key: cord- -c n w un authors: sokolov, andrii; mishagli, dmytro; giounanlis, panagiotis; bashir, imran; leipold, dirk; koskin, eugene; staszewski, robert bogdan; blokhina, elena title: simulation methodology for electron transfer in cmos quantum dots date: - - journal: computational science - iccs doi: . / - - - - _ sha: doc_id: cord_uid: c n w un the construction of quantum computer simulators requires advanced software which can capture the most significant characteristics of the quantum behavior and quantum states of qubits in such systems. additionally, one needs to provide valid models for the description of the interface between classical circuitry and quantum core hardware. in this study, we model electron transport in semiconductor qubits based on an advanced cmos technology. starting from d simulations, we demonstrate an order reduction and the steps necessary to obtain ordinary differential equations on probability amplitudes in a multi-particle system. we compare numerical and semi-analytical techniques concluding this paper by examining two case studies: the electron transfer through multiple quantum dots and the construction of a hadamard gate simulated using a numerical method to solve the time-dependent schrödinger equation and the tight-binding formalism for a time-dependent hamiltonian. this work is motivated by the development of complementary metal-oxide-semiconductor (cmos) charge qubits in one of the most advanced technologies, fdx by globalfoundries employing a nm fully-depleted silicon-on-insulator (fdsoi) process. building charge, spin or hybrid qubits by exploiting the fine-feature lithography of cmos devices is currently a dominant trend towards a large-scale quantum computer [ , , , , , , ] . although of all the mentioned cmos silicon qubits, charge qubits have quite short decoherence time [ , ] , they are revisited now in light of the high material interface purity, fine feature size and fast speed of operation of the latest mainstream nanometerscale cmos process technology (see the review section in ref. [ ] ). the speed of operation of quantum gates can now be ultra short due to the transistor cutoff frequency reaching half-terahertz in advanced cmos. thus, the number of quantum gate operations can be on the same order as with spin-based or hybrid qubits. for this reason, the paper is focused on the modelling of charge qubits. the development of quantum computer emulators requires high-level software representing the physics of quantum structures under study with high accuracy. at the same time, it should incorporate the control of quantum states of a large number of qubits, the realization of quantum gates, the act of measurement and transport of quantum information including the interface between classical circuitry and quantum registers, mentioning some of the major components needed for such an attempt. to facilitate an accurate modeling of interacting qubits, one is required to solve a many-body quantum system, which is a very resource intense task for classical simulators. there are some methods from computational quantum physics that could be used as a first approach for such problems. the density function theory (dft) is one of the most known and, in principle, exact ab initio method [ , ] . however, it is not applicable in practice for strongly correlated electron problems, since the exact exchange correlation functional is not known. in principle, the electrons in the position-based charge qubits described in this study are strongly interacting by coulomb interaction [ ] . from this point of view, any single-electron method such as dft cannot be reliably used. configuration interaction methods from quantum chemistry may also be considered exact ab initio methods, but of course they are limited to extremely small system sizes due to the well-known exponential scaling of the hilbert space with system size, making such methods essentially useless for our present purposes. by contrast, virtually all methods in quantum physics employ effective (or reduced) models that capture the essential physics of interest while throwing away irrelevant details [ ] . such approaches can even be quantitative semi-empirical, by fitting model parameters to experimental data. in this study, we will focus on the modelling of a specific type of cmos silicon qubits known as position-based charge qubits (or simply as charge qubits) [ ] . starting from d simulations, we demonstrate an order reduction and the steps necessary to obtain ordinary differential equations on probability amplitudes in a multi-particle system. we compare numerical and semi-analytical techniques concluding this paper by examining two case studies: electron transfer through multiple quantum dots and construction of a hadamard gate simulated using the time-dependent schrödinger equation and the tight-binding formalism. in this section, we provide the general description of the structures containing coupled quantum dots (qds) under study and key results of their fine-element method (fem) modelling employing comsol multiphysics. as we aim to penetrate the behaviour of a quantum processor fabricated in a commercial technology [ ] , fem simulations have been carried out on the structures whose dimensions and composition are inspired by the fdx technology of globalfoundries. the schematic d structure under study is shown in fig. (a) . the parameters and normalisation units used are presented in table . each structure can be seen as transistor-like devices arranged in a chain. each 'transistor' contains a control gate (which we call an imposer) made of a very thin sio layer, high-k dielectric layer and a thick heavily doped polysilicon layer. beneath a gate, there is a thin depleted silicon channel and a thin buried oxide (box) layer deposited on a thick lightly doped silicon wafer. an insulating coat is usually deposited on the top of the entire structure for electric isolation. the edges of the structure are connected to classic circuit devices known as single-electron injectors (detectors). semiconductor equilibrium simulations using the semiconductor module of comsol multiphysics have been carried out for temperatures ranging from to k to confirm that the silicon channel is completely depleted and there are no thermally generated carriers or carriers diffused from the interconnections with the heavily doped regions belonging to the injectors and detectors [ ] . electromagnetic simulations have been carried out to investigate the electric potential and electric field propagation through the structure when a given voltage is applied at the imposers. the electric potential developed in the silicon channel allows us to calculate the modulation of the edge of the conduction band and the formation of potential energy wells in the channel. an example of the potential energy on the surface of the silicon channel as a function of the coordinate along the channel is shown in fig. (b) where one can observe three potential wells forming in the region between the imposers. in general, there exist specific imposer voltages so that potential energy "barriers" are formed under the imposers and "wells" are formed in between the imposers. we refer to the region between the imposers where a potential energy well is formed as a quantum dot. in the figure, the minimum of the potential energy is conventionally placed at mev. in a typical scenario, barriers of to mev can be formed when a sub-threshold voltage is applied at the imposers. the resulting potential energy can be effectively approximated by an equivalent piece-wise linear function. the time-independent schrödinger equation (tise) with a piece-wise linear potential energy can be solved analytically or numerically in one, two or three dimensions to find a set of eigenfunctions and eigenenergies. the time-dependent schrödinger equation (tdse) can also be solved (as we will show later in the paper), but even in the d case, it requires substantial computational resources. the next section outlines the problem overview and the assumptions taken in this study. as the main model, we consider an isolated quantum system without external fluctuations. however, we will also present some results including effects of decoherence, which arise from the coupling between the quantum system under consideration with the environment. in this paper, the coupling appears as timedependent noise terms in the effective hamiltonian, but it should be noted that there are a number of approaches to model decoherence effects. coupling to a fermionic bath leads to kondo-type physics and the low-energy quenching of spin qubits, while coupling to a bosonic environment, leads to the localization through the caldeira-legget mechanism [ ] . in general, we note that both kinds of processes occur at some characteristic timescale (not instantaneously). in addition, we neglect other degrees of freedom (spin, valley and orbital) since we are interested in electron transfer in charge qubits (also called position-based qubits, as stated earlier). we start from the fundamental equation in quantum mechanics, the schrödinger equation. we have made some assumptions, which reduce the complexity of the problem: . we are interested in the transfer of an electron through the silicon channel of a quantum register containing multiple qds. since the channel is very thin, the electron wave function is "shallow" and we can neglect one dimension. in addition, fem simulations show the symmetry of the wave function, hence we use the reduction of the wave function along the symmetry line. in this case, it is reasonable to use the d modelling [ ] . . the complexity of the multi-electron model is significantly higher than that of a single-electron one. our first step is to consider the transfer of one electron through the channel by changing the imposer voltages. . in general, any changes of imposer voltages may cause non-trivial changes to the potential energy which can cause second-order effects on the wave function evolution. at the moment we do not take into account second-and third-order effects associated with abrupt imposer voltage changes of electronic noise. the starting point is the d time-dependent schrödinger equation: where is the reduced plank's constant, m * e is the effective mass of the electron, Φ(x, t) is the wave function of the particle, and v (x, t) is the d potential energy function. the the potential energy of the electron is obtained from the simulations presented in sect. , see fig. . the potential energy calculated from the fem simulations and its changes due to the variation of imposer voltages are exported as a table function from the comsol electrostatic simulator and is used as a 'pre-generated' input parameter of the quantum simulator. in order to have a useful simulator of the studied quantum structure, one needs to define a possible "localised" state of an electron injected in the structure, simulate its evolution with time at a given potential energy along the structure and calculate the probability of the electron to be measured at the edges of the structure by a detector device. the eigenenergies and eigenfunctions of the time independent case are particularly useful since they define the frequency of transitions, and, as the next step, we address the calculation eigenfunctions for an arbitrary shaped potential energy. in this section, we discuss a method for obtaining an approximate solution to a one-dimensional tise [ ] . a distinguishable feature of this method is that it allows one to obtain all the bound states and their corresponding wave functions at once. the method is closely related but not equivalent to the perturbation theory [ ] . assume that an electron is confined by a finite potential v (x) and this finite potential is located inside an infinite potential well v ∞ (x), so that the hamiltonianĤ of such a system readŝ hereĤ is the hamiltonian operator that corresponds to the problem of a particle (an electron) in an infinite potential well, the eigenvalues e since the functions ψ ( ) n form a complete basis set, for the required functions ψ n we can write the expansion where c nm are unknown coefficients. thus, the initial eq. ( ) yields multiplying both sides of the latter equation by ψ where the matrix element v km is determined by the potential v (x): thus, the problem of solving the differential equation ( ) is reduced to the square matrix equation problem ( ) that involves the integrals ( ) . the coefficients c nm form the eigenvectors of the hamiltonian matrix h km where n stays for the index of a given bound energy level. such a problem is usually solved by a matrix diagonalisation procedure, hence the name of the method. below we discuss different potentials v (x) and their impact on the solution. in case of a square well (potential barrier) structure, the integration in ( ) is trivial. indeed, for a piece-wise potential that takes either zero or some constant value v i for x ∈ [a, b], we have energy spectra of the potential generated from fem simulations (com-sol) and the six lowest energy levels with the corresponding wave functions for the three cases: realistic potential function integrated with splines (left), coarse piece-wise approximation (middle) and fine piece-wise approximation (right). left, realistic potential : the lowest energy levels (as well as the corresponding wave functions) exhibiting bound states 'localised' in each well. middle, coarse piece-wise approximation: the lowest energy levels are grouped in three, exhibiting 'non-localised' bound states. right, fine piece-wise approximation: the lowest energy levels are of the same order as those of the realistic potential energy; the wave functions match qualitatively. when the potential v (x) is given by some continuous but known function, the integration in ( ) should not be problematic. while it can be tedious, in principle this is a solvable problem. in the present study, we use the smooth potential energy generated by fem simulations as shown in fig. . for comparison, we create its coarse piece-wise approximation and also its fine piece-wise approximations as shown in fig. . the realistic smooth potential energy function is given in form of data points, and thus the easiest approach to the calculation of ( ) is numerical integration (e.g., using splines). placing the potential inside an infinite well of length l and separating it from the edges with a distance h, as described above, we obtain equivalent formulation of the problem within the matrix diagonalisation method. the result of the eigenenergy and eigenfunction calculations for the realistic potential energy is shown in fig. in the left column. we have used basis functions, and the width of the surrounding infinite well was l = . of dimensionless units, which gave bound states. one can see that such a potential has a nontrivial asymmetric allocation of the wave functions. the coarse and fine piece-wise approximations to the realistic function are shown in the same figure in the middle and right columns correspondingly. in the case of the coarse approximation, when the fine features of the potential energy such as "double-wells"are ignored, the lowest energy levels are grouped so that they are hardly distinguishable. there is also a significant difference in the values of the eigenenergies compared to the realistic case. on the other hand, the fine piecewise approximation allows one to preserve both qualitative and quantitative properties of the real potential energy. solving the time independent problem gives a good understanding of the system's properties at early stages of modelling. the time-dependent solution is discussed next. since we would like to model the evolution of an electron injected into a register of coupled qds and subject to a variable potential energy, we employ a split-operator method (som) to solve the time-dependent problem [ , ] . this method has been chosen due to its effectiveness at a moderate computational cost. since the method is well documented, we provide only its brief description, discuss its computational cost and show its application to the studied system. the split-operator method is based on the fact that in conventional cases it is possible to split the hamiltonian operator into two components, one being position dependentĤ r and the other being momentum dependentĤ k [ ] . moreover, it is possible to show that in the position space, theĤ r operator is reduced to the multiplication of the wave function by a position dependent function. the same reduction can be done for the momentum dependent component of the hamiltonian operator in the momentum space. this concept is illustrated in fig. . this method allows one to observe the evolution of the wave function with time, which is particularly useful in the case of a time-dependent hamiltonian. it also allows one to calculate the ground state of a system (in this case one can use the imaginary time step idt). in our case, when we deal with multiple potential wells (or as we say coupled quantum dots), it allows us to obtain corresponding localised states. the construction of the localised states in a system with the potential energy from sect. by the use of som is compared with that obtained by applying a unitary transformation on the eigenfunction set (obtained in sect. ). both methods show a good agreement. however, it is more convenient to use the matrix diagonalisation method in order to obtain the full spectrum of possible states. with regard to the computational cost of this method, it has two contributing aspects: the calculation of the forward and inverse fast fourier transforms (fft and ifft correspondingly) is proportional to the number of discretisation points n as n ln(n). a higher number n provides a higher resolution for the wave function, and therefore for the probability density function. note that in order to use the fft algorithm, the number of coordinate points should be a power of (in our case, ). this operation is repeated over a desired number of time steps dτ . the accuracy of the som is o(dt ), and thus the time step operation should be done with a relatively small time step (in our case − of dimensionless units of time). after we have implemented the split-operator method and ensured that it gives consistent results, our next task is to simulate the behaviour of an electron in a quantum register. we will show two examples: the transport of an electron from the first to the last qd in the register combined with electron probability oscillations and "spliting" electron's wave function between a number of qds. these simulations are presented in a later section using the coarse piece-wise approximation and by adjusting the height of the potential barriers separating the qds. in this section, we will introduce the tight binding formalism. this will allow one to capture the time dependent dynamics assuming an ideal quantum transport in the quantum structure (register) and can be easily extended to multi-particle and multi-energy level systems [ , ] . we use this approach for additional verification of the som modelling. in the tight binding formalism, we assume that electrons can be represented by wave functions associated with localised states in a discrete lattice. we can visualize the quantum register of fig. (a) as a pseudo- d lattice. for each qd, we consider one effective quantum state, which can be represented as |j , where j = , , ... is an integer denoting the position of each qd. then, the hamiltonian of the system can be written as: whereĉ † j (ĉ j ) are the creation (annihilation) operators, which create (annihilate) a particle at site j. the terms t s,jk are describing tunnelling, i.e., the hopping of electrons from site j to site k in the lattice. here, we will consider the symmetrical case, and therefore we will omit the potential energy of each qd (since it only shifts the total energy of the system by a constant and has no physical contribution to its evolution). we will also assume that sites k and j are immediate neighbors, and we will disregard any probability of a particle hopping to a distant qd. it should be noted that for single-electron tunneling processes through potential barriers, the tunneling rate is exponentially suppressed in the barrier height and width, therefore this is a reasonable assumption. in this representation, the wave function can be expressed as a linear combination in the position basis: where c k (t) are the complex probability amplitudes of the states |k , and the normalisation restriction applies k |c k (t)| = . furthermore, by considering the time-dependent schrödinger equation [ ] , one can write: where c(t) = {c (t), c (t), . . . , c k (t)} is the vector of the probability amplitudes. in this work, we are interested in describing the dynamics of the system for a time-dependent case where the hopping coefficients t s,jk do not remain constant with time (and can be increased or decreased by means of controlling the potential energy function). in order to perform quantum operations, one needs to apply a correct sequence of voltage pulses at the imposers (gates) at specific time instances, changing the tunnelling probabilities. in such a case, the hamiltonian of the system is changing with time. in the system under study we can consider a sudden change in the hamiltonian [ ] . also, the applied external fields (square voltage pulses) will be assumed of small magnitudes. as a consequence, the hamiltonian of the system takes the form: where each of the t h,jk hopping terms is a piece-wise time dependent-function of the form: where t jk, is the initial time instance when the pulse is applied at the imposer separating the quantum dots j and k, and t jk,width is the time duration for which the pulse is applied. note that one needs to match the initial conditions between the solutions of ( ), before and after the application of the pulse. the values used in this simulation are: t h,high = . e , t h,low = . e . figure demonstrates the transfer of an electron injected to dot and detected by two detectors ( and ) placed at the opposite edges of the structure. two pulses of . ns duration and mv amplitude are applied at imposers and respectively ( fig. (a) ). the heatmap ( fig. (b) ) demonstrates the pdf of the injected electron as a function of time (the horizontal axis) and coordinate along the register (the vertical axis), and its reaction to the applied pulses. the most informative is fig. (c) which shows the probability of electron being in each of the dots, and the final measurement in form of a probability histogram. it is obvious that in this case it is possible to transport the electron faster, but this graph was also made to demonstrate the feasibility of rabi oscillations with period t between the two dots when the barrier separating the dots is lowered. thus, to make the transport operation, we need to have the pulse duration t / + kt with integer k. an x-rotation gate is an operation which allows one to control the probability of detecting an electron. in order to "split" the electron's wavefunction into two equal parts, one needs to apply a pulse of duration equal to t / + kt (fig. (a) ). note that the second pulse applied is two times longer since we aimed at transporting a 'part' of the wave function to the third well. as one can see, the shown pulses allow one to realise an x-rotation gate. however, it is evident that each operation leaves some residual wave function in the dots, and thus it affects the accuracy (fidelity) of each operation. the presented results do not take into account decoherence effects or nonzero temperatures. however, it would have been unfair not to mention the decoherence that results from fluctuations, which always take place in a real system. using a simple two-levels telegraph noise model [ , , ] , we modified the algorithm described in sect. . we run simulations with the same initial conditions, where the height of the first potential barrier switches from v min to v max randomly. for each simulation, the switching time intervals were generated independently in accordance to the exponential distribution with the mean switching interval much grater than the simulation length. the corresponding results are shown in fig. . they demonstrate that the fluctuations of the potential energy result in the decay of rabi oscillations. the green shadowed area corresponds to the student's % confidence interval. in this paper, we discussed the the development of a quantum simulator for charge qubits based on fdsoi cmos technology. we started from the description of the system and proceeded with the discussion and comparison of numerical and semi-analytical techniques to model the behaviour of a single electron in such a structure. we presented a high-level multi-particle model to simulate the evolution of the various quantum states in such a system using the tight binding approach. we demonstrated two case studies: the electron transport through multiple qds and the construction of an x-rotation gate, and showed the effect of decoherence due to potential energy fluctuations. decoherence by quantum telegraph noise: a numerical evaluation improved exponential split operator method for solving the time-dependent schrödinger equation a mixed-signal control core for a fully integrated semiconductor quantum computer system-on-chip decoherence in qubits due to lowfrequency noise cmos position-based charge qubits: theoretical analysis of control and entanglement quantum dephasing induced by non-markovian random telegraph noise universal quantum hamiltonians rotation and phase-shift operations for a charge qubit in a double quantum dot photon enhanced interaction and entanglement in semiconductor position-based qubits modeling of semiconductor electrostatic qubits realized through coupled quantum dots split-operator spectral method for solving the timedependent schrödinger equation in spherical coordinates quantum mechanics -non-relativistic theory qubit gates with simultaneous transport in double quantum dots the harmonic oscillator in quantum mechanics: a third way two-channel kondo phases and frustration-induced transitions in triple quantum dots theoretical concepts of quantum mechanics. bod-books on demand quantum coherence in a oneelectron semiconductor charge qubit band-structure calculations for semiconductors within generalized-density-functional theory hubbard model description of silicon spin qubits: charge stability diagram and tunnel coupling in si double quantum dots correlated coherent oscillations in coupled semiconductor charge qubits condition for sudden approximation and its application in the problem of compression of an infinite well paired electron motion in interacting chains of quantum dots a two-qubit logic gate in silicon charge qubits and limitations of electrostatic quantum gates achieving high-fidelity single-qubit gates in a strongly driven charge qubit with /f charge noise from real materials to model hamiltonians with density matrix downfolding key: cord- -x pprjt authors: beyer, dirk; wendler, philipp title: cpu energy meter: a tool for energy-aware algorithms engineering date: - - journal: tools and algorithms for the construction and analysis of systems doi: . / - - - - _ sha: doc_id: cord_uid: x pprjt verification algorithms are among the most resource-intensive computation tasks. saving energy is important for our living environment and to save cost in data centers. yet, researchers compare the efficiency of algorithms still in terms of consumption of cpu time (or even wall time). perhaps one reason for this is that measuring energy consumption of computational processes is not as convenient as measuring the consumed time and there is no sufficient tool support. to close this gap, we contribute cpu energy meter, a small tool that takes care of reading the energy values that intel cpus track inside the chip. in order to make energy measurements as easy as possible, we integrated cpu energy meter into benchexec, a benchmarking tool that is already used by many researchers and competitions in the domain of formal methods. as evidence for usefulness, we explored the energy consumption of some state-of-the-art verifiers and report some interesting insights, for example, that energy consumption is not necessarily correlated with cpu time. there is a strong demand to save electrical energy, of which nowadays a large portion is used by computational processes. most importantly, we need to protect the environment that we live in, but we also need to consider that energy usage is one of the most important cost factors in data centers: after computing devices are purchased and installed, the operational cost is dominated by the cost of consumed electrical energy. and since most of the used electrical energy is turned into heat energy, there is follow-up cost for the cooling system, which sets the limits of used energy for each rack in a data center [ ] . in order to control energy consumption, we first need to measure it. work in the area of green software engineering identified a lack of data and insufficient tool support [ ] . energy consumption of an algorithm is often reduced to cpu time, which seems to be a natural choice at a first look, but after more accurate measurement we know that this reduction leads to wrong conclusions. why is energy usage of verification algorithms not measured but only cpu time? most likely it is technically too difficult for researchers to measure energy consumption, because it would require external hardware that is not common or because internal energy measurements are not well-known and complex to use. in order to provide a solution to this problem, we contribute an open-source lightweight tool that enables convenient energy measurement for a large range of modern cpus. the tool cpu energy meter makes it easy and convenient to access energy measurements done by the cpu for various of its parts. furthermore, we integrate energy measurement in the benchmarking framework benchexec, which is widely used by researchers and competitions (e.g., [ ] ). using cpu energy meter does not require any extra hardware, but accesses the existing feature for energy measurement called rapl that intel cpus provide. this convenience comes with a limitation: we can only access measurement values for those parts of the computing board that the cpu measures, but no external equipment, such as hard drives and the power supply itself. related work. energy measurements should be used for algorithm engineering [ ] , and there is a strong need for tool support, such as powerpack [ ] . rapl is being studied as a measurement method for energy consumption [ , , , , ] , and energy measurements that are based on rapl are being developed for specific scenarios [ , , , ] and used to evaluate algorithms [ ] . cpu energy meter makes energy measurement conveniently accessible to verification researchers. the most closely related project is the performance api (papi) analysis library, which also supports rapl [ ] , but this is a large library with a much larger scope than just energy measurements. in contrast, our tool is a ready-to-use solution for energy measurements that is easy to install and use. the intel running average power limit (rapl) [ ] is a feature of intel cpus that allows to measure and limit the energy consumption of cpus. it is available since the nd generation of the intel core architecture (code name "sandy bridge"), i.e., on intel core i /i /i and newer, as well as intel xeon e /e /e cpus. this covers a wide range of common cpus for notebooks, desktops, and servers. one part of rapl consists of access to a series of hardware counters in which the cpu accumulates the energy it has consumed. rapl supports measuring the energy consumption of so-called "domains", and up to five domains are supported by current cpus: package, pp , pp , dram, and psys. which hardware units are included in which domain is not clearly specified by intel, but in general we can use the following assumption: the package domain refers to the whole cpu, the pp domain refers to the processor cores, and the pp domain refers to other units such as an integrated graphics unit. the domains dram and psys may provide information on the energy consumption of the ram and other hardware on the mainboard, but both need special support from the hardware platform and its values may not be comparable between different systems. there is no official information by intel on the precision of the measurements except that the counters are updated approximately every ms. the resolution of the values varies between the cpus, but is typically j or j, i.e., in the order of − j. for the first generation of cpus with rapl, the energy consumption was approximated by the cpu and imprecise, but for subsequent generations the precision had been improved [ , , ] . our tool cpu energy meter provides access to the energy-measurement features of intel cpus to users. it was developed based on the tool intel power gadget for linux . our tool is available as open source under the permissive -clause bsd license and hosted on github . installation packages of cpu energy meter are available for debian-based distributions (e.g., ubuntu). cpu energy meter measures the energy consumption of the cpu(s) of a system for a specific time interval as reported by the rapl interface (cf. sect. ). in order to ensure the highest possible measurement precision with the lowest possible overhead, it reads the rapl energy counters as rarely as possible instead of using continuous sampling, while at the same time reading the counters often enough to safely detect and account for counter overflows. furthermore, our tool was developed to use a minimal amount of necessary dependencies and permissions in order to make its installation as easy as possible. requirements. cpu energy meter requires a system with one or more intel cpus that support the rapl feature. it needs direct access to the cpus, thus running in a virtual machine is not supported. accessing the model-specific registers of cpus with the energy measurements is done via the linux kernel module msr , which needs to be loaded and provides device files named /dev/cpu/*/msr. typically, access to these device files is granted only to the user root. in order to not need to execute cpu energy meter as root, one can change the file permissions of the device files appropriately (e.g., by granting read permissions to a group msr and making cpu energy meter always execute as this group using the "setgid" permission). furthermore, cpu energy meter needs the capability cap_sys_rawio , which can be granted using setcap . the installation packages of cpu energy meter attempt to automatically configure the system such that every user can execute the tool without granting any other non-standard permissions to users. in any case (whether executed as root or not), cpu energy meter drops all unnecessary permissions as soon as possible using the library "libcap" in order to reduce any risk related to the non-standard permissions. usage. cpu energy meter is intended primarily to be used by benchmarking frameworks, however, manual execution is also possible. when the tool is executed, it starts the measurements and prints the consumed energy for all supported domains and cpus of the system as soon as it is killed via the interrupt signal or ctrl+c. intermediate measurements are printed when the signal usr is received. to manually measure the energy consumption of the duration of a specific command, one can execute the following command line, for example: this will measure the energy consumption of all cpus during the whole time that the specified command is running, regardless of whether this energy consumption is caused by the specified command or by other processes running in parallel (this is a limitation of the rapl feature). thus, measuring the energy consumption during a specific time period (e.g., s) can be done by replacing some_command with sleep . the output values are given with the unit joule, and can be formatted either in a way that is optimized for being read by humans (cf. fig. ) or parsed by programs. integration into benchexec. we have contributed an integration of cpu energy meter into the benchmarking framework benchexec [ ] , because benchexec is widely used in the formal-methods community (e.g., sv-comp [ ] ). starting with version . , benchexec automatically executes cpu energy meter if the latter is installed, and it reports the energy results in the same manner as the results of its internal time and memory measurements (benchexec supports the creation of csv tables and interactive html tables with plots for its benchmarking results). benchexec will report the energy consumption only if all cores of one or more cpus are used for each tool execution, because we cannot distinguish between the energy consumption of individual processes. the th international competition on software verification (sv-comp' ) [ ] measured energy consumption of verification tools using benchexec and cpu energy meter and for the first time provided an alternative "green" ranking based on energy efficiency (cpu-energy usage divided by achieved score). this ranking was indeed considerably different from the main score-based ranking, with no overlap between the top three green verifiers and the top three verifiers in the category "c-overall". furthermore, the winner in the green ranking is two orders of magnitude more efficient than the last tool in the ranking ( j per score point vs. j per score point). this shows an enormous potential of efficiency improvements and energy savings if verification researchers get access to easy measurements of energy usage. in the following, we analyze in more detail some energy measurements of sv-comp' , which provides all raw results online . we pick the results for the submissions cbmc and cpa-seq across all categories. cpa-seq is the winner of the category "c-overall", written in java, and employs several different algorithms, some of which are partially parallelized. the garbage collector that is used by the jvm adds some more parallelism. cbmc is written in c++ and uses bounded model checking in a strictly sequential implementation. thus, we expect that the energy consumption of these tools has different characteristics. sv-comp' executed both tools for tasks (cpu-time limit s per task, intel xeon e - v cpu, quad-core with hyper-threading, . ghz, all processing units of the cpu and gb of memory were available to each tool execution, ubuntu . -bit with linux kernel . was the operating system). we now compare the energy consumption of the rapl domain "package" with the cpu time for cbmc in fig. and for cpa-seq in fig. . in the plot, all results that lie on the same line through the origin belong to tool executions for which the energy consumption per second of cpu time (in j s = w) was the same (this would be the average power of the cpu if measuring wall time instead of cpu time). we provide additional statistics in table and two graphs that compare the cpu time and the energy consumption of the two tools in fig. . insight: also for verification tools, high values for cpu time do not imply high values for energy. figure has a large vertical area of data points where the cpu time is close to the time limit. for those verification runs, the energy is in the range of . kj to kj. this shows that for a specific cpu time, the energy consumption (and average power, cf. table ) for different verification tasks can vary by a factor of . insight: comparing different verification tools regarding cpu time can lead to different conclusions than energy-based comparisons. the graph on the left of fig. compares cbmc and cpa-seq regarding cpu time, the graph on the right compares them regarding energy consumption. the difference between the shapes of these two graphs shows that looking at the energy consumption when comparing tools is an interesting addition to comparing only cpu time, and that table and figs. and ) can be misleading: if the power-usage characteristics of both tools were the same, the two graphs in fig. would look similar. verification algorithms consume large amounts of energy and thus, it is prohibitive to ignore the energy characteristics of algorithms when comparing their quality. although this matter is understood, the verification community does not measure energy. we believe that this is because measurement of energy is complex and requires a lot of additional effort. the lightweight tool cpu energy meter fills this gap: it supports reading intel-rapl-based energy measurements in a convenient way and -via integration into benchexec-using a tool environment that many verification researchers use anyway already. an analysis of a large data set from a verification competition invalidates a wide-spread assumption: the data quickly reveal that energy consumption can deviate significantly from the consumed cpu time. thus, it is not sufficient to measure cpu time. data availability statement. a replication package for this article including cpu energy meter and benchexec is available at zenodo [ ] . current versions of cpu energy meter are available at https://github.com/sosy-lab/ cpu-energy-meter and https://doi.org/ . /zenodo. . the dataset from sv-comp' [ ] that was analyzed in sect. is available online at https://sv-comp.sosy-lab.org/ /results/results-verified/all-raw.zip. a new energy aware performance metric reliable and reproducible competition results with benchexec and witnesses automatic verification of c and java programs: sv-comp reliable benchmarking: requirements and solutions replication package for article 'cpu energy meter: a tool for energy-aware algorithms engineering a validation of dram rapl power measurements energy footprint of advanced dense numerical linear algebra using tile algorithms on multicore architectures pow-erpack: energy profiling and analysis of high-performance systems and applications power measurement techniques on standard compute nodes: a quantitative comparison an energy efficiency feature survey of the intel haswell processor measuring energy consumption for short code paths using rapl green software engineering: the curse of methodology power measurements for compute nodes: improving sampling rates, granularity and accuracy green and sustainable computing conference (igsc) intel: intel and ia- architectures software developer's manual how much power does your server consume? estimating wall socket power using rapl measurements solutions for the data center's thermal challenges the shift from processor power consumption to performance variations: fundamental implications at scale evaluation of energy characteristics of mpi communication primitives with rapl measuring energy and power with papi ), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the creative commons license and indicate if changes were made. the images or other third party material in this chapter are included in the chapter's creative commons license, unless indicated otherwise in a credit line to the material. if material is not included in the chapter's creative commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use key: cord- -zx g dyg authors: hardon, anita title: chemical / date: - - journal: chemical youth doi: . / - - - - _ sha: doc_id: cord_uid: zx g dyg this chapter shines a light on what happens in the dark: specifically, we present ethnographic insights from the nightlife economy and how chemicals enable youth to work “ / .” producers, promoters, djs, hosts, artists, performers, drag queens, musicians, stage managers, bartenders, hospitality girls, and dancers from amsterdam, brooklyn, bira (indonesia), and puerto princesa (the philippines) share with the chemicalyouth team the various stimulants they use to stay awake and perform their jobs during non-typical working hours, and the other chemicals that they take in order to be able to sleep and recover afterwards. in chemical / we compare and contrast the chemical practices of youth working at leisure industry sites in the global north to those of the low-income service sector and manual workers in the global south, and discuss how these different working conditions perpetuate chemical use. our interlocutors rely on a range of chemicals for their work and social lives, and they develop practices to moderate their use in order to avoid adverse effects. yet their practices differ depending on the availability, marketing, and policing of the substances. nightwork-meaning all jobs that are executed during nighttimeincreased as cities became connected to electricity in the early twentieth century, and as economies became more connected globally through the internet. in the current "gig economy"-dominated by those jobs in which people are paid by the task, rather than receiving a fixed salarywork never stops. part of this "performance" has to do with adapting to the different temporal demands of the labor market-in other words, the management of sleep and wakefulness. as crary ( , p. ) notes, our modern economies " [undermine] distinction between day and night, between light and dark, and between action and repose … the planet becomes re-imagined as a non-stop work site or an always open shopping mall of infinite choices, tasks, selections, and digression." but working at night is not necessarily good for us. melatonin, the hormone involved in the regulation of our biological clock, is released when we are exposed to daylight. our bodies follow circadian rhythms of approximately -hour cycles, and as kamps warned me, these rhythms have an impact on our mental and metabolic health (roenneberg et al. ) . humans have a long history using chemicals to tinker with our circadian rhythms, with caffeine being the most ubiquitous substance used to stay awake, one that is accepted globally as beneficial despite its addictive properties. historians trace the use of coffee back to the fifth century, in the sufi monasteries of mocha, now known as yemen (weinberg and bealer ) . caffeine stimulates the central nervous system by blocking the action of adenosine (which causes drowsiness) on its receptors. the popular food writer pollan ( ) , in a recent analysis of caffeine, suggests that without this substance the industrial revolution wouldn't have happened. studies in sports medicine attest to caffeine's positive effects in adults, including increased endurance and strength, improved reaction time, and delayed fatigue (graham ; sökmen et al. ) . adverse effects of caffeine, if taken in high amounts, include disturbed sleep, increased blood pressure, and physical addiction. caffeine is considered safe to ingest up to about mg per day (or two cups of coffee). in addition to caffeine, those working at night often resort to cocaine and amphetamines for stamina and to stay awake. the use of cocaine for endurance goes back to the incas in peru who for thousands of years have chewed coca leaves for this purpose. the alkaloid cocaine, derived from the plant, was only isolated in the mid-nineteenth century. amphetamines were discovered shortly thereafter by chemists. in on speed rasmussen ( ) traces the history of this category of drugs, showing how early twentieth-century pharmacies in the united states sold invigorating tonics containing cocaine and nasal decongestants containing amphetamines. its first major use was during world war ii, when soldiers used it to boost their performance and alertness, and to suppress appetite (see also braswell ; rawson et al. ) . in japan, it was given to soldiers before they performed their "kamikaze" suicide bombing missions; in england, million amphetamine tablets were made available to pilots so they would not fall asleep (braswell ) . three years after the war, in , the japanese ministry of health prohibited the production of both tablet and powder form of methamphetamine. similar moves were made in the united states but, interestingly, the medical establishment continued to defend its legal status and deny its addictive potential. it was only when its use grew further, and more evidence about its addictive potential came to light, that the united states finally passed the drug control act (rawson et al. ) . nowadays cocaine is an illegal drug. amphetamines are sold legally as prescription tablets for adhd, while methamphetamine is an illegal drug, sold on the street as "crystal" and "ice," and consumed in many different ways: ingested pills, snorted powder, injected liquid, or smoked (rawson et al. ) . like caffeine, cocaine and methamphetamines increase alertness, strength, and coordination, while also increasing blood pressure and stimulating the heart rate (koob et al. ). both drugs cause pupils to dilate, allowing more light in, which activates our daytime metabolism (paul et al. ). the pharmacological actions of cocaine and methamphetamine differ: cocaine works fast and is quickly removed from the body, while methamphetamines have a much longer duration of action, making it harder to sleep after using them and increasing the risk of addiction. cocaine prolongs dopamine action in nerve cells, by blocking dopamine reabsorption, while methamphetamines work by both blocking dopamine re-uptake and increasing its release, leading to higher concentrations of the neurotransmitter in cells, which can be toxic. long-term adverse effects of methamphetamines include insomnia, confusion, memory loss, and psychiatric conditions such as psychosis (national institute on drug abuse ). social scientists have pointed to the widespread use of caffeinecontaining "energy drinks" and the off-label use of drugs indicated for attention deficit hyperactive disorder (adhd), such as ritalin and dexamphetamine, by students trying to increase their focus and attention when studying, and to stay up late when partying. but these studies generally focus on student populations. in this chapter, we present ethnographic insights on the use of various stimulants to stay awake and fight fatigue by workers in the nighttime leisure economy, the bartenders, djs, sound technicians, photographers, and event organizers who must perform professionally during the night. we contrast the / chemical practices in brooklyn and amsterdam, two leisure industry sites in the global north, with the / chemical practices of low-income service sector and manual workers in our field sites in the global south: puerto princesa and cagayan de oro (the philippines), and makassar (indonesia). here the substances are not only used to stay awake, but also to endure heavy physical labor. we find that practices differ depending on the availability, marketing, and policing of the various legal and illegal stimulants, and that risks are shaped by the structure of everyday life, the rhythms of stimulant use, and workplace policies. we also show howacross the sites-users moderate intake in order to avoid adverse effects, including their negative influence on the quality of sleep, and how they mitigate such effects by using other substances, such as cannabis or alcohol, to calm down. in brooklyn and amsterdam our youth ethnographers conducted focused research on the nighttime leisure industry, with tait mandler studying diy queer parties in brooklyn and daan kamps studying popular clubs in amsterdam. in these field sites, event managers organize the artists, barkeepers provide drinks, djs create music, and sound technicians fine tune it. mandler and kamps found that the workers in these entertainment spaces balanced their engagement in the party and staying fit for work. all moderated their alcohol intake and they took stimulants to stay alert till the end of the night. mandler ( ) observes that work in these sites is an inherently contradictory activity. when working, they have to appear to be enjoying themselves; leisure activities themselves become work. cocaine helps workers be productive and enjoy themselves in their nighttime jobs. our interlocutors in these two cities presented themselves as experienced moderators of circadian rhythms. they had developed personal strategies of stimulant use, aimed at generating the right amount of alertness, while also enabling pleasure at work. they scheduled their use around work and other responsibilities, monitored their dosage to ensure moderation, and took breaks from using when necessary. but all attested to the heavy toll that nightwork has on their bodies, especially if they combine nightwork with daytime jobs, or coursework, both of which require rapid transitions from night wakefulness to daytime alertness. in brooklyn, mandler ( mandler ( , found that the most common chemicals used to stay awake during the night shift were energy drinks, cocaine, and the adhd drug adderall. cocaine helped his interlocutors stay alert during shifts, while also engaging in the party, which was a challenge. jett, a bartender, said that after working in a bar for around six months, he realized that everyone around him was sniffing cocaine all the time. jett preferred energy drinks because they were free to employees in the establishment (which was sponsored by an energy drink manufacturer). mandler ( ) also found that many night workers combined day and nighttime jobs. joshua, a drag queen and visual artist, described how they (joshua's preferred pronoun) managed working hours in two days with only a few hours of sleep: that morning i go to work all day, so i'll have a coffee there. i get home around : pm or pm. … [i] get to the club around : pm … and drink a big non-alcoholic drink to bookend the night with. like seltzer and a fruit juice … then right around midnight i start drinking … something like vodka with a fruit mixer. throughout the night i'll probably have two and half of those. maybe someone had coke and i've done a bump [small snort] or two. around am or : am i'll have left the club … i'll sleep for three and half or four hours before i have to get up and go to work where i'll drink a little coffee. (mandler , p. ) alice produced underground queer events in warehouses that usually started around pm and continued well past am. she also worked for a nightlife magazine and was active on social media, which has made her a popular party host. alice explained that she did not really enjoy the nightlife culture and was mainly interested in her own friends. however, her job was to promote events as if they were going to make for the best night ever. she didn't drink much at these parties, but made sure to hold a drink; this made her feel as if she was engaged in the party, and dissuaded people from asking why she was not drinking. if she consumed alcohol, she said, she could not produce the parties well, and she would be tired before they were over. cocaine, in contrast, helped her be more assertive, "but sometimes this also [led] her to stand on the stage at the end of a party and watch the crowd dance to the final songs in awe" (mandler , p. ) . for cassandra, and many other nightlife workers, the use of cocaine was not the event of the night. they moderated use, spacing and sharing it, as dan explains: i take smaller bumps, i try not to do a whole line. i space it out throughout the night. also sharing kind of helps. if i'm going to do some and i have someone else to do it with, it sort of tricks me. (mandler , p. ) val explained that he preferred cocaine because it: doesn't really affect my ability to judge … so that's sort of the stimulant choice. i don't like coffee; it wrecks my stomach. i hate things like adderall, they're too strong. cocaine is light and it can keep me awake and after i get home i'll fall asleep maybe an hour later. (mandler , p. ) moderating their substance use was a common goal among these nightlife workers. they monitored the chemical use of their friends, specifically checking if it negatively affected their ability to function on the job or socially; and used the same criteria to evaluate their own chemical practice. some limited themselves to a few drinks or bumps. even so, at times, they felt that they had gone too far, at which point they took a break from using a specific drug, or even all chemicals (mandler ) . kamps interviewed people who work in amsterdam clubs. he recorded systematically which stimulants they used to stay alert and awake at work. out of the participants, drank energy drinks and/or coca cola, consumed amphetamines (including adhd drugs), and used cocaine. as was the case in brooklyn, the workers he spoke with asserted that they had developed personal strategies to stay awake and alert on the job. many smoked cigarettes and drank alcohol; the two go well together, they said. alcohol helped them feel more engaged with and connected to the clients at the clubs. but they felt compelled to moderate their alcohol consumption so as not to become too drunk to work. event organizers and venue programmers are responsible for the overall success of the party. they pick up the djs, manage the guest list, decorate the venue, and are present for the sound check. they feel responsible for getting the dance floor filled and creating the euphoric ambience. maarten, a venue manager used cocaine to stay alert and be sociable when preparing for events and to tune in with the atmosphere of the party. meike, an event organizer and hostess, said she often worked long, -hour shifts, till am the next morning. besides taking smoking breaks, she often drank club mate, which she combined with vodka. club mate is an energy drink with mg caffeine per ml and low sugar content (less sugar than red bull). nadine, too, who worked as a barkeeper, used cocaine for energy, alertness, and confidence. djs need to keep the crowd going through the night. sander, a well-known dj, talked about using adhd drugs to keep up the vibe. his girlfriend had been diagnosed with adhd and prescribed dexamphetamine. before he left for work in the evening, sander usually took two mg tablets of dexamphetamine, and then took another dose if he felt tired during the night. sander said that dextroamphetamine worked well: it kept him alert, without anyone noticing that he had taken drugs. the djs interviewed by kamps all attested to the highly desirable effects of amphetamines. the substances create very energetic states of being that contribute to the party atmosphere. the sound technician makes sure the music reaches the audience as well as possible. "being alert and focused-paying continuous attention to sound levels, depth, clarity, and space-is of utmost importance, and the longer the event lasts, the greater the challenge," explained one sound tech (kamps and hymans forthcoming, , p. ). another said that he used red bull in the early hours of the morning (around am), when he became unable to hear certain frequencies. kamps also talked with night workers about what they did to catch some sleep after work, especially after using amphetamines (the effects can last for around - hours, see keogh ) . his informants told him that, to ensure sleep, they stopped taking amphetamines around - am and smoked some cannabis once they got home. others used melatonin to reset their biological clocks. but other factors also could keep them awake. if a performance or event went particularly well, the excitement could still be palpable after returning home. for the event organizers, whether money was made or lost greatly affected their state of being; returning home, they often sat on the couch, contemplating, with images of the evening going through their heads, what went well and what went wrong. these emotions, together with the rhythm of their internal body clocks and the chemical stimulants still coursing through their bodies, made it hard to fall asleep, even if they actually felt tired. andy explained that one could be exhausted yet unable to fall asleep: you might lay in bed at seven in the morning, be half asleep for three hours and then be fully awake again around eleven." he would then get out of bed. bart described the same phenomenon: "your body is fully awake but your brain is lagging behind." (kamps and hymans forthcoming, , p. ) our fieldwork in leisure sites in amsterdam and brooklyn showed that these nightlife workers were cautious users of stimulants, striving to meet the various demands of their nighttime work. many used cocaine, which has as an advantage that its effect fades fast, allowing the workers to sleep when they get home. but amphetamines, in the form of adhd drugs or speed, were also used often, and these made sleeping harder. in addition, several workers managed their stamina with energy drinks, which generally contain around mg of caffeine per ml (similar to a cup of coffee). while moderating their stimulant use, and complementing it with other substances such as cannabis and melatonin to sleep, many of the interlocutors admitted to feeling burned out over time, which they attributed not only to their substance use but also simply to the lack of daylight in their lives. in the philippines and indonesia our focused ethnographies examined how young people used stimulants to have energy and strength enough to conduct physically challenging work, laboring long hours as porters, construction workers, and security guards. the use of amphetamines as fuel for labor in asia has been observed by sherman and colleagues ( ) , who describe how methamphetamines-called yaba (crazy drugs) in its pill form in thailand, and shabu in its powder form (also known as crystal meth) in indonesia and the philippinesentered the market in the s to enhance performance in physically demanding roles. a young construction worker in thailand reports: i felt i could work more and earn more as well… when we delivered cement powder, we got baht for one trailer… if we didn't take yaba we would be able to deliver only one or two trailers. but when we took yaba we became diligent. (sherman et al. , p. ) participating in the chemicalyouth project, lasco examined the use of shabu among unemployed young men hustling for work in a philippines harbor city. they worked as tambays (stand-by) porters in the harbor, vendors to the bus passengers that frequent the port, and occasionally at night as sex workers. their work comprised of long hours hanging around till boats and buses arrived. some of them combined working as a porter with selling freshly roasted peanuts and drinks to bus passengers. lasco learned that their work as street vendors also, ocassionally, involved stealing mobile phones from travelers, joining in "car-napping operations," and engaging in sex work. lasco described how his informants killed time while "standing by" by smoking cigarettes, as many as - cigarettes a day. shabu, they asserted, provided them with confidence and stamina, and reduced their inhibitions, allowing them to engage in a multitude of services. one told lasco ( ) , "we are not educated and we have nothing. where will we get the confidence to talk to others, if not from shabu?" (p. ). young men were initiated into shabu inhaling by their barkada, which is both a social and economic group consisting of peers. the cost of one small sachet of shabu, which can be used by three people, is pesos (us $ . ); the paraphernalia, consisting of three bits of aluminum foil and a lighter to heat the substance, was also shared. everyone in a barkada uses shabu, which expresses loyalty, thereby forging social bonding in the group. "scoring" sessions take place in ordinary port houses called "pwesto" (from the spanish "puesto," or place). the owner of the pwesto collects pesos from the users, in exchange for providing them with the security of being in a private home where the substance can be used away from the gaze of the police. the young men said that, after an immediate euphoria, they experience a sustained effect of being "kalmado" (calm) and "ganado" (enthusiastic). they said that using shabu boosted their skills, abilities, and industriousness. like kamps's informants in amsterdam, they treated any insomnia caused by their shabu use with cannabis and red horse beer, which they routinely used to fall asleep. several evenings a week, the barkadas gathered at night to drink alcohol together (inuman); this was leisure time. the costs for these evenings were shared by the whole barkada, unless someone was celebrating his birthday, in which case, the celebrant was expected to foot the bill. in the inuman, red horse often gave way to harder alcohol, such as a brandy called "empi light" (emperador light, % alcohol). alerted to the precariousness of his interlocutors' lives, lasco ( ) calculated how much they spent using multiple substances, as well as how much they earned from various sources. the results are presented in the table . . his findings reveal that the substances cost more than what was actually earned; the shortfall was met by occasionally doing sex work (earning around pesos for oral sex services provided to gay men, and more if anal sex is done), or stealing and selling a mobile phone. lasco writes that, while most of his informants used shabu, there were also a few young men who resisted doing so. one of them explained that users often lost the ability to distinguish between using in order to work, and working in order to use (lasco ) . the users asserted that the greatest danger in using shabu was its illegality, speaking of weekly raids, youths getting jailed, and worries about their safety. they nevertheless perceived the benefits to outweigh the costs. in publishing this case study, lasco decided to not publish the name of the city where he did fieldwork, and we followed his example in this book, worrying that philippine drug authorities might crack down on the young men working in the harbor. little did lasco know that just a year later rodrigo duterte would be elected president, and that he would declare a war on shabu, giving local police officers the green light to shoot any drug user without due process. another focused ethnography in the philippines was conducted by leo diego, who examined stimulant use among security guards in puerto princesa, palawan (diego ) . providing security is the most common job for young men in the philippines, and security guards are an omnipresent feature of contemporary philippine society, seen everywhere, in schools, malls, banks, and other big establishments where people frequent. diego observed that being alert during their long shifts was a key challenge for these workers, and that they relied on energy drinks as the main substance they use to help stay awake. the majority of the participants entered the security industry because of their lack of college degrees; most of them were high school graduates. they worked at pawnshops, banks, department stores, hotels, and schools. work circumstances differed at these sites. the pawnshops demanded a high level of security, as money was exchanged there and had to be protected. security guards in pawnshops were bound to follow a no-sitting policy while on duty. thus, alertness was crucial: as guards, they had to check the body language of customers, distribute forms to be filled out, and make sure that no trouble transpired. banks also hired security guards for the same reason-money matters. working in a bank was full of tension, especially for guards who drove armored vans. with their lives at stake, guards had to pay utmost attention to every movement in their surroundings. on the university campus, the work of security guards was very different. with its almost , students, palawan state university was the largest tertiary educational institution in the province, and security guards were needed to check that students entering the premises had proper identification: no id, no entry. in general, the work of security guards is undervalued in the philippines, with some seeing it as a job for lazy people. many people believe that security guards just stand there, not thinking, all day at their posts. for example, roland, a security guard who worked at a bank, always heard that being a security guard was a job for a bystander, because guards not only just stand and walk at their posts, but can also sleep if no one is watching. roland explained that, because of this misperception, some people from his neighborhood said that when you applied for a security job, it must be your last choice. but ric, a security guard at a mall, defended his work: guards must be conscious of everything that is happening in their vicinity at all times. they must constantly be reading the body language and facial expressions of the people around them. their minds must always be aware of what is to be done in case of unexpected trouble. they must be observant at all times. the greatest challenge reported by security guards was maintaining their alertness and fighting off sleep. this challenge had to do with the long and irregular working hours assigned to security guards. three guards often shared a single post; each of them had to have a shift of eight consecutive hours, and their work schedules could change with little or no notice. despite the stress involved, being a security guard was not a well-paid job. most security guards in puerto princesa earned the minimum wage of us $ per day, or approximately us $ per month. many paid rent to a boarding house, which in puerto princesa cost at least us $ - a month, excluding water and electricity. most guards commuted to work (spending us $ . daily for fare) and bought their lunch (us $ ). most of our interlocutors also supported families and other dependents, and struggled in the face of the rising costs of basic necessities, such as rice, fish, and gasoline. many fell into debt, and lived in a perpetual struggle to pay their bills and promissory notes. the precarious economic situation of most security guards meant that they depended on keeping their jobs, and any absence from work meant that they lost pay. furthermore, many feared being caught sleeping on the job, which could result in an instant dismissal. many security guards thus resorted to chemical stimulants, which they called "pampa-alert," their term for something that can be used to foster alertness. generally, "to be alert" meant being aware of anything in the vicinity. troubles and crimes could come along at any time. in this manner, the guards' lives were at risk, as they were expected to protect people and the establishment for which they are responsible. most security guards were men, and most were on duty at night. some security agencies told us that female guards were not permitted to work the night shift, because, they said, female guards were not on par with male guards in terms of alertness and self-defense. but still, female guards were often found at the entrances of department stores and malls, to name a few. fourteen of the security guards interviewed by diego drank instant coffee to keep themselves awake (nescafe -in- , great taste, and kopiko brown are popular; all contain large amounts of sugar), and of them also drank energy drinks during their shifts, see table . . table . shows the popularity of the cobra energy drink, which was used by of the informants. five of the cobra drinkers specified that they used the energy drink during night shifts. it also shows that half the informants did not smoke cigarettes; the reason for this is the strict anti-smoking policy in puerto princesa, where smoking is only allowed in designated areas. a ml bottle of cobra costs us $ . and contains mg caffeine (the same amount as two cups of coffee; this is about double the content of the energy drinks sold in amsterdam). it also contains b vitamins, ginseng, and sugar. cobra is the market leader in the energy drinks segment of the beverages market in the philippines, accounting for % of sales (euromonitor international ). the brand's bottles are sold in sari-sari stores (informal neighborhood shops) and the brand is heavily advertised on tv and through twitter, facebook, and youtube. everyone in the philippines knows cobra's slogans: "may laban ka" (you're up against it) and "tunay na lakas" (full of strength). its popularity is attributed to the fact that it is promoted by the award-winning filipino actor coco martin (the attractive muscular guy on the left in below advertisement) ( fig. . ) . see fig. . , for an image of a typical neighborhood outlet for cobra; notice how cobra is placed prominently in the store along with coca cola, sprite, and fortune cigarettes. despite the popularity of this energy drink, users' experiences are mixed. bryan, a -year-old security guard at a department store, told us that sometimes when he uses cobra he felt wide awake, but there were also times when he couldn't help falling asleep. charm, a female guard at a university, said that cobra caused her to suffer a urinary tract infection. when she stopped using cobra, she just walked around her post in order to avoid feeling sleepy while on duty. only a few of the security guards admitted to using shabu to stay alert during the night shift, perhaps because puerto princesa has a zero tolerance policy for drug use. one of the guards, joker, told us of how he used shabu when he needed to serve as a shift reliever, meaning he had to be at his post almost hours in a row. he also shared that there was a popular drug called fly high that could also be used to stay alert and was also effective in increasing stamina during sexual intercourse. he said that this drug was a combination of methamphetamine, viagra, and ecstasy, and could be bought for around us $ - per tablet. when asked about the effect of the drug, joker responded, "for three to four days you will not feel hungry, your being awake is continuous, your awareness will be active, you are unstoppable, and you have more stamina for sex" (diego , p. ) . for our final case study, we turn to the use of stimulants by two categories of low-income workers: porters and construction workers in makassar, indonesia. this research was carried out by amalia anwar ( ) in infrastructure development locations (such as housing and offices) that employed construction workers and in the seaport with dockworkers. the manual laborers involved in this study were construction workers ( men and women) and dockworkers (all men), aged between and years (fig. . ) . energy drinks, which are classified as "health drinks" in indonesia, were the most commonly used stimulants in these fieldwork sites. kuku bima and extra joss are popular local brands, sold in sachets (us $ . /sachet) in groceries and informal stalls, and mixed with water by vendors (as illustrated in fig. . ) . advertisements for such drinks in various print and electronic media are plentiful and varied, with provocative slogans such as "lelaki pemberani " (brave man), "jiwa laki bukan pengecut " (men's souls not cowardly), and "extra joss, perfect goal" (aired during the world football championships) that stimulate men to buy and consume them. the sachets are also marketed by sales promotion girls, see fig. . . the ad for kukubima ener-g drink features ade rai, an athlete and artist, and shows a picture of his muscular body, evoking strength and vitality, accompanied by a picture of ginseng, which is known for its virility enhancement effects. the slogans of such ads promote not only masculinity-for example, with slogans like these: ( country, fresh, full of energy, real energy)-but also competition (the essence of football, secret of the champions, premier energy drink in the world). although advertising plays an important role in promoting the use of energy drinks, workers generally learned about energy drinks from their coworkers who first consumed them. table . lists the contents of the energy drinks that were popular among manual laborers we spoke with. note how all three of the popular brands contain mg of caffeine per sachet along with ginseng, different kinds of vitamin b, flavors, and sweeteners (honey and/or sugar). the main difference is taste. limited rest periods and the heavy workload made it difficult for manual laborers to take a lunch break, so consuming energy drinks became a substitute for lunch. surti ( -year-old construction worker), for example, felt full and energetic after consuming kukubima ener-g, even when she had not eaten. ulla, a -year-old dockworker, admitted to frequently consuming kukubima ener-g (grape flavor) while resting in order to restore her stamina before her next shift. ella and her coworkers would regularly consume such energy drinks in large volumes, often mixing five or six sachets with a jug of cold water. energy drinks were used not only to work during the day but also for overtime shifts. foremen regularly asked workers to work hours a day and to continue working over the weekend to get the job done. ariana, a -year-old construction worker, said she drank energy drinks (extra joss active) only when working overtime, after a -hour shift. for some of our interlocutors, energy drinks were panaceas, used to overcome body aches, increase appetite, and improve sleep quality. the construction workers preferred kukubima ener-g. their foreman bought the sachets for them, and deducted these costs from their salary. ratih, a -year-old, explained: in the workplace, they buy it for us, usually bought in the morning, and also the afternoon, the foreman notes it. usually we make one box of grape flavored kukubima ener-g mixed with milk, mixed with water in a jug, and we drink it together. (anwar , p. ) energy drinks were consumed not only for work but also for fun. after receiving their wages, the construction and dock workers would gather and hang out with friends, staying up late watching movies together while eating junk foods and drinking energy drinks. energy drinks were mixed with milk or with cheap alcohol. our interlocutors explained that the alcoholic mixes made them sleep well, relieved body aches, and strengthened them for work the next day. the widespread use of energy drinks for both work and recreation in our field sites in makassar meant that the workers had a relatively high intake of caffeine. we wondered: did our interlocutors care about the dangers of consuming energy drinks? sari, a -year-old construction worker, claimed she did not know about the high level of caffeine, and was surprised that energy drinks were considered harmful in excess. ruslan, a -year-old dockworker, said that he had tried to consume a m- , but experienced heart palpitations. although extra joss active did not have a negative effect on his body, he preferred kukubima ener-g because of its grape flavor, which he found delicious. asril, a year-old construction worker, moved from one energy drink brand to another. while he found extra joss active tasty, he, like ruslan, preferred kukubima ener-g because of its grape taste; for him, kratingdaeng was not an option because it caused a variety of negative effects: heartburn, dizziness, stomach ulcers, and nausea. kamaruddin, a -year-old dockworker, also chose kukubima ener-g rather than extra joss active, because extra joss active caused a burning sensation in his throat every time he consumed it. among those concerned about the side effects of regularly consuming energy drinks, some had reduced their energy drink consumption, and some were looking for alternatives to overcome tiredness. jamal, a year-old construction worker, had limited his consumption of energy drinks, replacing them with other cold drinks that contain lots of sugar (like teh gelas) or water. others quit consuming energy drinks cold turkey. muhlis, a -year-old dockworker, for example, stopped consuming all energy drinks because he often experienced stomach pain and heat in his throat. he tried to prevent these adverse effects by consuming plain soda water mixed with milk and pilkita-an analgesic drug sold as a "strength drug"-because he believed that the mixture could relieve his pain. ulla, a -year-old dockworker, had replaced energy drinks with a mixture of soda water and raw chicken eggs. scholars of youth have described how young people use stimulantsmostly adhd drugs-to work long hours to keep up with academic requirements, a practice that is considered problematic because it is an "off-label" use and because it may create academic advantage in allowing users to unfairly enhance their performance (coveney et al. ; desantis and hane ; garnier et al. ; mccabe et al. ). however, young people's use of other stimulants like energy drinks to increase productivity has received much less scholarly attention. this is remarkable given the high sales of energy drinks across the globe, as well as the health risks associated with their frequent consumption. one of the rare studies that examines the use of energy drinks by youth found that nearly one in five students of a secondary school in ontario consumed energy drinks to be alert (reid et al. ) . another web-based study conducted across campuses in the united states found that almost half of the respondents had used energy drinks. this study reported that energy drink use was associated with poor sleep and tiredness the next day (patrick et al. ) , an observation also made in a study of energy drinks by us soldiers in afghanistan (cdc ) . researchers at the center for food policy and obesity at yale university (pomeranz et al. ) view the increasing use of energy drinks by youth in the united states as a public health hazard, because the high levels of caffeine in the drinks can lead to caffeine overdose. in addition, they warn that these products contain both high levels of sodium and novel ingredients, such as taurine, guarana, and ginseng, the combined effects of which have been understudied. finally, they point to the heavy advertising of these products to youth through digital media, facebook, and sports events and brands. our approach of examining situated chemical practices allowed our youth ethnographers to observe both the use of stimulants and the use of chemicals to address sleep problems. across our sites in amsterdam, brooklyn, puerto princesa, and makassar, we found that patterns of stimulant use differed. the porters in the philippines earned money not only by carrying wares from buses to boats and back. they also earned money by selling goods and sex. for this interactional labor, they valued the confidence enhancement that amphetamines offer. the security guards whom we interviewed in puerto princesa sought products to keep them awake during their night shifts. for them, energy drinks did the trick. but they earned very little money, and energy drinks took a substantial part of their limited income, which forced them to moderate their use. in indonesia, energy drinks are very cheap, and people used them as a panacea, not only to have stamina at work but also for virility and for bodily aches, and they valued the flavor that energy drinks brought to mixed alcoholic drinks. but the consumption of the caffeine in these drinks can lead to adverse effects, such as heart palpitations and nausea. several of our interlocutors were trying to quit using energy drinks for these reasons. in amsterdam, our ethnographic research found that nightlife workers also used amphetamines to stay alert, but they could easily get ahold of adhd drugs for this purpose. moreover, in both brooklyn and amsterdam night workers often used cocaine, which is much more expensive than crystal meth, to enhance their work performance. both adhd drugs and cocaine have less potential for addiction and less severe adverse effects than crystal meth (nida ). in both cities, users moderated their intake to manage sleep patterns, though the tiredness reported among students in the united states and soldiers in afghanistan is a common feature of the chemicalyouth narratives of our interlocutors. harm reduction programs, designed to mitigate drug harms, fail to recognize the health risks, including tiredness and sleep problems, related to the widespread use of energy drinks and other legal stimulants by youth (hardon and hymans ) . instead, such programs focus on risks of recreational drugs such as heroin, cannabis, and cigarettes and their potential for addiction (see also chapter ). however, since stimulant use for work and school is arguably a bigger problem than recreational use, as it takes place every working/school day and not only occasionally during free time, it is surprising that this area has been overlooked. this everydayness of use adds to the health risks. our field studies suggest that, to address these health risks, student and occupational health programs are needed to not only inform youth of the risks of using stimulants frequently but also to address the study demands and work conditions that give rise to the need for these drugs in the first place. academic cultures place high demands on students, normalizing night work. participating in stress-inducing academic cultures, working the night shift as security guards and club staff, and putting in long hours doing heavy labor on construction sites and in harbors-all of these fuel demands for energy drinks and amphetamines to stay alert, to have the stamina, and to feel the physical strength needed for the job. the tiredness and sleep problems experienced by our interlocutors need to be remedied by better work conditions, as pointed out by costa ( ) and wolf-meyer ( ) , who recommend that shift schedules should be designed to reduce stress and adverse effects on health, and to minimize circadian disruption, sleep deficits, and fatigue. sufficient time for recuperation after night shifts is needed, as is decent compensation for heavy and irregular work. workers engaged in hard, physical labor could be offered time to rest and provided with nutritious meals, rather than energy drinks, to fuel their bodies and give them time to recover. our study of young workers' situated chemical practices suggest that the widespread use of stimulants threatens to disrupt their circadian regimes even further, causing potentially severe metabolic disorders, especially when they use such products on a daily basis because they cannot afford to take a rest. daan kamps graduated from the research master's program in social sciences at the university of amsterdam. his current research interests lie in urban nightlife work, chronobiology, and drug use, which he studied as a researcher for the chemicalyouth project. for more than five years, he has been active within the amsterdam club circuit as a dj and event organizer, which provided him the opportunity to become familiar with the field (fig. . ). tait mandler carried out research in brooklyn, new york, on the lives of workers in queer nightlife spaces. their research explored the ways that workers use chemicals to get their jobs done and how they care for themselves and others (fig. . ). gideon lasco is a physician and medical anthropologist. he obtained his ph.d. from the university of amsterdam and his m.d. from the university of the philippines, where he currently teaches anthropology. his research examines the chemical practices of young people, the meanings of human height, the politics of health care, and the lived realities of the philippine "drug war." a palanca-winning essayist, he maintains a weekly column in the philippine daily inquirer, where he writes about health, culture, and society ( fig. . ) . ahsani amalia anwar was a researcher for the chemicalyouth project at the palawan studies center at palawan state university and conducted fieldwork on the social lives of energy drinks among physical laborers in indonesia. open access this chapter is licensed under the terms of the creative commons attribution . international license (http://creativecommons.org/ licenses/by/ . /), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the creative commons license and indicate if changes were made. the images or other third party material in this chapter are included in the chapter's creative commons license, unless indicated otherwise in a credit line to the material. if material is not included in the chapter's creative commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. bekerja versus bersenang-senang. social lives minuman berenergi pada pekerja fisik di makassar american meth: a history of the methamphetamine epidemic in america energy drink consumption and its association with sleep problems among u.s. service members on a combat deployment shift work and health: current problems and preventive actions the sociology of cognitive enhancement: medicalisation and beyond / : late capitalism and the ends of sleep adderall is definitely not a drug: justifications for the illegal use of adhd stimulants. substance use and misuse modernizing frontier: chemical transformations of young people's minds and bodies in puerto princesa passport: energy drinks in indonesiacontext. euromonitor international sharing and selling of prescription medications in a college student sample caffeine and exercise metabolism, endurance and performance guest editors' introduction: harm reduction from below the downside of uppers: chronobiology, stimulant use, and working in the nighttime leisure economy neurobiological mechanisms in the transition from drug use to drug dependence tamang tama: drug use in the everyday lives of male urban poor youth in a philippine port community (master's thesis) pampagilas: methamphetamine in the everyday economic lives of underclass male youths in a philippine port producing pleasure, minimizing harm producing pleasure: emotional labor and substance use in brooklyn's queer nightlife medical use, illicit use, and diversion of abusable prescription drugs methamphetamine. national institute on drug abuse energy drinks and binge drinking predict college students' sleep quantity, quality, and tiredness the role of retinal photoreceptors in the regulation of circadian rhythms caffeine: how caffeine created the modern world energy drinks: an emerging public health hazard for youth on speed: the many lives of amphetamine a comparison of contingency management and cognitive-behavioral approaches for stimulant-dependent individuals use of caffeinated energy drinks among secondary school students in ontario: prevalence and correlates of using energy drinks and mixing with alcohol life between clocks: daily temporal patterns of human chronotypes initiation of methamphetamine use among young thai drug users: a qualitative study extra joss energy drink boxes per package. shopee. https:// shopee.com.my/extra-joss-energy-drink- -boxes-per-package-i. caffeine use in sports: considerations for the athlete the world of caffeine: the science and culture of the world's most popular drug natural hegemonies sleep and the rhythms of american capitalism key: cord- -zjymmuuy authors: li, jun; long, yin; yang, fan; wang, xudong title: respiration‐driven triboelectric nanogenerators for biomedical applications date: - - journal: nan doi: . /eom . sha: doc_id: cord_uid: zjymmuuy as a fundamental and ubiquitous body motion, respiration offers a large amount of biomechanical energy with an average power up to the watt level through movements of multiple muscles. the energy from respiration featured with excellent stability, accessibility and continuality inspires the design and engineering of biomechanical energy harvesting devices, such as triboelectric nanogenerators (tengs), to realize human‐powered electronics. this review article is thus dedicated to the emerging respiration‐driven teng technology, covering fundamentals, applications, and perspectives. specifically, the human breathing mechanics are first introduced serving as the base for the developments of teng devices with different configurations. biomedical applications including electrical energy generation, healthcare monitoring, air filtration, gas sensing, electrostimulation, and powering implantable medical devices are then analyzed focusing on the design‐application relationships. at last, current developments are summarized and critical challenges for driving these intriguing developments toward practical applications are discussed together with promising solutions. [image: see text] respiration is a fundamental and ubiquitous body movement that serves as a critical metabolic process of body exchanging oxygen and carbon dioxide. besides, respiration is also a process of outputting work by converting chemical energy into mechanical energy, through the motion of intercostal muscles, lung muscles, and diaphragm. an average adult breathes at a normal rate of to times per minutes could provide a maximal power of up to the watt level, which is a significant biomechanical energy source in human body and is adequate to support many small electronics. [ ] [ ] [ ] [ ] if harvested effectively and appropriately, this energy source may allow us to bypass the bulky batteries in those electronics. more importantly, respiration is primarily an involuntary movement , (another typical one is heart beating) that consistently output biomechanical energy regardless of time and body status. it thus can be considered as a continuous and stable body energy source that other voluntary body movements (eg, muscle stretches from fingers, arms, legs, and feet , ) cannot compete with. compared to heart beating, the motion from respiration is more accessible and has a higher energy density. therefore, respiration could be the most appropriate biomechanical energy source for continuously powering wearable and implantable electronic devices to achieve % self-powered battery-free operation. among a number of mechanical energy harvesting principles, triboelectric nanogenerator (teng) stands out with its simple configuration, light weight, large power density, high energy conversion efficiency, and durability. [ ] [ ] [ ] [ ] [ ] [ ] [ ] the last decade has witnessed big advancements of teng from a basic concept to a well-established technology holding promises in a wide range of applications. [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] the broad selection of biocompatible materials, particularly those with a high flexibility and stretchability, for teng designs is an essential advantage for biomedical applications. for instance, tengs has been applied as active sensors for real-time healthcare monitoring through deciphering electrical signals into physiological information (eg, respiration, , heartbeats, , and blood pressure ). implantable tengs have been designed to generate μw-level electricity from regular body movements, which was sufficient to power implantable medical devices (imds) such as pacemakers. , intriguing interactions between teng and cell/tissue/organ activities , were also discovered enabling self-powered therapeutic stimulations. [ ] [ ] [ ] [ ] being aware of the unique advantages of biomechanical energy from respiration, a number of tengs prototypes were designed and demonstrated, based on which intriguing biomedical applications were implemented. although comprehensive review articles were published reporting the progress of teng, , , , , there is no focused review dedicating to respiration-driven teng technology. to fill this gap, this article provides an overview of respiration-driven teng and its biomedical applications. the driving mechanics from respiration are first introduced serving as the base for designing teng devices with different configurations. applications including electrical energy generation, healthcare monitoring, air filtration, gas sensing, electrostimulation, and powering imds are then reviewed focusing on the design-application relationships. at last, critical challenges for driving these intriguing developments toward practical applications are discussed together with potential solutions. breathing is a fundamental biological process that requires coordinated motions of different muscles with repeated constrictions and relaxations to realize the gas-exchange process ( figure a) . specifically, during inhalation, both the diaphragm and intercostal muscles between ribs contract leading to chest expansion, which increases the intrapulmonary volume of lung and decreases the intrapulmonary pressure down by to mm hg, forcing air in. in expiration, the relaxation of diaphragm and intercostal muscles decreases the intrapulmonary volume and increases pressure to to mm hg, and thereby moves air out of lungs. in the case of heavy breathing, the movement of abdomen is also involved. the mechanical energy associated with respirationrelated body motions has been well studied previously. [ ] [ ] [ ] to perform a respiration cycle, the body needs to overcome three major types of resisting forces, that is, elastic force of chest-lung system (p el ), air viscance and turbulence (p alv ) due to pressure gradient between the alveoli and the mouth, and non-elastic tissue deformation resistance (p def ) (deformation of tissue between lung surface and the alveoli) ( figure b ). results based on empirical studies showed that among the overall mechanical energy consumed in respiration, % is to overcome the elastic force, % is related to air resistance, and the remaining % is to deform tissues. to approximate the total biomechanical energy from respiration, first, the linear elastic force could be expressed as: where k is the elastance and v is the lung volume. together, p alv and p def are estimated as following: where (dv/dt) is the lung volume changing velocity and k and k are the constants. therefore, the total force required for a respiration is: assuming that the velocity of volume change is a sine wave, which is close in a real scenario, the output mechanical work per respiration could be calculated as: where v t and f referring to the tidal volume and respiration frequency, respectively. furthermore, expression of mechanical power could be deducted as according to equation ( ), given a reasonable respiration volume of l at a frequency of /min, it can be estimated that respiration of an average adult in a resting status could generate a power around mw. , for an air intake of l/min under normal activity, the power value could reach to approximately w. impressively, heavy and rapid breath could even produce a mechanical power up to w (at a frequency of /min and a maximal ventilation of l/min that an individual could perform). in general, there is a considerable power availability from respiration if one takes account of the energy consumption of common electronics. specifically, the sensor nodes have an power consumption at the nw or μw level. [ ] [ ] [ ] most implantable medical devices require a power supply in the range of μw to mw. [ ] [ ] [ ] even some portable electronics such as smart phone only demands w of power. this comparison revealed the promises of using biomechanical energy from human respiration for powering most biomedical electronic devices. all tengs operate through the coupling of contact electrification and electrostatic induction. , although teng embodies a plethora of configurations and structures, there are four common operation modes in general, that is, vertical contact-separation (cs), lateral in-plane sliding, single-electrode and freestanding mode, which have been comprehensively reviewed in a number of articles. [ ] [ ] [ ] , considering the specific motion patterns of respiration, to achieve high energy harvesting efficiency, most respiration-driven tengs were built based on the first two modes, that is, cs and sliding modes. as generally known, the electricity in a cs mode teng is generated by charge induction to balance the dynamic electrostatic field between triboelectric films that periodically separate and contact. the advantage of the cs mode is its high sensitivity to mechanical stimulus. however, the requirement of an air gap from separation raises engineering challenges for packaging and encapsulation. for a lateral sliding (ls) mode teng, the electricity is generated by creating potential and electron flow between two electrodes through in-plane displacing two triboelectric films back and forth. this mode is usually associated with enhanced output power compared to the cs mode especially when implementing a micrograting design; yet it requires larger area for operation. numerically, for a cs mode teng, the open-circuit voltage (v oc ) and short-circuit current (i sc ) can be expressed as: where l is the length, w is the width, σ is the charge density, d = d /ε + d / ε , d and d are the thickness, ε and ε are dielectric constants of dielectric films and , and velocity v(t) = dx/dt, respectively. analogously, v oc and i sc in the sliding mode can be expressed as a function of lateral displacement x(t) as: based on these equations, one could find that both modes have v oc and i sc related to variables due to mechanical stimuli (displacement or velocity of displacement). this relationship explains why simple deciphering the electricity signals of teng could obtain essential physiological information such as respiration rate (associated with v(t)) and respiration depth (associated with x(t)). as mentioned in previous section, the chest movement and air flow contribute to the majority of biomechanical energy from respiration at % and %, respectively. , therefore, two types of teng devices have been designed in response to this two types of mechanical energy ( figure c ). one type teng is an aeroelastic vibration device activated by air flow during breathing. this device is capable of being integrated with face masks that usually contain a triboelectric beam with either a cantilever (one-side fixed) or a bridge (two-side fixed) configuration. it works based on the effect of aeroelastic flutter due to the coupling of aerodynamic force and elastic deformation. [ ] [ ] [ ] [ ] [ ] [ ] specifically, when the energy of air flow exceeds the mechanical damping of the triboelectric beam, beam vibration could be sustained with a large amplitude that drives the beam to touch the package case, resulting in triboelectrification between the beam and the case. the amplitude of the triboelectric beam vibration under a respiratory airflow initially remains stable until the velocity of airflow exceeds a critical value. the critical flow speed at which destabilizing the aerodynamic effects is of interest for the design of the device. this speed u c could be simply estimated by balancing the bending forces (eh η/l ) with the aerodynamic forces (ρ f u η/l): where l is the length of beam, e is young's modulus, ρ f is the air density, h is the beam thickness, and η is the tilting angle. apparently, the critical velocity is related to the stiffness, geometry of the beam, and air density. once fluttering occurs, the flutter frequency is determined by the natural frequency of the beam that could be expressed as: where m is the mass per unit length, i is the moment of inertia of the beam, and λ i is a constant related to the modes of vibration. this equation applies to both cantilever beam and end-fixed beam yet λ i is much different between them. the first three constants of cantilever beam are exemplified, with λ = . , λ = . and λ = . . the flutter frequency should be equal to its lowest bending mode of natural frequency. moreover, the complete motion of the beam subjected to respiratory airflow could be given based on the euler-bernoulli equation considering the thin film structure: where l is the width of beam and Δp is the pressure difference on the two sides of beam due to airflow. , however, developing an analytical solution to this equation is complicated since the pressure difference is not constant during the vibration. overall, this type of device usually generates high-frequency electricity regardless of respiration rate as the frequency is determined by the natural frequency of triboelectric beam. another type teng device is motion triggered which is usually applied to the chest (thoracic respiration) or abdomen (abdominal respiration) to harvest energy from respiration. specifically, the regular constriction and relaxation of muscle due to respiration deform the device and make periodic displacement, either vertically or laterally (cs and ls modes, respectively), to generate triboelectric output. as exemplified in figure c , a ls-mode teng belt is wrapped around the chest. when air is inhaled, the chest expands and stretches the belt to pull the dielectric films apart from each other. when exhales, the chest contracts and the belt relaxes driving the films back to their original places. in response to this type of motion, the electrical output usually synchronizes with the respiration pattern at a low frequency. details of reported type i and type ii devices were compiled and compared in table . f i g u r e mechanics of respiration. a, schematics of muscle movement and air flow during inspiration (upper image) and expiration (bottom image). b, typical pressure-volume loop (one respiratory cycle) during breathing. p el , p def , and p alv are represented by the abscissal distance from the axis of ordinates to the diagonal, from the diagonal to the dashed curve, and from the dashed curve to the loop, respectively. c, schematics of two main types of respiration-driven teng that harvest energy from respiration at different locations. teng, triboelectric nanogenerator the triboelectrification effect could be found in almost all materials including polymers, ceramics, metals, and so on. based on the affinity to electrons, triboelectric series have already been established to serve as guidelines for designing tengs. , basically, a positively triboelectric material (low affinity to electrons) is usually paired with a negatively triboelectric material (high affinity to electrons) to enable the maximized output. however, regarding to harvesting biomechanical energy from human body, materials with tissue-compatible properties are more desired. for instance, metal thin film (such as gold, aluminum made by deposition) and low-modulus polymer film (such as polydimethylsiloxane [pdms], kapton, polytetrafluoroethylene [ptfe]) are usually exploited for building flexible/stretchable tengs. , [ ] [ ] [ ] in the consideration of wearability, tengs consisting of textile/fabric by weaving triboelectric yarns are developed. [ ] [ ] [ ] those yarns have core-shell structure with commercial threads (core) and coatings (shell) possessing strong electrostatic effects. another important material property is the biocompatibility, which must be taken account of when designing the implantable devices. , tengs will receive additional biocompatible encapsulations (mostly pdms) to avoid inflammatory reaction if they operate inside body. there are several strategies to enhance the triboelectrification effect in terms of materials selection and engineering. the surface of materials could be modified by physical techniques (such as photolithography and plasma etching) to create nano/micro patterns, which would enhance the surface area and thus the device output. , chemical methods including fluorinated surface, ion injection, sequential infiltration synthesis and molecular-targeting functionalization could also alter the surface properties and enable high performance. , in addition, compositing two or more pure materials such as embedding micro/nanomaterials into polymer matrix would effectively adjust the dielectric constant, and enhance the triboelectric performance of devices as well. , in general, clear understanding of the respiration mechanics together with triboelectric principles lays the foundation for the design and engineering of teng devices that could effectively convert respiration motions into continuous electricity for a variety of biomedical applications. the self-powering capability with other featured properties such as softness, flexibility, biosafety, and biocompatibility opens up many possibilities for tengs in biomedical engineering. hitherto, respiration-driven tengs have been implemented in a wide range of biomedical applications as a unique and self-sustainable electrical power/signal source. the applications mainly cover six directions including electrical energy generation, healthcare monitoring, air filtration, gas sensing, electrostimulation, and powering imds, which will be discussed in this section. the basic function of teng is to generate electrical energy from mechanical motions. both types of respiration energy from air flow and chest/abdomen movement have been actively investigated for teng designs for electricity generation. aeroelastic vibration devices capable of harvesting respiration energy were developed by multiple investigators. wang et al reported a device consisting of a triboelectric beam and acrylic frames. the bottom and top side frames were covered with ptfe and cu electrodes (figure a ), a kapton film covered by cu electrodes on both sides was fixed between the acrylic frames. finite element analysis (fea) simulation revealed the relationship between airflow and the vibration of the soft beam. six vibration modes and their corresponding natural frequencies were calculated, with the first-order and second-order modes corresponding to bending motion ( hz) and twisting motion ( hz) that determined the aeroelastic fluttering (twisting frequency higher than bending frequency) ( figure b ). under an airflow speed of m/s, this device output a high v oc over v at a frequency of hz ( figure c ). a maximum power output was estimated to be kw/m ( figure d ). driven by human breathing, output voltage and current can be up to v and μa under a loading resistance of . mΩ, respectively, resulting in an output power of . mw. a capacitor of μf could thus be charged from to . v in only . second. in another similar work, zheng et al demonstrated a cantilever structure with one fixed end. this device used a cu-covered acrylic film as the substrate and electrode-covered fluorinated ethylene propylene/polyvinylidene fluoride (pvdf) composite film as the cantilever beam ( figure e ). under an air flow speed of to m/s, the teng produced a low-frequency ( hz) voltage at -v level with a maximum of v at m/s ( figure f ). the significant frequency difference between this cantilever device and the above-mentioned bridge one is because of the different natural oscillation frequencies based on fixing types and beam materials. the output power of this teng could be up to . mw, where an extra power of . μw was contributed by the piezoelectric pvdf material. integrated with a face mask, this device could produce sufficient electricity ( v and . μa) to light green leds concurrently by harvesting energy from human breath. in a motion-triggered device for harvesting respiration energy, a cs mode teng (nylon and ptfe dielectric films with cu electrodes) was integrated with a belt through "z-shaped" connectors to be applied to the waist. during respiration, the decreased chest/abdomen circumference retracts connectors causing the full separation of polymer films, whereas expanded chest/abdomen during expiration stretches connectors to render dielectric pairs contact. this device on human volunteers produced a reasonable v oc of v yet a low current around . μa ( figure g ). the instantaneous power only reached a peak value of . μw ( figure h ). another similar belt reported by vasandani et al involved a cs teng with microstructures. it was able to charge a μf capacitor to . v in seconds when driven by respiration, corresponding to a power output at the nw level. these power values were significantly lower than those from aeroelastic devices, which were attributed to the coordinated low-frequency motions between the teng and the respiration rhythm ( . hz). in general, current respiration-driven tengs had a power output in the range of . μw to mw. although the chest movement contributes to the most mechanical energy, the motion-triggered devices exhibited significantly lower power output compared to the aeroelastic devices. considering the large amount of available energy from respiration, both types of devices need to be optimized to largely improve their biomechanical energy utilization rate and energy conversion efficiency. other useful strategies in teng designs for harvesting wind flow with high efficiency might be adapted for designing respiration-driven tengs with enhanced performance. respiration are closely associated with human health. electricity output of teng reflecting respiration characteristics thus may possess a great value for developing self-powered healthcare monitoring systems with potential applications for respiration behavior recognition, respiration rate and depth monitoring, and respiratory disease detection. , , [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] wang et al developed an intelligent wireless teng system to monitor the airflow during respiration. the operation of teng was based on aeroelastic fluttering of a flexible nanostructured ptfe (n-ptfe) thin film in an acrylic tube ( figure a) . it was found that the average values of voltage and current rose monotonically from . to . v and . to . μa, respectively, when the air flow rate increased from to l/min. this monotonic and sensitive response of teng to airflow rate enabled respiration monitoring. a mask built with the teng could provide distinguishing electric output features under different respiration patterns ( figure b) . specifically, slow breath in sleep induced low-frequency . v peaked at the middle of electrical envelop. rapid breath associated with exercise generated voltage envelop with a larger amplitude up to . v. shallow breath in a coma situation exhibited a much weaker voltage of only . v. deep breath was featured with a high voltage over v and the longest duration up to . seconds. therefore, human respiration behavior and related body status could be directly recognized based on the voltage patterns. based on this device, an intelligent wireless respiratory monitor and alert system was demonstrated. when the teng yielded voltage envelopes under normal breathing, active discrete square signal and zero switch signal was provided by the circuit (figure c ). once the breath pattern reached a critical situation (eg, no breath for more than seconds), an alarm would be triggered through a wireless module and a warning massage would be sent to the cell phone. an early intervention could be initiated to help the patient. instead of alerting at an emergency, zhang et al also proposed utilizing a similar teng device to build a human-machine interaction system to remotely manipulating appliances for disabled people by recognizing their breathing behaviors. a smart textile teng (t-teng) was developed by zhao et al to monitor respiration rate and depth. the t-teng was fabricated by direct weaving of cu-coated polyethylene terephthalate (cu-pet) warp yarns and polyimide (pi)-coated cu-pet (pi-cu-pet) weft yarns on an industrial sample weaving loom ( figure d ). the energy harvesting fabrics could generate electric output at the yarn crisscross intersections upon any mechanical displacement. a maximum v oc of v was reached. by directly integrating the fabrics into a chest strap, the rate and depth of respiration could be monitored in real-time ( figure e ). expansion and contraction of chest during respiration yielded a v oc at the . v level. counting the number of voltage peaks during a specific time interval, the respiration rate could be precisely deduced. furthermore, relationship between tidal volume v t and v oc was determined to be v t / v = oc , which allowed evaluation of respiration depth. other teng prototypes monitoring respiratory rate have also been reported. a soft band with a cs-mode teng was designed to work as a sheet without direct skin contact. with a high dynamic-pressure sensitivity of . v kpa − within a wide working range of kpa, this device could generate consistent electricity ( . v) when people lying on top of it. a respiration rate could also be directly obtained from the number of voltage peaks. a smart belt built with a sliding-mode teng and a wireless transmission chip was developed by zhang et al. the variation of the abdominal cavity circumference induced relative sliding of the triboelectric pair to generate voltage output. the electrical signal could be transmitted through a battery-powered wireless chip to a mobile phone in real time. through this device, the respiratory rate was precisely recorded when the person was lying, sitting, standing, and walking. in addition to respiration monitoring, the direct relationship between breath pattern and voltage output of tengs could be further used to detect obstructive sleep apnea-hypopnea syndrome (osahs), a respiratory disease due to upper airway obstruction during sleep. in this work, a conductive yarn composed of polyester and osahs, obstructive sleep apnea-hypopnea syndrome; teng, triboelectric nanogenerator stainless steel was enwrapped with silicone outer sheath to form the triboelectric fiber, with which a single-layered t-teng was fabricated ( figure f ). the t-teng exhibited a high sensitivity of . mv/pa at a wide frequency bandwidth ( - hz). being placed on a mattress as a bedsheet, this t-teng could record the real-time respiration rate once a patient was lying on top of it. unlike stable electrical signals from healthy person, the osahs patient had distinct blanks in the voltage patterns due to apnea caused by the narrowed airway ( figure g ). an osahs monitoring and intervention system was thus built based on this t-teng, which could identify the apnea episodes and provide a timely alarm to the patient for recovering the normal breath. in general, respiration-driven teng devices hold intriguing promises for respiratory healthcare monitoring with a few successful demonstrations. so far, the entire monitoring system usually consists of multiple modules including teng, signal processor, wireless transmission, signal receiver, and analyzer. these systems are bulky and not fully wearable, raising concerns for convenience and practicality. an all-in-one integrated wearable system with miniaturized size is desired. moreover, the accuracy of long-term monitoring as well as the stability of teng system should be further investigated particularly under real application environment. masks are an essential typical of personal protective equipment that filters hazardous particles including viruses from airborne, such as the covid- virus. , most particulate respirators have layered filters consisting of webs of nanofiber/microfiber to block particles while allow for air to go through. it is based on the mechanisms of gravitational settling, interception, diffusion, and electrostatic attraction. since triboelectrification is one of the common electrostatic phenomena, one could either use a teng to charge the filters or make filters as triboelectric pair to purify the air. [ ] [ ] [ ] liu et al. demonstrated a teng-based mask fully driven by respiration. the inlet of this mask had a cu film and electrospun pvdf (esp-pvdf) on a nonwoven substrate. a positive pressure from expiration pushed the cu film to make full contact with the esp-pvdf layer; while a negative pressure due to inspiration stretched the cu film back to separate from the esp-pvdf. this repeating process could generate and maintain the electrostatic charge on the fiber film ( figure a ). therefore, as large particles being removed by physical filtration through the porous structure, small particles were attracted and removed by electrostatic absorption. the teng-based mask showed almost the same efficiency as the mask only containing esp-pvdf at the initial stage ( . % particle removal rate). after minutes of continuous work, the tengbased mask showed a fairly stable removal efficiency, while this efficiency of non-teng masks were significantly reduced. particularly, for ultrafine particles ( nm to μm) the teng-based mask remained a . % to . % removal efficiency, while the value was dropped to only . % to . % for non-teng masks ( figure b) . impressively, the teng-based mask maintained a removal efficiency over . % for particles below . μm and over . % for particles over μm for days ( figure c ), illustrating high removal efficiency and great durability. although using teng might significantly enhance the electrostatic adsorption, a disadvantage of this electrostatic mask is that the static charge could fluctuate considerably and would be easily affected by multiple factors including temperature, humidity, and air speed. particularly, since the exhaled air from respiration contains high humidity, it could largely undermine the electrostatic charge generation capability. to make this intriguing development practical, it is necessary to design and engineer a teng device that can maintain a high performance with minimal impacts from environmental factors. because the absorption of gas molecules on the triboactive material surfaces could change its electrical properties (such as permittivity), the electrical output of teng would vary upon gas molecule absorption. therefore, by utilizing gas-responsive materials as the dielectric materials for charge generation, teng could be designed for gas sensing without the need of additional power. [ ] [ ] [ ] [ ] wang et al developed a respiration-driven teng system that could detect trace-level nh in the exhaled air. nh is a biomarker for diagnosing certain diseases (such as ulcers). this system contained an elastic balloon and a cs-mode teng consisting of nanostructured pdms and ce-doped zno-polyaniline nanocomposite films ( figure d ). the balloon was used to store the exhaled air and then to push the air to activate the teng. thus, a high sensitive to components in the exhaled air could be achieved. the output voltage monotonously decreased as the concentration of nh increases. this teng exhibited a good sensitivity ( . ppm − , r = . ) when exposed to trace-level nh with a concentration from . to ppm ( figure e ). an excellent selectivity was also observed to nh with a significantly higher response value of . compared to other gases at . - . . by using wo as the gas-responsive material, su et al made an alveolus-shaped teng sensor possessing a high sensibility toward no , which is the cause of pulmonary edema and respiratory diseases ( figure f ). the gas inflation and deflation due to respiration could enable the cs between the latex film and the sensitive wo film, f i g u r e filtration and gas sensing by respiration-driven tengs. a, schematic of a teng-based smart mask filtering particles and its working mechanism. inset is an sem image of pvdf-esnf. b, removal efficiencies of pvdf-esnf and teng masks. c, durability test on removal efficiency of the smart mask integrated with teng after days. reproduced with permission: copyright , the american chemical society. d, schematic illustration of a respiration-driven teng sensor. e, response-nh concentrations fitting curve of the teng. inset is the selectivity of teng to nh and other interference gases. reproduced with permission: copyright , elsevier. f, a digital image of a gas-sensing teng. inset is the schematic of the alveolus-inspired teng. g, selectivity of the teng to no and other interference gases. h, response-no concentrations fitting curve of the teng. reproduced with permission: copyright , the american chemical society. esnf, electrospun nanofiber film; pvdf, polyvinylidene fluoride; teng, triboelectric nanogenerator and generate electricity. a high response of . % and linearity of . were achieved when this sensor was exposed to ppm of no ( figure h ). in addition, the response toward no was over times higher than those from other gases such as co, h s, so , nh , and co ( figure g ), indicating an excellent selectivity. another alcohol analyzer was developed by using teng as the power source. instead of directly detecting the adsorbed gas molecules, wen et al utilized a respirationdriven sliding-mode teng to power a gas sensor for alcohol sensing. in this design, the solid-state sensor could be selected and design more independently to teng material selection. still powered by respiration energy, this tandem system achieved a high detection gas response of , fast response time of seconds, and recovery time of only seconds. compared to other applications, gas sensing of teng is largely immature. although a few good gas sensing phenomena of respiration-driven teng have been demonstrated, the general performance is still not comparable to regular solid state sensors. one key limitation is the selection of the gas-sensitive materials, which are typically not strong for triboelectric charge generation. since it is mostly used on human, several additional issues such as flexibility, biocompatibility, durability, and wearability also need to be investigated and improved. stimulation and activation of certain cells, organs and systems in human body by low-dose electricity have long been demonstrated. [ ] [ ] [ ] [ ] [ ] [ ] the periodic biphasic pulselike electrical signals generated from teng were also found capable of modulating cell activities, such as accelerating proliferation, adjusting orientation, stimulating motility, and improving differentiation. , therefore, the all-time accessible respiration energy guarantees a continuous operation of teng to provide consistent electric pulses for therapeutic electrostimulation. long et al fabricated a respiration-activated electrotherapy bandage consisting of a sliding-mode teng and a pair of dressing electrode to accelerate skin wound healing. the teng was made by overlapping the metal/ptfe layer with another metal layer on different sides of the pet substrate ( figure a ). when wrapping the device around the chest area of a sprague dawley rat, the expansion and relaxing of chest drove the ptfe layer sliding back and forth and provided a potential of . v between the dressing electrodes. the accelerated wound recovery was hypothesized based on the endogenous electric field effect on wound site recovery ( figure b ). the disruption of transepithelial potential enhanced the endogenous electric field at the wounded area for epithelial cells to initiate directional migration into the dermal wound bed until the skin regeneration process was completed. to demonstrate the accelerated wound healing process, a proximal wound was created on the rat and the two dressing electrodes were aligned over the wound. after days, the wound exposed to an electric field was nearly closed (figure c ), whereas the control wound was still largely open. quantitative study revealed that in the presence of electric fields, the wound reduced rapidly and reached a nearly complete closure ( % ± . %) within the first hours. without the electric field, the wounded area slowly reduced to % within the first hours ( figure d ). microscopy study of living fibroblasts showed that the electric field generated by teng could facilitate the fibroblasts differentiating into myofibroblasts, thereby providing a contraction force for wound closure. additionally, several important growth factors for wound recovery, such as transforming growth factor beta, epidermal growth factor (egf), and vascular egf, all showed enhanced expressions in tengstimulated tissues. this self-stimulated electrotherapy for wound healing could have large impacts on a range of related diseases (eg, raynaud's disease) and may resolve cosmetic concerns, such as chickenpox scars, acne, keloid scarring, or rosacea. one deficiency might be that this motiontriggered device delivered electricity with a frequency controlled by the respiration rate. clinical applications of electrotherapy may require an optimal combination of frequency and amplitude to deliver desired treatment. this discrepancy is very challenge to address in current motion-triggered teng designs. most current imds consume energy in the range of μw to mw, while the available energy from respiration could reach up to the watt level. owing to the capability of continuous electrical energy generation, respirationdriven teng may serve as a unique self-sustainable electric power supply for imds eliminating the bulky and rigid chemical batteries. diaphragm moves in a relatively large distance and involuntarily all day around. it is thus considered an ideal in vivo site for biomechanical energy supply. in this regard, li et al developed an ultrasoft and stretchable implantable sliding mode teng with higher output current and larger amounts of transported charge compared to cs-mode tengs. this teng had a micrograting electrode design with a multilayered structure, including two symmetric electrode layers and one mobile layer for electrification (middle layer), packaged by ecoflex elastomer ( figure a ). each electrode layer consisted of cu/cr interdigital electrodes (ides) deposited on a flexible pet substrate covered by a thin layer of ptfe. the middle mobile layer was comprised of a central pet film sandwiched between two ptfe film where cu/cr metal strips were deposited. in a typical micro-grating configuration, individual fingers of ides had a width of to μm (a ) with a length of cm (a ) and separated by a gap of μm (a ). the width (b ) and gap (b ) of metal strips in the middle layer were reconfigured accordingly following the relations: a = b ; and b = a + a . a central cavity was created inside encapsulation materials to ensure the free move of middle layer when the device was strained. this cavity design also significantly lowered the device's young's modulus to kpa, which was comparable to many soft tissues. when implanted in abdomen of a rat by connecting to the diaphragm, this teng could function as a battery-free direct current micropower supply ( figure b ). during normal breath, the up and down movement of diaphragm periodically stretched and relaxed the device, leading relative sliding of the center layers to produce groups of electric spikes ( . v measured at mΩ) as shown in figure c . when connected through a set of rectifier and capacitor, a led could be continuously and stably lighted up by the anesthetized rat at a breath rate of /min after experiencing a short charging period ( - seconds) ( figure d ). this result successfully demonstrated the feasibility of continuously powering a small electronic device solely by harvesting biomechanical energy. as one of the most important and broadly used imds, cardiac pacemaker consumes electrical energy of - μw, which is within the range of typical teng outputs. zheng et al. demonstrated the promises of powering a pacemaker by a respiration-driven teng. such a selfpowered pacemaker prototype was built by integrated a cs-mode teng with a pacemaker through a rectifying bridge and a capacitor. the teng was fabricated from a microstructured pdms film and an al foil. the teng device was either implanted under the chest skin or fixed in between the diaphragm and the liver. when the rat was in anesthesia, the device positioned on chest produced an ac electricity of ± v and ± . μa at a fast respiration rate of hz. the one placed under diaphragm output higher current up to . μa ( figure e ) at a lower respiration rate ( . hz). through the full-wave rectifying bridge, a μf capacitor was charged from to v within minutes by a teng in vitro (equivalent to breathing cycles if implanted under chest). this amount of electrical energy was used by the pacemaker to generate heart stimulation pulses at various f i g u r e electrostimulation by respiration-driven tengs. a, schematic of a teng-driven electrostimulation device for wound recovery. insets are a digital image of device (left bottom) and a rat wearing the device (right top), respectively. b, wound-healing mechanism under endogenous electric field. c, digital images of the healing process with and without the teng electric filed. d, wound area as a function of time with (experiment) and without the teng electric filed (control). reproduced with permission: copyright , the american chemical society. teng, triboelectric nanogenerator frequencies from to hz to regulate the heart rates of the rat ( figure f ). in general, the respiration-driven teng holds great promises as a self-sustainable power source for imds. however, the few preliminary studies are still very far away from clinical applications. many more fundamental developments including packaging, long-term impact to respiration, stability of electricity output, and power management and regulation need to be investigated to support future clinical studies. other technologies such as peng [ ] [ ] [ ] [ ] [ ] and electromagnetic generator (emg) [ ] [ ] [ ] [ ] [ ] have the capability of harvesting respiration energy and realize self-powered biomedical system as well. however, the tengs still stands out with unique merits. table compiles detailed information of each technology. apparently, teng has outperformed peng in terms of maximal power and energy conversion efficiency, although they have quite similar properties in other aspects (such as weight and size). the concurrent teng driven by human respiration could achieve . mw output, which was over times higher than that of peng. tengs possess huge advantages over emgs when the device volume and weight are critical, because they have close maximal power. the new generation of biomedical devices has the trend toward miniaturization and light weigh where the emgs could hardly be competent. while the majority of biomedical devices are still powered by batteries with rigid encapsulation, the batteries could contribute up to % weight or volume of the e, current output of a teng from diaphragmatic movement. inset is the teng sutured on diaphragm. f, stimulation of rat heart by a pacemaker powered by the teng in vitro. reproduced with permission: copyright , wiley-vc. imds, implantable medical devices; teng, triboelectric nanogenerator entire device. , despite the emergence of flexible/ stretchable batteries opening up possibilities for wearable and implantable bioelectronics, [ ] [ ] [ ] [ ] [ ] [ ] other potential issues including electrode delamination during deformation and leakage of toxic electrolyte still raise concerns for its practical applications. , moreover, taking account of imds, the replacement of or recharging the batteries requires substantial surgical or technical efforts, introducing additional suffering and complexity (infections and inflammations) to the patients. on the contrary, smaller, lighter, safer, and more effective and durable tengs with constant output exhibit great promise in broad biomedical applications. this article provides an overview of respiration-driven teng from both fundamental and application perspectives. it is well recognized by the community that the energy from respiration is sufficient and accessible, which can consistently fuel teng devices to achieve versatile biomedical applications, such as electrical energy generation, healthcare monitoring, air filtration, gas sensing, electrostimulation, and powering imds. as summarized in figure a , due to the best accessibility, % respirationdriven tengs were designed for chest and mouth/nose operation. among all application demonstrations, healthcare monitoring is the mostly studied application (> %) primarily because that respiration is an important physiological indication closely associated with multiple health problems ( figure b ). despite the exciting earlystage demonstrations of respiration-driven tengs, there exist a few critical challenges that need to be addressed to fulfill their promising role in practical applications. although theoretical calculations and in-lab studies have shown a high power density (up to kw/m ) and high energy conversion efficiency ( %) of teng, respirationdriven tengs only output an electrical power in the range of . μw to mw. given the available respiration energy of an average adult is . to w, the so far achieved energy conversion efficiency was less than %. the most likely reason was related to the low mechanical energy utilization. although all tengs utilized flexible polymers, the device modulus was still orders of magnitudes higher than that of body tissues. designing tengs with tissuecomparable mechanical properties may maximize the mechanical displacement in response to respiration actions and thus reduce the mechanical energy loss. . long-term device accuracy and stability. triboelectrification as a typical electrostatic phenomenon could be easily affected by the ambient environment, particularly temperature and humidity. though researchers have claimed that some specific designs of teng could work under a wide range of humidity and temperature, the long-term effect of these elements on the performance of respiration-driven teng (such as accuracy of monitoring and sensing) has not been systematically studied. appropriate packaging strategies without affecting device performance should be developed to isolate the functional component of a teng from the environment. meanwhile, the durability of the teng due to mechanical and chemical damage during friction should be considered simultaneously. . interference with other body movement. teng can pick up movements from all sensible body actions, which may result in interference with the electrical signals from respiration and lead to wrong conclusions. for a respirator monitoring teng placed on chest, large movements from arms could also induce chest motions and make teng to respond. this additional electrical signal would interfere the electrical signal for respiration rate or depth monitoring. how to differentiate the target signal from other interferences is critical for the achieving accurate sensing and monitoring. a potential solution might rely on advanced algorithms to filter interference and extract targeted data. . all-in-one self-powered system. at last but not least, while teng is a small and flexible membrane-like device, the entire biomedical electronic system may contain many other modules for signal processing, transmission, receiving, and analyzing. operation of multiple modules still require extra power supplies, and thus diminishes the meaningfulness of achieving a self-powered biomedical application. how to design an all-in-one miniaturized system that is fully integrated with and powered by a teng device is of great significance as well as a great engineering challenge. this challenge is also beyond respiration-driven tengs and is applicable to all other implantable energy harvesting devices for powering imds. above critical challenges need short or long-term dedicated research efforts from multiple disciplines, including material science, mechanical engineering, electrical engineering, and of course biomedical engineering. nevertheless, owing to its unique advantages, respiration-driven teng technology will likely play a significant role in the next generation power sources for a wide range of biomedical applications. human-powered wearable computing high-performance piezoelectric energy harvesters and their applications proceedings of the ieee international symposium on electronics and the environment energy harvesting from human and machine motion for wireless electronic devices control of human inspiratory motoneurones during voluntary and involuntary contractions effects of lung volume and involuntary breathing movements on the human diving response mechanisms of voluntary movement neural control of voluntary movement initiation triboelectric nanogenerators as new energy technology for self-powered systems and as active mechanical and chemical sensors progress in triboelectric nanogenerators as a new energy technology and self-powered sensors triboelectric nanogenerators as new energy technology and self-powered sensors-principles, problems and perspectives triboelectric nanogenerators as a new energy technology: from fundamentals, devices, to applications triboelectric nanogenerator: a foundation of the energy for the new era recent progress on flexible triboelectric nanogenerators for selfpowered electronics chemical modification of polymer surfaces for advanced triboelectric nanogenerator development flexible triboelectric generator non-contact cylindrical rotating triboelectric nanogenerator for harvesting kinetic energy from hydraulics effective anti-biofouling enabled by surface electric disturbance from water wave-driven nanogenerator a highly sensitive, self-powered triboelectric auditory sensor for social robotics and hearing aids sequential infiltration synthesis of doped polymer films with tunable electrical properties for efficient triboelectric nanogenerator development research update: materials design of implantable nanogenerators for biomechanical energy harvesting nanogenerator for biomedical applications a paper triboelectric nanogenerator for self-powered electronic systems single-electrode triboelectric nanogenerator for scavenging friction energy from rolling tires machine-washable textile triboelectric nanogenerators for effective human respiratory monitoring through loom weaving of metallic yarns expandable microspherebased triboelectric nanogenerators as ultrasensitive pressure sensors for respiratory and pulse monitoring self-powered pulse sensor for antidiastole of cardiovascular disease triboelectric nanogenerator enabled body sensor network for self-powered human heart-rate monitoring self-powered, one-stop, and multifunctional implantable triboelectric active sensor for real-time biomedical monitoring in vivo powering of pacemaker by breathing-driven implanted triboelectric nanogenerator symbiotic cardiac pacemaker triboelectric nanogenerator accelerates highly efficient nonviral direct conversion and in vivo reprogramming of fibroblasts to functional neuronal cells self-powered implantable electrical stimulator for osteoblasts' proliferation and differentiation investigation of low-current direct stimulation for rehabilitation treatment related to muscle function loss using self-powered teng system self-powered direct muscle stimulation using a triboelectric nanogenerator (teng) integrated with a flexible multiple-channel intramuscular electrode effective weight control via an implanted self-powered vagus nerve stimulation device self-activated electrical stimulation for effective hair regeneration via a wearable omnidirectional pulse generator triboelectric nanogenerators: fundamental physics and potential applications reviving vibration energy harvesting and self-powered sensing by a triboelectric nanogenerator human form, human function: essentials of anatomy & physiology mechanics of breathing in man mechanics of respiration the energy cost (work) of breathing improving power output for vibration-based energy scavengers paper presented at: vlsi circuits and systems ii comparison of energy harvesting systems for wireless sensor networks kinetic and thermal energy harvesters for implantable medical devices and biomedical autonomous sensors power approaches for implantable medical devices proceedings of the world congress on engineering usenix annual technical conference polymer-based nanogenerator for biomedical applications theoretical study of contact-mode triboelectric nanogenerators as an effective power source theory of sliding-mode triboelectric nanogenerators flutter-driven triboelectrification for harvesting wind energy aeroelastic flutter energy harvesters self-polarized by triboelectric effects flow-induced snap-through triboelectric nanogenerator a nanogenerator for harvesting airflow energy and light energy a flutter-effect-based triboelectric nanogenerator for breeze energy collection from arbitrary directions and self-powered wind speed sensor an aeroelastic flutter based triboelectric nanogenerator as a self-powered active wind speed sensor in harsh environment fluid-flow-induced flutter of a flag formulas for natural frequency and mode shape aeroelastic instability of cantilevered flexible plates in uniform flow fluttering flags: an experimental study of fluid forces elastoaerodynamics-driven triboelectric nanogenerator for scavenging air-flow energy concurrent harvesting of ambient energy by hybrid nanogenerators for wearable self-powered systems and active remote sensing air-flow-driven triboelectric nanogenerators for self-powered real-time respiratory monitoring breath-based human-machine interaction system using triboelectric nanogenerator waist-wearable wireless respiration sensor based on triboelectric effect triboelectric nanogenerator using microdome-patterned pdms as a wearable respiratory energy harvester stretchable-rubber-based triboelectric nanogenerator and its application as self-powered body motion sensors single-layered ultra-soft washable smart textiles for all-around ballistocardiograph, respiration, and posture monitoring during sleep a portable triboelectric nanogenerator for real-time respiration monitoring implanted battery-free direct-current micro-power supply from in vivo breath energy harvesting a semi-quantitative tribo-electric series for polymeric materials: the influence of chemical structure and properties single-electrode triboelectric nanogenerators based on sponge-like porous ptfe thin films for mechanical energy harvesting and self-powered electronics triboelectric touch-free screen sensor for noncontact gesture recognizing base-treated polydimethylsiloxane surfaces as enhanced triboelectric nanogenerators washable textile-structured single-electrode triboelectric nanogenerator for self-powered wearable electronics highly stretchable d fabrics for wearable triboelectric nanogenerator under harsh environments micro-cable structured textile for simultaneously harvesting solar and mechanical energy study of long-term biocompatibility and bio-safety of implantable nanogenerators biocompatibility and in vivo operation of implantable mesoporous pvdf-based nanogenerators transparent triboelectric nanogenerators and self-powered pressure sensors based on micropatterned plastic films nanopillar arrayed triboelectric nanogenerator as a self-powered sensitive sensor for a sleep monitoring system formation of triboelectric series via atomic-level surface functionalization for triboelectric energy harvesting enhancing performance of triboelectric nanogenerator by filling high dielectric nanoparticles into sponge pdms film surface texturing and dielectric property tuning toward boosting of triboelectric nanogenerator performance membrane-based self-powered triboelectric sensors for pressure change detection and its uses in security surveillance and healthcare monitoring noncontact heartbeat and respiration monitoring based on a hollow microstructured selfpowered pressure sensor self-powered nanofiber-based screen-print triboelectric sensors for respiratory monitoring can n respirators be reused after disinfection? how many times? rational use of face masks in the covid- pandemic on the minimum efficiency and the most penetrating particle size for fibrous filters triboelectric nanogenerator enhanced nanofiber air filters for efficient particulate matter removal removal of particulate matter emissions from a vehicle using a self-powered triboelectric filter washable multilayer triboelectric air filter for efficient particulate matter pm . removal self-powered electrostatic adsorption face mask based on a triboelectric nanogenerator a facile respiration-driven triboelectric nanogenerator for multifunctional respiratory monitoring alveolus-inspired active membrane sensors for self-powered wearable chemical sensing and breath analysis an integrated flexible selfpowered wearable respiration sensor blow-driven triboelectric nanogenerator as an active alcohol breath analyzer low intensity transcranial electric stimulation: safety, ethical, legal regulatory and application guidelines noninvasive brain stimulation with low-intensity electrical currents: putative mechanisms of action for direct and alternating current stimulation directly applied low intensity direct electric current enhances peripheral nerve regeneration in rats low-intensity electromagnetic and mechanical modulation of bone growth and repair: are they equivalent? transcutaneous electrical nerve stimulation the application of nanogenerators and piezoelectricity in osteogenesis self-powered electrical stimulation for enhancing neural differentiation of mesenchymal stem cells on graphene-poly ( , -ethylenedioxythiophene) hybrid microfibers effective wound healing enabled by discrete alternative electric fields from wearable nanogenerators development of a piezoelectric polyvinylidene fluoride (pvdf) polymer-based sensor patch for simultaneous heartbeat and respiration monitoring flexible piezoelectric nanogenerator in wearable self-powered active sensor for respiration and healthcare monitoring design of an ultrasensitive flexible bend sensor using a silver-doped oriented poly (vinylidene fluoride) nanofiber web for respiratory monitoring pvdf microbelts for harvesting energy from respiration an active self-driven piezoelectric sensor enabling real-time respiration monitoring paper presented at: active and passive smart structures and integrated systems xii paper presented at: th annual international conference of the paper presented at: iecon - th annual conference on ieee industrial electronics society paper presented at: ieee power and energy conference at illinois annual international conference of the ieee engineering in medicine and biology society mechanical efficiency of breathing a review on heat and mechanical energy harvesting from human-principles, prototypes and perspectives mechanical work of breathing during exercise in trained and untrained subjects flexible, solid electrolyte-based lithium battery composed of lifepo cathode and li ti o anode for applications in smart textiles progress in flexible lithium batteries and future prospects self-weaving sulfur-carbon composite cathodes for high rate lithium-sulfur batteries bendable inorganic thin-film battery for fully flexible electronic systems flexible and biocompatible high-performance solid-state micro-battery for implantable orthodontic system decoupling of mechanical properties and ionic conductivity in supramolecular lithium ion conductors batteries used to power implantable biomedical devices. electrochim acta issues and challenges facing flexible lithium-ion batteries for practical application flexible rechargeable lithium ion batteries: advances and challenges in materials and process technologies his current research interests include understanding the coupling effect between piezoelectric polarization and semiconductor functionalities; developing advanced nanomaterials and nanodevices for mechanical energy harvesting from human activities and ambient environment; and studying the growth mechanisms and developing assembly techniques of oxide nanostructures. he is the author of more than publications and holds more than patents on oxide and piezoelectric materials processing and applications.how to cite this article: li j, long y, yang f, wang x. respiration-driven triboelectric nanogenerators for biomedical applications. ecomat. ; - . https://doi.org/ . /eom . key: cord- -klvx g authors: tayfuroglu, omer; yildiz, muslum; pearson, lee-wright; kocak, abdulkadir title: an accurate free energy method for solvation of organic compounds and binding to proteins date: - - journal: biorxiv doi: . / . . . sha: doc_id: cord_uid: klvx g here, we introduce a new strategy to estimate free energies using single end-state molecular dynamics simulation trajectories. the method is adopted from ani- ccx neural network potentials (machine learning) for the atomic simulation environment (ase) and predicts the single point energies at the accuracy of ccsd(t)/cbs level for the entire configurational space that is sampled by molecular dynamics (md) simulations. our preliminary results show that the method can be as accurate as bennet-acceptance-ration (bar) with much reduced computational cost. not only does it enable to calculate solvation free energies of small organic compounds, but it is also possible to predict absolute and relative binding free energies in ligand-protein complex systems. rapid calculation also enables to screen small organic molecules from databases as potent inhibitors to any drug targets. the life cycle of the virus as many other viruses has an essential proteolytic auto-processing step. - the cl-protease takes an important role in freeing individual functional proteins from single-chain polyprotein that has been translated by the host cell translation machinery. interfering to this step has been shown to have capability of inhibiting virus replication. therefore, cl-protease is one of the valid and most attractive drug targets for covid- treatment. developing a drug molecule from scratch for curing a disease is quite expensive and time consuming. instead, repurposing an fda approved drug is a much faster and less expensive strategy since the time is very critical parameter in controlling such invasive viruses. even testing all fda approved drugs experimentally one by one may cause intolerable waste of the time. to help to ease the problem, computational calculations can be very handy. there have already been several computational studies about predicting an efficient fda approved drugs that can be repurposed for covid- . [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] in searching for drug candidates as inhibitors, there are two core questions that can be addressed: (a) what is the binding mode? (i.e. where does it bind from the enzyme?) (b) what is the binding affinity? (binding free energy). inhibition of an enzyme can be involved in various mechanisms. for instance, an inhibitor can bind to the enzyme from the active site in the absence of substrate (competitive inhibition) forming an additional or it can bind in the presence of the substrate (i.e. enzyme-substrate complexed) from the allosteric site (uncompetitive inhibition). alternatively, it can reduce the activity of the enzyme by binding from allosteric site of the enzyme either free or complex (non-competitive inhibition). in all these mechanisms the equilibrium constant, k s belonging to the reaction between the enzyme and substrate is shifted towards the reactants by existing inhibitor in the media. kinetic studies to understand the activity loss of the enzyme on substrate by the inhibitor report values such as inhibition equilibrium constant, k i or half maximal inhibitory concentration, ic . both these experimental parameters are proportional (they are equal in special cases). thermodynamic equilibrium constant k i is related to the standard binding gibbs free energy of the system by: the Δg o can also be calculated from the thermodynamic potentials. thus, it is possible to compare experimental Δg o determined from k i and theoretical Δg o predicted by thermodynamic potentials using computational methods. however, logarithmic relation between the k i and Δg o complicates the reliability of the calculations. an error of - kcal is acceptable for the most computations, but this makes thousands of times less efficient inhibitor. therefore, most computational methods fail to estimate the experimental binding affinity trend (relative binding free energies) among the inhibitors. reproducing the absolute standard free energies of binding is even more difficult for the computational methods. moreover, a trade-off between the computational accuracy and speed must be made. however, almost all of the studies screen databases listing the fda approved drugs at the molecular docking level, which is mostly based on geometrical alignment of a ligand into a binding pocket, namely the active site of c-like protease ( cl pro ). despite the speed of docking approach, they are very coarse methods and almost never predict the correct experimental binding affinity trend among the inhibitors. [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] more sophisticated methods to calculate the potential binding free energy of inhibitor candidate to the protein ranges from post molecular dynamics simulations such as molecular mechanics poisson-boltzmann surface area (mmpbsa) [ ] [ ] [ ] [ ] to perturbation methods such as bennett acceptance ratio (bar), - the latter being much more accurate. [ ] [ ] [ ] are also commonly used and proven to be sufficiently accurate in estimating solvation free energies along with relative and absolute binding free energies. however, all these methods require very high computational cost. screening all the drug candidates using these methods may not be very practical. for a typical free energy of binding, these methods require at least λ-states for the decoupling of l from pl complex and another that many for decoupling l from water (i.e. solvation free energy of ligand), which increases the computational cost by -folds. machine learning (ml) techniques have attracted a great interest for the past decade due to their successful algorithms to scientific questions including but not limited to chemical reactions, [ ] [ ] potential energy surfaces, [ ] [ ] [ ] [ ] forces, - atomization energies, - and proteinligand complex scorings. . one of the most promising aspects of the ml techniques is that the trained models can be applied to new systems (transferrable). recently several models using active learning such as ani- , ani- x and ani- cxx here, we introduce a new strategy to estimate free energies of solvation of small organic compounds and binding to proteins in explicit solvent using single end-state md simulations. the method is adopted from ani- ccx neural network potentials (machine learning) for the the insertion of the ligand to an environment of solvent (solvation free energy) or receptor (binding free energy) can be defined by a coupling parameter, λ. at each λ-state, the potential energy of the system would be: where v is the interaction energy between the ligand and environment. ܷ is the reference potential energy, which includes all energy terms except for the ligand-environment interaction. the partition function is; where f is the free energy depending on λ-state. re-organizing the above equation, the equation above is only valid when the ligand-environment interaction is proportional to coupling term λ. this results in; in the limiting case, this equation yields as; the equation implies that the free energy change is nearly half-the potential between the ligand-environment interaction in the complex configurational ensemble. for the binding studies, the protein-ligand complex (~ atoms) was placed in the center of a dodecahedron box. for the solvation studies, the ligand was placed in the center of a cubic box. each system was solvated in the tip p model type water energy minimization was carried out to a maximum kj.mol - .nm - force using verlet cutoff scheme. for both long range electrostatic and van der waals interactions, a cutoff length of Å was used with the particle mesh ewald method (pme) ( th order interpolation). the neighbor list update frequency was set to ps - . as with our earlier studies, [ ] [ ] a stepwise energy minimization and equilibration schemes were used. each minimization step consisted of a cycle of steepest descent and a subsequent cycles of l-bfgs integrators. after minimization, each system was equilibrated within three steps using langevin in order to test the ml-qm method, we run -ns md simulations for the molecules whose solvation free energies have been extensively studied. we first built a system in which the ligand is replaced in the center of box and the box is solvated with just single water molecule. the ligands studied are given in figure . we prepared other independent simulations in which we increased the number water molecules (nh o) in the box. each time the average ml-qm energies were almost . this has been the case until nh o= . figure a shows the interaction energy between the ligand and water molecules calculated by ml-qm energy difference: is the total energy of the system including ligand and water. are the energies of free ligand and free water molecules, respectively, which have been calculated by extracting from the trajectory of complex structure. when we kept adding more water in the system and running other md simulations, we found that starting from nh o= , the system undergoes from the unbound state to bound state by a drastic energy jump after ~ . ns. the degree of freedom for the water molecules in the bound state must be it is apparent that the ml-qm interaction energy is constant for the simulations with more than sufficient waters exist. the empirically determined linearity constant is α = / , thus the free energy change is approximately half of the interaction energy between the ligand and environment. however, considering the experimental conditions are more or less similar, the energy profile (i.e. the trend among the inhibitors) should at least be reproduced. here, we see that ml-qm is the most accurate method to yield the correct trend among the compared methods ( figure ). a novel coronavirus from patients with pneumonia in china coronavirus main proteinase ( cl pro ) structure: basis for design of anti-sars drugs virus-encoded proteinases and proteolytic processing in the nidovirales conservation of substrate specificities among coronavirus main proteases crystal structure of sars-cov- main protease provides a basis for design of improved α -ketoamide inhibitors in silico study the inhibition of angiotensin converting enzyme receptor of covid- by ammoides verticillata components harvested from western algeria state-of-the-art tools to identify druggable protein ligand of sars-cov- molecular docking analysis of n-substituted oseltamivir derivatives with the sars-cov- main protease drug repurposing for coronavirus (covid- ): in silico screening of known drugs against coronavirus cl hydrolase and protease enzymes reverse vaccinology approach to design a novel multi-epitope vaccine candidate against covid- : an in silico study repurposing of known anti-virals as potential inhibitors for sars-cov- main protease using molecular docking analysis covid- spike-host cell receptor grp binding site prediction virtual screening and repurposing of fda approved drugs against covid- main protease molecular docking analysis of selected natural products from plants for inhibition of sars-cov- main protease molecular docking analysis of withaferin a from withania somnifera with the glucose regulated protein (grp ) in comparison with the covid- main protease ligand binding free energy and kinetics calculation in an intuitive look at the relationship of k-i and ic : a more general use for the dixon plot the mm/pbsa and mm/gbsa methods to estimate ligand-binding affinities a. g_mmpbsa-a gromacs tool for high-throughput mm-pbsa calculations a comparative linear interaction energy and mm/pbsa study on sirt -ligand binding free energy calculation revisiting free energy calculations: a theoretical connection to mm/pbsa and direct calculation of the association free energy efficient estimation of free energy differences from monte carlo data efficiency of alchemical free energy simulations i: practical comparison of the exponential formula, thermodynamic integration and bennett's acceptance ratio method comparison of thermodynamic integration and bennett's acceptance ratio for calculating relative protein-ligand binding free energies bayesian estimation of free energies from equilibrium simulations unorthodox uses of bennett's acceptance ratio method multiscale free energy simulations: an efficient method for connecting classical md simulations to qm or qm/mm free energies using non-boltzmann bennett reweighting schemes on relation between the free-energy perturbation and bennett's acceptance ratio methods: tracing the influence of the energy gap comparison of efficiency and bias of free energies computed by exponential averaging, the bennett acceptance ratio, and thermodynamic integration binding thermodynamic cycles: hysteresis, the locally weighted histogram analysis method, and the overlapping states matrix calculations of solvation free energy through energy reweighting from molecular mechanics to quantum mechanics convergence of single-step free energy perturbation absolute hydration free energies of blocked amino acids: implications for protein solvation and stability bruckner, s.; boresch, s. efficiency of alchemical free energy simulations ii: improvements for thermodynamic integration qm/mm free-energy perturbation compared to thermodynamic integration and umbrella sampling: application to an enzymatic reaction separation-shifted scaling, a new scaling method for lennard-jones interactions in thermodynamic integration efficient determination of protein-protein standard binding free energies from first principles free-energy cost for translocon-assisted insertion of membrane proteins scalable molecular dynamics with namd efficient syntheses of diverse, medicinally relevant targets planned by computer and executed in the predicting reaction performance in c-n cross-coupling using machine learning the tensormol- . model chemistry: a neural network augmented with long-range physics machine learning of accurate energy-conserving molecular force fields quantumchemical insights from deep tensor neural networks first principles neural network potentials for reactive simulations of large molecular and condensed systems molecular dynamics with on-the-fly machine learning of quantum-mechanical forces accurate interatomic force fields via machine learning with covariant kernels energy-free machine learning force field for aluminum fast and accurate modeling of molecular atomization energies with machine learning prediction errors of molecular machine learning models lower than hybrid dft error protein-ligand scoring with convolutional neural networks ani- , a data set of million calculated offequilibrium conformations for organic molecules less is more: sampling chemical space with active learning linear interaction energy (lie) models for ligand binding in implicit solvent: theory and application to the binding of nnrtis to hiv- reverse transcriptase gromacs: high performance molecular simulations through multi-level parallelism from laptops to supercomputers improved side-chain torsion potentials for the amber ff sb protein force field molecular-dynamics study of atomic motions in water computational insights into the protonation states of catalytic dyad in bace -acyl guanidine based inhibitor complex docking, molecular dynamics and free energy studies on aspartoacylase mutations involved in canavan disease electrostatics of nanosystems: application to microtubules and the ribosome key: cord- - ddala r authors: pastukhova, maria; westphal, kirsten title: governing the global energy transformation date: - - journal: the geopolitics of the global energy transition doi: . / - - - - _ sha: doc_id: cord_uid: ddala r an effective and efficient governance is key for the global energy transformation. we argue that the process under the paris agreement, its ‘rulebook’ and the nationally determined contributions (ndcs) will have to be accompanied by focused and tailored governance mechanisms in the energy realm. the energy sector itself is key to limiting global warming to two degrees centigrade compared to the preindustrial level, because it is responsible for over two-thirds of global greenhouse gas emissions. yet, neither the energy transition nor energy governance start from scratch. energy governance is already happening on many levels: the local, the national, the regional and the global. these multi-level governance structures are necessary to enable, facilitate, and accelerate the energy transition(s) on the ground. they have to be adapted, however, to the changing and transforming energy world as we argue in the conclusions. in a first step, we conceptualize the notion of ‘energy transition’ and relate it to the concept of ‘energy transformation’. we argue that it is necessary to firstly move beyond the normative and target-driven idea(s) behind ‘transition’ and to secondly bring in the systemic aspects of energy transformation. moreover, energy security, economic efficiency, sustainability and climate neutrality have emerged over time as the guiding paradigms, forming a strategic quadrangle, as opposed to a strategic triangle, traditionally used to define energy security. in a second step, we present an overview of the current international energy governance system where multilayered governance structures have developed over time. we argue that the existing architecture is stemming from the past and is neither fit for governing the energy transition, nor even reflecting the proccesses underway in todays’ world. in a third step, we highlight that the energy transformation has and will have tremendous techno-economic, socio-technical and political (cherp et al. ) effects that have both internal and external dimensions. moreover, the transformation comes with (geo)political effects as it changes the political economy of energy on all levels: the global, the regional, the national and the local. in the final step, we look at ways forward. we argue that it is necessary to preserve existing multilateral institutions and to strengthen them. moreover, we assume that governance approaches towards and inside regions will have to be re-shaped or even created from scratch. we conclude that the crumbling of the global liberal order and the crises of multilateralism are complicating the approach to a better governance of the energy transition on the global level. moreover, we witness the emergence of illiberal tendencies in the western democracies as well. climate and energy are playing into the polarization of societies as the two topics emerged as a major cleavage and a conflict line. we emphasize that a just and inclusive energy transition, both on national and international levels, is necessary to keep countries and the world on a sustainable energy transformation path. the challenge faced by the planet is indeed systemic. national and the local. in the final step, we look at ways forward. we argue that it is necessary to preserve existing multilateral institutions and to strengthen them. moreover, we assume that governance approaches towards and inside regions will have to be re-shaped or even created from scratch. we conclude that the crumbling of the global liberal order and the crises of multilateralism are complicating the approach to a better governance of the energy transition on the global level. moreover, we witness the emergence of illiberal tendencies in the western democracies as well. climate and energy are playing into the polarization of societies as the two topics emerged as a major cleavage and a conflict line. we emphasize that a just and inclusive energy transition, both on national and international levels, is necessary to keep countries and the world on a sustainable energy transformation path. the challenge faced by the planet is indeed systemic. if governance of the energy transition is to be exercised effectively and efficiently, a common understanding of 'energy transition' seems to be helpful and necessary. nowadays, 'energy transition' is a concept widely accepted and operationalized by national governments, regional and international bodies and non-governmental organizations alike. although the term "energiewende" has been first introduced in the early s by the german Ökoinstitut (krause ) , it hasn't found its way into the vocabulary of policymaking until the twenty-first century. yet, when germany published the "energy concept for environmentally sound, reliable and affordable energy supply" (bmwi and bmu ), which was readapted after the nuclear accident in fukushima by the energy concept and the related package on the "energiewende", its english pendant 'energy transition' has become the international buzzword for a shift towards cleaner and more sustainable energy systems. as omnipresent and relevant the term 'energy transition' might be nowadays, it is remarkably difficult to grasp, not least because of the lacking conceptual clarity and uniformity. the lack of both a comprehensive definition and a theoretical framework to support the concept of energy transition is not only lamentable from a scientific point of view: the resulting lack of common understanding among (inter)national actors also incapacitates the development of functioning international governance mechanisms to address this global issue. the main reason for this lack of conceptual integrity lies in the broadly preferred focus on the "toolbox", that is, the single components or tasks of the energy transition. energy transition is most commonly defined extensionally (see fig. ), e.g. through its components such as the increasing share of renewable energy sources in the total energy mix (irena, iea), energy efficiency (eu, ipeec, irena), phase-out of fossil fuels (irena, eu) and nuclear energy (german fed. gov.), electrification of the transport sector (iea, eu), development of carbon capture and storage technologies (norway, saudi arabia). an important observation at this point is, that the set of these components differs among countries, regions and organizations according to their respective agenda. in other words: the global community lacks a uniformly agreed energy transition agenda. the respective policy approaches are guided by a set of paradigms, the central one often being energy security. traditionally, in the eu and in the oecd countries, energy security has been defined through the strategic energy triangle, consisting of the three objectives of security of supply, sustainability and economic efficiency. yet, there has always been the issue of prioritization of these objectives, given that there are not only synergies but also trade-offs between the policies addressing them. on the other side, the world energy council highlights that countries face an energy trilemma of addressing security of supply, ecological sustainability and energy justice simultaneously. the different wording chosen by the world energy council illustrates the variety of notions associated with the paradigms across the globe. while security aspects have been at the heart of energy governance since the emergence of the first energy institutions, the economic aspects have been gradually added afterwards, whereby their definition differs largely across the world. in the oecd countries, economic efficiency, competitiveness and affordability are prevailing notions. in other parts of the world, energy equity and energy justice underpin the economic, or better socio-economic angle of energy policies. the concept of energy transition is pervasively used as a normative one, it is also often tailored to fit certain policy objectives or to underpin specific measures and steps. therefore, international fora such as the g or the world energy council make the case for multiple energy transitions, i.e. structural shifts in the energy system of each country according to its respective goals and economic and resource potential (g ; wec ) . it is obvious that the various positions of countries in energy trading (influenced by their world market share/their position as a net importer/net exporter), in the globalized economy (trade surplus/deficit), with regard to their respective degrees of economic and social development (population growth/industrialization/urbanization) (bradshaw ) as well as to the state of the energy system and the level of access to modern energy supplies determine the weighing of objectives and the prioritization of energy policy goals. with climate change mitigation, adaption and resilience added to the set of objectives, this diversity of priorities has proven to be a heavy burden and at times an obstacle for energy and climate governance beyond national levels (ibid.). multilateral initiatives aiming to shape energy relations are in general hampered by widely scattered interests, which exacerbate the already considerable existing uncertainties. as a result, states have pursued very different pathways in energy governance: in the oecd area, it has been above all a matter of safeguarding prosperity; the post-socialist states have had to deal with the after-effects of the soviet era, including the task of socio-economic transformation and a search for a new position in the global economy. the 'resource curse' and rent-seeking patterns have determined the energy dilemma of the energy-rich countries, while the question of sufficient access to energy has occupied the energy-poor countries (ibid.). in addition to the traditional paradigms, sustainable development and growth have become key concerns. since the second decade of the s, the two key objectives of security of supply and climate protection have been accompanied by the goals of sustainable development and a fair and equal supply of energy worldwide, above all promoted by the united nations. at that time, the united nations also began to take an active stance on sustainable energy with its sustainable energy for all (se all) initiative. in the same vein, the millennium development goals were translated into the sustainable development goals (sdgs) in . goal is to ensure access to affordable, reliable, sustainable and modern energy for all by . sustainable development is very much connected to the issues of energy justice and energy poverty, but also to environmental protection, and more specifically, protection of water, soil and air. in the same year of , the paris agreement on climate change was signed. according to the paris agreement, countries' ambitions on ndcs have to progress in -year cycles. according to art . of the agreement, the ndcs should be formulated in line with the goal to keep global warming well below the degrees celsius compared to pre-industrial levels and pursue efforts to limit temperature increase to . °. the paris agreement, the consecutive conferences of parties (cops) and reports by the united nations framework convention on climate change (un fccc) have added a sense of urgency to the issue of climate protection, but at the same time possibly aggravated the dilemmas in addressing all four objectives even further. local air, soil and water pollution as part of sustainable development are in many countries a major driver and mitigating climate change comes as a transformation dividend (goldthau et al. ) , rather than as a policy goal on its own. although sustainable development has become a major underlying theme, e.g. also in the international energy agency and its world energy outlook(s), and climate is often subsumed under 'sustainability', we argue that both, climate and sustainability constitute paradigms in their own right. therefore, we suggest that a strategic energy quadrangle rather than a triangle is informing energy policies across the globe. energy security, economic efficiency, sustainable development and climate change mitigation, adaptation and resilience form four major angles or baskets, to which countries associate very different notions. at the same time, however, these four angles significantly overlap and create and numerous synergies to exploit and lift. to summarize, when it comes to energy transition governance, countries differ in terms of their starting points, their path dependencies and their future pathways as well as their ambitions. in view of this diversity, the paris agreement, its rulebook as well as the bottom-up mechanism of nationally determined contributions (ndcs) are important and necessary, but not sufficient preconditions to steer energy transition towards climate neutrality nor appropriate to govern energy transition(s) to meet the other objectives. indeed, if we are talking not about one, but multiple energy transitions, defining them through their respective components makes a lot of sense, since such a definition can be easily operationalized by, say, national policy makers. however, in order to enable global governance and international cooperation mechanisms on this issue, there must be an understanding of energy transition every stakeholder can identify itself with. although different stakeholders propose different measures and elements, there is indeed one common element such a definition can be based on: the characteristics of the future energy system they deem necessary and aim for are the same. all major stakeholders, some explicitly (g ; bmwi , p. ; g , p. ; mofa japan ), and some implicitly (iea a, b; ec ; irena ; national governments, e.g. the prc's government ) define sustainability, environmental safety, economic efficiency and security of supply to be the central goals and the end-state to which the process of energy transition should lead. a future energy system with these characteristics is indeed universally aspired-the sustainable development goal on energy, that is, access to affordable, reliable, sustainable and modern energy for all (un ), has been adopted by governments of countries. moreover, instead of energy transition, talking about energy transformation reflects the necessary systemic nature shifts in the energy system. sometimes both concepts are used interchangeably: in irena's report "global energy transformation-roadmap to " energy transformation is a means to achieve energy transition, which is conceptualized as the end-state itself: "the challenge that policy makers around the world face is how to accelerate the transition. fully delivering the energy transition will require a transformation in how we view and manage the energy system. transitioning in a few decades from a global fossil-fuel powered energy system, built-up over several hundred years, to one that is sustainable, will require a much greater transformation than current and planned policies (the reference case) envisage" (irena : ). as in several recent academic studies, in one if its newest reports "geopolitics of energy transformation", irena uses the term "energy transformation" intentionally instead of energy transition, to point out the broader implications a transition to low-carbon energy sources brings with it (irena ). against the above said, we suggest having an intensional definition of energy transition that is formulated as follows: a policy-driven process which involves systemic shifts towards (a) sustainable and climate-friendly, economically efficient and secure energy system(s). the measures and building blocks of such a transition will differ from country to country. yet, there should be a governance system behind these national efforts, to pave the way, facilitate, enhance and accelerate the energy transition(s). the existing energy governance landscape began emerging in the second half of the last century and has developed over time. it is sketchy and fragmented. within this landscape, there are very few multilateral institutions that tackle energy issues in a comprehensive way (see fig. ). this is the result of ( ) the different positions and roles of countries in the international energy system and ( ) the diverging national priorities in energy policies regarding the strategic quadrangle of energy. the traditional organizations such as the organization of oil exporting countries (opec), the gas exporting countries forum (gecf) or the international atomic energy agency (iaea) focus on specific energy sources, respectively oil, natural gas and nuclear energy. whereas opec and gecf are providing platforms for dialogue and cooperation among producing countries, the international energy agency (iea) was formed by the oecd countries as an organization of energy consumers and primarily in response to the first oil crisis of - . the iea has been dealing with different energy sources ever since, albeit it has always had a pillar on oil crisis management and prevention. the iea has been adjusting its role constantly to the new energy and climate realities. however, its membership structure, restricted to the oecd countries, came under increasing criticism as non-oecd countries like china and india have become powerful energy market players. in face of the changing dynamics, an association process has been currently under way with major non-oecd energy powers. in , the iea comprises member states, association countries and countries in accession. though being a display of iea's adaptability, the association process is certainly an attempt to maintain the existing order. the creation of the international renewable energy agency (irena) in meant a significant advance, both in renewable global governance as well as with regard to multilateralism (see also roehrkasten ). irena got a clearly defined mandate to "be the global voice and knowledge base for the use of renewable energy, to serve as a forum for international technological cooperation, and to advise the member states on these matters". (roehrkasten and westphal ; roehrkasten ) . the specific focus has been on renewables. irena has also been looking into the geopolitical implications of an energy transformation (irena ). as fig. shows, there are some organizations and fora that deal with specific energy sources or encompass a particular group of countries. this overview contains institutions on the global level, whereas regional organizations that specifically focus on energy (such as the latin american energy organization (olade)) or have energy in their portfolio (united nations economic commission for europe (unece), european union (eu), united nations economic and social commissions for western asia, for asia and the pacific and for latin america and the caribbean (unescwa, unescap, uneclac), etc.) are not included here. not included is also the world trade organization, which has played an important role in setting the rules for trade generally, but not in the energy sector (with an exception of energy services). the european energy charter in and the treaty in were an attempt to translate similar rules into the energy trade, transport and investment. yet, from today's perspective, it can be said that it is very doubtful whether the energy charter process can be revived and modernized in a way to provide a 'rule book' or a 'code of conduct' for international energy trade, transport and investments, despite the signed international energy charter. as fig. shows, very few existing institutions equally address energy policy objectives in an institutionalized manner. at the end of the s, there was a strong impetus to strengthen the coordination among the existing governance mechanisms and organizations. the initial idea was to better integrate the new powers such as china and india, and to have an outreach to the regions. the outreach and association process of iea as well the international platform of energy efficiency cooperation (ipeec) under the umbrella of iea resulted from initiatives of the group of eight (g ). it was the g that reacted to the fact that energy governance did neither reflect the energy landscape any longer nor the changes in global politics in general. in an increasingly multipolar world, energy governance (lesage et al. ) became a matter of steering committees and clubs, first and foremost of the g / and g . the g transformed back into an exclusive oecd-club with the crisis in and over ukraine, when russia was excluded from the process in . the group of carried on with the agenda of tackling climate change and energy security (with the primary focus on natural gas). in , the g emerged as the new 'club' to primarily address the financial crises. the g began to work on energy matters under the us presidency in , when g members declared their intent to phase out harmful and inefficient fossil based on westphal , updated fuel subsidies (van de graaf and westphal ). this new focus was also intended as an answer to the financial and economic crises as the member countries committed themselves to a resilient, sustainable and green recovery. the g is perfectly positioned to steer global energy transition. along with the g countries canada, france, germany, italy, the uk and the us, the g includes the european union (eu), argentina, australia, brazil, china, india, indonesia, mexico, russia, saudi arabia, south africa, south korea, as well as turkey. it comprises countries that are of utmost importance for a successful energy transition and includes major energy producers, consumers and key players in existing international institutions. also, in terms of climate policies, the g countries would make a huge difference, if acted together, as they account for % of global emissions (in comparison, g accounts for %). last but not least, the g includes all permanent members of the un security council, and major financiers of principal international organizations. the g has constantly stepped up its voluntary cooperation in energy-related areas such as subsidies, market transparency and price volatility, international energy collaboration, energy efficiency, energy access and renewable energies. the g summits provide countries with an opportunity to meet on an equal footing and to exchange national views and standpoints on energy topics, a major step forward being made in with the first g energy ministers meeting that took place under the turkish presidency. yet since then, every new presidency set its own priorities, which hampered continuity as an important precondition for efficient and effective energy governance. energy ministers have met each year since , except for under the german presidency. overall, though the g unites a representative group of industrialized countries and new powers that can have an impact in their respective regions, the members have very distinct and diverse policies and perspectives. this limits the role of the g when it comes to global energy governance and is also the reason for the group's focus on less controversial issues, such as energy efficiency. as a result, the g has only partly lived up to its potential as a steering committee (van de graaf and westphal ). in its current form, the g builds on the principle of voluntariness and on "soft" modes of steering, such as agenda setting, coordination among g members, information exchange and the steering of international organizations (ibid.). at the same time, the g has moved international energy governance up on its policy agenda, has rhetorically connected energy and climate policies and has enlarged its focus to sustainable development. since , the g has continued to exchange on and monitor the progress towards phasing-out of fossil fuel subsidies: in the iea, opec, oecd and the world bank published reports tracking fossil fuels subsidies (iea/opec/oecd/wb , ). in , the g endorsed a methodology for voluntary peer reviews "on inefficient fossil fuel subsidies that encourage wasteful consumption" (g , paragraph ) . since , the g has been addressing energy issues more comprehensively. at the g summit in brisbane, australia, the g endorsed the g principles on energy collaboration. the chinese presidency in continued this initiative to make energy institutions more inclusive and effective under the title "global energy architecture". the g affirmed its support for the sdg target number and pledged to increase the share of renewable energy substantially by . at the core of the g action on renewable energy is the toolkit of voluntary options, developed by irena. the following five options are presented as particularly beneficial for the g action: ( ) in-depth and country-specific analyses of renewable energy costs and reduction potentials, ( ) exchange good practice examples on enabling national policy frameworks, ( ) development of renewable energy-specific risk mitigation instruments, ( ) country-specific assessment of renewable energy technology potential and development of roadmaps and ( ) support the sustainability indicators and further actions of the global bioenergy partnership (gbep), in close cooperation with irena and iea bioenergy. in addition, g members decided to explore the potential for increased regional infrastructure connectivity and cross-border investment to enable greater levels of investments in renewable energy, and to continue the support for international cooperation, including capacity building for developing countries and encouraging the use of existing cooperation platforms. in , energy transformation has been officially put on the agenda at the ministerial meeting on "energy transitions and global environment for sustainable growth" in japan (g ). today's fragmented energy landscape increasingly amplifies the contours of a multipolar world. it is clear that in its current state, energy governance is far from being comprehensive, efficient and effective to steer a global energy transition. moreover, in the current geopolitical environment the efforts to strengthen theglobal cooperation and work on global public goods seem more and more futile. at the turn of the new decade of the s, personal ambitions of politicians determine politics. these are less directed to multilateral negotiations rather than to bilateral tit-for-tat zero-sum games. the volatility of personal relationships among the world leaders, where selfish nation-first policies dominate, increasingly compromises the stability and continuity of international relations. in the same vein, the global geopolitics around climate have changed fundamentally: since the adoption of the paris agreement in , the consensus among major powers has faded. cop in madrid in ended without a clear statement on raising the ambitions of the nationally determined contributions (ndcs), with the communiqué being watered down by the us, brazil and australia. the 'ndc explorer' shows, that the absolute majority of the countries put renewable energy first, while carbon capture, utilization and storage (ccus) technologies are hardly mentioned. even when taking into account that the ndcs have been produced under time pressure and that they may not be the best-grounded pledges, massive political and financial gaps are obvious and the ambitions are far too low (pauw et al. ). this altogether makes energy (transition) governance-albeit granular, selective and regional-more important than ever. policymakers at all levels face the herculean task of making energy systems more sustainable and climate friendly. moreover, at the same time, they have to ensure the supply of, e.g. fossil fuels, for the transitional period without perpetuating the existing energy system (westphal ) . if one looks to the horizon , in which the world aims to become carbon-neutral, the energy supply worldwide should be structured in such a way that the expected nine to ten billion people on earth have access to modern, affordable and sustainable energy supplies without further destroying the livelihoods of present and future generations (ibid.). we assume that energy transition pathways differ and depend on countries' respective preferences and imagined energy futures (see chapters in this volume). thus, we defined energy transitions as an intensional policy-driven process which involves systemic shifts towards (a) sustainable and climate-friendly, economically efficient and secure energy system(s). there is no single and simple solution to transitioning the energy system(s) in line with these paradigms, as stated by the iea in its world energy outlook of . the iea's weo has been very clearly stating that there is no silver bullet at hand, but a combination of technologies ranging from energy efficiency, renewables, fuel switch, nuclear, ccus, etc. as well as-not least-behavioural change are needed to put the world on track (see fig. ) . the systemic nature of energy transitions in general has been pointed out before, most notably in works on historical energy transformations (ex. smil ; kander et al. , etc.) . in its core, previous energy transitions have been transitions from one energy source (wood, coal, oil, electricity) and one type of energy converter (manpower, animal power, steam engine) to another. in all of these cases, major inventions of leading technologies such as the steam engine, electric lightning, etc., have kick-started processes of transition. however, all these transitions have been also accompanied by the profound and irreversible shifts on societal, ideological, political and economic levels (ibd.). in this regard, the energy transition that is taking place nowadays is no exception: it involves a shift to new, low-carbon energy sources. yet, this time, the range and speed of the transition is and needs to be different. moreover, the range of measures that will have to be deployed is enormous. as a result, the scale of socio-economic and political changes to be expected from the energy transitions happening around the world is not comparable to the historic cases. in other words, we have to think about energy transformation, in a way karl polanyi described the "great transformation"-neither national nor global energy systems are discrete elements. they are closely intertwined with politics, as well as with economic and social systems. a transition to a low-carbon economy doesn't just change the energy system. it has massive knock-on and distributional effects, causing re-allocation of resources both nationally and internationally. how to think about the new world (irena, ) and the difficult, painful, but promising transition phase? ( ) the energy transition(s) come with various structural shifts that create new patterns of energy supply and demand, investment and data flows, new infrastructure systems and new power balances. ( ) the new system will be more electrified, digitized, demand-side driven and distributed. this requires large infrastructure to adapt, to modernize or to be developed, depending on the respective countries. ( ) today's energy system rests on individual sectors (i.e. electricity, buildings, transport, industry), each characterized by a dominant mix of (fossil) fuels (goldthau et al. ). in the system of the future, the sectors (electricity, industry, heating and cooling, transport and mobility) will be coupled by the use of electricity and synthetic/decarbonized molecules and liquids. ( ) as a consequence of these changes in the system, a relocation of production and demand as well as a reconfiguration of energy spaces will take place. ( ) in the new energy world, the value is no longer generated primarily from the fossil fuel resource such as coal, oil or gas, but rather at the stage of conversion into end-user energy/services (ibid). in other words, more and more value will be created downstream of the energy supply chain and in services (e.g. lightning, heating, cooling, etc.). as a consequence, profits will be generated by the availability and use of low-carbon technologies. energy transformation does not only recalibrate energy value chains. it also (re)configures energy spaces, which are shaped by infrastructure, production chains, and industrial clusters. energy infrastructure can be viewed as an "infrastructured" geography of "long durée" that shapes spaces and even creates its own "ecology" and topography (högselius ) . this is particularly true for electricity grids and their different shapes (central, decentralized) as well as sizes (local, national, trans/continental). the spatial effects of the energy transition(s) result from technoeconomic change, e.g.in the shape of local micro grids or region-spanning super grids, such as those promoted by china's belt and road initiative. connectivity will be newly defined, knocking on existing interdependencies, alleviating old sensitivities and vulnerabilities, but also creating new ones. the interconnectedness of two critical infrastructures, the electric grid and the internet creates specific challenges and hybrid threats. if we assume that the energy transition has tremendous political, economic and social effects, the interaction with international political and geographical factor is evident (ivleva and tänzler ) . geopolitics can be understood as dynamics that stem from the interaction of geographical factors and international politics (ibid.; scholl and westphal ) . in international politics energy is (intended to be) used as a tool and means to influence political outcomes, achieve foreign policy goals and as a lever to project power (ivleva and tänzler ) . the geopolitics of energy transformation constitute a governance challenge in its own right. there is a growing body of literature on the energy transition having a geo-economic and geostrategic character (bradshaw ; scholten ; goldthau et al. ; bazilian et al. ; irena ) . importantly, the very notion of energy security will change along with the transformation of energy systems: to be more precise, in the oil-centered world of the past, national security and the issue of import dependencies were at the heart of energy security. in the new energy landscape, where electrification is a major trend, the stability of the power grid will be the defining feature of energy security. not surprisingly, energy is and will remain at the heart of national sovereignty and/or statecraft, as daniel yergin's definition of energy security as "adequate, reliable supplies of energy at reasonable prices in ways that do not jeopardize major national values and objectives" hints to (yergin ) . energy has always proven to be a major policy field, involving a strong role of the state, as it is closely related to its traditional tasks of providing prosperity, security and stability. the energy transition offers new opportunities to shape the energy system in a new vein, which is in line with national values and interests, while also providing and protecting global commons and goods. while traditional geopolitics is related to power relations, the energy transition implies power shifts and alters the political economy on the national and the international levels. it creates winners and losers (irena ; overland et al. ) . petrostates and coal-exporting countries are repositioning themselves in the international system as their major assets become de-valued (irena ). at the international level, fossil fuel producers are vulnerable to the fundamental changes caused by the energy transitions. resilience to the energy transition effects depends on the percentage of fossil fuel rents in the gdp and the diversification of their economy (irena ). if petrostates such as russia, saudi arabia or iraq, etc., are confronted with declining oil rents, their socio-economic model and political systems come under severe pressure. fossil fuel exporters are not only faced with a devaluation of their natural resources, but increasingly face fundamental challenges to their economic and social systems, since the resource wealth is part of the social contract. this in turn affects the political stability and economic growth in these countries. yet, it is fair to say that the us shale gas and tight oil revolution has already caused a landslide by creating a new situation of energy abundance, shaking up the position of energy rich countries and diminishing their respective rents. in a sense, the us shale revolution has already anticipated certain effects for the petrostates. transit countries such as ukraine, morocco or tunisia that gain rents from their midstream part in fossil fuel supply chains, will also feel the effects of energy transitions. obviously, the energy transformation will have knock-on effects along the whole fossil fuel value chain making the exporting and transit countries to losers of an energy transformation. evident winners are major importing countries, which will be able to produce more energy from renewables locally and at home or in cross-border cooperation within 'grid communities' (scholten ) , formed by political choice and not due to geological circumstances. at the same time, renewable technology leaders are emerging (irena ; goldthau et al. ) , gaining more and more political weight and a central place in the global markets. hence, energy governance has to tackle the geopolitical ramifications of energy transformation and aim for a transition that is as smooth as possible. in this respect, the notion of a 'just transition', energy justice or evenness, is key for the global energy transition, in particular with regard to the global south (see goldthau in this volume). finally, the energy transformation has profound and even disruptive structural effects. at the national level, it inherently entails structural ruptures and puts stress on the incumbent energy system. incumbent utilities like the german companies e. on and rwe lost significantly in their market capitalization and/or changed their asset base, which also split their renewable branches. in the socio-technical realm, a paradigm shift will have to take place, with the end consumer and/or the community moving into focus. consumers are becoming key actors as both, consumers and producers ("prosumers") of sustainable energy, which requires a behavioural change beyond energy saving and efficient energy use. the eu, for instance, has paid a tribute to this paradigm shift by focusing on the end consumer in its 'clean energy package for all europeans' of . in general, this paradigm shift from supply to the end consumer has three dimensions. first, consumer behaviour is critical to the success and speed of an energy transition: consumers have to take up responsibility, be empowered and become to a certain extend 'owners' of the transition. second, there is the social dimension of access, availability and affordability of (modern) energy: among others, governance measures are needed to deal with e.g. (temporary) price increases. last, but not least, structural ruptures such as a 'coal phase out' are part of the decarbonization. this requires states to mitigate social risks, e.g. ones expected from the coal phase-out negotiated in germany in (bmwi ). germany's decision to phase out coal by was achieved by a societal consensus after a long negotiation process and backed by a set of structural policies in coal regions. these policies translate into a long phase-out over almost years, depending on the age (and technology used) of the respective power plants. other countries might have the chance to leap-frog this technology, or might have to close down coal-fired power plants before their respective lifespan ends(as is likely to be the case for some countries in asia) (iea a, b) . in any case, the socio-economic dimension of the energy transformation cannot be underestimated. as mentioned above, energy transition affects societies. energy transition has a considerable effect on labor markets. germany is a case in point where the narrative of creating green jobs has not really (or only temporarily) delivered. when feed-in tariffs triggered the diffusion of pv in germany, the 'solar valley' in sachsen-anhalt boomed. yet, as china began to expand its solar panel manufacturing industry, many involved in the same sector in germany lost their green jobs. socio-technical dynamics have to be closely analysed and the respective policy measures developed: in germany, traditional energy sectors are covered by unions, primarily the respective labor union igbce (ig bergbau, chemie, energie), whereas workers in new industries such as solar and wind energy are not organized in trade unions and therefore don't have the same kind of support. this particular challenge to tackle the socio-economic effects of the energy transition is thus increasingly debated as the "just energy transition". the focus on a just transition is inextricably linked to the question of "who wins, who loses, how and why". it is imperative to ask this question both in relation to the existing distribution of energy (e.g. "who lives with the side effects of extraction, production and generation?"), and with regards to the ongoing energy transformation (e.g. "who will bear the social costs of decarbonizing energy sources and economies?") (newell and mulvaney , p. ) . this, in turn, necessitates addressing the issues of distribution and access to political power, natural, social and economic resources, and the political economy behind socio-technical energy transitions (goldthau and sovacool ) . attention has to be paid to the interrelation between a just energy transition and the speed of decarbonization, though. in the beginning, mitigating social effects can be an impediment to moving ahead with the rapid decarbonization, but a sound social consensus is needed as a stabilizing element to transform the energy system. the creation of green jobs can serve as a catalyst and is even more important than social measures to compensate for income losses and job cutbacks. these social aspects are moving to the political core of many western societies, where, i.e. resulting from such movements as "fridays for future", the energy-climate cleavage has started to influence the politics and polarize the societies. the message this chapter can't emphasize enough is that the energy transition(s) will play out differently in countries and regions, but they all will have a huge impact on all levels: the global, the regional, the national and the local. moreover, while the targets and paradigms are in place, creating the institutional framework fit to steer the transitions' pathways remains an open issue. as there is no simple and single solution (see fig. ), there is no one-size-fits-all approach to governance. instead, what is needed is a flexible multilevel architecture which is ( ) reflecting new connectivities and energy spaces, ( ) enabling, promoting and diffusing new technologies and knowhow and ( ) adapting the institutional and regulatory framework to the changes that come along with the transformation of the energy system(s) (see fig. ). there is a need for a better global and regional, and a good governance on the national and policies and cooperation mechanisms for global energy transition governance. source local level. particularly in today's world of nation-first policies and geo-economics, it is imperative to establish, maintain and improve the multilateral energy landscape. moreover, the governance task is not only to move forward with the energy transition, and to transform the system, but also to deal with the geopolitical aspects which the energy transition brings about. energy transformation comes with a cost, but the costs of doing nothing are higher, even if less immediate and more diffuse. the call on governance is evident, because it is assumed that this will make the transition(s) faster, smoother and more even. the transition period is assumed to have systemic transformational effects on political systems, economies and societies, and thus can be messy, disruptive and conflictive. furthermore, the energy transition(s) are not taking place in a vacuum but have the potential to add to the geo-economic rivalry. moreover, technology leadership and control over mineral resources can add to the struggles over political authority and power. the global environment of great power rivalry and the crises of multilateralism are clearly complicating the global energy transformation. there is less political will to work together to create and preserve global common goods than in the past. under these circumstances preserving the existing institutions such as wto, irena and un energy that build on 'altruism' and are aiming at a level-playing field is of the utmost importance. if the global consensus is shaky, it will remain important to act plurilaterally, in clubs, coalitions and alliances. the existing governance structure (figs. and ) can and has to ensure the functioning of today's energy system without perpetuating it. the format of clubs, the comprehensive institutions of iaea and iea will have a role to play. this is equally true for irena, un energy and se all, which are directed to changing the energy system(s) along the paradigms of the strategic energy quadrangle. in order to ensure that the measures undertaken (see fig. ) not only contribute to diversification, but in fact transform the system, the efforts in governing energy efficiency and renewable energy have to be stepped up. aside from the global level, new governance structures will have to be developed or adapted at the regional level. without an aspiration of being comprehensive, we recommend the following focus areas. governing energy regionalization and connectivity. the energy transition will reshape regions, but also create webs and routes within and between them (connectivity). so far they are largely un-or only partly governed. yet, the existence of large infrastructure (e.g. power grids) running across regulatory spaces will require new norms, rules and standards which deal with interoperability of systems and cross-border management of flows (scholl and westphal ; overland et al. ; balmaceda and westphal forthcoming) . energy regionalization takes place without a recognition of existing jurisdictions and polities. the question of who defines the rules of the game in the "infrastructured" space or across production and value chains is very acute. new governance schemes are necessary, also to prevent regulatory fault lines from feeding into geopolitical conflicts. this has systemic, structural and spatial implications of a transboundary nature that have repercussions on the regional and global level. among them are the global shift of investment and financial flows due to the changes in energy and technology markets; the emergence of new geographies of demand and supply; where the digitization comes with its own risks and challenges, as both energy, it and telecommunication sectors are connected by super infrastructures, which are highly critical to modern societies. the cascading effects in case of a crisis or a 'black-out' demand for specific resilience measures to be taken in smart/super grid communities. this issue is already very tangible in the eu, where electricity security and grid stability have gained utmost importance. the creation of synchronized grid communities that include turkey, and soon the baltics and ukraine, come with their own governance challenges, not least of them being connected to cyber security. a common set of global rules. one immediate blind spot to address in global energy governance is the lack of a code of conduct and/or a set of common rules. both are needed in order to create a level playing field as well as transparent and functioning markets. the more technology-driven the energy system will be, the more important will rule-setting organizations such as the wto become. patents and intellectual property rights will remain important in order to make profits from innovation, but at the same time, solutions will be needed to provide access to important technologies for developing countries. investments. one of the key challenges for a sustainable energy transition is to get the investments right and right in time. under the current price regime of low energy prices and in an era of abundance of energy sources, price signals to turn away from fossil fuels will be too weak or simply lacking. investments into production sites and infrastructure predetermine and cement path dependencies given the long lead times and lock-in effects they create. policy measures and regulatory frameworks will be key in the transition toward a sustainable global energy system. institutions will play a central role in incentivizing and realizing the big shifts in technology, as well as creating and capturing the value and creating new business models. this is also related to the question of who will finance the necessary infrastructure. therefore, 'shifting the trillions' and getting the financial and taxation framework right, is of a paramount importance. in many countries with high renewable energy and energy efficiency potential, the cost of capital is too high. new power grid infrastructure, renewable energy facilities, development of energy efficient buildings and appliances, restructuring transport sector, etc., require huge sums of infrastructure investments, great coordination efforts, and a stable regulatory framework to realize the shift. the unprecedented oil price slump triggered by the covid- pandemia in the first quarter of is burning capital which will be missing in the energy sector and for the transformation as a whole. technology-specific governance schemes and mechanisms. moreover, there are many issues around specific measures and technologies to be addressed by specific governance mechanisms. the table above is not considered comprehensive. yet, it aims to visualize the complexity of the tasks faced by the global community. the instrumental and operational level aims to grasp the multitude of the technologies, components and tools needed to bring forward energy transition, among them the deployment of low-carbon energy sources, power-to-x and synthetic fuels, but also the new approaches to power grid design (e.g. smart grids or super grids) as well as energy efficiency, sector coupling, and phase-out of fossil fuels. these elements and tools are employed altogether or in part, based on the political agenda and preferences of the respective countries-their efforts on the operational are therefore highly heterogeneous. a consumer-producer dialogue. one of the key mechanisms to ensure a successful energy transition is an enhanced and effective consumer-producer dialogue. such a dialogue is particularly important for depletion strategies and gradually phasing-out of fossil fuels. moreover, this dialogue can create new partnerships to produce, trade and transport 'de-carbonized' molecules and fuels (hydrogen and power-to-x) and coopt fossil fuel producers. the international energy forum (ief), whose primary focus is consumer-producer dialogue, is not delivering on that. it seems that it would be more fruitful to move ahead with the 'clubs' and 'coalitions of the willing' to e.g. gradually develop hydrogen markets. get the institutions right. steering energy transition on the global level requires enhanced technical and regulatory dialogue as well as a continuous exchange on best (and worst) practices among countries, regions and communities. there is no lack of targets, but the major challenge is to create effective incentives, frameworks and regulations to implement and accelerate the energy transformation. in addition, exchange and cooperation on a knowledge-and database on energy (including exchange on energy forecasts and common modelling exercises) must be developed, to provide transparency needed for an efficient energy transition governance. for these modes of inter-and transnational cooperation, the multilateralism of energy governance institutions should be kept up and preserved. coordination and coherence among the existing institutions, clubs, and coalitions of the willing must be strengthened, while governance structures where cooperation on energy transition can take place in a level-playing field and is not driven by geo-economic rivalry have to be developed. for this, countries and other relevant stakeholders have to abandon the traditional perception of the quadrangle of energy security, economic efficiency, climate and sustainable development as mutually exclusive dilemmas, and put synergies from coordinating these four elements to the forefront instead. tandems between global north and south are imperative to efficiently addressing the issues of energy poverty and just energy transition globally and to making sure that no region is left behind. with regard to the deployment of renewables, 'tandems' may be a way forward as pursued in the g with phasing-out fossil fuel subsidies. healey and barry ( ) rightfully highlight an "increasing inequality-of income, wealth and resource ownership" in general, and rising "inequality of access to safe and affordable energy" as well as "energy poverty" as major challenges. energy transition regimes must address inequalities in power and injustices across entire socio-energy systems. the issue of energy justice must be incorporated into all governance mechanisms. this can be done by paying tribute to the eight principles of energy justice: availability, affordability, due process and information, responsibility, sustainability, intra-generational and inter-generational equity (sovacool and dworkin ) . education, research and information. at the end of the day, the benefits of energy transition have to be communicated and pushed forward in the public debates: for instance, human security gains as improved air and water quality are among the 'dividends' of energy transition (goldthau et al. ) . education and information are key in addressing societies in general and in particular increasingly polarized societies. approach climate and energy security through the lens of public goods. energy transition has the potential of re-localizing the economy around human-scale enterprises rooted more closely in the communities they serve. internally, energy transition should be 'democratized' as entailing a shift towards empowerment and ownership, transforming end-users into "prosumers" in the true sense of the word. normatively, the aim should be a reconfiguration of "transition arenas" from spaces for 'coalitions of frontrunners' towards more open spaces for deliberation, dialogue and participation (barry et al. ) . for this, approaching energy and climate security through the lens of global public goods as opposed to a strategic national interest is important. we conclude that a just energy transition on all levels, but certainly on the national and the international level, is necessary to keep countries and the world on a sustainable energy transition path. it is essential for the international community to stick to the paris agreement in order to keep up the level of ambition nationally. but also vice versa, the international ambition cannot be sustained without an enduring social consensus in major countries. open access this chapter is licensed under the terms of the creative commons attribution . international license (http://creativecommons.org/licenses/by/ . /), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the creative commons license and indicate if changes were made. the images or other third party material in this chapter are included in the chapter's creative commons license, unless indicated otherwise in a credit line to the material. if material is not included in the chapter's creative commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. low carbon transitions and post-fossil fuel energy transformations as political struggles: analyzing and overcoming 'carbon lock-in' how the energy transition will reshape geopolitics global energy dilemmas: a geographical perspective global energy dilemmas. in: energy security, globalization, and climate change integrating techno-economic, socio-technical and political perspectives on national energy transitions: a meta-theoretical framework communication from the commission to the european parliament, the council, the european economic and social committee, the committee of the regions and the european investment bank: a framework strategy for a resilient energy union with a forward-looking climate change policy making a success of the energy transition: on the road to a secure, clean and affordable energy supply ) commission "growth, structural change and employment energy concept for an environmentally sound, reliable and affordable energy supply g karuizawa innovation action plan on energy transitions and global environment for sustainable growth g ( ) g leaders' declaration. st. petersburg the uniqueness of the energy security, justice, and governance problem the geopolitics of energy transformation. governing the shift: transformation dividends, systemic risks and new uncertainties politicizing energy justice and energy system transitions: fossil fuel divestment and a "just transition analysis of the scope of energy subsidies and suggestions for the g initiative world bankon fossilfuel and other energy subsidies: an update of the g pittsburgh and toronto commitments. prepared for the g meeting of finance ministers and central bank governors accelerating clean-energy transitions in major emerging economies global energy transformation: a roadmap to geopolitics of decarbonisation: towards an analytical framework power to the people evolving energy diplomacy-energy transition and the future of japan the political economy of the 'just transition' energy security and the osce: the case for energy risk mitigation and connectivity the gegalo index: geopolitical gains and losses after energy transition conditional nationally determined contributions in the paris agreement: foothold for equity or achilles heel? irena and germany's foreign renewable energy policy. aiming at multilevel governance and an internationalization of the energiewende? european energy security reimagined. mapping the risks, challenges and opportunities of changing energy geographies cham smil v ( , ) energy transitions. in: history, requirements, prospects united nations ( ) sustainable energy for all the g and g as global steering committees for energy: opportunities and constraints international energy governance revisited: fragmented landscapes, diverging dilemmas, and emerging (dis)orders global energy transitions: a comparative analysis of key countries and implications for the international energy debate speech at the th national congress of the communist party of china energy security in the s key: cord- -adhq zt authors: makarieva, anastassia m.; nefiodov, andrei v.; li, bai-lian title: life’s energy and information: contrasting evolution of volume- versus surface-specific rates of energy consumption date: - - journal: entropy (basel) doi: . /e sha: doc_id: cord_uid: adhq zt as humanity struggles to find a path to resilience amidst global change vagaries, understanding organizing principles of living systems as the pillar for human existence is rapidly growing in importance. however, finding quantitative definitions for order, complexity, information and functionality of living systems remains a challenge. here, we review and develop insights into this problem from the concept of the biotic regulation of the environment developed by victor gorshkov ( – ). life’s extraordinary persistence—despite being a strongly non-equilibrium process—requires a quantum-classical duality: the program of life is written in molecules and thus can be copied without information loss, while life’s interaction with its non-equilibrium environment is performed by macroscopic classical objects (living individuals) that age. life’s key energetic parameter, the volume-specific rate of energy consumption, is maintained within universal limits by most life forms. contrary to previous suggestions, it cannot serve as a proxy for “evolutionary progress”. in contrast, ecosystem-level surface-specific energy consumption declines with growing animal body size in stable ecosystems. high consumption by big animals is associated with instability. we suggest that the evolutionary increase in body size may represent a spontaneous loss of information about environmental regulation, a manifestation of life’s algorithm ageing as a whole. modern civilization aims to provide an increasing number of people with decent living conditions. keeping the civilization running requires continuous work on its maintenance. with the increasing reliance of the civilization on the information processing and computer power, the phenomenon of life began to be studied from the viewpoint of its information content [ ] [ ] [ ] [ ] [ ] [ ] . gorshkov [ ] estimated the information processing capacity of the global biota from the rate of photosynthesis at bit s − assuming that the biota computes at maximum possible efficiency of the order of kt ≈ − joules per bit [ ] [ ] [ ] [ ] [ ] . this exceeds the global computing capacity of the modern civilization by about fifteen orders of magntude. recent estimates of computing efficiency in protein synthesis supported the proposition that living systems are fairly close to the landauer limit and many orders of magnitude more efficient than modern computers [ ] . per unit surface area, the biota consumes two orders of magnitude less power but performs ten millions more operations per second than modern supercomputers demonstrating a billion times greater computing efficiency [ ] . in section , we discuss how the high energy consumption by modern civilization is unlikely a sign of high orderliness but a sign of unsteadiness warning of a potential collapse. in the final section , we discuss how life's major organizing principle, persistence via ensuring genetic and environmental stability, gives the meaning to biological information. we discuss how big disruptive animals, humans, could nevertheless culturally evolve into the guardians of the biosphere and prolong its existence using the scientific analysis of the laws of life functioning and adopting behaviors respecting those fundamental laws. a more complete description of the biotic regulation concept can be found in gorshkov [ ] and gorshkov et al. [ ] , see also gorshkov and makarieva [ , , ] . here, we introduce its main propositions at the simplified background of the more conventional ideas about life, evolution, and environment (figure a ). the key genetic information of life is assumed to be that about reproduction. copying of genetic information occurs with errors (mutations), which ensure that all organisms in a population differ (genetic diversity). in any given environment, some organisms reproduce better than others, their genetic information predominantly propagates. the environment may experience random changes, and the criteria of selection it imposes on the organisms, change as well. this causes the genetic information of a species change with time, which on a larger scale constitutes biological evolution. (a) main genetic information is about how to reproduce. mutations that accumulate during reproduction (copying of genetic information) serve as an ultimate source for adaptive genetic diversity. the environment undergoes random changes. in a given environment, some individuals survive better than others; this represents natural selection. (b) main genetic information is about how to stabilize the environment in an optimal state. the genetic information written in quantum molecular memory cells can be copied without errors (ageing). classical objects (organisms) encoded by this information stabilize the environment compensating for external and internal perturbations. the optimal environment is the one where the genetic information that encodes this environment features maximum competitiveness. in other words, life encodes and maintains an environment where the algorithm that does so possesses maximum fitness. this qualitative picture does not explain the long-term persistence of life and leaves plenty of room for alternative visions. indeed, as mutations accumulate in the course of copying of genetic information, some individuals with erroneous copies will, in a given environment, reproduce better than others, so there will always be a natural selection of some sorts. however, selection based on relative fitness will not guarantee that the absolute fitness, i.e., the ability of organisms to produce a sufficient amount of healthy progeny, will not decline with time. indeed, while it has become clear that, in the human population, natural selection is too weak to prevent accumulation of mutational load [ ] , it is not clear what general principles would guarantee the necessary efficiency of selection for other species of the biosphere. besides genetic degradation, another opportunity for life to go extinct comes from the unpredictable, uncontrollable, and unfavorable environmental changes. a logical way to account for life's persistence without appealing to a lucky chance is to assume that life's basic information kit includes, as its key component, the information about how to regulate the external environment ( figure b) . governed by this program, living organisms impose a stabilizing impact on the environment keeping it in a state optimal for life's functioning. the notion of optimality presumes that, in this environment, those individuals that perform environmental regulation must be "the fittest". this condition of a simultaneous genetic and environmental homeostasis imposes strict constraints on the properties of the optimal environment. a comprehensive quantitative analysis of these constraints represents a distinct feature of the biotic regulation concept in comparison to other propositions of life's stabilizing environmental impacts, including the gaia hypothesis [ ] . essentially, the optimal environment must be strongly non-equilibrium, such that, if left without biotic control, it would rapidly degrade to a state decreasing fitness of all organisms. this condition ensures that a mutant with eroded program of environmental regulation, even if initially competitive in the optimal environment, will be unable to spread globally as it will have rapidly destroyed its life-important resources. evolution and environmental change are considered as first-order corrections to the main picture of life's homeostasis (figure b) , see also haldane [ ] . evolution occurs in the direction of a more efficient program of environmental regulation. paraphrasing a well-known saying about evolution, one can say that nothing in life sciences makes sense except in the light of life's persistence. how can living organisms ensure persistence of non-equilibrium environmental conditions? the information about characteristics of the optimal environmental state has to be stored and copied. since the environment of life is macroscopic, it represents a classical object that ages-changes irreversibly with time. copying of classical objects is not possible without information loss; they undergo decay and are different at any point of time. thus, the information about environmental conditions, as well as all other life's information, must be written using quantum carriers-objects that do not age and possess the property of identity. in most biological species, the information about life's complexity is written in the polymer molecules of deoxyribonucleic acid (dna). total information written in these molecules constitutes a species' genome. once this information is lost in extinct species, it cannot be recovered. from paleodata, we know about the dinosaurs, mammoths, and other extinct species. we also know about species driven to extinction by humans-steller's cow, the dodo bird, the passenger pigeon, the elephant birds, and others. their genomes are irreversibly lost and irrecoverable. no extinct species ever came into existence again. the paleodata also indicate that the majority of extant species did not change morphologically for millions of years [ ] . it logically follows that their genetic program remained invariant as well [ ] . furthermore, all extant life shares a common ancestor, i.e., during the four billion years of life existence there was only one origin of persistent life. the genetic information can only be copied, not created anew. copying requires energy expenditures that come from the external environment. information of the polymer dna molecules is written with use of four molecular letters-nucleotides. these four letters can bind into complementary pairs to form the double-stranded four-letter dna molecule. as this molecule is to be copied, the double dna strand unravels, and, on each of the two strands, the complementary part is synthesized. in the result, two identical dna molecules are formed of two different cells belonging to one and the same or different individuals of the same species. during the copying process, errors may occur partially erasing the information dna carries. these copying errors obey the well-known pattern of radioactive decay. in a characteristic time period (the half-life time), one half of the initial number of the copied molecular objects acquire some errors. the other half remains error-free and identical to the previous generation. this identity is what constitutes the quantum nature of life. if life did not possess this property, i.e., there were no identical copies produced during copying, it would have been impossible to sustain the orderliness of life. with the probability of point mutation affecting a given nucleotide pair of about ν = − per cell division [ ] and division frequency of the order of τ − = q/k, where q = w kg − is the universal mass-specific metabolic rate and k = × j kg − is the energy content of living matter [ ] , the genetic information of life would have melted completely in about τ/ν ≈ one billion years. the observed level of tolerated genetic polymorphism in biological species, about one mutation per nucleotides, indicates that a loss of function occurs when about one thousandth of the total amount of information has been lost. this gives a time scale of genetic decay of about one million years. incidentally, this is close to the mean time of species' existence [ , ] . if the program of life contains information about how to recognize and delete the erroneous copies from the population, then it could be possible to maintain life's orderliness for an unlimited period of time-or at least to prolong its existence far beyond the half-life time of genetic information. the necessary condition is that erroneous copies should be deleted faster than they reproduce themselves. again, this condition constrains the properties of the optimal environment where life could persist. recognizing and deleting the erroneous copies cannot be realized on the quantum level of dna molecules. classical macroscopic organisms are required that are able to consume energy and matter from the environment and function on the basis of the genetic dna program. namely, in a population of such macroscopic classical individuals that all age, the program of recognizing and deleting the erroneous information copies can be realized. it is the most complex part of the genetic program itself. this statement is key to the biotic regulation concept. competitive interaction and natural selection are not merely imposed on the population by an external environment being passive outcomes of the organism-environment interaction (cf. figure a) . instead, competitive interaction and natural selection represent the key part of the genetic program itself. this property is not captured in the studies of complexity maintenance by cellular automata e.g., [ , , ] -there the program of selection is external and unrelated to the properties of the algorithm it selects. for example, in the well-known experiment of mitchell et al. [ ] , selection was set to favor the algorithms that correctly performed a certain calculation. this selection strategy got no feedback from the selected algorithms. more generally, among the many aspects studied by information theory in biological systems [ ] , the crucial aspect of how life interacts with its environment is practically missing. macroscopic physical processes in the earth's environment do not copy each other but arise anew triggered by external energy flows, of which on earth the most important one is the solar radiation. all life and civilization are maintained by the ordered solar radiation which is close to the blackbody radiation with temperature t s = k. the earth receives solar energy in the form of massless photons. after these photons have perturbed the ground states of molecules on earth, and the excited states relaxed back to the ground state, the solar photons turn to thermal photons with mean temperature t e = k. the power of solar radiation absorbed by the earth's surface undergoes decay to thermal radiation via a multitude of diverse channels provided by the living systems, civilization, and the inanimate nature of winds, oceanic currents, storms, hurricanes, and tornadoes. as the black body radiation consists of photons with mean energy kt, where k is the boltzmann constant, each solar photon with mean energy kt s decays into approximately t s /t e = thermal photons of the earth with mean energy kt e . this decay of solar photons into thermal photons shape all events and determine the time of all processes on the earth's surface. in most fields of theoretical physics, it is assumed that time is isotropic, which presumes that its direction can be reversed. the equations of motion in theoretical physics do not contain information about the decay of excited states of matter. these equations describe transitions of kinetic to potential energy and back for the two known long-range interactions, electromagnetic and gravitational. in the gravitational interaction, time defines the periods of potential-to-kinetic energy transitions, as in ideal pendulum, or rotation of interacting masses over elliptic orbits that characterize the energy of their interaction. in neither of these cases does anything change in the considered processes except the number of oscillations or rotations grows counted from an arbitrary initial state. this number is referred to as time. thus, defined time does not have a direction and it can be reversed, i.e., it conforms to the condition of isotropy. the considered processes change if only one takes into account dissipation and decay of excited states. a major achievement of quantum physics consists in the discovery of the identity of the ground and excited states of atoms, molecules, and atomic nuclei. two quantum objects being in the same states cannot be distinguished from one another. all excited states conform to the law of half-life time decay: starting from a certain initial number of identical excited states, since the so-called half-life time counted using the number of non-dissipating oscillations or rotations, the number of the excited states diminishes by half. the remaining excited states are identical to the initial excited states. the second half undergoes spontaneous or induced decay. induced decay diminishes the half-life time, but does not change the pattern: there always remain states that have not undergone decay and are identical to the initial states. those states that have not undergone decay do not change ("wear") or age. only those states that have undergone decay age and wear. the half-life time is a fundamental constant equal for all specific states irrespective of their "age". life is capable of selecting quantum programs with the smallest or optimal half-life time in the environment. let us define time as the number of arbitrarily chosen non-dissipating oscillations or rotations that have occurred from the moment when a certain initial amount of ordered states capable of undergoing decay has been prepared, to the moment when they have all undergone decay. if a new excited state has not been prepared by then, the time disappears. the direction of time is uniquely related to the diminishing number of the excited states, and thus automatically relates the cause and consequence. the decay of an excited state is accompanied by release of energy that can be routed along the additional decay channels. the power of a process is equal to the energy of the half of the initial states that have undergone decay divided by the half-life time. an event is the process of decay of an ordered state capable of undergoing decay. if there is no decay, there is no time and no events. if the sun had been sending the same radiation power but in the thermal part of the spectrum corresponding to t s = t e = k, the earth would have remained as warm as it is now, but the decay of solar radiation would have been impossible. no processes related to this decay, including the process of life, would be possible. time would have stopped. the ordered states that can undergo decay are slowly prepared at the expense of the energy of solar radiation. in the absence of a program governing how they will decay, their decay occurs explosively and the diversity of the possible channels for energy transformation is limited. rare classical macroscopic physical processes, like wind, rain, storms, hurricanes, and tornadoes, "die" and arise anew. they consume the available energy in an explosion-like manner and discontinue until new stores of energy arise in the environment. molecular quantum copying sometimes spontaneously appears in the inanimate nature at the expense of previously accumulated energy which is likewise spent in an explosive manner (for example, in chemical reactions with catalysts or nuclear chain reactions). such reactions do not lead to the formation of classical objects that recognize and delete erroneous copies. the explosion-like ordered processes in the inanimate nature discontinue as soon as the energy stores have been depleted, after which all objects that are being copied disappear. the combination of classical and quantum processes to ensure persistence uniquely differentiates life from the inanimate world. to account for the apparent absence of life elsewhere in the universe, chopra and lineweaver [ ] proposed that life may originate relatively often but evolves too slowly to gain control over the planetary environmental conditions. the life-compatible conditions are otherwise unstable and quickly deteriorate driving the "non-regulating life" to extinction. in comparison, from the biotic regulation viewpoint, a "life" that is not capable of controlling conditions perpetuating its persistence, is not a life. as we discussed, self-copying (reproduction) and metabolism (energy consumption) are common to many processes in the inanimate world. life's persistence corresponds to a genetic program that suppresses the explosive energy consumption. a good example is provided by how the biota handles the phase transitions of water on earth. water vapor evaporation under the influence of solar radiation is a slow distributed process. condensation of water vapor, in contrast, is governed by the vertical velocity of the ascending air (the faster it ascends, the faster it cools and moisture condenses), so it may occur at an arbitrarily high rate that exceeds by orders of magnitude the rate of evaporation. such explosive-like release of energy takes the form of hurricanes and tornadoes that quickly deplete all water vapor previously accumulated in the atmosphere [ ] , table . over natural undisturbed forests on land, where the hydrological cycle is under biotic control, the spatial and temporal fluctuations of precipitation and wind are strongly suppressed [ ] [ ] [ ] . the biota of the forest plants, fungi, and bacteria on land is able to slow down the rate of water vapor condensation sucking the ocean-evaporated moisture to land. the rates of evaporation and condensation become more equal, and there appears an opportunity of an uninterrupted time that follows the decay channels generated by life. civilization slowed down the decay of uranium in nuclear fission reactions and uses them for energy production (table ) . accidental loss of control over the slow-down leads to explosions at the nuclear power plants (chernobyl, fukushima). civilization did not succeed in slowing down the decay of the prepared initial state in the thermonuclear fusion reaction. consumption of fossil fuels by civilization has been exponentially increasing demonstrating explosion-like dynamics [ ] . destruction of the forest cover by civilization likewise proceeds in an explosion-like manner, with losses of the order of % over one tree life span [ ] . the biomass of the immobile life persists due to the equality between the rates of synthesis and decomposition of organic matter by plants, bacteria, and fungi on land and in the ocean. large animals including humans are able to destroy the biomass of plants at high rates that significantly exceed the slow rate of photosynthesis. the uninterruptedness of the time of life has been maintained because the share of biomass consumption by big animals remained small. if all synthesized biomass is consumed, in an explosion-like manner, by large animals and man, the uninterruptedness of time can be broken and the stability of life on earth destroyed. therefore, the uninterrupted time on earth is determined by life in the decay channels that life itself regulates, i.e., it is a consequence of the existence of life. (only within the volume of the sun the thermonuclear reaction is slowed down at the expense of radiation emission that prevents the star from the gravitational collapse. it is the only slow-down of energy flow that is independent of life on earth.) in what is to follow, we consider these statements in greater detail. table . "explosion" and "slow-down" energy consumption patterns in the biota and civilization. [ ] . note that the total power of thermonuclear explosion of the tsar bomba is just about times lower than the power output from the sun's surface. the only known way to slowdown the thermonuclear reaction is to arrange the thermonuclear fuel within the sun's volume. the data are taken from [ ] . average energy store per kilogram is twice as much as that in conventional fuel ( kg of tnt∼ . × j). the strategic stockpile of explosives in various forms is assumed to correspond to three months of use for explosions. the global average (and local) power of explosions is determined by using the time of explosion and average mass (∼ kt) of the tnt exploded. the global power of tnt explosions is j/[ − s] = w. energy store per kilogram of organic substance has the same order of magnitude as that in the fourth column. the global supply of fossil fuels is determined by the power consumption under the assumption that the strategic reserves of fossil fuels are equal to the -month consumption by civilization. local and average power per unit of earth's surface area is assumed to be equal to the power of cars; energy consumption of heating and industrial production are characterized by the same order of magnitude. the global power consumption of fossil fuels is known to be equal to . × w. in columns and , energy consumption of plant biomass is considered with energy content k = × j kg − and global store of the order of kg [ ] assuming most land ecosystems are disturbed; fires consume gtc yr − [ ] , which constitutes % of primary productivity on land gtc yr − [ ] ( × w), which amounts to × w globally or . w m − for land on average. wood consumption due to logging consumes globally about . gtc yr − [ ] ; however, in many regions of the world, logging facilitates forest fires [ , [ ] [ ] [ ] . instantaneous power for forest fire is estimated as the power of blackbody radiation at k as w m − . decay time for fires, s = day, is estimated as local biomass store in forests (∼ kg m − ) multiplied by k = × j kg − and divided by instantaneous local fire power; instantaneous local power of energy consumption by big herbivores, - w m − , is taken from figure a ; their total energy consumption in unstable ecosystems may reach % primary productivity with a global average of % [ ] . in intact forests, fires are suppressed by vegetation cover controlling the water regime and occur less frequently than once in a thousand years compared to disturbed ecosystems when burning may occur every years. this is reflected in the mean value of burnt areas, which for non-anthropogenic fires is two orders of magnitude smaller than for anthropogenic fires [ , ] . big herbivores in intact forests are allocated less than % of primary productivity (figure b ). global estimates are made assuming % of primary production on land from intact ecosystems. gravitational long-range interactions (via buoyancy and condensation-induced atmospheric dynamics [ ] ) determine atmospheric dynamics. explosion-like energy release in storms (hurricanes and tornadoes) is not controlled by the biota. the energy storage per unit mass is estimated from volume-specific energy storage ρ a v = j m − , where v∼ m s − is wind velocity in the eyewall of the storm and ρ a = kg m − is density of atmospheric air. instantaneous power per unit surface area for storms is estimated as ρ a v = w m − . energy storage in floods is gh = j kg − , where h∼ m is height of the surge, g = . m s − is the gravitational acceleration. assuming that during the flood the water rises by h∼ m in t = days, the local flood power is ρgh(h/t) = . w m − , where ρ = kg m − is density of liquid water. mean global power for floods is estimated assuming that every flood lasts about t = days and in one year the total globally affected area is about s f l = km [ ] , ρgh(h/t)( t/[ year])s f l = w. total energy storage in floods ρgh ( t/[ year])s f l = j. total energy storage in storms is estimated assuming a storm lasting on average days and there being globally storms each year [ ] with total energy ρ a v hl = j, where h = km is height of the atmosphere and l = km is storm's radius where v m s − . total storm power is ρ a v l = × w, global surface-specific power density divides this number by the earth's surface area s e . the biotic pump mechanism regulates precipitation and winds. the dry air can ascend and descend in the atmosphere of earth with zero net power expenditure; in contrast, water vapor condenses as it ascends, disappears from the gas phase and returns to the ground surface in the liquid or solid form. this water vapor disappearance from the gas phase creates a vertical pressure gradient (a deviation from the hydrostatic equilibrium) that acts as a vertical force pushing the air upward. work of this force per unit time represents the power of the biotic pump air circulation [ ] . the nearly instantaneous restoration of the hydrostatic equilibrium of the air occurs at the expense of the horizontal air inflow, mostly from the adjacent oceans. in a steady state, this incoming flow of moist air increases the precipitation rate over the forests by the magnitude of the river runoff. how to harmonize the fluxes of evaporation and precipitation such that their difference is equal to the amount of moisture needed to compensate the river runoff-at the same time minimizing the occurrences of hurricanes, tornadoes, floods and droughts-represents one of the most complex processes of the biotic regulation of the environment. in intact forests, fluctuations of precipitaton are suppressed by the biotic pump mechanism [ , ] . the energy store in the atmosphere is given by pa is partial pressure of atmospheric water vapor. total store is given by the product of p v h γ s f o = j, where h γ = km is the scale height for the vertical distribution of relative partial pressure of water vapor in the gravitational field [ ] and s f o = m is the total global area of intact forest landscapes [ ] . decay time is the turnover time of water in the atmosphere. mean power of wind associated with condensation rate controlled by forests is is the universal gas constant and t∼ k is absolute temperature. the estimate of local power assumes that precipitation events on average take about one tenth of the time. characteristics are estimated of the atomic bomb (little boy) dropped on hiroshima on august . the bomb with mass of . t contained kg of enriched uranium. blast yield is kt of tnt ( × j). initial radius of explosion is taken as m. the fission of one atom of uranium- releases on average mev ( × − j) with taking into account the decay of its fragments or × j per kilogram of u. for low-enriched uranium ( to % concentration of uranium- ), which is usually used as fuel for thermal-neutron reactors at nuclear power plants, it corresponds to the energy storage of about × j per kilogram of uranium. although uranium is quite widespread in nature, only a relatively small portion of it is concentrated in deposits that are economically profitable for industrial development and use in nuclear energetics. identified resources in situ recoverable at a cost not exceeding usd per kilogram of uranium are estimated to be ∼ t [ ] . since natural uranium contains about . % of fissile isotope u, total storage of energy is given by . × kg × × j/kg∼ × j. presently, there are about nuclear power reactors in operation worldwide with generating electric-power capacity of × w. the average efficiency of conversion of heat to electric power is about %. total (global) power of nuclear reactors is estimated as w, while the mean power per unit surface area is w/[ × km ]∼ × − w m − , where the earth's surface area s e is taken into account. a typical nuclear power station generates electricity at a rate of ∼ w. taking into account that a nuclear reactor core has an effective radius of m, one can estimate the local surface-specific power of nuclear reactor as w/[ m] ∼ w m − . nuclear stations are designed for at least a -year operating life. in a search for quantitative criteria of life's orderliness and complexity, a proposition was put forward by chaisson [ ] , see also chaisson [ , , ] that evolutionary progress and an increase of complexity with time in both animate and inanimate nature is reflected in the magntiude of the energy rate density. assuming, additionally, that "complexity generally increases with evolution" [ ] , higher energy rate densities in organisms that appeared later in the evolution were interpreted as a correlation between energy rate density and complexity. here, we reconsider these estimates and their more recent interpretations [ ] to show that there is no evidence for any systematic large-scale changes in mass-or volume-specific energy rate density in the course of biological evolution. in the biological context, individual rate of energy consumption is called metabolic rate, so these terms will be used here interchangeably. in addition, since the density of living matter is close to the density of liquid water ρ = kg m − , mass m and volume v in living objects are related as m = ρv, thus mass-and volume-specific rates differ by a constant ρ. figure chaisson [ ] summarized his previous estimates, according to which the more complex plants with their metabolic rate of about w kg − evolved from the more primitive protists that presumably had a lower metabolic rate of about . w kg − . the latter figure was obtained by chaisson [ ] (p. ), see also chaisson [ ] , for the biosphere as a whole by dividing the global rate of photosynthesis f by global plant mass. using modern data, this estimate can be obtained as here, m = gtc is the total plant mass in the biosphere in carbon units [ ] , f = gtc yr − is the global gross primary productivity, k c = × j (kgc) − is the energy content of organic matter [ ] . chaisson [ ] used a lower value for plant biomass, gt instead of gtc ≈ gt and a lower value for the biosphere energy consumption ( erg s − = w instead of fk c = × w) to obtain q b = × − w kg − . chaisson [ ] figure , see also table of chaisson [ ] , figure of chaisson [ ] , attributed q b = . w kg − to protists and referred to it as "valid for the great majority of earth's lower plant life". in table of chaisson [ ] , it is stated that examples of such low energy rate density is provided by "phytoplankton, algae." this is incorrect. the low value of q b ( ) is due to the fact that most part of plant biomass is wood, which is metabolically inactive e.g., [ , ] . wood performs mechanical functions not related to the biochemical energy conversion. to estimate the energy consumption of plants per unit wood mass is similar to estimating the energy consumption of birds per unit mass of their nests or energy consumption of the civilization per unit mass of buildings. in the ocean, plants lack such metabolically inactive parts. global biomass of oceanic phytoplankton m p ≈ . gtc is several hundred times lower than m. with gross primary production of the ocean about f p ≈ f/ ≈ gtc yr − , mean mass-specific photosynthetic rate of phytoplankton is this value for phytoplankton is significantly higher than the values quoted by chaisson [ ] [ figure and references therein] for the higher plants like gymnosperms and angiosperms ( . - w kg − ). it falls on the upper range of mass-specific metabolic rates of life as a whole ( figure ) and coincides with the metabolic rate of human brain, which in young healthy adults constitutes around . µmol o min − g − [ , ] , which corresponds to w kg − assuming j (ml o ) − . direct measurements of metabolic rates in phytoplankton and protists confirm that these organisms do not have lower metabolic rates than the higher plants and animals ( figure ) . notably, even if we calculate the metabolic rate of higher plants per unit mass of their photosynthetic tissue, still for plants on land we obtain a mean figure of about w kg − , since the biomass of green leaves is about ten times larger than phytoplankton biomass supplementary information bar-on et al. [ ] , while gross primary productivity on land is about the same as it is in the ocean. this is also consistent with direct estimates of respiration rates in green leaves (figure ). metabolic portrait of life in terms of whole-body metabolic rate q (w) and mass-specific metabolic rate q (w kg − ) of individual organisms and their brains. pink shading denotes the proposed optimal range for life's functioning, approximately between and w kg − [ , ] . red solid lines are the allometric dependencies of q on body mass m for groups of heterotrophic species from table of makarieva et al. [ ] , gray dotted lines are the same dependencies for q = qm. the thinner red line for protozoa represents starved cells from ikeda [ ] [ ] . green solid line is the mass-specific rate of dark respiration in green leaves depending on leaf thickness l calculated from the data of wright et al. [ ] . linear size l (upper horizontal axis) and body mass m (lower horizontal axis) relate as l = (m/ρ) / . the dependencies for the mass-specific brain metabolic rate in ectotherms and endotherms on body mass (measured in vivo, violet solid line, and estimated indirectly, violet dashed lines) are constructed using the data of mink et al. [ ] . see section for details. in a more recent analysis, kempes et al. [ ] recognized that there is no consistent change of mass-specific metabolic rate across all life. kempes et al. [ ] wrote that while "multicellular life obeys a certain economy of scale: as organisms grow larger, the metabolic rate required to support a unit of mass is decreasing and larger mammals support more tissues for the same amount of energy", more recently "it has been observed that this scaling relationship is not preserved across all the taxa of life." indeed, makarieva et al. [ ] established that "mean metabolic rates of major taxonomic groups...converge on...a remarkably small range compared with the -to , -fold difference between the mean metabolic rates of the smallest and largest organisms that would be observed if life as a whole conformed to universal quarter-power or third-power allometric scaling laws." the dataset of makarieva et al. [ ] included a large compilation of prokaryote metabolic rates that had not been previously analyzed. namely, these data for the smallest organisms allowed the generalizations about the metabolic portrait of life to be made. kempes et al. [ ] did not cite the study of makarieva et al. [ ] , but referred to delong et al. [ ] who used the data of makarieva et al. [ ] for bacteria, converted them from mass-specific to whole-body basis and observed that the scaling exponent in bacteria, listed in table of makarieva et al. [ ] , becomes greater than unity when the allometry is expressed per whole-body mass. converting those data back to the mass-specific basis, kempes et al. [ ] discussed how the scaling exponent changes with growing body size of the organisms, noting that q first grows with size in prokaryotes, then it remains relatively constant in protists and then declines in larger organisms ( figure ) . however, makarieva et al. [ ] emphasized that the methodological inaccuracy of measuring the link between organismal size and metabolic rate is profoundly different in the unicellular versus the multicellular organisms. in unicells, especially in prokaryotes, it is common to measure metabolic rate of a unit mass (e.g., taking g dry mass of the bacterial suspension). cell size is not simultaneously measured. makarieva et al. [ ] see supplementary information retrieved cell sizes from independent sources, often estimating cell mass from linear cell size. this procedure does not impact the value of mass-specific metabolic rate, but it should profoundly impact the dependence between mass-specific metabolic rate and cell size, especially given that the size of bacterial cells can change depending on their nutrition status (growth, starvation, etc.). this source of error is absent in larger organisms, where metabolic rate is commonly measured on a whole-body basis simultaneously with the body mass. delong et al. [ ] and kempes et al. [ ] did not assess the uncertainty associated with the poorly known cell sizes of unicellular organisms; at the moment, their conclusion about the difference in the scaling exponents between prokaryotes, unicellular eukaryotes, and higher organisms lacks statistical significance and cannot be meaningfully interpreted. a more up-to-date analysis of ikeda [ ] controlling for the physiological state in protozoa indicates a decline in mass-specific metabolic rate with growing body size that is not distinguishable from what is observed in the groups of larger organisms (figure , thin red line). in summary, given that the low q b ( ) assumed to characterize the lower life forms in the analyses of chaisson [ ] and previous work appears to be a miscalculation, while phytoplankton q p ( ) falls instead on the upper border of all life energy rate densities, little support remains for a progressive increase in energy rate densities or any other consistent change in metabolic allometry with evolution ( figure ), see also analyses by ikeda [ ] , johnson et al. [ ] , kiørboe and hirst [ ] , hatton et al. [ ] . instead, since within evolutionary close groups of organisms the mass-specific metabolic rate declines with growing body size, while evolution tends to produce larger body sizes from smaller ones, the more recently evolved bigger forms within a group face the danger of leaving the life's metabolic optimum range of - w kg − [ ] . once this happens, the bigger forms with low q could lose competitiveness and be forced out from the biosphere if a new group in the same body size interval evolves that has managed to elevate its rate back to the optimal range. in this context, chaisson [ ] 's proposition that endotherms who elevated their q rates above those of the similarly sized ectotherms might have been more evolutionarily advanced, at least in some aspects, remains meaningful. figure displays the interplay between metabolic optimality and ecological dominance by comparing two groups of species, lizards [ ] and mammals [ , ] . the green squares indicate population energy consumption of several hundred populations of mammalian species world over (mostly mainland) with a geometric mean of × − w m − and half of all values confined between . × − and × − w m − . (population energy consumption j is equal to population density (individuals per unit area or inverse area per one individual) multiplied by individual metabolic rate q, j = nq, see methods). the red circles in figure a show lizard populations on the mainland, i.e., where the reptiles have to co-exist with mammals. the geometric mean energy consumption rate of a mainland lizard population is × − w m − with half of all values confined between . × − and × − w m − . the population energy consumption by mammals is more than an order of magnitude higher than that of mainland lizards. on the ecosystem level, lizards are precluded from claiming the same amount of energy resources as mammals. things turn different on isands, where the competition with mammals is significantly reduced [ ] . the blue circles in figure b show population energy consumption in island populations of lizards-compared to the mainland, it rises to × − w m − with half of all values confined between . × − and × − w m − . remarkably, the geometric mean values of population energy consumption in mammals and island lizards practically coincide. these data are consistent with the idea that the metabolically suboptimal lizards lose to mammals in the competition for ecosystem energy resources but re-gain their share of resources where this competition weakens or disappears altogether. during evolution, the endotherms could have forced out some of the ectotherms with suboptimal metabolic rates (figure ) from their ecological niches causing their extinction-either by themselves or at the backstage of major environmental cataclysms. (for example, the metabolically 'sub-optimal' dinosaurs, whose metabolic levels continue to be debated, see e.g., [ ] [ ] [ ] and references therein, could have been outcompeted by the evolutionarily young metabolically optimal mammals.) figure illustrates a "metabolic footprint" of how this could have happened. further insights into ecological dominance and metabolic optimality are provided by consideration of individual surface-specific energy consumption rates as dependent on the organism's body size. if, generally, the volume-and mass-specific metabolic rate q is size-invariant across life (figure ) , then the surface-specific metabolic rate (or surface-specific energy rate density) j = q/s = qρl /l = ρql, where s is the area of the organism's projection on the ground surface, should grow linearly with linear size l of the organism. the flux of energy via the body surface of the smallest organisms like µm bacteria is about − w m − , while the biggest organisms like endotherms consume up to w m − (figure a ). in between lie the characteristic values of net primary productivity p∼ w m − that plants generate using the energy of solar photons. the critical linear size l c = p/(ρq)∼ − m divides all life into the small and the big, the immotile and the locomotive, the ecologically sustainable and the ecologically unstable [ , ] . figure . the dashed line shows a characteristic value of primary productivity p = w m − ; (b) share β of ecosystem energy flux consumed by heterotrophs from a given body size interval in stable ecosystems on land (dashed contour histogram) [ , ] and in the ocean (solid contour histogram) [ ] . the lower β values for the largest organisms in the ocean compared to land might be related to over-fishing, which reduced fish biomass in some body size intervals by at least an order of magnitude see, e.g., [ ] . note the logarithmic scale of the vertical axis in (b). organisms of linear size smaller than l c consume less power than the biosphere is able to generate, j = ρql < p, per unit area of their projection on the earth's surface (∼l ). such organisms do not need to move actively or destroy live plants. they can satisfy their energetic needs by sitting and waiting for the dead plant parts falling down to become their food. like plants themselves, such organisms can form a continuous cover, e.g., in the form of bacterial mats or fungi mycelia. conversely, species larger than the critical body size cannot sit and wait. they require more food per unit area per unit time than the biosphere is able to produce. such organisms have to move collecting biomass synthesized by plants over a large home territory h exceeding their body projection area s = l by many orders of magnitude, h s. importantly, these bigger locomotive organisms must feed on live plant biomass. indeed, at any moment of time, they occupy only a tiny portion s/h of their feeding territory and thus cannot compete for dead plant biomass with the immobile heterotrophs (bacteria and fungi) that are ubiquitously present. this explains the pattern noted by cebrian [ ] that vertebrate (i.e., bigger) detritivores are rare and their role is insignificant. the smallest heterotrophs, on the other hand, should preferentially consume dead plant biomass (i.e., they should be detritivorous) because live plants defend themselves biochemically, and it would be costly to overcome their defense. the bigger organisms have no choice but to accept these costs. plants represent the energetic basis for ecosystem functioning-indeed, "the removal of primary producers leaves no system at all" [ ] . as the bigger organisms consume live plant biomass, the big herbivores as an ecological and evolutionary group present a persistent threat to ecosystem stability. fires also consume live plant biomass at a rate that is comparable to herbivores in disturbed ecosystems ( table , column ) representing some of the more voracious "plant-feeders" [ ] . however, unlike living organisms, fires do not evolve. thus, a natural ecosystem can in principle evolve to a state where it becomes resistant to fires "once and for all", by employing efficient water retention and moisture transport mechanisms. meanwhile any resistance the plants would evolve against herbivores, e.g., [ ] figure d ,e, can be in principle overcome by evolution of the big herbivores themselves. this does not mean that any big herbivore the evolution has produced will destroy its own ecosystem by overfeeding. however, there are no general ecological, biological, or physical laws that would prohibit the occasional self-destructive increase in population numbers of big herbivores. persistent, stable ecosystems, both on land and in the ocean that apparently managed to keep population densities of big herbivores in check allocate a very low portion of total ecosystem flux to the biggest organisms (figure b) . the largest share of ecosystem productivity ( - %) goes via the detrital channel of the smallest heterotrophs, bacteria, fungi, and eukaryotic unicells. these organisms keep their mass-specific metabolic rates within the optimal range ( figure ) and do not exceed the critical linear size l c associated with ecological instability (figure a ). together with plants, they represent the main working unit of life whose functioning is stabilized in accordance with the law of large numbers. invertebrates of intermediate size are still metabolically optimal (figure ), but their size is already supercritical (figure a ). these organisms are allocated a smaller share of about % of ecosystem energy flux (figure b) . finally, the biggest organisms, vertebrates, have fallen out of the optimal metabolic range and increased their body size by two orders over the critical l c . this double suboptimality is associated with the lowest share of ecosystem energy flux (less than %) allocated to these organisms in stable conditions (figure b) . recently in a discussion of the ecological role of big animals opened in the russian journal of ecosystem ecology, e.g., [ , [ ] [ ] [ ] [ ] [ ] [ ] [ ] hatton and galbraith [ ] suggested that the idea of an ecological and environmental disruption associated with big animals might be in contradiction with the approximate constancy of population energy consumption observed in different-sized vertebrate species, as established by hatton et al. [ ] [their figure e ]. to address this criticism, we first note that the pattern shown in figure b is consistent with the data of hatton et al. [ ] and hatton and galbraith [ ] . indeed, share β of ecosystem energy flux consumed by all organisms in a given body size interval is equal to where n i (m − ) is population density of the i-th species, q (w) is whole-body metabolic rate of individuals in this species, β i = n i q i /p is population energy consumption of the i-th species, n is the total number of species in the considered body size interval, and p (w m − ) is ecosystem primary productivity. if population energy consumption β i is independent of body size, as figure e of hatton et al. [ ] suggests, the decline of β with increasing body size will occur at the expense of the declining number n of the bigger species (e.g., in most ecosystems, there are more species of rodents than of big ungulates), as also recognized by hatton and galbraith [ ] . (note that if n i is expressed in ind m − , q should be expressed in w ind − and body mass m in kg ind − such that the relationship between whole-body q and mass-specific q metabolic rates, q = qm, is preserved.) furthermore, any global compilation of β i = n i q i /p necessarily includes population density data from significantly perturbed ecosystems including some overgrazed nature reserves in africa [ ] . in such ecosystems, population energy consumption by big animals can be artificially elevated by providing extra food to the protected species. controlling for the degree of anthropogenic disturbance may change the size-related pattern for β i from the current size-invariance towards lower values at larger body sizes. makarieva et al. [ ] using the data of damuth [ ] showed that the scaling of n i is different in open (savanna, presumably less stable) versus closed (forests, presumably more stable) ecosystems: in closed canopy ecosystems, n i declines more rapidly with growing body size. (we note in passing that in their pan-eukaryotic compilation of n i q i estimates hatton et al. [ ] included multicellular plants, which, unlike the remaining species of the biosphere, are known to contain large amounts of metabolically inactive structural tissues (wood). this raises the problem of defining the metabolically relevant whole-plant mass, which is smaller than total plant mass. relocating the relatively high plant β i towards smaller body sizes in figures e and c of, respectively, hatton et al. [ ] and hatton and galbraith [ ] , would have made the overall dependence of n i q i on body size across all eukaryotes more negative.) finally, the logic of hatton and galbraith [ ] 's objection that big animals are not dangerous since their share of consumption declines with body size such that they may not claim all ecosystem productivity does not contradict the statement that big animals are potentially dangerous. as long as big animals are confined within the ecological corridor of relatively low β as outlined in figure b , they do not pose a threat to the ecosystem functioning; the ecosystem is balanced. however, since big herbivores are physiologically selected to destroy live plants, it appears to be just a matter of time when a big species with a sufficiently destructive potential arises in the course of evolution. homo sapiens appears to be a conspicuous example [ ] . while there is no general increase in energy rate density q in plants and animals to "parallel the emergence of major evolutionary stages on the scale of life's history" cf. [ ] , the human civilization does consume a relatively large amount of energy per unit time per unit live mass. for , the global energy consumption p c = × w ( quadrillion btu per year) [ ] divided by cumulative mass of all human bodies m h = × kg [ ] gives q c = p c /m h = w kg − for the modern civilization. this is more than an order of magnitude higher than a typical q h ≈ . w kg − of the human body. in countries consuming several times more energy power than the global average, the ratio q c /q h may well reach . do those high energy rate densities, q c ∼ w kg − , testify for an increased complexity and evolutionary advancement our civilization could be proud of? our species appears to be using so much energy because a certain part of the homo sapiens population was historically forced out of their natural ecological niche (a warm tropical climate with a high biological productivity). with technological progress they have attempted to recreate the "paradise" conditions in a significantly more hostile and less productive environment of the higher latititudes [ ] . this requires a lot of energy. however, such elevated rates are not unprecedented in the living world. growing bacteria and animal tissues during peak activity, e.g., during flight, consume energy at rates of up to several thousand watts per kilogram [ ] . however, living organisms do not normally maintain such rates for a prolonged period of time. this indicates that such levels of energy consumption are not sustainable in the long term. likewise, while global rates of synthesis and decomposition of organic matter in the biosphere balance each other with a high accuracy ensuring life's persistence in the long term, the energy consumption of the modern civilization mostly derives from fossil fuels that are not renewable. all major mineral and energy resources that our civilization consumes at an ever increasing rate are in decline. unlike in the rest of life, here we are apparently dealing with an unsteady process of an explosion-like exponentially accelerating energy consumption that will end in the depletion of energy resources and the collapse of the corresponding energy-consuming structure. the instantaneous unsteady rate of energy consumption can be significantly higher than our civilization's q c in many processes like nuclear bomb explosions that cannot claim high orderliness (table ) . biospheric processes, in contrast, are characterized by a slow-down of potentially explosion-like processes. in particular, the biotic control of water vapor condensation in natural forests stabilizes the terrestrial water cycle against such weather extremes with explosion-like energy release as hurricanes and tornadoes [ , , ] . per unit surface area, the energy consumption of our civilization j c = p c /s e = . w m − , s e = × m , is about an order of magnitude lower than the global gross photosynthetic power on earth fk c /s e ∼ . w m − . however, it exceeds the ecologically permissible energy quota for animals of human size by more than an order of magnitude (figure b) , illustrating the significant disruptive potential of our species with respect to destabilising the biosphere. (direct consumption of primary productivity of the biosphere (food, cattle fodder, wood) by humans appears, in power units, to be of the same order of magnitude as consumption of fossil fuels which mostly determines j c [ ] . fires provide a similar disturbance removing annually about % of net primary productivity on land (table ) .) the structure of anthropogenic energy consumption reveals its low information content. about one third of all energy flow is spent on transport. transport vehicles represent macroscopic objects whose behavior can be characterized by just a few variables like the velocity vector of its movement. its environmental function consists of consuming petrol and releasing carbon dioxide. in contrast, the continuous cover of plants and immobile heterotrophs covering the earth's surface consists of microscopic memory cells that independently censor environmental conditions on a fine scale and react to environmental perturbations in a non-random way. each such cell possesses an information-processing capacity comparable with that of a modern personal computer [ ] . for example, the functioning of soil biota can change the life-time of organic compounds turning normally short-lived substances like proteins (that rapidly degrade under laboratory conditions) into long-lived ones and vice versa [ ] . the meaning of "once there were bacteria, now there is new york" may be precisely the opposite to what this phrase is usually invoked to imply [ ] . generally, living organisms impose control over their external environment via the surface of their bodies. with the growing size of compact animal bodies, the relative number of body cells that are in contact with the external milieu diminishes inversely proportionally to linear body size l: where s = l and v = l are the animal body area and volume, s = l cell and v = l cell are the mean area and volume of cells in the animal body. for large animals cells that interact with the external environment represent a negligible proportion of total body cells, e.g., η = − for l = . m and l cell = µm. information flux in the animal body is proportional to total energy consumption of the animal. the larger the animal, the smaller the share of its information flux it can spend to participate in the biotic regulation of the external environment which allows for its very existence. large animals use the available fluxes of energy and information almost exclusively to maintain the orderliness of their internal milieu rather than the external environment [ ] . failure to process environmental information at a sufficient rate leads to ecological misbehavior and demise. in certain aspects, this can be compared to the economic phenomenon of a decline of big monopolies that focus too much on themselves while paying insufficient attention to, and failing to predict, the market trends their smaller competitors eagerly monitor [ ] . when large animals begin to dominate the ecosystem, the environment left without biotic control rapidly degrades. as it degrades, so does the efficiency of competitive interaction, which can no longer stabilize the genetic information of life. thus, the spontaneous occurence, in the course of evolution, of yet bigger life's forms may not represent some evolutionary advancement, but, on the contrary, can be manifestation of degradation (ageing) of life's algorithm as a whole. life is trying to counteract this decay process by limiting the energy resources allocated to big animals ( figure b ). when these limits are overcome by whatever reason, the environment degrades locally ( figure ) or globally depending on the spatial scale where the limits have been broken. the dependence reported by wright et al. [ ] table and supplementary information, log (q d /q d ) = − . log (lma/lma), where q d and lma are, respectively, the rate of dark respiration per unit dry leaf mass and dry leaf mass per unit leaf surface area, q d = . nmol o (g dry mass) − s − , lma = (g dry mass) m − , corresponds to log (q/q) = − . log (l/l), where q is the rate of dark respiration per unit live mass and l is leaf thickness estimated from lma, q = . w kg − , l = . × − m. (assuming % dry mass content in live mass and live matter density ρ = g m − , we have l [m] = lma/ . [(g dry mass) m − ]/ρ; assuming j per ml o [ ] we have q [w kg − the data for starved protozoa from ikeda [ ] , table s - (thin red line in figure ) were corrected to • c assuming q = as in makarieva et al. [ ] by multiplying the original metabolic rates by ( • c−t)/ • c , where t is the measurement temperature in degrees celsius. note that, in table s - of ikeda [ ] , the wet mass of cells is mistakenly represented in nanograms ( − mg), it should be picograms instead ( − mg) to match the (correct) values for cell volumes. data for starved cells correspond to those rows in table s - of ikeda [ ] , where variables "gr" and "uns" are both zeros. the violet solid line in figure describes five mammalian species where oxygen consumption of the brains was measured in vivo [ ] figure , the violet dashed lines also include the remaining indirectly obtained estimates from table of mink et al. [ ] . in figure , lizard population densities n (m − , an inverse area per one individual) and body masses m were taken from appendix s of novosolov et al. [ ] ( island and mainland populations). mammalian population densities n and body masses m were taken from the supplementary data of hatton et al. [ ] ( populations for species). given the highly uneven numbers of populations studied for different mammal species, a mean population density for each mammalian species was estimated by taking a geometric mean of all population densities for the considered species. to obtain population energy consumption j = nq (w m − ), each lizard population density and each mean mammalian population density were multiplied by field metabolic rate q f (w) as established by nagy [ ] for reptiles, q f /q = . (m/m ) . , and mammals, q f /q = . (m/m ) . , respectively, where q = kj day − = . w, m = g. note the relationship between population energy consumption j = nq and individual surface-specific energy consumption j = ρql = q/s (figure a) , where s = l is the projection area of the individual on the ground surface: j = jsn. we have considered several key statements of the biotic regulation of the environment that views life and environment as inseparable entities. in closed non-equilibrium systems, entropy diminishes. in open non-equilibrium systems that consume ordered energy, entropy may remain constant and the systems can be stabilized in the non-equilibrium state as long as this energy inflow is available. for example, as long as solar energy generates the fluxes of evaporation from the oceanic surface, there will be hurricanes. however, for living systems, their order (measured as the stabilization of the genetic information against decay) is not directly related to the availability of external energy supply. if the organism does not eat, it will die. however, even if it does eat, it will die. this allows the formulation of a constraint on the information entropy [ ] : if the external energy flow is low ordered compared to the information carrier, the information content can be stabilized if and only if this information carries a program of such stabilization. the measure of how disordered external energy is as compared to the ordered object in question is provided by the probability of spontaneous arisal of this object in the presence of this energy. unlike hurricanes, living objects never arise spontaneously. the genetic program of life must carry a subunit about how to recognize and delete the copies with erroneous information. the process of recognition of erroneous copies represents a measurement. this measurement is performed by classical objects (individuals) that all age and die. the deletion of erroneous copies must involve their deprivation of essential resources like energy. thus, the efficiency of the stabilization program depends on the environmental properties ( figure ). under conditions of unlimited resource abundance, the deletion of erroneous copies (and defective individuals) from the population would be impossible [ ] . individuals incapable of environmental regulation will propagate at the expense of consuming the available resources until they force out all "regulators", after which the biotic regulation discontinues and the environment degrades. a theoretical question is whether it is possible to conceive a program that will sustain itself eternally (provided the solar energy flux and other basic planetary characteristics remain constant). this is not obvious. the appearance of big animals, and generally the body size growth in the course of evolution, shows that, when the cells of the multicellular body act in concert (mutually correlated), they can at least sometimes outcompete the small organisms that represent independent individuals. this increase in individual competitive capacity comes hand in hand with the ability of large animals to destroy live plant biomass ( figure ) . apparently, both in the ocean and on land, the large-scale evolutionary increase in body size-from unicellular organisms to multicellular invertebrates to yet bigger vertebrates-was paralleled with a decline of the share of ecosystem energy consumption allocated to them-from, respectively, ∼ % to ∼ % to ∼ % (figure b) . it is most pronounced in the ocean [ ] , where there are no large primary consumers: the biggest animals reside at the top of the food pyramid with extremely low population energy consumption. the energetic deprivation of the biggest animals, and the destabilization their high population numbers can invoke, suggest that the spontaneous increase in body size during life's evolution may represent a drawback of the life's algorithm as a whole, a sign of its ageing and losing order. given that the key function of life is to maintain an environment where it can stabilize itself, big animals with their low surface-to-volume ratio are unable to perform efficient environmental regulation but are potentially capable of destruction. brains, and the human brain in particular, are tissues that display a close to optimum volume-specific energy rate density ( figure ) . apparently, having discovered external energy resources, the humanity has found itself in a temporary state of energy abundance and has been so far disturbing and destroying the biosphere. however, it is in principle possible that with use of their metabolically optimal brains humans will realize the principles of life stability and implement them into their culture. the danger of resource abundance for population organization has been intuitively recognized in some cultures, whereby the belongings of the deceased are destroyed preventing the accumulation of wealth [ ] . however, a scientific recognition of the danger of abundance is required. if this is done, then the degradation of life could be stopped via human knowledge. the biotic regulation concept gives meaning to the information content of the genome: the information makes sense if it fits the general program of keeping the environment stable. this information can be copied infinitely without loss as it is written on quantum carriers (dna molecules) that do not age. the combination of quantum and classical properties is a distinct feature of life as compared to processes in the inanimate nature. in modern computers, programs are written on macroscopic non-quantum memory cells. errors that arise in these programs do not obey the quantum law of radioactive decay. this copying does not necessarily produce identical copies. technical problems or improper handling of physical data carriers can lead to disappearance of all copies. however, program users are able to recognize and delete erroneous, virus-affected programs and by doing so they act as the classical individuals in the natural biota. the modern civilization is in this context fully classical. it does not contain any quantum program of the stationary norm and how to prevent decay. life, on the other hand, does not contain any information about the stationary state of the civilization. in the inanimate nature, there cannot be sustainable development; there is only the decay of an ordered state that determines the direction of time. the irreversibility of time is manifested in the impossibility of creating perpetuum mobiles of the second kind-one cannot get work from heat at the same temperature. in the living nature there is only one example of sustainable development-it is the programmed development of an embryo from the egg or a plant from the seed. this development occurs strictly in line with the genetic program of the species that determines the decay channels for energy transformations; and which processes must occur at each stage. the normal process of development, as well as deviations from the norm, are well defined. this sustainable development according to the genetic program formed during the billions of years of biological evolution culminates in the stationary life stage of the adult individual. this life continues for a known period of time and ends with the decay and death of the individual. for most species, the biosphere provides sustainable conditions for the development of all generations of organisms for several million years. in contrast to biological species, human civilization does not have a program of sustainable development. such a program can be created only on the basis of fundamental research. in a broad sense, sustainable development of the civilization can be understood as a steady-state process of cultural change: the civilization continues to evolve culturally (in particular, scientifically and technologically), but the environmental conditions persist that enable all generations to thrive [ ] [ ] [ ] . currently, attempts at climate stabilization are primarily based on technology and aimed at mitigating carbon dioxide emissions. meanwhile, protection and conservation of natural ecosystems are viewed as a related but separate goal. reflecting this duality, there are different international organizations dealing with the presumably different sets of problems, e.g., the intergovernmental panel on climate change and the intergovernmental science-policy platform on biodiversity and ecosystem services [ ] . the biotic regulation concept indicates that environmental sustainability cannot be achieved without understanding and quantifying the genetically encoded regulatory functions of the natural ecosystems. a wide international effort is needed to study the stabilizing climate impact of the still remaining least disturbed natural ecosystems [ ] [ ] [ ] . long-term climate stability, and thus sustainability on a planetary scale, is contingent upon the existence of vast areas where natural ecosystems are allowed to operate maintaining the environmental conditions in a suitable for life state. science and information theory adaptation toward the edge of chaos. in dynamic patterns in complex systems computation at the edge of chaos: phase transitions and emergent computation information theory, evolution, and the origin of life life: the final frontier for complexity principles of ecology revisited: integrating information and ecological theories for a more unified science stores and flows of information in biota and civilization irreversibility and heat generation in the computing process minimal energy requirements in communication minimal energy cost for thermodynamic information processing: measurement and information erasure comment on "minimal energy cost for thermodynamic information processing: measurement and information erasure the thermodynamic efficiency of computations made in cells across the range of life what can we learn from natural ecosystems to avoid a civilization breakdown? in global stability through decentralization? energy flows in low-entropy complex systems genetic programming: on the programming of computers by means of natural selection; complex adaptive systems revisiting the edge of chaos: evolving cellular automata to perform computations cosmic evolution: the rise of complexity in nature energy rate density as a complexity metric and evolutionary driver the natural science underlying big history on the possibility of physical self-organization of biological and ecological systems information in the animate and inanimate worlds physical and biological bases of life stability gaia and biotic regulation: understanding the homeostasis of the ecosphere biotic regulation of the environment: key issue of global change quantum and classical aspects of life organization time in life, technology and physics key ecological parameters of immotile versus locomotive life mutation and human exceptionalism: our future genetic load gaia as seen through the atmosphere the stasis of evolution fossilized nuclei and chromosomes reveal million years of genomic stasis in royal ferns the distribution of rates of spontaneous mutation over viruses, prokaryotes, and eukaryotes aging, senescence, and turnover in plants on the dependence of speciation rates on species abundance and characteristic population size the case for a gaian bottleneck: the biology of habitability fuel for cyclones: the water vapor budget of a hurricane as dependent on its movement biotic pump of atmospheric moisture as driver of the hydrological cycle on land temporal complexity of daily precipitation records from different atmospheric environments: chaotic and lévy stable parameters revisiting forest impact on atmospheric water vapor transport and precipitation global energy outlook : the next generation of energy deforestation and world population sustainability: a quantitative analysis astrophysical quantities the biomass distribution on earth historic global biomass burning emissions for cmip (bb cmip) based on merging satellite observations with proxies and fire models primary production of the biosphere: integrating terrestrial and oceanic components improving carbon stock estimates for in-use harvested wood products by linking production and consumption-a global case study fire history of dark needle coniferous forests in pechora-ilych nature reserve since second half of xix century to present time the impact of availability territory and terrain characteristics on location of burnt areas in dark coniferous forests pechora-ilych nature reserve the fire history in pine forests of the plain area in the pechora-ilych nature biosphere reserve (russia) before : possible anthropogenic causes and long-term effects comments on "is condensation-induced atmospheric dynamics a new theory of the origin of the winds? characteristics of river floods and flooding: a global overview resolution dependence of future tropical cyclone projections of cam . in the u.s. clivar hurricane working group idealized configurations mapping the world's intact forest landscapes by remote sensing red book") mean mass-specific metabolic rates are strikingly similar across life's major domains: evidence for life's metabolic optimum metabolic inequity of living tissues provides clues for the observed allometric scaling rules cerebral blood flow and cerebral metabolic rate of oxygen requirements for cerebral function and viability in humans noninvasive quantification of whole-brain cerebral metabolic rate of oxygen (cmro ) by mri the distribution of energy flow among the organisms of different dimensions an analysis of metabolic characteristics of planktonic heterotrophic protozoans the worldwide leaf economics spectrum ratio of central nervous system to body metabolism in vertebrates: its constancy and functional basis shifts in metabolic scaling, production, and efficiency across major evolutionary transitions of life universal constant for heat production in protists shifts in mass scaling of respiration, feeding, and growth rates across life-form transitions in marine pelagic organisms linking scaling laws across eukaryotes power in numbers. drivers of high population density in insular lizards cope's rule, the island rule and the scaling of mammalian population density dinosaur metabolism and the allometry of maximum growth rate formal comment on: myhrvold ( ) dinosaur metabolism and the allometry of maximum growth rate inferring the physiological regimes of extinct vertebrates: methods, limits and framework universal patterns of matter and energy fluxes in land and ocean ecosystems the empty sea. the future of the blue economy role of first-order consumers in ecosystem carbon flow playing chutes and ladders: heterogeneity and the relative roles of bottom-up and top-down forces in natural communities dangerous giants?-large herbivores, forest feedbacks and climate tipping points rus productivity and content of macro-and microelements in the phytomass of ground vegetation of typical and unique taiga forests of the northern urals (example of spruce-fir forests of the pechora-ilych nature reserve) key ecological parameters of immotile versus locomotive life gorshkov on the development of mathematical models of ecosystems what is most important to the universe? (comment on the article mass-specific versus whole-body metabolic rate in biological scaling analyses (commentary on territoriality and flock formation as possible mechanisms for maintaining species stability: commentary on v key ecological parameters of immotile versus locomotive life body size, energy consumption and allometric scaling: a new dimension in the diversity-stability debate how many times has the human population doubled? comparisons with cancer energetics of the smallest: do bacteria breathe at the same rate as whales? energetics of the biosphere persistence of soil organic matter as an ecosystem property x-inefficiency in monopolies field metabolic rate and body size destroyal of the personal belongings of the deceased. j. de la société des océanistes world commission on environment and development. environ. policy law three pillars of sustainability: in search of conceptual origins new paradigm of state policy in the field of ecology and environment and climate protection securing the climate benefits of stable forests the exceptional value of intact forest ecosystems the authors are grateful to mikhail s. onegin, antonio d. nobre, and two anonymous referees for useful comments. the authors declare no conflict of interest. the following abbreviations are used in this manuscript: btubritish thermal unit, btu = j dna deoxyribonucleic acid gtc gigaton of carbon, gt = t = kg ind individuals lma dry leaf mass per unit leaf surface area mevmegaelectronvolt, mev = ev = . × − j tnt trinitrotoluene key: cord- -vpw g authors: zhang, l.z.; zhu, d.s.; deng, x.h.; hua, b. title: thermodynamic modeling of a novel air dehumidification system date: - - journal: energy build doi: . /j.enbuild. . . sha: doc_id: cord_uid: vpw g a novel air dehumidification system is proposed. the proposed system incorporates a membrane-based total heat exchanger into a mechanical air dehumidification system, where the fresh air flows through the enthalpy exchanger, the evaporator and the condenser subsequently. thermodynamic model for the performance estimation of the combined system is investigated. processes of the fresh air and the refrigerant are studied. two additional specific programs are devised to calculate the psychrometrics and the thermodynamic properties of the refrigerant r a. annual energy requirement is . × ( ) kj per person, or % saving from a system without energy saving measures. it is often necessary to control and modify the water vapor content in the air: the operation is quite usual in air conditioning. normally the water vapor content of atmospheric air is small, some tens of grams per kilo of air; nonetheless, due to the very high heat of vaporization, the latent heat content in air conditioning is of the same order of the sensible one. the relative importance of latent load increases with the ventilation rates to buildings. higher ventilation rates are dictated both by better comfort requirements and by the most recent standards such as the ashrae / [ ] . more recently, people's concern on indoor air quality has been greatly deepened since the outbreak of the severe acute respiratory syndrome (sars) epidemic that molested south china and some other parts of the world in this spring and caused a loss of . billion us$ (or . % gdp) in china alone and billion us$ globally [ ] . the mechanisms of sars virus spreading is complex and remains a mystery till now. however, it is believed that enough fresh air ventilation is helpful in decreasing the possibility of being infected by the disease. ventilation air is the major source of moisture load in air conditioning. as shown in fig. for a moisture load estimation of a medium size retail store [ ] , ventilation air constitutes about % of the total moisture load in most commercial buildings. as a consequence, treatment of the latent load from the ventilation air is a difficult and imminent task for hvac engineers, especially in hot and humid climates like south china. traditionally, latent load and sensible load are treated in a coupled way. because air is not only for ventilation, but also a heat transfer medium, and large quantities of air is needed to extract the sensible load, energy requirements are very high. another problem with this technique is that in transit seasons, humidity will lose control [ ] . there is an increasing trend to separate the treatment of sensible and latent load by using an independent humidity control system. according to this concept, the latent load of a room is treated by an independent humidity control system, while the sensible load is treated with some other alternative cooling techniques such as chilled-ceiling panels. since the circulating air is dramatically reduced, energy consumption can be reduced substantially. another benefit is that chilled water or suction temperatures can be raised, resulting in increased equipment efficiency and decreased operating costs. it is estimated that % of the energy used www.elsevier.com/locate/enbuild energy and buildings ( ) - could be saved with chilled-ceiling panels combined with independent humidity control system, in comparison to a traditional coupled system [ , ] . nevertheless, due to the hot and humid climates in south china, energy for moisture control with an independent humidity control system still accounts for % of the total energy for air conditioning. thus, energy recovery measures must be combined to an independent humidity control system. in this study, a novel air dehumidification system, namely, mechanical dehumidification with membrane-based total heat exchanger, is proposed. the thermodynamic modeling of the system is performed. through hour-by-hour analysis, the annual primary energy consumptions for the systems proposed are discussed. a schematic of the new air dehumidification system modeled in this work is shown in fig. (a) and its psychrometrics are shown in fig. (b). in this system, a membrane based total heat exchanger is used to pre-cool the fresh air before it is pumped to a refrigeration system for air dehumidification. the total heat exchanger has a membrane core where the incoming fresh air exchanges moisture and temperature simultaneously with the exhaust air. in this manner, the total heat or enthalpy from the exhaust is recovered, and both the temperature and the humidity of the fresh air are decreased, which results in energy saving. then the cooled and dehumidified fresh air is flowed through the condenser of the refrigeration system, to satisfy the requirements of supply air: g/kg humidity and c in temperature. this system is relatively simple, since the membrane system has no moving parts, and is compact. desiccant wheels may be another choice, however, in some circumstances, gas or other thermal heat may be difficult to find. the control of the new system is easier than a conventional compression dehumidification system, because no other components except a membrane system is added to the system. the differences are the operating parameters are changed, and much fan power is needed. the membrane system operated in near atmospheric pressure condition, the maintenance is easy. this study is to estimate the energy performance of a novel air dehumidification system by thermodynamic analysis. the modeling methodology of the refrigeration cycle is a steady-state one. they are sufficient to reflect the coefficient of performance or the energy performance of the refrigeration cycle. even though more detailed models are proposed by some authors, see [ , ] , they are compli-list of symbols a tot total exchange area (m ) c constants in sorption curves cop coefficient of performance c p specific heat (kj kg À k À ) d wm water diffusivity in membrane (kg m À s À ) h specific enthalpy (kj/kg) k s convective mass transfer coefficient in supply side (kg m À s À ) m_ mass flow rate (kg/s) dp total pressure rise (pa) q heat (kw) cated and case-sensitive. in other words, the distributed parameter models in such studies are strongly based on design parameters of a specific refrigeration system. those detailed models just gave very generalized equations for the calculation of heat and mass transport in each component and rely heavily on manufacturers' product empirical data. further, this study gives a general view of energy savings in sub-tropical regions, which do not rely on a specific system. furthermoreover, the more detailed partial difference models in other studies are difficult and slow in finding a solution. it is difficult to use such models in a wholeyear-hour-by-hour simulation. those more complicated models are usually necessary to study transient responses and start-up characters of a refrigeration cycle, which is beyond the scope of this study. the effects of the refrigeration cycle on the whole system are demonstrable. a thermodynamic model of the refrigeration system is formulated based on the processes of refrigerant r a shown in fig. . saturated r a liquid at point flows through an expansion valve and becomes wet vapor at point . refrigerant at this state flows to the evaporator (also the dehumidifier) where it chills and dehumidifies the fresh air and evaporates to point and further superheats to point . then the refrigerant vapor is pumped by a compressor to point where the vapor is displaced to the condenser and condensates from state to through . the superheat is set to c. it should be noted that the exact degree of superheating may be affected by many factors, such as evaporator, expansion valve, and compressor, and are strongly related to operating conditions, control strategies. experiments found superheating are in the range of - c; and the superheating increases with air tempera- ture in the evaporator, from to c when the expansion valve is fully open. from viewpoint of energy use, too large superheating is not good. generally, - c superheating are possible. refrigerant superheating refers to the superheating in the evaporator. superheating from tubes can be neglected with well tube-insulating, since superheating from such sources is harmful to energy performance and should be prevented. the effects of heating in the compressor are included in the compressor's isentropic efficiency. the specific enthalpy of the refrigerant at the compressor exit is calculated by where h s is the isentropic efficiency; h , is the specific enthalpy at the condensing pressure by isentropic compression from the evaporating pressure. experimental results have shown that the isentropic efficiency is a weak function of the displacement volume, and varies linearly with the compressor speed. in this analysis, a constant isentropic efficiency of . is assumed, neglecting the rotational speed of the compressor. the specific enthalpy after the expansion valve is calculated by the degree of dryness at the inlet of the evaporator where h , is the specific enthalpy of the saturated liquid refrigerant at the evaporating pressure. the electricity consumed by the compressor where m_ f is the mass flow rate of refrigerant (kg/s); h motor is the motor efficiency, which is considered as . . the energy load of the evaporator heat rejected in the condenser refrigeration efficiency cooling and dehumidification of the incoming fresh air are performed in the evaporator. a detailed modeling of the evaporator and the condenser are rather complicated [ , ] . usually, they are divided into regions associated to the phase of the refrigerant. each region constitutes a separate heat exchanger. in the case of the condenser, the superheated vapor, the condensation and subcooled liquid regions are considered, whereas for the evaporator it is divided into the evaporating and superheated vapor regions. for each region, the refrigerant side and air side convective heat transfer coefficients need be calculated from the established correlations for single-phase and two-phase flow. for the evaporator, when the average fin surface temperature is calculated to be less than the local water dew point of the air stream, moisture condensation will occur. under these conditions, the air heat transfer coefficients can no longer be calculated as in dry conditions, and a water mass balance must be carried out. in this case, the enthalpic method, proposed by threlkeld [ ] and introduced in ashrae handbook [ ] was most adequate for use. according to this procedure, the driving force for heat transfer is assumed to be the difference between the saturated enthalpy of the air flowing over the fins and a fictitious saturated air enthalpy evaluated at the refrigerant temperature. the analysis of air cooling and dehumidifying coils requires coupled, non-linear heat mass transfer relationships. while the complex heat mass transfer theory that is presented in many textbooks is often required for cooling coil design, simpler models based on effectiveness concepts are usually more appropriate for energy estimation. these techniques are resulted from basic heat and moisture transfer equations for simultaneous heat and moisture transport. therefore, in this study, to ease the analysis, thermal performance of the heat exchangers regions is evaluated by the (e, ntu) method. according to this procedure, the heat exchanger effectiveness is defined as where t hi and t ci are the inlet temperatures of the hot and cold fluids, respectively (k). because the operations are set to fluctuate around the design points, constant evaporator and condenser effectiveness are assumed in the simulations. then the air states at the outlets of evaporator and condenser could be obtained. the heat extracted in the evaporator is calculated by where m_ a is the mass flow rate of fresh air stream (kg/s); h ab and h ac are the specific enthalpies of air at point b and c, respectively. similarly, heat rejected at this portion of the condenser is governed by it should be noted that an energy balance requires that eq. ( ) equals to eq. ( ); while q c calculated from eq. ( ) is only a portion of that calculated by eq. ( ). in the study, the evaporating temperature is fixed to c, while the refrigerant flow rate and the condensing temperature varies according to the cooling load of the evaporator and the outside weather conditions. usually, a c log mean temperature difference between the condensing refrigerant and the air flowing through it is required. energy saving for conditioning fresh air can be achieved by the application of heat recovery ventilators, in which a fraction of energy is recovered from the exhaust air to the supply air. there are presently two kinds of techniques available for heat recovery ventilators: sensible heat exchangers and energy wheels. the sensible heat exchangers are simple and reliable, but they cannot recover latent energy. energy wheels, which could save latent energy, are problematic due to rotating moving parts. hydrophilic polymer membranes provide a new alternative. some membranes such as polyethersulphone, cellulose triacetate, and polyvinylchloride, are useful in separating moisture from the vapor/air mixture, due to their strong affinity to the water molecule. the strong affinity also leads to the high permeation difference between water and air. the permeability ratio of water to air ranges from to , . in other words, gases other than vapor can hardly permeate through the membrane. these features have led to the development of a novel ventilator, the so-called membrane based enthalpy exchanger in which both the sensible heat and the moisture are transferred simultaneously through the membrane. since the membranes are very thin, both the heat and the moisture transfer rates can be very high. furthermore, no water condensation happens in the membrane system, which prevents hygienic problems of microorganism growth that is common for cooling coils. in this study, a membrane-based enthalpy recovery ventilator developed in the laboratory is used [ ] . two effectiveness: sensible effectiveness (e s ) and latent effectiveness (e l ) are defined. air state at point b in fig. is calculated by: the membrane-based energy recovery ventilator is just like a traditional plate-type heat recuperator. the only difference is that hydrophilic membranes are used in place of metal plates. a total number of transfer units is used to reflect the sensible heat transfer in an exchanger. for the membrane exchanger that has equal area on both sides of the air streams, the total number of transfer units for sensible heat is [ ] : where u is the total heat transfer coefficient (kw m À k À ), a tot is the total exchange area (m ), m_ a is the mass flow rate (kg/s), and c pa is the specific heat of air (kj kg À k À ). the sensible effectiveness is a function of two dimensionless parameters, ntu and c min =c max , the ratio of minimum to maximum heat capacity rate of the two air streams. for un-mixed cross flows, it can be expressed as [ ] [ ] moisture transfer is more complicated due to the couplings between moisture transfer and operating conditions, as well as membrane materials. by clarification of moisture resistance in membrane, a form similar to eq. ( ) for latent effectiveness has been proposed and validated by the authors as e l ¼ À exp expðÀntu : l m_ min =m_ max Þ À ntu À : and and where k s is convective mass transfer coefficient in supply side (kg m À s À ); d the membrane thickness, and d wm is the water diffusivity in membrane (kg m À s À ); c and w max are constants in sorption curves, which determine the equilibrium between the membrane and moisture at its surface by where u is the moisture uptake in membrane at two surfaces (kg kg À ). the convective mass transfer coefficient k can be estimated from convective heat transfer coefficient by a sensible effectiveness of . is easily obtained with a membrane system, and the latent effectiveness is about . of the sensible effectiveness according to a case study in [ ] [ ] . fan energy is an important factor in the annual energy consumption of an hvac system. fan (pump) performance can be characterized by its efficiency, which itself is dependent on operational air flow rate. mostly, rated volumetric flow rate, pressure rise and efficiency are available from the manufacturer. then rated power can be calculated as where v a is air (water) volumetric flow rate (m /h), dp is total pressure rise (pa), h fan is fan (pump) efficiency. the simulations are conducted on an hour-by-hour basis. the air flow rates are dictated as kg/h per person. the operating hours are from : to : . fan efficiency is selected as . . for the convenience of comparison, energy consumed in the form of electricity is converted to primary energy by a factor of . . in addition, two specific programs was written to calculate the psychrometrics and the thermodynamic properties of r a. it is based on a cubic equation of state [ ] . the calculations are on a per person basis. it is recommended that each person has kg/h of fresh air. the cop varies with both the evaporating temperature and the condensing temperature. the influence of the condensing temperatures on the cop is shown in fig. . as can be seen, the cop decreases with increasing condensing temperatures. when the condensing temperature increases from to c, the system cop decreases from around . - . . following correlation could be formulated for the relation for the refrigeration evaporating at c: the effects of the evaporating temperature on the cop are shown in fig. . the system cop rises with increasing evaporating temperatures. in fact, when the evaporating temperature increases from À to c, cop is improved from . to . . a correlation has been formulated for the analysis of the system performance: cop ¼ : t e þ : t e þ : t e þ : ( ) where the condensing temperature is fixed as c. fig. shows the distribution of the cop of the refrigeration system during a year. as indicated, in winter, the system has higher performance, in contrast, when it's hot in summer, the system cop decreases, which will in return deteriorate the energy requirements. in the analysis, the system is used to treat the latent load solely, and the sensible load of the room is around w/m , which will be extracted by chilled-ceiling panels. results indicate that the annual total energy requirement is .  kj per person. in comparison, an air dehumidification with no energy recovery measures would consume more than .  kj per person of primary energy. in other words, energy saving is %. considering local primary energy price of . usd/mj, the annual economic return for each person would be usd, which is not a small amount, considering china is still a developing country and the energy price is low. with oil prices growing very fast now, we believe the savings potential could be higher in future. fig. plots the primary energy requirements by the dehumidification system for each person in each month in a year. in hot and humid regions like guangzhou, air dehumidification is required most of the year. the energy values vary from .  to .  kj per month per person. in january and february, when it is the dry season, energy requirements are the least. in august, it is the most humid season, required energy is the largest. in office buildings, the moisture load from ventilation air comprises almost all the moisture load. the percentages of the energy required in each month to the annual total energy are shown in fig. . five months from may to september account for . % of the yearly energy load. other months account for the rest . %. south china has a long hot and humid summer. the energy for air dehumidification is substantially large. to save energy while ensuring a healthy built environment with enough fresh air ventilation, an independent air dehumidification system with energy recovery is necessary. concerns on indoor air quality have prompted the researches of novel air dehumidification techniques. this study proposed a new air dehumidification system in which a mechanical dehumidification is combined with a membranebased enthalpy exchanger. an hour-by-hour simulation reveals that the novel independent air dehumidification system could save % of primary energy. with this system, the annual total primary energy used for independent air dehumidification is around .  kj per person. standard - , ventilation for acceptable indoor air quality economic toll of sars, china youth daily dehumidification equipment advances energy savings potential of chilledceiling combined with desiccant cooling in hot and humid climates indoor humidity behaviors associated with decoupled cooling in hot and humid climates thermal comfort and energy consumption of the radiant ceiling panel system, comparison with the conventional all-air system cyrano: a computational model for the detailed design of plate-fin-and-tube heat exchangers using pure and mixed refrigerants numerical simulation of a variable speed refrigeration system thermal environmental engineering energy estimating and modeling methods membrane-based enthalpy exchanger: material considerations and clarification of moisture resistance effectiveness correlations for heat and moisture transfer processes in an enthalpy exchanger with membrane cores thermophysical properties of , , , -tetrafluoroethane (r a) this project is supported by national natural science foundation of china. this project is also supported by the natural science foundation of south china university of technology. key: cord- -efbfqnem authors: axelrod, simon; gomez-bombarelli, rafael title: geom: energy-annotated molecular conformations for property prediction and molecular generation date: - - journal: nan doi: nan sha: doc_id: cord_uid: efbfqnem machine learning outperforms traditional approaches in many molecular design tasks. although molecules are often thought of as d graphs, they in fact consist of an ensemble of inter-converting d structures called conformers. molecular properties arise from the contribution of many conformers, and in the case of a drug binding a target, may be due mainly to a few distinct members. molecular representations in machine learning are typically based on either one single d conformer or on a d graph that strips geometrical information. no reference datasets exist that connect these graph and point cloud ensemble representations. here, we use first-principles simulations to annotate over , molecules with the ensemble of geometries they span. the geometrical embedding of molecules (geom) dataset contains over million molecular conformers labeled with their relative energies and statistical probabilities at room temperature. this dataset will assist benchmarking and transfer learning in two classes of tasks: inferring d properties from d molecular graphs, and developing generative models to sample d conformations. machine learning outperforms traditional rulebased baselines in many molecule-related tasks, including property prediction and virtual screening [ ] [ ] [ ] , inverse design using generative models [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] , reinforcement learning [ ] [ ] [ ] [ ] , differentiable simulators [ , , ] , and synthesis planning and retrosynthesis [ , ] . these applications have been enabled by reference datasets and tasks [ ] , and by algorithmic improvements, especially in representation learning. in particular, graph convolutional [ ] [ ] [ ] , and more recently equivariant neural network architectures [ ] [ ] [ ] , achieve state-of-the-art performance in a variety of tasks. unlike other data structures, molecules do not have an obvious basic representation. strictly, they exist as ensembles of d point clouds [ ] . in chemistry, they are typically represented as graphs with domain-specific annotations to describe spatial arrangement. molecular representations in machine learning, and the existing reference datasets, typically use either graphs [ ] , or a single point cloud per molecule [ ] . because of the non-overlapping datasets and tasks, the interplay between graph and d features remains unexplored from a representation learning perspective. molecular representations geared for processing by humans are well-studied [ ] . a molecule is a stable spatial arrangement of atoms. this arrangement fluctuates in time, as it exists on an energy surface with many local minima. it is generally possible to identify chemical bonds that connect pairs of nearby atoms in a molecule. these bonds can be classified in qualitative classes (single, double, etc.). molecules are represented in chemistry through d projections of the atom point cloud onto onto a plane, with bonds symbolized as lines and atoms in the nodes represented as their atomic symbol. the stereochemical formula utilizes perspective and node and edge notation to capture d orientation beyond a simple undirected graph, and can also be transformed into a string representation like smiles [ ] or inchi [ ] . multiple d structures can have the same connectivity but different spatial arrangements. the set of stable spatial structures that can inter-convert at room temperature are called conformers. the ensemble of conformers a molecule can access, and their relative populations, are dictated by their relative energies. conformers are typically not represented explicitly, and the projection formula is understood to embed all possible conformers. it is possible to annotate a molecular entity with one or more valid geometries through physics-based simulations. finding the conformer with the lowest possible energy, or enumerating all thermally-accessible ones is computationally challenging [ ] . indeed, utilizing generative and autoregressive models to guess valid, high-likelihood conformations from a molecular connectivity is an exciting and active area of development [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] . thus, two classes of learning tasks and two corresponding representations are generally of interest. surrogate modeling tasks aim to replace physics simulators, and relate molecular entities existing in one specific point cloud state (conformer) to an expensive simulation outcome. these are natively d point cloud tasks. for predicting of experimental properties of chemical species, only the stereochemical projection formula is available as input. graph-based neural networks, however, cannot process stereochemical features natively and flatten the representation into a plain graph, and thus struggle to differentiate between stereoisomers. since the low energy conformers will be most abundant in the ensemble, it is common to annotate chemical species data with one arbitrary conformer to add stereochemical data back. these point cloud annotations of the graph are obtained from cheap simulations with poor guaranties of finding representative minima. furthermore, this addition does not result in significant performance gains [ ] . this may be due to the fact that the predicted property emerges from the ensemble of conformers, and not from one member. a number of open questions thus arise in relating these disparate tasks and representations, such as (i) the capacity of graph-based architectures to infer the ensemble of d conformers from which properties arise, (ii) novel methods to embed the stereochemical formula without relying on explicitly sampling d conformations, (iii) the ability of generative models to replace expensive physics-based generation of conformations, and (iv) whether exhaustive annotation with not only one but a complete conformer ensemble can enhance property prediction. because a reference dataset is needed to probe such questions, we report the geom (geometrical embedding of molecules) dataset of conformer ensembles annotated with their relative energies and populations. the dataset covers a broad chemical space of combinatorially generated small molecules and drug-like molecules. we propose synthetic regression tasks on properties of the conformational ensemble spanned by each stereochemical formula, and report the performance of existing and modified graph-and d-based baselines. in addition to benchmarks for regression models, geom provides data for pre-training on d-related tasks and for training generative models for molecular structure. a number of reference datasets exist for surrogate simulators and for chemical species property prediction. simulated data on molecular entities include qm [ ] , with density functional theory (dft) calculations of molecular properties for one low-energy equilibrium conformer of molecules with fewer than heavy atoms, and the ani suite of datasets that sample non-equilibrium conformations for qm and larger molecules, as well as with higher levels of theory [ ] [ ] [ ] . md- has thoroughly-sampled conformations for a small number of molecules with ab initio wavefunction methods and long molecular dynamics simulations [ ] . property prediction of macroscale experimental properties of molecules include quantitative (esol [ ] , freesolv [ ] , pdbbind-f [ ] ) and categorical (bace, hiv, clintox, tox , sider, bbbp). moleculenet [ ] and deepchem [ ] collects and hosts many of these. unlabeled molecular sets for generation tasks such as chembl [ ] , zinc [ ] and subsets [ ] , and related benchmarks are also reported [ , ] . the dataset is available online at [ ]. a tutorial for loading the data can be found at [ ] . we used the crest [ ] software to generate conformers for , drug-like molecules and , molecules from the qm dataset. the drug-like molecules were accessed as part of aicures [ ] , an open machine learning challenge to predict which drugs can be repurposed to treat covid- and related illnesses. in particular, we generated conformers for , drugs that have been tested for in-vitro inhibition of sars-cov cl [ ] (data accessed from [ ]; hits), , drugs from the broad repurposing hub [ ] (data accessed from [ ]; sars-cov cl activity treated here as unknown), and , molecules tested for in vitro inhibition of sars-cov pl protease [ , ] ( hits, with % of the molecules also contained in [ ] ). finally, the dataset contains , molecules that have been screened for growth inhibition of pseudomonas aeruginosa (data accessed by request from [ ]; hits) and , molecules screened for e. coli inhibition [ , ] ( hits). secondary infections of covid- patients can be caused by both of these pathogens. statistics of molecular descriptors for the dataset are given in table . the dataset of drug-like molecules consists of medium-sized organic compounds, containing an average of . atoms ( . heavy atoms), up to a maximum of atoms ( heavy atoms). they contain a large variance in flexibility, as demonstrated by the mean ( . ) and maximum ( ) number of rotatable bonds. % ( , ) of the molecules have specified stereochemistry, while % ( , ) have specified or unspecified stereochemistry. the qm dataset is limited to heavy atoms ( total atoms), with a much smaller molecular mass and few rotatable bonds. % ( , ) of the species have specified stereochemistry. generation of conformers ranked by energy is computationally complex. the exhaustive method is to enumerate all the possible rotations around every bond, but this approach scales exponentially [ , ] . basic algorithms are available in cheminformatics packages such as rdkit [ ] , but suffer from two flaws. first, they explore conformational space very sparsely through a combination of pre-defined distances and stochastic samples [ ] and can miss many low-energy conformations. second, conformer energies are determined with classical force fields, which are rather inaccurate [ ] . by contrast, molecular dynamics simulations, in particular meta-dynamics approaches, can sample conformational space more exhaustively but need to evaluate an energy function many times. likewise, ab initio methods, such as dft, can accurately assign energies to conformers but are also orders of magnitude more computationally demanding than force fields. an efficient balance is offered by the newly developed crest software [ ] . this program uses semi-empirical tight-binding density functional theory (gfn -xtb) for energy calculation. the predicted energies are significantly more accurate than classical force fields, accounting for electronic effects, rare functional groups, and bond-breaking/formation labile bonds, but are computationally less demanding than full dft. moreover, the search algorithm is based on metadynamics, a well-established thermodynamic sampling approach that can efficiently explore the low-energy search space. finally, the crest software identifies and groups rotamers, conformers that are identical except for atom re-indexing. it then assigns each conformer a probability through here p i is the statistical weight of the i th conformer, d is its degeneracy (i.e., how many chemically and permutationally equivalent rotamers correspond to the same conformer), e i is its energy, k b is the boltzmann constant, t is the temperature, and the sum is over all conformers. crest runs on the drug dataset took an average of . hours of wall time on cores on knights landing (knl) nodes ( . core hours), and . hours on cores on cascade lake and sky lake nodes ( . core hours). qm jobs were only performed on the latter two nodes, and took an average of . wall hours on cores ( . core hours). a total of million knl core hours and . million cascade lake/sky lake core hours were used in total. the geom dataset is significant for three key reasons. the first is that it provides high-quality d structures, energies and probabilities for a large number of drug-like molecules. these expensive annotations may result in increased performance in property prediction tasks. if one is interested in drug repurposing, rather than generation of entirely new molecules, the search space of existing drugs is already annotated and no new conformers are needed. second, the dataset can be used for training generative models to predict conformations. these models can be used to generate conformations of unseen molecules to bypass ab initio simulations. third and most important, the dataset provides summary statistics for each molecule that are related to conformational degrees of freedom (conformational entropy, gibbs free energy, average energy, and number of unique conformers). all of these are aggregate properties that represent the d ensemble, but emerge from the molecular graph in a known way. hence, this dataset allows to test representation learning strategies throughout across graph ⇔ single conformer ⇔ conformer ensemble on tasks that are ultimately d, but fully emergent. this is applicable both as a benchmark task for new architectures, or as a pre-training strategy to be transferred to low-data d-driven tasks like drug-target binding. where focus on the this third application. we compare different neural network architectures and their ability to predict summary statistics. moreover, we ask whether limited d information, such as that of only the highest-probability conformer, can improve predictive performance. here we discuss various d and d message-passing neural network architectures [ ] used to predict molecular properties. a molecule can be thought of as a graph, consisting of a set of nodes (atoms) connected to each other by a set of edges (bonds). both the nodes and edges have features. the atoms, for example, can be characterized by their atomic number and partial charge. the bonds can be characterized by bond order. message-passing neural networks use these node and edge features to create a learned fingerprint (representation) for the molecule. this is called the message passing phase. the fingerprint is used as input to a function that predicts a property. this stage is called the readout phase [ ] . the message passing phase consists of t steps, or convolutions. in what follows, superscripts denote the convolution number. the node features of the v th node are x v , and the edge features between nodes v and w are e vw . the atom features x v are initially mapped to another set of vectors h v , termed hidden states. in the t th convolution, a message m t+ v is created, which combines h v and h w for each pair of nodes v and w with edge features e vw [ , ] : where n (v) is the set of neighbors of v in graph g, and m t is a message function. the hidden states are updated using a vertex update function u t : the readout phase then uses a function r to map the final hidden states to a property y, througĥ for d graphs we adopt the directed message-passing approach of ref. [ ] with the implementation used in ref. [ ] , the latter of which is called chemprop. the detailed analysis of ref. [ ] showed that chemprop achieves state-of-the-art performance on a wide range of regression and classification tasks. the chemprop code was accessed through [ ] . in this implementation, hidden states h t vw and messages m t vw are used, rather than node-based states h t v and messages m t v . here the direction matters, as in general h t vw = h t wv and m t vw = m t wv . this implementation helps to avoid messages that loop back to the original node [ , ] . where w i ∈ r h×hi is a learned matrix, cat(x v , e vw ) ∈ r hi is the concatenation of the atom features x v for atom v and the bond features e vw for bond vw, and τ is the relu activation function [ ] . the message passing function is simply the edge update function is the same neural network at each step: where w m ∈ r h×h is a learned matrix with hidden size h. each message-passing phase is then for t ∈ , ..., t . after the final convolution, the atom representation of the molecule is recovered through the hidden states are then summed to give a feature vector for the molecule: h = v∈g h v . properties are predicted throughŷ = f (h), where f is a feed-forward neural network. in chemprop the atom features are atom type, number of bonds, formal charge, chirality, number of bonded hydrogen atoms, hybridization, aromaticity, and atomic mass. the bond features are the bond type (single, double, triple, or aromatic), whether the bond is conjugated, whether it is part of a ring, and whether it contains stereochemistry (none, any, e/z or cis/trans). all features are one-hot encodings. non-learnable features are incorporated through concatenation with h before applying the readout network. details of architecture hyperparameters can be found in the sm. a variety of graph convolutional models have been proposed for learning force fields, which map a set of d atomic positions of a molecular entity to an energy. architectures designed for force fields typically do not incorporate graph information [ , , , ] since these are broken during chemical reactions and may not be clearly defined. this is contrasted with architectures for property prediction, which are typically graph-based [ , , ] but can benefit from d information [ ] . here we explore both possibilities. in one case we modify the schnet force field architecture [ , ] (code adapted from [ ] ) to predict properties. in a second case we modify the chemprop model to include distance-based edge features between bonded-and non-bonded atoms. this is in addition to the regular graph edge features between bonded atoms. we call this model chemprop d. in the schnet model, the feature vector of each atom is initialized with an embedding function. this embedding generates a random vector that is unique to every atom with a given atomic number, and is also learnable. the edge features at each step t are generated through a so-called filter network w t . the filter network converts a distance between two atoms, ||r v − r w ||, into an edge vector e vw . this is accomplished by expanding the distance between atoms v and w in a basis of gaussian functions. the centers of these gaussians are evenly distributed up to a cutoff radius, taken here to be . Å. this converts a distance into a vector. further linear and non-linear (shifted-softplus) operations are applied. because only the distance between two atoms is used to create e vw , the features produced are invariant to rotations and translations. in each convolution t + , the new messages and hidden vectors are given by here, • denotes element-wise multiplication and i t denotes the so-called interaction block. the interaction block consists of a set of linear and non-linear operations applied atom-wise to the atomic features. these operations are applied before and after multiplication with w t . in the original schnet implementation, the readout layer converted each atomic feature vector into a single number, and the numbers were summed to give an energy. consistent with the chemprop model and the notion of property prediction, we here instead convert the node features into a molecular fingerprint, and then apply the readout function to the fingerprint. details of our implementation of the schnet model can be found in the sm. we follow the spirit of both schnet and chemprop to produce the chemprop d model. rather than only considering neighbors bonded to an atom, we consider all neighbors within a Å cutoff. for bonded neighbors, edge features are a concatenation of bond features and distance features. for non-bonded neighbors, edge features are a zero-array concatenated with distance features. distances are expanded in a set of gaussian functions, distributed evenly every . Å up to a maximum of Å. they are then followed by a fully-connected layer and activation function. that is, in the t th convolution, distances are converted to vectors through where r vw = ||r v − r w || is the distance, g i is the i th gaussian function, w t s is a learned schnet matrix, b t is a bias, and τ is the schnet activation function. consistent with the original schnet paper we use the shifted softplus for the distance activation, but use the relu in all other places. we also use the ring size as an atomic feature for atoms in rings. learnable graph d (lowest state) d ( lowest states) the above discussion applies to molecules associated with one geometry. in the geom dataset, however, multiple conformers can be used for a single stereochemical formula. there are two immediate possibilities for pooling these conformers. the first, which we call weightpool, is to create molecular fingerprints for each conformer, multiply each by its statistical weight, and add them. the second, which we call nnpool, is to use the fingerprint and the statistical weight as inputs to a neural network that generates a final fingerprint. the different pooling options are then: the first case multiplies the i th fingerprint by its weight p i and sums the result. the second case multiplies a learned matrix w pool , of dimension h i × (h i + ), with the concatenation of p i and h i before summing the result, adding a bias b pool , and applying a non-linear operation τ . nnpool is of interest for applications in which the target property is dominated by conformers of low statistical weight. this can often be the case in therapeutics, in which a single low-probability conformer can result in high-affinity binding. we trained different models to predict three quantities related to conformational information. the first quantity is the ensemble entropy, s = −r i p i log p i [ ] , where the sum is over the statistical probabilities p i of the i th conformer, and r is the gas constant. the conformational gibbs free energy is related to s through g = −t s [ ] . the conformational entropy is a measure of the conformational degrees of freedom available to a molecule. a molecule with only one conformer has an entropy of exactly , while a molecule with equal statistical weight for an infinite number of conformers has infinite conformational entropy. the conformational gibbs free energy is an important quantity for predicting the binding affinity of a drug to a target. the affinity is determined by the change in gibbs free energy of the molecule and protein upon binding, which includes the loss of molecular conformational free energy [ ] . the second quantity is the average conformational energy. the average energy is given by e = i p i e i , where e i is the energy of the i th conformer. each energy is defined with respect to the lowest-energy conformer. the third quantity is the number of unique conformers for a given molecule, as predicted by crest within a maximum energy window [ ] . the models include varying degrees of d information and various levels of learnable molecular embeddings. a summary of the information contained in each approach is given in table . in quantum chemistry one often attempts to optimize a geometry so that its energy is at a global minimum. we asked how much this ground state geometry could improve training by incorporating its d information in the schnet and chemprop d models. we also considered the impact of graph information, which is contained in all models except for schnet, as well as non-learnable features, through the inclusion of morgan [ ] and e fp [ ] fingerprints. morgan fingerprints contain only graph information, while e fp fingerprints also contain d information. it is informative to know if limited knowledge of the conformers of a molecule, e.g. through a short md run, could improve training further. to this end we also incorporated a statistical weight of e fp fingerprints using only the lowest conformers from each molecule. in this case a fingerprint was produced by multiplying the e fp fingerprint of each molecule by its statistical weight (properly re-normalized to account for missing conformers) and adding the results. a description of the architecture and training hyperparameters used for each model can be found in the sm. we used published architecture hyperparameter values and we optimized dropout rates with sigopt [ ] . , molecules were used, with % for training, % for validation, and % for testing. the same training, validation, and test splits were used for all models. d models were trained for epochs and d models for epochs due to slower convergence. we checked that training d models past epochs did not improve performance. the mean average error (mae) was used as a performance metric. in all cases the models with the best validation scores were selected for evaluation on the test set. the model performance is shown in table , and can be contextualized by analyzing the dataset statistics in table . note that chemical accuracy for energy prediction is typically considered to be kcal/mol, and sub-chemical accuracy to be . kcal/mol. it is clear that learnable fingerprint embeddings significantly improve performance, since morgan and e fp embeddings alone result in poor performance. the schnet model, trained on the d geometry of the lowest energy conformer, performs comparably to chemprop in all categories. the combination of chemprop with d information also leads to comparable performance, though it outperforms the chemprop entropy prediction by %. with this learning architecture, one-conformer d information can moderately improve performance in some contexts, but the advantage is far from decisive. finally, we asked whether d models trained on pooled conformers could outperform d models. specifically we asked whether schnet, a model built to predict energies, could implicitly learn the entropy and average energy associated with an ensemble of geometries. to this end we re-trained schnet on a sample of , species, using up to conformers per molecule, for a total of , geometries. we used both weightpool and nnpool for schnet, and compared results to chemprop trained on the stereochemical formula of the same species. to differentiate this model from the earlier instance of schnet, which used only a single geometry, we call the models schnet -weightpool and schnet -nnpool. details of the training can be found in the sm. the results are given in table . interestingly, we see that conformer pooling leads only to minor improvement over d models. in particular, the schnet -weightpool model is only % better than chemprop at predicting the entropy, while the nnpool model is significantly worse. the ordering is reversed for the average energy. to see why this is surprising, consider the average energy task as an example. if the model sees conformers per molecule, as well as the average energy, one would expect it to learn which conformations are high-energy. therefore, when shown a set of conformers for a new species, one would expect it to identify the high-energy structures. chemprop, by contrast, has no access to this information and must learn from the graph alone. it is therefore intriguing that d information from the conformer set would offer no clear advantage. given the similar performance of the weightpool model to chemprop, it appears that the state-of-the-art approaches to fingerprinting d structures can be improved for ensemble prediction tasks. this offers an attractive challenge to the machine learning and chemistry communities. d coordinates are important for predicting single-point properties such as energies and forces for one conformation of one molecular entity. however, here we have found mixed results regarding their ability to enhance the accuracy of ensemble-averaged quantity prediction. d-based approaches to ensemble property prediction are not significantly improved by d information. these results indicate that either d information is not useful for these prediction tasks, or that the current models we have used do not leverage d information in an optimal way. with access to our dataset, the community can develop improved models for leveraging d information for property prediction. using our data for training, they will also be able to develop generative models that may obviate the need for expensive conformer simulations. there are four datasets, organized by molecule type (drugs or qm ), and whether they contain the original crest information (drugs_crude.msgpack.tar.gz and qm _crude.msgpack.tar.gz) or post-processed feature information (drugs_featurized.msgpack.tar.gz and qm _featurized.msgpack.tar.gz). the notebook tutorial at [ ] explains how each dataset is organized and how to extract the data. to explain the necessity of the featurized files, consider that crest simulations allow for reactivity, so not all geometries arising from a calculation correspond to the same molecular graph that they started with. indeed, we have found a number of simulations in which bonds are broken and reformed, as in tautomerization. for this reason it was necessary to examine each geometry individually after simulation to determine its molecular graph. to this end we used a locally modified version of xyz mol [ ] (code accessed from [ ] ) to generate an rdkit mol object [ ] . the mol object's graph information is contained in the featurized files through dictionaries of atom and bond features. the smiles string generated by xyz mol, as well as the canonical form of this string, are also given. additionally, for d-based machine learning models, each convolution aggregates atomic information from atoms within a given cutoff radius r cut . the most efficient method of storing this information is to generate a so-called neighbor list for each atom before training. the neighbor list consists of a set of pairs of indices, each of which corresponds to two atoms that are within r cut of each other. we included a neighbor list with r cut = Å in the featurized files. two notes are in order: . both the smiles from xyz mol and its corresponding canonical form may be different from the original smiles. this may be because the graph contains more information than the original smiles (e.g., because the original did not specify stereochemistry, meaning that one random stereoisomer was chosen to seed the crest simulations), because the smiles strings are resonance structures, or because the connectivity and bond types are different. the latter is the case when a chemical reaction occurs, such as in the case of tautomerism. . not all conformers could be successfully converted to graphs, and so the featurized files contain fewer smiles strings than the crude files. our approach was to optimize dropout rates and use published values for other hyparameters when possible. this was based on our experience with smaller datasets, which showed that dropout rates were the most important factor for d models and models with non-learnable fingerprints. in all cases we optimized the natural logarithm of the dropout rate with sigopt [ ] , using a data subset of , , an optimization budget of , and a train/validation/test split of / / . the allowed range of log(dropout) was [- , ] in all cases. the dropout rate with the lowest test error was selected. the dropout rates were optimized separately for each architecture and for each prediction quantity. hidden state dimension readout layers convolutions activation relu we used the default architecture values given in [ ] and shown in table s . the hidden state dimension in the two readout layers was reduced according to → → . a dropout layer was placed after the activation functions following w m and w a (see main text), and before the linear layers in the readout phase, as implemented in [ ] . the optimized dropout rates are shown in table s . note that hyperparameters were optimized for the prediction of conformers, rather than log (conformers). these parameters were then used for models predicting conformers and for models predicting log (conformers). we only reported the prediction of log (conformers) in the main text as the prediction performance was far better. the fixed schnet hyperparameters are given in table s . the atomic fingerprint length, convolution activation, gaussian spacing, and number of readout layers are all those given in [ ] . the original schnet paper used three convolutions and a cutoff radius of Å. however, because chemprop used only three convolutions, and because bond distances are typically under Å, we reduced the cutoff radius to Å and used only two convolutions. also as in chemprop we used the relu activation for the readout and a molecular fingerprint length of . since the atomic and molecular fingerprints had different lengths, a single linear layer was used to convert the summed atomic fingerprints to a molecular fingerprint. as in the original schnet paper, the fingperint dimension dim was reduced in the readout layers according to dim → dim/ → . dropout layers were placed before the linear layers in the readout phase and before linear layers in the convolution phase. the dropout rates were optimized separately. optimized values are shown in table s . the same hyperparameters were used for schnet as for schnet, with the exception of the molecular fingerprint. this was reduced from to to reduce memory use. dropout rates optimized for schnet were also used for schnet . s dropout e dropout log (conformers) dropout convolution dropout . . . readout dropout . . . table s : optimized schnet dropout rates. s dropout e dropout log (conformers) dropout convolution dropout . . . readout dropout . . . table s : optimized chemprop d dropout rates. we used an identical architecture to that of chemprop, with the addition of gaussians, a linear layer, and the relu activation to map distances to edge features. the linear layer and relu activation converted the gaussians into an edge feature vector of length . we also used the dim → dim/ → schnet approach in the readout layer. dropout layers were placed before the linear layers in the readout phase and before linear layers in the convolution phase. the dropout rates were optimized separately. optimized values are shown in table s . in all cases we used the adam optimizer and mean square error loss for training. for chemprop we used the default training hyperparameters given in [ ] . the learning rate scheduler described in [ ] was used with an initial and final learning rate of − , a maximum learning rate of − , two warmup epochs, total epochs, and a batch size of . we verified that performance did not improve when using more than epochs. for all d models we used a batch size of and an initial learning rate of − . we used a scheduler that decreased the learning rate by half if validation performance had not improved in epochs. epochs were used in all models except for schnet , which required epochs for convergence. finally, the presence of a small number of outlier geometries initially led to divergences in the schnet training. to account for this, the optimizer did not take a step if the batch loss was divergent. our reported results in the main text exclude divergent predictions. a deep learning approach to antibiotic discovery design of efficient molecular organic light-emitting diodes by a high-throughput virtual screening and experimental approach deep learning enables rapid identification of potent ddr kinase inhibitors generative models for automatic chemical design automatic chemical design using a data-driven continuous representation of molecules junction tree variational autoencoder for molecular graph generation molgan: an implicit generative model for small molecular graphs learning deep generative models of graphs syntax-directed variational autoencoder for structured data boltzmann generators: sampling equilibrium states of many-body systems with deep learning molecular de novo design through deep reinforcement learning learning to navigate the synthetically accessible chemical space using reinforcement learning objective-reinforced generative adversarial networks (organ) for sequence generation models deep reinforcement learning for de novo drug design end-to-end differentiable learning of protein structure learning protein structure with a differentiable simulator planning chemical syntheses with deep neural networks and symbolic {ai} prediction of organic reaction outcomes using machine learning deep learning for the life sciences convolutional networks on graphs for learning molecular fingerprints molecular graph convolutions: moving beyond fingerprints analyzing learned molecular representations for property prediction cormorant: covariant molecular neural networks tensor field networks: rotation-and translation-equivariant neural networks for d point clouds directional message passing for molecular graphs gold book") a comprehensive survey on graph neural networks schnet: a continuous-filter convolutional neural network for modeling quantum interactions smiles, a chemical language and information system. . introduction to methodology and encoding rules inchi, the iupac international chemical identifier complexity of protein folding data-driven approach to encoding and decoding -d crystal structures reinforcement learning for molecular design guided by quantum mechanics adversarial reverse mapping of equilibrated condensed-phase molecular structures generating valid euclidean distance matrices deep generative models for d linker design molecular geometry prediction using a deep generative graph neural network bayesian optimization for conformer generation symmetry-adapted generation of d point sets for the targeted discovery of molecules generating equilibrium molecules with deep neural networks coarse-graining auto-encoders for molecular dynamics molecule attention transformer quantum chemistry structures and properties of kilo molecules ani- , a data set of million calculated offequilibrium conformations for organic molecules ani- : an extensible neural network potential with dft accuracy at force field computational cost less is more: sampling chemical space with active learning machine learning of accurate energy-conserving molecular force fields esol: estimating aqueous solubility directly from molecular structure freesolv: a database of experimental and calculated hydration free energies, with input files the pdbbind database: collection of binding affinities for protein-ligand complexes with known three-dimensional structures {moleculenet}: a benchmark for molecular machine learning chembl: towards direct deposition of bioassay data zinc -ligand discovery for everyone {guacamol}: benchmarking models for de novo molecular design alan aspuru-guzik, and alex zhavoronkov. molecular sets (moses): a benchmarking platform for molecular generation models geom: energy-annotated molecular conformations exploration of chemical compound, conformer, and reaction space with meta-dynamics simulations based on tight-binding quantum chemical calculations qfret-based primary biochemical high throughput screening assay to identify inhibitors of the sars coronavirus c-like protease ( clpro) qhts of yeast-based assay for sars-cov plp qhts of yeast-based assay for sars-cov plp: hit validation nontargeted metabolomics reveals the multilevel response to antibiotic perturbations conformations and d pharmacophore searching confab -systematic generation of diverse low-energy conformers rdkit: open-source cheminformatics conformational analysis using distance geometry methods a sobering assessment of small-molecule force field methods for low energy conformer predictions neural message passing for quantum chemistry analyzing learned molecular representations for property prediction discriminative embeddings of latent variable models for structured data chemprop machine learning for molecular property prediction extensions of marginalized graph kernels rectified linear units improve restricted boltzmann machines schnet-a deep learning architecture for molecules and materials neural networks for atomistic systems conformational entropy in molecular recognition by proteins extended-connectivity fingerprints a simple representation of three-dimensional molecular structure universal structure conversion method for organic molecules: from atomic connectivity to three-dimensional geometry converts and [sic] xyz file to an rdkit mol object attention is all you need the authors thank the xsede covid- hpc consortium, project che , for compute time. key: cord- -ukr a g authors: garcia, davide astiaso; groppi, daniele; tavakoli, siamak title: developing and testing a new tool to foster wind energy sector industrial skills date: - - journal: j clean prod doi: . /j.jclepro. . sha: doc_id: cord_uid: ukr a g the wind energy sector has seen an increasing growth in the last decade and this is foreseen to continue in the next years. this has posed several challenges in terms of skilled and prepared professionals that have always to be up to date in an industry that is constantly changing. thus, teaching tools have gained an increasing interest. the present research reviewed the state of the art in terms of digital interactive training tools pinpointing that the existing options do not feature the user involvement in the development of the training material. hence, the main aim of this paper is to develop and test an innovative method based on gamification to increase wind energy sector industrial skills, providing a digital interactive environment in the form of a new user-friendly software that can allow its users to train and contribute to the teaching and learning contents. the first methodological step deals with the associated background studies that were required at strategy implementation and development stages, including market analysis and technology trade-offs, as well as the general structure and the implementation steps of the software design. obtained results pinpointed that with minimal use of web-based database and network connectivity, a mobile phone application could work in the form of a time-scored quiz application that remotely located staff at wind energy farms could benefit from. the technological innovation brought by this research will substantially improve the service of training, allowing a more dynamic formative management contributing to an improvement in the competitiveness and a step towards excellence for the whole sector. the importance of greenhouse gas (ghg) emission reduction has been widely assessed by researchers from all over the world (li et al. ; zeng et al., a) . consequentially, several measures have been studied and applied to increase the energy efficiency (sun et al., ; zeng et al., b ) and the energy production from renewable energy sources (res) (pfeifer et al., ) . thus, the energy industry has gained a key role in tackling climate change. in this framework, training professionals is essential to face today's changes in the labour market and to support a competitive economy (stanitsas et al., ) , particularly in renewable energy (re) sectors since the energy transition to decarbonized systems is speeding up the innovation processes of these technologies (lin et al., ) . moreover, both in developed and developing countries there is a lack of studies that deal with stakeholders and professionals' awareness level about res (kacan, ) and energy efficiency (ciriminna et al., ) . as regard the wind industry, meeting the expectations of horizon is translated into an increase of % is also important to keep in mind the progressive ageing of maintenance workers who have difficulties to work in the harmful and narrow conditions of the old turbines. consequentially, a continuous turnover is needed and will offer potential opportunities for new professionals and green jobs. if we also consider the ageing of european wind farms and the tendency to increase their operating life, the european wind energy sector is clearly facing a challenge: the very limited availability of skilled operation and maintenance (o&m) staff and the future lack of it in the medium-term considering also the actual growth of the industry and the future projects needed to achieve the national energy and climate plan (necp) of each eu member state. on one hand, the topic of safety is being dealt with globally by the basic safety course of the global wind organization (gwo), an international organization linked with the safety training, and is becoming a global standard. on the other hand, few initiatives have been carried out in the re technology manufacturing industries to train technicians and mechanics working on both installation and o&m or re devices (kandpal and broman, ). consequentially, new approaches for the training of technicians able to supervise installations and o&m interventions specifics for wind and for other renewable technologies are essential to foster the development of each res (kandpal and garg, ; tsoutsos et al., ) . several for energy saving and management, a number of digital interactive tools exist that allow engagement of the users in the process of learning in full digital format, such as udemy (udemy, ) , litmos (litmos, ) and docebo (docebo, ) to mention a few of the recent and popular ones. udemy is one of the pioneers in supplying web-based environment for building new course in digital format with course material and course attendance facilities able to exchange most of the elements of an e- learning environment, developing an android application to enable users to follow their courses directly from their mobile phones (udemy, ) . the set of the stakeholders includes the instructor, the investors who invest on the marketing to attract students, and the ownership of udemy hosting service. nevertheless, the use of ict training tools alone does not ensure effective results. a major problem with fast-growing industries is the fact that training tools and education schemes must be always updated and engaging. in this context, ict tools can be effectively associated to game-based learning (gameffective, ; harbinger knowledge products, ). those basically increase the level of engagement and speed of access to the outcome of assessments by allowing users to act in a variety of game-style environments that are contextualized with learning contents of a domain topic. several existing digital interactive tools allow engagement of the users in the process of teaching and learning (mindflash, ; schoox, ) . these tools have at least one or both of the following two features: b. the right to authorship of the users is granted from a central originator of the created course. this intellect of central control to set who can or cannot collaborate could add a burden to both user account management and required security protocol. in this context, serious games, and gamification in general, have been identified as a valuable option to ). this statement is also corroborated by the inherent educational features of the game, being a stimulating mechanism for users, having great flexibility in use, achieving important learning while being playful, and therefore promoting teamwork as a key element of society today (hallinger et al., ) . in light of the above-mentioned current context, main research gaps include the standardization of the operational skills for the staff qualification and the development of an ad hoc serious game that considers j o u r n a l p r e -p r o o f and integrates the current approaches for professional trainings for installations and o&m activities in the wind energy sector. closing these research gaps is the main novelty of the present paper compared to the above mentioned state of the art. indeed, the development of a serious game to qualify professionals in the skills of the wind energy sector has never been done before and it will improve substantially the service of training given at present, allowing a more dynamic formative management and a technological development inside a company, contributing an improvement in the competitiveness and a step towards excellence. therefore, answering the three essential questions (what? how? why?) to be considered according to theory-development (whetten, ) , the main contribution of this research to theory is to standardize the operational skills needed for the qualification of employees of the wind energy companies (what) introducing a cutting-edge mode of training, developing and testing the first serious game on this industrial sector (how), in order to foster wind energy sector industrial skills enhancing the training in operation and maintenance to a higher level (why). moreover, the learning tool proposed in this research is based on the application of ict that allows the use of interactive information and quiz using a serious game environment thus supporting the development of efficient distance learning at any time. this feature is crucial since it aims to address one of the main issues affecting the wind energy sector trainings: the fact that personnel is often working in remote areas. hence, using ict, this research proposes the development of an innovative training tool in the re sector, particularly focused on wind energy sector. therefore, the main outcome of the research is the development of a mobile phone application with all the contents and elements required to improve the skills related to the ordinary activities of workers in the wind energy sector. furthermore, a new specific approach has been used compared to the several ones recently introduced to re education by means of the modern and flexible educational technologies (jennings, ). in this section the research methods to overcome all the issues that have been faced in different stage of the fundamental design are explained in detail. in particular, the technology integration and development of the proposed solution has been described, covering the general structure, the building blocks of the proposed software system, and the implementation steps of the new software design. the method section is structured as depicted in figure and described as follows: each of the afore-mentioned topics has been described in a specific paragraph where the related issues have been presented and the strategies to overcome such issues explained in detail. table . in particular, a power/interest matrix (olander and landin, ) has been selected as the most appropriate spanish in order to spread its use and eventual transnational initiatives. the above described procedures attained the software tool required. some screenshots of the current version in hand are shown in figures and . in this framework, future researches will be focused on the implementation of a simulator for o&m training in the wind energy sector, starting from the contents of the serious game and obtained data from end users feedbacks. in this way, it will be possible to update and tailor the training contents to the new technologies. that sector using a serious game. one of the main research objectives and novelties was to propose a model to standardise at european level the operational and transverse knowledge required to prepare adequate personnel for the wind energy sector. in order to make the app a feasible european standard, it had to be able to renovate its contents to match the wind energy sector transition. thus, the developed solution has been thought to be continuously updated thanks to users' feedback and inputs in order to be able to follow the market, technology and techniques changes that are happening faster than ever. modeling and simulation of ict network architecture for cyber-physical wind energy system wind power and job creation gamification-based framework for engagement of residential customers in energy applications a risk assessment tool for improving safety standards and emergency management in italian onshore wind farms. sustainable energy technologies and assessments training and certification of pv installers in europe a transnational need for pv industry's competitive growth how does the pedagogical design of a technology-enhanced collaborative academic course promote digital literacies, self-regulation, and perceived learning of students? internet and higher education learning visual importance for graphic designs and data visualizations proceedings of the th annual acm symposium on user interface software and technology practical and low-cost monitoring tool for building energy management systems using virtual instrumentation a framework for leading change in the uae public sector experimental investigation on co methanation process for solar energy storage compared to co -based methanol synthesis energy management supporting high penetration of solar photovoltaic generation for smart grid using solar forecasts and pumped hydro storage system reshaping the education of energy managers machine learning methods for short-term bid forecasting in the renewable energy market: a case study in italy a systematic literature review of empirical evidence on computer games and serious games offshore renewable energy standardization review, prepared for bsi innovative hybrid chp systems for high temperature heating plant in existing buildings energy retrofitting of dwellings from the 's in borgata trullo -rome overview of insular power systems under increasing penetration of renewable energy sources: opportunities and challenges ict in collaborative learning in the classrooms of primary and secondary education gaming for the energy transition. experimenting and learning in co- designing a serious game prototype home smart grid device for energy saves and failure monitoring a bibliometric review of research on simulations and serious games used in educating for sustainability, - . j. of cleaner production games based learning redefining engagement in elearning renewable energy and jobs -annual review future of wind -deployment, investment, technology, grid integration and socio- economic aspects new directions in renewable energy education renewable energy awareness in vocational and technical education renewable energy education for technicians/mechanics renewable energy education: a global status review. renewable a market-oriented wind power dispatch strategy using adaptive price thresholds and battery energy storage a study of utilizing backend as a service (baas) space for mobile applications assessing the policy impacts on non-ferrous metals industry's co reduction: evidence from china focusing on the right targets: economic factors driving non-hydro renewable energy transition litmos lms/?utm_source=capterra&utm_medium=cpc&utm_campaign=training_product_link (accessed th energy retrofitting of residential buildings-how to couple combined heat and power (chp) and heat pump (hp) for thermal management and off- design operation performance evaluation of thermal power plants considering co emission: a multistage pca, clustering, game theory and data envelopment analysis gaming for earth: serious games and gamification to engage consumers in pro-environmental behaviours for energy efficiency alternative tool for the energy evaluation and the management of thermal networks: the exergy analysis evaluation of stakeholder influence in the implementation of construction projects a roadmap toward the development of sapienza smart campus integration of renewable energy and demand response technologies in interconnected energy systems experimental results on a wireless wattmeter device for the integration in home energy management systems applying standards to systematize learning analytics in serious games environmental impacts of the national renewable energy targets -a case study from finland facilitating sustainability transition through serious games: a systematic literature review a closer look at cross-functional r&d cooperation for innovativeness: innovation-oriented leadership and human resource practices as driving forces uncovering energy use, carbon emissions and environmental burdens of pulp and paper industry: a systematic review and meta-analysis event tracking for real-time unaware sensitivity play and learn: serious games in breaking informational barriers in residential solar energy adoption in the united states what constitutes a theoretical contribution? academy of management review the present status and challenges of wind energy education and training in china rewards in gamification investment efficiency of the new energy industry in china china's so shadow prices and environmental technical efficiency at the province level this research has been carried out within the skillwind project co-funded by erasmus+ programme of the european union ( - -es -ka - ). key: cord- -t tannlh authors: vaka, mahesh; walvekar, rashmi; rasheed, abdul khaliq; khalid, mohammad title: a review on malaysia’s solar energy pathway towards carbon-neutral malaysia beyond covid’ pandemic date: - - journal: j clean prod doi: . /j.jclepro. . sha: doc_id: cord_uid: t tannlh covid’ pandemic has devastated several industries and solar energy is no exception. in its economic relief package, malaysia has announced approximately us$ . billion in expenditure for the installation of new grids, led street lights and rooftop solar panels. the government will also open the tender for a , mw solar power project in the year , which is expected to generate billion ringgit (us$ . billion) in investments. as these measures are intended to sustain the existing growth of solar energy potential in the country, it is vital to assess its status quo. hence, this paper aims to review the current status of renewable energy in malaysia as well as the initiatives taken before the pandemic to promote solar photovoltaic (pv) technology to meet the energy demands through the low-carbon pathway. the burning of fossil fuels, such as coal and oil to produce electricity is one of the main contributors to global warming and climatic changes. many countries are highly dependent on fossil fuels, particularly for the industrial sector to ensure sustainable socio-economic development (mohsin et al., ) . energy demand continues to rise and it will most likely increase fossil fuel consumption, resulting in a further increase of co emissions. therefore, governments across the world have been taking initiatives to address this issue by encouraging the implementation of renewable energy (re) through various national programs (iea, b) . re is generated from naturally abundant sources such as sun, wind, biomass, etc. it is, therefore, regarded as an eco-friendly form of energy that has zero to minimal amounts of co emissions. while renewable and alternative energy has great potential to replace the dependency on fossil fuels, the progress of bringing it into the mainstream has been slow in most developing countries (malahayati, ) . malaysia is no exception, introduced several measures in its th malaysia plan during for rapid re integration to its national grid (oh et al., ) . transition to re in malaysia has been challenging due to several issues such as difficulties in securing funding, unappealing tariffs and the absence of incentives for utilities, and lack of awareness among key decision-makers in the industry (oh et al., ) . currently, only % of malaysia's energy is generated from re while it has pledged to attain % by (seda, a) . according to the malaysian investment development authority (mida), thriving re technologies in malaysia include solar energy, hydroelectric and biomass. however, compared to most re technologies, recent developments in solar photovoltaic (pv) systems have led to its phenomenal growth in malaysia and across nations (sreenath et al., a; sreenath et al., b) . malaysia experiences hot and humid weather with a generous amount of rainfall all year round due to its geographic location. it receives an abundant amount of solar radiation throughout the year, with most places having daily solar radiation mean of . - . kwh/m (petinrin and shaaban, ) . therefore, applications involving solar energy have also been gaining popularity in malaysia due to favourable climate conditions of the country. realizing the solar energy potential and in general re (hannan et al., ; tang, ) , the government introduced several new programs and schemes. net energy metering (nem), the feed-in tariff (fit), large scale solar (lss), selfconsumption (selco) and re incentives are some examples of schemes intended to reduce the bills as well as the fiscal load to attain a carbon-neutral environment (chatri et al., ) . recent covid' pandemic has impacted energy industries and markets across the globe (anderson et al., ) . furthermore, the movement control orders and travel restrictions have closed the businesses, resulting in reduced pv cells production and subsequent installations. to keep the existing momentum as well as to achieve the paris agreement targets, the malaysian government and solar energy companies in the country must reshape the policies and strategy (abdullah et al., ) . therefore, this review aims to address the following objectives; ) determine the status quo of solar pv technology and related application in malaysia; ) establish the key factors affecting renewable energy development in malaysia; ) understand the updated energy framework of malaysia: energy policies, assessment, criticize, track the re progress; ) compare re growth in association of southeast asian nations (asean) countries; ) impact of covid' on the malaysian energy market and energy security; ) government's response to covid' pandemic to sustain the solar industry. furthermore, the solar energy field is fast evolving with some unprecedented developments in the recent past. reviews published lately focus broadly on analysis of re integration and enhancing grid requirements with control methods. other aspects published recently include impact and status of re in malaysia, policies influenced by public opinion, sustainable ideas for the development of re, climatic change mitigation in malaysia and feasibility studies on solar utilization in malaysia (abdullah et al., ; al-shetwi et al., ; ghazali et al., ; kaman et al., ; khan and go, ; qazi et al., ; wahid et al., ) . existing works do not provide any insight into how a potential framework is crucial to support and achieve future re goals. challenges, issues and conflicts are highlighted to ensure the long-term sustainability, reliability and energy security for the development of re in malaysia by considering different policies, assessing and monitoring solar pv. hence, this works presents an up to date overview of the solar energy technologies, factors affecting renewable energy and the policies in malaysia based on the qualitative approach. the development and promotion of renewable energy to fulfil the energy demands of future generations have been summarized with a particular focus on the post covid' scenario. in the case of solar thermal technology, the energy obtained from the solar source is directed to meet the requirements of different end-users in different sectors such as building, industry and residential sectors and applications (heng et al., ) . for example, the building sector, including both residential and commercial, covers a wide range of purposes from cooking to water heating (naghavi et al., ) . in the case of industry, it serves a variety of applications from low-temperature to high-temperature. to satisfy the use of heat ventilation and air conditioning (hvac) based on the category requires a considerable allocation of total final energy demand. for example, in malaysia, hvac in buildings and industry requires % and % of total energy consumption. according to the irena report, remap indicates the total energy demand and consumption by buildings and industries are % and %, as shown in figure a ) and b). moreover, the irena report shows that in malaysia, the district heating and cooling (dhc), in other words, hvac depends on non-renewable energy for the total energy demand in is about %. cooling is one of the prominent concepts and fast-growing in most emerging economies, that use waste-energy in buildings to minimize power consumption. over the last few decades, the usage of electricity for cooling in buildings across the region has increased drastically. till now, only % of households in southeast asia have air conditioners, showing the remarkable ability for further growth in major markets. by , the future of cooling in southeast asia investigates the increase in demand in energy consumption, peak electricity demand and co emission, and lays an alternative scenario that policy drives industry transformation to produce more efficient air conditioners. a sustainable development scenario, along with more robust policies, can address the efficiency in cooling equipment and buildings, which can lead to as much as twh savings by (iea, a). irena's remap analysis reports an increase in the use of renewable energy up to % by , where the majority of it will be contributed by bioenergy and solar thermal. solar energy has become one of the primary sources of renewable energy and widely used for different purposes such as generating electricity, heating and desalinating water. two ways can produce this: .) photovoltaics (pv) and .) concentrated solar power (csp). we only discuss the pv system because of climatic factors and other reasons restrict the development and usage of csp in malaysia. the main principle behind solar pv is converting the sunlight into electricity. the generation of electricity and making it accessible to every corner of the country is possible with the help of pv technology in combination with mini-grids. due to the reduction in the cost of solar panels, not only the electricity price is decreased but also becoming increasingly accessible to everyone. as a result, the solar pv installations have drastically increased in malaysia as shown in table . moreover, solar power generation shows no sign of greenhouse gas emission, making malaysia step forward towards a greener and cleaner energy. the promotion of solar power helps malaysia achieve its long-term goals to lower the carbon intensity to % by (malaysia, figure (irena, e). the gradual increase in electricity generation seen after the introduction of lsspv farms from the government and planning to add mw more annually from to . after the initiation of the fit scheme, the electricity generated from the producers utilise the power initially, and the excess made tends to sell. net energy metering (nem) has been launched in by the government to benefit the current fit scheme and large-scale solar programs (lssp) to replace the fit by (commission, ) . nem concept allows users to generate their electricity by installing solar panels and any excess power generated will be channelled back to the utility grid. however, one of the critical issues highlighted by the pv industry is the need to change the concept of nem from the existing net billing to true net energy metering. this change is to improve the return of investment of solar pv under the nem. therefore, effective from st january , the nem is improved by adopting the true net energy metering concept to allow excess solar pv generated energy to be exported back to the grid on a "one-on-one" offset basis. which means that every kwh exported to the grid will be offset against kwh consumed from the grid, instead of at the displaced cost previously (seda, d). despite all the efforts, the solar industry in malaysia still faces two major challenges: • lack of knowledge and awareness on the financial returns from solar pv investment and benefits among the malaysian public and the business community. • an easy application process and reasonable loan interest rate do not exist due to the lack of awareness on solar technologies and solar pv-related financing for bankers (seda, c several factors play a critical role in promoting or affecting the growth of renewable energy in malaysia. a culmination of these factors overcome issues faced by the renewable energy sector. this section summarizes the crucial elements affecting re implementation and aiding to develop a positive environment in which re exploitation can succeed (abdmouleh et al., ) . these factors are discussed in detail in this section. significant demand to develop re projects in a country requires enormous capital investment. moreover, certain projects involve high-risk factors due to fast-evolving technology and lack of sufficient resources. developing countries like malaysia need investments from both private and public sectors to implement re projects. the government should take the initiative to provide loans and funding to the organisations for research and development of re. during the initial stages, the government must come with a basic framework and encourage initial investments through banks for the growth of re. recently, the malaysian government announced a tender worth of rm . billion, which involves re and energy efficiency (ee) projects. financial security is also the biggest concern for renewable energy power purchase agreement does not offer enough cash flow for bankers that leads to reduced confidence between bankers when considering investment (petinrin and shaaban, ) . the malaysian government requires to make a collective attempt to confirm sustainable and effective funding mechanisms are to bring into effective action to facilitate the growth of re projects that would then promote the sustainable development of the country (sharvini et al., ) . hence, financial aspects play a significant role in the promotion and implementation of re. more investments, funding and other kinds of support such as loans should be provided to encourage the re projects. the government mainly controls this category, and it supports re projects through loans and grants to the public and private institutions. government grants awarded to the organisations are often non-returnable and are provided to encourage the growth of re in the country. carbon or energy taxes were introduced to help the incentives under different aspects such as efficient hvac systems, where the renewables are exempted from this. for instance, carbon tax merits, includes overtime, it may face ups and downs, assigned to external bodies, it assists most of the price signal and demerits such as execution will be a problem. this might be due to political interference, few industries might be exempted from this policy, and other factors might impact the effectiveness are considered to be important aspects under environmental taxes. the malaysian legislation provides petroleum entities with expenditurebased tax incentives that align with other countries in similar lower-middle-income brackets under the promotion of investment act (kraal, ) . malaysian government imposes carbon tax with a revenue recycling plan and the emission standard program to reduce the co emission level from fuel emissions. the co emission intensity of gdp reduces by . % under a carbon tax and . % under emission standards by introducing carbon dioxide emission policies (yahoo and othman, ) . to develop the renewable energy sector, the malaysian government has provided pioneer status and an investment tax allowance from . additionally, the energy commission and mida are the two agencies involved in the implementation of these incentives that made significant progress in renewable energy generation by (hashim and ho, ) . to promote investments and local businesses, the malaysian government introduces a stimulus package of usd . billion during the outbreak of covid' . the central bank has issued loans for small-and medium-sized enterprises (smes) worth of billion-ringgit and each sme entitled to receive up to million ringgits. additionally, the government also supported businesses worth million ringgits to upgrade their workers' skills (medina, ) . the government has announced an rm billion stimulus package that includes tax breaks for the influenced sectors, together with electricity bills discount of % and % trimmed of epf contribution by employees that are pointed to spur private consumption (kwek, ) . the primary concern for most of the green projects is accessing the finance towards the new technology that causes trouble to the investors, followed by the underlying investment framework. depending on the structure of the sector, the risks and challenges for investors differ. few barriers to green investments in developing countries have been identified from different studies, including the g development working group. based on various aspects, the risks and obstacles are categorized into technology risks, policy and regulatory risks, market risks, investment barriers, and capacity constraints (amin et al., ) . to overcome these conditions, financial incentives play a crucial role in the development of the current health and economic crisis due to covid' do not understand global efforts to take on the world's inevitable challenge of climate change. government launch sustainable stimulus packages to increase their climate goals taking advantage of the current situation by introducing clean energy technologies. the coronavirus crisis is already performing notable damage around the globe and needs to grab this opportunity to accelerate clean energy rather than obstructing clean transitions (iea, b). the main issue in market failures, especially in malaysia is the inconsistency in resources distribution by the suppliers to resolve the consumers' demand. erratic pricing structures is a drawback for renewables, uneven pricing of renewable energy products, power/information asymmetries, alteration in market power, fossil fuel subsidies, and failures to absorb social and environmental externalities into costs. the fossil fuel/nuclear subsidies, which obstruct the distribution of renewables on top of the energy tariffs that are not entirely cost-reflective. besides, trade barriers come into play by imposing high prices/taxes on imported re products such as import duties (murdock, ) . the other factors significantly affect the re development in malaysia such as the existence of market failure, technological constraints, lack of regulatory framework, lack of proper governance, no institutional measures, and finally limited oversight on implementation and achieving targets are to be considered. in malaysia, renewable energy is gradually making its footprints to improve or better the renewable energy usage step-by-step by focusing on different elements. again, these elements involve a combination or mixture of policies and programs to develop the country's economy. some of the critical policies and plans are established to meet the set goals and currently implement new strategies to provide re to future generations. these consist of (i) malaysian national renewable energy policy, (ii) renewable energy act , and (iii) sustainable energy development authority act . these policies are explained below in detail. currently, the malaysian government is focusing on the growth of "fifth fuel" as a renewable energy resource, particularly biomass under the country's fuel diversification policy. initially, the set target was % electricity generation through renewable energy by that the re policy is drafted to promote the importance and need for sustainable development by conveying the idea to all the stakeholders. the most and foremost thing for any re policy approval and acknowledgement is by combining energy, industry, environment, green technology, and information dissemination policies that contribute to excellent opportunity and challenge in its prototype. the government should impose a tax on the firms that release co , to reduce co emission or storage if they want to continue in the market. the main aspects that need to consider for any re policy are: to highlight the current market failures, to assign long-term sustainability; to encourage new firms; to understand the significance of the environment as an economic growth contributor, to advance the human capital resources in r&d technologies, and to enhance the consistency of current policy. these objectives, strategies, and action plans of the national re vision policy helps for the growth and development of any industry/firm mentioned in the below figure this act is responsible for beginning the production of re and other related matters, where a unique tariff system is to be established and implemented. this act involves several aspects and stages to achieve renewable energy. malaysia according to the renewable energy balance sheet of malaysia ( ) , the contribution of different renewable energy sources divided into three major parts such as supply by technology, transformation & losses, and consumption by sector. the overall renewable energy balance sheet is shown below in table . hydropower is with , . tj under-supply by technology category and under transformation and losses category electricity is contributing highest with , . tj. in the case of energy consumption, the residential sector has the highest with , . , followed by industry. the the new national green technology policy builds on four pillars and five strategic thrusts. this policy is introduced to minimize degradation of the environment, zero/low greenhouse gas emission, use of energy and natural resources, and promote the use of renewable resources (foo, ) . sustainable energy development authority (seda) is a malaysian government agency responsible for promoting and implementing sustainable energy. the main intention of this act is to use or produce the strength to fulfil the current requirements without affecting the needs of the future generation, which includes renewable energy also. moreover, malaysia aims to become a sustainably advanced nation by . therefore, the implementation of green technology as a driving force to increase the future economy that potentially helps to enhance sustainable development and green growth of the country. additionally, the national green technology policy mainly concentrates on a wide range of sectors such as energy, building, waste management, and transportation. the total energy consumption from each sector was collected and among all the sectors, residential and industry consume more energy of %, % compared to commercial ( %) and transport ( %) (irena, a). different financial aids should provide to support the small and medium scale industries at various levels of the business cycle. the government should take initiatives to help them from promotion to commercialisation through grants or subsidies or credits. these smallscale businesses or scale-ups can easily access to rural areas and assure the potential development of re. the malaysian government should bring more and more schemes and subsidies to support small and medium scale industries to develop re, which is not up to the standards yet. as a solar industry, all the alliances must be on board in search to develop the growth of malaysia's pv market (seda, c). (i) incorporation of solar energy with pv as a part of the government's vision set to install lower financing cost solar pv on all government buildings including schools, hospitals, and universities to promote solar energy as a practical form of re. (ii) in terms of pv service providers a high standard of customer service such as postsales, delivery needs to establish in the malaysian pv market and motivate higher involvement in the regional/worldwide pv market. (iii) to adapt green financing framework and encourage banks to offer loans for pv projects. malaysian government implements the eleventh malaysian plan as an initiative to meet the short-term goals and develop renewable energy successfully. the government is progressing according to the plan and very close to complete, the set targets within the time-bound. moreover, the government introduced a sustainability goal to decrease buildings electricity consumption by % and assuring the reduction of co emission by up to % per unit of gdp by . the energy commission with the help of seda implemented nem and set a goal to generate mw of electricity in peninsular malaysia by using solar pv. to become the hub of green technology by . this can be achieved by implementing electric vehicles, solar rooftops, sustainability buildings and ways to convert waste into energy. in the meantime, several efforts and initiatives taken by the government to achieve the target within the stipulated timeframe. sustainability energy development authority (seda) and energy commission are the central bodies to monitor the overall energy production from renewable sources. seda malaysia has its database (pv monitoring system, pvms) regularly to monitor the pv performance based on irradiance. moreover, the performance of the pv systems reported on a daily and monthly basis of over sites over malaysia (pvms, later, the national energy policies and programmes will be designed and structured from this data as a reference (seda, c). at this stage, the review of every individual program, schemes and policies are very critical to analyse the final report periodically, systematically and check the improvements related to technology, demand, market situations, strategies and new insights. these evaluations help to ensure the effectiveness, efficiencies, accuracy, and feasibility of these programs, schemes and policies to achieve future goals. this will provide a brief picture of the progress and helps to adjust the set targets if not met (gungah et al., ) . the best way to increase the renewable share is by using a mixed approach that includes sectors such as power, heating, cooking, transport and other renewable sources to meet the target less than a year. besides, there are several ways to increase the renewables in the energy system of a country but focusing on one particular sector alone compared to other industries may boost the rapid development and affects the economy/resource availability during the long run. the percentage of variable renewable energy (vre) compared to individual countries or within individual power systems over asean will be lower. but sometimes, if all remap options are executed, the generation will pass %. among the all, hydropower is contributing the most renewable energy share followed by solar pv and wind. solar pv and wind also play a crucial role in variable renewable energy, and the output is associated with the availability of the resource at a particular time, and against the power demand that differs with the country, as shown in figure . however, the stability of the grid faces challenges due to the high share of variable renewable power in a power system, where it needs to be variable. asean power grid (apg) is one of the best approaches to overcome the issues with integration vre into the grid. however, the main problem is the distribution of power supply among different member states with organised frameworks within the countries/ different countries. the implementation of power interconnectors, grid codes, trades for operation, design and maintenance of the market could be a better solution to resolve these issues (nicholas wagner, ) . in , asean countries set a goal to improve the share of renewable energy in its energy mix to % by (ace, ) . the uncertain timing of electricity generation remains an issue to maintain grid stability, with a higher percentage of vre sources like solar and wind (iea-etsap, ; iea, ) . increasing the grid's flexibility refers to a critical factor to address stability and reliability issues (iea-etsap, ; martinot, ) . to achieve grid reliability, it needs to remain stable by maintaining a balance of demand and supply at every second (huang et al., ) . for instance, as per stats, philippines produces % highest amount of electricity by renewable energy, and thailand maintains a high grid reliability score by integrating the most diverse renewable energy source to the grid (iea, a). this indicates that the grid supports the current level of integrated renewable energy. so, grid stability is often affected with the increase in grid integrated re; thus the current grid reliability is a good indicator to know the integration of existing renewable energy sources by a nation (cochran, ) . huang et al. studied asean grid flexibility to quantify and detail a load profile and calculate the worst-case ramp rate for each member nation (huang et al., ) . some asean countries like malaysia, brunei darussalam, singapore and thailand already reached full electrification and its % in the case of vietnam. some other countries like indonesia, lao pdr and the philippines are anticipated to attain full electrification by , as shown in figure . due to the reduced electrification rates in cambodia and myanmar, they formulated some schemes and national plans to attain % electrification in cambodia by and by in myanmar. a rapid increase in energy demand across asean countries, the energy systems including electricity generation, transmission, heating, cooling, cooking and transport needs significant investments. approximately, usd billion of total investment in renewable energy capacity estimated to meet asean's % renewable target by . out of which an estimation of usd billion per annum calculated only from present to , which usd billion per annum in reference case and remaining was with remap options. around usd billion yearly redirect the investments from fuel technologies into renewables under remap options. so, an additional investment of around usd billion per year required in the reference case. the higher capital cost of these renewable technologies requires a higher investment, including all except bio-energy based. from figure , the data showed that the two-third of total asean investment requires between and for renewable energy considered from indonesia, vietnam and supporting their citizens with tax breaks (medina, ) . the oil and gas industry plays a vital role in determining the country's economy and energy sector and nearly donates % of malaysian gross domestic product (gdp) in recent times. however, the purity and disposal lead to severe environmental issues such as air pollution, the current and proposed energy mix needs to be analysed and still depends on fossil fuels, and gas holds % of total energy in , followed by % of coal in the coming years. re sources have a less percentage of share compared to other sources, which needs to be raised in the next few years, as shown in figure . energy security is one of the significant problems that hide behind every country's energy policy. energy security is a critical topic, which needs to be addressed in assisting the economy's path towards a higher platform (ahmad, ) . malaysia has an excellent case study to evaluate the energy security scenario among all southeast asian countries. energy security is nothing but the availability and steady supply of energy sources at a reasonable price. the two main concerns related to energy security are an over-dependence on fossil fuels and coal, and the fluctuation in the country's supply-demand balance. the demand for energy is anticipated to increase remarkably in malaysia policymakers support to ensure that current and future systems remain secure after they are transformed by the rise of clean energy technologies and the significance of electricity. to counter this economic damage from the coronavirus, the government has drawn stimulus plans ensuring sustainable energy future does not effort from these blows (iea, b). the malaysian government mainly targets renewable energy and energy efficiency to minimise power bills and reduces co emission. malaysian renewable energy (re) supports the solar pv initiative from the ministry to uptake the excess energy through the net energy metering (nem) program. according to seda, nem is a solar photovoltaic (pv) program announced by prime minister under the budget as a replacement to the fit scheme. the electricity generated from solar pv systems consumed initially, and any leftover will be exported to the grid. later, they sell to the distribution licensee (tnb/sesb) at the premium rate predetermined by the energy commission, and the schematic representation of nem is illustrated in figure . nem applies to all the customers of tnb and sesb, including domestic, industrial and commercial sectors. as of jan , , under this scheme, mw of energy was saved and the government set a target of % by . the benefit of this scheme is motivating every individual to play their part in re generation that potentially solves the national energy security and climate agenda. apart from decreasing greenhouse gases emission, the nem also safeguards from any electricity tariff rise in the future. moreover, an additional attachment of a battery or energy storage system to the pv system to enhance the self-consumption facility. finally, the certified nem scheme holders have the facility to acquire electricity when the grid failure occurred by generating electricity from their pv system (seda, ). in malaysia, the nem has become challenging because of its slow take-up rate. the excessive electricity sold to distribution licenses for the low displaced cost is one of the significant challenges of nem (irena, b). large scale solar (lss) refers to electricity generation through a photovoltaic power station at a scale large enough to be classified as utility-scale or large-scale. the most large-scale solar project has the capacity of more significant than mw, with mw being the minimum capacity. in malaysia, companies that are interested in setting up a large scale solar plant will have to go through a bidding process announced by the energy commission. only the shortlisted companies are granted the license to develop the large-scale solar project. the main objective of lss is to accelerate electricity generation from solar pv and solar farms. moreover, the commission launched the third cycle of the lss scheme in february to improve the power generation from re. to date, the government has achieved an installed capacity of megawatts from the two lss project cycles. incentives must be initiated to motivate more involvement from the industry for lss (malaysia, e., ) . self-consumption (selco), where the electricity generated from pv panel is for individual usage and any excess production is not allowed to send back to the grid. the government has taken initiatives to support all individuals, commercial and industries to install their clean solar panels to reduce their own cost of electricity. the main benefit of this program is to save more power due to the increased cost of electricity (seda, e). the feed-in tariff (fit) program starts in to increase investments in renewable energy. the fit was implemented in malaysia since for solar pv, but now it is replaced with the net metering program. the fit rates differ from technology to technology and installed capacities. the main aim of this program is to sell clean energy to the distribution license for a while. moreover, the duration also depends on the specific renewable energy and technology used. for instance, the term for biomass is years, and for biogas, small hydropower and solar pv technology, the duration is years. the consumer or the government will pay money for every kwh of electricity you generate that guarantees you to regain the spent money for the technology. the malaysian government has taken these initiatives/ implementing different programs to boost renewable and clean energy using different technologies shown in figure . the government has taken a step forward to support and encourage all individuals, commercial and industries in all modes to completely utilise the resources towards a greener and sustainable energy. other asian hubs such as malaysia, vietnam, singapore, thailand, and south korea have been affected strongly by the covid' pandemic. another major concern for sustainable projects like solar arises in the form of tax incentives (kelley, , mar ) . covid- has affected not only the solar sector but also the other related markets such as renewable electricity, electric vehicles (evs), heating, cooling and the circular economy as officially announced by the world health organisation. the reports from the government that the global solar demand in has been cut down by %. bloomberg nef (bnef) expected solar demand to reach around - gigawatts (gw) in , whereas in the last three decades, solar capacity shows the first annual fall in between - gw. bnef and international energy agency (iea) reported that the virus impacts the clean energy investment and the government to use the drop in oil prices to check the fossil fuel subsidies. however, the main issues are with the growing tax receipts and most governments are planning to invest in high-carbon infrastructure by opting to trim the fuel taxes (murray, , mar ) . finally, covid- made an impact on society to change the path towards decarbonisation and achieving the sustainable development goals (macola, , mar ). although china declared success in its fight against covid' in mid-april , the rest of the world, including malaysia, continues to fight the pandemic. as a result, economies have devastated and that is expected to have a grave impact on future energy policies across the world. climate action following the paris agreement required malaysia to develop a new energy framework to meet its renewable energy goals. owing to the unfolding situation, malaysia will have to review its re policy seriously. we conclude the following points from this exhaustive review. • from the status-quo, it appears that the existing re projects will continue but any rapid development, once perceived in this sector, would be challenging in malaysia. • malaysia's solar energy pathway towards a low carbon society beyond covid' needs collective effort from the government, industries and small players to accomplish this vision. • the government is expected to generate rm billion (us$ . billion) in investments from solar power project by opening a tender for a capacity of , mw in the year . such investment should be continued in the future to keep the momentum. • the government is identifying the key factors affecting re development and actively promoting re and sustainability-related policies, assessments, incentives. they have introduced an updated energy framework and growing public awareness on net energy metering, green energy, and sustainability indicates malaysia's commitment to aim for a cleaner environment by avoiding co emission. • malaysia's strategy for the development of the energy sector compared to other asean countries has been practical and well-judged that gives priority to meeting demand and ensuring the security of supply. • there might be chances that renewable projects will get dropped while the government battles the effects by launching a stimulus package to promote the investments and local businesses. • the government has offered tax breaks discount on electricity bills of % approximately as well as % trimmed epf contribution by employees. • the government introduces sustainable stimulus packages to enhance the climatic goals taking advantage of the current situation by implementing clean energy technologies. • besides, the sustainable stimulus package introduced by the malaysian government, it could also learn from regional asean nations as well as other countries in the world, how they overcome the drag due to covid' pandemic and continue their efforts towards a cleaner future. the plausible recommendations will address the gaps, and suggest measures to be followed for the active development of re. • funds have to be disturbed equally between the private and public universities with a set of targets to entirely within the timeline. • standard and quality assurance from the fund receivers are considered and appreciable. • the government should take initiatives to conduct training programs and workshops to create self-employment and encourage start-ups, which can provide supporting/service to every corner of the country. • the government should be cautious about their projects and achieving goals on time, and plans have to be adequately organised or else cause a mix-up that leads to delay. • a separate policy or a framework needs to be introduced for regular monitoring of climatic changes, co emission and committee have to be formed to regulate renewable energy contribution in the reduction of greenhouse emission. • energy efficiency policy and renewable heat have to be monitored, and the team is assigned to make sure that the waste heat is reduced. • more awareness campaigns need to be conducted to educate the public about green technology and to protect the environment. • the government has to focus on green services by avoiding plastic and promote more green products. • more attention should be given to solar cars and bicycles to minimise pollution and co emission. malaysia aims and focuses on energy-efficient vehicles (eevs) by switching the combustion engines into eco-friendly electric vehicles (evs). moreover, the government has taken initiatives to be a marketing hub for electric vehicles by . to encourage the fast-charging stations for electric vehicles to reduce the emission of pollutants that helps to achieve a carbon-free environment by managing the indigenous energy resources. moreover, malaysia is on course to reduce carbon emissions by % in the coming years, % by and full carbon neutral by for a cleaner environment for future generations. additionally, the new economic policy (nep) and government-linked companies involved a free-market economic policy and blue ocean strategies employed to promote the development of re. the ministry of energy, green technology and water, malaysia is developing the renewable energy transition roadmap as a substitute to the current national renewable energy policy and action plan (hannan et al., ) . review of policies encouraging renewable energy integration & best practices the potential and status of renewable energy development in malaysia the malaysia's energy sector: in pursuit of a better future grid-connected renewable energy sources: review of the recent integration requirements and control methods designing smart green finance incentive schemes how will country-based mitigation measures influence the course of the covid- epidemic? energy demand and supply outlook the economic effects of renewable energy expansion in the electricity sector: a cge analysis for malaysia renewable energy grid integration:challenges and key issues commission a vision on the opportunities, policies and coping strategies for the energy security and green energy development in malaysia improving nigeria's renewable energy policy design: a case study approach review of baseline studies on energy policies and indicators in malaysia for future sustainable energy development renewable energy policies and initiatives for a sustainable energy future in malaysia performance of a small-scale solar cogeneration system in the equatorial zone of malaysia asean grid flexibility: preparedness for grid integration of renewable energy renewable energy integrationin power grid technology brief large-scale electricity interconnection: technology and prospects for cross-regional power networks southeast asia energy outlook southeast asia energy outlook. iea, a. data and statistics exploring the impacts of the covid- pandemic on global energy markets, energy resilience, and climate change irena global energy transformation: a roadmap to irena renewable energy technologies renewable power capacity and generation renewable energy and policy development in malaysia solar energy industry disrupted by coronavirus pandemic assessment of malaysia's large-scale solar projects: power system analysis for solar pv grid integration petroleum industry tax incentives and energy policy implications: a comparison between australia, malaysia, indonesia and papua new guinea beyond covid- : building back better for a more resilient economy and society. macola, i.g achieving renewable energies utilization target in south-east asia: progress, challenges, and recommendations malaysian building integrated photovoltaic project (mbipv), fianly evaluation report malaysia grid integration of renewable energy: flexibility, innovation, and experience asean incentives to counter covid- impact developing low carbon economies: an aggregated composite index based on carbon emissions renewable energy policies in a time of transition coronavirus dampens outlook for clean energy and electric vehicles ondemand dynamic performance of a thermal battery in tankless domestic solar water heating in the tropical region energy policy and alternative energy in malaysia: issues and challenges for sustainable growth-an update energy policy and alternative energy in malaysia: issues and challenges for sustainable growth renewable energy for continuous energy sustainability in malaysia pv monitoring system towards sustainable energy: a systematic review of renewable energy sources, technologies, and public opinions energy security in malaysia: current and future scenarios. seda national renewable energy policy & action plan seda, d. the net energy metering (nem) sustainable energy development authority green income tax exemption -gite green investment tax allowance -gita covid- : clean energy challenges and opportunitites malaysia to increase renewable energy output energy consumption trends and their linkages with renewable energy policies in east and southeast asian countries: challenges and opportunities technical assessment of captive solar power plant: a case study of senai airport solar pv energy system in malaysian airport: glare analysis, general design and performance assessment climate change in malaysia: trends, contributors, impacts, mitigation and adaptations a review on highlights and feasibility studies on solar energy utilization in malaysia employing a cge model in analysing the environmental and economywide impacts of co emission abatement policies in malaysia carbon-neutral malaysia beyond covid' pandemic . comparison between the asean countries and their strategies to reach renewable energy goals this work was supported by taylor's university through its taylor's university phd scholarship programme. the authors declare no conflicting interest regarding the publication of this manuscript.this statement is to certify that all authors have seen and approved the manuscript being submitted. on behalf of all co-authors, the corresponding author shall bear full responsibility for the submission. key: cord- -ev ghlwl authors: cao, lingyan; li, yongkui; zhang, jiansong; jiang, yi; han, yilong; wei, jianjun title: electrical load prediction of healthcare buildings through single and ensemble learning date: - - journal: energy reports doi: . /j.egyr. . . sha: doc_id: cord_uid: ev ghlwl healthcare buildings are characterized by complex energy systems and high energy usage, therefore serving as the key areas for achieving energy conservation goals in the building sector. an accurate load prediction of hospital energy consumption is of paramount importance to a successful healthcare building energy management. in this study, eight machine learning models of single learning and ensemble learning were developed for predicting healthcare facilities’ energy consumption. to validate the performance of the proposed model, an experiment was conducted on a general hospital in shanghai, china. it was found that the two ensemble models, extreme gradient boosting (xgboost) model and random forest (rf) model, outperformed single models in daily electrical load prediction. a further comparison between models trained with daily and weekly temporal resolution electrical data shows that it is more likely to achieve higher accuracy with finer time granularity. through feature importance analysis, the most influential features under the daily and weekly electrical load prediction were identified. based on the prediction results, it is expected that hospital facility managers will be able to conveniently assess the expected energy usage of their hospitals with the machine learning models. the building sector accounts for % of global energy consumption and more than % of global electricity consumption, generating % of energy-related co emissions worldwide (oecd/iea, ) . driven by the increasing floor area and rapidly growing demand for energy-consumption equipment and services in buildings, the energy use in the building sector has shown a continuous growth trend, with an annual average growth of . % since (oecd/iea, ). currently, the energy consumption of the building sector mainly comes from commercial and residential buildings. large-scale commercial buildings are reported to have a high energy consumption, which can be up to kw h/m , to times of that in residential buildings (liang et al., ) . in the commercial sector, healthcare buildings are particularly energy-intensive due to their constant need for power supply and strict requirements for air quality and disease control (garcía-sanz-calcedo et al., ; bawaneh * corresponding author. e-mail addresses: cly @tongji.edu.cn (l. cao), lyk@tongji.edu.cn (y. li), zhan @purdue.edu (j. zhang), jiang @purdue.edu (y. jiang), yilong.han@tongji.edu.cn (y. han), @tongji.edu.cn (j. wei). et al., a) . a report released by the energy information administration (eia) (eia, ) indicated that large hospitals were responsible for . % of major fuel consumption in commercial buildings, even though they only constitute . % of the total commercial building area. in addition, the healthcare industry market is expected to continuously increase in the future due to factors such as a higher number of chronic diseases, overpopulation, an increase of elderly population, and the lack of healthy lifestyle choices (gonzalez, ) . thus, healthcare buildings play an important role in overall energy consumption worldwide. in response to this increasing trend of building energy demand, much research has been conducted in the prediction of building energy consumption, especially the prediction of electrical loads. previous studies have shown that building energy prediction is helpful for implementing a series of energy conservation tasks, such as benchmarking building energy performance (zhao and magoulès, ) , detecting system fault , measuring building energy savings (heo and zavala, ) , and controlling demand response (pedersen et al., ) . the main functions of healthcare buildings include providing medical services and carrying out scientific research. compared to other commercial buildings, healthcare buildings are distinguished by overloaded schedules, increased electricity usage, diversified electricity forms, and higher electricity consumption per gross floor area. for example, in the hospital context, a large amount of electricity has to be provided to make sure the normal operation of cold-chain equipment for vaccine storage, pumps for clean water supply, lighting, and other life-saving medical equipment for night-time and emergency care (dholakia, ) . therefore, schemes to reduce the use of energy in complex healthcare buildings are important to understand. through literature review, it was found that numerous energy demand studies have been conducted on diverse building types, such as commercial buildings (yildiz et al., ) , office buildings (ding et al., ) , hotel buildings (shao et al., ) , and residential buildings (gao et al., ) . however, there is a paucity of research that focused on healthcare buildings due to the complexity of their energy consumption patterns. even though the amount of electrical load information related to diagnostic and medical treatment has been increased with the advancement of metering and sensing technologies, the detailed analysis based on the measured information remains scarce. therefore, in this paper, the authors propose a one day-ahead electrical load forecasting model based on single and ensemble machine learning algorithms. to validate the performance of the proposed model, an experiment was conducted on shanghai tenth people's hospital, a general hospital under the jurisdiction of the shanghai hospital development center (shdc) . daily electrical load consumption information was collected through an intelligent-building energy support system (i-bess). because energy consumption patterns in buildings can vary greatly depending on the use of buildings (park et al., ) , the ignorance of function related variables will result in a discrepancy between the predicted values and real values. to fill this gap, in this study, three types of patient occupants were taken into consideration, namely, the inpatient, outpatient, and emergency patients. in the present study, electrical load forecasting models of healthcare buildings are developed based on single and ensemble machine learning algorithms by taking account multi-factors simultaneously. features that are classified into four categories (weather parameters, occupancy data, day type information, and operation & maintenance measure) are specified as input to the forecasting models. the daily electrical load forecasting models are trained with a database of a general hospital in shanghai, containing instances with complete data. to test the impact of time granularity on the prediction performance, these models are also trained with a weekly load dataset. the performance of the prediction models is evaluated by statistical metrics such as the mean absolute percentage error (mape), coefficient of variation of the root mean square error (cvrmse), normalized root mean square error (nrmse). finally, a feature importance analysis is also presented to identify the critical attributes. the rest of this paper is organized as follows. in section , we discuss the relevant literature in the load prediction of buildings. section shows our proposed methodology. section introduces the experiment, ground truth, and evaluation metrics. section and section show the results and discussion of electrical load prediction, respectively. finally, in the last three section to , the contributions, limitations, and conclusions are presented, respectively. in the past decade, extensive research has been carried out to predict the load demand of buildings and various models have been proposed for real-world applications. these models can be broadly classified into two categories, namely physical models and data-driven models (amasyali and el-gohary, ) (see fig. ). in physical models, physical principles are used to calculate the thermal dynamics and energy behaviors of buildings by taking temperature, humidity, and other physical variables into consideration (wang et al., a; li, ) . several building energy modeling tools, such as energyplus, transient system simulation tool (trnsys), environmental systems performance-research (esp-r), and the quick energy simulation tool (equest), have been widely used in this area (bui et al., ) . however, the performance of physical models depends on a large number of building parameters, such as building envelope structure, lighting system setup, pump water distribution, etc., making it more suitable for buildings at the design stage rather than for as-built (shao et al., ) . to this end, data-driven models using machine learning algorithms to construct mapping functions between input and output data have gained immense popularity due to their ease of use, adaptability and high forecasting performance (wang et al., a; wang and srinivasan, ; somu et al., ) . in addition, data-driven models are more practical than physical models since the data used are more available from buildings, such as energy consumption, climatic, temporal, and occupancy, which can be collected via sensing and communication technologies (wang et al., a) . furthermore, data-driven prediction models can be categorized into single models and ensemble models based on the modeling structure and the number of prediction models (wang and srinivasan, ) . single prediction models were created by applying one prediction algorithm (wang and srinivasan, ) . examples of single prediction models include multiple linear regression (ji and xu, ) , artificial neural network (platon et al., ) , support vector machines (wang et al., b) , and long short term memory (lstm) algorithm (zhou et al., ; wang et al., ) . in ensemble learning prediction, instead of using one algorithm to build the forecasting model, multiple learning algorithms are needed to train its base models (wang and srinivasan, ) . the commonly used ensemble techniques are bagging (tuysuzoglu and birant, ) , boosting (kadkhodaei et al., ) , voting (tsai, ) , and stacking (mahendran et al., ) . among them, bagging and boosting are two of the most widely-used ensemble learning methods because of their theoretical superiority and strong experimental performance (oza, ) , with random forest (rf) and extreme gradient boosting (xgboost) as the representative algorithms for each, respectively. the main difference between rf and xgboost is that rf combines multiple predictors in a parallel way whereas xgboost combines them sequentially (wang et al., a) . based on the literature review, the prediction performance of single and ensemble prediction models in healthcare buildings context has been underinvestigated. since xgboost and rf are more advanced algorithms that could be used for electrical load consumption in buildings, these two algorithms are described in detail as follows. ( ) xgboost algorithm based on boosting the core idea of boosting is to start training a base learner from the initial training dataset, during which each sample (i.e., data point in the training dataset) has the same weight. then the weights of training samples are constantly adjusted in the subsequent iterations according to the performance of the base learner. a heavier weight will be given to the training samples that failed the training. this process is repeated until the number of base learners reaches a value specified in advance. finally, a strong model will be constructed by combining these base learners by their trained weights. in boosting, the data drawn for training the base learners depends directly on the previous steps (kadkhodaei et al., ) . xgboost is one of the boosting algorithms widely used in the field of machine learning and kaggle competitions for structured or tabular data in recent years (silvestro et al., ; kadkhodaei et al., ). xgboost can be used to solve both classification and regression problems. the mechanism of xgboost is to first train a decision tree by using the training dataset and then use this tree to obtain the corresponding predicted value. a residual can be obtained by subtracting predicted value from the corresponding real value. then, by inputting the new training sample and residual, a second tree is trained to optimize the previous residual. the iteration stops when the predefined threshold of parameters, such as max_depth, min_child_weight, are arrived at. the final predicted value is the sum of the predicted values of the previous predictors. after adding a base learner, the value of its objective function is calculated to ensure that the value of the objective function gradually decreases during the iteration process. xgboost can obtain much better performance than a single prediction algorithm due to the process of correcting the prediction errors of preceding models in the iterative process. ( ) random forest based on bagging bagging is the most famous representative of ensemble learning. the core idea of bagging is to obtain an aggregated predictor by using a combination rule (tuysuzoglu and birant, ) . in bagging, given a data set containing m samples, one sample is randomly picked into the sampling set for processing and then put back into the original dataset, so that the sample still has the possibility to be selected in the next sampling round. after m round of random sampling operations, a sampling set containing m samples is formed. in repeating this sampling t times, t datasets each containing m data can be generated. a base learner is then trained based on each sample set and all base learners are combined in the end. random forest (rf), one of the most popular machine learning algorithms, is an improvement of bagging methods. different from bagging where all features are considered for splitting a node, rf only selects a subset of features at random and uses the best splitting feature from the subset to split each node in a tree. a problem with bagging is that decision trees can have a lot of structural similarities since they choose which variable to split on using a greedy algorithm that minimizes errors, resulting in a high correlation in their predictions. rf addresses this problem by generating sub-trees in a way that the resulting predictions from all of the subtrees have fewer correlations. rf contains several weak predictors that are trained through bagging and random variable selection. therefore, rf has good anti-noise and generalization capabilities. previous research has shown that rf can perform well in the field of load forecasting (wang et al., a; morgenstern et al., ) . for data-driven models, parameters optimization plays an important role in improving the prediction accuracy of the proposed model. there are a variety of parameter tuning methods available. for example, a series of relevant work have been done by chen et al. ( ) 's team. they proposed an improved ant colony optimization for feature selection to identify the optimal subsets (zhao et al., ) . in addition, several methods such as enhanced moth-flame optimizer , improved whale optimization algorithm , enhanced bacterial foraging optimization , the chaos enhanced gray wolf optimization (zhao et al., ) have been developed and validated in different contexts such as medical diagnosis. based on the application context, following wang et al. ( a) 's method, gridsearchcv provided by scikit-learn (pedregosa et al., ) was used for hyper-parameter tuning in this study. understanding the drivers of building electrical load consumption is critical to the advancement of building energy systems and their management. according to the project report of international energy agency (iea) on total energy use in buildings, there are six types of factors that are influencing the total energy consumption of buildings, including climate, building envelope, building equipment, operation and maintenance, occupant behavior, and indoor environmental conditions (yoshino et al., ) . in addition to the general characteristics of the public buildings' energy consumption, healthcare buildings have important distinctions from other commercial buildings, including their continuous operation, a high percentage of included space types with special indoor environment requirements and a set of extremely energy-hungry diagnostic equipment, such as xray, computed tomography (ct) and magnetic resonance imaging (mri) (koulamas et al., ) . energy systems show different complexity even from hospital to hospital, depending on several factors such as the type and volume of the buildings, health care services offered, geographical location, and technological plants (silvestro et al., ) . in general, the electricity consumption in hospitals consists of air conditioning systems, lighting, electromedical devices, safety systems, information and communications technology (ict) systems, and treatment equipment (silvestro et al., ) . furthermore, each department of a hospital also may have different energy use patterns. taking the outpatient and inpatient departments as an example, the main function of the outpatient department is to receive patients and diagnose patients who do not need to be admitted to hospital stay (morgenstern et al., ) . therefore, the main energy systems or equipment of the outpatient departments are hvac systems, lighting systems, and medical equipment. while for the inpatient department, whose main function is to provide a place for patients who need to be hospitalized, the main energy consumption is related to the hvac system, lighting system, domestic hot water system, catering, and cooking appliances. however, the majority of research in healthcare buildings on energy prediction pays more attention to the useful floor area and number of beds, without taking healthcare occupancy types into consideration. similar to the research conducted in general buildings, electrical load prediction models for healthcare buildings can also be classified into physical and data-driven models. for example, by using dynamic thermal simulation and computational fluid dynamics, adamu et al. ( ) explored the alternative effects of four strategies on the performance of thermal comfort and heating load using a new ward of the great ormond street hospital london as a case study. ascione et al. ( ) investigated the energy, environmental and economic effects of rehabilitation of building envelope for healthcare facilities in mediterranean climates via energyplus and the designbuilder interface. due to the complexity and time-consuming nature of collecting buildings' detailed information needed by physical models, several data-driven models have been found to predict the energy consumption of healthcare buildings. for example, chen et al. ( ) used ann to predict a hospital's air-conditioning system's energy use by taking into account temperature, relative humidity, the previous-hour electricity, the time of a day, and some uncontrolled variables. bagnasco et al. ( ) performed electrical load forecasting for the cellini medical clinic of turin by proposing a multi-layer perception ann model with ( ) the type of the day, ( ) time of the day, and ( ) weather, as the input data. thinate et al. ( b) built a multiple linear regression model for the load prediction of large-scale hospital buildings in thailand by taking six affecting factors into account, including airconditioning area, non-air-conditioning area, in-patient department, out-patient department, staff number, and temperature. in ruiz et al.'s ( ) study, three machine learning techniques (i.e., multilayer perceptron, m rules algorithm, and tree ensemble learner algorithm) were used to predict electrical energy consumption in a hospital of granada. in spite of the several different aspects of energy use in healthcare facilities explored in previous studies, the main gap of extant research is the lack of consideration of healthcare occupancy variables. to address this gap, this study takes into account the occupancy of outpatients, emergency patients, and inpatients and employs single and ensemble machine learning algorithms to predict the electric load demand of healthcare buildings. the research methodology consists of module and module , which are for independent machine learning model development with different temporal granularity -daily and weekly, respectively as shown in fig. . it can be seen that the electric load prediction for the healthcare buildings includes three steps: ( ) identify the relevant features and gather data, ( ) train single and ensemble learning models with prepared dataset, and ( ) compare the prediction performance of different models. the electricity data of modules and are first randomly divided into two parts, % for training and % for testing. the generated training dataset is then used to train the machine learning models and the testing dataset is used to evaluate the performance of the trained models. machine learning is increasingly adopted in the big data era to enable data-driven decision making. empirical evidence shows that companies who adopt data-driven decision making will increase their efficiency and profitability significantly (bohanec et al., ) . data mining and machine learning methods are capable of addressing variable issues such as normality, correlation, missing value, and dependency. therefore, they can produce better prediction accuracies by mapping the nonlinear relationship between input and output more comprehensively. electrical load forecasting is naturally considered to be a regression problem in machine learning, aiming to accurately predict the energy demand of buildings based on its relationship with a given set of independent input variables. although machine learning techniques have provided good results in electrical load prediction of many types of buildings, electrical load prediction of healthcare buildings based on machine learning algorithms has been under-investigated, leading to a gap in knowledge on the most appropriate method to predict electrical load of healthcare facilities. to test the forecasting performance of different models, three performance measures are used including mape, cvrmse, and nrmse. the equations for calculating mape, cvrmse, and nrmse are defined as follows (kadkhodaei et al., ) : in which: ( ) n represents the number of instances in training or testing data; ( )ŷ i and y i represent the forecasted and real values, respectively, and ( ) y max and y min represent the maximum and minimum of the real values, respectively. for all the three indicators, a smaller value indicates a better prediction performance of the forecasting model. the method was applied to predicting the energy consumption of shanghai tenth people's hospital (stph), a general hospital located in jing'an district of shanghai, china. established in , stph provides healthcare across broad areas of general and specialty care. like other hospitals located in megacities of china, stph is extremely busy providing medical services for patients not only from local areas but also from the surrounding regions due to urban agglomeration (wang et al., a) . as a result, stph has experienced capacity strain over recent years. in , it had . million person-times of outpatients and emergency patients, thousand person-times of hospital discharge. the total floor area of stph is , m (fig. ) , consisting of various departments, such as operation theaters, intensive care units, examination and treatment rooms, and large-scale medical equipment, resulting in an annual electricity expenditure of million chinese yuan. electric power consumed in stph consists of space heating and cooling, ventilation, lighting, office equipment, and medical diagnostic facilities such as ct and mri. generally, hospital buildings can be seen as an integration of general-purpose building space and healthcare-specific building space. therefore, factors influencing energy consumption consist of common factors related to weather parameters (i.e., outdoor temperature, relative humidity, wind speed, barometric pressure, and precipitation) (wang et al., a) and some special factors relevant to occupancy, time and operation &maintenance (o&m). for occupancy, three types of patients are considered, including the number of outpatients, emergency patients, and inpatients. because hospitals usually have different schedules according to day type, a parameter representing weekday or weekend/holiday was also considered as an input to the forecasting model. in addition, different o&m measures related to the operational status of the central air-conditioning system are included to accommodate the changing indoor climate condition. the central air conditioning system will be turned on for heating or cooling and turned off at transition seasons, such as spring or autumn. finally, a total of parameters need to be considered to build a load forecasting model, as listed in table . due to different conditions such as geographic latitude and topography, the climate of china varies greatly from one location to another. to analyze the buildings according to local climate conditions, the chinese building climate is divided into severe cold area, cold area, hot-summer & warm-winter area, and temperate area (wei et al., ) . shanghai, a typical city in the hot-summer & cold-winter area, has a long summer and a short winter, resulting in high energy usage for cooling and heating. as illustrated in fig. , a u-shaped relationship exists between outdoor temperature and daily electricity consumption in shanghai. in this study, the weather data was collected from a weather station in the baoshan district, whose latitude and longitude are close to that of stph. the weather station consists of a complete set of weather sensors, including temperature, humidity, wind speed, air pressure, and precipitation. in this study, the weather data was downloaded on a daily average basis from the department web server. generally, healthcare facilities can be classified into different categories based on management and ownership types, type of care provided, facility size and patient type, etc. ahmed et al. ( ) . for healthcare buildings in chinese hospitals, the main classification is according to the type of patients, such as outpatient buildings and inpatient buildings. for example, the main components of inpatient buildings are patient bedrooms and the supporting spaces, e.g., nurses' rooms, storage space, and possible food heating facilities (morgenstern et al., ) . therefore, the occupancy of hospitals mainly consists of three types of patients, i.e., outpatients, emergency patients, and inpatients. in order to ensure careful control of the indoor climate, healthcare buildings consume more energy than other types of commercial buildings, to achieve a comfortable indoor environment since occupants in hospitals are more sensitive to the physical environment . occupancy fluctuations complicate decisions concerning the need for a variety of auxiliary facilities, including physical therapy, laboratory tests, surgical services, pharmacy, and housekeeping, and may ultimately impact the energy consumption (littig and isken, ) . these daily occupancy data were collected from the healthcare information system (his) of shanghai. fig. shows the normalized value of occupants and load relationship of stph for month. it can be seen that the number of inpatients and emergency patients is small compared to that of outpatients. in addition, it can be seen that both the number of outpatients and electricity consumption have the lowest levels on sundays. according to lusis et al. ( ) , the prediction performance of electrical load consumption can be improved by taking into account calendar effects because they can capture the change of energy consumption patterns in different calendar periods, such as daily or weekly energy consumption. to investigate the impact of the interaction between the healthcare buildings and calendar variables on the electrical load prediction, a dummy variable was added to distinguish between weekdays and weekends/holidays. for stph, weekday usually refers to monday to saturday while only sunday is the weekend. in addition, the calendar from the hospital's official website was used to determine the holiday schedule. all holidays and sundays were combined. in this study, the relationship between the day type and daily electrical load was statistically analyzed, and the violin plot is shown in fig. . as depicted in this plot, weekdays have higher load levels than the weekends/holidays. one possible explanation is that for weekdays, all departments will be under normal operations whereas, for weekends/holidays, only a small part of the departments will be open, e.g., the inpatient department. currently, there are four types of air conditioning terminals in stph, namely, central air-conditioning system, variable refrigerant volume (vrv) unit systems, large-sized test device for air-cooled heat pump unit, and split air-conditioning systems. only the split air-conditioning system can be kept in operation as wish. the other three types of air conditioning systems would not operate unless the outdoor temperature is higher or lower than an established threshold. according to the schedule of stph (table ) , the central air conditioning system will not operate unless the outdoor temperature is higher than • c in summer or lower than • c in winter, which means that the electricity consumption is not linear with regard to the outdoor temperature and it depends on the operation & maintenance policy. generally, there are two working patterns for these central air conditioning systems -cooling and heating. otherwise, they will be turned off when it is a transition season (i.e., spring or autumn). during transition seasons, the central air conditioning system does not operate. in this study, a categorical variable that represents the operational status of air conditioning systems is introduced (fig. ) . as fig. shows, the electrical load consumption of the whole hospital is highest when the central air conditioning system was in operation for cooling, followed by heating and turned off. in this experiment, the building electrical load data were acquired every hour from intelligent-building energy support system (i-bess) developed by the shanghai hospital development center (shdc) , the administrative agency for the investment, management, and operation of municipal public hospitals in shanghai, including stph. building electrical load data from january , , to december , (a total of days) were collected and used for training and testing. the time series of building electrical load in this experiment is shown in fig. . in this section, the prediction performance of different single and ensemble machine learning algorithms is compared. within the single machine learning category, linear regression, lasso regression, ridge regression, elastic net, support vector regression (svr), and gaussian process regression are selected. linear regression is a statistical method used for analyzing the linear relationship of multiple variables, and the simplest single machine learning algorithm (shine et al., ) . regularization technique is applied which can be used to prevent overfitting problems by adding a regularization term to the loss term. the regression model which uses l regularization term (i.e., the sum of absolute values) is lasso regression and the model which uses l regularization term (i.e., the sum of squared coefficients) is ridge regression. elastic net further combines the regularization terms of lasso and ridge regression to overcome their dependency on data and the resulting instability, to get the best of both models. svr is a powerful and versatile machine learning algorithm that has the ability to perform regression tasks. gaussian process is a generalization of nonlinear multivariate regression (heo and zavala, ) . in the ensemble machine learning category, xg-boost and random forest, are popular energy prediction models which builds a decision tree in a sequential and parallel way, respectively. besides, the optimal parameters via gridsearchcv function of these above-mentioned algorithms are presented in the appendix. the mape, cvrmse, and nrmse of the tested hospital for different forecast models over the entire training and testing period are summarized in table . because the models' rankings in all the three performance indicators are the same, mape will be used as an example to illustrate the comparison results of different models. for single learning models, svr was the most accurate model with a mape of . %, followed by gaussian process regression and the remaining four models (i.e., linear regression, lasso regression, ridge regression, and elastic net) with a similar mape. for ensemble learning models, rf performed slightly better than xgboost rf with a mape of . % and mape of . %, respectively. however, when comparing single models with ensemble models, the prediction performance of ensemble models was consistently better than that of single models, which could be ascribed to the way how ensemble models were developed. to investigate the prediction performance of the proposed model on longer timespans, weekly electrical load prediction was also tested corresponding to module of the methodology. in healthcare facilities management practice, it is very likely for facility managers to create weekly operation schedules for power systems. as was presented in section , there were four types of input variables and one type of output variable used in daily electrical load prediction (i.e., module ). when it comes to weekly data, the day type variable is not needed. therefore, in the weekly electrical load prediction, these models were trained with three types of input variables, namely, weather, occupancy, and o&m related variables. for the weather variables, such as outdoor temperature, relative humidity, wind speed, pressure, and precipitation, data were derived by averaging the daily data during the whole week. for occupancy variables, namely, the number of outpatient visits, emergency visits, and inpatients visits, the data were derived by summing the daily data during an entire week. as for the o&m variables, values were identified according to the operation schedule (table ) . for the output variable, weekly load prediction of stph, a sum of each week was used (fig. ) . the comparison results of weekly electrical load prediction through single and ensemble machine learning algorithms are shown in table . it can be observed that in single machine learning categories, svr outperformed the remaining five models with a mape of . % by a large margin. for ensemble learning models, the mape of xgboost and rf was . % and . %, respectively, indicating that rf is slightly better than xgboost. when comparing the results of single and ensemble machine learning models, it appeared that the best single model (i.e., svr) performed close to the best ensemble model (i.e., rf), with the ensemble model still outperforming the single model. traditionally, it is recognized that ensemble models always outperform single models. however, the performance of a prediction model depends on several factors, such as input variables, selected models, and model parameters. the results of module showed that in certain situations, a single model may get similar performance as ensemble models. due to the relatively high performance of svr, xgboost, and rf, they were selected as the base model for the subsequent analysis. by comparing the results of module and module in terms of svr, xgboost, and rf, it appears that prediction models trained with daily data have better performance than models trained with weekly data. the comparison shows that by dividing the data at a finer level of time granularity, the prediction performance of the machine learning model can be improved. therefore, the authors suggest that if there are different operating patterns in different periods, the data collected at a finer level of time granularity will be necessary to improve the prediction accuracy of building energy consumption. by comparing all machine learning models, including single and ensemble models, rf was found to be the model with the highest prediction accuracy, so rf was used for the subsequent feature importance analysis. figs. and depict the feature importance results for module and module , respectively. it can be seen from figs. and that the top most influential features for modules and were the same (i.e., outdoor temperature, pressure, and operation status of the central air conditioning system), indicating that the daily and weekly electrical load consumption are highly correlated with the same factors. due to the high energy use related to space heating, cooling and ventilation loads, it was expected that outdoor temperature was the most contributing factor of energy consumption in hospital buildings. the operation status of the central air conditioning system (i.e., ope), with its importance ranked the third, depends on the specific o&m measures in the tested hospital. given the same weather condition, hospitals taking different o&m measures will consume different levels of energy. for example, some hospitals decided to open the central air condition system based on the outdoor temperature while others based that decision on the day of the year solely. as to the remaining features, they followed a different importance pattern in daily and weekly load prediction. in fig. , the result shows that in the case of hospital buildings, day type was the least influential feature mainly due to the around-the-clock operations of hospitals. in this experiment, eight machine learning models were compared for load prediction, including six single learning models and two ensemble learning models. the scope of single prediction methods covers several ai-based prediction models, i.e., linear regression, ridge regression, lasso regression, elastic net, svr, and gaussian process. when it comes to ensemble machine learning, two of the most well-known models, xgboost and rf were selected to construct the load prediction model of the tested hospital. empirical results indicated that the most accurate model in the single and ensemble learning categories was svr and rf, respectively. the prediction result for svr, xgboost, and rf are shown in figs. and . while ensemble models outperformed single models in load prediction of the tested hospital in daily load prediction, demonstrating its ability to improve the prediction performance of single models by training with data of finer granularity. the energy consumption patterns of healthcare buildings are characterized by uninterrupted operation and high energy usage intensity. the input variables in our study are accessible to healthcare facility managers, such as weather, occupancy, day type, and o&m variables. it is feasible for them to conduct daily electrical load forecasting by adopting the machine learning algorithms in this study, especially ensemble models, such as xgboost and rf. besides, svr is also an excellent alternative single machine learning algorithm which has been recommended by various previous studies (thinate et al., b; shao et al., ) . as illustrated in section , there has been a large number of researches focused on building load forecasting over the past decades. however, few of them focused on healthcare buildings and the number is much less when it comes to electrical load forecasting of healthcare buildings via machine learning algorithms. however, healthcare buildings are characterized by energy-intensiveness due to the constant need for available power supply for medical equipment and stringent requirements for air quality, making them the key area of achieving the energy conservation goals in the building domain. in this study, the best prediction performance was . % of mape (table ) . cvrmse can be useful to indicate how much variation or randomness there is between the data and the model. for hourly and monthly load prediction, the cvrmse recommended by the american society of heating, refrigerating, and air-conditioning engineers (ashrae) is within % and %, respectively (landsberg et al., ) . on a daily basis, the cvrmse value results of ensemble models in our experiment were within %, indicating that the accuracy of our model is acceptable. in particular, considering the occupancy and o&m variables of the proposed procedure the cvrmse of xgboost in daily load prediction on the training set and the testing set was . % and . %, appeared to be improved with respect to the xgboost as exploited in wang et al. ( a) , in which the cvrmse on the training set and the testing set was . % and . %, respectively. even though the electrical load of healthcare buildings is affected by a large number of factors, such as climate conditions, building envelope, energy system, and occupancy behavior, etc. it is obvious that these factors impact the electrical load with different weights. in this paper, the outdoor temperature seems to be the most important feature in both module and module , which is consistent with many previous studies (e.g., thinate et al., b) . since in complex buildings such as a hospital, the energy consumption of the air conditioning system can account for % of total energy consumption, whose main function is to keep a comfortable and constant indoor climate against the outdoor climate. pressure came after temperature, which also has a great impact on energy performance. while for the third important feature, o&m related variable, the importance result is arguable. in most situations, the operation status of the air conditioning system has not been able to keep up with the change in the climate condition, that is it will operate on heating when the outdoor temperature is low and on cooling when the outdoor temperature is high. however, for the majority of public hospitals in china, there is an operation schedule for the central air conditioning system with a flexible period for heating and cooling. in addition, three types of patients were taken into consideration and they also had relatively high importance on electrical load consumption. with respect to the day type, it seems that the differentiation between weekdays and weekends/holidays is not sensitive to the prediction performance of these models. however, the rankings of these features are different in daily and weekly load predictions. one possible explanation is that these variables have different patterns in daily and weekly operations. for example, the number of outpatients is high on weekdays and is low on sundays since the outpatient department will close on sundays, which resulted in a significant increase in emergency patients on sundays. the experiments were performed on a machine with intel i - u . ghz cpu and gb memory. the operating system was windows . all the algorithms were implemented in python. table lists the data size and computation time of different algorithms used in module and module . notably, module used daily load dataset and module used weekly load dataset. the results showed that the computation time of ensemble learning algorithms were considerably greater than those of most single learning algorithms except for gaussian regression. the potential reason for the long computation time of gaussian regression was its working process in inferring a probability distribution over all possible values. as ensemble learning algorithms, both xgboost and rf had to operate by combining the results of several base learners, resulting in a relatively longer computation time. according to wang et al. ( b) , the prediction accuracy should be given the first priority when solving such problems. overall, the computation time of the ensemble algorithms were acceptable. by comparing the computation time of module and module , the influence of data size on computation time can be investigated. it can be observed that the computation time of all models trained with daily dataset were greater than those of weekly dataset, indicating that the increase of data size will result in an increment of computation time. however, the difference of computation time of xgboost and rf between module and module was acceptable and it is reasonable to infer that the ensemble learning algorithms would still be practically efficient when using large volume of data (e.g., big data). in recent years, various research focused on the energy analysis and consumption optimization in hospitals worldwide have been conducted, such as in the u.s. (bawaneh et al., ) , china (ji and qu, ) , german (gonzález et al., ) , etc. however, limited by the availability of reliable and fine-granularity data, most of them were descriptive analysis at a macro level. this paper makes several contributions in model design. focusing specifically in hospital modeling, the authors developed an electrical load prediction model for healthcare buildings via single and ensemble models. even though it is widely believed that ensemble models can deliver higher prediction performance than single models by combining multiple individual models together, it is not guaranteed and needs to be tested context-by-context. however, few empirical studies have been conducted to test it in the healthcare facility energy prediction context. using the data of a general hospital in shanghai, the experimental results of this paper confirmed that ensemble models indeed outperform single models in terms of almost all measurements. in addition, the scope of the involved independent variables of the models employed in this study is broader than the majority of previous studies. not only the well-known energy variables were included, such as weather and day type, but also explored is the impact of occupancy and o&m variables on the performance of the prediction model, making the model context closer to the actual operation situation of hospital buildings. furthermore, this study identified the most important features affecting energy consumption in the experimented hospital which can give insights to healthcare facility managers in how to create the o&m schedule more appropriately. by training the electrical load prediction with daily and weekly models, it shows that it is more accurate to conduct load prediction with finer time granularity. this research can have two direct practical applications. the first and most important application is that the proposed model can provide accurate forecasting results and will assist healthcare facility managers to conduct better planning of hospital activities and energy sources in a timely manner. it can also serve as the basis of some other relevant jobs, such as fault diagnosis, energy benchmarking, etc. with the aim of supporting administrators or facility managers of hospitals to make decisions when they are trying to achieve energy conservation goals, the prediction models are developed at the hospital level rather than building or floor level. in addition, this paper illustrates one possible way to improve the energy management performance by taking advantage of multi-sourced, heterogeneous data. for example, data of four types of independent variables and dependent variables involved in this study are gathered through different methods/tools, such as weather station, healthcare information system (his), and smart meter. with the increasing popularity of big data and artificial intelligence, more efforts will be devoted to collect data in the area of healthcare facility operations by using multiple technologies. from this perspective, the methodology used in this paper can achieve its effective applications not only in the energy management systems but also in other fields of healthcare facilities management in the future. in this study, eight algorithms from two load prediction approaches (single and ensemble machine learning) were compared, which has seldom been systematically conducted in previous studies. the ensemble models outperformed single models in electric load prediction of the tested hospital, demonstrating its ability to support the decision-making process of facility managers of hospitals. in addition, both general characteristics (e.g., weather parameters) and function-specific characteristics (e.g., the number of patients) were considered when building the prediction model, making the model context closer to the actual operation situation of hospital buildings. although the proposed model has satisfactory predictive performance, the following limitations are acknowledged. the nature of the proposed method is data-driven, meaning the prediction performance highly depends on the quality of data. even rigorous data preprocessing has been conducted before the formal experiment, there may still exist some data noise. thus, the characteristics of data collected from a specific hospital may affect its accuracy. it would be better to test the performance of the proposed procedure in several hospitals. besides, the occupancy in the hospital consists of several types of people, including doctors, nurses, patients, and their visitors, facilities managers, etc. in this study, due to the accessibility of data, only three types of patients were included. further research can be conducted for a deeper analysis of the effect of occupancy by taking all of them into consideration. healthcare facilities are a vital part of social and medical organizations providing the society with needed healthcare. in addition, they are also the main battlefield of the public health emergency system fighting a pandemic like coronavirus disease . serving as the lifeline for all activities, energy consumption plays an important role in ensuring the efficient operations of healthcare facilities. predicting the electrical load of healthcare buildings accurately can support the decision-making processes of healthcare facility managers to improve building energy performance. this study compared the precision of eight machine learning models trained with daily and weekly datasets from a general hospital in shanghai. it was found that for daily electrical load prediction, rf, xgboost, and svr were the most accurate ensemble and single learning models, with a mape on the test dataset of . %, . %, and . %, respectively. these can be considered as reliable intelligent prediction models for facility/energy managers to conduct daily electrical load prediction in the future. in addition, based on the same dataset, the impact of forecasting granularity on prediction performance was tested. by comparing the results of daily and weekly load prediction, it was found that the performance would improve by using more granular or detailed energy usage data. one possible explanation is that a detailed load profile can decrease the uncertainty in computing. in terms of the feature importance, outdoor temperature, air pressure, and operation status of the central air conditioning system were found to be the top contributing factors. the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. this study was supported by the international exchange program for graduate students of tongji university, china (no. ) , the support program for young and middle-tech leading talents of tongji university ''operation management of complex and mega projects'', china. shanghai hospital development center, china and shanghai tenth people's hospital, china were sincerely acknowledged for providing the original data. the number of features to consider when looking for the best split ( , , ) the number of features to consider when looking for the best split ( , , ) performance evaluation of natural ventilation strategies for hospital wards -a case study of great ormond street hospital a classification of healthcare facilities: toward the development of energy performance benchmarks for day surgery centers in australia a review of data-driven building energy consumption prediction studies rehabilitation of the building envelope of hospitals: achievable energy savings and microclimatic control on varying the hvac systems in mediterranean climates electrical consumption forecasting in hospital facilities: an application case energy consumption analysis and characterization of healthcare facilities in the united states energy consumption analysis and characterization of healthcare facilities in the united states explaining machine learning models in sales predictions enhancing building energy efficiency by adaptive façade: a computational optimization approach short-term electricity forecasting of airconditioners of hospital using artificial neural networks an enhanced bacterial foraging optimization and its application for training kernel extreme learning machine solar powered healthcare in developing countries research on short-term and ultra-shortterm cooling load prediction models for office buildings commercial buildings energy consumption survey: energy usage summary dilution effect of the building area on energy intensity in urban residential buildings electrical and thermal energy in private hospitals: consumption indicators focused on healthcare activity improving customer satisfaction of a healthcare facility: reading the customers evaluation of energy consumption in german hospitals: benchmarking in the public sector gaussian process modeling for measurement and verification of building energy savings investigation and evaluation of energy consumption performance for hospital buildings in china a bottom-up and procedural calibration method for building energy simulation models based on hourly electricity submetering data hboost: a heterogeneous ensemble classifier based on the boosting method and entropy measurement choosing measures for energy efficient hospital buildings measurement of energy, demand, and water savings designing a short-term load forecasting model in the urban smart grid system development of a conceptual benchmarking framework for healthcare facilities management: case study of shanghai municipal hospitals a data-driven strategy for detection and diagnosis of building chiller faults using linear discriminant analysis occupancy data analytics and prediction: a case study short term hospital occupancy prediction short-term residential load forecasting: impact of calendar effects and forecast granularity realizing a stacking generalization model to improve the prediction accuracy of major depressive disorder in adults benchmarking acute hospitals: composite electricity targets based on departmental consumption intensities? energy build world energy balances : overview online bagging and boosting development of a new energy benchmark for improving the operational rating system of office buildings using various data-mining techniques space heating demand response potential of retrofitted residential apartment blocks scikit-learn: machine learning in python hourly prediction of a building's electricity consumption using case-based reasoning, artificial neural networks and principal component analysis energy consumption modeling by machine learning from daily activity metering in a hospital prediction of energy consumption in hotel buildings via support vector machines machine-learning algorithms for predicting on-farm direct water and electricity consumption on pasture based dairy farms energy efficient policy and real time energy monitoring in a large hospital facility: a case study a hybrid model for building energy consumption forecasting using long short term memory networks sciencedirect sciencedirect sciencedirect sciencedirect energy performance study in thailand hospital building energy performance study in thailand hospital building nattanee the thinate, wongkot of assessing feasibility using the heat thailand demand fo new feature selection and voting scheme to improve classification accuracy enhanced bagging (ebagging): a novel approach for ensemble learning chaotic multi-swarm whale optimizer boosted support vector machine for medical diagnosis building thermal load prediction through shallow machine learning and deep learning forecasting district-scale energy dynamics through integrating building network and long short-term memory learning algorithm building energy efficiency for public hospitals and healthcare facilities in china: barriers and drivers a review of artificial intelligence based building energy use prediction: contrasting the capabilities of single and ensemble prediction models artificial intelligent models for improved prediction of residential space heating random forest based hourly building energy prediction random forest based hourly building energy prediction a study of city-level building energy efficiency benchmarking system for china enhanced moth-flame optimizer with mutation strategy for global optimization a review and analysis of regression and machine learning models on commercial building electricity load forecasting total energy use in buildings analysis and evaluation methods -final report of iea ebc annex feature selection based on improved ant colony optimization for online detection of foreign fiber in cotton a review on the prediction of building energy consumption chaos enhanced grey wolf optimization wrapped elm for diagnosis of paraquat-poisoned patients using long short-term memory networks to predict energy consumption of air-conditioning systems see tables a. -a. . see tables b. -b. . key: cord- -zgzq fe authors: kumar, durgesh; meena, mahendra kumar; kumari, kamlesh; patel, rajan; jayaraj, abhilash; singh, prashant title: in-silico prediction of novel drug-target complex of nsp of chikv through molecular dynamic simulation date: - - journal: heliyon doi: . /j.heliyon. .e sha: doc_id: cord_uid: zgzq fe literature reported that nsp of chikv is an important target for the designing of drug as it involves in the replication, survival etc. herein, about eighteen million molecules available in the zinc database are filtered against nsp using raspd. top five hit drug molecules were then taken from the total screened molecules ( ) from zinc database. then, a one pot-three components reaction is designed to get the pyrazolophthalazine and its formation was studied using dft method. authors created a library of compounds using the product obtained in the reaction and filtered against nsp of chikv based on docking using igemdock, a computational tool. authors have studied the best molecules after applying the the lipinski's rule of five and bioactive score. further, the authors took the best compound i.e. cmpd and performed the md simulations and tdmd simulations with nsp protease using amber . md trajectories were studied to collect the information about the nsp of chikv with and without screened compound and then, mm-gbsa calculations were performed to calculate change in binding free energies for the formation of complex. the aim of the work is to find the potential candidate as promising inhibitor against nsp of chikv. chikungunya virus (chikv) causes chikungunya fever (chikf) and this virus spread through the biting of mosquito [ , ] . it causes severe infection and the symptoms of chikf are high fever, polyarthralgia, myalgia etc. [ , , ] till date, there is no effective vaccine or drug for this disease available in the market, although few candidates as vaccine are under clinical trials [ ] . alphavirus is an enveloped viruses with a single stranded (þss) rna with non-structural proteins (nsp ) and structural proteins, capsid, envelope glycoproteins (e , e and e ) and k peptide [ , , , , ] . nsp of chikv is also known as macro-domain and have been initially obtained from databank [ ] . researchers reported baicalin as one of the potential drug molecule against the chikv based on binding affinity and π-π interaction between baicalin with tyr residue of nsp of chikv [ , ] . heterocyclic compounds have attracted the attention of the researchers due to biological potency in different aspects and they can be synthesized by number of steps as well one pot synthesis. further, one pot synthesis or the multi-component reactions are preferred due to less time consumption in the synthesis as well less or no time is wasted in the purification of the compound [ , , , ] . in silico methods are being explored by the researchers due to the efficiency and strategic approach. computational tools are used to create a library and filtering them to get the biological potent compound against a receptor [ , , , , , , , , ] . in this work, authors have designed a multi-component reaction (mcr) to produce pyrazolophthalazine via the one pot reaction between benzaldehyde, , -dihydrophthalazine- , -dione and oxazolidine- , -dione (ozd) and its feasibility was studied through dft method using gaussian . then, a library of molecules was designed based on pyrazolophthalazine. designed library was used for virtually screening against nsp of chikv, to get potential lead molecules based on minimum total binding energy, drug-likeness, and bioactivity score [ ] . the filtered compounds were subjected to molecular docking using pardock and their interaction profile was analyzed using ds visualizer, pymol, chimera. further, temperature dependent molecular dynamic simulations (tdmd) and mm-gbsa of screened compound-nsp of chikv complex was performed to analyze the structural stability of the complex. herein, cs chemdraw was used to draw the chemical reaction using from benzaldehyde, , -dihydrophthalazine- , -dione and oxazolidine- , -dione (ozd) to get pyrazolophthalazine i.e., the product molecule. it was used to design drug library by changing alkyl group (from r to r ) in aryl of aldehyde and these molecules were considered to be potential drug molecule targeting nsp of chikv [ , ] . literature reported that the oxazolidine- , -diones are based on five member heterocyclic compounds and many biological activity are reported. they have shown promising role as aldose reductase inhibitors, hypoglycaemic and hypolipidemic agents. a novel mcrs for the formation of novel pyrazolophthalazine molecules through a reaction between oxazolidine- , -dione, benzaldehyde and , -dihydrophthalazine- , -dione is designed as shown in scheme and was studied using dft. it is a proposed mechanism for the reaction shown in scheme . initially, there is a reaction between r i.e. ozd, has active methylene group and r i.e. benzaldehyde, carbonyl group. the reaction will give an unsaturated compound (im ) with an elimination of water molecule via knoevangel reaction. further, im reacts with r i.e. , -dihydrophthalazine- , -dione to give im . herein, the lone pair present on nitrogen of , -dihydrophthalazine- , -dione (nucleophilic site) attack on the unsaturated carbon (electrophilic site). it is azamichael addition followed by the rearrangement to im . further, im loose a molecule of water and cyclization occurs to give p, the product of interest. the adduct formation is justified based on energy diagram using b lyp/ - g*method [ , ] . the following parameters of global reacting indices were calculated from reactant to product such as total energy (e), e homo , e lumo & lumo-homo energy gap (Δe) are calculated [ , ] . the proposed mechanism of mcrs was studied using density functional theory (dft) calculation as in scheme . a library of molecules was created via different susbtitutents on pyrazolophthalazine using cs chemdraw as in table [ , ] . in designing, only aromatic aldehydes are varied to a library of the new compounds which may have better potency against the nsp of chikv. in this designed molecules only aromatic aldehydes have been varied by changing alkyl group r to r . library of designed molecules were used to screen against nsp of chikv through igemdock. authors have been taken best five molecules on the basis of minimum total binding energy. further, screening of best five molecules was filtered through admet properties. the crystal structure of nsp of chikv was obtained from the rcsb protein data bank (pdb id: gpo) in complex with adp-ribose at resolutions of . Ǻ respectively. the removal of extra atoms like water, missing atoms and added explicit hydrogen in the both model (ligand & target protein) was done using pymol (biovia ) and ucsf chimera- . . software [ ] . raspd is used for preliminary screening of potential molecules from zinc database based on minimum binding free energy. this is very fast protocol for accurate prediction of hit candidates for any target protein. in this way, authors screened drug molecules from zinc database based on binding affinity range of - . to . kcal/mol, but top five drug molecules were selected from screened molecules on the basis of molecular weight (mw < ) with minimum binding free energy for molecular docking and simulations [ ] . in this protocol, method a (protein-ligand complex) was used to estimation of binding free energy and these molecules are listed in table . screening is a method to design the drug in short span of time. it is used to investigate potential molecules against nsp of chikv. the purpose of this method is used to predict a best pose of molecule and it was selected best ligand conformations based on pose and their binding free energy [ ] . the designed library of molecules and screened top five molecules from raspd were screened against nsp of chikv using igemdock software [ ] . in this, top five best molecules from the designed library based on binding energy were taken and on other side, screened molecules from raspd are ignored due to high binding energy in comparison of designed best molecules. igemdock computes a ligand conformation and orientation relative to the active site of target protein based on ga and summarized results in term of minimum total binding energy of the complex in tables and [ ] . the bioactive properties like tpsa, chemical structure, logp and lipinski's "rule of five" value using molinspiration were calculated [ , ] . several other biological parameters of best five compounds were calculated using swiss adme as in tables and . thus, the absorption (% abs) was calculated by given equation according to the method [ ] . herein, authors used gusar, a webserver to predict ld values for rats with four types of administration like oral, intravenous, intraperitoneal, subcutaneous and inhalation. the acute toxicity of cmpd , , , & has been calculated for screened molecules. these results were obtained through gusar for prediction of rat acute toxicity and acute rodent toxicity with four type of administration are mentioned in scheme . synthesis of pyrazolophthalazine via the one pot three component reaction between benzaldehyde, , -dihydrophthalazine- , -dione and oxazolidine- , -dione (ozd). table . the acute rate toxicity end-points are based on the log representation of ld value (mg/kg) for the rats [ ] . pardock is an automated web server for rigid docking was used to determine the binding modes of compounds in the receptor [ ] . e is the total energy; eel is energy due to electrostatic interactions; evdw is due to van der waals interactions; ehpb is the due to hydrophobic interactions. the docking result was further validated using the molecular dynamics (md) simulations method. md simulations is used to predict the binding of compounds to the target protein and study the changes in binding strength with change in the temperature [ ] . md simulations, an important approach is to study the physical movements of the atoms of the receptor in presence and absence of the compound for a known time [ ] . three dimensional structure of the cmpd was drawn using marvin sketch and its optimization is done with the gaussian on applying b lyp/ - g(d) basis [ , ] . further, other parameters of screened cmpd for the md simulations were produced using antechamber module of amber suite molecular dynamics software utilizing generalized amber force field (gaff) [ ] . the input files were used to run by xleap command using amber ff sb force field for the created parameter and coordinate files. subsequently, solvate box tip p . was added with a Å buffering distance [ ] . during thermalization, initial velocities were produced based on the maxwell-boltzmann distribution with a temperature of k and constant volume (ntb ¼ ) for ps (nstlim ¼  dt ¼ . ) simulation time. further, the receptor or its complex was equilibrated at k and bar using the berendsen thermostat for constant pressure (ntp ¼ ) for another ps simulation time. once the equilibrium is reached, md simulations were performed for ns [ ] . different trajectories based on md simulations were analyzed [ ] . authors also checked the rmsd value by the variable temperature (non-isothermally) of drug-target complex at ns and according to david and konard approximation and this approximation is said to be temperature dependent md simulations. in tdmd simulation for ns, the input file (temp k to k) was used to set print energy output files every steps (ntwx&ntwr ¼ ) and save coordinates every (ntwx ¼ ) as in amber input. md simulations trajectories of complex system were used to determined relative change in binding free energy according to the mm-gbsa method [ , , , ] . in order to calculate binding free energies like for cmpd -nsp of chikv, nsp of chikv and cmpd was calculated for high accuracy results [ , ] . the binding free energy (Δg bind ) of the drug-target complex is calculated on the given eq. ( ). where, Δg bind and Δg bind , vacuum are the free energy difference between the bound and unbound forms of a complex in solvated and vacuum respectively. Δg solv,d-t, Δg solv,d and Δg solv,t represented the change in free energy between the solvated and vacuum states of a cmpd , nsp of chikv and cmpd -nsp of chikv complex. the change in solvation free energy from different systems are calculated by given eqs. ( ), ( ), ( ), and ( ). e mm -mm energy; e int -internal energy; e el -electrostatic energy and e vdw -energy due to van der waals interactions. bonding orbital calculations were performed by full nbo program as executed in the gaussian [ ] . different physiochemical descriptors scheme . the proposed mechanism for the formation of pyrazolophthalazine via one pot three component synthesis. (continued on next page) d. kumar et al. heliyon ( ) e ( ), ( ) , and ( ) as follows. authors have designed the chemical reaction for the synthesis of biologically potent pyrazolophthalazine as in scheme and it is considered as a novel compound to target nsp of chikv. initially, there is a reaction between r i.e. ozd, has active methylene group and r i.e. caronyl of aromatic aldehyde. the reaction will give an unsaturated compound (im ) with an elimination of water molecule via knoevangel reaction. further, im reacts with r i.e. , -dihydrophthalazine- , dione to give im . herein, the lone pair present on nitrogen of , -dihydrophthalazine- , -dione (nucleophilic site) attack on the unsaturated carbon (electrophilic site). it is aza-michael addition followed by the rearrangement to im . further, im loose a molecule of water and cyclization occurs to give p, the product of interest as in scheme . energy level (homo & lumo) of reactant, intermediate and the product are determined. the energy differences between the orbital energies are shown in table . the energy values of homo orbital and lumo orbital of product molecules were lying at an energy value of - . ev and - . ev respectively. the lumo-homo energy gap was obtained at - . ev in the isolated gas molecular calculations. if lumo-homo energy gap is higher implies the kinetic energy is higher and high chemical reactivity [ ] (see figure ). figure . the energy profile diagram of product formation using b lyp/ - g* basis set as in scheme through dft method. igemdock is used for the virtual screening of the compounds against the target protein [ , ] . the details of the binding energy of the designed compounds against the nsp of chikv is given in table and screened molecules by raspd from zinc data base against nsp of chikv is in table . then, the top five compounds are taken based on the least binding energy of the complex system for molecular docking. binding energy of the molecules or compounds from the obtained from the zinc database were further studied using igemdock, it found that the molecules (zinc_ ) showed minimum total binding energy but it was less than the designed best five compounds as in table . this molecule showed only one π-π interaction with tyr- and two h. bond interaction with leu and val in figure . best five molecules from the designed library as in table as well as the screened molecules from zinc database as in table are taken for the prediction of physicochemical properties, lipophilicity, water solubility, pharmacokinetics, drug-likeness and bioactivity score as in tables and . all best five compounds follow the criteria of biological parameters. if a compound having gpcr ligand values > . is mostly likely to possess considerable biological activities, while ligand values - . to . are expected to be moderately active and ligand values < - . , presumed to be inactive. for the prediction of acute toxicity, the adverse effects of a compound may result due to one or more than one time exposure. in present work, authors have determined the median lethal dose (ld ) of top five hit from the designed library (cmpd , , , & as in table ) via four types of administration: oral, intravenous, intraperitoneal and subcutaneous. ld is the amount of molecule, can causes the death or kill the % of test animal. therefore, the toxicologists can use different animals but rats and mice are usually considered for the study. it is expressed per g of the body weight of the small animals. the active site of receptor is a binding pocket due to hydrogen bonding, hydrophobic interactions. screened compounds showed the promising antiviral activity against nsp of chikv based on binding energy. molecular docking method was used for predicting the binding energy of newly formed drug-target complex. in this study, best five compounds from designed library were docked with active site of nsp of chikv using pardock to elucidate their molecular interactions as in table and figure . the best docking pose for each ligand was also recorded for better results. this analysis was showed that molecules fit to bind in the cavity of nsp of chikv and by forming a stable d-t complex. as is evident from figure a , b, drug interacts with nsp protease of chikv forming a most stable complex establishing hydrogen bond interactions with their minimum distance. the insight of various other residues are present in d-t complex interaction is depicted in d plot and these residues are play key role in the formation of stable d-t complex. the docking results were further evaluated in terms of rmsd value and binding free energy through mm-gbsa protocol. the amber program was used for md simulation to study the stability and flexibility of the nsp of chikv with and without cmpd receptor and its complex using different trajectories like rmsd, rmsf and hydrogen bond. rmsd plot showed that most of the complex system was relatively stable within - . Å for - ns simulation time as in figure . rmsf plot was used to understand the flexibility of the nsp of chikv with and without cmpd as in figure . less fluctuation are observed in the complex in comparison of the nsp of chikv alone. further, the hydrogen bond plot and analysis for the complex of nsp of chikv- are given in figure and table respectively. it was used to find the existence of hbs between a donor and acceptor, % occupancy and angle during the simulations. residues asp , arg , thr , leu , gly , ala and val are present in the active site of nsp of chikv and showed noteworthy fluctuations compared to other native residues. the total numbers of average hbs are formed during md simulations were predicted. the analysis to find the maximum number of hydrogen bonds is done and suggested maximum of intermolecular hydrogen bonds. average number of hbs for different donor-acceptor average distance cutoffs is . (strong bonding) with larger average angle. it was found that hbs between drug molecules and residues are gly_ @o with donor h & n of drg_ as in table . it was assume that formed hbs have distance between accepter residue o atom in the backbone with donor h & n in the drug molecules showed shorter distance ( . Å) and the angle of n-h-o is . with . % occupancy at k for ns simulations time observed. binding free energies was calculated of drug (cmpd ), target and drug-target complex using mm-gbsa methods are shown in table . figure . screened drug molecule from zinc data base showed only oneπ-π and hydrogen bonding are represented as a stick model. change in enthalpy (Δh) as in figure , differences of (drug-target complex) with target and drug was found to be - . kcal/mol. change in free energy (Δg) was determined by calculating change in entropy (Δs) and change in enthalpy (Δh) for the formation of complex between nsp of chikv and cmpd . for any spontaneous process or reaction, the change in free energy should be negative. tΔs was calculated for the complex system is - . kcal/mol as in table . Δg for the binding of the complex between nsp of chikv and cmpd comes out to be - . kcal/mol by using eq. ( ) . in the literature, authors were explained md simulation of backbone of nsp of chikv with and without cmpd (target protein and drug-target complex) at k (isothermally) and atm pressure. herein, based on david and konrad approximation, authors varied the temperature from to k (non-isothermally) and atm pressure for md simulation of drugtarget complex. the system minimization, heating, and equilibration were carried out in the same manner used for the optimization of drug-target complex described above. in this way tdmd simulations were performed for ns at , , and k and the rmsd trajectories are given in figure . note: where, in ad meaning the compound falls in applicability domain of models while out of ad means the compound is out of applicability domain of models. table . actual molecular docking results of cmpd drug molecule onto active site of apr ligand and also represented their interactions with distance analysis. the simulations and change in relative enthalpy energy results confirmed that actual stability of system at and k in figure and table . a total of snapshots were taken in a ns md simulations time to calculate the binding free energy difference using eq. ( ). further, rmsf curve for target and its complex with drug molecules was studied at ns at k, k, k, k and k as in figure . the hydrogen bond plot for the complex of nsp of chikv- for ns at , , , and k was studied and maximum number of hydrogen bonds for the complex at , , , and k are , , , and respectively and shown in figures , , , , and respectively. it means on increasing the temperature, number of hydrogen bonds decreases. further, hydrogen bond analysis for the complex of nsp of chikv- for ns at , , , and k was given in tables , , , , and respectively. prediction of the structural stability of intermolecular hydrogen bonds and total number of hydrogen bonds formed with nsp of chikv. md simulation of the drugtarget complex is used to study the stability during the trajectory period. hydrogen bond profiles between the selected drugs and nsp of chikv were calculated using the amber . this analysis revealed that average hydrogen bonds are formed during the simulations period sharing four to five hydrogen bonds with gly , arg , ile , lys , leu and these five hydrogen bonds showed poor hydrogen bond interactions with weak fractions of time at k for ns time period in figure and table . the same pattern was also observed in the case of variable temperature but at k, tyr showed maximum fraction of time in figure and table . dft calculations of best five compounds have been performed and frontier molecular orbitals taken as in table . homo-lumo energy gap plays an important role in stabilizing the interactions between compound and nsp of chikv. by using energy values of homo and lumo for top five screened hit drug molecule from designed library to calculated μ, χ, η and ω by using eqs. ( ), ( ), ( ) , and ( ) . table summarizes the homo, lumo and homo-lumo energy gaps (Δe) of top five hit drug molecules calculated at dft level in the b lyp/ - g* basis set. the energy different between homo and lumo is used to understand the chemical reactivity and kinetic of molecules. if a compound has small energy gap indicates more polarizable and therefore have high chemical reactivity and termed as soft molecule. global term is a primary descriptor for the chemical reactivity of compounds. chemical hardness is a measure to study the stability of compound. it explains the resistance towards polarization of the electron cloud under small perturbation. chemical potential is a form of energy and can be absorbed or released on changing the number of the species in a chemical reaction. larger the value of electronegativity indicates more the attractiveness for electrons. electrophilicity is a measure for the energy stabilization of compound. it is used to understand the the reactivity of compounds involved in chemical reactions. in the present work, finding the promising candidate against nsp of chikv was explored via screening, docking, md simulations, mm-gbsa calculation. a library of compounds is created based on the product obtained in one pot three component reaction. then, the compounds were subjected to docking and bioactive score. further, the results of screened compounds were compared with results of the compounds based on the compounds obtained from the raspd. then, nsp of chikv with and without cmpd were studied using md simulations for ns and change in binding energy is determined by mm-gbsa method. Δg for the formation of complex was found to be - . kcal/mol. subsequently, the effect of temperature was studied for the formation of the complex between the nsp of chikv and cmpd using the md simulations. the rmsd values and fluctuation increased on increasing the temperature. therefore, it is understood that the best inhibition is observed at k by the cmpd . author contribution statement durgesh kumar: performed the experiments; analyzed and interpreted the data; wrote the paper. kamlesh kumari, prashant singh: conceived and designed the experiments; wrote the paper. rajan patel: analyzed and interpreted the data. abhilash jayaraj: performed the experiments; analyzed and interpreted the data. this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. modeling dynamic introduction of chikungunya virus in the united states mapping of chikungunya virus interactions with host proteins identified nsp as a highly connected viral component design and validation of novel chikungunya virus protease inhibitors reemergence of chikungunya virus in indian subcontinent a dna vaccine against chikungunya virus is protective in mice and induces neutralizing antibodies in mice and nonhuman primates characterization of the early events in dengue virus cell entry by biochemical assays and single-virus tracking glycoprotein organization of chikungunya virus particles revealed by x-ray crystallography species-specific impact of the autophagy machinery on chikungunya virus infection molecular dynamics and quantum mechanics of rna: conformational and chemical change we can believe in the crystal structures of chikungunya and venezuelan equine encephalitis virus nsp macro domains define a conserved adenosine binding pocket putative papain-related thiol proteases of positive-strand rna viruses. identification of rubi and aphthovirus proteases and delineation of a novel conserved domain associated with proteases of rubi, alpha and coronaviruses mechanism of action of flavonoids as anti-inflammatory agents: a review nano-sized copper as an efficient catalyst for one pot three component synthesis of thiazolidine- , -dione derivatives copper nanoparticles in an ionic liquid: an efficient catalyst for the synthesis of bis-( -hydroxy- -oxothiazolyl)methanes copper nanoparticles in ionic liquid: an easy and efficient catalyst for the coupling of thiazolidine- , -dione, aromatic aldehyde and ammonium acetate phosphotungstic acid: an efficient catalyst for the synthesis of bis-( -hydroxycoumarin- -yl) methanes in water covid- : emergence of infectious diseases, nanotechnology aspects, challenges and future perspectives development of a theoretical model for the inhibition of nsp protease of chikungunya virus using pyranooxazoles understanding the binding affinity of noscapines with protease of sars-cov- for covid- using md simulations at different temperatures selective docking of pyranooxazoles against nsp of chikv eluted through isothermally and non-isothermally md simulations promising inhibitors of main protease of novel corona virus to prevent the spread of covid- using docking and molecular dynamics simulation computational approach to study the synthesis of noscapine and potential of stereoisomers against nsp protease of chikv a model to study the inhibition of arginase ii with noscapine & its derivatives a model to study the inhibition of nsp b-nsp protease of dengue virus with imidazole, oxazole, triazole thiadiazole, and thiazolidine based scaffolds pyrrolothiazolones as potential inhibitors for the nsp b-nsp protease of dengue virus and their mechanism of synthesis flavonoids as antioxidants and developmental regulators: relative significance in plants and humans virtual screening and docking studies of synthesized chalcones: potent anti-malarial drug dft theoretical study on the reaction mechanism of the nitrate radical with alkenes: -butene, isobutene, -methyl- -butene, and , -dimethyl- -butene efficient one-pot four-component synthesis of fused thiazolopyridin- -ones in ionic liquid density-functional theory of atoms and molecules applications of the conceptual density functional theory indices to organic chemistry reactivity chemdraw ultra . a theoretical model to study the interaction of erythro-noscapines with nsp protease of chikungunya virus ucsf chimera-a visualization system for exploratory research and analysis a rapid identification of hit molecules for target proteins via physico-chemical descriptors computational docking studies of noscapines: a potential bioactive agent gemdock: a generic evolutionary method for molecular docking impact of gemini surfactants on the stability of insulin using computational tools sanjeevini: a freely accessible web-server for target directed lead molecule discovery lead-and drug-like compounds: the rule-of-five revolution rate-limited steps of human oral absorption and qsar studies qsar modelling of rat acute toxicity on the basis of pass prediction pardock: an all atom energy based monte carlo docking protocol for protein-ligand complexes structural basis for modulation of a g-protein-coupled receptor by allosteric drugs molecular dynamics simulation of proteins: a brief overview a well-behaved electrostatic potential based method using charge restraints for deriving atomic charges: the resp model simmerling, ff sb: improving the accuracy of protein side chain and backbone parameters from ff sb binding free energy based structural dynamics analysis of hiv- rt rnase h-inhibitor complexes ptraj and cpptraj: software for processing and analysis of molecular dynamics trajectory data solvation free energy of biomacromolecules: parameters for a modified generalized born model consistent with the amber force field exploring protein native states and large-scale conformational changes with a modified generalized born model ligand affinities predicted with the mm/pbsa method: dependence on the simulation method and the force field absolute binding free energy calculation and design of a subnanomolar inhibitor of phosphodiesterase- theory and applications of the generalized born solvation model in macromolecular simulations results obtained with the correlation energy density functionals of becke and lee, yang and parr computational studies of global and local reactivity descriptors of some trimethyltetrathiafulvalenylthiophene molecules (tmettf-tp) by density functional theory (dft) green synthesis of tetrazines and their role as human cytomegalovirus (hcmv) protease inhibitor theoretical model to investigate the alkyl chain and anion dependent interactions of gemini surfactant with bovine serum albumin the authors declare no conflict of interest. no additional information is available for this paper. key: cord- -ap dzbp authors: iqbal, sajid; bilal, ahmad raza; nurunnabi, mohammad; iqbal, wasim; alfakhri, yazeed; iqbal, nadeem title: it is time to control the worst: testing covid- outbreak, energy consumption and co( ) emission date: - - journal: environ sci pollut res int doi: . /s - - -z sha: doc_id: cord_uid: ap dzbp during the covid- outbreak, managing energy consumption and co( ) emission remained a serious problem. the previous literature rarely solved this real-time issue, and there is a lack of public research proposing an effective way forward on it. however, the study examines the impact of the covid- outbreak on energy consumption and co( ) emission. the design of the study is quantitative, and the data is acquired from different online databases. the model of the study is inferred by using panel unit root test and ardl test. the robustness of study findings was checked through panel quantile regression. the findings highlighted that the covid- outbreak is negatively significant with energy consumption and co( ) emission. the study suggested revising the energy consumption patterns by developing and implementing the national action plan for energy consumption and environmental protection. the study also contributed in knowledge by suggesting the novel insight into co( ) emission and energy consumption patterns during covid- pandemic and recommended to consider renewable energy transition methods as an opportunity for the society. for a more effective management of energy consumption and environmental pollution, country-specific measures are suggested to be taken, and the national government should support the concerned public departments, ministries and private organizations on it. to the best of our study, this is one of the pioneer studies studying this novel link and suggesting the way forward on recent topicality. the world economy is facing two major problems: the spread of the new covid- outbreak and the current plunge in oil prices. the amalgamation of these two issues will probably trigger a long-term monetary slump and push the world economy into a subsequent downturn (baker et al. a ). the covid- outbreak continues to spread widely in the united states (usa), italy, china, iran and other countries, especially in europe, which has triggered special effects of stock market impulse and economic policy uncertainty. the recent stock market volatility level has exceeded from the levels of the stock market crashes in october and december and . during the same period, the uncertainty of the us economic policy indicated that by march , this number had jumped from to (disemadi and shaleh ) . similarly, the impact of the pandemic, such as the covid- outbreak commonly referred to as the coronavirus, has severely affected pakistan's energy sector. the petroleum and natural gas authority (ogra) of pakistan is committed to strengthening the national energy system and avoiding energy shortages not only due to local economic impacts but also due to international impacts. (chakraborty and thomas ) . likewise, it is widely accepted that the impact of the covid- outbreak is very big and structural in all the domains of life including the energy sector (nicola et al. ) . humans are the core regulator of society, and their health is the foremost important consideration for thriving in a productive and strong society. while, due to covid- outbreak, several health issues have been raised and such issues are becoming serious days by day, more specifically in frugal economies like pakistan, this impact is very critical, and now, an economic shock is being perceived; lockdown is being extended continuously; and by the effect of lockdown fuel consumption, co emission, energy demand and supply declined and market mechanism is altered very speedily. thus, to understand and identify the novel impact of covid- outbreak on co emission and energy consumption, the recent study is intended to investigate (solangi et al. b; hou et al. ) . this is the motivation of a recent study. deciding how much the impact of covid- is important, especially in the recent conditions, where many countries like the usa, china, italy, spain, iran, and india are facing 'pandemic effect' at large. by the fact, the covid- outbreak affected the energy sector of the world as a whole, and eventually, the demand graph of oil supplies have become bearish; oil market prices faced a decline; and big economies like the usa are bidding the oil-free of cost (malamud and núñez ) . according to bloomberg, a sudden decline has been observed in the oil and gas industry during march , and its future is still in an unpredictable state. importantly, the failure of opec negotiations is also the reason for the decline in oil prices and the covid- outbreak, which has expanded the greater impact on the energy industry of pakistan (solangi et al. a ). this is a very big impact with which existing theoretical propositions, assumptions, methods and models have not kept the pace. this is one of the big limitations and failures of previous literature. therefore, novel exertions are prerequisites to present advancement in the literature, empirical modelling and operational research by addressing the contemporary problem of the covid- outbreak (halkos and tsirivis ) . our study attempts to investigate this critical issue by testing the effect of covid- outbreak on the energy sector. more specifically, we inferred the effect of covid- outbreak on co emission and energy consumption. we incorporated the theory of economic efficiency to validate the association between co emission, energy consumption and the covid- outbreak. by considering the law of diminishing economic return due to the covid- outbreak, we authenticated the connection of the covid- outbreak with energy consumption and co emission (correia et al. ) . we test the inherent assumptions of economic efficiency theory and then validate an empirical model that forecasts the optimal points of energy consumption and co emission in pandemic where greater advantages are been achieved with the intent to sustain energy efficiency. we inquired the question how the covid- outbreak can reduce co emission and energy consumption (goodell ) . a better understanding of this question is the need of the time for academia, practitioners and regulators. in the energy sector, several energy consumptions and co emissionoriented frameworks, efficiency management policies and performance management mechanisms were presented. ironically, these policy frameworks and ways forward often increase energy demand and challenge the capacity of the energy sector to stay committed but not provide the way forward to adjust with the structurally imposed challenges, such as the covid- outbreak (department of economic and social affairs ). therefore, inquiries should give additional attention to understanding how structural changes like the covid- outbreak affect co emission and energy consumption (Öncü ) . in line with the concept of energy efficiency, we consider energy consumption as a contextual and market process that signals the expectation of an energy market (iqbal et al. b) . a so-called energy management system of ogra pakistan is expected to do this effectually but not essentially: recent declines in the local energy market of pakistan are big examples to support this argument. however, a policy way forward to manage the energy consumption and co emission is important (baloch et al. ) . and it is further important to give an alternative strategy in managing energy consumption by reducing the co emission in the pakistani context by taking the covid- outbreak as an opportunity. the objective of the current study is to investigate the impact of covid- outbreak on energy consumption and co emission, a way forward for sustainable energy markets. further, the study contributes to energy consumption patterns by suggesting how to cope and put up with the energy sector from the novel effect of the covid- outbreak. we propose sector-wide planning and administration in managing energy shortfalls and redressing the energy consumption habits. this is the first contribution. secondly, a recent study contributes to the novel covid- with the assumptions of the economic theory of efficiency by backing up the study arguments on energy consumption. thirdly, we fill the gap of theoretical and operational research by studying the novel covid- with co emission and energy consumption. fourth, by this study, we address the special call on 'secure and sustainable energy system' as this historical time is very crucial in developing the new avenues and/or ways forward to secure and stabilize energy system through energy markets-who have imagined a global lockdown and massive energy distress just a few months ago? fifth, we contribute to covid- , energy regulator (e.g. ogra pakistan) initiatives and energy market stability with the motivation to bring the best findings and policy ways forward to our readers. however, our study contributes to different avenues, most importantly in the covid- outbreak and energy consumption, to present a way forward for better planning and administration to meet the energy shortfalls. this article is one of the pioneering studies on the energy economic and environmental impact of the covid- pandemic. the rest of the paper is organized as follows: the 'review of literature' section describes the literature review, the 'research method and design' section describes methodology, the 'results and discussion' section describes the results and discussion while the 'conclusion and policy implications' section concludes the study. the pakistani economy is one of the rich oil-producing economies in the world and one of the self-sustainable economies in energy production resources in south asia. ironically, the national revenues, energy market returns, earning capacity, energy market microstructure and energy efficiency are adversely affected due to the covid- outbreak (connors ) . notably, the pakistani energy sector is broadly susceptible and sensitive to energy crust and turfs, energy preservation and consumption and environmental degradation. due to pandemic persistence, the role of covid- outbreak on the energy market and co emission has become an important area of study to study and guide the policymakers to sustain the energy sector at large. before the covid- lockdown, the energy consumption patterns of the pakistani economy were much alarming; and therefore, co emission and energy consumption have become a puzzle to solve (ataguba ) . in contrast, the covid- lockdown has proved the significance of less energy consumption due to lower co emission in the local context (wang et al. a) . in the emergence of , the covid- outbreak has become a lifetime emergency that affected the energy sector and economies as a whole. in response, national governments and regulatory authorities are combating with covid- pandemic resiliently (fornaro and wolf ) . in times of highly volatile momentum energy consumption and co emission, the covid- pandemic emerged as a big crisis (asbahi et al. ) . interestingly, the covid- outbreak locked the nations of nations into the self-isolation centres, and by the fact, this reduced co emission at large and co emission and energy consumption in so many countries like china, usa, spain, italy and pakistan. on this momentum, emission trading system (ets) and european union (eu) emission led a new policy framework on energy emission, such as co emission and energy consumption (liu et al. ; iqbal et al. b) . while, geographically, such policy frameworks were developed far away from asia, however, these are not considered, studied and implemented in the pakistani energy sector. considering the energy consumption way forward, it has been noticed from previous studies that many of the energy consumption and energy sustainability frameworks have been implemented in the annual year of . conversely, the covid- outbreak has postponed the entire activities related to the energy sector (disemadi and shaleh ) . likewise, due to covid- , such policy frameworks are being altered drastically ). thus, new policy frameworks on energy consumption, co emission leading towards energy sustainability (dong et al. ; zheng et al. ; iqbal et al. c) or energy efficiency are prerequisite in accordance to structurally imposed scenarios persistent in the world with the covid- pandemic (colenda et al. ) . in short, the energy sector needs adaptive policies that could enhance energy sustainability. a large-scale reduction in travel and transport activities has dampened the oil demand due to the covid- outbreak and by the fact (ghg) is also reduced. this is the common proposition that ghg emission is probable to be unmaintainable in the long run. however, a reduction in oil demand has raised an important point of concern that what would be the future of the climate and clean energy development. similarly, green credit assurance and assessment of the income which is produced from energy facilities provided by the supplier to the financial expert related to the environment by use of friendly power (khokhar et al. ) . it might endanger green capital and affect the revenues of environmental ventures. here advancement features are also described for the improvement of green money and speculation (ciaschini et al. ) . thus, recent research also intends to add two related structures sponsored by a hypothetical method like with green account and speculation which depend on task size. the impact of the pandemic on the energy market is phased into two sections. first is the effect of covid- on the energy sector in determining energy consumption pattern from the raw material of production (oil demand, supply and consumption) to end-product (electricity and end mean of fuel used in the travel and transport industry). second, how the energy market will reshape a shift and recover after a pandemic or, in other words, how energy market will revive after a pandemic is the most important question of recent times that need answer (igwe ) . endorsing the previous literature, a recent study is extending the theoretical contribution by testing these missing links between the covid- outbreak, energy consumption and co emission. moreover, based on published studies, our study enhanced the empirical evidence by considering the recent reality of pandemic. the covid- outbreak indicates that carbon dioxide emission will decline during this year and historically a drop-down in co emission was observed in , and the declining percentage ranged from . to . % approximately (burkle ) . thus, the covid- outbreak has locked down the entire business of life in so many countries around the globe, and mainly china is affected by this particular virus (chohan ) . due to said specific lockdown, megaindustries and small-and medium-sized (sme) businesses are in lockdown that reduced the demand for oil as china is the largest exporter of oil products. by this, oil consumption is reduced, and with this effect, co emission is also reduced. considering the pandemic and opportunity, when industries are in lockdown, this is the high time to shift the industries towards renewable energy with the mission to reduce oil consumption and co emission and to develop clean and green china for upcoming generations. however, there is dire need to redress energy margin and shift on renewable energy. considering the theory of economic efficiency supporting energy consumption in terms of energy efficiency in a recent study, we established various energy efficiency and energy sustainability frameworks into the question particularly energy consumption in the pakistani context due to the covid- effect (coccia ) . the covid- effect on the energy sector is temporal and multifold, such as short-run and long-run effects. in the short run, the pandemic lockdown, often termed as self-isolation, has decreased air pollution and co emission caused by various precautionary measures taken by the airline and transport industries and production schedule shutdowns, while the long-term effect of pandemic lockdown is depending on the structural implementation of such decisions in cited industries on a large scale and will result in energy crisis and/or an economic shock to all population (gilbert et al. ; iqbal et al. a) . notably, this situation of pandemic lockdown is and will be a great source of uncertainty and will scale larger implications for the energy sector (das ) . this led a probability to face the mighty challenges by the energy sector by deciding to ( ) revise the energy sustainability policies concerning covid- for the long-lasting sustainability in the energy sector and ( ) prioritize the policy framework that may lead to clean and green energy consumption by satisfying the 'clean and green pakistan vision'. however, endorsing the covid- outbreak as an opportunity, it is the need of the time to safeguard the local environment and make it carbon emission-free by transiting the energy consumption on modern and innovative tools (department of economic and social affairs ). thus, addressing the objective of study for sustainable energy development and environmental protection is important for the pakistani community as the population is increasing in the figure of . million (source: bauru of statistic ( ), pakistan). extending to it, the effect of the pandemic with carbon emission and energy has become much important as the pandemic effect raised the extent it lowers the carbon emission and energy consumption (wren-lewis ; wang et al. b) . from a practical perspective, the recent study would help the policymakers to understand that how they may stimulate the covid- impact on energy consumption and carbon emission, which they can facilitate and collaborate to develop a new way forward to remediate the pandemic impact on energy consumption. we found limited literature suggesting pandemic effect, more specifically, covid- outbreak on energy consumption and co emission combined, and literature lacks in suggesting the concrete solution to manage the energy consumption shortfall caused by covid- outbreak. we discussed the theory of economic efficiency to address and to explain the cause and effect of a recent study framework. the findings of solangi et al. ( ) supported that extended lockdown lowers co emission that causes a reduction in energy consumption. therefore, the extension in lockdown or self-isolation has a direct and adverse effect on energy consumption and co emission. thus, considering the cited arguments, we hypothesized that there is an adverse effect of covd- outbreak on co emission and energy consumption (Öncü ; parth ) . in doing a recent inquiry, we used daily data of covid- outbreak, co emission and energy consumption, taken from different national and international databases. the covid- outbreak is measured by the number of days of lockdown, and the data is acquired from covid. gov.pk and worldometers.info. the data on co emission is from the statistical review of world energy, and the energy consumption data is obtained from the daily summary statistics of economic surveys of pakistan and bauru of statistics (noy et al. ) . we collected the data with effect from the first day of pandemic lockdown in pakistan dated march until april (around days) ( table ) . co emission measurement co scaling method is used to measure co emission. arango-miranda et al. ( ) presented a significant and linear relationship between per capita gross domestic product (gdp) and per capita emission of co in developing economies. this relationship remained significant with the condition that the population of the respective country should remain stagnant and less mobile (wang et al. ; p. ) . notably, study authorized this assumption and assumed that study population remained static, under the structurally imposed lockdown of covid- pandemic, and during this period, a little physical movement of population is observed. therefore during the covid- outbreak, the co emission factors of pakistan showed a decline. in other words, the stationary level of co emission factors designed a decreasing trend in co emission line on a larger extent. considering these assumptions and real conditions of covid- outbreak, our study further endorsed the scaling method of in measuring co emission. for this, industrial classification and actual state of oil and gas sector, transport sector, electricity sector, and cement sector of pakistani context were used. hence, co emission is measured using the gdp of industry (gdp) i and carbon emission factors (ef) i , assuming (ef) i will remain stationary. if (ef) i remains the same, the decline in co emission is indicated with Δco emission (see eq. ). using these measures, on the basis of emission features, we parted study sectors into two groups (e.g. transport sector and non-transport sector). measurement the non-transport sector gdp of the country is taken, and for non-transport, traveling distance and decline in transport services is also obtained from different databases (national highway authority database and ministry of statistics database). however, the Δco emission of the transport sector is measured by using eq. , the emission of transport sector was combined with oil and gas, electricity and cement sectors for empirical analysis co emission in the recent study. the energy consumption is measured by taking the net energy consumption (ec) in all the provinces of pakistan. the estimate of energy consumption is further classified into different proxies, such as energy consumptions (ec) are substituted with electricity consumptions (ec ) and fossil energy consumptions (ec ). according to the pakistan economic survey ( - ), the installed electricity generation capacity reached , mw in . the maximum total demand coming from residential and industrial estates stands at nearly , mw, whereas the transmission and distribution capacity is stalled at approximately , mw. moreover, thermal power generation is more than % of total electricity consumption in pakistan. however, various secondary energy sources are suggested to adapt as primary energy sources. therefore, total electricity consumption and total fossil energy consumption (ec ) are good proxies suggested to use in measuring total energy consumption. considering the theoretical foundation to infer the estimation, unit root test including llc test presented by levin et al. ( ) , ffp and fadf test presented by choi ( ) and ips test given by pesaran ( ) are used. the adf, pp and ips unit root tests have individual unit root processes. these three unit root tests have the null hypothesis of unit root, where the alternative hypothesis does not contain a unit root. in this research, to explore the long-run and short-run association between estimated variables, we applied the panel ardl method due to the mixed nature of the stationarity of the variables. the panel ardl method has various advantages: traditional methods of cointegration only assess the long-term correlation in the equations, and the panel ardl technique is more compact (pesaran and shin ) . according to eq. , our studied variables are stationary at i( ), i( ) or the level at first difference (sulaiman and abdul-rahim ). our baseline model can be written as the algorithm form of eq. is developed and shown in eq. , where, i = , …, n as indicator sign, t is time period and ɛ is error term. ec indicates energy consumption and co is co emission. the study also used panel quintile regression (pqr) to infer the robustness of the results (lamarche ) . importantly, pqr reduces the probability of outlier's occurrence, when ɛ is not normal. however, pqr is most effective relevant test to infer robustness than the ordinary least square (ols) method. subsequent to study operationalization, pqr is relevant to test the impact of covid- outbreak on co emission and energy consumption, where the dynamics of study are more contextual. the empirical findings of growth regression are presented in table . we regress the covid- lockdown on national energy consumption and co emission shown in the first column. the resulting output of growth regression indicated that the covid- lockdown is adversely affecting co emission and energy consumption. likewise, this effect is significant in both series. the findings of study imply that % variation or extension in lockdown leads to − . × ( . )% variation in co emission and − . × ( . )% variation in energy consumption gauged from fixed effect modelling. this point estimation shows the similar variation in co emission as − . ( . ) and energy consumption as − . ( . ) acquired from -stage least square test. we identified a highly dependent island in the occurrence group during the complete sampling tenure, and the direction is generally sharped to the leftward. an upward arrow to the right can observe other coherence which shows the cyclic relationship between covid- and oil. the oil price shows a rapid reduction during the covid- outbreak (fig. ) . these results indicate that due to travel constraints and lower predictable production progression in european countries and china, the covid- pandemic seems to have had a serious impact on oil price volatility through the demand side. figure shows the world crude oil future. the results show that covid- has affected local oil prices that are clarified by imposing travel restrictions. the robustness test estimates the wavelet-based causality in the occurrence groups, explaining that the time-frequency changes the temporal series of the covid- -oil relationship since months. table shows descriptive statistics. the study used plas method to test the gdp-to-co emission reduction by taking the provincial statistics of pakistani context. the co emission were found to be decreasing in sindh, punjab, baluchistan and khyber pashtun khawah (kpk). the obtained values of gdp are tabulated in table with the significant difference. notably, this difference and decline in co emission is noteworthy. moreover, due to lack of detailed variation rate for plas sector data, during the covid- outbreak, the punjab province shown a higher variance (see table ). while sindh scored second position in co emission reduction with . emissions score, kpk reduced on third position with . and baluchistan remained in last with a . score. yasmeen et al. ( ) revealed that oil and gas is the largest sector of pakistani economy contributing to co emission transmission. our study findings are coherent with this narrative, and due to the covid- outbreak, a downward structural shift is inferred in this sector. secondly, the transport sector showed a significant decline in co emission. during this period of the covid- lockdown, from march to april , public transport, airways, urban transport, motorways, various production industries, oil and gas consumers were shut down. people were officially and publically notified to stay at home and maintain social distancing and standard procedures to mitigate threat of covid- pandemic. all these precautionary measures reduced public gathering, closed business activities, economic activities and movement of public. in result, a massive structural decline is observed in transport and oil and gas sector that supported structural and procedural cleaning of the environment. the findings show that panel unit root outcomes of study constructs were stationary at the l( ). this stationary level suggested applying ardl technique to infer a connection between covid- outbreak, energy consumption and co table ). pesaran and shin ( ) introduced ardl approach and is advanced by pesaran et al. ( ) . the ardl technique has several advantages over a cointegration test (johansen and juselius ; engle and granger ) . first, this approach does not impose the condition that the variables have the same order of integration. however, it takes into account variables that are order or order integrated. next, it is adapted to small samples. in fact, johansen's cointegration method requires a large number of observations for the estimation to be reliable. finally, in the ardl model, the dependent variable is explained by its past and by the past of the other independent variables. table indicates that co emission is negatively affected as − . * by the covid- outbreak with the p value as . (< . ). similarly, the total energy consumption (tec) is also negatively significant as − . * with the . p value as < . ; the total electricity consumption (ec ) is negatively affected by the covid- outbreaks as − . * with the . p value as . ; and the total fossil fuel consumption (ec ) is also negatively impacted by the structural imposed crises of covid- pandemic as − . * ( . ), and the p value of ec is also less than . level of significance. in addition − . * with ( . ) level of significance is acquired at full level. by this, the hypothesis of study is accepted that the covid- outbreak has negatively affected energy consumption and co emission in the context of pakistan. likewise, ardl results show that r of the study model is . . thus, considering the energy consumption and carbon emission, our findings are aligned with lin and raza ( ), revealing the analysis of co emission and energy consumption. one of the potential reasons of the decline in carbon emission during the covid- lockdown is the decrease in oil consumption and transportation mobility. energy and carbon intensity are the key antecedents causing reduction in energy consumption and carbon emission. according to official statistics of ogra, an % reduction rate in energy consumption is observed during the month of march ( ). and evidently, the pakistani energy sector is more inclined towards thermal energy consumption generated from petroleum products and fuel substitution. secondly, according to historic statistics of energy associations, around % of pakistani energy mix is dependent on fuel, and as mentioned earlier, this percentage faced a decline of % and redressed a new % of new energy mix. therefore, the covid- lockdown has resulted in a massive reduction in energy consumption in the study context. interestingly, this adverse effect leading to reduction in carbon emission is an opportunity of modern times to control this emission by maximizing the rapid growth through ideal energy sources. historical studies widely used ordinary least square (ols) technique to gauge robustness in the findings of these investigations, but this technique has some limitations that ols fails to portray a comprehensive look of empirical distributions of dependent variable. in a heterogeneous context like pakistan, the impact of the covid- outbreak on energy consumption and co emission are likely to be robust at different quantiles. for this, panel quantile regression (pqr) technique is suggested. this technique allows the coefficients to vary with multiple quantiles and has distinctive advantages of detecting the variation in the impact of covid- outbreak on energy consumption and co emission. moreover, the quantile regression approach is also useful for addressing problems that may severely affect the accuracy of estimation, including heteroscedasticity, outliers, and unobserved heterogeneity. therefore, this paper adopts the quantile regression to infer the robustness of the study results more comprehensively. the findings of pqr technique confirmed the results of ardl model and showed robustness, as the impact of covid- outbreak on energy consumption and co emission is negatively significant in all the quantiles, where, τ = th, τ = th, τ = th, τ = th and τ = th at % of level of significance (e.g. p value < . ) ( table ). in the recent topicality, the role of the covid- outbreak is evident and a big challenge for energy sustainability in upcoming time. therefore, a policy plan is much needed to enhance energy sustainability in pakistan and is suggested in the next section of this study. subsequent to the findings of the study, the covid- outbreak has several structural influences on the energy market of pakistan and environmental pollution, and importantly, these two aspects need more visionary attention to fix and to gain economic advantage on a national basis. for this, energy consumption indicators, energy efficiency and environmental pollution indicators should be carefully watched and managed. however, we suggest developing and implementing an economic action plan by considering energy consumption indicators and environmental pollution elements to give a boost to national economy of pakistan. incentivizing the energy consumption patterns could also generate a shift in consumption behaviour of the general public and corporate owners. in addition, most of the arrows turn left and left, which means that there is a counter-cyclical effect between covid- and the us stock index with covid- as the main index (fig. ) . uncertainty is mainly related to the long-term development of the pakistan economy and how the fed will deal with the significant increase in uncertainty and the bad news of covid- . this is an adverse effect on the potential output and unemployment rate in the usa, which are completely independent of monetary policy. the coronavirus (covid- ) epidemic spread from wuhan (hubei region to china), where the first case of infection is reported on december . forty-nine days after this, on january, the world health organization (who) released the first corona virus monitoring report. by , more than , people in more than countries around the world will be affected. although covid- does not present similar patterns in terms of mortality severe acute respiratory syndrome (sars) or in terms of global spread in - . compared with the spanish flu pandemic, the new coronavirus is highly contagious and creates a lot of uncertainty in the real economy and financial markets. creating short-term fluctuations in food prices affects aggregate demand and imminent the movement of workers and tourists. in addition, covid- creates fear and extra stress. financial markets, where price fluctuations are constantly increasing. hope to be strong. because of declining global demand in the coming period, saudi arabia started an oil price war from march , and flooding the market with oil. in a single day, the price of crude oil falls more than % of the shock spreads to falling financial markets in a single day. covid- seems to be the main geopolitical shock in the world. in the past few years, energy crises in pakistan are managed by the fossil fuels that raised the co emission at large, and because of the effect of the pandemic, energy association and regulatory authorities of pakistan have given less effort in managing energy sustainability. our study is one of the first studies to gain the attention of regulatory authorities in a local context and to present the a way forward to enhance the energy sustainability by reducing carbon emission and energy consumption. for instance, considering the bright side of covid- outbreak the energy consumption can be managed through innovative and advanced tools by replacing the fuelbased energy resources on renewable energy sources and/or green energy sources (gautret et al. ) . a significant reduction in carbon emission is one of the hard-core benefits of such renewable or green energy sources. covid- outbreak highlighted a structural impact on energy consumption and carbon emission, and this was the motivation of recent research to inspect the role. our findings are consistent with pegels ( ) and gugler et al. ( ) . we found a negatively inverse significant role of covid- outbreak on energy consumption and carbon emission. the findings are revealed by the co-efficient alpha of growth regression accepted by the study hypothesis. in short, a significant decline in energy consumption and carbon emission is observed due to pandemic effect. by the fact, the covid- outbreak extended the lockdown, and entire world is shifted in self-isolation. this impact lowered the burden of energy consumption; very less vehicles are mobilized around the globe that resulted in a massive decline in energy consumption and carbon emission. on this, it is difficult to persuade each and every stakeholder associated with energy sector, and realistically, this is the internal energy consumption position (kost, ). on energy production and consumption, pakistan is mainly depending on traditional sources of energy generation, from which, oil material and fossil fuels are most prominent (van de ven and fouquet ; , trotta ; iea ) . as previous literature suggested, this source of energy will be vanished from the world in upcoming sources (zameer and wang ) . thus, it is important to consider and plan about alternative energy generation sources to stabilize energy consumption and reduce environmental pollution (mirza and kanwal ) . it is important to consider the covid- outbreak as an opportunity to redesign the energy sector of pakistan as the energy demand is declined in most of the commercial sector. by underscoring the findings, we concur the results as model and country specific, and we warrant the caution that the comparability of findings with other context may result in heterogeneity in terms of energy consumption and the covid- outbreak. by endorsing the countryspecific findings, our study is providing certain policy measures. practically, responding to the covid- outbreak, oil prices and dampened oil demands should be managed especially in the wake of opec price game, and this affected energy consumption. these concerns are driving our research. this study is the first attempt to analyze the relationship between covid- outbreak, energy consumption and co caused by lead-lag interaction. here, due to differences in risk conditions, different expectations and different understandings of risks, investors from all over the world may respond differently to investment decisions during the investment period. for example, market traders are aware of the 'bad' news inherent in the world's rising cases of covid- infection, deaths, government alienation guidelines and the impact of oil price changes. fear of contagion and lack of vaccine availability worsen the private spending with a combined effect of declining income. service, tourism and entertainment sectors are being affected, which are more particularly associated with public events and catering services. income and job insecurity will be raised because of reduced working hours especially to those who have no access to social safety net. the panic and uncertainty of the pandemic will cause delay in private investment, but the demand of government will go up in order to meet emergency health assistance initiative. despite all the pandemic crisis of covid- , the negative net demand effect is assumed to be short lived. on the supply side, the manufacturing activity will be halted in most affected regions. reduced production will cause bottleneck in worldwide supply chain. unplanned accumulation of inventory would be depressing down production capacity resulting in sinking gdp. the covid- has already exhausted inventory stock by fluctuating the globalized production structure. such production variability will in turn generate extensive factory lockdowns for shortage of intermediary inputs. we contributed in literature by presenting a novel study on the covid- effect on carbon emission and energy consumption in modern time when the world is finding the solution for each and every sector and each and every aspect to make it sustainable. our study inferred the adverse effect of the covid- outbreak on energy consumption and co emission. we inquired and contributed by presenting the practical solution to stabilize energy consumptions and co emission in pakistan. we highlighted the negligence of energy authorities of pakistan and also contributed by directing the implications to sustain energy demand, energy prices by changing energy consumption and co emission behaviours in time. hence, to the best of our knowledge, this would be the one of the pioneer studies on covid- outbreak and energy consumption. the economic and social costs of the covid- pandemic are related to society, policy makers, and all financial market participants and individual investors. our findings provide novel and outstanding policy and practical significance. it is becoming more and more obvious as the covid- outbreak is causing an interruption to oil demand and energy consumption, while there is an abnormal increase in uncertainty of an economic policy. & policy : we suggest to manage the energy consumption more carefully because due to the covid- outbreak, the energy sector expects to face few massive shocks like health emergency leading to continuous lockdown, coping with low oil prices simultaneously and a decline in energy revenues due to lower oil revenues. to sustain energy sustainability by managing energy consumption, we suggest energy regulatory authorities to come up with contingent plans that may enhance operational effectiveness during and after covid- to reach the threshold level of energy consumption. in due course, when the threshold limit is achieved, then the upcoming energy demands should be replaced by the renewable energy sources. therefore, for the energy sector, we argue that the covid- is an opportunity to revive, redevelop and reconfigure energy consumption patterns. & policy : during covid- , we also observed few bitter realities in the energy sector of pakistan backing the study findings. first, poor attention in managing energy demand, oil prices and revenue shortfall has placed a big and clear question mark on the immediate future of energy sector. secondly, less visionary and less proactive leadership in energy regulatory authorities of pakistan is another big challenge to fix. thirdly, none of energy sustainability action plan is given by these regulatory authorities with respect to the covid- outbreak. this would not be false to say that such regulatory authorities as sleeping rabbits, and if they have not managed in time, there is a probability of energy chaos to knock at the door steps, just because the energy sector of pakistan is more fragile in comparison with developed countries. & policy : we suggest to ogra to develop a system to manage oil demand and oil prices mechanism as per local demographics instead of international spillover effects, to play a visionary and proactive role to enhance the energy sustainability in pakistan, to continuously plan implement and re-plan on energy consumption and carbon emission to achieve the threshold limit, to replace traditional sources by the renewable sources, and to disclose a national action plan for energy sector and then implement this plan phasewise. & policy : the government must acknowledge the electrical distribution organizations, such as wapda and paec, to provide all the support services at par so that energy consumption may be actively managed by considering the pre-and post-effect of the covid- outbreak. & policy : all the household and families should be provided with an energy consumption guide by the provincial and local governments. similarly, standard operating procedures for energy consumption must be given to the business sector. for greater awareness, a campaign on electronic, print and social media should be launched by the government of pakistan with the intent to stabilize energy consumption and co emission on a sustainable basis. we extend to guide that the government of pakistan should publically provide an 'energy consumption and co emission plan'. by this, the national government should sustain energy and the environment in recent time and the potential consequence of such outbreak(s) in future. just because, this is the high time to change the behaviour of energy consumers and co emitters in all over the pakistan. we further suggest to the pakistan bureau of statistics to keep the updated data files on energy consumption and carbon emission during the period of the covid- outbreak. this would help a lot to us researchers and will save our time in doing quality research. two of the major limitations in conducting the recent inquiry: one is the lack of literary evidences on covid- association with energy consumption and carbon emission, and secondly, scattered form of empirical data in national databases consumed much time to gather the facts and figures. author contributions conceptualization, methodology, writing of the original draft: sajid iqbal; review, supervision: ahmad raza bilal; data curation, visualization: wasim iqbal; visualization, editing: mohammad nurunnabi; writing and software: yazeed alfakhri; writing, visualization and editing: nadeem iqbal. data availability the data that support the findings of this study are openly available on request. competing interests the authors declare that they have no competing interests. ethical approval and consent to participate we declare that we have no human participants, human data or human issues. carbon dioxide emissions, energy consumption and economic growth: a comparative empirical study of selected developed and developing countries novel approach of principal component analysis method to assess the national energy performance via covid- pandemic, a war to be won: understanding its economic implications for africa trilemma assessment of energy intensity, efficiency, and environmental index: evidence from brics countries declining public health protections within autocratic regimes: impact on global public health security, infectious disease outbreaks, epidemics, and pandemics covid- and macroeconomic uncertainty: fiscal and monetary policy response a post-coronavirus world: points of discussion for a new political economy unit root tests for panel data environmental tax and regional government consumption expenditure in a fiscal federalism system factors determining the diffusion of covid- and suggested strategy to prevent future accelerated viral infectivity similar to covid covid- : financial stress test for academic medical centers singapore races to get on top of covid- crisis pandemics depress the economy, public health interventions do not: evidence from the flu impact of covid- pandemic into solar energy generation sector department of economic and social affairs ( ) the social impact of covid- banking credit restructuring policy amid covid- pandemic in indonesia regional development and carbon emissions in china co-integration and error correction: representation, estimation, and testing covid- coronavirus and macroeconomic policy hydroxychloroquine and azithromycin as a treatment of covid- : results of an open-label non-randomized clinical trial preparedness and vulnerability of african countries against importations of covid- : a modelling study covid- and finance: agendas for future research ownership unbundling and investment in electricity markets -a cross country study effective energy commodity risk management: econometric modeling of price volatility measuring energy efficiency and environmental performance: a case of south asia world energy outlook executive summary african development institute of research methodology iqbal w, altalbe a, fatima a et al ( a) a dea approach for assessing the energy, environmental and economic performance of top industrial countries assessment of wind energy potential for the production of renewable hydrogen in sindh province of pakistan nexus between covid- , temperature and exchange rate in wuhan city: new findings from partial and multiple wavelet coherence oil supply risk and affecting parameters associated with oil supplementation and disruption maximum likelihood estimation and inference on cointegration-with appucations to the demand for money evaluating the social sustainability criteria of supply chain management in manufacturing industries: a role of bwm in mcdm robust penalized quantile regression estimation for panel data unit root tests in panel data: asymptotic and finite-sample properties analysis of energy related co emissions in pakistan response to the covid- epidemic: the chinese experience and implications for other countries response+to+the+covid- +epidemic% a+the+chinese+ experience+and+implications+for+other+countries&stitle=int.+j.+ environ.+res.+public+health&title=international+journal+of+ environmental+research+and+public+health&volume= &issue= &spage=&epage=&aulast=liu&aufirst=wei&auinit= w.&aufull=liu+w.&coden=&isbn=&pages=-&date= &auinit =w& covid- in latin america: political challenges, trials for health systems and economic uncertainty energy consumption, carbon emissions and economic growth in pakistan: dynamic causality analysis the socio-economic implications of the coronavirus pandemic (covid- ): a review measuring the economic risk of covid- triggering a global financial crisis: covid- as the last straw the economic cost of covid- : a potential pandemic impact on indian economy renewable energy in south africa: potentials, barriers and options for support a simple panel unit root test in the presence of crosssection dependence an autoregressive distributed-lag modelling approach to cointegration analysis bounds testing approaches to the analysis of level relationships review on natural language processing (nlp) and its toolkits for opinion mining and sentiment analysis evaluating the strategies for sustainable energy planning in pakistan: an integrated swot-ahp and fuzzy-topsis approach analyzing renewable energy sources of a developing country for sustainable development: an integrated fuzzy based-decision methodology factors affecting energy-saving behaviours and energy efficiency investments in british households historical energy price shocks and their changing effects on the economy fluctuation behavior analysis of international crude oil and gasoline price based on complex network perspective risk management of covid- by universities in china short-term forecasts of the covid- epidemic in guangdong and zhejiang strategic renewable energy resources selection for pakistan: based on swot-fuzzy ahp approach the economic effects of a pandemic, mainly macro blog, energy production system optimization: evidence from pakistan regional development and carbon emissions in china publisher's note springer nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations consent for publication we do not have any individual person's data in any form. key: cord- -p ro zdj authors: brown, marilyn a.; soni, anmol; li, yufei title: estimating employment from energy-efficiency investments date: - - journal: methodsx doi: . /j.mex. . sha: doc_id: cord_uid: p ro zdj we develop a methodology for estimating the number and types of jobs that would result from investments in energy efficiency in homes, businesses, and industry. the methodology involves the development of input-output (i-o) bills of goods that characterize how energy-efficiency funds would be spent across sectors of the economy. the methodology builds on and adds greater articulation to the research conducted in prior studies of u.s. energy-efficiency policies. • the first two steps involve estimating the magnitude of investments in energy-efficient technologies and systems required to produce a unit of energy consumption reduction, and then identifying how these investments are expensed across the broad investment categories, which creates the preliminary “bills of goods” for investments in energy efficiency in homes, businesses, and industry. • the third step involves soliciting feedback on the preliminary bills of goods from experts in delivering and evaluating energy-efficiency programs, and then making necessary modifications. • in the final step we apply the input-output coefficients representing the bills of goods to estimate the direct, indirect and induced employment per million dollars of investment in energy efficiency. energy more specific subject area: energy efficiency method name: input-output estimates of clean energy jobs name and reference of original method: clean energy "bills of goods" resource availability: climate and energy policy lab, georgia institute of technology [methodological protocols should be in sufficient detail to be replicated. there is no word limit! you can include figures, tables, videos -anything that you feel will help others to reproduce the method. the main focus of the paper should be on the technical steps required for this method, more than results; where appropriate, guide the reader through the procedure and provide all extra observations or "tricks" alongside the protocol. results and discussion are not sections included in the methodsx format. however, providing data that validate the method is valuable and required. this section could become a "method validation" paragraph within the method details section.] prior work estimating employment from energy-efficiency investments comprises a wide range of studies, across different types of technologies, sectors of the economy, and scales. typically, these studies rely on an input-output modeling approach to estimate the macroeconomic impacts, including employment generation. the employment impacts can be categorized into direct, indirect and induced. the direct effects relate to sectors that get affected by direct economic activity due to higher investment through various programs. indirect effects primarily include the materials and industry demand as a second order effect. finally, induced effects reflect the increased spending on consumer goods and services by those earning higher incomes due to the direct and indirect effects across the economy. as the world grapples with a pandemic with devasting effects on health systems, consumer spending, and the entire u.s. economy, with widespread shutdowns causing significant economic retrenchment, there are major consequences in store for our energy systems. these may challenge the ability of energy economy models of historic u.s. conditions as used in this study to provide robust forecasts of employment from energy efficiency investments in the future. in the short-term, the reduction in industrial activity and closure of non-essential industries is likely to reduce investments in energy and related upgrades. one exception could be the expanded use of residential energy as the result of stay-at-home orders. "eia assumes, in particular, that household usage of electronic equipment such as computers and televisions will increase. other uses of electricity, such as for cooking and for heating water, may also rise. household use of air conditioning during the summer months is also likely to be higher than normal as more people stay home during the daytime." in the medium-term, as federal stimulus investments revive the global economy and household spending, the clean energy sector may gain some additional spending as witnessed in the - recession. legislators and stakeholders are already seeking funding for clean energy technologies in coronavirus stimulus packages. the international energy agency and many other cleantech advocates recommend that clean energy be put at the heart of stimulus plans to counter covid- , which could cause a resurgence in energy-efficiency investments, perhaps with altered patterns of investment that are yet to be determined. bell et al. [ ] provide an evaluation of different methodologies used to measure job creation in energy efficiency improvements. the authors summarize the prevailing studies as following one of two approaches -bottom-up where surveys and interviews are used to generate the number of jobs in the sector, and top-down approaches where economic modeling (such as computable general equilibrium, input-output, econometric models) is used to estimate the macroeconomic effect of investments in clean energy. the authors also describe a combination of the two major types, i.e. hybrid approaches where top-down and bottom-up analyses are combined. the us energy and employment report [ ] estimated that in there were nearly . million jobs in the energy efficiency sector. by , energy efficiency jobs had grown to . million jobs [ ] . more than half ( . million) of these employees work in the construction industry; others work in the design and manufacturing of products, and the delivery of professional services. in the report on energy efficiency jobs in america, environmental entrepreneurs and e thefuture [ ] find that jobs in the energy efficiency industry tend to be concentrated in smaller business, with or fewer employees. further, these companies focus primarily on installation, trade and distribution related aspects of the industry. the latest world employment and social outlook by the international labor organization deploys an i-o modeling approach to estimate the employment impacts of sustainability [ ] . similarly, the report by pollin et al. [ ] examines the net implications of expanded investments in clean energy and energy efficiency by using the implan i-o model [ ] . the authors find the net effects of rising clean energy investments and falling share of fossil fuels lead to an increase in the total jobs generated over two decades. the job growth is primarily because clean energy investments are more "labor intensive" and require a larger share of "domestic content". garett-peltier [ ] takes a similar approach, examining the net employment effects of redirecting fossil fuel investments towards clean energy. incorporating a similar input-output analysis into the results or a computable general equilibrium analysis of carbon taxes, brown et al. [ ] estimate significant employment growth from energy-efficiency investments. the novel application of input-output analysis to energy efficiency, in combination with general equilibrium modeling, is the subject of this methods-x paper. looking across metropolitan areas, yi [ ] uses an econometric approach to examine the employment effects of clean energy policies. he finds that overall, each clean policy adopted for the sector leads to a % increase in the number of green jobs. at a local scale, deshazo et al. [ ] also examine the wide range of clean energy programs in the los angeles county and use an i-o model to assess the actual expected job impacts. the authors find that more than job-years could be created for every million dollars invested in these programs operated by the los angeles department of water and power. and finally, in the evaluation of maryland's empower energy efficiency program, baatz and barrett [ ] estimate a total of jobs were generated in . several models are available to analyze employment impacts, including aceee's deeper model and nrel's jedi model. however, for this study we first deployed georgia tech's version of the national energy modeling system (nems), the premier and arguably most influential u.s. energy modeling tool. nems data is more up-to-date than the data in deeper, and it better represents energy-efficiency investments compared with jedi. the model uses an i-o approach to calculate employment across sectors of industry and services. the macroeconomic activity module documentation provides detailed information on industrial classification and employment calculations. preliminary analysis identified a gap in the nems employment calculations. it was detected empirically when the estimates showed a small net loss of u.s. jobs through , despite largescale investments in energy efficiency, which is a labor-intensive activity. examination of the nems architecture, and subsequent discussions with eia nems modelers revealed that the investments in energy efficiency are not recycled back to the ihs global insights macroeconomic model that estimates gdp and employment. as a result, nems underestimates the employment and gdp impacts of scenarios that model energy-efficiency incentives. it does not include the direct, indirect, and induced jobs generated by the incremental expenditures on high-efficiency equipment and materials. these overlooked jobs were then estimated through independent input-output (i-o) modeling, and the results added to the nems employment estimates to provide a more complete assessment. to estimate the employment impact of investments in energy efficiency, we develop an approach that applies employment coefficients from the implan input-output model to results from the national energy modeling system (nems) ( fig. ). the first step estimates investments in energy efficiency technologies and systems required to produce the energy consumption reductions. as noted earlier, the nems model predicts large scale improvements in energy efficiency as a result of a $ /ton carbon tax. however, in order to calculate the monetary value of the investments, we calculated the difference in electricity bills in the two cases. since the energy consumption in all three sectors (residential, commercial and industry) is expected to go down but the prices are expected to increases, utility revenues will likely increase, thus spurring additional investments in energy efficiency. the energy efficiency investments are assumed to be equivalent to the value of the energy saved in each (as would occur in an on-bill financing program). this involved estimating the energy consumption, prices and bills in the $ carbon tax scenario modeled in nems, by year and census region. for this, we first calculate the change in electricity consumption and prices. we multiply these to arrive at the bills for households and the resulting change in energy-efficiency jobs ( fig. ) . the results are presented in table . the second step involves distributing these investments across the broad investment categories. this step creates the "bills of goods" that characterize how energy efficiency expenditures are spent. this follows an approach similar to that of baer et al. [ ] and garrett-peltier [ ] , which focus on industry spending patterns. we build on the prior works as we combine the results of the nems (general equilibrium approach) and somewhat incomplete recycling of revenues in the nems i-o model by superimposing the energy-efficiency job gains from an external i-o model in implan. bills of goods are available for many green energy systems such as solar and wind, but they are not well defined for energy efficiency. to estimate the effects of energy-efficiency investments in each sector, we created separate bills of goods for each of the three major end-use sectors: residential, commercial, and industrial. for simplicity, we assume that energy-efficiency expenditures are spent similarly across the census regions. note: changes in prices are correct; they may differ from "e-b", as shown, due to rounding. step : solicit and review expert feedback the third step is to seek expert opinion on these estimates and validating the bill of goods created in step . draft bills of goods were developed by the authors and reviewed by a group of energyefficiency experts in the southface energy institute, aceee, the greenlink group, georgia public service commission, university of massachusetts, sterling energy and independent consultants. as a result of the experts' feedback, we incorporated the following changes: • increased the allocation to construction in residential and commercial sectors -the reviewers ' feedback converged in that the new investments in energy efficiency will require additional construction spending. responding to this, we increased the share of energy efficiency investment allocated to the sector. • reduced the level of investment in program administration -in our initial distribution of investments, we had assumed that a significant share would be allocated towards the administrative expenses of government-led energy-efficiency programs. however, the experts suggested that the shares would be lower than our estimates and accordingly, we reduced the share of related categories in the final distribution. • added a sector called architecture and engineering services -finally, one of the reviewers suggested including a new category given that some energy investments would also require changes to the current architectural and engineering approaches in building construction and design. accounting for this suggestion, we added this category in our distribution. this also allowed us to redistribute some of the investments from the reduced share of "program administration". we implemented a two-step approach, following up with the experts once the first round of changes had been incorporated. no additional changes were suggested in the second round. the final distribution of the bills of goods is shown in table . the fourth step uses the implan i-o coefficients to estimate the direct, indirect and induced employment per $ million of investment. the shares from step were further decomposed to reflect the specific industries covered in the implan software. the software lists industries reflecting the first -digits from the north american industry classification system (naics). this detailed breakdown is presented in tables - . the tables summarize the bills of goods for all three energy-efficiency sectors. these tables have four columns -the first represents the broad spending category as noted in table . the next column reflects the implan industry description/name as provided within the software. the next two columns are the shares we attribute to the sub-sector and the aggregate across the broad sector identified in the first column. it is interesting to note here that the indirect and induced effects surpass the direct effects in all cases. across the three energy-efficiency sectors, the jobs multipliers are highest in the commercial sectors, which is a function of the way spending is distributed across different sub-sectors ( table ). the spending in smart management and controls is higher in the commercial and industrial sectors than in the residential. further, spending on materials is a smaller share of the total investments in the sector. this distribution was then used to calculate the spending in each industry and the consequent implications on total additional jobs generated. we used implan version . for generating the multipliers ( fig. ) . fig. . the cumulative difference in employment, by region, with a $ carbon tax (figure created by authors using data published in [ ] ). the employment multipliers for investments in energy supply (based on implan-defined sectors) are lower than for investments in energy efficiency ( table ). as noted earlier, using the i-o model allows us to disaggregate the total employment effects into direct, indirect and induced effects. taking the example of investments in industrial energy efficiency here, as per table , an additional spending note: sectoral shares are correct; they may differ from the sum of the sub-sector shares as shown, due to rounding. of $ million increases the total jobs in sectors affected by higher investments in table creates . additional fte jobs. additionally, each sector that benefits directly also generates second-order effects in sectors that provide raw materials and support series to the sector. for example, as a result of spending in the construction of new structures (row in table ), jobs will be generated in sectors that produce construction materials. such second order effects constitute the indirect effects. in our example of industrial energy efficiency, the indirect jobs account for . additional fte jobs per million dollars of investment. finally, the increased employment and resultant wages in the hands of direct and indirect beneficiaries will lead to an increase in consumption spending in sectors such as restaurants, hotels etc. leading to . additional induced jobs as a result of industrial energy efficiency spending. to further illustrate the use of this methodology, we apply the multipliers to an analysis of the employment impact of implementing a $ carbon tax on the u.s. economy starting in and escalating % each year. we use gt-nems to analyze the employment impacts on the energy supplyside economic activities. we then estimate the additional employment that would occur as the result of energy-efficiency jobs based on the bills of goods shown in table through table . this methodology was used by brown and ahmadi [ ] in their analysis of a $ carbon tax, showing that a tax could boost u.s. employment significantly. if implemented in , a $ carbon tax could expand u.s. employment by . million jobs each year between and , which is nearly a percent increase above the baseline forecast of million jobs in . altogether, an estimated million "job years" would be created over the three decades with a $ carbon tax. (note that if one job continues after one year for another months, it represents two job years.) fig. summarizes these results. illustrations of how this methodology can be deployed are available in several recent publications [ , ] . fig. portrays our estimates of jobs per million dollars of investment (in $ ) across energy sectors of the u.s. economy, including three energy-efficiency domains. the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. policy, climate and energy policy lab, and global change program. gt's majid ahmadi helped to verify our data analytics and assisted with our visualizations. in addition, laura martin, russell tarver, erin boedecker, and others at the u.s. energy information administration provided helpful advice on key nems modeling issues. examining the results of empower maryland through the job generation impacts of expanding industrial cogeneration verifying energy efficiency job creation: current practices and recommendations are all jobs created equal? regional employment impacts of a u.s. carbon tax would a green new deal add or kill jobs? efficiently energizing job creation in los angeles environmental entrepreneurs (e ) & e thefuture, . energy efficiency jobs in america green versus brown: comparing the employment impacts of energy efficiency, renewable energy, and fossil fuels using an input-output model green growth a us program for controlling climate change and expanding job opportunities clean energy policies and green jobs: an evaluation of green jobs in us metropolitan areas several methodsx reviewers provided valuable and detailed comments, which are greatly appreciated. we also are grateful to the participants in our expert survey who provided detailed estimate the types of the expenditures required to complete energy-efficiency upgrades. during the course of the project we received valuable insights from discussions at georgia tech's school of public key: cord- -x sfwqnk authors: butler, colin d.; higgs, kerryn; mcfarlane, rosemary anne title: environmental health, planetary boundaries and limits to growth date: - - journal: encyclopedia of environmental health doi: . /b - - - - . - sha: doc_id: cord_uid: x sfwqnk published almost years ago, the limits to growth remains relevant to contemporary environmental health, though, paradoxically, this relevance is scarcely recognized. the seminal ideas it presented provide a useful background, as do the later planetary boundaries analyses, with which to consider key issues in contemporary environmental health. to be more than reactive, it is necessary to understand the complexity and interactions of integrated environmental health risks, including the possibility of significant global population decline within the current century. this contribution provides an overview to the limits to growth, linking it especially to the “planetary boundaries” of climate change, biodiversity loss and novel entities (including artificial substances and genetically modified organisms). the gradual increase in the amount of primary energy required to generate useable energy is also argued to be an under-recognized contributing factor to the decline in real wages growth for much of the world’s population since then, although this aspect may be improving. these elements have positive and negative health effects, which we discuss. only ones that allowed civilization to continue without crisis. if the human economy maintained business as usual, the team found, it would collide with the physical realities of a finite planet by the second half of the st century, triggering social collapse. initially, the book received a positive response and some of the recommendations were adopted by several countries. canadian prime minister pierre trudeau and us president jimmy carter each commissioned studies of the impact of physical limits on the global future and their national prospects. although these studies examined the outlook only as far as , their conclusions to that date confirmed those of the original ltg study. right from the start, however, economists were critical, even abusive, creating a negative impression that persists in some quarters, todayddespite the rapidly accumulating evidence of the basic robustness of the ltg projections and assumptions. robert gillette, who attended the ltg launch for the journal science, noted that the "assumption of inevitable economic growth" represents "the very foundation" of economics. any "limit" to growth challenged this foundation. it is unsurprizing that most economists attacked the ideas vigorously, an assault that illustrates the conflict between the core assumptions of economists and those of the physical sciences. economics adopts a standard model where production and consumption exist in a circular flow, without a natural context. it is a world of business and individual, producer and consumer, labor and goods. the physical world, which supplies resources and provides a site where wastes can be discharged, is not seen as essential and does not affect the equations, though, occasionally, the concept of "externalities" (which can be negative or positive) is mentioned. ecological economists reject the argument that human activity is independent of nature, which they consider a conceit. instead, nature is accepted as the indispensable foundation of human activities. physics really matters; questions of depletion and pollution are inescapable. several researchers have compared the mit projections with what has actually happened since, establishing that the correlation between the standard run and real world trends over the intervening years is extremely close. one of these researchers, graham turner, compared the standard run's modeled trajectory with years of historical data (see fig. ). he concluded that the data for - approximated the standard run of the ltg model, although the figure shows a slight but favorable divergence for the trajectory of non-renewable resources, such as fossil fuels, phosphate and concentrated, rich sources of ores. systems ecologists charles hall and john day also compared the standard run with actual data to . despite the common perception that the ltg work had failed, the model's performance was not invalidated, unlike models made by economists which are rarely, if ever, accurate over such a long time span. in , jørgen randers, part of the original ltg team, using an updated model, compared the ltg projections with real world data up to . he found that real world outcomes have approximated the second ltg scenario, the "standard run with extra resources," or "pollution crisis." based on observed data further processed by turner (up to ) trent modelled by the ltg study ( - ) (ltg) peak health? c : population declines due to increasing cases of regional overload meadows et al. for - and updated by turner with data to . it also introduces the concept of "peak health." this is the point at which human population well-being reaches its zenith, if the ltg model (of decline this century) proves reliable. although the timing is imprecise, peak health will precede the exact moment of maximum population. peak health and unwanted population decline are not inevitable; even today they could be postponed, perhaps indefinitely, by enlightened policies and technological breakthroughs. many resource analysts have identified declining "energy return on energy investment" as a key to understanding the slowing of the rate of improvement of living standards for most people in high-income countries. in turn, these indicators reflect the decline in easily accessible fossil fuels. this subject will be returned to. it is important to understand that the broad trends described in the figure and used in the ltg model do not capture the entire world. no model can. these trends were chosen because they captured many aspects of the material world, both human and natural, including feedback loops and potential crises that might threaten the human economy and thus wellbeing. indicators of these trends were chosen for a number of reasons, including researchers' attempts to choose representative indicators that would faithfully reflect the trends, the need for parsimony and, especially back in , the difficulty of finding accurate data. the decline in population that is modeled is a logical consequence of the decline in resources per capita, whether non-renewable, or as food, industrial output and services. if these inputs decline, the modelers assume, so will human population, which depends on them. the concept of the ecological footprint is among the most important developments in thinking related to the ltg. devised in the s by william rees and mathis wackernagel, this measure enables ecological impacts (individual, national or global) to be quantified and compared. on one hand, it estimates the ecological assets required to produce the resources consumed by any discrete population; this includes food and fiber plants, livestock and fish, timber and other forest products, space for urban infrastructure and whatever "sinks" are needed to absorb the waste produced, especially carbon dioxide emissions. the unit of measurement adopted is the area of biologically productive land and water, usually expressed in hectares. on the other hand, the ecological footprint also estimates the productivity of a country's actual ecological assets (cropland, grazing land, forest land, fishing grounds, and built-up land). researchers using the ecological footprint methodology calculated that, while the world's biocapacity averages . ha. per capita, high-income "developed" countries greatly exceed this average. examples include the united states ( . ha. per capita) and the united kingdom ( . ha. per capita). the us, which has far more productive land available than the united kingdom, appropriates . times its own biocapacity through imports, and the united kingdom almost three times. many island nations and arid countries such as saudi arabia exceed their biocapacity by a factor of more than ten. the ecological footprint has the strengths and weaknesses of any aggregate indicator: the concepts and units are easy to understand by policy-makers and the public, but it does not encompass all aspects of human environmental impact (methane, e.g., is not integrated). this matrix needs to be used in conjunction with other indicators. another related development is the framework called "planetary boundaries," devised by a large team led by johan rockström (see following section). although the environmental health literature has long identified links between health and indicators used in the ltg model, such as food, services, and pollution, there has been little recognition among the health community, including within public health, of the possibility of a reduction in population this century. such reductions, as mentioned above, are forecast by most ltg scenarios, including the standard run (see fig. ). such a reduction, were it to occur, will have impacts on public health. there are a few exceptions to this generalization. in , the human ecologist frederick sargent, in an article in the american journal of public health, warned that human "interventions in and manipulations of the processes of the planetary life supportsystem (ecosystem) have produced a set of complex problems" (page ). in , the visionary socialist economist barbara ward co-authored "only one earth" with the microbiologist, pioneering "earth physician" and pulitzer prize winner, rené dubos. this book stated in part "the charge to the [ stockholm] conference was clearly to define what should be done to maintain the earth as a place suitable for human life not only now, but also for future generations" (emphasis added) (page xiii). health is implicit in this statement, as is sustainable development. in mcmichael, who was influenced by dubos, echoed sargent's term, writing in the foreword to his influential book planetary overload, that "the most serious potential consequence of global environmental change is the erosion of earth's life-support systems. yet, curiously, the nature of this threat to the health and survival of the world's living speciesdincluding our owndhas received little attention" (page xiii). a quarter of a century later, little has changed. although keynote talks by mcmichael and john last at the conference of the international epidemiological association warned of the dangers to global public health of global environmental change, there has been barely any recognition or follow up, at the broad integrated dimension. ltg receives little recognition now. a literature search for the term "limits to growth" in association with "health" reveals little other than work involving the authors of this contribution and their close collaborators. this is unfortunate. the persistence of single-issue approaches to address complex problems retards our ability to act effectively. this is the case where there is singular focus on climate change. the impact on human health and wellbeing is modified by many interacting factorsdincluding population, global demand and availability of resources and services and the waste and pollution we generate. other than noting the exponential growth of carbon dioxide in the atmosphere, ltg did not address climate change as such, but it modeled these factors as part of a complex system. although infrequently, the issues of resource depletion and population pressure have featured in some medical curricula, from at least the s, preceding publication of the ltg by over a decade. pioneering writers and speakers have included colin bertram, peter parsons, and roger short. john guillebaud, the world's first clinician professor of family planning and reproductive health, has repeatedly spoken on the issue of both consumption and population, to diverse audiences including medical practitioners, nurses, medical students and others, since . in , a special issue of the american journal of public health focussed on peak oil, an important aspect of ltg. a scattering of other articles in the health literature have mentioned peak oil, but ltg is far more than peak oil. it is also far more than global warming. the reasons for the general failure of the public health literature to engage with ltg are complex but include an incorrect belief that ltg was discredited, over-specialization within the public health community, political suppression of the core ideas, and a lack of funders. the issue has had very few champions. this lack of engagement is not from lack of evidence. the term planetary boundaries (pbs) was first published in . these boundaries were defined, initially, as referring to nine earth system processes (see table ), each of which had been, is and will be modified by human actions. the first planetary boundary paper (published in in ecology and society, subtitled "exploring the safe operating space for humanity") explicitly acknowledges its debt to the ltg framework. a "safe operating space" implies the existence of multi-dimensional limits, just as does the word "boundaries". nonetheless, the links between pbs and the ltg are mostly implicit. although the focus of the pb work is on identifying the criteria for a "safe operating space" for humanity, rather than that of other living species, the concept acknowledges that humans depend on the diversity of life on earth. the first pb argued to be outside the safe operating space is biological diversity. analogous to nine bodily systems (renal, hepatic, neurological and so on) the large multidisciplinary team ( co-authors) that was responsible for the first pb articles argued that these earth system processes can still provide useful services, even if functioning outside their optimal range. however, pushed too far, even one aberrant bodily function can cause death, and just one extremely disturbed earth system process might trigger catastrophic consequences for humanity. perhaps, for example, a precipitous loss of insects could disrupt pollination, food supply, and the survival of birds and other vertebrates. in turn, loss of birds might trigger additional crop losses, as their biological control of insects and other pests (i.e., of pests that do survive) is lost. another example is the reduced complexity of the microbiome of those who live in cities and other modified environments. this in turn has been hypothesized to be a causal role in the emergence of auto-immune diseases such as type diabetes. further, just as with bodily processes, earth system components are linked to, interact with, and are influenced by common causes. humans may live for decades with chronic illness, but die quickly if multi-organ failure develops. so too, earth system processes interact, but exceeding multiple planetary boundaries, either simultaneously or in close proximity, risks precipitating a steep decline towards a civilization-crippling condition. other writers have also commented on the similarities between the earth and the human system, including james lovelock, the originator of the gaia hypothesis and an early user of the term "planetary medicine." table shows links between planetary boundaries, ltg and human health. the exact extent to which we are breaching planetary boundaries is still being explored. the team's paper argued that two problems are already extremely dangerous (red zone) and two others are well on the way (amber zone), also noting that the designated boundaries are inter-related and most have overlapping implications. the team considers loss of biosphere integrity as the most critical problem. rates of extinction are reckoned to be at least times the background rate, possibly as much as , times. populations of vertebrate species declined by more than half between and and the biomass of wild mammals is now only about % of the total, which is dominated by humans and livestock. that remaining % is under siege, including for substances such as rhinoceros horns and pangolin scales, which have alleged therapeutic benefit, even though chiefly constituted of keratin, just as are fingernails. biological diversity of lower order organisms (within soils, among pollinators, and in the species traditionally utilized for plant-origin food, resources and medicines) are similarly in decline. also under deliberate attack are forests, especially species with valuable timber, or growing on land that can be used for crops, including oil palm. many forests are also at unintended risk, due to roads and global warming, each of which also exacerbates the risk of fire. global warming is also likely to further hasten biodiversity loss. in some cases biodiversity decline and climate change, acting together or independently, also promote the survival of new pests. infestations of tree borers, able to survive warmer winters in large numbers, render trees, forests and their associated animal life more vulnerable to disease and fire. humans, a form of life, depend on the fabric of other life on earth for their survivaldfor food, clean air and water, and numerous other ecosystem "services" (see glossary and below), as well as for novel substances, including drugs. at some level of bio-alteration the reduction in ecosystem services will reduce in a non-linear way that could cascade in a manner harmful to all civilization. smaller scaled examples include the collapse of regional fisheries or the decimation of regional harvests by novel diseases or pests, such as in ireland in the late s. the khapra beetle, a pest from south asia that has evolved insecticide resistance threatens significant (up to %) loss of rice, post-harvest, in some regions. devastating drought in the "dry corridor" of guatemala, el salvador and honduras has been blamed for contributing to the influx of migrants attempting to enter the united states between and the present ( ). for rockström, steffen and colleagues the second most pressing danger is the radical disruption of the biogeochemical cycles, particularly nitrogen and phosphorous. in nature, most nitrogen was inert in the atmosphere, though some was mobilized by bacteria and leguminous plants. applied as fertilizer, nitrogen has greatly expanded food production, but is now cascading through our rivers, groundwater and continental shelves, initiating algal blooms and dead zones. in the case of phosphorous, the other widely dispersed fertilizer, there is an added dangerdphosphate rock is a resource in decline, with grim implications for future agriculture, especially where populations will lack the financial capacity to import it, as prices rise. land-system change is argued to be in the "amber zone," close to crossing the boundary into extreme danger, if it has not already crossed it. millions of hectares of vegetation are still being cleared every year and wetlands continue to be drained. stocks of "blue carbon," stored in plants and trees associated with water, such as kelp and mangroves, are also under threat. land-system changes enable more food, fiber and other financially valued products to be grown, but amplify the harm to several pbs: biological integrity, climate and biogeochemical cycles. oil palm plantations are displacing tropical forests in asia, africa and, increasingly, latin america, where clearing already provides cattle pasture, soybean and sugar cane. such plantations involve the death of vast numbers of individual animals and the annihilation of immense tracts of tropical forest. this boundary is underpinned by the declining remainder of tropical, temperate and boreal forests. these forests have a major role in land surfaceclimate coupling. in addition, agricultural land-system change may ultimately result in land degradation giving rise to erosion, loss of topsoil, sedimentation of waterways and degradation of coastal zones. in dryland regions, degradation is referred to as desertification. large areas are affected. the united nations organization considers that billion people are at risk of desertification globally, half of whom live in africa where they face major challenges to water and food security. increasing urbanization also drives land-system change, typically in areas of high agricultural productivity. vast urban regions impact surface energy (through the "heat island" effect), alter hydrological and biochemical cycles, net primary productivity and biological diversity. they are also major foci of pollutants. as humanity becomes predominantly urbanized it is with these land systems that most of us have most intimate contact. also in the amber zone is climate change. remaining below the c target, which is thought to provide a reasonable chance of avoiding catastrophic climate change, necessitates technologies which do not yet exist for extracting carbon from the atmosphere. most nascent carbon reducing technologies require considerable energy, although new forms of cement may soon be feasible and environmental health, planetary boundaries and limits to growth affordable on a large scale. research since suggests that the c target may need to be adjusted downwards to provide a reasonable chance of avoiding calamitous warming, in which case climate change may already belong to the red zone. even if the commitments made at the paris conference of the parties are all honored, it currently seems likely to many analysts that global temperatures will be c hotter than pre-industrial times by and nearly c higher by . these estimates depend on a number of variables: whether nations will adopt more ambitious pledges in the near term; whether technologies will emerge that can, at a low energetic cost, suck carbon back out of the atmosphere; whether unknown tipping points will be crossed, forcing a temperature surge. if these variables prove unfavorable, the aspirational . c maximum target may be reached by the early s. there is no guarantee that the damage can be held to approximately c, in particular due to the risk of amplifying feedbacks such as the release of carbon dioxide and methane from the arctic, and/or the drying and burning of the amazon forest. the capacity of the ocean to absorb co is also declining. that will slow the rate of ocean acidification, but increase atmospheric heat trapping. even if temperature rise and rainfall intensity can be contained, crop yields will decline and many places will become unliveable due to excessive heat and humidity or coastal inundation. glaciers that act as a bank to store water and in some cases whose melt supplies electricity to billions in asia and south america will shrink, coral reefs and many other species will disappear, and significantdeven catastrophicdsea level rise will result. in greenland and along the entire coast of west antarctica ice shelves are already retreating or collapsing as warm seawater intrudes underneath, grounding lines retreat, and the glaciers behind them accelerate in their march to the sea. climate scientist james hansen and many glaciologists warn that the disintegration of the polar icesheets involves non-linear processes, and the timing, though still unknown, may be far quicker than assumed, and may include rapid, even unstoppable collapse of ice cliffs in series in parts of antarctica and greenland. the impact upon human wellbeing resulting from stress on biological diversity will be compounded by climate change and the fragmentation of society. for example, a complex economic and social fabric enables the importation of food and other resources to an increasing number of regions, some of which have been in this vulnerable situation for decades. such mechanisms are fragile. today, five countries are recognized as afflicted by famine: yemen, somalia, south sudan, n.e. nigeria and two regions of the democratic republic of the congo (kasai and tanganyika). in the long run, if climate change and other aspects of adverse ecological change intensify, then it is also possible that regions that are current net food exporters will also experience famine; if this evolves then conditions in food-importing regions will inevitably deteriorate. alongside these four major crises, the researchers also identify the threat from various forms of pollution. most of these are discussed elsewhere in this encyclopedia. however, we briefly discuss novel entities. novel entities is a recently introduced term, first identified as a planetary boundary by the pb team in , evolving from chemical pollution in the earlier pb publications. the pb team defines novel entities as "forms of existing substances, and modified life forms that have the potential for unwanted geophysical and/or biological effects." most novel entities have been generated in the anthropocene, the human-dominated era, defined roughly as the time since the start of the widespread combustion of fossil fuels, in the th century. they include synthetic molecules such as chlorinated fluorocarbons (cfcs), ddt, dieldrin and other organochlorines used as biocides and compounds used in industry such as polyvinyl chloride. cfcs, by harming the stratospheric ozone layer, clearly impinge on an earth system function (and thus indirectly on human environmental health); the destruction of the stratospheric ozone layer causes uv light to reach the earth's surface to a greater extent than prior to the widespread use of cfcs, leading to the potential for an increased incidence of skin cancer, ocular problems and immunosuppression. here, however, we focus mainly on the biological effects of novel entities. novel entities are not confined to new chemical compounds, as the pb authors note. genetically altered organisms can be conceptualized as novel entities, as are nanoparticles (such as in sunscreens and cosmetics), and blue light from computer and phone screens. humans are also exposed to numerous other emerging environmental hazards, especially since world war ii, and to human-generated ionizing radiation (x-rays were once routinely used to help fit shoes). possible health risks of nonionizing radiation, such as from mobile phones, are discussed briefly below, as are novel behaviors, foods and other novel environments. a lancet commission report estimates that , compounds have been synthesized since , with perhaps widely disseminated in the global environment. although some are regulated, and a few have been banned, the pace of their introduction greatly exceeds that of epidemiological investigation and legal constraint. for example, the international agency for research into cancer (iarc), which is closely affiliated with the world health organization (who) has recently concluded that the widely applied herbicide glyphosate (commercially known as "round up") may be carcinogenic. these findings have been resisted by some companies and their agents and supporters. thousands of studies of novel entities have found or suggested that many are carcinogenic, while others act as endocrine disruptors or harm health in other ways. some have been linked with massive ecosystem disruption, including colony collapse disorder (of bees) and "insectageddon." the lancet commission on pollution reported that fewer than half of the most widely dispersed chemicals have undergone any testing for safety or toxicity. interactions between such chemicals have received even less examination. the immunological and allergenic effects of most novel entities are also barely explored, and could contribute to the changing pattern of allergic diseases, auto-immune conditions and autism. while some novel entities have been regulated (e.g., x-rays) and banned (such as the "dirty dozen," including the organochlorine dieldrin, which was, as a rare exception, strongly linked with breast cancer), hundreds or thousands of others are released annually onto the market. in both industrial and rural societies, almost the entire population has been exposed to hundreds of chemicals whose concentrations can be measured in tissue samples, while for thousands more, no test exists. there is little support from policy decision makers around the world for precautionary approaches to many potential risks. for example, there are concerns that mobile phones can cause brain tissue to warm up, if the receiver is held close to the ear. however, there are also concerns about the effects of non-ionizing radiation on brain tissue, and claims of an increased risk of malignant brain tumors in heavy users of mobile phones. cardiac and neurological disorders are also plausible consequences of the rapidly increasing use of wireless devices, including smart meters. infrasound from wind turbines is another novel entity. such sounds disturb the sleep of many people who live close to them, and there may also be other harmful effects including vertigo, as well as chronic diseases worsened by chronic poor sleep. such concerns have often been dismissed as "nocebic" (i.e., through apprehension and negative thoughts) as high quality evidence for health impacts is lacking. the precautionary principle would place the onus on industry to prove safety. novel behaviors, foods, organisms and environments are also emerging in the anthropocene. examples include reduced weight bearing exercise in childhood and adolescence (leading to a higher risk of early-onset osteoporosis), increased screen watching and the partial replacement of tangible, local friends and acquaintances for virtual social networks. novel diets include the widespread consumption of sweetened drinks, a known factor in obesity and harmful to health, while the greater variety of foods out of season, especially of fruit, is beneficial. there are also novel microbial and parasitic environments and novel microbiomes, each of which is likely to be associated with health benefits and risks. for example, humans and livestock farming provide opportunity for the amplification and spread of genes that convey antibiotic resistance. these genes are favored wherever antibiotics are used by humans or fed to livestock to promote growth and limit infectious disease. antibiotic resistance genes have been shown to spread to environmental microbes in soil and water systems, to wildlife and to human and livestock pathogens. identified mechanisms for this transfer include air-borne transport of particulate matter and direct and indirect contact with waste products. the augmented "wild" population of antibiotic resistant genes is an added risk to human health and has poorly understood implications for other environmental microbial systems. novel or increased contact with mammalian wildlife creates further potential for interspecies transfer of pathogens, particularly viruses. this is discussed below (in biodiversity and health). since the s, there has been increasing recognition of ways that anthropogenic emissions of greenhouse gases (manifest in phenomena including global warming, weather wilding, jetstream oscillations, sea level rise and ocean acidification) is likely to impact human health, both positively (e.g., fewer cold waves in some areas) and negatively. there are numerous mechanisms for this. one that is perhaps most obvious is an intensification of extreme weather events, including heatwaves, droughts, flooding, and major storms including cyclones, typhoons and hurricanes. such events can have complex and delayed effects, such as from the savage hurricanes that flooded and devastated houston, texas and the us territory of puerto rico, as well as other regions. there is also speculation that the frequency, severity and locations of tornadoes may be affected. very intense flooding events, where weather systems remain almost stationary, have generated the neologism "rainbomb." changes in vector-borne diseases, food security, and sea level rise have long been forecast to occur due to global warming. global warming is already affecting migration, conflict and mental health, and these effects are likely to intensify. over the longer timescale, of decades to centuries, adverse effects are forecast to exceed benefits, perhaps by orders of magnitude, especially if the ice sheets in greenland and antarctica continue to melt. there are many ways health effects related to climate change can be categorized, such as through changes in temperature and humidity, vector ecology, water quality, water and food supply impacts, severe weather effects, air pollution, allergens, and migration, conflict and related mental health implications. a simpler classification has three main classes, conceptualized as "direct" (e.g., heatwaves), "indirect" (e.g., changes in vector ecology) and a third category, causally more displaced, with the potential for the largest burden of disease, through means such as large-scale conflict, migration and famine. in this classification, effects on mental health are regarded as "cross-cutting." dislocation from one's home due to a storm surge or a prolonged blackout (some parts of puerto rico lacked power for months following hurricane irma) can lead to depression and even suicide. such stress is also likely to exacerbate domestic violence, especially if associated with increased economic insecurity. increased rates of post-traumatic stress and anxiety are also likely in survivors. even worse than the mental trauma of a single extreme weather event are the health consequences, including to mental health, from conflict, famine and forced migration. of course, such "tertiary" effects have multi-dimensional causes, from ancient rivalries to recent and emerging contests over scarce resources, often aggravated by "youth bulges" and brutal repression. all writers on these "tertiary" topics, publishing in the academic literature, recognize the complexity of this issue, and frequently try to convey this by using the term "risk multiplier" to indicate how changes in climate can worsen (or in some cases reduce) the co-factorial causal contributors to conflict. that is, climate change is conceptualized as similar to a catalyst or enzyme. famines, wars and migration can all occur without climate change, but in some cases climate change can make these phenomena much worse. in some cases, such as sea level rise, climate change can be conceived as by far the dominant factor. however, even for vulnerable lowlying pacific islands, co-factors such as high population growth have contributed to vulnerability and the risk of migration, for example by depleting fresh water lenses, leading to the salinization of garden soil. many important diseases, including parasitic, vector-borne and zoonotic diseases are associated with invertebrates such as ticks, mosquitoes and blackflies, or higher order vertebrates. ticks transmit diseases such as lyme disease, mosquitoes transmit many illnesses such as malaria and yellow fever, while black flies transmit river blindness (onchocerciasis). the distribution of these insects and animals are shaped, not only by climate but by many other aspects of their ecology. often, the identification of the precise attribution to climate change is elusive and possibly fruitless. less intuitively, the epidemiology of many vector-borne diseases, including malaria, dengue fever and zika virus is also influenced by the ambient temperature in another way, by determining the growth rate of the parasite or virus within the cold-blooded vector. more rapid growth of these pathogens (i.e., in slightly warmer vectors) can, in some cases, lead to additional cycles of transmission, leading to explosive increases in cases. another way to think of these organisms is that their numbers and disease potential exist within a window or "sleeve" of climate and ecological suitability. it would be wrong to think that a warmer or wetter climate will inevitably increase the burden of these infectious diseases. as temperatures rise, insect populations may too, but only to a point. beyond that point, vector populations may in fact decline. similarly, excessive rain may reduce vector habitat (e.g., flushing the population away), as may unusually prolonged droughts (drying out the habitat). however, the epidemiology of vector-borne diseases is also influenced by human factors, such as insecticides (including impregnated bednets) and molluscicides, and by treatments such as vaccines (e.g., for yellow fever) and antimalarial drugs such as quinine. the impact of biodiversity loss on human health is being realized slowly. the dimensions of biodiversity (the diversity of genes, species and ecosystems) are not experienced or understood by most individuals, or policy makers, and challenge health researchers. as such, the impacts are dispersed across multiple scales of biodiversity and multiple dimensions of health and wellbeing much of which is discussed elsewhere in this contribution. the pb team has examined the genetic diversity within and between species and ecosystems and its functional role within a global system, separately. they conclude that the loss of genetic diversity has exceeded a safe limit, with uncertainty remaining over how this impacts the function of ecosystems. the alarming rate and extent of loss of genetic biological diversity has been discussed earlier. the loss of genetic diversity undermines the resilience of ecosystems. under relentless ecological change, biological diversity is replaced by ecosystems dominated by fewer, highly adaptive species, inadvertently or purposefully promoted by human activities. these include domestic species, pests and wild synanthropes, humans and the novel entities described above. genetic diversity is also the source of pharmaceutical discovery as well as the storehouse of traditional medicines. most naturederived pharmaceuticals come from plants; some come from traditional medicine practice but much is the product of systematic searching, modification and trial. nature produces an inspirational variety and complexity of molecules to further manipulate. the diverse origins of the pharmaceutical armory against hiv aids includes betulinic acid, derived from the bark of the tree betula pubescens; bevirimat, extracted from a chinese herb syzygium claviflorum; and ganoderic acid b, isolated from the fruiting bodies and spores of the fungi ganoderma lucidum. such a utilitarian appreciation likewise extends to livelihoods dependent on different aspects of biodiversity. for some, particularly vulnerable groups and those in remote locations, survival is dependent on the ability to harvest freely (or illegally) from the natural environment. rich biological diversity is often helpful for the resilience of ecosystems functions, sometimes called "services." in the early s, the millennium ecosystem assessment, a global collaboration of over scientists, grouped these into four kinds, which they called supporting, provisioning, regulating and cultural. food production is classified as a provisioning service. for such a service, biological diversity is required for (supporting or underpinning) soil health, pest control (a regulating service), pollination and the genetics of livestock and crops. other products of provisioning services include clean water, bio-fuels and crop residues used to provide energy. other regulating services include carbon sequestration, climate regulation and disaster risk reduction. nutrient recycling is another example of a supporting ecosystem service. a sacred grove or an iconic species of deep significance to the beholder illustrate cultural services. disease-regulation as an ecosystem service is contested, but some diseases, such as lyme disease, are more prevalent in diminished and simplified ecosystems. the net effect of deforestation often favors mosquitoes that serve as vectors of human diseases including previously obscure pathogens such as zika and chikungunya viruses, or encourages urbanization or farm-foraging by fruit bat hosts of henipah viruses nipah and hendra. there is also a complex relationship between ecological change and malaria, which is, by far, the most important mosquito-transmitted disease. as discussed above, climate change also impacts these vector borne diseases. changes (driven by reductions) in biodiversity have increased zoonotic infectious disease risk especially due to intensive animal husbandry. livestock, which now dominate global vertebrate biomass, and intensive production, create the opportunity for viral amplification and mutations resulting in new and previously unrecognized animal diseases and zoonoses. these include h n (avian flu, via chickens), h n (swine flu, via chickens and pigs), possibly sudden acute respiratory syndrome (sars, via farmed civet cats and racoon dogs), nipah virus in malaysia (via pigs) and middle east respiratory syndrome (mers, via camels). novel or increased contact with mammalian wildlife creates further potential for interspecies transfer of pathogens, particularly viruses. such contact is facilitated by accelerated land-use change and wildlife harvesting and sometimes aided by domestic animals acting as amplification hosts. disease may transmit directly to humans or indirectly through domestic animals. many opportunities for viruses to jump between species may be required before a significant disease emerges. tropical areas of high biodiversity and under human pressure are considered "hotspots" for such diseases. novel zoonoses of wildlife origin such as hiv aids, ebola and sars corona virus have been the subject of strong interest in the late th century and early st century. the examples above have resulted in pandemics. many other smaller viral "spillover" events have occurred with localized impact only. natural or wild areas also reduce stress, depression and anxiety in those who visit them. this effect appears to be dependent on cultural and socioeconomic characteristics of the visitor and has deeper, religious dimensions for many indigenous people. as discussed earlier, the human microbiome links us to the external world. personal microbiodiversity is enriched by environmental and dietary diversity and, through mechanisms of immune regulation and the gut-brain axis, has a significant impact on physical and mental health. the benefits of experiencing biodiversity within natural settings appear to be physiological as well as psychological. however, the living environs of most people is one of reduced biodiversity, and for many most time is spent indoors. it is the capacity of earth's natural systems, the aggregate of species and ecosystem biodiversity, to provide resilience despite changing environmental conditions that should be of the most fundamental concern to health and well-being. the biosphere must absorb our wastes, including carbon emissions; buffer coastlines from extreme weather events; provide clean air, water, a moderate climate, and the renewable resources humanity seeks to consume. it is therefore of great concern that the global ecological footprint network (see "the ecological footprint" section) estimates that % of [global] biocapacity is consumed per annum. today, many determinants of health and wellbeing, including effective health services and their inputs, such as consumables and pharmaceuticals, are dependent on abundant and affordable energy. millions of people living in poverty, especially in sub-saharan africa and south asia, suffer multi-system consequences of air pollution, both indoor and outdoor, from smoke generated by their own household and by other households. in many locations, this is aggravated by the burning of fossil fuels such as coal and oil. many people, particularly women and children, undertake daily laborious effort to obtain fuel and water. access to electrical power, and even gas for cooking would bring significant improvements in health to the . billion people living without electricity. probably the least understood aspect of limits to growth is the concept and importance of declining energy return on energy investment (eroei). the number given for eroei is the ratio of useful energy obtained versus primary energy expended (see box ). the major energy carriers in use today are fossil fuels, especially coal, oil and gas. these are used not only for transport, heating and electrical power (over % globally), but also as a chemical stock to manufacture plastics and to make fertilizer. but, just as in the past when our ancestors bred, trained, housed and fed donkeys and draft horses for assistance with laborious tasks, fossil fuel needs to be wrested from the environment, whether drilled for, dug by hand or removed by robotic shovels. these processes themselves take energy. in addition, energy released or captured from these sources needs to be distributed and the infrastructure to do that needs to be maintained. coal needs to be transported and burned, with some of its energy captured through combustion. electrical energy needs to be distributed and regulated irrespective of its source (including solar, wind, hydro and tidal). to manufacture wind turbines or solar panels requires energy, as does the mining infrastructure described above. life-cycle assessment allows a full quantification of the energy invested in any form of energy extracted, which is clearly significant. in the heyday of fossil fuels, oil and coal were easy to extract, and their eroei was highdsome analysts report an average eroei of over in the late th century. in contrast, a review published in in nature communications found that, globally, up until , solar panels may have yielded no energy beyond that required for their manufacture and installation. in other words, under the least optimistic scenario, solar panels, cumulatively, have been a sink for energy, rather than a source until very recently. more encouragingly, the eroei for solar appears to have increased considerably in the last decade, perhaps to or , especially in locations with high insolation, such as in the tropics. the climate footprint of solar is much lower than of coal and will continue to decline, especially as the efficiency of panels increases and the electricity they generate is used to manufacture additional ones. the eroei for wind is widely agreed to be even higher than for solar, so these two sources have promise as major substitutes for fossil fuel energy, even though researchers still debate whether renewables will yield energy abundant enough to fuel the current consumption-oriented economy. in addition, ugo bardi and sgouris sgouridis argue that the window for a successful transition is narrow: a very large investment of available energy is required, while still maintaining adequate energy for ongoing services. moreover, the world's economic system may fail to allocate the necessary resources in the necessary timeframe (by in this analysis). bardi and sgouridis are skeptical that market forces can effect this transition. they calculated that, as of , capital investment is only about one tenth of what is required. energy investment is also inadequate. though not impossible, any transition to renewables will be challenging and requires a substantially greater rate of energy and capital investment than is currently allocated. there is a widespread understanding that fossil fuels have been crucial to the human colonization and domination of the biosphere. the importance of energy is explicit in the work of many environmental writers, and implicit in the military actions of many great powers, who have frequently acted with violence or duplicity to acquire or maintain energy resources, from the middle east to the timor sea. without fossil fuel, modern civilization could not have evolved in the way it did, whether to create highways, intensive agriculture, skyscrapers or the space age. although, in the middle ages, the harnessing of water power for work from milling grain to sawing wood ("sawmilling") was widespread, such industry was necessarily confined to suitable riversides. ancient mariners crossed straits and sometimes oceans, powered by oars and blown by the wind, but the scale of maritime trade was miniscule compared with that made possible by steam, oil and nuclear-powered vessels. while this dependence on energy is well-known, though rarely highlighted in economic histories, the fact that eroei is steadily declining is rarely mentioned in mainstream media or outside of specialist journals; it is claimed that fracking and shale oil now negate peak oil, though insufficient attention is paid to the instability of an industry reliant on proliferation of drilling sites and rising costs. the decline of eroei may be disconcerting to a public ill-prepared for the future austerity which such a decline implies. such consequences would not only affect health services, but the myriad other processes necessary for health which rely on affordable energy, including agriculture. concern about the impact of global ecological change on health is growing. so too is an understanding of the need for multi-sector collaborations. few groups are yet addressing the deeper issues of pbs. however, many once disparate groups are converging as they seek to improve equity in health with a focus on global problems of biodiversity decline, environmental degradation and climate change. "planetary health," promoted by the prestigious medical journal the lancet, is currently prominent. others include eco-health, one health and the in vivo planetary health group. predicting future human health (or survival) under the status quo is difficult. ecological systems typically demonstrate nonlinear responses to perturbations and it is likely that current consumption patterns will precipitate dramatic shifts in biodiversity, ecological function and health-supporting services. impacts of environmental change are disproportionately experienced by poor and rural communities. advocacy and action to prevent these health risks is an essential role for those concerned with public health. this entry has reviewed the issue of limits to growth, its more modern formulation as planetary boundaries and the relevance of both concepts to global population health. it has used these frameworks to classify and extend some environmental health risks. these include novel entities and behaviors, and global risks including climate change, biodiversity loss, land-system change and biogeochemical cycles. these risks are escalating and we recognize the shortfall in assessing the health risk of new pollutants, entities and behaviors. when considered together with economic and population growth, and with ever-increasing resource and energy use, these environmental health risks may foreshadow significant population decline. by using the ltg and pb frameworks in this contribution, society can frame preventative measures on the scale at which this is required. without urgent change, future global population health, and survival, is imperiled. environmental quality in a growing economy. resources for the future health, population, limits and the decline of nature climate change, food security and population health in the anthropocene a further critique of growth economics encyclical letter laudato si of the holy father francis on care for our common home collision course: endless growth on a finite planet the limits to growth great transition: the promise and lure of the times ahead union of concerned scientists, . world scientists' warning to humanity the interaction of human population, food production, and biodiversity protection is global collapse imminent? re-assessment of net energy production and greenhouse gas emissions avoidance after years of photovoltaics development come on! capitalism, short-termism, population and the destruction of the planet understanding social-ecological systems fischer: a critical look at food security strategies key: cord- - ixazg authors: morris, wyn; bowen, robert title: renewable energy diversification: considerations for farm business resilience date: - - journal: j rural stud doi: . /j.jrurstud. . . sha: doc_id: cord_uid: ixazg with a varied landscape, wales is resource rich in terms of wind and water and a suitable location to develop many different forms of sustainable energy. whilst farm businesses face increasing challenges in terms of economic stability and traditional production methods, this paper considers the role of renewable energy production as a form of diversification. the study adopts mixed methods as a means of undertaking an in-depth investigation into the role of renewable energy generation in supporting agribusinesses in wales. initially a questionnaire obtained responses from farmers in wales. subsequently, follow-up semi-structured interviews with farmers were conducted to further investigate the issues from the initial questionnaire. the theoretical contribution of this paper is a segmentation of farmer businesses which allows for distinctions to be made of different attitudes to off-farm income and the adoption of renewable energy sources. five farm types were identified, varying in relation to farm characteristics, attitudes to diversification, access to renewable energy and resource allocation. these farm types highlight the need for specific policies towards facilitating the increase in renewable energy along with sustaining farming incomes. furthermore the research provides valuable information to the farming industry on opportunities in renewable energy production, particularly for farmers and farm businesses who are considering diversification strategies. farming businesses are facing increasing challenges in particular the role of agriculture in the wider rural economy (barnes et al., ; loizou et al., ) , along with concerns regarding agriculture's impact on the environment in terms of resources and emissions. whilst some structural change is occurring in the rural economy, small-scale agricultural businesses remain at the core. the situation is even starker in large areas of wales where agriculture is dominated by upland sheep faming (morris et al., ) . these farm businesses are seen as having deep historical structural issues, being fragmented with limited value-added activity (roberts, ; armstrong, ) . as such upland sheep farms are regarded as being most at risk from agricultural policy reforms which focus on the reduction of direct payments and the greening of policies. the onset of brexit proposes further challenges to the industry in terms of trading agreements and standards. however, with a varied landscape, wales as a space is resource rich in terms of wind and water and a suitable location to develop many different forms of sustainable energy generation, particularly windfarms, solar parks, hydro-electric energy or biomass. the main aim of this study is to discover the possibilities for farmers in wales to utilise their resources and diversify into sustainable energy and build on the conceptual model of agri-environmental diversification behaviour established by sutherland et al. ( ) , as shown in fig. . whereas diversification in farming has received increasing attention in recent years (cf. brandth and haugen, ; mcfadden and gorman, ; morris et al., ) , the focus on renewable energy as a form of farm diversification has seen little research. this has largely been part of a wider discussion of agri-environmental diversification (sutherland et al., ; ge et al., ) , particularly in the context of scotland. thus, this study aims to develop a holistic understanding of the issues relating to farm diversification into renewable energy, focussing specifically on three research questions. . what drivers exist for farm businesses to diversify into renewable energy? . what barriers do farm businesses face in adopting renewable energy for diversification? . what types of farm businesses can benefit from diversifying into renewable energy? the research utilises a mixed methods approach to explore the opportunities for farmers to diversify into sustainable energy in response to current farming challenges and uncertainties. the research setting for the paper is wales, a predominantly rural country, where agrifood businesses represent a significant part of the economy, with % of the land area is used for agriculture (welsh government, ) . the rural geography of wales is considered abundant in natural resources, which is suitable for creating sustainable energy despite tis many challenges exist. as such, the study seeks to identify and understand the drivers and barriers that impact on the adoption of renewable energy generation as a form of farm diversification, and the types of farms that could benefit from these activities. the research contributes to previous research and proposes a sophisticated segmentation of farm business based on attitudes to diversification. the work informs both industry and policy of the opportunities from renewable energy diversification. the next section explores the role of agriculture in the rural economy and the themes of agricultural policy, farm diversification and renewable energy generation in the context of welsh agriculture. qualitative and quantitative analysis methods are explained in section and presented in section . the analysis identifies opportunities and barriers across all stages of renewable energy adoption, which can assist farmers and policy makers. with growing concerns regarding the increasing divide between urban and rural economies, as identified within the prosperity for all: economic action plan (welsh government, a) , sustainable agricultural businesses are essential to maintain upland communities. this is in contrast to the productivist view of agriculture and concerns regarding the industry's environmental impact from traditional farming practices, midmore ( ) comments that agriculture's contribution to the rural economy goes beyond its economic functioning, where it provides public services such as stewardship of the landscape, along with creating and managing biodiversity. more specifically, midmore ( ) adds that upland farmers in particular are becoming increasingly important, for example, in managing peat lands for carbon sequestration. on farm renewable energy generation could be an additional contribution where agriculture can assist in tackling climate change and support the rural economy. however, with uk farmers facing continuing economic pressures (house of commons, ), in addition, recent reforms, or 'greening', of agricultural policies require farmers to meet environmental targets, which may also have a negative impact on farm productivity (boere and van kooten, ; gittins et al., ) . in wales pillar support, that is non-direct subsidies as part of agricultural support to deliver climate objectives, has been delivered through a range of interventions including the agri-environment schemes, with financial support targeting tourism, renewable energy and improving ict, further reforms prioritising mitigation of climate change, water management and biodiversity, skills development, knowledge transfer and innovation. therefore, pillar provides potential funding for farm diversification into renewable energy generation. effective delivery of policies is dependent on the participation of farmers and farm managers (pollock, ) , with farmers facing tensions between adhering to policies and following strategies in response to their business aims and objectives. these strategies will impact on the farm's profitability, its contribution to the rural economy and the ecosystem services it produces. the success of these strategies and the future of family farms are reliant on investment in infrastructure surrounding connectivity as highlighted by bowen and morris ( ) , but also infrastructure in terms of national grid capacity. this investment will have spill over effects to the wider rural economy. for some time, farm diversification has been a prominent strategy in rural spaces as farmers seek to supplement farm incomes and explore business opportunities. there have been varying attempts to define diversification, for the purpose of this paper we will use the definition of vik and mcelwee ( , p. ) which defines farm diversification as "a movement away from core activities of the farm business by providing goods or services with a basis in a wide understanding of farm resources (human, physical, private, or collective)". farm household incomes have often included subsidies, food production, tourism or other forms of off-farm income, however, it is recognised that the natural resources of rural spaces in wales provide opportunities for growth in sustainable energy generation. in considering the above, the main aim of this study is to discover the possibilities for farmers in wales to utilise their resources and diversify into sustainable energy. the work considers the skills set and managerial mind-set highlighted by mcelwee and bosworth ( ) as essential for successful diversification strategies and seeking entrepreneurial opportunities. the aim of the research is to build on the conceptual model of agri-environmental diversification behaviour established by sutherland et al. ( ) , as shown in fig. . the model highlights the importance of farmer characteristics and farm business characteristics in adopting farm diversification strategies. farm diversification is one strategy that may provide spill-over effects for the wider community and highlights the entrepreneurial side of farmers (vik and mcelwee, ) . a pull factor towards diversification or pluriactivity may be related to household/family structure and the need to provide gainful employment for other family members. another factor could be the desire to contribute to wider social and environmental objectives such as providing employment opportunities for others in the specific rural area or contributing to the care of natural amenity and landscape (leck et al., ; suess-reyes and fuetsch, ) . renewable energy generation could be a solution to these diversification drivers and this form of entrepreneurship may be critical for the resilience of the family farm business by allocating resources away from mainstream food production (vik and mcelwee, ) . the european union has set targets that % of energy consumed will come from renewable sources by (european commission, ). however, the primary focus of this plan, along with previous reports, is on the energy sector, with the role of the agricultural sector in energy production generally ignored. in contrast, such reports consider agriculture to be a problem in achieving environmental targets due to the emissions produced from traditional production methods. it is apparent that the role of agriculture in renewable energy production requires greater attention. whilst there is a large back catalogue of literature on farm diversification, entrepreneurship and off-farm income, the literature on renewable energy generation on farms is limited with the exception of (cato et al., ; sutherland et al., sutherland et al., , . however, whilst cato et al. ( ) explores the renewable energy sector in wales, the focus is on the entrepreneurial elements. where all cases in the study demonstrated a drive to provide energy to their local community independent of the national grid, the majority of cases were concerned with sustainability. two of the cases found financial achievements as being the most important factor. sutherland et al. ( ) analysing agri-environmental diversification on scottish farms found that young, better educated farmers that receive subsidies and have off-farm income are more likely to engage in future environmental activities which include renewable energy production. this is consistent with the work of morris et al. ( ) analysing upland farm strategies in wales. sutherland et al. ( ) acknowledges agriculture's key role in renewable energy transition as agriculture is responsible for managing key resources such as land and biomass. the welsh government ( b) report on energy generation in wales highlights that between and energy consumption in wales fell by %. in addition, the government has set a target by that renewables are to generate electricity equivalent to % of wales's consumption. the report outlines that wales already generates % of this target. however, only % of total energy generated in wales is from renewables, as wales is a net exporter of electricity. of this renewable energy generation, wind power makes up % of renewable energy generation in wales. the welsh government ( b) report highlights considerable regional variations between local authorities in terms of renewable energy generation and the types of renewable energy generation. for example the neath port talbot local authority produces the largest amount of renewable energy which is dominated by onshore wind projects. whereas monmouth's renewable energy generation is dominated by biomass electricity, gwynedd's energy generation is dominated by hydro projects, with pembrokeshire focused on solar. some of these statistics are skewed by large commercial projects, however, the regional variation is also influenced by local resources and planning regulations. such factors must be considered if farmers are to adopt this form of diversification. as noted earlier, studies of renewable energy generation in agriculture are limited, however morris' ( ) study on technology adoption in agriculture captured data on renewable energy adoption by upland farms in wales. solar electricity was by far the most popular form of renewable energy with . % of respondents having electricity generating solar panels. the popularity of these panels is linked to government incentives, feed in tariffs and the electricity usage on farms particularly dairy farms. a total of ( . %) of the respondents to the survey had no renewables on the farm an area the welsh government must consider if it is set to meet its ambitious targets. the research aims to examine farm diversification activities and farmer attitudes towards renewable energy generation in supporting agribusinesses in wales, as such, the study uses a sequential mixed method design (creswell and plano clark, ) of two equally-weighted independent phases to undertake an in-depth investigation into the matter. initially an online questionnaire (november -february ) obtained responses from a database of farmers ( . % response rate) dispersed across wales (see fig. ) through a process of convenience sampling, with demographic questions within the questionnaire designed to confirm the suitability of respondents. questions focussed on farmer characteristics, farm income activities, diversification and engagement with renewable energy, with distinctions made between farmers that have and have not adopted farm diversification activities. questions were influenced by those employed by sutherland et al. ( ) , and were chosen to meet the aims of the research questions in understanding the opportunities for diversification into renewable energy, including the drivers and barriers to adoption. questionnaire findings were analysed initially through descriptive statistics, and later through a cluster analysis. subsequently, follow-up semi-structured interviews were conducted with questionnaire respondents (april-june ) based on a purposive sampling method to identify farmers already adopting renewable energy and those who do not (yin, ) . maximum variation sampling was used to ensure that the interview sample accounted for all characteristics of farm size, farmer age, location and adoption of renewable energy (see table ). the purpose of the interviews was to provide a deeper understanding of farmers' awareness, attitudes and barriers to renewable energy adoption as a form of diversification. the interviews (n = ) ranged between and min in length. the number of interviews is consistent with other studies on agriculture (for example warren, ; downey et al., ) . more importantly, the interviews achieved data saturation in terms of themes, and concepts (francis et al., ) . interview data was analysed using the six step process of thematic analysis by braun and clarke ( ) . the mixing of methods occurred through triangulation of the quantitative and qualitative data, with a final phase of data analysis conducted using a two-step cluster analysis. the cluster analysis was informed by the segmentation work of morris et al. ( ) and conducted in spss using survey data to investigate company typographies that could explain approaches to off-farm income (bacher et al., ; mooi and sarstedt, ) . results of the cluster analysis were analysed for validity using chi-square analysis to ensure that distinct segments were developed. table outlines the clusters obtained from the analysis. the next section provides detailed findings of the research, presented in chronological order. this section presents the findings of the data collection phases, with quantitative findings based on survey responses from farmers, along with follow-up interviews. of the survey respondents . % were aged between and years, . % were aged to , . % aged - years, . % aged to and a further . % aged over years. this reflects the aged nature of the industry. in terms of education . % of respondents had school only, . % has a-levels, . % had further education and . % had a higher education qualification. descriptive statistics from the survey show that . % of respondents were engaged in off-farm income. fig. shows that a range of activities were evident, however contracting was the most frequent activity with . % of respondents engaged in this. several respondents were also involved in property letting and tourism activities, with . % of respondents engaged in renewable energy generation. among the . % of respondents not involved in off-farm income, the reasons for non-adoption are documented in fig. . the most frequent reason was a lack of time, followed by limited resources. four respondents pointed to plans to retire rather than invest in the farm. other reasons include lack of viability, costs, deciding against adoption and uncertainty over what to do. a total of semi-structured follow-up interviews were conducted with farmers who had responded to the questionnaire. table outlines a profile of interviewees according to farm size, age range, location and whether they possess renewable energy sources. eight of the fifteen respondents possessed renewable energy. interview data was analysed using the six step process of thematic analysis by braun and clarke ( ) . verbatim transcripts of the interviews were coded through a process of first and second cycle coding (miles et al., ) , reducing the data into themes. the first cycle coding process led to codes from the interviews, which were reduced to unique codes by removing duplicates, and further reduced to unique codes through second cycle coding. this culminated in the formation of themes (see table ), which relate to renewable energy in farm diversification. these include resources available to farms and the opportunities that exist in diversification, the drivers and barriers to adopting renewable energy, and the overall farm activity. each theme is discussed hereafter. respondents acknowledge the abundance of natural resources that exist in wales provides opportunities for farmers to diversify into renewable energy, however, the type of renewable energy adoption varies according to the specific conditions of the farm. hydroelectric is seen as a desirable energy source due to potential high returns, however, this is dependent on suitable water flow levels. several respondents have installed solar panels or wind turbines on their farms, which are suited to farm locations. wind turbines can be accommodated on farm land, with the rooves of farm buildings suited for the positioning of solar panels. not only do farm resources provide opportunities for renewable energy adoption, other forms of diversification are also recognised, including tourism, food production, horticulture, or alternative farming activities, such as poultry. according to respondent g, "i think it's really important to maximise the farm's potential. every farm has got different aspects which can be utilised". respondents documented that the resource availability reduced their perceived risk in adopting in renewables, which represents a considerable investment for farmers. however, it is also recognised that support is essential in guiding farmers to invest in renewables, particularly financial resources, time and business advice. as mentioned above, respondents acknowledged that natural resources provide farmers with opportunities for farm diversification, especially in renewable energy, but also tourism or alternative farming activities. these opportunities were dependent on the location of the farm, as to whether certain forms of renewable energy production were viable, such as the placement of wind turbines, or access to water flow for hydroelectric. respondents commented that the alternative activities were a vital source of income for the farm to compensate for difficult periods in farming, and the difficulty in making a comfortable living from farm activities alone. off-farm diversification activities were seen as an important way of spreading the risk of farm activities, as this provided different income streams for the farm. "to make it a viable business you need income other than sheep. you could keep sheep and you still wouldn't make a living. but then you've got tourism. and the other thing is renewable energy. because we're by the sea i would've thought there's more wind here. that should justify the construction of a windmill." (respondent b) respondents c and g identified income generated from renewable energy as being half of the total farm income. significantly, for these respondents, renewable energy activities on the farm generate high profit margins, which adds to the appeal in investing in such activities. indeed, respondents pointed to opportunities to use income generated from initial renewable energy adoption to invest further in renewable energy sources later. additionally, the investments made into renewable energy sources were recognised as an opportunity to secure the longterm future of the farm for the future generations. not only were the benefits of renewable energy seen in income generation, but investing in renewable energy sources was also recognised as an important means for the farm to reduce costs, as renewable energy was used to power farm activities, thus making the farm more efficient. cost savings were observed in the short-term from reduced energy costs, but savings would increase in the long-term as farmers were able to pay back loans for their investment: "it's probably worth £ - , a year to me in electric and oil savings at the moment. so yeah, it's probably worth it. the projects will eventually be worth about £ , a year to me." (respondent f) a third theme from the interviews related to the drivers to adopting renewable energy as a source of off-farm income. despite the opportunities identified above, respondents pointed to drivers which influenced the decision to invest in renewables. this included the viability of the farm to generate income from renewable energy, which could be influenced by the scale of the farm. renewable energy sources are seen to be attractive as the return on investment (roi) is perceived to be favourable. respondents pointed to incentives influencing their decision to invest, including subsidies, financial support, advice, and good feedin tariffs. despite this, it is recognised that the conditions have become less favourable in recent years, particularly reductions to the feed-in tariff, which has made investment in renewables less attractive. as such, respondents called for government policy to support farmers to invest in renewables. "the number one thing was the feed in tariff at the time. they were just so good. that and the savings then that it gives you. the renewable industry would not have even got off its feet without the feed in tariff … the feed in tariff all finished on st march, so there's absolutely no incentive for anyone else to invest in it." (respondent f) as discussed above, the reduction in the feed-in tariffs was identified by respondents as a current issue, which acts as a barrier to further investment in renewables, and indeed as a barrier to adoption. for respondents without renewable energy, the lack of viability was cited as the main reason for non-adoption. other adoption barriers point to the cost of investment, financial risk, limited support, and limited awareness of where to get support. farm conditions, such as an isolated location and limited connectivity also impact on the viability of a farm to generate sufficient income from renewables. external environment barriers include planning restrictions, such as for respondent c, whose farm is located in a national park, regulations, and uncertainty in the industry, particularly related to brexit, which discourages farmers from investing. additional barriers to further investment in renewables included farmers gaining access to the national grid, particularly due to the grid being at full capacity, limiting farmers' ability to feed energy into the grid. "where we are there's quite stiff opposition to wind turbines and solar panels, and our grid connection is not sufficient to allow it. i don't think there's spare capacity left in the local grid anyway." (respondent k) additional responses from the interviews related to farm activity more broadly. diversification, especially in renewable energy sources, was acknowledged as an integral part of farm activity at present, representing an important means of spreading the risk across a range of activities, as off-farm income can compensate for difficult periods in farming. however, it is recognised that not all farms are suited to diversification in renewables, as this depends on the farm size, location and resources. "if a farm of this size can't make it, there's not a lot of hope for acre farms. and i think that we're strong enough to pass that. smaller farms, like half the size, they're going to struggle." (respondent a) given the level of investment, farms may consider other forms of diversification, such as tourism, food production, horticulture, or alternative means of farming. the timing of investment is important due to changing conditions in farming, including different levels of return from changing energy tariffs. respondents pointed to investment in offfarm income as a means of long-term investment in the farm, which would serve for future generations, but also innovate the way the farm operated, as this involved investing in technology, such as respondent f, who invested in automation alongside renewable energy adoption. this represents the continuous development of the farm and seen as good farm management. "i wanted £ , a year of income off farm that we could do something else with, or if farming had a bad cycle, like it does, that it could basically prop the farm up. so that's my aim, anyway." (respondent f) the themes derived from the thematic analysis underline several opportunities and barriers that farmers face in relation to farm diversification, especially involving renewable energy sources. fig. outlines the impact of these issues at different stages of the process of investing, adoption and operating renewable energy sources for farm diversification. opportunities in the investment stage exist for diversification in different ways, dependent on the nature of the farm and its resources, however, this is also impacted by the vision and proactivity in seeking to adopt renewables for off-farm income. barriers at this stage include limited support, limited resources, planning restrictions, high costs and risk, as well as farmers' resistance to change. opportunities in the adoption phase point to farms making full use of its resources to innovate and adapt to changes in the industry. diversification can also help spread the risk across a range of activities on the farm. challenges exist through regulations, regulations, risk and issues relating to a farm's isolated location, such as limited connectivity. once in operation, opportunities exist for farms to develop incremental growth. respondents pointed to battery storage as a potentially profitable activity, as this would enable for energy developed through renewable sources to be stored and then fed into the national grid. barriers exist at this stage, notably the cost of maintaining renewable activities, unfavourable return on investment and unfavourable deployment rates, depending on the type of renewable energy. respondents also acknowledged restrictions in grid capacity limiting the opportunities for farmers to feed energy back into the grid. additionally, respondents spoke of issues of companies exploiting opportunities in renewable energy, particularly when feed-in tariffs were high, which made it more difficult for individuals to invest in renewables. a two-step cluster analysis was conducted in spss using survey data to investigate farmer typographies that could explain approaches to offfarm income. the two-step cluster analysis was chosen over alternative clustering methods since it does not require for the number of clusters needed to segment the sample to be specified in advance. this allows for the number and types of clusters to be explored through the clustering process. ten variables observed in the questionnaire were used as inputs for the cluster analysis (table ) , selected to represent characteristics of the farmer, the farm and its activity, which were consistent with findings expressed from the interviews. alternative segment outcomes were explored, however, other solutions observed lower levels of cohesion, as the five cluster outcome obtained here displayed cluster sizes ranging from . % (n = ) to . % (n = ). the validity of the cluster analysis was supported using a chi-square analysis to indicate significant differences between the segments, as shown in table . the work was informed by the segmentation research of morris et al. ( ) which found the 'resource maximisers', i.e. those engaged in off farm income activities and participating in environmental schemes as being the most likely to adopt renewable technology. table outlines the clusters obtained from the analysis, with inputs listed in order of the predictor importance value, where farm size and off-farm income are listed as the findings show the main distinctions are observed between the inputs relating to off-farm income, farm size, education, age and renewables. observations show three clusters with off-farm income, of which cluster is the only one that possesses renewable energy sources. clusters and have off-farm income but no access to renewable energy. this implies that members of this cluster recognise opportunities in diversification but have pursued alternative activities. this could indicate the potential for farms within these clusters to pursue renewable energy activities in future. reasons for non-adoption require further investigation however, could be a lack of access to suitable renewable energy sources, or limited infrastructure, which could be improved through national policies towards improving rural infrastructure. two clusters operate without offfarm income, both of which have access to renewable energy sources. cluster is a mostly medium-sized upland cattle and sheep farm, whereas cluster represents a mostly small lowland cattle and sheep farm. as both have access to renewables, diversification in renewable energy is a possibility, however reasons for non-adoption could be due to a lack of desire, particularly in the case of cluster , as this mostly represents farmers in the and over age range who may be looking to retirement rather than investing in the farm. although the least important input, family involvement is high in each cluster, which indicates that family help is necessary on all farm types. cluster represents a large upland cattle and sheep farm with no diversification activities, but access to renewable energy. the farmer is experienced, aged - , well-educated and owns the farm. the characteristics point to a farm more focussed on its core activity, aligning with the farm focussed typography expressed by morris et al. ( ) , where the business focus is on utilising farm resources for income generation. here, it is likely that renewable energy is generated as a means of reducing costs and operating more efficiently, rather than generating additional income for the farm. however, they possess resources to be able to generate income, which could support growth in the farm business. strategies for this farm type could focus on developing diversified income streams through renewable energy, as the farm already possesses renewable energy sources. this would depend on the ability to expand on these existing resources, and whether suitable infrastructure is available, such as access to the national grid, or battery storage. such farm types could be incentivised by government policy to expand upon these activities, notably through favourable feed-in tariffs. cluster is a medium-sized upland cattle and sheep farm with access to renewable energy and engaged in diversification. the farmer is a well-educated, experienced tenant in the - age category. this implies that the business is more aware of the need to engage in diversification activities, this may be due to limited financial resources as a tenant. the inclusion of renewable energy as part of diversification activities indicates an openness to innovation and technology adoption, which relates to the resource maximiser typography (morris et al., ) . this farm type could be an example to other local farms interested in exploring diversification opportunities through renewable energy. indeed, such farms could play an integral role in community projects for producing renewable energy, such as ynni ogwen, a community social enterprise in the ogwen valley in north-west wales, which produces electricity through hydroelectric power, with profits being transferred to a fund aimed to fund community projects (partneriaeth ogwen, ) . policies towards these farms should ensure that adequate infrastructure is in place to enable such farms to explore further growth in the renewable energy income streams, where possible. clusters and share similar characteristics. both are involved in diversification activities but do not possess renewable energy sources. farmers are well-educated and experienced farms owners. both align with the lifestyle farmer typography (morris et al., ) with their activities based on lifestyle choices, where innovation is low and diversification activities are aimed at reducing risk and supplementing income. differences between both clusters are evident in the farm activity, size, and farmer age. whereas cluster represents a larger, upland farm with an older farmer, cluster is a smaller, hill farm with a farmer aged - . although both clusters could look to adopt renewable energy production, cluster may possess larger land resources for this, but lack a desire for innovation, whereas cluster may be more constrained by its size, but possess a farmer more open to innovation. thus distinctions could be classified between open and closed lifestyle farmers, referring to their attitude towards innovation. both farms could be incentivised to seek to supplement their income through support to adopt renewable energy production, particularly financial support or favourable feed-in tariffs. it is possible that both farm types have decided against renewables adoption due to infrastructure constraints, such as limited grid capacity, therefore greater national investment in suitable infrastructure would improve the possibility of developing renewable energy production. policies could seek to encourage higher levels of innovation within both farm types, especially cluster , where the farmer tends to younger than in cluster . this could be achieved through improving access to professional development and developing skills among farmers, as advocated by morris et al. ( ) . finally, cluster represents a medium lowland cattle and sheep farm with renewable energy access, but no diversification activities. the farmer is less educated, in the and over age category and owns the farm. these characteristics point to a farm that has maintained consistent activity over many years, keeping a focus on the farm rather than seeking to engage in off-farm income activities, possibly as the farmer is heading towards retirement. this aligns with the passive farmer typography of morris et al. ( ) , with renewable energy likely being ***p < . , **p < . , *p < . using chi-square tests. produced to cover energy costs on the farm, although there is potential that this could lead to income generation. such farms display opportunities for growth, which could largely be constrained by a lack of desire from the farmer. successors on the farm should thus be made aware of the growth potential and provided with suitable support in seeking to pursue these opportunities. this could be evident through financial incentives, and mentoring, especially where younger inexperienced farmers take over the management of the farm and may be more risk averse. farming and the rural economy have experienced increasingly difficult periods in recent years (marsden and sonnino, ; winter and lobley, ; marsden, ) , with further uncertainty evident from brexit (morris et al., ) and the coronavirus pandemic. as such, it is increasingly seen as essential for farms to diversify their activities to account for such downturns and enable resilient farm business models. these factors coincide with a period of increased focus on sustainability, following discussions and recognition of a climate emergency. given the natural resources available in rural areas, such as wales, there is an opportunity for farmers to explore diversified activities, such as tourism, food production, or renewable energy production. considering theoretical underpinnings of the resource-based view, the unique natural resources found in many rural areas offer rural businesses an opportunity to develop resilience and competitive advantage through the exploitation of such resources, which are valuable, rare, inimitable and non-substitutable to their specific place (barney, ) . respondents to this study pointed to diversification activities as an important way to spread the risk of farming across a range of activities. therefore, the exploitation of natural resources to produce renewable energy offers farmers an opportunity to develop new business activities on the farm. given the passive tendencies farm businesses show towards adopting change (bowen and morris, ) , support is necessary in assisting farmers to capitalise on the opportunities from renewable energy. respondents engaged in renewable energy spoke positively of government incentives in facilitating the adoption of renewable energy sources on the farm, however, the reduction of the feed-in tariffs was cited as a barrier to adoption, as investment in renewable energy sources has become less attractive as a consequence. the scale of investment in several forms of renewable energy is significant for farmers, especially considering the uncertainty in the industry, therefore a reduction in the perceived risk is essential in encouraging farmers to invest. some respondents acknowledged that this investment was not only a short-term benefit to the farm, but also a legacy for the future generations. findings in fig. outline opportunities and barriers along the process of renewable energy production, from investment to operation, highlighting the need for government policy to align better with farmers' needs on this matter, particularly in supporting investment through financial support and less restrictive planning regulations; encouraging adoption through improving connectivity and re-introducing favourable feed-in tariffs; and optimising operations through improved grid capacity and battery storage facilities. in recent times there has been an increasing emphasis on developing sustainability particularly in light of discussions around the climate emergency. renewable energy represents an important part of this, and the european union has set a target of achieving % of consumed energy from renewable sources by (european commission, ). findings from the cluster analysis show that many types of rural businesses possess opportunities to diversify, and are presently involved in off-farm income activities. clusters , and operate with off-farm income, but only cluster also possesses renewable energy sources. however, findings imply that rural business also possess opportunities to adopt renewable energy sources, as clusters and possess renewable energy sources despite not currently engaged in off-farm income activities. suitable support programmes could encourage rural businesses to seek off-farm income opportunities, particularly in adopting renewable energy sources, however, this is dependent on favourable conditions, as shown in fig. . findings imply that farmers display some entrepreneurial activity by engaging in off-farm income, however there is limited evidence of farmers exploiting the opportunities for off-farm income through renewable energy. this could be explained by farmers' passive tendencies to change (bowen and morris, ) , as the perceived risk of investing in renewable energy sources may be too great; or by limited support for farmers in these activities, including a lack of incentives, or inadequate infrastructure. as such, rural policies should look to overcome these challenges, by encouraging more proactivity to change, providing financial support or incentives, such as favourable feed-in tariffs, and ensuring adequate infrastructure is in place. the sudden loss of activities experienced by many businesses during the coronavirus pandemic underlines the precarity that many businesses face, thus diversification provides opportunities to spread the business risk across a variety of activities. indeed, as an essential commodity, energy provides opportunities for diversification in an industry that is likely to be impacted by sudden economic changes in future, particularly renewable energy, due to an increasing emphasis on the climate. the cluster analysis of this study underlines the differing opportunities and challenges that farms face in diversifying through renewable energy, according to their situation. the farm segments developed from this analysis align with the farm types developed by morris et al. ( ) , while also shedding further light on distinctions that could be observed within one of these types, the lifestyle farmer, with this study identifying two clusters that equate to this type, where differences exist in open and closed attitudes to innovation. the clusters developed within this study point to the need for specific policies to be tailored towards the farm type. farms in the farm focussed type could be incentivised to seek growth through diversification into renewable energy, particularly through favourable feed-in tariffs, and access to suitable infrastructure. resource maximiser types could be encouraged to pursue further growth, and to support community renewable energy generation projects. policies towards lifestyle farmer types could encourage farmers to engage in more innovative practice, and promote skills development, particularly among younger farmers to ensure a longer-term vision for farm activities. passive farmers should also be encouraged and supported to explore new opportunities through diversification, notably through financial incentives, as well as mentoring for younger generations of farmers who may take over from elderly farm managers. government policies in different places could also account for location-specific factors that may impact on farm diversification, such as the natural resources observed in wales, which present opportunities for engaging with renewable energy. the research presented in this paper finds a desire among welsh farmers to seek off-farm income opportunities to supplement farm income. the quantitative findings highlight that farmers are engaged in a range of diversification activities. however, despite recognition of diversification opportunities from renewable energy, this form of diversification only represents . % of diversification activities within the sample. whilst there is an existence of resources and opportunities to diversify into renewable energy, barriers to implementation exists. these are associated with an increased reliance on support, such as access to finance, favourable feed-in tariffs and less restrictive planning regulations. previous studies (bowen and morris, ; gittins et al., ) highlight that farmers have a reactive attitude towards technology adoption, hence government intervention in providing incentives to adoption is necessary. following empirical research among welsh farmers, the contribution of the paper is to propose a sophisticated clustering of farm businesses in terms of strategies adopted. findings show the main distinctions are observed between the inputs relating to off-farm income, farm size, education, age and renewables. observations find three clusters with off-farm income, of which cluster is the only one that possesses renewable energy sources. this categorisation identifies variation in a number of distinguishing characteristics of welsh farmers. the findings lead to the segmentation of farmers which allow for distinctions to be made of different attitudes to diversification and the adoption of renewable energy sources, resulting in a better understanding of environmental entrepreneurship and targeted policies. overall findings highlight farmers' ability and willingness to diversify despite significant challenges facing the rural economy. it must be noted that despite access to natural resources such as wind and water, not all farms are suited to renewable energy generation due to location, environmental or infrastructure restrictions. the research highlights that greater support for farm businesses and further investment in national infrastructure would enable farm diversification into renewable energy. findings underline opportunities in wales to exploit the natural resources available and enhance farm household with an increasing emphasis on the environment and sustainability, there is justification for investing in renewable energy sources to ensure a greener and future, whilst supporting more efficient and sustainable farming activity. as key actors within local rural communities, farmers could play a significant role in renewable community projects by sharing resources, notably land. . implications of the research are evident for both practice and policy. the data in fig. informs the farming industry of opportunities and barriers to diversification into renewable energy across all stages of the investment, adoption and operation process. in terms of policy, the research informs welsh government of the importance of renewable energy to the rural economy and how natural resources in rural spaces in wales could be harnessed for environmental entrepreneurship. additionally, research findings provide evidence for government in supporting farmers to diversify, and influence policies towards facilitating the increase in renewable energy generation. there is a requirement to amend planning, regulatory and infrastructure policies, which the qualitative data highlights as being restrictive. consequently, the research can also inform government in supporting the development of sustainable energy companies by utilising natural resources in rural places. in terms of renewable energy generation rural areas in wales have lost the opportunity to capture the value from large-scale projects and facilitating value. more often than not, more value is added outside wales than inside. therefore, the covid- pandemic has had major economic and social implications, while the rural economy has not been exempt from these impacts and has accelerated technology adoption. however, brexit will likely pose a greater threat to welsh agriculture than the covid- pandemic and as such diversification into the renewable energy sector may provide a more robust and resilient business model. the work has wider implications beyond wales in informing rural locations and governments in terms of the role of renewable energy generation in supporting rural economies, underlining the need for substantial investment in infrastructure of rural regions to embrace environmental entrepreneurship opportunities. research briefing: the farming sector in wales. national assembly of wales spss two step cluster -a first evaluation disadvantage and economic viability: evidence from scottish upland farming firm resources and sustained competitive advantage reforming the common agricultural policy: decoupling agricultural payments from production and promoting the environment the digital divide: implications for agribusiness and entrepreneurship. lessons from wales farm diversification into tourism -implications for social identity? using thematic analysis in psychology entrepreneurial energy: associative entrepreneurship in the renewable energy sector in wales designing and conducting mixed methods research what is the role of place identity in older farming couples' retirement considerations? renewable energy directive what is an adequate sample size? operationalising data saturation for theory-based interview studies exploring factors affecting on-farm renewable energy adoption in scotland using large-scale microdata discrete event simulation in livestock management food and rural affairs committee. farming in the uplands agriculture -who cares? an investigation of 'care farming' in the uk the role of agriculture as a development tool for a regional economy exploring the rural eco-economy: beyond neoliberalism rural development and the regional state: denying multifunctional agriculture in the uk exploring the strategic skills of farmers across a typology of farm diversification approaches exploring the concept of farm household innovation capacity in relation to farm diversification in policy context food and the economy in wales qualitative data analysis technology adoption, entrepreneurship and efficiency in agricultural businesses: the case of upland sheep farmers in wales farm diversification, entrepreneurship and technology adoption: analysis of upland farmers in wales repairing a fractured pipeline: improving the effectiveness of agricultural r&d in the uk review into the resilience of welsh farming the future of family farming: a literature review on innovative, sustainable and succession-oriented strategies conceptualising multi-regime interactions: the role of the agriculture sector in renewable energy transitions agrienvironmental diversification: linking environmental, forestry and renewable energy engagement on scottish farms diversification and the entrepreneurial motivations of farmers in norway farmers online: drivers and impediments in adoption of internet in uk agricultural businesses prosperity for all: economic action plan. cardiff: welsh government energy generation in wales what is land for? the food, fuel and climate change debate case study research: design and methods, revised edition both authors contributed equally to all aspects of this paper, from the beginning of the research to the writing of the paper. supplementary data to this article can be found online at https://doi. org/ . /j.jrurstud. . . . key: cord- -ygmkul authors: khrennikov, andrei title: social laser model for the bandwagon effect: generation of coherent information waves date: - - journal: entropy (basel) doi: . /e sha: doc_id: cord_uid: ygmkul during recent years our society has often been exposed to coherent information waves of high amplitudes. these are waves of huge social energy. often they are of destructive character, a kind of information tsunami. however, they can also carry positive improvements in human society, as waves of decision-making matching rational recommendations of societal institutes. the main distinguishing features of these waves are their high amplitude, coherence (homogeneous character of social actions generated by them), and short time needed for their generation and relaxation. such waves can be treated as large-scale exhibitions of the bandwagon effect. we show that this socio-psychic phenomenon can be modeled based on the recently developed social laser theory. this theory can be used to model stimulated amplification of coherent social actions. “actions” are treated very generally, from mass protests to votes and other collective decisions, such as, e.g., acceptance (often unconscious) of some societal recommendations. in this paper, we concentrate on the theory of laser resonators, physical vs. social. for the latter, we analyze in detail the functioning of internet-based echo chambers. their main purpose is increasing of the power of the quantum information field as well as its coherence. of course, the bandwagon effect is well known and well studied in social psychology. however, social laser theory gives the possibility to model it by using general formalism of quantum field theory. the paper contains the minimum of mathematics and it can be read by researchers working in psychological, cognitive, social, and political sciences; it might also be interesting for experts in information theory and artificial intelligence. during recent years, the grounds of the modern world have been shocked by coherent information waves of very high amplitude. the basic distinguishing property of such waves is that they carry huge amounts of social energy. thus, they are not just the waves widely distributing some special information content throughout human society. instead, their information content is very restricted. typically, the content carried by a wave is reduced to one (or a few) labels, or "colors": one wave is "green", another is "yellow". at the same time, information waves carry very big emotional charge, a lot of social energy. therefore, they can have strong destructive as well as constructive impact on human society. in this paper, we present a model of the generation of very powerful and coherent information waves; a model based on the recently developed theory of social laser [ ] [ ] [ ] [ ] [ ] [ ] . we stress that social laser theory is part of the extended project on applications of formalism of quantum theory outside of physics, quantum-like modeling (see, e.g., monographs [ ] [ ] [ ] [ ] [ ] and some selection of papers [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] ). this terminology was invented by the author to distinguish this modeling from attempts to reduce human consciousness, cognition, and consequently behavior to genuine quantum physical processes in the brain (see, e.g., penrose [ ] or hameroff [ ] ). we do not criticize • indistinguishability of people. the human gain medium, population exposed to the information radiation, should be composed of social atoms, "creatures without tribe": the role of national, cultural, religious, and even gender differences should be reduced as much as possible. content ignorance. social atoms should process information communications without deep analyzing of their contents; they extract only the basic labels ("colors") encoding the communications. of course, humans are still humans, not social atoms; thus, in contrast to quantum physics, it is impossible to create human gain mediums composed of completely indistinguishable creatures. people still have names, gender, nationality, but such their characteristics are ignored in the regime of social lasing. one of the basic components of lasers, both physical and social, is a resonator [ ] . it plays the double role: • amplification of the beam (of physical vs. information) radiation; • improving coherence of this beam. social laser resonators play a crucial role in generation of coherent information waves of high amplitude. they are established via internet-based echo chambers associated with social networks, blogs, and youtube channels. their functioning is based on the feedback process of posting and commenting, the process that exponentially amplifies the information waves that are initially induced by mass media. echo chambers improve the coherence of the information flow through the statistical elimination of communications that do not match the main stream. this statistical elimination is a consequence of the bosonic nature of the quantum information field (sections . and . ) . although this quantum process of coherence generation dominates in echo chambers, we should not ignore other technicalities increasing coherence (sections . and . ), such as censorship of moderators and the dynamical evaluation system of search engines of, e.g., google, youtube, or yandex. the latter system elevates approachability of posts, comments, and videos depending on the history of their reading (seeing) and reactions to them say in the form of new comments. this is a good place to recall that the quantum-like hilbert space formalism if widely used for the modeling of information processing by internet search engines, and, in particular, for information retrieval [ ] [ ] [ ] [ ] [ ] [ ] . we compare functioning of optical and information mirrors (section . ). the latter represents the feedback process in internet systems such as, e.g., youtube. in contrast to the optical mirror, the information mirror not only reflects excitations of the quantum information field, but also multiplies them. thus, this is a kind of reflector-multiplier (section . ). as the result of this multiplication effect, social resonators are more effective than physical ones. however, as in physics, resonator efficiency depends on a variety of parameters. one of such parameters is the coefficient of reflection-multiplication (section . ). we analyze the multilayer structure of an information mirror and dependence of this coefficient on the layer (section . ). the main output of this paper is presented in section describing the quantum-like mechanism of the generation of big waves of coherent information excitations. we start the paper with compact recollection of the basics of social laser theory distilled from technical details and mathematical formulas. we present the basic notions of this theory such as social energy (section . )) and social atom, human gain medium (section . ), information field (section . ), the energy levels structure of social atoms (section . ), and spontaneous and stimulated emission of information excitations (section . ). finally, we conclude the introduction by the schematic presentation of the functioning of social laser theory (section ). the role of information overload in approaching indistinguishability of information communications, up to their basic labels, quasi-colors, is discussed in section . . this is a good place to mention studies on coupling indistinguishability and contextuality [ ] . finally, we point to coupling of the social laser project with foundations of quantum theory (appendix b). the basic component of a physical laser is a gain medium, an ensemble of atoms. energy is pumped into this medium aimed to approach the state of population inversion, i.e., the state where more than % of atoms are excited [ ] . then, a coherent bunch of photons is injected into the gain medium and this bunch stimulates the cascade process of emission of the coherent photon beam. if the power of pumping is very high, i.e., it is higher than the so-called lasing threshold, all energy of pumping is transferred into the output beam of coherent radiation. to make this beam essentially stronger, the laser is equipped by an additional component, the laser resonator (typically in the form of an optical cavity). the laser resonator also improves the coherence of the output beam, by eliminating from the beam photons that were generated via spontaneous emission in the gain medium [ ] . typically, in physics, coherence is formulated in physical waves terms, as electromagnetic waves going in phase with the same direction of propagation and frequency. for us it is convenient to reformulate this notion by excluding any reference to waves in the physical space, since we want to move to the information space. instead of the wave picture we can use the photon picture, so a propagating wave is represented as a cloud of energy quanta. (this is the fock representation in quantum field theory.) coherence means that they have the same energy (frequency) and the direction of propagation-photon's wave vector. we remark that a photon also has additional characteristics such as polarization, the quantum version of the ordinary polarization of light. for convenience of further considerations, let us call all characteristics of a photon additional to its energy quasi-color. we recall that the usual light's color is determined by photon energy (frequency). therefore, a photon has its color and quasi-color. the notion of social energy is the main novel component of our quantum-like modeling. to justify the use of a social analog of the physical energy, we use the quantum-mechanical interpretation of energy, not as an internal feature of a system, but as an observable quantity. thus, like in the case of an electron, we cannot assign to a human the concrete value of the social energy. there are mental states in the superposition of a few different values of the social energy. however, by designing proper measurement procedures we can measure human energy; see [ , ] for details. social energy is a special form of the psychic energy. we recall that at the end of th/beginning of th century psychology was strongly influenced by physics, classical statistical physics and thermodynamics (in works of james and freud), later by quantum physics (in works of jung). in particular, the leading psychologists of that time have actively operated with the notion of psychic energy [ ] [ ] [ ] [ ] . later psychologists essentially lost interest in the construction of general theories and, in particular, operating with the notion of the social energy. recently, the notion of social energy attracted a lot interest in economics and finance, multi-agent modeling, evolution theory and industrial dynamics [ ] [ ] [ ] . of course, these novel as well as old (freud-jung) studies support our model. however, we emphasize that the application of the quantum (copenhagen) methodology simplifies and clarifies essentially the issue of the social energy. we treat it operationally as an observable on a system, a human being. in contrast to, say, freud, we are not interested in psychic and neurophysiological processes of generation of psychic energy (see appendix a for a brief discussion). the basic component of social laser is a gain medium, an ensemble of people. as already mentioned, to initiate lasing, such a gain medium should consist of indistinguishable people, i.e., without tribe, without cultural, national, religious, and ideally sex differences. such beings are called social atoms. (it is not clear whether they still can be called humans). of course, people still have aforementioned characteristics, in some contexts they remember that they are men or women, or even christian, or swedish. we discuss contexts in which people behave as indistinguishable, as social atoms. creation of such behavioral contexts is the first step towards initiation of social lasing. we recall that in quantum physics the electromagnetic field is treated as a carrier of interactions. in the quantum framework, interaction cannot be represented as it was done classically, by force-functions. quantum interaction is of the information nature. in quantum information theory, excitations of the quantum electromagnetic field, photons, are carriers of information. at the same time, each excitation also carries a quantum of energy. this quantum picture is very useful for general modeling of information fields generated by mass media and the internet. communications emitted by newspapers, journals, tv, social networks, and blogs are modeled as excitations of a quantum information field, as quanta of information and social energy. as we know, the quantum description is operational; this is only the mathematical symbolism used for prediction of probabilities. even the quantum electromagnetic field cannot be imagined as a "real wave" propagating in spacetime. (in the formalism, this is a distribution, generalized function, with operator values. hence, this is a very abstract mathematical structure. it is useful for accounting for the numbers of energy quanta and description of the processes of their emission and absorption.) on one hand, this impossibility of visualization is a disadvantage of the quantum description compared to the classical one (we remark that the visualization of the classical electromagnetic field is also not as straightforward as might be imagined. the electromagnetic waves were invented as the waves propagating in the special media, the aether, similarly to acoustic wave propagating in air. later, einstein removed aether from physics. the picture of a vibrating medium became inapplicable. therefore, electromagnetic waves are vibrations of a vacuum. this is not so natural picture for the visualization of this process.). on the other hand, this is a great advantage, since it provides the possibility for generalizations having no connection with physical spacetime. thus, we model the information field as a quantum field with communications (generated, e.g., by mass media) as quanta carrying social energy and some additional characteristics related to communication content. as was already emphasized, quantum description is applicable to fields with indistinguishable excitations, where indistinguishability is considered to observable characteristics. in addition, "observable" means those characteristics that people assign to communications. these are labels of communications, say "terrorism", "war in syria", "coronavirus" and so on. such labels we shall call quasi-colors of information excitations, these are analogs of photon wave vector and polarization. thus, each communication is endowed with a quasi-color. it also carries a quantum of energy; its value we consider as communication color. thus, allegorically we can speak about red, blue, or violet information. content ignorance (up to communication quasi-color and color) is the crucial feature of the applicability of the quantum formalism. why do social atoms compress contents of communications to quasi-colors? the most important is information overload. the information flows generated by mass media and the internet are so powerful that people are not able to analyze communication content deeply, they just scan its quasi-color and absorb a quantum of the social energy carried by this communication. they simply do not have computational and time resources for such an analysis. it is also crucial that people lose their identity, so they become social atoms. for a social atom, there are no reasons, say cultural or religious, to analyze news; he is fine with just absorption of labels (quasi-color) and social energy (color) assigned to them. consider for simplicity social atoms with just two energy levels, excited and relaxed, e and e . the difference between these levels, is the basic parameter of a social atom, its color. a social atom reacts only to a communication carrying energy e c matching his color: if a communication carries too high-energy charge, e c larger than e a ("a social atom is yellow, but a communication is blue"), then an atom would not be able to absorb it. say a communication carrying social energy e c is a call for an uprising against the government. in addition, an atom is a bank clerk in moscow, who has liberal views and hates the regime, but the energy of his excited state is too small to react to this call. if e c is less than e a ("an atom is blue, but a communication is yellow"), then an atom would not be excited by this communication. the communication would be simply ignored. as well as a physical atom, a social atom cannot collect social energy continuously from communications carrying small portions of energy (compared to e a = e − e ), it either absorbs communication (if the colors of an atom and communication match each other) or it does not pay attention to it. in the same way, a social atom cannot "eat" just a portion of energy carried by too highly charged communication. in physics textbooks, the condition of absorption of energy quantum by atom is written as the precise equality: however, precise equalities are only mathematical idealizations of the real situation. the photon-absorption condition ( ) is satisfied only approximately: the spectral line broadening is always present. the difference between the energies of atom levels is the mean value (average) of the gaussian distribution, a bell centered at this point of the energy axis. the dispersion of the gaussian distribution depends on an ensemble of atoms. ensembles with small dispersion are better as gain mediums for lasing, but deviations from exact law ( ) are possible. it is natural to assume gaussian distribution realization of exact laws even for social systems; in particular, absorption of of excitations of the quantum information field by social atoms. thus, deviations from ( ) are possible. however, a good human gain medium should be energetic homogeneous. therefore, the corresponding gaussian distribution should have very small dispersion. shock news, say a catastrophe, war, killed people, epidemic, terror attack, is very good for energy pumping to a social gain medium. the modern west is characterized by the high degree of excitation, the energy e of the excited level is sufficiently high-otherwise one would not be able to survive: life in the megalopolis, long distances, high intensity of the working day, and so on. on the other hand, the energy e of the relaxation level is very low-one who is living on state support, say, in sweden, has practically zero excitement, often his state is depressive. hence, e a = e − e is high and a social atom would absorb only communications carrying very high energy: as in aforementioned shock news or say in tv shows, people should cry loudly, express highly emotional psychic states. since e a is high (blue), people would not pay attention to plain news (say red colored). even scientific news attracts attention only if it is very energetic, carries big emotional charge (blue or, even better, violet). however, shock news is very good for energy pumping not only because it carries a high charge of social energy, but also because it is very good at peeling communications from content. labels (quasi-colors) such as "coronavirus is a bio-weapon" leads to immediate absorption of communications, and social atoms react immediately to the instinctive feeling of danger. in our quantum-like model (similarly to physical atoms), social atoms can both absorb and emit quanta of the social energy. as in physics, there are two types of emission-spontaneous and stimulated. the spontaneous emission happens without external interaction, a social atom spontaneously emits a quantum of social energy, in the form of some social action. such spontaneous actions are not coherent, different atoms do different things, quasi-colors of social energy quanta emitted spontaneously can be totally different. such emissions generate a social noise in a human media, noise that is unwanted in social lasing. in particular, spontaneous emission noise disturbs functioning of internet echo chambers. on the other hand, the emission of quanta of social energy can be stimulated by excitations of the information field. in the very simplified picture, it looks like this. an excited social atom by interacting with an information excitation emits (with some probability) quantum of social energy. the most important feature of this process is that the quasi-color of the emitted quantum coincides with the quasi-color of stimulating communication. this is the root of the coherence in output beam of lasers, both social and physical. (the colors also coincide; see section . ). in reality, the process of stimulated emission is more complicated. it is important that the information field (similarly to the quantum electromagnetic field) satisfies bose-einstein statistics. this is a thermodynamic consequence [ ] of indistinguishability of excitations: two excitations with the same social energy and quasi-color are indistinguishable. as was shown in [ ] , by using the gibbs' approach based on consideration of virtual ensembles of indistinguishable systems (or any origin) we obtain the standard quantum classification of possible statistics, bose-einstein, fermi-dirac, and parastatistics. indistinguishability is up to energy (for the fixed quasi-color). hence, by taking into account that the number of communications carrying the same charge of social energy can be arbitrary, we derive the bose-einstein statistics for the quantum information field (see [ ] for derivation's details). interaction of atomic-like structures with bosonic fields are characterized by the following property: probability of stimulated emission from an atom increases very quickly with increasing of the power of a bosonic field. an excited social atom reacts rather weakly to the presence of a few information excitations. however, if they are many, then it cannot stay indifferent. in fact, this is just a socio-physical expression of the well-known bandwagon effect in humans' behavior [ ] . in contrast to psychology, we can provide the mathematical field-theoretical model for such an effect. we consider the fixed energy (frequency) mode of the quantum electromagnetic field. for fixed quasi-color mode α, n-photon state |n, α , can be represented in the form of the action of the photon creation operator a α corresponding to this mode on the vacuum state | : this representation gives the possibility to find that the transition probability amplitude from the state |n, α to the state |n + , α equals to (n + ). on the other hand, it is well known that the reverse process of absorption characterized by the transition probability amplitude from the state |n, α to the state |(n − ), α equals to √ n . generally, for a quantum bosonic field increasing the number of its quanta leads to increasing the probability of generation of one more quantum in the same state. this constitutes one of the basic quantum advantages of laser-stimulated emission showing that the emission of a coherent photon is more probable than the absorption. since, as shown in [ ] , indistinguishability, up to energy (color) and quasi-color, of information excitations leads to the bose-einstein statistics, we can use the quantum operational calculus for bosonic fields even for the quantum information field and formalize in this way the bandwagon effect in psychology [ ] . this is the good place to recall that in our considerations the notion "social action" is treated very widely, from a purely information action, as posting a communication at facebook or commenting one of already posted communications, to a real physical action, as participating in a demonstration against putin or trump, or supporting government's policy on "self-isolation". the previous works on social laser [ ] [ ] [ ] [ ] emphasized external representation of social actions, say in the well-known color revolutions. in this paper, we are more interested in their representation in information spaces, e.g., spaces of social networks. however, we are even more interested in internal representation of some social actions as decision makings. in addition, a decision can have different forms, not only "to do"-decisions, but also "not to do"-decisions. the decisions of the latter type also consume energy and social atoms transit from the excited state to the relaxed one. it is also important to point to the unconscious character of many (or may be majority) of our decisions. for example, people can support (or not support) societal policies totally unconsciously. to make such decisions, they consume social energy. mass media and internet pump social energy into a gain medium composed of social atoms to approach the population inversion-to transfer most atoms into excited states. then a bunch of communications of the same quasi-color and energy (color) matching with the resonant energy of social atoms is injected in the gain medium. in the simplified picture, each communication stimulates a social atom to emit a quantum of social energy with the same quasi-color as its stimulator. resulting two excitations stimulate two social atoms to emit two quanta, the latter two quanta generate four and so on, after say steps there are , approximately one million of information excitations of the same (quasi-)color. in reality, the process is probabilistic: an atom reacts to stimulating information excitation only with some probability. the later increases rapidly with increasing of the density of the quantum information field. now, we discuss the basic counterparts of social lasing in more detail: • each information communication carries a quantum of social energy. the corresponding mathematical model is of the quantum field type, the information field. quanta of social energy are its excitations. each social atom is characterized by the social energy spectrum; in the simplest case of two levels, this is the difference between the energies of the excitation and relaxation states, besides of social energy, the excitations of the information field are characterized by other labels, quasi-colors. coherence corresponds to social color sharpness; ideal social laser emits a single mode of quasi-color, denoted say by the symbol α. humans in the excited state interacting with α-colored excitations of the information field also emit α-colored excitations. the amount of the social energy carried by communications stimulating lasing should match with resonance energy e a of social atoms in the human gain medium. to approach the population inversion, the social energy is pumped into the gain medium. this energy pumping is generated by the mass media and the internet sources. the gain medium should be homogeneous with respect to the social energy spectrum. in the ideal case, all social atoms in the gain medium should have the same spectrum, e a . however, in reality, it is impossible to create such a human gain medium. as in physics, the spectral line broadening must be taken into account. for example, a gain medium consisting of humans in the excited state and stimulated by the anti-corruption colored information field would "radiate" a wave of anti-corruption protests. the same gain medium stimulated by an information field carrying another social color would generate the wave of actions corresponding this last color. the general theory of resonators for social lasers is presented in [ ] . here we shall consider in more detail special, but at the same very important type of social resonators, namely internet-based echo chambers. we recall that an echo chamber is a system in that some ideas and behavioral patterns are amplified and sharped through their feedback propagation inside this system. in parallel to such amplification, communications carrying (as quasi-color) ideas and behavioral patterns different from those determined by the concrete echo chamber are suppressed. in our terms, an echo chamber is a device for transmission and reflection of excitations of the quantum information field. its main purpose is amplification of this field and increasing its coherence via distilling from "social noise". the latter function will be discussed later in more detail. the echo chamber is also characterized by the resonance social energy e a of its social atoms. for simplicity, it is assumed that all social atoms have the same resonance energy e a . (in reality, resonance energy of social atoms is a gaussian random variable with mean value e a .) we underline that in this paper an echo chamber is considered to be a component of the social laser, its resonator. compared to physics we can say that this is an analog of an optical cavity of the physical laser, not optical cavity by itself. the coherent output of an echo chamber, the quasi-color of this output, is determined not only by the internal characteristics of the echo chamber, but also by the quasi-color of stimulating emission. let us consider functioning of some internet-based echo chamber; for example, one that is based on some social group in facebook (or its russian version "vkontakte") and composed of social atoms. the degree of their indistinguishability can vary depending on the concrete echo chamber. say, names are still present in facebook, but they have some meaning only for the restricted circle of friends; in instagram or snapchat, even names disappear and social atoms operate just with nicknames. by a social group we understand some sub-network of say facebook, for example, social group "quantum physics". the main feature of a social group is that all posts and comments are visible for all members of this social group. thus, if one from the group puts a post, then it would be visible for all members of this social group, and they would be able to put their own comments or posts related to my initiation post. this is simplification of the general structure of posting in facebook, with constraints that are set by clustering into "friends" and "followers". we assume that the ensemble of social atoms of this echo chamber approached population inversion, so most of them are already excited. a bunch of communications of the same quasi-color α and carrying quanta of social energy e c = e a is injected in the echo chamber. excited social atoms interact with the stimulating communications and emit (with some probability) information excitations of the same quasi-color as the injected stimulators. these emitted quanta of social energy are represented in the form of new posts in echo chamber's social group. each post plays the role of a mirror, it reflects the information excitation that has generated this post. however, the analogy with the optics is not straightforward. in classical optics, each light ray is reflected by a mirror again as one ray. in quantum optics, each photon reflected by a mirror is again just one photon. an ideal mirror reflects all photons (the real one absorbs some of them). in contrast, "the mirror of an echo chamber", the information mirror, is a multiplier. a physical analog of such a multiplier mirror would work in the following way. each light ray is reflected as a bunch of rays or in the quantum picture (matching better the situation), each photon by interacting with such a mirror generates a bunch of photons. of course, the usual physical mirror cannot reflect more photons than the number of incoming ones, due to the energy conservation law. hence, the discussed device is hypothetical. this is a good place to remark that as mentioned, a photon should not be imagined as a metal ball reflecting from mirror's surface. a photon interacts with the macro-system, the mirror, and the latter emits a new photon that is identical to the incoming one, up to the direction of spatial propagation. it seems to be possible to create a kind of a mirror with the complex internal structure (composed of special materials) such that it would generate emission of a bunch of photons. of course, such a multiplier mirror cannot function without the energy supply. the internet-based system of posting news and communications works as a multiplier mirror. each posted news or communication emits a bunch of "information rays" directed to all possible receivers-the social atoms of echo chamber's social group. in the quantum model, each post works as an information analog of photon's emitter. it emits quanta of social energy; the power of the information field increases. consequently, excited social atoms emit their own posts and comments with higher probability. we repeat that new posts have the same quasi-color as the initiating information excitations that were injected in the echo chamber. it is also important to remind that the process of stimulated emission is probabilistic. members of the social group would react to newly posted message only with some probability. in addition, resulting from the bosonic nature of the quantum information field, this probability increases rapidly with increasing of field's power. by reaction we understood emission of a new message, say a comment. if a social atom simply reads a posted communication, but does not emit its own information excitation, then we do not consider such reading as a reaction. for the moment, we consider only the process of stimulated emission. later we shall consider absorption as well. in the latter, reaction means transition from the ground state to the excited state; so, not simply reading. (in principle, a relaxed atom can read a post or a comment without absorbing a quantum of social energy sufficient for approaching the state of excitement.) the crucial difference from physics is an apparent violation of the energy conservation law (see appendix a for the discussion on this question). each post in a social group works as a social energy multiplier. thus, information excitations in the echo chamber generated by posted communications not only increase the probability of emission of new information excitations by excited atoms, but they also perform the function of additional energy pumping into the gain medium (social group). relaxed social atoms can absorb social energy not only from externally pumped messages from mass media, tv and other social networks, but even from their own echo chamber. then they also emit new posts and so on. the main distinguishing feature of the quantum information field is its bosonic nature. we now emphasize the impact of the bosonic structure to coherence of the information field inside of an echo chamber. as was already noted (section . ), the interaction of a social atom with the surrounding bosonic field depends crucially on the power of this field, the probability of emission of energy quantum by an excited social atom increases very quickly with increasing of field's power. now, we stress again that a social atom (as well as a physical atom) distinguishes the modes of the field corresponding to different quasi-colors. the probability of emission of a quantum of the fixed quasi-color α depends on the power of the field's mode colored by α. thus, if the power of the α-mode essentially higher than the power of the mode colored by β, then with very high probability social atoms would emit α-colored energy quanta (in the form of posts, comments, and videos). social atoms would ignore the β-colored energy quanta, the probability of emission of such quantum (and hence the increase of the power of the β-mode) is practically zero. if a social atom emits a communication, colored by β, then this information excitation would not attract attention of social atoms who are busy with communications colored by α. as was already emphasized, the crucial role is played by indistinguishability, up to the quasi-colors, of the excitations of the information field. social atoms should process information in the regime of label scanning, without analyzing its content. as was discussed, the easiest way to establish the indistinguishability regime of information processing is to generate an information overload in the gain medium composed of social atoms. of course, the loss of individuality by social atoms is also very important, people "without tribe" are better accommodated to perceive information in the label-scanning regime. in this regime, one would never absorb the main information of the β-labeled communication, say statistical data. in this section, we considered the quantum-like nature of coherence of the information waves generated in echo chambers. this indistinguishability of information excitations, the label-scanning regime. the information overload and the loss of individuality by social atoms are the main socio-psychological factors leading to this regime. in following sections . and . , we consider supplementary factors increasing information field's coherence. now, we connect a social resonator, e.g., in the form of an internet-based echo chamber, to the social laser device described in section . as the result of the feedback processing of information in the echo chamber, the power and coherence of the information field increases enormously. one of the ways to consume the huge energy of this information field is to realize it in the form of physical social actions, mass protests, e.g., demonstrations or even a wave of violence. this is the main mechanism of color revolutions and other social tsunamis [ ] [ ] [ ] [ ] . however, in this paper we are more interested in the purely information consumption of the social energy of the coherent information field prepared in an echo chamber, namely for internal decision-making. decision-making on a question that important for society is also a social action; in particular, it consumes social energy. now, suppose that say a government needs some coherent and rational (from its viewpoint) decision on some question. it can use a powerful social laser. this is a good place to remark that an ensemble of echo chambers can be used coherently with stimulation by the same quasi-color α corresponding to the desired decision. by emitting the information excitation, a social atom confirms his-her support of the α-decision. such social action is realized in the mental space of social atoms, but, of course, it has consequences even for associated actions in the physical space. if the wave in the information space generated by a powerful social laser can approach the steady state, then social atoms live in the regime of the repeated confirmation of the internal α-decision: an atom emits and relaxes, then he/she again absorbs another α-excitation and moves to the state of excitement and so on. in this situation of surrounding by the information field of huge power concentrated on the same α-mode, the colors of the energy pumping and stimulated emission coincide. such repeating of the same α-decision is similar to concentration on the idea-fix and can lead to the state of psychosis and panic (see freud [ ] ). as in physical lasing, the above ideal scheme is complicated by a few factors related to losses of social energy in the echo chamber. as is known, not all photons are reflected by mirrors of the optical cavity, a part of them is absorbed by the mirrors. the coefficient of reflection plays the fundamental role. the same problem arises in social lasing. an essential part of posts is absorbed by the information mirror of the echo chamber: for some posts, the probability that they would be read by members of the social group is practically zero. additional (essential) loss of social energy is resulted from getting rid of communications carrying quasi-colors different from the quasi-color α of the bunch of the communications initiating the feedback dynamics in the echo chamber. such communications are generated by spontaneous emission of atoms in the social group. the real model is even more complex. the information mirror is not homogeneous, "areas of its surface" differ by the degree of readability and reaction. the areas can be either rigidly incorporated in the structure of the social group or be formed in the process of its functioning. for example, "quantum physics" group has a few layers that are rigidly incorporated in its structure. one of them is "foundations and interpretations". this sublayer of the information mirror "quantum physics" has rather low visibility, due to a variety of reasons. once, i posted in "quantum physics" a discussion on quantum information and quantum nonlocality. in addition, i discovered that the social group moderators control rigidly the layer structure. the message that my post should be immediately moved to this very special area of the information mirror, "foundations and interpretations", approached me in a few minutes. it looks that even in such a politically neutral social group moderators work in the online regime. as an example of functionally created information layers, we can point to ones which are coupled to the names of some members of the social group, say "area" related to the posts of a nobel prize laureate has a high degree of readability and reaction. however, of course, one need not be such a big name to approach a high level of readability and reaction. for example, even in science the strategy of active following to the main stream speculations can have a very good effect. top bloggers and youtubers create areas of the information mirror with high coefficients of reflection-multiplication (see below ( )) through collecting subscriptions to their blogs and youtube channels. it is clear that the probability of readability and reaction to a post depends heavily on the area of its location in the information space of a social group or generally facebook, youtube, or instagram. the reflection-multiplication coefficient of the information mirror varies essentially. consider first the physical mirror and photons reflected by it. from the very beginning, it is convenient to consider an inhomogeneous mirror with the reflection coefficient depending on mirror's layers. suppose that k-photons are emitted to area x and n of them were reflected, i.e., (k − n) were absorbed. then the probability of reflection by this area p(x) ≈ n/k, for large k. now, for the information mirror, consider a sequence of posts, j = , , ..., k, that were put in its area x. let n j denotes the number of group's members who reacts to post j. each n j varies between and n, where n is the total number of group's members. then coefficient of reflection-multiplication p(x) ≈ ( k ∑ j n j )/kn, for large k, n. if practically all posts generate reactions of practically all members of the group, then n j ≈ n and p(x) ≈ . we have already discussed in detail the multilayer structure of the information mirror of an echo chamber. this is one of the basic information structures giving the possibility to generate inside it the information field of the very high degree of coherence: a very big wave of information excitations of the same quasi-color, the quasi-color of stimulating communications. it is sufficient to stimulate atoms with the potential of posting in the areas of the information surface with the high coefficients of reflection-multiplication. these areas would generate a huge information wave directed to the rest of the social group. spontaneously emitted communications would be directed to areas with the low coefficients of reflection-multiplication. how is this process directed by the internet engines? it is described by the model of the dynamical evaluation of the readability history of a post. we shall turn to this model in section . . although the dynamical evaluation plays the crucial role in generating the coherent information waves, one has not to ignore the impact of straightforward filtering. we again use the analogy with physics. in the process of lasing, the dynamical feedback process in the cavity excludes the excitation of the electromagnetic field propagating in the wrong directions. in this way, laser generates the sharply directed beam of light. however, one may want some additional specification for excitations in the light beam. for example, one wants that all photons would be of the same polarization. it can be easily done by putting the additional filter, the polarization filter that eliminates from the beam all photons with "wrong polarization". of course, the use of an additional filter would weaker the power of the output beam. the latter is the price for coherence increasing. in social lasing, the role of such polarization filters is played by say google, facebook, instagram, or yandex control filtering, e.g., with respect to the political correctness constraints. besides numerous moderators, this filtering system uses the keywords search engines as well as the rigid system of "self-control". in the latter, users report on "wrongly colored posts and comments" of each other; the reports are directed both to the provider and to social groups-to attract the attention to such posts and comments. the dynamical evaluation system used, e.g., by youtube, increases post's visibility based on its reading history, more readings imply higher visibility (at least theoretically). however, the multilayer structure of the information mirror of youtube should also be taken into account. the main internet platforms assign high visibility to biggest actors of the mass media, say bbc, euronews, rt, that started to use actively these platforms. then, and this is may be even more important, these internet platforms assigns high visibility to the most popular topics, say presently the coronavirus epidemic, videos, posts, and comments carrying this quasi-color are elevated automatically in the information mirrors of google, youtube, or yandex. of course, the real evaluation system of the main internet actors is more complicated and the aforementioned dynamical evaluation system is only one of its components, may be very important. we would never get the answer to the question so widely discussed in communities of bloggers and youtubers: how are the claims on unfair policy of internet platforms justified? by unfair policy they understand assigning additional readings and likes to some internet communications or withdraw some of them from other communications. (i can only appeal to my own rather unusual experience from the science field. once, i was a guest editor of a special issue (so a collection of papers about some topic). in particular, my own paper was published in the same issue. this is the open-access journal of v top ranking, a part of nature publishing group. presently, all open-access journals qualify papers by the number of downloads and readings. (therefore, this is a kind of youtubing of science.) my paper was rather highly estimated in these numbers. however, suddenly i got email from the editors that since i put so much efforts to prepare this issue, i shall get as a gift an additional downloads. of course, i was surprised, but i did not act in any way and really received this virtual gift... after this event, i am very suspicious of numbers of downloads and readings that i can see in the various internet systems. if such unfair behavior is possible even in science, then one can suspect that it is really not unusual.) starting with presentation of the basics of social lasing, we concentrated on functioning of one of the most important kinds of social resonators, namely internet-based echo chambers. we analyzed similarities and dissimilarities of optical and information mirrors. the main distinguishing feature of the latter is its ability not only reflect excitations of the quantum information field, but also multiply them in number. the coefficient of reflection-multiplication is the basic characteristic of the information mirror. we point to the layer structure of the information mirror of an echo chamber; the coefficient of reflection-multiplication varies depending on mirror's layer. we emphasized the bosonic nature of the quantum information field. this is a straightforward thermodynamic consequence [ ] of indistinguishability of information excitations, up their quasi-colors. being bosonic, the information field increases tremendously the speed and coherence of stimulated emission of information excitations by excited social atoms. social atoms, "creatures without tribe", form the gain medium of a social laser. in contrast to quantum physics, we cannot treat real humans as totally indistinguishable. this is a good place to remind once again that our social lasing as well as generally decision-making modeling is quantum-like. quantum features are satisfied only approximately. this point is often missed in the presentation of "quantum models" for cognition and decision-making. in sections . and . , we discuss some technicalities related to functioning of internet-based social groups and generally google and youtube. this discussion plays only a supplementary role for this paper. it would be fruitful to continue it and especially to discuss exploring of the quantum-like features of users and information supplied to them by the internet (cf., for example, with studies on quantum-like modeling of information retrieval [ ] [ ] [ ] [ ] [ ] [ ] ). in appendix a, we discussed very briefly interrelation between the psychic energy and the physical energy of cells' metabolism. it is very important to continue this study in cooperation with psychologists and neurophysiologists. the main output of this paper is description of the mechanism of generation of big waves of coherent information carrying huge social energy, a kind of information tsunamis. we especially emphasize listing of the basic conditions on human gain media and the information field generated by mass media and amplified in echo chambers leading to successful generation of such waves. the author recognizes very well that this study is still one of the first steps toward well elaborated theory. motion) interpretation of quantum mechanics [ ] , whereas quite different from other interpretations, such as the many-world interpretation [ , ] and the wise (wave function is the system entity) interpretation [ ] . it should be also pointed out that in recent years, some physics-based social or network models have been studied [ , ] . some new intersection of quantum and operational research are emerging, such as quantum machine learning [ , ] . towards information lasers social laser: action amplification by stimulated emission of social energy social laser model: from color revolutions to brexit and election of donald trump on interpretational questions for quantum-like modeling of social lasing concept of information laser: from quantum theory to behavioural dynamics phase transitions, collective emotions and decision-making problem in heterogeneous social systems information dynamics in cognitive, psychological, social, and anomalous phenomena; series: fundamental theories of physics ubiquitous quantum structure: from psychology to finances quantum models of cognition and decision quantum concepts in the social classical and quantum mechanics on information spaces with applications to cognitive, psychological, social and anomalous phenomena. found. phys on quantum-like probabilistic structure of mental information pilot-wave theory and financial option pricing quantum dynamics of human decision making a quantum probability explanation for violations of 'rational' decision theory a quantum theoretical explanation for probability judgment errors decision theory with prospect interference and entanglement mathematical structure of quantum decision theory quantum-like model of behavioral response computation using neural oscillators a quantum probability explanation in fock space for borderline contradictions an operator-like description of love affairs can quantum probability provide a new direction for cognitive modeling? context effects produced by question orders reveal quantum nature of human judgments are quantum-mechanical-like models possible, or necessary, outside quantum physics? the visualizable, the representable and the inconceivable: realist and non-realist mathematical models in physics and beyond the role of information in a two-traders market conjunction and negation of natural concepts: a quantum-theoretic modeling a generalized probability framework to model economic agents' decisions under uncertainty quantum dynamics applied to cognition: a consideration of available options new fundamental evidence of non-classical structure in the combination of natural concepts the emperor's new mind quantum coherence in microtubules. a neural basis for emergent consciousness? brain and physics of many-body problems dissipation and memory capacity in the quantum brain model my double unveiled: the dissipative quantum model of brain enough! electoral fraud, collective action problems, and post-communist coloured revolutions why it's kicking off everywhere: the new global revolutions the color revolutions mistrust we trust: can democracy survive when we don't trust our leaders? the new digital age: reshaping the future of people why did people vote for brexit? deep-seated grievances lie behind this vote why did people vote for donald trump? voters explain; the guardian the science of structure: synergetics synergetics: an introduction-nonequilibrium phase transitions and self-organisation in physics laser light dynamics lasers and synergetics. a colloquium on coherence and self-organization in nature subjective probability: a judgment of representativeness prospect theory: an analysis of decision under risk critique des postulats et axiomes de l' cole amricaine risk, ambiguity, and the savage axioms ambiguity, and the dark-dependence axioms the geometry of information retrieval what is quantum information retrieval? how quantum theory is developing the field of information retrieval? supporting polyrepresentation in a quantum-inspired geometrical retrieval framework introduction to information retrieval and quantum mechanics deriving a quantum information retrieval basis the principles of psychology the standard edition of complete psychological works of sigmund freud on the nature of the psyche atom and archetype: the pauli/jung letters - competition between collective and individual dynamics from the financial crisis to sustainability? potsdam, european climate forum. available online: www.europeanclimate-forum.net/index.php?id=ecfreports interaction ritual chains oxford dictionary of psychology interpreting quantum mechanics in terms of random discontinuous motion of particles relative state" formulation of quantum mechanics many-worlds interpretation of quantum mechanics general quantum interference principle and duality computer modeling viral diffusion using quantum computational network simulation mechanics-an endless frontier quantum machine learning recent advances in quantum machine learning. quant. eng. , , e . [crossref] c by the author funding: this research received no external funding. the authors declare no conflict of interest. above we wrote about an "apparent violation" of the law of conservation of the social energy. we briefly discuss this point. the social energy is the special form of the psychic energy. hence, by discussing the conservation law we cannot restrict consideration solely to the social energy. the detailed analysis of transformation of different forms of the psychic energy and its origin in neurophysiological processes and finally the physical energy generated by cells' metabolism was presented by freud [ ] . we do not plan to discuss here the freud's hydrodynamical model for psychic energy transformations. we want to elevate the crucial difference of the energy transfer from the information field to social atoms from the energy transfer from the electromagnetic field to physical atoms. in physics, energy is assigned to photons carriers of information, an atom by absorbing a photon receives its energy. in our social model, an excitation of the information field just carries the social energy label e c . a social atom absorbs this label and generate the corresponding portion of energy by itself, by transforming its psychical energy into the social energy. in addition, the former is generated by neurophysiological activity in the brain and the nervous system from the physical metabolic energy. thus, by taking into account the psychic energy, we understand that even for cognitive systems the law of energy conservation is not violated. we remark that development of the social laser model has also some relevance to the interpretations of quantum mechanics. in this model, the quantum nature is apparent, because the smallest unit in a society is a human person. this is quite like the rdm (random discontinuous key: cord- -jspfwuqu authors: farangi, mostafa; asl soleimani, ebrahim; zahedifar, mostafa; amiri, omid; poursafar, jafar title: the environmental and economic analysis of grid-connected photovoltaic power systems with silicon solar panels, in accord with the new energy policy in iran date: - - journal: energy (oxf) doi: . /j.energy. . sha: doc_id: cord_uid: jspfwuqu in recent years, authorities in iran have introduced supporting policies for renewable energy resources but there is no comprehensive and updated survey from this perspective. this work aims to give a comprehensive survey on the country’s background from energy outlook and its prominent policies for renewable energy resources. due to the high co( ) emissions alongside with the high solar energy harvesting potential in iran, we have presented a clear simulation on kw and mw grid-connected photovoltaic (pv) power plants using retscreen software to determine the environmental and economic aspects based on the net greenhouse gases (ghg) emissions reduction, the annual electricity exported to the grid, the cumulative cash flows, and the payback period for the initial investment. according to this simulation, the annual ghg emissions reduction and the annual electricity exported to the grid for kw and mw pv power plants are . tco( ), tco( ), mwh, and mwh, respectively. from the economic outlook, based on the new feed-in tariff for power plants and the supposed initial costs, the payback period for the initial investments are between and , and years for kw and mw pv power plants, respectively. farangi and ebrahim asl soleimani conceived of the presented idea. farangi developed the theory and performed the computations. mostafa zahedifar, omid amiri and jafar poursafar verified the analytical methods. all authors discussed the results and contributed to the final manuscript. introduction worldwide primary energy demand increased at a rate of . % in , nearly double its -year average of . % from to , which is the highest rate since [ ] . due to this increasing demand for energy and burning of more fossil fuels, global warming has become one of the greatest consequential dilemmas facing the human being with considerable social, environmental and economic outcomes. there are three outstanding ethical dilemmas, making difficult the climate change discussions: how to settle the rights and obligation of the developed and developing countries; how to estimate geo-engineering schemes planned to slow or reverse climate change; and how to test our obligation to next generations who must struggle with an inferior climate we are changing today. in recent years, public awareness, the number of communities, national and international meetings about global warming have raised around the world. as prominent examples of international meetings, we can mention the paris agreement [ ] and the kyoto protocol [ ] as the two most important conventions by the united nations on climate change. at the same time, worldwide carbon emissions from energy consumption increased by . % in , again the highest rate for seven years, with emissions raising by around . gigatonnes. to a significant extent, the increase in carbon emissions is clearly a direct outcome of the growth in energy consumption [ ] . due to the important role of coal in carbon dioxide (co ) emissions, in , more countries obligated to phasing out or moving away from the coal consumption for electricity production (e.g., canada, france, etc.) [ , ] or do not more funding coal utilization (e.g., brazil's development bank) [ ] . opposing this trend, but several countries declared programs to increase coal production and utilization [ ] . however in there was a significant move back to coal with both production ( . %) and consumption ( . %) [ ] . in large number of countries, the emission quotas referring to each power company are limited. with the emission trading pattern they can determine the most preferred solution after achieving the pareto solution set regarding different emission quotas. this technique is economically useful for countries with this ability [ ] . the emission trading approach can be employed as a useful pattern by the power companies to maximize their profitability [ ] . comparatively low worldwide prices for coal, natural gas and oil, keep challenging renewable energy markets, particularly in the heating and transport sectors [ , ] . subsidies for fossil fuels, which stayed remarkably greater than renewable energy subsidies, also continued to influence renewable energy development. in over countries had obligated to phasing out subsidies for fossil fuels due to international commitments [ ] . also, subsidy revises were instituted in in several countries such as brazil, egypt, india, iran, nigeria, saudi arabia, sierra leone, thailand, tunisia, ukraine, venezuela [ ] . in the energy sector, the world needs novel trends that are secure, sustainable and favorable to all, and one of the most beneficial procedures is the utilization of sustainable energy resources instead of fossil fuels. the progression and consumption of sustainable energy resources are a fundamental alternative to climate change and global energy demand. utilization of sustainable, reliable and inexpensive energy will determine most standard aspects of life, in the future. as of , many countries directly provided renewable energy development and deployment with a broad range of policies. these policies prepare direct and indirect support, in an effort to economy-wide economic progression, environmental conservation, and national security. technology developments, descending costs and growing utilization of renewable energy resources are the results of these policies. in each country, authorities promote policies to merge renewable generation into their conventional national energy systems. due to the power sector is keeping to gain the most attention in energy subject, policymakers have introduced various support procedures and reformed existing policies to improve this sector by the utilization of renewable energy resources. these policies can be listed as follows: feed-in tariff (fit) policy is an energy-supply policy concentrated on supporting the progress of renewable energy plans by proposing long period purchase arrangements for the sale of renewable energy electricity. these arrangements propose purchasing every kilowatt-hour electricity for - years. the proposed payment levels for each kilowatt-hour can be distinguished by various factors such as project size, resource quality, technology type, and project location to properly cover main project costs. policymakers can also arrange the payment levels to decrease for installations in the following years, which will both follow and encourage changes in technology. the two most ordinary fit policies are the fixed fit and the feed-in premium. in the fixed fit, which is the most widely used fit design, payment quantity stays independent of the market price for electricity, proposing a guaranteed payment for a clearly described period. in the feed-in premium, which is being increasingly used, the payment quantity is based on a premium proposed above the market price for electricity and this premium can either vary, dependent upon a sliding scale, or it can be constant. several countries, especially in europe and asia, have shifted away from fit policies to auction and tender policies to support large-scale renewable energy project deployment. in spite of the fact that support for large-scale renewable energy projects is changing to a different mechanism in a growing number of countries, but fit policies continue to be valid in many countries for the deployment of small-scale renewable energy installations. policy designers continue to change fit rates as the technologies become more cost-competitive in each country. auctions and tenders are the most rapidly extending scheme of supporting mechanism for deployment of renewable energy projects and are becoming the preferred policy for supporting large-scale projects. generally, they are on the basis of the cost of electricity generation; although in auctions, the price is the only factor to be considered, tenders may contain extra criteria. net metering is a metering and billing agreement designed to compensate small-scale system owners for any electricity production that is exported to the grid. net metering allows utility customers with on-site distributed energy generation to offset the electricity they extract from the utility grid during the billing cycle (e.g., one month) and they pay for the net electricity consumed from the grid. net metering customers directly utilize the electricity produced on-site by their generation systems. if the amount of generation exceeds the utilized electricity, the excess electricity is exported to the utility grid. if a customer utilizes more electricity than distributed energy generation system produces, he or she imports electricity from the utility grid and pays the full retail rate for that amount of electricity, exactly similar to a traditional utility customer. renewable portfolio standard (rps) policy is a regulatory mandate to raise energy generation from renewable resources and it's also called a renewable electricity standard. the rps procedure usually places an obligation on power supply companies to generate a clearly described fraction of their power production from renewable energy resources. besides these main policies, some countries provided public funds by grants, loans or tax incentives to guide investment in renewable energy development. however, most of these incentives have been decreased or canceled in recent years in reaction to tightening fiscal budgets and/or reducing technology costs. although in recent years, policymakers in iran have introduced different supporting policies for renewable energy resources but there is no collective and updated survey from this point of view. this study examines the country background from energy outlook and some of its important policies for energy subject and introduces current supporting policy for various renewable and clean energy resources. due to the serious co emissions and air pollution in large cities of the country alongside with the high solar energy harvesting potential and growing trend of utilization of pv technology in iran, we investigate environmental and economic aspects of two different scales of pv systems, kw as a candidate for small-scale (for residential and commercial users) and mw as a candidate for large-scale (utility-scale) grid-connected pv power systems in tehran, iran, using retscreen software based on the new feed-in tariff policy. country background and energy policy . . iran iran, an asian country, is the th largest and th most populated country in the world. in this territory, population and technology growth has driven to the necessity for more energy production; while electricity production is mainly controlled by its fossil fuel resources. this country has the second-largest proven natural gas reserves ( . trillion cubic meters) and the fourth-largest proven crude oil reserves ( . thousand million barrels) in the world, around % and . % of the world's total reserves, respectively [ , ] . it has an outstanding regional occasion because it is surrounded by several countries which are more opportune for international economic progression due to their vast and various energy resources, tourism market, passenger and freight transportation. this occasion could be managed more appropriately in the energy field with a suitable energy business strategy to accomplish electrical, gas pipeline, and crude oil pipeline loops between neighboring countries and iran [ ] . energy policy however, iran's immense fossil fuel energy resources alongside with subsidization, have resulted in growing consumption of energy without seriously being worried about energy efficiency and the negative influences on the environment. during recent years, it has embarked several policies for production and consumption of energy. four remarkable policies that have affected energy demand, can be mentioned as: i. the first and the most prominent energy policy in iran is the large energy consumption subsidization, particularly in households and transport sectors. there are several distinctive approximations for energy subsidies in iran (between . to percent of gdp); however, it is accepted that iran's energy subsidies are one of the top-ranking energy subsidies in the world. ii. the second policy is assigning of oil production capacity in accord with the opec endorsements. meanwhile, faced with capital restrictions, iran identified the important role of international investment in the oil sector to develop new fields and improve the recovery factor in the existent fields, hence presented a "buy-back" contract to international investors. this contract permitted international companies to finance in oil and gas fields in iran and to share profits with the domestic counterparts. iii. the third prominent energy policy in iran has been the noticeable consumption and progression of natural gas fields from the s so far. this policy reinforced, especially when iran discovered its share of the south pars gas field, the world largest gas reservoir, which is located in the persian gulf. iran has been using most of its ever-growing gas production to replace relatively cheap and environmentally friendly natural gas for domestic consumption of crude oil products in various sectors. in , its energy consumption based on natural gas was . million tonnes of oil equivalent (mtoe) [ ] . iv. the fourth important energy policy in iran is providing rural areas with electricity by new transmission lines. this policy has assisted a lot of rural communities to receive clean and cheap energy and decrease environmental problems like for example deforestation. some other prominent policies in the energy sector in iran can be listed as follows: although high-impact low-probability (hilp) events such as earthquakes, hurricanes, and consequent flooding have prominent influence on power generation companies [ ] and the number of these natural disasters has increased in recent years in iran, but there is not a comprehensive and clear policy for these situations. generally government decides based on the event impact on local people life and, for example, provide them with free fuel and power for a certain period of time. as another example for emergency situation, during covid- crisis in iran the authorities have postponed the payments due for water and power bills in the country. renewable energy policy similar to other countries in the world, there has been a growing trend toward the utilization of sustainable energies in iran, too. besides enormous fossil fuel reserves, iran enjoys a perfect potential of using renewable energies (energy resources that are naturally inexhaustible and replenished) such as solar, wind, geothermal, biomass and hydropower. in iran, electrical customers participate in an electricity market and buy electricity generated from fossil fuels. due to the current levelized cost of electricity (lcoe) prices, production of electric power based on renewable energy resources is not economical on its own yet. therefore, the progression of the renewable energy division in iran is leaned upon the government incentive attitude and its encouraging policy on this subject. from the environmental aspects, noticeable troubles in iran are co emissions and air pollution. in , co emissions in iran were . million tonnes, increased by . % growth rate per annum that is above double its -year average of . % from to [ ] . so recently, the authorities have paid basic investment in harnessing renewable energies and laid down the new supporting policies to inspire people to use clean energy resources. due to the huge investments in hydropower, a large share of renewable power generation in iran is hydroelectricity, around . mtoe in [ ] . although in recent times, it has been financing on others, such as wind and solar power, too. solar energy as a worthwhile renewable energy source has attracted a lot of attention nowadays. living things, including the human being, depend on solar energy for warmth and food. however, the human being also harnesses solar energy in many distinctive ways. they use solar energy either indirectly as the form of fossil fuels, biomass, wind, hydropower, and … or directly by utilization solar thermal technology (using solar energy to generate low-cost, environmentally friendly thermal energy) and pv technology. pv devices or solar cells directly convert energy from the sunlight into electricity by the pv effect quietly, with no pollution or moving parts. a pv system is working differently than most electric-generating systems because it generally doesn't need a technician to be on-site for daily direct management due to its automated operation, and it just needs insignificant and slight oversight, monitoring, and maintenance. these systems are designed modularly and can be built on different scales. fortunately, solar energy is broadly achievable in most areas of iran, specifically in the southern and central regions (fig. ) . this country is potentially one of the best regions for solar energy harvesting because located in the global sunbelt, and experiences three hundred sunny days per year on over two-thirds of its land area, according to satba (renewable energy and energy efficiency organization), the ministry of energy, iran [ ] . the radiation distribution varies between . kwh/m in the southeast part to . kwh/m in central parts. in a country-wide analysis of irradiance, it is estimated that on percent of iran's land area, solar irradiance is between - kwh/m /year [ ] . the calculations show that the applicable solar radiation hours in iran surpasses hours per year [ , ] . according to the reports, by covering only % of the deserts in the country by solar collectors, the output energy would be five times greater than its annual gross electricity output [ , ] . besides iran's solar energy harvesting potential, several factors such as the price of fossil fuels in electricity generation and import of expensive pv instruments have limited applying pv technology in iran. as mentioned above, new supporting policies such as different feed-in tariff and subsidies have been described to stimulate using of renewable energies and turn them to competitive technologies with common electricity production methods based on the burning of fossil fuels. according to the new supporting policy of the government, the latest prices for electricity based on the feed-in tariff by offering long-term contracts to renewable energy resources are shown in table [ ]. the selected currency in this study is the iranian rial (irr) which can be converted to us dollar (usd) easily ( usd ≈ irr). according to table , the government will buy electricity from the producers at two prices: during the first years, the purchasing price is relatively high to investors gain their investment as soon as possible. however, during the second years, the price will be decreased to % of the prime bid for all resources except the wind systems (the price will be calculated according to their capacity factors), and after years the electricity can be sold in energy exchange. so, investments in different renewable and clean energy resources (especially pv technology) with different scales, are fostered by the new feed-in tariff to decrease consumption of fossil fuels in iran. known as turbo-expander or expansion turbine ( . ) ( . ) * the highest level capacity for the wind and solar farms will be determined by the policy of the ministry of energy on renewable and clean energy development policy, which is following up to , mw in a year by the private sector. ** during the second decade, the contract fee will calculate based on the capacity factor. for wind farm with capacity factors ≥ % and ≤ % during the first years, the prime fee will multiply in . and , respectively. for capacity factors between - %, the prime fee will multiply in a number proportionally. regarding the growing trend in using of pv technology around the globe, there is a considerable requirement for relatively simple, and user-friendly software packages, for the designing and performance assessment of pv systems by installers particularly during the prime design phases of a project. this requirement has led to the progress of many pv software packages such as pvwatts, pvsyst, polysun, homer, retscreen, pv jedi with various capabilities for analyzing these power systems. generally, simulation and analyzing of each pv power system include main divisions such as technology and performance analysis, energy systems analysis, environmental analysis, and economic and financial analysis. in this article the simulation has been carried out by applying retscreen, a clean energy management program for energy efficiency, renewable energy and cogeneration project feasibility examination and also ongoing energy performance analysis [ ] . this is an extremely user-friendly software and provides decisionmakers with primary or even meticulous detailed information about the project. one of the main advantages of this software is that it makes the project assessment procedure easier and a great number of projects have been investigated by this software. the investigated case of the pv installation is the grid-connected pv system with easy installation, and in locations with trustworthy grid power, it generally doesn't need the battery equipment for backup power. after installation, these systems do not need extra care and service, do not generate co and air pollution, and they are as quiet as the sun. a schematic diagram of the simulated grid-connected pv power system is shown in fig. . fig. . schematic diagram of a grid-connected pv power system. retscreen software is provided with nasa's satellite-derived meteorological data (developed by nasa' langley research center in collaboration with canmetenergy) for any location and the nasa prediction of worldwide energy resource (power) project. this data set is a helpful option when there is no access to ground-based data or itemized resource maps for the project location; it is calculated from data collected for a -year period starting in july , applying a -degree cell (at mid-latitudes ( °) the cell dimensions is around x km). solar rediation parameters are derived using satellite data of the atmosphere and earth's surface. the other meteorological values are adapted from goddard earth observing system (geos) meteorological analysis by the nasa's global modeling and analysis office (gmao). the selected site for this simulation is mehrabad national airport which its elevation, latitude, and longitude coordinates are m, . ˚ and . ˚ respectively. climate data for this site is gathered from the weather station and nasa database in retscreen ( table ). the capacity factor of pv module (the ratio of the average power produced by the power system over a year to its rated power capacity) is vital for selecting a proper site and solar system, and its quantity is . % for the fixed solar array in tehran [ ] . we used yingli silicon solar pv modules (mono-si-panda-yl c- b) wp with a module efficiency of . % for this simulation. the numbers of pv modules for kw and mw pv power plant are and modules, respectively. according to the pv market in iran, the estimated initial and periodic costs (due to the inverter replacement) for these two systems are shown in table . several factors such as site location, type of pv technology, maintenance and … may affect these estimated prices. kw pv power plant the first case, kw pv power plant, is a candidate for small-scale pv power plants. a small-scale pv system is normally mounted on places like residential or commercial roofs, the ground in backyards, or facade of the building, etc. along with the grid, these systems can take advantage of the battery equipment for backup power during a power outage, or while the sun is not shining. however, this advantage comes with intensified complexity, price, and maintenance. hence, in locations with trustworthy grid power, ignoring the battery backup system is the logical choice. table . equivalent cases substitute for kw pv power plant based on net annual ghg emissions reduction in iran. cars & light trucks not used liters of gasoline not consumed , barrels of crude oil not consumed . as mentioned before, global warming has become one of the greatest consequential dilemmas facing the human being in this century, thereby researching on ghg emissions is necessary for any power project. an emissions analysis worksheet is provided in retscreen to help studies on the ghg emissions mitigation potential of renewable energy projects. the main ghgs are water vapour, co , methane (ch ), nitrous oxide (n o), ozone (o ) and fluorinated gases. ghgs that are considered for energy project analysis are co , ch and n o which are expected in the retscreen emission reduction analysis. results from the ghg equivalence tool in the retscreen are presented in terms of the annual amount of co that would be equivalent to the total emission reduction, regardless of the actual gases. and it's done by converting ch and n o emissions to the equivalent co emissions based on their global warming potential. in table , one can find interesting data about kw pv power plant from net annual ghg emissions reduction outlook. in this table, important equivalent cases from the environmental perspective, such as the number of cars & light trucks that are not used, liters of gasoline not consumed, barrels of crude oil not consumed, people reducing energy use by %, acres of forest absorbing carbon, hectares of forest absorbing carbon, tons of waste recycled are mentioned. according to this simulation, the annual ghg emissions reduction and the annual electricity exported to the grid for kw pv power plant are . tco and mwh, respectively. a financial analysis worksheet in retscreen is provided to aid feasibility investigation of renewable energy projects. by considering a new supporting policy of the government for renewable energy resources, a financial analysis was carried out based on the new feed-in tariff for pv electricity in iran (table ) and estimated initial and periodic costs for kw pv power plant (table ). the cumulative cash flows from the simulation are plotted versus time in fig. . according to this figure the estimated initial costs for kw pv power plant is . birr based on the pv market in iran. after starting operation, the gained annual interest income is above mirr so the payback period for the initial investment is between - years. the change in linear trend of this plot is related to the estimated periodic costs ( mirr) for replacing invertors and other necessary services after years. following this payment, the same annual interest income can be gained till years. the average annual interest rate for this investment is about . % over years, base on the new feed-in tariff for this scale of pv power plant. the second case, mw pv power plant, is a candidate for large-scale pv power plants. large-scale (utilityscale) pv power plants, also known as solar parks, farms, or ranches (particularly when they are located in agricultural areas) are power stations that provide a considerable amount of electrical energy to great numbers of consumers. large-scale pv power plants are ground-mounted, usually with fixed tilted solar panels instead of utilizing expensive tracking systems. a similar examination was carried out on mw, same as kw pv power plant. first, the ghg emissions mitigation was studied and related data are presented in table . according to this simulation, the net annual ghg emissions reduction and the annual electricity exported to the grid for mw pv power plant are tco and mwh, respectively. table . equivalent cases substitute for mw pv power plant based on the net annual ghg emissions reduction in iran. fig. . according to this figure the estimated initial costs for mw pv power plant is birr and after starting operation, the obtained annual interest income is above birr so the payback period for the initial investment is about years. the change in linear trend of this plot is related to the estimated periodic costs ( . birr) for replacing invertors and other necessary services after years. following this payment, the same annual interest income can be gained till years. the average annual interest rate for this investment is about % over years, base on the new feed-in tariff for this scale of pv power plant. we have simulated two different scales of the pv power plant and investigated them from the environmental and economic aspects based on co emissions, and the cumulative cash flows after the new feed-in tariff, respectively. from the environmental (co emissions) and electricity generation perspective, a comparison between these two scales of pv power plant shows us that co emissions and the annual electricity exported to the grid, have a linear relationship with the scale of the power plant. we can reduce the quantity of co emissions by using pv technology as multiple small-scale pv power plants (by residential and commercial users), or a large-scale pv power plant (by the governments) in the same impact. from the economic outlook, there isn't a linear relation in cumulative cash flows rate and the average annual interest rate with the scale of the pv power plant. with a comparison between these two cases, as candidates for small-scale and large-scale pv power plants, we can realize that this difference comes from various amounts of the feed-in tariff for different scales of pv power plants in iran. according to the supposed initial costs, the payback period for the initial investments are between - , and years for kw and mw pv power plants, respectively. hence, in accord with the high initial costs for pv power plants, the ministry of energy in iran has formulated an incentive and supporting policy to persuade people, spatially residential or commercial users or private sector to invest in small-scale pv power plants. therefore, residential and commercial customers will have considerable long-term benefits, from taking part in an electricity market and selling their pv systems output. while those pv systems generally do not need a technician to be on-site for daily direct management due to its automated operation, and they just need insignificant and slight oversight, monitoring, and maintenance. on the other hand, the government itself has taken responsibility to set up large-scale pv power plants around the country. by focusing on these two procedures in pv subject, iran takes its first steps in lessening reliance on fossil fuels consumption and its related environmental issues. in future research, we will examine the various feasible renewable energy projects in iran, for different scales from the environmental and economic aspects in terms of this new feed-in tariff for each technology categories and scales. also, the authors will try to provide data from available operational cases to check the impacts of this supporting policy in reality. in conclusion, the intent of this paper is to give a brief and comprehensive survey on various energy policies and provide a technical outlook from the environmental and economic aspects for two different scale gridconnected pv power systems according to the new supporting policy for renewable energy resources in iran. we have presented a clear and efficient simulations on kw and mw grid-connected pv power plants using retscreen software to illustrate the mentioned aspects based on the net ghg emissions reduction, the annual electricity exported to the grid, the cumulative cash flows, and the payback period for the initial investment. from the environmental (co emissions) and electricity generation perspective, a comparison between these two scales of pv power plant demonstrates that co emissions and the annual electricity exported to the grid, have a linear relation with the scale of the power plant. from the economic outlook, due to varying amounts of the feed-in tariff for different scales of pv power plants, there isn't a linear relation in cumulative cash flows rate with the scale of the pv power plant. according to the supposed initial costs, the payback period for the initial investments are between - , and years for kw and mw pv power plants, respectively. hence, in accord with the high initial costs for pv power plants, the ministry of energy in iran has formulated an incentive and supporting policy to persuade residential, commercial users, and private sector to invest in small-scale pv power plants. furthermore, the government has taken responsibility to set up large-scale pv power plants around the country. it can be concluded that, by focusing on these two procedures in pv subject, iran takes its first steps in lessening reliance on fossil fuels consumption and its related environmental issues. coal and lignite production data | world coal production | enerdata n canada set to phase out coal-fired power by | the independent n france to shut down all coal-fired power plants by | the independent n update -brazil development bank scraps financing for coal-fired plants n coordinated wind-thermal-energy storage offering strategy in energy and spinning reserve markets using a multi-stage model cooptimized bidding strategy of an integrated wind-thermal-photovoltaic system in deregulated electricity market under uncertainties how do oil prices, macroeconomic factors and policies affect the market for renewable energy? natural gas prices | natural gas fossil-fuel subsidy reform : critical mass for critical change global subsidies initiative n.d iran's oil development scenarios by the potential of harnessing solar radiation in iran: generating solar maps and viability study of pv power plants solar photovoltaic power plants in five top oilproducing countries in middle east: a case study in iran risk-based probabilistic-possibilistic self-scheduling considering high-impact low-probability events uncertainty download free solar resource maps | solargis n solar potential and irradience map in iran | renewable energy and energy efficiency organization (satba) n.d estimation of height-dependent solar irradiation and application to the solar climate of iran environmental, technical and financial feasibility study of solar power plants by retscreen, according to the targeting of energy subsidies in iran wind and solar energy development in iran technical and economic assessment of the integrated solar combined cycle power plants in iran reference to any special commercial product, trademark, manufacturer, and so on, does not necessarily infer or insist on its confirmation, or approval by the writers. • we presented a brief and comprehensive survey on various energy policies in iran.• new incentive and supporting policy in iran for renewable energy resources is examined.• two different scales of grid-connected pv power systems are simulated by retscreen.• simulation results include annual ghg emission reduction and electricity production.• based on the payback period, its feed-in tariff policy targets low-capacity pv power systems. ☒ the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐the authors declare the following financial interests/personal relationships which may be considered as potential competing interests: key: cord- - pm fmd authors: almaktar, mohamed; elbreki, a. m.; shaaban, mohamed title: revitalizing operational reliability of the electrical energy system in libya: feasibility analysis of solar generation in local communities date: - - journal: journal of cleaner production doi: . /j.jclepro. . sha: doc_id: cord_uid: pm fmd abstract the political upheaval and the civil war in libya had a painful toll on the operational reliability of the electric energy supply system. with frequent power cuts and crumbling infrastructure, mainly due to the damage inflicted upon several power plants and grid assets as well as the lack of maintenance, many libyans are left without electricity for several hours a day. as the country has a staggeringly immense potential of solar energy, it is inevitable to exploit such potential, to avert system-wide blackouts. this paper investigates the use of small-scale pv systems in local communities as non-wires alternative (nwa), offering excess energy exchange within local/neighboring microgrids (mgs) for reliable electric power supply. different combinations of pv/storage/diesel distributed generations (dgs), with grid-interface options, were applied on a case study of a typical dwelling in the eastern libyan city of benghazi. technical and financial feasibility assessments were carried out to contrast between various supply combinations. sensitivity analysis of the pv-grid system was also conducted using net present value (npv) and the payback time indicators to determine the impacts of feed-in tariff (fit) rates, financial incentives, electricity tariff, and inflation rate on the economic viability of the pv grid system. results show that the pv-grid system has a promising potential under reasonable set of varying system parameters. on top of its social and environmental-friendly advantages, the pv-battery system is found to be more economical when adopted as a standalone nwa solution as compared to the diesel generator option, even at the lowest diesel price. the pv-grid system does not only provide a short-term remedy to the rolling blackouts in libya but also enhances system operational reliability by providing a nwa to rundown or shattered grid infrastructure, thus bolstering energy provision in residential neighborhoods. libya is blessed with abundant gas and oil resources. it has large quantities of indigenous oil supplies, which is currently the largest in africa and the ninth-largest globally; with b barrels of proven crude oil reserves (bindra et al., ) . the proven natural gas reserves stand at b cubic feet (eia, a). inasmuch as the libyan political economy was dominated by oil, not surprisingly, the electricity supply industry in the petro-state depends entirely on conventional power generation using fossil fuels. generally speaking, the electrical energy supply and provision enterprise performed reasonably well in libya, before , with the installed generation capacity superseding load demand with an adequate margin. following the arab spring protests in , libya had a full-fledged revolt against its reigning political regime; leading eventually to its downfall. however, the country has descended into civil war since then, with frequent infighting using heavy weaponry. the continuation of such crisis until this very day poses significant challenges to the power grid infrastructure. libya has suffered severe electricity shortages and power cuts in the past few years. this is basically due to the damage and destruction incurred, during the war, as well as sabotage and vandalism on some of its power plants and transmission network assets; particularly in eastern and western libya. the situation was further aggravated by the lack of cash and foreign companies to undertake maintenance and complete suspended projects. with actual electricity generation below load demand, grid system operators were left with no option but to implement rolling blackouts to avoid system-wide collapse. although some homeowners, businesses, and health centers have tended towards using mobile diesel generators, many libyans are still left out with no access to grid electricity supply few hours a day. the libyan economy and energy sector are still heavily dependent on fossil fuels. in temporary, yet uneconomic and environmentally unfriendly, solution to a chronic problem. the libyan historical load profile data show that the maximum power occurs during the summer season and the residential sector represents the highest share in electrical energy demand followed by the commercial and industrial sectors, as presented in fig. do not have the luxury, anymore, of diversifying energy resources to introduce re in the generation mix. in fact, gecol is currently struggling to tackle power outages using rotational load shedding, also known as rolling blackouts, with the aim of implementing an equitable and fair load shedding policy to all customers throughout the day. the misery of load shedding was further intensified very recently amid the quarantine caused by covid- pandemic, due to the substantial increase in the residential load demand. in the absence of a unified government, collapsing infrastructure and worsening security, it is imprudent to count on government initiatives to provide solutions, which can be ultimately available via damaged or vulnerable grid of traditional "wires". it is, therefore, imperative for local communities in libya to tap the vast re potential the country has and develop modular power supply via distributed renewable generation as a nwa connected directly to load centers. there is no good reason to rely on gecol for energy provision merely because it is mandated to do so. the blunt fact is the incumbent transmission provider, gecol, cannot meet the reliability needs and service obligations. as the country is already ravaged by civil war with damaged critical system infrastructure, an "ad-hoc" option to provide a regional solution could be the only practical alternative in the immediate and short- fit is defined as a policy initiative that encourages investment in re by providing green power producers long-run assured purchase contracts to sell their electricity to the grid at a premium rate. among the scheme aims to support investment in re by setting a target of , mw in the first regulatory load profile is depicted in fig. . as can be seen, the peak energy demand occurs between : pm and : pm with an average peak of . kw. according to ( ) (almaktar, ) , the nwa pv system capacity which satisfies the house demand is found to be kw, i.e., panels of w pv module. ( ) where psh is the peak sun hour in kwh/m /day; for benghazi it is . . losses of the designed pv system must be considered to ensure that the system will feed the load effectively. the system efficiency the merit of the nwa kw pv system is to provide an independent sustainable energy source to residential areas that is not reliant on intermittent power supply provided by gecol; due to its damaged t&d infrastructure. the excess energy can also be exchanged in the local community to fulfill another end user energy need within a mg context. if the local distribution networks are upgraded, and political stability is largely restored, the excess clean energy from the pv systems can be sold back to the grid under the fit policy. the specification and cost breakdown for the different components used in this study are listed in table . homer is utilized to investigate the feasibility of different hybrid energy systems to fulfil the energy on the other hand, npv is a standard method for using the time value of money to appraise long-term where i is the nominal interest rate. npv should be as large as possible and always positive so that the generated benefits are greater than costs. the initial cost (s) of the gcpv (without battery storage) system can be expressed as: s=c gen + c inv + c inst -c incn = c system -c incn ( ) where c gen is the cost of the nwa gcpv generator, c inv is the cost of the inverter. c inst is the cost of installation including supporting structures, wiring, protective elements, etc. c system is referred to as system it is assumed that no limitation is imposed for the amount of energy generated by the nwa fed into the utility grid i.e., all the produced energy can be sold which is, therefore, the most favorable situation for the pv installer. thus, e pvaut = . the annual operation and maintenance cost c o&m of the system installed was taken as % of the initial cost s (rahman, ) . also, c ins and c fin are assumed to be zero in the sense that there is no insurance or financing costs for the pv system installed. furthermore, c o&m increases with inflation (g); therefore, equation ( ) becomes; energy prices are highly subsidized in libya, in which fuel prices are among the lowest in the world. j o u r n a l p r e -p r o o f the investigation is focused on the analysis of several scenarios of battery amperage capacity, diesel generator fuel price, electricity tariff, and inflation rate. in terms of energy sale, the study initially assumes that the nwa system receives no incentive for injecting excess energy into the grid as this is the real case considering the grid electricity price equals to . $¢/kwh (current tariff), inflation rate at %, diesel fuel price in its lowest ( $¢/l), and $ for the price of energy sold back to the grid, it is found that the optimum configuration is for the pv-grid without battery storage, referring to fig. . this scenario offers the least npc and coe with $ , and . $¢/kwh respectively, as depicted in fig. showing the electrical simulation results of the system. as can be noticed, although the grid energy price is at the lowest tariff, yet the pv system covers % of the load demand. this system can yield an excess annual energy of , kwh that can later be sold to end users in the local communities . fit of $¢/kwh, at an inflation rate of %, the pv installation project is not feasible even when the project receives incentives up to % of capital cost, as shown in table . with such an inflation level, in order for the investment to be feasible, the fit must be higher than $¢/kwh. to investigate the impact of using unsubsidized electricity tariff rate on the financial viability of the pv nwa system, the tariff rate and fit are increased. as depicted in table , the pv project is financially feasible, even with an unsubsidized tariff rate of $¢/kwh, fit as twice as the tariff rate, inflation of %, and % incentives. however, at an inflation rate of %, the rate in libya, the sell- back price of electricity at $¢/kwh is not profitable even with up to % incentives of the capital cost. the results detailed in table , reiterates that at the highest inflation level ( %) the investment on pv technology in residential installations is not feasible even when the incentives to the pv projects reaches % of the capital cost. finally, table analyzes the npv and payback period of the kw solar home at % inflation rate when the electricity is unsubsidized, with fit increased to $¢/kwh (~ . ld/kwh). the results acquired emphasize that at % inflation level the investment on pv technology is untenable even when the fit is about seven times the base electricity price. ( . $¢/kwh), inflation rate at %, current subsidized diesel fuel price ( $¢/l), the most economic standalone nwa option goes to kw- kwh pv-battery system yielding to . $¢/kwh of electricity cost. whereas the incorporation of energy storage system (ess) in the pv system increases the cost of energy (coe) and the net present value (npv), utilizing renewable pv systems is more attractive financially than using the diesel generation option. furthermore, the pv options come with security of supply, cleaner environmental footprint, and a greater societal benefit. the latter can be achieved not only from the continuous clean energy supply, but also by maintaining people's comfort via avoiding the noise accompanying gas-guzzling diesel generators in densely-populated townships in eastern and western libya. for the nwa grid interfaced system, the most economic option is found to be pv-grid with % renewable fraction even at $ for the sell-back price; this offers a coe and npv of . $¢/kwh and $ , respectively. at a higher diesel price, the pv-battery option demonstrates its viability as the optimal standalone nwa solution. libya. while this study is primarily dedicated to the energy supply system in libya, the arguments presented herein can be extended to countries ravaged by political instability, insurgency and regional conflicts in the middle east such as iraq, syria and yemen. effect of full implementation of domestic solar water heaters on the electricity peak load in libya an investigation into the current utilisation and prospective of renewable energy resources and technologies in libya the market of solar panels in the united kingdom sizing of a hybrid power system for a house in libya annual information technology, electronics and mobile communication conference (iemcon) a mw very large-scale photovoltaic power plant for al- libya: energetic, economic and environmental impact analysis solar thermal and photovoltaic electrical generation in libya an improved algorithm for photovoltaic module temperature prediction and its general electricity company of libya (gecol) csp) a feasible option for sub-saharan africa?: investigating the techno-economic feasibility of csp in tanzania the potential of concentrating solar power (csp) for electricity generation in libya economical and environmental analysis of grid connected photovoltaic systems in spain potentials and prospects of renewables in libya a multiagent-based hierarchical energy management strategy for multi-microgrids considering adjustable power and demand response economic-bulletin- rd-quarter- , central bank of libya a novel control strategy for grid connected distributed generation system to maximize power delivery capability. energy current control based power management strategy for distributed power generation system comparing electricity transitions: a historical analysis of nuclear, wind and solar power in germany and japan feed-in tariff outlook in malaysia non-wire alternatives to capacity expansion energy storage as a non- ieee/pes transmission and distribution conference and exposition (t&d). ieee clean power from deserts, the desertec concept for energy economic analysis of different supporting policies for the production of electrical energy by solar photovoltaics in western european union countries renewable energy auctions in south africa outshine feed-in tariffs fossil co and ghg emissions of all world countries energy information administration international energy outlook with projection of support general electric network of libya by covering hot water load in the residential sector with solar water heaters, gecol energy efficiency and renewable energy libya -national study mediterranean and national strategies for sustainable development priority field of action : energy and climate change climate change over libya and impacts on agriculture baseload electricity and hydrogen supply based on hybrid pv-wind power plants solar energy: renewable energy and the environment recent facts about photovoltaics in germany the general electric company of libya [www document potential of hybrid system powering school in libya government of dubai media office are non-wire solutions the next big thing a study of grid-connected photovoltaics in the libyan power system hanwha q cells [www document hybrid optimization model for multiple energy resources compulsive policy-making -the evolution of the german feed-in tariff system for solar photovoltaic power solar energy mapping the road ahead energy policies of iea countries, the united kingdom rethinking energy theory and problems in financial management predictive power management strategy for pv/battery hybrid unit based islanded ac microgrid can a city reach energy self-sufficiency by means of rooftop photovoltaics? case study from poland a review paper on solar photovoltaic systems impact of political and economic barriers for concentrating solar power in sub-saharan africa forecasting power output of photovoltaic system energy procedia mohi-ud-din, g., . price volatility in the carbon market in china a comprehensive survey on control strategies of distributed generation power systems under normal and abnormal conditions evaluation of feed-in tariff-schemes in african countries future prospects of the renewable energy sector in proc. sbe dubai national aeronautics and space administration national oil corporation of libya [www document world oil outlook the future of the feed-in tariff (fit) scheme in europe: the case of photovoltaics energy estimation output simulation model and economic analysis for building integrated photovoltaic system under malaysia environment distributed multi-agent based coordinated power management and control strategy for microgrids with distributed energy resources country profile-renewable energy-libya provision of technical support/services for an economical environmental impact assessment of national regulations and incentives for renewable energy and energy national plan for developing the renewable energy in libya the prospects for cost competitive solar pv power fossil-fuel subsidies: a barrier to renewable energy in five middle east and north african countries determinants of electricity demand in libya: an empirical study for the period libya using time series stochastic method for long-term the use of renewable energy technologies in the libyan energy system case study: brak city region on the field performance of pv water pumping system in libya changes and driving forces of urban consumption-based carbon emissions: a case study of shanghai solar resource maps of libya [www document global market outlook for solar power united nations world atlas [www document environmental and climate policy integration: targeted strategies for overcoming barriers to nature-based solutions and climate change adaptation recent advances of feed-in tariff in analysis of feed-in tariff policies for solar photovoltaic in china country energy profile ( libya ) highlights: • decentralization can reinvigorate electricity system's operational reliability. • local energy provision is a viable remedy to the rolling blackouts in libya nwa is more economical than diesel generation. • fit along with inflation and subsidy are the main drivers for pv deployment. • government subsidies for fossil fuels should be the authors would like to thank gecol represented by managers of the power plants, for providing the necessary technical data. this research did not receive any specific grant from funding agencies in the public, commercial, or not- for-profit sectors. j o u r n a l p r e -p r o o f ☒ the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐the authors declare the following financial interests/personal relationships which may be considered as potential competing interests:j o u r n a l p r e -p r o o f key: cord- - gcmqh e authors: chiriboga, gonzalo; de la rosa, andrés; molina, camila; velarde, stefany; carvajal c, ghem title: energy return on investment (eroi) and life cycle analysis (lca) of biofuels in ecuador date: - - journal: heliyon doi: . /j.heliyon. .e sha: doc_id: cord_uid: gcmqh e in ecuador, the net energy contribution of biofuels is unknown or unnoticed. to address this issue, we determined the energy return on investment (eroi) for bioethanol and biodiesel. the selection of raw materials relied on their productive capacity, export and import records, and historical yields. consequently, the scope included three raw materials for ethanol (sugar cane, corn, and forest residues) and four for biodiesel (african palm, pinion, bovine fat, and swine fat). using a method based on the life cycle analysis (lca) of each biofuel, we assessed the entire production chain through statistical processing of primary and secondary information. then we calculated the calorific values in the laboratory, compared energy inputs/outputs, and finally obtained the energetic returns. erois for bioethanol were: . for sugarcane, . for corn, and . for wood. the results for biodiesel were: . for african palm, . for pinion, . for bovine fat, and . for swine fat. these values suggest feasibility only for sugarcane in the case of ethanol. in contrast, biodiesel has better prospects because all the feedstocks analyzed had erois higher than two. nevertheless, biodiesel is not available for trading in ecuador because energy policy has overlooked systems based on higher energy return. future studies should consider more comprehensive variables such as climate change, land use, and water management. globally, the use of biofuels in the transport sector increased % in (international energy agency, ). however, this growth was insufficient to achieve the international objectives set in the sustainable development scenarios for (united nations, ) , since this commitment would require tripling bioethanol and biodiesel content in final blends, involving around % of global transport (sawin et al., ) . several issues have slowed the incorporation of biofuels into worldwide transportation, for example, competition with the food sector for the use of feedstocks (ho et al., ) , the decrease in the calorific value due to the presence of oxygen (oh et al., ) , stillage handling and disposal (silva et al., ) , and the energy return on investment (eroi) (jessica g lambert, hall, balogh, gupta and arnold, ) . the eroi is directly or indirectly linked to the achievement of wellbeing, energy quality, and energy sovereignty (jessica g . it describes the amount of energy a source requires to deliver a unit of energy to society, and considers the energy flows involved in all stages of the production process . several methods for calculating the eroi have been published that contain points of agreement, but also methodological differences. the main disagreements relate to the way energy flows (moeller and murphy, ) , system boundaries, and residual energy embedded in co-products are identified and quantified (capell an-p erez, castro, javier and gonz alez, ) . the ecuadorean government has sought alternatives for reducing oil derivative imports to meet the local demand. these endeavors have intensified since last year, and in april , the ministry of agriculture announced the agrofuels plan, which would replace , ha of rice with sugar cane to produce bioethanol (el universo, ) . the program would also incorporate million liters of african palm oil per year to begin producing % v/v biodiesel (b ) (ministry of agriculture., ) (astm specification d , ). reducing imports would have a significant effect on ecuador's economy because, since the s, the country has maintained a subsidy on gasoline, diesel, and liquified petroleum gas (rivadeneira, ) . this public expenditure is increasingly unsustainable with demand increasing at around . % annually, fuel migrating to other consumer sectors, and the volatility of international derivative prices (espinoza and guayanlema, ) . in this context, ecuador has partially promoted the incorporation of biofuels into the energy supply (consejo nacional de planificaci on, ) (ministerio de electricidad y energía renovable, b) (presidencia del ecuador, ) . for example, since , a mixture of gasoline and anhydrous ethanol ( % v/v), has been available for trading in the local market (castro, ) . concerning biodiesel, the blends b , b , b , and b have been mentioned officially (agencia de regulaci on de hidrocarburos, ), but none have a real share in the transport sector. currently, the only energy use of vegetable oils is project "zero fossil fuels in galapagos" (programa de las naciones unidas para el desarrollo, ) (ministerio de electricidad y energía renovable, a). this initiative generates electricity through direct combustion of oil without previous transesterification. ecuador produces million boe (barrels of oil equivalent) of primary energy; it exports %, and about % is retained as feedstock for refineries (ministerio coordinador de sectores estrat egicos, ) . this production is insufficient to cover domestic demand. thus, in , about % of the local consumption of diesel, gasoline and liquefied petroleum gas was imported (c amara de comercio de quito, ) and from january to august , these imports increased . % compared to the same period of the previous year (banco central del ecuador, ) (planificaci et al., ) . consequently, the government has encouraged researchers and industrialists to design alternative fuels using economically viable and environmentally friendly feedstocks, as mentioned in the agrofuels plan (banerjee et al., ) (eduardo rosero, . the share of biomass in the energy matrix is less than %, and it is used mainly for cooking food and generating electricity (ministerio coordinador de sectores estrat egicos, ) . in second place is the production of anhydrous ethanol for the "gasolina ecopaís" project (about million liters) (petroecuador, ) . the production per inhabitant is comparable with countries of the region such as colombia (unidad de planeaci on minero energ etica, ) or uruguay (ministerio de industria energía y minería, ). however, comparison with world leaders such as brazil (energy research office, ) reveals a big gap of almost to . it is essential for ecuador to evaluate the actual energy contribution of biofuels and the degree of flexibility of their net output in relation to changes in production process and technology. eroi is a proper tool to carry out this evaluation since it considers the entire production cycle from planting until it is ready for blending (murphy and hall, ) . first, the study developed an extensive survey of the different raw materials with energetic potential (instituto nacional de preinversi on, ), namely agricultural and forestry crops with higher production records and yields, such as sugar cane, corn, wood, african palm (figueroa de la vega, ) , and pinion (instituto interamericano de cooperaci on para la agricultura, ). for livestock, the analysis included resources such as cattle, pigs, goats, and sheep, and focused on their transesterifiable fat content. then we determined the energy expenditure index (murphy et al., ) using the life cycle analysis (lca). this method permitted us to break down existing biodiesel and bioethanol production processes (tomi and schneider, ) . the analysis included the collection and statistical treatment of secondary information about industrial plants in operation in ecuador and other countries. the third part consisted of determining the lower calorific value and an elemental analysis by applying standardized methods for quantifying energy availability. finally, the relationship between the amount of energy produced and consumed was estimated using the eroi concept (jessica gail . few studies encompass the energy return of biofuels from different origins at the same time. furthermore, we included agricultural products with few records in the literature, such as animal fat, pinion oil, and forest residues. the objective was to group the most compelling possibilities and present their energy advantages in terms of eroi. this information is essential for allocating resources to programs that have the best energetic benefits. the presence of economic externalities does not influence eroi; instead, it relies on the concept that humans use the best resources first (hall, ) . the research includes biofuels that are being or could be used in ecuador, based on the characteristics of local industry. it incorporates the data treatment of the agricultural product to be analyzed, such as cultivation, consumption, import, and export, as well as the different levels of raw material allocation for biofuel production. the results permit us to see in a glance the effectiveness of policies implemented to meet energy requirements, given that sectors with more significant demands should be addressed first with higher eroi biofuels. this method is easy to replicate and allows the particularities of each country to be considered. the successful implementation of a biofuel program depends on technology, economics, environmental sustainability, and public policy support (saravanan et al., ) . governments of the region regulate their specifications by enacting minimum levels of ethanol or biodiesel content in blends (v azquez et al., ) (see table ). the prospects of biofuels depend on the behavior of international energy markets (pro ecuador, ) (energy information administration, ). for instance, the fall in the oil prices in (usd per barrel) would result in a severe decrease in the demand for biofuels, and lead to the collapse of their global price in the mid-term (getachew nigatu, kim hjort, agapi somwaru, ) . environmental standards, energy security, rural economic activation, and climate change will drive bioethanol consumption in the u.s. and the e.u., which, together with brazil, would remain as the leading producers worldwide (getachew nigatu, kim hjort, agapi somwaru, ) . their production would increase from billion liters in to about billion liters by . additionally, emerging economies like china, thailand, and india would contribute up to billion liters of ethanol by (u.s. department of energy, ). global expansion of biodiesel is expected to increase from to billion liters between and (union zur f€ orderung von oel -und proteinpflanzen e.v., ). again, the e.u., u.s., and brazil would dominate the market with good participation by argentina in south america. this production will utilize % of the world's vegetable oil (pro ecuador, ). ecuador began producing biodiesel from african palm in , and up to , all production was for export. in , when national production reached million liters, the government enacted executive decree establishing b blending for biodiesel. this proportion was supposed to increase gradually to b , which would mean achieving a production of million liters of biodiesel per year. for anhydrous ethanol, production started in with ecopaís gasoline, which was to contain up to % anhydrous bioethanol. the national fuel trade agency (arch) states that only ecopaís gasoline ( % v/v) is available in the current market, and biodiesel will have to wait for distribution and marketing policies (hernan, ) . the use of vegetable oil is limited to pilot projects such as zero fossil fuels for galapagos and the juan jos e castell o zambrano foundation, in cooperation with termopichincha; they have been burning pinion oil without transesterification to generate electricity since . agricultural zoning published by the ministry of agriculture (mag) identified the provinces with highest potential for the production of sugar cane (guayas %, loja %, cañar %, imbabura % los ríos % and carchi < %) and african palm (esmeraldas %, los ríos %, sucumbíos %, pichincha %, santo domingo de los ts achilas %, orellana %, and guayas %) (instituto nacional de preinversi on, ). this information is essential for evaluating the energy required to transport biofuels to blending centers (enclosed in thick lines on the maps). figure shows the geographical distribution of the energy potential of sugar cane on the left ( tj) and african palm on the right ( tj) (instituto ecuatoriano de estadística y censos, ). this record includes fermentation, transesterification, direct combustion, gasification, and pyrolysis. although the potentials do not include energy return, the advantage of african palm is clear in terms of available energy. the eroi calculated in this research includes the energy associated with refining and transporting fuel to the country's main point of distribution where blending would take place. the ratio of this amount of energy to the energy obtained when burning the fuel is called the energy return on investment -point of use (eroi pou ) (j. lambert, hall, balogh, poisson and gupta, ) . 〖eroi〗 pou ¼ ðenergy returned to societyÞ ðenergy used to get and deliver that energyÞ ( ) eq. ( ) described by ). the eroi is a useful decision-making tool before exploiting an energy resource or when defining public policy. for example, a value of or : means that society would benefit from this energy resource by %, and the remaining % is necessary to obtain that energy. this proportion varies considerably depending on the source. for example, gas and oil can have an eroi of : , but in the case of tar sands, the eroi decreases to : . the value for coal is usually higher and can be up to : . among the most compelling renewable energies, the eroi is : for hydroelectric generation and : for wind power (j. lambert et al., ) . for the specific case of biofuels, the values are less encouraging; for example, ethanol from corn has erois that range from . to . in u.s. distilleries (murphy and hall, ) . the source is not the only factor that determines the eroi; other inputs such as technological improvements or depletion can play crucial roles. gagnon et al. addressed this topic for oil and gas production worldwide. the eroi increased from : in to about : in , and then it decreased again to : in (gagnon et al., ). here it is clear that during the first period from to , the energy return increased thanks to technological advances and extraction methods; however, during the second period from to , depletion of the sources exceeded the benefits achieved through technological advances. charles hall (the originator of the concept of eroi) states that to keep our civilization working in the way we know it, energy systems should have erois higher than ). the eroi can vary depending on the system components; for example, boundaries and outputs/inputs assumed in the energy balance, and local particularities such as production methods, types of raw materials, and energy consumed for environmental remediation (see figure ). lca starts as a horizontal analysis tool and examines the inputs and outputs of every component of the process. then it carries out a vertical analysis of the activities of each stage (petraru and gavrilescu, ) , while seeking not to include irreversibilities that are not useful to society (arvesen and hertwich, ) . in general terms, this tool includes the definition of objectives, scope, inventory analysis, impact assessment, and interpretation of results. in ecuador, ethanol comes from sugar cane only; therefore, energy consumption data are from actual industrial plants. in contrast, there is no industrial production of biofuels based on corn, wood, fat, or african palm. hence, statistical tools and case studies are needed to determine the relationship between the energy consumption "dependent variable" and the raw material "independent variable." for biofuels production, this information allows the construction of four scenarios with different levels of corn, wood, fat, and african palm designated. this approach is based on the concept of economy of scale, where the unitary production cost decreases as the scale of operation increases. all investigations that seek to determine the eroi of any resource use one of the following three techniques: process analysis, economic inputoutput, or a hybrid of both (murphy et al., ) . looking for the implications of energy return in society (jessica gail , reviewed the eroi of different sources. the most relevant references are presented below with a description of the technique used in each case (see table ). the technique employed in each case defines the methodology and the instrument used to identify and account for energy flows. it consists of two dimensions. the first describes the boundaries of the production chain from cultivation to distribution; these are the energy outputs. the second sorts by levels and indicates the type of energy and materials directly or indirectly associated with the process. in this case, we chose level , which includes the energy inputs under investigation and the inputs from the other energy sectors (murphy et al., ) . this ensemble of dimensions results in a technique based on process analysis. the lca is the instrument that identifies the processes within the boundaries defined in dimension one, as well as the energy flows of dimension two. the aim is to define a roadmap for selecting the proper energy balance and the type of data to be collected. the scenarios vary the proportions of feedstock to estimate energy consumption through linear regression models. the variance analysis of the models and the t-test for the slopes show a statistically significant relationship between the amount of raw material destined for biofuel and energy consumption, since the p-value of each test is less than the level of significance chosen (α ¼ . ). moreover, this relationship demonstrates a high correlation between the variables according to the values of r (see tables , ; figure ). the selection criteria rely on the scenario that results in less energy consumption during the feedstock's industrial stage. the following are the best scenarios for each case. corn. -s ( %) with energy consumption in the industrial stage equal to . mj/kg bioethanol, which is higher than industrial plants in argentina . mj/kg, u.s. . mj/ kg, and chile . mj/kg. wood. -s with energy consumption of . mj/kg of bioethanol, a level comparable to other industrial plants, . mj/kg in the united kingdom, . mj/kg in canada, and . mj/kg in brazil. african palm. -s ( . mj/kg biodiesel), which represents . % of total energy consumption. it is within the range of preliminary studies . - . mj/kg biodiesel. animal fat. -s ( . mj/kg), which represents . % of total energy consumption; this is slightly higher than the values presented in preliminary studies ( . - . mj/kg). pinion. -s ( . mj/kg biodiesel), which represents . % of total energy consumption; this is higher than values presented in peru . mj/kg, argentina . mj/kg, and india . mj/kg. (murphy et al., ) and (jessica gail lambert et al., ) . reference technique ethanol and biodiesel production (pimentel and patzek, ) process analysis oil and gas discovery and production (guilford, hall, o'connor and cleveland, ) process analysis oil and gas production (guilford et al., ) hybrid oil gas and tar sand production process analysis oil and gas production (hu et al., ) economic input-output the production of biofuels generally involves the generation of some co-products; for example, glycerin in biodiesel, which accounts for approximately % of energy consumption. likewise, bioethanol from corn has multiple co-products that include oils and meal for animal feed; their exclusion or incorporation into the analysis produces essential changes in the final values of the eroi. hall et al. ( ) addressed this issue when comparing the eroi of corn alcohol, previously obtained by (kim and dale, ) and (pimentel and patzek, ) , as . : and . : , respectively. approximately % of this difference is due to the treatment and use of the co-products generated in the industrial process. this work excluded the subsequent treatment of co-products because of uncertainty about the allocation of the weighting factors of their energy consumption and their final use . hence, the scenarios developed in this work are conservative in this sense. similarly, we excluded the energy required for environmental remediations because it could change according to the specific obligations in each zone. finally, esmeraldas refinery was used as the final destination of biofuels, since this is where the mixing of ecopaís b gasoline take place. considering these methodological aspects, the calculated eroi is very close to the eroi at the point of use, with less than % difference ) ( % in our cases). we determined the energetic availability from the net amount of heat produced by fuel combustion under controlled conditions (cengel, yunus. boles, ) . local producers and research centers provided the samples. they are listed below with the respective selection criteria (see table ). finally, we obtained the net calorific value (ncv) from specialized tests, such as astm d - and (sader and oliveira, ) , for gross calorific value and elemental analysis, respectively. table . energy consumption involves the entire production chain, including the stages of cultivation, distribution, chemical transformation, and delivery to blending facilities. figures and show the extraction of biofuels from agricultural commodities and animal fat, respectively. the following is a model for calculating the eroi at the point of use for sugar cane in scenario . other raw materials follow the same procedure. the desegregation of formula ( ) shows the decrease in eroi through the production chain. this information is also shown as a percentage, taking the cultivation stage as a reference. eroi farming ¼ : : the eroi farming represents the energy return of sugar cane, considering cultivation only. after adding the other stages, the eroi becomes . , . , and . for transportation, transformation, and distribution (see figure ). the eroi farming begins at . and decreases by . %, . %, and . % by the end of its production chain. that is, . x ( - . )% ¼ . . this detail allows the analysis of consumption by subprocess. for example, the eroi of forest residues decreases by . % by the final stage. as a result, we obtain an eroi at the point of use that is less than one. the ncv of sugar cane, african palm, fat, and pinion was obtained experimentally, and ncv of corn and wood was theoretical. the following eight figures compare the results of the energy consumed per stage and the available ncv, to observe net benefits. the results confirm that energy consumption is strongly influenced by both the raw material and the industrial stage. in general terms, biodiesel has an advantage over ethanol (see table ). the calculation of the eroi has been adjusted not only for the agricultural and industrial reality of ecuador, such as ethanol from sugarcane, but also for raw materials, whose production is part of national development plans and public policies for future projects such as biodiesel. therefore, we propose substitutive goods to generate more inputs that will allow the prediction of the net energy impact of introducing biofuels from different origins under current production conditions. besides eroi, other socioeconomic considerations can arise, such as the creation of jobs and the activation of the agricultural sector, as well as reducing refined fuel imports resulting from the lack of internal production capacity. the fossil fuel subsidy policy impacts the national government in two ways. on one hand, subsidized fuel increases consumption due to its low price, and the country has to allocate around usd billion per year ( % of gdp) to meet the demand. on the other hand, since it does not have refining capacity to cover the domestic market, the government has to import derivatives at fluctuating prices, placing the local dollarized economy at risk year after year. the issue gained importance in the country after october , because the ecuadorean government attempted to eliminate gasoline and diesel subsidies. the measure provoked intense social protests from several sectors, such as transport, agriculture, and industry. finally, in the face of excessive pressure, it had to withdraw the decision. therefore, all options that are considered should adopt an integrated analysis that includes technical, economic, and social aspects. the eroi could provide vital information to address this issue from a more insightful standpoint. development is strongly related to the eroi on which societies base their economies. in ecuador, the production of primary energy from fossil fuels is close to %, and biofuels constitute less than %. however, increasing this share is a subject of constant debate and pressure from various sectors. this is where the concept of eroi plays an influential role, since it allows real-net contributions to be compared with the apparent benefits of green energy, driven mainly by actions to mitigate climate change. in many cases, those actions ignore the fact that fossil fuels provide energy for developing renewable technology. the eroi values for ecuador range from . to . for ethanol and . to . for biodiesel. moreover, the results show that the greatest energy demand is for cultivation ( . - . %) and industrial stages ( . - . %), so we compared them with regional and world values. biodiesel from african palm la fabril commercially, oils and fats are one of the most concentrated sectors in ecuador according to the center for economic and social rights. la fabril is one of eight companies that account for % of the national market. since , it has exported oil for biodiesel using the following method, astm d /b (blends with diesel) (lasso, ) . there is no industrialized refining of fat to biodiesel yet. therefore, the department of petroleum, environment, and contamination (dpec) provided a sample that complies with technical regulations in terms of calorific value. the producer is part of the dpec customer portfolio. biodiesel from pinion iner pinion oil, as an energy resource, is a pilot program of the ministry of energy and non-renewable natural resources, and iner is the implementing branch of the project (instituto interamericano de cooperaci on para la agricultura, ). the calculation for the other raw materials is available at https://uceedumy.sharepoint.com/personal/wgchiriboga_uce_edu_ec/_layouts/ /doc.aspx? energy consumption for growing sugar cane is . mj/kg, which on the average is . % more energy than brazil, but . % less than the u.s. the situation is different for corn, which in ecuador requires . mj/kg, compared to . ; . ; and . mj/kg in the u.s., chile, and argentina, respectively. for african palm, energy consumption is . mj/kg, . % higher than indonesia and . % higher than figure . from a to g, breakdown of the energy consumed to produce biofuel (left), and the total energy released by combustion (right) according to the feedstock and assumed scenarios. h is a summary of the eroipou for all the feedstocks considered and sorted by scenarios. the advantage of biodiesel is evident. colombia. for livestock, ecuador consumes about % more energy than mexico and brazil, and up to . % more than the u.s. energy consumption in pig raising is significantly lower due to space management and the type of feeding, so the energy demand comes from the transesterification of fat. this investigation reports the current situation of energy management for both alcohol fermentation and dehydration and the transesterification of fat. we also considered the pretreatment and refining stages of each raw material. in ecuador, the incorporation of biofuels into the energy matrix has two main objectives. on one hand, it seeks to reduce the environmental impact of greenhouse gas emissions by using biomass, whose carbon comes from photosynthesis. on the other hand, it seeks to displace imports of petroleum-derived fuels, mainly gasoline and diesel, while encouraging national agricultural production. in this context, ethanol from sugar cane has the most favorable eroi, at . , which leads to the following analysis. if the aim were to meet nationwide demand with ecopaís, the energy market for anhydrous ethanol would be , kboe ( , , mj). this amount of energy would require , , l of alcohol (energy intensity ¼ . mj per liter) and km of arable land (instituto interamericano de cooperaci on para la agricultura., ). fossil fuels could provide % of this energy; however, there would still be a contribution by renewables of about , , mj. for the other raw materials analyzed, there would not be a net energy contribution by ethanol. in the case of wood, there would be a negative energy balance since its eroi is between . and . . for biodiesel, we chose african palm to carry out a similar analysis, and the eroi calculated was . . the production of b blends to meet nationwide demand would represent , kboe or , , mj, and would involve around , , l of biodiesel and , km of land (energy intensity ¼ . mj per liter). pinion is worth highlighting because its eroi is . , and it constitutes an excellent opportunity because it does not compete directly with the food sector. only living fences are required to produce it, so it would therefore not jeopardize land use to a significant extent. biodiesel from animal fat (cattle . : and pigs . : ) appears to be more feasible than ethanol, as shown in figure h . the best production scenarios for both ethanol (sugar cane . ) and biodiesel (african palm . ) suggest that expending a unit of energy to produce biodiesel would return . more energetic units than bioethanol. besides, data from the last national energy balance showed that the demand for diesel is greater than gasoline ( , kboe and , kboe, respectively) due to the high energy consumption characteristics of this subsector, and the ease of fuel utilization for industrial activities. finally, it is worthwhile analyzing how ecuadorians use fuels for transportation. for example, individual or light cars consume % of the gasoline, and in the best case would transport five users at a time. and collective or heavy-duty transport utilizes the remaining %. in contrast, light and individual transport consumes % of the diesel and collective or heavy-duty transport utilizes up to %. so, since the biodiesel market would mean a higher energy return, better land use, and greater coverage of benefited users, it should be analyzed why, so far, ecuadoreans still cannot trade biodiesel locally. the study presents an initial analysis of the energy return of the biofuels considered in national development plans for transport. the energy return rate of bioethanol is feasible only for sugarcane because it has an energy surplus of . . for biodiesel, the values are favorable in all the selected scenarios, since its eroipou was always greater than . the stages of cultivation and industrial transformation are the most energy-demanding; therefore, energy efficiency policies should begin by addressing these stages, so that we can achieve world productive yields like those of brazil and the u.s. the market for bioethanol as fuel is million dollars ( million liters). petroecuador e.p. has awarded the administration of the project to three private companies and a % share to small farmers. this gasoline is available in of the provinces of the country. in , it achieved first place in sales with % of the total market. the numbers are encouraging but the energy ministry has questioned the project since , because it is cheaper to import ethanol from neighboring countries. the reasons are the lack of local production of agricultural inputs and the high cost of labor. based on this analysis, the project seems to be maintained solely by the , direct jobs it generates. however, even if the objective is to prioritize job stability, the eroi could provide public policymakers with adequate information on each stage in order to correctly direct incentive programs. the biofuels program was launched in april , and included biodiesel as a priority. that year, the organic law of energy efficiency called for the creation of the necessary policies for promoting the marketing of biofuels at the national level. as of the writing of this document, there are no clear implementation programs or plans for biodiesel. in the context of energy efficiency and renewable energy, the public policy proposes the electrification of the transport matrix. by , new units incorporated into public transport must only be electrically powered. this measure covers % of national diesel demand, but the actions to be taken for light and heavy units, which constitute %, are not clearly expressed. here, encouraging eroi results provide an alternative in the medium term, mainly because biodiesel blends do not incur the drawbacks of electrical units, such as battery life, limited range, dispatchability, and recharging points. the land required to meet domestic demand with ecopaís and biodiesel (b ) shows similar energy densities, since both have yields of about . mj per km . that is, the same amount of land would be committed to generating a unit of energy from sugar cane or african palm. however, this issue deserves further study that considers the water required and the net greenhouse gas emissions generated. we analyzed biofuels for use in transportation engines, which implies high-quality fuels and consequently, high energy demands during refining processes. diversifying the matrix and allocating fuels for direct combustion should be considered, such as pinion, for direct use in power generation. here, the eroipou would increase from . to . . the unprecedented crisis in the oil markets due to the covid- outbreak has caused severe impacts on oil-exporting economies, such as that of ecuador. in this regard, some analysts suggest that prices will rise considerably in the medium term, which would imply a new increase in the cost of derivatives. currently, ecuador's social environment makes it highly unlikely that subsidies will be withdrawn. this forces the ecuadorian government to generate guidelines focused on incorporating viable options for the diversification of the energy matrix to alleviate the fiscal deficit caused by the subsidy. in the current situation of low global energy demand, ecuador should use the opportunity to generate public policies aimed at defining how, when and what quantity of derivatives to acquire in the future, as well as the amount of raw materials to be dedicated to the production of biofuels. both decisions must consider, among other things, the eroi as a technical criterion to indicate which biofuel to produce to minimize the impact on other energy resources and economic sectors. norma para el manejo y control del biodiesel. quito: registro oficial del ecuador integrating agronomic factors into energy efficiency assessment of agro-bioenergy production -a case study of ethanol and biogas production from maize feedstock more caution is needed when using life cycle assessment to determine energy return on investment (eroi) standard specification for diesel fuel oil, biodiesel blend (b to b ) reporte del sector petrolero global scenario of biofuel production : past , present and future dynamic energy return on energy investment ( eroi ) and material requirements in scenarios of global transition to reflexiones en torno al desarrollo de los biocombustibles en ecuador. ceda, . centro ecuatoriano de desarrollo ambiental -temas de an alisis termodin amica plan nacional de desarrollo. plan nacional de desarrollo. quito: consejo nacional de planificaci on embodied energy and energy return on investment analyses in maize production for grain and ethanol under center pivot, subsurface drip, and surface (furrow) irrigation with disk tillage and no-till practices energías renovables observatorio de energías renovables en am erica latina y el caribe agrocombustibles dar an impulso a palma y caña energy information administration governo federal, rio de janeiro ep petroecuador firma contrato con empresas alcoholeras para la producci on de ecopaís balance y proyecciones del sistema de subsidios energ eticos en ecuador. an alisis, quito tablero comando para la promoci on de los biocombustibles en ecuador a preliminary investigation of energy return on energy investment for global oil and gas production projecting the effect of oil price regimes on biofuel markets a new long term assessment of energy return on investment (eroi) for u.s. oil and gas discovery and production will eroi be the primary determinant of our economic future? the view of the natural scientist versus the economist what is the minimum eroi that a sustainable society must have? energies seeking to understand the reasons for different energy return on investment (eroi) estimates for biofuels an alisis del uso de biocombustibles en ecuador periodo a mini review on renewable sources for biofuel energy return on investment (eroi) of china's conventional fossil fuels: historical and future trends encuesta de superficie y producci on agropecuaria continua. inec atlas de la agroenergía y los biocombustibles en las am ericas atlas bioenerg etico del ecuador life cycle assessment of various cropping systems utilized for producing biofuels : bioethanol and biodiesel eroi of global energy resources. preliminary status and trends. college of environmental science and forestry energy, eroi and quality of life large quantities of high quality energy eroi of different fuels and the implications for society la palma aceitera en el ecuador: ¿un cultivo social y sustentable? línea de fuego balance energ etico nacional plan maestro de electrictidad plan nacional de eficiencia energ etica - . plan nacional de eficiencia energ etica ecuador marca su rumbo en la industria de los agrocombustibles comments on energy return on investment ( eroi ): reconciling boundary and methodological issues year in review-eroi or energy return on (energy) invested order from chaos : a preliminary protocol for determining the recent developments and key barriers to advanced biofuels: a short review towards an improved methodology for energy return on investment (eroi) for electricity supply pollution prevention, a key to economic and environmental sustainability informe ethanol production using corn, switchgrass, and wood informe estadístico enero agosto time series eroi for canadian oil and gas dectreto ejecutivo . registro oficial del ecuador . viceministerio de promoci on de exportaciones e inversiones energía verde para gal apagos breve reseña hist orica de la exploraci on petrolera de la cuenca oriente quantification of total nitrogen according to the dumas method biofuel policy in india: a review of policy barriers in sustainable marketing of biofuel issues to consider , existing tools and constraints in biofuels sustainability assessments issues to consider , existing tools and constraints in biofuels sustainability assessments municipal solid waste system analysis through energy consumption and return approach alternative fuels data center balance energ etico nacional colombiano union zur f€ orderung von oel sustainable development goals documento de trabajo no. , gerencia de políticas y an alisis econ omico. osinergmin, lima we acknowledge the contributions of iner, dpec, and la fabril in providing biodiesel samples and soderal s.a., for permitting us to collect information on the energy consumption of its industrial processes. the authors declare no conflict of interest. no additional information is available for this paper. key: cord- - sm rlao authors: kazi, aamer; riyaz, mirza; tang, xin; staack, david; tai, bruce title: specific cutting energy reduction of granite using plasma treatment: a feasibility study for future geothermal drilling date: - - journal: procedia manufacturing doi: . /j.promfg. . . sha: doc_id: cord_uid: sm rlao abstract geothermal energy is one of the most consistent and viable sources of renewable energy. however, harnessing this energy has proved to be a challenge mainly due to the difficulty in drilling hard igneous rock formations that occur in and around geothermal wells. therefore, an energy efficient method that can drill hard rocks needs to be developed. in this paper, the effect of micro-scale energy delivery, in the form of plasma, to weaken rock by inducing micro-cracks is studied. two different types of granite (igneous rock) were sampled and used in this study, out of which the one control group was treated with five, kv, j pulses of plasma while the other was left uncracked. the effect of the cracks is quantified by conducting facing tests on the plasma cracked and uncracked samples and measuring a reduction in the specific cutting energy. two different methods were used to estimate the specific cutting energy, where the first method considered the entire cutting process and the second method considered only the stable cutting region. the plasma treatment showed a maximum of % and a minimum of % reduction in specific cutting energy and was regarded as being dependent on mainly the hardness and size of the samples. all results in this study are validated using statistical analysis. with the advent of global warming and the rise of greenhouse gases due to the excessive use of fossil fuel-based electricity, it has become imperative to search for cleaner alternatives to produce energy. geothermal energy has long been regarded as one of those viable alternatives. it is defined as the heat derived from within the sub-surface of the earth [ ] . it is one of the better sources of renewable energy because it is independent of the weather and the output is far more consistent [ ] . however, there are several physical and economic factors that prevent geothermal energy from competing with conventional fossil fuel-based (oil and gas) energy. one of the more significant physical factors is the difference between geothermal and petroleum rock formations. geothermal formations have primarily igneous rocks, such as granite, while oil formations consist of mainly sedimentary rocks, the former being significantly harder and more abrasive than the latter [ , ] . the harder rock encountered in geothermal drilling leads to higher tool wear, increased cutting forces and a lower rate of penetration. this increases the cost of production and reduces efficiency of the overall process [ ] . in order to overcome these issues, attempts have been made to develop deep geothermal drilling technologies that are economic. several studies revolve around the use of rock fragmentation techniques as a form of aid to induce cracks in hard rocks before drilling them. saadati et al. [ ] with the advent of global warming and the rise of greenhouse gases due to the excessive use of fossil fuel-based electricity, it has become imperative to search for cleaner alternatives to produce energy. geothermal energy has long been regarded as one of those viable alternatives. it is defined as the heat derived from within the sub-surface of the earth [ ] . it is one of the better sources of renewable energy because it is independent of the weather and the output is far more consistent [ ] . however, there are several physical and economic factors that prevent geothermal energy from competing with conventional fossil fuel-based (oil and gas) energy. one of the more significant physical factors is the difference between geothermal and petroleum rock formations. geothermal formations have primarily igneous rocks, such as granite, while oil formations consist of mainly sedimentary rocks, the former being significantly harder and more abrasive than the latter [ , ] . the harder rock encountered in geothermal drilling leads to higher tool wear, increased cutting forces and a lower rate of penetration. this increases the cost of production and reduces efficiency of the overall process [ ] . in order to overcome these issues, attempts have been made to develop deep geothermal drilling technologies that are economic. several studies revolve around the use of rock fragmentation techniques as a form of aid to induce cracks in hard rocks before drilling them. saadati et al. [ ] with the advent of global warming and the rise of greenhouse gases due to the excessive use of fossil fuel-based electricity, it has become imperative to search for cleaner alternatives to produce energy. geothermal energy has long been regarded as one of those viable alternatives. it is defined as the heat derived from within the sub-surface of the earth [ ] . it is one of the better sources of renewable energy because it is independent of the weather and the output is far more consistent [ ] . however, there are several physical and economic factors that prevent geothermal energy from competing with conventional fossil fuel-based (oil and gas) energy. one of the more significant physical factors is the difference between geothermal and petroleum rock formations. geothermal formations have primarily igneous rocks, such as granite, while oil formations consist of mainly sedimentary rocks, the former being significantly harder and more abrasive than the latter [ , ] . the harder rock encountered in geothermal drilling leads to higher tool wear, increased cutting forces and a lower rate of penetration. this increases the cost of production and reduces efficiency of the overall process [ ] . in order to overcome these issues, attempts have been made to develop deep geothermal drilling technologies that are economic. several studies revolve around the use of rock fragmentation techniques as a form of aid to induce cracks in hard rocks before drilling them. saadati et al. [ ] with the advent of global warming and the rise of greenhouse gases due to the excessive use of fossil fuel-based electricity, it has become imperative to search for cleaner alternatives to produce energy. geothermal energy has long been regarded as one of those viable alternatives. it is defined as the heat derived from within the sub-surface of the earth [ ] . it is one of the better sources of renewable energy because it is independent of the weather and the output is far more consistent [ ] . however, there are several physical and economic factors that prevent geothermal energy from competing with conventional fossil fuel-based (oil and gas) energy. one of the more significant physical factors is the difference between geothermal and petroleum rock formations. geothermal formations have primarily igneous rocks, such as granite, while oil formations consist of mainly sedimentary rocks, the former being significantly harder and more abrasive than the latter [ , ] . the harder rock encountered in geothermal drilling leads to higher tool wear, increased cutting forces and a lower rate of penetration. this increases the cost of production and reduces efficiency of the overall process [ ] . in order to overcome these issues, attempts have been made to develop deep geothermal drilling technologies that are economic. several studies revolve around the use of rock fragmentation techniques as a form of aid to induce cracks in hard rocks before drilling them. saadati et al. [ ] the presence of pre-existing cracks in granite resulted in a reduction of the cutting force required to reach a penetration depth. waterjet [ ] , thermal spallation [ ] and high-power laser [ ] are some of the current rock fragmentation techniques that use this concept of pre-cracking to improve the drilling process. however, these techniques suffer from various drawbacks, such as a poor area of effect in the case of thermal spallation and high-power laser, and high-pressure working fluid transportation issues in the case of waterjet [ ] . another technique that has been used for rock drilling and demolition for decades is electric pulsed power [ ] . it is one of the primary methods of non-mechanical contact rock breakage. however, majority of the applications of this technology, such as electro-pulse boring [ , ] , require very high voltage, high power, short electric pulses to be effective ( - kv, ns, ~ , j) [ ] . therefore, there is a requirement to develop efficient hard-rock drilling techniques that address these shortcomings. in this paper, the effectiveness of a novel methodology that will leverage micro-scale energy delivery, in the form of plasma, to the rock surface in order to cause fracture was studied. the goal of this research was to develop a more controlled and low energy alternative to enhance rock fragmentation in geothermal drilling. this technology will be used along with traditional drag-bit drilling operations (i.e., a hybrid approach). the technology aims to locally pre-crack rocks using under-liquid low energy (~ j and kv) nanosecond plasma pulses (~ ns). since the required energy is low, the power delivery is also achievable. micro-cracks on the rock substrate can be generated by inducing a nanosecond pulsed plasma discharge between two electrodes submerged under water [ ] . the electrical discharge between the electrodes generates extreme pressures due to the short timescale of the plasma event. this leads to a cavitation bubble generation in the fluid, which when collapses due to the pressure difference induces a shockwave. this shockwave leads to localized micro-cracks on the rocks which weaken them. the weakened rock becomes easier to drill, which in turn improves the efficiency of the drilling process. the effectiveness of the plasma induced micro-cracks is validated by comparing the specific cutting energy (p s) of plasma-cracked and uncracked granite. specific cutting energy is defined as the amount of energy required to remove a unit volume of the workpiece material. the hypothesis was that micro-cracks on the granite surface would lead to a reduction in ps and thus a reduction in cutting forces. granite is considered for this experiment as it is one of the more common igneous rocks encountered during geothermal drilling. two different varieties of granite (colonial white and westerly) are sampled with different dimensions to test the efficacy of the plasma treatment in two completely distinct scenarios, and to account for the inhomogeneous nature of the rock. the specific cutting energy of each granite is estimated by facing the samples on a cnc lathe, where the power expended during the cutting process and material reduction after the process are monitored. a facing process was considered in order to maintain simplicity of an orthogonal cutting configuration. a full-scale geothermal drilling process was not considered due to the process, environmental and geometric complexities that would be encountered [ ] . these experiments were done mainly to showcase the isolated effect of the plasma treatment. the experimental results were statistically validated. this paper is organized as follows: sample preparation procedure and the methodology used to calculate the specific cutting energy are given in section . an introduction of the plasma cracking setup and cutting test setup is given in this section as well. section presents the specific cutting energy results and section discusses the implications. lastly, section summarizes the study and draws the conclusions. in order to account for the inhomogeneity of rock and the uncontrollable nature of downhole drilling conditions, two different granite varieties are sampled with different dimensions and faced. multiple cylindrical samples were cut from colonial white (sample set ) and westerly granite (sample set ). the composition of these samples, obtained using x-ray diffraction, is given in table . the samples were then equally divided into a treated and untreated control group. each rock sample in the treated control group was cracked using five pulses of plasma in a circular pattern on the rock ( kv, j each). five pulses were selected as it was the number of pulses at which the effect of the cracking was observable through visual inspection. the cracks were generated equidistant and at a radial distance of mm from the center of the colonial white samples, and mm from the center of the westerly samples. the particulars of the specimens are shown in table . to crack the rocks, a nanosecond pulsing power circuit, with an air spark switch was used. the schematic of the experimental setup is shown in fig. . the test setup includes the following: (a) the electrical plasma generation system, (b) the test tank, and (c) the characterization/diagnostic equipment. the electrical plasma generation system includes a current source (spellman sl a negative polarity high voltage dc power supply) and a nanosecond pulse generation circuit ( nf capacitor bank and a mΩ ballast resistor, fig. ). the air spark gap (shown in fig. .) switch enables tuning of the breakdown voltage in the circuit and hence the submerged plasma discharge voltage. the air spark gap also allows for nanosecond pulsing. the test tank is an acrylic container that enables optical access for various characterizations and contains the test liquid, the test sample and the plasma generation electrodes. the electrodes are fed through a custom d printed electrode holder (enables inter-electrode spacing adjustment) for the various electrical, fluid, thermodynamic and emission characterizations, the test setup includes an oscilloscope (lecroy, waverunner mxi) to facilitate plasma discharge voltage and current measurements through voltage and current probes. the specific cutting energy was determined by performing a facing operation on an emco concept turn cnc lathe. the rocks were clamped in a -jaw chuck and faced using a tungsten carbide insert with a constant ° rake angle. an example facing operation on colonial white is shown in fig. . a facing operation was preferred to a turning operation due to limitations with treatment area. treating the flat surface was more viable than treating the curved surface since the discharge process required a certain minimum area which could not be obtained from the curved surface. moreover, the rock samples were procured from granite countertop manufacturers, who hone and resin the surface of the countertop. this is done in order to fill pits, crevices, and holes on the rock surface that can compromise with rock stability. however, the underside of the countertop slab is left unpolished. the plasma tests were conducted on this natural unpolished surface. the power expended during the cut was recorded by using a fast response universal power cell (load controls inc., sturbridge, massachusetts, us) with a response time of . s. this cutting data was collected using a ni-usb data acquisition unit with a sampling rate of hz and processed on labview. the cutting parameters are illustrated in table . the sample rotation speed was selected in order to adhere to the scale of cutting speeds seen in traditional geothermal drilling operations [ ] . the feed and depth of cut were selected to maintain machine stability. a tungsten carbide was selected as it is difficult to shape polycrystalline diamond compact (pdc) cutters to have a cutting edge suitable for a facing operation. to minimize the effects of tool wear over time, a new insert is used for every sample tested. the overall cutting test setup is shown in fig. . in this section, an overview of the methodology used to analyze the raw cutting data is presented. a sample power curve obtained from the facing operation is shown in fig. . the raw data presented shows an oscillatory trend and is primarily due to two factors: the nature of brittle fracture and the inhomogeneous nature of rock [ ] . figure also illustrates three distinct phases that the cutting data could be divided into. the first phase was the power measurement before the cut began, i.e., idle spindle rotation at rpm. this average of the idle spindle power is subtracted from the rest of the curve in the result section to show pure cutting power and to discount the machine power. the second phase occurred after the initial contact of the cutting tool with the rock, which resulted in a gradual cutting power increase. the third phase was the stable cutting phase which was defined by a decrease in the cutting power due to a linear decrease in the material removal rate as the cutting tool fed towards the center. this three-phase trend was exhibited by all the rock samples tested in this paper, and a similar trend has been reported in other studies as well [ ] . in this investigation, the specific cutting energy was calculated using two different approaches. the general formula for specific cutting energy is given by where p is the machining power and z is the material removal rate, defined by eq. ( ) for facing. the first method considered the entire duration of the cut, i.e., phase and phase of the facing process. the ps is calculated by the total machining energy divided by the actual volume removed. the total energy was obtained by integrating the power data with time and the volume removed was obtained by the weight change before and after the cutting (assuming a constant density). the result is defined as the apparent specific cutting here since this calculation takes advantage of the extra material removal caused by chipping or fracturing. occasionally, the excess edge effects can get exaggerated due to the proximity of the plasma treatment with the edge of the specimens. therefore, for a more conservative estimate of ps, a second approach is proposed which considers only phase of the cutting process. this phase occurs closer to the center of the specimen, and hence disregards the edge effects. this gives a value of specific cutting energy referred to as the true specific cutting energy, which is more suitable to gauge the effectiveness of the plasma treatment. this is calculated by first finding the rate of change of cutting power, such that as the cutter feeds towards the center with a constant feed rate in facing, the cutting speed decreases linearly with the decrease in diameter. the cutting speed is a function of the diameter in this process (since rotational speed is kept constant), and is given by from eqs. and , it is proven that power decreases linearly as well. however, due to the oscillatory nature of the raw data, a linear curve fitting was adopted to find the rate of change of cutting power during phase . this is illustrated in fig. . the slope then can be used to find ps using both equations. in this section, the apparent and true specific cutting energy results of colonial white granite are presented. figure compares the results of the facing operation between cracked and uncracked granite specimens. it is evident that the cutting power is lower for cracked samples during almost the entire cutting process except the initial contact and toward the center. figs. (a) and (b) . from visual observation, the cracked sample exhibited more chipping and loss of material. this is further supported by fig. , which shows less power (forces) required to cut the rock as it fractures apart during the cutting. also, the linear descending profile becomes less obvious due to the same reason. the apparent and true specific cutting energy of all six samples were averaged and tabulated in table . by comparing the means, the apparent specific cutting energy was reduced by . %, while the true specific cutting energy was reduced by . % after the plasma treatment. again, the more significant reduction in apparent specific cutting is because the calculation accounts for possible chipping and fracturing effects, whereas the true specific cutting energy only represents the stable cutting region. the statistical difference between the uncracked and cracked samples for both cases was confirmed using a paired two sample t-test with a confidence level of %. a comparison of the power vs. time curve between uncracked and cracked westerly granite specimens is shown in fig. . a reduction in the cutting power is seen as well. however, unlike the colonial white granite, the power data of cracked westerly granite does not have major fluctuation and plateau, which indicate a more stable cutting throughout. the rock samples after the cutting process are shown in figs. (a) and (b). the severity of edge chipping effect is much lesser than that of colonial white samples discussed in the previous section. this observation explains the smooth and consistent cutting profiles of both uncrack and cracked samples. the apparent and true specific cutting energy results are given in table . after plasma treatment, the apparent and true specific cutting energy reduce by . % and . %, respectively. the similar reduction percentages indicate minimal chipping and fracturing effects, but the plasma treatment still weakens the rock in certain way. for this sample set, the statistical difference of the apparent specific cutting energy between uncracked and cracked specimens could be validated at a % confidence level. however, a marginally significant difference for the true specific cutting energy was observed (p-value of . ). in this section, the data analysis results of both samples, limitations and possible improvements of the testing methodology are discussed. from the composition shown in table , colonial white was the harder rock between the two granite varieties. a higher hardness would result in a higher specific cutting energy and this can be supported by comparing the uncracked specific cutting energy results in sections . and . . colonial white granite shows a significant reduction in the apparent specific cutting energy after the plasma treatment because of the increased edge chipping effect. even though cutting around the edge is neglected, the outcome of the plasma treatment is still significant as there is still a . % reduction. in comparison, the reduction of westerly granite in both true and apparent specific cutting energy values are comparatively lesser. it can be inferred that an extra pulse or two may be required to make this result statistically significant. however, the practical significance of the treatment cannot be discounted as a reduction of the true specific cutting energy does exist. comparing the specific cutting energy results between colonial white and westerly granite, the plasma treatment had a bigger impact on the former although it was harder. the increased chipping seen in colonial white proves that the effect of plasma is dependent on more than just the hardness. perhaps this was a result of the plasma treatment being performed on a smaller surface area. factors such as a loosely packed grain structure, which facilitates material removal, are possible reasons as well. taking these factors into account, it is recommended to use the true specific cutting energy analysis for smaller samples, and apparent specific cutting energy for larger samples. this is because the effect of edge chipping is negligible in larger samples, and the apparent specific cutting energy is calculated using direct experiment data. the true specific cutting energy is an analytical approximation. the descending power profiles observed (phase ) for both rocks are fairly linear. from eqs. and , this linear relation implies that the specific cutting energy is indeed independent of cutting speed. this means the cutting force is also speed independent, which has been confirmed by other studies on the brittle failure mode of rocks [ , ] . from an energy perspective, plasma pre-treatment is also a loss of processing energy to trade for cutting energy reduction. in this study, a total of j of energy was spent to perform pulses of plasma ( j per pulse). cutting energy reduction can be calculated by the difference of power curves before and after plasma treatment. in the colonial white samples, approximately j of energy was saved, while in the westerly samples, j was lost. this indicates that an energy saving scenario requires proper plasma pre-treatment. however, it should be noted that the comparison does not consider other energy aspects, such as process time, tool life, and so on. finally, in this study, a couple of limitations could be addressed in future work. due to a facing process for this experiment, a tungsten carbide insert was used over a practical pdc insert for rock drilling. pdc inserts are usually manufactured for drag-bit type drilling operations and do not have the requisite cutting edge requirements for facing. therefore, as a result of using a carbide insert, the presence of tool wear in this experiment had to be accounted for, despite that a new tool was used for every cut. in addition, although the true specific cutting energy reveals the cutting force reduction in a stable cutting condition, a full factorial experiment is necessary to confirm the effects of rock type and size, and their interactions on the plasma-induced chipping and fracturing, which appear to be beneficial to real applications. in this investigation, the effect of micro-scale energy delivery, in terms of plasma pulses, on the specific cutting energy of granite is studied for the development of future geothermal technology. three major findings are concluded as follows. firstly, noticeable reduction of specific cutting energy (up to %) was confirmed on two different granite samples. secondly, the plasma treatment was deemed to be dependent on more than just the hardness of the sample. the size and rock grain structure may both play a major role in influencing the extent of edge chipping and fracturing. finally, between the two methods to calculate the specific cutting energy (namely true and apparent specific cutting energy), the true specific cutting energy is a more conservative approach which potentially eliminates the effect of size. having shown the effectiveness of plasma-assisted cutting process, the next step of this study is to quantify the extent of cracks to relate the plasma energy input and cutting energy reduction. this will provide a fundamental basis for the design and optimization of this concept at scale. the status and future of geothermal electric power worldwide status of geothermal development and international cooperation. geothermal resources council transaction geothermal drilling technology aerated drilling cutting transport analysis in geothermal well a study of geothermal drilling and the production of electricity from geothermal energy a numerical study of the influence from pre-existing cracks on granite rock fragmentation at percussive drilling drilling performance of rock drill by high pressure water jet under different configuration modes enhancing the drilling process for geothermal resources by combining conventional drilling and the spallation technology advanced rock drilling technologies using high laser power novel deep drilling technology based on electric plasma developed in slovakia. nd general assembly and scientific symposium of the international union of radio science drilling and demolition of rocks by pulsed power. digest of technical papers electro-pulse boring (epb): novel super-deep drilling technology for low cost electricity electro pulse boring: an experimental rock-breaking technology for low-cost access to ubiquitous, inexhaustible, autonomous, ultra-deep ( - km) geothermal heat influences on high-voltage electro pulse boring in granite microbubble generation by microplasma in water rock cutter interactions in linear rock cutting experimental study of force responses in polycrystalline diamond face turning of rock the mechanics of rock cutting this project was funded by the u.s. department of energy eere geothermal office, grant number #de-ee key: cord- - w ldm authors: kadir, m.a.; razak, f.i abdul; haris, n.s.h. title: experimental and dft data of p-chlorocalix[ ]arene as drugs receptor date: - - journal: data brief doi: . /j.dib. . sha: doc_id: cord_uid: w ldm the data in this article provide information on spectroscopic and theoretical data for p-chlorocalix[ ]arene when combined with selected drugs, such as paracetamol, ibuprofen, and cetirizine. the present spectroscopic data are generated from fourier transform infrared (ftir), nuclear magnetic resonance (( )h nmr and ( )c nmr), and ultraviolet-visible spectroscopy (uv-vis) as the key tools for molecular characterization. the measurement of the optimization energy, interaction energy, and the band gap energy between the molecules was calculated by gaussian software. it is interesting to note that of the three titled drugs identified, p-chlorocalix[ ]arene showed the highest interaction energy with paracetamol, followed by ibuprofen and cetirizine. keywords p-chlorocalix [ ] arene, paracetamol, interaction energy, molecular receptors, gaussian specifications table subject chemistry specific subject area synthetic chemistry, spectroscopy, computational chemistry type of data table figure how data were acquired ftir perkin elmer spectrum and the spectra were recorded in the range of - cm - utilizing potassium bromide (kbr) pellet, uv-vis (spectrophotometer shimadzu uv- ), h, and c nmr spectra analyzed by bruker avance iii spectrometer. computational calculations were performed using gaussian software package on the desktop cpu@ . ghz processor provided by faculty of science, utm, -bit operating system with an x -based processor, a . installed memory and . gb ram. the reaction mixture is heated up to °c until completion. the computational data are calculated at ground state and td-scf/dft/b lyp/ - g. the compound was characterized by a spectroscopic method and the application was observed by a uv spectrophotometer. gaussian software was used to calculate the interactions between host (pchlorocalix [ ] arene ) and guest molecules (paracetamol, ibuprofen, and cetirizine)  the dataset in this study can be used as a reference and guidance for further investigation of calix [ ] arene derivatives as a drug-receptor.  the discovery of new methods in computational chemistry offers research opportunities and further collaborations with other researchers who are interested in the host-guest chemistry of calix molecules.  since the outbreak of pandemic covid- , computational modelling has been utilized in explaining the chemical interactions between molecules. this study is an example of a contribution made by dft studies in enhancing understanding of molecular interactions between the host and guest molecules. compound p-chlorocalix [ ] arene was prepared from the reaction between calix [ ] arene, ferric chloride, and thionyl chloride in tetrachloromethane [ ] . the title compound was obtained as a brown solid after tetrachloromethane was removed under vacuum, and was further characterized by fourier transform infrared (ftir), nuclear magnetic resonance ( h nmr and c nmr) and ultraviolet-visible spectroscopy (uv-vis). fig. shows the illustration of computer modelling using gaussian software. the p-chlorocalix [ ] arene acted as molecular host, and three selected guest drugs namely paracetamol, ibuprofen, and cetirizine, acted as the guest molecules. the result showed that both hydrogen bonding and - interactions combined to stabilize the molecular structures [ ] . theoretical models proposed by gaussian were applied to measure the optimization energy, binding energy, and interaction energy of pchlorocalix [ ] arene with the drugs. the calculated data are listed in table . the descriptive measurement showed that strong interaction occurs between p-chlorocalix [ ] arene with paracetamol ( . kj/mol), which reflects a higher affinity of the interaction between both molecules [ ] as compared to ibuprofen ( . kj/mol) and cetirizine ( . kj/mol). this finding is in line with previous study that confirmed the interaction energy is in the range for a noncovalent interaction [ ] . spectroscopic data from ftir, nmr, and uv-vis are depicted in fig. , fig. , fig. and fig. , with the data tabulated in table and table , respectively. fig. indicates that pchlorocalix [ ] arene has the highest binding interaction with paracetamol as compared to ibuprofen and cetirizine, where the absorption peaks appeared at the lowest absorbance in the uv spectrum ( . , nm). the molecular orbital (mo) diagram of p-chlorocalix [ ] arene and the three title drugs are presented in fig. to elucidate the electronic transition within the complex. the diagram showed that pchlorocalix [ ] arene and cetirizine has the lowest energy band gap ( . ev) as compared to paracetamol ( . ev) and ibuprofen ( . ev). in theory, when conjugation increases, the band gap between homo-lumo decreases, thus less energy is required for the electron to excite from homo to lumo [ ] . this is applied to cetirizine because this compound exhibits more conjugated electrons when compared to paracetamol and ibuprofen. synthesis of p-chlorocalix [ ] arene was carried out accordingly to the literature procedure with some modifications [ ] . calix [ ] arene ( . g) was dissolved in tetrachloromethane, ccl ( ml). the mixture was left to stir before iron (iii) chloride, then the fecl ( . g) was added. after that, thionyl chloride, socl ( . ml) was added dropwise and heated at °c for hours. upon completion, the solvent was removed using a rotatory evaporator to give a brown solid. the residue was dissolved in ml of dichloromethane and washed with ml of saturated sodium bicarbonate two times. dichloromethane was dried over magnesium sulfate and the solvent was removed by using a rotatory evaporator to form the product as brown pale solid in % yield. the p-chlorocalix [ ] arene ( . mg, . mmol) was prepared in dimethyl sulfoxide ( ml). the solution of analytes was also prepared by dissolving paracetamol ( . mg, . mmol), ibuprofen ( . mg, . mmol) and cetirizine ( . mg, . mmol) in dimethyl sulfoxide ( ml). the solution was mixed and the obtaining spectrum was observed for any changes at nm. cetirizine ibuprofen paracetamol all compounds were calculated using density functional theory (dft)/b lyp method with a - g (d,p) basis set. the geometry was optimized without any symmetry constraints and performed at the gas phase. the value formula of uncorrected binding energy was collected from optimization calculation, as displayed in equation . the collected data of optimization energy was essential to obtain the corrected binding energy [ ] by adding the basis set superposition error (bsse) value. the correction value is required to remove the artificial energy lowering caused by the bsse [ ] . the formula of corrected binding energy was displayed in equation . meanwhile, the value of interaction energy was collected from interaction energy calculation, the formula was displayed in equation . the data of table can be used [ , ] as a guideline for further interpretation. the homo and lumo computational analysis have been used to clarify the electronic transition within the complex by td-scf/dft/b lyp method with a - g (d,p) basis set in a solvent phase, where dmso was used as a solvent match for the experimental method. synthesis and host -guest properties of a calix [ ] arene based receptor closed by an internal ion-paired cap theoretical approach of dft b lyp/ - g (d, p) on evaluating the performance of tert-butylhydroquinone and free fatty acids in inhibiting the oxidation of palm olein calix [n] arene-based drug carriers: a dft study of their electronic interactions with a chemotherapeutic agent used against leukemia the possibility of iron chelation therapy in the presence of different hpos; a molecular approach to the non-covalent interactions and binding energies synthesis and characterization of cinnamylidene acetone -a study on tuning of band gap by vibrational spectroscopic tools dft conformational study of calix[ ]arene and calix[ ]arene: hydrogen bond a new approach to counterpoise correction to bsse the authors greatly acknowledge the scientific and financial support from universiti malaysia terengganu for the success of this work. we would also like to express our gratitude to the center for the authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article. key: cord- -d qevnl authors: brown, stephen p.a.; brown, marilyn a.; madlener, reinhard; thomas, stephen; zhou, peng; antunes, carlos henggeler; yeh, sonia; du, huibin; goutte, stéphane title: the continuing evolution of energy policy date: - - journal: energy policy doi: . /j.enpol. . sha: doc_id: cord_uid: d qevnl nan available online april - /© published by elsevier ltd. the continuing evolution of energy policy as the world confronts the covid- pandemic, we hope that all of you are doing well. we know that many lives have been greatly disrupted, and that world economic activity is slowing and maybe declining in some places. we have read reports that energy consumption has been greatly affected by the slowdown in world economic activity-likely contributing to the sharp plunge in oil prices earlier this year. we do not know how long this pandemic may last. as we look forward to the end of the pandemic and a recovering world economy, however, we wonder if and how energy systems may have to be transformed, and whether new energy policy needs and approaches will emerge. will we see any change in the trajectory of adopting sustainable energy systems and reducing carbon emissions? in the academic world, many of us are now teleworking and teaching our courses online. this transition has proved time consuming-so we want to thank our many reviewers who are staying on or close to schedule. so far, energy policy has been mostly unaffected by the pandemic, but we must recognize that the elsevier employees who are responsible for the operations side of the journal may at some time be affected by in the meantime, we want to keep you informed about some recent developments regarding energy policy, including a little about its history and our editorial priorities. the first issue of energy policy was published years ago in june . in its first year of publication, energy policy had three issues that contained research articles and several reports. the focus was on oil, natural gas, electricity markets and nuclear energy. none of the articles in the first year focused on environmental issues, climate change issues, energy efficiency/conservation or renewable energy. john a.g. thomas was the editor with ivan f. klimes as the assistant editor. the international editorial board, as it was then called, included such well-known energy researchers as morris adelman, peter odell and sam schurr. over the years, the important policy issues in energy use and supply have changed, and the interest in energy policy issues has grown. as a result, energy policy's content has evolved and expanded, reflecting the pivotal role that policies play in shaping energy systems across the globe (fig. ). the volume had one article out of that addressed environmental issues related to energy use. the the , volumes had one article each on climate change issues related to energy use. the volume also had one article addressing environmental issues related to energy use. dominated by the oil crises, security of supply, and energy efficiency, the , , and volumes did not have any articles addressing environmental or climate change issues. the volume had one article that addressed energy efficiency/ conservation. the volume had several such articles. the volume had one article that addressed renewable energy. the , , volumes had no articles about renewable energy. by the mid- s, however, the journal regularly published articles addressing energy efficiency, energy conservation and renewable energy. today, these topics occupy regular space in every volume of energy policy. chernobyl (and later fukushima), acid rain, climate change and other environmental issues related to energy supply and use gradually changed the direction of research about policies affecting energy use and production. by the mid-to late s, the journal regularly published articles on environmental issues. articles about climate issues related to energy use took a bit longer to develop, and the journal published a special issue on climate policy in . today, both environmental and climate change topics are featured in every volume of energy policy fig. ). during its first ten years of publication, energy policy grew fairly robustly in size. volume (published in ) comprised four issues with a total of articles, representing a doubling of articles compared to and an annual average growth rate of . % ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) . volume (published in ) comprised issues with a total of articles, representing more than a tripling of articles published in comparison to volume and an annual average growth rate of . % ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) . perhaps reflecting the weakness in world oil prices, volume (published in ) comprised issues with a total of "only" articles, representing a . % increase of articles over volume and an annual average growth rate of merely . %. increased recognition about environmental issues and climate change associated with energy use and then rising oil prices have stimulated a strong surge in research about energy policy. in , energy policy had about a percent acceptance rate and published articles. the figure represents nearly a -fold increase over the number of articles published in , or an annual average growth rate of . % (from to ). the articles published in covered a wide variety of topics in energy policy including primary energy resources; energy conversion, transportation, transmission and storage; energy use and end-use technologies; energy markets and pricing; contents lists available at sciencedirect energy policy journal homepage: http://www.elsevier.com/locate/enpol https://doi.org/ . /j.enpol. . energy and society; energy and the environment; investment, financing and other economic issues; and technological change. clarivate reports a fairly steady climb in energy policy's two-year impact factor since . the respective figures are . in , . in , . in , . in and . in . the impact factor will become available in june . the impact factor places energy policy in the top quartile of journals in economics (ssci), environmental studies (ssci), environmental sciences (scie) and energy & fuels (scie). similarly, research papers in economics' (repec's) aggregate ranking for energy policy places it in the top of economics journals over the past ten years. energy policy is available in thousands of academic libraries and government institutes and had more than million full-text downloads in . after john a. g. thomas, patrick coyne served as editor for a number of years. with several changes in publication houses, the records of editorial leadership are less clear in the s and s. by , however, the editorial team was lyndon driscoll, managing editor and nicky france, editor. by , lyndon driscoll was the publisher and nicky france was the sole editor-a role she served in for many years before lorna greening and michael jefferson took over as editors in . with greening's departure in , the editorial team expanded to five people: stephen p. a. brown, michael jefferson, reinhard madlener, stephen thomas, and peng zhou. marilyn brown joined the team in . when michael jefferson retired as senior editor in early , carlos henggeler antunes and sonia yeh joined the editorial team. more recently huibin du and st� ephane goutte joined the editorial team, bringing the number to nine. as described above, energy policy recently added two members to the editorial team, huibin du and st� ephane goutte. huibin du joined energy policy as an associate editor on december , . prof. dr. du is a professor and the vice dean of the college of management & economics, tianjin university. her expertise is in resource and environmental management. as a principal investigator, she has conducted a national key r&d program of china, a national natural science foundation of china (nsfc) key project, and many other projects. based on these programs, she co-led a large collaborative team from georgia institute of technology, stony brook university, the university of adelaide, chinese academy of sciences, peking university and several other universities/institutes to implement research on air pollution regional joint governance, renewable energy development, and energy-water nexus, energy-economy-environment ( e) his interests lie in the area of mathematical finance and econometric applied to energy or commodities. he has published more than research papers in international peer-reviewed journals. he has also been a guest editor of various special issues of international peerreviewed journals and editor of many handbooks. he was a visiting professor at university of luxembourg and vietnam national university of hanoi, vietnam. although energy policy has evolved and taken on a greater academic relevance since its beginnings in , in many ways it remains the same. although the journal has become more technical as the field of energy-related research has matured, we expect the articles that we publish to inform energy-related policy. mathematical modeling, econometrics and other approaches should serve only to support the policy issues being examined. modeling should be a means rather than an end. papers that are focused on technology assessment, mathematical modeling, econometrics and other approaches with a few policy implications tacked on at the end, or no deeper and explicit new policy insights and implications derived from the analysis, do not belong in energy policy. they should be sent to more technically oriented journals. at energy policy, we consider a wide variety of topics that include fossil energy, renewable energy, nuclear power, behavioral, environmental and climate issues-provided that the manuscript focuses on the policy issues related to energy supply or use. we consider manuscripts with research methods from a wide variety of disciplines-including economics, engineering, law, political science, public policy, psychology and sociology. we expect these manuscripts to either advance research methods or represent the current state of the art in these disciplines, and for the manuscripts to address policy issues about energy supply or use. energy policy's editors do have the ability to make the direct transfer of a manuscript to some other elsevier journals and occasionally will suggest such a transfer (either pre-or post-review). a direct transfer does require author approval, and avoids the authors' burden of resubmission to another journal. in most cases, however, the editors prefer to make suggestions about other journals and let the authors decide which journal is most appropriate. first page of the first article ever published in energy policy (leslie dienes was associate professor in the department of geography-meteorology at the university of kansas), compared to the appearance of a specimen article (on regional energy inequality in the uk by a group of authors from leeds and sheffield university) in may . we have made a few additional changes at energy policy, as explained below in some detail. we have reduced considerably the delay in handling manuscripts. we have increased the word limit for policy perspectives. we are working to increase the number of invited review articles, and we continue to seek the submission of manuscripts addressing behavioral aspects of energy choices that need to be better understood in order to design effective programs and policies. surprisingly, a number of manuscripts fail initial technical checks and are returned to the authors for correction. such problems can greatly delay assignment to an editor, and we encourage the authors to take responsibility for the submission of appropriately formatted articles (i.e. such that they match the requirements described in the guide for authors). throughout most of , the editorial capacity of the energy policy was somewhat less than the more than submissions that the journal sees during a typical year. by fall ( ), energy policy had a backlog of unprocessed manuscripts that led to a delay of - weeks between the time a manuscript was submitted to the journal and it was assigned to an editor. the delay resulted in considerable author concern and frustration. in late december and early january , the editors undertook a special project to substantially reduce the backlog of manuscripts by culling out the considerable number of manuscripts that did not meet the aims and scope of the journal. by the end of january, the time between submission and assignment to an editor was reduced to several weeks. we are continuing the practice of quickly culling out manuscripts that do not meet the aims and scope of the journal, with hopes of being able to maintain relatively quick assignment of the surviving manuscripts to editors throughout and beyond. full length articles are the principal work that we publish. these articles should present rigorous research about energy policy issues. they are normally - words. the editors will consider papers of exceptional merit up to , words. authors submitting a full length article of more than words must submit a brief statement in their cover letter, explaining the exceptional merit of the submission to energy policy. research notes are shorter papers of less than words. research notes should present fully realized research but are shorter in length than full length articles. we have increased the word limit for policy perspectives from to words. a policy perspective is a relatively short contribution that offers judgment on an energy policy issue-normally without original research. a policy perspective should present well-reasoned and fully considered thinking to reach conclusions that are germane to important policy issues in energy supply or use. the number of policy perspectives per journal volume may be limited at the discretion of the editors. energy policy occasionally publishes invited review articles that are reviews of the literature. it does not publish reviews of the energy situation in a region, country or group of countries as invited review articles. invited review articles are typically initiated by one of the editors inviting a senior person to provide such an article. the editorial team will consider proposals for outstanding articles that review the literature and well capture the policy issues, but such proposals are typically expected to be received from individuals with senior standing in the profession. the editors of energy policy recognize that additional theoretical and empirical analysis of the behavioral aspects of energy choices is needed to better inform the design of energy programs and policies. we continue to seek more submissions examining the behavioral aspects of energy choices. what is the role of consumer trust and social norms, cognitive effort and rational inattention, environmental attitudes, time preferences, loss aversion, habits and habit formation, status quo bias, and more? these concepts need to be examined more fully to better understand how behavioral responses and shifts (including the rebound effect) could run counter to policy goals and alter policy effectiveness, and to assess how energy policy could be reformulated to address these behavioral responses. before it is assigned to an editor, each new manuscript is screened by elsevier's technical staff to assure that it complies with submission requirements. a surprising number of manuscripts are returned to the authors for failure to comply with the submission requirements. the technical expectations are: ) the submission includes all the expected files, including cover letter, highlights, manuscript file, tables (if needed) ) the authors listed on the manuscript match the list of authors specified in the submission; ) - keywords are present in the manuscript file; ) all headings and subheadings are numbered throughout and in the journal's style; ) the first main heading is labelled 'introduction' and the last main heading is labelled 'conclusion and policy implications'; ) references are provided in the journal's style (author þ year); ) the paper is formatted with double-line spacing; ) all of the submission questions have been answered correctly; ) the word count is below the maximum, and that the number matches the actual word count of the paper (according to the counting rules specified in the guide for authors); ) - reviewers are suggested, ideally with a doctoral degree, and none of them are at the same institution as any of the authors; and ) the abstract is - words as peter odell ( ) wrote on the tenth anniversary of this journal: "energy policy, which commands the interest and respect of both scholars and policymakers in so many aspects of the important energy issues, will remain an important forum for presentation and discussion …" energy policy has a continuing mission of advancing and informing policy issues about energy use and supply. fulfilling this mission requires well-researched articles using rigorous research methods and thinking about energy policy issues. we consider a continuum of papers, from those that make more substantial contributions to policy to those that make more substantial contributions to methodology, but we expect all papers to have a focus on policies about energy supply or use. by characterizing our priorities, the editors hope to continue to attract strong manuscripts with meaningful energy policy implications that can be published in future issues of energy policy. energy policy, - : retrospect and prospect key: cord- -fc wm authors: zhang, xiaqi; wang, fang; weng, ming; cao, meng title: calculations of energy deposition and ionization in the novel coronavirus by electron beam irradiation date: - - journal: radiat phys chem oxf engl doi: . /j.radphyschem. . sha: doc_id: cord_uid: fc wm using monte carlo methods, this study investigates energy deposition of energetic electrons and ionization in the novel coronavirus by electron irradiation, which are important characteristic quantities related with biological damage formation. the inelastic scattering of low-energy electrons (< kev) was calculated by dielectric theory. the optical energy-loss functions of viral proteins and rna were derived from an empirical method in the energy-loss range < ev and the calculation of optical parameters of the biomolecules. the densities and distributions of energy deposition and ionization were calculated from the stopping power and inelastic cross-sections in the electron-cascade simulation. electrons with primary energies of approximately – kev produced significant energy deposition and ionization in the target coronavirus. more energetic electrons were less effective due to the larger electron range and fewer scattering events in the coronavirus. the novel coronavirus ( -nocov) was responsible for the pandemic of (sohrabi et al., ; who, ) . to avoid exposure to covid- , effective methods that kill or inactivate the virus on contaminated media or in specific environments are demanded. electron beam irradiation is widely used for killing microorganisms, bacteria, and viruses (berovic et al., ; benson, ; feng et al., ) , because its penetration depth and dose can be controlled to comply with environmental protection requirements. moreover, under controlled irradiation, the virus can be partially or totally inactivated, providing useful information on its properties (lidzey et al., ; smolko and lombardo, ) . electron irradiation damage on biological macromolecules is mainly characterized by inactivity and the irreversibly chain broken (tan and liu, ) . the severity of these effects is highly correlated with the energy deposition and ionization in the molecules, which occur by inelastic interactions between the electrons and molecules (boudaïffa et al., ; kempner, ; kempner, ; tan et al., ; zhang and tan, ) . to properly understand electron irradiation effects on the novel coronavirus, the energy deposition and ionization must be calculated, because experimental evaluation with currently available methods is very difficult. high-energy electrons (above tens of kev) are usually applied for antiseptic purposes. when primary electrons interact with a target molecule by inelastic scattering, they lose energy and excite the shell electrons as secondary electrons (ses). low-energy electrons, including decelerated primary electrons and ses with energies below ev, significantly contribute to the large number of ses during the electron-cascade process, exerting a considerable ionization effect (emfietzoglou et al., ; nikjoo et al., ; zhang and tan, ) . therefore, the interaction of low-energy electrons with the main proteins and rna macromolecules of the novel coronavirus was the key issue of our calculation. the stopping power was suitable for describing the energy-deposition probability in the target, and the ionization events were determined as the inelastic cross-sections of collisions with the shell electrons of j o u r n a l p r e -p r o o f an atom. the stopping power and ionization events of low-energy electrons are usually calculated by dielectric theory, which requires the energy-loss function (elf). the elf can be derived from the optical elf (oelf) through a proper dispersion relation. however, as important input data for the calculation of the oelf, the optical parameters of macromolecules of proteins, rna are not available. tan et al. developed an empirical method that estimates the oelf of organic biomaterials at energy losses below ev (tan et al., a (tan et al., , b . the same approach is expected to be applicable to the novel coronavirus. in this work, we calculated the distributions of energy deposition and ionization in the novel coronavirus irradiated with electrons having primary energies below kev. for the calculations, we used a simplified physical model of the novel coronavirus with a multilayer spherical shell configuration. the model is based on published information of the novel coronavirus and similar known coronaviruses (cdc, ; lu, ) . the novel coronavirus is comparatively large (with an approximate diameter of nm), and its main proteins are spiked glycoproteins (s) on the outer layer, envelope proteins (e) in the next layer, a water layer, the nucleocapsid (n), and rna in the centre (see fig. ). the diameters of each shell are marked in fig. . the components of each shell were assumed as the typical amino acid sequences or nucleobase sequences of the main proteins within the shell, extracted from the sequence resources published in the national center for biotechnology information (ncbi, ). the statistical results j o u r n a l p r e -p r o o f yielded the average molecular formulas of the three types of proteins as follows: the energetic electrons interact with the novel coronavirus through elastic and inelastic scattering. elastic scattering describes the collision between electrons and the nuclei of the target atoms, which changes the direction of the electron trajectories. the elastic-scattering calculation of electrons with energy < kev was usually based on the mott cross-section. in this calculation, the atomic differential elastic-scattering cross-sections were taken from the nist electron elastic-scattering cross-section database (jablonski et al., ) . following the additivity rule (chiari et al., ; jiang et al., ) , the differential cross-section of each kind of molecule in the novel coronavirus was calculated by summing the differential cross-sections σ el of the individual atoms in the target molecule as follows: where n i is the atomic number of the i-th atom in the molecular formula, and Ω is the solid angle determined by the scattering angle θ. the inelastic cross-sections of low-energy electrons are usually calculated by dielectric theory. this calculation requires the elf, given by the negative of the reciprocal of the imaginary part of the dielectric function (im − , ∆ ⁄ ). penn ( ) and ashley ( ) obtained the elf by extending the dielectric function in the optical limit, where the momentum transfer is = . by fitting the oelf im − , ∆ ⁄ to the experimental optical data and introducing a suitable dispersion relation, the differential inelastic cross-section σ inel of the incident electrons colliding with the shell electrons can be calculated as (ashley, ) ,△ with in these expressions, ( is the bohr radius, is the number of molecules per unit volume in the target, is the electron energy, and Δ is the energy transfer. to calculate the energy loss along the electron trajectories, we require the stopping power of the electrons, which represents the average energy loss of an electron in the unit distance. the stopping power is given by however, the experimental oelf data of most complex compounds are lacking in the literature. for the constituent molecules in the novel coronavirus, which certainly lack available optical data, the oelfs at energy losses below ev were estimated by an empirical approach for bioorganic compounds developed by tan et al. ( a; b) . the oelf was expressed by the following single drude function: where the parameters g and h are linearly related to the average atomic number i ̅ of the molecule, and can be determined by inputting the mass density of the target, the molecular weight and the total number of electrons per molecule to the f-sum rule. for j o u r n a l p r e -p r o o f energy losses larger than ev, the atomic photoabsorption data of henke et al. ( ) are available, so the oelf can be calculated from the refraction index and the extinction coefficient (ding and shimizu, ) . for energy losses between ev and ev, the oelf was calculated by spline interpolation. if the electron energy decreases by - times the bandgap energy during the electron cascade, the main energy-loss mechanism should be electron-phonon interactions, and the cross-section can be treated by fröhlich's theory (fröhlich, ) . low-energy electrons are also affected by the polarization field induced by their own motions through the target. this interaction is known as the polaronic effect. in this study, the cross-section of the polaronic effects was calculated by a semi-empirical approach proposed by ganachaud and mokrani ( ) . as shown in fig. , uniformly distributed electrons with primary energies below kev were irradiated over the -nm diameter of the novel coronavirus. the number of primary electrons was > . the densities of protein, rna and water were set to . , . , and . g cm ⁄ , respectively. the electron trajectories were traced by two monte carlo strategies. the energy deposition was determined by a simple and fast monte carlo method based on the continuous slowing down approximation (csda). the csda assumes that electrons continuously lose energy along the electron trajectories, and change directions by elastic scattering. in the ionization-characterizing calculation, each energy loss and direction change along the electron trajectories was calculated by the energy straggling strategy. if the amount of energy lost in a single inelastic scattering event exceeded the binding energy of the atomic shell, the site became ionized, producing an inner secondary electron that was traced by the same procedure as the primary electrons (caleman et al., ). this simulated electron cascade considered the events of elastic scattering, electron-electron inelastic scatterings, and electron-phonon and electronpolaron interactions (dapor, ) . to describe the inelastic interactions between the electrons and molecules, the oefls of the constituent molecules in the novel coronavirus were calculated by using eq. ( ) and atomic photoabsorption data (henke et al., ) , as mentioned above. the oefl of water was adopted from heller et al. ( ) . as shown in fig. , the oefl curves of the five components peaked at energies between and ev. the envelope yielded the highest oefl peak, and rna has the maximum peak position. from the oefls, the probability of inelastic scattering events and the energy-loss distributions were determined. and rna. the oefl of water was adopted from heller et al. ( ) . the table . like the deposition energy, the ionization was maximized in the envelope. both the energy deposition and ionization densities appeared over a larger range of primary energies (~ ev- kev) in the envelope than in the other viral components (see figs. and ) . j o u r n a l p r e -p r o o f figure shows the distribution characteristics of the deposited energy and ionization densities through a vertical section of the novel coronavirus. to simplify the presentation, the sparse structure of the spike glycoproteins was neglected, and the deposited energy and ionization were assumed to be uniformly distributed through the shell volume. the primary energy was varied as ev, . kev, and kev. at ev, the energy deposition and ionization were concentrated in the upper shell (the envelope) because the penetration range of the primary electrons was small. approximately % of the primary electrons lost all their energy and were deposited in the target. at a primary energy of . kev, the energy deposition and ionization covered most of the electrons with energies below hundreds of ev will finally loss their energy and be deposited inside the target. as the primary energy decreases, the total amounts and densities of the energy deposition decrease accordingly. the estimated deposition depth of primary electrons with energies above kev in the thick materials of the envelope, nucleocapsid, and rna is nm (fitting, ) , larger than the coronavirus diameter. as fast electrons have lower probability of inelastic interactions with molecules than slow electrons, their energy deposition and ionization in the target will decrease, as shown in figs. and . therefore, the energy deposition and ionization densities are maximized over an optimal range of primary energies ( - j o u r n a l p r e -p r o o f kev). the presented results demonstrate that the characteristics of energy deposition and ionization depend on the energy loss and electron range in the coronavirus, which are mainly determined by the primary energy of the electrons. furthermore, the electron energy deposition is correlated with the temperature rise imparted by the electron irradiation. high temperature is expected to be an important deactivating factor of the novel coronavirus. although electrons with lower energies ( - kev) effectively deposit their energies and ionize the viral macromolecules, irradiating the novel coronavirus by low-energy electrons is difficult to achieve in practice. theoretical calculations may provide fundamental physical information on the electron irradiation of viruses. in this paper, we performed calculations of energy deposition and ionization on the novel coronavirus by electron irradiation, using monte carlo methods. the interaction of low-energy electrons with condensed matter: stopping powers and inelastic mean free paths from optical data use of radiation in biomaterials science the kinetics of radiation damage to the protein luciferase and recovery of enzyme activity after irradiation resonant formation of dna strand breaks by low-energy ( to ev) electrons radiation damage in biological material: electronic properties and electron impact ionization in urea total, elastic, and inelastic cross sections for positron and electron collisions with tetrahydrofuran transport of energetic electrons in solids: computer simulation with applications to materials analysis and characterization a monte carlo modeling of electron interaction with solids including cascade secondary electron production inelastic scattering of low-energy electrons in liquid water computed from optical-data models of the bethe surface electron beam irradiation on novel coronavirus (covid- ): a monte-carlo simulation transmission, energy distribution, and se excitation of fast electrons in thin solid films electrons in lattice fields theoretical study of the secondary electron emission of insulating targets collective oscillation in liquid water x-ray interactions: photoabsorption, scattering, transmission and reflection at e = - , ev, z= - . at. data nucl nist electron elastic-scattering cross-section database, national institute of standards and technology geometric shielding effects of electron scattering from polyatomic molecules effects of high-energy electrons and gamma rays directly on protein molecules direct effects effects of ionizing radiation on macromolecules a critical analysis of the use of radiation inactivation to measure the mass of protein genomic characterisation and epidemiology of novel coronavirus: implications for virus origins and receptor binding computational modelling of low-energy electron-induced dna damage by early physical and chemical events electron mean-free-path calculations using a model dielectric function virus inactivation studies using ion beams, electron and gamma irradiation world health organization declares global emergency: a review of the novel coronavirus (covid- ) simple and universal model for electron-impact ionization of complex biomolecules monte carlo calculations of energy deposition distributions of electrons below kev in protein cross sections of electron inelastic interactions in dna electron stopping power and mean free path in organic compounds over the energy range of - , ev who world health organization, . who statement on cases of covid- a new calculation on spectrum of direct dna damage induced by low-energy electrons key: cord- -nrzjedhi authors: dasgupta, s; auth, t; gompper, g title: nano- and microparticles at fluid and biological interfaces date: - - journal: j phys condens matter doi: . / - x/aa sha: doc_id: cord_uid: nrzjedhi systems with interfaces are abundant in both technological applications and biology. while a fluid interface separates two fluids, membranes separate the inside of vesicles from the outside, the interior of biological cells from the environment, and compartmentalize cells into organelles. the physical properties of interfaces are characterized by interface tension, those of membranes are characterized by bending and stretching elasticity. amphiphilic molecules like surfactants that are added to a system with two immiscible fluids decrease the interface tension and induce a bending rigidity. lipid bilayer membranes of vesicles can be stretched or compressed by osmotic pressure; in biological cells, also the presence of a cytoskeleton can induce membrane tension. if the thickness of the interface or the membrane is small compared with its lateral extension, both can be described using two-dimensional mathematical surfaces embedded in three-dimensional space. we review recent work on the interaction of particles with interfaces and membranes. this can be micrometer-sized particles at interfaces that stabilise emulsions or form colloidosomes, as well as typically nanometer-sized particles at membranes, such as viruses, parasites, and engineered drug delivery systems. in both cases, we first discuss the interaction of single particles with interfaces and membranes, e.g. particles in external fields, non-spherical particles, and particles at curved interfaces, followed by interface-mediated interaction between two particles, many-particle interactions, interface and membrane curvature-induced phenomena, and applications. systems with interfaces are abundant in both technological applications and biology. while a fluid interface separates two fluids, membranes separate the inside of vesicles from the outside, the interior of biological cells from the environment, and compartmentalize cells into organelles. the physical properties of interfaces are characterized by interface tension, those of membranes are characterized by bending and stretching elasticity. amphiphilic molecules like surfactants that are added to a system with two immiscible fluids decrease the interface tension and induce a bending rigidity. lipid bilayer membranes of vesicles can be stretched or compressed by osmotic pressure; in biological cells, also the presence of a cytoskeleton can induce membrane tension. if the thickness of the interface or the membrane is small compared with its lateral extension, both can be described using two-dimensional mathematical surfaces embedded in three-dimensional space. we review recent work on the interaction of particles with interfaces and membranes. this can be micrometer-sized particles at interfaces that stabilise emulsions or form colloidosomes, as well as typically nanometer-sized particles at membranes, such as viruses, parasites, and engineered drug delivery systems. in both cases, we first discuss the interaction of single particles with interfaces and membranes, e.g. particles in external fields, non-spherical particles, and particles at curved interfaces, followed by interface-mediated interaction between two particles, many-particle interactions, interface and membrane curvature-induced phenomena, and applications. keywords: membranes, nanoparticles, capillary interactions, lipid bilayers, emulsions, viruses, interfaces (some figures may appear in colour only in the online journal) original content from this work may be used under the terms of the creative commons attribution . licence. any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and doi. also compartmentalize cells and thereby define organelles. transmembrane transport is essential for the communication both inside a cell as well as of cells with their environment [ , ] . the interaction of particles and pathogens with biological membranes-and therefore also their cellular uptake and intracellular transport-crucially depends on the particle size, shape, softness, and surface functionalization. nowadays a whole zoo of micro-and nanoparticles can be fabricated from various materials, with engineered shapes and surface functionalizations. the particles can be used for applications in food science [ ] [ ] [ ] , cosmetics [ , , ] , as antimicrobials [ , ] , and in nanomedicine [ ] [ ] [ ] ; therefore systematic studies and a careful consideration of potentially toxic effects are required [ ] [ ] [ ] [ ] [ ] . figure shows examples for oblate, bullet-shaped, pill-shaped, and dumbbell-shaped microparticles that are made from a polymeric material. figure shows cube-like, rod-like, irregularly-shaped, and spindle-like metal and metal-oxide nanoparticles. all these particles can also be considered as model systems for 'particles' found in nature. for example, the malaria parasite is micrometer-sized and has an egg-like shape [ , ] . milk contains casein micelles with sizes below nm that stabilize fat globules [ ] . viruses resemble roundish, filamentlike, and bullet shapes with sizes below nm [ ] [ ] [ ] ; in particular, the filamentous ebola and marburg viruses are of much interest due to their enhanced virulence that leads to high mortality rates [ , ] . fluid interfaces are rough on the molecular scale and can be analytically well described by a hyperbolic tangent-shaped density profile [ , ] , see figure . however, the typical interface width is much smaller than the sizes of the particles that we consider. in order to study the interaction of particles with interfaces, the interface can therefore be thought of as mathematical surface with its physical properties characterized by an interface tension. lipid-bilayer membranes often consist of many components, e.g. different lipids and cholesterol, and biological membranes usually also contain membrane proteins. this can lead to phase separation within the membrane, as shown in figure . the typical thickness of a lipid bilayer membrane is ≈ d nm and cannot be neglected for small nanoparticles with sizes of few nanometers. for nanoparticles with radii of nm and above, the membrane can be described as mathematical surface with curvature-elastic properties. the possiblity to model both fluid interfaces and biological interfaces (membranes) using mathematical surfaces is our motivation for discussing particles at interfaces and at membranes in a single review article. for biological interfaces, we will focus on sufficiently large particles for which a continuum model is not only feasible, but also more appropriate than an atomistic model. the deformation energy of the surface can then be calculated using the helfrich hamiltonian [ ] , here, the interface conformation is characterized by the two principal curvatures at each point of the interface, c and c , that enter the hamiltonian via the mean curvature = + h c c ( )/ and the gaussian curvature = k c c . the total deformation energy is obtained by integration over the entire interface area s. tension γ, bending rigidity κ, spontaneous curvature c , and gaussian saddle splay modulus κ describe the mechanical and elastic properties of the interface. equation ( ) applies to biological interfaces if the bending energy contribution dominates, and to fluid interfaces if the energy is given only by the tension term. for spherical particles at planar fluid interfaces, the particle size, the interface tensions between the particles and the two phases, as well as the interface tension between both phases characterize the system. if the interface tensions between the particles and both phases are identical, the particles attach to the interface because their presence reduces direct contact between both phases without any additional costs for the contact of the particles with the fluids. for high-tension interfaces and micrometer-sized particles, such as for silica particles at oil-water interfaces, the attachment energy gain can be as high as k t b [ ] . therefore, such particles are irreversibly adsorbed to the interface. if the interface tensions of the particles with both fluids differ, the attachment energies of the particles can be strongly reduced. for particles attached to membranes, the membrane elastic properties in equation ( ) and the adhesion energy between particles and membranes characterize the system. here, s ad is the membrane area adhered to the particle, and the adhesion strength w for the contact interaction can be mediated by van der waals forces, by electrostatic interactions, and by specific adhesion (receptor-ligand bonds). for small spherical particles attached to nearly planar membranes and weak adhesion strengths, wrapping may not be energetically favourable, while for spherical particles with a radius of nm and for a high adhesion strength = − w k t . nm b the energy gain through wrapping can be as high as k t b . particle shape can strongly alter the attachment energy. table provides an overview of typical attachment energies of spherical particles to interfaces and membranes. for particles at interfaces, we assume that they have equal interface tensions with both fluid phases and that they are therefore half immersed in each phase. for particles at membranes, we assume that they are attached to a membrane with half of their surface area and that there is no deformation energy cost for the membrane surrounding the particles . interface deformations induced by particles lead to interface-mediated interactions and self-assembly; many-particle systems minimize the deformation energies also with respect to the particle positions. for example, capillary forces between micrometer-sized ellipsoidal particles increase with increasing aspect ratio and the energy gain at particle contact can be as high as k t b already for ellipsoid aspect ratios of - [ , ] . membrane-mediated binding energies of few k t b have been calculated for spherical particles at membranes [ , , ] . table provides an overview of interface-mediated and membrane-mediated bond energies for particles at contact. structures on the micrometer scale can readily be observed using light microscopy. in order to access the nanometer scale, more sophisticated techniques, such as electron microscopy or super-resolution microscopy, have to be employed [ ] [ ] [ ] [ ] [ ] [ ] . whereas ramsden and pickering have reported on particle-stabilised emulsions already in the early th century [ , ] , images of nanoparticles, such as bacteriophages, have only been reported in s, soon after electron microscopy has become available [ ] . since the very early studies of particles at fluid and biological interfaces, observation techniques and abilities to engineer particles have continuously advanced. besides these experimental developments, also mesoscopic and atomistic modeling and computer simulation techniques and speed have rapidly developed. both allows the characterization of particles at interfaces with increasing accuracy; this review article provides an overview of recent achievements. for both fluid and biological interfaces, we will discuss similar aspects: attachment to the interface, mechanisms for deforming the interface, particle orientation at the interface for nonspherical particles, long-range and short-range interactions, many-particle interactions, and applications. many concepts can easily be transferred between systems with fluid and with biological interfaces. we stress this parallelity by the analogous structure of the sections for both systems. section is devoted to particles at fluid interfaces, section to particles at biological membranes. the overview of the experimental studies of selfassembly of microparticles at fluid interfaces may not only benefit scientists investigating such systems, but also those interested in nanoparticles at biological membranes, where systems are less accessible experimentally and fewer studies are therefore available. particles adsorb at fluid interfaces because they reduce the interface area and thereby also the total interface energy. here, we have to account for the interface energies between the three phases, liquid , vapor (or a second liquid) v, and solid s. the system can be characterized by the three interface tensions γ sv , γ v , and γ s , see figure . the force balance at the contact line, where the liquid-vapor interface is located at the particle, is given by the young-dupré equation, which defines the contact angle θ c , see figure . the energy difference to bring a spherical particle with radius a from the bulk phase to the interface is the trapping energy [ ] [ ] . copyright © american chemical society. where τ is an effective line tension and l c is the length of the contact line. for micrometer-sized particles, the contrib ution of the line tension is negligible; the trapping energy is proportional to the liquid-vapor interface tension γ v and decreases with decreasing contact angle, see figure . for small particles with sizes below one micrometer line tension becomes relevant [ ] , for large particles with sizes of several micrometers gravity has to be taken into account [ ] [ ] [ ] . the eötvös or bond number compares the contributions of interface tension and gravity to the total energy, where ρ ∆ is the density difference of the two phases, g is the gravitational acceleration, and l is a characteristic length of the particle. similarly, the energies due to line tension and surface tension are compared using the dimensionless number ( ) . (a) a vertical slice of width σ . and height σ is shown with the interface region highlighted. (b) corresponding mean density profile z ( ) . reproduced with permission from [ ] . © epla. all rights reserved. for micrometer-sized particles and typical density differences between, for example, silica and water, ≈ − bo [ ] ; for line tensions and the corresponding surface tensions measured for polystyrene and poly(methyl methacrylate) particles at oil-water interfaces, = li . - . [ ] . in the following sections, we mainly discuss systems with bo and li , where both gravity as well as line tension can be neglected. the estimate for li indicates that line tension may not always be entirely negligible for small micrometer-sized and large nanometer-sized particles. line tension may qualitatively alter the behaviour of non-spherical particles at interfaces: for example, ellipsoidal and cylinderical particles may undergo orientational changes in order to minimise the length of the contact line. in [ ] , contact angles have been measured for spherical particles and for prolate ellipsoidal particles with various aspect ratios obtained by deforming initially spherical particles. here, an apparent decrease of the contact angle with increasing aspect ratio of the particles has been measured. this can be attributed to a line tension and a contact angle that is independent of particle shape [ ] . the experiment predicts an effective line tension τ ≈ nn that also includes experimentally-observed heterogeneities in the contact line. other values for line tensions reported in the literature are in the pn to µn range [ ] . one of the key reasons for the stability of colloidal assemblies at interfaces and of pickering emulsions are the very high trapping energies for the particles [ , ] , see table . calculations for non-spherical particles show that the trapping energies depend only weakly on particle shape and increase for both oblate and prolate deformations of spherical particles, see figure . at curved interfaces, the trapping energies of spherical particles have been shown to depend on the interface curvature and therefore on the laplace pressure difference at the interface [ ] . for spherical particles and a contact angle θ = c , the trapping energy decreases with increasing interface curvature. for contact angles θ ≠ c , the trapping energy either increases or decreases depending on the sign of the contact angle and on whether the interface is curved towards or away from the particles. the white arrow points to a cholesterol oriented in between the monolayer leaflets. reprinted with permission from [ ] . copyright © national academy of sciences. [ , ] . based on [ ] and [ ] . to satisfy the young-dupré equation locally at every point on the three-phase contact line, see figure , the contact lines and therefore also the interfaces are often not planar for non-spherical particles. also particle-surface inhomogeneities, either due to roughness or chemical surface patterning, e.g. for janus particles, may induce contact-line undulations. furthermore, imposed fields, such as gravity for large mm-sized particles or electromagnetic fields for electrically-charged or for magnetic particles, may lead to interface deformations. the capillary forces due to the system's tendency to reduce the total interface area between liquid and vapor is the origin of the capillary forces between particles, see table ; very strong bond energies of k t b for micrometer-sized particles correspond to interface height perturbations of only nm [ ] . the importance of hydrodynamic interactions for the dynamics of particles at interfaces is characterized by the capillary number with fluid viscosity η and typical particle velocity v. for typical velocities of µ − m s for particles with sizes of up to few micrometers in water [ ] , we find < − ca . therefore, for the systems discussed in this review article ca , such that hydrodynamic interactions can be neglected. particle velocities can therefore be directly related to the forces acting on the particles and the friction by the fluid. self-assembly of colloidal particles at fluid interfaces is governed by both direct interactions, such as van der waals and electrostatic interactions, and indirect interactions, such as forces due to overlap of interface distortions, popularly coined as capillary interactions [ , ] . in , pieranski reported a two-dimensional colloidal crystal of spherical polystyrene colloids with a triangular lattice structure at an air-water interface induced by an asymmetric charge distribution [ ] , forced into two dimensions by the interface. a large number of more recent studies on colloids at interfaces that assemble due to interface-mediated and direct interactions show a rich variety of two-dimensional structures. an overview of both single-particle and many-particle systems at interfaces is provided in the remainder of this section. in sections . - . , we focus on various aspects of the interaction of single particles with interfaces, while in sections . and . , we discuss two-particle and many-particle interactions, respectively. section . focuses on the special case of particles at interfaces that are half immersed into an ordered fluid. we finally discuss applications in section . . an undulating contact line at a particle distorts a surrounding planar fluid interface. for a cylindrically-symmetric system, such as a spherical particle at an interface, the young-laplace equation that describes the interface deformation is best expressed in cylindrical coordinates [ ] , the height profile φ h r, ( ) of the interface can then be expressed as product of a function of the radial coordinate r and a function of the angular coordinate φ around the sphere, the general solutions, are characterized by the contact line at the particle, described by Φ m, , φ m, , and r m, . the interface deformation decays faster with increasing distance from the particle the larger m, i.e. the larger the number of undulations along a circle around the particle. the contact-line undulations can be expressed as multipole expansion, where the contact radius r c is often similar to the particle radius, h m are the expansion coefficients, and φ m, the phase spherical particles at a fluid-fluid or fluid-gas interface in a system with a solid spherical particle (s), a fluid (l), and a gas/ second fluid (g). the contact angle θ c for the green particle is , while the contact angle for the red particle is smaller than . the three interface tensions γ sv , γ s , γ v are sketched for each particle using arrows. they indicate the force balance given by the young-dupré equation that holds for all points along the three-phase contact lines. angles. the first two terms of the expansion vanish, because without additional external forces the particles are at their optimal height and orientation at the interface. the lowest multipole contribution and the most important contribution for long-ranged interactions is the quadrupolar deformation with = m [ ] , where h characterizes the undulation amplitude of the contact line. the long-ranged interactions between two particles in the far field therefore decay with − d , where d is the interparticle distance. experimentally, imprinted contact-line shapes have to be distinguished from mere surface roughness. whereas surface roughness often leads to temporary and random pinning of the contact line, engineered contact-line deformations are stable and well controlled. for instance, undulating plates allow the engineering of the interface deformation and the tuning of the capillary interaction between particles from attractive to repulsive [ , ] . however, also nanometric roughness on microspheres or disc-like particles leads to strong capillary interactions due to contact-line pinning [ , [ ] [ ] [ ] . the temporary nature of contact-line pinning can be observed for instance for metastable orientations of dumbbell-shaped particles at interfaces; the distribution of particle orientations relaxes towards the globally stable particle orientation when the system ages [ ] . in , lucassen first suggested that particles with complex shapes can induce interface distortions in absence of gravity [ ] . he systematically calculated the interaction between sinusoidal interface deformations. however, the most common interface distortion due to non-spherical particles is the quadrupolar deformation, which is found for all elongated particles with homogeneous surface functionalization at planar interfaces in the far field [ , , ] . for ellipsoidal particles, quadrupolar interface deformations can also be found in the near field [ , , ] . for contact angles θ < c , the interface is pulled down at the tips and pulled up near the long sides of the particle-and reverse for the inverse-wetting condition with θ > c , see figure (a). for ellipsoidal particles and θ = c -and for spherical particles-a planar interface remains undeformed. strength and nature of the interface distortions can be characterized using different quantifications: contour maps of the interface distortion, see figures (a) and (b), shapes of contact lines, see figure (c), differential heights ∆u of the interface between the crest and trough along the contact lines, see figure (d), or height profiles along cross-sections, see figure (e). for well-defined particle shapes, in particular for ellipsoidal particles and quadrupolar interface deformations, the characterization of the interface deformation fields is uniquely determined by ∆ = − u z z max m in , where z max is for both particles. the spherical particle approaches the ellipsoidal particle at the side. reprinted with permission from [ ] . copyright ( ) american chemical society. (d) maximal height difference ∆u of the contact line for ellipsoidal particles with several aspect ratios b a ⩽ / ⩽ . the numerical data are normalized by the half the length of the minor axis a and plotted as function of the contact angle θ c . the maximum value of ∆u, depicted by ×, shifts to smaller contact angles with increasing particle aspect ratio, as indicated by the grey lines that serve as guides to the eye. reprinted with permission from [ ] . copyright ( ) american chemical society. the maximum and z min the minimum height along the contact line. the height difference ∆u for ellipsoidal particles vanishes for θ = c and for θ = c and assumes a maximal value ∆u max for θ < < c for ellipsoids with aspect ratios b a . ⩽ / ⩽ [ ] , see figure (d). the position of the peak shifts from larger to smaller contact angles with increasing aspect ratios of the particles [ ] , while the height of the peak increases from ∆ ≈ u a . . studies are available for ellipsoidal particles [ , , ] , for cylindrical [ ] , for cuboidal particles [ ] , and for rounded box-like particles [ ] . the height difference along the contact line of elongated particles can be thought of as a measure for their capillary interaction strength. systematic theoretical and experimental calculations thereby provide routes to tailor capillary assembly of multiple particles. the experimental determination of contact angles using light microcopy is difficult, because the same interface deformation can be derived for two different contact angles. this 'contact-angle mystery' arises because the differential interface height distortion, i.e. ∆u a / , does not show a monotonic increase with the contact angle θ c , see figure (d). due to the non-monotonic profile for ellipsoidal particles, for each value of ∆u a / there are two possible values for θ c , see figures (a) and (b). however, the 'mystery' can be resolved by measuring a second quantity, such as the excess area s s / plotted in figure (c), i.e. the ratio of the projected area by the contact line and the projected area at θ = c [ , ] . in figure , results from theoretical contact-angle calculations for ellipsoidal particles with various aspect ratios are plotted together with corresponding experimental measurements of ∆u a / and with s s / as function of the contact angle. the lower branch for smaller θ c has already been reported in [ ] , the upper branch more recently in [ ] . only with the knowledge of both, experimental values for ∆u a / and for s s / , the correct branch of contact angle solutions can be singled out. a new technique using electron microscopy provides means to measure contact angles more directly than optical microscopy. this so-called freeze-fracture shadow-casting cryo-sem (fresca) has been used to measure contact angles for wetting of spherical and ellipsoidal micro-and nanoparticles at liquid-liquid interfaces [ ] . for more complex particle shapes, the connection between interface deformation and particle aspect ratio can be different from the case of 'simple' elongated particles. for example, figures (a)-(e) shows deformations around rounded box-like particles, where rises and dips depend on local particle shape rather than aspect ratio. cuboidal particles can produce octupolar distortion fields with eight lobes (rises and dips), see figure (f). for rounded cylinders, there can even be multiple branches of possible contact angles due to the multiple peaks in the ∆u a / variation for certain aspect ratios (unpublished results). table provides an overview of the dominant multipole contributions for interface deformations and corresponding systems, several of them are discussed in more detail in the following. we discuss here gravity, buyoancy, and thin films in part and non-planar interfaces in part . . . . gravity, buyoancy, and thin films. the presence of graviational forces leads to floatation forces that cannot be neglected in the regime of large absolute values of the bond number [ , [ ] [ ] [ ] [ ] [ ] [ ] ] . particles either sink into the interface / , for ellipsoidal particles with aspect ratios in the range b a . ⩽ / ⩽ . the data from [ ] is plotted together with numerical data taken from [ ] . for a spherical particle, s s / varies as θ sin c , as shown by the solid line above. for all contact angles between and , s s / attains higher values for ellipsoidal particles in comparison to the analytical estimate obtained for a spherical particle. adapted with permission from [ ] . copyright ( ) american chemical society. if they are heavier than the fluid or float up if they are lighter than the fluid (buyoancy). gravitational forces therefore induce dominant monopole interface deformations, so-called 'capillary charges', see equation ( ) [ ] . some fascinating outcomes of the interplay of capillarity and gravity are water striders [ ] , meniscus-climbing insects [ , ] , and the cheerios effect in cereal bowls [ ] . monopole interface deformations are obtained as well for particles in thin films, where instead of gravitation the small thickness of the film compared with the particle size induces interface deformations [ , ] , see figure . the ideal interface positions on the particle are incompatible with the film thickness, which leads to immersion forces. for a thin film of fluid at a solid interface, the horizontal projection of the immersion force is [ ] πγ with the radius r c of the three-phase contact lines at the particles, the mean meniscus slope angle Ψ c at the contact line, and the distance d cc between the particles. this expression holds ( /( )) / , where ρ ∆ is the density difference between the fluid and the gas. figure compares the floatation forces between particles with immersion forces for polystyrene latex particles in a water film on a glass substrate; in this example, the floatation forces decrease faster with increasing interparticle distance than the immersion forces. as an instructive example, we discuss froth floatation as an application in more detail [ ] . here, grains of one solid are carried away with the froth, while grains of a different solid sink to the bottom of the floatation system. the selective adsorption of a collector chemical onto a mineral in a flotation plant determines-among others-the attachment of the mineral to bubbles used for separation. the stability of the froth with the particles depends mainly on the properties and the amounts of particles [ ] . the so-called capillary pressure due to the liquid that drains from the film because of gravity measures the pressure when the film ruptures. this critical pressure increases if particles stabilise the film, e.g. spherical particles with contact angles far below , and decreases if particles destabilise the film, e.g. particles with sharp edges. / . the heights are scaled by the length scale r. reprinted with permission from [ ] copyright of the royal society of chemistry (f) deformation profiles of an interface around a particle with hauser's cube shape at contact angle θ = . whether a particle stabilizes or destabilizes a film furthermore depends on the orientation that the particle assumes at the interface [ ] , see section . . figure shows how a thin film ruptures due to the presence of a non-spherical sharpedged particle. particles at curved interfaces experience forces not only due to the presence of the interface, but also because of the laplace pressure. curvature gradients of the interface lead to lateral forces, and curved interfaces modify interface-mediated interactions between particles [ , , , , , ] , see figure ; vice versa, particles at high densities can induce spontaneous interface curvature [ ] . mean curvature h and deviatoric curvature δ = − c c c determine the trapping energy [ ] where e f is the trapping energy at the flat interface, see equation ( ). for a spherical colloid of radius a on a spherical drop- , which is the interface curvature-induced contribution. this term is evaluated by considering contributions due to both the interface energies and the work done against the laplace pressure. a similar estimate for the trapping energies attempted previously in [ ] without including the work done by the laplace pressure resulted in the correction term to be . this result is consistent with equation ( ) when the contribution due to the pressure term, , is added to it [ ] . for a minimal surface with mean curvature = h , such as for a catenoidal interface shape, the correction term compared with the flat interface depends only on the deviatoric curvatue δc. the trapping energy of a colloidal particle on a catenoidal minimal surface is thus . on an interface with varying curvature, the lateral force on the trapped particle is given by [ thus, spherical particles on interfaces with curvature gradients experience forces depending on both the absolute values and the gradients of the mean and deviatoric curvature to move towards regions of high mean and deviatoric curvatures (and therefore also high gaussian curvatures because . recent experiments of microspheres on interfaces with different curvatures have evaluated these forces to be of the order = − ± [ ] . theoretical estimates of capillarity at curved interfaceswhich neglect pinning-suggest that capillary forces for particles that are smaller than the capillary length where ρ is the density of the fluid, are proportional to both a and the gradient of the gaussian curvature, ∇k [ ] . this has been verified in experiments where large microposts induce a curvature gradient and cause smaller particles to migrate along the deformed interface to assemble in regions of high gaussian curvature, see figure . experimental evidence further suggests that capillary migration on curved interfaces can be enhanced by contact-line pinning. contact-line undulations, which lead to finite local interface curvatures, induce capillary forces of the order ⋅ -⋅ k t b , which are much larger compared with the weak forces due to capillarity for perfectly smooth spherical particles. the experiments demonstrate that rough microspheres, microdisks, and rod-like particles move along deterministic trajectories to regions of maximum deviatoric curvature [ , , ] . non-spherical particles do not only migrate figure . comparison between immersion and floatation capillary forces between two spherical latex particles in a water film on a glass substrate: dependence of the capillary interaction energy, ∆w, on the particle radius, r. the distance between the particles is = l s , the contact angle θ α = c , and the liquid-vapor interface tension γ γ = v . see figure for a sketch of the system. reprinted with permission from [ ] . copyright ( ) american chemical society. translationally by sensing the background interface curvature, but also orient themselves to align their long axes, such that the excess area is minimized. for example, cylindrical particles reorient either parallel or perpendicular to the groove as the interface curvature changes from concave to convex [ ] . particle orientations for non-spherical particles, the orientation of the particles at interfaces, as well as particle shape, size, and surface properties have to be taken into account to determine adsorption energies and interface deformations. cube-like particles can be oriented in a corner-top or face-top orientation depending on the contact angle. elongated particles in a magnetic field or elongated janus particles in their stable orientations can be oriented with their long axes tilted with respect to the interface. one way to estimate the adsorption energy of a particle at an interface is to calculate the area of the fluid interface that is 'cut out'. this estimate can be exact if the interface tensions between particle and both phases are equal. for a particle that is symmetric with the interface acting as a mirror plane, the surrounding interface remains planar. however, in general particle-induced deformations of the surrounding interface can change adsorption energies and stable particle orientations even qualitatively. figure (a) sketches the various angles by which a cube-like particle can be rotated. figure for θ = c the flatinterface approximation predicts the edge-top orientation to be globally stable, while accounting for the deformation of the surrounding interface the corner-top orientation is found to be globally stable. figure (c) shows specific orientations for a cube-like particle at an interface. for a contact angle θ = . c , the globally stable state is the face-top orientation, while for θ = c the globally stable state is the corner-top orientation. figure (d) shows the predicted interface deformations for both cases using the same scale: hexapolar for the corner-top orientation and almost planar for the face-top orientation. capillary interactions between the cubes are therefore expected to be much stronger in the corner-top orientation compared with the facetop orientation. for particles with complex shapes, such as cube-like particles, a multitude of kinetically stabilised orientations and corresponding multipolar interface deformations is expected to be observed in experiments. a simple non-spherical particle with a stable tilted state is a janus dumbbell, which consists of two spherical particles made from different materials, see figures and . these particles do not deform planar interfaces, because the contact line around each of the spherical particles is a circle. figure (a) shows the experimentally observed orientations for dumbbell particles that consist of an hydrophobic spherical particle of radius r a and a hydrophilic spherical particle of radius r p . in their lowest-energy orientation, the spherical particles intersect the interface at different heights. the tilt angle of the dumbbell in the lowest energy state is [ ] see figure (b). here θ p is the contact angle at the polar particle, θ a is the contact angle at the apolar particle, α = r r a p / is the relative size of the two lobes, and with decreasing aspect ratio, the tilt angle of the janus dumbbell increases. for aspect ratio = b a / , only one of the spherical particles is in contact with the interface. however, also for cases where the tilted orientation of the dumbbell is predicted to have the lowest energy, a substantial fraction of particles are found experimentally in one of the kinetically stable orientations, where only one of the spherical particles intersects the interface [ ] . the lowest-energy orientation, where both spheres are at the interface, coexists with two kinetically stable orientations where only one of the spheres is at the interface. because the energy for an orientation where only one spherical particle is in contact with an interface does not depend on the tilt angle, an arrest in such a state could be caused by surface roughness. in these trapped states, the particles can therefore reorient to the tilted orientation only by diffusion. unlike janus dumbbell particles, janus ellipsoidal particles that are half hydrophobic and half hydrophilic do not show a continuous transition of their the orientation between a tilted long axis and a perpendicular long axis to the interface, see figures and . energy landscapes for various orientations of an ellipsoidal and a dumbbell particle are shown in figure . the lowest energy states for different aspect ratios are indicated in the figure using green symbols; the discontinuous transition in the particle orientation is clearly visible. the tilted orientation is only stable above a threshold aspect ratio and the orientation of the particle orientation jumps to the perpendicular orientation below this aspect ratio [ ] . these energies for various particle orientations have been calculated numerically, under the assumption of a flat interface surrounding the particles. whereas for ellipsoidal particles with homogeneous surface properties the deformations of the surrounding interface are quadrupolar with a dip at the tips and a rise at the long sides for contact angles below , see section . , the deformations of the interface around janus ellipsoids can show both a dip and a rise along their long sides [ ] , see figure . similar interface deformations have been observed for double-hydrophilic janus cylinders with aspect ratios . , . , and reprinted with permission from [ ] . copyright ( ) by the american physical society. . [ ] , see figure . the cylinders are found in kinetically trapped end-on orientations as well as globally stable tilted orientations. the cylinders have asymmetric hydrophilicity unlike most studies where the janus particles have amphiphilic properties [ ] . in their tilted orientations, they induce hexapolar interface deformations that lead to capillary interaction. complex particle assemblies have been observed due to the multi-lobed deformations and the non-determininistic assembly. fields. an external magnetic field can be used to tune the orientation of prolate ellipsoidal magnetic particles at fluid interfaces [ , , ] , see figure . the field tends to align the magnetic dipole with the direction of the applied magnetic field, where µ and h are the dipole and the field, respectively. the angle φ indicates the particle orientation and µ = | || | b h represents the field-dipole strength. the total free energy of the particle at the interface, neglecting particle-induced interface deformations, can therefore be written as where s is the area of the interface 'cut out' by the particle, and a sv is the area of the particle in contact with the vapor/the second liquid. if the field is oriented normal to the interface and if the direction of the permanent magnetic dipole coincides with the major axis of the ellipsoid, the analytical estimation of the tilt energy predicts that at a critical field strength the particle 'jumps' from a tilted orientation to a vertical orientation. here, φ = and φ = correspond to vertical and horizontal particle orientations, respectively. in figure , the energies of magnetic prolate ellipsoidal particles are shown as function of their orientation angle for various aspect ratios and field strengths. for particles with aspect ratio = b a . / and length of the minor axis a = nm , the energy barrier between vertical and tilted states can be several hundred k t b , such that the particles are trapped in one of both orientations. lattice-boltzmann simulations have been used to investigate the orientations of magnetic ellipsoidal particles in external fields including the deformations of the surrounding interface [ ] . the simulations show that the interface deformations around the particles significantly affect the tilt angles for a given dipole strengths, altering the properties of the reorientation transition. figure shows a simulation snapshot of the deformed interface and a plot of the tilt angle for various field strengths together with the analytical approximation discussed above. the simulation snapshot shows that the interface deformations remove more interface than in the planar-interface approximation, which lowers the free energy. deviations from the approximate result are found mainly for high aspect ratios. the discontinuous transitions allows the switching of the particle orientations using external magnetic fields, which could find applications for instance using its dynamically-tunable optical properties for electronic readers [ ] . furthermore, also the dipolar interface deformations can be switched on and off and thus lead to switchable capillary interactions between particles adsorbed at fluid interfaces. overlaps of interface deformations around particles lead to interface-mediated interactions, also called (lateral) capillary forces. capillary interaction energies between two particles, see figure , can be calculated based on the difference between the changes of the fluid-vapor interface area for placing two particles at given center-of-mass separation d cc and for placing two isolated particles at a planar interface. the corresponding capillary interaction energy is [ ] where ∆s ab is the change of the fluid-vapor interface area around the interacting particles, and ∆s a and ∆s b are the changes of the interface areas around the single particles. interface-mediated interactions follow power laws in the far field and are thus long-ranged. in the near field, the interactions strongly depend on the particle shapes. because the dynamics occurs in the stokes regime for small capillary numbers, figure . amphiphilic dumbbell particles at an oil-water interface. (a) in experiments, three dumbbell orientations are found: only the hydrophilic sperical particle intersects the interface, only the hydrophobic spherical particle intersects the interface, and both spherical particles intersect the interface. the circles and arrows indicate the size of the particle crossection at the interface and the shadow length obtained by freeze-fracture, shadow-casting (fresca) cryo-scanning electron microscopy, that can be used to measure the contact angle. (b) schematic diagram highlighting the geometry of the dumbbells at a liquid-liquid interface. reprinted with permission from [ ] . copyright ( ) american chemical society. see equation ( ), the particle velocities are proportional to the interaction forces and can therefore be extracted for example from videos. analytical solutions for the interaction forces are available in the far field, while numerical calculations have to be used in the near field. for large distances between particles, the deformation field of particle a can be assumed to be small at the position of particle b and vice versa. the capillary interaction energy can then be calculated using the superposition of the interface deformations around the single particles [ , , ] where h a and h b are the interface height deformation fields due to particle a and b, respectively. the lowest multipole contribution for a given system, see table , dominates the interaction. for sufficiently large particles for that gravity or buyoancy have to be considered, the capillary forces act between two monopole interface deformations [ ] πγ with the capillary length defined in equation ( ), the mass density ρ ∆ between the upper and the lower phase, and the capillary charges the angle ψ i is the slope of the interface at radius r i , the radius of the contact line. for )/( ), particle mass density ρ i , fluid mass density ρ , and upper fluid/gas mass density ρ g . stamou et al first presented an analytical result for the pair potential between two quadrupolar deformation fields in polar coordinates [ ] . in this quadrupolar approximation, the energy between two ellipsoidal particles is figure . janus ellipsoid and janus dumbbell at an interface with corresponding energy landscapes for particle orientations. while the dumbbell smoothly transitions to the perpendicular orientation with increasing aspect ratio, the ellipsoid jumps from a small tilt angle to the perpendicular orientation beyond a critical aspect ratio. reprinted with permission from [ ] . copyright ( ) american chemical society. interestingly, the magnitudes of the interaction potentials are equal in s-s, t-t, and t-s orientation for equal center-of-mass distances. kralchevsky et al extended the multipole approach to multipoles of arbitrary orders [ ] . whereas for weak deviations from circular contact lines a polar multipole expansion is most appropriate, for ellipsoidal particles with higher aspect ratios the appropriate choice are elliptical multipoles [ ] . ( )/ ( / ) , are observed for both cylindrical and ellipsoidal particles [ , ] . deviations are observed for small interparticle distances, which is discussed in section . . . elongated particles that touch each other have lower bond energies than predicted by the quadrupolar approximation in side-by-side orientation and higher bond energies in end-to-end orientation, see figure . capillary self-assembly is determined by the contact interactions between the particles, therefore near-field interactions are important for all many-particle systems. uncharged ellipsoidal particles at low bond numbers preferentially align in side-byside orientation [ ] . the higher stability of the side-by-side orientation over the tip-to-tip orientation is obvious from equation ( ) and is qualitatively unchanged by the deviation from the ideal quadrupolar approximation in the near field. using triangulated surfaces and energy minimisation, numerical calculations of deformation energies have been applied for various particle shapes, orientations, and contact angles. figure shows snapshots and interaction potentials for pairs of identical ellipsoidal particles with aspect ratios = b a / and = b a / [ ] . the bond energies increase quadratically as function of the bond angle φ | | that quantifies deviations from the side-by-side orientation with φ = . figure shows the bond-bending energies for two ellipsoids with shows a linear elastic regime with φ = t g , where γ = g a . [ ] ; the torques may reach values up to k t b . a bending modulus for the polymer-like assemblies of particles at the interface can be extracted from many-particle calculations. if two ellipsoids with different aspect ratios interact, the stable assembly is an arrow [ ] , see figure . unlike ellipsoidal particles, cylindrical particles preferentially assemble in end-to-end orientation, see figure . because of the flat ends of cylindrical particles, the contact figure . configurations of double-hydrophilic janus cylinders at the air-water interface. the first and second columns are sem images of janus cylinders embedded in pdms slabs prepared by the gel trapping method. arrows indicate the location of the wettability separation line. the schematic representations show the side view of particle configurations at the air-water interface where four colors represent four different particle-fluid surfaces: weakly polar surface in air (black), weakly polar in water (red), strongly polar in air (blue, rarely shown), and strongly polar in water (cyan). the third column shows the corresponding optical microscopy images. the scales bars are µm . reprinted with permission from [ ] . copyright ( ) american chemical society. figure . sketch of an ellipsoidal particle adsorbed at a liquidliquid interface in (a) vertical, (b) horizontal, and (c) tilted orientation. the variables defining the geometry and orientation of the particle are discussed in the text. the direction of the magnetic field is indicated by b. reprinted from [ ] . © iop publishing ltd. all rights reserved. line can adjust its height rather freely if the height of the surrounding interface changes because the contact angle remains unchanged. when two cylindrical particles approach each other, the energy gain for wetting the surfaces overcomes the costs for the deformation of the surrounding interface, thus the interface forms a capillary bridge between the two ends. the bond-bending energies for cylindrical particles around their preferred tip-to-tip state are very high, with restoring torques up to = t k t b [ ] . therefore, such chains are usually not distorted. two cylindrical particles may switch to the metastable side-by-side orientation only for bond angles larger than φ ≈ c - , which can be achieved for particulate monolayers under compression or shear stress. the height of the capillary bridge that forms between two cylindrical particles decreases when the distance between them is increased, compare snapshots for = d a . / with = d a . / in figure ; it changes also if the particles are tilted with respect to each other, compare snapshots for = d a . / and φ = , and for = d a . / and φ = . for cylindrical particles, bond bending is not elastic as for ellipsoidal particles, but shows non-elastic hinging behaviour. therefore, both bond energies and bond-bending energies are significantly affected by deformations of the surrounding interface and by changes of the wetting of the planar faces of the particles. this importance of wetting energy is a qualitative difference for the capillary interactions between ellipsoidal and between cylindrical particles. the crossover between elastic bond-bending and nonelastic hinging can be further explored using superegg-shaped particles with variable edge curvatures, as discussed in [ ] . . reprinted from [ ] . © iop publishing ltd. all rights reserved. / . (b) comparison of the tilt angle of the particle obtained from the analytical, planarinterface approximation in [ ] and the numerical data in [ ] . although the numerical data qualitatively confirms the prediction of a discontinuos transition, there are quantitative deviations in particular at higher aspect ratio. reprinted from [ ] with permission from the royal society of chemistry. and ω indicate the orientation of the particle or , respectively, with respect to the vector joining the centers of the two particles. the center-to-center distance is given by d cc for a particle of aspect ratio b a / . reprinted with permission from [ ] . copyright ( ) american chemical society. in general, the presence of one particle changes the contactline position on the other particle. figure (c) shows the deformation of the initially circular contact line around a spherical particle by a nearby ellipsoidal particle. figure shows that although the spherical particle at a planar interface by itself does not deform the interface and does not induce interfacemediated attraction, an ellipsoidal and a spherical particle mutually attract each other. the attractive interaction between spherical and ellipsoidal particles is larger for side-on configurations of the spherical particles than for tip-on configurations. in both configurations, however, the attraction between spherical and ellipsoidal particles is significantly weaker than the attraction between two ellipsoidal particles with similar sizes that have equal aspect ratios and surface properties. attractive energies for capillary bonds and energy barriers between locally stable configurations are often high, therefore computer simulations show self-assembly in kinetically-trapped dendritic and raft-like structures [ ] . numerical calculations for two-particle, three-particle, and four-particle interactions predict a variety of stable and metastable configurations [ , ] . many-particle studies of particles at interfaces can also be extended to polydisperse particle mixtures [ ] . , and ellipsoidal particles with aspect ratio = b a / that have been obtained by deformation of spherical particles with µ = a m [ ] . for prolate ellipsoidal particles mostly the side-by-side orientation is observed in experiments, hexagonal networks can be stable if an additional repulsive electrostatic repulsion contributes to the particle-particle interaction. figure (a) shows self-assembly of slightly charged micrometer-sized ellipsoidal particles. the structure initially shows many tip-to-tip contacts; after slow relaxation it compactifies slightly and shows less triangular and more chain-like aggregates in side-by-side orientation after h [ ] , see figure (b). the chains of particles in side-by-side orientation can be thought of as 'colloidal polymers': worm-like chains or rings with bending elasticity. for non-spherical particles at planar interfaces, particleparticle interactions may affect the orientations of particles and vice versa. for example, cube-like particles at lower interfacial densities assemble on hexagonal and honeycomb lattices in corner-top orientation [ ] , and at higher interfacial densities on a square lattice in face-top orientation [ ] . figure shows how particle orientations affect interparticle interactions: chains form for prolate ellipsoidal particles that are oriented with their long axes parallel to the interface, while particles disperse homogeneously if they are oriented with their long axes perpendicular to the interface. particle orientation can be controlled using an external magnetic field [ ] , see section . . . a similar tunable (dipolar) interface deformation and therefore tunable capillary interaction can be achieved using magnetic spherical janus particles [ ] . interface curvature alters particle-induced interface deformations and therefore many-particle self-assembly, see section . . . in order to systematically understand the interaction of many particles at non-planar interfaces, it is important to study model systems with controlled curvatures [ , [ ] [ ] [ ] [ ] . for example, spherical particles at interfaces with saddle-like shapes induce quadrupolar interface deformations and therefore at low densities assemble on a square lattice [ ] , see figure (a); at high densities, the optimal packing on a hexagonal lattice is observed. the local lattice structure can be investigated using bond-orientational order parameters, where n j indicates the number of neighbors of a particle. the angle θ j is the angle between the bond with a neighboring particle j and an arbitrary reference axis. figure (b) shows that the lattice order switches continuously from square to hexagonal with increasing particle density. particles embedded within a nematic liquid crystal (lc) interact with the nematic directors in the vicinity of the colloid and therefore impose boundary conditions on the nematic order parameter at the colloid-lc boundary. this leads to longranged anisotropic elastic interactions for spherical and ellipsoidal particles dispersed in nematogenic fluids [ , ] . due to varying nature of nematic defects at the colloid-lc boundary, typically elastic multipoles, such as dipoles and quadrupoles, are observed. large pair interaction strengths render the self-assembled aggregates insensitive to thermal or hydrodynamic fluctuations [ ] . capillary interactions dominate the elastic energies [ ] . for microspheres in nematic films, strength and nature of the elastocapillary interactions depend on film thickness and particle size [ ] . for small thicknesses of films, giant elastic dipoles occur due to interface distortions. defects appear around particles, elastic dipoles and nematic elasticity counterbalance the strongly attractive capillary interactions and stabilize particles pairs at finite distance. figure shows how cylindrical nanoparticles first assemble at a nematic interface in their energetically favourable tip-to-tip orientation and then align with the nematic director [ ] . the weak elastic interactions are able to manifest themselves at flat nematic interfaces, but under curvature gradients again capillarity dominates [ ] . particle anisotropy shall also play a significant role for defect formation at colloid-lc boundaries and shall thus also control nature and strength of pair-particle interactions. future experiments and theoretical investigations to elucidate these elusive interplay between capillarity and elasticity are warranted. applications for (engineered) particles at interfaces range from emulsion stabilisation and colloidosomes to suppression of the coffee-ring effect and froth floatation. in addition to capillary forces, also for example marangoni flows, surfactants, electric charges, or gravity have to be taken into account. a classical application is the stabilisation of emulsions. here, the interactions of particles at interfaces on the mesoscale can be expected to determine macroscopic rheologial properties. in general, the strong adsorption of particles to interfaces leads to thermodynamically stable droplets of oil (water) suspended in water (oil) [ , , [ ] [ ] [ ] . at low particle concentrations, the mechanism of limited coalescence generates narrow and reproducible droplet-size distributions [ ] . phase inversion of droplet emulsions is obtained by increasing the volume fraction of oil (water). for mixtures for small hydrophilic and hydrophobic particles also sponge-like, bicontinuous phases and non-spherical colloidosomes have been observed [ , ] . particles with anisotropic surface functionalization, such as janus particles, can be used as amphiphilic colloidal surfactants [ , ] . particle-stabilised emulsions are used for example in food and cosmetic industries [ ] [ ] [ ] [ ] . colloidosomes are solid capsules engineered with controlled permeability and mechanical strength that can have sizes from sub-micrometers to millimeters [ ] . the capsules are prepared by self-assembly of colloidal particles to emulsion droplets that are then locked together for example using sintering or electrostatic binding of an oppositely-charged polyelectrolyte. this ensures that the shells remain intact when they are transferred to a different fluid. with the help of centrifugation, the particles are typically transferred into a solvent that is identical to the internal phase. colloidosomes can be used for encapsulation of drugs, proteins, vitamins, flavors, gas bubbles, and even living cells. particles that are homogeneously dispersed over an entire drop often form ring-like deposits when the drop evaporates, so-called 'coffee rings' [ ] . addition of ellipsoidal particles with aspect ratio . , obtained by deforming spherical particles with µ = a . m , to droplets that contain the spherical particles has been found to lead to more homogeneous deposition [ ] . for droplets that contain ellipsoidal particles only, a strong suppression of the coffee ring effect is already observed for very moderate aspect ratios ≈ b a . / . numerical calculations predict capillary attraction between spherical and ellipsoidal particles [ ] ; the uniform deposition may therefore be caused by capillarity-induced cluster formation. applications for that a more uniform deposition of the material instead of 'coffee rings' may be desired are inkjet printing, fabrication of microand nanostructures, and coating. froth floatation is used to separate minerals from gangue. the separation efficiency depends on both the particle-bubble attachment and the froth stability [ , ] . while the particle-bubble attachment can be adjusted using collector chemicals that modify the particle's surface properties, the film stability is affected by particle shape. one complication that decreases froth stability can be particles with sharp edges [ ] . therefore, a systematic understanding of the interaction of non-spherical particles with thin films and potentially also of immersion forces may help to improve froth floatation [ , , , ] . particles adsorb at biological interfaces, often called membranes, because of an adhesion strength w between the particles and the membranes. in addition to the adhesion strength, the minimal ingredients required to study spherical particles are the bending ridigity κ and the tension γ of the membranes, and the radius a of the particles. for small particles, molecular interactions are important. coarse-grained or even atomistic computer simulations are used to investigate theoretically translocation through and incorporation within membranes [ ] [ ] [ ] [ ] . experimentally, the interaction of small particles with membranes can be investigated using a combination of microfluidic devices, fluorescence microscopy, and electrophysiological measurements [ ] , by scattering techniques [ ] , and by quartz crystal microbalance and afm [ ] . for larger particles with radii > a nm , wrapping is the dominant mechanism of the interaction between particles and membranes, as will be discussed in detail in this section. particles that interact with membranes can be engineered and are found in biological systems with a wide variety of sizes, shapes, and surface functionalizations, see figure . comparing the different energetic contributions, large spherical nanoparticle adhesion and wrapping is determined by two characteristic crossover radii, the radius κγ * a that compares the bending energy with the membrane tension characterizes the crossover between the bending-dominated regime for particles with < κγ * a a and the tension-dominated regime for larger particles. while for nanoparticles bending energy is thus the main player, for micrometer-sized particles tension plays the dominant role. within the bending-dominated regime, small particles with < κ * a a w remain unwrapped, while larger particles get wrapped, determined by the subtle balance of bending and adhesion energy [ , [ ] [ ] [ ] . for given particle radius, the threshold adhesion strength κ = * w a / therefore marks the transition between the unwrapped and the complete-wrapped regime. adhesion may be mediated by van der waals interaction [ ] , hydrophobic interaction [ ] , electrostatic interaction [ ] , and specific adhesion via receptor-ligand bonds [ ] [ ] [ ] [ ] [ ] [ ] [ ] . in biological media, nanoparticles can be surrounded with a corona of proteins that effectively changes their surface properties [ ] [ ] [ ] [ ] [ ] [ ] . throughout this section, we assume that the adhesion can be modeled by a continuous and mostly homogeneous adhesion strength, which is appropriate for many systems, but not always sufficient for / . an overview of both single-particle and many-particle systems at membranes is provided in this section. in sections . - . we focus on various aspects of the interaction of single particles with membranes, while in sections . and . we discuss two-particle and many-particle interactions, respectively. section . focuses on particles at membranes with spontaneous curvature. we finally discuss applications in section . . for a spherical particle and an infinitely large tensionless membrane, the membrane surrounding the particle assumes a catenoidal shape, see figure (a). this shape is found around all cylindrically-symmetric, 'conical' membrane inclusions, figure . interaction of a spherical particle with an ellipsoidal particle of aspect ratio = b a / . the contact angle θ = . c has been used for both particles. the energies are plotted for spherical particles with radii = r a and = r a that approach the ellipsoidal particle (a) at the side (b) and at the tip, here shown for a spherical particle with = r a . (c) interaction energies γ ∆e a / as function of d a cc / between the centers of mass of the particles. inset: doublelogarithmic plot and the fit of the numerical data to a power-law decay. reprinted with permission from [ ] . copyright ( ) american chemical society. which includes curved proteins [ , , ] and attached polymers [ ] [ ] [ ] [ ] . a catenoid is a minimal surface with vanishing mean curvature at every point and therefore with vanishing bending energy. the deformation energy cost for the membrane adhered to the particle and the adhesion energy gain for contact between particle and membrane can therefore be directly compared with each other in order to predict whether a particle gets wrapped or not. the wrapping transition is fully characterized using the critical particle radius κ * a w for wrapping in equation ( ) . however, in general the deformation energy of the membrane surrounding a particle will contribute to the total deformation energy of the membrane. a convenient way to characterize wrapping states of particles for various parameters are wrapping diagrams based on energy minimisation, analogous to phase diagrams in thermodynamics [ , , ] , see figure (b). spherical particles remain unwrapped below a threshold adhesion strength and get partialwrapped or complete-wrapped for higher adhesion strengths. particles at membranes with finite tension can be found in stable partial-wrapped states for adhesion strengths just above those for the binding transitions, see figure (b). the stable partial-wrapped states are separated by continuous transitions from the unwrapped states and by discontinuous transitions from the complete-wrapped states. the latter trans itions with energy barriers are associated with two spinodals that indicate those values for the adhesion strength beyond which particles transition spontaneously from partial-wrapped to completewrapped states and below which particles transition spontaneously from complete-wrapped to unwrapped states. membrane deformations induced by non-spherical particles depend on both particle shape, discussed in this section, and particle orientation, discussed in section . . in general, inhomogeneous surface curvature of particles corresponds to energy barriers for wrapping [ , ] . for non-spherical particles, membrane tension is therefore not required to stabilize partial-wrapped states; such particles are ideal membrane markers for imaging. thus not only size and aspect ratio, but also local particle surface curvature matters for wrapping of non-spherical particles [ ] . the importance of local particle surface curvature can be demonstrated well for hauser's cube-shaped particles. the phase diagram in figure shows that no membrane deformation energy costs arise if cube-like particles attach with a flat face to a membrane. the particles therefore adhere already for very small adhesion strengths and are found in shallow-wrapped states. the first energy barriers are encountered between shallow-wrapped and deep-wrapped states when the membrane has to bend around the highly-curved edges to increase wrapping from one face to five faces. the energy barriers between deepwrapped and complete-wrapped states correspond to the last four edges to be wrapped. both energy barriers shift to higher adhesion strengths for higher values of the membrane tension. we discuss here particles within the hydrophobic tail region of lipid bilayers in part and particles at curved membranes in part . particles with sizes of few nanometers may incorporate themselves in membranes and locally distort both lipid order and membrane thickness [ , , ] , see figure (a). while lipid order can only be investigated on the molecular scale, thickness variations can also be investigated using continuum models. here the headgroup positions of the monolayers can be modeled by mathematical surfaces with bending rigidity and monolayer tension, and a confinement potential which maintains the lipid bilayer thickness. analogous to integral membrane proteins with hydrophobic mismatch [ ] [ ] [ ] [ ] , particles that locally induce membrane-thickness deformations experience short-ranged deformation-mediated interactions. while the interactions may be repulsive at long distances as predicted by the continuum models, both continuum models and molecular dynamics simulations predict short-ranged attractive interactions and therefore clustering of nanoparticles within membranes. for high membrane tensions, the energy barrier for a third particle approaching a pair of particles is considerably decreased, such that particle aggregation may occur spontaneously [ ] , see figures (b) and (c). not only particle shapes, also membrane curvature prior to wrapping has to be taken into account for the interaction of particles with membranes. this can be demonstrated by calculating entry of particles into and exit of particles out of vesicles with different curvatures, see figure . the vesicles are assumed to freely adjust volume but keep a fixed membrane area. vesicles without particles thus adopt an overall spherical shape that is then locally distorted by binding a nanoparticle. the adhesion strength w and / , for vesicles with radius r v , are the relevant parameters to characterize this system. they are a subset of the full parameter space, determined in addition by membrane spontaneous curvatures and by osmotic pressures [ ] . for particles that enter vesicles from the outside, > c r , wrapping is hindered by an energy barrier. for particles that exit vesicles from the inside, < c r , upon increasing the adhesion strength the particles continuously transit from the free state via stable partial-wrapped states with increasing wrapping fractions to the complete-wrapped state. partial-wrapped particles can be used as probes for the local membrane curvature [ ] . a direct and barrierless transition between the free and the complete-wrapped state is only present for particles at infinitely large planar membranes. with decreasing absolute relative curvature c r , both the energy barriers for particle entry as well as the stability of partially-wrapped states for particle exit decrease. the adhesion strengths for the wrapping trans itions can be well approximated by the instability relations [ , ] for non-spherical particles, the orientation of particles at membranes-in addition to particle shapes, sizes, and surface properties-has to be taken into account to determine / and membrane tensions γ γ κ = a / . (a) the membrane deforms in a cylindrically symmetric way around the symmetry axis and the shape can be described by a radial deformation profile. for an infinitely large tensionless membrane, the shape of the free membrane is catenoidal. (b) the wrapping phase diagram shows that the nanoparticles are unwrapped below a critical adhesion strength = w , and completely enveloped for adhesion strengths beyond the thick solid line. the thin dotted line is the envelopment transition calculated neglecting the deformation energy of the free membrane. the thin dashed lines are the spinodals for spontaneous unwrapping from the complete-wrapped to the free/non-wrapped state and for spontaneous envelopment from the partially wrapped to the fully wrapped state. adapted with permission from [ ] . © epla. all rights reserved. wrapping states and membrane deformations. elongated particles can be oriented in rocket and in submarine orientation, with their long axes perpendicular and parallel to the membrane, respectively. janus particles preferably bind with their most adhesive side to the membrane. changing the orientation of particles in magnetic fields can be used to probe the elastic properties of membranes and cells. the orientations of elongated particles at membranes crucially depend on particle shapes, membrane elastic properties, and membrane-particle interactions, see figure . table summarizes wrapping states and transitions for various particles shapes and membrane elastic parameters based on the results of [ , , , ] . for prolate ellipsoidal particles, the particles bind to membranes with their points of lowest curvature at the sides of the particles. in these shallow-wrapped states, they are in the so-called 'submarine orientation'. for fast wrapping, if reorientation does not occur, the particles remain in submarine orientation until they reach the complete-wrapped state [ ] . for for two corresponding states at the w phase boundary: (a) a shallowwrapped state with approximately % of particle wrapped, and (b) a deep-wrapped state with approximately % of the particle wrapped. (c) phase diagram for wrapping of hauser's cube for reduced membrane tension γ γ κ = a / and reduced adhesion strength πκ = w wa /( ), where a is the particle surface area. we find a shallow-wrapped (sw), a deep-wrapped (dw), and a completewrapped (cw) state, separated by two discontinuous wrapping transitions, labeled as w and w . adapted with permission from [ ] . copyright ( ) american chemical society. morphology diagram of stable states of a particle adhering to a vesicle. the wrapping state is plotted for various values of rescaled adhesion energies κ = u wa / and relative curvatures c r of the vesicle membrane and the particle surface. the three black lines divide the diagram into three regions in which the particle is either partially wrapped, unwrapped, or fully wrapped. in the grey shaded region, the transitions between the unwrapped state and the wrapped state of a particle outside the vesicle require the crossing of an energy barrier. the red dashed lines are analytical instability lines derived from the stability relations in [ ] . reproduced from [ ] .-published by the royal society of chemistry. oa cc by . . slow wrapping, the particles are able to reorient to their minimal-energy states at every time, they transit from submarine orientation to the so-called 'rocket orientation' at deep wrapping. the rocket state is energetically preferable at deep wrapping, because only one of the pointed tips needs to be wrapped. from a stable deep-wrapped state, ellipsoidal particles then continuously transition to the complete-wrapped state [ ] . for rod-like particles, energy minimisation predicts that the particles readily bind with their blunt tips in rocket orientation at very small adhesion strengths. if the edges of the particles are sharp and their aspect ratios are small, the particles remain in rocket orientation until they reach complete wrapping; the transitions between shallow-wrapped and deep-wrapped, as well as between deep-wrapped and complete-wrapped states are discontinuous. for high aspect ratios or round edges of the particles, rod-like particles bind with their blunt tips in rocket orientation only with a very small fraction of their surface area. they then rotate to submarine orientation in the shallow-wrapped state, and back to rocket orientation in the deep-wrapped state [ , ] , see figure . in particular, the theoretical prediction for the rotation from submarine orientation to rocket orientation is in agreement with experimental observations for budding of filamentous viruses [ , ] . modes of entry for nanoparticle uptake by membrane wrapping: (i) submarine mode with the long axis of the particles oriented parallel to the membrane, (ii) rocket mode with the long axis oriented perpendicular to the membrane, and (iii) competition between submarine and rocket mode as observed for rod-like particles with high aspect ratios. the complete-wrapped particle is connected by an infinitely small catenoidal neck to the membrane; the particle orientation in this state is irrelevant. reprinted with permission from [ ] . copyright ( ) american chemical society. table . shape dependence of particle wrapping, based on the results of [ , , , ] . the membrane can be characterized by bending rigidity only, 'κ', or by bending rigidity and membrane tension, 'κ and γ'; the binding transition can occur at finite or vanishing adhesion strength w; the particle can be in submarine or rocket orientation; transitions can be continuous (cont.) or discontinuous (discont.) and may involve reorientation (reorient.). the binding transition for ellipsoids is independent of the membrane tension and is given in [ , ] . binding transition a fast wrapping at high adhesion strength, such that a bound ellipsoid cannot reorient to rocket orientation. b rocket mode for supereggs with blunt tips and small aspect ratio (e.g. = n and = b a . / ). reprinted with permission from [ ] . copyright ( ) american chemical society. the dynamics of wrapping of spherical nanoparticles is determined by the typical time scales for the relevant processes, such as membrane deformation [ ] , receptor or protein diffusion that may be hindered by a cortical cytoskeleton [ ] [ ] [ ] [ ] [ ] , and potential metabolic remodeling of the cytoskeleton [ ] [ ] [ ] . after initial contact between nanoparticles and membranes, the deformed area of the membrane surrounding the particles increases until half wrapping and then again decreases. while the membrane deformation is catenoid-like for small and for large wrapping fractions of particles, for finite membrane size the highest deformation energy costs are expected for about half-wrapped particles. formation of a defect in the neck towards the end of the wrapping process can induce the separation of bent and flat membrane and completes wrapping [ ] . the reorientation dynamics for elongated particles can be calculated using molecular dynamics simulations for nanoparticles that interact with initially flat lipid bilayer membranes [ , ] . also local free-energy analysis and incremental changes of the nanoparticle orientation in the direction of lowest energy at each time step allow to predict the wrapping pathway [ ] . in figure , the corresponding curvature-energy landscapes are displayed. a spherocylindrical nanoparticle that is initially oriented in the unfavourable rocket orientation first reorients towards submarine orientation. however, although energetically most favourable until half wrapping the particle may never actually reach submarine orientation. beyond half wrapping, the particle turns back to the then favourable rocket orientation, in agreement with the energetics discussed at the beginning of this section. we are not aware of systematic experimental studies for the interaction of lipid-bilayer membranes with nanoparticles that have anisotropic surface functionalization. however, micrometer-sized spherical particles that are half coated with ligands preferably orientate with the ligandcoated side towards the membrane during phagocytosis [ ] . furthermore, viruses have been modeled as partially adhesive particles [ ] . the reorientation of the malaria parasite in tipfirst orientation at the beginning of the invasion process may also be due to an adhesive gradient on the parasite surface [ ] . analytical calculations for partial-wrapped particles, e.g. janus particles, at non-spherical vesicles show that membrane curvature-induced forces pull the particles to regions with preferred membrane curvature [ ] . in analogy to magnetic particles with switchable orientation at fluid interfaces, micrometer-sized magnetic particles can also be attached to cell membranes with an underlying cytoskeleton [ ] . such microrheological measurements reveal glassy behaviour for various cell types [ ] [ ] [ ] [ ] . for red blood cells with their cortical spectrin cytoskeleton responsible for the shear elasticity of the complex cell membrane [ ] , the values of the elastic parameters obtained using magnetic particle microrheology agree well with those used for computer simulations for cell stretching and blood flow [ ] . membrane deformations induced by partial-wrapped particles lead to membrane-mediated interactions that minimise the sum of both membrane deformation energy and particlemembrane attachment energy [ ] . several recent studies are discussed in this section. however, much more is knownand this knowledge may partially be transferred to nanoparticles-about the related systems of lipid bilayer-mediated interactions between curved inclusions, both for membranedeformation mediated interactions [ , , , , ] , as well as for membrane-fluctuation mediated casimir interactions [ ] [ ] . membrane-mediated interaction between two parallel and long cylindrical particles at distance d attached to the same side of membranes under lateral tension is repulsive [ ] , / predicted by local energetics. the nanoparticles take a general laying-down-thenstanding-up sequence during endocytosis. the heat maps show the curvature energy for various particle orientation angles and wrapping fractions. nanoparticle wrapping at the turning points (i-v) along the endocytic pathways predicted by local free-energy analysis is schematically shown on the right: green-shaded areas are wrapped, while yellow-shaded areas are naked. reprinted with permission from [ ] . copyright ( ) american chemical society. where ξ γ κ = / is a characteristic reciprocal length, and a cyl is the cylinder radius. the interaction between two cylindrical particles attached to opposite sides of the membrane is attractive, here, the length of the cylinders is contained in the param eters for the bending rigidity, adhesion strength, and membrane tension for these effectively one-dimensional calculations. results for stronger membrane deformations can be found in [ ] . only few studies are available for far-field interactions between spherical nanoparticles that are partially attached to lipid bilayer membranes. figure shows both numerical calcul ations and experimental data. membrane-mediated particle attraction is found for distances below a , with an attractive energy well of κ ≈ − e . a for an interparticle distance of about a . [ ] . for typical lipid bilayer bending rigidities κ < < k t k t b b , this corresponds to binding energies the figure shows larger attraction strengths for membrane tensions γ < nn m / compared with membrane tensions γ µ > n m / . many computer simulation studies for membrane-mediated interactions between partial-wrapped nanoparticles, as shown in figure , rely on finite-element calculations. here, the bending energy is discretized on triangulated surfaces [ ] [ ] [ ] [ ] . large systems that require at the same time fine discretization in high-curvature regions around particles are computationally expensive, therefore membrane-mediated interactions between the particles have so far mostly been studied in the near field. however, long-ranged membrane-mediated interactions between partial-wrapped nanoparticles might be similar to long-ranged interactions between curved inclusions. for example, for two spherical-cap inclusions attached to the same side of planar membranes, the repulsive membranemediated interaction is [ ] where α and α are polar angles that determine the sizes of the spherical caps, a is their radius, and d is the distance between the centers of the caps. strongly-curved inclusions at very close distances experience an attractive interaction [ ] . interactions between two (spherical) nanoparticles have been shown to be attractive, see e.g. figure . this is surprising on the first view, because catenoid-like membrane deformations around partial-wrapped nanoparticles at large distances require only very small deformation-energy costs. if two spherical-cap inclusions or two particles approach each other on a planar membrane the ideal catenoid-like deformations cannot form any more because of the boundary conditions. therefore, the membrane-mediated interactions because of deformation-energy are expected to be repulsive [ , ] . however, for spherical particles the attractive membrane-mediated interactions because of membrane-particle adhesion energy dominate and lead to an overall attraction [ ] . for two partial-wrapped particles in the near field, not only the interparticle distance, but also the orientation of the pair of particles with respect to the membrane has to be taken into account. for example, in [ ] the connecting line between two particles adsorbed to a vesicle is parallel to the membrane at large distances and reorients to perpendicular orientation at small distances. the attractive interaction is significantly higher for this particularly stable tubular arrangement [ ] . many-particle interactions are important for membrane-mediated interactions, which has been demonstrated in several cases for integral membrane proteins with hydrophobic mismatch and for spherical-cap inclusions [ , , , ] . it is therefore essential to not only consider pair interactions between particles. we start our discussion with the 'inclusion case', i.e. with membrane deformation-mediated interactions only, where the membrane area attached to each particle is fixed. while two weakly-curved spherical-cap inclusions that are attached to the same side of the membrane repell each other as discussed in section . . , many inclusions have been observed to aggregate and to induce bud formation [ , , [ ] [ ] [ ] . a membrane that is curved prior to adhesion of inclusions or that gets curved by cooperative budding screens the repulsive interaction and can therefore lead to effective attraction. figure highlights catenoidal membrane deformations around inclusions on vesicles; the size of the catenoidal 'halo' shrinks with increasing background curvature, thereby screening the repulsive interaction between the inclusions. these catenoidal patches reduce the total bending energies of the vesicles, which vanish at optimal inclusion density. in comparison, on planar membranes curved inclusions always increase the deformation energy. a particle dimer switches from a linear aggregate on the membrane to a tubular aggregate for increasing wrapping fraction [ , ] , compare also section . for the orientation of elongated particles. on a vesicle, the wrapping fraction can be tuned by adjusting the reduced volume of the vesicle, where v is its actual volume and v sph is the volume of a spherical vesicle with the same membrane area. a small reduced volume also allows more than two particles to join the tube. the energy gain of such tubular assemblies compared with single, complete-wrapped particles strongly depends on the ratio of the range ρ of the particle-membrane interaction potential and the particle radius a. the finite potential range leads to a higher adhesion energy gain for tubular arrangements compared with single-particle buds, because some fraction of the tubular necks between particles are inside the interaction range; for example the energy gain per particle is about κ for ρ = a . / [ ] . simulation snapshots and energies for several configurations of three particles attached to membranes are shown in figure . if the particles are all located in the plane of the membrane, a third particle that attaches to form a linear aggregate gains membrane-mediated binding energy of few k t b and attaches without an energy barrier. in contrast, a particle that attaches from the side to the existing particle aggregate experiences an energy barrier and has a few k t b higher energy in the (metastable) bound state compared with the unbound state. bending energy has been shown to favour compact aggregation, . here, φ = corresponds to a linear arrangement of the particles. the four snapshots depict minimum-energy conformations at the angles φ = , , , and . reprinted with permission from [ ] . copyright ( ) by the american physical society. adhesion energy linear aggregation [ ] . also for tubular aggregates, the linear-tube configuration is preferred over the more compact, triangular configuration [ ] , see figure (b). linear aggregates in the plane of the membrane have been experimentally observed for colloidal particles bound to giant unilamellar vesicles (guvs) [ ] , tubular aggregates for the interaction of viruses with cells and guvs [ ] . figure (a) shows a phase diagram for many-particle systems in terms of bending rigidity κ and particle-membrane binding energy d [ ] . in the limit of small bending rigidities, partial-wrapped particles form a hexagonal cluster phase where the membrane penetrates in-between the particles. in the limit of high bending rigidities, the particles are barely attached to the membrane. they deform the membrane only weakly, therefore they also interact only weakly and are found in loose, mostly hexagonal aggregates. linear aggregates are observed inbetween both limites for biologically relevant bending rigidities κ < < k t k t b b . figure (b) shows a phase diagram in terms of particle diameter and particlemembrane binding energy. free unbound nanoparticles are found at low adhesion strengths and for small particle radii, then linear aggregates, tubular aggregates, and single-particle buds are observed with increasing adhesion strength [ ] . this sequence of configurations is consistent with the reorientation reported for elongated nanoparticles in [ ] , see section . . biological membranes are often not symmetric, the two monolayers usually consist of different lipids. this asymmetry can be modeled with the help of a spontaneous curvature c of the membrane. if the directions of spontaneous curvature and the curvature of the particle surface coincide, the spontaneous curvature facilitates complete wrapping compared with a symmetric membrane [ ] . at the same time, the direct transition between free and complete-wrapped states is replaced by a discontinuous transition. for a spontaneous curvature opposite to the curvature of the particle surface, the complete-wrapped state is shifted to higher adhesion strengths. furthermore, a new regime with partial-wrapped states is found. with increasing spontaneous curvature, also the regime of adhesion strengths where partial-wrapped states are stable increases. for fixed adhesion strengths, finite spontaneous curvatures lead to size selectivity for wrapping of nanoparticles, see figure . for vanishing or small spontaneous curvatures, all particles with radii beyond a threshold radius get figure . membrane-mediated interactions between many particles. (a) phase diagram for nanoparticle self-assembly in terms of membrane bending rigidity κ and particle-membrane binding energy d , which replaces the adhesion strength w in the simulations. the snapshots show typical aggregates in the h , the l, and the h phase (top to bottom). adapted with permission from [ ] . copyright ( ) by the american physical society. (b) phase diagram in terms of nanoparticle diameter a and d . with increasing d , the gaseous phase g with non-attached particles is followed by the linear aggregation phase l, the tubeformation phase t, and the single-particle bud phase b. the radius of the vesicle is σ = r v and the particle surface fraction is . . adapted with permission from [ ] . copyright ( ) by the american physical society. wrapped, see equation ( ) . with decreasing spontaneous curvatures, in addition to the lower threshold radius for complete wrapping, also an upper threshold radius beyond the that particles remain unwrapped is found [ ] . the regime with stable complete-wrapped states thus narrows to a small window in the particle radius for high negative values of the spontaneous curvature. such a preferred radius for particle wrapping has been observed in experiments [ , ] . size selectivity by spontaneous membrane curvature is therefore an alternative to receptor-based models for cellular uptake that are usually used to motivate an upper limit for the particle radius to achieve complete wrapping [ ] . on the one hand, particle-membrane systems can be used for applications in therapeutics and diagnostics. on the other hand, for numerous other applications in industry, potential toxic effects have to be considered. furthermore, nanostructured surfaces can be rationalised as nanoparticles bound to a substrate, which opens an entire new field for applications. for basic research, particle-membrane systems can serve as model systems to understand biological processes, such as viral budding, malaria invasion, and phagocytosis. . . . drug delivery. nanoparticles are potential drug-delivery vectors and tools for diagnosis [ ] [ ] [ ] [ ] [ ] . for diagnosis, in particular non-spherical nanoparticles with enhanced stability of partial-wrapped states can serve as membrane markers for imaging [ ] . for drug delivery, rough hydrophobic particles have been proposed to have a high drug-carrying capacity and high loading efficiency [ ] . such particles can prolong the time of release of a drug payload, which can be therapeutically advantageous. nanoparticles may even cross the blood-brain barrier via transcytosis and may therefore be applied for drug delivery in the brain [ , ] . recently hollow shell-shell nanocontainers with stimuli-responsive properties that could allow for controlled drug release have been suggested for drug delivery [ ] . for studies of potential toxic effects, not only single-particle properties, such as composition and size, but also particle concentrations play an important role [ ] . toxicity can be quantified by ec values that refer to the concentration of particles that induce a response of cells or organisms halfway between the base line and the maximum after h exposure time to nanoparticles. while agno leads to growth inhibition for algae already at concentrations of − − mg l , ag nanoparticles lead to growth inhibition only at concentrations between − . mg l and − mg l , see figure . most other organisms are less sensitive to nanoparticles and growth inhibition occurs only at higher particle concentrations compared with algae. in general, the ec values increase significantly with particle size, which means that the toxic effect is reduced. for mammalian cells they range from . . . nanostructured surfaces. multi-electrode arrays allow to electrically couple excitable cells to electronic devices, see figure . the challenge is to achieve an optimal coupling, which requires to minimize the cleft between the cell and the electrode and to achieve tight attachment of the cell to the substrate in general. while thin electrodes pierce cell membranes [ ] , micro-electrodes get wrapped [ , ] . a systematic study of different micro-electrode shapes reveals that mushroom-shaped pillars are engulfed more than cylindrical pillars without caps [ ] . furthermore, cells have been found to preferably engulf pillars in their center compared with their edge. quantitative evaluation of focused ion-beam cuts allows to extract normal cytoskeletal stresses between few pa for cylinders with caps and several hundred pa for cylinders without caps. sis. passive endocytosis of particles with a homogeneous adhesion strength between particles and membranes is often modified by specific adhesion and active processes for biological systems. figure shows viruses with different shapes and a malaria parasite that have similar sizes as the particles discussed earlier. one specific example for active wrapping is the invasion of the malaria parasite into an erythrocyte, see figure . reorientation of the parasite, possibly because of a gradient of adhesive molecules, is followed by invasion. during invasion, a tight junction forms and reseales the membrane, which completes the formation of the parasitophorous vacuole. for the egg-like shape of the malaria parasite, line tension at the tight junction, and anisotropic adhesion of the parasite leads to a complex phase diagram for passive endocytosis with stable non-wrapped, shallow-wrapped, deep-wrapped, and complete-wrapped states [ ] , see figure . as indicated in figure , secretion of unstructured membrane from the parasite and favourable spontaneous curvature of the erythrocyte membrane may help the parasite to overcome energy barriers for wrapping and to finally invade the cell. in addition, also motor forces have been proposed to assist invasion [ ] . another active biological 'wrapping' process is phagocytotic uptake, see figure . here, the growth of the phagocytotic cup with its actin cytoskeleton is the major dynamic process [ ] . quantification using microscopy and image analysis shows fast uptake at the beginning, followed by a plateau with weakly increasing wrapping fraction, and again fast uptake of the particle towards the end of the process [ ] . various mechanisms for phagocytotic uptake have been suggested, among them receptor diffusion and directed motion [ ] , a zipper-like mechanism based on membrane fluctuations and membrane adhesion to the particle [ ] , and hindered uptake by increase and relaxation of membrane tension [ ] . multi-phase fluid systems and cellular biological systems abound with interfaces. nano-and microparticles naturally collect at such interfaces, because their localization at the interfaces lowers their interaction energy with the environment. we have considered here two types of interfaces: fluid-fluid interfaces governed by interfacial tensions, and biological interfaces controlled by curvature elasticity. particles at both types of interfaces show many common behaviours. the interface attraction depends on particle size, shape, and surface properties. particles can orient in different ways at interfaces, they deform the interfaces around them, and these interface deformations lead to interface-mediated interactions and collective behaviour. although systems and concepts for particles at fluid and biological interfaces are very similar, and for instance sds stabilisation of droplets can drive the system from fluid interfaces towards membranes [ ] , there is a major difference. in many cases, particle sizes at fluid interfaces are in the micrometer range, while particle sizes at lipid bilayer membranes are in the nanometer range. this implies that different experimental techniques are required in both cases, where the nanometer scale makes particles at membranes more difficult to observe and more difficult to manipulate. therefore, we have a better knowledge about particles at fluid interfaces, and there is an urgent need for systematic and well-controlled experiments for particles at membranes. nevertheless, a unified numerical and theoretical description of both systems is possible-at least for particles above a threshold diameter of about − nm -on the basis of continuum models for two-dimensional surfaces and their deformations embedded in three-dimensional space. from the technological point of view, micrometer-sized particles at fluid interfaces can be used in many ways to control and tailor interface properties. such applications range for both the upper and lower lobes, after engulfment begins at ≈ t s there is an initial slow stage (light gray) followed by a much quicker second stage (dark gray). engulfment is complete by ≈ t s . reprinted from [ ] , copyright ( ), with permission from elsevier. from emulsion stabilisation through an effective reduction of the interface tension to the design of solid shells and surfaces with controlled optical properties. from a biological point of view, nanoparticles are interesting in nanomedicine as biomarkes and drug carriers, but their effect on cells also has to be assessed because of their potential nanotoxicity. in addition, there is a large range of biological particles, such as viruses and parasites, the interaction of which with cells is also highly desirable to be controlled. the interaction of single hard particles with interfaces is by now reasonably well understood. therefore, we believe that future research should move towards particle-mediated interactions and collective properties for many particles at both fluid and biological interfaces, as well as towards soft particles. for example, size and concentration effects for the interaction or nanoparticles with liposomes and polymersomes have been studied using electron microscopy and scattering [ ] [ ] [ ] . using force measurements, nanoparticlemediated adhesion between elastic gels has been measured [ ] . the hard particles can serve as 'glue' between soft interfaces. soft particles, e.g. microgel and polymeric particles, add further complexity by allowing the particle shape to adjust in response to the interaction with a fluid or biological interface [ , [ ] [ ] [ ] [ ] [ ] . finally, dynamical behaviour of particles at fluid and biological interfaces awaits further characterization. for instance, dynamics of wrapping of non-spherical particles by biological interfaces has been discussed in section . . , but calculations that include brownian motion are missing. colloids adsorbed to stabilised oil-water interfaces show different diffusion properties than colloids in bulk [ ] , systematic studies could be used to measure the viscosity of lipid bilayers. furthermore, nanoparticles in combination with superresolution microscopy can be used as probes to study dynamics in biological cells [ ] [ ] [ ] . to conclude, particles are already widely used for applications, but a systematic understanding of the interactions of engineered nano-and microparticles with soft and biological matter is often lacking. furthermore, our understanding of basic biological processes on the cellular scale, such as phagocytosis and blood-stage malaria, will benefit from a detailed understanding of particles at biological interfaces. we expect that in the future more systematic studies for particles at fluid and biological interfaces will allow the engineering of even better tailored nano-and microparticles for applications and to achieve a more thorough understanding of cellular uptake and invasion mechanisms. examples for areas where rational design of interface-particle systems may improve applications include targeted drug delivery for particles at biological interfaces, and a better control of the rheological properties of emulsions for particles at fluid interfaces. colloidal jamming at interfaces: a route to fluid-bicontinuous gels science separation of solids in the surfacelayers of solutions and 'suspensions' (observations on surface-membranes, bubbles, emulsions and mechanical coagulation).-preliminary account titanium dioxide nanoparticles in food and personal care products detection and characterization of engineered nanoparticles in food and the environment food addit food emulsions and foams: stabilization by particles liquid marbles: principles and applications soft matter silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications and toxicity effects int silver nanoparticles as antimicrobial agent: a case study on e. coli as a model for gram-negative bacteria novel hydrophilic chitosan-polyethylene oxide nanoparticles as protein carriers mesoporous silica nanoparticles in drug delivery and biomedical applications drug delivery systems: entering the mainstream how should the completeness and quality of curated nanomaterial data be evaluated? qsar model for cytotoxicity of sio nanoparticles on human lung fibroblasts size-dependent toxicity of silver nanoparticles to bacteria, yeast, algae, crustaceans and mammalian cells in vitro atomic force microscopy characterization of silver nanoparticles interactions with marine diatom cells and extracellular polymeric substance cuo and tio to bacteria vibrio fischeri and crustaceans daphnia magna and thamnocephalus platyurus membrane-wrapping contributions to malaria parasite invasion of the human erythrocyte cryo-sem images of native milk fat globule indicate small casein micelles are constituents of the membrane rsc adv making polymeric micro-and nanoparticles of complex shapes proc high-yield synthesis of monodisperse dumbbell-shaped polymer nanoparticles the effect of sedimentation and diffusion on cellular uptake of gold nanoparticles assembly and budding of ebolavirus plos pathog electron tomography reveals the steps in filovirus budding plos pathog directing the orientational alignment of anisotropic magnetic nanoparticles using dynamic magnetic fields faraday discuss enhanced wavelengthdependent surface tension of liquid-vapour interfaces the molecular face of lipid rafts in model membranes proc. natl acad. sci. usa statistical thermodynamics of surfaces, interfaces and membranes elastic properties of lipid bilayers: theory and possible experiments capillary force on a micrometric sphere trapped at a fluid interface exhibiting arbitrary curvature gradients shape transitions of fluid vesicles and red blood cells in capillary flows proc a multiscale red blood cell model with accurate mechanics, rheology and dynamics formation of supported bilayers on silica substrates langmuir adhesion energy of receptor-mediated interaction measured by elastic deformation novel method for measuring the adhesion energy of vesicles orientational transitions of anisotropic nanoparticles at liquid-liquid interfaces critical particle sizes for the engulfment of nanoparticles by membranes and vesicles with bilayer asymmetry capillary assembly of microscale ellipsoidal, cuboidal and spherical particles at interfaces langmuir lipid membrane-mediated attraction between curvature inducing objects capillary interactions between anisotropic colloidal particles tubulation and aggregation of spherical nanoparticles adsorbed on vesicles mechanism of membrane tube formation induced by adhesive nanocomponents membrane-mediated interactions between circular particles in the strongly curved regime probing bioinspired transport of nanoparticles into polymersomes internalization of silica nanoparticles into fluid liposomes: formation of interesting hybrid colloids control of the stability and structure of liposomes by means of nanoparticles soft matter threedimensional super-resolution imaging by stochastic optical reconstruction microscopy die sichtbarmachung der bakteriophagen lyse im Übermikroskop naturwissenschaften detachment energies of spheroidal particles from fluidfluid interfaces contact angles of microellipsoids at fluid interfaces langmuir the interaction of colloidal particles collected at fluid interfaces the 'cheerios effect capillary force acting on a colloidal particle floating on a deformed interface capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature proc nanoparticles at fluid interfaces two-dimensional interfacial colloidal crystals adsorption of colloidal particles to curved interfaces orientation and self-assembly of cylindrical particles by anisotropic capillary interactions long-range attraction between colloidal spheres at the air-water interface: the consequence of an irregular meniscus capillary forces between solid particles in fluid interfaces colloids surf capillary interactions between anisotropic particles soft matter capillary migration of microdisks on curved interfaces adsorption of submicron amphiphilic dumbbells to fluid interfaces langmuir wetting and contact lines of micrometer-sized ellipsoids ellipsoidal particles at fluid interfaces eur capillary bond between rod-like particles and the micromechanics of particle-laden interfaces how do mosquito eggs selfassemble on the water surface? oriented assembly of anisotropic particles by capillary interactions mechanism of formation of twodimensional crystals from latex particles on substrates langmuir the destabilization of froth by solids. i. the mechanism of film rupture capillary interactions between particles bound to interfaces, liquid films and biomembranes adv particles in thin liquid films and at interfaces capillary interactions between nearby interfacial objects mesoscale self-assembly: capillary bonds and negative menisci the interaction between floating particles math on the attraction of floating particles effective capillary interaction of spherical particles at fluid interfaces force balance of particles trapped at fluid interfaces interface deformations affect the orientation transition of magnetic ellipsoidal particles adsorbed at fluid-fluid interfaces magnetic cylindrical colloids at liquid interfaces exhibit non-volatile switching of their orientation in an external field role of geometry and amphiphilicity on capillary-induced interactions between anisotropic janus particles langmuir double hydrophilic janus cylinders at an air-water interface geometrically and chemically anisotropic particles at an oil-water interface shape induced deformation, capillary bridging and self-assembly of cuboids at fluid-fluid interface self-assembly of cubes into d hexagonal and honeycomb lattices by hexapolar capillary interactions modelling the self orientation of particles in a film miner the hydrodynamics of water strider locomotion fundamentals the effects of hydrophobicity and orientation of cubic particles on the stability of thin films miner. eng curvature-driven capillary migration and assembly of rod-like particles proc on the thermodynamics of particle-stabilized emulsions: curvature effects and catastrophic phase inversion curvature-induced capillary interaction of spherical particles at a liquid interface rotation and alignment of anisotropic particles on nonplanar interfaces langmuir equilibrium orientation of nonspherical janus particles at fluid-fluid interfaces influence of magnetic field on the orientation of anisotropic magnetic particles at liquid interfaces assembling ellipsoidal particles at fluid interfaces using switchable dipolar capillary interactions interactions between particles with an undulated contact line at a fluid interface: capillary multipoles of arbitrary order self-assembled capillary arrows self-assembly and rheology of ellipsoidal particles at interfaces shapeinduced capillary interactions of colloidal particles anisotropic capillary interactions and jamming of colloidal particles trapped at a liquid-fluid interface assembly of nanoparticles at liquid interfaces: crowding and ordering langmuir particle shape anisotropy in pickering emulsions: cubes and peanuts langmuir tunable dipolar capillary deformations for magnetic janus particles at fluid-fluid interfaces timescales of emulsion formation caused by anisotropic particles lattice boltzmann simulations of anisotropic particles at liquid interfaces comput nematic-wetted colloids in the isotropic phase: pairwise interaction biaxiality and defects elastocapillary interactions on nematic films proc. natl acad. sci. usa capillary-induced giant elastic dipoles in thin nematic films proc cellulosic nanorods of various aspect ratios for oil in water pickering emulsions shape anisotropic colloids: synthesis, packing behavior, evaporation driven assembly, and their application in emulsion stabilization capillary interactions in pickering emulsions can janus particles give thermodynamically stable pickering emulsions? exploiting particle shape in solid stabilized emulsions colloidosomes: selectively permeable capsules composed of colloidal particles capillary flow as the cause of ring stains from dried liquid drops suppression of the coffee-ring effect by shape-dependent capillary interactions the destabilization of froth by solids. ii. the rate-determining step lipid membranes as solvents for carbon nanoparticles computer simulation of the translocation of nanoparticles with different shapes across a lipid bilayer wrapping of ellipsoidal nano-particles by fluid membranes soft matter aggregation and vesiculation of membrane proteins by curvature-mediated interactions how shape influences uptake: interactions of anisotropic polymer nanoparticles and human mesenchymal stem cells small modeling the effect of nano-sized polymer particles on the properties of lipid membranes intracellular release of endocytosed nanoparticles upon a change of ligand-receptor interaction how hydrophobic nanoparticles aggregate in the interior of membranes: a computer simulation direct proof of spontaneous translocation of lipidcovered hydrophobic nanoparticles through a phospholipid bilayer sci softening of phospholipid membranes by the adhesion of silica nanoparticles-as seen by neutron spin-echo lipid tail protrusions mediate the insertion of nanoparticles into model cell membranes elastic deformation of a fluid membrane upon colloid binding adhesion of vesicles molecular mechanisms and forces involved in the adhesion and fusion of amphiphilic bilayers mechanics of receptormediated endocytosis proc the effect of interactions on the cellular uptake of nanoparticles the receptor-mediated endocytosis of nonspherical particles force-induced growth of adhesion domains is controlled by receptor mobility proc intermembrane adhesion mediated by mobile linkers: effect of receptor shortage a statistical-thermodynamic model of viral budding kinetics of receptor-mediated endocytosis of elastic nanoparticles coarse-grained model of adsorption of blood plasma proteins onto nanoparticles nanoparticle size and surface properties determine the protein corona with possible implications for biological impacts proc biomolecular coronas provide the biological identity of nanosized materials transferrin-functionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface serum albumin enhances the membrane activity of zno nanoparticles cell surface area regulation and membrane tension interaction of conical membrane inclusions: effect of lateral tension budding and vesiculation induced by conical membrane inclusions the shape of polymer-decorated membranes pressure patches for membranes: the induced pinch of a grafted polymer elastic properties of polymer-decorated membranes self-avoiding linear and star polymers anchored to membranes when do fluid membranes engulf sticky colloids? shape and orientation matter for the cellular uptake of nonspherical particles self-assembly of anionic, ligand-coated nanoparticles in lipid membranes nanoscale bilayer-thickness-mediated interactions between integral membrane proteins rigidity of transmembrane proteins determines their cluster shape lipid membranes with transmembrane proteins in shear flow contributions of gaussian curvature and nonconstant lipid volume to protein deformation of lipid bilayers membraneinduced interactions between inclusions the role of membrane curvature for the wrapping of nanoparticles adhesive nanoparticles as local probes of membrane curvature correction: wrapping of ellipsoidal nano-particles by fluid membranes role of nanoparticle geometry in endocytosis: laying down to stand up membrane skeletal dynamics: role in modulation of red cell deformability, mobility of transmembrane proteins and shape application of laser tweezers to studies of the fences and tethers of the membrane skeleton that regulate the movements of plasma membrane proteins lateral diffusion in membranes handbook of filament networks attached to membranes: cytoskeletal pressure and local bilayer deformation red blood cell membrane fluctuations and shape controlled by atp-induced cytoskeletal defects metabolic remodeling of the human red blood cell membrane proc equilibrium physics breakdown reveals the active nature of red blood cell flickering receptor-mediated endocytosis of nanoparticles of various shapes how half-coated janus particles enter cells uniform and janus-like nanoparticles in contact with vesicles: energy landscapes and curvature-induced forces scaling the microrheology of living cells implementation and application of a novel d magnetic twisting cytometry based on multi-pole electromagnet viscoelasticity of the human red blood cell cytoskeletal mechanics in adherent human airway smooth muscle cells: probe specificity and scaling of protein-protein dynamics fluctuations of coupled fluid and solid membranes with application to red blood cells fluid membranes can drive linear aggregation of adsorbed spherical nanoparticles long-range forces in heterogeneous fluid membranes casimir and meanfield interactions between membrane inclusions subject to external torques effect of chain length and unsaturation on elasticity of lipid bilayers indirect interactions of membrane-adsorbed cylinders eur adhesion of cylindrical colloids to the surface of a membrane triangulated surface models of fluctuating membranes statistical mechanics of membranes and network models of fluid, hexatic and polymerized membranes the conformation of fluid membranes: monte carlo simulations cooperative wrapping of nanoparticles by membrane tubes many-body forces between membrane inclusions: a new pattern-formation mechanism shape transitions in lipid membranes and protein mediated vesicle fusion and fission effect of protein shape on multibody interactions between membrane inclusions membrane mediated attraction and ordered aggregation of colloidal particles bound to giant phospholipid vesicles gm structure determines sv -induced membrane invagination and infection nat size-dependency of nanoparticle-mediated gene transfection: studies with fractionated nanoparticles int the mechanism of uptake of biodegradable microparticles in caco- cells is size dependent understanding particle margination in blood flow-a step toward optimized drug delivery systems magnetic nanoparticles: in vivo cancer diagnosis and therapy int the importance of nanoparticle shape in cancer drug delivery margination of micro-and nano-particles in blood flow and its effect on drug delivery sci nanoparticles in cancer therapy and diagnosis adv gold-silica quantum rattles for multimodal imaging and therapy proc. natl acad. sci. usa chapter two from the blood to the central nervous system: a nanoparticle's journey through the blood-brain barrier by transcytosis nanoparticle-mediated brain drug delivery: overcoming blood-brain barrier to treat neurodegenerative diseases could multiresponsive hollow shellshell nanocontainers offer an improved strategy for drug delivery? interfacing electrogenic cells with d nanoelectrodes: position, shape and size matter cell adhesion promotion strategies for signal transduction enhancement in microelectrode array in vitro electrophysiology: an introductory overview and critical discussion a feasibility study of multisite, intracellular recordings from mammalian neurons by extracellular gold mushroom-shaped microelectrodes immunoelectron microscopy of rift valley fever viral morphogenesis in primary rat hepatocytes the length of vesicular stomatitis virus particles dictates a need for actin assembly during clathrindependent endocytosis mechanics of neutrophil phagocytosis: experiments and quantitative models the mechanism of phagocytosis: two stages of engulfment role of target geometry in phagocytosis proc target shape dependence in a simple model of receptor-mediated endocytosis and phagocytosis proc the zipper mechanism in phagocytosis: energetic requirements and variability in phagocytic cup shape plasma membrane tension orchestrates membrane trafficking, cytoskeletal remodeling and biochemical signaling during phagocytosis proc kinetic control of the coverage of oil droplets by dna-functionalised colloids sci nanoparticle solutions as adhesives for gels and biological tissues microgel particles as model colloids: theory, properties and applications adv compression and deposition of microgel monolayers from fluid interfaces: particle size effects on interface microstructure and nanolithography cellular uptake of elastic nanoparticles size and dynamics of caveolae studied using nanoparticles in living endothelial cells protein-based fluorescent nanoparticles for super-resolution sted imaging of live cells super resolution imaging of nanoparticles cellular uptake and trafficking our research on the interaction of particles with biological membranes has been supported by the eu fp nmp collaborative project prenanotox ( ). key: cord- - n eo n authors: gil-alana, luis a.; martin-valmayor, miguel; wanke, peter title: the relationship between energy consumption and prices. evidence from futures and spot markets in spain and portugal date: - - journal: energy strategy reviews doi: . /j.esr. . sha: doc_id: cord_uid: n eo n abstract slow economic recovery, market concentration, and scant alternative energy sources make the iberian energy market quite idiosyncratic when compared to the rest of the eu. this paper focusses on the iberian energy market by dealing with the analysis of the relationship between energy consumpiton and energy prices by using fractional integration in the iberian market. this technique is used in order to examine the degree of persistence of the series, looking at the spot and futures markets in spain and portugal. the results indicate that all the series are fractionally integrated, showing long memory and mean reverting behaviour. moreover, a close relation between energy consumption and energy prices is found in the spot market whereas it is not found in the futures market. in fact, there is a weak relationship between the futures market and energy consumption. however, regarding energy pricing, the relationship is stronger but with the spot market itself. energy is the cornerstone of modern economies not only for the suppliers of physical goods and services but also as a means of social welfare and comfort for people in general. hence, it is crucial to know how price changes impact on the energy demand of suppliers and consumers. in the recent past, energy deregulation and sharp movements in the price of primary energy goods have stimulated an increased interest in this area. most econometric studies in this field are focused on the price elasticities of energy demand with some other macroeconomic factors [ ] , helping us to gain a better understanding of the economic consequences of varying energy prices. although the economic literature on energy demand dates back to the last century [ , ] , in recent years numerous academic studies have used various techniques to estimate both the short and the long-term price elasticity demand of different energy products in different countries. this paper, however, departs from that literature in the sense that we first examine the degree of persistence in both energy consumption and energy prices using updated time series techniques based on fractional integration. in addition, the relationship between these two variables has been investigated in the spot and futures markets in the case of spain and portugal. the iberian business case has presented a number of regulatory specificities and competition constraints when compared to other european energy markets. the main issues to resolve today in the spanish market are the scant competition, the tariff deficit, faulty tariff design, a raft of uncertainties, potential market integration and the introduction of new technologies [ ] . in the portuguese market, amorim et al. [ ] indicate that the two main issues to address are that of setting up balancing mechanisms to implement renewable energy sources and capacity incentives to allow new investments. these operational and financial constraints may be responsible for excessive volatility in pricing and energy consumption in the iberian region. ciarreta and zarraga [ ] found also relevant intra-day price and transmission volatility in the iberian market, arguing how results are driven by market structure, market design and the regulation of renewable generation. regarding the futures market, capit� an-herraiz and rodriguez-monroy [ ] documented its lack of liquidity in comparison with other north european markets. notwithstanding, the slow economic recovery experienced by the iberian peninsula following the global financial crisis of has also contributed to lack of investment in renewable sources. this earlier crisis has resulted in the absence of new players, which prefer to innovate in bigger and integrated markets, where future options and spot market trades can be transacted more easily, due to higher liquidity. this being the case, the energy market integration in the iberian peninsula, which is expected to take place from on, calls for more investigation on each country level current status. although volatility in energy prices and consumption in spot and future markets might be mitigated due to variance pooling effects; future investment prospects could be affected by country-level market idiosyncratic conditions. the current covid- crisis might highlight these weaknesses in the short future as has happened in the past. in summary, this paper departs from that literature in the sense that it examines the degree of permanence in both energy consumption and energy prices using updated time series techniques based on fractional integration. in addition, the relationship between the two variables is investigated in the spot and futures markets in the case of spain and portugal. the rest of the paper is structured in seven sections. the literature review is presented in section , while section focuses on the iberian case. the major methodological steps adopted in this research are presented in section . data descriptive and sources are detailed in section . results are analyzed in section and discussed in section . conclusions follow in section . the literature relating to energy models for demand forecasting and management in the last century is extensive, especially after the oil crisis during the s. after the s, as a result of the kyoto protocol, environmental problems were included in the equation and the relationship between social factors, natural resources consumption and dioxide emissions were also studied. a very popular contribution towards gaining an understanding of the different energy models is the that of jebaraj and iniyan [ ] in which different types of models such as energy planning, supply-demand structure or forecasting models where reviewed and presented, as well as renewable and emission reduction policies. a recent review of the different models for energy demand forecasting can be found in suganthi and samuel [ ] . during the first decade of the st century several new techniques were introduced to accurately predict future energy needs. traditional methods such as time series regressions as well as other computing techniques such as fuzzy logic, genetic algorithms and neural networks are being extensively used to study the demand side management. regarding the drivers that can affect energy demand, york [ ] analyzed the relationship between demographic trends and energy consumption for the period - in fourteen eu countries, concluding that the relationship between population size and energy consumption was highly elastic and close to one. the age structure of the population and its level of urbanization appear to play important roles in terms of energy consumption. other studies suggest that price or economic activity also have an important relationship with energy demand. sharimakin et al. [ ] studied different european industries in the period - and concluded that long-run elasticity with respect to price is negative (À . ), while long-run elasticity with respect to economic activity is positive ( . ). adeyemi et al. [ ] studied the asymmetric price responses and the underlying energy demand trends, concluding that changes in energy prices might induce asymmetric changes in the derived demand for energy. this process should depend upon whether the price falls, rises, or rises above a previous maximum, but the derived demand for energy might be driven by exogenous factors such as improvements in the efficiency of the capital or government regulations. a consequence of this is that the drivers of energy demand need not necessarily be the same for all countries in the estimation of demand models. analyzing energy consumption, wong et al. [ ] estimated the elasticities of changes in oil prices and income of twenty oecd countries for the period - . negative income elasticity was found for coal consumption but income elasticity for oil and gas was found to be positive, suggesting the importance of economic growth in the movement towards cleaner energy from coal to oil and gas. however, in the specific case of oil markets, its consumption fell significantly with higher oil prices. bhattacharyya and timilsina [ ] studied other indirect aspects for developed economies, concluding that current models were not resolving conceptual issues regarding the existence of non-monetized transactions, such as the poor-rich or urban-rural structures. in addition, traditional energy resources or differentiation between commercial and non-commercial energy commodities were often poorly reflected in models. other authors such as beunder and groot [ ] concluded that the consumers' preferences cannot be simply taken as given, as is customary in standard economic models, and they should interact with the structure of financial incentives. in consequence, taxes and subsidies, or changing fixed or flexible rates in energy bills, were interacting and modifying with people's preferences. salisu and ayinde [ ] documented other emerging issues for energy demand, ranging from asymmetric price responses, time varying demand parameters, triangulation analyses to seasonal and climate change effects. they proposed models assuming symmetric, asymmetric energy prices or non-parametric techniques with bayesian approaches, to make empirical captures using time-varying coefficient models such as rolling regressions. figueiredo et al. [ ] analyzed the effects of renewable energy output variations, particularly wind power, noting that its production is strongly influenced by weather conditions. a recent review of the latest current trends in energy systems can be found in lopion et al. [ ] as the requirements made on energy system models are changing due to the governments emissions regulation and the implementation of green energies. along with the climate goals of the paris agreement, the national greenhouse gas strategies of industrialized countries involve the total restructuring of their energy systems. in terms of the pricing discovery and the relationship between spot and futures markets, figuerola-ferretti and gonzalo [ ] studied the modelling of pricing in commodity markets, presenting an equilibrium model between spot and futures prices with finite elasticity of arbitrage services and convenience yields. this model was tested in non-ferrous metals prices traded in the london metal exchange (lme), concluding that most markets are in backwardation and futures prices are information dominant in highly liquid futures markets. other studies, as that of narayan and sharma [ ] proposed a time-varying price model structure based on a rolling-window error correction framework, showing that price discovery in nine general commodities is dominated by the spot market, while in another six, price discovery is dominated by the futures market. therefore, challenging the well-established view in commodity markets that it is the futures market which dominates the spot price discovery process. regarding energy pricing, a review of the different techniques can be found in weron [ ] explaining the complexity of the available solutions, and this review has been recently updated in nowotarski and weron [ ] focusing in a probabilistic perspective. shrestha [ ] analyzes empirically the price discovery process in the futures and spot markets for different types of energy, such as crude oil, heating oil and natural gas, discovering that almost all price discovery takes place in the futures markets for heating oil and natural gas but in the case of crude oil, price discovery takes place in both markets. in the specific case of the electricity market, malo [ ] studied electricity spot and futures price dependence with a multifrequency approach for modeling spot and weekly futures price dynamics. garcia-martos et al. [ ] worked with unobserved components, proposing a differential model to extract seasonal common factors from the vector of general electricity prices. lisi and pelagati [ ] considered the market time series comparing deterministic and stochastic approaches, and concluding that both approaches may give good results. le et al. [ ] proposed an algorithm to simulate the clearing of the integrated european intra-day market coordinating the discrete auction with the continuous trading, helping to solve the different intra-day market situations. monteiro et al. [ ] presented a probabilistic price forecasting model for day-ahead hourly price forecasts in electricity markets, based on a gaussian density estimator function for each input variable, allowing the parameters of a beta distribution to be calculated for the hourly price variable. de marcos et al. [ ] proposed a short-term hybrid electricity price forecasting model combining a cost-production optimization model with an econometric neural network model. manner et al. [ ] proposed a dynamic multivariate binary choice model, following a vector autoregressive (var) process. finally, lago et al. [ ] used deep learning algorithms with neural networks, and in lago et al. [ ] they improved the model results associating this specific focus with market integration. finally, regarding the specific usage of fractional integration in the context of energy, there are some studies that have used this methodology, including the contributions of elder and serletis [ ] regarding energy future prices, barros et al. [ ] focusing on u.s. renewable energy consumption, weron [ , ] and gil-alana et al. [ ] in the field of electricity prices, and barros et al. [ ] on energy prices. this section focuses on the cases of spain and portugal. to understand the specific iberian business case, an interesting analysis of the spanish market can be found in duarte et al. [ ] focusing in the specific disaggregation of the electricity industry into the generating, transmission, distribution and marketing businesses, which were decoupled in under legislation prohibiting any single company from conducting more than one of these businesses. conventional thermal and hydropower generating together make up more than % of total output, wind power produces % and nuclear power accounts for only % where almost all demand is covered by domestic production. the main issues to be resolved in the spanish market concern the scant competition, the tariff deficit, faulty tariff design, a raft of uncertainties, potential market integration and the introduction of new technologies. in the portuguese market, amorim et al. [ ] indicate that the two main issues to address are that of fulfilling balancing mechanisms to be able to manage more than % of renewable energy sources and the capacity incentives to allow new investments. in this line, as in portugal there is a commitment for the renewable electricity share to reach % by . several authors have worked in this industry green-renewal process. figueiredo et al. [ ] explain the issues around replacing traditional coal-based power plants with photovoltaics, while pereira and saraiva [ ] explain the implications of the penetration of wind power, since this process is putting the profitability of traditional stations under pressure. distributional costs of wind energy production in portugal under the liberalized iberian market regime can be found in prata et al. [ ] . another issue in the iberian market is the interconnection needs between different countries. as explained by rubino and como [ ] ; current eu energy policy calls for a well-integrated internal energy market by achieving interconnection of at least % of the installed electricity production capacity for all eu member states, with a % target in . figueiredo et al. [ ] track the iberian case, showing that iberia has already surpassed this value reaching . % and is aiming to achieve mw in the near future, which will represent % of the maximum demand considered in this study. an adequate cross-border interconnection capacity should avoid the internal development of dispatchable reserve capacity, helping balancing and grid security purposes. several studies have tried to explain the electric consumption and price evolution in the iberian market. ciarreta and zarraga [ ] studied the dynamic relationship between electric consumption and gdp in spain for the period to using a var model with differenced series in a unidirectional causality relationship. their results show a linear relationship running from gdp to electric consumption with no evidence of a non-linear relationship. in ciarreta and zarraga [ ] ; the same authors studied the volatility of hourly pricing from the iberian intra-day electricity market for the period - , concluding that the results show significant volatility transmissions between the sessions, arguing how results are driven by the market structure, the market design and the regulation of renewable generation. regarding the futures market, capit� an-herraiz and rodriguez-monroy [ ] documents its lack of liquidity compared with other north european markets, mentioning that the main significant drivers are the traded volumes in the otc trading and auctions. thus, it would be advisable to attract new players in order to increase liquidity and price efficiency. regarding pricing models, lagarto et al. [ ] studied the market power of generating firms in the day-ahead iberian electricity market (mibel) using a model where data on power plants, fuels, co and the day-ahead electricity market are provided as input data, and measuring the direct influence of the external market price drivers, such as fuel and co prices, renewable generation, or power plants availability. they conclude that major firms behaved much more competitively in off-peak than in peak periods, in some cases generating at market prices below marginal costs. monteiro et al. [ ] recently proposed another specific pricing model for the day-ahead price forecasting in the mibel market. input variables include hourly time series records of weather forecasts, previous prices, and regional aggregation of power generations and power demands. fractional integration is a time series technique that allows investigators to determine the dynamic specification of the data in a more flexible way than other approaches based on integer degrees of differentiation. it belongs to a broader category named long memory, characterized because the spectral density function is unbounded in at least one frequency on its spectrum. within this group of processes, a very popular analysis model within the time series studies is the fractional integration that is described in the following paragraph and that is characterized because its spectral density function tends to infinity as the frequency approaches . we say that a given process {x t , t ¼ , � , …} is integrated of order d, and denoted as i(d) (where d can be any real value) if it can be represented as: where l is the lag operator (lx t ¼ x t- ) and u t is integrated of order , i.e., i( ), defined as a covariance stationary process with a positive and bounded spectrum. thus, u t can be a white noise but also a weakly autocorrelated process, for example, of the autoregressive moving average (arma) form. the estimation of the differencing parameter d is crucial. ( ), and x t is said to be short memory as opposed to the case of long memory that takes place when d > . from a statistical viewpoint, the borderline point is . . thus, if d < . , x t is covariance stationary; however, if becomes nonstationary for d � . , and it is more nonstationary as we increase the value of d, noting that the variance of the partial sum increases in magnitude with d; finally, from a policy perspective, mean reversion occurs if d < and shocks will have permanent effects if d � . we estimate the value of d using the whittle function based on the frequency domain [ ] , and, for this purpose, we use a version of a testing procedure developed in robinson [ ] that is very convenient in the context of the series examined here, noting that it permits us to test any real value of d, including thus values in the nonstationary range (d � . ). using this method, we test the null hypothesis: in ( ), where x t can be the errors in a regression model of form: where z t can be either exogenous regressors or deterministic terms such as an intercept and/or a linear time trend. the test statistic proposed in robinson [ ] contains several important features. thus, its limiting distribution is standard normal (n( , ) ), so that we do not need to rely on critical values based on monte carlo simulation studies. moreover, the test statistic and its asymptotic behaviour remain valid for any real value d in ( ), including nonstationary cases, and thus, it does not require preliminary differencing to render the series stationary prior to the performance of the test; finally, it is the most efficient method in the pitman sense against local departures from the null. using alternative methods (also based on fractional integration) produced essentially the same results as those reported in this work. the dataset encompassing spot and futures daily prices and energy consumption was obtained from the omip website (http://www.omip. pt/downloads/tabid/ /language/pt-pt/default.aspx) for portugal and spain, during the period encompassed from to . table presents the descriptive statistics for these time series, while table presents the kendall's tau correlation coefficient. while table suggests that price and demand time series are, somehow, asymmetrically distributed, although dispersion maybe considered lowwith the exception of future energy demand -, table reveals a moderately strong correlation between future and spot prices and a very weak correlation between spot energy and spot prices. time series are depicted in figs. and for both energy and prices. this section starts with the analysis of the individual series. the initial point is to estimate the value of d in the model given by ( ) and ( ) with z t ¼ ( ,t) t , i.e., where y t refers to each of the observed time series (energy consumption and prices in the spot and future markets); β and β are unknown coefficients referring, respectively, to an intercept and a linear time trend, while x t is supposed to be i(d), where d can be any real value; finally, u t is i( ), expressed in terms of both uncorrelated and autocorrelated (bloomfield) errors. bloomfield [ ] proposed an alternative to the arma modelling in a non-parametric way. it is non-parametric because there is no explicit form for the model since it is exclusively presented in terms of its spectral density function. he showed that the log of that function approximates very well the log spectrum of ar processes, producing also autocorrelations that decay exponentially fast as in the ar model. in all cases, we present the results for the original data as well as for the log-transformed values. table displays the estimates of d (and their associated % confidence intervals) under the assumption of white noise errors. the results for the three standard cases of: i) no deterministic terms (i.e., β ¼ β ¼ in ( )), ii) an intercept (β ¼ in ( )), and iii) an intercept with a linear time trend (β and β unknown) have been displayed, marking in bold in the table the selected model for each series, based on the t-values of the estimated coefficients on the d-differenced series. the first thing that can be observed in table is that the time trend is not required in any single case, and the intercept is sufficient to describe the deterministic terms. while focusing on the estimated values of d, it can be seen that in all cases the values are constrained between and and both hypotheses (i( ) and i( )) are decisively rejected in favour of fractional integration. starting with the spot market, it is observed that the estimated value of d is . for consumption and . for the energy prices, and the values are slightly smaller ( . and . ) in the case of the log transformed data. for the futures market, the values are much smaller, being . (and . for the logged values) in the case of the energy consumption and . ( . ) for prices. thus, evidence of long memory (d > ) and mean reversion (d < ) is obtained in all cases, and thought consumption seems to be nonstatonary (d � . ), prices follow a stationary path (d < . ) in table we allow the error term to be autocorrelated. however, instead of imposing a specific modelling assumption for u t in ( ), we use here a non-parametric method due to bloomfield [ ] . it is called non-parametric in the sense that no functional form is explicitly presented for u t in ( ). the model is exclusively defined in terms of its spectral density function throughout an expression that approximates fairly well highly parameterized arma process. moreover, this approach accommodates extremely well in i(d) models (see ref. [ ] . the results using this approach are very similar to those given in table in the sense that all values are constrained between and implying fractional integration and mean reverting behaviour. thus, shocks affecting these series will have transitory though persistent effects. thereafter, the relationships between the two variables (in logs) were analyzed by taking a regression of one of the variables against the other. based on the fractional nature of the two series, one possibility here is to conduct a regression model under the assumption that the independent variables are exogenous to the system, allowing the errors to be potentially fractional. thus, the following regression model was considered first, where c refers to energy consumption and p to energy prices, and with k ¼ , , , , and . once more, we present the results for the two cases of uncorrelated (white noise) and autocorrelated (bloomfield) errors, in tables and respectively. the most noticeable feature observed in these two tables is that contemporaneously the slope is statistical significant in the two (spot and futures) markets, however, allowing for lags (k > ) the coefficient only remains significant in the case of the spot market, implying that prices affect the behaviour of energy consumption in this market. finally, the same experiment was carried out but in the opposite way, by testing energy prices against energy consumption, while still maintaining the possibility of long memory errors, i.e, the results for the two cases of uncorrelated and autocorrelated errors are respectively reported in tables and . it can be seen that similar to the previous tables, only lag effects are statistically significant in the case of the spot market. thus, energy prices and energy consumption are both related in a bi-directional way in the case of the spot market. however, this relationship does not hold in the futures market. these results suggest that the energy spot market in portugal and spain presents the price-elasticity of demand expected behaviour of micro-economics, where higher prices induces lower consumption and vice-versa, in a feedback process that is temporally persistent. this temporal persistence within the ambit of a feedback process of prices and consumption in the spot markets is consistent with results presented in table , where readers can easily note that variable dispersion is lower in spot markets, possibly as a consequence of a tied joint see ref. [ ] for an application using the same version of the tests of [ ] as the one used in this work. the same version of the tests has been used in refs. [ , ] ; etc. on the other hand, results for the future energy markets are counterintuitive. not only is temporal persistence not significant, but higher (lower) levels of energy prices tend to stimulate higher (lower) energy consumption levels and vice-versa. this behaviour is typical of speculative movements, where economic agents anticipate their purchases due to fear of future supply shortages. as long as energy supply in portugal and spain is controlled by a few companies with insufficient funding for generation and distribution capacity expansion, and which are scarcely integrated with other eu countries, this speculative behaviour in futures markets is quite justifiable. finally, it can be said that the main challenge of governments and regulators should be to use this anticipatory consumption that triggers price increases to stimulate new energy projects related to capacity expansion, especially with green energies. recent events such as the announcement of iberdrola to build a new "mega" photovoltaics plant in usagre -extremadura (an investment of € million, to be in service in september ), which will be the largest plant in europe, is a clear example. reductions in production costs and increases in the efficiency of solar panel plants are accelerating this process of green energy expansion. the values in parenthesis report the % confidence bands for the values of d, i. e., the values of d where the null hypothesis cannot be rejected at the % level. in both, the selected model in relation with the deterministic terms. the values in parenthesis report the % confidence bands for the values of d, i. e., the values of d where the null hypothesis cannot be rejected at the % level. in both, the selected model in relation with the deterministic terms. throughout this paper the stochastic properties of energy consumption and energy prices in spain and portugal have been examined by using fractional integration or i(d) techniques in the spot and futures markets. the following points can be concluded according to this study: . the univariate results clearly indicate that all the examined series display long memory patterns with mean reverting behaviour and thus the effects of the shocks disappear in the long run. in the multivariate setting we show that both variables are linked together in a bi-directional way in the case of the spot market, but this pattern does not hold in the futures market. . there is a weak relationship between the futures market and energy consumption, however regarding the energy pricing, there is a stronger relationship with the spot market itself. . in the case of energy consumption, our study is in line with other energy consumption studies, such as wong et al. [ ] for oil pricing that concluded higher oil prices lead to lower oil consumption. our results have shown that energy consumption behavior could be similar in the spot pricing, with no strong relationship in terms of future pricing, as final consumers are not directly affected by future energy price changes. . regarding energy pricing, our study seems to be in line with that of narayan and sharma [ ] completed for general commodities, which concluded that in % of these commodities the stock market was dominant while in the other % it is the futures market which is dominant. . finally, according to our study, it can be said that in the iberian energy market, spot dominates the futures market but both markets have a certain relationship in terms of electricity pricing. furthermore, correlation shows a direct relationship between both markets. this result might make sense, as the futures market is used to hedge peaks of the spot market production pull, while these peaks usually happen only at certain specific demand events (for instance, cool spells or heat waves), where fewer energy sources are entering in the energy pull increasing the spot price. . our results could be used by policy-makers to draw some regulatory changes, since the energy supply in portugal and spain is controlled by only a few suppliers. therefore, investment marks should be created so that speculative behaviour in futures markets could be avoided due to capacity expansion and better integration with eu energy lines. this being the case, the main challenge of a novel regulatory mark is to capture energy consumption in anticipationand the consequent price increase -to trigger new energy projects related to capacity expansion, especially with green energies, with other eu players. prof. luis alberiko gil-alana is the primary researcher in this work. he has contributed in all sections in this work, making special attention to the methodological part and the implications of the series. prof. peter wanke proposed the idea of this work. he obtained the data and contributed on the introduction, literature review and the implications of the results. prof. miguel martin-valmayor contributed with the introduction, literature review and the geographical context on section (the iberian case). also, with the implications of the results. for the revision, the three authors have jointly worked on it. estimated coefficients in the model in ( ) in bold, significant coefficients at the % level. estimated coefficients in the model in ( ) in bold, significant coefficients at the % level. estimated coefficients in the model in ( ) in bold, significant coefficients at the % level. in bold, significant coefficients at the % level. the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. energy models for demand forecasting-a review electricity tariffs in theory and practice some calculations of electricity consumption in great britain s� anchez-ch� oliz, the electricity industry in spain: a structural analysis using a disaggregated input-output model how much room for a competitive electricity generation market in portugal? modeling realized volatility on the spanish intra-day electricity market analysis of the traded volume drivers of the iberian power futures market a review of energy models demographic trends and energy consumption in european union nations dynamic multilevel modelling of industrial energy demand in europe asymmetric price responses and the underlying energy demand trend: are they substitutes or complements? evidence from modelling oecd aggregate energy demand energy consumption and energy r&d in oecd: perspectives from oil prices and economic growth modelling energy demand of developing countries: are the specific features adequately captured? energy consumption, cultural background and payment structure modeling energy demand: some emerging issues weather and market specificities in the regional transmission of renewable energy price effects a review of current challenges and trends in energy systems modeling modelling and measuring price discovery in commodity markets an analysis of time-varying commodity market price discovery electricity price forecasting: a review of the state-of-the-art with a look into the future recent advances in electricity price forecasting: a review of probabilistic forecasting price discovery in energy markets modeling electricity spot and futures price dependence: a multifrequency approach forecasting electricity prices and their volatilities using unobserved components component estimation for electricity market data: deterministic or stochastic? integrated european intra-day electricity market: rules, modeling and analysis new probabilistic price forecasting models: application to the iberian electricity market electricity price forecasting in the short term hybridising fundamental and econometric modelling modeling and forecasting multivariate electricity price spikes forecasting spot electricity prices: deep learning approaches and empirical comparison of traditional algorithms forecasting day-ahead electricity prices in europe: the importance of considering market integration long memory in energy futures prices evidence of long memory behavior in u.s. renewable energy consumption measuring long-range dependence in electricity prices shocks affecting electricity prices in kenya, a fractional integration study long range dependence and breaks in energy prices replacing coal-fired power plants by photovoltaics in the portuguese electricity system long term impact of wind power generation in the iberian day-ahead electricity market price distributional costs of wind energy production in portugal under the liberalized iberian market regime a regulatory assessment of the electricity merchant transmission investment in eu evaluating the market splitting determinants: evidence from the iberian spot electricity prices electricity consumption and economic growth in spain market power analysis in the iberian electricity market using a conjectural variations model maximum likelihood estimation of fractionally integrated time series models efficient parameter estimation for self-similar process efficient tests of nonstationary hypotheses testing of unit roots and other nonstationary hypotheses in macroeconomic time series uncovering the u.s. term premium.an alternative route term structure persistence an exponential model in the spectrum of a scalar time series the use of the bloomfield ( ) model as an approximation to arma processes in the context of fractional integration prof. luis a. gil-alana gratefully acknowledges financial support from the mineic-aei-feder eco - -r project from 'ministerio de economía, industria y competitividad' (mineic), 'agencia estatal de investigaci� on' (aei) spain and 'fondo europeo de desarrollo regional' (feder). he and dr. miguel martín-valmayor also acknowledges support from an internal project of the universidad francisco de vitoria entitled "sostenibilidad energ � etica y adaptaci � on al cambio clim � atico" (ufv - ). comments from the editor and three anonymous reviewers are also gratefully acknowledged.comments from the editor and three anonymous reviewers are gratefully acknowledged. supplementary data to this article can be found online at https://doi. org/ . /j.esr. . . key: cord- - hrs w r authors: bangotra, deep kumar; singh, yashwant; selwal, arvind; kumar, nagesh; singh, pradeep kumar; hong, wei-chiang title: an intelligent opportunistic routing algorithm for wireless sensor networks and its application towards e-healthcare date: - - journal: sensors (basel) doi: . /s sha: doc_id: cord_uid: hrs w r the lifetime of a node in wireless sensor networks (wsn) is directly responsible for the longevity of the wireless network. the routing of packets is the most energy-consuming activity for a sensor node. thus, finding an energy-efficient routing strategy for transmission of packets becomes of utmost importance. the opportunistic routing (or) protocol is one of the new routing protocol that promises reliability and energy efficiency during transmission of packets in wireless sensor networks (wsn). in this paper, we propose an intelligent opportunistic routing protocol (iop) using a machine learning technique, to select a relay node from the list of potential forwarder nodes to achieve energy efficiency and reliability in the network. the proposed approach might have applications including e-healthcare services. as the proposed method might achieve reliability in the network because it can connect several healthcare network devices in a better way and good healthcare services might be offered. in addition to this, the proposed method saves energy, therefore, it helps the remote patient to connect with healthcare services for a longer duration with the integration of iot services. . sensor node architecture with application in e-healthcare. with the ever-increasing use of term green computing, the energy efficiency of wsn has seen a considerable rise. recently, an approach for green computing towards iot for energy efficiency has been proposed, which enhances the energy efficiency of wsn [ ] . different types of methods and techniques were proposed and developed in the past to address the issue of energy optimization in wsn. another approach that regulates the challenge of energy optimization in sensor-enabled iot with the use of quantum-based green computing, makes routing efficient and reliable [ ] . the problem of energy efficiency during the routing of data packets from source to target in case of iotoriented wsn is significantly addressed by another network-based routing protocol known as greedi [ ] . it is imperative to mention here that iot is composed of energy-hungry sensor devices. the constraint of energy in sensor nodes has affected the transmission of data from one node to another and therefore, requires boundless methods, policies, and strategies to overcome this challenge [ ] . with the ever-increasing use of term green computing, the energy efficiency of wsn has seen a considerable rise. recently, an approach for green computing towards iot for energy efficiency has been proposed, which enhances the energy efficiency of wsn [ ] . different types of methods and techniques were proposed and developed in the past to address the issue of energy optimization in wsn. another approach that regulates the challenge of energy optimization in sensor-enabled iot with the use of quantum-based green computing, makes routing efficient and reliable [ ] . the problem of energy efficiency during the routing of data packets from source to target in case of iot-oriented wsn is significantly addressed by another network-based routing protocol known as greedi [ ] . it is imperative to mention here that iot is composed of energy-hungry sensor devices. the constraint of energy in sensor nodes has affected the transmission of data from one node to another and therefore, requires boundless methods, policies, and strategies to overcome this challenge [ ] . the focus of this paper was to put forward an intelligent opportunistic routing protocol so that the consumption of resources particularly during communication could be optimized, because the sensors , , of alleyway taken to transmit a data packet from a source node to the target node is determined by the routing protocol. routing is a complex task in wsn because it is different from designing a routing protocol in traditional networks. in wsn, the important concern is to create an energy-efficient routing strategy to route packet from source to destination, because the nodes in the wsn are always energy-constrained. the problem of energy consumption while routing is managed with the use of a special type of routing protocol known as the opportunistic routing protocol. the opportunistic routing (or) is also known as any path routing that has gained huge importance in the recent years of research in wsn [ ] . this protocol exploits the basic feature of wireless networks, i.e., broadcast transmission of data. the earlier routing strategies consider this property of broadcasting as a disadvantage, as it induces interference. the focal notion behind or is to take the benefit of spreading the behavior of the wireless networks such that broadcast from one node can be listened by numerous nodes. rather than selecting the next forwarder node in advance, the or chooses the next forwarder node robustly at the time of data transmission. it was shown that or gives better performance results than traditional routing. in or, the best opportunities are searched to transmit the data packets from source to destination [ ] . the hop-by-hop communication pattern is used in the or even when there is no source-to-destination linked route. the or protocols proposed in recent times by different researchers are still belligerent with concerns pertaining to energy efficiency and the reliable delivery of data packets. the proposed or routing protocol given in this paper was specifically meant for wsn, by taking into account the problems that surface during the selection of relay candidates and execution of coordination protocol. the proposed protocol intelligently selects the relay candidates from the forwarder list by using a machine learning technique to achieve energy efficiency. the potential relay node selection is a multi-class with multiple feature-based probabilistic problems, where the inherent selection of relay node is dependent upon each node's characteristics. the selection of a node with various characteristics for a node is a supervised multiclass non-linearly separable problem. in this paper, the relay node selection algorithm is given using naïve baye's machine learning model. the organization of this paper is as follows. section presents the related work in the literature regarding or and protocols. the various types of routing protocols are given in section . section describes or with examples, followed by the proposed intelligent or algorithm for forwarder node selection in section . section depicts the simulation results of the proposed protocol by showing latency, network lifetime, throughput, and energy efficiency. section presents a proposed framework for integration iot with wsn for e-healthcare. this architecture can be useful in many e-healthcare applications. section presents the conclusion and future. achieving reliable delivery of data and energy efficiency are two crucial tasks in wsns. as the sensor nodes are mostly deployed in an unattended environment and the likelihood of any node going out of order is high, the maintenance and management of topology is a rigorous task. therefore, the routing protocol should accommodate the dynamic nature of the wsns. opportunistic routing protocols developed in the recent past years provided trustworthy data delivery but they are still deficient in providing energy-efficient data transmission between the sensor nodes. some latest research on or, experimented by using the formerly suggested routing metrics and they concentrated on mutual cooperation among nodes. geraf [ ] (geographic random forwarding) described a novel forwarding technique based on the geographical location of the nodes involved and random selection of the relaying node via contention among receivers. exclusive opportunistic multi-hop routing for wireless networks [ ] (exor) is an integrated routing and mac protocol for multi-hop wireless networks, in which the best of multiple receivers forwards each packet. this protocol is based on the expected transmission count (etx) metric. the etx was measured by hop count from the source to the destination and the data packet traveled through the minimum number of hops. exor achieves higher throughput than traditional sensors , , of routing algorithms but it still has few limitations. exor contemplates the information accessible at the period of transmission only, and any unfitting information because of recent updates could worsen its performance and could lead to packet duplication. other than this, there is another limitation with exor, as it always seeks coordination among nodes that causes overhead, in case of large networks. minimum transmission scheme-optimal forwarder list selection in opportunistic routing [ ] (mts) is another routing protocol that uses mts instead of etx as in exor. the mts-based algorithm gives fewer transmissions as compared to etx-based exor. simple, practical, and effective opportunistic routing for short-haul multi-hop wireless networks [ ] . in this protocol, the packet duplication rate was decreased. this is a simple algorithm and can be combined with other opportunistic routing algorithms. spectrum aware opportunistic routing [ ] (saor) is another routing protocol for the cognitive radio network. it uses optimal link transmission (olt) as a cost metric for positioning the nodes in the forwarder list. saor gives better qos, reduced end-to-end delay, and improved throughput. energy-efficient opportunistic routing [ ] (eeor) calculates the cost for each node to transfer the data packets. the eeor takes less time than exor for sending and receiving the data packets. trusted opportunistic routing algorithm for vanet [ ] (tmcor) gives a trust mechanism for opportunistic routing algorithm. it also defines the trade-off between the cost metric and the safety factor. a novel socially aware opportunistic routing algorithm in mobile social networks [ ] considered three parameters, namely social profile matching, social connectivity matching, and social interaction. this gives a high probability of packet delivery and routing efficiency. ensor-opportunistic routing algorithm for relay node selection in wsns is another algorithm where the concept of an energy-efficient node is implemented [ ] . the packet delivery rate of ensor is better than geraf. economy-a duplicate free [ ] is the only or protocol that uses token-based coordination. this algorithm ensures the absence of duplicate packet transmissions. with the advent of the latest network technologies, the virtualization of networks along with its related resources has made networks more reliable and efficient. the virtual network functions are used to solve the problems related to service function chains in cloud-fog computing [ ] . further, iot works with multiple network domains, and the possibility of compromising the security and confidentiality of data is always inevitable. therefore, the use of virtual networks for service function chains in cloud-fog computing under multiple network domains, leads to saving network resources [ ] . in recent times, the cloud of things (cot) has gained immense popularity, due to its ability to offer an enormous amount of resources to wireless networks and heterogeneous mobile edge computing systems. the cot makes the opportunistic decision-making during the online processing of tasks for load sharing, and makes the overall network reliable and efficient [ ] . the cloud of things framework can significantly improve communication gaps between cloud resources and other mobile devices. in this paper, the author(s) proposed a methodology for offloading computation in mobile devices, which might reduce failure rates. this algorithm reduces failure rates by improving the control policy. in recent times, wsn used virtualization techniques to offer energy-efficient and fault-tolerant data communication to the immensely growing service domain for iot [ ] . with the application of wsn in e-healthcare, the wireless body area network (wban) gained a huge response in the healthcare domain. the wban is used to monitor patient data by using body sensors, and transmits the acquired data, based on the severity of the patients' symptoms, by allocating a channel without contention or with contention [ ] . eeor [ ] is an energy-efficient protocol that works on transmission power as a major parameter. this protocol discussed two cases that involved constant and dynamic power consumption models. these models are known as non-adjustable and adjustable power models. in the first model, the algorithm calculated the expected cost at each node and made a forwarder list on the source node based on this cost. the forwarder list was sorted in increasing order of expected cost and the first node on the list became the next-hop forwarder. as eeor is an opportunistic routing protocol, broadcasting is utilized and the packets transmitted might be received by each node on the forwarder list. in this, the authors propose algorithms for fixed-power calculation, adjustable power calculation, sensors , , of and opportunistic power calculation. this algorithm was compared with exor [ ] by simulation in the tossim simulator. the results showed that eeor always calculated the end-to-end cost based on links from the source to destination. eeor followed distance vector routing for storing the routing information inside each sensor node. the expected energy consumption cost was updated inside each node, after each round of packet transmission. data delivery was guaranteed in this protocol. additionally, according to the simulation results, packet duplication was significantly decreased. the mdor [ , ] protocol worked on the distance between the source to relay nodes. in this, the authors proposed an algorithm that calculated the distance to each neighbor from the source node and found out the average distance node. the average distance node was used by the source as a next-hop forwarder. the authors also stated that, to increase the speed and reliability of transmission, the strength of the signal was very important. the signal power depended on the distance between the sender and receiver. if a node sent a packet to the nearest node, then it might take more hops and this would decrease the lifetime of the network. another problem addressed in this protocol was to reduce energy consumption at each node through the dynamic energy consumption model. this model consumed energy according to the packet size and transmitted the packet by amplifying it according to the distance between the source and the relay nodes. mdor always chose the middle position node to optimize energy consumption in amplifying the packets. the mdor simulation results showed that the energy consumption was optimized and it was suitable for certain applications of wsn like environment monitoring, forest fire detection, etc. opportunistic routing introduced the concept of reducing the number of retransmissions to save energy and taking advantage of the broadcasting nature of the wireless networks. with broadcasting, the routing protocol could discover as many paths in the network as possible. the data transmission would take place on any of these paths. if a particular path failed, the transmission could be completed by using some other path, using the forwarder list that had the nodes with the same data packet. the protocols that were responsible for data transmission in wsn were broadly ordered into two sets [ ] , namely, (i) old-fashioned routing, and (ii) opportunistic routing. in the traditional routing, also known as old-fashioned routing techniques, the focus was on finding the route with a minimum number of intermediate nodes from the source to the destination, without taking into consideration some of the important factors like throughput, quality of links, reliability, etc. a small comparison [ ] of the routing categories is shown in table . as it is clear from the literature that energy consumption of a sensor node had a considerable impact on the lifetime and quality of the wireless sensor network, therefore, it becomes vital to design energy-efficient opportunistic routing protocols to maximize the overall lifetime of the network and also to enhance the quality of the sensor network. there are few methods in the literature listed below that might be useful to save the life of the sensor network. scheduling of duty cycle • energy-efficient medium access control (ee-mac) • energy-efficient routing • node replacements (not possible in unattended environments) of the above-mentioned methods for energy saving, energy-efficient routing is the most central method for the vitality of the wsn. as this method involved the transmission of signals, i.e., receiving and sending, it took about . percent of the total energy of the network [ ] . therefore, it became relevant that an opportunistic routing protocol that enhanced the vitality of the sensor network might be designed for enhancing the overall life span of the sensor network. or broadcasts a data packet to a set of relay candidates that is overheard by the neighboring nodes, whereas in traditional routing a node is (pre)-selected for each transmission. then, relay candidates that are part of the forwarders list and who have successfully acknowledged the data packet, run a protocol called coordination protocol between themselves, to choose the best relay candidate to onward the data packet. in other words, or is abstractly comprised of these three steps: step : broadcast a data packet to the relay candidates (this will prepare the forwarder list). step : select the best relay by using a coordination protocol among the nodes in the forwarder list. step : forward the data packet to the selected relay node. considering an example shown in figure , where the source node s sends a packet to the destination node d, through nodes r , r , r , r , and r . first, s broadcasts a packet. the relay nodes r , r , and r might become the forwarder nodes. further, if r is chosen as a potential forwarder, then r and r might become relay nodes. similarly, if r is the forwarder node, then it forwards the data packets to the destination node d. energy balance of the above-mentioned methods for energy saving, energy-efficient routing is the most central method for the vitality of the wsn. as this method involved the transmission of signals, i.e., receiving and sending, it took about . percent of the total energy of the network [ ] . therefore, it became relevant that an opportunistic routing protocol that enhanced the vitality of the sensor network might be designed for enhancing the overall life span of the sensor network. or broadcasts a data packet to a set of relay candidates that is overheard by the neighboring nodes, whereas in traditional routing a node is (pre)-selected for each transmission. then, relay candidates that are part of the forwarders list and who have successfully acknowledged the data packet, run a protocol called coordination protocol between themselves, to choose the best relay candidate to onward the data packet. in other words, or is abstractly comprised of these three steps: step : broadcast a data packet to the relay candidates (this will prepare the forwarder list). step : select the best relay by using a coordination protocol among the nodes in the forwarder list. step : forward the data packet to the selected relay node. considering an example shown in figure , where the source node s sends a packet to the destination node d, through nodes r , r , r , r , and r . first, s broadcasts a packet. the relay nodes r , r , and r might become the forwarder nodes. further, if r is chosen as a potential forwarder, then r and r might become relay nodes. similarly, if r is the forwarder node, then it forwards the data packets to the destination node d. opportunistic routing derived the following rewards: • the escalation in reliability. by using this routing strategy, the reliability of wsn increased significantly, as this protocol transmitted the data packet through any possible link rather than any pre-decided link. therefore, this routing protocol provided additional links that could act as back up links and thus reduced the chances of transmission failure. the escalation in transmission range. with this routing protocol, the broadcast nature of the wireless medium provided an upsurge in the transmission range, as all links irrespective of their location and quality of data packets were received. hence, the data transmission could reach the farthest relay node successfully. opportunistic routing derived the following rewards: • the escalation in reliability. by using this routing strategy, the reliability of wsn increased significantly, as this protocol transmitted the data packet through any possible link rather than any pre-decided link. therefore, this routing protocol provided additional links that could act as back up links and thus reduced the chances of transmission failure. the escalation in transmission range. with this routing protocol, the broadcast nature of the wireless medium provided an upsurge in the transmission range, as all links irrespective of their location and quality of data packets were received. hence, the data transmission could reach the farthest relay node successfully. in wsn, the sensor nodes could be deployed in two ways, randomly or manually. most applications require the random deployment of nodes in the area under consideration. initially, each node is loaded with the same amount of battery power. as soon as the network starts functioning, the nodes start consuming energy. to make the network energy efficient, the protocol used for transmitting data packets must consume less battery power and the calculation of the energy consumption network model and energy model should be formulated. in the upcoming subsection, these two models are discussed and these are depicted as assumptions, to carry out smooth working of the protocol. the n sensors are distributed in a square area of size * square meters. this network formed a graph g = (n, m), with the following possessions: . . , n n } is the set of vertices representing sensor nodes. • m is considered to be a set of edges representing the node-to-node links. the neighboring list nbl(n i ) consists of nodes that are in the direct link to the n i . the data traffic is assumed to be traveling from the sensor nodes toward the base station. if a packet delivery is successful, then the acknowledgment (ack) for the same is considered to travel the same path back to the source. the lifespan of a wsn depends on the endurance of each node, while performing network operations. the sensor nodes rely on the battery life to perform network operations. the energy cost model considered here is the first-order energy model for wsn [ ] . various terms used in equations ( )-( ) are defined in table . combined vitality cost of radio board of a sensor for communication of a data packets energy consumed in the transmission of n-bit packet up to l distance: energy consumed in the transmission of n-bit packet: sensors , , of sensor board-full operation, radio board-full operation, cpu board-sleep, wakeup for creating messages only. the proposed protocol uses these assumptions as preliminaries. a new algorithm is proposed in the next section, for solving the issue of energy efficiency and the reliability of opportunistic routing in wsn. let there be n nodes in the wsn, where each node has k neighbors, i.e., n , n , . . . , n k and each neighbor nodes are represented by x , x , . . . , x n attributes. in this case, the number of neighbors (k) might vary for the different nodes at a particular instance. additionally, it was assumed that the wireless sensor network is spread over an area of × square meters. let us assume that a node a ∈ n and had neighbors as na , na , . . . , na k , with respective features like node id, location, prr (packet reception ratio), residual energy (re) of nodes, and distance (d), which are represented by x , x , . . . , x n , respectively. the goal was to intelligently find a potential relay node a, say ar, such that ar ∈ {na , na , . . . , na k }. in the proposed machine learning-based protocol for the selection of potential forwarder, the packet reception ratio, distance, and outstanding energy of node was taken into consideration. the packet reception ratio (prr) [ ] is also sometimes referred to as psr (packet success ratio). the psr was computed as the ratio of the successfully received packets to the sent packets. a similar metric to the prr was the per (packet error ratio), which could be computed as ( -prr). a node loses a particular amount of energy during transmission and reception of packets. accordingly, the residual energy in a node gets decreased [ ] . the distance (d) was the distance between the source node and the respective distance of each sensor node in the forwarder list. the potential relay node selection was multi-class, with multiple features-based probabilistic problems, where the inherent selection of the relay node was dependent upon each node feature. the underlying probabilistic-based relay node selection problem could be addressed intelligently by building a machine learning model. the selection of a node with 'n' characteristics for a given node 'a' could be considered a supervised multiclass non-linearly separable problem. in this algorithm, the naïve baye's classifier was used to find the probability of node a to reach one of its neighbors, i.e., {n , n , . . . , n k }. we computed the probability, p(n , n , . . . , n k |a). the node with maximum probability, i.e., p(n , n , . . . , n k |a) was selected. the probability p of selecting an individual relay node of the given node a could be computed individually for each node, as shown respectively for each node in equation ( ). where p(na k |a) denotes the probability of node a to node k. furthermore, the probability computation of node a to na is such that na is represented by the corresponding characteristics x , x , . . . , xn, which means to find the probability to select the relay node na , given that feature x , na given that feature x , na given that feature x , and so on. the individual probability of relay node selection, given that the node characteristics might be computed by using naïve bayes conditional probability, is shown in equation ( ). sensors , , of where i = , , , . . . , n and p(xi|a) is called likelihood, p(a) is called the prior probability of the event, and p(xi) is the prior probability of the consequence. the underlying problem is to find the relay node a that has the maximum probability, as shown in equation ( ). table a-x represent the neighbor sets {na , na , . . . , na k } along with their feature attributes as {x , x , x , . . . , x n } of node a. the working of iop is comprised of two phases, i.e., phase i (forwarder_set_selection) and phase ii (forwarder_node_selection). in phase i, the authors used algorithm for the forwarder set selection. in this step, the information collection task was initiated after the nodes were randomly deployed in the area of interest, with specific dimensions. the beginning of the phase started with a broadcast of "hello packet" which contained the address and the location of the sending node. if any node received this packet, it sent an acknowledgment to the source and was added to the neighbor list. this process was repeated again and again, but not more than the threshold, to calculate the prr of each node and the neighbor list was formed using this procedure repeatedly. from the neighbor list and the value of prr, the forwarder set was extracted. the pre-requisite for the working of the second phase was the output of the first phase. the forwarder set generated from algorithm was the set of all nodes that had the potential to forward the data packets. however, all nodes in the set could not be picked for transmission, as this would lead to duplication of packets in the network. to tackle this situation, only one node from the forwarder list should be selected to transmit the packet to the next-hop toward the destination. this was accomplished using algorithm , which took a forwarder node list as input and selected a single node as a forwarder. algorithm used a machine-learning technique called naïve baye's classifier, to select the forwarder node intelligently. the proposed method of relay node selection using iop could be understood by considering an example of wsn shown in figure and using the naïve baye's algorithm on the generic data available in table , to find the optimal path in terms of energy efficiency and reliability from source node s to destination node d. therefore, by using the proposed naïve baye's classifier method, the probability of selection of a relay node r , r , or r from source node s was denoted by p(r , r , r |s), which could be calculated using equation ( ). where, putting the values in the above equations from table again, inputting the values in the above equations ( ) declare three float variables x , x , and x to represent the properties of ri, i.e., prr (packet reception ratio), re (residual energy), and d (distance), respectively. for each node ri∈ fl(s) repeat compute p(ri|s)//probability of selection of ri given s, i.e., p k = p(r i |s) for i = , . . . , n and assign k←i . compute the probability of p(r i |s) by computing the probability of each parameter separately, given s. make an unsorted array of probability values of n nodes, i.e., r , r , . . . , rn from step . for i = to n and k = i, arrprob[ri]←p k //to find the node with maximum probability. . select the first node of the array arrprob[ ] as the node with maximum value pmax i.e., pmax←arrprob[ ] . go through the rest of the elements of the array, i.e., from the nd element to the last (n − ) element, for i = to n − . for when the end of the array is reached, then the current value of the pmax is the greatest value in the array, pmax←arrprob[i]. . the node ri with pmax value is selected as a relay node from the forwarder list, as the node with the highest probability. the node with the next highest probability acts as a relay node in case the first selected relay node fails to broadcast. . broadcast transmission of the data packet as {ri, coordinates, data} . destination node d is reached, if yes, go to step . else, apply algorithm on ri s←ri and go to step . . end output: a potential forwarder node is selected from the list of forwarder nodes. again, putting the values in the above equations finally using the proposed method of relay node selection using naïve baye's algorithm, we could compute probability p(r , r , r s) , using equation ( ) . p(r , r , r s) = max(p(r s), p(r s), p(r s) = max( . , . , . ) ( ) thus, node r would be selected as the relay node in the forwarder list of r , r , and r for source node s. similarly, the process was followed again for the neighbors of s, which consequently would check the neighbors of r , r , and r . the tables - describe the features of neighboring nodes of r , r , and r , respectively. after the execution of phase i and phase ii on the above said example, the final route was intelligently selected for the onward transmission of the data packet from source node s to destination node d, using the naïve baye's algorithm shown in figure . node_id location prr (j) (m) r r ( , ) . . d after the execution of phase i and phase ii on the above said example, the final route was intelligently selected for the onward transmission of the data packet from source node s to destination node d, using the naïve baye's algorithm shown in figure . figure gives the details about the route selected using the iop. the source node s broadcasts the data packet among its neighboring nodes, using algorithm to create a forwarders list. the node r , r , and r in the figure, were selected as the nodes in the forwarders list. these were the potential nodes that would be used for the selection of a potential forwarder node. here, r was selected as the potential node using algorithm . the same procedure was adopted again and until the data reached its final destination. the final route was selected intelligently using iop is s→r →r →d. with the end goal of examination and comparison of the proposed or protocol, the simulation was performed in matlab. the simulation used the environment provided by the matlab to simulate the computer networks and other networks. matlab provides a good scenario to design a network of sensor nodes and also to define a sensor node and its characteristics. the simulation results were compared with the results of the eeor [ ] and the mdor [ ] protocols. table below shows the parameter setting of the network. figure gives the details about the route selected using the iop. the source node s broadcasts the data packet among its neighboring nodes, using algorithm to create a forwarders list. the node r , r , and r in the figure, were selected as the nodes in the forwarders list. these were the potential nodes that would be used for the selection of a potential forwarder node. here, r was selected as the potential node using algorithm . the same procedure was adopted again and until the data reached its final destination. the final route was selected intelligently using iop is s→r →r →d. with the end goal of examination and comparison of the proposed or protocol, the simulation was performed in matlab. the simulation used the environment provided by the matlab to simulate the computer networks and other networks. matlab provides a good scenario to design a network of sensor nodes and also to define a sensor node and its characteristics. the simulation results were compared with the results of the eeor [ ] and the mdor [ ] protocols. table below shows the parameter setting of the network. the motes are haphazardly deployed in × m field. the nodes are deployed in such a way that these can approximately cover the whole application area. the base station position is × m in the field. the field area was considered a physical world environment. the proposed or protocol started working immediately after the deployment process was complete. figure below represents the unplanned deployment of the nodes in the area of consideration. the motes are haphazardly deployed in × m field. the nodes are deployed in such a way that these can approximately cover the whole application area. the base station position is × m in the field. the field area was considered a physical world environment. the proposed or protocol started working immediately after the deployment process was complete. figure below represents the unplanned deployment of the nodes in the area of consideration. energy efficiency was the main objective of the proposed algorithm. it could be calculated as the overall energy consumption in the network for the accomplishment of diverse network operations. in matlab, the simulation worked based on simulation rounds. the simulation round was termed as packets transmission from a single source to a single destination. in matlab, when the simulation starts, a random source is chosen to start transmission and this node makes a forwarder list and starts executing the proposed protocol. one round of simulation represents successful or unsuccessful transmissions of packets from one source in the network. for each round, different source and relay nodes are selected. this process continues until at least one node is out of its energy. the energy efficiency was calculated as the total energy consumption after each round in the network. after the operation of the network starts, the sensor's energy starts decaying. this energy reduction was due to network operations like setting up the network, transmission, reception, and acknowledging the data packets, processing of data, and sensing of data. as the nodes decayed, their energy consumption kept increasing per round, as can be seen in figure below. it can be seen in the figure that energy consumption for the proposed or protocol was less, as compared to the other two algorithms. this was because the proposed or protocol distributed energy consumption equally to energy efficiency was the main objective of the proposed algorithm. it could be calculated as the overall energy consumption in the network for the accomplishment of diverse network operations. in matlab, the simulation worked based on simulation rounds. the simulation round was termed as packets transmission from a single source to a single destination. in matlab, when the simulation starts, a random source is chosen to start transmission and this node makes a forwarder list and starts executing the proposed protocol. one round of simulation represents successful or unsuccessful transmissions of packets from one source in the network. for each round, different source and relay nodes are selected. this process continues until at least one node is out of its energy. the energy efficiency was calculated as the total energy consumption after each round in the network. after the operation of the network starts, the sensor's energy starts decaying. this energy reduction was due to network operations like setting up the network, transmission, reception, and acknowledging the data packets, processing of data, and sensing of data. as the nodes decayed, their energy consumption kept increasing per round, as can be seen in figure below. it can be seen in the figure that energy consumption for the proposed or protocol was less, as compared to the other two algorithms. this was because the proposed or protocol distributed energy consumption equally to all nodes, so that every node could survive up to their maximum lifetime. hence, the proposed or protocol was more energy-efficient than mdor and eeor. sensors , , x for peer review of all nodes, so that every node could survive up to their maximum lifetime. hence, the proposed or protocol was more energy-efficient than mdor and eeor. latency can be measured as the time elapsed between sending the packet and receiving the same at the base station. this is also called as end-to-end delay for the packets to be reached at the destination. the communication in wireless sensor networks is always from source nodes to the sink station. latency can be measured as the time elapsed between sending the packet and receiving the same at the base station. this is also called as end-to-end delay for the packets to be reached at the destination. the communication in wireless sensor networks is always from source nodes to the sink station. in the random deployment of nodes, some nodes are able to communicate directly with the base station. while some nodes follow multi-hop communication, i.e., source nodes have to go through relay nodes to forward the data packet toward the base station. hence, in some cases, the network delay can be very low and in some cases, it can be high. hence in figure , the values of end-to-end delay after each communication in each round are plotted. it can be seen that the proposed or protocol has a good latency, as compared to the other two protocols. latency can be measured as the time elapsed between sending the packet and receiving the same at the base station. this is also called as end-to-end delay for the packets to be reached at the destination. the communication in wireless sensor networks is always from source nodes to the sink station. in the random deployment of nodes, some nodes are able to communicate directly with the base station. while some nodes follow multi-hop communication, i.e., source nodes have to go through relay nodes to forward the data packet toward the base station. hence, in some cases, the network delay can be very low and in some cases, it can be high. hence in figure , the values of end-to-end delay after each communication in each round are plotted. it can be seen that the proposed or protocol has a good latency, as compared to the other two protocols. the throughput of a network can be measured in different ways. throughput is calculated as the average number of packets received successfully at the base station per second in each round. figure represents the throughput for each round. the proposed or protocol has good throughput, as compared to the other two. as the proposed or protocol is efficient in energy consumption, the sensor nodes are able to survive and communicate for a long time in the network. as long as the communication goes on, the base station would continue to receive the packets. sensors , , x for peer review of the throughput of a network can be measured in different ways. throughput is calculated as the average number of packets received successfully at the base station per second in each round. figure represents the throughput for each round. the proposed or protocol has good throughput, as compared to the other two. as the proposed or protocol is efficient in energy consumption, the sensor nodes are able to survive and communicate for a long time in the network. as long as the communication goes on, the base station would continue to receive the packets. network lifetime for wireless sensor networks is dependent upon the energy consumption in the network. when the energy of the network is percent, the network lifetime would also be percent. however, as the nodes start operating in the network, the network lifespan would start to reduce. figure represents the percentage of lifetime remaining after each round of simulation. proposed or protocol has a good network lifetime due to the lower energy consumption in the network. network lifetime for wireless sensor networks is dependent upon the energy consumption in the network. when the energy of the network is percent, the network lifetime would also be percent. however, as the nodes start operating in the network, the network lifespan would start to reduce. network lifetime for wireless sensor networks is dependent upon the energy consumption in the network. when the energy of the network is percent, the network lifetime would also be percent. however, as the nodes start operating in the network, the network lifespan would start to reduce. figure represents the percentage of lifetime remaining after each round of simulation. proposed or protocol has a good network lifetime due to the lower energy consumption in the network. the packet loss is referred to as the number of packets that are not received at the destination. to calculate the number of packets lost during each round of the simulation, packet sequence numbers are used. whenever a source tries to send packets to a destination, it inserts a sequence number. later, on packet reception, these packet sequence numbers are checked for continuity. if a certain sequence number is missing then it is referred to as packet loss. packet loss recorded per round of simulation and presented in figure . it can be depicted from the figure that packet loss for the proposed protocol is less, as compared to eeor and mdor. this is because the forwarder node selection algorithm runs on each relay and source node. this algorithm calculates the probability of successful transmission through a neighbor node. this also increases the reliability of the protocol and provides accurate transmissions. sensors , , x for peer review of the packet loss is referred to as the number of packets that are not received at the destination. to calculate the number of packets lost during each round of the simulation, packet sequence numbers are used. whenever a source tries to send packets to a destination, it inserts a sequence number. later, on packet reception, these packet sequence numbers are checked for continuity. if a certain sequence number is missing then it is referred to as packet loss. packet loss recorded per round of simulation and presented in figure . it can be depicted from the figure that packet loss for the proposed protocol is less, as compared to eeor and mdor. this is because the forwarder node selection algorithm runs on each relay and source node. this algorithm calculates the probability of successful transmission through a neighbor node. this also increases the reliability of the protocol and provides accurate transmissions. a significant improvement could be seen in the graphs after the simulation is complete. figure shows the total energy consumption after each round of packet transmission is complete. here, the round was termed as packet transmissions in between single source and destination. mdor showed the highest energy consumption, followed by eeor and the proposed protocol. this was because mdor wasted more energy in the initial setup. however, the dynamic energy consumption considerations led the network to survive for a long time, as shown in figure . in the case of eeor in figure , it consumed lesser energy in transmission and the initial setup for opportunistic selection of relay nodes was based on the power level. however, when it comes to lifetime, eeor failed to perform better, as it considered the network to be dead when any one of the nodes ran out of its energy. eeor chose one node as a source and continued transmissions opportunistically, which resulted in a significant reduction in the power level of a single node. the proposed protocol gave the best results, as in each round, the source node was based on the intelligent model to change the next-hop relay node. figure presents the average end-to-end delay per round, generated by the simulation, and the proposed protocol worked significantly better as the next-hop selection was based on an intelligent algorithm. the proposed algorithm helped to significantly reduce average a significant improvement could be seen in the graphs after the simulation is complete. figure shows the total energy consumption after each round of packet transmission is complete. here, the round was termed as packet transmissions in between single source and destination. mdor showed the highest energy consumption, followed by eeor and the proposed protocol. this was because mdor wasted more energy in the initial setup. however, the dynamic energy consumption considerations led the network to survive for a long time, as shown in figure . in the case of eeor in figure , it consumed lesser energy in transmission and the initial setup for opportunistic selection of relay nodes was based on the power level. however, when it comes to lifetime, eeor failed to perform better, as it considered the network to be dead when any one of the nodes ran out of its energy. eeor chose one node as a source and continued transmissions opportunistically, which resulted in a significant reduction in the power level of a single node. the proposed protocol gave the best results, as in each round, the source node was based on the intelligent model to change the next-hop relay node. figure presents the average end-to-end delay per round, generated by the simulation, and the proposed protocol worked significantly better as the next-hop selection was based on an intelligent algorithm. the proposed algorithm helped to significantly reduce average end-to-end delays. figures and showed the reliability and availability performances of all protocols, including the proposed protocol that showed significantly better performance. this meant that the proposed protocol was a new generation protocol that has potential in many applications of wsn. in recent years, wsn saw its applications growing exponentially with the integration of iot. this gave a new purpose to the overall utility of data acquisition and transmission. with the integration of wsn with iot, the iot is making a big impact in diverse areas of life, i.e., e-healthcare, smart farming, traffic monitoring and regulation, weather forecast, automobiles, smart city, etc. all these applications are hugely dependent on the availability of real-time accurate data. healthcare with iot is one such area that involves critical decision making [ ] [ ] [ ] . the proposed approach makes use of intelligent routing and, therefore, would help in making reliable and accurate delivery of data to the integrated healthcare infrastructure, for proper care of the patients. the proposed framework for e-healthcare is shown in figure . as the proposed algorithm saves energy, the healthcare devices that are sensor-enabled can work for longer duration, and easy deployment and data analysis is possible due to iot integration [ ] [ ] [ ] [ ] [ ] . according to the proposed architecture, there can be any different kind of sensor nodes, such as smart wearables, sensors collecting health data like temperature, heartbeat, number of steps taken every day, sleep patterns, etc. these factors have a correlation with different existing diseases. the best part of the integration of iot and wsn is that, with the help of sensors, data are collected and the same is stored in the cloud due to iot integration. once the health data is stored in the cloud, this cloud is a health-record cloud that belongs to a specific hospital or a public domain cloud. these cloud data can be accessed by healthcare professionals in a different way, to analyze the data and also provide feedback to a specific patient and group of patients. in recent years, wsn saw its applications growing exponentially with the integration of iot. this gave a new purpose to the overall utility of data acquisition and transmission. with the integration of wsn with iot, the iot is making a big impact in diverse areas of life, i.e., e-healthcare, smart farming, traffic monitoring and regulation, weather forecast, automobiles, smart city, etc. all these applications are hugely dependent on the availability of real-time accurate data. healthcare with iot is one such area that involves critical decision making [ ] [ ] [ ] . the proposed approach makes use of intelligent routing and, therefore, would help in making reliable and accurate delivery of data to the integrated healthcare infrastructure, for proper care of the patients. the proposed framework for e-healthcare is shown in figure . as the proposed algorithm saves energy, the healthcare devices that are sensor-enabled can work for longer duration, and easy deployment and data analysis is possible due to iot integration [ ] [ ] [ ] [ ] [ ] . according to the proposed architecture, there can be any different kind of sensor nodes, such as smart wearables, sensors collecting health data like temperature, heartbeat, number of steps taken every day, sleep patterns, etc. these factors have a correlation with different existing diseases. the best part of the integration of iot and wsn is that, with the help of sensors, data are collected and the same is stored in the cloud due to iot integration. once the health data is stored in the cloud, this cloud is a health-record cloud that belongs to a specific hospital or a public domain cloud. these cloud data can be accessed by healthcare professionals in a different way, to analyze the data and also provide feedback to a specific patient and group of patients. in the recent epidemic of covid- , telemedicine had become one of the most popular uses of this platform. doctors also started e-consulation to the patients and getting access to their health records, using the smart wearables of patients. sill, there are many challenges, and lot of improvements are required. the proposed work add towards better energy efficiency of sensors, so that they can work for longer durations. thereafter these sensor data can be integrated using iot and cloud, as per the proposed approach shown in figure . in the recent epidemic of covid- , telemedicine had become one of the most popular uses of this platform. doctors also started e-consulation to the patients and getting access to their health records, using the smart wearables of patients. sill, there are many challenges, and lot of improvements are required. the proposed work add towards better energy efficiency of sensors, so that they can work for longer durations. thereafter these sensor data can be integrated using iot and cloud, as per the proposed approach shown in figure . in this paper, we proposed a new routing protocol (iop) for intelligently selecting the potential relay node using naïve baye's classifier to achieve energy efficiency and reliability among sensor nodes. residual energy and distance were used to find the probability of a node to become a next-hop forwarder. simulation results showed that the proposed iop improved the network lifetime, stability, and throughput of the sensor networks. the proposed protocol ensured that nodes that are far away from the base station become relay nodes, only when they have sufficient energy for performing this duty. additionally, a node in the middle of the source and destination has the highest probability to become a forwarder in a round. the simulation result showed that the proposed or scheme was better than mdor and eeor in energy efficiency and network lifetime. future work will examine the possibility of ensuring secure data transmission intelligently over the network. the authors declare no conflict of interest. an overview of evaluation metrics for routing protocols in wireless sensor networks comparative study of opportunistic routing in wireless sensor networks opportunistic routing protocols in wireless sensor networks towards green computing for internet of things: energy oriented path and message scheduling approach. sustain toward energy-oriented optimization for green communication in sensor enabled iot environments greedi: an energy efficient routing algorithm for big data on cloud. ad hoc netw an investigation on energy saving practices for and beyond opportunistic routing-a review and the challenges ahead a revised review on opportunistic routing protocol geographic random forwarding (geraf) for ad hoc and sensor networks: multihop performance opportunistic multi-hop routing for wireless networks optimal forwarder list selection in opportunistic routing simple, practical, and effective opportunistic routing for short-haul multi-hop wireless networks spectrum aware opportunistic routing in cognitive radio networks energy-efficient opportunistic routing in wireless sensor networks a trusted opportunistic routing algorithm for vanet a novel socially-aware opportunistic routing algorithm in mobile social networks opportunistic routing algorithm for relay node selection in wireless sensor networks economy: a duplicate free opportunistic routing mobile-aware service function chain migration in cloud-fog computing service function chain orchestration across multiple domains: a full mesh aggregation approach online learning offloading framework for heterogeneous mobile edge computing system virtualization in wireless sensor networks: fault tolerant embedding for internet of things traffic priority aware medium access control protocol for wireless body area network an energy efficient opportunistic routing metric for wireless sensor networks middle position dynamic energy opportunistic routing for wireless sensor networks an intelligent opportunistic routing protocol for big data in wsns recent advances in energy-efficient routing protocols for wireless sensor networks: a review radio link quality estimation in wireless sensor networks: a survey futuristic trends in network and communication technologies futuristic trends in networks and computing technologies communications in computer and information handbook of wireless sensor networks: issues and challenges in current scenario's lecture notes in networks and systems proceedings of icric introduction on wireless sensor networks issues and challenges in current era. in handbook of wireless sensor networks: issues and challenges in current scenario's congestion control for named data networking-based wireless ad hoc network deployment and coverage in wireless sensor networks: a perspective key: cord- - mxeq dg authors: cheshmehzangi, ali title: covid- and household energy implications: what are the main impacts on energy use? date: - - journal: heliyon doi: . /j.heliyon. .e sha: doc_id: cord_uid: mxeq dg this study explores the impacts of covid- on household energy use. some of these impacts are associated with longer-term energy demand changes and some could just be temporary. the study intends to present the results of a small pilot study conducted in china, by addressing household energy use. the samples are from households and particularly focus on primary energy use in three periods of pre-pandemic (and pre-lockdown), start of covid- outbreak and lockdown, and post lockdown. each period is identified as a timeframe of . months, from november to late june . the samples of this study highlight the primary implications of energy use, some that are understood as interim changes and some that may appear to be more prolonged. the results from the study highlight a variety of impacts on household energy use as well as prolonged impacts on transportation use. the primary household energy use are assessed in six fundamental elements of ( ) transportation for commuting and leisure (for both private and public modes), ( ) cooking, ( ) entertainment, ( ) heating and cooling, ( ) lighting, and ( ) the others. the results are summarized in three sections focused on major impacts on transportation use (comparison between private and public modes), cooking and entertainment, heating/cooling and lighting. the results could provide early suggestions for cities/regions that are experiencing longer lockdown. furthermore, this study provides insights for larger-scale research in assessing household energy use/demand during times of health emergency and crises, such as the event of a pandemic. by now, a little introduction is needed for the ongoing pandemic outbreak that has had major impacts on societies around the globe. the covid- outbreak was identified in late december in the city of wuhan, china, and was eventually recognized as a pandemic on the th of march . since the start of the outbreak in january , the impacts are increasingly seen on health and economies around the globe. in recent months, the covid- pandemic has gained research attention mostly on primary areas of health [ , , , , ] , economy [ , , , ] , social well-being [ , ] , resilience [ , ] , and disaster management [ , ] . to date, some studies also look at other primary factors, one of which is 'energy' [ , , , ] . the relationship between covid- and energy is discussed critically as a matter of energy crisis [ ] , an increase in energy demand [ , , ] , and potential transitions [ , ] . nevertheless, what has been studied so far are mostly associated with the study of intersections [ ] , and associated with energy systems, security, and services [ ] . while studies on energy and environmental footprints [ , , , , ] could shed light on short-term transitions, we could argue that it is perhaps too early to see how the energy crisis [ , ] could emerge and be potentially managed any time soon. some of the early recoveries [ , , , , ] , as seen in many parts of the world were just temporary. one of the early major energy demand changes were the unforeseen % reduction of energy use in china [ ] , which was mainly caused by temporary demand reductions that only lasted for less than two to three months. by april , despite several spikes across the country, most operations were back to normal or towards normalization in china, which then had a reverse impact on energy use and demand [ ] . it is envisaged the same pattern could appear in other countries or regions once they enter the recovery or post-recovery stages. of all covid- energy implications, 'household energy' is not yet studied extensively. while energy security has been debated already [ , ] , also from the financial perspective for decision making [ ] , the impacts on the increase of household energy consumption are so far studied from the perspectives of electricity use [ , ] , household energy in the informal economy [ ] , household energy choice [ ] , and home energy management [ ] . the latter is studied in correlation with the social-psychological factors that are also major drivers of energy use and demand. because of such change, the impacts on poorer households and communities [ ] are yet to be studied at a later stage. the higher energy use and energy costs would certainly have a wider impact on societies around the globe. with many countries under the widespread measures of lockdown and imposed curfew for weeks or months, the proposal for action plans to reduce energy consumption in buildings [ ] may not be necessarily applicable to the residential buildings or the households. in fact, the reverse impact is expected as it has been studied by chen et al. [ ] and as is evidenced in this research study. hence, this study aims to present the results of a small pilot study conducted in china, by addressing the so far impacts on household energy use. this is aimed to explore not only what could be the impacts on energy use exclusive to the households, but also the ones associated with daily household operations, such as the energy use that is needed for changes in transportation demand and mode. by exploring this overarching aim, the main objectives of this perspective paper are ( ) to evaluate the main impacts on the primary household energy use, ( ) to suggest what could become a longer-term energy implication for the households, and ( ) to address what needs to be studied at a larger scale in the future research. this pandemic cannot be simply seen as a driver for energy transition [ ] but rather as a major disruption [ ] that could potentially have longer impacts on household energy consumption behavior [ ] and longer-term environmental impacts [ ] . the study of global macroeconomic impacts of covid- [ ] already suggests potential scenarios that indicate significant impacts on households. hence, by studying the important topic of household energy implications, we could potentially reduce the impacts and pressure (e.g. energy costs) that seem to be overshadowing the households in the long run. the methodology package is designed based on a pilot study, evaluating the impacts of the covid- pandemic on household energy use and consumption. this is not aimed to suggest a transitional analysis but rather to evaluate what energy implications are important for the households. this study collected on-site survey data from households in the city of ningbo, china. based on the selection procedure, of the survey respondents were qualified for this study. the survey is designed based on the overall evaluation of main household energy use and associated energy implications. this is designed based on three main dimensions, namely the genera analysis of household energy consumption [ ] , implications for eco-environments [ ] , and the consideration of social emissions from energy consumption in households [ ] . in doing so, we are able to have an overview of generalities that suggest differences over the select period, as well as a ground for evaluating the results against the set conditions of the pandemic at multiple stages. the study follows the household category verification [ ] that provides us with a focused area of research for a better comparative analysis. data collection procedures follow this survey design to ensure the accuracy of data for the later evaluation and suggestions of the study. the study follows an estimation procedure [ , ] to create aggregated data of households in three consecutive timelines. the timeline for the survey is selected based on three different stages in a relatively short period (see section . ) to have a review of impacts of the covid- on energy consumption [ , ] , potential financial implications [ ] , and energy bills [ , ] . these could then be evaluated further for potential policy interventions [ ] that could lead to better socio-economic pathways [ ] after the recovery stage of the pandemic. given the increase in household consumption is inevitable [ ] the study is mainly designed to verify the implications that should be addressed in a short-to-midterm. the selection of ningbo as the case study is due to two factors of relatively minimal covid- impacts and accessibility to residential areas. the city experienced six weeks of lockdown (in february and march ) with a maximum of recorded inflected cases and no fatalities (to date, as of th of september ). in compared to many other cities in china, the city has not yet experienced any new spikes or further waves of the outbreak. as a result, most operations were back to normal by mid-may . the survey was conducted after the lockdown period followed by the normalization of operations in may and june . the households are selected from multiple residential areas, but all qualified respondents were identified as working-class residents, with three main selection criteria of ( ) living alone or with family, ( ) commuting to work daily (apart from the lockdown period), and ( ) having a private car. this selection is based on the mentioned category verification method [ ] , which is focused on specific demographic characteristics with the highest population in china. in doing so, the study focuses on current trends in household energy changes [ ] by avoiding the complexities of multiple categories [ ] , wide-range impacts [ ] , and other factors such as behavioural, physical, and socio-economic attributes [ ] . this is a verified approach that leads to a better analysis of data without cross-sectional variations [ ] and consideration of high-consumption [ ] and low-consumption categories. this study, therefore, aims to evaluate the household energy consumption behaviours [ ] or changes in requirements [ ] that are crucial for the users, policymakers, and developing any future action plans. the survey is conducted through the consideration of the abovementioned factors, and by defining multiple uses in and associated with the households. section . summarises the main parameters of the survey study for the households. finally, respondents were qualified for this pilot study. it is important to note that as of may , most daily operations in ningbo are back to normal and nearly all jobs require onsite operations (apart from some entertainment industries such as cinemas and theatres, and some public buildings, such as museums and libraries). therefore, the survey could only be conducted during a time when most industries were operational. the survey could not be conducted in separate timelines as the pandemic could not be predicted, the lockdown period was not fixed, and post-lockdown time was under highlevel safety and security measures. the following two sub-sections explain the details of the survey and the parameters of the data collection and analysis. the household cases were selected only if access was permitted. hence, the research was conducted based on the survey of multiple residential compounds across the city. the survey consisted of four parts. first, the survey started with explaining the aims and objectives of the study as well as the use of the data, to ensure all respondents are aware of the importance and accuracy of the studied areas. in this regard, the participants were asked about their knowledge of household energy use as well as daily activities and operations. second, the participants were requested to answer three questions to ensure they meet the selection criteria (as shown in section above); and finally, results were qualified. third, if qualified, the survey included a range of questions on household size, household type, household income, and demographic distribution. fourth, the participants were asked about household energy pre-covid me post-lockdown me among the participants, were selected for the analysis. all qualified participants are employed or have their own businesses, have to commute to their workplace on a daily basis, and have a private car. . % of participants indicated an annual household income of less than , rmb, . % between , to , rmb, and . % above , , rmb. regarding ethnic background, more than half of the participants were locally from ningbo ( . %), followed by other chinese but not local ( . %), non-chinese or foreign nationals ( . %), and chinese minority ethnics ( . %). more than third of the participants live with a family with one child ( . %), followed by couples only ( . %), family with two children ( . %), and larger families ( . %). single-living participants were intentionally disqualified in this survey. of all participants, the majority live in mid-to-highrise apartments ( . %) followed by low-to-midrise apartments/houses ( . %), and villa housing or individual houses ( . %), which is the factual representation of the chinese housing market. the parameters of the study were the primary energy use in six fundamental elements of ( ) transportation for commuting and leisure (for both private and public modes), ( ) cooking, ( ) entertainment, ( ) heating and cooling, ( ) lighting, and ( ) the others. the survey is divided in four packages, that includes ( ) the number of uses per week for transportation, both for private and public modes, ( ) the number of times per day for cooking and household entertainment activities that require energy use for preparation or operations, ( ) the estimated number of hours per day for indoor 'cooling and heating' and 'lighting'. to verify the latter, data for energy costs were also assessed. the data is then aggregated with the average figures amongst all participants, and in three phases as indicated in section . . the monthly average figures are then assessed to indicate changes in household energy use across all three phases. the results of this paper are presented across three combined areas, based on their energy use and daily/regular energy demand. first, the results of 'transportation use' indicate the changes over the total period of . months in three phases. the correlation between the decline in public transportation use and the increase in private car use is a primary result. second, the results of 'cooking' and 'household entertainment activities' are summarized together to indicate the changes between different phases and the correlation between these two daily needs that require energy use for preparation and operations. third, the results for two major household energy sources are summarized, namely indoor 'cooling and heating' and 'lighting'. these two categories account for the majority of our household energy use and represent the daily comfort needs of our indoor environments. the estimated energy use of these two fundamental elements are cross-checked with energy bills from the same time in . for this analysis, . % of the participants ( of the total of ) could verify the difference from their energy bills in both years. this is used only for the verification of energy demand changes during the time of this study. the results indicate no significant changes for the category of 'the others', which includes refrigeration, water heating, other household appliances, etc. hence, the results for this category is not presented. integrated across all three areas, the following sub-sections present the data followed by further analysis. the main implication here is the significant change in transportation use that may last longer than expected. the decline in public transportation use, as has been seen from the early days of the lockdown, is based on four main factors, ( ) early closure of public transportation systems as also indicated by [ , ] , ( ) social distancing measures that are used for safety and prevention procedures [ , ] , ( ) the general perception that rightly suggests public facilities are not safe during the pandemic [ , ] , and ( ) accessibility to public transportation systems [ , ] that requires decision making to walk outdoor to reach public transport. however, the main energy implication is that public transportation remains ostracized even after the lockdown. although ningbo has had no new cases since early march , the use of public transportation is minimized significantly. while the frequency of operations are back to normal since late april , the use of such systems are not even close to half of what they used to be. while public transport systems are managed by the government in china, the pressure would be on the provision of daily energy and operational management. in countries where public transportation is privatized, owners may face even further difficulties in managing the daily operations. the results from the survey indicate % increase in private car use with added traffic and energy demand in this sector. meanwhile, public transportation is facing an a. cheshmehzangi heliyon ( ) e estimated % decline in use, which has become prolonged with many empty buses, metro systems, and less demand for regular uses. the correlation between the increase and decline as shown in figure suggests a much larger energy demand in this sector. food and entertainment are part of our daily needs but are partially associated with outdoor activities. in china, the culture of eating outdoor [ ] is a major part of socializing activities and urban life. the growing outdoor entertainment [ ] also indicates the increasing popularity amongst chinese society. our survey results suggest an interesting correlation between the two, particularly during the lockdown and post-lockdown periods. the main impact on household cooking is the % increase during the lockdown in comparison to the pre-lockdown time. nevertheless, the trend did not keep up and our results indicate a significant decline in household cooking after the lockdown period. this indicates that household cooking is not returned to normal but instead lower than before. while larger demand for eating outdoor is economically viable for the post-recovery phase of the outbreak, it seems that people generally prefer to recover from several months of constantly cooking and eating inside their households. the same pattern is also seen for household entertainment [ , ] that constitutes a relationship between indoor stay and activities. for instance, household entertainment was almost tripled during the lockdown period but is reduced to its normal figures after the lockdown. the limited availability and closure of outdoor entertainment activities have enabled people to look for alternatives within the boundary of their households. this also means a short-term increase in household energy use. however, the sudden surge on computing entertainment could lead to longer-term impacts. the results do not suggest longer-term impacts but indicate a partial surge in household energy use and demand (figure ). although no statistically significant results were found that could suggest longer-term transitions, the relatively high increase of household energy demand (for household cooking and entertainment) in the lockdown period challenged assumptions and expectations. the results here touch on two main areas of human comfort for the indoor environments, namely 'heating and cooling' and 'lighting', which are both main energy consumption of households [ , , , , ] . considering the apparent impact of seasonal changes on energy demand, the results suggest an estimated % increase in cooling and heating, and % in lighting, just between january and february . this comparison is in the same season and indicates two different times of shorter 'cooking' and 'entertainment' indoor stay (pre-covid) and the lockdown period that stretched over most of february ( figure ). to verify the energy impacts, . % of the participants ( of the total of ) provided the information on their energy bills from jan-may and the same time in . the comparison indicates a significant increase in energy bills (i.e. by comparing and data) suggesting an average of % increase in electricity energy costs in february (in compared to february ), % in march , % in april, and % in may ( figure ). the unit price for both years have been the same. this verification adds to our concerns that household energy has been significantly affected, and could continue with a similar pattern of at least % increase. future research should aim to look at a much longer period to see if these could be identified as potential transitions in the household energy increase due to longer indoor stay. the results of the study cannot verify transitional changes. there are, however, temporary energy implications that are identified as part of this all-inclusive study on household energy consumption behaviour. the increasing demand for household energy use means higher consumption patterns, an increase in the use of household appliances, and longer energy use for cooling/heating and lighting. therefore, the main policy implications are on measures against the potentially increasing environmental footprint during and after the crisis [ ] , as well as policy implications for energy supply chain and decline in economic activities and energy consumption [ ] . give the reduction in co emissions only happened for a temporary period [ , , ] , the study verifies what has been associated with such reduction during that period. one example is the significant change in the selection of transportation mode, which lacks policy support and interventions. this requires action plans that could be responsive to the prolonged decline of public transportation use. the continuity of such a decline would have long term impacts on the industry and could encourage people to opt for private cars. apart from the already known long-lasting economic effects [ ] , there are growing concerns regarding short-term effects on behavioural changes that could potentially lead to longer-term behavioural patterns. for instance, the significant increase of household or in-house entertainment could have an adverse impact on outdoor entertainment or create an imbalance in some industries or sectors. for instance, the longer the public libraries remain closed, the more people may question the need for such buildings in their communities. thus, there is an obvious demand for new digital gadgets and tools that could put pressure on conventional methods of outdoor activities and functionalities. this study, however, does not delve into such arguments as it can only verify the household energy implications. nevertheless, there is enough evidence to indicate the need for future actions that could deal with potential transitions or changes that may change our day-to-day activities. as the pandemic continues, we could identify areas for policy interventions, some of which that could navigate the clean energy transition in the transportations sector [ ] , provide measures for energy sector responses [ ] , or create better energy governance [ , ] . moreover, issues of energy access [ ] may seem just about fine for the working class, as it is evidenced in this pilot study. however, this is unlikely to be the case for the people of lower income or deprived communities that have become more vulnerable [ ] due to the socio-economic impacts of the pandemic. the more self-sustained development patterns are the ones that could eventually help the better redevelopment of the communities, such as the development of actions for energy access [ ] , community-focused institutions [ ] , better investments that include stronger polices [ ] , and advocating methods of transitioning energy systems [ ] . as suggested by [ ] "instability makes the ability to adopt and implement…policy options more". therefore, we see an opportunity to enhance policies and actions that could lead to positive new normals [ ] , such as further investment in public facilities, public transportation, energy access, environmental policies, and policy interventions at the community level. in summary, policy implications and actions are essential in a long term and after the pandemic. these actions are essential to reflect on the losses in the progress of implementing and achieving the united nation's sustainable development goals (sdgs), such as the sustainable energy for all initiative [ ] . the current disruption in the patterns of household energy consumption could potentially impact the major initiatives of energy management and energy control, which then require to be carefully assessed and supported. therefore, active policies are needed to reflect on the conditions responsibly [ ] and by taking into consideration the long term effects of the covid- pandemic on households, household energy, energy consumption behaviour, and energy demand. altogether, the household energy implications should not be neglected as part of transitional opportunities or behavioural changes that may have occurred due to the pandemic. this study sheds light only a few examples on a small scale, but future research should evaluate larger datasets and potentially at multiple locales. it is important to note that the current variations in energy use, even if in specific sectors, could have significant implications for national-level or local-level policy initiatives. therefore, policy interventions should be carefully crafted to reflect on the socio-economic conditions as well as potential behavioural changes. by formulating these, the aim should be to establish long term action plans on major initiatives that are likely to be affected the most. in the following section, we summarise the findings of the study and highlight what could be a crisis and what could be an opportunity. these are highlighted as part of the conclusions of the study. this study is placed in the light of the ongoing covid- pandemic event and its focus is on household energy implications that suggest energy impacts on transportation, cooking, entertainment, cooling and heating, and lighting. it mainly investigates the changes that could suggest major impacts on the household energy use because of the covid- , and some that could potentially last longer than these few months of the pandemic. in light of this investigation, the main findings of this research are summarized in the followings: ( ) the impacts on transportation use, specifically from the household use perspective, is twofold: first, there is an inevitable increase in private transportation for commuting and leisure, and second, there is a significant decline in public transportation use that could lead into unforeseen pressures on public transportation suppliers/companies or even longer-term impacts; ( ) the impact on energy consumption related to household cooking is likely to be temporary with reverse impacts after the lockdown period; ( ) the impact on household entertainment is likely to increase in the longer term, with a potential increase in computing entertainment that became more popular in recent months. hence, we anticipate steady and higher energy consumption for household entertainment activities ( ) the impacts on household electricity costs associated with heating and cooling will largely depend on potential transitions for workfrom-home initiatives and longer indoor stays. it is likely to see longer impacts that could lead to more indoor stays in the future. ( ) the impacts on household lighting are similar to cooling and heating and mainly depend on forthcoming transitions. it is likely the indoor stays could be temporary during the covid- pandemic but could remain as longer-term norms even when the pandemic ends. hence, we could anticipate longer-term transitions should more people opt for work-from-home in the future. ( ) the impacts on other household energy use are unchanged and appear to have minimal impacts on the short-term. figure summarizes these impacts indicating how they would be seen from the household energy use perspective. the energy crises resulted from the impacts of covid- on daily operations/use suggest both long-term and short-term changes. through a pilot study, this research paper briefly assessed changes in household energy use in different phases before and during the pandemic (to date). the results could provide early suggestions for cities or regions that are experiencing longer lockdown or may face the new waves of the outbreak. as this study serves only as a pilot study, the findings indicate the need for larger-scale research in assessing household energy use and energy demand in the event of a pandemic. finally, we emphasize the importance of energy implications that could lead to better evaluation of potential transitions and the impacts on energy suppliers and the decision making of energy managers, policymakers, and end-users. if not properly planned, energy impacts could become adversities of the lower-income communities and could lead to potential conflicts in a phase in which the society needs more support than ever. author contribution statement a. cheshmehzangi: conceived and designed the experiments; performed the experiments; analyzed and interpreted the data; contributed reagents, materials, analysis tools or data; wrote the paper. this work was supported by the national natural science foundation of china ( ) ( ). figure . the summary of energy use impacts due to covid- . (legend: the long and thick arrow indicates high impact and long term effects, the short and think arrow represents short-term changes or insignificant impacts). the psychological impact of covid- on the mental health in the general population covid- -related infodemic and its impact on public health: a global social media analysis the spread of the covid- coronavirus: health agencies worldwide prepare for the seemingly inevitability of the covid- coronavirus becoming endemic coronavirus disease (covid- ): situation report covid and its mental health consequences the socio-economic implications of the coronavirus pandemic (covid- ): a review spillover of covid- : impact on the global economy covid- outbreak in italy: are we ready for the psychosocial and the economic crisis? baseline findings from the psycovid study covid- and the case for global development effects of the covid- pandemic and nationwide lockdown on trust, attitudes toward government, and well-being promoting older adults' physical activity and social well-being during covid- the city in need: urban resilience and city management in disruptive disease outbreak events risk and resilience in family well-being during the covid- pandemic hospital emergency management plan during the covid- epidemic will covid- generate global preparedness? minimising the present and future plastic waste, energy and environmental footprints related to covid- coronavirus comes home? energy use, home energy management, and the social-psychological factors of covid- here's why energy security is a vital tool in tackling a pandemic covid- impacts on energy demand, infrastructure yet to be known the energy crises revealed by covid: intersections of indigeneity, inequity, and health the short-run and longrun effects of covid- on energy and the environment when pandemics impact economies and climate change: exploring the impacts of covid- on oil and electricity demand in china analysis of the electricity demand trends amidst the covid- coronavirus pandemic what opportunities could the covid- outbreak offer for sustainability transitions research on electricity and mobility? covid- and the politics of sustainable energy transitions energy security, poverty, and sovereignty: complex interlinkages and compelling implications an outlook on the global development of renewable and sustainable energy at the time of covid- environmental and nutritional impacts of dietary changes in spain during the covid- lockdown impact of covid- outbreak measures of lockdown on the italian carbon footprint unlocking the impacts of covid- lockdowns: changes in thermal electricity generation water footprint and virtual water trade in europe navigating the clean energy transition in the covid- crisis effects of covid- on indian energy consumption covid- , climate change, and renewable energy research: we are all in this together, and the time to act is now will covid- fiscal recovery packages accelerate or retard progress on climate change? readiness of small energy markets and electric power grids to global health crises: lessons from the covid- pandemic a covid- recovery for climate covid- , further reform is necessary to accelerate china's clean energy future covid- assistance needs to target energy insecurity effects of covid- outbreak on environment and renewable energy sector household financial decision making amidst the covid- pandemic energy transition in a lockdown: an analysis of the impact of covid- on changes in electricity demand in lagos nigeria an empirical analysis of household energy choice in ghana sustainability and development after covid- review on government action plans to reduce energy consumption in buildings amid covid- pandemic outbreak understanding household energy consumption behavior: the contribution of energy big data analytics substantial changes in nitrate oxide and ozone after excluding meteorological impacts during the covid- outbreak in mainland china the global macroeconomic impacts of covid- : seven scenarios household energy consumption patterns and its environmental implications: assessment of energy access and poverty in nepal rural household energy consumption and its implications for eco-environments in nw china: a case study effects of household energy consumption on environment and its influence factors in rural and urban areas household enrgy and environmental analysis to highlight the impact of modern energy access in bangladesh what drives the change in uk household energy expenditure and associated co emissions? implication and forecast to modeling household energy expenditure in the united states emergency measures to protect energy consumers during the covid- pandemic: a global review and critical analysis covid- energy sector responses in africa: a review of preliminary government interventions energy demand in the state of kuwait during the covid- pandemic: technical, economic, and environmental perspectives long-term trends in direct and indirect household energy intensities: a factor in dematerialisation? complexities of household energy consumption and conservation the impact of household consumption on energy use and co emissions in china behavioural, physical and socio-economic factors in household cooling energy consumption an analysis of cross-sectional variations in total household energy requirements in india using micro survey data cognitive accessibility in judgments of household energy consumption evaluating the direct and indirect rebound effects in household energy consumption behavior: a case study of beijing energy requirements of household consumption: a case study of the netherlands covid- , social distancing and public policies adherence to social distancing and wearing of masks within public transportation during the covid pandemic easyband: a wearable for safety-aware mobility during pandemic outbreak explaining walking distance to public transport: the dominance of public transport supply prioritising accessible transit systems for sustainable urban development: understanding and evaluating the parameters of transportation system in mumbai food, eating behavior, and culture in chinese society featured insights/china/china and the world inside the dynamics of a changing relationsh ip/mgi-china-and-the-world-full-report recovering household preferences for digital entertainment entertaining or functional: an analysis of visuals in chinese and western household appliance manuals conference: nd annual international scientific conference of direct and indirect household energy consumption in china household energy consumption behavior user behavior and technology development the energy and environmental footprints of covid- fighting measures-ppe, disinfection, supply chains a preliminary assessment of the impact of covid- on environment-a case study of china the impact of different covid- containment measures on electricity consumption in europe temporary reduction in daily global co emissions during the covid- forced confinement the economic effects of covid- containment measures sustainable urban development in the age of climate change -people: the cure or curse the future of sustainable real estate investments in a post-covid- world impacts of covid- on a transitioning energy system, society and international cooperation sustainability and development after covid- the authors declare no conflict of interest. no additional information is available for this paper. key: cord- - rfb b authors: fell, michael j.; pagel, laura; chen, chien-fei; goldberg, matthew h.; herberz, mario; huebner, gesche m.; sareen, siddharth; hahnel, ulf j.j. title: validity of energy social research during and after covid- : challenges, considerations, and responses date: - - journal: energy res soc sci doi: . /j.erss. . sha: doc_id: cord_uid: rfb b measures to control the spread of coronavirus disease (covid- ) are having unprecedented impacts on people’s lives around the world. in this paper, we argue that those conducting social research in the energy domain should give special consideration to the internal and external validity of their work conducted during this pandemic period. we set out a number of principles that researchers can consider to give themselves and research users greater confidence that findings and recommendations will still be applicable in years to come. largely grounded in existing good practice guidance, our recommendations include collecting and reporting additional supporting contextual data, reviewing aspects of research design for vulnerability to validity challenges, and building in longitudinal elements where feasible. we suggest that these approaches also bring a number of opportunities to generate new insights. however, we caution that a more systemic challenge to validity of knowledge produced during this period may result from changes in the kinds of social research that it is practicable to pursue. the coronavirus disease (covid- ) pandemic is having tragic health consequences around the world, and measures to combat it are impacting people's lives in unprecedented ways. there is, as yet, no clarity on when and how measures such as suspension of certain businesses and physical distancing might end completely, or need to be reintroduced. the timescales required to develop a vaccine and deploy it globally suggest this could be well into and possibly later. during this time, the validity of energy social science research faces additional threats. validity generally refers to the truth of a knowledge claim or inference [ ] . national and global events continuously shape social worlds. but the magnitude, speed, and reach of the changes to our lives are of a different order to anything that most people alive today have experienced. given the scale and rapidity of change, how can we ensure that conclusions drawn from data collected during the pandemic are valid, representative, generalisable to a post-pandemic world, and comparable to the pre-pandemic one? while the answer is inherently unknowable [ ] , our aim in writing this paper is to highlight principles that we believe energy social science researchers can take to help mitigate this uncertainty, and ease future interpretation of research findings in the context of the progressing pandemic. broadly speaking, these principles involve giving consideration to possible impacts of the pandemic and associated response measures on findings; adjusting research design and data collection to reflect this; and reporting extra contextual detail. we argue that researchers who take reasonable steps in these areas will be able to ensure greater confidence in the validity of the work they conduct during this period. through consciously enhanced transparency for the 'extended peer community' that post-normal science scholars have long espoused [ , ] , their contributions will be better positioned to help address future challenges on the validity of findings by reviewers and users. we co-produced these principles as energy researchers who represent a variety of relevant disciplinary perspectives and subject interests, and are based in a range of institutions and countries. this allowed us to balance the will to draw on a breadth of input across the field, with the need to share these principles in a timely fashion. we set them out in the hope that researchers will find them helpful, but recognise that applicability will vary across energy social science research. our recommendations are likely to be most applicable to researchers employing quantitative research methods that are often restricted in the amount of contextual data they are able to collect [ ] . however, we hope that as a set of considerations they will be helpful to a broad range of energy social science scholars to employ as they see fit. the next section of this paper sets out the key challenges we identify for validity during the covid- pandemic, and justifies our focus on social science research in energy. we then expand on steps that researchers can take to address these challenges, and provide a simple checklist that can be applied by scholars in order to address the impacts of the pandemic on their research. we finally highlight additional opportunities these steps can yield, but also point out important potential implications for the nature of knowledge generated by contemporary research. decisions about validity inherently concern tradeoffs and priorities of a given research study [ ] . for instance, a researcher might prioritize internal validity (or "the degree to which a study establishes the cause-and-effect relationship" [ ] ) by conducting a randomized controlled laboratory experiment. artificial laboratory conditions enable strong experimental control, but limit generalizability across diverse, complex real-world situations. a field study, in contrast, might prioritize external validity (or "the generalization of research findings [...] to settings and populations other than those studied" [ ] ), but surrenders some ability to control and measure variables. both of these forms of validity are important. if we cannot trust the findings of a study because of methodological problems or unaccounted-for variables, generalisability is irrelevant. and findings that only apply in exceptionally narrow circumstances offer very limited value in applied research settings. external validity tends to be given special weight in applied research, including most energy research, where the generalisability of findings, and therefore any resulting conclusions and recommendations for action, often has primacy. our point of departure here is the impact of the covid- pandemic and associated response measures on internal, external, and subsidiary forms of validity. we argue that the pandemic merits explicit consideration for validity for a number of reasons. first, the response to covid- represents a departure from ordinary circumstances that is unprecedented in terms of its global nature, rapidity, diversity, and severity of impacts. at the time of writing in may , over countries and several billion people were under some form of lockdown, with restricted rights to movement and public assembly. in many cases, schools, non-essential businesses and hospitality venues were closed. evidence of prevalent psychological distress and anxiety had begun to emerge [ , ] . such a situation is far removed from the conditions under which knowledge is ordinarily produced and applied, and questions around the validity of findings generated during this circumstance are inevitable. second, an important consideration for external validity is how stable findings are over time. while there is always uncertainty about how closely the future will resemble the present, we argue that this uncertainty is now especially high. movement restrictions have already left millions of people unemployed, with millions more at risk of losing their jobs as businesses contract or close [ ] . governmental support packages are building up unprecedented levels of national debt that will have to be paid for, with little clarity around the effect this will have for public services and taxes. while some effects such as quarantine measures will be shorter-term, it is unknown whether the pandemic itself and associated consequences will result in long-term effects on the individual and societal level. realistic and symbolic threats induced by the pandemic are likely to affect individuals' values, identity, and worldviews and thus could exert long-term effects on various dimensions [ ] . moreover, research on past societal crises has shown that pandemic-related effects such as large-scale unemployment can lead to long-term effects on mental health [ ] ). taken together with the scale of current impacts, we believe this increased uncertainty in the short, medium, and long term justifies special consideration of validity of social research and, furthermore, a higher burden of proof on claims to such validity. why is a particular focus on energy studies important? energy use plays a prominent role in many aspects of human life. any changes on the scale being experienced during the pandemic have significant impacts not only on patterns of interaction with energy systems, but also on how people relate to and prioritise those systems. much energy research conducted today aims to inform transitions to clean, low-carbon energy systems that work for people and society. although research conducted now can shed light on how the extraordinary measures in place might impact energy use (such as evidence of reduced weekday electricity use [ ] and changing usage patterns [ ] ), it is challenging to disentangle these impacts from those that result from measures deployable absent a pandemic. moreover, the impact of such a drastic, globally shared experience impacts discursive and normative registers, with undetermined implications for public commitment to low-carbon energy transitions that become interwoven with other drivers of change pathways. although many of the principles we set out next could simply be viewed as good research practice, we think that they merit explicit attention during this pandemic and its aftermath. we argue that they are especially important for those domains of energy social research that claim broad generalisability to their findings and insights, with limited focus on context. for example, we think the points raised here are generally more applicable to survey-based than ethnographic research. by bringing these recommendations together here, we hope to stimulate a more consistent response by social researchers, allowing greater commensurability and comparability across studies in the future. furthermore, we recognise that scholars using social research approaches in energy have a wide variety of backgrounds and levels of experience. what we suggest may be self-evident to some, although for these we hope it will be helpful to have a checklist to compare their own responses against. to others, we hope it will provide both a prompt to consider challenges to validity, and a handy set of responses to consider. we have argued that challenges to the validity of social science energy research presented by the covid- pandemic warrant special recognition. we now lay out a set of principles for researchers to consider bringing to their practice for the duration of the pandemic period and its aftermath to help bolster the validity of their work, and to ensure that future use of their findings and recommendations is facilitated by requisite information to aid correct interpretation. our recommendations address data collection and the reporting of study conditions and context, as well as considerations for study designs in order to ensure high validity of energy social science research conducted during and after the pandemic. given the large number of possible new factors to be taken into account, we propose a 'core and consider' approach, allowing researchers in the field to prioritise and justify the measures they want to take to account for potential pandemic-related influences. where possible, we have drawn on existing good practice guidance, which itself has developed through conventional processes of cross-field engagement [ ] . while we think the validity challenges we have raised here are important, we also recognise that any responses to them must fit within existing research plans, budgets, timelines, labour constraints, and the heightened need for affective care, including researchers' own wellbeing under personal stress-inducing conditions. any response must be both proportionate to the anticipated vulnerability to validity challenges of the kind set out in the previous section. ethical and data protection concerns, while not directly related to validity, must be borne prominently in mind. any changes to planned research should not, unless it is explicitly justified, introduce collection of categories of data that are more sensitive than those that were originally (or would ordinarily be) planned and/or approved. this means, for example, that researchers should not (without careful thought and justification) begin to collect data on physical or mental health unless this was intended anyway. researchers should be mindful of the extra burden to participants that introducing additional data collection could bring. extra sensitivity is called for on the part of researchers to the potential impacts of collecting data on topics which may be more upsetting now than would ordinarily be the case. we suggest that additional and/or modified variables may need to be collected and reported for studies carried out during or after the covid- pandemic in order to account for the impact of the pandemic on research validity. already, researchers shouldand many doreport contextual factors of any study, and consider how these might impact the study findings [ ] [ ] [ ] . given the large number of possible new factors to be taken into account, we suggest researchers take a 'core and consider' approach. government restrictions and relevant demographic variables at the level of the unit of analysis (e.g., individuals or households) are core additional variables that should be reported and discussed. other factors should be considered for additional reporting depending on the precise topic of research. as in all studies, reporting of contextual factors should encompass date(s), place(s), and duration of data collection. as a core concern, we suggest that this should now be supplemented with information on pandemic-related national and local policies that were in force at the time and place of data collection. this could include factors such as levels of restriction of people's freedom to move around outside the home, including self-imposed precautionary behaviour, and the open/closed status of specific relevant services such as schools and certain businesses. significant changes in any of these measures during data collection should also be reported. researchers may consider it to be important for context to give a sense of the severity of the pandemic (including health, social and economic impacts, as relevant). we suggest using official government references for a description of such policies and impacts where possible, in ways that are cognizant of their rapid temporal evolution. a further core consideration is that local and national pandemic response measures affect individuals and households in diverse ways; specifying the national policies during data collection alone does not explain effects at the individual (or other analytical) level. more specific effects can be captured by measuring application of and compliance with response measures on the respective analytical level, and/or through collection of additional demographic variables from which application could be inferred. the nature and detail of measures will differ by locality, but could include whether someone is considered a 'key worker' (and hence still regularly leaves the home during lockdown) or comes under a highrisk category and has to observe stricter measures. other standard demographic variables may need amendment depending on the study aims. for instance, employment status can include categories such as being placed on government-subsidised furlough, working reduced hours, or working fully from home. other variables that might ordinarily have been judged as having limited importance, might gain relevance. impacts of the covid- pandemic are thought to be exacerbating existing inequalities in many societies, such as energy poverty issues [ ] . a key variable in many studies will likely be the financial situation of the individual, household, or other unit of interest. capturing information on recent (and risk of future) changes in factors such as income (including transfer payments), changes in employment status, increased receipt of benefits, or self-reported financial satisfaction may take on greater importance. unexpected deprivation from work income may have differential effects on energy-related measures, relative to foreseeable prolonged unemployment periods; while this is a consideration in samples at any time, it is likely to be especially common now. differentiated impacts on variables such as health, income or employment situation are already evident across individuals, notably across ethnicities, gender and income groups [ , ] . disaggregating on the basis of such variables, while always beneficial, may now be of more acute importance given heightened inequalities. at the individual level, we anticipate that covid- response measures will be associated with important changes in behaviour, as well as cognitive, affective, and other social and material dimensions [ ] . changes in energy-related behaviours and decision-making due to changes in daily routines, work and mobility might be more apparent and measurable, but changes in decisions and actions triggered by pandemic-related shifts in energy-related beliefs, attitudes, emotions, and judgments may be just as important to apprehend. for energy social science research focusing on the aforementioned dimensions it is important to assess to what extent these variables are different from a "normal" scenario and whether potential changes are durable or ephemeral. epidemiological research demonstrates the effect that pandemic response measures and consequences such as unemployment exert over time on personal well-being [ ] ). while empirical research on specific covid- measures is emergent, existing theoretical research on the psychological consequences of the crisis indicates that the fallout on current generations will linger in complex ways over time [ ] .the inability to accurately predict how such changes might be associated with energy-relevant outcomes, or which changes might be more or less enduring [ ] , makes it all the more important to capture and consider them in the long run. where additional measures are included, we suggest the use of standardized approaches to the extent possible, such as widely used and validated scales employed in regular national surveys. this will allow commensurability with pre-covid- levels, while minimising construct and instrument validity challenges and the resource-intensive efforts associated with developing new measures (which require substantial testing to ensure scale reliability and validity). we show an initial mapping of variables as 'core' and 'consider' , in table . we also provide a checklist (see appendix) suggesting where and how to report those additional variables (and other considerations) in studies. when thinking about the potential effects of the covid- pandemic on the validity of research findings, it is also important to consider how it might affect research design. in this section, we briefly introduce issues relating to study design, sample selection and recruitment, and data collection methodology, as well as implications for interpretation of findings. suggestions on ways to report such considerations are also provided in the checklist (see appendix). it is likely that the pandemic will affect non-experimental research in different ways than it will affect experimental research. research focused on identifying associations might be especially vulnerable to threats to internal and external validity. more specifically, if the pandemic affects both the independent and dependent variables of interest, it can induce a spurious correlation (confounding; [ ] ). for instance, the pandemic might harm mental health and increase energy usage, making it appear as though the variables are related when they might not be, absent the pandemic. researchers can address this concern in the way that is typically recommended for addressing confounding: anticipate how the pandemic might affect your variables of interest, measure this set of variables, and test whether they affect the study's primary results [ , ] . the idea that 'correlation is not causation' is wellknown --but worth keeping salient especially at times when non-experimental research is being planned or altered at short notice. experimental designs are still potentially vulnerable to other pandemic-induced issues. experiments, by design, manipulate a specific variable of interest. for example, an experiment aiming to improve people's motivation to purchase or support renewable energy by means of messaging strategies might focus on the harm caused by fossil fuels to increase people's fossil fuel risk perceptions. however, the salience of such risks, and therefore their malleability, may be substantially decreased if people are preoccupied with other worries related to covid- . thus, researchers should consider such influences and, if possible, take measures to ensure that they can indeed manipulate the causal variable of interest in an effective and meaningful way. this is an empirical question for each manipulated variable, but we advise that researchers attempt to anticipate such issues and design their research accordingly. a clear consequence of the pandemic is that it will make it more difficult to conduct betweenand within-country comparisons where covid- impacts and restrictions are different. for example, home energy usage will be higher in places where people are required to stay at home. a useful rule of thumb is, wherever reasonably possible, researchers should contextualize their research by considering how political and cultural circumstances might affect their results (see section "capture and report on extra relevant data"; [ ] ). it would be even better to anticipate how such factors might affect results and design the study to mitigate them, such as collecting a sample that is relatively homogeneous in orders to stay at home, limit travel, or any variable that might substantively affect the results. if substantial heterogeneity of restrictions is anticipated within a sample, increasing sample size to maintain statistical power should be considered. independent of study type, a powerful way to get a measure of stability and validity of findings over time is to build longitudinal elements into the research design. first, researchers could consider building replications into their research plan. this can be done by intentionally splitting data collection over waves separated by a period of time. this allows for comparison of the variables of interest over the two waves. variables that remain constant over this period are likely to be relatively less affected by pandemic response measures than those which show variation. this approach lends itself particularly well to collaborations between research groups, which could consider teaming up to add variables of interest reciprocally onto the end of each other's studies, saving on budget and potentially introducing opportunities for new analyses. please refer to the section "capture and report extra relevant data" for more information on variable dimensions to consider. another possible approach to demonstrate the robustness of research findings over time could be through attempting to reproduce previous research findings --either of related research by the researcher themselves, or of previously well-reproduced effects. the extent to which previous findings are reproduced, or change, could help 'calibrate' the more recent research and give some insight into whether or not the domain of interest is more or less impacted by the pandemic and the corresponding response (also accepting that failure to reproduce findings is not an unusual occurrence even under normal circumstances [ ] ). data collection with a given research method could produce different findings now compared to before pandemic-related restriction measures were put into place. for example, research conducted online could be more heavily influenced by distracting factors of the participant's environment. where people are confined to their homes, completing a survey or conducting an interview in a standardized way might be more difficult than before. this consideration is especially important, since persisting restrictions of contact might result in a shift towards more research being conducted online versus in person. it is thus recommended to explore the possibility of using more than one method to investigate the same research question, and to record potential limitations specific to a data collection method to account for their influence on the validity of the findings. this is another area where collaboration between research groups with complementary interests could bring significant additional value by allowing testing of the same research question through different approaches and in different settings [ ] [ ] [ ] . while elaborating on additional or alternative methods, it is again important to consider ethical aspects. as mentioned earlier, the extra sensitivity of collected data has to be thought through, and in terms of data collection methods, researchers and analysts should make sure that data privacy and confidentiality is not undermined by new approaches [ ] . in the previous subsection we already highlighted the importance of giving due consideration to contextual factors. in respect of covid- , this means paying particular attention to the extent to which pandemic response measures (and changes in them across time and the sample) might have contributed to the observation of particular results. if possible, researchers should attempt to communicate and justify their best estimate as to the impact such factors could have had on findings. for example, if little systematic difference is observed in an outcome variable across groups who were substantially differently impacted by pandemic response measures, this could be offered in support of a case that the impact of covid- of that particular variable could be small. as in many areas of research, transparency is likely to be key in allowing users to make informed judgements of their own. any recommendations for policy, practice, or further research should be similarly transparent and include appropriate caveats on the context of the findings to which they relate. employing the principles set out above presents a number of opportunities that go beyond simply mitigating threats to validity, and could help generate new insights or improve research practice in general. the introduction of longitudinal elements can provide important insights on stable and dynamic determinants of energy-relevant outcomes, especially if combined with new contextual, behavioural, and other data that may not previously have been collected. such longitudinal studies could moreover contribute to the research question whether observed changes on the individual and societal level are caused by the pandemic itself (e.g., due to perceived threats and vulnerability) or by associated measures and consequences (e.g., due to lockdown and job loss) and thus provide insights into short-term and long-term effects of the pandemic. moreover, where collected data suggests that different groups of people have been (or will be) systematically exposed to different conditions as a result of the pandemic, natural experiments could be possible. natural experiments provide a powerful opportunity to investigate causal associations which may otherwise be difficult or impossible to control for (for an example see: [ ] ). these fleeting windows of opportunity can provide novel research opportunities and should be considered by energy researchers. the same window of opportunity will likely extend to policy interventions introduced in the wake of the pandemic to aid economic recovery. we already highlighted the possible benefits that could accrue from collaboration with other groups to facilitate replication and support validity, but there is also a wider convergence research opportunity in energy social studies during and after covid- . convergence research is a way of addressing complex problems through highly integrated interdisciplinary approaches [ ] . given the range and scale of current and anticipated impacts of the pandemic, such an approach is likely to be especially valuable, and opportunities to build inter-and transdisciplinary collaborations should be proactively sought. such collaboration may also provide a route to adding in important contextual data, for example through matching datasets. finally, we suggest that responding to validity challenges presented by the covid- crisis is an opportunity for the energy research field to step up and embrace practices around transparency and reproducibility that are now seen as standard practice in other areas of research. for reasons likely connected with the multidisciplinary and applied nature of most energy research, tools such as reporting guidelines and pre-registration of analysis plans are still rarely employed [ ] . it is possible that the particularly pressing need to demonstrate validity at present will result in familiarity with, and adoption of, tools that subsequently become standard practice for an increasing number of energy researchers, potentially enhancing the overall validity of research in the field. in much of the social sciences, knowledge on the most severe and pressing problems is often difficult to create and therefore constitutes a smaller proportion of thematic scholarship than its implications merit. the flip side of this is that 'low-hanging fruits' can suffer from excessive coverage. this impacts the 'body of knowledge' validity, which we define as the representativeness of research in a field relative to the real-world problems the field is concerned with [ ] . energy social science research, with its diverse methodologies, spatial and scalar foci, and associated differences of requisite time and effort, is no stranger to these tendencies. consider, for instance, the wealth of scholarship on local and urban energy initiatives in the uk, home to many energy research scholars, versus the relatively thin body of work on energy practices in rural sub-saharan africa. both issues merit attention and are generative for conceptual insight, but the latter affects over a billion people, many of whom experience relatively severe degrees of energy poverty, and yet hardly registers in terms of volume in relevant energy social science research. we detect a risk that curtailment of field-based empirical research, especially in regions that face severe energy challenges and may be heavily impacted by the epidemic, will exacerbate existing biases in representation in terms of volume (more desk study over ethnographic research than usual), methodology (potentially more conceptual work over evidence-based research) and regional coverage (less pandemic-impacted areas over more pandemic-impacted areas). to some extent, this is a perennial problem in any interdisciplinary or transdisciplinary field of study: ethnographic work in challenging regions with marginalised populations takes time and the classics on such topics that have accumulated over the years (in quite large numbers) consequently receive considerable attention. it is similarly evident in other fields of energy research, such as modelling, and outside of the energy domain. yet research today is heavily metricised, and most scholars with access to most global peer-reviewed scholarship are based in global north institutions and typically urban contexts, often with pressure to publish frequently. this leads to the double jeopardy of being pressed for time to focus on short-term impact, and of being far more likely to access highly-cited and highvolume segments of the scholarship one engages with. since the pace of research outputs has escalated, few scholars are positioned to navigate a body of knowledge with adequate care to balance its in-built biases of representation. already, we see moves to run online surveys and study social perceptions; even with all the appropriate caveats and the best of informed intentions, these contribute to a likely disbalance by volume of the sort of concerns that will get platformed in energy research journals in the short-to medium-term. how much coverage of marginalised, hard-to-access concerns -such as migrants cast adrift with little energy access, subsistence farmers with crop loss and inability to pay for fuel costs -will be lost and substituted by low-hanging fruit? such exacerbation of an existing bias can cloud future accounts and understandings of the true effects of a pandemic on the subject of energy research, i.e., on the global lived experience of energy. but it is not inevitable -it is an artefact of choices we make as an epistemic community. informed by recognition of likely biases, our choices (and those of funders, who can prioritise research on marginalised research areas) can embody normative commitment to proportionally match research coverage to real-world problems. we can productively draw on approaches such as convergence research highlighted above. this drive captures the essence of our contribution, which is to work toward a reflexive understanding of our role as a scholarly community at this time of crisis and opportunity. in this paper we have set out what we see as important challenges to the validity --internal, external, and of other forms --of social research in energy associated with the covid- pandemic and measures put in place to control it. we have suggested a number of principles we think researchers should consider applying to give themselves and the users of their work confidence that the findings and recommendations they present will still be valid in the years to come. these focus mainly on the collecting and reporting of additional contextual data, and the review of research design elements to ensure they are as robust as possible to pandemic-related impacts. we think that these principles can be employed with relatively minimal impact on resources and timescales required for research. they even present some opportunities both to enrich insight into social aspects of energy, and draw attention to measures to improve research transparency that are still as-yet under-used in the energy field. however, we also need to be mindful that due to limits on the kind of research approaches that can be employed during the pandemic, there are likely to be important gaps in the knowledge generated during this period. we all hope that the period of direct applicability of this paper will be as short as possible, and that measures to control the spread of covid- will soon no longer be needed. nonetheless, we also think that the considerations we raise here have enduring relevance for energy social science in general, and the potential to contribute to more widespread use of transparent, contextually aware and valid research practices in the longterm. the authors declare no conflicts of interest. table : checklist of items to report or consider reporting in relation to covid- pandemic validity challenges. report: main details of covid- response measures in action at the time/place of data collection, at least including: level of freedom to move around in public; degree to which schools and businesses are open. methods "at the time of data collection, public movement in the uk was severely restricted by government measures to combat the covid- pandemic. people were instructed to stay at home at all times, except for doing essential shopping, one period of daily exercise, working outside the home if work at home was impossible, and providing support to vulnerable people. all schools, hospitality venues and nonessential shops were closed." consider reporting: how covid- restrictions are applying to individual participants. results "in our sample, % of participants reported staying at home at all times except for when conducting essential shopping and exercise. a further % also reported leaving home to undertake work or volunteering. % of the sample reported staying at home at all times." consider tailoring of the following aspects of the research: research design methods "in response to the rapidly changing circumstances connected with the response to the covid- pandemic, we introduced a longitudinal element to our data collection. the survey was administered over two waves separated by two months, allowing us to check whether any of the key independent variables changed over this time, and whether this was associated with any change in the outcome." data collected (see table for suggested dimensions) methods "in addition to employment status, we also collected data on the extent to which those in employment were working from home." consider possible implications for: findings discussion "we found a strong association between altruism and stated willingness to participate over both waves of the study. however, the association was weaker in the second wave, which, combined with the change in reported application of covid- response measures (while other variables remained stable), suggests that conditions surrounding the covid- pandemic could have affected this finding." conclusion "our findings suggest that policymakers should prioritise energy saving messaging framed in terms of benefits to the local environment. however, our participants reported spending more time in their local area as a result of covid- control measures which could have influenced our result. we therefore recommend that the effectiveness of such messaging be carefully monitored." experimental and quasi-experimental designs for generalized causal inference uncertainty, complexity and post-normal science extended peer communities and the ascendance of post-normal politics european energy poverty metrics: scales, prospects and limits establishing the internal and external validity of experimental studies theory-testing, generalization, and the problem of external validity a nationwide survey of psychological distress among chinese people in the covid- epidemic: implications and policy recommendations americans' risk perceptions and emotional responses to covid- covid- ) from pandemic to recovery: local employment and economic development conducting social psychological research in the wake of covid- long-term effects of youth unemployment on mental health: does an economic crisis make a difference? new data suggest covid- is shifting the burden of energy costs to households promoting novelty, rigor, and style in energy social science: towards codes of practice for appropriate methods and research design the importance of heterogeneity in large-scale replications the importance of social relations in shaping energy demand using in-home displays to provide smart meter feedback about household electricity consumption: a randomized control trial comparing kilowatts, cost, and social norms measures to tackle the covid- outbreak impact on energy poverty: preliminary analysis based on the italian and spanish experiences ethnicity and covid- : an urgent public health research priority how are americans coping with the covid- crisis? key findings from household survey survey tool and guidance: behavioural insights on covid- , who what sticks? ephemerality, permanence and local transition pathways, environmental innovation and societal transitions three conditions under which experiments and observational studies produce comparable causal estimates: new findings from withinstudy comparisons can nonrandomized experiments yield accurate answers? a randomized experiment comparing random and nonrandom assignments estimating the reproducibility of psychological science many labs : investigating variation in replicability across samples and settings crowdsourcing hypothesis tests: making transparent how design choices shape research results scientific utopia iii: crowdsourcing science on the responsible use of digital data to tackle the covid- pandemic mask-wearing increases after a government recommendation: a natural experiment in the us during the covid- pandemic convergence research in the age of big data: team science, institutional strategies, and beyond how to improve transparency when theories become tools: toward a framework for pragmatic validity while this work did not receive any dedicated funding in its own right, the individual authors gratefully acknowledge funding as follows. key: cord- -zt o co authors: sovacool, benjamin k.; furszyfer del rio, dylan; griffiths, steve title: contextualizing the covid- pandemic for a carbon-constrained world: insights for sustainability transitions, energy justice, and research methodology date: - - journal: energy research & social science doi: . /j.erss. . sha: doc_id: cord_uid: zt o co abstract the global covid- pandemic has rapidly overwhelmed our societies, shocked the global economy and overburdened struggling health care systems and other social institutions around the world. while such impacts of covid- are becoming clearer, the implications of the disease for energy and climate policy are more prosaic. this special section seeks to offer more clarity on the emerging connections between covid- and energy supply and demand, energy governance, future low-carbon transitions, social justice, and even the practice of research methodology. it features articles that ask, and answer: what are the known and anticipated impacts of covid- on energy demand and climate change? how has the disease shaped institutional responses and varying energy policy frameworks, especially in africa? how will the disease impact ongoing social practices, innovations and sustainability transitions, including not only renewable energy but also mobility? how might the disease, and social responses to it, exacerbate underlying patterns of energy poverty, energy vulnerability, and energy injustice? lastly, what challenges and insights does the pandemic offer for the practice of research, and for future research methodology? we find that without careful guidance and consideration, the brave new age wrought by covid- could very well collapse in on itself with bloated stimulus packages that counter sustainability goals, misaligned incentives that exacerbate climate change, the entrenchment of unsustainable practices, and acute and troubling consequences for vulnerable groups. the global covid- , or coronavirus disease, pandemic has overwhelmed our societies, shocked the global economy, thrown energy markets into disarray and overburdened struggling health care systems and other social institutions around the world. unlike earlier modern disease outbreaks such as severe acute respiratory syndrome (sars), swine flu (h n ), or ebola, the covid- virus is very easily transmitted by person-to-person contact. further, it has no known preexisting immunities, it is spread by people that do not appear to be sick, and the ratio between infections and fatalities is very high, particularly for older people and people with preexisting medical conditions. in medical terminology, society is undergoing a global pandemic with an immunologically naïve population. when addressing a group of sustainable development and medical professionals in april , columbia university professor jeffrey sachs estimated that the virus that causes covid- (i.e. sars-cov- ) could infect half the world's population within the next few years [ ] . although the global response to covid- may not be fully commensurate to the severity of the challenge, it has nevertheless disrupted longstanding notions of human resilience, disease preparedness, and even global health governance [ ] . national and subnational responses to the disease have often been far-reaching and at times transformative, including not only mandatory lockdowns, quarantines and restrictions on travel but key interventions such as evacuations, the distribution of hygiene and sanitation kits, and the suspension of all public visitors. some countries have utilized mass surveillance (as well as tracking and contact tracing apps) to monitor symptoms within their populations, funded community participation in the development and distribution of personal protective equipment, or participated in the design of intersectoral and transnational cooperation and aid packages. more than $ trillion in fiscal support measures had been announced by governments globally as of june to mitigate the economic impact from the pandemic, particularly impacts from the lockdown measures implemented to prevent spread of the disease [ ] . these relief packages amount to nearly % or more of gdp in germany, japan and the united states, with the united states alone signing a massive $ trillion covid- emergency bill and stimulus package in march [ ] . the european union set up a € billion coronavirus response investment initiative to provide liquidity to small businesses and the health care sector [ ] . the united kingdom also has invested heavily, launching a furlough program where the government paid the wages of . million affected workers (one quarter of the workforce) at a cost of more than £ billion with an additional £ billion in loans to businesses [ ] . initial assessments of the economic consequences of the pandemic are sobering, with estimations of a global gdp contraction of . % in [ ] , global trade shrinking by % [ ] and as many as million people losing their jobs [ ] . although the impacts of covid- on health systems and national economies are heavily covered in the media, and oft debated in the public, the implications of the disease for energy and climate policy are more prosaic. this special section of energy research & social science seeks to offer more clarity on the emerging connections between covid- and topics such as energy supply and demand, energy governance, future low-carbon transitions, social justice, and even the practice of research methodology. it features articles that ask, and answer: what are the known and anticipated impacts of covid- on energy demand and climate change? how has the disease shaped institutional responses and energy policy frameworks, especially in places such as africa where covid- is negatively affecting ongoing efforts to achieve access to modern energy? how will the disease impact ongoing patterns of innovation, social practices and future transitions, including not only adoption of renewable energy but also the electrification of mobility and mobility-as-a-service? how might the disease, and social responses to it, exacerbate underlying patterns of energy poverty, energy vulnerability, and energy injustice? lastly, what challenges and insights does the pandemic offer for the practice of research, and for research methodology? although ostensibly never intended as measures to reduce energy consumption, air pollution, or climate change directly, responses to the virus have had substantial connections with energy demand and greenhouse gas emissions. the most prominent drivers of these have been mandatory lockdowns or quarantines for households (people are only permitted to leave for essential reasons) and the related severe restrictions on travel. in late april , more than half of the entire global population ( %) was under some form of a coronavirus lockdown, with their movement actively restricted and controlled by their respective governments. the share of energy use that was exposed to containment measures reached % [ ] . as the top panel of fig. indicates, the largest lockdowns were in india, china, and the united states. one article calculated that more people were in lockdown due to covid- than were alive during world war ii [ ] . as the other panels of fig. indicate, more than countires had travel restrictions in place due to coronavirus in late march and the number of commerical flights has plummeted dramatically. abu-rayash and dincer (this volume [ ] ) add that road transport is also down significanty given the large number people forced to stay at home. they further show that in canada not only did civil aviation activities drop by % compared to business-as-usual in late , but also military aviatation activities were down by a significant % in . they also projected that for , greenhouse gas emissions for the canadian transport sector will be nearly % lower than than in . covid- has not only affected travel and the energy involved in providing it, but also global energy supply chains and the viability of energy firms. writing in this volume [ ] , hosseini argues that the most affected renewable energy sector has been solar energy and remarks that indeed, "the covid- pandemic has struck the renewable energy manufacturing facilities, supply chains, and companies and slowed down the transition to the sustainable energy world". the causes behind such shifts are manifold: governments have understandably redistributed public funding to combat the disease in a way that leaves less available for renewable energy incentives and tax credits. various renewable energy technology suppliers have placed staff on furlough and also adopted austerity measures and reduced operating capacity. projected installations are down significantly over earlier forecasts; one investment bank in the united states predicted residential-solar installations to fall by % year-over-year in the second quarter of and by % in the fourth quarter of . this reinforces the projections provided by irena that total new solar pv capacity additions in will be roughly on par , but this is as much as % below earlier expectations stated by several industry organizations [ ] . the off-grid renewable energy sector could face even more dire circumstances, with the world bank noting that the pandemic has seriously disrupted electrifications efforts, meaning that sdg (that encompasses universal energy access by ) is now unlikely to be met [ ] . it is in this context that mark mccarthy akrofi and colleagues (this volume [ ] ) caution that the pandemic could "reverse the enormous progress that off-grid energy companies have made to bring power to some million people in the last decade." solar pv alone is responsible for employing about % of the entire african workforce but solar firms and enterprises are already being forced to cut jobs, lay off staff, and confront declining liquidity. due to a strong dependence on imported solar pv technology from china, where manufacturing has declined due to the pandemic, dramatic reductions on future installed solar capacity are also projected for countries such as india [ ] . covid- is affecting global fossil fuel markets as well. hosseini (this volume [ ] ) adds that the coronavirus has disrupted global oil markets far more than any geopolitical event has (such as an embargo from opec), weakening the ability of oil suppliers to control markets and driving down natural gas spot prices into the $ /mmbtu (million british thermal units) range. although geopolitical tensions between saudi arabia and russia played an early role in the oil price collapse [ ] , demand destruction due to covid- has indeed been the driving force. jefferson (this volume) [ ] writes "in the run-up to the collapse of crude oil prices in early it was primarily a division between russia and saudi arabia within opec which appeared to be the main force at work, but then the covid- pandemic took over, followed by us oil prices turning negative in april , as may contracts expired and traders had to offload stocks with ongoing storage becoming extremely limited." he further states that despite the stimulus and recovery packages being offered by many nations, "there will be many oil sectors incurring losses, from us shale oil and canadian tar sands producers, to many standard crude oil exporters incurring problems with production equipment access and costs, or experiencing lack of competitiveness in key markets." recent data from the international energy agency confirms this point, noting severe reductions in global demand for oil and natural gas (see fig. ). although not representative of all countries and regions, the special section does feature some deep and nuanced assessments of the particular impacts the pandemic is having on national energy supply or demand. nima norouzi and colleagues (this volume) [ ] intimately trace the impacts of the virus where it first emerged in wuhan, china, looking at how it impacted not only national energy demand, but also precipitated steep declines (and future uncertainty) in patterns of electricity consumption and oil consumption, industrial productivity and energy markets. they specifically propose a methodology for analyzing such patterns during periods in which historical data becomes inaccurate because of a crisis event such as covid- . azzam abu-rayash and colleagues (this volume) [ ] closely analyze the impacts of the pandemic on electricity demand in ontario, canada, where they calculate declines in electricity consumption during april of about % or , gw and note distinct changes in demand patterns due to quarantine and travel restrictions. this corresponds with some positive externalities as well, including greenhouse gas emission reductions of , tons of co equivalent attributed to covid- with a monetary value of $ , for the month of april . fig. shows a similar trend in europe, with significant (and positive) reductions in air pollution noted across france, italy, and spain, largely from the curtailment of road transport. abouzar estebsari and colleagues (this volume [ ] ) offer a well-reasoned explanation for why related reductions in electricity demand occurred, having analyzed patterns of electricity demand in spain, italy, belgium and the united kingdom (countries with more severe covid- movement restrictions) as well as the netherlands and sweden (countries with less restrictive measures). they found that during the second week of april only in sweden demand remained more or less the same (actually rising slightly) relative to a reference week in . significant reductions were experienced in spain ( %), italy ( . %), belgium ( . %), the uk ( . %) and even the netherlands ( . %) due to covid- . the ramifications of covid- extend well beyond the avoided energy consumption and emissions associated with travel and household lockdowns; they are also drastically shaping the strength (or erosion) of some energy institutions and policy frameworks. for instance, the pandemic is having a particularly pronounced effect on institutions and policy frameworks in africa, even though it is not (at the time of this writing) a major center of infections or death. mulualem gebreslassie (this volume) [ ] writes that the closure of energy intensive businesses and industries in africa has meant a positive shift in that states can now provide scarce energy services to homes or national health care systems. as they conclude, the pandemic "may even convince the african continent to rethink and clear the way for investing more in clean and reliable energy resources and make business processes easy for those who are interested to enter the renewable energy sector." mark mccarthy akrofi and colleagues (this volume [ ] ) add that african states are already rushing to intervene and stimulate recovery but do not specifically address how stimulus packages will influence the clean energy transition. further research therefore needs to examine how government stimulus can strengthen the renewable energy sector via various aid packages, economic incentives, and monetary and fiscal incentives-efforts müller et al. note are all broadly consistent with many national policy frameworks across the continent [ ] . as already stated, the pandemic has significantly disrupted lives, businesses, and economies. furthermore, it could culminate in lasting effects on social norms and practices. to contextualize this claim, consider that the global response to covid- has necessitated unprecedented levels of coordination and information sharing with the intent of ultimately curtailing outbreaks and minimizing harm [ ] . this has occurred at multiple levels of society at once across many different types of institutions-making it what the nobel laureate elinor ostrom would have called "organizational multiplicity" and a "polycentric" phenomenon [ , ] . fig. displays the variety of messages received about covid- merely by the lead author, including those from the mass media (covid- dominated headlines in the uk for weeks), companies and travel providers, national government, grocery stores, universities, restaurants, social groups and charities, and even churches. this phenomenon parallels what scholar eve kosofsky sedgwick terms the "christmas effect" [ ] to describe the way that major parts of western society come together and speak "with one voice" for the christmas holiday. for it is annually during the christmas season that churches build nativity scenes and hold a greater number of masses; state and federal governments establish school and national holidays; the media run major advertising campaigns; and social events and domestic activities align. whenever society combines institutional inertia in this manner, it can exert profound and lasting influence over patterns of behavior, transcending individual firms and people. although certainly not festive, the "coronavirus effect" may be just as effective as the "christmas effect." such messages and strategies of communication underscore an immense amount of coordination across diverse and heterogeneous actors and organizations. the resulting messages were persistent, coming repeatedly and daily. they were prominent, in many times coming from sources people trust. they were multifaceted, coming from many sectors beyond health care including not only those in fig. , but also the mayor of london sadiq khan, banks, libraries, political groups, airlines, friends, and family. one of the authors even had his "smart printer" send an automated email about ink delivery during the pandemic, as well as six emails from his dentist about dental hygiene during the pandemic. and the messages were personal, often prescribing very specific actions or recommendations (about washing, essential travel, social distancing, self-quarantining, and mask wearing) connected to personal health and calling for immediate changes in behavior and practice. given the coronavirus' ability to achieve this "christmas effect," hundreds of millions of people immediately adopted the new behavior of "social distancing," with fig. showing its adoption in india, the united states, the united kingdom and singapore. when making the predictions mentioned in the introduction, jeffrey sachs even remarked that "we should expect to change our behaviors not just during this pandemic but perhaps forever." indeed, wisdom kanda and colleagues (this volume [ ] ) argue that in the context of sustainability transitions, the pandemic is causing "disruptive" change not only by potentially accelerating transformations in incumbent socio-technical systems, but also by also affecting emergent innovations and niches. in the mobility sector, they discuss how in finland and sweden the virus has weakened the push for mobility-as-a-service efforts (given they involve sharing rides, not ideal in an environment of social distancing) but had less impact on the push for electric vehicles (given they permit individualized, private transport). they therefore suggest that the impacts of covid- on mobility practices and transitions are important research streams moving forward. caroline kuzemko and colleagues (this volume [ ] ) take an even broader and more holistic view of the ways the pandemic can place pressure on sustainability transitions in the near-term and the longterm. they argue that covid- can alter the scope and pace of energy systems change with declining electricity demand and prices, the disruption of supply chains, and possible rebounds associated with recovery and stimulus packages. it could also shift financial investment flows away from incumbent industries and carbon intensive fuels. the pandemic is changing multi-scalar policy and politics by calling into question longstanding conventions about globalization and interconnectivity, as well as freedom of movement and geopolitical tensions between groups such as the united states and china or the united states and the world health organization. the pandemic is lastly transforming social and political practices, especially those related to telework/working from home as well a preferred modes of travel given the near-term focus on social distancing. here they warn that the lasting imprint of the pandemic is uncertain, with the potential that it entrenches unsustainable practices (such as driving a car) perhaps as great as its ability to introduce more sustainable practices (such as walking). they raise the critical question of whether there will be an acceleration of pre-pandemic drivers for sustainability across the dimensions they consider or whether momentum for sustainability will be lost as pandemic recovery plans are rolled out. kester et al. recently refer to this as the "dialectic" nature of future sustainability transitions, given they can reinforce dominant practices as much as they can reform existing ones [ ] . even electric mobility, an innovation kanda and colleagues noted may ultimately be less affected by the pandemic, has unclear and highly differentiated impacts on sustainability as noted in table . this means the adoption of electric vehicles is neither good nor bad in sustainability terms, it instead depends on how such innovations are governed and managed across areas such as vehicle use, daily life, social identity and systemwide environmental effects. the covid- pandemic has equally compelling linkages with energy crises, energy poverty, energy vulnerability and energy injustice. kathleen brosemer and colleagues (this volume [ ] ) write that the pandemic will only "illuminate and compound existing crises in energy sovereignty." it is worsening already terrible inequalities in health care access among the navajo nation in the united states, where hospitals were overburdened before covid- outbreaks with caring for indigenous peoples harmed from coal mining and extraction as well as increases in kidney disease and cancer that resulted from many years of living next to abandoned uranium mines. the pandemic is compounding environmental injustices as covid- most affects those with preexisting medical conditions, and yet decades of poor environmental and air quality leave minority groups at heightened risk of having those conditions. it is undermining the ability of energy firms to guarantee the provision of energy access and modern energy services in times of austerity and uncertainty. it is lastly serving as a mechanism for powerful incumbent interests to usurp various regulatory processes that back their own narrow interests at the expense of the public good. one particular example is enbridge "taking advantage of divided public attention and a fraught financial situation during the covid- crisis to push forward permit applications" for a major change in the routes of one of their pipelines. such attempts at regulatory manipulation are not limited to north america; kalyani writes how vested interests in india were using the pandemic as an excuse to increase employment in the coal and gas sectors, even though these sectors operate contrary to india's stated climate policies [ ] . paolo mastropietro and colleagues (this volume [ ] ) add that "the covid- pandemic and the consequent lockdown exacerbated energy poverty and insecurity worldwide." however, they also note that the collective response from policymakers has been to attempt to safeguard vulnerable citizens by an array of protection measures including: • disconnection bans; • energy bill deferral and payment extension plans; • enhancement of energy assistance programs; • energy bill reductions or cancellations; • support measures for commercial and small industrial activities; • creation of funds and other support measures to suppliers. after reviewing the global prevalence of these measures, they conclude that two are "best" at minimizing vulnerability: direct energy assistance programs and bans on disconnections, the latter being the most widespread measure introduced by governments during the pandemic. matthew henry and colleagues (this volume [ ] ) take an equally useful global analytical lens, reinforcing the recent call for a "just transition." this debate about a "just transition" is ongoing across many countries and provinces, with at least national commissions, policies, or task forces in place across canada, china, czech republic, germany, ghana, indonesia, new zealand, scotland, south africa, spain, the united states and vietnam. as table indicates, a "just transition" is backed by powerful coalitions and groups around the world. as henry and colleagues note, a just transition intends to ensure that as global society decarbonizes, it does not leave anyone behind. efforts must be made to offer income support for workers during the full duration of transition, to tailor local economic development tools for affected communities, and to offer realistic training or retraining programs that lead to decent work. they worry, however, that both the covid- pandemic and the global fall in oil prices could complicate ongoing attempts to realize a just transition-especially since the pandemic has resulted in the loss of more than , clean energy jobs and halted momentum in the push for solar energy and wind energy. they conclude however that the covid- crisis represents "a unique opportunity to adopt just transition principles into community and economic recovery efforts." the insights offered by this special section are not just topical or thematic. they also relate to the very art and craft of undertaking research, with some interesting insights for research design and research methodology. both jefferson (this volume [ ] ) and kanda and colleagues (this volume [ ] ) note how scholars, especially those designing energy programs (such as the global energy assessment) or utilizing table the differentiated impacts of electric mobility and electric vehicles on sustainability. strengthens sustainability weakens sustainability vehicle uptake evs substitute for conventional cars and motorcycle. evs increase car-based mobility by drawing people away from active and public modes of transport. evs used more in intermodal (active and public transport) systems and in combination with measures to discourage car use. evs encourage excessive driving and are bought as second or third (luxury) cars. evs increase the use of car sharing/ride sharing schemes. evs increase the preference for private, single-occupancy driving practices. evs are a wakeup call to address private vehicle use if alternatives are available -public transport, shared services etc. evs, through their cheaper variable costs, enable longer distances, thus supporting urban sprawl. they also compete with public transport and shared services. evs allow for more family time as commutes are part of office hours. evs allow office hours to be extended to include commuting time. expression of gender evs and ev marketing break with gender distinctions through alternative design, comfort and ease of operations. evs and ev marketing reinforce stereotypical car images of masculinity (large, sporty, pickup trucks) or femininity (small, quiet, early generation evs). evs and ev marketing point to new stereotypes around responsible and sustainable car use. evs and ev marketing reinforce stereotypical car discourses of joy and notions of freedom. evs break with class distinctions, as low variable costs enable more mobility for all. evs reinforce class/wealth distinctions as high capital costs imply that only rich can afford them and their benefits. evs, through their broad deployment, signal a need for more efficient low-carbon propellants, alternative modes of transport, less mobility and spur pro-environmental behavior in other sectors evs have lower emissions, which lead to rebound effects: more miles travelled, heavier vehicles, more private vehicles. this is especially relevant if the ecosystem around evs fails to materialize, e.g. no battery recycling, only dump charging, nonrenewable electricity, etc. oil independence evs minimize and signal lower oil/gas consumption, which reduces dependency among households and non-oil producers on oil companies and oil producing countries. evs cause a reduction in demand for oil, which reduces the oil price and makes fueling conventional vehicles cheaper. lower oil prices also reduce oil sector investments and thereby limit production to a smaller group of oil producing countries (those with low variable costs) and counterintuitively increasing oil dependence on a smaller group of countries. evs are designed and promoted by sustainably oriented firms with a focus on innovation and entrepreneurship. evs are co-opted and marginalized by transnational conglomerates with little desire for social change. source: authors modification from kester et al [ ] . selected organisations and movements supporting a "just transition" in . conceptual frameworks (such as the multi-level perspective) need to better account for epidemics and pandemics as landscape shocks. the persistence, prominence, multifaceted and personal nature of effective messaging about the virus (discussed in section ) also remind us about the importance of recognizing culture [ , ] whenever researchers engage in communication or outreach. fig. even shows the adapting to local culture of messages about social distancing and wearing masks. for instance, images about the virus in the western state of colorado (in the united states) feature skis and cowboys-symbols well embedded in local culture. lucha libre in mexico has played a relevant role in its culture since the late s, mainly due to its masked wrestlers, who have incorporated their own family traditions, beliefs and fears into the design of their masks [ ] . the louvre abu dhabi similarly adapted their messages about the pandemic to feature culturally appropriate attire for women, e.g. abayas on images of women performing social distancing. michael fell and colleagues (this volume [ ] ) suggest that the pandemic represents not only an existential threat to society, but also a threat to the practice of research, given that it calls into question the internal and external validity of our findings in the academy. this includes both the validly of research done before the pandemic (given that society may never be the same after) and the future robustness of any research conducted during the pandemic (a situation of extreme anxiety and stress far removed from "normal" life, potentially making findings less stable over time). they argue that covid- changes the context for research as it creates an environment that may be unprecedented and highly unusual compared to future years. they note the pandemic is reconfiguring demographics in rapid and unforeseen ways, with advanced morbidity and mortality and differentiated effects across age, gender, or ethnicity. they argue (much as we have in section ) that the pandemic is altering behaviors and daily routines; changing perceived personal and cognitive constraints and feelings; putting pressure on exiting social norms and identities; and materially changing homes and workplaces. taken together, these features of covid- may demand that we rethink in meaningful ways the design of future studies, how we determine demographically representative samples, how we collect data, how we interpret findings, and how we translate those findings into recommendations. such considerations are timely and relevant given the explosion of covid- publications that have appeared since the start of the pandemic. nearly , papers on the pandemic were published between february and may alone, and , of these were released through the preprint servers biorxiv, medrxiv and arxiv [ ] . chen and colleagues (this volume [ ] ) further these themes in their work on acceptance of and willingness to pay (wtp) for home energy management systems (hems) during the covid- pandemic in new york, usa. they note that the pandemic is having a distinct effect on survey participants with social-psychological variables, such as attitude toward hems and social norms, arising as important factors for explaining technology adoption intention. they also affirm some of the points raised by fell et al. about the unique situation survey respondents have found themselves in. many reported feeling "anxious" and others suggested that they felt they had a high chance of getting infected by coronavirus themselves-a salient message considering that the survey was conducted in new york, one of the global epicenters of the disease. the authors indicate that they hope that their survey results offer a "foundation for researchers to conduct larger-scale energy studies by considering the opportunities to build transdisciplinary collaborations through integrated methods and matching datasets." this might include future work on cultural differences in social distancing, how energy burdens are framed and distributed, what constitutes healthy built-home environments, and other social-psychological factors including perceived fairness or social networking. marius schwarz and colleagues (this volume [ ] ) offer additional insights regarding the impacts of the pandemic on research methodology that are perhaps obvious but nonetheless highlight important and perhaps persistent trends. they argue that covid- is opening up new ways of doing research, of being an academic, of collecting data and attending conferences. they argue "the pace with which researchers adopted digital formats for conferences, lectures, and meetings showed that currently available tools can substitute many of the physical interactions at work. it also showed that academics are willing to use digital tools for scientific exchange." the pandemic has showcased that academics and those in higher education can quickly and creatively change how they deliver lectures and are accessible to students; how they give guest seminars and discuss findings; even how they may interview for jobs, do research interviews, and host online workshops. they hope that "going digital" in many of these formats and contexts will continue, given the generally positive nature of the energy or carbon savings involved [ ] . they further suggest that such digital modes of interaction could come to substitute for physical modes in how academics work in groups, hold team meetings, and socially network. situated at the nexus of the covid- pandemic, energy systems, and climate change, this special section has revealed the complex, and often shifting, contours of how the disease is shaping global patterns of energy consumption, policymaking, and governance. it is altering the desirability of some emerging innovations and sustainability transitions, and heightening concerns over energy vulnerabilities and injustices. it is even challenging in fundamental ways how future energy and climate researchers go about their work. as table reveals, these intersections can be weighty and protean, but they are also perilous and precarious. for every noted positive intersection with some aspect of stainability or doing research, or benefit, we see an almost equally salient negative intersection, or risk. take one of these examples: lowering demand for, and prices of, fossil fuels. is this a blessing-foretelling that fossil fuels are becoming unviable-or a curse-cementing fossil fuels as cheap and abundant sources of energy to be utilized for many years to come? potently, it is the aspect of energy justice and vulnerability that particularly has more negative intersections (risks) than positive ones (benefits). covid- , as various authors presented in this special section, represents a strategic opportunity to work in parallel on designing and implementing economic and social recovery programs and advancing the global climate agenda towards a just transition. what is also evident from the special section is the multi-scalar and multifaceted nature of social responses to the pandemic, which have created a "christmas effect" or "coronavirus effect" of: • instructing people how to immediately alter and change their routines and practices in response to a crisis (e.g., social distancing, wearing masks, quarantining, and handwashing); • bolstering the strength and resilience of infrastructure and institutions (e.g., of hospitals and medical research institutions); • building capacity to monitor and manage emergency measures (e.g., trace infections, test people); • properly financing social responses in ways commensurate to a grand challenge (e.g., donations to national health services or the world health organization); • restoring economic activity gradually and via approaches that are backed by science (e.g., mandatory lockdowns and partial reopening, deployment of government rescue and stimulus funds); • harnessing innovation and rapidly developing critical new technologies (e.g., new therapeutics and vaccines); • utilizing a variety of trusted institutions and individuals to convey information and messages (e.g., the cdc, major news outlets, doctors and medical professionals); • while undertaking these steps, protecting the vulnerable (e.g., those with preexisting conditions, the unemployed and/or the indigent). although the impacts from the pandemic have so far been far from equitable or welcomed by the majority of people, this list of actions does offer a possible recipe for how future energy and climate planning could proceed as well, if policymakers and planners see the opportunity to transform social practices and institutions as much as the pandemic has. this could help achieve a "christmas" or "coronavirus" effect for energy and climate policy that encompasses: table the dialectic or dualistic impacts the covid- pandemic can have on energy and climate sustainability and research. energy and climate impacts of the virus -sharp reductions in travel related energy consumption and carbon emissions -immediate reductions in electricity consumption -depression of fossil fuel markets (particularly coal, oil and gas) -immediate reductions in global air pollution -redistribution of scarce energy resources in african nations to homes or national health care system -acceleration of african stimulus packages for low-carbon transitions -disruption of clean energy jobs -disruption of clean energy supply chains -risk of real and substantial rebounds in consumption accelerated by stimulus and recovery packages -disruption of off-grid energy markets and eroded progress on energy access programs -potentially bolstered trends in the electrification of private transport -shifted financial and investment flows away from carbon intensive assets -transformed social and professional practices in ways that are less energy intensive (e.g., working from home, walking, cycling) -undercutting of demand-side innovations such as ridesharing or mobility-as-a-service -dis-incentivizing mass-transit and public transport due to social distancing norms -calling into question the increasing interconnectivity and globalization of socio-technical systems -accelerating a geopolitical divide between the united states and other actors (e.g. china, world health organization) connections with energy justice an vulnerability -implementation of a variety of emergency protective measures including bans on disconnection and targeted assistance packages -increased attention to the principles of a "just transition" and the need for stimulus packages to be low-carbon and equitable • instructing people how to immediately reduce their carbon footprints (e.g. using energy efficient technologies in their homes, eating less meat, avoiding air travel [ ] ); • bolstering infrastructure, institutions and industrial strategy (e.g.. incentives for clean energy manufacturing and deployment including wind turbines, solar panels, electric vehicles [ ] ); • building capacity to mitigate, monitor and manage emergency measures (e.g., tracking plans for universal energy access and sdg , deployment of micro grids, bans on disconnection [ ] ); • properly financing social responses in ways commensurate to the challenge (e.g., substantially increase funding for national and multinational climate and development organizations or green investment banks, investment for deployment of low-carbon technologies and infrastructure [ , ] ); • restoring economic activity gradually and via approaches that are backed by science (e.g., development pathways synchronized to the ndcs of the paris accord or the findings of the ipcc, investment of economic stimulus funds in low-carbon technologies, green new deals [ ] [ ] [ ] ); • harnessing innovation and the development of new technologies (e.g., the next generation of transport fuels, energy storage, smart grids or hydrogen fuel cells) [ ] [ ] [ ] ; • utilizing trusted institutions and individuals to convey persistent and repeated information, messages and narratives in ways that resonate with audiences (e.g., major news outlets, the ipcc, governments, major corporations, churches, restaurants and celebrities sent persistently through various media channels) [ ] [ ] [ ] [ ] ; • while undertaking these steps, protecting the vulnerable (e.g., households in energy or mobility poverty, marginalized groups or indigenous peoples) [ ] [ ] [ ] [ ] . if such actions were taken in concert, progress on energy and climate would likely outpace all previous targets and milestones, rather than remaining chronically underfunded, underperforming and continually lagging behind expectations. both of these core findings-that covid- matches its promise of change with precariousness about the direction it goes, and that covid- responses offer a possible template for future energy and climate action-remind us that we remain at a critical but fragile crossroads. as much as we see great progress in efforts toward ameliorating the covid- crisis, we also see the same types of hindrances that have plagued progressive energy policy and climate action. specifically, lack of attention to warnings about a potential crisis, delayed responses to building evidence of crisis onset, nationalism at the expense of the global good, politics overshadowing social welfare, marginalized populations (e.g., people of low socio-economic status, or people in low and middle income countries) experiencing adverse consequences at higher rates, conspiracy theories and fatigue of mitigation measures. as fig. both comically and tragically seeks to depict, climate change is akin to a perpetual pandemic, but one that multiplies threats in steeper and more severe ways than covid- or its economic consequences. markard and rosenbloom have the right of it when they write that unlike the pandemic, "climate change, in particular, threatens the very basis for continued human prosperity and requires an equal, if not greater, societal mobilization" [ ] . hence, the opportunities emerging from the pandemic for energy systems and climate policy can be secured or squandered. without careful guidance, governance and consideration, the brave new age wrought by covid- could very well collapse in on itself with bloated stimulus packages, misaligned incentives, the embedding of unsustainable practices, and acute and troubling consequences for vulnerable groups. ssdn: epidemiology and economics of covid covid- gives the lie to global health expertise world economic outlook: the great lockdown trump signs $ trillion coronavirus stimulus bill jobs and economy during the coronavirus pandemic uk furlough scheme spending exceeds billion pounds trade set to plunge as covid- pandemic upends global economy more people are now in 'lockdown' than were alive during world war ii analysis of mobility trends during the covid- coronavirus pandemic: exploring the impacts on global aviation and travel in selected cities an outlook on the global development of renewable and sustainable energy at the time of covid- an agenda for resilience, development and equality, international renewable energy agency covid- intensifies the urgency to expand sustainable energy solutions worldwide covid- energy sector responses in africa: a review of preliminary government interventions challenges to just energy transitions in a post covid india a crude future? covid- s challenges for oil demand, supply and prices when pandemics impact economies and climate change: exploring the impacts of covid- on oil and electricity demand in china analysis of electricity demand amidst the covid- the impact of different covid- containment measures on electricity consumption in europe covid- and energy access: an opportunity or a challenge for the african continent? is green a pan-african colour? mapping african renewable energy policies and transitions in countries editorial, communication, collaboration and cooperation can stop the coronavirus polycentric systems for coping with collective action and global environmental change beyond markets and states: polycentric governance of complex economic systems what opportunities could the covid- outbreak offer for sustainability transitions research on electricity and mobility? covid- and the politics of sustainable energy transitions novel or normal: electric vehicles and the dialectic transition of nordic automobility the energy crises revealed by covid: intersections of indigeneity, inequity, and health emergency measures to protect energy consumers during the covid- pandemic: a global review and critical analysis just transitions: histories and futures in a post-covid world culture and low-carbon energytransitions the cultural barriers to a low-carbon future: a review of six mobility and energy transitions across countries the role of lucha libre in the construction of mexican male identity validity of energy social research during and after covid- : challenges, considerations, and responses scientific research on the coronavirus is being released in a torrent coronavirus comes home? energy use, home energy management, and the social-psychological factors of covid- covid- and the academy: it is time for going digital a systematic review of the energy and climate impacts of teleworking it starts at home? climate policies targeting household consumption and behavioral decisions are key to low-carbon futures harnessing innovation policy for industrial decarbonization: capabilities and manufacturing in the wind and solar power sectors of china and india sdgs in action: a novel framework for assessing energy projects against the sustainable development goals the politics of climate finance: consensus and partisanship in designing green state investment banks in the united kingdom and australia the misallocation of climate research funding the green new deal in the united states: what it is and how to pay for it canada's green new deal: forging the socio-political foundations of climate resilient infrastructure? a post mortem of the green deal: austerity, energy efficiency, and failure in british energy policy critical perspectives on disruptive innovation and energy transformation innovating innovation-disruptive innovation in china and the lowcarbon transition of capitalism are low-carbon innovations appealing? a typology of functional, symbolic, private and public attributes credibility, communication, and climate change: how lifestyle inconsistency and do-gooder derogation impact decarbonization advocacy climate change strategic narratives in the united kingdom: emergency, extinction,effectiveness using stories, narratives, and storytelling in energy and climate change research greenberg energy policy and research: the underappreciation of trust advancing an energy justice perspective of fuel poverty: household vulnerability and domestic retrofit policy in the united kingdom mobility justice in low carbon energy transitions justice, social exclusion and indigenous opposition: a case study of wind energy development on the isthmus of tehuantepec energy justice discourses in citizen deliberations on systems flexibility in the united kingdom: vulnerability, compensation and empowerment a tale of two crises: covid- and climate the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. key: cord- -rhu hp t authors: snyder, brian f. title: the genetic and cultural evolution of unsustainability date: - - journal: sustain sci doi: . /s - - -z sha: doc_id: cord_uid: rhu hp t anthropogenic changes are accelerating and threaten the future of life on earth. while the proximate mechanisms of these anthropogenic changes are well studied (e.g., climate change, biodiversity loss, population growth), the evolutionary causality of these anthropogenic changes have been largely ignored. anthroecological theory (aet) proposes that the ultimate cause of anthropogenic environmental change is multi-level selection for niche construction and ecosystem engineering. here, we integrate this theory with lotka’s maximum power principle and propose a model linking energy extraction from the environment with genetic, technological and cultural evolution to increase human ecosystem carrying capacity. carrying capacity is partially determined by energetic factors such as the net energy a population can acquire from its environment and the efficiency of conversion from energy input to offspring output. these factors are under darwinian genetic selection in all species, but in humans, they are also determined by technology and culture. if there is genetic or non-genetic heritable variation in the ability of an individual or social group to increase its carrying capacity, then we hypothesize that selection or cultural evolution will act to increase carrying capacity. furthermore, if this evolution of carrying capacity occurs faster than the biotic components of the ecological system can respond via their own evolution, then we hypothesize that unsustainable ecological changes will result. since the neolithic demographic transition, human societies have often lived along a continuum of unsustainability (ponting ; gowdy and krall ) , as depicted in fig. . at the most extreme end of this continuum is socio-ecological "collapse", defined here as a rapid decline in the population and/or development of a society due to a combination of ecological and social factors (cumming and peterson ) . civilizations that may have experienced socio-ecological collapse in whole or part due to their over-extraction of resources include the mayans, romans, greeks, the civilizations of easter and pitcairn islands, the norse colony in greenland, the cahokia in the american midwest, and the anasazi (lopinot and woods ; ponting ; hughes ; kennett and beach ) . in these cases, human systems may have expanded beyond their ability to absorb energy and materials from the environment, and these resource constraints interacted with socio-political conflict to generate socio-ecological collapse. the precise mechanisms and the relative weight of social versus ecological factors is debated in these and other cases (butzer ; butzer and endfield ; boersema ; cumming and peterson ) , and we do not imply that every case of social collapse is primarily resource driven. instead, we simply note that human populations have repeatedly experienced collapse and in many of these cases, environmental and resource constraints are implicated. while these cases of permanent collapse are particularly notable, humans have also spent a great deal of their history in a state of socio-ecological crisis. we define socio-ecological crisis as a situation in which human populations have expanded close to or beyond their ability to gather energy and materials from their environment which imperils the population and its standard of living. socio-ecological crisis may lead to the collapse, but societies might also be resilient. examples of socio-ecological crisis might include the years (out of ) between bce and ce in which there was a famine in at least one province in china; the european famine of - in which the population resorted to cannibalism; or the finish famine of - in which a quarter of the population perished (ponting ) . in each case, crisis did not lead to collapse, but for our purposes, it is only important that so much of recorded human history has been spent in a state of crisis. in addition to states of socio-ecological crisis and socioecological collapse, human populations have spent much of the remainder of our post-paleolithic history in a state of unsustainability. we define unsustainability as a growth phase in which humans extract increasing quantities of energy and materials from the environment and use them for both maintenance and growth. unsustainability is associated both with economic (daly ) and population growth (ehrlich and ehrlich ) and may lead to socio-ecological crisis. we might consider the growth phase of the ancient greek (hughes ) or contemporary western civilizations to exist in a state of unsustainability. given our history and our contemporary society, we might wonder why human civilization, since the neolithic revolution seems to be dominated by periods of unsustainability punctuated with periods of socio-ecological crisis and collapse (ponting ; gowdy and krall ) ? the purpose of this paper is to provide a conceptual model for understanding why humans may be predisposed to environmental unsustainability, socio-ecological crisis, and collapse. anthroecological theory (aet) hypothesizes that human social and cultural evolution is the ultimate cause of the ecological crises currently damaging earth systems (ellis ; ellis et al. ) . according to aet, human damage to earth systems is a consequence of socio-cultural niche construction which has evolved via a multi-level group selection process. in this understanding, humans have acted as ecosystem engineers and niche builders since at least the agricultural revolution, and perhaps since their burning of ancient savannahs for corralling game. this ecosystem engineering led to progressively greater "social scales" and population size, requiring ever-increasing levels of ecosystem engineering. here, we attempt to merge aet with lotka's maximum power principle (lotka ) and concepts from evolutionary ecology. lotka argued that natural selection acted so that organisms sought to maximize the rate at which it extracted energy from the environment; h.t. odum later named this hypothesis the maximum power principle (sciubba ) . if lotka was correct, then the ecosystem engineering and niche construction described by aet can be understood as a consequence of the maximum power principle acting via natural selection. while this energetic view is similar to ellis's aet model, we use energy extraction as a target of selection and as a metric of environmental load. this formalization might allow novel tests and models of aet. in the remainder of the paper, we first review the available literature on the evolution of unsustainability including prior approaches from agriculture, evolutionary psychology, and aet. we then describe our conceptual model of energetic aet and its relationship to the evolution of carrying capacity. finally, we discuss the implications of energetic aet for our understanding of two contemporary issues in socio-ecology and the paper ends with conclusions. as in the present work, gowdy and krall ( , attempted to understand the cause of human unsustainability. they argued that human ultra-sociality (called eusociality in the sociobiological literature) evolved as a consequence of the neolithic demographic transition and that this ultrasociality was the ultimate cause of the anthropocene's environmental crisis. to gowdy and krall, the ultra-social nature of human groups allowed for a shift in the primary level of selection from the individual level to the group level. thus, "with the transition to agriculture the group as an adaptive unit comes to constitute a wholly different gestalt driven by the imperative to produce surplus (gowdy and krall , ) ." this imperative to produce surplus leads to environmental crisis in gowdy and krall's model, but the same phenotype could also be understood as an expression of lotka's maximum power principle in our model. of course, gowdy and krall were not the first to link agriculture and socio-ecological crisis. thomas malthus' classic work on agriculture and population, and the responses to it, are to our knowledge, the first studies of the energetic sustainability of human societies. in is , an essay on the principle of population, malthus observed that population grew exponentially, while improvements in agricultural yields grew linearly at most (malthus and pullen ) . the result was what has been called a malthusian catastrophe in which the human demand for food energy exceeds our ability to extract it from the environment with consequent decreases in population size, standard of living, or both. phrased in the language of the present paper, malthus argued that the rate of increase of energy extraction from the environment was principally resource (rather than technology) limited and that this resulted in socio-ecological crisis when the rate of population growth exceeded the rate of energy extraction growth. malthus' ideas have been challenged many times since the eighteenth century, perhaps most notably by esther boserup ( ). boserup argued that agricultural productivity was principally limited by the technology and labor humans dedicated to agriculture. in her view, as population density rose, farming practices shifted through "agricultural intensification" which would serve to increase yields at the cost of increased labor. phrased in the language of the present paper, such a change would amount to technological and cultural evolution towards increasing energy extraction from the environment. this increasing energy extraction could then, contra malthus, support an exponentially growing population. since boserup's work, the green revolution increased staple crop productivity via new crop varieties and natural gas-made fertilizer. this revolution was able to ameliorate the potential socio-ecological crisis associated with the rapid population growth in the developing world in the latter half of the twentieth century (ehrlich and ehrlich ). thus, consistent with the outlines of boserup's thesis, humans were able to use technology to increase their energy extraction from the environment, this technologically-mediated energy extraction supported increased population size and occurred commensurate with a cultural shift (evolution) that allowed for increasing technological use in agriculture (possas et al. ) . this process is consistent with the energetic aet hypothesis developed here. while boserup and malthus provide important and contrasting lenses through which to understand the role of agriculture in human population, and while gowdy and krall identify agriculture as a critical turning point in human evolution, agriculture is no longer the predominant energy source for humans (smil ) . thus, we seek to build a conceptual evolutionary model of the human socio-ecological system that is consistent with these insights from agricultural systems but is more evolutionary and more general and incorporates extra-somatic energy, defined as energy that is used by humans but not used in direct human metabolism (price ) . furthermore, we propose a positive feedback that is missing from prior models of the energetics of socioecological systems, and we also integrate a ratchet-effect that causes the evolution of humans towards socio-ecological crisis to be unidirectional. where gowdy and krall ( , ) saw agriculture as the key to understanding human unsustainability, van vugt et al. ( ) saw the roots of unsustainability in the paleolithic, before the invention of agriculture. using an evolutionary psychological approach, van vugt et al. argued that ancestral selection in paleolithic humans created psychological conditions that make humans ill prepared to living sustainably. for example, they argue that relative values-valuing status rather than absolute quantities of goods-would have been adaptive in prehistory, but has become maladaptive for sustainability in the contemporary world. in the present paper, we understand the traits described by van vugt et al. ( ) as pre-adaptations that are exploited by cultural evolution. aet proposes that humans are predisposed for unsustainability through their biological and cultural evolution. specifically, aet proposes that human unsustainability has evolved via a multi-level selection process (see waring et al. ( ) for a relevant overview of multi-level selection) acting on the genome and occurring in concert with selective and non-selective mechanisms acting on culture and technology. in aet, this process results in a species that is prone to niche construction and ecosystem engineering, and the scale of these processes continues to increase as the population rises. this increasing scale coupled with human propensity for niche construction leads to human unsustainability (ellis ; ellis et al. ) . here, we hypothesize that humans have evolved to increase their carrying capacity (scale) by increasing their rate of energy extraction from the environment. this hypothesis is identical to that of aet, with the exception that it emphasizes the cause of the process (maximization of energy extraction) rather than the mechanism (niche construction and ecosystem engineering). that is, niche construction and ecosystem engineering are two possible mechanisms by which humans maximize their extraction of energy from the environment. because the substrate of this evolution is cultural and technological as well as genetic, it outpaces the ability of the ecological system to evolutionarily respond. the human and non-human ecological systems are thus locked in a form of red queen coevolution (van valen ; stenseth and smith ) , but human technology evolves faster than the biotic ecological system's ability to keep up. the red queen hypothesis is often invoked to describe coevolutionary systems in which one species coevolves to keep up with selective pressure from another species or species group and in which there is a difference in the evolutionary rate of the coevolutionary partners (e.g., pathogens and their hosts). here, we adapt the red queen to include coevolution between a species (humans) and the biotic components of the ecosystem (the biosphere). thus, we hypothesize that as human population size increases, human populations demand more energy from the environment. this places a selective pressure on the biotic environment, because energetic resources are limited and because of the nd law of thermodynamics, energetic resources are zero-sum; that is, if humans consume energy from the environment, there is necessarily less energy available for other organisms. however, the human population evolves via techno-cultural evolution, which is far faster than the biotic environment can evolve via genetic evolution. thus, the analogy between a fast-evolving parasite (humans) and a slow-evolving host (the biotic environment) is apt. note that we do not intend to imply that the environment itself coevolves with human techno-cultural evolution, but that the biotic populations that compose the ecosystem evolve, with consequent impacts on the abiotic environment (but see lovelock and margulis , levin , swenson et al. . while the conceptual differences between aet and the present hypothesis are modest, there are important differences in their implications. ellis's aet proposes that humans are somewhat unique, because we are expert ecosystem engineers and niche builders. the present hypothesis suggests the alternative. humans, just like all other species, maximize their energy extraction from the environment. just like all other species, humans are opposed in this process by a coevolutionary response in the biotic components of the ecosystem. humans are unique only, because the rate of cultural evolution in energy extraction exceeds our biotic environment's coevolutionary response. in this view, human unsustainability is a result of our uniquely advanced culture coupled with our non-unique drive towards for energy maximization; any species that developed a similar rate of cultural evolution would behave similarly. niche building and ecosystem engineering (ellis ) or agriculture (gowdy and krall ) are simply the means by which we maximize energy extraction from the environment. natural selection works to maximize the number of offspring an individual contributes to a following generation (i.e., fitness). however, energy and fitness are closely linked, because fitness is the result of a physiological process by which energy is captured from the environment and converted into offspring. that is, growth and reproduction at either the group or individual level require energy input from the environment coupled with high entropy waste output to the environment. this physiological understanding of fitness has been well studied in non-humans and is the foundation for much of life history theory [e.g., (weiner , garland jr and carter , ricklefs and wikelski ]. in this context, pianka ( ) argued that, "…natural selection will usually act to maximize the amounts of matter and energy gathered per unit time." brown et al. ( ) likewise offered an energetic definition in which fitness is "reproductive power, or the rate of conversion of energy into offspring." this reproductive power was taken to be a function of both the rate of assimilation of energy from the environment and the rate of conversion of energy to offspring (but see (kozlowski ) ). based on brown et al.'s definition, fitness (f) of individual i is a function of energy extracted (x) from the environment and the efficiency of energy conversion to offspring (e): where f is offspring number per lifetime, x is in calories extracted by the individual over its lifetime, and e is offspring produced per calorie. in this model, fitness is on the individual level, but identical logic applies at the group level, assuming heritable group variation in x or e. this physiological understanding of fitness is tautological when applied to non-humans, because the only source of energy non-human organisms use is somatic. for example, applied to a lion, eq. simply argues that the lion's offspring number is the total number of calories it eats multiplied by its offspring number divided by the number of calories it eats. however, both x and e can be selected independently, given heritable variation. that is, lions could be selected for better foraging ability (increased total energy gain from the environment), or for more efficient foraging, digestion, metabolism, etc. (increased efficiency). unlike non-humans, humans can use extra-somatic energy sources (e.g., fossil fuels), and can convert those energy sources into genetic fitness. for example, humans can burn savannas to harvest game (scherjon et al. ) , burn forests to create terra preta (glaser et al. ) , and reform fossil fuels to create fertilizer; all of these uses of energy use non-trophic energy to indirectly increase fitness. thus, for humans x and e are not limited by photosynthesis and respiration as they are in non-human populations. we hypothesize that humans have been selected for increased x and e and that this may have occurred through a combination of individual selection acting on genetic/ behavioral traits that favor high individual x, as well as group selection favoring groups which, due to their genes, culture, or technology, more rapidly absorb energy from the environment and convert that energy to fitness. we hypothesize that this selection has acted to increase both somatic x (e.g., food) and extra-somatic x that can contribute to fitness (e.g., fossil fuels). we hypothesize that humans have been preferentially selected to maximize x rather than e, that this is the cause of our predilection for socio-ecological crisis, and that this preferential selection on x occurs because of thermodynamic limits on the change in e. furthermore, even selection for increased resource efficiency can lead to increased environmental impacts. as resources are more efficiently converted into fitness, population size increases which in turns leads to increased absolute resource use. this is analogous to jevons' paradox and the ideas of steady state economics which propose that even increased energy efficiency can result in increased environmental impacts through increased economic growth (daly and cobb jr ) . at the individual level, we can see the impacts of selection to maximize energy extraction in human social behavior (penn ) . as we accumulate more energy from the environment, demonstrated socially in the form of material possessions, we improve our status in the group and presumably improve our mating success (kruger ; sundie et al. ). this might apply both to indirect material indicators of energy gain (e.g., objects) as well as direct physical indicators of energy gain [e.g., body mass as an indicator of male attractiveness (swami and tovée ) ]. of course, the aggregate accumulation of material possessions and status comes at an environmental cost. we use energy and materials to create and obtain status bearing objects (cars, houses, jewelry, clothes, etc.), and this resource use results in high entropy wastes output to the environment. thus, one way to understand our socio-ecological crisis is as a result of ancestral selection acting at the individual level and favoring social dominance expressed via the accumulation of embodied energy (odum ) . this adapted drive to accumulate material and embodied energy is a preadaptation for environmental extraction which is exploited by later cultural evolution (van vugt et al. ) . genetic selection might also operate at a group level (wilson and sober ) . in this case, groups of individuals that can more effectively accumulate resources outcompete groups that cannot or do not. if there is heritable (genetic) variation in the efficiency of resource extraction or resource use, these traits would be selected for (we consider nongenetic mechanisms in the next section). as in eq. , the fitness of the group is a function of the group's ability to extract energy from the environment and the group efficiency of conversion. for example, groups of hunter-gatherers that hunt more effectively due to genetic mutations in social intelligence might be selected over groups without such traits, even if the trait exhibits a cost at the individual level. see henrich ( ) for a discussion for both the potential and limits of genetic group selection. we might view human social organization in general in this lens: social organization exists to maximize the extraction of energy from the environment to the group and individual (x), and the efficiency of the conversion of extracted energy into offspring (e). this is identical to the claim that social organization exists to maximize the fitness of the group (wilson and sober ) and/or the individuals which compose the group (nowak et al. ) , given an energetic definition of fitness. what is unique is the implication. if social organization acts to maximize group fitness (or the fitness of individual group members), and if fitness is dependent on energy extraction from the environment, then social organization results in increasing energy extraction from the environment. again, either increased x or e leads to environmental unsustainability, and thus social organization is an evolutionary cause of the socioecological crisis. multi-level selection theory argues that the phenotypes, particularly social phenotypes, observed in nature can be understood as the result of a selective process that acts on both individual and higher levels of social organization simultaneously. in multi-level selection theory, it is the balance of variance and selective pressures at the group and individual levels that determine the genotypes and phenotypes that result. multi-level selection is increasingly used in biology as a means of explaining insect social behavior nowak et al. ( ) safarzyńska et al. , waring et al. , brooks et al. . one of the traditional weaknesses of multi-level selection theory is that ancestral human groups seemed poorly suited to maintaining the genetic variance between groups required for group-level selection (henrich ). however, selection is not limited to genetic transmission. cultural group selection posits that culture, rather than genes, is the source of heritable variation on which selection acts at the human group level. because there are differences in the transmissibility and variance generation between cultural and genetic inheritance, the maintenance of cultural variation across groups is more plausible (henrich ; bell et al. ; waring et al. ) , thus the attraction of group-level cultural selection as a means of explaining human traits. table describes the levels of selection acting to create human unsustainability and speed with which they act. the strength of selection is a function of the heritable variation in a trait and the trait's association with fitness (henrich ; freeman and herron ) . the speed of selection is a function of its strength and the generation time (van valen ) . cultural group selection can be more rapid than genetic forms of selection, because cultural change does not need to wait for biological reproduction to change phenotypic ratios, and new cultural innovations can be added to the population through non-random guided mutation (perreault ; brooks et al. ) . we hypothesize that genetic, individual level selection for behavioral and psychological traits that increase x serve results in pre-adaptations for a form of gene-culture coevolution (feldman and laland ; ambrose ) that results in technology that further increases x. technologicalcultural evolution spreads via cultural group selection (or other non-genetic means of transmission) (cavalli-sforza and feldman ; mesoudi et al. ; claidière et al. ; jordan ) . as a result, technology might change far more quickly than natural systems can respond via natural selection (wilson ) . in species without technology or a technological culture, changes in x and e will occur on evolutionary time and within a biological system that will evolve in response to any evolution. that is, in the absence of culture and technology, all of the biotic components of the system are limited to gradual changes in gene frequencies over time such that the rate of change in one species can be adapted to by another species. in humans, cultural evolution may have been too fast for other species to respond (perreault ) . thus, another way to understand our socioecological crisis is as a result of our ability to increase k by rapid, non-genetic processes. this rapid increase in technology creates an unsustainable situation in which the human system changes faster than the biotic components of the nonhuman system can co-evolutionarily respond. by analogy to the genetic definition of evolution (change in gene frequencies over time), consider technocultural evolution to be the change in the frequency of use of a specific technology over time. this frequency can change extremely rapidly. for example, the frequency of automobile use in the early twentieth century increased from , vehicles registered in the u.s. in , to million vehicles years later (nakicenovic ). we hypothesize that societies that heavily employed automobiles might have experienced greater economic and population growth in this period than those that did not, extracted more resources from the environment, and increased their carrying capacity. thus, in the early twentieth century, the u.s. increased x through a change in technology and this change occurred far more rapidly than the non-human system could respond via coevolution. this technologically mediated increase in x in the early twentieth century u.s. resulted in an increased survival and reproduction in the u.s., resulting in increased population growth. however, as population and affluence grew, new sources of energy were required to support the larger population and its energetic (e.g., economic) expectations. despite the challenge of maintaining the product of x and e during the twentieth century, the u.s. did so. several factors contributed to this capability, but as the twentieth century progressed the increasing population increased the number of minds that could be dedicated to increasing x and e. this increased the rate of innovation which increased the rate of energy extraction, which increased the ability of the society to support the population. this positive feedback loop is at the core of the energetic aet hypothesis (fig. ). the result of genetic and cultural evolution for increased x is lotka's maximum power principle (lotka (lotka , . the maximum power principle states that open systems tend to maximize the rate at which they can absorb useful energy from the environment. systems do not necessarily maximize energy gain, nor do they minimize energy loss, but instead systems maximize the useable power (energy divided by time) absorbed from the environment (hall ) . this is similar to the argument expressed in the preceding sections, because x is a rate (energy per lifetime). therefore, to say evolution acts to maximize x is to say selection acts to maximize power from the environment, consistent with lotka's principle. note that odum and pinkerton (odum and pinkerton ; odum ) expanded lotka's work and their model might draw different conclusions about efficiency than those presented here (hall et al. ). here, we use the maximum power principle sensu lotka rather than odum. lotka ( ) writes: if sources are presented, capable of supplying available energy in excess of that actually being tapped by the entire system of living organisms, then an opportunity is furnished for suitably constituted organisms to enlarge the total energy flux through the system … in every instance considered, natural selection will so operate as to increase the total mass of the organic system, to increase the rate of circulation of matter through the system, and to increase the total energy flux through the system, so long as there is presented a unutilized residue of matter and available energy" ( - ) thus, lotka imagines a system which absorbs exergy x from its environment and sustains n subsystems. if x increases, lotka argues that n will change to take advantage of the increased x. humans have been able to repeatedly increase x via technology and as a result, we increase n. according to lotka, we are expected to continue to do so, "so long as there is presented a unutilized residue of matter and available energy." unsustainability arises, because humans have evolved to employ increasingly sophisticated means of finding new unutilized sources of matter and energy. empirical tests of the maximum power principle are limited, but extant (hall ; cai et al. ; delong ; li et al. ) as are criticisms (månsson and mcglade ) . perhaps the most relevant example of the maximum power principle comes from the neolithic revolution. bowles ( ) compared the energy efficiency of hunter gatherers to early farmers and found that the efficiency in terms of energy extracted per unit of labor was higher for huntergatherers than for farmers (see also ponting ; smil ) . this led bowles to conclude that non-energetic factors explain the transition to agriculture. however, according to lotka, natural selection favors maximum power (energy per unit time) rather than maximum efficiency (energy per unit input). early farmers were able to extract more energy from the environment per unit time than hunter gatherers and this explains the success of the neolithic revolution. that is, in a given year (time), a farming society could extract more energy than a hunter-gatherer society (ponting ; smil ) and could convert this energy to fitness. thus, the transition to agriculture is consistent with the maximum power principle even while being inconsistent with explanations based on labor or energy efficiency. lotka stipulated that just because natural selection will act to maximize power flow through a system, evolution will not necessarily follow due to a lack of variance in the phenotypes leading to increased power flow; he called this variance "generating influences". we propose that human technology and culture is the primary generative influence that allows humans to obey the maximum power principle. in nonhumans, metabolic systems are highly conserved across species such that the same molecular pathways are present in diverse taxa. respiration, for example, is similar in plants, fungi and animals. this conservation is due to the lack of generative influence (variance) in respiration efficiency and results in a thermodynamic limit to the efficiency by which one generation can create the next generation. as a result, the evolution of e is limited. likewise, in non-humans, the evolution of x is limited by coevolution such that every adaptation that increases x in one species acts as a selective pressure on another species. using non-somatic energy, humans have freed x and e from these limitations, however, we hypothesize that there is more variation in the ability to capture energy flow into the system than in the efficiency of energy conversion. energy efficiency is limited by thermodynamic limits, while energy extraction is, because of rapid evolution through culture and technology, freed from the effects of coevolutionary responses. in other words, it has been easier for the system to evolve towards energy extraction than to evolve to energy efficiency. for example, we might expect that the rate of increase of global wood extraction will exceed the rate of increase in wood-fired energy efficiency. similar hypotheses could be generated for other fuels. human carrying capacity (k) is not a fixed quantity, but an emergent property of the earth system of which humans are a part (sayre ; chapman and byron ) . that is, k is not exogenous to humans but determined by the technology and behavior of humans interacting with climate, biodiversity, and biogeochemical cycles. over the past several centuries, humans have repeatedly increased k using technology to increase our extraction of energy and materials from the environment and to more efficiently convert those energy and materials into fecundity and survival. thus, selection has acted on individuals and groups to preferentially favor those groups that more rapidly increase the group-experienced k. in other words, carrying capacity is a group-level phenotype that is an important target of selections and, in humans, emerges from the interaction of genes, culture, technology and environment. we hypothesize that if there was heritable cultural or genetic variation in social ability to increase k, humans will have been selected towards increased k. that is, in the absence of top-down regulation, human populations have been selected to overcome bottomup regulation via genetic and cultural evolution. more formally, assume a discrete population growth system in which generation t + is composed only of the offspring of generation t (that is, generation t yields generation t + and dies). in this case where n t is the population size at time t and f is fitness as defined in eq. . thus, population size is simply the sum of all individual fitness. substituting from eq. : that is, the population in the next generation is the sum of all of the energy extracted by all members of the population, multiplied by each individual's conversion efficiency. assuming the population is at k, n t equals n t- , and k equals n t . therefore at the individual level, we assume that there is heritable (genetic) variation in either x or e. as this heritable variation is selected for, k increases, because they are positively related. at the group level, we suppose that each group experiences a local k, and a group-level x and e, and that there is heritable, between-group variation in x and e. in this case, groups with higher x or e would increase k, thereby increasing their population size. the increased population size relative to other groups implies might allow for social dominance which could increase the rate of spread of the genes and technologies used to increase x. the ability of a species to shift its carrying capacity is critical. if k is exogenously determined, selection cannot act to increase the extraction of materials and energy from the environment, because this has already been maximized. however, if k is endogenously determined, that is, if a species can determine its k through culture and technology, then we hypothesize that there may be cultural or genetic selection towards increasing k. the increase in k would, in turn, allow the population to expand to this new k, again placing a selective pressure on the population. however, the population is now larger with greater collective cognitive power and even better adapted at increasing k. thus, we might expect the rate of increase of k to increase over time ( fig. ; see meyer and ausubel ( ) ). this is analogous to an increase in the total frequency of mutation in a population as population size increases. as the size of a population increases, the probability of any given beneficial mutation increases in each generation. likewise, as the size of the human population increases, the probability of innovation also increases as the number of brains that may be dedicated to innovation increases. to illustrate the argument, we built a simple simulation population model that tracks population growth, energy extraction and the evolution of carrying capacity. the model is based on a standard discrete population growth model in which energy extraction from the environment replaces carrying capacity. thus where r is the intrinsic growth rate and is equal to f from eq. , x max is the energetic carrying capacity of the system and x t is the total population energy extraction. in other words, x max and x t substitute for k and n t in a standard discrete population growth model (as in eqs. and ) . fig. rate of change of k decreases as population size increases due to increasingly rapid technological innovation is determined by both by the energy available in the environment and the technology used to capture that energy. therefore, x max can change via technological innovation. we propose that the change in x max is a linear function of population size; however, we also propose that x max is more likely to change as x t approaches x max . that is, as the total energy extracted by the population nears the maximum energy available for extraction, it creates a selective pressure to increase x max . therefore, we define the probability of innovation, p, at time t as the coefficient . indicates that we assume a % chance of innovation per person per generation. the model generates a random integer between and and compares the random number to p t . if p t exceeds the random number, innovation occurs and x max increases by %; otherwise x max stays constant. changes to x max are assumed to be positive and permanent. substituting eqs. and into eq. and solving for x t yields where f and e are as defined in eq. , above. for this illustration, we assume that e is fixed at × - offspring per kcal and x i is fixed at × kcal per generation. these assumptions yield an r (or f) of . results of simulations are depicted in fig. . unsurprisingly, the energetic carrying capacity, x max , increases over time, indicating increasing environmental load on the however, the rate of increase of x max also increases over time. figure shows the mean x max from the simulations depicted in fig. , with a best-fit exponential equation. the fact that the relationship between generation number and x max is exponential, suggests that the rate of increase in energy extraction will itself increase over time. unless the biotic ecosystem can co-evolve to limit this increasing energy extraction, an unsustainable situation will result. note that this model does not include top-down factors such as parasites and pathogens that may act to limit human populations. parasites and pathogens may represent one way in which the biotic system can co-evolutionarily "keep up" with the techno-cultural evolution of the human system. the model we presented is not intended to explain socioecological collapse per se, but rather the human propensity towards unsustainability and socio-ecological crisis, which may lead to socio-ecological collapse. nonetheless, some of the critiques of the concept of socio-ecological collapse may be help clarify our argument. tainter ( ) argued that the role of ecological change in socio-ecological collapse is historically unsupported. instead, tainter attributes the collapse of ancient societies principally to social failures. for example, tainter ascribes the collapse of the sumerian population around ur in the late third millennia b.c.e. to poor irrigation practices combined with a failure of leadership to recognize the worsening agricultural situation. thus, tainter might disagree that population growth and environmental energy extraction were the primary causes of the collapse of sumer. however, phrased in the context of carrying capacity evolution, tainter is suggesting that the carrying capacity declined due to salinization of the soils, which was in turn a consequence of poor soil management. from our perspective, the decline in k was only possible, because k had been inflated by unsustainable irrigation practices. that is, societies use technology to increase x max (and thus k) and their populations grow accordingly. in some cases, societies might use this new technology to extract too many resources and the population might overshoot k with negative consequences; deforestation or prey extinction might be examples. in other cases, populations may not overshoot k, but k might decrease below the population size, because the system used to increase x was unsustainable (e.g., dryland agriculture in sumer). in either case, the "ecological" in socio-ecological collapse is critical. we propose that human populations face two problems related to carrying capacity evolution. first, continued increases in k may become increasingly difficult due to thermodynamic constraints, eventually leading to a situation in which the human population exceeds carrying capacity and the population collapses. second, increases in k may not be permanent and may depend on unsustainable extraction of energy and embodied energy from the environment. in this case, the population may not overshoot k but may nonetheless exceed k when k declines and experience collapse. butzer ( ) proposes socio-ecological collapse begins with economic and fiscal decline over decadal to centennial timescales, coupled with and precipitating economic crises at decadal timescales. butzer proposes that many of these economic and fiscal conditions are ecologic, for example, declining agricultural productivity and anthropogenic degradation, while others are socio-economic (economic depression; foreign attacks). however, from the perspective of the energetic version of aet described above, nearly all of the preconditions and triggers described by butzer are energetic and ecologic. this is due to the thermodynamic linkage between economic activity and energy (georgescu-roegen ; daly ) . that is, all economic activity implies the dissipation of energy so that when butzer identifies "economic depression" as a trigger for socio-ecological collapse, this implies that human societies are no longer able to extract energy from the environment and convert that energy into economic activity as they had in the recent past. similarly, when butzer identifies "foreign attacks" as a stimulus for collapse, the energetic-aet model proposed here sees invasion and conflict as a mechanism for extracting increasing quantities of energy from the environment and thereby increasing k. energetic-aet has implications for the ecomodernism versus technological pessimism debate and the interconnected environmentalist's paradox. the environmentalist's paradox is the observation that human wellbeing seems to be improving in the face of declining natural system wellbeing. raudsepp-hearne et al. ( ) both defined the environmentalist's paradox and evaluated four potential explanations for it. the four non-mutually exclusive potential explanations were that: ( ) human well-being has been measured improperly; ( ) human well-being is dependent only on food-related ecosystem services which have increased; ( ) technology has decoupled human well-being from ecosystem services; and ( ) time lags have insulated contemporary populations from future declines. while a complete critique of their analysis is beyond the scope of the present article, raudsepp-hearne et al. argued that human well-being has not been evaluated improperly but could not reject the other three hypotheses. alternatively, energetic-aet proposes that humans have been able to avoid the negative social impacts of environmental perturbation by increasing their energy demand on the environment. contra explanation ( ), technology has not decoupled human dependence on ecosystem services, but shifted which ecosystem services we depend on and increased our dependence on them. specifically, humans have used energy subsidies in the form of fossil fuels, renewables and nuclear energy to compensate for declines in energy flows from natural systems. for example, humans use energy in natural gas to reduce nitrogen for fertilizer production. human wellbeing increases, because energy extraction has increased faster than population growth such that per capita primary energy consumption increased from kg of oil equivalent per person in - kg of oil equivalent per person in . consequently, human wellbeing has increased. the suggestion that humans typically live on a continuum of unsustainability as depicted in fig. may seem inconsistent with the observed sustainability of some indigenous societies (trosper ; campbell and butler ) . nonetheless, it is a consequence of the present hypothesis. to phrase the energetic aet hypothesis in the language of game theory, we hypothesize that the evolutionary stable strategy of human societies is maximized and increasing rates of energy extraction. cases of sustainability in which societies fail to increase their energy extraction from the environment-as in some indigenous societies-are hence viewed as temporary, evolutionarily unstable strategies that will be outcompeted and replaced by more extractive strategies. this suggests a testable hypothesis: that societies with higher, less sustainable rates of energy extraction have outcompeted those with lower, more sustainable rates of energy extraction. note that evolution in general, and cultural evolution specifically, is value-neutral (sommers and rosenberg ) , so while it may be troubling to view sustainable cultures as evolutionarily unstable, this does not falsify the hypothesis. the model discussed here assumes human carrying capacity is controlled by bottom-up factors, specifically energy extraction from the environment (hopfenberg ) . as the global sars coronavirus- pandemic of demonstrates, humans are also susceptible to top-down population regulation by pathogens, as human pathogens may be one of the few parts of the ecosystem that can evolve as rapidly as human techno-culture. thus, human carrying capacity may be limited both by energy gain from the environment and by disease. future researchers may attempt to integrate disease evolution into the feedback loop, as depicted in fig. . all else equal, as population density increases, pathogen virulence may be expected to increase (van baalen and sabelis ; lively ; mennerat et al. ; borovkov et al. ) , suggesting that pathogens may place a constraint on the feedback loop in fig. . however, the evolution of pathogen virulence is complex and depends on ecological and genetic factors in both the pathogen and the host and the history of interactions between the two (knolle ; antia et al. ; levin ) . furthermore, the germ theory of disease, vaccination, and the development of antibiotic represent techno-cultural changes in how many human societies responded to pathogens, and this change may be positively associated with population density and energy extraction from the environment. thus, it may be interesting for future scholars to explore if pathogens act to limit population growth and energy extraction, or if technological innovation and population density have acted to remove the ability of pathogens to function as top-down population regulators. understanding how societies transition from unsustainable to sustainable states may be one of the most important questions in environmental social science in the twenty-first century. while such research is ongoing, less effort has focused on understanding why human societies are generally unsustainable in the first place. we propose that human societies are prone to unsustainability, because they have evolved to maximize their rate of energy extraction from the environment through a multi-level selective process acting on both genetic and cultural heritable variation. specifically, genetic evolution at the individual level creates behavioral pre-adaptations (van vugt et al ) that works with cultural group selection to favor traits and technologies that increase energy extraction per unit time. this increased energy extraction is used to support increased population sizes and this increased population size further improves the ability of the group to innovate new means of energy extraction, leading to a positive feedback loop that is the ultimate cause of human unsustainability (recall fig. ). cultivation of cereals by the first farmers was not more productive than foraging applying cultural evolution to sustainability challenges: an introduction to the special issue evolution of body size: consequences of an energetic definition of fitness collapse, environment, and society critical perspectives on historical collapse the maximum power principle: an empirical investigation archaeological evidence for resilience of pacific northwest salmon populations and the socioecological system over the last ~ years cultural transmission and evolution: a quantitative approach how darwinian is cultural evolution unifying research on social-ecological resilience and collapse steady-state economics: with new essays for the common good: redirecting the economy toward community, the environment, and a sustainable future the population bomb revisited. electron ecology in an anthropogenic biosphere evolving the anthropocene: linking multi-level selection with long-term social-ecological change gene-culture coevolutionary theory evolutionary analysis. pearson prentice hall, upper saddle river garland t jr, carter p ( ) evolutionary physiology energy and economic myths the'terra preta'phenomenon: a model for sustainable agriculture in the humid tropics the ultrasocial origin of the anthropocene agriculture as a major evolutionary transition to human ultrasociality the economic origins of ultrasociality the continuing importance of maximum power cultural group selection, coevolutionary processes and large-scale cooperation human carrying capacity is determined by food availability ancient deforestation revisited technology as human social tradition: cultural transmission among hunter-gatherers archeological and environmental lessons for the anthropocene from the classic maya collapse host density and the evolution of parasite virulence energetic definition of fitness? yes, but not that one male financial consumption is associated with higher mating intentions and mating success the evolution and maintenance of virulence in microparasites ecosystems and the biosphere as complex adaptive systems the maximum empower principle: an invisible hand controlling the self-organizing development of forest plantations in south china the ecology of virulence wood overexploitation and the collapse of cahokia. foraging farming east woodl note on the economic conversion factors of energy contribution to the energetics of evolution atmospheric homeostasis by and for the biosphere: the gaia hypothesis ecology, thermodynamics and ht odum's conjectures intensive farming: evolutionary implications for parasites and pathogens perspective: is human cultural evolution darwinian? evidence reviewed from the perspective of the origin of species carrying capacity: a model with logistically varying limits tr malthus: principles of political economy the automobile road to technological change: diffusion of the automobile as a process of technological substitution the evolution of eusociality environmental accounting: emergy and environmental decision making time's speed regulator: the optimum efficiency for maximum power output in physical and biological systems the evolutionary roots of our environmental problems: toward a darwinian ecology the pace of cultural evolution salles-filho s, da silveira j ( ) an evolutionary approach to technological innovation in agriculture: some preliminary remarks energy and human evolution ecosystem service bundles for analyzing tradeoffs in diverse landscapes cultural group selection plays an essential role in explaining human cooperation: a sketch of the evidence the physiology/life-history nexus evolutionary theorizing and modeling of sustainability transitions evolving power and environmental policy: explaining institutional change with group selection the genesis, history, and limits of carrying capacity burning the land: an ethnographic study of off-site fire use by current and historically documented foragers and implications for the interpretation of past fire practices in the landscape what did lotka really say? a critical reassessment of the "maximum power principle energy and civilization: a history darwin's nihilistic idea: evolution and the meaninglessness of life coevolution in ecosystems: red queen evolution or stasis? peacocks, porsches, and thorstein veblen: conspicuous consumption as a sexual signaling system male physical attractiveness in britain and malaysia: a cross-cultural study artificial ecosystem selection archaeology of overshoot and collapse northwest coast indigenous institutions that supported resilience and sustainability the dynamics of multiple infection and the evolution of virulence a group selection perspective on economic behavior, institutions and organizations a new evolutionary law evolutionary naturally green: harnessing stone age psychological biases to foster environmental behavior the coevolution of economic institutions and sustainable consumption via cultural group selection a multilevel evolutionary framework for sustainability analysis physiological limits to sustainable energy budgets in birds and mammals: ecological implications reintroducing group selection to the human behavioral sciences an evolutionary theory of largescale human warfare: group-structured cultural selection the author is grateful to leslie ruyle, jason lang, and two anonymous reviewers for their invaluable feedback on this manuscript. ambrose sh ( ) coevolution of composite-tool technology, constructive memory, and language: implications for the evolution of modern human behavior. curr anthropol :s -s antia r, levin br, may rm ( ) key: cord- -otbiiybs authors: lacey-barnacle, max title: proximities of energy justice: contesting community energy and austerity in england date: - - journal: energy res soc sci doi: . /j.erss. . sha: doc_id: cord_uid: otbiiybs spatial inequities are deeply embedded in low-carbon energy transition processes. as a result, new forms of contestation are emerging that reveal social inequalities at the heart of community-led responses to climate change. this paper uses four tenets of energy justice – distributional, procedural, restorative and recognition justice – to critically analyse and understand the politics and geography of local renewable energy deployment in bristol, england. focusing on the development of two solar pv farms in and around lawrence weston, an area of high deprivation in north west bristol, the paper demonstrates the critical nature of instances of both energy justice and injustice in a time of austerity. using primary data obtained via a participatory action research (par) approach in bristol during – , the paper draws on participant observation data and in-depth interviews (n = ) with a variety of local energy actors and community members active in lawrence weston. the primary data details the extent to which spatial configurations of new low-carbon energy infrastructures are integral to their justice implications. indeed, it is the proximity of projects both close to and within the lawrence weston community that shapes the participant’s thoughts and deliberations on how to achieve local energy justice, through appeal to the four tenets outlined. the findings emphasise the distributional justice impacts of creating new low-carbon energy infrastructures in deprived communities in a time of austerity, whilst also noting that ‘opening up’ local energy transitions to greater input from local communities’ offers opportunities to achieve procedural justice. shifting relationships between local energy actors and lawrence weston highlight opportunities for the remediation of past claims of injustice, facilitating processes of restorative justice, whilst local energy schemes that seek to advance greater ‘active participant’ (skills training & employment) opportunities for deprived communities in which they, or their projects, are embedded, may be underpinned by recognition justice concerns. this ‘active participant’ approach is shown to be key to advancing beyond ‘passive recipient’ approaches to community energy transitions and enhancing spatial equity. finally, the paper offers novel empirical insights into the contested role of geography, space and place in local transitions and contributes to bottom-up perspectives on issues of spatial (in)justice in community energy schemes. as policy responses to the challenge of anthropogenic climate change continue to intensify across the world, a new geography of lowcarbon energy infrastructures is rapidly emerging [ ] [ ] [ ] . while these new infrastructures operate at multiple sites and across many scales, reflecting a broad diversity of low-carbon technologies, local actors, such as community and civic energy organisations, are embedding new energy technologies within their communities in an era of growing energy decentralisation and distributed energy generation [ ] [ ] [ ] . this process of energy decentralisation has been gaining traction across the uk for over a decade, with both community energy [ ] and civic energy sector [ ] actors increasingly engaging in energy markets still dominated by market players that have formed an oligopoly over the uk energy market [ ] . one uk energy minister famously stated that the government was keen to see a shift from the 'big six to the big , ' [ ] , noting a trend towards a diversification of energy market competition and the proliferation of a new set of local energy market actors [ , ] . however, energy decentralisation has grown in complexity and in scope, featuring a variety of cross-sectoral actors collaborating across multiple levels of governance [ , ] . rather than being a core focus of uk energy policy, it is still somewhat marginalised and lacking a comprehensive regulatory framework and strategic direction. in addition, the uk policy framework for decentralised energy has begun to shift away from community energy towards 'local energy' more broadly, in which partnerships between public and private actors, alongside emphasis on the role of local authorities, play a key role in energy decentralisation initiatives and processes [ , ] . such developments in decentralised energy markets and the rapid growth of renewable energy technologies have been spurred in part by legislative developments, such as the eu renewables directive , the energy act and the uk climate change act , that have ensured an increase in renewable energy generation capacity through subsidy schemes supporting renewables and decarbonisation targets aiming at significantly lowering the uk's carbon footprint by [ ] . the introduction of the uk's feed-in tariff (fit) scheme in , in particular, has supported the growth of community renewables projects focused largely on solar [ ] and wind energy [ ] , as it provides guaranteed -year payments for the generation of renewable electricity. in addition, the cost of renewable energy technologies, such as solar pv and wind turbines, has been significantly reduced in recent years, with commercial-scale renewable energy power generation set to be cost-competitive by - [ ] . this is due, in part, to their rapid uptake within global energy markets over the past decade, the creation of new economies of scale and global systems of production supporting widespread market penetration and increased global investment [ , ] . while a new host of actors, institutions and market players are set to benefit from this transition, we are simultaneously living in an era of unprecedented social and economic inequality [ ] . thus, when seeking to explore the various ways in which climate change and social inequality intersect, it is vital to contrast the new wave of innovation, economic prosperity and era of growth brought about by the lowcarbon transition, with the worsening of social inequality in contemporary society. such a contrast is particularly pertinent to the uk. at the same time as renewable energy generation reaches record highs [ ] , alongside low-carbon energy generation accounting for the majority of electricity production in the uk [ ] , austerity measures have reconfigured the social landscape of the uk. austerity -seen here as a macroeconomic shift involving widespread fiscal cutbacks of state spending that has been definitive of both uk politics and local-level politics since -has been widely criticised for its divisive impact on society and negative impact on social equality generally [ , ] . recent research shows that social inequality has worsened in the uk, as central government has pursued an austerity agenda that drastically cuts back vital public expenditure for services such as education, health and welfare provision. over the last decade, this austerity agenda has been shown to be devastating for low-income families, communities and regions across the uk [ ] . thus, in a context where the uk has one of the highest levels of inequality amongst the developed oecd countries, policy research points towards evidence of huge wealth disparities in the uk; the richest % of the uk population are wealthier than the poorest % combined [ ] , million people have been classed as living below the uk poverty line [ ] and a 'cost of living crisis' has meant that the poor have become worse off in recent years, as 'income inequality has fallen back to levels last seen one or two decades ago' [ p. ] hood and waters [ ] predict that income inequality is projected to rise between the period - , while uk poverty rates are to remain roughly unchanged during the same period. however, the onset of a new economic crisis brought about by the covid- pandemic is drastically reshaping future forecasts for increases in social inequality, whilst also exposing a multitude of existing inequalities in the uk through disproportionately affecting the worst-off [ ] . combining the critical nature of the above areas presents new terrain for researchers at the interface of low-carbon energy transitions and social science research, as critical questions around the spatial distribution of new energy infrastructures and their embedding within landscapes of social inequality and material deprivation [ ] present new challenges to those seeking to mitigate against the worsening of social inequality as a result of energy transition processes. existing research that examines the interplay between new local energy systems and deprived communities demonstrates the relatively exclusive aspect of localised energy schemes, with more affluent communities with the necessary time, resources and capacity typically most likely to engage in, benefit from and develop their own local low-carbon energy schemes [ ] [ ] [ ] . however, there is also emerging research that looks at the opportunities and benefits for low-income and deprived communities that are arising from low-carbon transition processes [ ] , such as the material and wellbeing benefits arising from home energy efficiency schemes [ , ] , advice provision to low-income areas on energy usage /bill reduction [ ] and revenue generation from subsidy-backed renewables deployment [ ] which feeds into the development of 'community benefit funds' to support local organisations and local economies [ , , ] . in a highly unequal society/societies, the spatially uneven distribution of such low-carbon transition processes and the ability of disparate and divergent communities to benefit from such processes reflects a form of social inequality previously unseen and little explored. thus, this paper offers novel insights into new forms of social and spatial inequality -and opportunities to rectify and address those inequalities -that arise from local low-carbon energy transitions. in exploring this little researched terrain, the aim of this paper is to draw upon energy justice theory to investigate the broad social impacts of low-carbon transitions in bristol city, in a time in which increased public funding cuts and fiscal austerity measures are adversely affecting social inequality. in seeking to contribute this original insight, the paper draws on a distinctly spatial approach to understanding the interplay between an increase in local energy generation via energy decentralisation and social inequalities. thus, it is important to briefly address what previous and current literatures have had to offer when critically analysing local energy schemes. catney et al [ ] , in a powerful study of two different communities' engagement in energy schemes in the west midlands in england, critically explored the social impact of community-led energy schemes. seeing that highly unequal capacities for differing communities to engage in local energy schemes would be critical for their initiation, the authors suggest undertaking what they call a 'reality check' when exploring the potential for a deprived locality or community to engage in low-carbon energy generation projects [ ] . in this, they put forward three different points of analysis; taking stock of a community's social capital; assessing community capacity and understanding their cultural capacity, as they note that 'for people living in poverty in deprived areas, personal responsibility for carbon emissions may be the furthest thing from their minds' [ p. ] . additional analysis of catney et al.'s [ ] case studies drawn from the west midlands, in which they compare two relatively affluent wards to two highly deprived wards, sheds light on the critical importance of geographical differences and disparities underpinning socio-economic inequalities. indeed, bridge et al [ ] see energy transitions themselves as a fundamentally geographical process, arguing that the energy transition 'pathways' governments choose will shape the future geography of transitions. in their analysis of space and place in low-carbon transitions, they see the uneven and unequal landscape for the deployment of a diverse array of low-carbon technologies as embedded in 'spatial difference', emphasising that; there are significant opportunities […] for understanding the relationship between different trajectories of energy transition and the geographical conditions from which they emerge [ p. ] this spatial difference is not only intimately connected to a physical geography of resources, but also to the capacity of different regions, local authorities and communities to engage in energy transition processes. interestingly, more recent studies have taken this explicitly geographical focus and have integrated spatial justice [ ] approaches into energy justice. scholars have found that local and 'area-based' policy solutions have the potential to remedy geographically uneven patterns of energy injustice [ p. ] , whilst this geographical variation has been shown to be present in the spatially uneven deployment of renewable energy technology [ ] and in distributing the benefits of decarbonisation unevenly between households and localities [ ] . bringing these literatures together, bouzarovksi & simcock's [ ] call for scholars to acknowledge 'landscapes of material deprivation' when considering processes of energy injustice within energy systems, demonstrates strong connections to catney et al's [ ] analysis of the inability of deprived areas to engage in potentially beneficial forms of local energy activity. this highlights the socio-economic implications of bridge et al.'s [ ] 'spatial difference' and connects to de laurentis & pearson's [ ] examination of spatial unevenness and unequal local capacities in low-carbon energy transitions more specifically. additionally, while and eadson's [ ] analysis of socio-spatial disadvantages arising from decarbonisation processes evidences the disproportionate effect of rising energy prices and job losses on lowincome areas, whilst also shedding light on the relative exclusion of low-income households from benefitting from the fit scheme [ p. ]. building on these relations between space and energy injustice, golubchikov and o'sullivan [ ] and o'sullivan et al [ ] have introduced the concept of 'energy peripheries' that are integral to geographically uneven energy transition processes. connecting to notions of energy vulnerability and drawing on an analysis of unequal lowcarbon transitions in wales, both papers emphasise the extent to which transition processes reproduce distinctly spatial injustices and reinforce pre-existing spatial hierarchies. in addition, yenneti et al. [ ] demonstrate how the implementation of a large solar park in india leads to spatial injustices for vulnerable communities dependent on the land where the solar park is installed, highlighting a process of unjust land acquisition for renewable energy deployment as part of the low-carbon energy transition. it is apparent from these literatures, therefore, that space and place are integral features of unjust low-carbon energy transitions. thus, there are clearly strong overlaps and powerful interconnections at play when we see that the geographies of both social inequalities and the physical siting of new energy generation infrastructures are deeply interlinked. this also connects to previous insights derived from an explicitly geographical focus on environmental justice research, whereby 'first generation' understandings of environmental injustices relate to the close proximities of disadvantaged communities to the geographical site of environmental injustice [ ] . this overlap and interplay will only become more important for enhancing our understanding of energy policy responses to climate change as energy decentralisation continues to increase as a technological response to the mitigation of climate change, as well as featuring as an important component of the global energy transition. in order to make theoretical sense of this complex interaction between differing levels of community capacity and its relationship to spatial difference, an energy justice framework is drawn upon to help illuminate the core social aspects of the case study featured in the following sections. moreover, the first generation understanding of 'proximities' outlined above [ ] is drawn upon here and extended to the energy justice field, whilst also enriching energy justice perspectives on low-carbon transitions [ ] . thus, four principles of energy justice are used here to assist with this analysis; ( ) procedural justicerelating to the participation of people in energy-related decision-making processes; ( ) distributional justice -which concerns the sharing and distribution of energy system benefits and burdens; ( ) recognition justice -which seeks to ensure the acknowledgement of marginalised and/or disadvantaged groups in relation to energy systems, and ( ) restorative justice -a process of remediation in response to a perceived energy injustice [ , ] . in the analysis of the findings, these four tenets of energy justice act as thematic guides, providing a useful framework through which to sort, categorise and analyse the qualitative data collected. in addition, notions of 'space' and 'place' -and indeed ideas of 'spatial justice' -permeate throughout the research findings. next, this paper draws on the research methods used to engage with this vital theoretical overlap, using a bristol case study as a reference point. while this paper draws upon an energy justice framework to shed light on the interconnections between the geographies of both social inequalities and the physical siting of new energy generation infrastructures, the empirical data used to support this insight is derived from two of the traditional techniques of par -in-depth interviews (n = ) and participant observation. this data was collected over an -month period from mid- to early , forming part of the data collection process of a phd thesis [ ] . participant observation was used firstly as a means to gain familiarity with civic energy communities and networks in bristol and secondly, to record key discussions and occurrences at events in and around bristol. after attending many local events and connecting with various civic and community energy actors in bristol throughout and , appropriate participants were approached to gain a familiarity with all actors involved in the lawrence weston area of bristol after realising two energy projects were present within the area. in addition, it is vital to note that lawrence weston is one of the most deprived parts of bristol and in the most deprived % of areas in england [ ] , acting as a critical backdrop for advancing understandings of the empirical links between local lowcarbon transition initiatives and deprived communities. the case study mostly revolves around primary data collected during in-depth interviews with five key organisations present within bristol's civic energy network, focusing exclusively on their involvement with the lawrence weston community. these are; ambition lawrence weston -alw (n = ), low-carbon gordano -lcg (n = ), bristol energy co-operative -bec (n = ), bristol city council -bcc (n = ) and bristol energy network -ben (n = ). in addition, two solar pv projects associated with this case study, namely; lcg's -moorhouse solar array (msa) and bec's lawrence weston community solar farm (lwcs) are critical to the contestations at the heart of this case study. a total of interviews are featured in this case study, with one research participant featuring in two organisations. presented below, in table , is the identifier system for these organisations and actors, with unique identifiers assigned to each organisation and the associated participants interviewed, with anonymity ensured for all individuals involved. the data thus draws on research with and on civic energy actors in lawrence weston, however, the level of participation in the organisations themselves varied throughout the period of data collection. after integration into bristol's energy communities, subsequent attendance at for consistency in the definition of deprived communities, it is important to note that [ ] , state that the 'indices of deprivation have been produced using the same approach, structure and methodology used to create the previous indices of deprivation ′ [ ] , p. . ambition lawrence weston are a local regeneration charity set up in that seek to improve the lives of residents in the local area after a decline in local services. more information can be found here: https://www.ambitionlw. org/. the alw planning group meetings established deeper connections with lawrence weston residents, through forging links with key members of alw. despite this 'functional' level of participation in alw's activities [ ] , the in-depth semi-structured interviews, which lasted between and minutes, were conducted in a more classically 'extractive' fashion, where researchers seek to obtain knowledge and insight from key actors through a set of flexible pre-determined questions. however, room was given for research participant involvement in contributing understandings of local energy justice. while the participant observation technique was used to build connections to local energy communities, the in-depth interviews facilitated a much deeper conversation with research participants to explore the complexity of individual experiences and relationships between different organisations, alongside how these experiences and relationships relate to contesting local energy transitions and issues of local geography. in the in-depth interviews, participants expressed a shared interest in energy justice and saw the applicability of the theory in practice, offering their own interpretation of energy justice and describing how tenets such as distributional and procedural justice apply to their own experiences, activities and respective organisations. this collaborative approach to research contributes to local and bottom-up perspectives on energy justice and issues of spatial (in)justice in relation to community energy, one of the core contributions of the paper. in addition, the analysis offered in this paper was presented to members of alw (alw - ) and low-carbon gordano (lcg ) for feedback in april-june in the interests of transparency and accuracy, as well as to receive updates on the progress of alw and lcg. after this follow-up communication had taken place via email, the participants confirmed the accuracy of the paper and this continued communication also contributes to the participatory and open spirit of a par approach in academic research. given the 'local' scale of the paper's fieldwork, the use of par is intended to forward the energy justice and low-carbon transitions research agenda [ ] within bristol.theoretically, the paper also harnesses energy justice's analytical power to provide insights into the role of geography and its critical interconnections to social inequalities in local energy transitions. lastly, it is also important to acknowledge here the limitations of the data, as alw and alw are both lifelong residents of lawrence weston and active members of alw. in the presentation of the data below, both alw and alw are referred to as residents of lawrence weston and members of alw simultaneously, as they both occupy dual roles. finally, alw worked for both ben and alw in two separate roles, representing both organisations in the data presented. the origins of the case study stem from a heated debate between a resident of lawrence weston and a director of lcg. this was observed during the participant observation phase at an event in early held by ben in central bristol. during this event, one important recorded note summarised the nature of this dispute: this recorded dispute formed the foundation of this case study, proving critical to many of the topics discussed in the follow-up indepth interviews with actors from the five organisations outlined above. further activities that arose on the basis of this dispute also demonstrate tremendous resonance with different aspects of the three core tenets of energy justice, alongside the more recently proposed tenet of 'restorative justice' [ ] , expanded upon further in section . . . during the data collection period ( - ), the city council approved and supported the installation of two different solar arrays on council-owned land in and around lawrence weston -the 'moorhouse solar array' (msa) and the 'lawrence weston community solar farm' (lwcs). the msa, organised by lcg, consists of solar panels that produce enough annual electricity for around homes. with a £ minimum share offer, just over £ million pounds were raised through a community share offer developed by lcg in , and the project has been fully operational since april . the project received technical support from local renewables company solarsense (http://www. solarsense-uk.com/), based on the outskirts of bristol, and was praised by the then-incumbent mayor george ferguson, who also attended the launch of the new solar installation, pictured in fig. below: whilst the msa was widely supported as a key part of bristol's lowcarbon future, the project exhibited very little initial involvement with lawrence weston, despite its close proximity to the community, as detailed in fig. in contrast, the lwcs farm, organised by bec, is based on lawrence weston road and resides more decidedly 'within' the community's territory. the lwcs farm consists of . mw of annual solar generation capacity that is enough to power homes -close to double the capacity of the msa. the project has been fully operational since june and alongside a solar farm in puriton, is part of two of bec's key solar projects that raised over £ million in total through public share offers, with the opportunity to purchase a £ minimum share as part of this fundraising scheme. the lwcs farm received support from alw, as seen in fig. below: the lwcs farm was developed, in part, in reaction to claims of injustice by alw. as will be shown, bec partially reacted to the claims made by alw against lcg and against the city council's granting of planning permission to lcg in such a short timeframe, given their desire to be eligible for the fit rates at the time to ensure their business model worked and the rate of return to investors guaranteed. indeed, bec sought to create a more just solution to local energy deployment, and enhance engagement through an 'active participant' model, whileas will be explained further towards the end of the research findings -lcg have commendably attempted to involve themselves more closely with alw in response to these claims of energy injustice against lcg's development of the msa. underneath these shifting relationships and processes of remediation lie contestations over spatial injustice in the form of low-carbon siting dynamics [ ] . these siting dynamics fundamentally underpin the claims of injustice made against lcg by alw. as this paper will demonstrate, these justice claims are intimately tied to claims surrounding the proximity of projects and their closeness to the community of lawrence weston; a community that has felt as though it is on the geographical, economic and social margins of the city. moreover, lawrence weston is shown to be significantly affected by austerity through the powerful statements of the development manager at alw in section . as evidenced in the 'lawrence weston community plan' ( - ) [ ] , it is clear that the impact of austerity on the local area is a key consideration going forward: in the next five years we will face changes and challenges in lawrence weston. the government's ongoing austerity programme will undoubtedly result in more cuts to local authority spending. this means that bristol city council will provide fewer services and support for residents. it will also mean less funding and grants for organisations in the voluntary and community sector [ p. ] thus, the politics of austerity in the local area feature as a core concern for alw. drawing on secondary sources to generate further insight into the development of current and future relations between alw and lcg, the paper will demonstrate that it is the overtly geographical aspect of spatial proximities that informs the energy justice disputes at the heart of these transition processes. in addition, wider concerns about the economic impact of austerity on the local area, as demonstrated above, force into focus the emergence of new low-carbon activity in deprived parts of bristol, alongside the prospects of economic opportunity that this brings to new spaces and places in a time of austerity and economic crises. the following subsections address issues of both energy injustice and justice, detailing the extent to which participants from alw felt that processes of non-recognition, alongside a lack of inclusion within consultation measures around the installation of the msa, led to claims of both recognition and procedural injustice. after using recognition and procedural justice tenets to explore these tensions, the following subsections explore instances of energy justice through the lens of distributional and restorative justice, drawing on the impacts of the lwcs farm on lawrence weston in a time of austerity, as well as changing relations between alw and lcg. the following insights reveal the extent to which energy justice is capable of helping scholars to critically understand the complex nature of the politics of emerging local lowcarbon transitions in areas of high deprivation. as mentioned in the sections above, lawrence weston has long been recognised as an area of high deprivation and furthermore, is representative of some of the stark social, economic and geographical inequalities in bristol. as a result, the lawrence weston community has felt a sense of recognition injustice for some time, with persisting issues including crime, poverty, low quality housing, poor transport links into the city and high levels of unemployment. this sense of injustice connects quite intimately to issues of environmental injustice throughout lawrence weston's history. as fig. showed, lawrence weston is located close to avonmouth, an area that was historically a host to various industries in the mid to late th century, producing vast amounts of pollution that impacted upon surrounding areas. one local resident recalls how this industry and associated pollutants were once the norm amongst the local community: it's all dirty industry then so you had smelt works, you got britannia zinc, chemical plants and it was just accepted. back in the day that was it, you had these big funnels and they're bellowing out dirt, dust and other pollutants […] there wasn't a lot of concern given at that time because that was how people were working and getting a living. historically, air pollution and environmental injustice has been quite bad, really (alw ) as these industries began to go into decline or move operations elsewhere, one resident noted a significant improvement in the air quality of the local area: while the presence of local industry clearly brought economic benefits to the residents and families of local areas, this history of environmental injustice connects strongly to an ongoing scepticism within the community that is rooted in the lived experience of local residents and history of perceived environmental injustices. one participant noted that other parts of bristol haven't inherited this sense of continuing injustice against the community, whilst also possessing a greater capacity to object to imposing and potentially damaging infrastructures: there is a level of upset as soon as there is a mention of a power from waste burning plant. or any other waste. there's a level of sensitivity. there is also a sense of disempowerment, whereas in other parts of bristol […] immediately -there's an electric response amongst the community 'we're going to oppose this!' here there's a much more ready -a belief that nothing can be done -that 'they're doing it again! (alw ) fundamental to the recognition justice tenet is the acknowledgement of marginalised and deprived communities in energy systems and transitions, which also applies to the distribution of both environmental ills and environmental 'goods' [ , ] . while renewable energy infrastructures, such as wind and solar installations, are often described as environmental 'goods' due to their contribution to co emissions reductions, their imposition on local communities and landscapes, without some form of consultation and approval, potentially generates new forms of injustice [ ] . interestingly, alw's energy project officer, who as stated above, is also a member of ben, was conscious of this history of non-recognition in lawrence weston, stating that: 'not only have they not benefited, they've also been recipients of poor air quality, noise, and numerous amounts of health impacts without that being recognised and well supported' (alw ). alw's energy project officer therefore sought to use community renewables as a means to counter this history of the community existing at the margins of bristol, alongside bringing new economic opportunities to the local area. the residents/members of alw therefore felt that both lcg and bcc had ignored the community when seeking to deploy the msa, which threatened to repeat some of the mistakes of the past, in which the interests and voices of the local community are consistently ignored: a planning application was brought forward and was well advanced for putting the solar farm in. without any consultation with us -a neighbouring community -let alone as a neighbourhood planning forum […] it was a significant development, it was right up against the boundary of the planning area and i felt they had simply ignored the community -the planning authority had completely ignored the community (alw ) in addition, another participant felt that other new low-carbon energy infrastructures, including the msa, were deployed close to lawrence weston without recognition of the local community: the solar farm at moorhouse, the wind turbines, local authority solar farm and wind turbines, we didn't get to hear about any of that. only when we realised that there is a benefit for us getting involved, then we remonstrated and got highly involved, really (alw ) while these residents of lawrence weston / members of alw felt that local low-carbon energy transitions were failing to recognise a community within close proximity to new infrastructures, alongside seeing the potential benefit for greater involvement in transitions, a director of lcg felt that alw's claims of injustice were unjustified: in contrast, a director within bec acknowledged that there was an issue of non-recognition in relation to new energy infrastructures around lawrence weston, and saw this as an opportunity to foster deeper engagement, financial support and new relations with the community via the lwcs farm: we have a -year plan to rejuvenate the community. they're surrounded by energy -they're right in the shadow of the wind turbinesthere's a whole load of energy plants down there in avonmouth -on the whole they haven't benefitted from any of it really. they are just sitting right in the shadow of it […] we're working very hard to ensure that surplus profits are going directly to them' (bec ) while these different approaches of lcg and bec are clearly strongly opposed to one another, similar to the claims of injustice made by alw, the difference in these approaches can be linked to contrasting conceptions of the geographical boundaries and indeed, contested geographies, of energy infrastructure siting. for example, when questioned on some of the claims made by alw around the siting of the msa, a director from lcg responded by stating that: ' however, this geographical separation, while recognised by alw, was not sufficient enough to justify the non-recognition and exclusion of lawrence weston: 'there wasn't any recognition […] the solar farm at the moment and the wind turbines aren't really in our geographical area, or our border area, but it's so close to our border, i think we are affected by it' (alw ) 'they should've been here and the community feel that they should've been included much more formally […] the fact that it is just there. i think there is a general principle there as well' (alw ) interestingly, lcg themselves admitted that they could've done more initially, and that a sense of recognition injustice pervaded alw's claims of injustice: this data demonstrates the extent to which recognition justice is such a vital tenet within the energy justice framework, providing grounds upon which both the directors of community energy schemes (lcg & bec) and members of alw are able to voice their concerns around energy injustices in low-carbon transition processes. key to this sense of recognition injustice and non-recognition was the city councils and lcg's failure to consult the community and include them in any decision-making procedures surrounding the implementation of the msa. this is explored further in the next subsection addressing procedural injustices in the development of the msa. recognition justice can provide the foundation upon which both distributional and procedural justice can be realised. thus, it would logically follow that in the case of non-recognition, instances of procedural and distributional injustice can arise. in the case of procedural injustice in relation to the msa, the speed and short timeframes through which lcg had to act, in order to counter impending fit scheme reductions, are instrumental to their failure to include alw in their initial stages of decision-making and consultation. lcg also had to rely on voluntary directors for outreach work, which significantly reduced their capacity to connect with communities within close proximity to the msa. furthermore, lcg sought suitable sites for solar pv outside of north somerset (south west england) due to the organisations location in a hostile local authority area that proved highly sceptical and unsupportive towards new low-carbon energy projects, as made clear by both directors in the interviews: 'i don't think they believe in communities here in north somerset. the council here are dreadful. they've got in our way more than they've helped us […] we've really struggled to get any traction. we've had no support from them' (lcg ) in addition, a director within bec was sympathetic to the hostility lcg faced from their local council when speaking about the development of the msa in bristol: furthermore, this issue around timing and non-recognition was further reiterated by the energy project officer at alw: despite these admissions, a member of alw / resident of lawrence weston was adamant that the local community were ignored and that lawrence weston were excluded from consultation measures: this subsection shows that alw's sense of procedural and recognition injustice was amplified by the lack of consultation with the local community and ultimately the non-recognition of lawrence weston by lcg when they installed the msa. this sense of non-recognition also extended to the city council as well as lcg, who approved planning permission for the installation of the msa in such a short timeframe. while the restorative justice subsection details the efforts made by lcg to enhance community relations with alw, the above two subsections have detailed some of the energy injustices associated with new, emerging low-carbon energy infrastructures in bristol. the next subsection concerning distributional justice turns to a focus on bec's lwcs farm, seen here as a partial reaction on behalf of both the council and bec to some of the claims of both recognition and procedural injustice made in the above subsections. it also details the distributional impacts of the lwcs farm on alw, exploring what this means in a time of austerity. following the tensions between alw and lcg outlined above, it would appear that these occurrences had both a direct and indirect impact on future low-carbon energy initiatives in lawrence weston. indeed, much of the interview data suggests that bec and bcc acted, to some degree, to rectify these injustices. for example, when questioned on the relationship between bec and the city council with regards to the development of new projects, an investment manager at the city council was keen to emphasise his support for the lwcs farm: weston road, right […] that one we're really, really focusing on […] that would be a very large chunk of community owned asset there, which would be very exciting for the city (bcc ) furthermore, while bec had secured a partnership with alw during the planning of the lwcs farm, they also sought to emphasise the bottom-up nature of alw's involvement: it is really the ordinary people, local people that are driving that. there's no doubt. if you go to a meeting you'd be in no doubt that that is the case (bec ) while claims of injustice against lcg around the msa influenced the council and alw, it would be inaccurate to ignore the wider impacts of austerity on lawrence weston. furthermore, it would be wrong to assume that both the city council's drive to secure a local energy project in lawrence weston and alw's drive to assist the regeneration of the local area through involvement with the lwcs farm were only driven by this. rather, as attested to by alw's energy project officer, the origins of alw itself lie in broader inequalities and injustices in the city: this subsection on distributional justice therefore moves beyond criticism of the msa and directly addresses the impact of austerity on the local community, while detailing the contribution of bec to alw and considering the ways in which an 'active participation' approach to local energy schemes can extend distributional gains to localities. during the in-depth interviews, austerity was shown to be a significant concern for key members of alw, who, when questioned on the material and financial implications of austerity in the local area, noted the severe impacts of austerity measures since the introduction of fiscal cutbacks in : i think the biggest impact it can have on us is service provision and lack of it, community cohesion, more vulnerable people being created […] especially in the housing market […] i think it will all impact on that. crime, antisocial behaviour, drug use, more alcohol dependency simply because they are coping mechanisms to cope with all these cuts (alw ) thus, alw sought to prioritise new forms of economic activity that would benefit the local area to counter some of these harmful occurrences within the local community as a result of austerity. this localisation of new economic activity was therefore a key driver for alw that closely aligned with bec's desire to localise the economic benefits of low-carbon energy infrastructures. in addition, the city council were also supportive of this localisation agenda in lawrence weston: (footnote continued) current council are now comprised of cross-party councilors that are much more supportive of renewable energy and lcg, with a director of lcg also elected to the council. i think what is important is that any benefits that flow from the project become locally sited. i think that one of the benefits of the way that the finance on lawrence weston road is structured, is that there are lenders involved who are obligating the project to pay out to ambition lawrence weston because of their proximity to the project (bcc therefore, the location of the lwcs farm more decidedly 'within' the community led to concrete distributional benefits for alw, through direct payments to the organisation from bec's surplus revenues as detailed by alw : we'll be getting £ , . payment schedule is £ , up front for the first year […] then £ , for the next four years. in addition to thatso, that's the upfront payment -a minimum of £ a year from the yield from the solar farm (alw ) this demonstrates the extent to which community energy projects can move beyond offering benefits to investors, to supporting local organisations that are contributing to the regeneration of their local economy, as reiterated by a director within bec: people don't have to be invested in it to get some of that benefit -it will be going to alw who are doing projects for the whole community. that's the way we get our benefit out there (bec ) in addition, the creation of the lwcs farm and associated community benefits during a time of austerity proved highly valuable for alw as an organisation going forward: the beauty of this […] is that it's totally unrestricted. so, we can use it for whatever is needed to deliver our community development plan. which to me is a godsend […] in these austere times, it's an absolute luxury to have available to us £ , plus £ a year that could be spent on core funding should we need to, but ultimately to have that money unrestricted to spend it on the needs of the local area is absolutely brilliant (alw ) this data reveals the extent to which community energy models can support local organisations and local economies, particularly in regeneration and development efforts. the findings above show that this is key to the distributional justice impacts of local energy infrastructures in deprived areas. however, while this level of community engagement and involvement certainly provides a stark contrast to lcg's non-recognition of lawrence weston, particularly in a time of austerity, it is not without its criticisms. after some form of distributional justice had certainly been achieved through ensuring that alw were supported financially as an organisation, rather than the economic benefits remaining the preserve of affluent investors, questions arose around what exactly this money was then going to support and how. discussion around moving beyond a charitable 'passive recipient' approach to one which ensured the 'active participation' of local community residents and alw's members therefore followed, alongside general questions around the apportioning of surplus revenue. while bec's support for alw signalled a milestone for community energy directly supporting the regeneration of a deprived urban community, further examination of these links brings forth a certain politics around the allocation of surplus revenues. a participant from the city council noted that who decides on this allocation is crucial: where does that last tranche of funding go, once everything else has been paid? i can't comment on that because that is the job of that board of directors, and the shareholders. if they are all middle-class shareholders -well, you know, they would come up with a different answer than if they are all living in lawrence weston, which as we know, is quite a deprived area generally (bcc ) indeed, this assumption was proved correct, as from the perspective of alw , the agreement reached between alw and bec around surplus allocation was unsatisfactory: % of the surplus that is generated will come to lawrence weston and % will go to the bec community energy fund, there was never really any negotiation with the community about that […] furthermore, key to this idea of proximity requiring a greater level of community engagement and involvement, alw also sought to emphasise the need for deeper relations with the local community, moving beyond grants and awards to more active participation in the training, upskilling and empowerment of the local community: far from merely clarifying and understanding who benefits, this emphasis on an 'active participant' approach raises questions around how local communities benefit once local energy schemes facilitate engagement with the communities within close proximity to their associated infrastructures. this emphasis also connects strongly to social science perspectives on energy transitions that advocate for a move away from passive to active approaches to citizen involvement in energy transitions [ , ] . the next subsection explores this move 'beyond passive recipients', whilst also addressing the changing relationship between alw and lcg in response to claims of injustice via the lens of restorative justice. thus, the following restorative justice subsection will make clear that developing relations between alw and lcg have partially addressed issues of distributional injustice around the msa. as outlined in section , the concept of restorative justice in energy justice, stemming from the work of heffron and mccauley [ ] , relates quite broadly to a process of remediation in response to a perceived energy injustice within an energy system or as part of an 'unjust' energy transition process. this process of remediation may take place through formal or informal action, or through appeal to legal processes and procedures to ensure that justice is achieved. drawing on secondary sources in the form of information sourced from both lcg's and ben's websites, it is clear that alw, lcg, ben and bec have worked together to facilitate deeper forms of engagement between the lawrence weston community and local low-carbon energy projects. thus, this restorative justice tenet is relevant to this case study in two senses. firstly, lcg have now incorporated alw into their community benefit activities. secondly, both bec and lcg are wary of the need to move beyond a passive recipient approach to community energy that has indeed become the norm within the sector, whereby few community energy organisations offer training opportunities in relation to the development of new low-carbon energy infrastructures. the development of an active participant approach therefore still stands as the exception, rather than the rule, as attested to by a co-director within ben when speaking about bec: i think the energy co-op -although arguably you can say that as a bunch of, sort of white middle aged, middle-class techie types -they are very conscious of what they are doing, and so working with organisations like ambition lawrence weston, they are trying to create something that does deliver in a more inclusive way (ben ) lcg have recognised this and started to think of new ways to engage the lawrence weston community in some of their community benefit fund activities, as one director stated that 'finding a way of enabling the people who are, in this particular case local to the moorhouse, to benefit, is actually something that we'd be very keen to do' (lcg ). this is demonstrated by lcg involving alw more closely in their activities: 'we've had a meeting with low carbon gordano, and i'm now on the panel as an ambition lawrence weston representative and as the new energy officer' (alw ). this desire for closer involvement is evidenced by the community benefit section of lcg's website, which builds on an active participant approach: ambition lawrence weston, representing the community close to our moorhouse array, are going to train local, currently unemployed, people as energy advisers to help householders and businesses use energy more efficiently, and are working with local companies to ensure that there will be employment opportunities for the trainees after the project [ ] while lcg clearly sought to use some of their community benefit to assist local residents within lawrence weston, it is interesting to note the mention of the proximity of lawrence weston as a contributing factor to changing their relationship with and acknowledgement of alw. this shifting relationship also connects to assistance from other actors within bristol's local energy network, with ben working with lcg to deliver on this active participant approach: gordano community benefit fund. the grant was used to fund a community internship programme, with local long-term unemployed people working on various community energy projects in the lawrence weston area [ ] alw then responded to this need to advance forms of deeper engagement with the local community, and proved instrumental to the delivery of this internship scheme: we basically recognised, talking to marginalised groups […] that people didn't access green volunteering in energy, because they basically felt they couldn't afford to do so. by creating an internship, which creates job opportunities, linking them to potential employers and giving them life skills, that would actually open a door to other opportunities (alw ) in addition to this, bec wanted to encourage alw to use their contributions to fund training activities within the local community, as noted by a member of ben when discussing the passive recipient approach to local community engagement and support: furthering the creation of new economic opportunities in a time of austerity, this aspect of restorative justice connects powerfully to distributional justice and a focused, targeted approach to delivering the benefits of the low-carbon economy to deprived areas. this subsection has shown that, due to the claims of injustice around the proximity of the msa to lawrence weston, alongside passive recipient approaches that fail to fully engage and involve communities close to energy infrastructures, the tenet of restorative justice can be used to understand how lcg have sought to rectify these past claims of injustice and assist alw in wider regeneration efforts. this paper has demonstrated how the lcg moorhouse solar development is initially viewed as somewhat of an imposition that is not benefitting the community in a time when services are being cut. this imposition is therefore particularly pronounced, with the context of both austerity and high deprivation placing greater emphasis on localising wealth generation, rather than allowing a leakage of profits to external areas. this localisation of wealth generation and the activities that flow from new revenue generation are an particularly important distributional justice concern, whilst further correspondence with alw demonstrated that low-carbon energy would feature as a vital part of its continued regeneration going forward. interestingly, this is attested to throughout lawrence weston's community plan [ ] . building on the follow-up communication with alw in mid- , alw were successfully granted planning permission by the city council to deploy a m . mw onshore wind turbine in the local area, which will be owned by alw and will generate revenue for the local community. the projects revenues will also support the establishment of an 'energy learning zone', which will offer energy internships, energy events, workshops and focus on raising the skills of local residents [ p. ] . it is clear, therefore, that for both 'energy' and 'spatial' justice to be realised in local low-carbon transitions, deprived areas in which new energy infrastructures are deployed must be given the opportunity to benefit from those infrastructures, alongside opportunities for procedural engagement. these new infrastructures may then form a core part of their future regeneration efforts and plans, bringing a further cycle of benefits and localised revenue generation. once deployed, community-owned low-carbon infrastructures are in place for decades. this article has shown that how the organisations behind them choose to relate to the communities and people that surround them will shape the energy justice impacts of low-carbon transitions going forward. surprisingly, the majority of community energy literatures and policy reports have, to date, seen community energy schemes as largely beneficial to the localities in which they are located, with much research to date containing 'uncritical assumptions' that community energy overwhelmingly leads to positive outcomes [ ] . this paper has shown that, without careful consideration of the spatial hierarchies and inequalities embedded in the spaces and places in which low-carbon energy transitions take place, new injustices may occur that undermine the ability for local energy transitions to be socially just. furthermore, the backdrop of austerity measures reducing service provision and worsening social inequality in an area of high deprivation, should encourage energy justice scholars to further explore the potential of new low-carbon energy infrastructures to be embedded within community or organisational strategies for regeneration. this is a particularly pertinent point in light of the impacts of the economic crisis faced by the uk due to the covid- pandemic. as catney et al.'s [ ] 'reality check' reminds us, deprived communities are not primarily concerned with lowering their carbon emissions. rather, this paper shows that opportunities to combine lowcarbon transitions with economic development and local regeneration appeal to deprived areas. rather than simply making grants to local organisations and businesses, which is a ubiquitous feature of uk community energy organisations, local and community energy projects would themselves benefit from ensuring that they offer training to local residents in the installation, management and governance of local energy technologies and systems. in addition, this may also assist with gaining planning permission [ ] . these issues also broadly connect to debates around just transitions in local energy schemes [ ] , whereby new low-carbon jobs, procedural engagement and opportunities for learning are ensured for the communities in which future projects are situated. as community energy schemes begin to plateau and local energy schemes take a leading role in energy decentralisation processes [ ] , it will be vital for local energy strategies and policies to consider active participant approaches in policy. as fit's are locked in for years, the findings also have relevance for the policies of current community energy schemes that seek to use their surplus revenue in more productive ways, moving beyond opening up competitive bids for grants to local organisations and towards supporting local employment and skills training. in addition, advancing an active participant approach is integral to building the 'community capacity' [ ] needed to ensure the effective long-term management and governance of local energy technologies and systems, particularly as new innovations emerge. the uk does offer a 'community energy specialist' apprenticeship , however, this has not been widely used or supported to date. community energy schemes with large surplus revenues could engage with this this more fully, alongside forming partnerships with local authorities, energy intermediaries [ ] and local energy networks to access finance and funding to scale up this type of activity in tandem with the shift from community to local energy more broadly. intermediaries are also vital for raising awareness of the potential benefits of low-carbon energy in areas high in deprivation that are close to deployed low-carbon technologies. interestingly, two of the research participants (alw and lcg ) noted in their interviews, that an area in north bristol close to lawrence weston, henbury, contains similar levels of deprivation to lawrence weston [ ] , but was not involved in local energy projects. despite its proximity to newly deployed technologies, the area of henbury did not receive benefits from any of the community-owned solar or wind deployment outlined in this paperthough this may well change in future initiatives. this finding places an increased emphasis on the important work of intermediaries in connecting low-carbon transitions to low-income areas that would otherwise miss out on such opportunities, as intermediaries have been shown to be effective forums and mediums though which these concerns may be voiced, acted upon and resolved [ , ] . policy frameworks for local energy should therefore recognise the critical roles that intermediaries play in supporting energy justice concerns and prioritise them in outreach work and relevant strategies. furthermore, this point also relates to how future local energy schemes can relate more productively to marginalised 'energy peripheries' going forward [ , ] , alongside being integral to targeted and area-based approaches to spreading the benefits of future local energy schemes to communities in areas of high deprivation. the geographical underpinnings of many of the claims made in the findings are closely tied to contestations over the proximity of energy infrastructures. this connects to two fundamental aspects of spatial justice within a broader discussion of energy justice. the first, is that many of the grounds for claims of both injustice and more just relations by alw are based upon the proximity of projects to the area of lawrence weston. therefore, various civic and community energy actors should be acutely wary of the spatial proximity of their projects to deprived communities in future endeavors, considering how best to consult and engage with local communities to raise awareness, seek planning consent or spread the benefits of new energy infrastructures, drawing on the support of relevant intermediaries where possible. the second, is that through the deployment of solar pv farms close to the community, lcg expressed a desire to facilitate greater distributional justice through becoming an energy supply company that would provide low-cost electricity to fuel poor houses in lawrence weston. this kind of new energy supply set-up also relates to the closer proximity of lawrence weston to the source of energy generation, thereby reducing potential transmission losses and the transmission distance of electricity that is common to power provision within centralised grids. thus, further distributional gains may be achieved, should a system of decentralised provision offer the opportunity of lower energy prices and a reduction in transmission losses in power provision. such arrangements will require the critical lens of interdisciplinary energy justice scholars to understand how to embed social justice and equity concerns in future energy decentralisation initiatives, alongside interrogating how such initiatives perform in varying research contexts [ ] . as energy decentralisation begins to take on new technological forms, particularly via the integration of various energy storage technologies into local energy grid systems enhancing the prospect for continued renewables deployment, the potential for local low-carbon supply futures to benefit local populations will become a critical concern for energy justice scholars. this will prove a vital area of future research for two reasons. firstly, rapid energy market developments around the growth of energy storage technologies, flexibility markets, vehicle-to-grid services, smart meter deployment and smart grid development present a new wave of innovation in decentralised energy system development that also present a new set of challenges. one core issue that arises from such technological innovations will look at how social innovation -in the form of new social enterprise models and actors seeking to capture the values of such innovations for the benefit of the wider community -can counter the domination of incumbent market players and prevent the reproduction of the social and economic inequalities that undermine new low-carbon economies. secondly, if we are to mitigate against exacerbating social inequality in a post-covid society, in which social inequality is once again brought to the fore after a severe economic downturn, such concerns must be prioritised as we continually research the impact new low-carbon infrastructures have on the people and communities that exist around them. the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. geographies of energy transition: space, place and the low-carbon economy from 'energy geography' to 'energy geographies' perspectives on a fertile academic borderland the routledge research companion to energy geographies the economics of distributed energy generation: a literature review the local embedding of low carbon technologies and the agency of userside intermediaries social innovation in community energy in europe: a review of the evidence please see the 'institute for apprenticeships and technical education community energy: entanglements of community, state, and private sector financing the civic energy sector: how financial institutions affect ownership models in germany and the united kingdom green conservatism: move over big , we need the big , , green alliance a thousand flowers blooming? an examination of community energy in the uk transition pathways for a uk low carbon electricity future community versus local energy in a context of climate emergency governance institutions and prospects for local energy innovation: laggards and leaders among uk local authorities community energy business model evolution: a review of solar photovoltaic developments in england local impact of community renewable energy: a case study of an orcadian community-led wind scheme executive summary' international energy agency global wealth inequality austerity and inequality. exploring the impact of cuts in the uk by gender and age austerity bites: a journey to the sharp end of cuts in the uk the austerity state addressing economic inequality at root a tale of two britains: inequality in the uk living standards, poverty and inequality in the uk london: institute for fiscal studies why inequality could spread covid- spatializing energy justice big society, little justice? community renewable energy and the politics of localism community energy and equity: the distributional implications of a transition to a decentralised electricity system community acceptability and the energy transition: a citizens' perspective intermediating energy justice? the role of intermediaries in the civic energy sector in a time of austerity the impact of household energy efficiency measures on health: a meta-analysis targeting energy justice: exploring spatial, racial/ethnic and socioeconomic disparities in urban residential heating energy efficiency the drivers of energy-related financial hardship in australia-understanding the role of income, consumption and housing local energy generation projects: assessing equity and risks acceptance, acceptability and environmental justice: the role of community benefits in wind energy development exploring local energy justice in times of austerity: civic energy sector low-carbon transitions in bristol city (doctoral dissertation seeking spatial justice understanding the material dimensions of the uneven deployment of renewable energy in two italian regions households in place: socio-spatial (dis) advantage in energycarbon restructuring energy periphery: uneven development and the precarious geographies of low-carbon transition uneven energy transitions: understanding continued energy peripheralization in rural communities spatial justice and the land politics of renewables: dispossessing vulnerable communities through solar energy mega-projects beyond distribution and proximity: exploring the multiple spatialities of environmental justice energy justice in a changing climate: social equity and low-carbon energy energy justice: a conceptual review the concept of energy justice across the disciplines deprivation in bristol : the mapping of deprivation in bristol local authority area bristol city council participatory action research approaches and methods: connecting people, participation and place energy justice in the transition to low carbon energy systems: exploring key themes in interdisciplinary research the way fostering community energy and equal opportunities between communities procedural justice and the implementation of community wind energy projects: a case study from south yorkshire, uk the uk homeowner-retrofitter as an innovator in a socio-technical system expanding the scope and implications of energy research: a guide to key themes and concepts from the ambition lawrence weston case study community renewable energy: what does it do? walker and devine-wright ( ) ten years on summary findings of the english indices of deprivation within bristol local authority area bringing local energy benefits to deprived communities energy justice in the developing world: a review of theoretical frameworks, key research themes and policy implications the english indices of deprivation : technical report i am extremely grateful to all of the bristol participants for generously contributing their time to this research, both in the data collection phase of my phd and in the follow-up communication in that helped to update and improve this paper. in addition, i thank the encouraging reviewers at erss for their constructive feedback. their input significantly enhanced my first solo author paper. this research was also supported by an epsrc studentship from to , grant number bv / . key: cord- -t v zt authors: lee, p.; lam, p.t.i.; yik, f.w.h.; chan, e.h.w. title: probabilistic risk assessment of the energy saving shortfall in energy performance contracting projects–a case study date: - - journal: energy build doi: . /j.enbuild. . . sha: doc_id: cord_uid: t v zt lack of a proper assessment method on performance risks in energy performance contracting (epc) projects is one of the reasons hindering the further development of energy service companies (escos) market. this paper proposes a simulation-based method to evaluate the probability of energy saving shortfall taking into account the variations in the influential parameters, including weather conditions, occupancy, operating hours, thermostat set-point, etc., during the contract period. the proposed method involves the use of a detailed building energy simulation programme, sensitivity analysis and monte carlo simulation techniques. empirical data is also used to develop the probability distribution functions for the identified parameters to simulate the actual yearly variations in the post-retrofit conditions. a real case study of replacement of heat rejection system for a central chiller plant in hong kong is used to demonstrate the application of this probabilistic method. the result shows that the possible energy savings after a -year retrofit period ranges from , kw h ( . %) to , kw h ( . %) with % statistical significance. buildings account for % of the world's energy use, and most of the existing buildings are not so energy efficient as modern technology allows [ , ] . as such, energy retrofitting of existing building services equipment can yield significant amount of energy savings. however, the lack of upfront capital and technological know-how are usually hurdles to undertaking energy improvement projects although the benefits of such works, for example, a substantial reduction in utility costs and improvement of the built environment, are obvious. energy performance contracting (epc) is recognised as a means to tackle this problem in many countries, including the united states, australia, germany, japan, singapore and china [ , ] . the european parliament defines epc in the directive / /ec as "a contractual arrangement between the beneficiary and the provider (normally an esco) of an energy efficiency improvement measure, where investments in that measure are paid for in relation to a contractually agreed level of energy efficiency improvement." [ ] . it means that, under an epc arrangement, energy service companies (escos) guarantee or share the energy savings with building owners. building owners only make a series of payment to escos when the actual energy savings are materialised. in the case of shortfall in savings, escos will compensate the loss incurred by building owners. to ensure the guaranteed energy saving can be achieved, a proper assessment method on the probability of energy saving shortfall is needed to evaluate such project risks. mills et al. [ ] identified the risks associated with energyefficiency projects and classified them into five aspects, namely economic, contextual, technology, operation, and measurement and verification (m&v) risks. several risk management approaches (e.g. financial hedging, careful design, proper metering, etc.) were also introduced to mitigate the associated risks in their study. however, even though escos can better manage the performance risks by ensuring system efficiency, optimisation control and better maintenance, the actual energy saving is still uncertain. this is attributed to various extrinsic factors including weather conditions, economic circumstances, as well as occupants' behaviour, which can significantly affect the actual energy savings. for example, the occupancy rate of hotel may decrease dramatically due to economic downturn, resulting in a significant reduction in the actual energy savings. therefore, a dilemma is often observed from the escos' perspective in determining the amount of guaranteed energy savings. on one hand, escos try to mitigate the performance risks by being conservative on the guaranteed savings, but on the other hand, to increase chances of winning bids by offering higher energy saving guarantee and shorter contract period. several attempts were made to develop such an assessment method. rickard et al. [ ] adopted the technique of coefficient of . collect building & system info rmat ion , utilit y bills and measured data. . develop and ca librate two energ y model s usi ng utilit y bills and measured data. developmen t of pre -an d post -retrofit models . identif y inf lue ntial par ameters af fecting ener gy us e. . select the ran ge and in terval fo r sensitivit y analysi s. . calculate and rank the influential coeff icient for the influential pa rameters. . analyse the non -linearity situation and discard the non-inf luential pa rameters. developmen t of probability di stribution for the sel ected par ameters . collect the empirical data from st atistical data and previous research. . determine the repres entative p robabilit y distribution functions using curve fi tting techniqu es. simulation of possi ble energy saving analysis an d discussio n of simulation resul ts . generate a common set of post -retro fit period data using latin hypercube s ampl ing. . modify and reproduce the w eather fi les ba sed on the sampling resul ts. . incorporate c ommon data set into the calib rat ed energy mode ls. . run the simulat ions fo r each case of common data set. variation (cv) to compare saving uncertainties in different energy efficiency measures. however, some drawbacks were found in this technique, for example, several simplified assumptions had to be made for project comparison and a number of risk factors were excluded in the analysis. mathew et al. [ ] indicated the possible use of actuarial pricing approach to quantify the associated risks for project decision-making. however, this approach requires a large number of actual epc project data, but the non-standardised project information and poor data quality often hinder the development of a reliable actuarial database [ ] . mills et al. [ ] and jackson [ ] suggested using the monte carlo technique for quantifying the risks related to epc projects, but their studies only focused on the illustration of a proposed methodology and no real project data is used to demonstrate the credibility of their findings. this paper aims at developing a simulation-based method to evaluate the probability of energy saving shortfall taking into account the variations in the influential parameters. it is structured as follows. first, the probabilistic method is presented to quantify performance risks for energy saving shortfall under guaranteed epc projects. the method involves the use of a detailed building energy simulation programme, sensitivity analysis and the monte carlo simulation techniques. second, a case study of replacement of heat rejection system for a central chiller plant in hong kong is used for illustrating the application of this probabilistic method. finally, the results of this case study are presented. fig. shows the procedure and methods used for quantifying the probability of energy saving shortfall in guaranteed epc projects. the whole procedure consists of four main steps. i development of pre-and post-retrofit models: the first step is to develop two energy models that can predict representative energy consumption of the building at the pre-and post-retrofit stages. with the two models, the actual energy savings can be predicted taking into account any deviation in the post-retrofit conditions from the baseline conditions. the models should be developed by using a detailed building energy simulation programme, which allows users to input all essential building information, system & equipment specifications, as well as operational characteristics for realistic energy use predictions. the two models should be basically identical except the retrofitted systems and the conditions with significant changes (e.g. change of occupancy). to ensure the representativeness of the models, the models should be calibrated with the measured energy use data. details of the calibration procedures can be referred to other published literature and guidelines [ ] [ ] [ ] [ ] . ii sensitivity analysis: the second step is to identify the importance of influential parameters affecting energy use. in general, the influential parameters can be summarised into three categories, namely "building load", "system control and operation" and "equipment, system and plant". for the selection of influential parameters, attention should be paid to those parameters that are likely to change during the epc contract period, for example, weather conditions, occupancy rate, operating hours, etc. some of the influential parameters may be excluded, for example, building height, materials used in building facade, orientation, etc., since these parameters are unlikely to change during the contract period. in some projects, an exclusion clause is incorporated to protest the interest of escos and hosts in case of significant changes in the baseline conditions (e.g. large scale renovation works are conducted during the contract period). those parameters can also be discarded in the sensitivity analysis. there are three common techniques to conduct sensitivity analysis, namely differential sensitivity analysis (dsa), random sensitivity analysis (rsa) and stochastic sensitivity analysis (ssa) in the field of building energy study [ , ] . in comparison with these techniques, differential analysis by finite differences (fd) is most widely used because the calculations are easy and there are fewer problems to incorporate into the simulation programme. this technique has been widely used by researchers to determine the most sensitive parameters affecting building energy use [ ] [ ] [ ] [ ] [ ] . the selection of a proper range and interval is essential to obtain accurate results in sensitivity analysis. therefore, the range and intervals selected should cover the two extreme scenarios with a reasonably narrow interval. nonlinearity issues should also be studied when the standard deviation of the influence coefficient (ic) is large. the procedure of performing differential sensitivity analysis is presented in the later part of this paper. iii development of probability distribution for selected parameters: the third step is to develop the probabilistic distribution function (pdf) for each of the selected parameters. the selection of the representative pdf is critical in this analysis as it is used to simulate the yearly variations in those selected parameters during the post-retrofit period. empirical data from official database and previous research are used to determine the corresponding pdf for the selected parameters using curve-fitting techniques. three goodness-of-fit tests, namely the chi-square test, the kolmogorov-smirnov (k-s) test, and the anderson-darling (a-d) test, are performed to evaluate how well the assumed distributions fit a set of sample data [ ] . the chi-square test is used to determine the validity of two or more theoretical distribution models. the k-s test serves the same purpose, but with fewer limitations in application such as a large number of intervals. the a-d test is particularly useful when the tails of a distribution reflect an essential distribution characteristic. the lower the goodness-of-fit value of these tests is, the more representative the assumed pdf is selected. for those parameters without empirical data to determine, a triangular distribution is proposed to be the representative pdf, and the most likely value should be regarded as the baseline condition. iv simulation of possible energy saving: the fourth step is to simulate energy saving taking into account all possible combinations of selected parameters during the post-retrofit period. monte carlo simulation is performed to generate a common set of post-retrofit condition data based on the pdf of the selected parameters. monte carlo simulation is a mathematical method where output values are randomly generated based on the assumed distributions of the independent parameters. a smooth approximation of the output distribution is obtained with large sample sizes (e.g. by iterating , simulation runs). this technique has been applied in a number of probabilistic analysis [ ] [ ] [ ] [ ] [ ] .the latin hypercube sampling method is proposed to generate those random numbers, because it more precisely reflects the shape of a defined distribution with relative small sample sizes [ ] . detailed building energy simulation programmes usually require the weather and input data files to run the simulation. to simulate the energy saving uncertainty associated with yearly weather variations, it is necessary to modify and reproduce the typical weather file , times in accordance with the results of each monte carlo simulation. the algorithm of weather adjustment for the original weather file is based on a "morphing" method, developed by belcher et al. [ ] who constructed design weather data for future climates. chan [ ] also adopted this morphing method to modify the hong kong typical meteorological year (tmy) weather file taking into accounts the effect of urban heat islands. the procedure of this method will be illustrated in the later part of this paper. similarly, , input files are required to generate based on the result of monte carlo simulation. each weather and input file represents one of the possible yearly conditions during the post-retrofit period. these weather and input files are run on the detailed energy building simulation programme for the pre-and post-retrofit models to simulate possible range of energy savings. the above method for quantifying the probability of energy saving shortfall is illustrated through a real epc project in the composite buildings. this development consists of three commercial towers with a total gross floor area (gfa) of around , m , which were built in the late s. the first two towers, denoted as a and b, are symmetrical in building shape, and each comprises serviced apartment (sa) storeys and office storeys. the remaining tower, denoted as c, is solely for storeys of office premises. similar to other typical high-rise buildings below storeys [ ] , a reinforced concrete structure was adopted and the building facades are made up of curtain walls while the windowto-wall ratio (wwr) is around . for four orientations. reflective double glazing glasses are used for all towers. table shows the design parameters of these towers. a central chiller plant system is used to provide cooling to these towers. this chiller plant system comprises units of the day-mode ton chiller and units of the night-mode ton chiller. the primary-secondary pumping system is adopted and the seawater cooling system was used for heat rejection. the three day-mode chillers operating from : to : are capable of providing air the gross floor area of a building means the area contained within the external walls of the building measured at each floor level (including any floor below the level of the ground), including the thickness of the external walls of the building. the building authority may disregard essential building services areas from gross floor area calculation. (cap -building planning regulations for hong kong sar). conditioning for both the office and sa premises. for the remaining time, the ac operation is switched from the day-mode to the night mode, and only the sa premises are provided with air conditioning service. an energy audit was conducted by the esco after years operation of the building. a design problem was found in the seawater cooling system in that the central chilled water plant was supplied with seawater, which was discharged from an adjacent central chiller plant for chiller condenser cooling, after the seawater had been used to cool the chillers in the adjacent plant. as the "indirect" seawater supply was at much higher temperatures than the original design level, the chiller plant had been running at rather low coefficient of performance (cop). the poor quality of the seawater also exacerbated corrosion of condenser tubes, causing further lowering of the cop. in order to address these problems, the esco and host agreed that the existing seawater cooling system should be replaced with a fresh-water evaporative cooling tower system, and the project was implemented under an epc guaranteed saving package. the actual energy saving was calculated based on the common set of post-retrofit period conditions per annum. the isolation approach [ ] was adopted to measure the annual energy consumption of the whole chiller plant, including chillers, chilled water pumps and seawater pumps. other energy and cost-avoided savings (e.g. reduction in maximum demand use and maintenance costs) were not considered in this study. table shows the component of chiller plant equipment for energy saving calculation in this retrofit project. two building energy models, representing the energy consumption at the pre-and post-retrofit stages, were developed using energyplus [ ] . energyplus is a detailed building energy simulation program developed by the department of energy (doe) in the united states. this program has been tested and validated according to ashrae standard [ ] and a number of researchers have utilised energyplus to carry out sensitivity and parametric analysis for building energy use [ , ] . the composite buildings consist of two types of premises: office and serviced apartment, on a total of usable floors. for simplicity, a model for only three typical floors was developed to represent the whole composite buildings. as tower a and tower b are symmetrical to each other in shape, the first typical floor model, denoted as ty , represents the sa premises of towers a and b. similarly, the second typical floor model, denoted as ty , represents the office premises of towers a and b. the third typical floor model, denoted as ty , represents the office premises of the whole tower c. no roof and ground floors were modelled, because the top floors of all the three towers are used to house lift machine rooms, potable water, flush water and fire services water tank while the towers are atop a basement floor. therefore, it would be reasonable to assume that heat transfers to the air-conditioned area caused by direct solar heat gain and ground temperature variations would be limited. to ensure that the operating conditions of the chiller plant in the pre-retrofit period could be realistically modelled, a complete year of monthly energy use data of the chiller plant was collected and used as the basis for comparison while the operating conditions were tuned. a spot measurement was also conducted to evaluate the overall cop of the chiller plant. the other baseline conditions, including the occupancy rate of the office and sa premises, were obtained from relevant documentary records. table shows the energyplus input details. the pre-retrofit model was calibrated with reference to equipment nameplate data, operating schedules, occupancy patterns, etc. for those missing data which were required as inputs to energyplus, estimates were made based on common practices and regulatory requirements, such as the building energy code [ ] . the simulated results were compared to the monthly electricity bills data. the calibration procedures and requirements were in accordance with the ashrae guideline [ ] . the post-retrofit model was developed based on the pre-retrofit model except the retrofitted part. similarly, one complete year of post-retrofit data was collected for calibration of the post-retrofit model. other data and information, including new occupancy rate, operating schedules, as well as plant performance after retrofit, were also recorded. better chiller performance was observed after the retrofit. it was mainly attributed to the lower incoming condenser water temperature for chiller heat rejection (approximately • c reduction). apart from the chiller plant, there was no significant change from the baseline conditions, except the occupancy rate, which was % higher than the pre-retrofit conditions. the predictions of the calibrated models and the actual consumption figures are shown for comparison in table as well as figs. and . it should be noted that the measured values of total chiller plant energy use on april and september in the post-retrofit case were discarded, as these data were found erroneous. much effort had been made to account for the large deviation between the measured and predicted values of these two months, for example, checking on ( ) maintenance records; ( ) occupancy rate; ( ) monthly outdoor temperature; ( ) monthly relative humidity; ( ) [ ] . b seawater-cooled chiller system is not directly supported in energyplus. a "districtcooling" object with the specified leaving temperature on condenser loop is used to simulate the effect of using seawater as a heat rejection method in this study. numbers of holiday happening on weekdays; ( ) monthly billing period. the investigation concluded that the large deviation was most likely due to missing sub-meter readings but records of those readings could not be retrieved. according to the ashrae guideline, the two statistical indices, namely coefficient of variation of the root mean squared errors (cvrmse) and normalised mean bias error (nmbe), were used to assess how well the predicted values match with the measured values [ ] . the models may be declared to be calibrated when cvrmse and nmeb are less than % and % with monthly data respectively. both models in this study complied with the calibration requirements. twenty-two parameters were finally identified for sensitivity analysis. these are summarised in table . the range and intervals selected are plausible values found from the previous studies on parametric and sensitivity analysis [ , ] , with attention being paid to the selection of range and intervals, they should cover the two extreme scenarios with a reasonably narrow interval. for example, the range of annual mean dry bulb temperature was selected based on the highest and lowest values throughout the years of the hong kong observatory weather data, and the interval was selected based on the measurement error ± . • c for temperature sensor. the differential sensitivity analysis (dsa) was employed in this study, and the sensitivity influence coefficient (ic) was calculated as follows: where op is the new energy use in chiller plant; op bc is the base case energy use in chiller plant; ip is the new input parameter value; ip bc is the base case input parameter value. the base case value was same as the corresponding condition used to calibrate the pre-retrofit energy model. the advantage of using the above calculation approach is that ic is dimensionless, which can be used for comparison among different parameters. table shows the results of sensitivity analysis for the case study buildings. these parameters are ranked according to their absolute value of ic. it can be seen that the four most sensitive parameters affecting energy use are the annual mean dry bulb temperature, chiller cop, ac operating hours and annual mean dew point temperature. their ic values are at least . times larger than those of other parameters ranging from the fifth to the seventh, which include the thermostat set point for office premise, occupancy rate for office and sa premises, with the ic values ranging from . to . . other parameters, such as occupant density, lighting load, equipment load, chilled water supply temperature, ventilation rate and infiltration have relatively small effects on the building energy use in comparison with the first seven parameters. this suggests that the esco can neglect their impacts on actual energy savings even when a large deviation is observed between the pre-and postretrofit conditions. it is worth noting that the significance of the parameters may vary in different climatic conditions. for example, the ventilation rate is usually one of the most significant parameters contributing to the energy use of air-conditioning systems. however, for the hong kong weather conditions where four seasons are clearly distinct, the change of ventilation rate is insensitive to the total air-conditioning energy use on an annual basis because although the greater fresh air flow rate provides a larger rate of free cooling when the outdoor temperature is cool (thus reducing the energy use for air-conditioning during cool winter days), the saving would be compensated by the increase in air-conditioning energy use during hot summer days. high nonlinearity was found in several parameters. this means that the value of ic varies significantly from point to point. for instance, the parameter of ac operating hours is more sensitive to energy use when the presumed hour for switching off ac system is toward day-time in comparison to night-time due to the impact of solar radiation. however, the purpose of sensitivity analysis is to eliminate some parameters which are relatively less sensitive to energy use. the exact average ic value and ranking are not important in this study. the issue of high nonlinearity can be neglected when the average value of the most sensitive interval is still much lower than that of other parameters. based on the results of the sensitivity analysis, the first seven parameters were considered as the influential parameters and, for them, representative pdf were developed to simulate their yearly variations during the post-retrofit period. the selection of the representative distribution followed the three established tests, namely the chi-square test, the kolmogorov-smirnov (k-s) test, and the anderson-darling (a-d) test [ , ] . the k-s test was used when the sample sizes were less than . the chi-square test and a-d test were employed while the sample sizes equal to or more. all the calculated values from these tests were tested by the corresponding criteria values at the % significance level. when the calculated value is less than the critical value at the specified significance level, the assumed distribution can be declared as an acceptable model to describe sample data. for example, the observed data of dry bulb mean temperature (sample sizes = ) was assumed to be inferred by the normal distribution. in the k-s test, the calculated value of maximum discrepancy between the assumed and observed cumulative frequencies was . , which was less than the critical value of d˛= . n= = . at % significance level. by the k-s test, the normal distribution was verified as an acceptable model at % significance level for the dry bulb mean temperature parameter. the test results for all the selected parameters are listed in table . weather condition is one of the most critical factors affecting building energy consumption [ ] . although it is well recognised that mean temperature is generally increasing due to global warming and urbanisation [ ] , considerable variations may still be observed from year to year. for example, the location of this case study, hong kong, has a humid sub-tropical climate with four distinct seasons. in summer, the mean outdoor temperature reaches up to . • c but it can drop significantly to . • c in winter [ ] . the cooling degree-days (cdd) and heating degree-days (hdd) are and with a base of . • c, respectively [ ] . with such seasonal climate characteristics, the annual mean temperature varied from . • c to . • c within years (from to ), and the differences between the numbers of very hot days (daily maximum temperatures ≥ • c) and cold days (daily minimum temperatures ≤ • c) for two consecutive years can be as large as days (from to ) and days (from to ) respectively in hong kong [ ] . this uncertainty in yearround weather conditions can lead to volatility in energy savings for weather dependent retrofit measures. based on the latest years' daily measured data ( - ) obtained from the hong kong observatory [ ] , the four climatic variables, including annual maximum, mean and minimum daily dry bulb temperature and dew point temperature, were assigned to the most representative pdf using a distribution curve fitting technique. it is noted that the variations in diurnal temperature range is also considered in this study. diurnal temperature range is the temperature difference between the daily maximum and minimum temperature. the change in diurnal temperature range is an indication of the severity of global warming [ ] . occupancy rates in office and sa buildings vary from time to time, especially during the periods of economic growth or this sa study focused on the importance of parameters affecting the energy use of a chiller plant. the seasonal variation in these weather variables, therefore, was not included. the annual mean temperature was taken as the average value of the daily mean air temperature throughout a year. b ac operating hours (office) involves two parameters, the ac start-up time and operating duration, would be adjusted. in this study, the ac start-up time, which is : am, remained unchanged and only the operating duration was changed. c ac operating hours (sa) was assumed to be unchanged as it is very unlikely for sa operators to reduce the operating hours. d the data on occupancy rate is in terms of the annual mean percentage. the occupancy rate was converted into the number of floors being fully occupied. besides, it was assumed that a tenant rents the office floor in terms of a whole floor, instead of half-floor. similarly, the sa operator will try to occupy the whole floor for minimising the operation costs. downturn. in many epc projects, the esco and host both bear the risk of variations in occupancy, leading to uncertainty in actual energy savings. in this study, a large variation in occupancy rate was observed. in , the average occupancy rate dropped dramatically from . % to . % for the office premises and from . % to . % for the sa premises due to the economic impact of the severe acute respiratory syndrome (sars) outbreak in that year, and these figures increased gradually to nearly the highest (office: % and sa: %) in recent years. in this study, the pdfs of occupancy rate for the office and sa premises were derived from the years' data ( - ) of the developer's annual reports. to control the energy use within budget, the building owners provide tenants with air-conditioning service in fixed periods only. the operating hours of ac system for office premises in hong kong vary from buildings to buildings. in general, the ac operating hours is in line with the office working hours, which is typically from : am to : pm in hong kong. however, overtime working is very table results of chi-square, k-s and a-d tests and the assumed distribution for the selected parameters. as there is no occupancy rate of individual tower for office and sa premises in the annual report, the mean value of the whole composite buildings was used. all the parameters above are in term of annual mean. common in hong kong. there may be frequent requests for extension of ac operating hours, especially when there are changes of tenants. since the contract period is relatively long in epc projects (e.g. - years for chiller replacement), it is reasonable to expect that the operating hours in the first year of an epc contract would be different from those in the past year. therefore, the impact of possible extension or reduction of operating hours on the energy saving must be addressed. however, there are hardly any reliable records or research studies that report the long term variations in the operating hours of ac systems in buildings. an alternative way to estimate this variation is based on the ac operating hour data given by real estate agents. this approach assumed that the operating hours would be dependent on tenants' preference and relative negotiation power. as such, this study was based on the information from primeoffice to determine the pdf of operating hours. primeoffice is a property search website with the database of over hong kong office buildings. it provides the building information such as typical floor area, airconditioning hours and system types (e.g. central ac, split type) [ ] . based on the primeoffice database, the pdf of operating hours was determined. as real estate agents operate in a very competitive environment in hong kong and they pay particular attention to solicit patronage with good services, the data on this website is assumed to be adequate for the demonstration of methodology rather than reporting the actual results. the choice of indoor air temperature set-point can substantially affect the energy consumption of chiller plant [ , ] . the indoor air temperature setting can vary significantly as different occupants could have different thermal sensation to indoor environment. in the recent years, the government launched the "energy conservation charter" programme to encourage occupants to raise the indoor temperature to . • c for energy savings [ ] , but the thermostat set-point is not often adjusted as recommended. mui and wong's field survey [ ] on offices found that the average air temperature in typical office buildings is ± . • c. the pdf of thermostat set point was determined based on the survey results of mui and wong [ ] . despite the fact that this study was not focused on the variation of indoor air temperature in a single development as this case study represents, the finding was applicable since in general the decision on thermostat set point would be in relation to occupants' behaviours, instead of building characteristics and location. coefficient of performance (cop) is a primary indicator to reflect the actual energy efficiency of chillers; the higher the cop of chillers is, the less energy is consumed to provide the same amount of cooling. the performance of chiller plant will deteriorate with time of use due to two main factors: ( ) normal wear and tear over a long operating period; and ( ) contamination of chilled water tubes. masaaki et al. [ ] studied the degree of deterioration of chiller performance after years of operation. it was found that no performance deterioration was observed for the first months. after that, the cop deteriorated at an annual average of . %. the study also suggested that . % of chiller performance could be recovered when preventive maintenance, such as tube chemical cleaning, is regularly performed. the pdf of cop is difficult to determine, because the variations in the operating cop due to equipment deterioration depend on a number of factors, including operating hours, operation conditions (whether it is close to the standard operating conditions), the frequency and quality of maintenance work. as the maintenance is part of the scope of the contract in most epc projects, the esco has an incentive to ensure that the plant performance shall be maintained at the expected cop. when the plant performance is much lower than the expected cop, active maintenance, such as tube chemical cleaning, replacement of parts, would be carried out to avoid energy saving shortfall. in this case study, the existing chillers were still used after the retrofit. based on the previous study of existing chiller performance [ ] , an annual average of . % cop deterioration rate was assumed for the worst case while . % improvement of chiller performance will be used for the best case (assuming with high quality of maintenance work during the contract period). a triangular distribution was assumed for the pdf of cop. the most likely value in this pdf will be set equal to the existing cop. fig. illustrates the calculation procedures of , simulation runs. a risk analysis tool based on monte carlo simulation (@risk) [ ] was utilised to generate , common data sets of input parameters for two calibrated building energy models. the purpose of generating this common data set is to simulate all the possible cases for the yearly post-retrofit period conditions taking into account the variations in these selected parameters. in energyplus, the hong kong typical meteorological year (tmy) weather data file is used to represent the long-term typical weather condition over a year. this weather file consists of hourly climatic variable data, including dry bulb temperature, wet bulb temperature, solar radiation, wind speed, etc. in order to simulate all the possible yearly weather conditions during the post-retrofit period, this hong kong tmy weather file was modified and reproduced , times in accordance with the results of each monte carlo simulation run. the algorithm of weather adjustment is based on a "morphing" method, developed by belcher et al. [ ] who constructed design weather data for future climates. the main advantage of this method is that it preserves the characteristics of standard weather pattern after modification. in the "morphing" method, three operations: ( ) a shift; ( ) a liner stretch; and ( ) a shift and a stretch, as listed in eqs. ( ) to ( ) are used to modify the weather file. where x is the existing hourly climatic variable; x y is the absolute change in yearly mean climatic variable for the year y; ˛y is the fractional change in yearly mean climatic variable for year y; x y is the climatic variable x average over year y. in this study, the hourly dry bulb temperature (dbt) of the existing hong kong tmy weather file was morphed by a combination of a shift and a stretch to generate another set of hong kong tmy weather file. the equation for morphing is shown as follows (eq. where dbt max y , dbt y and dbt min y = yearly mean daily maximum, average and minimum temperature of energyplus weather file data respectively; tmax y , temp y and tmin y = absolute change in yearly mean daily maximum, average and minimum temperature of hong kong weather data respectively; dbt = existing hourly temperature of energyplus weather file. a stretch method was adopted to adjust the current hourly dew point temperature (dpt). as required in epw weather file, the other climatic variable-relative humidity (rh), was calculated from the hourly value of dbt and dpt using ashrae psychrometric formulae [ ] . all the morphing processes involved above were automatically performed using excel vba. by using the morphing method, a set of , modified weather files was developed, taking into account the yearly weather variations. after the generation of , tmy weather files, jeplus, an open-source parametric analysis tool for managing the energyplus simulations, was used to automatically substitute the base case value of two calibrated models with the results of monte carlo simulation. based on the representative pdf of those seven influential parameters, a group of values representing one of the post-retrofit conditions is randomly generated using the latin hypercube sampling method (please refer to fig. ). to instruct jeplus running all the possible conditions of the post-retrofit period, a csv-styled text file containing , different values of each influential parameter was created. by incorporating the calibrated energy model, tmy weather files and a csv-styled text file, jeplus can simultaneously perform the eight instructed simulations at maximum in each run, and the simulation results are automatically grouped together for a probabilistic analysis of actual energy savings [ ] . the , energyplus iterations ( , iterations for each model) were performed in computers with two quad-core processors, taking h to complete the calculation. in this demonstration, timesteps per hour was used and the conduction transfer function was adopted as a heat balance algorithm in energyplus. a point worth noting is that the common data set was applied to all selected parameters for both models, except the parameter "overall cop of chiller plant" in the pre-retrofit model, which remains unchanged as the pre-retrofit condition. figs. and show the actual energy saving for all possible combination of the selected parameters and the fitted distributions of energy savings in the case study buildings. the possible energy savings after year retrofit period ranges from , kw h ( . %) to , kw h ( . %) with % statistical significance, which is best fitted by a weibull distribution with a mean , kw h ( . %) and a standard deviation , kw h ( . %). this suggests that the variations in actual yearly energy savings can be significant. the maximum energy savings can be times higher than the minimum one. the results also provide information on the probability of energy saving shortfall when a certain amount of energy savings is anticipated. for example, only by a . % chance the esco will successfully achieve the mean value of energy saving per year , kwh ( . %) for the replacement of heat rejection system in this study. further studies are needed to benchmark this sort of probability values when data on more buildings are available, but since the objective of this paper is to demonstrate a plausible methodology, it still serves its purpose. this paper proposes a simulation-based method to evaluate the probability of energy saving shortfall taking into account the variations in the influential parameters. a real case study of replacement of heat rejection system for a central chiller plant in hong kong is used to demonstrate the application of this probabilistic method. the result shows that the possible energy savings after a -year retrofit period can range from , kw h ( . %) to , kw h ( . %) with % statistical significance. this assessment method can be useful for evaluating the performance risks when certain amount of energy saving is guaranteed for retrofit measures. it should be noted that the confidence of the result relies on the representativeness of two building energy models, the selection of proper ranges and intervals for sensitivity analysis, as well as the goodness-of-fits of probabilistic distribution functions for selected parameters. besides, this study only focuses on the energy savings from the retrofit work. however, the financial benefits from epc projects also include the avoided-cost savings, for instance, a reduction in operation and maintenance costs. the future works on the risk assessment in epc projects should include the variations in such avoided-cost savings. with the use of this proposed methodology, the risks of epc will be better understood and managed. energy saving by realistic design data for commercial buildings in hong kong world business for sustainable development (wdcsb), energy efficiency in buildings: transforming the market an international survey of the energy service company (esco) industry high-efficiency hvac systems, and energy efficient lighting: market analysis and forecasts directive / /ec of the european parliament from volatility to value: analysing and managing financial and performance risk in energy savings projects the investment risk in whole-buildings energy efficiency upgrades projects actuarial pricing of energy efficiency projects: lessons foul and fair evolution of the u.s. energy service company industry: market size and project performance from promoting energy efficiency investments with risk management decision tools management measurement & verification of performance contracting american society of heating refrigerating and air-conditioning engineers, measurement of energy and demand savings, ashrae guideline - m&v guidelines: measurement and verification for federal energy projects international performance measurement & verification protocol sensitivity analysis techniques for building thermal simulation programs sensitivity analysis of energy performance of office buildings multi-parameter building thermal analysis using the lattice method for global optimisation energy efficient building design using sensitivity analysis-a case study sensitivity analysis and energy conservation measures implications a comprehensive analysis of the impact of occupancy parameters in energy simulation of office buildings probability concepts in engineering: emphasis on applications in civil & environmental engineering practical application of uncertainty analysis comparative analysis of support mechanisms for renewable energy technologies using probability distributions uncertainty sensitivity analysis of building performance using probabilistic climate projections: a uk case study, automation in construction uncertainty analysis in building performance simulation for design support method and case study of quantitative uncertainty analysis in building energy consumption inventories constructing design weather data for future climates developing a modified typical meteorological year weather file for hong kong taking into account the urban heat island effect height construction costs of residential high-rise buildings in shanghai energyplus energy simulation software, version american society of heating refrigerating and air-conditioning engineers, standard method of test for the evaluation of building energy analysis computer programs, ashrae code of practice for energy efficiency of building services installation, the hong kong special administrative region climate change in hong kong in, the hong kong special administrative region monthly climatological normals for hong kong ashrae handbook: fundamentals, ashare climatological information services, extracts of climatological data, the hong kong special administrative region diurnal temperature range as an index of global climate change during the twentieth century commercial property for lease and for sale assessing energy performance in the latest versions of hong kong building environmental assessment method (hk-beam) a study on the energy penalty of various airside system faults in buildings electrical and mechanical services department, energy saving charter neutral temperature in subtropical climates-a field survey in air-conditioned offices electric chiller performance evaluation based on actual operating data for energy service business palisade corporation, @risk, version . . performing omplex parametric simulations with jeplus the work described in this paper was fully supported by a grant from the general research fund of the research grants council of the hong kong special administrative region (project no. polyu / e) key: cord- - bri f authors: fattahi, a.; sijm, j.; faaij, a. title: a systemic approach to analyze integrated energy system modeling tools: a review of national models date: - - journal: renewable and sustainable energy reviews doi: . /j.rser. . sha: doc_id: cord_uid: bri f we reviewed the literature focusing on nineteen integrated energy system models (esms) to: (i) identify the capabilities and shortcomings of current esms to analyze adequately the transition towards a low-carbon energy system; (ii) assess the performance of the selected models by means of the derived criteria, and (iii) discuss some potential solutions to address the esm gaps. this paper delivers three main outcomes. first, we identify key criteria for analyzing current esms and we describe seven current and future low-carbon energy system modeling challenges: the increasing need for flexibility, further electrification, emergence of new technologies, technological learning and efficiency improvements, decentralization, macroeconomic interactions, and the role of social behavior in the energy system transition. these criteria are then translated into required modeling capabilities such as the need for hourly temporal resolution, sectoral coupling technologies (e.g., p x), technological learning, flexibility technologies, stakeholder behavior, cross border trade, and linking with macroeconomic models. second, a multi-criteria analysis (mca) is used as a framework to identify modeling gaps while clarifying high modeling capabilities of markal, times, remix, primes, and metis. third, to bridge major energy modeling gaps, two conceptual modeling suites are suggested, based on both optimization and simulation methodologies, in which the integrated esm is hard-linked with a regional model and an energy market model and soft-linked with a macroeconomic model. the long-term energy strategy of the eu is aimed at a - % reduction of greenhouse gas (ghg) emissions by , relative to . reaching this goal requires a number of key actions to make a transition from a conventional energy system to a low-carbon energy system [ ] . as a result, low-carbon energy system models (esms) have been developed to guide decision-makers on taking long-term robust policy decisions towards energy system transition. however, every esm has been developed to answer specific policy questions, due to the complexity of the energy system and limited computational power. as a result, each model comes with specific capabilities and shortcomings. a large growing body of the literature has listed and classified esms with different aims and scopes. connolly et al. provided a comprehensive overview of suitable esms addressing issues related to renewable energy integration [ ] . similarly, bhattacharyya et al. compared energy models to identify their suitability for developing countries [ ] . aiming to find the prevalent modeling approaches for the u.k., hall et al. classified and compared esms based on their structure, technological detail, and mathematical approach [ ] . to find trends in energy system modeling, lopion et al. reviewed esms in a temporal manner [ ] . some reviews have emphasized the role of policy strategies and the corresponding modeling challenges. by grouping energy models into four categories, pfenniger et al. examined the policy challenges they face in each group [ ] . horschig et al. reviewed esms to provide a framework for identifying a suitable methodology for the evaluation of renewable energy policies [ ] . while savvidis et al. identified the gaps between low-carbon energy policy challenges and modeling capabilities with a focus on electricity market models [ ] , ringkjøb et al. classified esms with a focus on the electricity sector [ ] . lastly, li et al. reviewed socio-technical models emphasizing societal dynamics [ ] . the increasing share of variable renewable energy sources (vres) has caused the low-carbon energy system transition to face several major challenges, such as the increasing need for flexibility, further electrification, emergence of new technologies, technological learning, efficiency improvements, decentralization, macroeconomic interactions, and the deeper involvement of stakeholders in the energy system transition. additionally, some policy questions at the macro level, such as the impact of the energy transition on the macroeconomic indicators (e.g., economic growth and employment), require more indepth integrated analysis, i.e., analyzing the whole energy system consisting of technical, microeconomic, and macroeconomic aspects. however, current esms lack specific capabilities for adequately addressing low-carbon energy system changes that can cause debated conclusions. for instance, one study found no feasible way to achieve a % renewable power system by [ ] , while another study claims that a % renewable eu power system scenario would require % higher annual costs [ ] . separate analyses suggested that a % renewable eu energy system can be achieved by with only % higher annual energy system costs [ ] , while neglecting significant parameters such as electricity grid costs, location of renewables, key technological detail, and flexible electricity demand. brouwer et al. provided a detailed analysis of the west european power sector with high shares of renewables, while neglecting the heat and transport sectors [ ] . brown et al. analyzed the cross-sectoral and cross-border integration of renewables in europe, while assuming no national transmission costs, limited efficiency measures, and limited technology options [ ] . social aspects of the energy system transition are usually neglected in esms. to this end, some studies included actors' behavior in the energy system from the demand perspective, for example, the thermal demand transition [ ] or the efficiency of adaptation measures in households [ ] . analyzing each of the major changes in the energy system can be challenging for conventional esms as they need further capabilities such as fine technological detail, high temporal and spatial resolutions, and the presence of stakeholders' behavior. this study concentrates on the energy modeling challenges which result from the increasing share of vres, complexity, and system integration. the transition towards a decarbonized energy system involves other policies such as the higher energy efficiency and change in energy demand, the use of nuclear power supply, and using carbon capture utilization and storage (ccus) technologies. due to the diversity of esms, two major limitations were imposed in this review. first, we focused on energy models at the national level. therefore, the reviewed models were designed for national analysis (or they can be used for national assessments, e.g., primes). second, the models covered all energy system sectors (i.e., residential, services, agriculture, transport, and industrial sectors). the overarching research question of this study is "what are the potential solutions to address the shortcomings of current esms considering current and future low-carbon energy system challenges?". to answer this question, we first describe the current and future lowcarbon energy system modeling challenges. based on these modeling challenges, we identify the required modeling capabilities, such as the need for hourly temporal resolution, sectoral coupling technologies (i.e., p x), technological learning, flexibility and storage technologies, human behavior, cross border trade, and linking with market and macroeconomic models. the required capabilities were then translated into assessment criteria to be used in the multi-criteria analysis (mca). finally, potential model development solutions are discussed and a modeling suite is proposed as a model-linking solution to address the energy modeling challenges. (fig. ) seven major low-carbon energy system modeling challenges were identified. the challenges were translated into a number of required energy system modeling capabilities and criteria. nineteen models were selected from other reviews ( [ , ] ). primary inclusion criteria for the selected models (see table ) were: ( ) being used at national level, and ( ) covering the whole energy system (i.e., integrated energy system models). all the information from the selected models was gathered from officially published documents that may be incomplete or outdated (notably when this paper is published), as models are continuously developed. for each model, a brief description was provided in the appendix section. ahp multi criteria analysis was used as a transparent framework to analyze diverse esms from different perspectives. mca is a methodology that evaluates complex choices (i.e., various criteria, objectives, and indicators), which has been used extensively to analyze energy transition policies [ ] . the major advantage of mca is that it provides a rational structure of complex alternatives that presents substantial elements for identifying the desired choice [ ] . although mca may have different purposes, we were particularly interested in: first, breaking down complicated energy models into key criteria; and second, identifying the importance or relative weight of each criterion for each alternative. models were ranked based on known criteria, but this did not mean one model was superior to others. therefore, the intention was not to compare models but to identify modeling capabilities and gaps when used for structuring a low-carbon energy system modeling framework. based on the identified modeling gaps, a conceptual modeling suite was proposed to address future low-carbon energy system modeling challenges. the proposed suite included a core integrated energy system model that was hard-linked with a regional model and soft-linked with both an energy market model and a macroeconomic model. energy policies are designed to meet three key objectives, which are providing energy reliability (i.e., supply security), affordability (i.e., economics and job creation), and sustainability (i.e., environment and climate) [ ] . with the aim of reviewing electricity market models, savvidis et al. [ ] clustered twelve energy policy questions as a basis to quantify the gap between models and policy questions. based on the literature and experts' opinions, we divided energy modeling related policy questions into four categories as follows: . technical questions, such as a lack of insights in higher share of intermittent renewables, role of new technologies, and further electrification of the energy system. . microeconomic questions, such as a lack of insights in decentralization, human behavior, and liberalized energy markets. . macroeconomic questions, such as a lack of insights on economic growth and jobs due to the energy transition. . a mix of the above questions, such as lack of insights on the effect of further electrification on energy markets. providing a solution for each policy inquiry can be a challenge for energy system modeling. these challenges can alter the choice of modeling methodology and parameters. in this section, energy modeling challenges and the corresponding modeling parameters are described. some sources of renewable energy such as wind and solar energies have an intermittent characteristic i.e., they are (highly) variable and less predictable [ ] . the power generation from intermittent renewables is directly dependent on weather conditions [ ] . as wind and solar power generation technologies are becoming more competitive [ ] , it is expected that wind and solar power generation will cover up to % and % of the eu's electricity demand by , respectively ( [ , ] ). hence, a high share of intermittent renewables in the electricity generation sector is imminent. technically, the power system needs to be in balance at all temporal instances and geographical locations. therefore, the electricity sector should be structured in a way to ensure the balancing of demand and supply. the higher share of intermittent renewables entails variability on the power system balance [ ] . solutions to deal with power balance variabilities are called flexibility options (fos) as they provide flexibility to the power system against the variable and uncertain residual load profiles. traditionally, conventional power supplies and grid ancillary services were primary sources of flexibility. however, the power system needs further fos as the share of intermittent renewables in the power generation increases while the share of conventional power supplies -i. e., notably dispatchable gas-fired power plants -decreases. several review papers can be used as a starting point for a review on fos ( [ , ] ). lund et al. [ ] listed different fos as demand side management (dsm), storage, power to x, electricity market designs, conventional supply, grid ancillary services, and infrastructure (e.g., smart grids and microgrids). further, sijm et al. [ ] investigated fos by suggesting three fig. . proposed modeling suite approach. the reviewed models and their corresponding developers. causes of the demand for flexibility as the variability of the residual load, the uncertainty of the residual load, and the congestion of the grid. michaelis et al. [ ] divided fos based on the residual load in three groups: downward, upward, and shifting flexibility. due to high detail and complications regarding each fo, some studies focused mainly on one or a few technologies. to name a few examples: blanco et al. investigated the cost-optimal share of power to methane in the eu energy transition [ ] . the potential of power to heat and power to ammonia in the dutch energy system was investigated by hers et al. [ ] and ispt [ ] , respectively. some other studies followed an integrated approach that included several fos in different sectors; however, they made several assumptions as the computational capacity was limited (e. g., see ref. [ ] ). flexibility options can be divided into five main groups, i.e., storage, demand response (dr), vre curtailment, conventional generation, and cross border trade. instead of analyzing the pros and cons of each option, we were interested in identifying key energy modeling issues regarding each flexibility option. (fig. ) from a temporal perspective, storage fos can be divided into daily and seasonal storage options. on the one hand, solid-state and flow batteries, such as li-ion, ni-cd, nas, icb, vrb, and znbr batteries, provide high ramp rate with limited capacity, which is suitable for diurnal power storage. modeling these batteries with diurnal temporal resolution can be different to hourly temporal resolution (htr) or hourly time-slices (i.e., grouping hours featuring similar characteristics [ ] ). improvements in temporal resolution can have a significant impact on modeling results considering the high share of intermittent renewables (e.g., see ref. [ , , ] ). on the supply side, the uncertainty regarding weather forecasts needs to be implemented in the model as weather conditions have a significant impact on intermittent renewables' generation (e.g., see ref. [ ] [ ] [ ] ). on the other hand, technology options, such as pumped-hydro energy storage (phes), thermal energy storage (tes), large-scale hydrogen storage (lshs), and compressed air energy storage (caes), provide huge capacities that makes them suitable for seasonal energy storage. modeling seasonal storage options requires the inclusion of chronological order (cho) of the temporal parameter together with a fine temporal resolution, as the chronological order of time from summer to winter (and vice versa) determines the charge/discharge of seasonal storage options. dr refers to a set of schemes to shift the demand in a certain time period (e.g., an hour) to another time period of the day, week, or month, either forward or backward [ ] . currently, electricity comprises around % of eu final energy consumption. power to x (p x) technology options can provide further dr potentials by linking energy sectors and energy carriers together through converting electricity to other forms of energy, services, or products. in its latest report, the world energy council suggests that p x will be a key element for the transition to a low-carbon energy system [ ] . due to high detail and complications regarding each technology option, several studies focus mainly on one or a few options. at eu level, blanco et al. investigated the cost-optimal share of p g in the eu energy transition [ ] . at the national level, the potential of p heat [ ] and p ammonia [ ] in the dutch energy system was examined. there is a huge potential for demand response in the built environment sector as it is responsible for % of energy consumption and % of co emissions in the eu. while individuals can passively participate in either price-based or incentive-based demand response schemes [ ] , proactive participation of consumers can increase market efficiency and reduce price volatility [ ] . as heating demand averages % of eu household energy consumption, the dr potential can be realized by coupling electricity and heat demands. dr in the built environment can consist of three main components including p heat technologies (e.g., heat pumps and electric boilers), storage (e.g., thermal tank storage and thermally activate building), and smart controllers (that consider market participation, consumer behavior, and weather forecast) [ ] . as p x technology options bridge two different energy sectors or carriers, analysis of these options requires multi-sectoral modeling, and preferably, integrated energy system modeling. moreover, the hourly temporal resolution of the power sector should be maintained. table summarizes key modeling capabilities and concerning energy sectors and carriers for each p x technology option. vre curtailment and conventional generation options have been used as fos in the power sector. modeling these options is relatively straightforward, as they do not involve other sectors or energy carriers. still, the hourly temporal resolution remains the key modeling capability for these options. from the energy security perspective, modeling conventional generation may require modeling capacity mechanisms, preferably in combination with cross border power trade [ ] . the eu is promoting an internal single electricity market by removing obstacles and trade barriers (see e.g., com/ / final - / ). "the objective is to ensure a functioning market with fair market access and a high level of consumer protection, as well as adequate levels of interconnection and generation capacity" [ ] . one of the products of an internal eu electricity market is the potential to offer flexibility in the power system, as the load can be distributed among a larger group of producers and consumers. sijm et al. identified the cross-border power trade as the largest flexibility potential for the netherlands [ ] . similar to other flexibility options, one of the key modeling capabilities here is the hourly temporal resolution. table summarizes the required key modeling capabilities for representing and analyzing flexibility options in esms. the main requirement is the inclusion of (at least) an hourly temporal resolution. models' capabilities can improve substantially by adding seasonal storage options, which require the inclusion of chronological order and different energy carriers. moreover, the inclusion of cross border trade can play an important role in the optimal portfolio of flexibility options, especially in eu countries. higher shares of intermittent renewables affect the reliability of power generation and distribution as residual loads become less predictable. for instance, the prediction accuracy of a single wind turbine generation decreases from - %- % mean absolute error for the hour ahead and day-ahead forecasts, respectively [ ] . the increased uncertainty of the power generation due to higher shares of vre sources requires models to include short-term weather forecast and balancing mechanisms in their calculations. uncertainty analyses gain more importance for long-term esms as they model the energy system for several decades in an uncertain future that can get affected by parameters outside the energy system boundaries. energy system optimization models use four main uncertainty analysis methods, which are monte carlo simulation (mcs), stochastic programming (sp), robust optimization (ro), and modeling to generate alternatives (mga) [ ] . in , almost % of the eu final energy demand was satisfied by electricity, while heat consumption and transport accounted for the rest. current heating and cooling production in the eu come from fossil fuel sources, as renewable energy sources have a . % share of gross heating and cooling consumption. the transport sector is highly dependent on fossil fuels, with only . % of final energy consumption from renewables. therefore, decarbonization of the heat and transport sectors is getting more attention as it has a higher ghg emissions reduction potential. the eu commission suggests electricity as an alternative fuel for urban and suburban driving in its report entitled clean power for transport [ ] . further electrification of heating, cooling, and transport sectors may contribute to ghg reduction, assuming the electricity is generated from renewables rather than fossil fuels [ ] . due to the high seasonal variation of heating and cooling demand profiles (mainly in the built environment), further electrification of this sector requires huge seasonal storage capacities or other flexible supply options. currently, there are four main high capacity seasonal storage options, which are pumped hydro energy storage (phes), compressed air energy storage (caes), thermal energy storage (tes), and hydrogen energy storage (hes). by using tes technologies, hourly heat and power demand profiles can be decoupled resulting in a higher potential for dr flexibility option [ ] . tes technologies can be divided into three main groups based on their thermodynamic method of storing heat energy: sensible, latent, and chemical heat [ ] . sensible heat storage (shs) technologies stock the heat by the difference in the materials' temperature, for example by warming up water or molten salt tank. latent heat storage (lhs) technologies make use of phase-change materials (pcm) in a constant-temperature process to absorb or release thermal energy. chemical heat storage (chs) technologies make use of thermo-chemical materials (tcm) in a reversible endothermic or exothermic (i.e., a chemical reaction in which the heat is absorbed or released, respectively) process, for example, the reversible ammonia dissociation process (i.e., nh =n + h ). xu et al. [ ] provided an extensive review of current seasonal thermal energy storage technology options. further electrification of the energy system, which is expected to account for - % of final eu energy consumption by [ ] , generates higher interdependencies between energy sectors. single sector models, which are not able to capture sector coupling effects, may provide misleading conclusions by neglecting these interdependencies. as more sources of intermittent renewables are deployed in the energy system, the further electrification implies further volatility of the energy system that highlights the higher demand for flexibility options. moreover, analyzing sector coupling technologies such as evs (p mobility), heat pumps and electric boilers (p heat), and electrolyzers (p gas) become more important. inclusion of sector coupling options in the esm requires modeling of electricity, transport, and heat sectors simultaneously. due to high variations in the electricity supply, a fine temporal resolution should also be employed in the transport and heat sectors in order to adequately address the flexibility issues of sector coupling. development of new technologies and technological change are key drivers of the transition to a low-carbon energy system and are at the core of most energy-climate policies worldwide [ ] . for instance, the price decline of pv cells from . usd/w to . usd/w in the last years [ ] has made solar energy an economic option independent of subsidies. development of new technologies have made additional renewable energy supply sources available such as advanced biofuels, blue hydrogen, deep geothermal, wave, and seaweed. it also provides innovative opportunities for the further integration of the energy system by implementing p x technologies, which mainly consist of p heat, p g, p h , p l, and p mobility technology options. the seasonal variation of wind and solar increases the need for seasonal storage options such as thermal energy storage and caes. ccs and ccu technologies can be considered as alternative solutions for conventional ghg emission emitters. deep decarbonization of the industrial sector can be achieved by the development of new industrial processes while considering the whole value chain [ ] . the development of zero energy buildings [ ] and formation of energy-neutral neighborhoods [ ] can contribute to substantial energy savings in the built environment. esms currently represent technological learning either exogenously or endogenously [ ] . technological change is prevalently expressed as a log-linear equation relating technology cost to its cumulative production units. this one-factor equation provides the learning rate, which is the cost reduction that results from doubling the cumulative produced units of the concerned technology [ ] . the prominent alternative is the two-factor equation that incorporates both cumulative produced units and r&d investments [ ] . endogenous technological learning (etl) is widely used in long-term esm analysis (e.g., see ref. [ ] [ ] [ ] ). etl can be further elaborated as multi-cluster learning (mcl) and multi-regional learning (mrl) [ ] . mcl (or so-called compound learning) describes a cluster of technologies, which share the same component and learn together (e.g. see ref. [ ] ). mrl differentiates between region-specific technological learning and global technological learning. the consideration of new technologies and technological learning can greatly affect the energy system modeling results, particularly in long-term models. for instance, heuberger et al. [ ] . concluded that the presence of global etl will result in % more economically optimal offshore wind capacity by . as part of the clean energy for all europeans package, the eu sets binding targets of at least . % energy efficiency improvement by , relative to the business as usual scenario [ ] . this policy emphasizes particularly the built environment as the largest energy consumer in europe. although energy-efficient technologies provide financial and environmental costs reduction, they are not widely adopted by energy consumers. this "energy efficiency gap" can be a consequence of market failures, consumer behavior, and modeling and measurement errors [ ] . energy efficiency policies may induce the rebound effect (or backfire), in which energy efficiency improvements lead to an increase in energy use. the rebound effect may have a direct decreasing impact in energy consumption (e.g., a decrease in residential energy consumption), while having an indirect increasing impact (e.g., an increase in energy use by expansion of energy-intensive industries) [ ] . providing an accurate estimate of the magnitude of the rebound effect can be challenging ( [ ] , while the existence of this effect is a matter of discussion in the literature [ ] . although energy-efficient technologies can play an effective role in energy system transition, modeling and analyzing its direct and indirect effects is challenging. energy infrastructure has a key role in the low-carbon energy system transition by facilitating sectoral coupling, integrating renewable energies, improving efficiency, and enabling demand-side management. however, analyzing energy infrastructure can come up with some challenges, such as the complexities of distributing costs and benefits of investments and allocation of risk between investors and consumers [ ] . conventional energy infrastructure facilities are usually managed by a monopoly as public goods are not traded in a market. therefore, the clear disaggregation of costs and benefits of infrastructure changes due to energy transition needs further evaluation [ ] . long-term infrastructure investment and risk profiles of investors and consumers can be highly diverse as energy infrastructures can undergo drastic changes. moreover, social acceptance of energy infrastructure plays a key role in energy transition, particularly in decentralized infrastructures such as ccus networks, transmission lines, district heating, and local energy storage. modeling the social acceptance of energy infrastructure requires a combination of qualitative and quantitative datasets which can be highly locally dependent [ ] . assuming the above-mentioned datasets are available, esms would require specific capabilities to analyze energy infrastructure. the esm should be geographically resolved, as energy infrastructure can have both local and national scales. moreover, there is a need for gis-based geographical resolution of esms as costs and benefits of energy infrastructures can change drastically by their geographical location. over the past decades, energy used to be supplied by large power plants and then transmitted across to the consumers. by emerging renewable energy supplies, a new alternative concept of the energy system has been developed. the decentralized energy system, as the name suggests, is comprised of a large number of small-scale energy suppliers and consumers. a transition from a centralized fossil-fuel and nuclear-based energy system to a decentralized energy system based on intermittent renewable energy sources can be a cost-effective solution for europe [ ] . the local energy supply reduces transmission costs, transmission risks, environmental emissions, and to some extent promotes energy security for a sustainable society, with a competitive energy market. on the other hand, it can increase generation costs capacity investment, distribution, and energy reliability. therefore, there is a need to determine the optimal role of energy system decentralization by carefully analyzing costs and opportunities. conventional energy modeling tools were based on the centralized energy system and they have faced difficulties fulfilling the decentralized energy system demands. in conventional energy models, the location of the power plants does not play an important role, while spatial detail may be critically important for renewables. for instance, economic potentials, solar potentials, generation costs, environmental and social impacts, network constraints, and energy storage potentials are some location-dependent factors that can vary greatly across different regions. some other factors such as wind potential and infrastructural costs can vary greatly even with little dislocation. therefore, a fine spatial resolution is required in order to assess the role of locationdependent parameters in the energy system. esms can use national, regional, or gis (geographical information system) based spatial resolution. using a fine spatial resolution can be limited by the available computational power and spatial data. therefore, the choice of spatial resolution is the compromise between these two parameters. due to the huge computational load of gis-based esms, they are usually applied at urban level rather than national level. gisbased models can be used in a preprocessing phase in order to provide spatially resolved datasets for national esms. for instance, the global onshore wind energy potential dataset is produced at approximately km resolution [ ] . assuming the availability of spatial data, the computational limitation can be addressed by linking a coarse resolution energy model with a spatial modeling tool such as arcgis (e.g., see ref. [ ] ). conventional energy models neglected social stakeholders as the energy system was managed and controlled by central decision-makers. in order to reach a sustainable low-carbon energy system, technical and social insights should be integrated into these models [ , ] . according to the technology review of the u.s. department of energy, the balance of energy supply and demand is affected as much by individual choices, preferences, and behavior as by technical performance [ ] . the reliability of energy models is often low because they are excessively sensitive to cost analysis while ignoring major energy policy drivers such as social equity, politics, and human behavior [ ] . several studies have recently indicated the role of social sciences in energy research [ , ] . social parameters are usually difficult to quantify, and consequently, are usually neglected in quantitative energy models. however, there are practical methods of integrating human aspects into technical energy models, such as the inclusion of prosumers and agent-based modeling. originally coined by alvin toffler in his book the third wave [ ] , prosumer is the mixture of the words producer and consumer, explaining the active role of energy consumers in the production process. the conventional energy grid was dependent on the interaction between supplier and distributor, while consumers play an active role in the decentralized energy system. an important element of this new system is the role of prosumers i.e., consumers who also produce and share surplus of renewable energy generated with the grid and/or other consumers in the community [ ] . with the emerging renewable energies at the microscale, prosumers are not only an important stakeholder of the future smart grids but may also play a vital role in peak demand management [ ] . however, social acceptance of the decentralized energy system faces several drivers and barriers [ ] that need quantification in order to be imported into energy models. the emergence of prosumers has increased the diffusion of social sciences in energy system modeling (e.g., see refs. [ ] [ ] [ ] [ ] ). in order to grasp an adequate knowledge of the decentralized energy system, the behavior of the prosumers on energy grid should thus be considered alongside the techno-economical characteristics (e.g., see ref. [ ] [ ] [ ] ). based on the position of the decision-maker, esms can be divided into two main categories. the common approach is the assumption of a system planner who optimizes the single objective function (e.g., system cost minimization). contrary, agent-based models practice decentralized decision making by assuming autonomous agents who decide based on their own objectives. agent-based modeling has been proposed as a suitable modeling approach for complex socio-technical problems [ ] and it is used in modeling the wholesale electricity market considering human complexities [ ] . ringler et al. reviewed agent-based models considering demand response, distributed generation, and other smart grids paradigms [ ] . the term "agent" can be used to describe different types of players in the energy system such as prosumers, power generators, storage operators, or policy makers. agents can optimize their own objective function, which can be based on economic (e.g., capital, npv, and tariffs), technical (e.g., efficiency, emissions, and maximum capacity), and social (e.g., bounded rationality, neighborhood effect, and heterogeneity) factors. including techno-economic factors in the objective function is relatively easier due to the quantitative nature of these parameters, while integrating qualitative social parameters remains a complicated task. qualitative parameters such as the perceived weight of environmental costs and impacts, expected utilities, social networks, and communication can be estimated by socio-demographic factors and behavior curves (e.g., see ref. [ ] [ ] [ ] ). macroeconomic models follow a top-down analytical approach compared to techno-economic esms that use a bottom-up approach. the analytical approach is the way to break a system into elementary elements in order to understand the type of interactions that exist between them. this system reduction may be done in different ways. based on the reduction approach, esms are usually differentiated into three main groups: top-down, bottom-up, and hybrid models. top-down (td) models describe the energy-economy system as a whole to assess the energy and/or climate change policies in monetary units [ ] . these models mainly describe the relations between the energy system and the variations in macroeconomic and environmental factors such as economic growth, demographics, employment rate, global warming, and ghg emissions. consequently, top-down models lack detail on current and future technological options which may be relevant for an appropriate assessment of energy policy proposals [ ] . macroeconomic equilibrium models are an example of top-down models. bottom-up (bu) models, provide a higher degree of technological detail (in comparison to top-down models). characterized by a rich description of the current and prospective energy supply and end-use technologies, bottom-up models describe energy systems evolutions as resulting from a myriad of decisions on technology adoption [ ] . they can compute the least-cost solution of meeting energy balances subject to various systems constraints, such as exogenous emission reduction targets [ ] . hybrid models (i.e., linking td and bu models) can be a solution to integrate top-down consistency while maintaining bottom-up detail. the major advantage of top-down models is their consistency with welfare, market, economic growth, and other macroeconomic indicators that leads to a comprehensive understanding of energy policy impacts on the economy of a nation or a region. on the other hand, they lack an appropriate indication of technological progress, energy efficiency developments, non-economical boundaries of the system, and other technical details. instead, bottom-up models describe the energy system with detailed technological properties. moreover, bottom-up models lack feedback from the macro-effects of the technical changes in the overall economy. therefore, closing the gap between top-down and bottom-up energy models results in more consistent modeling outcomes (e.g., see ref. [ ] [ ] [ ] [ ] ). model linking is not an exclusive solution for td and bu models. hourcade et al. [ ] argued that the three main dimensions of an energy-economy system are: technological explicitness, microeconomic realism, and macroeconomic completeness. the main advantage of model linking (i.e., modeling suite) is the ability to provide consistent results while considering two or all three dimensions. each of these dimensions can be modeled with a number of different models depending on the complexity of the problem. the model linking approach can be classified into three subcategories, based on the level of linking [ ] . first, individual stand-alone models are linked together manually meaning that the processing and transferring of the information between models are controlled by the user, preferably in an iterative manner (i.e., soft-linking). second, a reduced version of one model exchanges data with the master model while both running at the same time (i.e., hard-linking). third, a combined methodology features an integrated model through a unified mathematical approach (e.g., mixed complementarity problems [ ] ). (fig. ) helgesen [ ] used another classification based on the linking type of models and the terminology proposed by wene (i.e., soft-linking and hard-linking) [ ] . the advantages of soft-linking can be summarized as practicality, transparency, and learning, while the advantages of hard-linking are efficiency, scalability, and control [ ] . the above discussion of the main challenges of the present and future esms identified several required modeling capabilities, which are summarized in table . in order to review models based on mentioned challenges, required capabilities are grouped into several model assessment criteria in table . it should be noted that the integrated energy system analysis capability is not mentioned further as all reviewed models were integrated. moreover, the linking esms with td models' capability is discussed further in section . apart from the criteria that results from emergent challenges of future esms, three additional criteria are considered in table , namely: (i) the underlying methodology of the model to separate calculator models from non-calculator ones; (ii) the source of the model's datasets to measure input-data quality; and (iii) the accessibility and the number of the model's applications to determine the models' use and acceptance. considering the criteria regarding the future low-carbon energy systems and available models, it can be concluded that no perfect model exists. models can be assessed based on the list of criteria such as temporal resolution, spatial resolution, the social aspect, data source quality, accessibility, and application ( table ). the capability of the model in each criterion is given a score from five (highest) to one (lowest) as presented in table . the results are highly dependent on the scores and weights, which are both -to some extent -subjective. readers can alter the results by incorporating new criteria or changing the perspective weights. in the following sections, these modeling capabilities and the corresponding scores are explained. there are two parameters that differ across integrated esms, which are the inclusion of fos and the inclusion of technological learning. therefore, models can be grouped into three groups: (i) no flexibility option and no technological learning that would score one; (ii) the inclusion of either flexibility options or technological learning that would score three; and (iii) the inclusion of flexibility options and technological learning that would score five. esms usually balance the supply and demand on a yearly basis or a limited amount of (hourly) time-slices per year. nevertheless, some models have a higher temporal resolution and balance the system on an hourly basis. reviewed models can be categorized in three groups: (i) temporal resolution on yearly basis that would score one; (ii) time-slice approach that would score three; and (iii) hourly temporal resolution that would score five. some models have the capability to model the regions inside a country. this ability can provide regional insights on energy system policies and vice versa. although the limited computational capacity and the lack of data make it difficult to perform a detailed regional analysis, some models balance the system in different regions inside the country based on different capacities and properties of the regions (e.g., esme in the uk). reviewed models are divided in three groups: (i) models without regional depth that would score one; (ii) models which consider regions that would score four, since it is a considerable improvement; and (iii) models which consider gis data that would score five. the role of social analysis in techno-economic models is usually negligible. however, some modeling tools practice multi-agent programming in order to model qualitative aspects of stakeholders' decision-making practice on energy systems. models are categorized into two groups: (i) models capturing socio-economic parameters only based on demand curves that would score one, and (ii) agent-based models considering a set of decision-making rules for different stakeholders in the energy system that would score five. reviewed models practice a different set of methodologies. in this review, the main categorization between methodologies can be made between the calculator and non-calculator methodologies. therefore, models can be grouped into two groups: (i) calculator models that would score one, and (ii) non-calculator models that would score five. the depth of technical detail and the quality of the data play a crucial role in providing accurate insights into the energy system with regard to new technologies and sectoral coupling. moreover, data access is the first limitation of energy system research as databases are rather private. models can then be divided into five groups: (i) models not indicating a data source that would score one; (ii) models using generalized opensource data that would score two; (iii) models using limited countryspecific data that would score three; (iv) models using detailed opensource data that would score four; and (v) models using detailed country-specific datasets, possibly in combination with global datasets that would score five. open-access models provide an opportunity to test the model and provide feedback. these models are divided into five groups: (i) models which provide no access that would score one; (ii) models which provide limited access that would score two; (iii) models which are commercial that would score three; (iv) models which are open-source but need permission that would score four, and (v) models which are completely open-source and accessible on internet that would score five. a model with more applications and users makes it easier to disseminate and discuss results. models are grouped in five sets: (i) models with no publication yet that would score one; (ii) models applied in one country that would score two; (iii) models applied in two countries that would score three; (iv) models applied across eu countries that would score four, and (v) models which applied in many countries and are well-known that would score five. table demonstrates the mca analysis with equal weight for all criteria. to calculate the score of each model for each criterion, the weighted percentage of that criteria in the model's total score is demonstrated. this percentage is calculated endogenously, as explained by (equation ( ) . it indicates the share of the models' score in each criterion out of the models' total score. primes would score high mainly due to the inclusion of social parameters, while the high score of remix is due to its high spatial resolution. these models merely demonstrate improved capabilities compared to others; therefore, it does not mean that these models are "best" models. moreover, some features of the models are not reflected in this table. for instance, metis works complementary to long-term esms as it only simulates one specific year. besides, the mca results can be changed considerably by assigning slightly different scores to various criteria as total scores are relatively close. models such as the markal family and metis demonstrate high scores mainly due to their high granularity; however, they lack the inclusion of social parameters. ensysi includes social parameters while lacking spatial resolution and application. addressing all the policy-induced challenges of the energy system requires a comprehensive esm that is not yet available. therefore, a compromise should be made based on the challenges that the model is designed to address. consequently, a weighted decision matrix can be formed by using the ahp method [ ] . in this method, the criteria are rated against each other with respect to the challenges. a consistency ratio (cr) is calculated to indicate the reliability of the weight table. saaty suggests that the crs of more than . are too inconsistent to be considered reliable [ ] . here the challenges are divided into two main groups, first: intermittency, flexibility, and further electrification; and second: human behavior and decentralization. the first group of challenges puts emphasis on the technological detail, the high temporal and spatial resolution; while the second group emphasizes the inclusion of social parameters and high spatial resolution. the pair-wise weighted decision matrix for the first group of challenges is formed in table . in each row, the importance of a criterion compared to other criteria is given a number in this order: would be equal importance, would be fairly important, and would be extremely important. it should be noted that these numbers are entirely subjective, thus, the user can make his own decision matrix. then, the table is normalized and the sum of each row is reported as the weight of the criterion. to calculate the cr, each column of the pair-wise table is multiplied by the corresponding weights. then, the sum of each row is divided by the corresponding weight to get λ values. the cr is then calculated by equation ( ), in which n is the number of criteria. repeating the same procedure for the second group of challenges leads to table . in both cases, the low cr indicates low levels of inconsistency in the assigned weights. using the weights in table to update the mca will lead to a slightly different result, presented in table . for the first group, it is expected that models with high scores in technological detail, temporal resolution, and spatial resolution will get higher total scores. the remix model gets a high total score mainly due to the inclusion of high spatial resolution with the use of gis data and the inclusion of key flexibility and storage technologies with the exogenous technological learning. the metis model provides lower technological detail by neglecting technological learning while incorporating hourly temporal resolution and gis-based spatial resolution. for the second group, the inclusion of social parameters and fine spatial resolution gains importance. models with the inclusion of social parameters such as primes and ensysi get higher scores. although the metis model does not include social parameters, it keeps a high score due to its fine spatial resolution. irrespective of the assigned weights, we find four models at the top of the mca table which are remix, primes, metis, and the markal family models. these models had high scores in nearly all criteria, while a low score in one criterion (for instance, lack of social parameters for remix) is compensated with a high score in another criteria (high temporal and spatial resolution). these four models were either developed recently (e.g., remix and metis) or are under constant development (e.g., markal family and primes). it shows how integrated energy system modeling points towards the models with improved capabilities in all the criteria. other models keep the same ranking position except for iwes, ensysi, and energyplan, which changed their position considerably (i. e., more than two steps change). this position change can be explained by the asymmetry of these models' scores in the mca table. for instance, the iwes model gets a high score in the first four criteria while getting a low score in the last four criteria. the mca represents an overview of the current state of esms with regard to low-carbon energy system modeling challenges. however, there is a need for adding new capabilities to current esms in order to address future modeling challenges. in the next section, we discuss two potential modeling solutions based on our observation from the current state. the overall solution is to expand single models and/or to link different models. it is not practical to decide on the best model that addresses challenges regarding low-carbon energy systems, as each model has specific pros and cons. from a techno-economic point of view, the mca indicates that for modeling the low-carbon energy system, current models require specific capabilities such as hourly temporal resolution, regional spatial resolution, inclusion of sectoral coupling technologies, technological learning, and inclusion of social parameters. there are major gaps between policy questions and modeling capabilities in the criteria, which were used to assess the models' performance. however, these criteria mainly focus on the technical policy questions rather than the entire technical, microeconomic, and macroeconomic aspects. although techno-economic models are rich in detail, they lack the capability to answer microeconomic and macroeconomic policy questions. therefore, specific models, such as energy market models and general equilibrium models, have been developed. due to the strong interconnection between energy and economy, mixed policy questions arise that require analyzing the technical, microeconomic, and note: percentages may not add up to due to rounding. macroeconomic aspects of the energy-economy system. such analysis can be conducted either by developing single models or by combining different models (i.e., soft-linking, hard-linking, or integrating). current single models can be developed and/or extended by incorporating further capabilities up to acceptable computational limits. considering the limitations, the modeler makes choices and/or tradeoffs on extensions to the model. developing a single model that can cover all the mentioned gaps could face limitations, such as complicated mathematical methodology and limited computational capacities (except generic limitations such as high data needs and lack of transparency). some common energy system modeling methodologies are optimization, simulation, accounting, multi-agent, and equilibrium. each mathematical methodology can be developed to answer specific energy modeling questions. integrating two different methodologies can be mathematically very complicated (e.g., mixed complementarity problems in which the optimization and equilibrium formulations are mixed) or not feasible (e.g., mixing optimization and simulation formulations). therefore, single esms are naturally limited by their underlying methodology. one of the main limitations for improving the temporal and geographical resolution of esms is the computational capacity. the computational limitation can be addressed either by hardware or software development. (fig. ) hardware development follows an exponential growth and relates to improvements in the number of transistors, clock frequency, and power consumption of processors. on the other hand, software methods can be divided into solver-related and modelspecific methods to improve computing times of linear optimization esms [ ] . solver-related methods focus on improving the solving methodology by using different off-the-shelf algorithms, such as lindo, cplex, gurubi, and mosek, or by practicing customized algorithms, such as bender's decomposition and parallelization. model-specific methods relate to heuristic methods, such as clustering, model reduction, decomposition, and parallelization. hardware-related developments proceed at a specific pace that is usually not affected by energy system modelers as users. solver-related developments are followed by a few energy system modelers (e.g., see the beam-me project [ ]), while the rest of the energy system modeling community follows model reduction and clustering methods that can be applied on temporal resolution, spatial resolution, and technological detail (e.g., see [ ] ). depending on the research questions, energy system modelers reduce or coarsen the resolution of the model in order to provide an answer in an adequate timeframe. therefore, a trade-off should be made between different modeling capabilities by making smart assumptions. an alternative approach to overcome the limitations of single model development is to form a modeling suite. model linking can be done between any set of desired models in order to enhance modeling capabilities. however, two types of energy model linking are more frequent in the literature: ( ) linking bu and td models such as optimization energy system models (oesms) linked with cge models, and ( ) linking two bu models such as oesms combined with energy market models (i. e., unit commitment or dispatch models). although linking models provides further modeling capabilities, it comes with certain challenges [ ] such as the identification of connection points in soft-linking (e.g., see ref. [ ] ), convergent solution in soft-linking (e.g., see ref. [ ] ), and mathematical formulation for integrated linking (e.g., see ref. [ , ] ). in summary, linking models can be resource-intensive as it requires the knowledge of different modeling frameworks. each model has its own set of assumptions and methodologies, which makes it complicated to maintain the harmonization of modeling assumptions in all steps of linking. the lack of harmonization in assumptions may result in inconsistent results from linked models. although this process seems straightforward, it is rather a puzzling procedure as esms are moderately complex. therefore, having an overview of different energy models and their capabilities is essential to provide the desired modeling suite. a linking approach is proposed for addressing current energy system modeling gaps. table provides an overview of identified energy modeling gaps and corresponding linking suggestions. these suggestions can form a modeling suite that involves four different models, namely, the energy system model (esm), the energy market model (emm), the macroeconomic model (mem), and the socio-spatial model (ssm). the suggestions in table can be framed in two separate modeling suites based on the methodology of the core esm. (fig. ) the first modeling suite can be formed around an optimization esm (oesm) that provides the cost-optimal state of the energy system assuming a fully rational central social welfare planner. the second modeling suite uses a socio-technical esm (stesm) that demonstrates a more realistic state of the energy system by assuming profit maximizer agents who consider social decision-making parameters in their decision-making process. such parameters include behavioral economics, bounded rationality, neighborhood effect, and technology diffusion curve. the core component of the suggested modeling suite is the presence of a central techno-economic esm as an information processor hub that exchanges the outputs with different models. based on the current state of the energy system and future scenarios, the esm can determine the technology and energy mix, commodity and energy prices, amount and price of emissions, and total energy system cost. however, this standalone analysis is based on specific scenario assumptions of demand profiles, energy import and export profiles, decentralized energy supply prospects, and macroeconomic expectations. it is suggested to use linear relations (i.e., linear optimization methodology) to keep the computational load manageable. while the optimization framework determines the theoretically optimal state of the energy system, the simulation methodology can demonstrate feasible pathways to reach the optimal state. therefore, by comparing the results of the optimization and simulation frameworks, the gap between the optimal solution and the feasible solution (symbolically demonstrated in fig. ) can be identified. several policy parameters can affect the width of this gap by bringing the feasible solution close to the optimal one. therefore, the analysis of the simulation and the optimization methodologies can provide a better understanding of the role of each parameter in reaching the optimal state of the energy system policy targets. based on the review and the mca, several optimization esms such as times and remix can be used as the core esm of the modeling suite, due to their fine temporal resolution and ample technological detail. agentbased simulation esms are not as common as optimization esms; therefore, from the reviewed models, only ensysi and primes can be selected as simulation core esms. current esms lack the capability to model the regional implications of the energy system such as decentralized supply and demand, infrastructure costs and benefits, land use, and resource allocation. although some local energy system models such as energis [ ] and gisa sol [ ] provide geographically resolved energy system analysis, they lack the interaction with other country regions. as regional variations of the energy system can have drastic effects on the system itself, it is suggested to hard-link the regional model into the core esm. the geographical resolution of esms can be improved depending on the research questions and available resources. for instance, after identifying spatially sensitive parameters of the energy system, such as heat supply location, renewable power production, transmission capacity expansion, and storage infrastructure, sahoo et al. provided a framework to integrate them into an esm (i.e., the opera model) [ ] . focusing on infrastructure, van den broek et al. clustered the co source regions using the arcgis software and then incorporated the spatially resolved data into the markal-nl-uu as the optimization-based esm [ ] . for well-connected countries, it is suggested to hard-link an emm with the core esm to capture the flexibility potential of the cross-border energy trade, albeit some studies that use a soft-linking approach (e.g., see ref. [ , ] ). in particular, for eu countries, this hard-linking is necessary as the interconnection flexibility option (fo) can be in direct competition with domestic fos such as demand response or storage. emms usually use the milp underlying methodology in order to model unit commitment; therefore, the inclusion of emm inside esm can be computationally intensive. it is suggested to use a linear optimization methodology in accordance with the core esm to reduce computational load, while reaching a fair estimate of the energy import and export flows, particularly for electricity. assuming the regional and interconnection capabilities are integrated into the core esm, in order to capture consistent economic analysis, one soft-linking loop is suggested as follows. this loop incorporates a macroeconomic model, which keeps demand and supply of commodities in equilibrium based on the statistical economic data such as capital stocks and investments, demographics, labor market, and trade and taxes. the esm outputs, such as energy prices, energy mix, and emissions are fed into the mem to update the supply and demand and price data of energy and fuel commodities. the mem provides the equilibrium demographics, gdp and income, monetary flows between economic sectors, trade, and employment rate. this loop can be performed once or it can continue until the results reach a convergence criterion, which is a user-defined criterion that determines the maximum gap between the results of two models. moreover, mem outputs can feed into an abm simulation esm in table model development and model linking suggestions based on the identified energy modeling gaps. lack of sectoral coupling technologies between electricity, heat, and transport sectors. developing a long-term planning optimization energy system model (esm) that involves all energy sectors, hourly temporal resolution, regional spatial resolution, seasonal storage options, and technological learning lack of new seasonal storage technology options such as tes and hes. lack of endogenous technological learning rates. lack of hourly temporal resolution for capturing intermittent renewables and corresponding potentials. lack of regional spatial resolution for analyzing energy flows between regions across a country. hard-linking esm with a regional energy system model (resm) that involves resolved spatial resolution, land use analysis, and infrastructure analysis lack of fine geographical resolution options such as gis, fine mesh, and clustering for analyzing decentralized intermittent supply and infrastructure costs and benefits lack of spatially resolved datasets such as infrastructure and local storage. simplistic modeling of human behavior in the current abms. developing an abm simulation socio-technical energy model (stesm) that involves stakeholders' behavior, local and neighborhood effects, bounded rationality, and perceived environmental values. the focus of current datasets is only on technological detail, rather than stakeholders' behavior. high dependence of esms on consumer load profiles. lack of national energy modeling consistency with a european (or an international) energy market. hard-linking esm with an international (or european) energy market model (emm) that involves an optimal dispatch electricity market, the gas and oil market, hourly temporal resolution, regional spatial resolution, and a detailed generation database lack of energy modeling consistency with macroeconomic indicators which consumer demand profiles are generated based on demographics, income, and employment (e.g., see ref. [ ] ). the stesm analyzes the social aspects of the energy system such as stakeholders' behavior, bounded rationality, imperfect communication, and environmental perceived value. the choice of models, connection points, and scenarios are dependent on the aims of the energy system modeling, available expertise and resources, and access to models and datasets. in summary, we identified the capabilities and shortcomings of current esms to analyze adequately the transition towards a low-carbon energy system. in this regard, we described seven current and future low-carbon energy system modeling challenges. finally, to bridge major energy modeling gaps, two conceptual modeling suites are suggested, based on both optimization and simulation methodologies, in which the integrated esm is hard-linked with a regional model and an energy market model and soft-linked with a macroeconomic model. model development and linking choices can be affected by major changes in the energy system outlook. for instance, the current covid- situation can have major impacts on economic activities, indicating the importance of soft-linking with macroeconomic models. a limitation of this study is that all the information about models has been gathered from published documents, which might be outdated as models are constantly under development. therefore, this review provides a rather static view on esms. only a limited number of energy system models was presented in this review, which is mainly due to limited time, resources, and access to modeling databases. other challenges of low-carbon energy systems modeling not included here are the need for energy policy harmonization, energy market design, business models of new technologies, legislation and legal aspect of the energy transition, and social acceptance implications of the energy transition. another limitation of this study is the subjective assignation of scores with the mca, however, a clear explanation for the assignation of scores was provided. furthermore, the mca only considered single esms while in practice a combination of models can be analyzed. a more comprehensive mca would consider the capabilities and limitations of suites of models. the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. the revised renewable energy directive: clean energy for all europeans a review of computer tools for analysing the integration of renewable energy into various energy systems a review of energy system models a review of energy systems models in the uk: prevalent usage and categorisation a review of current challenges and trends in energy systems modeling energy systems modeling for twenty-first century energy challenges are decisions well supported for the energy transition? a review on modeling approaches for renewable energy policy evaluation the gap between energy policy challenges and model capabilities a review of modelling tools for energy and electricity systems with large shares of variable renewables a review of socio-technical energy transition (stet) models burden of proof: a comprehensive review of the feasibility of % renewable-electricity systems broek mv d. is a % renewable european power system feasible by ? smart energy europe: the technical and economic impact of one potential % renewable energy scenario for the european union least-cost options for integrating intermittent renewables in low-carbon power systems synergies of sector coupling and transmission reinforcement in a cost-optimised, highly renewable european energy system agent-based modeling of a thermal energy transition in the built environment adoption of energy efficient technologies by households -barriers, policies and agent-based modelling studies dynemo: model documentation. london: ucl energy institute dynemo: a dynamic energy model for the exploration of energy, society, and environment metis technical note t : metis software introduction and architecture. european commission. brussels: directorate-general for energy australian energy projections to - the national energy modeling system. an over view. energy information administration the supply of flexibility for the power system in the netherlands a simulation model for the dutch energy system. the hague: pbl netherlands environmental assessment agency osemosys: the open source energy modeling system an introduction to its ethos, structure and development modelling low-carbon energy system designs with the eti esme model. eti poles-jrc model documentation. luxembourg: publications office of the european union primes model, version . national technical university of athens a time step energy process model for germany -model structure and results scenario analysis: electrification of commercial urban road transportation and impacts on the energy system future security of power supply in germany-the role of stochastic power plant outages and intermittent generation analysis of alternative uk heat decarbonisation pathways. imperial college london for the committee on climate change institute for sustainable solutions and innovations (isusi) stockholm environment institute system analysis: dtu, department of management engineering documentation for the markal family of models documentation for the times model, part i. international energy agency a review of multi criteria decision making (mcdm) towards sustainable renewable energy development sensitivity analysis of multicriteria decision making methodology developed for selection of typologies of earth-retaining walls in an urban highway the goals of energy policy: professional perspectives on energy security, economics, and the environment impact of the level of temporal and operational detail in energy-system planning models large-scale variability of weather dependent renewable energy sources. management of weather and climate risk in the energy industry trends reshaping climate and energy the european political strategy centre wind energy in europe: scenarios for an industrial policy for solar in europe. solarpower europe the potential of intermittent renewables to meet electric power demand: current methods and emerging analytical techniques flexibility requirements of renewable energy based electricity systems -a review of research results and methodologies a comprehensive survey of flexibility options for supporting the low-carbon energy future review of energy system flexibility measures to enable high levels of variable renewable electricity comparison of the techno-economic characteristics of different flexibility options in the european energy system potential of power-to-methane in the eu energy transition to a low carbon system using cost optimization potential for power-to-heat in the netherlands power to ammonia: feasibility study for the value chains and business cases to produce co -free ammonia suitable for various market applications. institute for sustainable process technology the importance of high temporal resolution in modeling renewable energy penetration scenarios. th conference on applied infrastructure research implications of temporal resolution for modeling renewables-based power systems high-resolution modeling framework for planning electricity systems with high penetration of renewables the effect of weather uncertainty on the financial risk of green electricity producers under various renewable policies weather forecasting error in solar energy forecasting impact of wind power uncertainty forecasting on the market integration of wind energy in spain international aspects of a power-to-x roadmap benefits of demand response in electricity markets and recommendations for achieving them from passive demand response to proactive demand participation decentralised storage and demand response: impact on renewable share in grids and buildings. world sustainable energy days (wsed) capacity mechanisms for electricity. eprs | european parliamentary research service internal energy market. fact sheets on the european union the demand for flexibility of the power system in the netherlands wind power myths debunked common questions and misconceptions a review of approaches to uncertainty assessment in energy system optimization models clean transport -support to the member states for the implementation of the directive on the deployment of alternative fuels infrastructure: good practice examples gas and the electrification of heating & transport: scenarios for heat electrification: the latest research in europe a comprehensive review of thermal energy storage a review of available technologies for seasonal thermal energy storage luxembourg: publications office of the european union lessons on technological learning for policy makers and industry. technological learning in the energy sector, lessons for policy. industry and science the transition of energy intensive processing industries towards deep decarbonization: characteristics and implications for future research the role of nearly-zero energy buildings in the transition towards post-carbon cities an assessment methodology of sustainable energy transition scenarios for realizing energy neutral neighborhoods technological learning in energy-environment-economy modelling: a survey a review of learning rates for electricity supply technologies a review of uncertainties in technology experience curves long-term payoffs of near-term low-carbon deployment policies decarbonising road transport with hydrogen and electricity: long term global technology learning scenarios modelling the evolutionary paths of multiple carbon-free energy technologies with policy incentives the role of technology diffusion in a decarbonizing world to limit global warming to well below • c: an assessment with application of global times model multi-cluster technology learning in times: a transport sector case study with tiam-ucl. informing energy and climate policies using energy systems models power capacity expansion planning considering endogenous technology cost learning clean energy for all europeans. luxembourg: publications office of the european union assessing the energy-efficiency gap residential energy efficiency policies: costs, emissions and rebound effects the rebound effect and energy efficiency policy energy efficiency and consumption -the rebound effect -a survey infrastructure, investment and the low carbon transition. new challenges in energy security infrastructure transformation as a socio-technical processimplications for the governance of energy distribution networks in the uk a conceptual framework for understanding the social acceptance of energy infrastructure: insights from energy storage decentralized energy systems. european parliament's committee on industry temporally-explicit and spatially-resolved global onshore wind energy potentials designing a cost-effective co storage infrastructure using a gis based linear optimization energy model energy research and the contributions of the social sciences: a retrospective examination energy research and the contributions of the social sciences: a contemporary examination integrating social science in energy research what kind of socio-technical research for what sort of influence on energy policy? the reality of cross-disciplinary energy research in the united kingdom: a social science perspective the third wave. united states: bantam books a novel prosumer-based energy sharing and management (pesm) approach for cooperative demand side management (dsm) in smart grid prosumer based energy management and sharing in smart grid distributed energy systems on a neighborhood scale: reviewing drivers of and barriers to social acceptance the flexible prosumer: measuring the willingness to co-create distributed flexibility self-sustainable community of electricity prosumers in the emerging distribution system an optimized energy system planning and operation on distribution grid level-the decentralized market agent as a novel approach incentivizing prosumer coalitions with energy management using cooperative game theory socio-technical transitions and policy changeadvocacy coalitions in swiss energy policy transformative policy mixes in socio-technical scenarios: the case of the low-carbon transition of the german electricity system socio-technical evolution of decentralized energy systems: a critical review and implications for urban planning and policy agent-based modeling: methods and techniques for simulating human systems . national academy of sciences agent-based modeling and simulation of competitive wholesale electricity markets. handbook of power systems ii agent-based modelling and simulation of smart electricity grids and markets -a literature review towards circular economy implementation: an agent-based simulation approach for business model changes agent-based modeling of energy technology adoption: empirical integration of social, behavioral, economic, and environmental factors . environmental modelling & software multi-agent based distributed control architecture for microgrid energy management and optimization introduction to energy systems modelling combining bottom-up and top-down reconciling topdown and bottom-up energy/economy models: a case of tiam-fr and imaclim-r. chaire modélisation prospective au service du développement technological change in economic models of environmental policy: a survey advances in techno-economic energy modeling: costs, dynamics and hybrid aspects useful models for simulating policies to induce technological change comparison of top-down and bottom-up estimates of sectoral and regional greenhouse gas emission reduction potentials closing the gap? top-down versus bottom-up projections of china's regional energy use and co emissions hybrid modeling: new answers to old challenges introduction to the special issue of top-down and bottom-up: combining energy system models and macroeconomic general equilibrium models integrated assessment of energy policies: decomposing top-down and bottom-up extension of gams for complementarity problems arising in applied economic analysis energy-economy analysis: linking the macroeconomic and systems engineering approaches hybrid modelling: linking and integrating top-down and bottom-up models. the h project. set-nav mathematical models for decision support methods to improve computing times in linear energy system optimization models integrating short term variations of the power system into integrated energy system models: a methodological review challenges in top-down and bottom-up soft-linking: lessons from linking a swedish energy system model with a cge model energy-economy analysis: linking the macroeconomic and systems engineering approaches bridging the gap using energy services: demonstrating a novel framework for soft linking top-down and bottom-up models from linking to integration of energy system models and computational general equilibrium models -effects on equilibria and convergence energis: a geographical information based system for the evaluation of integrated energy conversion systems in urban areas a gisbased decision support tool for renewable energy management and planning in semi-arid rural environments of northeast of brazil electricity sector flexibility analysis: the case of the north of the netherlands feasibility of storing co in the utsira formation as part of a long term dutch ccs strategy: an evaluation based on a gis/markal toolbox modelling flexible power demand and supply in the eu power system: soft-linking between jrc-eu-times and the open-source dispa-set model. institute of thermal technology soft-linking exercises between times, power system models and housing stock models linking agent-based energy market with computable general equilibrium model: an integrated approach to climate-economy-energy system the authors would like to thank paul koutstaal, pascal wissink, joost van stralen, somadutta sahoo, Ö zge Ö zdemir, bert daniels, german morales-españa, and other team members of the estrac project and other anonymous reviewers and the editor for their constructive comments, conversations, and feedback. the authors wish to acknowledge the support given by the estrac integrated energy system analysis project financed by the new energy coalition (finance code: ). the views expressed here are those of the authors alone and do not necessarily reflect the views of the project partners or the policies of the funding partners. supplementary data to this article can be found online at https://doi. org/ . /j.rser. . . optimization-based or simulation-based conceptual model linking framework for the low-carbon energy system modeling suite. key: cord- -kakxmc authors: achutha, a. s.; pushpa, v. l.; suchitra, surendran title: theoretical insights into the anti-sars-cov- activity of chloroquine and its analogs and in silico screening of main protease inhibitors date: - - journal: j proteome res doi: . /acs.jproteome. c sha: doc_id: cord_uid: kakxmc [image: see text] corona virus disease (covid- ) is a dangerous disease rapidly spreading all over the world today. currently there are no treatment options for it. drug repurposing studies explored the potency of antimalarial drugs, chloroquine and hydroxychloroquine, against sars-cov- virus. these drugs can inhibit the viral protease, called chymotrypsin-like cysteine protease, also known as main protease ( cl(pro)); hence, we studied the binding efficiencies of -aminoquinoline and -aminoquinoline analogs of chloroquine. six compounds furnished better binding energies than chloroquine and hydroxychloroquine. the interactions with the active site residues especially with cys and his , which are involved in catalytic diad for proteolysis, make these compounds potent main protease inhibitors. a regression model correlating binding energy and the molecular descriptors for chloroquine analogs was generated with r( ) = . and q( ) = . . this model was used to screen new analogs of primaquine and molecules from the asinex compound library. the docking and regression analysis showed these analogs to be more potent inhibitors of cl(pro) than hydroxychloroquine and primaquine. the molecular dynamic simulations of the hits were carried out to determine the binding stabilities. finally, we propose four compounds that show drug likeness toward sars-cov- that can be further validated through in vitro and in vivo studies. in december , patients were admitted in hospitals in wuhan, china due to pneumonia with fever and other symptoms. , in january , it was discovered that a novel coronavirus, which is similar to sars-cov and mers-cov genomes, is responsible for this disease. this virus is named as severe acute respiratory syndrome corona virus- (sars-cov- ) and the disease is called corona virus disease- . , it was declared as pandemic on march by the world health organization (who). as of september , , there are , , confirmed cases with , deaths worldwide according to who reports. coronavirus is a single-stranded positive sense rna with a membrane envelope composed of four types of viruses: α, β, γ, and δ coronaviruses. sars-cov- belongs to β-coronavirus family. , its genome encodes for structural proteins mainly spike glycoprotein (s), envelope glycoprotein (e), membrane glycoprotein (m), nucleocapsid protein (n), and nonstructural proteins consisting of chymotrypsin-like cysteine protease also known as main protease ( cl pro ) and papain-like protease (pl pro ). , , the viral rna is released to the host cell, which is then translated to polyproteins inside the cell. these viral polyproteins are cleaved to functional proteins by proteolysis, which is catalyzed by cl pro and pl pro , , . since the main protease or cl pro cleaves at sites of the polyprotein to produce smaller proteins for viral replication and because of its nonsimilarity with human proteins, cl pro is a potential target in anti-covid- drug design. , the main protease of sars-cov- has a cys-his catalytic diad involving cys and his and has four conserved binding subsites s , s , s , and s ′. main chains of cys , phe , and leu and side chains of asn , glu , his , and his residues are present in the s subsite. the side chains of his , met , tyr , and met , along with the alkyl side chain of asp forms the s subsite. the s subsite consists of met , leu , phe , and gln side chain residues and the main chain of gln . s ′ includes thr and thr . therefore, a molecule to show cl pro inhibitory property should interact with one or more residues among these amino acids. also, the inhibitory action can be assumed to enhance if they interact with cys or his , which is involved in the catalytic diad of main protease ( figure ). cysteine acts as a nucleophile and histidine as an acid/base catalyst in this catalytic reaction. , currently there are no specific approved treatment options for covid- . researches are in search of vaccine development, druggable small molecule, monoclonal antibodies and cell-based therapies. several drug repurposing studies have been conducted so far, and many of them gave positive results. the -aminoquinolines, chloroquine (cq), and its hydroxyl analog hydroxychloroquine (hcq) have been found to disrupt the viral replication and infectivity. their broad spectrum of activity as antibacterial, antiviral, and antifungal infections has also been reported. , hcq has been found out to be less toxic than cq, and it is currently being used to treat covid- patients. the present study deals with theoretical perspectives on the anti-sars-cov- activity of cq and hcq analogs by observing their main protease inhibitory property. molecular docking studies with the cl pro protein were performed to analyze the drug likeness as well as to correlate the binding energy of the docked complex with various physicochemical properties of the active molecules, which will aid in the design of new anti-covid- medicatives. analogs of cq and hcq as well as primaquine derivatives were obtained through literature search, from the database of small molecules pubchem as well as created manually. − all the molecules were drawn in marvin sketch and minimized their energy using avogadro software. , the structure of cl pro protein having pdb id lu was retrieved from rcsb protein data bank. , characterization studies of the protein were done by using expasy-protparam, an online server, which provides all the details regarding the protein. the energy minimization of the retrieved protein was done by employing swiss pbd viewer. , molecular docking was done using autodock . . . both protein and ligands were prepared in pdbqt format. polar hydrogens and gasteiger charges were added to the receptor. grid was prepared with × × Å with spacing . Å and centered at − . , . , and . Å along x, y, and z axes, respectively. grids were prepared for every atom present in the ligand data set. the genetic algorithm was employed as search parameter with runs, and , population size and number of generations, respectively. a multiple linear regression (mlr) model was generated to find the correlation with binding energy obtained from docking and the physicochemical properties using qsarins. , the molecular descriptors for the ligands were calculated utilizing padel-descriptor. to build the model, % of the data set were randomly divided as training set and test set in : ratio. thirty-five compounds ( training and test) including cq and hcq were employed for modeling purpose (supplementary tables s and s ). the models were generated using training set with mlr analysis of − variables. the generated models were examined by internal validation and external validation. internal validation was done by cross-validated leave-one-out (loo) method, which involves iteratively leaving one compound from the training set and generating regression model with the remaining molecules and predicting the value of response for the excluded one. for a good model, the regression coefficient (r ) as well as the cross validated r , that is, q has to be close and > . . , the model was validated using test set, which was not included in model generation. , the best model was used to predict the binding energy of novel set of compounds. all the md simulations were done using the namd package (version . ) developed by the theoretical and computational biophysics group in the beckman institute for advanced science and technology at the university of illinois at urbana−champaign with the charmm force field. , the docked structures were used as the initial coordinates for md simulations. tip p water box was used to solvate the complex with Å padding. the solvated system was minimized for ps with a time step of fs. the simulations were done with particle mesh ewald electrostatics and periodic boundary conditions. atom-based cutoff of Å was applied for nonbonding interactions. the temperature and pressure were kept constant at k and atm, respectively, using langevin dynamics. the system was equilibrated for ps followed by a production simulation for ns using the npt ensemble. all the preparation and analysis steps were done using the vmd package . . (available at http://www. ks.uiuc.edu/research/vmd/) (see figure ). being an inevitable enzyme for replication and transcription of the virus, the -chymotrypsin-like-cysteine protease ( cl pro ) having pdb id lu was retrieved from rcsb pdb and characterized by primary and secondary structure analysis as shown in table . the pi value (isoelectric point) of . shows the slightly acidic nature of the protein. the aliphatic index (ai) is a measure of the relative volume occupied by the side chains ala, leu, ile, and val, which are the aliphatic residues in a protein. high ai ranging from . to . implies high thermal stability and hydrophobicity, which help it for membrane penetration in biological system. , the value for grand average of hydropathy (gravy) indicates the hydrophilicity of the protein. the gravy value of − . , which is close to zero, shows that the protein is hydrophobic. instability index < shows that in vivo half-life is greater than h, which indicates the stability of the protein. , all the parameters show that the lu is a stable, hydrophobic protein. the lu protein consists of three domains in which the catalytically active site is present between domain i and ii. figure s (supporting information) shows the domains and active site of lu protein bound with its cocrystallized inhibitor n . , the antimalarial drugs chloroquine (cq) and its hydroxy analog hydroxychloroquine (hcq) are currently used as drugs for the treatment of covid- . , to compare its efficiency as an anti-covid- drug to that of an antimalarial drug, docking studies were carried out for both targets, cl pro and pfdhfr-ts. plasmodium falciparum dihydrofolate reductase thymidylate synthase (pfdhfr-ts) is one of the important targets for antimalarial drugs , (supplementary table s ). it was identified that for both the targets hcq has lower binding energy owing to its higher binding affinity to the protein. both the drugs are more active on pfdhfr-ts than cl pro . the d interaction diagrams and docked poses of cq and hcq with the target cl pro are given in figures s and s , respectively. hcq fits more perfectly to the active site of the target than cq, and hence, hcq has high negative binding energy, which imparts more stability to the docked complex (supplementary figure s ) . cq forms three hydrogen bonds with gly , cys , and his ; van der waals interaction with asn and gln ; πalkyl interaction with his ; and two π-donor hydrogen bond interactions with the −sh group of cys at distances . Å, . Å, . Å, . Å, . Å, . Å, . Å, and . Å, respectively (supplementary figure s a , table ). the cys -his diad is blocked by these interactions. the interaction of alkyl group of the cq with the π-cloud of imidazole ring of histidine may disturb the delocalization of π electrons. the basicity of the imidazole ring is due to the resonance stabilization of the positive imidazolium ion ( figure ). the alkyl−π interaction of the alkyl donor and aromatic acceptor increases the stability of the docked complex as well as reduces the ability of the imidazole ring to accept h + from the cys residue, which is the initial step in the catalytic cycle in proteolysis, thereby reducing the activity. , hcq forms two hydrogen bonds with phe , and one each with asn , ser , and glu at distances . Å, . Å, . Å, . Å, and . Å, respectively. it forms two van der waals interactions with phe , and one each with glu and his at distances . Å, . Å, . Å, and . Å, respectively. it also forms a π−σ interaction with asn and two π−alkyl interactions with cys (supplementary figure s b , table ). the π−alkyl interaction with cys may disturb the conformation required for the interaction with polypeptide in the catalytic cycle. there have been reports about the entry of sars coronavirus as acidic ph dependent in which the activation occurs by the fusion of the membranes of virus and cellular endosomes and viral genome enters the cytoplasm. , , the presence of amino side chain in cq and hcq makes them basic and increases the ph of cell organelles like endosomes and lysosomes, which interferes with the replication and inhibits the viral activation. , to find more potent inhibitors of cl pro , analogs of chloroquine were subjected to molecular docking, which were obtained from literature, pubchem database, by replacement with isosteres and functional group variations − of chloroquine (supplementary tables s and s ). the binding energy thus obtained from docking with lu protein is given in table . all the chloroquine analogs show some of the key interactions with the active site residues. the negative value shows a release of energy while forming a protein−ligand docked complex, which imparts stability. the more negative the binding energy, the higher will be the stability and binding affinity. the compounds , , , , , and have more negative binding energy than cq and hcq. their d ligand interaction diagrams are shown in supplementary figure s . from the structures of these six compounds, we can infer that if the side chain has an extra −nh group, it can introduce additional hydrogen bonds, which results in a decrease in binding energy. in compound , the tail of side chain has become a part of a ring, which can interact with met residue via π−alkyl interaction. because of the presence of an additional −nh group, the basicity of these compounds is higher than cq and hcq, and thus, they can act as better inhibitors against sars-cov- . compounds , , , , and form π-donor hydrogen bonds with cys , which will make the −sh hydrogen less available for catalytic cycle. compounds , , , , and have a π−alkyl interaction with cys . overall, these interactions may affect the catalysis of proteolysis reaction journal of proteome research pubs.acs.org/jpr article and hence block viral replication. compound is primaquine (an -aminoquinoline), which is an antimalarial drug. , the effect of the side chain in the chloroquinoline scaffold was studied by changing the chain length and methyl substitution of the side chain. compounds and are obtained by the removal of the branching methyl group from cq and hcq structures, which results in an increase in the binding energy to − . and − . kcal/mol, respectively. therefore, it is understood that the branching next to the −nh− group in -aminopentyl side chain is important. isosteric substitution of −ch group in compounds , , and with −oh, −nh , and −cf results in binding energies − . , − . , and − . kcal/mol, respectively. substitution with nh resulted in a decrease in binding energy compared to hcq by a factor of − . kcal/mol, which means that an extra . kcal/mol of energy is released while forming a docked complex, which is more stable than that of hcq. an increase in binding energy due to the variation of side chain length in cq and hcq structures of compounds , , , , , , , , and makes them less stable complexes with the protein than with cq and hcq. therefore, the chain length of -aminopentyl group is optimal for showing biological activity. when an additional −oh group is added to the ethyl chain of hcq resulting in -[( aminopentyl)( -hydroxyethyl)amino]ethan- -ol side chain as in compound , as a result, the binding energy is decreased to − . kcal/mol. therefore, the −oh group at one terminal ethyl chain only is required for their inhibitory activity. rearrangement of the amino side chain from the fourth position to fifth position of quinoline ring in hcq (molecule ) increased the binding energy by . kcal/mol. replacement of quinoline scaffold by isoquinoline scaffold also increased the binding energy by an amount of . kcal/ mol. the cq, hcq, and its analogs taken for this study were subjected to mlr analysis. regression models were generated with binding energy as the response and molecular descriptors as the variables. many models were generated by varying − variables at a time from a set of descriptors. the fitness criteria of a model include r ≥ . , r adj ≥ . , q loo ≥ . , high value for fisher ratio (f), low regression standard deviation (s), lower correlation between descriptors (k xx ), positive value for δ k , which is the difference in correlation between descriptors and the response (y) value and correlation among descriptors, and smaller root−mean−squared error for training calculation (rmse tr ). , the parameters of the best five models calculated are given in table . considering all the models generated, model has the highest fitness score. however, upon inspecting its external validation parameters rmse ext = . and r ext = . , the values did not meet the cutoff and hence show poor predictability. for a good prediction, rmse ext should not vary much from rmse tr (difference should be less) and r ext should be greater than . . model was selected for further studies since it was the best fit model with next highest r and q loo , which represents the fitness, robustness of the model, and the proximity of actual and predicted binding energy values. the model was built by incorporating the compounds , , , , , , and in the test set and all others in the training set. thus, the binding energy, the response value (y), can be expressed in terms of the descriptors considered for the generation of model in the form of a linear relationship y = Σm i x i + c where m i is the coefficient obtained for each descriptor in mlr model and x i is the value for the selected descriptor. the internal and external validation parameters determine the feasibility and predictivity of the model , (table s ). the linear equation correlating binding energy and descriptors generated by model can be written as shown in eq : the root−mean−square error for cross-validation rmse cv = . is greater than rmse tr = . , making the model stable and predictive. the criteria for y scrambling r y scr < . , q y scr < . , and r y scr > q y scr implies that there is no correlation between descriptors, and hence, the model is not simply correlated by chance. model was assessed with external validation parameters r ext > . and small difference between rmse ext and rmse tr and was hence acceptable due to its high predictivity. the predicted values of binding energy for both training and test set of molecules are given in table s . the plot of observed versus predicted binding energy of training and test set molecules is given in figure . substitution of −cl with −nh in quinoline scaffold in compound led to inaccurate prediction and hence was detected as an outlier. model shows that the binding energy is a linear combination of the descriptors sch- , nhsnh , minhbint , fp , and krfp . sch- is simple seventh order chi chain that is a topological descriptor based on interatomic distances calculated by the bonds between them representing molecular connectivity as a chemical graph like a bond-line formula of chemical structures. it considers the specificity of the structures at a fragment level rather than the whole molecule. the order represents the number of edges in the graph, which indicates the branching. , the negative value of its coefficient indicates its negative impact on biological activity. thus, a low value for sch- is required for a compound to show low binding energy, which makes a restriction on branching. nhsnh represents the number of nh groups and amine hydrogens. the positive coefficient of . indicates that as the number of nh groups increases, the binding energy decreases, which is in perfect agreement it is an atom-type electro-topological state descriptor in which both electronic and topological functions are considered. there is a positive dependence of minhbint with the binding energy because as the chances of h-bond increases, the binding energy will be more negative. fp and krfpc are fingerprint descriptors, which account for structure, specific properties, connectivity, or pharmacophores. krfpc accounts for the count of substructures also. both of these fingerprints are inversely related to binding energy. designing molecules in such a way that having high values for nhsnh and minhbint and low values for sch- , fp , and krfpc will help to reduce the binding energy considerably. compound , primaquine, shows the least binding energy among the cq analogs. it is the only antimalarial drug that can interfere with a majority of the life cycle stages of the malarial protozoan species. , the combined usage of chloroquine and primaquine may mask chloroquine resistance. however, its toxic effect is mainly due to the hemolytic lesions caused by methemoglobin production. , it is reported that introduction of a tert-butyl group at c position (r in scaffold given in table ) will increase the efficiency and is completely drained of from methemoglobin production as in compound pq . , by using the formulated regression model , we predicted the binding energy of some primaquine analogs obtained from the literature and pubchem database and then carried out their molecular docking studies on cl pro target to check the inhibitory potency of the ligands, given in table . also screened, , asinex compounds having antiviral properties using the regression model . it was observed that the predicted binding energy of some compounds obtained from journal of proteome research pubs.acs.org/jpr article the asinex database differed largely from its actual value, which was obtained from docking analysis. this may be due to their difference in scaffold from that of the compounds used to build the regression model. even though the predicted binding energy was less accurate, they have furnished better binding energies on docking with the target protein implying the reliability of the model. thirty molecules that showed lower binding energies were subjected to molecular docking analysis to identify the potent cl pro inhibitors (supplementary figure s ) . binding energies obtained through both the methods and their interactions with the receptor protein are given in table . all the primaquine analogs showed lower binding energies than cq and hcq. all the compounds except pq furnished binding energies lower than that of primaquine. the binding energies calculated using the regression model are in good agreement with the value obtained from docking analysis. all the compounds exhibited interactions with some of the active site residues including the catalytic diad residues either cys or his or both, which make them potent cl pro inhibitors. the compounds pq , pq , and pq exhibited lower binding energies of − . , − . , and − . kcal/mol. the d interaction diagrams of these ligands with the protein are given in figure . in accordance with the findings based on docking studies, the regression analysis of cq analogs reveals the presence of one extra −nh bond in their structure. inspecting the d interaction diagrams of compounds a , a , a , a , a , a , a , a it can be seen that there are unfavorable donor−donor or acceptor-acceptor interactions present between the compounds and target protein which may negatively affect the stability of the docked complexes (supplementary figure s ). hence these can be considered as poor inhibitors of cl pro protein even though they have binding energies less than hcq. from these results it is clear that binding energy as well as interactions play decisive roles in determining the druggability of compounds. asinex database compounds a , a , a , a , a , a , a , a , a , and a obtained lower binding energies among all ( figure and figure s ). these compounds form interactions with cys , his , or both along with other active site residues, which are responsible for their inhibitory property. the compounds a , a , a , a , a , and a form hydrogen bonding interactions with cys , which will obstruct the initial deprotonation step in the catalytic cycle of cl pro as shown in figure . the π−π interaction of his with π systems of the compounds a and a will affect the proton accepting ability of his . the π−sulfur interactions are present in aromatic rings with −sh group of the compounds a , a , a , a , a , and a with cys residue. it involves the interaction with the aromatic π orbitals and σ* acceptor orbital of sh bond of cys . s−h/π interactions are the important contributors to binding energy. the thiol group of cys is engaged in s−h/π comparing the structures of the hit compounds pq , pq , pq , and a with the rest, it was clear that the high flexibility of the structures owing to more single bonds and less compact rings makes them able to undergo conformational changes at the active site of the target leading to more interactions with cys and his along with other active site residues. hence, these four compounds were selected for further analysis. even though docking studies give the best binding poses, they do not account for the conformational changes taking place upon ligand binding as the docking analysis preferably treats protein as rigid. the conformational changes affecting the binding affinity could be analyzed using molecular dynamic simulations. four top ranked compounds via docking (pq , pq , pq , and a ) were selected for ns molecular dynamics simulation studies to understand the conformational changes in the protein on binding of the ligand. rmsd, rmsf, and radius of gyration plots were used to evaluate the stability of the complexes. the binding conformations of the compounds at the last frame of simulation are given in figure . the root−mean−square deviation (rmsd) plot of apoprotein cl pro , pq , pq , pq , and a with average rmsds . , . , . , . , and . Å, respectively, is given in figure a . it can be inferred that for the apo structure as well as the docked complexes except pq , rmsd values rose to . Å and then formed a plateau after ns of simulation, which indicates that the system has reached stable equilibrium state and has been confined in the active site. the rmsd of pq requires an extension of stabilization time to reach the root−mean−square fluctuation (rmsf) plot gives the fluctuations of individual residues in the protein backbone. higher rmsf denotes higher flexibility and vice versa. the rmsf plot (figure b ) showed greater residue flexibility for pq and pq compared to the unbound form. pq and a have comparable rmsf values with that of the apo form. the cys and his residues involved in the catalytic cycle have fluctuations with greater than . Å in apoprotein. in pq and pq , it fluctuates more than Å, while in pq and a , there is fluctuation less than . Å. in all the systems, the active site residues from to have the highest fluctuations. the structural flexibility or compactness of the protein molecule is analyzed by the radius of gyration. the protein is supposed to maintain a relatively steady value for r g . from inspection of figure c , it can be seen that r g has almost no significant variance with the average r g values of Å. the ligand bound form has lower r g values compared to apoprotein, which indicates that the bound structures are more compact. molecular docking analysis of chloroquine and hydroxychloroquine on main protease ( cl pro) protein has shown that hcq is more efficient than cq. more potent inhibitors of cl pro have been identified through docking studies. the interactions with the active site residues, especially with cys and his , which are the key residues involved in catalytic diad for proteolysis in the enzyme, are responsible for the activity of these compounds. a regression model with r = . and q = . was developed correlating binding energy with the molecular descriptors. this model was used to predict the binding energies of novel molecules. the primaquine derivatives and antiviral compounds obtained from asinex compound library were screened using the regression model, and the hit compounds thus obtained were further docked with cl pro protein. they showed less binding energies and proper interactions with the target, main protease ( cl pro ). molecular dynamics studies on these top four compounds pq , pq , pq , and a revealed their binding stability and conformational changes associated with the protein−ligand complexes. hence, these four compounds are proposed for validation and further studies as more efficient medication for covid- . the supporting information is available free of charge at https://pubs.acs.org/doi/ . /acs.jproteome. c . binding energy obtained for docking cq and hcq with cl pro and pfdhfr-ts; structure of cq analogs with -aminoquinoline scaffold; structure of chloroquine analogs with quinoline scaffold, values for internal and external validation criteria, binding energy values of training and test molecules predicted with model ; domains and active site of lu bound with inhibitor n ; d interaction diagrams of docked complexes of cq, hcq with cl pro ; docked poses of cq and hcq in active site of lu ; d interaction diagrams of , , , , , , and with lu ; structures of screened compounds from asinex compound library; d interaction diagram of compounds having unfavorable interaction with target; d interaction diagrams of asinex compounds with lu protein (pdf) research and development on therapeutic agents and vaccines for covid- and related human coronavirus diseases diagnosing covid- : the disease and tools for detection a review of the novel coronavirus (covid- ) based on current evidence coronavirus disease : coronaviruses and blood safety severe acute respiratory syndrome coronavirus (sars-cov- ): an overview of viral structure and host response covid- ) weekly epidemiological update and weekly operational update; who potential interventions for novel coronavirus in china: a systematic review structural basis of sars-cov- clpro and anti-covid- drug discovery from medicinal plants an overview of severe acute respiratory syndrome-coronavirus (sars-cov) cl protease inhibitors: peptidomimetics and small molecule chemotherapy department of medicinal chemistry, tokyo university of pharmacy and life sciences structure of mpro from covid- virus and discovery of its inhibitors distinct roles of catalytic cysteine and histidine in the protease and ligase mechanisms of human legumain as revealed by dft-based qm/mm simulations ongoing clinical trials for the management of the covid- pandemic chloroquine and hydroxychloroquine in the treatment of covid- with or without diabetes: a systematic search and a narrative review with a special reference to india and other developing countries review: hydroxychloroquine and chloroquine for treatment of sars-cov- (covid- ) new insights on the antiviral effects of chloroquine against coronavirus: what to expect for covid- ? recycling of chloroquine and its hydroxyl analogue to face bacterial, fungal and viral infections in the st century hydroxychloroquine, a less toxic derivative of chloroquine, is effective in inhibiting sars-cov- infection in vitro introducing new antimalarial analogues of chloroquine and amodiaquine: a narrative review. iran chloroquine analogs as antimalarial candidates with potent in vitro and in vivo activity chloroquine analogues in drug discovery: new directions of uses, mechanisms of actions and toxic manifestations from malaria to multifarious diseases update: improved access to chemical data avogadro: an advanced semantic chemical editor, visualization, and analysis platform avogadro: an open-source molecular builder and visualization tool. version .xx; avogadro chemistry the protein data bank an environment for comparative protein modeling. electrophoresis software news and updates autodock and autodocktools : automated docking with selective receptor flexibility a new software for the development, analysis, and validation of qsar mlr models insubria datasets and new qsar/qspr models for environmental pollutants in qsarins padel-descriptor: an open source software to calculate molecular descriptors and fingerprints comparative qsar model generation using pyrazole derivatives for screening janus kinase- inhibitors quantitative structure activity relationship study of anticonvulsant activity of α _ substituted acetamido-n-benzylacetamide derivatives scalable molecular dynamics on cpu and gpu architectures with namd scalable molecular dynamics on cpu and gpu architectures with namd ligand reader & modeler for charmm force field generation of small molecules vmd: visual molecular dynamics research paper state-of-the-art tools unveil potent drug targets amongst clinically approved drugs to inhibit helicase in sars-cov- physicochemical characterization and functional analysis of some snake venom toxin proteins and related non-toxin proteins of other chordates abstract: background: bioinformation genetic involvement of interleukin for asthma and identification of potential phytochemical scaffold through molecular docking studies understanding the relationship between the primary structure of proteins and its propensity to be soluble on overexpression in escherichia coli structure of mpro from covid- virus and discovery of its inhibitors structure -activity relationship and comparative docking studies for cycloguanil analogs as pfdhfr-ts inhibitors chalcone analogue as potent anti-malarial compounds against plasmodium falciparum: synthesis, biological evaluation, and docking simulation study. asian pac pi-interactions in proteins ph-dependent entry of severe acute respiratory syndrome coronavirus is mediated by the spike glycoprotein and enhanced by dendritic cell transfer through dc-sign primaquine or other -aminoquinolines for reducing plasmodium falciparum transmission primaquine therapy for malaria analysis for antioxidant activity of dipicolinic acid derivatives qsar study of anti-human african trypanosomiasis activity for -phenylimidazopyridines derivatives using dft and lipinski's descriptors. heliyon qsar with electro topological state atom index: antialirenergic activi ty of n, n-dimethyl- -bromo- -phenylethylamines the molecular connectivity chi indexes and kappa shape indexes in structure-property modeling. reviews in computational chemistry ) yap, c. w. padel-descriptor: an open source software to calculate molecular descriptors and fingerprints investigation of , -dihydro- -pyrones derivatives as potent anti-hiv agents inhibitors quantitative regression models for the prediction of chemical properties by an efficient workflow synthesis and blood-schizontocidal antimalarial activities of -substituted/ , -disubstituted- -quinolinamines and some of their amino acid conjugates discovery of a bulky -tert -butyl group containing primaquine analogue that exhibits potent blood-schizontocidal antimalarial activities and complete elimination of methemoglobin toxicity blood stage antimalarial efficacy of primaquine in plasmodium vivax malaria insights into thiol-aromatic interactions: a stereoelectronic basis for s -h/π interactions docking studies and molecular dynamics simulations of the binding characteristics of waldiomycin and its methyl ester analog to staphylococcus aureus histidine kinase understanding the structural features of jak inhibitors: a combined d-qsar, dft and molecular dynamics study molecular docking and molecular dynamics to identify a novel human immunodeficiency virus inhibitor from alkaloids of toddalia asiatica molecular docking and molecular dynamics simulation studies to identify potent aurka inhibitors: assessing the performance of density functional theory, mm-gbsa and mass action kinetics calculations the authors declare no competing financial interest. the authors gratefully acknowledge generous funding from kerala state council for science, technology and environment (kscste) for the junior research fellowship (no. / /kscste). key: cord- - oi w s authors: klemeš, jiří jaromír; fan, yee van; jiang, peng title: covid‐ pandemic facilitating energy transition opportunities date: - - journal: int j energy res doi: . /er. sha: doc_id: cord_uid: oi w s nan pandemics caused by covid- spread out to most countries around the world. as the energy sector is one of the imperatives for modern society; it has been influenced considerably. numerous studies and analyses appeared dealing with various aspects during the pandemics. however, the most decisive is going to be post-pandemic development. this is likely to shape the energy sector for some time, and it is representing both the challenges but also the opportunities. consumer habits tend to change over time, but the covid- outbreak is forcing consumers to reconfigure their lives, their habits and their spending patterns at speed and scale that the world has never seen. the nielsen company has created a global lens through which to analyse these changes and identified ways of prioritising what needs to get done, and when. he represented typical markers of these stages but are not always consistent, especially with the number of cases or deaths: (a) proactive health minded buying, (b) reactive health management, (c) pantry preparation, (d) quarantined living preparation, (e) restricted living, and (f) living as normal. however, the new normal is going to be influenced by a new experience, new discoveries and new opportunities. what does it mean for the energy sector? one strong issue is to focus on safer life preventing infections. it means a psychological move to single-use plastics. this means increased demand for plastics and consequently more energy for their production, logistics and disposal. it might also mean a psychological move to private cars with a lower exposure risk after pandemics. related to that have been more stress paid to hygiene, which means more antiseptic and disinfection, which again means more energy and consequently waste and effluents. they are serious indications about changes in the energy supply industry, which can accelerate the transition from fossil fuels to renewables. the other associated issues are related to energy supply and security. there has significantly arisen the importance of high capacity storage. worldwide mobility is expected to shrink due to possible fearful psychology. for example, some travel enthusiasts, mostly, the senior population who used to be making a considerable part of the holidaymakers, become more hesitating to travel to foreign destinations, and it has been considerably reducing energy and emissions for the transportation. this can perhaps return to near normal when the situation becomes under control; however, some sentiment with seniors may remain. there has been some unwanted impact on public mass transport, where it has been not easy to prevent the infection from spreading, and the population started to return to in many cases single used cars. however, there have not been only issues which are leading in the post-pandemic period to increase energy consumption. they include, but not only limited to, as the emerging developments have been by covid- pressure accelerating: . spread out of distance meeting and learning . massive home office . the growing popularity of e-shopping . raise in e-socialising . related to this intensifying the data transmissions as g . urban and sanitary reforms . remote and robotic health monitoring and even treatment . related preference to shortening the commuting . intelligent traffic control, strengthening to favour self-driving autonomous vehicles . advanced digital manufacturing challenging remote and distance production operating, and also remote construction and building as remote drilling . advanced and possible person-less waste management collection and treatment. . applications of novel ways for deliveries as, for example, drones and advancing delivery apps . promotion of renewable energy . setting up a post-covid- supply chain . industrial internet of things (iiot) many of those developments are based on "smart-city technology" which involved using smart sensors, machine learning, artificial intelligence (ai), blockchain and internet of things (iot) to improve infrastructure efficiency. they have been growing in use for transport, energy and housing. from the point of energy, there is an important issue if the new options are energy more efficient and to what proportion. figure shows the source of energy consumption of iot development, including data centre (main contributor), machine to machine communications, obsolescence of digital technologies and embodied energy. there have been works revealing that the ai can have substantial energy consumption and consequent ghgs footprint (see figure ). although ai has presented super advantages in "ai for good" applications, the related energy efficiency was an easily overlooked dimension, let alone that ai had also been used in some unreasonable scenarios. there have been, for example, analysis of the home office energy consumption. on one side, reduced travel, less need for lighting, heating and air conditioning offices; on the other side, raising need to provide this individually. they have also been issues as transporting children to schools and shopping on the way to the workplace and back. a similar analysis is important for energy consumption for e-shopping, where all the logistics should be considered from centralised to distributed and also in relation with, for example, home office. a very important direction is remote and robotic health monitoring and even treatment. it has been facilitated by g. the first small step has been now common intelligent watches monitoring the basic functions and connected via bluetooth with mobile phone applications. the next extension has been more sophisticated monitoring strips and the most recent development facilitated by the covid- pandemics is a remote online medical examination and even telerobotic spinal surgery based on g network. the first cases were reported in march . the considerably increased intensity of the data transmissions and the strongest need for g and in the future even g is going to have also some impact on the resources. g is expected to support data rates of and over terabyte per s (tbps). and even before the pandemics, g has been projected for a "dramatically increase" network energy consumption. for example, ericsson presented an overview where some statements from alessio zappone, assistant professor in signal transmission at the university of cassino and southern lazioas were given as "i think it can be stated that g will not meet the goal of reducing the energy consumption compared to g," he told euractiv in emailed comments. "one reason for this is the much larger volume of data that g must handle," he explains. "this has led to new transmission techniques which are able to provide much higher communication rates, but whose energy efficiency is doubtful." the highlighted concerns of global researchers do not mean the society should not embrace the new technologies. on the contrary, the society welcomes the innovations, especially when population are trapped by the epidemics. what should be stressed is to focus more on the energy efficiency and the resultant research, development and usage of such innovations. it means that intensive research and innovative solutions are needed from all potential providers as even when the efficiency is going to increase during the implementation and exploitation of g, the amount of massive data is going to be continuously increasing (figure ). the area chart with a trend projection was presented in the ericsson mobility report before the covid- pandemics struck. the purple curve in figure added by the authors shows a conjecture on the trend of g development by taking the covid- pandemic into consideration. it is noted that the curve presents a rough trend which will be finally determined by the pandemics. although the data obtained so far have been revealing that mobile data traffic has been increasing even more steeply, they are mostly based on g, and the g equipment supply and the device installation had been hit seriously during pandemics. as the covid- pandemic stimulated new markets in distance meeting/learning, home office, e-shopping and e-socialising, the promising development trend of g is highly expected after the pandemic is well controlled. it was found in , information and communications technology (ict) networks consumed . % of the total electricity grid supply globally and contributed to . % of the global carbon emissions related to energy. with new devices and use cases increasing the capacity of the networks, the demand to ensure low g energy consumption is critical to minimise operator expenses and ensure that they can still meet energy reduction goals. as it is obvious from the graph in figure , it is likely that the share and related emissions would increase folds and would start to play a major role in power consumption. the next figure is a summary of how ict helped and benefited during the pandemics. in the post-pandemic period, it is highly probable that the experienced benefits are going to be continuously used. transport and logistics are another crucial energyintensive area. many innovative and intensified services as e-shopping, advanced and possible person-less waste management collection and treatment, and applications of novel ways for deliveries, for example, drones, can change the energy requirements. on the one hand, they can reduce traffic jams escalating fuel consumption, reduce commuting frequency and distances; however, on the other hand, they can bring in some issues, for example, increased energy demands. an interesting development was the exploitation of drones for the delivery. a short time ago, was considered as an issue for the distant future has now moved closer to be implemented. the major obstacles seem not to be the available technology, but the legal framework and the legislation, as published at the end of april , for example, amazon moves closer with faa approval. regardless of the type of the services that iot is facilitating or enabling, one issue that needs to be comprehensively assessed is the marginal change in efficiency improvement and increase of service demand (see figure ). data centre workloads mean web requests, such as multimedia rendering, data analysis and other applications in the data centre. the compute instances mean managed and configured development environments in the cloud for big data, ai, machine learning and iot. the service demand is increased where the relative change is more significant than the efficiency improved. the need for reliable bottom-up estimates has been highlighted by masanet et al to ensure a low carbon emission and energy-efficient future of data centre energy use ( twh in ). they appeared various forecasts on how long and how extensive the pandemics are going to be. they have been some possible pessimistic side forecasts as, for example, "an estimated m people have been infected worldwide, and . m is dead" as megan scudellari estimated. they are some other possibilities as, for example, "another possibility is that immunity to sars-cov- is permanent. in that case, even without a vaccine, it is possible that after a world-sweeping outbreak, the virus could burn itself out and disappear by . however, if immunity is moderate, lasting perhaps about two years, then it might seem as if the virus has disappeared, but it could surge back as late as " as megan scudellari mentioned based on the the analysis from the harvard team. it means that with many options opened the new emerging options and opportunities for energy saving and making the generation, distribution and usage more efficient becomes a crucial issue and the research in this direction should be encouraged and facilitated. austrian economist joseph schumpeter in introduced a term of creative destruction "the essential fact about capitalism" and wrote the great new technologies and processes continuously revolutionise the economic structure from within, "incessantly destroying the old one, incessantly creating a new one." the economic disruptions have been facilitating faster changes and stronger creativity. innovations meet both cultural and material requirements for the acceleration. old and traditional structures preventing income of novel technologies are weakening. old economy has been collapsing, and the novel "clusters" of the innovation are becoming the core of a novel emerging economy. this had been happening during the past three centuries. it has been witnessed five substantial's "waves" regularly causing economic destructions and related re-clustering. the first wave was driven by employing the power of water, and the steam power was the second wave. coal and electricity brought the third wave, the fourth exploiting oil and gas, and the fifth wave was triggered by digital transformation. it is the opportunity that the humans are presently at the start of the sixth immense wave of innovation ( figure ), driven by renewable energy combined with emobility, e-activities and e-services, smart-city technology and the number of activities listed, including hydrogen energy. and this wave has been strongly initiated by the pandemics. it is interesting to see that the new waves are in most cases, coincided with some crises or critical situations where the society has been mobilising all possible researches strongly to overcome. the way ahead demands a continuous analysis of all novel emerging energy-related opportunities, under careful balancing of energy savings and energy increasing demands. not all novel smart and high-tech options are energy efficient, and each of them should specifically balance in casespecific conditions. however, with the started intensive development, the energy efficiency has been in most directions increasing. the enhancement of energy efficiency in digitalisation is promoting economic growth but regretfully also the usage and the energy demand. one issue becomes more and more evident that the largest energy carrier in the period ahead is going to be electrical power. as the final judgement should be quantified by ghg, energy and the other environmental footprints it becomes more and more obvious that a decisive issue will be how green (ie, with minimum environmental footprints) the electrical power is going to be. the future research should follow several avenues: novel opportunities continuously arising as a response to the new demands, energy efficiency and savings as well as reducing and minimising the environmental burden created by electrical power generation, transmission and distribution. covid- forces recalibration of priorities as world embraces new habits minimising the present and future plastic waste, energy and environmental footprints related to covid- plastics: friends or foes? the circularity and plastic waste footprint spatial-temporal potential exposure risk analytics and urban sustainability impacts related to covid- mitigation: a perspective from car mobility behaviour the energy and environmental footprints of covid- fighting measures -ppe, disinfection, supply chains covid- bankrupts energy (oil & gas) companies. . cleantechnica.com/ / / /covid- -bankrupts- -energy-oil-gas-companies security of supply, strategic storage and covid : which lessons learnt for renewable and recycled carbon fuels, and their future role in decarbonising transport? covid- and china's hotel industry: impacts, a disaster management framework, and postpandemic agenda internet of things for green cities transformation: benefits and challenges energy and policy considerations for deep learning in nlp paris: passive and continuous fetal heart monitoring system telerobotic spinal surgery based on g network: the first cases nasdaq: ttgt). . searchnetworking.techtarget.com/definition/ g ericsson: g could 'dramatically increase' network energy consumption. . www.euractiv. com/section/energy/news/ericsson- g-could-dramatically-increasenetwork-energy-consumption ericsson mobility report. g uptake even faster than expected ict ?utm_expid=.rnihqecnsxitpcj ucmtea. & utm_referrer=https% a% f% fwww.bing.com% f. accessed drone delivery? amazon moves closer with f.a.-a. approval, new york times recalibrating global data center energy-use estimates how the pandemic might play out in and beyond projecting the transmission dynamics of sars-cov- through the postpandemic period conversation au, . theconversation.com/-creative-destruction-the-covid- -economic-crisis-is-acceleratin g-the-demise-of-fossil-fuels- cities and climate: historical precedents and potential transitions for the new economy covid- coronavirus: closing carbon age, but opening hydrogen age environmental-socialeconomic footprints of consumption and trade in the asia-pacific region the authors gratefully acknowledge financial support from the eu project sustainable process integration laboratory -spil, funded as project no. cz key: cord- -puwf ab authors: yongjun, gao; liu, jingbo; bashir, sajid title: electrocatalysts for direct methanol fuel cells to demonstrate china's renewable energy renewable portfolio standards within the framework of the th five-year plan date: - - journal: catal today doi: . /j.cattod. . . sha: doc_id: cord_uid: puwf ab a unified treatment of the renewable portfolio standards is given concerning direct methanol fuel. the current mechanism of electrocatalysis of methanol oxidation on platinum and non-platinum-containing alloys is summarized for the systematic improvement of the rate of electro-oxidation of methanol are discussed. policy realignment under the five-year plan is discussed in length to demonstrate how policy, markets, and engineering designs contribute towards the development of model direct methanol fuel cells operational enhancement, and factors that affect critical performance parameters for commercial exploitation are summarized for catalytic formulations and cell design within the context of why this investment in technology, education, and finances is required within the global context of sustainable energy and energy independence as exposed by thirteenth the five-year plan. the prolog focuses on the way, whereas the section on methanol fuel cells on the how and the post log on what is expected post-covid- era in science and technology as china pivots to a post-fossil fuel economy. china's industrial growth has been through internal market reforms and supplies side economics from the chinese markets for fossil fuels except for petroleum. the latest renewable portfolio standards adopted have common elements as adopted from north american and the united kingdom in terms of adaptation of obligation in terms of renewable portfolio standards as well as a realization that the necessity for renewables standards for the thirteen five year plan (from to ) need to less rigorously implemented due to performance targets that were met during the eleventh ( – ) and twelfth five-year plans ( – ) in terms of utilization of small coal-ire power plants, development of newer standards, led to an improvement of energy efficiency of %, reduction of so(x)/no(x) by an average of % and pm . by % over the last two five-year plans. the current phase of the plan has a focus on energy generation from coal and a slowing down of renewables or renewable energy curtailment of approximately t wh renewables including t wh of non-hydro power, principally from guangdong, and jiangsu for transfer of hydropower and zhejiang, tianjin, henan for non-hydro power transfer with beijing and shanghai playing important roles in renewables energy curtailment and realignment using an integrated approach to optimize each provinces energy portfolio. the realignment of the renewable energy portfolio indicates that the newly installed capacity in sichuan, yunnan, inner mongolia, and zhejiang will account for less than % of the current renewable energy portfolio but with the no(x) so(x) and pm( . ) savings already accrued. the catalytic reduction of carbon dioxide to methanol ( / million metric tons from all sources in for china/world) is one technological approach to reduce global carbon dioxide emissions and suggests that catalytic methanol synthesis by co( ) hydrogenation may be a plausible approach, even if it is more expensive economically than methanol synthesis by the syngas approach. this is because the co( ) emissions of the synthesis are lower than other synthesis methodologies. the chinese government has placed a premium on cleaner air and water and may view such an approach as solving the dual issues of fuel substitution and reduction of co( ). thus, the coupling of hydrogen generation from sustainable energies sources (solar / gw) or wind ( / . gw in ) may be an attractive approach, as this requires slightly less water than coal gasification. due to the thermodynamic requirement of lower operating pressure and higher operating pressure, currently, there is no single operational approach, although some practice approaches ( °c at atm using copper) and zinc oxide/alumina are suggested for optimal performance. the chief aim of the state council through the issuance of the five-year plans was to meet 'current challenges (weng, ) , from positioning the republic to be a regional counterweight to soviet russia (malenbaum, ) to an international global economic superpower (wang, a) can be seen through measurement of certain key performance indicators, chiefly amongst them was power generation (yuan and zuo, ) , as it was recognized early on that independence from outside agencies necessitated sufficient industrial, mechanization which in al. a). the advantage of the proscribed approach is that it enables the grid utilities to integrate the renewable energy consumption obligation as part of the marketization process, where energy needs are met via a mix of renewable energy sources (shi, ) . the utilities can also act as a coordinator with local consumers and power exchange centers for on-time transfer of electricity derived from renewable energy sources (wang et al. b ). the above investment plan is based on the state council assessment that, the population and economic conditions of various regions on the chinese mainland in show that the chinese economy is still in a sound financial position with project growth (vu, ) . the table a . although a generalization, the population of china is steady at around . billion which requires food and energy. the energy in terms of electricity and as liquid fuel for cars. this has resulted in large increases of carbon dioxide (co ), particulate matter (pm), and sulfur oxides (sox) being released into the environment. one solution is to convert co directly to methanol and use methanol as a fuel in methanol fuel cells, as a blend with gasoline or as a precursor to generating other synthetic materials utilizing co and h . the case for which this should be considered will briefly be made, followed by a policy rationale of current and future policies as they're elated to energy and the environment and we will conclude with an extensive analysis of methanol hydrogenation and the catalyst and technologies utilized. according to the above figure, the economic growth rate in various regions of china is maintained at - . %, the strategic emerging industries are maintained at . - . %, and the natural population growth rate is between - . and . ‰. the growth rate and range span not only show that china's energy problems cannot be viewed centrally but at the provincial level (zhu, fan, shi, and shi, ; li, hong, and peng, b; shan, et al. ) . this suggests the methanol-based economy might assist china will the twin goals of energy independence and the lowering of carbon dioxide emissions. global production of methanol is around million tones ( billion usd) of which china contributes approximately %. china also consumes approximately % of the world methanol, therefore imports methanol. of the entire continuum of methanol consumed approximately % chemicals & fuels; . % in dimethyl ether (dme) fuels; and . % for traditional precursors. in , it was estimated that approximately . % of chemicals & fuels; . % in dme fuels; and . % for traditional precursors (zangeneh, sahebdelfar, and ravanchi, ) . most of the methanol to olefins (mto) , and methanol to propylene (mtp), methanol to gasoline (mtg), methanol to aromatics (mta), ethylene glycol (eg) with three or more plants in inner mongolia, henan, shaanxi, and shandong. methanol can be synthesized from biomass, natural gas, coal, or ta sand, via synthesis gas. syngas is often produced through the gasification of biomass, by catalytic reforming of the feedstock biomass to synthetic gas and then catalytic synthesis of methanol from the synthesis gas (surisetty, dalai, and kozinski, ) . with fossil fuels, this can be accomplished by steam reforming, oxy reforming, or co reforming steps. in the first step that is auto thermal in nature, the endothermic steam reforming process and exothermic oxy reforming step are coupled to generate methanol. methanol (physical properties summarized in table b ) can also be generated by direct oxidation of methane, using catalytic gas-phase or liquid-phase oxidations or conversion of mono halogenated methane to methanol or using bioreactors with enzymes. our favored approach is the chemical recycling of co to methanol (he, sun, and han, ) . as stated, earlier methanol can be used directly to generate electricity via direct methanol fuel cells. the fuel cells have electrodes, an electrolyte, and a membrane from which protons can migrate. the methanol feed is at the anode, whilst oxygen is taken at the cathode with platinum (cathode), platinum	ungsten-based (anode) catalyst (eqn: and figure b ). the anode can abstract a proton from methanol. when operated between - c enough electricity is generated to power storage batteries or small appliances. oxidation of carbon j o u r n a l p r e -p r o o f dioxide to methanol is energetically unfavorable, as carbon has a formal oxidation charge of c + to ch oh, with a formal change of c -, therefore requiring six electrons, requiring kj/mol. for photooxidation, the metal oxide bandgap (~ . ev) to the reduction potential of co would be required (linsebigler, lu, and yates jr, ) . figure b : a schematic of a direct methanol fuel cell anode: ch oh + h  co + h + + e ( a) cathode: . o + h + + e  h o ( b) overall reaction: ch oh + . o  co + h o ( c) methanol can also be blended into gasoline to increase the octane number of gasoline and increase the energy efficiency of the internal combustion engine. or directly as a methanol fuel cell in fuel cell cars or methanol powered vehicles and even as a fuel for heating. methanol to gasoline (mtg) or methanol to olefins (mto) to produce plastics is another application. lastly, methanol can be used to produce biodiesel via transesterification of vegetable oil or as a marine fuel. j o u r n a l p r e -p r o o f the tables above shown that methanol has a higher energy density than methanol, is safer to transport than ethanol and gasoline, although itself is a potential poison. the hydrogenation of co to methanol will be discussed in the concluding section. the current state of the economy within the framework of the current five-year plan will be described. j o u r n a l p r e -p r o o f based on the geographical location, climatic conditions, agricultural and industrial foundation, population distribution, and other factors, the development of the various provinces in the mainland has shifted from a managed command economy to the present more decentralized approach (wu, zuidema, and gugerell, ) . particularly during the development leading up to and beyond the beijing olympics industrial technology and energy development has geared up to the utility of renewable energy at the level of the province away from petrochemical coal and petroleum to non-hydro renewables (cherni, and kentish, ) . china's northwest region is famous for its abundant coal, wind, light, and oil and gas resources. the southwest region is characterized by abundant water resources and other renewable energy resources (di silvestre, favuzza, sanseverino, and zizzo, ) . the coastal areas are represented by nuclear energy and wind power (qin, liu, li, and li, ) . the state council has directed each province to meet the renewable energy portfolio obligation via a multimodal complementarity approach coordinated with regional energy providers. here, harmonized regional development is placed in the context of green energy obligations, where energy input and greenhouse gases and particulate matter as outputs development, are managed, which are currently implemented by regions in anhui, henan, hubei, and shanxi which has led to a reduction of carbon dioxide relative to the benchmark shown in figure a for and in figure b (kozyrev, ; chen, zhou, and yang, ) . j o u r n a l p r e -p r o o f based on the statistical analysis from the nbsc the reform related to the reduction of electricity price and the consumption of clean energy have not been met (fang, et al. (yang, chen, zhou, and ren, ) . seven provinces continued to emphasize energy reform, increase the consumption of renewable energy, optimize the energy structure, and adjust the proportion of clean energy mix, and seven regions focused on natural gas, summarized in table a . j o u r n a l p r e -p r o o f at present, every province in china needs to meet the expectations, but the mechanism can be different from each other (yang, hu, tan, and li, ) . first, continue to diversify the energy mix with a focus on renewable energy sources. the second distributed energy both temporarily and spatially. third, coordinated energy production and usage with enough overcapacity (dong, et al. ) . when comparing energy production and consumption at the provincial level through assessment of sox, nox, and co , some generalization can be stated starting from the th five -year plan to the thirteenth five-year plan, summarized in figure (hu, ) . the progressive decreases of nox and sox during the - decade, increased in the early s due to increased electricity generation and industrial production and infrastructure (qin et al. ; . these increases in emission were related to the beijing olympics, cement production peak in april and october of of a modal value of . thousand tons of cement, with production declining from jan-april (lei, zhang, nielsen, and he, ) . cement production then increased back to thousand tons and crept up to about thousand tons per year by and stayed constant except for a slight increase in (gao, et al. ) and a slight decrease in due to a slowdown in the chinese economy due to the coronavirus ). j o u r n a l p r e -p r o o f streets, and waldhoff, a; streets, tsai, akimoto, and oka, b; shi, et al. . note mole c/liter = . × - gt c/km , (using an atmospheric volume of .  km using an atmospheric mass of . × kg and an air density of . kg/km ), we calculate that gigaton of c is equivalent to . ppm of c, or ppm is equivalent to .; gigaton of carbon which is consistent with published data. a similar calculation for sulfur (yields gigaton to . ppm) and nitrogen ( gigaton to . ppm). the data from various sources was fin different units and was converted to ppm. in this manner, some artifacts were introduced, and some areas may be overestimated or underestimated in the graph should be viewed as a trend rather than specific end-point values). most of the emissions were from the generation of electricity from fossil fuel consumption, but emissions from heavy industries including the production of cement cannot be ignored (cai, et al. ) . in general co emissions increased from west to east and north to south. most reduction over the five-year plan ( th to th ) decreased by . % which is on target, with the greatest reductions occurring in xinjiang, shaanxi, guangxi, guangdong, and fujian, with j o u r n a l p r e -p r o o f current reductions occurring in the south and northwest provinces (tollefson, ) . the provinces have to balance its balance to generate a gross domestic product to that of transitioning to low-carbon sources for energy, such as beijing, shanghai, and guangdong focus will be on efficiency enhancements and development of solar, whereas shanxi, inner mongolia, xinjiang, ningxia, and guizhou focus will be on carbon capture due to an abundance of fossil resources (zhu, et al. ) . since the gross domestic product (gdp) and economic resources of central and western provinces in china are lower, utilization of low carbon energy sources or carbon capture may be more appropriate pathways towards increasing both gdp and lowering co emissions (zhang, and hao, ) . recently, the central government issued a consultative document entitled "opinions on accelerating the establishment of a green production and consumption regulatory and policy system through the national development and reform commission and the ministry of justice" on march , . the opinion if promogulated will be administered by the ministry of justice, strengthening law-based energy governance (shen, li, wang, and liao, ) . the core purpose of the opinions is to promote clean energy development, increase policy support for distributed energy, smart power grid, energy storage technology, and multi-energy complementarity, and research and formulate standards, regulations, and support policies for the development of new energy sources such as hydrogen energy and marine energy ). the energy balance should incorporate the whole life cycle, via the industrial chain to evaluate whether the energy supply and consumption meet the requirements of green and clean development. this may be promoted by recent rises in the particulate matter which were stable with a slight increase in and then a large rise in (yue, et al. ). in china's "completed of the thirteenth five-year plan and opening of the fourteenth five- year plan" period, we can see clearly that the chinese government is promoting "the coordinated development of beijing-tianjin-hebei region", (lei, et al. ab ) "the yangtze river economic belt", , "yangtze river delta integration development", "guangdong-hong kong-macao greater bay area" (bai, and li, a) and "the belt and road" (winter, ) new five regional development strategy, further formed the new pattern of linkage with whole areas, overall planning for regional and marine economic activities and coordinated development (xu, et al. ) . it shows that china's new space j o u r n a l p r e -p r o o f geographic economic phenomenon more and more clear, enters the new coordinated development stage of regional economic coordination and ecological environmental governance, comprehensive energy-using past experiences (zhou, chong, and wang, ) . the promulgation assumes all areas of the country continue to accelerate the development of renewable energy, strengthen local absorption capacity, reduce the amount of wastewater, wind, and light, and strive to build a highly clean energy supply system (vu, ) . in shanxi, inner mongolia, xinjiang, shaanxi, and shandong green mining technologies are expected to gradually replace traditional industries. the integration of science and technology in the field of energy development, through information technology and the introduction of a circular economy mode of production, will provide employment and opportunities and displace the traditional energy-intensive industries (he, wei, liu, and zhou, ) . provinces in the upper and middle reaches of the yangtze river and other central provinces are actively seizing the opportunity of natural gas and renewable energy sources to gradually release supply capacity to the central region to improve energy cleanliness (liu, et al, b) . the provinces and cities of the "yangtze river economic belt" strive for the promotion of the country, and enterprises have formed a benign mix of industrial transformation, environmental protection upgrading, government-enterprise cooperation, and the participation of private capital (zhuo, guan, & ye, ) . some regions in the five regions have the self-circulation of energy production, supply, and elimination, while some regions are still dominated by external energy supply. for example, one-third of the zhejiang province's electricity comes from outside the region (li, lei, li, and liu, a) . also, china's administrative governance has a special means, that is, the policy of poverty alleviation. this policy is not only poverty alleviation, but also has a great impact on energy production, supply, and consumption. for example, in xinjiang and ningxia province, the coal power supply, wind power supply, and natural gas supply have their consumption and absorption counterparts corresponding to the poverty-stricken provinces (lei, yao, and zhang, b ). china's urbanization process is still in the promotion stage, while urbanization plays an important role in china's energy consumption. the study of energy consumption in the process of urbanization from a spatial perspective is conducive to the coordinated development of urbanization and energy consumption (xie, yan, zhang, and wei, ) . in china, the previous energy problems in the process of urbanization are relatively extensive, in the future development of urbanization, the energy-saving strategy will be included in the process of j o u r n a l p r e -p r o o f urban planning and layout, starting from the demand side, the construction of economical and intensive mode of energy use, a new type of urbanization construction of ecological efficiency, energy conservation, and environmental protection, it will be china's new micro one of the symbols of the new space geographic economy (yu, huang, pan, and long, ). with the development of the chinese government's green and environmental protection law enforcement becomes legally enforceable (wang, c) , china's energy science and technology ministries, also strengthened laws related to the mining of coal, oil and gas exploration technology, recovery of smelting technology, environmental protection, as well as aspects related to clean coal and efficient conversion utilization of feedstocks (li, yang, wei, and zhang, c) . similarly, other laws have affected energy generation from nuclear, photovoltaic, wind power, and other aspects, whether in the design, manufacturing, or operation and maintenance (jiang, you, merrill, and li, a) . much of the focus has been on renewable energy, designed to stimulate technological innovation in areas of smart grid, energy storage to enable a transition to renewables and foster a new digital economy (zhu, fan, shi, and shi, ) . the current chinese market reforms (table b ) are designed to promote active research and development of new energy technologies and industries, particularly in green energy and transport (elliott and shanshan, ) . both state-owned enterprises and private investors are committed to seizing the commanding heights of a new round of green and low-carbon technologies (qian, wang, wang, and chen, ) . china is also investing heavily into artificial intelligence, cloud computing, big data, industrial internet, new materials, the large-scale generation of blockchain, and the sinking digital marketplace where technology commercialization is matched with angel investors has become one a major source of innovation and buy-ins (yue, et al. ) . with the development of first-line terminal sensing and control technology, the production efficiency of energy production and transportation will be significantly improved. according to artificial intelligence-based prediction, the efficiency in the manufacturing sphere will be improved by - %. with the direct collaboration of machines, the large-scale intelligent transportation upgrade will be closer to people's lives (sun and medaglia, ). in the supply or consumption terminals, driverless new energy vehicles, intelligent traffic dispatching applications, the crossregional industrial interconnection of energy production, and cross-type and proportionally j o u r n a l p r e -p r o o f dispatching of energy consumption have made steady progress (mann, ) . as shown in table b , much of the focus has been on the implementation of technical assistance to reduced co emissions as pm, through a transition to sustainable energy sources and digitization of the industrial economy to an industrial internet economy mirroring moves by other countries such as the usa and russian federation (zhang, and chen, ) . the further integration of the industrial internet and data has been widely applied in china's domestic market, which brings new development opportunities and challenges to the energy industry (yin, gong, guo, and wu, ) . based on the traditional energy industry, the energy industry will achieve great improvement by solving the "five core problems": (i) the transformation of energy digitalization, (ii) the collection of energy industry data, (iii) the value-added service technology of data comprehensive analysis, (iv) market demand, (v) and core products manufacturing & distribution (liu, ) . zhang and wen, ; sun, ; chen et al. ; and huang, zhao, and huang, ) . china, driven by the five-year plan has targeted environmental pollution as a major obstacle to increased efficiency and cost savings and envisions a transition to digital environmental as a benefit as approximately % of all carbon dioxide emissions up to were from heavy industries (zhou, et al. ) . the roll-out of artificial intelligence, industrial internet, and blockchain, the combination of an energy revolution and digital revolution is one approach to transition to local and more responsive environmental to both supply-side but also demand economics (li, wang, and zou, d) . the assumptions are that through the introduction of a smart digital economy, the energy system is increasingly digital and intelligent, especially the rapid development of clean energy represented by the production and supply of new energy and renewable energy, forming a new generation of energy digital technology economy. it is embodied in the multiple sharing of energy types, the mutual crossing of the main body's source-network-load, the mutual promotion of energy consumption and information consumption, and real-time data reporting and anticipates that it will incorporate elements of cloud computing, embedded device reporting, robotics, just-in-time deliveries, and payment. since this involves digital transactions, electrically operated devices with lower power demand the carbon footprint is anticipated to drop (zhao, jia, danlei, and shiwei, ) . under the policy influence of such technology, the raw materials, manufacturing technology, control technology, and management technology involved in the energy supply side, transportation network side, and consumption load side will all undergo qualitative changes such as in the field of agriculture . at present, the technology has gradually realized the real-time identification of the supply and consumption state of different types of energy, the timely installation of various energy storage regulation technologies, the statistical analysis of the proven-network-load operating curve of each province, and the prediction and response of potential risks in advance (jha, kumar, chatterjee, and khari, ) . in terms of top-level management and online supervision, online data collection, transmission, and cloud computing analysis will inevitably evolve to advance new intelligent automated operations, maintenance technologies, and most importantly, the supply chain (ben-daya, hassini, and bahroun, ). all these new technologies, summarized in figure a will give birth to the internet digital economy in the field of energy so that the energy economy is no longer the traditional asset-j o u r n a l p r e -p r o o f heavy economy, but both the traditional asset-heavy real economy and the digital asset economy. in the next five to years, china's energy sector will form a new type of business and a new model powered by energy numbers (guseva, dzusova, and kulikova, ) . according to the information released at several meetings of the financial and economic committee of the chinese government in , supply-side reform in the energy sector and the construction of an economy that emphasizes both green and quality will continue to be the keynote of the th five-year plan period . with the dual promotion of the country and the market, the energy technology field will further form an industrial system upgrading that combines points, lines, and faces (yilong, and jiaying, ) . with the implementation of the " th five-year plan" in the field of energy, how to build a high-quality green energy system reform transition, from sustained growth to more of a balanced holistic strategy in the " th five-year plan" is the central policy question which will occupy managers and decision-makers, as china continues to update part of its energy planning portfolios and specific policies seven in the " th five-year plan", to maintain energy consumption more emphasis will be given to production and distribution from various energy sustainable sources, with a local mix of solar pv, wind, it is anticipated that energy efficiency will improve requiring fewer coalpowered stations and thereby reducing carbon emissions and energy use costs, and promoting market-oriented energy trading of wind and solar companies even if electricity consumption continues to rise (lo, ) . the state council directives prioritize the production of clean and efficient utilization of petrochemical energy and the large-scale promotion of nuclear energy and renewable energy, building on from the best practices of the previous plan (yan and su, ) . based on the report card of energy conservation and emission reduction, the directive empowers the promotion of in-depth energy conservation and energy efficiency technologies. in terms of the reform of energy science and technology system, the directives also have setaside funding, tax adjustments to further develop clean technologies and iot integration such as the battery industry chain and the hydrogen energy industry chain is also continuously trying to adopt more flexible development policies and encourage the participation and development of various entities (jiang et al, a; li, e; and jingyu, et al. ). with the continuous development of the new normal of china's economy, china's energy development has entered the "three lows" trend. some of these are summarized in figures b and c. energy development is characterized by "low growth rate, low increment, and low carbonization", and the chinese government's continuous tightening of "constraints on the safe supply of resources, the protection of the ecological environment and the reduction of greenhouse gas emissions" has been further strengthened (figures d- f). during the period of the th five-year plan period, the carbon intensity of chinese provinces is expected to continue to decline significantly as electric vehicles and renewables kick-in. the chinese government is still the same as usual, on the demand side strongly advocated and encouraged revolution, the energy consumption in response to an increase in demand for energy, economic growth, and urbanization through the upgrade of industrial structure development of high and new technology industries, low energy consumption through realtime pricing, peak shaving, demand response to the demand side of the energy management, enhance the energy market competition mechanism, revitalize the enterprise vitality, eliminate backward production capacity, improve the efficiency of energy production enterprise for production (trubnikov, and richter, ) . whilst the policy directives are set forth at the state council, the actual implementations are left to the individual provinces. for example, clean energy, or the proportion of non-water renewable energy is achieved by wind or solar power, in the form of an integrated energy system and where systems can complement each other, promote energy system step by step in the direction of clean, green, low carbon transformation (sayigh, ) . in the comprehensive energy system, the traditional fossil energy such as coal power needs to be phased-out with wind power, photovoltaic power, and other renewable energy, and the proportion of renewable energy needs to be gradually increased, to reduce sufficient time for maturation of technologies and develop high storage capacities with cheaper operating costs (li, and taeihagh, b) . the industrial internet has been widely used in the field of energy and has penetrated and affected the integrated development of the secondary and tertiary industries covered by energy (shackelford, ) . under the influence of blockchain technology based on the industrial internet, the energy production relationship that can be reconstructed with the characteristics of decentralization in the digital economy era will gradually come to displace centralized systems and enhance redundancy (hou, wang, and & luo, ) . this new technology of integrated development will probably reshape the status and interrelationship of various subjects in the field of energy production, change the form of product distribution, and become a new engine to drive the development of energy digital economy (bai, cordeiro, and sarkis, b ). today's digital economy era based on blockchain softens the boundary between the producer, and end-user and the production materials no longer belong to a single party, as the "producer-consumer" linage is not strictly descriptive. in the field of energy digital economy, blockchain is profoundly changing the management, trading, and operation of distributed energy, and demand-side users are gradually playing the dual roles of consumers and producers (bai, and sarkis, c) . this aspect makes the energy supply-side and demand-side are the support of information technology, each data source, which changes the original traditional centralized energy distribution network and center, formed the new smart energy system construction direction, on the other hand, can complement each other, send parallel this new type of integrated energy storage mode to adapt to the market demand (saberi, kouhizadeh, sarkis, and shen, ) . with the acceptance and promotion of the market, the energy and j o u r n a l p r e -p r o o f digital resources supported by cloud technology will get the opportunity of coordinated development. surely, safety and reliability are still a problem that needs to be addressed before widespread adoption and replaced the traditional production workflow (abeyratne, and monfared, ) . methanol synthesis through co hydrogenation offers an attractive way to generate a synthetic precursor molecule, a fuel substitute, and a mechanism to lower the global co threshold (zangeneh, sahebdelfar, and ravanchi, ) . the economy of such an approach depends on whether the price of electricity is cheaper from coal, natural gas, solar, nuclear, or wind and are on average more expensive than conventional approaches. the conversion of co to methanol is also more expensive (~€ per ton vs € per ton) than the syngas process, although the price difference is decreasing, like how the price decrease from solar sources (jarvis, and samsatli, ) . the higher prices reflect the high stability of carbon dioxide and its associated activation ( kj/mol) and water production as a side-reaction which can lead to the deactivation of metal catalysts such as copper. one approach to minimize these potential disadvantages is to utilize the reverse water gas shift reaction which is separated from the main methanol synthesis route and then combined in the reactor. one final advantage is that net carbon dioxide emissions from hydrogenation are lower than from syngas emissions ( . -tons co per ton ch oh, versus . -ton co per ton ch oh) (din et al. ). the synthesis, operational parameters, and common catalyst configurations are summarized. methanol has several advantages as a fuel, due to its energy content . kj/mol, although its heat of combustion per gallon is lesser than gasoline ( , btu versus , for gasoline) (liu, and ma, ) . methanol is also a viable fuel substitute as their prices per gallon are similar with methanol being slightly cheaper ($ . /gallon versus . for a gallon, jan ), is a liquid at room temperature and has a lower freezing temperature than standard gasoline (- c versus - c for n-octane, although the value will depend on other additives) (carr, and riddick, ) . methanol having less carbon than gasoline combusts to only carbon dioxide and water, and has a lower flash point ( c versus . c for n-octane, although in typical gasoline with additives the flashpoint may be negative (~ c) and in this regards is a safer fuel choice. since gasoline can exhibit incomplete combustion products and particulate matter, j o u r n a l p r e -p r o o f inhalation of fumes from the combustion of gasoline is generally more toxic than for methanol (ghiotti, and boccuzzi, ) . methanol is synthesized commercially by syngas using zinc/chromic based catalysts at c and atm. substitution of zinc/chromic by cu/zno has enabled the synthesis to be favorable at lower pressures and temperatures ( - atm, - c) (rico et al. ). the present method for synthesis is related to the use of syngas and co over the cu-zno/al o catalyst at - c and - atm respectively (weigel, koeppel, baiker, and wokaun, ) . methanol seed material is carbon dioxide with carbon monoxide as surface oxygen, which is an attractive feature as it consumed co and has been proposed as a potential avenue away from the carbon economy to more clear methanol and ethanol economies, whereby methanol synthesis is via hydrogenation of co driven by solar or geothermal energy, at c and atm. in catalyst design, the three major obstacles are thermodynamic, kinetic, and cost considerations (yang, and jackson, ) . as co is a stable molecule, high pressures, and temperatures around c are required to drive the reaction forward (eqn: ), although the heat of formation suggests the reaction is favored at lower temperatures (gallucci, paturzo, and basile, ) . co + h  ch oh +h o h k = - . kj/mol ( a) therefore, the actual pressure and temperature regime is influence by the catalyst employed. recently co hydrogenation to methanol using a cu/zno/al o catalyst was achieved ay atm and at atm when using a ni(co) catalyst. one problem is water formation that leads to the deactivation of the catalyst, in addition to the use of hydrogen, which is greater than by syngas alone. water can also act as an oxidant at higher temperatures and oxidize the metal to the metal oxide (mahajan, and goland, ) . the water can be removed during the reaction, or co introduced to reduce the metal oxide. this would regenerate the co , or h gas been used for the reduction of cuo to cu. recently a new study showed that pre-addition of water suppressed the oxidation process, similar to the effects of water addition for co selectivity by the reverse water gas shift reaction (li, yuan, and fujimoto, ) . this reaction: co + h  co + h o h k = kj/mol ( d) is unfavored, thereby requiring higher temperatures to drive it, which also promotes the reverse j o u r n a l p r e -p r o o f water gas shift relative to hydrogenation of co to methanol. the current approach focuses on liquid phase methanol synthesis rather than gas-phase methanol hydrogenation (samimi, hamedi, and rahimpour, ) . the major metal catalyst for methanol synthesis is based on copper, zinc oxide, and alumina (yang, et al. ). silver as the active catalytic component with zro compared with cu/zno at temperatures lower than c, with enhanced selectivity for co hydrogenation, when added to cu/zno with % selectivity whereas the selectivity with cu/zro was % (köppel, stöcker, and baiker, ) . although the selectivity of silver is greater its activity is not as high as with cuo/zro catalyst (grabowski, et al. ) . palladium based catalysts at atm and c n over la o support, but with lower selectivity for the co hydrogenation reaction (~ %) (garcía-trenco, et al. ) . palladium (pd) on in catalyst also gave superior results relative to cu/zno/al o catalyst. other supports evaluated were pd on ceo at c and multi-walled carbon nanotubes supposed pd/zno or pd/tio at c gave higher selectivity due to stronger interactions between the metal catalyst and the support surface (liang, dong, lin, and zhang, ). in some of these studies, lower temperatures resulted in the production of methane, with indications that their selectivity for methanol may be greater than methanol (shen, okumura, matsumura, and haruta, ) . copper is the most widely used catalyst particularly when supposed by zno and is operated at higher temperatures than c, atm (behrens, ) . by using zno on silica the methanol formation from h and co can be increased, due to the availability of oxygen vacancies of zinc oxide, improving both stability and dispersion of the copper catalyst (sugawa, sayama, okabe, and arakawa, ) . therefore, the addition of support that enhances the stability of copper whilst increasing its dispersion generally leads to greater methanol selectivity (ovesen, et al. ). the addition of ga o to cu/zno led to better catalyst performance for hydrogenation of co to methanol, where the ga o facilitate the reduction fo cu, increasing the activity, suggesting that the interaction of cu with zno support is greater than with the sio support. whilst methanol is generated using copper alone, the addition of a promoter like ga o or support such as ceo or zno, because of the latter offer the probability of greater dispersion of cu on the support and thereby greater catalytic surfaces for the hydrogenation reaction to take place, relative to copper alone, in addition to stabilizing effect of the support material for the copper (i) species (toyir, de la piscina, fierro, and homs, ) . this reflects the complexity of the system in terms of catalyst half-life, selectivity, and activity, resulting in cu/zno/al o or cu/zro as being the default choice for the hydrogenation reaction (liu, lu, and yan, ) . the oxidation state of the metal catalyst is critical, it is generally observed that the zero-valent species are more stable and active. other support systems evaluated were silica, alumina, and zirconia, due to the availability of accessible oxygen sites and ion exchange pricing multiple reactive surfaces for the hydrogenation reaction. therefore, the correct choice of promoter and support can lead to greater activity, for example, cu/zro over cu/zno (nitta, et al. ) . zirconia can form some crystalline forms that are transformed at various ph, with the tetragonal form of zirconia is the most stable at basic ph environments, while at neutral ph the monoclinic form of zirconia is the most stable (zhuang, bai, liu, and yan, ) . lastly, the calcination temperature can also influence the allotropic, with the tetragonal form being most stable under c, but the monoclinic being formed at higher temperatures (rhodes, and bell, ) . the monoclinic zirconia (mzro ) is more active than the tetragonal allotrope (tzro ), due to greater interactions of the tetragonal form with intermediates than the monoclinic formation (jung, and bell, ) . doping with silver ion has also been shown to enhance activity via stabilization of the tzro form, suggesting that cu/zro is a better catalyst than cu/zno. the addition of zro or zno generally increased the activity of the cu catalyst by increasing the stability of the cu ion, but the rate was unchanged with zno but not zro with doped ag + (grabowski, et al. ) . this difference between zno and zro appears to be due to the stabilizing effect of zro on ag + that is lacking with zno. the ph-dependence for the hydrogenation reaction may be related to the mechanism of co-precipitation for cu/zno/al o due to aging, where hydroxide ions are release increasing the ph. the increase of ph can be countered by the addition of co , and a constant ph improves catalyst performance (bems, et al. ) . h o + co  h + + co -( b) thus, methanol selectivity is highly dependent upon the cu surface, morphology, and the phase of zro (guo, et al., ) , summarized in table a . j o u r n a l p r e -p r o o f the introduction of co in the aging process has several advantages, which are control of composition (purohit, sharma, pillai, and tyagi, ) , maintenance of constant ph (baltes, vukojević, and schüth, , increased in pore volume to promote gas diffusivity and increase surface area to promote catalysis (guo, et al. ) in addition to strong interactions between cu and specific stable phase of zro (zhuang, bai, liu, and yan, ) . the above studies with glycine or co-precipitation suggest that crystallinity and activity of the copper catalyst are counter to each other, where the dopant atom (e.g. ag) serves as a site for nucleation cu crystallization (maniecki, et al. ) . the extent of crystallization, in turn, depending on the degree of dispersion of the dopant or alloyed metal or metal substitution (e.g. la for cu) (guo, et al. ) , with activity being correlated with cu active sites (zhang, zhang, and chen, ) and selectivity being correlated with basic sites on the catalytic surface (yoneyama, ) , as shown in table b . as observed in earlier studies, the addition of ga o as a catalyst promoter increased activity, could be used instead of substitution of the metal catalyst itself. the promoter could enhance the catalyst to support structure or stabilize the metal catalyst itself by acceptance of an electron or promoting the reduction of the active metal (liu, lu, and yan, ) . as stated, earlier gallium oxide enhanced the activity of copper-based catalysts via oxidation of copper ( ) to copper (i), thereby maintaining a constant ratio between eh zerovalent and mono species increasing the catalyst half-life (toyir, et al. ) . niobium oxide (nb o ) as support has also been used and has been shown to exhibit excellent activity and selectivity in the hydrogenation reaction fo co and co for methanol production (furukawa, et al. ) . as this is an acidic oxide, it can also be used as a promoter. it is thought that the oxide increases cu dispersion, enhancing surface area sites better cu stability against water, and enhanced activity with co hydrogenation (hu, kunimori, and uchijima, ) . zinc oxide has been used as a catalyst in the co hydrogenation reaction, and as a promoter for cu by increasing its dispersion, thereby slowing potential agglomeration on the active copper catalyst when supported by alumina (saito, fujitani, takeuchi, and watanabe, ) . the zinc oxide is basic and can counteract the activity of the alumina support. this has been shown to slow down the conversion of methanol to dimethyl ether (toyir, et al. ). the interaction between cu and zno is thought to occur via interaction interactions cu + . o-zn, where the zinc oxide can adsorb h species and promote a stable intermediate (methoxy oxide) which is ultimately converted to methanol upon hydrogenation (kanai, et al. ) . it should be noted that with syngas based synthesis, the feed gas may have trace amounts of sulfur that can position that active catalyst surface, zno is thought to be able to abstract the sulfur forming zns and thereby lessening the deactivation of the cu species (centi, and perathoner, ). the zn was also able to adsorb with species such as hxco, increasing the rate of methanol synthesis (chen, et al. ). the role of the catalyst support is the dispersal of the active metal, but also to avoid sintering or aggregating the metal particles. the acidity or basicity of the support will affect catalyst performance (wang, wang, ma, and gong, ) . silica has high thermal stability and good dispersion capacity and has been used as a support material using co and h . some first two and second-row transition metals were evaluated ion silica supports, at c and atm resulting in higher selectivity of methane j o u r n a l p r e -p r o o f for ni, co, and co on pt (sugawa, sayama, okabe, and arakawa, ) . for methanol selectivity, cu, ag, fe, and pd were greater and may diver higher activities due to the greater surface area of silica relative to zno. silica can also transform silica hydroxide in the presence of steam, resulting in a search for substitutes such as alumina (takahashi, et al. ). alumina has been used as a support for methanol by co hydrogenation using cu/zno. however, over a prolonged operation that methanol yields have decreased, which could be lessened by the addition of cu/zno/al o (centi, and perathoner, ) . zirconia has been used as a support with cu (zuo) which gave good selectivity and stability that could be increased by the addition of al o as a cu/zno/zro /al o system, the higher thermal stability of zro -al o and selectivity of cu( )zro may be the reason or the improvement also, the cu/zno/zro system was found to be more tolerant to water poisoning during methanol synthesis than cu/zno/al o (li, yuan, and fujimoto, ) . recently carbon nanotubes or fibers have been used due to the high surface area and thermal stability of carbon and the ability to adsorb hydrogen via h-adsorption sites. catalyst particles dispersed on cnt support gave more active sites than on activated carbon, resulting in increased hydrogenation of methanol (liang, dong, lin, and zhang, ) . low rates were observed for pd/cnt suggesting that pd atoms required to be activated for the hydrogenation reaction to proceed and require a nearby metal oxide. nanocarbon fibers have also been used and can promote the hydrogenation to methanol from co at lower temperatures (wang, lu, li, and li, ) . whilst the macro-level mechanism is known in that co adsorption on metal oxide and h on metal, with the formation of intermediates being the rate-determining step in methanol synthesis through co hydrogenation on copper (rasmussen, et al. ) . the active species appears to be cu ( ), although other studies also suggest that cu(i) stabilized on the catalyst (cu( )) surface also assists with the co adsorption and has a bearing on methanol selectivity as well as activity (liu, lu, and yan, ) . this stabilization may also assist with the (chen, et al. (herman, et al. ) . also, studies on cu/zno/al o show that after adsorption of oxygen and carbon dioxide, carbonate (co ) and formate (hcoo) are generated as intermediates, with the carbonate being converted to formate upon additional hydrogenation, forming a methoxy species (ch -o) and methanol on the final reduction step (ch -oh) (fujitani, and nakamura, ) . using pd/ga o only these two species were identified when co was reduced to methanol, whilst the major species are formate, minor species often identified are varied such as carboxylate (hooch) and methylene peroxide (ch oo) (sahki, et al. ). the formate is coordinated with the surface metal oxide axially with an adjacent adsorbed carbon dioxide and hydrogen from the metal, with the monodentate formate being unstable at temperatures over c and is transformed into formic acid (hcooh) upon a reaction with the newly formed formate (jiang, et al. b) . is generated with upon hydrogenation yields formic acid, which in turn undergoes dehydration to product methylene peroxide (ch oo) (arena, et al. ) . the unstable methylene peroxide is converted to the methoxy species through reaction with adsorbed hydrogen (h ) and to methanol upon reduction. the application of bimetallic catalysts such as cu/zno and cu/zro suggest a dual mechanism operating on each catalyst surface, whereby co hydrogenation occurs on the metal surface with adsorbed hydrogen (h ) and carbon dioxide adsorption on the metal oxide, with molecular hydrogen adsorption occurring on the copper atoms. upon adsorption the hydrogen molecules dissociate to form atomic hydrogen and are transported from the cu surface to the zro surface where co is adsorbed by spillover, to reduce adsorbed co to formate, methyl species and reduction to methanol (gao, and au, ) . in cases of metal oxide supports, the optimal ratio is not uniform, for example for cu on znal o , the cu: zno ratio of . was found to yield the greater activity, whilst for al/zn the ratio was . , which reflects sites for synthesis and sites for coordination via monodentate or bidentate formate hydrogenation to methanol via a methoxy intermediate (frank, et al. ). with copper substitution by la, the range for a higher activity for lamn -xcuxo ( ≤x ≤), with a modal value of . . the range like with ag + stabilization that activity is related to the dispersion of cu + species that is inhibited by the reduction of cu + to cu , which is no longer stabilized by mn in the perovskite (jia, gao, fang, and li, (ahmed, shibata, taniguchi, and izumi, ) . the catalyst in the forms of beads or pellets can be fixed to the surface in the form of fixed bed reactors, or suspended in a solvent which allows for thermal motion, a form of a slurry reactor which may be charged and then discharged ('digital') or steady-state ('analog') configuration (nitta, et al. ). in general, fixed-bed reactors are applied to gas phase reactions, where hydrogenation of carbon dioxide to methanol occurs, from c to atm, using cu/zro /zno catalyst. higher conversion may be achieved by switching over to a different catalyst such as cuznga or a coprecipitated cu-zn-zr with gel-oxalate to provider greater active surface sites relative to coprecipitation with sodium carbonate and coordination with citric acid (gao, et al. a ). the activity of methanol synthesis is related to the number of exposed sites on the cu surface, whilst selectivity was related to the number of basic sites on the support. the introduction of an electronegative atom may improve activity as was demonstrated by the introduction of fluorine on cuznal catalyst for co hydrogenation to methanol (gao, et al. b) . the advantages of a fixed bed configuration are that gas and metal interaction does not require prior mixing, diffusion of reactants does not occur, and the higher volumetric loading of the catalyst and easier to upscale to higher quantities (sherwood, and farkas, ) . the deactivation of the catalyst at higher temperatures over time is one disadvantage, (bartholomew, ) which may be overcome with new catalysts such as mo coated by nitrogen and sulfur co-doped carbon (nsc) that as functional after almost h of operation on steam (han, geng, xiao, and wu, ) . it was further demonstrated that co/mn catalyst exhibited a selectivity of approximately % at c for h on steam, and might indicate that a bifurcated reactor design be implemented with separate hydrogen (h ) and water (h o) feed to pre-select the optimal ratio (stangeland, kalai, ding, and yu, ) . in a slurry reactor, the reaction is carried out in a liquid phase, such as the operating temperature can be reduced to promote the thermodynamic reaction to the right. in this manner, the catalyst deactivation observed at elevated temperatures can be minimized. the selectivity and activity of co hydrogenation to methanol was found to be greater with a slurry reactor than a fixed bed reactor design (kim, et al. ) . as the reaction occurs in solution, the rate j o u r n a l p r e -p r o o f of heating, over-temperature, the temperature gradient can be controller with greater precision than with a fixed bed reactor design. in a slurry, the metal catalyst can be dispersed in the form of a powder rather than pellets and are configured in three type configurations. type configuration is used for batch reaction stirred autoclaves, type pump stirred, and type reactant gas used to stir the mixtures (cybulski, stankiewicz, albers, and moulijn, ) . in the slurry, the excess heat is absorbed by the solvent, such as tetrahydroquinoline (c h n), which can be operated at less than c and atm (sun, et al. ) . the role of solvent is important, as well as co-additives in determining final operating temperature, pressure, activity, and selectivity (shreiber, and roberts, ) . as hydrogenation fo co to methanol is exothermic, thermodynamically, lower temperatures are favored. in practice, higher temperatures are utilized to give the gas and intermediate enough kinetic energy to interact and higher temperatures yield higher activity, up to where the equilibrium constant decreases with increasing temperature (le valant, et al. ) . the maximum temperature at which the equilibrium constant will decrease depending on the catalyst type, form, and support material but is from - c (fujitani, and nakamura, ) . this is due to the occurrence of side reactions or the reverse water gas shift reaction, which appears to have faster reaction kinetics than methanol synthesis concerning temperature (gallucci, and basile, ) . to illustrate the difference between reverse water gas shift reaction (jiang, et al. b) and methanol synthesis, the most common reaction conditions are summarized in table c (for reverse water gas shift reaction) and d (methanol synthesis). ( ) suggesting an upper limit of c, above which co is in part converted to co lessening the methanol yield (ahouari, et al. ) . the methanol synthesis via hydrogenation also appears to be more sensitive to temperature fluctuations than the reverse water gas shift reaction as can be seen by comparison of operating condition variance between the two (table a versus b variables) reactions (qi, zheng, fei and hou, ) . at c, the probability of methane formation is high. similarly, the selectivity of methanol decreased from approximately % at c to % at c (graaf, and winkelman, ) . therefore, the optimal temperature s appears to be between - c but is highly dependent on the catalyst (xin, yizan, zhang, and jinfu, ). while the thermodynamic yield favors lower temperatures, the thermodynamic calculations point to higher pressures for the reduction reaction, with the reverse water gas shift reaction would decrease at higher pressures (jun, shen, and lee, ) . higher pressures also favor oxygenated byproducts such as dimethyl ether, with additional safety concerns of chambers at very high pressure. most pressures are from atm to atm using cu/zn/al/zr fibrous catalyst or cu/al o or cu/zno/al o catalysts in a slurry reactor at c (liaw, and chen, ). j o u r n a l p r e -p r o o f the stoichiometric reaction indicates one mole of carbon dioxide to three molecules of hydrogen (h ) gas, thus a ratio of (h : co ) of is favored for co hydrogenation to methanol (bansode, and urakawa, ) . in reactor practical applications it has been demonstrated that at higher pressure, the reaction is controlled thermodynamically with a ration of co : h of > , but at lower pressures, it is kinetically controlled (ratio < ), with a suboptimal ratio between - depending on the final pressure (shen, jun, choi, and lee, ( ) . computational calculations at a fixed pressure ( atm) but at varied temperatures ( - c) or fixed temperature ( c) but at varied pressures ( - atm) show a linear relationship between h : co ratio and methanol yield (kim, et al. ) . in a slurry reactor, an increase of the h : co ration from - resulted in higher co conversion due to the availability of hydrogen to promote hydrogenation and methanol synthesis (potočnik, grabec, Šetinc, and levec, ) . a problem could also be viewed as an opportunity to be solved. in the current situation of the global epidemic, digital technology plays an irreplaceable role in social life and is also exerting a profound impact in the field of energy. the chinese government is making efforts to promote technological upgrading in the energy sector through policies and the market, especially in the integration of energy expertise and digital technology, as well as energy conservation and environmental protection technology and digital technology, to create an energy ecology based on local conditions, wisdom and comprehensively in energy-using, and security with science and technology. one technological approach is carbon dioxide hydrogenation to methanol via homogenous catalysis, which was inefficient due to lower catalyst recovery and regeneration. consequently, heterogeneous catalysis has been adopted using a reverse water gas shift reaction, whereby carbon dioxide and hydrogen gases are converted to carbon monoxide and water by the water gas shift reaction and the resulting gas mixture of co/co /h is channeled into a slurry reactor after removing water. the recent introduction of cu/zno based catalysts indicates higher selectivity and activity to methanol than prior approaches due to operation near-optimal thermodynamic conditions such as low temperature and moderate pressures and remove off heat due to efficient heat removing solvent. whilst direct co hydrogenation to methanol is a new technology, advances in a catalyst, reactor design, and operational at lower temperatures are pushing these technologies to be competitive with electricity generation from fossil fuels, j o u r n a l p r e -p r o o f with the catalyst being based around cu, such as cu/zno, nb o of ga o , with carbon nanotubes as support. due to the exothermic profile of the reaction, low temperature and high pressure will favor methanol selectivity over methane or other by-products, due to depression of the reverse water gas shift reaction and methanol decomposition. the stoichiometric ratio of h : co is is also favored for the hydrogenation reaction, but practical applications have a ratio of - . dr. gao conceived the thrust and wrote the first draft. dr. liu did figures , and and the section on catalysis. lastly, dr. bashir contributed to the analyses of emission data, catalytic technologies, figure , and references and copyright. two of the authors are from tamuk (drs. sajid bashir and jingbo liu) and dr. liu is also a guest editor. however the manuscript will still go through the peer-review process. the role of the state council modern economic growth in india and china: the comparison revisited, - . economic development and cultural change china and globalization: years of reform and opening-up and globalization . transition to low carbon energy policies in china-from the china's five-year planning system: implications for the reform agenda testimony for the us-china economic and security review commission environmental kuznets curve for co emissions in china: a spatial panel data approach international economic integration and environmental protection: the case of china an investigation of the spatial changing pattern of co emissions in china carbon emissions, logistics volume, and gdp in china: an empirical analysis based on a panel data model co emissions are embodied in interprovincial electricity transmissions in china the collective contribution of chinese cities to territorial and electricity-related co emissions estimating coal production peak and trends of coal imports in china statistics of china power industry. url: cec.org.cn nbsc ( ) global carbon budget decomposition analysis of carbon dioxide emissions in china's regional thermal electricity generation data and statistics tables sources of growth in the world economy: a comparison of g and e economies the methanol industry clean coal technologies in china based on the methanol platform china's use of fuel methanol and its implications on future energy trends china peoples' republic of efforts for a circular economy in china: a comprehensive review of policies a spatial panel analysis of carbon emissions, economic growth, and the high-technology industry in china an emissions-socioeconomic inventory of chinese cities conversion of carbon dioxide to valuable petrochemicals: an approach to clean development mechanism fossil and alternative fuels -energy content specific energy and energy density of fuels experimenting with decentralized energy governance in china: the case of the new energy demonstration city program renewable energy policy and electricity market reforms in china decarbonization, digitalization, and decentralization are changing key power infrastructures a multi-criteria decision analysis model for carbon emission quota allocation in china's east coastal areas: efficiency and equity harmonizing 'responsibility to protect': china's vision of a postsovereign world evaluation of china's electric energy efficiency under environmental constraints: a dea cross efficiency model based on game relationship will china peak its energy-related carbon emissions by ? lessons from chinese provinces regional energy efficiency evaluation in china: a super efficiency slack-based measure model with undesirable outputs china's renewable energy goals by study on china's renewable energy policy reform and improved design of renewable portfolio standard the five-year plan: a new tool for energy saving and emissions reduction characteristic and driving factors of aerosol optical depth over mainland china during trends in the chemical composition of global and regional population-weighted fine particulate matter are estimated for years an inventory of primary air pollutants and co emissions from cement production in china evolution and projection of co emissions for china's cement industry from to abrupt declines in tropospheric nitrogen dioxide over china after the outbreak of covid- present and future emissions of air pollutants in china: so , nox, and co sulfur dioxide emissions in asia in the period - emission inventory and trends of nox for china comparison of co emission scenarios and mitigation opportunities in china's five sectors in china's carbon emissions could peak sooner than forecast a five-year plan advances policy to reduce reliance on coal and expand renewable energy the development of energy blockchain and its implications for china's energy sector the allocation of carbon emission intensity reduction target j o u r n a l p r e -p r o o f by among provinces in china the effect of environmental policy tools on regional green innovation: evidence from china what influences the effectiveness of green logistics policies? a grounded theory analysis the stronger policy is required to substantially reduce deaths from pm . pollution in china estrogens in municipal wastewater and receiving waters in the beijing-tianjin-hebei region, china: occurrence and risk assessment of mixtures the assessment of forest ecological security and its determining indicators: a case study of the yangtze river economic belt in china evaluating regional eco-green cooperative development based on a heterogeneous multi-criteria decision-making model: example of the yangtze river delta region review of researches on talent cultivation models and approaches under the background of guangdong-hong kong-macao greater bay area geocultural power: china's belt and road initiative assessing progress towards sustainable development over space and time what is the future policy for photovoltaic power applications in china? lessons from the past spatial network analysis of carbon emissions from the electricity sector in china evaluation of the potential for salt cavern gas storage and integration of brine extraction: cavern utilization, yangtze river delta region prediction analysis of the coordinated development of j o u r n a l p r e -p r o o f the sports and pension industries: taking provinces and cities in the yangtze river economic belt of china as an example study on industrial selection of counterpart cooperation between jilin province and zhejiang province in china from the perspective of low carbon the competitiveness of provincial electric power supply in china: based on a bottom-up perspective does urbanization increase residential energy use? evidence from the chinese residential energy consumption survey community morphology and energy consumption. guidelines for community energy planning on the evolution of chinese environmental law and governance authoritarian environmentalism and environmental policy implementation in china. resources, conservation and recycling implementation of a multi-agent environmental regulation strategy under chinese fiscal decentralization: an evolutionary game-theoretical approach industrial activity and the environment in china: an industry-level analysis the resource curse, environmental regulation, and transformation of coal-mining cities in china review and challenges of policies of environmental protection and sustainable development in china a great leap forward how does new environmental law affect public environmental protection activities in china? evidence from structural equation model analysis on legal cognition. science of the total environment how policy tools utilized in open data policies in china cloud-fog architecture-based energy management and decision-making for next-generation distribution network with prosumers and internet of things devices mapping the challenges of artificial intelligence in the public sector: evidence from public healthcare blockchain technology-china's bid to high long-run growth china's digital economy: opportunities and risks what drives entrepreneurship in digital economy? evidence from china china's renewable energy law and policy: a critical review a roadmap for china to peak carbon dioxide emissions and achieve a % share of non-fossil fuels in primary energy by current situation and trend of research on application of blockchain technology in logistics field the assistance of digital economy to the revitalization of rural china state-of-the-art internet of things in protected agriculture collaborative handshaking approaches between the internet of computing and the internet of things towards a smart world internet of things and supply chain management: a literature review the financial and economic aspects of the digital economy insurtech trends china g: opportunities for ict industries top internet companies by total reached users in china for h china's top companies by market cap: banks and energy cos an in-depth analysis of the evolution of the policy mix for the sustainable energy transition in china from china's five-year plan and transformation of china's governance modernization. on china's road strong, sustainable, and inclusive growth in a new era for china-paper : challenges and ways forward economic performance of automobile industry in today's exchange rates. url: tradingeconomics governing energy consumption in china: a comprehensive assessment of the energy conservation target responsibility system what drives the changes in china's energy consumption and intensity during the th five-year plan period? energy policy who is the energy-poor? evidence from the least developed regions in china china's logistics development and prospects under the sharing economy in measuring the inclusive wealth of china: advances in the sustainable use of resources international energy outlook global bev and phev sales for china energy policy: evidence of china-russia cooperation solar and wind energy will supply more than % of world electricity by smart factories, dumb policy? managing cybersecurity and data privacy risks in the industrial internet of things how to improve the competitiveness of distributed energy resources in china with blockchain technology blockchain technology: business, strategy, the environment, and sustainability a supply chain transparency and sustainability technology appraisal model for blockchain technology blockchain technology and its relationships to sustainable supply chain management blockchain ready manufacturing supply chain using a distributed ledger technologies and infrastructures underpinning future co value chains: a comprehensive review and comparative analysis recent developments on heterogeneous catalytic co reduction to methanol the analysis of the energy and environmental impacts of microalgae-based fuel methanol in china physical properties of the methanol-water system chemical and physical properties of copper-based catalysts for co shift reaction and methanol synthesis evaluation of different dielectric barrier discharge plasma configurations as an alternative technology for green c chemistry in the carbon dioxide reforming of methane and the direct decomposition of methanol surface species in co and co hydrogenation over copper/zirconia: on the methanol synthesis mechanism china's growing methanol economy and its implications for energy and the environment an experimental study of co hydrogenation into methanol involving a zeolite membrane reactor integrating low-temperature methanol synthesis and co sequestration technologies: application to igcc plants development of a highly stable catalyst for methanol synthesis from carbon dioxide green methanol production process from indirect co conversion: rwgs reactor versus rwgs membrane reactor methanol synthesis from co -rich syngas over a zro doped cuzno catalyst copper-and silver-zirconia aerogels: preparation, structural properties, and catalytic behavior in methanol synthesis from carbon dioxide influence of polymorphic zro phases and the silver electronic state on the activity of ag/zro catalysts in the hydrogenation of co to methanol pdin intermetallic nanoparticles for the hydrogenation of co to methanol carbon nanotube-supported pd-zno catalyst for hydrogenation of co to methanol the influence of the support on the activity and selectivity of pd in co hydrogenation heterogeneous catalysis of co conversion to methanol on copper surfaces methanol synthesis from co and h over silver catalyst. energy conversion and management kinetic implications of dynamical changes in catalyst morphology during methanol synthesis over cu/zno catalysts highly effective conversion of co to methanol over supported and promoted copper-based catalysts: influence of support and promoter nanocrystalline zirconia as a catalyst support in methanol synthesis copper-zirconia catalysts for methanol synthesis from carbon dioxide: effect of zno addition to cu-zro catalysts the effects of zirconia morphology on methanol synthesis from co and h over cu/zro catalysts: part i. steady-state studies effects of zirconia phase on the synthesis of methanol over zirconia-supported copper relations between synthesis and microstructural properties of copper/zinc hydroxy carbonates the influence of la doping on the catalytic behavior of cu/zro for methanol synthesis from co hydrogenation ultrafine ceria powders via glycine-nitrate combustion correlations between synthesis, precursor, and catalyst structure and activity of a large set of cuo/zno/al o catalysts for methanol synthesis structure and performance of cu/zro catalyst for the synthesis of methanol from co hydrogenation bimetallic au-cu, ag-cu/cral o catalysts for methanol synthesis effect of promoter sio , tio , or sio -tio on the performance of cuo-zno-al o catalyst for methanol synthesis from co hydrogenation photoreduction of carbon dioxide on quantized semiconductor nanoparticles in solution solvent-free aerobic alcohol oxidation using cu/nb o : green and highly selective photocatalytic system interaction of hydrogen and oxygen with niobia-supported and niobia-promoted rhodium catalysts development of copper/zinc oxide-based multicomponent catalysts for methanol synthesis from carbon dioxide and hydrogen the synergy between cu and zno in methanol synthesis catalysts advances in catalysts and processes for methanol synthesis from co synergism between cu and zn sites in cu/zn catalysts for methanol synthesis recent advances in catalytic hydrogenation of carbon dioxide addition of zirconia in ni/sio catalyst for improvement of steam resistance a remarkable difference in co hydrogenation to methanol on pd nanoparticles supported inside and outside of carbon nanotubes methanol synthesis on cu ( ) from a binary gas mixture of co and h catalytic synthesis of methanol from coh : i. phase composition, electronic properties, and activities of the cu/zno/m o catalysts methanol synthesis from co and co hydrogenations over supported palladium catalysts cuo/zno/al o catalyst. reaction kinetics, mechanisms, and catalysis hydrogenation to methanol on pdcu bimetallic catalysts with lower metal loadings solid-state interactions, adsorption sites, and functionality of cu-zno/zro catalysts in the co hydrogenation to ch oh co hydrogenation to methanol on a yba cu o catalyst steam reforming of methanol over copper-containing catalysts: influence of support material on microkinetics influence of copper content on structural features and performance of pre-reduced lamn -xcuxo ( ≤ x< ) catalysts for methanol synthesis from co /h photocatalytic conversion of carbon dioxide into methanol using zinc-copper-m (iii)(m= aluminum, gallium) layered double hydroxides influence of zr on the performance of cu/zn/al/zr catalysts via hydrotalcite-like precursors for co hydrogenation to methanol influence of fluorine on the performance of fluorine-modified cu/zn/al catalysts for co hydrogenation to methanol studies of the slurry reactor mechanisms of catalyst deactivation high selective synthesis of methanol from co over mo c@ nsc mesoporous manganese-cobalt oxide spinel catalysts for co hydrogenation to methanol promotion of co hydrogenation to hydrocarbons in three-phase catalytic (fe-cu-k-al) slurry reactors monolithic reactors for fine chemical industries: a comparative analysis of a monolithic reactor and a mechanically agitated slurry reactor liquid/catalyst interactions in slurry reactors: changes in tetrahydroquinoline composition during methanol synthesis over zinc chromite methanol dehydrogenation in a slurry reactor: evaluation of copper chromite and iron/titanium catalysts the cu-zno synergy in methanol synthesis from co , part : origin of the active site explained by experimental studies and a sphere contact quantification model on cu + zno mechanical mixtures a theoretical analysis of methanol synthesis from co and h in a ceramic membrane reactor recent advances in carbon dioxide hydrogenation to methanol via heterogeneous catalysis catalytic activity of the m/( zno· zro ) system (m= cu, ag, au) in the hydrogenation of co to methanol co hydrogenation to methanol over cuznga catalysts prepared using microwave-assisted methods copper-gallia interaction in cu-ga o -zro catalysts for methanol production from carbon oxide (s) hydrogenation fluorine-modified zr catalysts via hydrotalcite-like precursors for co hydrogenation to methanol hydrogenation of co to ch oh over cu/zno catalysts with different zno morphology methanol synthesis from co hydrogenation over cu/γ-al o catalysts modified by zno, zro , and mgo bimetallic pd-cu catalysts for selective co hydrogenation to methanol study of cuznmox oxides (m= al, zr, ce, cezr) for the catalytic hydrogenation of co into methanol cu/zn/al/zr catalysts via phase-pure hydrotalcite-like compounds for methanol synthesis from carbon dioxide methanol synthesis from co hydrogenation over la-m-cu-zn-o (m= y, ce, mg, zr) catalysts derived from perovskite-type precursors methanol synthesis from co hydrogenation over copper-based catalysts low-temperature methanol synthesis catalyzed over cu/γ-al o -tio for co hydrogenation chemical equilibria in methanol synthesis including the water-gas shift reaction: a critical reassessment methanol synthesis from co hydrogenation with a cu/zn/al/zr fibrous catalyst concurrent production of methanol and dimethyl ether from carbon dioxide hydrogenation: investigation of reaction conditions the national science foundation (nsf-mri, cbet ), r. welch foundation (ac- ) from the texas a&m university-kingsville, and texas a&m energy institute are duly acknowledged for their financial support. key: cord- - ly to authors: skoczkowski, tadeusz; verdolini, elena; bielecki, sławomir; kochański, max; korczak, katarzyna; węglarz, arkadiusz title: technology innovation system analysis of decarbonisation options in the eu steel industry date: - - journal: energy (oxf) doi: . /j.energy. . sha: doc_id: cord_uid: ly to decarbonisation of the iron and steel (i&s) industry is crucial in the efforts to meet the eu ghg emission reduction objectives in … . promoting decarbonisation in this sector will necessarily require the identification, development, and diffusion of breakthrough technologies for i&s production. this paper uses an approach inspired by the technology innovation system (tis) to analyse the development of technology in the eu i&s industry and identify potential avenues of its decarbonisation. we have described key elements of the tis, analyse the functioning of these elements and their interactions in a more general context of innovation dynamics and policy design; the focus has been put on the role of actors and the identification of the main specific blocking and inducement mechanism in the tis to better explain its functioning. risks and uncertainties have also been discussed. we argue that deep decarbonisation in the i&s industry is feasible but its tis requires firm support, mostly political, to finance intensive r&d and reduce the business risk. to this end, all actors shall support more effectively the invention and implementation of new radical production technologies. the recommendations are mostly addressed to politicians although stressing the importance of collaboration of all actors. the i&s industry is on the good track reducing co emission by mtco between and however, observation of the efforts carried out in the i&s industry to increase energy efficiency, confirms that currently there is not enough incentive to encourage steel producers to autonomously undertake more sustainable and less ghg intensive production [ ] , [ ] . although increasing efficiency may lead to further savings, the industry has to make much effort to accelerate the development and diffusion of novel technologies to get out of the current standstill. this requires a technological change of a breakthrough nature [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] . a few breakthrough technologies have been proposed years ago [ ] , [ ] , [ ] , [ ] . although up to now, despite multiannual r&d works followed by the extremely long demonstration phase, these technologies are still not at the market phase [ ] . therefore it is of research interest to analyse the reasons for such a low rate of technology development. this article aims to analyse decarbonisation options in the eu i&s industry using the technology innovation system (tis) approach to deliver policy recommendations. apart from standard elements of tis, this analysis tries to embed considerations of sustainability (which include environmental, equity and competitiveness perspectives). therefore, the article has two purposes in the context of i&s industry decarbonisation: . identify the key elements of the innovation system. study the functioning of such systems as a basis for policy recommendations. this paper contributes to this task by harnessing the technology innovation system (tis) approach [ ] , [ ] , [ ] , [ ] to highlight the potential levers and barriers to promoting technological innovation in this i&s industry. tis is a useful heuristic framework that relies on the analysis of success or failure of a technology based on the performance of the surrounding technological system and trace development and di usion of innovations. tis approach enables to include socioeconomic elements to the analysis [ ] . twomey and gaziulusoy [ ] deliver an overview of concepts and frameworks for understanding and enabling transitions to a low carbon built environment. along with tis, they examine similar frameworks, e.g. multi-level perspective (mlp), strategic niche management (snm), and transition management (tm). a comprehensive review of the literature on innovative theory can be found in [ ] . diercks et al. [ ] stress that "…socio-technical understanding of innovation provides several appropriate analytical concepts that can help to shape our thinking and understanding of transformative innovation policy". the tis is considered as useful for policy recommendations and practitioners as it may provide for both sides novel insight in the understanding of functioning innovative systems. we use the tis approach to evaluate how the i&s industry is performing in a low-carbon transition with regards to some crucial aspects, e.g. a shrinking market in europe, and long transport distances to customers outside of europe. a hydrogen economy, smart grid development, including res booming, possible "green steel" market building. deep decarbonisation calls for an in-depth sociotechnical transition that also covers changes in users' behaviour, culture, policy, industry strategies, infrastructure, and science. if a tis analysis is to aim at improving policies or activities needed to a cost-effective and equitable transition, it must specifically account for sustainability and society implications. in-depth knowledge on innovation systems is needed to plan and control the transition process more effectively by providing the politicians with research-based conclusions [ ] . oda et al. [ ] investigated, based on an intensive and in-depth survey of steel-producing j o u r n a l p r e -p r o o f facilities and energy-efficient technologies in the steel sector. [ ] underline the importance of supporting the industry in their research efforts to make the innovations, often taken for granted, a reality from on. they stress how important it is to keep the values of the decision-making criterion, e.g. payback period, close to normal business conditions to exploit the possibilities offered by the prospective innovative technologies in this industry to the full, and the need to close the efficiency gap by making use of the policy options available. in the literature, a few analyses of national i&s industry development are to be found. two national cases of germany and sweden are worth commenting as the two countries have a specific position in the eu i&s industry -the former is the larger eu steel producer with traditional high technological culture, the latter boasts the high technologically advanced steel industry much focused on energy efficiency improvements. arens et al. [ ] claim that the german steel sector has two options to achieve its european co emissions reduction target for -if it strongly decreases its production output or technological changes are introduced. in this option, first, alternative steelmaking processes need to be developed including low-emission technologies and co -free processes, e.g. h-dr -eaf or electrolysis-based steel production with both routes based on co -free electricity. secondly, there should be a path on incremental co reductions in the short to medium term, e.g. heat recovery from bf slag, and from waste heat in eaf, production of high-quality steel from scrap-based secondary steelmaking, and the utilisation of by-products. arens and worrell [ ] examined the diffusion of six key energy-efficient technologies in the german steel industry and their impact on energy intensity. some novel technologies diffused at a quicker rate at the initial stage but since the s the rate levelled off. the diffusion rate depends much on developments in the sector, e.g. shutdowns or application of energy-efficient technologies. they estimated the primary energy efficiency potential of the selected technologies at . % for . in , the steel industry in sweden adopted a vision leading up to with three pillars -to lead technical development, to nurture creative individuals, and to create environmental benefits. these undertakings demonstrate importance on technological innovation with clear objectives in societal value creation and sustainability [ ] . the efforts of the swedish i&s industry to improving energy efficiency and implementing new technologies are very well documented [ ] , [ ] , [ ] . the main conclusion might be that the industry is aware of energy efficiency importance, but more effort is required as energy-saving potential remains untapped. regarding breakthrough technologies, sweden is proud of the hybrid project aimed at producing hydrogen by electrolyzing water and then using the hydrogen to make direct reduced iron (h-dri) [ ], [ ] . the eu reach is rarely addressed. recently, mayer et al. [ ] made a top-down macroeconomic analysis of a currently considered technological change in the eu i&s industry towards carbon-neutrality, based on techno-economic bottom-up literature. they analysed economic conditions (electricity and co price) for switches in the type of production process towards process-emission-free iron and steel technologies required for reaching climate targets, even though the current degree of alternative technology maturation varies considerably. they argued that if minimal criteria of cost-competitiveness are reached, macroeconomic benefits are feasible. yazdanparast et al. [ ] compared the gaps between service, product, and process innovations in one of the european steel companies. they claim that innovation success depends on cross-functional collaboration among members of the innovation network to share and leverage resources that are hardly ever available to one company. the research identifies internal and external success factors and challenges of each of the three innovations. vögele et al. [ ] assessed, using modelling, impacts of the global challenges, e.g. floor prices, tariffs, carbon price, on the i&s j o u r n a l p r e -p r o o f industry in the eu. they showed that moving eiis from the eu may increase global energy demand and co -emissions and bring disadvantages to developing countries participating in the value chain. they stressed the need for innovations to avoid relocations of production. the literature on transitions has so far not much addressed eiis [ ] . searching for tis analyses, we found that majority of them are based on the country-to-country and/or productto-product analysis whereas our case is classified as "sectorial". we cite a few recent examples. andreasen and sovacool [ ] used tis for analysing the hydrogen technological innovative system in denmark and the us focusing on fuel cell development. they conclude that although these two countries applied remarkably different tis strategy neither approach was effective. they also stressed the need for further research on tis as "better conceptual models of tis and innovation are needed". kochański et al. [ ] applied tis to analyse electricity smart meter in the eu. this an example of the tis approach focused on a single product (smart meter) discussed in the wide eu context. despite strong eu political support and the potential advantages for customers, the massive roll-out is slower than expected. they identified the major barrier at the level of implementation, e.g. insufficient regulatory framework which does not fully ensure interoperability, data protection, and security standards, or organisational effectiveness. clear presentation of benefits for the end-users has also failed. kushnir et al. [ ] studied the tis approach to adopting hydrogen direct reduction (h-dr) in the swedish steel industry. they identified several potential barriers, particularly in timely co-ordination with the power system regarding new infrastructure for h-dr and eaf electricity demand and noted that the i&s industry will have to compete for res-based electricity. they pointed out the necessity of political intervention to remove the barriers to make the swedish i&s industry the first nearly fossil-free industry in the world after . the paper is organized as follows (fig. ) . in section , the economic importance of the i&s industry for the eu economy, the need for the industry decarbonisation is underlined, and the reasons why the industry is hard for decarbonisation are given. in section , the methodology applied is outlined. the boundaries of the system under analysis are defined in section . section provides identification and discussion on the role of all structural components of the tis, namely infrastructure including physical, knowledge, financial and technology; actors; institutions and policies; institutions, and finally networks and interactions. in section , the mapping of the functional patters of the tis is done and then, in section , assessment of the functionality has been provided. section provides analysis and discussion of blocking mechanisms and inducements of innovation, and in section an outline of risks and uncertainties in the i&s industry is sketched. in section , conclusions and policy implications are presented. because of the complexity, the innovation process cannot be approached by solely focusing on standard measurable variables such as economic criteria, e.g. revenues, productivity, and quantities. understanding the dynamics of technological innovation requires the exploration and characterisation of the economic and social spaces in which the innovative activities take place and understanding of the interactions linking a wide range of actors and institutions [ ] , [ ] , [ ] , [ ] , [ ] . tis enables to identify key elements and then to analyse and assess the effectiveness of their functioning in multidimensional space which in majorities of analysis is simplified to fewer dimensions, e.g. technical and economic. tasks of this research covered: (a) mapping and description of key actors and institutions, and a qualitative assessment of how they interact at the supra-national, national, and sub-national levels, including a description of how the existing landscape evolved, and reasons for it, (b) mapping of innovation strategies, roadmaps and policy instruments across the innovation chain and their development and implementation, (c) identification of key barriers and inducements of innovation through desk research, and then adding supplementary comments on risks and uncertainties. there are some crucial trends (external factors) which make such tis approach in the i&s industry indispensable to make innovation feasible, e.g. global climate policy with the eu as a leader; "green" and circular economy; emerging hydrogen economy; transformation in the power system to the smart grid model which offers new symbiosis with industry, e.g. due to res penetration; increasing storage capacities, grid flexibility. there are also changes in seeking analogy between tis and the control theory, it can be stated that tis is like control system of timedependent dynamic nonlinear plant with highly distributed elements with a feedback. the plant is subjected to many, mainly stochastic noises which make its control highly unpredicted and difficult. some of the signal and j o u r n a l p r e -p r o o f the ways business operates nowadays, e.g. globalization, deregulation, advancements of information technology, and increasing customer demands which force the companies to continually deliver new products. we built on the existing knowledge but unlike other analysis of i&s industry, development our tis-based approach enables to a systematic analysis of the innovation system in a wider dimension than the standard methods, e.g. encompassing societal and environmental issues, networking, external factors. our paper tries to analyse the whole sector, namely the i&s industry in the eu. standard tis approaches are narrower, e.g. focused on the comparison of product development in different countries or industry in one country. to this end, following bergek et al. [ ] , we use a -stage approach for the tis performance assessment ( fig. specify key policy implications. the advantage of this paper is that it strictly follows the methodology of tis. first, we identify and described four key elements of tis, namely infrastructure and technology; actors; institutions; network and interactions [ ] . this approach highlights four constituent pillars which play a crucial role in innovation systems. then we analyse processes that are needed in each tis to stimulate technology development and diffusion. by mapping these processes (functions) over time, the insight into the dynamics of innovation systems can be understood. this step is based on the characterization of the seven functions specified in table and then detailed in section . the "functions" may be understood as key processes driving the development and diffusion of new technologies done in a wide sustainable context (table ) . a comprehensive latest literature review of the functions can be found e.g. in [ ] . [ ] , [ ] , [ ] tis is very flexible in methods of gaining the necessary information, e.g. by case studies, event history analysis, multiple data sources, and interviews [ ] . our research method was based on a systematic review of the literature (srl) since it provides context-specific insights based on systematic, transparent and reproducible review procedures [ ] . this choice is reasonable since the subject of our research, i.e. i&s industry has been very well described in academic literature, political documents, strategies and business reports which can hardly be supplemented by any complementary data acquisition. additionally, the eu dimension of our study would enormously extend the scope of potential interviewers and business confidentiality would make it tough to get data beyond the publicly available. the papers analysed were identified via scopus following the procedure described in appendix a. we also grabbed from the eu and tis national case studies -for the uk and italy made within the innopaths project [ ] . in the tis analysis the main technological drivers of transformation in the eu industry have been considered [ ] : . digitalisation (e.g. industry . ), . advanced materials development, . complex and global supply chains, . market competition and over-capacity, . life cycle design, pollution prevention, and product recyclability, . decarbonisation and energy efficiency, . evolution of customer requirements. the object of study is the innovation system in the i&s industry in the eu and its capacity to adopt new core technologies. this research is limited to nace . "manufacture of basic iron and steel and of ferro-alloys" which is broad and covers numerous technologies and products. the scope of its considered is rather limited to iron ore reduction technologies and does not include the production of semi-finished products of steel and manufacturing of hotrolled and cold-rolled products of steel. it is justified since most of the energy including electricity end-use in steel manufacturing is consumed by furnaces [ ] . the boundary for this analysis was confined geographically to the eu but essential externalities outside europe were considered to eliminate the risk of missing essential external factors. we consider that analysis of the i&s industry for the whole eu is feasible due to the high homogenisation of the whole surroundings secured by close integration of the mss forced by legislative and regulatory harmonization, common internal market rules, and the common framework of r&d. such an approach makes the result of our analysis useful both for the eu and ms levels. it is to note that lutz et al. [ ] observed that there cannot be a general approach for the transformation in the eiis since the capital structure may differ between countries and sectors. therefore, for some countries, analyses must be conducted individually. infrastructure and technology encompass four categories: physical, knowledge, financial, and technology. physical infrastructure includes artefacts, instruments, machines, etc.; financial infrastructure comprises subsidies, financial programs, and grants; and knowledge infrastructure encompasses knowledge, expertise, and strategic information [ ] . technology comprises the subset of knowledge about the full range of devices, methods, practices, and processes that enable the fulfilment of human purposes is a "specifiable and reproducible way" [ ] . silva and de carvalh [ ] provide an extensive account of the history of the steel industry. description of technologies in the i&s industry can be found anywhere, e.g. [ ] , [ ], [ ] , [ ] , [ ] , who summarise the present status of different kinds of steels and relative technologies (incumbent and emerging), review steels over past decades and also forecast of advanced steels in the future. over the last years, the i&s industry in the eu has undergone significant changes, e.g. the elimination of production in the traditional blast furnace (bf-ohf), the doubling of the share of production through the electric arc furnaces (eaf) technology (up to % now) and the almost complete transition to continuous casting [ ] , [ ] , [ ] . two main routes for steel production, i.e. basic oxygen furnace (bof) and eaf, are already well optimised thermodynamically, e.g. [ ] . since the s, steel specific energy consumption in the european steel industry has dramatically decreased by %. however, technical energy efficiency potential of … % still exists and will be essential to reduce emissions from existing, long-lived industrial assets [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] . specific co emissions in europe are some of the lowest in the world - . tco /t of steel, as compared with the global average of . tco /t in (global ccs institute), aiming at . tco /t of steel in assuming hypothetic diffusion of breakthrough technologies in combination with ccs [ ] . based on our literature research, ten ghg mitigation options, which can align the i&s industry with the objectives of the paris agreement, were identified several means of ghg emission reduction [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ ] , [ the iea lists several innovative technologies within the i&s industry [ ] : new smelting reduction process based on coal (trl - ); top gas recovery blast furnace (trl - ); top gas recovery blast furnace with coke oven gas reforming (trl - ); new direct reduction based on natural gas (trl ); direct reduction based on natural gas complemented with up to % electrolytic hydrogen (trl ); direct reduction based on hydrogen (trl ); direct use of electricity to reduce iron oxides (aqueous alkaline electrolysis, low-temperature °c) (trl - ); direct use of electricity to reduce iron oxides (molten oxide electrolysis, hightemperature > °c) (trl - ); carbon capture and storage (ccs) applied to commercial iron and steel technologies (trl - ); conversion of steel works arising gases to chemicals and fuels production (ccu) (trl - ); smelting reduction based on hydrogen plasma (trl ); electrolytic production of hydrogen. their market entry predicted in … is mostly delayed [ ] , [ ] , [ ] , [ ] , [ ] , [ ] . the technologies recently identified by european trl-technological readiness level. j o u r n a l p r e -p r o o f experts from the steel industry as innovative are improving energy efficiency beyond the state-of-the-art; new smelting reduction technologies; direct reduction technologies, based on natural gas; direct reduction technologies, based on hydrogen; direct use of electricity for iron ore reduction; use of biomass in steel production; more recycling of steel and other breakthrough solution paths for low-carbon steel production [ ] . the list of technologies which can be classified as "off-shelf" embraces a few items only, e.g. h-dr [ ] . this selection of reduction options which covers traditional stages of i&s production (e.g. coke making, sintering, bof, eaf) as well as a few breakthrough technologies, was done according to the potential to decarbonization till [ ] , [ ] . the best available technologies (bats) have the potential of emission reduction of … % in the eii, even when applied on a large scale [ ] , [ ] . current bat may contribute to short-term energy and ghg emissions savings in the i&s industry, but the switch to innovative technologies by the mid- st century is far more uncertain [ ] . other options for deep decarbonisation of the i&s industry are shifting to low carbon energy supply via either biomass, sustainable charcoal, nuclear energy, res-based electricity or ccs [ ] , [ ] , [ ] , [ ] . additionally, energy management can serve as an effective tool in improving energy efficiency [ ] , [ ] , [ ] , [ ] , [ ] , [ ] . the main conclusion from quantitative assessment has been that material and energy efficiency measures will help in decarbonisation process, but do not suffice to get the reductions needed. actors within an innovation system "typically include individuals and organizations operating at multiple scales" [ ] . different categories of actors within different sectors have different characteristics, motivations, and strategies which must be appropriately described and understood [ ] . the role of actors that contribute to the success/failure of the tis in the i&s industry is manifold and presents a complex array (table ) . role in i&s industry tis ec develops long-term social and economic strategies like climate-energy policy, industrial policy tries to improve co-ordination among complementary policies, e.g. innovation policy, tax policy, energy market regulation [ ] sets sustainable long-term priorities and objective strongly affected the i&s industry, e.g. political support for climate policy and the following decarbonisation of industry plays a crucial role in setting and the enforcement of climate-energy legislative framework (directives, regulations), e.g. eu legislation supporting deep industry decarbonisation, e.g. energy and material efficiency, eu ets introduces sectorial regulations and set market conditions via market regulations, e.g. taxes, import quotas initiates and finances r&d, e.g. finance i&s industry programs, establish innovation centres e.g. numerous programs supporting innovation policy to keep up with the world's innovation leaders launches short-term intervention programs in times of economic stagnation or crisis or natural disasters institutions are defined as a set of formal and informal rules, norms, decision-making procedures, beliefs, incentives and expectations that guide the interactions and behaviour of actors in an innovation system [ ] . institutions set the environment in which all actors operate [ ] . the ec has warned that "today, the european steel sector finds itself in a very difficult situation" [ ] , and to solve the issue, the ec has taken steps to strengthen the eu's defence against unfair trading practices. the ec called for immediate action for a european industrial renaissance in [ ] . the ec took planes to protect the industry from the unfair international competition including the steel industry, "…notably through modernisation and investments in innovation" [ ] . in , the ec reconfirmed: "energy-intensive industries, such as steel, chemicals, and cement, are indispensable to europe's economy, as they supply several key value chains" [ ] (table ) . trade improving the speed and efficiency with which the ec can begin and resolve trade defence investigations enabling better use of policy instruments to enforce trade defence intensifying discussions through the oecd with major steel producers like china, russia, and india to safeguard eu interests improving the access for eu steel exporters to "third markets" secure access to raw materials as crucial due to scarcity in the eu using eu funds to modernise the i&s industry, including retraining and j o u r n a l p r e -p r o o f development reintegration of redundant steelworkers into the labour market. engage high-level stakeholders in the industry to agree on a plan of action to modernise the industry implement the ec's "circular economy" strategy to reduce waste and increase efficiency in manufacturing energy compensate for energy prices as eu prices are higher than in most of its international competitors supporting energy-intensive industries within existing state aid rules reviewing the eu ets to ensure that the i&s industry remains competitive whilst also reducing emissions implementing the eu energy union source: own work. network and interactions describe the dynamic relationships and links between actors, but a "network" can also be seen as a higher form of "actors" organisation. interactions may take place within networks and can be analysed at the level of both networks and the level of individual contacts [ ] . analysis of networking usually poses a great challenge in tis research. even when the other components of tis are identified, to trace their interrelation is difficult both from the methodological and practical perspectives. the links may be multidimensional, overlapping, and tacit. even when properly recognised, there is neither a standard methodology nor metrics to measure their strength therefore narrative description or tracing connections in literature or patents must suffice. it is common to analyse an industrial sector as an isolated system with no or only a few links to the ambient constituted by other elements of the whole economy and society. however, combating climate change is such a global trend that it has enforced an interrelated transformation in other industries, e.g. a strong and immediate interdependence relationship between coal, power, chemical, and i&s industries [ ] . european companies, operating in a high-wage region, to compete try to create additional value, e.g., more and specialised variants of steel offered, highly sophisticated logistical services, and excellent after-sales service [ ] . analysis of networks in the i&s industry should embrace a wide range of actors and types of collaboration, e.g. suppliers and manufactures in the whole chain, customers, energy endusers, research institutions, multinational research, pilot and demonstration projects, innovative platforms, industrial and trade associates [ ] . r&d works in the i&s industry are often presented as cooperation among global players, e.g. top steel producers, novel technology providers, and leading research institutions. it is, however, to note that at the initial stage, the network also includes small companies, often not related to the specific sector, but with in-depth knowledge which can be supplementary to the steelmaking processes. the industry itself points at the overall immaturity of "collaborative solutions" and their frameworks [ ] . the discussion between the i&s industry and other actors can be led in two ways [ ] : • the institutional channels as the steel community is a part of society at local and global levels e.g. acting in corporate social responsibility, or participation in international initiatives, e.g. within un (global compact), business associations or business circles. • the science-based route related to the role of steel and analysed multidisciplinary as a mixture of soft and hard sciences. in this section, we will systematically analyse the seven functions of the tis in the i&s industry providing indicators of each of these functions (table ) . [ ] , [ ] , [ ] influence on the direction of research the top priority of climate-energy policy sends a clear signal to policymakers on the necessity of deep decarbonisation in i&s industry through technology innovation the high potential of material efficiency in the circular economy, e.g. scrap reuse, by-product utilisation the high potential of ghg reduction through breakthrough technology implementation low expectations of a breakthrough in core incumbent technologies a few identified technologies with limited energy and material efficiency improvements few emerging breakthrough technologies e.g. "green hydrogen", large use of res-based energy, electrowinning, dir, ccsu [ ] , [ ] , [ ] resource mobilisation well established research institutions, e.g. at universities, industrial institutes, and centres, with highly competent staff joint research centres of the academia and industry with public cofunding the co-operation of the main market players (manufactures) in r&d projects continuous sufficient inflow of educated staff at all levels of competence, e.g. trained workers, managers, engineers, scientists [ ] insufficient human and financial resources involved in the demonstrative phase of breakthrough technologies market formation mature market, without a niche, for steel products prone to economic cycles and crises unfair trade rules exercised by some manufactures make innovation technologies difficult to enter into the market evermore demanding environmental standards followed by penalty regulations accelerate r&d and market adoption market demand for improved products set by the main customers, e.g. automobile, construction sector ("learning by using") legitimation global political agreement on the urgency of ghg emission reduction broad consensus of all actors on the need to decarbonise the i&s industry actors, institutions are well established in multiannual historical processes low interest of public opinion in technology innovation in the i&s industry as such, but the high expectation to reduce environmental harm visibility of effects of environment protection measures build-ups of local support, e.g. reduction of air pollution eu and national environmental targets, e.g. ghg emission reduction, set indirectly the targets on i&s industry decarbonisation development of positive externalities acknowledged societal importance, national and local, e.g. retaining jobs flow of knowledge among different tiss, e.g. res-energy, chemical industry, cement industry, automobile, construction, resulting in mutual benefits strong complementarians among technologies, e.g. steel-hydrogen-res, electrolysis-res; in by-products utilisation, e.g. cement industry large potential contribution to the circular economy participation in global trend to the decarbonisation of eii realising the potential for ghg emission reduction and energy and material efficiency . assessment of the functionality of the tis . . knowledge development and diffusion innovation systems in the i&s industry are even more complex than in other sectors since the connections among actors and institutions occur at many stages of the innovation process in multiple sectors and countries and different scales, and are not "visible" to the public. additionally, the market is not directly driven by millions of customers as it happens in the case of many other products. most of the i&s large companies are involved in developing its since they are aware of the importance of ghg emission reduction and their key role in it. they recognise the need for co-operation at different stages of technology development, particularly in r&d and pilot phases despite clear business competitions. government's support is materialised in funding via r&d programs and creation of research centres which does not violate public aid rules and increases the attractiveness of the country to global manufactures [ ] , [ ] . the rate of innovation in carbon mitigation related technologies in the i&s industry has been increasing over the last decades what supports the thesis that climate policy is a strong driver of innovation [ ] , [ ] . the inertia of some tis components, not strictly of r&d nature, may amount to years, e.g. in political or standardisation decisions (see work plan of [ ] , and shall be accounted for in the tis assessment. the diffusion of technologies may therefore substantially vary. grubler [ ] , compared the development of four technologies used for steel production which competed simultaneously with decreasing and increasing market shares. the diffusion trajectories of the processes were diverse, with time constant ranging from less than two decades (replacement of the crucible process) to nearly seven decades (diffusion of eafs). the development of breakthrough technologies cannot take momentum also due to the complex and fast-changing externalities, e.g. energy and feedstock prices, fluctuation in demand for steel. our tis operates in a well-established industry facing a strong need for decarbonisation, although, at the same time, the industry faces limited options for breakthrough technologies soon. unlike many other industries, technological transformation should be mainly carried out with the active involvement of the industry through bottom-up initiatives rather than by new entrants or be directly transferred from academia to industry. the lack of new entrants in the mainstream business weakens the innovation drive among incumbent actors. the demonstration phase in the i&s industry is so risky that it cannot be jumped over or shortened radically. there are pieces of evidence of dropping or mothballing projects caused by economic hardships [ ] . research challenges are well recognised and are mostly initiated by environmental requirements and only partially by a limited demand for higher quality products [ ] . the eu and ms governments support r&d in the i&s industry but they have very limited possibilities to intervene directly into strictly business matters. the i&s industry in the eu can potentially remain a leader in its although competition from other countries is tough [ ] , [ ] . the i&s industry people are aware of the importance of the eu internal market, growing competition from globalised markets, the influence of financial markets on corporate strategies, and commodification. the development of its has suffered from the lack of sufficient r&d financing and resulting human resources involved. political support both at the eu and national levels despite different actions has not brought about the results expected by the i&s industry. therefore, pilot and demonstration stages remain a "bottleneck" in the whole innovation cycle. the industry raises several key business-oriented aspects essential for low-carbon innovation: . cost savings and competitiveness; . carbon price; . developing robust inter-industrial collaboration models; . reduced environmental externalities (delivering improved corporate sustainability reputation); . international competition for low-carbon products [ ] . at present, the energy consumption, ghg emission, and by-product utilisation in the i&s industry are serious political and public concerns that need to be addressed to avoid costs of pollution and make the technological processes sustainable. the i&s industry in the eu will be able to reduce its co emissions by % in an economically viable way until , compared to levels, while the steel market will grow by . % annually (to raise the eu crude steel production to mt in ) [ ] . the divergence between predicted ghg reduction possibilities and the production growth illustrates the market demand for breakthrough its. in response to these plans, the eu i&s industry declares that it will be able to reduce production's co emissions by % by and by … % by if breakthrough technologies are adopted [ ] . to end this, the i&s industry must undergo deep decarbonisation. the eu regulatory framework does not favour any of the emerging technologies postponing in this way possible competition for a more mature phase of technology development. the economic impacts of technological breakthroughs in the i&s industry will likely be nonlinear as system thresholds are breached and have knock-on effects. the market for its will emerge from the first success pilot installations which will be multiplied on other sites depending on the expected revenues, the scale of investment needed, and the threat of stray assets [ ] . . . legitimation steel as a product is very well recognised by people and enjoys high esteem [ ] , [ ] . i&s industry is highly valued by politicians as an economically and socially important and prestigious sector [ ] . steel is a key element of an industrial society and thus for meeting sustainable development goal [ ] . communities in which the steelworks are located also appreciate its importance to the local labour market and prosperity [ ] . the i&s industry tries to demonstrate its commitment to all aspects of "green economy", e.g. energy and material efficiency [ ] , [ ] , [ ] , [ ] . these efforts impact politicians although do not much affect the public therefore the i&s industry receives much less public attention as the environment polluter as compared e.g. with the power sector. the its in the i&s industry and other industries demonstrate in some respects close synergy, e.g. with power, automobile, construction, chemical, defence industries. the positive influence of each other results from common interests and objectives, e.g. these driven by res-based energy, material, and energy efficiency, complementary of technologies, easiness to adopt. the benefits of "spilling over" from one tis to another have not been yet fully recognised and valued although the symptoms of such synergy are "visible" and a prevailing tendency for the interdisciplinary research helps to create joint r&d programs and research centres. competition between the incumbent systems and the emerging ones is a key element in the development of tis. it is considered in categories of "blocking mechanisms" and "inducement" [ ] . the inducement mechanisms are understood as "believed in growth potential and government r&d policy" [ ] . presenting barriers and inducements against the functionalities increased the readability of the text. the vulnerability of r&d programs to external factors, e.g. economic crises ageing of current capacity leads to "greenfield" investments or at least to "brownfield" retrofits the main players in the eu steel industry recognise the decisive role of technological innovation in seeking global market advantage source: own work. r&d investments are needed, both in human resources and physical capacity, otherwise, rates of innovation and technology diffusion are apparent, and the support of different actors within the low-carbon innovation system is lacking. establishing industry and academia joint research programs and centres, e.g. in private-public partnership, gets the key actors closer [ ] . a high level of research in a country and public support helps to save domestic capacity from closing down [ ] . globalisation and overcapacity do not facilitate its in any eiis unless innovation secures high profits with short pay-back time [ ] , [ ] . low cost remains the decisive criterion in purchasing decisions on the global market with overcapacity of around million tonnes in , equivalent to almost % of global steel production capacity what effectively discourage innovative investments [ ] . there are several general trends in global development that give new impulses to technology change and innovation boost. these tendencies help to reject the traditional dogma of cost-effectiveness as a major criterion in technology assessment. on the other hand, periods of overcapacity are suitable for deep technological changes as there is no risk of losing important markets and customers assuming the company remains financially stable. additionally, local capacities will also weight, e.g. availability of qualified workforce, accessibility to res-based energy or reshydrogen, community acceptance for ccs [ ] , [ ] . the reduction of environmental burden due to innovative technology always builds better relationships between the investors and the community. all major actors of the i&s industry are active in the field of digitalisation this industry [ ] , [ ] integration of i&s technologies with other technologies, e.g. chemical, power industry, ict the r&d trajectories are set and it is hard to expect novel technologies to appear soon [ ] , [ ] . the progress in developing the currently researched breakthrough technologies is very slow and therefore requires public support at the eu and national levels [ ] , [ ] . more concentrated public financial support for r&d and then for breaking the demonstration and market barrier is a prerequisite if the i&s industry in the eu is to remain competitive especially in the light of the expected increase of costs due to the eu ets participation [ ] . r&d in the i&s industry is not considered highly innovative and, thus, is not a priority for governments in their national development strategies, neither for research institutions [ ] , [ ] even though these technologies are game-changers for deep decarbonisation. yet, the high value, traditionally attributed in the i&s industry to technological progress and innovation, allows the industry to remain highly advanced although progress in core technologies remains slow. it had been predicted that the currently used (standard) technologies would dominate until [ ] , [ ] . now it seems that the time horizon is likely to be pushed till … . a large number of technological projects in the i&s industry is co-financed from eu funds, e.g. the ulcos (ultra-low carbon dioxide (co ) steelmaking) is a consortium of european entities (all major eu steel companies, some engineering partners, research institutes and universities) [ ] , [ ] , [ ] . however, eu r&d programs seem to be too much dispersed, weakly focused on crucial decarbonisation challenges, and not tackled in a truly interdisciplinary way in a long-term perspective [ ] , [ ] , [ ] . the difficult economic position of the eu i&s industry in recent years -the dilemma of cost-cutting or the need for investments in new capacity possible unwillingness to finance industry operating at highly competitive markets at times of economic instability and hardship possible lack of access to investment capital especially in the difficult economic standing of the company the funding gap between trl - ("valley of death") [ ] , [ ] , inadequate availability of risk capital [ ] high capital involvement and low rate of return from financing high-emission investments lack of upfront clarity about the funding [ ] not fully recognised benefits of it in lca low r&d private funding insufficient to overcome barriers of pilot implementation at acceptable risk insufficient targeted economic incentives for ti, e.g. in the form of tax reduction, risksharing or loan guaranties from private and public financial institutions, governmental quarantines business risks and risks of perturbation in production deter large investments which may result in losing markets, crucial clients, or penalty payments lack of "green" criteria in public procurement [ ] low profits in incremental technological improvements the high share of energy in costs of final products (up to %) rising costs of energy make its more profitable the large share of public funds allocated for "green economy" envisaged in the eu financial perspective for - growing unwillingness or even ban on financing non-sustainable investments (like coal power stations) with a risk of extension on other eii, e.g. i&s industry the expected positive impact of eu ets on low-carbon technological up-take in i&s industry after (modernisation fund, innovation fund) technologies from environmental funds lack of new business models in i&s industries rewarding ti source: own work. very high investment costs in core technologies and long investment time in the unstable global market deter low-emission, high-cost transformation. financial incentives are indispensable to overcome the barriers for such investments to support private capital, e.g. via private-public-partnership [ ] , [ ] , [ ] , [ ] . for example, a demonstration hisarna technology plant of industrial size ( . … . mt/y) will require an investment of € … million [ ] . public intervention should complement and not overlap with existing eu and national funding programmes [ ] . there is a need for viable and robust business models for long-term and deep decarbonisation beyond incremental and short-payback measures. rules of support should be more flexible, e.g. simple two-stage application procedure, aligning the timing of support with funding needs ("funding against milestones"), ensure complementarity between different eu funds [ ] . the breakthrough technologies can hardly be classified as competing at this stage of their development when their actual costs and benefits are not yet properly assessed in the market scale [ ] , [ ] . their implementation will, to a large extent, depend on several criteria, sometimes local, e.g. availability of res-based energy and local feedstock, demand for waste heat, cost, and price structures in a specific country [ ] , [ ] . also, the time of implementation of process emission-free "high-cost" technology, e.g. or , plays its role as early implementation may increase the range of negative gdp implications in [ ] . the emission abatement in industry, e.g. in i&s, may turn out to be much more technologically challenging then emission reduction from energy use [ ] . the innovation diffusion in eiis exhibits a natural long time constant resulting from long decision cycle and investment phase even in pilot installations [ ] , [ ] . securing sufficient and stable financing would substantially reduce the duration of the premarket phases and lower the business risks. the ec intends to "support clean steel breakthrough technologies leading to a zero-carbon steel making process by " [ ] . the ec is aware of the costs of such large-scale innovative projects and plans to use for this purpose the funding from the european coal and steel community. financing options for modernisation opened by eu ets reform ( - ) seems to be the desired step but with some doubts about its potential for a truly deep technological transformation in the i&s industry. the i&s industry may in the future encounter a barrier of assessing to bank financing for high emission investments like it occurred in the power sector in coal-based technologies [ ] , [ ] . steel products are constantly evolving, driven in part by r&d conducted in collaboration with steel-using industries [ ] j o u r n a l p r e -p r o o f hydrogen" incremental improvements to core process technologies slow down pursuit for "breakthrough" technologies (lock-in) low use of res-based energy in technological processes, e.g. hydrogen res steel electrolysis high usage of coal in technologies where lower emission substitution is possible, e.g. as an energy carrier or feedstock not fully recognised impact of energy and material efficiency on operational costs high technological uncertainty between research and demonstration phases and then full commercialisation (scale uncertainty) "energy efficiency gap" -insufficient interest in energy savings in auxiliary technologies, e.g. waste heat recovery, electrical drives insufficient involvement in demand side management, e.g. in eafs a shift towards eaf would help i&s industry to move towards a circular value chain development of energy service market, e.g. energy management, energy audits, energy-saving obligation, enables quicker adoption of energy-efficient innovations [ ] , [ ] , [ ] high quality of domestic products reduces the risk of replacement of domestic products by import ("carbon leakage" consequence) [ ] the growing share of res in the eu power capacity may make res-based steel technologies economically viable [ ] natural obsolescence of some installations opens option for deep technology change the i&s industry, due to its characteristic is not predisposed to radical breakthroughs. the i&s technology although based on well-established knowledge when implemented is not straightforward replicable and on each site requires adaptation which creates additional risk. moreover, high technological integration entails that any change of one technological process requires changes to other parts of the process which increases the costs and the risk of technological incompatibility. the tis distinguishes between incremental innovations that track existing technological trajectories and radical innovations that lead to new technologies. the progress in the i&s industry mostly consists in the process innovation that tends to follow predefined technological trajectories through incremental innovation aimed at enhancing productivity [ ] . the radical case typically means investing in novel technologies for the basic conversion process or changes in feedstocks and low-carbon energy supply. for example, the eaf shift suitably combined with res-based energy could lead to the entire decarbonisation of steel production. since this deep decarbonization transition at present is proceeding very slowly, therefore, even incremental its can serve as an effective tool in ghg reduction [ ] , [ ] , [ ] , [ ] . through learning by doing, the practising engineers facilitated incremental innovations that triggered partial reinvestments. the leaders in the i&s industry employ many ancillary means of energy and material efficiency, e.g. waste heat utilisation, variable electric drives, advanced measuring and control systems, if only these are economically viable [ ] , [ ] , [ ] . however, these can only suitably complement mainstream measures. the variety of technologies under research, although not vast, will enable to compose the future technological structure in most suitable configuration depending on different j o u r n a l p r e -p r o o f geographical, social, economic, institutional environments criteria which characterize the different mss. for example, the mature technologies available for using biomass as fuel and feedstock in steel production are financially more attractive than the electrification of heat at electricity prices above approximately $ /mwh [ ] . electricity prices will be decisive in the choice between electricity-based decarbonization and ccs [ ] . innovations in the i&s industry are predominantly technological, with traditional organisational structures and business cases [ ] . i&s producers can use other options, e.g. consolidation and structural capacity reduction, customer orientation and commercial excellence, operational optimisation including material and energy efficiency [ ] , [ ] . long-lasting insufficient progress may demotivate actors from launching intensive r&d programs the crucial role of the world's largest steel companies may impede innovation process in some countries while supporting in others relatively slow deployment of bat due to lack of legal obligations or clear economic benefits [ ] the concentration of r&d programs on breakthrough technologies as the solemn options for deep decarbonisation the need for the i&s industry decarbonisation has been well recognised by all actors and is not questioned, see e.g. [ ] , [ ] , [ ] . since r&d directions in the i&s industry have been defined years ago, noting low pace of progress, and still pending pilot phase of key technologies, it can be assumed that further progress requires a strong involvement of key actors, i.e. the ec, ms governments and the i&s industry who shall play the leading role in acceleration the transformation. the other actors, i.e. the researches, are also important but innovative acceleration depends on the coherent action of the former group. that eu strong determination of decarbonisation helps to get synergy but has up to now turned out to be too weak to cause deep innovative changes. uncertainties around post-paris policy, unconvincing eu industrial policy which does not reflect the high climate ambitions and lack of economic incentives make main global i&s manufacturers reluctant to get fully involved in the it transformation. they remain unwilling to take the lead in r&d as long as eu financial incentives are apparent, and policies do not secure future stable regulatory framework. the push must, therefore, come from the actors who from different reasons have an interest in lowering ghg emission, namely the ec, ms governments, and society. for them, environmental protection is the common denominator enabling cooperation. relatively slow rate of i&s industry preparation to industry . as compared with highly innovative industries highly competitive global markets and weak faith in substantial benefits due to the fast implementation of breakthrough technologies conserve the "cost-efficient" criterion of technology development legislation insufficiently forces ecoinnovation developing or often-changing regulatory framework for less mature technologies, e.g. ccsu and hydrogen infrastructure [ ] ineffective use of eu ets revenues for lowemission technology transition in the steel industry [ ] i&s industry's objective to increase competitiveness may not coincide with cost optimal ghg emission reduction lack of interest to force the inclusion of external costs of energy into total costs of industry lack of agreed sectorial targeted energy and ghg reduction goals among big emitters, e.g. power, chemical, and steel incoherence of many eu politics and strategies aimed at supporting innovative technologies [ ] inadequate regulatory or legal frameworks efforts to remove distortion in the internal energy market to make it more competitive development of circular economy enforces better energy and material circulation, e.g. steel scrap, feedstock, by-material usage to support innovative technologies, e.g. tax realise, subsidies, public support to r&d steady risk of import substitution to the eu and difficulty with adoption common eu market defence and expansion strategies weak political, the organisational and economic power of few new entrants table . examples of blocking mechanisms and inducements in the i&s industry in the eu. the corporate style of management in large companies (multinational) impedes decisionmaking process and internal networking functioning [ ] corporate culture may not sufficiently support its difficulties to place deep decarbonisation projects as a priority in long-term strategies of i&s plants its are not a priority in the steel industry practice energy and material saving objectives not well integrated into operational, maintenance or purchase procedures low priority of improving industry corporate image as a "green" business (corporate social responsibility) entering of products into the market without obligation to trace "carbon foot" low interest of top management in implementing its especially in time of economic hardships or uncertainty unwillingness to undertake innovative projects by technical staff due to possible personal responsibility and the lack of financial gains or option for promotion a limited number of benchmarks mostly due to the unwillingness of industry to reveal energy, environmental and economic data [ ] natural trend of advancing technology towards more sustainable and competitive high pressure from employees and union trades on improving work conditions that can partly be accomplished by it implementation growing power of "green"-oriented parties on the eu political arena since the eu needs a long-term strategy to increase industrial competitiveness, a framework for building a new decarbonised industry and innovation policy strategy is required [ ] . the actual i&s industry decarbonisation options do not match the ambitious climate goals set by the ec [ ] , [ ] . the gap has been poorly assessed by politicians and the needed counteractions are not in place according to the i&s industry [ ] . the eu i&s industry is deeply embedded in the global business chain with the growing use of external subcontractors as part of their manufacturing operations, while changes of technological infrastructure on the national level require significant investments and, more importantly, a harmonised decarbonisation strategy of the whole national economy. this implies the need for tide coordination of actions among the key players in the long run. there are not "countervailing" policies which would intentionally impede the decarbonisation. the indirect impact is mainly by environmental legislation. the energy efficiency-related directives, e.g. energy efficiency directive [ ] , eco-design directive [ ] exert a weak impact on the i&s industry . the eu ets much helped to bring ghg emissions to corporate routines and culture and raised priority of the low-carbon technologies in the business hierarchy to strategically importance, e.g. by promotion energy management systems [ ] . similar to the analysis of the eu ets impact on the power sector [ ] , research on i&s industry interactions with res-based energy, chemical industry (res-hydrogen), and ccsu would bring interesting findings concerning r&d [ ] . unlike other sectors being under decarbonisation, eu legislation is less effective at enforcing the i&s industry decarbonisation by market rules, e.g. energy certificates for buildings, compulsory minimum energy efficiency regulations, appliance energy labels, car emission standards effectively help to support decarbonisation in other sectors. therefore, the eu should try to use indirect pull levers, e.g. public procurement and recent circular economy regulations affecting main steel-consuming industries, in particular the automotive, buildings and construction [ ] , [ ] , [ ] . similarly, to other eiis, energy costs are one of the main drivers of competitiveness for the eu i&s industry since energy costs represent up to % of total operational costs. intensification of markets for a quality product could be done by widening the scope of the eco-design directive, e.g. to better address co-design of products for material efficiency, durability, repairability, reuse, and recycling; public procurement, focusing on sustainable products and product design requirements [ ] , [ ] . assessing the necessary intervention in the post -covid- economy, it is recommended to increase funding for the acceleration of r&d and roll-out of pilot projects of low carbon technologies, also in the i&s industry, e.g. hydrogen-based steel making [ ] , [ ] . the number of industrial installations covered by the industrial emission directive (ied) and bat conclusions may serve as metrics of the effectiveness of eu regulation in establishing clean technologies and processes in the industry. the eea reports that there is continued progress in the number of installations covered by in the i&s industry, in total [ ] . a strong link between bats and reductions in air pollutants achieved was identified. as compared with what emissions would have been based on steel production data and emission factors from (per unit of steel produced), emissions of sox had been reduced by %, of nox by %, of pm by % and mercury by % [ ] . decarbonisation of the i&s industry does not encounter hostile coalitions in the eu, however, the roles of the two main actors, namely the ec and the manufacturers, have not been assigned. the i&s industry in the eu does not oppose decarbonisation being aware that the process is unavoidable [ ] . however, the i&s industry finds itself "squeezed" by the ghg reduction constantly forced by the eu ets, global competition, and perceived inability of the ec to protect the eu industry against unfair competition [ ] , [ ] , [ ] . the main global manufactures may threaten national governments with "carbon leakage" when seeking favourable economic privileges to continue or restore their business. the power of national governments seems to be inadequate and too weak to steer the i&s industry operating domestically towards more innovative transformation than it is due to the eu policies. therefore, the industry has tabled several postulates to the politician to empower the transformation and let this ue sector to survive [ ] , [ ] . many of them call for higher support to its through fostering the r&d works [ ] , [ ] . the eu steel companies were successful to achieve free allocation in phases i-iii of eu ets mostly due to effective lobbying. concerning participation in the eu ets the i&s industry constantly raises two issues -lack of abatement opportunities and inability to pass through costs. okereke and mcdaniels [ ] found that these arguments are only partially supported by evidence because of information asymmetry between the industry and politicians, inherent inappropriateness of adopting political decisions on environmental regulations, and privileged treatment in the eu ets, despite that all the key elements of the tis are in place and work towards the low carbon goal, the transition rate is low. seeking the obstacles, the ambiguous and week industrial policy towards eii of the eu can be blamed. this entails insufficient r&d public support to make a real breakthrough in its in the i&s industry. the global manufactures may benefit from the eu technology innovative system. the eu financed knowledge "leak" through global companies has also to be considered as a braking factor as the companies can control the rate of innovation according to their current business interest. on the other hand, using their r&d capacities, they also support eu research institutions [ ] . there are many policies and instruments the effect its in the i&s industry. they may embrace energy efficiency, e.g. energy audits, energy efficiency obligation schemes, voluntary agreements; energy policy, e.g. energy taxes; environmental policy, e.g. emission taxes and emission permits; financial incentives, e.g. subsidy-based "technology push" instruments, reward-based "market pull" instruments, and access to capital measures; regulatory measures, e.g. codes and standards; information and feedback provision [ ] , [ ] , [ ] . their interaction is complex and exacerbates the importance of policy coordination to secure the policies' effectiveness [ ] , [ ] , [ ] . the innovation system in the i&s industry unlike such systems in other non-eiis has not been driven by all customers pressing on radically improved products ("demand-side innovation") [ ] . there are customers demanding quality, but even they do not expect radical improvements due to innovative breakthroughs in technologies. the currently used high-emission technologies are capable to deliver the desired products at highly competitive prices. therefore, most customers show no direct interest in ghg reduction by the i&s industry and do not squeeze on the manufactures. the creation of the eu market for "green steel" is, therefore, if politically agreed, one of the fundamental steps to radically improve the economic viability of breakthrough technologies. public procurement (using shadow carbon prices as a bid criterion or setting limits on carbon intensity) and "green labelling" shall become the initial actions. then, more radical measures should follow, e.g. creation of investment incentives while ensuring "carbon leakage" protection by spreading carbon pricing globally, adjusting carbon prices at the border and stopping free allowance allocation, material "feed-in-tariffs", contracts for difference, applying consumption charges, promote the recycling of materials, also by extending producers' responsibility for the management of their end-of-life products. [ ] , [ ] . more attention must be paid to the industrial symbiosis and integration of i&s technologies with other technologies [ ] , [ ] , [ ] , [ ] . its from the i&s industry have very limited options to diffuse to other sectors because of their specific technology orientation. this limits the circle of their potential users ("market scale") and does not build up the inter industrial synergy. in the industrial symbiosis, the three most effective symbiotic measures for co abatement are bf gas recycling, coke oven gas recycling, and bf slag sold to the cement industry [ ] , [ ] , [ ] . participation in demand side management (dsm) ideally suitable for eafs should also be more exploited as a synergy with the power sector. conversely, it is predicted that radical technological change to the i&s industry will come from other industries, e.g. with res-based energy, "green hydrogen" technologies, electrolysis at affordable cost, and economically viable ccsu [ ] , [ ] , [ ] , [ ] . ccsu underscores coupling between the i&s industry and the chemical industry [ ] . at electricity prices below approximately $ /mwh, hydrogen use for greenfield steel production sites is more cost-competitive than applying ccs to conventional production processes [ ] . more extensive use of eafs would increase electricity demand. the eurofer [ ] predicts that the demand of the i&s industry for res-based energy in the eu amounts to approximately twh a year by (including for the production and use of hydrogen). this in turn would require public support for res and hydrogen industries to remain globally competitive [ ] , [ ] . power grids are getting pivotal for all industries facing the option of intensive electrification. eaf, h-dr technologies are only feasible when the availability and reliability of huge amounts of cheap energy are secured. h-dr gets cost-competitive with an integrated steel plant at a carbon price of € … eur per tonne co and electricity costs of €/mwh [ ] . this will take advantage for countries with well-developed res capacity and power systems meeting the standards of the smart grid. this requires closer than today long-term planning between the power sector and i&s industry in technical and co-financing aspects to retain energy security of the i&s industry [ ] . there is a threat that there may be competition for res-based electricity among different industries, e.g. transport, chemical. phasing-out nuclear capacity in some countries shall also be analysed in terms of being replaced by res-based energy especially in the light of options of use of hydrogen in steel production utilizing nuclear process heat [ ] . state ownership of the i&s industry and/or power enterprises poses an interesting challenge of large scale private-public partnership. novel technological options, e.g. hot briquetted iron from the dri combined with local res capacity may lead to a relocation of reduction/palletisation and steel production sites to avoid power grid congestions [ ] . the iea proposes identifying geographic clusters where key energy infrastructure can be built to support the decarbonisation of industry [ ] . lack of proper sectorial coordination between the i&s industry and the power sector may lead to a shift from process-related emission to combustion-related emission especially in countries with a high share of fossil fuels (coal, gas) in the energy mix [ ] . planning of the power system for a substantial increase in res is declared as one of the four key policy priorities to foster the eu energy transition [ ] . decarbonisation in the i&s industry may have a far-reaching impact on other industries, e.g. the global coal demand, and, consequently, poses societal problems in heavy steel and coaldependent regions ("fair transition") [ ] , [ ] . alongside efficiency improvements, this means that coal use in the i&s industry declines by around million mtce by [ ] . breakthrough transformation in core technology will entail deep changes in the entire supply chain, e.g. coal, gas, scrap, which will have to be restructured around these new methods [ ] . networking within the company or group in the same industry, between industries, and suppliers has been proved important for effective energy management [ ] . internal networking help to exchange ideas and discuss common strategies and future legislation, e.g. on the environment. industry calls for enabling and incentivization of cross-sector collaboration by supporting consortia with cross-sector technologies, e.g. to enlarge value chains, increase cross-industry cooperation, and to innovate horizontally applicable, integrated solutions and innovation that result in services replacing or complementing existing products. [ ] . public and political awareness needs to be increased by setting up communication channels, e.g. forums and platforms [ ] . okazaki and yamaguchi [ ] investigated possibilities of accelerating the effectiveness of the global voluntary sectoral approach for transfer and diffusion of energy-saving technologies in the i&s industry the authors claimed that the success depends on the four factors -sharing of information, the establishment of challenging numerical targets voluntarily, utilize communications, especially among experts, promoting more widespread use of technologies to achieve the set targets, and setting up and sharing of a common longterm vision. the findings show that non-technological factors, difficult to be included in the modelling, play important role in technology diffusion (see also [ ] ). the i&s industry in the eu is very well managed and supported by many organisations and platforms which work as lobby organisations, e.g. represent the industry in talks with the ec, co-ordinate eu wide activities, organise r&d programs [ ] , [ ] , [ ] . the i&s industry should more actively use the opportunity of building a positive atmosphere around the industry by participating in corporate social responsibility programs and "green" labelling the products to receive stronger public support for its decarbonisation needs [ ] . international collaboration and industry-government cooperation will be needed to further improve the energy and environmental performance of the i&s industry [ ] , [ ] , [ ] , [ ] . in some instances, coordinated action across multiple stakeholders may be required, e.g. sharing best practices driving innovation across industry groups [ ] . ti development in the i&s industry brings some long-term risks and uncertainties, some of them will become permanent barriers if timely not removed [ ] , [ ] . bachner et al. [ ] studied uncertainties in macroeconomic assessments of low-carbon transition pathways in the eu i&s industry. they show that effects strongly depend on technology choice, prevailing macroeconomic states as well as regional characteristics and to less extant on the underlying socio-economic development and the climate policy. based on our analyses, we provided a list of risk and uncertainties around technological innovation in the eu i&s industry (table ). the low share of costs of pollution in total manufacturing cost, e.g. these caused by the eu ets no progress in including "external costs" in eiis operation, e.g. in power sector "externalities are not priced") the continued gap between energy and environmental policies the inclination of some governments to "sacrifice" i&s industry at the price of meeting national climate objectives symptoms of "silos" among responsible central government bodies ("poor governance") technological risks socioeconomic economic risks the potential loss of market shares due to failures and delays in it expected implementation the economic failure of some key innovative technologies, e.g. ccsu the volatility of iron ore, energy carriers and scrap on global markets [ ] high and unpredicted costs of r&d work and transition to the demonstrative phase significant difficulties in obtaining commercial financing especially for basic and pre-commercial r&d [ ] large steel demand plunged following a change in the global economy volatility in financial markets and the vulnerability of emerging economies to a deterioration in financial conditions [ ] lack of "de-risking" instruments to reduce business risks the prevailing market tendency for "cheap products" over more costly "sustainable products" [ ] lack of reliable information, e.g. about future prices and costs, asymmetric information, principal-agent problems, learning by using [ ] the tendency to revert from grants to risk financing options for higher advanced developments [ ] lack of clear criteria and a highly transparent set of requirements, procedures, and decision making processes in the public financing schemes [ ] rising protectionism [ ] risk due to post covid- economic crisis [ ] the european business community has asked for the horizon' europe budget to be raised to at least € billion [ ] . through the analyses they identify some general trends which affect the i&s industry development through the diffusion of technologies. unused funding due to lack of deal flow [ ] the imposition of trade tari s by third countries (i.e. usa) that tend to increase the endeavour of countries like china, brazil or russia to export more steel to europe [ ] societal risk prolonged low public awareness on innovation benefits [ ] the public opinion focused on emissions of the power sector, not prioritising i&s industry public acceptance to import cheaper "dirty product" loss of legitimacy when public financial support is necessary [ ] source: own work. . conclusions and policy implication . . benefits of tis approach the main aim of the analysis was to apply the tis approach to highlight the actors, barriers, and inducements on the way of the i&s industry in the eu to deep decarbonisation. this paper identifies the key elements of its in this industry, and then analysis of the functions of innovation through the lens of the tis approach. it facilitates more in-depth insight into the highly complex and dynamic political, technological, economic, and societal environment at this climate-decisive moment. the eea warns "past trends for resource efficiency, the circular economy, and climate and energy are encouraging; the outlook is less positive" [ ] . our research, integrating a range of technological and non-technological aspects and thanks to identifying the involvement of many actors, their roles, and links among them in the functioning of the tis, should help to provide guidelines for political decisions. it contributes to a better understanding of sometimes divert interests among actors, to the prevention of duplication of efforts and to avoid excessive costs and stranded assets due to better coordination. this was indeed a challenging endeavour, yet worth taking because of its novelty. our tis analysis is close to the mission-oriented innovation system (mis) aiming to accomplish a widely shared societal challenge (mission) related to climate change. the notion of mis defined by hekkert et al. [ ] as "the network of agents and set of institutions that contribute to the development and diffusion of innovative solutions with the aim to define, pursue and complete a societal mission" should increase public awareness of the necessity of low-carbon transformation in the i&s industry and make the relevant r&d higher valued among scholars. power sector transformation to the smart grid concept, eii decarbonisation, stringent energy efficiency priorities, the digital revolution, closing material cycles are rather means than the individual initiative of completing the climate mission [ ] , [ ] , [ ] . we show that that deep decarbonisation in the i&s industry is feasible but requires firm support, mostly political, to finance intensive r&d and reduce the business risk. to that end, all actors need to come to a common strategy followed by an action plan to realise the decarbonisation vision. they shall support more effectively the further refinement and market implementation of breakthrough technologies. the major driving force for the low-carbon transformation in the i&s industry is the strategic vision of the all eu actors of radical reduction ghg emission through innovative technologies, and material and energy conservation [ ] , [ ] , [ ] , [ ] . j o u r n a l p r e -p r o o f technologies [ ] . policy, regulation, and energy price-induced technical change are welldocumented drivers for innovative technologies [ ] . public authorities at different levels, including local, are essential players in facilitating the dialogue among parties to set clear visions, mitigate divergent interests, balance costs, and benefits. the "climate" mission is not sufficient for all, especially for "steel dependent" communities, thus it shall be supported by presenting a fair cost-benefit assessment of transformation. the ec and the ms governments are firstly expected to support its by suitable legislation and regulations, e.g. setting realistic pollution limits, creation of "green steel" market, effective use of public procurement, setting material requirements for large steel consumers, reforming the eu ets, setting barriers against unfair steel import, world's regulation of scrap trade. the second desired support is to co-finance the decarbonisation under the state aid framework [ ] . in this respect, suitable energy prices and financing all stages of r&d, particularly important in the early stages of the innovation cycle, are highly required [ ] . there is a persistent state of the informational advantage of the i&s industry over politicians about costs and benefits of climate policy which in the long-term is harmful to both sidesdoes not enable to set effective and cost-efficient policies and adopt appropriate corporate strategy [ ] . more reliable data from the i&s industry and better access to public data banks are essential to eliminate the asymmetry of information among all actors [ ] , [ ] . modern means of data processing, e.g. big data, artificial intelligence, analytics, create opportunities for better economic effectiveness in the whole i&s business chain. the requirements of climate and environmental protection are getting stronger so that incumbent technologies are reaching their inherent limits and lose social acceptance. i&s industry will not be able to get closer to the eu reduction targets unless breakthrough technologies are introduced and prove their cost-effectiveness [ ] . decarbonisation consisting in material and energy efficiency will help, but it is not sufficient to get the reductions needed. other measures, e.g. organisational, managerial, logistical, business optimisation, can support but the technological breakthrough is a must. thus, national, and supra-nation support to technology research, development, and deployment play a key role. politicians should not allow breakthrough innovative investments to be placed outside of europe [ ] . the i&s industry is well suited to benefit from the increased priority of circular economy, e.g. recycle of scrap or utilisation of by-products or increased demand better products from other industries [ ] . reducing total steel demand via a shift to a more circular economy requires inter alia deep changes in the global scrap market [ ] , [ ] , [ ] . the rate of diffusion of breakthrough technologies in the i&s industry is not clear [ ] , [ ] , [ ] , [ ] , [ ] , [ ] . this analysis points to the need to accelerate r&d in the i&s industry to commercialise breakthrough core technologies and increase the role of material and energy efficiency. it also stresses the necessity of more res-based energy and importance of hydrogen technologies. in addition to a very much needed research focus on the technological side, more research on socio-technical drivers and barriers is needed to manage the transition process successfully [ ] . international collaboration and win-win industry-government cooperation will be essential to make a real breakthrough. domination of china as manufacture and the country's technological advances shall be carefully watched [ ] . the economics of the transition implies political involvement throughout the whole innovation cycle, from the preferred cost of capital, covering a large share of r&d costs, building energy infrastructure, e.g. electric energy, hydrogen, to the creation of competitive markets. the cost of deep decarbonisation in the i&s industry is high and therefore perceived unacceptable from a political point of view unless a trustful assessment of the long-term costs and benefits is presented and then accepted by the society which may take years. therefore, to make the transition viable, the future policies and regulations, e.g. environmental, market, should be far-reaching and encourage investors to employ these today breakthrough technologies and not to conserve the current state. the future economic framework should be conveyed to investors well in advance to avoid stray assets [ ] . many concerns shall be shown to the future impact of the eu ets on the i&s industry. the ineffectiveness of the eu ets as a driver for low-carbon technological transformation deters the industry to embark on large innovative projects. the new innovative eu ets built-in mechanisms are aimed to eliminate this insufficiency [ ] . it is postulated that benchmark used as a criterion for public support should be replaced by lca approach that can better value steel as a recycle product [ ] , [ ] . there should be an incentive for "degree of innovation" which should reward breaking innovations [ ] . our research also suggests that eu policy should be more focused on the development of knowledge-intensive and technologically complex industries, including. the i&s industry, as the main factor to retain industrial competitiveness. such a policy should enable rapid diffusion of technological innovations through the production and distribution networks of global corporations. this research is addressed to policymakers to elaborate an optimal policy strategy of technological change of the current functioning of the relevant technology-specific innovation system. it should lead to developing, modifying, and deploying the policy framework aiming at improving the functioning of tis by removing the blocking mechanisms. identification of structural elements of the tis, discovering the internal links among them and dynamics of functioning, control input signals, noises (barriers) and feedbacks in the tis have been done. the authors understand that more in-depth insight requires further research to build a coherent framework for it and contribute to meeting economic, sustainable, and societal objectives. further tis analysis and full risk assessment including technology and marketspecific risks would enable knowledge-based public funding granting for i&s projects, e.g. in modernisation or innovation funds of the eu ets. the research also provided a few recommendations for the managers, e.g. necessity for cost and risk management, the importance of building interfaces, and relations with supplier partners and customers [ ] . funding: the article has been prepared under project innopaths: innovation pathways, strategies, and policies for the low-carbon transition in europe. the project has received funding from the european union's horizon research and innovation programme under grant agreement no. . of "energy"; "environmental science"; "social science"; "multidisciplinary" and "business; management & accounting". this search was expanded via a snowballing procedure using the list of the literature of the collected contributions to gather additional sources. the literature on the tis was gathered by searching standard entries: "entrepreneurial activities"; "knowledge development"; "knowledge di usion"; "guidance of search"; "market formation"; "resources mobilisation"; "legitimacy"; "legitimation" and "positive externalities". additionally, considering a dynamic business characteristic of the i&s industry, the literature search was extended to cover the ec internet resources, political, and business websites. therefore, the feature of our analysis is its wide scope of the analysed sources and documents, e.g. advisory groups, eu and government-sponsored research projects, industry alliances, which are creating specifications. the slr used had some disadvantages, e.g. it relied only on one peer-reviewed database, the combination of the keywords used might miss some relevant papers and institutional insights. the role of the steel industry in a circular economy and its proposals ahead of the commission's launch of a revised package action plan for a competitive and sustainable steel industry in low and zero emissions in the steel and cement industries barriers, technologies and policies steel roadmap for a low carbon europe global warming of . °c an ipcc special report technical summary decarbonization of industrial sectors: the next frontier present needs, recent progress and future trends of energy-efficient ultra-low carbon dioxide (co ) steelmaking (ulcos) program the impact of the european steel industry on the eu economy breaking through industrial low-co technologies on the horizon european commission. finance for innovation, towards the ets innovation fund zero emissions platform. climate solutions for eu industry: interaction between electrification, co use and co storage european policies on climate and energy towards , and . european parliament navigating the roadmap for clean the european union energy transition: key priorities for the next five years the european green new deal the transition of energy intensive processing industries towards deep decarbonization : characteristics and implications for future research global climate policy and deep decarbonization of energy-intensive industries european commission. high-level panel of the european decarbonisation pathways. interim recommendations the transition of energy intensive processing industries towards deep decarbonization: characteristics and implications for future research steel 's contribution to a low carbon future and climate resilient societies european environment agency. emep/eea air pollutant emission inventory guidebook learnings from upstream integration of steelmakers pathways to a lowcarbon iron and steel industry in the medium-term -the case of germany technology map of the european strategic energy technology plan (set-plan): technology description a steel roadmap for a low carbon europe european commission. a clean planet for all a european strategic long-term vision for a prosperous, modern, competitive and climate neutral economy green deal on steel priorities european commission. long-term low greenhouse gas emission development strategy of the european union and its member states energy efficiency and co emissions reduction in the steel industry ulcos top gas recycling blast furnace process (ulcos tgrbf) : final report functions of innovation systems: a new approach for analysing technological change legitimation" and "development of positive externalities": two key processes in the formation phase of technological innovation systems systemic instruments for systemic innovation problems: a framework for policy makers and innovation scholars configurational innovation systems -explaining the slow german heat transition review of system innovation and transitions theories innovation theory: a review of the literature transformative innovation policy: addressing variety in an emerging policy paradigm diffusion of energy efficient technologies and co emission reductions in iron and steel sector the potential for improvements in energy efficiency and co emissions in the eu iron and steel industry under different payback periods diffusion of energy efficient technologies in the german steel industry and their impact on energy consumption steel industry -jernkontoret options for the swedish steel industry -energy efficiency measures and fuel conversion empirical investigation of barriers and drivers to the adoption of energy conservation measures, energy management practices and energy services in the swedish iron and steel industry improved energy efficiency within the swedish steel industry-the importance of energy management and networking first in fossil-free steel -ssab adopting hydrogen direct reduction for the swedish steel industry: a technological innovation system (tis) study macroeconomic implications of switching to process-emission-free iron and steel production in europe comparing service, product, and process innovations: insights from the internal supply chain network of a european steel manufacturing firm challenges for the european steel industry: analysis, possible consequences and impacts on sustainable development hydrogen technological innovation systems in practice: comparing danish and american approaches to fuel cell development technology innovation system analysis of electricity smart metering in the european union technological innovation systems in contexts: conceptualizing contextual structures and interaction dynamics case studies of national innovation systems, innopaths innovation pathways, strategies and policies for the low-carbon transition in europe analyzing the functional dynamics of technological innovation systems: a scheme of analysis case studies of national and eu innovation systems. innopaths innovation pathways, strategies and policies for the low-carbon transition in europe explaining the drivers of technological innovation systems: the case of biogas technologies in mature markets hydrogen technological innovation systems in practice: comparing danish and american approaches to fuel cell development towards a methodology for developing evidence-informed management knowledge by means of systematic review digital transformation in european steel industry : state of art and future scenario (deliverable . ) energy efficiency concepts and calculations endogenous technological change and emissions: the case of the german steel industry research and development, innovation and productivity growth in the steel sector advanced steels the future of european steel innovation and sustainability use of biomass in integrated steelmaking -status quo, future needs and comparison to other low-co steel production technologies steel's contribution to a low-carbon europe etp : tracking clean energy progress -trends in iron & steel integrated assessment of exergy, energy and carbon dioxide emissions in an iron and steel industrial network industrial energy efficiency project -benchmarking report for the iron and steel sector potential of energy savings and co emission reduction in china's iron and steel industry potential energy efficiency improvements for the brazilian iron and steel industry: fuel and electricity conservation supply curves for integrated steel mills jrc reference report best available techniques (bat) reference document for iron and steel production ( integrated pollution prevention and control ) comparison of co capture economics for iron and steel mills decarbonising the energy intensive basic materials industry through electrification -implications for future eu electricity demand co₂ abatement in the iron and steel industry a review of energy use and energy-efficient technologies for the iron and steel industry filling gaps in the policy package to decarbonise production and use of materials uk energy transition commission. reaching net-zero carbon emissions from harderto -abate sectors by mid -century a clean planet for all a european long-term strategic vision for a prosperous, modern, competitive and climate neutral economy prospective scenarios on energy efficiency and co emissions in the european iron & steel industry techno-economic evaluation of innovative steel production technologies a comprehensive review on energy efficient co breakthrough technologies for sustainable green iron and steel manufacturing modeling technological change and its impact on energy savings in the u.s. iron and steel sector a review of technology and policy deep decarbonization pathway options for making energy-intensive industry production consistent with the paris agreement a review of the technologies , economics and policy instruments for decarbonising energy-intensive manufacturing industries tracking clean energy progress analysis of the potential for energy demand and carbon emissions reduction in the iron and steel sector energy intensity in the iron and steel industry: a comparison of physical and economic indicators how benchmarking can improve cost competitiveness in steel, mckinsey & company technological transitions as evolutionary reconfguration processes: a multi-j o u r n a l p r e -p r o o f level perspeciteve and a case study sectoral systems of innovation and production impacts of innovation policy: synthesis and conclusions of the compendium of evidence on the effectiveness of innovation policy intervention project european commisssion. communication "for a european industrial renaissance investing in a smart, innovative and sustainable industry. a renewed eu industrial policy strategy european commission. the european green deal research and innovation performance strengthening the foundations for europe' s future eurofer. networking in european steel industries steel and humanity's grand challenges improving the world through entrepreneurship and innovation dec path to : decarbonizing the industrial sector a long road ahead for low-carbon manufacturing policy support for and r&d activities on digitising the european steel industry hydrogen steelmaking for a low-carbon economy a joint lu-sei working paper for the hybrit project guidelines on state aid for environmental protection and energy european commission. set-plan action n° -implementation plan the impact of standardization and standards on innovation time for a change: on the patterns of diffusion of innovation steel mothballing, not closing, uk electrical steel plant european commisssion. set-plan action n° -implementation plan -endorsed / game change in the steel industry a steel roadmap for a low carbon europe green deal on steel priorities the european environment: state and outlook : synthesis european commission. regional innovation monitor plus pathways to a resource-efficient and low-carbon europe technology and the market. demand, users and innovation the current capacity shake-up in steel and how the industry is adapting industrial decarbonisation and energy efficiency roadmaps to -iron and steel effects of monetary investment, payback time and firm characteristics on electricity saving in energy-intensive industry eu directorate-general for research and innovation. state of the innovation union new £ m research network to transform uk steel industry cato event -progress for dutch carbon capture research and innovation performance of the eu unlocking low carbon innovation research fund for coal and steel. synopsis of rfcs projects global challenges report innovation and diffusion of green technologies: the role of intellectual property and other enabling factors using public procurement as a decarbonisation policy: a look at germany energy transitions commission. reaching zero emissions from steel macro economic co-benefits and costs: the case of the european iron and steel industry european investment bank. eib climate strategy impact assessment of climate policy on poland's power sector energy management in industry -a systematic review of previous findings and an integrative conceptual framework innovation in times of financialization: do future-oriented innovation strategies suffer? examples from german industry world steel association. steel industry co-products -worldsteel position paper energy prices and emissions trading: windfall profits from grandfathering? union der deutschen akademien der wissenchaften. governance for the european energy union approaching sustainable energy management operations in a global gaps in clean energy research, developmetn, and demonstration. international energy agency directive / /eu of the european parliament and of the council of october on energy efficiency directive / /ec of the european parliament and of the council of october establishing a framework for the setting of ecodesign requirements for energy-related products energy savings by energy management systems: a review the impact of the eu ets on the sectoral innovation system for power generation technologies -findings for germany circular economy indicators in relation to ecoinnovation in european regions on the implementation of the circular economy action plan a government roadmap for addressing the climate and post covid- economic crises coronavirus batters steel sector to what extent are eu steel companies susceptible to competitive loss due to climate policy the roads ahead: narratives for shared socioeconomic pathways describing world futures in the st century mission-oriented innovation systems a review of technology and policy deep decarbonization pathway options for making energy-intensive industry production consistent with the paris agreement recent advances in carbon emissions reduction : policies , technologies , monitoring , assessment and modeling the potential of using biomass-based reducing agents in the blast furnace: a review of thermochemical conversion technologies and assessments related to sustainability an overview of utilization of blast furnace and steelmaking slag in various applications macroeconomic implications of switching to process-emission-free iron and steel production in europe assessment of hydrogen direct reduction for fossil-free steelmaking a techno-economic evaluation of the use of hydrogen in a steel production process, utilizing nuclear process heat the future of hydrogen -seizing today's opportunities. rep prep by iea g climate-change induced uncertainties, risks and opportunities for the coal-based region of silesia: stakeholders' perspectives ccus -a challenge for the iron and steel industry accelerating the transfer and diffusion of energy saving technologies steel sector experience-lessons learned diversity in the steel industry optimal international technology cooperation for the low-carbon transformation climate risk and response uncertainties in macroeconomic assessments of low-carbon transition pathways -the case of the european iron and steel industry where are the industrial technologies in energy-economy models? an innovative cge approach for steel production in germany policy-induced energy technological innovation and finance for low-carbon economic growth: study on the macroeconomics of energy and climate policies. deliverable d . study on the macroeconomics of energy and climate policies european energy transition : the big picture invention in energy technologies: comparing energy efficiency and renewable energy inventions at the firm level improving energy and climate indicators for the steel industry -the case of sweden oecd. going digital: shaping policies, improving lives the impact of climate targets on future steel productionan analysis based on a global energy system model steel institute vdeh. steel's contribution to a low-carbon europe learnings from upstream integration of steelmakers. oecd work cape t latest developments in steelmaking capacity industrial revitalization via industry . -a comparative policy analysis among china, germany and the usa the environmental impacts of iron and steel industry: a life cycle assessment study • problems, boundaries and difficulties in the i&s industry decarbonization • tis structural components, links and interactions of i&s industry decarbonisation. • mapping of functional patterns and evaluation of tis functionality in i&s industry. • blockades, incentives and innovation risks in the i&s industry decarbonisation. • tis analysis as a tool for granting public funds for i&s projects acknowledgements: we are in debt to ms ewa stefaniak for her friendly support and diligent proofreading of this paper. j o u r n a l p r e -p r o o f ☒ the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐the authors declare the following financial interests/personal relationships which may be considered as potential competing interests: j o u r n a l p r e -p r o o f key: cord- - xdtbbzb authors: remesar, xavier; alemany, marià title: dietary energy partition: the central role of glucose date: - - journal: int j mol sci doi: . /ijms sha: doc_id: cord_uid: xdtbbzb humans have developed effective survival mechanisms under conditions of nutrient (and energy) scarcity. nevertheless, today, most humans face a quite different situation: excess of nutrients, especially those high in amino-nitrogen and energy (largely fat). the lack of mechanisms to prevent energy overload and the effective persistence of the mechanisms hoarding key nutrients such as amino acids has resulted in deep disorders of substrate handling. there is too often a massive untreatable accumulation of body fat in the presence of severe metabolic disorders of energy utilization and disposal, which become chronic and go much beyond the most obvious problems: diabetes, circulatory, renal and nervous disorders included loosely within the metabolic syndrome. we lack basic knowledge on diet nutrient dynamics at the tissue-cell metabolism level, and this adds to widely used medical procedures lacking sufficient scientific support, with limited or nil success. in the present longitudinal analysis of the fate of dietary nutrients, we have focused on glucose as an example of a largely unknown entity. even most studies on hyper-energetic diets or their later consequences tend to ignore the critical role of carbohydrate (and nitrogen disposal) as (probably) the two main factors affecting the substrate partition and metabolism. at present, two main lines of study focus on metabolic acquisition, distribution and use of food energy to maintain efficiently human body functions. ( ) the analysis of foods and diets, which largely uses centuries-old methodologies, and its subject of study is the relationship to diet of the body in relation to health and disease. ( ) the analysis and function of cell and molecular effects of diet has developed during the last - decades, using the high pace of methodological advances and accumulated knowledge at the molecular and cellular level, with important inroads into the regulation of the cell, organ, and body homeostasis. unfortunately, both lines run parallel, and there is not enough shared-connecting-knowledge to use the enormous amount of knowledge accumulated to help explain the direct relationships of dietary components with metabolic modulation and regulation, despite the paramount importance of this nexus. the complexity (and variability at all levels) or the problem hampers any approach to the health (and survival) problems related to diet. in this focused review, we intend to present a few critical questions that may help to bridge the gap between these two lines. in most cases, the lack of hard research data is surprising [ ] . the excessive narrowness of these study goals is even more severe [ ] . the forfeiting of a large mass of knowledge accumulated just before the present century [ ] , and limited use of quantitative glucose, however, has considerable advantages as a primary energy-substrate source: it can be easily converted in two c fragments even under anaerobic conditions (via the classic embden-meyerhoff pathway), well preserved along evolution [ ] . this quality is seldom recognized, especially considering the growing awareness on the perils of oxidative free radicals generated from oxygen metabolic interventions [ , ] . splitting one c unit (i.e., glucose) yields a variety of (essentially) c molecules: pyruvate, l-lactate, glycerol, alanine, serine, and phospho-enol-pyruvate (pep), used for energy or synthetic pathways. c fragments are also generated from a number of key pathways in addition to straight glycolysis: the pentose-phosphate pathway, hexosamine metabolism, the leloir (galactose) pathway, the catabolism of fructose and other monosaccharides as substrates, the incorporation of glycerides-glycerol, lactate, and a number of amino acid hydrocarbon skeletons. not all three-carbon metabolites can be included in this c list. the clearest examples are propionate (yielding succinyl-coa, see section ) and d-lactate, a significant component of bacterial fermentation (including our microbiota), found in some foods. its degradation is difficult [ ] but does not proceed directly via pyruvate. in this review, we will reserve the term "lactate" for l-lactate as in most metabolic studies. pyruvate is the key c fragment from which the core of intermediary metabolism establishes the use of diet (or reserves/turnover) substrates (figure ), via direct oxidation for energy, used as building materials for biosynthesis or transport between pools (cell, organ, body) to achieve energy homeostasis and efficiency in metabolism. pyruvate is also a main source of oxaloacetate (oaa) to regulate the tca (tricarboxylic acid) cycle, i.e., the krebs cycle (the second one) [ ] , or regenerate c units via gluconeogenesis. these processes require a critical control of the crossing of the mitochondrial membrane [ ] . pyruvate helps maintain the redox state of cytoplasm via interconversion to lactate (lactate dehydrogenase) [ ] as well as the transport through the cell membrane [ , ] . in any case, the main drain of pyruvate is the formation of acetyl-coa via oxidative decarboxylation by pyruvate dehydrogenase [ ] ; this way, a c fragment becomes a c fragment and co . regulate the tca (tricarboxylic acid) cycle, i.e., the krebs cycle (the second one) [ ] , or regenerate c units via gluconeogenesis. these processes require a critical control of the crossing of the mitochondrial membrane [ ] . pyruvate helps maintain the redox state of cytoplasm via interconversion to lactate (lactate dehydrogenase) [ ] as well as the transport through the cell membrane [ , ] . in any case, the main drain of pyruvate is the formation of acetyl-coa via oxidative decarboxylation by pyruvate dehydrogenase [ ] ; this way, a c fragment becomes a c fragment and co . the regulation of glucose fate and circulating levels has been studied exhaustively, and it has been found that the alteration of these processes may cause serious harm to energy homeostasis. glucose is strictly controlled by a huge number of regulatory agents, including insulin, glucocorticoids, glucagon, intestinal peptides, catecholamines, cytokines, testosterone, estrogens, etc. [ ] . they regulate glucose splanchnic production [ ] and utilization [ ] [ ] [ ] . glucose modulates the production and secretion of insulin [ ] and, indirectly, its hepatic inactivation [ ] . however, insulin resistance affects very directly glucose uptake and metabolism, because of changes in insulin tissue receptors and signaling [ ] . on the other side, the c fragments (mainly pyruvate, lactate, glycerol) are regulated within the cells, but not as extensively as is glucose in their inter-organ relationships. c substrates, such as lactate or glycerol can be easily taken up by a wide diversity of cells, even using less specific (or quite different) transport systems [ , ] . when the cell takes up lactate, it can immediately provide nadh in the cytosol, and then follow a number of diverse paths to provide c or energy (via conversion to c). in comparison, after a strongly regulated maintenance of its circulating levels, glucose is transported into the cell, converted to glucose- p, and then it can be used for the production of c (and eventually c) through wellregulated mechanisms. the main potential inconvenient for plasma-carried c (specifically lactate) is its charge (a proton) and its reduced state, which necessarily has to be corrected via production of cytosolic nadh, but this is the same problem glucose generates at the level of triose-p dehydrogenase. in any case, glycerol or pyruvate do not comport these hindrances. it is well known the regulation of glucose fate and circulating levels has been studied exhaustively, and it has been found that the alteration of these processes may cause serious harm to energy homeostasis. glucose is strictly controlled by a huge number of regulatory agents, including insulin, glucocorticoids, glucagon, intestinal peptides, catecholamines, cytokines, testosterone, estrogens, etc. [ ] . they regulate glucose splanchnic production [ ] and utilization [ ] [ ] [ ] . glucose modulates the production and secretion of insulin [ ] and, indirectly, its hepatic inactivation [ ] . however, insulin resistance affects very directly glucose uptake and metabolism, because of changes in insulin tissue receptors and signaling [ ] . on the other side, the c fragments (mainly pyruvate, lactate, glycerol) are regulated within the cells, but not as extensively as is glucose in their inter-organ relationships. c substrates, such as lactate or glycerol can be easily taken up by a wide diversity of cells, even using less specific (or quite different) transport systems [ , ] . when the cell takes up lactate, it can immediately provide nadh in the cytosol, and then follow a number of diverse paths to provide c or energy (via conversion to c). in comparison, after a strongly regulated maintenance of its circulating levels, glucose is transported into the cell, converted to glucose- p, and then it can be used for the production of c (and eventually c) through well-regulated mechanisms. the main potential inconvenient for plasma-carried c (specifically lactate) is its charge (a proton) and its reduced state, which necessarily has to be corrected via production of cytosolic nadh, but this is the same problem glucose generates at the level of triose-p dehydrogenase. in any case, glycerol or pyruvate do not comport these hindrances. it is well known that a high number of tissues use lactate for energy under exercise [ ] , limited insulin resistance [ ] , or as a cryptic "universal cell fuel" [ ] . the brain is an active user of lactate [ ] and glycerol [ , ] . liver is a net lactate user, largely for gluconeogenesis [ , ] . white adipose tissue (wat) can take up lactate for lipogenesis [ ] or produce it from glucose in large amounts [ , ] . the intestine also provides c substrates, in part as a product of digestion [ ] . the transfer of energy to tissues via c has been found to be much higher than often considered [ , ] , constituting a clear alternative to intact glucose [ , ] . under conditions of excess glucose availability, its conversion to c eases the pressure over the regulation of glycaemia and allows for the direct use of its energy via c [ , ] , in a way comparable to the "pre-preparation" of fatty acids ( c n ) fragments to plasma-soluble ketone bodies ( c fragments). the relatively lax control and ease of direct metabolic incorporation allows for a loosely regulated use of c anywhere. this possibility is extensive to the nervous system, which can use c fragments to a large extent as a source of energy in addition to glucose (or as its substitute) [ ] . figure shows the relationship between dietary nutrients and the c and c substrates pools. in addition to the carbohydrate paths shown in figure , a large part of amino acid hydrocarbon skeletons can be incorporated to the c→ c pathways (largely glycolysis and gluconeogenesis) but also as intermediates of the tca cycle (which eventually will result in oaa and then to a c fragment used for energy or synthesis. lipids, essentially triacylglycerols (tag), also provide c (as glycerol), but their carbon is essentially structured in c units (acetate, acetyl-coa) or-massively-in c n chains, such as fatty acids. that a high number of tissues use lactate for energy under exercise [ ] , limited insulin resistance [ ] , or as a cryptic "universal cell fuel" [ ] . the brain is an active user of lactate [ ] and glycerol [ , ] . liver is a net lactate user, largely for gluconeogenesis [ , ] . white adipose tissue (wat) can take up lactate for lipogenesis [ ] or produce it from glucose in large amounts [ , ] . the intestine also provides c substrates, in part as a product of digestion [ ] . the transfer of energy to tissues via c has been found to be much higher than often considered [ , ] , constituting a clear alternative to intact glucose [ , ] . under conditions of excess glucose availability, its conversion to c eases the pressure over the regulation of glycaemia and allows for the direct use of its energy via c [ , ] , in a way comparable to the "pre-preparation" of fatty acids ( cn) fragments to plasma-soluble ketone bodies ( c fragments). the relatively lax control and ease of direct metabolic incorporation allows for a loosely regulated use of c anywhere. this possibility is extensive to the nervous system, which can use c fragments to a large extent as a source of energy in addition to glucose (or as its substitute) [ ] . figure shows the relationship between dietary nutrients and the c and c substrates pools. in addition to the carbohydrate paths shown in figure , a large part of amino acid hydrocarbon skeletons can be incorporated to the c→ c pathways (largely glycolysis and gluconeogenesis) but also as intermediates of the tca cycle (which eventually will result in oaa and then to a c fragment used for energy or synthesis. lipids, essentially triacylglycerols (tag), also provide c (as glycerol), but their carbon is essentially structured in c units (acetate, acetyl-coa) or-massively-in cn chains, such as fatty acids. glucose (in general terms, carbohydrate) is required as a main dietary macro-component for humans. [ ] , also probably being an essential component of diet, at least by default [ ] . the commonness, diverse forms, and high proportions of carbohydrates in many diets has masked this condition [ ] . nevertheless, the extended use of high-fat and high-protein diets resulting in figure . relationship between the main groups of dietary nutrients driving to the formation of c and c fragments. in red, the irreversible decarboxylative oxidation path of pyruvate ( c) to acetyl-coa ( c). glucose (in general terms, carbohydrate) is required as a main dietary macro-component for humans. [ ] , also probably being an essential component of diet, at least by default [ ] . the commonness, diverse forms, and high proportions of carbohydrates in many diets has masked this condition [ ] . nevertheless, the extended use of high-fat and high-protein diets resulting in inflammatory responses and metabolic alterations [ ] points to the requirement of a sufficient amount of c substrates (preferably as c n polysaccharides) in any normal health-sustaining diet, in proportions of c n not different at present from our early hominid ancestors [ ] . the notion that the brain only uses glucose as a substrate remains alive in many texts and studies, largely for the disproportionate basal consumption of glucose by the brain in comparison with most other organs [ ] . however, the widespread existence of intercellular lactate-glucose micro-cycles between glia and neurons suggests otherwise [ , ] . the main substrate for brain energy changes with development [ ] , but the nervous system continues using a large proportion of blood glucose under standard conditions [ ] , whether this is a consequence of glia cells (i.e., astrocytes) producing lactate from glucose to feed neurons [ ] or the neurons themselves using glucose directly is a question not yet settled [ , ] . the intensive utilization of lactate and glycerol by the brain as a whole has been known for more than half a century [ , ] and may be part of a system of protection against the chemical dangers posed by glucose reactivity. from the earliest stages of development, the nervous system has specific needs for some nutrients, such as glucose, as key source of energy [ ] ; oligosaccharides containing galactose and other sugars [ ] ; c fragments, as indicated above; specific essential fatty acids [ ] ; and enough amino n and essential amino acids [ ] . the needs of peripheral and enteric nervous systems are less known; in the last case, we have to include the direct relationships with intestinal microbiota [ ] . in any case, it is widely acknowledged that the brain has priority over the rest of the body with respect to glucose supply [ ] . the extent to which the requirements of c can be substituted by c is yet an object of discussion [ , ] . the erythrocytes (at least the non-nucleated mammal-including human-ones) are also peculiar with respect to the need for glucose. they require integer glucose, since they are not able to get energy via oxidation of c. thus, these cells are considered purely glycolytic, releasing lactate from glucose [ ] . since the red blood cells need little energy and are a fundamental component of the blood (which carries glucose), their needs can be easily covered by direct uptake from plasma [ ] . because their consumption is non-oxidative ( c to c), the return of two c units per glucose does not alter the global equation of glucose consumption and do not represent a quantitatively critical factor, as can be the case with parts of our nervous systems. the triad of tag, fatty acids, and acetate/acetyl-coa represents decreasing levels of complexity of most energy-related lipids; their mw is related directly to their physical conditioning and metabolic usage. a critical point is their lipophilic nature, which conditions transport by the blood and the crossing of intracellular and plasma membranes. acetate ( c) and easily metabolizable ketone bodies ( c ), as well as some short-chain fatty acids, are hydrophilic enough to be transported in blood or lymph and may cross easily most membranes [ ] . fatty acids ( c n , medium to long-chain with less than five to more than c units) are transported bound to proteins [ ] , and are incorporated into the cell by specific efficient binding-proteins [ ] and transporters [ ] . tag are too large and insoluble to be carried by blood plasma: they are transported within lipoproteins, structured with apolipoproteins and other lipids, such as phospholipids and other classes of lipophilic compounds as minority components. the intestine and the liver initially build up these complex lipid carriers, mainly chylomicra and vldl. they are fairly efficient systems for transporting large amounts of tag (i.e., heavy energy packages, mostly containing c n ) to provide fuel for energy and organ functions [ ] in addition to the transport to and from of critical lipophilic substrates such as cholesterol, a process reserved for the smaller lipoproteins (ldl, hdl) [ ] . within tissues, large amounts of lipid are transferred between cells by using at least two mechanisms. in the first, very large (often old) adipocytes, (or those marked for apoptosis), when broken up via apoptosis or autophagia, release a large amount of micro-drops of lipid. these vesicles are taken up via pinocytosis by macrophages, functional adipocytes [ ] , or other cells. a selective apoptotic (and packed groups of macrophages [ ] ) process has been proposed as a mechanism for tissue turnover, which is applied to dead or no longer functional adipocytes [ ] . this clearing process has the advantage to constrain the diffusion of cell debris and lipid drops that can cause damage to other cells, as well as limiting the clogging of individual macrophages with the remains of apoptosis [ ] . the other mechanism is the use of exosomes or vesicles, which can transfer signals, proteins, nucleic acids, but also tag between cells [ , ] . this (incomplete) list represents a wide panoply of mechanisms for transfer of c-based substrates, primarily between the splanchnic bed to peripheral tissues, for storage or direct utilization. the question of transport between cells and tissues is critical for the supply of energy on time, in the most efficient chemical form for immediate use, and with a sufficient transfer rate of to cover the needs. this is, probably the main reason why there are two main systems for sending energy substrates to the tissues via blood: a) lipophilic ( c-derived, energy-dense but large and difficult to handle) and b) hydrosoluble substrates, represented by glucose and c, but also the smaller c components soluble in plasma. the logistic advantages of having both systems rely essentially in the highly dense energy tag as substrates sent elsewhere for heavy needs, and a variety of other metabolites, usable directly by the cells faster to supply in a continuous way, and easily subjected to immediate regulation. the irreversible path of c to c is carried out by the pyruvate dehydrogenase complex [ ] (figure ), which is highly regulated [ , ] and controls the entry of c into the mitochondrion [ ] . we can use glucose to build fatty acids, but the reverse (regular fatty acids to glucose) is not possible because of this critical step at the confluence of the c and c worlds. this irreversibility is typical of animals, since plants and other phyla possess the "glyoxylate shunt" that we do not [ ] . probably, we lost this shunt along evolution because the main source of c to feed the tca cycle and fatty acid synthesis remained glucose-derived pyruvate. process has the advantage to constrain the diffusion of cell debris and lipid drops that can cause damage to other cells, as well as limiting the clogging of individual macrophages with the remains of apoptosis [ ] . the other mechanism is the use of exosomes or vesicles, which can transfer signals, proteins, nucleic acids, but also tag between cells [ , ] . this (incomplete) list represents a wide panoply of mechanisms for transfer of c-based substrates, primarily between the splanchnic bed to peripheral tissues, for storage or direct utilization. the question of transport between cells and tissues is critical for the supply of energy on time, in the most efficient chemical form for immediate use, and with a sufficient transfer rate of to cover the needs. this is, probably the main reason why there are two main systems for sending energy substrates to the tissues via blood: a) lipophilic ( c-derived, energy-dense but large and difficult to handle) and b) hydrosoluble substrates, represented by glucose and c, but also the smaller c components soluble in plasma. the logistic advantages of having both systems rely essentially in the highly dense energy tag as substrates sent elsewhere for heavy needs, and a variety of other metabolites, usable directly by the cells faster to supply in a continuous way, and easily subjected to immediate regulation. the irreversible path of c to c is carried out by the pyruvate dehydrogenase complex [ ] (figure ), which is highly regulated [ , ] and controls the entry of c into the mitochondrion [ ] . we can use glucose to build fatty acids, but the reverse (regular fatty acids to glucose) is not possible because of this critical step at the confluence of the c and c worlds. this irreversibility is typical of animals, since plants and other phyla possess the "glyoxylate shunt" that we do not [ ] . probably, we lost this shunt along evolution because the main source of c to feed the tca cycle and fatty acid synthesis remained glucose-derived pyruvate. the c→ c path irreversibility has important consequences for glucose and energy partition: while c→ c and c n→ c relationships are reversible, c→ c is unidirectional. in plants, fatty acid reserves can be converted into c [ ] . however, in humans and other animals, glucose (or other convertible c) is needed to provide the c fragments used in many metabolic paths, since despite the c→ c path irreversibility has important consequences for glucose and energy partition: while c→ c and c n → c relationships are reversible, c→ c is unidirectional. in plants, fatty acid reserves can be converted into c [ ] . however, in humans and other animals, glucose (or other convertible c) is needed to provide the c fragments used in many metabolic paths, since despite the possible excess of c, no c derivatives can be obtained from them. this leaves us with an inefficient system to obtain energy from c when converted to c, and later oxidized via tca cycle. an excess of c can be corrected only either storing it as fat or through its complete oxidation, whilst any excess of c or c can be used by a wider range of metabolic pathways, or ultimately derived into c. the reversible c→ c glycolytic conversion, and the easy entry of c in most cells results in a strategic advantage of distribution, limiting substrate buildups whilst maintaining their full homeostatic availability. this process is sustained by the existence of substrate cycles within adjoining groups of cells in a given tissue, as is the case of muscle [ ] or the brain, between glia and neurons [ ] . the substrate cycles between different organs are widely known, e.g., the cori cycle [ ] or the glucose-alanine cycle [ ] , in which exercising muscle converts glucose to c, later taken up by the liver, prompting gluconeogenesis (i.e., c→ c) with the overall result (cori cycle) of transfer of reducing power from peripheral tissues to the liver [ ] . in this case, the c→ c interconversion helps transfer reducing power (or -amino groups in the case of alanine) to the liver for their reutilization ( figure ) or disposal. this inter-organ coordination prompts a more efficient use of energy and oxygen (and -amino n), helping to maintain the levels and availability of substrates. most of the inter-organ substrate cycles were described as mechanisms preventing the dangers of reducing power or -amino n accumulation in muscle or other peripheral tissues under conditions of active use of glucose or amino acids (i.e., during exercise) for energy; they always present a time-delay component for maximal effectiveness. the exportation of c carrying the excess reducing power or n to the liver has the additional advantage of allowing the return of these c to the blood as glucose, completing a cycle. however, these "cycles" usually work, in real-time, as simple vectors for transfer-"open interrelationships" (figure ), making full use of the differential organ oxygen supply to transfer a reduced c (i.e., lactate) from active muscle to other muscles or the liver to regenerate glucose, resulting in a chain-transfer of reducing power [ ] . this situation can be sustained only when glucose is not in excess (in the liver), since it may block gluconeogenesis [ ] , but the excess reducing power can be easily corrected because of the high liver oxygen supply, removing lactate immediately or after a delay and even after a buildup of acidosis [ ] . the maximal "reduction" of open cycles can be found in the lung, which scarcely uses glucose [ ] but uses blood protons (as the liver do) exported by relatively hypoxic tissues, using their energy at the mitochondria and thus helping limit acidosis [ ] . a special situation is that of adipose tissue; it has been found to generate large amounts of c from glucose [ ] . this process has been suggested to help lower glycaemia (and its associated problems) under conditions of excess substrate availability [ ] . the extent of this transformation is considerable, especially in the mesenteric adipose mass, which receives the mixed c- c results of digestion before sending them via portal vein to the liver [ ] . this peculiarity is not limited to adipocytes, since the adipose stromal cells act in the same way: a practical anaerobic glycolytic conversion of c to c even under full oxygen availability [ ] . this may be considered either as another contribution to regulate glycaemia or as an alternative to produce c fragments (essentially lactate and glycerol) in massive amounts to supply ready-to-use energy to most organs (including the brain) to circumvent the regulatory difficulties of glucose utilization under situations of excess substrate and/or insulin resistance [ , , , ] . the ample use of c as main energy substrate agrees with this interpretation. int. j. mol. sci. , , x for peer review of figure . inter-organ substrate cycles ( c- c). the first and second panels present the cori cycle and glucose-alanine cycle [ ] . the lower panel shows an "open" inter-organ relationship ( c- c) such as that found between the adipose tissue and peripheral organs [ ] . inter-organ substrate cycles ( c- c). the first and second panels present the cori cycle and glucose-alanine cycle [ ] . the lower panel shows an "open" inter-organ relationship ( c- c) such as that found between the adipose tissue and peripheral organs [ ] . curiously, and despite their primeval importance, amino acids seldom are considered quantitatively important substrates for humans in analyses of overall energy metabolism. the most used explanations for this ellipsis are: • the often incomplete hydrolysis of dietary proteins [ ] ; • intervention of microbiota through transformation/catabolism or even synthesis of amino acids [ ] ; • further transformation/catabolism by the intestine and the liver before overall distribution [ ] ; • sparsely known real catabolic pathways for many amino acids [ - ] in humans; • the absence of specific amino acid/protein reserves; • the lack of knowledge on the regulation of essential amino acids; • the gross differences between measured calorimetric pump energy content of proteins and the real energy obtained in vivo from amino acids according to the known (or assumed) metabolic pathways [ ] ; • the assumed relatively small amount of actually oxidized amino acids derived from the diet compared with carbohydrates and lipids; • the uncertainty on how the n of amino acids is processed and excreted [ ] , which directly affects the estimations of dietary amino acid use [ ] ; • the "diversity and complexity" of amino acid catabolism; • the common absence of data on diet protein amino acid composition. in fact, the main question for eluding amino acids from most studies is the lack of knowledge. we do not know yet (in humans) the complete catabolic pathway of several essential amino acids or the implication and compartmentation of the catabolism of amino acids yielding c, c, c, and c/ c intermediates of the tca cycle. to complicate further the analysis, we have only an approximate knowledge on how the dietary protein (in fact, the amino acids resulting from their digestion if assimilated) translates into metabolizable energy. the role of a few amino acids in the maintenance of glycaemia via gluconeogenesis [ , ] is well known, but the focus is now on branched-chain amino acids [ , ] . these amino acids are catabolized to c fragments (leucine and isoleucine) and propionate (valine and isoleucine) [ ] (nor a c but an important anaplerotic precursor of c fragments [ ] ). some amino acids (such as alanine or serine), when oxidized, i.e., after their amino moiety has been removed, yield directly c (pyruvate). others (i.e., leucine, lysine) are mainly broken down to c, but most are oxidized to intermediate metabolites of the tca cycle (e.g., glutamate, aspartate, threonine). a simplified scheme of the fate of hydrocarbon moiety of amino acids is shown in figure . the amino acid hydrocarbon skeletons can, thus, provide c or (in a higher overall proportion) c, but also the high-energy containing c and c fragments, which, eventually will be converted into c along the tca cycle, hence their importance for gluconeogenesis under conditions of severe energy stress. however, the use of c for -ketoacid synthesis is almost nil, widening the c- c chasm. in fact, the variation of amino acid catabolic pathways results in a simplified handling of their complexity-losing in some cases energetic efficiency in the process-for gross energy purposes (as shown in figure ) than usually believed. as to the aspects of regulation cited above, we are yet in a serious state of ignorance, with few exceptions. catabolized to c fragments (leucine and isoleucine) and propionate (valine and isoleucine) [ ] (nor a c but an important anaplerotic precursor of c fragments [ ] ). some amino acids (such as alanine or serine), when oxidized, i.e., after their amino moiety has been removed, yield directly c (pyruvate). others (i.e., leucine, lysine) are mainly broken down to c, but most are oxidized to intermediate metabolites of the tca cycle (e.g., glutamate, aspartate, threonine). a simplified scheme of the fate of hydrocarbon moiety of amino acids is shown in figure . fragments, which revert essentially into c and c, during the human catabolism of amino acid hydrocarbon-skeletons. the pathways used to prepare this graph are the most common, including the main alternate pathways [ ] . the green lines show the carbon paths for each amino acid, the brown lines represent the relationship between the core of the tca cycle and pyruvate dehydrogenase (with the loss of one co between each substrate group box (marked in yellow). nonstandard abbreviations: hyp = l- -hydroxyproline; orn = ornithine; " c" = one-carbon fragment donor systems. the amino acid hydrocarbon skeletons can, thus, provide c or (in a higher overall proportion) c, but also the high-energy containing c and c fragments, which, eventually will be converted into c along the tca cycle, hence their importance for gluconeogenesis under conditions of severe energy stress. however, the use of c for -ketoacid synthesis is almost nil, widening the c- c chasm. in fact, the variation of amino acid catabolic pathways results in a simplified handling of their complexity-losing in some cases energetic efficiency in the process-for gross energy purposes (as shown in figure ) than usually believed. as to the aspects of regulation cited above, we are yet in a serious state of ignorance, with few exceptions. figure . summary of the final conversion of dietary protein amino acids in c, c, c, c, and c fragments, which revert essentially into c and c, during the human catabolism of amino acid hydrocarbon-skeletons. the pathways used to prepare this graph are the most common, including the main alternate pathways [ ] . the green lines show the carbon paths for each amino acid, the brown lines represent the relationship between the core of the tca cycle and pyruvate dehydrogenase (with the loss of one co between each substrate group box (marked in yellow). non-standard abbreviations: hyp = l- -hydroxyproline; orn = ornithine; " c" = one-carbon fragment donor systems. from an evolutionary point of view, our design evolved to preserve -amino n, since we cannot significantly use other sources of -amino n than amino acids themselves (obtained from dietary protein). all amino acids are synthesized by plants (and other phyla) and used to build their own proteins. we use (eat and digest) these same proteins to obtain the amino acids we need to form our self-proteins and other n-containing molecules (e.g., purines, pyrimidines, porphyrins, etc.). all our amino acids have been obtained (from the diet) either preformed-e.g., essential amino acids-or rebuilt by us from available hydrocarbon structures and -amino n suppliers, i.e., amino acids from plant or animal (formerly "plant") sources. since we are omnivores, the dietary protein is just another source of energy, used, for this purpose, in proportions that depend on their availability [ , ] . thus, the complex safety measures established to retain amino acid n necessarily should interfere with their utilization for energy. nevertheless, it is obvious that essential amino acids are continuously oxidized for energy irrespective of their source: if there are not changes in body protein (in addition to the "obligatory" protein losses: box ), the amount of these amino acids ingested in the diet should tally their oxidation, since they cannot be stored. source of energy, used, for this purpose, in proportions that depend on their availability [ , ] . thus, the complex safety measures established to retain amino acid n necessarily should interfere with their utilization for energy. nevertheless, it is obvious that essential amino acids are continuously oxidized for energy irrespective of their source: if there are not changes in body protein (in addition to the "obligatory" protein losses: box ), the amount of these amino acids ingested in the diet should tally their oxidation, since they cannot be stored. the main, basic studies on our handling of diet amino acids, protein synthesis, and recycling of amino n were done essentially more than half century ago, and they were invariably focused on the ways to preserve n, the mechanisms to survive under conditions of starvation [ ] , dietary protein deprivation [ ] and, globally, malnutrition [ , ] . amino acids as energy staple have been, since, considered "secondary" (or at most "complementary"), and their assumedly "complex" metabolism was oversimplified around their possible use as gluconeogenic substrate under glucose deficits or generators of ketones (ketogenic) during starvation [ ] . the epidemic nature of obesity, developed thereafter, and the need to find ways to cope with its ravages were centered on glucose and fats, a situation that continues with limited global interest on amino acids as energy substrates under conditions of plenty [ , ] . the key problems that remain and prevent further advances in the main, basic studies on our handling of diet amino acids, protein synthesis, and recycling of amino n were done essentially more than half century ago, and they were invariably focused on the ways to preserve n, the mechanisms to survive under conditions of starvation [ ] , dietary protein deprivation [ ] and, globally, malnutrition [ , ] . amino acids as energy staple have been, since, considered "secondary" (or at most "complementary"), and their assumedly "complex" metabolism was oversimplified around their possible use as gluconeogenic substrate under glucose deficits or generators of ketones (ketogenic) during starvation [ ] . the epidemic nature of obesity, developed thereafter, and the need to find ways to cope with its ravages were centered on glucose and fats, a situation that continues with limited global interest on amino acids as energy substrates under conditions of plenty [ , ] . the key problems that remain and prevent further advances in this direction are the diversity of metabolic pathways used to oxidize the hydrocarbon skeletons of amino acids, the relatively unknown mechanisms to retain essential amino acids, and, especially, the not yet clarified variable fate of the n moiety of amino acids during their catabolism. the canonic mechanism of excretion of the n moiety waste is the urea (or krebs-henseleit) cycle [ ] (the "first" krebs' cycle [ ] ), a very peculiar pathway between cytosol and mitochondria. it may also harbor a shunt to generate nitric oxide (no·) and citrulline from arginine [ ] . the daily losses of n via the no· pathway are a fraction of the overall n excretion, essentially made up from nitrogen oxides released through respiration [ ] (a few µg/day) or further oxidized to nitrite, nitrate, and other nitroxylated compounds [ , ] , which are excreted via saliva, urine, and stool [ , ] . however, there is proof of an additional, quantitatively significant, excretion of n as gas through respiration [ , ] that is supplementary to the standard and well-controlled urea excretion. when analyzing in detail n balances in experimental animals, the amount of n ingested is higher than the sum of the n accrued in the body and the n excreted and accounted for [ , ] (box ). the proportion of this "nitrogen gap" (assumedly n ) is in the range of - % of all nitrogen ingested and not accrued (i.e., it is actually excreted), and its amount is related to diet and energy status [ , ] . it has been found that this n loss is related to arginine metabolism [ ] (figure ). excretion. when analyzing in detail n balances in experimental animals, the amount of n ingested is higher than the sum of the n accrued in the body and the n excreted and accounted for [ , ] (box ). the proportion of this "nitrogen gap" (assumedly n ) is in the range of - % of all nitrogen ingested and not accrued (i.e., it is actually excreted), and its amount is related to diet and energy status [ , ] . it has been found that this n loss is related to arginine metabolism [ ] (figure ). the nitrogen "gap: in rats. a "nitrogen gap" was found when analyzing all the components of the nitrogen balance in young rats: i.e., the n ingested, that excreted by urine and feces as well as the total n accrued, thus proving the existence of a sizeable part of the n excreted not as urea, or through the other possible ways and means shown in box . different complete (measuring both sides of the n balance equation) studies repeated these findings, dependent on diet, and with a magnitude (in rodents at least) in the range of - % of all nitrogen excreted. redrawn with data from esteve et al. [ ] . in fresh-water plants [ ] or fish [ , ] living under high (cytotoxic) ammonia concentrations, the levels of no· are high, and the production of no· is increased several fold on exposure to ammonia, assumedly potentiating its oxidation [ ] . the most suggestive process is that of the anammox (anaerobic ammonia oxidation) bacteria [ ] , which assumedly use nox, probably via no· to oxidize nh + coupled to the reduction of no· [ ] . both ammonia and nitrite or nitric oxide can react spontaneously in an exothermic reaction, yielding n and water [ ] , provided that ammonia is protonated to ammonium and the extra electrons are removed figure . the nitrogen "gap: in rats. a "nitrogen gap" was found when analyzing all the components of the nitrogen balance in young rats: i.e., the n ingested, that excreted by urine and feces as well as the total n accrued, thus proving the existence of a sizeable part of the n excreted not as urea, or through the other possible ways and means shown in box . different complete (measuring both sides of the n balance equation) studies repeated these findings, dependent on diet, and with a magnitude (in rodents at least) in the range of - % of all nitrogen excreted. redrawn with data from esteve et al. [ ] . in fresh-water plants [ ] or fish [ , ] living under high (cytotoxic) ammonia concentrations, the levels of no· are high, and the production of no· is increased several fold on exposure to ammonia, assumedly potentiating its oxidation [ ] . the most suggestive process is that of the anammox (anaerobic ammonia oxidation) bacteria [ ] , which assumedly use nox, probably via no· to oxidize nh + coupled to the reduction of no· [ ] . both ammonia and nitrite or nitric oxide can react spontaneously in an exothermic reaction, yielding n and water [ ] , provided that ammonia is protonated to ammonium and the extra electrons are removed no + nh this is a reaction very similar to the integral oxidation of ammonia with nitrite [ ] , which can be reproduced very easily in the laboratory with minimal means. n is also produced by the reaction of nitrite with amino acids at low ph [ ] . the abundance of nitrite produced in the inactivation of no· could justify a small part of the production of n , in part via its reaction with amino acids [ ] . however, this process has been studied under conditions seldom found in a living human [ ] . nitrite may react more easily with ammonia, but their low circulating levels [ ] , and the small area of diffusion of newly-created no·, in the µm range, may prevent this reaction taking place, except, perhaps, in the gut lumen, where the levels of ammonium and no· (but not the environmental conditions) may be higher [ , ] . however, the fact that in axenic rodents the excretion of n is unchanged [ ] hint at the existence of a less "occasional" and regulated source for the production of n . the mechanism of nitrogen gas synthesis from ammonia used by anammox bacteria suggests a possible pathway in which this oxidation is carried out in two steps [ ] : evidently, the hypothesis we presented in figure with respect to the postulated origin of n from the mitochondrial reaction of ammonia and no· has a serious weak point, since, as far as we know, the enzymes that allow the oxidation of ammonia by no· (under anaerobiosis) are exclusive of anammox bacteria. however, the possibility of hydrazine being an intermediate step in the process could not be fully discarded given its limited toxicity (it has been used for the treatment of tuberculosis and cancer [ ] ) and its widespread effects on amino acid metabolism [ ] . inactivation of no· could justify a small part of the production of n , in part via its reaction with amino acids [ ] . however, this process has been studied under conditions seldom found in a living human [ ] . nitrite may react more easily with ammonia, but their low circulating levels [ ] , and the small area of diffusion of newly-created no·, in the µm range, may prevent this reaction taking place, except, perhaps, in the gut lumen, where the levels of ammonium and no· (but not the environmental conditions) may be higher [ , ] . however, the fact that in axenic rodents the excretion of n is unchanged [ ] hint at the existence of a less "occasional" and regulated source for the production of n . the mechanism of nitrogen gas synthesis from ammonia used by anammox bacteria suggests a possible pathway in which this oxidation is carried out in two steps [ ] : evidently, the hypothesis we presented in figure with respect to the postulated origin of n from the mitochondrial reaction of ammonia and no· has a serious weak point, since, as far as we know, the enzymes that allow the oxidation of ammonia by no· (under anaerobiosis) are exclusive of anammox bacteria. however, the possibility of hydrazine being an intermediate step in the process could not be fully discarded given its limited toxicity (it has been used for the treatment of tuberculosis and cancer [ ] ) and its widespread effects on amino acid metabolism [ ] . figure . hypothesis for the origin of ammonia and nitric-oxide generation of nitrogen gas in mitochondria. the coexistence in the liver mitochondrial matrix of both ammonia/ammonium and nitric oxide, within well-regulated pathways, in significant amounts, and related to the urea cycle, figure . hypothesis for the origin of ammonia and nitric-oxide generation of nitrogen gas in mitochondria. the coexistence in the liver mitochondrial matrix of both ammonia/ammonium and nitric oxide, within well-regulated pathways, in significant amounts, and related to the urea cycle, suggests the possibility of a reaction which may generate nitrogen gas at the expense of both. this is a speculative hypothesis, which has not been proven so far. in any case it is difficult to justify the presence of both reactants in a relatively high concentration without interacting, since the uncontrolled chemical reaction between them is spontaneous and exergonic. in this hypothesis, we include the findings of kartal et al. [ ] in their study of the mechanism of ammonia oxidation in anammox bacteria, which has an intermediate metabolite between them, hydrazine (n h ). the two enzyme activities of the complex hydrazine synthase and hydrazine dehydrogenase are intimately related to membrane of the anammoxosome particle. ammonia and nitric oxide are both produced in significant amounts in the mitochondria: ammonia through-mainly-glutamate dehydrogenase [ ] and glutaminase [ ] , and no· via no· synthase [ ] (figure ). one can speculate that within the mitochondria, the reaction can take place through a regulated mechanism. the main problems for this hypothesis to be confirmed are the so far unidentified catalyzer system, and the question of the low solubility of n in biological fluids but not on fat tissue, several-fold higher than in plasma [ , ] , to carry the gas away to be exhaled in respiration. this type of shunt is, probably, the base for the known excretion of n gas under certain circumstances (high arginine, high protein) resulting also in excess ammonium in the mitochondria [ ] . this uncharted metabolic path is affected by diet, sex, and excess energy and amino-n availability [ , , ] , and constitutes an example of our extremely low level of knowledge on the mechanisms and factors that govern substrate energy partition. this uncertainty affects seriously any quantitative study on this subject. we need (and thus maintain) reserves of all possibly scarce materials we need: essential metals, ions, sulfur, selenium, some vitamins, and especially -amino-n. evidently, we also store energy. the balance between reserves, their type and the problem of carrying them as part of our body weight has been extensively studied, but often, we tend to maintain excessive long-term reserves of lipid ( c n ). we retain a lower amount of c n reserves (glycogen) for hypoglycemic emergences, and we also keep a small supply of phosphagens for immediate support to the first line of response (atp). metabolic syndrome (ms) and similar conditions related to excess of energy supply create havoc with the management of reserves, since the unmanageable excess of c tends to end as lipid, which is massively stored for lack of alternatives. this problem derives largely from our taste for fat [ ] (inherited from our ancestors because of its high energy density), perhaps helped by our ingrained memories of lactation [ ] and the availability of "tasty" lipid-rich foods [ ] ; but it is also derived from an unbalanced supply of energy (especially in excess) of c vs. c as a main energy staple [ ] . our main (from a quantitative energy content point of view) physiological reserves are made of fat because wat contains up to % tag (in the range of mj/kg) [ ] ; thus, a few kg of wat may provide enough energy for our basic sustenance for months (table ). its main advantage is the high energy densities of fat and the adipose tissue holding it, especially when compared with polysaccharides. our reserves of glycogen are small [ ] and were devised to sustain glycaemia for a short time, since glycogen contains about half the energy than fat (on a dry weight comparison basis). in addition, it is highly hydrophilic and retains a large amount of water (added weight, limiting its accumulation in significant amounts) [ ] . a high weight (including water) with respect to energy content limits movement excessively in exchange for short-lived reserves; thus, the main reserves, the more effective in terms of energy/weight are lipids. however, their real effectiveness depends on the body mass of protein [ ] . [ ] . the data in the a part of the table were taken from frayn [ ] , modified with results of [ ] and including unpublished data in the calculations. we used standard body weights for men ( kg) and women ( kg) to homogenize the data. we assumed that from the whole body protein, only about % may be used (allowing recovery) under starvation to cover the body's energy needs. this datum was calculated from a study of long-term food deprivation in rats [ ] . similarly, an arbitrary limit of % minimum of body fat (i.e., not available for energy mobilization) was introduced in the calculations for lack of direct references. no information has been added with respect to more "immediate: energy reserves, such as phosphagens (e.g., creatine-p) and atp because of their low global energy entity in comparison with the three main storage pools described here. the data in the part b of the table were calculated only for plasma (i.e., estimated from blood volume minus blood cells, using normal standard concentrations, and a hematocrit value of . here, instead of referring the substrates to their energy content, we used molar concentrations, since they were the primary data. the main theoretical problems posed by body fat reserves are essentially two: a) its use as storage of energy may derive into being a c dump when energy intake is excessive, driving to obesity, inflammation and ms [ ] ; and b) we need, specifically, glucose/ c for inter-organ supply of energy. thus, sources of c should be taped to preserve our homeostasis under conditions of severe scarcity; even when there is a large excess of c reserves available, we keep needing a steady supply of c, which often requires the sacrifice of protein [ ] . in practical terms, the main c "reserve" of the body are the proteins (irrespective of their functionality). however, since we do not have protein reserves as such, we have had to rely on misadjusting the overall turnover rates to degrade faster and synthesize less protein [ ] , draining the amino acids freed to generate c, especially during starvation [ ] . the data shown in table are only general approximations, but the figures of storage substrates and circulating compounds used with different intensity as nutrients throughout the whole body illustrate clearly the enormous difference between the make-up of c substrates and the c ones that may be used for functions other than the generation of energy through the tca cycle. the c/ c ratio for all added-up energy reserves in normal weight healthy adults is about -fold higher when considering body reserves than when we analyze the nutrients carried by blood plasma. this highlights the differences (even with all logical caveats considered) between what is the homeostatic internal medium composition, akin to our immediate substrate supply needs, and what we have retained. the weight of c is overwhelming. in table , we have intended to obtain a value of the c /c ratio in the human diet. the problem is the absence of data (especially on protein composition of the enormous varieties of diets) we analyzed the c /c ratio for a "theoretical" adult healthy human eating a standard diet, such as those being recommended for a "healthy nutrition" by most specialists. the results were again shocking: the final ratio of the standard diet was in the range of / th of that of our "normal" body composition, and it was more than five times higher than the plasma nutrient ratio. these differences stress an innate deficit of c yielding substrates, necessary to maintain energy homeostasis with respect to the energy stores, strongly decanted toward the c supply, making a large part of these reserves not physiologically usable and, in fact, only "dead weight". this unchecked domination of c sources hint that our standard diets are probably inadequate, chosen more because of factors different from the best metabolic adequacy (taste, availability, social or historical factors, etc.). the recommendation of such types of diet adds to the problem they pose, since recommendations are based on population statistics with no 'controls' to refer to. they are not based on sound biochemical metabolic comparative data, simply because they have not been (sufficiently) investigated. the consequences are crystal-clear: a growing pandemic of diet-borne disorders, essentially undiagnosed, not treatable and affecting a large (and growing) proportion of our society. we used standard consensus-recommended diet compositions [ , ] adapted for a kg healthy adult man, assuming his body weight remains without changes (goals expressed by the who and efsa in the references cited above), that is with no accrual neither losses. the intake was adjusted to . mj/d ( kcal/d or w). obviously, the distribution in final metabolites for protein may be subjected to wider changes than lipids and carbohydrate, depending on the protein sources of the diet. we have not found published data for population-wide analysis of amino acids for diet protein composition related to complete and time-sustained normal human diets. in order to get an approximation to the sought data, we used instead data for rat cafeteria diet of previous studies from our research group [ , ] , on the assumption that the "cafeteria" diet was devised to mimic the usual consumption of food of young humans late in the past century in urban westernized settings [ ] . in the rat cafeteria diet used, the amino acid residues had a mean mw of . it is important to add an additional commentary on the methodology we use at present with diet (food) analyses. despite the considerable difficulties, assumptions and techniques available, the classical study of atwater [ ] remains the "current" basis for our energy intake/expenditure calculations. in decades, science has changed considerably, and precision is one of the critical points for accepting such widely used data. a recent critical analysis of the methodology used by atwater but applying present-day criteria [ ] showed that a significant deviation of the original data exists, and that we urgently need methodology more adapted to today's conditions. the dynamic situation of lipid reserves is clear and understandable. what is not is the reason why some body fat seems impossible to mobilize even using very-low energy diets [ , ] even with metabolic situations close to starvation, which resulted in scant (if any) mobilization of part of the fat reserves [ ] , often in spite of real body weight losses (water, protein, minerals). the extra weight and the inflammation accompanying the excess of adipose tissue fat are severely detrimental for the health and normal energy handling, and are maintained without any apparent reason [ ] . our energy metabolism overall can sustain, in a large proportion, the substitution (as energy substrates) of part of carbohydrate ( c-givers) by lipid ( c-providers). carbohydrate may be compensated in part by protein [ ] . however, the n moiety of protein and some amino acids could not be substituted (but we can lower our needs by modulating turnover rates) [ ] . these compensations include the use of internal reserves (mainly lipid) but also, in part, the lowering of the body protein pool [ ] . these measures do follow well-established priorities in the use of energy substrates (or, in the end, any substrate) ingested, and, when insufficient, compensated with the use of reserves [ ] . the order of precedence in consumption (that of preservation is just the reverse) [ ] is essentially: lipid ( c)→ carbohydrate ( c)→ protein (amino n) diet takes precedence in their use for energy over reserves, but changes in the diet may modify some of these evolutionary rules of precedence, thus protein is needed for lipid oxidation and to prevent its storage [ ] . these mechanisms were developed, and refined with efficient regulatory mechanisms, to enhance survival by maintaining energy homeostasis under conditions of insufficient food availability (including starvation), and incorporating the hypothesis of thrifty genes and their possible incidence in the development of diabetes/obesity [ , ] . however, we have not established a metabolic process (spendthrift) to cope with a simultaneous excess of energy and of all main nutrient classes in the diet. no process has evolved to solve this situation because this is a peculiarity, affecting practically only our species, which appeared in a very short time (in evolution terms) [ ] . the trend is fueled in part by the setting of epigenetic traits favoring the development of obesity, despite its real deleterious effects [ , ] . we have no historical evolutionary memory on how the problem of excess can be handled, since our tools are useful only to counter scarcity, and thus, the mechanisms/processes applied are often not only inadequate, but self-defeating and harmful. we ingest food for energy and growth/maintenance. evidently, a large part of the main substrates (amino acids, fatty acids, sugars and intermediate metabolites, as well as most essential components) are used in connection with turnover strategies of our own living matter, in order to maintain all mechanisms in their prime efficiency. however, from a theoretical (quantitative) point of view, intake should match excretion and energy loss (assuming that there is no real change in our mass) [ , ] . thus, the main types of substrate we ingest for energy (with all provisos stated above) belong to three groups: amino acids (n providers), c and c providers. after a large portion of amino acids is sieved and selected, they revert largely to "excess n" plus c, c and c (tca cycle intermediates) (figures , and ). the final proportion of c and c available during a certain stretch of time depends on digestion, rhythms etc., but we can just center the question in basic one-day periods. under no-growth conditions (i.e., no additional storage of energy: only turnover) almost all c will end as a source of energy via tca cycle. c have a higher variability of uses, but at last, all excess c is converted to c, which is then oxidized for energy (or stored as fat). if there is a large excess of amino acids, the elimination of n stresses the c/ c setup, both because of anaplerotic enhancement of tca cycle (via c) and an intense pressure for growth, which increases protein synthesis and "storage" as body protein. most of these effects/mechanisms remain rather unknown, because almost never come alone, and are largely mediated via gene expression and hormonal modulation affecting select different groups of cells. a large part of nutrients is used with little change (if any) for turnover (e.g., amino acids, fatty acids, glucose, etc. for, respectively, proteins, tag or glycogen), or to build-up reserves (i.e., fatty acids) or (almost all compounds) for growth and reposition of live matter lost (i.e., hair, epithelial cells or secretions). amino acids could not be substituted from the point of view of reposition and turnover, as well as for the synthesis of other n-containing body components. carbohydrates may be substituted, largely, by protein, but the loss of energy in the complex catabolism of some amino acids, plus the need to dispose-of -amino n markedly limits the extent of this substitution. on the other side, lipids (e.g., tag, but not including the essential fatty acids) can be entirely substituted because their sole specific metabolic contribution is to provide large amounts of c, which we are prepared to compensate with protein and, essentially carbohydrate. an excess of c, on the other side, limits the utilization of dietary fatty acids, which are then incorporated to the stored fat reserves, without previous oxidation to c [ ] . this is an efficient way to store dietary energy, quite different from the energetically expensive lipogenesis from acetyl-coa [ ] . this c molecule is also in excess (limited by the availability of coenzyme a because of insufficient capacity of the tca cycle to oxidize it, since reducing power/atp are produced on demand. this is compounded by limited lipogenesis, restrained because of the excess of dietary fatty acids [ ] . the large acetyl-coa availability, due to its limited need, inhibits the oxidative decarboxylation of pyruvate, the critical c→ c unidirectional process [ ] , thus secondarily provoking an unwanted accumulation of c. in parallel, glycolysis is also limited because of insufficient c removal [ ] , which results in lower glycolytic processing of c, which adds to the excess carbohydrate provided by the diet together with the unneeded excesses of dietary amino-n and fatty acids (figure ). acids [ ] . the large acetyl-coa availability, due to its limited need, inhibits the oxidative decarboxylation of pyruvate, the critical c→ c unidirectional process [ ] , thus secondarily provoking an unwanted accumulation of c. in parallel, glycolysis is also limited because of insufficient c removal [ ] , which results in lower glycolytic processing of c, which adds to the excess carbohydrate provided by the diet together with the unneeded excesses of dietary amino-n and fatty acids (figure ). figure . partition-related substitution of nutrients in the diet to fuel the metabolic processes. this graph intends to explain the absence of a total/complete substitution capability between the three main groups of nutrients: protein, carbohydrate and fat, which constitute most of our diet, at least from an energy point of view. solid lines show the direct relationship between the groups of figure . partition-related substitution of nutrients in the diet to fuel the metabolic processes. this graph intends to explain the absence of a total/complete substitution capability between the three main groups of nutrients: protein, carbohydrate and fat, which constitute most of our diet, at least from an energy point of view. solid lines show the direct relationship between the groups of substrates. the large red line emanating from c represents the oxidation of acetyl-coa in the tca cycle to obtain most of the energy we use. the thinner red dash-lines indicate other main sources of cell atp, adding up to the sum of energy available to cover our needs. part of our food is made up of other components (minerals, organic micro-components, fiber, etc.). their relationships with other compounds are marked with purple lines. sobc stands for: "synthesis of other body components" from the building blocks provided by the four groups of nutrients analyzed. their mixed paths have been marked in black. the lines in blue represent the metabolism of carbohydrates, including the part shared with amino acids and lipid. protein-amino acid paths are marked in green. the lines in dark yellow represent the paths exclusive of lipids. the serious difficulty lies on the iterative nature of the process along time. a few days of excesses can be modulated in part by decreasing appetite and voluntary intake [ ] , increasing protein turnover [ ] , thermogenesis [ ] and topping the reserves of glycogen and fat [ ] . nevertheless, these 'solutions' work only to a certain degree, not in a permanent way, and create a regulatory havoc that cannot be sustained indefinitely. the emergency measures only patch, do not solve the problem, it is just metabolic procrastination, and in short time deep problems begin to develop [ ] ; and shortly afterward, they also become chronic [ , ] . the excesses of substrates could not be disposed of, and the regular mechanisms of partition cannot function in a fluid way. obviously, oxidation of c is enhanced, but what to do with the unused atp? in a global setting, thermogenesis helps, but not at the level of each cell (largely those in the splanchnic bed). then, the priorities list ingrained in our metabolic control systems retake their place of reference. save as many amino n as possible and take special actions to prevent the toxicity of nh , perhaps via the alternative "nh + no·" production of n . • limit the processing of fatty acids to c fragments and thus dump them as tag (with a token c glycerol) [ ] . this process induces obesity [ ] , steatosis [ ] , and drives muscle to be essentially a fat-infiltrated c energy user, with glucose intolerance [ , ] . the toxicity of glucose (the same occurs with the excess of ammonia) represents an immediate danger that cannot be "stored" (as are the fatty acids in tag). the insulin basic controlling mechanisms of glycaemia no longer function properly [ ] , in fact they interfere, limiting the peripheral utilization of glucose as substrate [ , ] . hyperglycemia is a problem [ ] which is in part corrected by the conjunctive tissue (including adipose tissue), which actively takes up glucose and returns c to the blood [ ] . most tissues may work (including the brain) perfectly using c (largely lactate and glycerol) [ ] [ ] [ ] ] . thus, the blockage of liver metabolism, in its ↑ c-↑ c no-win situation, is in part corrected by an adipose tissue (also inflamed, engrossed by the excess lipid storage [ ] ) which generates large amounts of c at the expense of glucose [ ] . it also produces urea cycle intermediates, probably to compensate in part for the decreased capacity of the liver [ , ] . return to normalcy from the excess-driven picture of energy metabolism is difficult. the search for drugs is not a viable solution, because the problems observed have a known origin, and the severity of the damages is largely a consequence of the mechanisms established to ensure survival under scarcity. we cannot fight these mechanisms because a) we do not know them enough, b) we need them to sustain our "normal" homeostasis, and c) they have to be operative to achieve that normalcy. right now, the main systems in use to fight obesity are-essentially, and despite their limited effect-diet and exercise; but, what type of diet? hypocaloric? under starvation, the stored fat is progressively shed to last as much as feasible; our bodies adapt to lower energy, lower carbohydrate and limited protein intake diets, including the absence of fats, following the blueprints for starvation [ ] . the elimination of dietary carbohydrates [ , ] and lowering of energy intake share some characteristics, because of our adaptability to starvation, but there is a considerable discussion on the proposed benefits of ketogenic diets, which, in any case, could not be generalized from epilepsy to obesity [ ] [ ] [ ] . nevertheless, even after prolonged starvation or removal of dietary carbohydrates, a significant portion of body fat remains, even after prolonged exposure. unfortunately, in the practice and for most obese people, dietary treatments remain not effective [ ] . exercise is an alternative to increase energy expenditure with (or even without) restricted intake [ , ] . this approach is not always feasible, since obesity is syndromic with cardiovascular disease and problems of mobility [ ] and, despite numerous claims on the contrary, exercise it not sufficient to revert the damages of an established ms [ ] , and may not improve the health status [ ] . however, well dosed exercise may provide benefits to mild cases and young patients [ ] . in addition, the effectiveness of exercise is also limited from the point of view of energy: limited duration, limited proportion of increase in overall energy consumed, consequences in the availability and transport of oxygen and products of substrate oxidation. in fact, exercise is better suited to maintain functionality [ ] (when applicable) than to fight obesity. the chronicity of the "excess situation" described above, usually continue even when the dietary excesses cease. too often, very low-energy dieting and exercise combined (even using additional anti-obesity approaches) are unable to eliminate the excess fat and reverse the damages already induced by (or accompanying) this excess deposition. the size of fat depots is a critical point for the severity of the disorders and a barrier to a progressive and effective removal, often leaving only the alternative of surgical modification of nutrient intake [ ] . however, none of these procedures can revert the metabolic homeostasis to the situation prior to depot engrossment. nevertheless, drastic treatments may extend the patient life span, improve the lifestyle and ameliorate a few components of the ms [ , ] , but not cure it or its associated pathologies. the corollary to this exposition is our extreme resilience to change in the energy (and nutrient) equilibrium, which allows us to cope with the situation for a time and then alter, in a probably irreversible (and unknown) way, the common mechanisms for nutrient partition in a situation far from normal, which could not be sustained indefinitely. however, these changes allow a number of affected individuals to keep living despite the severe damages to metabolic processes and their control. a deeper layer of thought (and thorough research) are needed to understand how people can survive decades under ms conditions. probably, excess body fat is directly related to the severity of the disorder it causes: it is commonly accepted that the body mass index vs. mortality curves are u shaped [ ] . however, this index is not a real indexed measurement of the body fat content, and parallel studies analyzing body fat vs. mortality showed a lineal direct relationship [ ] . nevertheless, a certain degree of obesity helps protect the patient from some cardiovascular diseases [ ] . the discussion about the causes of the obesity paradox or even its existence continue, but part of the problem may lie on the inadequate use of body mass index to "measure" obesity [ ] , and the question of whether obesity is by itself a disease (or simply a part of a more severe disorder such as ms). the repeated references to "healthy obesity" (i.e., large body fat stores without the associated metabolic disorders of "proper" obesity) [ ] , have been relatively circumscribed by introducing factors such as age and gender [ ] . our group has postulated that a certain degree of obesity may help limit the ravages of type diabetes by removing excess glucose and releasing c, being more a (palliative) consequence than a cause for this disease [ , ] . in any case, the question is not settled, and perhaps there is also a margin for optimal (and not rigidly low, invariable and universal) mass of body fat reserves other than the one used at present. under conditions of excess energy intake, the metabolic handling of substrates is parallel to modifications in the hormonal mechanisms that regulate energy metabolism [ ] , since the main system of regulation of glycaemia (insulin) has been severely damaged [ ] . the other mechanisms complementary to insulin have a wider array of functions: the glucocorticoids, favor liver glucose output under conditions of stress or metabolic distress [ ] . glucocorticoids also affect the fate of the main gluconeogenic precursors, amino acids, and altering the excretion of n [ , ] . testosterone pairs with insulin as a main anabolic hormone [ ] , but glucocorticoids tend to limit testosterone production and availability [ ] , also affecting the availability of estrogen [ ] , which plays a critical function favoring the oxidation of c (i.e., saving c) in females [ ] via direct intervention in mitochondrial function [ , ] , and also preventing liver steatosis [ ] . an estrogen-derivative has been found to down-modulate the adjustment of the ponderostat, i.e., the oxidation/mobilization of lipids from adipose tissue [ , ] , by decreasing food intake and maintaining thermogenesis [ ] . unfortunately, there is insufficient mechanistic information on the effect of estrogen derivatives because only recently these hormones are considered important metabolic regulators [ , ] and act not only in the sex-related way indicated by its etymology. substitutive testosterone treatment normalizes the glycaemia of mature and old men, a situation that is slowly being accepted by endocrinologists (diabetologists, in fact) [ , ] after being a mainstay of the treatment of ms aging-related disorders by gerontologists [ ] . its soothing effect on the ms ravages [ ] is complemented by the already known effects of estrogen on energy partition [ , ] , limiting the storage of lipids. most of present-day studies on obesity (and of ms, as an afterthought) are focused on cytokine and regulatory circulating rna types [ ] and the paths they modulate, which add considerable knowledge on the possible regulation of their mechanisms of action, but not on the causes/mechanisms of the disorders or the ways to prevent and treat them. figure shows a simplified scheme of the main hormone-controlled mechanisms regulating glycaemia. partition [ , ] , limiting the storage of lipids. most of present-day studies on obesity (and of ms, as an afterthought) are focused on cytokine and regulatory circulating rna types [ ] and the paths they modulate, which add considerable knowledge on the possible regulation of their mechanisms of action, but not on the causes/mechanisms of the disorders or the ways to prevent and treat them. figure shows a simplified scheme of the main hormone-controlled mechanisms regulating glycaemia. in the liver, glucocorticoids increase glucose output [ ] and favor lipogenesis [ ] and tag deposition in most tissues [ ] ; testosterone induces the accrual of protein [ , ] and stabilizes the maintenance of glycaemia [ ] . estrogens favor c oxidation [ ] , increase oxidative metabolism in mitochondria [ ] , and limit lipogenesis and tag deposition [ ] . the role of these steroid hormones on the direct modulation of glucose is less clear, despite the large number of agents and effects uncovered. we already know a part of the puzzle, but there are not yet enough dots to draw a sufficiently clear line to understand their real function and help us fight the ravages of our own (effective) systems of protection of energy and protein. in the liver, glucocorticoids increase glucose output [ ] and favor lipogenesis [ ] and tag deposition in most tissues [ ] ; testosterone induces the accrual of protein [ , ] and stabilizes the maintenance of glycaemia [ ] . estrogens favor c oxidation [ ] , increase oxidative metabolism in mitochondria [ ] , and limit lipogenesis and tag deposition [ ] . the role of these steroid hormones on the direct modulation of glucose is less clear, despite the large number of agents and effects uncovered. we already know a part of the puzzle, but there are not yet enough dots to draw a sufficiently clear line to understand their real function and help us fight the ravages of our own (effective) systems of protection of energy and protein. man's main energy staple has been, in the last millions of years, of plant origin: seeds, starchy roots or other plant energy reserves, fruits, leafy foods, complemented with some products of animal origin. humans have evolved in parallel to their nutrition [ ] . foods from animals have been increasing their share with time [ ] , and our diets are clearly adapted to our pre-human (but pervading) basic food taste types. less exercise, better medical attention, longer lives and control of the sources of food have modified our present-day diets. culture, unproven ideas about food have been combined with religious or social taboos, increased availability of different presentations of food and the culture-driven extreme cult to taste. we are leaving starches to consume fats [ ] , and animal muscle protein and collagen instead of aleurone-like plant reserves [ ] . however, our digestive system and metabolic energy handling systems were adapted to a quite different diet [ ] , and have not been able to maintain the pace of change in eating habits occurring in the last centuries [ ] .thus, a gap between digestive system/nutrient utilization and diet composition exists and keeps growing. glucose continues being the main energy substrate, in spite of everything else, but its food form, ingestion, digestion, handling, and oxidation necessarily change with the composition of the diet. however, that of neanderthals showed little differences with our present day optimal diet types [ ] . the periodicity, the ratio of energy consumed (or needed) for a straightforward metabolic equilibrium versus that actually ingested is a powerful destabilizing factor for an effective maintenance of metabolic equilibrium. activity, feeding, light and internal rhythms control our hormones and metabolism, helping us to adapt to the variable conditions of the environment [ ] . probably this imbalance is a main cause of the ms together to the fattening of the diet [ ] . considerable observation and experimentation have shown that amino-n should be a part of our diet (in the range of - % of ingested energy) [ ] ; and, also, that protein should be ever present in our meals [ ] . this implies that we also need to ingest an adequate supply of a few special amino acids we cannot synthesize [ ] . in parallel, we also know that, today, most humans are taking in too much fat in their diets [ ] , often over % of all energy ingested [ , ] . an effect compounded by the ingestion of energy above our physiological needs [ ] . there is little quantitative analysis of necessities, amounts and proportions, as explained in detail above. these approximate proportions are quite different from those of all present-day apes, even more than most of the other primates [ ] . this comparison should include our earlier human ancestors, usually short in protein, and even shorter in lipids. hints on the postulated hunter-gatherer ancestors feeding standards and behavior, and the study of human dietary variability at present suggest that we are a remarkably adaptable species [ ] , but in all cases, c takes priority over c, often with the help of the highest protein intake of all primates [ , ] . evidently, within the enormous variety of human groups and their adaptation to all types of diet (the food available) and environmental conditions, it is expectable that a wide variety will be found -also-in the differential use of the main nutrients; provoked, in general, through epigenetic-driven adaptation to the foods available [ ] . but most humans not living under extreme conditions maintain diets which, despite the ample variability in foods and their proportions, provide enough amino-n, c and c for healthy survival [ ] (figure ). the problems arise when the carefully established compensatory mechanisms for diets markedly deviate from those of our ancestors, which result inoperative or deficient by excess of energy and, especially, of some nutrients [ , ] . it seems that the paleolithic (including ancient historical times) physiological blueprint has evolved little in regulation, despite our admirable adaptation, to occupy almost any ecological niche conceivable on earth, and thus, diet-provoked "inflammatory" diseases appear and remain unchecked [ ] . variable food supply, including in some cases its excesses and early death (for almost any cause imaginable including diseases) shortened the lifespan of our predecessors already in historical times [ ] . notwithstanding, in the present, our main health dangers seem to be related to our "excessive" success in providing food and health care to a large proportion of humans, coupled with an insufficiently fast evolutionary pace to let our bodies to adapt to this, so far, unique success in the extension of a species mean lifespan and its consequences [ ] . enter the problems of aging: until recently, a problem affecting a very small part of developed societies, that became a prime cause of health, lifestyle and social problems because of the success in expanding our longevity [ , ] . despite all that, we have not established (in times of plenty) an estimation of the magnitude of c-precursor nutrients we need to consume. essentially the question is: do we need a minimum intake of carbohydrate? [ ] . glucose is the main energy staple of our diet, and we base on c substrates most of our metabolic function and regulation [ , , ] . instead, we centered our attention on lipid ( c sources) [ ] [ ] [ ] , sugars as such [ ] , some minerals (e.g., salt), and, to a limited extent, on protein [ ] . it is unclear why our flag substrate, glucose, has not been given due importance except as a marker of disease. however, the pervading idea of almost any food-derived nutrient contributing effectively to our energy sustenance, with (almost) full substitution possibilities (as energy fuels) between carbohydrates, fats, protein (and even alcohol) is deeply rooted. this belief would render superfluous to analyze if there were a dietary minimum supply of c- c substrates, in the way we know that this minimum exists for amino-n and "loose" maximums are generally accepted for lipids and alcohol (a toxic substance and "pure" c). from the data available, the quest for lowering glycaemia and reducing body weight [ ] favor the use of low carbohydrate ketogenic diets [ ] . however, high-carbohydrate diets improve glucose metabolism [ ] in healthy individuals, and restriction of diet carbohydrates increases the risk of cardiovascular disorders, depending on the diet energy and composition, especially in patients with disorders of glucose metabolism [ ] (but not in healthy individuals [ ] ). not even glycaemia is better regulated in diabetics with excessive dietary carbohydrate restriction [ ] . the disarrangement provoked by the relative insufficiency of carbohydrate in some "low-carbohydrate" diets depends, essentially on four factors: (a) the metabolic "basal state" of the patients, since the results depend on gender, age and the incidence of ms-related disorders. (b) the overall energy intake with respect to the needs (or slimming goals) of the patient. (c) a diet low in carbohydrates must get the energy from either protein or lipid, the proportion and structure of these nutrients in the diet affects the incidence of lowering carbohydrate intake. (d) the type of carbohydrate present in the diet and its food associations, essentially its relationship to fiber and the mean molecular weight of the polysaccharides (including their digestibility and effects on the microbiota). the enormous variation of results, consequences, and effectiveness of the proposals coupled to the soundness of the results from the data published, results in a near-impossibility to draw conclusions. in addition, almost all diets studied have been applied for short periods of time to small numbers of individuals with scant information even for the point a) and were done in 'comparison' with other different types of diets. even the reviews and meta-analyses could not draw clear consequences from the huge amount of literature accrued on this question. there are too many factors to allow us to draw safe conclusions from partial, incomplete and not superimposable data. to face this type of analysis, a much-needed simplification is required, and reserve on the conclusions (and on their application to people) must be observed. diet studies largely analyze the consumption of food items (a huge, varied and socially peculiar group of products), which in addition have been cooked and mixed in varied proportions. this is "reduced" to the nutrients they contain, but this may forsake aspects such as synergisms, food structure (i.e., fiber), and the nature of the nutrient itself (fructose is as carbohydrate as amylose or a resistant-starch, for instance, and collagen-rich squid is as protein as gluten). we know what is eaten but not what is assimilated (the variable microbiota plays a critical role on this process). we need more information on-at least-what is ingested along longer periods of time. in any case, a multilateral approximation to the data known and the line of thought presented here allows us to assume that a minimum (both in proportion and in absolute terms) of daily dietary carbohydrate does exist [ ] , despite the possibility to substitute a large portion of the c intake by other sources of c. there is abundant literature but a dearth of information on diets. unfortunately, when dealing with the concept of diet industry, policy, fashion, absurdity and taste interact to produce dispersion, unproven assertions, expanded private interests and outright lies, with-unfortunately-scant material usable to advance scientific knowledge and improve the preservation of health. in most of the studies available, an enormous variability in all the factors implied can be observed, and the formal and bona fides results rarely go further than "hinting to," with excessive room for interpretation and discordance (or even actual overall relevance). the most recent and popular case in point is the mediterranean diet, which, in fact, has not been yet defined in nutritional terms [ ] but has generated, nevertheless, a considerable number of studies on its health benefits [ , ] . why do relatively small modifications in diet may induce so deep changes or no changes at all in functional parameters? we do not yet know enough to obtain a defendable and plausible answer. on one side, the nutritionists and dieticians usually analyze diets as a whole, use tables and measure our anthropometric (and metabolic) data and detailed food intake to calculate the needs of nutrients (translated to foods) to cover the energy expenditure, despite the fact that both factors are closely linked. on the other side, a growing number of molecular biologists analyze the specific mechanisms of control of endocrine and paracrine factors (largely those easily measurable), usually using isolated cells or cultures, since this approach is not viable in most in vivo models. both worlds of study are eons apart, and keep publishing large amounts of deep, sometimes excellent studies on "new" signaling factors or mechanisms, and the beneficial properties of some foods. our scientific careers have passed through different consecutive fashion periods: enzymes, hormone receptors, cyclic nucleotides, gene analysis, cytokines, gene expression, micrornas, gene modification, exosomes, stem cells, the transcendence of microbiome, "virome/pandemic" etc. however, surprisingly nobody has devoted sufficient time and funds to study such elementary "unknowns" as how "essential" are some amino acids (and which are the paths of their complete catabolism in humans), how the excess n is eliminated (signals, pathways, mechanisms, sites), or how much c (largely glycosyl monomers) we need to ingest daily? what is our dependence of c as energy substrates? how is regulated the utilization of c/ c for energy (not only in a type of cells, but overall)? where does this take place? why there are not enough quantitative studies on how much lactate or glycerol uses the brain, muscle or heart? is wat a real storage depot or a secondary supplier of c from excess glucose during hyperglycemia? is insulin the main hormone controlling use of glucose by tissues? what is the role of steroid hormones in the control of glycaemia? and so on. perhaps the plausible results of studies trying to answer these questions do not sound "flashy" enough for promotion, or perhaps they are not sufficiently "safe" to merit publication in "prestige" journals, but we need to carry on "risky" studies to get the answers we need in order to understand real problems such as how the substrates provided by the diet are distributed and used. we also need them to understand and fight the negative effects of disorders that right now affect large portions of humankind. right now, it is critical to obtain much more basic (and critical) knowledge to understand the nature (and causes) of "inflammation" (obviously, not that defined by celsus!) that is often used to justify everything that is wrong in ms and related disorders. funding: this study received no funding, and was in part financed by the researchers themselves, colleagues and the sparse funds available from the university. we want to specially thank the professionals working in the library of the university of barcelona (crai-ub) for their patience, support and constant help in maintaining the flow of information despite the prolonged adverse (largely financial) environmental conditions. the authors declare no conflict of interest. one obesity and the mediterranean diet: a systematic review of observational and intervention studies trends in biochemical literature insulin, the molecule of the century the story of how the western blot came into being pharmacologic treatments for coronavirus disease (covid- ): a review cross-species analysis of the glycolytic pathway by comparison of molecular interaction fields glucose toxicity is responsible for the development of impaired regulation of endogenous glucose production and hepatic glucokinase in zucker diabetic fatty rats chronic oxidative stress as a central mechanism for glucose toxicity in pancreatic isled beta cells in diabetes biochemistry of oxygen toxicity the anomeric nature of glucose and its implications on its analyses and the influence of diet: are routine glycaemia measurements reliable enough? anomeric compositions of d-glucose in tissues and blood of rat mutarotase effect on micro determinations of d-glucose and its anomers with β-d-glucose oxidase carbohydrate chemistry for food scientists marked increase in rat red blood cell membrane protein glycosylation by one-month treatment with a cafeteria diet anomeric specificity of d-glucose metabolism in rat brain cells oxygen-toxicity, oxygen radicals, transition-metals and disease d-lactate in human and ruminant metabolism metabolism of ketonic acids in animal tissues stimulation of pyruvate transport in metabolizing mitochondria through changes in the transmembrane ph gradient induced by glucagon treatment of rats lactate dehydrogenases: structure and function mechanistic basis of l-lactate transport in the slc solute carrier family comprehensive review on lactate metabolism in human health the mammalian pyruvate dehydrogenase complex: structure and regulation role of glucagon, catecholamines, and growth hormone in human glucose counterregulation. effects of somatostatin and combined a-and b-adrenergic blockade on plasma glucose recovery and glucose flux rates after insulin-induced hypoglycemia splanchnic regulation of glucose production glucagon and regulation of glucose metabolism the regulation of glucose metabolism: implications and considerations for the assessment of glucose homeostasis in rodents the role of estrogen in adipose tissue metabolism: insights into glucose homeostasis regulation nutrient and hormonal regulation of the threshold of glucose-stimulated insulin secretion in isolated rat pancreases hepatic insulin clearance in regulation of systemic insulin concentrations-role of carbohydrate and energy availability insulin resistance induced by high glucose and high insulin precedes insulin receptor substrate protein depletion in human adipocytes aquaporin- protein is the primary route of hepatocyte glycerol uptake for glycerol gluconeogenesis in mice monocarboxylate transporters: new players in body weight regulation lactate oxidation by skeletal muscle during sustained contraction in vivo. pflügers arch lactate generation following glucose ingestion. relation to obesity, carbohydrate tolerance and insulin sensitivity the ugly duckling of energy metabolism lactate fuels the human brain during exercise glycerol as a substrate for brain metabolism competition of glycerol with other oxidizable substrates in rat brain pastor-anglada, m. l-lactate uptake by rat liver. effect of food deprivation and substrate availability zonation of gluconeogenesis from lactate and pyruvate in the rat liver studied by means of anterograde and retrograde bivascular perfusion lipogenesis from lactate in rat adipose tissue lactate production in adipose tissue: a regulated function with extra-adipose implications use of c-glucose by primary cultures of mature rat epididymal adipocytes. marked release of lactate and glycerol, but limited lipogenesis in the absence of external stimuli gut exchange of glucose and lactate in basal state and after oral glucose ingestion in postoperative patients inter-organ relationships between glucose, lactate and amino acids in rats fed on high-carbohydrate or high-protein diets glucose feeds the tca cycle via circulating lactate evidences of basal lactate production in the main white adipose tissue sites of rats. effects of sex and a cafeteria diet higher lactate production from glucose in cultured adipose nucleated stromal cells than for rat adipocytes do active cerebral neurons really use lactate rather than glucose? the importance of dietary carbohydrate in human evolution on the essentiality of dietary carbohydrate cafeteria diet is a robust model of human metabolic syndrome with liver and adipose inflammation: comparison to high-fat diet an evolutionary perspective enhances understanding of human nutritional requirements the selfish brain: competition for energy resources evidence supporting the existence of an activity-dependent astrocyte-neuron lactate shuttle competition between glucose and lactate as oxidative energy substrates in both neurons and astrocytes: a comparative nmr study lactate utilization by the neonatal rat brain in vitro. competition with glucose and -hydroxybutyrate lactate shuttles in neuroenergetics-homeostasis, allostasis and beyond crosstalk proposal: an important astrocyte-to-neuron lactate shuttle couples neuronal activity to glucose utilisation in the brain crosstalk opposing view: lack of evidence supporting an astrocyte-to-neuron lactate shuttle coupling neuronal activity to glucose utilisation in the brain further observations on the oxidation of lactic acid by brain tissue sugar for the brain: the role of glucose in physiological and pathological brain function human milk oligosaccharides: every baby needs a sugar mama essential fatty acids in visual and brain development amino acid needs for early growth and development the gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems glucose transport in human red blood cells kinetics of glucose transport in human erythrocytes uptake and metabolism of the short-chain fatty acid butyrate, a critical review of the literature binding of long-chain fatty acids to serum albumin in healthy humans. relationship to obesity cellular uptake of long-chain fatty acids: role of membrane-associated fatty-acid-binding/transport proteins translocation of long chain fatty acids across the plasma membrane: lipid rafts and fatty acid transport proteins vldl triglyceride kinetics in lean, overweight, and obese men and women role of plasma lipoproteins and the plasma cholesterol esterification system effects of accumulation of lipid droplets on load transfer between and within adipocytes adipocyte death defines macrophage localization and function in adipose tissue of obese mice and humans dead adipocytes, detected as crown-like structures, are prevalent in visceral fat depots of genetically obese mice apoptotic cell clearance: basic biology and therapeutic potential characterisation of adipocyte-derived extracellular vesicles released pre-and post-adipogenesis interorgan communication by exosomes, adipose tissue, and adiponectin in metabolic syndrome regulation of pyruvate dehydrogenase in rat liver mitochondria by phosphorylation-dephosphorylation evidence for existence of tissue-specific regulation of the mammalian pyruvate dehydrogenase complex regulation by insulin of adipose tissue pyruvate dehydrogenase. a mechanism controlling fatty acid synthesis from carbohydrates the glyoxylate shunt, years on sucrose synthesis from acetate in the germinating castor bean: kinetics and pathway the possible role of glutamine substrate cycles in skeletal muscle quantitative estimation of the cori cycle in human the glucose-alanine cycle estimation of glucose-alanine-lactate-glutamine cycles in postabsorptive humans: role of skeletal muscle glycolytic end product and oxidative substrate during sustained exercise in mammals-the "lactate shuttle glucose load diverts hepatic gluconeogenic product from glucose to glycogen in vivo hepatic lactate uptake is enhanced by low ph at low lactate concentrations in perfused rat liver in vivo glucose metabolism in the rat lung rat splanchnic net oxygen consumption, energy implications glycerol is synthesized and secreted by adipocytes to dispose of excess glucose, via glycerogenesis and increased acyl-glycerol turnover quantifying the digestibility of dietary protein a review of the relationship between the gut microbiota and amino acid metabolism amino acid disposition by liver and gastrointestinal tract after protein and glucose ingestion absence of l-histidine ammonia lyase and histidine imidazole metabolites in human adenomatous prostate emerging aspects of gut sulfur amino acid metabolism metabolism of lysine in α-aminoadipic semialdehyde dehydrogenase-deficient fibroblasts: evidence for an alternative pathway of pipecolic acid formation modeling biochemical aspects of energy metabolism in mammals the problem of nitrogen disposal in the obese estimation of the metabolizable energy equivalence of dietary proteins gluconeogenesis and amino acid metabolism . comparison of various precursors for hepatic gluconeogenesis in vivo quantitative analysis of the whole-body metabolic fate of branched-chain amino acids dietary branched-chain amino acid restriction alters fuel selection and reduces triglyceride stores in hearts of zucker fatty rats the relation of α-methylbutyrate to isoleucine metabolism. ii. propionate formation propionate increases hepatic pyruvate cycling and anaplerosis and alters mitochondrial metabolism adaptation in muscle oxidation of leucine to dietary protein and energy intake effects of manipulating dietary protein and energy intake on energy balance and thermogenesis in the pig factors determining the preservation of protein status during dietary protein deprivation starvation in the rat. . effect of age and obesity on protein sparing and fuel metabolism protein turnover, synthesis and breakdown before and after recovery from protein-energy malnutrition protein-energy malnutrition: the nature and extent of the problem amino acids-their role as an energy source early changes in tissue amino acid metabolism and nutrient routing in rats fed a high-fat diet: evidence from natural isotope abundances of nitrogen and carbon in tissue proteins are there dietary requirements for dispensable amino acids and if so, how do we assess requirements? untersuchungen über die harnstoffbildung im tierkörper [studies on urea formation in animal carcasses krebs and his trinity of cycles the l-arginine-nitric oxide pathway reference values and determinants of exhaled nitric oxide in healthy korean adults cytochrome c oxidase rapidly metabolises nitric oxide to nitrite reactive nitroxidative species and nociceptive processing: determining the roles for nitric oxide, superoxide, and peroxynitrite in pain involvement of salivary glands in regulating the human nitrate and nitrite levels n -labelled nitrite/nitrate tracer analysis by lc-ms/ms: urinary and fecal excretion of nitrite/nitrate following oral administration to mice. free radic production of elemental nitrogen by certain mammals including man production of gaseous nitrogen in human steady-state conditions nitrogen balances of lean and obese zucker rats subjected to a cafeteria diet altered nitrogen balance and decreased urea excretion in male rats fed cafeteria diet are related to arginine availability nitric oxide supplementation alleviates ammonium toxicity in the submerged macrophyte hydrilla verticillata (lf.) royle influence of environmental ammonia on the production of nitric oxide and expression of inducible nitric oxide synthase in the freshwater air-breathing catfish hyper-ammonia stress causes induction of inducible nitric oxide synthase gene and more production of nitric oxide in air-breathing magur catfish, clarias magur (hamilton) anammox bacteria: from discovery to application effect of nitric oxide on anammox bacteria molecular mechanism of anaerobic ammonium oxidation kinetics and mechanism of the reaction between ammonium and nitrite ions: experimental and theoretical studies the reaction between nitrous acid and certain amino acids related compounds at • nitrogen gas formation by interaction of nitrites and amino acids partial pressure of ammonia versus ammonia in hepatic encephalopathy nitric oxide production by the human intestinal microbiota by dissimilatory nitrate reduction to ammonium intestinal handling of urea and ammonia biotransformation of hydrazine dervatives in the mechanism of toxicity influence of hydrazine on the distributions of free amino acids in mouse liver liver glutamate dehydrogenase controls whole-body energy partitioning through amino acid-derived gluconeogenesis and ammonia homeostasis control of rat-liver glutaminase by ammonia and ph mitochondrial nitric oxide synthase: current concepts and controversies diffusion coefficients and solubility coefficients for gases in biological fluids and tissues: a review solubility of nitrogen in marine mammal blubber depends on its lipid composition non-cirrhotic hyperammonemia-when high ammonia is not always from cirrhosis taste responses and preferences for sweet high-fat foods: evidence for opioid involvement different effects of hyperlipidic diets in human lactation and adulthood: growth versus the development of obesity dietary obesity in adult rats: similarities to hypothalamic and human obesity syndromes a high-fat, ketogenic diet induces a unique metabolic state in mice treatment of rats with a self-selected hyperlipidic diet, increases the lipid content of the main adipose tissue sites in a proportion similar to that of the lipids in the rest of organs and tissues fuel and energy metabolism in fasting humans glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition modeling of lipid and protein depletion during total starvation whole-rat protein-content estimation. applicability of the nx . factor metabolic regulation. a human perspective skeletal muscle mass and distribution in men and women aged - yr lower recovery of muscle protein lost during starvation in old rats despite a stimulation of protein synthesis abdominal obesity and metabolic syndrome the effect of total starvation and very low energy diet in lean men on kinetics of whole body protein and five hepatic secretory proteins protein turnover in skeletal muscle. ii. the effect of starvation and a protein-free diet on synthesis and catabolism of skeletal muscle proteins in comparison to liver starvation as a treatment of obesity: the need to conserve body protein nutrition and the prevention of chronic diseases scientific opinion on dietary reference values for energy unconnected body accrual of dietary lipid and protein in rats fed diets with different lipid and protein content in rats fed high-energy diets, taste, rather than fat content, is the key factor increasing food intake: a comparison of a cafeteria and a lipid-supplemented standard diet foods: nutritive value and cost; farmers calculating the metabolizable energy of macronutrients: a critical review of atwater's results les moyens mis en oeuvre pour perdre du poids chez sujets en surpoids ou obèses a systematic review of the evidence regarding efficacy of obesity prevention interventions among adults comparative effects of caloric restriction and total starvation on body composition in obesity risks of obesity contribution of several amino acids and lactate to gluconeogenesis in hepatocytes isolated from rats fed various diets protein sparing in skeletal-muscle during prolonged starvation: dependence on lipid fuel availability adjustment to dietary energy availability: from starvation to overnutrition dietary protein affects gene expression and prevents lipid accumulation in the liver in mice thrift: a guide to thrifty genes, thrifty phenotypes and thrifty norms evolutionary origins of the obesity epidemic: natural selection of thrifty genes or genetic drift following predation release? epigenetic germline inheritance of diet-induced obesity and insulin resistance epigenetic contribution to obesity energy balance in a respiration chamber: individual adjustment of energy intake to energy expenditure reciprocal compensation to changes in dietary intake and energy expenditure within the concept of energy balance preferential uptake of dietary fatty acids in adipose tissue and muscle in the postprandial period hepatic and whole-body fat synthesis in humans during carbohydrate overfeeding regulation of hepatic de novo lipogenesis in humans lactate downregulates the glycolytic enzymes hexokinase and phosphofructokinase in diverse tissues from mice regulation of pyruvate dehydrogenase kinase and phosphatase by acetyl-coa/coa and nadh/nad ratios energy density, diet composition and palatability: influences on overall food energy intake in humans effect of dietary protein and energy intakes on whole body protein turnover and its contribution to heat production in chicks effects of feeding a cafeteria diet on energy-balance and diet-induced thermogenesis in strains of rat body weight and tissue composition in rats made obese by a cafeteria diet acute exposure to a high-fat diet alters meal patterns and body composition chronic consumption of a high-fat/ high-fructose diet renders the liver incapable of net hepatic glucose uptake mice chronically fed a westernized experimental diet as a model of obesity, metabolic syndrome and osteoporosis glycerol: major contributor to the short-term sparing effect of fat emulsions in normal man persistent obesity in rats following a period of consumption of a mixed, high-energy diet alteraçðes bioquímicas e hepáticas em ratos submetidos à una dieta hiperlipídica/hiperenergenética {hepatic biochemical changes in rats submitted to a high-fat/high-energy diet} the impact of a high-fat diet in mice is dependent on duration and age, and differs between muscles contribution of hepatic and extrahepatic insulin resistance to the pathogenesis of impaired fasting glucose. role of increased rates of gluconeogenesis diet high in fat and sucrose induces rapid onset of obesity-related metabolic syndrome partly through rapid response of genes involved in lipogenesis, insulin signalling and inflammation in mice interactions between insulin resistance and insulin secretion in the development of glucose intolerance role of skeletal muscle in insulin resistance and glucose uptake usefulness of plasma glucose and insulin concentrations in identifying patients with insulin resistance inflammatory lipid mediators in adipocyte function and obesity the urea cycle of rat white adipose tissue white adipose tissue urea cycle activity is not affected by one-month treatment with a hyperlipidic diet in female rats body fuels and starvation consuming a ketogenic diet leads to altered hypoglycemic counter-regulation in mice effects of a ketogenic diet on muscle fatigue in healthy, young, normal-weight women: a randomized controlled feeding trial the ketogenic diet: pros and cons the 'epileptic diet'-ketogenic and/or slow release of glucose intervention: a review ketogenesis activates metabolically protective gdt cells in visceral adipose tissue dietary treatments for obesity are ineffective impact of high-intensity exercise on energy expenditure, lipid oxidation and body fatness exercise-induced energy expenditure: implications for exercise prescription and obesity obesity, functional mobility and quality of life adults with initial metabolic syndrome have altered muscle deoxygenation during incremental exercise maximal exercise electrocardiographic responses and coronary heart disease mortality among men with metabolic syndrome physical exercise improves low cardiorespiratory fitness associated with intramyocellular lipids in patients with metabolic syndrome exercise improves adiposopathy, insulin sensitivity and metabolic syndrome severity independent of intensity advances in the surgical treatment of morbid obesity the pluses and minuses of bariatric surgery for morbid obesity: an endocrinological perspective cardiovascular benefits of bariatric surgery in morbidly obese patients body weight and mortality among men and women in china hypothesis concerning the u-shaped relation between body mass index and mortality the obesity paradox. body mass index and outcomes in patients with heart failure obesity or bmi paradox? beneath the tip of the iceberg what is "metabolically healthy obesity"?: from epidemiology to pathophysiological insights gender and age related features of metabolically healthy obesity phenotype prevalence early endocrine and molecular changes in metabolic syndrome models longitudinal study of the effects of a high-fat diet on glucose regulation, hippocampal function, and cerebral insulin sensitivity in c bl/ mice regulation of glucose homeostasis by glucocorticoids glucocorticoids and acidosis stimulate protein and amino acid catabolism in vivo molecular regulation of urea cycle function by the liver glucocorticoid receptor testosterone supplementation improves insulin responsiveness in hfd fed male t dm mice and potentiates insulin signaling in the skeletal muscle and c c myocyte cell line do the interactions between glucocorticoids and sex hormones regulate the development of the metabolic syndrome? front glucocorticoids antagonize estrogens by glucocorticoid receptor-mediated activation of estrogen sulfotransferase estradiol determine liver lipid deposition in rats fed standard diets unbalanced with excess lipid or protein regitz-zagrosek, v. reduction of apoptosis and preservation of mitochondrial integrity under ischemia/reperfusion injury is mediated by estrogen receptor beta estrogenic control of mitochondrial function estrogen treatment after ovariectomy protects against fatty liver and may improve pathway-selective insulin resistance oleoyl-estrone is a precursor of an estrone-derived ponderostat signal rats receiving the slimming agent oleoyl-estrone in liposomes (merlin- ) decrease food intake but maintain thermogenesis impaired estrogen receptor action in the pathogenesis of the metabolic syndrome estrogen and voluntary exercise attenuate cardiometabolic syndrome and hepatic steatosis in ovariectomized rats fed a high-fat high-fructose diet the impact of testosterone replacement therapy on glycemic control, vascular function, and components of the metabolic syndrome in obese hypogonadal men with type diabetes effect of testosterone replacement therapy on sexual function and glycemic control among hypogonadal men with type diabetes mellitus the aging male: testosterone deficiency and testosterone replacement. an up-date metabolic effects of testosterone therapy in men with type diabetes and metabolic syndrome. sex the role of estrogens in control of energy balance and glucose homeostasis central regulation of energy metabolism by estrogens circulating micrornas and adipokines as markers of metabolic syndrome in adolescents with obesity regulation of lipogenesis by glucocorticoids and insulin in human adipose tissue role of glucocorticoids in the physiopathology of excessive fat deposition and insulin resistance effect of testosterone on muscle mass and muscle protein synthesis testosterone administration to elderly men increases skeletal muscle strength and protein synthesis men supplemented with b-estradiol have increased beta-oxidation capacity in skeletal muscle estrogens protect male mice from obesity complications and influence glucocorticoid metabolism nutrition and its role in human evolution humans, lipids and evolution when man met meat: meat in human nutrition from ancient times till today palaeolithic nutrition. a consideration of its nature and current implications the neanderthal meal: a new perspective using faecal biomarkers circadian rhythms, time-restricted feeding, and healthy aging evolutionary origins of obesity protein intake and energy balance dietary requirements of "nutritionally non-essential amino acids" by animals and humans dispensable and indispensable amino acids for humans a single day of excessive dietary fat intake reduces whole-body insulin sensitivity: the metabolic consequence of binge eating the effect of six weeks of overfeeding on the body weight, body composition, and energy metabolism of young men primate carnivory and its significance to human diets diet of the prehistoric population of rapa nui (easter island, chile) shows environmental adaptation and resilience emerging concepts on the role of epigenetics in the relationships between nutrition and health the metabolic syndrome: prevalence in worldwide populations origins of major human infectious diseases evolution of the human lifespan and diseases of aging: roles of infection, inflammation, and nutrition an upper limit to human longevity? is dietary carbohydrate essential for human nutrition? effect of acute and short-term dietary fat ingestion on postprandial skeletal muscle protein synthesis rates in middle-aged, overweight, and obese men preference for dietary fat: from detection to disease how dieting might make some fatter: modeling weight cycling toward obesity from a perspective of body composition autoregulation high-sugar diet leads to obesity and metabolic diseases in ad libitum-fed rats irrespective of caloric intake adéquation de l'apport en protéines et acides aminés dans les régimes végétariens a randomized trial of a low-carbohydrate diet for obesity a review of low-carbohydrate ketogenic diets a mediterranean and a high-carbohydrate diet improve glucose metabolism in healthy young persons low-carbohydrate ketogenic diets, glucose homeostasis, and nonalcoholic fatty liver disease effects of a carbohydrate-restricted diet on emerging plasma markers for cardiovascular disease systematic review and meta-analysis of dietary carbohydrate restriction in patients with type diabetes concepto de dieta mediterránea: ¿un grupo de alimentos saludables, una dieta o una panacea publicitaria? [the mediterranean diet: a group of healthy foods, a type of diet mediterranean diet and risk of falling in community-dwelling older adults mediterranean diet and health: a systematic review of epidemiological studies and intervention trials key: cord- -td m ojx authors: kirsch, stuart title: running out? rethinking resource depletion. date: - - journal: extr ind soc doi: . /j.exis. . . sha: doc_id: cord_uid: td m ojx since the s, environmentalists have warned that overconsumption, especially of minerals and fossil fuels, will lead to resource depletion. but there are compelling reasons to question the assertion that we are running out. on the one hand, new technologies and discoveries have increased the supply of petroleum and natural gas. on the other, concerns about global climate change and the competitiveness of renewable energy are turning coal into a sunset industry and threaten to transform oil reserves into stranded assets. in contrast to fossil fuels, which are consumed in the process of generating energy, virtually all of the metals excavated in the past remain available even after they have been put to use. even though the average size and degree of mineralization of recently-discovered ore bodies is on the decline, there has never been as much copper, silver, and gold available for human consumption as there is today. whether incorporated into digital technology or infrastructure, the majority of metals remain available for recycling, which is generally less expensive, uses less energy, and has fewer environmental impacts than extracting minerals from the earth. the threat posed by climate change from continued use of fossil fuels, and the impacts of environmental degradation caused by resource extraction, demand greater attention than the misleading specter of peak oil or running out of metals. a fundamental axiom of environmental thought since the s is that overconsumption will lead to resource depletion, especially with regard to minerals and fossil fuels, and thereby imperil the future. avoiding this fate requires moderating the demand for these resources to ensure that adequate supplies will be available to the members of future generations. these ideas were initially advanced by the limits to growth manifesto written by scholars affiliated with the club of rome (meadows et al., ) , and subsequently incorporated into the concepts of sustainability and sustainable development (mitcham, ) . recognition of the importance of recycling and reuse are also driven by these concerns. but in recent years, the malthusian fear of running out of minerals and fossil fuels has largely been overtaken by concerns about the contribution of greenhouse gas emissions to global climate change and environmental degradation resulting from resource extraction. there are compelling reasons to challenge the assumption that we are about to run out of fossil fuels. engineers have been predicting the exhaustion of oil and gas supplies for over a century. when the materialist anthropologist leslie white ( ) argued that the ability to capture ever larger amounts of energy was the driving force behind the evolution of culture, he expressed concern that the rising demand for oil was outpacing new discoveries. although the oil crisis of the s was more about cartel politics than petroleum shortages, it nonetheless provoked conversations about the end of oil. the first sentence of (ferry and limbert, ) edited volume on the temporality of resources raised the alarm about peak oil: "oil is running out. what's more, its final depletion now seems imminent." such concerns are logical, of course, because fossil fuels are consumed in their use. if more oil is burned than discovered, eventually it will all be gone. but the reality of the supply side of the equation is that proven energy reserves have increased with the development of new technology making it possible to exploit deposits that were previously unknown or inaccessible. fracking technology has made oil and gas supplies locked into shale formations available for extraction. deep sea oil now accounts for nearly one-third of global oil supplies, and the volume of offshore discoveries greatly outstrips new deposits found on land. while the petroleum industry has not overcome the challenges of oil extraction in the arctic, especially the outsized risks to fragile environments, its task may be eased somewhat by the melting of the polar ice caps, which will open up formerly inaccessible terrain. although oil is a finite resource, there are no signs that supplies are drying up. if anything, the trend is moving in the opposite direction, towards oversupply. this became apparent during the oil shock of early , when russia and saudi arabia broke their agreement to maintain oil prices by limiting production. with the expansion of renewable energy, which has become economically competitive with fossil fuels (hund et al., , p. ) , saudi arabia may be re-evaluating its longterm strategy. protecting its petroleum reserves by capping production rates may not be advisable in the long run if competition from renewables turns these resources into stranded assets, the value of which cannot be recovered. this is already occurring in some sectors of the petroleum market as a result of plummeting demand for oil during the early months of the covid- pandemic, which has meant that higher cost sources of oil, including fracking based on cheap money (mclean ) and oil sands, are no longer economically competitive. although the threat of peak oil has long managed to perch comfortably on a nearby horizon, never advancing too close or receding too far into the future, it has lost most of its influence over planning or pricing. far more troubling than running out of oil would be continued dependence on it, in part due to the risks of other accidents like the bp oil spill in the gulf of mexico ten years ago, which continues to surprise with the tenacity of its environmental impacts, or the oil spill in siberia that occurred while i was writing this essay. but even more disconcerting is the contribution of fossil fuel consumption to the myriad of detrimental consequences from global climate change. in contrast to oil, the story of coal has been one of abundance. coal fueled the industrial revolution and subsequently provided insurance against the advent of peak oil. despite coal being synonymous with the past, we asked it to guarantee our future. but the reduction and eventual elimination of coal consumption has become the first priority of the response to climate change due to its disproportionate contribution to greenhouse gas emissions. however, some countries have remained steadfast in their loyalty to coal. in the developing world, china, india, and indonesia all remain heavy coal users. australia wants to sell even more coal than it already does to both china and india, but its efforts have become a target of domestic and international criticism. in eastern europe, hungary, and poland refuse to sacrifice their coal supplies. japan is one of the few industrialized economies to build new coal-fired power generators, which it used to replace the nuclear power plants taken offline after fukushima in . in the united states, coal mining has become iconic of the fight between republicans and democrats even though it is no longer economically competitive with natural gas or renewable energy (plumer ) . despite the historical identification of union labor and the political left with coal, it has become the target of progressive environmental criticism, fueling climate change denialism on the right. in contrast to lingering coal pessimism on the part of some observers, the conviction that our economies will not be able to function without coal (eriksen (eriksen , , it now appears more likely that we will give up on coal long before it is gone. new investments in coal seek to lock in extraction before the inevitable moratorium, or receive compensation when that day arrives. as one industry observer notes, "overall, coal is still strong but its expansion is expected to stop and its future is bleak" (cornot-gandolphe , p. ). like the creative destruction resulting from the digital economy, coal mining is positioned to go the way of fax machines and video stores. a case in point is germany, which has the largest economy in the european union, and draws percent of its power from coal, but recently established a timetable to phase out coal power by (egenter and wehrmann ) . between and , the country will decrease coal use by . gigawatts. during this time, it plans to convert its reserve generators to natural gas, another . gigawatts in capacity. from until , it will reduce coal use by power generators an additional . gigawatts, which will be replaced by lowercost renewable energy. finally, by , and possibly earlier, it plans to end all coal-fired energy generation. germany hopes to encourage the other countries in the eu still dependent on coal to follow its lead, and to offer technical assistance to developing countries to make this transition as well (see kirsch ) . the world is not so much running out of coal as running away from it. what about metals and minerals? are we on the verge of running out, especially when considering the demand for new infrastructure to support renewable energy (hund et al., ) ? whereas proven reserves of oil and natural gas have been expanded through the application of new technologies, the conditions differ for minerals and metals. the general consensus is that many of the largest and most accessible ore bodies have already been developed. recently-discovered ore bodies tend to be smaller in size, to have lower rates of mineralization, and to be located deeper underground. this not only increases the costs of production but also the environmental costs of extraction, as more earth and rock need to be processed per quantity of ore recovered. the disposal of overburden and tailings from open-pit mines, along with the risk from acid mine drainage, have come to haunt the mining industry both in terms of financial obligations for their environmental impacts and the resulting opposition to new projects (kirsch ) . despite the higher costs and greater environmental impacts, new discoveries of metals and minerals have thus far kept pace with demand. periodic shortages are almost always revealed to be the result of political bottlenecks or strategic stockpiling. this holds true for most, if not all, minerals. bauxite, for example, the precursor to aluminum, is a very common element, and the limiting factor for the supply of aluminum is not access to bauxite but rather the accessibility of low-cost energy, as the process of production is energy intensive. even "rare earth" metals, in demand for everything from cell phones to wind power, are hardly rare. almost all are refined in china or malaysia, not because that is where the only deposits are located, but because of differences in environmental regulations and their enforcement. the limiting factor in access to rare earth metals is that they are found in conjunction with radioactive materials, including uranium and thorium, which make them uneconomical to extract and refine according to stricter environmental and health standards. but even more germane to the question whether we are running out of metals is the fact that, in contrast to fossil fuels, which are consumed in the process of generating energy, the total stock of metals remains largely unchanged by extraction and use rather than being exhausted by it. there has never been more copper, silver, or gold available for human consumption than there is today. of course, a great deal of the stock of metals is tied up in the cities of the world, but as infrastructure and architecture are renewed, these materials become available again. whether incorporated into today's digital technology, used for infrastructure, or discarded, the majority of these metals may eventually be recycled, which is generally less expensive, uses less energy, and has fewer environmental impacts than extracting metals from the earth. for nearly fifty years, concerns about resource depletion have motivated environmental politics by advancing the view that human society is at imminent risk of exhausting the supply of fossil fuels and metals needed to maintain our way of life. this concern is manifest in rhetoric about peak oil that continues to circulate despite new discoveries and the availability of econmically competitive forms of renewable energy that threaten to transform existing oil reserves into stranded assets. coal has already made this transition in many postindustrial countries, and despite its symbolic significance for both the right and the left, is already seen as a sunset industry by most external observers (cornot-gandolphe, , p. ). metals and minerals have different life-cycles than energy sources like coal and oil, as they are not consumed in their use. that many recent discoveries are smaller in size and yield lower returns does not mean that we are running out. in contrast, available stocks of metals have been increasing ever since humans first began to exploit them. virtually all of the metals excavated throughout the course of human history remain available for use through recycling and reuse. we are also gradually transitioning towards a more circular economy in which recycled materials play an expanded role in new production. this trend has already spawned a new movement in design that anticipates the reuse of an object's components in future commodities. this does not mean that the analysis of the problems posed by unlimited growth identified in the s was wrong then, or should be ignored today, but rather that the risks from climate change and environmental degradation resulting from resource extraction have eclipsed the threat of resource depletion. moreover, the response to climate change alters the way we make use of fossil fuels. to limit the global temperature rise to °c, while staying as close to . °above preindustrial levels as possible, as stipulated by the paris agreement, it will be necessary to replace fossil fuels with renewable sources of energy. some of these changes will come about as a result of social movement pressure and political change, but they are also being driven by the economic competitiveness of renewables (hund et al., , p. ) . similarly, we are less at risk of running out of metals, supplies of which are available through recycling, than we are vulnerable to the environmental impacts from the mining industry (kirsch ) . rethinking the risk of resource depletion does not imply that we no longer need to manage the earth's resources sustainably. rather, it encourages us to think about the problems caused by resource extraction in different ways: that the risks posed by the continued use of fossil fuels and the environmental impacts of resource extraction demand greater attention than the misleading specter of peak oil or that the world will run out of these important resources. the shift to renewable sources of energy and the increase in recycling and reuse of metals can help keep the world on track to minimize climate change while limiting environmental degradation from resource extraction. status of global coal markets and major demand trends in key regions german commission proposes coal exit by overheating: an anthropology of accelerated change boomtown: runaway globalisation on the queensland coast timely assets: the politics of resources and their temporality the world's last coal plant will soon be built. washington post minerals for climate action: the mineral intensity of the clean energy transition. the world bank group mining capitalism: the relationship between corporations and their critics why pacific islanders stopped worrying about the apocalypse and started fighting climate change coronavirus may kill our fracking fever dream. the new york times the limits to growth: a report for the club of rome's project on the predicament of mankind the sustainability question carbon democracy: political power in the age of oil in a first, renewable energy is poised to eclipse coal in u.s. the new york times energy and the evolution of culture this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. it represents the views of the author. i am grateful to robert brückmann, jessica smith, the editor, and the anonymous reviewer for their valuable comments and suggestions. key: cord- -dtsi qit authors: brauers, hanna; oei, pao-yu; walk, paula title: comparing coal phase-out pathways: the united kingdom’s and germany’s diverging transitions date: - - journal: environ innov soc transit doi: . /j.eist. . . sha: doc_id: cord_uid: dtsi qit political decisions and trends regarding coal use for electricity generation developed differently in the uk and germany, despite being subject to relatively similar climate protection targets and general political and economic conditions. the uk agreed on a coal phase-out by . in germany, a law schedules a coal phase-out by at the latest. this paper investigates reasons for the different developments and aims to identify main hurdles and drivers of coal phase-outs by using the triple embeddedness framework. the comparative case study approach reveals that policy outcomes regarding coal consumption are deeply influenced by several actor groups, namely, coal companies, unions, environmental ngos, and the government. the most discussed aspects of a coal phase-out in both countries are energy security concerns, whether coal is mined domestically, (regional) economic dependence, as well as the relative power of actors with vested interests in coal consumption. to meet the paris agreement target of limiting global warming to at most . • c to • c, coal consumption needs to be reduced drastically (unep, , chap. ; rockström et al., ) . the european union (eu) would have to cut its coal consumption to almost zero by to fulfil its already agreed upon climate protection commitments (rocha et al., ; climate analytics, a) . some major eu coal producing and consuming countries have agreed on a coal phase-out, while others still plan further expansions in coal generation capacity. this paper aims to identify the main hurdles and drivers of coal phase-outs on a country-specific level. it contributes to the literature by investigating and comparing the current state regarding coal consumption for electricity generation of two (former) eu states, namely the united kingdom (uk) and germany over the to era. both countries have a long history of coal production and consumption, being heavily dependent on coal for electricity supply. at the same time, they are (still) subject to the same eu climate and energy market regulations as well as the paris agreement (unfccc, ) , being required to reduce the amount of coal consumed. however, they are undertaking two contrasting strategies: namely a relatively rapid coal phase-out plan in the uk, compared to a strategy of conserving and delaying in germany. this paper aims to contribute to the literature by analysing why the developments in two major (formerly) coal producing and consuming countries are diverging so widely. it questions which actors and interests supported a continuation of coal's importance and the tef, a conceptual framework developed by geels ( ) , is part of the socio-technical transitions literature. industries suitable for this framework are reluctant to change, hold a high political influence, and are scale-intensive with many sunk investments, which is true for the coal sector. it recognises institutional change and includes strategic behaviour as well as the power of actors. by enabling the analysis of the co-evolution and the bi-directional relationships between an industry regime and its environments, it addresses shortcomings of previous methodologies (kungl and geels, ) . thereby, the framework refers to the situation of firms within an industry regime, which is itself embedded in two external environmentsthe socio-political and the techno-economic environments. an industry regime is under selection pressures from its socio-political environment, where the criteria include, among others, legitimacy and social fitness, and the techno-economic environment, which demands economic competitiveness, efficiency, and financial performance. the tef acknowledges the ability of firms to respond to their environments and influence them through strategic actions. the responses of the coal regime (adaptation strategies) are both externally-oriented (toward the economic and the socio-political environment) and internally-oriented (toward changing the firm's set-up to fit better to the environments). hence, the framework includes bi-directional relationships and co-evolution of the regime and its environments (geels, ) . it can be used as a tool for analysing the destabilisation of industry regimes. in the analysis included actor groups are the firms of the incumbent coal regime, non-governmental organisations (ngos), governments, labour unions, civil society and competitors for coal (this selection is based on hess ( ) and turnheim and geels ( ) and the actors influence on coal transitions). additional background on the triple embeddedness framework is presented in the appendix. to analyse drivers and hurdles away from coal, two eu countries, where coal mining and using coal for electricity generation played or still plays a major role for the economy, were chosen. in , the uk decided to phase out coal by (subsequently bringing the phase-out date forward to in ). in germany, the implementation of a phase-out plan is still under discussion; however, a coal phase-out by no later than is included in a draft law. the paper considers the to era, as the destabilisation of a regime is a long-term process and historic events can reveal broader societal and economic trends, creating path dependencies and lock-in effects (see also kungl and geels ( ) ). however, as most data (especially for east germany) is only available post- and climate concerns were only perceived as more pressing after , the paper focuses on to . in addition, information from earlier periods is included within the analysis to provide context for both case studies. in germany, the installation of the so-called "coal commission" and its proposed phase-out plan is considered, but the implementation process of the phase out law is not analysed as it is still ongoing at the time of writing. due to the close connection of coal use for downstream electricity generation and upstream coal mining, both are included in the coal regime analysis. the paper focusses on the usage of coal in the electricity sector, as heat, until now, is of lesser importance for coal companies. using the more commonly applied multi-level perspective (geels and schot, ) , would have diverted the attention to the niche part of the analysis. instead, we focus on the coal regime and incumbency, as well as the politics and power around a reduction in coal consumption. in the original framework from , the environment is called "economic" and not "techno-economic". data-collection is guided by the conceptual framework focusing on the relevant actors and contexts rather than on dependent and independent variables (kungl and geels, , ) . our data collection is based on a triangulation of document analysis, regular visits to the german coal regions, and a series of workshops. the document analysis uses primary data from databases regarding coal production, consumption, employment, and share of gdp, etc. as well as secondary sources from scientific peer-reviewed journals, other articles, and books. additionally, we draw on a wide range of grey literature including daily newspaper articles, blogs, company press reports, annual reports, and various website information, written in english or german and referenced throughout the text. informal background interviews with regionally affected stakeholders, while visiting german coal regions during three different research projects between and , allows us to test and complement the acquired information. we study the german context to highlight resistance against the phase-out. a first draft of different socio-political and techno-economic aspects of the coal phase-out, including response strategies of the coal regime, allowed us to organize ten thematic workshops in germany between and to acquire additional information on specific aspects as well as the underlying narratives of affected stakeholders within the coal phaseout process. participants varied between - representatives from governmental bodies, the (conventional and renewable) energy industry, unions, academia, and civil society. each workshops focused on a different set of topics, either touching more socio-political (e.g. health concerns, climate and environmental regulation options) or techno-economic (e.g. number of job losses and possible replacements, technical replacement of coal with renewable energies, grid stability, affordability) aspects as well as the response strategies of the coal regime (e.g. modelling phase-out pathways, liability issues). we did not do fieldwork in the uk; instead ongoing exchanges with academic experts on the uk validated the quality of our case study findings. the triangulation of this gathered information was used to develop the tef, mapping socio-political and techno-economic aspects of the coal phase-out including response strategies of the coal regime for each country. in addition, intermediate results of the tef were regularly refined following presentations and discussions with stakeholders at five international academic conferences. the main aim of the paper is to provide an overall picture of the political economy of coal in both countries in a novel way. many of the single elements included in the tef are studied by other authors. our main contribution is to bring these results into the descriptive framework to better understand the complexities influencing the political economy of coal. additionally, new findings are generated by comparing the diverging developments of these two countries. fig. provides a broad overview of coal mining and the total number of employees in coal mining (hard coal and lignite) in the uk and germany since . it is apparent that coal's importance is in decline in both countriesbut at different speeds. despite the strong reduction in coal mining and employment since the s, the share of electricity generated by coal is still % in germany in (bdew, ), whereas it constitutes only % in the uk (department for business, energy & industrial strategy, c). fig. shows the development of the electricity mixes for the two countries. it illustrates that the main substitutes for coal in the uk have been natural gas and renewables; in germany, renewable energy. this is also due to the fact that levelised costs of energy for renewables have fallen below the costs for conventional energy in both countries, especially due to falling capital costs and improving technologies (see for example for an analysis of energy prices in germany and the uk). the resulting strong increase of renewables has also resulted in new employment options for around , people for germany and slightly more than , for the uk (irena, ; oei et al., a,b) . the uk is one of the few eu member states where coal played an important role in the energy sector, but which nevertheless announced a coal phase-out by / and is a founding member of the powering past coal alliance (department for business, energy & industrial strategy ). the role of coal has changed dramatically since the s, especially in the last few years. while coal accounted for almost percent of the uk's electricity generation at the beginning of the s, it reached an all-time low in , as shown in fig. (department for business, energy & industrial strategy, c). coal was not needed at all to meet the uk's electricity requirements on days in (evans, ) , and is even further reduced in due to reduced energy demand because of covid- . coal production in the uk is almost eliminated with the closure of the last large deep mine in . the influence of the uk's coal unions on political decisions has changed over time. margaret thatcher fought against the power of unions during the s. reasons for this were the government's aspirations for power as well as the aim to liberalise the energy market and to increase competition (gouiffes, ; pollitt and haney, ) . after the end of the violent labour dispute (in ) , the union's influence had been reduced substantially (gouiffes, ; . nevertheless, all major unions supported coal and lobbied against mine and power plant closures. following the strikes, hard coal production and employment continued to decline substantially (see also fig. ), while overall coal consumption declined more slowly (department for business, energy & industrial strategy, a). an accelerated coal phase-out process, steered by the government, started much later. in , the socio-political environment in the uk observed a major shift in the perception of climate change, triggered by the 'big ask' campaign of the ngo friends of the earth (foe). an extensive media coverage of the campaign increased public and political awareness of climate change. the conservative party supported the 'big ask' campaign and adopted climate change accordingly as a major point of its strategy to modernise the party. within a month of this decision, members of parliament (out of ) signed the foe motion for a bill that would make emission reduction targets a law. the big three parties (conservatives, labour, and liberal democrats) started to compete by being greener than the others (carter and jacobs, ) . this made it more difficult for parties to openly support coal. starting in , the cross-party 'green' competition created opportunities for politics prioritising the environment. another main influence on climate friendly political decisions were inter-departmental institutions, e.g. the office for climate change (with members from all the main departments related to greenhouse gas (ghg) emissions (energy, business, transport, treasury, etc.)) and the the numbers for the electricity mix in germany in are preliminary. the numbers for the electricity mix in the uk in constitute the average of the first three quarters . for an overview of the longer term electricity trends in the uk and germany see fig. and fig. in the appendix. since the opening of an interconnector with france in , the uk has been a net electricity importer. at its peak in , electricity imports were responsible for less than . % of total primary energy supply and . % of uk electricity generation (bolten, ) . ~ % of the electricity imports come from france and the netherlands (bolten, ) . as both countries have a lower electricity carbon intensity than the uk, the phase-out of coal in the uk electricity mix did not lead to substantial additional emissions elsewhere. the strike resulted in more than , arrests, , wounded, imprisoned and more than , convicted (gouiffes, , ) . committee on climate change. by bringing different interests together and by being more independent, they managed to create consensus around integrated approaches that undermined pure economic considerations that had previously dominated (carter and jacobs, ) . the uk can be considered as a "liberal market economy" with a preference for market-based and non-technology specific policy instruments like the carbon price floor (cpf) (hall and soskice, ) . the focus on cost efficiencyand not on e.g. supporting new entrantsalso explains the preference for large-scale technologies (see section . . ). furthermore, the uk's 'liberal market economy' is characterized by "close-knit policy networks that are relatively open to incumbent industry actors but remain closed for outsiders and new entrants" (geels et al., , ) . as a mostly top-down policy style prevails, broad stakeholder engagement is limited . in general, there was a broad public consensus among civil society and ngos within the uk that tackling climate change was crucial (gillard, ; parkhill et al., ) . the declining role of coal combined with widely appreciated and available alternatives like local natural gas, nuclear energy, and renewable energy helped to generate public support for climate change policies. media coverage can shape public opinion and has also influenced the transition in the uk. isoaho and markard ( ) find in their discourse analysis of the guardian that incumbent actors first tried to legitimise coal until . however, as they had already started to shift to alternatives, there was little resistance in public media when the government announced its coal phase-out pledge (see also antal and karhunmaa ( ) for a comparison of reporting of the guardian and the times on the german energy transition). in , the government further increased its goals, deciding to target net-zero greenhouse gas emissions by (department for business, energy & industrial strategy, b). several factors of the techno-economic environment facilitated the reduction of coal in the uk. compared to other countries (e.g. colombia, south africa or russia), coal resources were deeper in the ground and labour costs were higher, such that international imports were much cheaper than domestic mining. instead of subsidising coal mining like other countries, e.g. germany (see section . . ), the uk started weaning itself off its dependence on coal mining. by taking the decision not to use public funds to support domestic mining in the s, international competition led to a quick decline of domestic coal production and related employment. several policies introduced after constrained coal's business opportunities long before the final phase-out decision in , especially the cpf, the renewables obligation (ro), the emissions performance standard (eps), as well as more in general the climate change act and the related carbon budgets. the climate change act of , a main cornerstone of its climate policy, commits the uk to reducing greenhouse gas emissions by at least percent by compared to levels, setting legally-binding carbon budgets. additionally, timetables for compliance with stricter eu pollution control regulations have required a response from all power plant operators and contributed to the closing decision of seven non-compliant and ageing power plants (~ g w) between and (littlecott et al., ) . older power plants are mostly more polluting (in terms of co and other emissions) and less efficient, which leads, next to higher amounts of pollution, to higher specific costs per mwh. in may , the four still operating coal plants have reached an average lifespan of years (power stations of the uk, ). the cpf and the eps, on the other hand, have restricted potential construction of new coal units (without carbon capture) (mendelevitch and oei, ) . renewable electricity policies, especially the renewables obligation, which required utilities to meet annual renewable electricity targets, incentivised incumbents to deploy a certain amount of renewable energies themselves, rather than enabling new market participants to enter the electricity market. entry barriers for new non-specialist market participants were high due to the complexity of the mechanism and related revenues were too uncertain for civil society actors (hall et al., ) . on the demand side, falling wholesale electricity prices, especially in the period after , put pressure on the coal industry (littlecott et al., ) . however, the coal industry is subsidised by the government through various policies: a capacity market was introduced in and serves to guarantee idle power plants a steady income. other policies in included various tax benefits, inherited liabilities related to coal mining, the supplementary balancing reserve ( - ), and others. the inherited liabilities related to coal mining amounted to annual average subsidies of € . million in the years - . estimates for the annual average budgetary support for the supplementary balancing reserve are € . million in (van der burg, ) . in addition, subsidies for renewables were cut back heavily in (johnstone et al., ) . renewable projects are, in most cases, smaller than conventional units and face problems in acquiring loans within a market based financial environment, such as the uk. this results in additional barriers for small scale renewable energy projects (especially with civil society ownership) to borrow funds from mostly centralised and internationalised private investment capital (hall et al., ) . this contributed to the fact that most installed renewable generation capacities in the uk are owned by firms that are already present in the energy market. additionally, the slowing down of the eps was part of the energy act and it sets a limit of gco /kwh for new power plants of more than mw. the carbon price floor was introduced in with £ /tco ; the price of £ /t co (~ €/t co ) was frozen in until (house of commons, ). climate change act , chapter , parliament of the united kingdom. the coal authority takes charge of inherited liabilities, for which coal-mine operators were not held responsible (van der burg, ) . the supplementary balancing reserve puts generation capacity into a reserve. the reserve is kept outside the electricity market and can be used when there is a shortage in supply (van der berg ). background talks with energy experts and see also https://www.gov.uk/government/publications/renewable-energy-planning-databasemonthly-extract. renewable energy investments increases the need to use natural gas as a replacement fuel for coal. so far, coal for electricity generation has been continuously replaced by cheaper electricity from both natural gas and renewables. however, in contrast to most eu countries, no renewable energy targets have been set for nor in the uk . this might further hinder renewable energy expansion and, therefore, increase the use of natural gas and potentially nuclear energy. lockwood et al. ( ) find that large electricity generators have structural power in relation to decision makers. this enabled companies' ideas and related lobbying to influence the design of the capacity market policy and other subsidies in the uk. additionally, high hopes among all incumbents were placed on cc(t)s (carbon, capture, (transport), and storage) as a 'silver bullet' to allow for emission free coal combustion. the political decision to implement the eps and the cps, accelerating the coal phase-out might have been different, if it had been clear for all actors that carbon capture, (transport,) and storage (ccs or ccts) would not be available as a so-called 'clean coal' alternative, potentially leading to more resistance (littlecott et al., ) . the coal industry used several framing techniques to influence public opinion and political decision makers. a main narrative was that without cheap coal, electricity prices would rise, which in turn would lower competitiveness of other british firms and hit households hard. the question of whether prices actually do increase because of climate policies or because the old power plants would have to go offline after ~ years in operation anyways, has been avoided. other powerful frames repeatedly pushed into the public debate by the coal regime are job losses and blackouts. an example for this is a report by the british infrastructure group saying that coal power station closures would lead to a "sustained danger of intermittent blackouts for the foreseeable future". the report was immediately refuted by several research institutes and ngos. the government reduced its support for onshore wind and solar pv substantially, and signals on support for tidal power and biomass are unclear. nuclear power is struggling with opposition, the long planning and construction times, high costs, and ever-increasing problems with hinkley point c (the guardian ( ): hinkley point nuclear plant building costs rise by up to £ . bn. https://www.theguardian.com/uk-news/ /sep/ / hinkley-point-nuclear-plant-to-run- m-over-budget). in , a new regulation stated that no coal power station would get a permission without ccts (carter and jacobs, ) . this prevented new coal-fired power plants from being built, as ccts never became technologically available. philpott, tim. . 'electric shock: will the christmas lights go out next winter?' a british infrastructure group (big) report. https://www. theguardian.com/environment/ /dec/ /campaigners-dismiss-christmas-electricity-blackout-report-as-laughable. fig. summarises the triple embeddedness framework analysis' results for uk. the aging infrastructure, uneconomic mining, and climate policies led to the unfavourable (economic) conditions for coal in the electricity sector. when coal mining became uneconomic in the s, state support was withdrawn, reducing the power of the unions. reducing the amount of domestic coal lowered further resistance to implement policies reducing coal's dominance in the electricity sector in subsequent years. the added focus on environmental protection and climate change by the government during the s led to the implementation of crucial policies like the cpf and the eps. together with eu emission reduction targets, the coal industry's business was further weakened, and finally the coal phase-out by / announced. the eps prevents new coal-fired power plants (without carbon capture) from being built, the cpf made electricity generation by coal less competitive and air pollution regulations forced older power plants to be closed. the policies incentivised incumbents to change their strategy: invest in renewables and natural gas projects instead of further holding on to coal as their main business model. however, policies in the uk did not support the entrance of new (small-scale renewable) generators but instead continued support for the incumbent energy companies. for an in-depth analysis of parallel developments regarding nuclear power, see . the characteristics of coal in germany are similar to the uk: in both countries hard coal mining has been uneconomic for decades, coal infrastructure is mostly old and hard coal import dependence is rising . the consequences for the coal regime, however, have been very different due to a different political direction. the german government subsidised domestic mining from the s onwards so that it could stay competitive with cheaper imported hard coal (matthes, ) . these numerous direct and indirect subsidies continued until they were forbidden by european regulation in (gençsü et al., ). as a consequence, hard coal mining experienced a continuous year controlled declinecompared to the abrupt collapse in the ukand ended in december . the consumption of hard coal stayed relatively constant over time, while power plants switched from domestic coal to imported hard coal. retired coal power plants were replaced with new units even after (pahle, ) . reasons for this were the underestimation of renewables and false hopes of operators to profit from the phase-out of nuclear energy. by the late s, the share of hard coal within the electricity mix was cut in half, reaching percent in , resulting in very low utilisation rates (oei et al., a,b) . the biggest drop in lignite production (and employment) already happened in the early s following the reunification of germany as mines in eastern germany were adopted to western standards (e.g. higher environmental standards and higher labour productivity), enforcing several closures (stognief et al., ) . in , lignite continues to be mined in three open cast mining regions in germany (oei et al., a,b) . the adjacent power plants profit from relatively low operating costs and, therefore, contributed percent of german electricity generation in (ag energiebilanzen, ). rising civil society pressure, as well as from the coal regions demanding financial support, pushed the government to introduce a 'commission on growth, structural change and employment' in -often also referred to as 'coal commission'. the commission included representatives of various social groups, such as unions, energy companies, industry, ngos, and residents of coal regions. it proposed a coal phase-out plan in january that foresees shutting down a total of . gw ( % of the active installed coal capacity at the end of ) of coal-fired power plants by . all coal-fired electricity should be phased-out by or by the latest (bmwi, ). the planned instrument to phase-out hard coal is an auction mechanism. in late , the government started negotiations with the lignite operators about the timing of decommissioning and the magnitude of compensations. in may , more than one year after the commission presented its recommendations, it is still not implemented as a law, and criticized by many actors previously involved in the negotiations of the commission (oei et al., b) . the following analysis focuses on historical hurdles that prevented an earlier coal phase-out in germany (compared to the uk). public opposition to coal began in the s due to high-stack emissions causing acid rains and forest diebacks. until the s, however, concerns and protests against coal remained a local issue. instead, the main focus of national protests by civil society and ngos was nuclear power, which was perceived as a more direct threat by the broad public. consequently, organizing anti-nuclear protests was the principal focus of environmental ngos like foe, greenpeace, and wwf (renn and marshall, ) . the german government slowed the decline of the coal industry since the s, lowering the negative impact on firms, workers, and regions, but also prolonging the difficulties of reducing the dependence of coal until this date. for a detailed description of government policies to support the hard coal industry from the s through , see oei et al. ( ) . internationally, germany is known as a strong supporter for climate change action. the focus on climate change protection and careful steps toward a government planned coal phase-out increased in . since then, germany's energy strategy has been called 'energiewende' (often translated as cumulative subsidies between and of € billion supported hard coal, while lignite received a total of € billion (meyer et al., ). next to the capacity payments for lignite power plants, there were several other state subsidies still in place in . these include royalty exemptions and reductions for resource extraction, support for the rehabilitation of mines, energy tax and electricity tax exemptions for power generation, and early retirement schemes for workers. for example, there were still € , million subsidies every year only for coal mining in north rhine westphalia until . there are interesting parallels to the uk, as there is a relatively newly introduced capacity reserve running in both countries until , costing € million in germany and € million in the uk (van der burg, ). energy transition). it is based on the goals of a nuclear phase-out, the reduced consumption of fossil fuels, and an increase in energy efficiency (renn and marshall, ; . however, the government fails to achieve its domestic emission reduction targets due to continued coal consumption. germany aimed to reduce emissions by % in compared to . in , germany was on track to reduce emissions only by . % (bmu, ). germany can be characterized as "coordinated market economy" (hall and soskice, ) . this can result in close interactions between the government and powerful incumbents, as well as civil society organisations. while coal incumbents received continuous governmental support stognief et al., ) , germany also has a relatively strong and organized civil society with active cooperatives, citizens' groups, and a strong environmental tradition. therefore, civil society protests were already an important lever enabling the phase-out of nuclear power in germany . from , the agreed upon nuclear phase-out relieved (human) resources of environmental actor groups. in parallel, concerns about coal intensified as knowledge about the impacts of climate change and human health impacts grew. tackling coal is more difficult for ngos, as it is not sufficient to simply address the risks of the energy technology (as in the nuclear case), but need to include also the potentially negative socio-economic aspects for coal workers and regions in their argumentation. rising international awareness of the climate crisis increased the pressure on the coal regime and the german government. consequently, ngos and activists managed to increase public attention, e.g. organizing a protest march in with more than , people into the hambach forest, which was planned to be cut down for the enlargement of an adjacent lignite mine . people living in the lignite mining regions have split opinions on a coal phase-out: one part of society fights against new mines to prevent their villages from being destroyed and to protect the environment. the other part lobbies to keep lignite as a main energy source in germany, mainly to protect their jobs and cultural heritage. both sides, however, believe that democratic processes have failed to make them actual stakeholders and part of the decisions shaping their energy futures (morton and müller, ) . the biggest unions in germany, representing workers of hard coal and lignite mines and power plants, are the ig bce and ver.di. both have a high influence on political decisions and were strong supporters of the gradual phase-out of coal in germany (compared to the uk) (renn and marshall, ) . the ig bce's position has been the most rigid, as they also represent workers in the energy intensive industries sector, which profits from low wholesale prices of electricity. before , a coal phase-out before was characterised as impossible. any measure to reduce coal consumption was seen as direct attack on their represented workers (ig bce, ). ver.di also lobbied against tighter air pollution controls and in favour of capacity payments to keep the coal industry alive. their focus, however, put benefits and retraining programs for affected workers as the highest priority, rather than only trying to postpone the phase-out date (enervis, ). the german electricity market was liberalised in , but competition remained limited resulting in continuously high market power of the four incumbent companies (rwe, enbw, e.on, and vattenfall). the renewable energy sources act (eeg), implemented in , substantially changed the dynamics of the electricity market. feed-in-tariffs were available for all electricity market participants and were especially attractive to, and supportive of, new market participants. the german green industrial policies were more stable, financially certain, and less bureaucratic than the british policies hall et al., ) . the green growth discoursethat germany with its substantial manufacturing sector could profit financially from the energy transition, building wind turbines and solar modulesfurther pushed the transition . the eeg also resulted in a reduction of the market share of the formerly 'big four' electricity generating companies as well as to a shift within their production portfolio (renn and marshall, ; . in , the domestic market share of the biggest five electricity generating companies ('big four' and leaga new company having bought all lignite assets from vattenfall) was reduced to % (bnetza and bundeskartellamt, ). this is comparable to the development of the wholesale electricity generation market share by the eight largest companies of the uk (edf, rwe, sse, drax, uniper, eex, scottishpower, and orsted) summing up to % (ofgem, ). in germany, big energy utilities face increasing re-municipalisation strategies as well as strong public support for nuclear phase-out and increasing renewables. in addition, many local small savings banks allocate capital to small and medium scale energy providers, like municipality owned stadtwerke (local public utilities), through an established framework of citizen investment to support regional development (hall et al., ). this regional financial support, paired with national renewable electricity policies of guaranteed feed-in tariffs, incentivised new small and community-based providers of renewable energies to enter the electricity market. continual market pressures on the coal business included overall decreasing energy demand due to the financial crisis, the rising market shares of renewables, and, consequently, decreasing wholesale electricity prices . in addition, the increasing price for allowances in the european emissions trading system, ~ euro/per tonne of co in , in combination with shrinking gas prices made coal combustion increasingly uneconomic. consequently, older hard coal units observed greater variable costs than gas units, resulting in lower utilization rates. this is the principal reason underlying the decline of coal's share in the electricity mix since (sandbag, ; agora energiewende, ). a paradox in germany is that despite big successes in growing wind, solar, and biomass capacities, greenhouse gas emissions remained relatively constant between and at around million tonnes of co -eq . the target for is million tonnes of co -eq (umweltbundesamt, (umweltbundesamt, , b . new estimations indicate that germany might achieve its target due to the recession caused by the covid- pandemic. this short-term decrease, however, will be evened out by the uptake of the economy in the following years and, therefore, does not reflect the desired structural reduction. the main strategy of the incumbent coal firms was to lobby for coal friendly regulation and further (financial) state support: this is visible in their success at opposing the first attempt by the german government in to introduce a 'climate contribution' (klimaabgabe) (morton and müller, ) . the 'climate contribution' would have led, similar to a carbon tax, to closures of mostly older coal units (goodman, ) . instead, a so-called 'carbon reserve' mechanism was introduced: old lignite-fired power stations were paid compensation while providing only a very small, if any, contribution to germany's climate goals. "the defeat of the 'climate contribution' is one clear example of how the politics of coal can undermine the policy aims of the energy transition" (morton and müller, , ) . another example illustrating the coal industry's power over german politics is air pollution regulations. in , germany lobbied with a small group of other (mostly eastern) eu countries against tighter eu air pollution rules , which set stricter emission limits (best available techniques (bat) requirements) for large combustion plants as part of the industrial emissions directive (climate analytics, b). nevertheless, a slim majority of european countries voted in favour of the stricter emission limits, taking effect for all eu member states in . however, in may germany is still not complying with european regulation not having transferred the new regulation into a corresponding law. the incumbent regime used several strategies to maintain the status quo of coal for as long as possible. one strategy was to misrepresent the effect of renewables on electricity prices for the general public. renewable feed-in-tariffs are mostly paid for by households and small industries, explicitly stated as such on all electricity bills. however, the increase of renewables actually lowered wholesale electricity prices -which especially benefited energy intensive industries. subsidies for conventional electricity, on the other hand, are directly paid for by the state budget and, thusly, are not clearly visible to consumers (lauber and jacobsson, ) . to save their business, electricity corporations additionally claimed that renewables threaten energy security because their fossil fuel plants would be rendered unprofitable and argued that renewables would make german industries uncompetitive by increasing energy costs. these claims were being made despite various studies showing that grid stability is not threatened by increasing amounts of renewables in the system and most energy intensive companies being freed entirely or at least partly from the eeg-surcharge (egerer et al., ) . the entanglement of rwe and municipal actors within the lignite region is a good example for the complexity of the coal regime in germany: traditionally, several city and regional governments in north-rhine westphalia are financially dependent on revenues of the rwe shares and have difficulties financing public services otherwise. municipal shareholders had little expertise (and belief) in renewables and consequently prevented a strategic reorientation of rwe away from coal, wanting to protect their regional coal interests . additionally, regional actors helped exert pressure on the national government to protect the overall coal regimeto safeguard local jobs and municipal services dependent upon the companies' financial success (oei, ) . rwe as well as the other members of the 'big four' in germany underestimated the fast growth of renewables and missed the opportunity to invest in non-fossil-fuel generation technologies. being used to large-scale projects, these companies did not want to participate in small-scale renewable projects and, additionally, they did not want to take some of their own profits from their conventional fleet away . consequently, medium-sized new actors formed, influencing and profiting from integrating renewable energy into the existing conventional wholesale power markets (wassermann et al., ) . this was strengthened through an overarching german trend toward re-municipalisation and the re-establishment of municipal utilities (stadtwerke). these served as key actors to promote structural change within the energy sector (berlo et al., ) . find that disruption in ownership in the electricity sector can help to support changing beliefs and practices. they distinguish between the "incumbent-led" energy transition in the uk and a "new-entrant-led disruptive" energy transition in germany. incumbents in the uk acted more strategically than incumbents in germany, saw change coming toward low carbon energy transition earlier, and deployed large-scale renewable energies themselves. nevertheless, incumbents in both germany and the uk lobbied for policies that supported their coal business activity. since , germany's 'big four' have also started to diversify their strategies (though not necessarily their portfolio): vattenfall sold all its lignite assets and is promoting a target of carbon neutrality within a generation; enbw wants to align its strategy according to the paris agreement; e.on sold all of its electricity assets (to rwe and fortum); and rwe aims at carbon neutrality by . furthermore, the bdew, the federal association of energy and water, which also represents the 'big four' together with most municipal utilities and renewable energy companies, was represented in the coal commission agreeing together with coal union representatives to the coal phase-out plan by / (bmwi, ). fig. summarises the tef analysis results for germany. this includes contextual information regarding the socio-political and economic environments as well as those forces (de-)stabilizing the coal regime. the long continuation of government subsidies for coal mining enabled the continuation of power generation and steel production with domestic energy sources. despite substantial pressure by international competition due to cheaper coal imports and climate protection measures, the political power of the coal regime limited changes to the status quo. climate change or air pollution concerns have not been strong enough to stop subsidies for the coal dw ( ): environmental groups hit back as german coal companies try to sue eu. https://www.dw.com/en/environmental-groups-hit-backas-german-coal-companies-try-to-sue-eu/a- . european commission ( ): news release -commission to review permits of large combustion plants. july . http://ec.europa.eu/ environment/pdf/ _ _ _news_en.pdf. industry or to implement policy instruments similar to those that forced closures in the uk. instead, concerns about high electricity prices, import independence, grid stability, as well as the implementation of the nuclear phase-out have resulted in a more gradual coal phase-out process. in , shortly before germany decided to phase out nuclear energy, the share of coal and nuclear energy in gross electricity generation was still %. to replace both energy carriers posed a substantially larger challenge than replacing the % share of coal generation in the uk in (see fig. ). thus, co emissions were not reduced in a similar manner as in the uk. germany's example powerfully demonstrates that only incentivising and expanding renewable energies is not enough to diminish coal's importance. however, small scale renewable energy deployment and citizen ownership has created broad civil society support for the german energiewende, providing a valuable lesson for other countries and an important basis for a future coal phase-out. furthermore, prices for renewables have been brought down with the help of deployment in germany, which helped other countries in their renewable energy investments, including the uk (morris, ) . the aim of this paper is to analyse which actors and interests prevented or, in contrast, enabled a reduction of coal's importance. the comparative case study of the uk and germany employs the triple embeddedness framework. for both countries, it is apparent that socio-political and techno-economic environment pressures influence the coal regime and that powerful incumbents exist. another commonality for these two countries is that incumbents successfully prevented policies reducing their business opportunities for several decades while also securing financial support. common frames used to generate this support are claiming disadvantages in e.g. domestic competitiveness, energy security, import dependence, rising energy prices, black-outs, and unemployment. however, the decline of coal happened at different speeds and under different policy tools, influenced by varying contextual national factors, diversity of actor power within the coal regime, and those opposing coal. table summarises the findings and highlights differences. in the uk, opposition of miners was already suppressed in the s -not for climate reasons but other political reasons. having to import coal lowered opposition to reducing coal's importance in the power sector over the following decades. a driving force was ngo campaigns influencing public opinion on climate change and health aspects, which facilitated a competition between political parties for 'green' policies and the implementation of policy instruments like the carbon price floor and emission performance standards in the s. this coincided with a point in time when, due to the age of coal-fired power plants, a decision between either major investments or a shutdown was necessary. furthermore, the decision for companies was comparatively easy as they were able to diversify into other domestic large-scale natural gas and renewables projects. in germany, since the s, coal unions and influential coal companies slowed the decline of coal. thereby, reductions within hard coal mining and related employment happened in a linear manner until with the help of large governmental subsidies. the lignite sector, on the other hand, observed a rapid structural break in the early s following german unification. a primary objective of east german mining was to create employment possibilitiesleading to 'inefficiencies' when having to compete with western mines optimized for capital return. after unification, this resulted in closures and layoffs as mining adapted to west european norms. our analysis shows that in germany the incumbent coal regime was able to uphold the status quo for a longer time than in the uk: in , regional governments as well as municipalities that are shareholders of energy corporations in mining areas in germany are still supportive of coal due to ongoing employment concerns. additionally, energy intensive industries have built a coalition with the coal regime as they perceived it as a means for achieving lower wholesale electricity prices. coal mining in the uk, on the other hand, was reduced to a negligible amount since the s, while germany still mined almost million tonnes of coal. therefore, the uk was less dependent on jobs and regional income generation related to coal. germany's previous nuclear phase-out decision, following the fukushima accident, made the coal phase-out more difficult due to concerns about sufficient installed electricity generation capacities. this, however, also released more human and financial capacities for ngos to put pressure on the coal industry. phasing-out coal and nuclear energy simultaneously meant having to replace the majority of electricity generation capacities both for germany as a whole and for those companies owning the power plants. moreover, in contrast to the uk, germany could not increase domestic natural gas production and were dependent on comparatively expensive imported gas. most large electricity corporations in germany underestimated the potential for renewable energy and did not change their strategy to investing in renewables until much later. other main reasons for the earlier reduction in coal production and consumption include the relatively old infrastructure of coal-fired power plants in the uk, requiring major investments in refurbishment or new capacities, as well as the stronger opposition to any decision restricting coal by miners' unions in germany. these experiences show that different actor groups have significantly more influence on political decisions than others, contributing to the diverging decisions regarding coal in countries otherwise comparatively similar and subject to the same eu energy and climate regulations. accepting this influence can make policy sequencing approaches more attractive (introducing policies that face little initial resistance, to upscale stringency and introduce more controversial policies later) (pahle et al., ). this appears more feasible than simply targeting most efficient policy instruments that go against the interest of a regime with close ties to policymakers. we show that the diverging situations regarding coal arise due to a complex interplay of pressures by the socio-political and techno-economic environments as well as the response strategies of the incumbent regime. without efforts to limit the influence incumbents have on policy making, or at least balance it with other civil society actors, more ambitious energy transitions seem unlikely, or will at least be significantly slower. some overarching policy recommendations that can be drawn from these past experiences are the following: -support for large scale renewable energy investments can either come through a renewables obligation, such as in the uk, or through the entrance of new renewable energy actors, like in germany. -however, supporting renewable energies is not sufficient to enable a coal phase-out in line with (inter-)national climate targets. this is reflected in the struggle of the german government to implement the agreement of the coal commission against continuing opposition of incumbents. importantly, the achieved compromise is neither in line with the paris agreement nor germany's climate targets (oei et al., b; kittel et al., ) . it is also slower than what citizens desire (rinscheid and wüstenhagen, ). -compatibility with the goal of ghg neutrality by needs to be included in transition planning. although the uk managed to achieve substantial ghg emission reductions with its shift from coal to natural gas, this will not be sufficient to achieve the upcoming more stringent climate targets for most countries. policies should be considered that prevent this next fossil fuel lock-in and instead create investments directly in renewables and energy storage as well as efficiency measures. -weakening the existing coal regime as well as showing them alternative business models enables change. margaret thatcher's political actions reduced the influence of the unions, but also resulted in other negative socio-economic consequences for mining regions still visible today. these impacts can be averted with targeted just transition policies, stopping coal use, and simultaneously providing social security for workers and new economic opportunities for dependent regions. -opportunities for change exist whenever larger investment decisions for plants or mines need to be taken. enforcing stringent climate and environmental regulation for new investments, as in the uk, can prevent stranded investments. missing such points in time can lead to ongoing legal debates regarding potential compensation payments, an ongoing discussion in germany. -phasing-out coal is not only about the replacement of coal with renewable energies within the energy system. for coal mining countries, like the uk and germany, the biggest challenge actually lies within the needed adjustments for the affected regional economies. past experiences show lessons of hardly managing (uk) or to passively delaying (germany) this process. current debates of the eu green deal try to reflect this by focusing on a "just transition" for all regions that will be affected by upcoming phase-out pathways. thereby, solutions strongly depend on regional contextual factors and must be adopted individually, as no single blueprint for a socially acceptable coal phase-out exists. we gratefully acknowledge support granted from the german ministry of education and research (bmbf) by financing the research group "coalexit" [grant number ln a] as part of the "global change" funding priority and the project "future of fossil fuels in the wake of greenhouse gas neutrality" [grant number la a] being part of the "economics of climate change" funding priority. the authors report no declarations of interest. firms-in-industries do "not only adapt to institutional pressures, but also respond strategically to shape them" (geels, , ) . aspects included from economic sociology highlight 'embeddedness', (cognitive, cultural and political). therefore, an important notion is "that economies and markets are underpinned by government regulations and institutions" (geels, , ) . another important contribution is also the recognition that "firms and industries use power and politics to shape formal institutions to their advantage" (geels, , ) and that "market elites and governmental elites often cooperate and that their voices are louder than those of labour unions, consumer groups and environmental groups" (geels, , ) , and that they can exert more political power than "ordinary citizens". the adaptation theory part acknowledges that firms act with deliberate and intentional strategies, rather than being mostly passive. both externally-and internally-oriented strategy schools are included. importantly, it is acknowledged that firms, in some contexts, have substantial scope to influence regulations and political environments. they use information strategies (e.g. setting up think tanks), financial incentives strategies (e.g. contributions to politicians and political parties), organize pressure strategies (e.g. creating industry associations, lobbying directly, confront using litigation, or threaten policymakers with layoffs), and discursive strategies (e.g. arguing that solutions are costly or technologically unfeasible). increasing pressures (from the economic and socio-political environment) and related performance problems can then incentivize actors to overcome lock-in mechanisms and tackle increasingly more foundational regime elements (geels, ) . the following two figures display long-term trends of electricity generation in the uk and germany. the effect of the miners' strikes in are clearly visible in the data for the uk. for germany, only data since its unification was available. bruttostromerzeugung in deutschland nach energieträger bruttostromerzeugung in deutschland ab nach energieträgern. arbeitsgemeinschaft energiebilanzen e die energiewende im stromsektor: stand der dinge . rückblick auf die wesentlichen entwicklungen sowie ausblick auf the german energy transition in the british, finnish and hungarian news media bdew, . bruttostromerzeugung in deutschland nach energieträger in den jahren die beendigung der energetischen nutzung von kohle in deutschland: ein Überblick über zusammenhänge. herausforderungen und lösungsoptionen the incumbents' conservation strategies in the german energy regime as an impediment to remunicipalization-an analysis guided by the multi-level perspective projektionsbericht für deutschland gemäß verordnung (eu) nr. / . bundesumweltministerium commission on growth, structural change and employment -final report energy imports and exports. briefing paper number . house of commons library the political economy of coal in poland: drivers and barriers for a shift away from fossil fuels cutting europe's lifelines to coal: tracking subsidies in countries -united kingdom. overseas development institute policy brief explaining radical policy change: the case of climate change and energy policy under the british labour government - integrating techno-economic, socio-technical and political perspectives on national energy transitions: a meta-theoretical framework a stress test for coal in europe under the paris agreement. scientific goalposts for a coordinated phase-out and divestment about % of eu and german, virtually all polish coal plants non-compliant with new eu air pollution regulations moving beyond the heuristic of creative destruction: targeting exnovation with policy mixes for energy transitions powering past coal alliance declaration. uk government historical coal data: coal production, availability and consumption supply and consumption of coal uk becomes first major economy to pass net zero emissions law historical coal data: coal production, availability and consumption historical electricty data energiewende 'made in germany' -low carbon electricity sector reform in the european context, st ed analysis: uk low-carbon electricity generation stalls in reconceptualising the co-evolution of firms-in-industries and their environments: developing an inter-disciplinary triple embeddedness framework the enactment of socio-technical transition pathways: a reformulated typology and a comparative multi-level analysis of the german and uk low-carbon electricity transitions ( - ) typology of sociotechnical transition pathways unravelling the united kingdom's climate policy consensus: the power of ideas, discourse and institutions the "climate dialectic" in energy policy: germany and india compared margaret thatcher & the miners - - -thirteen years that changed britain. e-book english translation financing the civic energy sector: how financial institutions affect ownership models in germany and the united kingdom sustainability transitions: a political coalition perspective out of the comfort zone! governing the exnovation of unsustainable technologies and practices energiewende 'made in germany': low carbon electricity sector reform in the european context. springer nature switzerland ag renewable energy and jobs -annual review ausstiegswettlauf führt in die irre -vassiliadis zum kohle-konzept der agora energiewende the politics of technology decline: discursive struggles over coal phase-out in the waves of disruption in clean energy transitions: sociotechnical dimensions of system disruption in germany and the united kingdom comparing nuclear trajectories in germany and the united kingdom: from regimes to democracies in sociotechnical transitions and discontinuities policy mixes for incumbency: exploring the destructive recreation of renewable energy, shale gas "fracking scenarios for coal-exit in germany -a model-based analysis and implications in the european context creative destruction or mere niche support? innovation policy mixes for sustainability transitions stewards or sticklers for change? incumbent energy providers and the politics of the german energy transition application and extension of a multi-dimensional framework. university of stuttgart institute for social sciences sequence and alignment of external pressures in industry destabilisation: understanding the downfall of incumbent utilities in the german energy transition the politics and economics of constructing, contesting and restricting socio-political space for renewables -the regime destabilization in energy transitions: the german debate on the future of coal insights from the uk coal phase out experience: report to chile decarbonization roundtable unpacking "regime resistance" in low-carbon transitions: the case of the british capacity market energy transition in germany: a case study on a policy-driven structural change of the energy system a just transition for coal miners? community identity and support from local policy actors the impact of policy measures on future power generation portfolio and infrastructure: a combined electricity and ccts investment and dispatch model (elco). energy syst. - staatliche förderungen der stein-und braunkohle im zeitraum - . Ö kologisch-soziale marktwirtschaft e.v. (fÖs). fÖs-studie im auftrag von greenpeace how germany helped bring down the costs of pv lusatia and the coal conundrum: the lived experience of the german energiewende energiewende 'made in germany' -low carbon electricity sector reform in the european context, st ed nrw im deutschen und europäischen kontext -energiewirtschaft, klimaziele und wirtschaftliche entwicklung, . politikberatung kompakt lessons from germany's hard coal mining phase-out: policies and transition from coal phase-out in germany -implications and policies for affected regions woran es beim kohleausstieg hakt und was zu tun ist. politikberatung kompakt, diw berlin wholesale electricity generation market shares by company largescale wind power in electricity markets with regular papers what stands in the way becomes the way sequencing in climate policy to ratchet up stringency over time transforming the uk energy system: public values, attitudes and acceptability -synthesis report dismantling a competitive electricity sector: the u.k.'s electricity market reform power stations of the uk, . power stations of the uk coal, nuclear and renewable energy policies in germany: from the s to the "energiewende germany's decision to phase out coal by lags behind citizens' timing preferences what does the paris climate agreement mean for finland and the european union? a roadmap for rapid decarbonization the politics of green transformations statistik der kohlenwirtschaft e.v, b. datenangebot statistik der kohlenwirtschaft beschäftigte der braunkohlenindustrie in deutschland statistik der kohlenwirtschaft e.v, b. steinkohle. statistik der kohlenwirtschaft approach to the distribution and orientation of power in socio-material change economic resilience of german lignite regions in transition regime destabilisation as the flipside of energy transitions: lessons from the history of the british coal industry ( - ) the destabilisation of existing regimes: confronting a multi-dimensional framework with a case study of the british coal industry ( - ) Übersicht zur entwicklung der energiebedingten emissionen und brennstoffeinsätze in deutschland - -unter verwendung von berechnungsergebnissen der nationalen koordinierungsstelle emissionsberichterstattung stromerzeugung erneuerbar und konventionell um , prozent zurück united nations environment programme unfccc, . paris agreement'. paris: united nations framework convention on climate change fakten und trends current challenges of germany's energy transition project and competing strategies of challengers and incumbents: the case of direct marketing of electricity from renewable energy sources we are grateful to all reviewers for helpful comments and suggestions that greatly improved earlier versions of the paper. a special thanks goes to all the experts on the uk and german energy sector that kindly provided us with their knowledge. we also thank adam lederer for language corrections. additional valuable input was provided by members of the coalexit research group, which we greatly appreciate. all potentially remaining errors are ours. the tef conceptualises industry environments and is based on evolutionary economics, neo-institutional theory, and economic sociology. it accommodates interactions between incumbent firms of a specific industry and a broader set of environments, including the economic and socio-political environments. the framework is based on schumpeter's idea to include social institutions relevant to economic behaviour in economic analyses (schumpeter ) . it recognises institutional change and includes strategic behaviour and power of actors. "embeddedness" means that the economy is embedded and not independent of social, political, and cultural dynamics.the tef framework builds on both selection theories and adaptation theories. it aims to integrate the two streams, not to choose either/or. the focus is on co-evolution, embeddedness, and bi-directional interactions (of industries and their economic, political, cultural, and social environments), which can only be analysed by combining the different theories and approaches. as geels ( ) states himself in the paper explaining the framework:' lewin and volberda ( ) suggest that selection theories and adaptation theories represent two levels of analyses, with the former emphasizing selection pressures that populations face from their environments, and the latter emphasizing (differences in) firmlevel strategies, capabilities and perceptions. […] "single-theme explanations for the adaptation-selection phenomenon have reached their limit. progress in the field requires combining and recombining multiple lenses instead of increasing fragmentation. we should consider the joint outcomes of managerial adaptation and environmental selection"' (geels, , ) .the tef framework is appropriate for our question and the coal industry, as it focusses on incumbent firms and the necessary pressure by policy makers and civil society to generate change (environmental selection). firms-in-industries are defined as "large, politically powerful, and scale-intensive with many sunk investments" (geels, , ) . further, the framework enables the analysis and comparison of coal phase-outs -non-linear processes involving a wide variety of actors -as it includes both lock-in and path dependence hindering reorientation of firms-in-industries and entire industriesas well as the reorientation of them, that means the change in the directionality of innovation. it includes insights from neo-institutional theory about the influences from the institutional environment, where "organizations compete for social fitness rather than economic efficiency" (geels, , ) . important is that key: cord- - jmo jc authors: ismail, saba; ahmad, sajjad; azam, syed sikander title: immuno-informatics characterization sars-cov- spike glycoprotein for prioritization of epitope based multivalent peptide vaccine date: - - journal: biorxiv doi: . / . . . sha: doc_id: cord_uid: jmo jc the covid- pandemic caused by sars-cov- is a public-health emergency of international concern and thus calling for the development of safe and effective therapeutics and prophylactics particularly a vaccine to protect against the infection. sars-cov- spike glycoprotein is an attractive candidate for vaccine, antibodies and inhibitor development because of many roles it plays in attachment, fusion and entry into the host cell. in this study, we characterized the sars-cov- spike glycoprotein by immune-informatics techniques to put forward potential b and t cell epitopes, followed by the use of epitopes in construction of a multi-epitope peptide vaccine construct (mepvc). the mepvc revealed robust host immune system simulation with high production of immunoglobulins, cytokines and interleukins. stable conformation of the mepvc with a representative innate immune tlr receptor was observed involving strong hydrophobic and hydrophilic chemical interactions, along with enhanced contribution from salt-bridges towards inter-molecular stability. molecular dynamics simulation in solution aided further in interpreting strong affinity of the mepvc for tlr . this stability is the attribute of several vital residues from both tlr and mepvc as shown by radial distribution function (rdf) and a novel analytical tool axial frequency distribution (afd). comprehensive binding free energies estimation was provided at the end that concluded major domination by electrostatic and minor from van der waals. summing all, the designed mepvc has tremendous potential of providing protective immunity against covid- and thus has the potential to be considered in experimental studies. in december , a new strain of coronavirus emerged in wuhan city of hubei province in china and has since spread globally. the virus belongs to clade b of family coronaviridae in the order nidovirales, and genera betacoronavirus and caused pulmonary disease outbreak [ , ] . it is positive-sense rna, enveloped and non-segmented virus and named as sars-cov- as it share % sequence identity with sars coronavirus (sars-cov) [ , ] . sars-cov- caused coronavirus disease- and evidence suggest a zoonotic origin of this disease [ ] . though the zoonotic transmission is not completely understood but facts provide the ground that it proliferates from the seafood market huanan in wuhan and human-to-human transmission resultant into the exponential increase in number of cases [ , ] . as of march , , cases are reported worldwide with , deaths and , recovered patients. among the active cases, , are currently infected, , ( %) are in mild conditions and , ( %) are seriously ill. serisouly illed. among the , closed cases, , ( %) are recovered whereas , ( %) die. on march , the world health organization (who) affirmed covid- as a pandemic (https://www.worldometers.info/coronavirus/). sars-cov- utilizes a highly glycosylated, homotrimeric class i viral fusion spike protein to enter into host cells [ ] . this protein is found in a metastable pre-fusion state which undergoes a structural rearrangement facilitating viral membrane fusion with the host cell [ ] [ ] [ ] . the binding of s subunit to a host-angiotensin-converting enzyme initiates this process and disrupts the prefusion trimeric structure resulting into s subunit dispersion and stabilizes the s subunit to a post-fusion conformation [ ] . the receptor-binding domain (rbd) of s goes through a hingelike conformational change that temporarily hides or exposes the determinants of receptor binding in order to occupy a host-cell receptor [ ] . down and up conformation states are recognized where former is related to the receptor-inaccessible state and the later one explains receptor-accessible state and considered as less stable [ ] [ ] [ ] [ ] . this critical role of the spike protein makes it an important target for antibody-mediated neutralization, and detailed study of the pre-fusion s structure would provide information at atomic-level helping in the design and development of a vaccine [ ] [ ] [ ] [ ] [ ] . current data indicates that sars-cov- spike and sars-cov spike both share the same functional receptor (host cell) -angiotensin-converting enzyme (ace ) [ , ] . interestingly, ace binds to sars-cov- spike ectodomain with ∼ nm affinity, about - folds higher than ace binding to sars-cov spike [ ] . one possible reason for sars-cov- capability of spreading infection from human-to-human is sars-cov- spike's high affinity for human ace [ ] . series of cellular immune and humoral responses can be triggered by sars-cov- infections [ ] . immunoglobulin g (igg) and igm were noticeable after the weeks of onset of infection which are specific antibodies to sars-cov- . high titers of neutralizing antibodies and sars-cov- specific cytotoxic t lymphocyte responses have been identified in the patients who have improved from sars-cov- . this phenomenon clearly suggest that both cellular and humoral immune reactions are vital to clearing the sars-cov- infection [ ] [ ] [ ] [ ] [ ] . the study presented, herein, is an attempt to get insights about antigenic determinants of sars-cov- spike glycoprotein and highlight all antigenic epitopes [ ] of the spike that can be used specifically for the design of a multi-epitope peptide vaccine construct (mepvc) [ ] to counter covid- infections. the epitopes predicted by immunoinformatics techniques were fused together as well as to β-defensin adjuvant [ , ] to boost the antibody production and long- the mepvc affinity for an appropriate immune receptor as an agonist was checked in the step of molecular docking [ ] . tlr available under pdb id of ziw was retrieved and used as a receptor molecule. tlr also named as cd is a transmembrane protein belongs to the family of pattern recognition receptor [ ] . it detects viral infection-associated dsrna and evoke the activation of interferon regulatory transcription factor (irf ) and (nuclear factor kappa-lightchain-enhancer) nf-kb [ ] . unlike other tlrs, tlr uses tir-domain-containing adapterinducing interferon-β (trif) as a primary adapter [ ] . irf eventually induces the development of type i interferons leading to the activation of innate immune system and eventually to long lasting adaptive immunity [ ] . the tlr receptor and mepvc were used in a blind docking approach through an online patchdock server interface [ ] . the interacting molecules were docked according to the shape complementarity principle. the clustering rmsd is allowed to default . Å. the output docked solutions were immediately refined with fast interaction refinement in molecular docking (firedock) server [ ] which provides an efficient framework for refining patchdock complexes. the refined complexes were examined and one with lowest global energy was considered as top ranked. the opted complex was subjected to in-depth mepvc conformation with respect to the tlr using ucsf chimera . . [ ] . md simulation was applied on the selected top complex for -ns to understand complex dynamics and stability for practical applications. this assay was categorized into three phases: (i) parameters file preparation (ii) pre-processing, and (iii) simulation production [ ] . in first phase using an antechamber module of amber [ ] , complex libraries and set of parameters for tlr and mepvc were generated. the complex system was solvated into Å tip p solvation box achieved through leap module of amber. the intermolecular and intramolecular interactions of the system were determined by ff sb force [ ] field. counter ions in the form of na + were added to the system for charge neutralization. in the system pre-processing stage, complex energy was optimized through several rounds: minimization of complete set of hydrogen atoms for steps, minimization of system solvation box energy for steps with restraint of kcal/mol -Å on the remaining system, minimization of complete set of system atoms again for steps with applied restraint of kcal/mol -Å applied on system carbon alpha atoms, and steps of minimization on system non-heavy atoms with restraint of kcal/mol -Å on other system components. the complex system then underwent a heating step where the complex was heated gradually to k through nvt ensemble, maintained through langevin dynamics [ ] and shake algorithm [ ] to restrain hydrogen bonds. complex equilibration was achieved for -ps. pressure on the system was maintained using npt ensemble allowing restraint on cα atoms of kcal/mol -Å . in the simulation production, trajectories of -ns were produced on time scale of -fs. non-bounded interactions were differentiated by describing cut-off distance of . Å.cpptraj module [ ] was lastly used for statistical computation of different structure parameters to probe complex stability. the md simulation trajectories were visualized and analyzed in visual molecular dynamics (vmd) . . [ ] . axial frequency distribution or simply afd [ ] is a novel analytical technique run on simulation trajectories to access ligand d conformation with respect to reference receptor atom. such local structural movements are not captured by any other available technique. afd can be mathematically presented by eq.i, where, i and j are ligand atom coordinates on x and y axis with cut-off value k and l, respectively. the mi,j sums interactions frequency that fall in the coordinate (i,j). the interaction energy and solvation free energy for tlr receptor, mepvc, tlr -mepvc complex were calculated utilizing the mmpbsa.py module [ ] of amber . also, an average of the above was estimated as a net binding free energy of the system. the binding free energy was computed through mm-pbsa method and its counterpart mm-gbsa of amber with objective to derive the difference between bound and unbound states of solvated conformations of the same molecule [ ] . . computational approach adopted for the design of a sars-cov- spike protein based mepvc. the sars-cov- spike protein was targeted for mepvc designing because of many filters it fulfilled required for a potential vaccine candidate. first, it does not share any significant homology to the human host and as such chances of autoimmune responses are negligible [ ] . second, the protein is also not found to have any sequence identity to the mouse proteome and thus accurate immunological findings can be deciphered from in vivo mice experimentations [ ] . this spike protein only harbored one transmembrane helix ensuring the wet lab protein cloning and expression for antigen analysis easy [ ] . antigenicity is another factor that make this candidate highly suitable for vaccine designing as this allows efficient binding to the products of host immune system [ ] . further, this protein is strongly adhesive which makes it an excellent target for creation of adhesion based vaccine [ ] . lastly, all the sequences of sars-cov- spike protein are highly conserved thus a vaccine based on its sequence will be highly likely to have broad spectrum immunological implications [ ] . prioritization of potential epitopes for the sars-cov- spike protein commenced with the mapping of b-cell epitopes that predicted total of epitopes of vary length ranging from one to (s table ). the average score predicted for these b cell epitopes is . , maximum (max) of . and minimum (min) of . (fig. ) . each bcell epitope was then analyzed in mhc- alleles binding regions prediction [ ] . the predicted epitopes were then screened and stringent criteria of lowest percentile score was used to choose the excellent binders. afterward, the b cell epitopes were simultaneously run in mhc-ii alleles binding [ ] . likewise mhc-i, reference set of mhc-ii binding were: hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , hla-drb * : , and hla-drb * : . the mhc-ii predicted epitopes were also filtered on basis of percentile score and then cross checked with the selected mhc-i allele and those common in both classes were considered only which were in numbers. the shortlisted common mhc-i and mhc-ii epitopes then subjected to antigenicity check. in this check, ability of the filtered b-cell derived t-cell epitopes ability to evoke and bind to products of adaptive immunity. this yielded epitopes all of which have strong ability to bind to the most prevalent drb* with average ic score of . , max of and min of . .the antigenic epitopes then underwent allergenicity check to discard allergic peptides that may cause allergic reactions [ ] . this resulted into epitopes. non-toxic epitopes were whereas were ifn-gamma producer (fig. ) . the set of epitopes obtained at different stages of epitope mapping phase is tabulated in table . these epitopes appear to provide coverage to % of the world population (fig. ) and green peaks are those predicted as epitopes and non-epitopes, respectively. prioritized t cell epitopes derived from b cells were fused together tandemly by aay linkers to make a multi-epitope peptide (mep). aay linker avoid formation of junctional epitopes and as such enhance epitope presentation [ ] . to the n-terminal of mep, eaaak linker was added to attach β-defensin as an adjuvant leading to the design of a mepvc. the mepvc is schematically shown in fig. a . mepvc offers many advantages compared to a separate antigenic peptide. such vaccines induce both cd + and cd + responses and the antigens optimization are optimal. eaaak is a rigid spacer and allow separation of the attached domain and promoting efficient immune processing of the epitopes [ ] . β-defensins are potent immune adjuvants as they are capable of significantly enhancing production of lymphokines resulting into antigen-specific ig production and t cell-dependent cellular immunity. the sequence of mepvc is: giintlckyycrvrggrccvcsccpkeeqigkcstrgrkccrrkkecaakyawnrk cisacyiapgqtgkiccyprrarsvcsacytvydpcqpcaayvydplcpelcayckn htscdv. physicochemical properties of the mepvc were evaluated in order to assist experimentalists in the field to setup experiments accordingly in vitro and in vivo. the length of mepvc is spanned across amino acids and has molecular weight of . kda. vaccine construct with weight less than kda is generally believed to effective vaccine target because of its easier purification. theoretical pi of mepvc is . and aids in locating mepvc on d gel. mepvc aliphatic index is . projecting the vaccine thermostable at different temperatures. the total number of negatively charged and positively charges residues are and , respectively. the grand average of hydropathicity (gravy) score computed for the mepvc is - . , illustrating hydrophilic nature of the protein and is likely to interact with water molecules. the estimated half-life of mepvc in mammalian reticulocytes, in vitro is hours, yeast, in vivo is greater than hours, and escherichia coli, in vivo higher than hours. the antigenicity of the mepvc was cross-checked and predicted highly antigenic with value of . . total entropy of the protein is . which is considered ideal and also the vaccine has no transmembrane helices (alpha helical transmembrane protein, . and beta barrel transmembrane protein, . ) hence no difficulties can be anticipated in cloning and expression analysis. the predicted solubility upon overexpression of mepvc is . reflecting higher solubility of mepvc. the d model of the mepvc was constructed using ab initio dpro predictor as no appropriate template was available for homology modeling and threading methods. the d structure of mepvc is shown in fig. b . the structure secured . % of residues in the ramachandran favored, . %, . % and % residues in additionally allowed, generously allowed and disallowed regions, respectively. as the predicted mepvc unit has number of loop regions that need to be modeled proper before moving forward. in total, five sets of residues: alas -lys , ile -gly , cys -arg , thr -pro , and asn -val were loop modeled. the loop modeled structure increased the ramachandran favored residues percentage to . %, residues in allowed region reduced to . %, residues of generously allowed region to . % and disallowed remained to %. the structure was subjected to structure perturbations and relaxations to obtain a refined model. among the generated structures (s- table ), the first model was selected as it has improved rama favored score, lowest stable galaxy energy of . , improved clash score of . and good molprobity value. similarly, the structure lacks poor rotamers in contrast to the original structure. the ramachandran statistics for the refined d structure are in following order: ramachandran favored residues ( . %), additionally allowed region ( . %), generously allowed region ( . %) and disallowed region ( %). the z-score of the refined mepvc is - . and within the score range of same size protein in structure data bases (s- fig. ). fig. . a. schematic depiction of the mepvc. b. the original predicted d mepvc structure and refined along with respective ramachandran plots. aay linkers are shown in red while epitopes are in coal and yellow is for eaaak linker. cyan color represents the β-defensin adjuvant. in the ramachandran plot, the torsion angles are shown by black squares dispersed across the core secondary structures (colored as red). the allowed regions can be understand by yellow, generously allowed by pale yellow and disallowed by white region. the top right, top left, bottom right and bottom left represent quadrants for left handed alpha helices, beta sheets, right handed alpha helix, and no elements, respectively. further, disulfide engineering of the mepvc was performed in order to optimize molecular interactions and confer considerable stability by attaining precise geometric conformation [ , ] . eight pairs of residues were selected to be replaced with cysteine amino acid. these pairs are: gln -ala (χ angle,+ , energy value, . kcal/mol), cys -leu (χ angle,+ . , energy value, . kcal/mol), lys -ala (χ angle,+ . , energy value, . kcal/mol), arg -ala (χ angle,+ . , energy value, . kcal/mol), ala -ala (χ angle,- . , energy value, . kcal/mol), ala -ala (χ angle, , energy value, kcal/mol), leu -glu (χ angle, - . , energy value, . kcal/mol), and phe -pro (χ angle,- . , energy value, . kcal/mol). these residues have either higher energy level i.e. > kcal/mol and χ angle out of range (< − and > + ) were selected on purpose to make them stable. the original and disulfide mutant mepvc structures are shown in fig. . the primary purpose of in silico cloning of the mepvc was guide molecular biologist and genetic engineers about the possible cloning sites and predicted level of expression in a specific expression system for instance here in this study we used e. coli k system. prior to cloning, reverse translation of the mepvc sequence was conducted to have an optimized codon usage as per e. coli k to yield its max expression. the cai value of the improved mepvc sequence is indicating ideal expression of the vaccine [ ] . the gc content whereas is . % nearly to the e. coli k and range within the optimum ranged between % and %. the cloned mepvc is shown in fig. . both primary and secondary immune responses seem to play a significant contribution against the pathogen and may be compatible to the actual immune response. the in silico host immune system response to the antigen is shown in fig. . high concentration of igg +igg and igm was characterized at the primary response, followed by igm, igg + igg and igg at both primary and secondary stages with concomitant of antigen reduction. additionally, robust response of interleukins and cytokines were observed. all this suggest the efficient immune response and clearance of the pathogen upon subsequent encounters. elevated b cell population including memory cells and different isotypes in response to the antigen, points to the long lasting formation of memory and isotype switching. the t helper cell population additionally with the cytotoxic t cell and their respective memory development are in strong agreement of strong response to the antigen. bioinformatic modelling driven molecular docking of the desingned mepvc to one representative innate immune response receptor tlr was carried out in order to decode mepvc potential of binding to the innate immune receptors. this was fundamental to understand as tlr is significant in recognition of virus associated molecular patterns and of activaiton of type i interferons and nf-kappa b. the docking assesment predicted top complexes sorted mainlny on scoring functions along with interacting molecules area size, desolvation energy, and complexes actual rigid transformation. following, the complexes were subjected to firedock web server for refinement assay. this ease in discarding flexibility errors of the docking procedure and provide a deep refinement of the predictions thus limiting the chances of false positive docking calculations. according to the global energy, solution was considered as a best complex with net global energy of - . kj/mol ( table ). this energy is the output of - . kj/mol attractive van der waals (vdw), . kj/mol repulsive vdw, . kj/mol atomic contact energy (ace), and - . kj/mol hydrogen bond energy. the docked conformation and chemical interacting residues of the mepvc with tlr is shown in fig. . visual inspection of the complex leads to observation of deep binding of the mepvc at the center of tlr and favor rigorously rigoursly hydrogen and weak van dar waals interactions with various residues of tlr . within Å, the mepvc was noticed to formed interactions with his ,val ,asn ,asp ,phe ,val ,asn ,gln ,his ,thr ,glu ,ser ,hi s ,thr ,his ,gln ,glu ,lys ,lys ,glu ,asn ,ser ,asp ,ser ,tyr ,tyr ,phe ,tyr ,lys ,tyr ,tyr ,asn ,his ,asn , and glu . the stability of mepvc with tlr was further investigated through md simulations. the trajectories of md simulations were used in vital statistical analysis to decode backbone stability and residual flexibility. root mean square deviation (rmsd) [ , ] was performed first that compute average distance of backbone carbon alpha atoms of superimposed frames (fig. a) . the average rmsd for the system is . Å with max of . Å at -ns. an initial sudden change in rmsd can be seen up to . -ns that may be due to adjustments adopted by the complex when exposed to dynamics forces and milieu. the second minor rmsd shift can be noticed between -ns to -ns. afterward, the system is quite stable with not global and local conformational changes specified. next, root mean square fluctuations (rmsf) [ ] was applied on the system trajectories (fig. b) . rmsf is the average residual mobility of complex residues from its mean position. mean rmsf for the mepvc-tlr complex calculated is . Å with max of . Å pointed at the n-terminal of the mepvc. most of the interacting residues of the mepvc with tlr are subject to minor fluctuations, a fact in analogy to complex high stability. the thermal residual deviation was assessed afterward by beta-factor (β-factor) [ ] , the outcomes of which is strongly correlated to the rmsf and hence further affirming system stability (fig. c) . the average β-factor of the system analyzed is . Ų with max of . Ų. lastly, we evaluated the compactness of the system by means of radius of gyration (rg) [ ] analysis (fig. d) . high rg and low rg illustrate the magnitude of system compactness and system less tight packing. it further tell us the whether the system of interest in order or not. highly compact system is an indication of system stability and vice versa. the mean rg for our system is . Å with max score of . reflecting higher ordered and compact nature of the system. hydrogen bonds are dipole-dipole attractive forces and formed when a hydrogen atom bounded to a highly electronegative atom such as f, n, and o is attracted by another electronegative atom [ ] . the strength of a hydrogen bond vary from kj to kj per mole. hydrogen bonds are deemed vital in molecular recognition and provide rigidity in achieving stable conformation [ ] . the frequency of hydrogen bonds in each frame of the md simulation trajectories can be visualized in fig. a . these hydrogen bonds are extracted by mean of vmd hbonds plugin and are in number as tabulated in table . the cut-off distance set is . Å and cut-off angle degrees. each residue pair may for one, two or more each of which is counted separately. the min, mean and max number of hydrogen bonds between mepvc and tlr are , , and , respectively. the distribution and bonding pattern of intermolecular interactions of the mepvc residues atom(s) with respect to the tlr were studied through radial distribution function (rdf) (abbasi et al., ; donohue, ; kouetcha et al., ) . rdf mainly describes distance 'r' between two entities and is represented by g(r). the factor 'r' is extracted from simulation trajectories and range from o to ∞ [ ] . the hydrogen bonds predicted by vmd were utilized in rdf that shown only interactions between mepvc and tlr with good affinity for each other. in these interactions, tlr residues (atoms) are: asp :od , gln :he , glu :oe , asp :od , lys :hz , asp :od , glu :oe , and glu :oe are found to have strong radii distribution to their counterpart mepvc residues (atoms): arg :hh , arg : o, lys :hz , arg :hh , glu :oe , asn :hd , arg :hh , and tyr : hh, respectively. the rdf plots for the above said interactions are illustrated in fig. b . the interaction between asp -od and arg -hh has a refined distribution pattern and highest density distribution among all. the max g(r) value for this interaction is . observed at distance range of Å. this is followed by glu -oe -tyr -hh with max g(r) value of . mostly interaction at distance range of . Å. the glu -oe -arg -hh is also much refined having g(r) value of . and mostly interacts within distance range of . Å. the remaining interactions density distribution is not confined and vary considerably but important from mepvc and tlr interaction point of view. salt bridges are non-covalent in nature and the outcome of interactions between two ionized states [ ] . these interactions comprised two parts: an electrostatic interaction and a hydrogen bond. in salt bridges, lysine or arginine typically behave as base where glutamine or aspartate as acid and the bridge is created when carboxylic acid group allows a proton migration to guanidine and amine group in arginine. salt bridges are the strongest among all non-covalent interactions and contribute to a major extent in biomolecular stability [ ] [ ] [ ] . in total, salt bridges were identified between tlr and mepvc within the cut-off distance of . Å as can be depicted from fig. c . the higher numbers of salt bridges were recorded for tlr -glu and mepvc-lys . the mean number of salt bridges for this interaction is , max, and min, . the count for other salt bridges from tlr to mepvc is in following order: asp -arg (mean, , max, and min, ), glu -lys (mean, , max, and min, ), asp -arg (mean, , max, and min, ), glu -arg (mean, max, and min, ), glu -lys (mean, max, and min, ), glu -lys gln -side . % the vital hydrogen bond interactions involved between tlr receptor and mepvc shortlisted by vmd were subjected to a novel afd analysis to elucidate d movements of mepvc atoms with respect to a reference tlr residues atom in simulation time. to this objective, interactions mentioned in the rdf were used in afd. preliminary investigation suggested that only three interactions: tlr -asp -mepvc-arg , tlr -glu -mepvc-tyr , and tlr -glu -mepvc-arg are mainly represented frequently and found in most of the simulation frames. the tlr -asp -mepvc-arg is uncovered in frames, tlr -glu -mepvc-tyr in , and tlr -glu -mepvc-arg in making these interactions ideal for interpreting density distribution of the interactions on xyz planes and also appropriate for gaining ideas about conformational changes of the interacting atoms with respect to each other. as the local structure movements and rotations are responsible for functional shifts, their understanding in our system is important to be unveiled. for tlr -asp -mepvc-arg (fig. ) , the density distribution is not uniform, dispersed and behave flexibility in affinity on all three axis for the receptor atom. parallel, the strength of interaction is also observed affected due to these minor structural movements of the mepvc residue atom. though, the mentioned interaction depicts mepvc is still within the vicinity of the tlr reference residue and enjoys this interaction flexibility with the said mepvc residue during simulation. tlr -glu -mepvc-tyr interaction (fig. ) has less distribution area and has much higher intensity illustrating strong affinity of the interacting atoms for each other. it also gives an idea of the lesser movements of the atoms with respect to each other, an indication of a correct system conformation. the distribution area tlr -glu -mepvc-arg is much dispersed though high intensity of the interaction can be seen in close vicinity (fig. ) . the net free energy of binding (Δtotal) in both gb and pb models are revealed favorable mepvc-tlr complex in pure water. the net gb and pb energy for the mepvc-tlr complex is - . kcal/mol and - . kcal/mol, respectively. to this energy, high contribution was noticed from gas phase energy (Δg gas) compared to highly insignificant contributions from solvation energy (Δg solv). in gb model, the Δg gas energy for the system is - . the net free energy of the simulated system was subjected to per residues and pairwise residues decomposition to point residues that contribute majorly in system stabilization and lower energy. molecular docking simulation studies demonstrated residues from the tlr receptor that are in direct contact with the mepvc but per residue decomposition assay illustrated that among the residues only hie , phe , glu , hie , met , ile , thr , asp , glu , glu , glu , ser , phe , asn , ser , met , asp , tyr , tyr , phe , tyr , tyr , glu , hie , and tyr are hotspot as they contribute rigoursly in binding interaction with mepvc at the docked side. the side chain of hie , thr , asp , glu , ser , tyr , and glu contribute significantly in chemical interactions and have energy value in following order: - . kcal/mol, - . kcal/mol, - . kcal/mol, - . kcal/mol, - . kcal/mol, - . kcal/mol, and - . kcal/mol, respectively. to these tlr hotspot residues, the mepvc interacting residues were also observed in quite lower energies illustrating high affinity for the receptor residues for chemical interactions. the binding free energy of the tlr -mepvc complex, tlr receptor, mepvc and the net system energy is further decomposed into frames extracted from simulation trajectories (s- fig. ). this information deemed vital in predicting the simulation time where higher intermolecular affinity was observed and can guide about the most suitable docked conformation. in general the complex, receptor and construct energies are higher in pb compared to gb but for the total energy, the pb energies are quite lower for frames in contrast to gb. for the complex, the min, max and average binding energy reported are - . kcal/mol, - . kcal/mol, and - . kcal/mol, respectively in gb. the pb max frame energy is - . kcal/mol, min is - . kcal/mol and average is - . kcal/mol. the gb receptor max is - . kcal/mol whereas the min is - . pair-wise energy contribution to the net energy of the system was accomplished in order understand pair residues role from both tlr and mepvc in complex stability. we found that the thr and asp (- . kcal/mol in gb and - . kcal/mol in pb), glu and ser (- . kcal/mol in gb and - . kcal/mol in pb), glu and hie (- . kcal/mol in gb and - . kcal/mol in pb) of tlr receptor have high combine contribution to the net energy. in case of mepvc, asn and thr (- . kcal/mol in both gb and pb), val and arg (- , kcal/mol in gb and - . kcal/mol in pb) and arg and arg (- . kcal/mol and . kcal/mol). taken together, we characterized sars-cov- spike glycoprotein for antigenic peptides and proposed a mepvc by means of several computational immunological methods and biophysical calculations. the outcomes of this study could save time and associated cost that go into experimental epitope targets study. the mepvc is capable of activating all components of the host immune system, have suitable structural and physicochemical properties. also, it seems to have very stable dynamics with tlr innate immune receptor and thus has higher chances of presentation to the host immune system. however, additional in vivo and in vitro experimentations are needed to disclose its potential in fight against covid- . no conflict of interest was reported by the authors. authors are highly grateful to the pakistan-united states science and technology cooperation program (grant no. pak-us/ / ) for granting the financial assistance. fig. . prosa-z energy plot for the mepvc. fig. . residue wise decomposition of net binding energy into tlr receptor and mepvc interacting residues. top (gb) and bottom (pb). fig. . binding energy decomposition per frame for tlr -mepvc complex (a), tlr receptor (b), mepvc (c) and net energy (d). s- table . b cell epitopes predicted for the sars-cov- spike glycoprotein. s- table . top refined model of the mepvc. the input mepvc is also provided. glu -arg (mean, max, and min, ), glu -lys (mean, max, and min, ), glu -arg (mean, max, and min, ), glu -lys (mean, max, and min, ), glu -lys (mean, max, and min, ), glu -lys (mean, max, and min, ), glu -arg (mean, max, and min, ), glu -arg (mean covid- , an emerging coronavirus infection: advances and prospects in designing and developing vaccines, immunotherapeutics, and therapeutics a review of the novel coronavirus (covid- ) based on current evidence emerging coronaviruses: genome structure, replication, and pathogenesis the deadly coronaviruses: the sars pandemic and the novel coronavirus epidemic in china zoonotic origins of human coronaviruses estimating clinical severity of covid- from the transmission dynamics in wuhan, china novel, others, the epidemiological characteristics of an outbreak of novel coronavirus diseases (covid- ) in china, zhonghua liu xing bing xue za zhi= zhonghua liuxingbingxue zazhi structure, function, and antigenicity of the sars-cov- spike glycoprotein structure, function, and evolution of coronavirus spike proteins the coronavirus spike protein is a class i virus fusion protein: structural and functional characterization of the fusion core complex cryo-em structure of the -ncov spike in the prefusion conformation tectonic conformational changes of a coronavirus spike glycoprotein promote membrane fusion cryo-electron microscopy structures of the sars-cov spike glycoprotein reveal a prerequisite conformational state for receptor binding shi, others, immunogenicity and structures of a rationally designed prefusion mers-cov spike antigen lanzavecchia, others, unexpected receptor functional mimicry elucidates activation of coronavirus fusion cryo-em structures of mers-cov and sars-cov spike glycoproteins reveal the dynamic receptor binding domains others, characterization of novel monoclonal antibodies against merscoronavirus spike protein wu, others, identification of the immunodominant neutralizing regions in the spike glycoprotein of porcine deltacoronavirus development of epitope-based peptide vaccine against novel coronavirus (sars-cov- ): immunoinformatics approach therapeutic options for the novel coronavirus ( -ncov) receptor recognition by the novel coronavirus from wuhan: an analysis based on decade-long structural studies of sars coronavirus greenough, others, angiotensin-converting enzyme is a functional receptor for the sars coronavirus the novel coronavirus ( -ncov) uses the sars-coronavirus receptor ace and the cellular protease tmprss for entry into target cells stabilized coronavirus spikes are resistant to conformational changes induced by receptor recognition or proteolysis others, a familial cluster of pneumonia associated with the novel coronavirus indicating person-to-person transmission: a study of a family cluster perspectives on therapeutic neutralizing antibodies against the novel coronavirus sars-cov- longitudinal profile of immunoglobulin g (igg), igm, and iga antibodies against the severe acute respiratory syndrome (sars) coronavirus nucleocapsid protein in patients with pneumonia due to the sars coronavirus disappearance of antibodies to sars-associated coronavirus after recovery an efficient method to make human monoclonal antibodies from memory b cells: potent neutralization of sars coronavirus anti--spike igg causes severe acute lung injury by skewing macrophage responses during acute sars-cov infection peptide vaccine: progress and challenges multi-epitope vaccines: a promising strategy against tumors and viral infections avian antimicrobial peptides: the defense role of $β$-defensins exploring the zika genome to design a potential multiepitope vaccine using an immunoinformatics approach exploring ns / a, ns a and ns b proteins to design conserved subunit multi-epitope vaccine against hcv utilizing immunoinformatics approaches molecular dynamics simulations of biomolecules the mm/pbsa and mm/gbsa methods to estimate ligandbinding affinities the immune epitope database (iedb): update bepipred- . : improving sequence-based b-cell epitope prediction using conformational epitopes gapped sequence alignment using artificial neural networks: application to the mhc class i system peptide binding predictions for hla dr, dp and dq molecules mhcpred: a server for quantitative prediction of peptide--mhc binding pangenome and immuno-proteomics analysis of acinetobacter baumannii strains revealed the core peptide vaccine targets virulentpred: a svm based prediction method for virulent proteins in bacterial pathogens vaxijen: a server for prediction of protective antigens, tumour antigens and subunit vaccines allertop-a server for in silico prediction of allergens peptide toxicity prediction designing of interferon-gamma inducing mhc class-ii binders development of an epitope conservancy analysis tool to facilitate the design of epitope-based diagnostics and vaccines exploring dengue genome to construct a multi-epitope based subunit vaccine by utilizing immunoinformatics approach to battle against dengue infection scratch: a protein structure and structural feature prediction server others, galaxy: a platform for interactive large-scale genome analysis galaxyrefine: protein structure refinement driven by sidechain repacking disulfide by design . : a web-based tool for disulfide engineering in proteins codon usage: nature's roadmap to expression and folding of proteins jcat: a novel tool to adapt codon usage of a target gene to its potential expression host innate immune pattern recognition: a cell biological perspective molecular docking, in: mol. model. proteins a family of human receptors structurally related to drosophila toll signaling to nf-$κ$b by toll-like receptors medical microbiology e-book: a guide to microbial infections: pathogenesis, immunity, laboratory diagnosis and control. with student consult online access recognition of doublestranded rna and activation of nf-$κ$b by toll-like receptor patchdock and symmdock: servers for rigid and symmetric docking firedock: fast interaction refinement in molecular docking ucsf chimera-a visualization system for exploratory research and analysis combating tigecycline resistant acinetobacter baumannii: a leap forward towards multi-epitope based vaccine discovery the ff sb force field langevin stabilization of molecular dynamics a fast shake algorithm to solve distance constraint equations for small molecules in molecular dynamics simulations cpptraj: software for processing and analysis of molecular dynamics trajectory data vmd: visual molecular dynamics afd: an application for bi-molecular interaction using axial frequency distribution mmpbsa.py: an efficient program for end-state free energy calculations assessing the performance of the mm_pbsa and mm_gbsa methods. . the accuracy.pdf identification of putative vaccine candidates against helicobacter pylori exploiting exoproteome and secretome: a reverse vaccinology based approach vaxign: the first web-based vaccine design program for reverse vaccinology and applications for vaccine development panrv: pangenome-reverse vaccinology approach for identifications of potential vaccine candidates in microbial pangenome prioritization of potential vaccine targets using comparative proteomics and designing of the chimeric multi-epitope vaccine against pseudomonas aeruginosa adhesins as targets for vaccine development exoproteome and secretome derived broad spectrum novel drug and vaccine candidates in vibrio cholerae targeted by piper betel derived compounds the mhc class i antigen presentation pathway: strategies for viral immune evasion mhc class ii proteins and disease: a structural perspective vaccine allergies predefined spacers between epitopes on a recombinant epitope-peptide impacted epitope-specific antibody response in silico design of multimeric hn-f antigen as a highly immunogenic peptide vaccine against newcastle disease virus disulphide bonds and protein stability protein disulfide engineering novel immunoinformatics approaches to design multi-epitope subunit vaccine for malaria by investigating anopheles salivary protein molecular dynamics simulation studies of novel $β$-lactamase inhibitor significance of root-mean-square deviation in comparing three-dimensional structures of globular proteins interaction mechanisms of a melatonergic inhibitor in the melatonin synthesis pathway binding mode analysis, dynamic simulation and binding free energy calculations of the murf ligase from acinetobacter baumannii radius of gyration as an indicator of protein structure compactness the hydrogen bond in molecular recognition hydrogen bonds in proteins: role and strength ultrafast scalable parallel algorithm for the radial distribution function histogramming using mpi maps radial distribution functions of some structures of the polypeptide chain defining the role of salt bridges in protein stability do salt bridges stabilize proteins? a continuum electrostatic analysis protein stabilization by salt bridges: concepts, experimental approaches and clarification of some misunderstandings contribution of surface salt bridges to protein stability: guidelines for protein engineering key: cord- -ezsy mx authors: rahman, hamidur; hossain, md. rakib; ferdous, tahmina title: the recent advancement of low-dimensional nanostructured materials for drug delivery and drug sensing application: a brief review date: - - journal: j mol liq doi: . /j.molliq. . sha: doc_id: cord_uid: ezsy mx in this review article, we have presented a detailed analysis of the recent advancement of quantum mechanical calculations in the applications of the low-dimensional nanomaterials (ldns) into biomedical fields like biosensors and drug delivery systems development. biosensors play an essential role for many communities, e.g. law enforcing agencies to sense illicit drugs, medical communities to remove overdosed medications from the human and animal body etc. besides, drug delivery systems are theoretically being proposed for many years and experimentally found to deliver the drug to the targeted sites by reducing the harmful side effects significantly. in current covid- pandemic, biosensors can play significant roles, e.g. to remove experimental drugs during the human trials if they show any unwanted adverse effect etc. where the drug delivery systems can be potentially applied to reduce the side effects. but before proceeding to these noble and expensive translational research works, advanced theoretical calculations can provide the possible outcomes with considerable accuracy. hence in this review article, we have analyzed how theoretical calculations can be used to investigate ldns as potential biosensor devices or drug delivery systems. we have also made a very brief discussion on the properties of biosensors or drug delivery systems which should be investigated for the biomedical applications and how to calculate them theoretically. finally, we have made a detailed analysis of a large number of recently published research works where theoretical calculations were used to propose different ldns for bio-sensing and drug delivery applications. by the world health organization [ ] . these three research works from the last three years are just some of many more recent research works done with ldns in the search for a biosensor. besides the application of ldns as drug and biomolecule sensors, their biocompatibility leads them to another crucial biomedical use, drug delivery systems. the drug delivery systems play an essential role in the pharmaceutical field by reducing the severe adverse effects of the various drug, especially chemotherapeutic anticancer drugs, by delivering the drugs to the targeted cell area. earlier in , xibo pei and his co-workers used polyethylene glycol attached graphene oxide (pgo) nanosheet as a dual-drug delivery system for antitumor drugs cisplatin (pt) and doxorubicin (dox) [ ] . in vivo data from their work confirmed that compared to the toxicity of free pt and dox drugs itself, pgo-pt/dox dual-drug delivery system displayed a significantly reduced toxicity. also, in vitro data from their study confirmed most prominent cell apoptosis and necrosis for pgo-pt/dox system compared to the free drugs and showed a higher growth inhibition property. the graphene and go nanosheets were further used as a drug delivery system for many other anticancer drugs including βlapachone [ ] , fluorouracil [ ] , camptothecin [ ] etc. and many other biological drugs including plasmid dna [ ] [ ] [ ] , sirna [ ] [ ] [ ] , proteins [ ] [ ] [ ] etc. other than the graphene nanosheets (gns), e. czarniewska and his team found that the oh functionalized bn (bn-oh-n) nanosheets showed very low cytotoxicity in both in vivo and in vitro hence bnnss can be applied in the platform like bio-imaging and drug delivery [ ] . furthermore, hollow bn spheres with anticancer drug paclitaxel were observed to suppress the tumour growth significantly with an increased prostate cancer cell apoptosis and decreasing cell viability [ ] . another allotrope of bn, bnnt functionalized with mesoporous silica was also found to perform as a potential drug delivery system for another anticancer drug dox to treat prostate cancer by increasing cancer cell killing ability [ ] . other than these gns and bn allotropes, other nanomaterials, e.g. metal-organic frameworks [ ] , phosphorene [ ] , gold nanoparticle [ ] etc. displayed their ability to carry many drugs by reducing adverse effects with lower cytotoxicity. figure : comparison between the normalized experimental and dft simulated absorption spectra of ssz in water. reproduced with permission from ref. [ ] . copyright springer nature, . choose the functionals and basis sets selectively, in case of the first-principles calculations through a computer simulation package. besides spectroscopic resemblance, dft theory also predicted the reactivity and reaction mechanism successfully with accordance to the experimental observations [ ] . the dft theory was also applied by m. darvish ganji et al. to observe the drug release mechanism using cnt [ ] . furthermore, they have also observed the interaction energy of - . kcal/mol in case of the interaction of benzene molecules with the graphene surface where it was observed as - . kcal/mol experimentally. due to these conveniences with the experimental results, first-principles calculations holds a potential application to explore various biosensor devices and drug delivery systems at the first place in a short time with a reduced cost. finally, considering a significant increase in the drug adsorption related work in the last years from figure , herein we have made a comprehensive review on the recent advancement of first-principles calculation on the applications of ldns in the biomedical fields including drug sensors and drug delivery. we have analyzed the properties which can be investigated through the first-principles calculations and application of those properties in search for promising drug sensors and drug delivery systems for different kind of drugs, especially the anticancer drugs. furthermore, we have explored the adverse effects of the drugs and several specific properties of the nanostructures, which provides it with an advantage to perform as a drug sensor or delivery system. finally, we have analyzed a wide range of research works that were reported in the last few years searching for promising drug sensors or delivery systems using first-principles calculations. biomedical fields like drug sensor and drug delivery. in this section, we will make a brief discussion on the properties of the drug sensors and drug delivery systems which can be calculated theoretically using computer simulation packages. the first thing first-principles calculations allows researchers is to optimize and relax their structures into the global minimum energy using many existing quantum mechanical theories like dft, md etc. with their respective exchange correlational functional basis sets. from the optimized geometry, it is possible to calculate the bond length and bond angle between the constituent atoms in the structures. these are essential parameters to investigate from which the interaction between the drug molecules and respective adsorbents can be confirmed, and their type of interactions can be identified. the different vibrational mode of the constituting atoms of a material can be observed through the ir spectroscopy. as it denotes every individual vibrational mode of a material, it is often used to identify the material hence works as a fingerprint of the material [ ] . by investigating the imaginary frequencies in the ir spectrum, researchers also achieve the information about the stability of the structures and the possibility of finding them into nature or synthesizing them into the laboratory. if any imaginary frequency for a vibrational mode in the structure is observed from the theoretical calculations, there will be a minimal possibility to find that material into nature as the naturally existing materials can not possess any imaginary frequencies. to investigate the structural stability of a nanostructure system, the cohesive energy ( ) of nanostructures can be calculated as [ ] : where n is the total number of constituent's atoms of the nanostructure, a and b represents the different constituent atoms of the nanostructure and and respectively represents their energies with x and y be the total number of them in the nanostructure. uv-vis spectrum usually provides researchers with information about the range of wavelength the material will absorb. the spectrum is also associated with the electronic bandgap of the material where a broader spectrum represents a wider bandgap of the material. besides, it is also useful to investigate the interaction of a biomolecule or drugs with the adsorbent material as an introduction of the new energy states usually creates a noticeable change in the spectrum [ ] . furthermore, the right shift of the spectrum or simply redshift due to the drug adsorption indicates with a decrease in the bandgap with an increase in the conductivity of the sensor material and an enhanced sensitivity towards the drug molecule [ ] . the nuclear magnetic resonance (nmr) usually allows researchers to investigate the magnetic field around an atomic nucleus. however, it is further applied extensively in structural biology to study the structure and dynamics of a biological sample. in drug sensing and drug delivery applications, nmr can also be used to investigate the chemical shift due to the interaction of an adsorbate molecule with an adsorbent [ ] . to investigate the adsorption process between the adsorbent and an adsorbate molecule, one of the most reliable and often used method is to examine the adsorption energy ( ) due to the adsorption which can be calculated as [ ] , where, represents the energy of adsorbate adsorbed adsorbent nanostructures and both and represents the isolated energy of the adsorbent and adsorbate, respectively. here a negative value for the adsorption energy represents a stable adsorption process, whereas the positive value for the adsorption energy represents no adsorption process. besides, if the adsorption energy value is less than ev, then the adsorption process is considered as weak physisorption, and no chemical interaction can be found between the adsorbate and adsorbent [ ] . but if the adsorption energy exceeds ev, then a strong chemical interaction is considered to have occurred between the adsorbate and adsorbent, and the adsorption process is then levelled as chemisorption. hence, more negative the value of adsorption energy gets, more strongly the system is considered to be bounded, representing a higher stable system. so, for the drug delivery and drug sensor devices, the adsorption process between the drug molecules and adsorbents are expected to have a negative value for the adsorption energy where in case of drug delivery systems the adsorbent is required to make a strong interaction with the drug molecule. but in the drug sensor devices, weak physisorption is desired as the strong chemical interactions often lead to a higher recovery time which is not suitable for the drug sensor device. several important information about the adsorption can also be found from the minimum distance between the adsorbate and adsorbent. a smaller distance between the adsorbate and absorbent often lead to a higher charge transfer between the adsorbent and the adsorbate molecules. hence the sensitivity of the adsorbent materials towards the adsorbate molecules can be understood which plays an important role in a drug sensor device development [ ] . several studies also claimed that a smaller adsorbent-adsorbate distance leads to a stronger interaction between and provides them with higher stability [ ] . to investigate the thermodynamical nature of the interaction, first-principles calculations allows calculating the change in the gibbs free energy ( ) using [ ] , where g represents the sum of electronic and thermal free energies. from the definition of the gibbs free energy, a negative change in the gibbs free energy represents a spontaneous interaction between the adsorbate molecule and adsorbent hence a negative change in desired in case of both drug delivery and drug sensor devices. the change in enthalpy ( ) can be calculated from [ ] , where h represents the sum of electronic and thermal enthalpies. a positive change in the enthalpy labels the reaction between the adsorbent and adsorbate as an endothermic reaction, whereas the negative changes in the change of enthalpy lead to an exothermic reaction. finally, the change in entropy ( ) can be calculated using, where t is the considered temperature depending on the systems. in most of the cases, the changes in entropy become negative due to the adsorption of a drug molecule by an adsorbent material which is because of the constrained movement of the structures due to their newly formed intermolecular bondings. j o u r n a l p r e -p r o o f . . homo and lumo energy the homo energy ( ) represents the energy state of the highest occupied molecular orbital (homo) whereas the lumo energy ( ) stands for the energy state of the lowest unoccupied molecular orbital (lumo). these are significant properties for a drug sensor or drug delivery systems as the difference between the homo and lumo energy, which is often expressed as h-l energy gap ( ), represents the conductive nature of the system where the conduction electron population (n) can be defined as [ ] , where, hence, by definition, a smaller h-l energy gap represents a higher conductivity which is desired for a drug sensor device. therefore, to inspect the sensitivity of the adsorbent towards the adsorbate, change in the h-l energy gap due to the adsorption plays an important role. for a drug sensor, if the h-l energy gap decreases significantly due to the adsorption of the drug on the nanostructure, then the nanostructure is considered to be sensitive towards the drug. this increase in the conductivity produces a detectable electrochemical signal from which the adsorption process can be confirmed, and the drug can be detected. besides just the homo and lumo orbital, first-principles calculations allow investigating all possible states for a given energy range by allowing to calculate the dos spectrum. hence the h-l energy gap can also be investigated from the dos spectrum. another vital application of dos spectrum for the drug sensor devices is that the interaction between the drug and the adsorbent can also be confirmed from the alteration of the dos spectrum due to the adsorption of the drug molecule. the resistance of a structure towards the deformation can be investigated from the global chemical hardness (η), which can be calculated from [ ] : hence, a higher value for the global hardness indicates higher chemical stability for the structure with reduced chemical reactivity. the global softness (s) has an inversely proportional relationship with the global hardness which can be expressed as [ ] , hence, opposite to the global hardness, an increase in the global softness indicates an increase in the chemical reactivity with the reduced chemical stability of the structure. using the koopmans' theorem, the chemical potential (µ) can be calculated as [ ] : the chemical potential also can be used to determine the stability of the investigated structures besides its another potential application to determine the direction of electron transfer from the adsorbate to adsorbent [ ] . the electrophilicity index ( ) from parr et al. also can be calculated using the formula [ ] : the electrophilicity can also be used to investigate the structural stability, reactivity and toxicity of a nanostructure where, similar to the global softness, an increasing value the electrophilicity index also indicates an increase in the chemical reactivity [ ] . the negative value of the chemical potential is known as the electronegativity ( ) of the structure and can be calculated as, to investigate the charge transfer between the adsorbate molecules and the adsorbent, the natural bond orbital (nbo) based charge transfer and the original basis function-based mulliken charge transfer can be calculated from theoretical calculations using computer simulations. these investigations of the charge transfer play an essential role to the development of a drug sensor device by observing if the adsorbent nanostructures are capable of making a detectable electrochemical signal on the presence of a drug molecule. to understand the charge transfer between the adsorbate and adsorbent more extensively, the quantum mechanical atoms in molecule (aim) analysis can be studied where the charge transfer between the adsorbate and adsorbent atoms can be observed from the bonded paths and the bond critical points (bcp), an appearance of which can confirm the charge transfer between the adsorbate and adsorbent atoms. the type of interaction can also be understood from aim analysis using several other parameters including the electron density at bcp ( ) and its laplacian ( ), kinetic electron energy density ( ), potential electron energy density ( ), and the total electron energy density ( ) which is the sum of kinetic and potential electron energy density [ ] . a closed-shell interaction can be confirmed from the positive value of the where the negative value represents a shared interactions. besides, if the negative ratio of the kinetic electron energy density to the potential electron energy density ( ) is greater than then the interaction is considered to be non-covalent and electrostatic in nature where < represent a covalent nature of the interaction. furthermore, at the bcp, if both and becomes negative, the interaction is considered as a strong covalent interaction following by weak electrostatic interaction for the positive value of both and [ ] . but if the becomes positive and remains negative, then the interaction can be labeled as a partial covalent and partial electrostatic interaction in nature. the molecular electrostatic potential (mep) map represents the regions where a positive test charge can be attracted or repelled. the positive electrostatic potential region, which is often coloured as blue in the mep map represents the regions with low electron density where a positive charge gets repelled by the atomic nuclei. furthermore, the negative electrostatic region is coloured as red in the mep map, which represents the region with higher electron density where a positive test charge can be attracted by the atomic nuclei. the interaction of a drug molecule with the adsorbent usually alters the electron density in the system hence an interaction can be detected from this alteration in the mep map which can further be used in the drug sensor device development. it is also possible to determine the direction of the charge flowing through the adsorbate and adsorbent from the calculation of the change in fractional charge ( ) using pearson's method [ ] : where µ and η represent the global chemical potential and chemical hardness, respectively. in this case, if the value for appears to be negative, then it can be concluded that the charge will flow towards the adsorbent from the adsorbate where a positive value will indicate the charge transfer to the adsorbate from the adsorbent. j o u r n a l p r e -p r o o f the dissolvability of the nanostructures into a polar medium like water etc. can be investigated using dipole moment (dm) which plays an integral part for drug delivery devices. an increasing dm represents a higher charge asymmetry for the structures which is desired in case of the drug delivery systems so that they can attract more random electrons and dissolve into the polar mediums. besides vacuum, theoretical calculations allow calculating the properties of nanostructures in many other mediums, e.g. water, acid, methanol etc. which plays a crucial role on investigating the behaviour of the drug sensors and drug delivery systems in many different targeted environments. for example, it is crucial to examine the performance of an anticancer drug delivery systems in a low ph cancerous cell region for a better understanding to the drug release performance of the nanostructures in the targeted region. the solubility and stability of the nanostructures in any solvent medium can be further investigated in terms of the solvation energy. for example, negative solvation energy of a nanostructure in a solvent medium represents spontaneous solvation and higher stability of that nanostructure in that solvent [ ] . hence for the drug delivery application, the solvation energy is essential to be negative in the polar solvent mediums like water etc. the solvation energy can be calculated from, where, represents the total energy of the structure in the solvent medium and represents the energy of the structure in the gaseous medium. in both drug delivery and drug sensor devices, the drug release mechanism plays a crucial to study the efficiency of the device. this can be observed from the interaction of the drug molecule with the adsorbent in the targeted environment. for example, if the adsorption energy of an anticancer drug on a nanostructure decreases or become positive in the low ph cancerous cell environment, the nanostructure is considered to desorb and release the drug ideally in a low ph environment. graphene is a d single-layer hexagonal network of carbon atoms bonded with sp hybridization. this honeycomb shaped allotrope of carbon along with its zero bandgap, exceptional hardness and other superior structural, electronic, and optical properties lead scientists to apply this material into many diverse fields like solar cells, gas sensor, biosensors, drug delivery system etc. [ ] [ ] [ ] [ ] [ ] . after the first synthesis of graphene by novoselov et al., from the university of manchester using the scotch tape method [ ] , several synthesis methods like exfoliation of natural graphite [ ] , chemical vapour deposition (cvd) [ ] , reduction of graphene oxide (go) [ ] etc. showed promising future in the graphene fabrication industry. though the method relating to the reduction of go into gns provides excellent cost-effectiveness, cvd can offer a large area on the gnss. the experimental c-c bond length of the graphene was observed as . - . Å [ ] with several other superior properties like very high strength with the value of young's modulus of tpa [ ] , the high thermal conductivity of w/mk [ ] , the electrical conductivity of s/m [ ] , and high carrier mobility at the room temperature as , cm /vs for carrier densities below × cm [ ] . besides these unique properties, the biocompatibility and reduced cytotoxicity of gnss made itself a promising candidate for the drug sensor and delivery applications [ , ] . but pristine gns shows weak interaction towards many drugs and amino acids which can be significantly enhanced by altering its properties with impurity atom doping. besides doping, the hexagonal ring of the graphene was also modified into a pentagonal and heptagonal ring to create a new type of nanomaterial named as phagraphene which shows promising applications in the drug delivery applications [ ] . besides, the theoretical calculations with gns showed significant similarity with experimental results, e.g. in figure we have optimized graphene quantum dot (gqd) using dft with b lyp/ - g (d,p) level of theory which showed comparable bond length, bond angles etc. with the experimental observations. thus the research on the theoretical implementation of pristine, doped or functionalized graphene in the field of drug delivery and drug sensor become very popular in recent years. β-lapachone (β-lap), a potential chemotherapeutic anti-cancer agent, possess an excellent value as it selectively kills or stops the growth of various tumour cells responsible for pancreas, prostate head and neck cancers [ ] [ ] [ ] . β-lap, containing naphthoquinone fused to a methylated hydropyran moiety, was originally j o u r n a l p r e -p r o o f isolated from a south american tree named lapacho. to carry this anti-cancer agent into the cancerous cell, the feasibility of using pristine and metal-doped (pt, au) graphene was investigated by zahra khodadadi et al. by a first-principles investigation [ ] . they observed the adsorption properties of β-lap into pure gns first, and then it's dipole moment to investigate the solubility into a polar medium like water. pristine graphene had a c-c bond length of . Å with a bond angle of ° and sp hybridization. but these properties were further modified by decorating metal atoms (pt, au) into the gns. the pt-c and au-c bond length for pt and au decorated gnss were increased to . Å and . Å respectively with a variation in the sp hybridization as the bond angles decrease to ° and ° respectively. but these modifications into the structural properties enhanced the adsorption properties of β-lap into the pt and au decorated graphene and their solvation properties into polar mediums. the adsorption energies of pt and au decorated graphene was increased as - . kcal/mol and - . kcal/mol which was - . kcal/mol for pristine graphene. hence it can be understood that the stability of the graphene was enhanced due to the metal doping. further, the dipole moment of the β-lap adsorbed graphene was increased by . and . debye by pt and au doping respectively while it was only . debye for the pristine gns. hence, β-lap was expected to dissolve into the polar medium more efficiently with an increased reactivity. so, it can be concluded that the metal-doped graphene performs better as a β-lap drug carrier rather than pristine graphene itself. doxorubicin, another chemotherapeutic drug for several cancer treatments, comes with high toxicity which causes many physical difficulties like hypertension and even a heart failure [ ] [ ] [ ] . m. z. tonel et al., made an investigation on the adsorption of doxorubicin on gns using dft theory with gga-pbe functional applied in the siesta code to decrease the side effects of the drug [ ] . they have found the binding energy of the doxorubicin with the pristine graphene can be as high as . kcal/mol with an adsorbate-adsorbent distance of . Å. however, this small adsorbate-adsorbent distance allowed a charge transfer of - . e between them. but depending on the orientation of the doxorubicin, the binding energy can drop down to . kcal/mol with an adsorbate-adsorbent distance of . Å. so, depending on the most stable orientation, they have reported stable adsorption of doxorubicin drug on gnss which were previously inconspicuous for carbon-based nanomaterial in many experimental and theoretical studies [ ] [ ] [ ] . aluminium (al) doped nanostructures were reported to adsorb -fluorouracil (fu), an anti-cancer drug for gastrointestinal, stomach etc. cancer treatment, strongly adsorption with an enhanced drug loading capacity [ , ] . to bring these research further, m. vatanparast et al., theoretically studied aln and bn doped gqd, another low toxic structure with high biocompatibility, as an efficient nanomaterial for the fu drug delivery [ ] . supporting the literature, the aln doped gqds showed some strong adsorption to the fu with a noticeable adsorption energy of - . kcal/mol for aln-fu gqd structure. in their work, they have worked with c h gqd whose central ring was further replaced by b-n, b-p, al-n and al-p bonds. besides high adsorption energy for the aln-fu gqd structure, negative values for the gibbs free energies of all other doped structures confirmed the spontaneous adsorption of fu with adsorption energies higher than that of the pristine gqd. further restriction to the translation degree of freedom lead to a decrease in the entropy with predicted exothermic adsorption with negative values for the change in enthalpy. these confirmed the ability of the pristine and doped gqds to load the fu drug. finally, an increase in the dipole moment up to . debye for aln-fu gqd, highest among the investigated structures, represents aln doped gqd's better solubility to the polar medium and enhanced reactivity towards fu drug made itself a potential candidate to carry fu to the target sites. carrier [ ] . the functionalization of the gns modified the adsorption process of the tegafur towards the structures significantly with a maximum value of the adsorption energy as - . kcal/mol for g-co/tg along with a minimum of - . kcal/mol for g-cooh/tg structure. the solvation energy of the g-cooh/tg structure was also found as - . kcal/mol with a - . kcal/mol of interaction energy. besides g-cooh, g-oh also showed very strong adsorption towards the tegafur with a remarkable adsorption energy of - . kcal/mol and solvation energy, and interaction energy of - . , - . kcal/mol respectively. though the dipole moment of the pristine gns is zero but increases significantly with the functionalization and hits as high as . debye for the tegafur adsorbed g-co structure. on the other side, the energy gap was reduced to as low as . ev for the tegafur adsorbed co functionalized gns while it was . ev for the pristine gns nanosheet. these indicated the batter reactivity of the tg adsorbed functionalized gns sheet with a higher polarity towards a polar medium like water which was further supported by the global parameters like chemical potential, global hardness, electrophilicity investigations. as it can be observed from figure that many anti-cancer drugs have structures akin to the nucleobases as the vital role of these drugs is to slow the growth rate of cancer cells by interfering their dna synthesis [ ] . this led c. rungnim et al., to investigate the adsorption properties, along with edge effect of the gnss, of three nucleobases with similar structures like anti-cancer drugs, mercaptopurine, thioguanine, and fluorouracil, on a graphene flake considering the weak dispersion forces caused by van der waals interaction [ ] . the lack of accuracy of many gga functional with dft due to their underestimation of π-π interaction lead rungnim et al., to use several functional like m - x, mp , ccsd(t) etc. [ ] . to validate their theoretical model, they have first investigated the adsorption properties of nucleobase uracil and then the anti-cancer drug akin to the uracil, fluorouracil, on the benzene ring. it was observed that the o on uracil and fluorouracil pointing to the benzene ring, and uracil/fluorouracil parallel to the benzene ring has better stability than any other investigated orientations. for o pointing to the benzene ring, benzene/uracil and benzene/fluorouracil configurations have adsorption energies as high as - . kcal/mol and - . kcal/mol respectively which becomes - . kcal/mol, and - . kcal/mol respective for uracil/fluorouracil parallel to the benzene ring. a favourable result from the meta gga based m - x functional led them to study the adsorption behaviour of the nucleobases towards the c , c , and c gnss. they have observed an edge effect which gradually decreased with the increased size of the graphene nanoclusters. less edge effect was observed in case of the adsorption of the nucleobases in the middle of the carbon clusters and depending on the alignment and position this effect can reduce the adsorption energies by < kcal/mol. further, the edge effect of c is almost as much as c lead them to adsorb mercaptopurine, thioguanine, and fluorouracil anti-cancer drugs in a parallel position with different alignments in the c nanosheet. finally, the adsorption energies of fluorouracil, mercaptopurine, and thioguanine were found around - . , - , and - kcal/mol respectively made c a promising candidate for the delivery of these drugs. adenine, another nucleobase with a structure akin to many drugs and biomolecule, showed enhanced adsorption properties on the ni decorated gnss compared to the pristine gns which was observed on an investigation made by s. gholami et al., [ ] . for a plane alignment of adenine to the pristine graphene surface, the adsorption energy was found as - . kcal/mol with a graphene-adenine distance of . Å and a charge transfer of - . e (mulliken) only. the adsorption energy was dramatically increased to a maximum of - . kcal/mol with an adsorbate-adsorbent distance of . Å, and a charge transfer of + . e (mulliken) in the ni decorated gns, where ni was adsorbed above the hexagonal ring of graphene with a strong chemical interaction of - . kcal/mol. adsorption of the adenine on the ni decorated graphene also decreased the bandgap and fermi level of the structure to . ev and - . ev respectively from a value of . ev and - . ev for ni-g itself. though the pristine graphene showed a weak interaction towards the pristine gns, decorating it with a ni atom increased its interaction significantly. hence the ni decorated graphene can be considered as a potential candidate for delivery of the drugs with structures similar to the adenine. furthermore, the adsorption of guanine nucleobase was investigated by a. s. rad et al., on pristine and al-doped graphene (alg) using dft theory with b lyp hybrid functional and - g basis set [ ] . it was observed that the doping of al to the pristine gns significantly alters the adsorption properties towards guanine. for pristine gns, the adsorption energy of guanine was observed only as - . kcal/mol with an adsorbateadsorbent distance of . Å. this allowed them to transfer a little amount of charge of - . e (based on mulliken charge transfer analysis), or - . e (based on natural population analysis) between adsorbate and the adsorbent. this was significantly enhanced by the doping of al atom to the pristine gns. for a specific orientation of guanine, o atom from guanine above al atom from alg, the adsorption energy increased as much as - . kcal/mol with an adsorbate-adsorbent distance of . Å only which allows them to transfer + . e (mulliken) amount of charge. for other orientations the adsorption energies were observed as - . , - . , - . , - . kcal/mol with an adsorbate-adsorbate distance of . Å, . Å, . Å, and . Å respectively. furthermore, along with the adsorption energy and charge transfer, the dipole moment of the alg structures was also enhanced significantly with a maximum of . debye. this excellent modification in the adsorption energy, charge transfer and dipole moment made alg nanostructure a suitable adsorbent or sensor for the guanine. other than the anti-cancer drugs, graphene was also reported to work as a drug delivery vehicle for -aminopyridine or dalfampridine, often marketed as ampyra with a chemical name of c h n-nh , helps to overcome walking difficulties for the adults by increasing nerve signal conduction through blocking the potassium channels on it [ , ] . but ampyra has several side effects like headaches, dizziness, nausea, insomnia etc. and an increased dose of it can also cause seizures [ ] . to reduce the possibility of a seizure, najme dastani et al. proposed pristine and functionalized gns (f-gns) for the transportation of ampyra using quantum mechanical calculations [ ] . they choose the dft theory with m - x functional and - g (d, p) basis set to optimize the structures due to its excellent agreement with the experiment. for gns, they observed c-c bond length as . Å while it was found as . Å experimentally [ ] . this encouraged them to study several f-gns (g-cooh, g-co, g-oh, and g-o) with the same functional and basis set. they have studied several essential properties like adsorption energies, homo-lumo energy gaps, chemical potential, dipole moment and several global parameters for both gaseous and aqueous phase. it was found that the dipole moment in the aqueous phase rose to . debye from a maximum of . debye in the gaseous phase. for the functionalized gnss this dramatic change on the dipole moment was continued and was found as high as . debye for g-cooh/ampyra complex. finally, the highest negative adsorption energies of - . kcal/mol for g-cooh/ampyra complex among the pristine gns and f-gns in the aqueous phase made g-cooh the best candidate for the transportation of ampyra drug. this was further supported by the lowest value for the energy gap as . ev, global hardness as . ev and the highest value for the change in global electrophilicity as . ev. besides the application of graphene as a potential sensor for the drugs and nucleobases, to understand the interaction of graphene with other biomolecules, the adsorption properties of amino acids on the gnss were also reported using first-principles investigations. b. saha et al. investigated the interaction of four amino acids (alanine, serine, phenylalanine and tyrosine) into pristine and b and/or n doped functionalized (-oh, -nh , -cooh) gnss [ ] . it was observed that the functionalized gnss interacted with the amino acids with interaction energy ranging from . - . kcal/mol depending on the adsorbent structures and dopants. furthermore, though the doping of b and/or n atoms changed the adsorption properties of amino acids to the -oh and nh functionalized graphene, it hardly affected the -cooh functionalized gns. on another dispersion corrected dft study, h. t. larijani et al., investigated the adsorption of several amino acids (glycine, histidine and phenylalanine) on pristine, defected and oxidized gnss [ ] . they have found that every interaction of the amino acids with the monolayer gnss was physisorption and the gnss is a potential candidate for the bio-related applications. as pyridinic n, pyrrolic n, and graphitic n [ ] . in their investigation with dft theory along with pbe functional, they have used nitrogen-doped d gnss along with pristine gns with hexagonal vacancy. the dft theory with pbe functional gave the c-c bond length as precise as . Å for the pristine gns. among three types of interaction between the amino acids and the substrates, the side chains perpendicular to the substrates was used as it was most energetically favourable. due to the adsorption of the several amino acids arginine, histidine, aspartic acid, asparagine, and tyrosine, to the pristine gns, the adsorption energy was found as low as - . kcal/mol for the aspartic acid with a maximum as - . kcal/mol for the arginine adsorption. but these values for the adsorption energies increased dramatically in case of the nitrogen atoms doping. for four nitrogendoped pyridinic n, this was found as high as - . kcal/mol for histidine with a minimum of - . kcal/mol for the arginine adsorption. this was again reduced in case of the hydrogenated nitrogen-doped structure disproportionally and finally for hydrogenated pyrrolic n it ranges between - . kcal/mol to - . kcal/mol. despite this low adsorption values for the hydrogenated structures, it increased dramatically again in case of a hydrogenated n-edge. for hydrogenated pyrrolic n-edge, it went as high as - . kcal/mol for arginine with a minimum value of - . kcal/mol for tyrosine adsorption. hence it was concluded that a pyridinic n nanosheet with a hydrogenated n-edge works best for the adsorption of amino acids. the modification of the hexagonal ring of the gns into the pentagonal and heptagonal ring made a noble kind of nanosheet known as phagraphene is also studied as a potential drug delivery nanomaterial for adrucil by r. bagheri et al., [ ] . the small adsorption energy of - . kcal/mol for phagraphene made it incompatible for the adrucil drug delivery. however, the adsorption energies increased dramatically to the - . , - . , and - . kcal/mol due to the doping of b, al and si atoms respectively. however, noticeable change in the electronic properties of b doped phagraphene made it unsuitable for adrucil drug delivery and despite having enormous adsorption energy, al-doped phagraphene showed a considerable response time of . × s. hence the sidoped graphene with a moderate adsorption energy of - . kcal/mol with a short response time of . s, was predicted to be a potential drug delivery system for adrucil drug. cnt is an allotrope of carbon made by a hexagonal network of carbon atoms which is cylindrically rolled up into a tubular shape. ever since its discovery, numerous research works were done on its various unique properties including exceptional mechanical strength, electrical, optical, and thermal properties etc. [ ] [ ] [ ] [ ] [ ] . similar to the gns, the sp hybridized carbon-carbon bond of cnt lead it to one of the strongest material with young's modulus of gpa and a tensile strength ranging from gpa to gpa [ ] . the density of the cnt was observed experimentally as large as ∼ . g/cm with a low room temperature resistivity of ∼ mΩ-cm [ ] . the thermal conductivity of cnt was predicted as high as ∼ w/mk at room temperature along with an electrical conductivity ranging from to s-cm - [ , ] . cnt can be classified in many subclasses but most simply into two, single-walled cnt (swcnt) and multi-walled cnt (mwcnt). where the swcnt is a single layer of graphene, mwcnt is a multi-layer of graphene rolled up cylindrically into a tubular shape as it is shown in figure [ ] . now, based on the chiral vector defined as (where n and m are the integer number of steps along the unit vectors and ) and chiral angle, defined as the rolling angle between the graphene and axis of the tube, cnt can be further classified into three chiralities as zigzag , armchair , and chiral ( ) [ ] . after the first synthesis of cnt through arc-discharge method [ ] , over the years cnt was reported to be synthesized using many techniques including chemical vapour deposition (cvd) [ ] , laser ablation [ ] , j o u r n a l p r e -p r o o f plasma jet [ ] and many more [ ] [ ] [ ] [ ] . though the arc-discharge method reports growth of swcnt with % figure : schematic diagram of various kind of cnt made by rolling up d graphene sheet. reproduced with permission from ref. [ ] . copyright elsevier science ltd., . purity and laser ablation method with %, cvd with - % purity still widely used due to its cost-effective solution for the mass production [ , ] . this wide range of methods to synthesize cnt along with a wide range of structural variation and unique properties led cnt to be applied in many fields like aerospace industry [ ] , electronics [ ] , energy harvesters [ ] , gas sensors [ ] , biosensors [ ] , drug delivery [ ] etc. among these widespread applications of cnt, our particular interest is in its adsorption ability of biomolecules (both for sensing and delivery purpose) as it offers biocompatibility in this field and has the ability to penetrate cells along with excellent stability, high reliability, faster response time, high adsorption strength towards the bio-molecules etc. [ ] . starting from small bio-molecules like glucose sensing [ ] , cnt can be used to sense and deliver several therapeutics, anaesthetic, anti-depression etc. drugs to the human body [ ] . to acquire the desired sensing and drug delivery performance, sometimes cnt is required to be doped or fictionalized by impurity atoms, and several studies have successfully reported enhanced performance towards biosensors and drug delivery due to the functionalization and doping to cnt [ ] [ ] [ ] . finally, due to the recent advancement on the accuracy of computer simulation methods with approximation theory like dft, e.g. a theoretically optimized swcnt is shown in figure , numerous research works were put forward on investigating cnt as an efficient system for the bio-molecule sensing and drug delivery. in this section, we aim to review recent research work exploring the bio-molecule sensing and drug delivery efficiency of the cnt. a first-principles study conducted by h. shaki et al. reported the adsorption of the penicillamine (pca), an anti-cancer drug with several vital side effects, on the pristine and functionalized swcnt [ ] . considering the dispersion terms, for pristine swcnt the pca drug make weak physisorption with a maximum adsorption energy of - . kcal/mol and an adsorbent-adsorbate distance of . Å. but this interaction was further enhanced by adding an extra -cooh functional group to the pristine swcnt. with -cooh functionalized swcnt (f-swcnt), the maximum adsorption energy of pca towards f-swcnt was observed as high as - . kcal/mol for a particular orientation of pca with a maximum dipole moment of . debye and an energy gap of . ev. thus, this study reveals that the -cooh f-swcnt performs better the pca drug delivery system, whereas all interactions were exothermic and stable with negative adsorption energies. these results were further compared with the md simulations, which successfully supported the result obtained from the dft investigations. isonicotinic acid hydrazide (inh), simply known as isoniazid, is a prodrug for the treatment of the infectious disease tuberculosis (tb) caused by mycobacterium tuberculosis (mtb) bacteria [ ] . as inh drug often comes with side effects like peripheral neuropathy, nausea, aplastic anaemia etc. n. saikia et al. proposed swcnt as a drug carrier to the target area [ ] . as the si doping in the cnt is less reported in the literature than the b/n doping, better electronic properties of si lead them to use si-doped swcnt to carry the inh drug using dft theory and molecular docking [ , ] . in a van der waals interaction corrected investigation it was found that inh parallel to the ( , ) swcnt have better stability with more adsorption energy of . kcal/mol compared to the perpendicular alignment of the inh with ( , ) swcnt with an adsorption energy of . kcal/mol. though the adsorbate-adsorbent distance of . Å was unchanged for both parallel and perpendicular alignment, electronic band gap decreased in the perpendicular alignment slightly to . ev compared to . ev for parallel alignment. for covalent functionalization of inh to the ( , ) swcnt, the adsorption energy was drastically increased to . kcal/mol with a change in the inh-( , ) swcnt distance of . Å and a change in bandgap as . ev. the quantum descriptors also reported an increase in the reactivity due to the covalent functionalization of inh. hence, ( , ) swcnt have a potential future as a drug delivery system for isoniazid drug. ', '-difluoro-deoxycytidine (dfdc) or simply know as gemcitabine is a popular therapeutic option to treat numerous cancers including breast cancer, pancreatic cancer and non-small cell lung cancer [ ] [ ] [ ] [ ] . it comes with relatively fewer side effects but as severe as fatal pulmonary toxicity and acute lung injury [ , ] . this lead h. moradnia et al., to investigate the pyrrolidine functionalized ( , ) swcnt (f-swcnt) as an efficient drug delivery system for gemcitabine drug using dft theory with m x functional and - g (d,p) basis set [ ] . in water solution, for a particular orientation ‗complex e', the gemcitabine was adsorbed towards f-swcnt with an adsorption energy of - . kcal/mol and a dipole moment of . debye with a minimum adsorbate-adsorbent distance of . Å. for another orientation complex a, the adsorption energy was slightly decreased to - . kcal/mol but with an increase in the dipole moment to . debye. the energy gap of the complex a and e was observed as . ev and . ev respectively. the global hardness of the structures ranges between . ev to . ev where the electrophilicity had a range between . ev to . ev. these findings lead them to declare the f-swcnt as a potential drug delivery system for the gemcitabine which was further confirmed through the aim, nbo, and dos analysis. flutamide, an anticancer drug with chemical name '-nitro- '-trifluoromethyl-isobutyranilide is a widely used drug to treat prostate cancer often comes with side effects like severe gynecomastia, liver toxicity etc. [ ] [ ] [ ] . to transfer this drug directly to the cancerous cell, to minimize the side effects, m. kamel et al., analyzed the potential of ( , ) swcnt for efficient delivery of flutamide drug, and how co-solvents like ethanol affects the interaction between the flutamide drug and ( , ) swcnt [ ] . in the water solution for a particular orientation labelled as configuration , the most negative adsorption energy value was observed with a minimum adsorbate-adsorbent distance and highest value for dipole moment. the values were - . kcal/mol, . Å, and . debye, respectively. so the flutamide drug made physisorption towards the swcnt, and the nature of the interaction was exothermic. the values of solvation energy indicated a spontaneous solvation with a range of - . to - . kcal/mol and the least value was for the configuration . a spontaneous flow of electron was observed from the adsorbent to the adsorbate with positive values of . ev and . ev for the charge transfers (Δn) and the energy change of the acceptor (Δe b (a) ). finally, from the md simulations, it was found that the addition of ethanol with . molar concentration increases the stability of the simulation system. however, another study lead by this group, m. kamel et al., investigated the cooh functionalized swcnt to use as a drug carrier for flutamide drug [ ] . in that study, they have found that the flutamide drug can be adsorbed in the swcnt with a maximum adsorption energy of - . kcal/mol in the water solvent where the dipole moment of the structure was found as . debye with a bandgap of . ev. the same cooh functionalized swcnt was used to investigate the carmustine drug delivery ability by the same group but this time lead by r. khorram [ ] . the performance was almost similar as for flutamide drug with a maximum adsorption energy of - . kcal/mol along with a dipole moment of . debye, the energy gap of . ev, and interaction energy of - . kcal/mol. an oral drug, metformin (mf), is used as a first-line medication to treat type diabetes especially patient with breast cancer, prostate cancer, and pancreatic cancer [ ] [ ] [ ] . to minimize the side effects, m. s. hoseininezhad-namin et al., investigated pristine, si and al-doped ( , ) swcnts as a promising mf drug carrier [ ] . weak physisorption of mf towards pristine ( , ) swcnt was observed with an adsorbateadsorbent distance of . Å, charge transfer of . e (nbo analysis), and adsorption energies of - . kcal/mol (b lyp) and - . kcal/mol (ωb xd) where an increment in the adsorption energy through ωb xd functional clearly indicated the role of dispersion in the adsorption of mf drug toward the pristine swcnt. however, doping the swcnt with si and al significantly increased the adsorption energy of mf to - . kcal/mol and - . kcal/mol, respectively in the solvent phase. the reactivity of the mf-doped swcnt configurations also increased in the solvent phase with an increment to the dipole moment to . debye and . debye for the mf adsorbed si and al doped swcnts respectively when it was only . debye for the adsorption of mf towards pristine swcnt. this increment in the reactivity was further supported by the global reactivity descriptors like chemical potential, global hardness and softness, and electrophilicity. hence si doped swcnt with a moderately high adsorption energy but with lowest band gap as . ev and highest reactivity in the solvation phase made itself most promising candidate for the mf drug delivery between pristine, si and al doped ( , ) swcnt. a theoretical investigation using dft theory with b lyp hybrid functional and - g (d, p) basis set, was made on the ca doped ( , ) swcnt to inspect its ability to perform as a drug carrier for atropine drug delivery [ ] . atropine is a drug taken by an injection to the muscle to treat several types of nerve agent and also performs as an antipode to the several poisonings [ ] . atropine drug was adsorbed by ca-swcnt with adsorption energy of - . kcal/mol for d-atropine, and - . kcal/mol for l-atropine with a dipole moment of . and . debye respectively. the homo-lumo energy gap was observed around . ev for both structures with a charge transfer of around + . e from the atropine to the ca-swcnt, which was confirmed by the nbo analysis. the solubility of the atrophine+ca-swcnt in the water medium was established through the negative solvent energy with a value of - . kcal/mol for d-atropine and - . kcal/mol for l-atropine. hence the ca-swcnt was predicted as a potential drug carrier for the atropine drug. ketamine, an n-methyl-daspartate (nmda) receptor antagonist, is clinically often used as an anaesthetic with limited use as an analgesic, anti-depression and anti-inflammatory drug, comes with numerous side effects like psychoactive effects, peripheral effects and neurotoxicity [ ] . so, the urgency of rapid determination of ketamine lead r. zhiani et al., to investigate swcnt and cooh, conhch functionalized swcnt as a sensor to detect ketamine in the gaseous medium along with several other polar mediums [ ] . it was found that the adsorption of ketamine in functionalized swcnt causes a change in the bond length of c-o, n-h and c=o groups noticeably. further, binding energy in the gaseous medium was observed as - . kcal/mol and - . kcal/mol for cooh and conhch functionalized swcnt. this value for binding energy was further increased as - . , - . , and - . kcal/mol in chloroform, methanol, and water medium respectively for cooh functionalized swcnt and became - . , - . , and - . kcal/mol respectively for conhch functionalized swcnt. furthermore, negative values for the change in enthalpy and gibbs free energies indicated spontaneous exothermic adsorption of ketamine in the functionalized swcnt. the response of swcnt to the ketamine was finally confirmed through the noticeable change in fermi energy to the positive values. finally, though the cooh functionalized swcnt responses better to the ketamine in the gaseous phase, conhch shows slightly better response towards ketamine in other medium like chloroform, methanol and water. another anti-inflammatory and analgesic, ibuprofen (ibp), comes with several side effects like indigestion, nausea, vomiting etc. [ , ] . hence c. parlak et al., made a first-principles investigation using dft theory along with b lyp/ m x functional - g(d) basis set and on the adsorption properties of ibp into si-doped swcnt and fullerene [ ] . the literature on the accuracy of m x functional to calculate the adsorption energies but the overestimation of the bandgap lead them to use b lyp hybrid functional for bandgap calculations [ , ] . after the correction of basis set superposition error (bsse), for a specific alignment of ibp where the o atom of (c-o) group of ibp was placed above si atom to the cnt, the adsorption energy was observed as - . kcal/mol with an adsorbate-adsorbent distance of . Å and bandgap . ev. furthermore, due to the adsorption of ibp, the work-function of si-doped swcnt increased by . % with a change in the fermi energy level from - . to - . ev. thus strong chemisorption with a change in the fermi energy constitutes swcnt a potential sensor for ibp drug detection. besides the swcnt as a drug sensor and delivery system, multi-walled cnt (mwcnt) was also investigated as the potential drug sensor for several drugs. d. shahabi et al. investigated several pristine and sulfur-doped swcnt along with several mwcnt (double-walled and triple-walled cnt) as potential drug sensor for the fluoxetine (fx), a widely used antidepressant drug [ ] . it was observed that sulfur atom slightly affected the adsorption processes of fx towards the swcnt where for most stable structure, ( , ) sulfur-doped swcnt, the adsorption energy in the gas (liquid) phase was observed as - . (- . ) kcal/mol while the fx drug was adsorbed inside the sulfur-doped swcnt, and only - . kcal/mol while the fx was adsorbed in the outside of the sulfur-doped swcnt. further to reduce time consumption, molecular docking study was initiated instead of dft to investigate the adsorption behaviour of fx towards systems with a large number of electrons like from ( , ) swcnt to ( , ) swcnt, double-walled cnt, triple-walled cnt. it was found that the stability was decreased from ( , ) swcnt with an increase in the chirality and the most stable structure, ( , ) swcnt, had adsorption energy of - . kcal/mol while the fx drug was adsorbed inside the ( , ) swcnt. the stability was increased slightly for the double and triple-walled cnt and the adsorption energies was found as - . kcal/mol and - . kcal/mol for ( , ) double-walled and ( , ) triple-walled cnt while the fx drug was adsorbed inside the cnt. however, another study lead by c. p. sousa et al., reported that the acetaminophen drug was also adsorbed inside an mwcnt more favourably than external surface [ ] . also, the functionalization of the mwcnt with polyethyleneimine polymer enhanced the stability of the acetaminophen adsorbed f-mwcnt complex with an adsorption energy of - kcal/mol while it was - kcal/mol for the adsorption of acetaminophen towards the pristine mwcnt. so, it was observed that both acetaminophen and fluoxetine could be sensed strongly with the mwcnt. other than directly the drug molecule itself, cnt was theoretically investigated to perform as an efficient sensor for several other molecules like bio-molecules, amino acids and lactic acid. the adsorption of five small bio-molecules co, h o no, so and po towards the swcnt was reported by y. xu et al., through the vibrational spectrum analysis using dft with gga-pbe level of theory [ ] . in another study, m. yoosefian et al. investigated ability of the pd doped swcnt to adsorb an amino acid, histidine, using dft and hf theory with b lyp hybrid functional [ ] . they reported strong chemisorption of the histidine towards the pd-swcnt with a maximum adsorption energy of - . kcal with an adsorbent-adsorbate distance of . Å. finally, the interaction of -hydroxypropanoic acid or simply know as lactic acid (la) with swcnt with different chirality was observed with a dft-d study from a. n. chermahini et al. [ ] . in their research, they have found that la interacts more with ( , ) swcnt than other swcnt with higher chirality with an adsorbate-adsorbent distance of . Å and maximum adsorption energy of - . kcal/mol in the gas phase and - . kcal/mol in the solvent phase. the solvation energy for la adsorbed ( , ) swcnt was observed as - . kcal/mol with an h-l energy gap of . ev. hence the ( , ) swcnt can work as a potential adsorbent for the la. so, it can be concluded that the swcnt can perform as a potential adsorbent for amino acids, lactic acid and biomolecules. akin to graphene and cnt another sp hybridized allotrope of carbon atoms with closed d structure, fullerene, got eminent attention on the field of biosensor and drug delivery application recently. fullerene was observed in the literature as early as in from h. p. schultz where he predicted a new possible topological structure of c h with truncated icosahedron shape with vertices until the first prediction of c fullerene came from e. osawa in [ , ] . finally, in , h. kroto et al. unintentionally observed the c fullerene while they were performing an experiment by vaporizing the carbon atom from a solid graphite surface into a high-density helium flow to understand the mechanism of long carbon chain formations in star and space [ ] . as shown in figure , the c fullerene is consists of pentagons along with hexagons like a soccer ball where pentagons cannot be adjacent as each of them is surrounded by five hexagons. with a fixed number of pentagons, fullerenes can be found with variable hexagons, and the closest stable one to c fullerene is c fullerene with pentagons and hexagons. though c is claimed to be the smallest stable fullerene structures, c unstable fullerene structure was reported to be stabilized in several ways, including metal doping [ ] [ ] [ ] . due to the mass commercial production of c fullerene, there is a wide range of methods available to synthesize it. after the discovery of c fullerene from h. kroto et al., the first macroscopic production of c was reported by w. krätschmer et al. in from electric arc heating of pure graphitic carbon soot in a helium atmosphere of around torr [ ] . following by the method of w. krätschmer et al., c was further produced by h. ajie et al. in from the evaporation of carbon rods but this time by heating it resistively [ ] . later in , growth of fullerenes was reported from r. f. bunshah et al. by electron beam evaporation and sputtering of graphite [ ] , further in , extraction of c ion beam was reported from s. chuanchen et al. from a hollow cathode ion source [ ] , and many more methods were used including the usage of low-pressure diffusion flame from p. hebgen et al. [ ] , arc discharge method from m. caraman et al. [ ] . besides this wide range of j o u r n a l p r e -p r o o f synthesis, due to their unique physical [ ] , electrical [ ] , optical [ ] and chemical properties [ ] of fullerenes lead them to many fields with potential applications in ion storage [ ] , photovoltaics [ ] , sensors [ ] , supercapacitors [ ] etc. despite fullerene's insolubility to the water which was further settled by functionalizing or doping with impurity atoms, it is soluble in a wide range of common solvents in room temperature, and of them were reported r. s. ruoff et al. for c fullerene back in [ ] . hence, moderated solubility in the polar mediums along with several other enchanted properties like hydrophobicity, biocompatibility [ ] etc. made fullerenes one of the front liner in the biological applications like antibacterial activity [ ] , antiviral activity [ ] , drug delivery [ ] , drug sensing [ ] etc. in this section, we aim to review the recent scientific (a) (b) figure : (a) c and (b) c fullerene nanostructures optimized using dft theory with b lyp hybrid exchange correlational functional and - g, - g (d,p) basis sets respectively. reports on the drug delivery and sensing application of carbon fullerenes which were made by the first-principles investigation. as several drugs require interaction with dna and rna, these drugs sometimes have a structure like dna and rna nucleobases which made the investigations on the adsorption properties of the nucleobases towards an adsorbent so crucial in drug delivery application. so, following the trend, a. s. rad made the firstprinciples investigation using dft theory on the adsorption properties of a purine derivative nucleobase, adenine, on the cr and ni-doped c fullerene [ ] . considering the dispersion forces and exchange-correlation energies, all structures were optimized using meta-hybrid functional ωb xd and a gga functional perdew-burke-ernzerhof (pbe) respectively along with - g (d, p) basis set which is widely used to investigate the drug delivery systems. chemisorption of the adenine nucleobase towards the both cr and ni-doped c fullerenes were reported with negative adsorption energies as high as - . and - . kcal/mol respectively with a charge transfer of . e and . e between the adenine and respective doped structure observed from nbo analysis. however, the adsorption process of adenine was spontaneous and exothermic in both cr and ni-doped structures with negative values for change in enthalpy (Δh) and gibbs free energy (Δg) ranging - . of fu with c fullerene using dft theory with dispersion corrected b lyp-d functional and - g* basis set [ ] . a very weak interaction of fu was observed towards the pristine c fullerene with a maximum adsorption energy of - . kcal/mol along with a h-l energy gap of . ev and an inferior charge transfer of . e (from nbo analysis). this interaction was further enhanced by doping a b atom to the fullerene structure. for b doped c fullerene the adsorption energy of fu was observed as high as - . kcal/mol with a decreased bandgap of . ev along with a significantly increased charge transfer of . e ( from nbo analysis). finally, they have reported a successful release of the fu drug to the low ph (< ) targeted area with a cancerous cell. similar to the adsorption behaviour of fu towards c fullerene, y. gökpek et al., observed a weak physisorption interaction between -phenylpyridine ( -phpy) and pristine c fullerene while the adsorption energy was increased significantly due to the doping of c fullerene with b or si [ ] . the dispersion corrected (with m x functional) dft study found that -phpy was adsorbed on a pristine c with an adsorption energy of - . kcal/mol in the water phase where this value was significantly increased to - . and - . kcal/mol for b and si-doped c fullerenes (bc and sic ) respectively. the solvation energy of -phpy was also increased to - . and - . ev for bc and sic structures respectively while it was only - . ev for pristine c fullerene. the h-l energy gap was decreased from . ev for -phpy-c to . and . ev for the phpy-bc and -phpy-sic respectively with an nbo charge transfer of - . e and - . e respectively. these adsorption properties of -phpy with pristine and b or si-doped c fullerenes was slightly diminished in the gaseous phase. observing these enhanced properties for the -phpy-bc and -phpy-sic systems led them to conclude bc and sic as potential structures to carry -phpy into drug delivery applications. the sic system was again subjected to study by m. moradi et al., but this time accompanied by alc to investigate their interactions with phenylpropanolamine (ppa) drug [ ] . ppa is used as a most used decongestant and also marked as a potentially hazardous drug due to its side effects like hypertension, cardiovascular side effects including a potential risk of hemorrhagic stroke [ ] [ ] [ ] . similar to -phpy, ppa had weak physisorption with pristine c fullerene structure with an adsorption energy of - . kcal/mol with a . % decrease in the h-l energy gap to . ev. this interaction was significantly enhanced due to the doping of c with al atom, where the adsorption energy of ppa was increased to - . kcal/mol with an . % decrease to the bandgap to . ev. but the most stable structure to adsorb ppa was found as si-doped c structure with the highest adsorption energy of - . kcal/mol with a significant . % drop in the energy gap to . ev. this fall in the bandgap increased the electrical conductivity of ppa-sic complex, which made sic structure most sensitive towards the ppa detection. but in another study lead by a. s. ghasemi et al., the al-doped c fullerene showed a promising behavior to detect and carry penicillamine drug which is commonly used to treat wilson's disease and rheumatoid arthritis [ ] [ ] [ ] . al-c adsorbed penicillamine with an adsorption energy of - . kcal/mol but increasing the dipole moment to as high as . debye and decreasing the work function as low as . ev. this increase in the reactivity was further confirmed by the global reactivity descriptors where the ionization potential along with the electrophilicity and global hardness decreased with an increase in the global softness for the al-c complex. the rising importance on the detection of the illicit drug to the medical community and law enforcing agency lead s. bashiri et al., to investigate pristine and several doped c fullerenes for its sensing ability to a central nervous system (cns) stimulant, amphetamine (aa) which is medically used to treat attention deficit hyperactivity disorder but is a habit-forming and highly potential drug for abuse [ , , ] . the pristine c fullerene showed a good sensitivity towards the aa drug with a low bandgap of . ev and a work function of . ev but with weak physisorption with an adsorption energy of - . kcal/mol. doping the fullerene with b, al, ga, si, and ge significantly increased the adsorption energy whereas the most stable structure was al-c with adsorption energy as high as - . kcal/mol while it was - . and - . for ga and b doped c fullerenes respectively. but the most promising performance was found from si and ge doped c fullerenes with a j o u r n a l p r e -p r o o f moderate adsorption energy of - . and - . kcal/mol but with a . % and . % reduction to the work function down to . ev for both case. hence si and ge doped c fullerenes were concluded as a potential sensor for the aa drug detection. c. parlak et al. further studied these structures for a drug sensor and carrier for antiviral drug amantadine, which is used to treat or prevent influenza-a, parkinson's disease but comes with side effects like corneal edema [ ] [ ] [ ] . all doped structures showed a promising performance as a sensor and carrier for the amantadine drug with adsorption energies ranging around - to - kcal/mol which was further increased in the water solution and energy gap around ev which was further reduced in the water solution. besides doping an adsorbent with impurity atoms, a noticeable change in the adsorption properties can be found due to the solvents, different isomers of the adsorbate drugs etc. which was further analyzed by o. ergürhan et al., in their investigation on the interaction of hydroquinone (hq) with pristine and doped c fullerenes [ ] . [ ] . for interaction between the -nh head of inh drug and a b atom of c b n heterofullerene, the adsorption energy was observed as - . kcal/mol with a significant decrease of . % to the bandgap which became . ev. for a drug delivery system of ibp drug e. alipour et al. modified c fullerene by substituting its five carbon atoms by n atoms and one tm atoms between fe, co, and ni which formed tmn c system [ ] . while nin c was reported to have a higher sensitivity towards ibp drug, nin c , con c , and fen c adsorbed ibp with acceptable adsorption energies of - . , - . , and - . kcal/mol, respectively including - . kcal/mol for the pristine c fullerene hence was considered potential systems for the ibp drug delivery. besides drug delivery and drug sensor, c fullerenes were also studied by m. f. kaya et al. to perform as a sensor for the phenylalanine (phe) amino acid, a high concentration of which in the blood can lead to mental retardation [ , , ] . using m x/ - g (d) level of theory, the maximum binding energy of the phe towards pristine c fullerene, alc and, sic was calculated as - . , - . , and - . kcal/mol respectively in the gas phase, except pristine c which was further increased to - . , - . , and - . kcal/mol respectively in the water solvent phase. the doping of al and si atoms reduces the bandgap of the structures j o u r n a l p r e -p r o o f significantly. for phe-c the bandgap in the gas(water) phase was observed as . ( . ) ev which dropped down as much as . ( . ) and . ( . ) ev for the al and si-doped c fullerenes with an nbo charge transfer of - . e and - . from n atom of phe to the al and si atoms of the adsorbent respectively. due to the alternation in the adsorption properties of phe towards alc and, sic made them a potential sensor for the phe amino acid while pristine c suffered from weak adsorption. currently, a popular method to synthesis the graphene is to reduce the go into gns [ ] . but the synthesis of the go was dated back to when b. c. brodie reported the first synthesis of go during his investigation on the various properties of graphite [ ] . this brodie synthesis method along with a slightly improved model from l. staudenmaier in was mostly used to synthesis until another improved model was proposed by w. s. hummers and r. e. offeman in by oxidizing the graphite with a water-free mixture of potassium permanganate (kmno ), sodium nitrate (nano ), and concentrated sulfuric acid (h so ) which is popularly known as the hummers method and is one of the most popular methods to synthesis go till now [ , ] . based on these methods till now there is an unambiguity on the exact structure of go, but this nonconductive hydrophilic allotrope of carbon lead it to be applied extensively in biomedical and therapeutic applications including the drug delivery and sensing [ , ] . pristine go was found to be a potential drug delivery system for sumatriptan (stt), a medicine used to treat migraine headaches [ ] . the dispersion corrected dft study lead by z. jafari et al. found that go adsorbed stt drug with acceptable adsorption energy to be used as a drug delivery system while the drug was reported to induce many chest symptoms [ ] . in the water phase, the stt drug was adsorbed with an adsorption energy of - . kcal/mol to go with a dipole moment of . debye and solvation energy of - . kcal/mol. the observed h-l energy gap of stt as . ev was further reduced to . ev for stt-go while it was . ev for go. a - . e charge transfer was observed from go to stt with a fermi energy level of - . ev. these interactions were further supported by the global reactivity descriptors where global hardness was increased to . ev with a decrease to the global softness and the electrophilicity to . ev - and . ev respectively. this result from the interaction of stt drug with go leads them to conclude go as a potential carrier for the stt drug. like other allotropes of carbon, go was further reported as a potential drug system for several anticancer drugs. z. hasanzade et al. made a dft investigation on the interaction of ellipticine (ept) anticancer drug with pristine go nanosheet (gons) and observed the effects of ph and solvents on the interaction using various solvents, e.g. water, ethanol and dimethyl sulfoxide (dmso) [ ] . in the gaseous environment, the ept drug was adsorbed with a maximum adsorption energy of - . kcal/mol where the maximum rise in the dipole moment was observed as . debye. in the water phase, a significant decrease in the adsorption energy was observed with a maximum of - . kcal/mol along with a considerable increase in the dipole moment to . debye where ept was dissolved with solvation energy ranging from - . to - . kcal/mol for different orientation of ept. the effects of dmso and ethanol was almost comparable with water as the adsorption energy and dipole moment were ranged between - . to - . kcal/mol and . to . debye for dmso. in contrast, for ethanol, it was - . to - . kcal/mol and . to . debye, respectively. as ept failed to alter the e g of gons, it may not work as a sensor for ept. still, it can be a potential drug delivery system which was further supported by the interaction of ept with gons in low ph regions as cancerous cells were reported to be slightly acidic. for another anticancer drug doxorubicin (dox) delivery, p. gong et al. decorated go with fluorine (fgo) to enhance the drug release mechanism in low ph regions [ ] . however, a high dox loading j o u r n a l p r e -p r o o f capacity was observed for the water-soluble fgo where non-covalent bonds were dominated in the loading and release mechanism of dox hence made fgo a promising candidate for the dox delivery. in their other work, they reported the synthesis of fgo with amino-polyethylene glycol and reported its potential use in the dox and another anticancer drug camptothecin delivery [ ] . besides the purely sp hybridized gns, another sp and sp hybridized allotrope of carbon, graphyne was also studied for medical applications using first-principles calculations. the graphyne nanosheet (gpns) was reported as a potential drug carrier for anticancer drug -fluorouracil ( -fu) and quercetin [ ] . in the surface of gpns, the most stable interaction of -fu was observed with an adsorption energy of - . kcal/mol where quercetin was adsorbed with - . kcal/mol. a charge transfer of . e and . e was observed for between the gpns and, -fu and quercetin respectively with a maximum drop of . % and . % in the energy gap lead to . ev and . ev respectively. with the increasing reactivity observed from the quantum reactivity descriptors, an increase in the adsorbent-adsorbate distance due to the protonation ensured the ability of gpns to deliver -fu and quercetin to the target cancerous cell. gpns was also investigated as a sensor to sense the cytosine and guanine nucleobases [ ] . gpns adsorbed the cytosine and guanine with an adsorption energy of - . and - . kcal/mol with a significant amount of . % and . % reduction in the h-l energy gap, respectively. this reduction in the bandgap indicated the increase in the electrical conductivity due to the adsorption of the nucleobases to the gpns ensured the cytosine and guanine sensing ability of the gpns. another graphyne like structure with carbon atoms is graphdiyne was reported to be synthesized by guoxing li et al. in by a cross-coupling reaction using hexaethynylbenzene on the copper surface [ ] . graphdiyne was also subjected to study as a potential drug delivery system for anticancer drugs. the interaction of two anticancer drugs sorafenib (stb) and regorafenib (rtb) with graphdiyne nanosheet (gdns) was investigated by u. srimathi et al. using dft theory with gga based pbe functional [ ] . stb that is used to treat thyroid [ ] and kidney cancer [ ] often come with several side-effects like alopecia, arthralgia, hypertension etc. [ ] [ ] [ ] whereas rtb is used to treat liver and colorectal cancer [ , ] but sometimes comes with deadly side effects with severe liver damage [ ] . stb was adsorbed by the gdns with a maximum adsorption energy of - . kcal/mol with solvation energy of - . kcal/mol and eg of . ev when for rtb these values were observed as - . kcal/mol, - . kcal/mol and . ev. a further alteration in the band structure was observed due to the adsorption of stb and rtb. finally, in the low ph regions similar to the cancer cells regions, the bond length between the gdns and stb, rtb increased noticeably, which ensured the drug release in the low ph regions. another anticancer drug, flutamide (flu), which was reported to make weak physisorption on cnt, a study by v. nagarajan et al. revealed strong chemisorption of flu drug with the graphdiyne nanotube (gdnt) [ ] . in the most stable interaction, flu was adsorbed by the gdnt with an adsorption energy of - . kcal/mol and solvation energy of - . kcal/mol along with a . % reduction to the energy gap to . ev which lead to a charge transfer of . e between the flu and gdnt. due to the interaction of the flu with gdnt, the chemical potential and global hardness decreased with an increase in the electrophilicity, which indicated the enhancement in the reactivity of the structures. while the minimum adsorbent-adsorbate distance was observed as . Å, this was raised up to . Å for lowering the ph by protonation, which ensured the drug release capability of gdns in slightly acidic cancerous cell environment. hence, gdns was concluded as a potential flu drug delivery system. the interaction of several other drugs like azathioprine, mesalamine, and hyoscyamine to be delivered to the targeted area using gdnt was also reported by the same group [ ] . in a first-principles investigation using dispersion corrected dft theory showed that the gdnt strongly adsorbed the azathioprine drug with an j o u r n a l p r e -p r o o f journal pre-proof adsorption energy of - . kcal/mol in its most stable position whereas the mesalamine and hyoscyamine were adsorbed with an adsorption energy of - . and - . kcal/mol respectively with solvation energy ranging from - . to - . kcal/mol. though a . % decrease in the energy gap to . ev was observed for the azathioprine drug adsorption on gdnt, it further dropped to . and . ev respectively for the mesalamine, and hyoscyamine with . % and . % decrease respectively. the reactivity of the structures was also studied using quantum reactivity descriptors. finally, a significant increase in the adsorbent-adsorbate bond length in the lower ph region ensured the drug release at the targeted site. the interaction of bcl with c h benzene at a very high temperature of ο c created a new type of graphite-like nanosheet but less stable than graphite known as bc , a theoretically relaxed structure of which is displayed on figure [ , ] . this bc nanosheet (ns) and nanotube (nt) was further studied by a. r. moosavi-zare et al. to sense an illicit cns stimulant amphetamine (aa) which was also reported to be adsorbed by pristine and si, ge doped c fullerenes [ , ] . it was observed that the bc nt adsorbed aa more strongly than the bc nt with an adsorption energy of - . kcal/mol where it was - . kcal/mol for the bc ns. despite stable adsorption, bc ns and nt were not considered as a sensible sensor for aa drug as a very poor decrease of . % and . % in the energy gap was observed. this was surmounted by doping bc with a si atom which reduced the energy gap by . % and . % for bc ns and nt respectively in case of aa adsorption. besides the si-doped bc ns and nt was found to adsorb aa drug more strongly with an adsorption energy of - . and - . kcal/mol respectively. despite this most stable and sensible for aa drug, si-doped bc nt suffers from a considerable recovery time of . s where it was only . s for si-doped bc ns. hence sidoped bc ns was considered as a potential sensor to sense the amphetamine drug. bc nt was further modified into bc n nt to work as a sensor for β-keto-amphetamine or simply cathinone (ct) [ ] . akin to the pristine bc ns and nt, bc n nt also suffers from a reduction in the energy gap by only % while it adsorbed ct with adsorption energy as high as - . kcal/mol. though al-doped bc n nt solved the problem with a . % reduction in the energy gap with a very strong adsorption of ct drug with an adsorption energy of - . kcal/mol, it suffers from a considerable recovery time. besides, si-doped bc n nt had a recovery time of . s and was considered as most sensible to the ct with a . % decrease in the energy gap due to the adsorption of ct with an adsorption energy of - . kcal/mol. finally, the interaction of an amino acid glycine with bc n nt was also reported by a. soltani et al. [ ] . glycine made strong chemisorption with the sidewall of bc n nt with a dipole moment ranging from . to . debye for different orientations resulting an increased reactivity due to the adsorption of glycine which was further verified from the global reactivity parameter analysis. another graphene alike d nanosheet, bnns made of boron and nitrogen atoms, is alternatively known as -white graphene‖ due white colour and graphene-like sp bonded hexagonal honeycomb structure with d h symmetry as shown in figure . the bnns is highly popular for its higher thermal and chemical stability compared to graphene while it has a very high melting point e.g. the hexagonal bnns (bnns) platelets showed thermal stability up to ~ o c in an investigation made by n. kostoglou et al. [ ] . the thermal conductivity of the bnns is also comparable to the graphene as the thermal conductivity for the bn nanoribbon is observed as ∼ - w m − k − at the room temperature [ ] . on the other hand, while graphene works as a zero bandgap semiconductor material, with a large bandgap of ~ . ev bnns works as an insulator or wide bandgap semiconductor material which help bnns to exhibit several unique optical properties [ ] . besides, the bnns j o u r n a l p r e -p r o o f can be synthesized with the large surface using numerous methods including the popular cvd methods for a large scale production [ ] [ ] [ ] . these alluring properties and sufficiently available synthesis methods made bnns to be applied as a catalyst [ , ] , dielectric material [ , ] , high temperature application [ ] , uv photodetector [ ] , energy storage device [ ] , sensor [ ] [ ] [ ] [ ] etc. finally, the biocompatibility of bnns [ ] leads them to the biomedical applications like drug sensors and drug delivery which will be reviewed in this section of our study. it was previously observed that many anticancer drugs have a structure like nucleobases as the operation of these drugs includes interactions with dna and rnas. several of these anticancer drugs -mercaptopurine (mp), -thioguanine (tg) and -fluorouracil (fu) which have structures akin to nucleobases adenine, guanine and uracil were subjected to be studied by m. vatanparast et al. for an efficient drug delivery system as they have a significant amount of side effects and they came up with bnns on this purpose [ ] . all three anticancer drugs made spontaneous adsorption to the bn, which was confirmed from the negative values for the adsorption energy and [ ] . it was observed that the among × , × , and × bn, thymine was adsorbed more strongly towards × bn with an adsorption energy of - . kcal/mol which was further increased to - . kcal/mol in case of an al atom doping. hence the size of the nanosheet along with doping it with impurity atoms plays a significant role in the drug adsorption. furthermore, using van der waals corrected dft theory (dft-d ), s. d dabhi et al. proposed a sensor to sense all dna and rna nucleobases using one-dimensional armchair and zigzag boron nanoribbons (bnnr) which can also be further applied for dna sequencing purpose [ ] . the adsorption profile of the nucleobases adsorbed in parallel with the armchair bnnr (a-bnnr) was observed as g > t > a > u > c with adsorption energies ranging from - . to - . kcal/mol with an adsorbent-adsorbate distance ranging as . Å to . Å. the a-bnnr responded towards all the nucleobases significantly by decreasing the h-l energy gaps ranging as . ev to . ev while it was . ev for the a-bnnr alone. the least h-l energy gap was observed for c + a-bnnr complex as . ev indicated that a-bnnr was most sensitive towards cytosine (c) and least towards adenine (a). on the contrary to the h-l energy gap, the work function of the a-bnnr increased noticeably with figure : hexagonal bnns optimized using dft theory with b lyp hybrid exchange correlational functional and - g basis set. adsorption of the nucleobases. the zigzag bnnr (z-bnnr) also followed the same trend upon the adsorption of nucleobases. but the adsorption energies were this time observed as g > c > a > t > u with a range of - . to - . kcal/mol. z-bnnr was also most sensitive towards the c with a least h-l energy gap . ev following by g, u, t, and a. here, the work function again increased upon the adsorption of the nucleobases towards the z-bnnr. hence the bnnr may not function as a work function based sensor but holds the potential of an electronic sensor to detect nucleobases. in several other theoretical studies, the performance of bnns was compared with other bn nanostructures for several other drug sensing. k. nejati et al. made a first-principles investigation using dft theory with b lyp hybrid functional on the interaction of cathinone drug with bnns, zigzag ( , ) bnnt, and b n nanocage (bnnc) [ ] . though the bnns showed a moderate sensitivity towards cathinone, it failed to adsorb the drug sufficiently. for different orientations of cathinone, bnns adsorbed with adsorption energies of - . and - . kcal/mol with a decrease in the h-l energy gap . % and . % respectively. the same trend was j o u r n a l p r e -p r o o f observed with bnnt while it failed to adsorb cathinone if shows sensitivity towards the drug. though bnnt still showed more enhanced performance than bnns by adsorbing the drug with adsorption energies as - . and - . kcal/mol for different orientations, with a decrease in the h-l energy gap by . % and . %. the nbo charge transfer was also greater in the bnnt from cathinone as . e and . e while it was only . e and . e respectively for bnns. the most alluring sensing properties towards cathinone was observed from bnnc while it adsorbed the drug with adsorption energies as - . and - . kcal/mol with a significant decrease in the h-l energy gap as . % and . % respectively. the nbo charge transfer from cathinone to bnnc was observed as . e and . e made it a potential candidate for the development of an electronic sensor to detect cathinone drug. besides, all three nanostructures benefit from a short recovery time of . s for bnnc following by . s for bnnt, and . ns for bnns at the room temperature of k. the bnns, bnnt, and bnnc also showed the same sensing properties towards another anticancer chemotherapeutic drug, mercaptopurine (mp), which was revealed by s. a. aslanzadeh from dft calculations using b lyp/ - g (d) level of theory [ ] . alike from cathinone, bnns also showed inferior adsorption properties towards mp with an adsorption energy of - . kcal/mol with a decrease in the h-l energy gap only by . %. this time also the most sensitivity and the most stable adsorption of mp was observed with bnnc. bnnc adsorbed the mp drug with maximum adsorption energy - . kcal/mol while the range of decrease in h-l energy gap was observed as . % to . %. but due to this strong adsorption, this time the bnnc suffered from an unrealistic high recovery time of . seconds. besides this time, the most promising adsorption behaviour of mp drug was observed from bnnt. bnnt adsorbed the drug with a decent maximum adsorption energy of - . kcal/mol while the decrease in h-l energy gap was observed from . % to . % for different orientations of the drug. besides, the bnnt also benefits from a shorter recovery time of . seconds at the room temperature of k. hence, bnnt holds the most potentiality in the development of an electrochemical sensor to detect mp drug. after the discovery of cnt in [ ] , the novel properties of bnns lead to the successful discovery of another polymorph of graphitic bn, bnnt in by n. g. chopra et al. [ ] shortly after its theoretical prediction in [ ] . by that time, the availability of many different methods to grow cnt and bns lead bnnts to be synthesized using many popular methods like arc discharge [ ] , ball mailing method [ ] , laser ablation method [ ] , and chemical vapour deposition (cvd) [ ] . being made of bns the bnnt also shares the similar properties as bnns like high thermal and chemical stability [ , ] , high thermal conductivity [ ] , high oxidation resistance [ ] and a wide insulating bandgap of ~ . ev [ ] . besides, having a tubular structure provided it excellent mechanical strength with the elastic modulus in tpa level as cnt [ ] . these properties made its applications as nanocomposites [ ] , nano light source [ ] , oil-polluted water treatment [ ] , radiation shielding [ ] , sensor [ , , ] etc. finally, bnnts were found to be non-toxic to the human body and biocompatible, which lead it to many biomedical applications [ ] [ ] [ ] [ ] . an efficient sensor for the broadly used sulfonamide (sa) antibacterial drugs is crucial to the medical community as it causes an adverse reaction to the % of its general consumers which rises % to the patients with human immunodeficiency virus (hiv) [ ] . hence z. rahmani et al. made a first-principles investigation on the bnnt and several other doped (al, si) bnnt using dft theory along with m - x functional and - g (d) basis set to study their sa drugs sensing ability [ ] . unlike the majority of the drug sensors, in this case, pristine bnnt performed as a better sa drugs sensor than si and al-doped bnnt. in the most stable position, bnnt adsorbed sa drugs with an adsorption energy of - . kcal/mol with an % reduction to the h-l energy gap. though the value for adsorption energy increased dramatically for al-doped bnnt to - . j o u r n a l p r e -p r o o f kcal/mol, it failed to decrease the energy gap significantly, which was only . %. hence with this poor sensing ability but strong adsorption of sa drug made al-bnnt a decomposition agent for sa drugs. for, si-bnnt the sa drug was adsorbed with an adsorption energy of - . kcal/mol at the most stable orientation but increased the h-l energy gap by . % which was enhanced in another orientation where sa decreased h-l energy gap by . % but was adsorbed with an adsorption energy of - . kcal/mol only. so, si-bnnt is not ideal to be used either as a sensor or to decompose sa drug. the popular anticancer drug -fluorouracil (fu) which was reported to be carried out by several carbon and boron-based nanoclusters, is also reported to make strong chemisorption with zigzag and armchair bnnt. from a first-principles investigation lead by a. soltani et al., it was observed that the ( , ) zigzag bnnt adsorbed fu more strongly with a reduction in the h-l energy gap significantly with an increase in the dipole moment (dm) compared to the ( , ) zigzag bnnt [ ] . the ( , ) zigzag bnnt adsorbed fu with an adsorption energy of - . kcal/mol with a dm of only . debye and an increase in the h-l energy gap by . % whereas the ( , ) zigzag bnnt adsorbed fu with an adsorption energy of - . kcal/mol with an increased dm of . debye and decrease in the h-l energy gap by . %. so they further doped ( , ) zigzag bnnt with al, ga and ge to enhance the adsorption of fu to bnnt. the most promising result was observed for al-doped ( , ) zigzag bnnt (al-bnnt) where it adsorbed fu strongly with chemisorption of - . kcal/mol with a significant decrease in the energy gap by . % where the dm was observed as high as . debye. after that, a promising result was also observed from the ga-bnnt where it adsorbed fu with an adsorption energy of - . kcal/mol and decreased the h-l energy gap by . % with a dm of . debye. among doped bnnt the least promising performance was observed from ge-bnnt but better than the pristine ( , ) zigzag bnnt. ge-bnnt adsorbed fu with an adsorption energy of - . kcal/mol with a cut to the h-l energy gap by . % and an increase in the dm to . debye. these increase in the reactivity was further verified from a decrease in the global hardness and changes in the global reactivity parameters accordingly. though the adsorption process of fu drug to the ( , ) zigzag bnnt wasn't spontaneous as it was seen from the change in gibbs free energy (Δg), for al and ga doped bnnt it was spontaneous with a negative value for Δg. and the adsorption process of fu to all adsorbent was exothermic with a decrease in the entropy. so analyzing the results, they came to a conclusion that ga-bnnt can be used as a potential drug delivery system for fu for its enhanced nbo charge transfer properties where al-bnnt can be a potentially stable sensor fu with high adsorption energy and reduction in the h-l energy gap. besides zigzag bnnt, k. shayan et al. investigated the interaction of fu with a wide number of armchair bnnt [ ] . though the armchair bnnts adsorbed fu with less adsorption energies compared to the zigzag bnnts, from a detailed analysis of thermodynamical parameters, charge transfer, and global reactivity descriptors it was revealed that armchair bnnts also could be a potential drug delivery systems to deliver fu drug. the dft theory with m - x and b lyp exchange correlational functional with - g* basis set was also employed to investigate the -oh functionalized ( , ) zigzag bnnt (f-bnnt) as a drug delivery system for another anticancer drug carmustine (bcnu) [ ] . bcmu is a potential anticancer drug that is used to treat many kinds of brain cancers for over few decades, but sometimes it induces unwanted side effects like acute interstitial pneumonitis, myocardial ischemia etc. [ ] [ ] [ ] . using the b lyp hybrid exchange correlational functional, it was observed that the bncu interacted with f-bnnt with a maximum adsorption energy of - . kcal/mol in the gas phase which decreased to - . kcal/mol in the water phase. this interaction energy was increased as high as - . (- . ) kcal/mol in the gas (water) phase, while the dispersion corrected m - x functional was used. this significant difference in the adsorption energies using two different functional indicated that the weak van der waals (vdw) interactions played an important role in the bncu adsorption on f-bnnt. this was then confirmed from the md simulations where vdw energy increased to - . kcal/mol from - . kcal/mol for a j o u r n a l p r e -p r o o f single drug molecule with an increase in the temperature to k from k. the adsorption process was spontaneous and thermodynamically possible with an exothermic one in both gaseous and water phase. but the adsorption of bncu barely affected the charge transfer and electronic properties with an increase in the h-l energy gap. besides the reactivity of the structures was also decreased with an increase in the global hardness of the bncu adsorbed f-bnnt. the biocompatibility and non-toxicity of bnnts encouraged s. ghahremani et al. to encapsulate an anticancer drug floxuridine (fudr) into a ( , - ) armchair bnnt [ ] . fudr is an anticancer drug to treat colorectal cancer and often causes side effects like toxicity, diarrhoea etc. which requires immediate medical attention and hospitalization [ ] [ ] [ ] . fudr was encapsulated inside the ( , - ) bnnt with interaction energy of - . kcal/mol only. but the encapsulation of fudr decreased the energy gap to . ev from . ev, which was occurred due to a significant increase in the lumo energy to - . ev from - . ev. more importantly, the dm of the fudr encapsulated ( , bnnt increased significantly to the . debye while it was . for the ( , bnnt. this increase in the dm indicated an enhanced reactivity of the structure in a polar medium. this enhancement in the reactivity was also reflected in the quantum reactivity descriptors where the global hardness of the structure was increased to . ev where it was . ev for the ( , - ) bnnt alone and the global softness increased to . ev - from . ev - along with an increase in the electrophilicity to . ev from . ev. from nbo analysis, it was observed that the electron is most like to flow towards bnnt from fudr which made fudr an electron donor and bnnt an electron acceptor. the weak physisorption was further confirmed from the qtaim analysis where it was observed that the interaction between the fudr and bnnt was weak van der waals interactions with a small value for the electron density and a negative value for where five hydrogen bond was also observed. these promising results lead them to propose a drug carrier for the fudr based on ( , bnnt to reduce the unwanted effects of the fudr drug in our body. besides the anticancer drug delivery, the sensing properties of bnnt on anti-fever and pain-reducing drugs like paracetamol (pa) and phenacetin (ph) was also observed from several studies as the overdose of these drugs may induce some liver and kidney damage [ ] . the interaction of both pa and ph with several armchair bnnt with different chirality was investigated by h. ghasempour et al. using dispersion corrected dft-d theory with gga functional [ ] . interestingly, instead of adsorbing pa, it was desorbed in the inside of ( , ) bnnt with a positive adsorption energy of . kcal/mol while it was adsorbed strongly with an adsorption energy of - . kcal/mol in the outside of the ( , ) bnnt. but the reverse effect was observed in case of the ( , ) and ( , ) bnnt where pa was adsorbed more stably inside the bnnt with an adsorption energy of - . and - . kcal/mol respectively while it was - . and - . kcal/mol respectively for the adsorption of pa on the outside of ( , ) and ( , ) bnnts. again more enhanced properties on sensing pa like a high drop in the h-l energy gap and an increase in the dm was observed while the drug was in the outside of ( , ) and ( , ) bnnts. the exact same adsorption properties like desorption inside ( , ) bnnt but more stable adsorption inside ( , ) and ( , ) bnnts, more decrease in the energy gap and more increase in the dm while the drug was adsorbed on the outer surface of ( , ) and ( , ) bnnts was also observed for the ph adsorption on the bnnts. the more effect on the pa adsorption towards bnnt was further investigated by z. iranmanesh-zarandy et al. using md simulations in terms of change in nanotube's size, length, chirality and temperature [ ] . the binding free energy of pa was increased with an increase in the diameter of the bnnt. the binding free energy of pa towards the ( , ) bnnt with diameter . Å was observed as - . kcal/mol while it was gradually increased to - . kcal/mol for the ( , ) bnnt with a diameter of . Å. but a significant decrease in the stability was observed in cases like an increase in the length of bnnt and chirality along with a minor decrease in the stability for increasing temperature. recently several computational works also had been done on investigating bnnt as a sensor for several harmful chemical compounds, a long exposure of which may induce harmful effect to the human body. b. makiabadi et al. investigated the sensing properties of ( , ) zigzag bnnt and three al-doped b al nnt with a diameter ranging . - . Å using b lyp/ - ++g(d) level of theory, to sense carcinogenic compounds nitrosamine (na) and thionitrosamine (tna) which can make an entry to the human body through cigarette smoke, water, foods etc. and induce gastric and oesophageal cancer [ ] [ ] [ ] [ ] . both bnnt and b al nnt adsorbed na and tna with stable negative adsorption energies along with a decrease in the h-l energy gap hence increase in the conductivity, and increase in the reactivity by a decreasing chemical hardness with increasing chemical softness and electrophilicity. b al nnt showed more stable adsorption of na and tna with adsorption energy (bsse corrected) ranging - . to - . kcal/mol while it was - . to - . kcal/mol for the bnnt. besides more charge transfer from na and tna to bnnt was observed than b al nnt and all the bonds between the adsorbent and adsorbate were covalent in nature. g. fan et al. proposed another sensor for acetone based on zigzag bnnts from a dispersion corrected dft-d study which can have a potential application on the detection of diabetes as a patient with diabetes produces more acetone in their body than a normal person [ ] . it was observed that the pristine bnnts adsorbed acetone with decent stability but hardly able to sense it which was further improved by doping impurity atoms to the bnnt hence an acetone sensor can be developed with flexible sensing properties based on the necessity. besides, the interaction of the oxazole and isoxazole with bnnt was investigated by j. kaur et al. as many drugs have a structure similar to these heterocyclic aromatic organic compounds hence plays an essential role in the development of many drugs [ ] . though the ( , ) zigzag bnnt adsorbed oxazole in both gaseous and solvent phase with an adsorption energy of - . and - . kcal/mol respectively, it adsorbed isoxazole only in the solvent phase with an adsorption energy of - . kcal/mol. but the ( , ) armchair bnnt desorbed both oxazole and isoxazole in both gaseous and solvent phase with a positive value for the adsorption energy. a higher reactivity with a significantly increased dm was also observed for the ( , ) bnnt than ( , ) bnnt. hence the solvent and the chirality of the bnnt affects the adsorption properties of oxazole and isoxazole significantly. prior to the advancement of the cnt and c fullerenes, the investigation on the bnnt and boron nitride nanocages (bnnc) also started with almost the same timeline. research on the bnncs got immense attention after a report from f. jensen and h. toftlund stating that b n nanocage offers higher stability compared to the c fullerenes [ ] . shortly after that, in the first accidental observation of the nested bnnc was reported by . stephan et al. during doping the cnt with b and n atoms using the electric arc-discharge method [ ] . furthermore, many groups reported the growth of the bnnc using various methods including the formation of octahedral b n bnnc ( figure ) using electron beam irradiation by d. golberg et al. [ ] , the formation of b n using an arc-melting method by t. oku et al. [ ] etc. being made of boron nitrides, bnncs also benefit from the unique properties shown by other bn polymorphs like wide bandgap, high resistance to the oxidation, high thermal and chemical stability etc. which lead its application as good lubrication [ ] , wastewater treatment [ ] , hydrogen storage [ ] , gas sensors [ ] etc. bnncs are also reported to have a potential application in the anticancer drug sensing and delivery system. thioguanine or -thioguanine (tg), a drug that has clinical applications to treat several types of acute leukaemia, have many unwanted side effects like bone marrow suppression, liver toxicity etc. [ ] [ ] [ ] . to reduce these adverse effects on the human body, m. noormohammadbeigi et al. investigated pristine b n nanocage to work as a potential nano-drug delivery vehicle for tg delivery [ ] . considering non-covalent calculations, they chose m - x functional along with widely used - g (d,p) basis set and dft theory as the m - x functional have a higher percentage of hartree-fock exchange ( %). the fascinating property upon tg j o u r n a l p r e -p r o o f adsorption on b n was the decrease in the h-l energy gap by a noticeable change ranging . - . % which was confirmed from the dos spectrum of structures hence made a significant rise to the electrical conductivity of tg adsorbed structures. besides this sensitivity towards tg, b n was also spontaneously adsorbed tg by strong chemisorption with an exothermic process. the adsorption energy of the tg on b n was in a range of - . to - . kcal/mol for different orientations and isomers of the drug in the gaseous phase. however, this range increased into - . to - . kcal/mol in the water solvent phase with a significant increase in the dm to as high as . debye. higher charge polarization transfer from tg to b n was also observed in the water phase. these properties made them conclude b n nanocage as a nano drug delivery system for tg drug. ifosfamide (ifo) is another anticancer drug which has a potential application to treat several kinds of cancer and tumours including testicular cancer, small cell lung cancer, ovarian cancer etc. and have relatively fewer side effects [ ] . but sometimes, it is capable of inducing life-threatening toxicities like cardiac toxicity, hemorrhagic cystitis, nephrotoxicity, encephalopathy and neuropathy [ ] . a. soltani et al. investigated the interaction of ifo with pristine b n and carbon atom doped b n c and b n c fullerenes which revealed that those unwanted side effects of ifo might be reduced by using bn fullerenes as a nano-drug delivery system for the ifo [ ] . besides the dft theory, they chose one gga and another hybrid functional with a high percentage of hf (hartree-fock) exchange as gga pbe- was observed to have results closer to the experimental outcomes for b n , and the hybrid m - x was used widely for b n c , graphene and other nanosystems. unlike many other nanostructures, pristine b n fullerene adsorbed ifo drug with strong chemisorption of - . kcal/mol in its most stable orientations which was further enhanced in the water solution where it became - . kcal/mol. this figure : b n nanocage relaxed using dft theory with b lyp hybrid exchange correlational functional and - g (d,p) basis set. interaction between the ifo and bnnc became stronger due to the substitution of carbon atoms, and the interaction energies were observed as - . and - . kcal/mol while the adsorbents were b n c and b n c fullerenes, respectively. the dm for the ifo adsorbed structures increased in the solvent medium and was observed as high as . debye for b n c and . debye for b n c fullerene. these properties ensured the ifo drug loading ability of b n c and b n c and the biocompatibility of the structures were increased with a decrease in the toxicity which was confirmed from an increasing reactivity observed from the increasing chemical potential and electrophilicity with a decrease in the global hardness. besides delivering the tg and ifo anticancer drugs, bnnc was also reported to be worked as a potential sensor candidate for another anticancer drug cisplatin (cp) which was revealed from a first-principles investigation made by s. onsori et al. [ ] . it was observed that at the most stable interaction, the b n nanocage adsorbed cp drug with an adsorption energy of - . kcal/mol. but one of the key features for sensor development, decrease in the h-l energy gap, was observed with the highest decrease of . %, which was analyzed from the dos spectrum. for the different orientation of cp drug the reduction in the h-l energy gap ranges from . % to . % which ensured that b n nanocage could detect cp drug in various orientations efficiently with an increase in the conductivity to produce a detectable signal. besides the recovery time of the sensor was also found as low as ~ ms ensured that pristine b n nanocage could be a potential candidate for cp drug sensor without any modification, doping or decoration. furthermore, bnnc was considered to be a potential sensor to detect another anticancer drug α-cyano- -hydroxycinnamic acid (chc) [ ] . frontier molecular orbital analysis with dos revealed that due to the adsorption of chc the h-l energy gap of b n nanocage decreased by a minimum of . % to a maximum of . % for different orientations which ensured its sensitivity towards chc drug. almost the same sensitivity was also observed in the water solvent where the decrease in the h-l energy gap was observed as . % to . % for different orientations of chc on b n nanocage. besides, it adsorbed chc with a maximum adsorption energy of - . kcal/mol, which leads the sensor to be suffered by a moderately large recovery time of . sec at the room temperature. hence the b n nanocage can be considered as a potential sensor candidate to detect cp and chc drug. in addition, bnnc was studied to design a nano-vehicle for an anti-inflammatory drug like celecoxib (cxb) and a sensor for metformin (mf) that is used to treat type diabetes. first, n. abdolahi et al. investigated the adsorption properties of cxb drug adsorption on b n fullerene (bnnc) and found that bnnc can be a potential candidate for the nano-vehicle of cxb to transfer it into the targeted cell [ ] . the rising importance on the drug delivery system is associated with adverse effects of cxb like hypertension, diarrhoea, gastrointestinal effects besides its use as a cox- selective nonsteroidal anti-inflammatory drug (nsaid) [ ] [ ] [ ] . the bnnc firmly bound the cxb drug by strong chemisorption with an adsorption energy of - . kcal/mol in a vacuum and with - . kcal/mol in water medium at its most stable state. besides the bnnc was also sensitive towards the cxb drug as a decrease of . % in the h-l energy gap was observed from the dos spectrum analysis. due to the adsorption of cxb, the reactivity of the structure also increased with a decreasing global hardness, chemical potential, and electrophilicity along with an increase in the global softness while the dm of the structure was also increased to as high as . debye from zero for the pristine symmetric b n fullerene which raised the potentiality of bnnc as a nano-vehicle for cxb in drug delivery application. in another study, a.s. ghasemi et al. initiated an investigation lead by dispersion corrected dft-d theory to find the drug delivery capability of pristine and doped b n and b n fullerenes to deliver mf but ended up with finding sensor application of bnnc to sense mf [ ] . without any doping or functionalization of b n and b n fullerenes, both interacted with mf strongly with an adsorption energy of - . and - . kcal/mol respectively with a decrease in the h-l energy gap by . % and . %. besides the reactivity of the structures increase with an increase in the dm up to . debye along with an increase in global softness and decrease in the global hardness, chemical potential, and electrophilicity. hence the pristine b n and b n fullerenes can be potential candidate in the sensor development of mf drug. due to doping b n fullerenes with al, si, ge and ga, while the most stable interaction of mf was observed with alb n with a large adsorption energy of - . kcal/mol, geb n was most sensitive towards mf drug with a decrease in the h-l energy gap by . % with an acceptable adsorption energy of - . kcal/mol. hence the study concludes geb n fullerene as the most potential nanostructure to work as a biosensor for mf drug. the popular pyridine nucleobase uracil like anticancer drug fluorouracil (fu) was further adsorbed with the quasi-planar b boron nanosheet ( figure ) in order to investigate if the b can be used as a novel drug carrier system for the fu drug [ ] . all the quantum mechanical calculations were carried out by timedependent dft (td-dft) theory, and for the exchange correlational functional they depended on the hybrid tpssh functional with - +g (d) basis set. first, the fu drug failed to generate any detectable signal where no noticeable change in the h-l energy gap was observed while the drug interacted with the concave and convex surface of b nanosheet with weak interaction energy of - . to - . kcal/mol. but these interactions were greatly enhanced while the drug interacted with its o atom on the edge of the b nanosheet. while a single molecule was adsorbed on the edge of b nanosheet, in the gaseous medium the adsorption energy was observed as high as - . kcal/mol with maximum deformation energy of . kcal/mol. the b also detected fu with a noticeable decrease in the h-l energy gap of % with an nbo charge transfer of . a.u. the dm of these structures was also observed as high as . debye, which indicated an increase in the reactivity in the polar medium. while instead of one fu, two fu molecule was adsorbed on the b nanosheet, the adsorption energy per molecule was slightly decreased with a maximum value of - . kcal/mol but increased the deformation energy as high as . kcal/mol. despite a less interaction the sensitivity and reactivity increased significantly where the decrease in the h-l energy gap was as high as % with nbo charge transfer ranging . to . a.u. while the dm was observed as high as . debye. besides, a more strong interaction of fu with b was observed in the aqueous solution where the adsorption energy was as high as - . kcal/mol with an increased reactivity where the highest dm was observed as . debye, but no significant change in the h-l energy gap was observed. hence these enhanced adsorption properties in the polar medium made b nanosheet a potential candidate for the nano-drug carrier of fu. besides, drug delivery application, b nanosheet was further investigated by c. xiao et al. in a search for an electrochemical sensor development to sense metronidazole (ml) drug [ ] . this antibiotic drug is used to treat a number of diseases including bacterial vaginosis, perineal crohn's disease, trichomoniasis etc. but an extensive usage of it can lead to unwanted carcinogenic effects on the human body [ ] [ ] [ ] . the dft theory based b lyp-gcp-d / - g* level of theory was applied to optimize the structures which further found that like fu, ml also interacted more strongly with the b nanosheet by its edge with adsorption energy as high as - . kcal/mol while the adsorption process was spontaneous with a negative value for the change in gibbs free energy as - . kcal/mol. but the maximum adsorption energy of the complexes was slightly decreased to - . kcal/mol with an increase in the solvation energy to - . kcal/mol. despite a very slight change in the work function of the b nanosheet due to the adsorption of ml, the change in the h-l energy gap was dramatic with the highest drop by . % to . ev from . ev ensuring a significant increase in the conductivity of the structure. this significant decrease in the h-l energy gap also caused an nbo charge transfer of . e between the ml and b nanosheet which will be able to induce a detectable electrochemical signal and can be used to develop a potential sensor to sense ml drug. the recovery time of the sensor was further found to be as low as . s for the most stable adsorption in the room temperature. using the different sensing properties towards the four dna nucleobases adenine, guanine, cytosine, thymine, the quasi-planar b nanosheet was further proposed for an application as a dna sequencing device by a dft investigation from a. rastgou et al. [ ] . it was observed that the b nanosheet was most sensitive towards the cytosine with its edge than other nucleobases with a massive decrease in the h-l energy gap by . %. for the thymine, this decrease in the h-l energy gap was observed within the range . % to . % and was the second most sensitive structure towards b nanosheet. the sensitivity of adenine and guanine was almost similar towards the b nanosheet, but the sensitivity was slightly higher for adenine with a decrease in the energy gap by . % to . % following by . % to . % for guanine although two orientations can decrease the j o u r n a l p r e -p r o o f energy gap by . % and . %. hence the highest peak in the conductivity will be observed for cytosine following by the thymine, adenine and guanine from which these dna nucleobases can be identified. though the electronic sensitivity was observed as cytosine>thymine> adenine ~ guanine, the energetic sensitivity of b nanosheet was observed as adenine>guanine> cytosine>thymine. another quasi-planar boron nanocluster, bowl-shaped b nanostructure was proposed to function as a drug delivery system for amantadine drug as it often comes with unwanted adverse effects like insomnia, depression, hallucinations etc. besides its application to treat parkinson disease and influenza a [ ] [ ] [ ] [ ] . like b nanosheet the strongest interaction of amantadine was observed on the edge of b nanostructure with an adsorption energy of - . kcal/mol while for other orientations it ranged between - . to - . kcal/mol ensuring strong chemisorption for every orientation. the amantadine adsorption by b nanostructure further got stronger on the water solvent while the range of the adsorption energy became - . to as high as - . kcal/mol. besides b nanostructure was more sensitive to amantadine by its edge but still not sufficient to develop a sensor as the maximum drop in the h-l energy gap was observed as only . % while for the other orientations this was observed with a range . % to . %. finally, the polarity and reactivity of the b nanostructure increased significantly with a major increase in the dm as high as . debye from . debye for the pristine b nanostructure. for other orientations, the dipole moment was also almost similar within the range of . to . debye. this increase in the polarity and reactivity with decent adsorption energy which also increased significantly in the aqueous solution made b nanostructure a potential candidate as a nano-drug delivery system for amantadine drug. as usual, metal oxide (mo) nanostructures were also studied as a drug delivery system for several therapeutic anticancer drugs. r. khorram et al. investigated the drug delivery properties maghemite (γ-fe o ) nanostructure to deliver carmustine (bcnu) anticancer therapeutic drug which was previously discussed in this study to be delivered using -oh functionalized ( , ) zigzag bnnt (f-bnnt) [ ] . like f-bnnt, bcnu was j o u r n a l p r e -p r o o f also made a weak interaction with maghemite with a maximum adsorption energy - . kcal/mol while other orientation of the drug it was also observed as low as - . kcal/mol. from thermodynamical parameter analysis, it was observed that the drug adsorption process was spontaneous and exothermic in nature as the change in the gibbs free energy and enthalpy was negative. the dm of the structures increased significantly to as high as . debye due to the adsorption of bcnu from . debye for the maghemite which increased the polarity and reactivity of the structures noticeably, and this played a crucial role into the delivery of bcnu using maghemite. the aim analysis was also done to investigate the type of interaction between the drug and maghemite which revealed the presence of partial covalent interaction between them. besides, nbo analysis identified the bcnu as electron donor where maghemite was a receiver, and this was further verified from a more negative value of chemical potential for maghemite as - . ev compared to - . ev for bcnu. this work with maghemite besides f-bnnt will surely advance the study to find a nano-drug carrier for bcnu drug. besides drug delivery, another study from s. onsori and e. alipour proposed another mo, zn o nanocluster, to develop an electrochemical sensor for another anticancer drug cisplatin (cp) with brand name platinol for which another sensor was discussed previously on this study using b n nanocage [ ] . the zn o nanocluster made a stronger interaction with cp compared to the b n nanocage but with a less sensitivity where the maximum adsorption energy and decrease in the h-l energy gap were observed as - . kcal/mol and . % respectively. the adsorption process was spontaneous with a negative value for the change in gibbs free energy as high as a - . kcal/mol with a maximum change transfer of . e between the cp and zn o nanocluster. the sensitivity of the zn o nanostructure towards cp was enhanced in the aqueous solution with a maximum drop in the h-l energy gap by . % with a slight reduction in the maximum adsorption energy to - . kcal/mol. the sensor also had a short recovery time of . sec in the combination of which made zn o nanostructure a promising sensor candidate for cp drug. the isonicotinic acid hydrazide (inh) with brand name isoniazid, a prodrug to treat the deadly infectious disease tuberculosis (tb), which was previously discussed to be delivered using swcnt by n. saikia et al., was also proposed to be delivered using another mo framework mg o nanocage by i. ravaei et al. [ ] . the pristine mg o nanocage made a strong interaction with inh drug with a maximum adsorption energy of - . kcal/mol but failed to alter the reactivity and electronic properties with no noticeable change in the global reactivity parameters and h-l energy gap of the structures. this problem was overcome by replacing an mg atom by al atom to the mg o nanocage, which decreased the h-l energy gap to . ev from . ev. the h-l energy gap was further reduced to . ev by . % due to the adsorption of inh drug on al-mg o nanocage with an increase in the reactivity by lowering the global hardness and chemical potential. due to the doping of al atom, the interaction of the inh drug also got stronger with an increase in the adsorption energy to as high as - . kcal/mol. besides from aim and nbo analysis, it was revealed that the interaction between the drug and carrier was partially covalent in nature and the electrons were transferred from inh drug to the al-mg o nanocage. in another first-principles investigation, m. rezaei-sameti et al. investigated the interaction of another mo, be o nanocluster with mercaptopyridine (mcp) drug [ ] . interestingly, pristine be o nanocluster showed more encouraging adsorption properties towards mcp than sc and ti-doped be o nanocluster in order to develop a nano-drug carrier system for mcp drug with maximum adsorption energy and dm of - . kcal/mol and . debye respectively. doping the nanocluster with sc and ti increased the adsorption energy to as high as - . kcal/mol but decreased the maximum dm to . debye. but the doping of sc and ti increased the sensitivity of the be o nanocluster towards the mcp drug by reducing the h-l energy gap significantly, which was not observed noticeably for pristine be o nanocluster. hence, those nanoclusters can hold future potential for the sensor development of mcp drug. furthermore, the adsorption process was spontaneous, j o u r n a l p r e -p r o o f exothermic, ordered for all investigated structures except the mcp adsorption with s atom towards the pristine be o nanocluster with a positive value for the change in gibbs free energy. besides mcp, another mo nanocluster, zno single-walled nanotube (swnt) was also proposed to be a potential sensor candidate for protein tyrosine nitration (ptn), -nitrotyrosine, which can be produced during the post-translational modifications in proteins and cause several human disorders like rheumatoid arthritis, parkinson's disease, alzheimer etc. [ ] . the interaction of the ptn increased significantly with the increasing chirality of the zno swnts. the maximum binding energy of the ( , ) zno swnt was observed as . kcal/mol while it was increased to . kcal/mol for zno swnt. finally, a noticeable alteration in the electronic band structure of the zno swnt indicated its sensitivity towards ptn. the interaction of isoniazid (inh) was also studied with the pristine and ni-doped ( , ) armchair gannts by m. rezaei-sameti et al. using the dft cam-b lyp/ - g(d) level of theory [ ] . it was observed that the pristine and ni-doped gannts adsorbed the inh drug with an adsorbate-adsorbent distance of . - . Å. the pristine gannt adsorbed the inh strongly with adsorption energies ranging - . to - . kcal/mol for different orientations for the drug which hadn't increased due to the doping with ni. the adsorption processes were exothermic in nature and thermodynamically favourable. all interactions were spontaneous and ordered with negative values for the change in gibbs free energy and entropy. the h-l energy for all of the investigated structures were ranging between . ev and . ev and a decrease in the energy gap was observed in the nidoped structures with an increase in the conductivity. besides, the work function of the investigated structures was observed as - . to - . ev. from the nbo analysis, it was also revealed that the inh worked as the electron donor in the inh-gannt complexes with a positive value for which agreed with the positive values for maximum electronic charge transfer ( ). these alluring adsorption properties may lead ( , ) armchair gannts to a potential sensor candidate for the inh drug. the sensor for another drug, benzoylethanamine (bea) or β-keto-amphetamine, was reported by a. hosseinian et al. using aln nanoclusters [ ] . another sensor for bea was previously discussed in this review besides, the aln nanosheet also has a very short recovery time of . s in the room temperature. though the aln nanoclusters hadn't shown better properties than the si-doped bc n nanotube, as pristine structures they showed better sensing properties than pristine bc nanotube, and these nanoclusters can be considered as potential candidates to develop a sensor for bea drug. besides the sensor for bea, aln nanocage was also reported to have a potential application in the development of a work function based sensor for antiparkinsonian drug amantadine (am) drug whose delivery was previously discussed by z. noroozi et al. [ , ] . at its most stable state, the aln nanocage adsorbed the am drug with an adsorption energy of - . kcal/mol with an adsorbent-adsorbate distance of . Å. though a charge transfer of . e from am to the nanocage which was confirmed by nbo analysis, am hardly able to decrease the h-l energy gap of the nanocage upon its adsorption. the decrease in the energy gap was observed by only . % leading no significant change in the conductivity of the nanocage. but the adsorption of am significantly decreased the work function by . % to . ev from . ev for pristine aln nanocage. hence the aln was considered to have potential on the development of a work function based biosensor for am drug. on the other hand, the bnnc was observed to decrease its h-l energy gap by . % to . ev on the adsorption of am drug. besides, bnnc also adsorbed the am drug with a decent adsorption energy of - . kcal/mol. hence the bnnc was considered as a potential electrochemical sensor to detect am drug. both aln and bn sensors were benefited from a shorter recovery time of s and . s at a high temperature of k, and their interactions with the am drug was electrostatic and covalent in nature, respectively. the similar kind of j o u r n a l p r e -p r o o f response was also observed on the adsorption of acetylsalicylic acid (asa) drug on the aln and bnnc [ ] . here, the asa was also adsorbed by aln nanocage strongly with an adsorption energy of - . kcal/mol but failed to alter the electronic properties of aln nanocage. besides, this time aln nanocage also suffered from an unrealistic large recovery time of . sec. on the other side, asa was adsorbed on the bnnc with a relatively weak adsorption energy of - . kcal/mol but decreased the h-l energy gap by . %. besides the bnnc also benefitted from a short recovery time of ~ seconds. again, the bnnc could not work as a work function based sensor as it increased the work function by % to . ev from . ev. hence bnnc can only be considered as a potential electrochemical sensor to detect asa. the result from adsorption of asa and am on aln and bn was also extended by r. padash et al. for -aminopyridine ( -ap) drug and exactly the same trends were followed [ ] . the al n nanocage was again adsorbed the -ap drug with the highest adsorption energy of - . kcal/mol followed by - . kcal/mol for b n nanocage, and - . kcal/mol for both al p and b p nanocages. following the same trend, while adsorption of -ap on bnnc decreased the h-l energy gap only to . ev from . ev, it hadn't decreased at all from . ev for alp nanocage. on the other side, the h-l energy gap was reduced to . ev from . ev on the adsorption of -ap towards bnnc following by . ev from . ev for bp nanocage. hence it was concluded that the sensitivity of the bn and bp was higher than aln and alp towards -ap made bn and bp structures a potential sensor candidate to detect -ap. finally, the aln nanoclusters were also proposed to be applied as a sensor for anticancer drug purinethol (pe) or mercaptopurine, by s. a. javarsineh et al. using dft theory with b lyp hybrid functional and the - g (d) basis set [ ] . in early s pe drug was first evaluated to treat leukaemia, but this hepatotoxic drug comes with several serious adverse effects like bone-marrow depression, abnormal liver function etc. which sometimes requires withdrawal of the drug from the human body which indicates rising importance for the pe sensor [ ] . the aln nanocage made spontaneous chemisorption with the pe drug with a maximum adsorption energy of - . kcal/mol. also, it showed relatively good sensitivity towards the pe drug with a maximum decrease in the h-l energy gap by . % to . ev with a maximum charge transfer of . e from drug to the nanocage. these made aln nanocage a promising candidate for the pe drug, but unfortunately, it suffers from a considerable recovery time of . seconds. on the other hand, the aln nanocone made a relatively weak interaction with pe with a maximum adsorption energy of - . kcal/mol but showed relatively higher sensitivity towards the pe drug with a maximum decrease in the h-l energy gap by . % to . ev. besides, the aln nanocone also benefits from a comparatively shorter recovery time of . seconds on the adsorption of pe in room temperature. hence, the aln nanocone holds a potential in the development of an electrochemical sensor to detect pe drug. b. khodashenas et al. used the gelatin-coated gold nanoparticles (gnps) to investigate the nanostructure's size effects on the curcumin drug encapsulations with the drug release mechanism using dft theory with b lyp hybrid functional and lanl dz basis set along with an experimental mechanism [ ] . in order to do that, they have first synthesized gnps with three different sizes ( , , and nm) and then coated them with gelatin. the characterization of the structures was further ensured by the ft-ir spectroscopy, uv-vis spectroscopy, dynamic light scattering, and scanning electron microscopy. from the dft investigation, a further strong interaction between the gnp and gelatin was revealed with a binding energy of - . kcal/mol and the gelatin works as an electron donor in the complex. finally, it was observed that the efficiency of the curcumin drug encapsulations was increased slightly with an increase in the nanocluster size. for au-gelatin ( nm) structure the efficiency was . % while the least was observed for the au-gelatin ( . nm) as . % following by . % for the au-gelatin ( . nm). besides the drug release rate was observed higher at a low ph ( . ) environment compared to the relatively neutral environment with . ph. j o u r n a l p r e -p r o o f investigate the drug delivery properties of silver nanoparticles for the aromatic organic compounds, anthraquinone derivatives, which induced a potential interest in the biological applications in recent years [ ] . they have prepared the anthraquinone derivative , -dimethoxy -nitro- -methylanthracene- , -dione (dmnmad) using an available method in the literature [ ] and the silver nanoparticles were synthesized solution combustion method. for the quantum mechanical calculations, they have used the b pw functional and lanl dz basis set with dft theory. from the surface-enhanced raman spectroscopy spectrum it was observed that the theoretical values from the dft calculations for different vibrational modes of the structures were very close to the experimental values which ensured the validity of first-principles calculations for this system. further from the dft calculations the h-l energy gap of the dmnmad was found as . ev which decreased to the . ev in the ag-dmnmad complex. this alteration in the electronic properties of dmnmad holds a promise in the future drug delivery of anthraquinone derivatives which was further investigated using uv-vis spectroscopy, molecular electrostatic potential etc. another micromolecule, poly (amido-amine) (pamam) dendrimers, recently had attention for working as a drug delivery system, electrochemical sensor etc. and the interaction of pamam with gnps was investigated by m. b. camarada using dft theory with b lyp hybrid exchange correlational [ ] . it was observed that the pamam interacted with the gnps with maximum interaction energy of . kcal/mol (bsse corrected) with an adsorbent-adsorbate distance ranging as . to . Å. this interaction increased the dm of the complex significantly to a maximum of . debye from . debye with a maximum decrease in the h-l energy gap to . ev from . ev. these alterations in the electronic properties indicate a promising application of au-pamam in the field of drug delivery and sensor. d. cortés-arriagada et al. used another graphene-like nanosheet, phosphorene, to investigate the interaction of nucleobases which plays an important role in designing drug molecules [ ] . for the dft calculations, they have used dft-d methods with pbe functional and def -svp basis sets. the nucleobases were observed to be adsorbed on the surface of phosphorene nanosheet more strongly than the gns where the most stable interaction was observed with guanine (g) nucleobase. the range of adsorption energies for the nucleobases on gns was observed on a range . to . kcal/mol which increased as . to . kcal/mol on the phosphorene nanosheet with weak long-range electrostatic closed-shell interactions. the stability was further increased while the nucleobases worked as a base pair and the most stable pair was c-g pair on the adsorption towards phosphorene with an adsorption energy of . kcal/mol following by . and . kcal/mol for a-t and a-u bases. during the interactions of nucleobases with phosphorene, a significant contribution to the van der waals dispersion energy was observed, and it was in the range of . to . kcal/mol for single nucleobases while was . to . kcal/mol for base pairs adsorption on phosphorene. but the adsorption of nucleobases almost failed to alter the electronic properties of phosphorene but increased the dm to as high as . debye in the base pairs and . debye for the single nucleobases while it was zero for the phosphorene nanosheet alone. these properties hold potential for the phosphorene nanosheet in the development of biosensors, nano-drug carrier vehicles or to be applied in dna/rna sequencing. the phosphorene nanosheet was further investigated by u. saikia et al. to find an efficient electrochemical sensor or nano-drug delivery vehicle for acetaminophen drug or more commonly known as paracetamol [ ] . it was observed that phosphorene adsorbed acetaminophen drug slightly more strongly compared to graphene with an adsorption energy of - . kcal/mol and an adsorbent-adsorbate distance of . Å following by - . kcal/mol and . Å for graphene. but the phosphorene clearly outnumbered the graphene and bnns in terms of charge transfer and dm which was . e and . debye respectively for phosphorene following by . e and . debye for graphene, and . e and . debye for bnns though bnns adsorbed j o u r n a l p r e -p r o o f acetaminophen more strongly than phosphorene with an adsorption energy of - . kcal/mol with a lower adsorbent-adsorbate distance of . Å. however, the most alluring interaction properties were observed for acetaminophen adsorption on the silicene, a two-dimensional nanosheet made of silicon atoms. when the drug was adsorbed in parallel with silicene, it was adsorbed with an adsorption energy of - . kcal/mol but with a small adsorbent-adsorbate distance of . Å. this lead to a higher amount charge transfer between the drug and nanosheet of . e along with a significantly increased dm of . debye. for the perpendicular orientation of the drug with silicene, a more stable interaction was observed with an adsorption energy of - . kcal/mol but with a slightly less charge transfer and dm of . e and . debye respectively. hence, the silicene surely holds a potential to be applied as a nano-drug carrier for acetaminophen drug, whereas other structures may work as a sensor to detect acetaminophen drug which can be explored through experimental research. after analyzing these vast number of research works, ldns can be concluded as promising candidate for the bio-sensing and drug delivery related applications. the biocompatibility and a great variety of the ldns with significant noble properties made these materials to work as sensors and delivery systems for many different types of drugs and biomolecules. besides, the quantum mechanical calculations have shown a considerable accuracy on predicting the different properties of the nanomaterials in the nanoscale range with a close resemblance to the experimental outcomes. furthermore, these first-principles calculation methods hold a promising future with the increasing computational abilities, which will significantly assist experimental researchers in developing any biomedical devices in a considerably short period of time during an emergency-response-situation. we have observed that the first-principles calculations allow researchers to calculate a wide range of essential properties from an atomic perspective to firmly understand the interaction of drug molecules with the nanomaterials. for the drug delivery systems, it also allows investigating the drug release mechanism in the targeted cell region. the excellent mechanical and electronic properties along with the biocompatibility of carbon-based ldns, e.g. graphene, cnt, fullerenes etc. made themselves evenhanded to be investigated more extensively than other nanomaterials to be applied in the stable drug sensor and drug delivery systems for various kind of drugs which show significant adverse effects in the human and animal bodies. among other nanomaterials, bnns and its allotropes, e.g. bnnt, bnnc showed a comparable mechanical strength, enhanced thermal stability, and other properties similar to the carbon-based nanomaterials which are being applied in the development of highly durable biosensors and drug delivery systems. other nanostructures like quasi-planar b , phosphorene, gold nanoparticles, metal nitrides etc. were investigated less extensively but showed promising sensing behaviour towards many drugs and biomolecules. especially, phosphorene, semimetal and post-transition metal nanostructures were studied to detect many toxic nerve agent, kidney biomarkers etc. hence, these nanomaterials can further be investigated to develop biosensors to detect many other drugs and biomolecules. in conclusion, the wide variety of ldns with many alluring novel properties holds a great potential in biomedical applications where first-principles investigations with rapidly increasing computational abilities will assist researchers in understanding these systems from the atomic perspective at a low cost with considerable accuracy. [ ] nanofood for thought, nat. nanotechnol. ( ) there's plenty of room at the bottom c : buckminsterfullerene a nontransferring dry adhesive with hierarchical polymer nanohairs role of dimensionality and quantum confinement in p-type semiconductor indium phosphide quantum dots synthesis, assembly and applications of semiconductor nanomembranes graphene-enabled and directed nanomaterial placement from solution for large-scale device integration non-lithographic direct patterning of carbon nanomaterial electrodes via electrohydrodynamic-printed wettability patterns by polymer brush for fabrication of organic field-effect transistor high-pressure-assisted design of porous topological semimetal carbon for li-ion battery anode with high-rate performance carbon nanomaterials for non-volatile memories combinatorial search for optimal hydrogen-storage nanomaterials based on polymers nanomaterials and nanostructures for efficient light absorption and photovoltaics in situ characterization of electrochemical processes in one dimensional nanomaterials for energy storages devices nanomaterials at work in biomedical research are carbon nanotubes safe? advanced hybrid nanomaterials for biomedical applications spontaneous insertion, helix formation, and hydration of polyethylene oxide in carbon nanotubes nano-bio interactions between carbon nanomaterials and blood plasma proteins: why oxygen functionality matters how to design preclinical studies in nanomedicine and cell therapy to maximize the prospects of clinical translation graphene in the sky and beyond synthesis, characterization of graphene oxide wrapped silicon carbide for excellent mechanical and damping performance for aerospace application grafting carbon nanotubes directly onto carbon fibers for superior mechanical stability: towards next generation aerospace composites and energy storage applications application of nanomaterials in civil engineering bt -nanomaterials and their applications nanotechnology: advantages and drawbacks in the field of construction and building materials nanotechnology: the future of fire safety nanotechnology innovations for the construction industry application of nanoparticles in percutaneous delivery of active ingredients in cosmetic preparations nanomaterials and regulation of cosmetics measurement of the elastic properties and intrinsic strength of monolayer graphene mechanics of carbon nanotubes optical properties of hexagonal boron nitride epitaxial growth of a silicene sheet phosphorene: an unexplored d semiconductor with a high hole mobility germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene large-gap quantum spin hall insulators in tin films the potential environmental impact of engineered nanomaterials nanoscience and nanotechnologies: opportunities and uncertainties safe handling of nanotechnology science policy considerations for responsible nanotechnology decisions fabrication, mechanical properties, and biocompatibility of graphene-reinforced chitosan composites preparation of carbon nanotube bioconjugates for biomedical applications the biocompatibility of carbon nanotubes nanomaterials and biocompatibility: carbon nanotubes and fullerenes bt -nanotechnology in drug delivery borophene is a promising d allotropic material for biomedical devices biocompatibility of boron nitride nanotubes: an up-date of in vivo toxicological investigation chemical sensors: definitions and classification state of the art in alcohol sensing with d materials ultrasensitive detection of nucleic acids using deformed graphene channel field effect biosensors enhanced surface plasmon resonance (spr) signals based on immobilization of core-shell nanoparticles incorporated boron nitride nanosheets: development of molecularly imprinted spr nanosensor for anticancer drug, etoposide fabrication of graphene film composite electrochemical biosensor as a pre-screening algal toxin detection tool in the event of water contamination pegylated nano-graphene oxide as a nanocarrier for delivering mixed anticancer drugs to improve anticancer activity anticancer efficacy and subcellular site of action investigated by real-time monitoring of cellular responses to localized drug delivery in single cells synthesis and drug-delivery behavior of chitosan-functionalized graphene oxide hybrid nanosheets water-soluble poly(n-isopropylacrylamide)-graphene sheets synthesized via click chemistry for drug delivery graphene based gene transfection graphene oxide-polyethylenimine nanoconstruct as a gene delivery vector and bioimaging tool engineered polyethylenimine/graphene oxide nanocomposite for nuclear localized gene delivery enhanced chemotherapy efficacy by sequential delivery of sirna and anticancer drugs using pei-grafted graphene oxide functionalized graphene oxide mediated adriamycin delivery and mir- gene silencing to overcome tumor multidrug resistance in vitro fabrication of mpegylated graphene oxide/poly( -dimethyl aminoethyl methacrylate) nanohybrids and their primary application for small interfering rna delivery folic acid-conjugated graphene oxide loaded with photosensitizers for targeting photodynamic therapy graphene multilayers as gates for multi-week sequential release of proteins from surfaces multilayered graphene nano-film for controlled protein delivery by desired electro-stimuli non-cytotoxic hydroxylfunctionalized exfoliated boron nitride nanoflakes impair the immunological function of insect haemocytes in vivo hollow boron nitride nanospheres as boron reservoir for prostate cancer treatment boron nitride nanotubes functionalized with mesoporous silica for intracellular delivery of chemotherapy drugs chiral nanoporous metal-organic frameworks with high porosity as materials for drug delivery black phosphorus nanosheet-based drug delivery system for synergistic photodynamic/photothermal/chemotherapy of cancer a novel nanoparticle vector for tumor directed drug delivery probing the solute-solvent interaction of an azo-bonded prodrug in neat and binary media: combined experimental and computational study experimental and theoretical studies of novel azo benzene functionalized conjugated polymers heteroleptic copper(i) complexes of -scorpionate‖ bis-pyrazolyl carboxylate ligand with auxiliary phosphine as potential anticancer agents: an insight into cytotoxic mode nmr and dft investigations of structure of colchicine in various solvents including density functional theory calculations transition-metal-free formal crosscoupling of aryl methyl sulfoxides and alcohols via nucleophilic activation of c-s bond molecular origin of drug release by water boiling inside carbon nanotubes from reactive molecular dynamics simulation and dft perspectives first principles study on the boron-nitrogen domains segregated within ( , ) and ( , ) single-wall carbon nanotubes: formation energy, electronic structure and reactivity high selectivity of cyclic tetrapyrrole over tetrafuran and tetrathiophene toward toxic chemicals; a first-principles study theoretical insight of polypyrrole ammonia gas sensor an ab initio study of the b boron nanocluster for application as atmospheric gas (no,no ,n o,nh ) sensor boron trifluoride interaction studies on graphdiyne nanotubes -a firstprinciples insight electronic properties of acetaminophen adsorbed on d clusters: a first principles density functional study a study on quercetin and -fluorouracil drug interaction on graphyne nanosheets and solvent effects -a first-principles study dft and md investigations on the functionalized boron nitride nanotube as an effective drug delivery carrier for carmustine anticancer drug amantadine antiparkinsonian drug adsorption on the aln and bn nanoclusters: a computational study a dft study on the geometrical structures, electronic, and spectroscopic properties of inverse sandwich monocyclic boron nanoclusters conbm (n = . ; m = - ) chemical hardness in density functional theory ordering of wave functions and eigenenergies to the individual electrons of an atom boron nitride nanotube (bnnt) as a sensor of hydroperoxyl radical (ho ): a dft j o u r n a l p r e -p r o o f study theoretical study of solvent and co-solvent effects on the interaction of flutamide anticancer drug with carbon nanotube as a drug delivery system hexagonal boron nitride nanosheet as novel drug delivery system for anticancer drugs: insights from dft calculations and molecular dynamics simulations behavior of ylides containing n, o, and c atoms as hydrogen bond acceptors absolute hardness: companion parameter to absolute electronegativity adsorption of oxazole and isoxazole on bnnt surface: a dft study -structural health monitoring of processes related to composite manufacturing quantum dots sensitized graphene: in situ growth and application in photoelectrochemical cells graphene and graphene oxide as new nanocarriers for drug delivery applications investigation of the solvent effect, molecular structure, electronic properties and adsorption mechanism of tegafur anticancer drug on graphene nanosheet surface as drug delivery system by molecular dynamics simulation and density functional approach recent advances in graphene based gas sensors recent advances in graphene-based biosensors electric field in atomically thin carbon films, science ( -. ) highly conducting graphene sheets and langmuir-blodgett films large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide chemical nature of boron and nitrogen dopant atoms in graphene strongly influences its electronic properties superior thermal conductivity of single-layer graphene thermal properties of graphene and nanostructured carbon materials approaching ballistic transport in suspended graphene cytotoxicity of graphene oxide and graphene in human erythrocytes and skin fibroblasts direct electrochemistry of glucose oxidase assembled on graphene and application to glucose detection phagraphene: a low-energy graphene allotrope composed of - - carbon rings with distorted dirac cones induction of apoptosis by β-lapachone in human prostate cancer cells efficacy of betalapachone in pancreatic cancer treatment: exploiting the novel, therapeutic target nqo selective killing of cancer cells by β-lapachone: direct checkpoint activation as a strategy against cancer studying metal-doped graphene nanosheet as a drug carrier for anticancer drug β-lapachone using density functional theory (dft) doxorubicin and mechanical performance of cardiac trabeculae after acute and chronic treatment: a review risk factors for doxorubicin-lnduced congestive heart failure doxorubicin pathways: pharmacodynamics and adverse effects a first-principles study of the interaction of doxorubicin with graphene fabrication and characterization of a triple functionalization of graphene oxide with fe o , folic acid and doxorubicin as dual-targeted drug nanocarrier controlled release of doxorubicin from graphene oxide based charge-reversal nanocarrier adsorption of ampyra anticancer drug on the graphene and functionalized graphene as template materials with high efficient carrier b n fullerene as a carrier for -fluorouracil anti-cancer drug delivery: dft studies a dft study of -fluorouracil adsorption on the pure and doped bn nanotubes aln and alp doped graphene quantum dots as novel drug delivery systems for -fluorouracil drug: theoretical studies process research and development of a dihydropyrimidine dehydrogenase inactivator: large-scale preparation of eniluracil using a sonogashira coupling -fluorouracil: mechanisms of resistance and reversal strategies screening of the structural, topological, and electronic properties of the functionalized graphene nanosheets as potential tegafur anticancer drug carriers using dft method recent and new targets for small molecule anti-cancer agents how strong is the edge effect in the adsorption of anticancer drugs on a graphene cluster? benchmark theoretical study of the π-π binding energy in the benzene dimer adsorption of adenine on the surface of nickel-decorated graphene study on the structure and electronic property of adsorbed guanine on aluminum doped graphene: first principles calculations sustained-release fampridine for symptomatic treatment of multiple sclerosis theoretical study of functionalized single-walled carbon nanotube ( , ) with mitoxantrone drug dalfampridine: review on its recent development for symptomatic improvement in patients with multiple sclerosis phonon dispersion curves of a bc honeycomb j o u r n a l p r e -p r o o f epitaxial sheet adsorption of amino acids on boron and/or nitrogen doped functionalized graphene: a density functional study trends of amino acid adsorption onto graphene and graphene oxide surfaces: a dispersion corrected dft study computational explanation for interaction between amino acid and nitrogen-containing graphene si-doped phagraphene as a drug carrier for adrucil anticancer drug: dft studies helical microtubules of graphitic carbon strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, science ( -. ) quantum transport in carbon nanotubes nanotube optoelectronic memory devices thermal conductance of an individual single-wall carbon nanotube above room temperature highly dense and perfectly aligned single-walled carbon nanotubes fabricated by diamond wire drawing dies unusually high thermal conductivity of carbon nanotubes carbon nanotube (cnt)-based composites as electrode material for rechargeable li-ion batteries: a review carbon nanotubes: a review on structure and their interaction with proteins advances in the science and technology of carbon nanotubes and their composites: a review catalytic growth of carbon microtubules with fullerene structure large-scale purification of single-wall carbon nanotubes: process, product, and characterization gas-phase synthesis of swnt by an atmospheric pressure plasma jet one-pot synthesis of carbon nanofibers from co synthesis of large arrays of well-aligned carbon nanotubes on glass large-scale production of single-walled carbon nanotubes by the electric-arc technique gas-phase catalytic growth of single-walled carbon nanotubes from carbon monoxide carbon nanotube growth by pecvd: a review a review featuring the fundamentals and advancements of polymer/cnt nanocomposite application in aerospace industry a review on carbon nanotube field effect transistors (cntfets) for ultra-low power applications a review on the use of carbon nanotubes nanofluid for energy harvesting system recent development in nanocarbon materials for gas sensor applications recent uses of carbon nanotubes & gold nanoparticles in electrochemistry with application in biosensing: a review applications of carbon nanotubes in drug delivery: a comprehensive review how do carbon nanotubes serve as carriers for gemcitabine transport in a drug delivery system? quaternized polymer-single-walled carbon nanotube scaffolds for a chemiresistive glucose sensor carbon nanotubes for the delivery of therapeutic molecules biomolecule-functionalized carbon nanotubes: applications in nanobioelectronics platinum(iv) prodrugs entrapped within multiwalled carbon nanotubes: selective release by chemical reduction and hydrophobicity reversal the application of carbon nanotubes in target drug delivery systems for cancer therapies modeling the interaction between anti-cancer drug penicillamine and pristine and functionalized carbon nanotubes for medical applications: density functional theory investigation and a molecular dynamics simulation tuberculosis and the tubercle bacillus si-doped single-walled carbon nanotubes interacting with isoniazid-a density functional and molecular docking study effect of b/n co-doping on the stability and electronic structure of single-walled carbon nanotubes by firstprinciples theory a randomized trial in patients with gemcitabine refractory pancreatic cancer. final results of the conko study efficacy and safety profile of gemcitabine in nonsmall-cell lung cancer: a phase ii study activity of gemcitabine in patients with non-small cell lung cancer: a multicentre, extended phase ii study gemcitabine plus paclitaxel versus paclitaxel monotherapy in patients with metastatic breast cancer and prior anthracycline treatment fatal pulmonary toxicity resulting from treatment with gemcitabine severe acute lung injury induced by gemcitabine a density functional theory-based analysis of the structural, topological and electronic properties of gemcitabine drug adsorption on the pyrrolidine functionalized single-walled carbon nanotube flutamide-induced hepatotoxicity: report of a case series severe gynecomastia due to anti androgens intake: a case report and literature review mechanism of action and pure antiandrogenic properties of flutamide assessment of the adsorption mechanism of flutamide anticancer drug on the functionalized single-walled carbon nanotube surface as a drug delivery vehicle: an alternative theoretical approach based on dft and md assessment of solvent effects on the interaction of carmustine drug with the pristine and cooh-functionalized single-walled carbon nanotubes: a dft perspective metformin use and prostate cancer in caucasian men: results from a population-based case-control study metformin and pathologic complete responses to neoadjuvant chemotherapy in diabetic patients with breast cancer antidiabetic therapies affect risk of pancreatic cancer quantum chemical study on the adsorption of metformin drug on the surface of pristine, si-and al-doped ( , ) swcnts, phys. e low-dimensional syst calcium-doped single-wall nanotubes (ca/swcnts) as a superior carrier for atropine drug delivery: a quantum-chemical study in gas and solvent phases chapter -drugs involved in drug-facilitated crime-pharmacological aspects ketamine and ketamine metabolite pharmacology: insights into therapeutic mechanisms functionalized single-walled carbon nanotube for ketamine sensing: dft and md studies an overview of clinical pharmacology of ibuprofen intermolecular and low-frequency intramolecular raman scattering study of racemic ibuprofen adsorption of ibuprofen on silicon decorated fullerenes and single walled carbon nanotubes: a comparative dft study density functional investigation of co and no adsorption on tm-decorated c fullerene a dft study on the functionalization of c fullerene with , -benzoquinone dft, nbo and molecular docking studies of the adsorption of fluoxetine into and on the surface of simple and sulfur-doped carbon nanotubes computational modeling of functionalized multi-walled carbon nanotubes dispersed in polyethylenimine for electrochemical sensing of acetaminophen absorption behavior of small biomolecules on carbon nanotube by density functional theory pd-doped single-walled carbon nanotube as a nanobiosensor for histidine amino acid, a dft study a dft-d study on the interaction between lactic acid and single-wall carbon nanotubes topological organic chemistry. polyhedranes and prismanes geometrical and electronic properties of the clusters of c cage doped with alkali metal atoms first-principles study of no adsorption on c fullerene stabilization of the c cage by encapsulation of h + and he + ions solid c : a new form of carbon characterization of the soluble all-carbon molecules c and c fullerene formation in sputtering and electron beam evaporation processes extraction of c cluster ion beam synthesis of fullerenes and fullerenic nanostructures in a lowpressure benzene/oxygen diffusion flame arc discharge instalation for fullerene production covalent fullerene chemistry, science ( -. ) electron-phonon coupling and the electrical conductivity of fullerene nanotubules fullerene-styrene random copolymers. novel optical properties fullerene chemistry for materials science applications fullerene materials for lithium-ion battery applications bt -perspectives of fullerene nanotechnology endohedral fullerenes for organic photovoltaic devices electrocatalytic properties and sensor applications of fullerenes and carbon nanotubes synthesis of c /graphene composite as electrode in supercapacitors, fullerenes, nanotub. carbon nanostructures solubility of fullerene (c ) in a variety of solvents antibacterial activity of fullerene water suspensions: effects of preparation method and particle size synthesis of a fullerene derivative for the inhibition of hiv enzymes a tumoral acidic ph-responsive drug delivery system based on a novel photosensitizer (fullerene) for in vitro and in vivo chemo-photodynamic therapy electrochemical behavior of an antiviral drug acyclovir at fullerene-c -modified glassy carbon electrode study on the electronic structure of cr-and ni-doped fullerenes upon adsorption of adenine: a comprehensive dft calculation a density functional theory study on the interaction between -fluorouracil drug and c fullerene adsorption mechanism, structural and electronic properties: -phenylpyridine & undoped or doped (b or si) c theoretical study on the phenylpropanolamine drug interaction with the pristine, si and al doped [ ] fullerenes, phys. e low-dimensional syst phenylpropanolamine: a potentially hazardous drug adverse drug effects attributed to phenylpropanolamine: a review of case reports phenylpropanolamine-induced hypertensive seizures a dft study of penicillamine adsorption over pure and al-doped c fullerene penicillamine, a new oral therapy for wilson's disease penicillamine in severe rheumatoid arthritis utility of extrinsic [ ] fullerenes as work function type sensors for amphetamine drug detection: dft studies fluorescence polarization immunoassay detection of amphetamine, methamphetamine, and illicit amphetamine analogues ge doped c fullerenes amantadine: the journey from fighting flu to treating parkinson disease amantadine caused corneal edema conformational and electronic properties of hydroquinone adsorption on c fullerenes: doping atom, solvent and basis set effects fullerene c containing porphyrin-like metal center as drug delivery system for ibuprofen drug application of c b n heterofullerene in the isoniazid drug delivery: dft studies, phys. e low-dimensional syst theoretical insight of alpha amino acid phenylalanine adsorption on pristine and decorated fullerenes adsorption behavior of amphetamine on the inorganic bc nanotube and nanosheet: dft studies the electronic response of pristine, al and si doped bc n nanotubes to a cathinone molecule: computational study a dft study of adsorption of glycine onto the surface of bc n nanotube potential of graphene oxide as a drug delivery system for sumatriptan: a detailed density functional theory study multifunctional fluorescent pegylated fluorinated graphene for targeted drug delivery: an experiment and dft study density functional theory calculations and molecular dynamics simulations of the adsorption of ellipticine anticancer drug on graphene oxide surface in aqueous medium as well as under controlled ph conditions investigation on graphdiyne nanosheet in adsorption of sorafenib and regorafenib drugs: a dft approach flutamide drug interaction studies on graphdiyne nanotube -a first-principles study adsorption behavior of cytosine and guanine nucleobases on graphyne nanosheets: a dft study a dft study on the detection of isoniazid drug by pristine, si and al doped c fullerenes brain dysfunction in phenylketonuria: is phenylalanine toxicity the only possible cause? pathogenesis of cognitive dysfunction in phenylketonuria: review of hypotheses on the atomic weight of graphite verfahren zur darstellung der graphitsäure preparation of graphitic oxide biomedical applications of graphene and graphene oxide new horizons for diagnostics and therapeutic applications of graphene and graphene oxide chest symptoms after sumatriptan: a two-year clinical practice review in consecutive migraine patients fluorinated graphene as an anticancer nanocarrier: an experimental and dft study architecture of graphdiyne nanoscale films phase ii trial of sorafenib in advanced thyroid cancer sorafenib for the treatment of advanced renal cell carcinoma dermatologic symptoms associated with the multikinase inhibitor sorafenib meta-analysis of dermatological toxicities associated with sorafenib sorafenib in radioactive iodine-refractory well-differentiated metastatic thyroid cancer regorafenib (bay - ) in advanced colorectal cancer: a phase i study regorafenib as second-line therapy in hepatocellular carcinoma acute liver failure due to regorafenib may be caused by impaired liver blood flow: a case report interaction of imuran, pentasa and hyoscyamine drugs and solvent effects on graphdiyne nanotube as a drug delivery system -a dft study a novel graphite-like material of composition bc , and nitrogen-carbon graphites calculation of electronic and structural properties of bc , phys. rev utility of extrinsic [ ] fullerenes as work function type sensors for amphetamine drug detection: dft studies thermal and chemical stability of hexagonal boron nitride (h-bn) nanoplatelets, vacuum thermal transport in hexagonal boron nitride nanoribbons synthesis of monolayer hexagonal boron nitride on cu foil using chemical vapor deposition synthesis of large-area multilayer hexagonal boron nitride for high material performance large scale growth and characterization of atomic hexagonal boron nitride layers nanorice-like structure of carbon-doped hexagonal boron nitride as an efficient metal-free catalyst for oxygen electroreduction doped h-bn monolayer as efficient noble metal-free catalysts for co oxidation: the role of dopant and water in activity and catalytic de-poisoning synthesis and characterization of hexagonal boron nitride as a gate dielectric on the use of two dimensional hexagonal boron nitride as dielectric boron nitride (bn) and bn composites for high-temperature applications high operating temperature and low power consumption boron nitride nanosheets based broadband uv photodetector sandwich-structured pvdf-based composite incorporated with hybrid fe o @bn nanosheets for excellent dielectric properties and energy storage performance d hexagonal boron nitride ( d-hbn) explored for the electrochemical sensing of dopamine ultra-sensitive hall sensors based on graphene encapsulated in hexagonal boron nitride study the gas sensing properties of boron nitride nanosheets boron nitride nanosheets as a platform for fluorescence sensing biocompatibility of boron nitride nanosheets thymine adsorption on two-dimensional boron nitride structures: first-principles studies nucleobases-decorated boron nitride nanoribbons for electrochemical biosensing: a dispersioncorrected dft study a comparative dft study on the interaction of cathinone drug with bn nanotubes, nanocages, and nanosheets adsorption of mercaptopurine drug on the bn nanotube, nanosheet and nanocluster: a density functional theory study theory of graphitic boron nitride nanotubes mass-production of boron nitride double-wall nanotubes and nanococoons synthesis of boron nitride nanotubes at low temperatures using reactive ball milling nanotubes in boron nitride laser heated at high pressure cvd growth of boron nitride nanotubes rate theory of yield in boron nitride nanotubes synthesis and characterization of ropes made of bn multiwalled nanotubes isotope effect on the thermal conductivity of boron nitride nanotubes boron nitride nanotubes: pronounced resistance to oxidation stability and band gap constancy of boron nitride nanotubes young modulus, mechanical and electrical properties of isolated individual and bundled single-walled boron nitride nanotubes electrically insulating polymeric composites with boron nitride nanotubes as fillers eu-doped boron nitride nanotubes as a nanometer-sized visible-light source superhydrophobic and superoleophilic boron nitride nanotube-coated stainless steel meshes for oil and water separation polyethylene/boron nitride composites for space radiation shielding boron nitride nanotube based nanosensor for acetone adsorption: a dft simulation detection of phosgene by sc-doped bn nanotubes: a dft study boron nitride nanotubes are noncytotoxic and can be functionalized for interaction with proteins and cells boron nitride nanotubes: biocompatibility and potential spill-over in nanomedicine boron nitride nanotube-based biosensing of various bacterium/viruses: continuum modelling-based simulation approach boron nitride nanotube as a delivery system for platinum drugs: drug encapsulation and diffusion coefficient prediction practical issues in the management of hypersensitivity reactions a density functional theory outlook on the possible sensing ability of boron nitride nanotubes and their al-and si-doped derivatives for sulfonamide drugs boron nitride nanotubes for delivery of -fluorouracil as anticancer drug: a theoretical study the chemotherapy of brain tumors: clinical experience with severe diffuse interstitial pneumonitis induced by carmustine (bcnu), chest. myocardial ischemia associated with high-dose carmustine infusion theoretical study of encapsulation of floxuridine anticancer drug into bn quality of life and survival with continuous hepatic-artery floxuridine infusion for colorectal liver metastases toxicities and complications of implanted pump hepatic arterial and intravenous floxuridine infusion adjuvant perioperative hepatic arterial mitomycin c and floxuridine combined with surgical resection of metastatic colorectal cancer in the liver electrochemical behavior of acetaminophen and its detection on the pani-mwcnts composite modified electrode theoretical studies of the paracetamol and phenacetin adsorption on single-wall boron-nitride nanotubes: a dft and md investigation molecular dynamics simulation of paracetamol drug adsorption on boron nitride nanotube: effects of temperature adsorption of the nitrosamine and thionitrosamine molecules as carcinogen compounds on the bn and b al n nanotubes: a dft study nitrosamine and related food intake and gastric and oesophageal cancer risk: a systematic review of the epidemiological evidence a study on carcinogenesis of endogenous nitrite and nitrosamine, and prevention of cancer ab initio investigation of pristine and doped single-walled boron nitride nanotubes as acetone sensor structure and stability of c and b n isomers doping graphitic and carbon nanotube structures with boron and nitrogen, science ( -. ) octahedral boron nitride fullerenes formed by electron beam irradiation formation and structure of b n clusters boron nitride nanocages synthesized by a moderate thermochemical approach controlled fabrication of ultrathin-shell bn hollow spheres with excellent performance in hydrogen storage and wastewater treatment fullerene nanocage capacity for hydrogen storage b n nano-cage as potential sensor for no detection treatment of adult acute leukemia with arabinosylcytosine and thioguanine hepatic veno-occlusive disease caused j o u r n a l p r e -p r o o f by -thioguanine -thioguanine treatment of psoriasis: experience in patients theoretical investigation of thioguanine isomers anticancer drug adsorption treatment on b n nanocage ifosfamide-pharmacology, safety and therapeutic potential side effects of ifosfamide a comparative theoretical study on the interaction of pure and carbon atom substituted boron nitride fullerenes with ifosfamide drug a computational study on the cisplatin drug interaction with boron nitride nanocluster interaction of α-cyano- -hydroxycinnamic acid drug with inorganic bn nanocluster: a density functional study adsorption of celecoxib on b n fullerene: spectroscopic and dft/td-dft study celecoxib associated esophagitis: review of gastrointestinal side effects from cox- inhibitors cyclooxygenase- inhibition with celecoxib enhances antitumor efficacy and reduces diarrhea side effect of cpt- adsorption behavior of metformin drug on boron nitride fullerenes: thermodynamics and dft studies quantum chemical assessment of the adsorption behavior of fluorouracil as an anticancer drug on the b nanosheet borophene as an electronic sensor for metronidazole drug: a computational study healing of perineal crohn's disease with metronidazole is metronidazole carcinogenic? dna sequencing by borophene nanosheet via an electronic response: a theoretical study a computational study for the b bowl-like nanostructure as a possible candidate for drug delivery system for amantadine amantadine in the treatment of parkinson's disease amantadine as treatment for dyskinesias and motor fluctuations in parkinson's disease specific structural alteration of the influenza haemagglutinin by amantadine the computational study of the γ-fe o nanoparticle as carmustine drug delivery system: dft approach a theoretical investigation on the adsorption of platinol drug on a zno nanocluster: solvent and density j o u r n a l p r e -p r o o f functional effect aim and nbo study of isoniazid drug delivery by mgo nanocage the capability of the pristine and (sc, ti) doped be o nanocluster to detect and adsorb of mercaptopyridine molecule: a first principle study exploring the sensitivity of zno nanotubes to tyrosine nitration: adft approach interaction of isoniazid drug with the pristine and ni-doped of ( , ) armchair gannts: a first principle study a computational study on the purinethol drug adsorption on the aln nanocone and nanocluster benzoylethanamine drug interaction with the aln nanosheet, nanotube and nanocage: density functional theory studies electronic and work function-based sensors for acetylsalicylic acid based on the aln and bn nanoclusters: dft studies p) nanocages for drug-delivery systems? a dft study on the adsorption property of -aminopyridine drug gelatin-gold nanoparticles as an ideal candidate for curcumin drug delivery: experimental and dft studies the clinical pharmacology of -mercaptopurine adsorption of , -dimethoxy- -nitro- -methylanthracene- , -dione onto silver nanoparticles first tdae approach in quinonic series: synthesis of new -substituted , -dimethoxy- , -anthraquinones dft investigation of the interaction of gold nanoclusters with poly(amidoamine) pamam g dendrimer phosphorene as a template material for physisorption of dna/rna nucleobases and resembling of base pairs: a cluster dft study and comparisons with graphene we thankfully acknowledge the higher education quality enhancement program (heqep) subproject cp- , university grant commission (ugc) of bangladesh, and the world bank for the financial assistance to set up the computational physics (cp) research lab in the department of physics at jahangirnagar university. also, we would like to give our special gratitude to ahmad azuad yaseer and shawon mahmud for their valuable assistance with the graphical content creation. ☒ the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐the authors declare the following financial interests/personal relationships which may be considered as potential competing interests: j o u r n a l p r e -p r o o f graphical abstract:in this review article, we have analyzed the application of low-dimensional nanostructured materials in the biomedical applications like drug delivery systems and drug sensors development.j o u r n a l p r e -p r o o f key: cord- -nevbssd authors: boulakhbar, m.; lebrouhi, b.; kousksou, t.; smouh, s.; jamil, a.; maaroufi, m.; zazi, m. title: towards a large-scale integration of renewable energies in morocco date: - - journal: j energy storage doi: . /j.est. . sha: doc_id: cord_uid: nevbssd renewable energies are a sustainable, unlimited and decarbonised solution to address future energy challenges. in this context, morocco has a considerable advantage to position itself on this promising market. furthermore, renewable energies have been highlighted as a key strategic source for the country's green growth. morocco has adopted the renewable energy path through a strategy targeted on the development of solar, wind and hydroelectric power to boost its energy policy by adapting it to the challenges posed by today's world. nowadays, morocco is facing a challenge to reach % by of its total renewable energy capacity, which will exceed % by the end of . the main objective of this paper is to study a scenario for for the moroccan electricity system and to identify the challenges that need to be addressed in order to accelerate the integration of renewable energies in the moroccan energy mix and to achieve a possible export of such green energy towards europe. the challenge of responding to the world's climate change is a worldwide environmental problem that will impact all countries around the globe. environmentalists alert international society and businesses that natural resources will run out faster than anticipated [ ] . indeed, energy demand in developed and developing countries is rising dramatically. by , % and % increases in energy consumption is expected in europe and in the usa, it will be doubled in india and it's expected to triple in china [ ] . since then, the global world interests to increase the use of renewable energy sources and reduce the ghge as a key solution. the use of renewable energy sources (res) can contribute to the decarbonization of the power system and to ensure a sustainable energy supply throughout the world [ , ] . over the past century, the share of renewable energy in the energy mix of many developed countries has increased considerably and this trend is expected to continue in the future [ ] . many governments around the world have directed their transition policies to more sustainable and accessible energy systems [ ] [ ] [ ] [ ] . in morocco, electricity consumption demand increases at an annual average of %, since [ ] . the electrical power production industry in morocco is facing challenges involved with sustained growth of demand, added to environmental protection requirements, that's why energy security [ ] and mitigation of emissions and environmental pollution are identified as the main motivating forces for the transformation of the existing electricity power supply system to a sustainable form of electricity [ ] [ ] [ ] [ ] [ ] [ ] . at cop conference held in paris, morocco is promising an optimistic and binding deal. it is in this perspective that the moroccan government has launched a holistic plan to boost the percentage of renewable energy in the energy mix and substantially increase energy efficiency. goals have been established to increase the percentage of renewable energy electricity generation capacity ( % by and % by -see fig. ) and objectives to decrease energy consumption by % by and % by through energy efficiency enhancements [ ] [ ] [ ] [ ] . for comparison, the european commission has adopted a mandatory goal of achieving % of renewable energy by , with the possibility of revising this target upwards by [ ] . however, as electrical systems incorporate higher levels of re, the quality and reliability of the power supply becomes more challenging to manage [ ] . although there are many alternative options to facilitate the integration of re systems, they are costly and complex [ ] . in addition, to ensure these options, significant changes in the organization and functioning of electrical systems are required. many papers [ , , ] have explored morocco's renewable energy potential under various perspectives with a focus towards its national energy strategy development. however, in this present paper, the current situation of the moroccan energy strategy is assessed with an indepth analysis of the main renewable energy projects completed or under development in morocco. as well as it focuses on a general scope of the main actual trails and challenges facing the national energy strategy, with a clear and detailed roadmap of the key elements and guidelines to be followed by morocco in order to achieve its objectives in terms of renewable energy and energy efficiency by . in addition to its commitments in favour of the climate (ghge reduction of % by ), the kingdom of morocco faces many challenges in its energy transition. efforts are aimed at matching the supply and demand of primary energy, which is increasing by % per year, driven by the electricity demand, which is growing at a fairly steady annual rate of more than %, through the development of new electricity production capacities, which should bring the installed capacity to , mw in . security of supply also remains one of the major challenges of the moroccan energy model, which it is attempting to address through the diversification of its energy resources. morocco's primary energy demand and electricity demand will both be expected to double by . figs. and show the evolution of the primary energy demand and electricity consumption in morocco respectively [ ] . through , in accordance with the sdgs (sustainable development goals), the kingdom of morocco is making good strides towards sustainable, secure and modern electricity. however, the ultimate target is to build a more diversified power system with a significant contribution from renewable sources. in , morocco installed % of renewable energy (i.e. , mw), divided as follows: , mw, , mw and mw respectively originate from hydroelectricity, wind power and solar energy [ ] . currently, morocco's renewable electricity system is widely diversified and has a mix of solar, wind and hydroelectric power plants. table presents the total installed and planned capacity in and in , respectively [ ] . the kingdom of morocco is currently considered as one of the leading countries in the world's energy transition, especially in africa, with several programmes to generate electricity from renewable sources. morocco has taken advantage of its geographical position and environment to gain an edge in the field of renewables, especially solar energy [ ] . the average incident solar radiation varies between . and . kwh/m /day with a number of hours of sunshine that varies from hours/year in the north of morocco to more than hours/year in the south. initiated in , the moroccan solar plan is a very ambitious project. a number of solar power plants have been planned and scheduled to be installed as part of this project. the moroccan agency for solar energy (masen) was set up specifically to execute these projects. its mission is to implement all projects related to the national energy strategy and to co-ordinate and supervise all other activities connected with this initiative. table lists the major projects completed, in the process or planned in sites, with total investment estimated at approximately usd billion through to . we note that pv technology is featured in all projects due to a decrease in the price of photovoltaic modules of more than % over the last ten years [ ] . as part of the mediterranean solar plan, ouarzazate plant has benefited from european co-financing. the overall ouarzazate project includes four power plants: noor , noor , noor and noor with different technologies. noor has a capacity of mw based on parabolic mirror technology and noor is equipped with a solar tower of mw capacity. noor based on photovoltaic technology has an output of mw. with a capacity of mw, noor is currently one of the largest concentrated solar thermal (csp) parabolic cylinder power plants in the world. the solar power plant noor is mainly equipped with the advanced concentrating solar power (csp) generation, with parabolic trough collector (ptc) [ ] . by comparing this technology to solar energy tower, linear fresnel reflector and parabolic dish collector, the ptc with thermal oil and molten salt storage is considered to be the simplest and most mature system [ , ] prospective sites for csp plants are generally selected based on the global distribution of direct normal irradiance (dni) [ ] . commercially viable csp plants should maintain a dni of at least - kwh/m /yr [ , ] . the rankine cycle with molten salt storage is the operating principle of the noor plant (see fig. ) [ , ] . as shown in fig. , the noor plant consists of three parts, which are the solar field, the power block and the thermal storage system. these parts are properly outlined by kuravi et al. [ ] . the noor power plant's solar field consists of parabolic trough loops arranged in parallel and connected to each other. each loop consists of arrays of solar collectors in series and each array is composed of solar collector elements. the solar collectors composed of very reflective parabolic mirrors and heat collection elements (hce) installed in the center of the dish. a monitoring system allows the collectors to follow the sun from sunrise to sunset [ ] . once the direct solar irradiation is received on the solar field and reflected by the parabolic collectors to the absorber, where the heat is transferred to the heat transfer fluid (htf). a synthetic oil which is used as htf circulates through the collectors. at the output of the solar field, the htf is collected and then pumped to an expansion tank, which is connected to the power block unit to transfer its energy to water. the power block includes a steam generator, preheater, steam turbine, power generator, condenser, cooling systems (air condenser and cooling tower) and auxiliary equipment. the steam generator has two heat exchanger trains including economizers, evaporators, superheaters and preheaters. the htf flows through the two heat exchanger trains in order to produce steam at high temperature and pressure. the noor plant has been designed with two tanks of an eutectic molten salt composed of a mixture of sodium nitrate and potassium nitrate ( % nano + % kno ). this mixture has a high heat transfer coefficient and high thermal storage capacity. the function of the thermal storage system is to store excess sensible heat from the solar field (charge mode) during daily sunshine hours, in order to extend plant operation during night or when solar irradiation is insufficient (discharge mode). the htf flows in heat exchanger to charge/discharge the thermal storage system. the molten salt circulates from the cold storage tank through the heat exchanger and enters the hot salt storage tank, with temperature of approximately °c. the temperature of the cold molten salt is about °c. when the storage system is discharged, the molten salt from the hot storage tank is sent back to cold storage tank through the heat exchanger that is used to heat up the cold htf. the heated htf is then sent to the power block. the favourable geographical location of morocco provides it an important wind energy potential, estimated at about mw [ , ] . most of morocco's windiest regions are located in the extreme north on the strait of gibraltar side in the tangier-tetouan region, the essaouira region, the south atlantic area from tarfaya to lagouira and the taza corridor between the atlas and rif mountain ranges. the wind field is characterized by average wind speeds above m/s for the windiest regions [ ] . under its energy strategy, morocco has implemented an ambitious wind energy program to promote the deployment of renewable energies. this program intends to expand installed wind power capacity to , mw by the end of and to boost this capacity to , mw by . table shows the commissioned wind power plants and table lists the projects in development [ ] . one of the most important projects in wind energy program is the giant tarfaya wind farm (see fig. ), which is operational. it is the largest wind energy project on the african continent. the year has witnessed the injection of the total capacity of this park of mw. in addition to electricity production, the wind program also includes industrial integration of the wind energy sector, as well as the promotion of research and development and technical training in this field. in this sense, the program includes the manufacture of equipment for wind farms in the national industrial fabric to amplify and sustain its impact on the national economy in general and the development of wind energy in particular. in morocco's new energy strategy, % of the country's energy production will come from hydropower by . installed hydropower capacity will be increased from , mw in to , mw in through the construction of new hydropower dams and pumped energy transfer station (pets). morocco currently has , mw of hydropower generation capacity, of which mw is in pets mode [ ] . this production capacity is really achievable only when water reservoirs are at their maximum. this is not always the case, rather the opposite; morocco is a semi-arid country. in hydraulics, the other element that must be taken into account in morocco is irrigation. thus, turbining to produce electricity is, therefore, dependent to a certain extent on irrigation needs. however, throughout the world, the production of hydroelectric power is always lower than the level of existing installed capacity dictates. in , for example, hydropower production is in sharp decline, with only . twh compared to . twh in , a year with abundant rainfall in morocco. petss that are constructed or under development are expected to serve as a storage mechanism for solar and wind energy fig. shows the pets of mw at the abdelmoumen site in the agadir region which will increase the hydraulic capacity of morocco to mw by the end of . meanwhile, morocco plans to build about sixty large dams over the next twenty years; however, most of them should be dedicated to water resource management, and therefore not necessarily to power generation. table shows the current situation of the hydro projects [ ] , and table shows the future hydropower projects in morocco [ ] . in addition to solar, wind and hydraulic power, the process of diversification of energy resources in morocco also concerns biomass. currently, morocco has considerable biomass potential thanks to a forest area of more than , , ha, halfa areas of nearly , , ha, an agricultural area of nearly , , ha and a highly diversified livestock (cattle, sheep, goats, etc.) of around , , livestock units [ ] . despite its enormous resources in biomass, morocco currently has only less than % of its potential capacity because of its high initial expenditure and the lack of knowledge about energy production techniques and processes [ ] . nevertheless, its main potential has yet to be covered by national policies, although some small companies already are involved in this sector. in order to organise the use of biomass efficiently, the department of energy and mines in morocco has initiated a national strategy for the energy recovery of biomass. this initiative has been financed by the european union, as part of the support for the reform of the energy sector. this initiative was initially based on an evaluation of the business potential of biomass, with an analysis of the main material flows, coming from the sectors of agriculture, forestry, waste management and wastewater treatment, according to the indications of the department of energy. until now, two agricultural regions (northen and souss-massa) have been studied to evaluate their biomass energy potential. these two regions generate agricultural waste of the order of . million tonnes per year and , tonnes per year respectively. the recovery of this waste shows a potential of , mwh in the northern region, i.e. a saving of . million tons of oil. moreover, even if the potential exists, this does not mean that it is exploitable. the costs as well as the profitability have yet to be determined. in the souss-massa area, a few pilot projects, financed by donors, have already been tested. other projects are under development to promote the exploitation of biomass as an energy source, and the most important of them are: • program for disseminating biogas digesters in the souss-massa region; • development of new biofuels technologies. masen (moroccan agency for solar energy) has also started to explore options for initiating waste-to-energy projects. while, iresen (institute of research in solar energy and new energies) has commissioned in a prototype combining solar thermal collectors and biomass for electricity production [ ] . it is interesting to outline that large-scale biogas production is still at the stage of feasibility studies, particularly by private investors. the legislative framework remains insufficient since there is no obligation for biogas recovery. the major obstacles to the dissemination of biogas technologies in morocco are probably the non-availability of water and the insufficient technical monitoring of the installations and the inadequacy of incentives. based on the analysis of the results obtained in the first half of , we can recognize and appreciate the considerable progress accomplished in recent years by morocco, leading it to achieve the targets. however, to achieve the ambitious targets set for , the moroccan government needs to diversify financing models for renewable energy projects and stimulate private sector investment in re. in addition, it needs to capitalize on the high potential of biomass through concrete projects and immediate investments. in morocco, renewable energy policy has gained attention as an effective solution to recognize ecological problems and achieve sustainable growth and with high economic impact [ ] . fulfilling the targets for renewable electrical energy development in morocco by presents a new challenge regarding the integration of renewable energy sources. this must not involve any systems integration problems but opportunities abound the further increase power system flexibility, efficiency and remove constraints in the current power system operation. for a productive electricity transition focused on a broad renewable portion, a systemic approach is required, given the evolution trajectories of supply and demand, electricity infrastructure and the competition of various flexibility options to ensure the stability of the system (interconnections, active demand management, energy storage). a forward-looking study in electricity allows this increasing need for flexibility to be measured while recognizing other pathways for maximizing renewable energy adoption in morocco. energy transition in morocco is expected to have a significant impact on the national power grid stability, generating both a significant need for a network (to integrate a growing fraction of renewable production and benefit from the proliferation of intermittent production) and a decrease in its utilization rate (linked to self-consumption and decentralization of production). the transition to a high proportion of re in morocco will represent a complete redesign of the power grid, requiring a comprehensive reflection to optimize investments in transmission (or perhaps distribution) networks and production plants. congestion problems observed in systems where generation assets are located far from consumption areas (e.g. offshore wind farms in northern germany, solar and wind generation in northern and western china for industrial consumption centers in the east and south) demonstrate the importance of these challenges. the moroccan power system has an extensive and complicated network, comprising a dense transmission grid with , km of kv lines, about , km of kv lines, km of kv lines and about , km of kv lines [ ] . the network was created fifty years ago and is a combination of old and new technological elements. the majority of the network's system is outdated and subject to aging due to the effects of stress, such as extreme temperatures, vibrations, water infiltration and damage due to civil engineering works [ , ] . several initiatives have been implemented by the national agency for electricity and water (onee) to reinforce the electricity grid. table summarizes the grid expansion planned between and [ ] . however, these initiatives are unfortunately insufficient to meet morocco's objectives. there is an urgent need to modernize and improve the moroccan grid infrastructure to ensure a wide penetration of wind in the energy mix [ ] . most wind farms are either remote from the power grid or table planned grid reinforcement added between and . have poor electrical infrastructure that limits their level of penetration into the power grid. today, the large amounts of electricity from renewable sources and solidarity between territories are the main vectors for the evolution of the power grid and new challenges for transmission system operators. some regions will essentially be importing and others will be strongly exporting. the mesh and density of the electricity network will be a key point in guaranteeing access to electricity and security of supply from renewable energy sources. the integration of renewable energies in the moroccan electricity system also requires the mobilization of flexible modes of production to address their intermittency and improve the stability of the power grid. today, the introduction of combined cycle power plants operating on natural gas is positioned in morocco as one of the most appropriate means to meet the challenges of intermittent power generated by renewable energies. gas is expected to play a major role in the electricity mix and according to [ ] in the gas demand in the mena countries grew faster than in other regions., since morocco plans to import billion cubic meters (bcm) of lng via a new lng import terminal, which will provide , mw of new combined cycle gas turbines (ccgts).morocco's needs for flexibility will increase and will mainly be provided via decentralized tools (energy storage, erasure, consumption modulation, electric vehicles batteries, decentralized production) requiring the aggregation of a large number of diffuse points; distribution network operators will become real operators, responsible for active network management and the organization of local flexibility markets. the exploitation and optimization of the sources of flexibility (question of global optimization / local optimization) will become an essential issue in morocco. the principal challenge for electricity distribution in morocco is associated to environmental and climatic conditions caused by long land distances, vast forests, severe winter seasons and high number of overhead lines [ ] . these problems require advanced automatic solutions for fast defect management and long term grid forecasting. accordingly, in the onee installed a new more modern and efficient national distribution control centre called "dispatching". the new system, which has been installed in casablanca city, manages in real time and under different conditions, between the change in electricity production facilities and a steadily rising of the national demand. despite the dispatching system, there are still production losses based on future energy forecasts and emergency needs. another important problem is that most of the electrical energy produced in the grid cannot be stored. therefore, the smart grid is essential to correlate electricity generation with demand [ ] . the development of smart grids is an essential prerequisite for moving from a unidirectional to a bidirectional system, making it possible to act on demand and to adapt consumption in part to instantaneous production capacities. smart grids are designed to improve control of the electrical system throughout the entire chain of value from the producer to the end consumer. by making a portion of consumption (industrial and domestic) dependent on available production, they make it possible to reduce demand peaks and thus reduce maximum production capacities in a given geographical area. similarly, it is perfectly possible to program certain equipment (e.g. electric vehicles) to receive energy when there is a given overproduction. the smart grid can reduce transmission and distribution losses by monitoring the capacity to distribute electrical energy efficiently through communication technologies. digitalisation of network will in some ways be a condition for the success of the energy transition [ ] . the deployment of renewable energies is challenging the way in which the supply-demand balance has been achieved in the electricity sector until now. flexibility and security of the energy system must rely on the operating capability to allow both generation and usage dispersal and distortion between service quality and continuity [ ] . that's why the smart grid remains an essential element to develop in order to meet the ambitious target of . one of the most practical ways to reduce the intermittency of renewable energy is to interconnect them in order to mitigate the variations in electricity generated from such intermittent sources. for that purpose, morocco needs to reinforce electricity interconnection infrastructures at the regional level and with the european continent (see fig. ). electricity importations represent the main source of flexibility in morocco since they play an important role in balancing supply and demand [ ] . by exporting green electricity to europe, considering its proximity to spain, morocco has the potential to become an important actor in the export of renewable electricity to a large regional market. in this regard, several eu countries have interestingly implemented a "roadmap for sustainable electricity trade" (set roadmap) and signed an official declaration during the cop with morocco. in this perspective, morocco has already achieved significant electricity interconnection capacities with spain ( , mw). currently, the interconnection with spain is the unique link between europe and north africa. morocco is also interconnected with algeria, with an exchange capacity of , mw. the african market is very promising since it is relatively poorly electrified and represents real investment opportunities for future years. currently, morocco continues the process of regional integration of energy markets. firstly, the country has a project to establish an electrical interconnection line to portugal with a capacity of , mw. morocco is also planning to expand the interconnection with spain by a third line with a capacity of mw. discussions are under way to establish new interconnection lines with mauritania. thanks to the electricity interconnections with algeria and spain, morocco is positioned as a leading electricity market player in the western mediterranean region and fully plays an important role both as a regional energy hub and as a transit country for cross-border electricity exchanges. an ambitious project (xlinks) is under consideration to develop a new gw submarine cable linking morocco to the uk, which will allow green electricity to be sent directly to the uk without using existing infrastructure in spain and france [ ] . the project will generate % of the uk's electricity demand. given the important role of interconnections in improving reserves capacity, the development of electricity generation from renewable sources and the increase of re integration capacity from new interconnection projects are under consideration. in line with the objective, morocco is expected to significantly boost investment in electricity trading and interconnections and to play an important role in the development of the regional electricity market in west africa and its integration into the european market. onee is currently the major player in morocco's electricity market; it is the sole purchaser and responsible for power imports and exports and the purchase of electricity generated by independent power producers (ipps), surplus electricity from self-generators and all renewable electricity production from masen projects. [ ] . onee holds longterm power purchase agreements (ppas) with these entities. onee also owns generation plants, including coal, gas and wind (which will be transferred to masen by ). onee's own generation market share has decreased, with the growth of renewable energy projects developed by masen [ ] . otherwise, under law - , onee has to transfer all renewable energy generation assets within five years to masen (with the exception of pump storage hydro plants, plants that are critical for the national electricity supply security and plants under . in terms of market shares in , onee supplied power to the national market from its own plants ( . %), and through ipps ( . %) and imports ( . %), with power from private industrial producers accounting for the remainder ( . %) [ ] . the structure of the electricity industry is detailed in the fig. . two observations can be drawn from the analysis of fig. : • the national agency for electricity regulation, which was created in , has not yet initiated its principal missions to ensure effective operation of the electricity market and to control the transmission and distribution operators. there is an urgent need to allocate financial and human resources to this agency to ensure its function in the moroccan electricity market. • the reorganisation of the onee and its business model by separating the activities of the electricity value chain (i.e. generation, transmission, distribution and marketing) is required to ensure a more effective operation of the moroccan electricity market. one of the main drawbacks of using renewable energy sources is the management of their intermittent production. thus, even if morocco holds the world record, especially in wind energy, the load factor, i.e. what the installation actually produces in relation to its capacity, is % for wind energy projects and falls at best to % for photovoltaic projects. for the latter, it is therefore necessary to use electricity storage [ ] . energy storage can render several services to power grids [ ] : • it can be used to address erratic and rapid variations in energy demand and prevent the possible requirement for frequency adjustment from the main power system. it can also resolve temporary power interruptions, minimize harmonic distortions, and prevent voltage drops and bursts. • it avoids a partially loaded main power system, which is held operational to meet unplanned, unexpected demands and electrical urgencies resulting from the breakdown of generation plants and/or transmission lines. • it helps to handle the peaks of the daily demand curve. • it allows excess electricity generated during off-peak hours to be stored to meet increased demand during peak hours. • it ensures the storage of electricity produced by renewable energies in order to adapt fluctuating supply to shifting demand. the first large-scale electricity storage project in morocco is the mw afourer pumped storage power station (pets), commissioned in . it consists of a hydraulic system composed of two . million-m water reservoirs connected by a pipeline with two hydroelectric production units between the basins. the abdelmoumen wwtp located in taroudant province will enhance hydraulic storage capacity in morocco. this station, piloted by the onee, has been under construction since july after the project was awarded to the consortium led by the french company vinci construction and including the company andritz hydro. the € million contract consists of the construction of a wwtp (waste water treatment plan) with two basins connected by a km transfer line with a mw reversible hydropower plant located in the middle. it is interesting to mention that the noor power plant is equipped with a hours thermal storage system. for noor and plants, the thermal storage time is up to hours. this will guarantee continuity of energy distribution, even in the evening, at times of peak consumption [ ] . csp thermal storage was also chosen to ensure hours of autonomy for the first phase of the mw noor midelt station in hybrid technology: csp and pv. a nd phase, currently being prequalified by masen, is competing between different solar technologies with storage, in particular pv and csp associated with different thermal storage or battery technologies, with the aim of ensuring a stable power injected into the grid up to mw. energy storage technologies (est) can be classified in to [ ] : • mechanical storage systems [ ] like pumped hydro-storage (phs), compressed air energy storage (caes) and flywheel energy storage (fes) technologies. • electrochemical storage systems [ ] like batteries (lead acid, nicd/nimh, li-ion, metal air, sodium sulphur and sodium nickel chloride) and flow batteries (redox flow battery (rfb) and hybrid flow battery (hfb)). • electrical storage systems [ ] like supercapacitors (sc) and superconducting magnet energy storage (smes) systems. • chemical energy storage [ ] , which emphasizes hydrogen (h ) and synthetic natural gas (sng) as secondary energy, vectors, as they could have a considerable impact on the storage of large quantities • thermal storage systems (tss) [ ] , which includes sensible, latent and thermochemical storage technologies. thermal sensible storage is the most mature technology but has the lowest energy density, which is followed by the latent storage and then by thermochemical storage. thermal storage can provide important services to moroccan power system and increase the flexibility of the network. many thermal storage options can be developed in morocco such as the storage of excess renewable electrical energy in buildings (e.g. domestic hot water tank). the development of district heating networks in morocco can also give a growing role to the massive thermal storage in morocco [ ] . the principle of the above technologies has been presented in detail in various articles [ , ] . power density and energy density are two main characteristics of energy storages technologies [ ] . the higher the power and energy density, the lower the required volume for the storage system. so, est can be classified according to discharge time [ , , ] : • short discharge time (seconds to minutes): smes and fes. the energy-to-power ratio is less than one. • medium discharge time (minutes to hours): fes and for large capacities, electrochemical storage systems, which is the dominant technology: lead acid, li-ion and sodium sulphur batteries. • long discharge time (days to months): h and sng. for these est, the energy-to-power ratio is greater than . the main advantage of h and sng is the high energy density, superior to all other storage systems. phs, caes flow batteries systems are situated between storage systems for medium and long discharge times [ , ] . like h and sng systems, these est have external storage tanks. however, the energy densities are rather low, which limits the energy-to-power ratio to values between approximately and . among all existing technologies, whether commercially available or under development, there is no technology that can achieve both power and energy density at the same time. in this context, the hybridization of high-energy systems in combination with high power systems appears to be more efficient est [ ] . high power storage systems produce energy at very high rates, but typically for short time periods. conversely, high-energy storage systems can generate energy for longer periods [ , ] . to ensure its place in an electrical system, the hybrid energy storage system must not only demonstrate its technical relevance but also prove its economic viability. the most appropriate energy storage technology for a given storage situation should be chosen according to needs, available space and financial resource. actually, no legislative or regulatory framework exclusively dedicated to the regulation of energy storage exists in morocco. however, the electricity storage legislation is expected to change in order to address the evolutions and challenges presented by the recent dynamic of energy transition in morocco. to ensure a sustainable energy strategy in morocco, the implementation of energy storage solutions adapted to the moroccan context is essential. as well as developing mature solutions such as petss and csp storage [ ] , it is time to achieve benchmarks with new technologies such as lithium batteries and storage via hydrogen [ ] as part of the ambitious power-to-x techniques in the r&d phase. the promulgation of a legislation to regulate energy storage is necessary to initiate the development of new large-scale storage projects. in addition, it is recommended to integrate tax incentives to encourage entrepreneurship in the field of energy storage with a view to opening, through smart grids, the national electricity grid to the surplus injections of industrial and private owners. "power-to-x" is a way of storing electrical energy for greater flexibility. the excess of the available energy can be stored in other forms: chemical or industrial products, etc. the first step of the ptx pathway consists in using low-carbon electricity and water to produce hydrogen by means of water electrolysis: the power-to-hydrogen (pth) segment. hydrogen can be used immediately (e.g. as a fuel for mobility or as feedstock in industry), or used in further synthesis steps with carbon, nitrogen or oxygen to produce chemical compounds such as methane, ammonia or gasoline that replace fossil fuels [ ] . fig. shows the power to x applications [ ] . with its geographical position and outstanding wind and solar capacity, moroccan government is able to achieve a valuable share of the 'power-to-x' market expected to be between % and % of global production in [ ] . otherwise, economic assessment of hydrogen production potential from solar energy in morocco is detailed in [ ] . according to a study carried out by the world energy council germany, morocco is among the countries with a high potential in terms of power to x. power to x requires an energy mix that allows plants to run for as long as possible during the hours. solar energy can cover about % of the need. if we add the contribution of wind power, we can reach %. this means that up to - % can even be achieved if storage is used. the other goal is to reach a balance between the cost of hydrogen or fossil-fuel ammonia production and the cost of the photovoltaic and wind energy output of these technologies. in this sense, "green ammonia" will provide morocco with opportunities to fulfil the long-term demands of its local fertilizer industry and foreign market [ ] . morocco will therefore draw up a roadmap for hydrogen and ptx products, a roadmap for hydrogen technology and related ptx products for morocco, and establish sustainability requirements as part of the hydrogen / ptx roadmap. otherwise, several exporting industries are facing a critical situation due to the implication of the carbon tax on the products exported by most european countries. for this reason, the moroccan industry must promptly respond to the new requirements and constraints of the european market in which the power to x represents one of the best potential solutions to promote the national economy. freshwater is a crucial factor in regional economic development. domestic users, agriculture and industry require large quantities of freshwater. meeting current and future demands for freshwater has become a serious challenge in many countries of the world [ , ] . however, seawater and sometimes brackish water desalination constitute an important option as a very safe water source comparatively to conventional water supply. nevertheless, the world desalination market has experienced rapid expansion since the beginning of the s, with growth in contracted capacity increasing by an average of . % per year [ ] . fig. shows the evolution of water desalination market between and [ ] . the current technologies of water desalination are classified into two categories, according to the principle applied [ , ] : • thermal processes involving a change of phases: freezing and distillation. • processes using membranes: reverse osmosis and electro dialysis. among the above methods, distillation and reverse osmosis are technologies with proven efficiency in desalining seawater. indeed, these two processes are the most commercialized in the world desalination market. the other techniques have not experienced a significant development in the field due to problems generally related to energy consumption and/or the size of the investments they require. fig. shows awarded membrane and thermal desalination capacity between and [ ] . regardless of the salt-water separation process envisaged, all desalination plants consist of four stages: • seawater intake with a pump and coarse filtration, • pretreatment with finer filtration, addition of biocidal compounds and anti-pattern products, • the desalination process itself, • post-treatment with possible remineralization of produced water. at the end of these four stages, the sea water is made potable or industrially usable; it must then contain less than . g of salts per liter [ ] . however, energy consumption accounts for about % of the total costs of a reverse osmosis desalination plant [ ] . table represents a comparative study of the energy consumption of the different desalination technologies [ ] . otherwise, to minimize energy consumption, more studies have been conducted [ , ] . several studies indicate that the combination of desalination technologies and renewable sources is among the most promising approaches for the development of the sector [ ] . during the drought periods in the last three decades, morocco is facing a real issue in water supply, due to the water demand increasing and because of the climate changes [ , ] . the first desalination plants in morocco were installed in to address the shortage of potable water in the southern regions, and all subsequent schemes contribute to water supplies in southern moroccan areas that shortage fresh water and have insufficient brackish water availability [ ] . agadir's seawater desalination plant is the africa's largest desalination station with a capacity of , m per day, expandable to , m a day. in addition, to reduce production costs, the station will be coupled to a wind power plant. table shows more details about water desalination plants in morocco [ ] . since desalination is such an energy-intensive operation, its economic feasibility is directly affected by the resources needed to generate fresh water [ ] . that's why the interest in renewable energy -driven desalination systems have been growing very rapidly, the number of developed plants is still limited, and the applications are primarily in early stages of development [ ] . with a huge capacity of renewable energy sources and with the and goals, the use of the energy surplus coming from renewable sources or the alimentation of the desalination plants by renewable energy sources represent one of the most pioneer's solution to reduce the production cost in the desalination plants. moreover, more studies had been contacted by many research shows how morocco could use its high potential of renewable energy sources coupled with the desalination plants [ , ] . in morocco, the seawater desalination market seems promised to continue to grow in the coming years. however, the current technologies can only meet certain targeted needs concentrated in a few regions. the high costs of these plants limit their dissemination throughout the country, which suffers from fresh water shortages for economic reasons and whose hydraulic infrastructures are generally deficient. the energy consumption of desalination plants coupled with environmental uncertainties implies imperative technological evolutions in order to support the development of this sector. cooperation between project developers and energy specialists makes it possible to envisage the large-scale development of photovoltaic and wind-powered structures. in the absence of an efficient distribution network and sufficient financing capacities, decentralized desalination systems are more relevant than large-capacity plants to fulfil morocco's demands. moreover, small-scale infrastructure would make it possible to reduce the amount of investment required and reach isolated populations fig. . awarded membrane and thermal desalination capacity, - [ ] . while reducing the energy consumption of the devices by exploiting the great potential of renewable energy in morocco. with over million vehicles, transport sector is the pillar of moroccan economy accounts for % of gdp and employs % of the urban active population. morocco has a road network of about , km of roads, , km of expressways and , km of motorways [ ] . however, transport is the second polluting sector in morocco and a major source of gas emissions; it is responsible for % of total emissions of the kingdom. the major problem is that the transport sector absorbs % of national energy consumption including % of petroleum products [ ] . for these reasons and because of the transport remains an essential link in the development of the country's economy, the interest in electric vehicles has increased in recent years in morocco. many automobile manufacturers have installed in the kingdom at this point developed and commercialized their first modern electric models, proving that the electric drive is technically viable, environmentally friendly and affordable and it's a better solution in order to improve moroccan economy. as well as the renewal of the state's vehicle fleet with electric and hybrid vehicles are one of the first measures that the government intends to put in place as part of the kingdom's sustainable development strategy. clean cars should make up % of the fleet by [ ] . meanwhile, the deployment of a strong charging infrastructure is the backbone of the electric vehicle adoption. through iresen, morocco has started some initiatives to encourage the development of electric mobility. the example is the green miles project that focuses on the installation of charging points to cover more than km highway. furthermore, the implementation of charging units coupled to photovoltaic panels in rabat city [ ]. fig. and fig. represent respectively the evolution of charging pools number in morocco between the last trimester of and the second trimester of and the distribution of plugs by charging speed [ ] . transport always goes with energy, and the major question is where the energy needed comes from? otherwise, given the impact of transport on the consumption of fossil fuels and greenhouse gas emissions, the implementation of a policy allowing the development of electro mobility in morocco represented an important fraction of the renewable energy objectives. in this context a socio-economic study of electric vehicles in morocco was conducted by [ ] , it shows the reasons influencing the moroccan choices of transportation modes, in particular, those taken according to electric vehicles technologies. it also explores potential options for incorporating this green transport style into the moroccan context, while respecting their preferences and limitations. in several studies, rechargeable electric vehicles are used in combination with renewable energies at different levels of the electrical system [ ] [ ] [ ] . the integration rate of electric vehicles in was estimated at . % [ ] . a literature review and prospects for sustainability about adoption of electric vehicles are detailed in [ ] . otherwise, [ ] describes the challenges and assessment of electric vehicles integration, with a comprehensive analysis of political, economic, social, technical, legislative and environmental aspects and rigorously assesses achievability of the ev integration. thus, electric mobility contributes to the independence of imported fossil energies, constitutes a lever for the integration of re in the energy mix because partial electrification of transport encourages the installation of (decentralized) renewable energy production units, storage (v g: vehicle to grid) and the valorization of surpluses for the production of hydrogen [ , ] . based on an in-deep analysis of the current electric mobility situation and on data collected from electric mobility actors in morocco, barriers of electric vehicles adoption are categorized on three major elements. table presents the matrix of these barriers. morocco expects a real growth in electric-vehicle sales in coming years. however, the market is currently in a period of transition, as companies and cities scale up to meet the demands. the demand for electric vehicles comes with a few factors that require collaboration between cities and car owners. research agencies, vehicles manufacturers and operating entities are encouraged to maximize electric vehicles adoption based on local conditions, and to develop responsibilities for implementation. fig. shows the four key elements for a successful transformation for ev adoption acceleration in morocco. a voluntarist policy of the government, through concrete actions and subsidies aimed to encourage consumers to buy green vehicles at competitive prices, are the main acts allowing the development of electric mobility in morocco. finally, it is necessary to ensure the compatibility of charging, communication, and billing and payment systems and to adapt them to the moroccan context. according to the national energy strategy adopted at the end of , energy efficiency is considered a key element of economic and social progress [ ] . in this context, a number of measures to save energy and control energy consumption in various sectors (industry, buildings, agriculture, public lighting and transport) have been adopted in morocco. to support energy efficiency programmes, law - on energy efficiency was published in [ ] . it focuses on energy audits, energy impact studies, energy performance in several sectors, rationalisation of the energy used by public establishments and local authorities, the creation of the status of energy service companies and the introduction of technical controls for audits by accredited companies. the new thermal building regulation, which defines energy performance rules in buildings, was drafted in . in , the energy audit of industries is mandated. the goals for energy efficiency, which have been adjusted from ′s initial ambition, are now % by (compared to % initially) and % by [ , ] . this delay in implementing the energy efficiency objectives is due to the positioning of the amee (moroccan agency for energy efficiency), its organisation and the lack of human and financial resources needed to carry out this important project. current analysis of morocco's energy sector reveals that there is significant potential for additional energy savings in the country [ ] . we consider that the success of the energy transition policy in morocco can only be achieved through local authorities (region, municipalities and communes), which are in the first line to apply and adapt the national objectives in terms of energy efficiency to the local context. local and regional authorities should be committed to a process of achieving a balance between energy consumption and production at local level by reducing energy needs as far as possible and respecting the national energy system's equilibrium. in their policies, they must promote energy efficiency, the reduction of greenhouse gas emissions, the reduction of fossil fuel consumption and the deployment of renewable energies. different instruments can be implemented locally in each region to achieve the energy efficiency targets and accelerate the transition to a more energy-efficient society: • assess the potential of energy savings, renewable energy and heat recovery in each region [ ] . waste heat recovery can lead to two complementary heat valorisation processes [ ] : ■ internal valorization, to meet the heat needs in the company; ■ external valorization, to meet the heat needs of other companies or, more generally, of a region, via a district heating network. in addition to thermal recovery, the heat can also be transformed into electricity, for internal or external use. • reducing energy consumption: in particular, by improving the thermal isolation of public buildings, switching off public lighting after a certain period, promoting car sharing as well as clean and collective transport, mutualising facilities, encouraging local product, etc. • development of renewable energies: for example, through a regional programme for the installation of photovoltaic panels on public ■ establishment of a national energy efficiency fund. ■ implement norms and financial mechanisms to support energy efficiency policies. ■ reinforcing the expertise, the human and the financial resources of the amee. ■ creation of an amee office at the level of each region. the covid sanitary crisis that recently affected the entire world has clearly revealed the necessity to develop locally an economic, energy and social policy in relation to the specificities of each region. ■ a legislative framework to regulate and control the conformity in terms of quality and safety must govern renewable energy equipments introduced in the national market. ■ national competence and expertise must also be created to develop testing laboratories to facilitate the study and certification of energy equipments and regional construction materials. morocco has outstanding re prospects, including solar, wind and biomass technologies. such technologies have different needs in terms of support for research and development, demonstration and market development [ ] . moreover, innovation remains an important link for a wide integration of these technologies [ ] . the energy research, development and innovation policies remain mandatory to enhance the morocco's ambitious energy policy priorities, boosting the use of renewable energy technology, and helping to develop a local manufacturing industry. masen and iresen are responsible for implementing r&d projects and identify strategic topics to guide the r&d and create a real and concrete research map. iresen is a network of applied research platforms at the service of researchers and innovation actors. based on the implementation of current projects, iresen will have to assess the progress, priorities and organization of r&d governance in order to ensure the success of morocco's energy transition for . continued support is needed for universities and educational centres to ensure that students, scientists and operators are informed and trained in re technologies. to this end, it is recommended that research, education and training in re be included in the legislative framework and educational policies. in addition, it becomes necessary to strengthen the coordination of energy technologies and r&d between different agencies, universities and government in order to avoid duplication of activities and to develop stronger synergies between industry and universities. morocco has made the transition to renewable energy a high priority since the national energy strategy. after , the moroccan government has set an ambitious long-term target for renewable energy by reaching % of total installed capacity by , by taking advantage of the country's high potential conditions for wind and solar power in addition to the contributions of hydropower, thus demonstrating a clear long-term commitment. however, morocco must implement several measures and strategies in order to achieve the ambitious target of . among these measures: the modernization of the electricity network with the introduction of intelligent metering and analysis systems, the development of regional and international interconnections and the promotion of energy storage. otherwise, the kingdom must complete the regulatory framework for open and transparent access to low-voltage grid, including through harmonized permitting, and tariff structures. it is urgent for policymakers to explore possibilities for developing the "power to x" concept in industry and the feasibility of exporting it into europe. moreover, it is necessary to promote electric mobility start-ups including operators from all fields: very light, light and heavy rolling stock, infrastructures, business models for sharing and recharging, batteries and their recycling. it is also essential to promote local research to adapt international experience to local needs in terms of recharging systems and use; stimulate local production of electrical vehicles components. meanwhile, research and innovation, in relation to all res applications must be encouraged, strengthen the coordination of energy r&d programs across government, universities and agencies, and boost the kingdom energy innovation ecosystem by developing synergies between business and universities. the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. real options analysis for renewable energy technologies in a ghg emissions trading environment management and control of smart grid systems: opportunities and challenges in morocco renewable energy resources: current status, future prospects and their enabling technology renewable energy and biodiversity: implications for transitioning to a green economy towards % renewable energy systems: uncapping power system flexibility flexible electricity generation, grid exchange and storage for the transition to a % renewable energy system in europe energy transition to a future low-carbon energy society in japan's liberalizing electricity market: precedents, policies and factors of successful transition transition to renewable energy and sustainable energy development in azerbaijan energy policy in the context of sustainable development: case of morocco and algeria promotion of renewable energy in morocco evaluating the energy security of electricity interdependence: perspectives from morocco a review and assessment of energy policy in the middle east and north africa region renewable energy potential and national policy directions for sustainable development in morocco morocco's strategy for energy security and low-carbon growth the renewable energy plan in morocco, a divisia index approach evaluating the energy security of electricity interdependence: perspectives from morocco morocco's strategy for energy security and low-carbon growth energy needs for morocco , as obtained from gdpenergy and gdp-energy intensity correlations yearly performance of low-enthalpy parabolic trough collectors in mena region according to different sun-tracking strategies technical feasibility of a sustainable concentrated solar power in morocco through an energy analysis kingdom of the sun: a critical, multiscalar analysis of morocco's solar energy strategy hybrid renewable energy systems for renewable integration in microgrids: influence of sizing on performance deploying storage assets to facilitate variable renewable energy integration: the impacts of grid flexibility, renewable penetration, and market structure renewable energy in emergent countries: lessons from energy transition in morocco moroccan energy outlook : achievements and opportunities analysis of renewable energy integration into the transmission network feuille de route pour un maroc % énergie renouvelable a geographical information system-based multi-criteria method for the evaluation of solar farms locations: a case study in souss-massa area, southern morocco irena: pv prices have declined % since -pv magazine international a comprehensive review of state-ofthe-art concentrating solar power (csp) technologies: current status and research trends policies to keep and expand the option of concentrating solar power for dispatchable renewable electricity economic justification of concentrating solar power in high renewable energy penetrated power systems global potential of concentrating solar power the potential of concentrating solar power (csp) for electricity generation in libya water consumption analysis of moroccan concentrating solar power station parabolic trough solar thermal power plant noor i in morocco thermal energy storage technologies and systems for concentrating solar power plants evaluation of wind energy potential in morocco's coastal regions nareva holding réalise le plus grand parc éolien en afrique | www.le . ma maroc : le parc éolien de khalladi exploité par besta entre en service près de tanger | afrik morocco to build € mln hydroelectric plant near agadir | the north africa post energetic recovery of biomass in the region of rabat office national de l'electricité, électrification rurale (onee) a simulation of the economic impact of renewable energy development in morocco a review on renewable energy and electricity requirement forecasting models for smart grid and buildings morocco's sustainable energy transition and the role of financing costs: a participatory electricity system modeling approach energy demand and environmental impact of various construction scenarios of an office building in morocco development prospect of smart grid in morocco weaknesses and drivers for power-to-x diffusion in europe. insights from technological innovation system analysis xlinks - / solar energy from the sahara to the uk energy storage technologies and real life applications -a state of the art review État des lieux et perspectives a review of multi-criteria decision making approaches for evaluating energy storage systems for grid applications a review of energy storage types, applications and recent developments hybrid energy storage system for microgrids applications: a review hydrogen energy, economy and storage: review and recommendation a review and evaluation of thermal insulation materials and methods for thermal energy storage systems a literature review of energy flexibility in district heating with a survey of the stakeholders' participation energy storage: applications and challenges review of energy storage system for wind power integration support emergence of hybrid energy storage systems in renewable energy and transport applications -a review review of system topologies for hybrid electrical energy storage systems technoeconomic assessment of thermal energy storage solutions for a mwe csp-orc power plant the role of electricity storage and hydrogen technologies in enabling global low-carbon energy transitions linking the power and transport sectors -part : the principle of sector coupling le maroc se met à la technologie «power-to-x» a technical and economical assessment of hydrogen production potential from solar energy in morocco renewable energydriven desalination technologies: a comprehensive review on challenges and potential applications of integrated systems future needs for desalination in south mediterranean countries global desalination capacity growing substantially, finds study | water tech online home -global water intelligence emerging desalination technologies for water treatment: a critical review fouling mitigation in forward osmosis and membrane distillation for desalination economic analysis of wind-powered desalination in the south of morocco an analysis of the overall adoption of rpa | sia partners evaluation and minimisation of energy consumption in a medium-scale reverse osmosis brackish water desalination plant water desalination by pervaporation -comparison of energy consumption desalination experience in morocco perspective of renewable desalination by using membrane distillation hybrid concentrated solar thermal power systems: a review hybrid concentrated solar thermal power systems: a review design analysis of mvc desalination unit powered by a grid connected photovoltaic system ministry of equipment, transport, logistics moroccan climate change policy charging stations' statistics in socio-economic analysis of electric vehicles in morocco application of microgrids in addressing distribution network net-load ramping co-benefits of large scale plug-in hybrid electric vehicle and solar pv deployment a comprehensive study of economic unit m. boulakhbar commitment of power systems integrating various renewable generations and plug-in electric vehicles adoption of electric vehicle: a literature review and prospects for sustainability review of challenges and assessment of electric vehicles integration policy goals: integrated risk analysis approach environmental effects of electromobility in a sustainable urban public transport the ultimate smart mobility combination for sustainable transport? a case study on shared electric automated mobility initiatives in the netherlands loi n° - relative à l'efficacité énergétique promulguée par le dahir n° - - du er kaada efficacité énergétique methods to estimate the industrial waste heat potential of regions -a categorization and literature review external use of industrial waste heat -an analysis of existing implementations in austria innovations for sustainable development: moving toward a sustainable future sustainability-oriented service innovation: an emerging research field the authors acknowledge funding provided by the research institute for solar energy and new energies (iresen). key: cord- - m k t authors: kuzemko, caroline; bradshaw, michael; bridge, gavin; goldthau, andreas; jewell, jessica; overland, indra; scholten, daniel; van de graaf, thijs; westphal, kirsten title: covid- and the politics of sustainable energy transitions date: - - journal: energy res soc sci doi: . /j.erss. . sha: doc_id: cord_uid: m k t in this perspectives piece, an interdisciplinary team of social science researchers considers the implications of covid- for the politics of sustainable energy transitions. the emergency measures adopted by states, firms, and individuals in response to this global health crisis have driven a series of political, economic and social changes with potential to influence sustainable energy transitions. we identify some of the initial impacts of the ‘great lockdown’ on sustainable and fossil sources of energy, and consider how economic stimulus packages and social practices in the wake of the pandemic are likely to shape energy demand, the carbon-intensity of the energy system, and the speed of transitions. adopting a broad multi-scalar and multi-actor approach to the analysis of energy system change, we highlight continuities and discontinuities with pre-pandemic trends. discussion focuses on four key themes that shape the politics of sustainable energy transitions: (i) the short, medium and long-term temporalities of energy system change; (ii) practices of investment around clean-tech and divestment from fossil fuels; (iii) structures and scales of energy governance; and (iv) social practices around mobility, work and public health. while the effects of the pandemic continue to unfold, some of its sectoral and geographically differentiated impacts are already emerging. we conclude that the politics of sustainable energy transitions are now at a critical juncture, in which the form and direction of state support for post-pandemic economic recovery will be key. covid- is, above all, a global health crisis with devastating implications for a great many as people lose their lives and as we live through an array of direct and indirect effects of lockdown and social distancing measures. this perspectives piece is written at a time when the pandemic is still unfolding, but some of its dramatic and varied impacts on the global economy, energy and financial markets, governance, and our ways of living are already evident. our purpose here is to explore how the changes wrought by the pandemic might influence the complex and dynamic politics of sustainable energy transitions. this question is particularly pertinent now, as governments, companies, and wider publics consider what the pandemic means, how to respond and, importantly, the extent to which responses should be 'green'. there had been some positive trends in the politics of sustainable energy transitions, as broadly defined below, in the years running up to the outbreak of the pandemic. for example, the paris agreement instituted nationally determined climate goals; sustainability transitions were placed on the agendas of many local, national and global governing bodies; the cost of renewable energy continued to fall rapidly, making it an increasingly politically and economically viable option; divestment campaigns were taking off; and there was a surge in public buy-into the argument that urgent action was required to address climate change. the hope was that cop- , due to take place in glasgow in november , would see increased ambition to meet the goals of the paris agreement. meanwhile, however, global greenhouse gas (ghg) emissions continued to rise rather than fall, albeit not in [ ] , and there remains a considerable emissions gap between the paths we are on and where we need to be [ ] . early reports of the economic impact of the pandemic, and the 'great lockdown', are bleak: the global economy is predicted to shrink by % in , with the possibility that million people lose their jobs [ ] . there will, however, be significant variance in impacts with some sectors and countries harder hit, and some recovering more quickly than others. predictions are that the open, service-oriented economies that dominate the oecd are likely to suffer more for longer [ ] , whilst china's economy is already showing strong signs of recovery. equally, those economies already carrying significant debt and/or a reliance on fossil fuel exports are also likely to be harder hit. in april , almost % of the global population were subject to complete or partial lockdowns and, as such, the share of energy use that was exposed to containment measures reached % [ ] . unsurprisingly, therefore, the early implications of covid- were also significant but varied for emissions, fossil fuel and sustainable energy. daily global co emissions fell by % in april , compared to april , with just under half this reduction coming from surface transport as social practices changed [ ] [ ] , and expectations are of an overall % drop in taking emissions to levels of years ago [ ] . lower emissions are connected, in turn, to energy use: demand for, and prices of, fossil fuels and electricity fell quite dramatically. the biggest drop was for oil, which saw a % fall in april , with us oil prices falling negative for a period of time [ ] . renewable demand was, however, less affected and is expected to rise overall, by %, in . as a result, the share of renewables within the overall energy mix may jump several years ahead of pre-pandemic expectations [ ] . the debate has, however, already started to turn to what kind of recovery, in sustainability terms, we can expect. there is considerable concern that, as with the post- recovery, there will be a rapid return to high levels of emissions and urban air pollution, and severe inequalities in terms of social outcomes. by may air pollutant levels in china had already over-shot their pre-crisis levels [ ] , whilst it is evident that a green recovery is not a luxury that all can afford and short-term survival strategies, that support business-as-usual, are underway in many parts of the world. at the same time, however, many are arguing forcefully that sizeable global stimulus packages provide an historic opportunity to drive sustainable energy transitions whilst, at the same time, delivering positive societal outcomes such as jobs, green growth and equity [ ] . as such, the economic and social impacts of covid- will do much to shape the politics of sustainable energy transitions over the next few years. we structure our discussions below around how important trends emerging in four thematic areas: energy system change; finance and investment; multi-scalar governance; and social practices, might be affected by covid- . whist we recognise limitations in reaching conclusions at a time of rapid change and uncertainty, indications so far are that the pandemic overall is likely to be continuous with, and to accelerate, many of these trends. our emphasis on the politics of transitions tends to foreground the notion that policy decisions taken as we emerge out of lockdown and into prolonged periods of social distancing will be vital to the success of sustainable energy transitions. it is important, before we proceed, to provide some key definitions. sustainable energy transitions are conceived here as complex socio-technical processes of decarbonisation within energy systems, and involve both bringing in low, or zero, carbon energy and phasing out old, high carbon energy [ ] . our understanding of sustainable also includes due consideration for social issues of energy poverty, equity and justice. in turn, energy systems, old and new, are understood as being made up not just of supply, but also demand and social infrastructures [ ] . energy systems and practices are, of course, already undergoing sustainable changes, in particular in electricity, whilst there is significant variety between countries, in terms of pace, scale and technologies [ ] , partly related to political approaches to sustainability. politics is broadly understood here as consisting of power relations, formal and informal political processes, and their outcomes. energy politics is increasingly multi-scalar in that it involves a growing multiplicity of actors at global, national and sub-national scales [ ] [ ] , a theme to which we return below. sustainable energy transitions and politics are deeply intertwined: politics can shape the nature of energy systems, i.e. the degree to which they become sustainable, but politics is also, in turn, affected by energy systems [ ] [ ] . this observation informs our choice of energy system change as one of our themes. sustainable energy policy is, in turn, shaped by embedded power relations and institutions, but exists today because of the successful articulation of new ideas, particularly about climate change [ ] [ ] . within our definition, energy power relations also include institutionalised financial practices, and investment choices, that have long facilitated fossil fuel lock-in in energy systems [ ] , to which we return in section . below. lastly, as part of our multi-actor view of the politics of sustainable energy transitions we consider social practices, and the role of the public, to be of paramount importance: as voters, particularly within democracies; as participants in political movements; and as consumers and, increasingly, generators of energy [ ] [ ] . indeed, habits, norms and culture, can be considered both a constituent element of existing energy systems [ ] , as well as a key aspect of how systems can change given the right political conditions [ ] . this aspect of the politics of sustainable energy becomes particularly relevant given that lockdown led to, more or less temporary, new social practices. partly for these reasons, but also because of wider socio-technical lock-ins [ ] , sustainable energy transitions have frequently required conscious efforts by public actors to steer towards a more sustainable path. the nature of policy responses to the covid- pandemic emerge as key given that these have the potential to speed up or slow down sustainable energy transitions [ ] [ ] [ ] . or, put more dramatically, to determine whether or not political pandemic responses prevent the world from leaping from the covid- frying pan into the climate fire [ ] . equally it is important to consider whether covid- has the potential to change the politics of energy and, if so, in what ways. we approach these questions by identifying continuities and discontinuities with sustainable energy politics trends, outlined above and below, and by thinking in terms of whether these trends are accelerating or decelerating. this is what we turn to next. the below is clearly not intended as an exhaustive discussion of all possible implications of covid- for the politics of sustainable energy. the thematic areas that shape the discussion tie in with our understanding of the politics of sustainable energy transitions outlined above, and are further informed by emerging analyses of the effects of the pandemic and related debates. what this represents is an early attempt at analysing complex politics at a time of ongoing change and uncertainty, with some emphasis on the oecd countries. questions of acceleration and deceleration highlight the importance of time frames, and the analysis below is sensitive to the temporalities of covid- : i.e. in some parts of the world, the short-term, defined as the period of lockdown, is over; whilst the medium-term can be defined as the period over which social distancing and recovery take place; and the longer term, mid s to , where the consequences of decisions made now will be most apparent [ ] . what's key in this thematic area is the impact of the pandemic on the pace and nature of whole energy system change, an issue that was already the subject of considerable debate [ ] , on the growth of the low carbon energy system, and the looming demise of the incumbent fossil-fuel based system [ ] . historical price crashes and demand shocks left indelible marks on the evolution of the global energy system, and the current crisis is no different. the counterfactual when considering implications for whole energy systems is to consider what the structure of the global energy system might have been in had there not been a pandemic. the short-term impact is clear: an unprecedented fall in energy demand, especially for oil, along with a more modest, but still significant, decline in electricity demand and prices. after the march oil price war, opec+ reached an agreement, that was subsequently supported by the g , to reduce global oil production, but, as is always the case with such deals, the final outcome will only be perceptible later on. the initial impact on natural gas demand was more muted, but global production of liquefied natural gas was constrained by a lack of demand and the future is increasingly uncertain [ ] . coal demand in china was hit early by falls in industrial output and electricity demand, both have swiftly rebounded in china, but remained constrained elsewhere [ ] . natural gas and coal demand are both linked to power generation, the relative impact there was related to the extent and duration of the 'lockdown', and its varied impact on industrial activity, and this complicates matters in relation to coal, domestic gas and electricity demand [ ] . renewable power generation has fared relatively well, particularly in those markets where capacity is already significant, and it tops the merit order. at the same time, the pandemic has impacted on the operation of energy installations, such as offshore wind platforms, and also slowed the construction of new production facilities and infrastructure. first, because construction activity was hindered by new safety measures and second because the breakdown in international trade disrupted supply chains [ ] . indeed, the iea, forecasts approximately % less growth in than in , with growth rebounding in which is a discontinuity with pre-pandemic trends, albeit the growth of renewables as a percent of the overall mix is continuous with longer-term trends [ ] . the pandemic has also exposed the vulnerabilities of relying on international supply chains for vital healthcare products and appliances, and the energy industry has been affected here too. for renewables and batteries, government-ordained work stoppages and border and port closures have also led to a disruption of trade in materials, components and assembled goods [ ] . as the reliability of global supply chains can no longer be taken for granted, governments and corporations are considering 're-shoring' essential and strategic industries, which typically includes the energy sector. as such, the pandemic might accelerate an ongoing trend of 'de-globalization' and the re-shoring of critical energy industries, especially those in which china has obtained a pivotal position in the supply chain and production line. covid- has also underscored the need to closely monitor security of supply for certain minerals that are essential for the energy transition, including cobalt, nickel and copper [ ] . in the medium term we will need to closely watch recovery programmes and the degree to which struggling fossil fuel companies are supported, and whether there are any decarbonisation conditions. and the struggle is apparent: already, many energy companies have slashed their investment plans, final investment decisions (fids) have been delayed and the longer-term prospects for new production are threatened, though not everywhere. the iea estimates that total energy investment will fall by % in [ ] . the lng industry is instructive with fids delayed in north america and mozambique, whilst prospects in the eastern mediterranean now seem bleak, although qatar is going ahead with its expansion. as such, whether or not fossil fuel producing states decide to support their ailing producers is a critical factor in determining the medium-term oil, gas and coal outcome. the plight of the shale industry in the us is also instructive: the rig count has plummeted, production is falling, and bankruptcies are rising. just as in - , the us shale industry will survive, but production will probably never return to its - peak [ ] . this will take the shine off us 'energy dominance' with potentially wide-ranging geopolitical consequences. although it is still early days, companies invested in renewable energy are more optimistic about their future, but it remains to be seen whether international oil companies (iocs), such as bp, shell and total, will accelerate their diversification into 'new energy' as they grapple with the loss of fossil fuel revenue. much also depends on the pace and scale of demand recovery, but there are those who argue that might turn out to be the date of global peak fossil fuel demand [ ] , and, as such, in hindsight covid- may be viewed as having accelerated the demise of fossil fuels. the long-term outlook will be shaped by the pace of economic recovery and the degree to which the trillions of dollars of government stimulus support fossil-fuel incumbents and to which they accelerate clean energy production and demand side management. equally, reduced electricity demand growth may weaken the appetite for new coal power in emerging economies. the sentiment of the financial sector is also a critical factor here, and, see below, accelerated fossil fuels divestment seems one likely outcome [ ] . the medium-term cuts in investment in production, discussed above, may result in high oil and gas prices and volatility in the second half of the decade, although bp have revised their long-term oil price outlook, and announced a usd bn to . bn write-off [ ] . however, it is worth remembering that over % of states are not net fossil fuel exporters. the very prospect of future high oil and gas prices may accelerate the transition away from such fuels; and fossil-fuel demand destruction would gather pace, which would constrain prices. thus, we can conclude that, for most states, investing in the low-carbon transition is a win-win strategy that both stimulates economic recovery and reduces the cost of future fossil-fuel imports. an historically intransigent aspect of sustainable energy transitions has been the financial practices that have heretofore supported fossil fuel industries, as well as the financial power of many incumbent actors. transnational, and national, oil and gas companies have kept up investments in long-term projects; coal investments, often by japan and china, have continued in developing countries thereby underpinning the expansion of coal fired electricity; whilst state subsidies for fossil fuels continue to far outstrip support for sustainable energy [ ] . prior to this crisis, and the implications for fossil fuel companies listed above, these investment practices were partly responsible for locking-in difficulties associated with phasing out fossil fuels [ ] . over the past few years, however, there have been growing moves to divest away from fossil fuels by increasingly high profile private and quasi-state actors in many oecd countries. there is also growing recognition of financial risks associated with continued fossil fuel investment, as well as re-evaluations of fossil fuel reserves associated with concerns about stranded assets. lastly, energy policy has played a strong role in, directly or indirectly, supporting investment in renewables, energy efficiency, grid improvements, and storagealbeit investment levels remain too low [ ] . evidence thus far suggests that the implications of covid- may accelerate some of these more recent trends. the stronger demand and price performance of green energy compared to fossil fuels through the crisis is a core aspect of expected longer-term sustainable energy transitions [ ] . this potential for relatively improved financial returns for green versus brown energy is further underpinned by recent analysis showing superior investment returns from renewable versus fossil fuel shares since the pandemic, and indeed over the past years [ ] . we have already seen, above, that low oil and gas demand and prices have resulted in falling investment in, especially, us shale but also a range of other petroleum provinces. there is also, however, and this is more of a discontinuity with existing trends, potential for a fall in investment flows into coal plants as economic growth in emerging economies weakens [ ] . it is also important to also think about who is investing at the moment given that so many national governments, and some international actors, are currently implementing, and devising, significant rescue and stimulus packages which might offer an historic chance for sustainable investment [ ] . indeed, the iea has already pointed out that % of funds invested in energy come, directly or indirectly, from the state [ ] , and that governments, globally, are planning to spend usd tn in the next months on recovery packages [ ] . thurs far, short-term government spend has been focused on reacting to the health challenge and protecting livelihoods, jobs and businesses and, as such, tends to support 'business-as-usual' [ ] . indeed, a point of comparison regularly made is with the recovery process post which, given limited green stimulus, returned the world quite quickly to an upward trajectory of emissions [ ] , [ ] , [ ] . there is more hope, however, this time around, of medium and longer-term stimulus packages leading to green outcomes. significant cleantech market progress [ ] , mainly in efficiency and electricity sectors, means that 'business-as-usual' in energy is now greener than in for a lot of countries. what can be inferred from this is that, for those countries that have strong and/or growing cleantech sectors, focusing investments on green energy may well mean effective short-and medium-term stimulus. hepburn et al [ ] , argue that green investments, for example in energy efficiency building retrofits, renewables, and clean energy infrastructure, can be delivered quickly and have high economic and jobs multipliers, see also [ ] , [ ] . indeed, relative fossil fuel and sustainable energy share performances and the longer-term demand outlook for oil and coal provides more evidence to support the argument that sustainable initiatives offer superior economic returns for government spending [ ] , as well as contributing towards longer term resilience and national emissions targets. although the evidence base for green stimulus is much stronger this time around, it is not yet clear whether, or to which extent, policymakers in oecd countries will choose that path. what is clear is the emergence of high-profile, and widely disseminated, arguments that state actions in this time period are crucial to a recovery that supports, and perhaps even accelerates, sustainable energy transitions [ ] [ ] [ ] . it is also worth noting that there will be significant variety in whether countries pursue green stimulus, partly in relation their existing commitments to sustainable energy, and how financially embedded clean and fossil fuel energy sectors are. sustainable energy transitions have played out against an historical backdrop of globalisation -in the sense of increasing interdependence of energy systems, global supply chains, and energy-associated externalities -albeit more recent trends, exacerbated by the pandemic, have been towards 're-shoring'. yet, there has been a general lack of coordinated and inclusive global energy governance that spans across all actors and sectors. the historically dominant global governance institutions typically consist of either producer or consumer clubs, and they tend to be preoccupied with energy security (of supply or demand) rather than with decarbonization per se [ ] . the last decade, however, has seen major innovations in intergovernmental governance, notably the creation of the international renewable energy agency (irena) in , the adoption of un sustainable development goals, and the paris agreement. the latter, in particular, now requires most national governments to devise and regularly update their climate pledges, the so-called nationally determined contributions (ndcs). while this has prompted countries like the uk and regions like the eu to adopt or propose net zero emission targets by the middle of the century, other major players, most significantly the united states, have backtracked at the national level. even within the eu there are divisions: most western eu member states have embraced the energy transition as a means to green and diversify their energy supply, and as an industrial opportunity, whilst many eastern eu members are more reluctant, for example poland is opting to secure jobs in coal [ ] . in this sense, the world in general and the eu in particular face a multi-speed energy transition. the paris agreement has, importantly, both underpinned the notion of sub-national and non-state action and galvanized new actors, including cities, civil society groups, investors, transnational movements and corporations. overall, one could say that the site of sustainable energy governance has been gravitating away from multilateral diplomacy and across national, transnational and local scales [ ] . this dynamic was explicitly supported by the paris agreement which, in starting from nationally determined pledges, took an explicitly more bottom-up approach. as things stand, however, policies and regulatory frameworks in almost every country are insufficient in terms of reaching the new emissions targets [ ] . such was the state of affairs when covid- struck. the pandemic will have multiple implications for multi-scalar energy governance. one immediate consequence is that the cop climate summit, which was planned to take place in november in glasgow, has been postponed by a year. this raises the possibility that the us is represented at the cop by a new administration with a more positive climate stance, depending on the outcome of the upcoming us elections. more broadly, the response of governments to the covid- crisis thus far seems to bode ill for the system of multilateral cooperation. regional and international organizations from the eu to the un have struggled to muster a coordinated response to the pandemic, the us has announced its withdrawal from the world health organization (who), and geopolitical tensions between china and the united states have escalated. the frailty of the current system of global cooperation might reinforce the decentralization of energy governance from the multilateral to national, transnational and local scales marking some continuity with direction of travel in governance. it will also be interesting to see in this regard whether, for example, covid- exacerbates or diminishes the aforementioned differences in speed and enthusiasm with which the eu member states pursue the energy transition and how the european commission will cope with that. another impact of covid- on the multi-scalar nature of sustainable energy governance is that the role of national governments has been stepped up, markedly in many places, in order to respond to the pandemic [ ] , [ ] . indeed, the pandemic has led to levels of government intervention in markets and private life not seen in many decades and, as such, marks some discontinuity with longer term trends. the effectiveness of government intervention, however, will partly depend on their economic and institutional capacities [ ] , which may be stretched thin as a result of the unprecedented responses required so far to covid- . at the same time, there is also evidence of cities around the world responding quite rapidly, often by changing transport modes and enabling distancing while travelling [ ] , [ ] , [ ] , sometimes even as national governments take a different course. again, this appears to be an acceleration of the pre-covid- trend of greater multi-scalarity in how energy is governed, as the pandemic so far shows signs of re-localizing and re-calibrating places and spaces of energy governance. clearly, how different social groups are affected by sustainable transitions differs markedly between and within countries. those employed within fossil fuel industries may feel very differently from those living within regions at high risk from rising sea levels -hence recent calls to adjust for such inequalities when governing for sustainable energy transitions [ ] . within many oecd countries, however, in the years immediately preceding covid- , public support for action on climate change was at an all-time high [ ] , [ ] . for example, mass transnational movements, like extinction rebellion and the youth climate movement, took a considerable step up in the late s, whilst opinion polls showed increasing levels of concern about climate change as well as support for solutions, like renewables. reports, in particular ipcc . degrees [ ] , provided a far clearer picture of the human and social implications of not mitigating, whilst more publicly visible, physical evidence of climate change had also been mounting. all of which led to a consensus in many oecd countries that the s are vital for action to mitigate. at the time of writing, june , much of society is understandably focused on human security, improved health, protection of jobs and incomes, and economic recovery. those working in high carbon and clean energy industries will seek support as part of recovery packages. arguably, however, pre-covid- surges in support for climate action as well as how attitudes evolve during the pandemic will be important considerations for policymakers as they make decisions about what priority they give to green stimulus, and to developing much needed new sustainable policies over the medium term. this, in turn, raises the relevance of debates in the public sphere, across newspapers, social media and civil society, on what a post-covid- world will look like -i.e. the 'new normal'. one of the key outcomes of lock-down and ongoing social distancing has been considerable, albeit partly non-voluntary, changes in social practices -including in mobility and work practices [ ] . transport has been one of the hardest hit sectors, especially air, rail, car and bus travel, as people have stayed home. by contrast, in many countries walking and cycling has proven the obvious travel replacement for shorter journeys [ ] , [ ] . as we have seen, these practice changes have had clear implications for oil demand, whilst reduced high carbon travel has been a major contributor to covid- related emissions reductions. the key question here is whether social practice changes persist firstly beyond lock-down, and then through social distancing phases -i.e. staying with the example of transport, will demand for transport overall be lower longer term, and how will transport choices differ? there are various clues that we can consider in relation to this question. firstly, in terms of preferred modes of transport, some national and many local governments, as mentioned above, have announced new policies aimed at structurally reinforcing moves towards cycling and walking within cities. conversely, with relevance for longer journeys, social distancing lowers demand for public transport, which may mean a switch to more car journeys for those that have that choice. at the same time, however, although car sales have fallen dramatically, and car companies are amongst those clamouring for government support, electric vehicle sales are still up globally [ ] . secondly, lockdown has provided new evidence about the effectiveness of working from home, not least due to the time saved from not having to commute [ ] , [ ] . because social distancing also affects people's willingness to return to work, and some workplaces may not have sufficient space, the duration of social distancing is a key variable in determining longer term travel demand. this is also because, as some sociologists have noted [ ] , the longer the time period over which people are compelled to change practices the more likely some behavioural changes become new norms or habits. in sum, in terms of the carbon content of travel, covid- appears so far to be continuous with and accelerated existing trends, like cycling and working from home, but may present some difficulties in the medium-term for policies encouraging public transport as an alternative to cars. lastly, when thinking about public responses to the pandemic, there is evidence emerging that covid- has demonstrated, in more vivid terms, links between human activity, biodiversity loss, environmental degradation and health [ ] . air pollution was already climbing up political agendas in many parts of the world and the who estimates that annually . million deaths result from exposure to outdoor air pollution [ ] . now it has also become a key focus within the pandemic. various studies linking covid- deaths with air pollution have been widely circulated, including comments from the who that if you are exposed to air pollution your chances of being severely affected are much higher [ ] , [ ] . at the same time, it has not gone unnoticed that air pollution has dropped significantly and, in the case of china, started to rise again as lockdown eases. indeed, a recent ipsos mori poll, undertaken in europe, shows not only that people have noticed the clean air, but that they are now asking policymakers to refocus on wellbeing over other indicators such as gdp [ ] . indeed, covid- , like climate change, was no 'black swan' event -there have been several warnings of a pandemic of this nature [ ] , [ ] . what covid- has more widely demonstrated, therefore, is the devastating consequences of ignoring such warnings, thereby offering some potential to argue for an accelerated shift in political focus onto long-term measures of broad resilience, and away from short-term gains. it is clear that the pandemic occurred at a critical juncture in terms of the relationship between politics and sustainable energy transitions. state support and policy intervention has been key to promoting efficiency and accelerating decarbonisation of the energy system, particularly in a just manner; now the need for the state to invest to support post-pandemic economic recovery presents an opportunity to energise green growth. many of the main drivers of what happens next represent a continuation of processes that pre-date the pandemic. a key question that has emerged here is whether or not there will be an acceleration of trends towards a more sustainable future, or whether the desire to protect existing jobs and incumbent industry will retard the momentum that was emerging in some countries under the banner of a 'green new deal' or 'green growth'. one lesson from the crisis was that, when it comes to emissions, a rebound to the ways of old is as likely as not. however, this perspectives piece has found good reasons to think that this time might be somewhat different. given relative economic performances between fossil fuels and sustainable energy during the pandemic, there appears to be a greater chance of green stimulus this time around. much also depends on whether changes imposed in the lockdown result in longer term behavioural and structural change in relation to issues like fossil fuel demand, air quality, and support for climate change mitigation. new global accords now exist, in the form of the paris agreement and the un's agenda and associated sdgs, that provide targets and direction for politicians and policy makers to strive towards and, importantly, against which increasingly active publics can hold them to account. furthermore, the covid- crisis has explicitly exposed a lack of political response to warnings of human disaster and of resilience in public health and welfare, which provides further support for arguments that a post-pandemic world should not be politics, or indeed business, as usual. rising diversity and inequality, both within and between countries, were also a hallmark of recovery from the global financial crisis, but these issues may well become even more significant as some parts of the world, europe, some us states and cities, focus more on sustainable change, whilst others cannot afford, or will not be politically incentivised, to do so. clearly, it will be critical to see what happens in the major economies, china, the us and the eu, but as over % of future demand growth between now and lies outside the oecd, the road to recovery in the emerging economies of asia, latin america and sub-saharan africa is just as significant. the oil price crash that accompanied the pandemic has made clear the need for so the so-called 'producer economies' to finally put themselves on a more sustainable path, particularly if a green recovery results in an earlier peak in fossil fuel demand and an acceleration of permanent demand destruction. failure of fossil fuel-dominated economies to adapt to such a trajectory will likely result in instability and conflict, both within and between states. in this context, there is an urgent need to explore further what these geographical diversities mean for the future politics of sustainable energy transitions, whilst not forgetting the growing significance of scale and diversity in political responses within countries. last, but far from least, there is the matter of publics and political participation. some argue that publics will now be focused on jobs/recovery only, but there are some early indications that this is an over-simplification. thus, it will be important that those policymakers tasked with ensuring sustainable transitions appeal to new behaviours, values, and evidence as they design recovery packages, alongside reviving some aspects of business-as-usual in the economy. it is in this wider societal context that academics can play a critical role in helping to understand possible futures, making clear that what is done today can shape those futures in a positive way. rather like the archivist in the film, 'the age of stupid', who in reflects back on why society failed to take the actions necessary to avoid catastrophic climate change, we do not want to look back on - as a time when we were unable to turn a global health crisis into an opportunity to finally put the world on a more sustainable path, both in terms of human security and environmental sustainability. supplementary data to: le quere et al ( ) temporary reduction in daily global co emissions during the covid- forced confinement' global progress report on climate change sustainable recovery imf ( ) world economic outlook temporary reduction in daily global co emissions during the covid- forced confinement covid- , changing social practices and the transition to sustainable production and consumption. version . china's air pollution overshoots pre-crisis levels for the first time global energy politics a climate for change? the impacts of climate change on energy politics re-scaling ipe: local government, sustainable energy, and change how the energy transition will reshape energy geopolitics' caution! transitions ahead: politics, practice and sustainable transition management toward a cultural politics of climate change: devices desires, and dissent understanding carbon lock-in will covid- fiscal recovery packages accelerate or retard progress on climate change? navigating the clean energy transition in the covid- crisis the history and politics of energy transitions: comparing contested views and finding common ground the speed of the energy transition: gradual or rapid quarterly gas review: the impact of covid- on global gas markets anouke honoré ( ) natural gas demand in europe: the impacts of covod- and other influences in . oxford: oxford institute for energy studies covid- weakens both sides in the battle between coal and renewables. behavioural and social sciences in nature research susceptibilities of solar energy supply chains. global policy opinion (blog). a clean energy progress after the covid- crisis will need reliable supplies of critical minerals accessed the oil crash's unlikely winner: saudi arabia. foreign policy was the peak of the fossil fuel era? carbon tracker progressing strategy development, bp revises long-term price assumptions energy investing: exploring risk and return in the capital markets ministerial roundtable on economic recovery through investments in clean energy $ tn us coronavirus relief comes without climate stipulations', the guardian pandemic, price wars, petrostates and the new energy order the political economy of decarbonisation: from green energy 'race' to green 'division of labour fiscal impacts of energy efficiency programmes -the example of solid wall insulation investment in the uk green versus brown: comparing the employment impactsof energy efficiency, renewable energy, and fossil fuels using an input-output model global mayors launch covid- economic recovery task force a place in the sun? irena's position in the global energy governance landscape new directions in the international political economy of energy prospects for powering past coal city leaders aim to shape green recovery from coronavirus crisis biking provides a critical lifeline during the coronavirus crisis covid- crisis hammers auto industry could climate change and biodiversity loss raise the risk of pandemics? ambient air pollution: health impacts is air pollution making the coronavirus even more deadly?', guardian th assessing nitrogen dioxide (no ) levels as a contributing factor to coronavirus fatality addressing climate change in post-pandemic world covid- stimulus measures must save lives, protect livelihoods, and safeguard nature to reduce the risk of future pandemics', ipbes website th the multi-speed energy transition in europe: opportunities and challenges for eu energy security