The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is f...The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is frictional work dissipated,particularly in cases where material damage and wear are not involved.The initiation of energy dissipation,the role of structural commensurability,and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model,the Frenkel-Kontorova model,and the cobblestone model,respectively.The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping.The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included.As an example,we analyzed a specific process of dissipation in multilayer graphene,on the basis of results of molecular dynamics(MD)simulations,which reveal a reversible part of energy that circulates between the system and the external driver.This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation.展开更多
Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and applications.We first note that the intermolecular excitonic coupling is muc...Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and applications.We first note that the intermolecular excitonic coupling is much weaker in strength than the intramolecular electron-vibration coupling for a majority of newly termed AIEgens,which leads to the emission peak position insensitive to excitonic coupling,hence the conventional excitonic model for J-aggregation cannot effectively explain their AIE phenomena.Then,using multiscale computational approach coupled with our self-developed thermal vibration correlation function rate formalism and transition-state theory,we quantitatively investigate the aggregation effect on both the radiative and the nonradiative decays of molecular excited states.For radiative decay processes,we propose that the lowest excited state could convert from a transition dipole-forbidden“dark”state to a dipole-allowed“bright”state upon aggregation.For the radiationless processes,we demonstrate the blockage of nonradiative decay via vibration relaxation(BNR-VR)in harmonic region or the removal of nonradiative decay via isomerization(RNR-ISO)or minimum energy crossing point(RNR-MECP)beyond harmonic region in a variety of AIE aggregates.Our theoretical work not only justifies a plethora of experimental results but also makes reliable predictions on molecular design and mechanism that can be experimentally verified.Looking forward,we believe this review will benefit the deep understanding about the universality of AIE phenomenon and further extending the scope of AIE systems with novel applications.展开更多
The increasing number of gas-fired units has significantly intensified the coupling between electric and gas power networks.Traditionally,nonlinearity and nonconvexity in gas flow equations,together with renewable-ind...The increasing number of gas-fired units has significantly intensified the coupling between electric and gas power networks.Traditionally,nonlinearity and nonconvexity in gas flow equations,together with renewable-induced stochasticity,resulted in a computationally expensive model for unit commitment in electricity-gas coupled integrated energy systems(IES).To accelerate stochastic day-ahead scheduling,we applied and modified Progressive Hedging(PH),a heuristic approach that can be computed in parallel to yield scenario-independent unit commitment.Through early termination and enumeration techniques,the modified PH algorithm saves considerable com,putational time for certain generation cost settings or when the scale of the IES is large.Moreover,an adapted second-order cone relaxation(SOCR)is utilized to tackle the nonconvex gas flow equation.Case studies were performed on the IEEE 24.bus system/Belgium 20-node gas system and the IEEE 118-bus system/Belgium 20-node gas system.The computational efficiency when employing PH is 188 times that of commercial software,and the algorithm even outperforms Benders Decomposition.At the same time,the gap between the PH algorithm and the benchmark is less than 0.01% in both IES systems,which proves that the solutions produced by PH reach acceptable optimality in this stochastic UC problem.展开更多
Polymer dielectrics with excellent dielectric properties and energy storage performance under elevated temperature are urgently needed in electrical power systems.Polyetherimide(PEI),which is supposed to be the most p...Polymer dielectrics with excellent dielectric properties and energy storage performance under elevated temperature are urgently needed in electrical power systems.Polyetherimide(PEI),which is supposed to be the most promising candidate among polymer dielectric materials,has a limitation for high-temperature dielectric applications especially at high electric field owing to secondary relaxation.Herein,a series of self-cross-linkable oligomers are prepared by combining the advantages of PEI and phenylethynyl groups.Cross-linked polymer dielectric films with enhanced voltage resistance and low leakage current density are obtained by cross-linking under oxygen.The occurrence ofβ-relaxation is diminished by cross-linking,which makes polymer dielectrics exhibit desirable dielectric stability over a broad temperature and frequency range.Particularly,the dielectric loss of c-10%PEPA-PEI at 1000 Hz is 0.0037 and 0.0043 at room temperature and 150℃,respectively.Simultaneously,the polymer dielectric maintains a still low dielectric loss(<0.010)between 10^(2)and 10^(6)Hz.Furthermore,c-10%PEPA-PEI possesses excellent hightemperature energy storage performance owing to much interchain reaction originating from proper chain length,and exhibits ultrahigh charge–discharge efficiency(>95.0%)and improved energy density(3.6 J/cm^(3))at 150℃.The authors believe that these cross-linked films showing excellent dielectric performance have a promising future in high-temperature applications.展开更多
基金The authors would like to express their appreciations to the financial support from the National Natural Science Foundation of China under the grant Nos.of 51075526,51005129,and 51021064.
文摘The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is frictional work dissipated,particularly in cases where material damage and wear are not involved.The initiation of energy dissipation,the role of structural commensurability,and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model,the Frenkel-Kontorova model,and the cobblestone model,respectively.The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping.The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included.As an example,we analyzed a specific process of dissipation in multilayer graphene,on the basis of results of molecular dynamics(MD)simulations,which reveal a reversible part of energy that circulates between the system and the external driver.This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation.
基金National Natural Science Foundation of China,Grant/Award Numbers:21788102,21973099,21973043Ministry of Science andTechnology of ChinaNationalKeyR&DPlan,Grant/Award Number:2017YFA0204501。
文摘Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and applications.We first note that the intermolecular excitonic coupling is much weaker in strength than the intramolecular electron-vibration coupling for a majority of newly termed AIEgens,which leads to the emission peak position insensitive to excitonic coupling,hence the conventional excitonic model for J-aggregation cannot effectively explain their AIE phenomena.Then,using multiscale computational approach coupled with our self-developed thermal vibration correlation function rate formalism and transition-state theory,we quantitatively investigate the aggregation effect on both the radiative and the nonradiative decays of molecular excited states.For radiative decay processes,we propose that the lowest excited state could convert from a transition dipole-forbidden“dark”state to a dipole-allowed“bright”state upon aggregation.For the radiationless processes,we demonstrate the blockage of nonradiative decay via vibration relaxation(BNR-VR)in harmonic region or the removal of nonradiative decay via isomerization(RNR-ISO)or minimum energy crossing point(RNR-MECP)beyond harmonic region in a variety of AIE aggregates.Our theoretical work not only justifies a plethora of experimental results but also makes reliable predictions on molecular design and mechanism that can be experimentally verified.Looking forward,we believe this review will benefit the deep understanding about the universality of AIE phenomenon and further extending the scope of AIE systems with novel applications.
基金supported by the National Key Research and Development Program(SQ 2020YFE0200400)the National Natural Science Foundation of China(No.52007123)the Science,Technology and Innovation Commission of Shenzhen Municipality(No.JCYJ 20170411152331932).
文摘The increasing number of gas-fired units has significantly intensified the coupling between electric and gas power networks.Traditionally,nonlinearity and nonconvexity in gas flow equations,together with renewable-induced stochasticity,resulted in a computationally expensive model for unit commitment in electricity-gas coupled integrated energy systems(IES).To accelerate stochastic day-ahead scheduling,we applied and modified Progressive Hedging(PH),a heuristic approach that can be computed in parallel to yield scenario-independent unit commitment.Through early termination and enumeration techniques,the modified PH algorithm saves considerable com,putational time for certain generation cost settings or when the scale of the IES is large.Moreover,an adapted second-order cone relaxation(SOCR)is utilized to tackle the nonconvex gas flow equation.Case studies were performed on the IEEE 24.bus system/Belgium 20-node gas system and the IEEE 118-bus system/Belgium 20-node gas system.The computational efficiency when employing PH is 188 times that of commercial software,and the algorithm even outperforms Benders Decomposition.At the same time,the gap between the PH algorithm and the benchmark is less than 0.01% in both IES systems,which proves that the solutions produced by PH reach acceptable optimality in this stochastic UC problem.
基金supported by the National Natural Science Foundation of China(nos.51973080 and 51573070)the Jilin Province Science and Technology Development Plan Project(no.20190302051GX).
文摘Polymer dielectrics with excellent dielectric properties and energy storage performance under elevated temperature are urgently needed in electrical power systems.Polyetherimide(PEI),which is supposed to be the most promising candidate among polymer dielectric materials,has a limitation for high-temperature dielectric applications especially at high electric field owing to secondary relaxation.Herein,a series of self-cross-linkable oligomers are prepared by combining the advantages of PEI and phenylethynyl groups.Cross-linked polymer dielectric films with enhanced voltage resistance and low leakage current density are obtained by cross-linking under oxygen.The occurrence ofβ-relaxation is diminished by cross-linking,which makes polymer dielectrics exhibit desirable dielectric stability over a broad temperature and frequency range.Particularly,the dielectric loss of c-10%PEPA-PEI at 1000 Hz is 0.0037 and 0.0043 at room temperature and 150℃,respectively.Simultaneously,the polymer dielectric maintains a still low dielectric loss(<0.010)between 10^(2)and 10^(6)Hz.Furthermore,c-10%PEPA-PEI possesses excellent hightemperature energy storage performance owing to much interchain reaction originating from proper chain length,and exhibits ultrahigh charge–discharge efficiency(>95.0%)and improved energy density(3.6 J/cm^(3))at 150℃.The authors believe that these cross-linked films showing excellent dielectric performance have a promising future in high-temperature applications.
