Carbonate electrolytes are one of the most desirable electrolytes for high-energy lithium-sulfur batteries(LSBs)because of their successful implementation in commercial Li-ion batteries.The low-polysulfide-solubility ...Carbonate electrolytes are one of the most desirable electrolytes for high-energy lithium-sulfur batteries(LSBs)because of their successful implementation in commercial Li-ion batteries.The low-polysulfide-solubility feature of some carbonate solvents also makes them very promising for overcoming the shuttle effects of LSBs.However,regular sulfur electrodes experience undesired electrochemical mechanisms in carbonate electrolytes due to side reactions.In this study,we report a catalytic redox mechanism of sulfur in propylene carbonate(PC)electrolyte based on a compari-son study.The catalytic mechanism is characterized by the interactions between polysulfides and dual N/O functional groups on the host carbon,which largely prevents side reactions between polysulfides and the carbonate electrolyte.Such a mechanism coupled with the low-polysulfide-solubility feature leads to stable cycling of LSBs in PC electrolyte.Favorable dual N/O functional groups are identified via a density functional theory study.This work provides an alternative route for enabling LSBs in carbonate electrolytes.展开更多
Selective coupling of methyl radicals to produce C_(2) species(C2H4 and C2H6)is a key challenge for oxidative coupling of methane(OCM).In traditional OCM reaction systems,homogeneous transformation of methyl radicals ...Selective coupling of methyl radicals to produce C_(2) species(C2H4 and C2H6)is a key challenge for oxidative coupling of methane(OCM).In traditional OCM reaction systems,homogeneous transformation of methyl radicals in O_(2)‐containing gases are uncontrollable,resulting in limited C_(2) selectivity and yield.Herein,we demonstrate that methyl radicals generated by La_(2)O_(3)at low reaction temperature can selectively couple on the surface of 5 wt%Na2WO4/SiO_(2).The controllable surface coupling against overoxidation barely changes the activity of La_(2)O_(3)but boosts the C_(2)selectivity by three times and achieves a C_(2)yield as high as 10.9%at bed temperature of only 570℃.Structure‐property studies suggest that Na_(2)WO_(4) nanoclusters are the active sites for methyl radical coupling.The strong CH_(3)·affinity of these sites can even endow some methane combustion catalysts with OCM activity.The findings of the surface coupling of methyl radicals open a new direction to develop OCM catalyst.The bifunctional OCM catalyst system,which composes of a methane activation center and a CH_(3)·coupling center,may deliver promising OCM performance at reaction temperatures below the ignition temperature of C2H6 and C2H4(~600℃)and is therefore more controllable,safer,and certainly more attractive as an actual process.展开更多
The scene matching navigation is a research focus in the field of autonomous navigation,but the real-time performance of image matching algorithm is difficult to meet the needs of real navigation systems.Therefore,thi...The scene matching navigation is a research focus in the field of autonomous navigation,but the real-time performance of image matching algorithm is difficult to meet the needs of real navigation systems.Therefore,this paper proposes a fast image matching algorithm.The algorithm improves the traditional line segment extraction algorithm and combines with the Delaunay triangulation method.By combining the geometric features of points and lines,the image feature redundancy is reduced.Then,the error with confidence criterion is analyzed and the matching process is completed.The simulation results show that the proposed algorithm can still work within 3°rotation and small scale variation.In addition,the matching time is less than 0.5 s when the image size is 256 pixel×256 pixel.The proposed algorithm is suitable for autonomous navigation systems with multiple feature distribution and higher real-time requirements.展开更多
Ab initio CCSD(T)/CBS//B3LYP/6-311G(d,p)calculations of the potential energy surface for possible dissociation channels of HOC2H3F,as well as Rice-Ramsperger-Kassel-Marcus(RRKM)calculations of rate constants,were carr...Ab initio CCSD(T)/CBS//B3LYP/6-311G(d,p)calculations of the potential energy surface for possible dissociation channels of HOC2H3F,as well as Rice-Ramsperger-Kassel-Marcus(RRKM)calculations of rate constants,were carried out,in order to predict statistical product branching ratios in dissociation of HOC2H3F at various internal energies.The most favorable reaction pathway leading to the major CH2CHO+HF products is as the following:OH+C2H3F→i2→TS14→i6→TS9→i3→TS3→CH2CHO+HF,where the rate-determining step is HF elimination from the CO bridging position via TS11,lying above the reactants by 3.8 kcal/mol.The CH2O+CH2F products can be formed by F atom migration from Cαto Cβposition via TS14,then H migration from O to Cαposition via TS16,and C-C breaking to form the products via TS5,which is 1.8 kcal/mol lower in energy than the reactants,and 4.0 kcal/mol lower than TS11.展开更多
The generalized quantum master equation(GQME)provides a general and exact approach for simulating the reduced dynamics in open quantum systems where a quantum system is embedded in a quantum environment.Dynamics of op...The generalized quantum master equation(GQME)provides a general and exact approach for simulating the reduced dynamics in open quantum systems where a quantum system is embedded in a quantum environment.Dynamics of open quantum systems is important in excitation energy,charge,and quantum coherence transfer as well as reactive photochemistry.The system is usually chosen to be the interested degrees of freedom such as the electronicstates in light-harvesting molecules or tagged vibrational modes in a condensed-phase system.The environment is also called the bath,whose influence on the system has to be considered,and for instance can be described by the GQME formalisms using the projection operator technique.In this review,we provide a heuristic description of the development of two canonical forms of GQME,namely the time-convoluted Nakajima-Zwanzig form(NZ-GQME)and the time-convolutionless form(TCL-GQME).In the more popular NZ-GQME form,the memory kernel serves as the essential part that reflects the non-Markovian and non-perturbative effects,which gives formally exact dynamics of the reduced density matrix.We summarize several schemes to express the projection-based memory kernel of NZ-GQME in terms of projection-free time correlation function inputs that contain molecular information.In particular,the recently proposed modified GQME approach based on NZ-GQME partitions the Hamiltonian into a more general diagonal and off-diagonal parts.The projection-free inputs in the above-mentioned schemes expressed in terms of different system-dependent time correlation functions can be calculated via numerically exact or approximate dynamical methods.We hope this contribution would help lower the barrier of understanding the theoretical pillars for GQME-based quantum dynamics methods and also envisage that their combination with the quantum computing techniques will pave the way for solving complex problems related to quantum dynamics and quantum information that are currently intractable even with today’s state-of-the-art classical supercomputers.展开更多
The product branching ratio between different products in multichannel reactions is as important as the overall rate of reaction,both in terms of practical applications(e.g.models of combustion or atmosphere chemistry...The product branching ratio between different products in multichannel reactions is as important as the overall rate of reaction,both in terms of practical applications(e.g.models of combustion or atmosphere chemistry)in understanding the fundamental mechanisms of such chemical reactions.A global ground state potential energy surface for the dissociation reaction of deuterated alkyl halide CD_(3)CH_(2)F was computed at the CCSD(T)/CBS//B3 LYP/aug-cc-p VDZ level of theory for all species.The decomposition of CD_(3)CH_(2)F is controversial concerning C-F bond dissociation reaction and molecular(HF,DF,H_(2),D_(2),HD)elimination reaction.RiceRamsperger-Kassel-Marcus(RRKM)calculations were applied to compute the rate constants for individual reaction steps and the relative product branching ratios for the dissociation products were calculated using the steady-state approach.At the different energies studied,the RRKM method predicts that the main channel for DF or HF elimination from1,2-elimination of CD_(3)CH_(2)F is through a four-center transition state,whereas D_(2) or H_(2) elimination from 1,1-elimination of CD_(3)CH_(2)F occurs through a direct three-center elimination.At 266,248,and 193 nm photodissociation,the main product CD_(2)CH_(2)+DF branching ratios are computed to be 96.57%,91.47%,and 48.52%,respectively;however,at 157 nm photodissociation,the product branching ratio is computed to be 16.11%.Based on these transition state structures and energies,the following photodissociation mechanisms are suggested:at 266,248,193 nm,CD_(3)CH_(2)F→absorption of a photon→TS5→the formation of the major product CD_(2)CH_(2)+DF;at 157 nm,CD_(3)CH_(2)F→absorption of a photon→D/F interchange of TS1→CDH_(2)CDF→H/F interchange of TS2→CHD_(2)CHDF→the formation of the major product CHD_(2)+CHDF.展开更多
The Yangtze River(YZR) regions have experienced rapid changes after opening up to economic reforms, and human activities have changed the land cover, ecology, and wildlife habitat quality. However, the specific ways i...The Yangtze River(YZR) regions have experienced rapid changes after opening up to economic reforms, and human activities have changed the land cover, ecology, and wildlife habitat quality. However, the specific ways in which those influencing factors changed the habitat quality during different periods remain unknown. This study assessed the wildlife habitat quality of the middle and lower YZR in the past(1980–2018) and in future scenarios(2050, 2100). We analyzed the relationships between habitat quality and various topological social-economic factors, and then mapped and evaluated the changes in habitat quality by using the Integrated Valuation of Environmental Services and Tradeoffs(InVEST) model. The results show that the slope(R = 0.502, P < 0.01, in 2015), elevation(R = 0.003, P < 0.05, in 2015), population density(R = –0.299, P < 0.01, in 2015), and NDVI(R = 0.366, P < 0.01, in 2015) in the study area were significantly correlated with habitat quality from 2000 to 2015. During the period of 1980–2018, 61.93% of the study area experienced habitat degradation and 38.07% of the study area had improved habitat quality. In the future, the habitat quality of the study area will decline under either the A2 scenario(high level of population density, low environmental technology input, and high traditional energy cost) or the B2 scenario(medium level of population density, medium green technology and lack of cooperation of regional governments). The results also showed that habitat in the lower reaches or north of the YZR had degraded more than in the middle reaches or the south of YZR. Therefore, regional development should put more effort into environmental protection, curb population growth, and encourage green technology innovation. Inter-province cooperation is necessary when dealing with ecological problems. This study can serve as a scientific reference for regional wildlife protection and similar investigations in different areas.展开更多
As a mega-city constrained by resources and the environment, Beijing has developed a leading service sector, and it is necessary to evaluate the service sector circular economy in this major global city. Here, we esta...As a mega-city constrained by resources and the environment, Beijing has developed a leading service sector, and it is necessary to evaluate the service sector circular economy in this major global city. Here, we estab- lish an indicator system including internal subsystem （economic production, resources consumption, waste emis- sions, and waste recycling）, external subsystem （industry correlation） and mutualistic subsystem （society devel- opment）, and use AHP modeling to evaluate the period from 2000 to 2013. We found that the development of the service sector circular economy in Beijing experienced an increase from 2000 to 2008, then a decrease from 2009 to 2013. This change mainly resulted from the decrease in Beijing＇s GDP following the international financial crisis in 2008. The internal subsystem greatly influences the service sector circular economy：synthetic weight of eco- nomic production, resource consumption, waste emissions and waste recycling was 0.367,0.136,0.136 and 0.075, respectively. Within the external subsystem, industrial correlation has a weak connection with Beijing＇s service sector circular economy with asynthetic weight of 0.143, this result illustrates that the development of the service sector circular economy has an intimate relationship with other cities or provinces around Beijing, such as Tianjin and Hebei. As are presentative of the mutualistic subsystem, society development has a positive nexus with the service sector circular economy with asynthetic weight of 0.143, proving that the development of the service sector circular economy can improve the service sector employment ratio in Beijing. We conclude with some suggestions on how to develop the service sector circular economy in Beijing.展开更多
文摘Carbonate electrolytes are one of the most desirable electrolytes for high-energy lithium-sulfur batteries(LSBs)because of their successful implementation in commercial Li-ion batteries.The low-polysulfide-solubility feature of some carbonate solvents also makes them very promising for overcoming the shuttle effects of LSBs.However,regular sulfur electrodes experience undesired electrochemical mechanisms in carbonate electrolytes due to side reactions.In this study,we report a catalytic redox mechanism of sulfur in propylene carbonate(PC)electrolyte based on a compari-son study.The catalytic mechanism is characterized by the interactions between polysulfides and dual N/O functional groups on the host carbon,which largely prevents side reactions between polysulfides and the carbonate electrolyte.Such a mechanism coupled with the low-polysulfide-solubility feature leads to stable cycling of LSBs in PC electrolyte.Favorable dual N/O functional groups are identified via a density functional theory study.This work provides an alternative route for enabling LSBs in carbonate electrolytes.
文摘Selective coupling of methyl radicals to produce C_(2) species(C2H4 and C2H6)is a key challenge for oxidative coupling of methane(OCM).In traditional OCM reaction systems,homogeneous transformation of methyl radicals in O_(2)‐containing gases are uncontrollable,resulting in limited C_(2) selectivity and yield.Herein,we demonstrate that methyl radicals generated by La_(2)O_(3)at low reaction temperature can selectively couple on the surface of 5 wt%Na2WO4/SiO_(2).The controllable surface coupling against overoxidation barely changes the activity of La_(2)O_(3)but boosts the C_(2)selectivity by three times and achieves a C_(2)yield as high as 10.9%at bed temperature of only 570℃.Structure‐property studies suggest that Na_(2)WO_(4) nanoclusters are the active sites for methyl radical coupling.The strong CH_(3)·affinity of these sites can even endow some methane combustion catalysts with OCM activity.The findings of the surface coupling of methyl radicals open a new direction to develop OCM catalyst.The bifunctional OCM catalyst system,which composes of a methane activation center and a CH_(3)·coupling center,may deliver promising OCM performance at reaction temperatures below the ignition temperature of C2H6 and C2H4(~600℃)and is therefore more controllable,safer,and certainly more attractive as an actual process.
基金supported by the Fundation of Graduate Innovation Center in Nanjing University of Aeronautics and Astronautics (No.kfjj20191506)
文摘The scene matching navigation is a research focus in the field of autonomous navigation,but the real-time performance of image matching algorithm is difficult to meet the needs of real navigation systems.Therefore,this paper proposes a fast image matching algorithm.The algorithm improves the traditional line segment extraction algorithm and combines with the Delaunay triangulation method.By combining the geometric features of points and lines,the image feature redundancy is reduced.Then,the error with confidence criterion is analyzed and the matching process is completed.The simulation results show that the proposed algorithm can still work within 3°rotation and small scale variation.In addition,the matching time is less than 0.5 s when the image size is 256 pixel×256 pixel.The proposed algorithm is suitable for autonomous navigation systems with multiple feature distribution and higher real-time requirements.
基金supported by the National Natural Science Foundation of China (No.91641116).
文摘Ab initio CCSD(T)/CBS//B3LYP/6-311G(d,p)calculations of the potential energy surface for possible dissociation channels of HOC2H3F,as well as Rice-Ramsperger-Kassel-Marcus(RRKM)calculations of rate constants,were carried out,in order to predict statistical product branching ratios in dissociation of HOC2H3F at various internal energies.The most favorable reaction pathway leading to the major CH2CHO+HF products is as the following:OH+C2H3F→i2→TS14→i6→TS9→i3→TS3→CH2CHO+HF,where the rate-determining step is HF elimination from the CO bridging position via TS11,lying above the reactants by 3.8 kcal/mol.The CH2O+CH2F products can be formed by F atom migration from Cαto Cβposition via TS14,then H migration from O to Cαposition via TS16,and C-C breaking to form the products via TS5,which is 1.8 kcal/mol lower in energy than the reactants,and 4.0 kcal/mol lower than TS11.
基金support from NYU Shanghai,the National Natural Science Foundation of China(No.21903054)the Hefei National Laboratory for Physical Sciences at the Microscale(No.KF2020008)+1 种基金the Shanghai Sailing Program(No.19YF1435600)the Program for Eastern Young Scholar at Shanghai Institutions of Higher Learning。
文摘The generalized quantum master equation(GQME)provides a general and exact approach for simulating the reduced dynamics in open quantum systems where a quantum system is embedded in a quantum environment.Dynamics of open quantum systems is important in excitation energy,charge,and quantum coherence transfer as well as reactive photochemistry.The system is usually chosen to be the interested degrees of freedom such as the electronicstates in light-harvesting molecules or tagged vibrational modes in a condensed-phase system.The environment is also called the bath,whose influence on the system has to be considered,and for instance can be described by the GQME formalisms using the projection operator technique.In this review,we provide a heuristic description of the development of two canonical forms of GQME,namely the time-convoluted Nakajima-Zwanzig form(NZ-GQME)and the time-convolutionless form(TCL-GQME).In the more popular NZ-GQME form,the memory kernel serves as the essential part that reflects the non-Markovian and non-perturbative effects,which gives formally exact dynamics of the reduced density matrix.We summarize several schemes to express the projection-based memory kernel of NZ-GQME in terms of projection-free time correlation function inputs that contain molecular information.In particular,the recently proposed modified GQME approach based on NZ-GQME partitions the Hamiltonian into a more general diagonal and off-diagonal parts.The projection-free inputs in the above-mentioned schemes expressed in terms of different system-dependent time correlation functions can be calculated via numerically exact or approximate dynamical methods.We hope this contribution would help lower the barrier of understanding the theoretical pillars for GQME-based quantum dynamics methods and also envisage that their combination with the quantum computing techniques will pave the way for solving complex problems related to quantum dynamics and quantum information that are currently intractable even with today’s state-of-the-art classical supercomputers.
基金supported by the National Natural Science Foundation of China(No.91641116,No.21433004,No.91753103,and No.21933010)the NYU Global Seed Grantthe Laboratory and Equipment Management Office of ECNU。
文摘The product branching ratio between different products in multichannel reactions is as important as the overall rate of reaction,both in terms of practical applications(e.g.models of combustion or atmosphere chemistry)in understanding the fundamental mechanisms of such chemical reactions.A global ground state potential energy surface for the dissociation reaction of deuterated alkyl halide CD_(3)CH_(2)F was computed at the CCSD(T)/CBS//B3 LYP/aug-cc-p VDZ level of theory for all species.The decomposition of CD_(3)CH_(2)F is controversial concerning C-F bond dissociation reaction and molecular(HF,DF,H_(2),D_(2),HD)elimination reaction.RiceRamsperger-Kassel-Marcus(RRKM)calculations were applied to compute the rate constants for individual reaction steps and the relative product branching ratios for the dissociation products were calculated using the steady-state approach.At the different energies studied,the RRKM method predicts that the main channel for DF or HF elimination from1,2-elimination of CD_(3)CH_(2)F is through a four-center transition state,whereas D_(2) or H_(2) elimination from 1,1-elimination of CD_(3)CH_(2)F occurs through a direct three-center elimination.At 266,248,and 193 nm photodissociation,the main product CD_(2)CH_(2)+DF branching ratios are computed to be 96.57%,91.47%,and 48.52%,respectively;however,at 157 nm photodissociation,the product branching ratio is computed to be 16.11%.Based on these transition state structures and energies,the following photodissociation mechanisms are suggested:at 266,248,193 nm,CD_(3)CH_(2)F→absorption of a photon→TS5→the formation of the major product CD_(2)CH_(2)+DF;at 157 nm,CD_(3)CH_(2)F→absorption of a photon→D/F interchange of TS1→CDH_(2)CDF→H/F interchange of TS2→CHD_(2)CHDF→the formation of the major product CHD_(2)+CHDF.
基金The National Natural Science Foundation of China (41271534)The China Scholarship Council (201906770044)。
文摘The Yangtze River(YZR) regions have experienced rapid changes after opening up to economic reforms, and human activities have changed the land cover, ecology, and wildlife habitat quality. However, the specific ways in which those influencing factors changed the habitat quality during different periods remain unknown. This study assessed the wildlife habitat quality of the middle and lower YZR in the past(1980–2018) and in future scenarios(2050, 2100). We analyzed the relationships between habitat quality and various topological social-economic factors, and then mapped and evaluated the changes in habitat quality by using the Integrated Valuation of Environmental Services and Tradeoffs(InVEST) model. The results show that the slope(R = 0.502, P < 0.01, in 2015), elevation(R = 0.003, P < 0.05, in 2015), population density(R = –0.299, P < 0.01, in 2015), and NDVI(R = 0.366, P < 0.01, in 2015) in the study area were significantly correlated with habitat quality from 2000 to 2015. During the period of 1980–2018, 61.93% of the study area experienced habitat degradation and 38.07% of the study area had improved habitat quality. In the future, the habitat quality of the study area will decline under either the A2 scenario(high level of population density, low environmental technology input, and high traditional energy cost) or the B2 scenario(medium level of population density, medium green technology and lack of cooperation of regional governments). The results also showed that habitat in the lower reaches or north of the YZR had degraded more than in the middle reaches or the south of YZR. Therefore, regional development should put more effort into environmental protection, curb population growth, and encourage green technology innovation. Inter-province cooperation is necessary when dealing with ecological problems. This study can serve as a scientific reference for regional wildlife protection and similar investigations in different areas.
基金The Educational Committee Foundation of Beijing(sm201410005006JJ104001201501)the Ri-Xin Talent Project of Beijing University of Technology(033000514116001)
文摘As a mega-city constrained by resources and the environment, Beijing has developed a leading service sector, and it is necessary to evaluate the service sector circular economy in this major global city. Here, we estab- lish an indicator system including internal subsystem （economic production, resources consumption, waste emis- sions, and waste recycling）, external subsystem （industry correlation） and mutualistic subsystem （society devel- opment）, and use AHP modeling to evaluate the period from 2000 to 2013. We found that the development of the service sector circular economy in Beijing experienced an increase from 2000 to 2008, then a decrease from 2009 to 2013. This change mainly resulted from the decrease in Beijing＇s GDP following the international financial crisis in 2008. The internal subsystem greatly influences the service sector circular economy：synthetic weight of eco- nomic production, resource consumption, waste emissions and waste recycling was 0.367,0.136,0.136 and 0.075, respectively. Within the external subsystem, industrial correlation has a weak connection with Beijing＇s service sector circular economy with asynthetic weight of 0.143, this result illustrates that the development of the service sector circular economy has an intimate relationship with other cities or provinces around Beijing, such as Tianjin and Hebei. As are presentative of the mutualistic subsystem, society development has a positive nexus with the service sector circular economy with asynthetic weight of 0.143, proving that the development of the service sector circular economy can improve the service sector employment ratio in Beijing. We conclude with some suggestions on how to develop the service sector circular economy in Beijing.
