Aims From the light-competition hypothesis,competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light.Greater ...Aims From the light-competition hypothesis,competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light.Greater plant height provides pre-emptive access to light and produces increased height differences among species.The question is what produces these differences in plant height or height growth response among species in response to fertilization.Methods In 2009,a field experiment of N,P and N+P enrichments at three levels each was initiated in an alpine meadow on the northeast Qinghai-Tibet Plateau.Effects of fertilization on species richness,aboveground net primary production(ANPP),relative light intensity and plant height of different plant functional groups were determined.Festuca ovina(grass),Kobresia humilis(sedge),Oxytropis ochrocephala(legume),Taraxacum lugubre(rosette forb)and Geranium pylzowianum(upright forb)were selected as exemplars of each of the indicated functional groups.The N:C ratios in aboveground biomass,gibberellic acid(GA_(3))concentrations in leaves,plant heights and height relative growth rate(RGR)of these exemplar species were analyzed in detail.Important Findings Species richness of grasses significantly increased with increasing N+P levels.Species richness of legumes and upright forbs decreased after N and N+P additions.P addition had no significant effect on species richness.The effects of N+P addition on species richness and ANPP were consistently stronger than those of the single N or P fertilization.Reductions in species richness caused by nutrient addition paralleled the increases in ANPP and decreases in light intensity under the canopies,indicating indirect effect of nutrient addition on species richness via ANPP-induced light competition.The exemplar species that responded most positively to fertilization in height and RGR also displayed stronger increases in their GA_(3) content and N:C ratios.GA_(3) concentrations and N:C ratios were positively correlated with height RGR展开更多
Proton exchange membrane fuel cells(PEMFCs)as promising alternatives to traditional internal combustion engines have attracted massive concerns to promote their wide application in society.However,the biggest challeng...Proton exchange membrane fuel cells(PEMFCs)as promising alternatives to traditional internal combustion engines have attracted massive concerns to promote their wide application in society.However,the biggest challenge to the commercialization of PEMFCs remains the high cost due to the adoption of the platinum group metal(PGM)catalysts in the cathode.展开更多
Microbial fuel cells(MFCs)have a simple structure and excellent pollutant treatment and power generation performance.However,the slow kinetics of the oxygen reduction reaction(ORR)at the MFC cathode limit power genera...Microbial fuel cells(MFCs)have a simple structure and excellent pollutant treatment and power generation performance.However,the slow kinetics of the oxygen reduction reaction(ORR)at the MFC cathode limit power generation.The electrochemical performance of MFCs can be improved through electrocatalysis.Thus far,metal-based catalysts have shown astonishing results in the field of electrocatalysis,enabling MFC devices to demonstrate power generation capabilities comparable to those of Pt,thus showing enormous potential.This article reviews the research progress of meta-based MFC cathode ORR catalysts,including the ORR reaction mechanism of MFC,different types of catalysts,and preparation strategies.The catalytic effects of different catalysts in MFC are compared and summarized.Before discussing the practical application and expanded manufacturing of catalysts,we summarize the key challenges that must be addressed when using metal-based catalysts in MFC,with the aim of providing a scientific direction for the future development of advanced materials.展开更多
The slow oxygen reduction process at the cathode and the scarcity of platinum-based metals lead to limited applications in fuel cells and metal-air cells.Recently,transition metal and nitrogen co-doped carbon-based ca...The slow oxygen reduction process at the cathode and the scarcity of platinum-based metals lead to limited applications in fuel cells and metal-air cells.Recently,transition metal and nitrogen co-doped carbon-based catalysts(M–N–C)are regarded as the most prospective non-precious metal catalysts for future fuel cell applications.It is verified theoretically and experimentally that the metal and nitrogen coordination structure is the main catalytic activity center of oxygen reduction reaction(ORR),so constructing M–N–C materials with high available surface area and structural stability is an effective way to accelerate ORR.Herein,we deliberately synthesize a one-dimensional ZIF structure to fabricate one-dimensional porous Fe–N–C nanostick via two-step pyrolysis.Excitingly,the as-synthesized exhibited an outstanding ORR activity in alkaline medium(E_(1/2)of 0.928 V),as well as superior stability(only changed 7 mV after 10,000 cycles in alkaline medium).Our results show that the reduction of electrocatalyst dimensionality can promote mass transport and increase the accessibility of active sites,thus optimizing their performance in ORR.This work is a good demonstration of the importance of a rational design of catalyst structure for efficient ORR.展开更多
NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conducti...NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conductivity,limited activity,durability.To address these issues,herein,by utilizing three-dimensional covalent organic framework(3D-COF)with porous confined structures and abundant coordinate N sites as the precursor,the partially oxidized Ni_(3)Fe nanoalloys wrapped by Ndoped carbon(N-C)layers are constructed via simple pyrolysis and subsequent oxidization.Benefiting from the 3D curved hierarchical structure,high-conductivity of Ni_(3)Fe and N-C layers,well-distributed active sites,the as-synthesized O-Ni_(3)Fe-NC catalyst demonstrates excellent activity and durability for catalyzing OER.Experimental and theoretical analyses disclose that both high-temperature oxidization and the OER process greatly promote the formation and exposure of the Ni(Fe)OOH active species as well as lower charge transfer resistance,inducing its optimized OER activity.The robust graphitized N-C layers with superior conductivity and their couplings with oxidized Ni_(3)Fe nanoalloys are beneficial for stabilizing catalytic centers,thereby imparting O-Ni_(3)Fe-N-C with such outstanding stability.This work not only provides a rational guidance for enriching and stabilizing high-activity catalytic sites towards OER but also offers more insights into the structural evolution of NiFe-based OER catalysts.展开更多
Single atom catalysts(SACs)with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction(ORR)and ox...Single atom catalysts(SACs)with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),showing great application potential in Zn-air batteries.However,because of the complex structure-performance relationships of carbon-based SACs in the oxygen electrocatalytic reactions,the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous.In this study,SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets(M-N@Gs,M=Co,Fe and Ni),featured with similar physicochemical properties and M-N@C configurations,are obtained.By comparing the on-set potentials and the maximum current,we observed that the ORR activity is in the order of Co-N@G>Fe-N@G>Ni-N@G,while the OER activity is in the order of Co-N@G>Ni-N@G>Fe-N@G.The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G.This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants.This study could improve our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level.展开更多
The benzophenone-initiated photoaddition of N-methyl ammes 2 to the chiral synthon1 proceeds in a regiospecitlc and highlyr stereocontrolled thshion to give the C-C photoadductscontaining a ne\viy stereogenic center 3...The benzophenone-initiated photoaddition of N-methyl ammes 2 to the chiral synthon1 proceeds in a regiospecitlc and highlyr stereocontrolled thshion to give the C-C photoadductscontaining a ne\viy stereogenic center 3a-3c. The enantiomerically pure N-C photoadducts, aminobutenolides 5a-5c have been obtained from the enantioselective photoaddition of secondary cyclicammes 4 with the chiral synthon 1 under the same conditions.展开更多
Single C3N4 crystals with 1-3μm in length and 300 nm in cross area was obtained on nickel substrate.The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth w...Single C3N4 crystals with 1-3μm in length and 300 nm in cross area was obtained on nickel substrate.The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth was on silicon.The X-ray diffraction and transmission electron microscopy with selective-area electron diffraction give the lattice constants a=0.624 nm and c=0.236 nm for β-C3N4,and a=0.638 nm and c=0.464 8 nm for αC3N4,which are respectively 2.5% and 1.3% lower than those of the latest first-principle calculations.An N:C ratio of 1.30-1.40 was determined by energy dispersive X-ray.Based on the experimental lattice constants,the bulk modulus of the obtained β-C3N4 are in the region of 425-445 GPa.展开更多
Voltage-gated potassium channels comprise 12 subtypes （Kv1-Kv12）. Kv2.1, which is expressed in most mammalian central neurons, provides the majority of delayed-rectifier K＋ current in cortical and hippocampal pyram...Voltage-gated potassium channels comprise 12 subtypes （Kv1-Kv12）. Kv2.1, which is expressed in most mammalian central neurons, provides the majority of delayed-rectifier K＋ current in cortical and hippocampal pyramidal neurons, and plays an especially prominent role in repolarizing membrane potential, as well as in facilitation of exocytosis. Kv2.1-encoded K＋ efflux is essential for neuronal apoptosis programming. The human form of the Kv2.1 potassium channel contains large intracellular regions. The cytoplasmic C-terminal plays a key role in modulating Kv2.1 gating. The present manuscript summarized Kv2.1 structure and modulation in neurons and analyzed the roles of the cytoplasmic C-terminal.展开更多
It has been made a proposal of new ideal cycle for power plants which is working by a turbine gas, for both closed and open systems. It has been designed a special device for adding heat at constant volume. The aim of...It has been made a proposal of new ideal cycle for power plants which is working by a turbine gas, for both closed and open systems. It has been designed a special device for adding heat at constant volume. The aim of special device is to decrease the amount of added heat for the new cycle. We have made a comparison between the simple gas turbine cycle & the new cycle. The results has been shown, that the efficiency of new cycle is greater than the simple cycle of gas turbine.展开更多
This study proposes a ladder gradient method for neutron and gamma-ray discrimination.The proposed method exhibited state-of-the-art performance with low time consumption,which incorporates two parts:information extra...This study proposes a ladder gradient method for neutron and gamma-ray discrimination.The proposed method exhibited state-of-the-art performance with low time consumption,which incorporates two parts:information extraction and discrimination factor calculation.A quasi-continuous spiking cortical model was proposed to extract information from the radiation pulse signals,thus generating an ignition map corresponding to each pulse signal.The ignition map can be used to calculate the discrimination factor.A ladder gradient calculation was introduced to obtain a discrimination factor with low computational complexity.The proposed method was compared with five other discrimination methods to evaluate its robustness and efficacy.Furthermore,the filter adaptability of the pulse-coupled neural network and ladder gradient methods was investigated.Possible reasons for adapting the conditions with different discrimination methods and filters were analyzed.Experiments were conducted in 20 filtering situations with 11 types of filters to determine the most suitable filters for discrimination methods.The experimental results revealed that the three most adaptive filters of the pulse-coupled neural networks and ladder gradient methods are the wavelet,elliptic,and median filters and the elliptic,moving average,and wavelet filters,respectively.展开更多
A family of tropos ligands bearing a N-heterocyclic carbene and a chiral oxazoline coordination group with a N-phenyl framework were easily prepared,and their coordination behavior with Pd（Ⅱ）acetate was performed,a...A family of tropos ligands bearing a N-heterocyclic carbene and a chiral oxazoline coordination group with a N-phenyl framework were easily prepared,and their coordination behavior with Pd（Ⅱ）acetate was performed,affording a series of axially chiral palladium complexes in good yields.展开更多
Lithium carbon dioxide(Li-CO_(2))batteries deliver a theoretical energy density of 1876 W h kg^(-1) in terms of effective utilization of greenhouse gases.This battery system is considered to be an encouraging electroc...Lithium carbon dioxide(Li-CO_(2))batteries deliver a theoretical energy density of 1876 W h kg^(-1) in terms of effective utilization of greenhouse gases.This battery system is considered to be an encouraging electrochemical energy storage device and a promising alternative to Li-ion batteries.However,the main drawback of Li-CO_(2) batteries is their accumulative discharge product of Li_(2)CO_(3)/C,which leads to large overpotential and poor cycling performance.Thus,specific and efficient catalysts must be explored to enhance the decomposition of Li_(2)CO_(3)/C.Single-atom catalysts(SACs)are regarded as promising heterogeneous catalysts owing to their maximized utilization of metal atoms and strong interfacial electronic interactions.Herein,single-metal atoms of Fe,Co,and Ni uniformly anchored on N-doped reduced graphene oxide(rGO),designated as Fe_(1)/N-rGO,Co1/N-rGO,and Ni_(1)/N-r GO,respectively,are designed and fabricated to investigate their catalytic activity toward the decomposition of Li_(2)CO_(3)/C.Among them,Fe_(1)/N-rGO delivers a high discharge capacity of 16,835 mA h g^(-1) at 100 mA g^(-1) and maintains stability for more than 170 cycles with a discharge voltage of 2.30 V at 400 mA g^(-1).Therefore,this catalysts are overwhelmingly superior to other types.This work reveals the advances of SACs in Li-CO_(2) batteries and offers an effective method for realizing high-performance Li-CO_(2) batteries.展开更多
Atomically dispersed transition metal(M)and nitrogen(N)co-doped carbon(M-N-C)electrocatalysts hold excellent application potentials for several critical reactions required in electrochemical conversion processes and e...Atomically dispersed transition metal(M)and nitrogen(N)co-doped carbon(M-N-C)electrocatalysts hold excellent application potentials for several critical reactions required in electrochemical conversion processes and energy storage devices,including oxygen reduction reaction,oxygen evolution reaction,hydrogen evolution reaction,carbon dioxide reduction reaction and nitrogen reduction reaction.Despite significant progress achieved in the past few decades,their commercialization is hindered by their fast degradation.This perspective article outlines the historical development of M-N-C electrocatalysts,the current understanding of their active catalytic sites,and crucial degradation mechanisms.We highlight that many methods used to tailor M-N-C electrocatalysts likely cause contradictory effects on activity and stability.More emphasis is needed to address their degradation issues under industryrelevant working conditions.展开更多
In this work,the detailed oxygen reduction reaction(ORR)catalytic performance of M-N_(4−x)O_(x)(M=Fe,Co,and Ni;x=1−4)has been explored via the detailed density functional theory method.The results suggest that the for...In this work,the detailed oxygen reduction reaction(ORR)catalytic performance of M-N_(4−x)O_(x)(M=Fe,Co,and Ni;x=1−4)has been explored via the detailed density functional theory method.The results suggest that the formation energy of M-N_(4−x)O_(x)shows a good linear relationship with the number of doped O atoms.The adsorption manner of O_(2)on M-N_(4−x)O_(x)changed from end-on(x=1 and 2)to side-on(x=3 and 4),and the adsorption strength gradually increased.Based on the results for binding strength of ORR intermediates and the Gibbs free energy of ORR steps on the studied catalysts,we screened out two highly active ORR catalysts,namely Co-N_(3)O_(1)and Ni-N_(2)O_(2),which possess very small overpotentials of 0.27 and 0.32 V,respectively.Such activities are higher than the precious Pt catalyst.Electronic structure analysis reveals one of the reasons for the higher activity of Co-N_(3)O_(1)and Ni-N_(2)O_(2)is that they have small energy gaps and moderate highest occupied molecular orbital energy levels.Furthermore,the results of the density of states reveal that the O doping can improve the electronic structure of the original catalyst to tune the adsorption of the ORR intermediates.展开更多
Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design o...Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design of a fast-neutron detector based on the scintillating fiber (Sci-Fi) to provide D-T neutron yield through Geant4simulation. The effect on the detection performance is concerned when changing the number of the Sci-Fis embedded in the probe head, minimum distance between the fibers, length of the fibers, or substrate material of the probe head. The maximum number of scintillation photons generated by the n/γ source particles and output by the light guide within an event (event:the entire simulation process for one source particle) was used to quantify the n/γ resolution of the detector as the main basis. And the intrinsic detection efficiency was used as another evaluation criterion. The results demonstrate that the optimal design scheme is to use a 5 cm probe head whose substrate material is pure aluminum, in which 463 Sci-Fis with the same length of 5 cm are embedded, and the minimum distance between the centers of the two fibers is 2 mm. The optimized detector exhibits clear directionality in the simulation, which is in line with the expectation and experimental data provided in the literature. This study presents the variation trends of the performance of the SciFi detector when its main parameters change, which is beneficial for the targeted design and optimization of the Sci-Fi detector used in a specific radiation environment.展开更多
The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO2 have been investigated using the first-principles calculation. Co-doping these two elements results in...The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO2 have been investigated using the first-principles calculation. Co-doping these two elements results in the local lattice distortion and volume expansion of CeO2. Compared with the energy hand structure of pure CeO2, some local energy levels appear in the forbidden band, which may facilitate the light absorption. Moreover, the enhanced photo-catalytic properties of CeO2 were explained through the absorption spectra and the selection rule of the band-to-band transitions.展开更多
基金National Natural Science Foundation of China(31270472)Specific Fund for Agro-scientific Research in the Public Interest(201203006).
文摘Aims From the light-competition hypothesis,competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light.Greater plant height provides pre-emptive access to light and produces increased height differences among species.The question is what produces these differences in plant height or height growth response among species in response to fertilization.Methods In 2009,a field experiment of N,P and N+P enrichments at three levels each was initiated in an alpine meadow on the northeast Qinghai-Tibet Plateau.Effects of fertilization on species richness,aboveground net primary production(ANPP),relative light intensity and plant height of different plant functional groups were determined.Festuca ovina(grass),Kobresia humilis(sedge),Oxytropis ochrocephala(legume),Taraxacum lugubre(rosette forb)and Geranium pylzowianum(upright forb)were selected as exemplars of each of the indicated functional groups.The N:C ratios in aboveground biomass,gibberellic acid(GA_(3))concentrations in leaves,plant heights and height relative growth rate(RGR)of these exemplar species were analyzed in detail.Important Findings Species richness of grasses significantly increased with increasing N+P levels.Species richness of legumes and upright forbs decreased after N and N+P additions.P addition had no significant effect on species richness.The effects of N+P addition on species richness and ANPP were consistently stronger than those of the single N or P fertilization.Reductions in species richness caused by nutrient addition paralleled the increases in ANPP and decreases in light intensity under the canopies,indicating indirect effect of nutrient addition on species richness via ANPP-induced light competition.The exemplar species that responded most positively to fertilization in height and RGR also displayed stronger increases in their GA_(3) content and N:C ratios.GA_(3) concentrations and N:C ratios were positively correlated with height RGR
文摘Proton exchange membrane fuel cells(PEMFCs)as promising alternatives to traditional internal combustion engines have attracted massive concerns to promote their wide application in society.However,the biggest challenge to the commercialization of PEMFCs remains the high cost due to the adoption of the platinum group metal(PGM)catalysts in the cathode.
基金supported by the National Natural Science Foundation of China(Nos.52170019 and 51973015)the Fundamental Research Funds for the Central Universities(No.06500100)the“Ten thousand plan”-National High-level Personnel of Special Support Program.National Environmental and Energy Science and Technology International Cooperation Base.
文摘Microbial fuel cells(MFCs)have a simple structure and excellent pollutant treatment and power generation performance.However,the slow kinetics of the oxygen reduction reaction(ORR)at the MFC cathode limit power generation.The electrochemical performance of MFCs can be improved through electrocatalysis.Thus far,metal-based catalysts have shown astonishing results in the field of electrocatalysis,enabling MFC devices to demonstrate power generation capabilities comparable to those of Pt,thus showing enormous potential.This article reviews the research progress of meta-based MFC cathode ORR catalysts,including the ORR reaction mechanism of MFC,different types of catalysts,and preparation strategies.The catalytic effects of different catalysts in MFC are compared and summarized.Before discussing the practical application and expanded manufacturing of catalysts,we summarize the key challenges that must be addressed when using metal-based catalysts in MFC,with the aim of providing a scientific direction for the future development of advanced materials.
基金the National Natural Science Foundation of China(22071202,21931009,and 21721001).
文摘The slow oxygen reduction process at the cathode and the scarcity of platinum-based metals lead to limited applications in fuel cells and metal-air cells.Recently,transition metal and nitrogen co-doped carbon-based catalysts(M–N–C)are regarded as the most prospective non-precious metal catalysts for future fuel cell applications.It is verified theoretically and experimentally that the metal and nitrogen coordination structure is the main catalytic activity center of oxygen reduction reaction(ORR),so constructing M–N–C materials with high available surface area and structural stability is an effective way to accelerate ORR.Herein,we deliberately synthesize a one-dimensional ZIF structure to fabricate one-dimensional porous Fe–N–C nanostick via two-step pyrolysis.Excitingly,the as-synthesized exhibited an outstanding ORR activity in alkaline medium(E_(1/2)of 0.928 V),as well as superior stability(only changed 7 mV after 10,000 cycles in alkaline medium).Our results show that the reduction of electrocatalyst dimensionality can promote mass transport and increase the accessibility of active sites,thus optimizing their performance in ORR.This work is a good demonstration of the importance of a rational design of catalyst structure for efficient ORR.
基金the National Natural Science Foundation of China(Nos.22075062 and 21871167)and the Volkswagen Foundation(Freigeist Fellowship)。
文摘NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conductivity,limited activity,durability.To address these issues,herein,by utilizing three-dimensional covalent organic framework(3D-COF)with porous confined structures and abundant coordinate N sites as the precursor,the partially oxidized Ni_(3)Fe nanoalloys wrapped by Ndoped carbon(N-C)layers are constructed via simple pyrolysis and subsequent oxidization.Benefiting from the 3D curved hierarchical structure,high-conductivity of Ni_(3)Fe and N-C layers,well-distributed active sites,the as-synthesized O-Ni_(3)Fe-NC catalyst demonstrates excellent activity and durability for catalyzing OER.Experimental and theoretical analyses disclose that both high-temperature oxidization and the OER process greatly promote the formation and exposure of the Ni(Fe)OOH active species as well as lower charge transfer resistance,inducing its optimized OER activity.The robust graphitized N-C layers with superior conductivity and their couplings with oxidized Ni_(3)Fe nanoalloys are beneficial for stabilizing catalytic centers,thereby imparting O-Ni_(3)Fe-N-C with such outstanding stability.This work not only provides a rational guidance for enriching and stabilizing high-activity catalytic sites towards OER but also offers more insights into the structural evolution of NiFe-based OER catalysts.
基金funding support from the National Natural Science Foundation of China(Nos.U2032202,22125902 and 21975243)DNL cooperation Fund,CAS(No.DNL202020)+1 种基金Fundamental Research Funds for the Central Universities(Nos.WK2060000013 and YD3430002001)Users with Excellence Program of Hefei Science Center CAS(No.2021HSC-UE002)。
文摘Single atom catalysts(SACs)with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),showing great application potential in Zn-air batteries.However,because of the complex structure-performance relationships of carbon-based SACs in the oxygen electrocatalytic reactions,the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous.In this study,SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets(M-N@Gs,M=Co,Fe and Ni),featured with similar physicochemical properties and M-N@C configurations,are obtained.By comparing the on-set potentials and the maximum current,we observed that the ORR activity is in the order of Co-N@G>Fe-N@G>Ni-N@G,while the OER activity is in the order of Co-N@G>Ni-N@G>Fe-N@G.The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G.This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants.This study could improve our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level.
文摘The benzophenone-initiated photoaddition of N-methyl ammes 2 to the chiral synthon1 proceeds in a regiospecitlc and highlyr stereocontrolled thshion to give the C-C photoadductscontaining a ne\viy stereogenic center 3a-3c. The enantiomerically pure N-C photoadducts, aminobutenolides 5a-5c have been obtained from the enantioselective photoaddition of secondary cyclicammes 4 with the chiral synthon 1 under the same conditions.
文摘Single C3N4 crystals with 1-3μm in length and 300 nm in cross area was obtained on nickel substrate.The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth was on silicon.The X-ray diffraction and transmission electron microscopy with selective-area electron diffraction give the lattice constants a=0.624 nm and c=0.236 nm for β-C3N4,and a=0.638 nm and c=0.464 8 nm for αC3N4,which are respectively 2.5% and 1.3% lower than those of the latest first-principle calculations.An N:C ratio of 1.30-1.40 was determined by energy dispersive X-ray.Based on the experimental lattice constants,the bulk modulus of the obtained β-C3N4 are in the region of 425-445 GPa.
基金the Department of International Cooperation, Hebei Province Science and Technology Research Council, China, No. 09396427D
文摘Voltage-gated potassium channels comprise 12 subtypes （Kv1-Kv12）. Kv2.1, which is expressed in most mammalian central neurons, provides the majority of delayed-rectifier K＋ current in cortical and hippocampal pyramidal neurons, and plays an especially prominent role in repolarizing membrane potential, as well as in facilitation of exocytosis. Kv2.1-encoded K＋ efflux is essential for neuronal apoptosis programming. The human form of the Kv2.1 potassium channel contains large intracellular regions. The cytoplasmic C-terminal plays a key role in modulating Kv2.1 gating. The present manuscript summarized Kv2.1 structure and modulation in neurons and analyzed the roles of the cytoplasmic C-terminal.
文摘It has been made a proposal of new ideal cycle for power plants which is working by a turbine gas, for both closed and open systems. It has been designed a special device for adding heat at constant volume. The aim of special device is to decrease the amount of added heat for the new cycle. We have made a comparison between the simple gas turbine cycle & the new cycle. The results has been shown, that the efficiency of new cycle is greater than the simple cycle of gas turbine.
基金supported by the National Natural Science Foundation of China(Nos.U19A2086,41874121,12205078).
文摘This study proposes a ladder gradient method for neutron and gamma-ray discrimination.The proposed method exhibited state-of-the-art performance with low time consumption,which incorporates two parts:information extraction and discrimination factor calculation.A quasi-continuous spiking cortical model was proposed to extract information from the radiation pulse signals,thus generating an ignition map corresponding to each pulse signal.The ignition map can be used to calculate the discrimination factor.A ladder gradient calculation was introduced to obtain a discrimination factor with low computational complexity.The proposed method was compared with five other discrimination methods to evaluate its robustness and efficacy.Furthermore,the filter adaptability of the pulse-coupled neural network and ladder gradient methods was investigated.Possible reasons for adapting the conditions with different discrimination methods and filters were analyzed.Experiments were conducted in 20 filtering situations with 11 types of filters to determine the most suitable filters for discrimination methods.The experimental results revealed that the three most adaptive filters of the pulse-coupled neural networks and ladder gradient methods are the wavelet,elliptic,and median filters and the elliptic,moving average,and wavelet filters,respectively.
基金the National Natural Science Foundation of China for financial support (Nos. 21372075 and 61376003)
文摘A family of tropos ligands bearing a N-heterocyclic carbene and a chiral oxazoline coordination group with a N-phenyl framework were easily prepared,and their coordination behavior with Pd（Ⅱ）acetate was performed,affording a series of axially chiral palladium complexes in good yields.
基金supported by the National Natural Science Foundation of China (52034011)the Key R&D Program of Shaanxi (2019ZDLGY04-05)+2 种基金the National Natural Science Foundation of Shaanxi (2020JQ-189, 2019JLM-29 and 2019JLZ-01)the Fundamental Research Funds for the Central Universities (G2020KY05129)the Research Fund of the State Key Laboratory of Solidification Processing (NPU),China (2020-BJ-03 and 2019-TS-06)
文摘Lithium carbon dioxide(Li-CO_(2))batteries deliver a theoretical energy density of 1876 W h kg^(-1) in terms of effective utilization of greenhouse gases.This battery system is considered to be an encouraging electrochemical energy storage device and a promising alternative to Li-ion batteries.However,the main drawback of Li-CO_(2) batteries is their accumulative discharge product of Li_(2)CO_(3)/C,which leads to large overpotential and poor cycling performance.Thus,specific and efficient catalysts must be explored to enhance the decomposition of Li_(2)CO_(3)/C.Single-atom catalysts(SACs)are regarded as promising heterogeneous catalysts owing to their maximized utilization of metal atoms and strong interfacial electronic interactions.Herein,single-metal atoms of Fe,Co,and Ni uniformly anchored on N-doped reduced graphene oxide(rGO),designated as Fe_(1)/N-rGO,Co1/N-rGO,and Ni_(1)/N-r GO,respectively,are designed and fabricated to investigate their catalytic activity toward the decomposition of Li_(2)CO_(3)/C.Among them,Fe_(1)/N-rGO delivers a high discharge capacity of 16,835 mA h g^(-1) at 100 mA g^(-1) and maintains stability for more than 170 cycles with a discharge voltage of 2.30 V at 400 mA g^(-1).Therefore,this catalysts are overwhelmingly superior to other types.This work reveals the advances of SACs in Li-CO_(2) batteries and offers an effective method for realizing high-performance Li-CO_(2) batteries.
基金supported by the Australian Research Council under the Future Fellowships scheme(FT160100107)。
文摘Atomically dispersed transition metal(M)and nitrogen(N)co-doped carbon(M-N-C)electrocatalysts hold excellent application potentials for several critical reactions required in electrochemical conversion processes and energy storage devices,including oxygen reduction reaction,oxygen evolution reaction,hydrogen evolution reaction,carbon dioxide reduction reaction and nitrogen reduction reaction.Despite significant progress achieved in the past few decades,their commercialization is hindered by their fast degradation.This perspective article outlines the historical development of M-N-C electrocatalysts,the current understanding of their active catalytic sites,and crucial degradation mechanisms.We highlight that many methods used to tailor M-N-C electrocatalysts likely cause contradictory effects on activity and stability.More emphasis is needed to address their degradation issues under industryrelevant working conditions.
基金the Applied Basic Research Project of Science and Technology Department of Sichuan Province(Grant No.2020YJ0418)the Youth Science and Technology Innovation Team of Southwest Petroleum University(Grant No.2018CXTD05)+1 种基金the Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation of Southwest Petroleum University(Grant No.PLN201925)the Postgraduate Research and Innovation Fund of Southwest Petroleum University(Grant No.2019cxzd027).
文摘In this work,the detailed oxygen reduction reaction(ORR)catalytic performance of M-N_(4−x)O_(x)(M=Fe,Co,and Ni;x=1−4)has been explored via the detailed density functional theory method.The results suggest that the formation energy of M-N_(4−x)O_(x)shows a good linear relationship with the number of doped O atoms.The adsorption manner of O_(2)on M-N_(4−x)O_(x)changed from end-on(x=1 and 2)to side-on(x=3 and 4),and the adsorption strength gradually increased.Based on the results for binding strength of ORR intermediates and the Gibbs free energy of ORR steps on the studied catalysts,we screened out two highly active ORR catalysts,namely Co-N_(3)O_(1)and Ni-N_(2)O_(2),which possess very small overpotentials of 0.27 and 0.32 V,respectively.Such activities are higher than the precious Pt catalyst.Electronic structure analysis reveals one of the reasons for the higher activity of Co-N_(3)O_(1)and Ni-N_(2)O_(2)is that they have small energy gaps and moderate highest occupied molecular orbital energy levels.Furthermore,the results of the density of states reveal that the O doping can improve the electronic structure of the original catalyst to tune the adsorption of the ORR intermediates.
基金supported by the Users with Excellence Program of Hefei Science Center CAS(No.2020HSC-UE012)the Comprehensive Research Facility for Fusion Technology Program of China(No.2018-000052-73-01-001228)the Institute of Energy,Hefei Comprehensive National Science Center(No.21KZS205,21KZL401).
文摘Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design of a fast-neutron detector based on the scintillating fiber (Sci-Fi) to provide D-T neutron yield through Geant4simulation. The effect on the detection performance is concerned when changing the number of the Sci-Fis embedded in the probe head, minimum distance between the fibers, length of the fibers, or substrate material of the probe head. The maximum number of scintillation photons generated by the n/γ source particles and output by the light guide within an event (event:the entire simulation process for one source particle) was used to quantify the n/γ resolution of the detector as the main basis. And the intrinsic detection efficiency was used as another evaluation criterion. The results demonstrate that the optimal design scheme is to use a 5 cm probe head whose substrate material is pure aluminum, in which 463 Sci-Fis with the same length of 5 cm are embedded, and the minimum distance between the centers of the two fibers is 2 mm. The optimized detector exhibits clear directionality in the simulation, which is in line with the expectation and experimental data provided in the literature. This study presents the variation trends of the performance of the SciFi detector when its main parameters change, which is beneficial for the targeted design and optimization of the Sci-Fi detector used in a specific radiation environment.
基金Project supported by the National Natural Science Foundation of China(Grant No.61306098)
文摘The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO2 have been investigated using the first-principles calculation. Co-doping these two elements results in the local lattice distortion and volume expansion of CeO2. Compared with the energy hand structure of pure CeO2, some local energy levels appear in the forbidden band, which may facilitate the light absorption. Moreover, the enhanced photo-catalytic properties of CeO2 were explained through the absorption spectra and the selection rule of the band-to-band transitions.
