Two-dimensional(2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo-or ...Two-dimensional(2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo-or heterojunctions, which show novel emission properties caused by interface engineering. In this review, we will first give an overview of the basic strategies that have been employed in interface engineering, including changing components, adjusting interlayer gap, and tuning twist angle. By modifying the interfacial factors, novel emission properties of emerging excitons are unveiled and discussed. Generally, well-tailored interfacial energy transfer and charge transfer within a 2D heterostructure cause static modulation of the brightness of intralayer excitons. As a special case, dynamically correlated dual-color emission in weakly-coupled bilayers will be introduced, which originates from intermittent interlayer charge transfer. For homobilayers and type Ⅱ heterobilayers, interlayer excitons with electrons and holes residing in neighboring layers are another important topic in this review. Moreover, the overlap of two crystal lattices forms moiré patterns with a relatively large period, taking effect on intralayer and interlayer excitons. Particularly, theoretical and experimental progresses on spatially modulated moiré excitons with ultra-sharp linewidth and quantum emission properties will be highlighted. Moiré quantum emitter provides uniform and integratable arrays of single photon emitters that are previously inaccessible, which is essential in quantum many-body simulation and quantum information processing. Benefiting from the optically addressable spin and valley indices, 2D heterostructures have become an indispensable platform for investigating exciton physics, designing and integrating novel concept emitters.展开更多
The trajectory of the compact torus(CT)within a tokamak discharge is crucial to fueling.In this study,we developed a penetration model with a vacuum magnetic field region to accurately determine CT trajectories in tok...The trajectory of the compact torus(CT)within a tokamak discharge is crucial to fueling.In this study,we developed a penetration model with a vacuum magnetic field region to accurately determine CT trajectories in tokamak discharges.This model was used to calculate the trajectory and penetration parameters of CT injections by applying both perpendicular and tangential injection schemes in both HL-2A and ITER tokamaks.For perpendicular injection along the tokamak's major radius direction from the outboard,CTs with the same injection parameters exhibited a 0.08 reduction in relative penetration depth when injected into HL-2A and a 0.13reduction when injected into ITER geometry when considering the vacuum magnetic field region compared with cases where this region was not considered.In addition,we proposed an optimization method for determining the CT's initial injection velocity to accurately calculate the initial injection velocity of CTs for central fueling in tokamaks.Furthermore,this paper discusses schemes for the tangential injection of CT into tokamak discharges.The optimal injection angle and CT magnetic moment direction for injection into both HL-2A and ITER were determined through numerical simulations.Finally,the kinetic energy loss occurring when the CT penetrated the vacuum magnetic field region in ITER was reduced byΔEk=975.08 J by optimizing the injection angle for the CT injected into ITER.These results provide valuable insights for optimizing injection angles in fusion experiments.Our model closely represents actual experimental scenarios and can assist the design of CT parameters.展开更多
The performance of an electrocatalyst is closely correlated with the binding strength of key oxygencontaining intermediates,i.e.,*OOH,*O and*OH,in the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).F...The performance of an electrocatalyst is closely correlated with the binding strength of key oxygencontaining intermediates,i.e.,*OOH,*O and*OH,in the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).Facile strategies to achieve favorable binding strength of these oxygen-containing species are urgently demanded,yet it still remains great challenges.Herein,the Zn-Co bimetallic isolation,which serves as an ideal model,is studied systematically by the density functional theory(DFT).Reaction activity volcano plots are built from 48 models,among them the ZnCoN6-gra(I)configuration is confirmed to be the most stable,featured of the strongest interaction with the oxygen-containing species.Optimal △G*O(free energy change of an atomic oxygen containing intermediate)is facilitated,which effectively drifts the volcano peaks of ORR and OER closer to each other,enabling promising bifunctional catalyst.Moreover,the small overpotential in the simulation of protonation and oxidation by hydroxy groups rationalizes the durability of the catalyst in both acid and alkaline media.展开更多
The nuclear mean-field potential built up during the ^(12)C+^(12)C and ^(16)O+^(16)O collisions at low energies relevant for the carbon-and oxygen-burning processes is constructed within the double-folding model(DFM) ...The nuclear mean-field potential built up during the ^(12)C+^(12)C and ^(16)O+^(16)O collisions at low energies relevant for the carbon-and oxygen-burning processes is constructed within the double-folding model(DFM) using the realistic ground-state densities of^(12)C and^(16)O, and CDM3Yn density-dependent nucleon–nucleon(NN) interaction. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus–nucleus potential predicted through this low-energy version of the DFM was tested in the optical model(OM) analysis of the elastic^(12)C+^(12)C and ^(16)O+^(16)O scattering data at energies below 10 MeV/nucleon.These OM results provide a consistently good description of the elastic angular distributions and 90 excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions very well over a wide range of energies.展开更多
Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, ...Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science.展开更多
We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to twoferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach.We first developa B1oc...We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to twoferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach.We first developa B1och-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics,and then developexplicit analytical expressions for the local magnetization,current,and its fluctuations.On this basis,we predict a novelzero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration,and asymmetric peak splitting in a magnetic field.Also,for the same system with large polarization,we find a negativezero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapidspin-reversal due to underlying spin-flip cotunneling.展开更多
High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr2RuO4.Unlike previous rep...High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr2RuO4.Unlike previous reports,which found that a high cleaving temperature can suppress the surface Fermi surface,we find that the surface Fermi surface remains obvious and strong in Sr2RuO4 cleaved at high temperature,even at room temperature.This indicates that cleaving temperature is not a key effective factor in suppressing surface bands.On the other hand,the bulk bands can be enhanced in an aged surface of Sr2RuO4 that has been cleaved and held for a long time.We have also carried out laser ARPES measurements on Sr_(2)RuO_(4) by using a vacuum ultra-violet laser (photon energy at 6.994eV) and found an obvious enhancement of bulk bands even for samples cleaved at low temperature.This information is important for realizing an effective approach to manipulating and detecting the surface and bulk electronic structure of Sr2RuO4.In particular,the enhancement of bulk sensitivity,along with the super-high instrumental resolution of VUV laser ARPES,will be advantageous in investigating fine electronic structure and superconducting properties of Sr_(2)RuO_(4) in the future.展开更多
This study develops an optimal performance monitoring metric for a hybrid free space optical and radio wireless network, the Outage Capacity Objective Function. The objective function—the dependence of hybrid channel...This study develops an optimal performance monitoring metric for a hybrid free space optical and radio wireless network, the Outage Capacity Objective Function. The objective function—the dependence of hybrid channel outage capacity upon the error rate, jointly quantifies the effects of atmospheric optical impairments on the performance of the free space optical segment as well as the effect of RF channel impairments on the radio frequency segment. The objective function is developed from the basic information-theoretic capacity of the optical and radio channels using the gamma-gamma model for optical fading and Ricean statistics for the radio channel fading. A simulation is performed by using the hybrid network. The objective function is shown to provide significantly improved sensitivity to degrading performance trends and supports of proactive link failure prediction and mitigation when compared to current thresholding techniques for signal quality metrics.展开更多
The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the stru...The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the structural domain formation in this material often complicates the study of intrinsic material properties.It is crucial to fully characterize the structural domains for unrevealing underlying physics.Here,we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence.The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal,and gives rise to a peculiar contrast.The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements.A distinct contrast in reflectance is also found in the opposite cleavage surfaces,owing to the polar mode of the RuO6 octahedra.More importantly,the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain.Such an approach provides an efficient yet feasible method for structural domain characterization,which can also find applications in noncentrosymmetric crystals in general.展开更多
Chromium (Cr) doped Zinc oxide ZnO thin films were deposited onto glass substrates by Metal Organic Chemical Vapour Deposition (MOCVD) technique with varying dopant concentration at a temperature of 420°C. The ef...Chromium (Cr) doped Zinc oxide ZnO thin films were deposited onto glass substrates by Metal Organic Chemical Vapour Deposition (MOCVD) technique with varying dopant concentration at a temperature of 420°C. The effect of the chromium concentration on morphological, structural, optical, electrical and gas sensing properties of the films were investigated. The scanning electron microscopy results revealed that the Cr concentration has great influence on the crystallinity, surface smoothness and grain size. X-ray diffraction (XRD) studies shows that films were polycrystalline in nature and grown as a hexagonal wurtzite structure. A direct optical band energy gap of 3.32 to 3.10 eV was obtained from the optical measurements. The transmission was found to decrease with increasing Cr doping concentration. Rutherford Backscattering Spectroscopy (RBS) analysis also demonstrates that Cr ions are substitutionally incorporated into ZnO. I-V characteristic of the film shows a resistivity ranges from 1.134 × 10-2 · cm to 1.24 × 10-2 · cm at room temperature. The gas sensing response of the films were enhanced with incorporation of Cr as a dopant with optimum operating temperature around 200°C.展开更多
Zinc Oxide (ZnO) and Aluminium doped ZnO (AZO) thin films were deposited on soda lime glass by Metal Organic Chemical Vapour deposition technique (MOCVD), using prepared compound mixtures of Zinc Acetate di-hydrate (Z...Zinc Oxide (ZnO) and Aluminium doped ZnO (AZO) thin films were deposited on soda lime glass by Metal Organic Chemical Vapour deposition technique (MOCVD), using prepared compound mixtures of Zinc Acetate di-hydrate (Zn(CH3COO)2⋅2H2O;ZAD) and Aluminium Acetyl-Acetonate (Al(C5H702)3;AAA) precursors at a temperature of 420°C. Effects of the varying mole percent concentrations of AAA precursor additives on the Al dopant concentrations in ZnO were systematically studied. The observations were made via investigations carried out on the morphological, optical, electrical and compositional properties of the deposited thin films. The thin films morphology was found to be strongly dependent on the varying concentration of AAA in the precursor mixtures. The average optical transmittance of the thin films in the uv-visible region was over 85% except 5 mol.% Al. While the energy band gaps were found to be in range of 3.27 - 3.36 eV. There is a blue-shift of the energy band edge observed between 0 and 5 mol.% AAA, which may be due to Burstein-Moss’ band gap widening effect and an opposing band gap renormalization effect at 10 mol.% AAA along with an extra band gap stabilization effect (Roth’s effect) at 15 mol.% AAA in rather quasi-sinusoidal or anomalous behaviour. The optical transmittance and electrical conductivity of ZnO were enhanced with addition of Al dopants. The RBS confirm the presence of Al, Zn and O, and evidence that Al dopants were successfully incorporated into the ZnO.展开更多
Positron annihilation in TiO2 rutile crystal is studied by an assumption that a positron binds with valance electrons of a titanium dioxide to form a pseudo TiO2-positron molecule before it annihilates with these elec...Positron annihilation in TiO2 rutile crystal is studied by an assumption that a positron binds with valance electrons of a titanium dioxide to form a pseudo TiO2-positron molecule before it annihilates with these electrons. The orbital modification consisting of explicit electron-positron and electron-electron correlation in each electronic orbital is used for the electrons and positron wave functions. By these wave functions, the calculation results of the positron lifetimes in unmitigated and defective TiO2 crystals are about 170 ps, 266 ps and 243 ps, respectively. These results are in good agreement with experimental data of the positron lifetimes in vacancies of TiO2 from 180 ps to 300 ps.展开更多
Graphene Oxide (GO) was chemically synthesized from Natural Flake Graphite (NFG). The GO was chemically reduced to Reduced Graphene Oxide (RGO) using hydrazine monohydrate. Thin films of GO and RGO were also deposited...Graphene Oxide (GO) was chemically synthesized from Natural Flake Graphite (NFG). The GO was chemically reduced to Reduced Graphene Oxide (RGO) using hydrazine monohydrate. Thin films of GO and RGO were also deposited on sodalime glass substrate using spray pyrolysis technique (SPT). The samples were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDS) facility attached to it, UV-Visible Spectrometry and Four-Point probe. The FTIR spectra showed the addition of oxygen functionality groups in GO while such groups was drastically reduced in RGO. SEM micrograph of GO thin film showed a porous sponge-like structure while the micrograph of RGO thin film showed evenly distributed and well connected graphene structure. The EDX spectrum of RGO showed that there was decrease in oxygen content and increase in carbon content of RGO when compared to GO. The optical analysis of the GO and RGO thin films gave a direct energy bandgap of 2.7 eV and 2.2 eV respectively. The value of sheet resistance of GO and RGO films was determined to be 22.9 × 10<sup>6</sup>Ω/sq and 4.95 × 10<sup>6</sup>Ω/sq respectively.展开更多
Starting from the groundbreaking work in graphene[1],the active research in two-dimensional(2D)layered materials has unveiled a number of exotic phenomena that are unique in the 2D limit.In addition to the semimetal g...Starting from the groundbreaking work in graphene[1],the active research in two-dimensional(2D)layered materials has unveiled a number of exotic phenomena that are unique in the 2D limit.In addition to the semimetal graphene,the semiconducting transition metal dichalcogenides(TMDs)and the insulating hexagonal boron nitride(hBN)are also the main driving forces of the field.展开更多
Ammonia borane(AB)is an excellent candidate for the chemical storage of hydrogen.However,its practical utilization for hydrogen production is hindered by the need for expensive noble-metal-based catalysts.Herein,we re...Ammonia borane(AB)is an excellent candidate for the chemical storage of hydrogen.However,its practical utilization for hydrogen production is hindered by the need for expensive noble-metal-based catalysts.Herein,we report Co-Co3O4 nanoparticles(NPs)facilely deposited on carbon dots(CDs)as a highly efficient,robust,and noble-metal-free catalyst for the hydrolysis of AB.The incorporation of the multiinterfaces between Co,Co3O4 NPs,and CDs endows this hybrid material with excellent catalytic activity(rB=6816 mLH2 min^-1 gCo^-1)exceeding that of previous non-noble-metal NP systems and even that of some noble-metal NP systems.A further mechanistic study suggests that these interfacial interactions can affect the electronic structures of interfacial atoms and provide abundant adsorption sites for AB and water molecules,resulting in a low energy barrier for the activation of reactive molecules and thus substantial improvement of the catalytic rate.展开更多
A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues ass...A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues associated with interaction between a compact torus(CT)and RFP.The key interests include fueling directly into the reactor center,confinement improvement,and the injection of momentum and helicity into the RFP discharges.The CT velocity and mass have been measured using a multichannel optical fiber interferometer,and for the first time the time evolution of the CT density profile during CT propagation is obtained.The effects of discharge parameters on the number of injected particles,CT velocity and CT density have been characterized:the maximum hydrogen CT plasma mass,m,CTis 50μg,corresponding to 30%of the mass in a typical KTX plasma;the CT velocity exceeds 120 km s-1.It is observed for the first time that multiple CTs can be produced and emitted during a very short period(<100μs)in one discharge,which is significant for the future study of repetitive CT injection,even with an ultra-high frequency.展开更多
In furtherance to improving agreement between calculated and experimental nuclear data, the nuclear reaction code GAMME was used to calculate the multistep compound(MSC) nucleus double differential cross sections(DDCs...In furtherance to improving agreement between calculated and experimental nuclear data, the nuclear reaction code GAMME was used to calculate the multistep compound(MSC) nucleus double differential cross sections(DDCs) for proton-induced neutron emission reactions using the Feshbach-Kerman-Koonin(FKK) formalism. The cross sections were obtained for reactor structural materials involving ^(52)Cr(p, n)^(52)Mn,^(56)Fe(p,n)^(56)Co, and ^(60)Ni(p, n)^(60)Cu reactions at 22.2 MeV incident energy using the zero-range reaction mechanism. Effective residual interaction strength was 28 MeV, and different optical potential parameters were used for the entrance and exit channels of the proton-neutron interactions. The calculated DDCs were fitted to experimental data at the same backward angle of 150°, where the MSC processes dominate. The calculated and experimental data agree well in the region of pre-equilibrium(MSC) reaction dominance against a weaker fit at the lower emission energies. We attribute underestimations to contributions from the other reaction channels and disagreement at higher outgoing energies to reactions to collectively excited states. Contrary to the FKK multi-step direct calculations, contributions from the higher stages to the DDCs are significant. Different sets of parameters resulted in varying levels of agreement of calculated and experimental data for the considered nuclei.展开更多
The design of the poloidal field (PF) system includes the ohmic heating field system and the equilibrium (EQ) field system, and is the basis for the design of a magnetic confinement fusion device. A coupling betwe...The design of the poloidal field (PF) system includes the ohmic heating field system and the equilibrium (EQ) field system, and is the basis for the design of a magnetic confinement fusion device. A coupling between the poloidal and plasma currents, especially the eddy current in the stabilizing shell, yields design difficulties. The effects of the eddy current in the stabilizing shell on the poloidal magnetic field also cannot be ignored. A new PF system design is thus proposed. By using a low-μ material (μ = 0.001, ε = 1) instead of a conductive shell, an electromagnetic model is established that can provide a continuous eddy current distribution on the conductive shell. In this model, a 3D time-domain problem with shells translates into a 2D magnetostatic problem, and the accuracy of the calculation is improved. Based on these current distributions, we design the PF system and analyze how the EQ coils and conductive shell affect the plasma EQ when the plasma ramps up. To meet the mainframe design requirements and achieve an efficient power-supply design, the position and connection of the poloidal coils are optimized further.展开更多
基金supported by the Natural Science Foundation of China(22203042,21873048 and 22173044)。
文摘Two-dimensional(2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo-or heterojunctions, which show novel emission properties caused by interface engineering. In this review, we will first give an overview of the basic strategies that have been employed in interface engineering, including changing components, adjusting interlayer gap, and tuning twist angle. By modifying the interfacial factors, novel emission properties of emerging excitons are unveiled and discussed. Generally, well-tailored interfacial energy transfer and charge transfer within a 2D heterostructure cause static modulation of the brightness of intralayer excitons. As a special case, dynamically correlated dual-color emission in weakly-coupled bilayers will be introduced, which originates from intermittent interlayer charge transfer. For homobilayers and type Ⅱ heterobilayers, interlayer excitons with electrons and holes residing in neighboring layers are another important topic in this review. Moreover, the overlap of two crystal lattices forms moiré patterns with a relatively large period, taking effect on intralayer and interlayer excitons. Particularly, theoretical and experimental progresses on spatially modulated moiré excitons with ultra-sharp linewidth and quantum emission properties will be highlighted. Moiré quantum emitter provides uniform and integratable arrays of single photon emitters that are previously inaccessible, which is essential in quantum many-body simulation and quantum information processing. Benefiting from the optically addressable spin and valley indices, 2D heterostructures have become an indispensable platform for investigating exciton physics, designing and integrating novel concept emitters.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2022YFE03100004 and 2022YFE03060003)National Natural Science Foundation of China(Nos.12375226,12175227 and 11875255)the China Postdoctoral Science Foundation(No.2022M723066).
文摘The trajectory of the compact torus(CT)within a tokamak discharge is crucial to fueling.In this study,we developed a penetration model with a vacuum magnetic field region to accurately determine CT trajectories in tokamak discharges.This model was used to calculate the trajectory and penetration parameters of CT injections by applying both perpendicular and tangential injection schemes in both HL-2A and ITER tokamaks.For perpendicular injection along the tokamak's major radius direction from the outboard,CTs with the same injection parameters exhibited a 0.08 reduction in relative penetration depth when injected into HL-2A and a 0.13reduction when injected into ITER geometry when considering the vacuum magnetic field region compared with cases where this region was not considered.In addition,we proposed an optimization method for determining the CT's initial injection velocity to accurately calculate the initial injection velocity of CTs for central fueling in tokamaks.Furthermore,this paper discusses schemes for the tangential injection of CT into tokamak discharges.The optimal injection angle and CT magnetic moment direction for injection into both HL-2A and ITER were determined through numerical simulations.Finally,the kinetic energy loss occurring when the CT penetrated the vacuum magnetic field region in ITER was reduced byΔEk=975.08 J by optimizing the injection angle for the CT injected into ITER.These results provide valuable insights for optimizing injection angles in fusion experiments.Our model closely represents actual experimental scenarios and can assist the design of CT parameters.
基金the National Natural Science Foundation of China(No.21403185 and 51774251)the Hebei Natural Science Foundation for Distinguished Young Scholars(B2017203313)the Hundred Excellent Innovative Talents Support Program in Hebei Province(SLRC2017057)for financial support。
文摘The performance of an electrocatalyst is closely correlated with the binding strength of key oxygencontaining intermediates,i.e.,*OOH,*O and*OH,in the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).Facile strategies to achieve favorable binding strength of these oxygen-containing species are urgently demanded,yet it still remains great challenges.Herein,the Zn-Co bimetallic isolation,which serves as an ideal model,is studied systematically by the density functional theory(DFT).Reaction activity volcano plots are built from 48 models,among them the ZnCoN6-gra(I)configuration is confirmed to be the most stable,featured of the strongest interaction with the oxygen-containing species.Optimal △G*O(free energy change of an atomic oxygen containing intermediate)is facilitated,which effectively drifts the volcano peaks of ORR and OER closer to each other,enabling promising bifunctional catalyst.Moreover,the small overpotential in the simulation of protonation and oxidation by hydroxy groups rationalizes the durability of the catalyst in both acid and alkaline media.
基金supported,in part,by the National Foundation for Scientific and Technological Development(NAFOSTED Project No.103.04-2017.317)
文摘The nuclear mean-field potential built up during the ^(12)C+^(12)C and ^(16)O+^(16)O collisions at low energies relevant for the carbon-and oxygen-burning processes is constructed within the double-folding model(DFM) using the realistic ground-state densities of^(12)C and^(16)O, and CDM3Yn density-dependent nucleon–nucleon(NN) interaction. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus–nucleus potential predicted through this low-energy version of the DFM was tested in the optical model(OM) analysis of the elastic^(12)C+^(12)C and ^(16)O+^(16)O scattering data at energies below 10 MeV/nucleon.These OM results provide a consistently good description of the elastic angular distributions and 90 excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions very well over a wide range of energies.
文摘Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science.
基金The project supported by National Natural Science Foundation of Chinathe Shanghai Municipal Commission of Science and Technology+2 种基金the Shanghai Pujiang Programthe Program for New Century Excellent Talents in Universities (NCET)NJMH is supported by the DURINT program administered by the US Army Research Office, DAAD Grant No. 19-O1-1-0592
文摘We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to twoferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach.We first developa B1och-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics,and then developexplicit analytical expressions for the local magnetization,current,and its fluctuations.On this basis,we predict a novelzero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration,and asymmetric peak splitting in a magnetic field.Also,for the same system with large polarization,we find a negativezero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapidspin-reversal due to underlying spin-flip cotunneling.
基金Support by the National Natural Science Foundation of China under Grant Nos 10734120 and 91021006the National Basic Research Program of China under Grant Nos 2011CB921703 and 2011CB605903.
文摘High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr2RuO4.Unlike previous reports,which found that a high cleaving temperature can suppress the surface Fermi surface,we find that the surface Fermi surface remains obvious and strong in Sr2RuO4 cleaved at high temperature,even at room temperature.This indicates that cleaving temperature is not a key effective factor in suppressing surface bands.On the other hand,the bulk bands can be enhanced in an aged surface of Sr2RuO4 that has been cleaved and held for a long time.We have also carried out laser ARPES measurements on Sr_(2)RuO_(4) by using a vacuum ultra-violet laser (photon energy at 6.994eV) and found an obvious enhancement of bulk bands even for samples cleaved at low temperature.This information is important for realizing an effective approach to manipulating and detecting the surface and bulk electronic structure of Sr2RuO4.In particular,the enhancement of bulk sensitivity,along with the super-high instrumental resolution of VUV laser ARPES,will be advantageous in investigating fine electronic structure and superconducting properties of Sr_(2)RuO_(4) in the future.
文摘This study develops an optimal performance monitoring metric for a hybrid free space optical and radio wireless network, the Outage Capacity Objective Function. The objective function—the dependence of hybrid channel outage capacity upon the error rate, jointly quantifies the effects of atmospheric optical impairments on the performance of the free space optical segment as well as the effect of RF channel impairments on the radio frequency segment. The objective function is developed from the basic information-theoretic capacity of the optical and radio channels using the gamma-gamma model for optical fading and Ricean statistics for the radio channel fading. A simulation is performed by using the hybrid network. The objective function is shown to provide significantly improved sensitivity to degrading performance trends and supports of proactive link failure prediction and mitigation when compared to current thresholding techniques for signal quality metrics.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2019YFA0308602 and 2016YFA0300500)the National Natural Science Foundation of China(Grant Nos.11804220,11774305 and 11974237)Natural Science Foundation of Shanghai(Grant No.20ZR1428900).
文摘The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the structural domain formation in this material often complicates the study of intrinsic material properties.It is crucial to fully characterize the structural domains for unrevealing underlying physics.Here,we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence.The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal,and gives rise to a peculiar contrast.The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements.A distinct contrast in reflectance is also found in the opposite cleavage surfaces,owing to the polar mode of the RuO6 octahedra.More importantly,the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain.Such an approach provides an efficient yet feasible method for structural domain characterization,which can also find applications in noncentrosymmetric crystals in general.
文摘Chromium (Cr) doped Zinc oxide ZnO thin films were deposited onto glass substrates by Metal Organic Chemical Vapour Deposition (MOCVD) technique with varying dopant concentration at a temperature of 420°C. The effect of the chromium concentration on morphological, structural, optical, electrical and gas sensing properties of the films were investigated. The scanning electron microscopy results revealed that the Cr concentration has great influence on the crystallinity, surface smoothness and grain size. X-ray diffraction (XRD) studies shows that films were polycrystalline in nature and grown as a hexagonal wurtzite structure. A direct optical band energy gap of 3.32 to 3.10 eV was obtained from the optical measurements. The transmission was found to decrease with increasing Cr doping concentration. Rutherford Backscattering Spectroscopy (RBS) analysis also demonstrates that Cr ions are substitutionally incorporated into ZnO. I-V characteristic of the film shows a resistivity ranges from 1.134 × 10-2 · cm to 1.24 × 10-2 · cm at room temperature. The gas sensing response of the films were enhanced with incorporation of Cr as a dopant with optimum operating temperature around 200°C.
文摘Zinc Oxide (ZnO) and Aluminium doped ZnO (AZO) thin films were deposited on soda lime glass by Metal Organic Chemical Vapour deposition technique (MOCVD), using prepared compound mixtures of Zinc Acetate di-hydrate (Zn(CH3COO)2⋅2H2O;ZAD) and Aluminium Acetyl-Acetonate (Al(C5H702)3;AAA) precursors at a temperature of 420°C. Effects of the varying mole percent concentrations of AAA precursor additives on the Al dopant concentrations in ZnO were systematically studied. The observations were made via investigations carried out on the morphological, optical, electrical and compositional properties of the deposited thin films. The thin films morphology was found to be strongly dependent on the varying concentration of AAA in the precursor mixtures. The average optical transmittance of the thin films in the uv-visible region was over 85% except 5 mol.% Al. While the energy band gaps were found to be in range of 3.27 - 3.36 eV. There is a blue-shift of the energy band edge observed between 0 and 5 mol.% AAA, which may be due to Burstein-Moss’ band gap widening effect and an opposing band gap renormalization effect at 10 mol.% AAA along with an extra band gap stabilization effect (Roth’s effect) at 15 mol.% AAA in rather quasi-sinusoidal or anomalous behaviour. The optical transmittance and electrical conductivity of ZnO were enhanced with addition of Al dopants. The RBS confirm the presence of Al, Zn and O, and evidence that Al dopants were successfully incorporated into the ZnO.
文摘Positron annihilation in TiO2 rutile crystal is studied by an assumption that a positron binds with valance electrons of a titanium dioxide to form a pseudo TiO2-positron molecule before it annihilates with these electrons. The orbital modification consisting of explicit electron-positron and electron-electron correlation in each electronic orbital is used for the electrons and positron wave functions. By these wave functions, the calculation results of the positron lifetimes in unmitigated and defective TiO2 crystals are about 170 ps, 266 ps and 243 ps, respectively. These results are in good agreement with experimental data of the positron lifetimes in vacancies of TiO2 from 180 ps to 300 ps.
文摘Graphene Oxide (GO) was chemically synthesized from Natural Flake Graphite (NFG). The GO was chemically reduced to Reduced Graphene Oxide (RGO) using hydrazine monohydrate. Thin films of GO and RGO were also deposited on sodalime glass substrate using spray pyrolysis technique (SPT). The samples were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDS) facility attached to it, UV-Visible Spectrometry and Four-Point probe. The FTIR spectra showed the addition of oxygen functionality groups in GO while such groups was drastically reduced in RGO. SEM micrograph of GO thin film showed a porous sponge-like structure while the micrograph of RGO thin film showed evenly distributed and well connected graphene structure. The EDX spectrum of RGO showed that there was decrease in oxygen content and increase in carbon content of RGO when compared to GO. The optical analysis of the GO and RGO thin films gave a direct energy bandgap of 2.7 eV and 2.2 eV respectively. The value of sheet resistance of GO and RGO films was determined to be 22.9 × 10<sup>6</sup>Ω/sq and 4.95 × 10<sup>6</sup>Ω/sq respectively.
文摘Starting from the groundbreaking work in graphene[1],the active research in two-dimensional(2D)layered materials has unveiled a number of exotic phenomena that are unique in the 2D limit.In addition to the semimetal graphene,the semiconducting transition metal dichalcogenides(TMDs)and the insulating hexagonal boron nitride(hBN)are also the main driving forces of the field.
基金financially supported by the National Natural Science Foundation of China(21774041 and 51433003)the China Postdoctoral Science Foundation(2018M640681 and 2019T120632)。
文摘Ammonia borane(AB)is an excellent candidate for the chemical storage of hydrogen.However,its practical utilization for hydrogen production is hindered by the need for expensive noble-metal-based catalysts.Herein,we report Co-Co3O4 nanoparticles(NPs)facilely deposited on carbon dots(CDs)as a highly efficient,robust,and noble-metal-free catalyst for the hydrolysis of AB.The incorporation of the multiinterfaces between Co,Co3O4 NPs,and CDs endows this hybrid material with excellent catalytic activity(rB=6816 mLH2 min^-1 gCo^-1)exceeding that of previous non-noble-metal NP systems and even that of some noble-metal NP systems.A further mechanistic study suggests that these interfacial interactions can affect the electronic structures of interfacial atoms and provide abundant adsorption sites for AB and water molecules,resulting in a low energy barrier for the activation of reactive molecules and thus substantial improvement of the catalytic rate.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2017YFE0301700 and 2017YFE0301701)National Natural Science Foundation of China(Nos.11875255,11635008,11375188 and 11975231)。
文摘A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues associated with interaction between a compact torus(CT)and RFP.The key interests include fueling directly into the reactor center,confinement improvement,and the injection of momentum and helicity into the RFP discharges.The CT velocity and mass have been measured using a multichannel optical fiber interferometer,and for the first time the time evolution of the CT density profile during CT propagation is obtained.The effects of discharge parameters on the number of injected particles,CT velocity and CT density have been characterized:the maximum hydrogen CT plasma mass,m,CTis 50μg,corresponding to 30%of the mass in a typical KTX plasma;the CT velocity exceeds 120 km s-1.It is observed for the first time that multiple CTs can be produced and emitted during a very short period(<100μs)in one discharge,which is significant for the future study of repetitive CT injection,even with an ultra-high frequency.
文摘In furtherance to improving agreement between calculated and experimental nuclear data, the nuclear reaction code GAMME was used to calculate the multistep compound(MSC) nucleus double differential cross sections(DDCs) for proton-induced neutron emission reactions using the Feshbach-Kerman-Koonin(FKK) formalism. The cross sections were obtained for reactor structural materials involving ^(52)Cr(p, n)^(52)Mn,^(56)Fe(p,n)^(56)Co, and ^(60)Ni(p, n)^(60)Cu reactions at 22.2 MeV incident energy using the zero-range reaction mechanism. Effective residual interaction strength was 28 MeV, and different optical potential parameters were used for the entrance and exit channels of the proton-neutron interactions. The calculated DDCs were fitted to experimental data at the same backward angle of 150°, where the MSC processes dominate. The calculated and experimental data agree well in the region of pre-equilibrium(MSC) reaction dominance against a weaker fit at the lower emission energies. We attribute underestimations to contributions from the other reaction channels and disagreement at higher outgoing energies to reactions to collectively excited states. Contrary to the FKK multi-step direct calculations, contributions from the higher stages to the DDCs are significant. Different sets of parameters resulted in varying levels of agreement of calculated and experimental data for the considered nuclei.
基金supported by the National Magnetic Confinement Fusion Research Program of China (2011GB106000)
文摘The design of the poloidal field (PF) system includes the ohmic heating field system and the equilibrium (EQ) field system, and is the basis for the design of a magnetic confinement fusion device. A coupling between the poloidal and plasma currents, especially the eddy current in the stabilizing shell, yields design difficulties. The effects of the eddy current in the stabilizing shell on the poloidal magnetic field also cannot be ignored. A new PF system design is thus proposed. By using a low-μ material (μ = 0.001, ε = 1) instead of a conductive shell, an electromagnetic model is established that can provide a continuous eddy current distribution on the conductive shell. In this model, a 3D time-domain problem with shells translates into a 2D magnetostatic problem, and the accuracy of the calculation is improved. Based on these current distributions, we design the PF system and analyze how the EQ coils and conductive shell affect the plasma EQ when the plasma ramps up. To meet the mainframe design requirements and achieve an efficient power-supply design, the position and connection of the poloidal coils are optimized further.