bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress of refactoring first principle package of Beijing Simulation Tool for Atom TEchnology
Authors: Ma Ying-Jin , Zhang Tan , He Lian-Hua , Jin Zhong ,   Computer Network Information Center, Chinese Academy of Science, Beijing 100190, China,   Center of Scientific Computing Applications & Research, Chinese Academy of Science, Beijing 100190, China,   Beijing National Research Center for Condensed Matter Physics, Institute of Physics, Chinese Academy of Science, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The development of first principle methods can represent the summit of the sciences in the material computing and molecular modeling, and the corresponding first principle software packages are closely related with the accumulation of theories and algorithms in this field. In this paper, we reported our recent progress in refactoring the first principle package BSTATE. The key points in the reconstruction are lowering the doorsill, extending the scope of application, as well as adjusting package to the popular computer hardware. And as such, we updated the Makefile system to the new CMake system, in which the GUI can be used and many math libraries can be configured automatically; we added the support for the Libxc library, in which a large quantity of density functionals are included; we updated the interface for supporting GPU, in order to support the heterogeneous computing system. After refactoring, the Makefile system of BSTATE can supply both the Makefile and CMake system, and the Fourier transform libraries such as FFTW2, FFTW3, and Cufftw, the math libraries such as Intel MKL library, Openblas, and the density functional library such as Libxc, can be automatically or manually assigned. The integration of FFTW3 can slightly prompt the calculating efficiency in Intel’s many integrated core (MIC) architecture, and the integration of Cufftw can supply the initial support for the graphics processing unit (GPU) architecture, respectively. The usage of Libxc library makes the BSTATE package has the capacity to use hundreds density functionals, and the usages of various functionals were demonstrated by calculating the density of states of GaAs compound. Beyond the integration of various libraries, the parallel performance of BSTATE was also investigated. It can be found that the Fourier transformation and the solving for the eigenvalue equations are the major contributions. Using the tuning and analysis utilities (TAU) tool, we found that the tasks can be well distributed in modern HPC clusters. It implied that the refactoring didn’t affect the parallel efficiency of original BSTATE package. In a following benchmark test of graphene fragments, one can found that the refactored BSTATE package showed the best performance, its FFTW3 & Libxc version owns about 0–17% acceleration comparing to that of FFTW2 version.
Prediction of short range order in high-entropy alloys and its effect on the electronic, magnetic and mechanical properties
Authors: Ren Xian-Li , Zhang Wei-Wei , Wu Xiao-Yong , Wu Lu , Wang Yue-Xia ,   Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433, China,   The First Sub-Institute, Nuclear Power Institute of China, Chengdu 610005, China
Published: December 2020

The prediction of stable state of high-entropy alloys (HEAs) is crucial to obtain fundamental insight to the excellent properties of HEAs. Taking a FeCuCrMnMo alloy as a case study, we combined Monte Carlo (MC) method with the density functional thoery (DFT) calculations (MC/DFT) to predict the equilibrium structure of high-entropy alloys in a finite unit cell. Instead of approaching the ideal random state obtained from special quasi-random approximation (SQS) method, physical factors such as atomic size, mixing enthalpy of atomic pairs, and interatomic interactions in the alloy are fully considered and implemented in our simulation by MC/DFT calculations. MC codes ensure the energy convergence of the system to the equilibrium state through the atom exchange process. The equilibrium structures exhibit Cu-rich short-range orders (SRO), which is consistent with the observation in experiments. Comparing with ideal random state structure, SRO structure is more stable in energy, and more closely packed in atomic arrangement. Moreover, the analyses of order parameters and radial distribution functions (RDFs) are performed to character the structure of high-entropy alloy. The order parameter of Cu-Cu atomic pair reaches to –0.53 in the SRO equilibrium structure, which indicates that Cu-rich regions appear in the alloy. The RDFs show that the atomic distance distribution of the SRO structure is between 2.25 Å to 2.7 Å, which is smaller than the range of 2.16 Å to 2.84 Å in the SQS structure, indicating that the lattice distortions is relatively small in the SRO structure after structural optimization. The appearing of SRO phenomena is attributed to the inherent characteristics of atoms, including (i) atomic size, (ii) interatomic mixing enthalpy and (iii) the interaction of atoms. Atomic sizes in the FeCuCrMnMo alloy are in the order of Fe (11.78) < Cu (11.81) < Cr (11.97) < Mn (14.38) < Mo (15.58), in unit of Å3/atom. The relatively large sizes of Mn and Mo atoms should disadvantage the pairing of Mo-Mo and Mn-Mn. The mixing enthalpy of Cu with other atoms are all positive values, indicating that Cu is not favor of pairing other elements and precipitate itself. The analyses of density of state (DOS) and Crystal Orbital Hamilton Population (COHP) also support the results. The reason is exactly attributed to the inactive valence electrons of Cu. Furthermore, the effect of SRO on the magnetic and mechanical properties are investigated. The existence of SRO decreases the mean value of magnetic moment, and results in an increase of elastic moduli (B, G and E) and a decrease in the ductility and anisotropy properties.
Interaction between monodisperse fine particles in a standing wave acoustic field
Authors: Qu Guang-Ning , Fan Feng-Xian , Zhang Si-Hong , Su Ming-Xu ,   School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China,   Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China,   Division of Thermo Engineering and Energy Sources Measurement Technology, Shanghai Institute of Measurement and Testing Technology, Shanghai 201203, China
Published: December 2020

The external acoustic field can be used to promote the interactions between fine particles suspended in the gas phase. Due to the particle interaction, collision and agglomeration between fine particles occur, causing the average particle size to increase and the particle number concentration to decrease. This offers an important technical route to controlling the emissions of fine particles. However, the interaction behaviors between the fine particles under the acoustic field are still not well understood, which severely hinders the technology from developing for fine particle emission control by using acoustic agglomeration. In order to reveal the interaction between monodisperse fine particles in a standing wave acoustic field, a particle interaction model with consideration of the drag force, gravity and acoustic wake effect is developed. The particle motion equations in the model are solved by using the classical Runge-Kutta method combined with the second-order implicit Adams interpolation method. The particle velocity due to acoustic entrainment and the interaction process between particles obtained from the numerical simulation are compared with the corresponding analytical solutions and experimental results to validate the accuracy of model prediction. Good agreement is found, which indicates that the model and the numerical method are capable of accurately predicting the interaction between fine particles in the standing wave acoustic field. On this basis, the effects of initial conditions and diameters of particles on the interaction behaviors are explored. The results show that when the initial particle centerline is closer to the acoustic wave direction or the initial particle position is closer to the wave antinode, the acoustic wake effect between the particles becomes stronger, and shorter time is required for particles to collide. It is also found that the influence of particle diameter on particle interaction depends on the initial deviation of particle centerline from the acoustic wave direction. When the deviation is small, the larger the particle diameter, the shorter the time required for particles to collide is. When the deviation is large, the collision between particles with smaller diameters occurs, while the collision between particles with larger diameters may not occur.
Numerical simulation of shear-thinning droplet impact on surfaces with different wettability
Authors: Shen Xue-Feng , Cao Yu , Wang Jun-Feng , Liu Hai-Long ,   School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

Controlling impact dynamics of droplets on solid surfaces is a significant problem in a variety of applications, such as inkjet printing, spray cooling and coating and so on. Most of fluids used in industries always contain various kinds of additives such as surfactants, polymers and particles. Therefore, these fluids exhibit non-Newtonian behaviors, for instance, yield-stress, viscoelastic, shear-thickening and shear-thinning. The impact dynamics of Newtonian droplets on solid surfaces has been extensively investigated. However, the number of researches about fluids with non-Newtonian properties is comparatively very small. In this work, we employ the finite element scheme coupled with level set method to simulate the impact process of droplets on solid surfaces. The numerical simulation models the presence of shear-thinning viscosity by using the truncated power-law rheological model. We first conduct a mesh convergence study and verify the numerical model. The simulation results are found to be in good agreement with experimental data in the literature. By performing extensive numerical simulations and varying the rheological parameters and surface wettabilities, the influences of these parameters on the impact dynamics are evaluated, and the dominant effects that govern the spreading and receding process are determined. The simulation results show that for the case of droplet impacting on surface with contact angle θ = 55°, the spreading is stronger with power-law index decreasing as evidenced by larger shape deformation and faster interface moving speed. As power-law index decreases, we expect the maximum dimensionless diameter to increase and the minimum dimensionless height to decrease during inertial spreading. For the case of droplet with lower power-law index (m = 0.85 and 0.80), which indicates lower viscous dissipation during impact, the dimensionless parameters have significant differences. After first receding, the impacting droplet is not balanced any more and it starts to spread again until its kinetic energy is completely damped by fluid viscous dissipation. For the case of droplet (m = 0.80) impacting on surface, the center breakage can be observed during droplet spreading, which results from the effect of strong shear-thinning property. When a shear-thinning droplet impacts on a surface with contact angle θ = 100°, the oscillation behavior can be observed and the oscillation amplitude increases as power law index decreases. Bouncing phenomenon can be observed when a droplet impacts on surface with contact angle θ = 160°, regardless of rheological property. Finally, we propose an empirical model to predict the maximum dimensionless diameter of shear-thinning droplet impacting on the surface with contact angle θ = 55° as a function of non-Newtonian Reynolds number Ren.
Nonlinear mechanism of excitatory autapse-induced reduction or enhancement of firing frequency of neuronal bursting
Authors: Hua Hong-Tao , Lu Bo , Gu Hua-Guang ,   School of Mathematical Science, Henan Institute of Science and Technology, Xinxiang 453003, China,   School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China
Published: December 2020

Excitatory and inhibitory effect always induces the enhancement and inhibitory effect of neural electronic activities, which is the common viewpoint of the modulations to the neural firing and plays important roles in the information processing of the nervous system. In the present paper, the Homoclinic/Homoclinic bursting pattern with alternation behavior between burst containing multiple spikes and subthreshold oscillations and the tough value of the burst lower than that of the subthreshold oscillations is chosen as representative, and the excitatory effect on the complex nonlinear dynamics of the representative bursting pattern is studied. For the excitatory autapse with suitable autaptic time delay and strength, the autaptic current pulse applied to the trough of the burst can induce the number of spikes within a burst to decrease and then the average firing frequency to decline, which presents a novel example different from the common viewpoint of the excitatory effect. The excitatory autapse induces the average firing frequency to increase in the remained parameter region of two-parameter plane of the autaptic time delay and strength. With bifurcations acquired by the fast/slow variable dissection method and phase trajectory, the subthreshold oscillations of the bursting correspond to a subthreshold limit cycle of the fast subsystem and the spike within burst corresponds to a suprathreshold limit cycle, and excitatory autaptic current can induce the transition from suprathreshold limit cycle to subthreshold limit cycle, which leads the spike to terminate in advance and is the cause for reducing the average firing frequency. The results is the present paper are compared with the phenomenon and bifurcation mechanism that the excitatory autapse can induce the spike number to decrease within a burst but the average firing frequency to increase as indicated in a recent study on the Fold/Homoclinic bursting. These results enrich the uncommon phenomenon of the neuronal electrical activities, reveal the underlying nonlinear mechanism, provide a new way to regulate the bursting pattern, and disclose the potential functions of the excitatory autapse.
Experimental investigation of lower hybrid current drive induced plasma rotation on the experimental advanced superconducting tokamak
Authors: Yang Jin , Chen Jun , Wang Fu-Di , Li Ying-Ying , Lyu Bo , Xiang Dong , Yin Xiang-Hui , Zhang Hong-Ming , Fu Jia , Liu Hai-Qing , Zang Qing , Chu Yu-Qi , Liu Jian-Wen , Wang Xun-Yu , Bin Bin , He Liang , Wan Shun-Kuan , Gong Xue-Yu , Ye Min-You ,   School of Nuclear Science and Technology, University of South China, Hengyang 421001, China,   Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China,   Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China,   School of Electrical Engineering, University of South China, Hengyang 421001, China
Published: December 2020

Rotation and its shear can reduce the magnetohydrodynamic instabilities and enhance the confinement. The LHCD has been proposed as a possible means of rotation driving on a future fusion reactor. Exploring the mechanisms of LHCD rotation driving on the current tokamaks can provide important reference for future reactors. On EAST, it was previously shown that 2.45 GHz LHCD can drive plasma toroidal rotation and the change of edge plasma rotation leads the co-current core rotation to increase. At higher frequency, 4.6 GHz lower hybrid wave can more effectively drive co-current plasma toroidal rotation. On EAST, at the lower current, the effects of different LHCD power on plasma toroidal rotation are analyzed. Higher power LHCD has a better driving efficiency. The effect of safety factor (q) profile on toroidal rotation is also presented. The LHCD can change the profile of safety factor due to current drive. It is found that when the power exceeds 1.4MW, the q profile remains unchanged and the rotation changes only very slightly with LHCD power, suggesting that the current profile is closely related to rotation. In order to further analyze the dynamic process of plasma toroidal rotation driven by lower hybrid current drive on EAST, the toroidal momentum transport due to LHCD is deduced by using the modulated LHCD power injection. Based on the momentum balance equation, the toroidal momentum diffusion coefficient (χφ) and the toroidal momentum pinch coefficient (Vpinch) are obtained by the method of separation of variables and Fourier analysis for the region where the external momentum source can be ignored. It is found that the momentum diffusion coefficient (χφ) and momentum pinch coefficient (Vpinch) tend to increase from the core to the outer region. This is consistent with the characteristic that the toroidal rotation velocity first changes in the outer region and then propagates to the core when the toroidal rotation is driven by LHCD.
Study on the effect of thermal annealing process on ohmic contact performance of AuGeNi/n-AlGaInP
Authors: Wang Su-Jie , Li Shu-Qiang , Wu Xiao-Ming , Chen Fang , Jiang Feng-Yi ,   National Institute of LED on Si Substrate, Nanchang University, Nanchang 330047, China
Published: December 2020

In this paper, Ni/Au/Ge/Ni/Au laminated metals were deposited on the n-(Al0.27Ga0.73)0.5In0.5P by electron beam evaporation, the ohmic contact with low contact resistance was successfully prepared by optimized annealing process. The specific contact resistance reached 1.4 × 10–4 Ω·cm2 when annealed at 445 ℃ for 600 s. The result of the secondary ion mass spectrometer shows that the solid-state reaction takes place at the interface between the laminated metal Ni/Au/Ge/Ni/Au and n-AlGaInP, then the germanium atoms and indium atoms diffuse outwards due to thermal decomposition and leave vacancies in the lattice. In this paper, the reason for the formation of ohmic contact is attributed to the fact that the germanium vacancy and indium vacancy are occupied by gallium atoms as donors to increasing the N-type doping concentration. The optimized annealing process can improve the ohmic contact performance of n-(Al0.27Ga0.73)0.5In0.5P with low doping concentration, but the specific contact resistivity has no obvious relationship with the annealing process when the of doping concentration of n-(Al0.27Ga0.73)0.5In0.5P increased. The Schottky barrier is high at low doping concentration of n-(Al0.27Ga0.73)0.5In0.5P. So inter diffusion in the annealing process could significantly increase the doping concentration of n-(Al0.27Ga0.73)0.5In0.5P and reduce the Schottky barrier height. Nevertheless, the Schottky barrier of the sample with high doping concentration is low enough what is not sensitive with inter diffusion. It provides a new method for the preparation of N-electrode of AlGaInP thin film light-emitting-diodes chip, as so as avoid the problem of n+-GaAs absorption in the conventional N-electrode preparation method and the problem of electrode dropping. However, there are still some shortcomings in this paper. The disadvantage is that the high doping concentration of n-AlGaInP will affect the crystal quality, which will reduce the luminous efficiency of LED. Therefore, in order to prepare ohmic contact with excellent properties on n-AlGaInP with lower doping concentration, optimizing the electrode design and the surface treatment of semiconductor materials are the keys to follow-up research.
Numerical simulation of gas-liquid two-phase flow in gas lift system
Authors: Zuo Juan-Li , Yang Hong , Wei Bing-Qian , Hou Jing-Ming , Zhang Kai ,   State Key Labortory of Eco-hydraulic in Northwest Arid Region of China, Xi’an University of Technology, Xi’an 710048, China
Published: December 2020

The gas-lift system has a lot of significant advantages in sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters. The densities of different liquid media and gas media have great influences on the performance of gas lift system. Therefore, based on Fluent simulation software, using Euler model and k-ω SST (shear stress transport) turbulence model, the gas-liquid two-phase flow behaviors in nitrogen-water, nitrogen-kerosene, nitrogen-mercury and air-water, argon-water, nitrogen-water of gas lift system are studied. The rules of gas volume fraction and liquid flow rate at lifting pipe, liquid radial velocity at lifting pipe outlet, promoting efficiency are analyzed. The results are shown as follows. 1) In the nitrogen-water, nitrogen-kerosene and nitrogen-mercury system, the higher the density of liquid medium, the smaller the gas volume fraction in the lifting pipe is; the greater the flow rate of lifting liquid, the higher the promoting efficiency is. 2) In the air-water, argon-water and nitrogen-water systems, the higher the density of gas medium, the smaller the gas volume fraction in the lifting pipe is; the larger the flow rate of lifting liquid, the smaller the peak value of promoting efficiency is. 3) With the increase of gas flow rate, the liquid radial velocity at the lifting pipe outlet increases with overall fluctuation rising. Finally, the liquid velocity near the center of pipe axis is large, near the pipe wall is small. These research results provide the scientific theoretical basis for optimizing the gas lifting technology in applications such as sewage treatment, deep well oil recovery, liquid metal cooled reactor and magnetohydrodynamic power converters.
Reverse osmotic characteristics and mechanism of hydrogenated porous graphene
Authors: Zhang Zhong-Qiang , Yu Fan-Shun , Liu Zhen , Zhang Fu-Jian , Cheng Guang-Gui ,   Institute of Intelligent Flexible Mechatronics, Jiangsu University, Zhenjiang 212013, China,   School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China,   State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Graphene-based materials have aroused great interest for their potential applications in water desalination and purification membranes attributed to their ultrathin thickness, high mechanical strength, and anti-foiling properties. Reverse osmosis (RO) technology is currently the most progressive, energy-saving and efficient separation technology by membranes, therefore the new materials with high strength, strong pollution resistance and excellent performance are urgently needed. The ability of porous graphene to serve as a kind of novel advanced RO membrane is due to two major potential strengths of this atomically thin two-dimensional material, i.e., ultrahigh permeability and super selectivity. Thus, the reverse osmotic properties of the porous graphene membranes should be further investigated theoretically. In this paper, classical molecular dynamics method is used to investigate the reverse osmosis characteristics of brine in hydrogenated porous graphene reverse osmosis membrane. The results show that the water permeation rate increases with the driving force, pore size and temperature increasing, for the pore diameter larger than the hydration radius. The ion rejection rate decreases with the driving force and temperature increasing. Interestingly, as the porous graphene moves in the tangential direction to perform a shearing process, the interception rate of the salt ions can be effectively improved and the concentration difference polarization phenomenon can be reduced with the tangential velocity increasing, although the water flux decreases slightly. The influence mechanism of each parameter on permeability and on water flux are explored by analyzing the hydrogen bond distribution, the ionic hydration in feed solution, and the energy barrier of the water molecules in penetrating process. In order to further evaluate the effects of various parameter changes on the benefits of reverse osmosis membranes, both the selectivity and permeability are calculated to evaluate the tradeoff between permeability and selectivity, indicating that the increase of the pore diameter can obtain both high permeability and selectivity under the shearing circumstance of the membrane. The research results in this paper will provide a theoretical understanding of porous graphene-based desalination membrane and also may be helpful in designing the shearing graphene-based water filtration devices.
Structure, magnetic and transport properties of Fe3O4 near verwey transition
Authors: Liu Xiang , Mi Wen-Bo ,   Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, School of Science, Tianjin University, Tianjin 300354, China
Published: December 2020

As the first known metal-insulator transition, Verwey transition of Fe3O4 attracts much attention due to its fascinating physics. With the decreasing temperature across Verwey temperature, Fe3O4 undergoes the transition of lattice distortion, charge ordering, electricity, magnetic anisotropy, etc, but the magnetic ground state keeps the ferrimagnetism. The comprehension of the underlying physics in Verwey transition facilitates the understanding of metal–insulator transition in other strongly-correlated systems. Nevertheless, the mechanism of Verwey transition is still debated after the first glimpse of Verwey transition. In this paper, we summarize the research history and current status of Verwey transition in Fe3O4. The investigations of lattice structure, charge ordering, electronic transport, magnetic and ferroelectric properties of Fe3O4 across Verwey transition are reviewed. Finally, the summary and outlook are given.
Application research of ant colony cellular optimization algorithm in population evacuation path planning
Authors: Wang Pei-Liang , Zhang Ting , Xiao Ying-Jie ,   Merchant Marine College, Shanghai Maritime University, Shanghai 201306, China,   Marine College, Shandong Transport Vocational College, Weifang 261206, China,   Weifang University of Science and Technology, Weifang 262700, China
Published: December 2020

With the improvement of people's living standards, large-scaled public activities have increased considerably, and the emergency probability has increased greatly. When an emergency occurs, the emergency evacuation can effectively reduce casualties and economic losses. Therefore, how to quickly evacuate crowd is a current research hotspot in this field. The path planning of emergency evacuation is one of the effective ways to implement the crowd evacuation. Aiming at the problem of path planning for emergency evacuation and taking the grid map as the background, the ant colony cellular optimization (ACCO) algorithm is proposed as the path planning algorithm based on the cellular automata theory and ant colony algorithm. Firstly, in order to solve the problem of inconsistent time steps in the quadrilateral grid map, the grid map based on hexagonal cell is established and the ACCO algorithm is developed based on the hexagonal grid map. And the method of solving grid coordinate is given. Then, in order to improve the convergence speed and search ability of the ACCO algorithm, the static field is used to optimize the heuristic function, and the segment update rule is used to optimize the pheromone update method. Finally, the parameters of ACCO algorithm are optimized through the particle swarm optimization (PSO) algorithm. The method of designing the fitness evaluation function is proposed, and the optimal combination of parameters of the ACCO algorithm is implemented according to the fitness function. In order to verify the scientificity and effectiveness of the algorithm proposed in this research and also to systematically verify the optimization strategy, in this research the exhibition hall on the B-deck of a large cruise ship is used as the engineering background, and the traditional algorithm and the ACCO algorithm are adopted to perform the simulations. The simulation results show that compared with the traditional quadrilateral grid, the hexagonal grid proposed in this research unifies the simulation time step and can be used as the division method of the simulation environment. At the same time, the ACCO algorithm can effectively perform the evacuation path planning, and the optimization strategy proposed in this research not only acceletates the search speed, but also increases the solution space and improves the search ability, which can effectively avoid falling into the local optimal solution.
Investigation of interaction between α-Fe metal and H atom by ab-initio method
Authors: Cheng Ying-Jin , Yang Chao-Fei , Xue Gang , Wang Tao , Zhang Lei , Li Mei-E ,   Luoyang Ship Material Research Institute, Luoyang 471023, China,   State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

Hydrogen-induced cracking (HIC) is a key problem restricting the application of ultra-high strength steel. It is necessary to analyze the distribution of diffusible hydrogen to reveal the mechanism of HIC. The site occupation tendency of H in interstitial and vacancy positions are investigated by the ab-initio method, and the stable configuration and steady state energy are obtained. The solution tendency of H atom in interstitial and vacancy positions is analyzed based on the aforementioned results. Specifically, the Mulliken population, density of states, charge density difference are calculated and used to analyze the interaction between α-Fe metal and H atom. The results show that the dissolved H tends to occupy the interstitial sites of the body-centered cubic, the weak hybridization interaction between the interstitial hydrogen and its nearest neighbour Fe atom is contributed by the H 1s orbital and Fe 4s orbital. Vacancies can capture H atoms easily and H atoms tend to occupy the isoelectric surface near the inwall of the vacancies. A vacancy defect can hold up to three H atoms which are difficult to combine with each other to form H2 molecule by covalent bond. H atoms in vacancies and at interstitial positions change the charge distribution of the Fe lattice, which weakens the binding force of the atoms and forms anti-bonding orbital in local area. The proposed thermodynamical model allows the determining of the equilibrium vacancy and the dissolved H concentration for a given temperature and H chemical potential in the reservoir, and the calculated results are in good agreement with the actual results.
Comparison of electrical wire explosion characteristics of single wire and wire array in air
Authors: Li Chen , Han Ruo-Yu , Liu Yi , Zhang Chen-Yang , Ouyang Ji-Ting , Ding Wei-Dong ,   School of Physics, Beijing Institute of Technology, Beijing 10081, China,   State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, China,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

In this paper, discharge characteristics of a planar copper wire array explosion driven by a microsecond pulsed current source (500 J stored energy) in atmospheric air medium were studied. Meanwhile, controlled experiments were performed with single wire cases. With a 2 cm distance between electrodes, 2-16 copper wires with a diameter of 100 μm were selected to form planar copper wire arrays, and single copper wires with diameter of 50-400 μm were selected for comparisons. Load voltage, circuit current and light radiation intensity were measured. Electric power and deposited energy were calculated. The experimental results show that for the single wire case, with the increase of mass (diameter), the process of vaporization and ionization become slower, manifested as a delay of the voltage peak and an increase of the full width half maximum (FWHM) of the voltage pulse from 0.07 μs to 0.64 μs. In contrast, although the explosion time of wire array load was delayed with the increase of mass, the duration of vaporization and ionization did not change significantly with a FWHM of 0.11 ± 0.01 μs. In addition, the deposited energy of wire array load before breakdown was lower than that of single wire load with the same mass. As for the optical radiation intensity, under three cases with the same mass, the peak intensity of wire array explosion is about 28%, 49% and 52% higher than that of single wire explosion. There may be two reasons which cause the difference between the single wire load and wire array load. First, the larger specific surface area of the wire array load makes faster phase transitions. Second, the development of thermal or magnetohydrodynamics for the two kinds of loads was different, which should be responsible for the differences in energy deposition and optical emission.
Compound relaxation oscillations connected by pulse-shaped explosion
Authors: Song Jin , Wei Meng-Ke , Jiang Wen-An , Zhang Xiao-Fang , Han Xiu-Jing , Bi Qin-Sheng ,   Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

Relaxation oscillations are ubiquitous in various fields of natural science and engineering technology. Exploring possible routes to relaxation oscillations is one of the important issues in the study of relaxation oscillations. Recently, the pulse-shaped explosion (PSE), a novel mechanism which can lead to relaxation oscillations, has been reported. The PSE means pulse-shaped sharp quantitative changes related the variation of system parameters in branches of equilibrium points and limit cycles, which leads the system’s trajectory to undertake sharp transitions and further induces relaxation oscillations. Regarding externally and parametrically excited nonlinear systems with different frequency ratios, some work on PSE has been reported. The present paper focuses on the PSE and the related relaxation oscillations in a externally and parametrically excited Mathieu-van der Pol-Duffing system. We show that if there is an initial phase difference between the slow excitations with the same frequency ratio, the fast subsystem may compose of two parts with different expressions, each of which determines a different vector field. As a result, the bistable behaviors are observed in the system. In particular, one of the vector fields exhibits two groups of bifurcation behaviors, which are symmetric with respect to the positive and negative PSE, and each can induce a cluster in the relaxation oscillations. Based on this, we present several routes to compound relaxation oscillations, and obtain new types of relaxation oscillations connected by pulse-shaped explosion, which we call compound “subHopf/fold-cycle” relaxation oscillations and compound “supHopf/supHopf” relaxation oscillations, respectively. Our results show that the two clusters in the resultant relaxation oscillations are connected by the PSE, and the initial phase difference plays an important role in transitions to different attractors and the generation of relaxation oscillations. Although the research in this paper is based on a specific nonlinear system, we would like to point out that the bistable behaviors, the PSE and the resultant compound relaxation oscillations can also be observed in other dynamical systems. The reason is that the fast subsystem composes of two different vector fields induced by the initial phase difference, which dose not rely on a specific system. The results of this paper deepen the research about PSE as well as the complex dynamics of relaxation oscillations.
Theoretical calculations on photoelectron angular distribution of sequential two-photon double ionization for Ar atom
Authors: Ma Kun , Xie Lu-You , Dong Chen-Zhong ,   School of Information Engineering, Huangshan University, Huangshan 245041, China,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China,   Engineering Technology Research Center of Intelligent Microsystems Anhui Province, Huangshan University, Huangshan 245041, China
Published: December 2020

With the development of the intense light source, such as free electron lasers, the experiments on the nonlinear process in atomic photo absorption in the XUV and X-ray region became more and more feasible. As one of the simplest possible nonlinear processes, the sequential two-photon double ionization, in which the first photon produces an ion which is subsequently ionized by the second photon, attracts increasing attention of theorists and experimentalists. Study on the angular distributions and angular correlations of the photoelectrons in the sequential two-photon double ionization process are especially attractive, which provides valuable information about the electronic structure of atom or molecule systems and allows the obtaining of additional information about mechanism and pathway of the two-photon double ionization. In this paper, the expression for the photoelectron angular distribution in a sequential two-photon process is given based on the multi-configuration Dirac-Fock method and the density matrix theory. And then, the relativistic calculation program for photoelectron angular distribution is further developed with the help of the program packages GRASP2K and RATIP which are based on the multi-configuration Dirac-Fock method. By using this code, the sequential two-photon double ionization of the 3p shell in atomic argon is studied theoretically. The cross section, magnetic cross section, alignment of residual ions and the asymmetry parameter of the photoelectron angular distribution, each as a function of photon energy, for the first and the second step of sequential two-photon double ionization of argon are presented. The calculations predict that the alignment has a maximum value and the asymmetry parameter has a minimum value in the region of the cooper minimum. The angular distribution of the first step ionization for Ar atom and the second step ionization for Ar+ ion are given at 33.94 eV and 55.34 eV photon energy, respectively. In addition, the difference in property between the angular distributions of the first photoelectron in sequential two-photon double ionization and in conventional one-photon single ionization is discussed. The present calculated results are compared with other available results, showing that they are in good agreement with each other. The results of this paper will be helpful in studying nonlinear processes in the XUV range.
Time-resolved ultrafast dynamics in triple degenerate topological semimetal molybdenum phosphide
Authors: Jiang Cong-Ying , Sun Fei , Feng Zi-Li , Liu Shi-Bing , Shi You-Guo , Zhao Ji-Min ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   Strong-Field and Ultrafast Photonics Lab, Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China,   Songshan Lake Materials Laboratory, Dongguan 523808, China
Published: December 2020

We employ the time resolved pump probe experiment to investigate the ultrafast dynamics in a topological semimetal molybdenum phosphide (MoP), which exhibits triple degenerate points in the momentum space. Two relaxation processes with the lifetime of 0.3 and 150 ps have been observed. We attribute the fast component to the electron-phonon scattering and the slow component to the phonon-phonon scattering, respectively. Temperature dependence investigation shows that both the lifetimes of the fast and slow components enhance slightly with increasing temperature. We also successfully generate and detect a thermal-stress-induced coherent acoustic phonon mode with a frequency of 0.033 THz, which does not vary with temperature. Our ultrafast spectroscopy investigation of the quasiparticle dynamics and the coherent phonon in MoP provides useful experimental facts and information about the overall excited state dynamics and the temperature dependence of electron-phonon coupling.
Link predictability of complex network from spectrum perspective
Authors: Tan Suo-Yi , Qi Ming-Ze , Wu Jun , Lu Xin ,   College of Systems Engineering, National University of Defense Technology, Changsha 410073, China,   College of Liberal Arts and Sciences, National University of Defense Technology, Changsha 410073, China,   International Academic Center of Complex Systems, Beijing Normal Univerdity, Zhuhai 519087, China
Published: December 2020

Link prediction in complex networks has attracted much attention in recent years and most of work focuses on proposing more accurate prediction algorithms. In fact, “how difficultly the target network can be predicted” can be regarded as an important attribute of the network itself. In this paper it is intended to explain and characterize the link predictability of the network from the perspective of spectrum. By analyzing the characteristic spectrum of the network, we propose the network link predictability index. Through calculating the index, it is possible to learn how difficultly the target network can be predicted before choosing algorithm, and to solve the problem whether the network is unpredictable or the algorithm is inappropriate. The results are useful for the selecting and matching the complex network and link prediction algorithms.
Investigation on equation of state and ionization equilibrium for aluminum in warm dense matter regime
Authors: Wang Tian-Hao , Wang Kun , Zhang Yue , Jiang Lin-Cun ,   State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300130, China,   Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province, Hebei University of Technology, Tianjin 300130, China
Published: December 2020

Warm dense matter is widely found in the high-energy-density-physics researches, such as inertial confinement fusion, X-ray source and wire-array Z-pinch. The equation of state and ionization equilibrium of material in warm dense matter regime play a significant role in explaining experimental results and simulations of physical process. In this paper, the Coulomb interaction between charged particles, and the excluded volume effect due to high density and polarization effect between neutral atoms and charged particles are considered in the equation of state for aluminum in warm dense matter regime. A non-ideal Saha equation is used to account for the ionization equilibrium. The data for pressure and concentration of particles of aluminum plasma are derived by iteration between equation of state and ionization equilibrium model. The pressure and average ionization degree of aluminum plasma are consistent with the calculation results from other models and relevant experimental data. The Coulomb interaction, which dominants the non-ideal effects, is insensitive to temperature and increases with density rising especially near the region of critical density. The excluded volume effect peaks at a density of ～0.5 g/cm3. The polarization effect first becomes stronger with density increasing and then decreases at a density of ～0.4 g/cm3. The ionization equilibrium results with density ranging from 1.0 × 10–4 g/cm3 to 3.0 g/cm3 and temperature ranging from 1.0 × 104 K to 3.0 × 104 K reveal that the average ionization degree increases with density sharply increasing near the critical density. The non-ideal effects, which lead the ionization energy to decline and the effective ionization potential of specific ions in aluminum plasma to decrease substantially, are responsible for the sharp increase of average ionization degree near the region of critical density. When the temperature is lower than 12000 K, first and second stage of ionization occur in aluminum plasma, and the system is mainly composed of Al1+, Al2+ and electrons. The average ionization degree can reach 2 at critical density. The third stage of ionization is dominant in the aluminum plasma when plasma temperature is higher than 12000 K. And then, the charged particles in the plasma are composed of Al3+ and electrons, allowing the average ionization degree to reach 3 at critical density.
Design of microscope eyepiece with high magnification and wide field of view based on freeform surface
Authors: Guo Yu-Tong , Chang Jun , Hu Yao-Yao , Zhong Yue , Song Da-Lin ,   School of Opto-Electronics, Beijing Institute of Technology, Beijing 100081, China,   The First Research Institute of the Ministry of Public Security, Beijing 100048, China
Published: December 2020

With the great improvement of microscope property, the eyepiece of microscope is required to have a larger field of view, high magnification, and better imaging quality. Because of the external aperture stop and short focal length, the design difficulty of microscope eyepiece lies in how to correct the distortion and other off-axis aberrations caused by the large field of view, and how to obtain an eye relief that meets the requirements for human observation is also important. The main aberrations of the eyepiece optical system, especially the effect of the optical system with distortion on imaging is analyzed in this paper. The freeform surface is applied to the distortion correction of the optical system of the microscope eyepiece. A wide-angle microscope eyepiece with field of vision of 60° and a magnification of 25× is described in this paper. The full-field distortion is less than 5%. The microscope eyepiece adopts a five-piece three-element structure, in which the freeform surface lens is made of plastic material and is symmetrical about the XOZ plane and YOZ plane. A high-performance microscope eyepiece design with simple structure, easy processing, and low cost is realized.