bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction of Lennard-Jones pair potential and pairwise many-body potential for crystal α-boron
Authors: Yu Zhi-Qing  , Wang Xun  , Liu Yan-Xia  , Wang Mei  , Yang He  , Xue Xiang-Xin  ,   School of Materials and Metallurgy, Northeastern University, Shenyang 110819, China;,   School of Science, Shenyang Jianzhu University, Shenyang 110168, China;,   School of Physics, Liaoning University, Shenyang 110036, China;,   Titanium Alloys Division, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Published: December 2020

For α-boron, R3m group, Lennard-Jones (L-J) pair potential function is fitted, and a pairwise many-body potential is constructed. For constructing both interatomic potentials, only the atomic average cohesive energy and geometric information are needed. And the cohesive energy and geometry of α-boron crystal are calculated by first-principles code Castep. The fitting procedure for the potentials is as follows. For L-J potential, the minimum of the function is set to be located at the nearest neighbors. For the pairwise many-body potential, L-J potential is minimal, and the form of the function is chosen as a piecewise function, which consists of the L-J function and polynomial function. The minima of L-J potential are located at the distances between the different neighbors of atoms, and the potential barriers are at the midpoints of the distances of the two neighbor minima. L-J potential, L-J pair potential, and Tersoff potential for boron are tested and compared with each other, by energy minimization method in molecular dynamics (MD) simulation. The radial distribution function is used to analyze the structure obtained from the simulation results obtained by using different potentials. The results show that the structure after minimization deviates significantly from the initial crystal of α-boron by L-J potential, and final structure is consistent well with the initial ideal crystal, with L-J potential used. The NVT ensemble is used in MD simulation, where the temperature is set to be 2000 K, and the α-boron crystal experiences the thermodynamic evolutions for 10 fs and 100 fs, to obtain the deviated initial structures. Then the minimization by MD simulation is made to test the three potentials, which also shows that the L-J potential can give the much better result than the other two potentials.
Modeling and simulation of the background light in underwater imaging under different illumination conditions
Authors: Zhao Xin-Wei  , Jin Tao  , Chi Hao  , Qu Song  ,   Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

The underwater visibility is very important in underwater vision research and target detection. However, most underwater vision systems cannot guarantee to possess the performance under complex water conditions. This is because underwater images are usually degraded by light-water interactions of absorption and scattering. The ambient light is scattered into the cameras line of sight by water molecules and suspended particles in the water medium, which adds a layer of haze to the image and reduces the contrast of the image. This part of scattered light is usually called background light, which is the main reason for underwater image degradation. In this paper, the formations of background light in underwater imaging under two different lighting conditions: natural illumination and artificial lighting, are analyzed by setting up physical models. The models developed include the parameters such as camera parameters, light source parameters, inherent optical properties, and camera-source-object geometry. Based on the models, the relationship between the background light and the above parameters is studied. Computer analysis shows that the global background light under two illumination conditions has a close relationship between the inherent optical properties of water medium and camera parameters. The global background light under natural illumination is proportional to the scattering coefficient and inversely proportional to the attenuation coefficient. The background light under the two illumination conditions both can be described in simple exponential falloff expressions of the global background light. The simple expression greatly reduces the computational complexity of simulations. The intensity of background light mainly depends on the inherent optical properties, camera-scene distance, camera-source distance and cameras imaging angle. The relationship between the global background light and the inherent optical properties can be used to estimate the attenuation coefficient, scattering coefficient and scene depth information. The result of this paper can be very useful for designing and improving the underwater imaging systems.
Shock wave amplification by shock wave self-generated magnetic field driven by laser and the external magnetic field
Authors: He Min-Qing  , Dong Quan-Li  , Sheng Zheng-Ming  , Zhang Jie  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   School of Physics and Optoelectronic Engineerings, Ludong University, Yantai 260405, China;,   Key Laboratory for Laser Plasmas (MoE) and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Shock wave is a common phenomenon in astrophysics. Shock wave acceleration has been regarded as a source of high-energy cosmic rays. Very strong magnetic field exists in the surrounding of the shock wave at the edge of the supernova remnants. But the mechanisms of generation and amplification of such a strong magnetic field are not clear yet. In this paper, the properties of shock wave driven by the laser irradiating on un-magnetized and magnetized plasmas are investigated using two-dimensional particle-in-cell (PIC) simulations. It is found that very strong spontaneous magnetic field can be generated around the laser-driven shock front in the un-magnetized plasma. The spontaneous magnetic field can store energy and accelerate electrons further. When an external magnetic field is introduced, the electrons and ions are accelerated more efficiently by the shock wave than in the un-magnetized plasma. The external magnetic field can transfer its energy to electrons and ions, and strengthen the shock wave. In simulations, the introduced external magnetic field has three different strengths: 1072 MG, 107.2 MG and 10.72 MG, which determine the shock structures through the driven currents. There are two single-polar magnetic arcs that constitute the shock structure when the external magnetic field is 1072 MG, i.e., one is the shock itself and the other is actually the reverse shock, whereas only one magnetic arc is produced but with a bipolar structure in the direction perpendicular to the shock propagation when the externally added magnetic fields are much lower (107.2 MG and 10.72 MG). The two bipolar magnetic structures will evolve into a single-polar arc when the externally added magnetic field is 107.2 MG, but they are kept for all the time when the external magnetic field is 10.72 MG. It can be explained by taking the Larmor radius into the consideration. That the amplification ratio of the magnetic field decreases as the introduced external magnetic field increases implies that the magnetic amplification in the space is possibly due to the local field generation rather than the field compression. An amplification ratio of tens of the external magnetic field is achieved due to the pseudo Rayleigh-Taylor instability, but still much smaller than that around the astrophysical shock front, indicating that other efficient mechanisms are responsible for the observed magnetic amplification around shocks in the supernova remnants.
Interaction between low energy proton ring-beam and plasma with one-dimentional hybrid simulations
Authors: Jin Yuan-Wei  , Wang Ya-Bing  , Gu Bin  , Zhao Lei  , Zhang Xiao-Xin  ,   Department of Physics, Nanjing University of Information Science and Technology (NUIST), Nanjing 210044, China;,   Institute of Space Weather, NUIST, Nanjing 210044, China;,   National Center for Space Weather, Beijing 100081, China
Published: December 2020

In this paper, the interaction between the low energy proton ring-beam with an initial velocity perpendicular to the background magnetic field, and the background plasma is studied by one-dimensional (1D) hybrid simulations. In the initial stage, the excited plasma waves experience a fast growth exponentially, which is consistent with the linear theory. After that, three non-linear stages, including the saturation process, the fast damping process and the relatively stable stage, follow in sequence. In the linear stage, the mode-resonance damps with the pitch angle scattering of the injected protons, and the plasma oscillation reaches the peak quickly. The continuing pitch angle scattering makes the velocity distributions of the proton beam and the background ions uniformly distributed. Meanwhile, the initially excited right-handed resonant instability decreased, with only the Alfven waves left in the stable stage. The results also show that the effective heating of the background plasma is achieved after the linear stage, instead from the very beginning of the injection of the protons. This demonstrates that the excited plasma waves lead to the energy transferring from the injected proton beams to the background plasma.
Phase field crystal simulation of grain boundary annihilation under strain strain at high temperature
Authors: Gao Ying-Jun  , Qin He-Lin  , Zhou Wen-Quan  , Deng Qian-Qian  , Luo Zhi-Rong  , Huang Chuang-Gao  ,   Guangxi Colleges and Universities Key Laboratory of Novel Energy Materials and Related Technology, College of Physics Science and Technology, Guangxi University, Nanning 530004, China
Published: December 2020

Grain boundary (GB) research is always the most fundamental and active study field in interface science. Grain boundary premelting (GBPM) is induced as a consequence of local inner strain around defects in material at high temperature. When GB premelting is under an external stress, it is referred to as stress induced GBPM (SIGBPM). Owing to the fact that the width of a GB usually is a few atoms thick, it is difficult to observe the GBPM directly in experiment, thus the development of computational simulation experiment can make up for the shortcomings in experiment. For this reason, a new method which is named phase field crystal (PFC) model based on density functional theory is proposed. Because the method can be used to simulate the evolution of macroscopic structure of polycrystalline material on a diffusive time and atomic scale, therefore, PFC has a great advantage in simulating the evolution of microstructure. In this paper, PFC method is used to investigate the annihilation process of dislocation pairs of premelted grain boundary under strain at high temperature. Simulated results show that the essence of separation process of sub-GB (SGB) from original GB is that sub-grain structures are generated. The SGB migration is the process of the new grain swallowing up the old one. The annihilation process of GBPM under applied strain at high temperature can be divided into two stage features. The first stage is the stage of system energy increasing, which is corresponding to the process of SGB migration, dislocation gliding; the second stage is the energy decreasing, which corresponds to the interaction of SGBs and annihilation of dislocations, while the speed of annihilation in this process is slow and the peak of energy curve is wide and smooth. According to the changing process of the atomic density distribution projected along the directions of x and y axis with strain increasing, we can reveal that the nature of annihilation of double dislocation pairs at high temperature is the process of two-step annihilations, of which the detailed process is not easy to observe at low temperature due to its fast annihilating speed of dislocation pairs.
Phase diagram of the one-dimensional extended ionic Hubbard model
Authors: Zhao Hong-Xia  , Zhao Hui  , Chen Yu-Guang  , Yan Yong-Hong  ,   Key Laboratory for Advanced Microstructure Materials of the Ministry of Education and Department of Physics, Tongji University, Shanghai 200092, China;,   Department of Physics, Shaoxing University, Shaoxing 312000, China
Published: December 2020

We use a density-matrix renormalization group method to study quantitatively the phase diagram of the half-filled one-dimensional (1D) extended Hubbard model in the presence of a staggered ionic potential Δ. An extensive finite-size scaling analysis is carried out on the relevant structure factors and localization operator to characterize the Mott-insulator (MI)-bond-ordered insulator (BOI)-band-insulator (BI) transitions. The intermediate BOI phase occupies a small region of the phase diagram, and this region is enlarged in the presence of Δ. In addition, the phase diagram of ionic Hubbard (the nearest-neighbor electron-electron interaction V=0) is also given.
Design and optimization of integrated micro optical gyroscope based on a planar ring resonator
Authors: Liu Jun  , Zhang Tian-En  , Zhang Wei  , Lei Long-Hai  , Xue Chen-Yang  , Zhang Wen-Dong  , Tang Jun  ,   Key Laboratory of Instrumentation Science and Dynamic Measurement Ministry of Education of China, Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China
Published: December 2020

In order to optimize the performance of the coupled resonator optical waveguide (CROW) gyroscope, a well-designed structure by optimizing the ring number and the transmission coefficient of the coupler is used as the core component of the planar waveguide optical gyroscope. The structure with double coupled ring resonator may possess large effective group refractive index to enhance angular sensing sensitivity was proposed. The concept of the Sagnac effect in this new double coupled ring resonator structure with a large effective group refractive index is investigated, it’s found that the rotation-induced phase shift is proportional to the effective group refractive index. On the basis of this effect, we calculate the general relation expression of theoretical rotation sensitivity and the effective group refractive index for this two-ring bidirectional CROW gyroscope by numerically simulation. Based on the relation, the phase shift characteristics of double coupled ring resonator and single ring resonator was analyzed. And the changing characteristics of the transmission coefficient of the couplers and the effective group refractive index was discussed based on the double cascaded ring resonator coupling mode theory. In the case of R1=R2=100 μm and ring transmission loss coefficient t1=t2=0.95, the generating condition of the largest effective group refractive index was obtained, according to the different effects of the couplers between rings and waveguide on the effective group refractive index. By using the parameters of R=100 μm and t=0.95, the sensitivity of a single ring resonator gyroscope is (104-105) °/h, and the sensitivity of double coupled ring resonator gyroscope can reach to 10 °/h. In summary, we show that the theoretical sensitivity of the double coupled ring gyroscope and single ring gyroscope are comparable when both have the same parameters. Using numerical and analytical methods, we demonstrated that coupling multiple resonators together can enhance rotation sensitivity. This research is important for applications of coupled ring resonator in optical angular velocity detection, and a promising regime to realize highly compact optical gyroscope.
Three-dimensional numerical analysis of interaction between arc and pool by considering the behavior of the metal vapor in tungsten inert gas welding
Authors: Fan Ding  , Huang Zi-Cheng  , Huang Jian-Kang  , Wang Xin-Xin  , Huang Yong  ,   Lanzhou University of Technology, Material Science and Engineering institute, Lanzhou 730050, China;,   State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050, China
Published: December 2020

A three-dimensional (3D) numerical analysis model of tungsten inert gas welding arc interacting with an anode material is presented based on the local thermodynamic equilibrium assumption and taking the behavior of metal vapor into account. The thermodynamic parameters and transport coefficients of plasma arc are dependent on the local temperature and metal vapor concentration. A second viscosity approximation is used to express the diffusion coefficient which describes the metal vapor diffuse in the argon plasma. The weld pool dynamic is described by taking into account the buoyancy, Lorentz force, surface tension, and plasma drag force. The temperature coefficient of the surface tension at the weld pool surface is considered in two ways: one is taken as a function of temperature with only oxygen being the active component, and the other is taken as a constant value. The distributions of temperature field and velocity field of arc plasma and weld pool, metal vapor concentration and current density in the arc plasma are investigated by solving the Maxwell equations, continuity equation, momentum conservation equation, energy conservation equation and the components of the transport equation. The influence of metal vapor on arc plasma behavior and that of arc plasma on the weld pool are studied and compared with the non-metal vapor results. It is shown that the distribution of Fe vapor concentrates around the weld pool surface. Metal vapor has obvious shrinkage effect on arc plasma, and weak influences on velocity and potential of the arc plasma. In addition, the metal vapor has a weak effect on the distributions of velocity and shear force on the weld pool surface and no obvious influence on the molten pool shape. We test two different methods to illustrate this point in the case with or without metal vapor. The method used for a variable temperature coefficient of surface tension allows the prediction of a depth-to-width ratio and weld pool shape in agreement with experimental result when taking the behavior of metal vapor into account. The results in this paper, obtained by simulation are in good agreement with experimental results and also with the simulation results by some other authors.
Modeling and failure monitor of Li-ion battery based on single particle model and partial difference equations
Authors: Huang Liang  , Li Jian-Yuan  ,   School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044, China;,   School of Physics, Peking University, Beijing 100871, China
Published: December 2020

Li-ion battery is a complicated distributed parameter system that can be described precisely by field theory and partial differential equations. In order to reduce the calculation amount and the solution difficulty, a distributed parameter system is often described by ordinary differential equation model during the design and the analysis. As a result, systemic error is caused, and the reliability of the system model is reduced. The rechargeable Li-ion batteries are widely used in many fields because of their excellent properties. The research on the modeling and failure monitor of Li-ion battery can evaluate its working state, and improve the security during its servicing. Li-ion battery system is regarded as a distributed parameter system in this paper. Single particle model is a simplification of a Li-ion battery under a few assumptions. According to the measured data, single particle model can be used for estimating the parameter at a fast simulation speed. Li-ion battery model based on partial difference equations and single particle model is proposed to detect the failure and evaluate the working state of Li-ion battery system. Lithium ion concentration is an unmeasurable distributed variable in the anode of Li-ion battery. The failure monitor system can track the real-time Li ion concentration in the anode of Li-ion battery, calculate the residual which is the difference between the measured value and the ideal value. A failure can be judged when the residual is beyond a predefined failure threshold. A simulation example verifies that the accuracy and the effectiveness of Li-ion battery failure monitor system based on parabolic partial difference equations and single particle model is reliable.
Tooth-shaped plasmonic filter based on graphene nanoribbon
Authors: Sheng Shi-Wei  , Li Kang  , Kong Fan-Min  , Yue Qing-Yang  , Zhuang Hua-Wei  , Zhao Jia  ,   School of Information Science and Engineering, Shandong University, Jinan 250100, China;,   College of Physics and Electronics, Shandong Normal University, Jinan 250014, China;,   School of Information and Electrical Engineering, Shandong Jianzhu University, Jinan 250101, China
Published: December 2020

A class of single tooth-shaped plasmonic filter based on graphene nanoribbon is proposed in this paper, and the structure is numerically analysed by using finite-difference time-domain method. The tooth-shaped structure of graphene nanoribbon can induce a sharp band-stop effect in the transmission spectrum, and the filtering characteristics can be analysed by the scattering matrix method. The effective refractive index of the plasmonic waveguide mode in the graphene nanoribbon is analysed numerically, and it is found that the effective refractive index is influenced by both the chemical potential and the width of the nanoribbon, and when the width is narrower than 30 nm, the higher order mode disappears and the ribbon becomes a single mode waveguide. According to the scattering matrix method, the central frequencies of the transmission dips can be changed by changing the length and the width of the tooth. Flexible electrical tunability of this kind of filter by tiny change of the chemical potential of the graphene through electrical gating is also validated. In addition, transmission spectrum of multi-teeth shaped plasmonic filter is also studied. This kind of structure can possess the broad band-stop filtering property. The influences of tooth number and tooth period on transmission spectrum are investigated. We find that the transmission value can be reduced down to almost zero by adjusting the number of the teeth, also the tooth period can influence the central frequency of the stop band because of the coupling effects between each other. Like the single-tooth filter based on graphene nanoribbon, the multi-tooth broad band-stop filter can also be flexibly tuned by the geometric parameters of the structure and the chemical potential of the graphene. This work provides an effective method of designing graphene based ultra-compact tunable devices, and has extensive potential for designing all-optical integrated architectures for optical networks, communication and computing devices.
Numerical simulation of fuel dispersal into cloud and its combustion and explosion with smoothed discrete particle hydrodynamics
Authors: Chen Fu-Zhen  , Qiang Hong-Fu  , Miao Gang  , Gao Wei-Ran  ,   Faculty 601, Second Artillery Engineering University, Xi’an 710025, China;,   Non-commissioned Officer Institute, Second Artillery Engineering University, Qingzhou 262500, China;,   First Institute, Second Artillery Equipment Academe, Beijing 100085, China
Published: December 2020

A fuel air cloud is formed under the driving force of the explosive detonation and then it’s ignited to explosion to attack the target. The existing numerical simulations are mainly limited to the fuel dispersal processes which are all based on mesh methods. The fuel particles in the air cloud are difficult to traced. Otherwise, the computing process is complex and could not be solved by the exiting methods for the chemical reaction and the forming and propagation of shock waves are both involved in the fuel combustion and explosion. Smoothed discrete particle hydrodynamics (SDPH), as a new method to solve the gas-particle two-phase flow, has been successfully used to simulate the aeolian sand transport, heat transfer and evaporation. Based on the previous work, the Jones-Wilkins-Lee (JWL) function is imported to describe the explosive detonation to expansion and it is solved by finite volume method. The fuel drops dispersed by explosion are traced by the improved smoothed particle hydrodynamics. The drop evaporation model and the EBU-Arrhenius combustion model for gas high-speed combustion are introduced to describe the combustion and detonation of fuel drops. Then we build a new SDPH method to simulate the warhead initiation, fuel dispersal, and the fuel second explosion. Firstly, we design a test that is the dispersal of circular fuel drops drove by explosive detonation to validate our new method. The changing of the explosive detonation pressure and the velocity fields of explosive and particles are analyzed and they are consistent with the theory. And then, the forming and developing of FAE cloud are simulated. Through comparing with the experiments, the shapes of the cloud by the two methods coincide with each other. The effects of different initiations on the cloud forming are also analyzed. Finally, based on the cloud group forming, the evaporation and combustion models are introduced to study the combustion and explosion of FAE. We obtain the velocity field and the distribution of combustion product. The result indicates that the fuel dispersal into cloud and its explosion can be simulated better with the mathematical model and computational method built in this paper. This finding supplies a more effective numerical method for the design and research on this type of weapon equipments.
Investigations on the nuclear charge radii
Authors: Sheng Zong-Qiang  , Fan Guang-Wei  , Qian Jian-Fa  ,   School of Science, Anhui University of Science and Technology, Huainan 232007, China
Published: December 2020

Experimental nuclear charge radii for 885 nuclei with N8 and Z8 have been systematically investigated. Results show that the formula for single parameter Z1/3 law is superior to that for the A1/3 law in describing nuclear charge radii. For two-parameter and three-parameter formulae, the Z1/3 law is as good as the A1/3 law. Considering the importance of shell effect and deformations for nuclear charge radii, we add a term including the Casten factor P into the conventional three-parameter formula and thus obtain very good results. The corresponding root-mean-square deviation falls to =0.0273 fm, i.e. reduced by about 50% when compared with the result obtained with the old three-parameter formula. Shell effect can be well reproduced for some elements by adding the Casten factor term. It is shown that the Casten factor plays a key role for nuclear charge radii. The odd-even staggering is a common phenomenon in many nuclear fields. This phenomenon can be observed with nuclear charge radii for most elements. For this reason, we add a term into the formula (10) in this paper. The root-mean-square deviation falls to =0.0266 fm. A five-parameter formula can well reproduce the variation of the nuclear charge radii for most elements. Calculated results are well consistent with the experimental data available. The differences between the experimental nuclear charge radii and the results calculated using the conventional three-parameter formula and the present five-parameter formula for the 885 selected nuclei are presented. A comparison of the formulae mentioned in this paper is given. The present five-parameter formula including the Casten factor P and the odd-even staggering is the best formula to fit available RC data and gives the smallest root-mean-square deviation . Our calculated results may be useful for future experiments.
Investigation of ultrafast relaxation dynamic process of water-soluble TGA-CdTe quantum dots
Authors: Han Yuan-Chun  , Bao Tmurbagan  ,   College of Physics and Electronic Information, Inner Monggolia University for Nationalities, Tongliao 028043, China
Published: December 2020

In the present paper, we study the average fluorescence lifetimes, detected by using the time-correlated single-photon-counting (TCSPC) technique, of three thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs), which are ～6 ns, ～9 ns and ～11 ns; and the fluorescence kinetic process includes two parts:the slow process and the fast process. With the increase of the particle size, the slow process becomes longer, but the fast process becomes shorter. Afterwards, by using both femtosecond transient absorption and fluorescence up-conversion time-resolved spectrum techniques, we have investigated the interband relaxation process of three TGA-CdTe QD samples, with the nanoparticle diameters of 2.3, 2.8 and 3.5 nm. Investigation indicates that for the three QD samples, exciton filling rate becomes slower in the highest excited state and the lowest excited state, among them, the time of exciton filling increases from 0.33 to 0.79 ps for the highest excited state, while the time of exciton filling increases from 0.53 ps to 1 ps for the lowest excited state. Moreover, the two kinds of experiment provide complementary information and obtain the full image of interband relaxation process. Result shows that the bleach recovery of the 1 S transition shows an initial rise, but the fluorescence up-conversion signal for the 1 S transition is slower in rise time, which can provide help in the application of optoelectronic devices.
A 303 MHz fundamental repetition rate femtosecond Er:fiber ring laser
Authors: Liu Huan  , Gong Ma-Li  , Cao Shi-Ying  , Lin Bai-Ke  , Fang Zhan-Jun  ,   Center for Photonics and Electronics, Department of Precision Instrument, Tsinghua University, Beijing 100084, China;,   Division of Time and Frequency Metrology, National Institute of Metrology, Beijing 100029, China
Published: December 2020

High-repetition-rate fiber laser has widely applications in the field of femtosecond frequency comb, ultra-fast optical sampling, and so on. In this paper, an Er-doped femtosecond fiber laser with a repetition rate of 303 MHz is demonstrated based on the mechanism of nonlinear polarization rotation. By means of optimization of cavity dispersion, the net dispersion in fiber cavity is a little negative nearby zero point. After mode locking, the laser is operating in the stretched-pulse regime. At a pump power of 817 mW, the output power of the laser is 125 mW in continue-wave state, and 69 mW in mode-locking state. The laser directly generates 90 fs before dispersion compensation. Mode locking can self-start at the pump power of 700-817 mW. Repetition rate drift of the mode-locked laser is 30 Hz in five hours.
Mesoscale simulation of the sedimentation of melting elliptical particle
Authors: Liu Han-Tao  , Jian Shan  , Wang Yan-Hua  , Wang Chan-Juan  , Li Hai-Qiao  ,   The Lab. Of Energy&Environment Engineering and Computational Fluid Dynamics, North University of China, Taiyuan 030051, China;,   Department of Civil & Environmental Engineering, University of Missouri, Columbia, MO USA 65211
Published: December 2020

In this paper, a mathematical relationship between particle melting rate and its surface heat flux is established to solve the problem of melting of elliptical particle sedimentation based on the direct numerical simulations of particle sedimentation when taking account of thermal convection within the framework of the arbitrary Lagrangian-Eulerian technique. The elliptical particle with different initial angles is released in a mesoscale channel under gravity. Compared with the isothermal elliptical particle sedimentation, the melting elliptical particle shows large differences in moving trajectories, the forces exerting on the particle and velocities, which come from the consideration of fluid convection, mass loss, and shape change. More specifically, 1) in the case of isothermal elliptical particle sedimentation, the velocity, the horizontal trajectory, and the force vary periodically. However, the amplitude recedes gradually, and finally becomes zero in the case of the melting elliptical particle, which is caused by the mass lost and shape change. 2) The equilibrium position of the major axis will finally be perpendicular to the direction of sedimentation. So, the initial angle of slope (θ) usually affects the sedimentation in the beginning, and vanishes after a period of time. 3) The downward convection induced by the cold fluid accelerates the velocity of the melting particle. The angular velocity, force and horizontal amplitude of the melting particle become smaller than those of the isothermal particle, and finally recedes to zero. In our study, the investigation of coupled heat transfer, fluid-solid system and shape change is carried out, and some new features are found out.
Study of the shock wave induced by closing partial road in traffic flow
Authors: Sun Xiao-Yan  , Zhu Jun-Fang  ,   School of systems Science, Beijing Normal University, Beijing 100875, China;,   College of Physics and Electronic Engineering, Guangxi Teacher Education University, Nanning 530023, China;,   School of Science, Southwest University of Science and Technology, Mianyang 621010, China
Published: December 2020

There often occurs traffic accident or road construction in real traffic, which leads to partial road closure. In this paper, we set up a traffic model for the partial road closure. According to the Nagel-Schreckenberg (NS) cellular automata update rules, the road can be separated into cells with the same length of 7.5 m. L = 4000 (corresponding to 30 km) is set to the road length in the simulations. For a larger system size, our simulations show that the results are the same with those presented in the following. In our model, vmax rtial road is closed (for convenience, we define the road length as L1), vmax 2= 2 (corresponding to 54 km/h) in the section of normal road (we define the road length as L2). In our simulations, let L1= L2 = 2000. We would like to mention that changing these parameter values does not have a qualitative influence on the simulation results. The simulation results demonstrate that three stationary phases exist, that is, low density (LD), high density (HD) and shock wave (SW). Two critical average densities are found:the critical point ρcr 1= 3/8 separates the LD phase from the SW phase, and ρcr 2= 1/2 separates the SW phase from the HD phase. We also analyze the relationship between the average flux J and average density ρ. In the LD phase J = 4/3ρ, in the HD phase J= 1 -ρ and J is 0.5 in the SW phase. We investigate the dependence of J on ρ. It is shown that with the increase of ρ, J first increases, at this stage J corresponds to the LD phase. Then J remains to be a constant 0.5 when the critical average density ρcr 1 is reached, and J corresponds to the SW phase (this time,J reaches the maximum value 0.5). One goal of traffic-management strategies is to maximize the flow. We find that the optimal choice of the average density is 3/8 ρρcr 2 is reached, J decreases with the increase of average density, which corresponds to the HD phase. We also obtain the relationship between the shock wave position and the average density by theoretical calculations, i.e. Si = i+4-8ρ, which is in agreement with simulations.
Preparation of BST nanotube and its infrared absorption properties
Authors: Zou Chao  , Xu Zhi-Mou  , Ma Zhi-Chao  , Wu Xing-Hui  , Peng Jing  ,   School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China;,   College of Science, Wuhan University of Science and Technology, Wuhan 430081, China
Published: December 2020

Ba0.6Sr0.4TiO3 (BST) nanotubes are fabricated successfully by sol-sel method with the through-hole anodic aluminum oxide (AAO) template for the first time so far as we know. This fabrication method is easy to realize at low cost because the through-hole AAO template and the BST sol can be acquired easily at low cost, so this is very valuable in the fabrication of other similar nanostructures. First, the steady BST sol is prepared and the well aligned through-hole anodic aluminum oxide template is fabricated by a two-step anodization method; second, the BST sol is introduced into the ordered nanohole arrays of the through-hole AAO template by dipping and spinning; and finally, the samples are fired in air at 650℃ for 1 h to get BST nanotubes. X ray diffraction (XRD) patterns reveal that the BST nanotubes are of cubic perovskite structures, and grow mainly along [110] crystal orientation. Scanning electron microscope (SEM) results show that the thickness and pore size of the through-hole AAO template are about 16 μm and 75 nm, respectively. The length, external and inner diameters of the BST nanotubes are about 16 μm, 75 nm and 50 nm, respectively. Measurements of BST nanotubes give results highly matched with that of the through-hole AAO template. Fourier transform infrared spectroscopy (FTIR) results shows that in the 1350-1650 cm-1 waveband, the composite structure of AAO/BST nanotubes has two obvious absorption peaks which are respectively at 1470 and 1550 cm-1, while the BST film does not have; the absorption property of the composite structure is about two times of the pure through-hole AAO membrane. Finally, the possible reasons of this phenomenon about infrared absorption are discussed.
Configuration interaction study on electronic structures and transitional properties of excited states of GeO molecule
Authors: Liu Xiao-Jun  , Miao Feng-Juan  , Li Rui  , Zhang Cun-Hua  , Li Qi-Nan  , Yan Bing  ,   College of Science, Qiqihar University, Qiqihar 161006, China;,   Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy, Jilin University, Changchun 130012, China;,   College of Communications and Electronics Engineering, Qiqihar University, Qiqihar 161006, China;,   Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
Published: December 2020

GeO molecule, which plays an important role in fabricating integrated optics and semiconductor components, has received much attention. However, the electronic state density of the molecule is very large, and the electric structures and transitional properties of the molecule have not been well investigated. In this work, the 18 Λ -S states correlated to the lowest dissociation limit (Ge(3Pg)+O(3Pg)) are calculated by a complete active space self-consistent field (CASSCF) method, through using the previous Hatree-Fock molecular orbitals as the starting orbitals. Furthermore, we take all configurations in the configuration interaction expansions of the CASSCF wave functions as a reference configuration, and calculate the energies of the 18Λ-S states by a high-level multireference configuration interaction method. The core-valence correlation effect of the 3d orbit of Ge atom, the scalar relativistic effect, and the Davidson correction are taken into consideration in the calculations. On the basis of the calculated potential energy curves of the bound and quasibound electronic states, the spectroscopic constants (Re, Te, ωe, ωeχe, and Be), vibrational energy levels, vibrational wave functions, and Franck-Condon factors (FCFs) are obtained by solving the radical Schrödinger equation. The computed spectroscopic constants of these electronic states are well consistent with previously available experimental results. We calculate the electric dipole moments of electronic states with different bound lengths, and analyze the influences of the variation of electron configuration on the electric dipole moment. The calculated potential energy curves indicate that the adiabatic transition energies of A1Π, 11Σ-, D1Δ, a3Π, a’3Σ+, d3Δ, and e3Σ- sates are located in a range of 26000-37000 cm-1, and the spin-orbit coupling of the states can obviously affect the corresponding vibrational wave functions. With the help of calculated spin-orbit coupling matrix elements, the perturbations of the nearby states to a3Π and A1Π are discussed in detail. Our calculation results indicate that the spin-orbit coupling between A1Π and e3Σ- states has an evident perturbation on the v’> 4 vibrational levels of A1Π, and the v’≥ 0 vibrational levels of a3Π state are perturbed by the crossing states a’3Σ+, d3Δ, e3Σ-, 11Σ-, and D1Δ. On the basis of computed transition dipole moments and FCFs of A1Π-X1Σ+ and A’1Σ+-X1Σ+ transitions, the radiative lifetimes of the six lowest vibrational levels of the two singlet excited states are computed.
Diffraction optical field of the Bessel beam through elliptical annular aperture
Authors: Xie Xiao-Xia  , Wang Shuo-Chen  , Wu Feng-Tie  ,   Fujian Key Laboratory of Optical Beam Transmission and Transformation, College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

Based on Fresnel diffraction theory and complex Gaussian function expansion of hard-edged aperture, the optical field formula of Bessel beam propagating through an elliptical annular aperture is derived, and the transverse intensity distribution of the beam is numerically simulated. The changes of the optical field and the propagation process of the diffracted beam behind the elliptical annular aperture are studied. In the experiment for the first time, a quasi non-diffracting beam is generated by an axicon and the patterns that are due to the beam diffraction by an elliptical annular aperture at different propagation distances are observed with a charge-coupled device camera. The theoretical analysis and experimental results both show that Bessel beam passing through an elliptical annular aperture can generate a hollow beam.
Improving coherent field imaging quality by suppressing the influence of transmitting aperture spacing error
Authors: Cheng Zhi-Yuan  , Ma Cai-Wen  , Luo Xiu-Juan  , Zhang Yu  , Zhu Xiang-Ping  , Xia Ai-Li  ,   Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Coherent field imaging is based on the assumption of equal transmitting apertures spacing and equal spectrum of laser, and high-resolution image is reconstructed by iteratively computing the frequency spectrum. However, the inevitable transmitting aperture spacing error of laser is a key factor to affect the coherent field imaging quality in the application. Aiming at the problem of degrading imaging quality caused by the transmitting aperture spacing error, we discuss the mechanism of influence of aperture spacing error on imaging quality and propose a novel method of improving imaging quality from the perspective of suppressing the influence of transmitting aperture spacing error. Firstly, the mechanism of the influence of aperture spacing error on imaging quality and laser echo spectrum is analyzed in detail. Then we derive a frequency spectrum error propagation model. Based on the model, the iterative effect of frequency spectrum error is investigated and the trend of variation in imaging quality with frequency spectrum error is given. We propose a theoretical equation, in which the transmitting aperture spacing error has no influence on frequency spectrum nor imaging quality. To solve the above equation, an optimized method of linear programming is proposed and the optimized matrix of aperture spacing error is obtained. In practice, the influence of aperture spacing error on imaging quality can be largely counteracted by reasonably allocating aperture spacing error according to the optimized spacing error matrix. The correctness and validity of the theoretical model are verified by a simulation experiment. The results show that the Strehl ratio of imaging quality index can be improved by about 100% through using the proposed method, the greater the aperture spacing error, the higher the Strehl ratio of imaging quality index obtained by the method will be. In addition, the method is easy to use practically and less costly as well. Finally, it is concluded that the proposed method can easily and effectively counteract the degrading effect of aperture spacing error on imaging quality. The research can provide a theoretical basis for improving imaging quality and reasonably assigning transmitter aperture spacing accuracy of coherent field imaging telescope.
Multi-source remote sensing image registration based on scale-invariant feature transform and optimization of regional mutual information
Authors: Zhao Liao-Ying  , Lü Bu-Yun  , Li Xiao-Run  , Chen Shu-Han  ,   Institute of Computer Application Technology, Hangzhou Dianzi University, Hangzhou 310018, China;,   College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

In order to further improve the precision of remote sensing image registration, we propose a new registration scheme by combining the scale-invariant feature transform (SIFT) and the optimization of regional mutual information in this paper. Firstly, taking advantage of the randomness and ergodicity of chaotic sequence, we present a new chaos quantum-behaved particle swarm optimization (CQPSO) algorithm to solve the premature convergence problem of the quantum particle swarm optimization (QPSO) algorithm. By taking full account of the quantity differences among the values of different dimensions for the particle location information, small disturbances are generated as the Hadamard product of chaotic sequence and the particle location information. Before being added to the particle location information, the small disturbances are adjusted by an evolutionary parameter to ensure that each new particle location information is within the scope of reasonable evolution. The image registration scheme consists of two processes, namely the pre-registration process and fine coregistration process. The pre-registration process is implemented by the SIFT approach with a reliable outlier removal procedure. By the repetitive fine-tuning of several selected matched feature point coordinates, a series of registration parameters is estimated by a least square method and used to construct initial particle swarms. Next, the fine coregistration process is implemented to obtain the optimal match parameters by maximizing regional mutual information based on CQPSO. The proposed CQPSO algorithm is tested on several benchmark functions and compared with QPSO as well as standard PSO experimentally. Furthermore, comparative experiments are carried out on the registration of remote sensing images with different ground resolutions and the registration of remote sensing images at different phases by using four algorithms: the SIFT algorithm, SIFT combined with PSO algorithm, SIFT combined with QPSO algorithm, and SIFT combined with CQPSO algorithm. The regional mutual information, root mean square error, and the joint histogram are used to evaluate the performance of the algorithms. The experimental results verify the superiority of CQPSO and the effectiveness of the proposed registration scheme.
Guo-Åberg-Crasemann theory for high harmonic generation and its cutoff law
Authors: Yu Chao  , Sun Zhen-Rong  , Guo Dong-Sheng  ,   State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China;,   School of Physics, Peking University, Beijing 100871, China
Published: December 2020

Based on the scattering theory of Guo-Åberg-Crasemann (GAC), which has no artificial assumptions, high harmonic generation (HHG) is studied by using first-principles. The HHG spectra of different rare atoms are also calculated. Using the properties of ordinary Bessel functions and the Einstein photoelectric law in the strong-field case, we reveal a new cutoff law qcħω = (9 -4√2) Up + (2√2-1) Ip ≈ 3.34 Up + 1.83 Ip of HHG based on a mathematical deduction method and a graphical method, which accords well with the Popmintchev’s experimental result published on Science in 2012. This cutoff law also agrees well with our own calculation using the HHG transition rate formula derived from the GAC scattering theory. Thus, we have four pieces of independent evidence for the same cutoff law of HHG. The cutoff orders predicted by this theory are higher due to the absorption of the extra photons. These photons only participate in the photon-mode up-conversion and do nothing in the photoionization process.