bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiconfiguration time-dependent Hartree-Fock treatment of electron correlation in strong-field ionization of H2 molecules
Authors: Zhang Bin  , Zhao Jian  , Zhao Zeng-Xiu  ,   Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   Department of Physics, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Electron correlation plays an important role in the multielectron interactions of many physical and chemical processes.The investigation of correlation effects in the non-perturbative electronic dynamics (e.g.non-sequential double ionization) when atoms and molecules are subjected to strong laser fields requires non-perturbative theoretical treatments. The direct numerical integration of the time-dependent Schrödinger equation successfully explains many experimental results,but it is computationally prohibitive for systems with more than two electrons.There is clearly a need for a theory which can treat correlation dynamics self-consistently in strong time-dependent electric fields.In this paper we develop a three-dimensional multiconfiguration time-dependent Hartree-Fock method,which can be applied to the non-perturbative electronic dynamics for diatomic molecules,and it can also investigate the effect of electron correlation in strong-field ionization of H2 molecules.This method adopts the prolate spheroidal coordinates (which can treat the two-center Coulomb potential accurately) and the finite-element method together with discrete-variable representation (which lowers the calculation burden from two-electron integrations).For the temporal propagation,we use the efficient short iterative Lanczos algorithm for the equation which governs the configuration expansion coefficients,while an eight-order Runge-Kutta (RK) method and an Bulirsch-Stoer (BS) extrapolation method,both with adaptive precision controls,are implemented to solve the nonlinear orbital equation.While both methods yield correct results,the BS method displays a better stability in the realtime propagation,while the RK method demands less computation.The alignment-dependent ionization probabilities of H2 molecules in intense extreme ultraviolet pulses are calculated.Comparisons between multi-configuration and single-configuration results show that electron correlation has little effect on the single ionization process,but it plays an important role in double ionization,leading to the decrease in the ionization probability.The double ionization probability from the single-configuration space 1σ is about three times larger that from 4σ1π.The ionization probability increases monotonically when the alignment angle increases from 0° to 90°, yielding a ratio of 2.6(1.5) between 90° and 0° for the double (single) ionization process.This method presents the basis for the future study of electron correlation in strong-field processes.
Rectifying performances of oligo phenylene ethynylene molecular devices based on graphene electrodes
Authors: Cui Yan  , Xia Cai-Juan  , Su Yao-Heng  , Zhang Bo-Qun  , Chen Ai-Min  , Yang Ai-Yun  , Zhang Ting-Ting  , Liu Yang  ,   School of Science, Xi'an Polytechnic University, Xi'an 710048, China
Published: December 2020

With the experimental advances in microscale fabrication technology, the designing of functional devices by using single molecules has become one of the most promising methods for the next generation of electronic devices. Molecular rectifier, as a basic component almost for any electronic device, has become a research hotspot in molecular electronics. Recently, one-dimensional graphene nanoribbons (GNRs) which cut off from the novel two-dimensional material-graphene were used as the electrodes for several molecular devices due to their unique electronic structures and transport characteristics. The GNRs have less serious contact problems than metallic electrode materials like gold. In this paper, we investigate the rectifying performances of oligo phenylene ethynylene molecular devices based on graphene electrodes by using the density-functional theory and the non-equilibrium Green's function method. The effect of functional group on the rectifying performances of molecular device is discussed. The results show that the functional group plays a significant role in determining the rectifying performances of oligo phenylene ethynylene molecular device. The rectifying ratio can be effectively tuned by the functional group: adding the donor group (NH2) can lead to the positive rectifying phenomenon, adding the acceptor group (NO2) can trigger the negative rectifying phenomenon, and simultaneously adding NH2 and NO2 groups can bring about an alternate phenomenon between positive and reverse rectifying . The physical mechanism of the rectifying behavior is explained based on the transmission spectra and molecular projected self-consistent Hamiltonian. The transmission spectra of four models (M1-M4) bias voltages in range from-1.0 V to 1.0 V are given. The main transmission peak of M1 for positive bias is similar to that for negative bias, resulting in a weak rectification ratio. However, for M2 and M3, the main transmission peaks for positive and negative bias are significantly different from each other, which shows obviously a rectifying behavior. For M4, the main transmission peak is higher for the bias of (0.44-0.83 V) and also for the bias (0.95-1.00 V), showing an alternate phenomenon between positive and reverse rectifying. The maximum rectification ratio reaches 2.71 by adding an acceptor group (NO2), which suggests that this system has attractive potential applications in future molecular circuit.
Fluorescent investigation on process of tBid inducing membrane permeabilization
Authors: Ma Li  , He Xiao-Long  , Li Ming  , Hu Shu-Xin  ,   Key Laboratory of Soft Matter Physics, 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;,   National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
Published: December 2020

The proapoptotic protein tBid is a member of Bcl-2 family, and it plays an important role in apoptosis by inducing mitochondrial outer membrane permeabilization (MOMP) and lysosomal membrane permeabilization (LMP). Previous studies have shown that the mechanism of tBid-dependent MOMP and LMP depends on tBid interacting with membranes. Researchers hold different opinions about whether tBid itself could induce MOMP and LMP. Some of the researchers insist that tBid must trigger other proteins like Bax or Bak inserting into the membrane, and assembly of tBid itself could not form pores large enough to release cytochrome c. Some others think that tBid just like Bax, can permeabilize mitochondrial outer membrane releasing cytochrome c and lysosomal membrane with the leakage of lysosomal cathepsin B. Here, we want to know whether the tBid itself can induce membrane permeabilization in our model system at low concentration. We use 3 ways to observe tBid and membranes interactions. They are confocal imaging of GUVs (giant unilamellar vesicles), traditional single molecular fluorescence assay, and a recently developed approach, single molecular surface-induced fluorescence attenuation (sm-SIFA). So we can obtain information from single vesicle level and single molecule level. At single vesicle level, we can directly find out whether the GUVs are permeabilized and at the same time the shape of the GUVs is changed. At a single molecule level, we can know the properties of one protein. Especially by using the sm-SIFA, we can obtain the insertion depth of exact residue. Combining the results obtained from different ways under the same conditions, we find that tBid itself can induce the model membrane to permeate, releasing the fluorescent molecules, by oligomerization. What is more, we suggest that the mechanism is that in oligomers some tBids can be inserted deep into the membrane although in oligomers not all the proteins have the same insertion depth. It is indicated that the conformations of tBids in oligomers are diversified. We also prove that the ways we use here are efficient. The GUVs and supported lipid bilayers are indeed tenable model systems. Sm-SIFA has a grand future in the study of protein and membrane interactions.
Numerical simulation of effect of pump distribution on spherical aberration of end-pumped laser
Authors: Yao Qiang-Qiang  , Wang Qi-Han  , Feng Chi  , Chen Si  , Jin Guang-Yong  , Dong Yuan  ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

In order to study the spherical aberration of thermal lens when the laser crystal is pumped with the pump light distributed differently and the pump light under the end-pumping condition, in this paper we establish a single-ended pump and constant temperature thermal model to analyze the working characteristics of the Nd:YVO4 crystal. The steady state heat conduction equation and Zernike polynomials are solved, and the relationship between thermal spherical aberration and distribution of pump laser is established. The model is used in simulation, and the simulation results are further analyzed theoretically, showing that under the same pump power, the spherical aberration is greatest when the pump beam is of 2-order super-Gaussian distribution. The spherical aberration decreases with the increase of pump distribution coefficient k (except the Gaussian distribution). With the increase of pump power, the influence of pump distribution coefficient k on spherical aberration is aggravated gradually, and the difference in spherical aberration caused by different values of distribution coefficient k increases gradually. The range of strongest laser power of the 2-order super-Gaussian distribution pump is analyzed and simulated. Under same pump power, the maximum range of the strongest laser power of 2-order super-Gaussian distribution pump is 0.3-0.63 times the Gauss radius. The research methods and conclusions obtained in this paper have universal applicability and can be used for quantitatively analyzing the temperature distributions, thermal deformations, optical path difference distributions, and spherical aberration distributions of other laser crystals. At the same time, this study also provides a theoretical reference for improving spherical aberration from the perspective of changing the distribution of pump light and the laser output characteristics.
Field effect transistor photodetector based on graphene and perovskite quantum dots
Authors: Zheng Jia-Jin  , Wang Ya-Ru  , Yu Ke-Han  , Xu Xiang-Xing  , Sheng Xue-Xi  , Hu Er-Tao  , Wei Wei  ,   College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China;,   College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China;,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of Chinese Academy of Sciences, Xi'an 710119, China
Published: December 2020

Graphene is an attractive optoelectronic material for various optoelectronic devices, especially in the field of photoelectric detection due to its high carrier mobility and fast response time. However, the relatively low light absorption cross-section and fast electron-hole recombination rate can lead to rapid exciton annihilation and small light gain, which restrict the commercial applications of pure graphene-based photodetector. The perovskite has attracted much attention because of its high photoelectric conversion efficiency in the field of solar cells. The perovskite has the advantages of long carrier diffusion distance and high optical absorption coefficient, which can effectively make up for the shortcomings of pure graphene-based field-effect transistor. In this work, a field-effect transistor photodetector is demonstrated with the combination of graphene and halide perovskite quantum dots (CsPbI3) serving as conductive channel materials. The graphene is prepared by plasma enhanced chemical vapor deposition, and the quantum dots are CsPbI3 perovskite. The electrical properties of graphene and pure graphene-based field-effect transistor are detected and analyzed by using the Raman spectrum. The results show that the graphene has good intrinsic electrical properties. Unlike previous report in which bulk perovskite was used, the perovskite quantum dot field-effect transistor photodetector has an obvious light response to 400 nm signal light, and shows the excellent photoelectrical performance. Under the illumination of 400 nm light, the signal light could be detected steadily and repeatedly by the graphene-perovskite quantum dot photodetector and converted into photocurrent. The photocurrent of the photodetector has a rapid rise, and the maximum value can reach 64 A at a light power of 12 W. The corresponding responsivity is 6.4 AW-1, which is two orders of magnitude higher than that of the general single graphene photodetector (10-2 AW-1), and it is also higher than that of perovskite-based photodetector (0.4 AW-1). In addition, the photoconductive gain and detectivity arrive at 3.7104 and 6107 Jones (1 Jones=1 cmHz1/2W-1), respectively. The results of this study demonstrate that the graphene-perovskite quantum dot photodetector can be a promising candidate for commercial UV light detectors.
Glass transition in binary mixture of colloidal ellipsoids and spheres
Authors: Sun Yan-Li  , Wang Hua-Guang  , Zhang Ze-Xin  ,   Centre for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, Suzhou 215006, China
Published: December 2020

The nature of glass and glass transition are considered to be one of the most fundamental research problems in condensed matter physics. Colloidal suspension provides a novel model system for studying glass and glass transition, since the structures and dynamics of a colloidal system can be quantitatively probed by video microscopy. Traditional systems for studying glass transition typically are single-component systems composed of either isotropic or anisotropic colloidal particles. Recently, glass transition of mixture of isotropic and anisotropic colloids has attracted great attention, such as the observation of rotational glass and translational glass, and the establishment of the two-step glass transition. Similarly, computer simulations have also shown that mixture of isotropic and anisotropic colloidal particles could manifest interesting, new glassy behaviors. However, the experimental study of the glass transition in such a colloidal mixture is still rare. In this paper, we experimentally investigate the glass transition of a binary mixture of colloidal ellipsoids and spheres. The colloidal spheres are polystyrene microspheres with a diameter of 1.6 m, and the ellipsoids are prepared by physically stretching from polystyrene microspheres of 2.5 m in diameter. The major and minor axes of the as-prepared ellipsoid are 2.0 m and 1.2 m, respectively. The mixture is confined between two glass slides to make a quasi-two-dimensional sample. To prevent the mixture from crystallizing, the mixing ratio of ellipsoids and spheres is chosen to be 1/4 in number, which is similar to the mixing ratio used in the classical Kob-Anderson model of binary sphere mixture. We systemically increase the area fraction of colloidal mixture to drive the glass transition. We then employ bright-field video microscopy to record the motion of the particles in the colloidal suspension at a single particle level, and the trajectories of individual particles are obtained by standard particle tracking algorithm. Through the analysis of radial distribution function, Voronoi diagram and local order parameter, we find that the ellipsoids can effectively inhibit the spheres from crystalizing, and the structure of the system remains disordered when increasing the area fraction. For dynamics, mean square displacement and self-intermediate scattering function are calculated. We find that the dynamic process of the system slows down substantially when increasing the area fraction, and the relaxation time of the system increases rapidly and diverges close to the glass transition point predicted by the mode coupling theory. Moreover, we analyze the fast particles that participate in cooperative rearrangement regions (CRRs) in the system, and find that the shapes, sizes and positions of CRRs are closely related to the locations of the ellipsoids in the system.
Coupling effects of surface elasticity and disjoining pressure on film drainage process
Authors: Ye Xue-Min  , Li Ming-Lan  , Zhang Xiang-Shan  , Li Chun-Xi  ,   Key Laboratory of Condition Monitoring and Control for Power Plant Equipment, North China Electric Power University, Baoding 071003, China
Published: December 2020

The aim of the present paper is to investigate the gravity-driven draining process containing insoluble surfactants, with the coupling effects of surface elasticity and disjoining pressure taken into consideration. A set of evolution equations including liquid film thickness, surface velocity and surfactant concentration, is established based on the lubrication theory. Assuming that the top of the liquid film is attached to the wireframe and the bottom is connected to the reservoir, the drainage stability is simulated with the FreeFem software. The characteristics of film evolution under the coupled effects of surface elasticity and disjoining pressure are examined, respectively. The simulated results show that the surface elasticity and the disjoining pressure have significant influences on the vertical thin film draining process. Under the effect of the surface elasticity alone, the initial film thickness increases with the elasticity increasing and the black film only forms on the top of the liquid film, but cannot stably exist and breaks quickly. The addition of the surface elasticity can increase the liquid film thickness and the drainage time, reduce the surface velocity, and rigidify the interface. When the disjoining pressure is applied merely, the surfactant flows into the reservoir continuously; hardly can the liquid film form a surface tension gradient and thus cannot form a countercurrent phenomenon. Under the coupling effect of the surface elasticity and disjoining pressure, a more stable liquid film forms. In the early stage of drainage, surface elasticity increases the film thickness, reduces the surface speed and generates the liquid countercurrent to slow the drainage process. When the black film appears, the electrostatic repulsion of the disjoining pressure is notable and makes the black film stable. The results obtained in the paper are in agreement with some of the experimental results in the literature. However, the elasticity-related surface tension and surfactant concentration model used is a simplified model. The nonlinear relationship between surface tension and surfactant concentration should be further considered in future theoretical models.
Multipactor in parallel-plate transmission line partially filled with dielectric material
Authors: Zhai Yong-Gui  , Wang Rui  , Wang Hong-Guang  , Lin Shu  , Chen Kun  , Li Yong-Dong  ,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   National Key Laboratory of Science and Technology on Space Microwave, China Academy of Space Technology(Xi'an), Xi'an 710100, China
Published: December 2020

Due to the poor conductivity of the dielectrics, if an electron collides with the dielectric material, a charge will be deposited on the surface as a consequence of the secondary electron emission. Thus, the multipactor process in dielectric-loaded microwave devices differs from those in metallic devices. The objective of this paper is to study the self-extinguishing physical mechanism of the multipactor in parallel-plate transmission lines partially filled with dielectric layers by particle-in-cell simulation. The self-consistent field generated by the electrons in the simulation is assumed to be neglected, since there do not exist too many electrons in the self-extinguishing process. To illustrate the self-extinguishing phenomenon in a dielectric-loaded waveguide device, the strength of electric field in the vacuum area needs to be the same as that in a metallic device. When the input power is slightly higher than the multipactor threshold, the self-extinguishing phenomenon occurs after the initial electron multiplication while the number of electrons increases exponentially with the simulation duration in metallic device. Based on this fact, the physical mechanism of self-extinguishing phenomenon is investigated in detail. By analyzing the temporal evolution of the electrons and the average secondary electron yield (SEY), it can be concluded that the self-extinguishing phenomenon is caused by the electrostatic field generated by the charges deposited on the surface of the dielectric. Moreover, the average SEY of the dielectric tends to be one or greater than one when the number of electrons drops to nearly zero. Hence, it is necessary to further analyze the ability to continue accumulating charges on the dielectric surface when extra electrons are injected into the simulation region at the instant when the number of electrons is close to zero. For the former case, the charges deposited on the dielectric surface remain steady all along, while the charges reach to a stable state eventually as the number of injected electrons increases for the latter one. Both of them mean that the average SEY of the dielectric surface will be unity in the end. Since the electrostatic field generated by the charge deposited on the dielectric surface can reduce the risk of occurrence of multipactor, the electret material could be used in the design of the dielectric-loaded microwave devices to improve the multipactor threshold.
Design and simulation of output mode conversion structure of relativistic magnetron with all cavity output
Authors: Yang Wen-Yuan  , Dong Ye  , Dong Zhi-Wei  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

A relativistic magnetron using all cavity extraction and semi-transparent cathode has the virtues of compactness, high output power and high efficiency. The three-dimensional particle-in-cell simulations show that 1.15 GW output microwave with an efficiency about 50% can be obtained at S-band with pure TE11 mode of the fan waveguide.
However, due to the fact that the output structure is composed of three detached fan waveguides, mode conversion structure in the output region is required for the convenience of practical applications. Therefore, two mode conversion structures are studied for the output mode conversion. The first structure is to widen gradually or abruptly the fan waveguide in the azimuthal direction from a given position (starting point) along the microwave transport direction. And then the three fan waveguides are connected into one coaxial waveguide. The effects of the position of the starting point on the beam-wave interaction and microwave extraction are numerically studied. For the convenience of description, we define L as the axial distance between the center of the output coupling hole and starting point. Simulation results show that for the abrupt and gradual variation case, when the length of L changes in a relatively wide region, the output power is larger than 1.0 GW in TEM mode at S-band. It is about 90% of the conventional fan waveguide with 1.15 GW. For the gradual variation case, the optimal value of L equals 10.0 cm, and the corresponding output power is beyond 1.0 GW. For the abrupt variation case, the optimal value of L equals 13.75 cm, the corresponding output power is about 1.15 GW. But in the abrupt variation case, the output power is a little more sensitive to the value of L. The second structure is to convert the fan waveguide into a rectangular waveguide. Ａcompound waveguide composed of a section of fan waveguide and a section of rectangular waveguide is designed for studying its feasibility. In the compound waveguide, the wide edges of the cross section of the rectangular waveguide are tangent to the inner and outer arc of the fan cross section respectively. And the narrow edges cross the end points of the outer arc. Simulation results show that in the compound waveguide the microwave with TE11 mode of the fan waveguide input at the inlet can be changed into the TE10 mode of the rectangular waveguide at the outlet with almost no power loss. In all, the output microwave power larger than 1.0 GW could be obtained after using the two proposed mode conversion structures. In practical applications, one could choose the relevant mode conversion structure according to the requirement.
Microstructure and thermoelectric properties of In2O3/poly(3, 4-ethylenedioxythiophene) composites
Authors: Tao Ying  , Qi Ning  , Wang Bo  , Chen Zhi-Quan  , Tang Xin-Feng  ,   Hubei Nuclear Solid Physics Key Laboratory, School of Physics and Technology, Wuhan University, Wuhan 430072, China;,   State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430072, China
Published: December 2020

Poly(3, 4-ethylenedioxythiophene) (PEDOT) has applications in many areas due to its exciting electrical performance and high stability. Since it has very low thermal conductivity, it is also a good organic thermoelectric material. However, the ZT value of pure PEDOT is rather low, because the electrical properties such as conductivity are still not satisfactory. It is found that the thermoelectric performance can be enhanced by adding inorganic thermoelectric materials into PEDOT to form composites. In this paper, we synthesize a composite of In2O3/PEDOT by chemical oxidation. Microstructure of the composite is studied by X-ray diffraction, infrared spectroscopy, transmission electron microscope, and positron annihilation spectroscopy. The XRD measurements show that the pure PEDOT sample is amorphous, and the crystallinity in composite sample is contributed by In2O3. Besides, the diffraction peaks become sharper with increasing the In2O3 content. Transmission electron microscope measurements confirm that the PEDOT sample is amorphous and the shapes of In2O3 particles are regular. The surfaces of the In2O3 particles are wholly coated with thin layers of PEDOT, and when the In2O3 content is higher than 22 wt%, the In2O3 particles cannot be uniformly dispersed in pure PEDOT layers. The positron annihilation measurements reveal the interface structure in the In2O3/PEDOT composite, which can capture positron and cause the lifetime of positron to increase. The relative quantity of interface increases with In2O3 content increasing. However, when the In2O3 content is more than 22 wt%, the interface structure is destroyed. All the measurements show that when the In2O3 content is lower than 22 wt%, the In2O3 nanoparticles are well dispersed in PEDOT. The electrical conductivity of In2O3/PEDOT composite increases with In2O3 content increasing. At room temperature, the electrical conductivity of PEDOT is 7.5 S/m, while in the In2O3/PEDOT sample with 12.3 wt% In2O3, a maximum electrical conductivity of 25.75 S/m is obtained. When the In2O3 content increases from 0 to 22 wt%, the power factor of the composite increases rapidly from 14.5×10-4 to 68.8×10-4 μW/m·K2. On the contrary, the thermal conductivity shows decrease compared with the thermal conductivity of pure PEDOT. The ZT value of the composite increases from 0.015×10-4 to 0.073×10-4. Our results indicate that the thermoelectric properties of In2O3/PEDOT composite can be effectively improved compared with those of the pure PEDOT
Effect of twining on dynamic behaviors of beryllium materials under impact loading and unloading
Authors: Pan Hao  , Wang Sheng-Tao  , Wu Zi-Hui  , Hu Xiao-Mian  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

As a rare metal material with low density, high strength and high melting point, beryllium (Be) is widely utilized in many fields including aerospace and vehicles. Dynamic loadings such as impact and high-rate compression often happen in the applications of Be materials in these fields. However, the dynamic behaviors of Be materials under high pressure and high-rate loading have not been fully investigated, although they are valuable for better applications of Be materials. articularly, the effect of twinning on dynamic behaviors of Be material is very important for better understanding the plasticity deformation mechanism of Be material. In this paper, a thermoelastic-viscoplastic crystal plasticity model is developed for dynamic behaviors of Be material under high pressure and high strain-rate loading based on the physical mechanism of plasticity deformation. Besides, the dislocation motion and work hardening are considered within the constitutive framework by the Orowan relation and the Taylor equation respectively, and the contribution of twinning to the plasticity deformation is also considered via twinning fraction evolution and fragmentation of crystal due to twinning deformation. With the model, dynamic behaviors of Be material are investigated, including effect of pressure on the dynamic yield strength, the quasi-elastic unloading behavior, and evolution of twinning in shock loading and unloading. Compared with the classical SG model, the model developed in this paper accords better with the experimental results in predicting yield strength of Be material under impact loading, especially with high pressure. Moreover, it is revealed that the condition of yield strength of the Be material is divided into three cases, namely the non-twinning under low pressure, the twinning deformation under moderate pressure, and the twinning fragmentation under high pressure. The unloading behavior of Be material under impact loading is also studied with the model, and the quasi-elastic unloading behavior observed in experiments many times, is faithfully predicted. It is found that the quasi-elastic unloading phenomenon of the material is closely related to the variation of the shear velocity of shock wave with the shear strain, which suggests that the non-linear elastic property of the material is an important reason for this phenomenon. Finally, the evolution of twinning of Be material in the shock loading is studied, showing that the increasing of twinning friction happens not only in the loading process but also in the unloading process of the shock waves. Some crystals break up into sub-crystals due to the fact that the volume fraction of twinning exceeds the critical fraction in the evolution of twinning.
First-principles study of stacking effect on second harmonic generation of graphene-like two-dimensional silicon carbide
Authors: Shi Jia-Yu  , Lan You-Zhao  ,   College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

Two-dimensional layered silicon carbide (2d-SiC), a semiconductor with graphene-like structure, has potential applications in nonlinear optical frequency conversion. The effect of stacking and strain on the nonlinear second harmonic generation (SHG) coefficient are studied by using the first-principles calculation of the all-electron full-potential linearized augmented-plane wave combined with the sum-over-states method. The analysis of physical origin of the SHG process shows that the single-particle transition channel formed by three bands dominates the SHG process of 2d-SiC. The interband motion of electrons is significantly tuned by the intraband motion. The angle dependence of the SHG coefficient of 2d-SiC is given as a reference for future experiments. A tunable SHG enhancement could be obtained by straining 2d-SiC.
Orientation effect of asymmetric diatomic molecules in transport diffusion
Authors: Jiang Zhi-Liang  , Chen Pei-Rong  , Zhong Wei-Rong  , Ai Bao-Quan  , Shao Zhi-Gang  ,   Department of Physics and Siyuan Laboratory, Jinan University, Guangzhou 510632, China;,   Guangdong Province Key Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
Published: December 2020

Non-equilibrium transport is an important research area in statistical physics. The influences of the structures of polyatomic molecules on their transport have attracted the attention of researchers. Up to now, most of researchers deemed that temperature gradient is the main factor for molecular orientation and neglected the effect of the chemical potential gradient on the molecular orientation. To make up the deficiency in the study of chemical potential gradients, we build a non-equilibrium system with both chemical potential gradient and temperature gradient, and study the transport diffusion behavior of asymmetric diatomic molecules by using molecular dynamics and Monte Carlo methods. It is found that the diatomic molecules implement the orientation effect during non-equilibrium transport. Under the chemical potential gradient, the molecular orientation effect leads to the fact that the large atom tends to be in the direction of low concentration particle bath, while the small atom tends to be in the direction of high concentration particle bath. The molecular orientation is opposite to the direction of the flow. Under the temperature gradient, the molecular orientation effect leads to the fact that the large atom tends to be in the direction of high temperature particle bath, while the small atom tends to be in the direction of low temperature particle bath. The molecular orientation is the same as the direction of the flow. The orientation direction caused by concentration gradients is opposite to that caused by temperature gradients and it appears as a competitive relationship. At the same time, the influence of the asymmetry of the molecule itself on the molecular orientation is also studied. The larger the asymmetry of the molecule itself (σB/σA), the more obvious the molecular orientation effect is. When σB/σA>1.6, the influence of the asymmetry of the molecule itself on the orientation effect is gradually saturated. When σB/σA=1, which is also for a symmetric molecule, even if neither the temperature gradient nor the chemical potential gradient is zero, no molecular orientation occurs. We explain the physical mechanism of orientation through the principle of minimum entropy production. This work is of theoretical significance for in depth understanding the relationship between mass transport and molecular structure under non-equilibrium conditions.
Theoretical and experimental study of self-reconstruction property of astigmatic Bessel beam
Authors: Yang Yan-Fei  , Chen Jing  , Wu Feng-Tie  , Hu Run  , Zhang Hui-Zhong  , Hu Han-Qing  ,   Fujian Key Laboratory of Light Propagation and Transformation, College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

In this paper, the self-reconstruction property of astigmatic Bessel beam is studied experimentally and theoretically. Based on the Fresnel diffraction integral theory and Babinet principle, the general expression of the intensity distribution of astigmatic Bessel beams passing through a circular obstacle is derived. The cross-section light intensity at transmission distance of, 10, 30, and 80 mm after astigmatism of the astigmatic Bessel beam are occluded by circular obstacles. The self-reconstruction process of the light field is observed and verified by using an specially designed experimental setup. In the experiment, we choose He-Ne laser as a light source, collimate and expand the beam through a telescope system, and a zero-order astigmatic Bessel beam is generated by a beam vertically incident on the tilted axicon after the diaphragm. A circular obstacle with a radius of 0.2 mm is placed at a distance of 200 mm behind the axicon. Finally, the cross-section intensities at different distances are observed and recorded by a microscope. The experimental phenomena are in good agreement with the theoretical prediction. The results show that the reconstruction of the zero-order astigmatic Bessel beams will occur after passing through the on-axis and off-axis obstacles. And as the transmission distance increases, the outer contour size of the astigmatic Bessel beam becomes larger, and the number of central spot arrays increases, and the complete beam is gradually reconstructed. Particularly, this feature is different from the behavior of the non-diffracting Bessel beam, which maintains the light field unchanged during transmission and has a single central spot. It is expected to be applied to multi-layer multi-particle control. And a new optical property is discovered in the experiments: the reconstruction speed of the beam in the horizontal and vertical direction are not consistent in the reconstruction process, and there is a certain speed difference. Further, we add a spiral phase plate between the diaphragm and the axicon to produce a high-order astigmatic Bessel beam. And it is verified that the high-order astigmatism Bessel beam has the same self-reconstruction characteristics after being shielded by obstacles. Compared with the zero-order aperture system, the high-order beam can not only expand the operating range, but also use the orbital angular momentum carried by the beam to achieve light rotation, which makes the particle manipulation more flexible. The research proves the self-reconstruction characteristics of astigmatic Bessel beams theoretically and experimentally, and broadens the research range of astigmatic Bessel beams. The research results have practical significance and application value in the field of optical micro-manipulation.
Research progress about 111-typed iron based superconductor
Authors: Wang Xian-Cheng  , Jin Chang-Qing  ,   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
Published: December 2020

111-typed iron based superconductors have three members: LiFeAs, NaFeAs and LiFeP. The family of LiFeAs itself does not show any long range magnetic order but become superconductor without chemical doping. NaFeAs displays the separation of structural and magnetic transition, suitable to investigate the origin of the two transitions. LiFeP has been proved to be a nodal superconductor. The structure of 111 compounds consists of[FeAs/P] layers intercalated with two alkali metal layers, which makes single crystals easy to be cleaved into two equal counterparts with non-polar surface and thus is favored by the surface characterization techniques, such as the research of angleresolved photoemission experiment and scanning tunneling microscope measurement. Up to now, fruitful results have been achieved about the study of 111 family. In this paper, we summarize recent progresses on this family.
Bifurcation mechanism of not increase but decrease of spike number within a neural burst induced by excitatory effect
Authors: Cao Ben  , Guan Li-Nan  , Gu Hua-Guang  ,   School of Aerospace and Applied Mechanics, Tongji University, Shanghai 200092, China
Published: December 2020

Nonlinear dynamics is identified to play very important roles in identifying the complex phenomenon, dynamical mechanism, and physiological functions of neural electronic activities. In the present paper, a novel viewpoint that the excitatory stimulus cannot enhance but reduce the number of the spikes within a burst, the novel viewpoint which is different from the traditional viewpoint, is proposed and is explained with the nonlinear dynamics. When the impulse current or the autaptic current with suitable strength is used in the suitable phase within the quiescent state of the bursting pattern of the Rulkov model, a novel firing pattern with reduced number of spikes within a burst is evoked. The earlier the application phase of the current within the quiescent state, the higher the threshold of the current strength to evoke the novel firing pattern is and the less the number of the spikes within a burst of the novel firing pattern. Moreover, such a novel phenomenon can be explained by the intrinsic nonlinear dynamics of the bursting combined with the characteristics of the current. The nonlinear behaviors of the fast subsystem of the Rulkov model are acquired by the fast and slow variable dissection method, respectively. For the fast subsystem, there exist a stable node with lower membrane potential, a stable limit cycle with higher membrane potential, a saddle serving as the border between the stable node and limit cycle, a saddle-node bifurcation, and a homoclinic orbit bifurcation. When external simulation is not received, the bursting pattern of the Rulkov model exhibits behavior alternating between the spikes corresponding to the limit cycle of the fast subsystem and quiescent state of the fast subsystem, which is located within the parameter region between the saddle-node bifurcation point and the homoclinic orbit bifurcation point of the fast subsystem. The spikes begin with the saddle-node bifurcation and end with the homoclinic orbit bifurcation. As the bifurcation parameter turns close to the homoclinic orbit bifurcation, the disturbation or stimulus that can induce the transition from the quiescent state to the spikes becomes strong. Therefore, as the application phase of the current within the quiescent state becomes earlier, the strength threshold of the current that can induce the transition from the quiescent state to the spikes becomes stronger, and the initial phase of the spikes becomes closer to the homoclinic orbit bifurcation, which leads the parameter region of the spikes to become shorter and then leads the number of spikes within a burst to turn less. It is the dynamical mechanism of the decrease of the spike number induced by the excitatory currents. The results enrich the nonlinear phenomenon and dynamical mechanism, present a novel viewpoint for the excitatory effect, and provide a new approach to modulating the neural bursting patterns.
Periodic solution and its stability of spring pendulum with horizontal base motion
Authors: Zhang Li-Juan  , Zhang Hua-Biao  , Li Xin-Ye  ,   1. Institute of Mechanical Engineering, Hebei University of Technology, Tianjin 300130, China;,   2. Institute of Mechanical Engineering, Tianjin University of Commerce, Tianjin 300134, China
Published: December 2020

In this paper, the nonlinear dynamic response of spring pendulum with horizontal base motion is studied. The dynamical equations of the system are established by using Lagrange equation. The discrete Fourier transform, harmonic balance method and homotopy continuation method are combined to solve the periodic response of the system, which avoids the limitation of the small amplitude caused by the Taylor expansion in the traditional analytical method. The comparison with the numerical results shows that the proposed method in this paper can not only be used to solve the large amplitude vibration of spring pendulum, but also has a high accuracy. The stability of periodic response is studied by using Floquet theory. The effects of amplitude and frequency of base motion on the periodic response of the system are given, and the bifurcation characteristics of the periodic solution are analyzed. The results show that the influence curve of the base frequency on the periodic response has two peaks, and with the increase of the amplitude of the base motion, the two peaks will shift to the different sides respectively. When the base amplitude is large, the periodic response amplitude changes with the frequency of the foundation motion, and there will be two jumps. The amplitude of the periodic solution increases with the base amplitude. For some base frequencies, the amplitude of the periodic solution will jump with the change of the base amplitude. When the amplitude and frequency of the system are large, the periodic response of the system may be unstable. After the instability, the spring pendulum enters the continuous rotation state, and the amplitude in the breathing direction is great, the system will be destroyed. It is found that Hopf bifurcation may occur in the periodic response of the system corresponding to some base frequencies and amplitudes. The variation of the system response with the base frequency and amplitude after the Hopf bifurcation is studied numerically by the Runge-Kutta method. Complex dynamical behaviors such as periodic motion, almost periodic motion, torus doubling and chaos are found. It is shown that the main path of the system entering chaos is almost periodic torus rupture and paroxysmal. Finally, the influence analysis of the base frequency and amplitude is synthesized, and the transition of the response form on the plane of the basic motion parameters is given. The results of this paper provide a theoretical reference for the analysis and design of spring pendulum in engineering.
Theoretical study on potential curves and spectroscopic constants of low-lying electronic states of Na2+ cation
Authors: Wei Chang-Li  , Liao Hao  , Luo Tai-Sheng  , Ren Yin-Shuan  , Yan Bing  ,   1. School of Physics and Electronics, Qiannan Normal University for Nationalities, Duyun 558000, China;,   2. Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy(Jilin University), Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
Published: December 2020

In this paper, high-level ab initio calculations by using multi-configuration self-consistent field method with atomic effective core potential, polarization potential, and uncontracted Gaussian basis function, are performed to compute the potential energy curves of a total of 36 low-lying ∧-S states with ∑g,u, Πg,u, △g,u symmetries of Na2+ cation associated with the lowest 9 dissociation limits Na (3s, 3p, 4s, 3d, 4p, 5s, 4d, 4f, 5p)+Na+. On the basis of the potential energy curves, the spectroscopic constants (Te, Re, ωe, ωeχe, Be, α e, De) of the bound states are determined, which are in good agreement with the existing available experimental and theoretical values. Our results indicate that 52∑g+-72∑g+, 32∑u+-72∑u+, 22Πg, 42Πg, 12△u and 22△u states are repulsive, which supports Berriche's results, and we report 10 electron states for the first time, that is, 82∑g, u+-92∑g, u+, 52Πg, u-72Πg, u and 32△g, u. The vibrational-rotational spectroscopic constants and lowest vibrational-rotational energy levels (ν=0-20) of the bound states are also presented. Moreover, in order to illustrate the strong state interactions of adjacent states with same symmetry, the information about the avoided crossing points is shown in detail. Finally, the transition dipole moments from a few low-lying excited states (12Πu-32Πu) to the ground state X2∑g+ are computed. Therefore, it is expected that our computational results in the present calculations are significant for the molecular spectroscopy, ion-atom interaction and molecular cold collision fields.