bluuebunny/crossref_metadata_2025 huggingface dataset:
Perpendicular magnetic anisotropy in the CoFeB/Pt multilayers by anomalous Hall effect
Authors: Liu Na  , Wang Hai  , Zhu Tao  ,   Department of Physics, Capital Normal University, Beijing 100048, China;,   State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The perpendicular magnetic anisotropy (PMA) in as-deposited [CoFeB/Pt]n multilayer is studied by using anomalous Hall effect. A clear PMA is observed in the ultrathin (～ 0.5 nm) amorphous CoFeB layer sandwiched by Pt. The PMA in as-deposited [CoFeB/Pt]n multilayers is strongly dependent on the thicknesses of CoFeB, Pt, and the number of CoFeB/Pt bilayers. With the increase of the number of CoFeB/Pt bilayers (n ≥ 5), the hysteresis loop changes from rectangular to bow-tie shaped, and then the net moment approaches to zero in the remnant state. Moreover, the coercivty of [CoFeB/Pt]n multilayers is much low, which meets the requirement for free perpendicular electrode in the future spintronic device.
Properties and coherence-controlling of entanglement of a two-qubit Heisenberg XY chain with intrinsic decoherence
Authors: Jiang Chun-Lei  , Liu Xiao-Juan  , Liu Ming-Wei  , Wang Yan-Hui  , Peng Zhao-Hui  ,   School of Physics, Hunan University of Science and Technology, Xiangtan 411201, China
Published: December 2020

By solving the Milburn equation, we investigate the thermal entanglement properties of a two-qubit Heisenberg XY chain in the presence of intrinsic decoherence. The controls of nonuniform magnetic field, the initial state of two qubits, the relative phases and the amplitudes of the polarized qubits on thermal entanglement are studied. The results show that for a particular initial state, the thermal entanglement can be increased by the external magnetic field. The time behavior of the entanglement exhibits a strong dependence on the initial state of two qubits, and it can be manipulated by changing the relative phase and the amplitudes of the polarized qubits. It is also notable that stable entanglement, which is dependent on initial state of the qubit, occurs even in the presence of decoherence. The magnetic field may have a constructive effect on the stable entanglement for a certain initial state, and the Bell-diagonal state turns out to be a dark state of the system in the absence of the magnetic field.
Suprathreshold stochastic resonance of a non-linear multilevel threshold neuronal networks system
Authors: Guo Yong-Feng  , Tan Jian-Guo  ,   School of Science, Tianjin Polytechnic University, Tianjin 300387, China
Published: December 2020

Suprathreshold stochastic resonance can be used to explain some biologic phenomena. In this paper, the suprathreshold stochastic resonance of a non-linear multilevel threshold neuronal network system is studied. The expression of the mutual information is derived, and the effects of the noise intensity and the system parameter on mutual information are discussed. The numerical computation results show that in the process of information transmission the selection of the threshold is very important according to the different effects of additive noise and multiplicative noise on system. Moreover, we also find that the more the number of devices, the more apparent the phenomenon of suprathreshold stochastic resonance is.
Information entropies and dynamics in the stochastic ecosystem of two competing species
Authors: Xie Wen-Xian  , Cai Li  , Yue Xiao-Le  , Lei You-Ming  , Xu Wei  ,   Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Using the models of stochastic population dynamics, the competitions and interactions of interspecies and between species and the stochastic environment are studied. In this paper, the stochastic ecosystems (in Itô or Statonovich model) of two competing species are investigated through evaluating probability densities and information entropy fluxes and productions of two species. The formulas of entropy flux (i.e. expectation of divergence) and entropy production are educed for numerical calculations, through the corresponding Fokker-Planck equation with its condition and the definition of Shannon entropy. The nonlinear characteristics of entropy fluxes are captured and the relationships are found between the extremal points of entropy productions and the rapid transitions or bifurcations. The numerical results obtained with path integration method show that the probability densities and Shannon entropies of these two stochastic models (in Itô or Statonovich meaning) have the same evolutional tendency but with different points of extrema.
Saturation property of mean growth of initial error for chaos systems
Authors: Yang Jin-Hui  , Song Jun-Qiang  ,   School of computer, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The saturation property of mean growth of initial error and the relation between saturation value and predictability limit of chaos system are studied in a frame of the nonlinear error growth dynamics. Firstly, the saturation property of mean relative growth of initial error (RGIE) of Lorenz96 system is investigated. It is found that there exists a simple linear relationship between the logarithm of saturation value of mean RGIE and initial error. The sum of logarithms of the two is constant that is independent of the magnitude of the initial error. It is proven by experiment that this conclusion is suitable for other chaotic systems too. With this conclusion, once the constant sum has been determined, the saturation values of mean RGIE at any magnitude of initial error can be calculated easily. Furthermore, to make the study of the relation between error growth saturation and the predictability limits more convenient, just as the definition of the mean RGIE, a definition of the mean absolute growth of initial error (AGIE) is introduced and theoretical analysis reveals that the AGIE has a similar saturation property as RGIE. The saturation value of mean AGIE is constant, which means for a given chaos system, once the control parameters of the system has been determined, the saturation of AGIE is determined. Finally a model for calculating predictability limit quantitatively is given as follows: Tp=1/∧ln(Es/δ0)+c, where Es is the saturation value of mean AGIE. It is shown that this model can work with complicated and high dimension chaos system very well.
Propagation of helical beams through amplitude diffractive optical elements and the measurement of topological charge
Authors: Xin Jing-Tao  , Gao Chun-Qing  , Li Chen  , Wang Zheng  ,   School of Optical-Electronics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

A new method is proposed to generate amplitude diffractive optical elements such as Young's double-slits and triangular apertures from a spatial light modulator (SLM). With the help of plane wave angular spectrum diffraction formula and Collins formula, the propagation property of helical beams passing through those two amplitude optical elements is studied, and the measurement of topological charge of helical beams is also achieved with those two amplitude diffractive optical elements. Due to the fact that the SLM can flexibly and accurately change the configurations and locations of optical elements, the measurements can be conveniently achieved.
Fabricating three-dimensional periodic micro-structure with planar defects via a single exposure
Authors: Chen Xiao-Jun  , Zhang Zi-Li  , Ge Hui-Liang  ,   Department of Physics, HongKong University of Science and Technology, HongKong, China;,   Hangzhou Institute of Applied Acoustics, Hongzhou 310012, China
Published: December 2020

In this paper, we introduce a method to incorporate a planar defect into the fcc-like photonic crystal structure by utilizing a negative photoresistor SU8. This method in which multi-coating and a single exposure are used simplifies the experiment much more than other methods. In the paper, we exhibit the SEM images for the intact and defective structures. Corresponding to each structure, the reflection spectrum in (1 1 1) direction fabricated shows obviously characteristic peaks and pits. For the intact structure, the spectrum contains two peaks whose wavelengths approach to 1.2 μm and 2.2 μm. These two peaks corresponds to two optical forbidden gaps. For the structure with planar defect, a pit which splits the optical forbidden gap is considered to be a defect mode exhibited on spectral curve. The structure parameters are extracted from the SEM image and used to simulate the reflectance spectra via FDTD program. The simulation results almost match the experiment data accurately.
Application of leading structure on thermal protection of nosetip
Authors: Sun Jian  , Liu Wei-Qiang  ,   Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The structure of embedded high thermal conductivity carbon material leading thermal protection is considered as thermal protection system to prevent hypersonic vehicle nosetip which requires sharp figure during hypersonic flying, from being seriously aerodynamically heated. By fluid structure interaction method, we analyze leading thermal protection of nosetip and validate that embedded high thermal conductivity carbon material structure has a good effect on thermal protection. The maximal temperature of the nosetip which uses leading thermal protection structure is reduced by 21.9% and the lowest temperature of aft is increased by 15.2% when Mach number is 9. The transfer of heat from head to after-body is achieved, the thermal load of the front head is weakened and the ability of leading-edge thermal protection is strengthened. The influences of structure parameter and material attributes of coating and thermal conductivity of high conductivity carbon material on thermal protection are discussed. The highest temperature of the nosetip decreases with thermal conductivity of coating increasing to a steady value and descends with blackness level of coating ascending and increases with the thickness of coating increasing, and it descends in parabola form as thermal conductivity of carbon materials increases.
Statistical modeling arbitrary diversitiy multi-input multi-output systems
Authors: Hai Lin  , Zhang Ye-Rong  ,   College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210003, China
Published: December 2020

A new form of power matrix is proposed to correct the unreasonable points in traditional statistical multi-input multi-output (MIMO) channel model which mishandles different power variations in different polarization direction. Based on the analysis of modeling theory of different diversities, a composite calculation method of power matrix and covariance matrix is proposed to build a general-purpose statistical channel model which exactly represents statistical characteristics under the effects of space-diversity and polarization-diversity, and thus can be applied to arbitrary diversity MIMO systems.
Design of metamaterial absorber and its applications for waveguide slot antenna
Authors: Liu Tao  , Cao Xiang-Yu  , Gao Jun  , Zheng Qiu-Rong  , Li Wen-Qiang  ,   Telecommunication Engineering Institute of Air Force Engineering University, Xi'an 710077, China
Published: December 2020

A metamaterial absorber is designed and applied to the waveguide slot antenna. The absorber is composed of two metallic layers separated by a lossy dielectric spacer. The top layer consists of etched oblique cross-gap patch set in a periodic pattern and the bottom one is of a solid metal. By fine adjusting the geometric parameters of the structure, we can obtain a polarization-insensitive, wide-incident-angle ultra-thin absorber that has an absoption of 99.1% and a thickness of only 0.01λ. The absorber is applied to the waveguide slot antenna. The radar cross secction (RCS) of antenna is reduced by 3 dB or more in an the operation band from 5.48 GHz to 5.7 GHz, and by 5 dB or more in the boresight direction from -25° to +25°, and the most reduction value exceeds 12 dB, but the forward gain of antenna reduces only 0.53 dB. The experimental results are in good agreement with the simulation results, which verifies that the absorer has a good characteristic of RCS reduction and can be applied to the stealth of antenna.
Polarization stable vertical-cavity surface-emitting laser with surface sub-wavelength gratings
Authors: Li Shuo  , Guan Bao-Lu  , Shi Guo-Zhu  , Guo Xia  ,   Photonic Device Research Laboratory, Beijing University of Technology, Beijing 100124, China
Published: December 2020

By introducing sub-wavelength grating into an oxide-confined 980-nm vertical-cavity surface-emitting laser (VCSEL), the VCSEL with a stable polarization is realized. A sub-wavelength zero-order grating period is smaller than the wavelength in the semiconductor medium. This choice avoids a reduction in efficiency due to higher diffracting light. After the grating is etched, the threshold gains of E-fields parallel and perpendicular to the grating groves direction are different. The polarization therefore would be controlled. Good laser characteristics are obtained: the orthogonal polarization suppression ratio is over 12 dB and the threshold current increases just 7.14%.
Numerical optimization of volume production efficiency of the JAERI 10 A ion source
Authors: Yang Chao  , Liu Da-Gang  , Xia Meng-Zhong  , Wang Hui-Hui  , Wang Xiao-Min  , Liu La-Qun  , Peng Kai  ,   University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

In this paper, the particle-in-cell/Monte Carlo method simulation algorithm with independent intellectual property is described in-depth, and discharge properties of the JAERI 10 A multicusp ion source are investigated by using the algorithm. The effects of discharge parameters (such as air pressure, discharge electrode position, magnitute of the filter magnetic field, discharge voltage, etc) on volume production efficiency are analyzed. The results show that in order to obtain high volume production of negative hydrogen ions, filter magnetic field should not be too large, and the discharge voltage should not be too small, but the filter magnetic field and discharge voltage should be appropriately selected, and primarily regulating air pressure and discharge location simultaneously can optimize the ion source.
Properties and order-disorder competition of spin-1/2 XY model in the ferrimagnetic diamond chain
Authors: Cheng Tai-Min  , Ge Chong-Yuan  , Sun Shu-Sheng  , Jia Wei-Ye  , Li Lin  , Zhu Lin  , Ma Yan-Ming  ,   Department of Mathematics and Physics, Shenyang University of Chemical Technology, Shenyang 110142, China;,   National Laboratory of Superhard Materials, Jilin University, Changchun 130012, China;,   Department of Physics, Northeastern University, Shenyang 110004, China
Published: December 2020

The elementary excitation spectra of the one-dimensional spin-1/2 XY model in the ferrimagnetic diamond chain at low temperature are calculated by using invariant eigenvector in this paper. And the elementary excitation energies in different cases are discussed. Therefore, analytic solutions of the three critical magnetic field intensities HC1, HC2 and Hpeak in the system are given. It is found that the analytic solutions of three critical magnetic field intensities are correct from the law of the magnetization changing with temperature under different external magnetic fields, and it is explained by the contributions of the three elementary excitations to the magnetization. The external magnetic field dependent magnetization presents a 1/3 magnetized plateau at low temperature. The variation of magnetic susceptibility either with temperature or with external magnetic field shows a double peak structure, this phenomenon indicates that the double peak structure originates from the competition among the ferromagnetic exchange interaction energy of intramolecular electronic spin parallel arrangement in dimer, the antiferromagnetic exchange interaction energy of intermolecular electronic spin antiparallel arrangement in dimer-monomer, the thermal disorder energy and the spin magnetic moment potential energy related to external magnetic field.
Chaotic impulse synchronization of opto-electronic feedback
Authors: Hu Han-Ping  , Yu Zhi-Liang  , Liu Ling-Feng  ,   Institute for Pattern Recognition and Artificial Intelligence, Huazhong University of Science & Technology, Wuhan 430074 China
Published: December 2020

In this paper, a chaotic impulse synchronization is proposed by using opti-electronic feedback. The laser chaos dynamical equations are numerically calculated, and the different chaotic states are obserred by modulating the coefficient of feedback or impulse which realizes the control of chaotic dynamics. Then, the impulse synchronization equations are numerically calculated, and the simulation image of synchronization is plotted. Experiments show the scheme can achieve the chaotic synchronization.
Multiple ionization effect of Ta induced by heavy ions
Authors: Wang Xing  , Zhao Yong-Tao  , Cheng Rui  , Zhou Xian-Ming  , Xu Ge  , Sun Yuan-Bo  , Lei Yu  , Wang Yu-Yu  , Ren Jie-Ru  , Yu Yang  , Li Yong-Feng  , Zhang Xiao-An  , Li Yao-Zong  , Liang Chang-Hui  , Xiao Guo-Qing  ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   Department of Physics, School of Science, Xi'an Jiaotong University, Xi'an 710049, China;,   Xianyang Normal University, Xianyang 712000, China
Published: December 2020

The M X-ray spectra of Ta induced by H+, He2+, Ar11+ and Xe20+ are measured in Heavy Ion Research Facility in Lanzhou. The intensities of M (M3N5) and N (M4,5N6,7), i.e. I and I, are also derived from the spectra. It is found that the intensity ratio of I/I increases with the increase of projectile atomic number. The results show that the M3-subshell fluorescence yield 3 of Ta target is greatly enhanced, owing to multiple ionization effect in collision with heavy ions.
Two kinds of optical pulse compression approaches based on cross phase modulation
Authors: Li Bo  , Lou Shu-Qin  , Tan Zhong-Wei  , Su Wei  ,   School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

Time lens based on cross phase modulation can realize accurate quadratic phase modulation. However, its application in optical pulse compression is restricted by the pump pulse with a high peak power. The formula of the peak power is deduced. It is proposed to use an output fiber with positive dispersion to lower the high peak power requirement for the pump pulse. It is also proposed to use a 4f system which consists of two time lenses to realize optical pulse compression, thereby more effectively lowering the peak power of the pump pulse. The formulas of the peak power and the resolution of the 4f system are deduced. The optical pulse compression is simulated and analysed. The research results demonstrate that in a 4f system based on cross phase modulation, femtosecond pulses can be generated by using pump pulses with small peak power; With compression factor increasing, the pulse width of the output pulse is restricted mainly by the solution of the 4f system. The method of improving the solution of the 4f system is discussed.
Multi-spectral and panchromatic image fusion based on HIS-wavelet transform and MOPSO algorithm
Authors: Zhao Liao-Ying  , Ma Qi-Liang  , Li Xiao-Run  ,   Institute of Computer Application Technology, HangZhou Dianzi University, Hangzhou 310018, China;,   College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Effective fusion method of remote sensing multispectral and panchromatic image must ensure maximizations of spectrum and space information. Using the fusion algorithm framework with combining HIS transformation and wavelet transform (HIS-wavelet), in this paper we propose a new method to extract high frequency coefficients and a new multispectral and panchromatic image fusion method by using multi-objective particle swarm optimization (MOPSO) algorithm. According to the physical characteristics that the edge information in the high frequency has the nature of direction and noise points in the high frequency are generally isolated, a high frequency coefficient extraction method based on Gauss first order differential is proposed. The final resulting image is optimally combined by two images obtained by using different fusion rules in HIS-wavelet. Multiple fusion evaluation indicators are used as object functions and the MOPSO algorithm is used to find the optimal weights. The experiments on TM multi-spectral image and SPOT panchromatic image are carried out. Experimental results demonstrate that the improved method has a better improvement in spectral and spatial information. At the same time, the resulting image which is obtained using MOPSO algorithm has obvious advantages in retaining the spectral information and the spatial information is also greatly improved.
Calculation of two-temperature transport coefficients of helium plasma
Authors: Wang Hai-Xing  , Sun Su-Rong  , Chen Shi-Qiang  ,   School of Astronautics, Beihang University, Beijing 100191, China
Published: December 2020

The knowledge of two-temperature transport coefficients over wide temperature and pressure range is essential to model the flow and heat transfer in plasma process. In this study, the plasma composition is calculated using the Saha equation and the transport coefficients are worked out using Chapman-Enskog method expanded up to higher approximation. The electron temperature Te is assumed to be different from that of heavy species Th. The evolutions of viscosity, thermal conductivity, and electric conductivity of helium plasma are presented in elctron temperature range from 300 K to 40 000 K. It is shown that the transport coefficients strongly depend on pressure and non-equilibrium parameter (θ= Te/Th). These values in local thermodynamic equilibrium state accord well with previously reported data.
Experimental and theoretical studies on gas discharge and plasma oscillation at atmospheric pressure
Authors: Wu Jin-Ze  , Tang Jin-E  , Dong You-Er  , Zhang Guo-Feng  , Wang Yan-Hua  ,   College of Physics and Electronics Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

The gas discharge and plasma oscillation between the electrodes of high-voltage alternating current arc generator are studied, and the nanosecond pulsed phenomenon in the gas discharge process is observed at atmospheric pressure. Electron accumulation phenomenon under the action of alternating electric field is described by using a function. Based on the equation of electron fluid motion and Maxwell equations, the discharge voltage between the electrodes is depicted theortically. Theoretical and experimental results are consistent with each other basically, and the electron density is estimated to be 1.3 1012/m3.
Relaxation properties of graphene nanoribbons at different ambient temperatures: a molecular dynamics study
Authors: Wang Wei-Dong  , Hao Yue  , Ji Xiang  , Yi Cheng-Long  , Niu Xiang-Yu  ,   School of Electrical and Mechanical Engineering, Xidian University, Xi'an 710071, China;,   State Key Laboratory of Wide Bandgap Semiconductor Technology Disciplines, Xidian University, Xi'an 710071, China
Published: December 2020

At different thermodynamic temperatures (between 0.01 and 4000 K), the relaxation properties of three kinds of graphene nanoribbons with different aspect ratios are simulated by molecular dynamics method based on Tersoff-Brenner and AIREBO potential functions separately. Then we compare the energy curves and surface morphologies of nanoribbon relaxation with two kinds of potential functions, and study the dynamic equilibrium process of the graphene nanoribbons during their relaxation simulation. The simulation results show that the single layer graphene nanoribbon is not of a perfect planar structure and that a certain degree of fluctuations and folds occur at the edges and inside of nanoribbons, which are consistent with the existing experimental results; the surface fluctuation level of graphene nanoribbons decreases with the reduction of the aspect ratio, and the system kinetic energy has a dramatic influence on the relaxation deformation of the graphene nanoribbons at different temperatures, which indicates that the higher the system temperature, the greater the deformation is. Curl phenomenon could appear even on the surface of the nanoribbon with a high aspect ratio at a certain temperature. Finally, the simulations of graphen molecular dynamics by using the Tersoff-Brenner and AIREBO potential are deeply analyzed.
Study on Lagrangian analysis for solving the stress gradually along the time
Authors: Tao Wei-Jun  , Huan Shi  ,   Earthquake Engineering Research and Test Center, Guangzhou University, Guangzhou 510405, China
Published: December 2020

Lagrangian analysis method is re-analyzed, in which by measuring the physical variables of each Lagrangian positions the other physical variables of these positions of the material is analyzed, and then the dynamic mechanical properties of materials can be determined. However, the existing Lagrangian analysis methods are still inadequate when the particle velocity is known. In this paper, a new Lagrangian analysis method, with only particle velocity known, is developed, which is called step by step method along the time. The method does not make any assumption, and it can solve the problem when only particle velocity wave profiles are measured. A set of experimental data of concrete under impact is processed with the method, and the corresponding strain wave, stress wave, and stress-strain relations of the whole process of loading and unloading are calculated. Thus the strain rate dependent elastic-elastic constitutive characteristics of the concrete are revealed.
Optimal working point of a Brillouin amplifier for a weak input signal in the transient regime
Authors: Gao Wei  , Lü Zhi-Wei  , He Wei-Ming  ,   Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, Harbin University of Science and Technology, Harbin 150080, China;,   Department of Optics Information Science and Technology, College of Applied Science, Harbin University of Science and Technology, Harbin 150080, China;,   Institute of Opto-Electronics, Harbin Institute of Technology, Harbin 150080, China
Published: December 2020

In order to improve the working performances of a transient Brillouin amplifier, the dependences of the signal-noise-ratio, sensitivity, energy extraction efficiency and signal amplification factor on exponential gain G are numerically studied based on the theoretical model of transient Brillouin amplification including distributed noise, and an optimal working point of a Brillouin amplifier is obtained. Experimental verifications are performed by choosing CS2 and FC-72 as nonlinear media. A frequency-doubled Nd:YAG pulse laser is used. Results show that when the pump pulse lags behind the Stokes signal pulse by an amount of time equal to half the pulse width, Gopt can be set to be above the SBS threshold exponential gain Gth. For a collinear Brillouin amplifier, Gopt is 1.1-1.3 times Gth; while for a non-collinear structure, Gopt can be set to be over 1.3 times Gth. Nearly saturated amplification is achieved.
A time-dependent nonlinear theory and simulation for gyroklystron amplifier
Authors: Ma Jun-Jian  , Zhu Xiao-Fang  , Jin Xiao-Lin  , Hu Yu-Lu  , Li Jian-Qing  , Yang Zhong-Hai  , Li Bin  ,   National Key Laboratory of Science and Technology on Vacuum Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

A time-dependent nonlinear theory for gyroklystron amplifier is presented. The theory includes a time-dependent description of the electromagnetic fields and a self-consistent analysis of the electrons. The generalized telegrapher equations represent the electromagnetic fields. The equations of motion of the electrons are described in the framework of the guiding-center approximation. All trajectories are calculated and used as current sources for the fields. The nonlinear theory of interaction is investigated in which mode coupling is taken into account in varying wall radius. Transverse velocity of the electrons from the gyroklystron amplifier satisfies Gaussian distribution. Distribution model of the velocity spread in the gyroklystron amplifier beam-wave interaction is established. A code for the self-consistent nonlinear beam-wave interaction is developed based on the presented theory. The electron beam-wave interaction of a Kα band gyroklystron amplifier is thoroughly studied and analyzed by the code. Numerical verification using MAGIC simulation is also given. The numerical results are in good agreement with the self-consistent nonlinear simulations.
A unified bifurcation control strategy for voltage source inverter
Authors: Wu Jun-Ke  , Zhou Luo-Wei  , Lu Wei-Guo  ,   State Key Laboratory of Power Transmission Equipment and System Security & New Technology, Chongqing University, Chongqing 400044, China
Published: December 2020

There exist fast scale and slow scale nonlinear dynamic behaviors in the voltage source inverter. Period doubling bifurcation and low-frequency oscillation instability phenomena are investigated. A unified bifurcation control strategy based on frequency-domain transfer function is proposed to suppress the fast-scale and slow-scale instabilities under the guarantee of the inverter's good dynamic and static performance. The stability boundary of the inverter is greatly expanded with the help of the controller. Harmonic balance method and small-signal averaged model are used to verify the effectiveness of the proposed control method when it is used to suppress the period-doubling bifurcation and the low-frequency oscillation, the stability domain border is also derived with the help of the analysis method. Theoretical analysis and simulation results show that the proposed control strategy is correct and feasible.
The quantum properties of three-parameter two-mode squeezed number state
Authors: Lu Dao-Ming  ,   Department of Electronic Engineering, Wuyi University, Wuyishan 354300, China
Published: December 2020

The three-parameter two-mode squeezed number state is proposed by the technique of integration in an ordered product of operators. Its squeezing, antibunching effect and Cauchy-Schwartz inequality are analysed. The conditions under which squeezing or antibunching effect is displayed, are given. The effects of the complex parameter and photon number on squeezing , antibunching effect and Cauchy-Schwartz inequality of the field are discussed. The results indicate that its squeezing, antibunching effect and the degree of violation of Cauchy-Schwartz inequality of two-mode field are all weakened with the increase of photon number; on the other hand, its antibunching effect and the degree of violation of Cauchy-Schwartz inequality of two-mode field are weakened with the increase of the complex parameter modulus, while its squeezing is strengthened with the increase of the complex parameter modulus.
A first principles study on Mn2NiGa Heusler alloy
Authors: Zhao Jian-Tao  , Zhao Kun  , Wang Jia-Jia  , Yu Xin-Quan  , Yu Jin  , Wu San-Xie  ,   School of Materials Science and Engineering, Southeast University, Nanjing 211189, China;,   Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China;,   School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
Published: December 2020

Tetragonal distortion of Mn2NiGa Heusler alloy is calculated by first-principles based on density functional theory with projector augmented wave pseudopotential, and the magnetism, electronic structure, elastic constants and phonon frequencies are also calculated and analyzed. The contribution of the spin magnetic moments of Mn atom to the total moment is largest for Mn2NiGa, and the Mn2NiGa alloy shows ferrimagnetism in these two cases, owning to the antiparallel but unbalanced magnetic moments of Mn (A) atom and Mn (B) atom. Analysis of tetragonal distortion shows that there is a local minimum total energy at c/a=0.94 and c/a=1.27, which corresponds to a stable martensitic phase. Elastic constants of Mn2NiGa reveal that cubic structure does not satisfy stability conditions, but tetragonal structure (c/a=0.94 and c/a=1.27) does. The imaginary values of phonon frequencies in cubic structures validate that tetragonal structure (c/a=0.94 and c/a=1.27) of Mn2NiGa is more stable than cubic structure. The phase transition temperature of c/a=1.27 tetragonal structure converting to cubic structure is about 315 K.
Experimental study of rovibrational spectrum of ultracold polar RbCs molecules
Authors: Yang Yan  , Ji Zhong-Hua  , Yuan Jin-Peng  , Wang Li-Rong  , Zhao Yan-Ting  , Ma Jie  , Xiao Lian-Tuan  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Laser Spectroscopy Laboratory, Shanxi University, Taiyuan 030006, China
Published: December 2020

Ultracold polar RbCs molecules are produced via photoassociation in a dual dark-SPOT magneto-optical trap, in which ultracold rubidium and cesium atoms with high densities are formed by laser cooling and trapping. The a3∑+ triplet metastable state ultracold RbCs molecules with 104/s production rate are detected using resonance-enhanced two-photon ionization. The ultra-high resolution rovibrational spectra of (2)0+, (3)0- and (2)0- rovibrational states are observed by scanning the photoassociation laser frequency. The rotational constants of (2)0+, (3)0- and (2)0- vibrational states are 0.00349 cm-1, 0.00649 cm-1 and 0.00372 cm-1 by fitting respectively.
Ultra-low field magnetic resonance imaging based on high Tc dc-SQUID
Authors: Wang Ning  , Jin Yi-Rong  , Deng Hui  , Wu Yu-Lin  , Zheng Guo-Lin  , Li Shao  , Tian Ye  , Ren Yu-Feng  , Chen Ying-Fei  , Zheng Dong-Ning  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

A systematic research on ultra-low field magnetic resonance imaging (MRI) is conducted based on high-Tc dc-SQUID senor. The coil system is first updated to reach the requirements of MRI experiment. After that one-dimensional and two-dimensional imaging are performed and images consistent well with original phantoms are obtained successfully. Two different methods are used to rebuild the image: direct back projection and Fourier transform reconstruction. Both of them can obtain the profile of water phantom. A comparative discussion between these methods is proposed: the Fourier transform method has a better profile, while the direct back projection has a better signal-to-noise ratio. Imaging of biological sample such as green pepper and celery is also performed, and it is consistent well with the physical object.
Chirped pulse amplification of femtosecond pulse sequences in a Ti: sapphire laser
Authors: Ge Xu-Lei  , Ma Jing-Long  , Zheng Yi  , Lu Xin  , Jiang Gang  , Li Yu-Tong  , Wei Zhi-Yi  , Zhang Jie  ,   Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China;,   Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Key Laboratory for Laser Plasmas of Ministry of Education, Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

An amplified femtosecond pulse sequence is generated in a multi-TW Ti: sapphire chirped pulse amplification system (JG-II facility). The pulse interval of the pulse sequence is 14.8 ns, corresponding to a frequency of 67.5 MHz. The compressed pulse sequence can reach 122 mJ in 19 independent pulses with a pulse width of about 60 fs. The energy of the pulses declines from 20 mJ to 0.5 mJ, corresponding to a peak power from 1011 W to 1010 W. The pulse sequence has important applications in lengthening the lifetime of the laser produced plasma channel in air and in microfabrication.
The strong hydrophobic properties on nanoparticles adsorbed core surfaces
Authors: Wang Xin-Liang  , Di Qin-Feng  , Zhang Ren-Liang  , Ding Wei-Peng  , Gong Wei  , Chen Yi-Chong  ,   Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China;,   Shanghai Key Laboratory of Mechanics in Energy and Environment Engineering, Shanghai 200072, China
Published: December 2020

A compact hydrophobic nanoparticle (HNP) adsorption layer, which has miro- and nano-dual structural properties like lotus leaf, can be built by adsorbing HNP on core surfaces. A slip velocity on the surface can be produced with the purpose of reducing the water resistance and increasing water injection rate. The results are of significance for the study of HNP drag reduction technology. In this paper we give a briefing of the super hydrophobic properties of the lotus leaf, mosquito legs, and striders leg. The strong hydrophobic surface preparation method with HNP adsorption layer is presented, and physical mechanism of strong hydrophobic surfaces with regular arrangement of HNPs is given. According to the real HNP adsorption core samples, the contact angle range is given, the calculation results accord well with experimental data. Core displacement experimental results show that the average drag reduction rate can be up to 94%.
An MHD simulation study on the location and shape of magnetopause in equatorial plane
Authors: Li Chuan-Qi  , Gu Bin  , Mu Li-Li  , Zhang Qing-Mei  , Chen Mei-Hong  , Jiang Yong  ,   College of Physics and Optical Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   School of Electronic Engineering, Guangxi Normal University, Guilin 541004, China;,   College of Math and Statistics, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

The determination of the varying position and shape of magnetopause is one of the important Gordian knots in geophysics and space physics. According to the solar wind-magnetosphere-ionosphere coupling global magnetohydrodynamic (MHD) simulation, and with the maximum electric current criterion, we study the position and shape of the magnetopause under several solar wind dynamic pressure (Dp) and interplanetary magnetic field conditions. The simulation results show that the subsolar position (r0) of the magnetopause is controlled mainly by Dp with the significant decrease of r0 as Dp increases. At a certain Dp, when southword Bz (Bz0) decreases to zero, then shifts to northward (Bz0) and increases, the subsolar position r0 keeps increasing. For all cases studie here, the flare angle () of the magnetopause experiences small changes. This provide an evidence for the structural self-similarity of magnetopause in equatorial plane. Compared with the empirical low-latitude magnetopause model of Shue98, MHD simulation can reproduce the dependence of the subsolar point r0 on Dp, while the saturation effect of r0 varying with Bz in empirical model is represented only with slow solar wind. As to the flare angle , although the difference between MHD simulation and empirical model is less than 2.5, the variation of with Bz in MHD simulations is nonlinear and different from the linear trend in empirical model.
Ground state phase diagram of the quantum spin 1 Blume-Capel model: reduced density fidelity study
Authors: Zhao Jian-Hui  ,   Postdoctoral Research Station of Materials Science and Engineering, Chongqing University, Chongqing 400030, China
Published: December 2020

The reduced density fidelity is a measure of distance between two reduced density matrix, which can be used to characterize quantum phase transitions in quantum many-body systems. In this paper, we use the multi-scale entanglement reorganization ansatz (MERA) algorithm to simulate the spin 1 quantum Blume-Capel model and determine its ground-state phase diagram through calculating the reduced density fidelity. The qualitative relevant information contained in one site reduced density matrix is different from that contained two-site reduced density matrix, which can be detected by using the reduced density fidelity. In addition, we also characterize quantum phase transitions in quantum many-body systems by using the local parameters and energy gaps.
Effects of nonlinearity on quantum resonance ratchet
Authors: Zhao Wen-Lei  , Dou Fu-Quan  , Wang Jian-Zhong  ,   School of Physics, Beijing Institute of Technology, Beijing 100081, China;,   National Key Laboratory of Science and Technology on Computation Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   HEDPS, Center for Applied Physics and Technology, Peking University, Beijing 100084, China
Published: December 2020

We investigate the effect of the nonlinear interaction on the quantum resonance ratchet for the periodically kicked Bose-Einstein condensate that is realized on a ring. In the noninteracting case, the wave packet spreads asymmetrically in momentum space, leading to a directed current. We show that for the weak nonlinear interaction, the probability density distribution in momentum space has two peaks which linearly shift to ward positive and negative momentum, respectively. The force periodically acting on each peak is a constant with time evolution. The competition between the motions of the two parts of cold atoms leads to the reduce or the revival of the momentum current. For the strong nonlinearity, the momentum distribution has only one peak which does not shift with time. The force on this peak is almost zero with time evolution, thus the directed current varnishes.
Study on the mean absolute growth of model error for chaos system
Authors: Yang Jin-Hui  , Song Jun-Qiang  ,   School of computer, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Mean absolute growth of model error which is used to describe the initial error growth for chaos system, is employed in this paper to investigate the model error growth, and some meaningful conclusions are drew from it. It is found that the mean absolute growth of model error is initially exponential with a growth rate which has no direct relationship with the largest Lyapunov exponent. Afterwards model error growth enters into a nonlinear phase with a decreasing growth rate, and finally reaches a saturation value. If the difference between the attractor of real system and that of the model system is very small, the model error saturation level is consistent with the initial error saturation level of real system. With these conclusions one can obtain the predictability limit of a model easily, which is meaningful for weather prediction models. Also the predictability limit of model can be used for model comparison. The exacter model has a higher predictability limit which is useful for new model development.
First-principles study on W-S co-doped anatase titanium dioxide
Authors: Wu Guo-Hao  , Zheng Shu-Kai  , Liu Lei  , Jia Chang-Jiang  ,   College of Electronic and Informational Engineering, Hebei University, Baoding 071002, China;,   Research Center for Computational Materials, Hebei University, Baoding 071002, China
Published: December 2020

The electronic structures and optical properties of pure anatase TiO2, W doped, S doped and W-S co-doped anatase TiO2 are calculated using the plane-wave ultra-soft pseudo-potential (PWPP) method based on the density functional theory. The results indicate that the lattice is distorted and the lattice constant is enlarged due to doping. The doping also introduces impurity energy levels into the forbidden band. For the S-doped TiO2, its forbidden band width decreases and the introduction of impurity energy levels result in the red shift of the absorption band edge, but for the W-doped and W-S co-doped anatase TiO2, their obviously increased forbidden band gaps result in the blue shifts of the absorption spectra.
Core condition analysis of radiation driven implosion for maximum compression
Authors: Dong Jian-Jun  , Ding Yong-Kun  , Cao Zhu-Rong  , Zhang Ji-Yan  , Cheng Bo-Lun  , Yang Zheng-Hua  , Deng Bo  , Yuan Zheng  , Jiang Shao-En  ,   Laser Fusion Research Center,Chinese Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Core condition studies of radiation driven implosion for maximum compression time are the key contents of inertial confinement fusion research. Core conditions refer to the electron temperature and mass density in core region. The spatial distribution of core emission is calculated based on local thermal equilibrium by Multi one-dimensional simulation of core temperature and density. Assumption is made that the core temperature and density distributions each meet a Gauss distribution. Peak values and full widths at half maximum of temperature and density spatial distribution can be inferred by parameter optimization. The data-processing for implosion experiment on Sheng-GuangIII prototype facility indicates that the peak values of temperature and density are 1.7 keV and 1.2 g/cm3 respectively. The full widths at half maximum of temperature and density distribution are 20 μm and 18 μm respectively.
Preparation and red long-lasting luminescence properties of Eu3+ doped CaO
Authors: Li Hai-Ling  , Wang Yin-Hai  , Zhang Wan-Xin  , Wang Xian-Sheng  , Zhao Hui  ,   School of Physics and Optoelectronic Engineering Guangdong University of Technology Guangzhou 510006, China
Published: December 2020

The red long-persistent phosphor CaO: Eu3+ is prepared by a co-precipitation method with further thermal decomposition. The X-ray diffraction analysis shows that the crystal structure of calcium carbonate sample transforms into a single-phase structure and then generates a single-phase calcium oxide structure with the increase of sintering temperature. The excitation spectrum of CaO: Eu3+ shows a broad band around 255 nm, which is attributed to the charge transfer of Eu3+-O2-, and a sharp peak at 393 nm. The emission spectral limes of sample correspond to Eu3+ transitions between 5D and 7FJ (J=0, 2, 3, 4) electron configurations. The red long afterglow is observed at room temperature. A trap level located at 0.69 eV is found by thermolumihnescence measurement, which arises from the fact that Eu3+ is substituted for Ca2+ and enters into the lattice The afterglow luminescence mechanism of sample was discussed according to quantum tunneling.
Quantitative phase-field model for dendritic growth with two-sided diffusion
Authors: Pan Shi-Yan  , Zhu Ming-Fang  ,   Jiangsu Key Lab for Advanced Metallic Materials, Southeast University, Nanjing 211189, China
Published: December 2020

A quantitative phase-field (PF) model with an anti-trapping current (ATC) is developed to simulate the dendritic growth with two-sided diffusion. The asymptotic analysis is performed at the second-order for the PF equations coupled with nonlinear thermodynamic properties and an ATC term under the equal chemical potential condition. The PF mobility and ATC are derived based on the asymptotic analysis in the thin interface limit, and the solute drag model. Then the model is reduced to the dilute solution limit for dendrite solidification of binary alloys. The test of convergence with respect to the interface width exhibits an excellent convergent behavior of the proposed model. The performance of the model is then validated by comparing PF simulations with the predictions of the Gibbs-Thomson relation, the linearized solvability theory, and the modified-Lipton-Glicksman-Kurz (M-LGK) analytical model, for the isothermal dendritic growth of an Fe-0.15 mol%C alloy. The results demonstrate quantitative capabilities of the model that effectively suppresses the abnormal solute trapping effect when the interface is taken artificially to be wide. It is also found that the present model can quantitatively describe dendrite growth with various solid diffusivities, ranging from the case with one-sided diffusion to the symmetrical model.