bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum chaos for two-dimensional Sinai billiard
Authors: Qin Chen-Chen  , Yang Shuang-Bo  ,   School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

We study the classical and quantum correspondence for a two-dimensional Sinai billiard system. By using the Stationary state expansion method and Gutzwiller's periodic orbit theory, we analyze the quantum length spectrum obtained through the Fourier transformation of the quantum density of state for the Sinai billiard system, and by comparing the peak position with the length of the classical periodic orbit we find their excellent correspondence. We observe that some quantum states are localized near some short period orbits, forming the quantum scarred states or superscarred states. In this paper we also investigate the nearest-neighbor spacing distribution of levels for both concentric and nonconcentric Sinai billiard systems, and find that the concentric Sinai billiard system is nearintegrable, and for the nonconcentric Sinai billiard system with =3/8 its nearest-neighbor spacing distribution of levels transits from nearintegrable to the Wigner distribution as the distance between the two centers increases.
Absorption spectra and crystal-field modeling of Er3+ doped in Y3Sc2Ga3O12 crystal
Authors: Gao Jin-Yun  , Sun Dun-Lu  , Luo Jian-Qiao  , Li Xiu-Li  , Liu Wen-Peng  , Zhang Qing-Li  , Yin Shao-Tang  ,   The Key Laboratory of Photonic Devices and Materials, Anhui Province, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

Er3+-doped Y3Sc2Ga3O12 (Er:YSGG) single crystal is grown by Czochralski method successfully, and the absorption spectra are measured in a wider spectral wavelength range (340-1700 nm). The experimental energy levels are analyzed and identified. The free-ion and crystal-field parameters are fitted by the experimental energy levels with a root mean square deviation of 10.34 cm-1, and 102 Stark energy levels of Er3+ in YSGG host crystals are assigned. It indicates that the fitting results of Stark energy levels are more satisfactory with the experimental spectra. Finally, the fitting results of free-ion and crystal-field parameters are compared with those already reported of Er:YAG crystal. A conclusion is drawn that the Er:YSGG has higher laser efficiency than Er:YAG, which may result from Er:YSGG that has a strong crystal field interaction.
Fluid dynamic analysis on solar heating error of radiosonde humidity measurement
Authors: Mao Xiao-Li  , Xiao Shao-Rong  , Liu Qing-Quan  , Li Min  , Zhang Jia-Hong  ,   Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   School of Electronic and Information Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

The error of humidity sensor induced by solar radiation seriously affects the accuracy of the relative humidity measurement. To solve this problem, this paper presents a novel numerical analysis method of correcting the error of relative humidity based on computational fluid dynamics. In view of the external thermal environmental conditions of radiosonde humidity sensors, the convection-solar radiation coupled thermal boundary conditions are adopted in the numerical simulation with analysis method of fluid-solid coupled heat transfer. The temperature error analysis model is first established from the ground to 32 km altitude with different pressures and temperatures. Combined with Goff-Gratch approximation formulas of saturation vapor pressure, the corresponding fluid dynamic numerical analysis model of relative humidity is put forward for error correction. Moreover, the relative humidity errors are reported in the different physical parameters such as the direction of the solar radiation, the reflectivity of sensor, thermal conductivity of the substrate material, the size of sensor, etc. The data analysis shows that the error of relative humidity, caused by solar radiation nonlinearly increases with altitude. The humidity measurement accuracy is affected notably by the direction of solar radiation. Among the errors caused by solar radiation, the error in the direction perpendicular to the front of the sensor is biggest, the error in the direction of the top of the sensor is the next, and the error in the direction of the side of the sensor is smallest. The data analysis also indicates that the solar heating error of the relative humidity can be reduced by reducing the size of the sensor, reducing the thermal conductivity of the substrate material, or improving the reflectivity of sensor. However, the solar heating error can not be neglected under low air pressure at high altitude. A comparison with experimental results shows that the numerical analysis method of the relative humidity error based on fluid dynamics simulation provides a new way to enhance the radiation error correction.
An improved pre-processing method for somooth particle hydrodynamics
Authors: Lei Juan-Mian  , Huang Can  ,   School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

An improved pre-processing method for smooth particle hydrodynamics is proposed, which can rapidly distribute the uniform particles for the fluid field with an arbitrary boundary. The improved pre-processing method is obtained by improving the algorithm proposed by Colagrossi et al., whose method can distribute the uniform particles in a simple shape. However, when the ratio of the smoothing length to the initial particle space is bigger than unity, the algorithm proposed by Colagrossi et al. has a numerical oscillation and a slow convergence rate; and the fluid particles may penetrate the solid boundary. For solving the problems, the XSPH model is added to improve the algorithm stability, and the boundary force is exerted on the fluid particles near the solid boundary to prevent fluid particles from penetrating wall surface. Verified by showing some exmples, the improved pre-processing method can rapidly distribute the more uniform particles for the fluid field with an arbitrary boundary and prevent fluid particles from penetrating wall surface.
Quantitative analysis of chromium in edible gelatin by using laser-induced breakdown spectroscopy
Authors: Zhang Ying  , Zhang Da-Cheng  , Ma Xin-Wen  , Pan Dong  , Zhao Dong-Mei  ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

We quantitatively analyze the concentration of element chromium in edible gelatin sample by the laser-induced breakdown spectroscopy. As the excitation source, Nd:YAG pulsed laser (wavelength 355 nm) is used to generate a laser plasma in edible gelatin. We study the relationship between spectral intensity and delay time, and find that the optimal condition is 1.7 μs. The experimental data show that the relation between the spectral line intensity (CrI: 425.43 nm) and the concentration of chromium is linear when we use the internal standard method to quantitatively analyze the concentration of chromium in a range from 10 ppm to 200 ppm. This study shows that internal standard method of quantitative analysis works well on measuring the chromium concentration in edible gelatin.
Evolution of laser-induced plasma spectrum intensity under magnetic field confinement
Authors: Li Cheng  , Gao Xun  , Liu Lu  , Lin Jing-Quan  ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

In this paper, the evolution of laser-induced copper plasma spectrum intensity under magnetic field confinement is studied. The evolution process of plasma spectrum intensity and laser energy effect on spectral enhancement are analyzed. Experimental results show that the atomic spectrum and ion spectrum of copper plasma are enhanced as magnetic field increases. In the spectral intensity evolution plot of Cu I 510.55 nm there appears double peak structure in a time range from 1.2 μs to 5.7 μs. The spectral intensity of Cu I 510.55 nm is significantly enhanced in a space range from 0 mm to 1.4 mm away from the target surface. The spectral enhancement factors of Cu I 510.55 nm and Cu I 515.32 nm monotonically decrease with the laser pulse energy increasing, and the maximum enhancement factors for Cu I 510.55 nm and Cu I 515.32 nm are 11 and 8 respectively at the laser energy 20 mJ. The enhancement mechanism of magnetic confinement plasma spectrum is also discussed.
Numerical simulation of energy deposition improvment in electrical wire explosion using a parallel wire
Authors: Shi Huan-Tong  , Zou Xiao-Bing  , Zhao Shen  , Zhu Xin-Lei  , Wang Xin-Xin  ,   Department of Electrical Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

The energy deposition process of electrical wire explosion under vacuum or low gas pressure circumstances is usually terminated prematurely, owing to the flashover along the surfaces of wires. Therefore energy deposited into wires can be far less than the amount needed to fully vaporize them. In this paper, a parallel connection method of wire is introduced in order to improve the energy deposition of the concerned wire before flashover takes place. Wire explosion driven by a current with a rise time of tens of ns and an amplitude of about 1 kA is studied numerically, and the simulation results show that by connecting a wire of a certain size in parallel with both ends of the exploding wire, the voltage rising rate is suppressed and the flashover is delayed; therefore the energy deposited into the concerned wire is increased effectively.
Negative piezo-optical effect and the inverse mode piezo-o ptical effect of stressed liquid crystals
Authors: Fan Zhi-Xin  , Li Zhen-Yuan  , Zhou Xuan  , Zhang Zhi-Dong  ,   School of Science, Hebei University of Technology, Tianjin 300401, China;,   Tianjin Tianshi School, Tianjin 301700, China
Published: December 2020

The concepts of polymer dispersed liquid crystal (PDLC) and stressed liquid crystal (SLC) are introduced; the three kinds of definitions, i.e., “positive piezo-optical effect”, “negative piezo-optical effect” and “inverse mode piezo-optical effect” of PDLC switchable glass are given. The new types of stressed switchable glass samples of negative piezo-optical effect and inverse mode piezo-optical effect are prepared. The experimental results show that the haze is above 90% in a scattering state and the transmittance is nearly 30% in a translucent state. The principle of piezo-optical effect is analyzed with polarization microscopy. The results show that the vertical surface pressure or stretching stress applied to the sample will result in the special reorientation of LC molecules in LC droplets, which causes the optical characteristics of the sample to change significantly. The mode of vertical stretched liquid crystal droplet is proposed, the computation results and graph plotting conform with the results from the micrographs of polarizing microscope very well, so that the experimental phenomena are reasonably explained. The research on SLC piezo-optical effect has the fundamental significance for studying the PDLC and the application value for developing non-electro-optic switchable glass.
Influence of air exposure on the structure and properties of cesium iodide film
Authors: Fan Long  , Yang Zhi-Wen  , Chen Tao  , Li Jin  , Li Yu-Kun  , Cao Zhu-Rong  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Polycrystalline cesium iodide (CsI) thin films were prepared on glass substrates by thermal evaporation. The Influences of air exposure on the structure, resistivity and infrared transmittance of CsI film were investigated by scanning electron microscopy, X-ray diffraction (XRD), high resistance meter and infrared spectrophotometer (IR). It is found that the coalescence of grains occurs and the average grain size increases from 0.36 μm to 1.25 μm. The mechanism of grain growth is attributed to the diffusion of water molecules along grain boundaries and the migration of grain boundaries driven by minimization of total free energy. XRD results indicate the formation of (110/220) texture when exposed to ambient air and the relaxation of tensile stress during recrystallization. The average crystallite sizes obtained from Debye-Scherrer's formula are 25.6 nm, 28.4 nm and 45.1 nm respectively. The resistivity of the film decreases from the order of 1010 Ω·cm to 108 Ω· cm. The IR absorption bands in the ranges of 3675-3750 cm-1 and 3560-3640 cm-1 closely resemble that of free water rather than liquid water. The observed split bands are assigned to the non-hydrogen-bonded OH associated with ion-dipole bonds and dangling OH at air-water interface respectively.
First-principle study of the effects of oxygen vacancy on the electronic structure and the absorption spectrum of ZnO
Authors: Hou Qing-Yu  , Guo Shao-Qiang  , Zhao Chun-Wang  ,   College of Sciences, Inner Mongolia University of Technology, Hohhot 010051, China
Published: December 2020

Nowadays, the studies of the influence of oxygen vacancy on forming impurity level of ZnO have obtained contrary conclusions. The experimental results about both the deep impurity level and the shallow impurity level are reported. However, under the high temperature heating condition, the origin of free electron increasing in conduction band of ZnO with oxygen vacancy is not sufficiently understood. To slove this problem, according to the first-principles plane-wave ultrasoft pseudopotential of the density functional theory, we set up the models for a pure ZnO cell and two different oxygen vacancy concentration supercells of ZnO, and perform the geometrical optimization for three models. The density of state, band structure, population and differential electron density are also calculated. Calculation results indicate that with the increase of oxygen vacancy concentration, the total energy increases and the formation energy will be greater. It makes the stability decline and the oxygen vacancy harder. Meanwhile, its conduction band minimum shifts toward low energy, the electron transition width decreases, and the absorption spectrum is red-shifted. It shows that these results may be helpful for the future experimental design and also for the preparation of optical device with oxygen vacancy of ZnO.
Electric characteristics and resistive switching mechanism of Ni/HfO2/Pt resistive random access memory cell
Authors: Pang Hua  , Deng Ning  ,   Institute of Microelectronics, Tsinghua University, Beijing 100084, China
Published: December 2020

Electric characteristics and resistive switching mechanism of Ni/HfO2/Pt cell are investigated. The cell has a forming-free property and shows an abnormal non-polar switching behavior. A high ON/OFF resistance ratio (>105) is obtained. The resistance of the on-state is independent of cell size, which implies that a conductive filament is formed in HfO2 film. X-ray photoelectron spectroscopy is used to investigate the compositions and valences of Ni and Hf in HfO2 film for the on-state cell. The results show that there is a hybrid filament comprised of a Ni filament and an oxygen vacancy filament in the HfO2 film for the on-state.
Adsorption of H2O by the Li decorated C6Li molecule
Authors: Zhang Yi-Jie  , Tang Chun-Mei  , Gao Feng-Zhi  , Wang Cheng-Jie  ,   College of Science, Hohai University, Nanjing 210098, China
Published: December 2020

The generalized gradient approximation based on the density functional theory is used to study the adsorption process of H2O molecules by the Li decorated C6Li and the catalytic process of decomposition of H2O molecules. The geometry optimization shows that the most stable adsorption position of the Li is above the C atom of C6. Research shows that the adsorption of the first H2O molecule on C6Li needs to overcome an energy barrier of 1.77 eV, then H2O is decomposed into H and OH and bonding with Li atoms. Furthermore, the adsorption of the second H2O molecule needs to overcome an energy barrier of 1.2 eV and then the H2O molecule is decomposed into H and OH, the H atom in which and the H atom on the Li atom combine into an H2 molecule. OH replacing H atoms on Li atoms combines with the Li atom. Therefore, C6Li can be used as a catalyst for H2O molecules, and thus provide a new train of thought for the preparation of hydrogen storage material. The analysis shows that C6Li mainly adsorbs the H2O molecules through the dipole moment formed by the positive charge of Li and negative charge of H2O.
Band-structure optimization of triangular lattice magnonic crystals
Authors: Hu Xiao-Ying  , Huhemandula  , Cao Yong-Jun  ,   Department of Physics, Jining Teacher's College, Jining 012000, China;,   College of Physics and Electronic Information, Inner Mongolia Normal University, Hohhot 010002, China
Published: December 2020

In this paper, band structure of two-dimensional magnotic crystal composed of elliptic rods triangularly arranged is calculated by using the plane-wave expansion method. The results show that under the condition of the same filling ratio, the width and central frequency of band gap obviously change with the ratio between two radii of ellipse, and that elliptic cylinder scattering body can open the lower frequency band gap or widen the low frequency band gap.
Basic problem in the first-order phase transition magnetic refrigeration material
Authors: Chen Xiang  , Chen Yun-Gui  , Tang Yong-Bo  , Xiao Ding-Quan  , Li Dao-Hua  ,   Department of Physics and Electronic Informational Engineering, Neijiang Teachers College, Neijiang 641112, China;,   School of Materials Science and Engineering, Sichuan University, Chengdu 610065, China
Published: December 2020

Due to the cell volume mutations and the phase transition latent heat existing during phase transition of the first-order phase transition magnetic refrigeration material, many basic problems need to further explore in the magnetization process. In this paper, taking LaFe13-xSixalloys as the research object, we discuss in detail some problems, such as a phase-change, entropy change, isothermal entropy change, adiabatic temperature change, thermal and magnetic hysteresis, the temperature range and magnetic field range in which the ferromagnetic and paramagnetic state coexist, and magnetic refrigeration capacity calculation, The analysis shows that the magnetic entropies calculated by Maxwell equation and Clausius-Clapeyron equation are equivalent when neglecting the contributions of ferromagnetic and paramagnetic state to magnetocaloric effect. The area surrounded by the curve in heating of isothermal magnetization process and curve in cooling of isothermal magnetization process (hysteresis size) is actually the net work done by magnetic field during the heating process and cooling process. The values of magnetic and thermal hysteresis are related to the measurement time: the longer the measurement time, the smaller the hysteresis is. When the transformation is of the equilibrium phase, the hysteresis should be equal to zero. In addition, the temperature and magnetic field induced magnetic transition processes are discussed, and different calculation models of the first-order phase transition material for magnetic refrigeration refrigeration capacity are proposed.
Monte-Carlo method of computing multipactor threshold in microwave devices
Authors: Lin Shu  , Yan Yang-Jiao  , Li Yong-Dong  , Liu Chun-Liang  ,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

In order to find a rapid and accurate numerical method to compute the multipactor threshold in microwave device, three enhanced Monte-Carlo (MC) methods are proposed which are single particle-multiple collision MC, multiple particle-single collision MC and multiple particle-multiple collision MC method. The three MC methods all give the random nature of the secondary electrons, including their initial energies, phases and angles. And in all of the methods, the electron trajectory is computed with Runge-Kutta method and the secondary electron yield (SEY) per collision is computed with Furman model. The effective SEY is taken as the criterion to judge whether multipactor occurs, the definition of which is a little different from those of the three MC methods. As a verification, the multipactor in a parallel plate transmission line is investigated with the presented MC methods and the traditional MC method. The numerical results of the four MC methods are compared with the results of the statistical theory. It is demonstrated that the single particle-multiple collision MC method has the smallest error and the best stability.
First-principles characterization of lanthanum occupying tendency in -Fe and effect on grain boundaries
Authors: Wang Hai-Yan  , Gao Xue-Yun  , Ren Hui-Ping  , Zhang Hong-Wei  , Tan Hui-Jie  ,   School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China;,   Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Baotou 014010, China;,   Beris Engineering and Research Corporation, Baotou 014010, China
Published: December 2020

The -Fe 3[110] (112) symmetrical tilt grain boundary model is established by the coincidence site lattice theory. First-principles plane wave ultrasoft pseudopotential method based on the density functional theory is used to calculate the La occupying tendency in -Fe. The results show that La elements tend to be located at grain boundary in the -Fe since the impurity formation energy keeps lowest. On this basis, the electronic structure of La doped in -Fe grain boundary is also calculated. The results indicate that the charges in the system are redistributed to provide more electrons for the grain boundary bonding when the La occupies -Fe grain boundary. Meanwhile, Fe atoms obtain more electrons, and the La doped region combination has the ion-tendency toward strengthening the interaction between La atom and Fe atoms in the adjacent boundary region, and the Fe atom bonds in the grain boundaries and on both sides of the grain boundary also strengthen, which is the reason why the mechanical properties change from the energy point of view. Moreover, La addition also makes the atomic density of states on the grain boundary move to the left, reduce the total energy of the system, and make the grain boundary more stable.
The microstructural and electrochemical properties of oxygen ion implanted nanocrystalline diamond films
Authors: Wang Rui  , Hu Xiao-Jun  ,   College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Published: December 2020

The nanocrystalline diamond (NCD) films are implanted by oxygen ions with a dose of 1×1012 cm-2 and subsequently annealed at 700, 800, 900 and 1000 ℃, respectively. The microstructure and electrochemical properties of these NCD films are investigated systematically and the results show that the potential windows of the unannealed sample (O120) and 1000 ℃ annealed sample (O121000) increase up to 4.6 V and 3.61 V, respectively. The mass transfer efficiencies of the two samples are also better, indicating that the oxygen ion implantation and 1000 ℃ annealing can improve the mass transfer efficiency of NCD film. The results of infrared spectrum measurements show that there are no hydrogen atoms that are terminated to the surfaces of samples O120 and O121000, while hydrogen atoms terminate to the surfaces of the other samples. It is indicated that oxygen ion implantation and 1000 ℃ annealing can damage hydrogen terminations in the surface, which improves the electrochemical performances of NCD films. Raman spectrum measurements suggest that high content of diamond phase, small internal stress and more disordered amorphous carbon can improve the electrochemical properties of NCD films. When the number or size of sp2 carbon clusters in amorphous carbon grain boundaries decreases, the electrochemical properties of NCD films become better.
Application of quantum dot infrared photodetectors in space photoelectric systems
Authors: Zhou Yan-Ping  , Li Fa-Jun  , Che Chi  , Tan Li-Ying  , Ran Qi-Wen  , Yu Si-Yuan  , Ma Jing  ,   National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Space environment and space resources have become a new field of competition among countries, and this field is to be developed. To achieve these purposes, some countries have established the detection sites and communication network by launching satellites, space stations, space shuttles and other spacecrafts into the space. Photoelectric systems in space play a crucial role in developing new fields and exploring new resources. Presently, the space environment factors including point-to-point long distance, intense space radiation, large temperature difference challenge the high requirements of the stability and reliability for the optoelectronic system. A new type of technology with quantum dot infrared photodetector, which may be used in the space, is proposed, which potentially provides higher detectivity, operation temperature, radiation tolerance, responsive bandwidth, etc. The basic working principle and the advantages of the quantum dot infrared photodetectorare discussed. And the basic technical requirements for the quantum dot infrared photodetector in space application are pointed out. Finally, feasible applications of the quantum dot infrared photodetector in the field of space laser radar, satellite optical communications and imaging system are analyzed.
Research on SiGe heterojunction bipolar transistor with a trench-type emitter
Authors: Liu Jing  , Wu Yu  , Gao Yong  ,   Department of Electronic Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

A novel SiGe heterojunction bipolar transistor (HBT) with a trench-type emitter is presented. Effects of the trench-type emitter on device performance are analyzed in detail, and current transport mechanism of the novel device is studied. The emitter resistances are parallel partitions by changing current path. Under the precondition without increasing the junction capacitance, the resistances of the new emitter are reduced effectively, and the frequency characteristics of the device are improved. Results show that the cutoff frequency and the maximum oscillation frequency of the new device are increased to 100.2 GHz and 134.4 GHz, respectively. More important is that the frequency characteristics are improved by the introduction of the trench-type emitter, while the current gain is not reduced and the junction capacitance is also not increased. A good trade-off is achieved among frequency, current gain, and junction capacitance. The trench-type emitter is designed to be optimal. With the change in sidewall height, no effects are found on the emitter resistances, and the frequency characteristics do not change, while the frequency characteristics are reduced when the sidewall width is increased.
Improvement in the range resolution of THz radar using phase compensation algorithm
Authors: Liang Mei-Yan  , Zhang Cun-Lin  ,   School of Opto-Electronic, Beijing Institute of Technology, Beijing 100081, China;,   Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Capital Normal University, Beijing 100048, China
Published: December 2020

The paper describes the principle of 0.2 THz stepped-frequency radar system which is utilized to achieve a one-dimensional range profile and range resolution. Terahertz (THz) stepped frequency radar is more susceptible to the phase error which will cause the spread and shift of range profile, thus affecting the quality of the high resolution range profile and signal-to-noise ratio. Therefore, a method of phase compensation is proposed to improve the range resolution. After phase compensation, the resolution and signal-to-noise ratio are improved remarkably. The range resolution can reach centimeter scale. Experimental and simulation results indicate that THz stepped frequency radar can reach high resolution range profile with the phase compensation method, which provides a foundation for further research on two-dimensional and three-dimensional image in the THz band.
Numerical model error estiamtion by derivative-free optimization method
Authors: Huang Qi-Can  , Hu Shu-Juan  , Qiu Chun-Yu  , Li Kuan  , Yu Hai-Peng  , Chou Ji-Fan  ,   College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China;,   School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000, China
Published: December 2020

Initial error and model error are key factors restricting the accuracy of numerical weather prediction (NWP). The purpose of the present study is to estimate the errors of spatiotemporal evolution model by using recent observations. By considering the continuous evolution of atmosphere, the observed data (ignoring the measurement error) can be viewed as a series of solutions of accurate model governing the actual atmosphere, and the model errors can be objectively assumed to be an unknown functional term (a missing forcing term) of the numerical model, thus the NWP can be considered as an inverse problem to uncover the unknown model error term by using the long periods of observed data. In this study, we first construct an inverse problem model with its optimization problem, which is constrained by the numerical model, to estimate the errors of spatiotemporal evolution model, then we present a derivative-free optimization (DFO) method to find the minimum solution of the optimization problem by running the numerical model with an external forcing term. The DFO method does not need to compute the gradient of the objective functional and the tangent linear model or adjoint model of the original numerical model. The numerical study of Burgers equation indicates that the presented methods can effectively uncover the model errors from the past data and evidently improve the numerical prediction. The precedures described in this paper open up possibilities for utilizing the past observation data to extract useful information about model errors and enhance the prediction efficiency in the operational models.
Steadystate charging characteristics of polymer irradiated by multi-energetic electrons
Authors: Liu Jing  , Zhang Hai-Bo  ,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Department of Electronic Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Charging characteristics of polymer irradiated by multi-energetic electrons is a basis to study and prevent electrostatic discharge in space radiation environment. The polymer irradiated by multi-energetic electrons is modeled and simulated. The space charge distribution, surface potential, space potential, surface potential and maximum field strength under the condition of sample parameters are obtained. The results show that because of electron drift and diffusion, electrons can transit through the electron scattering region, forming negative space charges. Some electrons can flow to the substrate of polymer. In the equilibrium state, the surface potential of the film negatively charged decreases with film thickness and trap density increasing, and it increases with electron mobility and relative permittivity increasing. The maximum field strength increases with film thickness and trap density increasing, and it decreases with electron mobility and relative permittivity increasing. The high-energy electrons section of multi-energetic electrons will shorten the equilibrium of charging process.
Stability of dipolar soliton in crossed linear and nonlinear optical lattices
Authors: Yong Wen-Mei  , Chen Hai-Jun  ,   College of Science, Gansu Agricultural Univerisity, Lanzhou 730070, China;,   Electrical Engineering College, Longdong University, Qingyang 745000, China
Published: December 2020

Stability of a dipolar Bose-Einstein condensate (BEC) soliton in crossed linear and nonlinear optical lattices is investigated using variational approximation. The Euler-Lagrange equations for variational parameters and the effective potential are derived by means of a cylindrically symmetric Gaussian ansatz, while the equilibrium widths are determined by minimization of the effective potential. In the presence of a periodic spatial variation of short-range contact interaction, the localized bound states can exist for both attractive and repulsive dipolar interactions. And the domain of stable dipolar BEC solitons is illustrated in a phase plot of the nonlinearities. Finally, we give the evolution of the variational width for different values of the nonlinearities.
Numerical simulations of dynamic properties of the restricted solid-on-solid model on fractal substrates
Authors: Yang Yi  , Tang Gang  , Song Li-Jian  , Xun Zhi-Peng  , Xia Hui  , Hao Da-Peng  ,   Department of Physics, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

In order to investigate the effect of the structure of a non-complete substrate on the dynamic behaviors of a growing surface, the restricted solid-on-solid model on Sierpinski arrowhead and Crab fractal substrates, which have the same fractal dimensions but of different spectrum dimensions, are extensively studied by means of numerical simulations. The surface width and the maximal height of the saturated surface are calculated. It is found that the microscopic structure of the substrates affects significantly the dynamic properties of the surfaces. Although the restricted solid-on-solid model evolving on two kinds of fractal substrates exhibits dynamic scaling behavior, the standard Family-Vicsek scaling is still satisfied for different dynamic scaling exponents. The maximal height of the width of saturated surface can be fitted by Asym2Sig distribution, not by the three kinds of usual extreme statistical distribution, i.e. Weibull, Gumbel, and Frechet distributions.
Time-varying singularity spectrum distribution of sea clutter based on wavelet leaders
Authors: Xiong Gang  , Zhang Shu-Ning  , Zhao Hui-Chang  ,   Institute of Photoelectric Information/School of Optical Electrical and Computer Engineering, University of Shanghai for S&T, Shanghai 200093, China;,   School of Electronic and Optical Engineering, Nanjing University of S&T, Nanjing 210094, China
Published: December 2020

Singularity spectrum analysis of sea clutter is the key technology of detecting radar for sea target, which can discover the dynamic mechanism of the sea surface theoretically. In this paper, based on wavelet leaders the time-varying singularity spectrum distribution of sea clutters is proposed, which introduces time information to the traditional singularity spectrum, and displays the time-varying characteristic of singularity spectrum analytically. In theory, by way of self-windowed fractal signal, we introduce the time information to the traditional singularity spectrum, and realize multifractal spectrum distribution of sea clutters. In algorithm, based on the wavelet leaders, we adapt the process of embodying chirp-type and cusp-type singularities, and obtain the time-varying singularity spectrum distribution of sea clutters by the Legendre transform of the time-varying scaling function. In practice, we analyze the classical multifractal modelrandom wavelet series and the real sea clutter data of continuous wave Doppler radar in level III sea state. Experiments indicate that (1) the time-varying singularity spectrum distribution based on wavelet leaders can trace the time-varying scale characteristic and display the time-varying singularity spectrum distribution of sea clutters; (2) the algorithm possesses good statistical convergence, low computational cost, and passive moment property. The time-varying singularity spectrum distribution based on wavelet leaders may serve as a reference sample for nonlinear dynamics and multifractal signal processing.
Prediction of methane PVT relations at high temperatures by a simplified virial equation of state
Authors: Han Yong  , Long Xin-Ping  , Guo Xiang-Li  ,   Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, China;,   China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

In order to meet the demand of describing the supercritical gas under high temperature and medium-high pressure conditions, such as in detonation circumstance, a simplified virial equation of state (EOS), named Han-Long (HL), is presented, which is based on Lennard-Jones potential function. One hundred and twelve sets of theoretical data for methane above 1000 K are calculated using HL EOS. We obtain that the volume average absolute deviation (AAD) is about 1% and the maximum error is 3.28%; this error is far lower than the calculation deviation of DMW (Duan-Moller-Weare) EOS and BS (Belonoshko-Saxena) EOS. The shockwave data of methane is also calculated by HL EOS and the AAD are less than 3%. Results show that HL EOS can well describe the thermodynamic state of CH4 at high temperatures.
Molecular dynamics study of cascade damage at SiC/C interface
Authors: Wang Cheng-Long  , Wang Qing-Yu  , Zhang Yue  , Li Zhong-Yu  , Hong Bing  , Su Zhe  , Dong Liang  ,   College of Nuclear Science and Technology, Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin 150001, China;,   Nuclear and Radiation Safety Center, MEP, Beijing 100082, China
Published: December 2020

Continuous silicon carbide (SiC) fiber-reinforced SiC (SiCf/SiC) composites have been considered to be used as structural materials in advanced nuclear reactors for its excellent properties. Their mechanical properties have been greatly improved during the last decade. But the radiation damage at the SiC and pyrolytic carbon interface would degrade the mechanical integrity of the composites, while the mechanism of degradation is remaining unknown at present. In this study, molecular dynamics simulations have been used to model the irradiation cascade of five SiC/C composite systems. According to the angle between the graphite layer and the interface, the models are marked as M0, M28, M56, M77 and M90, in which the number represents the angle. Forty primary knock-on atoms (PKAs) at different positions in each composite system are used to bombard the interface. In each run a collision cascade may be initiated by giving one of the 40 atoms 1.5 keV kinetic energy. The relationships between the distribution of defects and simulation time and PKA position are systematically studied, and compared with those in bulk SiC, which are marked as MW. Results show that the radiation damage resistance of SiC/C interface is significantly lower than bulk SiC, and the interface structure has an impact on the number of defects. Radial distribution function (RDF) is employed to examine the coordination of interfacial atoms. The results show that the higher the density of graphite atoms in the interface, the larger impact the irradiation on the RDF and coordination.
Zeeman slowing and magneto-optically trapping of lithium atoms in atomic interferometry experiments
Authors: Yang Wei  , Sun Da-Li  , Zhou Lin  , Wang Jin  , Zhan Ming-Sheng  ,   State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Center for Cold Atom Physics, Chinese Academy of Sciences, Wuhan 430071, China
Published: December 2020

To prepare cold lithium atoms for atomic interferometry experiments, we have carried out experimental researches on Zeeman deceleration and magneto-optical trap (MOT) of lithium atoms. We have also designed and implemented a compact adjustable Zeeman slower with an inner water cooling chamber, to decelerate the velocity of the 7Li atom beam from 600 m/s down to 60 m/s, and load them into the MOT. The loading rate is 5108 /s, the total trapped atom number is 1109 , and the lowest temperature of the atom cloud is 220 30 K. Then we investigate the dependence of lifetime of 7Li atoms in optical molasses on the detuning of trapping laser beams. The above results lay a foundation for further sub-Doppler cooling, optical trap based on evaporative cooling, and atomic interferometry experiments.
Research on indoor channel measurement and simulation at 340 GHz
Authors: Wang Min  , Wang Jun-Feng  , Wu Qiu-Yu  , Huang Yi-Xin  ,   College of Computer Science, Sichuan University, Chengdu 610064, China;,   College of Computer Science and Information Technology, Yunnan Normal University, Kunming 650092, China;,   Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621900 China
Published: December 2020

Ultra-broadband terahertz communication systems are expected to help satisfy the ever-growing need for unoccupied bandwidth. Due to high attenuation of terahertz wave, it can be widely used in indoor WLAN data communication. Future THz WLANs will rely on not only the line-of-sight (LOS) but also the nonline-of-sight (NLOS) channels to perform data communication. Hence, both kinds of channels have to be characterized. In this paper, we present the measures of ultra-broadband channel at 340 GHz for an indoor scenario. The measured channel transfer function is compared with a ray tracing simulation performed with the indoor scenario. Additionally, we show the reflection losses of some building and plastic materials which could be required as input data for the ray tracing algorithm.
Resonance experiment on a microwave resonator system
Authors: Shi Feng  , Yang Juan  , Tang Ming-Jie  , Luo Li-Tao  , Wang Yu-Quan  ,   College of Astronautics, Northwestern Polytechnic University, Xi'an 710072, China
Published: December 2020

A microwave resonator system is made, which has a tapered resonant cavity, a microwave source, and a transmission device. Because of the electromagnetic pressure gradient on the tapered resonant cavity, a net electromagnetic force along the axis of the cavity may be observed, which is needed to verify experimentally the use of the independent microwave resonator system. It is also needed to keep the independent microwave resonator system in resonating state, which is the important procedure to demonstrate the possibility of net electromagnetic force. Thus, a low-signal resonating experiment on the tapered resonant cavity combined with resonating parts is completed to accurately find out the resonant frequency of 2.45 GHz and to analyze the influence of temperature on the resonant state. Experimental result shows that the resonant frequency and quality factor of the independent microwave resonator system are 2.44895 GHz and 117495.08 respectively. When the temperature of the tapered resonant cavity wall rises, the resonant frequency will be decreased and the quality factor changed separately.
Electric and magnetic polarization singularities of focused Gaussian vortex beams in the focal region
Authors: Luo Ya-Mei  , Gao Zeng-Hui  , Tang Bi-Hua  , Lü Bai-Da  ,   Department of Biomedical Engineering, Luzhou Medical College, Luzhou 646000, China;,   Key Laboratory of Computational Physics, Yibin University, Yibin 644000, China;,   Institute of Laser Physics & Chemistry, Sichuan University, Chengdu 610064, China
Published: December 2020

Taking the Gaussian vortex beam as an example, the variation of electric and magnetic polarization singularities of focused Gaussian vortex beams is studied. It is shown that in the focal region there exist two- and three-dimensional (2D and 3D) electric and magnetic polarization singularities of focused Gaussian vortex beams, which do not coincide in general. By suitably varying the distance from the focal plane and the truncation parameter, the motion, creation, and annihilation of circular polarization singularities will take place. The critical valuse of the parameters at which a pair of circular polarization singularities of 2D and 3D electric and magnetic fields will annihilate, are not the same. In the 2D electric field the V-point may appear at the focal plane.
Investigation of the scattering characteristics from discrete random scatterers based on recursive aggregate T-matrix algorithm
Authors: Cui Shuai  , Zhang Xiao-Juan  , Fang Guang-You  ,   Key Laboratory of Electromagnetic Radiation and Sensing Technology, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

In this paper, we derive in vector form the recursive aggregate T-matrix algorithm based on the principles of electromagnetic wave multipole expansion of vector spherical wave functions and the vector addition theorem. After that we establish a three-dimensional electromagnetic scattering model for multiple spherical scatterers by simulating the scattering of subsurface discrete random scatterers using the derived algorithm. Calculating the scattering from different sizes, randomly distributed spherical scatteres and analyzing the high-order scattering effects, we can conclude that the vector recursive aggregate T-matrix algorithm has a high computation accuracy, and contains the interaction effects among multiple scatterers, therefore we can calculate the total scattering effects accurately from multiple scatterers. The established model can be served as a powerful tool in applications for retrieving the impact caused by the scattering of subsurface discrete random scatterers in soil moisture from radar measurements.
Conversion of cylindrical vector beams on the higher-order Poincar sphere
Authors: Luo Zhao-Ming  , Chen Shi-Zhen  , Ling Xiao-Hui  , Zhang Jin  , Luo Hai-Lu  ,   Key Laboratory of Micro/Nano Optoelectronic Devices of Ministry of Education, College of Physics and Microelectronics Science, Hunan University, Changsha 410082, China;,   College of Information and Communication Engineer, Hunan Institute of Science and Technology, Yueyang 414006, China
Published: December 2020

A conversion approach for cylindrical vector beams on the high-order Poincar sphere based on half-wave plate is studied theoretically and experimentally in this paper. The theoretical analysis using the Jones matrix method shows that the latitudes of two corresponding points produced by the cylindrical vector beams on the high-order Poincar sphere before and after conversion are situated oppositely, and the longitudes are changed with different azimuth angles of the half-wave plate. Finally, an experimental system for the generation and conversion of the cylindrical vector beams is established with the spatial light modulator, and the experimental results demonstrate the feasibility of this approach.
Laser diode end-pumped continuous-wave Nd：YVO4 self-Raman laser at 1175 nm
Authors: Fan Li  , Chen Hai-Tao  , Zhu Jun  ,   School of Physics Science and Technology, Yangzhou University, Yangzhou 225002, China
Published: December 2020

In this paper, an LD (laser diode) end-pumped continuous-wave Nd:YVO4 self-Raman laser at 1175 nm is reported. The doping concentration and structure of the self-Raman crystals are optimized to reduce the thermal effects of the crystal, and a high-efficient diode-end-pumped continuous-wave self-Raman laser operated at 1175 nm is demonstrated. Finally, the thermal effects are efficiently improved by using a double-end diffusion-bonded composite Nd:YVO4 crystal as a gain medium. An output power up to 3.4 W of the first-order Stokes line 1175 nm is achieved at the incident diode pump power of 25.5 W, corresponding to a diode-to-Stokes optical conversion efficiency of 13.3% and a slope efficiency of 14.6%. The Raman threshold is as low as 2.21 W of diode power at 808 nm.