bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanosecond electrical explosion of twisted aluminum wires
Authors: Sheng Liang  , Li Yang  , Wu Jian  , Yuan Yuan  , Zhao Ji-Zhen  , Zhang Mei  , Peng Bo-Dong  , Hei Dong-Wei  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

The experiments on nanosecond electrical explosion of twisted aluminum wires with different wavelengths (λt=0.37, 0.5, 0.75, 1.0 mm) are carried out. The experimental results indicate that a specific wavelength can strongly affect the energy deposition, expansion velocity, and radiation intensity. The energy deposition is about 3.3 times the atomic enthalpy of aluminum when the twisted wavelength is 0.5 mm. While for the other three twisted wavelengths, the energy depositions are all about 1.8 times the atomic enthalpy. The expansion velocity is about 3.8×103 m·s-1 for the wavelength 0.5 mm, and the optical radiation intensity is also strongest for this wavelength. The initial twisted structure is strongly imprinted in the freely expanding aluminum column after the electrical explosion. In the experiments for the wavelength 0.5 mm, a neural particle column with a diameter of 1.6 mm is formed and its density is about 1019 cm-3 at t=246 ns. A periodic structure with the wavelength 0.5 mm and the amplitude 0.3 mm is observed on the surface of this column.
Properties of Cu1-xWx alloys at high pressure and high temperature from first-principles calculations
Authors: Zhai Dong  , Wei Zhao  , Feng Zhi-Fang  , Shao Xiao-Hong  , Zhang Ping  ,   College of Science, Beijing University of Chemical Technology, Beijing 100029, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

The electronic structures, elastic properties and thermodynamic properties of three different proportions of copper tungsten alloys (Cu3W, CuW, CuW3) at ground state, high temperature and high pressure are investigated by using the combined method of the first-principles calculation method based on density function theory. The calculated elastic constants indicate that Cu3W has an unstable structure and the CuW and CuW3 have the stable structures, which are in agreement with the phonon spectrum result. The metallic bond increases and the curve of the density of states moves toward the deep level with the increase of pressure. The quasi harmonic Debye model and the quasi harmonic approximation model are employed to calculate the bulk moduli, thermal expansion coefficients, Debye temperatures and specific heats of the Cu1-xWx alloys at different temperatures and different pressures.
First-principles calculations of phosphorene doped with carbon, oxygen and sulfur
Authors: Tan Xing-Yi  , Wang Jia-Heng  , Zhu Yi-Yi  , Zuo An-You  , Jin Ke-Xin  ,   School of Science, Hubei Minzu University, Enshi 445000, China;,   Shannxi Key Laboratory of Condensed Matter Structures and Properties, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Using first-principles calculations based on density functional theory and plane pseudo-potential method, we investigate the geometric structures, magnetic properties and electronic structures of phosphorene with phosphorus substituted by carbon (CP), oxygen (OP) and sulfur (SP). The results show that the phosphorene with SP presents a less geometric distortion than with OP and CN. Although the pure phosphorene is non-magnetic, all the doped systems are magnetic, each with a magnetization value of 1 μB per cell. The doped systems with stable ferromagnetism play an important role in developing spin electric devices.
Complexity analysis of power system energy flow based on multi-scale entropy
Authors: Gou Jing  , Liu Jun-Yong  , Wei Zhen-Bo  , Gareth Taylor  , Liu You-Bo  ,   School of Electrical Engineering and Information, Sichuan University, Chengdu 610065, China;,   Brunel Institute of Power Systems, Brunel University, London UB8 3PH, United Kingdom
Published: December 2020

Complexity of power system energy flow is mainly reflected in the features of dynamic behavior such as real-time, nonlinear, uncertainty, etc. The analysis of dynamics on network is a critical means. The potential energy function models of system and branches are established, which are based on power system dynamic equilibrium equation to extract the system energy information after the fault duration. And the complexity of the system energy flow evolution is analyzed by using the multi-scale entropy method. The analysis results show that the system complexity under steady operation is much low. In addition, the complexity of the fault system increases with the increase of fault duration. Moreover, the system complexity under unstable operation shows a strong uncertainty in a small time scale and obvious regularity in a large time scale. And the most important is that the system complexities of the critical stable state and the critical unstable state are clearly distinct in different time scales. Such a difference can be used as a positive reference to the identification of the critical point in the dynamic state. Research results reveal the evolution of power energy flow in physical dynamic process. This can provide new ideas and methods for analyzing the dynamics behavior of power system.
Mass retrieval in mammogram based on hashing theory and linear neighborhood propagation
Authors: Li Yan-Feng  , Chen Hou-Jin  , Cao Lin  , Han Zhen-Zhong  , Cheng Lin  ,   School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044, China;,   Center for Breast, Peking University People's Hospital, Beijing 100044, China
Published: December 2020

Mass detection in mammograms usually has high false positive (FP) rate. Content based mass retrieval can effectively reduce the FP rate by comparing the image which is to be determined with mass images which have already been diagnosed. In this paper, a method combining discriminating anchor graph hashing (DAGH) and linear neighborhood propagation (LNP) is proposed for mammogram mass retrieval. Original AGH image representation does not consider pathological relevance in defining image similarity. To solve this problem, DAGH is put forward as a new image representation, which introduces the pathological class into image similarity. Furthermore, LNP is employed as a relevance feedback technique. Finally, interactive retrieval for mammogram masses is implemented based on the learning strategy between the underlying features and high-level semantic for images. Mammograms provided by the Breast Center of Peking University People's Hospital (BCPKUPH) are used to test the proposed method. Experimental results show that the DAGH image representation introducing pathological class is superior to original AGH in analyzing the similarity of mass images. Compared with existing methods, the proposed method shows obvious improvement in mass retrieval performance.
Review of sparse optimization-based computed tomography image reconstruction from few-view projections
Authors: Wang Lin-Yuan  , Liu Hong-Kui  , Li Lei  , Yan Bin  , Zhang Han-Ming  , Cai Ai-Long  , Chen Jian-Lin  , Hu Guo-En  ,   National Digital Switching System Engineering and Technological Research Center, Zhengzhou 450002, China;,   Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian 116000, China
Published: December 2020

Computed tomography (CT) is a technology widely used in medicine and industrial non-destructive testing, and the image reconstruction algorithm is a core technology of CT. Now, the image reconstruction from few-view projections is a hot point in the study of reconstruction algorithm. With the advancements in theories and algorithms, the sparse optimization has recently been applied to few-view reconstruction for CT image, and shown to have a good performance in both accuracy and speed. In this paper, basic conclusions and classical algorithms in sparse optimization are introduced. Furthermore, the spare optimization based few-view reconstruction algorithms for CT image, in particular the main results and the values of spare optimization, are summarized. Finally, the future research direction of sparse optimization based few-view reconstruction for CT image is discussed.
Application of heart rate variability analysis to pain detection for newborns
Authors: Zeng Chao  , Jiang Qi-Yun  , Chen Chao-Yang  , Xu Min  ,   College of Information Science and Technology, Shihezi University, Shihezi 832000, China;,   School of Geoscience and Info-Physics, Central South University, Changsha 410083, China;,   Department of Biomedical Engineering, Wayne State University, Detroit MI48201, USA
Published: December 2020

To investigate the influence of pain exposure on autonomic nervous system of newborns, and develop a detection model based on heart rate variability (HRV) indexes, 40 newborns are recruited in the study and short-term HRV analyses are performed on electrocardiogram before and after pain exposure using time-domain, frequency domain and nonlinear methods. Wilcoxon signed rank test is adopted for statistical comparison, and the support vector machine (SVM) is used for developing a detection model. The results demonstrate that 3 linear indexes such as the mean of RR intervals aRR, absolute powers of low frequency band LF and absolute powers of high frequency band HF, and 9 nonlinear indexes such as approximate entropy ApEn, sample entropy SampEn, and determinism DET before pain exposure are significantly different from after pain exposure; and that a detection accuracy of 83.75% could be achieved by the model based on the combination of 5 indexes, i.e., aRR, proportion of adjacent intervals greater than 50 ms pNN50, ApEn, correlation dimension D2 and recurrence rate REC, and SVM. It suggests that HRV indexes can reveal the response of autonomous nervous system to pain exposure of newborns, and the model based on HRV indexes and SVM could be employed for the detection of pain.
An improved synchronous algorithm based on Kendall for analyzing epileptic brain network
Authors: Dong Ze-Qin  , Hou Feng-Zhen  , Dai Jia-Fei  , Liu Xin-Feng  , Li Jin  , Wang Jun  ,   Key Laboratory Image Processing and Image Communications of Jiangsu Nanjing University of Posts and Telecommunications, Nanjing 210003, China;,   School of Science, China Pharmaceutical University, Nanjing 210009, China;,   Nanjing General Hospital of Nanjing Military Command, Nanjing 210002, China;,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

In this study, we propose a kendall rank correlation based synchronous algorithm inverse rank correlation (IRC). The kendall rank correlation is a generalized algorithm of nonlinear dynamics analysis which can effectively measure nonlinear correlations between variables. The study of complex networks has gradually penetrated into various fields of the social sciences. We use our algorithm to construct functional brain networks based on the data from electroencephalogram (EEG). The average node degree of complex brain networks is analyzed to investigate whether epileptic functional brain networks are distinctly different from normal brain networks. Results show that our method can distinguish between epileptic and normal functional brain networks and needs to record a very small number of EEG data. Experimental data show that our method suited to distinguish between epilepsy and normal brain node degree, which may contribute to further deepening the study of the brain neural dynamic behaviors, and provide an effective tool for clinical diagnosis.
Emergence of scaling in non-uniform hypernetworksdoes the rich get richer lead to a power-law distribution?
Authors: Guo Jin-Li  ,   Business School, University of Shanghai for Science and Technology, Shanghai 200093, China;,   Center for Supernetwork Research, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

In this paper, we propose a hypernetwork model with a nonlinear preferential attachment, and study the evolving mechanism and topological properties of the hypernetwork. We analyze the model by using a Poisson process theory and a continuous technique, and give a characteristic equation of hyperdegrees. We obtain the stationary average hyperdegree distribution of the hypernetwork by the characteristic equation. The analytical result shows that the hypernetwork has a phenomenon of the rich get richer, and it accords well with the simulation. It is shown in this paper that the hyperdegree distribution of the dynamic model exhibits a stretched exponential distribution with the increase of the hypernetwork size. It proves that the rich get richer does not necessarily induce a power-law distribution.
An evolution model of microblog user relationship networks based on complex network theory
Authors: Wang Ya-Qi  , Wang Jing  , Yang Hai-Bin  ,   Network and Information Security Key Lab of Armed Police Force, Electronics Technology Department, Engineering College of Armed Police Force, Xi'an 710086, China
Published: December 2020

Microblog provides convenience to the society, but at the same time, it also brings some adverse effects. To obtain the propagation mechanism of microblog rumor, and then take effective measures to prevent its spread, according to the complex network theory, in this paper we investigate the internal characteristics of microblog user relationship networks, and present a microblog user relationship network evolution model. By using the mean-field theory, the topological statistical property of our evolution model, and the dynamical behaviors of rumor spreading on such a model are analyzed. Theoretical analysis and simulation results show that such an evolving network exhibits a scale-free property. The degree distribution exponent not only is related to the reverse connection probability, but also depends on the node attraction degree distribution. It is also found that when the node attraction degree follows a power-law distribution, the steady-state rumor prevalence is great compared with the exponential distribution and uniform distribution. Moreover, as the reverse connection probability or the number of node initial edges increases, the probability of rumor outbreak and the number of nodes finally infected by the rumor will also increase.
Application of moving cut data-rescaled variance analysis in dynamic structure mutation testing
Authors: Sun Dong-Yong  , Zhang Hong-Bo  , Huang Qiang  ,   Key Laboratory of Subsurface Hydrology and Ecological Effect in Arid Region of Ministry of Education, School of Environmental Science and Engineering, Chang'an University, Xi'an 710054, China;,   Key Laboratory of Northwest Water Resources and Environment Ecology of Ministry of Education, Institute of Water Resources and Hydro-electric Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Scaling exponent is a valid nonlinear dynamics index, and can effectively detect the dynamic structure mutations in the correlation time series by means of moving a fixed widow and the moving cut a fixed window technique. When there is short-term correlation, sequence with short-term correlation and the calculation result of scaling exponent with rescaled range will be influenced to a certain degree, resulting in a certain deviation for the scaling exponent calculation of a moving cut window sequence, and some false mutations point and mutations range for abrupt change detection. In view of this, we present a new method of the dynamic structure mutation detection-moving cut data-rescaled variance analysis. The numerical testing of ideal time series shows that the moving cut data-rescaled variance analysis has strong stability and accuracy, which is much better than the moving rescaled variance and the moving approximate entropy. The test results have not false mutation point and interval when the moving window is small. The further application to practically measured data validates the reliability of the new method.
Interdecadal variation of precipitation pattern and preliminary studies during the summer of late-1990s in East Asia
Authors: Hu Po  , Qiao Shao-Bo  , Feng Guo-Lin  ,   College of Physical Science and Technology, Yangzhou University, Yangzhou 225002, China;,   Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing 100081, China
Published: December 2020

Based on the analyses of monthly precipitation, National Centers Environmental Prediction/University Corporation for Atmospheric Research reanalysis dataset, and 2°×2° sea surface temperature (sst) data of extended reconstructed sea surface temperature during 1983-2011, we discuss the interdecadal variations of precipition around late-1990s in East Asia, the contributions of the atmospheric internal dynamic processes, and the extra-forcing factors such as sst that presents interdecal characteristics corresponding to the results obtained by using regress analysis. The results show that the interdecadal variations of the summer rainfall over Northern East Asia around late-1990s were more obvious than over Southern East Asia, and the summer rainfall over Southern East Asia experienced a notable interdecadal change around early-1990s and early-2000s. The summer geopotential height at 500 hPa, the summer wind at 850 hPa, the summer U-wind at 200 hPa, the water vapor transportation field, the index of EAP and EASM all have the notable characteristics of the interdecadal variations, which further validate the interdecadal change of precipition of late-1990s from the angle of the atmospheric internal dynamic process. At the same time the sea surface temperature interdecadal anomalies of North Pacific and West Pacific may also be one of the important reasons for causing the interdecadal change over East Asia of the late-1990s.
Hopf bifurcation and chaos in the solar-forced El Niño /Southern Oscillation recharge oscillator model
Authors: Zhang Wu-Fan  , Zhao Qiang  ,   School of Physics, Peking University, Beijing 100871, China
Published: December 2020

A class of solar-forced recharge oscillator model for the El Niño /Southern Oscillation (ENSO) is considered. By transforming the ENSO model equations into the van der Pol-Duffing oscillator with periodic forcing, we obtain the Hopf bifurcation conditions by the harmonic balance method. Numerical simulations also show that the 11-yr solar-cycle forced ENSO system undergoes a transition from the quasi-periodicity route to chaos as the solar-cycle forcing is increased.
Recognition technology for obtaining micro-motion characteristics of rotating rough targets
Authors: Yang Zhi-Qiang  , Wu Zhen-Sen  , Zhang Geng  , Gong Lei  ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China;,   School of Photoelectrical Engineering, Xi'an Technological University, Xi'an 710032, China
Published: December 2020

Recognition of micro-motion characteristics has important research values in target detection field, which can be realized by employing the dynamic speckle technology. Based on the rough surface scattering theory, this paper studies the dynamic speckle time correlation function for rotating rough convex targets, and provides the dynamic speckle time correlation function for rotating cones. Comparison of the simulation results with those obtained under the experimental conditions confirms the validity of target time correlation length for cone targets. The angular velocity and line-of-sight angle for rotating cones are inversed by adopting particle group algorithm. Results show that this method is capable to identify the line-of-sight angle within 2090 and the angular velocity within 0.56 r/min for rotating cones, thus providing theoretical and experimental bases for recognition of micro-motion characteristics.
Optical system design of the coded aperture imaging spectrometer
Authors: Pei Lin-Lin  , Lü Qun-Bo  , Wang Jian-Wei  , Liu Yang-Yang  ,   Academy of Opto-Electronic, Chinese Academy of Sciences, Beijing 100094, China
Published: December 2020

The coded aperture imaging spectrometer system based on the double-Amici-prism is designed in this paper, which includes the telescope objective, the coded template, the double-Amici-prism, the collimator lens and the imaging lens. This optical system can obtain a high diffraction efficiency. Compared to the imaging spectrometer system with a slit for this kind of system, the field of view is a two-dimensional spatial expansion, increasing the difficulty of design. For the subsequent data inversion algorithm, perfect imaging is needed, and based on this, the optical aberration of the system should be corrected carefully wildly. In this paper, we design and analyse the features of the imaging spectrometer system based on the double-Amici-prism, then the comple imaging spectrometer system. Telescope objective is designed to be telecentric, its MTF at 39 line pairs is 0.8, implying that good images can be obtained. Innovatively, an inverted telescope objective is used as a collimation system.The imaging spectrometer system's MTF at 39 line pairs is higher than 0.65. The imaging of the outdoor target scene, obtained by the coded aperture imaging spectrometer, proves that the design principle is feasible,the system is of high diffraction efficiency, the full-field imaging is of good quality, and the full spectrum of data is creditabe.
Spin polarization and potential energy function of FeH2
Authors: Zheng Yuan-Yuan  , Ren Gui-Ming  , Chen Rui  , Wang Xing-Ming  , Chen Xiao-Hong  , Wang Ling  , Yuan Li  , Huang Xiao-Feng  ,   School of Physics-Chemistry, Xihua University, Chengdu 610039, China;,   Research Center for Advanced Computation, Xihua University, Chengdu 610039, China
Published: December 2020

Among the three methods (B3LYP, BP86 and B3LYP*) in density functional theory (DFT), the best tools for predicting the ground state of metal hydride, the B3LYP method for predicting the harmonic frequencies and geometric parameters of the ground state of FeH2 gives result in good accordance with the experimental data; so it is employed to optimize the structure of molecules FeH and FeH2 in possible geometries and multiplicities based on 6-311++g(d,p) level in searching of the structure with the lowest energy. Results show that their electronic states in the ground states are FeH(4Δ) and FeH2(5A1), supposing that the two molecules have three and four unpaired electrons respectively, with spin polarization effect, and they are paramagnetic substances, and the stable structure of molecule FeH2 is of C2v symmetry. The Murrell-Sorbie potential energy function-the sufficient analytical potential function form for biatomic molecules-with 4 parameters in molecule FeH is derived via the least square method. Their spectra data and force constants are deduced according to the results. The analytical potential energy function of FeH2 is also obtained from the many-body expansion theory, which gives the analytical potential function of triatom molecules of the single-value potential surface consisting of three parts with single body terms, two body terms, and three body terms. The deduced analytical functions for FeH2 in this paper predict successfully a global minimum stable structure of quintet FeH2 with a 4.68 eV depth potential trap, and other higher energy stable and saddle structures. This potential function predicts the balanced ground structure and the second derivative force constants of this molecule. According to the potential function of FeH2(C2v), when it is formed from H and FeH, a potential trap with its depth being 4.68 eV is excited and the complex molecule of H–Fe–H is easily formed. The reaction of Fe+H2 → HFeH is exothermic with ΔH=-0.08305 eV.
Analysis of one-dimensional electromagnetic wave transmission characteristics of plasma based on a kinetic theory model
Authors: Chen Wen-Bo  , Gong Xue-Yu  , Lu Xing-Qiang  , Feng Jun  , Liao Xiang-Bai  , Huang Guo-Yu  , Deng Xian-Jun  ,   School of Electrical Engineering, University of South China, Hengyang 421001, China;,   School of Nuclear Technology, University of South China, Hengyang 421001, China
Published: December 2020

This paper utilizes a kinetic theory model to gain the accurate electromagnetic (EM) wave characteristics in the plasma region, based on the solution of Maxwell-Boltzmann (MB) equation system. The system is solved by finite-difference time-domain (FDTD) algorithm, which gives the results of the electric field intensity and particle velocity distribution function. Furthermore, the validity and effectiveness of the proposed method is verified by comparing the results of reflection coefficient and transmission coefficient of the wave that impinges on plasma plate region with that of the analytic solution.
Studies on the mechanism of refractive index gradient surface
Authors: Liu Xiao-Bo  , Shi Hong-Yu  , Chen Bo  , Jiang Yan-Sheng  , Xu Zhuo  , Zhang An-Xue  ,   Department of Information and Communication Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

These years, with the development of material fabrication technology, some new synthetic materials that have unique electromagnetic properties have come out, one of which, the gradient meta-surface constructed into a special topological structure, gains rising popularity among experts. This paper establishes a refractive index gradient meta-surface and discusses its physical mechanism in optics. Normal reflection, anomalous reflection, and transformation from plane wave to medium wave can be realized by using this meta-surface. If the refractive index is larger than some threshold, the sine value of the reflection angle will vary linearly with that of the incidence angle, implying that parallel incident waves will become parallel emergent waves. If refraction index gradient is larger than some threshold, the plane wave at any incidence angle will give out a total reflection inside the medium, in other words, it is bound within the medium. Therefore the control of direction and intensity of beams can be achieved by adjusting parameters, providing a new engineering implementation method of artificial controllable full-medium gradient meta-surface.
Tight focusing properties of off-center Gaussian vortex beams
Authors: Wang Hui  , Ding Pan-Feng  , Pu Ji-Xiong  ,   College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

The properties of off-center Gaussian vortex beams focused by a high numerical aperture are investigated on the basis of vector Debye integral. A complex amplitude of off-center Gaussian vortex beams through a high numerical aperture objective is derived and numerical calculation is performed to analyze the intensity and phase distributions of the beams in the focal plane. It is shown that the intensity and phase distributions change significantly with the variation of off-axial distance; the intensity distribution in the focal plane is different in the direction of y-axis which is enhanced with the increase of off-axial distances; the sign of off-axial distance determines the direction in which the intensity is concentrated. On the other hand, different from the 1st order off-axial vortex beam, high-order off-axial vortex will split in the tightly focused field. Multiple phase singularities will appear and the number of singularities is equal to the topological charge of the original beam. Besides, the split singularities are symmetric, obviously. It is found that the splitting of high-order vortex is due to the tight focusing.
Theoretical and experimental researches on Tm and Ho codoped Q-switching laser
Authors: Qiao Liang  , Yang Fu-Gui  , Wu Yong-Hua  , Ke You-Gang  , Xia Zhong-Chao  ,   Centre of Electronic Information and photoelectric technology, Fujian Jiangxia University, Fuzhou 350108, China
Published: December 2020

The distribution of population inversion has been obtained by solving the rate equations of a Tm and Ho codoped laser system. A giant pulse laser output of 88.4 mJ with pulse duration of 426 ns has been predicted at 0.1% duty cycle of LD pump source. In a 2 m ring resonator, the Tm, Ho:LuLF laser material has been side-pumped from three directions and Q-switched for acoustic-optic device. The slope efficiency is 6.36% in free running mode and 2.9% in Q-switching mode. When 3.25 J pump energy in 1 Hz repetition frequency is injected, it has been demonstrated that the laser pulse energy of 103.2 mJ with an optical-to-optical efficiency of 3.17% in the free running mode and 30.3 mJ with 0.93% optical-to-optical efficiency. When 3.5 J pump energy is injected, it has been obtained that the pulse energies of 129.3 mJ and 35.9 mJ in the two modes with optical-to-optical efficiencies of 3.69% and 1.02% respectively. The greatest dynamic to static ratio is 32.8%. The pulse duration is 417.2 ns when 3.25J pump energy is injected. If the ring resonator operates unidirectionally, the laser energy and the corresponding optical efficiency will be doubled, the result being in agreement with the theoretical analysis of rate equations.
A 28.2-W wave-locked 878.6 nm diode-laser-pumped multi-segmented Nd:YVO4 laser operating at 1064 nm
Authors: Li Bin  , Ding Xin  , Sun Bing  , Sheng Quan  , Jiang Peng-Bo  , Zhang Wei  , Liu Jian  , Fan Chen  , Zhang Hai-Yong  , Yao Jian-Quan  ,   Key Laboratory of Opto-Electronics Information Science and Technology, Ministry of Education, College of Precision Instrument and Opto-Electronics Engineering, Institute of Laser and Opto-Electronics, Tianjin University, Tianjin 300072, China;,   Tianjin Maiman Laser Technology Co., Ltd, Tianjin 300111, China
Published: December 2020

We report a wave-locked 878.6 nm diode-laser-pumped multi-segmented Nd:YVO4 laser operating at 1064 nm, which is compared with the high doping concentration and the low doping concentration monolithic Nd:YVO4 lasers. Experimental results show that the configuration of the wave-locked 878.6 nm diode-laser-pumped multi-segmented crystals not only can reduce thermal effects of the laser but also can improve the optical-to-optical conversion efficiency. We have achieved an output power of 28.2 W at 1064 nm with an incidence pump power of 40 W, corresponding to the optical-to-optical efficiency of 70.5%, slope efficiency of 70.6%. For absorbed pump power, the optical-to-optical efficiency is 76% and the slope efficiency is 76.4%. The laser also has an excellent output stability while the temperature is varied from 10 ℃ to 40 ℃.
Acoustic scattering from the finite periodically ribbed two concentric cylindrical shells
Authors: Pan An  , Fan Jun  , Wang Bin  , Chen Zhi-Gang  , Zheng Guo-Yin  ,   State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;,   China Ship Development and Design Center, Wuhan 430064, China;,   Wuhan No.2 Shipbuilding Institute, Wuhan 430064, China
Published: December 2020

Acoustic scattering from the submerged finite periodically ribbed two concentric cylindrical shells, insonified by an incident plane wave, is studied. Motion of the shell is described by Donnell equations, while the motion of the disks is described by thin plate motion equations and plane ströss equations ignoring the effects of axial forces on the disks. Through angle-frequency spectra, besides the elastic waves of the shells, the contributions of the fluid between the inner and outer shells and the interaction of the inner and outer shells with the disks play an important role in the far scattering field. There are fine echo waves such as Bragg scattering and fluid-added waves excited on the angle-frequency spectra. Finally the theories are verified by experiments.
A virtual time reversal method for passive source localization in a range-dependent waveguide
Authors: Zhang Tong-Wei  , Yang Kun-De  ,   National Deep Sea Center, Qingdao 266061, China;,   College of Marine, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Matched-field replica vector should be calculated using parabolic equation in a range-dependent waveguide, this means that the matched-field localization is too computationally intensive, hence its engineering application is seriously hindered. A virtual time-reversal method for passive source localization for a range-dependent waveguide is presented. The number of parabolic equation computational grids in virtual time-reversal method is much smaller than that in matched-field processing for a range-dependent waveguide. Thus, the computational cost can be greatly reduced. Different from the matched-field processing, the virtual time-reversal method is a back-propagation process, which explores and utilizes the properties of reciprocity and superposition. It can be realized by weighting the replica surface with the complex conjugate of the data received on the corresponding element, followed by a summation of the processed received data. This performance of virtual time-reversal method for source localization is validated through numerical simulations and data from the Mediterranean Sea.
Numerical study of convection heat transfer in ordered three-dimensional porous media
Authors: Wang Ping  , Yin Yu-Zhen  , Shen Sheng-Qiang  ,   School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Saturated fluid convective heat transfer in ordered three-dimensional porous media has been investigated numerically using a CFD software. Spherical particles with diameters dp equal to respectively 14, 9.4, 7 mm have orderly arrangements constituting the porous media skeleton. There is a copper plate of constant heat flux density above the porous skeleton. The distribution of temperature and local convective heat transfer coefficient in the channel, as well as factors affecting the convective heat transfer are investigated by the method of fluid-solid coupling. Results show that the thickness of the thermal penetration and the thermal boundary layer increase in the flow direction, and decrease with the flow rate. When the thermal conductivity of the skeleton is relatively high, the convective heat transfer increases slightly with decreasing particle diameter. The convective heat transfer coefficient decreases with the increase in mass concentration of polyacrylamide solution, because the viscous dissipation weakens convection heat transfer.
Granular coal crack propagation study under uniaxial compression based on J integral
Authors: Xu Jun  , Xiao Xiao-Chun  , Pan Yi-Shan  , Ding Xin  ,   School of Mechanics and Engineering, Liaoning Technical University, Fuxin 123000, China
Published: December 2020

Granular coal is a kind of multilayer and structured solid matter, which consists of a large assemblage of individual granular solids and has dual characters of coal and granular materials. Its crack propagation law can be studied using the coal mechanics and multi-scale characteristics. First of all, the linear elastic material may be damaged under compression; and the cause of crack propagation is explained from the viewpoint of energy that the dynamics of crack propagation is due to the release of strain energy. And then, further study on the granular coal crack propagation under uniaxial compression from macroscopic and microscopic raspects is carried out by physical experiment and numerical simulation. Results show that a cone is formed at the bottom of the heap, the crack propagation is slowed down with the decrease of coal particle size, mutation points in crack propagation will appear, and the crack will not be smooth after the granular coal is damaged completely. Besides, due to the influence of granular coal particle size, uniformity has an important effect on crack propagation. The greater the homogeneity coefficient, the later the fractures occur. The acoustic emission energy release becomes frequent and severe in the mild, moderate and deep stages of crack propagation. These results will be conducive to further study on the law of geotechnical granular materials crack propagation under compression.
A study of capillary flow in variable interior corners under microgravity
Authors: Li Yong-Qiang  , Liu Ling  ,   Institute of Applied Mechanics, College of Science, Northeastern University, Shenyang 110819, China
Published: December 2020

This paper investigates the capillary flows in variable interior corners along the axis when a microgravity environment and the Concus-Finn condition are satisfied. The governing equation for capillary-driven flows in variable interior corners is established, and an approximately analytic solution is obtained. Then we compare the approximately analytic solution with the numerical simulation results obtained using the software FLOW-3D. Results show that the relative error between the approximately analytical and numerical solutions is getting smaller and smaller with increasing time, and it will be less than 5% after 6 s. The influence of different parameters on the interior corner flow is studied using a set of typical parameters. Numerical results show that the liquid-front position and meniscus height decrease with increasing interior angles, contact angle, slope, and power exponent. The liquid meniscus height increases with the duration at different times. But it remains constant at the initial time. The conclusion of this paper can be applied when designing containers and choosing the suitable solution in the space fluid management.
Theoretical study on charging equation of dust plasmas in double Maxwellian distribution
Authors: Li Xue-Liang  , Shi Yan-Xiang  ,   Department of Electronics and Information Engineering, Yili Normal University, YiNing 835000, China
Published: December 2020

According to the charging equation and charge conservation, the charging frequency (electric relaxation rate) is deduced and the formulation of charging electric current of the weakly ionized dust plasma is given according to the double Maxwellian distribution. It is shown that the directional speed have an influence on charging frequency; the charging frequency will decrease with the increase of directional speed; the charging frequency expression are the same as that in the literature when the directional speed is much smaller than the electron thermal velocity.
Polarization smoothing design for improving the whole spatial frequency at focal spot
Authors: Li Ping  , Wang Wei  , Zhao Run-Chang  , Geng Yuan-Chao  , Jia Huai-Ting  , Su Jing-Qin  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Polarization smoothing is a technique for reducing speckle pattern contröst on a target by overlaying two uncorrelated speckle patterns with orthogonal polarizations, and it can reduce focal spot contröst by a factor of 1/√2. Improvement of focal spot contröst by using traditional polarization wedge for polarization smoothing is usually concentrated at some special spatial frequency and is lack of effect in physical experiments. To improve the spatial spectrum of polarization smoothing, a new method is proposed, in which two orthogonal polarization states are separated by the angle distribution differences of the beam direction angle and the uniaxial crystal optic axis; the angle can induce the optical phase differences between “o” and “e” light. Theoretical analysis and numerical simulation are carried out to analyze the new method. Results show that based on the viable control of beam random polarization state at near field, besides the reduction of the focal spot contröst by 1/√2, the new method can improve the whole spatial spectrum at the focal spot. The boundary conditions that continuous phase plate is used as the way to induce the been direction angle for polarization smoothing is obtained.
Spectra study of He-irradiation induced defects in 6H-SiC
Authors: Du Yang-Yang  , Li Bing-Sheng  , Wang Zhi-Guang  , Sun Jian-Rong  , Yao Cun-Feng  , Chang Hai-Long  , Pang Li-Long  , Zhu Ya-Bin  , Cui Ming-Huan  , Zhang Hong-Peng  , Li Yuan-Fei  , Wang Ji  , Zhu Hui-Ping  , Song Peng  , Wang Dong  ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Specimens of 6H-SiC were irradiated by 300keV He ions at temperatures of RT, 450, 600 and 750 ℃ with fluences ranging from 11015 to 11017 cm-2. Post-irradiation, virgin and irradiated 6H-SiC specimens are measured and studied by microscopic laser confocal Raman spectrometer and UV-visible transmission apparatus. Analyses of both experimental results shown that production and recovery of defects caused by irradiation are directly related to the fluences and temperatures. Amorphization of 6H-SiC irradiated at RT occurrs, which is reflected by the disappearance of the Raman peaks and the saturation of the relative Raman intensity(simultaneously a strong Si-Si peak appears). Recovery of defects may exist in high-temperature irradiation, when helium bubbles do not exist, so that irradiation-induced defects can be easily recovered during irradiation process at elevated temperatures; but when helium bubbles are present, they can inhibit defects to recover, as shown in the trend of slopes of curves representing the relative Raman intensity and the relative absorption coefficients. This paper mainly focuses on the effects of helium bubbles on defect accumulation and recovery under the condition of high temperature irradiation, and then the comparison with the results of 6H-SiC irradiated by Si ions at elevated temperatures.
Effect of strain on Li adsorption on silicene
Authors: Li Xi-Lian  , Liu Gang  , Du Tao-Yuan  , Zhao Jing  , Wu Mu-Sheng  , Ouyang Chu-Ying  , Xu Bo  ,   College of Physics and Communication Electronics, Jiangxi Normal University, Nanchang 330022, China;,   School of software, Jiangxi Normal University, Nanchang 330022, China;,   Department of Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Structure and stability of the Li-adsorbed silicene under a biaxial strain are studied by using the first-principles plane-wave pseudopotential method based on the density functional theory. Results show that Li-adsorbed silicenes keep their original configurations basically when the tensile and certain compressive strains are applied, while the silicene plane bulges towards the Li atom when a larger compressive strain is applied, and the total energy of the corresponding system becomes distinctly lower. We also calculate the phonon spectra of the silicene under various strains, and analyze the reason why the Li-adsorbed silicene is unstable under the compressive strain.
Investigation into the reverse recovery voltage peak mechanism of freewheeling diode at a switching transition
Authors: Luo Yi-Fei  , Xiao Fei  , Tang Yong  , Wang Bo  , Liu Bin-Li  ,   National Key Laboratory of Vessel Integrated Power System Technology, Naval University of Engineering, Wuhan 430033, China
Published: December 2020

The freewheeling diode in power electronic converters may generate a voltage peak on the load during the reverse recovery process, and the peak voltage becomes larger when the forward conduction time is smaller, which very likely induces the over-voltage failure of the power devices. To effectively guide the reliability design of power electronic devices, the switching transition mechanism of the PIN freewheeling diode is discussed thoroughly based on semiconductor physics and the essential structure of power diodes. The law of reverse recovery voltage peak variation with switching transition time is deduced by methods of stored charge analysis, which shows that the peak voltage is larger for shorter conduction time and decreases abruptly as the transient conduction time increases. Experiments are carried out using the two-level half-bridge inverter unit with insulated-gate bipolar transistors and PIN diodes. Results show that the reverse recovery voltage peak decreases with the increase of the transition time, following an exponential rule, and tends to be constant after the freewheeling current becomes stable and finally approaches a steady state as the steady forward conduction current vanishes, thus proving the correctness of the presented analysis. This paper shows the theoretical and application values in the optimization of the reverse recovery mechanism of power diodes and the reliability improvement of power converters.
Research on the emission process of doped PhOLED by transient EL and delay luminescence measurement
Authors: Long Man-Man  , Zhao Su-Ling  , Xu Zheng  , Shen Chong-Yu  , Zhang Cheng-Wen  , Yang Zhao-Kun  , Huang Di  ,   Institute of Optoelectronic Technology, Beijing Jiaotong University, Key Laboratory for Information Storage, Displays and Materials, Beijing 100044, China
Published: December 2020

The organic phosphorescent OLED (PhOLED) has been widely studied because its inner quantum efficiency can reach 100%, but there has been much debate about the internal luminescence mechanism and process, mainly because they are explained using the luminescence theory of inorganic LED. In this paper, we set up a transient electroluminescence (EL) and delay EL measurement system, and for the first time asfar as we know use this measurement system to study the internal luminescence mechanism and process of PhOLED. In these studies we first fabricate a PhOLED which uses a kind of new efficient red-emitting iridium(III) complexes (Bis[2-(9, 9-dimethyl-9H-flouren-2-yl) benzothiazolato-N, C2'] iridium(III) (acetylacetonate)) doped with TAZ as the emitting layer. From the results, we find that there exists an overshoot at the end edge of the driving pulse; through the research we find that this is reasonable for the holes and electrons to accumulate in the object materials Irf and host TAZ, respectively. We also find that at the interface between host transfer layer and emission layer there exist a large number of holes. Through the delay luminescence measurement, we have proved that the emission of this doped system mainly comes from the directly trapped holes and electrons in Irf, and then excitons are formed.
Fabrication and optical-electrical properties of VO2/AZO composite films
Authors: Yuan Wen-Rui  , Li Yi  , Wang Xiao-Hua  , Zheng Hong-Zhu  , Chen Shao-Juan  , Chen Jian-Kun  , Sun Yao  , Tang Jia-Yin  , Liu Fei  , Hao Ru-Long  , Fang Bao-Ying  , Xiao Han  ,   School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China;,   Shanghai Key Laboratory of Modern Optical Systems, Shanghai 200093, China;,   Department of Computer and Information Engineering, Shanghai University of Electric Power, Shanghai 200090, China
Published: December 2020

Vanadium dioxide (VO2) thin film have been fabricated on the ZnO-doped Al conductive glass (AZO) substrates by DC magnetron sputtering and after thermal annealing. Effect of different annealing temperature and time olunation on the VO2/AZO composite films has been studied, then the structure, components and optical-electrical properties of the composite films are tested and analyzed by suitable instruments. Results show that the AZO film deposited on the conductive glass substrate dose not change the preferred orientation growth of the VO2 thin film, but its surface morphology characteristics are changed. Compared with those fabricated on ordinary glass substrates by the same processes and conditions, the phase transition temperature of the VO2/AZO composite film is decreased by about 25 ℃, and the width of thermal hysteresis is narrowed to about 6 ℃. Before and after phase transition, the visible light transmittance remains higher than 50%, and the infrared transmittances at a wavelength of 1500nm are 55% and 21% respectively. Furthermore, the resistivity rangeability is also up to three orders of magnitude before and after phase transition. In conclusion, the VO2/AZO composite films are easy to be fabricated and have a high degree of stability, smooth ness and compact surface morphology, thus they may be used to make new photoelectric devices