bluuebunny/crossref_metadata_2025 huggingface dataset:
Chaotic time series prediction using add-delete mechanism based regularized extreme learning machine
Authors: Zhao Yong-Ping  , Wang Kang-Kang  ,   School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Considering a regularized extreme learning machine (RELM) with randomly generated hidden nodes, an add-delete mechanism is proposed to determine the number of hidden nodes adaptively, where the extent of contribution to the objective function of RELM is treated as the criterion for judging each hidden node, that is, the large the better, and vice versa. As a result, the better hidden nodes are kept. On the contrary, the so-called worse hidden nodes are deleted. Naturally, the hidden nodes of RELM are selected optimally. In contrast to the other method only with the add mechanism, the proposed one has some advantages in the number of hidden nodes, generalization performance, and the real time. The experimental results on classical chaotic time series demonstrate the effectiveness and feasibility of the proposed add-delete mechanism for RELM.
Laser frequency scale system in carbon isotopic abundance measurement
Authors: Li Qin-Lei  , Fan Feng-Ying  , Xiong Wei-Jia  , Chen An-Ying  , Li Yan  ,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China
Published: December 2020

The real-time laser frequency scale system is developed for measuring the carbon isotopic abundance. By using confocal Fabry-Perot interferometer with different free spectral ranges, the diode laser frequency tuning characteristic is acquired in each laser frequency scanning period. During the course of measurements, two nonlinear analysis techniques are tested, i.e., linear interpolation and polynomial fitting. The absorption line center position for CO2 between 4976 and 4980 cm-1 is obtained by 100 average measurements from our experiments. A comparison between the measured absorption spectra and the spectral line positions from the HITRAN-2008 database, shows that the two method can both reach an accuracy of 10-4 cm-1 for the laser frequency scale. The best results are obtained with a linear interpolation method. The result shows that the laser frequency real-time scale system is applicable in carbon isotopic abundances measurement.
Dissociative adsorptions of NO on Yn (n=1–12) clusters
Authors: Yao Jian-Gang  , Gong Bao-An  , Wang Yuan-Xu  ,   Department of Basic Education, Yantai Nanshan University, Yantai 265713, China;,   Institute of Computational Materials Science, Henan University, Kaifeng 475004, China
Published: December 2020

The geometry structures, stabilities and chemical bonding properties of the YnNO(n=1–12) clusters are studied in the generalized gradient approximation based on the density functional theory with the consideration of spin multiplicities. The results show that NO adsorption changes the basic frameworks of the corresponding Yn clusters with n=5, 7, 8, 10. The obvious elongation of N–O bond length and the attenuate vibrational frequency indicate that the adsorption of NO on Yn cluster can be regarded as the dissociative adsorption. The chemical bondings of N–Y and O–Y both simultaneously play an important role in enlarging the adsorption energy of YnNO clusters. Specially, Y3NO, Y5NO, and Y8NO have the giant adsorption energies (9.92, 9.24, and 9.82 eV) coupled with the break of the N–O bond. The calculated second-order energy differences suggest that the NO adsorption has influences on the stabilities and bonding properties of Yn clusters. The appearance of the couple electrons, arising from the sp3 hybridization of N and O atom, not only leads to the fracture of N–O bond, but also enhances the ability to form N–Y bond and O–Y bond, which has important effects on the high stabilities of Y3NO, Y5NO, and Y8NO clusters.
Monte Carlo simulation of phonon ballistic diffusive heat conduction in silicon nanofilm
Authors: Hua Yu-Chao  , Dong Yuan  , Cao Bing-Yang  ,   Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
Published: December 2020

A Monte Carlo (MC) method is proposed by establishing a new model of phonon scattering processes with random sampling according to a scattering probability function. The MC scheme is used to simulate steady and transient ballistic-diffusive heat conduction in silicon nanofilm. In the MC simulations, we trace the phonon bundles that emit into media from the boundaries, and obtain the temperature profiles through statistics of the distribution of phonon bundles. It is found that the size effect of phonon transport leads to a boundary temperature jump which increases with the Knudsen number increasing. The thermal conductivity of the silicon nanofilm is calculated and the results suggest that nanofilm thermal conductivity increases with film thickness increasing, which is in good agreement with the experimental data as well as the results from the theoretical model. The temperature profiles vary with time in the transient simulations, which shows that the heat wave is related to not only time scale but also spatial scale. When the spatial scale becomes smaller, the ballistic transport is more dominant, which leads to stronger heat waves.
Molecular dynamics simulation of Lag effect in fluorine plasma etching Si
Authors: Wang Jian-Wei  , Song Yi-Xu  , Ren Tian-Ling  , Li Jin-Chun  , Chu Guo-Liang  ,   Institute of Microelectronics, Tsinghua University, Beijing 100084, China;,   Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, China
Published: December 2020

We present a simulation model of fluorine plasma etching of silicon. A mechanism for lag effect in the silicon surface etched by an inductively coupled plasma is investigated using molecular dynamics simulation. The results show that the lag effect is popular in etching process and that the etching rate of wide grooves is higher than that of the narrow ones. A probable reason is that the wide groove is produced more easily than the narrow groove. And the escape rate of product in narrow groove is lower than in wide groove. This is because a lot of products huddle together in the groove, which causes the speed of incident ions to decrease, and thus the energy of ions reaching the surface is reduced. The etching rate increases with the decrease of energy under otherwise identical conditions. On the other hand, the incident F particles are more close to the sidewall, which leads to the fact that the incident F particles will be easier to deposit on the surface of the wall. Then the width of the groove becomes narrower and narrower. The subsequent incident particles will be more difficult to reach the bottom of the groove. The lag effect increases not only with the decrease of the width of the groove but also with the enhancement of energy, and it decreases with temperature rising.
Time behavior and optimum conditions for the Xe gas extreme ultraviolet source
Authors: Zhao Yong-Peng  , Xu Qiang  , Xiao De-Long  , Ding Ning  , Xie Yao  , Li Qi  , Wang Qi  ,   National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin 150080, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Published: December 2020

The time behavior and the optimum conditions for the Xe gas capillary discharge extrem ultraviolet source are investigated theoretically and experimentally. By setting up a one-dimensional magneto-fluid-mechanics model, the plasma compressing characteristics and the emission characteristics are simulated under different gas pressures and different discharge currents. The time characteristic and the intensity of the 13.5 nm (2% bandwidth) emission are measured experimentally. The theoretical and experimental results show that there are the optimum gas pressures for different discharge currents. Meanwhile, the optimum gas pressure increases with the discharge current increasing. Moreover, the time to generate the highest 13.5 nm (2% bandwidth) emission should decrease by the increase of the discharge current. All the results should be useful to better understand the plasma condition for the discharge experiments and the EUV source. And it can be used to increase the power of the extreme ultraviolet source as well.
Modelling of edge plasma transport during H-mode of EAST by SOLPS5.0
Authors: Du Hai-Long  , Sang Chao-Feng  , Wang Liang  , Sun Ji-Zhong  , Liu Shao-Cheng  , Wang Hui-Qian  , Zhang Ling  , Guo Hou-Yang  , Wang De-Zhen  ,   School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116023, China;,   Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

This work aims at modeling the ELMing H-mode of the experimental advanced superconducting Tokamak (EAST) using edge plasma code package SOLPS5.0. The steady-state H-mode is obtained by adjusting the perpendicular radial anomalous transport coefficient according to the given upstream profiles of experimental measurements (shot 36291). The downstream divertor region can be then modeled once the simulated upstream electron density and temperature agrees well with the experimental measurements. On the basis of the H-mode simulation, the effect of the drift on divertor targets power asymmetry and that of the power damping width of scrape-off layer (SOL) on the peak power density to the divertor target are modeled, the simulation results indicate that the drift (E×B, B×▽B) is one of the main reasons for targets power asymmetry, and the increasing of power damping width of the SOL will reduce the peak power load on the divertor target sharply; besides, due to the presence of interaction between plasma and neutral gas or radiation in divertor region, the effect of the power damping width on the divertor target power load is decreased.
Influence of water on the tensile properties of amorphous silica：a reactive molecular dynamics simulation
Authors: Zhang Yun-An  , Tao Jun-Yong  , Chen Xun  , Liu Bin  ,   Science and Technology on Integrated Logistics Support Laboratory, College of Mechatonics Engineering and Automation, National University of Defense Technology, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Humidity has an important influence on the strength of the silica (SiO2). We examine the influence of liquid water on the tensile properties of amorphous silica (a-SiO2) using reactive molecular dynamics simulation. The results of the quasi-static tension show that liquid water reduces the tensile strength of a-SiO2 significantly. The tensile strength of dry a-SiO2 is 9.4 GPa while the tensile strength of a-SiO2 in the presence of liquid water is only 4.7 GPa. The strain-stress curve of dry a-SiO2 indicates that the stiffness of the a-SiO2 structure becomes stable with the increase of strain. On the other hand, the stiffness of the a-SiO2 with liquid water is gradually reduced with the increase of tensile strain. Moreover, the strain-stress curve of a-SiO2 in a strain range of 16% to 20% in the presence of liquid water is similar to the yielding phenomenon of plastic metal. The snapshots of the a-SiO2 in the presence of liquid water during the tension show that no plastic deformation is observed. We propose that the stress-enhanced hydrolysis releases part of the stress for the rupture of the Si–O bonds, so that the stiffness of the a-SiO2 in the presence of liquid water decreases with the increase of strain.
Quasi-periodic excitation and dynamic stability for strained superlattice
Authors: Luo Xiao-Hua  , He Wei  , Wu Mu-Ying  , Luo Shi-Yu  ,   College of Electric Engineering, Chongqing University, Chongqing 400044, China;,   Library of Chongqing Jiaotong University, Chongqing 400074, China;,   College of Electronic Engineering, Dongguan University of Technology, Dongguan 523808, China
Published: December 2020

In this paper, the action exerted by a superlattice sawtooth-shaped channel on the particle is assumed to be equivalent to that exerted by a periodic field with a similar shape. In the framework of classical mechanics, by introducing the sines-quared potential, the particle motion equation is reduced to pendulum equation with a damping term and dual-frequency excitation term. The bifurcation and chaos of single-frequency excitation system are analyzed with the Melnikov method. The stability of dual-frequency excitation system is discussed by using the Lyapunov exponent. The results show that in the case of weak nonlinearity, local instability can be found in the dual frequency excitation system, and it will be expanded globally until chaos appears. The dual excitation intensity leading to chaos is far less than that of single-frequency excitation. The application of an appropriate ultrasonic field is likely to make such a sensitivity passivated, and the stability of the system improved as well.
Growth and thermoelectric properties of Ge doped n-type Sn-based type-Ⅷ single crystalline clathrate
Authors: Meng Dai-Yi  , Shen Lan-Xian  , Shai Xu-Xia  , Dong Guo-Jun  , Deng Shu-Kang  ,   Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology of Ministry of Education, Solar Energy Research Institution, Yunnan Normal University, Kunming 650092, China
Published: December 2020

Single crystalline samples of type-Ⅷ Ba8Ga16-xGexSn30 (0 ≤ x ≤ 1.0) clathrates are fabricated by the Sn flux method. The structures and thermoelectric properties of the samples at temperatures ranging from 300 to 600 K are studied. Research results show that the actual content of Ge is relatively small in single crystal. The lattice parameters of the samples decrease slightly with the increase of the doping composition of Ge. The Ge doped samples have lower carrier density and higher carrier mobility than undoped samples. The Seebeck coefficients of all the doped samples are negative, and their absolute values are smaller than those of the undoped one. However, the electrical conductivity of the sample is increased by 62% after doping Ge and the sample of x=0.5 obtains a maximum value of ZT (1.25) at about 500 K.
Influence of sputtering power on the optical properties of metal manganese film
Authors: Tang Hua-Jie  , Zhang Jin-Min  , Jin Hao  , Shao Fei  , Hu Wei-Qian  , Xie Quan  ,   Institute of New Optoelectronic Materials and Technology, College of Electronic Information, Guizhou University, Guiyang 550025, China
Published: December 2020

In this paper, spectroscopic ellipsometry with an incident photon energy range of 2.04.0 eV is used to investigate the optical properties of Mn films deposited on silicon substrates at different sputtering powers. The ellipsometric data are analyzed by Drude and Lorenz oscillators dispersion model. The results show that the refractive index of the film decreases with the increase of the sputtering power. The extinction coefficient of the Mn film increases when the energy of photons is less than 3.0 eV and decreases when the energy of photons is in a range of 3.04.0 eV, and it arrives at an extremum at about 3.0 eV. The extremum shows a red-shift with the sputting power increasing from 60 to 100 W, which is dependent on the quality of the Mn film. With the increase of sputtering power, the extinction coefficient of the film approaches to that of metal manganese. The results also imply that the voids in the film decrease with the increase of the sputtering power, which is conducive to the growth of the films.
Composite interfaces and electrode properties of resistive random access memory devices
Authors: Yang Jin  , Zhou Mao-Xiu  , Xu Tai-Long  , Dai Yue-Hua  , Wang Jia-Yu  , Luo Jing  , Xu Hui-Fang  , Jiang Xian-Wei  , Chen Jun-Ning  ,   School of Electronics and Information Engineering, Anhui University, Hefei 230601, China;,   School of Physics and Electronic Information, Huaibei Normal University, Huaibei 235000, China
Published: December 2020

For the three kinds of composite materials, i.e., Cu(111)/HfO2(001), Cu(111)/HfO2(010) and Cu(111)/HfO2(100), the first-principles method based on the density functional theory is adopted to calculate their rates of mismatching of interface model, interface adhesion energies, the electric charge densities, the electron localization functions, and the charge density differences separately. The results indicate that the rate of mismatching of the Cu(111)/HfO2(010) interface model is lowest and its interface adhesion energy is higher than the others’, which means that the Cu(111)/HfO2(010) is most stable. From the analyses of charge densities and electron localization functions of the three interfaces, it can be found that only the Cu(111)/HfO2(010) interface is able to form the connective electronic channel along the vertical direction of the Cu electrode. This indicates that electrons possess the localizabilty and connectivity along the HfO2(010) direction, which corresponds to the switching-on direction of the resistive random access memory (RRAM) device. The charge density difference analysis reveals that the charge density distributions overlap, the electrons transfer mutually and bond at the interface of the Cu(111)/HfO2(010). In addition, based on the model of Cu (111)/HfO2 (010) interface, the formation energies of the interstitial Cu at different positions are also calculated. The results show that the closer to the interface the Cu atom, the more easily it migrates into HfO2. This indicates that the electrochemical reaction takes place more easily under the applied voltage, which results in the formation and rupture of Cu conductive filaments. All the above findings will provide a theoretical guidance for improving the performances of RRAM devices.
An implicit Monte Carlo method for thermal radiation transport
Authors: Li Shu  , Li Gang  , Tian Dong-Feng  , Deng Li  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The equations of thermal radiative transfer are mathematical models that describe the physical processes of photons scattering through and being absorbed in and emitted by a high-energy background material. These processes are important research objects of inertial confinement fusion (ICF). Numerical simulation is an indispensable method for this transportation equation. As an important method in the field of particle transportation, the Monte Carlo method has been widely employed in the fields of linear transportation of neutrons and high energy photons. However, traditional Monte Carlo method does not hold true when it is applied to the simulation of thermal radiation. In this research, an implicit Monte Carlo method based on calculable modeling and numerical simulation is studied. An integral transport equation that is suitable to Monte Carlo simulation is derived. A three-dimensional simulation code is developed, by which some thermal radiative transportation problems are simulated. The results of numerical experiments support that the implicit Monte Carlo method is applicable for thermal radiation transfer simulating. The work is expected to provide an important calculation method and tool for the thermal radiative transfer simulations of ICF.
Nonlinearity of the attitude motion of space robots subjected to gravitational gradient torque
Authors: Guo Sheng-Peng  , Li Dong-Xu  , Fan Cai-Zhi  , Meng Yun-He  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The attitude dynamics equation of free-floating space robots subjected to gravitational gradient effect is investigated. A two-link space robot is employed to analyze nonlinear properties of the perturbed yaw motion of the system in depth, when the manipulator configuration is fixed. Its nonlinear dynamical behavior is described by phase plane plot and Poincaré section. It is shown that the perturbed motion is sensitive to orbital eccentricity. The system takes on periodic motion and tumbling in circular orbit, while additional quasi-periodic motion in elliptic orbit. Furthermore, these nonlinearities are quantitatively studied by means of bifurcation and power spectrum.
Variable frequency range finding technology based on double polarization modulation method and system implementation
Authors: Hei Ke-Fei  , Yu Jin-Long  , Wang Ju  , Wang Wen-Rui  , Jia Shi  , Wu Qiong  , Xue Ji-Qiang  ,   School of Electronic Information Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Traditional laser range technology has a poor phase measurement accuracy and an additional phase of the system, which restricts the improvement of its accuracy. In this article, by using the technology of variable frequency measurement based on double polarization modulation the phase shift range-finding technology is improved. With the method of double polarization modulation, the demodulation of the phase information is directly implemented on the phase modulator, which can make the system simpler. The variable frequency technology is used to replace the traditional phase discrimination technology; therefore the measurement accuracy of the system will not be persecuted with the phase crimination any more. The theoretical curve of sine (cosine) relation between modulation frequency and output light intensity is proved experimentally. Owing to the fact that the stability of frequency can be better than 10-6, the measurement accuracy can reach ±10.6 u m@4.5 m. By using this system to measuring a 200 m-long fiber, the clear curve of modulation frequency versus output of system is obtained.
Electric field effects on the excited properties of Si2N2 molecule with special configuration：a density-functional study
Authors: Xu Guo-Liang  , Zhang Lin  , Lu Zhan-Sheng  , Liu Pei  , Liu Yu-Fang  ,   College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China
Published: December 2020

In order to understand in depth the electroluminescence mechanism, the influences of the external electric field on the geometric and electronic structure in ground state, the molecular vibrational spectra of Si2N2 molecule with Cs special symmetry are studied by density functional theory with B3LYP exchange-correlation prescription at the aug-cc-pVTZ basis set level. Following each optimization, the vibrational frequencies are calculated and all optimized structures are stable. The results show that the molecular vibrational Stark effect, i.e., red-shift for the low-frequency modes and blue-shift for the high-frequency modes are observed with the increase of the applied field strength. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the energy gap between HOMO and LUMO of Si2N2 molecule diminish with the increase of external field. A time-dependent density functional theory is used to investigate the excited properties of Si2N2 (Cs) molecule. The calculated absorption spectra of Si2N2 molecule with Cs symmetry are in agreement with the experiment values. The analysis reveals that the absorption spectrum wavelength increases in the visible region with a concomitant increase in the electronic transition oscillator strengths in the course of the increase of the external electric field strength. The results reveal that the excited properties of Si2N2 molecule can be easily tuned by the external electric field, which indicates that the silicon nitride is an interesting optoelectronic functional material. These investigations on the various properties of Si2N2 molecule with Cs symmetry under an external electric field are useful to understand the electroluminescence mechanism for silicon nitride used in molecular electronics.
Study of argon/hydrogen mixed cluster in supersonic gas jet
Authors: Guo Er-Fu  , Han Ji-Feng  , Li Yong-Qing  , Yang Chao-Wen  , Zhou Rong  ,   Key Laboratory of Radiation Physics and Technology of Ministry of Education, College of Physical Science and Technology, Sichuan University, Chengdu 610064, China
Published: December 2020

The average mixed cluster sizes in different mixing proportions of Ar-CH4 mixed cluster and Ar-H2 mixed cluster in supersonic gas jet are studied by Rayleigh scattering method. It is found that Ar-CH4 mixed cluster could form easily when the mixed Ar and CH4 gas are used in gas jet, and the maximum cluster size is achieved when the content of Ar is 50%. The maximum cluster size of Ar-CH4 mixed cluster is larger than that of either Ar cluster or CH4 cluster. Being different from pure hydrogen cluster which only forms at liquid nitrogen temperature, Ar-H2 mixed cluster can form at room temperature. So this is the first time we have obtained hydrogen cluster at room temperature. Ar-H2 mixed cluster starts to form at H2 content value higher than 40% and it reaches maximum size when the content of H2 is 60%. Hydrogen (deuterium) mixed clusters introduce heavier Ar element on the basis of hydrogen (deuterium) clusters. It will further accelerate the deuterium ions to higher energy in deuterium cluster laser fusion experiments, so we can obtain higher neutron yield and fusion efficiency.
Numerical simulation and experimental investigation of the production of multiply charged ions by the ionization of benzene cluster with a moderate intensity laser
Authors: Zhao Wu-Duo  , Wang Wei-Guo  , Li Hai-Yang  ,   Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The production of multiply charged ions by the interaction of intense femtosecond laser with clusters has been widely reported. Recently, many groups discovered the multiply charged ions when the cluster was irradiated by a 532 nm nanosecond laser with the intensity as low as 1010 W/cm2. Although this interesting phenomenon could be explained by the mechanism of multiphoton ionization triggered-inverse bremsstrahlung heating-electron impact ionization, there is a lack of numerical simulation to explain the generation of multiply charged ions. In this paper, numerical simulation is performed to study the generation process of multiply charged ions in the moderate intensity laser. Firstly, the electron energy is calculated according to ponderomotive potential. Secondly, the cross section of electron impact ionization is calculated on the basis of Lotz formula. Finally, the evolution of multiply charged ions in the cluster is calculated with the kinetic reaction rate equation. The effects of cluster size and electron density on multiply charged ions are investigated in detail. Simulation results show that the ionization process is completed and the balance among C2+, C3+ and C4+ is achieved in 0.7 ns. The relative intensity sequence of multiply charged ions is C2+ C3+ C4+, which is consistent with the experimental results. In addition, numerical simulation results show that the charge state of ions is increased with the increase of cluster size, which is consistent with the experimental results.
Newmark method for finite-difference time-domain modeling of wave propagation in frequency-dispersive medium
Authors: Wang Fei  , Wei Bing  , Li Lin-Qian  ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China
Published: December 2020

The complex polarizations of three kinds of general dispersive medium models, i.e. Debye model, Lorentz model, Drude model, are described by rational polynomial fraction in jω. The relationship between the polarization vector P and the intensity of electric field E in time domain is obtained by utilizing the transformation relationship from frequency domain to time domain jω→∂/∂t. Then, the time domain second order equation is solved by using the Newmark β and γ method, which has higher accuracy than the traditional center difference method. Once the recursive formulations for E and P are obtained, the recursive formulations for D and E in time domain can be also obtained based on the constitutive relation. Therefore for a dispersive medium the iterative electromagnetic field calculation is conducted by finite-difference time-domain (FDTD) method. The present numerical results demonstrate that the proposed method is a general algorithm for three kinds of general dispersive medium models, and has higher accuracy than the shift operator-FDTD, which is based on the central difference discrete scheme.
Analyses on limitations of coherent field imaging principle
Authors: Si Qing-Dan  , Luo Xiu-Juan  , Zeng Zhi-Hong  ,   Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The theoretical basis of coherent field imaging technique (also called the Fourier telescopy) is reconsidered. The limitations of the technique principle are analyzed by defining the measured object and deriving rigorously mathematical expressions. The reconstructed image of the technique ineluctably contains the gradient information about the object; as a result the technique cannot acquire the reflectivity of the object exactly. The computer simulation verifies the conclusion. Based on the conclusion, the reconstructed image of the technique can be evaluated and three-dimensional coherent field imaging technique may be developed.
Influence of Raman effect on the state of polarization evolution in a low-birefringence fiber
Authors: Wang Mei-Jie  , Jia Wei-Guo  , Zhang Si-Yuan  , Qiao Hai-Long  , Yang Jun  , Zhang Jun-Ping  , Menke Nei-Mu-Le  ,   School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
Published: December 2020

In this paper, the linear polarization light satisfied nonlinear coupled differential equations containing the Raman effect are utilized in a low birefringence fiber. The coupling model equation satisfied by the Stokes parameters is derived by introducing the Stokes parameters. Poincaré sphere is used to analyze the influence of Raman scattering effect on the state of polarization evolution in the low-birefringence fiber. The results show that the state of polarization evolution can be changed and the polarization ellipticity can also be changed due to Raman scattering effect in the low birefringence fiber when between the input power and motion constants satisfy a certain relation.
Simulation of X-ray refraction information extraction using multiple image-collecting strategies
Authors: Wang Yun-Bo  , Li Gong-Ping  , Pan Xiao-Dong  , Xu Nan-Nan  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
Published: December 2020

With different strategies collecting images, the extraction results of refraction information using the diffraction-enhanced imaging (DEI), generalized diffraction-enhanced imaging (G-DEI) or multiple-image radiography (MIR) algorithm of analyzer-based imaging technique are greatly different from each other. Compared with the conventional strategy in which the images are acquired at the waist positions of rocking curve (RC), the one with the positions closer to the central axis of RC can obtain more accurate refraction information for the DEI algorithm. For the G-DEI algorithm taking three images, if the positions, where images are obtained, are symmetrical with respect to the central axis of RC, the extraction result of refraction information is better when the positions are asymmetrical. Besides, by comparison with the strategy in which the images are acquired at the waist or toe positions, the one with the positions closer to central axis of RC can obtain better result. If the angle interval of neighbor positions is larger than the full-width at half-maximum (FWHM) of RC, the extraction result of the MIR algorithm is bad. When the angle interval is smaller than the FWHM, and the value of angle range of all positions collecting images is close to the maximum theoretical value of sample, the extraction result is very good. This study will be helpful for reasonably choosing the image-collecting strategies in experiment, and further understanding the extraction algorithms of refraction information.
Frequency difference modulation of microchip Nd：YAG laser induced by laser feedback
Authors: Zhang Song  , Tan Yi-Dong  , Zhang Shu-Lian  ,   State Key Laboratory of Precision Measurement Technology and Instruments, Tsinghua University, Beijing 100084, China
Published: December 2020

Microchip laser can output two orthogonal frequency splitting modes due to its own internal residual stress. In this paper it is found that the frequency difference of microchip laser is modulated by laser feedback. The modulation is a sinusoid-like curve whose center is the original frequency difference and period is half-wavelength. The amplitude of the modulation curve is proportional to feedback level. But when the feedback is too strong, so that the polarization switching occurs and only one polarization exists sometimes. In a range of external cavity, the amplitude of the modulation curve is also proportional to original frequency difference. The theoretical analysis and simulation based on the composite laser cavity theory and self-consistent theory are in good agreement with the experimental results. The potential applications of this phenomenon in precision measurement are discussed.
A 4 mJ femtosecond Ti：sapphire regenerative amplifier at 1 kHz repetition rate
Authors: Shen Zhong-Wei  , Wang Zhao-Hua  , Fan Hai-Tao  , Qin Shuang  , Teng Hao  , He Peng  , Wei Zhi-Yi  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710126, China
Published: December 2020

To meet the application requirements for high energy kHz repetition rate femtosecond laser, a high-efficiency femtosecond Ti:sapphire linear regenerative amplifier is designed. By optimizing the parameters of the cavity, 5.8 mJ chirped pulses at 800 nm are obtained, under pump energy of 20 mJ with wavelength of 527 nm at 1 kHz repetition rate, corresponding to a slope efficiency of 30.7%. By compensating for the dispersion, 4 mJ laser pulses at 800 nm with pulse duration of 45.7 fs are achieved. The energy fluctuation is 0.18% (RMS) in 5 h.
Continuous-wave modulation differential absorption lidar system for CO2 measurement
Authors: Liu Hao  , Shu Rong  , Hong Guang-Lie  , Zheng Long  , Ge Ye  , Hu Yi-Hua  ,   Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China;,   State Key Laboratory of Pulsed Power Laser Technology, Electronic Engineering Institute, Hefei 230037, China
Published: December 2020

An intensity modulation hard-target differential laser absorption lidar system for CO2 sensing is demonstrated. On and off wavelength lasers are modulated with 10 kHz and 12 kHz sinusoidal waves. The echo is extracted using coherent detection technique. The system is fiber based, which makes it compact and removable. We obtain three day variation of horizontal column averaged CO2 concentration of Shanghai district. We also propose an accuracy evaluation method based on electronic noise analysis combined with laser frequency modulation. The result shows that the measurement precision for the column corresponds to 3.39×10-6 (rms) with 1s integral time and 450 m path.
Rogue solution of Hirota equation and its transmision
Authors: Li Shu-Qing  , Yang Guang-Ye  , Li Lu  ,   Department of Science, Taiyuan Institute Technology, Taiyuan 030008, China;,   Department of Physics, Shanxi Medical University, Taiyuan 030001, China;,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China
Published: December 2020

A breather soliton solution of the higher-order Hirota equation is given under the integrable condition, and the rogue solution of Hirota equation is obtained on the basis of the breather soliton solutions, which is helpful to understand the characteristics and the physical reason of rogue wave. The excitation of rogue wave is studied by a cw and periodic perturbation or a Gaussian type perturbation. As an example, by distribution Fourier method, the transmission characteristics of rogue wave is studied with considering the frequency shift and the Raman gain, and the effects of the frequency shift and Raman gain on the interaction between rogue waves are also analyzed.
Sensing detection and quenching method for InGaAs single-photon detector
Authors: Zheng Li-Xia  , Wu Jin  , Zhang Xiu-Chuan  , Tu Jun-Hong  , Sun Wei-Feng  , Gao Xin-Jiang  ,   Wuxi Branch, Southeast University, Wuxi 214135, China;,   National ASIC System Engineering Research Center, Southeast University, Nanjing 210096, China;,   The 44th Research Institute, China Electronics Technology Group Corporation, Chongqing 400060, China
Published: December 2020

A gated operation dynamic bias control strategy of InGaAs single-photon avalanche diode (SPAD) and circuit implementation are proposed based on the research of the SPAD performances. By the gated operation active quenching method the quenching time can be lowered, also dark count and afterpulsing effect are inhibited. The circuit fabricated by standard complementary metal oxide semiconductor (CMOS) technology and SPAD fabricated by non-standard CMOS technology are interconnected through the indium column interconnection hybrid packaging process. In the low temperature (-30 ℃) test conditions, the avalanche current signal triggered by light is extracted and avalanche phenomenon is quickly quenched. Studies in this paper are the sensing resistance and critical sensing voltage effect on electrical performance of the detector and the implementation method of the detection circuit. The recovery time and transfer delay of the SPAD are 575 and 563 ps, respectively and the quenching time is 1.88 ns. These characteristics meet the requirements for the nanosecond precision sensor detection application.
Research progress of silicon-based photonic integration
Authors: Zhou Pei-Ji  , Li Zhi-Yong  , Yu Yu-De  , Yu Jin-Zhong  ,   State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

The research progress of the silicon-based photonic integration in the world and the results of our group in recent years are reported in this paper, including exploration of design and improvement on process of the optical transceiver modules, Ⅲ-V/silicon lasers and other integrated photonics. The silicon photonics is predicted to have a great prospect in many fields due to its good compatibility with complementary metal oxide semiconductor technology. It is concluded that the trend of photonic integration on silicon substrate is toward high data rate, low power consumption and large integration density, and the silicon based photonic integration will become a main research subject of silicon photonics in the future.
Spatial filter design based on compressed replica vectors
Authors: Su Lin  , Ma Li  , Sun Bing-Wen  , Guo Sheng-Ming  ,   Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   Key Laboratory of Underwater Acoustics Environment, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Matched field processing techniques have been studied extensively in recent decades, and a lot of detail algorithms have been put forward for practical use. When the underwater target is obscured by the strong surface interferences, the performance of matched field processing localization will degrade severely. The now existing spatial filter technique can be used to suppress the surface interferences, but the burden of calculation is heavy and the memory usage is large. In this paper, a scheme of optimizing spatial filter design based on the compressed replica vectors is presented, and the broadband data are processed incoherently. In contrary to the existing spatial filter, the optimized spatial filter can effectively reduce the computational complexity and memory usage when the number of array elements N is greater than the number of the effective modes Q, meanwhile, it also retains the original performance of interference suppression. Numerical simulations in a littoral shallow water environment are performed to validate the performance of the spatial filter and the promotion of computation speed. Then, data processing results obtained from an experiment conducted in the littoral shallow water environment are presented. It follows from the results that the weak underwater target can be distinguished from the strong surface interference clearly by use of the incoherent matched field processing with the application of the spatial filter based on compressed replica vectors.
Influence of separation ratio on Rayleigh-Bénard convection solutions in a binary fluid mixture
Authors: Ning Li-Zhong  , Wang Na  , Yuan Zhe  , Li Kai-Ji  , Wang Zhuo-Yun  ,   State Key Laboratory of Eco-Hydraulic Engineering in Shaanxi, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

The Rayleigh-Bénard convection in a binary fluid mixture is one of typical models for studying the nonlinear dynamics of nonequilibrium convection. In this paper, using the numerical simulations of the two-dimensional full equations of hydrodynamics, we study the bifurcation and evolution of patterns in the traveling wave convection in binary fluid mixtures with strong Soret effect (separation ratio Ψ=-0.60) in a rectangular cell. The system exhibits 5 types of traveling wave convection solutions with the increasing of reduced Rayleigh number r along the upper branch of the bifurcation curve. They are localized traveling wave convection, traveling wave convection with defects, traveling wave convection, undulation traveling wave convection, and stationary overturning convection. Second, the influence of separation ratio on convection solutions is investigated. By comparing the convection solutions with strong Soret effect (Ψ=-0.60) with those of weakly Soret effect (Ψ=-0.11), we find that those with strong Soret effect are richer. Because of the complexity in convection with strong Soret effect, the convection solutions at Ψ=-0.60 are different from those at Ψ=-0.20, -0.4.
Perturbation to Noether symmetries and adiabatic invariants for Birkhoffian systems based on El-Nabulsi dynamical models
Authors: Chen Ju  , Zhang Yi  ,   College of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China;,   College of Civil Engineering, Suzhou University of Science and Technology, Suzhou 215011, China
Published: December 2020

In this paper, we study the problem of perturbation to Noether symmetries and adiabatic invariants for a Birkhoffian system under small disturbance based on the El-Nabulsi dynamical model. First, the dynamical model presented by El-Nabulsi, which is based on the Riemann-Liouville fractional integral under the framework of the fractional calculus, is extended to the Birkhoffian system, and El-Nabulsi-Birkhoff equations for the Birkhoffian system are established. Then, by using the invariance of the El-Nabulsi-Pfaff action under the infinitesimal transformations, the definition and criterion of the Noether quasi-symmetric transformation are given, and the exact invariant caused directly by the Noether symmetry is obtained. Furthermore, by introducing the concept of high-order adiabatic invariant of a mechanical system, the relationship between the perturbation to the Noether symmetry and the adiabatic invariant after the action of small disturbance is studied, the condition that the perturbation of symmetry leads to the adiabatic invariant and its formulation are presented. As a special case, the perturbation to Noether symmetries and corresponding adiabatic invariants mechanics of non-conservative systems in phase space under El-Nabulsi models and classical Birkhoffian systems are discussed. At the end of the paper, taking the well-known Hojman-Urrutia problem for example, its Noether symmetries under the El-Nabulsi dynamical model is investigated and corresponding exact invariants and adiabatic invariants are presented.
Conformal invariance and conserved quantity of relative motion holonomic dynamical system in phase space
Authors: Wang Ting-Zhi  , Sun Xian-Ting  , Han Yue-Lin  ,   School of Science, Jiangnan University, Wuxi 214122, China;,   School of Electric and Information Engineering, Pingdingshan University, Pingdingshan 467000, China
Published: December 2020

Conformal invariance and conserved quantity of relative motion holonomic dynamical system in phase space are studied. The definition of conformal invariance of relative motion holonomic dynamical system in phase space is provided. The necessary and sufficient conditions that conformal invariance of the system would be Lie symmetry are deduced. By use of a structure equation that the gauge function satisfies, the corresponding conserved quantity of the system is derived. Finally an illustrative example is given to verify the results.
Inhibition effect of low-temperature pre-irradiation of helium ions on the growth of helium bubble in stainless steel：a Monte Carlo simulation
Authors: Zheng Hui  , Zhang Chong-Hong  , Chen Bo  , Yang Yi-Tao  , Lai Xin-Chun  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China;,   State Key Laboratory for Surface Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621907, China
Published: December 2020

Zhang Chong-Hong group has found that pre-irradiation of helium ions at low temperature with very low dose could effectively suppress helium bubble growth in materials. This experimental result lacks theoretical explanation. In this paper, we use Monte Carlo simulation to study the effects of different temperature modes on helium bubbles based on a three-dimensional lattice gas model under continued particle injection, and find that the phenomenon that pre-irradiation of helium atoms at low temperature can suppress the helium bubble growth occurs in simulation results as it does in the experiments. The reason is that small helium bubbles with high number density are produced by pre-irradiation at low temperature, and the high number density of bubbles controls the increase of sizes of helium bubbles.
Preliminary experimental research of electron emission characteristics on surface area of two kinds of electrodes
Authors: Su Zhao-Feng  , Yang Hai-Liang  , Zhang Peng-Fei  , Lai Ding-Guo  , Guo Jian-Ming  , Ren Shu-Qing  , Wang Qiang  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

The principle of measuring electron emission threshold of surface area metal electrode is presented. The measurement system of electron emission thresholds of two electrodes is developed. The electron emission characteristics of materials with different roughness degrees or Cr2O3 coating-deposit 40 um are measured in “Chenguang” accelerator. The results show that polishing can suppress electron emission. The higher the roughness degree of material, the lower the electron emission threshold is. Material coated with Cr2O3 has higher electron emission threshold than polished material.