bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of visible and infrared broadband dispersive waves in photonic crystal fiber cladding
Authors: Zhao Xing-Tao  , Zheng Yi  , Han Ying  , Zhou Gui-Yao  , Hou Zhi-Yun  , Shen Jian-Ping  , Wang Chun  , Hou Lan-Tian  ,   Laser Institute of Science College, Beijing Jiaotong University, Beijing 100044, China;,   Measurement Technology and Instrumentation Key Laboratory of Hebei Province, State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

The optical properties of photonic crystal fiber cladding knot among the three air holes are analyzed. The mode area, nonlinear coefficient and dispersion characteristics of the core and cladding knot are contrasted. Cladding knot of photonic crystal fiber has a small core and highly nonlinear characteristics. For larger cladding air holes, double zero dispersion curves are obtained. According to the dispersion curve, phase-matching features are analyzed for dispersive wave generation. Variation rules of the central wavelength of the dispersive wave with pump power and wavelength are achieved. The photonic crystal fiber designed is fabricated. The visible and infrared broadband dispersive waves above 300 nm are obtained in experiment. Experimental and theoretical results are completely consistent with each other. These are foundation for wavelength conversion and supercontinuum broadband light source.
Analysis of underwater sound absorption of visco-elastic composites coating containing micro-spherical glass shell
Authors: Yu Li-Gang  , Li Zhao-Hui  , Wang Ren-Qian  , Ma Li-Li  ,   School of Electronic Engineering and Computer Science, Peking University, Beijing 100871, China
Published: December 2020

Underwater sound absorption coating is significant to the stealth of a submarine, so it attracts a lot of attention. Underwater sound absorption of visco-elastic composites coating containing micro-spherical glass shell was investigated theoretically. The mechanical and acoustic properties of the composites in response to the volume of the micro-spherical glass shell were analyzed by the effective parameters method. Sound absorption of a single layer composites coating containing different volume of micro-spherical glass shell was calculated by the one-dimensional model, in which sound propagates in multi-layer media. The calculated results show that the sound absorption at low frequencies can be promoted by increasing the volume of micro-spherical glass shell, but the sound absorption at high frequencies is depressed. The volume distribution of the micro-spherical glass shells across the thickness of the coating was optimized by the genetic algorithm. The optimal multi-layer structure can promote the sound absorption at low frequencies, and keep the sound absorption coefficients above a limited value (0.7) at high frequencies. The optimal multi-layer composite coating can work at high pressure since it does not contain hollow macro-structure. Its structure is simple, so the technique of its fabrication should not be complicated. The theoretical method achieved in this paper can be applied in the design of underwater sound absorption coating.
Orthogonal code shift keying spread spectrum underwater acoustic communication
Authors: Yu Yang  , Zhou Feng  , Qiao Gang  ,   National Laboratory of Underwater Acoustic Technology, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Code shift keying (CSK) is generally used to overcome the spreading gain versus data rate limitation in underwater acoustic (UWA) communication as generalized M-ary spread spectrum technology. In addition, the concept of orthogonal CSK is introduced into the UWA communication to achieve higher rate, mitigate crosstalk from the other thoroughfare and utilize the redundant information of CSK adequately. In this paper, we propose a new scheme employing orthogonal double thoroughfare CSK spread spectrum UWA communication with utilizing code phase information combined. First, each symbol integration output form of the proposed method is deduced. Furthermore, the property of orthogonal CSK is analyzed and its bit error rate is investigated as compared with conventional CSK and double thoroughfare CSK via simulation. Finally, the validity of simulation comparison is verified in experiment. 580.6 bps data rate of the proposed communication scheme is realized in 104 bit volume and 4 kHz bandwidth efficiently. It is shown that the proposed method provides significantly improved communication performance through formula, simulation and test.
Linear wave propagation in the bubbly liquid
Authors: Wang Yong  , Lin Shu-Yu  , Zhang Xiao-Li  ,   Institute of Applied Acoustics Shaanxi Normal University, Xi’an 710062, China
Published: December 2020

In order to get the factor of influence of bubbly liquid on the acoustic wave propagation, the linear wave propagation in bubbly liquid is studied. The influence of bubbles is taken into account when the acoustic model of bubbly liquid is established, and we can get the corrected oscillation equation of the bubble when the interaction of bubbles is taken into the Keller's model. One can get the acoustic attenuation coefficient and the sound speed of the bubbly liquid through solving the linearized equation of wave propagation of bubbly liquids and the oscillation equation of bubbles when (ωR0)/c << 1. After the numerical analysis, we find that the acoustic attenuation coefficient increases and the sound speed will turn smaller as the numbers of bubbles increases and the bubbles gets smaller when the driving frequency of sound field keeps constant; when the driving frequency is far bellow the resonance frequency of bubble and both the volume fraction and the size of bubbles are kept constant, the sound speed will changes in a way contrary to the case of driving frequency of sound field; it is not evident that the bubble interaction influences the acoustic attenuation coefficient and the sound speed. Finally, we deem that the volume concentration, the size of bubble and the driving frequency of sound field are the important parameters which determine the deviations of the sound speed and the attenuation from those of bubble-free water.
On the first integrals of linear damped oscillators
Authors: Ding Guang-Tao  ,   College of Physics and Electronic Information, Anhui Normal University, Wuhu 241000, China
Published: December 2020

By introducing fundamental integrals of one-dimensional linear damped oscillators the other first integrals can be constructed, including time-irrelevant integrals. The above method is extended to multidimensional systems, in order to construct different integrals of two-dimensional and n-dimensional linear damped oscillators. It is proved that there are three independent time-irrelevant integrals for all kinds of two-dimensional linear damped oscillators, and 2n-1 independent time-irrelevant integrals for n-dimensional linear damped oscillators. Using the transformation of variables the first integrals of linear damped oscillator transform into ones of harmonic oscillator.
Experimental research on bubble dynamics near circular hole of plate
Authors: Wang Shi-Ping  , Zhang A-Man  , Liu Yun-Long  , Wu Chao  ,   College of Shipbuilding Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Traditional studies on bubble dynamics near solid boundaries mainly focus on its pulsation and jet features near a full plate. A hole will be formed when a warship is attacked by an underwater weapon and it may be subjected to a subsequent attack generated by charge explosion. And the hole on the plate would affect the blow effect of the underwater explosion bubble nearby. To study the bubble pulsation and jet features near a plate with a hole in the middle, a series of experiments is carried out using a spark bubble generator and high-speed camera. We find that when a bubble is generated homocentricly near the hole, cavity-attraction effect of the bubble will be formed due to the effect of the hole, and the opposite-jets can then be formed. Then the influences of dimensionless standoff distance and hole size are analyzed. Finally, the dynamic behavior of a bubble which is generated decenteredly near the hole is studied to show that the blow effect of a bubble increases with decentered position increasing.
Friction and wear performance of the 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 piezoelectric film
Authors: Zhang Yan  , Wang Zeng-Mei  , Chen Yun-Fei  , Guo Xin-Li  , Sun Wei  , Yuan Guo-Liang  , Yin Jiang  , Liu Zhi-Guo  ,   School of Mechanical Engineering, Jiangsu Key Laboratory for Design, Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing 210096, China;,   School of Materials Science and Engineering, Jiangsu Key Laboratory of Construction Materials, Southeast University, Nanjing 211189 China;,   State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China;,   School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;,   Department of Materials Science and Engineering, National Laboratory of Solid State Microstructure, Nanjing University, Nanjing 210093, China
Published: December 2020

As a lead-free piezoelectric material with potential application, 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) ceramics, which has a morphotropic phase boundary composition, deserves much attention due to its excellent ferroelectric and piezoelectric properties. BZT-0.5BCT lead-free piezoelectric film has been synthesized on a Si (100) substrate by Sol-Gel process. The topography of the film measured using an atomic force microscope and a scanning electron microscope shows that the surface of the prepared film is smooth, and the grain is in the shape of hemisphere with a diameter of 80-100 nm. The film is 1.7 μm in thickness, with pores inside. Friction experiments show that the friction between the tip and the piezoelectric film is much larger than that between the tip and the SiO2 substrate, because of the existence of electrostatic force between the film and the silicon tip. However, the friction coefficients obtained are approximately equal. Nano-scratch experiments show that the BZT-0.5BCT film has a high normal carrying capacity, but a poor tangential wear resistance. The average elastic modulus of the film is 23.64 GPa ± 5 GPa, and its hardness is 2.7-4 GPa, both being slightly lower than those of the bulk value in PZT ceramics.
Electronic state of zigzag graphene nanoribbons
Authors: Deng Wei-Yin  , Zhu Rui  , Deng Wen-Ji  ,   Department of Physics, South China University of Technology, Guangzhou 510641, China
Published: December 2020

Based on the tight-binding model, the electronic state and band of zigzag graphene nanoribbons are given analytically by a new method. The results show that there are only two kinds electronic states, i.e., the standing wave state and edge state. For the standing wave state, the wave function is sine function and the vector is real; for the edge state, the wave function is hyperbolic sine function and the vector is complex, whose real part is 0 or π/2. The energy band is composed of the energy of standing wave state and the energy of edge state. The accurate ranges of infinite direction wave vector and energy of the edge state are deduced. Then we discuss the transition point between the edge state and the standing wave state and find that the two kinds of electronic states tend to the linear relationship regarding the site of carbon lattice in different ways at the phase transition point. When the width of two restricted boundary goes to infinity, the result of the limited graphene tends to the infinite case.
Photoluminescence studies of the neutral vacancy defect known as GR1 centre in diamond
Authors: Wang Kai-Yue  , Li Zhi-Hong  , Tian Yu-Ming  , Zhu Yu-Mei  , Zhao Yuan-Yuan  , Chai Yue-Sheng  ,   School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030014, China;,   Key Laboratory of Advanced Ceramics and Machining Technology, Ministry of Education, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

The single isolate vacancy in diamond exists in three charged states, neutral, negative and positive; and many complicated defects such as di-vacancies, impurities-vacancy complexes could also be formed in diamond. In this paper, we investigate the optical properties of the irradiation-induced neutral vacancy in diamond by low-temperature micro-photoluminescence technology, which will play a guiding significant role in the further studies of the complex defects in diamond.
Sub-diffraction-limit fabrication of 6H-SiC with femtosecond laser
Authors: Yun Zhi-Qiang  , Wei Ru-Sheng  , Li Wei  , Luo Wei-Wei  , Wu Qiang  , Xu Xian-Gang  , Zhang Xin-Zheng  ,   The KOE Laboratory of Weak-Light Nonlinear Photonics, School of Physics & TEDA Applied Physics School, Nankai University, Tianjin 300457, China;,   State Key Labboratory of Crystal Materials, Shandong University, Jinan 250100, China
Published: December 2020

Sub-diffraction-limit fabrication of 6H-SiC is investigated with femtosecond laser direct-write setup. Micro/nano-fabrication on 6H-SiC is studied with a home-made micro/nano-fabrication platform, which is integrated with a fluorescence microscope and a Ti:sapphire laser with a central wavelength of 800 nm and pulse duration of 130 fs. Micro/nano-structures are characterized with scanning electron microscope. It is found that the spatial resolution is improved with the decrease of laser power and the increase of scanning velocity. The smallest resolution achieved is 125 nm and line array with a line width of 240 nm and a period of 1 μm is fabricated. This work paves the new way for integrated micro electro-mechanical systems devices.
Friction phenomena in two-dimensional Frenkel-Kontorova model with hexagonal symmetry lattice
Authors: Jia Ru-Juan  , Wang Cang-Long  , Yang Yang  , Gou Xue-Qiang  , Chen Jian-Min  , Duan Wen-Shan  ,   College of Physics and Electronic Engineering and Joint Laboratory of Atomic and Molecular Physics of NWNU & IMP CAS, Northwest Normal University, Lanzhou 730070, China;,   State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, Lanzhou 730070, China
Published: December 2020

Locked-to-sliding phase transition is studied based on the two-dimensional Frenkel-Kontorova model in this paper. The method of molecular dynamics simulation is used. The effect of the static friction force on system parameter is investigated numerically when the upper layer atoms are of the hexagon symmetric structure.
Control of electron localization in the dissociation of H2+ using attosecond and two-color femtosecond pulses
Authors: Xu Tian-Yu  , He Feng  ,   Key Laboratory for Laser Plasma (Ministry of Education), Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

We study the control of electron localization in the dissociation of H2+ using three laser pulses by numerically simulating the time-dependent Schrödinger equation. First, we use an attosecond pulse to excite the wave packet of H2+ from 1sσg to 2pσu. Then, two-color femtosecond pulses (800 nm+400 nm) are used to control the dissociation of H2+. By manipulating the phases of two femtosecond pulses, the electron localization can be controlled effectively. For the proper laser parameters, the maximal probability that the electron is located on the selective nucleus is up to 90%. This theoretical scheme can be realized by the state-of-art laser technology.
The damage effect and mechanism of bipolar transistors induced by injection of electromagnetic pulse from the base
Authors: Ren Xing-Rong  , Chai Chang-Chun  , Ma Zhen-Yang  , Yang Yin-Tang  , Qiao Li-Ping  , Shi Chun-Lei  ,   School of Microelectronics, Xidian University, Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices,Xi’an 710071, China
Published: December 2020

A two-dimensional electrothermal model of the bipolar transistor (BJT) is established, and the transient behaviors of the BJT originally in the forward-active region are simulated with the injection of electromagnetic pulse from the base. The results show that the damage location of the BJT shifts with the amplitude of the pulse. With a low pulse amplitude, the burnout of the BJT is caused by the avalanche breakdown of the emitter-base junction, and the damage location lies in the cylindrical region of this junction. With a high pulse amplitude, the damage first occurs at the edge of the base closer to the emitter due to the second breakdown of the p-n-n+ structure composed of the base, the epitaxial layer and the substrate. The burnout time increases with pulse amplitude increasing, while the damage energy changes in a decrease-increase-decrease order with it, thus generating both a minimum value and a maximum value of the damage energy. A comparison between simulation results and experimental ones shows that the transistor model presented in the paper can not only predict the damage location in the BJT under intense electromagnetic pulses, but also obtain the damage energy.
Theoretical and experimental study of two-phase-stepping approach for hard X-ray differential phase contrast imaging
Authors: Du Yang  , Lei Yao-Hu  , Liu Xin  , Guo Jin-Chuan  , Niu Han-Ben  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering,Shenzhen University, Shenzhen 518060, China;,   CAS Key Laboratory of Ultrafast Diagnostics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119, China
Published: December 2020

To satisfy the need of low-dose and high-speed in practical application of hard X-ray differential phase contrast imaging, according to the theoretical analysis and the optimal design of parameters for the experimental system, we propose a two-stepping phase shift algorithm to retrieve the object phase information. The method can effectively reduce the radiation dose and substantially improve the speed of retrieving phase information, which lays the foundation for the X-ray phase contrast imaging in medical and industrial applications.
Fiber Fabry-Perot tunable filter based Fourier domain mode locking swept laser source
Authors: Chen Ming-Hui  , Ding Zhi-Hua  , Wang Cheng  , Song Cheng-Li  ,   Shanghai Institute for Minimally Invasive Therapy, School of Medical Instrument and Food Engineering, University of Shanghai for Science andTechnology, Shanghai 200093, China;,   State Key Laboratory of Modern Optical Instrumentation, Department of Optical Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

An all-fiber Fourier domain mode locking (FDML) swept laser source at 1300 nm for swept source optical coherence tomography is reported. The swept laser source is realized with power amplification and laser resonator which includes gain medium, tunable filter and dispersion managed delay line. FDML swept laser can realize high-speed tuning, and phase is stable since its highly stable mode locking operation. The turning range of fiber Fabry-Perot tunable filter (FFP-TF) based FDML swept laser is 130 nm, and the 3 dB bandwidth is 70 nm with an average output power of 11 mW. The tunable speed of FDML laser is 48.12 kHz compared with 8 kHz of short-cavity FFP-TF based swept laser. The axial resolution in OCT imaging of FDML swept laser is 7.8 μm (in tissue), which is improved by 1.9 μm compared with that of short-cavity swept laser.
Severe hail identification model based on saliency characteristics
Authors: Wang Ping  , Pan Yue  ,   School of Electrical and Automation Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

There are always high false alarm ratios when warning against the severe hail with the severe hail index (SHI) which is supplied by digital weather radar system. To solve this problem, the extraction algorithm with several novel features, such as "overhang", is designed and realized, and these features can describe the severe hail conceptual model from different aspects. Then we take short-time heavy rainfall cells which are easy to be confused with severe hail cells as counter examples to perform statistic analysis for these features and the SHI. Test results show that they have more significant difference between two kinds of samples and hence each of them can reflect one aspect characteristic of severe hail cells. Then a severe hail recognition model that is the Support Vector Machine with radial primary kernel function is learned. Finally, the normalized distance between the sample to be recognized and the optimal separating hyper-plane is determined as a new SHI for warning against the severe hail. Experimental results show that the method proposed in this paper makes severe hail hit ratio higher than the SHI being used and the false alarm ratio is reduced substantially.
Construction of new infinite sequence complexion soliton-like solutions of nonlinear evolution equations
Authors: Taogetusang  ,   College of Mathematical Science, Inner Mongolia Normal University, Huhhot 010022
Published: December 2020

The G'(ξ)/G(ξ) expansion method is further studied for constructing new infinite sequence complexion soliton-like solutions of nonlinear evolution equations. First, to solve a linear ordinary differential equation with constant coefficients of second order is changed into the solving of one unknown quadratic equation and Riccati equation by a function transformation. Then a nonlinear superposition formula of the solutions to Riccati equation is presented to seek new infinite sequence complexion solutions of a second order linear ordinary differential equation with constant coefficients. Based on this, the new infinite sequence complexion soliton-like solutions to (2+1)-dimensional modified dispersive water wave system and (2+1)-dimensional dispersive long-wave equation are obtained with the help of symbolic computation system Mathematica.
The stability of matter-wave solitons in 2D linear and nonlinear optical lattices
Authors: Chen Hai-Jun  , Li Xiang-Fu  ,   Electrical Engineering College, Longdong University, Gansu 745000, China
Published: December 2020

By means of variational solution and direct numerical simulation of the Gross-Pitaevskii equation (GPE), we have studied the stability of matter-wave solitons in two-dimensional (2D) Bose-Einstein condensations (BECs), with 2D linear and nonlinear optical lattices (OLs). Using the static variational approach and Vakhitov-Kolokolov criterion necessary for stability, we obtain the stability condition for solitons in different combinations of OL's parameters. We show that the 2D linear and nonlinear optical lattices allow us to stabilize 2D solitons for both attractive and repulsive interactions. We also study the time-evolution problems of 2D BECs, using the time-dependent variational approach and numerical solution of GPE for 2D linear and nonlinear OLs. Very good agreement between the results corresponding to both treatments is observed.
Influnce of the external force on the directed transport of feedback-coupled Brownian ratchet
Authors: Wang Li-Fang  , Gao Tian-Fu  , Huang Ren-Zhong  , Zheng Yu-Xiang  ,   College of Physical Science and Technology, Shenyang Normal University, Shenyang 110034, China;,   Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China
Published: December 2020

The directed transport performance of two coupled Brownian particles in the double-well ratchet potential under the external force has been studied in this paper. Langevin equation in the overdamped regime is solved numerically. The influence of the external force, the thermal noise, and the asymmetric parameter of the potential on the transport properties of the coupled Brownian particles including the average velocity, the effective diffusion coefficient Deff , and the Pe number, is discussed in detail. It is found that the average velocity changes periodically under the external force. Meanwhile, there is an optimal value of the intensity of the thermal noise at which the current reaches the maximum. It is worthwhile to point out that the enhancement of the current can be achieved by changing the structure of the ratchet potential.
Retrieving dynamic forecast model of the western pacific subtropical high in abnormal years based on GA
Authors: Hong Mei  , Zhang Ren  , Liu Ke-Feng  ,   Institute of Meteorology, PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

On the basis of the potential field data on 500 hPa from 2000-2010 from NCEP/NCAR, introducing the ideas of EOF(empirical orthogonal function) time-space separation and the dynamic system reconstruction of time series, with the advantages of the global optimization and parallel calculation by genetic assistance, dynamic model inversion is carried out, thus a nonlinear forecast model of the subtropical high activity and aberrance is established. And a mid/long-range forecast of subtropical high activity was carried out. The results of dynamic model forecast experiment showed that the mid/long-range forecast of subtropical high pressure by our model can be very actual. Especially, the aberrance of the subtropical high pressure can be drawn and forecast. A new method of idea is presented for diagnosing and forecasting such complicated weathers as subtropical high activity.
Synchronization processes in clustered networks with different inter-cluster couplings
Authors: Feng Cong  , Zou Yan-Li  , Wei Fang-Qiong  ,   College of Electronic Engineering, Guangxi Normal University, Guilin 541004
Published: December 2020

This paper studies the synchronizability and the synchronization processes of three kinds of clustered networks with different inter-cluster couplings, where each clustered network is composed of two BA scale-free subnets. The clustered network is called a TWD network if the inter-cluster coupling is a two-way coupling, but it is called a BDS network if the small subnet is driven by the big one, and is called an SDB network if the big subnet is driven by the small one. The result shows that when the ratio of node number of small subnet to that of big one is larger than a critical value, the whole synchronizability of the TWD networks is better than that of the BDS networks; however, when this ratio is smaller than the critical value, the whole synchronizability of the TWD networks is weaker than that of the BDS ones, the whole synchronizability of the SDB networks is always the worst. For a one-way-driven clustered network, the synchronizability is just related to the node number of the driven subnet and the number of the inter-links, but has nothing to do with the node number of the driving subnet. The increase in the inter-links can reduce the synchronous speed of the subnet at the beginning but may enhance the synchronizability of the whole network eventually. The Kuramoto phase oscillators are taken as the network nodes to further study the synchronization process of the three-clustered networks for different cases, and the correctness of the above conclusions are evidenced.
Analysis of an innovative method for large-scale high-precision absolute distance measurement based on multi-heterodyne interference of dual optical frequency combs
Authors: Wang Guo-Chao  , Yan Shu-Hua  , Yang Jun  , Lin Cun-Bao  , Yang Dong-Xing  , Zou Peng-Fei  ,   College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Femtosecond optical frequency comb (FOFC) has been widely used in time-frequency technique and precision spectral measurement. The derivative technique for absolute distance measurement by FOFC, which has features of high-speed, large-scale and high-precision, has become a worldwide research hotspot and is promising to be directly applied in some precision ranging missions, such as large equipment manufacturing, satellites formation flying, laser radar and space gravitation measurement, etc. An innovative method for large-scale and high-precision absolute distance measurement based on multi-heterodyne of dual FOFCs, is proposed in this paper. This method combines the multi-heterodyne cross-correlation distance measurement of dual optical combs with the beat-frequency distance measurement based on repetition frequency of the comb, so that it achieves large-scale and high-precision absolute distance measurement without relying on the earlier judgment with time-of-flight measurement, scanning the repetition frequency or scanning the reference beam path. Based on the basic theory of FOFC and the ranging scheme, the theoretical model for large scale distance measurement chain based on dual FOFCs has been constructed; influence of the multi-heterodyne lowest spectral lines and the repetition frequency stability on the measurement results has been discussed, and lots of simulation calculations have been done. Simulation results show that the method has achieved measurement errors better than ± 50 pm on the premise of not considering the phase demodulation accuracy, and the impact caused by the deviation of the lowest multi-heterodyne spectrum is figured out to be far below the ranging resolution of the multi-heterodyne measurement, which has verified that the proposed method may be used to realize large-scale and high-precision absolute distance measurement.
Closed-loop displacement control system for piezoelectric transducer based on optical frequency comb
Authors: Zhu Min-Hao  , Wu Xue-Jian  , Wei Hao-Yun  , Zhang Li-Qiong  , Zhang Ji-Tao  , Li Yan  ,   State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China
Published: December 2020

A sub-nanometric closed-loop displacement control system for piezoelectric transducers has been set up based on an optical frequency comb, an external cavity diode laser and a Fabry-Perot interferometer. The external cavity diode laser is locked to the optical frequency comb, so that the optical frequency can be set precisely in the working range by tuning the repetition frequency of the optical frequency comb. As a sensor of the piezoelectric transducer, the Fabry-Perot cavity is locked to the external cavity diode laser by means of the Pound-Drever-Hall locking technique. With the aid of precisely controlling the diode laser frequency, displacements of the piezoelectric transducer can be obtained with a sub-nanometric resolution. Experimental results show that the Allan deviation of the diode laser frequency is 1.68×10-12 after locked to the optical frequency comb. The displacement range of 4.8 μm can be generated by the piezoelectric transducer through continuously and precisely tuning the diode laser frequency in the range of 30.9496 GHz. Meantime, the displacement resolution of 450 pm is achieved by scanning the repetition frequency of the optical frequency comb at a step of 3.75 Hz. Besides, the hysteresis characteristic of the piezoelectric transducer is measured using this system. Compared to those methods based on heterodyne interferometers to calibrate the displacement of piezoelectric transducers, the nonlinear errors are eliminated and the measurement results are traceable to an Rb clock.
Structural properties of ZnO molecules under an external electric field
Authors: An Yue-Hua  , Xiong Bi-Tao  , Xing Yun  , Shen Jing-Xiang  , Li Pei-Gang  , Zhu Zhi-Yan  , Tang Wei-Hua  ,   Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Hangzhou 310018, China;,   Department of Applied Physics, School of Science, Zhejiang University of Science and Technology, Hangzhou 310023, China;,   School of Science, Beijing University of posts and Telecommunications, State Key Laboratory of Information Photonics & Optical Communication, Beijing University Posts and Telecommunications, Beijing 100876, China
Published: December 2020

Based on the equilibrium structure obtained, the ground states of ZnO molecule under external electric fields ranging from -0.05 to 0.05 a.u. were optimized using the density functional theory B3P86 at 6-311++g(d,p) level. Effects of electric fields on the bond length, total energy, charge distribution, energy levels, HOMO-LUMO gap and the infrared spectrum of the ground states of ZnO molecule have been investigated systematically. The results show that the molecular geometry and electronic properties were dependent on the magnitude and direction of the external electric field considerebly. With the increase of electric field along the molecular axis O-Zn, the equilibrium bond length first decreased and then increased, while the total energy, the harmonic frequency and infrared spectrum first increased and then decreased. But the HOMO, LUMO energy levels and the energy gap decreased monotonically, indicateing that the molecule could be excited easily by a specific electric field. We think that the present results are useful for better understanding the physical mechanism underlying the electroluminescence properties of ZnO molecule.
Investigation of state-selective cross-sections for excitation processes of the collisions of He2++ H(1s) in strong magnetic fields
Authors: He Bin  , Ding Ding  , Qu Shi-Xian  , Wang Jian-Guo  ,   Data Center for High Energy Density Physics, Institute of Applied Physics and Computational Mathematics, Bei jing 100088, China;,   Institute of theoretical & computational physics, school of physics and information technology, Shannxi Normal University, Xi'an 710062, China
Published: December 2020

Based on the excitation cross-sections in collisions of H(1s) atoms with He2+ obtained by using the classical trajectory Monte Carlo method, the state-selective cross-sections of excitation processes for different n and m, where n and m are the principal and magnetic quantum numbers respectively, are studied with the application of strong longitudinal and transverse magnetic fields. Meanwhile, the precise energy levels for atom H in strong magnetic fields are obtained by non-perturbative quantum method. It is found that there is some strong separation of the state-selective cross-sections among different magnetic quantum states. Such behaviors are related to the variation of the energy levels and the diamagnetic terms induced by the applied magnetic fields. The diamagnetic terms in transverse magnetic fields result in the rapid increase of the cross-sections for the state of negative m at 25keV/u, which is further indicated by the trajectory in this case. In some cases the decrease of the total excitation cross-sections is found to be due to the rise of the energy levels caused by the magnetic fields. The orbital angular momentum along the direction of the magnetic field is not conserved absolutely; this phenomenon is found also in the trajectories and agrees with our analysis.
First-principle study of vacancy-induced cubic boron nitride electronic structure and optical propertiy changes
Authors: Li Yu-Bo  , Wang Xiao  , Dai Ting-Ge  , Yuan Guang-Zhong  , Yang Hang-Sheng  ,   Institute of Microelectronics and Optoelectronics, Department of Information Science and Electronic Engineering, Zhejiang University, Zhejiang 310027, China;,   State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Zhejiang 310027, China
Published: December 2020

Influences of vacancies on the electronic and optical properties of cubic boron nitride were investigated by using first-principles ultra-soft pseudopotential approach of the plane wave, based on the density functional theory. It was found that the formation of B vacancy is stable from the view of energy. Only the nearest atom were affected by vacancy, and the bandgap decreased from 6.3 eV to 2.86 eV or to 3.43 eV, by the introduction of 4.17% B or N vacancy . In addition, the boron vacancy also induce the emergence of an absorption band in the visible region, with the increase in vacancy concentration, the absorption in the visible region increased gradually, while the absorption in the ultraviolet region decreased.
Investigation on integral model of heat-pipe-cooled leading edge of hypersonic vehicle
Authors: Sun Jian  , Liu Wei-Qiang  ,   Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The structure of leading edge embedded high temperature heat-pipe (HTHP) is considered as thermal protection system to prevent hypersonic vehicle's leading edge that requires sharp figure during hypersonic flying from the serious aerodynamic heating. Under the complex flow and heat transfer condition of the heat pipe, the model of leading edge embedded HTHP is established. In contrast with experimental results, the model of heat pipe which is a core component of leading edge embedded HTHP has good accuracy. Using a numerical method, we analyze the thermal protection effect of leading edge embedded HTHP under the given condition. The maximum temperature of leading edge can be decreased by 11.6% and the minimum temperature of the leading edge increases by 8%. Both high temperature areas and low temperature areas are closed in the outer zone of the leading edge. While the temperature distribution of the inner zone is almost uniform, the heat transfer from high temperature areas to low areas is achieved. Thus the thermal load in high temperature areas is reduced. The influence of contact thermal resistance on the thermal protection effect of heat-pipe cooled leading edge is also studied.
Numerical studies of ignition and combustion of pulverized magnesium particle cloud
Authors: Yang Jin-Zhao  , Xia Zhi-Xun  , Hu Jian-Xin  ,   Science and Technology on Scramjet Laboratory, College of Aerospace and Material Engineering National University of Defense Technology, Changsha 410073, China
Published: December 2020

A one-dimensional unsteady ignition and combustion model is established for the pulverized magnesium particles in a spherical cloud. The behavior of ignition and combustion of magnesium particle cloud is numerically simulated. The result shows that the ignition of particle cloud occurs at the boundary of particle cloud first, then the initial of which bifurcates into two flames, one of which propagates into the particle cloud, and the other moves away from it. Finally, the inner flame disappears because of O2 depletion, and only the outer flame, which maintains and controls the combustion of magnesium particle cloud, exists at the outside of it. The flame propagation velocity accelerates, while the flame temperature decreases during the process of the inner flame going into the magnesium particle cloud. The effects of the interior and the environmental parameters on the ignition and combustion of the magnesium particle cloud were analyzed. With the increase in the particle concentration, the ignition delay time increases slightly, but the propagation velocity of the inner flame becomes faster, and the steady particle cloud flame sphere is enlarging. With increasing initial temperature of the particle cloud, the ignition delay time canbe reduced significantly, the propagation of inner flame speeds up, but the size of steady particle cloud flame sphere keeps almost constant. The effect of ambient temperature on ignition and combustion of particle cloud is complicated. The higher the ambient temperature, the shorter the ignition delay time, however, the propagation velocity of inner flame becomes slower, and the size of the steady particle cloud flame sphere changes very insignificantly. Both the size of particle and the temperature of radiation source have great influences on the ignition and combustion of particle cloud. The smaller the particle size or the higher the temperature of radiation source, the shorter the ignition delay time of particle cloud, the faster the propagation velocity of inner flame, and the bigger the size of steady flame sphere. The results of numerical simulation are in good agreement with experimental data published in the literature.
Influence of nitrogen in diamond films on plasma etching
Authors: Wu Jun  , Ma Zhi-Bin  , Shen Wu-Lin  , Yan Lei  , Pan Xin  , Wang Jian-Hua  ,   School of Material Science and Engineering, Key Laboratory of Plasma Chemical and Advanced Materials of Hubei Province, Wuhan Institute of Technology Wuhan 430073, China
Published: December 2020

Nitrogen-doped and undoped diamond films grown by microwave plasma chemical vapor deposition (CVD) were etched by electron cyclotron resonance (ECR) plasma with asymmetric magnetic mirror field. The influences of nitrogen doping on the etching characteristic of CVD diamond films are studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy(XPS), and surface roughness measuring instrument; and the etching mechanism is explicated in detail by etching models. It is found that the crystal edges are dramatically etched for the nitrogen-doped diamond film, while the (111) facets are etched and crystalline grains collapse for the undoped diamond film. And after etching by ECR plasma for 4 h, the nitrogen-doped diamond film surface roughness decreases from 4.761 μm to 3.701 μm, while the surface roughness of the undoped film decreases from 3.061 μm to 1.083 μm. The results indicate that nitrogen doping has great influence on the etching characteristic of the CVD diamond films. Nitrogen-doping deteriorates the film quality and increases the defect density in the crystallites. And the defects distributed in the crystal edge lead to dramatically etching of the crystal edge. Compared with the nitrogen-doped diamond film, the defect density in undoped diamond film is relatively low and the distribution of defects is comparatively uniform, resulting in the fact that (111) facets would suffer from oxygen cyclotron ion beams bombardment and so grains of the film collapse. The reason why the surface roughness of nitrogen-doped diamond film decreases less than the undoped diamond film is that the movement of ions is affected by the electrons emitting from crystal edge, which weakens the ion bombardment on (111) facets.
Simulation of laser to X-ray conversion features influenced by low density gold foam
Authors: Dong Yun-Song  , Yang Jia-Min  , Zhang Lu  , Shang Wan-Li  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China
Published: December 2020

In the laser indirect-driven inertial confinement fusion, laser light is converted into X-rays by laser-plasma interactions in the hohlraum, then at the surface of the capsule the re-emission of hohlraum inner wall would drive a symmetrical radiation source to motivate implosion. It is of great importance to improve the features of laser to X-ray conversion in the hohlraum. The influence of low density gold foam on conversion features was investigated numerically with the help of one-dimensional hydrodynamics code. The numerical simulation results show that conversion efficiency increases with the decrease in gold density under the given laser condition. In particular, it can indeed have more than 19% extra conversion efficiency relatively when solid gold is replaced by gold foam of 0.1 g/cm3 density. In addition, the percentage of M-band decreases. There is an appropriate density of gold foam, at which the movement of plasma are restrained. According to the simulation results of energy balance, we get a higher radiation energy proportion when low density gold foam is selected as the target, and this is due to the decrease of kinetic energy losses compared with solid gold. Anyway, it is an effective approach to optimize the hohlraum by using low density gold foam to improve the features of laser to X-ray conversion, and these simulations would provide a scientific basis for further attempting correlative experiments.
Investigation of copper precipitation in denuded zone in Czochralski silicon
Authors: Zhang Guang-Chao  , Xu Jin  ,   College of Materials, Xiamen University, Xiamen 361005, China;,   State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
Published: December 2020

The precipitation behavior of copper in denuded zone (DZ) of Czochralski silicon has been systematically investigated by means of etching and optical microscopy (OM). Firstly, the samples were treated in a conventional furnace by high-low-high annealing for the formation of denuded zone. Subsequently, copper contamination was introduced at different temperatures. Finally, samples were treated with rapid thermal annealing (RTA) and conventional furnace annealing separately. It was found that, copper precipitates could be observed in DZ through OM only in the samples which experienced RTA followed by contamination in 900 ℃ and 1100 ℃. This indicates that the out-diffusion of vacancy which is produced in the process of RTA is the main cause for the copper precipitation in DZ.
Effects of irradiation on PNP input bipolar operational amplifiers in different radiation environments and under various post-annealing treatments
Authors: Hu Tian-Le  , Lu Wu  , Xi Shan-Bin  , Guo Qi  , He Cheng-Fa  , Wu Xue  , Wang Xin  ,   Xinjiang Technical Institute of Physics & Chemistry CAS, Urumqi, Xinjiang 830011, China;,   College of Physical Science and Technology, Xinjiang University, Urumqi, Xinjiang 830046, China;,   Xinjiang key laboratory of electronic information materials and devices, Urumqi, Xinjiang 830011, China
Published: December 2020

Radiation responses and variation characteristics of PNP input bipolar operational amplifier LM837 have been studied in two different radiation environments under the 1MeV electron and 60Coγ irradiation. The parametric failure mechanism of LM837 caused by a total dose radiation for different biases has been discussed through analyzing the characteristics of LM837 which is annealed at room temperature, 100 ℃ and 125 ℃ after irradiation. The results show that the ionization damage is the primary damage for LM837 caused by 1MeV electron irradiation, and it is larger than that by 60Coγ source irradiation under forward bias condition. In the different radiation environments, bias current under forward bias condition changes larger than that with zero bias. Annealing characteristics of LM837 after irradiation are dependeut on the annealing temperatures, and this relationship is directly related to the increase of radiation-induced interface traps during irradiation.
Thermal conductivity and thermal rectification of carbon nanotube Y junctions
Authors: Li Wei  , Feng Yan-Hui  , Tang Jin-Jin  , Zhang Xin-Xin  ,   School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100084, China
Published: December 2020

The thermal conductivity of carbon nanotube (CNT) Y junctions and the thermal rectification behavior in the Y junctions have been investigated by means of classical non-equilibrium molecular dynamics simulation with quantum effects considered. The results indicate that the thermal conductivity of a CNT Y junction is about 12%–85% lower than a (10,10) pristine CNT. The thermal conductivity of the Y junction in the positive direction, when the heat flux is directed from the stem to branches, is always higher than that of the reverse direction, i.e. from branches to the stem. The decline of the thermal conductivity due to the existence of Y junctions decreases with increasing temperature. The thermal rectification coefficient of the Y junction first decreases and then increases with the increase of temperature.