bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-time α/γ pulse shape discrimination in CsI(Tl) scintillators
Authors: Li Kui-Nian  , Li Bin-Kang  , Zhang Mei  , Li Yang  ,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

A real-time α/γ pulse shape discriminator based on CsI(Tl) scintillators is developed. The charge comparison method is adopted as an inserted algorithm. In this paper, the design scheme of the system is introduced and the real-time system is tested with a 60Co-γ source and a 241Am-α source. The influence of parameter setting on the discrimination result is investigated and the best parameter setting is provided. The results show that the designed real-time system has a small size. The best figure of merits is above 1.4. The system can discriminate α/γ events exactly and its counting rate of events can achieve 3×105 per second.
Single isolated attosecond pulse generated by helium atom exposed to the two laser pulses with the same color and midinfrared intense laser pulse in the plasmon
Authors: Zeng Ting-Ting  , Li Peng-Cheng  , Zhou Xiao-Xin  ,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

We have investigated the characteristics of high harmonic and attosecond pulse generated by helium atom exposed to the combined field of two laser pulses with the same color and a midinfrared laser pulse in nano-structure plasmon by solving the one-dimensional time-dependent Schrödinger equation. It is shown that the cut-off position of the harmonics is obviously extended in the combined field, however, the plasmon structure determined effect of absorbing the electron in the continuum states has an important influence on the cut-off position of the harmonics. It is found that the contribution from some single trajectory of electron is enhanced and other trajectories are suppressed by changing the plasmon position, so a single isolated attosecond pulse is obtained. Comparison with the scenario of atoms driven in homogeneous field, the width of the pulse decreases greatly, and an isolated pulse is achieved to be as short as 28 attoseconds.
Optomechanically induced transparency and normal mode splitting in an optical parametric amplifier cavity
Authors: Yan Xiao-Bo  , Yang Liu  , Tian Xue-Dong  , Liu Yi-Mou  , Zhang Yan  ,   College of Electronic Science, Northeast Petroleum University, Daqing 163318, China;,   College of Physics, Jilin University, Changchun 130012, China;,   School of Physics, Northeast Normal University, Changchun 130024, China
Published: December 2020

We study the properties of optomechanically induced transparency and normal mode splitting in an optical parametric amplifier (OPA) cavity. We find that the value of phase of the field driving the OPA and the nonlinear gain of the OPA will evidently affect the width of the optomechanically induced transparency window and the property of the normal mode splitting. In particular, when the coupling field works at the mechanical red sideband, narrower transparency window than the case of empty cavity (no OPA) can be realized by adjusting the value of phase of the field driving the OPA and the nonlinear gain of the OPA, accompanied by the steep dispersion curve. These results may be applied to the realization of fast/slow light, and light storage in optomechanical system.
Localized high pressure near an aspheric encapsulated microbubble
Authors: Shao Wei-Hang  , Chen Wei-Zhong  ,   Key Laboratory of Modern Acoustics, Ministry of Education, Institution of Acoustics, Nanjing University, Nanjing 210093, China
Published: December 2020

Based on hydrodynamics, the pressure of the liquid outside an aspheric encapsulated bubble driven by ultrasound is studied, and its analytical expression is derived. Numerical simulation shows that 1) the aspheric shape of an encapsulated bubble makes little influence on the pressure of the liquid far away from the bubble; 2) the pressure is extremely high at some local places of the liquid near an aspheric encapsulated bubble, and the pressure values at these places are apparently larger than those for a spherical encapsulated bubble at the same conditions. This phenomenon is of significance in the applications such as high intensity ultrasound therapy, drug delivery, cell membrane perforation, etc. As the ultrasound frequency shifts to the resonance frequency of an encapsulated bubble, or bubble shape deviates from sphericity, the localized high pressure becomes even greater.
Molecular dynamics study on the stability and properties of α-Cgeyne
Authors: Zhang Jiao-Jiao  , Xin Zi-Hua  , Zhang Ji-Hua  , Yan Xiao  , Deng Mi-Hai  ,   Department of Physics, Shanghai University, Shanghai 200444, China;,   Guizhou Provincial Key Laboratory of Computational Nano-material Science, Guizhou 550018, China
Published: December 2020

A structural stable crystalline analogue of α-graphyne is predicted by an efficient semi-empirical Hamiltonian scheme based on quantum mechanics. This analogue can be derived by substituting carbon atoms in six corners of α-graphyne with Ge atoms, which is referred to as α-CGeyne. We investigate the structure stability, electronic and thermodynamic properties of this analogue, and the calculations indicate that the most stable structure is a hexagonal honeycomb planar structure with a lattice constant of 8.686 Å. This material is a semiconductor with a band gap of 1.078 eV and it can keep intact until 2280 K and recovers to its initial structure through quenching.
InGaN/GaN blue light emitting diodes grown on Si(110) and Si(111) substrates
Authors: Liu Zhan-Hui  , Zhang Li-Li  , Li Qing-Fang  , Zhang Rong  , Xiu Xiang-Qian  , Xie Zi-Li  , Shan Yun  ,   School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China;,   School of Biochemical and Environmental Engineering, Nanjing Xiaozhuang College, Nanjing 211171, China
Published: December 2020

In this paper, InGaN/GaN multiple quantum-well blue light emitting diodes (LEDs) are successfully grown on Si(110) and Si(111) substrates. The micro-structural properties of the LEDs are characterized by means of high-resolution X-ray diffraction, atomic force microscopy, Raman spectra, and temperature dependent photoluminescence measurements. The results show that the sample on Si(110) substrate exhibits the high crystal quality, weak tensile strain, and large internal quantum efficiency. The optoelectronic properties of the LED devices are also investigated. The I-V curves indicate that the LED devices fabricated on Si(110) and Si(111) substrates have similar series resistances and low reverse leakage currents, but the LED devices fabricated on Si(110) substrate possess lower turn-on voltages. The relationship between light output intensity and injection current suggests that the LED device fabricated on Si(110) substrate has a strong light output efficiency. The study on the variation of spectral peak energy with injection current of the LED device reveals that LED device on Si(110) substrate presents a smaller spectral shift range when increasing the injection current. And the smaller spectral shift range reflects the weak quantum-confined Stark effect in the device, which can be attributed to the high crystal quality and weak strain between well layer and barrier film in the LED sample grown on Si(110).
Performance evaluation of Chinese air temperature simulated by Beijing Climate Center Climate System Model on the basis of the long-range correlation
Authors: Zhao Shan-Shan  , He Wen-Ping  ,   National Climate Center, China Meteorological Administration, Beijing 100081, China;,   Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

The traditional evaluation of simulation perfomance for numerical model is based on the differences in average, trend, probability density distribution, extreme value, variance and self-correlation between observational data and the simulated data by numerical model. These evaluation methods mainly depend on the comparison of statistical difference between the simulation and observation, but ignore the comparison in the dynamical characteristics of climate system. In view of this, in the present paper we use detrended fluctuation analysis (DFA) method to analyze the scaling characteristics of daily temperature from observational data and the corresponding simulated data by climate model, and investigate whether the long-range correlation of meteorological elements can exist in the simulated data of climate model. If so, we can assess the performance of climate model based on the comparison of scaling index between the observational data and the simulated data. As an example, the performances of Beijing Climate Center Climate System Model (BCC_CSM1.1(m)) model, including simulated daily average temperature, daily maximum temperature and daily minimum temperature, are assessed by using DFA. The results indicate that the long-range correlation characteristics of temperature in China can be simulated by BCC_CSM1.1(m). But the simulation errors are relatively large in Qinghai-Tibet Plateau, most West China, North China, and Huanghuai district. Thereinto, and the performance of BCC_CSM1.1(m) in Qinghai-Tibet Plateau and western West China is worst in China.
Research of deep dielectric charging characteristics of polytetrafluoroethene irradiated by energetic electrons
Authors: Li Guo-Chang  , Min Dao-Min  , Li Sheng-Tao  , Zheng Xiao-Quan  , Ru Jia-Sheng  ,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Deep-layer dielectric charge and discharge in insulating material irradiated by energetic electrons are one of the major factors causing spacecraft anomalies. In this paper we establish a two-dimensional physical model of deep-layer dielectric charging, based on charge distribution and energy deposition of incident electrons and conductivity properties. The model is accomplished by finite element method, and the deep-layer dielectric charging characteristics of polytetrafluoroethene irradiated by energetic electrons are calculated. The calculation results show that in the vacuum environment, in the surface of the dielectric there exists a weak reverse electric field, and it first decreases to zero and then increases with the increase of depth. The maximum electric field appears near the ground, but the electric field presents a slight reduction at the position of ground point. Space-time evolution characteristics of the maximum potential and maximum electric field in different radiation times (one hour, one day, ten days and 30 days) within dielectric are analyzed. With the increase of radiation time, the maximum potential increases from -128 V to -7.9× 104 V, and the maximum electric field increases from 2.83×105 V·m-1 to 1.76×108 V·m-1. Finally, the influence of electron-beam density on the maximum electric field is discussed. In a typical space environment (1×10-10 A·m-2), the maximum electric field reaches 2.95×106 V/m·m-1 for ten days. However, in severe space environment (2×10-8 A·m-2, the maximum electric field rapidly reaches 108 V/m for 42 hours, exceeding the breakdown threshold (about 108 V·m-1), which may easily cause electrostatic discharge). The physical model and numerical method can be used as a research basis of multi-dimension electric filed simulation of spacecraft complex parts.
New infinite sequence solutions to equations of sine-Gordon type
Authors: Taogetusang  , Yi Li-Na  ,   The College of Mathematical Science, Inner Mongolia Normal University, Huhhot 010022, China
Published: December 2020

The following steps are given to search for new solutions to equations of sine-Gordon type. Step one, according to function transformation, the solving of sine-Gordon equation and sinh-Gordon equation is changed into the solving of two kinds of nonlinear ordinary differential equations. Step two, two kinds of nonlinear ordinary differential equations and quasi-Bcklund transformation of the first kind of elliptic equation are obtained. Finally, new infinite sequence solutions to equations of sine-Gordon type are constructed by applying Bcklund transformation and new solutions of the first kind of elliptic equation.
A corrected smoothed particle hydrodynamics approach to solve the non-isothermal non-Newtonian viscous fluid flow problems
Authors: Jiang Tao  , Ren Jin-Lian  , Xu Lei  , Lu Lin-Guang  ,   Department of Mathematics, School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou 225002, China
Published: December 2020

In this paper, a corrected smoothed particle hydrodynamics (SPH) method is proposed to solve the problems of non-isothermal non-Newtonian viscous fluid. The proposed particle method is based on the corrected kernel derivative scheme under no kernel derivative and incompressible conditions, which possesses higher accuracy and better stability than the traditional SPH method. Meanwhile, a temperature-discretization scheme is deduced by the concept of SPH method for the purpose of precisely describing the evolutionary process of the temperature field. Reliability of the corrected SPH method for simulating the non-Newtonian viscous fluid flow is demonstrated by simulating the isothermal Poiseuille flow and the jet fluid of filling process; and the validity and accuracy of the proposed SPH discrete scheme in a temperature model for solving the non-isothermal fluid flow are tested by solving the non-isothermal Couette flow and 4:1 contraction flow. Subsequently, the proposed corrected SPH method combined with the SPH temperature-discretization scheme is tentatively extended to include the simulation of the non-isothermal non-Newtonian viscous free-surface flows in the ring-shaped and C-shaped cavities. Especially, the convergence of numerical simulations is analyzed, and the influences of heat flow parameters on the temperature and fluid flow at different positions are discussed.
Analysis on a class of double-wing chaotic system and its control via linear matrix inequality
Authors: Wang Bin  , Xue Jian-Yi  , He Hao-Yan  , Zhu De-Lan  ,   College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, China
Published: December 2020

This paper presents a class of quadratic nonlinear system by introducing a linear term x of the third equation into the second equation of a chaotic system based on analyzing and studying some chaos. Using nonlinear dynamics method we analyze the steady, quasi-periodic and chaotic transition process when the system parameter varies. Experiment results are in good agreement with the Matlab simulation results. The Lyapunov exponent of the system with absolute value operation is larger than the original system, and the absolute value operation makes the wing of the original system doubled. Based on Takagi-Sugeno (T-S) fuzzy model and linear matrix inequality, a robust fuzzy controller is designed for the double-wing chaotic system being in asymptotical stability. Simulation results are provided to illustrate the effectiveness of the proposed scheme.
Broad-band time domain terahertz radar cross-section research in scale models
Authors: Liang Da-Chuan  , Wei Ming-Gui  , Gu Jian-Qiang  , Yin Zhi-Ping  , Ouyang Chun-Mei  , Tian Zhen  , He Ming-Xia  , Han Jia-Guang  , Zhang Wei-Li  ,   Center for Terahertz Waves, College of Precision Instrument and Opto-electronics Engineering Tianjin University, Tianjin 300072 China;,   Academy of Photoelectric Technology, Hefei University of Technology, Hefei 230009 China
Published: December 2020

Based on terahertz time-domain spectrscopy (THz-TDS) technology, a broad-band time domain terahertz radar system can be used to do research on scattering characteristics of objects. At present, the optical structure and mechanism of this system-showing the radar detection principle and imaging mechanism-has attracted a lot of interest in the terahertz research field. Based on the femtosecond Ti: sapphire osillators pumped terahertz time-domain spectrscopy system, this paper constructs the first terahertz radar system in this country (0.11.3 THz). System calibration is carried out by measurements on standard metallic spheres. Three military scale models are measured by the Radar system. The shapes of the models are retrieved by the improved back projection algorithm, which verifies the new imaging mechanism based on time domain scattering signal. With high frequency broad band spectrum and high imaging resolution, the terahertz radar would make great contribution to stealth military units design and become a new research platform on terahertz scattering characteristics.
Study on the temperature dependence of oxygen A-band absorption coefficient
Authors: Li Jin-Hua  , Wang Zhao-Ba  , Wang Zhi-Bin  , Zhang Min-Juan  , Cao Jun-Qin  ,   North University of China, Key Laboratory of Instrumentation Science and Dynamic Measurement, Ministry of Education, Taiyuan 030051, China;,   North University of China, Engineering Technology Research Center of Shanxi Province for Opto-Electronic Information and Instrument, Taiyuan 030051, China
Published: December 2020

Oxygen A-band is an ideal inversion channel. Absorption coefficient is one of the important parameters, its precision determines the accuracy of inversion result. The influence factor for the absorption of oxygen A-band is analyzed using HITRAN2012 database and temperature profiles of atmosphere. The temperature dependence is deduced for each influence factor, and then for the absorption coefficient. It is found that the influence of temperature on the coefficient is poor for HWHM (half width at half maximum) of the spectral line, but the HWHM of the line is greatly influenced by the temperature. The linetype function has two changes during the variation of temperature: The function value decreases with increasing temperature beyond the HWHM; it, however, slowly increases from the center frequency to HWHM of the line. The line intensity is strongly dependent on the temperature. Using the line by line integral algorithm, the absorption of oxygen A-band is calculated. The temperature dependences are considered to come from the pressure broadening effect, spectral line intensity, and HWHM. A conclusion is given that the temperature dependence of absorption of oxygen A-band comes from line intensity, and especially the center frequency. While, the temperature dependence of the linetype function with Lorentzian is not obvious. Finally, the absorption of oxygen A-band is measured at 63m using BRUKER spectrometer with 1 cm-1. The error is less than 0.83% as compared with that in theoretical model under the same condition. The correctness of the temperature calibration model is thus verified.
Diagnosis of high-Z plasma with soft X-ray laser probe
Authors: Wang Chen  , An Hong-Hai  , Jia Guo  , Fang Zhi-Heng  , Wang Wei  , Meng Xiang-Fu  , Xie Zhi-Yong  , Wang Shi-Ji  ,   Shanghai Institude of Laser Plasma, Shanghai 201800, China
Published: December 2020

It is important to diagnose electron density of a plasma irradiated by lasers for inertial confinement fusion, in high energy density physics and related fields, especially for measuring high-Z plasma near the interface. Use of soft X-ray laser as a probe is an important method in diagnosis of plasma electron density distribution. However, it is difficult to carry out the research in high-Z laser plasma, because of the problem of excessive plasma spontaneous radiation. In view of the characteristics of soft X-ray laser, several specific experimental techniques have been developed. By using these techniques, which can greatly suppress effects of spontaneous radiation, diagnosis of high-Z plasma with soft X-ray laser probe method becomes possible. As a typical example, an experiment of diagnosing gold plasma is performed and clear images are obtained, indicating that the techniques are effective and feasible.
PL enhancement of MoS2 by Au nanoparticles
Authors: Wei Xiao-Xu  , Cheng Ying  , Huo Da  , Zhang Yu-Han  , Wang Jun-Zhuan  , Hu Yong  , Shi Yi  ,   School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China;,   Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China
Published: December 2020

Molybdenum disulphide (MoS2), a layered quasi-two dimensional (2D) chalcogenide material, is a subject of intense research because of its electronic, optical, mechanical and physicochemical properties. Since the monolayer MoS2 is a direct-gap seminconductor, it is widely used in the field of light-emitting area. However, its photoluminescence (PL) efficiency is very low due to excessive doping in monolayer MoS2 and rich non-radiative centers. In this letter, we reportits synthesis using the gold nanoparticles which have a resonance absorption peak around 514 nm. The gold nanoparticles are dispersed on the surface of the MoS2 samples by means of spin-coating. Then, we measure the photoluminescence (PL) of the monolayer, bilayer and multilayer samples before and after the spin-coating, and find a great enhancement in the PL intensity of the monolayer sample. Also the PL intensities of bi-layer and multiple layer MoS2 samples are slightly enhanced. Our work shows that gold nanoparticles may impose an obvious p-doping effect to the monolayer and bi-layer MoS2 samples to enhance the PL, and a surface plasmon polariton effect of the gold nanoparticles is also a positive factor for the enhancement.
Electroluminescence properties of vertical structure GaN based LED on silicon and copper submount at different temperatures and current densities
Authors: Huang Bin-Bin  , Xiong Chuan-Bing  , Zhang Chao-Yu  , Huang Ji-Feng  , Wang Guang-Xu  , Tang Ying-Wen  , Quan Zhi-Jue  , Xu Long-Quan  , Zhang Meng  , Wang Li  , Fang Wen-Qing  , Liu Jun-Lin  , Jiang Feng-Yi  ,   National Engineering Technology Research Center for LED on Si Substrate, Nanchang University, Nanchang 330047, China
Published: December 2020

GaN-based light-emitting diode (LED) thin films grown on Si(111) substrates are successfully detached and transferred to copper and silicon submounts, and then become 40mil high power vertical structure LED chips. Electroluminescence properties of the two kinds of chips with the same expitaxial structure are investigated at different forward current densities and ambient temperatures. The obtained results are as follows. 1) at the same temperature, the EL peak wavelength of the chip with copper submount is longer than that of the chip with silicon submount. Under 13 K, the EL peak wavelength of the chip with copper submount is about 6 nm longer than that of chip with silicon submount as the driving current increases from 0.01 mA to 400 mA. While under 300 K, the difference in EL peak wavelength between the two kinds of chips at 0.01 mA is only about 3 nm; as the current increases to 400 mA, the difference will tend to zero and the spectra will coincide. 2) At the same current density, as the temperature increases from 13 K to 320 K, the EL peak wavelengths of the two kinds of chips are S-shaped, and the spectra tend to coincide. 3)When the temperature is below 100 K, the current density droop effect of the chips with copper submount is more abvious than that of chips with silicon submount, while above 100 K, the results are just inverse. Perhaps, it is due to the fact that the differences in thermal expansion coefficient and thermal conductivity between the two kinds of submounts lead to the diffrent EL properties.
Mechanism of phase transition induced by high temperatures and its influences on the luminescence of Ca0.64WO4:Eu0.24 ceramics
Authors: Chen Lian-Ping  , Chen Yi-Bin  , Cao Jun  ,   School of Materials Science and Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
Published: December 2020

Ca0.64WO4:Eu0.24 also crystalizes in the phase of CaWO4 with about 12 mol% of Schottky defects on Ca2+-sites in the crystal lattice of CaWO4. The question whether such a phase is well stable at high temperatures remains to be studied, so the impacts of over-sintering on the structure of Ca0.64WO4:Eu0.24 ceramics are examined. The probable origins resulting in the phase transition at high temperatures are discussed, and the influences of such a phase transition on the luminescence properties are also studied. Observations reveal that some oxygen ions bonded to Schottky defects may be released when the sintering temperature is over 1100 ℃. This leads to the shortage of oxygen element for the bulk Ca0.64WO4:Eu0.24 ceramics, and a phase transition in CaWO4 may have occurred. A monoclinic phase of the formula Eu2 WO6 is generated. It is found that the distance between crystal planes in CaWO4 becomes larger after the phase transition. This may be one of the primary reasons accounting for the sharp decrease of luminescent intensities of Ca0.64WO4:Eu0.24 ceramics.
Effect of external field shape on the ultracold atom-polymer molecule conversion efficiency
Authors: Zhao Xiu-Niao  , Sun Jian-An  , Dou Fu-Quan  ,   College of Physics and Electronic Engineering Northwest Normal University, Laboratory of Atomic Molecular Physics and Functional Material in Gansu province, Lanzhou 730070, China
Published: December 2020

By changing the Rabi frequency of the photoassociation laser and the atom-polymer coupling strength, we investigate the effect of external field shape on atom-polymer conversion efficiency. First, by defining time-index, the external filed shape given in literature is improved. We discuss the influence of time-index on conversion efficiency, and then choose a more optimized external filed shape, it has good parameter robustness. Under the action of the external field, the adiabatic process has almost no oscillation, the adiabatic fidelity is close to 1, and the error of the system is less. The ultracold atom-polymer molecules conversion can be realized stably and efficiently.
Effect of the oscillation of substrate potential in driven Frenkel-Kontorova chains
Authors: Lei You-Ming  , Li Yi-Wei  , Zhao Yun-Ping  ,   Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710129, China
Published: December 2020

In this paper, the effect of the oscillation of the substrate potential in a one-dimensional Frenkel-Kontorova model is considered. The relationship between the oscillating amplitude, frequency of the substrate and the nanofriction phenomena such as hysteresis, maximum static friction force, super-lubricity are investigated. Similar results are obtained for the two cases in which the ratios of the atomic distance to the period of potential field of the substrate potential field are incommensurate and commensurate respectively. The results show that on one hand, with the appropriate frequency, the area of the hysteresis will decrease while the amplitude increases, and the tendency of the decrease depends on the frequency. In particular, suitable frequency and amplitude give rise to super-lubricity. However, when the frequency is too high, the result is the same as those in the case without oscillation. On the other hand, fixing the amplitude, the area of the hysteresis will increase with the increase of frequency in spite of tendencies being different. At the same time, on a whole, the maximum static friction force has an increasing tendency. Interestingly and importantly, for a certain amplitude, as the frequency increases, the maximum static friction force first decreases to zero (corresponding to super-lubricity), and then increases. That is, there is an optimum oscillating frequency which makes the system have the minimum static friction force. Furthermore, the difference between the above two circumstances lies in that for commensurate interfaces, there are the same start-up velocities for a certain frequency and various small amplitudes, which is different from the incommensurate mating contacts. Hence, it shows that the latter has a more complex dynamic behavior under the same hypothesis.
A broad-band gain improvement and wide-band, wide-angle low radar cross section microstrip antenna
Authors: Zheng Yue-Jun  , Gao Jun  , Cao Xiang-Yu  , Zheng Qiu-Rong  , Li Si-Jia  , Li Wen-Qiang  , Yang Qun  ,   Information and Navigation College of Air Force Engineering University, Xi'an 710077, China
Published: December 2020

A novel high-gain and low radar cross section (RCS) microstrip antenna is designed and fabricated. The proposed antenna obtained broad-band 3 dB gain bandwidth and wide-band, wide-angle low RCS properties after applying the frequency selective surface (FSS) as a superstrate of original microstrip antenna. The FSS cell is composed of two metallic layers separated by a dielectric substrate. A metallic square loop with four resistors mounted on each side of the loop is enched on the top layer and a metallic plane with a central cross slot and four fringe slots is enched on the bottom layer. The four resistors of top layer are mainly used to absorb radar incoming wave and reduce antenna RCS. The patch of bottom layer can constructe a Fabry-Perot resonance cavity with ground plane and improve the antenna gain. The reflection coefficient S22 and transmission coefficient S12 of top layer are all below -10 dB at 5.75-11.37 GHz. The reflection phase gradient of bottom layer is positive and the reflection magnitude value is above 0.86 from 11.21 GHz to 11.54 GHz. Measurement results show that the antenna gain is enhanced by about 3.4 dB at 11.73 GHz, and the half-power beam width of E-plane and H-plane is reduced 16° and 50° respectively. The 3 dB gain bandwidth is about 2.4 GHz which from 10.0 GHz to 12.4 GHz and well cover the impedance bandwidth. The proposed antenan achieved an RCS reduction of more than 3 dB in the normal direction at 4.10-11.30 GHz, the largest reduction reached 23.08 dB in comparison with the original antenna. The monostatic and bistatic RCS reduction are over 3 dB from -20° to 20° and -37° to 37° respectively at 4.95 GHz. The results proved the FSS superstrate can be applied to improve the radiation and scattering performance simultaneously.
Dynamic generation and manipulaition of electromagnetically induced 2D phtonic band-gaps
Authors: Zhang Yan  , Liu Yi-Mou  , Han Ming  , Wang Gang-Cheng  , Cui Cui-Li  , Zheng Tai-Yu  ,   School of Physics, Northeast Normal University, Changchun 130024, China;,   College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

We study the steady optical responses of a four-level Tripod cold 87Rb atomic system, which is driven by two mutually perpendicular strong standing-wave laser fields. It is found that satisfying the condition of a proper detuning between two strong fields, one nearly perfect structure of double photonic band-gap, where reflectivity can reach 95%, can be generated along each direction, respectively. Shifting a strong field (two strong fields) to a travelling-wave field (two travelling-wave fields), we can achieve a reflectivity platform and a transmissivity window (two transmissivity windows). Our new findings are beneficial to a novel all-optical switching and routing, which may have applications in complex all-optical information networks.
Laser diode pumped Nd:YAG laser with high repetition and high average power
Authors: Wang Chao  , Wei Hui  , Wang Jiang-Feng  , Jiang You-En  , Fan Wei  , Li Xue-Chun  ,   Joint Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In our work we build a high repetition, high peak power and high average power laser which contains three main components: the fiber oscillator, the Nd:YAG regenerative amplifier, and the four-pass amplifier side-pumped by laser diode. The wavelength is 1064 nm. The laser operates at 100 Hz with pulse energies up to 112 mJ. And the average power is 11 W. The pulse width is tunable from 500 ps to 2 ns. The radius of the beam is 6.8 mm. The spatial profile of the beam presents nearly a top hat in the near filed and 1.5× diffraction-limited in the far filed.
Impact sound synthesis method of complex structures and the experimental verification
Authors: Zhang Bing-Rui  , Chen Ke-An  , Ding Shao-Hu  ,   Department of Environmental Engineering, School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

In order to simulate the structural vibration and acoustic field in time domain, we discuss the calculation method of the structural damping and provide an integrated numerical method for impact sound synthesis which is finally well verified experimentally. Firstly, since the damping is considered to be one of the factors influencing the time-varying characteristics of the transient vibration, the detailed information are obtained by both of modal damping calculating methods. Secondly, the vibration and sound radiation of damping impacted plates are simulated in the time domain, showing that they are highly consistent with the results from the finite-difference time-domain method. Finally, the comparison between the impact sound of the finite cylindrical shell and the experimental results is performed, indicating that the two sounds are much the same in the temporal envelope, spectral structure and decay trend. What is more, the results imply that it is quite effective to use the these numerical methods to synthesize impact sounds.
Effects of high magnetic field on structure and optical properties of metal ions doped modified CaTiO3
Authors: Li Qiang  , Yang He  , Xue Xiang-Xin  , Li Qing-Wei  ,   Liaoning Key Laboratory of Metallurgical Resources Recycling Science, School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China;,   School of Science, Shenyang Jianzhu University, Shenyang 110168, China
Published: December 2020

In the paper, the changes of structures and optical properties of metal ions doped modified CaTiO3 prepared under different magnetic field intensities (up to 12 T) and 800 ℃ are studied. The results indicate that the photo absorption performances are enhanced with the ions doped concentration increasing and red shift occurs significantly. With the same doped concentration, the photo absorption performances of the samples prepared under magnetic field are improved compared with under no magnetic field, while there are little differences among the absorption curves of these samples prepared under different magnetic field intensities. Furthermore, it is observed that the X-ray diffraction curve peaks of pure CaTiO3 prepared under magnetic field are all left-shifted and cutoff wavelengths of UV-vis are augmented, which indicates that the interplanar spacing and lattice constant are increased while the band gap is narrowed.
Simulations of the interactions between dislocations and solute atoms in different loading conditions
Authors: He Yan-Sheng  , Fu Shi-Hua  , Zhang Qing-Chuan  ,   CAS Key Laboratory of Mechanical Behavior and Design of Material, Department of Modern Mechanics, University of Science and Technology of China, Hefei 230027, China
Published: December 2020

Dynamic strain aging, i.e. the interaction between dislocations and solute atoms, affects the mechanical properties of alloys. In this paper, a 2D-kinetic Monte Carlo model relating to the interaction between dislocations and solute atoms is developed to simulate the motions of edge dislocations in four different conditions. In “single dislocation with constant stress rate” condition, single dislocation is pinned under low stress rate, moves continuously under high stress rate, and moves intermittently under middle stress rates. In “multi-dislocation with zero stress” condition, the solute atoms gather below positive dislocations and above negative dislocations. In “multi-dislocation with constant stress” condition, the influence of solute atoms on dislocation motion becomes stronger with stress decreasing. In “multi-dislocation with constant stress rate” condition, the collective pinning and unpinning result in the stepped curve of total displacement. The simulated results present the process of dynamic strain aging in a microscopic scale and are consistent with theoretical results.
Macro-micro coupled simulation of competitive dendrite growth in different areas of the welding pool
Authors: Han Ri-Hong  , Dong Wen-Chao  , Lu Shan-Ping  , Li Dian-Zhong  , Li Yi-Yi  ,   Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Published: December 2020

A macro-micro coupled model is developed to simulate the competitive dendrite growths in different areas of the welding pool in the solidification process. The transient solidification conditions in welding pool are obtained by the three-dimensional (3D) macro-scale FEM model. The thermal conditions used in the micro-scale cellular automata model is obtained from the macro-scale FEM model by using the interpolation algorithm. The simulation results indicate that the micro-scale cellular automata model developed in this paper can simulate the morphologies of dendrites with various growth directions accurately. The solidification conditions in welding pool have obvious effects on the competitive dendrite growth. The dendrites with their preferential orientations parallel to the direction of the highest temperature gradient are more competitive. The morphology of grain structure is determined by the competition among different dendritic arrays. The dendritic arrays with more favorable growth direction can gradually crowd out other dendritic arrays and occupy more space through dendrite branching. The area near the central line of welding pool has a lower temperature gradient, a higher solidification rate, and a higher cooling rate in the solidification process, and such solidification conditions lead to the finer microstructure. The simulation results of the secondary dendrite arm spacing are in agreement with the experimental results under the corresponding solidification conditions.
Reconstruction verification for random demodulator based compressed sampling
Authors: Zheng Shi-Lian  , Yang Xiao-Niu  , Zhao Zhi-Jin  ,   School of Telecommunications Engineering, Xidian University, Xi'an 710071, China;,   Science and Technology on Communication Information Security Control Laboratory, Jiaxing 314033, China;,   School of Telecommunications Engineering, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

A reconstruction failure detection method for random demodulator based compressed sampling is proposed, which utilizes the correlation between two consecutive reconstructed supports of the sparse signal. The method is easy to realize because of its low-computational complexity. Simulations show that the proposed method can judge whether the reconstruction is successful with high accuracy and it can reduce the interference probability with primary users when the signal is not that sparse.
Spectrum allocation of cognitive radio network based on artificial physics optimization
Authors: Chai Zheng-Yi  , Wang Bing  , Li Ya-Lun  ,   School of Computer Science and Software Engineering, Tianjin Polytechnic University, Tianjin 300384, China;,   Department of Maritime, Henan Vocational and Technical College of Communications, Zhengzhou 450005, China;,   Key Laboratory of Universal Wireless Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

To study the spectrum allocation problem based on graph coloring model in cognitive radio network, an algorithm to maximize total network revenue is proposed, which is based on artificial physics optimization because of its NP-based features. In artificial physics optimization algorithm, the solution of spectrum allocation problem is mapped into a particle with mass. It establishes the relation between particle mass and its fitness value, and defines the virtual force between the particles by the law of gravity so that the entire group can move to the better direction and achieve population optimization. The detailed spectrum allocation process is given and the particle position updating equation is improved because of its binary coding features. Simulation results show that the proposed algorithm can better maximize network revenue.
Analysis of the drought vulnerability characteristics in Northeast China based on the theory of information distribution and diffusion
Authors: Wang Wen-Xiang  , Zuo Dong-Dong  , Feng Guo-Lin  ,   Department of Physics Yangzhou University, Yangzhou 225000, China
Published: December 2020

The drought vulnerability characteristics from 1971 to 2012 in Northeast China are analysed and the risk in Northeast China is calculated based on the theory of information distribution and diffusion, combining with the standardized precipitation index (SPI) and the drought damage index (DDI) in Northeast China, with considering the meteorological factors and social factors. The probability density function (PDF) of DSI is estimated by using the method of information distribution. The vulnerability of the relationship between DSI and DDI is constructed by using the method of two-dimensional normal information diffusion. Then the average risk can be obtained by calculating the sum (discrete distribution) or integral (continuous distribution) of the product of the PDF of DSI and the vulnerability curve. The results show that the introduction of information distribution and diffusion method to analyze the problem of vulnerability for the situation of small sample could render the PDF of DSI smoother. What is more, the vulnerability of the relationship between DSI and DDI through the DSI to obtain the DDI has clearer physical meaning. Therefore the results could be realistic. More significantly, similar results can be obtained with different simple lengths, which means that the method is insensitive to the simple length and it can well overcome the instability of analysis of the small sample.
Direct transport of fractional overdamped deterministic motors in spatial symmetric potentials driven by biharmonic forces
Authors: Xie Tian-Ting  , Zhang Lu  , Wang Fei  , Luo Mao-Kang  ,   College of Mathematics, Sichuan University, Chengdu 610064, China;,   Science and Technology on Electronic Information Control Laboratory, Southwest China Research Institute of Electronic Equipment, Chengdu 610036, China
Published: December 2020

Physical significance of fractional damping for order 0 p 2 is demonstrated from the perspective that it can be explained as the memory of acceleration. Based on Caputo's fractional derivatives, the transport phenomenon of fractional overdamped deterministic motors in spatial symmetric potentials driven by biharmonic forces is investigated numerically. Relationships between transport velocity and model parameters are analyzed. The effect of fractional order is discussed in detail. Research shows that the contribution of historical acceleration increases or decreases monotonously with the historical moment varying with different fractional orders. With certain parameters the transport velocity can show generalized resonance when the spatial potential depth or the external force frequency varies. Furthermore, for some large orders, the velocity varies in step with the variation of potential depth and is in a direct proportional to the frequency if there is transport. Effect of fractional damping is intimately linked with the shape of the force. The memory of damping force can promote or inhibit the particle transport under different conditions, thus triggering abundant transport behaviors.
Numerical simulation of positive glow corona discharge initiated from long ground wire under thundercloud field
Authors: Sima Wen-Xia  , Fan Shuo-Chao  , Yang Qing  , Wang Qi  ,   State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China
Published: December 2020

With the slow effect of electric field of thundercloud, a kind of positive glow corona without streamers is initiated from the surface of object near the ground, and a large number of positive space charges are injected into the surrounding space, consequently, lighting targets selected by the lighting leader can be changed. In this paper, a numerical simulation of positive glow corona discharge initiated from the long ground wire with the effect of the electric field of thundercloud is presented. In consideration of the attachment and collision effects between positive ions and other ions, an accurate two-dimensional positive glow corona model is established. Meanwhile, a high-voltage corona discharge experiment is done in the laboratory to measure the corona current in different background electric fields, and the results are compared with the simulation results in order to verify the correctness of the model established in this paper. According to the established model, the initiation and development progress of glow corona with the effect of thundercloud are simulated and the corona current, laws of positive ion density distribution and migration are revealed. Results show that positive ions generated from the glow corona discharge present a circular symmetric distribution in the plane perpendicular to the ground wire at their early stage of migration, but the distribution is shaped as an elongated oval later when the ions move farther from the ground wire for the effect of electric field of thundercloud, that is to say, the overwhelming majority of the ions will be finally distributed in the upper area of the ground wire and gradually migrate towards the thundercloud. Due to the accumulation effects of positive ions in the upper migration area near the ground wire, the positive space charge background is formed, which has a damping effect on the electron beam. Thus the formation of electron avalanche is suppressed and the probability for electron avalanche to be converted into streamer is reduced. Meanwhile, the positive space charge background improves the collision surface of the gas and increases the compound probability between positive ions and electrons. Therefore, the conversion processes from electron avalanche and streamer to upward leader are impeded and the initiation of upward leader is suppressed.
First-principles study on the uniaxial pressure induced topological quantum phase transitions of Ge2X2Te5 (X =Sb, Bi) thin films
Authors: Zhang Mei  , Wen Li-Wei  , Ding Jun  , Zhang Ying  ,   Department of Physics, Beijing Normal University, Beijing 100875, China;,   College of Science, Henan Institute of Engineering, Zhengzhou 451191, China
Published: December 2020

Since the topological insulator was discovered, the investigation of topological properties has become the hot spot in condensed matter physics. In this paper, we study topological properties of chalcogenide compounds Ge2X2Te5 (X=Sb, Bi) crystals and their monolayer and bilayer films as well as the vertical uniaxial pressure induced topological quantum phase transitions in monolayer and bilayer films. The results show that for A-type crystal, the bulk structures of these two compounds are topological insulators, the monolayer structures of these two compounds are conventional metals, and bilayer structures are topological metals. There is no topological quantum phase transition in monolayer nor bilayer film under the uniaxial compression. While for B-type crystal, the bulk structures of these two compounds are conventional insulators, the monolayer Ge2Sb2Te5 is conventional metal, its bilayer structure as well as monolayer and bilayer of Ge2Bi2Te5 films is conventional insulator. All the B-type monolayer and bilayer films each undergo a topological quantum phase transition to the topological metals under the uniaxial compression.