bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical transition of the charged excitons in InAs single quantum dots
Authors: Li Wen-Sheng  , Sun Bao-Quan  ,   College of Chemical Engineering, Tongliao ProfessionalEducation College, Tongliao 028000, China;,   The State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Quantum dot (QD) samples studied in the experiment are grown by molecular-beam epitaxy on semi-insulating GaAs substrates. The photoluminescences (PLs) of the excitons in a single QD are measured at 5 K. The PL spectra of the excitons, biexcitons and charged excitons are identified by measuring and analyzing both PL peaks of the circular and linear polarization and power-dependent PL properties. The charged exciton emissions can be tuned by applying a bias voltage, i.e., negatively charged excitons are changed into positively charged excitons by changing the voltage from 1.0 to -1.0 V. It is shown that the electron-spin will slowly relax compared with that of the hole when they relax from wetting layer into the QD.
Theoretical and experimental investigation on thermophysical properties of metal rubber
Authors: Ma Yan-Hong  , Tong Xiao-Long  , Zhu Bin  , Zhang Da-Yi  , Hong Jie  ,   School of Jet Propulsion, Beihang University, Beijing 100191, China;,   AVIC Commercial Aircraft Engine Co., Ltd., Shanghai 200241, China
Published: December 2020

Metal rubber (MR) is a new-type damping material with special raw material and manufacturing process. The helix wire is considered as the geometric unit of MR. The thermal expansion model of the MR is established based on the thermal expansion analyses of micro-springs in different contact states with the Schapery model. Thermal experiments are conducted to analyze the effects of relative density and temperature on the thermal expansion property of metal rubber. The heat transfer process of the MR and the heat transfer model of helix wires are obtained based on MR microstructure. Under certain conditions, the heat transfer can be simplified into the single thermal conductions. Based on the Fourier law, thermal conduction of MR microstructure is analyzed using the thermoelectric analogy method. Combined with the equivalent coefficient law of the thermal conduction, the thermal conduction model of MR is established. The formula of the thermal conduction coefficient is derived. The accuracy of the theoretical model is verified by the experimental results. The theoretical and experimental results of the thermal expansion and heat transfer provide strong theoretical and calculative analytical foundation for the application of the MR in the heat insulation material field at high temperature.
Effect of substitution Fe2+ on physical properties of MgSiO3 perovskite at high temperature and high pressure
Authors: Wu Di  , Zhao Ji-Jun  , Tian Hua  ,   School of Science, Shenyang Aerospace University, Shenyang 110136, China;,   School of Physics and Optoelectronic Technology, College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
Published: December 2020

(Mg, Fe)SiO3-perovskite is currently considered to be the most abundant mineral in the earth’s lower mantle. Its behavior at high temperature and high pressure is crucial for interpreting conditions at the deep level of the mantle, variations of seismic waves, and so on. Equilibrium crystal structures and mechanics properties of MgSiO3 and (Mg0.75, Fe0.25)SiO3 are determined using first-principles calculations in a series of hydrostatic pressures up to 140 GPa. Seismic wave velocity as a function of pressure is derived from the Voigt-Reuss-Hill scheme. Their thermodynamic quantities under the conditions of the lower mantle’s pressures and temperatures are computed by means of the Debye model within the quasi-harmonic approximation. The substitution effect of Fe2+ on the thermoelastic property for silicate perovskite is discussed. Substitution of Fe2+ for Mg2+ can provoke softening wave velocity phenomenon arising from the minerals containing Mg element located in the earth interior. The present theoretical results are useful for interpreting seismic wave velocity softened in certain areas of the mantle.
Influence of thermal decomposition temperature of zinc acetate on the structural and the optical properties of ZnO nanorods
Authors: Chen Xian-Mei  , Gao Xiao-Yong  , Zhang Sa  , Liu Hong-Tao  ,   Key Laboratory of Materials Physics of Ministry of Education of China, School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052, China
Published: December 2020

ZnO nanorods are fabricated by hydrothermal method on glass substrates that are covered with a ZnO seed layer by the thermal decomposition of zinc acetate. The influences of the thermal decomposition temperature on the structural and the optical properties of the obtained ZnO nanorods are carefully studied by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. It is found that the crystalline quality, head-face dimension, macro stress, and transmissivity are found to be dependent on the thermal decomposition temperature. The 〈002〉c-axis-preferred orientation of the obtained ZnO nanorod is first enhanced and then weakened; the macro tensile stress first decreases and then increases; the average transmissivity first increases and then decreases as thermal decomposition temperature increases. When the thermal decomposition temperature reaches 350 ℃, the c-axis preferred orientation is strongest; the tensile stress is smallest; the average transmissivity in the visible region is maximal for the obtained ZnO nanorod. The surface scattering induced by the head-face dimension is the key mechanism of the average transmissivity of the obtained ZnO nanorod in the visible region.
Study on weak signal detection method with Duffing oscillators
Authors: Liu Hai-Bo  , Wu De-Wei  , Jin Wei  , Wang Yong-Qing  ,   Information and Navigation Institute, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

By numerical simulations we find that the Duffing state transition from big-cycle motion to chaotic motion is more suited to weak signal detection. Based on this, in this paper, we propose a new weak periodic signal detection method from the angle of theoretical analysis. The principle of the proposed method is introduced and its feasibility is analyzed. Then, the proposed method and the traditional method are compared and analyzed both in transition zone effect and detection probability, and then a contrast simulation is carried out. The analysis and simulation results both indicate, the Duffing oscillator state transition from big-cycle motion to chaotic motion is affected less by transition zone under the same condition, based on which the proposed detection method possesses better detection capability. The simulation data also show that weak signal detection with Duffing oscillator must be based on unilateral state transition. The frequency difference detection based on intermittent chaos is suited only for the case where the signal-to-noise ratio of the detected signal is relatively high.
Effects of time-periodic modulation of cross-correlation intensity between noises on stochastic resonance of over-damped linear system
Authors: Tian Yan  , Huang Li  , Luo Mao-Kang  ,   College of Mathematics, Sichuan University, Chengdu 610065, China
Published: December 2020

For an over-damped linear system subjected to correlated additive and multiplicative noise and a periodic signal, when the cross-correlation intensity between noises is a time-periodic function, the analytical expression of the output signal-to-noise ratio (SNR) is derived by means of the stochastic averaging method. It is found that this system has richer dynamic behaviors than the linear systems in which cross-correlation intensity between noises is constant, that the evolution of the output SNR with the cross-correlation modulation frequency presents periodic oscillation, and that the parameters of cross-correlation intensity between noises diversify the stochastic resonance phenomena.The time-periodic modulation of cross-correlation intensity between noises is conductive to enhancing the sensitivity to weak periodic signal detection and implementing the frequency estimation of weak periodic signal.
Bright and dark solitons in metamaterials obtained by extended F-expansion method
Authors: Zhuang Bin-Xian  , Guo Jun  , Xiang Yuan-Jiang  , Dai Xiao-Yu  , Wen Shuang-Chun  ,   Key Laboratory for Micro-/Nano-Optoelectronic Devices of Ministry of Education, College of Information Science and Engineering, Hunan University, Changsha 410082, China
Published: December 2020

The ultra-short pulse equation in a metamaterial is solved by the extended F-expansion method. The new phenomena and characteristics of solitons, caused by the anomalous self-steepening effect and the second-order nonlinear dispersion in metamaterials, are discussed. The results show that the second-order nonlinear dispersion in the positive-index region may take the place of the linear dispersion to form the bright and dark solitons. Due to the switchable sign of the anomalous self-steepening effect in the positive-index and negative-index regions, the bright and dark solitons separately exist in the anomalous and normal dispersion regions under some specific conditions. The moving directions of the centers of bright and dark solitons can be controlled by the sign of the anomalous self-steepening effect or by the combination of the anomalous self-steepening effect and third-order linear dispersion.
Auto-alignment in four-pass amplifier with wavefront correction system
Authors: Wang Yu-Yu  , Gao Yan-Qi  , Zhu Hai-Dong  , Lu Xing-Hua  , Zhang Jun-Yong  , Guo Ya-Jing  , Hui Hong-Chao  , Zhu Bao-Qiang  ,   Joint Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   Shanghai Institute of Laser and Plasma, China Academy of Engineering Physics, Shanghai 201800, China
Published: December 2020

In order to solve the interaction problem between the wavefront distortion correction and optical alignment in a high-power laser system, especially in a multi-pass amplification system, based on fresnel diffraction integral theory, the beam propagation model of 310 mm×310 mm aperture beam in four-pass amplifier is built by analyzing the properties of this system. The problem of excessive amount of calculation, caused by high resolution in traditional calculation, is solved by coordinate transformation method, Using this model, the differences of far-field accuracy among centroid method, circle fitting and pure phase matching filter in beam with wavefront distortion are discussed; what influence the wavefront correction has on focal spot position is analyzed. This article provides an important basis for optimizing collimation adjustment programs in four-pass amplifier.
Molecular dynamics simulation of the critical and subcritical nuclei during solidification of nickel melt
Authors: Jian Zeng-Yun  , Gao A-Hong  , Chang Fang-E  , Tang Bo-Bo  , Zhang Long  , Li Na  ,   School of Materials Science and Engineering, Xi'an Technological University, Xi'an 710032, China
Published: December 2020

The microstructures of nickel solidified at different cooling rates are studied by using molecular dynamics simulation and the critical condition for nickel melt to form ideal metallic glass is calculated. The simulation results show that the crystal structure is obtained after the nickel melt has been solidified at a cooling rate that is lower than 1011 K/s; while a mixture is composed of crystal structure and amorphous structure when the cooling rate is in a region from 1011 K/s to 1014.5 K/s. The solidified crystal of nickel is of fcc structure when the cooling rate is lower than 1010 K/s, while it changes into crystal structure composed of fcc and hcp when the cooling rate is between 1010 K/s and 1014.5 K/s. By analyzing the calculation and simulation results, it is determined that the critical cooling rate for nickel melt to form ideal metallic glass is 1014.5 K/s. Moreover, it is found that the structures of the subcritical nuclei (the cooling rate is higher than 1014.5 K/s), critical nuclei (the cooling rate is 1014.5 K/s), and the growing crystal (the cooling rate is lower than 1014.5 K/s) are the lamellar structures composed of fcc and hcp atoms, which indicates that the subcritical nuclei, critical nuclei and the growing crystal have the same structures.
Investigation on the fabrication of Ag-doped ZnO nanorods by hydrothermal method
Authors: Chen Xian-Mei  , Wang Xiao-Xia  , Gao Xiao-Yong  , Zhao Xian-Wei  , Liu Hong-Tao  , Zhang Sa  ,   Key Laboratory of Materials Physics of Ministry of Education, School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052, China
Published: December 2020

Ag-doped ZnO nanorods with different morphologies and optical properties are synthesized by hydrothermal method on the DC magnetron-sputtered Al-doped ZnO (AZO) seed layers. The influences of the molar ratio of Ag ions to Zn ions (RAg/Zn) and the AZO seed layer on the structural and optical properties of the Ag-doped ZnO nanorods are carefully studied by using X-ray diffractometry, scanning electron microscopy, spectrophotometry, EDS spectrum, etc. The changes in the microstructure and optical property of Ag-doped ZnO nanorods are closely related to the change in the average head-face dimension induced by Ag doping as RAg/Zn increases, owing to the different relative proportions of Ag ions doped in ZnO nanorods resulting from the different particle sizes and densities of the seed layers. The photoluminescence intensity in the visible region for the ZnO nanorods growing on the 15 min-sputtered AZO is stronger than that of the ZnO nanorods growing on the 10 min-sputtered AZO seed layer at the same RAg/Zn, which results from the increased defects in ZnO. More point defects caused by Ag doping are produced as RAg/Zn increases, resulting in the broadening of PL envelope in the visible region. The microstructure of pure ZnO nanorod is related to the seed layer thickness-related degree of crystallinity and particle size.
First-principles study on electronic structures of Al, N Co-doped ZnO nanotubes
Authors: Wang Ping  , Guo Li-Xin  , Yang Yin-Tang  , Zhang Zhi-Yong  ,   State Key Laboratory of Integrated Service Networks, School of Telecommunications Engineering, Xidian University, Xi'an 710071, China;,   School of Science, Xidian University, Xi'an 710071, China;,   School of Microelectronics, Xidian University, Xi'an 710071, China;,   School of Information Science and Technology, Northwest University, Xi'an 710127, China
Published: December 2020

By using first principles calculation based on density functional theory, band structures, densities of states and electron density differences for an ideal (6, 0) ZnO nanotube (ZnONT), Al doped, N doped and Al, N co-doped nanotubes are investigated. The calculated results reveal that the doped nitrogen atom results in the formation of acceptor level in the band gap of the ZnONT, which indicates that the doped nanotube has the characteristic of a p-type semiconductor. While the high locality of the acceptor level leads to a lower solubility for the doped nitrogen atoms, the acceptor level is broadened and shows delocalizing characteristics in nanotube with Al, N co-doped. This co-doping may be an efficient method of preparing p-type ZnONTs.
Growth mechanism and optoelectronic properties of vanadium oxide films prepared by Sol-Gel
Authors: He Qiong  , Xu Xiang-Dong  , Wen Yue-Jiang  , Jiang Ya-Dong  , Ao Tian-Hong  , Fan Tai-Jun  , Huang Long  , Ma Chun-Qian  , Sun Zi-Qiang  ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Vanadium oxide films are prepared by Sol-Gel at different annealing temperatures. Their surface morphologies, valence states, electrical and optical properties are characterized by SEM, XRD, resistance meter, UV-Vis spectrometer and FTIR, respectively. Results reveal that the optimal temperature for producing V2O5 films by Sol-gel is 430 ℃, the organics in the films cannot be decomposed completely below 430 ℃ while the V-O bonds will be broken under a higher temperature (>430 ℃). The as-prepared vanadium pentoxide films exhibit higher TCR and larger light absorption, so that they are suitable to be used as bolometric materials for uncooled infrared detectors. The growth mechanism of vanadium oxide film prepared by Sol-Gel is also presented in this paper.
Calculation of crystal-melt interfacial free energy of Cu by molecular dynamics simulation
Authors: Zhou Hua-Guang  , Lin Xin  , Wang Meng  , Huang Wei-Dong  ,   State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

The growing and melting of crystal nuclei in liquid Cu are investigated by molecular dynamics simulation. The critical undercooling is proportional to the reciprocle of the nanoparticle radius. The Gibbs-Thomson coefficient of Cu is 1.12× 10-7 K·m. Then the crystal-melt interfacial free energy of Cu is 0.146 J/m2 estimated from the Gibbs-Thomson coefficient, and the Turnbull coefficient of Cu is 0.416. All the values by simulation are consistent with the experimental results of Turnbull.
Research on the capacitance-voltage characteristic of strained-silicon NMOS accumulation capacitor
Authors: Wang Bin  , Zhang He-Ming  , Hu Hui-Yong  , Zhang Yu-Ming  , Shu Bin  , Zhou Chun-Yu  , Li Yu-Chen  , Lü Yi  ,   Key Laboratory for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

Accumulation MOS capacitor is more linear than inversion MOS capacitor and is almost independent of the operation frequency. In this paper, we present first the formation mechanism of the plateau, observed in the C-V characteristic of the strained-Si NMOS capacitor, and then a physical model for strained-Si NMOS capacitor in accumulation region. The results from the model show to be in excellent agreement with the experimental data. The proposed model can provide valuable reference for the strained-Si device design, and is has been implemented in the software for extracting the parameter of strained-Si MOSFET.
Electronic structure and spin-polarization of boron-nitride nanoflake
Authors: Wang Dao-Jun  ,   School of Automotive Engineering Linyi University, Linyi 276005, China
Published: December 2020

Boron-nitride graphene-like monolayer possesses a similar atomic arrangement to that of the famous graphene. However, due to the large difference in electronegetivity between boron and nitrogen atoms, the electronic properties of the two nanomaterials are different significantly. Here, we report on our theoretical investigation of the electronic structure and spin-polarization of zigzag-edged boron-nitride triangular nanoflake using a Hubbard model and the first-principles calculations within density-functional theory. Our numerical results indicate that in contrast to graphene nanoflake with spin-polarized ground state, the boron-nitride nanoflak has the zero-energy state that is either empty or fully occupied, and its ground state is thus spin-unpolarized which breaks the Lieb's law. However, the electron occupation and spin-polarization of the zero-energy state of boron-nitride nanoflake can be tuned by doping it with electrons or holes. These results are expected to offer the theoretical basis for the applications of boron-nitride nanomaterials in spintronics.
Numerical study of the superconductor-insulator transition in double-layer graphene driven by disorder
Authors: He Long  , Song Yun  ,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

The kernel polynomial method is employed to study the disorder effects of impurities on the superconductivity of double-layer graphene. The Bogoliubov-de-Gennes equations are solved self-consistently by the kernel polynomial method, and the spatial fluctuations of the superconducting order parameters caused by disorder are obtained. Furthermore, we calculate the density of states, the optical conductivity and the general inverse participation ratio, and we find that the energy gap in the density of states can be constrained by increasing disorder, accompanied with the disappearance of the Drude weight in optical conductivity. We also find that the electron states are Anderson localized by disorder and the superconductor-insulator transition happens in double-layer graphene.
Measurement of refractive index of luminescent photoelastic coating
Authors: Hua Shi-Qun  , Luo Yin  ,   Faculty of Science, Jiangsu University, Zhenjiang 212013, China;,   School of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

The refractive index of the coating is one of the essential parameters used for principal strain separation in luminescent photoelastic coating (LPC) method by oblique incidence technique. According to the theoretical analysis of the amplitude of the emitted light exciting the coating, which returns along the same path as the oblique incident excitation light, we propose a new online method of measuring the refractive index of the LPC based on optical Fresnel response of the coating. The refractive index of the coating containing Rhodamine B as luminescent dye, is measured under the excitation at a wavelength of 465 nm and an incident angle of 60. The experimental result proves the feasibility of the new method, and the present method is also applicable to the refractive index measurement of other luminescent coating.
Design of a low-frequency broadband circuit analog absorbers based on wire media
Authors: Xu Yang-Qiu  , Zhang Hui-Bin  , Zhou Pei-Heng  , Lu Hai-Peng  , Liang Di-Fei  , Xie Jian-Liang  ,   Northeast Light Alloy Co., Ltd., Haerbin 150008, China;,   State Key Laboratory of Electronic Thin-films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

A circuit analog absorber (CA) with wire medium is presented. Both the original CA and the structure presented are analyzed. It is shown that original CA cannot have more than one resonant frequency in low frequency band, owing to the limitation by the effective resistance. The presented structure breaks the limitation using artificial plasma resonance, with the wave dispersion in the structure analyzed using the quasi-static model. The experimental results, consistent with simulation results based on the finite-difference time-domain (FDTD) method, show that the structure obtains dual-band absorption, thus broadening the absorption band in low frequency band.
Influences of growth orientation on strain and strain relaxation of quantum dots
Authors: Ye Ying  , Zhou Wang-Min  ,   College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310032, China
Published: December 2020

Different growth orientations influence the mechanical properties and behavior of quantum dots, due to the anisotropy of elasticity and surface energy of the material. In this paper, the relations of the strain energy, strain relaxation energy and free energy to growth orientation are analyzed for the self-assembled InAs/GaAs semiconductor quantum dots, based on finite element method of cubic elasticity theory. The results show that the strain relaxation of the (211) quantum dots is biggest, and that of the (100) quantum dots is smallest. These can provide the theoretical basis for the growth of quantum dots in a controlled fashion.
Subwavelength antenna array based on far-field time reversal
Authors: Liang Mu-Sheng  , Wang Bing-Zhong  , Zhang Zhi-Min  , Ding Shuai  , Zang Rui  ,   Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054
Published: December 2020

Based on far-field time reversal, the super-resolution focusing property of the subwavelength array is analyzed theoretically according to signal processing in this paper. A novel subwavelength array is proposed. It is demonstrated experimentally that the array has super-resolution focusing property in the far-field zone and each element has an independent channel. With this kind of subwavelength array used in time reversal mirror, better super-resolution focusing result is achieved. The proposed subwavelength array may be useful in the applications of multi-antenna ultra-wideband (UWB) wireless communications.
Influences of the multiple electron overtaking on the bunching process of the wide-gap klystron amplifier under high power injection condition
Authors: Bai Xian-Chen  , Yang Jian-Hua  , Zhang Jian-De  , Jin Zhen-Xing  ,   College of Opto-Electronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Under the high power injection condition of the wide-gap klystron amplifier (WKA), a second peak current appears besides the conventional optimally bunching current (or the first peak current) in the distribution of the fundamental integral current. Considering the electron bunching theory and the Particle-in-cell (PIC) simulation results together, the formation mechanism of the second peak current is discussed. The results indicate that the second peak current has a close relation with the electron multiple-overtaking phenomenon in the case of high voltage modulation coefficient. When the diode voltage is 600 kV, beam current is 5 kA and working frequency is 3.6 GHz, the beam modulation depth of the WKA is enhanced to 92% from 80% according to the multiple-overtaking mechanism. Simultaneously, the bunching current power is improved from 2.2 GW to 2.8 GW, and a 27 percent increment is obtained.
Photothermal response of extracellular solution to the near-infrared laser irradiation determined by its optical absorption properties
Authors: Guan Kui-Wen  , Li Xin-Yu  , Liu Jia  , Sun Chang-Sen  ,   Lab of Biomedical Optics, College of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116023, China
Published: December 2020

Photothermal effect has been proved to mediate the interaction of near-infrared laser with biological tissue. However, the generation and transformation mechanism of the photothermal effect is still unclear. In this paper, we combine a patch clamp technique with the laser simulation to figure out the chromophores, which are responsible for the photothermal effect generation. This method is based on the fact that temperature dependence of solution can be measured as resistance changes. A dual-wavelength infrared light irradiating the open pipette in extracellular solution is designed to study the relation between the photothermal effect and the absorption property of solution. The principle is based on that the nearly ten times difference in the magnitude of the optical absorption coefficient in water (0.502 cm-1 at 980 nm and 0.0378 cm-1 at 845 nm), makes the corresponding proportional absorption-driven temperature rise. The photothermal effect in laser-tissue interaction can be assessed in two stages: the establishment and the dissipation of the temperature rise. In the establishment stage, an open pipette method is employed to measure the temperature rise by fabricating a glass pipette which is filled with electrolyte solution. In the dissipation stage, the electrophysiological function of a living neuron cell is studied based on a patch clamp. Theoretical calculation and experimental results show that the optical absorption properties of solution determine the photothermal effect. The results can be used to study the photothermal effect in laser-tissue interaction.
Fractal characteristics research of lightning and its application to automatic recognition
Authors: Huo Yuan-Lian  , Zhang Guang-Shu  , Lü Shi-Hua  , Yuan Ping  ,   Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China;,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

By analyzing the fractal feature of 120 cloud-to-ground lightning signals and 77 intracloud lightning signals obtained by the fast antenna system in Qinghai area during the summer of 2009, the results show fractal dimension of cloud-to-ground lightning signal is obviously different from that of intracloud lightning signal. Then 5 characteristic values of fractal dimension are used to recognize the discharge types of lightning signal via support vector machine, and the recognition rate is higher than 95%. The construction of cloud-to-ground lightning time series signal fractal dimension trajectory map shows that the fractal dimension minimum value corresponds to the return stroke of the original time series signal, which can be used to quickly and accurately detect the return stroke of lightning signal, and the detection rate can reach 100%.The fractal dimension is a discriminatively physical property which can be used for intelligently analyzing and automatically processing the lightning signal.
The early warning signals of abrupt climate change in different regions of china
Authors: Wu Hao  , Feng Guo-Lin  , Hou Wei  , Yan Peng-Cheng  ,   College of Physical Science and Technology, Yangzhou University, Yangzhou 225002, China;,   National Climate Center, Beijing 100081, China;,   College of physics and electronic engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

In recent years, critical slowing down phenomenon has shown great potentials in disclosing whether a complex dynamic tends toward critical cataclysm. Based on the concept of critical slowing down, the observed data of temperature in different regions in China which have different noises are processed in this article to study the precursory signal of abrupt climate change. First, Mann-Kendall(M-K)method is used to find the locations of the abrupt climate change in different regions, then the autocorrelation coefficient which can characterize critical slowing down is calculated; the appearance-time moments of early warning signals of abrupt climate change under the influence of different noises are also stadied. The results show that for different signal-to-noise ratios, the critical slowing down phenomenon has appeared in the data 5-10 years before the abrupt climate change took place, which indicateds that critical slowing down phenomenon is a possible early warning signal for abrupt climate change and the noise has less influence on the test results for early warning signals of abrupt climate change. Accordingly, it demonstrates the reliability of critical slowing down phenomenon to test the precursory signals of abrupt climate change, which provideds an experimental basis for the wide applications of the present method in real observation data.
The effect of the radiative pressure on the potential function in asynchronous rotational binary
Authors: Song Han-Feng  , Wang Jing-Zhou  , Li Yun  ,   College of Science, Guizhou University, Guizhou 550025, China;,   School of Physics and Electronic Engineering, Kaili University, Kaili 556000, China
Published: December 2020

Radiative pressure is an important physical factor and can affect the structure and evolution of the massive star. The Roche lobe, three Lagrangian points and the corresponding Roche potentials are calculated according to the asynchronous rotational Roche potential which includes the radiative pressure. They are compared with the corresponding synchronous rotational Roche potentials. It is found that the centrifugal force greatly reduces the gravitational acceleration at the equator while the radiative pressure can reduce the gravitational acceleration of the massive star. Both the asynchronous rotation and the radiative pressure have an obvious influence on the Roche lobe, the positions of three Lagrangian points, the Roche potentials and the time of mass overflow. Therefore, it is very important to calculate the asynchronous rotational Roche potential which includes the radiative pressure in the massive close binaries.
Critical data processing technology for spectral image inversion in a static computational spectral imager
Authors: Liu Yang-Yang  , Lü Qun-Bo  , Zeng Xiao-Ru  , Huang Min  , Xiang Li-Bin  ,   Academy of Opto-electronics, Chinese Academy of Sciences, Key Laboratory of Computational Optics Imaging Technology, Beijing 100094, China
Published: December 2020

To carry out spectral image inversion in a static computational spectral imager is a crucial step for accomplishing its theoretical advantages, so the data processing technology for spectral image inversion will determine the final spectral image achieved. Focusing on the spectral image inversion, we have investigated various algorithms such as image reconstruction, image compressed sensing and spectral image inversion theories, and compared them carefully. By taking into account the data transmission link of the system and the error in the engineering development process, a comprehensive simulation is carried out. The key issue of spectral image inversion, and also how to use the inversion algorithms to achieve its optimized routes are pointed out. So a detailed analysis for realizing the theoretical advantages and ensuring instrument technology development is provided.
Entangled quantum heat engines based on two-qubit XXZ model with Dzyaloshinski-Mariya interaction
Authors: Wang Tao  , Huang Xiao-Li  , Liu Yang  , Xu Huan  ,   School of Physics and Electronic Technology, Liaoning Normal University, Dalian 116029, China
Published: December 2020

We construct an entangled quantum heat engine based on two-coupled-qubit XXZ model with Dzyaloshinski-Mariya interaction. The work done and the heat transfer are discussed according to the definition first given by Kieu, The relations between the entanglement and heat transfer, work output and efficiency are analyzed for different anisotropic parameters. The results show that the second law of thermodynamics holds in entangled systems and the isolines for the efficiency are looped curves. When the anisotropic parameter Δ is small enough, the heat engine can operate in both C1 > C2 and C1C2, however, when Δ is large, the heat engine operates in C1 > C2 only.
Simulating dnamical Casimir effect at finite temperature with magnons in spin chain within an optical lattice
Authors: Zhao Xu  , Zhao Xing-Dong  , Jing Hui  ,   State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China;,   College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China
Published: December 2020

In this paper, we study the dynamical characteristics of magnons generated by the static magnetic dipole-dipole interaction and the external-laser induced dipole-dipole interaction in spin chain within an optical lattice. Specially, we choose a blue-detuned optical lattice and define an effective temperature for the system. We make a comparison between the generation process of magnons and that of photons in an optical vibration cavity. The results show that by suitably choosing the system parameters, the dynamical Casimir effect at finite temperature in the magnon system can be reproduced.
A two-dimensional magneto-optical trap for a cesium fountain clock
Authors: Wu Chang-Jiang  , Ruan Jun  , Chen Jiang  , Zhang Hui  , Zhang Shou-Gang  ,   National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China;,   Graduate University of Chinese Academy of Sciences, Beijing 100049, China;,   Key Laboratory of Time and Frequency Primary Standards, Chinese Academy of Sciences, Xi'an 710600, China
Published: December 2020

To study the relationship of atomic beam flow with cooling intensity, laser detuning, and magnetic field gradient, the numerical simulation is performed and a two-dimensional magneto-optical trap setup is built. A low-velocity atomic beam flow is generated with a total flux of 2.1 109/s. Theoretical analysis and experimental results are in good consistence. Optimal detuning and magnetic field gradient can produce the largest atomic beam flow.
First-principles study on the piezoelectric properties of hydrogen modified graphene nanoribbons
Authors: Liu Yuan  , Yao Jie  , Chen Chi  , Miao Ling  , Jiang Jian-Jun  ,   School of Optical and Electronic Information of Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

This paper focuses on the piezoelectric properties of zigzag graphene nanoribbons with hydrogen selective modifications by first-principles calculations. The structures of hydrogen modified graphene nanoribbons are optimized and the calculated hydrogen binding energies indicate that these structures are very stable. Owing to the hydrogen atom selective adsorption, the adjacent carbon atoms have different charge states and breaking inversion symmetries of nonpiezoelectric graphene. So, the positive charge centers and the negative charge centers of the hexatomic carbon ring in these structures separate from each other under uniaxial tensile strain, inducing the macroscopical electric polarization. Furthermore, the gradient of strain induced dipole moment density is related to ribbon width, i.e., the wider the ribbon, the better the piezoelectric property is. Besides, the dipole moment density of hydrogen selective modified graphene nanoribbons without strain could be controlled by changing the edge modification configuration of hydrogen atoms effectually.
Tunable split ring resonators in terahertz band
Authors: Dai Yu-Han  , Chen Xiao-Lang  , Zhao Qiang  , Zhang Ji-Hua  , Chen Hong-Wei  , Yang Chuan-Ren  ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Split ring resonators (SRRs) can be used as a negative permeability medium near its magnetic resonance frequency. In this paper, a new type of THz-band magnetic resonance structure is proposed by introducing metal wires into traditional SRRs, and the effect of metal wires on the transmission characteristics of SRRs is numerically investigated. The results show that the resonant frequency of SRRs significantly decreases with the number of metal wires increasing. The parameters of metal wires, such as length Lx, width Wx and distance Gx also have influence on the resonant frequency of SRRs. Meanwhile, the results verify that the introduction of metal wires play an important role in reducing the size of the device, and cannot be affected by the presence of dielectric substrate. The new magnetic resonance structure proposed in this paper provides a reference for the design and practical applications of metamaterials in the future.
Design of low-radar cross section microstrip antenna based on metamaterial absorber
Authors: Yang Huan-Huan  , Cao Xiang-Yu  , Gao Jun  , Liu Tao  , Ma Jia-Jun  , Yao Xu  , Li Wen-Qiang  ,   Information and Navigation Institute of Air Force Engineering University, Xi’an 710077, China
Published: December 2020

A metamaterial absorber with high absorptivity, wide incident angle and no surface ullage layer is designed and applied to microstrip antenna to reduce its radar cross section (RCS). The results show that the absorber can exhibit an absorption of 99.9% with a thickness of 0.3 mm. Compared with the conventional microstrip antenna, the proposed antenna has an RCS reduction of more than 3 dB in the boresight direction in the working frequency band, and the largest reduction can reach 16.7 dB, the monostatic and bistatic RCS reduction are over 3 dB from -30° to +30° and -90° to +90° respectively, while the radiation performance is kept, which proves that the absorber has an excellent absorptivity and could be applied to microstrip antennas to achieve in-band stealth.
Cognitive physics-based method for image edge representation and extraction with uncertainty
Authors: Wu Tao  , Jin Yi-Fu  , Hou Rui  , Yang Jun-Jie  ,   School of Information Science and Technology, Zhanjiang Normal University, Zhanjiang 524048, China
Published: December 2020

Image edge detection is an important tool of image processing, in which edge representation and extraction with uncertainty is one of key issues. Based on the physics-like methods for image edge representation and extraction, a novel cognitive physics-based method with uncertainty is proposed. The method uses data field to discover the global information from the image and then to map it from grayscale space to the appropriate potential space. From the point of view of the field theory, the method establishes an extensible theoretical framework and unifies the existing physics-like methods. On the other hand, the method defines the ascending half-cloud to construct the internal relationship between the range of cloud uncertainty degree and the edge representation and extraction. Finally, the method achieves image edge representation and extraction with uncertainty using the cognitive physics. The time complexity of the proposed algorithm is approximately linear in the size of the original image. It is indicated by the quantitative and qualitative experiments that the proposed method yields accurate and robust result, and is reasonable and effective.
Splitting of electromagnetically induced transparency window and appearing of gain due to radio frequency field
Authors: Li Xiao-Li  , Shang Ya-Xuan  , Sun Jiang  ,   College of Physical Science and Technology, Hebei University, Baoding 071002, China;,   State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Two resonant radio frequency fields are added to lambda three-level system in this paper. By discussing the behaviors of probing field absorption profiles under the effect of different Rabi frequencies of two radio frequency fields, the splitting of electromagnetically induced transparency (EIT) can be seen and the overlapping between EIT and gain can be obtained. The results show that the two radio frequency fields have different control functions on the system. The radio frequency field which interacts with hyperfine levels of ground state plays a role in the splitting of EIT, but the radio frequency field which interacts with hyperfine levels of excited state does not work on it. In addition only when the Rabi frequency of radio frequency field interacting with hyperfine levels of ground state is greater than with hyperfine levels of excited state, can the new features about the overlapping between EIT and gain be obtained.
High power bessel ultrashort pulses directly output from a fiber laser system
Authors: Xie Chen  , Hu Ming-Lie  , Xu Zong-Wei  , Wu Wei  , Gao Hai-Feng  , Zhang Da-Peng  , Qin Peng  , Wang Yi-Sen  , Wang Qing-Yue  ,   Ultrafast Laser Laboratory, College of Precision Instruments and Opto-Electronics Engineering, Key Laboratory of Opto-Electronics Information Technology (Ministry of Education), Tianjin University, Tianjin 300072, China;,   State Key Laboratory of Precision Measuring Technology and Instruments, Centre of MicroNano Manufacturing Technology, Tianjin University, Tianjin 300072, China
Published: December 2020

High power Bessel pulses directly output from a fiber-based amplifier system are demonstrated. A compact solution based on the inverse micro-axicon (IMAX) on fiber end is proposed for the conventional ultrashort pulse fiber laser system to enable the direct generation of high power Bessel pulses from lasers without any additional exhausting alignments. The IMAX is fabricated on one facet of a ytterbium-doped large mode area fiber by focusing ion beam technique and constitutes an integrated beam shaper in combination with an inherent collimating lens in the fiber laser system. The experimental results accord qualitatively with the simulations. The system can directly generate chirped Bessel pulses with diffraction-free propagation in meter-scaled free space. The highest average power of such a wavepacket can reach 10.1 W, correspongding to 178 nJ, and the pulse duration can be dechirped to 140 fs.
Research on the key parameters of illuminating beam for imaging via ptychography in visible light band
Authors: Wang Ya-Li  , Shi Yi-Shi  , Li Tuo  , Gao Qian-Kun  , Xiao Jun  , Zhang San-Guo  ,   University of the Chinese Academy of Sciences, Beijing 100049, China;,   State Key Laboratory of Information Security, Institute of Information Engineering, Chinese Academy of Sciences, Beijing 100093, China
Published: December 2020

Some key parameters of illuminating beam and the influence on imaging quality are investigated via ptychography in visible light band. The influences of overlap ratio, size and shape of illuminating beam on imaging quality and their relationship are studied using ptychographical iterative engine algorithm. The simulation results show that the overlap ratio of illuminating beam is a main factor influencing imaging quality. Shape of illuminating beam mainly influences the convergence of ptychography. And the size of illuminating beam less influences directly the imaging quality and convergence. Therefore, the simulation results play an important theoretic guiding role in optimizing the beam parameters in visible light, the X-ray and electronic band and other bands.
Self-diffraction based self-reference spectral interferometry
Authors: Li Fang-Jia  , Liu Jun  , Li Ru-Xin  ,   State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

A new method of characterizing the femtosecond pulse is proposed based on the self-diffraction process in a thin transparent bulk medium and the self-reference spectral interferometry. A simple device is designed based on this technique and is successful in characterizing a ～40 fs pulse at 800 nm centeral wavelength. The result is in accordance with that measured by a commercial self-reference spectral phase interferometry for direct electric reconstruction. Pulses in a spectral range from deep UV to middle IR are expected to be measured by this new method and corresponding simple device.
Characterization and comparison of 7-core and 19-core large-mode-area few-mode fibers
Authors: Lin Zhen  , Zheng Si-Wen  , Ren Guo-Bin  , Jian Shui-Sheng  ,   Key Laboratory of All Optical Network and Advanced Telecommunication Network of EMC, Beijing Jiaotong University, Beijing 100044, China;,   Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

A novel multi-core large-mode-area few-mode fiber (MC-LMA-FMF) is proposed in this paper. The special structure of air holes makes it operate in few modes (HE11 and HE21 mode only). Numerical analysis shows that the 7-core-LMA-FMF can maintain a stable dual-mode operation and the effective area of the fundamental mode can reach 866.54 μm2. The regular pattern that fiber structure parameters affect mode characteristics and the effective area is investigated, and the similarities and differences brought in by increasing the number of cores is also analyzed. The advanced 19-core-LMA-FMF inherits the few-mode characteristic, meanwhile, the effective area of the fundamental mode can be as high as 3617.55 μm2. Compared with the reported few-mode fibers, MC-LMA-FMF obtains a large effective area and good bending characteristics. These advantages enable this new type of fiber to be a potential candidate for high-speed large-capacity optical fiber transmission systems or high power fiber amplifiers and lasers.