bluuebunny/crossref_metadata_2025 huggingface dataset:
Thorium capture ratio determination through γ-ray off-line method
Authors: Yang Yi-Wei  , Liu Rong  , Yan Xiao-Song  ,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China;,   Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China;,   Key Laboratory of Particle and Radiation Imaging, Tsinghua University, Beijing 100084, China
Published: December 2020

To determine the thorium capture ratio and thorium-uranium conversion ratio in the thorium cladding of the fusion-fission reactor model, a new approach, activated thorium sample decay γ -ray off-line measurement, is introduced in this paper. This method is based on the measurement of the 311.98 keV characteristic decay γ-ray emitted by 233Pa which is produced through decay of 233Th, the capture product of 232Th. Then some reverse mathematic approach is brought in and finally the 232Th (n, γ ) 233Th reaction ratio is determined, with an uncertainty of 6% in the test experiment (233Th/232Th under the order of magnitude 10-17). In the paper, we introduce the detail of the approach including the background, principle and the result of a simple test experiment which shows that this approach can work well in thorium capture ratio determination. Compared with prompt γ-ray method and mass spectrometer method, this decay γ-ray off-line method has many advantages in determining the thorium capture ratio and thorium-uranium conversion ratio in the thorium cladding. It is also promising in the measurement of other relevant parameters.
The differential cross sections and mechanisms of ionization and in the collisions of He2++H(1s) with strong magnetic fields
Authors: Ding Ding  , He Bin  , Shi Xian  , Jian Guo  ,   Institute of Theoretical and Computational Physics, School of Physics and Information Technology, Shannxi Normal University, Xi'an 710062, China;,   Institute o f Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

The ionization processes in collisions of H (1s) atoms with He2+ are studied by the classical trajectory Monte Carlo method. The first-order differential cross sections for ionization are calculated for different field strengths of both transverse and parallel magnetic field, and they increase obviously with the fields applied. Instead of monotonic decline, a peak appears for the differential cross section, with the fields applied. According to the analysis of trajectories, the ionization mechanisms become quite different. In this paper, the influences the strength and direction of the applied field including the incident energy on the ionization mechanisms are also explained.
A broadband artificial magnetic conductor composite structure for radar cross section reduction
Authors: Lu Lei  , Qu Shao-Bo  , Ma Hua  , Xia Song  , Xu Zhuo  , Wang Jia-Fu  , Yu Fei  ,   Science College, Air Force Engineering University, Xi'an 710051, China;,   Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

We propose a broadband artificial magnetic conductor (AMC) composite structure for reducing radar cross section (RCS). By combining multiple periodic metal square patches together, we further broaden the working bandwidth of the AMC composite structure. The tested results indicate that the reflection is below -10 dB in a frequency range of 7.7—13.1 GHz, and the relative bandwidth is 51.9%. We study the scattering characteristics of the AMC composite structure at different frequencies by full wave simulation. Reflection peaks in the opposite quadrant bisector of plane shift close to the normal direction with the increase of frequency, but the backscattering RCS of the AMC composite structure is still about -8 dB smaller than that of the metal plate. The AMC composite structure has the advantages of broad working bandwidth, simple design, easy processing, etc, and has important application foreground.
Generation of autofocusing beams with multi-Airy beams
Authors: Zhang Ze  , Liu Jing-Jiao  , Zhang Peng  , Ni Pei-Gen  , Prakash Jai  , Hu Yang  , Jiang Dong-Sheng  , Christodoulides Demetrios N  , Chen Zhi-Gang  ,   National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Heilongjiang 150001, China;,   Department of Physics and Astronomy, San Francisco State University, San Francisco 94132, USA;,   CREOL/ The College of Optics & Photonics, University of Central Florida, Orlando, Florida 32816, USA;,   School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Thus far, focusing a single beam and combining multi-optical Gaussian beams have become two major methods of locally enhancing output laser intensity. In this paper, we propose a method of generating free space auto-focusing beams by combining multiple one-dimensional Airy beams. By employing split-step beam propagation method, auto-focusing beams generated by four and eight one-dimensional Airy beams are numerically simulated, and their intensity distributions are displayed from both transverse plane and side-view propagation. By utilizing a spatial light modulator and computer generated phase masks, these auto-focusing beams are experimentally demonstrated. Our experimental results accord well with the numerical simulations.
Study on resonance frequency and equivalent circuit parameters of a thin disk in flexural vibration
Authors: Zhang Xiao-Li  , Lin Shu-Yu  , Fu Zhi-Qiang  , Wang Yong  ,   Institute of Applied Acoustics, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

The electro-mechanical equivalent circuit is the most common method of analyzing and designing composite transducers. However, for the thin disk, because of the complexity of flexural vibration, equivalent lumped parameters are difficult to obtain, and so this method is rarely used. From the point of equivalent view of the distributed parameter system and lumped parameter system, according to the kinetic energy equal principle and the potential energy equal principle in this paper, we give the lumped parameter equivalent mass and equivalent elasticity coefficient of the flexural vibration, and the resonance frequency equations as well. The results from the analytical method are in good agreement with those from the finite element method. Finally, the equivalent circuit of lumped parameter model of the thin disk in analyzing the composite vibration system is given. These results can serve as a reference for designing flexural vibration composite transducers.
Neutral beam injection induced discrete Alfvn instabilities on experimental advanced superconducting tokamak
Authors: Wang Jun  , Hu Chun-Dong  , Hu Shuang-Hui  , Wu Bin  , Ding Si-Ye  , Wang Jin-Fang  ,   Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031, China;,   College of Science, Guizhou University, Guiyang 550025, China
Published: December 2020

The neutral beam injection (NBI) system is applied to the experimental advanced superconducting tokamak (EAST). It will excite some Alfvn instabilities when the plasma characteristics are improved. The numerical research on the NBI-induced discrete Alfvn eigenmode (TAE) and toroidal effect-induced Alfvn eigenmode (TAE) in the pedestal region is presented in the paper. The research results show that plenty of TAEs appear in this region. The TAE is very different from the TAE. These modes are trapped by the -induced potential wells along the magnetic field line. Due to negligible continuum damping via wave energy tunneling, similar to TAE, the TAE can also be readily destabilized by energetic particles. Differently, TAE frequency spectrum is more broad than TAE, and they are existed not only inside the gap but also outside the gap. The growth rate increases with injected power increasing. This instability maybe affects the physical behavior of the tokamak and the confinement of the plasma.
Molecular dynamics investigation of shock front in nanocrystalline copper
Authors: Ma Wen  , Lu Yan-Wen  ,   Department of Physics, College of Science, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The elasto-plastic deformation behavior, yield strength and strain rate of material under shock compression can be represented by shock front, and the shock front is also related to the variation of strength after shock compression. In this paper, we study the dynamic plastic deformation processe of nanocrystalline copper under shock compression through molecular dynamics simulations. We also explore the dependences of the shock front and the mechanism of elasto-plastic deformation on grain boundary, and make a comparison with the case of the shock response of nanocrystalline aluminum. This investigation shows that the contribution of grain boundary to the shock-front width of nanocrystalline copper are smaller than that of nanocrystalline aluminum. The plastic mechanism of nanocrystalline copper is dominated by the emission and propagation of partial dislocations, and the full dislocation and deformation twin are rarely found in the samples. From the simulations are also found that the shock-front width decreases with the increase of loaded shock stress. A quantitative inverse relationship between the shock wave front width and the shock intensity is obtained. This quantitative inverse relationship is close to other simulation result of nanocrystalline copper and quite different from results of coarse-grained copper compression experiments.
Density functional theory studies of O2 and CO adsorption on the graphene doped with Pd
Authors: Sun Jian-Ping  , Miao Ying-Meng  , Cao Xiang-Chun  ,   Electrical and Electronic Engineering Institute, North China Electric Power University, Beijing 102206, Chian
Published: December 2020

Based on density functional theory, the single O2 and CO adsorption on pristine and palladium (Pd) doped graphene are studied using first-principles calculations. By calculating the system adsorption energy, charge transfer, band structure and density of states (DOS), we find that compared with O2 and CO adsorbed on the pristine graphene, the Pd doped systems have high adsorption energies and large charge transfers. The reason is that the new energy levels which are brought into pristine graphene by the dopant Pd strengthened the interaction between graphene and the adsorbed gas molecule. Oxidizing gas O2 and reducing gas CO have obviously different effects on band structure and DOS of graphene. The DOS near the Fermi level of graphene has great change after adsorbing O2 and the change becomes smaller when O2 is adsorbed on Pd doped graphene, while there is almost no change in DOS when graphene adsorbs CO, which indicates that doping Pd on graphene adsorbing CO will not enhance the gas sensitivity. However, the adsorption energy increases, which can improve the gas sensing response speed when graphene adsorbs reducing gas.
Roughening and pre-roughening processes on InGaAs surface
Authors: Luo Zi-Jiang  , Zhou Xun  , Wang Ji-Hong  , Guo Xiang  , Zhang Bi-Chan  , Zhou Qing  , Liu Ke  , Ding Zhao  ,   College of Science, Guizhou University, Guiyang 550025, China;,   School of Education Administration, Guizhou University of Finance and Economics, Guiyang 550004, China;,   School of Physics and Electronics Science, Guizhou Normal University, Guiyang 550001, China
Published: December 2020

Roughening and pre-roughening processes on InGaAs surface are studied using scanning tunneling microscopy. There are different roughening and pre-roughening processes for InGaAs films at different substrate temperatures and As beam equivalent pressure. Under low temperature and low As beam equivalent pressure, pits is main mechanism in the beginning of InGaAs morphology evolution, with the increase of annealing time, a great number of pits and islands are observed which make the surface rough. Small islands should play a leading role during the InGaAs morphology evolution at high temperature and high As beam equivalent pressure, and the number of islands will increase gradually with the increase of annealing time till it reaches an equilibrium state.
Phase transition of ultrathin Bi2Se3 film sandwiched between ferromagnetic insulators
Authors: Wang Huai-Qiang  , Yang Yun-You  , Ju Yan  , Sheng Li  , Xing Ding-Yu  ,   National Laboratory of Solid State Microstructure and Department of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

For an ultra-thin Bi2Se3 film sandwiched between two ferromagnetic insulators (FIs), we investigate how its topological properties change with the angle between the magnetizations of the two FIs. The Chern numbers are calculated from the low-energy effective Hamiltonian for electrons in the surface states, and the bulk energy band and the edge states are simulated from the tight-binding model of a long ribbon with armchair edges on a two-dimensional honeycomb lattice, from which the topological phase of the system can be determined. It is found that with the magnetizations of the FIs varying from parallel to antiparallel, there appears a topological phase transition from the anomalous quantum Hall phase to the trivial insulating one at a critical angle.
Local ferromagnetic structure in Heusler alloy Mn2CoGa and Mn2CoAl doped by Cr, Fe and Co
Authors: Zhang Yu-Jie  , Li Gui-Jiang  , Liu En-Ke  , Chen Jing-Lan  , Wang Wen-Hong  , Wu Guang-Heng  , Hu Jun-Xiong  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, China
Published: December 2020

The crystal structures and magnetic properties of Mn2CoMxGa1-x and Mn2CoMxAl1-x (M=Cr, Fe, Co) alloys are investigated through experiment and calculation. Due to the covalent effect, the doped Fe and Co atoms preferentially occupy the A sites. It causes that some MnA (-2.1 B) atoms become MnD (3.2 B) and a local ferromagnetic structure of MnB-CoC-MnD is generated in the ferrimagnetic matrix, showing that an increment of molecular moment is as high as 6.18 B. The achievement of the ferromagnetic structure consumes the exchange interaction energy, consequently, reducing the TC in Fe doping alloys. It is found that the toleration for doping Co in Mn2CoAl reaches up to x=0.64, much more than that in Mn2CoGa (x=0.36), and the change from ordered B2 to A2 structures along with the decrease of Al content. These observations reveal the importance of the covalent effect in these intermetallic compounds. The Cr doping shows an abnormal increment of molecular moment of 3.65 B and increases the TC rapidly, which implies that Cr atoms may take an atomic configuration thereby disobeying to the occupation rule.
Morphology and ferromagnetism of Ge nanostructure
Authors: Zhao Cui-Lian  , Zhen Cong-Mian  , Ma Li  , Pan Cheng-Fu  , Hou Deng-Lu  ,   Hebei Advanced Thin Films Key Laboratory, Department of Physics, Hebei Normal University, Shijiazhuang 050024, China;,   Library of Heibei Engineering and Technical College, Cangzhou 061001, China
Published: December 2020

A series of Ge films with varying thickness is prepared by plasma enhanced chemical vapor deposition technology. With the thickness of the sample becoming thinner, the sample shows ferromagnetism. When the 12-nm-thick sample is annealed at 300℃, the partile size becomes smaller, and thus the number of interface defects between the particles increases, so the sample gives a largest magnetic signal at room temperature (50 emu/cm3). FC-ZFC measurement shows that Curie temperature is 350 K. For a higher temperature (600 ℃, the coalescence of small Ge particles makes surface area decline, so magnetic signal becomes weak. With the thickness being 6 nm, the paramagnetism and the ferromagnetism coexist in the 6-nm-thick Ge film. When the 6-nm-thick sample is annealed under nitrogen atmosphere at 300 ℃, the sample only shows ferromagnetism. However, annealed at 600 ℃, the sample only presents paramagnetism. With the annealing temperature changing, the 12-nm-thick film and the 6-nm-thick film show different magnetic phenomena. Particle size and particle distribution cause different magnetic phenomena. It is supposed that the Ge nannostructure unpaired electrons are provided mainly by the interface defect between Si matyix and Ge film and the surface defect of Ge particles. The ferromagnetism coupling of the unpaired electrons is related to the distribution of sample particles and the junction among particles. The fusion between particles will reduce the ferromagnetism of the sample.
Method of accurately measuring silicon sphere density difference based on hydrostatic suspension principls
Authors: Wang Jin-Tao  , Liu Zi-Yong  ,   Division of Mechanics and Acoustic, National Institute of Metrology, Beijing 100013, China
Published: December 2020

The micro density difference between silicon single crystal spheres is not only important for the research on the redefinition of Avogadro constant based on quantum standard, but also a key solution for quality control for the production of silicon single crystal with ultra-high purity in semi-conductor industry. To overcome the complexity of non-contact laser interferometer method and improve the accuracy of hydro-weight method, a method based on the hydrostatic suspension principle is realized. The silicon single spheres to be measured are immersed into mixture liquid including 1,2,3-tribromopropane and 1,2-dibromoethane, and floated freely by adjusting the temperature and pressure of the liquid. The micro density difference between two silicon single crystal spheres is calculated based on a mathematical model by using liquid temperature, pressure, and central floatation height difference in the floatation condition. The stable constant temperature liquid with maximal error ± 100 μ K is realized by two-cycle water bath and PID control system. The floatation height of silicon single crystal sphere is determined by binary image and iterative algorithm. The stable suspension is achieved by the PID pressure control system, and the temperature fluctuation due to Joule-Thomson effect is reduced. By means of linearity between changes of temperature and pressure in hydrostatic suspension model, the compressibility of mixture liquid is measured. The experimental results show that the influence from liquid surface tension is avoided by using the hydrostatic suspension method, and accurate measurement of density difference between silicon single crystal spheres can be achieved with an uncertainty of 2.1× 10-7 (expand factor k=1).
Effect of molecule polarity on the resonance raman spectrum of caroteniod
Authors: Wu Yong-Ling  , Liu Tian-Yuan  , Sun Cheng-Lin  , Qu Guan-Nan  , Li Zuo-Wei  ,   State Key Laboratory of Superhard Materials, Changchun 130012, China;,   College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

The resonance Raman spectra of nonpolar molecule all-trans--carotene and polar molecule canthaxanthin in nonpolar CS2 and polar 1,2-dicholoroethane in a temperature range from 243K to 293K are measured. The results show that polarities of the solute and solvent have a great effect on Raman spectrum. Raman scattering cross-section of nonpolar all-trans--carotene in nonpolar solvent CS2 is biggest and its bandwidth is narrowest. Raman scattering cross-section of polar canthaxanthin in polar solvent 1,2-dicholoroethane is smallest and its bandwidth is widest. The experimental phenomena are explained by solvent effects, coherent weakly damped electron-lattice vibration and effective conjugated length.
Preparation and near-infrared luminescence properties of Bi2O3-B2O3-BaO glasses
Authors: Liu Jun-Fang  , Su Liang-Bi  , Xu Jun  ,   College of Materials Science and Engineering, Tongji University, Shanghai 200092, China;,   Key Laboratory of Advanced Civil Engineering Materials (Tongji University), Ministry of Education, Shanghai 200092, China;,   Key Laboratory of Transparent and Opto-Functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

xBi2O3-50B2O3-(50-x)BaO glasses are prepared by melting method. Their infrared luminescence spectra, fluorescence decay curves and Raman scattering spectra are measured. No obvious near-infrared (NIR) luminescence is observed in 50Bi2O3-50B2O3 glass under 808 nm laser diode (LD) pumping. Adding BaO, broadband NIR luminescences are observed in 40Bi2O3-50B2O3-10BaO glass, 45Bi2O3-50B2O3-5BaO glass and 49Bi2O3-50B2O3-1BaO glass. With the increase of BaO concentration, no obvious NIR luminescences are observed in 30Bi2O3-50B2O3-20BaO glass, 20Bi2O3-50B2O3-30BaO glass and 10Bi2O3-50B2O3-40BaO glass. The NIR emissions with several emission peaks appear in 0.5Bi2O3-50B2O3-50BaO glass and 1Bi2O3-50B2O3-50BaO glass. The mechanism for the emission is investigated preliminarily.
Tunable properties of localized surface plasmon resonance wavelength of gold nanoshell
Authors: Zhang Xing-Fang  , Yan Xin  ,   College of Optoelectronics Engineering, Zaozhuang University, Zaozhuang 277160, China
Published: December 2020

The effects of shell thickness, inner core size, and dielectric constants of core and embedding medium on the localized surface plasmon resonance wavelength of gold nanoshell are investigated by Mie theory. The results show that the extinction peak of gold nanoshell is first blue-shifted and then red-shifted with the increase of shell thickness, that the shift shell thickness corresponding to quadrupolar wavelength is greater than that corresponding to dipolar wavelength, and that the ratio of the shift shell thickness to the inner core size decreases with the increase of inner core size, and increases with the increase of dielectric constant of inner core or embedding medium. The resonance peaks in the scattering spectra have similar phenomena to those in extinction spectra as the shell thickness increases. The shift of the spectral peak is ascribed to the plasmon hybridization and phase retardation effect.
Extraction of effective constitutive parameters of active terahertz metamaterial with negative differential resistance carbon nanotubes
Authors: Si Li-Ming  , Hou Ji-Xuan  , Liu Yong  , Lü Xin  ,   Department of Electronic Engineering, School of Information and Electronics, Beijing Key Laboratory of Millimeter Wave and Terahertz Technology, Beijing Institute of Technology, Beijing 100081, China;,   Department of Physics, Southeast University, Nanjing 211189, China
Published: December 2020

A strategy is presented to acquire active terahertz (THz) metamaterial by incorporating negative differential resistance carbon nanotubes. Furthermore, we propose a method of extracting active metamaterial effective parameters. This new method can effectively solve the problems of signs and multi-branches, while the traditional parameter extraction method becomes powerless for active case. Our results indicate that the active THz metamaterial with metal wires array not only has negative value of the imaginary part of the permittivity but also presents magnetic-dispersion characteristics.
Effect of annealing atmosphere on characteristics of MONOS with LaTiON or HfLaON as charge storage layer
Authors: Zhu Jian-Yun  , Liu Lu  , Li Yu-Qiang  , Xu Jing-Ping  ,   School of optical and electronic information, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Charge-trapping memory capacitor with LaTiON or HfLaON serving as charge storage layer is fabricated by reactive sputtering method, and influences of post-deposition annealing (PDA) in NH3 or N2 ambient on its memory characteristics are investigated. It is found that before PDA, the LaTiON sample exhibits better retention characteristic than the HfLaON sample, but the later shows larger memory window (4.8 V at +/-12 V/1 s), and after PDA, the NH3-annealed sample has faster program/erase speed, better retention and endurance properties than the N2-annealed sample, owing to nitridation role of NH3. Furthermore, the HfLaON sample with PDA in NH3achieves a large memory window of 3.8 V at +/-12 V/1 s, and also shows better retention and endurance properties than the LaTiON sample with PDA in NH3.
Modelling and structure optimization of flat-panel thermal concentrated solar thermoelectric device
Authors: Liu Lei  , Zhang Suo-Liang  , Ma Ya-Kun  , Wu Guo-Hao  , Zheng Shu-Kai  , Wang Yong-Qing  ,   College of Electronic and Information Engineering, Hebei University, Baoding 071002, China
Published: December 2020

Solar thermoelectric conversion is another way to convert solar radiation directly into electricity besides photovoltaic technology, and has become a new hot spot of solar energy utilization in recent years. In this paper a model of flat-panel thermal concentrated solar thermoelectric device is built based on the material of Bi2Te3. And finite element analysis is used to analyze the temperature distribution of the device under AM1.5 illumination. Furthermore, the influences of thermal concentration, cross section area and length of thermal legs on open voltage, maximum output power and conversion efficiency of the device are calculated based on temperature-dependent physical parameters. The results indicate that thermal concentration and length of thermal legs haved a significant influence on device performance, while the cross section area changes the conversion efficiency of device relatively weakly, and the conversion efficiency of the device reaches 1.56% in this model.
Crosslayer parameter configuration for TCP throughput improvement in cognitive radio networks
Authors: Jiang Hong  , Liu Cong-Bin  , Wu Chun  ,   School of Information Engineering, Southwest University of Science and Technology, Mianyang 621010, China
Published: December 2020

In cognitive radio network (CRN), TCP end to end throughput is one of the key issues to measure its performance. However, most of existing research efforts devoted to TCP performance improvement have two weaknesses as follows. First, most of them only consider the underlying parameters to optimize the physical performance, but the TCP performance is neglected. Second, they are largely formulated as a Markov decision process (MDP), which requires a complete knowledge of network and cannot be directly applied to CRNs. To solve the above problems, a Q-BMDP algorithm is proposed in this paper. Each user in CRN combines modulation type and transmitting power at the physical layer, access channels at the media access control layer and TCP congestion control factor to maximize the TCP throughput. Due to the existence of perception error of environment, this issue is formulated as a partial observable Markov decision process (POMDP) which is then converted to belief state MDP, with Q-value iteration to find the approximately optimal strategy. Simulation and analysis results show that the proposed algorithm can be approximately converged to optimal strategy under a maximum error limit, and can effectively improve TCP throughput in a dynamic wireless network under the premise of the limited power consumption.
Empirical analysis of microblog centrality and spread influence based on Bi-directional connection
Authors: Yuan Wei-Guo  , Liu Yun  , Cheng Jun-Jun  , Xiong Fei  ,   Key Laboratory of Communication & Information Systems, Beijing Jiaotong University, Beijing 100044, China;,   Computer Network Information Center, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The identifying of the most influential nodes in the complex network is of great significance for information dissemination and control. We collect actual data from Sina Weibo and establish two user relationship networks based on bi-directional concern. By analyzing the statistical characteristics of the network topology, we find that each of them has a small world and scale free characteristics. Moreover, we describe four network centrality indicators, including node degree, closeness, betweenness and k-Core. Through empirical analysis of four-centrality metric distribution, we find that the node degrees follow a segmented power-law distribution; betweenness difference is most significant; both networks possess significant hierarchy, but not all of the nodes with higher degree have the greater k-Core values; strong correlation exists between the centrality indicators of all nodes, but this correlation is weakened in the node with higher degree value. The two networks are used to simulate the information spreading process with the SIR information dissemination model based on infectious disease dynamics. The simulation results show that there are different effects on the scope and speed of information dissemination under different initial selected individuals. We find that the closeness and k-Core can be more accurate representations of the core of the network location than other indicators, which helps us to identify influential nodes in the information dissemination network.
Influence of sea spray droplets on drag coefficient in high wind speed
Authors: Shi Jian  , Zhou Lin  , Yang Long-Ying  ,   Institute of Meteorology, PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

Sea spray droplets change the distribution of air-sea momentum fluxes in the sea surface, and then influence sea surface drag coefficient considerably. In order to estimate the influence of sea spray droplets on drag coefficient exactly, a new sea spray generation function (SSGF) which depends on wind and wave, is deduced. Then the SSGF is integrated into the spray momentum flux formula to calculate the spray momentum flux. The result shows that revised spray momentum flux formula are sensitive to the wave state remarkably. It indicates that the new sea spray flux formulae can be used in any wave state. The total momentum flux of sea surface contains sea spray momentum flux and air-sea interface momentum flux. Based on this theory, the formula of drag coefficient which is influenced by sea spray droplets at high wind speed is acquired. The theoretical result of the drag coefficient formula shows that the drag coefficient reduces at the high wind speed, which indicates that the sea spray droplets can restrict the increase of drag coefficient at high wind speed. Comparison between theoretical value and measured value of sea surface drag coefficient in field and laboratory shows that the theoretical value of drag coefficient cover the measured value almost. Meanwhile, with the new sea surface drag coefficient, ocean wave model can model the significant wave height very well in typhoon condition. All the results show that the new drag coefficient can be used properly at high wind speed.
The variation features of the surface mixed layer depth in Erhai Lake and Taihu Lake in spring and autumn and their mechanism analyses
Authors: Zhao Qiao-Hua  , Sun Ji-Hua  ,   Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing 210044, China;,   College of Remote Sensing, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Yunnan Institute of Meteorological Science, Kunming 650034, China;,   Dali Meteorological Bureau of Yunnan, Dali 671003, China
Published: December 2020

The variation of the surface mixed layer depth may affect not only the evolution of aquatic ecosystem, but also the temporal-spatial distribution of precipitation and climate in the basin. Based on the meteorological data and water temperature profiles observed in Erhai Lake (located in the Tibetan Plateau) and Taihu Lake (located in the Taihu Plain), the variation features and the mechanisms of the surface mixed layer depths are investigated. The stratification in Erhai Lake can be established and sustained in summer; the diurnal stratification in Erhai Lake can also be established, However, in both summer and autumn, stratification may exist in Taihu Lake. The time length of stratification is longer in Erhai Lake than that in Lake Taihu in the autumn. And the surface mixed layer depths in Erhai Lake are shallower than those in Taihu Lake in summer and autumn. The transformation frequency between establishment and destruction of stratification in Taihu Lake is faster than that in Erhai Lake, which illustrated that the response of water body in Taihu Lake to atmospheric variation is quicker than that in Erhai Lake. The water depth is a key factor which prevents such shallow lakes as Taihu Lake from establishing and maintainaning stratifications and in a suitable radiation condition the stratification will exist. The net radiation is a key factor that determines the stratification and the length of the time when the stratification can be sustained in lakes whose depths are the same as that of Erhai Lake. The research result in this paper is helpful for exploring the coupling mechanism of the turbulence of water and air and the evolution law of aquatic ecosystem.
Global characteristics of the double tropopause derived from the COSMIC radio occultation data
Authors: Jiang Yu  , Sheng Zheng  , Shi Han-Qing  ,   Institute of Meteorology and Oceanography, PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

The global distribution of the second lapse-rate tropopause (LRT2) is investigated with the radio occultation measurements from the constellation observing system for meteorology, ionosphere and climate (COSMIC) covering December 2006-November 2008 Comparisons between COSMIC and radiosonde in terms of the tropopause are examined in three stations to check the difference. The research results are as follows. 1) In the winter, occurrence frequency for LRT2 in the northern hemisphere (NH) is of 50%-70% and in the southers hemisphere is of 20%-40%. 2) The second tropopause over the equatorial zone with 20%-26% occurrence seems to be related to the equatorial jet stream and subvisual cirrus above the first tropopause. 3) In the tropic, the difference in altitude and occurrence between the first and second tropopause decrease with latitude. In the extratropic zone, the difference increases with latitude and reaches a maximum of 7-8 km in the winter of the NH. 4) The second tropopause occurs frequently over the subtropical jet stream region, in which the first tropopause temperature is almost higher than the second one. 5) The more intense the single station daily variations of tropopause height, the bigger the difference between COSMIC and radiosonde is.
Using the principle of critical slowing down to discuss the abrupt climate change
Authors: Wu Hao  , 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 to critical cataclysm. Based on the concepts of critical slowing down, the observed data of temperature and the pacific decadal oscillation (PDO) index and the intensity of Aleutian low pressure, which have different noises are processed in this article to study the precursory signals of abrupt climate change. Take the abrupt climate change in the late1970s-early 1980s as an example, then variances and autocorrelation coefficients which can characterize critical slowing down will be calculated separately; the occurring time of precursory signal of abrupt climate change under the noises influence is studied. The results show that the critical slowing down phenomenon appears in the data with different signal-to-noise ratios before the abrupt climate change takes place, which indicates 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 precursory 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 provides an experimental basis for the wide applications of the present method in real observation data.
Transport of fractional coupled Brownian motor in asymmetric periodic potential
Authors: Wang Fei  , Deng Cui  , Tu Zhe  , Ma Hong  ,   College of Mathematics, Sichuan University, Chengdu 610065, China;,   Science and Technology on Electronic Information Control Laboratory, Chengdu 610036, China
Published: December 2020

In this paper, we first discuss the physical meaning of the fractional Frenkel-Kontorova model and depict the transport phenomenon of elastically coupled particles in a memorable medium, then give the effects of various parameters on the motion of coupled particles. According to the numerical value, the memory effect of system has a significant influence on the motion of coupled particles, in addition, the current reversal which does not exist in a non-memorable system appears, this is an abnormal phenomenon. What is more in this research we find that there appears the generalized resonance in the system mean velocity as the spring constant and the fractional order are varied, and the generalized stochastic resonance will appear with noise intensity changing.
Optical vortex solitons in self-defocusing Kerr-type nonlocal medium
Authors: Ouyang Shi-Gen  ,   Laboratory of Nanophotonic Functional Materials and Devices, SouthChina Normal University, Guangzhou 510631, China
Published: December 2020

The propagation and interaction properties of optical vortex solitons in a self-defocusing Kerr-type nonlocal medium are investigated by the numerical simulation method. It is indicated that the singly charged vortices are stable and the multicharged vortices are topologically unstable in both the nonlocal and local cases. And in the nonlocal and local cases the point vortices model is applicable for describing the interactions of vortices provided that the interval distances between vortices are much larger than the size of the core of the vortices. However, vortices interact differently in short distance, depending on the nonlocality, and the larger the characteristic nonlocal respond length, the larger the rotating period of two singly charged vortices.
Influence of the strong beam impedance on injection and bunching features of the relativistic klystron amplifier
Authors: Zhang Ze-Hai  , Shu Ting  , Zhang Jun  , Qi Zu-Min  ,   College of Opto-Electric Science and Engineering, National University of Defence Technology, Changsha 410073, China
Published: December 2020

With numerical calculation and particle simulation program, the influences of the intense electron beam impedance, voltage and current characteristics on the beam modulation and bunching characteristics in relativistic klystron amplifier (RKA) are analyzed. Within the particle-in-cell simulation program, the beam emission method is used to accurately control the impedance of the electron beam. The results show that the electron beam of low-impedance can reduce the bunching distance and shorten the overall length of the RKA devices but degrade the injected modulation of the electron beam. Electron beam of high impedance is just opposite. When the electron beam impedance is constant, the increase of the electron beam accelerating voltage is similar to the increase of the impedance of the electron beam. In addition, with the particle simulation method, the beam loaded conductance of a specific input cavity loaded by a different impedance of the electron beam is determined, thereby meeting the demand of the power level of the seed, and the requirements for the externally loaded quality factor of the input cavity.
Tunability THz metamaterials base on the dielectric nonlinear of barium strontium titanate
Authors: Zhao Qiang  , Wen Qi-Ye  , Dai Yu-Han  , Zhang Ji-Hua  , Chen Hong-Wei  , Yang Chuan-Ren  , Zhang Wan-Li  ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

We present the tunable resonance behavior of laminated metal mesh metamaterial embedded by barium strontium titanate (BST) thin film. The electromagnetic frequency response shows a redshift when the dielectric constant of BST thin film increases, and the tunability is about 22.6%. For the tunable metamaterial proposed in this paper, the structural unit of metal graphics is used as electrodes to apply the electric potential, which simplifies the preparation and application of tunable THz metamaterials greatly. It has potential application in the THz media modulators.
Magnetic properties of permanent magnet for cryogenic undulator of permanent Shanghai synchrotron radiation facility
Authors: He Yong-Zhou  , Zhou Qiao-Gen  ,   Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
Published: December 2020

M-H and M-T curve at cryogenic (10-300 K) of domestic Nd2Fe14B (N50M) permanent magnet are tested by physical property measurement system (PPMS). Br-T and Hci-T figure under the cryogenic condition for N50M are obtained. The orientation degree and three-dimensional magnetization are also analyzed and researched under the cryogenic conditon. The results show that N50M has a strong spin reorientation effect(SRT) between 80 and 150 K, Br shows a peak between 120 and 130 K and Hci increases linearly with temperature decresing. At 130 K, Br increases 15.6% and Hci increases 220% compared with at room temperature (300 K), reaching 1.65 T and 3638 kA/m respectively. Between 150 and 300 K, with temperature declining, the macroscopic orientation degree uniformity and the external magnetic field uniformity of N50M are improved gradually. Between 80 and 235 K, the micro-external magnetic field uniformity shows a deterioration phenomenon. The experimental research also indicates that near 235 K the N50M perpendicular to orientation direction presents a “remanent magnetization jump” phenomenon. The experimental results provide a reference for the physical design of cryogenic undulator for Shanghai Synchrotron Radiation Facility II and other high-precision cryogenic permanent magnet instruments and equipment.
Simulation and analysis of nonlinear self-focusing phenomenon based on ray-tracing
Authors: Ruan Wang-Chao  , Cen Zhao-Feng  , Li Xiao-Tong  , Liu Yang-Zhou  , Pang Wu-Bin  ,   State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China
Published: December 2020

The simulation of nonlinear self-focusing phenomenon using ray-tracing method can macroscopically provide an intuitive picture of the propagation of light in a self-focusing material, without adopting paraxial approximation or self-similar hypothesis. In this paper, propagation of light is sampled by discrete slices along a certain direction. Thus nonlinear propagation is turned into the combination of optical modulation of the refractive index on separate slices and linear propagation between each two adjacent slices. On each slice, after calculating the flux, we use a novel algorithm to suppress the quantized errors. For the linear propagating process, Adams method is adopted to solve the ray equations, which solve the problem that the widely used Runge-Kutta method cannot be used in simulation of light in nonlinear materials. The simulation results reveal that there are several foci along the propagating axis and the location of the first focus becomes closer to the incident plane as the power of light goes up. Furthermore, because the program traces real rays, it is possible to reach the non-paraxial region and reveal the phenomenon of ring-structure flux distributions caused by self-focusing. This is significant for the safety of high-power laser systems. Some commercial optical design and simulation software are also based on ray-tracing methods. Thus the systems including both nonlinear and linear materials are possible to simulate, which can guide people to set up the corresponding experimental systems.
Differential compressive correlated imaging
Authors: Bai Xu  , Li Yong-Qiang  , Zhao Sheng-Mei  ,   Institute of Signal Processing and Transmission, Nanjing University of Posts and Telecommunications, Nanjing 210003, China
Published: December 2020

Correlated imaging offers great potentiality, with respect to standard imaging, to obtain the imaging of objects located in optically harsh or noisy environment. It can solve the problems which are difficult to solve by conventional imaging techniques. Recently, it has become one of the hot topics in quantum optics. In this paper, we propose a new scheme of correlated imaging with differential correlated imaging based on compressive sensing, named differential compressive correlated imaging. The new scheme takes advantage of the high signal-to-noise ratio of the differential correlated imaging and low-imaging sampling frequency of the compressed sensing technique. In the scheme, we utilize the intensity of the thermal light, which is in line with the Gaussian distribution, as the measurement matrix of compressive sensing. We extract the differential object information as the image object information which could be recovered via orthogonal matching pursuit algorithm with high quality. By numerical simulations, we verify the proposed scheme. Here, we select the two gray-scale images, such as double-slit and NUPT, as well as the two multi-grayscale images (Lena and Boats) as the object. We take sampling 350 times in differential compressive correlated imaging for measurement. The numerical simulation results show that for the above image objects, the average mean-square error (MSE) over 10 times for the differential compressive correlated imaging scheme is reduced by 97.7%, 93.9%, 92.5% and 71.4% respectively with respect to that of the differential correlated imaging scheme. Moreover, compared with the compressive ghost imaging, the MSE value of the same double-slit in CDGI, as well as Lena and Boats under the same conditions, is reduced by 50.4%, 72.9% and 66.8% separately, which indicates that the compressive differential correlated imaging scheme can greatly improve the signal-to-noise ratio of the imaging, and significantly reduce the imaging time.
High power and low quantum-defect Yb-doped fiber amplifier based on tandem pumping
Authors: Jiang Man  , Xiao Hu  , Zhou Pu  , Wang Xiao-Lin  , Liu Ze-Jin  ,   College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

We show experimentally that a tandem-pumped Yb-doped fiber amplifier with high power and low quantum-defect can be reached. And a high power 21 W output power at 1018 nm is demonstrated finally. We use this 1018 nm fiber laser as a pumping source of the 1080 nm fiber laser to demonstrate the tandem-pumped double-cladding Yb-doped fiber amplifier, and obtain an output power of 18.6 W at 1080 nm with a slope efficiency of 90.86%.
Quantitative analysis of cadmium in navel orange by laser-induced breakdown spectroscopy combined with partial least squares
Authors: Zhang Xu  , Yao Ming-Yin  , Liu Mu-Hua  ,   Key Laboratory of Optics-Electronics Application of Biomaterials, College of Engineering, Jiangxi Agricultural University, Nanchang 330045, China
Published: December 2020

The navel orange is analysed quantitatively for cadmium by laser-induced breakdown spectroscopy. The laser-induced breakdown spectroscopy is used to obtain the characteristic spectrum of Cd in sample. The concentration of sample is detected as a reference concentration by atomic absorption spectrophotometer. The partial least squares method is applied to the data of 39 samples which are preprocessed by combining the five smoothing formula and centerization method to establish quantitative analysis of cadmium model. Other 13 samples are used to be compared with the results from the quantitative analysis model. In this model, the correlation coefficient of fitting curve is 0.9806 and the relative error of 12 samples is 10.94 percent. The research results show that laser-induced breakdown spectroscopy can nondestructively and accurately detect heavy metals in agricultural products without preparing any sample and provides a technology for the safety of agricultural products.