bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental study on multiple-ring vortex beams
Authors: Huang Su-Juan  , Gu Ting-Ting  , Miao Zhuang  , He Chao  , Wang Ting-Yun  ,   Key Laboratory of Special Fiber Optics and Optical Access Networks, School of Communication and Information Engineering, Shanghai University, Shanghai 200072, China
Published: December 2020

The generation, propagation and application of vortex beams have been hot research topics in recent years. In this paper we introduce the novel multiple-ring vortex beams, including double-ring vortex beams and triple-ring vortex beams, which are generated by the coaxial superposition of multiple Laguerre-Gaussian vortex beams with different topological charge numbers and different waist parameters, and their intensity distribution is of multiple-ring. We study the generation and distribution characteristics of multiple-ring vortex beams theoretically, obtain the computer generated hologram of multiple-ring vortex beams based on conjugate symmetric extension Fourier computer generated holography, and experimentally generate quality multiple-ring vortex beams using a spatial light modulator. Excellent agreement between theoretical and experimental results is observed. The study indicates that each ring of multiple-ring vortex beams carries different orbital angular momentum, and the spatial distribution is independent. The novel multiple-ring vortex beams provide more controllable parameters and more diverse structure distributions, which enable their applications in the fields of micro-manipulation as optical tweezers or optical spanner. Furthermore, they also have potential applications as available encoding tools in optical communication.
Construction of a strongly coupled cavity quantum electrodynamics system with easy accessibility of single or multiple intra-cavity atoms
Authors: Wen Rui-Juan  , Du Jin-Jin  , Li Wen-Fang  , Li Gang  , Zhang Tian-Cai  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The long-time trap and control of neutral atoms in an optical micro-cavity is a crucial problem in cavity quantum electrodynamics (QED), which greatly restricts the coherent manipulation of the interaction process between single atom and light. In this paper, we design a strongly coupled cavity QED system based on the traditional Fabry-Perot cavity. The parameters of the cavity are 3.5 millimeters in length, about 57000 in fineness, (g0,,)=2 (1.48, 0.375, 2.61) MHz, 1.54 and 0.89 in critical photon and atom number, respectively. The system allows building the magneto-optical trap (MOT) and optical lattice directly inside the cavity, which provides the possibility of long-time trapping deterministic single neutral atom or a number of neutral atoms in the cavity. By setting up a dipole trap and atomic imaging system, the capture, detection and imaging of single atom or several atoms in the cavity can be realized. The system overcomes some difficulties in transferring atoms in the usual cavity QED and has potential applications in robust intracavity atom control for quantum information processing.
Evolution of vortex configuration for superconducting ring in the presence of an externally applied field
Authors: Shi Liang-Ma  , Zhou Ming-Jian  , Zhu Ren-Yi  ,   College of Electronic Engineering and Electricial Automation, Chaohu University, Hefei 238000, China
Published: December 2020

The evolution of vortex configuration for superconducting ring is simulated by the Ginzburg-Landau theory in the presence of an externally applied field. The effects of the applied field, the material parameter, the size of ring on the entrance of vortices into the ring and distributing of steady vortices are discussed. Research results show that the higher the applied field, the bigger the material parameter κ is, and the larger the width of the ring, the bigger the number of the vortices which the ring accommodates. The vortices enter into the ring only from the inner boundary when the applied field is low enough, otherwise the vortices enter into the ring first from the outer boundary and then from the inner boundary.
Static magnetization and demagnetizing field distribution of the amorphous wire in non-uniform applied field
Authors: Zhao Yin  , Xu Hong-Guang  , Zhang Qin-Yu  ,   Communication Engineering Research Center, Harbin Institute of Technology Shenzhen Graduate School, Shenzhen 518055, China
Published: December 2020

Currently, the giant magneto-impedance effect of amorphous wires is usually investigated on the hypothesis that demagnetizing field can be ignored. This hypothesis is not true for amorphous wires with small size. We propose a model for calculating the static magnetization and magnetic field distribution inside CoFe-rich amorphous wires, which divides the amorphous wire into coaxial and nonoverlaped circular rings with the same width and height and different radii. Calculating the impulse response of the demagnetizing field at point r to the magnetization in each ring, the impulse response matrix is obtained. Using the impulse response matrix, the static magnetization and demagnetizing field distribution in the amorphous wire placed in an uniform or non-uniform DC applied field can be obtained.
First-principles study of the effect of lanthanum on the Cu diffusion mechanism in bcc-Fe
Authors: Gao Xue-Yun  , Wang Hai-Yan  , Li Chun-Long  , Ren Hui-Ping  , Li De-Chao  , Liu Zong-Chang  ,   Beris Engineering and Research Corporation, Baotou 014010, China;,   Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Baotou 014010, China;,   Baotou Iron and Steel (Group) Corporation, Baotou 014010, China
Published: December 2020

The influence of La on the Cu precipitation in bcc-Fe is determined by first-principles density functional calculations. The binding energies of La-vacancy, Cu-vacancy pairs, and La-Cu pair are calculated, and the effects of La atoms on the diffusion activation energy of Cu atoms in bcc-Fe are considered. It is found that there exist strong attractive interactions between La atom and vacancy and between La atom and adjacent Cu atom. In addition, the formation energy of the vacancy adjacent to Cu atom increases significantly with the La addition, suggesting that vacancy is difficult to form in the La and Cu segregation zone. Meantime, we find that the migration energy of Cu atom is enhanced due to the attractions of La atom to adjacent vacancy and Cu atom. The calculated results of the vacancy formation energy and migration energy indicate that Cu atom possesses a higher diffusion activation energy after the La addition, and in turn, delays the segregation and precipitation process of the Cu rich phase in bcc-Fe.
Process parameters of large single crystal graphene prepared by chemical vapor deposition
Authors: Han Lin-Zhi  , Zhao Zhan-Xia  , Ma Zhong-Quan  ,   SHU-SolarE Research and Development Laboratory, Department of Physics, Shanghai University, Shanghai 200444, China
Published: December 2020

Graphene, as a two-dimensional sp2 hybridization allotropicity of carbon element, possesses unique properties of electricity, photology, thermology and mechanics. For industrialization, graphene possessing large dimension and homogeneous property is required. It can be prepared by chemical vapor deposition technology. In this paper, based on the progress of graphene research this year, we summarize the influence factors of graphene preparation, including substrate selection and preprocessing, carbon source and assist gas flow control, chamber temperature, pressure control, cooling rate, and deposition time setting, etc. Finally, we outlook the research direction of preparing the large-dimensional and single crystal graphenes.
Phase transition and structure of LuTaO4
Authors: Xing Xue  , Wang Xiao-Fei  , Zhang Qing-Li  , Sun Gui-Hua  , Liu Wen-Peng  , Sun Dun-Lu  , Yin Shao-Tang  ,   Key Laboratory of Photonic Devices and Materials of Anhui Province, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Since LuTaO4 is a scintillator host with the highest density, it is important to investigate the structure and phase transition for its single crystal preparation. The polycrystalline formed by the mixture of Lu2O3:Ta2O5 with the molar ratio 1:1 is prepared by solid state reaction method at different temperatures. The phase transitions and structures of the polycrystalline powders are investigated by X-ray diffraction and Rietveld refinement. The results show that the polycrystalline has a single phase M'-LuTaO4 when sample is prepared at 1740 ℃, it presents a mixture phase of M'-LuTaO4 and M-LuTaO4 at 1800 ℃, and it displays a single phase M-LuTaO4 at 1840 ℃. The sample is melted when the calcined temperature is 2058 ℃, the melt is quenched and the polycrystalline is the mixture of M-LuTaO4, Lu3TaO7 and Ta2O5, whose structural parameters, including the lattice parameters, atomic fraction coordinates, etc. are obtained by Rietveld refinement to their X-ray diffraction pattern, and the results show their weight ratios are 78.1%, 18.9% and 3.0%, respectively. These results are valuable for the single crystal growth of the heavy scintillators with the host LuTaO4.
Outline design and performance analysis of navigation constellation near earth-moon libration point
Authors: Meng Yun-He  , Chen Qi-Feng  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The outline design problem of navigation constellation near libration point is studied for deep space exploration. Firstly, the model of circular restricted three body problem near libration point is given, and the differential correction method is provided to calculate periodic orbits, of which the stability factor is also introduced. Secondly, the concept of effective coverage is defined, and the elements and the steps to design the constellation are proposed. Then, the outline design, performance analysis and evaluation of the navigation constellation are carried out concretely from aspects of orbits selection, space coverage, geometric dilution of precision factor, signal transmission and navigation precision. Compared with the case of global position system, the feasibility of the navigation constellation in libration point orbit is proved, and the performance index is provided. By analysis, the designed navigation constellation in L3-Vertical orbit with 5 satellites is able to provide navigation service for most of the spacecrafts in the space of between the earth and the moon, and the navigation precision is better than 10 m if the orbit determination errors of the constellation are not considered.
Phase noise induced single or double coherence resonances of neural firing
Authors: Ding Xue-Li  , Li Yu-Ye  ,   Foundation Department, Fuyang Vocational and Technical College, Fuyang 236031, China;,   Mathematics and Statistics institute, Chifeng University, Chifeng 024000, China
Published: December 2020

Neuronal firing activity can be changed from the resting state to firing state either through Hopf bifurcation where the firing exhibits a fixed period or through saddle-node bifurcation where the firing frequency is nearly zero. Phase noise with periodicity can induce coherence resonances near Hopf and saddle-node bifurcation points. When the period of phase noise is shorter than the internal period of firing near the Hopf bifurcation point, the phase noise can induce single coherence resonance appearing near the frequency of the phase noise. When the period of phase noise is longer than the internal period of firing near the Hopf bifurcation point, the phase noise can induce double coherence resonances. The resonance at low noise intensity appears near the frequency of the phase noise, and the one at large noise intensity occurs near the frequency of the firing near the Hopf bifurcation. The mechanism of the double resonances is explained. Unlike the Hopf bifurcation point, only a single coherence resonance can be induced near the saddle-node bifurcation point by the phase noise with long or short periods. The results not only reveal the dynamics of phase noise induced coherence resonance of the equilibrium point and identify the distinction between two types of neuronal excitabilities corresponding to two kinds of bifurcations, but also provide an explanation about the different results of phase noise induced single or double resonances simulated in recent studies.
The characteristics of the summer atmospheric water cycle over China and comparison of ERA-Interim and MERRA reanalysis
Authors: Su Tao  , Feng Guo-Lin  ,   College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China;,   Laboratory for Climate Studies of China Meteorological Administration, National Climate Center, Beijing 100081, China
Published: December 2020

Atmospheric water cycle process includes precipitation, evaporation, water vapor transport and other links. The temporal and spatial characteristics of the atmospheric water cycle over China in summer are investigated by using the ERA-Interim and MERRA reanalysis from 1979 to 2012. Comparison and performance analyses of these two reanalysis data are given. The obtained results are as follows. 1) the spatial distributions of precipitation, evaporation and precipitable water are highly similar to each other, and all gradually decrease from southeast coast to northwest inland regions. Because the differences in physical condition, precipitation and evaporation among different underlying surfaces, mutually promot or mutually restrict each other, the interactions among them have positive and negative feedback mechanisms. Precipitable water mainly concentrates in the ground to the 700 hPa height, accounts for about 75% of the total quantity. 2) All of the atmospheric water cycle elements have obvious characteristics of climate change, especially in these areas like Northwest China, Tibet and Northeast China. The zonal flux of water vapor transport significantly decreases in most parts of the northern, while the meridional flux of water vapor transport significantly increases in the northern region of Northwest China. 3)The reproduction ability to change characteristics of precipitation is better than that of evaporation based on these reanalyses. The temporal and spatial distribution characteristics of moisture transport situation and the various levels of atmospheric water vapor content are highly consistent with each other. The simulations of flux climate change trend of precipitation and water vapor transport are more accurate and more reliable. 4) Interim reanalysis is applicable to the study of the southwest, Southeast and northeast regional atmospheric water balance, water cycle elements can maintain balance well, while MERRA reanalysis is more reasonable in Southwest and northwest.
Sensitivity analysis of sample number on the drought descriptive model built by Copula function in southwest China
Authors: Zuo Dong-Dong  , Hou Wei  , Wang Wen-Xiang  ,   Department of Physics, Yangzhou University, Yangzhou 225002, China;,   Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing 100081, China
Published: December 2020

Based on the standardized precipitation index data of 89 meteorological stations in southwest China (Sichuan Province, Yunnan Province, Guizhou Province, Chongqing) during 1961-2010, probability model containing drought duration and drought severity is established by using the theory of run and the Copula function. The influences of the drought sample number on the distribution parameters, the probability and drought return period are discussed. The result shows that the stability of distribution parameters needs larger sample number. The sample number is greater than 50 in some regions and the requirements for sample number of each parameter is not consistent. The sample number of severity distribution parameters is largest. The probability and return period obtained in the case where the sample number is about 10 have no significant difference (the significant level is 0.05) from those in the case where the sample number is 40 in most of region. With the results used as the standard, statistical model can greatly reduce the requirements for the sample number. And then it demonstrates that the distribution function of drought duration and drought severity can still be established in the lack of measurement data and the inconsistency between starting and ending time. Climate warming has no influence on the minimum of sample number. The fluctuation is mostly between -5 to 5. Statistical model has a certain stability. Meanwhile, the division of climate state reduces the need for distribution test sample number and makes it easier to build model.
Interpolating particle method for mechanical analysis of space axisymmetric components
Authors: Du Hong-Xiu  , Wei Hong  , Qin Yi-Xiao  , Li Zhong-Hua  , Wang Tong-Zun  ,   College of Architecture and Civil Engineering, Taiyuan University of Technology, Taiyuan 030024, China;,   College of Mechanical Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China;,   Shantui Construction Machinery Co., Ltd, Shandong 272000, China
Published: December 2020

For the mechanical analyses of the axisymmetric structures in civil and mechanical engineering, combining the interpolating reproducing kernel particle method and the principle of minimum potential energy of space axisymmetrical elastic problems, the interpolating particle method for space axisymmetrical problem of elasticty is presented. And the corresponding matrix equations are deduced. This method employs the shape function with interpolating properties of scatter points and forms the displacement trial function to get rid of dependence on meshes, so it has an advantage that it can directly exert boundary conditions and can increase the computation efficiency. This method can obtain the global continuous stress field directly and avoid the fitting calculation error of stress in the post-processing of finite element method, then it is a high-precision numerical simulation method. Numerical examples are given to show the validity of the new mesh-less method in the paper.
Mechanism for the coexistence phenomenon of random phase suppressing chaos and stochastic resonance in Duffing system
Authors: Li Shuang  , Li Qian  , Li Jiao-Rui  ,   School of Statistics, Xi’an University of Finance and Economics, Xi’an 710100, China;,   College of Art and Design, Shaanxi University of Science and Technology, Xi’an 710021, China
Published: December 2020

Noise, which is ubiquitous in real systems, has been the subject of various and extensive studies in nonlinear dynamical systems. In general, noise is regarded as an obstacle. However, counterintuitive effects of noise on nonlinear systems have recently been recognized, such as noise suppressing chaos and stochastic resonance. Although the noise suppressing chaos and stochastic resonance have been studied extensively, little is reported about their relation under coexistent condition. In this paper by using Lyapunov exponent, Poincaré section, time history and power spectrum, the effect of random phase on chaotic Duffing system is investigated. It is found that as the intensity of random phase increases the chaotic behavior is suppressed and the power response amplitude passes through a maximum at an optimal noise intensity, which implies that the coexistence phenomenon of noise suppressing chaos and stochastic resonance occurs. Furthermore, an interesting phenomenon is that the optimal noise intensity at the SR curve is just the critical point from chaos to non-chaos. The average effect analysis of harmonic excitation with random phase and the system’s bifurcation diagram shows that the increasing of random phase intensity is in general equivalent to the decreasing of harmonic excitation amplitude of the original deterministic system. So there exists the critical noise intensity where the chaotic motion of large range disintegrates and non-chaotic motion of small scope appears, which implies the enhancing of the regularity of system motion and the increasing of the response amplitude at the input signal frequency. After that, the excess noise will not change the stability of the system any more, but will increase the degree of random fluctuation near the stable motion, resulting in the decreasing of the response amplitude. Therefore, the formation of stochastic resonance is due to the dynamical mechanism of random phase suppressing chaos.
Multispectral image enhancement based on irradiation-reflection model and bounded operation
Authors: Bi Guo-Ling  , Xu Zhi-Jun  , Zhao Jian  , Sun Qiang  ,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Science, Beijing 100049, China
Published: December 2020

According to irradiation-reflection model, by combining the generalized bounded operation model with guide filter, the problem of enhancement for multispectral degraded images with blurred details can be effectively solved and the contrast and low signal-to-noise ratio can be improved. The multi-scale reflection component image, i.e., final enhanced image is obtained through the following procedures: using the adaptive different scales of guide filter function as surround function estimate reaction; separating out the high-low-frequency information; obtaining the different scales Irradiation images which react the overall structure of the image; using the bounded generalized logarithmic ratio (GLR) model addition to replace the Retinex logarithmic transformation; taking a similar logarithmic transformation to the original image to improve the contrast of the image and make the dark area of image details enhanced; again using GLR model subtraction to remove illuminate components from the original image to segment the different scales of the reflection image, thereby avoiding the loss of small details and the big details caused halo effect and noise interference. With four direction Sobel gradient image which reflects the comprehensive edge details of image information the adaptive gain function can be obtained. To avoid the smooth area noise amplification, by using the GLR model multiplication and addition to fuse the effective information of different scales images, the multi-scale reflection image, namely the final enhanced image are obtained. The effective suppression of the emergence of halo effect and computing overflow, which can retain a large number of image details; the comparision of subjective visual effect and the quantitative parameter analysis of the visible low illumination image, haze image, infrared image and X-ray medical images (a total of four groups of multispectral degraded images), the use of the contrast and entropy as evaluation indices, qualitative and quantitative comparison with a variety of image enhancement algorithms, show that the proposed algorithm strengthens and keeps the details of the image texture and edge, realizes the image contrast enhancement and the effective dynamic range compression, has a strong anti-noise ability, and can meet a variety of practical engineering image enhancement needs. The results of the study has been used in the infrared thermal imager, and good results have been achieved. The proposed algorithm is only for 8-bit grayscale image enhancement, and the color image enhancement will be studied in the future.
Optimal calculation of detection efficiency for thermal neutron sensitive microchannel plate
Authors: Wang Sheng  , Li Hang  , Cao Chao  , Wu Yang  , Huo He-Yong  , Tang Bin  ,   Institute of Nuclear Physics and Chemistry, CAEP, Mianyang 621900, China
Published: December 2020

The traditional digital imaging of neutron radiography is based on neutron scintillation screen cooperated with charge coupled device (CCD) camera, whose spatial resolution and neutron detection efficiency are contradictory. Neutron detection method based on microchannel plates (MCP) could solve the problem appearing in traditional method. It could supply high spatial resolution, high neutron detection efficiency and high time resolution. It is of benefit to high-resolution neutron radiography and neutron energy choice imaging. Tremsin et al. [Tremsin A S, Feller W B, Downing R G, Mildner D R 2004 U. S. Government Work not Protected by U. S. Copyright p340] calculated the detection efficiency of thermal neutron sensitivity MCP in 2004. Then his team fabricated a prototype of neutron detection system based on MCP and carried out the neutron imaging experiments on several neutron sources. The experimental results show that spatial resolution is nearly 15 μm and neutron detection efficiency for cold neutron is more than 70%. In China, Yang Y G et al.[15] from Tsinghua University developed a neutron detection system based on MCP, and preliminary neutron experimental results indicate that spatial resolution is about 200 μm.#br#In order to find the optimal structure of MCP, in this paper we calculate the detection efficiency of thermal neutron sensitive MCP doped (or coated) by boron and gadolinium with Monte-Carlo method. The neutron detection efficiency P is determined by three terms P1, P2 and P3, which are related by P=P1× P2× P3. Here, P1 is the possibility that the neutrons are absorbed by MCP solid parts, P2 is the possibility that the secondary particle escapes into MCP channel and generates an electron avalanche, and P3 is the possibility that the electron avalanch is recorded by readout system. Theoretical analysis indicates that more solid parts of MCP can make P1 higher and increase the difficulty for secondary particle to escape, and make P2 lower. There may be an optimal geometry to make the total P maximal. This paper gives the calculation method of P1 and P2, and approximates P3 to 1. #br#The calculation results show that the neutron detection efficiency depends on channel diameter (or coated thickness) and material, but not on the structure of MCP. When the thickness of MCP is 0.4 mm, the pixel of MCP is 15 μm, and the neutron sensitivity material is 10B2O3, the optimal thermal neutron detection efficiency is more than 40% with a channel diameter of 8.0 μm for the doped MCP, and it is nearly 60% with a coated thickness of 1.5 μm for the coated MCP. With the same geometry parameters and the neutron sensitive material such as natural Gd2O3, the optimal thermal neutron detection efficiency is more than 30% with a channel diameter of 9.0 μm for the doped MCP, and it is more than 50% with a coated thickness of 0.5 μm for the coated MCP.
Heat transfer analysis of rotating tritium target of deuterium-tritium fusion neutron generator
Authors: Wang Gang  , Yu Qian-Feng  , Wang Wen  , Song Gang  , Wu Yi-Can  ,   Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

Fusion reactor is considered as one of the solutions for the sustaining development of nuclear energy. International Thermonuclear Experimental Reactor (ITER) is the biggest fusion reactor research plan in the world. High-intensity D-T fusion neutron generator can generate 14 MeV neutrons, and it matches the neutrons generated in ITER and be competently used for imitating the neutron environment in nuclear fusion reactor, which is important for the relevant experimental researches of blanket materials of fusion reactors. It can also be used for validating the correctness and reliability of the simulations and analyses in fusion basic studies, and can guide the subsequent material improvement and innovation of calculation methodology. A rotating tritium target system for D-T fusion neutron generator with a neutron yield of 1012 n·-1, i.e., a high intensity D-T fusion neutron generator, is proposed in this paper and the design, main parameters, technical difficulties and heat transfer enhancement method are introduced. The key and innovative technology of this rotating target system is the integration of the sprayed water cooling, mechanical seal and magnetic fluid seal technologies, which focuses on the heat transfer of the high heat power density in the target system. The most important technical index is that the maximum temperature on the target should not be above 200 ℃ as the tritium ions run away heavily from the tritium target when the target temperature is bigger than 200 ℃. To investigate the heat transfer characteristics of this rotating target system, the effects of water layer thickness, water flow rate and rotating speed on the heat transfer of this rotating target system are analyzed by computational fluid dynamics method. And the heat transfer processes of the target system under different heat power densities are also simulated and studied. The analysis results show that big water layer thickness, big water flow rate and high rotating speed are good for the heat transfer enhancement of the rotating target system, but the effects of the changes of the water layer thickness and water flow rate on the heat transfer process are both very small. Due to the design index, the heat power density on the target should be under a limit value, which is about 12 kW·cm-2 in the calculation results of this paper.
Collision dynamic behaviors of CO(X1Σ+) molecule with Mg atom in cold and ultracold temperatures
Authors: Han Yu-Long  , Zhang Kan  , Feng Er-Yin  , Huang Wu-Ying  ,   College of Physics and Electronics Information, Anhui Normal University, Wuhu 241000, China;,   Mechanical and Electrical College, Anhui Polytechnic University, Wuhu 241003, China
Published: December 2020

Sympathetic cooling is one of the most promising techniques for producing ultracold molecules from precooled molecules. The previous work has shown that it is inadequate to use the ultracold alkali-metal atoms as coolant for sympathetic cooling. Whether the ultracold alkali-earth-metal atoms can be used as coolant deserves to be investigated. In this paper, the cold collision dynamic behaviors for Mg atom and CO molecule are investigated by quantum scattering calculations. The influences of electric field on the elastic and inelastic collision cross sections of low field seeking state within cold and ultracold temperature are explored. The results show that sympathetic cooling CO molecule with ultracold Mg atom might be difficult to perform.
Theoretical and experimental study of thrust produced by corona discharge exciter in wire-aluminum foil electrode configration
Authors: Wang Wei  , Yang Lan-Jun  , Liu Shuai  , Huang Yi-Zhi  , Huang Dong  , Wu Kai  ,   Department of Electrical Engineering, State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

Air corona discharge ionic wind exciter can generate driving force without any rotating component, which makes it commonly used in aviation and aerospace field. Although there are many explanations of the thrust generating mechanism of the air corona discharge ionic wind exciter, no existing theories can unify the experiment results obtained under various conditions. A further study is still needed. The paper focuses on the characteristics of wire-aluminum foil exciter. The experiments show that the electrostatic force acting on the wire-aluminum foil is asymmetric and the variations of the height in lengthways aluminum foil and the air pressure can change the electrostatic force. Meanwhile, with the theoretical analysis the calculation model of the force of the wire-aluminum foil exciter’s corona discharge is established by taking the influences of corona layer and space charge into consideration. The calculation fits the measured value. By combining with the theoretical analysis, the thrust of wire-aluminum foil electrode corona discharge exciter is proved to come from the space charge produced by wire electrode corona discharge, which exerts an asymmetric electrostatic force on the electrode system and generates a net electrostatic force for the exciter.
Fabrication and microstucture of spray formed powder metallurgy superalloy FGH4095M
Authors: Wang Tian-Tian  , Ge Chang-Chun  , Jia Chong-Lin  , Wang Jie  , Gu Tian-Fu  , Wu Hai-Xin  ,   School of Materials Science and Engineering, Institute of Powder Metallurgy and Advanced Ceramics, University of Science and Technology Beijing, Beijing 100083, China;,   Beijing Beiye Functional Materials Corporation, Institute of High Temperature Materials, Beijing 100192, China;,   School of Materials Science and Engineering, Southwest JiaoTong University, Chengdu 610031, China
Published: December 2020

Spray forming is a kind of near-net-shaped rapid solidification process based on powder metallurgy gas atomization technology. In this work, the FGH4095M is fabricated by spray forming. The pre-alloy is prepared by vacuum induction melting and vacuum arc remelting techniques. Then the alloy is sprayed by SK2 facility with atomization gas nitrogen at University of Bremen in Germany. In this paper we study the density and microstructure of the spray-formed billet, especially the special morphology of γ’ phase. The results show that density is associated with different parts of the deposited billet. The relative density of the bottom part is higher (99.63%) than those in the other parts. The relative density of top part (98.91%) is lowest. After hot isostatic pressing, the relative density can be up to 100%. Uniform and fine equiaxed grains are the remarkable morphology of spray-formed alloy without prior particle boundary. The sizes of grains are in a range of about l0-40 μm and the grains at bottom part of billet are finest. The grain sizes of primary γ’ phase are in a range of about 0.6-0.8 μm, and the grain sizes of secondary γ’ phase in a range of about 0.1-0.5 μm as well as dispersed spherical tertiary γ’ particles with the sizes of 10-20 nm. The special morphology of secondary γ’ phase occurs with the splitting of γ’ particle, which is related to the low cooling rate of the depositing process. The splitting behavior reduces the total energy of γ’ particle. Total energy of γ’ particle includes elastic interaction energy, elastic strain energy and surface energy, among which the elastic strain energy is invariable. The surface energy increases with the splitting process and the elastic interaction energy reduces. The effect of elastic interaction energy on particles is the major reason why the total energy is reduced. The trend of splitting behavior is analyzed by calculating the equivalent diameter of splitting γ’ particle. It indicates that when the equivalent diameter is over 0.40 μm, there is the possibility to split. Subsequently, spray-formed FGH4095M billet is treated by hot isostatic pressing, isothermal forging and heat treatment process to obtain the FGH4095M alloy turbine disk. The research of tensile property of FGH4095M alloy turbine disk shows an excellent property either at room temperature or at high temperature for the optimized alloy. The relationship between special morphology of γ’ phase and excellent property needs further investigating.
Sound velocity and phase transition for low porosity tin at high pressure
Authors: Song Ping  , Cai Ling-Cang  , Li Xin-Zhu  , Tao Tian-Jiong  , Zhao Xin-Wen  , Wang Xue-Jun  , Fang Mao-Lin  ,   Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics, 919-102, Mianyang 621900, China
Published: December 2020

Shock and release experiments are performed on the porous Sn with sub-micropores with porosity m=1.01. Time-resolved interfacial velocities between the porous Sn and LiF window are measured with Doppler pins system under seven pressure points from 31.8 GPa to 66.1 GPa. From the interfacial velocity, the Euler longitudinal sound velocities and the bulk sound velocities are obtained. The corresponding Poisson ratio and shear modulus are determined, too. From the transition of longitudinal sound velocity to bulk sound velocity at high pressures, the shock-induced melting of Sn with porosity 1.01 occurs at about 49.1 GPa. With the Euler longitudinal sound velocities, the bulk sound velocities and the shear moduluses of porous and dense Sn, the melting pressure zone of dense Sn can be determined to be between 53.5 GPa and 62.3 GPa. Comparing the melting zone of porous Sn and that of dense Sn, micropores in the material reduce the the shock melting pressure obviously. The Exact shock melting pressure of dense Sn needs further experimental data in the corresponding pressure zone. From the longitudinal velocity of porous Sn in the measured solid zone, no bcc phase transition takes place for this material. This may relate with the micropores in the material or the difference in material component, which needs further investigating.
Optical properties of graphene plasmons and their potential applications
Authors: Yang Xiao-Xia  , Kong Xiang-Tian  , Dai Qing  ,   National Center for Nanoscience and Technology, Beijing 100190, China
Published: December 2020

Graphene plasmons have aroused a great deal of research interest in recent years due to their unique features such as electrical tunability, ultra-strong field confinement and relatively low intrinsic damping. In this review paper, we summarize the fundamental optical properties of localized and propagating plasmons supported by graphene, and the experimental techniques for excitation and detection of them, with focusing on their dispersion relations and plasmon-phonon coupling mechanism. In general, the dispersion of graphene plasmons is affected by the Fermi level of graphene and the dielectric environment. The graphene plasmons can exist in a broad spectrum range from mid-infrared to terahertz. This has been experimentally verified for both the localized and propagation plasmons in graphene. On the one hand, the excitation frequency and confinement of localized plasmons supported by graphene micro/nano-structures are constrained by the structural geometry. Additionally, influenced from the tunability of the optical conductivity of graphene, the excitation frequency of graphene plasmons can be tuned by electrostatic or chemical doping. On the other hand, propagating plasmons have been launched and detected by using scattering-type scanning near-field optical microscopy. This technique provides the real-space imaging of the electromagnetic fields of plasmons, thereby directly confirming the existence of the graphene plasmons and verifying their properties predicted theoretically. In a similar regime, the launching and controlling of the propagating plasmons have also been demonstrated by using resonant metal antennas. Compared to metal plasmons, graphene plasmons are much more easily affected by the surroundings due to their scattering from impurity charges and coupling with substrate phonons. In particular, graphene plasmons can hybridize strongly with substrate phonons and there are a series of effects on plasmon properties such as resonance frequency, intensity and plasmon lifetime. The designing of the dielectric surrounding can effectively manipulate the graphene plasmons. Finally, we review the emerging applications of graphene plasmon in the mid-infrared and terahertz, such as electro-optical modulators and enhanced mid-infrared spectroscopy.
Effect of thermal annealing on the structure and properties of plasma enhanced chemical vapor deposited SiCOH film
Authors: Tan Zai-Shang  , Wu Xiao-Meng  , Fan Zhong-Yong  , Ding Shi-Jin  ,   Department of Materials Science, Fudan University, Shanghai 200433, China;,   School of Microelectronics, State Key Laboratory of ASIC and System, Fudan University, Shanghai 200433, China
Published: December 2020

The development of high-performance integrated circuit chips and the shrinkage of feature sizes according to Moore’s law bring forward continuously the requirements for low dielectric constant (low-k) materials with various excellent properties in the back-end-of-the-line (BEOL) interconnect. Porous SiCOH films prepared by plasma enhanced chemical vapor deposition (PECVD) through a porogen approach are widely applied to industry and extensively studied. Thermal annealing is an important process for fabricating the porous low-k films, which has a great influence on film structure as well as properties. SiCOH films are deposited by PECVD using tetraethoxysilane and limonene as precursors, and annealed at 450 ℃ for 1.5 h under nitrogen atmosphere. The evolutions of film structure and properties during thermal annealing are revealed, and the reaction mechanism for structure change is also proposed. Fourier transform inferred spectroscopy and solid state nuclear magnetic resonance results show that the as-deposited film is an organic-inorganic hybrid film composed of various kinds of Si-O-Si, -CHx, Si-O-CH2CH3, etc. The organic component is removed almost completely during thermal annealing, making a porous film with a Si-O-Si inorganic skeleton. The skeleton is also rearranged at the same time. Deconvolution of the Si-O-Si absorption band of the FTIR spectrum reveals that the cage-like Si-O-Si occupies the major part for both as-deposited and annealed films, while the amount of silicon suboxide Si-O-Si decreases and that of network Si-O-Si increases during thermal annealing, making the film more robust. More C=C and Si-C are formed through chemical reactions between Si-H, -CHx and Si-O-CH2-CH3, and crosslinking is further enhanced. Nitrogen adsorption/desorption isothermal measurement reveals that a large number of micropores with diameter less than 2-3 nm are created during thermal annealing, which is consistent with the removal of organic groups and the existence of cage-like Si-O-Si. As a result, both the refractive index and dielectric constant decrease significantly from 1.476 (λ =630 nm) and 3.45 to 1.365 and 2.60, respectively. Because of the increase of C=C after annealing, extinction coefficient and leakage current density increase. Although there is a shrinkage of 14.7% in film thickness and a reduction of mechanical properties after annealing, the Young’s modulus is still larger than 4 GPa. Considering all kinds of properties, the obtained film appears to be a competitive candidate as inter layer dielectrics in the BEOL interconnect of integrated circuits.
Effects of growth angle and solidification rate on crystal growth of precious metal prepared by electron beam floating zone method
Authors: Li Shuang-Ming  , Geng Zhen-Bo  , Hu Rui  , Liu Yi  , Luo Xi-Ming  ,   State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China;,   Kuming Institute of Precious Metals, Kuming 650106, China
Published: December 2020

Precious metals exhibit fascinating properties and extensive applications in chemical engineering, high-temperature measurement, and electronic industry. The microstructures of these metals are generally polycrystalline and the precious metals like Ir and Ru with polycrystalline microstructures are difficult to deform at room temperature. However, the single crystal of precious metal can be well deformed to the final product, and it can be effectively used as a material. In this paper, electron beam floating zone method (EBFZM) is employed to prepare single crystals of precious metals, due to the fact that precious metals, e. g. Ir and Ru have high melting points of 2443 ℃ and 2310 ℃ respectively, and no crucible can be used for this processing. Considering the fact that the height of floating zone plays a key role in EBFZM, we deduce the expression for height of floating zone in EBFZM based on pedestal growth and zone melting techniques. The effects of crystal growth angle, interface growth mechanism, and solidification rate on the height of floating zone are discussed. The results show that the heights of floating zone for six precious metals are in a sequence order of Ru >Pd >Ir >Pt >Ag >Au. The crystal growth angles of these metals are calculated in a range of 8.4°-10.7°. For the same growth angle, the heights of floating zone, calculated by the Pedestal growth, zone melting and Czochralski-like growth techniques, are close to each other. But for different growth angles, the height of floating zone increases with increasing the growth angle for pedestal growth and Czochralski-like growth techniques, different from zone melting technique. Meanwhile, the height of floating zone changes with interface growth mechanism and solidification rate. For the pedestal growth technique, the height of floating zone is low for continuous growth mechanism, and for zone melting technique, its height of floating zone, calculated from continuous growth mechanism, is larger than those from the dislocation and faceting growth mechanisms. Furthermore, it reveals that the growth angle and height of floating zone vary slightly with continuous growth mechanism. In addition, a predicted solidification rate of 2.4 mm/min, available for single-crystal growth of precious metals, is in agreement with the previous experimental results of single crystals Ir and Ru prepared by EBFZM.
Fluorescence resonance energy transfer in a aqueous system of CdTe quantum dots and Rhodamine B with two-photon excitation
Authors: Li Mu-Ye  , Li Fang  , Wei Lai  , He Zhi-Cong  , Zhang Jun-Pei  , Han Jun-Bo  , Lu Pei-Xiang  ,   Laboratory of Optical Information and Technology, School of Science, Wuhan Institute of Technology, Wuhan 430073, China;,   School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China;,   Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Fluorescence resonance energy transfer (FRET) is non-radiation energy transfer that occurs between a donor (D) molecule in an excited state and an acceptor (A) molecule in a ground state by dipole-dipole interactions. The efficiency of FRET is dependent on the extent of spectral overlap between the donor photoluminescence peak and the absorption spectrum of acceptor, the quantum yield of the donor, and the distance between the donor and acceptor molecules. Currently, FRET is commonly used for determining the metal ion, analyzing the protein, biological molecular fluorescence probe, etc. In this study, the FRET between CdTe quantum dots (QDs) with different sizes and Rhodamine B (RhB) in aqueous solution is investigated by using the time-resolved fluorescence test system under two-photon excitation. In this two-photon FRET aqueous system, QD is used as donor while RhB as acceptor. The time resolved two-photon photoluminescence and fluorescence lifetime measurements are performed for analyzing the two-photon-excited luminescence by using a titanium sapphire femtosecond laser with a wavelength of 800 nm, pulse width of 130 fs, repetition frequency of 76 MHz, with the power fixed at 500 mW. The fluorescence spectrum is measured by fluorescence spectrometer and the fluorescence decay curves are recorded by single photon counter. Besides, the steady state photoluminescence is also studied with a JASCO FP-6500 Fluorescence Spectrometer. The result shows that with the increase of spectral overlap of the CdTe emission spectrum and the Rhodamine B absorption spectrum, the FRET efficiency of the QDs-RhB system becomes higher. Specifically, the fluorescence intensity of QDs decreases and the lifetime of QDs becomes shorter while RhB shows the opposite tendency. By means of the Förster theory of energy transfer, the spectral overlap integral J(λ), Foster radius R0 and the FRET efficiency E are calculated and the FRET characteristics of QD-RhB system is characterized. Theoretical analysis reveals that the physical source is the increase of the sample’s Forster radius. Moreover, the relationship between the ratio of acceptor/donor concentration and the FRET efficiency is investigated experimentally. When the ratio of acceptor/donor concentration increases, the lifetime of QDs turns shorter, and the FRET efficiency of the QDs-RhB system becomes higher. The two-photon excited FRET efficiency can reach 40.1% when the concentration of RhB is 3.0×10-5 mol·L-1. This study shows a brighter future in biological and optoelectronic applications.