bluuebunny/crossref_metadata_2025 huggingface dataset:
Explanation of Cr-C eutectic points using the cluster-plus-glue-atom model
Authors: Wang Tong  , Hu Xiao-Gang  , Wu Ai-Min  , Lin Guo-Qiang  , Yu Xue-Wen  , Dong Chuang  ,   Key Laboratory of Materials Modification by Laser, Ion and Electron Beams Ministry of Education, Dalian University of Technology, Dalian 116024, China;,   Dalian Nano-Crystal Tech Co. Ltd, Dalian 116600, China
Published: December 2020

Cr-C system is an important protective coating material for its high hardness, good corrosion resistance and electrical conductivity. It is also a typical eutectic system, where all stable phases are involved in the eutectic reactions. According to our previous work, binary eutectic liquids satisfy the dual-cluster short-range-order structural model, i.e., a eutectic liquid is composed of two stable liquid subunits respectively issued from the two eutectic phases and each one formulates the same ideal metallic glass [cluster] (glue atom)1 or 3, where the nearest-neighbor cluster is derived from a devitrification phase. Therefore a eutectic liquid can always be formulated as two nearest-neighbor clusters plus two, four, or six glue atoms. The key step towards understanding a eutectic composition is then to obtain the right clusters from the two eutectic phases for use in the formulation of the glassy/eutectic composition, which we call the principal clusters. In this paper, Friedel oscillation and atomic dense packing theories are adopted to identify the principal clusters of Cr-C eutectic phases for the objective of establishing the dual cluster formulas for the eutectic compositions. First, clusters in eutectic phases Cr, Cr23C6, Cr7C3 and Cr3C2 are defined by assuming that all the nearest neighbors are located within the first negative potential minimum zone in Friedel oscillation, which causes a cutoff distance to be less than 1.5 times the innermost shell distance. Second, by comparing all the radial distribution profiles of total atomic density centered by each cluster in a given phase structure, the one exhibiting the most distinct spherical periodicity feature is selected as the principal cluster. Moreover, the principal clusters are the most separated from each other among all the clusters in the same phase, showing the highest degree of cluster isolation. Under the criteria of the cluster distribution following spherical periodicity order and of the cluster isolation, the following principal clusters are derived: rhombidodecahedron CN14 [Cr-Cr14] from Cr, capped trigonal prism CN9 [C-Cr9] from Cr23C6 and Cr7C3, and [C-Cr8] from Cr3C2. Via these examples, the principal cluster identification procedures are detailed. Third, the thus selected principal clusters are matched with appropriate glue atoms to construct the dual cluster formulas for the Cr-C eutectics Cr86C14 and Cr67.4C32.6, i.e., [Cr-Cr14+C-Cr9]CrC3Cr86.2C13.8 and [C-Cr9+C-Cr8]C6Cr68.0C32.0, respectively. This work proves the universality of the cluster-plus-glue-atom model in explaining the composition of binary eutectics and lays a theoretical foundation for the composition design of Cr-C based materials.
Comprehensive evaluation and analysis of the weighted-sum-of-gray-gases radiation model
Authors: Chu Hua-Qiang  , Feng Yan  , Cao Wen-Jian  , Ren Fei  , Gu Ming-Yan  ,   School of Energy and Environment, Anhui University of Technology, Ma'anshan 243002, China;,   Key Laboratory of Metallurgical Emission Reduction and Resources Recycling of Ministry of Education, Anhui University of Technology, Ma'anshan 243002, China
Published: December 2020

In oxy-fuel combustion with CO2 recycle, the non-gray gas radiative heat transfer characteristics of gaseous participating media are different from those in air-fuel combustion. Therefore, the choice of a non-gray gas radiation model should be carefully made since it plays an important role in modeling the oxy-fuel combustion system. Using the statistical narrow-band model as a benchmark, in this paper we provide a comprehensive assessment of the development of the weighted-sum-of-gray-gase (WSGG) model, which has been achieved in recent years. The results show that the predicted values obtained by the WSGG model are generally reasonably accurate, though some significant differences still exist. For the total emissivity, the WSGG models by Dorigon et al. (2013 Int. J. Heat Mass Transfer 64 863) and Bordbar et al. (2014 Combust. Flame 161 2435) are consistent well with the benchmark model, within a relative error of less than about 20%. Under the conditions of PH2O/PCO2=1 and 2, the magnitudes of radiative heat transfer between two planar plates are calculated using the discrete-ordinate method and WSGG model. It is found that the radiative source and radiative net heat flux obtained using the WSGG model parameters of Dorigon et al. and Bordbar et al. are more accurate than using other parameters developed in the literature (about 10% relative errors). It is worth noting that the WSGG model parameters of Jonhansson et al. (2011 Combust. Flame 158 893) and Bordbar et al. have a wider range of applications.
Low-frequency wide-band mechanism of a new type acoustic metamaterial with negative modulus
Authors: Zhang Yong-Yan  , Wu Jiu-Hui  , Zhong Hong-Min  ,   School of Mechanical Engineering and State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an 710049, China;,   School of Mechanical Engineering, Sichuan University of Science and Engineering, Zigong 643000, China
Published: December 2020

In this paper, a new type of acoustic metamaterial with negative modulus is proposed, and the formation and broadening mechanism of the low frequency bandgap are revealed. The expression of the normalized effective modulus of the structure is derived theoretically. Since the zero value of the effective modulus is closely related to the system parameters, the appropriate parameters can be adjusted to reduce the zero point, and the lower bound of the bandgap is reduced, thus the low-frequency bandgap is realized. The theoretical results show that the elastic modulus of the system is negative and the region of the negative modulus is widened in a certain frequency range, therefore, the widening of the bandgap can be realized through the enlargement of the negative modulus region. This new mechanism for achieving low-frequency bandgap overcomes the shortcomings both in the traditional local resonance with too large additional mass, and in the inertial amplification structures with narrow bandgaps. At the same time, the transmission of this periodic structure obtained by the finite element method is highly consistent with that by the theoretical analysis, with a low-frequency band of 40-180 Hz, from which the new mechanism presented here is verified. This new idea of achieving low-frequency bandgap is of great theoretical significance for controlling low-frequency sound waves.
Dynamic instability of super-long elastic rod in viscous fluid
Authors: Wang Peng  , Xue Yun  , Lou Zhi-Mei  ,   School of Civil Engineering and Architecture, University of Jinan, Jinan 250022, China;,   School of Mechanical Engineering, Shanghai Institute of Technology, Shanghai 201418, China;,   Department of Physics, Shaoxing University, Shaoxing 312000, China
Published: December 2020

The external environment affects the structural form of biological system. Many biological systems are surrounded by cell solutions, such as DNA and bacteria. The solution will offer a viscous resistance as the biological system moves in the viscous fluid. How does the viscous resistance affect the stability of biological system and what mode will be selected after instability? In this paper, we establish a super-long elastic rod model which contains the viscous resistance to model this phenomenon. The stability and instability of the super-long elastic rod in the viscous fluid are studied. The dynamic equations of motion of the super-long elastic rod in viscous fluid are given based on the Kirchhoff dynamic analogy. Then a coordinate basis vector perturbation scheme is reviewed. According to the new perturbation method, we obtain the first order perturbation representation of super-long elastic rod dynamic equation in the viscous fluid, which is a group of the second order linear partial differential equations. The stability of the super-long elastic rod can be determined by analyzing the solutions of the second order linear partial differential equations. The results are applied to a twisted planar DNA ring. The stability criterion of the twisted planar DNA ring and its critical region are obtained. The results show that the viscous resistance has no effect on the stability of super-long elastic rod dynamics, but affects its instability. The mode selection and the influence of the viscous resistance on the instability of DNA ring are discussed. The amplitude of the elastic loop becomes smaller under the influence of the viscous resistance, and a bifurcation occurs. The mode number of instability of DNA loop becomes bigger with the increase of viscous resistance.
Time-resolved spectra and measurements of temperature and electron density of laser induced nitrogen plasma
Authors: Yang Wen-Bin  , Zhou Jiang-Ning  , Li Bin-Cheng  , Xing Ting-Wen  ,   The Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

As an important analytical tool, laser-induced breakdown spectroscopy (LIBS) has been widely used in material analysis, environmental monitoring, and other fields. In recent years, due to increasingly serious air pollution, various LIBS-based on-line air pollution detection techniques are being developed. The temporal evolution of nitrogen plasma characteristics is of great importance for investigating the atmospheric plasma dynamics and developing the LIBS-based air pollution monitoring techniques. Temperature and electron density, which are the most important parameters of a plasma state, directly influence the kinetic behaviors of plasma formation, expansion and degradation processes, as well as the energy transfer efficiency in plasma. In this paper, the temporal evolutions of continuous background radiation, molecular spectral strength, and signal-to-background ratio (SBR) are studied based on time-resolved spectra. The results show that the lifetime of the continuous background radiation is about 700 ns, the N2+(B2u+-X2g+, v: 0-0) transition line strength reaches a maximum value within 12-15 s, the SBR first increases and then stabilizes. Accordingly, the optimal observation period for N2+(B2u+-X2g+) band system based plasma temperature investigation should be selected to be between 10 and 25 s. The temporal evolution of plasma temperature is determined by fitting experimental spectra to theoretical ones simulated by LIFBASE (a spectral simulation program). As the radiation loss is less than the loss due to the collision cooling, the plasma temperature decays exponentially from ~10000 K to ~6000 K within 10-28 s. By taking into account the instrumental broadening lineshape (Voigt lineshape), the temporal evolutions of Stark broadening and Stark shift of N 746.831 nm atomic line are obtained via Nelder-Mead simplex algorithm, and then the electron density is calculated accordingly. The results show that the electron density decays between 1017 and 1016 cm-3 in magnitude. By comparing the experimental electron decay rate with theoretical values calculated from different mechanisms, it is concluded that a three-body collision recombination is the main mechanism of electron decay.
Analysis of optical scattering of micro-nano particles
Authors: Fu Cheng-Hua  ,   High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China;,   University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The micro-nano-scale science is rapidly developing. In order to study the properties of micro-nano-scale particles by the optical method, we discuss the scattering effects of sub-micrometer wires and sub-micrometer balls on photo-electromagnetic wave in this paper. For the optical scattering of micro-nano-scale particles, the scattering particle size can meet the Mie scattering conditions compared with the incident light wavelength, that is to say, the scatterer and the incident wavelength have comparable size. In this article, the analysis results are clearly displayed in the form of simulation graphs obtained by the Matlab numerical simulation. The Mie scattering analysis method can be used for discussing the scattering of electromagnetic waves in the cases of layered particles which meet the size requirements and any number of scattering particles. Multi-particle scattering is analyzed to investigate the effects of scatterers at different positions on the scattering. By analyzing the differential scattering cross section and the electromagnetic field distribution of near-field scattering related to the scattering light field, we obtain the variation trend of the scattering light field with scattering angle and the effects of various factors on the scattering light field, including the polarization of incident wave, the size of the scatterer, the structure of scattering particles, the number of particles, the number of scattering particles, and some hidden factors such as the relative refractive index of scatterer and surrounding medium. The scientific significance of the paper is reflected through the fact that the sub-micron scale particle can be used as a sensor of detecting the displacement, which can be realized by optical means. So it has a certain reference value for studying the influence of particle own characteristic on the scattering light, thereby rendering the optical readout of the mechanical displacement very accurate. The obtained results have a guiding significance for studying the optical detection of mechanical vibrations of sub-micron wires.
Influence of filler content on trap and space charge properties of epoxy resin nanocomposites
Authors: Yuan Duan-Lei  , Min Dao-Min  , Huang Yin  , Xie Dong-Ri  , Wang Hai-Yan  , Yang Fang  , Zhu Zhi-Hao  , Fei Xiang  , Li Sheng-Tao  ,   Pinggao Group Co. LTD., Pingdingshan 467001, China;,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Epoxy resin nanocomposites have excellent properties such as the suppression of space charge accumulation, high resistivity, and high electrical breakdown strength, which play an important role in developing the direct current power equipment. However, the influencing mechanisms of filler content on trap, conductivity, and space charge of nanocomposites have not been clear to date. In the present paper, a method to calculate the densities of shallow traps and deep traps in interaction zones is proposed based on the multi-region structure model of interaction zones, and the dependence of shallow traps and deep traps on filler content is obtained. It is found that the shallow trap density increases with the increase of filler content, while the deep trap density first increases and then decreases with increasing the filler content, which is caused by the overlap of interaction zones. Then, the relation between the shallow trap controlled carrier mobility and the filler content is investigated. With the filler content increasing, the density of shallow traps increases and their mean distance decreases, leading to an increase in the shallow trap controlled carrier mobility.
Considering the charge injection from cathode into dielectrics, carrier hopping in shallow traps, charge trapping into and detrapping from deep traps, a unipolar charge transport model is established to study the conductivity and distributions of space charges and electric field in epoxy resin nanocomposites. At relatively low filler content, the charge transport is dominated by deep traps in interaction zones and the conductivity decreases with the increase of filler content. However, the charge transport is determined by shallow traps at relatively high filler content and the conductivity increases.
Low temperature depositions of GaN thin films by plasma-enhanced atomic layer deposition
Authors: Tang Wen-Hui  , Liu Bang-Wu  , Zhang Bo-Cheng  , Li Min  , Xia Yang  ,   School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266000, China;,   Institute of Microelectronics of Chinese Academy of Sciences, Beijing 100029, China;,   Jiaxing Microelectronic Equipment Research Center, Chinese Academy of Sciences, Jiaxing 314006, China
Published: December 2020

Metalorganic chemical vapour deposition and molecular beam epitaxy have already been demonstrated to be successful techniques for obtaining high-quality epitaxial GaN layers with low impurity concentrations and pretty good electrical properties. However, high growth temperature employed in both of these methods give rise to some intrinsic defects of the thin films, such as high background-carrier concentrations. As a low-temperature thin film deposition method, plasma-enhanced atomic layer deposition (PE-ALD) has more unique advantages compared to both methods for epitaxial growth of GaN. In this paper, the polycrystalline GaN thin films were fabricated on Si (100) substrates at 150-300℃ by PE-ALD. Trimethylgallium and N2/H2 plasma gas mixture were used as the Ga and N precursors. The growth rate of the thin films was demonstrated by the spectroscopic ellipsometer. The crystal structrue and composition of the GaN thin films were characterized by X-ray diffractometer and X-ray photoelectron spectrometer (XPS). It is showed that the growth window for PE-ALD grown GaN thin films is 210-270℃, where the growth rate remains constant at 0.70 /cycle. And it is known that it is the self-limiting nature of PE-ALD that is ascribed to the plateau of the growth rate. Films grown at relatively higher temperature are polycrystalline with a hexagonal wurtzite structure, while films grown under relatively lower temperature are amorphous. The grazing incidence X-ray diffraction (GIXRD) patterns of the polycrystalline thin films reveal three main peaks located at 2=32.4, 34.6 and 36.9, which are corresponding to the (100), (002) and (101) reflections. It is showed that the Ga, N atoms would get higher energy for more effective migration to positions with lowest energy to form ordered crystalline arrange at higher growth temperature. The XPS results show that all the N elements of the as-grown thin films are in the form of NGa bond, indicating that all the N elements are formed into GaN thin films; and there is a little amount of the Ga elements that exist in GaO bond. The fact that there is no Ga2O3-related peaks in the GIXRD pattern suggests that there is small amount of amorphous Ga2O3 dispersed in the polycrystalline GaN thin films. In the future work, reducing the concentration of the C and O impurities may be achieved by increasing the time of the reaction and plasma pules in the process formula and replacing the inductively coupled plasma with the hollow cathode plasma, respectively.
Three-dimensional simulations and analyses of spherical hohlraum experiments on SGⅢ laser facility
Authors: Li Shu  , Chen Yao-Hua  , Ji Zhi-Cheng  , Zhang Ming-Yu  , Ren Guo-Li  , Huo Wen-Yi  , Yan Wei-Hua  , Han Xiao-Ying  , Li Zhi-Chao  , Liu Jie  , Lan Ke  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Center for Applied Physics and Technology, Peking University, Beijing 100871, China;,   Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

A new type of laser fusion indirect drive octahedral spherical hohlraum has been built up by Chinese researchers in recent years. The hohlraum with 6 laser entrance holes (LEHs) has superiority over other hohlraum configurations in both robust inherent high symmetry and high coupling energy efficiency from laser to hotspot for inertial confinement fusion study. Recently, an experimental investigation on radiation emission from the spherical hohlraum with two LEHs has been performed on the SGⅢ laser facility. In this experiment, 32 laser beams (24 beams from the top, 8 beams from the bottom) are injected into the hohlraum within 3 ns, and the total laser energy is 86.4 kJ. The hohlraum radius is 1.8 mm, and the radius of laser entrance hole is 0.6 mm. The experiments are conducted under two conditions:one is that a 0.48-radius capsule is located at the center of the hohlraum, and the other is that nothing is located in the hohlraum. Some flat response X-ray detectors (FXRDs) are installed at different angles on the target wall to collect the radiation energy. We carry out three-dimensional (3D) simulations of the experiment by using our 3D radiation implicit Monte Carlo code IMC3D. This code was developed in recent years based on fleck and Cumming's ideas. The hydrodynamics is not taken into consideration in the simulations, so we deduct 30% laser energy lost to hohlraum wall movements and back scattered by laser plasma instabilities. Based on the approximation, the simulation results are reasonable in principle. As a result, the radiation temperature of the hohlraum with capsule is 230 eV, and the radiation temperature of the hohlraum without capsule is 238 eV. At the end of laser injection, the capsule reflection ratio is 0.83. Compared with the experimental data, most of the simulation data agree well with the detector observations, except the data at 0 angle. The possible reasons for the difference are analyzed. The flux at 0 angle is more sensitive to the wall plasma movements than at the other angles. So if we ignore this phenomenon, then the witch will occur both in experiment and in simulation, yielding obvious differences for those quantities which strongly relate to the hydrodynamics of wall plasma. Finally, the methods of eliminating the difference are proposed and the prospect of IMC3D is presented.
Low-energy ion beam modified surface property and mechanism of high temperature superconductor YBa2Cu3O7- thin film
Authors: Wang San-Sheng  , Li Fang  , Wu Han  , Zhang Zhu-Li  , Jiang Wen  , Zhao Peng  ,   Key Laboratory of Micro-nano Measurement, Manipulation and Physics, Ministry of Education, Beihang University, Beijing 100191, China;,   Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China
Published: December 2020

The interaction between ion beam and solid target is widely used in material modification. For the high temperature superconducting thin film modification, however, earlier experiments show that the samples are accompanied by the degradation in superconducting properties due to the structural damage of materials. In order to improve surface morphologies and superconducting properties of YBa2Cu3O7- (YBCO) thin films, we introduce a new ion beam structure modification (ISM) method. Although the ion bombardment time parameter effect is not clear, the related mechanism should be clarified. In this paper, the bombardment processes with duration times of 8 min, 10 min and 12 min are investigated in a vacuum chamber with an Ar+ Kaufman ion source, and the direction between the incident ion beam and the normal of sample is fixed at a certain angle. Surface morphologies and the microstructures of YBCO samples are characterized by scanning electron micrographs and X-ray diffraction patterns, respectively. In the respect of superconducting properties, the critical current density Jc is measured by Jc-scanning test. The results indicate that the needle-like a-axis grains and pores disappear gradually with the increase of the ion bombardment time. In order to characterize the effects of ion beam bombardment time on the internal strain in YBCO thin films, the relationship between the full width at half maximum and the Bragg diffraction angle of YBCO (00l) peak is studied by the William-Hall equation. The results show that the internal strain in YBCO thin film increases with increasing the ion beam bombardment time. At the same time, the critical current density Jc value of the sample after ISM processing increases, which is more than 2.2 times higher than that of the initial sample. The main reason for the increases of critical current density Jc in YBCO thin film is due to the drastic shrink of CuO bond caused by the increasing internal strain. Based on the bond contraction pair theory, the shrink of CuO bond improves the energy to break Cooper-pairs, and then increases the current carrying capacity of high temperature superconducting YBCO thin film, especially in copper-oxygen (CuO2) plane. The ISM process might be a useful method of markedly improving the surface morphology, meanwhile, the critical current density Jc value also increases in high temperature superconducting YBCO thin film.
Experimental study of electromagnetic wave transmission characteristics in S-Ka band in plasma
Authors: Ma Hao-Jun  , Wang Guo-Lin  , Luo Jie  , Liu Li-Ping  , Pan De-Xian  , Zhang Jun  , Xing Ying-Li  , Tang Fei  ,   Hypervelocity Aerodynamics Institute, China Aerodynamics Research and Development Center, Mianyang 621000, China
Published: December 2020

When hypersonic vehicle flies in the atmosphere at a high altitude with a high speed, plasma sheath is generated around the vehicle, and thus attenuating the electromagnetic wave signals and even interrupting the communication. Therefore the control, guidance, and navigation of hypersonic vehicle can be affected seriously by the plasma sheath. It is necessary to study this problem in reasonable ground experiment.
The inductively coupled plasma (ICP) wind tunnel is an ideal equipment for studying electromagnetic transmission characteristics in plasma because it can produce uncontaminated plasma and the electrode cannot be ablated in the process of plasma production. We carry out the experiment in ICP wind tunnel. A thin slice of plasma jet is generated by a rectangular nozzle with an outlet size of m 50 mm250 mm. Plasma jets with different parameters are obtained by adjusting the operating power and inlet flow of the wind tunnel. Four kinds of states are provided with the electron densities of 7.01010, 5.01011, 3.51012 and 1.01013/cm3, and the collision frequencies of 1.5109, 1.6109, 2.0109 and 9.0109 Hz, respectively.
The amplitude attenuations and phase changes of the electromagnetic waves are measured with microwave diagnostics system consisting of a vector network analyzer and high gain antennas. And electron density and collision frequency of plasma are obtained according to the transmission characteristics of electromagnetic waves in plasma.
The attenuations of the electromagnetic wave in plasmas of different states are measured via microwave transmission system which is composed of a vector network analyzer and pairs of horn antennas covering a frequency range of 2.6-40 GHz. The results show that both the amplitude attenuation and attenuation band increase with the increase of electron density. The classical theory and thin layer theory are used to simulate the transmission attenuation. The results are compared with the experimental ones. The results in this paper provide basic data for further theoretical and numerical study of electromagnetic wave transmission characteristics in plasma.
Theoretical models and experiments for the time-space characteristics of internal waves generated by towed bodies
Authors: Chen Ke  , Wang Hong-Wei  , Sheng Li  , You Yun-Xiang  ,   State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;,   Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China;,   China Ship Development and Design Center(Shanghai), Shanghai 201108, China;,   No. 92537 Unit of PLA, Beijing 100161, China
Published: December 2020

In this paper, we perform experiments on the time-space characteristics of internal waves generated by horizontally towed bodies with three aspect ratios in a stratified fluid with a halocline. By the real-time measurements of conductivity probe arrays which are arranged symmetrically in the transverse section of the stratified fluid tank, it is shown that the transition between the body-generated internal wave and the wake-generated internal wave is related to a critical Froude number Frc, which is linearly dependent on the aspect ratio. For FrFrc, the correlation velocities of internal waves are consistent with the towing speeds of the towed bodies, indicating that such internal waves in this range are dominated by the body-forced effect. The heights of such body-generated internal waves first increase with the increase of Fr until Fr reaches a certain value of Frp, which is also linearly dependent on the aspect ratio, and then decrease. For FrFrc, the correlation velocities of internal waves are noticeably lower than the towing speeds, indicating that such internal waves in this range are dominated by the wake-forced effect, and that the Froude numbers with respect to the correlation velocities of such internal waves vary in a range from 0.43 to 1.18. The heights of such wake-generated internal waves nearly linearly increase with Fr increasing regardless of the aspect ratio. Moreover, the patterns of body-generated waves are symmetric, while the patterns of wake-generated waves are not symmetric. Based on the experimental results and the equivalent source method which has been proposed to simulate the internal waves generated by a towed sphere, a new equivalent source method is developed to calculate the internal waves generated by towed slender bodies. For the body-generated waves, the method of designing the speed, length and diameter of the equivalent source is proposed. The symmetrical and anti-symmetrical equivalent source and their speed and size are also proposed for the wake-generated waves. The numerical results are in good accordance with the experimental results in the heights and patterns of waves, indicating that such a theoretical method and its parameter settings are reasonable and effective.
First-principle study on quantum thermal transport in a polythiophene chain
Authors: Wu Yu  , Cai Shao-Hong  , Deng Ming-Sen  , Sun Guang-Yu  , Liu Wen-Jiang  ,   College of Big Data and Information Engineering, Guizhou University, Guiyang 550025, China;,   Institute of Applied Physics, School of Physics and Electronic Science, Guizhou Education University, Guiyang 550018, China;,   Guizhou Provincial Key Laboratory of Computational Nano-material Science, Guizhou Education University, Guiyang 550018, China;,   Guizhou Provincial Key Laboratory of Economic System Simulation, Guizhou University of Finance and Economics, Guiyang 550025, China
Published: December 2020

Bulk polythiophene material is usually regarded as thermal insulator because it has low thermal conductivity (less than 1 Wm-1K-1). However, the report demonstrates that along the amorphous polythiophene nanofiber axis, the pure polythiophene nanofibers have high thermal conductivity (more than 4.4 Wm-1K-1), which is obviously higher than that of the bulk polythiophene material. In order to throw light on this situation, molecular dynamics (MD) method is used to detect the high thermal conductivity of a polythiophene chain. However, the MD method is highly sensitive to the choice of empirical potential function or simulation method. Even if the same potential function (ReaxFF potential function) is adopted, the thermal conductivity of a polythiophene chain could also have obviously different results. To overcome the instability of MD method, we use the first-principles to calculate the force constant tensor. In such a case the properties of quantum mechanics in a polythiophene chain can be reflected. In our algorithm, several disadvantages of MD that different potential functions or different simulation methods probably lead to very different thermal conductivities for the same transport system are avoided. Based on the density functional theory (DFT), the central insertion scheme (CIS) method and nonequilibrium Green's function (NEGF) approach are used to evaluate the isotope effect on thermal transport in a polythiophene chain, which includes 448 atoms in a scattering region and has a length of 25.107 nm. It is found that the thermal conductivity of a 32-nm-long pure polythiophene chain reaches 30.2 Wm-1K-1, which is close to the thermal conductivity of lead at room temperature. The reduction of average thermal conductance caused by C atom impurity is more remarkable than by S for a pure polythiophene chain when the mixing ratios of 13C to 12C and 36S to 32S are equal. The most outstanding isotope effect on quantum thermal transport appears when the mixing ratio of 13C to 12C is 1:1. It will cause the average thermal conductance to decrease by at least 30% in the polythiophene chain at room temperature. Moreover, we find that the thermal conductance of a pure polythiophene chain is inversely proportional to the atomic weight of carbon, and increases nonlinearly with the increasing atomic weight of sulfur. It is of significance to optimize the thermal conductance properties of polythiophene function material.
A new model for the profiles of optical turbulence outer scale and Cn2 on the coast
Authors: Cai Jun  , Li Xue-Bin  , Zhan Guo-Wei  , Wu Peng-Fei  , Xu Chun-Yan  , Qing Chun  , Wu Xiao-Qing  ,   Key Laboratory of Atmospheric Optics, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China;,   Maoming Meteorological Bureau of Guangdong Province, Maoming 525000, China
Published: December 2020

Atmospheric optical turbulence severely restricts the performances of electro-optical systems. The turbulent atmosphere causes the intensity of a light beam to fluctuate or scintillate, leads the light beam to wander and makes the images randomly displace, which directly relates to the refractive index structure parameter Cn2. Therefore the knowledge of Cn2 is essential to evaluate and to predict the effects of optical turbulence on electro-optical imagery systems. During the period from December 13, 2016 to January 2, 2017, 30 sets of sounding data, which include temperatures, humidities, pressures, wind speeds, wind directions and atmospheric refractive index structure parameters, are obtained by using a self-developed meteorological radiosonde for turbulence at Marine Meteorological Science Experiment Base at Bohe of Maoming. On the basis of the HMNSP99 outer scale model, an atmospheric optical turbulence outer scale formula of Maoming is obtained by fitting the sounding data. At the same time, the experimental data of the turbulence profiles are statistically averaged, and then based on the Hufnagel-Valley model, a statistical model is obtained, which is appropriate to the variation of the turbulence profile on the coast. According to Tatarski turbulence parameterization and the Maoming outer scale formula, the new estimated Cn2 values are compared with their experimental observations and the results from other already defined models, respectively. Statistical analysis shows that the overall correlation coefficients of log10(Cn2) between observed values and estimated values by using the new fitting Maoming outer scale formula, the HMNSP99 model, the Dewan model and the Coulman model are 0.924, 0.848, 0.763 and 0.651, respectively. Also, both the trends and magnitudes for these four outer scale models are consistent with each other. The errors of the above four outer scale models are very small:their overall average absolute errors and average relative errors are 0.514 and 2.963%, 0.627 and 3.612%, 0.943 and 5.439%, 0.766 and 4.417%, respectively, and the error of the Maoming outer scale model is smallest. The reliabilities and validities of the new outer scale and Cn2 models are further verified. In addition, it is found that the occurrence of upper air optical turbulence is closely related to wind shear and temperature gradient. The results support the prediction of the atmospheric optical turbulence profile required for electro-optical engineering on the coast.
Lattice scattering in n-type Ge-on-Si based on the unique dual-valley transitions
Authors: Huang Shi-Hao  , Xie Wen-Ming  , Wang Han-Cong  , Lin Guang-Yang  , Wang Jia-Qi  , Huang Wei  , Li Cheng  ,   College of Information Science and Engineering, Fujian University of Technology, Fuzhou 350118, China;,   College of Physical Science and Technology, Xiamen University, Xiamen 361005, China
Published: December 2020

Silicon-based light emitting materials and devices with high efficiency are inarguably the most challenging elements in silicon (Si) photonics. Band-gap engineering approaches, including tensile strain and n-type doping, utilized for tuning germanium (Ge) to an optical gain medium have the potential for realizing monolithic optoelectronic integrated circuit. While previous experimental research has greatly contributed to optical gain and lasing of Ge direct-gap, many efforts were made to reduce lasing threshold, including the understanding of high efficiency luminescence mechanism with tensile strain and n-type doping in Ge. This paper focuses on the theoretical analysis of lattice scattering in n-type Ge-on-Si material based on its unique dual-valley transition for further improving the efficiency luminescence of Ge direct-gap laser. Lattice scattering of carriers, including inter-valley and intra-valley scattering, influence the electron distribution between the direct valley and indirect L valleys in the conduction of n-type Ge-on-Si material. This behavior can be described by theoretical model of quantum mechanics such as perturbation theory. In this paper, the lattice scatterings of intra-valley scattering in valley and L valleys, and of inter-valley scattering between the direct valley and L valleys in the n-type Ge-on-Si materials are exhibited based on its unique dual-valley transition by perturbation theory. The calculated average scattering times for phonon scattering in the cases of valley and L valleys, and for inter-valley optical phonon scattering between valley and L valleys are in agreement with experimental results, which are of significance for understanding the lattice scattering mechanism in the n-type Ge-on-Si material. The numerical calculations show that the disadvantaged inter-valley scattering of electrons from the direct valley to indirect L valleys reduces the electrons dwelling in the direct valley slightly with n-type doping concentration, while the strong inter-valley scattering from the indirect L valleys to indirect valleys increases electrons dwelling in the direct valley with n-type doping concentration. The competition between the two factors leads to an increasing electrons dwelling in the direct valley with n-type doping in a range from 1017 cm-3 to 1019 cm-3. That the electrons in the indirect L valleys are transited into the direct valley by absorbing inter-valley optical phonon modes is one of the effective ways to enhance the efficiency luminescence of Ge direct-gap laser. The results indicate that a low-threshold Ge-on-Si laser can be further improved by engineering the inter-valley scattering for enhancing the electrons dwelling in the valley.
A thermodynamic model of grain-grain contact force
Authors: Jiang Yi-Min  , Liu Mario  ,   School of Physics and Electronics, Central South University, Changsha 410083, China;,   Theoretische Physik, Universität Tübingen, Tübingen 72076, Germany
Published: December 2020

The starting premise of any soft discrete element method simulation, widely used in granular physics and granular mechanics, is the modelling of grain-grain contact force. Most of models often used in the literature including the famous ones by Hertz-Mindlin and Luding, do not present the algorigthy of total elastic potential, or the rate of dissipation which is mainly due to the partially frictional character of the forces. This renders the question of thermodynamic consistency unsettled. A model that possesses explicit expressions for both is proposed here. It is conceptually closely related to the continuum-mechanical theory of granular solid hydrodynarmics (GSH). This theory contains expressions for the total elastic potential and the thermal energy, it accounts for energy conservation and the positivity of entropy production, and it clarifies the equilibrium properties of granular media. All these are lacking (or hidden) in the contact models widely used in the literature. A preliminary calculation shows that the restitution coefficient varies with the impact velocity, which is an added bonus, and demonstrates the model's increased realism. For simplicity, the equations presented in this work are limited to the 2D-case and neglect granular rotations. Nevertheless, the generalization to the 3D-case and the inclusion of granular rotations are carefully discussed, clarifying how to treat rolling and the torsional forces in a thermodynamically consistent fashion. A key point of the present approach, and the major difference to other force models, is the fact that, starting from the characteristic thermodynamic potential, we employ the Onsager reciprocity relation to set up the transport coefficients. The contact forces (usually postulated) are then derived from them. This difference is both conceptually and methodologically relevant. We discussed in detail off-diagonal transport coefficients, especially the so called gear ratio that is particular to granular matter. It reflects the difference between the elastic and the total strain, and is closely related to the slip movement of contact surface, which occur during shear, rolling and torsional deformations. It is relevant to both the macroscopic GSH scales, and the mesoscopic granular scale.
Numerical simulation of a spinning sphere moving in granular matter
Authors: Cheng Qi  , Ran Xian-Wen  , Liu Ping  , Tang Wen-Hui  , Raphael Blumenfeld  ,   Institute of Engineering Physics, College of Science, National University of Defence Technology, Changsha 410073, China;,   Cavendish Laboratory, University of Cambridge, Cambridge CB30HE, The United Kingdom
Published: December 2020

Recently, how the desert lizards run, hide or swim in the sand has attracted much attention of many scientists in granular matter field, and many valuable results have been published, except for the Phrynocephalus mystaceus, a type of the desert lizard, which can embeds itself into the sand through a motion mode which is completely different from other types of desert lizards. To illuminate the roles played by the spinning-mode in the Phrynocephalus mystaceus' motion in the sand, the three-dimentional (3D) numerical simulation using the Hertz model on the system, in which one sphere is spinning in the granular matter, is carried out with the open-source code LIGGGHTS released by the Sandia National Laboratory in USA. In the numerical simulations for all the cases, the initial conditions are the same and the sphere spins around X-axis while the X-Y plane is the horizontal plan and the Z axis is the vertical direction. According to the numerical results and analyses, for the spinning sphere deeply embedded in the granular matter we can draw some conclusions. 1) The X-axis spinning motion can cause the sphere embedded in the granular to notably displace along the Z-axis and Y-axis, but the displacement along the spinning direction is smaller than the sphere diameter. 2) The friction coefficient between the sphere and the granular matter has a notable influence on the motion of the sphere in granular matter, the spinning sphere can move vertically and horizontally only when the friction coefficient between the sphere and the granular matter is larger than that of the granular matter; and the bigger the , the more violent the movement of the sphere is. This can be used to explain why most of the desert creatures each have a coarse skin. 3) On the premise that the friction coefficient between the sphere and the granular matter is larger than that of the granular matter, the spinning velocity of the sphere also has a great influence on the movement of the sphere in the granular matter. In a spinning velocity range between 10 rad/s and 640 rad/s, the larger the , the more obvious the movement of the sphere is. When the spinning velocity reaches 1280 rad/s, the movement of the sphere slightly decreases compared with when the spinning velocity is 640 rad/s. 4) For the spining sphere in granular matter, the sphere always moves upward in the Z direction, but in the Y direction the sphere may move in a positive or negative direction depending on the and . The sphere moves in the positive direction of Y axis if the and are relatively small, while it moves in the negative direction if the and are larger.
Thrust density characteristics of ion thruster
Authors: Long Jian-Fei  , Zhang Tian-Ping  , Yang Wei  , Sun Ming-Ming  , Jia Yan-Hui  , Liu Ming-Zheng  ,   Key Laboratory of Science and Technology on Vacuum Technology and Physics, Lanzhou Institute of Physics, Lanzhou 730000, China
Published: December 2020

Thrust density distribution of ion thruster is an important factor that affects the orbit correction and station keeping of the spacecraft. Current empirical models mainly concern themselves with the overall thrust of the ion thruster, yet the thrust density distribution has not been fully understood. Hence it is necessary to investigate the thrust density characteristics of the ion thruster to devise the approach to optimizing the thruster performances. In this study, the thrust density characteristics of the ion thruster is analyzed and discussed by combining the empirical and theoretical methods. An ion thruster utilizes biased grids to extract ions from discharge chamber and accelerate them to high velocities, thereby forming a beam and generating thrust. In this paper, we analyze the working process of the ion thruster. The thrust expression as a function of beam micro-particle parameters is presented. Meanwhile the transport process of the plasma in the beam stream is simulated by the particle in cell-Monte Carlo (PIC-MCC) method for two-grid optics. The motion behavior of ions is modeled by the PIC method, while the collisions of particles are modeled by the MCC method. In the simulation, the particle trajectories are traced and the micro information about ejected charged ions is recorded with respect to singly charged ion, doubly charged ion and charge exchanged (CEX) ion. By analyzing the density and axial velocity of the charged particles in the beam stream, the thrust of the beam from a single grid hole can be calculated, based on which the thrust distribution of the thruster can be inferred by considering the distribution of plasma density at the exit of discharge chamber. Moreover, the above theoretical analysis of the thrust density is tested experimentally. The studies show that the thrust contribution percentages of the singly charged ion, doubly charged ion and CEX ion in the beam current are 84.63%, 15.35%, and 1.82%, respectively. Apparently, the main contributions to the thrust are made by the singly charged ions and doubly charged ions in the beam plasma, while the CEX ions have a trivial effect on the variation of the thrust. The distribution of the thrust density shows good symmetry along the central axis and it levels off after a fast decline in the radial direction. Comparisons of empirical and numerical results with the experimental results show that the empirical results have an error of about 4.1% and the numerical results have an error of about 2.8%. This indicates that the computational accuracy of our numerical model is better than that of the empirical model This work provides a reference for optimizing the thrust density uniformity of an ion thruster.