bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy transfer and dissipation in vibrational granular bed
Authors: Liu Chuan-Ping  , Wang Li  , Zhang Fu-Weng  ,   School of Mechanical Engineering, University of Science and Technology, Beijing 100083, China;,   Beijing Engineering Research Center for Energy Saving and Environmental Protection, Beijing 100083, China
Published: December 2020

By using numerical simulation, the kinetic energy/temperature, the energy dissipation and the volume fraction in a 1D vertical vibrational bed are studied. Discrete element simulation shows that the granular bed moves up and down as an ensemble and the kinetic energy of the particles increases along the bed height when the bed bottom vibrates at a low-frequency and low-amplitude. For high-frequency vibrations, the particles in the bed move randomly and their kinetic energy decreases along the bed height. The energy dissipation and the volume fraction of the particles are also influenced by the vibrations frequency obviously, and they show different distributions at the high and low frequencies. In addition, we have compared the result of the discrete element simulation with that of the hydrodynamic simulation. When the bed bottom vibrates at high frequency, the two simulation methods can get the similar results. However, for the low-frequency and low-amplitude vibrations, the computed results are opposite to each other. Since the particles in the bed do not move and collide randomly, the application of the hydrodynamic simulation to the bed with low-frequency and low-amplitude vibrations should be investigated and discussed further.
First-principles calculations on the electronic and optical properties of ZnO codoped with Cu-Co
Authors: He Jing-Fang  , Zheng Shu-Kai  , Zhou Peng-Li  , Shi Ru-Qian  , Yan Xiao-Bing  ,   College of Electronic and Informational Engineering, Hebei University, Baoding 071002, China
Published: December 2020

The electronic structures and optical properties of intrinsic, Cu, Co doped and Cu-Co codoped ZnO compounds are calculated using first-principles plane-wave ultrasoft pseudopotential method based on the the density functional theory. The results show that the conductivity of ZnO can be improved by doping Cu and Co because of the increase of the carrier concentration under the order of magnitude of doping concentration in this paper. Cu-Co codoping leads to the degeneration and makes ZnO metallic. Thses three kinds of dopings can cause light absorption enhancement phenomenon in the visible and near ultrasoft regions, in which Cu-Co codoping greatly increases the absorption of solar light due to the synergistic effect between Cu ions and Co ions, which can be used to prepare the high efficiency solar cells.
Phase transition, electronic and optical properties of Si3N4 new phases at high pressure with density functional theory
Authors: Yu Ben-Hai  , Chen Dong  ,   College of Physics and Electronic Engineering, Xinyang Normal University, Xinyang 464000, China
Published: December 2020

Characteristics of the hexagonal polymorph Si3N4 i.e., phase transition, electronic and optical properties (band structure, dielectric function, reflectivity and energy loss function) are investigated by the first-principles pseudo-potential method. The results suggest that it is feasible that the P6 transition takes place at room temperature. The critical pressures of the P6 and P6 transformations are 42.9 and 47.7~GPa, respectively. The phase transition from P6 is accompanied by the volume shrinkage. The calculated results also show that the P6 and P6' phases belong to direct bandgap and indirect bandgap semiconductors, respectively. The calculated band gaps are 4.98 and 4.01 eV for the P6 and P6' phases, respectively. Besides, the static dielectric constants are also obtained. The reflectivity shows that the two phases can serve as the shielding and detecting devices for ultraviolet radiation and they have optical transparent behaviors in the visible light region.
Impedance and dielectric spectroscopy analysis of high TC lead-free BaTiO3-(Bi1/2Na1/2)TiO3 positive temperature coefficient resistivity ceramics
Authors: Leng Sen-Lin  , Shi Wei  , Long Yu  , Li Guo-Rong  ,   Department of Physics and Electronic Science, Tongren University, Tongren 554300, China;,   Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Published: December 2020

92 mol%BaTiO3-8 mol% (Bi1/2Na1/2)TiO3 (BBNT8) lead-free positive temperature coefficient resistivity (PTCR) ceramics doped with Y2O3 are prepared by the solid state reaction method. The microstructure of the sample is observed by transmission electron microscope. Results show that the microstructure of the sample mainly consists of grain and grain boundary, and no obvious shell structure is found. The electrical properties of the sample are further analyzed using the impedance spectroscopy. It is found that the total resistance of BBNT8 is composed of the resistances of grain and grain boundary. The resistance of grain is low and slightly changes with temperature when the temperature is above the Curie temperature. The PTCR effect of the material is mainly dominated by the grain boundary resistance. As the temperature increases up to above the Curie temperature, the grain boundary permittivity decreases, leading to the increase of the potential barrier height and the resistivity of the grain boundary. As a result, the distinct PTCR effect takes place. Finally, the room-temperature resistivity of the BBNT8 is studied by measuring the permittivity-frequency characteristics.
Effect of neutron irradiation on the electrical properties of AlGaN/GaN high electron mobility transistors
Authors: Gu Wen-Ping  , Zhang Lin  , Li Qing-Hua  , Qiu Yan-Zhang  , Hao Yue  , Quan Si  , Liu Pan-Zhi  ,   School of Electronic and Control Engineering, Chang'an University, Xi'an 710064, China;,   Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

SiN-passivated AlGaN/GaN high electron mobility transistors (HEMTs) are exposed to 1 MeV neutron at fluences up to 1015 cm-2. The device shows a negligible degradation at neutron fluences below 1014 cm-2, while the gate leakage current (Ig) slightly changes (the forward IF increases, the reverse IR decreases.) at low fluencies and the IR degrades dramatically at fluences higher than 1014 cm-2. Moreover, near the knee voltage, the transconductance decreases at fluences up to 1015 cm-2, but the Schottky characteristicis become degraded after neutron irradiation. And the 20-hour annealing results do not show any significant annealing recovery effect at room temperature, while the parameters also continues to degrade a little. Therefore, the drain current (near the knee voltage) and the IF degradation of SiN-passivated AlGaN/GaN HEMT can be attributed to the irradiation induced defects in SiN passivation layers, demonstrating that the effectiveness of the SiN layer in passivating surface state in the source-gate spacer and gate-drain spacer is undiminished by neutron irradiation. And the Ohmic contact is so relatively robust to neutron, but the Schottky characteristics degrade obviously. The annealing results prove that the damage induced by neutron may be recovered more difficultly. SiN-passivated AlGaN/GaN HEMT appear to be an attractive candidate for space and terrestrial applications where resistance to displacement damage is required.
Influences of post-heat treatment on microstructures, optical and magnetic properties of unintentionally doped GaN epilayers implanted with Mn ions
Authors: Xu Da-Qing  , Zhang Yi-Men  , Lou Yong-Le  , Tong Jun  ,   School of Electrical and Control Engineering, Xi'an University of Science and Technology, Xi'an 710054, China;,   Key Laboratory for Wide Band-Gap Semiconductor Materials and Devices of Ministry of Education, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

In this study, GaN:Mn thin films are fabricated by implementing Mn ions into the undoped GaN material. The effects of annealing temperature on microstructures, optical and magnetic properties of the thin films are investigated. The Raman spectra measured from Mn-implanted GaN samples at different annealing temperatures show that new phonon modes, which are related to macroscopic disorder or vacancy-related defects caused by Mn-ion implantation and the local vibrational mode of Mn atoms in the (Ga, Mn)N, are created. The results of photoluminescence measurement show that new peaks appear at 2.16, 2.53, and 2.92 eV. Among these, the new emission around 2.16 eV, besides some contributions from optical transitions from the conduction band or shallow donor to a deep acceptor, cannot exclude the contribution from optical transitions of free electrons in the conduction band to Mn acceptor level. The Hall test shows that the annealed samples are of n type. Ferromagnetism is observed in the Mn doped GaN thin film at 300 K and found to be sensitive to the density of holes that mediate the Mn-Mn magnetic exchange interaction in this Mn-related impurity band.
Magnetism of MgO nanoparticles
Authors: Fan Wei  , Zeng Zhi  ,   Key Laborarory of Materials Physics, Institute of Solid-State Phyics, Hefei Institutes of Hefei Physical Science, Chinese Academy of Science, Hefei 230031, China
Published: December 2020

MgO polycrystal is found to be weakly magnetic experimentally, although its single crystal is non magnetic. In this work, the magnetic properties of surfaces of crystal and nano-particles of MgO are studied by the first-principles density functional theory. The obtained results show that there are the oxygen-rich regions in all the magnetic surfaces discussed in this work, especially in the (111) surface with pure oxygen layer and the (114) surface with pure oxygen chains. Other surfaces with high Miller indices generally have the oxygen-rich regions. For MgO nano-particles, the facets with high Miller indices and the edges and vertexes formed by different orientation surfaces are oxygen-rich possibly and have strong magnetism. The itinerant magnetism is indentified for the magnetism on the surfaces of MgO crystal and the surfaces of MgO nano-particles. That the special MgO ∑ 7[111] grain boundary is not magnetic means that the magnetism of MgO grain boundary is weak if the chemical composition in grain-boundary region is slightly different from that in the crystal. It can be inferred that the magnetism of MgO polycrystal is mainly contributed by the polycrystal surface, the micro-pores, micro-voids and micro-cracks.
Characterization of typical infrared characteristic peaks of hydrogen in nitrogen and hydrogen co-doped diamond crystals
Authors: Yan Bing-Min  , Jia Xiao-Peng  , Qin Jie-Ming  , Sun Shi-Shuai  , Zhou Zhen-Xiang  , Fang Chao  , Ma Hong-An  ,   State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China;,   College of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

The 3107 cm-1 peak is observed in the infrared absorption spectra of all types of Ia diamonds, but it has not been observed in the iron-based catalyst. A series of nitrogen and hydrogen-doped diamond crystals is successfully synthesized using P3N5 as the nitrogen source in a catalyst-carbon system at a lower pressure and temperature (6.3 GPa, 1500 ℃). Fourier transform infrared micro-spectroscopy reveals that the hydrogen atoms existing in the synthesized diamond are in two forms. The one is attributed to the CH bond stretching (3107 cm-1) and bending (1405 cm-1) vibrations of the vinylidene group (C＝CH2). The other is due to sp3 hybridization CH bond symmetric (2850 cm-1) and anti-symmetric (2920 cm-1) vibrations. According to our result, we find that the 3107 cm-1 hydrogen absorption peak is related to the aggregated nitrogen in synthetic diamond. The 3107 cm-1 peak could not be observed in synthetic diamond without aggregated nitrogen, even if it has a high nitrogen concentration. And the hydrogen absorption peaks at 2920 and 2850 cm-1 are more widespread than the absorption peak at 3107 cm-1, this suggests that the sp3 CH bond more widely exists in diamond than the vinylidene group (C＝CH2). Infrared spectra analysis indicates that the hydrogen impurity mainly exists in the natural diamond as vinylidene group as seen from the absorption peak intensity. We believe that our results provide a new way to study the formation mechanism of the natural diamond. Moreover, the ideal synthesis condition in our system supplies a possible way for us to design n-type diamond semiconductor.
Influence of the cross section area on the conductive characteristics of titanium oxide memristor
Authors: Tian Xiao-Bo  , Xu Hui  , Li Qing-Jiang  ,   School of Electronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The conduction of nano-scale titanium oxide memristor exhibits complex characteristics, owing to the change of self-parameters and the coexistence of different conductive mechanisms. However, there has been no detailed discussion about the influence of the cross section area change on the conductive characteristics of memristor. Based on dopant drift and tunnel barrier mechanisms, the conductive process of memristor is analysed, and the relevance between cross section area and key physical factors of the conductive process is studied, then the influences of the changes of titanium oxide and tunnel barrier cross section area on conductive characteristics of memristors are studied, respectively. The differences and connections between the two cases are analysed. In the case of the coexistence of those two mechanisms, compared with the change of titanium oxide cross section area, the change of tunnel barrier cross section area is proved to be the chief factor which causes changes of memristor conductive characteristics, it is also a possible factor causing the change of non-ideal conductive characteristics of memristor. The research results contribute to further explaining the complexity of memristor conductions and providing basis for optimizing memristor modeling.
Mechanism and characteristic analysis and optimization of SiGeC heterojunction bipolar transistor with super junction
Authors: Liu Jing  , Guo Fei  , Gao Yong  ,   Department of Electronic Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

A novel SiGeC heterojunction bipolar transistor (HTB) with super junction is presented. The effects of SiGeC base and super junction on device performance are analyzed in detail, and current transport mechanism of novel device is studied. Based on SiGeC/Si heterojunction technology, the high frequency characteristic of the novel device can be excellent. The breakdown voltage of device is improved greatly, because of two-dimensional direction of the electric field distribution in the collector region. The results show that the breakdown voltage of SiGeC HBT with super junction is increased by 48.8%, compared with that without super junction. More importantly, the introduction of super junction changes neither the high current gain nor the high frequency characteristics of SiGeC HBT. Compared with the Si bipolar transistor (BJT) with the same parameters, the novel device has a current gain that increases 10.7 times, and its cutoff frequency and maximum oscillation frequency are also improved greatly. A good trade-off is achieved among high current gain, high frequency and high breakdown voltage, in the novel SiGeC HBT with super junction. The layers and width of column region are designed to be optimal. With the increase in the number of column region layers, the breakdown voltage of the novel device is increased significantly, the current gain is improved somewhat, and the cutoff frequency and maximum oscillation frequency are reduced slightly. Taken together, the pnpn four-layer structure of super junction region is reasonable.
Analysis of Doppler shift in a three-dimensional scattering channel model
Authors: Jiang Hao  , Zhou Jie  , Hisakazu Kikuchi  , Shao Gen-Fu  ,   Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Department of Electronic and Electrical Engineering, Niigata University, Xinxie 950-2181, Japan;,   Department of Automation, Hangzhou University of Electronic Science and Technology, Hangzhou 310018, China
Published: December 2020

In this paper we investigate a generalized three-dimensional (3D) scattering channel model for microcell environments, which idealizes a directional antenna at the center of the semi-spheroid. The joint and marginal PDFs of angle of arrival and Doppler spectra are derived. According to the theory of the relative motion, with the movement at the mobile station, the base station is relatively moving, which will also produce Doppler spectra. Comparisons between our theoretical calculations and customary 3D results show that the analyses are correct and applicable to microcell environments, which promotes the research of the 3D scattering channel models.
Laser wavelength influence on capture and delivery of polystyrene microspheres using nanofibers
Authors: Li Ying  , Hu Yan-Jun  ,   School of Information Engineering, Guangdong Medical College, Dongguan 523808, China
Published: December 2020

In the paper we study the effects of laser wavelength on capture and delivery of polystyrene microspheres using a nanofiber. Theoretical analysis shows that when the fiber diameter and the power of the laser are fixed, with the increase of the laser wavelength, the range and intensity of evanescent wave outside optical fiber become large and light gradient and scattering forces exerted on spheres also increase, which means that the ability to capture and transportation of spheres using nanofiber increases with the laser wavelength. The experimental phenomena and theoretical predictions are completely consistent with each other, when the lasers with three wavelengths are separately injected into the fiber with a diameter of 600 nm, with the increase of the wavelength, the critical power becomes small, and when the laser power is constant, with the increase of the wavelength, velocities of spheres also increase, showing that the ability to capture and transport the microsheres is enhanced.
Variability periodicity and chaotic property of quasars based on ensemble empirical mode decomposition
Authors: Tang Jie  ,   School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001, China
Published: December 2020

The radio fluxes of the quasars 3C 345, 3C 279 and 3C 273 at a frequency of 8.0 GHz were collected in a time period from 1965 to 2012 based on the database of University of Michigan Radio Astronomy Observatory. The time series of the quasar variability is decomposed into trend components, periodic components and high frequency components by the ensemble empirical mode decomposition. Then chaotic characteristic quantities of the high frequency component is analyzed, that is, saturation correlation dimension, maximum Lyapunov exponent and Kolmogorov entropy. The results show that the variability of quasars has the chaotic characteristic as well as the characteristic of periodicity. The variability of quasars is due to the comprehensive consequence of a physical mechanism of the periodic phenomenon combined with the nonlinear mechanism of the chaos phenomenon.
Trust, evolution, and consensus of opinions in a social group
Authors: Su Jiong-Ming  , Liu Bao-Hong  , Li Qi  , Ma Hong-Xu  ,   College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha 410073, China;,   College of Information System and Management, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Most dynamical models with continuous opinion lack the considerations of trust between individuals and different weights of opinions. This article extends the Hegselmann-Krause model by introducing the trust between individuals and the similarity between opinions, and extending the hypothesis of bounded confidence to bounded influence. Finally, the model of opinion updating with weights is proposed. We have studied the formation, evolution of opinions in a social group and consensus-building process under the influence of a few of narrow-minded and authoritative individuals. Simulation results show that decreases of the difference between the initial opinions of two types of individuals and the midpoint of distribution range (0.5), or increases of the influence thresholds of narrow-minded individuals and the trust degree of authoritative individuals would form larger and fewer opinion clusters. As the influence thresholds of narrow-minded individuals increases, the opinion of maximum cluster concentrates at near 0.5, but the trust degree of authoritative individuals will increases to make the opinion of maximum cluster constantly approach the final opinion of authoritative individuals. These results can reflect and explain the realistic social phenomenon with narrow-minded individuals and authoritative individuals to a certain extent.
Chaotic control of the interconnected power system based on the relay characteristic function
Authors: Min Fu-Hong  , Ma Mei-Ling  , Zhai Wei  , Wang En-Rong  ,   School of Electrical and Automation Engineering, Nanjing Normal University, Nanjing 210042, China;,   State Grid Electric Power Research Institute, Nanjing 210003, China
Published: December 2020

Chaotic oscillation in a power system is very harmful for the large-scale interconnected power grid. Here, the basic dynamic properties of the interconnected power system are investigated under the disturbance of electromagnetic power through the Lyapunov exponent spectrum, bifurcation diagram, phase plane, and power spectrum. The sensitivity to the disturbance of electromagnetic power is also studied. Meanwhile, from the sliding mode variable structure control and relay characteristic function, a new method to control the chaotic oscillation is presented, which can quickly and smoothly make the system reach the expected target. Simulation results show that the method can not only shorten the control time, but also reduce the possibility of the impulse response from the system, due to the large parameters. It can inhibit the high-frequency buffeting effectively and has strong robustness.
An authenticated key agreement protocol based on extended chaotic maps
Authors: Shu Jian  ,   Department of Electronic Commerce, Jiangxi University of Finance and Economics, Nanchan 330013, China;,   School of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

Recently, many chaotic maps-based authenticated key agreement protocols using smart cards have been proposed. Unfortunately, tamper-resistant card readers make these protocols costly and unpractical. In addition, the digital signature scheme based on chaotic maps requires high computational resources. There exists security problem in publishing public keys which depend on signature schemes. In this paper, we will present a novel authenticated key protocol without smart cards while using extended Chebyshev maps. The proposed protocol eliminates the process of publishing the public key. Security and performance analysis show that our protocol can resist various attacks and yet is reasonably efficient. Therefore, our protocol is more suitable for practical applications.
Effect of defect on the programming speed of charge trapping memories
Authors: Wang Jia-Yu  , Zhao Yuan-Yang  , Xu Jian-Bin  , Dai Yue-Hua  ,   School of Electronics and Information Engineering, Anhui University, Hefei 230039, China
Published: December 2020

The programming speed of charge trapping memories (CTM) with different defects were studied based on the first principle and VASP package. The defects include threefold oxygen vacancy (VO3), fourfold oxygen vacancy (VO4), hafnium vacancy (VHf), and interstitial oxygen (IO). Trapping energy, energy band offset, and the trapping density were calculated and compared. Results show that VO3, VO4 only trap holes, VHf only trap electrons, and IO trap electrons and holes; the most important is the trapping energy which is greater in VHf. It is the best for trapping charges; because the charge tunneling into trapping layer is easy in VHf. It can also reduce the tunneling time. Finally, the trapping densities were compared with each other: VHf's trapping density is greater than other defects, i.e. charges can be trapped easier than by other defects. All of these show that VHf is the best one for reducing programming time. This paper will provide a theoretical guidance for increasing the programming speed ofCTM.
First principles calculation of dielectric properties of Al and N codoped 3C-SiC
Authors: Zhou Peng-Li  , Zheng Shu-Kai  , Tian Yan  , Zhang Shuo-Ming  , Shi Ru-Qian  , He Jing-Fang  , Yan Xiao-Bing  ,   College of Electronic and Informational Engineering, Hebei University, Baoding 071002, China;,   Research Center for Computational Materials and Device Simulations, Hebei University, Baoding 071002, China;,   School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

We have performed geometry optimizations of crystal structure and contrasted the calculated results of band structure, density of states, and permittivity of 3C-SiC for four kinds of doped supercell models: undoped, Al-doped, N-doped and Al-N codoped ones, by using the first principles plane wave ultrasoft pseudopotential method based on the density functional theory. Results show that Al doping increases the lattice constant of 3C-SiC, while N doping has little effect on the SiC lattice. The Fermi energy level introduced into valence band and the band gap is slightly widened through Al doping for 3C-SiC, and the SiC becomes a p-type semiconductor. Both the conduction band and the valence band of N-doped SiC move toward low energy side, and its band gap is slightly reduced. Intrinsic 3C-SiC has shown poor dielectric loss properties in the microwave range, but the dielectric property can be improved significantly through the Al doping or N doping, especially the former. The microwave dielectric loss performance of 3C-SiC doped with Al and N in the range of 8.2–12.4 GHz declined sharply, which validates the results of experiments. We finally analyzed and discussed the reason for the decrease of permittivity.
An unusual pulse compression of stimulated Brillouin scattering in water
Authors: Zhang Lei  , Li Jin-Zeng  ,   National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
Published: December 2020

Pulse compression is an important property of stimulated Brillouin scattering (SBS), and the SBS pulse duration becomes smaller with the increase of pump energy. An unusual pulse compression was investigated of the stimulated Brillouin scattering in water, it was found that the SBS pulse duration becomes larger as the pump energy increases. The pulse duration of SBS alters differently with the change of pump energy in strong focusing and weak focusing. Numerical simulation of pump light transmission in water cell has been made to explain the unusual pulse compression phenomena. Different real gain lengths in strong and weak focusing make different SBS pulse compression.
Introduction of two-dimensional defects in inverse opal films by means of planar lithography and sol-gel co-assembly methods
Authors: Li Long  , Wang Ming  , Ni Hai-Bin  , Shen Tian-Yi  ,   Key Laboratory on Opto-Electronic Technology of Jiangsu Province, School of Physics Science and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

By applying planar lithography and sol-gel co-assembly methods, the designed two-dimensional defects were introduced in inverse opal films. Composite colloidal crystal films which can turn into inverse opal films after calcination were fabricated by sol-gel co-assembly method. Photoresist patterns produced by planer lithograph either on silicon or composite colloidal film/silicon substrate were used as the sacrificial structure to form the designed defects. To form the embedded defects in inverse opal films, a layer of composite colloidal crystal film was assembled on the photoresist patterns. After calcination, both PS spheres and photoresist were removed, and the designed defects were introduced in the inverse opal films. Influence of the photoresist patterns on self-assembled PS particles was also characterized.
Phase singularities of an ultrasonic speckle field back-scattered from an underwater Gaussian interface
Authors: Zheng Wei-Hua  , Jia Hu  ,   School of Civil Engineering and Architecture, Nanyang Normal University, NanYan 473061, China
Published: December 2020

In order to describe the characteristics of the ultrasonic speckle field accurately, a computation-simulated generation of ultrasonic speckle field is proposed. Using the Gaussian correlation random surfaces that are generated by the simulation, the simulation of the speckle field produced by this kind of surfaces in the far field, the sound intensity distribution, and phase distribution can also be obtained. To compare the difference between speckle field from experiment and that by the simulation, the ultrasonic speckle field receiving experimental system is established, taking the same parameters to calculate and simulate, the experimental speckle field is obtained. By contrast, phase singularity exists in the simulated speckle field and the phase distribution is similar to the swirl around singular points, The intensity distribution of the simulated speckle field and that obtained experimentally are similar, but the former has a bigger strength, more highlight speckles carrying useful information, dark speckle being less, so that it is more conducive to the research and analysis.
Research and design of thermal concentrator with arbitrary shape based on transformation thermodynamics
Authors: Li Ting-Hua  , Mao Fu-Chun  , Huang Ming  , Yang Jing-Jing  , Chen Jun-Chang  ,   Wireless Innovation Lab of Yunnan University, Kunming 650091, China;,   School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

How to control and manipulate the heat flow in a flexible way is a hotspot of current research. According to transformation thermodynamics method, material parameter expressions for thermal concentrator with an arbitrary cross section are derived, and thermal concentrator with special symmetrical profiles, such as circle, ellipse, and pentagon, as well as thermal concentrator with arbitrary conformal/non-conformal cross section are designed on this basis. Full wave simulation results show that these thermal concentrators can bend the isotherm and heat flux towards their compressive regions, making the heat diffuses faster on the side near heat source and slower on the opposite side. Heat concentrated into a tiny region may have potential applications in thermal engineering. In addition, research on layered realization method of cylindrical thermal concentrator is conducted. Results reveal that the thermal concentrator can be realized through alternatively filling isotropic materials into layers along the angular direction. This work has a guiding significance for the design and manufacturing of thermal concentrator.
Lattice Boltzmann simulation of slip flow and drag reduction characteristics of hydrophobic surfaces
Authors: Huang Qiao-Gao  , Pan Guang  , Song Bao-Wei  ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China;,   Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580, Japan
Published: December 2020

The relationship between the surface wettability and the interaction strength of liquid-wall particles is first investigated using a lattice Boltzmann method, and then the liquid flow over hydrophobic surfaces is simulated in a microchannel. Effect of surface wettability on the slip flow and drag reduction characteristics of hydrophobic surfaces is obtained. Existence of the apparent slip on hydrophobic surfaces is confirmed and its mechanism is revealed. Simulation results show that the hydrophobicity induces a low density layer near the wall of hydrophobic surfaces and the apparent slip is observed on the low density layer. It is shown that the apparent slip is a direct cause of hydrophobic surfaces' drag reduction effect. Thus the drag reduction effect increases with increasing slip length. For a specific fluid system, the slip length is an inherent property of the hydrophobic surfaces and is a single function of the surface wettability. The slip length does not change with the external flow property.
Vortex structures in turbulent channel flow modulated by a steadily distributed spanwise Lorentz force
Authors: Wu Wen-Tang  , Hong Yan-Ji  , Fan Bao-Chun  ,   National Key Laboratory of Laser Propulsion and Application, Academy of Equipment, Beijing 101416, China;,   National Key Laboratory of Transient Physics, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Turbulence control and drag reduction in a channel flow by using a steadily distributed spanwise Lorentz force are investigated numerically via a direct numerical simulation (DNS). The characteristics of controlled flow fields and vortex structures are described. Meanwhile, the mechanisms of turbulence suppression and drag reduction by the Lorentz force are also discussed. Calculated results indicate that: (1) The shear layers with a arge gradient of spanwise velocity are created in the laminar boundary layer induced by the spanwise Lorentz force, where the streamwise vortices are easily generated by perturbations. (2) Under the action of the distributed Lorentz force with proper control parameters, only periodically well-organized streamwise vortices are observed in the near-wall region of the turbulent channel flow. (3) After controlling, the averaged lift height of inclined streamwise vortices is reduced significantly as compared with the uncontrolled turbulence flow, resulting in the reduction of the burst strength and subsequent drag reduction on the wall.
Study on a rising bubble bouncing near a rigid boundary
Authors: Li Shuai  , Zhang A-Man  ,   School of Shipbuilding Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Some numerical studies were carried out on micrometer-sized rising bubble bouncing near a rigid boundary. Taking surface tension into consideration, the bubble motion could be solved using the potential flow theory. A correction should be made in Bernoulli equation because the pressure gradient was caused by the viscosity between the bubble and the wall. The numerical result agree well with the experimental data. Based on the fundamental phenomenon, we have studied the influence of characteristic parameter on bubble bouncing behavior, and the balanced shape due to the action of the wall. With the increase of the rising distance of the bubble, the distance of the bubble bouncing downward and the period of bouncing would increase. However, they would not change obviously when the rising distance is large enough. Surface tension has great effect on the dynamic behavior of the bubble. The bouncing period decreases when surface tension becomes large, but the bouncing distance will have an increase before it gradually decreases. Finally, the balanced shape of the bubble due to the wall effect can be mainly controlled by buoyance parameter and the Weber number.
Experimental study of insulated aluminum planar wire array Z pinches
Authors: Sheng Liang  , Li Yang  , Yuan Yuan  , Peng Bo-Dong  , Li Mo  , Zhang Mei  , Zhao Ji-Zhen  , Wei Fu-Li  , Wang Liang-Ping  , Hei Dong-Wei  , Qiu Ai-Ci  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect Northwest Institute of Nuclear Technology, Xi'an, 710024;,   Northwest Institute of Nuclear Technology, Xi'an, 710024
Published: December 2020

The planar wire array Z pinch experiments with insulated aluminum wires coated with 2 μm polyimide were carried out on "QiangGuang-I" facility (100ns, 1.3 MA) and compared to those with ordinary aluminum wires. Experimental results indicate that surface insulation can affect the implosion dynamics and radiation character of Z pinches. The resistive heating energy and imploding mass may be increased by exploiting the effect of surface insulation. In the surface-insulated wire array Z pinch experiments the multi-peak phenomena were considerably suppressed, whereas the improvement on the X-ray yield was not observed.
Switching dynamic behavior of a ferroelectric bilayer film
Authors: Cui Lian  , Qiu Zhong-Yang  , Li Rui-Ying  , Liu Yong-Hao  , Li Yu-Chun  , Xia Zun-Yi  , Hu Tong-Rui  , Lü Tian-Quan  ,   Department of Physics, Daqing Normal University, Daqing 163712, China;,   Center of Condensed Matter Science and Technology, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Based on the Landau-Khalatnikov equation of motion, the switching dynamic behaviors, (including the average polarization, switching time, switching current and coercive field) of a ferroelectric bilayer film with a surface transition layer within each constituent thin film and a ferroelectric interfacial coupling between two thin films have been investigated. Results reveal that there is a competitive mechanism in the bilayer film, the action of surface transition layer and the interfacial coupling. The abnormal behavior is discovered in the polarization reversal process of the bilayer film, which can be attributed to the competition between the surface transition layer and the interfacial coupling. The combined action of surface transition layer and interfacial coupling plays a decisive role on the dynamic properties of a ferroelectric bilayer film.
Thermoelectric properties of chalcopyrite Cu3Ga5Te9 with Sb non-isoelectronic substitution for Cu and Te
Authors: Sun Zheng  , Chen Shao-Ping  , Yang Jiang-Feng  , Meng Qing-Sen  , Cui Jiao-Lin  ,   Materials Science and Engineering College, Taiyuan University of Technology, Taiyuan 030024, China;,   School of Materials, Ningbo University of Technology, Ningbo 315016, China
Published: December 2020

Thermoelectric materials, which allow the conversion between heat and electricity, can be directly applied in the fields of cooling and power generation. Here we report an effective approach: non-isoelectronic substitution of Sb for Cu and Te in Cu3Ga5Te9 to increase the Seebeck coefficient and electrical conductivity. This improvement is attributed to the enhancement in carrier concentration n and effective mass as well as the conservation of the carrier mobility μ. The enhancement of the carrier concentration is caused by the hole doping effect due to the drop of the Fermi level into the valence band when Sb occupies the Te lattice sites, and also due to the increase of the copper vacancy (V-1Cu) concentration when Cu content decreases. In addition, the non-isoelectronic substitution can yield extra crystal structure defects. These defects, which are represented by the alterations of anion (Te2-) position displacement (u) and tetragonal deformation (η), directly govern the lattice thermal conductivity (κL) on an atomic scale. The maximum ZT value is 0.6 at 766 K with proper Sb substitution, which is about 25% higher than that of Cu3Ga5Te9. Therefore, we are able to effectively manipulate the electrical and thermal properties through proper selections of the substituting / substituted elements and their quantities, and prove that the non-isoelectronic substitution approach in the chalcopyrite semiconductors is an effective way to improve the thermoelectric performance.
Effect of temperature and external magnetic field on the structure of electronic state of the Si-uniformlly-doped GaAs quantum well
Authors: Yang Shuang-Bo  ,   School of Physical Science and Technology Nanjing Normal University, Nanjing 210023, China
Published: December 2020

By solving the Schrödinger equation and the Poisson equation self-consistently, we have calculated the electronic structure for the Si-uniformally-doped GaAs/AlGaAs quantum well system at T=273 K and B=25 T in the effective mass approximation. We also studied the influence of the temperature and the external magnetic field on the subband energies, eigen-envelope functions, self-consistent potential, density distribution of the electrons, and the Fermi energy. It is found that at the given magnetic field B≠0, with the increase of temperature, the subband energies increase monotonically, the Fermi energy decreases monotonically, the width of the self-consistent potential well decreases, the depth of the well increases, the distribution of the electron density becomes wider, and the peak value is reduced. At the given temperature, with the increase of the strength of the magnetic field, the subband energies and Fermi energy increase monotonically, the depth of the self-consistent potential well is reduced, the peak of the electron density distribution becomes higher, and concentrated around the center of the well.
Nuclear magnetic resonance experimental study on the characteristics of pore-size distribution in muck under several typical loading cases
Authors: Li Zhang-Ming  , Zeng Wen-Xiu  , Gao Mei-Lian  , Luo Zhi-Bin  ,   Institute of Geotechnical Engineering, Guangdong University of Technology, Guangzhou 510090, China;,   Shanghai Niumag Corporation, Shanghai 200333, China
Published: December 2020

Several typical loads are applied to muck specimens to simulate muck ground treatment conditions. Then tests of pore structural distribution of the soil are performed by the method of nuclear magnetic resonance (NMR), for seeking variation of their internal structure under the typical load level and rate, and thus to further determine the muck ground reinforcement mechanism and responses in micro-structure aspect. The results suggest that: (1) the max-pore decreases under a certain load, and the reduction increases with load level; nevertheless, when the impact load reaches a considerable level, both the max-pore and small-pore decrease; (2) the confining stiffness effect of constraint samples induces a decrease in the proportion of large-pore; (3) at a certain load level (680 kPa or less), the loading rate is the key factor determining the relative proportion of maximum void ratio: smaller lading rate will make the void ratio increase, larger lading rate will make the void ratio reduced, and its boundary value is between > 0.8 MPa/s and ≤ 1.6 MPa/s; (4) with a certain load level and rate, an the number of impact times increses, namely as the total energy is enhanced, the large-pore as well as the max-pore considerably decreases; however, this effect will be reduced when the interval time is short and as the number of impact times increases further. i.e. the large-pore effectively decreases. There exists a suitable value of the number of impact times for the muck specimens. These results reflect the rule of different loading effects in the micro of micro fine structue and provide a basis for the design and construction optimization for muck ground improvement.
Influences of gold/silver nanoparticles on fluorescence of europium-doped films
Authors: Wang Qing-Ru  , Li Shu-Hong  , Shi Qiang  , Wang Wen-Jun  ,   School of Physical Science and Information Engineering, Liaocheng University, Shandong Provincial Key Laboratory of Optical Communication Science and Technology, Liaocheng 252000
Published: December 2020

Spherical silver (Ag) nanoparticles, triangular Ag nanoprisms, and triangular gold (Au) nanoparticles were separately deposited on the Eu(TTFA)3-doped Su8 films. Compared with the fluorescence of films without nanoparticles, the fluorescence of the doped films was greatly enhanced by the two kinds of the Ag nanoparticles, the enhancement is greater for the spherical Ag nanoparticles than that for the triangular Ag nanoprisms. The fluorescence was quenched for the film with Au nanoparticles. Results show that the nanoparticles can both enhance and quench the fluorescence of the films, which depend mainly on the local surface plasmon resonance (LSPR) of the nanoparticles. When the LSPR of nanoparticles overlaps with the excitation or the emission spectrum of the films, the fluorescence would be enhanced. Otherwise the fluorescence of the films would be quenched.
Design and evaluation of a pre-traveling wave deflector magnetic solenoid lens focused streak image tube
Authors: Liu Rong  , Tian Jin-Shou  , Li Hao  , Wang Qiang-Qiang  , Wang Chao  , Wen Wen-Long  , Lu Yu  , Liu Hu-Lin  , Cao Xi-Bin  , Wang Jun-Feng  , Xu Xiang-Yan  , Wang Xing  ,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Xi'an Technological University, Xi'an 710032, China
Published: December 2020

Owing to the excellent feature of ultrahigh temporal resolution, the streak image tube has been the indispensable scientific instrument for the application to measurement of ultrafast phenomena on subpicosecond time scale. In this paper, a new femtosecond streak image tube with both high temporal and spatial resolution is designed. To improve its integrated performance, a pair of traveling wave deflectors is located before a magnetic solenoid lens in the tube, which minimizes the electron transit time from anode to deflection plates and therefore reduces time dispersion and space charge effects. Using CST microwave studio finite element method, bandwidth and deflection sensitivity of traveling wave deflector have been studied numerically. The result shows that the wide bandwidth of the traveling wave deflectors designed is beneficial to slow down the electrical deflecting pulse to match the beam velocity in a wide frequency range, which can improve the deflection sensitivity. After tracing the trajectory of electrons and calculating the modulation transform function, we get temporal resolution of 220 fs and spatial resolution above 100 lp/mm. Based on the aberration theory, the aberration formulas of electron trajectory are deduced, which systematically evaluate the imaging quality of streak image tube with modulation transfer function. Finally, static experiment is carried out, and the result shows that the static spatial resolution is better than 35 lp/mm.
Review of reconstruction algorithms with incomplete projection data of computed tomography
Authors: Yang Fu-Qiang  , Zhang Ding-Hua  , Huang Kui-Dong  , Wang Kun  , Xu Zhe  ,   Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, Ministry of Education, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

This paper mainly reviews the progress of methods, and research development in the field of computed tomography(CT) with incomplete projection data, at home and abroad, on limited angle projection data reconstruction with the detector fully covered, and truncated data reconstruction with the detector partially covered. Firstly, the discrete model iterative reconstruction algorithm and the compressed sensing(CS) sampling reconstruction algorithm are discussed for the sparsely uniform and limited-view angle sampling in the case that the detector fully covers the detected object. Secondly, the reconstruction algorithm of back-projection filtration(BPF) for helical cone beam and improved ones for cone beam FDK are discussed in the case that the detector could not fully cover the detected object. This paper could provide the researchers in CT reconstruction field the criticism of methods and summaries. Furthermore, it also points out current focus of the study and the research direction in the future.