bluuebunny/crossref_metadata_2025 huggingface dataset:
A new approach to identify influential spreaders in complex networks
Authors: Hu Qing-Cheng  , Yin Yan-Shen  , Ma Peng-Fei  , Gao Yang  , Zhang Yong  , Xing Chun-Xiao  ,   Research Institute of Information Technology Tsinghua National Laboratory for Information Science and Technology Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China
Published: December 2020

In the research of the propagation model of complex network, it is of theoretical and practical significance to detect the most influential nodes. Global metrics such as degree centrality, closeness centrality, betweenness centrality and K-shell centrality can be used to identify the influential spreaders. Each of these approaches is simple but has a low accuracy. We propose K-shell and community centrality (KSC) model. This model considers not only the internal properties of nodes but also the external properties, such as the community which these nodes belong to. The susceptible-infected-recovered model is used to evaluate the performance of KSC model. The experimental result shows that our method is better to detect the most influential nodes. This paper comes up with a new idea and method for the study in this field.
Fast self-similar amplification through passive nonlinear pulse pre-shaping
Authors: Wang Si-Jia  , Gu Cheng-Lin  , Liu Bo-Wen  , Song You-Jian  , Qian Cheng  , Hu Ming-Lie  , Chai Lu  , Wang Qing-Yue  ,   Key Laboratory of Opto-electronic Information Science and Technology of Ministry of Education, College of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

A nonlinear pre-shaper which optimizes initial pulses for self-similar evolution in a following short fiber amplifier is demonstrated. It consists of a pair of transmission gratings and a segment of single mode fiber, by which pulses are shaped temporally and spectrally before amplification. To confirm the benefit of nonlinear pre-shaping for the self-similar evolution, pulse amplifications with and without the nonlinear pre-shaper are simulated. From comparison, pulses optimized by nonlinear pre-shaper show a shorter pulse duration, less pedestal and broader spectrum after amplification and compensation. With this optimization, the self-similar amplification can be realized in a 2.2-meter Yb3+-doped fiber in a large range of pump power, generating 60 fs transform-limited pulses after compression. This nonlinear pre-shaping method can efficiently shorten the fiber length and release the seed quality required for self-similar amplification. An all-normal dispersion mode-locked fiber laser is employed as the seed of a self-similar amplifier for the first time, thus facilitating an all-fiber system.
Electrical transport properties of InSe under high pressure
Authors: Wu Bao-Jia  , Li Yan  , Peng Gang  , Gao Chun-Xiao  ,   Department of Physics, College of Science, Yanbian University, Yanji 133002, China;,   State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
Published: December 2020

Electrical resistivity and Hall-effect in InSe under high pressure are accurately measured in situ. The measurement results of electrical resistivity and the temperature dependence of electrical resistivity show that InSe undergoes semiconductor-to-metal transition at 5-6 GPa and transforms from rhombohedral layered phase P1 (InSe-I) to metallic rocksalt cubic phase P3 (InSe-III) at 12 GPa. Certainly, the pressure-induced metallization of InSe results from the pressure-induced structural phase transition. In addition, Hall-effect measurements display the carrier transport behavior of InSe under pressure, which indicates that InSe undergoes a carrier-type inversion around 6.6 GPa and the increases of the carrier concentration is the dominant factor producing the decrease of the resistivity after 9.9 GPa.
Thermodynamic properties of Li-N-H hydrogen storage: first-principles study
Authors: Zhao Yu-Na  , Gao Tao  , Lü Jin-Zhong  , Ma Jun-Gang  ,   Beijing Jiaotong University Haibin College, Huanghua 061100, China;,   Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610064, China
Published: December 2020

According to the plane wave pseudo-potential method of the first-principles based on density functional theory, we systematically investigate the cell parameters, the formation heat and the reaction enthalpy in the Li-N-H hydrogen storage process. The calculated lattice parameters of these compounds are in good agreement with previous theoretical and experimental results. The values of formation heat at 298 K for (lithium nitride) Li3N, (lithium hydride) LiH, (lithium amide) LiNH2 and (lithium imide) Li2NH are estimated to be -168.7, -81.0, -173.0 and -190.8 kJ/mol, respectively. The reaction enthalpy of this system is calculated to be 78.5 kJ/mol H2 at T=298 K and this value accords with the experimental value of 75.67 kJ/mol H2 at T=300 K. As a result, the reaction enthalpies for the two-step reactions are very close to their calculation results respectively.
Stable structures of Ge65, Ge70, Ge75 and their electronic properties
Authors: Li Peng-Fei  , Zhang Yan-Ge  , Lei Xue-Ling  , Pan Bi-Cai  ,   Department of Physics, University of Science and Technology of China, Hefei 230026, China;,   Department of Physics and Electronic, Jiangxi Normal University, Nanchang 330022, China
Published: December 2020

The low-lying candidates of Ge65, Ge70 and Ge75 are extensively investigated through combining the tight-binding potential of germanium with two kinds of global minima search strategies: compressing liquid and genetic algorithm. Then, we perform accurate ab initio calculations to optimize the atomic structures of these low-lying candidates and identify the ground state structures. Our calculations predict that there exist two kinds of stable isomers characterizing the sphere- and ellipsoid-like structural features for each sized cluster, and the two kinds of isomers are energetically competitive. This is consistent with the observation for the large sized clusters Gen (65 ≤ n ≤ 80) in experiment. Meanwhile, we also briefly analyze the electronic properties of these three kinds of clusters.
Analysis and measurments of path loss effects for ultra high frequency radio-frequency identification in real environments
Authors: Zuo Lei  , He Yi-Gang  , Li Bing  , Zhu Yan-Qing  , Fang Ge-Feng  ,   School of Electrical and Automation Engineering, Hefei University of Technology, Hefei 230009, China;,   College of Electrical and Information Engineering, Hunan University, Changsha 410082, China;,   National Key Laboratory of National Defense Science and Technology on Electronic Test and Measurement, Qingdao 266555, China
Published: December 2020

Based on the principles of radio-frequency identification (RFID) technology and Friis propagation equation, the path loss expression of ultra high frequency (UHF) RFID in free space is provided. The Fresnel clearance and horizontal interval between reader antenna and tag are employed as dependent variables, and then the obstructing effect of the first Fresnel zone on path loss is discussed. By the methods of linear regression and minimum mean-square error, a dual-slope Logarithm distance path losses model is proposed. The path losses of UHF RFID under different parameters are measured in open indoor environment. The measurement results indicate that RFID system experiences less fading when the Fresnel clearance is 1.5 times higher than the first Fresnel radius. The standard deviation of the proposed model with two slopes reduces ten percent or more compared with that of traditional logarithm distance path loss model.
The effect of soil model on earth surface potential and reasonable selection method for soil model
Authors: Li Wen-Feng  , Yang Hong-Geng  , Xiao Xian-Yong  , Li Xing-Yuan  ,   School of Electrical Engineering and Information, Sichuan University, Chengdu 610065, China
Published: December 2020

The Green's function of three-dimensional combined-layer soil model is firstly derived using simulated image method. Based on the specified soil model, the influence of soil model on the earth surface potential (ESP) is analyzed for different soil structure configurations. It is found that difference in soil model only changes the absolute value of ESP, but the influence of ESP difference can be ignored under certain conditions. And the physical mechanism for the effect of soil parameter change on ESP is explained theoretically. One of the challenges that have not been solved effectively is how to establish the proper soil model to calculate DC current flowing through the neutral point of transformer accurately. For this challenge, the criteria and threshold value for selecting the soil model reasonably are introduced. Therefore, the arbitrariness and blindness of selecting the soil model can be avoided. The results are useful for calculating accurate results, which can further provide theoretical references for selecting substations near the HVDC ground electrode.
Characteristics of electron motion in a short-wavelength free-electron laser
Authors: Wang Shi-Jian  , Xu Yong-Gen  , Ji Yu-Pin  , Xu Jing-Yue  , Lu Hong  , Liu Xiao-Xu  , Zhang Shi-Chang  ,   School of Physics and Chemistry, Xihua University, Chengdu 610039, China;,   Institute of Photoelectronics, Southwest Jiaotong University, Chengdu 610031, China
Published: December 2020

Transport channel of the electron beam in a short-wavelength free-electron laser is quite narrow and long, which is needed for the electrons to have excellent motion feature so as to prevent the transverse divergence. In this paper the characteristics of the ultra-relativistic electron motion in a planar wiggler filed with transverse distribution are studied by analytical derivation, nonlinear simulations and Kolmogorov entropy calculations. Results show that the wiggler not only forces the electron to periodically wiggle on the transverse plane, but also superpose a transverse shift motion leaving away from the wiggler axis, which leads to the transverse divergence of the electron motion in the absence of an external magnetic focusing system. However, it is shown that the proper choice of the initial value of the electron transverse velocity could suppress the transverse motion divergence, where the electron can smoothly pass through a narrow and long channel with a length of 10 m and a width of 0.09 mm and the electron motion is stable even if there is no external magnetic focusing system.
Ridgelet transform for quantum optical states
Authors: Yu Hai-Jun  , Zhong Guo-Bao  , Ma Jian-Guo  , Ren Gang  ,   Department of Physics and Electronic Information Engineering, Huinan Normal Colledge, Huainan 232038, China;,   Shool of Physics and Material Science, Anhui University, Hefei 230039, China
Published: December 2020

We derive a useful formula for the normal ordering of two-mode operator by the technique of integration within an ordered product (IWOP) of operators. Furthermore, we also calculate the Radon transformations for the coherent state, special squeezed coherent state, intermediary entangled state in the view of the quantum mechanics. Based on the results above, the Mexican hat's mother wavelet function is selected to analyse Ridgelet transformations of these three quantum optical states.
Shape-variant astigmatic elliptical breathers in strongly nonlocal nonlinear medium
Authors: Lu Da-Quan  ,   Laboratory of Nanophotonic Functional Materials and Devices, South China Normal University, Guangzhou 510631, China
Published: December 2020

The analytical solution for the shape-variant astigmatic elliptical breathers in strongly nonlocal nonlinear medium is obtained, and the propagation properties of this type of breather is investigated according to the solution. During propagation, the beam in x- and y-direction keeps Gaussian, the beam width and the curvature of the cophasal line vary periodically but asynchronously. For the two-dimensional off-waist input case, the initial convergence (divergence) makes the width narrowed (broaden) first near the entrance plane, no matter what the input power is; then varies periodically but asynchronously in x- and y-direction. For the one-dimensional on-waist input case, the beam might breathe only in one direction. The breather of the beam width induces the periodical variation of the curvature for the elliptically cophasal surface and the ellipticity of the pattern. If the location of the waist in x-direction and that in y-direction are identical with each other, the product of the maximum and the minimum of the ellipticity keeps equal to unify. In this case, the position of the entrance plane does not affects the maxima and the minima of the ellipticity, but affects the uniformity for the variation velocity of the ellipticity in a period.
Demodulation and multi-input multi-output equalization for mode division multiplexing system using a novel few-mode fiber
Authors: Yao Shu-Chang  , Fu Song-Nian  , Zhang Min-Ming  , Tang Ming  , Shen Ping  , Liu De-Ming  ,   National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

In order to solve the mode crosstalk in a mode division multiplexing (MDM) transmission system, we design and fabricate a novel few-mode fiber (FMF) with high mode differential group delay (MDGD) that ensure that all supporting modes can transmit through the FMF independently. Then, we propose a cascaded multi-input multi-output (MIMO) delay equalization method, in order to further suppress the mode crosstalk from the mode division multiplexer/demultiplexer (MUX/DeMUX) and improve the transmission distance and spectrum efficiency of MDM system. Our simulation results verify that the cascaded MIMO delay equalization method together with the novel FMF can effectively mitigate the mode crosstalk of MDM transmission. Compared with the traditional MIMO equalization method, our proposed equalization method can be successfully applied to the QPSK signal transmission through the FMF with large MDGD, while no obvious increase of computation complexity is observed. Our results show that for a 40 Gbps two-mode division multiplexing system, the Q factor can be improved by 1.7 dB after 40 km FMF transmission using the proposed cascaded MIMO equalization method. Therefore, all those results are very conducive to the next-generation high capacity fiber-optic transmission.
Bionic underwater acoustic communication using dolphin sounds
Authors: Liu Song-Zuo  , Qiao Gang  , Yin Yan-Ling  ,   Science and Technology on Underwater Acoustic Laboratory, Harbin Engineering University, Harbin 150001, China
Published: December 2020

An underwater acoustic communication scheme using intrinsic dolphin sounds is proposed to overcome the sound exposure derived from traditional fixed carrier modulation for covert communication in this paper. The communication signal can be detected but it could easily be excluded in the process of recognition/classification by an adversary. This is because the signal resembles dolphin sounds. Properties of dolphin sounds are investigated in this paper. Synchronization in this scheme is achieved by using dolphin whistles while dolphin clicks are used as information carrier. The time interval between dolphin clicks conveys information. Channel equalization is performed by passive time reversal mirror technique, whereas channel estimation is done through matching pursuit method under the theory of compressive sensing. The efficiency and feasibility of the proposed method are verified by lake trial. The received signal and emission mimic bio-signal are very similar. Bit error rate less than 10-4 is achieved above 29 bps to a distance of about 2 km.
Nanofluid Raleigh-Benard convection in rectangular cavity: simulation with lattice Boltzmann method
Authors: Guo Ya-Li  , Xu He-Han  , Shen Sheng-Qiang  , Wei Lan  ,   School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China
Published: December 2020

The lattice Boltzmann method is used to simulate the thermal field and flow field of nanofluid Raleigh-Benard convection in a rectangular cavity. The heat transfer characteristics of nanofluid are compared under different Raleigh numbers, volume fractions of nanoparticles and particle sizes. The results show that under the same Raleigh number and volume fraction, the convection heat transfer of nanofluid becomes weakened by increasing the particle size. Under the same Raleigh number and particle size, the convection heat transfer of nanofluid becomes strengthened by increasing the volume fraction of nanoparticles.
Bubble velocities in the nonlinear Rayleigh-Taylor and Richtmyer-Meshkov instabilities in non-ideal fluids
Authors: Huo Xin-He  , Wang Li-Feng  , Tao Ye-Sheng  , Li Ying-Jun  ,   State Key Laboratory for GeoMechanics and Deep Underground Engineering, China University of Mining and Technology, Beijing 100083, China;,   HEDPS, Center for Applied Physics and Technology, Peking University, Beijing 100871, China
Published: December 2020

In a reference system moving with the bubble vertex we investigate the effects of fluid viscosity and surface tension on the bubble velocity in the nonlinear Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities, by extending the ideal fluid model [Goncharov V N, Phys. Rev. Lett. 88 134502 (2002)] to the non-ideal fluid case. First of all, the governing equation (i.e. self-consistent differential equations) describing the dynamic of the bubble front in RT and RM instabilities is obtained. Then, the numerical and asymptotic solutions of the bubble velocity in two-dimensional planar geometry and three-dimensional cylindrical geometry are obtained. Moreover, we quantitatively study the effects of fluid viscosity and surface tension on the RT and RM bubble velocities. It is found that in the fully nonlinear evolutions of RT and RM instabilities, the bubble velocity and amplitude in the non-ideal fluid are both less than those in its ideal fluid counterpart. That is to say, the effects of fluid viscosity and surface tension tend to stabilize the RT and RM instabilities.
In situ high temperature X-ray diffraction study of anatase and rutile
Authors: Wang Ling  , Wang He-Jin  , Li Ting  ,   School of Earth and Space Sciences, Peking University, Beijing 100871, China
Published: December 2020

In situ X-ray diffraction patterns of the powder titania polymorphs are recorded in a temperature range from room temperature (RT) to 1200℃ in static air and vacuum. The results show that the temperature converting anatase into rutile is at 850℃ in static air and at 855℃ in vacuum. Lattice parameters for anatase (RT-850℃) and rutile (RT, 900-1200℃) in static air and those for anatase (27-850℃) and rutile (950-1200℃) in vacuum are refined. The variations of lattice parameters of anatase and rutile with temperature (℃) are therefore well described. Linear () and volume () thermal expansion coefficients of anatase (RT-850℃) and rutile (RT, 900-1200℃) are calculated. The change laws of and with temperature for anatase and rutile in static air and vacuum are summarized. At RT, the thermal expansion coefficients for anatase are a=4.5506310-6/℃, c=7.754310-6/℃, and =16.8583610-6/℃ in static air and a=4.6942910-6/℃, c=9.0285010-6/℃, and =18.6968810-6/℃ in vacuum while those for rutile are a=6.8124310-6/℃, c=8.7164410-6/℃, and =22.2217810-6/℃ in static air and a=6.0583410-6/℃, c=8.3928010-6/℃, and =20.5236210-6/℃ in vacuum, respectively.
Variable gap and gap state distribution of film silicon
Authors: Zhang Zhi-Guo  ,   Institute of Functional Material, Quanzhou Normal University, Quanzhou 362000, China
Published: December 2020

A method of preparing film silicon with variable optical gap is introduced, and the relevant results are given. An easy way to determine the film optical gap by transmittivity curve tangent is shown, and the preparation craftwork and conditions are given. The gap state distribution maps of various materials are presented. In experiment, it is found that the optical gap width of material is related not only to the quantum size effect, but also to the height and width of the barrier formed by lacuna, and to the length of short range order (atom cluster length) as well. A relationship between optical gap of silicon film and atom cluster length is given. Computations show that electron liquid level lifts in potential well with atom cluster length increasing, and the scattering of carrier is weakened by defect barrier. When the atom cluster length is shorter, the electron liquid level does not always lift with atom cluster length increasing, but fluctuates heavily and forms an indention wave. The computations also show that in the case of a constant ratio of the barrier width to the length of the atomic string, the electronic liquid level is also related to the barrier height.
Magnetic field-induced martensitic transformation, superspin glass and exchange bias in Heusler alloys NiCoMnSn
Authors: Zhang Hong-Wu  , Zhou Wen-Ping  , Liu En-Ke  , Wang Wen-Hong  , Wu Guang-Heng  ,   Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China;,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Beijing Institute of Business and Technology, East Yanjiao 065202, China
Published: December 2020

The crystal structures and magnetic properties of Ni50-xCoxMn39Sn11 (8≤x≤10) Heusler alloys are investigated. As a result, we achieve the magnetic field induced martensitic transformation in Ni42Co8Mn39Sn11. It is found that the saturation magnetic moments of alloys increase with Co content increasing. Moreover, a superspin glass behavior and a large exchange bias effect are also found in samples with Co content being higher than 8. We confirm the coexistence of superspin glass of the martensite and ferromagnetic parent phase, which is the physical origin of the exchange bias effect. On the other hand, we propose that the origin of superspin glass in our NiMnCoSn system is due to the occurence of Mn-Mn cluster as reported by Ma et al. in Heusler Mn2Ni1.6Sn0.4 alloys [Ma L, Wang W H, Liu J B, Li J Q, Zhen M, Hou D L and Wu G H 2011 Appl. Phys. Lett. 99 182507].
Fabrication of SU8-based chip suitable for genomic sequencing
Authors: Han Wei-Jing  , Wei Qing-Quan  , Li Yun-Tao  , Zhou Xiao-Guang  , Yu Yu-De  ,   State Key Laboratory of Integrated Optoelectronics, Institute of Semicnductorss, Chinese Academy of Sciences, Beijing 100083, China;,   The Joint Laboratory of Bioinformation Acquisition and Sensing Technology, Institute of Semicnductorss, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

DNA sequencing technology has markedly advanced the development of biological and medicinal sciences. High-throughput pyrosequencing instruments that combine the pyrosequencing with microfabricated high-density picoliter reactors have been proved to be suitable for de novo sequencing and metagenome sequencing. In the present work, we report on an alternative sequencing chip consisting of hundreds of thousands of picoliter sized honeycombed SU8 reaction vessels on a fiber-optic slide by lithography technique for high-throughput pyrosequencing instruments. Highly reproducible fabrication process of SU8 sequencing chip is achieved through the improvement on SU8 film thickness uniformity and relaxation of SU8 residual stress during fabrication. To achieve the optical isolation required for SU8 reaction wells, metal film is selectively deposited on the side walls of the reaction vessels by reformating vacuum coating. With the metal coating, the average value of optical cross talking between SU8 reaction vessels is reduced from 25% to 1%. The SU8 sequencing chip demonstrates an excellent light transmission characteristic and meets the need of pyrosequencing application.
Area effect of isolated conductor's surface charging inside spacecraft
Authors: Cao He-Fei  , Liu Shang-He  , Sun Yong-Wei  , Yuan Qing-Yun  ,   Electrostatic and Electromagnetic Protection Institute, Ordnance Engineering College, Shijiazhuang 050003, China;,   Department of physics, Shijiazhuang College, Shijiazhuang 050035, China
Published: December 2020

The negative effect of spacecraft inside isolated conductor surface charging is more unobvious, causing more serious direct and potential harm. Considering the electrons and ions, the secondary electron emission, according to the kinetic theory of gases and combing the theory of particle in Maxwell velocity distribution function, calculate general expression in a plasma environment unbiased solid surface charging. Using the voltage general expression, we deduce the expression of energy and electric quantity, discuss the relationship between energy of isolated conductor's electrostatic field and surface as well as space environment in special environment, compare the energies of electrostatic field in different environments and different surfaces with electromagnetic pulse discharge damage of ground electronic components, and finally summarize the rules of area effect of isolated conductor's surface charging.
Control method for complex network topological connection optimization
Authors: Zhou Xuan  , Yang Fan  , Zhang Feng-Ming  , Zhou Wei-Ping  , Zou Wei  ,   Material Management and Safety Engineering College, Air Force Engineering University, Xi’an 710051, China;,   Navy Academy of Armament, Beijing 100161, China;,   Normal College, Tibet University, Lasa 850000, China
Published: December 2020

In order to enhance complex network connection income and reduce network connection cost, a network topological connection optimization control method was proposed based on network efficiency and average connection degree, which used network efficiency and average connection degree to denote the gain and cost of network connection respectively, and an optimized arithmetic whose time complexity was O(Mpn2) was provided. Experimental analysis shows that the topological connection of complex network can be optimized by some measures, and an average degree threshold existed in small world network and scale-free network which can make the network’s income reach the maximum value.
Control and modeling of suspending stabilization problom for floated inertial platform
Authors: Li An-Liang  , Cai Hong  , Zhang She-Feng  , Bai Xi-Bin  ,   College of Aerospace Science and Engineering, National University of Defence Technology, Changsha 410073, China
Published: December 2020

Focusing on the suspending stabilization problem for the floated inertial platform, the 6-DOF (degree-of-freedom) equation of motion for the stabilized platform is derived based on the disturbance analysis of the platform and the mode of the suspending support system. To solve the disturbance of the external environments, mode parameter uncertainty, unmodeled dynamics and measurement noise, the sliding mode controller based on the extended high-gain observer are proposed. Simulations indicate that the stabilization structure could isolate the external disturbance and improve the anti-interference ability of the platform; the high precision and quick stabilization control are realized by the proposed controller. Compared with the previous research, the dynamic and stabilization performance of the proposed controller is increased by 50%.
Study on survival function of noise quantum channel and its simulation
Authors: Zhang Lin  , Nie Min  , Liu Xiao-Hui  ,   College of Communication and Information Engineering, Xi’an University of Posts and Telecommunications, Xi’an 710061
Published: December 2020

In order to build a quantum signaling network with high survivability, quantum channel survival function and survivability of signaling network have been proposed based on the concept of fidelity. The survival coefficient in optical fiber or free space is analyzed, fidelity in noisy quantum channel with the decoherence mechanisms is calculated and survival function test model is proposed. Simulation analysis shows that, by reducing the quantum state transition rate, controlling fiber attenuation coefficient and atmospheric attenuation coefficient, decreasing the time of quantum states evolution, and setting quantum repeaters, we can construct a high survivability of quantum channel and provide a theoretical foundation for the formulation of quantum entanglement signaling network standard.
Analytic model of discrete random magnetizing Halbach PM motor
Authors: Liang Jing-Hui  , Zhang Xiao-Feng  , Qiao Ming-Zhong  , Xia Yi-Hui  , Li Geng  , Chen Jun-Quan  ,   College of electric Engineering, Naval University of Engineering, Wuhan 430033, China;,   National Key Laboratory of Vessel Integrated Power System Technology, Naval University of Engineering, Wuhan 430033, China
Published: December 2020

Halbach motors have attracted lots of attention in novel ship propelling and ocean current generators as they have much dominance. Under the condition of ideal ferromagnetic material and slotless stators, randomly magnetized Halbach array is considered as an equivalence of two 90° Halbach (180° Halbach) arrays, and a new analytic method is proposed in this paper to analyze the randomly magnetized Halbach motors. Fourier series of magnetic scalar potential is calculated, and the expression of air-gap flux density of a 90° Halbach motor is given in polar coordinate system. On the basis of calculations above, the magnetization intensity expression of a randomly magnetized Halbach motor in a pole, and the air-gap flux density distribution of randomly magnetized Halbach motor are obtained; and the relationship of air-gap flux density between the numbers of poles, permanent magnet thickness as well as magnetizing angle are analyzed. The finite element method and experimental results verify the effectiveness of the methods above.
The mean first-passage time for piecewise nonlinear system driven by colored correlated additive and multiplicative colored noises
Authors: Li Bei  , Jin Yan-Fei  ,   Department of Mechanics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

In this paper, We have studied the effects of intensity and correlation time of noises on the mean first-passage time in a picecewise nonlinear system driven by multiplicative and additive colored noises with colored cross-correlation. We derived the expression of the mean first-passage time (MFPT) by applying the unified colored approximation method and the steepest-descent approximation. Results show that the MFPT of the system exhibits a mono-peak structure and the “resonance” phenomena enhance with the increase of multiplicative noise intensity. The value of the peak decreases with increasing additive noise intensity and the correlation between the additive and multiplicative noises. However, the MFPT of the system increases with the increase of additive noise intensity. That is, the effects of the additive noise and the multiplicative noise on MFPT are different. Moreover, the negative and passive correlations play different roles in the MFPT.
Nonlinear phenomena in the hybrid step-up converter with switched-inductor structure
Authors: Liu Hong-Chen  , Yang Shuang  , Wang Guo-Li  , Li Fei  ,   School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Inserting the switched-inductor structure into a traditional Boost converter can increase its line-to-output voltage ratio significantly, decrease the current stresses in the switching elements, reduce losses, and improve efficiency at the same time, which makes it find wide applications in prospect. The bifurcation and chaos phenomenon occurring in the hybrid step-up converter with switched-inductor structure is studied for the first time so far as we know. The discrete iterated mapping model under continuous current mode is established, while the effects of circuit parameters on system performance are analyzed by using bifurcation diagrams. Not only period-doubling bifurcation, border collision bifurcation, tangent bifurcation and intermittent chaos are found in this converter, but a special phenomenon can also be observed according to the simulation result. With the decrease of the capacitance C and inductance L2, the circuit experiences roughly a period, double-period and quadruple-period, and during the quadruple period, two of the bifurcation lines will cross, which leads to the system exhibiting a period-3 behavior at that point. Finally, the existence of this special phenomenon is confirmed by the typical time-domain waveforms and phase portraits of the converter. Results obtained indicate that there can be more complicated and diversiform phenomena in the hybrid step-up converter with switched-inductor structure than in the traditional low-dimensional Boost converter as the circuit parameters vary.
Solution refractive index sensor with wide-range high-resolution linear response based on short no-core fiber
Authors: Zheng Jing-Jing  , Jian Shui-Sheng  , Ma Lin  , Bai Yun-Long  , Pei Li  , Ning Ti-Gang  , Wen Ying-Hong  ,   Key Laboratory of All Optical Network ＆ Advanced Telecommunication Network of the Ministry of Education, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China;,   EMC Research Section, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

The feasibility of applying mode propagation analysis (MPA) method in solving single mode- multimode- single mode (SMS) fiber structure is confirmed by comparing the experimental data with the theoretical results. The method of searching for linear response points on SMS based on MPA was proposed, applied to finding a wide-range high-resolution linear response wavelength theoretically, and confirmed in experiment. By using a 104 μ-in-diameter no-core fiber as short as 4.4 mm, we archived a linear transmission variation of 19.10 dB in the refractive index range of 1.326–1.417, which means a refractive index resolution of 4.76×10-5 according to the resolution of common commercial optical powermeter, and realizes a wide-range high-resolution linear response under the direction of the theory.
Theoretical analysis and numerical simulation of rising sun magnetron with sector cavities
Authors: Shi Di-Fu  , Wang Hong-Gang  , Li Wei  , Qian Bao-Liang  ,   College of Opto-electric Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Field analysis method is used to deduce the dispersion relation of rising-sun magnetron with sector cavities, which is proved correct by the high frequency field analysis software, and the influence of each structure parameter of the magnetron on the cutoff frequency of π mode and the mode isolation is investigated. The results show that the relative errors between the theoretical values and the simulation values of the dispersion relation are less than 3%, and the relative errors between the theoretical and simulation cutoff frequencies of π mode are less than 1%. Cutoff frequency of π mode is in direct proportion to the cathode radius Rc, anode radius Ra and big cavity angle 2θ1, but in inverse proportion to small cavity radius Rd0, big cavity radius Rd1 and small cavity angle 2θ0. However, these qualitative relationships are not entirely consistent with those of the same cavity magnetron. In radial orientation, the structure parameters, the influence of which on frequency is sorted in descending order, are as follows: anode radius, big cavity radius, small cavity radius and cathode radius. In angular orientation, the influence of big cavity angle on frequency is greater than that of small cavity angle. In addition, mode isolation γ is in direct proportion to big cavity radius Rd1, but in inverse proportion to cathode radius Rc, small cavity radius Rd0, and small cavity angle 2θ0, and it increases first and then decreases with the increase in anode radius Ra or big cavity angle 2θ1.
Simulations using Monte Carlo method and expriment on dynamics of two-dimensional collimated thermal atomic beam of strontium
Authors: Cong Dong-Liang  , Xu Peng  , Wang Ye-Bing  , Chang Hong  ,   National Time Service Center, Chinese Academy of Sciences, Key Laboratory of Time and Frequency Primary Standards of Chinese Academy of Sciences, Xi’an 710600, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Considering the stochastic factors and using Monte Carlo method, we have studied the dynamics of two-dimensional (2D) collimated thermal atomic beam of strontium theoretically. Taking into account transverse divergence, initial position of each atom, longitudinal velocity distribution, and isotopes, we show the theoretical transverse distribution and the results of the Monte Carlo method as functions of detuning and power of laser, respectively. The theoretical results agree excellently with the experimental data, showing that the Monte Carlo method has precisely described the dynamics of 2D collimated thermal atomic beam of strontium. The method can provide an analytical tool for precisely controlling the 2D collimated thermal atomic beam and optimizing the atomic clock system.
The influence of alkali metal ions on crystallization habits of nonlinear optical crystal containing [B3O7] groups
Authors: Wang Di  , Zhang De-Ming  , Zhang Ji  , Wang Xiao-Fei  , Zhang Qin-Li  , Wan Song-Ming  , Yin Shao-Tang  ,   Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

LiB3O5 and CsB3O5 are two excellent nonlinear optical borate crystals containing [B3O7] groups. With a difference of aikali metal ions in structure, LiB3O5 and CsB3O5 exhibit different crystallization habits. The former is an incongruent compound, which cannot crystallize from its melt; however, the latter is a congruent compound obtained by cooling its melt directly. In this work, using Raman spectroscopy and ab initio calculation, the structures of LiB3O5 and CsB3O5 melts have been investigated, and then the influence of alkali metal ions on melt structures is discussed, finally, the relationship between crystallization habits of LiB3O5 and CsB3O5 and their melts is proposed. Results suggest that the boron oxide species of LiB3O5 and CsB3O5 melts are in the form of six-membered rings B3Ø7 and B3Ø6 (Ø represents a bridging oxygen); Raman frequency of the symmetric breathing vibration of six-membered rings shifts to low frequency with the addition of BØ4 tetrahedrons in rings; the relatively large amount of BØ4 tetrahedrons is found in LiB3O5 melts. However, Cs+ ions with larger ion radius hinder the formation of BØ4 tetrahedrons, and then reduc, the BØ4/BØ3 ratio of the melt. Finally, considering the growth mechanism of LiB3O5 and CsB3O5 crystals (Wang D, Wan S M et al. 2011 Cryst. Eng. Comm. 13 5239), we propose that the amount of BØ4 tetrahedrons in melts, which is influenced by aikali metal ions, determines LiB3O5 and CsB3O5 crystallization habits, therefore, and suggest the reduction of BØ4 tetrahedrons in melts is an effective way to crystallize LiB3O5.
Properties of over-the-horizon propagation of infrasonic wave in the inhomogeneous atmosphere
Authors: Zhou Chen  , Wang Xiang  , Zhao Zheng-Yu  , Zhang Yuan-Nong  ,   School of Electronic Information School, Wuhan University, Wuhan 430072, China
Published: December 2020

This paper explores the properties of over-the-horizon propagation of infrasonic wave in the inhomogeneous atmosphere using the nonlinear progressive equation (NPE). It has been calculated for propagation and path transmission loss of infrasonic wave all the year round in Wuhan. Results show that it is obviously influenced due to infrasonic wave propagation with properties of the inhomogeneous atmosphere and winds in the inhomogeneous atmosphere. Refraction in stratosphere is related to the speed of winds and propagation direction of infrasonic wave. The minimum propagation loss is achieved when the main frequency of gauss infrasonic wave source is 0.1Hz.
Investigation of the inversion of rainfall field based on microwave links
Authors: Jiang Shi-Tai  , Gao Tai-Chang  , Liu Xi-Chuan  , Liu Lei  , Liu Zhi-Tian  ,   Institute of Meteorology and oceanography, PLA Univ. of Sci. & Tech., Nanjing 211101, China
Published: December 2020

The accurate measurements of rainfall distribution with high spatial and temporal resolution have important implications in meteorology, hydrology, agriculture, environmental policies, flood warning and weather forecasting. Based on the rain-induced power-law attenuation equation, a method is presented to reconstruct the rainfall field using rain-induced attenuation data from microwave links, and a tomographic model is formulated. Simutareous itesative reconstruction technigue (SIRT) algorithm and regularization method are employed in the tomographic model separately. The simulated result shows that the tomographic model and iterative algorithms are able to reconstruct the intensity and features of original rainfall field preferably. The distribution of rain rate with high spatial and temporal resolution is also available. Therefore, rain estimation exploiting microwave attenuation measurement data is a useful complement to traditional rain gauge and radar derived estimations.
Applicability of resonating valence bond wave function with quantum Monte Carlo method for modeling high pressure liquid hydrogen
Authors: Li Ming-Rui  , Zhou Gang  , Chu Zhe  , Dai Xiang-Hui  , Wu Hai-Jun  , Fan Ru-Yu  ,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China;,   Northwest Institute of Nuclear Technology, Xi’an 710024, China
Published: December 2020

Based on the resonating valence bond theory, the linear combinations of the main orbits occupied by liquid hydrogen electrons are selected as the basis sets to construct the Jastrow antisymmetrized geminal product. The resonating valence bond (RVB) wave function which takes into consideration electron correlation effects provides lower energy than the local density approximation (LDA) function. In order to improve the nodal accuracy of the variational trial wave function, the backflow correlations are suggested to be employed whenever rs1.75 or T 15000 K, the improved wave function has about 1 mHa/atom decrease in local energy with respect to the one without backflow effects at the VMC level, and has a lower variance simultaneity. After combining the coupled electron-ion Monte Carlo (CEIMC) method with the RVB wave function, the simulation results we have obtained are in good agreement with the experimental and other ab-initio ones; the deuterium principal Hugoniot curve passing through the error bars of various existing experiments conducted via different high-pressure technologies has a maximum compression of 4.48 at about 50.3GPa, but the phenomenon of apparent increase in compression ratio along the Hugoniot between 100120 GPa has not been found. The RVB wave function discussed in this paper when adopted the CEIMC method is not only quite suitable for the simulation of liquid hydrogen within a wide range of density and temperature (1.0 rs2.2, 2800 K T60000 K), but also can give some more applicable thermodynamic properties of hydrogen under shock loading.
Computer simulation of radiation damage caused by low energy neutron in zirconium
Authors: Cui Zhen-Guo  , Gou Cheng-Jun  , Hou Qing  , Mao Li  , Zhou Xiao-Song  ,   Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610065, China;,   China Academy of Engineering Physics, Mian Yang 621900, China
Published: December 2020

Based on the Geant4 program-the package for simulating particle transportation in materials, simulations of the irradiation by neutrons with 1 MeV energy in zirconium were conducted The two adjacent elastic collisions between injected neutron and target atoms produce numerous primary knock-on atoms (PKA). It is found that the average distance of adjacent collisions is 29.47 mm, and the kinetic energy of most PKAs ranges from 1 keV to 15 keV. The damaged area induced by the PKAs is in nanometer scale, which is far less than the distance between the two PKAs. According to the fact that, the subsequent cascade collisions caused by the two PKAs can be considered as a set of independent processes, it is reasonable to study the cascade collisions of the PKAs by means of molecular dynamics method. The cascade collision progress of PKAs with different energies was performed, and the number of interstitial atoms and the size of the damaged regions in the material were extracted. Through the combination of Monte Carlo method and molecular dynamics simulation, a complete physical picture of the primary damage caused by the 1 MeV neutrons in the zirconium was obtained.
Solving dispersion relations of one-dimensional diatomic chain with on-site potential by invariant eigen-operator method
Authors: Ren Yi-Chong  , Fan Hong-Yi  ,   Department of Materials Science and Engineering,University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The dispersion law of a one-dimensional diatomic lattice with on-site potential cross on its dispersion relation is solved under the harmonic approximation with quantized invariant eigen-operator method (IEO) and the influences of on-site potential and force constant are discussed. It is shown that due to the existence of on-site potential the lattice vibration spectra induced are shifted. Under certain conditions, the point of intersection exist between optical branch and acoustic branch in the boundary of Brillioun zone, which means the frequency gap between optical branch and acoustic branch is zero.
Degradation mechanism of leakage current in AlGaN/GaN high electron mobility transistors
Authors: Ren Jian  , Yan Da-Wei  , Gu Xiao-Feng  ,   Key Laboratory of Advanced Process Control for Light Industry (Ministry of Education), Department of Electronic Engineering, Jiangnan University, Wuxi 214122, China
Published: December 2020

In order to study the degradation mechanism of leakage current in AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated AlGaN/GaN heterojunction Schottky diodes having equivalent structure and characteristics to AlGaN/GaN HEMTs. Step stress tests were then performed to compare the leakage current changes at different gate voltages. The transport mechanism of leakage current before and after degradation was validated based on the current-voltage and capacitance-voltage measurements. The light emission from the device surface was examined by emission microscopy (EMMI) to investigate the time-dependent degradation of leakage current. Experimental results show that the leakage current increases with increasing time and is accompanied by a large noise when the applied gate voltage exceeds a critical value. After introducing the polarization field into the current-field dependence, log(IFT/E) exhibits a good linear relationship with E both before and after degradation, indicating that the leakage current is dominated by the Frenkel-Poole (FP) emission. The slope of log(IFT/E)-E curve decreases after degradation, and the hot spots corresponding to defects are directly observed by EMMI at the gate edge of the degraded device, suggesting that the degradation mechanism is: New defects are induced by high electric field in the AlGaN layer, and the increase of defect density leads to the increase of FP emission current.