bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiphase equation of states of solid and liquid phases for bismuth
Authors: Li Ying-Hua  , Chang Jing-Zhen  , Li Xue-Mei  , Yu Yu-Ying  , Dai Cheng-Da  , Zhang Lin  ,   Science and Technology on Shock Wave and Detonation Physics Laboratory, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China;,   Institute of Structural Mechanics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Element bismuth (Bi) will experience complex phase transitions under high temperature and high pressure, which means significant changes in physical properties, such as density, energy, etc. Multiphase equations of states (EOSs) of both solid and liquid phases for Bi are presented. The EOSs are based on the three-term expression for Helmholtz free energy, where the ion vibration free energy is evaluated from the mean field potential model we recently proposed. The calculated results show that our multiphase EOSs can well reproduce the experimental data, including phase diagram, isotherms of solid phases, density measurements of liquid phase and shock-wave compression data, which proves the rationality of the parameter values and the universal nature of this model.
Investigation of polarons in perovskite manganites
Authors: Yi Ding  , Qin Wei  , Xie Shi-Jie  ,   State Key Laboratory of Crystal Materials, School of Physics, Shandong University, Jinan 250100, China
Published: December 2020

Perovskite manganites have aroused a great interest in their outstanding electrical and magnetic properties, but the characteristics of carriers in these materials are still under debate. According to the Mn-O chain, we build a one-dimensional tight-binding model to study the characteristics of charge carriers in manganites. It is obtained that at doping concentration x=0.5, the system shows a ferromagnetic state and the energy bands of spin up and spin down are completely splitted. A gap exists between valence band and conduction band, and all the electronic states are extended. With further doping, a localized electronic state appears, which we call a polaron. Accompanied with the electronic state, local distortions of the lattice and deep levels appear in the gap. The depth of the polaron increases with the doping quantity of electrons. It is also found that the polaron is spin polarized and has a maximum electronic charge of 0.621 e in the present parameters, beyond which the polaron will be divided into two separate states called solitons.
Influence of magnetic anisotropy thermoelectric effect on spin-dependent devices
Authors: Chen Jia-Luo  , Di Guo-Qing  ,   Jiangsu Key Laboratory of Thin Films, Department of Physics, Soochow University, Suzhou 215006, China
Published: December 2020

While researching the thermoelectric effect of the nanocontact, we find that the thermoelectric voltage between both ends of the "Γ"-shaped Ni wire changes significantly by applying an external magnetic field, which we attribute to the influence of magnetic anisotropy of Ni wire. The effect of the external magnetic field always produces an extra force whose direction goes against the temperature gradient. And the extra force clearly corresponds to the magnetic field and temperature difference between both ends of the Ni wire. These results suggest that during studying spin-dependent devices, the testing methods and the configuration of magnetic material need to be noticed seriously in order to avoid interfusing additional electromagnetic signals which may bring about a miscarriage of justice to the experimental results.
Effects of B additive on structure and magnetic properties of Co-Zr-Mo alloys
Authors: Hou Zhi-Peng  , Zhang Jin-Bao  , Xu Shi-Feng  , Wu Chun-Ji  , Wang Zi-Han  , Yang Kun-Long  , Wang Wen-Quan  , Du Xiao-Bo  , Su Feng  ,   College of Physics, Jilin University, Changchun 130023, China;,   College of Science, Shenyang Aerospace University, Shenyang 110136, China
Published: December 2020

The phases and magnetic properties of Co77Zr18-xBxMo5 (x=1.0, 1.5, 2.0, 2.5, and 4.0) are studied by X-ray diffraction analysis and magnetic measurements. Proper addition of Ti could improve the magnetic properties of Co-Zr alloy significantly. The largest value of Hc=7.0 kOe (1 Oe =79.5775 A/m) is obtained in the Co77Zr16Mo5B2 melt-spun ribbon. The grain size of Co5Zr phase decreases with the increase of B content, which contributes significantly to the enhancement of exchange-coupling effect. The coercivity values of the Co77Zr18-xMo5Bx (x=1.0, 1.5, 2.0, 2.5) melt-spun ribbons are affected mainly by the grain size of the Co5Zr phase. The coercivity value first increases and then decreases with the decrease of the Co5Zr phase. On the other hand, the coercivity mechanisms of Co77Zr18-xBxMo5 (x=1.0, 1.5, 2.0, 2.5) melt-spun ribbons are found to be of the pinning type.
Dielectric properties of CaCu3Ti4O12 ceramics prepared by a simplified coprecipitation method
Authors: Jia Ran  , Gu Fang  , Wu Zhen-Hua  , Zhao Xue-Tong  , Li Jian-Ying  ,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Precursor powder of CaCu3Ti4O12 is prepared by a simplified coprecipitation process, in which an optimum reaction condition with ammonium acetate is used as buffer solution and pH=3.0 is proved by X-ray diffraction and scanning electron microscope. The CaCu3Ti4O12 ceramics samples are prepared by sintering the calcined powder at different temperatures (1040℃-1100℃). It is found that higher sintering temperature of CaCu3Ti4O12 ceramics will lead to lager grain size, higher dielectric constant and lower dielectric loss. The dielectric loss of CaCu3Ti4O12 ceramics is suggested to be due to DC electric conductivity, low-frequency relaxation loss and high-frequency relaxation loss. The low-frequency and high-frequency relaxations are related to grain boundary and oxygen vacancy defects respectively.
Influences of Y- and La-dopant on the thermal conductive properties and dielectric relaxation of Al2O3-based ceramics
Authors: Wu Jun-Bo  , Tang Xin-Gui  , Jia Zhen-Hua  , Chen Dong-Ge  , Jiang Yan-Ping  , Liu Qiu-Xiang  ,   School of Physics and Optoelectric Engineering, Guangdong University of Technology, Guangzhou 510006, China
Published: December 2020

Al2O3 ceramics doping with Y3+ and La3+ are synthesized by conventional solid state reaction method. The structures, thermal conductivities properties and the effects of sintering temperature on the electrical properties of the samples are measured. X-ray diffraction results indicate that all the ceramics are formed to be of pure solid solution when the samples are sintered at 1500℃. Thermal conductivities of Al2O3 ceramics reach up to 8.60 W/(m· K). All the ceramics show temperature-stable dielectric characteristics. Typical dielectric relaxation behaviors are observed in Y- and La-doped Al2O3 ceramics, and the relaxation mechanism is also analyzed.
Study on the light extraction efficiency of GaN-based light emitting diode by using the defects of the photonic crystals
Authors: Yue Qing-Yang  , Kong Fan-Min  , Li Kang  , Zhao Jia  ,   School of Information Science and Engineering, Shandong University, Jinan 250100, China
Published: December 2020

Many studies have shown that the photonic crystals and surface nanostructures can improve the light extraction efficiency of light emitting diode (LED). The defects and disorders exist in photonic crystals inevitably as the manufacturing technology limitations, and so the light extraction efficiency of LED will be changed correspondingly. In this work we perform a simulation study on defects and disorder of photonic crystals by the finite-difference time-domain (FDTD) method, and we speed up the FDTD by GPU acceleration technology. Simulation results show that a small number of defects in photonic crystals LED do not reduce the LED light extraction efficiency. Instead, the light extraction efficiency of LED will be increased by adding some defects into the photonic crystals. We give a detailed analysis of its physical mechanism. We design a kind of photonic crystals with defects, and its light extraction efficiency achieves 1.6 times that of the perfect photonic crystals.
Changes of entropy and power spectrum in circadian rhythm for heart rate variability signals
Authors: Li Jin  , Liu Da-Zhao  ,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

Physiologic systems generate complex fluctuations in their output signals that reflect the underlying dynamics. In order to detect the effect of circadian rhythm for heart rate variability signals, we apply base-scale entropy method and power spectral analysis to the 24-hour heart rate variability signals. The results show that 1) such profound circadian- and pathologic-dependent changes are accompanied by changes in base-scale entropy and power spectral distribution, but by little changes in approximate entropy; 2) the circadian regulating ability of vagal nerve is clearly decreasing for congestive heart failure subjects; 3) the base-scale entropy is more sensitive than spectral analysis method to distinguishing wake/sleep states and identifying patterns generated from healthy and pathologic states, meanwhile, the base-scale entropy changes reflect corresponding changes in autonomic nerve outflow. With the suppression of vagal tone and dominance of sympathetic tone in congestive heart failure subjects, there are more variabilities in the m-words form π due to the trends in the data. So the higher base-scale entropy belongs to congestive heart failure subjects. With the decrease of sympathetic tone during sleep, the base-scale entropy drops in both healthy and congestive heart failure subjects. Finally, in order to further investigate the effect of series length, we calculate the base-scale entropy for different length series and find that the series length nearly has no influence on the result.
Periodic solution of relative rotation nonlinear dynamic model with commonly damped force and forcing periodic force
Authors: Li Xiao-Jing  , Chen Xuan-Qing  ,   College of Mathematics and Physics, Jiangsu Teachers University of Technology, Changzhou 213001, China
Published: December 2020

The periodic problem of the corresponding autonomous system is discussed. Some results on the existence and uniqueness of periodic solutions of the system are obtained by using the continuation theorem of coincidence degree theory. The results available from the literature are generalized. Furthermore, an example is given to illustrate our results are new.
Study of KDP crystal lattice strain and stress by high resolution X-ray diffraction
Authors: Sun Yun  , Wang Sheng-Lai  , Gu Qing-Tian  , Xu Xin-Guang  , Ding Jian-Xu  , Liu Wen-Jie  , Liu Guang-Xia  , Zhu Sheng-Jun  ,   China State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
Published: December 2020

The lattice strain of large-scale KDP crystal is characterized by using high resolution X-ray diffraction technique, and the lattice stress is analysed quantitatively in detail. The results indicate that KDP crystal may cleave easily along the [001] direction, which corresponds to the cracking phenomenon in the practical work. The major factors of introducing the internal stress and causing crack in the crystal growth process are summarized. Those conclusions provide important theoretical basis for proposing crack control measures of the large-scale KDP crystals.
Quantum phase transition and ground state entanglement of the quantum spin system: a MERA study
Authors: Zhao Jian-Hui  , Wang Hai-Tao  ,   Postdoctoral Research Station of Materials Science and Engineering, Chongqing University, Chongqing 400030, China;,   College of Physics, Chongqing University, Chongqing 400030, China
Published: December 2020

We use the multi-scale entanglement reorganization ansatz algorithm to simulate the spin 1/2 quantum XYX model and determine its ground-state phase diagram and entanglement phase diagram by using local order parameter and characterizing quantum entanglement: one-tangle, concurrence, and entanglement ratio R. We find that the information in entanglement phase diagram is more than in ground-state phase diagram. In addition, we extract the critical exponents β and ν from the numerical data near critical point.
Features extraction based on singular value decomposition and stochastic resonance
Authors: Zheng An-Zong  , Leng Yong-Gang  , Fan Sheng-Bo  ,   School of Mechanical Engineering, Tianjin University, Tianjin 300072, China;,   Key Laboratory of Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin 300072, China
Published: December 2020

In order to detect the weak characteristic signal submerged in heavy noise with extremely low signal-to-noise ratio, a method based on singular value decomposition (SVD) and stochastic resonance is proposed. The sampling signal is first preprocessed and reconstructed by means of SVD, and then we search for a component signal. In the component signal, the components of the characteristic signal match noise strength. Then the component signal is processed with the non-linear bistable system to obtain stochastic resonance response, thus the goal of detecting the weak characteristic signal submerged in a heavy background noise is realized.
Synchronization of two spiral waves interacting through a passive medium
Authors: Chen Xing-Ji  , Tian Tao-Tao  , Zhou Zhen-Wei  , Hu Yi-Bo  , Tang Guo-Ning  ,   College of Physics and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Synchronization of two spiral waves in two-dimensional excitable systems interacting through a passive medium is studied by using the Bär model. The passive medium is composed of excitable elements. There are no couplings among these elements. The numerical results show that synchronization of spiral waves is significantly affected by the passive medium. When two subsystems have the same initial spiral waves, the passive medium can induce meander of stable spiral waves and cause spiral waves to transform into multi-spiral waves or anti-target waves. When initial spiral waves are in an asynchronization state, the synchronization and phase-synchronization between two spiral waves are established if the relevant parameters are properly chosen. In addition, the following phenomena are observed: the tips of two spiral waves repel each other, multi-spiral waves coexist, synchronized spatiotemporal pattern repeats periodically, and the two systems evolves into the resting state. Wave patterns can generally be observed in passive medium. However, passive medium can exhibit synchronous oscillation in certain circumstances. These results can help one understand the formation of spatiotemporal patterns in the cardiac system.
Raman spectrum research on graphene modification under high intensity laser
Authors: Zhang Qiu-Hui  , Han Jing-Hua  , Feng Guo-Ying  , Xu Qi-Xing  , Ding Li-Zhong  , Lu Xiao-Xiang  ,   Department of Electrical Information Engineering, Henan Institute of Engineering, Zhengzhou 451191, China;,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China;,   Electrical and Computer Engineering, University of Houston, USA
Published: December 2020

The graphene samples with different numbers of layers are prepared by chemical vapor deposition, the relation between the number of graphene layers and the transmission at 550 nm is analyzed by graphene transmission spectrum. Besides, the damage characteristics of graphene under high intensity laser irradiation are analyzed. The results show that under the laser irradiation, for the single layer graphene, G band and 2D band shift toward high frequeney but for the multilayer graphene, only G band shifts a litile; the ratio between intensities of G band and 2D band in Raman spectrum characterizes the number of graphene layers, and it increases with the irradiated time, so the high intensity laser can peel the graphene.
Displacement damage effect on the characteristics of quantum well laser
Authors: Ma Jing  , Che Chi  , Han Qi-Qi  , Zhou Yan-Ping  , Tan Li-Ying  ,   National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Quantum well lasers are irradiated by electrons with a total fluence of 1 10-16 cm-2. The output power is reduced and the threshold current is increased under electron irradiation. The displacement damage effect on quantum well laser is analyzed theoretically and we deduce the relationship between the radiation induced output power and threshold current change and the electron fluence. The formula fits the experiment data very well, and can describe the change trend of the laser performance under electron irradiation, it can also predict the behavior of quantum well laser under radiation environment and is valuable for practical application.
Characteristics and optimization of traffic flow in a two-off-ramp system
Authors: Jiang Jin-Sheng  , Dong Li-Yun  ,   Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China;,   Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai 200072, China
Published: December 2020

In this paper, a multi-lane cellular automata model is adopted to investigate the evolution of traffic flow in a two-off-ramp system. The variable message sign (VMS) is used to realize traffic flow guidance. More attention is paid to the decision-making behaviors of the driver, i.e., choosing the target off-ramp and its influence on road capacity. The original model without VMS and the improved model with VMS are proposed respectively. Through numerical simulation, the corresponding phase diagram, the capacity, the flux of each section and typical patterns are obtained, then the effects of the injection probabilities, the fraction of leaving vehicles and the length of the exit lane on capacity are analyzed in detail. When the length of the exit lane is rather short but the entering probability and the fraction of leaving vehicles are rather large, the road capacity is increased noticeably with the help of VMS and therefore the state of traffic flow is improved. It is shown that the utilization efficiency of downstream off-ramp is enhanced and traffic jams are alleviated due to the guidance of VMS.
Influence of diode gap distance on space charge effects in field emission
Authors: Zuo Ying-Hong  , Wang Jian-Guo  , Fan Ru-Yu  ,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China;,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Under intense electric field, the electrons emitted from the cathode by field emission have strong space charge effects, so the space charge limited current of a diode is an important parameter in the design of many intense electron beam apparatus, such as the high power microwave source devices. The field emission current density depends on cathode material and electric field at the cathode surface, while the space charge limited current density is a function of applied voltage and diode gap distance. To investigate the influence of the diode gap distance on space charge effect in field emission, in the paper we build a model of a planar vacuum diode operating with a field emission cathode. The time evolutions of the electric field at the cathode surface with various diode gap distance and applied voltage are studied using the particle-in-cell method, and the steady value of the electric field at the cathode surface is obtained. The electric field at the cathode surface first oscillates and finally reaches a steady state. At a given applied electric field, the longer the diode gap distance, the higher the absolute value of the electric field at the cathode surface is, and it takes more time to reach the steady state for longer diode gap distance; the distribution of the electric field in the diode gap region is steeper for shorter diode gap distance after the electric field at the cathode surface has reached a steady state.
Phase constitution and microstructure evolution of rapidly solidified Ti-Cu-Fe alloy
Authors: Lu Xiao-Yu  , Liao Shuang  , Ruan Ying  , Dai Fu-Ping  ,   Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Ternary Ti61.2Cu32.5Fe6.3 quasiperitectic alloy is rapidly solidified in drop tube. The diameter of the obtained droplets varies from 80 to 1120 m. The theoretical analysis indicates that the range of undercooling is from 34 to 293 K (0.23TL). Due to the influences of containerless, microgravity, ultrahigh vacuum, etc, the microstructure of solidified alloy is composed of Cu0.8Fe0.2Ti phase, CuTi2 phase and CuTi3 phase. This result deviates appreciably from the equilibrium state. CuTi3 phase exhibits a conspicuous solute trapping effect during rapid solidification. The microstructure of alloy consists chiefly of eutectic (Cu0.8Fe0.2Ti and CuTi2 phases) and dendrites (Cu0.8Fe0.2Ti, CuTi3) structure. With the increase of undercooling, the microstructure of eutectic experiences a transition from strip eutectic cell to ellipsoidal eutectic cell to spherical eutectic cell; the morphology of Cu0.8Fe0.2Ti dendrite experiences a transition from coarse dendrites to broken dendrites to anomalous grain; while the morphology of CuTi3 dendrite changes from small block to coarse dendrite.
Electronic structure and photoelectric properties of OsSi2 epitaxially grown on a Si(111) substrate
Authors: Yu Zhi-Qiang  ,   Department of Electrical Engineering, Hubei University for Nationalities, Enshi 445000, China;,   Institute of Advanced Optoelectronic Materials and Technology, Guizhou University, Guiyang 550025, China
Published: December 2020

The electronic structure and photoelectric properties of semiconductor material OsSi2 epitaxially grown on a Si(111) substrate are invesligated using the pseudo potential plane wave method based on first principles method. The calculated results show that OsSi2 is an indirect semiconductor material with a band gap of 0.625 eV. The valence band of OsSi2 epitaxially grown on a Si(111) substrate is composed mainly of Si 3s, 3p and Os 5d, and the conduction band is comprised mainly of Os 5d as well as Si 3s, 3p. The static dielectric function is 15.065, the reflectivity is 3.85, and the biggest peak of the absorption coefficient is 3.9665× 105 cm-1. Furthermore, the static dielectric function, refractivity index, reflectivity, absorption, conductivity and loss function of OsSi2 epitaxially grown on a Si(111) substrate are analyzed in terms of the calculated band structure and density of states. The results offer theoretical data for the design and application of OsSi2.
The effects of Ag-doping on thermoelectric properties of p-type Pb0.5Sn0.5Te compound
Authors: Yu Bo  ,   h Research Institute, CSIC, Wuhan 430064, China
Published: December 2020

A series of Ag-doped p-type Agx(Pb0.5Sn0.5)1-xTe compounds is prepared by melting followed by slow-cooling process, and the phase compositions, microstructures and thermoelectric properties are also systematically investigated. The introduction of Ag in Pb/Sn site effectively increases the hole density which is much lower than the theoretically predicated value in the approximation of complete substitution and single acceptor of Ag, in spite of the fact that all samples show finely single phase for the 5% Ag-doped sample. This implies that part of Ag atoms enter into the interstitial sites acting as electron donor to reduce the hole density. With the increase of Ag content, the electrical conductivity increases gradually and the Seebeck coefficient shows an opposite variation tendency, mainly owing to the variation of hole density. Interestingly, the anomalous crossover of Seebeck coefficient at about 450 K indicates the transition of dominating valence valley from light-band to heavy-band while temperature is higher than 450 K. Consequently, due to the optimization of hole density and the domination of heavy band with large effective mass, 1% Ag-doped sample obtains a highest power factor of 2.1 mWm-1K-2 at 750 K, which results in a highest ZT of 1.05 combined with the suppressed lattice thermal conductivity via intensifying point defect phonon scattering. This high ZT is ～ 50% higher than that of Ag-free sample and also higher than commercial p-type PbTe material. Further, the 50% substitution of toxic and heavy Pb by Sn is beneficial for the practical application and environmental sustainability of PbTe-based materials.
Band structure and optical absorption in InAs/GaSb quantum well
Authors: Liu Zhu  , Zhao Zhi-Fei  , Guo Hao-Min  , Wang Yu-Qi  ,   Applied Technology Laboratory of Materials, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

An analysis of band structure, wave function distribution and absorption of linearly polarized light along the [110] direction in InAs/GaSb quantum well grown along the [001] direction is performed by the eight-band K-P model and finite difference method. Our study shows that the band structure and wave function distribution could be regulated effectively by changing the thickness of InAs or GaSb layer. When the bottom of conduction subband and the top of the valence subband are in resonance, the hybridization of ground electron and light-hole state at the zone-center is very weak, and the overlap between the wave function of the ground and the first-excited electron state is considerable, according to the theory of wave function engineering, so the transition rate between the ground and the first-excited electron state at the zone-center is larger than that when the bottom of conduction subband and the top of the valence subband are not in resonance. This is very important for designing advanced optoelectronic devices such as far-infrared or mid-infrared cascade lasers and detecters based on InAs/GaSb quantum wells.
Hot deformation behavior of spray formed FGH4095
Authors: Zhang Yu  , Ge Chang-Chun  , Guo Biao  , Shen Wei-Ping  ,   Institute of Special Ceramics and Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

For the numerical simulation of hot working process of spray-formed FGH4095, the high temperature deformation behavior of spray-formed FGH4095 is studied at different deformation temperatures (1010-1140 ℃) and different strain rates (0.001-10.0 s-1) using Gleeble 3800 thermal simulator. The constitutive equation is established with the sinh model. The calculative results are consistent with the experimental data. It indicates that the accurate material model is provided for the numerical simulation for hot working process of spray-formed FGH4095.
The characteristics of turbulent momentum and heat similarity function and bulk transfer coefficient over grassland surface
Authors: Yue Ping  , Zhang Qiang  , Niu Sheng-Jie  , Wang Run-Yuan  , Sun Xu-Ying  , Wang Sheng  ,   Key Laboratory of Arid Climate Change and Reducing Disaster of Gansu Province, Key Laboratory of Arid Climate Change and Reducing Disaster of CMA, Institute of Arid Meteorology, CMA, Lanzhou 730020, China;,   Zhangye National Meteorological Observatory, Zhangye 734000, China;,   Nanjing University of information Science and Technology, Nanjing 210044, China
Published: December 2020

The turbulent momentum and sensible heat transfer over land surface have a notable influence on the change of global climate and atmospheric circulation, and Monin-Obukhov similarity function is a most important method to calculate the turbulent momentum and sensible heat flux near the surface, and ascertaining the right bulk transfer coefficient is a most effective way of improving the atmospheric model simulation capabilities. The characteristic of Monin-Obukhov similarity function is analyzed and the empirical formula is fitted, and the changes of bulk transfer coefficients of momentum and sensible heat over grassland with mean wind speed at 10 m high are discussed by using the data of the flux observations over Xilin Gol grassland in Spring 2008. Comparison with the observation values by eddy correlation method shows that the revised Monin-Obukhov similarity function underestimates the momentum flux by 10.8% and over estimates the sensible heat flux by 6.5%, but the typical Businger-Dyer similarity function underestimates the momentum flux by 37.0% and over estimates the sensible heat flux by 16.1%. Under unstable stratification, the bulk transfer coefficients of momentum (CD) and sensible heat (CH) vary with mean wind speed at 10 m high (U) according to the power law, which take the forms CD=0.009U-0.322 and CH=0.184U-1.978 respectively. Under stable stratification, the bulk transfer coefficients are found to increase in the manner of the logarithm law over grassland surface and tend to neutral or nearly neutral values with wind speed increasing. The revised Monin-Obukhov similarity function can significantly improve the accuracy of turbulent momentum and sensible heat flux computed by average gradient data, and the relations between bulk transfer coefficients and wind speed at 10 m high provide the useful parameterization schemes for accurately expressing the transportation characteristics of near surface turbulence.
Research on different time-scale prediction models for the total electron content
Authors: Sheng Zheng  ,   Institute of Meteorology and Oceangraphy, PLA University of Science and Technology, Nanjing 211101, China;,   Sate Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

In the solar-terrestrial space environment, the ionosphere couples tightly with the upper magnetic layer as well as the lower middle atmosphere in various forms. Meanwhile, the ionosphere can affect radio-communication and satellite navigations, so the research on ionosphere prediction model is very important. Now, the accuracy of statistic prediction mode is about 60%, but cannot meet the practical requirements. In order to solve the problem, the prediction model of total electron content (TEC) data is achieved in three major phases: decomposition of the spatiotemporal variability of the TEC data, noise reduction of the encoded space, and time variability and the prediction, by a nonlinear forecasting technique of the time variability. Experiments show that the new prediction model is better than traditional prediction model. The prediction data shows realistic features and a reliable physical distribution, and the relative accuracies of prediction for 1, 2, 4, and 7 d obtained by our method is 0.32, 0.48, 0.68 and 0.94 TECU.
Group consensus analysis of multi-agent systems with delays
Authors: Ji Liang-Hao  , Liao Xiao-Feng  , Liu Qun  ,   State Key Lab. of Power Transmission Equipment & System Security and New Technology, College of Computer Science, Chongqing University,Chongqing 400044, China;,   College of Computer Science and Technology, Chongqing University of Posts and Telecommunications, Chongqing 400065, China
Published: December 2020

In this paper, a new consensus problem is investigated which is group consensus. It contains such consensus problem as a special case that all agents in a network reach a consistent value asymptotically. Consider a dynamic multi-agent system with connected undirected or connected bipartite graph topology and delays, two novel consensus protocols are introduced to solve the group consensus problem. The convergence analysis is discussed and the sufficient condition for system group convergence is obtained based on the frequency-domain analysis and generalized Nyquist criterion, respectively. And we know that the condition of group convergence is only depended on system's time delay and the adjacent weight between the agents, meanwhile, delay can affect the dynamic characteristics of the system. Finally, simulations are provided to demonstrate the effectiveness of our theoretical results.
The mechanism of energy input to bistable system to generate stochastic resonance
Authors: Lin Min  , Huang Yong-Mei  ,   College of Metrology Technology and Engineering, China Jiliang University, Hangzhou 310018, China
Published: December 2020

According to the Langevin equation that describes the Brownian particle motion, the instantaneous power and average power of Brownian particle provided by periodic external force are analyzed. The mechanism of energy input to a bistable system to generate stochastic resonance is revealed. The theoretical analysis and numerical simulation manifest that the instantaneous power absorbed by Brownian particle changes periodically. The change frequency is twice that of periodical external force, and its amplitude and average are controlled by the noise intensity. The energy input form of periodic external force can be controlled effectively by changing the parameters of thermal environment where Brownian particle is located.
Berry phase and quantum phase transition in spin chain system with three-site interaction
Authors: Shan Chuan-Jia  ,   College of Physics and Electronic Science, Hubei Normal University, Huangshi 435002, China
Published: December 2020

In this paper, we diagonalize the Hamiltonian of the one-dimensional spin chain system with three-body interaction. Then we solve geometric phase of ground state in the system through a rotating operation. By the numerical calculation of the geometric phase and its derivative, we consider the three-body interaction effects on the geometric phase and quantum phase transition, the results show that the geometric phase can be well used to characterize quantum phase transition in this system, and find that three-body interaction not only can move the criticality region, but also can generate a new critical point.
Dynamics of current controlled switching converters under wide circuit parameter variation
Authors: Bao Bo-Cheng  , Yang Ping  , Ma Zheng-Hua  , Zhang Xi  ,   School of Information Science and Engineering, Changzhou University, Changzhou 213164, China;,   School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China
Published: December 2020

With current-controlled buck-boost converter used as an example, through a detailed description of the switch state of the switching converter under wide circuit parameter variation, such as input voltage and load resistance variation, two inductor current borders in the current controlled switching converter are derived and an accurate discrete-time model is established. The validation of the discrete-time model is verified by a piecewise-linear model. Based on the discrete-time model, the complex dynamical behaviors existing in switching converter, such as period-double bifurcation, border-collision bifurcation, robust chaos and intermittent chaos, etc., are revealed. By formulating the Jacobian, the maximum Lyapunov exponent and the movement trajectories of eigvalues with the variations of circuit parameters are obtained. By utilizing the parameter-space maps, the operation-state regions corresponding to circuit parameter regions are estimated. Finally, an experimental setup is implemented, the corresponding observation results are consistent with those of theory analyses. In this paper the dynamics theory in switching converters is investigated systematically; the analysis methods and research results are helpful for designing and controlling switching converters.
A novel free-space method of mearsuring of electromagnetic parameters based on the resonance property of reflectivity
Authors: Ding Shi-Jing  , Huang Liu-Hong  , Li Yue-Bo  , Xue Fan-Xi  ,   The Third Engineer Scientific Research Institute of the Headquarters of the General Staff, Luoyang 471023, China
Published: December 2020

The free-space method is a analysis method applicable for measuring electromagnetic parameters of materials, owing to its non-contact and non-destructibility. Base on the resonance property of reflectivity under sweep frequency mode, a novel free-space method is presented. For the study of constructive interference or destructive interference, the method is used to measure the real component of complex dielectric constant through the thickness of material and the interference frequency. The method can also measure the imaginary component of complex dielectric content by the positions of peaks and valleys of waveform or/and their correlation. The study also demonstrates the higher precision obtained by using the valley-to-valley ratio than by using the standing waveform ratio (peak-to-valley ratio).
Electrical and mechanical properties of a Cu-Cr-Zr alloy aged under an imposed DC current and static magnetic field
Authors: Rao Xian-Jun  , Zhong Yun-Bo  , Zhang Zeng-Guang  , Wang Zhi-Qiang  , Deng Kang  , Ren Zhong-Ming  , Xu Kuang-Di  ,   Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072, China
Published: December 2020

In this paper, Cu-0.41wt.%Cr-0.21wt.%Zr alloy is subjected to an isochronal aging treatment with a DC electric current (100A/cm2) and a static magnetic field simultaneously imposed. The alloy in the form of plate with a thickness of 2 mm is solid-solution-treated and cold deformed with a total area reduction of more than 98% before aging. The results indicate that the conductivity and micro hardness of the sample are significantly improved by the imposed electric-magnetic field. The conductivity of the sample increases with magnetic flux density (MFD) improving, especially at a lower aging temperature (350 ℃), and a maximum improvement of 22.1% IACS in conductivity could be obtained with a 10 T magnetic field. For the property of micro hardness, it increases with MFD increasing at a lower aging temperature (350 ℃), while at a higher aging temperature, it first increases and then decreases with MFD increasing. The effects of the DC current and magnetic field on the microstructure of the alloy are investigated by transmission electron microscopy. A lower dislocation density and more Cr precipitation are observed under electric-magnetic couple field than under the DC current only. It indicates that the electric and magnetic fields enhance the aging process of Cu-Cr-Zr alloy distinctly. According to the experimental results, we believe that the main mechanism of the influence of electric and magnetic fields on the Cu-Cr-Zr alloy is that the magnetic field enhances the interaction between solute atoms, vacancies, dislocations and electron wind force, thereby intensifing the effect of the dc current.
Influences of isotopic variant and collision energy on the stereodynamics of the N(4S)+H2 reactive system
Authors: Xia Wen-Ze  , Yu Yong-Jiang  , Yang Chuang-Lu  ,   School of Physics and Opto-Electronic Engineering, Ludong University, Yantai 264025, China
Published: December 2020

The influences of isotopic variant and collision energy on the stereodynamics in the N(4S)+H2 reaction are investigated by using the quasi-classical trajectory method on the calculated DMBE potential energy surface. The angular distributions of P(r), P(r) and P(r, r), which reflect the vector correlation of k-j' and k-k'-j', differential cross sections,integral cross sections are calculated and discussed in detail. Moreover,the influences of collision energy variant in a collision energy range of 25-80~kcal/mol in the three reactions N+H2,N+D2 and N+T2 are also studied The results indicate that the stereodynamic properties of the reactions are influenced by intermolecular isotope and collision energies.
Simulation and design of a W-band extended interaction klystron amplifier
Authors: Wu Yang  , Xu Zhou  , Zhou Lin  , Li Wen-Jun  , Tang Chuan-Xiang  ,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China;,   Institute of Applied Electronics, CAEP, Mianyang 621900, China;,   Science and Technology on High Power Microwave Laboratory, Mianyang 621900, China
Published: December 2020

Extended interaction klystron amplifier is a very important high power millimeter wave source with many actual and potential applications. Based on the electromagnetic simulation software and 3D PIC code, a W-band extended interaction klystron amplifier is designed. In the PIC simulation, when the beam voltage is 30 kV and current is 8 A, the device can generate a 43 kW output power at 96.8 GHz with an efficiency of 18% and a gain of 49.3 dB.
Optical bistability via active Raman gain in an n-type atomic medium
Authors: Yang Jin-Jin  , Li Hui-Jun  , Wen Wen  , Huang Guo-Xiang  ,   Department of Physics, and Institute of Nonlinear Physics, Zhejiang Normal University, Jinhua 321004, China;,   Department of Mathematics and Physics, Hohai University, Changzhou Campus, Changzhou 213022, China;,   Department of Physics, and State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200061, China
Published: December 2020

We study the optical bistability (OB) in an active Raman gain atomic medium by means of a unidirectional ring cavity. The system considered is a resonant n-type four-level atomic ensemble, which can be realized at room temperature and not only have a lot of tunable parameters, such as detuning, atomic concentration, pump and control field, but also possess gain-free (or little gain) transparent windows. We discuss the conditions and the range of these parameters for realizing OB, and also the condition for realizing optical multistability. Our results will provide the theoretical basis for experimental realization.
Improvement on stress instability in smoothed particle hydrodynamics
Authors: Yang Xiu-Feng  , Liu Mou-Bin  ,   Key Laboratory for Hydrodynamics and Ocean Engineering, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Smoothed particle hydrodynamics (SPH) is a Lagrangian meshfree particle method. It has special advantages in modeling large deformation and free surface flow, and has been widely applied to different problems in engineering and science. However, the classical SPH suffers from stress instability which resticts its further development and applications. The fundamental reason of stress instability is that the stress state and the kernel do not match each other. For frequently used bell-shaped kernel function, in tensile state the attraction between particles increases as particle spacing decreases, thereby leading to tensile instability. In a compressible state, the repulsive force between particles increases, and then decreases as particle spacing decreases, thereby leading to compressible instability. In this paper is presented an approach to removing stress instability in SPH by proposing a new kernel function and a modified SPH discrete form. In the modified SPH, the force between particles is always repulsive and it increases as particle spacing decreases. Two numerical examples are given to test the proposed approachs, and the obtained numerical results clearly demonstrate that the new approach can eliminate stress instability effectively.
Research on interaction between bubble and surface waves based on BEM
Authors: Liu Yun-Long  , Zhang A-Man  , Wang Shi-Ping  , Tian Zhao-Li  ,   College of Shipbuilding Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

In order to study the interaction between underwater explosion bubble and surface waves, numerical and analytical methods are combined in this paper to solve the singular problem of the opened free surface and to consider the influence of far field. Then we decompose the velocity potential into incident potential due to the waves and the disturbing potential due to the bubble to consider the influence of waves. With the numerical model, interaction between the underwater explosion bubble and surface waves and the influence of wavelength and initial phase on the bubble dynamics are analyzed in this paper. Through the analysis of the numerical results, following conclusions are reached. During the collapsing phase of the bubble, the existence of the waves would budge the upside bubble and the downward liquid jet, while for the spike of the free surface, the influences on its height and width are considerable besides its migration. These magnitudes of influence are changed with the initial phase periodically, and decrease with the increase of wavelength in the range considered in this paper.
Heating mechanism of hot electrons in the interaction between laser and nanolayered target
Authors: Yu Jin-Qing  , Jin Xiao-Lin  , Zhou Wei-Min  , Li Bin  , Gu Yu-Qiu  ,   Vacuum Electronics National Laboratory, University of Electronic Science and Technology of China, Chengdu 610054, China;,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The generation of hot electrons and the coupling efficiency from laser to hot electrons are very important issues in fast ignition of inertial confinement fusion, which are important for optimizing the parameters of laser pulse and plasma and reducing the requirement for laser pulse. Laser interaction with nanolayered target is considered to be one of available ways of enhancing the coupling efficiency of laser to hot electrons. In order to understand the heating mechanism of hot electrons in the interaction between laser and nanolayered target in great detail, two-dimensional particle-in-cell simulation is carried out in this paper. Reflux for cold electrons moving to the interaction-face and then being accelerated near the interaction-face is detected by observing the tracks of electrons in the nanolayered target. It is found that the energies of inverse electrons are far smaller than those of forward electrons and the most inverse electrons are from the reflux of cold electrons by investigating the variations of the electron density and the electron energy density in one laser period. The J B heating mechanism is found to be a dominate mechanism in the generation of hot electrons by comparing the field and the locations of hot electrons at different times.
Numerical simulation of enhanced glow discharge plasma immersion ion implantation using three-dimensional PIC/MC model
Authors: He Fu-Shun  , Li Liu-He  , Li Fen  , Dun Dan-Dan  , Tao Chan-Cai  ,   School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China
Published: December 2020

Enhanced glow discharge plasma immersion ion implantation is self-consistently simulated using a three-dimensional PIC/MC model. The information about ion counts, space potential, plasma density and ion incident dose is obtained. The results show that the sheath has fully expanded at 5 μs. There is a stable equilibrium of ion counts at 15 μs, which corroborates the characteristic of self-sustaining glow discharge of EGD-PIII. In the space just below anode where is found a highest plasma density, verifying the electron focusing effect. The rate of implantation is steady and the incident dose is relatively uniform except at the rim of target. A higher pulse negative bias may increase the injection rate but reduce the dose uniformity at the same time.
Experimental investigation of delayed double pulse laser produced plasma in air
Authors: Liu Ke  , Yi You-Min  , Li Liang-Bo  ,   Experiment Center, Anhui Sanlian University, Hefei 230601, China;,   Department of Information and Communication Technology, Anhui Sanlian University, Hefei 230601 China
Published: December 2020

By using Mach-Zehnder interferometer, we gain time series interference patterns of delayed double pulse laser and three-monopulse laser produced air plasmas. And then we gain electron density values in the centre of plasma region at different moments. We compare electron density values of the plasmas produced, respectively, by delayed double pulse laser and three-monopulse laser. The results show that the electron density of the plasma produced by the delayed double pulse laser is greater than by the three-monopulse laser at the same time after the second laser effects. The electron density time change processes of the plasma produced by delayed double pulse laser and monopulse laser of the same injection energy are analyzed theoretically. The analysis results show that when the same laser energy is injected, the delayed double pulse method can increase the plasma existing time effectively.