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共有20条相似文献,以下是第1-20项 搜索用时 93 毫秒

1.  Circuit-field coupled finite element analysis method for an electromagnetic acoustic transducer under pulsed voltage excitation  
   郝宽胜  黄松岭  赵伟  王珅《中国物理 B》,2011年第20卷第6期
   This paper presents an analytical method for electromagnetic acoustic transducers (EMATs) under voltage excitation and considers the non-uniform distribution of the biased magnetic field. A complete model of EMATs including the non-uniform biased magnetic field, a pulsed eddy current field and the acoustic field is built up. The pulsed voltage excitation is transformed to the frequency domain by fast Fourier transformation (FFT). In terms of the time harmonic field equations of the EMAT system, the impedances of the coils under different frequencies are calculated according to the circuit-field coupling method and Poynting’s theorem. Then the currents under different frequencies are calculated according to Ohm’s law and the pulsed current excitation is obtained by inverse fast Fourier transformation (IFFT). Lastly, the sequentially coupled finite element method (FEM) is used to calculate the Lorentz force in the EMATs under the current excitation. An actual EMAT with a two-layer two-bundle printed circuit board (PCB) coil, a rectangular permanent magnet and an aluminium specimen is analysed. The coil impedances and the pulsed current are calculated and compared with the experimental results. Their agreement verified the validity of the proposed method. Further- more, the influences of lift-off distances and the non-uniform static magnetic field on the Lorentz force under pulsed voltage excitation are studied.    

2.  Performance characteristics and optimal analysis of a nonlinear diode refrigerator  
   王秀梅  何济洲  梁红妮《中国物理 B》,2011年第20卷第2期
   This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures.Based on the theory of thermal fluctuations,the expressions of the heat flux absorbed from the heat reservoirs are derived.After the heat leak between the two reservoirs is considered,the cooling rate and the coefficient of performance are obtained analytically.The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail.    

3.  Performance characteristics a nonlinear diode and optimal analysis of refrigerator  
   Wang Xiu-Mei  He Ji-Zhou  Liang Hong-Ni《中国物理 B》,2011年第2期
   This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of thermal fluctuations, the expressions of the heat flux absorbed from the heat reservoirs are derived. After the heat leak between the two reservoirs is considered, the cooling rate and the coefficient of performance are obtained analytically. The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail.    

4.  Research on coupling between thermoacoustic resonance pipe and piezoelectric acoustic source  
   FAN Li ZHANG Shuyi WANG Benren《Chinese Journal of Acoustics》,2007年第26卷第2期
   Piezoelectric loudspeakers have been used in thermoacoustic refrigerators for operating at the high frequency to miniaturize the system. Then the coupling between the piezoelectric loudspeaker and resonance pipe becomes an important factor for improving the performances of the system. By the equivalent circuit model, the expressions of the acoustic output power and electroacoustic transfer efficiency at a low operating frequency are obtained, and then the structures of the piezoelectric loudspeaker and resonance pipe, as well as the operating frequency, are optimized to achieve a high electroacoustic transfer efficiency and a large acoustic output power. It is also shown that when the total reactance of the system equals zero, the resonance frequency of the resonance pipe is the optimized operating frequency and a high acoustic output power can be achieved. However, the highest transfer efficiency and largest acoustic power cannot be obtained simultaneously, therefore a trade-off condition must be adopted.    

5.  Influence of resonator shape on nonlinear acoustic field in a thermoacoustic engine  
   LIU Danxiao  ZHOU Chengguang  LIU Ke《Chinese Journal of Acoustics》,2012年第3期
   The influence of the resonator shape on nonlinear acoustic field in a thermoacoustic engine is studied.The resonator of themoacoustic engine is boundary driving by a piston at one end,and the other end of it is rigid closed.A one-dimensional wave equation that accounts for gas dynamic nonlinearities and viscous dissipation in the resonator is established based on the governing equations of viscous hydromechanics.The nonlinear wave equation is solved using approximate Galerkin method.The nonlinear acoustic field in four different types of shaped resonators including hyperbolical,exponential,conical and sinusoidal are obtained and compared with that of a cylindrical resonator.It is found that the amplitude and waveform of the pressure are strongly affected by the resonator shape,the driving amplitude and the oscillation frequency of the piston.Waveform distortion,resonance frequency shift and hysteresis are observed,when the piston oscillation amplitude is large enough.The advantages of shaped resonator for thermoacoustic engine lie in inhibition of higher order harmonics and improvement of pressure ratio,etc.    

6.  Effects of Trapped Electrons on Off-axis Lower Hybrid Current Drive  
   JIAO Yiming LONG Yongxing DONG Jiaqi GAO Qingdi WANG Aike LIU Yong《核工业西南物理研究院年报(英文版)》,2006年第1期
   The effects of trapped electrons on off-axis lower hybrid current drive (LHCD) in tokamaks are studied. The influence of the resonance regime on the current drive efficiency as well as the influence of trapped particle fraction on the current drive efficiency are emphasized.    

7.  Non-monotonic dependence of current upon i-width in silicon p–i–n diodes  
   庞正鹏  王欣  陈健  杨盼  张洋  田永辉  杨建红《中国物理 B》,2018年第6期
   Silicon p–i–n diodes with different i-region widths are fabricated and tested. It is found that the current shows the non-monotonic behavior as a function of i-region width at a bias voltage of 1.0 V. In this paper, an analytical model is presented to explain the non-monotonic behavior, which mainly takes into account the diffusion current and recombination current contributing to the total current. The calculation results indicate that the concentration ratio of p-region to n-region plays a crucial role in the non-monotonic behavior, and the carrier lifetime also has a great influence on this abnormal phenomenon.    

8.  Investigation on bubble dynamics characteristics and power spectral variation in acoustic field  
   YANG Desen  SHI Jie  SHI Shengguo  ZHANG Haoyang  JIANG Wei  JIN Shiyuan《Chinese Journal of Acoustics》,2013年第2期
   Based on Keller-Miksis model,the influences of multiple control parameters,such as acoustic pressure amplitude,acoustic frequency and bubble radius at rest,on the complicated dynamics characteristics of nonlinear bubble oscillation driven by acoustic wave are discussed by utilizing a variety of numerical analysis methods,and the restrictive relationships among different parameters are analyzed.It is shown that chaotic state can occur only in the condition of all of the parameters in the suitable threshold,as the same time,chaotic state is the result of interaction of multiple control parameters.Furthermore,the power spectral expansion and energy conversion are existed in this nonlinear system.It is certified that the stronger acoustic pressure amplitude,the greater the sub-harmonic energy,besides,the energy attenuation of fundamental harmonic is also much greater.    

9.  Interaction between encapsulated microbubbles:A finite element modelling study  
   蔡晨亮  于洁  屠娟  郭霞生  黄品同  章东《中国物理 B》,2018年第8期
   Theoretical studies on the multi-bubble interaction are crucial for the in-depth understanding of the mechanism behind the applications of ultrasound contrast agents(UCAs) in clinics. A two-dimensional(2 D) axisymmetric finite element model(FEM) is developed here to investigate the bubble–bubble interactions for UCAs in a fluidic environment. The effect of the driving frequency and the bubble size on the bubble interaction tendency(viz., bubbles' attraction and repulsion),as well as the influences of bubble shell mechanical parameters(viz., surface tension coefficient and viscosity coefficient)are discussed. Based on FEM simulations, the temporal evolution of the bubbles' radii, the bubble–bubble distance, and the distribution of the velocity field in the surrounding fluid are investigated in detail. The results suggest that for the interacting bubble–bubble couple, the overall translational tendency should be determined by the relationship between the driving frequency and their resonance frequencies. When the driving frequency falls between the resonance frequencies of two bubbles with different sizes, they will repel each other, otherwise they will attract each other. For constant acoustic driving parameters used in this paper, the changing rate of the bubble radius decreases as the viscosity coefficient increases,and increases first then decreases as the bubble shell surface tension coefficient increases, which means that the strength of bubble–bubble interaction could be adjusted by changing the bubble shell visco-elasticity coefficients. The current work should provide a powerful explanation for the accumulation observations in an experiment, and provide a fundamental theoretical support for the applications of UCAs in clinics.    

10.  Analysis of each branch current of serial solar cells by using an equivalent circuit model  
   易施光  张万辉  艾斌  宋经纬  沈辉《中国物理 B》,2014年第23卷第2期
   In this paper,based on the equivalent single diode circuit model of the solar cell,an equivalent circuit diagram for two serial solar cells is drawn.Its equations of current and voltage are derived from Kirchhoff’s current and voltage law.First,parameters are obtained from the I–V(current–voltage)curves for typical monocrystalline silicon solar cells(125 mm×125 mm).Then,by regarding photo-generated current,shunt resistance,serial resistance of the first solar cell,and resistance load as the variables.The properties of shunt currents(Ish1and Ish2),diode currents(ID1and ID2),and load current(IL)for the whole two serial solar cells are numerically analyzed in these four cases for the first time,and the corresponding physical explanations are made.We find that these parameters have different influences on the internal currents of solar cells.Our results will provide a reference for developing higher efficiency solar cell module and contribute to the better understanding of the reason of efficiency loss of solar cell module.    

11.  Observation of a diverse deviation from macropore-formation theory in silicon electrochemistry  
   包晓清  葛道晗  焦继伟《中国物理 B》,2008年第17卷第8期
   Via anodizing patterned and unpatterned samples with a high HF concentration ([HF]), the degree of deviation from pore-formation theory was found to be markedly different. Based on the analysis of scanning electron microscope (SEM) micrographs and current-voltage (I - V) curves, the variation of physical and chemical parameters of patterned and unpatterned substrates was found to be crucial to the understanding of the observations. Our results indicate that the initial surface morphology of samples can have a considerable influence upon pore formation. The electric-field effect as well as current-burst-model was employed to interpret the underlying mechanism.    

12.  Transient demonstration of exciton behaviours in solid state cathodoluminescence under different driving voltage  被引次数:1
   张福俊  赵谡玲  徐征  黄金昭  徐叙瑢《中国物理》,2007年第16卷第5期
   In the solid state cathodoluminescence (SSCL), organic materials were excited by hot electrons accelerated in silicon oxide (SiO2) layer under alternating current (AC). In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence (exciton emission and recombination radiation), it was demonstrated that recombination radiation should benefit from the exciton ionization.    

13.  Environmental Impacts on Spiking Properties in Hodgkin-Huxley Neuron with Direct Current Stimulus  
   袁常青  赵同军  展永  张素花  柳辉  张玉红《中国物理快报》,2009年第11期
   Based on the well accepted Hodgkin-Huxley neuron model, the neuronal intrinsic excitability is studied when the neuron is subject to varying environmental temperatures, the typical impact for its regulating ways. With computer simulation, it is found that altering environmental temperature can improve or inhibit the neuronal intrinsic excitability so as to influence the neuronal spiking properties. The impacts from environmental factors can be understood that,the neuronal spiking threshold is essentially influenced by the fluctuations in the environment. With the environmental temperature varying, burst spiking is realized for the neuronal membrane voltage because of the environment-dependent spiking threshold. This burst induced by changes in spiking threshold is different from that excited by input currents or other stimulus.    

14.  Properties of Graphene Based Parametric Pump  
   罗松林  卫亚东《中国物理快报》,2009年第26卷第11期
   The adiabatic parametric electron pump of the infinite zigzag graphene ribbons and the infinite armchair graphene ribbons is investigated by the tight binding method. The pumping signals are added by two gates around the ribbons. It is shown that the de current can be pumped out by cyclically varying the two gate voltages and the pumped current strongly depends on the driving frequency, the pumping amplitude and the phase difference of the gate voltages. The pumped current is mediated by the graphene energy levels and its peaks occur around the energies where transmission coefficients and density of states are large. The pump current may give one peak or two opposite peaks corresponding to each transmission peak or transmission pair peaks. The height and width of the current peaks increase with the amplitude of the pumping driving voltages. The pumped current is antisymmetric about the phase difference Ф=π and for small pumping amplitude the pumped current is a sinusoidal function of the phase difference. Some graphene ribbons, although with different widths, have very similar contours of the transmission coefficients and give the same pumped current figures.    

15.  Experimental observations of nonlinear effects of the Lamb waves  被引次数:1
   DENGMingxi D.C.Price D.A.Scott《Chinese Journal of Acoustics》,2004年第23卷第3期
   The experimental observations of nonlinear effects of the primary Lamb waves have been reported. Firstly, the brief descriptions have been made for the nonlinear acoustic measurement system developed by Ritec. The detailed considerations for the acoustic experiment system established for observing of the nonlinear effects of the primary Lamb waves have been carried out. Especially, the analysis focuses on the time-domain responses of second harmonics of the primary Lame waves by employing a straightforward model. Based on the existence conditions of strong nonlinearity of the primary Lamb waves, the wedge transducers are designed to generate and detect the primary and secondary waves on the surface of an aluminum sheet. For the different distances between the transmitting and receiving wedge transducers,the amplitudes of the primary waves and the second harmonics on the sheet surface have been measured within a specified frequency range. In the immediate vicinity of the driving frequency,where the primary and the double frequency Lamb waves have the same phase velocities, the quantitative relations of second-harmonic amplitudes with the propagation distance have been analyzed. It is experimentally verified that the second harmonics of the primary Lamb waves do have a cumulative growth effect along with the propagation distance.    

16.  Ab initio investigation of boron nanodevices:conductances of the different geometric conformations  
   李桂琴《中国物理 B》,2010年第19卷第1期
   Conductances of different geometric conformations of boron ribbon devices are calculated by the ab initio method. The I-V characteristics of three devices are rather different due to the difference in structure. The current of the hexagonal boron device is the largest and increases nonlinearly. The current of the hybrid hexagon-triangle boron device displays a large low-bias current and saturates at a value of about 5.2 μA. The current of the flat triangular boron flake exhibits a voltage gap at low bias and rises sharply with increasing voltage. The flat triangular boron device can be either conducting or insulating, depending on the field.    

17.  Parameter identification and state-of-charge estimation approach for enhanced lithium–ion battery equivalent circuit model considering influence of ambient temperatures  
   《中国物理 B》,2019年第10期
   It is widely accepted that the variation of ambient temperature has great influence on the battery model parameters and state-of-charge(SOC) estimation, and the accurate SOC estimation is a significant issue for developing the battery management system in electric vehicles. To address this problem, in this paper we propose an enhanced equivalent circuit model(ECM) considering the influence of different ambient temperatures on the open-circuit voltage for a lithium–ion battery. Based on this model, the exponential-function fitting method is adopted to identify the battery parameters according to the test data collected from the experimental platform. And then, the extended Kalman filter(EKF) algorithm is employed to estimate the battery SOC of this battery ECM. The performance of the proposed ECM is verified by using the test profiles of hybrid pulse power characterization(HPPC) and the standard US06 driving cycles(US06) at various ambient temperatures, and by comparing with the common ECM with a second-order resistance capacitor. The simulation and experimental results show that the enhanced battery ECM can improve the battery SOC estimation accuracy under different operating conditions.    

18.  Mode transition in homogenous dielectric barrier discharge in argon at atmospheric pressure  
   刘富成  贺亚峰  王晓菲《中国物理 B》,2014年第7期
   The influence of driving frequency on the discharge regime of a homogenous dielectric barrier discharge in argon at atmospheric pressure is studied through a one-dimensional self-consistent fluid model. The simulation results show that the discharge exhibits five notable discharge modes, namely the Townsend mode, stable glow mode, chaotic mode, asymmetric glow, and multiple period glow mode in a broad frequency range. The transition mechanisms of these modes should be attributed to the competition between the applied voltage and the memory voltage induced by the surface charges.    

19.  Generation of Helical and Axial Magnetic Fields by the Relativistic Laser Pulses in Under—dense Plasma:Three—Dimensional Particle—in—Cell Simulation  
   郑春阳 朱少平 等《中国物理快报》,2002年第19卷第7期
   The quasi-static magnetic fields created in the interaction of relativistic laser pulses with under-dense plasmas have been investigated by three-dimensional particle-in-cell simulation.The relativistic ponderomotive force can drive and intense electron current in the laser propagation direction,which is responsible for the generation of a helical magnetic field.The axial magnetic field results from a difference bean of wave-wave,which drives a solenoidal current.In particular,the physical significance of the kinetic model for the generation of the axial magnetic field is discussed.    

20.  Influence of Wall Charges on Discharge Characteristics of Surface Discharge  
   李雪辰 王龙 苒俊霞 董丽芳《中国物理快报》,2005年第22卷第3期
   The discharge current and the inception voltage in a surface discharge device have been measured to investigate the influence of wall charges on the discharge characteristics in argon. The results show that the inception voltage decreases as the amplitude of the applied voltage Up increases. However, the sum of the inception voltage and the applied voltage almost keeps constant when Up is changed, due to the fact that the wall charges are generated in the discharge process. This phenomenon suggests that net electric field between the electrodes almost keeps constant when the amplitude of the applied voltage is changed. The electron temperature calculated by the intensity ratio of emitted spectral lines has been estimated to be less than 0.3eV and almost keeps constant under different amplitudes of the applied voltage. The result is consistent with nearly constant net field. The duty ratio of the discharge current increases as the amplitude of the applied voltage increases.    

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