Acta Physica Sinica

A non-Noether conserved quantity, i.e. Hojman conserved quantity, for nonholonomic mechanical systems

Luo Shao-Kai, Mei Feng-Xiang — 2004-03-15

Author(s): Luo Shao-Kai, Mei Feng-Xiang

A non-Noether conserved quantity, i.e. Hojman conserved quantity, of the nonholonomic mechanical systems is presented. Using the special Lie symmetry under infinitesimal transformations in which the time is not variable, the determining equations, the constrained restriction equations and the additional restriction equations of the nonholonomic mechanical systems are given. The Hojman conserved quantity of the corresponding holonomic systems, the weakly Hojman conserved quantity and the strongly Hojman conserved quantity of the nonholonomic systems are obtained. An example is given to illustrate the application of the result.

Acta Physica Sinica. 2004 53(3): 6-10. Published 2004-03-15

Effects of non-conservative forces and nonholonomic constraints on Noether symmetries of a Lagrange system

Zhang Yi, Mei Feng-Xiang — 2004-03-15

Author(s): Zhang Yi, Mei Feng-Xiang

The effects of non-conservative forces and nonholonomic constraints on Noether symmetries and conserved quantities of a Lagrange system are studied. When non-conservative forces or nonholonomic constraints are inserted in a Lagrange system, the Noether symmetries and the conserved quantities of the system may vary. Some Noether symmetries disappear, some new Noether symmetries emerge, and under certain conditions, some Noether symmetries will still remain. The conditions under which the Noether symmetries and the conserved quantities of the system will remain are given, and two examples are given to illustrate the application of the results.

Acta Physica Sinica. 2004 53(3): 661-668. Published 2004-03-15

Simulation of thermal convection in a vertical slot using the lattice Boltzmann model

Zhao Ying, Ji Zhong-Zhen, Feng Tao — 2004-03-15

Author(s): Zhao Ying, Ji Zhong-Zhen, Feng Tao

A new distribution function of energy is introduced and coupled with a velocity distribution function of particle and applied to study a hot fluid field. Thus, a new lattice Boltzmann model is constructed by both energy and velocity distribution functions and Boltzmann equation in the BGK form, which satisfies the conservation criteria of mass, momentum and energy. Thermal convection in a vertical slot is calculated by using the present lattice Boltzmann model. The numerical results have shown that multi-vortexes in the flow field will take place for Prandtl number Pr=1 and Grashof number 1.3×1026. The numerical results are in good agreement with Lee's studies.

Acta Physica Sinica. 2004 53(3): 671-675. Published 2004-03-15

Jacobi elliptic function expansion method under a general function transform and its applications

Liu Guan-Ting, Fan Tian-You — 2004-03-15

Author(s): Liu Guan-Ting, Fan Tian-You

A Jacobi elliptic function expansion method under a general function transform, which is more general than the Jacobi elliptic function expansion method under a traveling wave transform, is proposed to construct the exact solutions of nonlinear evolution equations. It is shown that some new exact periodic solutions of them are obtained by this method and these new solutions include previous solutions. Meanwhile, it is proved that the periodic solutions of some nonlinear evolution equations must be traveling solutions.

Acta Physica Sinica. 2004 53(3): 676-679. Published 2004-03-15

Bound states for Dirac equation with Wood-Saxon potential

Chen Gang — 2004-03-15

Author(s): Chen Gang

The s wave exact bound state solutions of Dirac equation are obtained when the Wood-Saxon -type scalar potential is not less than its vector potential.

Acta Physica Sinica. 2004 53(3): 680-683. Published 2004-03-15

Bound states of relativistic particles in Rosen-Morse potential

Chen Gang — 2004-03-15

Author(s): Chen Gang

The exact bound state solutions of the Klein-Gordon equation and Dirac equation with scalar and vector Rosen-Morse potentials are obtained in this paper. In addition, we use the supersymmetric quantum mechanics and shape invariance to get the bound state energy spectrum and use a change of variable to obtain the wave function. The above methods are extended to relativistic quantum mechanics.

Acta Physica Sinica. 2004 53(3): 684-687. Published 2004-03-15

Exact solutions to the Schr?dinger equation for the anharmonic oscillator potential

Lu Fa-Lin, Chen Chang-Yuan — 2004-03-15

Author(s): Lu Fa-Lin, Chen Chang-Yuan

The radial wave function of Schr?dinger equation for the anharmonic oscillator potential V(r)=ar2+br4+cr6 can be written in the form of a product of an exponential function and a polynomial function .The exact energy and wave function of the potential are obtained by using the relation for the coefficient of the polynomial function. In the bound states, the results show that parameters a,b and c in the model potential have to satisfy relevant restraint conditions.

Acta Physica Sinica. 2004 53(3): 688-692. Published 2004-03-15

The minimum optical wavepackets

Deng Wen-Ji, Xu Ji-Huan, Liu Ping — 2004-03-15

Author(s): Deng Wen-Ji, Xu Ji-Huan, Liu Ping

The explicit expressions of minimum classical wavepackets are generally derived by using the operator technique of quantum mechanics.The problem of optical wavepackets travelling in vacuum is taken as an example to investigate the meaning of complex functions and negative frequency in classical physics.The central frequency of complex Gaussian wavepackets can be freely adjusted through the displacement parameter and squeeze factor. Some other characters of the minimum optical wavepackets are also studied.

Acta Physica Sinica. 2004 53(3): 693-697. Published 2004-03-15

Single-photon interference and router-control in an optic fiber Sagnac interferometer

Wu Guang, Zhou Chun-Yuan, Zeng He-Ping — 2004-03-15

Author(s): Wu Guang, Zhou Chun-Yuan, Zeng He-Ping

A novel scheme to realize stable single-photon interference and router-control is demonstrated in this paper. Phase difference between clockwise and counter-clockwise single-photons is controlled by time-division phase modulation in an optic fiber Sagnac loop. Due to the annular geometric configuration of the Sagnac loop, clockwise and counter-clockwise single-photons travel the same optical path and have the same slowly-varying phase drifts, which are automatically compensated. Furthermore, clockwise and counter-clockwise single-photons encounter the same polarization mode dispersion, which is also automatically compensated at the exit port of the Sagnac interferometer. Long-distance single-mode optic fiber at 1550 nm is used in our experimental realization. Fringe visibility of single-photon interference higher than 98% and fidelity of single-photon router-control higher than 90% have been obtained in a Sagnac fiber loop of 5 km. We also realized a stable single-photon interference in Sagnac fiber loops as long as 27 and 52 km. The corresponding fringe visibilities were higher than 94% and 84%, respectively.

Acta Physica Sinica. 2004 53(3): 698-702. Published 2004-03-15

Phase Landau states

Tian Xu, Zhao Zhong-Yun, Li Jian-Qing — 2004-03-15

Author(s): Tian Xu, Zhao Zhong-Yun, Li Jian-Qing

Phase eigenstates for the Landau system (planar charged particle moving in a uniform magnetic field) are built. It is convenient to use these states to describe the circular motion of the charged particle. The results obtained do not depend on gauges.

Acta Physica Sinica. 2004 53(3): 703-705. Published 2004-03-15

A parameter-modulated method for chaotic digital communication based on state observers

Li Guo-Hui, Xu De-Ming, Zhou Shi-Ping — 2004-03-15

Author(s): Li Guo-Hui, Xu De-Ming, Zhou Shi-Ping

By designing an appropriate state observer, we have constructed two subsystems which alternately synchronize the chaotic drive system. When the parameter of the transmitter is modulated using the binary digital signal, the two systems can alternately be synchronized with the chaotic system. In the receiver, information is demodulated by analyzing synchronization error. An observer-based parameter modulation and demodulation Henon system was chosen to be a typical example. Numerical simulation is carried out to illustrate the effectiveness and efficiency of the proposed method.

Acta Physica Sinica. 2004 53(3): 706-709. Published 2004-03-15

A DCT domain quadratic predictor for real-time prediction of continuous chaotic signals

Zhang Jia-Shu, Li Heng-Chao, Xiao Xian-Ci — 2004-03-15

Author(s): Zhang Jia-Shu, Li Heng-Chao, Xiao Xian-Ci

A DCT domain quadratic predictor with normalized least mean square (NLMS) algorithm, efficient implementing structure of the reduced parameter second-order Vloterra filter (RPSOVF), is proposed to investigate nonlinear real-time multi-step prediction performance of three kinds of continuous chaotic signals. Experimental results show that the real-time ahead one-step prediction mean square errors of the DCT domain quadratic predictor proposed in this paper are at least 100 times smaller than that of RPSOVF, which indicates that this predictor has better predictive performance, its structure is simple and easy to implement. Multi-step prediction performance of this DCT domain quadratic predictor to three continuous chaotic time series is superior to the one of local prediction method obviously, and its mean square errors do not increase exponentially according as the prediction step.

Acta Physica Sinica. 2004 53(3): 710-716. Published 2004-03-15

Power spectrum research of twice sampling stochastic resonance response in a bistable system

Leng Yong-Gang, Wang Tai-Yong, Qin Xu-Da, Li Rui-Xin, Guo Yan — 2004-03-15

Author(s): Leng Yong-Gang, Wang Tai-Yong, Qin Xu-Da, Li Rui-Xin, Guo Yan

The characteristics of Lorentzian distribution in the power spectrum of a stochastic resonance(SR) from a bistable system have been investigated, and then the viewpoint of producing an identifiable SR peak only at the lower frequency area where the power energy being concentrated has been proposed. With big values of parameters, the spectral properties of a twice sampling stochastic resonance(TSSR) from a bistable system is probed in detail. Take the detection of a weak signal overwhelmed in heavy noise as an example, the application of the TSSR technique is shown finally.

Acta Physica Sinica. 2004 53(3): 717-723. Published 2004-03-15

The principles of pressure sensors based on photonic crystal

Xu Zhen-Yu, Zhang Ruo-Jing, Gong Yi-Ling — 2004-03-15

Author(s): Xu Zhen-Yu, Zhang Ruo-Jing, Gong Yi-Ling

The mechanism of photonic crystal pressure sensor was described in this paper, after an examination of the relationship of the pressure on a one-dimensional photonic crystal and its photonic band gap (PBG) property. The results show that there is a simple relationship between the pressure and the stop wave length. This makes it possible to know the load by studying the PBG property or to change the PBG property by loading; the loads can be mechanical loads or thermal loads. Since the structure scale is similar to the wave length, it is possible to realize a series of sensors with very high exactness.

Acta Physica Sinica. 2004 53(3): 724-727. Published 2004-03-15

On micro scanning forces under the coupling deformation of atomic force microscope probe

Zhang Xiang-Jun, Meng Yong-Gang, Wen Shi-Zhu — 2004-03-15

Author(s): Zhang Xiang-Jun, Meng Yong-Gang, Wen Shi-Zhu

Micro cantilever probe of atomic force microscope (AFM) is a typical micro mechanical component, which is under a coupling deformation during the contact scanning process. Numerical simulations of micro scanning forces and micro topography are presented to investigate the influence of the coupling deformation of AFM probe under the AFM contact mode. It is demonstrated that the normal scan force is actually not constant, which is coupled with the lateral force on an asperity of sample surface, increasing together uphill and decreasing together downhill. The coupling relationship increases with the surface slope, tip height, etc. Coupling deformation of the probe proves to play a minor role on the AFM micro topography image and the perpendicular scan force. However, surface slope plays an important role on the variation of lateral force, and the peak positions of lateral force are not accordant with that of surface topography. These results are in good agreement with those previous AFM experiments.

Acta Physica Sinica. 2004 53(3): 728-733. Published 2004-03-15

Microscopic approach of the spectral property of 1+ and high-spin states in 124 Te nucleus

Shi Zhu-Yi, Ni Shao-Yong, Tong Hong, Zhao Xing-Zhi — 2004-03-15

Author(s): Shi Zhu-Yi, Ni Shao-Yong, Tong Hong, Zhao Xing-Zhi

Using a microscopic sdIBM-2+2q.p. approach, the spectra of the low-spin and partial high-spin states in 124Te nucleus are relatively successfully calculated. In particular, the 1+1, 1+2, 3+1, 3+2 and 5+1 states are successfully reproduced, the energy relationship resulting from this approach identifies that the 6+1, 8+1 and 10+1 states belong to the aligned states of the two protons. This can explain the recent experimental results that the collective structures may coexist with the single-particle states. So this approach becomes a powerful tool for successfully describing the spectra of general nuclei without clear symmetry and of isotopes located at transitional regions. Finally, the aligned-state structure and the broken-pair energy of the two-quasi-particle are discussed.

Acta Physica Sinica. 2004 53(3): 734-737. Published 2004-03-15

Effect of nucleon momentum distribution on the calculation of semiclassical distorted wave model

Hu Ze-Hua, Sun Wei-Li, Zhang Ben-Ai, Tian Dong-Feng — 2004-03-15

Author(s): Hu Ze-Hua, Sun Wei-Li, Zhang Ben-Ai, Tian Dong-Feng

The semiclassical distorted wave(SCDW)model is applied to the analysis of the multistep direct processes of 90Zr(p,p′x) at 80 and 160MeV incident energies with the single particle momentum distribution of target nucleons given by the coherent density fluctuation model. The calculated double differential cross sections are compared with the experimental data and the results of the previous SCDW model calculations. The agreement of the calculated double differential cross sections with the experimental data is improved, compared with the previous calculations. The effect of the momentum distribution of target nucleons on the calculated cross sections is discussed.

Acta Physica Sinica. 2004 53(3): 738-744. Published 2004-03-15

High frequency response of Salisbury screen and its related factors

Wu Rui-Xin, Wang Xiang-Yuan, Qian Jian, Zhang Ming-Xue, Zhu Hang-Fei, Xu Pei-Hua — 2004-03-15

Author(s): Wu Rui-Xin, Wang Xiang-Yuan, Qian Jian, Zhang Ming-Xue, Zhu Hang-Fei, Xu Pei-Hua

In this work, the high-frequency response of the Salisbury screen made of metallic thin film was investigated. The formulas of reflectivity and bandwidth coefficient were derived. Theoretical and numerical studies show that the spectrum of reflectivity presents a resonance type, which is symmetric to the resonance frequency. The reflectivity is determined only by the normalized surface resistance α of the metallic film at resonance, and by both α and wave impedance η2 of the isolation layer at other frequencies. For the bandwidth coefficient Δ, it is determined by the examined reflectivity Γa, η2 and α. Bandwidth coefficient can be improved by changing the wave impedance η2, and tuning the surface resistance to the optimum value αc which is correlated to Γa and not equal to the one in most cases. It is also noted that the thickness of the metallic thin film should be in the order of sub-micron or nanometers.

Acta Physica Sinica. 2004 53(3): 745-749. Published 2004-03-15

Investigation of the high harmonic generation and ionization of atoms with long-range and short-range potentials in intense laser fields

Li Peng-Cheng, Zhou Xiao-Xin, Dong Chen-Zhong, Zhao Song-Feng — 2004-03-15

Author(s): Li Peng-Cheng, Zhou Xiao-Xin, Dong Chen-Zhong, Zhao Song-Feng

By using numerical solutions of the time-dependent Schrdinger equation for a one-dimensional atom in intense laser fields, We investigate the high harmonic generation and ionization of the long-range and short-range potential atoms. It is found that the intensities of high harmonic generation for both cases are similar, but the short-range potential atom does not radiate the low-order harmonic spectra, and the ionization probabilities of the long-range and short-range potential atoms as functions of the laser intensity are obviously different. Our results show that the excited states of the atom play an important role in the low-order harmonic spectra and ionization probabilities.

Acta Physica Sinica. 2004 53(3): 750-755. Published 2004-03-15

Study on hyperspectral detection system with the harmonic diffractive element in infrared dual-band

Sun Qiang, Yu Bin, Wang Zhao-Qi, Mu Guo-Guang, Lu Zhen-Wu — 2004-03-15

Author(s): Sun Qiang, Yu Bin, Wang Zhao-Qi, Mu Guo-Guang, Lu Zhen-Wu

In this paper, the application of harmonic diffractive element（HDE） in the infrared hyperspectral detection system is investigated based on the special large dispersion capability of HDE and window character of infrared bands. The fundamental principle of the new infrared hyperspectral imaging is described, and a design sample is presented. It is shown that the resolution is improved and the optical power received is enlarged. The rectification of the ray aberrations in both band has been simultaneously accomplished. Wave front aberrations are less than 1/4 wavelength,and the modulation transfer function of the dual-band in every zoom focus location approaches or attains the diffraction limit of 20 cycles/mm.

Acta Physica Sinica. 2004 53(3): 756-761. Published 2004-03-15

Influence of AC-Stark shift on cavity field spectra in the non-degenerate Raman process

Gao Yun-Feng, Feng Jian — 2004-03-15

Author(s): Gao Yun-Feng, Feng Jian

The cavity field spectrum of an atom interacting with two-mode field through non-degenerate Raman coupling with the presence of AC-Stark shift in an ideal cavity is investigated. The results for the atom in the low-level state and the initial fields in pure number states, coherent states, and squeezed vacuum states are calculated. When the initial fields are in number states, the three-peak structure of each model cavity field spectra appear for weak fields, and two-peak or single-peak structure appear for strong fields. When both field modes are in a superposition of number states initially, the cavity field spectra are generally of two-peak structure. With the increase of γ=g2/g1,one peak rises and the other peak reduces.

Acta Physica Sinica. 2004 53(3): 762-766. Published 2004-03-15

Interaction between photovotaic spatial solitons with difference wavelengths

Ouyang Shi-Gen, Wang Xiao-Sheng, She Wei-Long — 2004-03-15

Author(s): Ouyang Shi-Gen, Wang Xiao-Sheng, She Wei-Long

The interaction between photovoltaic spatial solitons with difference wavelengths in photovoltaic-photorefractive crystals is investigated by numerical method. Our numerical study indicates that the interaction between these solitons is inelastic, and these solitons keep their shapes only within some propagation distance. Besides the attraction with each other, the energy of soliton would be coupled from one waveguide to other waveguide during propagation.

Acta Physica Sinica. 2004 53(3): 767-772. Published 2004-03-15

Lattice Boltzmann simulation for nonlinear flow in porous media with coupling reaction

Xu You-Sheng, Li Hua-Bing, Fang Hai-Ping, Huang Guo-Xiang — 2004-03-15

Author(s): Xu You-Sheng, Li Hua-Bing, Fang Hai-Ping, Huang Guo-Xiang

Based on the lattce Boltzmann method and theory of fluid flow in porous media,a numerical model is discussed for the nonlinear flow in porous media with coupling reaction.The numerical simulation results agree well with the analytical solution;and the reconstructed digital images show that there are strong coupling and anti-coupling effect between the fluid flow and the reaction,which results in the self-organization cingulum forms.All these also agree well with the experimental and theoretical prediction.

Acta Physica Sinica. 2004 53(3): 773-777. Published 2004-03-15

A novel FDTD simulation for plasma piecewise linear current density recursive convolution

Liu Shao-Bin, Mo Jin-Jun, Yuan Nai-Chang — 2004-03-15

Author(s): Liu Shao-Bin, Mo Jin-Jun, Yuan Nai-Chang

A novel finite-difference time-domain (FDTD) method, called piecewise linear current density recursive convolution method,is developed for dispersive media. The formulation of this method is derived using the convolution relationship between the current density and the electric field. The high accuracy and efficiency of this method are confirmed by computing the reflection and transmission coefficients of electromagnetic waves through a collisional plasma slab in one dimension.

Acta Physica Sinica. 2004 53(3): 778-782. Published 2004-03-15

A JEC-FDTD implementation for anisotropic magnetized plasmas

Liu Shao-Bin, Mo Jin-Jun, Yuan Nai-Chang — 2004-03-15

Author(s): Liu Shao-Bin, Mo Jin-Jun, Yuan Nai-Chang

A JEC finite-difference time-domain (JEC-FDTD) methodology for dispersive media is extended to anisotropic magnetized plasmas. The problem which incorporates both anisotropy and frequency dispersion at the same time is solved for the electromagnetic wave propagation. The JEC-FDTD formulation for anisotropic magnetized plasmas is derived. The high efficiency and accuracy of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer, with the direction of the propagation parallel to the direction of the biasing field. A comparison with frequency-domain analytic results is included.

Acta Physica Sinica. 2004 53(3): 783-787. Published 2004-03-15

Numerical study of supersonic plasma torch

Yuan Xing-Qiu, Li Hui, Zhao Tai-Zhe, Wang Fei, Guo Wen-Kang, Xu Ping — 2004-03-15

Author(s): Yuan Xing-Qiu, Li Hui, Zhao Tai-Zhe, Wang Fei, Guo Wen-Kang, Xu Ping

The magnetic hydrodynamics(MHD) model which is used to describe the heat and fluid flow inside the plasma torch under atmosphere condition was presented. Numerical simulation of the plasma torch with convergence-divergence nozzle shape was carried out by using a two-dimensional mathematical model. Plasma temperature, velocity, pressure, Mach number contours,which describe the characteristic of heat and fluid flow inside the plasma torch, were obtained. Results show that the plasma field can be divided into three regions named subsonic region, transonic region, and the supersonic region.

Acta Physica Sinica. 2004 53(3): 788-792. Published 2004-03-15

The Bohm criterion for the dusty plasma sheath

Wang Zheng-Xiong, Liu Jin-Yuan, Zou Xiu, Liu Yue, Wang Xiao-Gang — 2004-03-15

Author(s): Wang Zheng-Xiong, Liu Jin-Yuan, Zou Xiu, Liu Yue, Wang Xiao-Gang

The hydrodynamic-fluid model and the self-consistent dust charging model are used to investigate the Bohm criterion for the dusty plasma sheath. The variation of the ion critical Mach number and the dust Mach number with dust density are presented, and the relation between the dust surface potential and the dust density at the sheath edge is discussed. It is shown that the ion velocity entering the sheath would exceed the ion sound velocity due to the existence of dust particles. The ion critical Mach number began declining after a maximum with the incessant increase of the dust density. The numerical results satisfy the qualitative analysis of the Sagdeev potential.

Acta Physica Sinica. 2004 53(3): 793-797. Published 2004-03-15

Solitons formed by ultrashort laser pulses propagating in a plasma

Zhang Qiu-Ju, Sheng Zheng-Ming, Zhang Jie — 2004-03-15

Author(s): Zhang Qiu-Ju, Sheng Zheng-Ming, Zhang Jie

Using one-dimensional particle-in-cell simulations, we observed the formation of solitons which can move with high group velocities when ultrashort laser pulses at a few cycles only propagate in underdense plasma near the critical density. There exist reflection and transmission when the solitons arrive at the plasma-vacuum boundary. When the intensity of initial laser pulses increases, the velocity of the formed solitons decreases. When a laser pulse at a few tens of cycles propagates in such a plasma, a cluster of solitons are left behind, and trapped in the plasma.

Acta Physica Sinica. 2004 53(3): 798-802. Published 2004-03-15

Calculation of high-energy ions exploded from argon clusters in high intensity femtosecond laser pulses

Zhu Pin-Pin, Liu Jian-Sheng, Xu Zhi-Zhan — 2004-03-15

Author(s): Zhu Pin-Pin, Liu Jian-Sheng, Xu Zhi-Zhan

The modified nanoplasma model has been used to simulate the interaction of large Ar clusters with high intensity femtosecond laser pulses. The modified model has weakened the huge enhancement of electric field inside the clusters, thus provides a more reasonable explanation. The calculated mean kinetic energy of Ar ions is in good agreement with our previous experimental results. For further experimental work, it is the quantitative analysis of the variation of the mean kinetic energy and charge states of Ar ions exploded from the interactions with thecluster size and laser intensity.

Acta Physica Sinica. 2004 53(3): 803-807. Published 2004-03-15

Optimization design of a wire array load for Z-pinch plasma implosion experiments

Ding Ning, Yang Zhen-Hua, Ning Cheng — 2004-03-15

Author(s): Ding Ning, Yang Zhen-Hua, Ning Cheng

The Z-pinch implosion from a wire array load is one of the ways to generate strong x-ray radiation. Under the conditions of a pulsed power accelerator, the x-ray radiation yield is determined by the initial diameter chosen and mass per length of a wire array load. In this paper, the effects of the mass, the array diameter and wire diameter, as well as the array material on the implosion time, the implosion trajectory, the implosion velocity and the kinetic energy are estimated by using an infinitely thin annular shell model. The relationship among the implosion time, the implosion kinetic energy and the initial array load parameters is analyzed. The optimized parameters of a wire array load are obtained under the given conditions of a driven current. Our conclusions by using the thin shell model are in agreement with the experimental results. Hence, the thin shell model can be used to design a wire array load of Z-pinch implosion experiment.

Acta Physica Sinica. 2004 53(3): 808-817. Published 2004-03-15

PIC simulation of the wake field acceleration driven by triangle-shaped laser pulse

Xu Han, Chang Wen-Wei, Yin Yan, Zhuo Hong-Bin — 2004-03-15

Author(s): Xu Han, Chang Wen-Wei, Yin Yan, Zhuo Hong-Bin

“Electron trapping” is the main acceleration mechanism in the laser wakefield acceleration, and the theoretical analysis indicates that more electrons are trapped when the initial velocity of the electrons are increased. A new wakefield acceleration scheme named “triangle-shaped laser pulse wakefield acceleration” is proposed and tested by 2D3V PIC simulation. The slow-rising part of the triangle-shape will excites stimulated Raman scattering(SRS) which preheats electrons while the sharp-descending part of the pulse drives the wakefield to trap more electrons. Our simulation also indicates that the side stimulated Raman scattering (SSRS) is the main instability when the length of the incident laser pulse is greater than the plasma wavelength. Furthermore, the electrostatic wave mode with the greatest growth rate in SSRS is always the one with the largest wave vector kp=(2ωp/ω0)1/2, and the scattering angle satisfies θ=cos-1(2ωp/ω0).

Acta Physica Sinica. 2004 53(3): 818-823. Published 2004-03-15

The effect of external magnetic field, current and arc column radiuson the arc helical instability

Zou Xiu, Gong Ye, Liu Jin-Yuan, Gong Ji-Quan — 2004-03-15

Author(s): Zou Xiu, Gong Ye, Liu Jin-Yuan, Gong Ji-Quan

The effect of external magnetic field, current and arc column radius on the helical instability is studied by using linear time perturbation theory in this paper. The arc has the effect of gas flow. The stability conditions and the growth rate of the helical instability are given.

Acta Physica Sinica. 2004 53(3): 824-828. Published 2004-03-15

A new approach to extract reliable intensities of non-equivalent systematical overlapping reflections from powder diffraction data

Ma Hong-Wei, Liang Jing-Kui — 2004-03-15

Author(s): Ma Hong-Wei, Liang Jing-Kui

A new approach to extract reliable intensities from systematical non-equivalent overlapping reflections has been proposed and tested by simulated powder diffraction pattern of known structures. By using both crystallographic and structural chemistry knowledge, the IDM-UAIC reconstructs the intensities and solves the structure through an iterative procedure. The results show that IDM-UAIC succeeds when more than 30% of the total scattering power can be located in a reasonable precise from the equivalent systematical overlapping reflections. The IDM-UAIC procedure is superior to the simple equi-partition methods for the nonequivalent systematical overlapping reflections while it is equivalent to simple equi-partition methods for the equivalent systematical overlapping reflections.

Acta Physica Sinica. 2004 53(3): 829-834. Published 2004-03-15

Study of gas-solid interface via low-energy pulsed electron beams

Zhang Tong, Hu An, Wu Qiang, Mao Fu-Ming, Yang Xue-Qian, Cui Yi-Ping — 2004-03-15

Author(s): Zhang Tong, Hu An, Wu Qiang, Mao Fu-Ming, Yang Xue-Qian, Cui Yi-Ping

The principle and method for gas-solid interface study via low-energy pulsed electron beams are introduced, and the processes of adsorption-desorption and displacement are experimentally investigated. The desorption yields, threshold energies, and cross sections for N2 and O2 from polycrystalline Ni and W in vacuum (1×10-3Pa) at (T=300K) are measured. At the end of the paper, the conclusions are given.

Acta Physica Sinica. 2004 53(3): 835-839. Published 2004-03-15

The study of self-simulating properties of spherical shock front attenuation

Bian Bao-Min, Yang Ling, Li Zhen-Hua, Chen Xiao, He An-Zhi, Shen Zhong-Hua — 2004-03-15

Author(s): Bian Bao-Min, Yang Ling, Li Zhen-Hua, Chen Xiao, He An-Zhi, Shen Zhong-Hua

In an isotropic medium the self-simulating theory is used in characterizing the spherical shock front attenuation. We first deduce the self-simulating equation of decaying spherical shock front propagation. Then the decaying propagation equation of the spherical shock front is shown in good agreement with experimental data.

Acta Physica Sinica. 2004 53(3): 840-843. Published 2004-03-15

Superconductivity and negative temperature coefficient of the resistivity of bulk metallic glass Zr46.75Ti8.25Cu7.5Ni10Be27.5

Li Yong, Wen Ping, Liu Zhen-Xing, Jing Xiu-Nian, Wang Wan-Lu, Bai Hai-Yang — 2004-03-15

Author(s): Li Yong, Wen Ping, Liu Zhen-Xing, Jing Xiu-Nian, Wang Wan-Lu, Bai Hai-Yang

Electrical-resistivity measurements between 1.5 K and 300 K were performed on the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glasses (BMGs) before and after annealing. Results of the superconducting transition temperature measurements are presented for the BMG Zr46.75Ti8.25Cu7.5Ni10Be27.5. The superconducting critical temperature Tc is 1.84K for the as-prepared metallic glassy sample and 3.76K for the annealed sample at zero magnetic fields. The as-prepared metallic glassy sample exhibits negative temperature coefficient of the resistivity in the temperature range from 5 to 300 K. The negative temperature coefficient of the resistivity of the as-prepared metallic glassy sample can be reasonably understood with the extended Faber-Ziman theory in terms of the diffraction model for metallic glasses if it is assumed that Zr, Ti, Cu, Ni and Be contribute 1.5, 1.5, 0.5, 0.5 and 2 conduction electrons, respectively. The R(T) of the BMG Zr46.75Ti8.25Cu7.5Ni10Be27.5 over the temperature range from 5 to 300 K was analyzed by fitting it to a polynomial using a least-squares procedure.

Acta Physica Sinica. 2004 53(3): 844-849. Published 2004-03-15

A new Pr-based bulk metallic glass and its properties

2004-03-15

Author(s): Zhao Zuo-Feng, Zhang Zhi, Li Zheng, Wen Ping, Zhao De-Qian, Pan Ming-Xiang, Wang Wan-Lu, Wang Wei-Hua

A new rare-earth Pr-based bulk metallic glass (BMG) is obtained in the shape of rod up to 5 mm in diameter by die cast. Unlike other rare-earth based BMGs, it exhibits a distinct glass transition, Tg=409K,the lowest glass transition temperature among the known BMGs, a large and stable supercooled liquid region and paramagnetic property. The glass transition as well as its kinetic nature and the fragility parameters m of the BMG have been studied. The BMG offers an ideal model to investigate the nature of glass transition as well as the relaxation and nucleation with a large experimentally accessible time and temperature window at very low temperature region.

Acta Physica Sinica. 2004 53(3): 850-853. Published 2004-03-15

Fabrication, morphology and structure of carbon nanotube arrays and bundles fabricated by a three-step rising temperature procedure

2004-03-15

Author(s): Cao Pei-Jiang, Gu You-Song, Liu Fei, Liu Hong-Wen, Zhang Qi-Feng, Wang Yan-Guo, Gao Hong-Jun

In a simple-structured single-temperature furnace, a three-step rising temperature process has been used to fabricate carbon nanotube (CNT) arrays and carbon nanotube bundles by pyrolysis of ferrocene/melamine mixtures on silica and ceramic wafers, respectively. The structure and composition of the CNTs are investigated by scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and electron energy-loss spectroscopy (EELS). EELS spectrum shows that CNTs grown on the two different kinds of substrates are pure carbon tubes. CNTs on smoothing silica wafer are highly orientated and have uniform outer diameters of about 22 nm and varying lengths from 10 to 40 μm. CNTs grow in top growth mode and exhibit the stacked-cup-like structures. CNT bundles on rough ceramics wafer are randomly orientated. They have varying outer diameters of 15—80nm and lengths up to one hundred of micrometers. They exhibit two types of shapes, bell-like and dome-like. The effect of substrate morphologies on the morphology and structure of CNTs has been discussed.

Acta Physica Sinica. 2004 53(3): 854-860. Published 2004-03-15

Thermodynamic calculation of energy consumed for boundary friction during martensitic transformation in single crystal Ni2MnGa

Cui Yu-Ting, Zhu Ya-Bo, Liao Ke-Jun, Wang Wan-Lu — 2004-03-15

Author(s): Cui Yu-Ting, Zhu Ya-Bo, Liao Ke-Jun, Wang Wan-Lu

Based on the boundary friction phenomenological theory,a general equation for calculating the thermodynamic parameters of Ni2MnGa system was deduced.According to the measured results of the ac magnetic susceptibility or strain during the martensitic transformation for three non-stoichiometric Ni2MnGa single crystal samples with martensitic transition occurring at temperatures below,near,and above room temperature,respectively,the energies consumed for boundary friction in the three samples during their martensitic transformations were calculated using the general equation.It was also indicated that the thermal hysteresis of martensitic transformation originates from the friction of phase boundary motion;moreover,the large differences of the energy consumed for boundary friction and the thermal hysteresis result from the different structures of martensites produced for the three samples during the martensitic transformation.

Acta Physica Sinica. 2004 53(3): 861-866. Published 2004-03-15

Photoluminescence centers and shift of ZnO films deposited by rf magnetron sputtering

Li Huo-Quan, Ning Zhao-Yuan, Cheng Shan-Hua, Jiang Mei-Fu — 2004-03-15

Author(s): Li Huo-Quan, Ning Zhao-Yuan, Cheng Shan-Hua, Jiang Mei-Fu

ZnO films deposited by rf magnetron sputtering with different stoichimetries were made by varing Ar/O2 flow rate during the depositions, and annealed in vacuum. The photoluminescence measurements show that the films have strong blue emission. As O2 gas flow decreases, the blue emission peak moves to long wavelength side. The blue emission may correspond to the electron transition from the bottom of the conduction band to the acceptor level composed of zinc defects.

Acta Physica Sinica. 2004 53(3): 867-870. Published 2004-03-15

Growth of single domain monatomic In chain arrays on vicinal Si(001) surface

2004-03-15

Author(s): Dou Rui-Fen, Jia Jin-Feng, Xu Mao-Jie, Pan Ming-Hu, He Ke, Zhang Li-Juan, Xue Qi-Kun

Using a vicinal Si(001) surface with 4°miscut along ［110］ direction as a substrate, we have fabricated single-domain monatomic In chain arrays on a large scale. High-resolution scanning tunneling microscopic images reveal that the deposited In atoms preferentially form In dimers between the two neighboring Si dimer rows on the lower terrace along the step edge, due to the high coordination of these positions. Indium dimers remove dangling bonds of the Si dimers and saturate all In valency,andthen develop into a long monatomic In chain along the step edge. It is worth highlighting that the ordered narrow terrace and the straight DB steps edge are key to the formation of the monatomic In chains.

Acta Physica Sinica. 2004 53(3): 871-876. Published 2004-03-15

In situ investigation of structural properties during formation of pentacene thin film on Ag (110) with MBE-LEED

2004-03-15

Author(s): Wang Ye-Liang, Shi Dong-Xia, Ji Wei, Du Shi-Xuan, Guo Hai-Ming, Liu Hong-Wen, Gao Hong-Jun

The structural transition of pentacene thin films on single Ag (110) crystals has been directly observed using a home-designed in situ low-energy electron diffraction during the course of absorption and subsequently changes of substrate temperature.The pentacene moleculs showed the evolution from disordered structure in the submonolayer region to a well-ordered structure in the monolayer on the substrate at room temperature.The experimental and theoretical results showed that the molecules lay flat on the Ag (110) surface with two domain orientations mirrored with respect to the crystal axis of the silver substrate.Furthermore, the ordered structures can keep stable when the substrate temperature is below the sublimation temperature of pentacene.

Acta Physica Sinica. 2004 53(3): 877-882. Published 2004-03-15

Fullerene-like nano-crystalline CNx films and its characteristics of field electron emission

2004-03-15

Author(s): Zhang Lan, Ma Hui-Zhong, Li Hui-Jun, Yang Shi-E, Yao Ning, Hu Huan-Ling, Zhang Bing-Lin

CNx films were prepared by using microwave plasma-enhanced chemical vapor phase deposition. As-deposited films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy and Raman spectroscopy. Field electron emission characteristics of thin films were studied. Experimental results indicate that the film structure and properties of the field electron emission are related to flow ratio of N2 to H2 while the flow rate of CH4 was kept at 8 sccm. When the flow ratio of N2 to H2 was 50/50 sccm, the obtained film had a nano-crystalline graphitic structure with curved basal planes (fullerene-like structure) and excellent properties of field electron emission. The turn-on field decreased to 1.1 V/μm. At an electric field of 5.9V/μm, the average current density was 70μA/cm2 and emission sites density was larger than 1×104cm-2.

Acta Physica Sinica. 2004 53(3): 883-887. Published 2004-03-15

Study on the definite direction growth of carbon nanotubes by the microwave plasma-enhanced chemical vapro phase deposition

Wang Miao, Li Zhen-Hua, Takegawa Hitosi, Saito Yahachi — 2004-03-15

Author(s): Wang Miao, Li Zhen-Hua, Takegawa Hitosi, Saito Yahachi

Using the microwave plasma-enhanced chemical vapor phase deposition,in the gas mixture of the methane and hydrogen, the aligned growth of the carbon nanotubes was observed and analyzed with a scanning electron microscope.The carbon nanotubes have the tidy arrangement in the perpendicular direction on a solid substrate.Its length is the same as the uniform caliber.This kind of carbon nanotubes can be used as the potential electron source material.

Acta Physica Sinica. 2004 53(3): 888-890. Published 2004-03-15

Study on fabrication of sol-gel glass containing chiral micro-crystal and its depolarization

Tao Wei-Dong, Dong Jian-Feng, Xia Hai-Ping, Bai Gui-Ru, Lu Zu-Kang — 2004-03-15

Author(s): Tao Wei-Dong, Dong Jian-Feng, Xia Hai-Ping, Bai Gui-Ru, Lu Zu-Kang

By dry crush way, the bulk chiral crystal was smashed to chiral micro-crystal which particle size was 70μm. The chiral micro-crystal was disseminated homogeneously in the gel by sol-gel process. So sol-gel glass containing chiral micro-crystal which thickness was 4 mm has been manufactured successfully. It was found that sol-gel glass containing chiral micro-crystal displayed its depolarization effect. We replaced the chiral micro crystal by glass powder which particle size was also 70 μm, and manufactured the sol-gel glass containing glass powder by the same way. It was found that the sol-gel glass containing glass powder displayed its polarization-held characteristic. The cause was analyzed.

Acta Physica Sinica. 2004 53(3): 891-894. Published 2004-03-15

Crystal growth of quasi-two-dimensional purple bronze KxMo6O17

2004-03-15

Author(s): Wang Jun-Feng, Xiong Rui, Yu Heng, Li Hui, Tang Wu-Feng, Yu Zu-Xin, Shi Jing, Tian De-Cheng, Tian Ming-Liang, Zhang Yu-Heng

Purple bronze KxMo6O17 single crystals are successfully grown by electrolytic reduction method from the melts of K2CO3 and MoO3.The detailed process of the preparation is reported.The structure of the single crystals are investigated with x-ray diffraction and Transmission electron microscope.The results show that the crystals have large sizes and high qualities.The unit cell parameters are:a=b=0.5540nm,c=1.3508nm，and the crystal structure is refined to be trigonal with space group P3.The temperature dependence of resistance reveals that the compounds undergo Peierls phase transition at 112K.

Acta Physica Sinica. 2004 53(3): 895-899. Published 2004-03-15

Cu-W Thin film characterized by surface fractal and resistivity

Wang Yuan, Xu Ke-Wei — 2004-03-15

Author(s): Wang Yuan, Xu Ke-Wei

Thin films of Cu-W were deposited on Si wafers by magnetron sputtering,and characterized by atomic force microscopy(AFM).Power spectra density was used to calculate the fractal dimension of the AFM images.The results show that the fractal dimension values increase with the film thickness and there is a relationship between the fractal dimension and the resistivity of the films.The change of resistivity is directly proportional to the fractal dimension.

Acta Physica Sinica. 2004 53(3): 900-904. Published 2004-03-15

The magnetic anisotropic effect on giant magnetoimpedance in sandwiched films

Wang Ai-Ling, Liu Jiang-Tao, Zhou Yun-Song, Jiang Hong-Wei, Zheng Wu — 2004-03-15

Author(s): Wang Ai-Ling, Liu Jiang-Tao, Zhou Yun-Song, Jiang Hong-Wei, Zheng Wu

The sandwiched film structured by two soft magnetic layers with the Cu layer as the central one is proposed,which is based on the experimental samples of giant magnetoimpedance (GMI) effect.Its characteristics are discussed theoretically using Maxwell equations and Landau-Lifshitz equation wiuh calculating the anisotropy of the magnetic layers.Application of the theoretical model to real materials is examined.Predictions of the model compare well qualitatively with experimental data.The anisotropic constant Hk of the magnetic layer is very important.The GMI effect is modified by both the magnitude and the orientation of Hk.The best Hk is about 400A/m along the normal to the current.It is also proved that any magnetostriction in the magnetic layer of the sandwiched film damages the GMI effect.

Acta Physica Sinica. 2004 53(3): 905-910. Published 2004-03-15

Optimizing boron implantation dose of HgCdTe infrared detectors

2004-03-15

Author(s): Chen Gui-Bin, Lu Wei, Cai Wei-Ying, Li Zhi-Feng, Chen Xiao-Shuang, Hu Xiao-Ning, He Li, Shen Xue-Chu

Using the material chip technology,large area photodiodes of n-on-p structure with different boron implantation dose are fabricated on the Hg1-xCdxTe film for mid-infrared wavelength region(x=0.291).Current-voltage characteristics of the photodiodes are measured at 77K and zero bias resistance-area products of different photodiodes are fitted from the data in the voltage range of -0.2—0.08V.The study indicated that the R0A products of different elements depended distinctly upon the implanted boron dose.A large R0 value has also obtained in another chip with x=0.2743.All the samples in this study are grown by Riber 32P molecular-beam epitaxy system and all the junctions-forming process is same to the standard planar technology but using a series of metallic masks during the boron ion implantation.

Acta Physica Sinica. 2004 53(3): 911-914. Published 2004-03-15

X-ray photoemission studies of Yb intercalated C60 thin film

2004-03-15

Author(s): He Shao-Long, Li Hong-Nian, Li Hai-Yang, Zhang Han-Jie, Lü Bin, He Pi-Mo, Bao Shi-Ning, Xu Ya-Bo

Yb-intercalated C60 thin film was prepared in a ultra-high-vacuum system. The binding energies of C 1s, Yb 4f and Yb 4d during the compound formation were studied by x-ray photoemission technique. The stoichiometry of the phase-pure sample was determined by the peak intensities of Yb 4f and C 1s. The result turned to be very near to that for Yb2.75C60 that was first determined for bulk-phase sample by x-ray diffraction measurement. The positions and intensities of the Yb 4f and Yb 4d peaks revealed the charge state of Yb2+ in Yb2.75C60. The C 1s core level for the phase-pure sample shifted towards lower binding energy by ≈0.5 eV relative to C60, which exhibited that some Yb 6s electrons transferred from Yb to the lowest unoccupied molecular orbital band of C60. The shift and the FWHM of C 1s x-ray photoemission spectroscopic peak can be used as sample characterization in future researches on Yb/C60 compounds.

Acta Physica Sinica. 2004 53(3): 915-921. Published 2004-03-15

Study on the electronic structure and superconductivity of MgCNi3

Chen Li, Li Hua — 2004-03-15

Author(s): Chen Li, Li Hua

The electronic structures and superconductivity of a new superconducting perovskite material MgCNi3 are studied using MS-Xα calculation. In MgCNi3, the peak of density of states is located below the Fermi level, which is dominated by Ni d band. The electronic structures of MgCNi2T(T=Co，Mn，Cu) have been also investigated. It is confirmed that Co dopants in MgCNi3 behave as a source of d-band holes, and the suppression of superconductivity occurs faster for the Mn-doped case than for the Co-doped case. We study the effects of electron (Cu) doping on the superconductivity. It is found that both electron (Cu) doping and hole (Co, Mn) doping quench superconductivity. Comparing with the hole (Co) doping, we found that the suppression of superconductivity occurs faster for the Co-doped case than for the Cu-doped case.

Acta Physica Sinica. 2004 53(3): 922-926. Published 2004-03-15

Substitution effect of Ta in EuSr2Ru1-xTaxCu2O8 system

2004-03-15

Author(s): Fang Ming-Hu, Lin Yang-Fan, Lu Jun-Sheng, Zhang Guo-Fang, He Qing, Wang Hang-Dong

The measurements on the structure, resistance and magnetization were carried out for EuSr2Ru1-xTaxCu2O8 (x=0.0, 0.1, 0.2, 0.5 and 1.0) samples. It is found that the EuSr2RuCu2O8 compound exhibits a ferromagnetic order of Ru moments below Tc=130.2K, and becomes superconducting at a much lower temperature Tc=35K, and shows the typical characteristics of underdoped high-Tc superconductors. The ferromagnetic transition temperature and superconducting transition temperature decrease with increasing the substitution concentration x value of Ta for Ru. The effect of element substitution, the coexistence of magnetism and superconductivity in this system are discussed in detail.

Acta Physica Sinica. 2004 53(3): 927-931. Published 2004-03-15

Optical absorption of Au/BaTiO3,Fe/BaTiO3 nanocomposite films prepared by PLD

Wang Wei-Tian, Yang Guang, Guan Dong-Yi, Wu Wei-Dong, Chen Zheng-Hao — 2004-03-15

Author(s): Wang Wei-Tian, Yang Guang, Guan Dong-Yi, Wu Wei-Dong, Chen Zheng-Hao

Nanocomposite thin films formed by nanometer-sized metal particles embedded in BaTiO3 matrices (Au/BaTiO3,Fe/BaTiO3) were fabricated using pulsed laser deposition technique.The morphology and chemical state of the embedded metal particles were analyzed by transmission electron microscopy and x-ray photoelectron spectroscopy,respectively.The absorption peak due to the surface plasmon resonance of Au particles was observed at the wavelength of about 580nm in Au/BaTiO3 films.However,optical absorption spectra in the wavelength range of 330—800nm showed no significant resonance peak in Fe/BaTiO3 films.The results were explained by Mie theory.

Acta Physica Sinica. 2004 53(3): 932-935. Published 2004-03-15

The effect of hydrogen and nitrogen on the growth of boron carbonitride nanotubes

Chao Ming-Ju, Ding Pei, Zhang Hong-Rui, Guo Mao-Tian, Liang Er-Jun — 2004-03-15

Author(s): Chao Ming-Ju, Ding Pei, Zhang Hong-Rui, Guo Mao-Tian, Liang Er-Jun

On the basis of the study of different temperature and catalyst, the effect of hydrogen and nitrogen on the morphology and yield of boron carbonitride(BCN) nanotubes produced by thermal decomposition at 860℃ was studied. It is found that nitrogen has a little effect on the growth of BCN nanotubes. Different from nitrogen, transmission electron microscopy(TEM) images reveal that hydrogen is important to the growth of BCN nanotube. Bamboo-shaped thinner wall nanotubes with higher yield are produced with hydrogen flow rate of 40 sccm, whereas curved nanotubes with lower yield and are generated with hydrogen flow rate of 0 sccm. BCN nanotubes with some holes on were produced with the flow rate of 80 sccm. Basic on previous analysis, we think that the appropriate range of N2 should be 150—210 sccm, and that of H2 should be about 40 sccm. At last, the reasons were also analysised.

Acta Physica Sinica. 2004 53(3): 936-941. Published 2004-03-15

Luttinger parameter of carbon nanotubes investigated by shot noise experiment

Zhang Zhi-Yong, Wang Tai-Hong — 2004-03-15

Author(s): Zhang Zhi-Yong, Wang Tai-Hong

Fermi liquid model with elemental charge of e*(e*=ge) is used to describe the electrical transport in carbon nanotubes, so the scattering theory can be used to calculate the zero-frequency shot noise in nanotubes. When the temperature is 0K, the nanotube with a strong barrier has the shot noise of 2geI. A new approach to measure the Luttinger g-factor of nanotubes is created: forming a strong barrier in nanotube, measuring its shot noise S, and then calculating the g-factor.

Acta Physica Sinica. 2004 53(3): 942-946. Published 2004-03-15

A new search method to solve the magnetoencephalography inverse problem

Zhu Hong-Yi, Shen Jian-Qi, Li Jun — 2004-03-15

Author(s): Zhu Hong-Yi, Shen Jian-Qi, Li Jun

A new search method is presented to solve the magnetoencephalography(MEG) inverse problem in a realistic head model. This method is based on the relationship between the magnetic fields generated by two closely located current dipoles. If we know the magnetic field produced by a current dipole, we can get the magnetic field generated by another current dipole located in somewhere close to it through this relationship. Doing it again and again, we can calculate the magnetic field generated by the dipole located anywhere in the brain, and obtain the difference between the calculated magnetic field and the measured magnetic field. The place where the square of the difference is the least will be the solution to our problem. Compared with boundary element method, this method can get the accurate solution to MEG inverse problem simpler, as well as costing less time.

Acta Physica Sinica. 2004 53(3): 947-951. Published 2004-03-15

The influence of thermal effects in a beam control system and spherical aberration on the laser beam quality

Ji Xiao-Ling, Tao Xiang-Yang, Lü Bai-Da — 2004-03-15

Author(s): Ji Xiao-Ling, Tao Xiang-Yang, Lü Bai-Da

With the strehl ratio, power in the bucket, β parameter and beam widths taken as the characteristic parameters of laser beam quality in the far field, the influence of thermal effects in a beam control system and spherical aberration on the laser beam quality in the far field is studied. Detailed calculations are performed using a four-dimensional simulation code, and numerical results are given and analyzed physically. It is shown that the thermal effects in the propagation channel and positive spherical aberration give rise to an expansion of intensity distributions and reduce the focus ability in the far field, and degrade the beam quality. It is interesting that a suitable choice of the negative spherical aberration would result in a higher peak intensity and a better focus abilty at the geometrical focal plane than that of the spherical-aberration-free case, as the emissive power reaches a certain value; whereas a similar result is achieved at the real focal plane due to the focal shift as in the previous work. The physical interpretation is that there exists the nonlinear thermal blooming, which is illustrated with numerical examples.

Acta Physica Sinica. 2004 53(3): 952-960. Published 2004-03-15

A study of characteristics for deep dielectric charging on satellites

Huang Jian-Guo, Chen Dong — 2004-03-15

Author(s): Huang Jian-Guo, Chen Dong

Deep dielectric charging is one of the key factors that induce malfunction and failure on geosyncronous satellites. In this paper, the relations between the maximum electric field generated during charging and high energy spectrum, thickness of dielectric and that of shield applied are studied, and the main characteristics about the maximum electric field are provided

Acta Physica Sinica. 2004 53(3): 961-966. Published 2004-03-15

Effects of target thickness on spectral characteristics of x-ray flux from the laser-produced plasmas

Wang Wei, Zhang Jie, Dong Quan-Li, V.K.Senecha — 2004-03-15

Author(s): Wang Wei, Zhang Jie, Dong Quan-Li, V.K.Senecha

A detailed numerical simulation study of spectral characteristics of the x-ray flux from gold foil targets of different thickness irradiated by a 1ns laser pulse with 1014W/cm2 intensity at 0.35μm wavelength using the one dimensional radiation hydrodynamic code MULTI is investigated using one dimensional radiation hydrodynamic code MULTI.This is very important in the diagnosis of the x-ray spectrum and the design of an x-ray source.

Acta Physica Sinica. 2004 53(3): 967-972. Published 2004-03-15