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Chin. Phys. B  
  Chin. Phys. B--1999, Vol.8, No.5
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GENERAL

UNDULATION MODES IN BILAYER MEMBRANES

Zhang Shao-guang, Ouyang Zhong-can
Chin. Phys. B 1999, 8 (5): 0321;  doi: 10.1088/1004-423X/8/5/001
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Through the complete analysis of the solution for one dimensional bilayer membranes, it has been shown that under the Helfrich spontaneous curvature model, periodic shapes only exist in the case of \bar{Δp}=0. The undulation modes under force balance which correspond to positive, negative and zero tensile stresses have been given.

A SIMPLE SOLITON SOLUTION METHOD FOR THE (2+1) DIMENSIONAL LONG DISPERSIVE WAVE EQUATIONS

Zhang Jie-fang, Wu Feng-min
Chin. Phys. B 1999, 8 (5): 0326;  doi: 10.1088/1004-423X/8/5/002
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A simple and direct method is presented to solve the (2+1) dimensional long dispersive wave equation. We introduced a variable dependent transformation in order to convert this equation into the simple forms, which are three coupled linear and bilinear partial differential equations, and give the single and double soliton solutions and the (1, N) dromion solution.
ATOMIC AND MOLECULAR PHYSICS

ELECTRON IMPACT IONIZATION OF HELIUM FROM ITS GROUND AND METASTABLE STATES

Chen Zhang-jin, Xu Ke-zun
Chin. Phys. B 1999, 8 (5): 0331;  doi: 10.1088/1004-423X/8/5/003
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The triple differential cross sections for the ionization of helium from its ground state 11S and metastable states 21S and 23S in coplanar asymmetric geometry by 150, 250 and 400 eV electrons have been calculated in the BBK model. The present results are compared with the experimental data and/or the other theoretical ones. It has been found that the structures for the metastable states differ markedly from those for the ground state. The collision mechanisms for the new structures appearing in the cross sections for the ionization from metastable states have been analysed. And it has been shown how the intensity of recoil peak changes due to the size of the electron orbital. In addition, the optimal kinematical situations for the cross sections are explored for future experiment.
CLASSICAL AREAS OF PHENOMENOLOGY

DYNAMICS OF A TRAPPED ATOM INTERACTING WITH AN ELECTROMAGNETIC WAVE OF CIRCULAR POLARIZATION

Zhang Jing-tao, Zeng Gao-jian
Chin. Phys. B 1999, 8 (5): 0342;  doi: 10.1088/1004-423X/8/5/004
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In this paper the dynamics of a trapped two-level atom interacting with a beam of electromagnetic wave of circular polarization is studied. In a frame rotating with the atomic transition frequency ω0, the motion of the atom is governed by a nonlinear coupled Jaynes-Cummings (JC) Hamiltonian. By means of this nonlinear Hamiltonian, we study the atomic inversion, squeezing effect of the vibration mode and that of the atomic dipole, and the phase property as well as its fluctuation of the vibration mode. In the Lamb-Dicke limit, we get the results similar to those of the JC model; beyond the Lamb-Dicke limit, we find the evolution of these quantities becomes very complicated. The nonlinearity weakens the collapse-revival phenomenon of the atomic inversion and the squeezing effect; the evolution of the cosine phase operator becomes less predetermined with its fluctuation not enlarged.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

THOMSON SCATTERING MEASUREMENT OF LASER-HEATED PLASMAS

Zhai Kan, Han Shen-sheng, Lu Hai-he, Li Ming-fu, Yang Xiao-dong, Tang Yu-hui, Xu Zhi-zhan
Chin. Phys. B 1999, 8 (5): 0351;  doi: 10.1088/1004-423X/8/5/005
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Experiment on characterizing the laser-heated plasmas using Thomson scattering measurement has been carried out. An incoherent Thomson scattering system with a 90° scattering angle has been established. The influence of the gas density and the pumping laser energy on the temperature of the laser-heated plasma has been examined. The results show that the temperature of the laser-heated plasma increases with the increase of pumping laser energy and the plasma density, which agrees well with the explanation of inverse Bremsstrahlung absorption.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

ELECTRONIC STRUCTURES AND GEOMETRY OF THE Al12Si CLUSTER SOLID

Zhu Zi-zhong, Zhao Jing-tai
Chin. Phys. B 1999, 8 (5): 0356;  doi: 10.1088/1004-423X/8/5/006
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The electronic structures and geometry of a solid assembled out of cubic close packing of Al12Si clusters have been studied with an ab initio pseudopotential method and within the local density functional theory. Both the lattice constant of the solid formed and the atomic geometry of the clusters in it have been optimized through the ab initio method without adjustable variables. Our results show that the crystal composed of Al12Si clusters is a metal rather than a semiconductor. Interactions between Al12Si clusters in the solid are strong and the clusters are no longer inert under crystal field.

DOUBLE BOUND POLARON IN QUANTUM WELLS

Liu Zi-xin, Huang Yong-chang, Liu Ya, Jia Tian-qing
Chin. Phys. B 1999, 8 (5): 0361;  doi: 10.1088/1004-423X/8/5/007
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We have proposed the Hamiltonian of the single or double polaron bound to a helium-type donor impurity in semiconductor quantum wells (QWs) in the case of positively charged donor center and neutral donor center. The couplings of an electron with various phonon modes are considered; in particular, the interaction of the impurity with the various phonon modes is included. We have calculated the binding energy of a bound polaron in Al(xl)Ga1-(xl)As/GaAs/Al(xr)Ga1-(xr) As symmetric and asymmetric QWs. The results are obtained as a function of barrier height (or equivalently of Al concent ration x), well width, and the position of impurity in the QWs. Our numerical calculations show clearly that for a thin well the cumulative effects of the electron-phonon coupling and the impurity-phonon coupling can contribute appreciably to the donor binding energy. The enhancement of polaronic effect is also found in the case of ionized donor.

REDUCED QUANTUM FLUCTUATION IN MESOSCOPIC JOSEPHSON JUNCTION WITH SCHR?DINGER-CAT STATE FIELD

Shao Bin, Zou Jian
Chin. Phys. B 1999, 8 (5): 0368;  doi: 10.1088/1004-423X/8/5/008
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We consider the system of a mesoscopic Josephson junction interacting with a quantized radiation field and investigate the fluctuation properties of the junction variables with time evolution. Our results show that, due to the quantum entanglement between the field and junction, the mesoscopic Josephson junction subsystem can exhibit squeezing behavior.

CRITICAL CURRENT DENSITY AND FLUX PINNING CHARACTERISTICS IN MELT-TEXTURED Y0.6Er0.4Ba2Cu3Oy SUPERCONDUCTOR

Feng Yong, Zhou Lian, Shi Lei, Yang Wan-min, Zhang Cui-ping, Wang Jing-rong, Du Ze-hua, Yu Ze-min, Wu Xiao-zu, Zhang Yu-heng
Chin. Phys. B 1999, 8 (5): 0374;  doi: 10.1088/1004-423X/8/5/009
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We prepared highly textured YBa2CuOy and Y0.6Er0.4Ba2Cu3Oy bulk samples by a powder melting process method under the same conditions and studied the magnetic properties and flux pinning character istics. It is found that the Jc estimated by the Bean's model decreases with the magnetic field according to a power law Jc∝B-n (n<0.55), suggesting that Jc values of these materials are controlled by the flux pinning rather than weak links. Also, Jc and flux pinning are improved by the Er addition. The reduction of the size of Y2BaCuO5 particles, magnetic pinning and stress-field pinning caused by the Er addition may be responsible for the enhancement of Jc and flux pinning.

SOLVATION DYNAMICS OF METHANOL INVESTIGATED BY FEMTOSECOND TIME-RESOLVED FLUORESCENCE UP-CONVERSION TECHNIQUE

Zhang Tie-qiao, Wang Shu-feng, Yang Hong, Li Jian-liang, Gong Qi-huang
Chin. Phys. B 1999, 8 (5): 0383;  doi: 10.1088/1004-423X/8/5/010
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The solvation dynamics of methanol has been investigated using a femtosecond time-resolved fluorescence up-conversion technique. Transient fluorescence spectra of Coumarin 152A dissolved in methanol at different time were reconstructed from the measured fluorescence decays. The Stokes shift was obtained and the solvent response function Sv(t) was fitted using a bimodal function with a fast Gaussian component and a slow bi-exponential component. The Gaussian component was attributed to the effect of free streaming motion of the solvent molecules, whereas the bi-exponential component was caused by the rotational diffusion motion of the solvent molecules. A comparison of our results with reported data was made.
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