Table of contents

15 May 1999, Volume 8 Issue 5 Previous issue    Next issue

GENERAL

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UNDULATION MODES IN BILAYER MEMBRANES Zhang Shao-guang (张劭光), Ouyang Zhong-can (欧阳钟灿) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  321-325.  DOI: 10.1088/1004-423X/8/5/001 Abstract ( 1326 )   PDF (184KB) ( 373 )   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 $\overline{Δp}$ = 0. The undulation modes under force balance which correspond to positive, negative and zero tensile stresses have been given.

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A SIMPLE SOLITON SOLUTION METHOD FOR THE (2+1) DIMENSIONAL LONG DISPERSIVE WAVE EQUATIONS Zhang Jie-fang (张解放), Wu Feng-min (吴锋民) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  326-330.  DOI: 10.1088/1004-423X/8/5/002 Abstract ( 1150 )   PDF (169KB) ( 426 )   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

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ELECTRON IMPACT IONIZATION OF HELIUM FROM ITS GROUND AND METASTABLE STATES Chen Zhang-jin (陈长进), Xu Ke-zun (徐克尊) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  331-341.  DOI: 10.1088/1004-423X/8/5/003 Abstract ( 1114 )   PDF (261KB) ( 364 )   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

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DYNAMICS OF A TRAPPED ATOM INTERACTING WITH AN ELECTROMAGNETIC WAVE OF CIRCULAR POLARIZATION Zhang Jing-tao (张敬涛), Zeng Gao-jian (曾高坚) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  342-350.  DOI: 10.1088/1004-423X/8/5/004 Abstract ( 939 )   PDF (247KB) ( 465 )   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 $\omega$0, 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

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THOMSON SCATTERING MEASUREMENT OF LASER-HEATED PLASMAS Zhai Kan (翟侃), Han Shen-sheng (韩申生), Lu Hai-he (陆海鹤), Li Ming-fu (李明富), Yang Xiao-dong (杨晓东), Tang Yu-hui (汤宇辉), Xu Zhi-zhan (徐至展) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  351-355.  DOI: 10.1088/1004-423X/8/5/005 Abstract ( 998 )   PDF (208KB) ( 502 )   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

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ELECTRONIC STRUCTURES AND GEOMETRY OF THE Al12Si CLUSTER SOLID Zhu Zi-zhong (朱梓忠), Zhao Jing-tai (赵景泰) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  356-360.  DOI: 10.1088/1004-423X/8/5/006 Abstract ( 1338 )   PDF (204KB) ( 304 )   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.

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DOUBLE BOUND POLARON IN QUANTUM WELLS Liu Zi-xin (刘自信), Huang Yong-chang (黄永畅), Liu Ya (刘亚), Jia Tian-qing (贾天卿) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  361-367.  DOI: 10.1088/1004-423X/8/5/007 Abstract ( 901 )   PDF (234KB) ( 354 )   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.

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REDUCED QUANTUM FLUCTUATION IN MESOSCOPIC JOSEPHSON JUNCTION WITH SCHR$\ddot{\rm O}$DINGER-CAT STATE FIELD Shao Bin (邵彬), Zou Jian (邹健) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  368-373.  DOI: 10.1088/1004-423X/8/5/008 Abstract ( 997 )   PDF (181KB) ( 397 )   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.

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CRITICAL CURRENT DENSITY AND FLUX PINNING CHARACTERISTICS IN MELT-TEXTURED Y0.6Er0.4Ba2Cu3Oy SUPERCONDUCTOR Feng Yong (冯勇), Zhou Lian (周廉), Shi Lei (石磊), Yang Wan-min (杨万民), Zhang Cui-ping (张翠萍), Wang Jing-rong (汪京荣), Du Ze-hua (杜泽华), Yu Ze-min (于泽民), Wu Xiao-zu (吴晓祖), Zhang Yu-heng (张裕恒) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  374-382.  DOI: 10.1088/1004-423X/8/5/009 Abstract ( 1287 )   PDF (266KB) ( 520 )   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.

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SOLVATION DYNAMICS OF METHANOL INVESTIGATED BY FEMTOSECOND TIME-RESOLVED FLUORESCENCE UP-CONVERSION TECHNIQUE Zhang Tie-qiao (张铁桥), Wang Shu-feng (王树峰), Yang Hong (杨宏), Li Jian-liang (李建良), Gong Qi-huang (龚旗煌) Acta Physica Sinica (Overseas Edition), 1999, 8 (5):  383-388.  DOI: 10.1088/1004-423X/8/5/010 Abstract ( 1110 )   PDF (242KB) ( 570 )   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.