Table of contents

20 September 1998, Volume 7 Issue 9 Previous issue    Next issue

GENERAL

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DETERMINATION OF THE PERIOD OF A TORSION PENDULUM BY THE FITTING METHOD IN REAL TIME Fu Xiang-hui (傅湘辉), Luo Jun (罗俊), Hu Zhong-kun (胡忠坤), Tang Meng-xi (唐孟希) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  641-648.  DOI: 10.1088/1004-423X/7/9/001 Abstract ( 994 )   PDF (222KB) ( 1082 )   A phenomenological study on the fitting method in real time has been done, and the method was applied to process and analyze the extensive data of a long period torsion pendulum used to determine Newtonian gravitational constant G. The result shows that the fitting method in real time is effective to determine the period of a torsion pendulum with a relative precision of 10-5 orders.

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B?CKLUND TRANSFORMATION, LAX PAIRS, SYMMETRIES AND EXACT SOLUTIONS FOR VARIABLE COEFFICIENT KdV EQUATION Fan En-gui (范恩贵), Zhang Hong-qing (张鸿庆), Lin Gang (林钢) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  649-654.  DOI: 10.1088/1004-423X/7/9/002 Abstract ( 1076 )   PDF (187KB) ( 577 )   The homogeneous balance method is extended to seek for B$\ddot{\rm a}$cklund transformation, Lax pairs, non-local symmetries of variable coefficient KdV equation (VCKdVE). Then based on the B$\ddot{\rm a}$cklund transformation and general solutions of a fourth-order nonlinear ordinary differential equation, five kinds of exact solutions of VCKdVE are derived. The soliton-like solution also belongs to these solutions.

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DEPENDENCE OF DOMAIN STRUCTURES ON Au THICKNESS IN Co/Au MULTILAYER FILMS Xu Hai (徐海), Li Jian (李建), Han Bao-shan (韩宝善), Wang Yin-jun (王荫君) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  655-661.  DOI: 10.1088/1004-423X/7/9/003 Abstract ( 996 )   PDF (201KB) ( 451 )   The magnetic force images and surface topography images of sputtered Co/Au multilayer films in remnant state were measured by magnetic force microscopy. From the surface magnetic structures shown in the magnetic force images it can be seen that the domain pattern and size vary with the increase of the thickness t of the non-ferromagnetic Au layer remarkably. With the measurements of the effective perpendicular anisotropy Ku and the domain period d, it was found that there are similar trends of d and Ku as functions of t. The variations of the domain pattern and size were qualitatively interpreted in terms of magnetic domain theory. the theoretical relations of d and the domain wall energy $\sigma$w vs t were calculated. As t=8.5 AL(1 AL=0.235 nm), the largest $\sigma$w is 11 mJ/m2.

ATOMIC AND MOLECULAR PHYSICS

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STEADY STATE BEHAVIOR OF A THREE-LEVEL ATOM IN A TWO-MODE PARAMETRICALLY DRIVEN CAVITY Li Gao-xiang (李高翔), Peng Jin-sheng (彭金生), Zhou Peng (周鹏) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  662-669.  DOI: 10.1088/1004-423X/7/9/004 Abstract ( 1122 )   PDF (211KB) ( 640 )   We have studied the steady-state behavior of a cascade three-level atom in a two-mode bad cavity which is parametrically driven by a classical field. In the weak field limit, it has been found that the atomic population trapping in the upper-level depends on the cavity photon number not only linearly but also quadratically, and the atomic dipole squeezing can occur.

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DETERMINATION OF FLOQUET STATES AND QUASI-ENERGY BY CORRELATION FUNCTION Xie Bai-song (谢柏松), Chen Shi-gang (陈式刚) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  670-680.  DOI: 10.1088/1004-423X/7/9/005 Abstract ( 1109 )   PDF (256KB) ( 1517 )   The Floquet spectrum generated by the use of time correlation function has been developed to extract the Floquet functions with Fourier transform method for wave function at integral multiples of optical period. The quasi-energy position and ionization width of those Floquet states have also been determined by least-squares fit method. Numerical calculation shows that the Fourier transform method is powerful and the resultant Floquet functions are in excellent agreement with that obtained by orthogonality projection method developed in our previous work.

CLASSICAL AREAS OF PHENOMENOLOGY

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COMPUTER SIMULATION OF VISCOUS FINGERING IN SIERPINSKI CARPET Tian Ju-ping (田巨平), Yao Kai-lun (姚凯伦) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  681-687.  DOI: 10.1088/1004-423X/7/9/006 Abstract ( 1083 )   PDF (310KB) ( 552 )   A new method—mapping dilation method is proposed in this paper to construct Sierpinski carpet. Viscous fingering (VF) in Sierpinski carpet, based on the assumption that bond radii are beta distribution, is investigated by means of successive over-relaxation techniques. The topology and the geometry of the porous media have a strong effect on displacement processes. In the Sierpinski network, the VF pattern of porous media in the limit M→∞ is found to be similar to the diffusion-limited-aggregation pattern. The fractal dimension for VF in fractal space is calculated and the fractal dimension D can be reasonably regarded as a useful parameter to evaluate the sweep efficiencies and oil recoveries. We have also found that the geometry of the porous medium also has strong effects on the displacement processes and the structure of the VF. Moreover, we find that the sweep efficiency of the displacement processes mainly depends upon the length of the network system and also on the viscosity ratio M. This shows that the current method can be used to solve VF problems in complex structures if the structures are self-similar, or they can be reduced to a self-similar structure.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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MAGNETIC FIELD GRADIENT EFFECTS ON ION FLUX BEHAVIORS IN ECR PLASMA SOURCES Shao Fu-qiu (邵福球), Wang Long (王龙), Wu Han-ming (吴汉明), Yao Xin-zi (姚鑫兹) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  688-694.  DOI: 10.1088/1004-423X/7/9/007 Abstract ( 1113 )   PDF (230KB) ( 626 )   The available electron cyclotron resonance plasma source has been simulated in two-dimensional configuration space (z, r) and three-dimensional velocity space (Vz, Vr, V$\theta$). The simulation is focused on the magnetic field gradient effects on ion flux behaviors in electron cyclotron resonance plasma sources. The simulation results show that, when the magnetic field gradients increase, electron temperature, plasma density, ionization rate, and ion flux in Z-direction would decrease, while ion energy and plasma potential would increase.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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THE DISTRIBUTION OF Sb ATOMS IN $\delta$-DOPED SILICON CRYSTAL Jia Quan-jie (贾全杰), Zheng Wen-li (郑文莉), Wang Zhou-guang (王洲光), Wang Jun (王俊), Jiang Xiao-ming (姜晓明), Jiang Zui-min (蒋最敏), Pei Cheng-wen (裴成文), Qin Jie (秦捷), Hu Dong-zhi (胡冬枝) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  695-702.  DOI: 10.1088/1004-423X/7/9/008 Abstract ( 1203 )   PDF (241KB) ( 376 )   The distribution of Sb atoms in $\delta$-doped silicon crystals grown by molecular beam epitaxy at different temperatures was measured using the technique of synchrotron radiation X-ray low angle reflection. The esults indicate that the doped Sb atoms are distributed exponentially in the epitaxial layers, and the 1/e decay lengths are 0.45, 0.95 and 3.5 nm for the samples grown at temperatures of 250, 300 and 350℃, respectively. For samples grown at 400℃, the 1/e decay length of the Sb atomic distribution increases drastically because of the segregation of Sb atoms during the growth process.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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TUNNEL MAGNETORESISTANCE IN THE FERROMAGNETIC TUNNEL JUNCTION WITH FERROMAGNETIC LAYERS OF FINITE THICKNESS SUBJECTED TO AN ELECTRIC FIELD Zhang Xiang-dong (张向东), Wang Jun-zhong (王俊忠), Li Bo-zang (李伯臧), Pu Fu-cho (蒲富恪) Acta Physica Sinica (Overseas Edition), 1998, 7 (9):  703-710.  DOI: 10.1088/1004-423X/7/9/009 Abstract ( 1032 )   PDF (236KB) ( 476 )   Based on the two-band model, we investigate the tunnel magnetoresistance(TMR) in ferromagnet/insulator (semiconductor)/ferromagnet(FM/I(S)/FM) tunnel junction covered on both sides by nonmagnetic metal layers subjected to an electric field. Our results show that TMR oscillates with the thickness of ferromagnetic layers owing to the quantum-size effect and can reach very large value under suitable conditions, which may in general not be reached in FM/I(S)/FM with infinitely thick ferromagnetic layer. Although the electric field causes the change of the oscillation period, phase and amplitude of the TMR, a large TMR is still obtained in some situations with the electric field. Furthermore, the electric field does not change the feature that TMR varies monotonously with the change of magnetization angle of the middle ferromagnetic layer.