Table of Content

15 December 1999, Volume 8 Issue 12 Previous Issue    Next Issue

GENERAL

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INTERFACE SHAPE AND CONCENTRATION DISTRIBUTION IN CRYSTALLIZATION FROM SOLUTION UNDER MICROGRAVITY LIU YONG-CAI, CHEN WAN-CHUN, HUO CHONG-RU, GE PEI-WEN 1999, 8 (12):  881-888.  doi: 10.1088/1004-423X/8/12/001 Abstract ( 0 )   PDF (246KB) ([an error occurred while processing this directive])   The influence of the gravity and interface kinetics on interface shape and interfacial concentration distribution was numerically investigated by using Galerkin finite element method.A boundary mapping technique was used for dealing with free boundary problem. A two-dimensional steady-state model of TGS crystal growth was developed. The results show that with the increase of the gravity level, the growth rate becomes faster, the growth face becomes more curved and interfacial concentration distribution more non-uniform. The consideration of interface kinetics will cause the decrease of growth rate as compared with the pure transport model. It seems that the interface shape does not change very much within two cases of k=5.7cm4/(mol·s) and k=∞, but its position does.

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NEW B?CKLUND TRANSFORMATION AND EXACT SOLUTIONS FOR VARIABLE COEFFICIENT KdV EQUATION YAN ZHEN-YA, ZHANG HONG-QING 1999, 8 (12):  889-894.  doi: 10.1088/1004-423X/8/12/002 Abstract ( 0 )   PDF (128KB) ([an error occurred while processing this directive])   In this paper, with the aid of Lax pairs, a new B?cklund transformation for the variable coefficient KdV equation is found, Based on the B?cklund transformation, only if integration is needed, a series of exact solutions can be obtained. This method is important for finding more new and physical-signficant solutions.

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A NEW STRATEGY OF CHAOS CONTROL AND A UNIFIED MECHANISM FOR SEVERAL KINDS OF CHAOS CONTROL METHODS LUO XIAO-SHU, FANG JIN-QING, WANG LI-HU, KONG LING-JIANG, JIANG FENG 1999, 8 (12):  895-901.  doi: 10.1088/1004-423X/8/12/003 Abstract ( 0 )   PDF (233KB) ([an error occurred while processing this directive])   Based on a general principle of physics that a physical system is in the most stable state if it is of the lowest energy stale, a new method for chaos control is proposed. A calculable generalized energy function in a nonlinear system is suggested for measuring control process, The Henon map and Lorenz system are taken as two typical examples to demonstrate the method. A series of stabilized periodic orbits as well aa inverse sequence of chaotic bands are obtained. At the same time, a unified mechanism of physics for several kinds of current cbaos control methods is studied using the idea proposed in this paper.

CLASSICAL AREAS OF PHENOMENOLOGY

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OPTICAL BISTABILITY IN V MEDIUM BY SQUEEZED VACUUM INPUT CHEN ZHAO-YANG, ZHANG JING-TAO, XU ZHI-ZHAN 1999, 8 (12):  902-907.  doi: 10.1088/1004-423X/8/12/004 Abstract ( 0 )   PDF (184KB) ([an error occurred while processing this directive])   We discuss the optical bistable behavior of a system of N V-type three-level atoms pumped by a coherent input field and coupled to a squeezed vacuum field by treating the optical hist ability of such a system as an input-output problem. It is shown that bistability can be realized due to the squeezed vacuum input.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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INFLUENCE OF HIGHER ORDER TOROIDICITY ON COUPLING OF TEARING MODES WANG CHUAN-BING, LI DING 1999, 8 (12):  908-912.  doi: 10.1088/1004-423X/8/12/005 Abstract ( 0 )   PDF (165KB) ([an error occurred while processing this directive])   he general dispersion relation for toroidally coupled tearing mode including pressure and other O(ε2) order corrections is naturally derived based on the structure of ideal magnetohydro-dynamic solutions in the outer region. It is found that the inclusion of the O(ε2) order terms in the diagonal element of E-matrix does not change physical properties of the toroidally coupled tearlng mode and only make negligible contribution to the magnitude of growth rate.

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NEUTRON TIME OF FLIGHT ENERGY SPECTROMETER FOR ICF ION TEMPERATURE DIAGNOSTIC TANG ZHENG-YUAN, YANG JIAN-LUN, WEN SHU-HUAI, WANG GEN-XING, GUO YU-ZHI, YANG HONG-QIONG, MA CHI 1999, 8 (12):  913-918.  doi: 10.1088/1004-423X/8/12/006 Abstract ( 0 )   PDF (175KB) ([an error occurred while processing this directive])   A current-mode neutron time-of-flight(nTOF) energy spectrometer for inertial confinement fusion(ICF) ion temperature measurements has been designed which will reduce measuring error of fusion neutron energy spectra when the neutron yield is low. The spectrometer consists of a shallow cup-shaped ST1422 fast plastic scintillator with a thicknees of 3mm and full effective volume of 104cm3, a microchannel plate photomultiplier tube(MCP-PMT), a piece of coaxial cable(SUJ-50-7) with a length of 20m, and a transient oscilloscope with a bandwidth of 7GHz. The main performances of the spectrometer and its components have been calibrated. The rise-time and FWHM of the temporal response function are 260ps and 850 ps, respectively. This spectrometer will be used to measure ion temperature in the direct-driven implosion experiments on Sheng-Guang 2 laser facility at Shanghai Institute of Optics and Fine Mechanica(SIOFM) next year.

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

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CONTRIBUTION FROM MOLDCULAR FIELD TO THE TEMPERATURE DEPENDENCE OF TUNNELING MAGNETORESISTANCE WANG JUN-ZHONG, LI BO-ZANG, GAO JUN-SHAN 1999, 8 (12):  919-926.  doi: 10.1088/1004-423X/8/12/007 Abstract ( 0 )   PDF (240KB) ([an error occurred while processing this directive])   Based on the nearly free-electron approximation, we have investigaed the temperature (T) dependence of spin-polarized tunneling in the magnetic tunnel junction with an asymmetrical barrier, with emphasis on the variation of molecular field with T in the same way as that of surface magnetization. It is found that the Slonczewski model can describe well the T depen-dence of spin-polarized tunneling, while the Julliere model only describes the T dependence of JMR qualitatively, but does accurately that of the difference of tunneling conductance between the parallel and antiparallal alignments for the magnetizations of FMs; Differing from the pre-vious finding, we find the electron spin polarization is not strictly proportional to the surface magnetization, for the former decreases with the increasing T more rapidly than the latter does.

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LECTRONIC STRUCTURE STUDIES OF Bi2Sr2CaCu2-xSnxO8+δ SYSTEM LI QI, PAN HAI-BIN, ZHU CHUAN-GANG, XU PENG-SHOU, ZHOU YING-XUE, ZHANG XIN-YI 1999, 8 (12):  927-931.  doi: 10.1088/1004-423X/8/12/008 Abstract ( 0 )   PDF (180KB) ([an error occurred while processing this directive])   Photoemission measurements have been carried out for Bi2Sr2CaCu2-xSnxO8+δ system with conventional x-ray photoemission spectroscopy for core-level spectra and synchrotron radiation photoemission spectroscopy for valence band. With Sn doping, all core levels shift differently in binding energy, and the intensity near fermi energy becomes smaller in valence hand. From the experiment, we can deduce that the shifts of all core levels and valence hands may involve some other mechanisms, such ms electrostatic effects, in addition to binding energy referencing effects. We argue that the chemical environment plays a crucial role in the electronic structure of high-temperature superconductors.

CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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GROWTH MODEL OF TEXTURED DIAMOND (111) FILM IN CH4/O2/H2 ATMOSPHERE WU JIN, XIE FANG-QING, ZHANG QING-ZHE, LIU JI-WEN, CHEN YOU-CUN, LIN ZHANG-DA 1999, 8 (12):  932-937.  doi: 10.1088/1004-423X/8/12/009 Abstract ( 0 )   PDF (237KB) ([an error occurred while processing this directive])   Partially oriented and highly textured diamond films on Si( 111 ) substrates were achieved by hot-filament chemical vapor deposition(HFCVD). High nucleation density greater than 5×108cm-2 was realiged in 3 min by near-surface glow discharge. The os-grown films were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD) and Raman spectroscopy. It was found that by adding a small amount of oxygen to the mixture of CH4/H2, the appearance of facet(111) was well controlled, and the secondary nucleation on the facet(111) was suppressed greatly. Growth feature of homoepitaxy on diamond (111) surface was demonstrated to be in Stranski-Krastanov model by SEM.

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TOMOGRAPHY FORMULA FOR BIOCHEMICAL IMAGING OF THIN TISSUE WITH DIFFUSE-PHOTON DENSITY WAVES DONG GUANG-JIONG, HAN RU-SHAN, HUANG YUN, KAORU SAKATANI, ZHUANG FENG-YUAN 1999, 8 (12):  938-943.  doi: 10.1088/1004-423X/8/12/010 Abstract ( 0 )   PDF (182KB) ([an error occurred while processing this directive])   Using the transport theory to describe the near infrared light propagating in tissue with finite parallel-plane geometry, and taking the zero-boundary condition, we obtain the analytical expression of average photon density and Green's function incorporating the boundary effects in the homogeneous tissure. Making use of perturbation theory we also obtain the analytical expression of scattered wave induced by the heterogeneity, and present the 2-dimensional spatial transform of scattered wave with respect to transverse coordinate. If the information of heterogeneity on depth and thickness is available, diffraction tomography formula is presented to save the time of image reconstruction; if the information is unknown, we suggest to obtain the inhomogeneous function from the one-dimensional integral equation of 2-dimensional spatial transform of scattered wave applying the direct matrix method or iterative method for image reconstruction. This approach avoids directly solving three-dimensional integral equation of scattered wave. In our proposed approach the strong points of the direct matrix method, iterative method, and diffraction tomography are fully combined.