Table of contents

20 June 1995, Volume 4 Issue 6 Previous issue    Next issue

GENERAL

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NEW SYMMETRIES AND LIE ALGEBRAS OF THE GENERAL KdV EQUATION ZHANG JIE-FANG (张解放) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  401-405.  DOI: 10.1088/1004-423X/4/6/001 Abstract ( 1116 )   PDF (97KB) ( 347 )   The strong symmetry of the general KdV equation is factorized to a simple form and then the inverse strong symmetry is obtained explicitly. Acting a strong symmetry of the general KdV equation on the trivial symmetry and the known $\tau_{\rm c}$ symmetry, we obtain four new sets of symmetries of the general KdV equation. All these sets of symmetries constitute an infinite dimensional Lie algebra.

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GEOMETRIC PHASES AND SCHR?DINGER'S CAT STATE WU JIN-WEI (吴锦伟), GUO GUANG-CAN (郭光灿) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  406-419.  DOI: 10.1088/1004-423X/4/6/002 Abstract ( 1121 )   PDF (234KB) ( 409 )   A matrix method is presented for treating the dynamical phases, adiabatic phases and nonadiabatic phases of quantum superposition states. It is effective for any parameter-varying Hamiltonian system. As two examples, the evolution of mass-varying harmonic oscillator and the evolution of coherent states under parameter-varying displaced operator have been studied, Some new phenomena are obtained in the first case and the possible producing of so-called Schr$\ddot{\rm o}$dinger's cat state by geometric phases is pointed out. The quantum state useful for the quantum optical verification of Berry's phase is introduced.

CLASSICAL AREAS OF PHENOMENOLOGY

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EFFECT OF LIGHT-INDUCED SCATTERING ON DIFFRACTION EFFICIENCY IN PHOTOREFRACTIVE CRYSTALS ZHOU ZHONG-XING (周忠祥), SUN WAN-JUN (孙万钧), SUN XIU-DONG (孙秀冬), ZHAO HUA (赵桦), XU KE-BIN (许克彬), JIANG QUAN-ZHONG (姜全忠), CHEN HUAN-CHU (陈焕矗) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  420-427.  DOI: 10.1088/1004-423X/4/6/003 Abstract ( 1086 )   PDF (196KB) ( 340 )   The coupled wave equations and their analytic solutions in photorefractive crystals are presented for the case of two-beam writing, while the light-induced scattering is considered, Using this result, the diffraction efficiency for each writing beam is discussed in doped KNSBN crystals with unidirectional fan, which is explained theoretically and verified exper-imentally.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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EFFECT OF INTERFACE LAYER ON LAMB WAVE PROPAGATION IN SOLID ADHESIVE JOINTS: A PERTURBATION MODEL NING WEI (宁伟), WANG YAO-JUN (王耀俊) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  428-433.  DOI: 10.1088/1004-423X/4/6/004 Abstract ( 1164 )   PDF (150KB) ( 403 )   This paper presents a perturbation model for calculating the approximate Lamb wave velocities in solid adhesive joints. The numerical computations show that the approximate values of the Lamb wave velocities are very close to the exact ones if the thickness of the interface layer is small. A comparison of the perturbation analysis with the approximate "spring" model is given. The significance of the perturbation model is discussed for the inverse deduction of the mechanical properties of the interface layer from Lamb wave measurements.

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

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RESONANT TUNNELING THROUGH COUPLED DOUBLE-QUANTUM-WELL LIU LI-JUN (刘立军), NIU CHENG (牛成), LIN ZONG-HAN (林宗涵) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  434-440.  DOI: 10.1088/1004-423X/4/6/005 Abstract ( 998 )   PDF (160KB) ( 446 )   A double-well resonant tunneling structure has been investigated carefully using the nonequilibrium Green's function method. We find that in the transmission probability two maxima appear even when the two levels have the same energy. This characteristic is at-tributed to the resonant tunneliug through mixed quasibound states. The tunneling current formula through this system under a dc voltage has been derived exactly. Three different cases are considered and several novel properties are found, which manifest coherent charac-teristics of the tunneling process.

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ANISOTROPY OF CRITICAL CURRENT DENSITY IN c-AXIS ORIENTED EPITAXIAL YBa2Cu3O7-$\delta$ FILMS XU XIAO-JUN (许小军), FANG JUN (方军), CAO XIAO-WEN (曹效文), LI KE-BIN (李可斌) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  441-447.  DOI: 10.1088/1004-423X/4/6/006 Abstract ( 1156 )   PDF (179KB) ( 373 )   The dependence of critical current density Jc on the angle $\alpha$ between the directions of the applied magnetic field H (which was rotated in the c-axis-I plane) and the in-plane current I was measured on a c-axis oriented epitaxial YBa2Cu3O7-$\delta$ films at 81 K, with the magnetic field strength up to 6T. Analysis of the experimental results on the basis of the classical scaling law of pinning force shows that there exist simultaneously planar-pinning and volume-pinning mechanisms, and the contribution of volume pinning increases wish decreasing $\alpha$ while that of the planar pinning decreases. We propose that the decrease of Lorentz-force-independent critical current density with increasing H for H∥I results from the suppression of superconductivity by the magnetic field, The fact that the contribution of volume pinning increases with decreasing $\alpha$ also arises from the suppression of superconductivity in CuO2 plane by the magnetic field.

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PHASE TRANSITIONS IN Bi2Sr2(Cu1-zFez)O6+$\delta$ PAN GUO-QIANG (潘国强), G. COLLIN, S. MEGTERT Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  448-456.  DOI: 10.1088/1004-423X/4/6/007 Abstract ( 1115 )   PDF (271KB) ( 311 )   We have investigated, by X-ray diffraction, a series of single crystals of Bi-based oxides with the nominal composition Bi2Sr2(Cu1-zFez)O6+$\delta$ (0≤z≤0.55). In this system we observed two structural phase transitions with the increase of the doping content. The first transition, from an incommensurate monoclinic phase to an incommensurate orthorhombic phase, occurs at a doping content of iron zFe=0.027. The second one corresponds to a phase transition from an incommensurate orthorhombic phase to a commensurate orthorhombic phase at zFe=0.34. The comparison of these results with those for more limited substitutions of Zn and Ni indicates the significant role of the insertion of the extra oxygen in the (Bi-O)$\infty$ double layers.

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EFFECT OF THE SUBSTITUTION OF Ga ON THE STRUCTURE AND MAGNETIC PROPERTIES OF Dy2Fe17 COMPOUND LUO YOU-QUAN (罗有泉), LU GUO-RONG (卢国荣), ZHANG ZHI-YOU (张志友), LIANG BING (梁兵) Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  457-461.  DOI: 10.1088/1004-423X/4/6/008 Abstract ( 1091 )   PDF (121KB) ( 353 )   Dy2Fe17-xGax (x = 0,1,2,3,4, 5 and 6) compounds were prepared by arc melting. These compounds are of single phase, having a hexagonal Th2Ni17-type structure fox x=0 and rhombohedral Th2Zn17-type structure for x≥1. The substitution of Ga for Fe in the Dy2Fe17 leads to a linear increase of unit-cell volumes. The saturation magnetization Ms at 1.5K is found to decrease linearly with increasing Ga concentration, from 65emu/g for x= 0 to 5emu/g for x = 6; and the Fe magnetic moment $\mu$Fe is almost independent of Ga concentration. The Curie temperature TC is found first to increase with increasing Ga content x, and goes through a maximum value of 559 K at about x = 3, then decreases. The sharp increase of TC at lower Ga content may result from the increase of unit cell volumes. Dy2Fe17-xGax compounds with x≤5 exhibit easy plane anisotropy at room temperature, and those with x = 6 possess easy-axis.

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RADIAL CONTRACTION OF THE FIRST KIND OF DUMBBELL DOMAINS SUBJECTED TO A STATIC BIAS FIELD LIU DA-PENG (刘大鹏), HAN BAO-SHAN (韩宝善), NIE XIANG-FU (聂向富), J. Ben Youssef, J. M. Desvignes, H. Le Gall Acta Physica Sinica (Overseas Edition), 1995, 4 (6):  462-469.  DOI: 10.1088/1004-423X/4/6/009 Abstract ( 1032 )   PDF (272KB) ( 382 )   On the basis of the "exercise" experiment and the phenomenon of "self-shrink", the behavior of "less-stable" IDs (first kind of dumbbell domains) in radial contraction under an "exercise" bias field, (Hb)e, was statistically investigated in detail. It was found that the histograms of their stripe-to-bubble transition field, Hsb after exercise, become narrower and shift towards the side of lower Hsb with the increase of (Hb)e. It illustrates how the less-stable IDs lose part of their vertical Bloch lines under different (Hb)e. In addition, it was also found that the curve of the upper boundary of these histograms, (Hsb)max vs. (Hb)e, consists of two segments of straight lines. This discontinuity was proved to be due to self shrink, and the crosspoint of these two lines is just the lower limit of the self-shrink region. Furthermore, a series of photographs were taken to show the effect of radial contraction on less-stable IDs intuitively.