Table of contents

20 October 1998, Volume 7 Issue 10 Previous issue    Next issue

GENERAL

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ENVELOPE SOLITON UNDER DISSIPATION IN A FLUID-FILLED ELASTIC TUBE Duan Wen-shan (段文山), Zhao Cun-yuan (赵存元), Lü Ke-pu (吕克朴), Wang Ben-ren (王本仁), Wei Rong-jue (魏荣爵) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  721-726.  DOI: 10.1088/1004-423X/7/10/001 Abstract ( 1344 )   PDF (193KB) ( 481 )   By using the reductive perturbation method, the carrier wave modulation propagating in a weakly viscous fluid-filled elastic tube is investigated. It is shown that such a process can be described by equation A$\tau$+iBA$\xi\xi$+iC|A|2A+DA=0 and the amplitude of envelope soliton will decrease as it propagates away.

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AN INTEGRAL EXPRESSION OF EXACT SOLUTION FOR HARMONIC OSCILLATOR WITH TIME-VARYING FREQUENCY Li Li-xiang (李立祥), Guo Guang-can (郭光灿) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  727-731.  DOI: 10.1088/1004-423X/7/10/002 Abstract ( 1192 )   PDF (182KB) ( 488 )   Using Feynman's method of disentangling operators, an exact expression of evolution operator of harmonic oscillator with time-varying frequency is obtained. The parameters in this expression are related to the time-varying frequency directly. Some implications are further investigated, including general form of linear and quadratic invariants and evolution of Wigner function.

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THE IMMISCIBLE DISPLACEMENT IN PERCOLATION CLUSTER Tian Ju-ping (田巨平), Yao Kai-lun (姚凯伦) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  732-738.  DOI: 10.1088/1004-423X/7/10/003 Abstract ( 1071 )   PDF (231KB) ( 335 )   The percolation clusters with varying occupy probability were constructed in this paper. Viscous fingering (VF) in percolation cluster, based on the assumption that bond radii are Rayleigh distribution, is investigated by means of successive over-relaxation technique. The fractal dimension for VF in percolation cluster is calculated. The result shows that it can increase fractal dimension of VF as increase of percolation probability of reduce of viscous ratio. VF's fractal dimension of porous media in the limit viscous ratio →$\infty$ is found to be identical with that in diffusion limited-aggregation. We have found that the topology and the geometry of the porous medium have strong effects on the displacement processes and the structure of the VF. 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. Moreover, the fractional flow of injected fluid as a function of mean saturation is obtained.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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SINE-GORDON MODEL WITH LOCAL SYMMETRIC POTENTIALS Ye Fei (叶飞), Xu Bo-wei (许伯威) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  739-743.  DOI: 10.1088/1004-423X/7/10/004 Abstract ( 1010 )   PDF (178KB) ( 370 )   Effects of spatial inhomogeneity with symmetric potentials in one-dimensional quantum sine-Gordon model are treated by use of the variational Gaussian wave functional method. The properties of the ground state and the critical point of the system are investigated.

CLASSICAL AREAS OF PHENOMENOLOGY

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PERFORMANCE OF VERTICAL VIBRATION ISOLATION SYSTEM WITH GRAVITATIONAL POSITIVE FEEDBACK Zhao Peng-fei (赵鹏飞), Zhang Ping-hua (张平华), Tang Jia-xiang (唐家祥), Luo Jun (罗俊) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  744-750.  DOI: 10.1088/1004-423X/7/10/005 Abstract ( 1113 )   PDF (222KB) ( 378 )   A new model of vertical vibration isolation system is presented in the paper. It is principally constructed by mounting an additional mass on the simplest passive vertical isolator, which can give rise to gravitational positive feedback. By theoretical analyzing and numerical calculating, we come to a conclusion that the resonant frequency is decreased in the new system, which agrees with the result of the experiment.

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

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STUDY OF IRON OVERLAYER ON SULPHUR PASSIVATED GaAs(100) BY SYNCHROTRON RADIATION PHOTOEMISSION Zhu Chuan-gang (祝传刚), Xu Peng-shou (徐彭寿), Xu Fa-qiang (徐法强), Lu Er-dong (陆尔东), Pan Hai-bin (潘海斌), Guo Hong-zhi (郭红志) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  751-756.  DOI: 10.1088/1004-423X/7/10/006 Abstract ( 1166 )   PDF (221KB) ( 392 )   We have studied the interface electronic structures and the chemical reaction of the Fe overlayer deposited on S-passivated GaAs(100). The chemical bond and electronic structure are different from Fe/GaAs, and the reaction between As and Fe is weakened by S atoms. This is beneficial to the magnetism in the interface. In the first stage of deposition, Fe clusters is form near S atoms due to the large electronegativity of S. The S atoms remain at the interface with Fe coverage. Magnetic ordering feature is found at a coverage higher than 0.6 nm. According to the large exchange splitting in valence band spectra, we suggest that Fe phase transition from bcc to fcc occurs with increasing coverage.

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GRAIN SIZE DEPENDENT MAGNETISM IN GRANULAR MANGANESE PEROVSKITE La0.82Sr0.18MnO3 Zhang Ning (张宁), Zhang Sheng (张胜), Xu Yin-lin (徐寅林), Ding Wei-ping (丁维平), Zhong Wei (钟伟), Du You-wei (都有为) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  757-763.  DOI: 10.1088/1004-423X/7/10/007 Abstract ( 1214 )   PDF (230KB) ( 530 )   La0.82Sr0.18MnO3 have been investigated. With grain growth, both an evident decrease of magnetization and the lattice distortions have been simultaneously observed. The phenomenon suggests a structure-coupled change of magnetism in the hole-doped manganese perovskite.

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LOW-FREQUENCY INTERNAL FRICTION STUDY FOR SrBi2Ta2O9 FERROELECTRIC CERAMICS Wang Zhi-yong (王志勇), Chen Ting-guo (陈廷国), Zhu Wei-min (朱为民), Fu Jian (傅剑), Yan Hai-xue (宴海学), Li Cheng-en (李承恩) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  764-772.  DOI: 10.1088/1004-423X/7/10/008 Abstract ( 1309 )   PDF (253KB) ( 450 )   Low-frequency internal friction (IF) of SrBi2Ta2O9(SBT) ceramics has been measured at temperatures ranging from 293 to 623 K. Two IF peaks, with their locations around 393 K (P1) and 569 K (P2) (f≈1.58 Hz), respectively, are observed. P1 is found to be associated with a relaxation process with activation energy of 0.97 eV and pre-exponential factor of 3.58×10-14 s. Peak shape analyses reveal that P1 can be well described by a broadened Debye peak with the width parameter $\beta$ from 2.70 to 2.92. The mechanism responsible for P1 is proposed to be relaxation of oxygen vacancies near domain walls(DWs). P2 is considered to arise from viscous motion of DWs since it shows characteristics of static hysteresis type. Comparisons for the IF behavior between SBT and Pb(Zr, Ti)O3(PZT) suggest that in SBT oxygen vacancies are much less localized near DWs than that in PZT. This result provides a possible explanation for the weak DW pinning due to oxygen vacancies in SBT.

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UPCONVERSION FLUORESCENCE DYNAMICS OF Tm3+ IONS IN LiYF4 CRYSTAL Chen Xue-yuan (陈学元), Luo Zun-du (罗遵度) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  773-783.  DOI: 10.1088/1004-423X/7/10/009 Abstract ( 1485 )   PDF (260KB) ( 530 )   According to Judd-Ofelt parameter calculation and energy transfer theory, the cross-relaxation process of the Tm3+ ions is investigated. A four-level system of coupled rate equations is established to study the fluorescence dynamics of Tm3+ in LiYF4 crystal. Attentions are focused on the upconversion luminescence 1G4→3H6 (483.0 nm) in Tm3+:LiYF4. The relationship between the avalanche properties (critical pump rate, fluorescence intensity and buildup time) originated by resonant excited state absorption and the doped Tm3+ concentration is discussed, and some useful conclusions are drawn.

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POSITRON ANNIHILATION STUDY OF THERMOELASTIC MARTENSITE STABILIZATION IN A THERMALLY CYCLED CuZnAl ALLOY--A DISCUSSION OF ORIGIN OF THERMOELASTIC MARTENSITE STABILIZATION Wang Jing-cheng (王景成), You Fu-qiang (尤富强), Shao Zi-chang (邵自昌), Qi Jin-lin (祁金林), Tang Xue-feng (汤学峰) Acta Physica Sinica (Overseas Edition), 1998, 7 (10):  784-788.  DOI: 10.1088/1004-423X/7/10/010 Abstract ( 1200 )   PDF (174KB) ( 426 )   The thermally cycled samples of Cu-23at%Zn-10at%Al have been studied by means of positron annihilation. It is shown that vacancies and their movement seem to be the leading factors resulting in thermoelastic martensite stabilization based on the fact that stabilization was no longer present and the great decrease of positron parameters after the samples in martensite were thermally cycled.