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1998年, 第7卷, 第10期　刊出日期：1998-10-20 上一期    下一期

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ENVELOPE SOLITON UNDER DISSIPATION IN A FLUID-FILLED ELASTIC TUBE 段文山, 赵存元, 吕克朴, 王本仁, 魏荣爵 1998 (10):  721-726.  doi: 10.1088/1004-423X/7/10/001 摘要 ( 1319 )   PDF(193KB) ( 475 )   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 Aτ+iBAξξ+iC|A|2A+DA=0 and the amplitude of envelope soliton will decrease as it propagates away. 相关文章 | 计量指标

GENERAL

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AN INTEGRAL EXPRESSION OF EXACT SOLUTION FOR HARMONIC OSCILLATOR WITH TIME-VARYING FREQUENCY 李立祥, 郭光灿 1998 (10):  727-731.  doi: 10.1088/1004-423X/7/10/002 摘要 ( 1178 )   PDF(182KB) ( 483 )   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. 相关文章 | 计量指标

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THE IMMISCIBLE DISPLACEMENT IN PERCOLATION CLUSTER 田巨平, 姚凯伦 1998 (10):  732-738.  doi: 10.1088/1004-423X/7/10/003 摘要 ( 1054 )   PDF(231KB) ( 331 )   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 →∞ 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. 相关文章 | 计量指标

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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SINE-GORDON MODEL WITH LOCAL SYMMETRIC POTENTIALS 叶飞, 许伯威 1998 (10):  739-743.  doi: 10.1088/1004-423X/7/10/004 摘要 ( 997 )   PDF(178KB) ( 366 )   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. 相关文章 | 计量指标

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PERFORMANCE OF VERTICAL VIBRATION ISOLATION SYSTEM WITH GRAVITATIONAL POSITIVE FEEDBACK 赵鹏飞, 张平华, 唐家祥, 罗俊 1998 (10):  744-750.  doi: 10.1088/1004-423X/7/10/005 摘要 ( 1096 )   PDF(222KB) ( 376 )   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. 相关文章 | 计量指标

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 祝传刚, 徐彭寿, 徐法强, 陆尔东, 潘海斌, 郭红志 1998 (10):  751-756.  doi: 10.1088/1004-423X/7/10/006 摘要 ( 1150 )   PDF(221KB) ( 387 )   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. 相关文章 | 计量指标

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GRAIN SIZE DEPENDENT MAGNETISM IN GRANULAR MANGANESE PEROVSKITE La0.82Sr0.18MnO3 张宁, 张胜, 徐寅林, 丁维平, 钟伟, 都有为 1998 (10):  757-763.  doi: 10.1088/1004-423X/7/10/007 摘要 ( 1195 )   PDF(230KB) ( 528 )   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. 相关文章 | 计量指标

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LOW-FREQUENCY INTERNAL FRICTION STUDY FOR SrBi2Ta2O9 FERROELECTRIC CERAMICS 王志勇, 陈廷国, 朱为民, 傅剑, 宴海学, 李承恩 1998 (10):  764-772.  doi: 10.1088/1004-423X/7/10/008 摘要 ( 1297 )   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 β 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. 相关文章 | 计量指标

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UPCONVERSION FLUORESCENCE DYNAMICS OF Tm3+ IONS IN LiYF4 CRYSTAL 陈学元, 罗遵度 1998 (10):  773-783.  doi: 10.1088/1004-423X/7/10/009 摘要 ( 1466 )   PDF(260KB) ( 524 )   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. 相关文章 | 计量指标

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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 王景成, 尤富强, 邵自昌, 祁金林, 汤学峰 1998 (10):  784-788.  doi: 10.1088/1004-423X/7/10/010 摘要 ( 1184 )   PDF(174KB) ( 423 )   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. 相关文章 | 计量指标