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1999年, 第8卷, 第7期　刊出日期：1999-07-15 上一期    下一期

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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SELF-SIMILAR GLOBAL TEXTURES AND MEMBRANES—A NEW INTERPRETATION FOR THE COSMIC MATTER-STRUCTURE FORMATION 陶必修 1999 (7):  481-484.  doi: 10.1088/1004-423X/8/7/001 摘要 ( 1106 )   PDF(165KB) ( 348 )   The existence and evolution of spherical membrane configurations in spherical-symmetric and self-similar spacetimes are studied, and a solution for the dynamics of membranes is obtained. A new interpretation for the origin and evo lution of the cosmic matter-structures is acquired. It agrees well with the survey of astronomy. 相关文章 | 计量指标

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CROSSOVER FROM THERMAL HOPPING TO QUANTUM TUNNELING IN FERROMAGNETIC PARTICLE 寇谡鹏, 梁九卿, 张云波, 王小兵, 蒲富恪 1999 (7):  485-489.  doi: 10.1088/1004-423X/8/7/002 摘要 ( 1088 )   PDF(214KB) ( 462 )   The crossover from thermal hopping to quantum tunneling is studied. We show that the decay rate Γ with dissipation can accurately be determined near the crossover temperature. Besides considering the Wentzel-Kramers-Brillo uin exponent, we also calculate contribution of the fluctuation modes around the saddle point and give an extended account of a previous study of crossover region. We deal with two dangerous fluctuation modes whose contribution cannot be calculated by the steepest descent method and show that higher order couplings between the two dangerous modes need to be taken into consideration. 相关文章 | 计量指标

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RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTRA OF THE HALOGEN ATOMS 陈旸, 裴林森, 金瑾, 冉琴, 陈从香, 俞书勤, 马兴孝 1999 (7):  490-495.  doi: 10.1088/1004-423X/8/7/003 摘要 ( 1256 )   PDF(221KB) ( 410 )   The resonance-enhanced multiphoton ionization (REMPI) spectra of atomic chlorine and bromine in the range of 230-245 nm and 250-285 nm were obtained by using REMPI and time of flight (TOF) techniques. There are twenty-six lines for Cl and twenty-three for Br in the spectra, among which five transitions of Cl and four of Br are observed for the first time. These lines are due to transitions from the Cl(3p 2P03/2, 2P01/2) and Br(4p2P03/2, 2P01/2) states to upper states induced by two-photon excitation. It is found that the Stark shift of different excited states are almost the same, and they are independent of the S, L, and J quantum numbers of the excited state. 相关文章 | 计量指标

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MOMENTUM CORRELATION OF ELECTRON-HYDROGEN IONIZATION 张穗萌, 陈长进 1999 (7):  496-502.  doi: 10.1088/1004-423X/8/7/004 摘要 ( 1034 )   PDF(228KB) ( 355 )   Following the work of Berakdar, the momentum correlation in the three-body Coulomb continuum problem is considered by the introduction of effective Sommerfeld parameters for both symmetric and asymmetric geometry. The triple differential cross sections for electron impact ionization of atomic hydrogen at incident energies of 54.4 and 150 eV in asymmetric geometry are calculated. Results are compared with the related measurements and the only existing theoretical results of the convergent close-coupling method. They are in good agreement with experiment, though some small quantitative discrepancies remain. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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PHYSICAL CHARACTERISTICS OF ELECTROMAGNETIC LEVITATION PROCESSING 王楠, 解文军, 魏炳波 1999 (7):  503-513.  doi: 10.1088/1004-423X/8/7/005 摘要 ( 1218 )   PDF(252KB) ( 1219 )   Electromagnetic levitation has developed from a pure physical phenomenon into a practical containerless processing technique in the fields of both applied physics and materials science. In order to obtain a better understanding of this processing technique, two typical levitation coils were designed and the physical characteristics in levitation droplets suspended in these two coils, such as electromangetic field, levitation force field, total levitation force, and power absorption, were analyzed numerically and calculated in this paper. It was found that the eddy current density, together with the magnetic flux density and levitation force density, increases rapidly with radius as it approaches sample surface. The maximum levitation force produced by coil A is larger than that of coil B, whereas the levitated sample can obtain less power absorption at the equilibrium position in the former coil than that in the latter one. Moreover, the calculated results also demonstrated that the levitation ability decreases as the atomic number increases. The larger the material's electrical resistivity, the easier the samples can obtain more power absorption. 相关文章 | 计量指标

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RADIATION OF DRESSED EXCITONS IN THE SEMICONDUCTOR MICROCAVITY 刘世安, 林世鸣, 王启明 1999 (7):  514-520.  doi: 10.1088/1004-423X/8/7/006 摘要 ( 1352 )   PDF(225KB) ( 391 )   In this paper, we introduced the dressed exciton model of the semiconductor micro-cavity device. In the semiconductor micro cavity of vertical-cavity surface-emission device, the excitons first coupled with the cavity through an intra-electromagnetic field and formed the dressed excitons. Then these dressed excitons decayed into the vacuum cavity optical mode, as a multi-particle process. Through the quantum electrodynamics method, the dipole emission density and system energy decayed equation were obtained. And it was predicted that the excitons decay into a very narrow mode when the exciton-cavity coupling becomes strong enough. 相关文章 | 计量指标

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STUDY OF SPATIAL HOLE BURNING IN DISTRIBUTED PHASE-SHIFTED DISTRIBUTED FEEDBACK SEMICONDUCTOR LASERS 沈丹勋, 顾畹仪, 徐大雄 1999 (7):  521-525.  doi: 10.1088/1004-423X/8/7/007 摘要 ( 1302 )   PDF(199KB) ( 672 )   A new algorithm based on transfer matrix method is given to analyse a new distributed feedback (DFB) structure—the distributed phase- shifted (DPS) DFB laser. In the small signal analysis, a new model is proposed with this algorithm. Considering different structures of DFB laser diode, we define a spatial-hole-burning (SHB) factor to measure the SHB effect. Compared with the λ/4 phase-shifted DFB and 3 phase-shifted DFB, the DPS-DFB structure shows a superior characteristics both in static and dynamic behavior. 相关文章 | 计量指标

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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APPROXIMATION ANALYTICAL SOLUTION FOR A CURRENT-CARRYING ION SHEATH AND ITS CHAOS CONTROL 方锦清, 陈关荣 1999 (7):  526-532.  doi: 10.1088/1004-423X/8/7/008 摘要 ( 1274 )   PDF(216KB) ( 476 )   A higher-order approximation analytical solution for a current-carrying ion sheath is automatically derived in computer by decomposition method. Chaos behaviors in the system driven by an external periodic oscillation are controlled using feedback control strategy. Its effectiveness is verified by numerical simulations. 相关文章 | 计量指标

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EFFECT OF GRAIN-ALIGNMENT ON THE LEVITATION FORCE OF MELT-PROCESSED YBCO BULK SUPERCONDUCTORS 杨万民, 周廉, 冯勇, 张平祥, 吴民智, 吴晓祖 1999 (7):  533-538.  doi: 10.1088/1004-423X/8/7/009 摘要 ( 1197 )   PDF(190KB) ( 491 )   Single-domain YBCO bulk superconductors have been fabricated by Top Seeded Melt Slow Cooling Growth(TSSCG) process. Two typical YBCO cylinder samples with differential grain-alignment were selected for the investigation of the relationship between the grain-alignment and the levitation force under the same testing condition at liquid nitrogen temperature. It is found that the levitation force values is much different for the two samples, the levitation force of the sample with H∥c-axis is more than two times higher than that of the samples with H⊥c-axis. So it is necessary to take account of this anisotropy in practical applications. The relationship between a magnet and a superconductor can be well described with a double exponential function. All the results are discussed in details. 相关文章 | 计量指标

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ANNIHILATION OF VERTICAL-BLOCH-LINE CHAINS IN THE WALLS OF THE SECOND KIND OF DUMBBELL DOMAINS SUBJECTED TO JOINT STATIC BIAS FIELD AND IN-PLANE FIELD 王远飞, 韩宝善 1999 (7):  539-544.  doi: 10.1088/1004-423X/8/7/010 摘要 ( 1214 )   PDF(193KB) ( 340 )   Experiments were statistically carried out on the behavior of vertical-Bloch-line(VBL) chains in the walls of the second kind of dumbbell domains (IIDs) is garnet bubble films subjected to joint action of static bias field Hb and in-plane field Hip. The curves of the four critical in-plane fields, (Hip)IID-ID (Hip)IID-OHB (Hip)IID-SB and H'ip vs Hb were measured and explained. In particular, in terms of two series of IID photos, a new experimental manifestation of the unknown "number effect" of VBL chains was found. 相关文章 | 计量指标

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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STRUCTURE AND MORPHOLOGY OF CARBON NANOTUBES GROWN ON ZEOLITE-SUPPORTED CATALYSTS BY CHEMICAL VAPOR DEPOSITION 孙连峰, 毛健民, 常保和, 潘正伟, 王刚, 周维亚 1999 (7):  545-550.  doi: 10.1088/1004-423X/8/7/011 摘要 ( 926 )   PDF(191KB) ( 546 )   The zeolite-supported catalysts were prepared in nickel and cobalt nitrate aqueous solutions by ion exchange method. After reducing these substrates by hydrogen, we grew carbon nanotubes on them by chemical vapor deposition under different conditions. The results reveal that nickel/zeolite, cobalt/zeolite and nickel+cobalt/zeolite have different optimal conditions. When nickel+cobalt/zeolite was used as the catalyst, we can get straight carbon nanotubes. The Raman spectrum of the straight nanotubes shows they have fewer defects. We propose a growth mechanism for the growth of these nanotubes. 相关文章 | 计量指标