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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--1999, Vol.8, No.7
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CLASSICAL AREAS OF PHENOMENOLOGY

PHYSICAL CHARACTERISTICS OF ELECTROMAGNETIC LEVITATION PROCESSING

Wang Nan, Xie Wen-jun, Wei Bing-bo
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 503-513 doi: 10.1088/1004-423X/8/7/005
Full Text: [PDF 252 KB] (Downloads:942)
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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.

RADIATION OF DRESSED EXCITONS IN THE SEMICONDUCTOR MICROCAVITY

Liu Shi-an, Lin Shi-ming, Wang Qi-ming
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 514-520 doi: 10.1088/1004-423X/8/7/006
Full Text: [PDF 225 KB] (Downloads:320)
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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.

STUDY OF SPATIAL HOLE BURNING IN DISTRIBUTED PHASE-SHIFTED DISTRIBUTED FEEDBACK SEMICONDUCTOR LASERS

Shen Dan-xun, Gu Wan-yi, Xu Da-xiong
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 521-525 doi: 10.1088/1004-423X/8/7/007
Full Text: [PDF 199 KB] (Downloads:527)
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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.
ATOMIC AND MOLECULAR PHYSICS

RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTRA OF THE HALOGEN ATOMS

Chen Yang, Pei Lin-sen, Jin Jin, Ran Qin, Chen Cong-xiang, Yu Shu-qin, Ma Xing-xiao
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 490-495 doi: 10.1088/1004-423X/8/7/003
Full Text: [PDF 221 KB] (Downloads:298)
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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.

MOMENTUM CORRELATION OF ELECTRON-HYDROGEN IONIZATION

Zhang Sui-meng, Chen Zhang-jin
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 496-502 doi: 10.1088/1004-423X/8/7/004
Full Text: [PDF 228 KB] (Downloads:292)
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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.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

SELF-SIMILAR GLOBAL TEXTURES AND MEMBRANES—A NEW INTERPRETATION FOR THE COSMIC MATTER-STRUCTURE FORMATION

Tao Bi-xiu
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 481-484 doi: 10.1088/1004-423X/8/7/001
Full Text: [PDF 165 KB] (Downloads:283)
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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.

CROSSOVER FROM THERMAL HOPPING TO QUANTUM TUNNELING IN FERROMAGNETIC PARTICLE

Kou Su-peng, Liang Jiu-qing, Zhang Yun-bo, Wang Xiao-bing, Pu Fu-ke
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 485-489 doi: 10.1088/1004-423X/8/7/002
Full Text: [PDF 214 KB] (Downloads:348)
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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.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

APPROXIMATION ANALYTICAL SOLUTION FOR A CURRENT-CARRYING ION SHEATH AND ITS CHAOS CONTROL

Fang Jin-qing, Chen Guan-rong
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 526-532 doi: 10.1088/1004-423X/8/7/008
Full Text: [PDF 216 KB] (Downloads:395)
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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.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

EFFECT OF GRAIN-ALIGNMENT ON THE LEVITATION FORCE OF MELT-PROCESSED YBCO BULK SUPERCONDUCTORS

Yang Wan-min, Zhou Lian, Feng Yong, Zhang Ping-xiang, Wu Min-zhi, Wu Xiao-zu
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 533-538 doi: 10.1088/1004-423X/8/7/009
Full Text: [PDF 190 KB] (Downloads:402)
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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.

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

Wang Yuan-fei, Han Bao-shan
Acta Phys. Sin. (Overseas Edition), 1999, 8 (7): 539-544 doi: 10.1088/1004-423X/8/7/010
Full Text: [PDF 193 KB] (Downloads:262)
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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.
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