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1998年, 第7卷, 第11期　刊出日期：1998-11-20 上一期    下一期

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INFLUENCE OF INTERFACE KINETICS ON THE RELAXATION BEHAVIOR IN SOLUTION SYSTEM FOR CRYSTAL GROWTH UNDER MICROGRAVITY 朱振和, 葛培文, 许政一, 霍崇儒 1998 (11):  801-809.  doi: 10.1088/1004-423X/7/11/001 摘要 ( 1271 )   PDF(234KB) ( 374 )   The influence of the interface kinetics at the growth face of a crystal and at the surface of material of solute source on the relaxation behavior in a solution system for crystal growth under microgravity is studied. Because the variation of the solution density caused by the solute concentration change can be omitted and only that caused by the temperature change is taken into account, the interface kinetics does not influence the relaxation behaviors of the fluid velocity and the temperature distribution index Sθ (see text). The relaxations of the concentration distribution index Sφ (see text) and dimensionless average growth rate of crystal \bar{V}cg are calculated under the square pulsed fluctuations of the gravity level or the temperature at the growth face of crystal. Introduction of the interface kinetics makes the value of Sφ enlarged and the perturbation peak of the Sφ-τ curve caused by the gravity level or temperature fluctuation lowered. While the perturbation peak and the valley of the \bar{V}cg-τ curve caused by the negatively and positively pulsed temperature fluctuation, respectively, is lowered and shallowed by the interface kinetics. 相关文章 | 计量指标

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ROOM TEMPERATURE LIGHT-THERMO-DETECTOR MADE OF HIGH-Tc SUPERCONDUCTOR 张鹏翔, 李国桢, 张燕, 文小明, H. U. Habermeier 1998 (11):  810-816.  doi: 10.1088/1004-423X/7/11/002 摘要 ( 1041 )   PDF(216KB) ( 587 )   Based on the anisotropic Seebeck tensor coefficients, a light-thermo-radiation detector made of high-Tc superconductor (YBa2Cu3O7-δ) was fabricated, which can function at room temperature. The induced voltaic signals at various modulation frequencies for radiation from He-Ne laser and from a 500 K black body were measured. The noise ratio for detecting He-Ne laser radiation and the D* for black body were evaluated. Compared with bolometer made of high-Tc superconductor which functions at liquid nitrogen, and with pyroelectric detector, it was found that the advantages of this new device are that the device can work at room temperature with very low noise and very fast response. Although having a lower D* value than that of bolometer for the present device construction, we point out the possibility and the direction for improving the D* value, hence the promising prospect of this kind of device. 相关文章 | 计量指标

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ENERGETIC ABOVE THRESHOLD IONIZATION SPECTRA OF HELIUM-ATOMS 陈宝振 1998 (11):  817-822.  doi: 10.1088/1004-423X/7/11/003 摘要 ( 1100 )   PDF(200KB) ( 399 )   A new analytic model for the energetic above threshold ionization spectra of He is proposed. The experimental spectra by Mohideen et al. can be accurately described. The serious intensity unconsistency, which appears in the previous calculation, is actually reduced by the present calculation. 相关文章 | 计量指标

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BEHAVIOR OF PLASMA FORMED IN A PAGODA-SHAPED RADIO FREQUENCY PLASMA SOURCE 姚鑫兹, 江德仪, 刘训春, 叶甜春 1998 (11):  823-831.  doi: 10.1088/1004-423X/7/11/004 摘要 ( 1201 )   PDF(239KB) ( 448 )   A large volume, high density, and pagoda-shaped radio frequency (rf) plasma source has been developed for use in large scale plasma processing. The inductively coupled plasma (ICP) is created by a pagoda-shaped 13.65 MHz antenna to improve the plasma uniformity on substrate. Plasma densities and electron temperatures are measured by using a Langmuir probe and their radial and axial profiles are attained. Electron density of >1×1011 cm-3 on the substrate and uniform to ≦±1.6% over 16 cm diameter can be produced at argon pressure of 6.65×10-1 Pa and input rf power of 1 kW. ICP etching photoresist in O2 plasma has been tested and the etching uniformity consists with that of the plasma density on the substrate. A large scale etched sample with the uniformity to ≦±1.1% over 10 cm diameter or to ≦±2.2% over 13 cm diameter has been obtained. 相关文章 | 计量指标

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STRUCTURAL PHASE TRANSITION IN BISMUTH HIGH-Tc SUPERCONDUCTING MATERIALS UNDER SYMMETRY OF D174h(I4/mmm) 潘国强 1998 (11):  832-840.  doi: 10.1088/1004-423X/7/11/005 摘要 ( 1250 )   PDF(253KB) ( 334 )   By applying the Landau's second-order phase transition theory, the symmetry changes due to the continuous phase transition from the phase of D174h symmetry were studied. The possible low symmetry phases were obtained by minimizing the thermodynamic potential expanded in the order parameters up to fourth order. Some related experimental results were discussed. 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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LATTICE DYNAMICS OF WURTZITE SEMICONDUCTORS GaN AND AlN 韦广红, 资剑, 张开明, 谢希德 1998 (11):  841-850.  doi: 10.1088/1004-423X/7/11/006 摘要 ( 1474 )   PDF(260KB) ( 1187 )   The lattice dynamics of wurtzite GaN and AlN is studied within the framework of a rigid-ion model. Short-range interactions up to the third nearest neighbors are described by using a valence-force-field potential and the long-range Coulomb interactions between ions are calculated via an Ewald summation. Phonon dispersion curves, density of states and specific heats are presented. 相关文章 | 计量指标

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A DISCRETE VARIATIONAL METHOD STUDY ON THE ELECTRONIC STRUCTURES OF CaMnO3 AND LaMnO3 杨中芹, 孙强, 叶令, 谢希德 1998 (11):  851-863.  doi: 10.1088/1004-423X/7/11/007 摘要 ( 1480 )   PDF(289KB) ( 639 )   The electronic structures of the perovskite oxides, LaMnO3 and CaMnO3, with various magnetic structures are studied using the first-principles discrete variational (DV) cluster method based on ab initio local-spin-density approximation (LSDA). The ground states of different magnetic phases (including ferromagnetic (FM), A-type antiferromagnetic (A-AFM), and G-type antiferromagnetic (G-AFM)) have been described in this work. The cubic CaMnO3 with observed G-AFM magnetic order is found to have a 0.1 eV calculated gap. Both FM CaMnO3 and LaMnO3 have "half-metallic" character, which is in agreement with other works. LaMnO3 with both A-type and G-type antiferromagnetic order have metallic band structures. Part of Jahn-Teller (JT) distortion (Q2 type) has been taken into consideration for A-AFM LaMnO3. Under Q2 type JT distortion, the occupied and unoccupied states of O 2p and Mn 3d states move farther away from the Fermi energy. It is also found that the distortion can further stabilize the structure. The density of states and the binding energy of the distorted A-AFM LaMnO3 are given in this paper. 相关文章 | 计量指标

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

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REPLICA SOLUTION TO QUANTUM INFINITE RANGE HEISENBERG MODEL 商育民, 姚凯伦 1998 (11):  864-869.  doi: 10.1088/1004-423X/7/11/008 摘要 ( 1165 )   PDF(190KB) ( 379 )   By using replica method and Matsubara imaginary-time functional-integral technique, the quantum infinite range Heisenberg model is solved. The solution shows that the quantum infinite range Heisenberg model also has phase transition. 相关文章 | 计量指标