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1993年, 第2卷, 第10期　刊出日期：1993-10-20 上一期    下一期

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EFFECTS OF BOOTSTRAP CURRENT ON ENERGY CONFINEMENT OF TOKAMAK PLASMAS 袁鹰, 高庆第, 邱孝明, 牟宗泽 1993 (10):  721-730.  doi: 10.1088/1004-423X/2/10/001 摘要 ( 1247 )   PDF(215KB) ( 517 )   Based on the principle of profile consistency and ηi-mode induced anomalous transport model, the enery confinement in tokamak plasmas is studied with inclusion of the bootstrap curreut in which the poloidal magnetic field is consistently deter-mined. The results show that bootstrap current has a significant effect on plasma confinement. If the bootstrap current is (15-30)% of the total current, global energy confinement time may increase by (20-45)%, and the maximum of related energy store is almost as much as twice the value without bootstrap current. Variation of the energy confinement time with the plasma parameters is of similar trend with Kaye-Goldston scaling. In addition, it can be seen that the radius of q=l surface decreases with bootstrap current, which may be one of the possible mechanisms for some experimental results where sawtooth oscillation disappears because of auxiliary heating. 相关文章 | 计量指标

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ATOMIC SHORT-RANGE ORDER OF AMORPHOUS Ta-Cu ALLOYS PREPARED BY MECHANICAL ALLOYING 柳林, 董远达, 何怡贞 1993 (10):  731-736.  doi: 10.1088/1004-423X/2/10/002 摘要 ( 1268 )   PDF(133KB) ( 395 )   In the present work, the atomic short-range ordering structure of the amorphous Ta-Cu alloys formed by mechanical alloying was investigated through radial distribution function (RDF) analysis. The results suggest that the elemental powders of Ta and Cu were well mixed by mechanical alloying at atomic level. The regions of short-range order (rs) increase with Cu concentration in Ta-Cu alloys, This means that the short-range ordering becomes stronger in those alloys with higher Cu content. The coordination number was estimated to be 12-13 from the area under the first maximum of the RDF (r) curves for all the Ta-Cu amorphous alloys. This result indicates that the amorphous alloys formed by mechanical alloying are also of topologically dense-packing structure. 相关文章 | 计量指标

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ABNORMAL ENERGY DEPENDENCE OF AXIAL MINIMUM CHANNELING YIELDS IN GexSi1-x/Si(100) STRAINED 黄孟兵, 赵国庆, 周筑颖, 汤家镛, 杨福家 1993 (10):  737-744.  doi: 10.1088/1004-423X/2/10/003 摘要 ( 1382 )   PDF(208KB) ( 393 )   An energy dependence of the axial minimum channeling yield in GexSi1-x/Si(100) Strained-layer superlattice is observed in the energy range of impinging He+ ione from 1.2 to 3.0 MeV. For [100] axial channeling, the measurements ere in agreement with what have been known in a single crystal. However, for [110] axial channeling, it is found that the minimum channeling yields increase markedly with the increase of He+ ion energy, which is contrary to the general channeling behaviors in a single crystal. A tentative model is suggested to explain this aberrance. 相关文章 | 计量指标

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A STUDY ON ABSORPTION OF Na ATOMS ON Si(100) 2×1 SURFACES WITH DV-Xα METHOD 徐世红, 徐彭寿, 李嘉, 麻茂生, 张裕恒, 许振嘉 1993 (10):  745-753.  doi: 10.1088/1004-423X/2/10/004 摘要 ( 1112 )   PDF(231KB) ( 392 )   The Na absorption on Si(100) 2×1 surface is studied with quantum chemistry molecular cluster method. The calculated results show that the most favourable absorption site of Na is the cave site and the charge transfer of Na atom to Si is large when the Na coverage is smaller than 0.5 monolayer (ML). A Na chain is formed along the cave sites at the 0.5 ML Na coverage, the charge transfer then becomes small. The calculated density of states show that the Na atoms are metallic along the chain. At 1 ML coverage, the Na atoms occupy both the cave and pedestal sites and form a double-layer. There is a charge transfer of 0.5e from each Na atom to the Si surface. The calculated surface energy shows that the saturation absorption of Na on Si surface is 1 ML. 相关文章 | 计量指标

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THE SCREENING EFFECT OF PHONON MODES IN HIGH-Tc OXIDE SUPERCONDUCTOR 叶红娟, 黄叶肖, 傅柔励, 陆晓峰, 史国良, 蔡培新, 顾为芳, 冉中原, 刘竞青, 赵忠贤, 杨秉川, 阎少林 1993 (10):  754-763.  doi: 10.1088/1004-423X/2/10/005 摘要 ( 1354 )   PDF(317KB) ( 466 )   This paper presents three different kinds of infrared (IR) spectra of oxide materials. The first one is the IR reflection spectra of Ti2Ba2Ca2Cu3O10 superconducting film at the incident angles 7°, 12° and 30°. The second one is the IR spectra of nonsuperconducting ceramic materials YBa2Cu3O6 and PrBa2Cu3O7. The third one is the IR spectra of superconductor YBa2Cu3O7-δ and of its film with the c-axis perpendicular to the film plane, as well as the changes in the spectra of these materials after annealing at different temperatures. It is found that in the spectra of high-Tc oxide superconductor, only the phonon modes along c-axis can be observed while the modes in a-b plane are absent. But in the spectra of nonsuperconductors the modes in a-b plane can be observed, particularly in the absorption spectra of the semiconductor YBa2Cu3O6, all eleven allowed IR active modes have been detected. We suggest that the above experimental phenomena may result from the fact that the phonon modes vibrating in the a-b plane of the high-Tc oxide superconducting materials are almost screened by the free carriers which can move only in a-b plane. 相关文章 | 计量指标

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MEASUREMENT OF ANISOTROPIC ACTIVATION ENERGIES IN HIGH-Tc SUPERCONDUCTORS 范宏昌, 张贻瞳, 金新, 姚希贤 1993 (10):  764-770.  doi: 10.1088/1004-423X/2/10/006 摘要 ( 1367 )   PDF(198KB) ( 450 )   For single crystalline and melt-textured samples there exist several different activation energies for fluxoid creep, which are related to various vortex orientations and hopping directions. We discuss how to obtain these anisotropic activation energies from magnetic relaxation data and present measured results of a melt-textured YBCO sample. 相关文章 | 计量指标

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BLUE-GREEN UP-CONVERSION LUMINESCENCE OF NONCHYSTALLINE HoP5O14 INDUCED BY PULSE DCM DYE LASER 陈晓波, 张光寅, 王虹, 刘言滨, 陈金铠, 商美茹, 李江卫 1993 (10):  771-775.  doi: 10.1088/1004-423X/2/10/007 摘要 ( 1381 )   PDF(113KB) ( 432 )   This paper reports the up-conversion luminescence phenomenon in blue-green wave-range of noncrystalline HoP5O14 induced by pulse DCM dye laser and gives some simple analyses. 相关文章 | 计量指标

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PHOTOLUMINESCENCE PROPERTIES OF NANO-SIZE CRYSTALLINE SILICON FILMS 唐文国, 龚涛, 李自元, 刘湘娜, 何宇亮 1993 (10):  776-781.  doi: 10.1088/1004-423X/2/10/008 摘要 ( 1268 )   PDF(170KB) ( 384 )   Photoluminescence (PL) at low temperature is reported for nc-Si:H films grown by PECVD. A characteristic luminescence peak was observed in the wavelength range of 1.1-1.2μm. The temperature dependence of PL has been studied in the temperature range of 4.2-180 K. The PL mechanism of nc-Si:H films is discussed. The emission peak at 1.1-1.2 μm is attributed to the interface atoms between grains, and the emission peak around 0.9μm is due to a little amount of amorphous component. 相关文章 | 计量指标

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SCALING LAW FOR CBr4-C2Cl6 LAMELLAR EUTECTIC IN DIRECTIONAL SOLIDIFICATION 刘俊明, 刘治国, 吴状春 1993 (10):  782-790.  doi: 10.1088/1004-423X/2/10/009 摘要 ( 1022 )   PDF(218KB) ( 331 )   A coupling equation of directional solidification of CBr4(α)-C2Cl6(β) eutectic is solved numerically. Profiles and profile bifurcation of the solidifying interface as functions of the interlamellar spacing are studied in detail. It is believed that the critical bifurcating point of the solidifying interface of each lamella coincides with its marginally stable position and hence, a new scaling law is derived. Existence of the band of spacing selection is also studied. For a given solidifying rate, the critical bifurcating point of β/liquid interface is the upper limit of this band, and its lower limit corresponds to the critical bifurcating point of α/liquid interface. Our analyses interpret the latest relevant experimental data reasonably. 相关文章 | 计量指标