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1996年, 第5卷, 第3期　刊出日期：1996-03-20 上一期    下一期

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CONJUGATE POINTS ALONG NULL GEODESICS IN A CLASS OF SPACETIMES 邝志全, 梁灿彬, 吴月江 1996 (3):  161-169.  doi: 10.1088/1004-423X/5/3/001 摘要 ( 1435 )   PDF(223KB) ( 431 )   The existence and location of conjugate points along null geodesics in Taub's vacuum spacetime is investigated in detail. It is shown that every null geodesic η not confined in a t-z plane contains two pairs of segments (M,M) and (N, N) such that each point p in M(resp.N) has a unique conjugate point p along η that is located in M (resp. N) and vice versa, and what is more interesting, if p and p are conjugate points along η with p∈J+(p), then p∈I+(p). This presents a realistic example illustrating that there do exist null geodesics emanating from p that can get into I+(p) before meeting a point conjugate to p. All results are generalized to a class of spacetimes. 相关文章 | 计量指标

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EXTENDED SSH MODEL FOR C58B2 AND C58N2 徐强, 董锦明, 蒋杰, 邢定钰 1996 (3):  170-175.  doi: 10.1088/1004-423X/5/3/002 摘要 ( 1628 )   PDF(186KB) ( 372 )   The extended Su-Schrieffer-Heeger model is used to study the electronic energy levels and molecular structures for two kinds of isomers of C58X2(X=B, or N). In each case we obtain two sets of stable solutions. For C58X2 (1, 2), both sets of solutions are found to be reasonable, indicating two different phases. For C58X2(1, 60 ), only one set of solutions which satisfy the central inversion symmetry is physically reasonable. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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IONS CONFINEMENT IN ELECTRON BEAM ION TRAP 刘明海, 王善才, 胡希伟 1996 (3):  176-184.  doi: 10.1088/1004-423X/5/3/003 摘要 ( 1082 )   PDF(237KB) ( 522 )   This paper shows the evolution of density and temperature of multi-charged ions in an electron beam ion trap (EBIT). Three cases are studied: the continuous neutral gas injection, ion source injection, and evaporative cooling. The effects of the neutral gas density, axial potential, and the beam current density on the ions evolution are discussed. 相关文章 | 计量指标

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WHISPERING-GALLERY MODE STRUCTURE IN SEMICONDUCTOR MICRODISK LASERS AND CONTROL OF THE SPONTANEOUS EMISSION FACTOR 郭长志, 陈水莲 1996 (3):  185-194.  doi: 10.1088/1004-423X/5/3/004 摘要 ( 1434 )   PDF(286KB) ( 404 )   The mode density and cross-sectional area of whispering-gallery modes of various possible polarizations existing in a microdisk cavity structure have been investigated and compared in some detail. Their variations with the disk thickness and radius have been calculated and the behavior of the spontaneous emission factor controlled by the microdisk structure have been shown. It is found that for a given microdisk thickness, the spontaneous emission factor increases with decreasing microdisk radius, but decreases after passing a maximum value, This non-monotonic behavior has never been noted before by others. The variation of spontaneous emission factor with respect to microdisk thickness also exhibits similar behavior. For a microdisk laser emitting at 1.5 μm wavelength, the enhanced spontaneous emiasion factor can barely exceed 0.2. A device configuration for improving the coupling between the whispering-gallery mode and the active region, and for leading the laser beam out of this high-Q microcavity is proposad, and its feasibility in realizing a thresholdless laser is discussed. 相关文章 | 计量指标

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OPTICAL BISTABILITY IN A RING CAVITY WITH A PHOTOREFRACTIVE TWO-WAVE MIXER 洪艳华, 戴建华, 谢平, 张洪钧 1996 (3):  195-200.  doi: 10.1088/1004-423X/5/3/005 摘要 ( 1111 )   PDF(149KB) ( 361 )   We observed the phenomenon of optical bistability in a ring cavity with a photorefractive two-wave mixer. The experimental results are in agreement with those of theory. 相关文章 | 计量指标

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TRANSVERSE MODULATION OF BEAM PROFILES IN PUMP-PROBE CONFIGURATIONS WITH BaTiO3:Ce 谢平, 戴建华, 王鹏业, 张洪钧 1996 (3):  201-206.  doi: 10.1088/1004-423X/5/3/006 摘要 ( 1184 )   PDF(159KB) ( 415 )   Transverse spatial modulation of beam profiles for a probe beam counterpropagating to a pump beam in a 45°-cut BaTiO3:Ce crystal with an externally applied electric field is studied numerically studied. For the case that the direct ion of the external field makes an angle of 45° with the c-axis of the crystal, the probe beam, which propagates in the direction perpendicular to the external field and has a waist wider than that of the pump beam, can acquire deep spatial modulation. In contrast, the pump beam shows no spatial modulation but diffracts only. For the case the external field is directed opposite to the direction mentioned above, the probe beam shows much stronger spatial modulation as compared to the pump. 相关文章 | 计量指标

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SOFT-X-RAY PHOTOEMISSION STUDY OF Mn/GaP(100) INTERFACE 徐世红, 徐彭寿, 陆尔东, 余小江, 张新夷, 杨风源 1996 (3):  207-212.  doi: 10.1088/1004-423X/5/3/007 摘要 ( 1279 )   PDF(198KB) ( 378 )   The interface formation and electronic structures of the Mn/GaP(100) interface are studied with synchrotron radiation photoemission, At the early stage of Mn deposition, Mn covers the whole GAP(100) surface. With the increase of coverage, Ga atoms can be exchanged by Mn atoms and diffuse into the Mn overLaycr. However, P atoms remain always near the interracial region. A sigaificant difference of the electronic structures is observed between the ultra-thin and the thick Mn films. The explanations for this are given in the text. 相关文章 | 计量指标

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THIRD-HARMONIC COEFFICIENT IN A BILATERAL ROUGH GOLD FILM PERCOLATION SYSTEM 叶高翔, 张其瑞, 文自立, 焦正宽, 张宣嘉, 许宇庆 1996 (3):  213-218.  doi: 10.1088/1004-423X/5/3/008 摘要 ( 1358 )   PDF(173KB) ( 413 )   In this paper, the third-harmonic coefficient in a bilateral rough Au-film percolation system deposited on the self-affine substrates is studied. It is proved experimentally that both the critical current and the film resistivity an functions of the third-harmonic coefficient yield power law critical behaviors. However, compared with flat systems, the critical exponents are significantly changed. The discussion for the universality behavior in this special system is also presented. 相关文章 | 计量指标

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GROWTH MODE OF Cu-RICH PARTICLES ON LASER-ABLATED YBa2Cu3O7 THIN FILMS 杨晔, 刘军政, 李林, 周玉清, 周岳亮, 陈正豪, 吕惠宾, 崔大复, 杨国桢 1996 (3):  219-224.  doi: 10.1088/1004-423X/5/3/009 摘要 ( 1274 )   PDF(243KB) ( 447 )   The microstructure of the laser-ablated YBa2Cu3O7 (YBCO) thin film deposited on heated (100) SrTiO3 substrate was examined by transmission electron microscope. The par-ticles on the film mainly consist of CuO and few CuYO2. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height, A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure. 相关文章 | 计量指标

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PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS 聂家财, 陈烈, 杨涛, 郭丽萍, 吴培钧, 刘贵荣, 李林, 赵忠贤 1996 (3):  225-230.  doi: 10.1088/1004-423X/5/3/010 摘要 ( 1218 )   PDF(201KB) ( 359 )   The a-axis oriented YBa2Cu3Ox(YBCO) thin films could be grown on (100) SrTiO3(STO) substrates with STO buffer layers by dc and rf magnetron sputtering either by low-ering the deposition temperature, or by using a self-template technique. For the latter, the resistivity of the thin film at 290K along the substrate [001] direction is about four times larger than that in the [010] direction. The zero resistance temperatures Tc0 are 89 K in both directions. So high quality a-axis oriented YBCO thin films can be prepared by the self-template technique. Also the Tc0 increase monotonously with the reduction of the thickness of the YBCO seed layer. 相关文章 | 计量指标