Table of Content

20 March 1992, Volume 1 Issue 3 Previous Issue    Next Issue

GENERAL

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PLANE SYMMETRIC GENERAL SOLUTION TO EINSTEIN-MAXWELL EQUATIONS IN HIGHER DIMENSIONS LIANG CAN-BIN, SHANG YU-MING 1992, 1 (3):  161-166.  doi: 10.1088/1004-423X/1/3/001 Abstract ( 0 )   PDF (97KB) ([an error occurred while processing this directive])   The plane symmetric general solution to the Einstein-Maxwell equations in D =n+2 dimensions is presented. In addition to the n(n+1)/2 spacelike Killing vector fields characterizing the higher dimensional plane symmetry, there is also an extra Killing vector field in the solution, suggesting that the generalized Birkhoff theorem proved for 4-dimensional spacetimes might also be valid in higher dimensions.

ATOMIC AND MOLECULAR PHYSICS

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THE 82S1/2→62D EXCITATION TRANSFER OF RUBIDIUM ATOMS INDUCED BY COLLISIONS WITH GROUND-STATE RUBIDIUM AND HYDROGEN MOLECULES SUN XIAN-PING, HU ZHI-LIN, ZENG XI-ZHI, WANG QING-JI, ZHENG LE-MIN 1992, 1 (3):  167-172.  doi: 10.1088/1004-423X/1/3/002 Abstract ( 0 )   PDF (176KB) ([an error occurred while processing this directive])   The processes of excitation transfer from the 82S1/2 state to the 62D state of rubidium in Rb(82S1/2)-Rb(52S1/2) and Rb(82S1/2)-H2 collisions have been studied experimentally. During irradiating the Rb vapor, mixed with H2, by two light beams for selective stepwise excitation, the Rb 82S1/2→52P3/2 direct fluorescence and the Rb 62D3/2→52P1/2 sensitized fluorescence have been measured as a function of H2 gas pressure. The measurements yielded the cross-sections σ(82S1/2→62D) and σ*(82S1/2→62D) of Rb 82S1/2→62D excitation tranfer induced by collisions with 52S1/2 atom and H2 molecules respectively. The results are discussed in detail.

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STUDY OF OPTICAL PUMPING OF ALKALI ATOMIC BEAM IN STRONG MAGNETIC FIELDS MEI GANG-HUA, HUANG GUI-WEN, ZHU XI-WEN, ZHANG YUAN, LIU ZHI-YUAN, ZENG XIAO-YUN 1992, 1 (3):  173-182.  doi: 10.1088/1004-423X/1/3/003 Abstract ( 0 )   PDF (255KB) ([an error occurred while processing this directive])   Using rate equation formalism, we got an analytic expression describing the optical pumping of an alkali atomic beam in strong megnetic fields. By comparing with the traditional description in single velocity approximation, the influence of velocity distribution in a practical alkali atomic beam on the pumping effect was quantitatively discussed. It turned out that the rate equation treatment in velocity approximation might result in an error within twenty percent. Laser optical pumping of 7Li atomic beam in a strong magnetic field (0.15T) was experimentally studied, and the results are in agreement with the theory in which the velocity distribution is taken into account.

CLASSICAL AREAS OF PHENOMENOLOGY

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STUDIES ON THE DYNAMICS OF OPTICAL BISTABILITY SWITCHING IN THE INTERNAL FABRY-PEROT CAVITY WITH A CdSxSe1-x-DOPED GLASS CHANNEL WAVEGUIDE PENG WEN-JI, LI QING-XING, YU ZHEN-XIN, AN NING, XU MAI 1992, 1 (3):  183-190.  doi: 10.1088/1004-423X/1/3/004 Abstract ( 0 )   PDF (177KB) ([an error occurred while processing this directive])   We report the optical bistability in CdSxSe1-x-doped glass channel waveguide with rise and fall times of about 24 and 30ps, respectively, in bistable switching by means of fiber coupling input with a power of about 3mW. The third-order nonlinear susceptibility (x(3)) of CdSxSe1-x-doped glass is estimated experimentally to be 1.8×10-9 esu. The high speed switching and the value of x(1) show that the optical bistability is caused by an optical nonlinearity which can be attributed to the band-filling effect.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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FI-STM STUDY OF HYDROGEN ADSORPTION ON Si(100) SURFACE LU HUA, WANG XIANG-DONG, K.MOTAI, T.HASHIZUME, T.SAKURAI 1992, 1 (3):  191-201.  doi: 10.1088/1004-423X/1/3/005 Abstract ( 0 )   PDF (505KB) ([an error occurred while processing this directive])   Chemisorption of atomic hydrogen on the Si(100)2×1 surface has been investigated in detail by using a field ion-scanning tunneling microscope (FI-STM). The results showed that the adsorption geometry changed from the 2×1 monohydride phase to the 1×1 dihydride phase with increasing exposure of hydrogen. The data of desorption of the hydrogen-saturated Si surface showed that on annealing at 670K the surface becomes highly disordered: the 1×1 dihydride structure is eliminated and the 2×1 reconstructed monohydride is also hardly to identify. When the temperature rises to as high as 730 K, the surface is domi-nated by the 2×1 structure with missing dimer rows, and some adatom chains occur on the Si substrate ler-races. We attribute the formation of these atomic chains to an epitaxial growth of Si atoms which are formed by the dissociation of SiHx (x= 1, 2, 3 or 4) compounds on the Si surface.

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

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AB INITIO CALCULATIONS OF OPTICAL PHONON DEFORMATION POTENTIALS IN DIAMOND AND ZINC-BLENDE SEMICONDUCTORS WANG REN0-ZHI, KE SAN-HUANG, HUANG MEI-CHUN 1992, 1 (3):  202-210.  doi: 10.1088/1004-423X/1/3/006 Abstract ( 0 )   PDF (274KB) ([an error occurred while processing this directive])   Ab initio calculations of optical-phonon deformation potentials (ODP's), i.e., d0, d30, d10 (val) and d10 (con) for sixteen semiconductors were carried out systematically. The calculations are based on the LMTO-ASA band-structure method within the framework of the frozen-phonon approximation model, in which the displacement of empty sphere is considered to match its atomic sphere partners, We have compared the d0 values obtained by several different theoretical calculation methods and studied the main factors affecting them. It is pointed out that the two different models (rhombohedral strain model and frozen-phonon model) for calculations will lead to different results of d0.

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SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS LI YI-JIE, XIONG GUANG-CHENG, GAN ZI-ZHAO, REN CONG-XIN, CHEN GUO-LIANG, ZOU SHI-CHANG 1992, 1 (3):  211-218.  doi: 10.1088/1004-423X/1/3/007 Abstract ( 0 )   PDF (255KB) ([an error occurred while processing this directive])   High quality epitaxial YBa2Cu3O7-x thin films have been succcessfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO3, LaAlO3 and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a Jc (at 77 K, H=0) over 106A/cm2. It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by X-ray diffraction. Rutherford backscattering and channeling spectroscopy, X-ray double-crystal diffraction and transmission election microscopy. The experimental results demonstrated that the epitaxial YBa2Cu3O7-x films had excellent superconducting properties and quite perfect structure.

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POSITRON ANNIHILATION STUDY OF YBa2(Cu1-xSnx)3Oy SUPERCONDUCTORS CHEN ANG, ZHI YU, LI BIAO-RONG, ZHANG XU-LI, TANG CHAO-QUN, LI XIAO-HUA, WANG SHAO-JIE 1992, 1 (3):  219-223.  doi: 10.1088/1004-423X/1/3/008 Abstract ( 0 )   PDF (148KB) ([an error occurred while processing this directive])   The positron annihilation lifetime spectra and their temperature dependence for the YBa2Cu3Oy superconducting ceramics doped with Sn have been studied. The resutts of analyses indicate that the element Sn is substituted for Cu(1) sites, and this leads to the ordering of the oxygen atoms as well as the increase of local electronic density in the Cu(1)-O layer where Cu(1) is substituted by Sn.