Table of contents

20 May 1995, Volume 4 Issue 5 Previous issue    Next issue

CLASSICAL AREAS OF PHENOMENOLOGY

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A THEORETICAL AND EXPERIMENTAL STUDY OF FREQUENCY REDSHIFT IN OPTICAL-FIELD-INDUCED FREEDERICKSZ TRANSITION IN A NEMATIC LIQUID CRYSTAL FILM YE MAO (叶茂), WANG PENG-YE (王鹏业), DAI JIAN-HUA (戴建华), ZHANG HONG-JUN (张洪钧) Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  321-328.  DOI: 10.1088/1004-423X/4/5/001 Abstract ( 1155 )   PDF (252KB) ( 436 )   The frequency redshift in the optical-field-induced Freedericksz transition in a nematic liquid crystal film is investigated, We derive a theoretical expression for the frequency shift, and then measure the temporal evolution of the frequency shift and the light-intensity de-pendence of the maximum frequency shift. The theory agrees with the measurements.

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SIMULATING STUDY ON INTERNAL SELF-PUMPED PHASE CONJUGATORS WITH EXTERNAL CONFIGURATIONS DOU SHUO-XING (窦硕星), WANG MAO-GANG (王茂岗), ZHANG JIA-SEN (张家森), YE PEI-XIAN (叶佩弦), Lü XIN-LIANG (吕新亮), JIANG QUAN-ZHONG (姜全忠), CHEN HUAN-CHU (陈焕矗) Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  329-336.  DOI: 10.1088/1004-423X/4/5/002 Abstract ( 1244 )   PDF (223KB) ( 360 )   A new method is proposed to study the properties of stimulated photorefractive backscat-tering and four-wave-mixing (SPB-FWM) and total-internal-reflection (TIR) self-pumped phase conjugators. The phase conjugators are simulated with external configurations using a KNSBN:Cu crystal, a plane mirror and a prism. As a result, the parameters such as beamwidth and intensity of the contra-directionally propagating pump beams for the FWM interactions in the crystal can be easily controlled. The dependence of self-pumped phase conjugation reflectivity and FWM coupling strength on these parameters of the pump beams have been studied.

GENERAL

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SYMMETRIES OF THE ELECTROMAGNETIC FIELDS IN GENERAL RELATIVITY ZAFAR AHSAN Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  337-343.  DOI: 10.1088/1004-423X/4/5/003 Abstract ( 1057 )   PDF (159KB) ( 416 )   Using the null tetrad approach of Newman and Penrose, the symmetries of the electro-magnetic fields are investigated. It is found that null electromagnetic fields admit Maxwell collineation, and the existence of Ricci collineation and motion is possible only under certain conditions on the spin-coefficients.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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PROOF OF THE VALIDITY OF THE VIRIAL THEOREM IN THE EQUATION OF STATE BY THE THOMAS-FERMI-DIRAC MODEL CHENG KAI-JIA (程开甲), CHENG SHU-YU (程漱玉) Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  344-349.  DOI: 10.1088/1004-423X/4/5/004 Abstract ( 1252 )   PDF (121KB) ( 454 )   The present paper is to demonstrate the validity of the virial theorem for electrons in the revised Thomas-Fermi-Dirac model, which has not yet received a rigorous proof. The theorem has actually a wider sense in application both in classical and quantum-mechanical dynamics.

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SHOCK COMPRESSIBILITIES OF Fe UP TO 0.8 TPa AND SiO2 UP TO 0.4 TPa FU SI-ZU (傅思祖), GU YUAN (顾援), WU JIANG (吴江), WANG SHI-JI (王世绩) Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  350-355.  DOI: 10.1088/1004-423X/4/5/005 Abstract ( 1165 )   PDF (163KB) ( 341 )   Using uniform illumination of high-power laser on targets and the principle of impedance-match, the shock wave velocities in the standard material and the test sample have been measured experimentally on "Shenguang-I" laser facility from high-quality luminant signals produced at the back surface of target, and the shock adiabats of Fe and SiO2 were obtained, respectively, in the pressure ranges of 0.35-0.82 and 0.21-0.41 TPa.

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

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ELECTRON-INTERFACE PHONON SCATTERING IN ASYMMETRIC SEMICONDUCTOR QUANTUM WELL STRUCTURES SHI JUN-JIE (史俊杰) Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  356-364.  DOI: 10.1088/1004-423X/4/5/006 Abstract ( 1127 )   PDF (239KB) ( 420 )   Electron-interface phonon scattering rates in asymmetric single quantum well and step quantum well structures are calculated by means of the interaction Fr?hlich-like Hamiltonian between an electron and interface optical phonons in a four-layer heterostructure given re-cently. The intrasubband and intersubband electron scattering rates are given as functions of quantum well width, step width and step height. We have found that the electron scattering depends strongly on the potential parameters and the usual selection rules for these tran-sitions are broken down in asymmetric heterostructures; the interface LO modes are more important than the interface TO modes for the electron-interface phonons scattering in het-erostructures; the intrasubband scattering rates are insensitive functions of step width and step height, and the intersubband scattering rates are complicated functions of step height and step width in step quantum wells. Moreover, we have also observed that the scattering rates for intrasubband and intersubband transitions have no obvious changes in the case that the first or second subband energy level crosses the step height in a step quantum well.

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DIELECTRIC RELAXATIONS IN FERROELECTRIC COPOLYMER VINYLIDENE FLUORIDE(65)/TRIFLUOROETHYLENE(35) ZHANG XING-YUAN (张兴元), TAKEO FURUKAWA Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  365-379.  DOI: 10.1088/1004-423X/4/5/007 Abstract ( 1149 )   PDF (438KB) ( 378 )   The molecular motion characteristics of ferroelectric copolymer vinylidene fluo-ride(65)/trifluoroethylene(35) have been investigated by means of dielectric relaxation. The frequency spectra of the copolymer consisting of low-frequency and high-frequency compo-nents are observed below room temperature. With the rise of crystallinity, the Curie point decreases while the dielectric constant increases in the region of ferroelectric-to-paraelectric phase transition. Based on the fitting results using one or two Cole-Cole functions, and cal-culating with the WLF equation and an Arrhenius formula, the glass transition temperature (= -28℃) and the activation energy of local relaxation (= 54.4 kJ·mol-1) of the copolymer are obtained. It is found that the distribution of relaxation time in the molten and the ferroelectric phases is located at a same line, which complies with the Arrhenius rule. This indicates that the elementary motions are of the same type for molecular motions provided by the high-temperature process and the low-temperature local mode process.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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A STUDY OF THERMAL DESORPTION OF HELIUM FROM HIGH-PURE $\alpha$-Ti AND HYDROGENATED Ti SAMPLES GOU CHENG-LING (芶成玲), WANG PEI-XUAN (王佩璇), YAO YU-QIN (姚玉琴), FANG ZHENG-ZHI (方正知), ZHU PEI-RAN (朱沛然) Acta Physica Sinica (Overseas Edition), 1995, 4 (5):  380-388.  DOI: 10.1088/1004-423X/4/5/008 Abstract ( 758 )   PDF (258KB) ( 309 )   Helium ions have been implanted into highly pure $\alpha$-Ti and hydrogenated Ti samples with energy of 140keV and at dose of 5.2×1017He·cm-2. The retained amount and depth pro-files of helium in the samples were determined by means of proton-enhanced-backscattering (PEBS) at room temperature. The changes of He peaks during isochronical annealing at 100, 200, 300℃,… were monitored in-situ by PEBS for groups of samples. The process of temperature ramping was not stopped until He peaks almost disappeared and hence the release curves were obtained. It was found that ～ 60% of helium was released at 200℃ for high-pure $\alpha$-Ti samples, whereas massive release occurred at 300℃ for the samples with H/Ti=0.9 and at 350℃ for the samples with H/Ti=0.2. The mechanism of He release and the effect of hydrogen were also discussed.