中国物理B

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A THEORETICAL AND EXPERIMENTAL STUDY OF FREQUENCY REDSHIFT IN OPTICAL-FIELD-INDUCED FREEDERICKSZ TRANSITION IN A NEMATIC LIQUID CRYSTAL FILM

叶茂, 王鹏业, 戴建华, 张洪钧

1995 (5): 321-328. doi: 10.1088/1004-423X/4/5/001

摘要 ( 1154 )

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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

窦硕星, 王茂岗, 张家森, 叶佩弦, 吕新亮, 姜全忠, 陈焕矗

1995 (5): 329-336. doi: 10.1088/1004-423X/4/5/002

摘要 ( 1243 )

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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.

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SYMMETRIES OF THE ELECTROMAGNETIC FIELDS IN GENERAL RELATIVITY

1995 (5): 337-343. doi: 10.1088/1004-423X/4/5/003

摘要 ( 1056 )

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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.

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PROOF OF THE VALIDITY OF THE VIRIAL THEOREM IN THE EQUATION OF STATE BY THE THOMAS-FERMI-DIRAC MODEL

程开甲, 程漱玉

1995 (5): 344-349. doi: 10.1088/1004-423X/4/5/004

摘要 ( 1252 )

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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

傅思祖, 顾援, 吴江, 王世绩

1995 (5): 350-355. doi: 10.1088/1004-423X/4/5/005

摘要 ( 1164 )

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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.

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ELECTRON-INTERFACE PHONON SCATTERING IN ASYMMETRIC SEMICONDUCTOR QUANTUM WELL STRUCTURES

史俊杰

1995 (5): 356-364. doi: 10.1088/1004-423X/4/5/006

摘要 ( 1127 )

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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)

张兴元

1995 (5): 365-379. doi: 10.1088/1004-423X/4/5/007

摘要 ( 1149 )

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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.

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A STUDY OF THERMAL DESORPTION OF HELIUM FROM HIGH-PURE α-Ti AND HYDROGENATED Ti SAMPLES

芶成玲, 王佩璇, 姚玉琴, 方正知, 朱沛然

1995 (5): 380-388. doi: 10.1088/1004-423X/4/5/008

摘要 ( 757 )

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Helium ions have been implanted into highly pure α-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 α-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.

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