Chin. Phys. B
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Chin. Phys. B  
  Chin. Phys. B--1996, Vol.5, No.9
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GENERAL

ON A SUFFICIENT CONDITION FOR THE METRIC COEFFICIENTS TO BE CONFORMALLY TIME-INDEPENDENT

KUANG ZHI-QUAN, LIANG CAN-BIN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 641-645 doi: 10.1088/1004-423X/5/9/001
Full Text: [PDF 123 KB] (Downloads:250)
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The statement in Rindler's book "Essential Relativity" [(Springer-Verlag, New York, 1977), p. 119] claiming that "the metric coefficients are time-independent if light signals tracing out the same path always take the same coordinate time" has two problems, the first one has been pointed out by us in a recent paper "relation between choosing ‘good' coordinates and the behavior of light signals" [Acta Physica Sinica (Overseas Edition), 3(1994), 881], while the second is the main focus of the present article.

EXACT RESULTS FOR A SYMMETRIC 27-VERTEX MODEL

MI XIANG-DONG, YANG ZHAN-RU
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 646-653 doi: 10.1088/1004-423X/5/9/002
Full Text: [PDF 193 KB] (Downloads:264)
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Wu study a symmetric 3-state 27-vertex model and summarize three ways con-tributing to obtaining information of a higher-spin (more-vertex) model in terms of lower-spin (less-vertex) models. We find that this model is equivalent to a symmet-ric 2-state 8-vertex model or an arbitrary 3-state spin models on Kagome lattice in different eases. And 21 exact critical lines and a multicritical point (add something that I cannot recognize) are obtained in ten-dimensional weight space.
CLASSICAL AREAS OF PHENOMENOLOGY

RELATIONSHIP BETWEEN THE SPONTANEOUS AND THE STIMULATED RADIATIONS IN A NOVEL WIGGLER FREE-ELECTRON LASER

ZHU JIA-QING
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 654-661 doi: 10.1088/1004-423X/5/9/003
Full Text: [PDF 184 KB] (Downloads:270)
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The spontaneous and the stimulated radiations, as well as the relationship between them, are calculated for an electron moving in the wiggler with the independent magnetostatic-field on the axial (z) coordinates. It is shown that the Madey's law is still valid in the novel wiggler case. The small signal gain of free-clectron laser is calculated in a novel wiggler.

RELAXATION DYNAMICS OF PHOTOINDUCED EXCITON BLEACHING IN POLYMERS

WANG HUI, LAN WEN-GUANG, LIN WEI-ZHU, MO DANG
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 662-669 doi: 10.1088/1004-423X/5/9/004
Full Text: [PDF 228 KB] (Downloads:349)
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Presented in this paper are systematic studies of photoiuduced exciton bleaching dynamics in the polymers with nondegenerate ground state, such as polydiacetylene, polythiophene and polyaniline. From a three-level model, the photoexcitation and relaxation of the exciton bleaching in the polymers are simulated. The results show that the exciton bleaching decay is composed of two components, the fast component and the slow component. For the fast component, the speed of exciton bleaching decay depends on the way in which the excitons relax. When the relaxation of the exciton to the ground state is dominant, the polymers exhibit an ultrafast initial bleaching relaxation; when the relaxation of the exciton to the self-trapped exciton state is dominant, the polymers exhibit a slower initial bleaching relaxation than that in the former case, For the slow component, the exciton bleaching decay is due to the relaxation of the self-trapped excitons to the ground state. Using femtosecond time-resolved pump-probe technology, we measured the relaxation dynamics of the photoinduced exciton bleaching in the emeraldine base form of polyaniline. Fitting the experimental data to the theoretical model indicates that the fast component arises from the relaxation of excitons to the ground state (~100fs) and the slow component arises from the relaxation of self-trapped excitons to the ground state (~30 ps).

TWO-WAVE COUPLING IN PHOTOREFRACTIVE TRANSITION METAL DOPED POTASSIUM SODIUM BARIUM STRONTIUM NIOBATE CRYSTALS

ZHU DE-RUI, ZHANG YUE-LI, MO DANG
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 670-676 doi: 10.1088/1004-423X/5/9/005
Full Text: [PDF 214 KB] (Downloads:274)
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Large values of the exponential gain coefficient are obtained (Γ= 8-20cm-1) in photorefractive potassium sodium barium strontium niobate crystals doped with transition metal elements: Co, Gu, Fe, Cr and Ni by using two-wave coupling experiments with argon ion laser (λ = 488nm). The response time is measured to be 60-1000ms at an intensity of 5W/cm2 for various samples. We find that in all the crystals electrons are the dominant photorefractive charge carriers, and the typical density of carriers is 1016-1017 cm-3.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

NUMERICAL SIMULATION OF ECR PLASMA SOURCES

SHAO FU-QIU, WANG LONG, YAO XIN-ZI, WU HAN-MIN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 677-691 doi: 10.1088/1004-423X/5/9/006
Full Text: [PDF 476 KB] (Downloads:467)
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The available electron cyclotron resonance plasma source has been simulated in two-dimensional configuration space (z, r) and three-dimensional velocity space (Vz, Vr, Vθ). Using a hybrid model, we treat ions as particles and electrons as fluid. The motion of ions and electrons is determined by external magnetic field and self- consistent electrostatic field. For a given magnetic distribution, the spatial profiles of electron temperature, plasma potential, plasma density and ionization rate have been obtained. The influences of microwave power, neutral gas pressure and magnetic field on plasma parameters have been studied. The comparisons between simulation and experimental results are made and the explanations for some physical phenomena are given.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

A POSSIBLE WAY TO MEASURE LITHIUM ION DIFFUSION COEFFICIENT FOR Li INSERTION THIN FILM WITH UNKNOWN Li COMPOSITION: APPLICATION TO LiαCoO2 and WO3

WEN SHI-JIE, CHEN LI-QUAN
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 692-699 doi: 10.1088/1004-423X/5/9/007
Full Text: [PDF 203 KB] (Downloads:335)
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In this paper, a new experimental method of lithium ion diffusion coefficient measurement for lithium intercalation thin film material is presented. This exper-imental method is feasible and can be applied to thin films with unknown lithium composition such as LiαCoO2 etc. To check its validity, we used the impedance spec-troscopy method to make a verification on the WO3 thin film sample with known lithium composition.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

SUPPRESSION OF BALLISTIC ELECTRON TRANSMISSION THROUGH A SEMICONDUCTOR Π-STRUCTURE BY AN EXTERNAL TRANSVERSE ELECTRIC FIELD

SHENG WEI-DONG, XIA JIAN-BAI
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 700-704 doi: 10.1088/1004-423X/5/9/008
Full Text: [PDF 161 KB] (Downloads:289)
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We have conducted numerical studies of ballistic electron transport in a semicon-ductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.

EFFECTS OF BANDGAP SHRINKAGE IN FEMTOSECOND ABSORPTION SATURATION MEASUREMENTS OF GaAs FILM

CHEN ZHONG, PI FEI-PENG, HU XIANG-WEI, LAI TIAN-SHU, XU GENG, MO DANG, LIN WEI-ZHU
Acta Phys. Sin. (Overseas Edition), 1996, 5 (9): 705-712 doi: 10.1088/1004-423X/5/9/009
Full Text: [PDF 208 KB] (Downloads:304)
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Using CPM dye laser and self-mode-locked Ti sapphire laser as pump-probe optical sources, the effects of bandfilling and bandgap shrinkage on the femtosecond absorption saturation spectra of GaAs film have been studied, For exciting photon energy of 1.97eV and carrier density of 1×1018cm-3, an optical-induced absorption increase is observed and is attributed to bandgap shrinkage, The dependence of the absorption coefficient change on the carrier temperature and the carrier densities is discussed.
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