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Vol. 42, No. 1 (1993)

1993-01-05
GENERAL
UNIFORMIZATION IN RIEMANN SURFACES AND LIOUVILLE FIELD THEORY
SHENG ZHENG-MAO, SHEN JIAN-MIN, LI YOU-QUAN
1993, 42 (1): 1-8. doi: 10.7498/aps.42.1
Abstract +
The monodromy of Liouville field in the punctured Riemann sphere is disc us-sed. The exchange algebras and exchange matrix of the field are obtained by means of uniformization in Liouville theory. A relation between the exchange matrix and SL(2n,R) is also presented.
NUCLEAR PHYSICS
RELATIVISTIC MICROSCOPIC OPTICAL POTENTIALS FOR NUCLEON-NUCLEUS IN THE IMPROVED LOCAL DENSITY APPROXIMATION
ZHU PING, XU JIA-BAO, GAO QIN
1993, 42 (1): 9-16. doi: 10.7498/aps.42.9
Abstract +
Based on Walecka model, the refativistic microscopic optical potentials (RMOP) for nu-cleon-nucleus are investigated in the improved local density approximation (ILDA). The RMOP in ILDA, which include the effect of interaction range, are obtained by folding RMOP in LDA with Gaussian form factors. The parameters in Gaussian form factors are adjusted to fit the empirical values of the volume integral and root mean squar radius of the optical potential for p-Ca. By analysing the elastic scattering of proton from nuclei, we get a better agreement of ILDA with experiment data than that of LDA.
A STUDY OF THE SYSTEMATICS FOR (n,T) AND (n, 3He) REACTION CROSS SECTIONS AT 14 MeV
YAO LI-SHAN, JIN YU-LING, CAI DUN-JIU
1993, 42 (1): 17-24. doi: 10.7498/aps.42.17
Abstract +
The systematics charaters of the (n,T) and (n,3He)reaction cross sections have been studied. On the basis of odd-even effect, the systematics formulae of the reaction cross sections are obtained as σu,q=(A1/3+1)2aexp[β(N-Z+δ)/A]. A set of fitting empirical para meters by using the least square method are extracted. For the (n,T) reactions, α and β values are 327.602, 9.592 and -24.495,-14.038, respectively; for (n,3He) reactions, α and β values are 0.918 and -11.340, respectiv ely The (n, T) and (n, 3He) reaction cross sections of some nuclei are calculated by using the theoretical model, and a good agreement with existing data are obtained. In addition, the Ω-value effect and possible reaction mechanism are also discussed.
ATOMIC AND MOLECULAR PHYSICS
ELECTRONIC STRUCTURE OF MOLECULAR RYDBERG STATES OF SOME SMALL MOLECULES AND MOLECULAR ION
SUN BIAO, LI JIA-MING
1993, 42 (1): 25-31. doi: 10.7498/aps.42.25
Abstract +
Based on an independent-particle-approximation (i.e. the multiplescattering self-consistent-field theory), we studied the electronic structures of Rydberg states of the small diatomic molecules H2, He2 and the He2+ molecular ion. The principal quantum number of the first state of the Rydberg series is determined from a convention of the limit of the molecular electronic configuration. The dynamics of the excited molecules and molecular ion has been elucidated. Our theoretical results are in fair agreement with the existing experimental measurements, thus they can serve as a reliable basis for future refined treatment such as the configuration interaction calculation.
ASSOCIATIVE IONIZATION OCCURRING IN COLLISIONS BETWEEN TWO Na(3P) ATOMS
SHEN YI-FAN, LI WAN-XIN
1993, 42 (1): 32-39. doi: 10.7498/aps.42.32
Abstract +
We have measured the cross section [σAl=4.2×10-17cm2±36%] for associative ioniza-tion occurring in collisions between two Na(3P) atoms, by measuring the current reselting from excitation of Na vapor with CW-laser radiation. The major experimental difficulty in measurements of this type is in the determination of the number density and spatial distribution of excited atoms. Here we have measured the excited-atom density by three independent methods, and we have studied the spatial distribution of excited atoms in detail. We have compared the cross section obtained by us at =523k with other experimental results.
ELECTRON IMPACT IONIZATION CROSS SECTIONS OF BORON-LIKE IONS
FANG DU-FEI, WANG YAN-SEN, HU WEI, GAO HAI-BIN, LU FU-QUAN
1993, 42 (1): 40-45. doi: 10.7498/aps.42.40
Abstract +
By using a distorted-wave Born exchange approximation, the direct ionizarion cross section of boron-like ions by electron impact have been calculated. The interferences between direct and exchange amplitudes make important contribution in the process of ionization. The calculated results indicate that the "Natural Phase" approximation is better than the "Maximum Interference" approximation, while the latter agrees better with experiments for some other species of ions. Compared with Coulomb-Born approximation of Moores et al., our calculation gives better agreement with the experiment data available.
CLASSICAL AREA OF PHENOMENOLOGY
INVESTIGATION OF a-C:H FILMS DEPOSITED ON SILICON SOLAR CELL AS ANTIREFLECTIVE COATING
XIA YI-BEN, AN QI-LIN, JU JIAN-HUA, SHI WEI-MIN, WANG HONG
1993, 42 (1): 46-50. doi: 10.7498/aps.42.46
Abstract +
α-C:H films produced on various substrate materials by using radio frequency plasma vapor deposition method have been analysed by Raman spectroscopy, indicating both diamond-like and diamond phases appear in these films. After analysing the transmittance and the refractive index of the films in the visible range, we suggest that the deposited film on silicon solar cell can be used as antireflective coating. The spectrum response value of the solar cell can be improved obviously over a wide range of wavelength from 0.55 to 1.0 μm and the short-circuit cxurent(lsc) of the solar cell is increased by 38% over the uncoated ones.
LENGTH-BIT-RATE PRODUCT LIMIT DUE TO GAIN NOISE IN OPTICAL SOLITON COMMUNICATION SYSTEMS
YANG XIANG-LIN, CHEN JIAN
1993, 42 (1): 51-57. doi: 10.7498/aps.42.51
Abstract +
The system's product of length with bit rate is limited by the Gordon-Haus effect of pulse arrival time in the all-optical soliton communication systems with energy compensated periodically. We analyze effect of perturbation on the group velocity shift in a lossy fiber, and jitter of the soliton arrival time caused by gain noise in a lumped or distributed energy compensated system. The maximum length-bit-rate product is thus estimated. The result shows that in a practical system the maximum length-bit-rate product in a distributed energy compensated system is generally over twice as much as that in a lumped one.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
PROFILES OF H BALMER LINES EMITTING FROM A LASER-INDUCED SILANE PLASMA
LI XIAO-WEI, FU GUANG-SHENG, HAN LI, ZHANG LIAN-SHUI, Lü FU-RUN, WANG JIN-GUO
1993, 42 (1): 58-65. doi: 10.7498/aps.42.58
Abstract +
Profiles of Hα,Hβ and Hγ lines, cmited from a TEA CO2 laser induced silane plasma, are measured with an optical multichannel analizer (OMA Ⅲ) The experimental results show that FWHM (full width of half maximum) of the three lines increases with the main quantum number of the corresponding upper level of the transiti ons, i.e. △λ1/2(Hα)1/2(Hβ)1/2(Hγ), this suggests that the dominant broadening mechanism of the lines is Stark broadening. Fitting the measured Hα profile to theretical data of Stark broadening, two parameters of the plasma are obtained: average electron density N = 1017cm-3 and electron temperature T = 40 000 K. From time tesolved measurements of Hβ profile, a curve of electron density versus time is derived.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
STUDIES ON HIGH TEMPERATURE TRAP OF AlGaAs/GaAs GRIN SCH SQW LASER FABRICATED BY MBE
LU LI-WU, ZHONG ZHAN-TIAN, XU JUN-YING, ZHOU JIE
1993, 42 (1): 66-71. doi: 10.7498/aps.42.66
Abstract +
The high temperature traps of AlGaAs/GaAs GRIN-SCH SQW lasers fabricated by MBE has been studied using DLTS technique.The majority and minority carrier DLTS spectra show that high temperature trap, having larger capture cross section and concentration, exist in n-AlGaAs layer of lasers. This trap may correlate strongly with oxygen content of AlGaAs layer grown by MBE. It may be responsible for the degradation of laser performance. High temperature hole trap may spatially localize between the interface of xAl= 0.2→0.43 and xAl= 0.43 n-AlGaAs layers. And high temperature electron trap may spatially localize in the interface regions of discontinous variation Al mole fraction of AlGaAs layer with xAl= 0.43.
A STUDY OF DEFEETS AND PHASE TRANSITION IN LaAlO3 SINGLE CRYSTAL
XU XIU-YING, ZHANG XING-KUI, FAN DE-PEI, JIANG DONG-MEI
1993, 42 (1): 72-77. doi: 10.7498/aps.42.72
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In situ observation o phase transition in LaAlO3 crystal with the convergent polarized interference pattern at 20° to 800℃ was done. The experiment revealed the phase transition from rhombohedral to cubic at 560℃. The morphology of twin and its concentration, the cry-stallograpliic orientation of domain and the change of topography image of domain and inclusion near Tc have also been studied.
FORMATION PROCESS OF PHASES IN BINARY PLANAR DIFFUSION COUPLE
WU ZI-QIN, ZHAO YUE-CHAO, XIAN DING-CHANG
1993, 42 (1): 78-86. doi: 10.7498/aps.42.78
Abstract +
In this paper a description for the phase formation in a binary planar diffusion couple is presented in the form of a system of differential equations. Not only diffusivity of constituents but also interfacial reaction at phase boundary are introduced in this system of equations. The formation process of phases including the sequence, the growth or shrinkage of the phases can be described clearly with this system of equations. The analysis on the basis of these equations indicates that the formation process of phases depends on interfacial reaction as well as of diffusion. Finally, two typical experimental results are expounded.
A STUDY ON THE RECONSTRUCTION OF DIAMOND(100) SURFACE WITH LOCAL DENSITY FUNCIONAL THEORY
YE LING
1993, 42 (1): 87-91. doi: 10.7498/aps.42.87
Abstract +
The reconstruction of diamond C(100) surface is studied with local density functional theory and extended numerical basis set. A cluster C49H36 is adopted to simulate the surface, where H atoms are saturation atoms. According to the calculation of forces exerted on the surface C atoms, an optimized C(100) surface atomic structure is achieved with the surface dimerized bond length, C-C, equals 1.415?. The nature of the bonding and the corresponding electronic structures, especially the distribution of surface states, are investigated and discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
ENERGY LEVEL NUMBER AND DISSOCIATION ENERGY OF DIATOMIC MOLECULES DESCRIBED BY THE q-DEFORMED OSCILLATOR MODEL
YANG GUANG-CAN
1993, 42 (1): 92-94. doi: 10.7498/aps.42.92
Abstract +
The formula of dissociation energy and total energy level number of diatomic molecules is obtained by using the q-deformed oscillator model- It is shown that the dissociaron energy of the model is greater than the experimental value up to about 10 percent. The method is much in advance of the usual Birge-Sponer method and can be used as a new approximate method to evaluate the dissociation energy of diatomic molecules.
MOBILITY EDGE IN THE AUBRY MODEL OF ONE-DIMENSIONAL INCOMMENSURATE SYSTEMS
WANG WEN-ZHENG, WANG CHUAN-KUI, SUN JIN-ZUO, WANG JI-SUO
1993, 42 (1): 95-100. doi: 10.7498/aps.42.95
Abstract +
In this paper, we show that: when the wave vector Q is not infinitesimal but sufficiently small, there exist mobility edges in the region of V c=±|2-V|, The result is different from that of duality theory.
SPECTRA AND CRYSTAL PARAMETERS OF HOST LUMINESCENT CRYSTAL Na5Eu(MoO4)4 UNDER HIGH PRESSURE
GUO CHANG-XIN, LI BI-LIN
1993, 42 (1): 101-105. doi: 10.7498/aps.42.101
Abstract +
Na5Eu(MoO4)4 is a stoichiometrlc host luminescent material. The light emessioB comes from high concentration host ions Eu3+. In the present work, the effects of hydropressure on fluorescence of Eu3+ in Na5Eu(MoO4)4 are invistigated under 0-5.0 GPa using a diamon anvil high pressure microspectroscopic system. According to crystal field theory, the energy level fexpressinns of Eu3+ (in approximatry D2d symmetry site) are calculated and fit with the experimental data of energy levels, under high pressure, then the ratios of crystal parameter variation △Bkq (kq= 20,40 44, 60 and 64) with pressure variation △P are determind. A comparison of above results with that of YVO4:Eu3+, in which Eu3+ is an active impurity, is also made.
EFFECT OF INTERSUBBAND IMPURITY SCATTERING IN TWO DIMENSIONAL DISORDERED ELECTRON SYSTEMS
YANG YONG-HONG, XING DING-YU, GONG CHANG-DE
1993, 42 (1): 106-113. doi: 10.7498/aps.42.106
Abstract +
By using the Green's function method, we have studied effect of intersubband impurity scattering on the quantum correlation of conductivity and Hall coefficient. It is shown that crossover behaviors appears in both coductivity and Hall coefficient when the situation changes from one-subband occupation to two-subband occupation.
MAGNETIC TRANSITION IN La2CuO4 INDUCED BY MAGNETIC FIELD PARALLEL TO CuO2 PLANE
YU ZHI-MING, WU HANG-SHENG
1993, 42 (1): 114-117. doi: 10.7498/aps.42.114
Abstract +
In this letter, we develop a theory in the mean-field approximation for the spin-flop transition in La2CuO4 when the magnetic field is parallel to the CuO2 plane. The temperature dependence of the critical field predicted by our theory agree qualitatively with the experiment. However, there is no multicritical point according to our theory. The origin of this disagreement is discussed briefly.
MASTER EQUATION OF A SPIN IN PERIODIC FIELD AND THE STEADY STATE
ZHANG YU-MEI
1993, 42 (1): 118-127. doi: 10.7498/aps.42.118
Abstract +
Robertson's theory is applied to derive the master equations of a spin under the action of a static longitudinal field and a rotating transverse field. The damping and the steady state of the spin are obtained as functions of field strength, frequency and the coupling with the bath The structure of the steady state and its origin are discussed.
MONTE CARLO STUDY ON THE PHASE DIAGRAM OF THE FERROMAGNETIC BOND-DILUTE BLUME-CAPEL MODEL
ZHANG GUO-MIN, YANG CHUAN-ZHANG
1993, 42 (1): 128-133. doi: 10.7498/aps.42.128
Abstract +
We have used the Monte Carlo method to study the phase diagram of the ferromagnetic bond-dilute Blume-Capel model, combined with the finite-size scalar theory, and obtained the transition temperatures in zero crystal field, Comparison is made between the results of this simulation and other methods. The influence of the bond-dilute concentration on the tricriti-cal points is determined using the Monte Carlo method.
SPONTANEOUS MAGNETIZATION OF SMALL PARTICLE SPIN SYSTEM
SUN JI-RONG, SHEN ZHONG-YI, LIU YONG, PU FU-KE
1993, 42 (1): 134-141. doi: 10.7498/aps.42.134
Abstract +
Based upon the spin wave theory, the spontaneous magnetization of small particle system at low temperatures is studied by means of solving the Heisenberg model directly. Investigations show that the spin waves are frozen out at ultra-low temperature, and the Bloch T3/2 law is no longer correct in any region of temperature. At the same time, the distribution of the probability for spins to be activated versus positions is obtained, which indicates that there exists no spin layers with obviously high probability to flip.
PHOTOCONDUCTIVITY FOR POLYDIACETYLENE SINGLE CRYSTAL
PENG JING-CUI
1993, 42 (1): 142-148. doi: 10.7498/aps.42.142
Abstract +
The photoconductivity along the polymer hain direction for poly [bis(p-toluene sulpho-nate) ester of 2,4-hexadiyne-l,6-diol] (PDA-TS) single crystal is investigated. After analyzing the limitation of Onsager's model for bimolecular geminate pair thermalizing, a new model of photogenerated charge carries is presented and it is used to explain the dependence of stationary photocurrent Iph on the energies of incident photon.
MECHANISM OF PHOTO-CARRIER GENERATION IN POLYMER WITH CONJUGATED TRIPLE BOND
PENG JING-CUI
1993, 42 (1): 149-153. doi: 10.7498/aps.42.149
Abstract +
In this paper, the mechanism of photo-carrier generation in polymer with conjugatedtriple bond-poly(bis(p-toluene sulphonate)ester of 2,4-hexadiyne-l,6-diole)(PDA-TS) isstudied. We infer that photo-carriers are generated by dissociation electron-hole pairs which were produced by photo-excitation initially, and by thermalization of polaron-excitons which were formed through relaxation, respectively, The formation and characters of triple exciton in PDA-TS are analyzed in detail.
VIBRATIONAL SPECRTA OF SINGLE CRYSTAL Li2B4O7
ZENG LING-ZHI, JIANG YI-JIAN, FU YI, ZHOU YA-DONG
1993, 42 (1): 154-160. doi: 10.7498/aps.42.154
Abstract +
Polarized Raman spectra of single crystal Li2B4O7 have been measured in the wavenum-ber shift range of 50-3000cm-1 at room temperature. The infrared absorption spectrum of Li2B4O7 has also been measured in the range of 200-4000cm-1 for powder samples dispersed in the pressed KBr disks. Based upon the experimental results of LO-TO splitting, the effective charge and mode strength of polar modes are calculated. A comparison of the structure and B-O stretching vibration frequency of various borate species suggests comparatively high nonlinear optical efficiency of Li2B4O7 crystals.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
THE PROPERTIES OF RADIATION NEAR THE BLACK HOLE'S HORIZON AND THE SEDOND LAW OF THERMODYNAMICS
LI LI-XIN, LIU LIAO
1993, 42 (1): 161-168. doi: 10.7498/aps.42.161
Abstract +
By considering a gedankenexperiment of adiabatically lowering a box containing matter with rest energy E and entropy S to a black hole, Bekenstein claimed that the necessary condition for the validity of the generalized second law of thermodynamics is S/E ≤ 2πR, where R is the effective radius of the box, Unruh and Wald claimed that this condition is not necessary but the acceleration radiation can guarantee the generalized second law. In this paper, we point out that Unruh and Wald's conclusion does not hold because the Hawking radiation near the horizon is not thermal. Bekenstein's conclusion also does not hold because the thin box approximation is not correct near the horizon. Neither Hawking radiation nor S/E ≤ 2πR. can guarantee the second law. We have sufficient reasons to conjecture that the gravitation can influence the state equation of matter. For radiation, the usual state equation ρ = αT4 and s =4/3αT3 do not hold in the strong gravitation field, e.g., near theblackhole's horizon. We have derived the state equation for radiation near ths horizon and find that it is very different from that in flat spacetime. The second law may be valid if some restrictions on one parameter of the state equation are imbo-sed. As a corollary, an upper bound on S/E which resembles the Bekenatein's result is found.