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Vol. 41, No. 1 (1992)

1992-01-05
GENERAL
THE HAUSDORFF DIMENSION OF DIFFUSION-LIMITED AGGREGATION CLUSTERS WITH ANISOTROPIC DIFFUSION
FENG YUE-XIN, LIU SHEN-ZHI, FENG CHANG-JING
1992, 41 (1): 1-9. doi: 10.7498/aps.41.1
Abstract +
We obtain effective exterion half angle of the anisotropic diffusion DLA clusters β= min {βx, βy} by analytical calculation. The hypothesis of Yu Jiang about β = max{βx,βy} is modified and the formula of Hausdorff dimension D of the anisotropic diffusion DLA clusters varying with the anisotropic diffusion probability p is also modified. We also made simulation tests and find that the modified formula agrees well with experimental results. Finally, we compare our result with the numerical result of Jullien, and find a good coincidence when
ATOMIC AND MOLECULAR PHYSICS
ELECTRONIC STRUCTURES OF RYDBERG STATES FOR MOLECULES WITH Ne AS THEIR UNITED ATOMS
YANG HUAN-WANG, LIU LEI, LI JIA-MING
1992, 41 (1): 10-17. doi: 10.7498/aps.41.10
Abstract +
Based on the multiple-scattering self-consistent-field theory, we have studied the molecular Rydberg states of the molecules B2,HF,H2O,NH3 and CH4 with Ne as their united atoms. From the united atomic limite of molecular electronic configuration, we set a convention to determine the principal quantum number of fhe initial states of a Rydberg series. The dynamics of the excited molecules are elucidated. The theoretical calculations are in fair agreement with the available experimental results.
CLOSE COUPLING WAVE PACKET THEORY OF ATOM- DIATOM SCATTERING
YANG HUAN-WANG, ZHANG YI-CI, REN TING-QI
1992, 41 (1): 18-25. doi: 10.7498/aps.41.18
Abstract +
In the space-fixed(SF)coordinate frame and body-fixed(BF) coordinate frame, we cal-culete the state to state transitional probabilities for the He-H2 system by using the rencently developed close coupling wave packet method. The results shows that (1) the two theories formulated in the SF frame and BF frame are equivalent, and the calculated results of the two method coincide with that of close coupling method, (2) the calculational efficience in the SF, frame is higher than that in the BF frame as the number of coupled terms increases.
CLASSICAL AREA OF PHENOMENOLOGY
RESONANCE FLUORESCENCE SPECTRUM OF TWO-LEVEL ATOM IN CONSIDERATION OF SELF-REACTION
LIU REN-HONG, TAN WEI-HAN
1992, 41 (1): 26-36. doi: 10.7498/aps.41.26
Abstract +
In this paper, the resonance fluorescence spectrum of two level atom is investigated under the influence of both the driving field and the emission field from the atom itself. Some new features are revealed. The most important one the disappearence of the central peak resulting from the vacuum Rabi splitting, and the presence of the new central peak resulting from the interaction between side peak and self emission at the same time.
INTERACTION OF ULTRASONIC WAVE WITH VOID- CONTAINING LAYER IN SOLID
WANG YAO-JUN
1992, 41 (1): 37-45. doi: 10.7498/aps.41.37
Abstract +
Using a general model for sound reflection from multilayered media, we present in this paper the expressions for sound reflection and transmission coefficients on voidcontaining interface layer in solid and derive the characteristic equation for symmetric and antisymmetric modes of the interface waves along the layer. The method for evaluating the effective elasric moduli of void-containing solid is also introduced. The numerical calculation given in this paper shows the influence of the void volume concentration and layer thickness on the sound reflection coefficients and interface wave velocity, providing a theoretical basis for inverse deduction of the mechanical properties of void-containing layer based on ultrasonic measurements.
A THEORY OF HYDROGEN-INDUCED CRACK PROPAGATION IN AN ELASTIC CONTINUOUS MEDIUM
JIANG SHENG-RUI, QUAN HONG-SHUN
1992, 41 (1): 46-55. doi: 10.7498/aps.41.46
Abstract +
Induced by the crack stress field, hydrogen atoms tend to gather together to form hydro-gen atmosphere in an elastic continuous medium. The average hydrogen concentration of this hydrogen atmosphere is calculated in this paper. By regarding this hydrogen atmosphere at the crack tip as an elastic inclusion, the eigen-strain of the inclusion is calculated and the influence of the stress field pij to crack dislocation density is studied. Thus the total stress intensity factor of the crack tip is obtained. We infer that the mechanism of the hydrogen embritt-lement is the enlargement of the crack stress intensity factor by this hydrogen atmosphere. The physical process of the hydrogeninduced crack propagation is also discussed. The calculated propagation rate of the crack agrees quite well with the experimental result.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
A STUDY ON DYNAMICS OF dc GLOW DISCHARGE PLASMA AT AXIAL DIRECTION
LI ZAI-GUANG, LIU ZU-LI, SONG WEN-DONG, WEI HE-LIN
1992, 41 (1): 56-61. doi: 10.7498/aps.41.56
Abstract +
We study one dimensional dynamics of dc glow discharge for parallel plates, taking into account the effect of inelastic collisions between electrons and neutral particles on the energy and momentum loss by the MHD theory. The distributions of density, velocity and temperature of plasma and the electric field for Ar plasma are obtained. It is found that the gas pressure and the electrode spacing give significant influence on electron density in the cathode region, but the influence on ion density is small.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
EXTENDED ONE-DIMENSIONAL FIBONACCI STRUCTURES
HU AN, JIANG SHU-SHENG, PENG RU-WEN, ZHANG CHUN-SHENG, FENG DUAN
1992, 41 (1): 62-68. doi: 10.7498/aps.41.62
Abstract +
A one-dimensional k-component Fibonacci structure, which includes k incommensurate intervals, is the natural extension of the Fibonacci structure with two intervals. The projection method is applied to deal with the pattern and indexing problems of X-ray diffraction. The theoretical simulation is performed to prove the projection method for this extended Fibonacci structures. The diffraction spectrum will lead to chaos for a finite chain provided that k is sufficiently large.
DISLOCATION IN MOVING NEAR THE FREE SURFACE ——ANISOTROPIC CASE
YANG SHUN-HUA, LI GUO-WANG, HUANG LIN-GEN
1992, 41 (1): 69-79. doi: 10.7498/aps.41.69
Abstract +
In this paper, the Eshelby theory of static dislocation in infinite anisotropic medium is extended, and combining the integration method with Green tensor function, to treat a dislocation moving uniformly near free surface. We take the system of γ-Fe/free space as an example to perform numerical calculation, the result shows the influence of dislocation motion on its elastic fields. As the velocity of dislocation v→0, the result coincide with that of static disloca-tion. On field point more close to the surface, the influence of the surface becomes more significant. The calculated "image force" acting on the dislocation shows that the action of the surface is attractive in nature. The simple theory and method suggested in this paper can be applied to calculate the elastic field of and "image force" on moving dislocation in any anisotropic medium, and would be significant in investigation of mechanical properties of the me dium.
ELECTRON CORRELATION AND TWO-DIMENSIONAL LATTICE INSTABILITY
LIU JING-NAN, SUN XIN
1992, 41 (1): 80-86. doi: 10.7498/aps.41.80
Abstract +
Starting from the screened Coulomb electron interaction, the energy band and electron wave function of two-dimensional unstable lattice system are calculated by using the Wannier function. The effect of electron correlation on two-dimensional lattice instability is studied by means of the electron correlation function. Our results show that the electron interaction reduces the two-dimensional lattice dimerization, which is different from the one-dimensional case.
BOND-BENDING EFFECT ON LOCALIZED VIBRATIONS OF SOLITON FOR TRANS-(CH)x
YAO KAI-LUN, LI ZHAN-JIE, XING BIAO
1992, 41 (1): 87-96. doi: 10.7498/aps.41.87
Abstract +
We study the lattice vibrations of soliton in two-dimensional model and find that the vibrational amblitudes of carbon atoms normal to chain is comparable to that along the chain for most of the modes. Compared with the results of SSH model, a number of new modes have been found. They depend on the coupling constant and the bond-bending.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
ZERO FIELD STEPS IN AN ANNULAR SYMMETRIC JOSEPHSON JUNCTION
YAO XI-XIAN, XU KUN-MING, LU DAO-FANG
1992, 41 (1): 97-105. doi: 10.7498/aps.41.97
Abstract +
A numerical study of a perturbed sine-Gordon equation (SGE) in an annularly symmetric Josephson junction by considering the cosΦ-term is carried out in this paper. The numerical results show that in the absence of external applied field there are two branches of the zero field steps (ZFS) in the I-V characteristic; the lower voltage ZFS corresponds to the single soliton excitation (1-ZFS) and the higher voltage one corresponds to three solitons exicitation (3-ZFS). In our calculations for the definite size and parameters of the annularly symmetric Josephson junction, the two solitons excitation is unstable. The three solitons excitation is similar to the 3-ZFS with the symmetric mode in the one-dimensional overlap Josephson junction except that there exist amplitude molulation for the time behaviour in both of the voltages 〈φτ〉ρ and φτ(ρ1,τ).
INFLUENCE OF NON-MAGNETIC IMPURITIES ON THE HIGH-Tc SUPERCONDUCTIVITY
LI ZHENG-ZHONO, XIAO MING-WEN, SHI DA-NING
1992, 41 (1): 106-114. doi: 10.7498/aps.41.106
Abstract +
In this paper, we have proved that the non -magnetic doping can also produce pair-breaking effect in the Anderson lattice model of the high-Tc cuprate superconductorts due the energy dependence of the order parameter. In the case of dilute doping, we have obtained a linear decreasing behavior of Tc with the increasing of non-magnetic impurity concentration in agreement with experimental results. Furthermore, we have also calculated the influence of doping on the superconducting energy gap in the density of states. The results indicate that the decreasing of the gap at T = 0 is much slower than the dropping of Tc with the increasing of non-magnetic impurities. Therefore, the gapless region may not appear before the system transforms into the normal state in different from the conventional BCS superconductors with magnetic impurities.
RETURNING EFFECT AND THE FIRST ZERO FIELD STEP IN AN ANNULAR JOSEPHSON JUNCTION
WANG QIANG-HUA, WANG WEI, YAO XI-XIAN
1992, 41 (1): 115-122. doi: 10.7498/aps.41.115
Abstract +
The returning effect of soliton in an annular Josephson junction is analysed in detail theoretically. Some results are compared with directly numerical simulation ones. To avoid the return effect of soliton, the conditions which relate to the minimum bias current of the first zero step of annular junctions with different geometric and dissipative parameters are discussed. A disscusion of the difference between in-line and annular junction is also made.
CORRELATION BETWEEN THE IRREVERSIBILITY LINE AND PINNING POTENTIAL IN HIGH-Tc SUPERCONDUCTOR YBa2Cu3O7-δ
JIN XIN, ZHANG YI-TONG, LU RUI-XI, YAO XI-XIAN, LIU FENG-SHENG, MOU HUI-LIN, WU XIAO-ZU, ZHOU LIAN
1992, 41 (1): 123-127. doi: 10.7498/aps.41.123
Abstract +
We have studied the irreversibility line and pinning potential U0 of high-Tc melt-textured YBa2Cu3O7-δ samples and found that the irreversibility line takes an exponential form B*-e(-T/Tc) over the temperature range of 72-85K, whereas the corresponding magnetic measurement at 77K gave a nonvanishing critical current density It is shown in the present paper that the functional expression of irreversibility line and pinning potential U0 of samples are closely associated.
ION COORDINATION AND STRUCTURAL TRANSITION OF YBa2Cu3-xFexOy
LIN MING-XI, CHEN GUAN-MIAN, A SHA, XU XIAO-ZHEN
1992, 41 (1): 128-135. doi: 10.7498/aps.41.128
Abstract +
Critical temperature, phase structure, oxygen content and coordination of oxygen atoms were studied for Fe doped superconducting oxides YBa2Cu3-xFexOy(0.01≤x≤ 0.2) after an-nealing at different temperatures by use of M?ssbauer spectroscopy and X-ray diffraction. The result shows that Fe ion occupies mainly Cu(l) position. Both the increase of Fe content and vacuum annealing at high temperature lead to the structural transition from orthorhombic, to tetragonal phase, and the critical temperature Tc goes to zero. However, in the former case, during the increase of Fe content the transition occurs when appreciable amount of Fe3+ ion with sixfold coordinate oxygen atoms exists, and is thus accompanied by the increase of oxygen content. But for vacuum annealing at high temperature, with the increase of annealing temperature the number of Fe ion with double oxygen coordination increases and oxygen content decreases, and the transition occurs when this double oxygen coordination dominates. Both these processes destroy the planar Cu-O configuration and lead to the decrease of Tc .Besides, the valence states of Fe atoms at different lattice sites are also determined and discussed.
METAL-INSULATOR TRANSITION IN YBa2Cu3O7-x
YANG YONG-HONG, XING DING-YU, GONG CHANG-DE
1992, 41 (1): 136-143. doi: 10.7498/aps.41.136
Abstract +
On the basis of the scalinp: theory of locallzation, we introduce an effective dimensionality for layered structure systems, which depends on the conductivity anisotropy or the interlayer coupling. We propose that both decrease of conductance and drop in effective dimensionality account for the metal-insulator transitions in YBa2Cu3O7-x and other oxide compounds. The scaling theory in finite temperatures is also discussed to explain the temperature dependence of the normal state resistivities.
PROPAGATING CHARACTERISTICS OF ULTRASONIC WAVE IN THE MAGNETIC LIQID
DU YOU-WEI, TONG XING-WU, ZHONG WEI, WANG TING-XIANG, GAN CHANG-MING, ZHANG XIAO-RONG
1992, 41 (1): 144-148. doi: 10.7498/aps.41.144
Abstract +
Here we report experimental results of propagating characteristics of ultrasonic wave and explain it in light of existing theories. First, we study the relaxation process after magnetic field built up. It is known that the particles form chain-like clusters when the magnetic field is applied. The process of the cluster for mation is a relaxation process. The ultrasonic velocity v as a function of magnetic field at field angle θ= 0 and π/2 at 4MHz were measured. We have studied the dependence of velocity on. Concentrations of the magnetic particles and frequency. The experimental results can be explain by Tarapov's theory rather than th approach used by Parsons.
MAGNETIC PROPERTIES OF ULTRAFINE NICKEL PARTICLES
DU YOU-WEI, WU JIAN, SHI YING-BING, LU HUAI-XIAN, XU MINO-XIANG, XUE RONG-HUA
1992, 41 (1): 149-154. doi: 10.7498/aps.41.149
Abstract +
In this paper we report the magnetic properties of ultrafine Ni particles. The specific magnetic moment drastically decreases with reducing the diameter d of particles when d≤15 nm. The coercivity Hc also approaches zero when d is about 15nm. The value of effective magnetic anisotropy constant is determined as K=-5.8×105 (erg/c.c.). It is found to be larger than the bulk one. The mechanism of reversal magnetization can be understood by sphere chain model. Curie temperature Tc is obviously lower for 9nm average diameter particles as compared with the bulk, this may result from the lattice contraction.
THE FREE AND RANDOM DIELECTRIC RELAXATIONS
LI JING-DE, LI JIA-BAO, FU SHI-LIU, SHEN WEN-BIN
1992, 41 (1): 155-161. doi: 10.7498/aps.41.155
Abstract +
A method of Fourier transform dielectric spectrometer is described, it leads to simplifying the process of solving spectrum and to save the memory capacity for data. Using this method, it is shown that for the same dielectric sample the free and random relaxation will appear under different condition in the time range of 106 to 10-4 seconds, that was predicted by the phe-nomenoiogical theory. The relaxation times are related to the resistance R of the measurement circuit joinning the two electrodes of the sample.. Large value of R leads to a relaxation time of open circuit, and small ones lead to the limit of short circuit; the relaxation time of open ciecuit may be as large as 106 times of the short circuit one. The variation in frequancy domain spectrums of complex dielectric constant is given from open to short circuit cases.
INFLUENCE OF HYDROGEN AND TEMPERATURE ON POSITRON TRAPPING IN PROTON-IRRADIATED SILICON
XIONG XING-MIN
1992, 41 (1): 162-169. doi: 10.7498/aps.41.162
Abstract +
Positron lifetime measurements are used to investigate positron trapping in silicon irradiated with protons at a high dose of 3.2×1017cm-2 and a lower dose of 3.6×1016cm-2, respectively. The irradiation-induced vacancy defects are mainly divacancies. During the irradiations, the divacancies in high dose samles have almost trapped hydrogens, while a part of the divacancies in low dose samples have not trapped hydrogensyet. In the measurements of the two warm-up of high dosed samples and the first warm-up of low dose samples, the further trapping of hydrogens into divacancies is observed., With increasing temperature the charge state of the divacancies decorated by hydrogens takes a transition from negative to neutral around 145K. With increasing the amount of the trapped hydrogens per divacancy, the lifetimes of the negatively charged divacancy and the neutral one are both shortened, while both their trapping cross sections are increased. The trapping of hydrogens into the negatively charged divacancies has no influence on the temperature dependence of its trpping cross sections.
A STUDY ON CORROSION-RESISTING MECHANISM OF THE ANCIENT MIRROR "HEI QI GU"
WU YOU-SHI, FAN CHONG-ZHENG, WANG SHENG-JUN, LI ZHI-CHAO, WANG CHANG-SUI
1992, 41 (1): 170-176. doi: 10.7498/aps.41.170
Abstract +
The surface layer of the bronze mirror "Hei Qi Gu" is composed of non-metal layer and transition layer. The valent electron structure analysis points out that the main phase of tran-sition Sn1-xCuxO2 is similar to SnO2 in stablility. It was found from study of experimental data that there is the coincidence site lattice structure at the phase boundary between the δ-phase Cu-Sn alloy and Sn1-xCuxO2 in the transition layer. This structure reduces the energy of Cu atoms at the phase boundary and makes the δ-phase Cu-Sn alloy stable, which is the main reason for corrosion resistant of the "Hei Qi Gu".