1998年, 第29卷, 第3期　
刊出日期：1998-04-30

  

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  Nonequilibrium Green's Function Approach to Resonant Magnetotunneling Through a Quantum Dot

  ZHOU Hong, LIN Tsunghan

  理论物理通讯. 1998, 29(3): 321-328.

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  Keldysh's nonequilibrium Green's function is applied to studying resonant magnetotunneling through a quantum dot. We propose a microscopic Anderson-impurity-like Hamiltonian in which two kinds of the on-site Coulomb interactions are introduced:the interaction of two electrons at the same Landau level with different spins, U₁ and the interaction for the electrons between different Landau levels, U₁. I-V curves are obtained under different magnetic fields in asymmetrical structures which can display both the energy quantization and singleelectron charging effect. The theoretical results are in good agreement with the experiments qualitatively. The linear-response conductance is also discussed.
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  Stark Effect of Polarons in Parabolic Quantum Wells

  PENG Jianping, W.S. LI, GU Shiwei, Y.Y. YEUNG

  理论物理通讯. 1998, 29(3): 329-336.

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  We report the study of Stark effect of polarons in infinite parabolic quantum wells under an electric field, taking into account the effects of interaction with bulk LO-phonons. The electron-phonon interaction and the.effective mass in the plane perpendicular to the growth direction for excited states of free polarons have been calculated as functions of the degree of confinement. The general behavior of the excited states is found to be in agreement with previous works on the ground state. It is shown that in the limit of strong confinement the differences in electron-phonon interaction and effective mass between the ground state and excited states vanish. Although the applied electric field has no effect on the electronphonon interaction or the effective mass of a free polaron system, our numerical results for an AlGaAs parabolic quantum well have demonstrated its significance in determining the coupling of electrons with bulk LO-phonons of bound polaron systems.
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  Polaronic Effects on the Impurity Binding Energy in a Polar Crystal Slab Within an Electric Field

  ZENG Zhushi, CHEN Chuanyu, HE Guangping, XIE Hongjing

  理论物理通讯. 1998, 29(3): 337-342.

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  The effects of the interaction between electron and bulk longitudinal optical (LO) phonon and surface optical (SO) phonon on the impurity binding energy of the ground state in a polar crystal slab within an external electric field are derived by using the method of a variational wavefunction. The binding energy of the bound polaron is obtained as a function of the impurity position, the slab thickness and the electric field strength. It is found that the polaronic correction to the impurity binding energy by the SO phonon may be enhanced and that by the LO phonon may be reduced with increasing electric field strength. And the effect of the electron-phonon interaction is quite important in increasing the values of binding energy.
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  Strong Electron-Phonon Interaction Effect in Quantum Dots

  LI Waisang, ZHU Kadi

  理论物理通讯. 1998, 29(3): 343-346.

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  Strong-coupling polaron in a parabolic quantum dot is investigated by the Landau-Pekar variational treatment. The polaron binding energy and the average number of virtual phonons around the electron as a function of the effective confinement length of the quantum dot are obtained in Gaussian function approximation. It is shown that both the polaron binding energy and the average number of virtual phonons around the electron decrease with increasing the effective confinement length. The results indicate that the polaronic effects are more pronounced in quantum dots than those in two-dimensional and three-dimensional cases.
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  Spin Stiffness of 2D Isotropic Heisenberg Antiferrornagnet

  QI Jun, JI Yanjiang, LI Meirong, GONG Changde

  理论物理通讯. 1998, 29(3): 347-350.

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  The spin stiffness of spin-1/2 two-dimensional isotropic Heisenberg antiferromagnet is calculated by a perturbation method based on the extended Schwinger-Boson mean-field theory. We arrive at a value of the spin stiffness, p_s = 0.176J, which is in quite well agreement with experiments and the numerical results.
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  The Microscopic Model of Composite Fermion-Type Excitations for υ = l/m Edge States

  YU Yue, ZHU Zhongyuan

  理论物理通讯. 1998, 29(3): 351-356.

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  We derive a microscopic theory of the composite fermion-type quasiparticles describing the low-lying edge excitations in the fractional quantdm Hall liquid with υ = 1/m. Using the composite fermion transformation, one finds that the edge states of the system in a disc sample are described by the Calogero-Sutherland-like model (CSLM) in the one-dimensional limit. This result presents the consistency between one-dimensional and two-dimensional statistics. It is shown that the low-lying excitations, indeed, have the chiral Luttinger liquid behaviors because there is a gap between the right-and left-moving excitations of the CSLM.
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  Analytical Results for the Critical Exponents of Fully Directed Levy Flights

  J.F. WANG, K.L. YA0, Z.Y. LEE

  理论物理通讯. 1998, 29(3): 357-362.

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  In this paper we generalize the definition of Levy flight (LF). With the help of a useful definition for the critical exponents of LF by introducing the concept of cutoff steplength, we calculate analytically the exponents of FDLFs in arbitrary d dimensions, utilizing the generating function method.
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  Photon-Number Distributions of Lasers Generated via Pump-Noise Suppression

  YANG Ming, CAO Li, WU Dajin, LI Zaiguang

  理论物理通讯. 1998, 29(3): 363-368.

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  The photon-number distribution of lasers generated via pump-noise suppression is derived in the photon-number representation. The derivation shows that the negative probability emerging in the calculation of the photon-number distribution in the photon-number representation is not caused by the representation itself but by the truncation of the master equation. Here without truncating the master equation we derive the characteristic function and the distribution function of the photon-number distribution of the laser system with regular pump and with spontaneous atomic decays being eliminated. It is convenient to use the characteristic function to calculate any order of the moment of the photon-number distribution. Such a method can be used to some more general cases, in which the laser system has imperfectly regular pump and the spontaneous atomic decays are also considered.
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  Symbolic Dynamics of the Piecewise Linear Standard Map

  ZHENG Weimou

  理论物理通讯. 1998, 29(3): 369-376.

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  The symbolic dynamics of the sawtooth map is extended to the dissipative piecewise linear standard map. The ordering rules of foliations are derived, and the admissibility condition for allowed symbolic sequences is obtained. A symbolic analysis is given for invariant circles of the piecewise linear standard map without dissipation.
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  On the Graded Quantum Yang-Baxter and Reflection Equations

  ZHANG Yaozhong

  理论物理通讯. 1998, 29(3): 377-380.

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  We clarify the extra signs appearing in the graded quantum Yang-Baxter reflection equations, when they are written in a matrix form. We find the boundary K-matrix for the Perk-Schultz six-vertex model, thus give a general solution to the graded reflection equation associated with it.
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  Solutions of CDG Equation and Modified CDG Equation

  TIAN Yongbo and CHENG Yi

  理论物理通讯. 1998, 29(3): 381-384.

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  This article puts forward a new way to find solutions of CDG equation. The main results are:(i) According to the Lax pair of CDG equation, we introduce the modified CDG equation. (ii) An invariance depending on two parameters of M-CDG equation is found. (iii) Some solutions for CDG equation are obtained by using the invariance.
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  Time Evolution of the Time-Dependent Harmonic Oscillator

  XU Jingbo, YU Youhong

  理论物理通讯. 1998, 29(3): 385-388.

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  The time evolution of the time-dependent harmonic oscillator is studied by a sequence of unitary transformations and the exact evolving state for the system is obtained. A specific model of frequency variation for the time-dependent harmonic oscillator is discussed as an illustrative example.
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  Drinfeld-Sokolov Construction of Heterotic Toda Model

  WANG Yanshen, CHAO Liu, HOU Boyu

  理论物理通讯. 1998, 29(3): 389-398.

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  A free field representation for the left-right asymmetric conformal Toda theory based on simplf-laced even-rank Lie algebras is given. It is shown that the classical chiral exchange algebra for such theories can be reconstructed from free chiral bosons via Drinfeld-Sokolov linear systems, and is a bit more complicated than that of the standard Toda due to some additional δ-function terms and extra degrees of freedom.
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  Wide Existence of the ΔI = 4 Bifurcation in the A～190 Superdeformed Bands

  WU Chongshi, ZHOU Zhining

  理论物理通讯. 1998, 29(3): 399-404.

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  The superdeformed bands in A～190 region were systematically investigated to indicate the existence of ΔI = 4 bifurcation in this region. The behavior of bifurcation was also discussed.
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  One-Neutron Halos in N = 9 Isotones

  REN Zhongzhou, CHEN Baoqiu, MA Zhongyu, XU Gong'ou

  理论物理通讯. 1998, 29(3): 405-410.

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  We have studied the ground-state properties of N = 8 and N = 9 isotones in the framework of the nonlinear relativistic mean-field (RMF) theory using force parameters NL-SH. It is shown that the RMF theory provides a good description of the ground-state properties. One-neutron halos in ¹⁵C and ¹⁴B are predicted. A simple discussion on, the level inversion in N = 9 isotones is given.
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  The F-Spin Formalism of the Neutron-Proton Interacting Boson Model

  SUN Hongzho, LONG Guilu, ZHANG Jinyu, HAN Qizhi

  理论物理通讯. 1998, 29(3): 411-424.

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  The neutron-proton interacting boson model is presented in the F-spin formalism. Hamiltonian and transition operators are rewrit ten in the F-spin formalism based on group chain U(12)⊃U(6)⊗SU_F(2). Matrix elements are given explicitly in terms of the cfp's with F-spin. Different forms of Hamiltonian in IBM-2 are compared, and their relations are given.
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  Spin Structure of Baryons in Orbiting Valence Quark Model

  CHEN Hong

  理论物理通讯. 1998, 29(3): 425-430.

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  The quark model with orbital motion of the valence quarks is constructed to reproduce the spin structure of baryons. The relations between the spin-averaged sum rules and baryon magnetic moments found in the previous works do not remain, unless the small orbital magnetic moments are neglected. In particular, when the orbital motion of the valence quarks leads to the small contribution of quark orbit-spin to baryon magnetic moments, the sum rules for polarized nucleon are in agreement with the recent experiment.
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  Precision Data and Implications on the Parameters of TC Theory

  XIAO Zhenjun, LIU Shunmin, WANG Xuelei, WAN Lingde, LU Gongru

  理论物理通讯. 1998, 29(3): 431-436.

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  Assuming that the actual values of mt and the data set (Γ_b,Γ_h,Γ_Z, R_b,R_c,R_l) are within their 1-σ errors as reported by CDF, DO and by LEP Collaborations, the parameter Δ_b^new which measures the nonoblique corrections on the Zbb vertex from new physics can be determined experimentally. According to the precision data one can obtain updated constraints on the parameters ξ and the masses of the charged PGBs.
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  A QCD-Inspired Model for the Deuteron Form Factors in the Intermediate-Q² Region

  WU Huifang, CAO Jun

  理论物理通讯. 1998, 29(3): 437-442.

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  Based on a perturbative QCD analysis of the deuteron form factors a QCD-inspired model is suggested. The contributions of helicity-flip matrix elements to the deuteron form factors are discussed. Our numerical results are consistent with the data in the intermediate-Q² region.
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  Lagrangian Form of the Self-Dual Equations for SU(N) Gauge Fields on Four-Dimensional Euclidean Space

  HOU Boyu, SONG Xingchang

  理论物理通讯. 1998, 29(3): 443-446.

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  By compactifying the four-dimensional Euclidean space into S₂×S₂ manifold and introducing two topological relevant Wess-Zumino terms to H_n≡SL(n, c)/SU(n) nonlinear sigma model, we construct a Lagrangian form for SU(n) self-dual Yang-Mills field, from which the self-dual equations follow as the Euler-Lagrange equations.
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  Equation of Motion in Hybrid Monte Carlo

  LOU Xiangqian

  理论物理通讯. 1998, 29(3): 447-452.

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  The equation of motion and molecular dynamics for simulating lattice field theory using the Hybrid Monte Carlo (HMC) algorithm are described. Some techniques for improving the HMC efficiency are discussed.
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  Ion Viscosity Stabilization of Tokamak Resistive Internal Kink Modes

  SHI Bingren, SUI Guofang

  理论物理通讯. 1998, 29(3): 453-456.

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  For most of small and medium sized Tokamaks, the unstable mode responsible for the sawtooth crash is the resistive internal kink mode. However, the plasma parameters can be in the ion kinetic regime. In this paper, we consider the dependence of the mode growth rate on the magnetic shear which is changeable during a sawtooth cycle and find that the ion viscosity effect can completely stabilize the mode only for shear smaller than some critical value, corresponding to the stable phase of the sawtooth evolution. This is consistent with one of the salient phenomena of the sawtooth, the sudden onset.
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  Relativistic BBGKY Theory and Collision Integral of Generalized Boltzmann Equation in a Relativistic Magnetized Plasma

  LU Quankang

  理论物理通讯. 1998, 29(3): 457-462.

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  Usually, only Coulomb interactions between charged particles which are independent of time are considered in BBGKY theory of a nonrelativistic plasma. In relativistic case, the induced electromagnetic forces between charged particles which are dependent on time obviously should be considered. A Lorentz-covariant generalized n-time Liouville equation for classical plasma is established. A convenient form applicable to the laboratory frame of this equation is also given. The relativistic BBGKY hierarchy is developed in which both Coulomb and electromagnetic forces between particles are included. A method for solving the relativistic pair correlation equation is given in polarization approximation. A new formula for calculating collision integral in terms of discrete particle Green functions is given. A number of generalized Boltzmann equations for relativistic plasmas are derived.
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  Velocity Profiles of Slow Blood Flow in a Narrow Tube

  CHEN Jinyu, HUANG Zuqia, ZHUANG Fengyuan, ZHANG Hui

  理论物理通讯. 1998, 29(3): 463-468.

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  A fractal model is introduced into the slow blood motion. When blood flows slowly in a narrow tube, red cell aggregation results in the formation of an approximately cylindrical core of red cells. By introducing the fractal model and using the power law relation between area fraction φ and distance from tube axis ρ, rigorous velocity profiles of the fluid ia and outside the aggregated core and of the core itself are obtained analytically for different fractal dimensions. It shows a blunted velocity distribution for a relatively large fractal dimension (D～2), which can be observed in normal blood; a pathological velocity profile for moderate dimension (D = 1), which is similar to the Segre-Silberberg effect; and a parabolic profile for negligible red cell concentration (D = 0), which likes in the Poiseuille flow.
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  A Barrier Problem in Luttinger Liquid

  DING Guohui, XU Bowei

  理论物理通讯. 1998, 29(3): 469-472.

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  By using Gaussian wave functional method, the problem of a single barrier in a one-dimensional interacting electron system is studied. We have constructed the ground state of the system and discussed the phase diagram at the weak barrier limit.
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  Density-Dependence of Quark Mass in Scaling Chiral Lagrangian

  CHEN Hong, LIU Bo

  理论物理通讯. 1998, 29(3): 473-476.

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  We calculate the quark mass in dense medium at one-loop order for an effective chiral Lagrangian supplemented by the scale anomaly of QCD. It is found that the tadpole diagram corrections lead to the decreasing mass of quark with density, while the effect of radiative corrections is opposite to that of the tadpole diagrams.
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  New Derivation for Cranking Hamiltonian and Tensor Form of Angular Velocity

  FAN Hongyi, LI Liangshi

  理论物理通讯. 1998, 29(3): 477-480.

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  We present an alternative approach for deriving the Coriolis term ω(t) J of cranking model Hamiltonian, which is based on the technique of integration within an ordered product of operators. The merit of this approach is that the tensor form of angular velocity ω, which describes the body frame rotation, naturally appears. Remarkablx the angular velocity we obtained here can be time-dependent.