1999年, 第32卷, 第1期　
刊出日期：1999-07-30

  

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  A New Expanding Basis in Variational Calculation

  SHI TingYun, BAO ChengGuang

  理论物理通讯. 1999, 32(1): 1-4.

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  A modified basis of harmonic oscillator wavefunctions with adjustable asymptotic behavior is introduced for variational calculation. A test of validity is carried out for hydrogenatom and rare gas dimer Ne₂.
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  The Influence of the Micromotion on the Internal Dynamics of an Ion in a Paul Trap

  FANG XiMing, FENG Mang, SHI Lei, YAN Min, GAO KeLin, ZHU XiWen

  理论物理通讯. 1999, 32(1): 5-12.

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  For the case of standing wave laser field, we investigate the internal dynamics of a Paul-trapped ion for different cases of the micromotion frequency by means of nonlinear Jaynes-Cummings model and compare our model with the pseudopotential model. The specific calculations show that, when values of dc and ac voltages are fixed, the larger the micromotion frequency is, the smaller the difference between the two models becomes and the larger the Rabi frequency is, for both within and beyond the Lam b-Dicke regime. Moreover, the property of the trapped ion staying whether on the node or on the antinode of the standing wave field is first presented.
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  Ionization Problem for Hydrogen Atom in Intense Circularly Polarized Laser Field Revisited

  XIE BaiSong, CHEN ShiGang

  理论物理通讯. 1999, 32(1): 13-18.

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  Ionization rate for circular polarization laser field is reformulated in length gauge. The Volkov state or the Coulomb-correctsd Volkov one is served at the final wavefunction and would lead to that the ionization rate in length gauge is closer to the experimental data than the corresponding result in velocity gauge. It is also found that the ionization rate as a function of laser intensity has nevertheless the stabilization effect, although in the sense more weakly in length gauge than in velocity gauge, when the field is to be comparable or exceeds to the atomic binding field.
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  Energy Spectrum and g Factor of MgO:Cr³⁺ and Their Pressure-Induced Shifts

  MA DongPing, MA Ning, ZHANG HongMeil, CHEN JuRong

  理论物理通讯. 1999, 32(1): 19-26.

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  The unified calculation of the whole energy spectrum and g factor of the ground state for MgO:Cr³⁺ at normal pressure and their pressure-induced shifts has been carried out on the basis of the theory of pressure-induced shifts and the diagonalization of the complete d³ energy matrix in a regular octahedral field. All the calculated results are in very good agreement with a lot of experimental data. For the first time, by using the wavefunctions obtained by diagonalization of the complete energy matrix, the pressure-induced shifts of g factor have satisfactorily been calculated and explained by microscopic theory. The rates of change of levels with respect to various parameters and the contributions to levels from various parameters have been calculated. The distinct differences in magnitude and/or sign of pressure-induced shifts of various levels are immediately determined by their characteristic dependencies on the parameters of interactions. The pressure-induced shifts of levels and g factor have provided important criteria for the correctness of the calculations and assignments of the energy spectrum and wavefunctions, and it is quite necessary and important to carry out the unified calculation of the whole energy spectrum and g factor at normal pressure and their pressure-induced shifts.
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  Electronic Transport Through Three-Dimensional Metal Point Contact with Rough Boundaries

  DAI ZhenHong, SUN JinZuo, YANG FuMin

  理论物理通讯. 1999, 32(1): 27-32.

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  We have studied numerically the electronic transport properties of metal point contact with rough boundaries. According to the forming process of the metal point contact, we add the roughness as stochastic variance on the cross-sectional radius of the metal point contact, the calculations are performed by making use of the mode matching technique and the transfer-matrix method. In this paper, we mainly study variation of the conductance with cross-sectional radius and length of the point contact. It shows that conductance quantization is influenced by the roughness of the metal point contact, when the roughness arrives at a certain degree, at the customary conductance plateaus, the conductance oscillates strongly with the variance of cross-sectional radius and length of the point contact.
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  The Spectra of Low-Lying States of Three-Dimensional Quantum Dots in a Magnetic Field

  XIE WenFang, CHEN ChuanYu

  理论物理通讯. 1999, 32(1): 33-36.

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  We have studied three-electron systems in three-dimensional anisotropic parabolic quantum dots with the cylindrical symmetry in magnetic fields by means of the method of few-body physics. The results show that the energy levels of a number of states are the lowest, as the magic angular momentum states of two-dimensional quantum dots.
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  The Linear Optical Polarizability Spectra of Five C₇₈ Isomers

  JIANG Jie, DONG JinMing, WAN XianGang, XING DingYu

  理论物理通讯. 1999, 32(1): 37-42.

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  Effects of anisotropy, symmetry, atom arrangement and Coulomb interaction on the linear optical polarizability spectra of five C₇₈ isomers are theoretically studied by using the extended Su-Schrieffer-Heeger model with and without Coulomb interaction. The main results are as follows. 1) The spectra become anisotropic with respect to the direction of the electric field of light. The property is common in the niorlel with and without Coulomb interaction. 2) The symmetry and atom arrangement have grcat effects on the peak positions, strengths, and number. 3) The Coulomb interaction tends to shift peaks to higher energies and enhances the oscillator strengths at higher energies.
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  Large Bipolarons in Two and Three Dimensions

  CHEN QingHu, REN YuHang, JIAO ZhengKuan

  理论物理通讯. 1999, 32(1): 43-46.

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  The large bipolaron in two and three dimensions is investigated by combining the reasonable asymptotic relative wavefunctions and the Lee-Low-Pines-Huybrechts (LLP-H) variational method. The values of the critical coupling constant α_C above which bipolarons may exist and the critical ratio of dielectric constants η_c below which bipolarons may exist are evaluated, which are very close to the recent results obtained within totally different variational approaches. It is also found that low-dimensional materials are more favorable for the formation of bipolarons.
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  Soliton-Like Bi-plasma Polaron

  WU JuHao, LIU YueRan FENG Mang, WANG KeLin, LIN XiaoDong

  理论物理通讯. 1999, 32(1): 47-56.

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  In the framework of phonon-plasmon cooperative effect mechanism, the differential equation for the wavefunction of the travelling soliton-like bi-plasma polaron (BPP) is derived. Then it is proven that the solution can be simply one-dimensional form. Meanwhile, the velocity range of the travelling soliton-like BPP is studied, thereby, we found that the quantity η=ε_∞/ε₀ of the materials, where the travelling soliton-like BPP can exist, should be very small, i.e. η→0. This result is consistent with the recently reported ones. Finally, an analytic approximation solution is given.
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  Effective Nonlinear Response of the Nonlinear Random Mixed Composites

  LU WenGang, LI ZhenYa

  理论物理通讯. 1999, 32(1): 57-62.

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  A simple self-consistent mean-field theory is used to study the nonlinear composites consisting of linear and strongly nonlinear materials or strongly nonlinear materials with different nonlinear exponents. The effective nonlinear response obtained is compared with simulation data. Good agreement is found. Meanwhile, we study the effect of granular shapes (depolarization factor g) in different external applied fields on the nonlinear response of nonlinear random composites. It is found that the factor g affects the effective nonlinear response greatly in certain conditions.
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  Numerical Study of the Magnetic Phase Diagram of Perovskite Mn Oxides at Low Temperatures

  HUANG MingSheng, ZHU PeiChen

  理论物理通讯. 1999, 32(1): 63-66.

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  We obtain the magnetic phase diagram of perovskite Mn oxides at low tempera tures. Our results show that when temperature T→0 a spiral state is stable in a lower doping concentration, a canted state is stable in a higher doping concentration and a ferromagnetic (FM) state becomes stable in the intermediate doping concentration. With temperature increasing, a paramagnetic (PM) state appears at the higher doping concentration and then the canted state disappears.
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  Phase Diagrams of a Transverse Ising Model with Interfaces

  ZHOU JianHua, YANG ChuanZhang

  理论物理通讯. 1999, 32(1): 67-70.

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  A transverse Ising model for a magnetic superlattice of spin-1/2 Ising layered media intercalated by periodic interfaces described by the spin-1/2 Ising model is considered. Phase diagrams and different profiles of magnetization determined by the parameters of the model are discussed within a variational procedure based on Bogoliubov's inequality for the free energy. Our results agree to those of the other's work at the limit of Ω = 0.
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  An Approach to the Study of Quantum Phase Problem Based on Action-Angle Wigner Distribution

  JIE QuanLin, WANG ShunJin

  理论物理通讯. 1999, 32(1): 71-76.

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  Quantum phase distribution is expressed in terms of action-angle Wigner distribution function. It turns out to coincide with the limit case of Pegg-Barnett theory. This discrete phase space approach, in which some concepts such as quantum phase operator are not needed, can express phase-related quantities in a unified way. The expectation values and variances of cosθ and sinθ are the same as those of Susskind-Glogolver theory. The phase-(particle) number uncertainty has a simple form in this formalism.
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  Effects of the Form of Correlation Between Noises on Dynamic Properties of Linear System

  ZHOU XiaoJi, CAO Li, WU DaJin

  理论物理通讯. 1999, 32(1): 77-82.

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  We have derived exact expressions for the correlation function, power spectrum and correlation time of a one-dimensional non-Markovian linear system driven by correlated noises with correlation forms of delta function and different-time-region exponential function, respectively. We find that these dynamic properties of system for delta form are much different from those for different-time-region exponential form. Especially, the power spectrum for the former only has one peak but for the latter can have one, two or three peaks.
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  The Universal Plateau Structure of Lyapunov Exponents for Period Doubling Cascade Attractors

  WANG BingHong, LI XiaoHu, SUN Yong, CHEN LongKang

  理论物理通讯. 1999, 32(1): 83-90.

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  Using algebraic. analysis method for periodic orbits of Hknon map, we derive the boundary equations of stable window and Lyapunov exponent plateau region on the space of nonintegrability parameter A and dissipation parameter J. Ekom the real root of these equations, we obtain the plateau width of Lyapunov exponent W_p = A_p,max - A_p,min and the stable tvindorv width W_s = A_p,max - A_p,min for high periodic orbits. The calculated result of plateau structure ratio α4 = W_p/W_S for period-4 orbit agrees with the conjectural analytical formula: α4 = 2J²/(1+J⁴). Hence our result presents further evidence of universal dependence of Lyapunov exponent plateau structure on the dissipation parameter for period doubling cascade attractors of nonlinear system in transition from order to chaos.
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  Neuronal Oscillatory Network with Stored Patterns

  JI DaoYun, CHEN TianLun

  理论物理通讯. 1999, 32(1): 91-96.

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  We consider a neuronal oscillatory network in which the interactions among neurons are constructed by Hebb rule with finite stored patterns. A general master equation is obtained by dividing the lattice into sublattices. In some simple cases, the dynamics of the system is explicitly solved.
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  The Structure of Affine Hecke Algebra H_N for the XXZ Model with Boundary

  HOU BoYu, YANG WenLi

  理论物理通讯. 1999, 32(1): 97-102.

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  A new affine Hecke algebra is found in studying the XXZ model with a diagonal boundary condition. In the special case of T = 0, we give the double structure of this new affine Hecke algebra, which is similar to the B_n type affine Hecke algebra.
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  Free Boson Representation of DY_h(sl₂)_k and the Deformation of the Feigin-Fuchs

  DING XiangMao, ZHAO Liu

  理论物理通讯. 1999, 32(1): 103-108.

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  A realization of the Yangian double with center DY_h(sl₂)_k of level-k(≠ 0, -2) in terms of free boson fields is constructed. The screening currents are also presented, which commute with DY_h(sl₂) modulo total difference. In the n → 0 limit, the currents of Yangian double DY_h(sl₂)_k become the Feigin-Fuchs realization of affine Lie Sl(2)k, while the screening currents of Yangian double DY_h(sl₂)_k become the screening currents of the affine Lie algebra sl(2)k.
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  Dromion Structures of (2+l)-Dimensional sine-Gordon System

  RUAN HangYu, LOU SenYue

  理论物理通讯. 1999, 32(1): 109-114.

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  Starting from n line soliton solutions of an integrable (2+1)-dimensional sine-Gordon system, one can find a dromion solution which is localized in all directions for a suitable potential. The dromion structures for a special (2+1)-dimensional sine-Gordon equation are studied in detail. The interactions among dromions are not elastic. In addition to a phase shift, the "shape" and the velocity of these dromions may also be changed after interaction.
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  Spinor Representation Reduction Factors for O(N) ⊃ O(N - 1)

  RUAN Dong, SUN HongZhou

  理论物理通讯. 1999, 32(1): 115-118.

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  In this paper, the spinor irreducible representations of O (N) for (σ 1/2 1/2 ± 1/2) with some O (N) U-functions, are obtained by the building-up process.
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  Relativistic RPA and Giant Resonances in β Stable and Unstable Nuclei

  MA ZhongYu, CHEN BaoQiu, Hiroshi Toki, Nguyen Van Giai

  理论物理通讯. 1999, 32(1): 119-126.

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  The nuclear isoscalar and isovector giant resonances in stable and unstable nuclei are studied in the framework of the relativistic random phase approximation. The classical meson propagators with nonlinear self-interactions are constructed in momentum space from the second variation of the action. The relativistic models with the parameter sets, TMI and NLSH, which provide good account of static ground state properties, can also well describe the collective states of nuclei, such as giant resonances. The isovector giant dipole resonances in the unstable Ar isotope chain are investigated.
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  Hadronic Correction to Coulomb Potential Between Quarks and Diquark Structure

  GUO XinHeng, LI XueQian, SHEN PengNian, WANG Chuang

  理论物理通讯. 1999, 32(1): 127-136.

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  We have studied the hadronic correction from the background pion fields due to the chiral symmetry breaking to the Coulomb potential that governs the short-distance behavior of the interactions between the bound quarks. The background fields are associated with the constituent quark mass. We find a modified potential form which favors the diquark structure. We also roughly estimate an influence of this correction on the phase shifts in nucleon-nucleon scattering and find that it may cause an extra middle range attraction between nucleons which is expected.
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  Partonic Structure of the Pomeron in the Modified GLR Equation

  ZHU Wei, RUAN JianHong

  理论物理通讯. 1999, 32(1): 137-144.

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  The gluon recombination effect in the pomeron is studied by using the modified Gribov-Levin-Ryskin evolution equation. We find that the measured parton distributions in the pomeron can be generated dynamically from a purely gluonic input on assuming a small size for the pomeron.
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  The Signatures of the Neutral Top-Pion at the NLC and the Tevatron in Topcolor-Assisted MWTC Model

  YUE ChongXing, LU GongRu

  理论物理通讯. 1999, 32(1): 145-150.

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  The neutral top-pion π_t⁰ can couple to the gluons and the photons through the top quark triangle-loop. we calculate the corrections of the neutral top-pion π_t⁰ to the tt production cross section in topcolor-assisted multiscale walking technicolor model. We find that, for a heavy neutral top-pion, the corrections are quite significant. For m_t = 175 GeV, 5 GeV ≤ m_t¹ ≤ 20 GeV and M_πt = 350 GeV, the relative correction Δσ/σ₀ is larger than 10% which might be observed at a high-luminosity Tevatron. We further estimate the production cross section of π_t⁰ at the NLC experiment. We find that the production rate is significantly large. The neutral top-pion π_t⁰ may be detected in future e⁺e^- linear collider experiments.
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  Number-Difference Orthonormal Representation

  FAN HongYi, ZOU HuiFAN HongYi, ZOU Hui

  理论物理通讯. 1999, 32(1): 151-154.

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  We study the properties of two-mode phase operator √(a⁺+b)/(a+b⁺) and the phase state by constructing the number-difference orthonormal state |q, г). We prove that |q, г ) constitutes a complete and orthonormal representation (number-difference representation). We show that two-mode phase operator √(a⁺+b)/(a+b⁺) exhibits its phase behavior explicitly in the number-difference representation, which resembles the single-mode phase operator e^iψ ≡ (1/√a⁺a+1)a. The corresponding phase state is also studied.
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  Multiple and Strong Luminosity Evolution in the Population of Elliptical Galaxies

  HE Ping, ZHANG YuanZhong

  理论物理通讯. 1999, 32(1): 155-160.

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  The traditional single burst and passive evolution model for elliptical galaxies should not be accepted. In this paper we demonstrate further by comparison of the model predictions with the observed B-K color distribution of galaxies, that the internal extinction by dust cannot save the traditional scenario for ellipticals either. Hence we do not agree with Zepf's (S.E. Zepf, Nature 390 (1997) 377) argument that such a scenario could still survive if ellipticals might have formed in dusty starburst environments. Furthermore, we have also found that the luminosity evolution within the population of ellipticals should be strong, complicated or multiple, which is not favored by our previous study of number counts for ellipticals. The conflicting results simply suggest that the pure luminosity evolution model should not be accepted, and hence the number evolution for ellipticals is a straightforward inference. Our conclusions hold in any one of the three cosmological models, i.e., flat, open, or Λ-dominated, under consideration.