1993年, 第20卷, 第1期　
刊出日期：1993-07-30

  

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  Extension Theory for Magnetic Excitations of Ordered Ferromagnetic Systems

  Song PAN, Tsung-Han LIN

  理论物理通讯. 1993, 20(1): 1-10.

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  The extension theory for lattice Green functions is used to study the magnetic excitations of some ordered ferromagnetic systems. The local density of magnon states for the bulk as well as for the surface, edge and corner is presented.
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  Polaron Effects in a Quantum Box

  Ka-Di ZHU, Shi-Wei GU

  理论物理通讯. 1993, 20(1): 11-18.

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  The interaction Hamiltonian of an electron with LO phonons in a quantum box is derived. Within the framework of the effective-mass approximation, the electron self-energies due to the interaction of the electron with the confined LO-phonons that incorporate effects of phonon confinement in a quantum box have been calculated as a function of the size of the boxes by a perturbative method. The results show that for small boxes, the electron self-energy increases rapidly to a maximum and then. decreases slowly to the limit of the wire value as the box trends to infinity in one direction while remaining fixed in the other two directions. The smaller the size of the box, the larger the absolute maximum of the self-energy These results imply that the effects of phonon confinement are dominant in small boxes.
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  Polaron Effects on the Stark Shift of a Bound Polaron in Finite Quantum Wells

  You-Cheng LI, Shi-Wei GU

  理论物理通讯. 1993, 20(1): 19-28.

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  With both LO and SO modes being taken into account, the influence of electron-phonon interaction on QCSE of a bound polaron in a finite quantum well (QW) is investigated by means of the perturbation-variation method. It is found that the presence of an ionized impurity decreases the energy shift and weakens the effect of a finite barrier height. LO and SO mode effects will give significant corrections to the Stark energy shift individually and their influences on the shift just are contrary.
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  CDW and SDW Groundstates of the Extended Hubbard Model

  Zhi SONG, Zhen-Qing YANG, Guo-Zhu HE

  理论物理通讯. 1993, 20(1): 29-34.

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  4-site and 6-site small systems are chosen to study the charge-density-wave and spin-densitywave groundsta tes of ex tended Hu bbard model in order to reveal the physics explicj t1y and find analytic results as well. The effections of two kinds of fluctuation processes are analyzed in detail. The compositions of the two groundstates are also analyzed. The general energy formulas of the two groundstates and the phase transition line between them are obtained.
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  Simultaneous Failures of the Nonuniform-Stressed Fiber Bundle

  Y. N. LU, E. J. DING

  理论物理通讯. 1993, 20(1): 35-40.

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  The burst process in a load-carrying bundle of the identical fibers, in which each fiber is initially stressed randomly, js considered. The distribution function of the simultaneous burst sizes is obtained analy tically. It is shown that this model belongs to the same class of universality as the model discussed by Hemmer and Hansen (1991).
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  First-Order-Like Transition of Dye Laser Colored Gain Model

  Ling LIN, Li CAO and Da-Jin WU

  理论物理通讯. 1993, 20(1): 41-48.

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  A unified colored-noise approximation, a novel approximative theory, is applied to solve the colored gain model for dye laser. The stationary probability of the colored gain model is derived. The first-order-like transition is discussed. The effect of the noise correlation time τ on the first-order-like transition is analysed. It's found that the size of the regions in the parameter plane is related with r and three different regions are turned into two different regions in the parameter plane as r >> 1/2a₁. By comparison, we find that the res.ults of the unified colored-noise approximation are more close to simulation's results than those of the best Fokker-Planck equation.
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  Bifurcation and Chaos in Two-Photon Optical Multistability

  Ying-Hai WANG, Hua-Wei YIN

  理论物理通讯. 1993, 20(1): 49-54.

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  Investigation of the two-photon optical multistability (tristability and double-bistability) has revealed the existence of the spontaneous oscillation and chaotic motion. By the information obtained from the time-dependent solution, power spectra, Lyapunov exponents and phase trajectory, we proved evidence of the bifurcation structure for tristability, and show the existence of two coexisting at tractors for the double-bistability.
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  The spin-1/2 Heisenberg Chains in Constant Magnetic Field and Coherent states1

  H. YAN, S. M. FEI, J. ZHANG

  理论物理通讯. 1993, 20(1): 55-64.

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  In the ferromagnetic Heisenberg chains of XXX and XXZ types with the hidden symmetries of Lie bi-algebra su(2) and quantum bi-algebra su_q(2), we show that at thermodynamic limit the algebra contractions give the boson algebra h(4) and the q-deformed boion algebra h_q(2) as the hidden symmetries respectively. The chains in constant magnetic field are studied and the ground states and lowest excited states are given explicitly with energy spectra. The phonon (or angular momentum) excitations are shown to be bosonic for the isotropic case and q-bosonic for the anisotropic case, and the ground states and lowest excited states of the systems of the chains in field are given explicitly. We give the phonon coherent states in the isotropic Heisenberg chain and the q-coherent states of the anisotropic chain at the thermodynamic limit. The q-coherent states are shown to be a squeezed states of phonon excitations.
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  Multiple Pole Solutions of the Modified Nonlinear Schrödinger Equation

  Jue-Ping LIU

  理论物理通讯. 1993, 20(1): 65-72.

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  A general formula for the N-tuple polesoliton solutions of the modified nonlinear Schrödinger equation, which corresponds to a nonzero pole of order N of the Jost solution to the corresponding Lax-pair equations, is derived.
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  Similarity Reductions and Painlev6 Properties for the Kupershmidt Equations

  Hang-Yu RUAN, Sen-Yue LOU

  理论物理通讯. 1993, 20(1): 73-80.

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  Five types of similarity reductions of the Kupershmidt equations which admit a tri-Hamiltonian structure are found by a direct method. Two types of reduction equations which are Painlevé Ⅱ and IV types are coincident with those obtained by classical Lie approach. Both algebraic and logarithmic branch points for time t can be entered into the solutions of Kupershmidt equations. The integrability of the Kupershmidt equations is re-examined by the singularity analysis using the Weiss-Kruskal approach and the A blowitz-Ramani-Segur algorithm.
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  Pion-Nucleus Scattering and the Interacting Boson Model

  Yu-Shun ZHANG, Yu-Xin LIU

  理论物理通讯. 1993, 20(1): 81-88.

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  A procedure of combining the medium energy scattering theory in the Eikonal approximation with the interacting boson model is proposed to study the pion-nucleus scattering. The channel coupling effects in the excitation of nuclear collective state with ρ^- and ρ⁺ elastic and inelastic scattering are analyzed. The calculated cross sections for the excitation of 2₁⁺ state of ²¹⁸Sn agree with experimental data quite well.
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  Wave Function of Non-Vacuum Universe in Ashtekar Theory

  Hao-Gang DING, Chao-Guang HUANG, Yao-Yang LIU, Yuan-Zhong ZHANG

  理论物理通讯. 1993, 20(1): 89-94.

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  In this paper, we studied the wave function of the universe in the (anti-) self-dual representation for the cosmological-model in which the closed Robertson- Walker spacetime is minimally coupled to a massless scalar field and the cosmological constant is equal to zero. We found that some wave functions in the (anti-) self-dual representation cannot be mapped into the σ-representation, or the metric representation, and vice versa.
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  SU(2) Gauge System with Dynamical Fermions in Cumulant Expansion Treatment

  Xi-Te ZHENG, Gang CHEN

  理论物理通讯. 1993, 20(1): 95-100.

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  The SU(2) lattice gauge system with dynamical Wilson fermions is investigated by the variational cumulant expansion method with the novel criterion to determine the variational parameters. The agreement of calculated order parameter Ep of the pure gauge sector with Monte Carlo data is much improved, especially, in the intermediate coupling region. The fermionic contributions are small to k⁶ hopping parameter expansion, but the general feature is in accordance with the Monte Carlo data qualitatively. The necessity of higher order calculations in the intermediate coupling region is discussed.
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  BFV Quantization of the Minimal Chiral Schwinger Model

  Yan-Gang MIA0, Yao-Yang LIU

  理论物理通讯. 1993, 20(1): 101-106.

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  Both the gauge-invariant and the gaugenoninvariant versions of the minimal chiral Schwinger model are quantized by using the BFV formalism for the two cases of the regularization'parameter a > 1 and a = 1. The equivalence of these two versions of the model is then established in a gauge-independent manner.
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  Wormhole Solutions with Perfect Fluid Energy-Momentum Tensors

  Jian-Jun XU

  理论物理通讯. 1993, 20(1): 107-112.

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  Wormhole solutions are found in various theories with a perfect fluid energy-momentum tensor added to the right-hand side of classical Euclidean-Einstein equation. We found that wormhole solutions indeed exist for a lot of models in the presence of such a perfect fluid energy-momentum tensor, which is coincident with the conclusion obtained by Hawking and Page.
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  Twin-Gap in High-T_c Perovskite Copper Oxides

  Xiao-Jian YUAN, Ming SHAW, Fu-Sui LIU

  理论物理通讯. 1993, 20(1): 113-116.

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  This paper shows that the gap in high-T, perovskite copper oxides is always twin, which corresponds to the two kinds of attractive potentials in different regions of κ. The twingap has been observed in a lot of experiments. The special temperature-dependence of the twin-gap can quantitatively explain the observed data of penetration depth vs temperature.
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  Soliton Chains of a Generalized Toda Lattice

  Ying WU, Xi-Xue YANG

  理论物理通讯. 1993, 20(1): 117-120.

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  We consider a strongly anisotropic multi-dimensional lattice model which has a Toda-type nonlinearity along one direction and is considered as a linear continuous medium in other directions. Soliton chains on this lattice are obtained, and their various variants are discussed in detail.
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  A Discussion on the Existence of the Saddle Point Solution

  Jia-Ru WEN, Yu-Dong YIN, Tao HUANG

  理论物理通讯. 1993, 20(1): 121-124.

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  We prove that there is no saddle point solution in the (1 + 1)-dimensional O(3) nonlinear σ model with a term explicitly breaking symmetry ddwn to O(2). In the standard model, it is shown that the ansatz of Monton is not sufficient to get a saddle point solution of the theory. Thus the question of baryon number violation based on the saddle point solution in the electroweak theory should be reexamined.
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  An Alternative Lorentz-Type Symmetry of the Theory of Chiral Bosons with Interactions

  Yan-Gang MIAO, Yi-Shi DUAN

  理论物理通讯. 1993, 20(1): 125-128.

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  We canonically quantize the extended theory of chiral bosons described by the Floreanini-Jackiw Lagrangian to include an interaction potential, and obtain that the commutation relations of interacting chiral bosons coincide. with those of free ones. We then construct an alternative Lorentz-type symmetry for this theory in terms of the basic commutation relation.