1996年, 第25卷, 第2期　
刊出日期：1996-03-15

  

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  ATI Spectra and Angular Distributions of the Ionized Electrons in Strong Fields: Classical Approaches

  Jie LIU, Shi-Gang CHEN, De-Hai BAO

  理论物理通讯. 1996, 25(2): 129-134.

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  In this paper classical approaches are identified to be a powerful treatment in above- threshold ionization processes in strong fields. Numerical results are compared with existing theories and some new phenomena on angular distributions are showed.
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  Double-Cusp Susceptibility of Quantum Heisenberg Spin Glasses: Ferromagnetic Coupling and Anisotropy interaction

  Y. S. XIONG, L. YI, K. L. YAO, Z. G. LI

  理论物理通讯. 1996, 25(2): 135-140.

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  With the help of the generalized static replica symmetric spin-glass theory, a quantum Heisenberg S = 112 spin-glass model with the infinite-ranged random Dzyaloshinskii-Moriya (DM) interactions and ferromagnetic coupling is investigated. The dependence of the local susceptibility and the corresponding order parameters on temperature is calculated numerically for different ferromagnetic interactions and fixed anisotropy It has been found that the local susceptibility exhibits double-cusp features for different ferromagnetic coupfings (J_o). In addition, the dependence of the spontaneous moment on temperature is studied numerically, too.
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  Spectral Weight Function and Charge-Excitation Gap of the Half-Filled 2D Hubbard Model

  Feng CHEN, He-Ping YING, Tie-Feng XU, Wen-Zhu LI

  理论物理通讯. 1996, 25(2): 141-144.

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  Using the combination of the quantum Monte-Carlo and the maximum entropy methods, we study the singleparticle spectral weight function for the half-fiUed two-dimensional Hubbard model including the next-nearest-neighbor hopping. In both the weak- and strong-coupling regimes, it is found that a gap persists as the next-nearest-neighbor hopping is turned on. This indicates that a well-defined chargeexcitation gap is a universal nature of the model, irrespective of its band structure.
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  Infrared Magneto-Optical Absorption of Shallow Donors in GaAs/GaAsAl Quantum Dots

  Ka-Di ZHU and Shi-Wei GU

  理论物理通讯. 1996, 25(2): 145-148.

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  Infrared magneto-optical absorption spectra of shallow donor impurity states in GaAs/Ga-AsAl quantum dot are investigated theoretically using the effective-mass, approximation within the strong confinement regime. The numerical results show that for high magnetic fields, the transition energies for (0, 0) + (0, 1) increase linearly with enhancement of magnetic field strength, while the transition energies for (0, 0) → (0, -1) appear to diminish with increasing magnetic field strength.
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  Symbolic Analysis of NMR-Laser Chaos

  Jun-Xian LIU, Zuo-Bing WU, Wei-Mou ZHENG

  理论物理通讯. 1996, 25(2): 149-158.

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  For the extended Bloch-type model of the NMR laser, a binary partition is determined directly from tangencies between forward and backward foliations of the Poincar6 map. Both forward and backward foliations are well ordered according to their symbolic sequences as those of the H6non map with a positive Jacobian. Based on the symbolic dynamics of the H6non map the admissibility condition for allowed sequences is derived and admissible periods are obtained, among which some were formally regarded as forbidden. The allowed periodic orbits are numerically verified. Allowed chaotic sequences are also constructed.
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  The Spectral Density of Nonlinear O-U Noise and the Influence of Nonlinear Fluctuation on the Transition of Bistable System

  Ya JIA, Li CAO, Da-Jin WU

  理论物理通讯. 1996, 25(2): 159-170.

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  A stochastic differential equation driven by N-order nonlinear fluctuation is investigated by defining a novel stochastic process Г(t). The spectral densities of Г(t) for N = 1,2,3 and 4 are obtained. We compare the results of the linear fluctuation case with the nonlinear fluctuation case and find that the extremum of the spectral density for linear case is directly proportional to the noise intensity D and independent of the correlation time τ, the extremum of the spectral density for nonlinear case is determined by both D and τ. An approximate Fockker-Planck equation of the N-order nonlinear fluctuation is derived by Hanggi-like ansatz. The infl uences of nonlinear fluct uation on the transition of bistable system are studied. It is found that the area of unimodal region and bimodal region of the stationary probability is independent of D and τ for linear case, however, the area of two regions is related to D and τ for nonlinear case.
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  Wetting Transitions of Thin Multilayer Films with Opposite Surface Fields

  G. M. XIONG, F. C. ZHAO, X. T. ZHENG

  理论物理通讯. 1996, 25(2): 171-178.

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  Wetting transitions of very thin three-dimensional ferromagnetic Ising films with opposite surface fields are studied by using a self-consistent duster method. The main result is that the wetting transitions of a thin film depend on the thickness L of the film. When L is small the quasiwetting is suppressed and only the layering exists; while as L ≥ L_C (L_C = 20 in our model), both the quasiwetting and the layering can be observed. The question of critical-point shift in the thin film is also discussed.
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  Dynamical Phase Transitions in the Disordered Two-Dimensional XY Model

  Ce-Jun LIU, Jia-Zhen HU

  理论物理通讯. 1996, 25(2): 179-182.

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  We study the time evolution of the distance between two configurations of the site-disordered two-dimensional (2D) XY model submitted to metropolis dynamics on a square lattice. For concentrations between p = 0.6 and p = 0.9 (p_c = 0.59), dynamical transitions and three temperature regimes, similar to the case of pure 2D XY model, are found.
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  Method of Darboux Transformation Matrix for the KdV Equation

  Gou-Jun LIAO, Nian-Ning HUANG

  理论物理通讯. 1996, 25(2): 183-188.

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  For the KdV equation, the method based upon the Darboux transformation matrix is developed. All the conditions are shown to hold by suitably choosing the constants involved. Exphiit expressions of Darboux matrices are determined in a recursive manner.
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  Operator Ordering Problem and Coordinate-Free Nature of Geometric Quantization

  De-Hai BAO, Z. Y. ZHU

  理论物理通讯. 1996, 25(2): 189-194.

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  Operator ordering problem in geometric quantization is investigated. While the quantum operator for p²f(q) given by geometric quantization is found to be ordered via the rule invariant under general coordinate transformations, it is shown that the quantum operators for pⁿ f(q) when n > 2 cannot be well-defined by geometric quantization. This is considered as a natural consequence of the coordinate-free nature of geometric quantization and the Van Hove's theorem.
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  Disappearance of Collective Rotation in Heavy Ion Collisions

  Yu-Gang MA and Wen-Qing SHEN, Zhi-Yuan ZHU

  理论物理通讯. 1996, 25(2): 195-202.

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  A theoretical analysis of collective rotation is performed in heavy ion collisions below 100 MeV/nucleon in the quantum molecular dynamics approach. Both methods are contributed to this analysis, one is based on the shapes of azimuthal distribution, and the other is based on the numerical semiclassical calculation of rotation. The collective rotation becomes weaker with the increasing of beam energy, and tends to fade out at a certain beam energy. The impact parameter dependence of collective motion is also discussed. In connection with recent experiments, theoretical results and experimental data are compared by taking into account the fluctuation of experimental reaction plane determination.
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  Discussion on Weakly Bound States of Three-Body Systems

  Zhong-Zhou REN, Gong-Ou XU

  理论物理通讯. 1996, 25(2): 203-212.

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  The equivalent two-body method for a three-body system has been generalized to an arbitrary three-body system with short-range two-body interactions. An analytical expression for the long-range effective potential is obtained for the Gaussian potential, the Yukawa potential and the exponential potential. The asymptotic behavior of the effective potential at very large distance is found to be universal and an explanation on the significance of universality is given. The weakly bound excited state for the system is first obtained although there is no bound state for two-body subsystems.
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  The Electroweak Correction of Decay H → bb in Standard Model

  Wen-Gan MA, Chao-Hsi CHANG

  理论物理通讯. 1996, 25(2): 213-218.

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  We reevaluated the decay H → bb up to one-loop order of electroweak corrections in standard model with the nowadays parameters, determined by the best measurements including thelatest ones from LEP and SLC. Within error range of the CDF measurement of top-quark; mass, the electroweak correction reduces the decay width less than 0.7% and the correction value varies in the range of 0.5%.
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  The Decay H₀ → W⁺W^- in the Two-Higgs-Doublet Model

  Zeng-Hui YU, Wen-Gan MA, La-Zhen SUN, Yao-Yang LIU

  理论物理通讯. 1996, 25(2): 219-226.

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  The additional weak corrections at one-loop level to process H₀ → W⁺W^- in the two-fliggsdoublet model are calculated. The corrections from the extra Higgs sector depend strongly on the masses of Higgs sectors and the ratio of vacuum expectation values tanβ. It is shown that the general two-Higgs-doublet model admits flexibility in adjusting the one-loop corrections for the decay. In particular, for the heavy Ho boson the additional corrections imply a 5~14% reduction, when M_Ho < 1 TeV, due to relative light H₁ mass and heavy H₂, Φ masses which we used.
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  Transport Theory for Friedberg-Lee Model

  H. GUO, S. J. WANG

  理论物理通讯. 1996, 25(2): 227-232.

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  By means of correlation density matrix theory and in terms of Wigner distribution function for quark, we obtain the transport equation for Friedberg-Lee model, which includes the coUision terms consis ten tly.
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  Collapse of Quasi-Energies and Destruction of Zener Tunneling in Semiconductors Driven by Laser Fields

  Xian-Geng ZHAO

  理论物理通讯. 1996, 25(2): 233-236.

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  The eigenvalue problem of electrons in a semiconductor superlattice driven by a laser field is studied by taking in to account the in terminiband coupling. The closed-form solutions for the quasi-energy minibands are carried out with the help of SU(2) symmetry, from which the conditions for the appearance of the band collapse and the miniband crossing are obtained.It is demonstrated that the emergence of the miniband crossing is coincident with the onset of the destruction of Zener tunneling.
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  The Asymptotic Functional integrals and Critical Temperature of the Dicke Model

  Jun YAN, Xiao-Ming QIU

  理论物理通讯. 1996, 25(2): 237-240.

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  A corrective effective action of the Dicke model is derived by means of the operator determinant identity. An asymptotic expression of functional integral (Z/Z₀) is obtained at critical temperature T_c. The error of the partition function is estimated.
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  Similarity Reductions and Nonlocal Symmetry of the KdV Equation

  Sen-Yue LOU, Hang-Yu RUAN

  理论物理通讯. 1996, 25(2): 241-244.

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  Using some local and nonlocal symmetries of the KdV equation we get two types of nontrivial new similarity reductions. The first type of reduction equation can be solved by means of the Weierstrass elliptic function and the Riemann's zeta function while the solutions of the other type of reduction can be changed to the Painlevd Ⅱ equation.
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  The Definition of Physical Observable in Singular Systems

  An-Min WANG, TU-an RUAN

  理论物理通讯. 1996, 25(2): 245-248.

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  The explicit expression of evolution of the phase space function in time is derived. The physical observables are shown, in general, not always to have weakly vanishing Poisson brackets with all the first-class constraints according to Bergmann's physical requirement and then the corrected definition of the physical observable is given. The relations between this definition with the extended Dirac's conjecture and the gauge conditions are discussed.
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  Non-Oblique Correction on Zbb Vber tex from ETC Dynamics in One-Family Technicolor Model

  Chong-Xing YUE, Gong-Ru LU, Ling-De WAN

  理论物理通讯. 1996, 25(2): 249-252.

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  We calculate the non-oblique correction on Zbb vertex arising from extended technicolor dynamics in one-family technicolor model. We show that this correction is rather large and clearly disfavored by the recently experimental data.
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  Supersymmetric Pair Coherent States

  Hong-Yi FAN, Yue FAN

  理论物理通讯. 1996, 25(2): 253-256.

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  Based on the permu table property between the two-mode boson-fermion annihilator for a supersymmetric harmonic oscillator, which is described by H = b^↑b + f^↑f, and the "charge" operators b^↑b - f^↑f we construct the supersymmetric pair coherent state. The super-lie algebra associated with the supersymmetric pair coherent state is analyzed.