1997年, 第27卷, 第2期　
刊出日期：1997-03-15

  

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  The Effect of the Electron-Phonon Interaction on Giant Magnetoresistance in Magnetic Multilayers

  Ling-Yun ZHANG, Bo-Zang LI, Ping-Bo ZHAO, Fu-Cho PU

  理论物理通讯. 1997, 27(2): 129-134.

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  We built electron and phonon free energies and attempted to investigate the effect of the electron-phonon interaction on giant magnetoresistance in magnetic multilayers. Starting from a jellium-like model, we found that the electron-phonon interaction can have an important effect on the spin splitting of electronic energy band. The expression of giant magnetoresistance has been obtained by considering the spin splitting of electronic energy band,indicating that the effect of phonon could not be neglected. Numerical calculations using our approach demonstrate the agreement between experimental and theoretical values.
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  Coherent Resonant Tunneling Model in Double-Barrier Nanostructures

  Ying WU, Guo-Qin GE, Xiao-Xue YANG

  理论物理通讯. 1997, 27(2): 135-140.

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  We propose a coherent resonant tunneling model in double-barrier nanostructutes in which besides an interference effect originated from coherent tunneling of single electron through two barriers, the effects of one-electron charging, discrete energy spectrum and electron interactions between barriers are also important. The interference effect, like that for light in Fabry-Perot cavity, will occur no matter whether a magnetic field exists or not, and is shown to have significant effect on the systems' tunneling current. Our model agrees
  surprisingly well with all the main experimental features of the phenomenon discovered by Scott Thomas et al.
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  Solitary Frenkel Excitons in One-Dimensional Molecular Aggregates with Static Dipole Moment

  Ka-Di ZHU

  理论物理通讯. 1997, 27(2): 141-144.

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  It is shown theoretically that solitary Frenkel excitons in one-dimensional molecular aggregates can exist and propagate when the Frenkel exciton is accompanied by a static dipole moment along the aggregate axis.
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  Thresholds and Universality of the Site Percolation on the Sierpinski Carpets

  Zhen-Quan LIN, Z. R. YANG

  理论物理通讯. 1997, 27(2): 145-152.

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  Following the methods proposed by Yonezawa, Sakamoto and Hori, we have calculated the percolation thresholds P_c, their error bars ΔP_c, and the correlation length exponents v of a family of the Sierpinski carpets for the site percolation problems by making use of MonteCarlo simulations and finite size scaling. We have found the dependence of P_c and v on the fractal dimensionality D_f and the lacunarity. We ascertain that the site percolation problems on a family of Sierpinski carpets with central cutouts and different D belong to different universal classes, and those on Sierpinski carpets with same D_f but of different lacunarities belong to different universal classes.
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  Thermal Properties and Fluctuations of Non-Interacting "M-ons"

  Yun WANG, Jian-Xin ZHU, Z. D. WANG, J. WANG

  理论物理通讯. 1997, 27(2): 153-156.

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  We investigate low and high temperature properties of a two-dimensional gas of noninteracting "M-ons", in which only an integer number of identical particles can occupy a single-particle state. The fluctuation of statistical distribution is calculated. We also compare our results with those derived from Haldane's theory of exclusion statistics.
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  Brownian Motion Theory of Oxide High-T_c, Superconductor and Inertial Effects of Vortices

  Zhi-Gang ZHENG, Gang HU

  理论物理通讯. 1997, 27(2): 157-162.

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  The flux dynamics in high-T_c, oxidc superconductors is investigated by using Brownian motion theory, and the inertial effect is studied. Because of the layer structure of the superconductor,the dynamics can be described by the Brownian motion of a particle in a biased periodic potential field.
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  Saturation Effects and the Colored Pump Noise in a Dye Laser

  Jian HE, Zhi-You ZHONG, Da-Jin WU, Li CA0

  理论物理通讯. 1997, 27(2): 163-168.

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  We investigate the statistical properties of two single-mode dye-laser models-the colored-loss-noise model and the colored-gain-noise model. Analytic expressions of the probability,the mean and the variance of the steady-state laser intensity are obtained through the unified expansion theory [Phys. Rev. A43 (1991) 700]. By comparison we find that when the cavity decay rate for the electric field is large and the pump parameter a₀ is small, the differences of the results of the two laser models are small. Otherwise, the differences are large. And the correlation time of the noise has very obvious influence on the results of the two models.
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  New Solutions of Reflection Equation and Yang-Baxterization of K-Matrix with Three Eigenvalues

  Xiang-Jun MENG, Kang XUE

  理论物理通讯. 1997, 27(2): 169-172.

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  For the standard representation of braid group with two and three distinct eigenvalues, a class of new constant solutions to reflection equation has been found for the standard solutions of braid group represen tations (BGRs) with three distinct eigenvalues. An explicit prescription for the trigonometric Yang-Baxterization of K-matrix with three eigenvalues is presented.
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  The qs-Hermite Polynomial and the Representations of Heisenberg and Quantum Heisenberg Algebra

  Xi-Wen GUAN, Dian-Min TONG, Huan-Qiang ZHOU

  理论物理通讯. 1997, 27(2): 173-178.

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  By introducing a pair of canonical conjugate two-parameter deformed operators D_qs, X_qs,we can naturally obtain the form of qs-analogous Taylor series for an arbitrary analytic function, and explicitly construct the realizations of Heisenberg and two-parameter deformed quantum Heisenberg algebra by means of the operators D_qs and X_qs, and it is shown that the qs-analogous Hermite polynomials are the representations of Heisenberg and the quantum Heisen berg algebra.
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  Clebsch-Gordan Coefficients for the Two-Parameter Deformed Quantum Algebra SU (1,1)_q,s (I)

  Zhao-Xian YU, Ge YU, De-Xing ZHANG

  理论物理通讯. 1997, 27(2): 179-184.

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  The Bargmann representations in the tensor product space of the irreducible representations for the two-parameter deformed quantum algebra SU(1,1)_q,s corresponding to the positive discrete series (a) are in trod uced, and the corresponding Bargmann expressions for the bases of irreps, the coherent state and the operators are also derived. The Clebsch-Gordan coefficients (CGC) for the two-parameter deformed quan tum algebra SU(1,1)_q,s corresponding to the positive discrete series (a) are obtained.
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  An Analysis of One-Body Densities of Three-Body Systems Based on Symmetry

  W. F. XIE, C. G. BAO

  理论物理通讯. 1997, 27(2): 185-192.

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  A three-identical particle model system with the spatial wavefunction being all-symmetric has been proposed to calculate the one-body densities. A11 L≤4 states with even or odd parity are involved in the calculation. The emphasis is placed on exploring the physics underlying the features of the densities. It is shown that the quantum mechanical symmetry plays an essential role in determining the features.
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  Regional Systematics for Even-Even Medium-Heavy Nuclei

  Y. M. ZHAO, Y. CHEN

  理论物理通讯. 1997, 27(2): 193-202.

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  The fluctuation of the δV_np, and δV_NN is taken into account to evaluate the np interaction and pairing strength of nuclei more precisely than the simple N_πN_v[or N_nN_p/(N_n+N_p)]parametrization. Regionally elegant systematics are noticed for the excited energy of the ground β and γ bands. The systematics of the β and γ bands are presented in detail for the first time. Correlation phenomenon of the general behavior of different bands in the same region is pointed out.
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  A Formula for E₂ Transition Rates of the SU(7) Limit of the Fermion Dynamical Symmetry Model

  Guang-Zhou LIU, Wei LIU, En-Guang ZHAO

  理论物理通讯. 1997, 27(2): 203-208.

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  The SO(7) limit of the fermion dynamical symmetry model (FDSM) is discussed. Using the vector coherent state theory (VCST), we construct the matrix elements of quadruple pair (D⁺) and quadrupole (P²) operators explicitly, then obtain a selection rule for E₂ transition and a formula for the E₂ transition rates of the SO(7) limit. As an experimental evidence of the FDSM's SO(7) limit, the B(E₂) values for the Pd-Ru region in this way are calculated,and the predicted results are in good agreement with the experimental data.
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  On Observation of e⁺e^-→bqb⁰ at LEP Ⅱ with Two Higgs Doublets

  Chao-Hsi CHANG, Yi-Bing DING, Xue-Qian LI, Jian-Xiong WANG, Yue-Hong XIE

  理论物理通讯. 1997, 27(2): 209-216.

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  We study possible observational effects of the two Higgs doublets in the e⁺e^-→bqb⁰ at the LEP Ⅱ energy. We have found that the observational values can be obviously different from those predicted by the minimal standard model (MSM), but the results depend on the parameters of the extended model. The possibilities of the observation are discussed in some details.
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  An Improved Perturbative Expression for the Pion Form Factor with Sudakov Suppression

  F. G. CAO, T. HUANG

  理论物理通讯. 1997, 27(2): 217-224.

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  We present an improved perturbative expression for the pion form factor with Sudakov suppression, in which the running coupling constant is suggested to be frozen at α_s, (T>) and the intrinsic transverse momentum dependence associated with pion wavefunction is re-analysed. This expression is available for momentum transfer of the order of a few GeV as wed as for Q→∞. Our scheme can be extended to evaluate contributions to the pion form factor beyond the leading order.
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  Extended Technicolor Corrections to the Zbb Vertex

  Chong-Xing YUE, Yu-Ping KUANG, Gong-Ru LU, Ling-De WAN

  理论物理通讯. 1997, 27(2): 225-228.

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  We reconsider the non-oblique corrections to the Zbb vertex from the sideways and diagonal ETC boson exchange. We find that the sideways ETC boson exchange decreases the Zbb width while the diagonal ETC boson exchange increases it. For N_TC = 2, the correction to the Zbb branching ratio is consistent with the recent measurements.
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  Temperature Dependence of Two- and Three-Gluon Condensates in the Instanton Vacuum

  Jue-Ping LIU, Ping-Xiong YANG

  理论物理通讯. 1997, 27(2): 229-240.

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  The two-gluon and three-gluon condensates at finite temperature are calculated in the framework of the grand partition function for a weak-interacting instanton medium of a disordered phase. The interference parts of both chromomagnetic and chromoelectric two-gluon condensates are found to be small but still significant for a quantitative determination of the value of the condensates at very low temperature, and negligible at the temperature above 1.5Λ_MS, with respect to their non-interference ones. The interference parts of the threegluon condensates are found to be quite small even at very low temperature. With the QCD scale parameter fixed by the value of the Lorentz invariant two-gluon condensate at zero temperature, the value of the three-gluon condensate at zero temperature is found to be coincident with the phenomenological estimate. The values of the gluon condensates decrease when temperature increases, and are negligible when the temperature goes beyond 2.5Λ_MS in the case of the SU_C(3) pure gauge theory.
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  Remarks on Small Superconducting Specimens in Magnetic Field and Measurements of the Lower Critical Field

  Y. B. XIE, T. N. RUAN, Y. H. ZHANG

  理论物理通讯. 1997, 27(2): 241-244.

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  We shall discuss the magnetic behaviors associated with the boundary effects for type-Ⅱ superconductors in general orientations. Using previous results, we speculate that the relation among the lower critical field H_c1, the thermodynamic critical field H_c and the upper critical field H_c2, namely H_c²～H_c1H_c2, is still approximately valid for general experimental orientations. More precisely, the magnitudes of H_c1, H_c and H_c2 are consistent with the formulae given for bulk superconductors when the typical size of the superconducting specimen is greater than the coherence length ε, provided the penetration depth λ is substituted by a modified value λ_m. Consequently, the criterion for observing type-Ⅱ superconducting magnetic behaviors also becomes λ_m>ε, although the London equation is still governed by λ. In the second part of the paper, we shall also suggest an experiment, based on the fact of H_c1. of superconducting thin films in parallel magnetic field being much higher than that of bulk superconductors, to measure H_c1 precisely, especially for extreme type-Ⅱ superconductors,without influence of the penetration barrier.
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  Correlated Holstein-Primakoff Transformation for Correlated Spin Coherent State

  Hong-Yi FAN, Bo-Zhan CHEN

  理论物理通讯. 1997, 27(2): 245-248.

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  We show that by introducing the two-mode correlated Holstein-Primakoff transformation the correlated spin coherent state can be identified as a two-mode correlated binomial state.This fact can be used to describe populations on the three levels of an assembly of identical atoms.
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  (2+l)-Dimensional Integrable Models from the Constraints of the KP Equation

  Sen-Yue LOU

  理论物理通讯. 1997, 27(2): 249-252.

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  Starting from an inner parameter-dependent symmetry constraint of the Kadomtsev-Petviashvili (KP) equation, the asymmetric multi-component Davey-Stewartson extension and the asymmetric multi-component modified Nizhnik-Novikov-Veselov extension are obtained.
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  Another Proof of the Equivalence Between the Duality Symmetric and Maxwell's Action

  Yan-Gang MIA0, Chuan-Hong CHEN

  理论物理通讯. 1997, 27(2): 253-256.

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  We show that the duality symmetric action is equivalent to the Maxwell's action at the quantum level by means of the Dirac's method, and find out that the set of Dirac's brackets on the full phase space is invariant under the dual transformation.