1994年, 第22卷, 第3期　
刊出日期：1994-10-30

  

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  Excitons and Optical Nonlinearities in Conjugated Polymers

  C.Q. WU

  理论物理通讯. 1994, 22(3): 257-264.

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  Within the random phase approximation, single-exciton states in the 1D Peierlas-extended Hubbard model are investigated. Two low-lying bound-exciton states (lB_a and 2A_g) are found for a moderate interaction. The excitons are of an intermediate size. The electron correlation strongly affects energles of the bound-exciton states and leads to the change of the order between lB_a and 2A_g. The lB_a and 2A_g excitons are almost, degenerate for some interaction parameters. The calculated third-harmonic generation clearly shows a three-photon resonance at 0.6 eV and a two-photon resonance at 0.9 eV observed experimentally in polyacetylene.
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  Perturbation Expansion Method and Effective Medium Approximation for Effective Conductivity of Nonlinear Composite Media

  Ge CHEN, Hong-An CRE, Guo-Qing GU

  理论物理通讯. 1994, 22(3): 265-272.

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  In this paper, we establish an effective medium approximation (EMA) for effective conductivity of nonlinear composite media. As an example, we consider a two-dimensional composite medium with a cylindrical inclusion embedded in a homogeneous host, both the host and the inclusion having nonlinear current-voltage constitutive relations, and apply the perturbation expansion method to derive its analytic series solution. Using the nonlinear EMA we derive the formulae of the first, the third and the fifth-order effective conductivities, which are valid for nonlinear composite media with middle concentration of inclusion.
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  Finite-Temperature Optical Conductivity of the Two-Dimensional Hubbard Model

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

  理论物理通讯. 1994, 22(3): 273-276.

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  The finite-temperature optical conductivity of the two-dimensional Hubbard model is studied by means of the grand canonical quantum Monte Carlo method. Results are reported for the half-filled and nonhalf-filled band. The formation and variation of Hubbard gap are observed. For the half-filled band case, our results support that there exists a high-temperature insulator-metal transition.
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  Relation Between the Anderson Transition Zone and the Wave Vector in the Aubry Model

  Fu-Min YANG, Jin-Zuo SUN, Chuan-Kui WANG, Ji-Suo WANG

  理论物理通讯. 1994, 22(3): 277-282.

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  In a previous work of ours the numerical results have proved that there exists the Anderson transition zone in the Aubry model of one-dimensional incommensurate systems. In this paper, we further investigate the relation between the Anderson transition zone and the wave vector in this model. Our numerical results show that the Anderson transition zone is relative immediately to the wave vector, that is to say, the smaller the wave vector, the lower the value of the potential strength V in which the Anderson transition zone lies.
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  A Biased Double-Well Heterostructure in a Free-Electron Laser

  Xian-Geng ZHAO

  理论物理通讯. 1994, 22(3): 283-288.

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  The eigenvalue problem of electrons in a biased double-well heterostructure driven by a laser, field is studied. The closed-form solutions for the quasi-energy and the Floquet states are obtained with the help of SU(2) symmetry. A remarkable feature is found to be that of the occurrence of the quasi-energy crossing, which implies that the coherent tunneling of electrons between two wells can be suppressed almost completely through the choice of the field parameters. Such a coherent destruction of tunneling should be observed in experiments by using freeelectron laser facilities.
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  The Statistical Properties of Loss-Noise Model for Single-Mode Laser

  Li-Mei CHEN, Li CAO, Da-Jin WU

  理论物理通讯. 1994, 22(3): 289-298.

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  The statistical properties of loss-noise model for single-mode laser with multiplicative white noise are studied. By means of expansion in eigenmodes, we derive the accurate analytic expressions of stationary in tensity distribution, stationary moments, transition probability density, stationary joint probability distribution, transient moments, correlation functions, correlation times, and power spectrum. Some significant conclusions are obtained by discussing the transient moments, correlation functions and power spectrum under approximative conditions.
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  Symbolic Dynamics for the Sin Map

  Bin DUAN, Ying-Hai WANG, Hong ZHAO

  理论物理通讯. 1994, 22(3): 299-306.

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  By investigating the sin map, the symbolic dynamics on the two-dimensional map was generalized. We constructed the infinite-word symbolic dynamics, and reduced it to the definiteword symbolic dynamics composed of a suitable number of the words. In the examples of the symbol analysis, all the permitted periodic objects up to period four were identified, and some chaotic trajectors were derived.
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  Temperley-Lieb-Jones Algebraic Structures in Higher Spin Chain Models

  Shao-Ming FEI

  理论物理通讯. 1994, 22(3): 307-314.

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  We investigate the Temperley-Lieb-Jones algebraic structures in isomorphic higher spin chain modgls with nearest neighbour interactions and SU(2) symmetry. The Ternperley-Lieb-Jones algebraic constructions for such chains of spins from 1 to 7/2 are presented. For the case of spin-1 we also give the Temperley-Lieb-Jones algebraic representations related to the anisomorphic spin chain with q-deformed SU_q(2) symmetry. Their related spin chain Harniltonians with SU(2) and SU_q(2) symmetries as well as the corresponding solutions of Yang-Baxter equation are also discussed.
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  Irreducible Representations and Reduced Coefficients of Quantum Algebra SU_q(4) in the SU_q(4)⊃ SU_q(2)⊕SU_q(2) Basis

  Ya-Ping YANG, Zu-Rong YU

  理论物理通讯. 1994, 22(3): 315-322.

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  In this paper, the tensor-like method is presented, and the applications to quantum algebra SU_q(4) are given. The irreducible representation of SU_q(4) and a recurrent formula to calculate reduced coefficients of SU_q(4)⊃ SU_q(2)⊕SU_q(2) is obtained. Some of reduced matrix elements and q-reduced scalar factors (qRF) are tabulated.
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  Long-Range Effective Potential in Halo Nuclei

  Zhong-Zhou REN

  理论物理通讯. 1994, 22(3): 323-330.

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  A way to derive the long range effective potential and the corresponding eigenequation for halo nuclei¹¹ Ll, ¹⁴Be and ¹⁷B is presented by using the equivalent two body method for a three body system. The results agree with both Efimov' s conclusions and experimental data for halo nuclei.
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  QCD Interaction in Pion-Nucleus DCX Reaction

  Xiao-Fu LU, En-Guang ZHAO, Yu-Xin LIU, Jie MENG

  理论物理通讯. 1994, 22(3): 331-336.

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  The pion-nucleus double charge exchange (DCX) transition matrix element is under consideration in the framework of QCD. The interactions including the perturbative effect and nonperturbative contributions ofgluon condensate and quark condensate in the DCX process are discussed. The interaction operators are given.
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  Study on the Hadronic Structure of Charmed Baryons from

  Xin-Heng GUO, Xue-Qian LI

  理论物理通讯. 1994, 22(3): 337-344.

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  By contrast to the traditional consideration about the structure of the heavy flavor baryons (cqq') where the two light quarks are combined as a (qq') system, we propose two other possible structures of (cqq') where in one case (cq) or (cq') constitlltes a color triplet scalar or spin-1 system according to the group analysis and Clebsch-Gordon recombination; in the other case there are diquark structures (cq), (cq') and (qq') in (cqq'). Applying the superflavor symmetry, we calculate the cross sections and as well as their relative ratios which can be measured in experiments with sufficient accuracy. A comparison of the results with that obtained in terms of the three possible structures is given. The distinction is observable and can be tested in sophisticated experiments.
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  Z₂ × Z₂ Discrete Symmetry in the Left-Right Symmetric Model SU(2)_L × SU(2)_R × U(l)_B-L

  Bin CHEN, Ke WU

  理论物理通讯. 1994, 22(3): 345-352.

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  From the point that the Higgs fields can be regarded as the gauge fields on a discrete group, we construct a gauge theory of the leftright symmetric model SU(2)_L × SU(2)_R × U(1)_B-L (LRSM) over Z₂ ⊙ Z₂ discrete symmetry.
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  Theory of a Forced Hydromagnetic Cavity (I)

  Ying.WU, Guo-Qin GE, Zhong-Dang XIAO

  理论物理通讯. 1994, 22(3): 353-364.

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  In this paper, we study a one-dimensional hydromagnetic cavity into which A1fvi.n waves are fed by harmonic shear motion of its boundaries, where they interact with slow magnetosonic waves. The nonlinear equations governing the space slow-varying amplitudes of the forward and backward Alfven waves are derived and are subsequently solved under the characteristic conditions for the A1fvèn waves excited at the boundaries where the magnetosonic oscillations are required to vanish. The forced hydromagnetic cavity is shown to exhibit rnultistable behaviors under certain circumstances.
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  Gravitational Scalar-Driving Inflation Ⅱ

  Mian WANG, Bao-Liang CHENG

  理论物理通讯. 1994, 22(3): 365-372.

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  In the given scalar-tensor theory of gravity, the gravitational scalar ф plays the role of inflaton field, the cosmological function λ(ф) together with the coupling function ω(ф) provides a double-well potential for the motion of ф. After inflation, the universe expands according to 2/3 power law different from the Friedmann cosmology. There is no reheating and there is no need of reheating. The model predicts consistency between the Jeans mass and the mass of galaxies.
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  Holstein-Primakoff Boson Realization for the Hydrogen Atom

  Bong-Yi FAN, Zhong-Xi ZHANG

  理论物理通讯. 1994, 22(3): 373-374.

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  We apply the Holstein-Primakoff transformation to the orbital angular momentum and the Runge-Lenz operators of a hydrogen atom to study its classical Kepler's problem. In this way the classical Kepler's frequency can be directly obtained without in troducing Schwinger's boson realization and boson coherent states.
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  Coherent State Realization of Exponential Solutions of Yang-Baxter Equation and Its Generalizations

  Chang-Pu SUN

  理论物理通讯. 1994, 22(3): 375-376.

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  In this letter, it is shown that the generator of coherent state can be used to realize exponential solutions of Yang-Baxter equation with a spectral parameter. Based on generalization of this observation, the non-unitary finite dimensional solutions of Yang-Baxter equation are constructed in terms of the Heisenberg-Weyl algebra. The unitary realization of the solutionis also obtained in connection with the Hamiltonian of the system of forced harmonic oscillators.
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  Diagonalization of the Single Spin's Quadratic Hamiltonian

  Lei MA, Yong-De ZHANG

  理论物理通讯. 1994, 22(3): 377-378.

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  In this letter, the linear transformation of the single spin operators is studied, the existent condition and the form of this transformation are obtained. From this transformation, a diagonahzation of the single spin's quadratic Hamiltonian is discussed.
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  The Dyson Realization of the Quantum Group SU(1,1)_q and Its Coherent state

  Guo-Xing JU, Jin-He TAO, Mian WANG

  理论物理通讯. 1994, 22(3): 379-382.

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  The Dyson realization of the quantum group SU(1,1)_q is constructed and the transformation matrix, which turns the Dyson realization into the Holstein Primakoff realization, is given. The coherent state for the Dyson realization is discussed and is found to be the qdeformed Weyl Heisenberg coherent state.
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  Exactly-Analytical Approach for Neutrons in Magnetic Field and Berry's Phase Effect in Moving Translation Reference Frame

  Xiao-Guang WANG, Chang-Pu SUN

  理论物理通讯. 1994, 22(3): 383-384.

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  In connection with Bitter-Dubbers experiment, an exact solution for the quantum dynamics of neutrons in magnetic field which is harmonically inhomogeneous (helical) and changes harmonically with time is obtained by invoking a time-dependent transformation with spin space coupling. It predicts that a beam of neutrons with monotonous momentum will be split into two beams by the magnetic field. As its limiting case, the Berry's geometric phase in moving reference frame appears while the field is very strong.