中国物理B

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PATH INTEGRAL IN CORRELATED EIGENSTATE BASIS OF COMPLEX SCALAR FIELDS φ(x) AND φ^?(x)

范洪义, 范悦

1999 (3): 161-166. doi: 10.1088/1004-423X/8/3/001

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Using the technique of integration within an ordered product of operators, we construct a new common eigenvector set of the complex scalar fields φ(x) and φ^?(x), which is a set of particle-antiparticle correlated states. On the basis of the new eigenstates we develop the path integral formuation. The new eigenvectors' properties are investigated, they are qualified to be a new representation.

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DOUBLE DIFFERENTIAL CROSS SECTIONS FOR ELECTRON IMPACT IONIZATION OF HELIUM

姚云飞, 陈长进

1999 (3): 167-173. doi: 10.1088/1004-423X/8/3/002

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The double differential cross sections for electron impact ionization of helium at incident energies of 200 eV, 100 eV and 64.6 eV have been calculated in the BBK model. The present results are found to be in generally good agreement with the latest measurements of R?der et al. and the theoretical results of the convergent close-coupling method although some quantitative discrepancy remains.

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EFFECTS OF CROSS-CORRELATED NOISES ON A SINGLE-MODE LASER MODEL: STEADY STATE ANALYSIS

梅冬成, 谢光中, 曹力, 吴大进

1999 (3): 174-179. doi: 10.1088/1004-423X/8/3/003

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The stationary properties of a single-mode laser with positive and negative correlations between additive and multiplicative white-noise terms are investigated. By virtue of a simple rule and decoupling ansatz, the intensity correlation function and correlation time for the laser model are derived. We found that: (1) the fluctuation of light intensity with negative correlations between the noise terms are reduced in comparison with those for positive correlations; (2) the coupling between additive and multiplicative noises enhances the rate of decay of intensity correlation; (3) the effects of negative correlations between the noise terms are more remarkable than those of positive correlations.

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STATIONARY PROBABILITY DISTRIBUTION FOR COLORED-LOSS-NOISE MODEL OF A SINGLE-MODE DYE LASER

陈黎梅, 傅海翔, 曹力, 吴大进, 丘军林

1999 (3): 180-184. doi: 10.1088/1004-423X/8/3/004

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We apply the interpolation procedure to calculate the stationary probability distribution of the colored-loss-noise model of a single-mode dye laser operating above the threshold with correlation time τ covering a very wide range. By stochastic Runge-Kutta algorithm, we also carry out numerical simulations of steady-state properties. Comparing the results of the interpolation procedure and the unified colored-noise approximation with simulation results, we find that the agreement between the results of the interpolation procedure and the simulation results is much better than that of the unified colored-noise approximation when correlation time τ covers a range from moderate to large. We conclude that the interpolation procedure really improve the accuracy of predictions for this system.

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SPIN POLARIZATION IN A MODEL QUANTUM WIRE WITH A CROSS-SECTION

王传奎, 王洪松, 张庆刚

1999 (3): 185-192. doi: 10.1088/1004-423X/8/3/005

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Numerical investigation of the electronic structure of a small closed quantum system fabricated on the two-dimensional electron gas forming on the interference between GaAs and Al_xGa_1-xAs is reported. The Kohn-Sham spin-density-fun ctional theory is applied. Self-consistent results show that the quantum system assumes unequal numbers of electrons for spin up and spin down because of the existence of bound states. The profiles of effective potential energies for spin up and spin down electrons are then found to be very different, which will result in different transmission coefficients. It is notable that this spin polarization is caused by the geometry of the nanostructure.

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A POSSIBLE SOLITON-LIKE POLARON MODEL FOR SUPERCONDUCTORS Y_1-xCa_xBa₂Cu_3-xM_xO_7-δ(M=Fe, Ni)

王忆, 陈传誉, 黄效吾, 汪克林

1999 (3): 193-198. doi: 10.1088/1004-423X/8/3/006

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Using 1+1 soliton-like polaron model of a deformable continuum, the critical temperature and the energy gap in high-temperature superconductors Y_1-xCa_xBa₂Cu_3-xM_xO_7-δ(M=Fe,Ni) are studied in the framework of finite temperature Green's function theory. The ratio 2Δ/k_BT_c=3.9 is obtained. Theoretical results are found in good agreement with the experimental data.

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TEMPERATURE DEPENDENCES OF THE ORDER PARAMETERS OF A MAGNETIC ISING SUPERLATTICE OF TWO FERROMAGNET MATERIALS WITH SPINS μ=1/2 and S=1

B. Laaboudi, M. Saber, A. Benaboud, M. Kerouad

1999 (3): 199-207. doi: 10.1088/1004-423X/8/3/007

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The temperature dependences of the layer parameters σ_n,zand q_n,z=2_n,z> of a magnetic Ising superlattice consisting of two ferromagnetic Ising materials with spins μ=1/2 and S=1 respectively, on a simple cubic structure, are examined using the effective field theory based on the use of a probability distribution technique that correctly accounts for the single site kinematic relations. According to the values of the exchange interactions, different qualitative types of phase diagrams are expected.

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THE INFLUENCE OF Co SUBSTITUTION ON THE MAGNETIC PROPERTIES AND THE GIANT MAGNETO-IMPEDANCE EFFECT OF (Fe_1-xCo_x)₈₄Zr_3.5Nb_3.5B₈Cu₁

何峻, 郭慧群, 沈保根, 何开元, 刘宜华, 胡季帆

1999 (3): 208-215. doi: 10.1088/1004-423X/8/3/008

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The microstructure, magnetic properties and the giant magneto-impedance (GMI) effect of the nanocrystalline (Fe_1-xCo_x)₈₄Zr_3.5Nb_3.5B₈Cu₁ ribbons have been studied. With increasing Co concentration, the nanocrystallized grain size and volume fraction of the α-Fe(Co) phase decrease under the same annealing condition, while the coercivity H_c increases from 1.92 A/m at x=0.0 to 30.38 A/m at x=0.8. The effective permeability drops sharply with increasing Co concentration so that the GMI effect goes down. A value of more than 380% for the magneto-impedance(MI) ratio was measured at frequency f=2.5 MHz and the sensitivity can reach 0.9% (A/m)^-1 for Fe₈₄Zr_3.5Nb_3.5B₈Cu₁ ribbon. When x is equal to 0.8, the MI ratio drops to about 30% and the sensitivity only reaches a value of lower than 0.025% (A/m)^-1. The concise analysis in theory is also expounded.

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NON-RESONANT UPCONVERSION ENERGY TRANSFER OF CRYSTAL ErP₅O₁₄

陈晓波, 张光寅, 李美仙, 李昆, 冯衍, 毕诗章, 郝昭, 宋峰, 宋增福, 孟广政, 孙寅官, 杨展如, 聂玉昕

1999 (3): 216-222. doi: 10.1088/1004-423X/8/3/009

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This paper reports the upconversion luminescence phenomenon of crystal ErP₅ O₁₄ in ultraviolet to blue-green wave range induced by red DCM dye laser. The upconversion passage of each upconversion fluorescence is confirmed. It is found that the upconversion mechanism is mainly non-resonant upconversion energy transfers between rare earth ions when laser wavelength is near 650 nm. It is very interesting that the non-resonant upconversion energy transfer is achieved directly through a kind of coupling state of rare earth ion cluster and the ions do not exchange their phonon energy with crystal lattice.

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EMISSION AND MASS SPECTRAL ANALYSES OF LASER ABLATED AlN PLUMES

陈金海, 王培南, 郭钊, 李富铭

1999 (3): 223-228. doi: 10.1088/1004-423X/8/3/010

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The emission spectrum of the ³Π_i-³Π_i (0－0) AlN band and some N⁺ and N emission lines have been studied in the visible region for the laser ablated plumes. The Stark-shift and Stark broadening were observed. The component species in the ablated plumes were analyzed by time of flight mass spectroscopy. The electron density and the temperature were calculated from the Stark-shift and Stark broadening of N(²D) emission line. The densities of AlN⁺, Al⁺, N⁺, AlN, N and Al were estimated by the mass spectra and the Saha equation.

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