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.

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.

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.

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.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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_{x}Ga_{1-x}As 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.

Using 1+1 soliton-like polaron model of a deformable continuum, the critical temperature and the energy gap in high-temperature superconductors Y_{1-x}Ca_{x}Ba_{2}Cu_{3-x}M_{x}O_{7-δ}(M=Fe,Ni) are studied in the framework of finite temperature Green's function theory. The ratio 2Δ/k_{B}T_{c}=3.9 is obtained. Theoretical results are found in good agreement with the experimental data.

The temperature dependences of the layer parameters σ_{n,z}and 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.

The microstructure, magnetic properties and the giant magneto-impedance (GMI) effect of the nanocrystalline (Fe_{1-x}Co_{x})_{84}Zr_{3.5}Nb_{3.5}B_{8}Cu_{1} 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 Fe_{84}Zr_{3.5}Nb_{3.5}B_{8}Cu_{1} 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.

Chen Xiao-bo, Zhang Guang-yin, Li Mei-xian, Li Kun, Feng Yan, Bi Shi-zhang, Hao Zhao, Song Feng, Song Zeng-fu, Meng Guang-zheng, Sun Yin-guan, Yang Zhan-ru, Nie Yu-xin

Chin. Phys. B 1999, 8 (3): 0216; doi: 10.1088/1004-423X/8/3/009
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This paper reports the upconversion luminescence phenomenon of crystal ErP_{5} O_{14} 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.

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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