Chin. Phys. B

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The periodic wave solutions for the generalized Nizhnik－Novikov－Veselov equation

Zhang Jin-Liang, Ren Dong-Feng, Wang Ming-Liang, Wang Yue-Ming, Fang Zong-De

Chin. Phys., 2003, 12 (8): 825-830 doi: 10.1088/1009-1963/12/8/001
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The periodic wave solutions expressed by Jacobi elliptic functions for the generalized Nizhnik－Novikov－Veselov equation are obtained using the F-expansion method proposed recently. In the limiting cases, the solitary wave solutions and other types of travelling wave solutions for the system are obtained.

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The calculating formula for radial matrix elements of a relativistic harmonic oscillator

Qiang Wen-Chao

Chin. Phys., 2003, 12 (8): 831-835 doi: 10.1088/1009-1963/12/8/002
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A universal practical formula is given for calculating an integral which includes two confluent hypergeometric functions, power and exponential functions; then by means of this formula, the expressions of the radial matrix elements for a relativistic harmonic oscillator are given.

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Chaos in a gravitational field with dipoles

Chen Ju-Hua, Wang Yong-Jiu

Chin. Phys., 2003, 12 (8): 836-840 doi: 10.1088/1009-1963/12/8/003
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In this paper we investigate the dynamics of a test particle in the gravitational field with dipoles. At first we study the gravitational potential by numerical simulations, we find that, for appropriate parameters, there are two different cases in the potential curve: one is the one-well case with a stable critical point, and the other is the three-well case with three stable critical points and two unstable critical points. By performing Poincaré sections for different values of the parameters and initial conditions, we find a regular motion and a chaotic motion. From these Poincaré sections, we further confirm that the chaotic motion of the test particle originates mainly from the dipoles.

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A set of Lie symmetrical non-Noether conserved quantity for the relativistic Hamiltonian systems

Luo Shao-Kai, Jia Li-Qun, Cai Jian-Le

Chin. Phys., 2003, 12 (8): 841-845 doi: 10.1088/1009-1963/12/8/004
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For the relativistic Hamiltonian system, a new type of Lie symmetrical non-Noether conserved quantities are given. On the basis of the theory of invariance of differential equations under infinitesimal transformations, and introducing special infinitesimal transformations for q_s and p_s, we construct the determining equations of Lie symmetrical transformations of the system, which only depend on the canonical variables. A set of non-Noether conserved quantities are directly obtained from the Lie symmetries of the system. An example is given to illustrate the application of the results.

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Directed transport of coupled systems in symmetric periodic potentials

Zheng Zhi-Gang, Liu Feng-Zhi, Gao Jian

Chin. Phys., 2003, 12 (8): 846-850 doi: 10.1088/1009-1963/12/8/005
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In this paper, we discuss the damped unidirectional motions of a coupled lattice in a periodic potential. Each particle in the lattice is subject to a time-periodic ac force. Our studies reveal that a directed transport process can be observed when the ac forces acting on the coupled lattice have a phase shift (mismatch). This directed motion is a collaboration of the coupling, the substrate potential, and the periodic force, which are all symmetric. The absence of any one of these three factors will not give rise to a directed current. We discuss the complex relations between the directed current and parameters in the system. Results in this paper can be accomplished in experiments. Moreover, our results can be generalized to the studies of directed transport processes in more complicated spatially extended systems.

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Quantum teleportation of one- and two-photon superposition states

Li Ying, Zhang Tian-Cai, Zhang Jun-Xiang, Xie Chang-De

Chin. Phys., 2003, 12 (8): 861-865 doi: 10.1088/1009-1963/12/8/008
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Quantum teleportation of one- and two-photon superposition states based on EPR entanglement of continuous-wave two-mode squeezed state is discussed. The fidelities of teleportation are deduced for two different input quantum states. The dependence of the fidelity on the parameters of EPR entanglement and the gain of the classical channels are shown numerically. Comparing with the teleportation of Fock state and coherent state, it is pointed out that for given EPR entanglement and classical gain, the higher the nonclassicality of the input state, the lower the accessible fidelity of teleportation.

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Linear entropy dynamics of the field in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation

Li Chun-Xian, Fang Mao-Fa

Chin. Phys., 2003, 12 (8): 866-871 doi: 10.1088/1009-1963/12/8/009
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We present the linear entropy dynamics of the field state in the dispersive cavity in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation, and investigate the influence of dissipation on entanglement between the field and the atoms. We show that the coherence properties of the field are also affected by the cavity when the nonlinear process of the field interacting with the atoms with an intensity-dependent coupling is involved, and find that the dissipation constant, the intensity of the field and the atomic distribution angle have different influence on the coherence properties of the field.

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Atomic emission and cavity field spectra of the Jaynes－Cummings model

Li Fu-Li, Gao Shao-Yan, Zhao Yong-Tao

Chin. Phys., 2003, 12 (8): 872-878 doi: 10.1088/1009-1963/12/8/010
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Atomic emission and cavity field spectra of the Jaynes－Cummings model are analytically compared. We show that the two spectra are in general different, except for the special case where the interaction is resonant, the cavity is initially empty and the retarded time of one-photon emission is considered in calculations of the spectra. In this case, the two spectra are the same. We also show that this result comes from the fact that the two-time autocorrelation function of the cavity field is not directly proportional to that of the atom.

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Propagation of ultrashort pulsed beams in dispersive media

Liu Zhi-Jun, Lü Bai-Da

Chin. Phys., 2003, 12 (8): 879-885 doi: 10.1088/1009-1963/12/8/011
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Starting from the Rayleigh diffraction integral, the propagation equation of ultrashort pulsed beams in dispersive media is derived without making the paraxial approximation and slowly varying envelope approximation (SVEA). The spatiotemporal properties of ultrashort pulsed beams in dispersive media, such as spectrum redshifting, narrowing and pulse distortion are illustrated with pulsed Gaussian beams. It is stressed that the "antibeam" behaviour of ultrashort pulsed beams can be avoided, if a suitable truncation function is chosen.

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Passive mode locking of a Nd:YAG laser with co-doped Nd, Cr:YAG as saturable absorber

Yang Lin, Feng Bao-Hua, Zhang Zhi-Guo, Gaebler Volker, Liu Bai-Ning, Eichler Hans

Chin. Phys., 2003, 12 (8): 886-889 doi: 10.1088/1009-1963/12/8/012
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We demonstrate the characteristics of relatively low saturation intensity using co-doped Nd, Cr:YAG as saturable absorber for passively mode locking the Nd:YAG laser. The difference of the saturation intensity between Q-switched and mode-locked operation in co-doped Nd, Cr:YAG was only one to two orders of magnitude, while Cr:YAG was generally reported at a difference of five orders of magnitude. More than 80% mode locking modulation depth was achieved at an incident pump power of 4.4W, corresponding to an intracavity intensity of 6×10^4W/cm^2, using a 68cm long plano-concave cavity.

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Laser spectroscopy of jet-cooled CuF in visible region

Zhang Xiao-Peng, Guo Jing-Ru, Wang Ting-Ting, Pei Lin-Sen, Chen Cong-Xiang, Chen Yang

Chin. Phys., 2003, 12 (8): 851-855 doi: 10.1088/1009-1963/12/8/006
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The laser-induced fluorescence excitation spectra of jet-cooled CuF have been recorded in the range of 19000－21470cm^{-1}, in which the CuF radicals were produced by the reaction of SF_6 with copper atoms from a dc discharge-sputtering source under supersonic jet conditions. Eight observed vibronic transition bands have been assigned as the transition from the ground state X(^1Σ^+) to B(^1Σ^+), C(^1Π) and an unreported upper state. The rotational structure of all observed bands has been analysed at the estimated rotational temperature 80K. We determined the newly observed band to be the (^1Π, v=1)－X(^1Σ^+v=0) transition according to the character of the rotational structure and the isotopic shift analysis. In addition, the lifetimes of the states involved in these bands were measured.

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Investigation of the time characteristics of a pulsed flow of large rare gas clusters

Li Shao-Hui, Liu Bing-Chen, Ni Guo-Quan, Xu Zhi-Zhan

Chin. Phys., 2003, 12 (8): 856-860 doi: 10.1088/1009-1963/12/8/007
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The time characteristics of a flow of large rare gas atomic clusters formed by supersonic expansion of a gas into vacuum through conic nozzles are studied using the time resolving Rayleigh scattering method. The results show a two-region structure of the time resolved spectrum of the scattered light from the clusters. The average cluster size in the second region is much, even orders of magnitude, larger than that in the first one. Three designs of the valve-nozzle assembly have been used to investigate the origin of this finding. Finally, the potential application of the observation is proposed.

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Phasing of lysozyme using one-wavelength anomalous scattering of sulphur atoms through the combination of direct methods and density modification

Jiang Fan, Gu Yuan-Xin, Zheng Chao-De, Fan Hai-Fu

Chin. Phys., 2003, 12 (8): 890-894 doi: 10.1088/1009-1963/12/8/013
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A new method of combining one-wavelength anomalous scattering (OAS) phasing and density modification has been described, in which the improved phases from density modification are re-introduced into OAS phasing. In this way, the phases could be improved iteratively until convergence. The OAS phasing method is based on the previously established sign-probability formula, which breaks the phase ambiguity in the OAS phasing. The implementation of this method has been available in CCP4 as OASIS. This method, although based on direct-methods, could also incorporate known phases and figures of merit into its sign-probability formula. In the implementation of OASIS, the known phases are from the positions of the anomalous scatters. In the current method, the known phases are from the density modification. The current method was tested on phasing a lysozyme crystal using anomalous scattering of sulphur atoms with diffraction data collected on an in-house x-ray source. The resulting map was well connected for the backbone atoms and clearly traceable, with an average map correlation coefficient of 0.6622 for the backbone atoms.

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Numerical modelling of anisotropy in 4H-SiC MESFET's

Lü Hong-Liang, Zhang Yi-Men, Zhang Yu-Ming

Chin. Phys., 2003, 12 (8): 895-898 doi: 10.1088/1009-1963/12/8/014
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A numerical model for 4H-SiC MESFET anisotropy is presented in this paper and the device performances, such as breakdown, temperature and transient characteristics, are demonstrated. The simulation results show obvious effects of the anisotropy for 4H-SiC and are in better accordance with the experimental results. The anisotropy for 4H-SiC should be involved in the device design to acquire better performances.

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Dynamical properties of two-band superlattices with strong interband coupling in real space under the action of ac and dc－ac fields

Duan Su-Qing, Wang Zhi-Gang, Zhao Xian-Geng

Chin. Phys., 2003, 12 (8): 899-904 doi: 10.1088/1009-1963/12/8/015
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Within a two-band tight-binding model driven by ac and dc－ac electric fields, using numerical methods, we investigate the dynamics of electrons and the quasi-energy spectrum of the system with strong interband coupling in real space. We find that when the bandwidth is suppressed to a value much smaller than the field frequency, the dynamical localization can exist in the system. The corresponding regions are found for the occurrence of dynamical localization in the parameter space.

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Bifurcation of a periodic instanton and quantum-classical transition in the biaxial nano-ferromagnet with a magnetic field along hard axis

Nie Yi-Hang, Li Zhi-Jian, Liang Jiu-Qing, Yan Qi-Wei

Chin. Phys., 2003, 12 (8): 905-910 doi: 10.1088/1009-1963/12/8/016
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Crossover from classical to quantum regimes of the barrier transition rate in a biaxial ferromagnetic magnet with a magnetic field applied along hard anisotropy axis is investigated. We show that the type of action-temperature diagrams can be determined by counting the number of bifurcation points. The model possesses not only the known type I and II, but also the interesting type III and IV of transition which do not occur in general.

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Large magnetic entropy change and magnetic properties in La(Fe_1-xMn_x_11.7Si_1.3H_y compounds

Wang Fang, Chen Yuan-Fu, Wang Guang-Jun, Sun Ji-Rong, Shen Bao-Gen

Chin. Phys., 2003, 12 (8): 911-914 doi: 10.1088/1009-1963/12/8/017
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Magnetic properties and magnetic entropy change in La(Fe_{1-x}Mn_x)_{11.7}Si_{1.3}H_y compounds have been investigated. A significant increase of the Curie temperature T_C and a small increase of the saturation magnetizations μ_S have been observed after the introduction of interstitial H, which caused a slight volume expansion. The first-order field-induced itinerant-electron metamagnetic (IEM) transition remains and brings about a large magnetic entropy change around room temperatures for the compounds. The maximal magnetic entropy change is about 23.4, 17.7 and 15.9J/kg·K under a magnetic field change from 0 to 5T for x=0.01, 0.02 and 0.03, respectively. Therefore, the compounds appear to be potential candidates for magnetic refrigerants around room temperatures.