Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2003, Vol.12, No.7
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Lie symmetries and conserved quantities of controllable nonholonomic dynamical systems

Fu Jing-Li, Chen Li-Qun, Bai Jing-Hua, Yang Xiao-Dong
Chin. Phys., 2003, 12 (7): 695-699 doi: 10.1088/1009-1963/12/7/001
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This paper concentrates on studying the Lie symmetries and conserved quantities of controllable nonholonomic dynamical systems. Based on the infinitesimal transformation, we establish the Lie symmetric determining equations and restrictive equations and give three definitions of Lie symmetries before the structure equations and conserved quantities of the Lie symmetries are obtained. Then we make a study of the inverse problems. Finally, an example is presented for illustrating the results.

NMR analogue of the generalized Grover's algorithm of multiple marked states and its application

Zhang Jing-Fu, Lu Zhi-Heng, Deng Zhi-Wei, Shan Lu
Chin. Phys., 2003, 12 (7): 700-707 doi: 10.1088/1009-1963/12/7/002
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The generalized Grover's algorithm for the case in which there are multiple marked states is demonstrated on a nuclear magnetic resonance (NMR) quantum computer. The Walsh-Hadamard transform and the phase inversion are all replaced. NMR analogues of Einstein-Podolsky-Rosen states (pseudo-EPR states) are synthesized using the above algorithm.

Nonadiabatic effects on population transfer of two Bose-Einstein condensates induced by atomic interaction

Hu Zheng-Feng, Du Chun-Guang, Li Shi-Qun
Chin. Phys., 2003, 12 (7): 708-713 doi: 10.1088/1009-1963/12/7/003
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We investigate the stimulated Raman adiabatic passage for Bose-Einstein condensate (BEC) states which are trapped in different potential wells or two ground states of BEC in the same trap. We consider that lasers are nearly resonant with the atomic transitions. The difference of population transfer processes between BEC atoms and usual atoms is that the atomic interaction of the BEC atoms can cause some nonadiabatic effects, which may degrade the process. But with suitable detunings of laser pulses, the effects can be remedied to some extent according to different atomic interactions.

The bifurcation threshold value of the chaos detection system for a weak signal

Li Yue, Yang Bao-Jun, Du Li-Zhi, Yuan Ye
Chin. Phys., 2003, 12 (7): 714-720 doi: 10.1088/1009-1963/12/7/004
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Recently, it has become an important problem to confirm the bifurcation threshold value of a chaos detection system for a weak signal in the fields of chaos detection. It is directly related to whether the results of chaos detection are correct or not. In this paper, the discrimination system for the dynamic behaviour of a chaos detection system for a weak signal is established by using the theory of linear differential equation with periodic coefficients and computing the Lyapunov exponents of the chaos detection system; and then, the movement state of the chaos detection system is defined. The simulation experiments show that this method can exactly confirm the bifurcation threshold value of the chaos detection system.

Spectral property and its shape transition on 72-84Kr isotopes in microscopic core plus two-quasiparticle approach

Shi Zhu-Yi, Zhao Xing-Zhi, Tong Hong
Chin. Phys., 2003, 12 (7): 732-737 doi: 10.1088/1009-1963/12/7/006
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By using a microscopic sdIBM-2+2q.p. approach, the levels of the ground-band, γ-band and partial two-quasi-particle bands for {}^{72-84}Kr isotopes are calculated. The data obtained are in good agreement with the recent experimental results, and successfully reproduce the nuclear shape phase transition of {}^{72-84}Kr isotopes at zero temperature. The ground-state band is described successfully up to J^π=18^+ and E_x=10.0MeV. Based on this model, the aligned requisite minimum energy has been deduced. The theoretical calculations indicate that no distinct change of nuclear states is caused by the abruptly broken pair of a boson, and predict that the first backbending of Kr isotopes may be the result of aligning of two quasi-neutrons in orbit g_{9/2}, which gains the new experimental support of the measurements of g factors in the {}^{78-86}Kr isotopes.

The periodic magnetic cylinder tube for atom guidance: transport efficiency analysis

Li Dai-Jun, Hu Zheng-Feng, Li Shi-Qun
Chin. Phys., 2003, 12 (7): 738-744 doi: 10.1088/1009-1963/12/7/007
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We have proposed a model of periodic axial magnetized hollow tube for atom guidance (1999 Opt. Commun. 160 72-4). In the present paper, an analytic solution of the magnetic field inside the tube is obtained and the transport efficiency of the cold atoms in the magnetic tube at different tube intensities of magnetization is discussed. The effect of the curvature of magnetic tube on the atom transport efficiency is also considered. We have found that the tube has a cooling effect on the transverse temperature of the transported atoms.

The penetration, diffusion and energy deposition of high-energy photon

Luo Zheng-Ming, Gou Cheng-Jun, Wolfram Laub
Chin. Phys., 2003, 12 (7): 803-808 doi: 10.1088/1009-1963/12/7/019
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This paper presents a new theory for calculating the transport of high-energy photons and their secondary charged particles. We call this new algorithm characteristic line method, which is completely analytic. Using this new method we cannot only accurately calculate the transport behaviour of energetic photons, but also precisely describes the transport behaviour and energy deposition of secondary electrons, photoelectrons, Compton recoil electrons and positron-electron pairs. Its calculation efficiency is much higher than that of the Monte Carlo method. The theory can be directly applied to layered media situation and obtain a pencil-beam-modelled solution. Therefore, it may be applied to clinical applications for radiation therapy.

Feynman propagator for an arbitrary half-integral spin

Huang Shi-Zhong, Zhang Peng-Fei, Ruan Tu-Nan, Zhu Yu-Can, Zheng Zhi-Peng
Chin. Phys., 2003, 12 (7): 721-731 doi: 10.1088/1009-1963/12/7/005
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Based on the solution to Bargmann-Wigner equation for a particle with arbitrary half-integral spin, a direct derivation of the projection operator and propagator for a particle with arbitrary half-integral spin is worked out. The projection operator constructed by Behrends and Fronsdal is re-deduced and confirmed and simplified, the general commutation rules and Feynman propagator with additional non-covariant terms for a free particle with arbitrary half-integral spin are derived, and explicit expressions for the propagators for spins 3/2, 5/2 and 7/2 are provided.

Study of hot bands in the B2Σ+u-X2Σ+g system of C-2 anion

Yu Shan-Shan, Yang Xiao-Hua, Li Ben-Xia, Kaniki Kakule, Wu Sheng-Hai, Guo Ying-Chun, Liu Yu-Yan, Chen Yang-Qin
Chin. Phys., 2003, 12 (7): 745-749 doi: 10.1088/1009-1963/12/7/008
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Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy was employed to observe the visible absorption spectra of the B^2Σ^+_u-X^2Σ^+_g electronic transition of C^-_2. Four hot bands (0,1), (1,2), (2,3) and (3,4) have been observed and the band (3,4) is measured directly for the first time, so far as we know, by absorption. A rotational analysis was carried out to obtain molecular constants. With the Franck-Condon principle and the vibrational Boltzmann distribution, we have estimated the vibrational temperature of C^-_2 to be about 3000K.

Electron scattering from molecule CH4 at 10-5000eV

Liu Yu-Fang, Zhu Zun-Lüe, Sun Jin-Feng, Cong Shu-Lin, Han Ke-Li
Chin. Phys., 2003, 12 (7): 750-752 doi: 10.1088/1009-1963/12/7/009
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Electron scattering from molecules in the intermediate-and high-energy range is investigated employing the developed semi-empirical formula for electron scattering from diatomic molecules. Total cross sections of e-CH_{4} scattering are obtained over an incident energy range of 10-5000eV. The results agree well with other available experimental and theoretical data. According to our formula, some quantitative information of single Yukawa potential are also obtained.

Influence of second sideband excitation on the dynamics of trapped ions in a cavity

Liu Xiang, Fang Mao-Fa
Chin. Phys., 2003, 12 (7): 753-758 doi: 10.1088/1009-1963/12/7/010
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We study the dynamics of a trapped ion placed at an antinode of the standing wave inside a high finesse cavity with consideration of the second sideband excitation between the ionic internal levels and the light field. We investigate the entanglement of the three subsystems embodying the ionic internal levels, the vibrational mode of the ion and the cavity field.

Modulational instability of a weakly relativistic ion acoustic wave in a warm plasma with nonthermal electrons

S. K. El-Labany, M. S. Abdel Krim, S. A. El-Warraki, W. F.El-Taibany
Chin. Phys., 2003, 12 (7): 759-764 doi: 10.1088/1009-1963/12/7/011
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An investigation has been made of modulational instability of a nonlinear ion acoustic wave in a weakly relativistic warm unmagnetized nonthermal plasma whose constituents are an inertial ion fluid and nonthermally distributed electrons. Up to the second order of the perturbation theory, a nonlinear Schr?dinger type (NST) equation for the complex amplitude of the perturbed ion density is obtained. The coefficients of this equation show that the relativistic effect, the finite ion temperature and the nonthermal electrons modify the condition of the modulational stability. The association between the small-wavenumber limit of the NST equation and the oscillatory solution of the Korteweg-de Varies equation, obtained by a reductive perturbation theory, is satisfied.

Structure and phase transition of a two-dimensional dusty plasma

Liu Bin, Liu Yan-Hong, Chen Yan-Ping, Yang Si-Ze, Wang Long
Chin. Phys., 2003, 12 (7): 765-770 doi: 10.1088/1009-1963/12/7/012
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The structure and phase transition of a two-dimensional (2D) dusty plasma have been investigated in detail by molecular dynamics simulation. Pair correlation function, static structure factor, mean square displacement, and bond angle correlation function have been calculated to characterize the structural properties. The variation of internal energy, shear modulus, particle trajectories and structural properties with temperature has been monitored to study the phase transition of the 2D dusty plasma system. The simulation results are in favour of a two-step continuous transition for this kind of plasma.

Self-assembly behaviour of amphiphilic diblock copolymer in selective solvents studied by synchrotron small-angle x-ray scattering

Rong Li-Xia, Wei Liu-He, Dong Bao-Zhong, Hong Xin-Guo, Li Fu-Mian, Li Zi-Chen
Chin. Phys., 2003, 12 (7): 771-777 doi: 10.1088/1009-1963/12/7/013
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The aggregation behaviour of styrene-vinyl benzoic acid (PS_m-b-PVBA_n) amphiphilic diblock copolymers in selective solvents with different m and n was investigated by synchrotron small-angle x-ray scattering (SAXS). We have carried out a detailed analysis of scattering intensity, dimension, shape and microstructure of the diblock copolymers of narrow distribution in water, methanol, ethanol and isopropanol selective solvents, respectively. We have found that the aggregation behaviour of the copolymer depends on the nature of the solvent and the micelle forms flat disc objects with the ratio of radius ω=0.4. The average radius gyration R_g of the copolymer decreases as solvents change from isopropanol to ethanol and to methanol, and increases with increasing pH in aqueous solution, but decreases with the addition of CoCl_2 in ethanol solvent. The scattering intensity of diblock copolymer micelle follows I(h)∝h^{-α} in different selective solutions, suggesting that the PS_m-b-PVBA_n coils have self-similar structure behaviour or a fractal structure in the selective solvents. All of these revealed that the aggregation behaviour of the diblock copolymer changes dramatically with experimental condition in the selective solvent. The increase of mass fractal dimension (D_m) from 2.12 to 2.47 indicates that the copolymer chain changes from a swollen coil to a rather compact disc in the course of changing solvents, decreasing surface fractal dimension (D_s) from 2.98 to 2.58 indicates that the copolymer micelle change from a rather rough surface to a smooth form in the course of increasing pH in aqueous solutions, and increasing D_m and D_s from 2.29 to 2.35 and 2.70 to 2.90, respectively, indicates the shrinkage of copolymer micelle to a rather compact and rough disc form by adding CoCl_2 in ethanol solvents.

Monte Carlo simulation of the effect of atomic diagonal transition on cluster diffusion

Xie Feng, Wang Xiao-Ping, Shi Qin-Wei, Zhao Te-Xiu
Chin. Phys., 2003, 12 (7): 778-784 doi: 10.1088/1009-1963/12/7/014
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The effect of atomic diagonal transition on the cluster diffusion and its size dependence is simulated by kinetic Monte Carlo method. The thresholds of atomic diagonal transition barriers E_{dt} are found to be 0.2eV and 0.4eV, corresponding to with and without evaporation and condensation mechanism, respectively. The results indicate that the cluster diffusion is controlled primarily by the atomic diagonal transition, and the cluster diffusion coefficient D decreases drastically with increasing E_d when E_dE_{dt}, and the relationship between D and N changes into D∝N^{-1.08±0.027}.

Photocurrent properties of high-sensitivity GaN ultraviolet photodetectors

Zhou Jian-Jun, Jiang Ruo-Lian, Sha Jin, Liu Jie, Shen Bo, Zhang Rong, Zheng You-Dou
Chin. Phys., 2003, 12 (7): 785-788 doi: 10.1088/1009-1963/12/7/015
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GaN epilayers were grown on sapphire substrates by metal-organic chemical vapour deposition. Metal-semiconductor-metal photoconductive detectors were fabricated using this material. The photocurrent properties of the detectors were measured and analysed. The spectrum response shows a high sensitivity in the wavelength region from 330 to 360nm, with a peak at 358nm and a sharp cutoff near 360nm. The maximum responsivities at 358nm were 700A/W (2V) and 7000A/W (30V). The relationship between responsivity and bias indicates that the responsivity increases linearly with bias until 30V. The influence of the spacing between two electrodes on the detector responsivity was also studied.

Magnetic properties of Nd0.5Pb0.5-xSrxMnO3 materials

Lu Yi, Li Qing-An, Di Nai-Li, Ma Xiao, Kou Zhi-Qi, Luo Zhi, Cheng Zhao-Hua
Chin. Phys., 2003, 12 (7): 789-791 doi: 10.1088/1009-1963/12/7/016
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The structure and magnetic properties of Nd_{0.5}Pb_{0.5-x}Sr_xMnO_3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state. Curie temperature T_C and the MI transition temperature T_p increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling.

Anomalous magnetostrictive effects in (La1-xTbx)2/3S1/3MnO3

Wu Jian, Zhang Shi-Yuan
Chin. Phys., 2003, 12 (7): 792-795 doi: 10.1088/1009-1963/12/7/017
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A series of (La_{1-x}Tb_x)_{2/3}Sr_{1/3}MnO_3 polycrystalline samples has been studied by means of x-ray diffraction, magnetostriction, and thermal expansion measurements. It has been found that this series undergoes a phase transition from a rhombohedral to an orthorhombic form at the doping level x≈0.20 at room temperature accompanied by an anisotropic magnetostriction up to -50×10^{-6} under a magnetic field of 1T. The linear and volume magnetostrictions vary with chemical composition, even change sign. At T=80K, the magnetostrictions for the samples of x=0.20 and 0.40 exhibit different behaviours. The sample of x=0.20 has positive volume and linear magnetostrictions and a negative anisotropic magnetostriction, while the sample of x=0.40 has an opposite behaviour. The magnitude of volume magnetostriction for both the samples is essential (~10^{-4}) at T=80K under a magnetic field of 4T. We conclude that these anomalous effects are due to the charge delocalization and the structural phase transition between orthorhombic and rhombohedral forms induced by the applied magnetic field.

Numerical investigations on the current conduction in bilayer organic light-emitting devices with ohmic injection of charge carriers

Peng Ying-Quan, Zhang Fu-Jia, Song Chang-An
Chin. Phys., 2003, 12 (7): 796-802 doi: 10.1088/1009-1963/12/7/018
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A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trapped charge limited conduction. The dependences of the current density on the operation voltage, the thickness and trap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trap depth, total trap density, and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL to the sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance, can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentially with the mean reduced trap depth.
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