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Chin. Phys. B  
  Chin. Phys. B--2003, Vol.12, No.1
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New explicit exact solutions for a generalized Hirota-Satsuma coupled KdV system and a coupled MKdV equation

Cheng Yong, Yan Zhen-Ya, Li Biao, Zhang Hong-Qing
Chin. Phys. B 2003, 12 (1): 01;  doi: 10.1088/1009-1963/12/1/001
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In this paper, we make use of a new generalized ansatz in the homogeneous balance method, the well-known Riccati equation and the symbolic computation to study a generalized Hirota--Satsuma coupled KdV system and a coupled MKdV equation, respectively. As a result, numerous explicit exact solutions, comprising new solitary wave solutions, periodic wave solutions and the combined formal solitary wave solutions and periodic wave solutions, are obtained.

Exact solution and exotic coherent soliton structures of the (2+1)-dimensional generalized nonlinear Schrodinger equation

Zheng Chun-Long, Zhang Jie-Fang, Sheng Zheng-Mao, Huang Wen-Hua
Chin. Phys. B 2003, 12 (1): 011;  doi: 10.1088/1009-1963/12/1/002
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In this paper, a variable separation approach is used to obtain localized coherent structures of the (2+1)-dimensional generalized nonlinear Schrodinger equation:$\i\varphi_t-(\alpha \beta)\varphi_{xx}+(\alpha+\beta)\varphi_{yy}-2\lambda \varphi \bigg[(\alpha+\beta)\bigg(\dint_{-\infty}^x|\varphi|_{y}^2\dd x+u_1(y,t)\bigg) $$-(\alpha-\beta)\bigg(\dint_{-\infty}^y|\varphi|_{x}^2\ddy+u_2(x,t)\bigg)\bigg]=0.$ By applying a special B\"{a}cklund transformation and introducing arbitrary functions of the seed solutions, the abundance of the localized structures of this model are derived. By selecting the arbitrary functions appropriately, some special types of localized excitations such as dromions, dromion lattice, breathers and instantons are constructed.

Suppressing chaos by parametric perturbation at doubled frequency of periodic perturbation

Peng Jie-Hua, Tang Jia-Shi, Yu De-Jie, Hai Wen-Hua, Yan Jia-Ren
Chin. Phys. B 2003, 12 (1): 017;  doi: 10.1088/1009-1963/12/1/003
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An analysis of the chaos suppression of a nonlinear elastic beam (NLEB) is presented. In terms of modal transformation the equation of NLEB is reduced to the Duffing equation. It is shown that the chaotic behaviour of the NLEB is sensitively dependent on the parameters of perturbations and initial conditions. By adjusting the frequency of parametric perturbation to twice that of the periodic one and the amplitude of parametric perturbation to the same as the periodic one, the chaotic region of the nonlinear elastic beam driven by periodic force can be greatly suppressed.

Global exponential convergence analysis of delayed cellular neural networks

Zhang Qiang, Ma Run-Nian, Wang Chao, Xu Jin
Chin. Phys. B 2003, 12 (1): 022;  doi: 10.1088/1009-1963/12/1/004
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Some sufficient criteria have been established to ensure the global exponential stability of delayed cellular neural networks by using an approach based on delay differential inequality. Compared with the method of Lyapunov functionals as in most previous studies, our method is simpler and more effective for a stability analysis of delayed system. Some previously established results in the literature are shown to be special cases of the present result.

The equivalence between B-W and K-G band R-S equations

Huang Shi-Zhong, Ruan Tu-Nan, Wu Ning, Zheng Zhi-Peng
Chin. Phys. B 2003, 12 (1): 025;  doi: 10.1088/1009-1963/12/1/005
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The equivalence between the Bargmann--Wigner (B-W) equations and the Klein--Gordon (K-G) equations for integral spin, and the Rarita--Schwinger (R-S) equations for half integral spin is established by explicit derivation, starting from the lowest spin cases. It is demonstrated that all the constraints or subsidiary conditions imposed on the K-G or R-S equations are included in the B-W equations.

New amplitude equation of single-mode laser

Zhang Li, Cao Li, Wu Da-Jin
Chin. Phys. B 2003, 12 (1): 033;  doi: 10.1088/1009-1963/12/1/006
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The white-gain model and the white-loss model of a single-mode laser are investigated in the presence of cross-correlations between the real and imaginary parts of quantum noise as well as pump noise. It was found that, like the white cubic model (2001 Chin. Phys. Lett. 18 370), the amplitude equations are all decoupled from the phase equations for the two models, and the same novel term appears in the amplitude equations of the two models. So we can put the amplitude equations of all the models into a general form, that is, the new amplitude equation. We further use this new amplitude equation to study specifically the stationary properties of the laser intensity for the white-gain model.

The probe gain with and without inversion in a four-level atomic model: light amplification at a short wavelength

Wu Jin-Hui, Wang Deng-Pan, Zhang Hui-Fang, Xiao Zhi-Hong, Gao Jin-Yue
Chin. Phys. B 2003, 12 (1): 039;  doi: 10.1088/1009-1963/12/1/007
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We propose a new four-level atomic model for achieving light amplification at a short wavelength, where direct incoherent pumping into the top level is avoided by the advantage of coherent pumping. In this model, the lower level of the probe transition is an excited state but not the usual ground state. By analytical as well as numerical calculations, we find that the probe gain, either with or without population inversion, which depends on the relation between spontaneous decay rates $\g_{42}$ and $\g_{21}$, can be achieved with proper parameters. We note that the Raman scattering gain always plays an important role in achieving the probe amplification.

The effect of degenerate atomic levels on the field state dissipation in two-photon Jaynes--Cummings model

Zhou Ling, Song He-Shan, Li Chong, Guo Yan-Qing
Chin. Phys. B 2003, 12 (1): 045;  doi: 10.1088/1009-1963/12/1/008
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The dissipation of the field in the two-photon Jaynes--Cummings model (JCM) with degenerate atomic levels was studied. The initial degenerate atomic state affects the field coherence loss. When the degenerate atom is initially in an equal probability superposition state, the field coherence loss is smallest. It is found that the degeneracy of the atomic level increases the period of entanglement between the atom and the field. When the degeneracy was considered, the coherence properties of the field could be affected by the reservoir qualitatively, if a nonlinear two-photon process is involved. This is different from the dissipation of one-photon JCM with degenerate atomic levels.

Quantum nondemolition measurement of photon-number distribution for a weak cavity field with resonant atoms

Zheng Shi-Biao
Chin. Phys. B 2003, 12 (1): 051;  doi: 10.1088/1009-1963/12/1/009
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We propose a quantum nondemolition measurement of the photon-number distribution for a weak cavity field with no more than two photons. The scheme is based on the resonant interaction of atoms with the cavity field, and thus the required interaction time is much shorter than that using dispersive interaction. This is important in view of decoherence. Our scheme can also be used to generate even and odd coherent states for a weak cavity field with resonant atoms.

Characteristics of ultrafast K line hard x-ray source from femtosecond terawatt laser-produced plasma

Chen Min, Chen Jian-Wen, Gao Hong-Yi, Lu Pei-Xiang, Xu Zhi-Zhan
Chin. Phys. B 2003, 12 (1): 055;  doi: 10.1088/1009-1963/12/1/010
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Theoretical studies and analytical scalings were carried out to find the optimized laser parameters and target conditions so that ultrashort hard x-ray pulses and high x-ray power could be achieved. The dependence of laser intensity and wavelength on the yield of $K$-shell x-ray emission was studied. We propose an optimal design for a foil target for producing high-yield hard x-ray pulses of customizing duration.

Numerical simulation for thermohaline multiple equilibrant system in non-rectangular domains

Zhan Jie-Min, Li Yok-Sheung
Chin. Phys. B 2003, 12 (1): 060;  doi: 10.1088/1009-1963/12/1/011
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In this paper, incompressible, double-diffusive convection is simulated using finite-difference schemes. The Navier--Stokes equations are expressed in terms of stream function and vorticity. Because of the existence of large velocity, temperature and salinity gradients in boundary layers, a boundary-fitted coordinate system is used to concentrate the grid points near the wall and fit complex boundaries. The finite-difference methods used include the high-order accurate upwind difference scheme. It is shown that the scheme is a good candidate for direct simulations of double-diffusive convection flows. The proposed method is first applied to symmetry breaking and overturning states in thermohaline-driven flows in trapezoid basins. The basic phenomena agree well with those by Dijkstra and Molemaker (1997 {\em J. Fluid Mech.} {\bf 331} 169) and Quon and Ghil (1992 {\em J. Fluid Mech.} {\bf 245} 449), but symmetry breaking and overturning states can occur in an asymmetric geometrical region without perturbations. Then the method is applied to double-diffusive convections in a cavity with opposing horizontal temperature and concentration gradients at large thermal ($Rt$), solutal ($Rs$) Rayleigh numbers and Lewis number. There are three straight sides and a sine curve side in the cavity. Basically, numerical results are in agreement with those of Lee and Hyun (1990 {\em Int. J. Heat Mass Transfer} {\bf 33} 1619) qualitatively, but eddies mixing in the top left-hand corner near the curved wall affects the layered structure.

Lattice-BGK simulation of a two-dimensional channel flow around a square cylinder

Guo Wei-Bin, Wang Neng-Chao, Shi Bao-Chang, Guo Zhao-Li
Chin. Phys. B 2003, 12 (1): 067;  doi: 10.1088/1009-1963/12/1/012
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The confined flow around a square cylinder mounted inside a two-dimensional channel (blockage ratio $\be=1/8$) was investigated in detail by a newly developed incompressible nonuniform lattice-BGK model. It is found that the vortex shedding behind the cylinder induces periodicity in the flow field, and the periodicity of the flow will lose for $Re>$300. A detailed analysis for a range of Reynolds numbers between 1 and 500 was presented. Quantitative comparisons with other methods show that the model gives accurate results for complex flows.

Nanocrystalline silicon films prepared by laser-induced crystallization

Fu Guang-Sheng, Yu Wei, Li She-Qiang, Hou Hai-Hong, Peng Ying-Cai, Han Li
Chin. Phys. B 2003, 12 (1): 075;  doi: 10.1088/1009-1963/12/1/013
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The excimer laser-induced crystallization technique has been used to investigate the preparation of nanocrystalline silicon (nc-Si) from amorphous silicon ($\al$-Si) thin films on silicon or glass substrates. The $\al$-Si films without hydrogen grown by pulsed-laser deposition are chosen as precursor to avoid the problem of hydrogen effluence during annealing. Analyses have been performed by scanning electron microscopy, atomic force microscopy, Raman scattering spectroscopy and high-resolution transmission--electron microscopy. Experimental results show that silicon nanocrystals can be formed through laser annealing. The growth characters of nc-Si are strongly dependent on the laser energy density. It is shown that the volume of the molten silicon predominates essentially the grain size of nc-Si, and the surface tension of the crystallized silicon is responsible for the mechanism of nc-Si growth.

The two-dimensional alternative binary L-J system: liquid--gas phase diagram

Zhang Zhi, Chen Li-Rong
Chin. Phys. B 2003, 12 (1): 079;  doi: 10.1088/1009-1963/12/1/014
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A two-dimensional (2D) binary system without considering the Lennard-Jones (L-J) potential has been studied by using the Collins model. In this paper, we introduce the L-J potential into the 2D binary system and consider the existence of the holes that are called the ``molecular fraction". The liquid--gas phase diagram of the 2D alternative binary L-J system is obtained. The results are quite analogous to the behaviour of 3D substances.

Theoretical study on defects associated with lead vacancies in PbWO2 crystals

Yao Ming-Zhen, Gu Mu, Liu Feng-Song
Chin. Phys. B 2003, 12 (1): 084;  doi: 10.1088/1009-1963/12/1/015
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The defects associated with lead vacancies ($V_{\rm Pb}$) in lead tungstate crystals (PbWO$_4$) are investigated by the relativistic self-consistent discrete variational embedded cluster method. We focus on the density of states and the effect of $V_{\rm Pb}$ on surroundings. The results show that the existence of $V_{\rm Pb}$ can diminish the bandwidth of WO$_4^{ \ 2-}$ group, however, it can neither produce O$^-$ and Pb$^{3+}$ ions nor result in absorptions at 350 and 420\,nm. The charge balance of $V_{\rm P\!b}$ may be evenly compensated by the surrounding oxygen ions.

Theoretical investigation of incomplete ionization of dopants in uniform and ion-implanted 4H-SiC MESFETs

Wang Shou-Guo, Zhang Yi-Men, Zhang Yu-Ming
Chin. Phys. B 2003, 12 (1): 089;  doi: 10.1088/1009-1963/12/1/016
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The effects of incomplete ionization of nitrogen in 4H-SiC have been investigated. Poisson's equation is numerically analysed by considering the effects of Poole--Frenkel, and the effects of the potential on $N^+_\dd$ (the concentration of ionized donors) and $n$ (the concentration of electrons). The pinch-off voltages of the uniform and the ion-implanted channels of 4H-SiC metal-semiconductor field-effect transistors (MESFETs) and the capacitance of the gate are given at different temperatures. Both the Poole--Frenkel effect and the potential have influence on the pinch-off voltage $V_{\rm p}$ of 4H-SiC MESFETs. Although the $C$-$V$ characteristics of the ion-implanted and the uniform channel of 4H-SiC MESFETs have a clear distinction, the effects of incomplete ionization on the $C$-$V$ characteristics are not significant.

Parameter extraction for a Ti/4H-SiC Schottky diode

Wang Shou-Guo, Zhang Yi-Men, Zhang Yu-Ming
Chin. Phys. B 2003, 12 (1): 094;  doi: 10.1088/1009-1963/12/1/017
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Based on the MIS model, a simple method to extract parameters of SiC Schottky diodes is presented using the $I$-$V$ characteristics. The interface oxide capacitance $C_\i$ is extracted for the first time, as far as we know. Parameters of 4H-SiC Schottky diodes fabricated for testing in this paper are: the ideality factor $n$, the series resistance $R_{\rm s}$, the zero-field barrier height $\phi_{\rm B0}$, the interface state density $D_{\rm it}$, the interface oxide capacitance $C_\i$ and the neutral level of interface states $\phi_0$.

A method to obtain ground state electroluminescence from 1.3μm emitting InAs/GaAs quantum dots grown by molecular beam epitaxy

Kong Yun-Chuan, Zhou Da-Yong, Lan Qing, Liu Jin-Long, Miao Zhen-Hua, Feng Song-Lin, Niu Zhi-Chuan
Chin. Phys. B 2003, 12 (1): 097;  doi: 10.1088/1009-1963/12/1/018
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1.3 um emitting InAs/GaAs quantum dots (QDs) have been grown by molecular beam epitaxy and QD light emitting diodes (LEDs) have been fabricated. In the electroluminescence spectra of QD LEDs, two clear peaks corresponding to the ground state emission and the excited state emission are observed. It was found that the ground state emission could be achieved by increasing the number of QDs contained in the active region because of the state filling effect. This work demonstrates a way to control and tune the emitting wavelength of QD LEDs and lasers.

Optical resonance of metal-coated nanoshell

Diao Jia-Jie, Chen Guang-De, Xi Cong, Z Y Fan, Yuan Jin-She
Chin. Phys. B 2003, 12 (1): 0100;  doi: 10.1088/1009-1963/12/1/019
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Metal-coated nanoshell, the nanoparticle consisting of a nanometre-scale dielectric core coated with a thin metallic shell, exhibits three distinct optical resonant forms, the sphere cavity resonance (SCR), plasmon resonance (PR), and concentric dielectric sphere resonance (CDSR). The SCR, PR and CDSR of the metal-coated nanoshell reveal a geometric tunability controlled by the core radius and by the ratio of the core radius to the total radius. Classical electrodynamics and Mie scattering theory are used to treat the resonant forms and the transition state between the resonant forms. Based on previous experimental research, we present a group of resonant equations for all the resonant forms, which depend on the geometric structure of the metal-coated nanoshell.

A study on the short-wavelength and high-numerical-aperture phase-change recording

Liu Bo, Ruan Hao, Gan Fu-Xi
Chin. Phys. B 2003, 12 (1): 0107;  doi: 10.1088/1009-1963/12/1/020
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In this paper, we discuss the phase-change recording at a short-wavelength (514nm) and a high numerical aperture (0.85). Effects of recording power and pulse width on the size of the recording marks are studied. The minimum recording mark with a length of approximately 220nm has been observed. The capacity of about 17GB for a single-layer disc of a 12cm diameter can be obtained. The maximum carrier-to-noise ratio reaches 45dB at a writing power of 13--14mW.
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