Table of contents

20 December 2006, Volume 15 Issue 12 Previous issue    Next issue

GENERAL

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The derivative-dependent functional variable separation for the evolution equations Zhang Shun-Li(张顺利), Lou Sen-Yue(楼森岳), and Qu Chang-Zheng(屈长征) Chinese Physics, 2006, 15 (12):  2765-2776.  DOI: 10.1088/1009-1963/15/12/001 Abstract ( 1450 )   PDF (145KB) ( 817 )   This paper studies variable separation of the evolution equations via the generalized conditional symmetry. To illustrate, we classify the extended nonlinear wave equation $u_{tt}=A(u, u_x)u_{xx}+B(u,u_x, u_t)$ which admits the derivative-dependent functional separable solutions DDFSSs). We also extend the concept of the DDFSS to cover other variable separation approaches.

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Integrating factors and conservation theorems of constrained Birkhoffian systems Qiao Yong-Fen(乔永芬), Zhao Shu-Hong(赵淑红), and Li Ren-Jie(李仁杰) Chinese Physics, 2006, 15 (12):  2777-2781.  DOI: 10.1088/1009-1963/15/12/002 Abstract ( 1300 )   PDF (100KB) ( 489 )   In this paper the conservation theorems of the constrained Birkhoffian systems are studied by using the method of integrating factors. The differential equations of motion of the system are written. The definition of integrating factors is given for the system. The necessary conditions for the existence of the conserved quantity for the system are studied. The conservation theorem and its inverse for the system are established. Finally, an example is given to illustrate the application of the results.

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Immunization for scale-free networks by random walker Hu Ke(胡柯) and Tang Yi(唐翌) Chinese Physics, 2006, 15 (12):  2782-2787.  DOI: 10.1088/1009-1963/15/12/003 Abstract ( 1590 )   PDF (173KB) ( 665 )   Based on the random walk and the intentional random walk, we propose two types of immunization strategies which require only local connectivity information. On several typical scale-free networks, we demonstrate that these strategies can lead to the eradication of the epidemic by immunizing a small fraction of the nodes in the networks. Particularly, the immunization strategy based on the intentional random walk is extremely efficient for the assortatively mixed networks.

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Noether's theorem and one-step corrections method for holonomic system Shang Mei(尚玫) and Chen Xiang-Wei(陈向炜) Chinese Physics, 2006, 15 (12):  2788-2791.  DOI: 10.1088/1009-1963/15/12/004 Abstract ( 1427 )   PDF (105KB) ( 434 )   In this paper, a new computational method for improving the accuracy of numerically computed solutions is introduced. The computational method is based on the one-step method and conserved quantities of holonomic systems are considered as kinematical constraints in this method.

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Noether--Lie symmetry and conserved quantities of mechanical system in phase space Fang Jian-Hui(方建会), Liao Yong-Pan(廖永潘), Ding Ning(丁宁), and Wang Peng(王鹏) Chinese Physics, 2006, 15 (12):  2792-2795.  DOI: 10.1088/1009-1963/15/12/005 Abstract ( 1608 )   PDF (92KB) ( 514 )   In this paper, a new kind of symmetry and its conserved quantities of a mechanical system in phase space are studied. The definition of this new symmetry, i.e. a Noether--Lie symmetry, is presented, and the criterion of this symmetry is also given. The Noether conserved quantity and the generalized Hojman conserved quantity of the Noether--Lie symmetry of the system are obtained. The Noether--Lie symmetry contains the Noether symmetry and the Lie symmetry, and has more generalized significance.

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A set of Boussinesq-type equations for interfacial internal waves in two-layer stratified fluid Song Jin-Bao(宋金宝) Chinese Physics, 2006, 15 (12):  2796-2803.  DOI: 10.1088/1009-1963/15/12/006 Abstract ( 1341 )   PDF (126KB) ( 513 )   Many new forms of Boussinesq-type equations have been developed to extend the range of applicability of the classical Boussinesq equations to deeper water in the study of the surface waves. One approach was used by Nwogu (1993. J. Wtrw. Port Coastal and Oc. Eng. 119, 618--638) to improve the linear dispersion characteristics of the classical Boussinesq equations by using the velocity at an arbitrary level as the velocity variable in derived equations and obtain a new form of Boussinesq-type equations, in which the dispersion property can be optimized by choosing the velocity variable at an adequate level. In this paper, a set of Boussinesq-type equations describing the motions of the interfacial waves propagating alone the interface between two homogeneous incompressible and inviscid fluids of different densities with a free surface and a variable water depth were derived using a method similar to that used by Nwogu (1993. J. Wtrw. Port Coastal and Oc. Eng. 119, 618--638) for surface waves. The equations were expressed in terms of the displacements of free surface and density-interface, and the velocity vectors at arbitrary vertical locations in the upper layer and the lower layer (or depth-averaged velocity vector across each layer) of a two-layer fluid. As expected, the equations derived in the present work include as special cases those obtained by Nwogu (1993, J. Wtrw. Port Coastal and Oc. Eng. 119, 618-638) and Peregrine (1967, J. Fluid Mech. 27, 815-827) for surface waves when the density of the upper fluid is taken as zero.

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A new method of new exact solutions and solitary wave-like solutions for the generalized variable coefficients Kadomtsev--Petviashvili equation Mao Jie-Jian(毛杰健) and Yang Jian-Rong(杨建荣) Chinese Physics, 2006, 15 (12):  2804-2808.  DOI: 10.1088/1009-1963/15/12/007 Abstract ( 1463 )   PDF (96KB) ( 748 )   Using the solution of general Korteweg--de Vries (KdV) equation, the solutions of the generalized variable coefficient Kadomtsev--Petviashvili (KP) equation are constructed, and then its new solitary wave-like solution and Jacobi elliptic function solution are obtained.

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The Jacobi elliptic function-like exact solutions to two kinds of KdV equations with variable coefficients and KdV equation with forcible term Taogetusang(套格图桑) and Sirendaoerji(斯仁到尔吉) Chinese Physics, 2006, 15 (12):  2809-2818.  DOI: 10.1088/1009-1963/15/12/008 Abstract ( 1646 )   PDF (117KB) ( 714 )   By use of an auxiliary equation and through a function transformation, the Jacobi elliptic function wave-like solutions, the degenerated soliton-like solutions and the triangle function wave solutions to two kinds of Korteweg--de Vries (KdV) equations with variable coefficients and a KdV equation with a forcible term are constructed with the help of symbolic computation system Mathematica, where the new solutions are also constructed.

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A method of solving the stiffness problem in Biot's poroelastic equations using a staggered high-order finite-difference Zhao Hai-Bo(赵海波), Wang Xiu-Ming(王秀明), and Chen Hao(陈浩) Chinese Physics, 2006, 15 (12):  2819-2827.  DOI: 10.1088/1009-1963/15/12/009 Abstract ( 1359 )   PDF (1013KB) ( 416 )   In modelling elastic wave propagation in a porous medium, when the ratio between the fluid viscosity and the medium permeability is comparatively large, the stiffness problem of Biot's poroelastic equations will be encountered. In the paper, a partition method is developed to solve the stiffness problem with a staggered high-order finite-difference. The method splits the Biot equations into two systems. One is stiff, and solved analytically, the other is nonstiff, and solved numerically by using a high-order staggered-grid finite-difference scheme. The time step is determined by the staggered finite-difference algorithm in solving the nonstiff equations, thus a coarse time step may be employed. Therefore, the computation efficiency and computational stability are improved greatly. Also a perfect by matched layer technology is used in the split method as absorbing boundary conditions. The numerical results are compared with the analytical results and those obtained from the conventional staggered-grid finite-difference method in a homogeneous model, respectively. They are in good agreement with each other. Finally, a slightly more complex model is investigated and compared with related equivalent model to illustrate the good performance of the staggered-grid finite-difference scheme in the partition method.

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Entanglement in the supermolecular dimer [Mn4]2 Xu Chang-Tan(许长谭), Chen Gang(陈刚), He Ming-Ming(贺明明), and Liang Jiu-Qing(梁九卿) Chinese Physics, 2006, 15 (12):  2828-2834.  DOI: 10.1088/1009-1963/15/12/010 Abstract ( 1361 )   PDF (284KB) ( 486 )   This paper investigates the entanglement in the supermolecular dimer [Mn4]2 consisting of a pair of single molecular magnets with antiferromagnetic exchange-coupling J. The conventional von Neumann entropy as a function of the exchange-coupling is calculated explicitly for all eigenstates with the quantum number range from M=M1+M2=-9 to 0. It is shown that the von Neumann entropy is not a monotonic function of the coupling strength. However, it is significant that the entropy of entanglement has the maximum values and the minimum values for most eigenstates, which is extremely useful in the quantum computing. It also presents the time-evolution of entanglement from various initial states. The results are useful in the design of devices based on the entanglement of two molecular magnets.

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A new representation and probabilistic teleportation of an arbitrary and unknown N -particle state Dong Li(董莉), Xiu Xiao-Ming(修晓明), and Gao Ya-Jun(高亚军) Chinese Physics, 2006, 15 (12):  2835-2839.  DOI: 10.1088/1009-1963/15/12/011 Abstract ( 1788 )   PDF (109KB) ( 593 )   A new representation of an arbitrary and unknown N-particle state is presented at first. As an application, a scheme for teleporting an arbitrary and unknown N-particle state is proposed when N pairs of two-particle non-maximally entangled states are utilized as quantum channels. After Alice (sender) makes Bell-state measurement on her particles, Bob (recipient) introduces an auxiliary particle and carries out appropriate unitary transformation on his particle and the auxiliary particle depending on classical information from Alice. Then, von Neumann measurement that confirms whether the teleportation succeeds or not is performed by Bob on the auxiliary particle. In order to complete the teleportation, another N-1 times operations need to be performed which are similar to the above ones. It can be successfully realized with a certain probability which is determined by the product of the smaller coefficients of non-maximally entangled pairs. All possible unitary transformations are given in detail.

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Teleportation of atomic entangled states with a thermal cavity Zheng Xiao-Juan(郑小娟), Fang Mao-Fa(方卯发), Cai Jian-Wu(蔡建武), and Liao Xiang-Ping(廖湘萍) Chinese Physics, 2006, 15 (12):  2840-2846.  DOI: 10.1088/1009-1963/15/12/012 Abstract ( 1465 )   PDF (127KB) ( 583 )   We propose a most simple and experimentally feasible scheme for teleporting unknown atomic entangled states in driven cavity quantum electrodynamics (QED). In our scheme, the joint Bell-state measurement (BSM) is not required, and the successful probability can reach 1.0. Furthermore, the scheme is insensitive to the cavity decay and the thermal field.

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Preparation of entangled atomic states through simultaneous nonresonant atom--field interaction Chen Mei-Feng(陈美锋) Chinese Physics, 2006, 15 (12):  2847-2849.  DOI: 10.1088/1009-1963/15/12/013 Abstract ( 1234 )   PDF (85KB) ( 550 )   A scheme is proposed for generating a three-atom maximal entanglement W state. It is based on the simultaneous nonresonant interaction of atoms with a single-mode cavity field. Our scheme is insensitive to the cavity field, so the cavity field in our scheme can be initially in thermal states.

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Late-time evolution of massive Dirac fields in the Kerr background He Xi(贺喜) and Jing Ji-Liang(荆继良) Chinese Physics, 2006, 15 (12):  2850-2855.  DOI: 10.1088/1009-1963/15/12/014 Abstract ( 1150 )   PDF (195KB) ( 414 )   The late-time tail of massive Dirac fields in Kerr spacetime is investigated by using the black hole Green function. It is shown that in the intermediate late times there are two kinds of new properties. The one is that the asymptotic behaviour of the massive Dirac fields is dominated by a decaying tail without any oscillation, which is different from the oscillatory decaying tails of the massive scalar field; the other is that the dumping exponent for the massive Dirac field depends not only on the multiple number of the wave mode and the mass of the Dirac particle but also on the rotating parameter of the black hole.

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The instability conditions of a weakly interacting Fermi gas trapped in weak magnetic field Men Fu-Dian(门福殿) and Liu Hui(刘慧) Chinese Physics, 2006, 15 (12):  2856-2860.  DOI: 10.1088/1009-1963/15/12/015 Abstract ( 1511 )   PDF (108KB) ( 570 )   In this paper the analytical expression of free energy expressed by small parameter r of a weakly interacting Fermi gas trapped in weak magnetic field is derived by using `the maximum approximation' method and the ensemble theory. Based on the derived expression, the exact instability conditions of a weakly interacting Fermi gas trapped in weak magnetic field at both high and low temperatures are given. From the instability conditions we get the following two results. (1) At the whole low-temperature extent, whether the interactions are repulsive or attractive with $\alpha n+4\varepsilon_{\rm F}$ (n and $\varepsilon_{\rm F}$ denote the particle-number density and the Fermi energy respectively, $\alpha=4\pi a\hbar^2/m$, and $a$ is s-wave scattering length) positive, there is a lower-limit magnetic field of instability; in addition, there is an upper-limit magnetic field for the system of attractive interactions with $(\alpha n+4\varepsilon_{\rm F}/3)$ negative. (2) At the whole high-temperature extent, the system with repulsive interactions is always stable, but for the system with attractive interactions, the greater the scattering length of attractive interactions $|a|$ is, the stronger the magnetic field is and the larger the particle-number density is, the bigger the possibility of instability in the system will be.

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Statistical fluctuations in a saturation laser model with correlated noises Chen Shi-Bo(陈世波) and Mei Dong-Cheng(梅冬成) Chinese Physics, 2006, 15 (12):  2861-2866.  DOI: 10.1088/1009-1963/15/12/016 Abstract ( 1331 )   PDF (164KB) ( 456 )   We study the effects of correlations between quantum and pump noises on fluctuations of the laser intensity in a saturation laser model. An approximative Fokker--Planck equation and analytic expressions of the steady-state probability distribution function (SPD) of the laser system are derived. Based on the SPD, the normalized mean, the normalized variance, and the normalized skewness of the steady-state laser intensity are calculated numerically. The results indicate that (i) the correlation strength $\lambda$ of correlated noises always enhances the fluctuation of laser intensity; (ii) the correlation time $\tau$ of correlated noises strengthens the fluctuation of laser intensity for the below-threshold case but $\tau$ weakens it for the above-threshold case.

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Parameter-induced stochastic resonance with a periodic signal Li Jian-Long(李建龙) and Xu Bo-Hou(徐博侯) Chinese Physics, 2006, 15 (12):  2867-2871.  DOI: 10.1088/1009-1963/15/12/017 Abstract ( 1622 )   PDF (471KB) ( 650 )   In this paper conventional stochastic resonance (CSR) is realized by adding the noise intensity. This demonstrates that tuning the system parameters with fixed noise can make the noise play a constructive role and realize parameter-induced stochastic resonance (PSR). PSR can be interpreted as changing the intrinsic characteristic of the dynamical system to yield the cooperative effect between the stochastic-subjected nonlinear system and the external periodic force. This can be realized at any noise intensity, which greatly differs from CSR that is realized under the condition of the initial noise intensity not greater than the resonance level. Moreover, it is proved that PSR is different from the optimization of system parameters.

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A new chaotic system and its circuit realization Wang Guang-Yi(王光义), Qiu Shui-Sheng(丘水生), Li Hong-Wei (李宏伟), Li Cai-Fen(李彩芬), and Zheng Yan(郑艳) Chinese Physics, 2006, 15 (12):  2872-2877.  DOI: 10.1088/1009-1963/15/12/018 Abstract ( 1708 )   PDF (1075KB) ( 1002 )   Based on the Lü system, a new chaotic system is constructed, which can generate a Lorenz-like attractor, Chen-like attractor, Lü-like attractor and new attractor when its parameters are chosen appropriately. The detailed dynamical behaviours of this system are also investigated, including equilibria and stability, bifurcations, and Lyapunov exponent spectrum. Moreover, a novel analogue circuit diagram is designed for the verification of various attractors.

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A new multi-scroll chaotic system Wang Fa-Qiang(王发强) and Liu Chong-Xin(刘崇新） Chinese Physics, 2006, 15 (12):  2878-2882.  DOI: 10.1088/1009-1963/15/12/019 Abstract ( 1665 )   PDF (1422KB) ( 692 )   This paper proposes a new simple autonomous chaotic system which can generate multi-scroll chaotic attractors. The characteristic of this new multi-scroll chaotic system is that the $4n+2m+4$-scroll chaotic attractors are generated easily with $n$ and $m$ varying under $n \leq m$. Various number of scroll chaotic attractors are illustrated not only by computer simulation but also by the realization of an electronic circuit experiment on EWB (Electronics Workbench).

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Perfect synchronization of chaotic systems: A controllability perspective Sun Ming-Xuan(孙明轩), He Xiong-Xiong(何熊熊), and Yu Li(俞立) Chinese Physics, 2006, 15 (12):  2883-2889.  DOI: 10.1088/1009-1963/15/12/020 Abstract ( 1317 )   PDF (209KB) ( 555 )   This paper presents a synchronization method, motivated from the constructive controllability analysis, for two identical chaotic systems. This technique is applied to achieve perfect synchronization for Lorenz systems and coupled dynamo systems. It turns out that states of the drive system and the response system are synchronized within finite time, and the reaching time is independent of initial conditions, which can be specified in advance. In addition to the simultaneous synchronization, the response system is synchronized un-simultaneously to the drive system with different reaching time for each state. The performance of the resulting system is analytically quantified in the face of initial condition error, and with numerical experiments the proposed method is demonstrated to perform well.

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Impulsive control for synchronization of a nonlinear Rössler's chaotic systems Li Yang(李阳), Liao Xiao-Feng(廖晓峰), Li Chuan-Dong(李传东), and Chen Guo(陈果) Chinese Physics, 2006, 15 (12):  2890-2893.  DOI: 10.1088/1009-1963/15/12/021 Abstract ( 1428 )   PDF (227KB) ( 699 )   This paper reports that an impulsive control theory for synchronization of nonlinear Rössler chaotic systems is developed. A new framework for impulsive synchronization between such chaotic systems is presented, which makes the synchronization error system a linear impulsive control system. Therefore, it is easy to derive the impulsive synchronization law. The proposed impulsive control scheme is illustrated by nonlinear R?ssler chaotic systems and the simulation results demonstrate the effectiveness of the method.

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Open-loop frequency response for a chaotic masking system Huang Xian-Gao(黄显高), Yu Pei, and Huang Wei(黄伟) Chinese Physics, 2006, 15 (12):  2894-2901.  DOI: 10.1088/1009-1963/15/12/022 Abstract ( 1257 )   PDF (178KB) ( 542 )   In this paper, a new numerical simulation approach is proposed for the study of open-loop frequency response of a chaotic masking system. Using Chua's circuit and the Lorenz system as illustrative examples, we have shown that one can employ chaos synchronization to separate the feedback network from a chaotic masking system, and then use numerical simulation to obtain the open-loop synchronization response, the phase response, and the amplitude response of a chaotic masking system. Based on the analysis of the frequency response, we have also proved that changing the amplitude of the exciting (input) signal within normal working domain does not influence the frequency response of the chaotic masking system. The new numerical simulation method developed in this paper can be extended to consider the open-loop frequency response of other systems described by differential or difference equations.

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Broadband amplified spontaneous emission from Er3+-doped single-mode tellurite fibre Chen Dong-Dan(陈东丹), Zhang Qin-Yuan(张勤远), Liu Yue-Hui(刘粤惠), Xu Shan-Hui(徐善辉), Yang Zhong-Min(杨中民), Deng Zai-De(邓再德), and Jiang Zhong-Hong(姜中宏) Chinese Physics, 2006, 15 (12):  2902-2905.  DOI: 10.1088/1009-1963/15/12/023 Abstract ( 1342 )   PDF (260KB) ( 531 )   This paper reports on the fabrication and characterization of a newly erbium-doped single-mode tellurite glass-fibre applicable for 1.5-μm optical amplifiers. A very broad erbium amplified spontaneous emission in the range 1450--1650nm from erbium-doped single-mode tellurite glass-fibre is obtained upon excitation of a 980-nm laser diode. The effects of the length of glass-fibre and the pumping power of laser diode on the amplified spontaneous emission are discussed. The result indicates that the tellurite glass-fibre is a promising candidate for designing fibre-optic amplifiers and lasers.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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On the mass of the s$\bar{s}$ member of the 13D1 meson nonet Feng Xue-Chao(冯学超), Wei Ke-Wei(魏科伟), and Zhang Gui-Jie(张贵杰) Chinese Physics, 2006, 15 (12):  2906-2908.  DOI: 10.1088/1009-1963/15/12/024 Abstract ( 1212 )   PDF (96KB) ( 461 )   In the framework of Regge phenomenology and meson--meson mixing, this paper estimates the mass of isoscalar state (s$\bar{\rm s}$) of the 13D1 meson nonet, and the results given by two different approaches are 1735.51$\pm$59MeV and 1730.29$\pm$46.8MeV.

ATOMIC AND MOLECULAR PHYSICS

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Laser-phase determination methods and transfer equations for direct temporal structure measure- ments of atto- and femtosecond XUV pulses Ge Yu-Cheng(葛愉成) Chinese Physics, 2006, 15 (12):  2909-2919.  DOI: 10.1088/1009-1963/15/12/025 Abstract ( 1318 )   PDF (1784KB) ( 606 )   In this paper the laser-phase determination methods and transfer equations are presented to directly reconstruct the detailed temporal structures of ultra-short extreme ultraviolet (xuv) pulses from the measured photoelectron energy spectra (PES). Each transfer equation includes one of PID (proportional-integral-differential) terms of PES. The intensity and instantaneous frequency of attosecond xuv can be retrieved from the integral term of PES. The intensity profiles of narrow bandwidth atto- and femtosecond xuvs can be rebuilt from the proportional and differential terms of PES respectively. The methods and equations may be used to improve time resolutions in measuring ultrashort pulses.

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Collisional quantum interference on rotational energy transfer: Physical interpretation of the differential interference angle Li Yong-Qing (李永庆), Li Jian(李健), and Ma Feng-Cai(马凤才) Chinese Physics, 2006, 15 (12):  2920-2927.  DOI: 10.1088/1009-1963/15/12/026 Abstract ( 1111 )   PDF (150KB) ( 433 )   Collisional quantum interference (CQI) on the intramolecular rotational energy transfer is observed in an experiment with a static cell, and the integral interference angles are measured. To obtain more accurate information, an experiment with a molecular beam is carried out, and thereby the relationship between the differential interference angle and the scattering angle is obtained. Based on the first-Born approximation of time-dependent perturbation theory, the theoretical model of CQI is developed in an atom--diatom system in the condition of the molecular beam, with the long-range interaction potential taken into account. The method of measuring correctly the differential interference angle is presented. The tendencies of the differential interference angle changing with the impact parameter and relative velocity are discussed. The theoretical model presented here is important for understanding or performing the experiment in the molecular beam.

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Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B1$\Pi$ of 7LiH Shi De-Heng(施德恒), Liu Yu-Fang(刘玉芳), Sun Jin-Feng(孙金锋), Zhu Zun-Lüe(朱遵略) and Yang Xiang-Dong(杨向东) Chinese Physics, 2006, 15 (12):  2928-2933.  DOI: 10.1088/1009-1963/15/12/027 Abstract ( 1335 )   PDF (138KB) ( 541 )   The reasonable dissociation limit of the second excited singlet state B1$\Pi$ of 7LiH molecule is obtained. The accurate dissociation energy and equilibrium geometry of the B1$\Pi$ state are calculated using a symmetry-adapted-cluster configuration--interaction method in full active space. The whole potential energy curve for the B1$\Pi$ state is obtained over the internuclear distance ranging from about 0.10nm to 0.54nm, and has a least-square fit to the analytic Murrell--Sorbie function form. The vertical excitation energy is calculated from the ground state to the B1$\Pi$ state and compared with previous theoretical results. The equilibrium internuclear distance obtained by geometry optimization is found to be quite different from that obtained by single-point energy scanning under the same calculation condition. Based on the analytic potential energy function, the harmonic frequency value of the B1$\Pi$ state is estimated. A comparison of the theoretical calculations of dissociation energies, equilibrium interatomic distances and the analytic potential energy function with those obtained by previous theoretical results clearly shows that the present work is more comprehensive and in better agreement with experiments than previous theories, thus it is an improvement on previous theories.

CLASSICAL AREAS OF PHENOMENOLOGY

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Mode hopping in single-mode microchip Nd:YAG lasers induced by optical feedback Tan Yi-Dong(谈宜东), Zhang Shu-Lian(张书练), Wan Xin-Jun(万新军), and Cheng Xiang(程翔) Chinese Physics, 2006, 15 (12):  2934-2941.  DOI: 10.1088/1009-1963/15/12/028 Abstract ( 1261 )   PDF (374KB) ( 593 )   The mode hopping phenomenon induced by optical feedback in single-mode microchip Nd:YAG lasers is presented. With optical feedback, mode hopping strongly depends on two factors: the ratio of external cavity length to intra-cavity length, and initial gains of the two hopping modes. When external cavity length equals an integral multiple of intra-cavity length, there is almost no mode hopping. However, if the external cavity length does not equal an integral multiple of intra-cavity length, mode hopping occurs. The ratio of external cavity length to intra-cavity length determines the position of two-mode hopping. The initial gains of the two hopping modes determine the corresponding peak values and oscillating periods of them in the intensity modulation curves.

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Hanbury-Brown and Twiss type double-slit interference with photorefractive fanning light Xiong Jun(熊俊), Li Hong-Guo(李洪国), Sun Xu-Juan(孙绪娟), Lin Lu-Fang(林露芳), and Wang Kai-Ge(汪凯戈) Chinese Physics, 2006, 15 (12):  2942-2946.  DOI: 10.1088/1009-1963/15/12/029 Abstract ( 1171 )   PDF (436KB) ( 599 )   This paper reports that when an intense extraordinary-polarized laser beam illuminates a photorefractive BaTiO3 crystal, the dynamic beam fanning light is formed to be a thermal-like light source with a long correlation time and wide spectral bandwidth. The experimental results of the first- and second-order double-slit interference with such photorefractive fanning light source, can be understood with the theoretical simulation in terms of Hanbury-Brown and Twiss effect.

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Entangling two single-mode Gaussian states by use of a beam splitter Li Hong-Rong(李宏荣), Li Fu-Li(李福利), and Yang Yang(杨杨) Chinese Physics, 2006, 15 (12):  2947-2952.  DOI: 10.1088/1009-1963/15/12/030 Abstract ( 1283 )   PDF (967KB) ( 630 )   Considering two light beams which are in general single-mode Gaussian states and incident on input ports of an ideal beam splitter, respectively, this paper investigates how separability and entanglement of the output lights depend on degrees of nonclassicality and purities of the input states. The minimum and maximum amounts of attainable entanglement in the output state are found.

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Entanglement concentration for multi-atom GHZ class state via cavity QED Jiang Chun-Lei(姜春蕾), Fang Mao-Fa(方卯发), and Zheng Xiao-Juan(郑小娟) Chinese Physics, 2006, 15 (12):  2953-2958.  DOI: 10.1088/1009-1963/15/12/031 Abstract ( 1323 )   PDF (126KB) ( 532 )   In this paper, we propose a physical scheme to concentrate non-maximally entangled atomic pure states by using atomic collision in a far-off-resonant cavity. The most distinctive advantage of our scheme is that the non-maximally entangled atoms may be far from or near each other and their degree of entanglement can be maximally amplified. The photon-number-dependent parts in the effective Hamiltonian are cancelled with the assistance of a strong classical field, thus the scheme is insensitive to both the cavity decay and the thermal field.

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Micromechanical tunable vertical-cavity surface-emitting lasers Guan Bao-Lu(关宝璐), Guo Xia(郭霞), Deng Jun(邓军), Qu Hong-Wei(渠红伟), Lian Peng(廉鹏), Dong Li-Min(董立敏), Chen Min(陈敏), and Shen Guang-Di(沈光地) Chinese Physics, 2006, 15 (12):  2959-2962.  DOI: 10.1088/1009-1963/15/12/032 Abstract ( 1213 )   PDF (711KB) ( 565 )   We report the study on a short wavelength-tunable vertical-cavity surface-emitting laser utilizing a monolithically integrated bridge tuning microelectromechanical system. A deformable-bridge top mirror suspended above an active region is utilized. Applied bridge-substrate bias produces an electrostatic force which reduces the spacing of air-gap and tunes the resonant wavelength toward a shorter wavelength (blue-shift). Good laser characteristics are obtained: such as continuous tuning ranges over 11 nm near 940 nm for 0--9 V tuning bias, the peak output power near 1 mW and the full-width-half-maximum limited to approximately 3.2--6.8 nm. A detailed simulation of the micromechanical and optical characteristics of these devices is performed, and the ratio of bridge displacement to wavelength shift has been found to be 3:1.

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Temperature-related performance of Yb3+:YAG disk lasers and optimum design for diamond cooling Cao Ding-Xiang(曹丁象), Yu Hai-Wu(於海武), Zheng Wan-Guo(郑万国), He Shao-Bo(贺少勃), and Wang Xiao-Feng(王晓峰) Chinese Physics, 2006, 15 (12):  2963-2969.  DOI: 10.1088/1009-1963/15/12/033 Abstract ( 1178 )   PDF (773KB) ( 578 )   In this paper the temperature-related performances of the Yb3+:YAG disc laser has been investigated based on quasi-three level rate equation model. A compact diamond window cooling scheme also has been demonstrated. In this cooling scheme, laser disc is placed between two thin discs of single crystal synthetic diamond, the heat transfer from Yb3+:YAG to the diamond, in the direction of the optical axis, and then rapidly conducted radically outward through the diamond to the cooling water at the circumference of the diamond/Yb3+:YAG assembly. Simulation results show that increasing the thickness of the diamond and the overlap-length (between diamond and water) decreases the disc temperature. Therefore a 0.3--0.5mm thick diamond window with the overlap-length of 1.5--2.0mm will provide acceptable cost effective cooling, e.g., with a pump intensity of 15kW/cm2 and repetitive rate of 10Hz, to keep the maximum temperature of the lasing disc below a reasonable value (310K), the heat exchange coefficient of water should be about 3000 W/m2K.

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(3+1)-dimensional nonlinear propagation equation for ultrashort pulsed beam in left-handed material Hu Yong-Hua(胡勇华), Fu Xi-Quan(傅喜泉), Wen Shuang-Chun(文双春), Su Wen-Hua(苏文华), and Fan Dian-Yuan(范滇元) Chinese Physics, 2006, 15 (12):  2970-2976.  DOI: 10.1088/1009-1963/15/12/034 Abstract ( 1310 )   PDF (167KB) ( 642 )   In this paper a comprehensive framework for treating the nonlinear propagation of ultrashort pulse in metamaterial with dispersive dielectric susceptibility and magnetic permeability is presented. Under the slowly-evolving-wave approximation, a generalized (3+1)-dimensional wave equation first order in the propagation coordinate and suitable for both right-handed material (RHM) and left-handed material (LHM) is derived. By the commonly used Drude dispersive model for LHM, a (3+1)-dimensional nonlinear Schr?dinger equation describing ultrashort pulsed beam propagation in LHM is obtained, and its difference from that for conventional RHM is discussed. Particularly, the self-steeping effect of ultrashort pulse is found to be anomalous in LHM.

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The photorefractive sensitivity and the effective electron transport length in two-centre holographic recording Zhou Yu(周煜), Liu Li-Ren(刘立人), Liu De-An(刘德安), Luan Zhu(栾竹), and Yan Ai-Min(闫爱民） Chinese Physics, 2006, 15 (12):  2977-2983.  DOI: 10.1088/1009-1963/15/12/035 Abstract ( 1255 )   PDF (294KB) ( 470 )   In this paper the photorefractive sensitivity defined for single-centre holographic recording is modified to adapt two-centre holographic recording. Based on the time analytic solution of Kukhtarev equations for doubly doped crystals, the analytical expression of photorefractive sensitivity is given. For comparison with single-centre holographic recording and summing the electron competition effects between the deeper and shallower traps, an effective electron transport length is proposed, which varies with the intensity ratios of recording light to sensitive light. According to analyses in this paper, the lower photorefractive sensitivity in two-centre holographic recording is mainly due to the lower concentration of unionized dopants in the shallower centre and the lower effective electron transport length.

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Different localized states of travelling-wave convection in a rectangular container Li Guo-Dong(李国栋) and Huang Yong-Nian(黄永念) Chinese Physics, 2006, 15 (12):  2984-2988.  DOI: 10.1088/1009-1963/15/12/036 Abstract ( 1314 )   PDF (226KB) ( 451 )   We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of the rolls perpendicular to their axes. For a negative enough separation ratio, two types of quite different confined states were documented by applying different control processes. One branch of localized travelling waves survives only in a very narrow band within subcritical regime, while another branch straddles the onset of convection existing both in subcritical and supercritical regions. We elucidated that concentration field and its current are key to understand how confined convection is sustained when conductive state is absolutely unstable. The weak structures in the conducting region are demonstrated too.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Experimental characteristics of a lower hybrid wave multi-junction coupler in the HT-7 tokamak Ding Bo-Jiang(丁伯江), Shan Jia-Fang(单家方), Liu Fu-Kun(刘甫坤), Fang Yu-De(方瑜德), Wei Wei(韦维), Wu Zhen-Wei(吴振伟), Chen Zhong-Yong(陈忠勇), Xu Han-Dong(徐汉东), Wang Mao(王茂), Jiang Min(蒋敏), Zhang Gong-Rang(张公让), Huang Feng(黄峰), Zhao Yan-Ping(赵燕平), Kuang Guang-Li(匡光力), and HT-7 team Chinese Physics, 2006, 15 (12):  2989-2999.  DOI: 10.1088/1009-1963/15/12/037 Abstract ( 1318 )   PDF (528KB) ( 555 )   A phase-controlled lower hybrid wave (LHW) multi-junction (MJ) coupler (3(rows)×(columns)× (subwaveguides)) has been developed in the HT-7 tokamak. Simulations show that it is more effective for driving plasma current than an ordinary phase-controlled LHW antenna (3(rows)×12(columns)) (traditional coupler). The plasma--wave coupling experiments show that the reflection coefficient (RC) is below 10%, implying that the MJ grill can launch the wave into the plasma effectively. The effect of power spectrum launched by the MJ coupler on RC indicates that an optimal condition is requisite for a better coupling in the lower hybrid current drive (LHCD) experiments. Studies indicate that the drive efficiency of the MJ antenna is higher than that of the traditional one, which is mainly ascribed to the discrepancy in impurity concentration, plasma temperature, and spectrum directivity. An improved confinement with an electron internal transport barrier is obtained by LHCD. The analysis shows that the modified negative (low) magnetic shear and the change of radial electric field profile due to LHCD are possible factors responsible for the eITB formation.

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Simulation of radiation losses using non-coronal model on HL-2A Chen Wei(陈伟), Yang Qing-Wei(杨青巍), and Li Wei(李伟) Chinese Physics, 2006, 15 (12):  3000-3004.  DOI: 10.1088/1009-1963/15/12/038 Abstract ( 1269 )   PDF (212KB) ( 563 )   In this paper, the radiation losses of impurity on HL-2A have been simulated by assuming the profiles electron temperature and density and solving ionization rate equation under conditions of non-coronal radiation. The time required for an impurity species to establish equilibrium is proved to be sensitively dependent on the plasma electron temperature, and it is strongly correlated with the ionization state distribution during equilibrium establishment of impurity species. It is found from simulation results that the residence parameter plays an important role in the enhancement of radiation losses of plasma.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Structural classification and a binary structure model for superconductors Dong Cheng(董成) Chinese Physics, 2006, 15 (12):  3005-3013.  DOI: 10.1088/1009-1963/15/12/039 Abstract ( 1200 )   PDF (431KB) ( 678 )   Based on structural and bonding features, a new classification scheme of superconductors is proposed to classify them into three classes: three-dimensional, two-dimensional and molecule-assembled superconductors. The sandwich model' for the high-Tc cuprates is extended to a `binary structure model': i.e., the crystal structure of most superconductors can be partitioned into two parts, a superconducting active component and a supplementary component. Partially metallic covalent bonding is found to be a common feature in all superconducting active components, and the electron states of the atoms in the active components usually make a dominant contribution to the energy band near the Fermi surface. Possible directions to explore new superconductors are discussed based on the structural classification and the binary structure model.

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

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Structural and thermodynamic properties of AlB2 compound Zhou Xiao-Lin(周晓林), Liu Ke(刘科), Chen Xiang-Rong(陈向荣), and Zhu Jun(朱俊) Chinese Physics, 2006, 15 (12):  3014-3018.  DOI: 10.1088/1009-1963/15/12/040 Abstract ( 1527 )   PDF (135KB) ( 821 )   We employ a first-principles plane wave method with the relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter (HGH) scheme in the frame of DFT to calculate the equilibrium lattice parameters and the thermodynamic properties of AlB2 compound with hcp structure. The obtained lattice parameters are in good agreement with the available experimental data and those calculated by others. Through the quasi-harmonic Debye model, obtained successfully are the dependences of the normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized primitive cell volume V/V0 on pressure P, the variation of the thermal expansion $\alpha$  with pressure P and temperature T, as well as the Debye temperature $\varTheta_{\rm D}$ and the heat capacity CV on pressure P and temperature T.

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Intrinsic Hall effect and separation of Rashba and Dresselhaus spin splittings in semiconductor quantum wells Song Hong-Zhou(宋红州), Zhang Ping(张平), Duan Su-Qing(段素青), and Zhao Xian-Geng(赵宪庚) Chinese Physics, 2006, 15 (12):  3019-3025.  DOI: 10.1088/1009-1963/15/12/041 Abstract ( 1328 )   PDF (284KB) ( 692 )   We have proposed a method to separate Rashba and Dresselhaus spin splittings in semiconductor quantum wells by using the intrinsic Hall effect. It is shown that the interference between Rashba and Dresselhaus terms can deflect the electrons in opposite transverse directions with a change of sign in the macroscopic Hall current, thus providing an alternative way to determine the different contributions to the spin--orbit coupling.

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Critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume--Capel model in the presence of an applied field Yan Shi-Lei(晏世雷) and Zhu Hai-Xia(朱海霞) Chinese Physics, 2006, 15 (12):  3026-3032.  DOI: 10.1088/1009-1963/15/12/042 Abstract ( 1267 )   PDF (223KB) ( 604 )   This paper studies the critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume--Capel model (BCM) in the presence of an applied field within the effective field theory. The trajectory of tricritical point, reentrant transitions and degenerate patterns of anisotropy are obtained both for the bond and the anisotropy dilutions. The global phase diagrams demonstrate unusually reentrant phenomena. The temperature dependences of magnetization curves undergo remarkable spin glass behaviour at low temperatures, and transform from ferromagnetism to paramagnetism at high temperature in applied fields. Temperature dependence of magnetic susceptibility curve is in qualitative agreement with experimental result.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Research on the optimum hydrogenated silicon thin films for application in solar cells Lei Qing-Song(雷青松), Wu Zhi-Meng(吴志猛), Geng Xin-Hua(耿新华), Zhao Ying(赵颖), Sun Jian(孙健), and Xi Jian-Ping(奚建平) Chinese Physics, 2006, 15 (12):  3033-3038.  DOI: 10.1088/1009-1963/15/12/043 Abstract ( 992 )   PDF (185KB) ( 646 )   Hydrogenated silicon (Si:H) thin films for application in solar cells were deposited by using very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at a substrate temperature of about 170℃. The electrical, structural, and optical properties of the films were investigated. The deposited films were then applied as i-layers for p-i-n single junction solar cells. The current--voltage (I-V) characteristics of the cells were measured before and after the light soaking. The results suggest that the films deposited near the transition region have an optimum properties for application in solar cells. The cell with an i-layer prepared near the transition region shows the best stable performance.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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A hybrid quantum encoding algorithm of vector quantization for image compression Pang Chao-Yang (庞朝阳), Zhou Zheng-Wei(周正威), and Guo Guang-Can(郭光灿) Chinese Physics, 2006, 15 (12):  3039-3043.  DOI: 10.1088/1009-1963/15/12/044 Abstract ( 1412 )   PDF (328KB) ( 578 )   Many classical encoding algorithms of vector quantization (VQ) of image compression that can obtain global optimal solution have computational complexity O(N). A pure quantum VQ encoding algorithm with probability of success near 100% has been proposed, that performs operations $45\sqrt{N}$ times approximately. In this paper, a hybrid quantum VQ encoding algorithm between the classical method and the quantum algorithm is presented. The number of its operations is less than $\sqrt{N}$ for most images, and it is more efficient than the pure quantum algorithm.

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The Casimir effect of Reissner--Nordström black hole Xiao Kui(肖奎) and Liu Wen-Biao(刘文彪) Chinese Physics, 2006, 15 (12):  3044-3048.  DOI: 10.1088/1009-1963/15/12/045 Abstract ( 1470 )   PDF (102KB) ( 535 )   The stress tensor of a massless scalar field satisfying a mixed boundary condition in a ( 1+1)-dimensional Reissner--Nordstr?m black hole background is calculated by using Wald's axiom. We find that Dirichlet stress tensor and Neumann stress tensor can be deduced by changing the coefficients of the stress tensor calculated under a mixed boundary condition. The stress tensors satisfying Dirichlet and Neumann boundary conditions are discussed. In addition, we also find that the stress tensor in conformal flat spacetime background differs from that in flat spacetime only by a constant.