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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.11
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GENERAL

Multi-symplectic method for generalized fifth-order KdV equation

Hu Wei-Peng, Deng Zi-Chen
Chin. Phys. B, 2008, 17 (11): 3923-3929 doi: 10.1088/1674-1056/17/11/001
Full Text: [PDF 1054 KB] (Downloads:1298)
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This paper considers the multi-symplectic formulations of the generalized fifth-order KdV equation in Hamiltonian space. Recurring to the midpoint rule, it presents an implicit multi-symplectic scheme with discrete multi-symplectic conservation law to solve the partial differential equations which are derived from the generalized fifth-order KdV equation numerically. The results of the numerical experiments show that this multi-symplectic algorithm is good in accuracy and its long-time numerical behaviour is also perfect.

The second-order dynamic phase transition and Lee--Yang zeros in Eggers urn model

Liu Xiao-Xian, Tong Pei-Qing
Chin. Phys. B, 2008, 17 (11): 3930-3935 doi: 10.1088/1674-1056/17/11/002
Full Text: [PDF 205 KB] (Downloads:610)
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A second-order dynamic phase transition in a non-equilibrium Eggers urn model for the separation of sand is studied. The order parameter, the susceptibility and the stationary probability distribution have been calculated. By applying the Lee--Yang zeros method of equilibrium phase transitions, we study the distributions of the effective partition function zeros and obtain the same result for the model. Thus, the Lee--Yang theory can be applied to a more general non-equilibrium system.

Pattern formation induced by cross-diffusion in a predator--prey system

Sun Gui-Quan, Jin Zhen, Liu Quan-Xing, Li Li
Chin. Phys. B, 2008, 17 (11): 3936-3941 doi: 10.1088/1674-1056/17/11/003
Full Text: [PDF 3206 KB] (Downloads:981)
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This paper considers the Holling--Tanner model for predator--prey with self and cross-diffusion. From the Turing theory, it is believed that there is no Turing pattern formation for the equal self-diffusion coefficients. However, combined with cross-diffusion, it shows that the system will exhibit spotted pattern by both mathematical analysis and numerical simulations. Furthermore, asynchrony of the predator and the prey in the space. The obtained results show that cross-diffusion plays an important role on the pattern formation of the predator--prey system.

Symplectic-energy-first integrators of discrete mechanico-electrical dynamical systems

Fu Jing-Li, Chen Ben-Yong, Tang Yi-Fa, Fu Hao
Chin. Phys. B, 2008, 17 (11): 3942-3952 doi: 10.1088/1674-1056/17/11/004
Full Text: [PDF 199 KB] (Downloads:762)
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A discrete total variation calculus with variable time steps is presented for mechanico-electrical systems where there exist non-potential and dissipative forces. By using this discrete variation calculus, the symplectic-energy-first integrators for mechanico-electrical systems are derived. To do this, the time step adaptation is employed. The discrete variational principle and the Euler--Lagrange equation are derived for the systems. By using this discrete algorithm it is shown that mechanico-electrical systems are not symplectic and their energies are not conserved unless they are Lagrange mechanico-electrical systems. A practical example is presented to illustrate these results.

Adomian decomposition method and Padé approximants for solving the Blaszak--Marciniak lattice

Yang Pei, Chen Yong, Li Zhi-Bin
Chin. Phys. B, 2008, 17 (11): 3953-3964 doi: 10.1088/1674-1056/17/11/005
Full Text: [PDF 268 KB] (Downloads:607)
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The Adomian decomposition method (ADM) and Pad\'{e} approximants are combined to solve the well-known Blaszak--Marciniak lattice, which has rich mathematical structures and many important applications in physics and mathematics. In some cases, the truncated series solution of ADM is adequate only in a small region when the exact solution is not reached. To overcome the drawback, the Pad\'{e} approximants, which have the advantage in turning the polynomials approximation into a rational function, are applied to the series solution to improve the accuracy and enlarge the convergence domain. By using the ADM-Pad\'{e} technique, the soliton solutions of the Blaszak--Marciniak lattice are constructed with better accuracy and better convergence than by using the ADM alone. Numerical and figurative illustrations show that it is a promising tool for solving nonlinear problems.

Non-isospectral integrable couplings of Ablowitz--Kaup--Newell--Segur (AKNS) hierarchy with self-consistent sources

Yu Fa-Jun, Li Li
Chin. Phys. B, 2008, 17 (11): 3965-3973 doi: 10.1088/1674-1056/17/11/006
Full Text: [PDF 170 KB] (Downloads:578)
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A hierarchy of non-isospectral Ablowitz--Kaup--Newell--Segur (AKNS) equations with self-consistent sources is derived. As a general reduction case, a hierarchy of non-isospectral nonlinear Schr\"{o}dinger equations (NLSE) with self-consistent sources is obtained. Moreover, a new non-isospectral integrable coupling of the AKNS soliton hierarchy with self-consistent sources is constructed by using the Kronecker product.

A new variable coefficient algebraic method and non-travelling wave solutions of nonlinear equations

Lu Bin, Zhang Hong-Qing
Chin. Phys. B, 2008, 17 (11): 3974-3984 doi: 10.1088/1674-1056/17/11/007
Full Text: [PDF 1152 KB] (Downloads:573)
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In this paper, a new auxiliary equation method is presented of constructing more new non-travelling wave solutions of nonlinear differential equations in mathematical physics, which is direct and more powerful than projective Riccati equation method. In order to illustrate the validity and the advantages of the method, (2+1)-dimensional asymmetric Nizhnik--Novikov--Vesselov equation is employed and many new double periodic non-travelling wave solutions are obtained. This algorithm can also be applied to other nonlinear differential equations.

Quantum mechanical description of waveguides

Wang Zhi-Yong, Xiong Cai-Dong, He Bing
Chin. Phys. B, 2008, 17 (11): 3985-3990 doi: 10.1088/1674-1056/17/11/008
Full Text: [PDF 171 KB] (Downloads:568)
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Applying the spinor representation of the electromagnetic field, this paper present a quantum-mechanical description of waveguides. As an example of application, a potential qubit generated by photon tunnelling is discussed.

Construction and application of multi-partner communication network

Xiu Xiao-Ming, Dong Li, Gao Ya-Jun, Chi Feng
Chin. Phys. B, 2008, 17 (11): 3991-3995 doi: 10.1088/1674-1056/17/11/009
Full Text: [PDF 154 KB] (Downloads:609)
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In this paper, we present a multi-partner communication network protocol. The supervisor prepares numerous Einstein--Podolsky--Rosen (EPR) pairs and auxiliary qubits. He then performs a controlled-NOT(CNOT) gate operation on one qubit of each EPR pair and an auxiliary, which induces the entanglement between the EPR pair and the auxiliary. The supervisor keeps one qubit sequence in his laboratory and sends the others to the outside world. After security approval, the network can be constructed successfully, which can be applied to quantum secret sharing and quantum secure direct communication.

Nonlinear transport of Bose--Einstein condensates in a double barrier potential

Fang Jian-Shu
Chin. Phys. B, 2008, 17 (11): 3996-4001 doi: 10.1088/1674-1056/17/11/010
Full Text: [PDF 538 KB] (Downloads:2006)
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The stable nonlinear transport of the Bose--Einstein condensates through a double barrier potential in a waveguide is studied. By using the direct perturbation method we have obtained a perturbed solution of Gross--Pitaevskii equation. Theoretical analysis reveals that this perturbed solution is a stable periodic solution, which shows that the transport of Bose--Einstein condensed atoms in this system is a stable nonlinear transport. The corresponding numerical results are in good agreement with the theoretical analytical results.

Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbouring interactions

Shan Chuan-Jia, Cheng Wei-Wen, Liu Tang-Kun, Huang Yan-Xia, Li Hong
Chin. Phys. B, 2008, 17 (11): 4002-4008 doi: 10.1088/1674-1056/17/11/011
Full Text: [PDF 269 KB] (Downloads:599)
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By using the method of density-matrix renormalization-group to solve the different spin--spin correlation functions, the nearest-neighbouring entanglement (NNE) and the next-nearest-neighbouring entanglement (NNNE) of one-dimensional alternating Heisenberg XY spin chain are investigated in the presence of alternating the-nearest-neighbouring interaction of exchange couplings, external magnetic fields and the next-nearest neighbouring interaction. For a dimerised ferromagnetic spin chain, the NNNE appears only above a critical dimerized interaction, meanwhile, the dimerized interaction a effects a quantum phase transition point and improves the NNNE to a large extent. We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighbouring (NNN) interaction on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction increases and shrinks the NNE below and above a critical frustrated interaction respectively, while the antiferromagnetic NNN interaction always reduces the NNE. The antiferromagnetic NNN interaction results in a large value of NNNE compared with the case where the NNN interaction is ferromagnetic.

Multiple attractors and generalized synchronization in delayed Mackey--Glass systems

Li Dong, Zheng Zhi-Gang
Chin. Phys. B, 2008, 17 (11): 4009-4013 doi: 10.1088/1674-1056/17/11/012
Full Text: [PDF 205 KB] (Downloads:528)
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Nonlinear dynamics of the time-delayed Mackey--Glass systems is explored. Coexistent multiple chaotic attractors are found. Attractors with double-scroll structures can be well classified in terms of different return times within one period of the delay time by constructing the Poincar\'{e} section. Synchronizations of the drive--response Mackey--Glass oscillators are investigated. The critical coupling strength for the emergence of generalized synchronization against the delay time exhibits the interesting resonant behaviour. We reveal that stronger resonance effect may be observed when different attractors are applied to the drivers, i.e., more resonance peaks can be found.

A new R?sslor hyperchaotic system and its realization with systematic circuit parameter design

Wang Guang-Yi, He Hai-Lian
Chin. Phys. B, 2008, 17 (11): 4014-4021 doi: 10.1088/1674-1056/17/11/013
Full Text: [PDF 1824 KB] (Downloads:835)
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Based on two modified R\"{o}sslor hyperchaotic systems, which are derived from the chaotic R\"{o}sslor system by introducing a state feedback controller, this paper proposes a new switched R\"{o}sslor hyperchaotic system. The switched system contains two different hyperchaotic systems and can change its behaviour continuously from one to another via a switching function. On the other hand, it presents a systematic method for designing the circuit of realizing the proposed hyperchaotic system. In this design, circuit state equations are written in normalized dimensionless form by rescaling the time variable. Furthermore, an analogous circuit is designed by using the proposed method and built for verifying the new hyperchaos and the design method. Experimental results show a good agreement between numerical simulations and experimental results.

New robust chaotic system with exponential quadratic term

Bao Bo-Cheng, Li Chun-Biao, Xu Jian-Ping, Liu Zhong
Chin. Phys. B, 2008, 17 (11): 4022-4026 doi: 10.1088/1674-1056/17/11/014
Full Text: [PDF 345 KB] (Downloads:679)
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This paper proposes a new robust chaotic system of three-dimensional quadratic autonomous ordinary differential equations by introducing an exponential quadratic term. This system can display a double-scroll chaotic attractor with only two equilibria, and can be found to be robust chaotic in a very wide parameter domain with positive maximum Lyapunov exponent. Some basic dynamical properties and chaotic behaviour of novel attractor are studied. By numerical simulation, this paper verifies that the three-dimensional system can also evolve into periodic and chaotic behaviours by a constant controller.

An improved image encryption algorithm based on chaotic maps

Xu Shu-Jiang, Wang Ji-Zhi, Yang Su-Xiang
Chin. Phys. B, 2008, 17 (11): 4027-4032 doi: 10.1088/1674-1056/17/11/015
Full Text: [PDF 973 KB] (Downloads:943)
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Recently, two chaotic image encryption schemes have been proposed, in which shuffling the positions and changing the grey values of image pixels are combined. This paper provides the chosen plaintext attack to recover the corresponding plaintext of a given ciphertext. Furthermore, it points out that the two schemes are not sufficiently sensitive to small changes of the plaintext. Based on the given analysis, it proposes an improved algorithm which includes two rounds of substitution and one round of permutation to strengthen the overall performance.

Realization of fractional-order Liu chaotic system by a new circuit unit

Xu Zhe, Liu Chong-Xin
Chin. Phys. B, 2008, 17 (11): 4033-4038 doi: 10.1088/1674-1056/17/11/016
Full Text: [PDF 2499 KB] (Downloads:950)
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A new circuit unit for the analysis and the synthesis of the chaotic behaviours in a fractional-order Liu system is proposed in this paper. Based on the approximation theory of fractional-order operator, an electronic circuit is designed to describe the dynamic behaviours of the fractional-order Liu system with $\alpha =0.9$. The results between simulation and experiment are in good agreement with each other, thereby proving that the chaos exists indeed in the fractional-order Liu system.

A new hyperchaotic system and its linear feedback control

Cai Guo-Liang, Zheng Song, Tian Li-Xin
Chin. Phys. B, 2008, 17 (11): 4039-4046 doi: 10.1088/1674-1056/17/11/017
Full Text: [PDF 5137 KB] (Downloads:764)
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This paper reports a new hyperchaotic system by adding an additional state variable into a three-dimensional chaotic dynamical system, studies some of its basic dynamical properties, such as the hyperchaotic attractor, Lyapunov exponents, bifurcation diagram and the hyperchaotic attractor evolving into periodic, quasi-periodic dynamical behaviours by varying parameter $k$. Furthermore,effective linear feedback control method is used to suppress hyperchaos to unstable equilibrium, periodic orbits and quasi-periodic orbits. Numerical simulations are presented to show these results.

Formation and instability of spiral wave induced by Gaussian coloured noise

Gan Zheng-Ning, Ma Jun, Zhang Guo-Yong, Chen Yong
Chin. Phys. B, 2008, 17 (11): 4047-4055 doi: 10.1088/1674-1056/17/11/018
Full Text: [PDF 294 KB] (Downloads:629)
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In this paper, we studied the effect of Gaussian coloured noise on the formation and instability of spiral waves described by one class of modified FitzHugh--Nagumo equation. It was found that Gaussian coloured noise plays a constructive role in the formation, transition and instability of spiral wave. Too weak or too strong noise may act against the formation of spiral waves. At a certain noise level, spiral wave is maintained in a medium, in which spiral wave cannot be observed in the absence of the noise. It is difficult to make a stable spiral wave into unstable state by Gaussian coloured noise, unless the noise level is very high. The parameter regions of Gaussian coloured noise for spiral forming and spiral instability were given and discussed with numerical simulations.

A unified approach to fuzzy modelling and robust synchronization of different hyperchaotic systems

Zhang Hua-Guang, Zhao Yan, Yu Wen, Yang Dong-Sheng
Chin. Phys. B, 2008, 17 (11): 4056-4066 doi: 10.1088/1674-1056/17/11/019
Full Text: [PDF 804 KB] (Downloads:702)
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In this paper, a Takagi--Sugeno (T--S) fuzzy model-based method is proposed to deal with the problem of synchronization of two identical or different hyperchaotic systems. The T--S fuzzy models with a small number of fuzzy IF--THEN rules are employed to represent many typical hyperchaotic systems exactly. The benefit of employing the T--S fuzzy models lies in mathematical simplicity of analysis. Based on the T--S fuzzy hyperchaotic models, two fuzzy controllers are designed via parallel distributed compensation (PDC) and exact linearization (EL) techniques to synchronize two identical hyperchaotic systems with uncertain parameters and two different hyperchaotic systems, respectively. The sufficient conditions for the robust synchronization of two identical hyperchaotic systems with uncertain parameters and the asymptotic synchronization of two different hyperchaotic systems are derived by applying the Lyapunov stability theory. This method is a universal one of synchronizing two identical or different hyperchaotic systems. Numerical examples are given to demonstrate the validity of the proposed fuzzy model and hyperchaotic synchronization scheme.

Adaptive projective synchronization with different scaling factors in networks

Guo Liu-Xiao, Xu Zhen-Yuan, Hu Man-Feng
Chin. Phys. B, 2008, 17 (11): 4067-4072 doi: 10.1088/1674-1056/17/11/020
Full Text: [PDF 547 KB] (Downloads:652)
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We study projective synchronization with different scaling factors (PSDF) in $N$ coupled chaotic systems networks. By using the adaptive linear control, some sufficient criteria for the PSDF in symmetrical and asymmetrical coupled networks are separately given based on the Lyapunov function method and the left eigenvalue theory. Numerical simulations for a generalized chaotic unified system are illustrated to verify the theoretical results.

Adaptive generalized projective synchronization of two different chaotic systems with unknown parameters

Zhang Ruo-Xun, Yang Shi-Ping
Chin. Phys. B, 2008, 17 (11): 4073-4079 doi: 10.1088/1674-1056/17/11/021
Full Text: [PDF 242 KB] (Downloads:591)
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This paper presents a general method of the generalized projective synchronization and the parameter identification between two different chaotic systems with unknown parameters. This approach is based on Lyapunov stability theory, and employs a combination of feedback control and adaptive control. With this method one can achieve the generalized projective synchronization and realize the parameter identifications between almost all chaotic (hyperchaotic) systems with unknown parameters. Numerical simulations results are presented to demonstrate the effectiveness of the method.

Synchronization of stochastically hybrid coupled neural networks with coupling discrete and distributed time-varying delays

Tang Yang, Zhong Hui-Huang, Fang Jian-An
Chin. Phys. B, 2008, 17 (11): 4080-4090 doi: 10.1088/1674-1056/17/11/022
Full Text: [PDF 745 KB] (Downloads:716)
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A general model of linearly stochastically coupled identical connected neural networks with hybrid coupling is proposed, which is composed of constant coupling, coupling discrete time-varying delay and coupling distributed time-varying delay. All the coupling terms are subjected to stochastic disturbances described in terms of Brownian motion, which reflects a more realistic dynamical behaviour of coupled systems in practice. Based on a simple adaptive feedback controller and stochastic stability theory, several sufficient criteria are presented to ensure the synchronization of linearly stochastically coupled complex networks with coupling mixed time-varying delays. Finally, numerical simulations illustrated by scale-free complex networks verify the effectiveness of the proposed controllers.

Exponential stability of cellular neural networks with multiple time delays and impulsive effects

Li Dong, Wang Hui, Yang Dan, Zhang Xiao-Hong, Wang Shi-Long
Chin. Phys. B, 2008, 17 (11): 4091-4099 doi: 10.1088/1674-1056/17/11/023
Full Text: [PDF 150 KB] (Downloads:552)
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In this work, the stability issues of the equilibrium points of the cellular neural networks with multiple time delays and impulsive effects are investigated. Based on the stability theory of Lyapunov--Krasovskii, the method of linear matrix inequality (LMI) and parametrized first-order model transformation, several novel conditions guaranteeing the delay-dependent and the delay-independent exponential stabilities are obtained. A numerical example is given to illustrate the effectiveness of our results.

Numerical study of IP3-induced Ca2+ spiral pattern evolution

Tang Jun, Ma Jun, Yi Ming, Jia Ya
Chin. Phys. B, 2008, 17 (11): 4100-4106 doi: 10.1088/1674-1056/17/11/024
Full Text: [PDF 4841 KB] (Downloads:410)
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The effect of change in concentration of messenger molecule inositol 1,4,5-trisphosphate (IP$_{3})$ on intracellular Ca$^{2 + }$spiral pattern evolution is studied numerically. The results indicate that when the IP$_{3}$ concentration decreases from 0.27\,$\mu $M, a physiologically reasonable value, to different values, the spiral centre drifts to the edge of the medium and disappears for a small enough IP$_{3}$ concentration. The instability of spiral pattern can be understood in terms of excitability-change controlled by the IP$_{3}$ concentration. On the other hand, when the IP$_{3}$ concentration increases from 0.27\,$\mu $M, a homogeneous area with a high Ca$^{2 + }$ concentration emerges and competes with the spiral pattern. A high enough IP$_{3}$ concentration can lead the homogeneous area to occupy the whole medium. The instability of spiral pattern is ascribed to the change in stability of a stationary state with a high Ca$^{2 + }$ concentration.

Synchronization of spiral waves in a two-layer coupled inhomogeneous excitable system

Zhang Guo-Yong, Ma Jun, Yu Lian-Chun, Chen Yong
Chin. Phys. B, 2008, 17 (11): 4107-4113 doi: 10.1088/1674-1056/17/11/025
Full Text: [PDF 4161 KB] (Downloads:587)
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We studied synchronization behaviours of spiral waves in a two-layer coupled inhomogeneous excitable system. It was found that phase synchronization can be observed under weak coupling strength. By increasing the coupling strength, the synchronization is broken down. With the further increase of the coupling strength, complete synchronization and phase synchronization occur again. We also found that the inhomogeneity in excitable systems is helpful to the synchronization.

Periodic solutions and flip bifurcation in a linear impulsive system

Jiang Gui-Rong, Yang Qi-Gui
Chin. Phys. B, 2008, 17 (11): 4114-4122 doi: 10.1088/1674-1056/17/11/026
Full Text: [PDF 937 KB] (Downloads:592)
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In this paper, the dynamical behaviour of a linear impulsive system is discussed both theoretically and numerically. The existence and the stability of period-one solution are discussed by using a discrete map. The conditions of existence for flip bifurcation are derived by using the centre manifold theorem and bifurcation theorem. The bifurcation analysis shows that chaotic solutions appear via a cascade of period-doubling in some interval of parameters. Moreover, the periodic solutions, the bifurcation diagram, and the chaotic attractor, which show their consistence with the theoretical analyses, are given in an example.

High-codimensional static bifurcations of strongly nonlinear oscillator

Zhang Qi-Chang, Wang Wei, Liu Fu-Hao
Chin. Phys. B, 2008, 17 (11): 4123-4128 doi: 10.1088/1674-1056/17/11/027
Full Text: [PDF 430 KB] (Downloads:538)
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The static bifurcation of the parametrically excited strongly nonlinear oscillator is studied. We consider the averaged equations of a system subject to Duffing--van der Pol and quintic strong nonlinearity by introducing the undetermined fundamental frequency into the computation in the complex normal form. To discuss the static bifurcation, the bifurcation problem is described as a 3-codimensional unfolding with $Z_{2}$ symmetry on the basis of singularity theory. The transition set and bifurcation diagrams for the singularity are presented, while the stability of the zero solution is studied by using the eigenvalues in various parameter regions.

Wavefront depinning in semiconductor superlattices due to discrete-mapping failure

Wang Jun, Zheng Zhi-Gang
Chin. Phys. B, 2008, 17 (11): 4129-4136 doi: 10.1088/1674-1056/17/11/028
Full Text: [PDF 223 KB] (Downloads:698)
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We investigate the wavefronts depinning in current biased, infinitely long semiconductor superlattice systems by the method of discrete mapping and show that the wavefront depinning corresponds to the discrete mapping failure. For parameter values near the lower critical current in both discrete drift model (DD model) and discrete drift--diffusion model (DDD model), the mapping failure is determined by the important mapping step from the bottom of branch $\gamma$ to branch $\alpha$. For the upper critical parameters in DDD model, the key mapping step is from branch $\gamma$ to the top of the corresponding branch $\alpha$, and we may need several active wells to describe the wavefronts.

Consensus problems of multi-agent systems with noise perturbation

Sun Yong-Zheng, Ruan Jiong
Chin. Phys. B, 2008, 17 (11): 4137-4141 doi: 10.1088/1674-1056/17/11/029
Full Text: [PDF 194 KB] (Downloads:748)
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In this paper, by using the stability theory of stochastic differential equations, the average-consensus problem with noise perturbation is investigated. It is analytically proved that the consensus could be achieved with a probability of one. Furthermore, numerical examples are taken to illustrate the effectiveness of the theoretical result.

The analysis of the integral gated mode single photon detector

Wei Zheng-Jun, Li Kai-Zhen, Zhou Peng, Wang Jin-Dong, Liao Chang-Jun, Guo Jian-Ping, Liang Rui-Sheng, Liu Song-Hao
Chin. Phys. B, 2008, 17 (11): 4142-4148 doi: 10.1088/1674-1056/17/11/030
Full Text: [PDF 246 KB] (Downloads:612)
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This paper critically analyses and simulates the circuit configuration of the integral gated mode single photon detector which is proposed for eliminating the transient spikes problem of conventional gated mode single photon detector. The relationship between the values of the circuit elements and the effect of transient spikes cancellation has been obtained. With particular emphasis, the bias voltage of the avalanche photodiode and the output signal voltage of the integrator have been calculated. The obtained analysis results indicate that the output signal voltage of the integrator only relates to the total quantity of electricity of the avalanche charges by choosing the correct values of the circuit elements and integral time interval. These results can be used to optimize the performance of single photon detectors and provide guides for the design of single photon detectors.

Simulation of time bunching for a pulsed positron beam

Gao Chuan-Bo, Xiong Tao, Xi Chuan-Ying, Weng Hui-Min, Ye Bang-Jiao, Han Rong-Dian, Zhou Xian-Yi
Chin. Phys. B, 2008, 17 (11): 4149-4152 doi: 10.1088/1674-1056/17/11/031
Full Text: [PDF 791 KB] (Downloads:561)
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Simulate anneal arithmetic has been used to settle the problem of time bunching on a pulsed slow-positron beam device. This paper has searched for the parameters of the device in a large scope and achieved the time resolution within 150ps at the target with accelerating voltage in a range of 0.5--30kV.
CLASSICAL AREAS OF PHENOMENOLOGY

Superposition of orbital angular momentum of photons by a combined computer-generated hologram fabricated in silica glass with femtosecond laser pulses

Guo Zhong-Yi, Qu Shi-Liang, Sun Zheng-He, Liu Shu-Tian
Chin. Phys. B, 2008, 17 (11): 4199-4203 doi: 10.1088/1674-1056/17/11/040
Full Text: [PDF 3011 KB] (Downloads:468)
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This paper introduces a novel method to realize the superposition of orbital angular momentum of photons by combined computer-generated hologram (CCGH) fabricated in silica glass with femtosecond laser pulses. Firstly, the two computer-generated holograms (CGH) of optical vortex were obtained and combined as a CCGH according to the design. Then the CCGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any pre- or post-treatment of the material. The vortex beams with different vortex topological charges (including new topological charges) have been restructured using a collimated He--Ne laser beam incidence to the CCGH normally. A theoretical and experimental explanation has been presented for the generations of the new topological charges.

Exact analytical solution for quantum spins mixing in spin-1 Bose--Einstein condensates

Chen Ai-Xi, Qiu Wan-Ying, Wang Zhi-Ping
Chin. Phys. B, 2008, 17 (11): 4204-4206 doi: 10.1088/1674-1056/17/11/041
Full Text: [PDF 141 KB] (Downloads:438)
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This paper solves exactly a set of fully quantized coupled equations describing the quantum dynamics of quantum spins mixing in spin-1 Bose--Einstein condensates by deriving the exact explicit analytical expressions for the evolution of creation and annihilation operators.

Generation of cluster states for cavity fields

Jia Lian-Jun, Yang Zhen-Biao, Wu Huai-Zhi, Zheng Shi-Biao
Chin. Phys. B, 2008, 17 (11): 4207-4210 doi: 10.1088/1674-1056/17/11/042
Full Text: [PDF 267 KB] (Downloads:562)
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This paper proposes an alternative scheme for generating cluster-type of entangled coherent states. This scheme is based on resonant interaction of a two-mode cavity with a two-level atom driven by strong classical fields. Thus the required interaction time is greatly shortened, which is very important in view of decoherence.

Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

Liu Ji-Cai, Wang Chun-Xin, Gel'mukhanov Faris, Wang Chuan-Kui
Chin. Phys. B, 2008, 17 (11): 4211-4217 doi: 10.1088/1674-1056/17/11/043
Full Text: [PDF 223 KB] (Downloads:443)
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This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultrashort laser pulse by solving numerically the full-wave Maxwell--Bloch equations. The 4, 4$'$-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.

An all-optical time-delay relay based on a bacteriorhodopsin film

Chen Gui-Ying, Xu Xu-Xu, Zhang Chun-Ping, Qi Shen-Wen, Song Qi-Wang
Chin. Phys. B, 2008, 17 (11): 4218-4225 doi: 10.1088/1674-1056/17/11/044
Full Text: [PDF 223 KB] (Downloads:481)
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Using a special property of dynamic complementary-suppression-modulated transmission (DCSMT) in the bacteriorhodopsin (bR) film, we have demonstrated an all-optical time-delay relay. To extend our work, the relationship between the delay time of the all-optical time-delay relay and parameters of a bR film is numerically studied. We show how the delay time changes with the product of concentration and thickness (PCT) of a bR film. Furthermore, the shortest and longest delay times are given for the relay of `switch off'. The saturable delay time and maximum delay-time of `switch on' are also given. How the wavelengths (632.8, 568, 533 and 412\,nm) and intensities of the illuminating light influence the delay time is also discussed. The simulation results are useful for optimizing the design of all-optical time-delay relays.

All-optical error-bit amplitude monitor based on NOT and AND gates in cascaded semiconductor optical amplifiers

Dong Jian-Ji, Zhang Xin-Liang, Huang De-Xiu
Chin. Phys. B, 2008, 17 (11): 4226-4231 doi: 10.1088/1674-1056/17/11/045
Full Text: [PDF 1654 KB] (Downloads:411)
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This paper proposes and simulates a novel all-optical error-bit amplitude monitor based on cross-gain modulation and four-wave mixing in cascaded semiconductor optical amplifiers (SOAs), which function as logic NOT and logic AND, respectively. The proposed scheme is successfully simulated for 40\,Gb/s return-to-zero (RZ) signal with different duty cycles. In the first stage, the SOA is followed by a detuning filter to accelerate the gain recovery as well as improve the extinction ratio. A clock probe signal is used to avoid the edge pulse-pairs in the output waveform. Among these RZ formats, 33{\%} RZ format is preferred to obtain the largest eye opening. The normalized error amplitude, defined as error bit amplitude over the standard mark amplitude, has a dynamic range from 0.1 to 0.65 for all RZ formats. The simulations show small input power dynamic range because of the nonlinear gain variation in the first stage. This scheme is competent for nonreturn-to-zero format at 10Gb/s as well.

Cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate

Xiang Yan-Xun, Deng Ming-Xi
Chin. Phys. B, 2008, 17 (11): 4232-4241 doi: 10.1088/1674-1056/17/11/046
Full Text: [PDF 1229 KB] (Downloads:514)
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The physical process of cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate is presented by using the second-order perturbation and the technique of nonlinear reflection of acoustic waves at an interface. In general, the cumulative second-harmonic generation of a dispersive guided wave propagation does not occur. However, the present paper shows that the second-harmonic of Lamb wave propagation arising from the nonlinear interaction of the partial bulk acoustic waves and the restriction of the three boundaries of the solid plates does have a cumulative growth effect if some conditions are satisfied. Through boundary condition and initial condition of excitation, the analytical expression of cumulative second-harmonic of Lamb waves propagation is determined. Numerical results show the cumulative effect of Lamb waves on second-harmonic field patterns.
ATOMIC AND MOLECULAR PHYSICS

Study of dynamical behaviour and fermionization of a bosonic gas in funnel potential

Xu Guang-Yuan, Yan Li, Wang Yong-Jun, Liu Xian-Feng, Han Jiu-Rong, Wang Yu-Zhu
Chin. Phys. B, 2008, 17 (11): 4158-4162 doi: 10.1088/1674-1056/17/11/033
Full Text: [PDF 189 KB] (Downloads:576)
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This paper presents a funnel external potential model to investigate dynamic properties of ultracold Bose gas. By using variational method, we obtain the ground-state energy and density properties of ultracold Bose atoms. The results show that the ultracold Bose gas confined in a funnel potential experiences the transition from three-dimensional regime to quasi-one-dimensional regime in a small aspect ratio, and undergoes fermionization process as the aspect ratio increases.

Ab initio calculations of the ionization spectrum of SO2

Zhang Yong-Feng, Wang Mei-Shan, Yang Chuan-Lu, Ma Mei-Zhong, Pang Wei-Xiu, Ma Rong-Cai
Chin. Phys. B, 2008, 17 (11): 4163-4169 doi: 10.1088/1674-1056/17/11/034
Full Text: [PDF 703 KB] (Downloads:684)
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The ionization spectrum of sulfur dioxide has been successfully studied by using the symmetry-adapted-cluster configuration-interaction (SAC-CI) general-$R$ and SD-$R$ methods and the basis set correlation-consistent polarized valence triple-zeta (cc-pVTZ). The SAC-CI general-$R$ method reproduces the experimental spectrum well for both the main peaks and the satellite peaks of ionization spectrum of SO$_{2}$. The sequence of ionic states corresponding to main peaks of SO$_{2}$ has been re-determined according to the SAC-CI conclusions and it is reordered as ${\tilde {X}}{ }^{\rm 2}{A}_1 $, ${\tilde {A}}^{\rm 2}{B}_{\rm 2} $, ${\tilde {B}}{ }^{\rm 2}{A}_{\rm 2} $, ${\tilde {C}}^{\rm 2}{B}_{\rm 1} $, ${\tilde {D}}{ }^{\rm 2}{A}_{\rm 1} $, ${\tilde {E}}^{\rm 2}{B}_{\rm 2} $ and ${\tilde {F}}^{\rm 2}{A}_1 $. Besides, the equilibrium structures and adiabatic ionization potentials (AIPs) of ionic states of main peaks of SO$_{2}$ are calculated by using the SAC-CI SD-$R$ method.

Zitterbewegung in quantum field theory

Wang Zhi-Yong, Xiong Cai-Dong
Chin. Phys. B, 2008, 17 (11): 4170-4174 doi: 10.1088/1674-1056/17/11/035
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Traditionally, the zitterbewegung (ZB) of the Dirac electron has just been studied at the level of quantum mechanics. Seeing the fact that an old interest in ZB has recently been rekindled by the investigations on spintronic, graphene, and superconducting systems, etc., this paper presents a quantum-field-theory investigation on ZB and obtains the conclusion that, the ZB of an electron arises from the influence of virtual electron--positron pairs (or vacuum fluctuations) on the electron.

Wavefunction and energy of the 1s22sns configuration in a beryllium atom

Huang Shi-Zhong, Ma Kun, Yu Jia-Ming, Liu Fen
Chin. Phys. B, 2008, 17 (11): 4175-4179 doi: 10.1088/1674-1056/17/11/036
Full Text: [PDF 179 KB] (Downloads:416)
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A new set of trial functions for 1s$^{2}$2s$n$s configurations in a beryllium atom is suggested. A Mathematica program based on the variational method is developed to calculate the wavefunctions and energies of 1s$^{2}$2s$n$s ($n=3-6$) configurations in a beryllium atom. Non-relativistic energy, polarization correction and relativistic correction which include mass correction, one- and two-body Darwin corrections, spin-spin contact interaction and orbit-orbit interaction, are calculated respectively. The results are in good agreement with experimental data.

Light-induced evaporative cooling in a magneto-optical trap

Ma Hong-Yu, Cheng Hua-Dong, Wang Yu-Zhu, Liu Liang
Chin. Phys. B, 2008, 17 (11): 4180-4183 doi: 10.1088/1674-1056/17/11/037
Full Text: [PDF 364 KB] (Downloads:414)
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This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. The remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.

Retrieval algorithm of quantitative analysis of passive Fourier transform infrared (FTRD) remote sensing measurements of chemical gas cloud from measuring the transmissivity by passive remote Fourier transform infrared

Liu Zhi-Ming, Liu Wen-Qing, Gao Min-Guang, Tong Jing-Jing, Zhang Tian-Shu, Xu Liang, Wei Xiu-Li
Chin. Phys. B, 2008, 17 (11): 4184-4192 doi: 10.1088/1674-1056/17/11/038
Full Text: [PDF 1275 KB] (Downloads:604)
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Passive Fourier transform infrared (FTIR) remote sensing measurement of chemical gas cloud is a vital technology. It takes an important part in many fields for the detection of released gases. The principle of concentration measurement is based on the Beer--Lambert law. Unlike the active measurement, for the passive remote sensing, in most cases, the difference between the temperature of the gas cloud and the brightness temperature of the background is usually a few kelvins. The gas cloud emission is almost equal to the background emission, thereby the emission of the gas cloud cannot be ignored. The concentration retrieval algorithm is quite different from the active measurement. In this paper, the concentration retrieval algorithm for the passive FTIR remote measurement of gas cloud is presented in detail, which involves radiative transfer model, radiometric calibration, absorption coefficient calculation, {\it et al}. The background spectrum has a broad feature, which is a slowly varying function of frequency. In this paper, the background spectrum is fitted with a polynomial by using the Levenberg--Marquardt method which is a kind of nonlinear least squares fitting algorithm. No background spectra are required. Thus, this method allows mobile, real-time and fast measurements of gas clouds.

The direct ionization processes in the collisions of partially stripped carbon and oxygen ions with helium atoms at low-to-intermediate energies

Zhou Chun-Lin, Shao Jian-Xiong, Chen Xi-Meng, Sun Guang-Zhi, Zou Xian-Rong
Chin. Phys. B, 2008, 17 (11): 4193-4198 doi: 10.1088/1674-1056/17/11/039
Full Text: [PDF 603 KB] (Downloads:414)
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The values of direct double- to-single ionization ratio $R$ of helium atoms induced by C$^{q + }$, O$^{q + }$ ($q=1-4$) ions at incident energies from 0.2 to 8.5MeV are measured. Based on the existing model (Shao J X, Chen X M and Ding B W 2007 \wx{Phys. Rev. {\rm A}}{75} 012701) the effective charge of the projectile is introduced to theoretically estimate the value of $R$ for the partially stripped ions impacting on helium atoms. The results calculated from our ``effective charge'' model are in good agreement with the experimental data, and the dependence of the effective charge on the ionization energy of the projectile is also discussed qualitatively.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Classical integrability of strings in γ-deformed backgrounds

Xie Xiao-Ning, Yue Rui-Hong
Chin. Phys. B, 2008, 17 (11): 4153-4157 doi: 10.1088/1674-1056/17/11/032
Full Text: [PDF 175 KB] (Downloads:539)
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This paper considers classical strings propagating in $\gamma$-deformed $AdS_3\times S^3$ backgrounds generated by certain shift T-dualities accompanied (TsT) transformations on $S^3$ and $AdS_3$, respectively. It finds that the $U(1)$ currents of strings with the twisted boundary conditions are equal to those in $\gamma$-deformed backgrounds generated by TsT transformations on both $S^3$ and $AdS_3$. Applying the TsT transformations, it derives the local Lax connections and the monodromy matrices in $\gamma$-deformed backgrounds with the spectral parameter which ensure the classical integrability of the string theories.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Improving the uniformity of RF-plasma density by a humped variable-gap spiral antenna

Xu Xu, Li Lin-Sen, Liu Feng, Zhou Qian-Hong, Liang Rong-Qing
Chin. Phys. B, 2008, 17 (11): 4242-4246 doi: 10.1088/1674-1056/17/11/047
Full Text: [PDF 611 KB] (Downloads:577)
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This paper develops a humped spiral antenna of top inductively coupled plasma with variable gap. Comparing with planar spiral antennae, it investigates the performance of humped spiral antennae in the calculated electromagnetic configurations and experimental results. It finds that the humped antenna has the improved uniformity of plasma density in the radial direction and the decreased electron temperature in the top inductively coupled plasma. By experimental and theoretical analyses, the plasma performance in the case of humped antennae is considered to be the combined results of the uniform electromagnetic configurations and the depressed capacitively coupling effect.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Single crystalline boron carbide nanobelts: synthesis and characterization

Bao Li-Hong, Li Chen, Tian Yuan, Tian Ji-Fa, Hui Chao, Wang Xing-Jun, Shen Cheng-Min, Gao Hong-Jun
Chin. Phys. B, 2008, 17 (11): 4247-4252 doi: 10.1088/1674-1056/17/11/048
Full Text: [PDF 9569 KB] (Downloads:414)
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This paper reports that the large-scale single crystalline boron carbide nanobelts have been fabricated through a simple carbothermal reduction method with B/B$_{2}$O$_{3}$/C/Fe powder as precursors at 1100${^\circ}$C. Transmission electron microscopy and selected area electron diffraction characterizations show that the boron carbide nanobelt has a B$_{4}$C rhomb-centred hexagonal structure with good crystallization. Electron energy loss spectroscopy analysis indicates that the nanobelt contains only B and C, and the atomic ratio of B to C is close to 4:1. High resolution transmission electron microscopy results show that the preferential growth direction of the nanobelt is [101]. A possible growth mechanism is also discussed.

Numerical distortion and effects of thermostat in molecular dynamics simulations of single-walled carbon nanotubes

Li Rui, Hu Yuan-Zhong, Wang Hui, Zhang Yu-Jun
Chin. Phys. B, 2008, 17 (11): 4253-4259 doi: 10.1088/1674-1056/17/11/049
Full Text: [PDF 1935 KB] (Downloads:684)
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In this paper, single-walled carbon nanotubes (SWCNTs) are studied through molecular dynamics (MD) simulation. The simulations are performed at temperatures of 1 and 300\,K separately, with atomic interactions characterized by the second Reactive Empirical Bond Order (REBO) potential, and temperature controlled by a certain thermostat, i.e. by separately using the velocity scaling, the Berendsen scheme, the Nose--Hoover scheme, and the generalized Langevin scheme. Results for a (5,5) SWCNT with a length of 24.5\,nm show apparent distortions in nanotube configuration, which can further enter into periodic vibrations, except in simulations using the generalized Langevin thermostat, which is ascribed to periodic boundary conditions used in simulation. The periodic boundary conditions may implicitly be applied in the form of an inconsistent constraint along the axis of the nanotube. The combination of the inconsistent constraint with the cumulative errors in calculation causes the distortions of nanotubes. When the generalized Langevin thermostat is applied, inconsistently distributed errors are dispersed by the random forces, and so the distortions and vibrations disappear. This speculation is confirmed by simulation in the case without periodic boundary conditions, where no apparent distortion and vibration occur. It is also revealed that numerically induced distortions and vibrations occur only in simulation of nanotubes with a small diameter and a large length-to-diameter ratio. When MD simulation is applied to a system with a particular geometry, attention should be paid to avoiding the numerical distortion and the result infidelity.

Deposition mechanism of nano-structured single-layered C36 film on a diamond (100) crystal plane

Chen Ming-Jun, Liang Ying-Chun, Yuan Yi-Jie, Li Dan
Chin. Phys. B, 2008, 17 (11): 4260-4267 doi: 10.1088/1674-1056/17/11/050
Full Text: [PDF 3527 KB] (Downloads:508)
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The Brenner--LJ potential is adopted to describe the interaction between C$_{36}$ clusters and diamond surface, and the deposition mechanism of multi-C$_{36}$ clusters on the diamond surface is also studied by using the method of molecular dynamics simulation. The simulation results show that the competition effects of two interactions, i.e. the interaction between cluster and cluster and the interaction between cluster and crystal plane, are studied, and then the influence of these competition effects on C$_{36}$ cluster deposition is analysed. The finding is that when an incident energy is appropriately chosen, C$_{36}$ clusters can be chemically adsorbed and deposited steadily on the diamond surface in the form of single-layer, and in the deposition process the multi-C$_{36}$ clusters present a phenomenon of energy transmission. The experimental result shows that at a temperature of 300K, in order to deposit C$_{36}$ clusters into a steady nano-structured single-layered film, the optimal incident energy is between 10 and 18\,eV, if the incident energy is larger than 18\,eV, the C$_{36}$ clusters will be deposited into an island nano-structured film.

Two-vibron bound states in the β--Fermi--Pasta--Ulam model

Hu Xin-Guang, Tang Yi
Chin. Phys. B, 2008, 17 (11): 4268-4272 doi: 10.1088/1674-1056/17/11/051
Full Text: [PDF 2407 KB] (Downloads:534)
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This paper studies the two-vibron bound states in the $\beta $--Fermi--Pasta--Ulam model by means of the number conserving approximation combined with the number state method. The results indicate that on-site, adjacent-site and mixed two-vibron bound states may exist in the model. Specially, wave number has a significant effect on such bound states, which may be considered as the quantum effects of the localized states in quantum systems.

Finite element analysis of three-dimensional laser-induced transient thermal grating in diamond/ZnSe system

Cheng Ying, Huang Qiao-Jian, Liu Xiao-Jun
Chin. Phys. B, 2008, 17 (11): 4273-4278 doi: 10.1088/1674-1056/17/11/052
Full Text: [PDF 1440 KB] (Downloads:508)
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This paper uses finite element method to obtain the three-dimensional temperature field of laser-induced transient thermal grating (TTG) for two-layered structure of diamond film on ZnSe substrate. The numerical results indicate that unique two-times heating process is gradually experienced in the area between two adjacent grating stripes. However, there is a little change for the temperature field along the depth direction for the diamond film due to its great thermal conductivity. It further finds that the thickness of the diamond film has a significant influence on the temperature field in diamond/ZnSe system. The results are useful for the application of laser-induced TTG technique in film/substrate system.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

First-principle study of native defects in CuScO2 and CuYO2

Fang Zhi-Jie, Shi Li-Jie, Liu Yong-Hui
Chin. Phys. B, 2008, 17 (11): 4279-4284 doi: 10.1088/1674-1056/17/11/053
Full Text: [PDF 782 KB] (Downloads:607)
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This paper studies the electronic structure and native defects in transparent conducting oxides CuScO$_{2}$ and CuYO$_{2}$ using the first-principle calculations. Some typical native copper-related and oxygen-related defects, such as vacancy, interstitials, and antisites in their relevant charge state are considered. The results of calculation show that, Cu$M$O$_{2}$($M=$ Sc, Y) is impossible to show n-type conductivity ability. It finds that copper vacancy and oxygen interstitial have relatively low formation energy and they are the relevant defects in CuScO$_{2}$ and CuYO$_{2}$. Copper vacancy is the most efficient acceptor, and under O-rich condition oxygen antisite also becomes important acceptor and plays an important role in p-type conductivity.

Excitonic optical absorption in semiconductors under intense terahertz radiation

Zhang Tong-Yi, Zhao Wei
Chin. Phys. B, 2008, 17 (11): 4285-4291 doi: 10.1088/1674-1056/17/11/054
Full Text: [PDF 247 KB] (Downloads:555)
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The excitonic optical absorption of GaAs bulk semiconductors under intense terahertz (THz) radiation is investigated numerically. The method of solving initial-value problems, combined with the perfect matched layer technique, is used to calculate the optical susceptibility. In the presence of a driving THz field, in addition to the usual exciton peaks, 2p replica of the dark 2p exciton and even-THz-photon-sidebands of the main exciton resonance emerge in the continuum above the band edge and below the main exciton resonance. Moreover, to understand the shift of the position of the main exciton peak under intense THz radiation, it is necessary to take into consideration both the dynamical Franz--Keldysh effect and ac Stark effect simultaneously. For moderate frequency fields, the main exciton peak decreases and broadens due to the field-induced ionization of the excitons with THz field increasing. However, for high frequency THz fields, the characteristics of the exciton recur even under very strong THz fields, which accords with the recent experimental results qualitatively.

Theoretical study of electromechanical property in a p-type silicon nanoplate for mechanical sensors

Zhang Jia-Hong, Huang Qing-An, Yu Hong, Lei Shuang-Ying
Chin. Phys. B, 2008, 17 (11): 4292-4299 doi: 10.1088/1674-1056/17/11/055
Full Text: [PDF 309 KB] (Downloads:465)
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Electromechanical property of a p-type single-crystal silicon nanoplate is modelled by a microscopic approach where the hole quantization effect and the spin--orbit coupling effect are taken into account. The visible anisotropic subband structures are calculated by solving self-consistently the stress-dependent 6$\times $6 ${\bm k} \cdot {\bm p} $ Schr\"{o}dinger equation with the Poisson equation. The strong mixing among heavy, light, and split-off holes is quantitatively assessed. The influences of the thickness and the temperature on the piezoresistive coefficient are quantitatively investigated by using the hole concentrations and the effective masses from the complex dispersion structure of the valence band with and without stresses. Our results show that the stress determines the extent to which the band is mixed. The hole quantization effect increases as the thickness decreases, and therefore the valence band is strongly reshaped, resulting in the size-dependent piezoresistivity of the silicon nanoplate. The piezoresistive coefficient increases almost 4 times as the thickness reduces from the bulk to 3\,nm, exhibiting a promising application in mechanical sensors.

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Liang Song, Zhu Hong-Liang, Pan Jiao-Qing, Zhao Ling-Juan, Wang Lu-Feng, Zhou Fan, Shu Hui-Yun, Bian Jing, An Xin, Wang Wei
Chin. Phys. B, 2008, 17 (11): 4300-4304 doi: 10.1088/1674-1056/17/11/056
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Photoluminescence (PL) and lasing properties of InAs/GaAs quantum dots (QDs) with different growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the low growth rate sample shows a greater blueshift of PL peak wavelength. This is caused by the larger InAs layer thickness which results from the larger 2--3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named {indium flush method,} is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blueshift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.

Interface dipole induced by asymmetric exchange effect in Mott-insulator/Mott-insulator heterojunction

Hao Lei, Wang Jun
Chin. Phys. B, 2008, 17 (11): 4305-4311 doi: 10.1088/1674-1056/17/11/057
Full Text: [PDF 523 KB] (Downloads:453)
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We study theoretically the interfacial electronic property of a heterojunction made from two Mott insulators (MI) with different magnetic structures. By means of unrestricted Hartree-Fock calculations in real space, we find that a charge dipole can form spontaneously near the interface of the MI/MI heterojunction. The magnitude of this charge dipole depends strongly on the magnetic states of both sides of the heterojunction. Combining with the result from an exactly solvable two-site toy model, we argue that the interface dipole arises from exchange effects as well as its asymmetry intrinsic to the heterojunction near the interface. Our study may shed light on the fabrication of ultrathin ferroelectric and magnetoelectric devices.

Performance and analytical modelling of halo-doped surrounding gate MOSFETs

Li Zun-Chao
Chin. Phys. B, 2008, 17 (11): 4312-4317 doi: 10.1088/1674-1056/17/11/058
Full Text: [PDF 1287 KB] (Downloads:546)
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Halo structure is added to sub-100\,nm surrounding-gate metal--oxide--semiconductor field- effect-transistors (MOSFETs) to suppress short channel effect. This paper develops the analytical surface potential and threshold voltage models based on the solution of Poisson's equation in fully depleted condition for symmetric halo-doped cylindrical surrounding gate MOSFETs. The performance of the halo-doped device is studied and the validity of the analytical models is verified by comparing the analytical results with the simulated data by three dimensional numerical device simulator Davinci. It shows that the halo doping profile exhibits better performance in suppressing threshold voltage roll-off and drain-induced barrier lowering, and increasing carrier transport efficiency. The derived analytical models are in good agreement with Davinci.

The effect of doped ions on single-molecule magnets of the Mn12-Ac family

Zhang Jun-Rong, He Lun-Hua, Cao Hui-Bo, Wang Fang-Wei, Zhang Pan-Lin
Chin. Phys. B, 2008, 17 (11): 4318-4322 doi: 10.1088/1674-1056/17/11/059
Full Text: [PDF 432 KB] (Downloads:476)
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This paper investigates the single-molecule magnets of pure and Cr/Fe-doped Mn$_{12}$-Ac. The components of the mixed crystals are identified by AC susceptibility technique. The ground-state spin and anisotropy parameters of doped \mbox{Mn$_{12}$-Ac} are obtained: (i) \mbox{Mn$_{11}$Cr-Ac} ($S$=19/2, $D$=0.62\,K, $B$=0.0009\,K, $\De$=63\,K), and (ii) \mbox{Mn$_{11}$Fe-Ac} ($S$=21/2, $D$=0.39\,K, $B$=0.001\,K, $\De$=55\,K). The single-ion origin of the magnetic anisotropy is discussed.

Enhanced mechanical behaviour of lead zirconate titanate piezoelectric composites incorporating zinc oxide nanowhiskers

Lin Hai-Bo, Cao Mao-Sheng, Yuan Jie, Wang Da-Wei, Zhao Quan-Liang, Wang Fu-Chi
Chin. Phys. B, 2008, 17 (11): 4323-4327 doi: 10.1088/1674-1056/17/11/060
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This paper reports that the lead zirconate titanate (PZT) piezoelectric composites incorporating zinc oxide nanowhiskers (ZnO$_{\rm w})$ were prepared by the conventional solid state processing. The whisker-dispersed PZT composites (PZT/ZnO$_{\rm w})$ presented a significant enhancement in the mechanical properties such as Young's modulus, tensile strength and compressive strength. Especially, the compressive strength increased from 153\,MPa for the PZT to 228\,MPa for the PZT/ZnO$_{\rm w}$ composites. The reinforcement mechanism in strength of the composites was discussed. The mechanical quality factors of the PZT/ZnO$_{\rm w }$ composites increased considerably, while the piezoelectric constants and electromechanical coupling coefficient decreased slightly. The composites with good electrical and excellent mechanical properties are promising for further applications.

Spectroscopic study of thulium doped transparent glass ceramics

Zhang Xiang-Yu, Zheng Hai-Rong, Gao Dang-Li
Chin. Phys. B, 2008, 17 (11): 4328-4332 doi: 10.1088/1674-1056/17/11/061
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A systematic investigation on °uorescence spectroscopy of trivalent thulium doped in oxy°uoride glass ceramics containing LaF3 nanocrystals has been carried out in a spectral range from 400 to 900nm under the direct excitation of 1D2 level at a low temperature. Speciˉc optical transitions related to the °uorescence emissions are studied based on experimental measurements in frequency and time domain. Fluorescence emissions from the ions in crystal phase are distinguished from what in glass phase and their spectroscopic properties are explored. The dynamical process shows that the temporal decay of °uorescence emission consists of two parts: a rapid decay from the ions in glass phase and a slower decay from the ions in crystal phase.

Low-field electron emission from pinaster-like MoO2 nanoarrays as two-stage emitters

Zhang Jing-Yuan, Liu Yong-Gang, Shi Song-Lin, Wang Yan-Guo, Wang Tai-Hong
Chin. Phys. B, 2008, 17 (11): 4333-4336 doi: 10.1088/1674-1056/17/11/062
Full Text: [PDF 2117 KB] (Downloads:551)
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Low-field electron emission is obtained from the pinaster-like MoO$_{2}$ nanoarrays. The turn-on field of the pinaster-like MoO$_{2}$ nanoarrays is found to be as low as 2.39\,V/$\mu $m with the current density of 10\,$\mu $A/cm$^{2}$. The enhancement factor is extracted to be 3590 from the Fowler--Nordheim plot. These excellent emission properties are attributed to the special structure of the pinaster-like MoO$_{2}$ nanoarrays and confirmed by the calculation in the frame of the two -stage model. Our results show that the pinaster-like MoO$_{2}$ nanoarrays are promising candidate in realizing field emission displays.
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