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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.2
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GENERAL

Template identification technology of nuclear warheads and components

Liu Su-Ping, Gong Jian, Hao Fan-Hua, Hu Guang-Chun
Chin. Phys. B, 2008, 17 (2): 363-369 doi: 10.1088/1674-1056/17/2/001
Full Text: [PDF 545 KB] (Downloads:924)
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Template identification technology (TIT) is designed for the scenarios where a batch of disarmed nuclear weapons or components would be dismantled to observe a nuclear disarmament treaty. The core function played by the TIT is to make a judgment on whether the verified item belongs to a certain kind of nuclear weapons or component (NW/NC) or to which kind the verified item belongs. This paper analyses the functions played by the TIT in the process of NW/NC dismantlement, and proposes that two phases would be followed when applying the TIT: firstly to establish NW/NC templates with a sample of size n drawn from a certain kind of disarmament NW; secondly to authenticate NW/NC by means of the TIT. This paper also expatiates some terms related to the concept of the TIT and investigates on the development status of NW/NC TIT based on radiation signatures. The study concludes that the design of template structure is crucial to the establishment of an effective TIT and that starting from different research angles and aiming at the same goal of classification different template structures and corresponding template identification methods can be built up to meet specific identification requirements.

Asymptotic solution for a class of sea--air oscillator model for El Nino--southern oscillation

Mo Jia-Qi, Lin Wan-Tao
Chin. Phys. B, 2008, 17 (2): 370-372 doi: 10.1088/1674-1056/17/2/002
Full Text: [PDF 119 KB] (Downloads:713)
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The El Ni\~{n}o--Southern Oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific Ocean--atmosphere interactions. In this paper, an asymptotic method of solving the nonlinear equation for the ENSO model is used. And based on a class of oscillator of ENSO model, the approximate solution of a corresponding problem is studied by employing the perturbation method. Firstly, an ENSO model of nonlinear time delay equation of equatorial Pacific is introduced, Secondly, by using the perturbed method, the zeroth and first order asymptotic perturbed solutions are constructed. Finally, from the comparison of the values for a figure, it is seen that the first asymptotic perturbed solution using the perturbation method has a good accuracy. And it is proved from the results that the perturbation method can be used as an analytic operation for the sea surface temperature anomaly in the equatorial Pacific of the atmosphere-ocean oscillation for the ENSO model.

A dynamic epidemic control model on uncorrelated complex networks

Pei Wei-Dong, Chen Zeng-Qiang, Yuan Zhu-Zhi
Chin. Phys. B, 2008, 17 (2): 373-379 doi: 10.1088/1674-1056/17/2/003
Full Text: [PDF 175 KB] (Downloads:716)
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In this paper, a dynamic epidemic control model on the uncorrelated complex networks is proposed. By means of theoretical analysis, we found that the new model has a similar epidemic threshold as that of the susceptible-infected-recovered (SIR) model on the above networks, but it can reduce the prevalence of the infected individuals remarkably. This result may help us understand epidemic spreading phenomena on real networks and design appropriate strategies to control infections.

The relativistic bound states for a new ring-shaped harmonic oscillator

Zhou Yan, Guo Jian-You
Chin. Phys. B, 2008, 17 (2): 380-384 doi: 10.1088/1674-1056/17/2/004
Full Text: [PDF 114 KB] (Downloads:570)
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In this paper a new ring-shaped harmonic oscillator for spin 1/2 particles is studied, and the corresponding eigenfunctions and eigenenergies are obtained by solving the Dirac equation with equal mixture of vector and scalar potentials. Several particular cases such as the ring-shaped non-spherical harmonic oscillator, the ring-shaped harmonic oscillator, non-spherical harmonic oscillator, and spherical harmonic oscillator are also discussed.

The Lie symmetries and Noether conserved quantities of discrete non-conservative mechanical systems

Shi Shen-Yang, Fu Jing-Li, Chen Li-Qun
Chin. Phys. B, 2008, 17 (2): 385-389 doi: 10.1088/1674-1056/17/2/005
Full Text: [PDF 105 KB] (Downloads:605)
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This paper investigates the Lie symmetries and Noether conserved quantities of discrete non-conservative mechanical systems. The variational principle of discrete mechanics, from which discrete motion equations of systems are deduced, is generalized to the case of including the time variational. The requirement for an invariant group transformation is defined to be the Lie symmetry and the criterion when the Noether conserved quantities may be obtained from Lie symmetries is also presented. An example is discussed for applications of the results.

Hojman conserved quantity deduced by weak Noether symmetry for Lagrange systems

Xie Jia-Fang, Gang Tie-Qiang, Mei Feng-Xiang
Chin. Phys. B, 2008, 17 (2): 390-393 doi: 10.1088/1674-1056/17/2/006
Full Text: [PDF 87 KB] (Downloads:422)
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This paper studies the Hojman conserved quantity, a non-Noether conserved quantity, deduced by special weak Noether symmetry for Lagrange systems. Under special infinitesimal transformations in which the time is not variable, its criterion is given and a method of how to seek the Hojman conserved quantity is presented. A Hojman conserved quantity can be found by using the special weak Noether symmetry.

A new type of conserved quantity of Mei symmetry for relativistic nonholonomic mechanical system in phase space

Zhang Xiao-Ni, Fang Jian-Hui, Pang Ting, Lin Peng
Chin. Phys. B, 2008, 17 (2): 394-398 doi: 10.1088/1674-1056/17/2/007
Full Text: [PDF 105 KB] (Downloads:458)
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In this paper, a new type of conserved quantity induced directly from the Mei symmetry for a relativistic nonholonomic mechanical system in phase space is studied. The definition and the criterion of the Mei symmetry for the system are given. The conditions for the existence and form of the new conserved quantity are obtained. Finally, an example is given to illustrate the application of the result.

A new expansion method of first order nonlinear ordinary differential equation with at most a sixth-degree nonlinear term and its application to mBBM model

Pan Jun-Ting, Gong Lun-Xun
Chin. Phys. B, 2008, 17 (2): 399-402 doi: 10.1088/1674-1056/17/2/008
Full Text: [PDF 99 KB] (Downloads:618)
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Based on a first order nonlinear ordinary differential equation with at most a sixth-degree nonlinear term which is extended from a type of elliptic equation, and by converting it into a new expansion form, this paper proposes a new algebraic method to construct exact solutions for nonlinear evolution equations. Being concise and straightforward, the method is applied to modified Benjamin--Bona--Mahony (mBBM) model, and some new exact solutions to the system are obtained. The algorithm is of important significance in exploring exact solutions for other nonlinear evolution equations.

Some new exact solutions of Jacobian elliptic function about the generalized Boussinesq equation and Boussinesq--Burgers equation

Zhang Liang, Zhang Li-Feng, Li Chong-Yin
Chin. Phys. B, 2008, 17 (2): 403-410 doi: 10.1088/1674-1056/17/2/009
Full Text: [PDF 119 KB] (Downloads:665)
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By using the modified mapping method, we find some new exact solutions of the generalized Boussinesq equation and the Boussinesq--Burgers equation. The solutions obtained in this paper include Jacobian elliptic function solutions, combined Jacobian elliptic function solutions, soliton solutions, triangular function solutions.

Scheme for realizing assisted cloning of an unknown two-atom entangled state via cavity QED

Zhan You-Bang
Chin. Phys. B, 2008, 17 (2): 411-414 doi: 10.1088/1674-1056/17/2/010
Full Text: [PDF 93 KB] (Downloads:502)
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This paper proposes a scheme where one can realize quantum cloning of an unknown two-atom entangled state with assistance of a state preparer in cavity QED. The first stage of the scheme requires usual teleportation. In the second stage of the scheme, with the assistance of the preparer, the perfect copies of an unknown atomic entangled state can be produced.

Multi-proxy quantum group signature scheme with threshold shared verification

Yang Yu-Guang
Chin. Phys. B, 2008, 17 (2): 415-418 doi: 10.1088/1674-1056/17/2/011
Full Text: [PDF 102 KB] (Downloads:565)
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A multi-proxy quantum group signature scheme with threshold shared verification is proposed. An original signer may authorize a proxy group as his proxy agent. Then only the cooperation of all the signers in the proxy group can generate the proxy signature on behalf of the original signer. In the scheme, any $t$ or more of $n$ receivers can verify the message and any $t-1$ or fewer receivers cannot verify the validity of the proxy signature.

Circular threshold quantum secret sharing

Yang Yu-Guang, Wen Qiao-Yan
Chin. Phys. B, 2008, 17 (2): 419-423 doi: 10.1088/1674-1056/17/2/012
Full Text: [PDF 108 KB] (Downloads:508)
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This paper proposes a circular threshold quantum secret sharing (TQSS) scheme with polarized single photons. A polarized single photon sequence runs circularly among any $t$ or more of $n$ parties and any $t$ or more of $n$ parties can reconstruct the secret key when they collaborate. It shows that entanglement is not necessary for quantum secret sharing. Moreover, the theoretic efficiency is improved to approach 100{\%} as the single photons carrying the secret key are deterministically forwarded among any $t$ or more of $n$ parties, and each photon can carry one bit of information without quantum storage. This protocol is feasible with current technology.

Generation of unconventional geometric phase gates in ion trap-optical cavity system by squeezed operators

Zhang Ying-Qiao, Jin Xing-Ri, Zhang Shou
Chin. Phys. B, 2008, 17 (2): 424-430 doi: 10.1088/1674-1056/17/2/013
Full Text: [PDF 144 KB] (Downloads:385)
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Based on squeezed operators this paper has implemented an ideal unconventional geometric quantum gate (GQG) in ion trap-optical cavity system by radiating the trapped ions with the cavity field of frequency $\omega_c}$ and an external laser field of frequency $\omega_L}$. It can ensure that the gate time is shorter than the coherence time for qubits and the decay time of the optical cavity by appropriately tuning the ionic transition frequency $\omega_{0}$, the frequencies of the cavity mode $\omega_c}$ and the vibrational mode $\nu$. It has also realized the unconventional GQG under the influence of the cavity decay based on the squeezed-like operators and found that the present scheme works well for the smaller cavity decay by investigating the corresponding fidelity and success probability.

Scheme for implementing quantum dense coding with four-particle decoherence-free states in an ion trap

Zheng Xiao-Juan, Cao Shuai, Fang Mao-Fa, Liao Xiang-Ping
Chin. Phys. B, 2008, 17 (2): 431-434 doi: 10.1088/1674-1056/17/2/014
Full Text: [PDF 182 KB] (Downloads:473)
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This paper proposes an experimentally feasible scheme for implementing quantum dense coding of trapped-ion system in decoherence-free states. As the phase changes due to time evolution of components with different eigenenergies of quantum superposition are completely frozen, quantum dense coding based on this model would be perfect. The scheme is insensitive to heating of vibrational mode and Bell states can be exactly distinguished via detecting the ionic state.

Factors influencing entanglement of two excitons in a coupled exciton--photon system

Yang Xiong, Xiang Shao-Hua, Song Ke-Hui
Chin. Phys. B, 2008, 17 (2): 435-439 doi: 10.1088/1674-1056/17/2/015
Full Text: [PDF 144 KB] (Downloads:399)
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The relation between the excitonic purity and the concurrence in a system of two coupled large semiconduction quantum dots mediated by a single-mode cavity field is investigated by using linear entropy theory. The results show the difference in describing two modes of excitonic entanglement between linear entropy and concurrence. The relation between nonclassical property of cavity field and the entanglement degree of excitons is also discussed. The results show that two modes of exciton can reach maximal entanglement when the cavity exhibits an antibunching effect.

Relation between quantum NOT gate speed and asymmetry of the potential of RF-SQUID

Ji Ying-Hua, Cai Shi-Hua, Hu Ju-Ju
Chin. Phys. B, 2008, 17 (2): 440-444 doi: 10.1088/1674-1056/17/2/016
Full Text: [PDF 179 KB] (Downloads:450)
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This paper investigates the relationship between the speed of a quantum not gate and the asymmetry of the potential in an interactive system formed by a two-level RF-SQUID qubit and a classical microwave pulse. The RF-SQUID is characterized by an asymmetric double well potential which gives rise to diagonal matrix elements that describe the interaction of the SQUID with the microwave pulse. And the diagonal matrix elements account for the interaction of the microwave pulse with the SQUID. The results indicate that, when the angular frequency of the microwave field is chosen as near resonate with the transition $\left| 0 \right\rangle \leftrightarrow \left| 1 \right\rangle$, i.e. $\omega_1-\omega_0 \approx \omega_{\rm m}$, (1) the gate speed is decided by three factors, the Rabi frequency, the difference of the diagonal matrix elements between the two levels, and the angular frequency of the applied microwave pulse $\omega _{\rm m} $; (2) the gate speed descends when the asymmetry of the potential is considered.

Scheme for probabilistic remotely preparing a multi-particle entangled GHZ state

Ma Peng-Cheng, Zhan You-Bang
Chin. Phys. B, 2008, 17 (2): 445-450 doi: 10.1088/1674-1056/17/2/017
Full Text: [PDF 115 KB] (Downloads:460)
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This paper presents a scheme for probabilistic remote preparation of a three-particle entangled Greenberger--Horne--Zeilinger (GHZ) state via three-particle orthonormal basis projective measurement, and then directly generalize the scheme to multi-particle case. It is shown that by using $N$ pairs of bipartite non-maximally entangled states as the quantum channel and $N$-particle orthonormal basis projective measurement, the multi-particle remote preparation can be successfully realized with a certain probability.

Scheme for teleportation of unknown states of trapped ion

Chen Mei-Feng, Ma Song-She
Chin. Phys. B, 2008, 17 (2): 451-455 doi: 10.1088/1674-1056/17/2/018
Full Text: [PDF 106 KB] (Downloads:403)
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A scheme is presented for teleporting an unknown state in a trapped ion system. The scheme only requires a single laser beam. It allows the trap to be in any state with a few phonons, e.g. a thermal motion. Furthermore, it works in the regime, where the Rabi frequency of the laser is on the order of the trap frequency. Thus, the teleportation speed is greatly increased, which is important for decreasing the decoherence effect. This idea can also be used to teleport an unknown ionic entangled state.

Entanglement of a two-qubit anisotropic Heisenberg XYZ chain in nonuniform magnetic fields with intrinsic decoherence

Xu Xiao-Bo, Liu Jin-Ming, Yu Peng-Fei
Chin. Phys. B, 2008, 17 (2): 456-461 doi: 10.1088/1674-1056/17/2/019
Full Text: [PDF 523 KB] (Downloads:620)
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Taking the intrinsic decoherence effect into account, this paper investigates the entanglement of a two-qubit anisotropic Heisenberg XYZ model in the presence of nonuniform external magnetic fields by employing the concurrence as entanglement measure. It is found that both the intrinsic decoherence and the anisotropy of the system give a significant suppression to the entanglement. Moreover it finds that the initial state of the system plays an important role in the time evolution of the entanglement, which means that the entanglement of the system is independent of the nonuniformity and uniformity of the magnetic field when the system is in the initial state \left| \Ps \left( 0\right) \right\rangle =\left| 00\right\rangle and \left| \Ps’\left( 0\right) \right\rangle =m\left| 01\right\rangle +n\left| 10\right\rangle , respectively.

Scheme for splitting quantum information via W states in cavity QED systems

Yu Xi-Mei, Gu Yong-Jian, Ma Li-Zhen, Zhou Bang-An
Chin. Phys. B, 2008, 17 (2): 462-466 doi: 10.1088/1674-1056/17/2/020
Full Text: [PDF 143 KB] (Downloads:557)
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Assisted by multipartite entanglement, Quantum information may be split so that the original qubit can be reconstructed if and only if the recipients cooperate. This paper proposes an experimentally feasible scheme for splitting quantum information via W-type entangled states in cavity QED systems, where three-level Rydberg atoms interact with nonresonant cavities. Since W-type states are used as the quantum channel and the cavities are only virtually excited, the scheme is easy to implement and robust against decoherence, and the dependence on the quality factor of the cavities is greatly reduced.

Entropy of quantum field in toroidal black hole without brick wall

Wang Bo-Bo
Chin. Phys. B, 2008, 17 (2): 467-472 doi: 10.1088/1674-1056/17/2/021
Full Text: [PDF 122 KB] (Downloads:388)
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In this paper the entropy of a toroidal black hole due to a scalar field is investigated by using the DLM scheme. The entropy is renormalized to the standard Bekenstein--Hawking formula with a one-loop correction arising from the higher curvature terms of the gravitational action. For the scalar field, the renormalized Newton constant and two renormalized coupling constants in the toroidal black hole are the same as those in the Reissner--Nordstrom black hole except for other one.

An extended master-equation approach applied to aggregation in freeway traffic

Li Jun-Wei, Lin Bo-Liang, Huang Yong-Chang
Chin. Phys. B, 2008, 17 (2): 473-478 doi: 10.1088/1674-1056/17/2/022
Full Text: [PDF 230 KB] (Downloads:460)
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We restudy the master-equation approach applied to aggregation in a one-dimensional freeway, where the decay transition probabilities for the jump processes are reconstructed based on a car-following model. According to the reconstructed transition probabilities, the clustering behaviours and the stochastic properties of the master equation in a one-lane freeway traffic model are investigated in detail. The numerical results show that the size of the clusters initially below the critical size of the unstable cluster and initially above that of the unstable cluster all enter the same stable state, which also accords with the nucleation theory and is known from the result in earlier work. Moreover, we have obtained more reasonable parameters of the master equation based on some results of cellular automata models.

Transitions in a genotype selection model driven by coloured noises

Wang Can-Jun, Mei Dong-Cheng
Chin. Phys. B, 2008, 17 (2): 479-485 doi: 10.1088/1674-1056/17/2/023
Full Text: [PDF 289 KB] (Downloads:496)
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This paper investigates a genotype selection model subjected to both a multiplicative coloured noise and an additive coloured noise with different correlation time $\tau_{1}$ and $\tau_{2}$ by means of the numerical technique. By directly simulating the Langevin Equation, the following results are obtained. (1) The multiplicative coloured noise dominates, however, the effect of the additive coloured noise is not neglected in the practical gene selection process. The selection rate $\mu$ decides that the selection is propitious to gene $A$ haploid or gene $B$ haploid. (2) The additive coloured noise intensity $\alpha$ and the correlation time $\tau_2$ play opposite roles. It is noted that $\alpha$ and $\tau_2$ can not separate the single peak, while $\alpha$ can make the peak disappear and $\tau_2$ can make the peak be sharp. (3) The multiplicative coloured noise intensity $D$ and the correlation time $\tau_1$ can induce phase transition, at the same time they play opposite roles and the reentrance phenomenon appears. In this case, it is easy to select one type haploid from the group with increasing $D$ and decreasing $\tau_1$.

Stochastic resonance in an asymmetric bistable system driven by coloured correlated multiplicative and additive noise

Ning Li-Juan, Xu Wei, Yao Ming-Li
Chin. Phys. B, 2008, 17 (2): 486-491 doi: 10.1088/1674-1056/17/2/024
Full Text: [PDF 432 KB] (Downloads:571)
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This paper investigates the stochastic resonance (SR) phenomenon in an asymmetric system with coupling between multiplicative and additive noise when the coupling between two noise terms is coloured. The approximate expression of signal-to-noise ratio has been obtained by applying the two-state theory and SR exhibits in the bistable system. Moreover, the potential asymmetry $r$ and cross-correlation strength $\lambda$ can weaken the SR phenomenon, while the cross-correlation time $\tau $ can strengthen the SR phenomenon.

Passive control and synchronization of hyperchaotic Chen system

Zhang Qun-Jiao, Lu Jun-An
Chin. Phys. B, 2008, 17 (2): 492-497 doi: 10.1088/1674-1056/17/2/025
Full Text: [PDF 135 KB] (Downloads:595)
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This paper investigates the control and synchronization of hyperchaotic Chen system based on the passive theory. By using two outputs, novel passive controllers are respectively designed to realize the globally asymptotical stability of the hyperchaotic Chen system and the error dynamical system, which avoids mistakes in Ref.[11], where function $W(z)$ cannot guarantee that $f_0(z)$ is globally asymptotically stable via only one output and $W(z)$ is the Lyapunov function of $f_0(z)$. Furthermore, numerical simulations are given to show the effectiveness of our method.

Backstepping synchronization of uncertain chaotic systems by a single driving variable

Lü Ling, Zhang Qing-Ling, Guo Zhi-An
Chin. Phys. B, 2008, 17 (2): 498-502 doi: 10.1088/1674-1056/17/2/026
Full Text: [PDF 612 KB] (Downloads:594)
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In this paper a parameter observer and a synchronization controller are designed to synchronize unknown chaotic systems with diverse structures. Based on stability theory the structures of the observer and the controller are presented. The unknown Coullet system and Rossler system are taken for examples to demonstrate that the method is effective and feasible. The artificial simulation results show that global synchronization between the unknown Coullet system and the Rossler system can be achieved by a single driving variable with co-operation of the observer and the controller, and all parameters of the Coullet system can be identified at the same time.

Adaptive synchronization of uncertain Liu system via nonlinear input

Hu Jia, Zhang Qun-Jiao
Chin. Phys. B, 2008, 17 (2): 503-506 doi: 10.1088/1674-1056/17/2/027
Full Text: [PDF 105 KB] (Downloads:534)
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This paper addresses the adaptive synchronization for uncertain Liu system via a nonlinear input. By using a single nonlinear controller, the approach is utilized to implement the synchronization of Liu system with total parameters unknown. This method is simple and can be easily designed. What is more, it improves the existing conclusions in Ref [12]. Simulation results prove that the controller is effective and feasible in the end.

Controlling chaos based on an adaptive nonlinear compensator mechanism

Tian Ling-Ling, Li Dong-Hai, Sun Xian-Fang
Chin. Phys. B, 2008, 17 (2): 507-519 doi: 10.1088/1674-1056/17/2/028
Full Text: [PDF 1110 KB] (Downloads:476)
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The control problems of chaotic systems are investigated in the presence of parametric uncertainty and persistent external disturbances based on nonlinear control theory. By using a designed nonlinear compensator mechanism, the system deterministic nonlinearity, parametric uncertainty and disturbance effect can be compensated effectively. The renowned chaotic Lorenz system subjected to parametric variations and external disturbances is studied as an illustrative example. From the Lyapunov stability theory, sufficient conditions for choosing control parameters to guarantee chaos control are derived. Several experiments are carried out, including parameter change experiments, set-point change experiments and disturbance experiments. Simulation results indicate that the chaotic motion can be regulated not only to steady states but also to any desired periodic orbits with great immunity to parametric variations and external disturbances.

Robust adaptive synchronization of chaotic neural networks by slide technique

Lou Xu-Yang, Cui Bao-Tong
Chin. Phys. B, 2008, 17 (2): 520-528 doi: 10.1088/1674-1056/17/2/029
Full Text: [PDF 164 KB] (Downloads:577)
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In this paper, we focus on the robust adaptive synchronization between two coupled chaotic neural networks with all the parameters unknown and time-varying delay. In order to increase the robustness of the two coupled neural networks, the key idea is that a sliding-mode-type controller is employed. Moreover, without the estimate values of the network unknown parameters taken as an updating object, a new updating object is introduced in the constructing of controller. Using the proposed controller, without any requirements for the boundedness, monotonicity and differentiability of activation functions, and symmetry of connections, the two coupled chaotic neural networks can achieve global robust synchronization no matter what their initial states are. Finally, the numerical simulation validates the effectiveness and feasibility of the proposed technique.

Anticontrol of chaos for discrete-time fuzzy hyperbolic model with uncertain parameters

Zhao Yan, Zhang Hua-Guang, Zheng Cheng-De
Chin. Phys. B, 2008, 17 (2): 529-535 doi: 10.1088/1674-1056/17/2/030
Full Text: [PDF 330 KB] (Downloads:443)
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This paper proposes a new method to chaotify the discrete-time fuzzy hyperbolic model (DFHM) with uncertain parameters. A simple nonlinear state feedback controller is designed for this purpose. By revised Marotto theorem, it is proven that the chaos generated by this controller satisfies the Li--Yorke definition. An example is presented to demonstrate the effectiveness of the approach.

Multi-step-prediction of chaotic time series based on co-evolutionary recurrent neural network

Ma Qian-Li, Zheng Qi-Lun, Peng Hong, Zhong Tan-Wei, Qin Jiang-Wei
Chin. Phys. B, 2008, 17 (2): 536-542 doi: 10.1088/1674-1056/17/2/031
Full Text: [PDF 192 KB] (Downloads:584)
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This paper proposes a co-evolutionary recurrent neural network (CERNN) for the multi-step-prediction of chaotic time series, it estimates the proper parameters of phase space reconstruction and optimizes the structure of recurrent neural networks by co-evolutionary strategy. The searching space was separated into two subspaces and the individuals are trained in a parallel computational procedure. It can dynamically combine the embedding method with the capability of recurrent neural network to incorporate past experience due to internal recurrence. The effectiveness of CERNN is evaluated by using three benchmark chaotic time series data sets: the Lorenz series, Mackey--Glass series and real-world sun spot series. The simulation results show that CERNN improves the performances of multi-step-prediction of chaotic time series.

Gradient control and synchronization of Julia sets

Zhang Yong-Ping, Liu Shu-Tang
Chin. Phys. B, 2008, 17 (2): 543-549 doi: 10.1088/1674-1056/17/2/032
Full Text: [PDF 483 KB] (Downloads:433)
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This paper firstly introduces the control methods to fractals and give the definition of synchronization of Julia sets between two different systems. Especially, the gradient control method is taken on the classic Julia sets of complex quadratic polynomial $z_{n+1}=z_n^2+c$, which realizes its Julia sets control and synchronization. The simulations illustrate the effectiveness of the method.

Synchronization of chaos in resistive-capacitive-inductive shunted Josephson junctions

Feng Yu-Ling, Shen Ke
Chin. Phys. B, 2008, 17 (2): 550-556 doi: 10.1088/1674-1056/17/2/033
Full Text: [PDF 2243 KB] (Downloads:461)
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We present a scheme for chaotic synchronization in two resistive- capacitive-inductive shunted Josephson junctions (RCLSJJs) by using another chaotic RCLSJJ as a driving system. Numerical simulations show that whether the two RCLSJJs are chaotic or not before being driven, they can realize chaotic synchronization with a suitable driving intensity, under which the maximum condition Lyapunov exponent (MCLE) is negative. On the other hand, if the driving system is in different periodic states or chaotic states, the two driven RCLSJJs can be controlled into the periodic states with different period numbers or chaotic states but still maintain the synchronization.

Chaotic motion of the dynamical system under both additive and multiplicative noise excitations

Li Xiu-Chun, Xu Wei, Li Rui-Hong
Chin. Phys. B, 2008, 17 (2): 557-568 doi: 10.1088/1674-1056/17/2/034
Full Text: [PDF 343 KB] (Downloads:559)
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With both additive and multiplicative noise excitations, the effect on the chaotic behaviour of the dynamical system is investigated in this paper. The random Melnikov theorem with the mean-square criterion that applies to a type of dynamical systems is analysed in order to obtain the conditions for the possible occurrence of chaos. As an example, for the Duffing system, we deduce its concrete expression for the threshold of multiplicative noise amplitude for the rising of chaos, and by combining figures, we discuss the influences of the amplitude, intensity and frequency of both bounded noises on the dynamical behaviour of the Duffing system separately. Finally, numerical simulations are illustrated to verify the theoretical analysis according to the largest Lyapunov exponent and Poincar\'{e} map.

Dynamical behaviour of Liu system with time delayed feedback

Qian Qin, Wang Lin, Ni Qiao
Chin. Phys. B, 2008, 17 (2): 569-572 doi: 10.1088/1674-1056/17/2/035
Full Text: [PDF 1402 KB] (Downloads:2476)
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This paper investigates the dynamical behaviour of the Liu system with time delayed feedback. Two typical situations are considered and the effect of time-delay parameter on the dynamics of the system is discussed. It is shown that the Liu system with time delayed feedback may exhibit interesting and extremely rich dynamical behaviour. The evolution of the dynamics is shown to be complex with varying time-delay parameter. Moreover, the strange attractor like `wormhole' is detected via numerical simulations.

Space radiation effect on fibre optical gyroscope control circuit and compensation algorithm

Zhang Chun-Xi, Tian Hai-Ting, Li Min, Jin Jing, Song Ning-Fang
Chin. Phys. B, 2008, 17 (2): 573-577 doi: 10.1088/1674-1056/17/2/036
Full Text: [PDF 145 KB] (Downloads:474)
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The process of a $\gamma $-irradiation experiment of fibre optical gyroscope (FOG) control circuit was described, in which it is demonstrated that the FOG control circuit, except for D/A converter, could endure the dose of 10krad with the protection of cabin material. The distortion and drift in D/A converter due to radiation, which affect the performance of FOG seriously, was indicated based on the elemental analysis. Finally, a compensation network based on adaptive neuro-fuzzy inference system is proposed and its function is verified by simulation.
NUCLEAR PHYSICS

The mass effect of the quark phase transition in supernova core

Lai Xiang-Jun, Liu Men-Quan, Liu Jing-Jing, Luo Zhi-Quan
Chin. Phys. B, 2008, 17 (2): 585-591 doi: 10.1088/1674-1056/17/2/038
Full Text: [PDF 152 KB] (Downloads:739)
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Constituent quark mass model is adopted as a tentative one to study the phase transition between two-flavour quark matter and more stable three-flavour quark matter in the core of supernovae. The result shows that the transition has a significant influence on the increasing of the core temperature, the neutrino abundance and the neutrino energies, which contributes to the enhancement of the successful probability of supernova explosion. However, the equilibrium values of these parameters (except the temperature) from the constituent quark mass model in this work are slightly bigger than those obtained from the other model. And we find that the constituent quark mass model is also applicable to describing the transition in the supernova core.
CLASSICAL AREAS OF PHENOMENOLOGY

The transient scattering mechanism of dipole array with reflector

Zhang Xue-Qin, Wang Jun-Hong, Li Zeng-Rui
Chin. Phys. B, 2008, 17 (2): 608-617 doi: 10.1088/1674-1056/17/2/041
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The transient backscattering mechanisms of a dipole array with reflector have been investigated from different aspects: time-domain, frequency-domain, and combined time-frequency domain, using $4\times 8$ dipole arrays with reflector as an example. The data of scattering from the arrays under the incidence of Gaussian pulses are obtained by finite differential time domain method. The influences of the array structural parameters, incident wave parameters, and incident angles on the waveforms, spectrum, and time-frequency representations of the backscattered fields of the arrays are analysed and conclusions are drawn. From these characteristics and conclusions, it is possible to deduce the array structure inversely from the backscattered field.

The entropic squeezing of superposition of two arbitrary coherent states

Lu Dao-Ming
Chin. Phys. B, 2008, 17 (2): 618-623 doi: 10.1088/1674-1056/17/2/042
Full Text: [PDF 954 KB] (Downloads:385)
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In this paper the superpositions of two arbitrary coherent states $\left| \psi \right\rangle = a\left| \beta \right\rangle + b{\rm e}^{{\rm i}\varphi }\left| {m\beta {\rm e}^{{\rm i}\delta }} \right\rangle $ are constructed by using the superposition principle of quantum mechanics. The entropic squeezing effects of the quantum states are studied. The numerical results indicate that the amplitudes, the ratio between the amplitudes of two coherent states, the phase difference between the two components and the relative phase of the two coefficients play important roles in the squeezing effects of the position entropy and momentum entropy.

Quantum state sharing of an arbitrary qudit state by using nonmaximally generalized GHZ state

Tao Ying-Juan, Tian Dong-Ping, Hu Ming-Liang, Qin Meng
Chin. Phys. B, 2008, 17 (2): 624-627 doi: 10.1088/1674-1056/17/2/043
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We present a scheme for quantum state sharing of an arbitrary qudit state by using nonmaximally entangled generalized Greenberger--Horne--Zeilinger (GHZ) states as the quantum channel and generalized Bell-basis states as the joint measurement basis. We show that the probability of successful sharing an unknown qudit state depends on the joint measurements chosen by Alice. We also give an expression for the maximally probability of this scheme.

Incoherent and coherent beam combination for master oscillator/power amplifier system with stimulated Brillouin scattering mirror

Fu Shi-You, Tian Zhao-Shuo, Shi Xiao-Li, Sun Zheng-He
Chin. Phys. B, 2008, 17 (2): 628-632 doi: 10.1088/1674-1056/17/2/044
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In this paper, we studied incoherent and coherent beam combining for the master oscillator/power amplifier (MOPA) system with stimulated Brillouin scattering (SBS) mirror. Optic field intensity distributions in the near and far field are numerically calculated for the two kinds of system. The results show that good beam quality in the far field could be obtained. It provides a theoretical basis for experimental research in the future.

1-W, high-repetition-rate room temperature operation of mid-infrared optical parametric oscillator based on periodically poled MgO-doped LiNbO

Zhang Tie-Li, Zhang Bai-Gang, Xu De-Gang, Wang Peng, Ji Feng, Yao Jian-Quan
Chin. Phys. B, 2008, 17 (2): 633-636 doi: 10.1088/1674-1056/17/2/045
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In this paper a high-repetition-rate mid-infrared (mid-IR) optical parametric oscillator based on periodically poled MgO-doped LiNbO$_{3}$ (PPMgLN) at room temperature was demonstrated. The maximum average mid-IR output power at 3.63\textit{$\mu $}m was 1.02 W with the repetition rate of 60kHz and corresponding efficiency from the pump to the idler was 26.7{\%}. The temperature tuning and the period tuning characteristics were also discussed.

Correlation dimension analysis and capillary wave turbulence in Dragon-Wash phenomena

Peng Huai-Wu, Li Rui-Qu, Chen Song-Ze, Li Cun-Biao
Chin. Phys. B, 2008, 17 (2): 637-643 doi: 10.1088/1674-1056/17/2/046
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This paper describes the evolution of surface capillary waves of deep water excited by gradually increasing the lateral external force at a single frequency. The vertical velocities of the water surface are measured by using a Polytec Laser Vibrometer with a thin layer of aluminium powder scattering on the surface to reflect the laser beam. Nonlinear interaction processes result in a stationary Fourier spectrum of the vertical surface velocities (the same as the surface elevation), i.e. $I_\omega \sim \omega ^{ - 3.5}$. The observed spectrum can be interpreted as a wave-turbulent Kolmogorov spectrum for the case of `narrowband pumping' for a direct cascade of energy. Correlation dimension analysis of the whole development process reveals four distinct stages during the wave structure development and identifies the wave turbulence stage.
ATOMIC AND MOLECULAR PHYSICS

Excitation and decay dynamics of 1s2s inner-shell double-vacancy states of neon atoms

Ding Xiao-Bin, Dong Chen-Zhong, Fumihiro Koike, Takako Kato, Stephan Fritzsche
Chin. Phys. B, 2008, 17 (2): 592-598 doi: 10.1088/1674-1056/17/2/039
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The photo-excitation and Auger decay processes of inner-shell double vacancy states 1s2s2p$^6(^{1,3}$S)3s3p of neutral neon atoms have been studied theoretically. Multi-configuration Dirac--Fock (MCDF) calculations have been carried out, with electron correlation effects taken into consideration. The relaxation of core and excited orbitals and configuration interaction are found to be crucial to creating the double vacancy states by single photo-absorption. The predominant decay paths for the double vacancy states turn out to be of the LLM Auger decay to 1s 2s$^2$2p$^5$3s(3p), KLL Auger decay to 1s$^2$2s2p$^4$3s3p, and KLM Auger decay to 1s$^2$2p$^6$3s(3p). They lead to further Auger decay, creating the neon ions of multiple charge states. For both double and single vacancy states the spectator type of Auger process is dominated in all the Auger decay processes. Theoretical Auger electron spectra are presented for further investigations, experimental and theoretical.

Semiclassical calculation of recurrence spectra of Rydberg He2+ molecular ion in a magnetic field

Wang De-Hua, Song Xin-Xiu, Ding Shi-Liang
Chin. Phys. B, 2008, 17 (2): 599-607 doi: 10.1088/1674-1056/17/2/040
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Making use of the molecular closed-orbit theory and a new model potential for the Rydberg molecule, we have calculated the recurrence spectra of He$_{2}^{ + }$ molecular ion in a magnetic field for different quantum defects. The Fourier transform spectra of He$_{2}^{ + }$ molecular ion may be used to perform a direct comparison between peaks in the spectra and the scaled action values of closed orbits of the excited electron in external fields. We find that the spectral modulations can be analysed in terms of the scattering of the excited electron on the molecular core. Unlike the case of the Rydberg atom where the elastic scattering is predominant, modulations produced by inelastic scattering are also vital to the photoabsorption spectrum of the Rydberg molecule. Our results are in good agreement with the quantum results, which suggests that our method is correct.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Interference nature of light

Yao Zhi-Xin, Zhong Jian-Wei, Mao Bang-Ning, Pan Bai-Liang
Chin. Phys. B, 2008, 17 (2): 578-584 doi: 10.1088/1674-1056/17/2/037
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Interference of light has been reinvestigated theoretically by linear superposition of two different state-vector functions, of which each describes the photons from one of two different light sources in both polarization and intensity. By the use of microscopic parameters for a photon, namely probability amplitude and phase, it is again validated that interference of light occurs only between the same photons possessing a set of the selfsame eigenvalues.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Intensity modulation characters of orthogonally polarized HeNe lasers with different optical feedback level

Cui Liu, Zhang Shu-Lian, Wan Xin-Jun
Chin. Phys. B, 2008, 17 (2): 644-648 doi: 10.1088/1674-1056/17/2/047
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This paper demonstrates the intensity modulation characters of orthogonally polarized HeNe lasers with different optical feedback level generated by the variable reflectivity of external reflector. The modulation depths of the orthogonally polarized frequencies are increased when the optical feedback level becomes strong. It also observes that the modulation amplitudes are different for different external cavity length. Based on the vectorial extension of Lamb's semi-classical theory, it finds that the calculations are consistent with the experimental results.

Effect of an axial magnetic field on a DC argon arc

Li Lin-Cun, Xia Wei-Dong
Chin. Phys. B, 2008, 17 (2): 649-654 doi: 10.1088/1674-1056/17/2/048
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In this paper a commercial CFD (computational fluid dynamics) code FLUENT has been used and modified for the axisymmetric swirl and time-dependent simulation of an atmospheric pressure argon arc in an external axial magnetic field (AMF). The computational domain includes the arc itself and the anodic region. Numerical results demonstrate that the AMF substantially increases the tangential component of the plasma velocity. The resulting centrifugal force for the plasma rotation impels it to travel to the arc mantel and as a result, a low-pressure region appears at the arc core. With the AMF, the arc presents a hollow bell shape and correspondingly, the maximal values of the temperature, pressure and current density on the anode surface are departing from the arc centreline.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Ab initio study of oxygen-vacancy LaAlO2(001) surface

Tang Jin-Long, Zhu Jun, Qin Wen-Feng, Xiong Jie, Li Yan-Rong
Chin. Phys. B, 2008, 17 (2): 655-661 doi: 10.1088/1674-1056/17/2/049
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Density functional theory is used to investigate the surface structures and the energies of two possible terminated LaAlO$_{3}$ (001) surfaces with oxygen vacancies, i.e. LaO- and AlO$_{2}$-terminated surfaces. The large displacements of ions, deviated from their crystalline sites, can lead to the formation of the surface rumpling. From thermodynamics analysis, the AlO$_{2}$-terminated surface with oxygen-vacancies is less stable than the LaO-terminated one. Some states in the gap lie under the Fermi level by about --1eV in the LaO-terminated surface with oxygen vacancies. For the AlO$_{2}$-terminated oxygen-vacancy surface, some O 2p states move into the mid-gap region and become partially unoccupied. The two types of termination surfaces exhibit conduction related to oxygen vacancies. Our results can contribute to the application of LAO films to high dielectric constant materials.

Atomistic simulation of kink structure on edge dislocation in bcc iron

Chen Li-Qun, Wang Chong-Yu, Yu Tao
Chin. Phys. B, 2008, 17 (2): 662-668 doi: 10.1088/1674-1056/17/2/050
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Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 $\lan111\ran${\{}011{\}} and 1/2 $\lan111\ran${\{}112{\}} edge dislocations (EDs) in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 $\lan111\ran${\{}011{\}} and 1/2 $\lan111\ran${\{}112{\}} EDs are calculated, the formation energies are 0.05\,eV and 0.04\,eV, and widths are 6.02b and 6.51b, respectively (b is the magnitude of the Burgers vector). The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe.

Formation mechanism of ordered stress-relief patterns in a free sustained Cu film system

Chen Miao-Gen, Xie Jian-Ping, Jin Jin-Sheng, Xia A-Gen, Ye Gao-Xiang
Chin. Phys. B, 2008, 17 (2): 669-673 doi: 10.1088/1674-1056/17/2/051
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A nearly free sustained copper (Cu) film system has been successfully fabricated by thermal evaporation deposition of Cu atoms on silicone oil surfaces, and a characteristic ordered pattern has been systematically studied. The ordered pattern, namely, band, is composed of a large number of parallel key-formed domains with different width $w$ but nearly uniform length $L$; its characteristic values of $w$ and $L$ are very susceptible to the growth period, deposition rate and nominal film thickness. The formation mechanism of the ordered patterns is well explained in terms of the relaxation of the internal stress in the films, which is related to the nearly zero adhesion of the solid-liquid interface. By using a two-time deposition method, it is confirmed that the ordered patterns really form in the vacuum chamber.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Characterizing localization properties of two spinless electrons in a one-dimensional Harper model with concurrence

Gong Long-Yan, Tong Pei-Qing
Chin. Phys. B, 2008, 17 (2): 674-679 doi: 10.1088/1674-1056/17/2/052
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By mapping the Fock space of many local fermionic modes isomorphically onto a many-qubit space and using the measure of concurrence, this paper studies numerically the mode entanglement of two spinless electrons with on-site interaction $U$ moving in the one-dimensional Harper model. Generally speaking, for electrons in extended regimes (potential parameter $\lambda<2$), the spectrum-averaged concurrence $N\langle C\rangle$ first decreases slowly as $\lambda$ increases until its local minimum, then increases with $\lambda$ until its peak at $\lambda=2$, while for electrons in localized regimes ($\lambda>2$), $N\langle C\rangle$ decreases drastically as $\lambda$ increases. The functions of $N\langle C\rangle$ versus $\lambda$ are different for electrons in extended and localized regimes. The maximum of $N\langle C\rangle$ occurs at the point $\lambda=2$, which is the critical value in the one-dimensional single-particle Harper model. From these studies it can distinguish extended, localized and critical regimes for the two-particle system. It is also found for the same $\lambda$ that the interaction $U$ always induce the decreases of concurrence, i.e., the concurrence can reflect the localization effect due to the interaction. All these provide us a new quantity to understand the localization properties of eigenstates of two interacting particles.

Magnetoresistance in the ferromagnet/insulator/ferromagnet tunnel junction

Lu Hong-Xia, Dong Zheng-Chao, Fu Hao
Chin. Phys. B, 2008, 17 (2): 680-684 doi: 10.1088/1674-1056/17/2/053
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Recently experiments and theories show that the tunnel magnetoresistance (TMR) does not only depend on the ferromagnetic metal electrodes but also on the insulator. Considering the rough-scattering effect and spin-flip effect in the insulator, this paper investigates the TMR ratio in a ferromagnet/insulator/ferromagnet (FM/I/FM) tunnelling junction by using Slonczewsik's model. A more general expression of TMR ratio as a function of barrier height, interface roughness and spin-flip effect is obtained. In lower barrier case, it shows that the TMR ratio depends on the rough-scattering effect and spin-flip effect.

A novel 10-nm physical gate length double-gate junction field effect transistor

Hou Xiao-Yu, Huang Ru, Chen Gang, Liu Sheng, Zhang Xing, Yu Bin, Wang Yang-Yuan
Chin. Phys. B, 2008, 17 (2): 685-689 doi: 10.1088/1674-1056/17/2/054
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A novel double-gate (DG) junction field effect transistor (JFET) with depletion operation mode is proposed in this paper. Compared with the conventional DG MOSFET, the novel DG JFET can achieve excellent performance with square body design, which relaxes the requirement on silicon film thickness of DG devices. Moreover, due to the structural symmetry, both p-type and n-type devices can be realized on exactly the same structure, which greatly simplifies integration. It can reduce the delay by about 60{\%} in comparison with the conventional DG MOSFETs.

Growth temperature dependent evolutions of microstructural, optical and magnetic properties of Zn0.75Co0.25O films

Qiu Dong-Jiang, Feng Chun-Mu, Feng Ai-Ming, Wu Hui-Zhen
Chin. Phys. B, 2008, 17 (2): 690-696 doi: 10.1088/1674-1056/17/2/055
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Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-ray diffraction, selected area electron diffraction, field emission scanning electron microscope, high resolution transmitting electron microscope, photoluminescence (PL), field dependent and temperature dependent DC magnetization, and x-ray photoelectron spectroscopy (XPS). It is shown that Zn0.75Co0.25OO films grown at low temperatures (250--350\du) are of single-phase wurtzite structure. Films synthesized at 300 or 350\du\ reveal room temperature (RT) ferromagnetism (FM), while superparamagnetism for 250\du\ fabricated films is found above 56K. PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75Co0.25O film, while the superparamagnetism of 250\du\ fabricated film is attributed to the small size effect of nanoparticles in Zn0.75Co0.25O film.

Cooper-pair number-phase quantization analysis in double-Josephson-junction mesoscopic circuit coupled by a capacitor

Liang Bao-Long, Wang Ji-Suo, Fan Hong-Yi
Chin. Phys. B, 2008, 17 (2): 697-701 doi: 10.1088/1674-1056/17/2/056
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This paper examines the quantization of mesoscopic circuit including Josephson junctions. Following Feynman's assumption, via the Hamilton dynamic approach and by virtue of the entangled state representation, it constructs Hamiltonian operator for the double-Josephson-junction mesoscopic circuit coupled by a capacitor. Then it uses the Heisenberg equation of motion to derive the induction voltage across each Josephson junction. The result manifestly shows how the voltage is affected by the capacitance coupling.

Quantum communication in spin star configuration

Deng Hong-Liang, Fang Xi-Ming
Chin. Phys. B, 2008, 17 (2): 702-709 doi: 10.1088/1674-1056/17/2/057
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This paper considers a generalized spin star system which can be solved exactly, with the central spin-$\ddfrac{1}{2}$ system embedded in an outer ring of $N$ spin-$\ddfrac{1}{2}$ particles(denoted as spin bath). In this model, in addition to the central-outer interaction, each pair of nearest neighbour of the bath interacts within themselves. The general expressions of the eigenstates as well as the eigenvalues of the model are derived with the use of the symmetries of system. It analyses the quantum state transfer and the dynamical behaviour of entanglement created during quantum communication. It also analyses the efficiency of the configuration regarded as quantum phase covariant clone or decoherence model. Some interesting results are discovered concerning the properties of quantum communication in this model.

Theoretical analysis of the anisotropy of the magnetization of the Ho3+ ion in holmium iron garnet single crystals

Yang Jie-Hui, Ma Sheng-Can, Xu You
Chin. Phys. B, 2008, 17 (2): 710-715 doi: 10.1088/1674-1056/17/2/058
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The spontaneous magnetization of the Ho$^{3+}$ ion in holmium iron garnet (HoIG) single crystals in the temperature range of 4.2--294\,K along the directions [111], [110], and [100] are calculated, taking into account the effects of six magnetically inequivalent sites occupied by the Ho$^{3+}$ ions based on the quantum theory. The calculated results show that the magnetization of the Ho$^{3+}$ ion in HoIG is obviously anisotropic. The theoretical results are in agreement with those of experiments. A primary interpretation of the anisotropy of magnetization of the Ho$^{3+}$ ion in HoIG is put forward.

Electron field emission characteristics of nano-catkin carbon films deposited by electron cyclotron resonance microwave plasma chemical vapour deposition

Gu Guang-Rui, Wu Bao-Jia, Jin Zhe, Ito Toshimichi
Chin. Phys. B, 2008, 17 (2): 716-720 doi: 10.1088/1674-1056/17/2/059
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This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/$\mu $m corresponding to a current density of about 1$\mu $A/cm$^{2}$ and a current density of 3.2mA/cm$^{2}$ at an electric field of 10V/$\mu $m were obtained from the carbon film deposited at CH$_{4}$ concentration of 8{\%}. The mechanism that the threshold field decreased with the increase of the CH$_{4}$ concentration and the high emission current appeared at the high CH$_{4}$ concentration was explained by using the Fowler--Nordheim theory.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Trend of extreme precipitation events over China in last 40 years

Zhang Da-Quan, Feng Guo-Lin, Hu Jing-Guo
Chin. Phys. B, 2008, 17 (2): 736-742 doi: 10.1088/1674-1056/17/2/062
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Using the daily precipitation data of 740 stations in China from 1960 to 2000, the analysis on the variations and distributions of the frequency and the percentage of extreme precipitation to the annual rainfall have been performed in this paper. Results indicate that the percentage of heavy rains (above 25mm/day) in the annual rainfall has increased, while on average the day number of heavy rains has slightly reduced during the past 40 years. In the end of 1970s and the beginning of 1980s, both the number of days with extreme precipitation and the percentage of extreme precipitation abruptly changed over China, especially in the northern China. By moving t test, the abrupt change year of extreme precipitation for each station and its spatial distribution over the whole country are also obtained. The abrupt change years concentrated in 1978--1982 for most regions of northern China while occurred at various stations in southern China in greatly different/diverse years. Besides the abrupt change years of extreme precipitation at part stations of Northwest China happened about 5 years later in comparison with that of the country's average.
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