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Chin. Phys. B  
  Chin. Phys. B--2010, Vol.19, No.10
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GENERAL

L2L learning of dynamic neural networks

Choon Ki Ahn
Chin. Phys. B 2010, 19 (10): 100201 ;  doi: 10.1088/1674-1056/19/10/100201
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This paper proposes an L2L learning law as a new learning method for dynamic neural networks with external disturbance. Based on linear matrix inequality (LMI) formulation, the L2L learning law is presented to not only guarantee asymptotical stability of dynamic neural networks but also reduce the effect of external disturbance to an L2L induced norm constraint. It is shown that the design of the L2L learning law for such neural networks can be achieved by solving LMIs, which can be easily facilitated by using some standard numerical packages. A numerical example is presented to demonstrate the validity of the proposed learning law.

Leader-following formation control of multi-agent networks based on distributed observers

Luo Xiao-Yuan, Han Na-Ni, Guan Xin-Ping
Chin. Phys. B 2010, 19 (10): 100202 ;  doi: 10.1088/1674-1056/19/10/100202
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To investigate the leader-following formation control, in this paper we present the design problem of control protocols and distributed observers under which the agents can achieve and maintain the desired formation from any initial states, while the velocity converges to that of the virtual leader whose velocity cannot be measured by agents in real time. The two cases of switching topologies without communication delay and fixed topology with time-varying communication delay are both considered for multi-agent networks. By using the Lyapunov stability theory, the issue of stability is analysed for multi-agent systems with switching topologies. Then, by considering the time-varying communication delay, the sufficient condition is proposed for the multi-agent systems with fixed topology. Finally, two numerical examples are given to illustrate the effectiveness of the proposed leader-following formation control protocols.

Homotopic mapping method of solitary wave solutions for generalized complex Burgers equation

Mo Jia-Qi, Chen Xian-Feng
Chin. Phys. B 2010, 19 (10): 100203 ;  doi: 10.1088/1674-1056/19/10/100203
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A class of generalized complex Burgers equation is considered. First, a set of equations of the complex value functions are solved by using the homotopic mapping method. The approximate solution for the original generalized complex Burgers equation is obtained. This method can find the approximation of arbitrary order of precision simply and reliably.

Maintenance of cooperation induced by punishment in public goods games

Wang Zhen, Xu Zhao-Jin, Huang Jian-Hua, Zhang Lian-Zhong
Chin. Phys. B 2010, 19 (10): 100204 ;  doi: 10.1088/1674-1056/19/10/100204
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In this paper, we study the public goods games with punishment by adopting the well-known approximate best response dynamics. It shows that the evolution of cooperation is affected by two aspects when other parameters are fixed. One is the punishment mechanism which can avoid the dilemma of lacking investment, and the other is the degree of rationality. Theoretical analysis and numerical results indicate that the existence of punishment mechanism and distribution of rationality are the keys to the enhancement of cooperation level. We also testify that they can heavily influence the payoffs of system as well. The findings in this paper may provide a deeper understanding of some social dilemmas.

Interaction behaviours of solitoffs: fission, fusion, reconnection and annihilation

Li Jun-Min, Liang Zu-Feng, Tang Xiao-Yan
Chin. Phys. B 2010, 19 (10): 100205 ;  doi: 10.1088/1674-1056/19/10/100205
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The interactions between solitoffs are extensively investigated. Besides the known solitoff fission and fusion interactions, two new types of solitoff interactions are discovered, named the solitoff reconnection and the solitoff annihilation. Taking the asymmetric Nizhnik–Novikov–Veselov equation as an illustrative system, five types of solitoff interactions are graphically revealed on the basis of the analytical solution obtained by the modified tanh function expansion method.

Instantaneous solitons and fractal solitons for a (2+1)-dimensional nonlinear system

Pan Zhen-Huan, Ma Song-Hua, Fang Jian-Ping
Chin. Phys. B 2010, 19 (10): 100301 ;  doi: 10.1088/1674-1056/19/10/100301
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By an improved projective equation approach and a linear variable separation approach, a new family of exact solutions of the (2+1)-dimensional Broek–Kaup system is derived. Based on the derived solitary wave solution and by selecting appropriate functions, some novel localized excitations such as instantaneous solitons and fractal solitons are investigated.

Solving (2+1)-dimensional sine-Poisson equation by a modified variable separated ordinary differential equation method

Su Ka-Lin, Xie Yuan-Xi
Chin. Phys. B 2010, 19 (10): 100302 ;  doi: 10.1088/1674-1056/19/10/100302
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By introducing a more general auxiliary ordinary differential equation (ODE), a modified variable separated ordinary differential equation method is presented for solving the (2+1)-dimensional sine-Poisson equation. As a result, many explicit and exact solutions of the (2+1)-dimensional sine-Poisson equation are derived in a simple manner by this technique.

Two new integrable couplings of the soliton hierarchies with self-consistent sources

Xia Tie-Cheng
Chin. Phys. B 2010, 19 (10): 100303 ;  doi: 10.1088/1674-1056/19/10/100303
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A kind of integrable coupling of soliton equations hierarchy with self-consistent sources associated with s~l(4) has been presented (Yu F J and Li L 2009 Appl. Math. Comput. 207 171; Yu F J 2008 Phys. Lett. A 372 6613). Based on this method, we construct two integrable couplings of the soliton hierarchy with self-consistent sources by using the loop algebra s~l(4). In this paper, we also point out that there are some errors in these references and we have corrected these errors and set up new formula. The method can be generalized to other soliton hierarchy with self-consistent sources.

Preliminary analysis of resonance effect by Helmholtz–Schrödinger method

Yan Er-Yan, Meng Fan-Bao, Ma Hong-Ge, Chen Chao-Yang
Chin. Phys. B 2010, 19 (10): 100304 ;  doi: 10.1088/1674-1056/19/10/100304
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The Helmholtz–Schrödinger method is employed to study the electric field standing wave caused by coupling through a simple slot. There is a good agreement between the numerical results and the resonant conditions presented by the Helmholtz–Schrödinger method. Thus, it can be used in similar cases where the amplitude of the electric field is the important quantity or eigenfunctions of the Schrõdinger equation are needed for complicated quantum structures with hard wall boundary conditions.

Tripartite states Bell-nonlocality sudden death in a quantum-critical environment

Zhang Deng-Yu, Xie Li-Jun, Tang Shi-Qing, Zhan Xiao-Gui, Chen Yin-Hua, Gao Feng
Chin. Phys. B 2010, 19 (10): 100305 ;  doi: 10.1088/1674-1056/19/10/100305
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We demonstrate that multipartite Bell-inequalities violations can be fully destroyed in finite time in three-qubit states under a quantum-critical environment, which is an Ising model in a transverse field. We use the Mermin–Ardehali–Belinksii–Klyshko (MABK) inequality to detect the degree of nonlocality as measured by the extent of their violations. The effects of system-environment couplings, the size of degrees of freedom of environment and the strength of transverse field on the Bell-inequality violations are given for two different initial states, namely, the W class and GHZ class states. The results indicate that the Bell-inequality violations of the tripartite states will be completely destroyed by the decoherence under certain conditions.

Energy band structure of spin-1 condensates in optical lattices

Li Zhi, Zhang Ai-Xia, Ma Juan, Xue Ju-Kui
Chin. Phys. B 2010, 19 (10): 100306 ;  doi: 10.1088/1674-1056/19/10/100306
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The energy band structure of spin-1 condensates with repulsive spin-independent and either ferromagnetic or antiferromagnetic spin-dependent interactions in one-dimensional (1D) periodic optical lattices is discussed. Within the two-mode approximation, Bloch bands of spin-1 condensates are presented. The results show that the Bloch bands exhibit a complex structure as the atom density of mF=0 hyperfine state increases: bands splitting, reversion, intersection and loop structure are excited subsequently. The complex band structure should be related to the tunneling and spin-mixing dynamics.

Pairwise thermal entanglement in a three-qubit Heisenberg XX model with a nonuniform magnetic field and Dzyaloshinski–Moriya interaction

Ren Jin-Zhong, Shao Xiao-Qiang, Zhang Shou, Yeon Kyu-Hwang
Chin. Phys. B 2010, 19 (10): 100307 ;  doi: 10.1088/1674-1056/19/10/100307
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Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform magnetic field and the Dzyaloshinski–Moriya interaction are included. We find that the nonuniform magnetic field and Dzyaloshinski–Moriya interaction are the more efficient control parameters for the increase of entanglement and critical temperature. For both the nearest neighbour sites and the next nearest neighbour sites, the magnetic field can induce entanglement to a certain extent and the Dzyaloshinski–Moriya interaction can enhance the entanglement to a stable value. The steady value of the nearest neighbour site entanglement C12 is larger than the next nearest neighbour site entanglement C13. An interesting phenomenon is that the entanglement curve of C12 appears a peak value when the Dzyaloshinski–Moriya interaction is considered in a nonuniform magnetic field.

Comparative studies of open qubit via Bloch equation and master equation of Redfield form

Shen Yan, Lu Yu-Ping, Liang Xian-Ting
Chin. Phys. B 2010, 19 (10): 100308 ;  doi: 10.1088/1674-1056/19/10/100308
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In this paper, we investigate the dynamics of an open qubit model by solving two sets of its reduced dynamical equations. One set of the equations is the well-known Bloch equations and the other is the widely investigated master equations of Redfield form. Both of them are obtained from the perturbation approximation which demands the system of interest weakly coupled to its environment. It is shown that the qubit has a longer decoherence and relaxiation time as the dynamics is described by the Redfield equantions.

Bound states of the Schrödinger equation for the Pöschl–Teller double-ring-shaped Coulomb potential

Lu Fa-Lin, Chen Chang-Yuan
Chin. Phys. B 2010, 19 (10): 100309 ;  doi: 10.1088/1674-1056/19/10/100309
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Põschl–Teller double-ring-shaped Coulomb (PTDRSC) potential, the Coulomb potential surrounded by Pöschl–Teller and double-ring-shaped inversed square potential, is put forward. In spherical polar coordinates, PTDRSC potential has supersymmetry and shape invariance in φ, θ and r coordinates. By using the method of supersymmetry and shape invariance, exact bound state solutions of Schrödinger equation with PTDRSC potential are presented. The normalized φ, θ angular wave function expressed in terms of Jacobi polynomials and the normalized radial wave function expressed in terms of Laguerre polynomials are presented. Energy spectrum equations are obtained. Wave function and energy spectrum equations of the system are related to three quantum numbers and parameters of PTDRSC potential. The solutions of wave functions and corresponding eigenvalues are only suitable for the PTDRSC potential.

Monogamy relations in tripartite quantum system

Li Jiao-Jiao, Wang Zhi-Xi
Chin. Phys. B 2010, 19 (10): 100310 ;  doi: 10.1088/1674-1056/19/10/100310
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This paper presents monogamy relations for three-qubit quantum states by using convex-roof extended negativity, which inspires studying the difference between the three entanglement measures, concurrence, negativity and convex-roof extended negativity. It finds that the convex-roof extended negativity is a stronger entanglement measure than concurrence in multipartite higher-dimensional quantum system.

Quantum thermal discord in a two-spin-1/2 XXZ model

Wang Qiong, Liao Jie-Qiao, Zeng Hao-Sheng
Chin. Phys. B 2010, 19 (10): 100311 ;  doi: 10.1088/1674-1056/19/10/100311
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We study the quantum discord in a two-spin-1/2 XXZ model in thermal equilibrium at temperature T in the presence of an external magnetic field B. Special attention is paid to the dependence of quantum discord on the temperature T and magnetic field B. It is found that quantum thermal discord is more robust than concurrence against temperature, in the sense that quantum thermal discord does not vanish at finite temperatures, but concurrence vanishes completely at a critical temperature.

Passive decoy state SARG04 quantum-key-distribution with practical photon-number resolving detectors

Xu Fang-Xing, Wang Shuang, Han Zheng-Fu, Guo Guang-Can
Chin. Phys. B 2010, 19 (10): 100312 ;  doi: 10.1088/1674-1056/19/10/100312
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SARG04 protocol has its advantages in defending photon number splitting attack, benefited from two-photon pulses part. In this paper, we present a passive decoy state SARG04 scheme combining with practical photon number resolving (PNR) detectors. Two kinds of practical detectors, transition-edge sensor and time-multiplexing detector, are taken into consideration. Theoretical analysis shows that both of them are compatible with the passive decoy state SARG04. Compared with the original SARG04, two detectors can boost the key generation rate and maximal secure distance obviously. Meanwhile, the result shows that quantum efficiency and dark count of the detector influence the maximal distance slightly, which indicates the prospect of implementation in real quantum key distribution system with imperfect practical PNS detectors.

Simple schemes for generation of W-type multipartite entangled states and realization of quantum- information concentration

Zhang Deng-Yu, Tang Shi-Qing, Xie Li-Jun, Zhan Xiao-Gui, Chen Yin-Hua, Gao Feng
Chin. Phys. B 2010, 19 (10): 100313 ;  doi: 10.1088/1674-1056/19/10/100313
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We propose simple schemes for generating W-type multipartite entangled states in cavity quantum electrodynamics (CQED). Our schemes involve a largely detuned interaction of Λ-type three-level atoms with a single-mode cavity field and a classical laser, and both the symmetric and asymmetric W states can be created in a single step. Our schemes are insensitive to both the cavity decay and atomic spontaneous emission. With the above system, we also propose a scheme for realizing quantum-information concentration which is the reverse process of quantum cloning. In this scheme, quantum-information originally coming from a single qubit, but now distributed into many qubits, is concentrated back to a single qubit in only one step.

External electric field control in the charge qubits including three Josephson junctions

Liu Hai-Yan, Wang Ji-Suo, Liang Bao-Long
Chin. Phys. B 2010, 19 (10): 100314 ;  doi: 10.1088/1674-1056/19/10/100314
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Based on the standard canonical quantization principle, this paper gives the quantization scheme for the charge qubits mesoscopic circuit including three Josephson junctions coupled capacitively. By virtue of the Heisenberg equation, the time evolution of the phase difference operators across the polar plates and the number operators of the Cooper-pairs on the island are investigated and the modification of the Josephson equation is discussed. The time evolution of the phase difference operators is analysed when the Josephson junctions are irradiated by the external electrical field, which is referred to as also the obtainable controlling parameter.

A new four-dimensional hyperchaotic Chen system and its generalized synchronization

Jia Li-Xin, Dai Hao, Hui Meng
Chin. Phys. B 2010, 19 (10): 100501 ;  doi: 10.1088/1674-1056/19/10/100501
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Based on the Chen chaotic system, a new four-dimensional hyperchaotic Chen system is constructed, and the basic dynamic behaviours of the system were studied, and the generalized synchronization has been observed in the coupled four-dimensional hyperchaotic Chen system with unknown parameters. The Routh–Hurwitz theorem is used to derive the conditions of stability of this system. Furthermore based on Lyapunov stability theory, the control laws and adaptive laws of parameters are obtained to make generalized synchronization of the coupled new four-dimensional hyperchaotic Chen systems. Numerical simulation results are presented to illustrate the effectiveness of this method.

A hyperchaotic system stabilization via inverse optimal control and experimental research

Yang Ning-Ning, Liu Chong-Xin, Wu Chao-Jun
Chin. Phys. B 2010, 19 (10): 100502 ;  doi: 10.1088/1674-1056/19/10/100502
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In this paper, some basic dynamical properties of a four-dimensional autonomous hyperchaotic system are investigated by means of Poincaré mapping, Lyapunov exponents and bifurcation diagram. The dynamical behaviours of this new hyperchaotic system are proved not only by performing numerical simulation and brief theoretical analysis but also by conducting an electronic circuit experiment. An efficient approaching is developed for global asymptotic stabilization of this four-dimensional hyperchaotic system. Based on the method of inverse optimal control for nonlinear systems, a linear state feedback is electronically implemented. It is remarkably simple as compared with other chaos control ways, like nonlinear state feedback.

Adaptive generalized synchronization between Chen system and a multi-scroll chaotic system

Chen Long, Shi Yue-Dong, Wang De-Shi
Chin. Phys. B 2010, 19 (10): 100503 ;  doi: 10.1088/1674-1056/19/10/100503
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Based on Lyapunov theory, the adaptive generalized synchronization between Chen system and a multi-scroll chaotic system is investigated. According to the form of target function a proper adaptive controller is designed, by which the controlled Chen system can be synchronized with a multi-scroll chaotic system including unknown parameters. The Lyapunov direct method is exploited to prove that the synchronization error and parameter identification error both converge to zero. Numerical simulation results verify the feasibility of the proposed method further.

Sliding mode control of a new chaotic system

Li Ming, Liu Chong-Xin
Chin. Phys. B 2010, 19 (10): 100504 ;  doi: 10.1088/1674-1056/19/10/100504
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In this paper, a sliding mode controller (SMC) is designed to control a new dynamical system with canonical chaos characters. With the proposed SMC, the new chaotic system can be regulated to a fixed point in the state space. Simulation shows that the chattering phenomenon is greatly alleviated.

Anti-synchronization of a new hyperchaotic system via small-gain theorem

Xiao Jian
Chin. Phys. B 2010, 19 (10): 100505 ;  doi: 10.1088/1674-1056/19/10/100505
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Based on the small-gain theorem, the anti-synchronization between two identical new hyperchaotic systems is investigated, moreover, the general sufficient conditions to achieve anti-synchronization between the new hyperchaotic system and the new hyperchaotic Lorenz system are obtained via small-gain theorem. Numerical simulations are performed to verify and illustrate the analytical results.

The stability control of fractional order unified chaotic system with sliding mode control theory

Qi Dong-Lian, Yang Jie, Zhang Jian-Liang
Chin. Phys. B 2010, 19 (10): 100506 ;  doi: 10.1088/1674-1056/19/10/100506
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This paper studies the stability of the fractional order unified chaotic system with sliding mode control theory. The sliding manifold is constructed by the definition of fractional order derivative and integral for the fractional order unified chaotic system. By the existing proof of sliding manifold, the sliding mode controller is designed. To improve the convergence rate, the equivalent controller includes two parts: the continuous part and switching part. With Gronwall's inequality and the boundness of chaotic attractor, the finite stabilization of the fractional order unified chaotic system is proved, and the controlling parameters can be obtained. Simulation results are made to verify the effectiveness of this method.

Function projective synchronization between fractional-order chaotic systems and integer-order chaotic systems

Zhou Ping, Cao Yu-Xia
Chin. Phys. B 2010, 19 (10): 100507 ;  doi: 10.1088/1674-1056/19/10/100507
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This paper investigates the function projective synchronization between fractional-order chaotic systems and integer-order chaotic systems using the stability theory of fractional-order systems. The function projective synchronization between three-dimensional (3D) integer-order Lorenz chaotic system and 3D fractional-order Chen chaotic system are presented to demonstrate the effectiveness of the proposed scheme.

Effects of memory on scaling behaviour of Kardar–Parisi–Zhang equation

Tang Gang, Hao Da-Peng, Xia Hui, Han Kui, Xun Zhi-Peng
Chin. Phys. B 2010, 19 (10): 100508 ;  doi: 10.1088/1674-1056/19/10/100508
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In order to describe the time delay in the surface roughing process the Kardar–Parisis–Zhang (KPZ) equation with memory effects is constructed and analysed using the dynamic renormalization group and the power counting mode coupling approach by Chattopadhyay [2009 Phys. Rev. E 80 011144]. In this paper, the scaling analysis and the classical self-consistent mode-coupling approximation are utilized to investigate the dynamic scaling behaviour of the KPZ equation with memory effects. The values of the scaling exponents depending on the memory parameter are calculated for the substrate dimensions being 1 and 2, respectively. The more detailed relationship between the scaling exponent and memory parameter reveals the significant influence of memory effects on the scaling properties of the KPZ equation.

Stationary patterns in a discrete bistable reaction–diffusion system: mode analysis

Zou Wei, Zhan Meng
Chin. Phys. B 2010, 19 (10): 100509 ;  doi: 10.1088/1674-1056/19/10/100509
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This paper theoretically analyses and studies stationary patterns in diffusively coupled bistable elements. Since these stationary patterns consist of two types of stationary mode structure: kink and pulse, a mode analysis method is proposed to approximate the solutions of these localized basic modes and to analyse their stabilities. Using this method, it reconstructs the whole stationary patterns. The cellular mode structures (kink and pulse) in bistable media fundamentally differ from stationary patterns in monostable media showing spatial periodicity induced by a diffusive Turing bifurcation.

Discrete-time movement model of a group of trains on a rail line with stochastic disturbance

Yang Li-Xing, Li Feng, Gao Zi-You, Li Ke-Ping
Chin. Phys. B 2010, 19 (10): 100510 ;  doi: 10.1088/1674-1056/19/10/100510
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This paper presents a discrete-time model to describe the movements of a group of trains, in which some operational strategies, including traction operation, braking operation and impact of stochastic disturbance, are defined. To show the dynamic characteristics of train traffic flow with stochastic disturbance, some numerical experiments on a railway line are simulated. The computational results show that the discrete-time movement model can well describe the movements of trains on a rail line with the moving-block signalling system. Comparing with the results of no disturbance, it finds that the traffic capacity of the rail line will decrease with the influence of stochastic disturbance. Additionally, the delays incurred by stochastic disturbance can be propagated to the subsequent trains, and then prolong their traversing time on the rail line. It can provide auxiliary information for rescheduling trains when the stochastic disturbance occurs on the railway.

The relationship between energy consumption and train delay in railway traffic

Li Ke-Ping, Fan Hong-Qiang
Chin. Phys. B 2010, 19 (10): 100511 ;  doi: 10.1088/1674-1056/19/10/100511
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Based on deterministic NaSch model, we propose a new cellular automation model for simulating train movement. In the proposed model, the reaction time of driver/train equipment is considered. Our study is focused on the additional energy consumption arising by train delay around a traffic bottle (station). The simulation results demonstrate that the proposed model is suitable for simulating the train movement under high speed condition. Further, we discuss the relationship between the additional energy consumption and some factors which affect the formation of train delay, such as the maximum speed of trains and the station dwell time etc.

General solution of the modified Korteweg-de-Vries equation in the lattice hydrodynamic model

Yu Han-Mei, Cheng Rong-Jun, Ge Hong-Xia
Chin. Phys. B 2010, 19 (10): 100512 ;  doi: 10.1088/1674-1056/19/10/100512
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Traffic congestion is related to various density waves, which might be described by the nonlinear wave equations, such as the Burgers, Korteweg-de-Vries (KdV) and modified Korteweg-de-Vries (mKdV) equations. In this paper, the mKdV equations of four different versions of lattice hydrodynamic models, which describe the kink–antikink soliton waves are derived by nonlinear analysis. Furthermore, the general solution is given, which is applied to solving a new model —— the lattice hydrodynamic model with bidirectional pedestrian flow. The result shows that this general solution is consistent with that given by previous work.

Topological probability and connection strength induced activity in complex neural networks

Wei Du-Qu, Zhang Bo, Qiu Dong-Yuan, Luo Xiao-Shu
Chin. Phys. B 2010, 19 (10): 100513 ;  doi: 10.1088/1674-1056/19/10/100513
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Recent experimental evidence suggests that some brain activities can be assigned to small-world networks. In this work, we investigate how the topological probability p and connection strength C affect the activities of discrete neural networks with small-world (SW) connections. Network elements are described by two-dimensional map neurons (2DMNs) with the values of parameters at which no activity occurs. It is found that when the value of p is smaller or larger, there are no active neurons in the network, no matter what the value of connection strength is; for a given appropriate connection strength, there is an intermediate range of topological probability where the activity of 2DMN network is induced and enhanced. On the other hand, for a given intermediate topological probability level, there exists an optimal value of connection strength such that the frequency of activity reaches its maximum. The possible mechanism behind the action of topological probability and connection strength is addressed based on the bifurcation method. Furthermore, the effects of noise and transmission delay on the activity of neural network are also studied.
ATOMIC AND MOLECULAR PHYSICS

Influence of pressure effect on Fermi resonance in binary solution

Jiang Xiu-Lan, Yang Guang, Li Dong-Fei, Zhou Mi, Sun Cheng-Lin, Gao Shu-Qin, Li Zuo-Wei
Chin. Phys. B 2010, 19 (10): 103301 ;  doi: 10.1088/1674-1056/19/10/103301
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The Fermi resonance behaviours of the two groups of binary solutions —— pyridine and methanol, benzene and carbon tetrachloride, under different pressures are investigated according to their Raman spectra. The effect of pressure on Fermi resonance in binary solution differs significantly from that in pure liquid. In a binary solution, with the intermolecular distance shortening, the intermolecular interaction potential increases, the shift rates of the Raman spectral lines increase, the spectral line splitting occurs ahead of that in pure liquid, and the wavenumber separation Δ0 between the unperturbed harmonic levels shifts more quickly, too. The Fermi resonance parameters, the coupling coefficient W and the intensity ratio R of the two Raman bands, decrease rapidly with pressure increasing, and the pressure at which Fermi resonance phenomenon disappears is much lower than that in pure liquid, especially in the solution whose molecules are of the same polarity. This article is valuable in the identification and the assignment of spectral lines under high pressure, as well as the study of high pressure effect, intermolecular interaction, and solvent effects in different cases, etc.

Time-energy properties of an attosecond extreme ultra-violet pulse

Ge Yu-Cheng, He Hai-Ping
Chin. Phys. B 2010, 19 (10): 103302 ;  doi: 10.1088/1674-1056/19/10/103302
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The time-energy properties of high-order harmonic generation (HHG) are calculated for a linearly polarized 7-fs laser pulse with different carrier-envelope phases (CEPs). The quantum trajectory paths that contribute to an as (1 as=10-18 s) pulse in HHG are identified. The laser-duration dependence and the CEP dependence of HHG energy property are investigated. The study shows that an as extreme ultra-violet (XUV) pulse can be selected from HHG spectrum near cut-off energy with a bandpass optical filter. The theoretical prediction of the pulse duration is proportional to bandwidth. Analysis suggests that a measured narrowband as XUV pulse may consist of instantaneous shorter pulses each dependent on laser pulse duration, intensity, and CEP. These information can be used as references for producing, selecting, improving and manipulating (timing) as pulses.

Control of reaction channels of CsI molecule by ultra-short laser pulse

Xiong De-Lin, Wang Mei-Shan, Yang Chuan-Lu, Tong Xiao-Fei, Ma Ning
Chin. Phys. B 2010, 19 (10): 103303 ;  doi: 10.1088/1674-1056/19/10/103303
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The influence of the ultra-short pulse wavelength on the populations in the three electronic states of CsI molecule is investigated using the time-dependent wave packet method. The calculated results show that the populations in the two excited states approach to the maxima at the wavelengths of 369 nm and 297 nm, respectively. The photodissociation reaction channels of the CsI molecule can be chosen by controlling the pump pulse wavelength.

Two-photon absorption properties of aggregation systems on the basis of (E)-4-(2-nitrovinyl) benzenamine molecules

Wang Chuan-Kui, Zhang Zhen, Ding Ming-Cui, Li Xiao-Jing, Sun Yuan-Hong, Zhao Ke
Chin. Phys. B 2010, 19 (10): 103304 ;  doi: 10.1088/1674-1056/19/10/103304
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Aggregation effect caused by the intermolecular hydrogen-bonding interactions on two-photon absorption properties of (E)-4-(2-nitrovinyl) benzenamine molecules is studied at a hybrid density functional level. The geometry optimization studies indicate that there exist two probable conformations for the dimers and three for the trimers. A strong red-shift of the charge-transfer states is shown. The two-photon absorption cross sections of the molecule for certain conformations are greatly enhanced by the aggregation effect, from which a ratio of 1.0:2.6:3.6 is found for the molecule and its dimer and trimer with nearly planar structures. Namely, a 30 or 20 percent increase of the two-photon absorption cross section is observed.

Theoretical investigations of spectroscopic parameters and molecular constants for electronic ground state of Cl2 and its isotopes

Shi De-Heng, Zhang Xiao-Niu, Liu Hui, Zhu Zun-Lue, Sun Jin-Feng
Chin. Phys. B 2010, 19 (10): 103401 ;  doi: 10.1088/1674-1056/19/10/103401
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The potential energy curve of the Cl2(X1Σg+) is investigated by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with the largest correlation-consistent basis set, aug-cc-pV6Z, in the valence range. The theoretical spectroscopic parameters and the molecular constants of three isotopes, 35Cl2, 35Cl37Cl and 37Cl2, are studied. For the 35Cl2(X1Σg+), the values of D0, De, Re, ωe, ωeχe, αe and Be are obtained to be 2.3921 eV, 2.4264 eV, 0.19939 nm, 555.13 cm-1, 2.6772 cm-1, 0.001481 cm-1 and 0.24225 cm-1, respectively. For the 35Cl37Cl(X1Σg+), the values of D0, De, Re, ωe, ωeχe, αe and Be are calculated to be 2.3918 eV, 2.4257 eV, 0.19939 nm, 547.68 cm-1, 2.6234 cm-1, 0.00140 cm1 and 0.23572 cm-1, respectively. And for the 37Cl2(X1Σg+), the values of D0, De, Re, ωe, ωeχe, αe and Be are obtained to be 2.3923 eV, 2.4257 eV, 0.19939 nm, 540.06 cm-1, 2.5556 cm-1, 0.00139 cm-1 and 0.22919 cm-1, respectively. These spectroscopic results are in good agreement with the available experimental data. With the potential of Cl2 molecule determined at the MRCI/aug-cc-pV6Z level of theory, the total of 59 vibrational states is predicted for each isotope when the rotational quantum number J equals zero (J = 0). The theoretical vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J = 0, which are in excellent accordance with the available experimental findings.

Positron scattering and ionization of neon atoms —— theoretical investigations Hot!

Harshit N. Kothari, K. N. Joshipuravs
Chin. Phys. B 2010, 19 (10): 103402 ;  doi: 10.1088/1674-1056/19/10/103402
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Although positron scattering with inert gas atoms has been studied in theory as well as in experiment, there are discrepancies. The present work reports all the major total cross sections of e–neon scattering at incident energies above ionization threshold, originating from a complex potential formalism. Elastic and cumulative inelastic scatterings are treated in the complex spherical e–atom potential. Our total inelastic cross section includes positronium formation together with ionization and excitation channels in Ne. Because of the Ps formation channel it is difficult to separate out ionization cross sections from the total inelastic cross sections. An approximate method similar to electron–atom scattering has been applied to bifurcate ionization and cumulative excitation cross sections at energies from threshold to 2000 eV. Comparisons of present results with available data are made. An important outcome of this work is the relative contribution of different scattering processes, which we have shown by a bar-chart at the ionization peak.
CLASSICAL AREAS OF PHENOMENOLOGY

Study correlation vortices in the near-field of partially coherent vortex beams diffracted by an aperture

Li Jian-Long
Chin. Phys. B 2010, 19 (10): 104001 ;  doi: 10.1088/1674-1056/19/10/104001
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We have derived the analytical expression of the electric cross-spectral density in the near- field of partially coherent vortex beams diffracted by an aperture. Taking the Gaussian Schell-model vortex beam as a typical example of partially coherent vortex beams, the spatial correlation properties and correlation vortices in the near-field of partially coherent vortex beams diffracted by a rectangle aperture are studied. It is shown that the off-axis displacement, spatial degree of coherence parameter, propagation distance, and the opening factor of the aperture affect the spectral degree of coherence and positions of correlation vortices. With the optimization algorithm, we obtain the symmetric distributing coherent vortex.

Study on tapered crossed subwavelength gratings by Fourier modal method

Chen Xi, Zhong Yuan, Wang Qing, Zhang Ye-Jin, Chen Liang-Hui
Chin. Phys. B 2010, 19 (10): 104101 ;  doi: 10.1088/1674-1056/19/10/104101
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Fourier modal method incorporating staircase approximation is used to study tapered crossed subwavelength gratings in this paper. Three intuitive formulations of eigenvalue functions originating from the prototype are presented, and their convergences are compared through numerical calculation. One of them is found to be suitable in modeling the diffraction efficiency of the circular tapered crossed subwavelength gratings without high absorption, and staircase approximation is further proven valid for non-highly-absorptive tapered gratings. This approach is used to simulate the ''moth-eye'' antireflection surface on silicon, and the numerical result agrees well with the experimental one.

Analysis of restriction factors of widening diffraction bandwidth of multilayer dielectric grating

Wang Jian-Peng, Jin Yun-Xia, Ma Jian-Yong, Shao Jian-Da, Fan Zheng-Xiu
Chin. Phys. B 2010, 19 (10): 104201 ;  doi: 10.1088/1674-1056/19/10/104201
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In order to design a multilayer dielectric grating with wide-bandwidth diffraction spectrum, the restriction factors of both the reflection bandwidth of multilayer dielectric high-reflectivity mirror and the guided-mode resonance phenomenon are studied in detail. The reflection characteristics of high-reflectivity mirror in zeroth and -1st transmitted diffraction orders are quantitatively evaluated. It is found that the reflection bandwidth of high-reflectivity mirror in -1st transmitted diffraction order, which determines the final diffraction bandwidth of multilayer dielectric grating, is evidently compressed. Furthermore, it is demonstrated that the reducing of grating period is an effective approach to the elimination of guided mode resonance over a required broad band range both spectrally and angularly. In addition, the expressions for calculating the maximum period ensuring no guided mode resonance in the required bandwidth are derived. Finally, two high-efficiency pulse-compression gratings with broad-band are presented.

Relation between Debye series and generalized Lorentz–Mie theory of laser beam scattering by multilayer cylinder

Li Hai-Ying, Wu Zhen-Sen, Li Zheng-Jun
Chin. Phys. B 2010, 19 (10): 104202 ;  doi: 10.1088/1674-1056/19/10/104202
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With the recursive relations of Bessel function and applying inductive approach, the consistency between the scattering coefficient formula of Debye series and that of the generalized Lorentz–Mie theory (GLMT) in the scattering of a multilayer cylinder illuminated by a laser beam is proved in detail. As an application example, rainbow phenomenon in the scattering of a two-layer cylinder is discussed by the Debye series components. It can be concluded that the radius and the refractive index of a two-layer cylinder have an effect on the twin-primary rainbow, and the high-order Debye series components which are associated with the high-order rainbows are more complex than those of a homogeneous cylinder.

Spin-image surface matching based target recognition in laser radar range imagery

Wang Li, Sun Jian-Feng, Wang Qi
Chin. Phys. B 2010, 19 (10): 104203 ;  doi: 10.1088/1674-1056/19/10/104203
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We explore the problem of in-plane rotation-invariance existing in the vertical detection of laser radar (Ladar) using the algorithm of spin-image surface matching. The method used to recognize the target in the range imagery of Ladar is time-consuming, owing to its complicated procedure, which violates the requirement of real-time target recognition in practical applications. To simplify the troublesome procedures, we improve the spin-image algorithm by introducing a statistical correlated coefficient into target recognition in range imagery of Ladar. The system performance is demonstrated on sixteen simulated noise range images with targets rotated through an arbitrary angle in plane. A high efficiency and an acceptable recognition rate obtained herein testify the validity of the improved algorithm for practical applications. The proposed algorithm not only solves the problem of in-plane rotation-invariance rationally, but also meets the real-time requirement. This paper ends with a comparison of the proposed method and the previous one.

Operators' s-parameterized ordering and its classical correspondence in quantum optics theory

Fan Hong-Yi, Yuan Hong-Chun, Hu Li-Yun
Chin. Phys. B 2010, 19 (10): 104204 ;  doi: 10.1088/1674-1056/19/10/104204
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In reference to the Weyl ordering , where X and P are coordinate and momentum operator, respectively, this paper examines operators' s-parameterized ordering and its classical correspondence, finds the fundamental function-operator correspondence and its complementary relation , where Hm,n is the two-variable Hermite polynomial, are bosonic annihilation and creation operators respectively, s is a complex parameter. The s'-ordered operator power-series expansion of s-ordered operator in terms of the two-variable Hermite polynomial is also derived. Application of operators' s-ordering formula in studying displaced-squeezed chaotic field is discussed.

Generalized photon-added coherent state and its quantum statistical properties

Yuan Hong-Chun, Xu Xue-Xiang, Fan Hong-Yi
Chin. Phys. B 2010, 19 (10): 104205 ;  doi: 10.1088/1674-1056/19/10/104205
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In this paper, we propose a class of the generalized photon-added coherent states (GPACSs) obtained by repeatedly operating the combination of Bosonic creation and annihilation operatoes on the coherent state. The normalization factor of GPACS is related to Hermite polynomial. We also derive the explicit expressions of its statistical properties such as photocount distribution, Wigner function and tomogram and investigate their behaviour as the photon-added number varies graphically. It is found that GPACS is a kind of nonclassical state since Wigner function exhibits the negativity by increasing the photon-added number.

Measurement of the carrier recovery time in SOA based on four-wave mixing on narrow-band ASE spectrum

Cheng Cheng, Zhang Xin-Liang, Zhang Yu, Liu Lei, Huang De-Xiu
Chin. Phys. B 2010, 19 (10): 104206 ;  doi: 10.1088/1674-1056/19/10/104206
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Carrier recovery time is a key parameter that determines the performance of a semiconductor optical amplifier (SOA). A measurement method of carrier recovery time in SOA based on a nearly degenerate four-wave mixing of narrow-band amplified spontaneous emission (ASE) spectra is presented. The results show the carrier times are 50.2, 44.6, and 23.6 ps when the injected currents are 120, 180, and 240 mA, respectively, which are in agreement with the nominal values of the sample.

Diffraction of white-light supercontinuum by femtosecond laser-induced transient grating in carbon bisulfide

Huang Li, Yang Yan-Qiang, Wang Ying-Hui, Zheng Zhi-Ren, Su Wen-Hui
Chin. Phys. B 2010, 19 (10): 104207 ;  doi: 10.1088/1674-1056/19/10/104207
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Experiments on fs laser-induced transient grating (LITG) in carbon bisulfide (CS2) are carried out to explore the chirp characteristics of a white-light supercontinuum (SC) generated by a 800-nm, 160-fs laser pulse in a 4-mm thick Al2O3 crystal. Two orders of diffraction signals of SC by fs LITG in CS2 are observed, demonstrating that both the third-order process and the fifth-order process are present simultaneously. The experimental results also imply that the formation of an fs transient refractive-index grating in CS2 is mainly due to the electronic polarization process.

Study on pulse compression in tapered holey fibres

Ma Wen-Wen, Li Shu-Guang, Yin Guo-Bing, Fu Bo, Zhang Lei
Chin. Phys. B 2010, 19 (10): 104208 ;  doi: 10.1088/1674-1056/19/10/104208
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This paper proposes three kinds of tapered holey fibres with a multi-layer of holes whose pitch of air holes at the end of untapered and tapered are 5.8 μm and 1.8 μm. The central wavelength which locates in the anomalous dispersion region is 1.55 μm. An adaptive split-step Fourier method is numerically used to study the pulse propagation in tapered holey fibres. For the considered convex tapered holey fibre, at a wavelength of 1.55 μm, a compression factor of 136.7 can be achieved by initial width of 800 fs propagation through a length of 0.8 m. It demonstrates that in anomalous dispersion region, pulse can be compressed with the increase of nonlinearity coefficient and the decrease of dispersion coefficient.

A new tracking error detection method using amplitude difference detection for signal waveform modulation multi-level discs

Yan Ming-Ming, Pei Jing, Pan Long-Fa
Chin. Phys. B 2010, 19 (10): 104209 ;  doi: 10.1088/1674-1056/19/10/104209
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The sub-land/sub-pit affects the characteristic of the tracking error signal which is generated by the conventional differential phase detection (DPD) method in the signal waveform modulation multi-level (SWML) read-only disc. To solve this problem, this paper proposes a new tracking error detection method using amplitude difference. Based on the diffraction theory, the amplitude difference is proportional to the tracking error and is feasible to be used for obtaining the off-track information. The experimental system of the amplitude difference detection method is developed. The experimental results show that the tracking error signal derived from the new method has better performance in uniformity and signal-to-noise ratio than that derived from the conventional DPD method in the SWML read-only disc.

Sampling strong tracking nonlinear unscented Kalman filter and its application in eye tracking

Zhang Zu-Tao, Zhang Jia-Shu
Chin. Phys. B 2010, 19 (10): 104601 ;  doi: 10.1088/1674-1056/19/10/104601
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The unscented Kalman filter is a developed well-known method for nonlinear motion estimation and tracking. However, the standard unscented Kalman filter has the inherent drawbacks, such as numerical instability and much more time spent on calculation in practical applications. In this paper, we present a novel sampling strong tracking nonlinear unscented Kalman filter, aiming to overcome the difficulty in nonlinear eye tracking. In the above proposed filter, the simplified unscented transform sampling strategy with n+2 sigma points leads to the computational efficiency, and suboptimal fading factor of strong tracking filtering is introduced to improve robustness and accuracy of eye tracking. Compared with the related unscented Kalman filter for eye tracking, the proposed filter has potential advantages in robustness, convergence speed, and tracking accuracy. The final experimental results show the validity of our method for eye tracking under realistic conditions.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

A numerical analytic method for electromagnetic radiation accompanying with fracture of rocks

Chen Zhen, Huang Ka-Ma
Chin. Phys. B 2010, 19 (10): 105201 ;  doi: 10.1088/1674-1056/19/10/105201
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This paper studies Rabinovitch's compression experiments on granite and chalk and proposes an oscillating dipole model to analyse and simulate the electromagnetic radiation phenomenon caused by fracture of rocks. Our model assumes that the electromagnetic radiation pulses are initiated by vibrations of the charged rock grains on the tips of the crack. The vibrations of the rock grains are stimulated by the pulses of the cracks. Our simulations show comparable results with Rabinovitch's compression experiments. From the simulation results, it verifies an assumption that the crack width is inversely proportional to the circular frequency electromagnetic radiation, which is presented by Rabinovitch et al. The simulation results also imply that, by using our oscillating dipole model together with Rabinovitch's two equations about the crack length and crack width, we can quantitatively analyse and simulate the electromagnetic radiation phenomenon, which is induced from the fracture of the rocks.

Theoretical study of wave propagation along the coaxial waveguide filled with moving magnetized plasma

Zhang Ya-Xin, Jia Jia, Liu Sheng-Gang, Yan Yang
Chin. Phys. B 2010, 19 (10): 105202 ;  doi: 10.1088/1674-1056/19/10/105202
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This paper presents detailed theoretical study on the theory of wave propagation along the coaxial waveguide filled with moving magnetized plasma (CWMMP). Making use of the Lorentz transformation and the constitutive transformation, Maxwell's equations lead to the coupled non-homogeneous differential equations which govern the wave propagation in CWMMP, and then analytical solutions have been obtained. The discussion about the eigenvalues of the waves and detailed studies on the fields are carried out. It finds that the fields of the CWMMP are composed of two parts with different eigenvalues. Numerical calculations show that because of Doppler shift effect, the eigenvalues of the modes in such a case is quite different from those of the CWMMP. And a detailed discussion on the dispersion characteristic of CWMMP is presented.

The interaction of an atmospheric pressure plasma jet using argon or argon plus hydrogen peroxide vapour addition with bacillus subtilis

Deng San-Xi, Cheng Cheng, Ni Guo-Hua, Meng Yue-Dong, Chen Hua
Chin. Phys. B 2010, 19 (10): 105203 ;  doi: 10.1088/1674-1056/19/10/105203
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This paper reports that an atmospheric pressure dielectric barrier discharge plasma jet, which uses argon or argon + hydrogen peroxide vapour as the working gas, is designed to sterilize the bacillus subtilis. Compared with the pure argon plasma, the bacterial inactivation efficacy has a significant improvement when hydrogen peroxide vapour is added into the plasma jet. In order to determine which factors play the main role in inactivation, several methods are used, such as determination of optical emission spectra, high temperature dry air treatment, protein leakage quantification, and scanning electron microscope. These results indicate that the possible inactivation mechanisms are the synergistic actions of chemically active species and charged species.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Improvement of a new rotation function for molecular replacement by designing new scoring functions and dynamic correlation coefficient

Jiang Fan, Ding Wei
Chin. Phys. B 2010, 19 (10): 106101 ;  doi: 10.1088/1674-1056/19/10/106101
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A previously published new rotation function has been improved by using a dynamic correlation coefficient as well as two new scoring functions of relative entropy and mean-square-residues to make the rotation function more robust and independent of a specific set of weights for scoring and ranking. The previously described new rotation function calculates the rotation function of molecular replacement by matching the search model directly with the Patterson vector map. The signal-to-noise ratio for the correct match was increased by averaging all the matching peaks. Several matching scores were employed to evaluate the goodness of matching. These matching scores were then combined into a single total score by optimizing a set of weights using the linear regression method. It was found that there exists an optimal set of weights that can be applied to the global rotation search and the correct solution can be ranked in the top 100 or less. However, this set of optimal weights in general is dependent on the search models and the crystal structures with different space groups and cell parameters. In this work, we try to solve this problem by designing a dynamic correlation coefficient. It is shown that the dynamic correlation coefficient works for a variety of space groups and cell parameters in the global search of rotation function. We also introduce two new matching scores: relative entropy and mean-square-residues. Last but not least, we discussed a valid method for the optimization of the adjustable parameters for matching vectors.

STM observation of pit formation and evolution during the epitaxial growth of Si on Si(001) surface

Xu Mao-Jie, Jeyanthinath Mayandi, Wang Xue-Sen, Jia Jin-Feng, Xue Qi-Kun, Dou Xiao-Ming
Chin. Phys. B 2010, 19 (10): 106102 ;  doi: 10.1088/1674-1056/19/10/106102
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Pit formation and surface morphological evolution in Si(001) homoepitaxy are investigated by using scanning tunneling microscopy. Anti-phase boundary is found to give rise to initial generation of pits bound by bunched DB steps. The terraces break up and are reduced to a critical nucleus size with pit formation. Due to anisotropic kinetics, a downhill bias diffusion current, which is larger along the dimer rows through the centre area of the terrace than through the area close to the edge, leads to the prevalence of pits bound by {101} facets. Subsequent annealing results in a shape transition from {101}-faceted pits to multi-faceted pits.

Study of nanocrystalline VO2 thin films prepared by magnetron sputtering and post-oxidation

Luo Zhen-Fei, Wu Zhi-Ming, Xu Xiang-Dong, Wang Tao, Jiang Ya-Dong
Chin. Phys. B 2010, 19 (10): 106103 ;  doi: 10.1088/1674-1056/19/10/106103
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Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and post-oxidation. These films undergo semiconductor–metal transition at 70 du, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction (XRD) and atomic force microscope (AFM), respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy (XPS) results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p–3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, Eopt2p–3d=1.81 eV, is in good agreement with that previously obtained by theoretical calculation.

Synthesis of monodisperse palladium nanocubes and their catalytic activity for methanol electrooxidation Hot!

Ding Hao, Shi Xue-Zhao, Shen Cheng-Min, Hui Chao, Xu Zhi-Chuan, Li Chen, Tian Yuan, Wang Deng-Ke, Gao Hong-Jun
Chin. Phys. B 2010, 19 (10): 106104 ;  doi: 10.1088/1674-1056/19/10/106104
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The single crystalline palladium nanocubes with an average size of 7 nm were prepared in the presence of poly (vinyl pyrrolidone) (PVP) and KBr using the polyol method. The as-prepared Pd nanocubes were highly uniform in both size and shape. The ordered packing structures including monolayer and multilayer can be fabricated via the rate-controlled evaporation of solution solvent. The electrochemical catalytic activity of these Pd nanocubes towards methanol oxidation was found to be higher than that of spherical Pd nanoparticles of similar size.

Laser-induced damage on large-aperture fused silica gratings

Han Wei, Huang Wan-Qing, Wang Fang, Li Ke-Yu, Feng Bin, Li Fu-Quan, Jing Feng, Zheng Wan-Guo
Chin. Phys. B 2010, 19 (10): 106105 ;  doi: 10.1088/1674-1056/19/10/106105
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Two sets of laser-damage experiments on large-aperture fused silica optics have been carried out in a high-power laser facility. Severe damage has been found on the grating which presented dense craters on the front surface. This phenomenon is quite different from other fused silica optics, which are damaged on the rear surface. The damage possibility due to the redeposition layer was ruled out by acid-etching the grating's front surface. The remarkable stimulated Brillouin scattering (SBS) effect was observed in grating and the reason for the front surface damage is thought to be the backward SBS.

Influence of nitrogen implantation into the buried oxide on the radiation hardness of silicon-on-insulator wafers

Tang Hai-Ma, Zheng Zhong-Shan, Zhang En-Xia, Yu Fang, Li Ning, Wang Ning-Juan
Chin. Phys. B 2010, 19 (10): 106106 ;  doi: 10.1088/1674-1056/19/10/106106
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In order to improve the total-dose radiation hardness of the buried oxide of separation by implanted oxygen silicon-on-insulator wafers, nitrogen ions were implanted into the buried oxide with a dose of 1016 cm- 2, and subsequent annealing was performed at 1100 ℃. The effect of annealing time on the radiation hardness of the nitrogen implanted wafers has been studied by the high frequency capacitance-voltage technique. The results suggest that the improvement of the radiation hardness of the wafers can be achieved through a shorter time annealing after nitrogen implantation. The nitrogen-implanted sample with the shortest annealing time 0.5 h shows the highest tolerance to total-dose radiation. In particular, for the 1.0 and 1.5 h annealing samples, both total dose responses were unusual. After 300-krad(Si) irradiation, both the shifts of capacitance--voltage curve reached a maximum, respectively, and then decreased with increasing total dose. In addition, the wafers were analysed by the Fourier transform infrared spectroscopy technique, and some useful results have been obtained.

Right on time: measuring Kuramoto model coupling from a survey of wrist-watches

Reginald D. Smith
Chin. Phys. B 2010, 19 (10): 106401 ;  doi: 10.1088/1674-1056/19/10/106401
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Using a survey of wrist-watch synchronization from a randomly selected group of independent volunteers, we model the system as a Kuramoto-type coupled oscillator network. Based on the phase data both the order parameter and likely size of the coupling are derived and the possibilities for similar research to deduce topology from dynamics are discussed.

A new model for the formation of contact angle and contact angle hysteresis

Gong Mao-Gang, Liu Yuan-Yue, Xu Xiao-Liang
Chin. Phys. B 2010, 19 (10): 106801 ;  doi: 10.1088/1674-1056/19/10/106801
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The formation mechanism of the contact angle and the sliding angle for a liquid drop on a solid surface plays an important role in producing hydrophobic surfaces. A new half soakage model is established in this paper as a substitute for Wenzel (complete soakage) and Cassie (no soakage) models. The model is suited to many solid surfaces, whether they are hydrophilic or hydrophobic, or even superhydrophobic. Based on the half soakage model, we analyse two surfaces resembling lotus, i.e. taper-like surface and corona-like surface. Furthermore, this new model is used to establish a quantitative relationship between the sliding angle and the parameters of surface morphology.

Evaluation of both composition and strain distributions in InGaN epitaxial film using x-ray diffraction techniques

Guo Xi, Wang Hui, Jiang De-Sheng, Wang Yu-Tian, Zhao De-Gang, Zhu Jian-Jun, Liu Zong-Shun, Zhang Shu-Ming, Yang Hui
Chin. Phys. B 2010, 19 (10): 106802 ;  doi: 10.1088/1674-1056/19/10/106802
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The composition and stain distributions in the InGaN epitaxial films are jointly measured by employing various x-ray diffraction (XRD) techniques, including out-of-plane XRD at special planes, in-plane grazing incidence XRD, and reciprocal space mapping (RSM). It is confirmed that the measurement of (204) reflection allows a rapid access to estimate the composition without considering the influence of biaxial strain. The two-dimensional RSM checks composition and degree of strain relaxation jointly, revealing an inhomogeneous strain distribution profile along the growth direction. As the film thickness increases from 100 nm to 450 nm, the strain status of InGaN films gradually transfers from almost fully strained to fully relaxed state and then more In atoms incorporate into the film, while the near-interface region of InGaN films remains pseudomorphic to GaN.

Deposition pressure effect on the surface roughness scaling of microcrystalline silicon films

Zhu Zhi-Li, Ding Yan-Li, Wang Zhi-Yong, Gu Jin-Hua, Lu Jing-Xiao
Chin. Phys. B 2010, 19 (10): 106803 ;  doi: 10.1088/1674-1056/19/10/106803
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The scaling behaviour of surface roughness evolution of microcrystalline silicon (μc-Si:H) films prepared by very-high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) has been investigated by using a spectroscopic ellipsometry (SE) technique. The growth exponent β was analysed for the films deposited under different pressures Pg. The results suggest that films deposited at Pg = 70 Pa have a growth exponent β about 0.22, which corresponds to the definite diffusion growth. However, abnormal scaling behaviour occurs in the films deposited at Pg = 300 Pa. The exponent β is about 0.81 that is much larger than 0.5 of zero diffusion limit in the scaling theory. The growth mode of μ c-Si:H deposited at Pg= 300 Pa is clearly different from that of μc-Si:H at Pg = 70 Pa. Monte Carlo simulations indicate that the sticking process and the surface diffusion of the radicals are two key factors to affect the growth mode under different pressures. Under Pg= 300 Pa, β>0.5 is correlated with the strong shadowing effect resulting from the larger sticking coefficient.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Modeling of 4H–SiC multi-floating-junction Schottky barrier diode

Pu Hong-Bin, Cao Lin, Chen Zhi-Ming, Ren Jie, Nan Ya-Gong
Chin. Phys. B 2010, 19 (10): 107101 ;  doi: 10.1088/1674-1056/19/10/107101
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This paper develops a new and easy to implement analytical model for the specific on-resistance and electric field distribution along the critical path for 4H–SiC multi-floating junction Schottky barrier diode. Considering the charge compensation effects by the multilayer of buried opposite doped regions, it improves the breakdown voltage a lot in comparison with conventional one with the same on-resistance. The forward resistance of the floating junction Schottky barrier diode consists of several components and the electric field can be understood with superposition concept, both are consistent with MEDICI simulation results. Moreover, device parameters are optimized and the analyses show that in comparison with one layer floating junction, multilayer of floating junction layer is an effective way to increase the device performance when specific resistance and the breakdown voltage are traded off. The results show that the specific resistance increases 3.2 mΩ·cm2 and breakdown voltage increases 422 V with an additional floating junction for the given structure.

Effect of Co on magnetic property and phase stability of Ni–Mn–Ga ferromagnetic shape memory alloys: A first-principles study

Tan Chang-Long, Jiang Jiu-Xing, Tian Xiao-Hua, Cai Wei
Chin. Phys. B 2010, 19 (10): 107102 ;  doi: 10.1088/1674-1056/19/10/107102
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The effect of Co content on magnetic property and phase stability of Ni50-xMn25Ga25Cox ferromagnetic shape memory alloys has been investigated using first-principles calculations. The total energy difference between paramagnetic and ferromagnetic state of austenite plays an important role in the magnetic transition. The high Curie temperature can be attributed to the stronger Co–Mn exchange interaction as compared to the Ni–Mn one. The phase stability of Ni50-xMn25Ga25Cox austenite increases with increasing Co content, which is discussed based on the electronic structure.

Theoretical study of small Mo clusters and molecular nitrogen adsorption on Mo clusters

Lei Xue-Ling
Chin. Phys. B 2010, 19 (10): 107103 ;  doi: 10.1088/1674-1056/19/10/107103
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This paper studies the small molybdenum clusters of Mon (n=2–8) and their adsorption of N2 molecule by using the density functional theory (DFT) with the generalized gradient approximation. The optimized structures of Mon clusters show the onset of a structural transition from a close-packed structure towards a body-centred cubic structure occurred at n=7. An analysis of adsorption energies suggests that the Mo2 is of high inertness and Mo6 cluster is of high activity against the adsorption of N2. Calculated results indicate that the N2 molecule prefers end-on mode by forming a linear or quasi-linear structure Mo–N–N, and the adsorption of nitrogen on molybdenum clusters is molecular adsorption with slightly elongated N–N bond. The electron density of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the partial density of states of representative cluster are also used to characterize the adsorption properties of N2 on the sized Mon clusters.

Trends in the band-gap pressure coefficients and bulk moduli in different structures of ZnGa2S4, ZnGa2Se4 and ZnGa2Te4

Jiang Xiao-Shu, Yan Ying-Ce, Yuan Shi-Min, Mi Shu, Niu Zhen-Guo, Liang Jiu-Qing
Chin. Phys. B 2010, 19 (10): 107104 ;  doi: 10.1088/1674-1056/19/10/107104
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We have performed a first-principles investigation for the family of compounds ZnGa2X4 (= S, Se, Te). The properties of two possible structures, defect chalcopyrite and defect famatinite are both calculated. We reveal that ZnGa2S4 and ZnGa2Se4 have direct band gaps, while ZnGa2Te4 has an indirect band gap. The local density approximation band gaps are found to be very different in two structures, while the lattice parameters and bulk moduli are similar. We extend Cohen's empirical formula for zinc-blende compounds to this family of compounds. The pressure coefficients are calculated and metallization pressures are discussed. We find that agi remains fairly constant when the group-VI element X is varied in ZnGa2X4(II–III2–VI4).

First-principle calculation on the defect energy level of carbon vacancy in 4H–SiC

Jia Ren-Xu, Zhang Yu-Ming, Zhang Yi-Men
Chin. Phys. B 2010, 19 (10): 107105 ;  doi: 10.1088/1674-1056/19/10/107105
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First, electronic structures of perfect wurtzite 4H–SiC were calculated by using first-principle ultra-soft pseudo-potential approach of the plane wave based on the density functional theory; and the structure changes, band structures, and density of states were studied. Then the defect energy level of carbon vacancy in band gap was examined by substituting the carbon in 4H–SiC with carbon vacancy. The calculated results indicate the new defect energy level generated by the carbon vacancy, and its location in the band gap in 4H–SiC, which has the character of deep acceptor. A proper explanation for green luminescence in 4H–SiC is given according to the calculated results which are in good agreement with our measurement results.

Laser-induced voltage effects in Ca3Co4O9 thin films on tilted LaAlO3(001) substrates grown by chemical solution deposition

Wang Shu-Fang, Chen Ming-Jing, Zhao Shu-Rui, Chen Jing-Chun, He Li-Ping, Yu Wei, Wang Jiang-Long, Fu Guang-Sheng
Chin. Phys. B 2010, 19 (10): 107201 ;  doi: 10.1088/1674-1056/19/10/107201
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Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10° tilted LaAlO3 (001) substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, open-circuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions.

Coherence destruction of tunneling in a quantum-dot molecule with bias

Zhong Guang-Hui, Wang Li-Min
Chin. Phys. B 2010, 19 (10): 107202 ;  doi: 10.1088/1674-1056/19/10/107202
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This paper studies the constraint conditions for coherence destruction in tunneling by using perturbation theory and numerical simulation for an AC-field with bias and Coulomb interaction between electrons in a quantum dot molecule. Such conditions can be described by using the roots of a Bessel function Jn(x), where n is determined by both the bias and the Coulomb interactions, and x is the ratio of the amplitude to the frequency of the AC-field. Under such conditions, a coherent suppression of tunneling occurs between localized electronic states, which results from the dynamical localization phenomenon. All the conditions are verified with numerical simulations.

The transverse laser induced thermoelectric voltages in step flow growth (1-x)Pb(Mg1/3Nb2/3)O3xPbTiO3 thin films

Shang Jie, Zhang Hui, Li Yong, Cao Ming-Gang, Zhang Peng-Xiang
Chin. Phys. B 2010, 19 (10): 107203 ;  doi: 10.1088/1674-1056/19/10/107203
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This paper reports that the transverse laser induced thermoelectric voltages (LITV) are observed for the first time in the step flow growth (1-x)Pb(Mg1/3Nb2/3)O3xPbTiO3 (PMN–PT, x=0.20, 0.33, 0.50) thin films deposited on vicinal-cut strontium titanate single crystal substrates. Because lead magnesium niobate-lead titanate is a solid solution of lead magnesium niobate (PMN) and lead titanate (PT), there are two types of signals. One is wide with a time response of a microsecond, and the other superimposed with the wide signal is narrow with a time response of a nanosecond. The transverse LITV signals depend on the ratio of PMN to PT drastically. Under the irradiation of 28-ns pulsed KrF excimer laser with the 248-nm wavelength,the largest induced voltage is observed in the 0.50Pb(Mg1/3Nb2/3)O3–0.50 PbTiO3 films. Moreover, the effects of film thickness, substrates, and tilt angles of substrates are also investigated.

The etching of a-plane GaN epilayers grown by metal–organic chemical vapour deposition

Xu Sheng-Rui, Hao Yue, Zhang Jin-Cheng, Zhou Xiao-Wei, Cao Yan-Rong, Ou Xin-Xiu, Mao Wei, Du Da-Chao, Wang Hao
Chin. Phys. B 2010, 19 (10): 107204 ;  doi: 10.1088/1674-1056/19/10/107204
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Morphology of nonpolar (1120) a-plane GaN epilayers on r-plane (1102) sapphire substrate grown by low-pressure metal–organic vapour deposition was investigated after KOH solution etching. Many micron- and nano-meter columns on the a-plane GaN surface were observed by scanning electron microscopy. An etching mechanism model is proposed to interpret the origin of the peculiar etching morphology. The basal stacking fault in the a-plane GaN plays a very important role in the etching process.

No-catalyst growth of vertically-aligned AlN nanocone field electron emitter arrays with high emission performance at low temperature

Liu Fei, Mo Fu-Yao, Li Li, Su Zan-Jia, Huang Ze-Qiang, Deng Shao-Zhi, Chen Jun, Xu Ning-Sheng
Chin. Phys. B 2010, 19 (10): 107205 ;  doi: 10.1088/1674-1056/19/10/107205
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The AlN nanostructures with a wide band-gap of 6.28 eV are considered as ideal cold cathode materials because of their low electron-affinity. Many methods have been devoted to fabricating AlN nanostructures, but high growth temperature over 800 ℃ and the use of the catalysts in most methods limit their practical application and result in their poor field-emission behaviours in uniformity. This paper reports that without any catalysts, a simple chemical vapour deposition method is used to synthesize aligned AlN nanocone arrays at 550 ℃ on silicon substrate or indium tin oxide glass. Field emission measurements show that these nanocones prepared at low temperature have an average turn-on field of 6 V/μm and a threshold field of 11.7 V/μm as well as stable emission behaviours at high field, which suggests that they have promising applications in field emission area.

GaP layers grown on GaN with and without buffer layers

Li Shu-Ti, Cao Jian-Xing, Fan Guang-Han, Zhang Yong, Zheng Shu-Wen, Su Jun
Chin. Phys. B 2010, 19 (10): 107206 ;  doi: 10.1088/1674-1056/19/10/107206
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The growth of GaP layer on GaN with and without buffer layers by metal-organic chemical vapour deposition (MOCVD) has been studied. Results indicate that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature (HT) GaP growth. These sites can promote the two-dimensional (2D) growth of HT GaP and reduce the surface roughness. A GaP single crystal layer grown at 680℃ is obtained using a 40-nm thick GaP buffer layer. The full-width at half-maximum (FWHM) of the (111) plane of GaP layer, measured by DCXRD, is 560 arcsec. The GaP layer grown on GaN without low temperature GaP buffer layer shows a rougher surface. However, the FWHM of the (111) plane is 408 arcsec, which is the indication of better crystal quality for the GaP layer grown on GaN without a low temperature buffer layer. Because it provides less nucleation sites grown at high growth temperature, the three-dimensional (3D) growth is prolonged. The crystalline quality of GaP is lightly improved when the surface of GaN substrate is pretreated by PH3, while it turned to be polycrystalline when the substrate is pretreated by TEGa.

Effect of diode size and series resistance on barrier height and ideality factor in nearly ideal Au/n type-GaAs micro Schottky contact diodes

M. A. Yeganehx, Sh. Rahmatallahpur, A. Nozad, R. K. Mamedov
Chin. Phys. B 2010, 19 (10): 107207 ;  doi: 10.1088/1674-1056/19/10/107207
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Small high-quality Au/n type-GaAs Schottky barrier diodes (SBDs) with low reverse leakage current are produced using lithography. Their effective barrier heights (BHs) and ideality factors from current–voltage (IV) characteristics are measured by a Pico ampere meter and home-built IV instrument. In spite of the identical preparation of the diodes there is a diode-to-diode variation in ideality factor and barrier height parameters. Measurement of topology of a surface of a thin metal film with atomic force microscope (AFM) shows that Au-n type-GaAS SD consists of a set of parallel-connected micro and nanocontacts diodes with sizes approximately in a range of 100–200 nm. Between barrier height and ideality factor there is an inversely proportional dependency. With the diameter of contact increasing from 5 μm up to 200 μm, the barrier height increases from 0.833 up to 0.933 eV and its ideality factor decreases from 1.11 down to 1.006. These dependencies show the reduction of the contribution of the peripheral current with the diameter of contact increasing. We find the effect of series resistance on barrier height and ideality factor.

The study on two-dimensional analytical model for gate stack fully depleted strained Si on silicon-germanium-on-insulator MOSFETs

Li Jin, Liu Hong-Xia, Li Bin, Cao Lei, Yuan Bo
Chin. Phys. B 2010, 19 (10): 107301 ;  doi: 10.1088/1674-1056/19/10/107301
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Based on the exact resultant solution of two-dimensional Poisson's equation in strained Si and Si1 - XGeX layer, a simple and accurate two-dimensional analytical model including surface channel potential, surface channel electric field, threshold voltage and subthreshold swing for fully depleted gate stack strained Si on silicon-germanium-on-insulator (SGOI) MOSFETs has been developed. The results show that this novel structure can suppress the short channel effects (SCE), the drain-induced barrier-lowering (DIBL) and improve the subthreshold performance in nanoelectronics application. The model is verified by numerical simulation. The model provides the basic designing guidance of gate stack strained Si on SGOI MOSFETs.

Study on two-dimensional analytical models for symmetrical gate stack dual gate strained silicon MOSFETs

Li Jin, Liu Hong-Xia, Li Bin, Cao Lei, Yuan Bo
Chin. Phys. B 2010, 19 (10): 107302 ;  doi: 10.1088/1674-1056/19/10/107302
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Based on the exact resultant solution of two-dimensional Poisson's equation, the novel two-dimensional models, which include surface potential, threshold voltage, subthreshold current and subthreshold swing, have been developed for gate stack symmetrical double-gate strained-Si MOSFETs. The models are verified by numerical simulation. Besides offering the physical insight into device physics, the model provides the basic designing guidance of further immunity of short channel effect of complementary metal-oxide-semiconductor (CMOS)-based device in a nanoscale regime.

Effect of transparency on Josephson junction between s+g-wave superconductors

Gholamreza Rashedi
Chin. Phys. B 2010, 19 (10): 107303 ;  doi: 10.1088/1674-1056/19/10/107303
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In this paper, a dc Josephson junction between borocarbide superconductors has been studied theoretically. The s+g-wave pairing symmetry which is observed in rare earth complex of borocarbides has a huge anisotropy and is an interesting form of unconventional superconductivity. We calculate the Josephson current in a superconductor–insulator–superconductor (SIS) Josephson junction with s+g-wave superconducting pairing symmetry. In our planar junction c-axis is parallel to an interface with finite transparency but ab-planes of two tetragonal superconductors are misorientated by angle α. We obtain that the Josephson current is strongly dependent on mis-orientation between the left and the right ab-planes. An insulator sandwiched between two superconductors which acts as a potential barrier is demonstrated by a transparency coefficient. The effects of the potential barrier and the mis-orientation on the current are studied analytically and numerically. Occurrence of 0π  transition in this s+g-wave junction is investigated in this paper. A comparison between d-wave Josephson junction and s+g-wave one is also made in the present paper.

Study and optimal simulation of 4H–SiC floating junction Schottky barrier diodes' structures and electric properties

Nan Ya-Gong, Pu Hong-Bin, Cao Lin, Ren Jie
Chin. Phys. B 2010, 19 (10): 107304 ;  doi: 10.1088/1674-1056/19/10/107304
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This paper stuides the structures of 4H–SiC floating junction Schottky barrier diodes. Some structure parameters of devices are optimized with commercial simulator based on forward and reverse electrical characteristics. Compared with conventional power Schottky barrier diodes, the devices are featured by highly doped drift region and embedded floating junction layers, which can ensure high breakdown voltage while keeping lower specific on-state resistance, and solve the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with optimized structure parameter, the breakdown voltage can reach 4.36 kV and the specific on-resistance is 5.8 mΩ·cm2 when the Baliga figure of merit value of 13.1 GW/cm2 is achieved.

Significant performance enhancement in AlGaN/GaN high electron mobility transistor by high-κ organic dielectric

Wang Ze-Gao, Chen Yuan-Fu, Chen Cao, Tian Ben-Lang, Chu Fu-Tong, Liu Xing-Zhao, Li Yan-Rong
Chin. Phys. B 2010, 19 (10): 107305 ;  doi: 10.1088/1674-1056/19/10/107305
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The electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) with and without high-κ organic dielectrics are investigated. The maximum drain current ID max and the maximum transconductance gm max of the organic dielectric/AlGaN/GaN structure can be enhanced by 74.5%, and 73.7% compared with those of the bare AlGaN/GaN HEMT, respectively. Both the threshold voltage VT and gm max of the dielectric/AlGaN/GaN HEMT are strongly dielectric-constant-dependent. Our results suggest that it is promising to significantly improve the performance of the AlGaN/GaN HEMT by introducing the high-κ organic dielectric.

Structure distortion, optical and electrical properties of ZnO thin films co-doped with Al and Sb by so–gel spin coating

Zhong Wen-Wu, Liu Fa-Min, Cai Lu-Gang, Zhou Chuan-Cang, Ding Peng, Zhang Huan
Chin. Phys. B 2010, 19 (10): 107306 ;  doi: 10.1088/1674-1056/19/10/107306
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ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl3 to SbCl3 at 1:2, are prepared by a sol–gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×108, 3.26×108, 5.23×108, and 6.97×108 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm.

Invariable optical properties of phosphor-free white light-emitting diode under electrical stress

Long Hao, Fang Hao, Qi Sheng-Li, Sang Li-Wen, Cao Wen-Yu, Yan Jian, Deng Jun-Jing, Yang Zhi-Jian, Zhang Guo-Yi
Chin. Phys. B 2010, 19 (10): 107307 ;  doi: 10.1088/1674-1056/19/10/107307
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This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours' current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode.

Glassy phase and thermodynamics for random field Ising model on spherical lattice in magnetic field

Khalid Bannora, Galal Ismail, Wafaa Hassan
Chin. Phys. B 2010, 19 (10): 107501 ;  doi: 10.1088/1674-1056/19/10/107501
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Phase diagram and thermodynamic parameters of the random field Ising model (RFIM) on spherical lattice are studied by using mean field theory. This lattice is placed in an external magnetic field (B). The random field (hi) is assumed to be Gaussian distributed with zero mean and a variance < hi2 > = HRF2 . The free energy (F), the magnetization (M) and the order parameter (q) are calculated. The ferromagnetic (FM) spin-glass (SG) phase transition is clearly observed. The critical temperature (TC) is computed under a critical intensity of random field . The phase transition from FM to paramagnetic (PM) occurs at TC = J / k in the absence of magnetic field. The critical temperature decreases as HRF increases in the phase boundary of FM-to-SG. The magnetic susceptibility (χ) shows a sharp cusp at TC and the specific heat (C) has a singularity in small random field. The internal energy (U) has a similar behaviour to that obtained from the Monte Carlo simulation.

Polydispersity effects on the magnetization of diluted ferrofluids: a lognormal analysis

Wang Xu-Fei, Shi Li-Qun
Chin. Phys. B 2010, 19 (10): 107502 ;  doi: 10.1088/1674-1056/19/10/107502
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Based on a lognormal particle size distribution, this paper makes a model analysis on the polydispersity effects on the magnetization behaviour of diluted ferrofluids. Using a modified Langevin relationship for the lognormal dispersion, it first performs reduced calculations without material parameters. From the results, it is extrapolated that for the ferrofluid of lognormal polydispersion, in comparison with the corresponding monodispersion, the saturation magnetization is enhanced higher by the particle size distribution. It also indicates that in an equivalent magnetic field, the lognormally polydispersed ferrofluid is magnetically saturated faster than the corresponding monodispersion. Along the theoretical extrapolations, the polydispersity effects are evaluated for a typical ferrofluid of magnetite, with a dispersity of σ =0.20. The results indicate that the lognormal polydispersity leads to a slight increase of the saturation magnetization, but a noticeable increase of the speed to reach the saturation value in an equivalent magnetic field.

Response of colloidal liquids containing magnetic holes of different volume densities to magnetic field characterized by transmission measurement

Deng Hai-Dong, Sun Ting, Zhao Wei-Ren, Fu Zhi-Cheng, Dai Qiao-Feng, Wu Li-Jun, Lan Sheng, Achanta Venu Gopal
Chin. Phys. B 2010, 19 (10): 107503 ;  doi: 10.1088/1674-1056/19/10/107503
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This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhancement in the transmission of such a colloidal liquid under a magnetic field exhibits a strong dependence on the volume density of magnetic holes. A linear increase in the maximum enhancement factor is observed when the volume density of magnetic holes is below a critical level at which a maximum enhancement factor of ~150 is achieved in the near infrared region. Once the volume density of magnetic holes exceeds the critical level, a sharp drop of the maximum enhancement factor to ~2 is observed. After that, the maximum enhancement factor increases gradually till a large volume density of ~9%. By monitoring the arrangement of magnetic holes under a magnetic field, it reveals that the colloidal liquids can be classified into three different phases, i.e., the gas-like, liquid-like and solid-like phases, depending on the volume density of magnetic holes. The response behaviour of colloidal liquids to magnetic field is determined by the interaction between magnetic holes which is governed mainly by their volume density. A phase transition, which is manifested in the dramatic reduction in the maximum enhancement factor, is clearly observed between the liquid-like and solid-like phases. The optical switching operations for colloidal liquids in different phases are compared and the underlying physical mechanisms are discussed.

Effects of thin MnAl buffer layer on structural and magnetic properties of MnAl films

Zhang Xu-Hui, Ma Bin, Zhang Zong-Zhi, Jin Qing-Yuan
Chin. Phys. B 2010, 19 (10): 107504 ;  doi: 10.1088/1674-1056/19/10/107504
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Thin Mn(2 nm)/Al(2 nm) bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic τ-phase forms in the buffer layers at an optimum substrate temperature. As a template it induces the growth of following MnAl film. Compared with the case of film without buffer layer, the growth of non-ferromagnetic phase is suppressed and the structural and magnetic properties of MnAl film are improved. Weak dipolar inter-grain coupling is revealed in the MnAl film, and the magnetic reversal process is dominated by magnetic moment rotation.

Structure, dielectric and magnetodielectric properties of Bi1-xGdxFeO3 Ceramics

Li Jing-Bo, Rao Guang-Hui, Xiao Yin-Guo, Luo Jun, Liu Guang-Yao, Chen Jing-Ran, Liang Jing-Kui
Chin. Phys. B 2010, 19 (10): 107505 ;  doi: 10.1088/1674-1056/19/10/107505
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Different magnetodielectric effects were observed in Bi1-xGdxFeO3 ceramics depending on gadolinium content. A positive one was observed in the samples with x ≤ 0.10 at 295 K and 16 K, and a negative one in the sample with x = 0.4 at 16 K. Structure analysis by x-ray diffraction (XRD) reveals that the samples crystallize in the R3c structure (ferroelectrics) for x < 0.08 and in the Pbnm structure (paraelectrics) for x ≥ 0.3 at room temperature. Temperature-dependent dielectric response and x-ray diffraction confirm the occurrence of a structural transition in the Pbnm phase at low temperature for the samples with x ≤ 0.4. While the positive magnetodielectric effects can be attributed to a coupling of magnetic and crystallographic structures of the R3c phase, the observed negative magnetodielectric effect in the Pbnm phase can be associated with a low-temperature modification of the Pbnm structure. The observed dual-signed magnetodielectric effects suggest that the Bi1-xGdxFeO3 oxides are a good prototype for understanding the magnetodielectric coupling mechanism in this kind of materials.

Lanthanum-doped Bi4Ti3O12 ceramics prepared by high-pressure technique

Lin Xue, Guan Qing-Feng, Liu Yang, Li Hai-Bo
Chin. Phys. B 2010, 19 (10): 107701 ;  doi: 10.1088/1674-1056/19/10/107701
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We present an effective way in this paper to increase the density of lanthanum doped bismuth titanate ceramics, Bi4-xLaxTi3O12 (BLT), thereby significantly improving the performance of the BLT ceramics. Dense BLT ceramicses, Bi4-xLaxTi3O12 (x = 0.25, 0.5, 0.75, 1.0), are prepared by using nanocrystalline powders fabricated by sol–gel method and high-pressure technique. The microstructures of the BLT ceramicses prepared separately by conventional-pressure and high-pressure techniques are investigated by using x-ray diffraction and transmission electron microscope. The influence of La-doping on the densification of bismuth titanate ceramics is investigated. The experimental results indicate that the phase compositions of all samples with various lanthanum dopings sintered at 900℃ possess layer-structure of Bi4Ti3O12. The green compacts are pressed under 2.5 GPa, 3.0 GPa, 3.5 GPa and 4.0 GPa, separately. It is found that the density of BLT ceramics is significantly increased due to the decreasing of porosity in the green compacts by high-pressure process.

Polarization fatigue in poly(vinylidene fluoride (78%)-trifluoroethylene (22%)) ferroelectric thin films: a pulse train study

Luo Xiao-Ya, Zhang Ji-Hao, Yan Xue-Jian, Zhu Guo-Dong
Chin. Phys. B 2010, 19 (10): 107702 ;  doi: 10.1088/1674-1056/19/10/107702
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This paper investigates the influences of polarization fatigue on remanent polarization and switching time by pulse train measurements in ferroelectric poly(vinylidene fluoride (78%) and trifluoroethylene (22%)) thin films. Fatigue was carried out by a series of bipolar switching pulses with constant pulse width (on-time) and various interval times between pulses (off-time). The experimental observations indicated that the off-time period showed no obvious influence on fatigue rate and the switching time increased with the increase of fatigue cycles. The origination of these phenomena was discussed according to the charge injection model.

General formula for phonon-assisted n-photon absorption in solids

Deng Hong-Xiang, Jiang Xiao-Dong, Xiang Xia, Sun Kai, Yuan Xiao-Dong, Zheng Wan-Guo, Gao Fei, Zu Xiao-Tao
Chin. Phys. B 2010, 19 (10): 107801 ;  doi: 10.1088/1674-1056/19/10/107801
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A general formula for phonon-assisted n-photon absorption in solids is obtained by (n+1)-th order perturbation technique. The complicated calculation process for transition element of n-photon absorption is simply demonstrated by a diagram approach that is proposed in this work. We find that the transition element for the n-photon absorption has a simple form, i.e., it is just the first term of the n-th order fist kind Bessel function.

Controlling electric field distribution by graded spherical core-shell metamaterials

Wei En-Bo, Sun Lei, Yu Kin-Wah
Chin. Phys. B 2010, 19 (10): 107802 ;  doi: 10.1088/1674-1056/19/10/107802
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This paper investigates analytically the electric field distribution of graded spherical core-shell metamaterials, whose permittivity is given by the graded Drude model. Under the illumination of a uniform incident optical field, the obtained results show that the electrical field distribution in the shell region is controllable and the electric field peak's position inside the spherical shell can be confined in a desired position by varying the frequency of the optical field as well as the parameters of the graded dielectric profiles. It has also offered an intuitive explanation for controlling the local electric field by graded metamaterials.
CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Effect of physical disturbance on the structure of needle coke

Zhao Shi-Gui, Wang Bao-Cheng, Sun Quan
Chin. Phys. B 2010, 19 (10): 108101 ;  doi: 10.1088/1674-1056/19/10/108101
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Through different preparation technology, this paper reports that the needle coke is prepared with coal-tar pitch under the effect of magnetic field and ultrasonic cavitation. It studies the effect of physical disturbance on the structure of needle coke. The structure of needle coke is characterized by scanning electron microscope and x-ray diffractometer, and the influence mechanism is analysed. Results showed that the structure and property of needle coke could be effectively improved by magnetic field and ultrasonic cavitations, such as degree of order, degree of graphitization and crystallization. Comparatively speaking, the effect of magnetic field was greater. The graphitization degree of needle coke prepared under the effect of magnetic field is up to 45.35%.

Preparation of size controllable copper nanocrystals for nonvolatile memory applications Hot!

Wang Li, Sun Hong-Fang, Zhou Hui-Hua, Zhu Jing
Chin. Phys. B 2010, 19 (10): 108102 ;  doi: 10.1088/1674-1056/19/10/108102
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A method of fabricating Cu nanocrystals embedded in SiO2 dielectric film for nonvolatile memory applications by magnetron sputtering is introduced in this paper. The average size and distribution density of Cu nanocrystal grains are controlled by adjusting experimental parameters. The relationship between nanocrystal floating gate micro-structure and its charge storage capability is also discussed theoretically.

Non-equilibrium statistical theory about microscopic fatigue cracks of metal in magnetic field

Liu Zhao-Long, Hu Hai-Yun, Fan Tian-You, Xing Xiu-San
Chin. Phys. B 2010, 19 (10): 108103 ;  doi: 10.1088/1674-1056/19/10/108103
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This paper develops the non-equilibrium statistical fatigue damage theory to study the statistical behaviour of micro-crack for metals in magnetic field. The one-dimensional homogeneous crack system is chosen for study. To investigate the effect caused by magnetic field on the statistical distribution of micro-crack in the system, the theoretical analysis on microcrack evolution equation, the average length of micro-crack, density distribution function of micro-crack and fatigue fracture probability have been performed. The derived results relate the changes of some quantities, such as average length, density distribution function and fatigue fracture probability, to the applied magnetic field, the magnetic and mechanical properties of metals. It gives a theoretical explanation on the change of fatigue damage due to magnetic fields observed by experiments, and presents an analytic approach on studying the fatigue damage of metal in magnetic field.

Influence of Pb adatom on adsorption of oxygen molecules on Pb(111) surface: a first-principles study

Yang Yu
Chin. Phys. B 2010, 19 (10): 108201 ;  doi: 10.1088/1674-1056/19/10/108201
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Using first-principles calculations, we systematically study the influence of Pb adatom on the adsorption and the dissociation of oxygen molecules on Pb(111) surface, to explore the effect of a point defect on the oxidation of the Pb(111) surface. We find that when an oxygen molecule is adsorbed near an adatom on the Pb surface, the molecule will be dissociated without any obvious barriers, and the dissociated O atoms bond with both the adatom and the surface Pb atoms. The adsorption energy in this situation is much larger than that on a clean Pb surface. Besides, for an adsorbed oxygen molecule on a clean Pb surface, a diffusing Pb adatom can also change its adsorption state and enlarge the adsorption energy for O, but it does not make the oxygen molecule dissociated. And in this situation, there is a molecule-like PbO2 cluster formed on the Pb surface.

Intrinsic noise analysis and stochastic simulation on transforming growth factor beta signal pathway

Wang Lu, Ouyang Qi
Chin. Phys. B 2010, 19 (10): 108202 ;  doi: 10.1088/1674-1056/19/10/108202
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A typical biological cell lives in a small volume at room temperature; the noise effect on the cell signal transduction pathway may play an important role in its dynamics. Here, using the transforming growth factor-β signal transduction pathway as an example, we report our stochastic simulations of the dynamics of the pathway and introduce a linear noise approximation method to calculate the transient intrinsic noise of pathway components. We compare the numerical solutions of the linear noise approximation with the statistic results of chemical Langevin equations, and find that they are quantitatively in agreement with the other. When transforming growth factor-β dose decreases to a low level, the time evolution of noise fluctuation of nuclear Smad2–Smad4 complex indicates the abnormal enhancement in the transient signal activation process.

Effect of number density on velocity distributions in a driven quasi-two-dimensional granular gas

Sajjad Hussain Shah, Li Yin-Chang, Hou Mei-Ying
Chin. Phys. B 2010, 19 (10): 108203 ;  doi: 10.1088/1674-1056/19/10/108203
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The motion of mono-disperse spherical steel particles in a vibration driven quasi-two-dimensional (2D) square cell is studied. The cell is horizontally vibrated to eliminate the effect of gravity compaction. The velocity distributions at different particle number densities are studied and found to obey the form exp [-β (|vy|σy)α], in which vy and σy are velocity and its variance in the transverse direction, and α and β are fitting parameters. The value of α is found to decrease with the number density of particles increasing. To investigate the effect of the bottom plate, the molecular dynamics simulation without considering any bottom friction is performed. The accordance between the simulation result and the experimental result shows that the influence of bottom plate friction force on the high energy tail of the velocity distribution can be neglected.

Depletion interactions in binary mixtures of repulsive colloids

Li Wei-Hua, Qiu Feng
Chin. Phys. B 2010, 19 (10): 108204 ;  doi: 10.1088/1674-1056/19/10/108204
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Acceptance ratio method, which has been used to calculate the depletion potential in binary hard-sphere mixtures, is extended to the computation of the depletion potential of non-rigid particle systems. The repulsive part of the Lennard–Jones pair potential is used as the direct pair potential between the non-rigid particles. The depletion potential between two big spheres immersed in a suspension of small spheres is determined with the acceptance ratio method through the application of Monte Carlo simulation. In order to check the validity of this method, our results are compared with those obtained by the Asakura–Oosawa approximation, and by Varial expansion approach, and by molecular dynamics simulation. The total effective potential and the depth of its potential well are computed for various softness parameters of the direct pair potential.

Effects of fractal gating of potassium channels on neuronal behaviours

Zhao De-Jiang, Zeng Shang-You, Zhang Zheng-Zhen
Chin. Phys. B 2010, 19 (10): 108701 ;  doi: 10.1088/1674-1056/19/10/108701
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The classical model of voltage-gated ion channels assumes that according to a Markov process ion channels switch among a small number of states without memory, but a bunch of experimental papers show that some ion channels exhibit significant memory effects, and this memory effects can take the form of kinetic rate constant that is fractal. Obviously the gating character of ion channels will affect generation and propagation of action potentials, furthermore, affect generation, coding and propagation of neural information. However, there is little previous research on this series of interesting issues. This paper investigates effects of fractal gating of potassium channel subunits switching from closed state to open state on neuronal behaviours. The obtained results show that fractal gating of potassium channel subunits switching from closed state to open state has important effects on neuronal behaviours, increases excitability, rest potential and spiking frequency of the neuronal membrane, and decreases threshold voltage and threshold injected current of the neuronal membrane. So fractal gating of potassium channel subunits switching from closed state to open state can improve the sensitivity of the neuronal membrane, and enlarge the encoded strength of neural information.

Research on the response model of microbolometer

Sui Xiu-Bao, Chen Qian, Gu Guo-Hua, Liu Ning
Chin. Phys. B 2010, 19 (10): 108702 ;  doi: 10.1088/1674-1056/19/10/108702
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There are certain limitations in the application of uncooled focal plane array (FPA) detector due to the lack of an effective response model which reliably transforms the target temperature to analog output voltage. This paper establishes the response model of microbolometer through researching the detection theory of microbolometer and the heat balance equation under the condition of the pulsed voltage bias. In the establishing process, we simplified the heat balance equation to acquire a simple answer. The experimental data show that, in the temperature dynamic range of 30 K, the biggest tolerance between the model data and the experiment data is 0.2 K; while in the temperature dynamic range of 100 K, it is 1 K. This model can reflect the real response of the microbolometer with only small differences which are acceptable in engineering applications.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Swelling of K+, Na+ and Ca2+-montmorillonites and hydration of interlayer cations: a molecular dynamics simulation

Liu Tao, Tian Xiao-Feng, Zhao Yu, Gao Tao
Chin. Phys. B 2010, 19 (10): 109101 ;  doi: 10.1088/1674-1056/19/10/109101
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This paper performs molecular dynamics simulations to investigate the role of the monovalent cations K, Na and the divalent cation Ca on the stability and swelling of montmorillonite. The recently developed CLAYFF force field is used to predict the basal spacing as a function of the water content in the interlayer. The simulations reproduced the swelling pattern of these montmorillonites, suggesting a mechanism of their hydration different (K+ < Na + < Ca2 + ) from that of K + -, Na + -, and Ca2 + -montmorillonites. In particular, these results indicate that the valence of the cations has the larger impact on the behaviour of clay--water systems. It also finds that the differences in size and hydration energy of K + , Na + and Ca2 + ions have strong implications for the structure of interlayer. This leads to the differences in the layer spacings of the simulated K + -, Na + -, and Ca2 + -montmorillonites. Furthermore, these simulations show that the K cations interact strongly with the clay sheets for the dehydrated clay sheets, but for the hydrated clays the Ca cations interact clearly strongly with the clay sheets.

Spectral dispersion of cloud droplet size distributions and radar threshold reflectivity for drizzle

Xie Xiao-Ning, Liu Xiao-Dong
Chin. Phys. B 2010, 19 (10): 109201 ;  doi: 10.1088/1674-1056/19/10/109201
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From first principles, we find that the radar threshold reflectivity between nonprecipitating clouds and precipitating clouds is strongly related to not only the cloud droplet number concentration but also the spectral dispersion of cloud droplet size distributions. The further investigation indicates that the threshold value is an increasing function of spectral dispersion and cloud droplet number concentration. These results may improve our understanding of the cloud-precipitation interaction and the aerosol indirect effect.
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