Table of contents

15 January 2011, Volume 20 Issue 1 Previous issue    Next issue

GENERAL

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Synchronisation of chaotic systems using a novel sampled-data fuzzy controller Feng Yi-Fu(冯毅夫) and Zhang Qing-Ling(张庆灵) Chin. Phys. B, 2011, 20 (1):  010101.  DOI: 10.1088/1674-1056/20/1/010101 Abstract ( 2077 )   PDF (406KB) ( 1131 )   This paper presents the synchronisation of chaotic systems using a sampled-data fuzzy controller and is meaningful for many physical real-life applications. Firstly, a Takagi–Sugeno (T–S) fuzzy model is employed to represent the chaotic systems that contain some nonlinear terms, then a type of fuzzy sampled-data controller is proposed and an error system formed by the response and drive chaotic system. Secondly, relaxed LMI-based synchronisation conditions are derived by using a new parameter-dependent Lyapunov–Krasovskii functional and relaxed stabilisation techniques for the underlying error system. The derived LMI-based conditions are used to aid the design of a sampled-data fuzzy controller to achieve the synchronisation of chaotic systems. Finally, a numerical example is provided to illustrate the effectiveness of the proposed results.

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Second-order nonlinear differential operators possessing invariant subspaces of submaximal dimension Zhu Chun-Rong(朱春蓉) Chin. Phys. B, 2011, 20 (1):  010201.  DOI: 10.1088/1674-1056/20/1/010201 Abstract ( 1719 )   PDF (215KB) ( 903 )   The invariant subspace method is used to construct the explicit solution of a nonlinear evolution equation. The second-order nonlinear differential operators that possess invariant subspaces of submaximal dimension are described. There are second-order nonlinear differential operators, including cubic operators and quadratic operators, which preserve an invariant subspace of submaximal dimension. A full description of the second-order cubic operators with constant coefficients admitting a four-dimensional invariant subspace is given. It is shown that the maximal dimension of invariant subspaces preserved by a second-order cubic operator is four. Several examples are given for the construction of the exact solutions to nonlinear evolution equations with cubic nonlinearities. These solutions blow up in a finite time.

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Reductions and conserved quantities for discrete compound KdV–Burgers equations He Yu-Fang(何玉芳), Liu Yong-Song(刘咏松), and Fu Jing-Li(傅景礼) Chin. Phys. B, 2011, 20 (1):  010202.  DOI: 10.1088/1674-1056/20/1/010202 Abstract ( 1859 )   PDF (201KB) ( 846 )   We present two methods to reduce the discrete compound KdV–Burgers equation, which are reductions of the independent and dependent variables: the translational invariant method has been applied in order to reduce the independent variables; and a discrete spectral matrix has been introduced to reduce the number of dependent variables. Based on the invariance of a discrete compound KdV–Burgers equation under infinitesimal transformation with respect to its dependent and independent variables, we present the determining equations of transformation Lie groups for the KdV–Burgers equation and use the characteristic equations to obtain new forms of invariants.

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Special Lie symmetry and Hojman conserved quantity of Appell equations in a dynamical system of relative motion Xie Yin-Li(解银丽), Jia Li-Qun(贾利群), and Luo Shao-Kai(罗绍凯) Chin. Phys. B, 2011, 20 (1):  010203.  DOI: 10.1088/1674-1056/20/1/010203 Abstract ( 1919 )   PDF (139KB) ( 1075 )   Special Lie symmetry and the Hojman conserved quantity for Appell equations in a dynamical system of relative motion are investigated. The definition and the criterion of the special Lie symmetry of Appell equations in a dynamical system of relative motion under infinitesimal group transformation are presented. The expression of the equation for the special Lie symmetry of Appell equations and the Hojman conserved quantity, deduced directly from the special Lie symmetry in a dynamical system of relative motion, are obtained. An example is given to illustrate the application of the results.

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Noether's theory of generalized linear nonholonomic mechanical systems Dong Wen-Shan(董文山) Huang Bao-Xin(黄宝歆), and Fang Jian-Hui(方建会) Chin. Phys. B, 2011, 20 (1):  010204.  DOI: 10.1088/1674-1056/20/1/010204 Abstract ( 1706 )   PDF (188KB) ( 773 )   By introducing the quasi-symmetry of the infinitesimal transformation of the transformation group Gr, the Noether's theorem and the Noether's inverse theorem for generalized linear nonholonomic mechanical systems are obtained in a generalized compound derivative space. An example is given to illustrate the application of the result.

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The Hirota bilinear method for the coupled Burgers equation and the high-order Boussinesq–Burgers equation Zuo Jin-Ming(左进明) and Zhang Yao-Ming(张耀明) Chin. Phys. B, 2011, 20 (1):  010205.  DOI: 10.1088/1674-1056/20/1/010205 Abstract ( 1925 )   PDF (148KB) ( 1839 )   This paper studies the coupled Burgers equation and the high-order Boussinesq–Burgers equation. The Hirota bilinear method is applied to show that the two equations are completely integrable. Multiple-kink (soliton) solutions and multiple-singular-kink (soliton) solutions are derived for the two equations.

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Prolongation structure of the variable coefficient KdV equation Yang Yun-Qing(杨云青) and Chen Yong(陈勇) Chin. Phys. B, 2011, 20 (1):  010206.  DOI: 10.1088/1674-1056/20/1/010206 Abstract ( 1837 )   PDF (163KB) ( 822 )   The prolongation structure methodologies of Wahlquist–Estabrook [Wahlquist H D and Estabrook F B 1975 J. Math. Phys. 16 1] for nonlinear differential equations are applied to a variable-coefficient KdV equation. Based on the obtained prolongation structure, a Lie algebra with five parameters is constructed. Under certain conditions, a Lie algebra representation and three kinds of Lax pairs for the variable- coefficient KdV equation are derived.

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Time-delay feedback control in a delayed dynamical chaos system and its applications Ye Zhi-Yong(叶志勇), Yang Guang(杨珖),and Deng Cun-Bing(邓存兵) Chin. Phys. B, 2011, 20 (1):  010207.  DOI: 10.1088/1674-1056/20/1/010207 Abstract ( 1760 )   PDF (561KB) ( 1802 )   The feedback control of a delayed dynamical system, which also includes various chaotic systems with time delays, is investigated. On the basis of stability analysis of a nonautonomous system with delays, some simple yet less conservative criteria are obtained for feedback control in a delayed dynamical system. Finally, the theoretical result is applied to a typical class of chaotic Lorenz system and Chua circuit with delays. Numerical simulations are also given to verify the theoretical results.

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Disturbed solution of the El Niño-southern oscillation sea–air delayed oscillator Xie Feng(谢峰), Lin Wan-Tao(林万涛), Lin Yi-Hua(林一骅), and Mo Jia-Qi(莫嘉琪) Chin. Phys. B, 2011, 20 (1):  010208.  DOI: 10.1088/1674-1056/20/1/010208 Abstract ( 1870 )   PDF (222KB) ( 810 )   A class of delayed oscillators of El Niño-southern oscillation (ENSO) models is considered. Using the delayed theory, the perturbed theory and other methods, the asymptotic expansions of the solutions for ENSO models are obtained and the asymptotic behaviour of solution of corresponding problem is studied.

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Symplectic eigenvector expansion theorem of a class of operator matrices arising from elasticity theory Wang Hua(王华), Alatancang(阿拉坦仓), and Huang Jun-Jie(黄俊杰) Chin. Phys. B, 2011, 20 (1):  010209.  DOI: 10.1088/1674-1056/20/1/010209 Abstract ( 1748 )   PDF (164KB) ( 772 )   This paper deals with the completeness of the eigenvector system of a class of operator matrices arising from elasticity theory, i.e., symplectic eigenvector expansion theorem. Under certain conditions, the symplectic orthogonality of eigenvectors of the operator matrix is demonstrated. Based on this, a necessary and sufficient condition for the completeness of the eigenvector system of the operator matrix is given. Furthermore, the obtained results are tested for the free vibration of rectangular thin plates.

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An analytical model for coplanar waveguide on silicon-on-insulator substrate with conformal mapping technique He Da-Wei(何大伟), Cheng Xin-Hong(程新红), Wang Zhong-Jian(王中健), Xu Da-Wei(徐大伟), Song Zhao-Rui(宋朝瑞), and Yu Yue-Hui(俞跃辉) Chin. Phys. B, 2011, 20 (1):  010210.  DOI: 10.1088/1674-1056/20/1/010210 Abstract ( 1891 )   PDF (978KB) ( 1906 )   In this paper, the authors present an analytical model for coplanar waveguide on silicon-on-insulator substrate. The four-element topological network and the conformal mapping technique are used to analyse the capacitance and the conductance of the sandwich substrate. The validity of the model is verified by the full-wave method and the experimental data. It is found that the inductance, the resistance, the capacitance and the conductance from the analytical model show they are in good agreement with the corresponding values extracted from experimental S-parameter until 10 GHz.

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A generalized Hadamard transformation from new entangled state Xu Xing-Lei(徐兴磊), Xu Shi-Min(徐世民), Zhang Yun-Hai(张运海), Li Hong-Qi(李洪奇), and Wang Ji-Suo(王继锁) Chin. Phys. B, 2011, 20 (1):  010301.  DOI: 10.1088/1674-1056/20/1/010301 Abstract ( 1672 )   PDF (210KB) ( 704 )   A new entangled state $| {\eta ;\theta } \rangle $ is proposed by the technique of integral within an ordered product. A generalized Hadamard transformation is derived by virtue of $| {\eta ;\theta } \rangle $, which  plays a role of Hadamard transformation for $(\hat {a}_1 \sin \theta - \hat {a}_2 \cos \theta )$ and $(\hat {a}_1 \cos \theta + \hat {a}_2 \sin \theta )$.

RAPID COMMUNICATION

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Nonlinear dynamical symmetries of Smorodinsky–Winternitz and and Fokas–Lagerstorm systems Li You-Ning(李佑宁) and Huang Hua-Jun(黄华俊) Chin. Phys. B, 2011, 20 (1):  010302.  DOI: 10.1088/1674-1056/20/1/010302 Abstract ( 2060 )   PDF (224KB) ( 1303 )   General solutions of the Smorodinsky–Winternitz system and the Fokas–Lagerstorm system, which are superintegrable in two-dimensional Euclidean space, are obtained using the algebraic method (structure function). Their dynamical symmetries, which are governed by deformed angular momentum algebras, are revealed.

GENERAL

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Drinfeld twist and the domain wall partition function of the eight-vertex model Hao Kun(郝昆),Chen Xi(陈曦),Shi Kang-Jie(石康杰),and Yang Wen-Li(杨文力) Chin. Phys. B, 2011, 20 (1):  010303.  DOI: 10.1088/1674-1056/20/1/010303 Abstract ( 1660 )   PDF (366KB) ( 687 )   With the help of the F-basis provided by the Drinfeld twist or factorising F-matrix for the spatial optical soliton model associated with the eight-vertex model, we calculate the partition function for the eight-vertex model on an N × N square lattice with domain wall boundary condition.

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Solving ground eigenvalue and eigenfunction of spheroidal wave equation at low frequency by supersymmetric quantum mechanics method Tang Wen-Lin(唐文林) and Tian Gui-Hua(田贵花) Chin. Phys. B, 2011, 20 (1):  010304.  DOI: 10.1088/1674-1056/20/1/010304 Abstract ( 1681 )   PDF (199KB) ( 845 )   The spheroidal wave functions are found to have extensive applications in many branches of physics and mathematics. We use the perturbation method in supersymmetric quantum mechanics to obtain the analytic ground eigenvalue and the ground eigenfunction of the angular spheroidal wave equation at low frequency in a series form. Using this approach, the numerical determinations of the ground eigenvalue and the ground eigenfunction for small complex frequencies are also obtained.

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Einstein–Podolsky–Rosen entanglement in time-dependent broadband pumping frequency non-degenerate optical parametric amplifier Zhao Chao-Ying(赵超樱) and Tan Wei-Han(谭维翰) Chin. Phys. B, 2011, 20 (1):  010305.  DOI: 10.1088/1674-1056/20/1/010305 Abstract ( 1853 )   PDF (387KB) ( 689 )   This paper investigates quantum fluctuations characteristic of time-dependent broadband pumping frequency non-degenerate optical parametric amplifier for below and above threshold regions. It finds that a high squeezing and entanglement can be achieved.

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Optimal approach to rotational state reconstruction of linear molecules Qin Xiao(覃晓) and Gao Jun-Yi(高军毅) Chin. Phys. B, 2011, 20 (1):  010306.  DOI: 10.1088/1674-1056/20/1/010306 Abstract ( 1524 )   PDF (881KB) ( 640 )   We present a simulation for the reconstruction of the rotational quantum state of linear molecules to retrieve the density matrix. An optimal approach in the sense of minimal error limit is proposed, in which a variable set of angular frequency is properly chosen and the least square inversion is then applied. This approach of reconstruction from time-dependent molecular-axis angular distribution is proved adaptable for various object states, which has a good numerical stability independent of the selected rotational space.

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Deterministically distinguishing a remote Bell state Zhao Zhi-Guo(赵志国), Peng Wei-Min(彭卫民), and Tan Yong-Gang(谭勇刚) Chin. Phys. B, 2011, 20 (1):  010307.  DOI: 10.1088/1674-1056/20/1/010307 Abstract ( 1714 )   PDF (167KB) ( 876 )   It has been proven that, with a single copy provided, the four Bell states cannot be distinguished by local operations and classical communications (LOCC). Traditionally, a Bell basis projective measurement is needed to distinguish the four Bell states, which is usually carried out with a local interference between two particles. This paper presents an interesting protocol that allows two remote parties to distinguish four Bell states deterministically. We prove that our protocol of distinguishing remote Bell states is beyond LOCC.

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Large-scale cluster state generation with nuclear spins in diamonds Chen Qiong(陈琼), Feng Mang(冯芒), Du Jiang-Feng(杜江峰), and Hai Wen-Hua(海文华) Chin. Phys. B, 2011, 20 (1):  010308.  DOI: 10.1088/1674-1056/20/1/010308 Abstract ( 1807 )   PDF (797KB) ( 950 )   The cluster state is an indispensable resource for one-way quantum computing (1WQC). We propose a practical scheme for constructing cluster states among nuclear spins in nitrogen-vacancy defect centres (NV centres) in different diamonds. The entanglement of nuclear spins within an NV centre is made by hyperfine coupling via electron spin, and the entanglement between remote NV centres is accomplished using the parity projection of emitted photons. We discus the possibility to build large-scale nuclear-spin cluster states with diamonds.

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Dark soliton in one-dimensional Bose–Einstein condensate under a periodic perturbation of trap Liu Chao-Fei(刘超飞),Hu Ke(胡柯),Hu Tao(胡涛),and Tang Yi(唐翌) Chin. Phys. B, 2011, 20 (1):  010309.  DOI: 10.1088/1674-1056/20/1/010309 Abstract ( 1706 )   PDF (2503KB) ( 850 )   The perturbation of a confining trap leads to the collective oscillation of a Bose–Einstein condensate, thereby the propagation of a dark soliton in the condensate is affected. In this study, periodic perturbation is employed to match the soliton oscillation. We find that the soliton dynamics depends sensitively on the coupling between the moving direction of the trap and that of the soliton. The soliton energy/depth evolves periodically, and a relevant shift in the soliton trajectory occurs as compared with the unperturbed case. Overall, the soliton oscillation frequency changes little even if the perturbation amplitude and frequency vary.

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The spin evolution of spin-3 52Cr Bose–Einstein condensate Situ Shu-Ping(司徒树平) and He Yan-Zhang(贺彦章) Chin. Phys. B, 2011, 20 (1):  010310.  DOI: 10.1088/1674-1056/20/1/010310 Abstract ( 1614 )   PDF (4779KB) ( 838 )   This paper studies theoretically the spin evolution of a Bose–Einstein condensate starting from a mixture of two or three groups of 52Cr (spin-3) atoms in an optical trap. The initial state is so chosen that the condensate has total magnetization zero so that the system does not distinguish up and down. It is assumed that the system is very dilute (particle number is very small), the temperature is very low, and the frequency of the harmonic trap is large enough. In these situations, the deviation caused by the neglect of the dipole–dipole interaction and by using the single-mode approximation is reduced. A theoretical calculation beyond the mean field theory is performed and the numerical results are helpful for the evaluation of the unknown strength g0.

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Dynamics of Bose–Einstein condensate in a harmonic potential and a Gaussian energy barrier Hua Wei(花巍), Li Bin(李彬), and Liu Xue-Shen(刘学深) Chin. Phys. B, 2011, 20 (1):  010311.  DOI: 10.1088/1674-1056/20/1/010311 Abstract ( 1762 )   PDF (412KB) ( 1090 )   We have studied the dynamics of Bose–Einstein condensate by solving numerically the Gross-Pitaevskii (GP) equation. We examined the periodic behaviour of the condensate in a shifted harmonic potential, and further demonstrated the tunneling effect of a condensate through a Gaussian energy barrier, which is inserted after the condensate has been excited by shifting the harmonic trapping potential to a side. Moreover, it is shown that the initial condensate evolves dynamically into two separate moving condensates after the tunneling time under certain conditions.

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Stochastic resonance in a time-delayed mono-stable system with correlated multiplicative and additive white noise Zhou Yu-Rong(周玉荣) Chin. Phys. B, 2011, 20 (1):  010501.  DOI: 10.1088/1674-1056/20/1/010501 Abstract ( 1989 )   PDF (436KB) ( 1060 )   This paper considers the stochastic resonance for a time-delayed mono-stable system, driven by correlated multiplicative and additive white noise. It finds that the output signal-to-noise ratio (SNR) varies non-monotonically with the delayed times. The SNR varies non-monotonically with the increase of the intensities of the multiplicative and additive noise, with the increase of the correlation strength between the two noises, as well as with the system parameter.

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Horseshoe and entropy in a fractional-order unified system Li Qing-Du(李清都), Chen Shu(陈述), and Zhou Ping(周平) Chin. Phys. B, 2011, 20 (1):  010502.  DOI: 10.1088/1674-1056/20/1/010502 Abstract ( 1846 )   PDF (381KB) ( 971 )   This paper studies chaotic dynamics in a fractional-order unified system by means of topological horseshoe theory and numerical computation. First it finds four quadrilaterals in a carefully-chosen Poincar'e section, then shows that the corresponding map is semiconjugate to a shift map with four symbols. By estimating the topological entropy of the map and the original time-continuous system, it provides a computer assisted verification on existence of chaos in this system, which is much more convincible than the common method of Lyapunov exponents. This new method can potentially be used in rigorous studies of chaos in such a kind of system. This paper may be a start for proving a given fractional-order differential equation to be chaotic.

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Effects of potential functions on stochastic resonance Li Jian-Long(李建龙) and Zeng Ling-Zao(曾令藻) Chin. Phys. B, 2011, 20 (1):  010503.  DOI: 10.1088/1674-1056/20/1/010503 Abstract ( 1785 )   PDF (266KB) ( 842 )   In this paper, the effects of a bistable potential function $U(x)=-ax^2/2+b|x|^{2\gamma }/{(2\gamma)}$ on stochastic resonance (SR) is discussed. We investigate the effects of index $\gamma$ on the performance of the SR system with fixed parameters a and b, and with fixed potential barriers, respectively. To measure the performance of the SR system in the presence of an aperiodic input, the bit error rate is employed, as is commonly used in binary communications. The numerical simulations strongly support the theoretical results. The goal of this investigation is to explore the effects of the shape of potential functions on SR and give a guidance of nonlinear systems in the application of information processing.

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Non-smooth bifurcations in a double-scroll circuit with periodic excitation Zhang Yin(张银)and Bi Qin-Sheng(毕勤胜) Chin. Phys. B, 2011, 20 (1):  010504.  DOI: 10.1088/1674-1056/20/1/010504 Abstract ( 1885 )   PDF (1661KB) ( 1097 )   The fast-slow effect can be observed in a typical non-smooth electric circuit with order gap between the natural frequency and the excitation frequency. Numerical simulations are employed to show complicated behaviours, especially different types of busting phenomena. The bifurcation mechanism for the bursting solutions is analysed by assuming the forms of the solutions and introducing the generalized Jacobian matrix at the non-smooth boundaries, which can also be used to account for the evolution of the complicated structures of the phase portraits with the variation of the parameter. Period-adding bifurcation has been explored through the computation of the eigenvalues related to the solutions. At the non-smooth boundaries the so-called 'single crossing bifurcation' can occur, corresponding to the case where the eigenvalues jump only once across the imaginary axis, which leads the periodic burster to have a quasi-periodic oscillation.

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Protein structural classification and family identification by multifractal analysis and wavelet spectrum Zhu Shao-Ming(朱少茗), Yu Zu-Guo(喻祖国), and Ahn Vo Chin. Phys. B, 2011, 20 (1):  010505.  DOI: 10.1088/1674-1056/20/1/010505 Abstract ( 1615 )   PDF (451KB) ( 1244 )   Family identification is helpful for predicting protein functions. It has been known from the literature that longer sequences of base pairs or amino acids are required to study patterns in biological sequences. Since most protein sequences are relatively short, we randomly concatenate or link the protein sequences from the same family or superfamily together to form longer protein sequences. The 6-letter model, 12-letter model, 20-letter model, the revised Schneider and Wrede scale hydrophobicity, solvent accessibility and stochastic standard state accessibility are used to convert linked protein sequences into numerical sequences. Then multifractal analyses and wavelet analysis are performed on these numerical sequences. The parameters from these analyses can be used to construct parameter spaces where each linked protein is represented by a point. The four classes of proteins, namely the $\alpha$, $\beta$,  $\alpha+\beta$ and $\alpha/\beta$ classes, are then distinguished in these parameter spaces. The Fisher linear discriminant algorithm is used to assess the discriminant accuracy. Numerical results indicate that the discriminant accuracies are satisfactory in separating these classes. We find that the linked proteins from the same family or superfamily tend to group together and can be separated from other linked proteins. The methods are helpful for identifying the family of an unknown protein.

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Synchronization of chaotic Lur'e systems with delayed feedback control using deadzone nonlinearity S.M. Lee, O.M. Kwon, and Ju H. Park Chin. Phys. B, 2011, 20 (1):  010506.  DOI: 10.1088/1674-1056/20/1/010506 Abstract ( 1814 )   PDF (242KB) ( 950 )   In this paper we present a synchronization method for chaotic Lur'e systems by constructing a new piecewise Lyapunov function. Using a delayed feedback control scheme, a delay-dependent stability criterion is derived for the synchronization of chaotic systems that are represented by Lur'e systems with deadzone nonlinearity. Based on the Lyapunov–Krasovskii functional and by using some properties of the nonlinearity, a new delay-dependent stabilization condition for synchronization is obtained via linear matrix inequality (LMI) formulation. The criterion is less conservative than existing ones, and it will be verified through a numerical example.

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Hölder continuity of two types of bidirectionally coupled generalised synchronisation manifold Guo Liu-Xiao(过榴晓), Xu Zhen-Yuan(徐振源), and Hu Ai-Hua(胡爱花) Chin. Phys. B, 2011, 20 (1):  010507.  DOI: 10.1088/1674-1056/20/1/010507 Abstract ( 1634 )   PDF (908KB) ( 840 )   This paper studies the existence of Höolder continuity of bidirectionally coupled generalised synchronisation (GS). Based on the slaving principle of synergetics and the modified system approach, it classifies the GS into several types. The existences of two main types of Hölder continuous bidirectionally coupled GS inertial manifolds are theoretically analysed and proved by using the Schauder fixed point theorem. Numerical simulations illustrate the theoretical results.

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Projective synchronization of a complex network with different fractional order chaos nodes Wang Ming-Jun(王明军), Wang Xing-Yuan(王兴元), and Niu Yu-Jun(牛玉军) Chin. Phys. B, 2011, 20 (1):  010508.  DOI: 10.1088/1674-1056/20/1/010508 Abstract ( 1956 )   PDF (829KB) ( 1380 )   Based on the stability theory of the linear fractional order system, projective synchronization of a complex network is studied in the paper, and the coupling functions of the connected nodes are identified. With this method, the projective synchronization of the network with different fractional order chaos nodes can be achieved, besides, the number of the nodes does not affect the stability of the whole network. In the numerical simulations, the chaotic fractional order Lü system, Liu system and Coullet system are chosen as examples to show the effectiveness of the scheme.

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A new four-dimensional hyperchaotic Lorenz system and its adaptive control Si Gang-Quan(司刚全), Cao Hui(曹晖), and Zhang Yan-Bin(张彦斌) Chin. Phys. B, 2011, 20 (1):  010509.  DOI: 10.1088/1674-1056/20/1/010509 Abstract ( 1940 )   PDF (474KB) ( 2889 )   Based on the Lorenz chaotic system, this paper constructs a new four-dimensional hyperchaotic Lorenz system, and studies the basic dynamic behaviours of the system. The Routh–Hurwitz theorem is applied to derive the stability conditions of the proposed system. Furthermore, based on Lyapunov stability theory, an adaptive controller is designed and the new four-dimensional hyperchaotic Lorenz system is controlled at equilibrium point. Numerical simulation results are presented to illustrate the effectiveness of this method.

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Synchronization of spatiotemporal chaos in a class of complex dynamical networks Zhang Qing-Ling(张庆灵) and Lü Ling(吕翎) Chin. Phys. B, 2011, 20 (1):  010510.  DOI: 10.1088/1674-1056/20/1/010510 Abstract ( 2008 )   PDF (1364KB) ( 1110 )   This paper studies the synchronization of complex dynamical networks constructed by spatiotemporal chaotic systems with unknown parameters. The state variables in the systems with uncertain parameters are used to construct the parameter recognizers, and the unknown parameters are identified. Uncertain spatiotemporal chaotic systems are taken as the nodes of complex dynamical networks, connection among the nodes of all the spatiotemporal chaotic systems is of nonlinear coupling. The structure of the coupling functions between the connected nodes and the control gain are obtained based on Lyapunov stability theory. It is seen that stable chaos synchronization exists in the whole network when the control gain is in a certain range. The Gray–Scott models which have spatiotemporal chaotic behaviour are taken as examples for simulation and the results show that the method is very effective.

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Global exponential stability of mixed discrete and distributively delayed cellular neural network Yao Hong-Xing(姚洪兴) and Zhou Jia-Yan(周佳燕) Chin. Phys. B, 2011, 20 (1):  010701.  DOI: 10.1088/1674-1056/20/1/010701 Abstract ( 1667 )   PDF (245KB) ( 716 )   This paper concernes analysis for the global exponential stability of a class of recurrent neural networks with mixed discrete and distributed delays. It first proves the existence and uniqueness of the balance point, then by employing the Lyapunov–Krasovskii functional and Young inequality, it gives the sufficient condition of global exponential stability of cellular neural network with mixed discrete and distributed delays, in addition, the example is provided to illustrate the applicability of the result.

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Cardiac magnetic source imaging based on current multipole model Tang Fa-Kuan(唐发宽), Wang Qian(王倩), Hua Ning(华宁), Lu Hong(陆宏), Tang Xue-Zheng(唐雪正), and Ma Ping(马平) Chin. Phys. B, 2011, 20 (1):  010702.  DOI: 10.1088/1674-1056/20/1/010702 Abstract ( 1682 )   PDF (3303KB) ( 884 )   It is widely accepted that the heart current source can be reduced into a current multipole. By adopting three linear inverse methods, the cardiac magnetic imaging is achieved in this article based on the current multipole model expanded to the first order terms. This magnetic imaging is realized in a reconstruction plane in the centre of human heart, where the current dipole array is employed to represent realistic cardiac current distribution. The current multipole as testing source generates magnetic fields in the measuring plane, serving as inputs of cardiac magnetic inverse problem. In the heart-torso model constructed by boundary element method, the current multipole magnetic field distribution is compared with that in the homogeneous infinite space, and also with the single current dipole magnetic field distribution. Then the minimum-norm least-squares (MNLS) method, the optimal weighted pseudoinverse method (OWPIM), and the optimal constrained linear inverse method (OCLIM) are selected as the algorithms for inverse computation based on current multipole model innovatively, and the imaging effects of these three inverse methods are compared. Besides, two reconstructing parameters, residual and mean residual, are also discussed, and their trends under MNLS, OWPIM and OCLIM each as a function of SNR are obtained and compared.

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Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy Tian Lu(田璐), Zhou Qing-Li(周庆莉), Zhao Kun(赵昆), Shi Yu-Lei(施宇蕾), Zhao Dong-Mei(赵冬梅), Zhao Song-Qing(赵嵩卿), Zhao Hui(赵卉), Bao Ri-Ma(宝日玛), Zhu Shou-Ming(朱守明), Miao Qing(苗青), and Zhang Cun-Lin(张存林) Chin. Phys. B, 2011, 20 (1):  010703.  DOI: 10.1088/1674-1056/20/1/010703 Abstract ( 1976 )   PDF (782KB) ( 2150 )   The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz–Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS2) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS2-lithium grease than that of lithium grease.

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Real-time and label-free detection of biomolecular interactions by oblique-incidence reflectivity difference method Hot! Wang Xu(王旭), Lu Heng(陆珩), Dai Jun(戴俊), Wen Juan(温娟), Yuan Kun(原昆), Lü Hui-Bin(吕惠宾), Jin Kui-Juan(金奎娟), Zhou Yue-Liang(周岳亮), and Yang Guo-Zhen(杨国桢) Chin. Phys. B, 2011, 20 (1):  010704.  DOI: 10.1088/1674-1056/20/1/010704 Abstract ( 1644 )   PDF (256KB) ( 735 )   We successfully conduct the label-free and real-time detection of the interactions between epoxy groups and rabbit IgG and 5' CTT CAG GTC ATG AGC CTG AT 3' oligonucleotide, and between the hybridization of 5' CTT CAG GTC ATG AGC CTG AT 3' and its complementary 3' GAA GTC CAG TAC TCG GAC TA 5' oligonucleotide, by the oblique-incidence reflectivity difference (OI-RD) method. The dynamic curves of OI-RD signals, corresponding to the kinetic processes of biomolecular combination or hybridization, are acquired. In our case, the combination of epoxy groups with rabbit IgG and 5' CTT CAG GTC ATG AGC CTG AT 3' oligonucleotide need almost one and a half hours and about two hundred seconds, respectively; and the hybridization of the two oligonucleotides needs about five hundred seconds. The experimental results show that the OI-RD is a promising method for the real-time and label-free detection of biomolecular interactions.

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Measurement of integral diffraction coefficients of crystals on beamline 4B7 of Beijing Synchrotron Radiation Facility Yang Jia-Min(杨家敏), Gan Xin-Shi(甘新式), Zhao Yang(赵阳), Cui Ming-Qi(崔明启), Zhu Tuo(朱托), Zhao Yi-Dong(赵屹东), Sun Li-Juan(孙丽绢), Zheng Lei(郑雷), Yan Fen(鄢芬), Hu Zhi-Min(胡智民), Wei Min-Xi(韦敏习), Zhang Ji-Yan(张继彦), and Yi Rong-Qing(易荣清) Chin. Phys. B, 2011, 20 (1):  010705.  DOI: 10.1088/1674-1056/20/1/010705 Abstract ( 1868 )   PDF (1160KB) ( 896 )   Integral diffraction coefficients of the crystal are the essential data of a crystal spectrometer which is extensively used to measure quantitative x-ray spectra of high temperature plasmas in kilo-electron-volt region. An experimental method has been developed to measure the integral diffraction coefficients of crystals on beamline 4B7 of Beijing Synchrotron Radiation Facility. The integral diffraction coefficients of several crystals including polyethylene terephthalate (PET), thallium acid phthalate (TlAP) and rubidium acid phthalate (RAP) crystals have been measured in the x-ray energy range 2100–5600 eV and compared with the calculations of the 'Darwin Prins' and the 'Mosaic' models. It is shown that the integral diffraction coefficients of these crystals are between the calculations of the 'Darwin Prins' and the 'Mosaic' models, but more close to the 'Darwin Prins' model calculations.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Noether's theory of Lagrange systems in discrete case Lü Hong-Sheng(吕洪升), Zhang Hong-Bin(张宏彬), and Gu Shu-Long(顾书龙) Chin. Phys. B, 2011, 20 (1):  011101.  DOI: 10.1088/1674-1056/20/1/011101 Abstract ( 1523 )   PDF (172KB) ( 863 )   In this paper, Noether theory of Lagrange systems in discrete case are studied. First, we briefly overview the well-known Noether theory of Lagrange system in the continuous case. Then, we introduce some definitions and notations, such as the operators of discrete translation to the right and the left and the operators of discrete differentiation to the right and the left, and give the conditions for the invariance of the difference functional on the uniform lattice and the non-uniform one, respectively. We also deduce the discrete analog of the Noether-type identity. Finally, the discrete analog of Noether's theorem is presented. An example was discussed to illustrate these results.

ATOMIC AND MOLECULAR PHYSICS

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Si3O cluster: excited properties under external electric field and oxygen-deficient defect models Xu Guo-Liang(徐国亮), Liu Xue-Feng(刘雪峰), Xie Hui-Xiang(谢会香), Zhang Xian-Zhou(张现周), and Liu Yu-Fang(刘玉芳) Chin. Phys. B, 2011, 20 (1):  013101.  DOI: 10.1088/1674-1056/20/1/013101 Abstract ( 1885 )   PDF (261KB) ( 1079 )   This paper investigates the excited states of Si3O molecule by using the single-excitation configuration interaction and density functional theory. It finds that the visible light absorption spectrum of Si3O molecule comprises the yellow and the purple light without external electric field, however all the visible light is included except the green light under the action of external electric field. Oxygen-deficient defects, which also can be found in Si3O molecule, have been used to explain the luminescence from silicon-based materials but the microstructures of the materials are still uncertain. Our results accord with the experimental values perfectly, this fact suggests that the structure of Si3O molecule is expected to be one of the main basic structures of the materials, so the oxygen-deficient defect structural model for Si3O molecule also has been provided to research the structures of materials.

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Comparative analysis of energy-level splitting of Pr3+ doped in LiYF4 and LiBiF4 crystals: a complete energy matrix calculation Duan Mei-Ling(段美玲), Kuang Xiao-Yu(邝小渝), Zhang Cai-Xia(张彩霞), and Chai Rui-Peng(柴瑞鹏) Chin. Phys. B, 2011, 20 (1):  013102.  DOI: 10.1088/1674-1056/20/1/013102 Abstract ( 1679 )   PDF (428KB) ( 868 )   Based on the combination of Racah's group-theoretical consideration with Slater's wavefunction, a 91 × 91 complete energy matrix is established in tetragonal ligand field D2d for Pr3+ ion. Thus, the Stark energy-levels of Pr3+ ions doped separately in LiYF4 and LiBiF4 crystals are calculated, and our calculations imply that the complete energy matrix method can be used as an effective tool to calculate the energy-levels of the systems doped by rare earth ions. Besides, the influence of Pr3+ on energy-level splitting is investigated, and the similarities and the differences between the two doped crystals are demonstrated in detail by comparing their several pairs of curves and crystal field strength quantities. We see that the energy splitting patterns are similar and the crystal field interaction of LiYF4:Pr3+ is stronger than that of LiBiF4:Pr3+.

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Excited state refraction of C70/toluene studied by using 4f coherent imaging system with phase object Liu Nan-Chun(刘南春), Shi Guang(石光), Yang Jun-Yi(杨俊义), and Song Ying-Lin(宋瑛林) Chin. Phys. B, 2011, 20 (1):  013103.  DOI: 10.1088/1674-1056/20/1/013103 Abstract ( 1676 )   PDF (520KB) ( 950 )   Dynamic nonlinearities of C70/toluene solution are measured and analysed by an improved picosecond time-resolved pump-probe system based on a nonlinear imaging technique with phase object. The photophysical parameters are determined by the five-level model, which is adopted to interpret the experimental data. The change of refraction index per unit density of the excited state obtained by a numerically simulation is a critical factor to determine the nonlinear behaviour of C70 in picosecond time regime.

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Frequency stabilization of a 399-nm laser by modulation transfer spectroscopy in an ytterbium hollow cathode lamp Wang Wen-Li(王文丽), Ye Jie(叶捷), Jiang Hai-Ling(蒋海灵), Bi Zhi-Yi(毕志毅), Ma Long-Sheng(马龙生), and Xu Xin-Ye(徐信业) Chin. Phys. B, 2011, 20 (1):  013201.  DOI: 10.1088/1674-1056/20/1/013201 Abstract ( 1749 )   PDF (568KB) ( 1811 )   The modulation transfer spectroscopy in an ytterbium hollow cathode lamp at 399 nm is measured. The error signal for frequency locking is optimized by measuring the dependences of its slope, linewidth and magnitude on various parameters. Under the optimum condition, the laser frequency at 399 nm can be stabilized. The long-term stability of laser frequency is measured by monitoring the fluorescence signal of the ytterbium atomic beam induced by the locked laser. The laser frequency is shown to be tightly locked, and the stabilized laser is successfully applied to the cooling of ytterbium atoms.

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Transmission of 18 keV negative ions Cl- through nanocapillariesin Al2O3 membrane Lü Xue-Yang(吕学阳),Chen Lin(陈林),Chen Xi-Meng(陈熙萌),Jia Juan-Juan(贾娟娟), Zhou Peng(周鹏),Zhou Chun-Lin(周春林), Qiu Xi-Yu(邱玺玉),Shao Jian-Xiong(邵剑雄), Cui Ying(崔莹),Yin Yong-Zhi(尹永智),Wang Hong-Wei(王宏伟),and Ji Ming-Chao(姬明超) Chin. Phys. B, 2011, 20 (1):  013401.  DOI: 10.1088/1674-1056/20/1/013401 Abstract ( 1622 )   PDF (1957KB) ( 837 )   We investigate the angular distribution of the transmitted 18keV negative ions Cl- through Al2O3 nanocapillaries of 50 nm in diameter and 10 μm in length. Elastic scattering ions and inelastic scattering ions are obtained simultaneously. The experimental result is partially consistent with the guiding effect. We can qualitatively explain our experimental result through a dynamic process.

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Experimental study of cross-section ratios in the collisions of Cq+ and Oq+(q=1–4) on atomic helium in strong-interaction region Chen Xi-Meng(陈熙萌), Jiang Li-Juan(江丽娟), Zhou Peng(周鹏), Zhou Chun-Lin(周春林), Gao Zhi-Min(高志民), Qiu Xi-Yu(邱玺玉), Cui Ying(崔莹), Wang Xing-An(王兴安), Lou Feng-Jun(娄凤君), Lü Xue-Yang(吕学阳), Jia Juan-Juan(贾娟娟), Chen Lin(陈林), Shao Jian-Xiong(邵剑雄), Lü Ying(吕瑛), and Wang Fan(王幡) Chin. Phys. B, 2011, 20 (1):  013402.  DOI: 10.1088/1674-1056/20/1/013402 Abstract ( 1835 )   PDF (2245KB) ( 917 )   We have measured the cross-section ratios of helium induced by Cq+ and Oq+ (q=1–4) in an energy range from 20 keV/amu to 500 keV/amu, and obtained the two-dimensional spectra by employing the coincidence method combined with the MPA-3 data acquisition system. Hence, we obtain the ratios of total single-ionization cross-sections (SI, SC, SLSI, and DLSI), total double-ionization cross-sections (DI, DC, TI, SLDI, and DLDI) and cross-sections of every process (SI, SC, SLSI, DLSI, DI, DC, TI, SLDI, and DLDI), which induce the single-ionization and double-ionization, to the total cross sections respectively. The competitive relations between the reaction-channels and the experimental data law of each reaction-channel are revealed explicitly, and the qualitative explanations involved in those results are also presented accordingly.

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Semiclassical calculation of ionisation rate for Rydberg helium atoms in an electric field Wang De-Hua(王德华) Chin. Phys. B, 2011, 20 (1):  013403.  DOI: 10.1088/1674-1056/20/1/013403 Abstract ( 1715 )   PDF (205KB) ( 725 )   The ionisation of Rydberg helium atoms in an electric field above the classical ionisation threshold has been examined using the semiclassical method, with particular emphasis on discussing the influence of the core scattering on the escape dynamics of electrons. The results show that the Rydberg helium atoms ionise by emitting a train of electron pulses. Unlike the case of the ionisation of Rydberg hydrogen atom in parallel electric and magnetic fields, where the pulses of the electron are caused by the external magnetic field, the pulse trains for Rydberg helium atoms are created through core scattering. Each peak in the ionisation rate corresponds to the contribution of one core-scattered combination trajectory. This fact further illustrates that the ionic core scattering leads to the chaotic property of the Rydberg helium atom in external fields. Our studies provide a simple explanation for the escape dynamics in the ionisation of nonhydrogenic atoms in external fields.

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Theoretical study of stereodynamics for the O(3P) + H2 → OH + H reaction Liu Shi-Li(刘世莉) and Shi Ying(石英) Chin. Phys. B, 2011, 20 (1):  013404.  DOI: 10.1088/1674-1056/20/1/013404 Abstract ( 1724 )   PDF (296KB) ( 973 )   This paper employs the quasi-classical trajectory calculations to study the influence of collision energy on the title reaction on the potential energy surface of the ground 3A' triplet state developed by Rogers et al. (J. Phys. Chem. A 2000 104 2308). It calculates the product angular distribution of $P( {\theta _{\rm r} } )$, $P( {\phi _{\rm r} } )$ and $P( {\theta _{r}, \phi _{\rm r} } )$ which reflects  vector correlation. The distribution $P( {\theta _{\rm r} } )$ shows that product rotational angular momentum vectors j$'$ of the products are strongly aligned along the relative velocity direction k. The  distribution of $P( {\phi _{\rm r} } )$ implies a preference for left-handed product rotation in planes parallel to the scattering plane. Four different polarisation-dependent cross-sections  are also presented in the  centre-of-mass frame. Results indicate that {OH} is sensitively affected by collision energies of H$_{2}$.

CLASSICAL AREAS OF PHENOMENOLOGY

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All-dielectric left-handed metamaterial based on dielectric resonator: design, simulation and experiment Yang Yi-Ming(杨一鸣), Wang Jia-Fu(王甲富), Xia Song(夏颂), Bai Peng(柏鹏), Li Zhe(李哲), Wang Jun(王军), Xu Zhuo(徐卓), and Qu Shao-Bo(屈绍波) Chin. Phys. B, 2011, 20 (1):  014101.  DOI: 10.1088/1674-1056/20/1/014101 Abstract ( 2053 )   PDF (5522KB) ( 1775 )   Dipoles with Lorentz-type resonant electromagnetic responses can realise negative effective parameters in their negative resonant region. The electric dipole and magnetic dipole can realise, respectively, negative permittivity and negative permeability, so both the field distribution forms of electric and magnetic dipoles are fundamentals in designing left-handed metamaterial. Based on this principle, this paper studies the field distribution in high-permittivity dielectric materials. The field distributions at different resonant modes are analysed based on the dielectric resonator theory. The origination and influence factors of the electric and magnetic dipoles are confirmed. Numerical simulations indicate that by combining dielectric cubes with different sizes, the electric resonance frequency and magnetic resonance frequency can be superposed. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial composed by this means.

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Wave propagation in parallel-plate waveguides filled with nonlinear left-handed material Burhan Zamirand Rashid Ali Chin. Phys. B, 2011, 20 (1):  014102.  DOI: 10.1088/1674-1056/20/1/014102 Abstract ( 1907 )   PDF (430KB) ( 1582 )   A theoretical investigation of field components for transverse electric mode in the parallel-plate waveguides has been studied. In this analysis two different types of waveguide structures have been discussed, i.e., (a) normal good/perfect conducting parallel-plate waveguide filled with nonlinear left-handed material and (b) high-temperature-superconducting parallel-plate waveguide filled with nonlinear left-handed material. The dispersion relations of transverse electric mode have also been discussed for these two types of waveguide structures.

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Interaction of two edge dislocations in free-space propagation He De(何德), Gao Zeng-Hui(高曾辉), Yan Hong-Wei(闫红卫), and Lü Bai-Da(吕百达) Chin. Phys. B, 2011, 20 (1):  014201.  DOI: 10.1088/1674-1056/20/1/014201 Abstract ( 1811 )   PDF (1122KB) ( 1316 )   This paper studies in detail the interaction of two edge dislocations nested in a Gaussian beam propagating in free space. It shows that in free-space propagation the edge dislocations are unstable and vanish, and  two noncanonical vortices with opposite topological charge take place when off-axis distances $c_{1}$ and $c_{2}$ of two edge dislocations are non-zero, and the condition $k^{2}w_{0}^{8}+32c_{1}c_{2}(w_{0}^{2}-2c_{1}c_{2})z^{2}>0$ is fulfilled ($k$-wave number, $w_{0}$-waist width). A noncanonical vortex appears when one off-axis distance is zero. However, one edge dislocation is stable when  two edge dislocations are perpendicular and one off-axis distance is zero. Two perpendicular edge dislocations both with zero off-axis distance are also stable. The analytical results are illustrated by numerical examples.

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Tight focusing of femtosecond elliptically polarised vortex light pulses Hua Li-Min(华黎闽),Chen Bao-Suan(陈宝算),Chen Zi-Yang(陈子阳),and Pu Ji-Xiong(蒲继雄) Chin. Phys. B, 2011, 20 (1):  014202.  DOI: 10.1088/1674-1056/20/1/014202 Abstract ( 1723 )   PDF (8238KB) ( 1206 )   This paper studies the tight focusing properties of femtosecond elliptically polarised vortex light pulses. Based on Richards–Wolf vectorial diffraction integral, the expressions for the electric field, the velocity of the femtosecond light pulse and the total angular momentum of focused pluses are derived. The numerical calculations are also given to illustrate the intensity distribution, phase contour, the group velocity variation and the total angular momentum near the focus. It finds that near the focus the femtosecond elliptically polarised vortex light pulse can travel at various group speeds, that is, slower or faster than light speed in vacuum, depending on the numerical aperture of the focusing objective system. Moreover, it also studies the influence of the numerical aperture of the focusing objective and the time duration of the elliptically polarised vortex light pulse on the total angular momentum distribution in the focused field.

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A corrected method of distorted printed circuit board image Qiao Nao-Sheng(乔闹生), Ye Yu-Tang(叶玉堂), and Huang Yong-Lin(黄永林) Chin. Phys. B, 2011, 20 (1):  014203.  DOI: 10.1088/1674-1056/20/1/014203 Abstract ( 1791 )   PDF (3091KB) ( 1035 )   This paper proposes a corrected method of distorted image based on adaptive control. First, the adaptive control relationship of pixel point positions between distorted image and its corrected image is given by using polynomial fitting, thus control point pairs between the distorted image and its corrected image are found. Secondly, the value of both image distortion centre and polynomial coefficient is obtained with least square method, thus the relationship of each control point pairs is deduced. In the course of distortion image processing, the gray value of the corrected image is changed into integer with bilinear interpolation. Finally, the experiments are performed to correct two distorted printed circuit board images. The results are perfect and the mean square errors of residual error are tiny.

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A new finite-dimensional thermal coherent state and its Wigner distribution function Meng Xiang-Guo(孟祥国), Wang Ji-Suo(王继锁), and Liang Bao-Long(梁宝龙) Chin. Phys. B, 2011, 20 (1):  014204.  DOI: 10.1088/1674-1056/20/1/014204 Abstract ( 1667 )   PDF (785KB) ( 845 )   This paper constructs a new type of finite-dimensional thermal coherent states (FDTCS), which differs from the proceeding thermal coherent state in construction, as realisations of SU(2) Lie algebra. Using the technique of integration within an ordered product of operator, it investigates the orthonormality and completeness relation of the FDTCS. Based on the thermal Wigner operator in the thermal entangled state representation, the Wigner function of the FDTCS is obtained. The nonclassical properties of the FDTCS are discussed in terms of the negativity of its Wigner function.

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Mechanical effects of light on the $\Xi$-type three-level atom in a high-finesse optical cavity Liu Li-Wei(刘利伟), Tan Lei(谭磊), and Huang Gang(黄刚) Chin. Phys. B, 2011, 20 (1):  014205.  DOI: 10.1088/1674-1056/20/1/014205 Abstract ( 1727 )   PDF (1024KB) ( 691 )   A theoretical study is carried out for the modification and implication of the effect on the $\Xi$-type three level atom in a high-finesse optical cavity driven by light field including spontaneous emission and the cavity decay. Analytic expressions for the dipole force, the friction force, the optical potentials and the friction coefficient are obtained. Then the numerical and graphical methods are used to investigate the friction coefficient with the controlling parameters. It is shown that the friction coefficient is strongly dependent on the controlling parameters. The cooling rate can increase by one order of magnitude more than that of a two-level atomic system. The reason can be given using the dressed states and the Sisyphus cooling mechanism, which would stimulate further experimental investigations.

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Simultaneous measurements of global vibrational spectra and dephasing times of molecular vibrational modes by broadband time-resolved coherent anti-Stokes Raman scattering spectrography Hot! Yin Jun(尹君), Yu Ling-Yao(于凌尧), Liu Xing(刘星), Wan Hui(万辉), Lin Zi-Yang(林子扬), and Niu Han-Ben(牛憨笨) Chin. Phys. B, 2011, 20 (1):  014206.  DOI: 10.1088/1674-1056/20/1/014206 Abstract ( 1678 )   PDF (693KB) ( 1792 )   In broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy with supercontinuum (SC), the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science.

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Long- and short-term average intensity for multi-Gaussian beam with a common axis in turbulence Chu Xiu-Xiang(储修祥) Chin. Phys. B, 2011, 20 (1):  014207.  DOI: 10.1088/1674-1056/20/1/014207 Abstract ( 1704 )   PDF (311KB) ( 881 )   With the help of the extended Huygens–Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam (MGB) in the turbulent atmosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.

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Numerical investigation of multi-beam laser heterodyne measurement with ultra-precision for linear expansion coefficient of metal based on oscillating mirror modulation Li Yan-Chao(李彦超), Wang Chun-Hui(王春晖), Qu Yang(曲杨), Gao Long(高龙), Cong Hai-Fang(丛海芳), Yang Yan-Ling(杨彦玲), Gao Jie(高洁), and Wang Ao-You(王遨游) Chin. Phys. B, 2011, 20 (1):  014208.  DOI: 10.1088/1674-1056/20/1/014208 Abstract ( 1708 )   PDF (301KB) ( 962 )   This paper proposes a novel method of multi-beam laser heterodyne measurement for metal linear expansion coefficient. Based on the Doppler effect and heterodyne technology, the information is loaded of length variation to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by temperature variation after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain length variation accurately, and eventually obtain the value of linear expansion coefficient of metal by the calculation. This novel method is used to simulate measurement for linear expansion coefficient of metal rod under different temperatures by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.4%.

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Band gap control of phononic beam with negative capacitance piezoelectric shunt Chen Sheng-Bing(陈圣兵), Wen Ji-Hong(温激鸿), Yu Dian-Long(郁殿龙), Wang Gang(王刚), and Wen Xi-Sen(温熙森) Chin. Phys. B, 2011, 20 (1):  014301.  DOI: 10.1088/1674-1056/20/1/014301 Abstract ( 1764 )   PDF (902KB) ( 2408 )   Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.

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Influence of adhesive layer properties on laser-generated ultrasonic waves in thin bonded plates Sun Hong-Xiang(孙宏祥), Xu Bai-Qiang(许伯强), Zhang Hua(张华), Gao Qian(高倩), and Zhang Shu-Yi(张淑仪) Chin. Phys. B, 2011, 20 (1):  014302.  DOI: 10.1088/1674-1056/20/1/014302 Abstract ( 1747 )   PDF (458KB) ( 906 )   This paper studies quantitatively the generation of Lamb waves in thin bonded plates subjected to laser illumination, after considering the viscoelasticity of the adhesive layer. The displacements of such plates have been calculated in the frequency domain by using the finite element method, and the time domain response has been reconstructed by applying an inverse fast Fourier transform. Numerical results are presented showing the normal surface displacement for several configurations: a single aluminum plate, a three-layer bonded plate, and a two-layer plate. The characteristics of the laser-generated Lamb waves for each particular case have been investigated. In addition, the sensitivity of the transient responses to variations of material properties (elastic modulus, viscoelastic modulus, and thickness) of the adhesive layer has been studied in detail.

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A novel macroscopic traffic model based on generalized optimal velocity model Zhou Xuan-Hao(周玄昊) and Lü Yong-Zai(吕勇哉) Chin. Phys. B, 2011, 20 (1):  014501.  DOI: 10.1088/1674-1056/20/1/014501 Abstract ( 1690 )   PDF (284KB) ( 950 )   In this paper, we adopt the coarse graining method proposed by Lee H K et al. to develop a macroscopic model from the microscopic traffic model-GOVM. The proposed model inherits the parameter p which considers the influence of next-nearest car introduced in the GOVM model. The simulation results show that the new model is strictly consistent with the former microscopic model. Using this macroscopic model, we can avoid considering the details of each traffic on the road, and build more complex models such as road network model easily in the future.

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Anisotropic character of atoms in a two-dimensional Frenkel–Kontorova model Wang Cang-Long(王苍龙), Duan Wen-Shan(段文山), Chen Jian-Min(陈建敏), andShi Yu-Ren(石玉仁) Chin. Phys. B, 2011, 20 (1):  014601.  DOI: 10.1088/1674-1056/20/1/014601 Abstract ( 1778 )   PDF (1786KB) ( 1002 )   The dynamics of a certain density of interacting atoms arranged on a two-dimensional square lattice, which is made to slide over a two-dimensional periodic substrate potential with also the quare lattice symmetry, in the presence of dissipation, by an externally applied driving force, is studied. By rotating the misfit angle θ, the dynamical behaviour displays two different tribological regimes: one is smooth, the other becomes intermittent. We comment both on the nature of the atomic dynamics in the locked-to-sliding transition, and on the dynamical states displayed during the atom motion at different values of the driving force. In tribological applications, we also investigate how the main model parameters such as the stiffness strength and the magnitude of the adhesive force affect the static friction of the system. In particular, our simulation indicates that the superlubricity will appear.

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Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma Sankar Moni Borah,Arup Ratan Pal,Heremba Bailung,andJoyanti Chutia Chin. Phys. B, 2011, 20 (1):  014701.  DOI: 10.1088/1674-1056/20/1/014701 Abstract ( 1682 )   PDF (1263KB) ( 3405 )   Study of electron drift velocity caused by E×B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investigated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the conventional theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Numerical studies of surface and bulk modes in attenuated total reflection spectra Yan Bao-Rong(燕保荣),Lü Jian-Hong(吕建红), Kong Ling-Hua(孔令华),and Hu Xi-Wei(胡希伟) Chin. Phys. B, 2011, 20 (1):  015101.  DOI: 10.1088/1674-1056/20/1/015101 Abstract ( 1712 )   PDF (1564KB) ( 737 )   The dispersion relations of normal modes in the layered constructions are studied. In the frequency region with negative permittivity, we investigate the normal modes near the air–metal and the air–matematerial interfaces and compare them. An extra bulk mode appearing in a pass band of two media is found near the air–matematerial interface, which is different from the air--metal case. Moreover, the bulk mode will be further proved by the attenuated total reflection (ATR) technique, in which the coupling between the incident electromagnetic waves and the normal modes is studied. For p-polarized incident waves, the ATR spectra based on the Otto and the Kretschmann configurations are obtained numerically, where the dips present the excitations of the surface and bulk modes. Furthermore, we also discuss the influences of the middle layer thickness, the incident angle and the damping term on the reflection in detail. It is found that the coupling frequencies and the maximum strength are strongly dependent on the above media parameters.

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Concentric-ring structures in an atmospheric pressure helium dielectric barrier discharge Shang Wan-Li(尚万里), Zhang Yuan-Tao(张远涛), Wang De-Zhen(王德真), Sang Chao-Feng(桑超峰), Jiang Shao-En(江少恩), Yang Jia-Min(杨家敏), Liu Shen-Ye(刘慎业), and M.~G. Kong Chin. Phys. B, 2011, 20 (1):  015201.  DOI: 10.1088/1674-1056/20/1/015201 Abstract ( 1774 )   PDF (2944KB) ( 819 )   This paper performs a numerical simulation of concentric-ring discharge structures within the scope of a two-dimensional diffusion–drift model at atmospheric pressure between two parallel circular electrodes covered with thin dielectric layers. With a relative high frequency the discharge structures present different appearances of ring structures within different radii in time due to the evolvement of the filaments. The spontaneous electron density distributions help understanding the formation and development of self-organized discharge structures. During a cycle the electron avalanches are triggered by the electric field strengthened by the feeding voltage and the residual charged particles on the barrier surface deposited in the previous discharges. The accumulation of charges is shown to play a dominant role in the generation and annihilation of the discharge structures. Besides, the rings split and unify to bring and annihilate rings which form a new discharge structure.

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Analysis of Ar line spectra from indirectly-driven implosion experiments on SGII facility Pu Yu-Dong(蒲昱东),Zhang Ji-Yan(张继彦),Yang Jia-Min(杨家敏), Huang Tian-Xuan(黄天晅),and Ding Yong-Kun(丁永坤) Chin. Phys. B, 2011, 20 (1):  015202.  DOI: 10.1088/1674-1056/20/1/015202 Abstract ( 1784 )   PDF (590KB) ( 788 )   This paper reports on the indirectly-driven implosion experiments on SGII laser facility in which Ar emission spectrum from Ar-doped D-filled plastic capsule is recorded with the crystal spectrometer. Spectral features of Ar Heβ line and its associated satellites are analysed to extract the electron temperature and density of the implosion core. Non local thermal equilibrium (NLTE) collisional-radiative atomic kinetics and Strark broadening line shape are included in the present calculation. By comparing the calculated spectrum with the measured one, the core electron temperature and density are inferred to be 700 eV and 2.5×1023 cm-3 respectively. With these inferred values of electron temperature and density, neutron yield can be estimated to agree with the measured value in magnitude despite of the very simple model used for the estimation.

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Dynamical behaviour of transverse plasmons in pair plasmas Liu San-Qiu(刘三秋), Liu Yong(刘勇), and Li Xiao-Qing(李晓卿) Chin. Phys. B, 2011, 20 (1):  015203.  DOI: 10.1088/1674-1056/20/1/015203 Abstract ( 1988 )   PDF (203KB) ( 680 )   This paper analytically investigates the nonlinear behaviour of transverse plasmons in pair plasmas on the basis of the nonlinear governing equations obtained from Vlasov–Maxwell equations. It shows that high frequency transverse plasmons are modulationally unstable with respect to the uniform state of the pair plasma. Such an instability would cause wave field collapse into a localized region. During the collapse process, ponderomotive expulsion is greatly enhanced for the increase of wave field strength, leading to the formation of localized density cavitons which are significant for the future experimental research in the interaction between high frequency electromagnetic waves and pair plasmas.

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Control of plasmonic wave propagating in nanocavity with tooth-shaped configuration Li Xu-Feng(李旭峰), Pan Shi(潘石), Guo Ying-Nan (郭英楠), and Wang Qiao(王乔) Chin. Phys. B, 2011, 20 (1):  015204.  DOI: 10.1088/1674-1056/20/1/015204 Abstract ( 1783 )   PDF (1242KB) ( 901 )   Characteristics of plasmonic wave propagating in nanocavity formed by two silver films are studied numerically. The groove etched inside wall of the top film makes it possible to control the propagation when light goes through the top film along a nanoslit into the cavity. It is found that the transmission wave through the channel of groove etched side can be filtered linearly with the groove of a certain depth; while the other side is still open for this wave and its intensity can be enhanced periodically with the variable groove position in both films, which are explained well based on the interference of plasmonic waves in the system.

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Investigation on the resonance phenomena of multi-solitons for the (3+1)-dimensional Kadomtsev–Petviashvili equation Shi Yu-Ren(石玉仁), Zhang Juan(张娟), Yang Hong-Juan(杨红娟), Duan Wen-Shan(段文山), and Karl E. Lonngren Chin. Phys. B, 2011, 20 (1):  015205.  DOI: 10.1088/1674-1056/20/1/015205 Abstract ( 1670 )   PDF (721KB) ( 1098 )   In this paper, we theoretically investigate the four-soliton interaction and their resonance phenomena of the (3+1)-dimensional Kadomtsev–Petviashvili (KP) equation. We find that the maximum amplitude of the resonantly created soliton can be 16 times that of one of the four equi-amplitude initial interacting solitons. We also find that the maximum amplitude can only be 4 times the initial soliton amplitude when the resonance phenomena does not take place. The case of four solitons with different amplitudes also has been studied analytically. The results indicate that the resonance phenomena still exists in this case. Numerical results confirm the theoretical predictions.

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Suppression of multiple ion bunches and generation of monoenergetic ion beams in laser foil-plasma Zhang Shan(张闪), Xie Bai-Song(谢柏松), Hong Xue-Ren(洪学仁), Wu Hai-Cheng(吴海城), Aimierding Aimidula(艾米尔丁·艾米都拉), Zhao Xue-Yan(赵学燕), and Liu Ming-Ping(刘明萍) Chin. Phys. B, 2011, 20 (1):  015206.  DOI: 10.1088/1674-1056/20/1/015206 Abstract ( 1657 )   PDF (772KB) ( 888 )   In one-dimensional particle-in-cell simulations, this paper shows that the formation of multiple ion bunches is disadvantageous to the generation of monoenergetic ion beams and can be suppressed by choosing an optimum target thickness in the radiation pressure acceleration mechanism by a circularly polarised laser pulse. As the laser pulse becomes intense, the optimum target thickness obtained by a non-relativistic treatment is no longer adequate. Considering the relativistic Doppler-shifted pressure, it proposes a relativistic formulation to determine the optimum target thickness. The theoretical predictions agree with the simulation results well. The model is also valid for two-dimensional cases. The accelerated ion beams can be compelled to be more stable by choosing the optimum target thickness when they exhibit some unstable behaviours.

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Diagnosis of a low pressure capacitively coupled argon plasma by using a simple collisional-radiative model Yu Yi-Qing(虞一青), Xin Yu(辛煜), and Ning Zhao-Yuan(宁兆元) Chin. Phys. B, 2011, 20 (1):  015207.  DOI: 10.1088/1674-1056/20/1/015207 Abstract ( 1837 )   PDF (272KB) ( 2560 )   This paper proposes a simple collisional-radiative model to characterise capacitively coupled argon plasmas driven by conventional radio frequency in combination with optical emission spectroscopy and Langmuir probe measurements. Two major processes are considered in this model, electron-impact excitation and the spontaneous radiative decay. The diffusion loss term, which is found to be important for the two metastable states (4s[3/2]2, 4s'[1/2]0), is also taken into account. Behaviours of representative metastable and radiative states are discussed. Two emission lines (located at 696.5 nm and 750.4 nm) are selected and intensities are measured to obtain populated densities of the corresponding radiative states in the argon plasma. The calculated results agree well with that measured by Langmuir probe, indicating that the current model combined with optical emission spectroscopy is a candidate tool for electron density and temperature measurement in radio frequency capacitively coupled discharges.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Structures and luminescence properties of Yb3+ in the double perovskites Ba2YB'O6 (B'=Ta5+, Nb5+) phosphors Zhou Wen-Long(周文龙), Zhang Qing-Li(张庆礼), Gao Jin-Yun(高进云), Liu Wen-Peng(刘文鹏), Ding Li-Hua(丁丽华), and Yin Shao-Tang(殷绍唐) Chin. Phys. B, 2011, 20 (1):  016101.  DOI: 10.1088/1674-1056/20/1/016101 Abstract ( 1923 )   PDF (830KB) ( 2146 )   The Yb3+ doped Ba2YB'O6 (B'=Ta5+, Nb5+) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb3+:Ba2YB'O6 (B'=,Ta5+, Nb5+) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO6 or NbO6 centre with large Stokes shift. The Yb3+ doped into these hosts are situated at Y3+ sites of cubic symmetry (Oh). The experimental energy levels of Yb3+ in Ba2YTaO6 and Ba2YNbO6 were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg–Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb3+:Ba2YB'O6(B'=Ta5+, Nb5+) from (2F5/2)$\varGamma$8- to the low-energy states were calculated.

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A continuous analytic channel potential solution to doped symmetric double-gate MOSFETs from the accumulation to the strong-inversion region He Jin(何进), Liu Feng(刘峰), Zhou Xing-Ye(周幸叶), Zhang Jian(张健), and Zhang Li-Ning(张立宁) Chin. Phys. B, 2011, 20 (1):  016102.  DOI: 10.1088/1674-1056/20/1/016102 Abstract ( 1750 )   PDF (589KB) ( 1365 )   A continuous yet analytic channel potential solution is proposed for doped symmetric double-gate (DG) MOSFETs from the accumulation to the strong-inversion region. Analytical channel potential relationship is derived from the complete 1-D Poisson equation physically, and the channel potential solution of the DG MOSFET is obtained analytically. The extensive comparisons between the presented solution and the numerical simulation illustrate that the solution is not only accurate and continuous in the whole operation regime of DG MOSFETs, but also valid to wide doping concentration and various geometrical sizes, without employing any fitting parameter.

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Structural transition, dielectric and bonding properties of BeCN2 Gou Hui-Yang(缑慧阳), Gao Fa-Ming(高发明), Zhang Jing-Wu(张静武), and Li Zhi-Ping(李志平) Chin. Phys. B, 2011, 20 (1):  016201.  DOI: 10.1088/1674-1056/20/1/016201 Abstract ( 1706 )   PDF (1454KB) ( 1144 )   By means of first principle total energy calculations, this paper studies the structural transition, elastic, mechanical, dielectric and electronic properties of BeCN2. The calculations in total energy indicate that under ambient condition, the orthorhombic BeSiN2-type BeCN2 (space group Pna21) is a more favoured structure than the tetragonal chalcopyrite-type one (space group I-42d). The results of elastic properties reveal that BeCN2 in both orthorhombic and tetragonal structure has higher bulk and shear moduli and smaller Poisson's ratio. The calculated Vicker hardness of tetragonal phase is 36.8 GPa, indicating a hard material. The analyses of electronic structure and electron density difference demonstrate that these excellent mechanical properties are attributed to the stronger covalent-bonding of CN4 and BeN4 subunits in BeCN2 crystal. Also, the orthorhombic BeCN2 phase is found to be a transparent semiconductor material with the calculated direct band gap of about 5.56 eV, superior to the indirect band gap of diamond and c-BN. Moreover, it also calculates Born effective charges and dielectric constants of BeCN2. These results suggest that BeCN2 may have some useful applications as optoelectronic, optical window and wear resistant materials.

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Experimental investigation of evaporative cooling mixture of bosonic 87Rb and fermionic 40K atoms with microwave and radio frequency radiation Wang Peng-Jun(王鹏军), Xiong De-Zhi(熊德智), Fu Zheng-Kun(付正坤), and Zhang Jing(张靖) Chin. Phys. B, 2011, 20 (1):  016701.  DOI: 10.1088/1674-1056/20/1/016701 Abstract ( 1717 )   PDF (2620KB) ( 1112 )   We investigate sympathetic cooling fermions 40K by evaporatively cooling bosonic 87Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states |F=9/2, mF=9/2$\rangle$ for 40K and |F=2, mF=2$\rangle$ for 87Rb, which is trapped in Quadrupole–Ioffe–Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic 87Rb atoms with sympathetically cooling Fermi gas 40K, we find that the presence of rubidium atoms in the |2,1$\rangle$ Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of 40K due to inelastic collisions. Thus, the rubidium atoms populated in the |2, 1$\rangle$ Zeeman states should be removed in order to effectively perform sympathetically cooling 40K with the evaporatively cooled 87Rb atoms.

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A new method for the determination of surface tension from molecular dynamics simulations applied to liquid droplets Zhu Ru-Zeng(朱如曾) and Yan Hong(闫红) Chin. Phys. B, 2011, 20 (1):  016801.  DOI: 10.1088/1674-1056/20/1/016801 Abstract ( 1639 )   PDF (274KB) ( 1787 )   For the determination of surface tension of liquid droplets by molecular dynamics simulations, the most time-consuming part is the calculation of pressure tensor in the transition layer, which makes it difficult to enhance the precision of the computation. A new method for the calculation of surface tension of liquid droplets to reduce the calculation quantity of pressure tensor in transition layer to the minimum is proposed in this paper. Two thousand particles are taken as example to show how to carry out our scheme.

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

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First-principles calculation of electronic structure of MgxZn1-xO codoped with aluminium and nitrogen Zhang Ming(张明), Zhang Chuan-Hui(张川晖), and Shen Jiang(申江) Chin. Phys. B, 2011, 20 (1):  017101.  DOI: 10.1088/1674-1056/20/1/017101 Abstract ( 1781 )   PDF (707KB) ( 1315 )   Aiming at developing p-type semiconductors and modulating the band gap for photoelectronic devices and band engineering, we present the ab initio numerical simulation of the effect of codoping ZnO with Al, N and Mg on the crystal lattice and electronic structure. The simulations are based on the Perdew–Burke–Ernzerhof generalised-gradient approximation in density functional theory. Results indicate that electrons close to the Fermi level transfer effectively when Al, Mg, and N replace Zn and O atoms, and the theoretical results were consistent with the experiments. The addition of Mg leads to the variation of crystal lattice, expanse of energy band, and change of band gap. These unusual properties are explained in terms of the computed electronic structure, and the results show promise for the development of next-generation photoconducting devices in optoelectronic information science and technology.

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Electronic structures and thermodynamic stabilities of aluminum-based deuterides from first principles calculations Ye Xiao-Qiu(叶小球), Luo De-Li(罗德礼), Sang Ge(桑革), and Ao Bing-Yun(敖冰云) Chin. Phys. B, 2011, 20 (1):  017102.  DOI: 10.1088/1674-1056/20/1/017102 Abstract ( 1720 )   PDF (1080KB) ( 1201 )   The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen densities and are among the most promising solid-state hydrogen-storage materials. In this work, the electronic structures and the formation enthalpies of seven typical aluminum-based deuterides have been calculated by the plane-wave pseudopotential method, these being AlD3, LiAlD4, Li3AlD6, BaAlD5, Ba2AlD7, LiMg(AlD4)3 and LiMgAlD6. The results show that all these compounds are large band gap insulators at 0 K with estimated band gaps from 2.31 eV in AlD3 to 4.96 eV in LiMg(AlD4)3. The band gaps are reduced when the coordination of Al varies from 4 to 6. Two peaks present in the valence bands are the common characteristics of aluminum-based deuterides containing AlD4 subunits while three peaks are the common characteristics of those containing AlD6 subunits. The electronic structures of these compounds are determined mainly by aluminum deuteride complexes (AlD4 or AlD6) and their mutual interactions. The predicted formation enthalpies are presented for the studied aluminum-based deuterides.

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First-principles study of metallic carbon nanotubes with boron/nitrogen co-doping Chen Ling-Na(陈灵娜), Ma Song-Shan(马松山), OuYang Fang-Ping(欧阳芳平), Xiao Jin(肖金), and Xu Hui(徐慧) Chin. Phys. B, 2011, 20 (1):  017103.  DOI: 10.1088/1674-1056/20/1/017103 Abstract ( 1664 )   PDF (747KB) ( 988 )   Using the first-principles calculations, we investigate the electronic band structure and the quantum transport properties of metallic carbon nanotubes (MCNTs) with B/N pair co-doping. The results about formation energy show that the B/N pair co-doping configuration is a most stable structure. We find that the electronic structure and the transport properties are very sensitive to the doping concentration of the B/N pairs in MCNTs, where the energy gaps increase with doping concentration increasing both along the tube axis and around the tube, because the mirror symmetry of MCNT is broken by doping B/N pairs. In addition, we discuss conductance dips of the transmission spectrum of doped MCNTs. These unconventional doping effects could be used to design novel nanoelectronic devices.

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Transport properties of a ladder with two random dimer chains Hu Dong-Sheng(胡冬生),Zhu Chen-Ping(朱陈平),and Zhang Yong-Mei(张永梅) Chin. Phys. B, 2011, 20 (1):  017104.  DOI: 10.1088/1674-1056/20/1/017104 Abstract ( 1716 )   PDF (1453KB) ( 855 )   We investigate the transport properties of a ladder with two random dimer (RD) chains. It is found that there are two extended states in the ladder with identical RD chains and a critical state regarded as an extended state in the ladder with pairing RD chains. Such a critical state is caused by the chiral symmetry. The ladder with identical RD chains can be decoupled into two isolated RD chains and the ladder with pairing RD chains can not. The analytic expressions of the extended states are presented for the ladder with identical RD chains.

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Monte Carlo study of single-barrier structure based on exclusion model full counting statistics Chen Hua(陈华), Du Lei(杜磊), Qu Cheng-Li(曲成立), He Liang(何亮), Chen Wen-Hao(陈文豪), and Sun Peng(孙鹏) Chin. Phys. B, 2011, 20 (1):  017201.  DOI: 10.1088/1674-1056/20/1/017201 Abstract ( 1687 )   PDF (241KB) ( 669 )   Different from the usual full counting statistics theoretical work that focuses on the higher order cumulants computation by using cumulant generating function in electrical structures, Monte Carlo simulation of single-barrier structure is performed to obtain time series for two types of widely applicable exclusion models, counter-flows model, and tunnel model. With high-order spectrum analysis of Matlab, the validation of Monte Carlo methods is shown through the extracted first four cumulants from the time series, which are in agreement with those from cumulant generating function. After the comparison between the counter-flows model and the tunnel model in a single barrier structure, it is found that the essential difference between them consists in the strictly holding of Pauli principle in the former and in the statistical consideration of Pauli principle in the latter.

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Detailed analysis of ultrathin fluorescent red dye interlayer for organic photovoltaic cells Zang Yue(臧月), Yu Jun-Sheng(于军胜), Wang Na-Na(王娜娜), and Jiang Ya-Dong(蒋亚东) Chin. Phys. B, 2011, 20 (1):  017202.  DOI: 10.1088/1674-1056/20/1/017202 Abstract ( 1662 )   PDF (1115KB) ( 941 )   The influence of an ultrathin 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) fluorescent dye layer at donor/acceptor heterojunction on the performance of small-molecule organic photovoltaic (OPV) cell is studied. The structure of OPV cell is of indium-tin oxide (ITO)/copper phthalocyanine (CuPc)/DCJTB/fullerene (C60)/bathophenanthroline (Bphen)/Ag. The results show that open circuit voltage (VOC) increases to 0.57 V as the film thickness of DCJTB layer increases from 0.2 to 2.0 nm. By using an equivalent circuit model, the enhancement of VOC is found to be attributed to the reduced reverse saturation current density (JS) which is due to the lower highest occupied molecular orbital (HOMO) level in DCJTB than that in CuPc. Also, the short circuit current density (JSC) is affected when the DCJTB layer becomes thicker, resulting from the high series resistance RSA due to the low charge carrier mobility of fluorescent red dye.

RAPID COMMUNICATION

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Development and characteristic analysis of a field-plated Al2O3/AlInN/GaN MOS–HEMT Mao Wei(毛维), Yang Cui(杨翠), Hao Yao(郝跃), Zhang Jin-Cheng(张进成), Liu Hong-Xia(刘红侠), Bi Zhi-Wei(毕志伟), Xu Sheng-Rui(许晟瑞), Xue Jun-Shuai(薛军帅), Ma Xiao-Hua(马晓华), Wang Chong(王冲), Yang Lin-An(杨林安), Zhang Jin-Feng(张金风), and Kuang Xian-Wei(匡贤伟) Chin. Phys. B, 2011, 20 (1):  017203.  DOI: 10.1088/1674-1056/20/1/017203 Abstract ( 2021 )   PDF (823KB) ( 1672 )   We present an AlInN/AlN/GaN MOS–HEMT with a 3 nm ultra-thin atomic layer deposition (ALD) Al2O3 dielectric layer and a 0.3 μm field-plate (FP)-MOS–HEMT. Compared with a conventional AlInN/AlN/GaN HEMT (HEMT) with the same dimensions, a FP-MOS–HEMT with a 0.6 μm gate length exhibits an improved maximum drain current of 1141 mA/mm, an improved peak extrinsic transconductance of 325 mS/mm and effective suppression of gate leakage in both the reverse direction (by about one order of magnitude) and the forward direction (by more than two orders of magnitude). Moreover, the peak extrinsic transconductance of the FP-MOS–HEMT is slightly larger than that of the HEMT, indicating an exciting improvement of transconductance performance. The sharp transition from depletion to accumulation in the capacitance–voltage (C–V) curve of the FP-MOS–HEMT demonstrates a high-quality interface of Al2O3/AlInN. In addition, a large off-state breakdown voltage of 133 V, a high field-plate efficiency of 170 V/μ m and a negligible double-pulse current collapse is achieved in the FP-MOS–HEMT. This is attributed to the adoption of an ultra-thin Al2O3 gate dielectric and also of a field-plate on the dielectric of an appropriate thickness. The results show a great potential application of the ultra-thin ALD-Al2O3 FP-MOS–HEMT to deliver high currents and power densities in high power microwave technologies.

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

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Internal quantum efficiency drop induced by the heat generation inside of light emitting diodes (LEDs) Hot! Chen Yi-Xin(陈依新),Shen Guang-Di(沈光地),Guo Wei-Ling(郭伟玲), Xu Chen(徐晨), and Li Jian-Jun(李建军) Chin. Phys. B, 2011, 20 (1):  017204.  DOI: 10.1088/1674-1056/20/1/017204 Abstract ( 1848 )   PDF (651KB) ( 1419 )   The reasons for low output power of AlGaInP Light Emitting Diodes (LEDs) have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency (EQE) has serious impaction on the internal quantum efficiency (IQE), because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.

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Two-dimensional analytical models for asymmetric fully depleted double-gate strained silicon MOSFETs Liu Hong-Xia(刘红侠), Li Jin(李劲),Li Bin(李斌), Cao Lei(曹磊),and Yuan Bo(袁博) Chin. Phys. B, 2011, 20 (1):  017301.  DOI: 10.1088/1674-1056/20/1/017301 Abstract ( 1683 )   PDF (935KB) ( 1346 )   This paper develops the simple and accurate two-dimensional analytical models for new asymmetric double-gate fully depleted strained-Si MOSFET. The models mainly include the analytical equations of the surface potential, surface electric field and threshold voltage, which are derived by solving two dimensional Poisson equation in strained-Si layer. The models are verified by numerical simulation. Besides offering the physical insight into device physics in the model, the new structure also provides the basic designing guidance for further immunity of short channel effect and drain-induced barrier-lowering of CMOS-based devices in nanometre scale.

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Effect of vacancy defect on electrical properties of chiral single-walled carbon nanotube under external electrical field Luo Yu-Pin(罗煜聘), Tien Li-Gan(田力耕), Tsai Chuen-Horng(蔡春鸿), Lee Ming-Hsien(李明宪), and Li Feng-Yin(李丰颖) Chin. Phys. B, 2011, 20 (1):  017302.  DOI: 10.1088/1674-1056/20/1/017302 Abstract ( 2075 )   PDF (941KB) ( 974 )   Ab initio calculations demonstrated that the energy gap modulation of a chiral carbon nanotube with mono-vacancy defect can be achieved by applying a transverse electric field. The bandstructure of this defective carbon nanotube varying due to the external electric field is distinctly different from those of the perfect nanotube and defective zigzag nanotube. This variation in bandstructure strongly depends on not only the chirality of the nanotube and also the applied direction of the transverse electric field. A mechanism is proposed to explain the response of the local energy gap between the valence band maximum state and the local gap state under external electric field. Several potential applications of these phenomena are discussed.

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Electronic transport through a quantum ring coupled to ferromagnetic leads Chi Feng(迟锋), Sun Lian-Liang(孙连亮), Huang Ling(黄玲) and Zhao Jia(赵佳) Chin. Phys. B, 2011, 20 (1):  017303.  DOI: 10.1088/1674-1056/20/1/017303 Abstract ( 1668 )   PDF (1729KB) ( 829 )   We study the spin-dependent transport through a one-dimensional quantum ring with taking both the Rashba spin–orbit coupling (RSOC) and ferromagnetic leads into consideration. The linear conductance is obtained by the Green's function method. We find that due to the quantum interference effect arising from the RSOC-induced spin precession phase and the difference in travelling phase between the two arms of the ring, the conductance becomes spin-polarized even in the antiparallel magnetic configuration of the two leads, which is different from the case in single conduction channel system. The linear conductance, the spin polarization and the tunnel magnetoresistance are periodic functions of the two phases, and can be efficiently tuned by the structure parameters.

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Improved performance of 4H-SiC metal-semiconductor field-effect transistors with step p-buffer layer Deng Xiao-Chuan(邓小川), Zhang Bo(张波), Zhang You-Run(张有润), Wang Yi(王易), and Li Zhao-Ji(李肇基) Chin. Phys. B, 2011, 20 (1):  017304.  DOI: 10.1088/1674-1056/20/1/017304 Abstract ( 2115 )   PDF (602KB) ( 1001 )   An improved 4H-SiC metal-semiconductor field-effect transistors (MESFETs) with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.

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Investigation of resistive switching behaviours in WO3-based RRAM devices Li Ying-Tao(李颖弢), Long Shi-Bing(龙世兵), Lü Hang-Bing(吕杭炳), Liu Qi(刘琦), Wang Qin(王琴), Wang Yan(王艳), Zhang Sen(张森), Lian Wen-Tai(连文泰), Liu Su(刘肃), and Liu Ming(刘明) Chin. Phys. B, 2011, 20 (1):  017305.  DOI: 10.1088/1674-1056/20/1/017305 Abstract ( 1698 )   PDF (2008KB) ( 1555 )   In this paper, a WO3-based resistive random access memory device composed of a thin film of WO3 sandwiched between a copper top and a platinum bottom electrodes is fabricated by electron beam evaporation at room temperature. The reproducible resistive switching, low power consumption, multilevel storage possibility, and good data retention characteristics demonstrate that the Cu/WO3/Pt memory device is very promising for future nonvolatile memory applications. The formation and rupture of localised conductive filaments is suggested to be responsible for the observed resistive switching behaviours.

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Performance improvement in pentacene organic thin film transistors by inserting a C60 ultrathin layer Sun Qin-Jun(孙钦军), Xu Zheng(徐征), Zhao Su-Ling(赵谡玲), Zhang Fu-Jun(张福俊), and Gao Li-Yan(高利岩) Chin. Phys. B, 2011, 20 (1):  017306.  DOI: 10.1088/1674-1056/20/1/017306 Abstract ( 1580 )   PDF (480KB) ( 1242 )   The contact effect on the performances of organic thin film transistors is studied here. A C60 ultrathin layer is inserted between Al source–drain electrode and pentacene to reduce the contact resistance. By a 3 nm C60 modification, the injection barrier is lowered and the contact resistance is reduced. Thus, the field-effect mobility increases from 0.12 to 0.52 cm2/(V·s). It means that inserting a C60 ultra thin layer is a good method to improve the organic thin film transistor (OTFT) performance. The output curve is simulated by using a charge drift model. Considering the contact effect, the field effect mobility is improved to 1.15 cm2/(V·s). It indicates that further reducing the contact resistance of OTFTs should be carried out.

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Shot noise of the spin inelastic tunneling through a quantum dot with single molecule-magnet Chang Bo(常博)and Liang Jiu-Qing(梁九卿) Chin. Phys. B, 2011, 20 (1):  017307.  DOI: 10.1088/1674-1056/20/1/017307 Abstract ( 1633 )   PDF (949KB) ( 940 )   We have studied the quantum fluctuations of inelastic spin-electron scattering in quantum dot with an embedded biaxial single molecule-magnet and particularly investigated the zero-frequency shot noise and Fano factor in different magnetic fields. It is found that the shot noise and Fano factor exhibit a stepwise behaviour as bias increases in the presence of interaction between the electron and molecule-magnet for a weak magnetic field. As magnetic field becomes strong, a dip is displayed in the shot-noise-bias curve due to the suppression of inelastic shot noise caused by the quantum tunneling of magnetisation. Because of the spontaneous inelastic tunneling at zero bias, a small shot noise occurs, which results in the case of Fano factor F >> 1. Moreover, our results show that the sweeping speed can also influence the shot noise and Fano factor obviously.

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Multilayer transition in a spin-1 Blume–Capel model with RKKY interaction and quantum transverse anisotropy N. Tahiri, H. Ez-Zahraouy, and A. Benyoussef Chin. Phys. B, 2011, 20 (1):  017501.  DOI: 10.1088/1674-1056/20/1/017501 Abstract ( 1629 )   PDF (304KB) ( 899 )   Using mean-field theory, we have studied the effect of quantum transverse anisotropies with RKKY interaction on the multi-layer transition and magnetic properties of the spin-1 Blume–Capel model of a system formed by two magnetic multi-layer materials, of different thicknesses, separated by a non-magnetic spacer of thickness M. It is found that the multilayer magnetic order--disorder transition temperature depends strongly on the value of the transverse anisotropy. The multilayer transition temperature decreases when increasing the transverse anisotropy. Furthermore, there exists a critical quantum transverse anisotropy ΔxL beyond which the separate transitions occur in the two magnetic layers. The critical transverse anisotropy ΔxL decreases (increases) on increasing the non-magnetic spacer of thickness M (on increasing the crystal field), and ΔxL undergoes oscillations as a function of the Fermi level.

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Analyses of crystal field and exchange interaction of Dy3Ga5O12 under extreme conditions Wang Wei(王维), Qi Xin(祁欣), and Yue Yuan(岳元) Chin. Phys. B, 2011, 20 (1):  017502.  DOI: 10.1088/1674-1056/20/1/017502 Abstract ( 1843 )   PDF (279KB) ( 889 )   This paper theoretically investigates the effects of crystal field and exchange interaction field on magnetic properties in dysprosium gallium garnet under extreme conditions (low temperatures and high magnetic fields) based on quantum theory. Here, five sets of crystal field parameters are discussed and compared. It demonstrates that, only considering the crystal field effect, the experiments can not be successfully explained. Thus, referring to the molecular field theory, an effective exchange field associated with the Dy–Dy exchange interaction is further taken into account. Under special consideration of crystal field and the exchange interaction field, it obtains an excellent agreement between the theoretical results and experiments, and further confirms that the exchange interaction field between rare-earth ions has great importance to magnetic properties in paramagnetic rare-earth gallium garnets.

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Two-dimensional quantum compass model in a staggered field: some rigorous results He Pei-Song(何培松), You Wen-Long(尤文龙), and Tian Guang-Shan(田光善) Chin. Phys. B, 2011, 20 (1):  017503.  DOI: 10.1088/1674-1056/20/1/017503 Abstract ( 1919 )   PDF (414KB) ( 965 )   We study the properties of the two-dimensional quantum compass model in a staggered field. Using the Perron–Fröbenius theorem and the reflection positivity method, we rigorously determine the low energy spectrum of this model and its global ground state $\varPsi_0$. Furthermore, we show that $\varPsi_0$ has a directional long-range order.

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

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Multiband terahertz metamaterial absorber Gu Chao(顾超), Qu Shao-Bo(屈绍波), Pei Zhi-Bin(裴志斌), Xu Zhuo(徐卓), Liu Jia(刘嘉), and Gu Wei(顾巍) Chin. Phys. B, 2011, 20 (1):  017801.  DOI: 10.1088/1674-1056/20/1/017801 Abstract ( 1959 )   PDF (1181KB) ( 1700 )   This paper reports the design of a multiband metamaterial (MM) absorber in the terahertz region. Theoretical and simulated results show that the absorber has four distinct and strong absorption points at 1.69, 2.76, 3.41 and 5.06 THz, which are consistent with `fingerprints' of some explosive materials. The retrieved material parameters show that the impedance of MM could be tuned to match approximately the impedance of the free space to minimise the reflectance at absorption frequencies and large power loss exists at absorption frequencies. The distribution of the power loss indicates that the absorber is an excellent electromagnetic wave collector: the wave is first trapped and reinforced in certain specific locations and then consumed. This multiband absorber has applications in the detection of explosives and materials characterisation.

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An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field Yang Guo(杨国), Zhang Guo-Ying(张国营), Gao Jiao(高娇), Xue Liu-Ping(薛刘萍), Xia Tian(夏天), and Zhang Xue-Long(张学龙) Chin. Phys. B, 2011, 20 (1):  017802.  DOI: 10.1088/1674-1056/20/1/017802 Abstract ( 1682 )   PDF (232KB) ( 1036 )   The superexchange interaction on a magnetic ion may be represented by an effective field Hm = $\lambda$M in some paramagnetic materials, here λ is the coefficient of effective field and M = $\chi$He with $\chi$ being the magnetic susceptibility and He being the applied field. The variation of the equivalent $\lambda_{\chi}$ with the dynamic applied field is given and the crystal field-splitting levels of the excited configuration 4f75d1 of the Tb3+ ion are calculated in the Tb3Ga5O12. By means of the effective field Hm and the applied field He, the Faraday rotation of Tb3Ga5O12 at 6 K and 41 K, under the high magnetic field and at 0.63 μm wavelength, are presented. Our calculated results are in agreement with the experimental data.

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Optical parameters of Nd3+:Er3+:Yb3+ co-doped borosilicate glasses and their energy transfers at high temperature Li Cheng-Ren(李成仁), Li Shu-Feng(李淑凤), Dong Bin(董斌), Cheng Yu-Qi(程宇琪), Yin Hai-Tao(殷海涛), Yang Jing(杨静), and Chen Yu(陈宇) Chin. Phys. B, 2011, 20 (1):  017803.  DOI: 10.1088/1674-1056/20/1/017803 Abstract ( 1687 )   PDF (724KB) ( 1081 )   This paper reports that a series of Nd3+:Er3+:Yb3+ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J–O intensity parameters Ωk (k=2, 4, 6), spontaneous radiative lifetime τrad, spontaneous transition probability A, fluorescence branching ratio β and oscillator strength fed of the Nd3+ ions at room temperature are calculated based on Judd–Ofelt (J–O) theory. The temperature dependence of the up-conversion photoluminescence characteristics in a Nd3+:Er3+:Yb3+ co-doped sample is studied under a 978 nm semiconductor laser excitation, and the energy transfer mechanisms among Yb3+, Er3+ and Nd3+ ions are analysed. The results show that the J–O intensity parameters Ω2 increase when the Nd3+ concentration of the Nd3+:Er3+:Yb3+ co-doped borosilicate glasses increases. The possibility of spontaneous transition is small and lifetimes are long at levels of 4F5/2 and 4F3/2. The intensity of Nd3+ emissions at 595, 691, 753, 813 and 887 nm are markedly enhanced when the sample temperature exceeds 400 K. The reasons being the cooperation of the secondary sensitization from Er3+ to Nd3+ and the contribution of a multi-phonon.

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Nonpolar a-plane light-emitting diode with an in-situ SiNx interlayer on r-plane sapphire grown by metal-organic chemical vapour deposition Fang Hao(方浩),Long Hao(龙浩),Sang Li-Wen(桑立雯), Qi Sheng-Li(齐胜利),Xiong Chang(熊畅),Yu Tong-Jun(于彤军), Yang Zhi-Jian(杨志坚),and Zhang Guo-Yi(张国义) Chin. Phys. B, 2011, 20 (1):  017804.  DOI: 10.1088/1674-1056/20/1/017804 Abstract ( 1692 )   PDF (1916KB) ( 989 )   We report on the growth and fabrication of nonpolar a-plane light emitting diodes with an in-situ SiNx interlayer grown between the undoped a-plane GaN buffer and Si-doped GaN layer. X-ray diffraction shows that the crystalline quality of the GaN buffer layer is greatly improved with the introduction of the SiNx interlayer. The electrical properties are also improved. For example, electron mobility and sheet resistance are reduced from high resistance to 31.6 cm2/(V·s) and 460 Ω/口 respectively. Owing to the significant effect of the SiNx interlayer, a-plane LEDs are realized. Electroluminescence of a nonpolar a-plane light-emitting diode with a wavelength of 488nm is demonstrated. The emission peak remains constant when the injection current increases to over 20 mA.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Investigation of AlGaN/GaN fluorine plasma treatment enhancement-mode high electronic mobility transistors by frequency-dependent capacitance and conductance analysis Quan Si(全思), Hao Yue(郝跃), Ma Xiao-Hua(马晓华), and Yu Hui-You(于惠游) Chin. Phys. B, 2011, 20 (1):  018101.  DOI: 10.1088/1674-1056/20/1/018101 Abstract ( 1806 )   PDF (634KB) ( 1128 )   This paper reports fluorine plasma treatment enhancement-mode HEMTs (high electronic mobility transistors) EHEMTs and conventional depletion-mode HEMTs DHEMTs fabricated on one wafer using separate litho-photography technology. It finds that fluorine plasma etches the AlGaN at a slow rate by capacitance–voltage measurement. Using capacitance–frequency measurement, it finds one type of trap in conventional DHEMTs with $\tau$T=(0.5–6) ms and DT= (1–5) × 1013 cm-2·eV-1. Two types of trap are found in fluorine plasma treatment EHEMTs, fast with τT(f)=(0.2–2) μs and slow with $\tau$T(s)=(0.5–6) ms. The density of trap states evaluated on the EHEMTs is DT(f)=(1–3) × 1012 cm-2·eV-1 and DT(s)=(2–6) × 1012 cm-2·eV-1 for the fast and slow traps, respectively. The result shows that the fluorine plasma treatment reduces the slow trap density by about one order, but introduces a new type of fast trap. The slow trap is suggested to be a surface trap, related to the gate leakage current.

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Molecular beam epitaxy growth of GaAs on an offcut Ge substrate He Ji-Fang(贺继方), Niu Zhi-Chuan(牛智川), Chang Xiu-Ying(常秀英), Ni Hai-Qiao(倪海桥), Zhu Yan(朱岩), Li Mi-Feng(李密锋), and Shang Xiang-Jun(尚向军) Chin. Phys. B, 2011, 20 (1):  018102.  DOI: 10.1088/1674-1056/20/1/018102 Abstract ( 1775 )   PDF (6465KB) ( 2362 )   Molecular beam epitaxy growth of GaAs on an offcut Ge (100) substrate has been systemically investigated. A high quality GaAs/Ge interface and GaAs film on Ge have been achieved. High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains. The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition. The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed. High quality In0.17Ga0.83As/GaAs strained quantum wells have also been achieved on a Ge substrate. Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate. These results indicate a large application potential for III–V compound semiconductor optoelectronic devices on Ge substrates.

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First-principles studies of Mn-doped LiCoPO4 Lin Zhi-Ping(林志萍), Zhao Yan-Ming(赵彦明), and Zhao Yu-Jun(赵宇军) Chin. Phys. B, 2011, 20 (1):  018201.  DOI: 10.1088/1674-1056/20/1/018201 Abstract ( 1634 )   PDF (363KB) ( 1409 )   This paper investigates Mn-doped LiCoPO4 material using first-principles calculations. Results indicate that the volume change of LiMnxCo1-xPO4 to MnxCo1-xPO4 is smaller than that of undoped LiCoPO4, which is responsible for the excellent tolerance of repeated cycling in lithium ion batteries. Combining first-principles calculations with basic thermodynamics, we calculate the average intercalation voltage of Mn-doped LiCoPO4. It is shown that the redox couple Mn3+/Mn2+ can be observed with increasing Mn content. Therefore, the Mn ion displays some electrochemical activity during discharge/charge of LiMnxCo1-xPO4 due to the coexistence of Co and Mn.

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A statistical RCL interconnect delay model taking account of process variations Zhu Zhang-Ming(朱樟明), Wan Da-Jing(万达经), Yang Yin-Tang(杨银堂), and En Yun-Fei(恩云飞) Chin. Phys. B, 2011, 20 (1):  018401.  DOI: 10.1088/1674-1056/20/1/018401 Abstract ( 1603 )   PDF (736KB) ( 704 )   As the feature size of the CMOS integrated circuit continues to shrink, process variations have become a key factor affecting the interconnect performance. Based on the equivalent Elmore model and the use of the polynomial chaos theory and the Galerkin method, we propose a linear statistical RCL interconnect delay model, taking into account process variations by successive application of the linear approximation method. Based on a variety of nano-CMOS process parameters, HSPICE simulation results show that the maximum error of the proposed model is less than 3.5%. The proposed model is simple, of high precision, and can be used in the analysis and design of nanometer integrated circuit interconnect systems.

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Thermal stability improvement of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations using non-uniform finger spacing Chen Liang(陈亮), Zhang Wan-Rong(张万荣), Jin Dong-Yue(金冬月), Shen Pei(沈珮), Xie Hong-Yun(谢红云), Ding Chun-Bao(丁春宝),Xiao Ying(肖盈),Sun Bo-Tao(孙博韬), and Wang Ren-Qing(王任卿) Chin. Phys. B, 2011, 20 (1):  018501.  DOI: 10.1088/1674-1056/20/1/018501 Abstract ( 1650 )   PDF (4405KB) ( 1385 )   A method of non-uniform finger spacing is proposed to enhance thermal stability of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations. Temperature distribution on the emitter fingers of a multi-finger SiGe heterojunction bipolar transistor is studied using a numerical electro-thermal model. The results show that the SiGe heterojunction bipolar transistor with non-uniform finger spacing has a small temperature difference between fingers compared with a traditional uniform finger spacing heterojunction bipolar transistor at the same power dissipation. What is most important is that the ability to improve temperature non-uniformity is not weakened as power dissipation increases. So the method of non-uniform finger spacing is very effective in enhancing the thermal stability and the power handing capability of power device. Experimental results verify our conclusions.

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Analytical base–collector depletion capacitance in vertical SiGe heterojunction bipolar transistors fabricated on CMOS-compatible silicon on insulator Xu Xiao-Bo(徐小波), Zhang He-Ming(张鹤鸣), Hu Hui-Yong(胡辉勇), Ma Jian-Li(马建立), and Xu Li-Jun(许立军) Chin. Phys. B, 2011, 20 (1):  018502.  DOI: 10.1088/1674-1056/20/1/018502 Abstract ( 1712 )   PDF (263KB) ( 1095 )   The base–collector depletion capacitance for vertical SiGe npn heterojunction bipolar transistors (HBTs) on silicon on insulator (SOI) is split into vertical and lateral parts. This paper proposes a novel analytical depletion capacitance model of this structure for the first time. A large discrepancy is predicted when the present model is compared with the conventional depletion model, and it is shown that the capacitance decreases with the increase of the reverse collector–base bias–and shows a kink as the reverse collector–base bias reaches the effective vertical punch-through voltage while the voltage differs with the collector doping concentrations, which is consistent with measurement results. The model can be employed for a fast evaluation of the depletion capacitance of an SOI SiGe HBT and has useful applications on the design and simulation of high performance SiGe circuits and devices.

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Multifunctional silicon-based light emitting device in standard complementary metal–oxide–semiconductor technology Wang Wei(王伟), Huang Bei-Ju(黄北举), Dong Zan(董赞), and Chen Hong-Da(陈弘达) Chin. Phys. B, 2011, 20 (1):  018503.  DOI: 10.1088/1674-1056/20/1/018503 Abstract ( 1905 )   PDF (1499KB) ( 1088 )   A three-terminal silicon-based light emitting device is proposed and fabricated in standard 0.35 μm complementary metal–oxide–semiconductor technology. This device is capable of versatile working modes: it can emit visible to near infra-red (NIR) light (the spectrum ranges from 500 nm to 1000 nm) in reverse bias avalanche breakdown mode with working voltage between 8.35 V–12 V and emit NIR light (the spectrum ranges from 900 nm to 1300 nm) in the forward injection mode with working voltage below 2 V. An apparent modulation effect on the light intensity from the polysilicon gate is observed in the forward injection mode. Furthermore, when the gate oxide is broken down, NIR light is emitted from the polysilicon/oxide/silicon structure. Optoelectronic characteristics of the device working in different modes are measured and compared. The mechanisms behind these different emissions are explored.

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InP-based evanescently coupled high-responsivity photodiodes with extremely low dark current density integrated diluted waveguide at 1550 nm Zuo Yu-Hua(左玉华),Cao Quan(曹权),Zhang Yun(张云), Zhang Ling-Zi(张岭梓), Guo Jian-Chuan(郭剑川),Xue Chun-Lai(薛春来),Cheng Bu-Wen(成步文),and Wang Qi-Ming(王启明) Chin. Phys. B, 2011, 20 (1):  018504.  DOI: 10.1088/1674-1056/20/1/018504 Abstract ( 1863 )   PDF (1079KB) ( 937 )   In this paper, we have demonstrated a high performance waveguide photodiode integrated diluted waveguide serving as a fibre-to-waveguide coupler to achieve high coupling efficiency. High responsivity (> 1 A/W), high saturation power (> 45 mA) in the static state and extremely low dark current density (0.04 pA/μm2) with 3 dB bandwidth at 13.4 GHz have been achieved.

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Extended triplet set C343 of DNA sequences and its application to the p53 gene Yan Yan-Yan(闫艳艳) and Zhu Ping(朱平) Chin. Phys. B, 2011, 20 (1):  018701.  DOI: 10.1088/1674-1056/20/1/018701 Abstract ( 1541 )   PDF (282KB) ( 1062 )   Recently, much research has indicated that more and more cancers pose a threat to human life. Cancers are caused by oncogenes. Many human oncogenes have been found and most of them are located on chromosomes. The discovery of the oncogene plays a significant role in the treatment of cancer. The p53 tumor suppressor gene has received much attention because it frequently mutates or deletes in tumor cells of most people. Thus, the study of oncogenes is significant. In order to establish the Galois field (GF(7)), the indefinite gene is introduced as D and oncogene is introduced as O, and P. Taking the polynomial coefficients a0, a1, a2 ∈ GF(7) and the bijective function f:GF(7) → {D,A,C,O,G,T,P}, where f(0) = D, f(1) = A, f(2) = C, f(3) = O, f(4) = G, f(5) = T, and f(6) = P, the bijective φ may be written as φ(a0 + a1x + a2x2). Based on the algebraic structure, we can not only analyse the DNA sequence of oncogenes, but also predict possible new cancers.

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Multi-target pursuit formation of multi-agent systems Yan Jing(闫敬), Guan Xin-Ping(关新平), and Luo Xiao-Yuan(罗小元) Chin. Phys. B, 2011, 20 (1):  018901.  DOI: 10.1088/1674-1056/20/1/018901 Abstract ( 1544 )   PDF (777KB) ( 1059 )   The main goal of this paper is to design a team of agents that can accomplish multi-target pursuit formation using a developed leader–follower strategy. It is supposed that every target can accept a certain number of agents. First, each agent can automatically choose its target based on the distance from the agent to the target and the number of agents accepted by the target. In view of the fact that all agents are randomly dispersed in the workplace at the initial time, we present a numbering strategy for them. During the movement of agents, not every agent can always obtain pertinent state information about the targets. So, a developed leader–follower strategy and a pursuit formation algorithm are proposed. Under the proposed method, agents with the same target can maintain a circle formation. Furthermore, it turns out that the pursuit formation algorithm for agents to the desired formation is convergent. Simulation studies are provided to illustrate the effectiveness of the proposed method.

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Community detection with consideration of non-topological information Zou Sheng-Rong(邹盛荣), Peng Yu-Jing(彭昱静),Liu Ai-Fen(刘爱芬), Xu Xiu-Lian(徐秀莲),and He Da-Ren(何大韧) Chin. Phys. B, 2011, 20 (1):  018902.  DOI: 10.1088/1674-1056/20/1/018902 Abstract ( 1820 )   PDF (2312KB) ( 843 )   In a network described by a graph, only topological structure information is considered to determine how the nodes are connected by edges. Non-topological information denotes that which cannot be determined directly from topological information. This paper shows, by a simple example where scientists in three research groups and one external group form four communities, that in some real world networks non-topological information (in this example, the research group affiliation) dominates community division. If the information has some influence on the network topological structure, the question arises as to how to find a suitable algorithm to identify the communities based only on the network topology. We show that weighted Newman algorithm may be the best choice for this example. We believe that this idea is general for real-world complex networks.

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Preliminary research on the relationship between long-range correlations and predictability Zhang Zhi-Sen(张志森), Gong Zhi-Qiang(龚志强), Zhi Rong(支蓉), Feng Guo-Lin(封国林), and Hu Jing-Guo(胡经国) Chin. Phys. B, 2011, 20 (1):  019201.  DOI: 10.1088/1674-1056/20/1/019201 Abstract ( 1761 )   PDF (1337KB) ( 1012 )   By establishing the Markov model for a long-range correlated time series (LRCS) and analysing its evolutionary characteristics, this paper defines a physical effective correlation length (ECL) $\tau$, which reflects the predictability of the LRCS. It also finds that the ECL has a better power law relation with the long-range correlated exponent $\gamma$ of the LRCS: $\tau$ = Kexp (-$\gamma$/0.3)+Y, ($0<\gamma <1$)-the predictability of the LRCS decays exponentially with the increase of γ. It is then applied to a daily maximum temperature series (DMTS) recorded at 740 stations in China between the years 1960–2005 and calculates the ECL of the DMTS. The results show the remarkable regional distributive feature that the ECL is about 10–14 days in west, northwest and northern China, and about 5–10 days in east, southeast and southern China. Namely, the predictability of the DMTS is higher in central-west China than in east and southeast China. In addition, the ECL is reduced by 1–8 days in most areas of China after subtracting the seasonal oscillation signal of the DMTS from its original DMTS; however, it is only slightly altered when the decadal linear trend is removed from the original DMTS. Therefore, it is shown that seasonal oscillation is a significant component of daily maximum temperature evolution and may provide a basis for predicting daily maximum temperatures. Seasonal oscillation is also significant for guiding general weather predictions, as well as seasonal weather predictions.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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The interaction of nonlinear waves in two-dimensional dust crystals Jiang Hong(姜虹), Yang Xiao-Xia(杨晓霞), Lin Mai-Mai(林麦麦), Shi Yu-Ren(石玉仁), and Duan Wen-Shan(段文山) Chin. Phys. B, 2011, 20 (1):  019401.  DOI: 10.1088/1674-1056/20/1/019401 Abstract ( 1699 )   PDF (709KB) ( 881 )   This paper investigates the collision between two nonlinear waves with different propagation directions in two-dimensional dust crystals. Using the extended Poincaré–Lighthill-Kuo perturbation method, two Korteweg–de Vries equations for nonlinear waves in both the ξ and η directions are obtained, respectively, and the analytical phase shifts and trajectories after the collision of two nonlinear waves are derived. Finally, the effects of parameters of the lattice constant a, the arbitrary constant u0η, the forces f(r), and the colliding angle θ on the phase shifts of both colliding nonlinear waves are examined.