Table of Content

01 November 2012, Volume 21 Issue 12 Previous Issue    Next Issue

GENERAL

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A target group tracking algorithm for wireless sensor network using azimuthal angle of arrival information Zhang Chun, Fei Shu-Min, Zhou Xing-Peng 2012, 21 (12):  120101.  doi: 10.1088/1674-1056/21/12/120101 Abstract ( 0 )   PDF (225KB) ([an error occurred while processing this directive])   In this paper, we explore the technology of tracking a group of targets with correlated motions in a wireless sensor network. Since a group of targets moves collectively and is restricted within a limited region, it is not worth consuming scarce resources of sensors in computing the trajectory of each single target. Hence, in this paper, the problem is modeled as tracking a geographical continuous region covered by all targets. A tracking algorithm is proposed to estimate the region covered by the target group in each sampling time. Based on the locations of sensors and the azimuthal angle of arrival (AOA) information, the estimated region covering all the group members is obtained. Algorithm analysis provides the fundamental limits to the accuracy of localizing a target group. Simulation results show that the proposed algorithm is superior to the existing hull algorithm due to the reduction in estimation error, which is between 10% and 40% of hull algorithm, with a similar density of sensors. And when the density of sensors increases, the localization accuracy of the proposed algorithm improves dramatically.

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A type of new conserved quantity deduced from Mei symmetry for Nielsen equations in a holonomic system with unilateral constraints Han Yue-Lin, Sun Xian-Ting, Wang Xiao-Xiao, Zhang Mei-Ling, Jia Li-Qun 2012, 21 (12):  120201.  doi: 10.1088/1674-1056/21/12/120201 Abstract ( 0 )   PDF (87KB) ([an error occurred while processing this directive])   A type of new conserved quantity deduced from Mei symmetry for Nielsen equations in a holonomic system with unilateral constraints are investigated. Nielsen equations and differential equations of motion for the holonomic mechanical system with unilateral constraints are established. The definition and the criterion of Mei symmetry for Nielsen equations in the holonomic systems with unilateral constraints under the infinitesimal transformations of Lie group are also given. The expressions of the structural equation and a type of new conserved quantity of Mei symmetry for Nielsen equations in the holonomic system with unilateral constraints are obtained. An example is given to illustrate the application of the results.

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Multi-symplectic wavelet splitting method for the strongly coupled Schrödinger system Qian Xu, Chen Ya-Ming, Gao Er, Song Song-He 2012, 21 (12):  120202.  doi: 10.1088/1674-1056/21/12/120202 Abstract ( 0 )   PDF (4162KB) ([an error occurred while processing this directive])   We propose a multi-symplectic wavelet splitting method to solve the strongly coupled nonlinear Schrödinger equations. Based on its multi-symplectic formulation, the strongly coupled nonlinear Schrödinger equations can be split into one linear multi-symplectic subsystem and one nonlinear infinite-dimensional Hamiltonian subsystem. For the linear subsystem, multi-symplectic wavelet collocation method and symplectic Euler method are employed in spatial and temporal discretization, respectively. For the nonlinear subsystem, the mid-point symplectic scheme is used. Numerical simulations show the effectiveness of the proposed method during long-time numerical calculation.

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Riemann theta function periodic wave solutions for the variable-coefficient mKdV equation Zhang Yi, Cheng Zhi-Long, Hao Xiao-Hong 2012, 21 (12):  120203.  doi: 10.1088/1674-1056/21/12/120203 Abstract ( 0 )   PDF (126KB) ([an error occurred while processing this directive])   In this paper, a variable-coefficient mKdV equation is considered. Bilinear forms is presented to explicitly construct periodic wave solutions based on a multidimensional Riemann theta function, then the one and two periodic wave solutions are presented, and it is also shown that the soliton solutions can be reduced from the periodic wave solutions.

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Approximate solutions of nonlinear PDEs by the invariant expansion Wu Jiang-Long, Lou Sen-Yue 2012, 21 (12):  120204.  doi: 10.1088/1674-1056/21/12/120204 Abstract ( 0 )   PDF (89KB) ([an error occurred while processing this directive])   It is difficult to obtain exact solutions of the nonlinear partial differential equations (PDEs) due to the complexity and nonlinearity, especially for non-integrable systems. In this paper, some reasonable approximations of real physics are considered, and the invariant expansion is proposed to solve real nonlinear system. A simple invariant expansion with quite a universal pseudopotential is used for some nonlinear PDEs such as Korteweg-de Vries (KdV) equation with fifth-order dispersion term, perturbed fourth-order KdV equation, KdV-Burgers equation, and Boussinesq type of equation.

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Asymptotic solving method for period solution to a class of disturbed nonlinear evolution equation Yao Jing-Sun, Lin Wan-Tao, Du Zeng-Ji, Mo Jia-Qi 2012, 21 (12):  120205.  doi: 10.1088/1674-1056/21/12/120205 Abstract ( 0 )   PDF (862KB) ([an error occurred while processing this directive])   A class of disturbed evolution equation is considered using a simple and valid technique. We first introduce periodic traveling-wave solution of a corresponding typical evolution equation. And then the approximate solution for an original disturbed evolution equation is obtained using the asymptotic method. And we point out that the series of approximate solution is convergent and the accuracy of the asymptotic solution is studied using the fixed point theorem for the functional analysis.

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A new complex variable meshless method for transient heat conduction problems Wang Jian-Fei, Cheng Yu-Min 2012, 21 (12):  120206.  doi: 10.1088/1674-1056/21/12/120206 Abstract ( 0 )   PDF (204KB) ([an error occurred while processing this directive])   In this paper, based on the improved complex variable moving least-square (ICVMLS) approximation, a new complex variable meshless method (CVMM) for two-dimensional (2D) transient heat conduction problems is presented. The variational method is employed to obtain the discrete equations, and the essential boundary conditions are imposed by the penalty method. As the transient heat conduction problems are related to time, Crank-Nicolson difference scheme for two-point boundary value problems is selected for the time discretization. Then the corresponding formulae of the CVMM for 2D heat conduction problems are obtained. In order to demonstrate the applicability of the proposed method, numerical examples are given to show the high convergence rate, good accuracy, and high efficiency of the CVMM presented in this paper.

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Alternative routes to equivalent classical models of a quantum system M. Radonjić, Slobodan Prvanović, Nikola Burić 2012, 21 (12):  120301.  doi: 10.1088/1674-1056/21/12/120301 Abstract ( 0 )   PDF (194KB) ([an error occurred while processing this directive])   Coarse-graining of some sort is the fundamental and unavoidable step in any attempt to derive the classical mechanical behavior from the quantum formalism. We utilize two-mode Bose-Hubbard model to illustrate how different coarse-grained systems can be naturally associated with a fixed quantum system if it is compatible with different dynamical algebras. Alternative coarse-grained systems generate different evolutions of the same physical quantities, and the difference becomes negligible only in the appropriate macro-limit.

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Approximate any l-state solutions of Dirac equation for modified deformed Hylleraas potential by the Nikiforov–Uvarov method H. Hassanabadi, E. Maghsoodi, S. Zarrinkamar, H. Rahimov 2012, 21 (12):  120302.  doi: 10.1088/1674-1056/21/12/120302 Abstract ( 0 )   PDF (795KB) ([an error occurred while processing this directive])   We inquire into spin and pseudospin symmetries of Dirac equation under modified deformed Hylleraas potential via a Pekeris approximation and the Nikiforov-Uvarov technique. A tensor interaction of Coulomb form is considered and its degeneracy-removing role is discussed in detail. The solutions are reported for arbitrary quantum number in a compact form and useful numerical data are included.

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Transport properties in multi-terminal regular polygonal quantum ring with Rashba spin-orbit coupling Tang Han-Zhao, Zhai Li-Xue, Liu Jian-Jun 2012, 21 (12):  120303.  doi: 10.1088/1674-1056/21/12/120303 Abstract ( 0 )   PDF (181KB) ([an error occurred while processing this directive])   Transport properties in multi-terminal regular polygonal quantum ring with Rashba spin-orbit coupling (SOC) are investigated analytically using quantum networks and transport matrix method. The results show that conductances remain at exactly the same values when the output leads are located at axisymmetric positions. However, for the nonaxisymmetrical case, there is a phase difference between the upper and lower arm, which leads to zero conductances appearing periodically. An isotropy of the conductance is destroyed by the Rashba SOC effect in the axisymmetric case. In addition, the position of zero conductance is regulated with the strength of the Rashba SOC.

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Approximate solution of the spin-one Duffin-Kemmer-Petiau (DKP) equation under a non-minimal vector Yukawa potential in (1+1)-dimensions H. Hassanabadi, Z. Molaee 2012, 21 (12):  120304.  doi: 10.1088/1674-1056/21/12/120304 Abstract ( 0 )   PDF (221KB) ([an error occurred while processing this directive])   We solve the Duffin-Kemmer-Petiau (DKP) equation with a non-minimal vector Yukawa potential in (1+1)-dimensional space-time for spin-1 particles. The Nikiforov-Uvarov method is used in the calculations, and the eigenfunctions as well as the energy eigenvalues are obtained in a proper Pekeris-type approximation.

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Arbitrated quantum signature scheme based on entanglement swapping with signer anonymity Li Wei, Fan Ming-Yu, Wang Guang-Wei 2012, 21 (12):  120305.  doi: 10.1088/1674-1056/21/12/120305 Abstract ( 0 )   PDF (107KB) ([an error occurred while processing this directive])   In this paper an arbitrated quantum signature scheme based on entanglement swapping is proposed. In this scheme a message to be signed is coded with unitary operators. Combining quantum measurement with quantum encryption, the signer can generate the signature for a given message. Combining the entangled states generated by the TTP's Bell measurement with the signature information, the verifier can verify the authentication of a signature through single quantum state measurement. Compared with previous schemes, our scheme is more efficient and less complex, furthermore, our scheme can ensure the anonymity of the signer.

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Performance of superconducting single photon detector with nano-antenna Zhang Chao, Jiao Rong-Zhen 2012, 21 (12):  120306.  doi: 10.1088/1674-1056/21/12/120306 Abstract ( 0 )   PDF (1387KB) ([an error occurred while processing this directive])   The performance of single-photon detectors can be enhanced by using nano-antenna. The characteristics of the superconducting nano-wire single-photon detector with cavity plus anti-reflect coating and specially designed nano-antenna is analysed. The photon collection efficiency of the detector is enhanced without damaging the detector's speed, thus getting rid of the dilemma of speed and efficiency. The characteristics of nano-antenna are discussed, such as the position and the effect of the active area, and the best result is given. The photon collection efficiency is increased by 92 times compared with that of existing detectors.

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Application of the homotopy analysis method for the Gross-Pitaevskii equation with a harmonic trap Shi Yu-Ren, Liu Cong-Bo, Wang Guang-Hui, Zhou Zhi-Gang 2012, 21 (12):  120307.  doi: 10.1088/1674-1056/21/12/120307 Abstract ( 0 )   PDF (160KB) ([an error occurred while processing this directive])   The Homotopy Analysis Method (HAM) is adopted to find the approximate analytical solutions of the Gross-Pitaevskii equation, a nonlinear Schrödinger equation is used in simulation of Bose-Einstein condensates trapped in a harmonic potential. Comparisons between the analytical solutions and the numerical solutions have been made. The results indicate that they are agreement very well with each other when the atomic interaction is weakly.

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Area spectrum of the three-dimensional Gödel black hole Li Hui-Ling 2012, 21 (12):  120401.  doi: 10.1088/1674-1056/21/12/120401 Abstract ( 0 )   PDF (100KB) ([an error occurred while processing this directive])   The aim of this paper is to investigate the area spectrum of the three-dimensional Gödel black hole by using two different methods. The result shows that the area spectrum of the black hole is ΔA=8πlP2, which confirms the initial proposal of Bekenstein that the area spectrum is independent of the black hole parameters and the spacing is 8πlP2.

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Time evolution of information entropy for a stochastic system with double singularities driven by quasimonochromatic noise Guo Yong-Feng, Tan Jian-Guo 2012, 21 (12):  120501.  doi: 10.1088/1674-1056/21/12/120501 Abstract ( 0 )   PDF (1064KB) ([an error occurred while processing this directive])   This paper deals with the time evolution of information entropy for a stochastic system with double singularities driven by quasimonochromatic noise. The dimension of Fokker-Planck equation is reduced by the linear transformation. The exact expression of the time dependence of information entropy is obtained based on the definition of Shannon's information entropy. The relationships between the properties of dissipative parameters, system singularity strength parameter, quasimonochromatic noise, and their effects on information entropy are discussed.

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Stochastic resonance of a damped oscillator with frequency fluctuation driven by a periodic external force Zhang Ling-Ying, Jin Guo-Xiang, Cao Li, Wang Zhi-Yun 2012, 21 (12):  120502.  doi: 10.1088/1674-1056/21/12/120502 Abstract ( 0 )   PDF (205KB) ([an error occurred while processing this directive])   Considering a damped linear oscillator model subjected to a white noise with an inherent angular frequency and a periodic external driving force, we derive the analytic expression of the first moment of output response, and study the stochastic resonance phenomenon in a system. The results show that the output response of this system behaves as a simple harmonic vibration, of which the frequency is the same as the external driving frequency, and the variations of amplitude with the driving frequency and the inherent frequency present a bona fide stochastic resonance.

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Stability analysis of nonlinear Roesser-type two-dimensional systems via homogenous polynomial technique Zhang Tie-Yan, Zhao Yan, Xie Xiang-Peng 2012, 21 (12):  120503.  doi: 10.1088/1674-1056/21/12/120503 Abstract ( 0 )   PDF (551KB) ([an error occurred while processing this directive])   This paper is concerned with the problem of stability analysis of nonlinear Roesser-type two-dimensional (2D) systems. Firstly, the fuzzy modeling method for the usual one-dimensional (1D) systems is extended to the 2D case, then the underlying nonlinear 2D system could be represented by the 2D Takagi-Sugeno (TS) fuzzy model which is convenient to implement the stability analysis. Secondly, a new kind of fuzzy Lyapunov function which is homogeneous polynomially parameter-dependent on fuzzy membership functions is developed to conceive less conservative stability conditions for the TS Roesser-type 2D system. In the process of stability analysis, the obtained stability conditions approach to exactness in the sense of convergence by applying some novel relaxed techniques. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is also given to demonstrate the effectiveness of the proposed approach.

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Variational iteration method for solving the time-fractional diffusion equations in porous medium Wu Guo-Cheng 2012, 21 (12):  120504.  doi: 10.1088/1674-1056/21/12/120504 Abstract ( 0 )   PDF (90KB) ([an error occurred while processing this directive])   The variational iteration method is successfully extended to the case of solving fractional differential equations, and the Lagrange multiplier of the method is identified in a more accurate way. Some diffusion models with fractional derivatives are investigated analytically, and the results show the efficiency of the new Lagrange multiplier for fractional differential equations of arbitrary order.

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Adaptive fuzzy nonlinear inversion-based control for uncertain chaotic systems Liu Heng, Yu Hai-Jun, Xiang Wei 2012, 21 (12):  120505.  doi: 10.1088/1674-1056/21/12/120505 Abstract ( 0 )   PDF (1122KB) ([an error occurred while processing this directive])   This paper presents a robust output feedback control method for uncertain chaotic systems which comprises a nonlinear inversion-based controller with a fuzzy robust compensator. The proposed controller eliminates the unknown nonlinear function by using a fuzzy system, whose inputs are not the state variables but feedback error signals. The underlying stability analysis as well as parameter update law design are carried out by Lyapunov-based technique. The proposed method indicates that the nonlinear inversion-based control approach can also be used to uncertain chaotic systems. Theoretical results are illustrated through two simulation examples.

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Generalized projective synchronization of fractional-order complex networks with nonidentical nodes Liu Jin-Gui 2012, 21 (12):  120506.  doi: 10.1088/1674-1056/21/12/120506 Abstract ( 0 )   PDF (550KB) ([an error occurred while processing this directive])   This paper investigates the synchronization problem of fractional-order complex networks with nonidentical nodes. The generalized projective synchronization criterion of fractional-order complex networks with order 0 < q < 1 is obtained based on the stability theory of the fractional-order system. The control method which combines active control with pinning control is then suggested to obtain the controllers. Furthermore, the adaptive strategy is applied to tune the control gains and coupling strength. Corresponding numerical simulations are performed to verify and illustrate the theoretical results.

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Synchronization between a novel class of fractional-order and integer-order chaotic systems via sliding mode controller Chen Di-Yi, Zhang Run-Fan, Ma Xiao-Yi, Wang Juan 2012, 21 (12):  120507.  doi: 10.1088/1674-1056/21/12/120507 Abstract ( 0 )   PDF (509KB) ([an error occurred while processing this directive])   In order to figure out the dynamical behaviours of fractional-order chaotic system and its relation to integer-order chaotic system, in this paper we investigate the synchronization between a class of fractional-order chaotic systems and integer-order chaotic systems via sliding mode control method. Stability analysis is performed for the proposed method based on stability theorems in the fractional calculus. Moreover, three typical examples are carried out to show that the synchronization between fractional-order chaotic systems and integer-orders chaotic systems can be achieved. Our theoretical findings are supported by numerical simulation results. Finally, results from numerical computations and theoretical analysis are demonstrated to be a perfect bridge between fractional-order chaotic systems and integer-order chaotic systems.

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Adaptive generalized matrix projective lag synchronization between two different complex networks with non-identical nodes and different dimensions Dai Hao, Jia Li-Xin, Zhang Yan-Bin 2012, 21 (12):  120508.  doi: 10.1088/1674-1056/21/12/120508 Abstract ( 0 )   PDF (677KB) ([an error occurred while processing this directive])   The adaptive generalized matrix projective lag synchronization between two different complex networks with non-identical nodes and different dimensions is investigated in this paper. Based on Lyapunov stability theory and Barbalat's lemma, generalized matrix projective lag synchronization criteria is derived by using the adaptive control method. Furthermore, each network can be undirected or directed, connected or disconnected, and nodes in either network may have identical or different dynamics. The proposed strategy is applicable to almost all kinds of complex networks. In addition, numerical simulation results are presented to illustrate the effectiveness of this method, showing that the synchronization speed is sensitively influenced by the adaptive law strength, the network size, and the network topological structure.

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Wronskian and Grammian solutions for (3+1)-dimensional Jimbo–Miwa equation Su Peng-Peng, Tang Ya-Ning, Chen Yan-Na 2012, 21 (12):  120509.  doi: 10.1088/1674-1056/21/12/120509 Abstract ( 0 )   PDF (4412KB) ([an error occurred while processing this directive])   In this paper, based on the Hirota's bilinear method, the Wronskian and Grammian technique, as well as several properties of determinant, a broad set of sufficient conditions consisting of systems of linear partial differential equations are presented, which guarantees that the Wronskian determinant and the Grammian determinant solve the (3+1)-dimensional Jimbo-Miwa equation in the bilinear form, and then some special exact Wronskian and Grammian solutions are obtained by solving the differential conditions. At last, with the aid of Maple, some of these special exact solutions are shown graphically.

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Novel delay-distribution-dependent stability analysis for continuous-time recurrent neural networks with stochastic delay Wang Shen-Quan, Feng Jian, Zhao Qing 2012, 21 (12):  120701.  doi: 10.1088/1674-1056/21/12/120701 Abstract ( 0 )   PDF (117KB) ([an error occurred while processing this directive])   In this paper, the problem of delay-distribution-dependent stability is investigated for continuous-time recurrent neural networks (CRNNs) with stochastic delay. Different from the common assumptions on time delays, it is assumed that the probability distribution of the delay taking values in some intervals is known a priori. By making full use of the information concerning the probability distribution of the delay and by using a tighter bounding technique (reciprocally convex combination method), less conservative asymptotic mean-square stable sufficient conditions are derived in terms of linear matrix inequalities (LMIs). Two numerical examples show that our results are better than the existing ones.

ATOMIC AND MOLECULAR PHYSICS

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First-principles study of the electronic structure and optical properties of defect chalcopyrite CdGa2Te4 Jiao Zhao-Yong, Guo Yong-Liang, Zhang Xian-Zhou, Ma Shu-Hong 2012, 21 (12):  123101.  doi: 10.1088/1674-1056/21/12/123101 Abstract ( 0 )   PDF (741KB) ([an error occurred while processing this directive])   The electronic and optical properties of the defect chalcopyrite CdGa2Te4 compound are studied based on the first-principles calculations. The band structure and density of states are calculated to discuss the electronic properties and orbital hybridized properties of the compound. The optical properties, including complex dielectric function, absorption coefficient, refractive index, reflectivity, and loss function, and the origin of spectral peaks are analysed based on the electronic structures. The presented results exhibit isotropic behaviours in a low and a high energy range and an anisotropic behaviour in an intermediate energy range.

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Theoretical study of potential energy curves, spectroscopic constants, and radiative lifetimes of low-lying states in SeO molecule Li Rui, Lian Ke-Yan, Li Qi-Nan, Miao Feng-Juan, Yan Bing, Jin Ming-Xing 2012, 21 (12):  123102.  doi: 10.1088/1674-1056/21/12/123102 Abstract ( 0 )   PDF (648KB) ([an error occurred while processing this directive])   The low-lying potential energy curves of SeO molecule are computed by means of ab initio multireference configuration interaction technique, taking into account relativistic (scalar plus spin-orbit coupling) effects. The spectroscopic constants of Ω states for X3Σ-, a1Δ, b1Σ+, A3Π, A'3Δ, and A"3Σ+ states are obtained, and they are in good accordance with available experimental values. The Franck-Condon factors and transition dipole moments to the ground state are computed, and the natural radiative lifetimes of low-lying Ω states are theoretically obtained. Comparisons of the natural lifetimes of Ω states with previous experimental results and those of isovalent TeO molecule are made.

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Static electric dipole polarizability of lithium atom in Debye plasmas Ning Li-Na, Qi Yue-Ying 2012, 21 (12):  123201.  doi: 10.1088/1674-1056/21/12/123201 Abstract ( 0 )   PDF (296KB) ([an error occurred while processing this directive])   The static electric dipole polarizabilities of the ground state and n ≤ 3 excited states of lithium atom embedded in a weekly coupled plasma environment are investigated as a function of the plasma screening radium. The plasma screening of the Coulomb interaction is described by the Debye-Hückel potential and the interaction between the valence electron and the atomic core is described by a model potential. The electron energies and wave functions for both the bound and continuum states are calculated by solving the Schrödinger equation numerically using the symplectic integrator. The oscillator strengths, partial-wave, and total static dipole polarizabilities of the ground state and n ≤ 3 excited states of lithium atom are calculated. Comparison of present results with those of other authors, when available, is made. The results for the 2s ground state demonstrated that the oscillator strengths and the static dipole polatizabilities from np orbitals do not always increase or decrease with the plasma screening effect increasing, not like that for hydrogen-like ions, especially for 2s → 3p transition there is a zero value for both the oscillator strength and the static dipole polatizability for screening length D=10.3106a0, which is associated with the Cooper minima.

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Polarization and phase control of two-photon absorption in an isotropic molecular system Lu Chen-Hui, Zhang Hui, Zhang Shi-An, Sun Zhen-Rong 2012, 21 (12):  123202.  doi: 10.1088/1674-1056/21/12/123202 Abstract ( 0 )   PDF (130KB) ([an error occurred while processing this directive])   We theoretically and experimentally study the polarization and phase control of two-photon absorption in an isotropic molecular system. We theoretically show that the two-photon transition probability decreases when the laser polarization changes from linear through elliptical to circular, and the laser polarization does not affect the control efficiency of two-photon transition probability by shaping the spectral phase. These theoretical results are experimentally confirmed in coumarin 480. Furthermore, we propose that the combination of the laser polarization with the spectral phase modulation can further increase the control efficiency of the two-photon absorption.

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Chiral asymmetry of anti-symmetric coordinates studied by the Raman differential bond polarizability of S-phenylethylamine Shen Hong-Xia, Wu Guo-Zhen, Wang Pei-Jie 2012, 21 (12):  123301.  doi: 10.1088/1674-1056/21/12/123301 Abstract ( 0 )   PDF (455KB) ([an error occurred while processing this directive])   The Raman optical activity (ROA) study on S-phenylethylamine is presented by the intensity analyses via bond polarizability and differential bond polarizability. Ample information concerning the physical picture of this chiral system is obtained, and its ROA mechanism is constructed. Especially, we propose that the asymmetric modes and/or the off-diagonal elements of the electronic polarizability tensor are the potential keys to the exploration of ROA.

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Study of the H+HS reaction on a newly built potential energy surface using the quasi-classical trajectory method Bai Meng-Meng, Ge Mei-Hua, Yang Huan, Zheng Yu-Jun 2012, 21 (12):  123401.  doi: 10.1088/1674-1056/21/12/123401 Abstract ( 0 )   PDF (236KB) ([an error occurred while processing this directive])   The quasi-classical trajectory (QCT) method is used to study the H+HS reaction on a newly built potential energy surface (PES) of the triplet state of H2S (3A") in a collision energy range of 0-60 kcal/mol. Both scalar properties, such as the reaction probability and the integral cross section (ICS), and the vector properties, such as the angular distribution between the relative velocity vector of the reactant and that of the product, etc., are investigated using the QCT method. It is found that the ICSs obtained by the QCT method and the quantum mechanical (QM) method accord well with each other. In addition, the distribution for the product vibrational states is cold, while that for the product rotational states is hot for both reaction channels in the whole energy range studied here.

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Quasiclassical calculation of the chemical reaction Ba+C3H7Br→BaBr+C3H7 Jiang Yong-Chao, Li Gui-Xia, Shi Xiao-Feng, Huang Shu-Lai 2012, 21 (12):  123402.  doi: 10.1088/1674-1056/21/12/123402 Abstract ( 0 )   PDF (123KB) ([an error occurred while processing this directive])   The quasi-classical trajectory (QCT) method based on extended the London-Eyring-Polanyi-Sato potential energy surface is used to investigate the product vibrational distribution, angular distribution and angle resolved kinetic distribution of the reaction Ba+C3H7 Br→ BaBr+C3H7 at 2.58 kcal/mol. The calculated results show that the product BaBr vibrational distribution is quite hot, the vibrational population peaks are located at ν= 12, and the angular product distribution tends to backward scattering. The calculated angle resolved kinetic distribution shows that the kinetic distribution is obviously related to angle. The QCT results are always qualitatively acceptable and sometimes even quantitatively.

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Unnatural parity resonance states in positron-excited hydrogen scattering Ma Jia, Zhou Ya-Jun, Wang Yuan-Cheng 2012, 21 (12):  123403.  doi: 10.1088/1674-1056/21/12/123403 Abstract ( 0 )   PDF (94KB) ([an error occurred while processing this directive])   The coupled-channels optical method for positron scattering has been applied to investigate resonance states with unnatural parities in positron-excited hydrogen system. The positronium formation channels and continuum channel are included via a complex equivalent local potential. Resonance states with angular momenta L=1 to L=2 and parities (-1)L+1 are calculated. Resonance energies and widths are reported and compared with other theoretical calculations. We found that the opening positronium formation channels play an important role in forming nondipole Feshbach resonances.

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Structures, stabilities, and electronic properties of GaAs tubelike clusters and single-walled GaAs nanotubes Liu Li-Ren, Zhu Heng-Jiang, Liu Zhi-Feng, Wu Peng 2012, 21 (12):  123601.  doi: 10.1088/1674-1056/21/12/123601 Abstract ( 0 )   PDF (906KB) ([an error occurred while processing this directive])   The geometric structures, stabilities, and electronic properties of (GaAs)n tubelike clusters at up to n=120 and single-walled GaAs nanotubes (GaAsNTs) were studied by density functional theory (DFT) calculations. A family of stable tubelike structures with Ga-As alternating arrangement were observed when n≥8 and their structure units (four-membered rings and six-membered rings) obey the general developing formula. The average binding energies of the clusters show that the tubelike cluster with eight atoms in the cross section is the most stable cluster. The size-dependent properties of the frontier molecular orbital surfaces explain why the long and stable tubelike clusters can be obtained successfully. They also illustrate the reason why GaAsNTs can be synthesized experimentally. We also found that the single-walled GaAsNTs can be prepared by the proper assembly of tubelike clusters to form semiconductors with large bandgap.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Dual-band left-handed metamaterials fabricated by using tree-shaped fractal Xu He-Xiu, Wang Guang-Ming, Wang Jia-Fu, Yang Zi-Mu 2012, 21 (12):  124101.  doi: 10.1088/1674-1056/21/12/124101 Abstract ( 0 )   PDF (9193KB) ([an error occurred while processing this directive])   A method of fabricating dual-band left-handed metematerials (LHMs) is investigated numerically and experimentally by single-sided tree-like fractals. The resulting structure features multiband magnetic resonances and two electric resonances. By appropriately adjusting the dimensions, two left-handed (LH) bands with simultaneous negative permittivity and permeability are engineered and are validated by full-wave eigenmode analysis and measurement as well in the microwave frequency range. To study the multi-resonant mechanism in depth, the LHM is analysed from three different perspectives of field distribution analysis, circuit model analysis, and geometrical parameters evaluation. The derived formulae are consistent with all simulated results and resulting electromagnetic phenomena, indicating the effectiveness of the established theory. The method provides an alternative to the design of multi-band LHM and has the advantage of not requiring two individual resonant particles and electrically continuous wires, which in turn facilitates planar design and considerably simplifies the fabrication.

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Photoluminescence degradation mechanism of BaMgAl10O17:Eu2+ phosphor by vacuum ultraviolet irradiation Zhang Jia-Chi, Zhou Mei-Jiao, Wang Yu-Hua 2012, 21 (12):  124102.  doi: 10.1088/1674-1056/21/12/124102 Abstract ( 0 )   PDF (357KB) ([an error occurred while processing this directive])   A real high power vacuum ultraviolet light source is applied to the investigation on the vacuum ultraviolet irradiation degradation of BaMgAl10O17:Eu2+ phosphor. The degradations of emission intensity and colour quality of sample are clearly observed after irradiation. It reveals that the oxidation of Eu2+ during irradiation is partly responsible for the degradations. The excitation and absorption spectra show that some traps generated during irradiation have negative influence on the luminescence of sample and these traps have been identified as positively charged oxygen vacancies by positron annihilation. The investigations on host emission and decay curve further confirm that these oxygen vacancies are involved in the perturbation of energy transfer from host to Eu2+ and finally result in the degradation.

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Spin Hall effect of light beam in anisotropic metamaterials Tang Ming, Zhou Xin-Xing, Luo Hai-Lu, Wen Shuang-Chun 2012, 21 (12):  124201.  doi: 10.1088/1674-1056/21/12/124201 Abstract ( 0 )   PDF (3531KB) ([an error occurred while processing this directive])   We theoretically investigate a switchable spin Hall effect of light (SHEL) in reflection for three specific dispersion relations at an air-anisotropic metamaterial interface. The displacements of horizontal and vertical polarization components vary with the incident angle at different dispersion relations. The transverse displacements can be obtained with the relevant metamaterial whose refractive index can be arbitrarily tailed. The results of the SHEL in the metamaterial provide a new way for manipulating the transverse displacements of a specific polarization component.

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Lasing without inversion in a four-level diamond system Gao Qiang, Song Tong-Qiang 2012, 21 (12):  124202.  doi: 10.1088/1674-1056/21/12/124202 Abstract ( 0 )   PDF (825KB) ([an error occurred while processing this directive])   We study the lasing without inversion in a four-level diamond configuration in the case of incoherent pumping field within the framework of the bare-state basis. With the strong fields limit, we obtain the approximate steady-state solution, and discuss the dependence of population distribution and system gain on probe detuning and auxiliary field Rabi frequency.

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Compact temperature-insensitive modulator based on silicon microring assistant Mach–Zehnder interferometer Zhang Xue-Jian, Feng Xue, Zhang Deng-Ke, Huang Yi-Dong 2012, 21 (12):  124203.  doi: 10.1088/1674-1056/21/12/124203 Abstract ( 0 )   PDF (538KB) ([an error occurred while processing this directive])   On the silicon-on-insulator platform, an ultra compact temperature-insensitive modulator based on cascaded microring assistant Mach-Zehnder interferometer is proposed and demonstrated with numerical simulation. According to the calculated results, the tolerated variation of ambient temperature can be as high as 134℃ while the footprint of such silicon modulator is only 340 μm2.

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Harmonic and attosecond pulse enhancement in the presence of noise Feng Li-Qiang, Chu Tian-Shu 2012, 21 (12):  124204.  doi: 10.1088/1674-1056/21/12/124204 Abstract ( 0 )   PDF (2351KB) ([an error occurred while processing this directive])   In this paper, we theoretically investigate the effect of noise on the photoionization, the generations of the high-order harmonic and the attosecond pulse irradiated from a model He+ ion. It shows that by properly adding the noise fields, such as the Gaussian white noise, the random light or the colour noise, both the ionization probabilities (IPs) and the harmonic yields can be enhanced by several orders of magnitude. Further, by tuning the noise intensity, a stochastic resonancelike curve is observed, showing the existence of an optimal noise in the ionization enhancement process. Finally, by superposing a properly selected harmonic, an intense attosecond pulse with a duration of 67 as is directly generated.

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Infrared emissivities of Mn, Co co-doped ZnO powders Yao Yin-Hua, Cao Quan-Xi 2012, 21 (12):  124205.  doi: 10.1088/1674-1056/21/12/124205 Abstract ( 0 )   PDF (6093KB) ([an error occurred while processing this directive])   Infrared emissivities of Zn0.99-xMn0.01CoxO (x=0.00, 0.01, 0.03, 0.05) powders synthesized at different calcination temperatures by solid-state reaction are investigated. Their phases, morphologies, UV absorption spectra, and infrared emissivities are studied by XRD, SEM, UV spectrophotometer, and IR-2 Dual-Band Infrared Emissometer in a range of 8 μm-14 μm. Doped ZnO is still of wurtzite structure, and no peaks of other phases originating from impurities are detected. The optical band-gap decreases as the Co content and calcination temperature ascend, and of which the smallest optical band-gap is 2.19 eV. The lowest infrared emissivity, 0.754, is observed in Zn0.98Mn0.01Co0.01O with the increase in Co concentration. The infrared emissivity experiences fluctuations with calcination temperature going up, and its minimum value is 0.762 at 1100℃.

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Polarization properties in prism laser gyro with mechanical dither bias Yao Cheng-Kang, Zeng Xiao-Dong, Cao Chang-Qing 2012, 21 (12):  124206.  doi: 10.1088/1674-1056/21/12/124206 Abstract ( 0 )   PDF (1381KB) ([an error occurred while processing this directive])   Specially for the phenomenon that amplitude of output voltage signal is modulated by dither bias in the laser gyros consisting of totally reflecting prisms, theoretical analysis and experimental research on the polarization properties of output light in gyro are carried out. Taking the effect of stress birefringence of prism into account, analytical formula of output light intensity in gyro and the relationship between polarization parameter and the amplitude modulation of the output signal are obtained and discussed. For the first time, the polarized power value of output light is adopted as a basis to estimate the output signal amplitude fading extent of laser gyros. Experimental results demonstrate that when the value of polarized power of output light is below 25.5% of that in ideal static case, the standard error is over 0.0337 dBm, and the displacement extent of prism is higher than 53% of radius of the beam waist in gyro cavity, the amplitude modulation extent of gyro output signal can reach up to 16%, which badly influences measurement accuracy of laser gyro. Using this polarized power detecting measurement method can make gyro repaired in its fabricating process immediately, improve the testing and producing efficiency and shorten the product development cycle.

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Research on reliable acoustic path: Physical properties and a source localization method Duan Rui, Yang Kun-De, Ma Yuan-Liang, Lei Bo 2012, 21 (12):  124301.  doi: 10.1088/1674-1056/21/12/124301 Abstract ( 0 )   PDF (6946KB) ([an error occurred while processing this directive])   The physical properties of the reliable acoustic path (RAP) are analysed and subsequently a weighted-subspace-fitting matched field (WSF-MF) method for passive localization is presented by exploiting the properties of the RAP environment. The RAP is an important acoustic duct in the deep ocean, which occurs when the receiver is placed near bottom where the sound velocity exceeds the maximum sound velocity in the vicinity of the surface. It is found that in the RAP environment the transmission loss is rather low and no blind zone of surveillance exists in a medium range. The ray theory is used to explain these phenomena. Furthermore, the analysis of the arrival structures shows that the source localization method based on arrival angle is feasible in this environment. However, the conventional methods suffer from the complicated and inaccurate estimation of the arrival angle. In this paper, a straightforward WSF-MF method is derived to exploit the information about the arrival angles indirectly. The method is to minimize the distance between the signal subspace and the spanned space by the array manifold in a finite range-depth space rather than the arrival-angle space. Simulations are performed to demonstrate the features of the method, and the results are explained by the arrival structures in the RAP environment.

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Statistical model for combustion of high-metal magnesium-based hydro-reactive fuel Hu Jian-Xin, Han Chao, Xia Zhi-Xun, Huang Li-Ya, Huang Xu 2012, 21 (12):  124501.  doi: 10.1088/1674-1056/21/12/124501 Abstract ( 0 )   PDF (6001KB) ([an error occurred while processing this directive])   We investigate experimentally and analytically the combustion behavior of a high-metal magnesium-based hydro-reactive fuel under high temperature gaseous atmosphere. The fuel studied in this paper contains 73% magnesium powders. An experimental system is designed and experiments are carried out in both argon and water vapor atmospheres. It is found that the burning surface temperature of the fuel is higher in water vapor than that in argon and both of them are higher than the melting point of magnesium, which indicates the molten state of magnesium particles in the burning surface of the fuel. Based on physical considerations and experimental results a mathematical one-dimensional model is formulated to describe the combustion behavior of the high-metal magnesium-based hydro-reactive fuel. The model enables the evaluation of the burning surface temperature, the burning rate and the flame standoff distance each as a function of chamber pressure and water vapor concentration. The results predicted by the model show that the burning rate and the surface temperature increase when the chamber pressure and the water vapor concentration increase, which are in agreement with the observed experimental trends.

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Parameter design of a liquid-filled sloshing system Zhong Shun, Chen Yu-Shu 2012, 21 (12):  124701.  doi: 10.1088/1674-1056/21/12/124701 Abstract ( 0 )   PDF (583KB) ([an error occurred while processing this directive])   The nonlinear governing equations of the liquid sloshing modals in cylindrical storage tank are established. Through analytical analysis, the analytical expressions of the solutions of this kind of system are obtained. With different parameters, the dynamical behaviours of the solutions are different from the trivial ones. To prevent system instability, two selection principles that the stiffness equations are positive-definite and the nonlinear terms of the system are not regenerative elements are given. Meanwhile, numerical simulations are also given, which confirm the analytical results.

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Experimental investigations of detonation initiation by hot jets in supersonic premixed flows Han Xu, Zhou Jin, Lin Zhi-Yong 2012, 21 (12):  124702.  doi: 10.1088/1674-1056/21/12/124702 Abstract ( 0 )   PDF (1492KB) ([an error occurred while processing this directive])   A new method to initiate and sustain the detonation in supersonic flow is investigated. The reaction activity of coming flow may influence the result of detonation initiation. When a hot jet initiates a detonation wave successfully, there may exist two types of detonations. If the detonation velocity is greater than the velocity of coming flow, there will be a normal detonation here. Because of the influence of boundary layer separation, the upstream detonation velocity is much greater than the Chapman-Jouguet (CJ) detonation velocity. On the other hand, if the detonation velocity is less than the velocity of coming flow, an oblique detonation wave (ODW) will form. The ODW needs a continuous hot jet to sustain itself. If the pressure of jet is lower than a certain value, the ODW will decouple. In contrast the normal detonation wave can sustain itself without the hot jet.

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Multi-relaxation-time lattice Boltzmann front tracking method for two-phase flow with surface tension Xie Hai-Qiong, Zeng Zhong, Zhang Liang-Qi, Liang Gong-You, Hiroshi Mizuseki, Yoshiyuki Kawazoe 2012, 21 (12):  124703.  doi: 10.1088/1674-1056/21/12/124703 Abstract ( 0 )   PDF (265KB) ([an error occurred while processing this directive])   In this paper, an improved incompressible multi-relaxation-time lattice Boltzmann-front tracking approach is proposed to simulate two-phase flow with sharp interface, where the surface tension is implemented. The lattice Boltzmann method is used to simulate the incompressible flow with a stationary Eulerian grid, an additional moving Lagrangian grid is adopted to track explicitly the motion of the interface, and an indicator function is introduced to update accurately the fluid properties. The interface is represented by using a four-order Lagrange polynomial through fitting a set of discrete marker points, and then the surface tension is directly computed by using the normal vector and curvature of the interface. Two benchmark problems, including the Laplace's law for a stationary bubble and the dispersion relation of the capillary wave between two fluids are conducted for validation. Excellent agreement is obtained between the numerical simulations and the theoretical results in the two cases.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Fusion flame spreading in depth with deuterium–tritium plane fuel density profile for plasma block ignition B. Malekynia, S. S. Razavipour 2012, 21 (12):  125201.  doi: 10.1088/1674-1056/21/12/125201 Abstract ( 0 )   PDF (180KB) ([an error occurred while processing this directive])   The solid state fuel ignition was given by Chu and Bobin according to the hydrodynamic theory at x=0 qualitatively. A high threshold energy flux density, i.e., E*=4.3×1012 J/m2, has been reached. Recently, fast ignition by employing clean petawatt-picosecond laser pulses was performed. The anomalous phenomena were observed to be based on suppression of prepulses. The accelerated plasma block was used to ignite deuterium-tritium fuel at solid state density. The detailed analysis of the thermonuclear wave propagation was investigated. Also the fusion conditions at x≠0 layers were clarified by exactly solving hydrodynamic equations for plasma block ignition. In this paper, the applied physical mechanisms are determined for, such as, nonlinear force laser driven plasma blocks, thermonuclear reaction, heat transfer, electron-ion equilibration, stopping power of alpha particles, bremsstrahlung, expansion, density dependence, and fluid dynamics. New ignition conditions may be obtained by using temperature equations, including the density profile that is obtained by continuity equation and expansion velocity. The density is only a function of x and independent of time. The ignition energy flux density, Et*, for the x≠0 layers is 1.95×1012 J/m2. Thus threshold ignition energy in comparison with that at x=0 layers would be reduced to less than 50 percent.

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Electron temperature diagnostics of aluminium plasma in z-pinch experiment on “QiangGuang-1” facility Li Mo, Wu Jian, Wang Liang-Ping, Wu Gang, Han Juan-Juan, Guo Ning, Qiu Meng-Tong 2012, 21 (12):  125202.  doi: 10.1088/1674-1056/21/12/125202 Abstract ( 0 )   PDF (642KB) ([an error occurred while processing this directive])   Two curved crystal spectrometers are setup on "QiangGuang-1" generator to measure the z-pinch plasma spectra emitted from planar aluminum wire array loads. The Kodak Biomax-MS film and IRD AXUVHS5# array are employed to record time-integrated and time-resolved free-bound radiation respectively. The photon energy recorded by each detector is ascertained by using the L-shell lines of molybdenum plasma. Based on the exponential relation between the continuum power and photon energies, the aluminum plasma electron temperatures are measured. For the time-integrated diagnosis, several "bright spots" indicate electron temperatures between (450 eV～520 eV)± 35%. And for the time-resolved ones, the result shows that the electron temperature reaches about 800 eV±30% at peak power. The system satisfies the demand of z-pinch plasma electron temperature diagnosis on ～1 MA facility.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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The response of temperature and hydrostatic pressure of zinc-blende GaxIn1-xAs semiconducting alloys A. R. Degheidy, E. B. Elkenany 2012, 21 (12):  126101.  doi: 10.1088/1674-1056/21/12/126101 Abstract ( 0 )   PDF (330KB) ([an error occurred while processing this directive])   The electronic band structure of GaxIn1-xAs alloy is calculated by the local empirical pseudo-potential method including the effective disorder potential in the virtual crystal approximation. The compositional effect of the electronic energy band structure of this alloy is studied with composition x ranging from 0 to 1. Various physical quantities such as band gaps, bowing parameters, refractive indices, and high frequency dielectric constants of the considered alloys with different Ga concentrations are calculated. The effects of both temperature and hydrostatic pressure on the calculated quantities are studied. The obtained results are found o be in good agreement with the available experimental and published data.

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Sodium beta-alumina thin films as gate dielectrics for AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors Tian Ben-Lang, Chen Chao, Li Yan-Rong, Zhang Wan-Li, Liu Xing-Zhao 2012, 21 (12):  126102.  doi: 10.1088/1674-1056/21/12/126102 Abstract ( 0 )   PDF (411KB) ([an error occurred while processing this directive])   Sodium beta-alumina (SBA) is deposited on AlGaN/GaN by using co-deposition process with using sodium and Al2O3 as the precursors. X-ray diffraction (XRD) spectrum reveals that the deposited thin film is amorphous. The binding energy and composition of the deposited thin film, obtained from the X-ray photoelectron spectroscopy (XPS) measurement are consistent with those of SBA. The dielectric constant of the SBA thin film is about 50. Each of the capacitance-voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and AlGaN. The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor (MISHEMT) is measured to be (3.5～9.5)×1010 cm-2·eV-1 by the conductance method. The fixed charge density of SBA dielectric is on the order of 2.7×1012 cm-2. Compared with the AlGaN/GaN metal-semiconductor heterostructure high-electron-mobility transistor (MESHEMT), the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively. However, the threshold voltage of the AlGaN/GaN MISHEMT with using SBA as gate dielectric shifts positively from -5.5 V to -3.5 V. From XPS results, the surface valence-band maximum (VBM-EF) of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition. The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum (VBM-EF), the reduction of interface traps and the effects of sodium ions, and/or the fixed charges in SBA on the two-dimensional electron gas (2DEG).

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First-principles investigation on diffusion behaviours of H isotopes: From W(110) surface into bulk and in bulk W Liu Yue-Lin, Lu Wei, Gao An-Yuan, Gui Li-Jiang, Zhang Ying 2012, 21 (12):  126103.  doi: 10.1088/1674-1056/21/12/126103 Abstract ( 0 )   PDF (215KB) ([an error occurred while processing this directive])   The diffusion behaviours of hydrogen (H), deuterium (D), and tritium (T) from W(110) surface into bulk and in bulk W are investigated using a first-principles calculations combined with simplified models. The diffusion energy barrier is shown to be 1.87 eV from W(110) surface to the subsurface, along with a much reduced barrier of 0.06 eV for the reverse diffusion process. After H enters into the bulk, its diffusion energy barrier with quantum correction is 0.19 eV. In terms of the diffusion theory presented by Wert and Zener, the diffusion pre-exponential factor of H is calculated to be 1.57×10-7 m2·s-1, and it is quantitatively in agreement with experimental value of 4.1×10-7 m2·s-1. Subsequently, according to mass dependence (√1/m ) of H isotope effect, the diffusion pre-exponential factors of D and T are estimated to be 1.11×10-7 m2·s-1 and 0.91×10-7 m2·s-1, respectively.

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Experimental and theoretical analysis of package-on-package structure under three-point bending loading Jia Su, Wang Xi-Shu, Ren Huai-Hui 2012, 21 (12):  126201.  doi: 10.1088/1674-1056/21/12/126201 Abstract ( 0 )   PDF (4079KB) ([an error occurred while processing this directive])   High density package is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package (PoP) is a promising three-dimensional high-density packaging method that integrates chip scale package (CSP) in the top package and fine-pitch ball grid array (FBGA) in the bottom package. In this paper, in-situ scanning electron microscopy (SEM) observation is carried out to detect the deformation and damage of the PoP structure under three-point bending loading. The results indicate that the cracks occur in the die of the top package, then cause the crack deflection and bridging in the die attaching layer. Furthermore, the mechanical principles are used to analyse the cracking process of the PoP structure based on the multi-layer laminating hypothesis. And the theoretical analysis results are found to be in good agreement with the experimental results.

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Effects of wave propagation anisotropy on the wave focusing by negative refractive sonic crystal flat lenses S. Alagoz 2012, 21 (12):  126202.  doi: 10.1088/1674-1056/21/12/126202 Abstract ( 0 )   PDF (1195KB) ([an error occurred while processing this directive])   In this study, wave propagation anisotropy in a triangular lattice crystal structure and its associated waveform shaping in a crystal structure are investigated theoretically. A directional variation in wave velocity inside a crystal structure is shown to cause bending wave envelopes. The authors report that a triangular lattice sonic crystal possesses six numbers of a high symmetry direction, which leads to a wave convergence caused by wave velocity anisotropy inside the crystal. However, two of them are utilized mostly in wave focusing by an acoustic flat lens. Based on wave velocity anisotropy, the pseudo ideal imagining effect obtained in the second band of the flat lens is discussed.

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Tuning of band-gap of phononic crystals with initial confining pressure Feng Rong-Xin, Liu Kai-Xin 2012, 21 (12):  126301.  doi: 10.1088/1674-1056/21/12/126301 Abstract ( 0 )   PDF (592KB) ([an error occurred while processing this directive])   The mechanism of the shift of the band-gap in phononic crystal (PC) with different initial confining pressures is studied experimentally and numerically. The experimental results and numerical analysis simultaneously indicate that the confining pressure can efficiently tune the location in and the width of the band-gap. The present work provides a basis for tuning the band-gap of phononic crystal in engineering applications.

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Enhancing the thermal conductivity of polymer-assisted deposited Al2O3 film by nitrogen doping Huang Jiang, Zhang Yin, Pan Tai-Song, Zeng Bo, Hu Guo-Hua, Lin Yuan 2012, 21 (12):  126501.  doi: 10.1088/1674-1056/21/12/126501 Abstract ( 0 )   PDF (758KB) ([an error occurred while processing this directive])   Polymer-assisted deposition technique has been used to deposit Al2O3 and N-doped Al2O3 (AlON) thin films on Si(100) substrates. The chemical compositions, crystallinity, and thermal conductivity of the as-grown films have been characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and 3-omega method, respectively. Amorphous and polycrystalline Al2O3 and AlON thin films have been formed at 700 ℃ and 1000 ℃. The thermal conductivity results indicated that the effect of nitrogen doping on the thermal conductivity is determined by the competition of the increase of Al–N bonding and the suppression of crystallinity. A 67% enhancement in thermal conductivity has been achieved for the samples grown at 700 ℃, demonstrating that the nitrogen doping is an effective way to improve the thermal performance of polymer-assisted-deposited Al2O3 thin films at a relatively low growth temperature.

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Modeling effective viscosity reduction behaviour of solid suspensions Wei En-Bo, Ji Yan-Ju, Zhang Jun 2012, 21 (12):  126601.  doi: 10.1088/1674-1056/21/12/126601 Abstract ( 0 )   PDF (137KB) ([an error occurred while processing this directive])   Under a simple shearing flow, the effective viscosity of solid suspensions can be reduced by controlling the inclusion particle size or the number of inclusion particles in a unit volume. Based on the Stokes equation, the transformation field method is used to model the reduction behaviour of effective viscosity of solid suspensions theoretically by enlarging the particle size at a given high concentration of particles. With a lot of samples of random cubic particles in a unit cell, our statistical results show that at the same higher concentration, the effective viscosity of solid suspensions can be reduced by increasing the particle size or reducing the number of inclusion particles in a unit volume. This work discloses the viscosity reduction mechanism of increasing particle size, which is observed experimentally.

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A facile way to fabricate aluminum sheet with superhydrophobic and self-cleaning properties Yang Zhou, Wu Yi-Zhi, Ye Yi-Fan, Gong Mao-Gang, Xu Xiao-Liang 2012, 21 (12):  126801.  doi: 10.1088/1674-1056/21/12/126801 Abstract ( 0 )   PDF (9417KB) ([an error occurred while processing this directive])   A superhydrophobic aluminum sheet is fabricated via hot water immersing process and subsequently surface modification with heptadecafluorodecyltrimethoxy-silane (HTMS). As revealed by the scan electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectrophotometer (FTIR) results, a rough pseudoboehmite film is formed on the aluminum sheet, and HTMS molecules are grafted on the film surface successfully. These two factors make the treated aluminum sheet present superhydrophobicity with a water contact angle larger than 160° and sliding angle less than 5°, and possess self-cleaning property. Furthermore, the flexible superhydrophobic aluminum sheet could be pasted to cylinder surface without destroying its superhydrophobicity. At the end, the effect of hot water treatment time on superhydrophobicity is investigated.

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Molecular dynamics study of mechanical characteristics of Ni/Cu bilayer using nanoindentation Muhammad Imran, Fayyaz Hussain, Muhammad Rashid, S. A. Ahmad 2012, 21 (12):  126802.  doi: 10.1088/1674-1056/21/12/126802 Abstract ( 0 )   PDF (2694KB) ([an error occurred while processing this directive])   In the present work, a three-dimensional molecular dynamics simulation is carried out to perform the nanoindentation experiment on Ni single crystal. The substrate indenter system is modeled using hybrid interatomic potentials including many-body potential embedded atom method (EAM), and two-body morse potential. To simulate the indentation process, spherical indenter (diameter=80 Å, 1 Å=0.1 nm) is chosen. The results show that mechanical behaviour of a monolithic Ni is not affected by crystalline orientation. To elucidate the effect of heterogeneous interface, three bilayer interface systems are constructed, namely Ni(100)/Cu(111), Ni(110)/Cu(111), and Ni(111)/Cu(111). The simulations along these systems clearly describe that mechanical behaviour directly depends on the lattice mismatch. The interface with smaller mismatch between the specified crystal planes is proved to be harder and vice versa. To describe the relationship between film thickness and interface effect, we choose various values of film thickness ranging from 20 Å to 50 Å to perform nanoindentation experiment. It is observed that the interface is significant only for the relatively small thickness of film and the separation between interface and the indenter tip. It is shown that with the increase in film thickness, the mechanical behaviour of film shifts more toward that of monolithic material.

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A density-functional theory investigation on disorption of O2 on Sn(111) and its comparison with initial oxidation on the X(111) (X=Si, Ge, Sn, Pb) surfaces Hu Zi-Yu, Wan Ping-Yu, Hou Zhi-Ling, Shao Xiao-Hong 2012, 21 (12):  126803.  doi: 10.1088/1674-1056/21/12/126803 Abstract ( 0 )   PDF (2881KB) ([an error occurred while processing this directive])   The first-principles calculations are performed to investigate the adsorption of O2 molecules on an Sn(111) 2×2 surface. The chemisorbed adsorption precursor states for O2 are identified to be along the parallel and vertical channels, and the surface reconstructions of Sn(111) induced by oxygen adsorption are studied. Based on this, the adsorption behaviours of O2 on X(111) (X=Si, Ge, Sn, Pb) surfaces are analysed, and the most stable adsorption channels of O2 on X(111) (X=Si, Ge, Sn, Pb) are identified. The surface reconstructions and electron distributions along the most stable adsorption channels are discussed and compared. The results show that the O2 adsorption ability declines gradually and the amount of charge transferred decreases with the enhancement of metallicity.

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Influence of double AlN buffer layers on the qualities of GaN films prepared by metal–organic chemical vapour deposition Lin Zhi-Yu, Zhang Jin-Cheng, Zhou Hao, Li Xiao-Gang, Meng Fan-Na, Zhang Lin-Xia, Ai Shan, Xu Sheng-Rui, Zhao Yi, Hao Yue 2012, 21 (12):  126804.  doi: 10.1088/1674-1056/21/12/126804 Abstract ( 0 )   PDF (3284KB) ([an error occurred while processing this directive])   In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire (0001) substrate with double AlN buffer layers. The buffer layer consists of a low-temperature (LT) AlN layer and a high-temperature (HT) AlN layer that are grown at 600℃ and 1000℃, respectively. It is observed that the thickness of LT-AlN layer influences the quality of GaN thin film extremely, and that the optimized 4.25-min-LT-AlN layer minimizes the dislocation density of GaN thin film. The reason for the improved properties is discussed in this paper.

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

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Study of electronic and magnetic properties of MnS layers R. Masrour, E. K. Hlil, M. Hamedoun, A. Benyoussef, O. Mounkachi 2012, 21 (12):  127101.  doi: 10.1088/1674-1056/21/12/127101 Abstract ( 0 )   PDF (345KB) ([an error occurred while processing this directive])   Self-consistent ab initio calculations, based on density functional theory (DFT) and using full potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnS layers. Polarized spin and spin-orbit coupling are included in the calculations within the framework of the antiferromagnetic state between two adjacent Mn layers. Magnetic moments considered to lie along axes are computed. Obtained data from ab initio calculations are used as input data for the high temperature series expansion (HTSE) calculations to compute other magnetic parameters. The zero-field high temperature static susceptibility series of the spin-4.39 nearest-neighbour Heisenberg model on centred face cubic (FCC) and lattices is thoroughly analysed by a power series coherent anomaly method (CAM). The exchange interactions between the magnetic atoms, the Néel temperature, and the critical exponent associated with the magnetic susceptibility are obtained for MnS layer.

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Thermodynamics and elastic properties of Ta from first-principles calculations Li Qiang, Huang Duo-Hui, Cao Qi-Long, Wang Fan-Hou, Cai Ling-Cang, Zhang Xiu-Lu, Jing Fu-Qian 2012, 21 (12):  127102.  doi: 10.1088/1674-1056/21/12/127102 Abstract ( 0 )   PDF (287KB) ([an error occurred while processing this directive])   Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties of Ta, including phonon density of states (DOS), equation of state, linear thermal expansion coefficient, entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young's modulus, microhardness, and sound velocity, are studied using the first-principles projector-augmented wave method. The vibrational contribution to Helmholtz free energy is evaluated from the first-principles phonon DOS and Debye model. The thermal electronic contribution to Helmholtz free energy is estimated from the integration over the electronic DOS. By comparing the experimental results with the calculation results from the first-principles and Debye model, it is found that the thermodynamic properties of Ta are depicted well by the first-principles. The elastic properties of Ta from the first-principles are consistent with the available experimental data.

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First-principles calculations on the elastic and thermodynamic properties of NbN Ren Da-Hua, Cheng Xin-Lu 2012, 21 (12):  127103.  doi: 10.1088/1674-1056/21/12/127103 Abstract ( 0 )   PDF (253KB) ([an error occurred while processing this directive])   The elastic and thermodynamic properties of NbN at high pressures and high temperatures are investigated by the plane-wave pseudopotential density functional theory (DFT). The generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) method is used to describe the exchange-correlation energy in the present work. The calculated equilibrium lattice constant a0, bulk modulus B0, and the pressure derivative of bulk modulus B0' of NbN with rocksalt structure are in good agreement with numerous experimental and theoretical data. The elastic properties over a range of pressures from 0 to 80.4 GPa are obtained. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. It is indicated that NbN is highly anisotropic in both longitudinal and shear-wave velocities. According to the quasi-harmonic Debye model, in which the phononic effect is considered, the relations of (V-V0)/V0 to the temperature and the pressure, and the relations of the heat capacity CV and the thermal expansion coefficient α to temperature are discussed in a pressure range from 0 to 80.4 GPa and a temperature range from 0 to 2500 K. At low temperature, CV is proportional to T3 and tends to the Dulong-Petit limit at higher temperature. We predict that the thermal expansion coefficient α of NbN is about 4.20×10-6/K at 300 K and 0 GPa.

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Electronic structures and optical properties of Zn-doped β-Ga2O3 with different doping sites Li Chao, Yan Jin-Liang, Zhang Li-Ying, Zhao Gang 2012, 21 (12):  127104.  doi: 10.1088/1674-1056/21/12/127104 Abstract ( 0 )   PDF (1057KB) ([an error occurred while processing this directive])   The electronic structures and optical properties of intrinsic β-Ga2O3 and Zn-doped β-Ga2O3 are investigated by first-principles calculations. The analysis about the thermal stability shows that Zn-doped β-Ga2O3 remains stable. The Zn doping does not change the basic electronic structure of β-Ga2O3, but only generates an empty energy level above the maximum of valence band, which is shallow enough to make the Zn-doped β-Ga2O3 a typical p-type semiconductor. Because of Zn doping, absorption and reflectivity are enhanced in the near infrared region. The higher absorption and reflectivity of ZnGa(2) than those of ZnGa(1) are due to more empty energy states of ZnGa(2) than those of ZnGa(1) near Ef in the near infrared region.

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Optical design of adjustable light emitting diode for different lighting requirements Lu Jia-Ning, Yu Jie, Tong Yu-Zhen, Zhang Guo-Yi 2012, 21 (12):  127105.  doi: 10.1088/1674-1056/21/12/127105 Abstract ( 0 )   PDF (1837KB) ([an error occurred while processing this directive])   Light emitting diode (LED) sources have been widely used for illumination. Optical design, especially freedom compact lens design is necessary to make LED sources applied in lighting industry, such as large-range interior lighting and small-range condensed lighting. For different lighting requirements, the size of target planes should be variable. In our paper we provide a method to design freedom lens according to the energy conservation law and Snell law through establishing energy mapping between the luminous flux emitted by a Lambertian LED source and a certain area of target plane. The algorithm of our design can easily change the radius of each circular target plane, which makes the size of target plane adjustable. Ray-tracing software Tracepro is used to validate the illuminance maps and polar-distribution maps. We design lenses for different sizes of target planes to meet specific lighting requirements.

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Analysis on electrical characteristics of high-voltage GaN-based light-emitting diodes Guo Wei-Ling, Yan Wei-Wei, Zhu Yan-Xu, Liu Jian-Peng, Ding Yan, Cui De-Sheng, Wu Guo-Qing 2012, 21 (12):  127201.  doi: 10.1088/1674-1056/21/12/127201 Abstract ( 0 )   PDF (462KB) ([an error occurred while processing this directive])   In order to investigate their electrical characteristics, high-voltage light-emitting-diodes (HV-LEDs) each containing four cells in series are fabricated. The electrical parameters including varying voltage and parasitic effect are studied. It is shown that the ideality factors (IFs) of the HV-LEDs with different numbers of cells are 1.6, 3.4, 4.7, and 6.4. IF increases linearly with the number of cells increasing. Moreover, the performance of the HV-LED with failure cells is examined. The analysis indicates that the failure cell has a parallel resistance which induces the leakage of the failure cell. The series resistance of failure cell is 76.8 Ω, while that of normal cell is 21.3 Ω. The scanning electron microscope (SEM) image indicates that different metal layers do not contact well. It is hard to deposit the metal layers in the deep isolation trenches. The fabrication process of HV-LED needs to be optimized.

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The quantum Hall's effect: A quantum electrodynamic phenomenon A. I. Arbab 2012, 21 (12):  127301.  doi: 10.1088/1674-1056/21/12/127301 Abstract ( 0 )   PDF (109KB) ([an error occurred while processing this directive])   We have applied Maxwell's equations to study the physics of quantum Hall's effect. The electromagnetic properties of this system are obtained. The Hall's voltage, VH=2πh2ns/em, where ns is the electron number density, for a 2-dimensional system, and h=2πh is the Planck's constant, is found to coincide with the voltage drop across the quantum capacitor. Consideration of the cyclotronic motion of electrons is found to give rise to Hall's resistance. Ohmic resistances in the horizontal and vertical directions have been found to exist before equilibrium state is reached. At a fundamental level, the Hall's effect is found to be equivalent to a resonant LCR circuit with LH=2πm/e2ns and CH=me2/2πh2ns satisfying resonance condition with resonant frequency equals to the inverse of the scattering (relaxation) time, τs. The Hall's resistance is found to be RH=√LH/CH. The Hall's resistance may be connected with the impedance that the electron wave experiences when propagates in the 2-dimensional gas.

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A wideband metamaterial absorber based on magnetic resonator loaded with lumped resistors Cheng Yong-Zhi, Gong Rong-Zhou, Nie Yan, Wang Xian 2012, 21 (12):  127801.  doi: 10.1088/1674-1056/21/12/127801 Abstract ( 0 )   PDF (4592KB) ([an error occurred while processing this directive])   A wideband metamaterial absorber (MA) based on a magnetic resonator loaded with lumped resistors is presented. It is composed of a one-dimensional periodic array of double U shape structured magnetic resonators loaded with lumped resistors, dielectric substrate, and metal plate. We simulated, fabricated, measured, and analyzed the MA. The experimental results show that the reflectance (S11) is below -10 dB at normal incidence in the frequency range of 7.7 GHz-18 GHz, and the peak value is about -20 dB. Simulated power loss density distributions indicate that wideband absorption of the MA is mainly attributable to the lumped resistors in the magnetic resonator. Further investigations indicate that the distance between two unit cells along the magnetic field direction significantly influences the performance of the MA.

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Difference in effect of temperature on absorption and Raman spectra between all-trans-β-carotene and all-trans-retinol Qu Guan-Nan, Li Shuo, Sun Cheng-Lin, Liu Tian-Yuan, Wu Yong-Ling, Sun Shang, Shan Xiao-Ning, Men Zhi-Wei, Chen Wei, Li Zuo-Wei, Gao Shu-Qin 2012, 21 (12):  127802.  doi: 10.1088/1674-1056/21/12/127802 Abstract ( 0 )   PDF (551KB) ([an error occurred while processing this directive])   Temperature dependences (81 °C-18 °C) of visible absorption and Raman spectra of all-trans-β -carotene and all-trans-retinol extremely diluted in dimethyl sulfoxide are investigated in order to clarify temperature effects on different polyenes. Their absorption spectra are identified to be redshifted with temperature decreasing. Moreover, all-trans-β -carotene is more sensitive to temperature due to the presence of a longer length of conjugated system. The characteristic energy responsible for the conformational changes in all-trans-β -carotene is smaller than that in all-trans-retinol. Both of the Raman scattering cross sections increase with temperature decreasing. The results are explained with electron-phonon coupling theory and coherent weakly damped electron-lattice vibrations model.

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Calibration-free wavelength modulation spectroscopy for gas concentration measurements under low-absorbance conditions Che Lu, Ding Yan-Jun, Peng Zhi-Min, Li Xiao-Hang 2012, 21 (12):  127803.  doi: 10.1088/1674-1056/21/12/127803 Abstract ( 0 )   PDF (2631KB) ([an error occurred while processing this directive])   We derive the expressions of the first and second harmonic signals on the basis of absorption spectral and the lock-in theories, and determine the gas concentration according to the ratio of second and first harmonic signals. It is found that the X and Y components of the harmonic signals are influenced by the phase shift between the detection and reference signal, and the phase shift can be any value in a range from 0 to 2π, which is different from the results obtained previously. Meanwhile, an additional item caused by the residual amplitude modulation will make a great contribution to the second harmonic signal, and may not be neglected under low absorbance conditions. Theoretical analysis indicates that subtracting back-ground signal from the second harmonic signal can remove the influence of this item, and can improve the measurement accuracy of gas concentration. On this basis, we select the transition of CO2 at 6527.64 cm-1 to analyse the approximation errors during the derivation by numerical simulation and then measure the CO2 concentration under low absorbance conditions, with absorbance varying from 1‰ to 6‰.

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Ca2BO3Cl:Ce3+, Tb3+: A novel tunable emitting phosphor for white light-emitting diode Li Pan-Lai, Wang Yong-Sheng, Zhao Su-Ling, Zhang Fu-Jun, Xu Zheng 2012, 21 (12):  127804.  doi: 10.1088/1674-1056/21/12/127804 Abstract ( 0 )   PDF (1721KB) ([an error occurred while processing this directive])   Ca2BO3Cl:Ce3+, Ca2BO3Cl:Tb3+, and Ca2BO3Cl:Ce3+, Tb3+ phosphors are synthesized by a high temperature solid-state reaction. The emission intensity of Ce3+ or Tb3+ in Ca2BO3Cl is influenced by the Ce3+ or Tb3+ doping content, and the optimum concentrations of Ce3+ and Tb3+ are 0.03 mol and 0.05 mol, respectively. The concentration quenching effect of Ce3+ or Tb3+ in Ca2BO3Cl occurs, and the concentration quenching mechanism is d-d interaction for either Ce3+ or Tb3+. The Ca2BO3Cl:Ce3+, Tb3+ can produce colour emission from blue to green by properly tuning the relative ratio between Ce3+ and Tb3+, and the emission intensity of Tb3+ in Ca2BO3Cl can be enhanced by the energy transfer from Ce3+ to Tb3+. The results indicate that Ca2BO3Cl:Ce3+, Tb3+ may be a promising double emission phosphor for UV-based white light emitting diode.

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Soft magnetic properties of amorphous Fe52Co34Hf7B6Cu1 alloy treated by pulsed magnetic field and annealing Gu Yue, Chao Yue-Sheng, Zhang Yan-Hui 2012, 21 (12):  127805.  doi: 10.1088/1674-1056/21/12/127805 Abstract ( 0 )   PDF (4366KB) ([an error occurred while processing this directive])   The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cu1 alloy are studied. Amorphous Fe52Co34Hf7B6Cu1 alloys are first treated by pulsed magnetic field with a medium frequency, and then annealed at 100℃-400℃ for 30 min in vacuum. The rise in temperature during the treatment by pulsed magnetic field is measured by a non-contact infrared thermometer. The soft magnetic properties of specimens are measured by a vibrating sample magnetometer (VSM). The microstructure changes of specimens are observed by Mössbauer spectroscopy and transmission electron microscope (TEM). The results show the medium-frequency pulsating magnetic field will promote nanocrystallization of the amorphous alloy with lower temperature rise. The nanocrystalline phase is α-Fe(Co) with bcc crystal structure, and the grain size is about 10 nm. After vacuum annealing at 100℃ for 30 min, scattering nanocrystalline phases become more uniform, the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.

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Manipulated localized surface plasmon resonances in silver nanoshells coated with a spherical anisotropic layer Jiang Shu-Min, Wu Da-Jian, Cheng Ying, Liu Xiao-Jun 2012, 21 (12):  127806.  doi: 10.1088/1674-1056/21/12/127806 Abstract ( 0 )   PDF (3459KB) ([an error occurred while processing this directive])   The influences of the anisotropy of outer spherically anisotropic (SA) layer on the far-field spectra and near-field enhancements of the silver nanoshells are investigated by using a modified Mie scattering theory. It is found that with the increase of the anisotropic value of the SA layer, the dipole resonance wavelength of the silver nanoshell first increases and then decreases, while the local field factor (LFF) reduces. With the decrease of SA layer thickness, the dipole wavelength of the silver nanoshell shows a distinct blue-shift. When the SA layer becomes very thin, the modulations of the anisotropy of SA layer on the plasmon resonance energy and the near-field enhancement are weakened. We further find that the smaller anisotropic value of the SA layer is helpful for obtaining the larger near-field enhancement in the Ag nanoshell. The geometric average of the dielectric components of SA layer has a stronger effect on the plasmon resonance energy of the silver nanoshell than on the near-field enhancement.

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Charging dynamics of polymer due to electron irradiation: A simultaneous scattering-transport model and preliminary results Cao Meng, Wang Fang, Liu Jing, Zhang Hai-Bo 2012, 21 (12):  127901.  doi: 10.1088/1674-1056/21/12/127901 Abstract ( 0 )   PDF (464KB) ([an error occurred while processing this directive])   We present a novel numerical model and simulate preliminarily the charging process of polymer subjected to electron irradiation of several 10 keV. The model includes the simultaneous processes of electron scattering and ambipolar transport and the influence of a self-consistent electric field on the scattering distribution of electrons. The dynamic spatial distribution of charges is obtained and validated by existing experimental data. Our simulations show that excess negative charges are concentrated near the edge of the electron range. However, the formed region of high charge density may extend to the surface and bottom of a kapton sample, due to the effects of electric field on electron scattering and charge transport, respectively. Charge trapping is then demonstrated to significantly influence the charge motion. The charge distribution can be extended to the bottom as the trap density decreases. Charge accumulation is therefore balanced by the appearance and increase of leakage current. Accordingly, our model and numerical simulation provide a comprehensive insight into the charging dynamics of polymer irradiated by electrons in the complex space environment.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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The influence of SixNy interlayer on GaN film grown on Si(111) substrate Peng Dong-Sheng, Chen Zhi-Gang, Tan Cong-Cong 2012, 21 (12):  128101.  doi: 10.1088/1674-1056/21/12/128101 Abstract ( 0 )   PDF (1326KB) ([an error occurred while processing this directive])   A method to drastically reduce dislocation density in a GaN film grown on an Si(111) substrate is newly developed. In this method, the SixNy interlayer which is deposited on an AlN buffer layer in situ is introduced to grow the GaN film laterally. The crack-free GaN film with thickness over 1.7 micron is grown on an Si(111) substrate successfully. Synthesized GaN epilayer is characterized by X-ray diffraction (XRD), atomic force microscope (AFM), and Raman spectrum. The test results show that the GaN crystal reveals a wurtzite structure with the <0001> crystal orientation and the full width at half maximum of the X-ray diffraction curve in the (0002) plane is as low as 403 arcsec for the GaN film grown on the Si substrate with an SixNy interlayer. In addition, Raman scattering is used to study the stress in the sample. The results indicate that the SixNy interlayer can more effectively accommodate the strain energy. So the dislocation density can be reduced drastically, and the crystal quality of GaN film can be greatly improved by introducing SixNy interlayer.

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Field emissions of graphene films deposited on different substrates by CVD system Wang Xiao-Ping, Liu Xiao-Fei, Liu Xin-Xin, Wang Li-Jun, Yang Can, Jing Long-Wei, Li Song-Kun, Pan Xiu-Fang 2012, 21 (12):  128102.  doi: 10.1088/1674-1056/21/12/128102 Abstract ( 0 )   PDF (11618KB) ([an error occurred while processing this directive])   Graphene films are deposited on copper (Cu) and aluminum (Al) substrates, respectively, by using microwave plasma chemical vapour deposition technique. Furthermore, these graphene films are characterized by a field emission type scanning electron microscope (FE-SEM), Raman spectra, and field emission (FE) I-V measurements. It is found that the surface morphologies of the films deposited on Cu and Al substrates are different: the field emission property of graphene film deposited on Cu substrate is better than that on Al substrate, and the lowest turn-on field of 2.4 V/μm is obtained for graphene film deposited on Cu substrate. The macroscopic areas of the graphene samples are all above 400 mm2.

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Stereo-dynamics of the exchange reaction Ha+LiHb→LiHa+Hb and its isotopic variants Zhai Hong-Sheng, Yin Shu-Hui 2012, 21 (12):  128201.  doi: 10.1088/1674-1056/21/12/128201 Abstract ( 0 )   PDF (250KB) ([an error occurred while processing this directive])   Quasi-classical trajectory (QCT) method is used to calculate the stereo-dynamics of the exchange reaction Ha+LiHb→LiHa+Hb and its isotopic variants based on an accurate potential energy surface reported by Prudente et al. [Prudente F V, Marques J M C and Maniero A M 2009 Chem. Phys. Lett. 474 18]. The reactive probability of the title reaction is computed. The vector correlations and four polarization-dependent generalized differential cross sections (PDDCSs) at different collision energies are presented. The influences of the collision energy and the reagent rotation on the product polarization are studied in the present work. The results indicate that the product rotational angular momentum j' is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The product polarization distributions of the title reaction and its isotopic variants exhibit distinct differences which may arise from different mass combinations.

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Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ spinels: A first-principles study Xin Xiao-Gui, Shen Jing-Qin, Shi Si-Qi 2012, 21 (12):  128202.  doi: 10.1088/1674-1056/21/12/128202 Abstract ( 0 )   PDF (879KB) ([an error occurred while processing this directive])   Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ are investigated using density-functional theory calculations. Results indicate that nonstoichiometric LiNi0.5Mn1.5O4-δ and stoichiometric LiNi0.5Mn1.5O4 exhibit two different structures, i.e., the face-centred cubic (Fd-3m) and primitive, or simple, cubic (P4332) space groups, respectively. It is found that the magnetic ground state of LiNi0.5Mn1.5O4 (P4332 and Fd-3m) is ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the [110] direction whereas they are antiferromagnetic with respect to each other. We demonstrate that it is the presence of O-vacancy in LiNi0.5Mn1.5O4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi0.5Mn1.5O4 with the P4332 space group.

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A novel four-legged loaded element thick-screen frequency selective surface with a stable performance Tang Guang-Ming, Miao Jun-Gang, Dong Jin-Ming 2012, 21 (12):  128401.  doi: 10.1088/1674-1056/21/12/128401 Abstract ( 0 )   PDF (203KB) ([an error occurred while processing this directive])   Because thick-screen frequency selective surface (FSS) has not only a broad bandwidth but also an advantage of overcoming multilayer FSS shortcoming of complex structure and low transmittance of centre frequency due to the cascade of FSSs, it has a potential application to the stealth curved streamlined radome. However, there are an unsteadiness of centre frequency in a wide range of incident angle and another unsteadiness of polarization in a big incident angle. In order to solve the problems, in this paper we provide a novel four-legged loaded element thick-screen FSS. The structure is analysed and simulated using mode matching method and moment method. The centre frequency, the transmittance of centre frequency, and bandwidth of the structure are investigated when some parameters including the polarization at a big incident angle and the incident angles of TE & TM waves are changed. The novel four-legged loaded element thick-screen FSS has better transmission properties with a better steadiness of polarization and incident angle independence. The novel structure of four-legged loaded element thick-screen FSS provides a valuable reference for the application in stealth curved streamlined radome.

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Enhanced performance in organic photovoltaic devices with KMnO4 solution treated indium tin oxide anode modification Yang Qian-Qian, Zhao Su-Ling, Zhang Fu-Jun, Yan Guang, Kong Chao, Fan Xing, Zhang Yan-Fei, Xu Xu-Rong 2012, 21 (12):  128402.  doi: 10.1088/1674-1056/21/12/128402 Abstract ( 0 )   PDF (1183KB) ([an error occurred while processing this directive])   The properties of poly(3-hexylthiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) organic photovoltaic devices (OPVs) with indium tin oxide (ITO) anode treated by KMnO4 solution are investigated. The optimized KMnO4 solution has a concentration of 50 mg/L, and ITO is treated for 15 min. The modification of ITO anode results in an enhancement of the power conversion efficiency (PCE) of the device, which is responsible for the increase of the photocurrent. The performance enhancement is attributed to the work function modification of the ITO substrate through the strong oxygenation of KMnO4, and then the charge collection efficiency is improved.

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Improvement of breakdown characteristics of AlGaN/GaN HEMT with U-type gate foot for millimeter-wave power application Kong Xin, Wei Ke, Liu Guo-Guo, Liu Xin-Yu 2012, 21 (12):  128501.  doi: 10.1088/1674-1056/21/12/128501 Abstract ( 0 )   PDF (641KB) ([an error occurred while processing this directive])   In this study, physics-based device simulation tool Silvaco ATLAS is used to characterize the electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) with a U-type gate foot. The U-gate AlGaN/GaN HEMT mainly features a gradually changed sidewall angle, which effectively mitigates the electric field in the channel, thus obtaining enhanced off-state breakdown characteristics. At the same time, only a small additional gate capacitance and decreased gate resistance ensure excellent RF characteristics for U-gate device. U-gate AlGaN/GaN HEMTs are of great feasibility through adjusting the etching conditions of inductively coupled plasma system, without introducing any extra process step. The simulation results are confirmed by the experimental measurements. These features indicate that U-gate AlGaN/GaN HEMTs might be promising candidates for millimeter-wave power application.

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Investigation of inhomogeneous barrier height of Au/Bi4Ti3O12/n-Si structure through Gaussian distribution of barrier height M. Gökcen, M. Yildirim 2012, 21 (12):  128502.  doi: 10.1088/1674-1056/21/12/128502 Abstract ( 0 )   PDF (534KB) ([an error occurred while processing this directive])   Au/Bi4Ti3O12/n-Si structure is fabricated in order to investigate its current-voltage (I-V) characteristics in a temperature range of 300 K-400 K. Obtained I-V data are evaluated by thermionic emission (TE) theory. Zero-bias barrier height (ΦB0) and ideality factor (n) calculated from I-V characteristics, are found to be temperature-dependent such that ΦB0 increases with temperature increasing, whereas n decreases. Obtained temperature dependence of ΦB0 and linearity in ΦB0 versus n plot, together with lower barrier height and Richardson constant values obtained from Richardson plot, indicate that the barrier height of the structure is inhomogeneous in nature. Therefore, I-V characteristics are explained on the basis of Gaussian distribution of barrier height.

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Junction barrier Schottky rectifier with improved P-well region Wang Ying, Li Ting, Cao Fei, Shao Lei, Chen Yu-Xian 2012, 21 (12):  128503.  doi: 10.1088/1674-1056/21/12/128503 Abstract ( 0 )   PDF (359KB) ([an error occurred while processing this directive])   A junction barrier Schottky (JBS) rectifier with improved P-well on 4H-SiC is proposed to improve the VF-IR trade-off and the breakdown voltage. The reverse current density of the proposed JBS rectifier at 300 K and 800 V is about 3.3×10-8 times that of the common JBS rectifier at no expense of the forward voltage drop. It is because that the depletion layer thickness in P-well region at the same reverse voltage is larger than in P+ grid, resulting in the lower spreading current and tunneling current. As a result, the breakdown voltage of the proposed JBS rectifier is over 1.6 kV that is about 0.8 times more than that of the common JBS rectifier due to the uniform electric field. Although the series resistance of the proposed JBS rectifier is a little larger than that of common JBS rectifier, the figure of merit (FOM) of the proposed JBS rectifier is about 2.9 times that of the common JBS rectifier. Based on simulating the values of susceptibility of the two JBS rectifiers to electrostatic discharge (ESD) in the human body model (HBM) circuits, the failure energy of the proposed JBS rectifier increases 17% compared with that of the common JBS rectifier.

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Improved efficiency droop characteristics in InGaN/GaN light-emitting diode with a novel designed last barrier structure Wang Tian-Hu, Xu Jin-Liang 2012, 21 (12):  128504.  doi: 10.1088/1674-1056/21/12/128504 Abstract ( 0 )   PDF (210KB) ([an error occurred while processing this directive])   In this study, the characteristics of the nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the less polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.

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Experimental observation of multirhythmic pattern in chains of Rossler circuits Liu Wei-Qing, Deng Jing-Fa, Xiao Jing-Hua 2012, 21 (12):  128701.  doi: 10.1088/1674-1056/21/12/128701 Abstract ( 0 )   PDF (237KB) ([an error occurred while processing this directive])   The influences of parameter mismatches on multirhythmic pattern in chains of coupled Rossler circuits are explored experimentally. The parameter mismatches in coupled chaotic oscillators are found helpful to form a kind of multirhythmic pattern as reported in chains of biological coupled oscillators [Phys. Rev. Lett. 92 228102]. Moreover, a new type of multirhythmic pattern based on the envelope of time series is observed.

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Multidimensional subdiffusion model: Arbitrage-free market Li Guo-Hua, Zhang Hong, Luo Mao-Kang 2012, 21 (12):  128901.  doi: 10.1088/1674-1056/21/12/128901 Abstract ( 0 )   PDF (121KB) ([an error occurred while processing this directive])   To capture the subdiffusive characteristics of financial markets, the subordinated process, directed by the inverse α-stale subordinator Sα(t) for 0 < α <1, has been employed as the model of asset prices. In this article, we introduce a multidimensional subdiffusion model that has a bond and K correlated stocks. The stock price process is a multidimensional subdiffusion process directed by the inverse α-stable subordinator. This model describes the period of stagnation for each stock and the behavior of the dependency between multiple stocks. Moreover, we derive the multidimensional fractional backward Kolmogorov equation for the subordinated process by Laplace transform technique. Finally, using martingale approach, we prove that the multidimensional subdiffusion model is arbitrage-free, and also gives an arbitrage-free pricing rule for contingent claims associated with the martingale measure.

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Stochastic bounded consensus tracking of leader-follower multi-agent systems with measurement noises and sampled-data Wu Zhi-Hai, Peng Li, Xie Lin-Bo, Wen Ji-Wei 2012, 21 (12):  128902.  doi: 10.1088/1674-1056/21/12/128902 Abstract ( 0 )   PDF (560KB) ([an error occurred while processing this directive])   This paper is concerned with the stochastic bounded consensus tracking problems of leader-follower multi-agent systems, where the control input of an agent can only use the information measured at the sampling instants from its neighbours or the virtual leader with a time-varying reference state, and the measurements are corrupted by random noises. The probability limit theory and the algebra graph theory are employed to derive the necessary and sufficient condition guaranteeing the mean square bounded consensus tracking. It is shown that the maximum allowable upper bound of the sampling period simultaneously depends on the constant feedback gains and the network topology. Furthermore, the effects of the sampling period on the tracking performance are analysed. It turns out that from the view point of the sampling period, there is a trade-off between the tracking speed and the static tracking error. Simulations are provided to demonstrate the effectiveness of the theoretical results.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Multi-coupled single scattering method of solving vector radiative transfer equations Sun Bin, Wang Han, Sun Xiao-Bing, Hong Jin, Zhang Yun-Jie 2012, 21 (12):  129501.  doi: 10.1088/1674-1056/21/12/129501 Abstract ( 0 )   PDF (269KB) ([an error occurred while processing this directive])   A new method of multi-coupled single scattering (MCSS) for solving vector radiative transfer equation is developed and public on Internet. Recent solutions got from Chandrasekhar's X-Y method is used to validate the MCSS's result, which shows a high precision. The MCSS method is theoretically simple and clear, so it can be easily and credibly extended to simulation of aerosol/cloud atmosphere's radiative property, which provides effective support for the research of polarized remote sensing.