Table of contents

15 November 2010, Volume 19 Issue 11 Previous issue    Next issue

GENERAL

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Punishment in optional public goods games Wang Zhen(王震),Xu Zhao-Jin(许照锦), and Zhang Lian-Zhong(张连众) Chin. Phys. B, 2010, 19 (11):  110201.  DOI: 10.1088/1674-1056/19/11/110201 Abstract ( 1535 )   PDF (702KB) ( 931 )   In this work, the optional public goods games with punishment are studied. By adopting the approximate best response dynamics, a micro model is given to explain the evolutionary process. Simultaneously, the magnitude of rationality is also considered. Under the condition of bounded rationality which provides a light to interpret phenomena in human society, the model leads to two types of equilibriums. One is the equilibrium without punishers and the other is the equilibrium including only punishers and cooperators. In addition, the effects of rationality on equilibriums are briefly investigated.

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Statistical Elmore delay of RC interconnect tree Dong Gang(董刚), Yang Yang(杨杨), Chai Chang-Chun(柴常春), and Yang Yin-Tang(杨银堂) Chin. Phys. B, 2010, 19 (11):  110202.  DOI: 10.1088/1674-1056/19/11/110202 Abstract ( 1468 )   PDF (529KB) ( 1154 )   As feature size keeps scaling down, process variations can dramatically reduce the accuracy in the estimation of interconnect performance. This paper proposes a statistical Elmore delay model for RC interconnect tree in the presence of process variations. The suggested method translates the process variations into parasitic parameter extraction and statistical Elmore delay evaluation. Analytical expressions of mean and standard deviation of interconnect delay can be obtained in a given fluctuation range of interconnect geometric parameters. Experimental results demonstrate that the approach matches well with Monte Carlo simulations. The errors of proposed mean and standard deviation are less than 1% and 7%, respectively. Simulations prove that our model is efficient and accurate.

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New approximate solution for time-fractional coupled KdV equations by generalised differential transform method Liu Jin-Cun(刘金存) and Hou Guo-Lin(侯国林) Chin. Phys. B, 2010, 19 (11):  110203.  DOI: 10.1088/1674-1056/19/11/110203 Abstract ( 1294 )   PDF (1139KB) ( 1521 )   In this paper, the generalised two-dimensional differential transform method (DTM) of solving the time-fractional coupled KdV equations is proposed. The fractional derivative is described in the Caputo sense. The presented method is a numerical method based on the generalised Taylor series expansion which constructs an analytical solution in the form of a polynomial. An illustrative example shows that the generalised two-dimensional DTM is effective for the coupled equations.

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A type of new conserved quantity deduced from Mei symmetry for Appell equations in a holonomic system with unilateral constraints Jia Li-Qun(贾利群), Xie Yin-Li(解银丽), Zhang Yao-Yu(张耀宇), and Yang Xin-Fang(杨新芳) Chin. Phys. B, 2010, 19 (11):  110301.  DOI: 10.1088/1674-1056/19/11/110301 Abstract ( 1391 )   PDF (151KB) ( 825 )   A type of new conserved quantity deduced from Mei symmetry of Appell equations for a holonomic system with unilateral constraints is investigated. The expressions of new structural equation and new conserved quantity deduced from Mei symmetry of Appell equations for a holonomic system with unilateral constraints expressed by Appell functions are obtained. An example is given to illustrate the application of the results.

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Nonlinear waves in a fluid-filled thin viscoelastic tube Zhang Shan-Yuan(张善元) and Zhang Tao(张涛) Chin. Phys. B, 2010, 19 (11):  110302.  DOI: 10.1088/1674-1056/19/11/110302 Abstract ( 1267 )   PDF (1025KB) ( 785 )   In the present paper the propagation property of nonlinear waves in a thin viscoelastic tube filled with incompressible inviscid fluid is studied. The tube is considered to be made of an incompressible isotropic viscoelastic material described by Kelvin–Voigt model. Using the mass conservation and the momentum theorem of the fluid and radial dynamic equilibrium of an element of the tube wall, a set of nonlinear partial differential equations governing the propagation of nonlinear pressure wave in the solid–liquid coupled system is obtained. In the long-wave approximation the nonlinear far-field equations can be derived employing the reductive perturbation technique (RPT). Selecting the exponent $\alpha$ of the perturbation parameter in Gardner–Morikawa transformation according to the order of viscous coefficient $\eta$, three kinds of evolution equations with soliton solution, i.e. Korteweg–de Vries (KdV)–Burgers, KdV and Burgers equations are deduced. By means of the method of traveling-wave solution and numerical calculation, the propagation properties of solitary waves corresponding with these evolution equations are analysed in detail. Finally, as a example of practical application, the propagation of pressure pulses in large blood vessels is discussed.

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Entanglement of two atoms interacting with a dissipative coherent cavity field without rotating wave approximation Kang Guo-Dong(康国栋), Fang Mao-Fa(方卯发), Ouyang Xi-Cheng(欧阳锡城), and Deng Xiao-Juan(邓小娟) Chin. Phys. B, 2010, 19 (11):  110303.  DOI: 10.1088/1674-1056/19/11/110303 Abstract ( 1363 )   PDF (352KB) ( 812 )   Considering two identical two-level atoms interacting with a single-model dissipative coherent cavity field without rotating wave approximation, we explore the entanglement dynamics of the two atoms prepared in different states using concurrence. Interestingly, our results show that the entanglement between the two atoms that initially disentangled will come up to a large constant rapidly, and then keeps steady in the following time or always has its maximum when prepared in some special Bell states. The model considered in this study is a good candidate for quantum information processing especially for quantum computation as steady high-degree atomic entanglement resource obtained in dissipative cavity.

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Entanglement dynamics of two distant atoms in two detuning cavities Ji Xin(计新), Lü Tian-Quan(吕天全), and Zhang Shou(张寿) Chin. Phys. B, 2010, 19 (11):  110304.  DOI: 10.1088/1674-1056/19/11/110304 Abstract ( 1263 )   PDF (976KB) ( 730 )   We investigate the entanglement dynamics via the concurrence of two distant atoms interacting off-resonantly with two cavity fields in Fock states, respectively. We find that the evolution of entanglement has sudden death and sudden birth phenomena, that with the increase of photon numbers in the two cavities, the alternate frequency of sudden death and sudden birth turns fast, and that the amplitude of concurrence oscillates regularly with oscillation frequency becoming slow when the cavity fields have the same photon numbers. While, the maximum of concurrence declines and the amplitude of concurrence oscillates irregularly when the two cavity fields have different photon numbers. In addition, we find the length of death time is dependent on the initial entanglement.

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Controlled decoherence of floating flux qubits Ji Ying-Hua(嵇英华) and Xu Lin(徐林) Chin. Phys. B, 2010, 19 (11):  110305.  DOI: 10.1088/1674-1056/19/11/110305 Abstract ( 1172 )   PDF (195KB) ( 661 )   In Born–Markov approximation, this paper calculates the energy relaxation time T1 and the decoherence time T2 of a floating flux qubit by solving the set of Bloch–Redfield equations. It shows that there are two main factors influencing the floating flux qubits: coupling capacitor in the circuit and the environment resistor. It also discusses how to improve the quantum coherence time of a qubit. Through shunt connecting/ series connecting inductive elements, an inductive environment resistor is obtained and further the reactance component of the environment resistor is improved，which is beneficial to the enhancement of decoherence time of floating flux qubits.

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Faithful quantum secure direct communication protocol against collective noise Yang Jing(杨静), Wang Chuan(王川), and Zhang Ru(张茹) Chin. Phys. B, 2010, 19 (11):  110306.  DOI: 10.1088/1674-1056/19/11/110306 Abstract ( 1481 )   PDF (161KB) ( 824 )   An improved quantum secure direct communication (QSDC) protocol is proposed in this paper. Blocks of entangled photon pairs are transmitted in two steps in which secret messages are transmitted directly. The single logical qubits and unitary operations under decoherence free subspaces are presented and the generalized Bell states are constructed which are immune to the collective noise. Two steps of qubit transmission are used in this protocol to guarantee the security of communication. The security of the protocol against various attacks are discussed.

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Relative entropy of entanglement of two-qubit 'X' states Huang Jie-Hui(黄接辉), Liu Nian-Hua(刘念华), Liu Jiang-Tao(刘江涛), Yu Tian-Bao(于天宝), and He Xian(何弦) Chin. Phys. B, 2010, 19 (11):  110307.  DOI: 10.1088/1674-1056/19/11/110307 Abstract ( 1364 )   PDF (154KB) ( 799 )   Two closest single-qubit states could be diagonalised by the same unitary matrix, which helps to find the relative entropy of entanglement of a two-qubit 'X' state. We formulate two binary equations for the relative entropy of entanglement and the corresponding closest separable state of a given two-qubit 'X' state. This approach can be applied to get the relative entropy of entanglement of many widely-discussed two-qubit states, such as pure states, Werner states, and so on.

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The ground-state entanglement in the spin-XX chain with a magnetization current Zhang Yong(张勇), Wang Chuan(王川), and Jin Guang-Sheng(金光生) Chin. Phys. B, 2010, 19 (11):  110308.  DOI: 10.1088/1674-1056/19/11/110308 Abstract ( 1431 )   PDF (302KB) ( 851 )   The ground-state entanglement in a transverse spin-1/2 XX chain with a magnetization current is studied. By introducing a magnetization current to the system, a quantum phase transition to current-carrying phase may be presented with the variation of the driving field $\lambda$ for the magnetic field h >1; and the ground-state entanglement arises simultaneously at the critical point of quantum phase transition. In our model, the introduction of magnetization current may result in more entanglement between any two nearest-neighbour spins.

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Two quantum oscillators coupled with a planar radio frequency ion trap Chen Liang(陈亮) and Gao Ke-Lin(高克林) Chin. Phys. B, 2010, 19 (11):  110309.  DOI: 10.1088/1674-1056/19/11/110309 Abstract ( 1365 )   PDF (274KB) ( 661 )   In this scheme, two quantum oscillators in a planar radio frequency ion trap are coupled by the trap electrodes. The ions motional states encode the quantum bits (qubits), and a swap gate could be achieved. Under different conditions of the experiments, the intensity of the coupling between two quantum oscillators and the dissipation of the system are calculated. We compute fidelities for a quantum swap gate and discuss experimental issues.

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Unconventional geometric phase gate and multiqubit entanglement for hot ions with a frequency-modulated field Zhong Wen-Xue(钟文学), Cheng Guang-Ling(程广玲), and Chen Ai-Xi(陈爱喜) Chin. Phys. B, 2010, 19 (11):  110310.  DOI: 10.1088/1674-1056/19/11/110310 Abstract ( 1281 )   PDF (190KB) ( 722 )   We present an alternative scheme for implementing the unconventional geometric two-qubit phase gate and preparing multiqubit entanglement by using a frequency-modulated laser field to simultaneously illuminate all ions. Selecting the index of modulation yields selective mechanisms for coupling and decoupling between the internal and the external states of the ions. By the selective mechanisms, we obtain the unconventional geometric two-qubit phase gate, multiparticle Greenberger–Horne–Zeilinger states and highly entangled cluster states. Our scheme is insensitive to the thermal motion of the ions.

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Scheme for teleportation of unknown single qubit state via continuous variables entangling channel Wang Zhong-Jie(王中结), Zhang Kan(张侃), and Fan Chao-Yang(范朝阳) Chin. Phys. B, 2010, 19 (11):  110311.  DOI: 10.1088/1674-1056/19/11/110311 Abstract ( 1336 )   PDF (163KB) ( 642 )   A new scheme for quantum teleportation of single quantum bit state with using continuous variables entangling channel is presented. In our scheme two entangled light fields are employed. An outstanding characteristic of this scheme is that one atomic state is transmitted directly to another atom without using the third atom as the mediate.

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The high squeezing and entanglement in regular loss modulated optical parametric amplifier Zhao Chao-Ying(赵超樱) and Tan Wei-Han(谭维翰) Chin. Phys. B, 2010, 19 (11):  110312.  DOI: 10.1088/1674-1056/19/11/110312 Abstract ( 1481 )   PDF (211KB) ( 604 )   We investigate the quantum fluctuation characteristic for time dependent regular loss modulated optical parametric amplifier for below and above threshold regions. It is found that a high squeezing and entanglement can be achieved.

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Thermal entanglement in molecular spin rings Hou Jing-Min(侯净敏), Du Long(杜龙), Ding Jia-Yan(丁伽焱), and Zhang Wen-Xin(张文新) Chin. Phys. B, 2010, 19 (11):  110313.  DOI: 10.1088/1674-1056/19/11/110313 Abstract ( 1276 )   PDF (2269KB) ( 875 )   The thermal entanglement in the triangular molecular spin ring with Dzyaloshinskii–Moriya interaction is studied. The concurrences of arbitrary two spins of the triangular molecular spin ring for various cases are evaluated. The tendency of the concurrence with Dzyaloshinskii–Moriya interaction and temperature is analysed and discussed. We note that the concurrence arrives at its maximum in the regime with the large Dzyaloshinskii–Moriya interaction and low temperature, and gradually decreases to zero with the increase of temperature. The concurrence has different features for the ferromagnetic and antiferromagnetic cases. For completeness, we also numerically calculate the concurrence of spin rings with N>3 spins and analyse their behaviours.

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Teleparallel equivalent theory of (1+1)-dimensional gravity Gamal G.L. Nashed Chin. Phys. B, 2010, 19 (11):  110401.  DOI: 10.1088/1674-1056/19/11/110401 Abstract ( 1180 )   PDF (198KB) ( 581 )   A theory of (1+1)-dimensional gravity is constructed on the basis of the teleparallel equivalent of general relativity. The fundamental field variables are the tetrad fields $e_i^{\mu}$ and the gravity is attributed to the torsion. A dilatonic spherically symmetric exact solution of the gravitational field equations characterized by two parameters M and Q is derived. The energy associated with this solution is calculated using the two-dimensional gravitational energy–momentum formula.

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Gravitational radiation fields in teleparallel equivalent of general relativity and their energies Gamal G.L. Nashed Chin. Phys. B, 2010, 19 (11):  110402.  DOI: 10.1088/1674-1056/19/11/110402 Abstract ( 1161 )   PDF (188KB) ( 512 )   We derive two new retarded solutions in the teleparallel theory equivalent to general relativity (TEGR). One of these solutions gives a divergent energy. Therefore, we use the regularized expression of the gravitational energy–momentum tensor, which is a coordinate dependent. A detailed analysis of the loss of the mass of Bondi space–time is carried out using the flux of the gravitational energy–momentum.

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Real scalar field scattering in the nearly extremal Schwarzschildben--de Sitter space Guo Guang-Hai(郭广海) Chin. Phys. B, 2010, 19 (11):  110403.  DOI: 10.1088/1674-1056/19/11/110403 Abstract ( 1294 )   PDF (202KB) ( 551 )   Reasonable approximations are introduced to investigate the real scalar field scattering in the nearly extremal Schwarzschild–de Sitter (SdS) space. The approximations naturally lead to the invertible x(r) and the global replacement of the true potential by a P?shl–Teller one. Meanwhile, the Schr$\ddot{\rm o}$dinger-like wave equation is transformed into a solvable form. Our numerical solutions to the wave equation show that the wave is characteristically similar to the harmonic under the tortoise coordinate x, while the wave piles up near the two horizons and the wavelength tends to its maximum as the potential approaches to the peak under the radial coordinate r.

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Massive particle radiation from Gibbons–Maeda black hole Fang Heng-Zhong(方恒忠) Chin. Phys. B, 2010, 19 (11):  110404.  DOI: 10.1088/1674-1056/19/11/110404 Abstract ( 1168 )   PDF (148KB) ( 549 )   This paper investigated the massive particle radiation from Gibbons–Maeda black hole by using a semi-classical method. The calculations showed that, if the self-gravitation of the radiated particle is taken into account, the radiation spectrum deviates from exact black body spectrum and the rate of tunneling equals precisely the exponent of the difference of the black hole entropies before and after emission. The conclusion supports the viewpoint of information conservation.

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Synchronization between different motifs Li Ying(李莹) and Liu Zeng-Rong(刘曾荣) Chin. Phys. B, 2010, 19 (11):  110501.  DOI: 10.1088/1674-1056/19/11/110501 Abstract ( 1270 )   PDF (885KB) ( 535 )   In this paper, we study the synchronization between different motifs. First, the synchronization between two networks with different topology structures and different dynamical behaviours is studied. With the open-plus-closed-loop(OPCL) method, conditions for two different networks to realize synchronization are given. Then based on the theoretical results achieved, the synchronization between different motifs is studied, which verifies the effectiveness and feasibility of the synchronization scheme.

RAPID COMMUNICATION

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Prediction of protein binding sites using physical and chemical descriptors and the support vector machine regression method Sun Zhong-Hua(孙重华) and Jiang Fan(江凡) Chin. Phys. B, 2010, 19 (11):  110502.  DOI: 10.1088/1674-1056/19/11/110502 Abstract ( 1534 )   PDF (212KB) ( 751 )   In this paper a new continuous variable called core-ratio is defined to describe the probability for a residue to be in a binding site, thereby replacing the previous binary description of the interface residue using 0 and 1. So we can use the support vector machine regression method to fit the core-ratio value and predict the protein binding sites. We also design a new group of physical and chemical descriptors to characterize the binding sites. The new descriptors are more effective, with an averaging procedure used. Our test shows that much better prediction results can be obtained by the support vector regression (SVR) method than by the support vector classification method.

GENERAL

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Nonlinear analysis of traffic jams in an anisotropic continuum model Arvind Kumar Gupta and Sapna Sharma Chin. Phys. B, 2010, 19 (11):  110503.  DOI: 10.1088/1674-1056/19/11/110503 Abstract ( 1335 )   PDF (1662KB) ( 1286 )   This paper presents our study of the nonlinear stability of a new anisotropic continuum traffic flow model in which the dimensionless parameter or anisotropic factor controls the non-isotropic character and diffusive influence. In order to establish traffic flow stability criterion or to know the critical parameters that lead, on one hand, to a stable response to perturbations or disturbances or, on the other hand, to an unstable response and therefore to a possible congestion, a nonlinear stability criterion is derived by using a wavefront expansion technique. The stability criterion is illustrated by numerical results using the finite difference method for two different values of anisotropic parameter. It is also been observed that the newly derived stability results are consistent with previously reported results obtained using approximate linearisation methods. Moreover, the stability criterion derived in this paper can provide more refined information from the perspective of the capability to reproduce nonlinear traffic flow behaviors observed in real traffic than previously established methodologies.

RAPID COMMUNICATION

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Enhancement of scale-free network attack tolerance Qu Ze-Hui(瞿泽辉), Wang Pu(王璞), Song Chao-Ming(宋朝鸣), and Qin Zhi-Guang(秦志光) Chin. Phys. B, 2010, 19 (11):  110504.  DOI: 10.1088/1674-1056/19/11/110504 Abstract ( 1372 )   PDF (1293KB) ( 852 )   Despite the large size of most communication and transportation systems, there are short paths between nodes in these networks which guarantee the efficient information, data and passenger delivery; furthermore these networks have a surprising tolerance under random errors thanks to their inherent scale-free topology. However, their scale-free topology also makes them fragile under intentional attacks, leaving us a challenge on how to improve the network robustness against intentional attacks without losing their strong tolerance under random errors and high message and passenger delivering capacity. Here we propose two methods (SL method and SH method) to enhance scale-free network's tolerance under attack in different conditions.

GENERAL

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Structural properties of effective potential model by liquid state theories Xiang Yuan-Tao(向远涛), Andrej Jamnik, and Yang Kai-Wei(杨开巍) Chin. Phys. B, 2010, 19 (11):  110505.  DOI: 10.1088/1674-1056/19/11/110505 Abstract ( 1119 )   PDF (842KB) ( 685 )   This paper investigates the structural properties of a model fluid dictated by an effective inter-particle oscillatory potential by grand canonical ensemble Monte Carlo (GCEMC) simulation and classical liquid state theories. The chosen oscillatory potential incorporates basic interaction terms used in modeling of various complex fluids which is composed of mesoscopic particles dispersed in a solvent bath, the studied structural properties include radial distribution function in bulk and inhomogeneous density distribution profile due to influence of several external fields. The GCEMC results are employed to test the validity of two recently proposed theoretical approaches in the field of atomic fluids. One is an Ornstein–Zernike integral equation theory approach; the other is a third order + second order perturbation density functional theory. Satisfactory agreement between the GCEMC simulation and the pure theories fully indicates the ready adaptability of the atomic fluid theories to effective model potentials in complex fluids, and classifies the proposed theoretical approaches as convenient tools for the investigation of complex fluids under the single component macro-fluid approximation.

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Feedback control of two-headed Brownian motors in flashing ratchet potential Zhao A-Ke(赵阿可), Zhang Hong-Wei(张红卫), and Li Yu-Xiao(李玉晓) Chin. Phys. B, 2010, 19 (11):  110506.  DOI: 10.1088/1674-1056/19/11/110506 Abstract ( 1605 )   PDF (2011KB) ( 736 )   We presented a detailed investigation on the movement of two-headed Brownian motors in an asymmetric potential under a feedback control. By numerical simulations the direct current is obtained. The current is periodic in the initial length of spring. There is an optimal value of the spring constant. And the dependence of the current on the opposing force is reversed. Then we found that when the change of the temperature and the opposing force have optimal values, the Brownian motors can also obtain the optimal efficiency.

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Analysis of convergence for initial condition estimation of coupled map lattices based on symbolic dynamics Sun Li-Sha(孙丽莎), Kang Xiao-Yun(康晓云), and Lin Lan-Xin(林兰馨) Chin. Phys. B, 2010, 19 (11):  110507.  DOI: 10.1088/1674-1056/19/11/110507 Abstract ( 1216 )   PDF (676KB) ( 727 )   A novel approach to the inverse problem of diffusively coupled map lattices is systematically investigated by utilizing the symbolic vector dynamics. The relationship between the performance of initial condition estimation and the structural feature of dynamical system is proved theoretically. It is found that any point in a spatiotemporal coupled system is not necessary to converge to its initial value with respect to sufficient backward iteration, which is directly relevant to the coupling strength and local mapping function. When the convergence is met, the error bound in estimating the initial condition is proposed in a noiseless environment, which is determined by the dimension of attractors and metric entropy of the system. Simulation results further confirm the theoretic analysis, and prove that the presented method provides the important theory and experimental results for better analysing and characterizing the spatiotemporal complex behaviours in an actual system.

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Optical patterns in spatially coupled phase-conjugate systems Yue Li-Juan(岳立娟) and Sang Jin-Yu(桑金玉) Chin. Phys. B, 2010, 19 (11):  110508.  DOI: 10.1088/1674-1056/19/11/110508 Abstract ( 1419 )   PDF (3766KB) ( 591 )   Various pattern evolutions are presented in one- and two-dimensional spatially coupled phase-conjugate systems (SCPCSs). As the system parameters change, different patterns are obtained from the period-doubling of kink–antikinks in space to the spatiotemporal chaos in a one-dimensional SCPCS. The homogeneous symmetric states induce symmetry breaking from the four corners and the boundaries, finally leading to spatiotemporal chaos with the increase of the iteration time in a two-dimensional SCPCS. Numerical simulations are very helpful for understanding the complex optical phenomena.

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Nonlinear feedback synchronisation control between fractional-order and integer-order chaotic systems Jia Li-Xin(贾立新), Dai Hao(戴浩), and Hui Meng(惠萌) Chin. Phys. B, 2010, 19 (11):  110509.  DOI: 10.1088/1674-1056/19/11/110509 Abstract ( 1273 )   PDF (229KB) ( 829 )   This paper focuses on the synchronisation between fractional-order and integer-order chaotic systems. Based on Lyapunov stability theory and numerical differentiation, a nonlinear feedback controller is obtained to achieve the synchronisation between fractional-order and integer-order chaotic systems. Numerical simulation results are presented to illustrate the effectiveness of this method.

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The 0-1 test algorithm for chaos and its applications Sun Ke-Hui(孙克辉), Liu Xuan(刘璇), and Zhu Cong-Xu(朱从旭) Chin. Phys. B, 2010, 19 (11):  110510.  DOI: 10.1088/1674-1056/19/11/110510 Abstract ( 1778 )   PDF (489KB) ( 1380 )   To determine whether a given deterministic nonlinear dynamic system is chaotic or periodic, a novel test approach named zero-one (0-1) test has been proposed recently. In this approach, the regular and chaotic motions can be decided by calculating the parameter K approaching asymptotically to zero or one. In this study, we focus on the 0-1 test algorithm and illustrate the selection of parameters of this algorithm by numerical experiments. To validate the reliability and the universality of this algorithm, it is applied to typical nonlinear dynamic systems, including fractional-order dynamic system.

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Impulsive control of stochastic system under the sense of stochastic asymptotical stability Niu Yu-Jun(牛玉俊) and Ma Ge(马戈) Chin. Phys. B, 2010, 19 (11):  110511.  DOI: 10.1088/1674-1056/19/11/110511 Abstract ( 1355 )   PDF (1264KB) ( 743 )   This paper studies the stochastic asymptotical stability of stochastic impulsive differential equations, and establishes a comparison theory to ensure the trivial solution's stochastic asymptotical stability. From the comparison theory, it can find out whether the stochastic impulsive differential system is stable just by studying the stability of a deterministic comparison system. As a general application of this theory, it controls the chaos of stochastic Lü system using impulsive control method, and numerical simulations are employed to verify the feasibility of this method.

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An linear matrix inequality approach to global synchronisation of non-parameter perturbations of multi-delay Hopfield neural network Shao Hai-Jian(邵海见), Cai Guo-Liang(蔡国梁), and Wang Hao-Xiang(汪浩祥) Chin. Phys. B, 2010, 19 (11):  110512.  DOI: 10.1088/1674-1056/19/11/110512 Abstract ( 1566 )   PDF (166KB) ( 591 )   In this study, a successful linear matrix inequality approach is used to analyse a non-parameter perturbation of multi-delay Hopfield neural network by constructing an appropriate Lyapunov-Krasovskii functional. This paper presents the comprehensive discussion of the approach and also extensive applications.

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Bending localization of nitrous oxide under anharmonicity and Fermi coupling: the dynamical potential approach Zhang Chi(张弛), Fang Chao(房超) and Wu Guo-Zhen(吴国祯) Chin. Phys. B, 2010, 19 (11):  110513.  DOI: 10.1088/1674-1056/19/11/110513 Abstract ( 1340 )   PDF (2601KB) ( 622 )   This paper studies the vibrational nonlinear dynamics of nitrous oxide with Fermi coupling between the symmetric stretching and bending coordinates by classical dynamical potential approach. This is a global approach in the sense that the overall dynamics is evidenced by the classical nonlinear variables such as the fixed points and the focus are on a set of levels instead of individual ones. The dynamics of nitrous oxide is demonstrated to be not so much dependent on the excitation energy. Moreover, the localized bending mode is shown to be ubiquitous in all the energy range studied.

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System dynamics of behaviour-evolutionary mix-game models Gou Cheng-Ling(苟成玲), Gao Jie-Ping(高洁萍), and Chen Fang(陈芳) Chin. Phys. B, 2010, 19 (11):  110514.  DOI: 10.1088/1674-1056/19/11/110514 Abstract ( 1056 )   PDF (281KB) ( 630 )   In real financial markets there are two kinds of traders: one is fundamentalist, and the other is a trend-follower. The mix-game model is proposed to mimic such phenomena. In a mix-game model there are two groups of agents: Group 1 plays the majority game and Group 2 plays the minority game. In this paper, we investigate such a case that some traders in real financial markets could change their investment behaviours by assigning the evolutionary abilities to agents: if the winning rates of agents are smaller than a threshold, they will join the other group; and agents will repeat such an evolution at certain time intervals. Through the simulations, we obtain the following findings: (i) the volatilities of systems increase with the increase of the number of agents in Group 1 and the times of behavioural changes of all agents; (ii) the performances of agents in both groups and the stabilities of systems become better if all agents take more time to observe their new investment behaviours; (iii) there are two-phase zones of market and non-market and two-phase zones of evolution and non-evolution; (iv) parameter configurations located within the cross areas between the zones of markets and the zones of evolution are suited for simulating the financial markets.

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Harmonic stochastic resonance-enhanced signal detecting in NW small-world neural network Wang Dao-Guang(王道光), Liang Xiao-Ming(梁小明), Wang Jing(王晶), Yang Cheng-Fang(杨成方), Liu Kai(刘凯), and LÜ Hua-Ping(吕华平) Chin. Phys. B, 2010, 19 (11):  110515.  DOI: 10.1088/1674-1056/19/11/110515 Abstract ( 1597 )   PDF (405KB) ( 1136 )   The harmonic stochastic resonance-enhanced signal detecting in Newman-Watts small-world neural network is studied using the Hodgkin–Huxley dynamical equation with noise. If the connection probability p, coupling strength gsyn and noise intensity D matches well, higher order resonance will be found and an optimal signal-to-noise ratio will be obtained. Then, the reasons are given to explain the mechanism of this appearance.

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Using three-dimensional discrete spherical Fourier descriptors based on surface curvature voxels for pollen particle recognition Xie Yong-Hua(谢永华) and Michael OhEigeartaigh Chin. Phys. B, 2010, 19 (11):  110601.  DOI: 10.1088/1674-1056/19/11/110601 Abstract ( 1390 )   PDF (1079KB) ( 1255 )   This paper presents a new method for extract three-dimensional (3D) discrete spherical Fourier descriptors based on surface curvature voxels for pollen particle recognition. In order to reduce the high amount of pollen information and noise disturbance, the geometric normalized curvature voxels with the principal curvedness are first extracted to represent the intrinsic pollen volumetric data. Then the curvature voxels are decomposed into radial and angular components with spherical harmonic transform in spherical coordinates. Finally the 3D discrete Fourier transform is applied to the decomposed curvature voxels to obtain the 3D spherical Fourier descriptors for pollen recognition. Experimental results show that the presented descriptors are invariant to different pollen particle geometric transformations, such as pose change and spatial rotation, and can obtain high recognition accuracy and speed simultaneously.

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Stable 85Rb micro vapour cells: fabrication based on anodic bonding and application in chip-scale atomic clocks Su Juan(苏娟), Deng Ke(邓科), Guo Deng-Zhu(郭等柱), Wang Zhong(汪中), Chen Jing(陈兢), Zhang Geng-Min(张耿民), and Chen Xu-Zong(陈徐宗) Chin. Phys. B, 2010, 19 (11):  110701.  DOI: 10.1088/1674-1056/19/11/110701 Abstract ( 1387 )   PDF (841KB) ( 1745 )   We describe the microfabrication of 85Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions, the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm3 internal volumes during the cell sealing process. At an ambient temperature of 90 ℃ the optical absorption resonance of 85Rb D1 transition with proper broadening and the corresponding coherent population trapping (CPT) resonance, with a signal contrast of 1.5% and linewidth of about 1.7 kHz, have been detected. The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status. In addition, the physics package of chip-scale atomic clock (CSAC) based on the cell was realized. The measured frequency stability of the physics package can reach to 2.1×10-10 at one second when the cell was heated to 100 ℃ which proved that the cell has the quality to be used in portable and battery-operated devices.

ATOMIC AND MOLECULAR PHYSICS

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Si2O2 molecule: structure of ground state and the excited properties under different external electric fields Xu Guo-Liang(徐国亮), Liu Xue-Feng (刘雪峰), Xie Hui-Xiang(谢会香), Zhang Xian-Zhou(张现周), and Liu Yu-Fang(刘玉芳) Chin. Phys. B, 2010, 19 (11):  113101.  DOI: 10.1088/1674-1056/19/11/113101 Abstract ( 1573 )   PDF (187KB) ( 815 )   Geometry and vibrational frequencies of the ground state of Si2O2 molecule are studied using density function theory (DFT) at the level of cc-pvtz and 6-311++G**. It is found that the optimizing value by B3lyp/cc-pvtz is closer to the experimental data. The excited properties under different external electric fields are also investigated by the time-dependent-DFT method. Transitions from the ground state of Si2O2 molecule to the first singlet state under different external electric fields can take place more easily. The corresponding absorption spectral line is about 360 nm in wavelength and the excitation energy is about 3.4 eV.

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Accurate calculations of the helium atom in magnetic fields Hot! Zhao Ji-Jun(赵继军), Wang Xiao-Feng(王晓峰), and Qiao Hao-Xue(乔豪学) Chin. Phys. B, 2010, 19 (11):  113102.  DOI: 10.1088/1674-1056/19/11/113102 Abstract ( 1371 )   PDF (219KB) ( 867 )   The 110+, 11(-1)+and 11(-2)+ states of the helium atom in the magnetic field regime between 0 and 100 a.u. are studied using a full configuration-interaction (CI) approach. The total energies, derivatives of the total energy with respect to the magnetic field and ionisation energies are calculated with Hylleraas-like functions in spherical coordinates in low to intermediate fields and Hylleraas–Gaussian functions in cylindrical coordinates in intermediate to high fields, respectively. In intermediate fields, the total energies and ionisation energies are determined in terms of Hermite interpolation, based on the results obtained with the two above-mentioned basis functions. Calculations show that the current method can produce lower total energies and larger ionisation energies, and make the two ionisation energy curves obtained with the two above-mentioned basis functions join smoothly in intermediate fields. Comparisons are also made with previous works.

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Temporal electronic structure of non-resonant Raman excited virtual state of P-nitroaniline by 514 nm excitation via bond polarisabilities Hot! Wang Pei-Jie(王培杰), Fang Yan(方炎), and Wu Guo-Zhen(吴国祯) Chin. Phys. B, 2010, 19 (11):  113201.  DOI: 10.1088/1674-1056/19/11/113201 Abstract ( 1148 )   PDF (303KB) ( 557 )   We have studied the temporal bond polarisabilities of para-nitroaniline from the Raman intensities by the algorithm proposed by Wu et al. in 1987 (Tian B, Wu G, Liu G 1987 J. Chem. Phys. 87 7300). The bond polarisabilities provide much information concerning the electronic structure of the non-resonant Raman excited virtual state. At the initial moment by the 514.5 nm excitation, the tendency of the excited electrons (mapped out by the bond polarisabilities) is to spread to the molecular periphery, and the electronic structure of the Raman virtual state is close to the pseudo-quinonoidic state. When the final stage of relaxation is approached, the bond polarisabilities of those peripheral bonds relax faster than those closer to the molecular core, the phenyl ring. The molecule is in the benzenoidic form as demonstrated by the bond polarisabilities after relaxation.

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Fluorescence properties in a single driven four-level atomic system Jiang Xiang-Qian(姜向前), Lü Zhi-Wei(吕志伟), Zhang Bing(张冰), and Sun Xiu-Dong(孙秀冬) Chin. Phys. B, 2010, 19 (11):  113202.  DOI: 10.1088/1674-1056/19/11/113202 Abstract ( 1425 )   PDF (444KB) ( 585 )   The spontaneous emission decay dynamics of a tripod configuration four-level atom driven by a single laser field is studied. Under different initial conditions, we discuss the effects of quantum interference and detuning of external driving field on atomic spontaneous emission properties. For the larger detuning, the interesting phenomena of the spectral line narrowing are found which stem from the contribution of external driving field.

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Control of high-order harmonic generation with two-colour laser field Dai Jun(戴君), Zeng Zhi-Nan(曾志男), Li Ru-Xin(李儒新), and Xu Zhi-Zhan(徐至展) Chin. Phys. B, 2010, 19 (11):  113203.  DOI: 10.1088/1674-1056/19/11/113203 Abstract ( 1230 )   PDF (388KB) ( 685 )   We numerically investigate the high-order harmonic generation with two-colour optical field, taking into consideration the propagation effects. Some harmonics can be dramatically enhanced at a certain delay between the fundamental pulse and its second harmonics. Choice of the enhanced harmonics can be realised by changing the time delay between the two laser pulses.

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Multi-photon resonance enhanced super high-order harmonic generation Lin Zheng-Zhe(林正喆), Zhuang Jun(庄军), and Ning Xi-Jing(宁西京) Chin. Phys. B, 2010, 19 (11):  113204.  DOI: 10.1088/1674-1056/19/11/113204 Abstract ( 1139 )   PDF (2481KB) ( 843 )   This paper proposes highly charged ions pumped by intense laser to produce very high order harmonics. Numerical simulations and full quantum theory of Ne9+ ions driven by laser pulses at 1064 nm in the power range of 109 W/cm2 ～ 1015 W/cm2 show that the emission spectrum corresponds to the electronic transitions from the excited states to the ground state, which is very different from the spectrum of general high-order harmonic generation. In such situation, harmonic order as high as 1000 can be obtained without producing lower order harmonics and the energy conversion efficiency is close to general high order harmonic generation of hydrogen atom in the same laser field.

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Chaos in a Bose–Einstein condensate Wang Zhi-Xia(王志霞), Ni Zheng-Guo(倪政国), Cong Fu-Zhong(从福仲), Liu Xue-Shen(刘学深), and Chen Lei(陈蕾) Chin. Phys. B, 2010, 19 (11):  113205.  DOI: 10.1088/1674-1056/19/11/113205 Abstract ( 1264 )   PDF (644KB) ( 814 )   It is demonstrated that Smale-horseshoe chaos exists in the time evolution of the one-dimensional Bose–Einstein condensate driven by time-periodic harmonic or inverted-harmonic potential. A formally exact solution of the time-dependent Gross–Pitaevskii equation is constructed, which describes the matter shock waves with chaotic or periodic amplitudes and phases.

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Measurement of the secular motion frequency and the space charge density in the linear ion trap Zhou Fei(周飞), Xie Yi(谢艺), Xu You-Yang(徐酉阳), Huang Xue-Ren(黄学人), and Feng Mang(冯芒) Chin. Phys. B, 2010, 19 (11):  113206.  DOI: 10.1088/1674-1056/19/11/113206 Abstract ( 1340 )   PDF (1756KB) ( 1169 )   This paper reports that a cloud of laser-cooled 40Ca+ is successfully trapped and manipulated in the home-built linear ion trap constructed for quantum information processing (QIP). The frequency of the secular motion and the space charge density of the ion cloud are measured, which help knowing the characteristic of the trapping potential and are the prerequisite of QIP with the trapped ions.

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Autler–Townes doublet in the absorption spectra for the transition between excited states of cold cesium atoms Liang Qiang-Bing(梁强兵), Yang Bao-Dong(杨保东), Yang Jian-Feng(杨建峰), Zhang Tian-Cai(张天才), and Wang Jun-Min(王军民) Chin. Phys. B, 2010, 19 (11):  113207.  DOI: 10.1088/1674-1056/19/11/113207 Abstract ( 1361 )   PDF (415KB) ( 652 )   Autler-Townes splitting in absorption spectra of the excited states 6 2P3/2 - 82S1/2 of cold cesium atoms confined in a magneto-optical trap has been observed. Experimental data of the Autler–Townes splitting fit well to the dressed-atom theory, by which the fact of the cold atoms dressed by cooling/trapping laser beams is revealed. The results of the theoretical fitting with experiment not only told us the effective Rabi frequency cold atoms experienced, but also could be used for measuring the probability amplitudes of the dressed states.

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Coherent control of non-resonant two-photon transition in molecular system Zhang Hui(张晖), Zhang Shi-An(张诗按), Wang Zu-Geng(王祖赓), and Sun Zhen-Rong(孙真荣) Chin. Phys. B, 2010, 19 (11):  113208.  DOI: 10.1088/1674-1056/19/11/113208 Abstract ( 1431 )   PDF (159KB) ( 660 )   In this paper, we study theoretically and experimentally the coherent control of non-resonant two-photon transition in a molecular system (Perylene dissolved in chloroform solution) by shaping the femtosecond pulses with simple phase patterns (cosinusoidal and $\pi$ phase step-function shape). The control efficiency of the two-photon transition probability is correlated with both the laser field and the molecular absorption bandwidth. Our results demonstrate that, the two-photon transition probability in a molecular system can be reduced but not completely eliminated by manipulating the laser field, and the control efficiency is minimal when the molecular absorption bandwidth is larger than twice the laser spectral bandwidth.

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Electromagnetically induced transparency based six-wave mixing in a Doppler-broadened folded four-level system Niu Jin-Yan(牛金艳), Pei Li-Ya(裴丽娅), Wu Ling-An(吴令安), and Fu Pan-Ming (傅盘铭) Chin. Phys. B, 2010, 19 (11):  113209.  DOI: 10.1088/1674-1056/19/11/113209 Abstract ( 1404 )   PDF (258KB) ( 887 )   We study phase-conjugate six-wave mixing spectroscopy based on electromagnetically-induced-transparency in a Doppler-broadened folded four-level system. It is found that the six-wave mixing spectrum can be either Doppler-free or very broad, depending on whether the interference between the polarisations of atoms with different velocities is constructive or destructive. To obtain the Doppler-free six-wave mixing spectrum in the folded four-level system, the conditions are more stringent in comparison with those in the cascade and N-type four-level systems. This polarisation interference can be controlled in the presence of a strong coupling field.

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Ionisation of Rydberg hydrogen atom near a metal surface by short pulse laser Wang Lei(汪磊), Yang Hai-Feng(杨海峰), Liu Xiao-Jun(柳晓军), and Liu Hong-Ping(刘红平) Chin. Phys. B, 2010, 19 (11):  113301.  DOI: 10.1088/1674-1056/19/11/113301 Abstract ( 1165 )   PDF (210KB) ( 690 )   In the ionisation of Rydberg hydrogen atoms near a metal surface, the electron will escape from the nucleus and arrive at the detector in a time sequence. This probability flux train relies on the initial electron wave packet irradiated by the laser pulse. For simplicity, the laser pulse is usually simplified to a delta function in energy domain, resulting in a sharp initial arrival time with an exponentially decaying tail at the detector. Actually and semiclassically, the initial outgoing wave should be modeled as an ensemble of trajectories propagating away from the atomic core in all directions with a range of launch times and a range of energies. In this case, each pulse in the pulse train is averaged out rather than a sharp profile. We examine how energy and time averaging of the electron wave packet affects the resolution of escaping electron pulses and study the energy dependence of the arrival time for each pulse in the ionisation train. An optimization condition for the laser pulse shape to generate narrow ionisation electron pulse in the train is obtained. The ionisation rates with various excitation energy are calculated also, which show the excitation to higher N Rydberg states will narrow the electron pulse as well.

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Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide Feng Wen-Ke(冯文科), Feng Yi-Yu(冯弈钰), Wang Shu-Feng(王树峰), Feng Wei(封伟), Yi Wen-Hui(易文辉), and Gong Qi-Huang(龚旗煌) Chin. Phys. B, 2010, 19 (11):  113401.  DOI: 10.1088/1674-1056/19/11/113401 Abstract ( 1678 )   PDF (233KB) ( 1436 )   This paper studies the intramolecular photoinduced electron-transfer (PET) of covalent bonded azobenzene-perylene diimide (AZO-PDI) in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 1011 s-1 is found. This PET process is also consolidated by femtosecond transient absorption spectra.

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Ab initio investigations of the charge transport properties of endohedral M@C20 (M= Na and K) metallofullerenes An Yi-Peng (安义鹏), Yang Chuan-Lu(杨传路), Wang Mei-Shan(王美山), Ma Xiao-Guang(马晓光), and Wang De-Hua(王德华) Chin. Phys. B, 2010, 19 (11):  113402.  DOI: 10.1088/1674-1056/19/11/113402 Abstract ( 1543 )   PDF (2391KB) ( 879 )   Using density functional theory and quantum transport calculations based on nonequilibum Green's function formalism, we investigate the charge transport properties of endohedral M@C20 (M= Na and K) metallofullerenes. Our results show that the conductance of C20 fullerene can be obviously improved by insertion of alkali atom at its centre. Both linear and nonlinear sections are found on the I-V curves of the Au-M@C20-Au two-probe systems. The novel negative differential resistance behaviour is also observed in Na@C20 molecule but not in K@C20.

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Investigation of the lateral spread of erbium ions implanted in silicon crystal Qin Xi-Feng(秦希峰), Chen Ming(陈明), Wang Xue-Lin(王雪林), Liang Yi(梁毅), and Zhang Shao-Mei(张少梅) Chin. Phys. B, 2010, 19 (11):  113403.  DOI: 10.1088/1674-1056/19/11/113403 Abstract ( 1514 )   PDF (389KB) ( 667 )   The erbium ions at energy of 400 keV and dose of 5×1015 ions/cm2 were implanted into silicon single crystals at room temperature at the angles of 0°, 45°and 60°. The lateral spread of 400 keV erbium ions implanted in silicon sample was measured by the Rutherford backscattering technique. The results show that the measured values were in good agreement with those obtained from the prediction of TRIM'98 (Transport of Ions in Matter) and SRIM2006 (Stopping and Range of Ions in Matter) codes.

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Accurate ab initio study of low-lying electronic states of phosphorus nitride radical Wang Jie-Min(王杰敏), Sun Jin-Feng(孙金锋), and Shi De-Heng(施德恒) Chin. Phys. B, 2010, 19 (11):  113404.  DOI: 10.1088/1674-1056/19/11/113404 Abstract ( 1297 )   PDF (157KB) ( 681 )   This paper employs the highly accurate valence internally contracted multireference configuration interaction method to investigate the potential energy curves (PECs) for the ground state (X1$\varSigma$+) and two low-lying excited states (A1$\varPi$ and D1$\varDelta$ of phosphorus nitride (PN) radical with the correlation-consistent basis set, aug-cc-pV6Z, in the valence range. Relativistic effects are considered in these calculations. The spectroscopic constants of the X1$\varSigma$+ and A1$\varPi$ states are calculated based on the PECs, and the results are in good accord with the available experimental data. The first 30 vibrational states for the A1$\varPi$ state and the first 40 vibrational states for the A1$\varPi$ state are determined when J =0. For each vibrational state, molecular constants $G(v)$, $B(v)$ and $D(v)$ are also attained.

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Positron-impact ionisation of atomic hydrogen in the presence of a bichromatic laser field Lou Jun(娄俊) and Li Shu-Min(李书民) Chin. Phys. B, 2010, 19 (11):  113405.  DOI: 10.1088/1674-1056/19/11/113405 Abstract ( 1039 )   PDF (601KB) ( 639 )   The positron impact-ionisation of atomic hydrogen in the presence of a linearly polarised bichromatic field is investigated in the first Born approximation. The field is composed of a fundamental frequency and its second harmonic. The state of positron in the field is described by the Volkov wavefunction, and the continuum state of the ejected electron is described by the Coulomb-Volkov wavefunction. The dressed ground state of target is a first order time-dependent perturbative wavefunction. The triple differential cross sections and their dependencies on laser field parameters are discussed and compared with the results modified by a monochromatic field. Numerical results show that the coherent phase control is significant and the laser-assisted ionisation cross sections caused by positron and electron are different.

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Molecular constants of LiCl(X1Σ+) and elastic collisions of two ground-state Cl and Li atoms at low and ultralow temperatures Zhu Zun-Lue(朱遵略), Zhang Xiao-Niu(张小妞), Kou Su-Hua(寇素华), Shi De-Heng(施德恒), and Sun Jin-Feng(孙金锋) Chin. Phys. B, 2010, 19 (11):  113501.  DOI: 10.1088/1674-1056/19/11/113501 Abstract ( 1279 )   PDF (473KB) ( 595 )   Interaction potentials for LiCl(X1Σ+) are constructed by the highly accurate valence internally contracted multireference configuration interaction in combination with a number of large correlation-consistent basis sets, which are used to determine the spectroscopic parameters (D0, De, Re, ωe, ωeχe, Be and αe. The potentials obtained at the basis sets, i.e., aug-cc-pV5Z-JKFI for Cl and cc-pV5Z for Li, are selected to study the elastic collision properties of Li and Cl atoms at the impact energies from 1.0×10-12 to 1.0×10-4 a.u. The derived total elastic cross sections are very large and almost constant at ultralow temperatures, and their shapes are mainly dominated by the s-partial wave at very low impact energies. Only one shape resonance can be found in the total elastic cross sections over the present collision energy regime, which is rather strong and obviously broadened by the overlap contributions of the abundant resonances coming from various partial waves. Abundant resonances exist for the elastic partial-wave cross sections until l = 22 partial waves. The vibrational manifolds of the LiCl(X1Σ+) molecule, which are predicted at the present level of theory and the basis sets cc-pV5Z for Li and the aug-cc-pV5Z-JKFI for Cl, should achieve much high accuracy due to the employment of the large correlation-consistent basis sets.

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Density functional study of AunCu (n=1–7) clusters Guo Jian-Jun(郭建军), Wei Cheng-Fu(魏成富), Yang Ji-Xian(杨继先), and Die Dong (迭东) Chin. Phys. B, 2010, 19 (11):  113601.  DOI: 10.1088/1674-1056/19/11/113601 Abstract ( 1451 )   PDF (1205KB) ( 943 )   The possible stable geometrical configurations and the relative stabilities of the lowest-lying isomers of copper-doped gold clusters, AunCu (n=1–7), are investigated using the density functional theory. Several low-lying isomers are determined. The results indicate that the ground-state AunCu clusters have planar structures for n = 1–7. The stability trend of the AunCu clusters (n=1–7), shows that odd-numbered AunCu clusters are more stable than the neighbouring even-numbered ones, thereby indicating the Au5Cu clusters are magic cluster with high chemical stability.

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The density functional calculations on the structural and electronic properties of the endohedral fullerene dimer (N2@C60)2 Gao Hong(高虹), Zhu Wei-Hua(朱卫华), Tang Chun-Mei(唐春梅), Geng Fang-Fang(耿芳芳), Yao Chang-Da(姚长达), Xu Yun-Ling(徐云玲), and Deng Kai-Ming(邓开明) Chin. Phys. B, 2010, 19 (11):  113602.  DOI: 10.1088/1674-1056/19/11/113602 Abstract ( 1589 )   PDF (1574KB) ( 753 )   The generalised gradient approximation based on density functional theory is used to study the structural and electronic properties of the endohedral fullerene dimer (N2@C60)2. Four N atoms sit at the cage centres in the form of two N2 molecules. The density of states and Mulliken charge analysis explore that the energy levels from -6 to -10 eV are mainly influenced by the N2 molecules.

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The density functional study of the stabilities, bond characters, static linear polarisabilities, and aromaticities of the `in-out' isomerism Hn-60@CnH60 (n=70, 72, 74) Tang Chun-Mei(唐春梅), Zhu Wei-Hua(朱卫华), and Deng Kai-Ming(邓开明) Chin. Phys. B, 2010, 19 (11):  113603.  DOI: 10.1088/1674-1056/19/11/113603 Abstract ( 1462 )   PDF (703KB) ( 553 )   This paper uses the density functional theory to analyse the stabilities, bond characters, static linear polarisabilities, and aromaticities of the 'in-out' isomerism Hn-60@CnH60 (n=70, 72, 74). The binding energies, C–H bond energies, and energy gaps explore that the 'in-out' isometric perhydrogenation of Cn (n=70, 72, 74) can remarkably improve the stabilities. The static linear polarisabilies of Hn-60@CnH60 (n=70, 72, 74) are indeed relative to their shapes, while they show almost nonaromatic character. This study can suggest that the 'in-out' isometric perhydrogenation of fullerenes could lead to the invention of entirely novel potential hydrogen storage nanomaterials.

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Irregular phenomenon induced by Ag atomic segregation during the heating process of Ag–Pd cluster Xiao Xu-Yang(肖绪洋) Chin. Phys. B, 2010, 19 (11):  113604.  DOI: 10.1088/1674-1056/19/11/113604 Abstract ( 1278 )   PDF (789KB) ( 674 )   This paper studies the melting of icosahedral Ag–Pd bimetallic clusters by using molecular dynamics with the embedded atom method. It finds that the mixed Ag–Pd cluster shows an irregular phenomenon before melting, i.e., the atomic energy decreases with the increase of temperature. It indicates that the segregation of Ag atoms results in this phenomenon by analysing atomic radius distribution. Since the surface energy of Ag is lower than that of Pd, this leads to the result that the decreased energy by the Ag atomic segregation is larger than the increased energy by the heating. This provides a new method to obtain irregular thermodynamic properties.

CLASSICAL AREAS OF PHENOMENOLOGY

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A simple and effective model for Jones matrix to evaluate the transmission performance of Savart polariscope Wu Hai-Ying(吴海英), Zhang Chun-Min(张淳民), and Li Jie(李杰) Chin. Phys. B, 2010, 19 (11):  114201.  DOI: 10.1088/1674-1056/19/11/114201 Abstract ( 1119 )   PDF (479KB) ( 962 )   Starting from the wave normal tracing treatment in the Savart polariscope that relates the Jones matrix to its transmission performance, this paper establishes a simple and effective model for the Jones matrix at an arbitrary incidence in the spatial domain. Analytical expressions of all the matrix components are determined with the consideration of all the main impact factors. This model needs only a few parameters hence it is convenient to be employed to evaluate the propagation performance of any birefringent optical system. The simulated results obtained with it demonstrate that this model gives a precise representation of the characteristic of light propagation in the Savart polariscope. This would provide useful suggestions for the design, calibration, and performance improvement of any other birefringent polarisation element and optical system.

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Transmittance investigation on capacitive mesh on thick dielectric substrates as output windows for optically pumped terahertz lasers Qi Chun-Chao(祁春超), Zuo Du-Luo(左都罗), Lu Yan-Zhao(卢彦兆), Tang Jian(唐建), and Cheng Zu-Hai(程祖海) Chin. Phys. B, 2010, 19 (11):  114202.  DOI: 10.1088/1674-1056/19/11/114202 Abstract ( 1314 )   PDF (613KB) ( 871 )   This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm thick). Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation, a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s. A transmittance spectrum of the output window in a certain frequency range (say, from zero to 1 THz) has been obtained by using THz time domain spectroscopy. Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model (TLM) containing attenuation component from dielectric substrate. The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz. Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.

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Research of photolithography technology based on surface plasmon Li Hai-Hua(李海华), Chen Jian(陈健), and Wang Qing-Kang(王庆康) Chin. Phys. B, 2010, 19 (11):  114203.  DOI: 10.1088/1674-1056/19/11/114203 Abstract ( 1539 )   PDF (1928KB) ( 1188 )   This paper demonstrates a new process of the photolithography technology, used to fabricate simply fine patterns, by employing surface plasmon character. The sub-wavelength periodic silica structures with uniform silver film are used as the exposure mask. According to the traditional semiconductor process, the grating structures are fabricated at exposing wavelength of 436 nm. At the same time, it provides additional and quantitative support of this technique based on the finite-difference time-domain method. The results of the research show that surface plasmon characteristics of metals can be used to increase the optical field energy distribution differences through the silica structures with silver film, which directly impact on the exposure of following photosensitive layer in different regions.

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The anomalous radiation force of light on a left-handed material Yi Xu-Nong(易煦农), Liu Jin-Song(刘劲松), Chen Huan(陈欢), and Du Qiu-Jiao(杜秋姣) Chin. Phys. B, 2010, 19 (11):  114204.  DOI: 10.1088/1674-1056/19/11/114204 Abstract ( 1590 )   PDF (719KB) ( 740 )   This paper derives the force of the electromagnetic radiation on left-handed materials (LHMs) by a direct application of the Lorentz law of classical electrodynamics. The expressions of radiation force are given for TE-polarised and TM-polarised fields. The numerical results demonstrate that electromagnetic waves exert an inverse lateral radiation force on each edge of the beams, that is, the lateral pressure is expansive for TE-polarised beams and compressive for TM-polarised beams. The investigation of the radiation force will provide insights into the fundamental properties of LHMs and will provide to better understanding of the interaction of light with LHMs.

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Comprehensive research on self phase modulation based optical delay systems Yang Ai-Ying(杨爱英) and Sun Yu-Nan(孙雨南) Chin. Phys. B, 2010, 19 (11):  114205.  DOI: 10.1088/1674-1056/19/11/114205 Abstract ( 1301 )   PDF (7181KB) ( 641 )   This paper comprehensively investigates the properties of self phase modulation based optical delay systems consisting of dispersion compensation fibre and highly nonlinear fibres. It researches into the impacts of power level launched into highly nonlinear fibres, conversion wavelength, dispersion slope, modulation format and optical filter bandwidth on the overall performance of optical delay systems. The results reveal that, if the power launched into highly nonlinear fibres is fixed, the time delay generally varies linearly with the conversion wavelength, but jumps intermittently at some conversion wavelengths. However, the time delay varies semi-periodically with the power launched into highly nonlinear fibres. The dispersion slope of highly nonlinear fibres has significant influence on the time delay, especially for the negative dispersion slope. The time delay differs with modulation formats due to the different combined interaction of nonlinearity and dispersion in fibres. The bandwidth of the optical filters also greatly affects the time delay because it determines the bandwidth of the passed signal in the self phase modulation based time delay systems. The output signal quality of the overall time delay systems depends on the conversion wavelength and input power level. The optimisation of the power level and conversion wavelength to provide the best output signal quality is made at the end of this paper.

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Solving nonlinear master equation describing quantum damping by virtue of the entangled state representation Fan Hong-Yi(范洪义), Ren Gang(任刚), Hu Li-Yun(胡利云), and Jiang Nian-Quan(姜年权) Chin. Phys. B, 2010, 19 (11):  114206.  DOI: 10.1088/1674-1056/19/11/114206 Abstract ( 1334 )   PDF (164KB) ( 690 )   This paper solves the newly constructed nonlinear master equation dρ/dt=κ[2f(N)aρ(1/f(N-1) )a$\dagger$-a$\dagger$aρ -ρa$\dagger$a] , where f(N) is an operator-valued function of N=a$\dagger$a, for describing amplitude damping channel, and derives the infinite operator sum representation of quasi-Kraus operators for the density operator. It also shows that in this nonlinear process the initial pure number state density operator will evolve into the binomial field (a mixed state) when f(N)=1/√(N+1).

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Nonlinear images of scatterers in chirped pulsed laser beams Hu Yong-Hua(胡勇华), Wang You-Wen(王友文), Wen Shuang-Chun(文双春), and Fan Dian-Yuan(范滇元) Chin. Phys. B, 2010, 19 (11):  114207.  DOI: 10.1088/1674-1056/19/11/114207 Abstract ( 1193 )   PDF (1071KB) ( 609 )   The bandwidth and the duration of incident pulsed beam are proved to play important roles in modifying the nonlinear image of amplitude-type scatterer. It is found that the initially positive chirp-type bandwidth can suppress the nonlinear image, while the negative one can enhance it, and that both effects are inversely proportional to the incident pulse duration. Numerical simulations further demonstrate that the location of nonlinear image is at the conjugate plane of the scatterer and that, for negatively pre-chirped pulsed beam, the nonlinear image peak intensity can be higher than that in the corresponding monochromatic case under certain conditions. Moreover the effect of group velocity dispersion on nonlinear image is found to be similar to that of chirp-type bandwidth.

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Second-harmonic generation circular dichroism spectroscopy from tripod-like chiral molecular films Wang Xiao-Ou(王晓鸥), Chen Li-An(陈立安), Chen Li-Xue(陈历学), Sun Xiu-Dong(孙秀冬), Li Jun-Qing(李俊庆), and Li Chun-Fei(李淳飞) Chin. Phys. B, 2010, 19 (11):  114208.  DOI: 10.1088/1674-1056/19/11/114208 Abstract ( 1250 )   PDF (320KB) ( 992 )   The second-harmonic generation (SHG) circular dichroism in the light of reflection from chiral films of tripod-like chiral molecules is investigated. The expressions of the second-harmonic generation circular dichroism are derived from our presented three-coupled-oscillator model for the tripod-like chiral molecules. Spectral dependence of the circular dichroism of SHG from film surface composed of tripod-like chiral molecules is simulated numerically and analysed. Influence of chiral parameters on the second-harmonic generation circular dichroism spectrum in chiral films is studied. The result shows that the second-harmonic generation circular dichroism is a sensitive method of detecting chirality compared with the ordinary circular dichroism in linear optics. All of our work indicates that the classical molecular models are very effective to explain the second-harmonic generation circular dichroism of chiral molecular system. The classical molecular model theory can give us a clear physical picture and brings us very instructive information about the link between the molecular configuration and the nonlinear processes.

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Compact and tunable mid-infrared source based on a 2 μm dual-wavelength KTiOPO4 intracavity optical parametric oscillator Geng You-Fu(耿优福), Tan Xiao-Ling(谭晓玲), Li Xue-Jin(李学金), and Yao Jian-Quan(姚建铨) Chin. Phys. B, 2010, 19 (11):  114209.  DOI: 10.1088/1674-1056/19/11/114209 Abstract ( 1512 )   PDF (600KB) ( 789 )   Using a double resonant KTiOPO4 (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42-19.52 μm, and a peak power of 834 W for type-I phase matching scheme and 730 W for type-II phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range.

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Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal Liu Zheng-Qi(刘正奇), Feng Tian-Hua(冯天华), Dai Qiao-Feng(戴峭峰), Wu Li-Jun(吴立军), Lan Sheng(兰胜), Ding Cai-Rong(丁才蓉), Wang He-Zhou(汪河洲), and Gopal Achanta Venu Chin. Phys. B, 2010, 19 (11):  114210.  DOI: 10.1088/1674-1056/19/11/114210 Abstract ( 1310 )   PDF (3161KB) ( 793 )   This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal. In experiments, semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated. The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements. The modification of the spontaneous emission rate, which is reflected in the change of spectral shape and PL lifetime, is clearly observed. While an obvious increase in the PL lifetime is found at most wavelengths in the band gap, a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge. Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal. It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously. This finding provides a simple and effective way for improving the performance of light emitting devices.

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A time reversal damage imaging method for structure health monitoring using Lamb waves Zhang Hai-Yan(张海燕), Cao Ya-Ping(曹亚萍), Sun Xiu-Li(孙修立), Chen Xian-Hua(陈先华), and Yu Jian-Bo(于建波) Chin. Phys. B, 2010, 19 (11):  114301.  DOI: 10.1088/1674-1056/19/11/114301 Abstract ( 1291 )   PDF (532KB) ( 1075 )   This paper investigates the Lamb wave imaging method combining time reversal for health monitoring of a metallic plate structure. The temporal focusing effect of the time reversal Lamb waves is investigated theoretically. It demonstrates that the focusing effect is related to the frequency dependency of the time reversal operation. Numerical simulations are conducted to study the time reversal behaviour of Lamb wave modes under broadband and narrowband excitations. The results show that the reconstructed time reversed wave exhibits close similarity to the reversed narrowband tone burst signal validating the theoretical model. To enhance the similarity, the cycle number of the excited signal should be increased. Experiments combining finite element model are then conducted to study the imaging method in the presence of damage like hole in the plate structure. In this work, the time reversal technique is used for the recompression of Lamb wave signals. Damage imaging results with time reversal using broadband and narrowband excitations are compared to those without time reversal. It suggests that the narrowband excitation combined time reversal can locate and determine the size of structural damage more precisely, but the cycle number of the excited signal should be chosen reasonably.

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Time-domain analysis of second-harmonic generation of primary Lamb wave propagation in an elastic plate Deng Ming-Xi(邓明晰) and Xiang Yan-Xun(项延训) Chin. Phys. B, 2010, 19 (11):  114302.  DOI: 10.1088/1674-1056/19/11/114302 Abstract ( 1270 )   PDF (5027KB) ( 1107 )   Within the second-order perturbation approximation, this paper investigates the physical process of generation of the time-domain second harmonic by a primary Lamb wave waveform in an elastic plate. The present work is performed based on the preconditions that the phase velocity matching is satisfied and that the transfer of energy from the primary Lamb wave to the double frequency Lamb wave is not zero. It investigates the influences of the difference between the group velocities of the primary Lamb wave and the double frequency Lamb wave, the propagation distance and the duration of the primary Lamb wave waveform on the envelope shape of the time-domain second harmonic. It finds that the maximum magnitude of the envelope of the second-harmonic waveform can grow within some propagation distance even if the condition of group velocity matching is not satisfied. Our analyses also indicate that the maximum magnitude of the envelope of the second-harmonic waveform is kept constant beyond a specific propagation distance. Furthermore, it concludes that the integration amplitude of the time-domain second-harmonic waveform always grows with propagation distance within the second-order perturbation. The present research yields new physical insight not previously available into the effect of generation of the time-domain second harmonic by propagation of a primary Lamb wave waveform.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Properties of plasma radiation during discharges with improved confinement on HL-2A Tokamak Gao Jin-Ming(高金明), Liu Yi(刘仪), Li Wei(李伟), Cui Zheng-Ying(崔正英), Zhou Yan(周艳), Huang Yuan(黄渊), and Ji Xiao-Quan(季小全) Chin. Phys. B, 2010, 19 (11):  115201.  DOI: 10.1088/1674-1056/19/11/115201 Abstract ( 1043 )   PDF (2315KB) ( 834 )   In the recent experiment on the HL-2A tokamak, two types of improved confinement regimes have been achieved in different configurations. One is the improved confinement regime in limiter configuration during electron cyclotron resonant heating (ECRH), characterized by a sharp decrease in Hα emission accompanied by an increase in the total radiation of plasma, the line averaged electron density and the stored energy of plasma. The other is high confinement regime (H-mode) in divertor configuration during a combination of ECRH and Neutral beam injection (NBI) heating, characterized with edge localized modes (ELMs) besides the features mentioned above. The ELMs are found to be localized on the plasma edge (r/a ≥ 0.8), causing average losses of particles and stored energy in the ranges of about 1–3% and 3–5% respectively during a single ELM event. So far, the ELMs observed in the HL-2A are type III ELMs with low amplitude and high repetition frequency in a range from 200 Hz to 350 Hz. An investigation of the radiated power density profiles shows that radiative cooling effect plays a significant role in the transition back to the L-mode and the triggering of ELM events.

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Influence of core property on multi-electron process in slow collisions of isocharged sequence ions with neon Lu Rong-Chun(卢荣春), Yu De-Yang(于得洋), Shao Cao-Jie(邵曹杰), Ruan Fang-Fang(阮芳芳), and Cai Xiao-Hong(蔡晓红) Chin. Phys. B, 2010, 19 (11):  115202.  DOI: 10.1088/1674-1056/19/11/115202 Abstract ( 1349 )   PDF (1884KB) ( 1044 )   Influence of core property on multi-electron process in the collisions of q=6-9 and 11 isocharged sequence ions with Ne is investigated in the keV/u region. The cross-section ratios of double-, triple-, quadruple- and total multi-electron processes to the single electron capture process as well as the partial ratios of different reaction channels to the relevant multi-electron process are measured by using position-sensitive and time-of-flight techniques. The experimental data are compared with the theoretical predictions including the extended classical over-barrier model, the molecular Columbic barrier model and the semi-empirical scaling law. Results show a core effect on multi-electron process of isocharge ions colliding with Neon, which is consistent with the results of Helium we obtained previously.

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Nonlinear acoustic waves in a collisional self-gravitating dusty plasma Guo Zhi-Rong(郭志荣), Yang Zeng-Qiang(杨增强), Yin Bao-Xiang(殷保祥), and Sun Mao-Zhu(孙茂珠) Chin. Phys. B, 2010, 19 (11):  115203.  DOI: 10.1088/1674-1056/19/11/115203 Abstract ( 1270 )   PDF (241KB) ( 873 )   Using the reductive perturbation method, we investigate the small amplitude nonlinear acoustic wave in a collisional self-gravitating dusty plasma. The result shows that the small amplitude dust acoustic wave can be expressed by a modified Korteweg-de Vries equation, and the nonlinear wave is instable because of the collisions between the neutral gas molecules and the charged particles.

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Investigation of electric fields inside and outside a magnetised cold plasma sphere Li Ying-Le(李应乐), Wang Ming-Jun(王明军), and Dong Qun-Feng(董群峰) Chin. Phys. B, 2010, 19 (11):  115204.  DOI: 10.1088/1674-1056/19/11/115204 Abstract ( 1398 )   PDF (353KB) ( 744 )   Based on the scales transformation of electromagnetic theory, the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter. The obtained results are in good agreement with that in the literature. The angle between the direction of inside field and that of outside field is derived. In S wave band, calculations for the effects induced by parameters of the inner field are established. Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably. The inner field will increase as the electron density increases. The inner field varies with frequency nonlinearly. There is an angle between the inner field and the incident field, it changes nonlinearly with the frequency.

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Finite Larmor radius magnetohydrodynamic analysis of the ballooning modes in tokamaks Jiang Hai-Bin(蒋海斌), Wang Ai-Ke(王爱科), and Peng Xiao-Dong(彭晓东) Chin. Phys. B, 2010, 19 (11):  115205.  DOI: 10.1088/1674-1056/19/11/115205 Abstract ( 1168 )   PDF (982KB) ( 757 )   In this paper, the effect of finite Larmor radius (FLR) on high n ballooning modes is studied on the basis of FLR magnetohydrodynamic (FLR-MHD) theory. A linear FLR ballooning mode equation is derived in an '$\hat{s}$- \alpha' type equilibrium of circular-flux-surfaces, which is reduced to the ideal ballooning mode equation when the FLR effect is neglected. The present model reproduces some basic features of FLR effects on ballooning mode obtained previously by kinetic ballooning mode theories. That is, the FLR introduces a real frequency into ballooning mode and has a stabilising effect on ballooning modes (e.g., in the case of high magnetic shear $\hat{s}$ ≥ 0.8). In particular, some new properties of FLR effects on ballooning mode are discovered in the present research. Here it is found that in a high magnetic shear region ($\hat{s}$ ≥ 0.8) the critical pressure gradient (αc,FLR ) of ballooning mode is larger than the ideal one (αc,IMHD ) and becomes larger and larger with the increase of FLR parameter b0 . However, in a low magnetic shear region, the FLR ballooning mode is more unstable than the ideal one, and the αc,FLR is much lower than the αc,IMHD . Moreover, the present results indicate that there exist some new weaker instabilities near the second stability boundary (obtained from ideal MHD theory), which means that the second stable region becomes narrow.

RAPID COMMUNICATION

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Brillouin scattering study on elastic and piezoelectric properties of laser irradiated ZnO single crystals Liu Jie(刘洁) and Jiang Yi-Jian(蒋毅坚) Chin. Phys. B, 2010, 19 (11):  116201.  DOI: 10.1088/1674-1056/19/11/116201 Abstract ( 1520 )   PDF (183KB) ( 829 )   Brillouin light scattering technique can be successfully used to determine the whole set of elastic and piezoelectric constants of a ZnO single crystal irradiated by different laser energy densities, into a micron range (radiation layer thickness). It is found that the scattering intensity, the linewidth and the Brillouin scattering shift of acoustic phonons are all strongly dependent on laser energy density. Based on the sound propagation equations and these results, the directional dependences of the compressional and shear moduli of the irradiated ZnO sample in the (001) plane are investigated. It is found that under an appropriate laser condition, 248 nm KrF excimer laser irradiation can significantly improve the surface quality and increase the elastic properties of ZnO single crystal. This procedure has potential applications in the fabrication of ZnO-based surface acoustic wave and optic-electronic devices.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Stochastic systems with cross-correlated Gaussian white noises Wang Cheng-Yu(王成玉), Gao Yun(高云), Song Yu-Min(宋玉敏), Zhou Peng(周鹏), and Yang Hai(杨海) Chin. Phys. B, 2010, 19 (11):  116401.  DOI: 10.1088/1674-1056/19/11/116401 Abstract ( 1378 )   PDF (225KB) ( 1391 )   This paper theoretically investigates three stochastic systems with cross-correlation Gaussian white noises. Both steady state properties of the stochastic nonlinear systems and the nonequilibrium transitions induced by the cross-correlated noises are studied. The stationary solutions of the Fokker-Planck equation for three specific examples are analysed. It is shown explicitly that the cross-correlation of white noises can induce nonequilibrium transitions.

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Effects of AlN nucleation layer thickness on crystal quality of AlN grown by plasma-assisted molecular beam epitaxy Ren Fan(任凡), Hao Zhi-Biao(郝智彪), Hu Jian-Nan(胡健楠), Zhang Chen(张辰), and Luo Yi(罗毅) Chin. Phys. B, 2010, 19 (11):  116801.  DOI: 10.1088/1674-1056/19/11/116801 Abstract ( 1334 )   PDF (2257KB) ( 2129 )   In this paper, the effects of thickness of AlN nucleation layer grown at high temperature on AlN epi-layer crystalline quality are investigated. Crack-free AlN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy. The AlN crystalline quality is analysed by transmission electron microscope and x-ray diffraction (XRD) rocking curves in both (002) and (102) planes. The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope. A critical nucleation thickness for realising high quality AlN films is found. When the nucleation thickness is above a certain value, the (102) XRD full width at half maximum (FWHM) of AlN bulk increases with nucleation thickness increasing, whereas the (002) XRD FWHM shows an opposite trend. These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AlN main layer growth.

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

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First-principle study on phase Al0.8Ni3Sn0.2 in Sn-Ni-Al alloy as anode for lithium ion battery Huang Zhao-Wen(黄钊文), Hu She-Jun(胡社军), Hou Xian-Hua(侯贤华), Zhao Ling-Zhi(赵灵智), Ru Qiang(汝强),Li Wei-Shan(李伟善), and Zhang Zhi-Wen(张志文) Chin. Phys. B, 2010, 19 (11):  117101.  DOI: 10.1088/1674-1056/19/11/117101 Abstract ( 1419 )   PDF (1743KB) ( 836 )   The mechanism of lithium intercalation/deintercalation for phase Al0.8Ni3Sn0.2 as anode material used in lithium ion battery was studied carefully based on the first-principle plane wave pseudo-potential method. The calculated results indicated that Sn–Ni–Al alloy had high theoretical capacity when used as anode material, however, there was high initial irreversible capacity loss because of the large volume expansion. Therefore the technological parameters during preparing the Sn–Ni–Al anode should be controlled strictly to make the content of Al0.8Ni3Sn0.2 phase as low as possible and to make the anode consist of promising Sn–Ni and Al–Ni phases. For comparison, an experiment based on magnetron sputtering was done. The result showed that the calculation is in good agreement with the experiment. We found that the first-principle investigation method is of far-reaching significance in synthesising new commercial anode materials with high capacity and good cycle performance.

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Comparisons of ZnO codoped by group IIIA elements (Al, Ga, In) and N: a first-principle study Li Ping(李平), Deng Sheng-Hua(邓胜华), Zhang Li(张莉), Yu Jiang-Ying(余江应), and Liu Guo-Hong(刘果红) Chin. Phys. B, 2010, 19 (11):  117102.  DOI: 10.1088/1674-1056/19/11/117102 Abstract ( 1777 )   PDF (525KB) ( 1171 )   The electronic structures and effective masses of the N mono-doped and Al–N, Ga–N, In–N codoped ZnO system have been calculated by a first-principle method, and comparisons among different doping cases are made. According to the results, the impurity states in the codoping cases are more delocalised compared to the N mono-doping case, which means a better conductive behaviour can be obtained by codoping. Besides, compared to the Al–N and Ga–N codoping cases, the hole effective mass of In–N codoped system is much smaller, indicating the p-type conductivity can be more enhanced by In–N codoping.

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Electronic and optical properties of pure and Ce3+-doped CaS single crystals: a first-principles prediction Chen Zhong-Jun(陈中钧) and Tian Dong-Bin(田东斌) Chin. Phys. B, 2010, 19 (11):  117103.  DOI: 10.1088/1674-1056/19/11/117103 Abstract ( 1211 )   PDF (2008KB) ( 824 )   This paper investigates the electronic and optical properties for pure and Ce3+-doped CaS crystals by using the first-principles total energy calculations. The results show that CaS:Ce has a direct band gap of 2.16 eV, and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states, respectively. Our results validate that the yellow emission from CaS:Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration. The Ce–S bond shows more covalent character than the Ca–S bond.

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Strain effects on optical polarisation properties in (1122) plane GaN films Hao Guo-Dong(郝国栋), Chen Yong-Hai(陈涌海), Fan Ya-Ming(范亚明), Huang Xiao-Hui(黄晓辉), and Wang Huai-Bing(王怀兵) Chin. Phys. B, 2010, 19 (11):  117104.  DOI: 10.1088/1674-1056/19/11/117104 Abstract ( 1415 )   PDF (986KB) ( 587 )   We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the (1122)-plane. The calculations are performed by the κ• p perturbation theory approach through using the effective-mass Hamiltonian for an arbitrary direction. The results show that the transition energies decrease with the biaxial strains changing from –0.5% to 0.5%. For films of (1122)-plane, the strains are expected to be anisotropic in the growth plane. Such anisotropic strains give rise to valence band mixing which results in dramatic change in optical polarisation property. The strain can also result in optical polarisation switching phenomena. Finally, we discuss the applications of these properties to the (1122) plane GaN-based light-emitting diode and lase diode.

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The complex band structure for armchair graphene nanoribbons Zhang Liu-Jun(张留军) and Xia Tong-Sheng(夏同生) Chin. Phys. B, 2010, 19 (11):  117105.  DOI: 10.1088/1674-1056/19/11/117105 Abstract ( 1330 )   PDF (741KB) ( 1616 )   Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N=3M-1. The band gap is almost unchanged for N=3M+1, but decreased for N=3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons, and is also classified into three classes.

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Influence of annealing conditions on impurity species in arsenic-doped HgCdTe grown by molecular beam epitaxy Yue Fang-Yu(越方禹), Chen Lu(陈璐), Li Ya-Wei(李亚巍), Hu Zhi-Gao(胡志高), Sun Lin(孙琳), Yang Ping-Xiong(杨平雄), and Chu Jun-Hao(褚君浩) Chin. Phys. B, 2010, 19 (11):  117106.  DOI: 10.1088/1674-1056/19/11/117106 Abstract ( 1405 )   PDF (232KB) ( 1027 )   Based on our previous work, the influence of annealing conditions on impurity species in in-situ arsenic (As)-doped Hg1-xCdxTe (x≈ 0.3) grown by molecular beam epitaxy has been systematically investigated by modulated photoluminescence spectra. The results show that (i) the doped-As acting as undesirable shallow/deep levels in as-grown can be optimized under proper annealing conditions and the physical mechanism of the disadvantage of high activation temperature, commonly assumed to be more favourable for As activation, has been discussed as compared with the reports in the As-implanted HgCdTe epilayers (x≈ 0.39), (ii) the density of VHg has an evident effect on the determination of bandgap (or composition) of epilayers and the excessive introduction of VHg will lead to a short-wavelength shift of epilayers, and (iii) the VHg prefers forming the VHg–AsHg complex when the inactivated-As (AsHg or related) coexists in a certain density, which makes it difficult to annihilate VHg in As-doped epilayers. As a result, the bandedge electronic structures of epilayers under different conditions have been drawn as a brief guideline for preparing extrinsic p-type epilayers or related devices.

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Disorder-induced enhancement of conductance in doped nanowires Xu Ning(徐宁),Wang Bao-Lin(王保林), Sun Hou-Qian(孙厚谦), and Kong Fan-Jie(孔凡杰) Chin. Phys. B, 2010, 19 (11):  117201.  DOI: 10.1088/1674-1056/19/11/117201 Abstract ( 1385 )   PDF (839KB) ( 598 )   A new mechanism is proposed to explain the enhancement of conductance in doped nanowires. It is shown that the anomalous enhancement of conductance is due to surface doping. The conductance in doped nanowires increases with dopant concentration, which is qualitatively consistent with the existing experimental results. In addition, the I-V curves are linear and thus suggest that the metal electrodes make ohmic contacts to the shell-doped nanowires. The electric current increases with wire diameter (D) and decreases exponentially with wire length (L). Therefore, the doped nanowires have potential application in nanoscale electronic and optoelectronic devices.

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A theoretical extraction scheme of transport information based on exclusion models Chen Hua(陈华), Du Lei(杜磊), Qu Cheng-Li(曲成立), Li Wei-Hua(李伟华), He Liang(何亮), Chen Wen-Hao(陈文豪), and Sun Peng(孙鹏) Chin. Phys. B, 2010, 19 (11):  117202.  DOI: 10.1088/1674-1056/19/11/117202 Abstract ( 1299 )   PDF (193KB) ( 562 )   In order to explore how to extract more transport information from current fluctuation, a theoretical extraction scheme is presented in a single barrier structure based on exclusion models, which include counter-flows model and tunnel model. The first four cumulants of these two exclusion models are computed in a single barrier structure, and their characteristics are obtained. A scheme with the help of the first three cumulants is devised to check a transport process to follow the counter-flows model, the tunnel model or neither of them. Time series generated by Monte Carlo techniques is adopted to validate the abstraction procedure, and the result is reasonable.

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Preparation and study on performance of submicron nickel powder for multilayer chip positive temperature coefficient resistance Hot! Chen Yong(陈勇), Gong Shu-Ping(龚树萍), Fu Qiu-Yun(傅邱云), Zheng Zhi-Ping(郑志平), Huang Ri-Ming(黄日明), and Su Peng(苏鹏) Chin. Phys. B, 2010, 19 (11):  117301.  DOI: 10.1088/1674-1056/19/11/117301 Abstract ( 1167 )   PDF (1553KB) ( 888 )   Base metal nickel is often used as the inner electrode in multilayer chip positive temperature coefficient resistance (PTCR). The fine grain of ceramic powders and base metal nickel are necessary. This paper uses reducing hydrazine to gain submicron nickel powder whose diameter was 200–300 nm through adjusting the consumption of nucleating agent PVP properly. The submicron nickel powder could disperse well and was fit for co——fired of multilayer chip PTCR. It analyes the submicron nickel powder through x-ray Diffraction (XRD) and calculates the diameter of nickel by PDF cards. Using XRD analyses it obtains several conclusions: If the molar ratio of hydrazine hydrate and nickel sulfate is kept to be a constant, when enlarging the molar ratio of NaOH/Ni2+, the diameter of nickel powder would become smaller. When the temperature in the experiment raises to 70–80℃, nickel powder becomes smaller too. And if the molar ratio of NaOH/Ni2+ is 4, when molar ratio of (C2H5O)2/Ni2+ increases, the diameter of nickel would reduce. Results from viewing the powders by optical microscope should be the fact that the electrode made by submicron nickel powder has a better formation and compactness. Furthermore, the sheet resistance testing shows that the electrode made by submicron nickel is smaller than that made by micron nickel.

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Coherent spectroscopy of a strongly driven triple quantum dot molecule Xie Yan(解研), Duan Su-Qing(段素青), Chu Wei-Dong(楚卫东), and Yang Ning(杨宁) Chin. Phys. B, 2010, 19 (11):  117302.  DOI: 10.1088/1674-1056/19/11/117302 Abstract ( 1466 )   PDF (2430KB) ( 769 )   Based on a calculation model, we study the interference phenomena of serially coupled V-type and Λ-type triple quantum dots (CTQDs) driven simultaneously by a strong driving field and a weak probe field. Strongly depending on the configuration of the three-level CTQD, the probe absorption spectra, which are shown in the tunneling current, exhibit various quantum coherence properties. In the case where the two pairs of transitions of the CTQD have a small eigenfrequency difference Δω, the double-coupling effect of the driving field results in two Autler-Townes doublets and one weak Mollow triplet in one spectrum. With the value of Δω increasing, only one Autler-Townes splitting remains due to the single-coupling of the field. We also find that the effect of spontaneous emission of phonons may lead to an obvious background current, which can be used to distinguish which transition is driven by the driving field in experiment. The interesting quantum property of a CTQD revealed in our results suggests its potential applications in quantum modulators and quantum logic devices.

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Electron tunneling effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells Ji Zi-Wu(冀子武), Zheng Yu-Jun(郑雨军), and Xu Xian-Gang(徐现刚) Chin. Phys. B, 2010, 19 (11):  117303.  DOI: 10.1088/1674-1056/19/11/117303 Abstract ( 1341 )   PDF (524KB) ( 590 )   We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Also, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures.

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Optimizing bowtie structure parameters for specific incident light Wang Qiao(王乔), Wu Shi-Fa(吴世法), Li Xu-Feng(李旭峰), and Wang Xiao-Gang(王晓钢) Chin. Phys. B, 2010, 19 (11):  117304.  DOI: 10.1088/1674-1056/19/11/117304 Abstract ( 1572 )   PDF (401KB) ( 704 )   We investigate optical properties of a bowtie-shaped aperture using the finite difference time domain method to optimize its geometric parameters for specific incident lights. The influence of the parameters on local field enhancement and resonant wavelength in the visible frequency range is numerically analysed. It is found that the major resonance of the spectrum is exponentially depended on the bowtie angle but independent of the whole aperture size. The simulation also demonstrates that increasing the aperture size raises the local field intensity on the exit plane due to an enlarged interaction area between the light and the metal medium. And the near-field spot size is closely related to the gap. Based on these results, the design rules of the bowtie structure can be optimized for specific wavelengths excited.

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On the tunneling time of arbitrary continuous potentials and the Hartman effect Yin Cheng(殷澄), Wu Zhi-Jing(吴至境), Wang Xian-Ping(王贤平), Sun Jing-Jing(孙晶晶), and Cao Zhuang-Qi(曹庄琪) Chin. Phys. B, 2010, 19 (11):  117305.  DOI: 10.1088/1674-1056/19/11/117305 Abstract ( 1247 )   PDF (181KB) ( 920 )   This paper obtains a generalized tunneling time of one-dimensional potentials via time reversal invariance. It also proposes a simple explanation for the Hartman effect using the useful concept of the scattered subwaves.

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Effect of film thickness on interfacial barrier of manganite-based heterojunctions Xie Yan-Wu (谢燕武), Guo De-Feng (郭得峰), Sun Ji-Rong(孙继荣), and Shen Bao-Gen(沈保根) Chin. Phys. B, 2010, 19 (11):  117306.  DOI: 10.1088/1674-1056/19/11/117306 Abstract ( 1364 )   PDF (942KB) ( 662 )   Interfacial barrier is a key factor that determines the performances of heterojunctions. In this work, we study the effect of manganite film thickness on the effective interfacial barrier for La0.67Sr0.33MnO3/Nb:SrTiO3 junctions. The barrier is extracted from the forward current--voltage characteristics. Our results demonstrate that the barrier decreases gradually from ～0.85 eV to ～0.60 eV when the film thickness decreases from 150 nm to 2 nm. The overall value of the barrier is only about 50% of the corresponding one determined from the photovoltaic effect.

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

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Impact of the displacement damage in channel and source/drain regions on the DC characteristics degradation in deep-submicron MOSFETs after heavy ion irradiation Xue Shou-Bin(薛守斌), Huang Ru(黄如), Huang De-Tao(黄德涛), Wang Si-Hao(王思浩), Tan Fei(谭斐), Wang Jian(王健), An Xia (安霞), and Zhang Xing(张兴) Chin. Phys. B, 2010, 19 (11):  117307.  DOI: 10.1088/1674-1056/19/11/117307 Abstract ( 1636 )   PDF (2091KB) ( 994 )   This paper mainly reports the permanent impact of displacement damage induced by heavy-ion strikes on the deep-submicron MOSFETs. Upon the heavy ion track through the device, it can lead to displacement damage, including the vacancies and the interstitials. As the featured size of device scales down, the damage can change the dopant distribution in the channel and source/drain regions through the generation of radiation-induced defects and thus have significant impacts on their electrical characteristics. The measured results show that the radiation-induced damage can cause DC characteristics degradations including the threshold voltage, subthreshold swing, saturation drain current, transconductance, etc. The radiation-induced displacement damage may become the dominant issue while it was the secondary concern for the traditional devices after the heavy ion irradiation. The samples are also irradiated by Co-60 gamma ray for comparison with the heavy ion irradiation results. Corresponding explanations and analysis are discussed.

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Study on the negative bias temperature instability effect under dynamic stress Ma Xiao-Hua(马晓华), Cao Yan-Rong(曹艳荣), and Hao Yue(郝跃) Chin. Phys. B, 2010, 19 (11):  117308.  DOI: 10.1088/1674-1056/19/11/117308 Abstract ( 1501 )   PDF (320KB) ( 618 )   This paper studies negative bias temperature instability (NBTI) under alternant and alternating current (AC) stress. Under alternant stress, the degradation smaller than that of single negative stress is obtained. The smaller degradation is resulted from the recovery of positive stress. There are two reasons for the recovery. One is the passivation of H dangling bonds, and another is the detrapping of charges trapped in the oxide. Under different frequencies of AC stress, the parameters all show regular degradation, and also smaller than that of the direct current stress. The higher the frequency is, the smaller the degradation becomes. As the negative stress time is too small under higher frequency, the deeper defects are hard to be filled in. Therefore, the detrapping of oxide charges is easy to occur under positive bias and the degradation is smaller with higher frequency.

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An analytical threshold voltage model for dual-strained channel PMOSFET Qin Shan-Shan(秦珊珊), Zhang He-Ming(张鹤鸣), Hu Hui-Yong(胡辉勇), Dai Xian-Ying(戴显英), Xuan Rong-Xi(宣荣喜), and Shu Bin(舒斌) Chin. Phys. B, 2010, 19 (11):  117309.  DOI: 10.1088/1674-1056/19/11/117309 Abstract ( 1190 )   PDF (694KB) ( 880 )   Based on the analysis of vertical electric potential distribution across the dual-channel strained p-type Si/strained Si1-xGex/relaxd Si1-yGey(s-Si/s-SiGe/Si1-yGey) metal–oxide–semiconductor field-effect transistor (PMOSFET), analytical expressions of the threshold voltages for buried channel and surface channel are presented. And the maximum allowed thickness of s-Si is given, which can ensure that the strong inversion appears earlier in the buried channel (compressive strained SiGe) than in the surface channel (tensile strained Si), because the hole mobility in the buried channel is higher than that in the surface channel. Thus they offer a good accuracy as compared with the results of device simulator ISE. With this model, the variations of threshold voltage and maximum allowed thickness of s-Si with design parameters can be predicted, such as Ge fraction, layer thickness, and doping concentration. This model can serve as a useful tool for p-channel s-Si/s-SiGe/Si1-yGey metal-oxide-semiconductor field-effect transistor (MOSFET) designs.

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Tunable surface-plasmon-resonance wavelength of silver island films Wang Ji-Fei(王继飞), Li Hong-Jian(李宏建), Zhou Zi-You(周子游), Li Xue-Yong(李雪勇), Liu Ju(刘菊), and Yang Hai-Yan(杨海艳) Chin. Phys. B, 2010, 19 (11):  117310.  DOI: 10.1088/1674-1056/19/11/117310 Abstract ( 1522 )   PDF (1502KB) ( 1479 )   This paper experimentally and theoretically investigates the effect of the underlayer medium on tuning of the surface plasmon resonance (SPR) wavelength of silver island films, and the effect of substrate temperature on the morphologies and optical properties of the films. From the absorption spectra of single Ag with various thickness and overcoated (Ag/TiO2) films deposited on glass substrates at various substrate temperatures by RF magnetron sputtering, we demonstrate that the surface plasmon resonance wavelength can be made tunable by changing the underlayer medium, the thickness of metal layer and the substrate temperature. By varying substrate temperatures, the interparticle coupling effects on plasmon resonances of nanosilver particles enhance as the spacing between the particles reduces. When the substrate temperature is up to 500 ℃, the absorption peak decreases sharply and shifts to shorter wavelength side due to the severe coalescence between silver islands in the film.

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Crossover from a pseudogap state to a superconducting state Cao Tian-De(曹天德) Chin. Phys. B, 2010, 19 (11):  117401.  DOI: 10.1088/1674-1056/19/11/117401 Abstract ( 1292 )   PDF (247KB) ( 619 )   This paper deduces that the particular electronic structure of cuprate superconductors confines Cooper pairs to be first formed in the antinodal region which is far from the Fermi surface, and these pairs are incoherent and result in the pseudogap state. With the change of doping or temperature, some pairs are formed in the nodal region which locates the Fermi surface, and these pairs are coherent and lead to superconductivity. Thus the coexistence of the pseudogap and the superconducting gap is explained when the two kinds of gaps are not all on the Fermi surface. It also shows that the symmetry of the pseudogap and the superconducting gap are determined by the electronic structure, and non-s wave symmetry gap favours the high-temperature superconductivity. Why the high-temperature superconductivity occurs in the metal region near the Mott metal-insulator transition is also explained.

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Josephson junction of two-species Bose–Einstein condensates in a high-finesse optical cavity Wang Bin(王彬), Tan Lei(谭磊), Lü Chun-Hai(吕纯海), and Tan Wen-Ting(谭文婷) Chin. Phys. B, 2010, 19 (11):  117402.  DOI: 10.1088/1674-1056/19/11/117402 Abstract ( 1641 )   PDF (1469KB) ( 686 )   The mean-field dynamics of undistinguishable two-species Bose Josephson junction coupled to a single mode high-finesse optical cavity is investigated. From the Hamiltonian, the phase portrait and the stationary points are given. It is shown that the role of the interspecies interaction equals the intraspecies interaction under suitable conditions. As the interspecies interaction increases, the trapped atoms will start tunneling between the two wells unnaturally for some special cases.

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Thermal effect mechanism of magnetoresistance in p-type diamond films Qin Guo-Ping(秦国平), Kong Chun-Yang(孔春阳), Ruan Hai-Bo(阮海波), Huang Gui-Juan(黄桂娟), Cui Yu-Ting(崔玉亭), and Fang Liang(方亮) Chin. Phys. B, 2010, 19 (11):  117501.  DOI: 10.1088/1674-1056/19/11/117501 Abstract ( 1502 )   PDF (161KB) ( 666 )   Based on the analysis and the discussion of the influence of thermal ionization energy and various scatterings on magnetoresistance(MR) of p-type diamond films, a revised model of valence band split-off over temperature is put forward, and a corresponding calculation formula is given for the MR of p-type diamond films (Corbino discs). It is shown that the theoretical calculation that the MR of diamond films changes with temperature is consistent with the experiment. The influence of Fermi energy level on MR of diamond films is discussed. Additionally, the thermal effect mechanism of MR in p-type diamond films is also explored.

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Influence of Dzyaloshinskii-Moriya and Kaplan-Shekhtman-Entinwohlman-Aharony superexchange interactions on ground state properties of the one-dimensional spin-Peilers model in open chain Liu Hai-Lian(刘海莲), Huang Xian-Shan(黄仙山),Wang Zhi-Guo(王治国), and Shi Yun-Long(石云龙) Chin. Phys. B, 2010, 19 (11):  117502.  DOI: 10.1088/1674-1056/19/11/117502 Abstract ( 1552 )   PDF (811KB) ( 816 )   The effects of the Dzyaloshinskii–Moriya (DM) and the Kaplan–Shekhtman–Entinwohlman–Aharony (KSEA) superexchange interactions on the ground state properties of the one-dimensional spin-Peilers system in open chain are studied by using the Lanczos numerical method. The study concentrates mainly on the influence of systemic dimerisation in open chain. The results show that systemic ground state energy density varies with dimerisation parameter $\delta$ in different DM interactions, and there exists a special point $\delta$c where the DM interaction has no influence on the systemic dimerisation, no matter whether the DM interaction is relative or irrelative to systemic dimerisation (η = 1 or η = 0). The KSEA interaction has no fixed special point, but the points of intersection are dense relatively in a certain numberical value range, and sparse in other numberical value ranges. So we can conclude that the antisymmetric anisotropy DM interaction differs from the symmetric anisotropy KSEA interaction, but they are analogous in the sense of the influence of systemic dimerisation in open chain.

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Effects of pre-deformation on the martensitic transformation and magnetocaloric property in Ni–Mn–Co–Sn ribbons Ma Sheng-Can(马胜灿), Xuan Hai-Cheng(轩海成), Zhang Cheng-Liang(张成亮), Wang Liao-Yu(王辽宇), Cao Qing-Qi(曹庆琪), Wang Dun-Hui(王敦辉), and Du You-Wei(都有为) Chin. Phys. B, 2010, 19 (11):  117503.  DOI: 10.1088/1674-1056/19/11/117503 Abstract ( 1203 )   PDF (205KB) ( 808 )   This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni–Mn–Co–Sn ribbons. The experimental results show that the reverse martensitic transformation temperature TM increases with the increasing pre-pressure, suggesting that pre-deformation is another effective way to adjust TM in ferromagnetic shape memory alloys. Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well. It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni–Mn–Co–Sn ribbons.

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Magnetostriction of Fe81Ga19 oriented crystals Wang Zhi-Bin(王智彬), Liu Jing-Hua(刘敬华), and Jiang Cheng-Bao(蒋成保) Chin. Phys. B, 2010, 19 (11):  117504.  DOI: 10.1088/1674-1056/19/11/117504 Abstract ( 1361 )   PDF (2213KB) ( 770 )   The effect of the orientation on the magnetostriction in Fe81Ga19 alloy has been investigated experimentally and theoretically. The Fe81Ga19 [001] and [110] oriented crystals were prepared and the magnetostriction was measured under different pre-stress. The saturation magnetostriction of the [001] oriented crystal increases from 170×10-6 to 330×10-6 under the pre-stress from 0 to 50 MPa. The [110] oriented crystal has a saturation magnetostriction from 20×10-6 to 140×10-6 with the compressive pre-stress from 0 to 40 MPa. The magnetostriction of [001] and [110] oriented crystals has been simulated based on the phenomenological theory. The domain rotation path has been determined and the resultant magnetostriction calculated under different pre-stress. The experimental and simulated results both show that the [001] oriented crystal exhibits better magnetostriction than [110] oriented crystal. The enhancement of the saturation magnetostriction by the compressive pre-stress in the [110] oriented crystal is higher than that in the [001] oriented crystal.

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The exciton-longitudinal-optical-phonon coupling in InGaN/GaN single quantum wells with various cap layer thicknesses Hu Xiao-Long(胡晓龙), Zhang Jiang-Yong(张江勇), Shang Jing-Zhi(尚景智), Liu Wen-Jie(刘文杰), and Zhang Bao-Ping(张保平) Chin. Phys. B, 2010, 19 (11):  117801.  DOI: 10.1088/1674-1056/19/11/117801 Abstract ( 1494 )   PDF (207KB) ( 1157 )   This paper studies the exciton–longitudinal-optical-phonon coupling in InGaN/GaN single quantum wells with various cap layer thicknesses by low temperature photoluminescence (PL) measurements. With increasing cap layer thickness, the PL peak energy shifts to lower energy and the coupling strength between the exciton and longitudinal-optical (LO) phonon, described by Huang–Rhys factor, increases remarkably due to an enhancement of the internal electric field. With increasing excitation intensity, the zero-phonon peak shows a blueshift and the Huang–Rhys factor decreases. These results reveal that there is a large built-in electric field in the well layer and the exciton–LO–phonon coupling is strongly affected by the thickness of the cap layer.

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Self-consistent field method and non-self-consistent field method for calculating the positron lifetime Zhang Jie(张杰), Liu Jian-Dang(刘建党),Chen Xiang-Lei(陈祥磊), and Ye Bang-Jiao(叶邦角) Chin. Phys. B, 2010, 19 (11):  117802.  DOI: 10.1088/1674-1056/19/11/117802 Abstract ( 1337 )   PDF (457KB) ( 2093 )   Many methods are used to calculate the positron lifetime, these methods could be divided into two main types. The first method is atomic superposition approximation method and the second one is the so called energy band calculation method. They are also known as the non-self-consistent field method and self-consistent field method respectively. In this paper, we first introduce the two basic methods and then, we take Si as an example and give our calculation results, these results coincide with our latest experimental results, finally, we discuss the advantages and disadvantages of the two methods.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Synthesis of large diamond crystals containing high-nitrogen concentration at high pressure and high temperature using Ni-based solvent by temperature gradient method Huang Guo-Feng(黄国锋), Jia Xiao-Peng(贾晓鹏), Li Shang-Sheng(李尚升), Zhang Ya-Fei(张亚飞), Li Yong(李勇), Zhao Ming(赵明), and Ma Hong-An(马红安) Chin. Phys. B, 2010, 19 (11):  118101.  DOI: 10.1088/1674-1056/19/11/118101 Abstract ( 1194 )   PDF (795KB) ( 1974 )   This paper reprots that with Ni-based catalyst/solvent and with a dopant of NaN3, large green single crystal diamonds with perfect shape are successfully synthesized by temperature gradient method under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus (SPD-6×1200), and the highest nitrogen concentration reaches approximately 1214-1257 ppm calculated by infrared absorption spectra. The synthesis conditions are about 5.5 GPa and 1240-1300 ℃. The growth behaviour of diamond with high-nitrogen concentration is investigated in detail. The results show that, with increasing the content of NaN3 added in synthesis system, the width of synthesis temperature region for growth high-quality diamonds becomes narrower, and the morphology of diamond crystal is changed from cube-octahedral to octahedral at same temperature and pressure, the crystal growth rate is slowed down, nevertheless, the nitrogen concentration doped in synthetic diamond increases.

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Structure, room-temperature magnetic and optical properties of Mn-doped TiO2 nano powders prepared by the sol–gel process Ding Peng(丁芃),Liu Fa-Min(刘发民),Zhou Chuang-Cang(周传仓), Zhong Wen-Wu(钟文武), Zhang Huan(张嬛), Cai Lu-Gang(蔡鲁刚), and Zeng Le-Gui(曾乐贵) Chin. Phys. B, 2010, 19 (11):  118102.  DOI: 10.1088/1674-1056/19/11/118102 Abstract ( 1257 )   PDF (4128KB) ( 2074 )   TiO2 nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol–gel process, and were annealed at 500 ℃ and 800 ℃ in air for 2 hrs. X-ray diffraction (XRD) measurements indicate that the Mn–TiO2 nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 ℃ are of pure anatase and rutile, respectively. The scanning electron microscope (SEM) observations reveal that the crystal grain size increases with the annealing temperature, and the high resolution transmission electron microscopy (HRTEM) investigations further indicate that the samples are well crystallized, confirming that Mn has doped into the TiO2 crystal lattice effectively. The room temperature ferromagnetism, which could be explained within the scope of the bound magnetic polaron (BMP) theory, is detected in the Mn–TiO2 samples with Mn concentration of 2 at%, and the magnetization of the powders annealed at 500 ℃ is stronger than that of the sample treated at 800 ℃. The UV–VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO2 powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping.

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Thermal diffusivity of light-emitting diode packaging material determined by photoacoustic piezoelectric technique Sun Qi-Ming(孙启明), Gao Chun-Ming(高椿明), Zhao Bin-Xing(赵斌兴), and Rao Hai-Bo(饶海波) Chin. Phys. B, 2010, 19 (11):  118103.  DOI: 10.1088/1674-1056/19/11/118103 Abstract ( 998 )   PDF (519KB) ( 721 )   Thermal property is one of the most important properties of light-emitting diode (LED). Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric (PAPE) technique has been employed to investigate the thermal properties of polyvinyl alcohol (PVA) and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.

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Finite element modeling of heating phenomena of cracks excited by high-intensity ultrasonic pulses Chen Zhao-Jiang(陈赵江), Zheng Jiang(郑江), Zhang Shu-Yi(张淑仪), Mi Xiao-Bing(米小兵), and Zheng Kai(郑凯) Chin. Phys. B, 2010, 19 (11):  118104.  DOI: 10.1088/1674-1056/19/11/118104 Abstract ( 1301 )   PDF (5627KB) ( 1679 )   A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.

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Development of silicon purification by strong radiation catalysis method Chen Ying-Tian(陈应天), Ho Tso-Hsiu(何祚庥), Lim Chern-Sing(林晨星), and Lim Boon Han(林文汉) Chin. Phys. B, 2010, 19 (11):  118105.  DOI: 10.1088/1674-1056/19/11/118105 Abstract ( 1496 )   PDF (505KB) ( 813 )   Using a new type of solar furnace and a specially designed induction furnace，cost effective and highly efficient purification of metallurgical silicon into solar grade silicon can be achieved. It is realized by a new method for extracting boron from silicon with the aid of photo-chemical effect. In this article, we discussed the postulated principle of strong radiation catalysis and the recent development in practice. Starting from ordinary metallurgical silicon, we achieved a purification result of 0.12 ppmw to 0.3 ppmw of boron impurity in silicon by only single pass of a low cost and simple process, the major obstacle to make `cheap' solar grade silicon feedstock in industry is thus removed.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Influence of small-molecule material on performance of polymer solar cells based on MEH-PPV:PCBM blend Liu Xiao-Dong(刘晓东), Xu Zheng(徐征), Zhang Fu-Jun(张福俊), Zhao Su-Ling(赵谡玲), Zhang Tian-Hui(张天慧), Gong Wei(龚伟), Song Jing-Lu (宋晶路), Kong Chao(孔超), Yan Guang(闫光), and Xu Xu-Rong(徐叙瑢) Chin. Phys. B, 2010, 19 (11):  118601.  DOI: 10.1088/1674-1056/19/11/118601 Abstract ( 1446 )   PDF (318KB) ( 886 )   In this work, the influence of a small-molecule material, tris(8-hydroxyquinoline) aluminum (Alq3), on bulk heterojunction (BHJ) polymer solar cells (PSCs) is investigated in devices based on the blend of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). By doping Alq3 into MEH-PPV:PCBM solution, the number of MEH-PPV excitons can be effectively increased due to the energy transfer from Alq3 to MEH-PPV, which probably induces the increase of photocurrent generated by excitons dissociation. However, the low carrier mobility of Alq3 is detrimental to the efficient charge transport, thereby blocking the charge collection by the respective electrodes. The balance between photon absorption and charge transport in the active layer plays a key role in the performance of PSCs. For the case of 5 wt.% Alq3 doping, the device performance is deteriorated rather than improved as compared with that of the undoped device. On the other hand, we adopt Alq3 as a buffer layer instead of commonly used LiF. All the photovoltaic parameters are improved, yielding an 80% increase in power conversion efficiency (PCE) at the optimum thickness (1 nm) as compared with that of the device without any buffer layer. Even for the 5 wt.% Alq3 doped device, the PCE has a slight enhancement compared with that of the standard device after modification with 1 nm (or 2 nm) thermally evaporated Alq3. The performance deterioration of Alq3-doped devices can be explained by the low solubility of Alq3, which probably deteriorates the bicontinuous D-A network morphology; while the performance improvement of the devices with Alq_3 as a buffer layer is attributed to the increased light harvesting, as well as blocking the hole leakage from MEH-PPV to the aluminum (Al) electrode due to the lower highest occupied molecular orbital (HOMO) level of Alq3 compared with that of MEH-PPV.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Improvement of the axial trapping effect using azimuthally polarised trapping beam Li Xue-Cong(李雪璁) and Sun Xiu-Dong(孙秀冬) Chin. Phys. B, 2010, 19 (11):  119401.  DOI: 10.1088/1674-1056/19/11/119401 Abstract ( 1468 )   PDF (1105KB) ( 687 )   A dual optical tweezers system, which consists of a doughnut mode optical tweezer (DMOT) with the azimuthally polarised trapping beam and a solid mode optical tweezer (SMOT) with the Gauss trapping beam was constructed to compare the axial trapping effect of DMOT and SMOT. The long-distance axial trapping of ST68 microbubbles (MBs) achieved by DMOT was more stable than that of SMOT. Moreover the axial trapping force measured using the viscous drag method, was depended on the diameter of the particle, the laser power, and the numerical aperture (NA) of the objective lens. The measurement of the axial trapping force and the acquisition of CCD images of trapping effect confirmed that the DMOT showed excellent axial trapping ability than SMOT. A simple and effective method is developed to improve axial trapping effect using the azimuthally polarized beam as trapping beam. This is helpful for the long-distance manipulating of particles especially polarised biological objects in axial direction.

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Cognitive radio resource allocation based on coupled chaotic genetic algorithm Zu Yun-Xiao(俎云霄),Zhou Jie(周杰), and Zeng Chang-Chang(曾昶畅) Chin. Phys. B, 2010, 19 (11):  119501.  DOI: 10.1088/1674-1056/19/11/119501 Abstract ( 1435 )   PDF (1039KB) ( 1079 )   A coupled chaotic genetic algorithm for cognitive radio resource allocation which is based on genetic algorithm and coupled Logistic map is proposed. A fitness function for cognitive radio resource allocation is provided. Simulations are conducted for cognitive radio resource allocation by using the coupled chaotic genetic algorithm, simple genetic algorithm and dynamic allocation algorithm respectively. The simulation results show that, compared with simple genetic and dynamic allocation algorithm, coupled chaotic genetic algorithm reduces the total transmission power and bit error rate in cognitive radio system, and has faster convergence speed.

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Exact solution of phantom dark energy model Wang Wen-Fu(王文福), Shui Zheng-Wei(税正伟), and Tang Bin(唐斌) Chin. Phys. B, 2010, 19 (11):  119801.  DOI: 10.1088/1674-1056/19/11/119801 Abstract ( 1577 )   PDF (137KB) ( 948 )   We investigate the phantom dark energy model derived from the scalar field with a negative kinetic term. By assuming a particular relation between the time derivative of the phantom field and the Hubble function, an exact solution of the model is constructed. Absence of the `big rip' singularity is shown explicitly. We then derive special features of phantom dark energy model and show that its predictions are consistent with all astrophysical observations.