Table of contents

15 May 2014, Volume 23 Issue 5 Previous issue    Next issue

GENERAL

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Collective surrounding control in multi-agent networks Wei Ting-Ting (魏婷婷), Chen Xiao-Ping (陈小平) Chin. Phys. B, 2014, 23 (5):  050201.  DOI: 10.1088/1674-1056/23/5/050201 Abstract ( 454 )   PDF (553KB) ( 444 )   We study the collective encirclement control problem of a multi-agent system in this paper, where the agents move collectively to encircle the multiple targets. An algorithm is proposed and a sufficient condition is derived to realize the collective encirclement motion. Some simulation results are provided to show the effectiveness of the obtained theoretical results.

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A high order energy preserving scheme for the strongly coupled nonlinear Schrödinger system Jiang Chao-Long (蒋朝龙), Sun Jian-Qiang (孙建强) Chin. Phys. B, 2014, 23 (5):  050202.  DOI: 10.1088/1674-1056/23/5/050202 Abstract ( 496 )   PDF (649KB) ( 395 )   A high order energy preserving scheme for a strongly coupled nonlinear Schrödinger system is proposed by using the average vector field method. The high order energy preserving scheme is applied to simulate the soliton evolution of the strongly coupled Schrödinger system. Numerical results show that the high order energy preserving scheme can well simulate the soliton evolution, moreover, it preserves the discrete energy of the strongly coupled nonlinear Schrödinger system exactly.

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A new coupled map car-following model considering drivers’ steady desired speed Zhou Tong (周桐), Sun Di-Hua (孙棣华), Li Hua-Min (李华民), Liu Wei-Ning (刘卫宁) Chin. Phys. B, 2014, 23 (5):  050203.  DOI: 10.1088/1674-1056/23/5/050203 Abstract ( 691 )   PDF (2157KB) ( 443 )   Based on the pioneering work of Konishi et al., in consideration of the influence of drivers' steady desired speed effect on the traffic flow, we develop a new coupled map car-following model in the real world. By use of the control theory, the stability condition of our model is derived. The validity of the present theoretical scheme is verified via numerical simulation, confirming the correctness of our theoretical analysis.

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Statistical properties of coherent photon-subtracted two-mode squeezed vacuum and its application in quantum teleportation Zhang Guo-Ping (张国平), Zheng Kai-Min (郑凯敏), Liu Shi-You (刘世右), Hu Li-Yun (胡利云) Chin. Phys. B, 2014, 23 (5):  050301.  DOI: 10.1088/1674-1056/23/5/050301 Abstract ( 578 )   PDF (957KB) ( 534 )   We introduce a kind of non-Gaussian entangled state, which can be obtained by operating a non-local coherent photon-subtraction operation on a two-mode squeezed vacuum. It is found that its normalization factor is only related to the Legendre polynomials, which is a compact expression. Its statistical properties are discussed by the negative region Wigner function with the analytical expression. As an application, the quantum teleportation for coherent states is considered by using the non-Gaussian state as an entangled channel. It is found that the teleportation fidelity can be enhanced by this non-Gaussian operation.

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Ocean internal waves interpreted as oscillation travelling waves in consideration of ocean dissipation Jiang Zhu-Hui (姜祝辉), Huang Si-Xun (黄思训), You Xiao-Bao (游小宝), Xiao Yi-Guo (肖义国) Chin. Phys. B, 2014, 23 (5):  050302.  DOI: 10.1088/1674-1056/23/5/050302 Abstract ( 463 )   PDF (538KB) ( 333 )   Most studies of the synthetic aperture radar remote sensing of ocean internal waves are based on the solitary wave solutions of the Korteweg-de Vries (KdV) equation, and the dissipative term in the KdV equation is not taken into account. However, the dissipative term is very important, both in the synthetic aperture radar images and in ocean models. In this paper, the traveling-wave structure to characterize the ocean internal wave phenomenon is modeled, the results of numerical experiments are advanced, and a theoretical hypothesis of the traveling wave to retrieve the ocean internal wave parameters in the synthetic aperture radar images is introduced.

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Doppler shift of a laser pulse beam scattered by a rotating cone and cylinder Wang Bao-Ping (王保平), Wang Ming-Jun (王明军), Wu Zhen-Sen (吴振森), Li Ying-Le (李应乐), Xiang Ning-Jing (向宁静) Chin. Phys. B, 2014, 23 (5):  050303.  DOI: 10.1088/1674-1056/23/5/050303 Abstract ( 584 )   PDF (370KB) ( 430 )   Based on laser radar equations, a Doppler shift model of a laser pulse beam scattered by a rotating arbitrary convex target is reported in this paper. The boundary relations between an incident pulse beam and the detected area elements are analyzed by geometric methods. The Doppler shift characteristics of the rotating cone and cylinder are discussed and the difference between the laser pulse beam and the plane wave scattered from the same rotating target is compared accordingly. Numerical simulations show that the Doppler shift is tightly relevant to their dimensions, speeds, and so on. In the same incidence conditions, the pulse beam and plane wave have difference peak values and the same Doppler shift bandwidth. If the waist radius of the pulse beam is larger, the peak value is higher, and the Doppler shifts are proportional to the speed of the rotating target. By virtue of our theoretical model, we probe into the scattered characteristics of the Doppler shifts of a laser pulse beam, which would benefit target identification in national defense.

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Thermal quantum and total correlations in spin-1 bipartite system Qiu Liang (仇亮), Ye Bin (叶宾) Chin. Phys. B, 2014, 23 (5):  050304.  DOI: 10.1088/1674-1056/23/5/050304 Abstract ( 717 )   PDF (5491KB) ( 435 )   Thermal quantum and total correlations of a two spin-1 Ising model in the presence of an external homogeneous magnetic field and the Dzyaloshinski-Moriya (DM) interaction are investigated. The result indicates that the DM interaction plays a leading role in the quantum correlation measured by measurement-induced disturbance except for the region with small DM interaction and low temperature, while the DM interaction and the external magnetic field play competing roles in the negativity. The thermal total correlations measured by an alternative new measure defined in terms of the Wigner-Yanase skew information and the quantum mutual information display differences in the same region.

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Thermal entanglement in the mixed three-spin XXZ Heisenberg model on a triangular cell Seyit Deniz Han, Ekrem Aydiner Chin. Phys. B, 2014, 23 (5):  050305.  DOI: 10.1088/1674-1056/23/5/050305 Abstract ( 823 )   PDF (383KB) ( 490 )   We numerically investigate the thermal entanglements of spins (1/2, 1) and spins (1/2, 1/2) in the three-mixed (1/2, 1, 1/2) anisotropic Heisenberg XXZ spin system on a simple triangular cell under an inhomogeneous magnetic field. We show that the external magnetic field induces strong plateau formation in the pairwise thermal entanglement for fixed parameters of the Hamiltonian in the cases of ferromagnetic and antiferromagnetic interactions. We also observe an unexpected critical point at finite temperature in the thermal entanglement of spins (1/2, 1) for the antiferromagnetic case, while the entanglement of spins (1/2, 1) in the ferromagnetic case and the entanglement of spins (1/2, 1/2) in both ferromagnetic and antiferromagnetic cases almost decay exponentially to zero with increasing temperature. The critical point in the entanglement of spins (1/2, 1) in the antiferromagnetic case may be a signature of the quantum phase transition at finite temperature.

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Complete hyperentangled state analysis and generation of multi-particle entanglement based on charge detection Ji Yan-Qiang (计彦强), Jin Zhao (金钊), Zhu Ai-Dong (朱爱东), Wang Hong-Fu (王洪福), Zhang Shou (张寿) Chin. Phys. B, 2014, 23 (5):  050306.  DOI: 10.1088/1674-1056/23/5/050306 Abstract ( 541 )   PDF (284KB) ( 373 )   We propose the schemes for implementing hyperentangled state analysis and generating four-electron high entangled states (including cluster state, |χ> state, and symmetric Dicke state) based on the charge detection of free electrons. These schemes are deterministic and rely only on charge detection and single-spin rotations. This method, which uses noninteracting electrons, is not only efficient but also saves on quantum resources.

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Cavity-assisted quantum computing in a silicon nanostructure Tang Bao (唐宝), Qin Hao (秦豪), Zhang Rong (张融), Liu Jin-Ming (刘金明), Xue Peng (薛鹏) Chin. Phys. B, 2014, 23 (5):  050307.  DOI: 10.1088/1674-1056/23/5/050307 Abstract ( 543 )   PDF (373KB) ( 314 )   We present a scheme of quantum computing with charge qubits corresponding to one excess electron shared between dangling-bond pairs of surface silicon atoms that couple to a microwave stripline resonator on a chip. By choosing a certain evolution time, we propose the realization of a set of universal single- and two-qubit logical gates. Due to its intrinsic stability and scalability, the silicon dangling-bond charge qubit can be regarded as one of the most promising candidates for quantum computation. Compared to the previous schemes on quantum computing with silicon bulk systems, our scheme shows such advantages as a long coherent time and direct control and readout.

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Consequent entanglement concentration of a less-entangled electronic cluster state with controlled-not gates Zhou Lan (周澜) Chin. Phys. B, 2014, 23 (5):  050308.  DOI: 10.1088/1674-1056/23/5/050308 Abstract ( 650 )   PDF (248KB) ( 435 )   We present a highly efficient entanglement concentration protocol (ECP) for a four-electron system in a less-entangled cluster state. In this ECP, we only require one pair of less-entangled electron cluster states and one ancillary electron to complete the task. With the help of the controlled-not (CNOT) gate, the concentrated maximally entangled state can be retained for further application with some success probability. On the other hand, the discarded items can be reused to obtain a high success probability. All the features make this ECP useful in the current quantum information field.

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Measures of genuine multipartite entanglement for graph states Guo Qun-Qun (郭群群), Chen Xiao-Yu (陈小余), Wang Yun-Yun (王赟赟) Chin. Phys. B, 2014, 23 (5):  050309.  DOI: 10.1088/1674-1056/23/5/050309 Abstract ( 637 )   PDF (220KB) ( 381 )   Graph states are special multipartite entangled states that have been proven useful in a variety of quantum information tasks. We address the issue of characterizing and quantifying the genuine multipartite entanglement of graph states up to eight qubits. The entanglement measures used are the geometric measure, the relative entropy of entanglement, and the logarithmic robustness, have been proved to be equal for the genuine entanglement of a graph state. We provide upper and lower bounds as well as an iterative algorithm to determine the genuine multipartite entanglement.

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Measurement-induced disturbance in Heisenberg XY spin model with Dzialoshinskii-Moriya interaction under intrinsic decoherence Shen Cheng-Gao (沈诚诰), Zhang Guo-Feng (张国锋), Fan Kai-Ming (樊开明), Zhu Han-Jie (朱汉杰) Chin. Phys. B, 2014, 23 (5):  050310.  DOI: 10.1088/1674-1056/23/5/050310 Abstract ( 634 )   PDF (698KB) ( 618 )   Quantum correlations measured by measurement-induced disturbance (MID) in a two-qubit Heisenberg XY spin model with Dzialoshinskii-Moriya (DM) interaction under intrinsic decoherence are investigated. MID is studied under various circumstances and the influences of the external dependencies on the final quantum state which has stable MID are discussed. Two kinds of initial quantum states are considered as well as different conclusions. MID appears to decay periodically during the processing of intrinsic decoherence; both DM interaction and intrinsic decoherence have a negative impact on the correlations. The MID of the stable state depends on several factors, except the parameter of the intrinsic decoherence. Moreover, we find a special initial state that is able to maintain the maximum quantum correlations during the processing of intrinsic decoherence.

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Spin-star environment assisted entanglement generation in weakly coupled bipartite systems Wang Gen-Fang (王艮芳), Lü Jian-Mei (吕建美), Wang Lin-Cheng (王林成) Chin. Phys. B, 2014, 23 (5):  050311.  DOI: 10.1088/1674-1056/23/5/050311 Abstract ( 591 )   PDF (616KB) ( 324 )   We study the entanglement evolution in a weakly coupled bipartite system with a large energy level difference under the influence of spin-star environments. The subsystems can be coupled to a pure state or a thermal equilibrium state spin-star environment. Our results show that, in the case of the coupling strength being less than the energy level difference of the subsystems (weakly coupled), the spin-star environment can always be used to assist the entanglement generation of the bipartite system.

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Mechanical properties of the thermal equilibrium Friedmann-Robertson-Walker universe model Wei Yi-Huan (魏益焕), Lan Tian-Bao (兰天葆), Zhang Yue-Zhu (张月竹), Fu Yan-Yan (付妍妍) Chin. Phys. B, 2014, 23 (5):  050401.  DOI: 10.1088/1674-1056/23/5/050401 Abstract ( 456 )   PDF (199KB) ( 301 )   The mechanical property of the thermal-equilibrium Friedmann-Robertson-Walker (TEFRW) universe is first studied. The equation of state and the scale factor of the TEFRW universe take the forms of w=w(a;zT) and a=a(a;zT,H0). For the universe consisting of the nonrelativistic matter and the dark energy, the behavior of the dark energy depends on the value of the present-day matter fraction. For the TEFRW universe consisting of N ingredients, the effective temperature is introduced. Lastly, a simple TEFRW universe model is analyzed.

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A statistical model for predicting thermal chemical reaction rate Lin Zheng-Zhe (林正喆), Li Wang-Yao (李王尧), Ning Xi-Jing (宁西京) Chin. Phys. B, 2014, 23 (5):  050501.  DOI: 10.1088/1674-1056/23/5/050501 Abstract ( 614 )   PDF (1646KB) ( 369 )   A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 (2011)] or molecules [Chin. Phys. Lett. 29 080504 (2012)] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.

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Motion of spiral tip driven by local forcing in excitable media Liu Gui-Quan (刘贵泉), Ying He-Ping (应和平) Chin. Phys. B, 2014, 23 (5):  050502.  DOI: 10.1088/1674-1056/23/5/050502 Abstract ( 2176 )   PDF (538KB) ( 696 )   We study the motion of a spiral wave controlled by a local periodic forcing imposed on a region around the spiral tip in an excitable medium. Three types of trajectories of spiral tip are observed: the epicycloid-like meandering, the resonant drift, and the hypocycloid-like meandering. The frequency of the spiral is sensitive to the local periodic forcing. The dependency of spiral frequency on the amplitude and size of local periodic forcing are presented. In addition, we show how the drift speed and direction are adjusted by the amplitude and phase of local periodic forcing, which is consistent with a theoretical analysis based on the weak deformation approximation.

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Adaptive step-size modified fractional least mean square algorithm for chaotic time series prediction Bilal Shoaib, Ijaz Mansoor Qureshi, Shafqatullah, Ihsanulhaq Chin. Phys. B, 2014, 23 (5):  050503.  DOI: 10.1088/1674-1056/23/5/050503 Abstract ( 586 )   PDF (675KB) ( 1062 )   This paper presents an adaptive step-size modified fractional least mean square (AMFLMS) algorithm to deal with a nonlinear time series prediction. Here we incorporate adaptive gain parameters in the weight adaptation equation of the original MFLMS algorithm and also introduce a mechanism to adjust the order of the fractional derivative adaptively through a gradient-based approach. This approach permits an interesting achievement towards the performance of the filter in terms of handling nonlinear problems and it achieves less computational burden by avoiding the manual selection of adjustable parameters. We call this new algorithm the AMFLMS algorithm. The predictive performance for the nonlinear chaotic Mackey Glass and Lorenz time series was observed and evaluated using the classical LMS, Kernel LMS, MFLMS, and the AMFLMS filters. The simulation results for the Mackey glass time series, both without and with noise, confirm an improvement in terms of mean square error for the proposed algorithm. Its performance is also validated through the prediction of complex Lorenz series.

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A new approach of optimal control for a class of continuous-time chaotic systems by an online ADP algorithm Song Rui-Zhuo (宋睿卓), Xiao Wen-Dong (肖文栋), Wei Qing-Lai (魏庆来) Chin. Phys. B, 2014, 23 (5):  050504.  DOI: 10.1088/1674-1056/23/5/050504 Abstract ( 554 )   PDF (1515KB) ( 397 )   We develop an online adaptive dynamic programming (ADP) based optimal control scheme for continuous-time chaotic systems. The idea is to use the ADP algorithm to obtain the optimal control input that makes the performance index function reach an optimum. The expression of the performance index function for the chaotic system is first presented. The online ADP algorithm is presented to achieve optimal control. In the ADP structure, neural networks are used to construct a critic network and an action network, which can obtain an approximate performance index function and the control input, respectively. It is proven that the critic parameter error dynamics and the closed-loop chaotic systems are uniformly ultimately bounded exponentially. Our simulation results illustrate the performance of the established optimal control method.

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Generation of a novel spherical chaotic attractor from a new three-dimensional system Sun Chang-Chun (孙常春), Zhao En-Liang (赵恩良), Xu Qi-Cheng (徐启程) Chin. Phys. B, 2014, 23 (5):  050505.  DOI: 10.1088/1674-1056/23/5/050505 Abstract ( 594 )   PDF (4279KB) ( 434 )   A new three-dimensional (3D) system is constructed and a novel spherical chaotic attractor is generated from the system. Basic dynamical behaviors of the chaotic system are investigated respectively. Novel spherical chaotic attractors can be generated from the system within a wide range of parameter values. The shapes of spherical chaotic attractors can be impacted by the variation of parameters. Finally, a simpler 3D system and a more complex 3D system with the same capability of generating spherical chaotic attractors are put forward respectively.

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Collective dynamics in a non-dissipative two-coupled pendulum system Chen Zi-Chen (陈子辰), Li Bo (李博), Qiu Hai-Bo (邱海波), Xi Xiao-Qiang (惠小强) Chin. Phys. B, 2014, 23 (5):  050506.  DOI: 10.1088/1674-1056/23/5/050506 Abstract ( 569 )   PDF (9813KB) ( 778 )   We study the collective dynamics of a non-dissipative two-coupled pendulum system, including phase synchronization (PS) and measure synchronization (MS). We find that as the coupling intensity between the two pendulums increases, the PS happens prior to the MS. We also present a three-dimensional phase space representation of MS, from which a more detailed information about evolution can be obtained. Furthermore, the order parameters are introduced to describe the phase transition between PS and MS. Finally, through the analysis of the Poincaré sections, we show that the system exhibits separatrix crossing behavior right at the MS transition point, and as the total initial energy increases, the Hamiltonian chaos will arise with separatrix chaos at the chaotic MS transition point.

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Hyper-chaos encryption using convolutional masking and model free unmasking Qi Guo-Yuan (齐国元), Sandra Bazebo Matondo Chin. Phys. B, 2014, 23 (5):  050507.  DOI: 10.1088/1674-1056/23/5/050507 Abstract ( 423 )   PDF (813KB) ( 387 )   In this paper, during the masking process the encrypted message is convolved and embedded into a Qi hyper-chaotic system characterizing a high disorder degree. The masking scheme was tested using both Qi hyper-chaos and Lorenz chaos and indicated that Qi hyper-chaos based masking can resist attacks of the filtering and power spectrum analysis, while the Lorenz based scheme fails for high amplitude data. To unmask the message at the receiving end, two methods are proposed. In the first method, a model-free synchronizer, i.e. a multivariable higher-order differential feedback controller between the transmitter and receiver is employed to de-convolve the message embedded in the receiving signal. In the second method, no synchronization is required since the message is de-convolved using the information of the estimated derivative.

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Linear and nonlinear generalized consensuses of multi-agent systems Guo Liu-Xiao (过榴晓), Hu Man-Feng (胡满峰), Hu Ai-Hua (胡爱花), Xu Zhen-Yuan (徐振源) Chin. Phys. B, 2014, 23 (5):  050508.  DOI: 10.1088/1674-1056/23/5/050508 Abstract ( 556 )   PDF (733KB) ( 649 )   Consensus in directed networks of multiple agents, as an important topic, has become an active research subject. Over the past several years, some types of consensus problems have been studied. In this paper, we propose a novel type of consensus, the generalized consensus (GC), which includes the traditional consensus, the anti-consensus, and the cluster consensus as its special cases. Based on the Lyapunov's direct method and the graph theory, a simple control algorithm is designed to achieve the generalized consensus in a network of agents. Numerical simulations of linear and nonlinear GC are used to verify the effectiveness of the theoretical analysis.

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Pinning sampled-data synchronization for complex networks with probabilistic coupling delay Wang Jian-An (王健安), Nie Rui-Xing (聂瑞兴), Sun Zhi-Yi (孙志毅) Chin. Phys. B, 2014, 23 (5):  050509.  DOI: 10.1088/1674-1056/23/5/050509 Abstract ( 582 )   PDF (286KB) ( 440 )   We deal with the problem of pinning sampled-data synchronization for a complex network with probabilistic time-varying coupling delay. The sampling period considered here is assumed to be less than a given bound. Without using the Kronecker product, a new synchronization error system is constructed by using the property of the random variable and input delay approach. Based on the Lyapunov theory, a delay-dependent pinning sampled-data synchronization criterion is derived in terms of linear matrix inequalities (LMIs) that can be solved effectively by using MATLAB LMI toolbox. Numerical examples are provided to demonstrate the effectiveness of the proposed scheme.

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Synchronization transition of a coupled system composed of neurons with coexisting behaviors near a Hopf bifurcation Jia Bing (贾冰) Chin. Phys. B, 2014, 23 (5):  050510.  DOI: 10.1088/1674-1056/23/5/050510 Abstract ( 575 )   PDF (624KB) ( 489 )   The coexistence of a resting condition and period-1 firing near a subcritical Hopf bifurcation point, lying between the monostable resting condition and period-1 firing, is often observed in neurons of the central nervous systems. Near such a bifurcation point in the Morris-Lecar (ML) model, the attraction domain of the resting condition decreases while that of the coexisting period-1 firing increases as the bifurcation parameter value increases. With the increase of the coupling strength, and parameter and initial value dependent synchronization transition processes from non-synchronization to compete synchronization are simulated in two coupled ML neurons with coexisting behaviors: one neuron chosen as the resting condition and the other the coexisting period-1 firing. The complete synchronization is either a resting condition or period-1 firing dependent on the initial values of period-1 firing when the bifurcation parameter value is small or middle and is period-1 firing when the parameter value is large. As the bifurcation parameter value increases, the probability of the initial values of a period-1 firing neuron that lead to complete synchronization of period-1 firing increases, while that leading to complete synchronization of the resting condition decreases. It shows that the attraction domain of a coexisting behavior is larger, the probability of initial values leading to complete synchronization of this behavior is higher. The bifurcations of the coupled system are investigated and discussed. The results reveal the complex dynamics of synchronization behaviors of the coupled system composed of neurons with the coexisting resting condition and period-1 firing, and are helpful to further identify the dynamics of the spatiotemporal behaviors of the central nervous system.

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Complex solutions and novel complex wave localized excitations for the (2+1)-dimensional Boiti-Leon-Pempinelli system Ma Song-Hua (马松华), Xu Gen-Hai (徐根海), Zhu Hai-Ping (朱海平) Chin. Phys. B, 2014, 23 (5):  050511.  DOI: 10.1088/1674-1056/23/5/050511 Abstract ( 579 )   PDF (629KB) ( 342 )   With the help of the symbolic computation system Maple, the Riccati equation mapping approach and a linear variable separation approach, a new family of complex solutions for the (2+1)-dimensional Boiti-Leon-Pempinelli system (BLP) is derived. Based on the derived solitary wave solution, some novel complex wave localized excitations are obtained.

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Exit selection strategy in pedestrian evacuation simulation with multi-exits Yue Hao (岳昊), Zhang Bin-Ya (张滨雅), Shao Chun-Fu (邵春福), Xing Yan (邢燕) Chin. Phys. B, 2014, 23 (5):  050512.  DOI: 10.1088/1674-1056/23/5/050512 Abstract ( 684 )   PDF (1575KB) ( 667 )   A mixed strategy of the exit selection in a pedestrian evacuation simulation with multi-exits is constructed by fusing the distance-based and time-based strategies through a cognitive coefficient, in order to reduce the evacuation imbalance caused by the asymmetry of exits or pedestrian layout, to find a critical density to distinguish whether the strategy of exit selection takes effect or not, and to analyze the exit selection results with different cognitive coefficients. The strategy of exit selection is embedded in the computation of the shortest estimated distance in a dynamic parameter model, in which the concept of a jam area layer and the procedure of step-by-step expending are introduced. Simulation results indicate the characteristics of evacuation time gradually varying against cognitive coefficient and the effectiveness of reducing evacuation imbalance caused by the asymmetry of pedestrian or exit layout. It is found that there is a critical density to distinguish whether a pedestrian jam occurs in the evacuation and whether an exit selection strategy is in effect. It is also shown that the strategy of exit selection has no effect on the evacuation process in the no-effect phase with a low density, and that evacuation time and exit selection are dependent on the cognitive coefficient and pedestrian initial density in the in-effect phase with a high density.

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Output power analyses for the thermodynamic cycles of thermal power plants Sun Chen (孙晨), Cheng Xue-Tao (程雪涛), Liang Xin-Gang (梁新刚) Chin. Phys. B, 2014, 23 (5):  050513.  DOI: 10.1088/1674-1056/23/5/050513 Abstract ( 639 )   PDF (291KB) ( 671 )   Thermal power plant is one of the important thermodynamic devices, which is very common in all kinds of power generation systems. In this paper, we use a new concept, entransy loss, as well as exergy destruction, to analyze the single reheating Rankine cycle unit and the single stage steam extraction regenerative Rankine cycle unit in power plants. This is the first time that the concept of entransy loss is applied to the analysis of the power plant Rankine cycles with reheating and steam extraction regeneration. In order to obtain the maximum output power, the operating conditions under variant vapor mass flow rates are optimized numerically, as well as the combustion temperatures and the off-design flow rates of the flue gas. The relationship between the output power and the exergy destruction rate and that between the output power and the entransy loss rate are discussed. It is found that both the minimum exergy destruction rate and the maximum entransy loss rate lead to the maximum output power when the combustion temperature and heat capacity flow rate of the flue gas are prescribed. Unlike the minimum exergy destruction rate, the maximum entransy loss rate is related to the maximum output power when the highest temperature and heat capacity flow rate of the flue gas are not prescribed.

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Cellular automata model for traffic flow with safe driving conditions María Elena Lárraga, Luis Alvarez-Icaza Chin. Phys. B, 2014, 23 (5):  050701.  DOI: 10.1088/1674-1056/23/5/050701 Abstract ( 856 )   PDF (642KB) ( 623 )   In this paper, a recently introduced cellular automata (CA) model is used for a statistical analysis of the inner microscopic structure of synchronized traffic flow. The analysis focuses on the formation and dissolution of clusters or platoons of vehicles, as the mechanism that causes the presence of this synchronized traffic state with a high flow. This platoon formation is one of the most interesting phenomena observed in traffic flows and plays an important role both in manual and automated highway systems (AHS). Simulation results, obtained from a single-lane system under periodic boundary conditions indicate that in the density region where the synchronized state is observed, most vehicles travel together in platoons with approximately the same speed and small spatial distances. The examination of velocity variations and individual vehicle gaps shows that the flow corresponding to the synchronized state is stable, safe and highly correlated. Moreover, results indicate that the observed platoon formation in real traffic is reproduced in simulations by the relation between vehicle headway and velocity that is embedded in the dynamics definition of the CA model.

ATOMIC AND MOLECULAR PHYSICS

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Spectroscopic properties and radiative lifetimes of SiTe：A high-level multireference configuration interaction investigation Li Rui (李瑞), Zhang Xiao-Mei (张晓美), Jin Ming-Xing (金明星), Xu Hai-Feng (徐海峰), Yan Bing (闫冰) Chin. Phys. B, 2014, 23 (5):  053101.  DOI: 10.1088/1674-1056/23/5/053101 Abstract ( 569 )   PDF (396KB) ( 357 )   The 18 Λ-S states correlated to the lowest dissociation limit of SiTe were calculated by using a high-level multireference configuration interaction (MRCI) method, including scalar relativistic and spin-orbit coupling effects. Based on the calculated potential energy curves, the spectroscopic constants of bound states were determined, which are well consistent with previous experimental results. The spin-orbit matrix elements between the Λ-S states were computed, which lead to an in-depth understanding of perturbations on the electronic state a3Π. Finally, the transition dipole moments of allowed transitions A1Π-X1Σ+, E1Σ+-X1Σ+, a3Π-d3Δ, a3Π-a'3Σ+, a3Π-e3Σ-, and the radiative lifetimes of A1Π, E1Σ+, and a3Π were evaluated.

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Probing dynamic interference in high-order harmonic generation from long-range molecular ion：Bohmian trajectory investigation Wang Jun (王俊), Wang Bing-Bing (王兵兵), Guo Fu-Ming (郭福明), Li Su-Yu (李苏宇), Ding Da-Jun (丁大军), Chen Ji-Gen (陈基根), Zeng Si-Liang (曾思良), Yang Yu-Jun (杨玉军) Chin. Phys. B, 2014, 23 (5):  053201.  DOI: 10.1088/1674-1056/23/5/053201 Abstract ( 686 )   PDF (1489KB) ( 377 )   Using Bohmian trajectory (BT) method, we investigate the dynamic interference in high-order harmonic generation from diatomic molecular ions. It is demonstrated that the main characteristics of the molecular harmonic spectrum can be well reproduced by only two BTs which are located at the two ions. This happens because these two localized trajectories can receive and store the whole collision information coming from all of the other re-collision trajectories. Therefore, the amplitudes and frequencies of these two trajectories represent the intensity and frequency distribution of the harmonic generation. Moreover, the interference between these two trajectories shows a dip in the harmonic spectrum, which reveals the molecular structure information.

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Investigation on the influence of atomic potentials on the above threshold ionization Tian Yuan-Ye (田原野), Li Su-Yu (李苏宇), Wei Shan-Shan (魏珊珊), Guo Fu-Ming (郭福明), Zeng Si-Liang (曾思良), Chen Ji-Gen (陈基根), Yang Yu-Jun (杨玉军) Chin. Phys. B, 2014, 23 (5):  053202.  DOI: 10.1088/1674-1056/23/5/053202 Abstract ( 550 )   PDF (1481KB) ( 336 )   We systematically investigate the influence of atomic potentials on the above-threshold ionization (ATI) spectra in one-dimensional (1D) cases and compare them with the three-dimensional (3D) case by numerically solving the time-dependent Schrödinger equation. It is found that the direct ionization plateau and the rescattering plateau of the ATI spectrum in the 3D case can be well reproduced by the 1D ATI spectra calculated from the supersolid-core potential and the soft-core potential, respectively. By analyzing the factors that affect the yield of the ATI spectrum, we propose a modified-potential with which we can reproduce the overall 3D ATI spectrum. In addition, the influence of the incident laser intensities and frequencies on the ATI spectra calculated from the proposed modified potential is studied.

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Projectile electron loss in collisions of light charged ions with helium Yin Yong-Zhi (尹永智), Wang Yun (王赟), Chen Xi-Meng (陈熙萌) Chin. Phys. B, 2014, 23 (5):  053401.  DOI: 10.1088/1674-1056/23/5/053401 Abstract ( 439 )   PDF (291KB) ( 250 )   We investigate the single-electron loss processes of light charged ions (Li1+,2+, C2+,3+,5+, and O2+,3+) in collisions with helium. To better understand the experimental results, we propose a theoretical model to calculate the cross section of projectile electron loss. In this model, an ionization radius of the incident ion was defined under the classical over-barrier model, and we developed “strings” to explain the processes of projectile electron loss, which is similar with the molecular over-barrier model. Theoretical calculations are in good agreement with the experimental results for the cross section of single-electron loss and the ratio of double-to-single ionization of helium associated with one-electron loss.

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Electron impact ionization of neon and neonic ions under distorted-wave Born approximation Zhou Li-Xia (周丽霞), Yan You-Guo (燕友果) Chin. Phys. B, 2014, 23 (5):  053402.  DOI: 10.1088/1674-1056/23/5/053402 Abstract ( 542 )   PDF (421KB) ( 236 )   The (e, 2e) triple differential cross sections of 2s orbitals of neon and neonic ions (Z=11-14) are calculated using a distorted-wave Born approximation under coplanar asymmetric geometry. The calculated results show that, with the increase in the nuclear charge number Z, the amplitude of triple differential cross sections decreases. The angle difference between the binary peak position and the direction of momentum transfer gradually increases with the increase in the nuclear charge Z, and a new structure appears at an ejected angle 90°<θ 2<120°. Three kinds of collision processes are proposed to illustrate the formation mechanism of such collision peaks.

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Decay pathways of superexcited states of nitrous oxide Lin Mei (林梅), Liu Ya-Wei (刘亚伟), Zhong Zhi-Ping (钟志萍), Zhu Lin-Fan (朱林繁) Chin. Phys. B, 2014, 23 (5):  053403.  DOI: 10.1088/1674-1056/23/5/053403 Abstract ( 521 )   PDF (381KB) ( 285 )   The ionization and ionic dissociation of the superexcited state of N2O are studied by using electron energy loss spectroscopy and positive ion time-of-flight mass spectroscopy at different momentum transfers; that is, 0 and 0.23 a.u. (atomic unit). The transitions at 13.8 eV and 14.0 eV are reassigned as 3pπ (000) and 3pσ (000) converging to A2Σ+, respectively. The competition between the main decay pathways of superexcited states at different momentum transfers is revealed. It is found that 3dσ converging to C2Σ+ mainly decays into N2O+ while 4dσ can decay into both N2O+ and NO+.

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

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Design of two-dimensional elliptically cylindrical invisible cloaks with multiple regions Luo Xiao-Yang (罗孝阳), Liu Dao-Ya (刘道亚), Liu Jin-Jing (刘锦景), Dong Jian-Feng (董建峰) Chin. Phys. B, 2014, 23 (5):  054101.  DOI: 10.1088/1674-1056/23/5/054101 Abstract ( 493 )   PDF (4384KB) ( 371 )   Two-dimensional (2D) elliptically cylindrical invisible cloaks with multiple regions are designed based on the transformation optics and the complementary media theory. Multiple invisible cloak regions can be obtained by properly using the compressed or folded transformation in each space layer. The constitutive parameter tensor expressions for each region have been obtained. The results of full wave simulations by using finite element software confirm the validity of the constitutive parameter tensor expressions. In addition, the parameters are relatively easier to realize.

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Inverse design-based metamaterial transparent device and its multilayer realization Li Ting-Hua (李廷华), Huang Ming (黄铭), Yang Jing-Jing (杨晶晶), Yuan Gang (袁刚), Cai Guang-Hui (蔡光卉) Chin. Phys. B, 2014, 23 (5):  054102.  DOI: 10.1088/1674-1056/23/5/054102 Abstract ( 537 )   PDF (884KB) ( 363 )   We propose an inverse method to determine the material parameters of a transparent device without any knowledge of the corresponding transformation function. The required parameters are independently obtained and expressed as functions of the introduced generator. Moreover, to remove the inhomogeneity and anisotropy of material parameters, a layered transparent device composed of only homogeneous and isotropic materials is presented based on the effective medium theory. The feasibility of using the layered device in antenna protection is also investigated. Full-wave simulation is carried out for verification. This work paves a new way toward designing metamaterial devices without specifying the underlying coordinate transformation, and has great guiding significance for the practical fabrication of transparent devices.

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The polarization effect of a laser in multiphoton Compton scattering Liang Guo-Hua (梁国华), Lü Qing-Zheng (吕清正), Teng Ai-Ping (滕爱萍), Li Ying-Jun (李英骏) Chin. Phys. B, 2014, 23 (5):  054103.  DOI: 10.1088/1674-1056/23/5/054103 Abstract ( 655 )   PDF (497KB) ( 456 )   The multiphoton Compton scattering in a high-intensity laser beam is studied by using the laser-dressed quantum electrodynamics (QED) method, which is a non-perturbative theory for the interaction between a plane electromagnetic field and a charged particle. In order to analyze in the real experimental condition, a Lorentz transformation for the cross section of this process is derived between the laboratory frame and the initial rest frame of electrons. The energy of the scattered photon is analyzed, as well as the cross sections for different laser intensities and polarizations and different electron velocities. The angular distribution of the emitted photon is investigated in a special velocity of the electron, in which for a fixed number of absorbed photons, the electron energy will not change after the scattering in the lab frame. We obtain the conclusion that higher laser intensities suppress few-laser-photon absorption and enhance more-laser-photon absorption. A comparison between different polarizations is also made, and we find that the linearly polarized laser is more suitable to generate nonlinear Compton scattering.

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Scattering and propagation of terahertz pulses in random soot aggregate systems Li Hai-Ying (李海英), Wu Zhen-Sen (吴振森), Bai Lu (白璐), Li Zheng-Jun (李正军) Chin. Phys. B, 2014, 23 (5):  054201.  DOI: 10.1088/1674-1056/23/5/054201 Abstract ( 488 )   PDF (649KB) ( 480 )   Scattering and propagation of terahertz pulses in random soot aggregate systems are studied by using the generalized multi-particle Mie-solution (GMM) and the pulse propagation theory. Soot aggregates are obtained by the diffusion-limited aggregation (DLA) model. For a soot aggregate in soot aggregate systems, scattering characteristics are analyzed by using the GMM. Scattering intensities versus scattering angles are given. The effects of different positions of the aggregate on the scattering intensities, scattering cross sections, extinction cross sections, and absorption cross sections are computed and compared. Based on pulse propagation in random media, the transmission of terahertz pulses in random soot aggregate systems is determined by the two-frequency mutual coherence function. Numerical simulations and analysis are given for terahertz pulses (0.7956 THz).

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Subwavelength Fourier-transform imaging without a lens or a beamsplitter Liu Rui-Feng (刘瑞丰), Yuan Xin-Xing (袁新星), Fang Yi-Zhen (方一珍), Zhang Pei (张沛), Zhou Yu (周宇), Gao Hong (高宏), Li Fu-Li (李福利) Chin. Phys. B, 2014, 23 (5):  054202.  DOI: 10.1088/1674-1056/23/5/054202 Abstract ( 835 )   PDF (1129KB) ( 468 )   The fourier-transform patterns of an object are usually observed in the far-field region or obtained in the near-field region with the help of lenses. Here we propose and experimentally demonstrate a scheme of Fourier-transform patterns in the Fresnel diffraction region with thermal light. In this scheme, neither a lens nor a beamsplitter is used, and only one single charge coupled device (CCD) is employed. It means that dividing one beam out of a light source into signal and reference beams is not as necessary as the one done by the use of a beamsplitter in usual ghost interference experiments. Moreover, the coincidence measurement of two point detectors is not necessary and data recorded on a single CCD are sufficient for reconstructing the ghost diffraction patterns. The feature of the scheme promises a great potential application in the fields of X-ray and neutron diffraction imaging processes.

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Correspondence normalized ghost imaging on compressive sensing Zhao Sheng-Mei (赵生妹), Zhuang Peng (庄鹏) Chin. Phys. B, 2014, 23 (5):  054203.  DOI: 10.1088/1674-1056/23/5/054203 Abstract ( 2335 )   PDF (398KB) ( 959 )   Ghost imaging (GI) offers great potential with respect to conventional imaging techniques. It is an open problem in GI systems that a long acquisition time is be required for reconstructing images with good visibility and signal-to-noise ratios (SNRs). In this paper, we propose a new scheme to get good performance with a shorter construction time. We call it correspondence normalized ghost imaging based on compressive sensing (CCNGI). In the scheme, we enhance the signal-to-noise performance by normalizing the reference beam intensity to eliminate the noise caused by laser power fluctuations, and reduce the reconstruction time by using both compressive sensing (CS) and time-correspondence imaging (CI) techniques. It is shown that the qualities of the images have been improved and the reconstruction time has been reduced using CCNGI scheme. For the two-grayscale “double-slit” image, the mean square error (MSE) by GI and the normalized GI (NGI) schemes with the measurement number of 5000 are 0.237 and 0.164, respectively, and that is 0.021 by CCNGI scheme with 2500 measurements. For the eight-grayscale “lena” object, the peak signal-to-noise rates (PSNRs) are 10.506 and 13.098, respectively using GI and NGI schemes while the value turns to 16.198 using CCNGI scheme. The results also show that a high-fidelity GI reconstruction has been achieved using only 44% of the number of measurements corresponding to the Nyquist limit for the two-grayscale “double-slit” object. The qualities of the reconstructed images using CCNGI are almost the same as those from GI via sparsity constraints (GISC) with a shorter reconstruction time.

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Transient responses of transparency in a far-off resonant atomic system Hu Zheng-Feng (胡正峰), Du Chun-Guang (杜春光), Deng Jian-Liao (邓见辽), Wang Yu-Zhu (王育竹) Chin. Phys. B, 2014, 23 (5):  054204.  DOI: 10.1088/1674-1056/23/5/054204 Abstract ( 700 )   PDF (308KB) ( 354 )   Transient coherent oscillations in a closed Λ system under far-off resonant Raman fields were investigated theoretically. It has been found that the coherent superposition of the ground states can be formed due to the absorption even for initial maximal mixed ground states. The absorption oscillates with a period depending on the two-photon detuning when the system is initially in a transparent state and the two-photon Raman detuning is suddenly changed. The amplitude of the absorption decays with the decay rate of the ground states, which is different from the case when the lasers are applied resonantly. These transient coherent oscillations can be used to measure the relaxation rate of the ground states.

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Off-resonant double-resonance optical-pumping spectra and their application in a multiphoton cesium magneto-optical trap Hot! Yang Bao-Dong (杨保东), He Jun (何军), Wang Jun-Min (王军民) Chin. Phys. B, 2014, 23 (5):  054205.  DOI: 10.1088/1674-1056/23/5/054205 Abstract ( 604 )   PDF (557KB) ( 446 )   We present an investigation of double-resonance optical pumping (DROP) spectra under the condition of single-photon frequency detuning based on a cesium 6S1/2 -6P3/2 -8S1/2 ladder-type system with a room-temperature vapor cell. Two DROP peaks are found, and their origins are explored. One peak has a narrow linewidth due to the atomic coherence for a counterpropagating configuration; the other peak has a broad linewidth, owing to the spontaneous decay for a copropagating configuration. This kind of off-resonant DROP spectrum can be used to control and offset-lock a laser frequency to a transition between excited states. We apply this technique to a multiphoton cesium magneto-optical trap, which can efficiently trap atoms on both red and blue sides of the two-photon resonance.

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Switching from positive to negative absorption with electromagnetically induced transparency in circuit quantum electrodynamics Li Hai-Chao (李海超), Ge Guo-Qin (葛国勤) Chin. Phys. B, 2014, 23 (5):  054206.  DOI: 10.1088/1674-1056/23/5/054206 Abstract ( 489 )   PDF (245KB) ( 428 )   We present a theoretical study of electromagnetically induced transparency (EIT) in a superconducting quantum circuit with a tunable V-shaped energy spectrum derived from two superconducting Josephson charge qubits coupled with each other through a superconducting quantum interference device. Using the density matrix formalism and the steady-state approximation, we obtain the analytical expressions of the first-order matrix element associated with the absorption and dispersion of the probe field for two different V-type schemes. Our results show that, for this superconducting quantum system, it is possible to realize a remarkable phenomenon that dynamic conversion between EIT and EIT with amplification without population inversion. Such a unique optical feature has potential applications in quantum optical devices and quantum information processing.

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Diode-pumped self-starting mode-locked femtosecond Yb：YCa4O(BO3)3 laser Hot! Gao Zi-Ye (高子叶), Zhu Jiang-Feng (朱江峰), Tian Wen-Long (田文龙), Wang Jun-Li (王军利), Wang Qing (王庆), Zhang Zhi-Guo (张治国), Wei Zhi-Yi (魏志义), Yu Hao-Hai (于浩海), Zhang Huai-Jin (张怀金), Wang Ji-Yang (王继扬) Chin. Phys. B, 2014, 23 (5):  054207.  DOI: 10.1088/1674-1056/23/5/054207 Abstract ( 637 )   PDF (768KB) ( 476 )   A self-starting mode-locked femtosecond laser is accomplished with an oxoborate self-frequency doubling crystal Yb:YCa4O(BO3)3 (Yb:YCOB) as the gain medium and a semiconductor mirror as the saturable absorber. Pumped by a 976-nm fiber-coupled diode laser with 50-u m core diameter, stable mode-locked laser pulses up to 430 mW were obtained at a repetition rate of 83.61 MHz under 5-W pump power. The autocorrelation measurement shows that the pulse duration is as short as 150 fs by assuming the sech2 pulse shape at a central wavelength of 1048 nm. This work has demonstrated a compact and reliable femtosecond laser source for prospective low-cost applications.

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A novel 2-μm pulsed fiber laser based on a supercontinuum source and its application to mid-infrared supercontinuum generation Yang Wei-Qiang (杨未强), Zhang Bin (张斌), Hou Jing (侯静), Yin Ke (殷科), Liu Ze-Jin (刘泽金) Chin. Phys. B, 2014, 23 (5):  054208.  DOI: 10.1088/1674-1056/23/5/054208 Abstract ( 646 )   PDF (674KB) ( 562 )   A new method to achieve 2-μm pulsed fiber lasers based on a supercontinuum (SC) is demonstrated. The incident pump light is a pulsed SC which contains a pump light and a signal light at the same time. The initial signal of the seed laser is provided by the incident pump light and amplified in the cavity. Based on this, we obtain a 2-μm pulsed laser with pulse repetition rate of 50 kHz and pulse width of 2 ns from the Tm-doped fiber laser. This 2-μm pulsed laser is amplified by two stages of fiber amplifiers, then the amplified laser is used for mid-infrared (mid-IR) SC generation in a 10-m length of ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. An all-fiber-integrated mid-IR SC with spectrum ranging from 1.8 μm to 4.3 μm is achieved. The maximal average output power of the mid-IR SC from the ZBLAN fiber is 1.24 W (average output power beyond 2.5 μm is 340 mW), corresponding to an output efficiency of 6.6% with respect to the 790-nm pump power.

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Multi-component optical azimuthons of four-wave mixing Wang Rui-Min (王瑞敏), Wang Xing-Peng (王兴鹏), Wu Zhen-Kun (吴振坤), Yao Xin (姚鑫), Zhang Yi-Qi (张贻齐), Zhang Yan-Peng (张彦鹏) Chin. Phys. B, 2014, 23 (5):  054209.  DOI: 10.1088/1674-1056/23/5/054209 Abstract ( 576 )   PDF (521KB) ( 516 )   We report the multi-component optical azimuthons of four-wave mixing (FWM) composed of several modulated vortex beams, the so-called azimuthons, in V-type three-level and two-level atomic systems. We analyze the formation mechanisms of the FWM azimuthons theoretically and experimentally. In addition, we illustrate the interactions between the co-propagating azimuthon components. Finally, we also compare the stabilities of azimuthons in V-type three-level and two-level atomic systems.

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Low-loss terahertz waveguide with InAs-graphene-SiC structure Xu De-Gang (徐德刚), Wang Yu-Ye (王与烨), Yu Hong (于红), Li Jia-Qi (李佳起), Li Zhong-Xiao (李忠孝), Yan Chao (闫超), Zhang Hao (张昊), Liu Peng-Xiang (刘鹏翔), Zhong Kai (钟凯), Wang Wei-Peng (王卫鹏), Yao Jian-Quan (姚建铨) Chin. Phys. B, 2014, 23 (5):  054210.  DOI: 10.1088/1674-1056/23/5/054210 Abstract ( 461 )   PDF (2137KB) ( 736 )   We demonstrate a low-loss terahertz waveguide based on the InAs-graphene-SiC structure. By analyzing the terahertz waveguide proposed in this paper, we can obtain that it is the characteristic of a low transmission loss coefficient (αloss ≈ 0.55 dB/m) for fundamental mode (LP01) when the incident frequency is larger than 3.0 THz. The critical radii of the inside and outside cylinders have been found for the high-quality transmission. The large inside radius and the high transmission frequency result in a flat transmission loss coefficient curve. As a strictly two-dimensional material, the double graphene surface rings perform better to improve the quality of transmission mode. These results provide a new idea for the research of the long-distance THz waveguide.

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Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells Liang Ming-Ming (梁明明), Weng Guo-En (翁国恩), Zhang Jiang-Yong (张江勇), Cai Xiao-Mei (蔡晓梅), Lü Xue-Qin (吕雪芹), Ying Lei-Ying (应磊莹), Zhang Bao-Ping (张保平) Chin. Phys. B, 2014, 23 (5):  054211.  DOI: 10.1088/1674-1056/23/5/054211 Abstract ( 723 )   PDF (446KB) ( 610 )   The structural and optical properties of InGaN/GaN multiple quantum wells (MQWs) with different barrier thicknesses are studied by means of high resolution X-ray diffraction (HRXRD), a cross-sectional transmission electron microscope (TEM), and temperature-dependent photoluminescence (PL) measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodicity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization potentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence, and the corresponding activation energy (or the localization potential) increases with the increase of the barrier thickness. The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers, i.e., clusters with lower In contents aggregate into clusters with higher In contents.

RAPID COMMUNICATION

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Manipulation of extraordinary acoustic transmission by a tunable bull’s eye structure Wang Ji-Wei (王继伟), Cheng Ying (程营), Liu Xiao-Jun (刘晓峻) Chin. Phys. B, 2014, 23 (5):  054301.  DOI: 10.1088/1674-1056/23/5/054301 Abstract ( 692 )   PDF (769KB) ( 499 )   Extraordinary acoustic transmission (EAT) has been investigated in a tunable bull's eye structure. We demonstrate that the transmission coefficient of acoustic waves can be modulated by a grating structure. When the grating is located at a distance of 0.5 mm from the base plate, the acoustic transmission shows an 8.77-fold enhancement compared to that by using a traditional bull's eye structure. When the distance increases to 1.5 mm, the transmission approaches zero, indicating a total reflection. Thus, we can make an efficient modulation of acoustic transmission from 0 to 877%. The EAT effects have been ascribed to the coupling of structure-induced resonance with the diffractive wave and the waveguide modes, as well as the Fabry-Perot resonances. As a potential application, the modulation of far-field collimation is illustrated in the proposed bull's eye structure.

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

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Molecular structure dependence of acoustic nonlinearity parameter B/A for silicone oils Zhang Zhe (张喆), Chen Gong (陈功), Zhang Dong (章东) Chin. Phys. B, 2014, 23 (5):  054302.  DOI: 10.1088/1674-1056/23/5/054302 Abstract ( 452 )   PDF (232KB) ( 328 )   Exploring new acoustic parameters is essential to develop a noninvasive imaging technique for the surgery of silicone oil tamponades. In this study, the acoustic nonlinearity parameters B/A of varied silicone oil samples (e.g., linear or hyper-branched) are experimentally measured by using a modified thermodynamic method. The results show that: (i) when the concentration of the silicone oil with a molecular weight of 5× 104 increases from 0.5 g/100 ml to 8 g/100 ml, the corresponding B/A value increases by about 18%, but the acoustic velocity only increases by about 0.1%; (ii) when the molecular weight of the hyper-branched silicone oil is enhanced from 2× 105 to 1× 106, the B/A value increases by about 22%, while the acoustic velocity is only raised by about 0.2%. This study suggests that the B/A parameter of the silicone oil is more sensitive to the change in its molecular structure than that of the acoustic velocity. Thus, the B/A parameter might be utilized as an effective index for the development and optimization of the noninvasive imaging of the surgery of silicone oil tamponades.

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Noether symmetry and conserved quantity for a Hamilton system with time delay Jin Shi-Xin (金世欣), Zhang Yi (张毅) Chin. Phys. B, 2014, 23 (5):  054501.  DOI: 10.1088/1674-1056/23/5/054501 Abstract ( 682 )   PDF (226KB) ( 396 )   In this paper, the Noether symmetries and the conserved quantities for a Hamilton system with time delay are discussed. Firstly, the variational principles with time delay for the Hamilton system are given, and the Hamilton canonical equations with time delay are established. Secondly, according to the invariance of the function under the infinitesimal transformations of the group, the basic formulas for the variational of the Hamilton action with time delay are discussed, the definitions and the criteria of the Noether symmetric transformations and quasi-symmetric transformations with time delay are obtained, and the relationship between the Noether symmetry and the conserved quantity with time delay is studied. In addition, examples are given to illustrate the application of the results.

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Reactionless robust finite-time control for manipulation of passive objects by free-floating space robots Guo Sheng-Peng (郭胜鹏), Li Dong-Xu (李东旭), Meng Yun-He (孟云鹤), Fan Cai-Zhi (范才智) Chin. Phys. B, 2014, 23 (5):  054502.  DOI: 10.1088/1674-1056/23/5/054502 Abstract ( 616 )   PDF (393KB) ( 400 )   On-orbit servicing requires efficient techniques for manipulating passive objects. The paper aims at developing a reactionless control method that drives the manipulator to manipulate passive objects with high precision, while inducing no disturbances to its base attitude. To this end, decomposition of the target dynamics from the base dynamics is discussed, so that they can be considered as two independent subsystems. A reactionless nonlinear controller is presented, which ensures high-precision manipulation of the targets and that the base orientation is unchanged. This is achieved by combining the robust finite-time control with the reaction null space. Finally, the performance of the proposed method is examined by comparing it with that of a reactionless PD controller and a pure finite-time controller.

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Properties of surface waves in granular media under gravity Zheng He-Peng (郑鹤鹏) Chin. Phys. B, 2014, 23 (5):  054503.  DOI: 10.1088/1674-1056/23/5/054503 Abstract ( 498 )   PDF (392KB) ( 349 )   Acoustical waves propagating along the free surface of granular media under gravity are investigated in the framework of elasticity theory. The influence of stress on a surface wave is analyzed. The results have shown that two types of surface waves, namely sagittal and transverse modes exist depending on initial stress states, which may have some influence on the dispersion relations of surface waves, but the influence is not great. Considering that the present experimental accuracy is far from distinguishing this detail, the validity of elasticity theory on the surface waves propagating in granular media can still be maintained.

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MHD flow of nanofluids over an exponentially stretching sheet in a porous medium with convective boundary conditions T. Hayat, M. Imtiaz, A. Alsaedi, R. Mansoor Chin. Phys. B, 2014, 23 (5):  054701.  DOI: 10.1088/1674-1056/23/5/054701 Abstract ( 570 )   PDF (423KB) ( 1594 )   This article concentrates on the steady magnetohydrodynamic (MHD) flow of viscous nanofluid. The flow is caused by a permeable exponentially stretching surface. An incompressible fluid fills the porous space. A comparative study is made for the nanoparticles namely Copper (Cu), Silver (Ag), Alumina (Al2O3) and Titanium Oxide (TiO2). Water is treated as a base fluid. Convective type boundary conditions are employed in modeling the heat transfer process. The non-linear partial differential equations governing the flow are reduced to an ordinary differential equation by similarity transformations. The obtained equations are then solved for the development of series solutions. Convergence of the obtained series solutions is explicitly discussed. The effects of different parameters on the velocity and temperature profiles are shown and analyzed through graphs.

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Existence of a Hartmann layer in the peristalsis of Sisko fluid Saleem Asghar, Tayyaba Minhas, Aamir Ali Chin. Phys. B, 2014, 23 (5):  054702.  DOI: 10.1088/1674-1056/23/5/054702 Abstract ( 584 )   PDF (331KB) ( 554 )   Analytical solutions for the peristaltic flow of a magneto hydrodynamic (MHD) Sisko fluid in a channel, under the effects of strong and weak magnetic fields, are presented. The governing nonlinear problem, for the strong magnetic field, is solved using the matched asymptotic expansion. The solution for the weak magnetic field is obtained using a regular perturbation method. The main observation is the existence of a Hartman boundary layer for the strong magnetic field at the location of the two plates of the channel. The thickness of the Hartmann boundary layer is determined analytically. The effects of a strong magnetic field and the shear thinning parameter of the Sisko fluid on the velocity profile are presented graphically.

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Newtonian heating effects in three-dimensional flow of viscoelastic fluid A. Qayyum, T. Hayat, M. S. Alhuthali, H. M. Malaikah Chin. Phys. B, 2014, 23 (5):  054703.  DOI: 10.1088/1674-1056/23/5/054703 Abstract ( 499 )   PDF (425KB) ( 369 )   A mathematical model is constructed to investigate the three-dimensional flow of a non-Newtonian fluid. An incompressible viscoelastic fluid is used in mathematical formulation. The conjugate convective process (in which heat the transfer rate from the bounding surface with a finite capacity is proportional to the local surface temperature) in three-dimensional flow of a differential type of non-Newtonian fluid is analyzed for the first time. Series solutions for the nonlinear differential system are computed. Plots are presented for the description of emerging parameters entering into the problem. It is observed that the conjugate heating phenomenon causes an appreciable increase in the temperature at the stretching wall.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Validity of the two-term Boltzmann approximation employed in the fluid model for high-power microwave breakdown in gas Zhao Peng-Cheng (赵朋程), Liao Cheng (廖成), Yang Dan (杨丹), Zhong Xuan-Ming (钟选明) Chin. Phys. B, 2014, 23 (5):  055101.  DOI: 10.1088/1674-1056/23/5/055101 Abstract ( 787 )   PDF (437KB) ( 684 )   The electron energy distribution function (EEDF), predicted by the Boltzmann equation solver BOLSIG+ based on the two-term approximation, is introduced into the fluid model for simulating the high-power microwave (HPM) breakdown in argon, nitrogen, and air, and its validity is examined by comparing with the results of particle-in-cell Monte Carlo collision (PIC/MCC) simulations as well as the experimental data. Numerical results show that, the breakdown time of the fluid model with the Maxwellian EEDF matches that of the PIC/MCC simulations in nitrogen; however, in argon under high pressures, the results from the Maxwellian EEDF were poor. This is due to an overestimation of the energy tail of the Maxwellian EEDF in argon breakdown. The prediction of the fluid model with the BOLSIG+ EEDF, however, agrees very well with the PIC/MCC prediction in nitrogen and argon over a wide range of pressures. The accuracy of the fluid model with the BOLSIG+ EEDF is also verified by the experimental results of the air breakdown.

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Numerical simulation of electron cyclotron current drive characteristics on EAST Wei Wei (韦维), Ding Bo-Jiang (丁伯江), Zhang Xin-Jun (张新军), Wang Xiao-Jie (王晓洁), Li Miao-Hui (李妙辉), Kong Er-Hua (孔二华), Zhang Lei (张磊) Chin. Phys. B, 2014, 23 (5):  055201.  DOI: 10.1088/1674-1056/23/5/055201 Abstract ( 495 )   PDF (546KB) ( 390 )   Electron cyclotron current drive (ECCD) will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of ECCD with the parameters of EAST have been carried out by using TORAY-GA code based on the understanding of ECCD mechanisms. ECCD efficiencies achieved in different plasma and electron cyclotron (EC) wave parameters are given. The dependences of ECCD characteristics on EC wave injection angle, toroidal magnetic field, plasma density, and temperature are presented and discussed.

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Effect of inner-surface roughness of conical target on laser absorption and fast electron generation Wang Huan (王欢), Cao Li-Hua (曹莉华), Zhao Zong-Qing (赵宗清), Yu Ming-Yang (郁明阳), Gu Yu-Qiu (谷渝秋), He Xian-Tu (贺贤土) Chin. Phys. B, 2014, 23 (5):  055202.  DOI: 10.1088/1674-1056/23/5/055202 Abstract ( 628 )   PDF (340KB) ( 436 )   The effect of inner-surface roughness of conical targets on the generation of fast electrons in the laser-cone interaction is investigated using particle-in-cell simulation. It is found that the surface roughness can reduce the fast-electron number (in the energy range E > 1 MeV) and energy, as compared to that from a cone with smooth inner wall. A scaling law for the laser reflectivity based on the vacuum-heating model is derived. Both theory and simulation indicate that laser reflection increases with the height-to-width ratio of the periodic inner surface structure and approaches that of a smooth cone as this ratio becomes zero.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Icosahedral quasicrystals solids with an elliptic hole under uniform heat flow Li Lian-He (李联和), Liu Guan-Ting (刘官厅) Chin. Phys. B, 2014, 23 (5):  056101.  DOI: 10.1088/1674-1056/23/5/056101 Abstract ( 554 )   PDF (264KB) ( 253 )   The complex variable method for solving the two-dimensional thermal stress problem of icosahedral quasicrystals is stated. The closed-form solutions for icosahedral quasicrystals containing an elliptical hole subjected to a remote uniform heat flow are obtained. When the hole degenerates into a crack, the explicit solutions for the stress intensity factors is presented.

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Finite size specimens with cracks of icosahedral Al–Pd–Mn quasicrystals Yang Lian-Zhi (杨连枝), Ricoeur Andreas, He Fan-Min (何蕃民), Gao Yang (高阳) Chin. Phys. B, 2014, 23 (5):  056102.  DOI: 10.1088/1674-1056/23/5/056102 Abstract ( 470 )   PDF (529KB) ( 338 )   Icosahedral quasicrystals are the most important and thermodynamically stable in all about 200 kinds of quasicrystals currently observed. Beyond the scope of classical elasticity, apart from a phonon displacement field, there is a phason displacement field in the elasticity of the quasicrystal, which induces an important effect on the mechanical properties of the material and makes an analytical solution difficult to obtain. In this paper, a finite element algorithm for the static elasticity of icosahedral quasicrystals is developed by transforming the elastic boundary value problem of the icosahedral quasicrystals into an equivalent variational problem. Analytical and numerical solutions for an icosahedral Al-Pd-Mn quasicrystal cuboid subjected to a uniaxial tension with different phonon-phason coupling parameters are given to verify the validity of the numerical approach. A comparison between the analytical and numerical solutions of the specimen demonstrates the accuracy and efficiency of the present algorithm. Finally, in order to reveal the fracture behavior of the icosahedral Al-Pd-Mn quasicrystal, a cracked specimen with a finite size of matter is investigated, both with and without phonon-phason coupling. Meanwhile, the geometry factors are calculated, including the stress intensity factor and the crack opening displacement for the finite-size specimen. Computational results reveal the importance of phonon-phason coupling effect on the icosahedral Al-Pd-Mn quasicrystal. Furthermore, the finite element procedure can be used to solve more complicated boundary value problems.

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Coulombic interaction in the colloidal oriented-attachment growth of tetragonal nanorods Li Jun-Fan (李峻樊), Wen Ke-Chun (文克春), He Wei-Dong (何伟东), Wang Xiao-Ning (王晓宁), Lü Wei-Qiang (吕维强), Yan Peng-Fei (严鹏飞), Song Yuan-Qiang (宋远强), Lu Hong-Liang (路红亮), Lin Xiao (林晓), Dickerson J. H. Chin. Phys. B, 2014, 23 (5):  056103.  DOI: 10.1088/1674-1056/23/5/056103 Abstract ( 695 )   PDF (364KB) ( 351 )   In this report, the analytical expression of Coulombic interaction between a spherical nanoparticle and a tetragonal nanorod is derived. To evaluate the Coulombic interaction in the oriented attachment growth of tetragonal nanorods, we analyze the correlation between the Coulombic interaction and the important growth parameters, including: nanoparticle-nanorod separation, aspect ratio of the nanorods, and surface charge density. Our work opens up the opportunity to investigate interparticle interactions in the oriented attachment growth of tetragonal nanorods.

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Role of helium in the sliding and mechanical properties of a vanadium grain boundary：A first-principles study Zhou Hong-Bo (周洪波), Jin Shuo (金硕), Zhang Ying (张颖), Shu Xiao-Lin (舒小林), Niu Liang-Liang (牛亮亮) Chin. Phys. B, 2014, 23 (5):  056104.  DOI: 10.1088/1674-1056/23/5/056104 Abstract ( 517 )   PDF (2499KB) ( 373 )   The effects of helium (He) on the sliding and mechanical properties of a vanadium (V) Σ5(310)/[001] grain boundary (GB) have been investigated using a first-principles method. It has been found that He was energetically favorable sitting at the GB region with a segregation energy of -0.27 eV, which was attributed to the special atomic configurations and charge density distributions of the GB. The maximal sliding energy barrier of the He-doped GB was calculated to be 1.73 J/m2, ～ 35% larger than that of the clean GB. This suggested that the presence of He would hinder the V GB mobility. Based on the thermodynamic criterion, the total energy calculations indicated that the embrittlement of V GB would be enhanced by He segregation.

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Controllable synthesis of high aspect ratio Mg2B2O5 nanowires and their applications in reinforced polyhydroxyalkanoate composites Mo Zhao-Jun (莫兆军), Chen Jin-Peng (陈金鹏), Lin Jing (林靖), Fan Ying (范英), Liang Chun-Yong (梁春永), Wang Hong-Shui (王洪水), Xu Xue-Wen (徐学文), Hu Long (胡龙), Tang Cheng-Chun (唐成春) Chin. Phys. B, 2014, 23 (5):  056201.  DOI: 10.1088/1674-1056/23/5/056201 Abstract ( 456 )   PDF (2505KB) ( 397 )   Highly pure magnesium borate (Mg2B2O5) nanowires with an average diameter of ～ 30 nm, an average length of ～ 15 μm, and a high aspect ratio of ～ 500 have been synthesized on a large scale via a two-step method. MgBO2(OH) nanowires with high aspect ratios were first prepared via a PVP-assisted hydrothermal technique. Using these nanowires as precursors, single crystalline Mg2B2O5 nanowires were synthesized by post-annealing treatment at a relatively low temperature of 700 ℃. The important effect of the MgBO2(OH)-Mg2B2O5 conversion process on the morphology of the Mg2B2O5 nanowires was investigated and it was indicated that the recrystallization process plays an important role in the protection of the one-dimensional (1D) nanostructure. Moreover, the rigidity and the toughness of the Mg2B2O5 nanowire-reinforced PHA composites were tremendously improved compared to those of the pure PHA. Our results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcement applications in polymer composites.

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Effect of Gd doping on the magnetism and work function of Fe1-xGdx/Fe (001) Tang Ke-Qin (汤可嵚), Zhong Ke-Hua (钟克华), Cheng Yan-Ming (程燕铭), Huang Zhi-Gao (黄志高) Chin. Phys. B, 2014, 23 (5):  056301.  DOI: 10.1088/1674-1056/23/5/056301 Abstract ( 674 )   PDF (533KB) ( 323 )   The magnetism and work function Φ of Fe1-xGdx/Fe (001) films have been investigated using first-principles methods based on the density functional theory. The calculated results reveal that Gd doping on the Fe (001) surface would greatly affect the geometrical structure of the system. The restruction of the surface atoms leads to the transition of magnetic coupling between Gd and Fe atoms from ferromagnetic (FM) for 0.5 ≤ x ≤ 0.75 to antiferromagnetic (AFM) for x=1.0. For Fe1-xGdx/Fe (001) (x=0.25, 0.5, 0.75, 1.0), the charge transfer from Gd to Fe leads to a positive dipole formed on the surface, which is responsible for the decrease of the work function. Moreover, it is found that the magnetic moments of Fe and Gd on the surface layer can be strongly influenced by Gd doping. The changes of the work function and magnetism for Fe1-xGdx/Fe (001) can be explained by the electron transfer, the magnetic coupling interaction between Gd and Fe atoms, and the complex surface restruction. Our work strongly suggests that the doping of the metal with a low work function is a promising way for modulating the work function of the magnetic metal gate.

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Diverse solid and supersolid phases of bosons in a triangular lattice Chen Qi-Hui (陈起辉), Li Peng (李鹏) Chin. Phys. B, 2014, 23 (5):  056701.  DOI: 10.1088/1674-1056/23/5/056701 Abstract ( 651 )   PDF (489KB) ( 325 )   We investigate the ground state of bosons with long-range interactions in the large U limit on a triangular lattice. By mapping this system to the spin-1/2 XXZ model in a magnetic field, we can apply the spin wave theory to this study. We demonstrate how to construct the phase diagrams within the spin wave theory. The phase diagrams are given in an extensive parameter region, where, besides the superfluid phase, diverse solid and supersolid phases are shown to exist in this model. Especially, we find that the phase diagram obtained in this method is consistent with the one obtained previously using numerical techniques in the Ising limit. This confirms the effectiveness of our method. We analyze the stability of all the obtained supersolids and show that they will not be ruined by the quantum fluctuations. We observe that the quantum fluctuations in the stripe supersolid phase could be enhanced by the external field. We also discuss the relevance of our result with the experiment that may be realized with ultracold bosonic polar molecules in a triangular optical lattice.

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Corrosion related properties of iron (100) surface in liquid lead and bismuth environments：A first-principles study Song Chi (宋驰), Li Dong-Dong (李冬冬), Xu Yi-Chun (许依春), Pan Bi-Cai (潘必才), Liu Chang-Song (刘长松), Wang Zhi-Guang (王志光) Chin. Phys. B, 2014, 23 (5):  056801.  DOI: 10.1088/1674-1056/23/5/056801 Abstract ( 457 )   PDF (492KB) ( 313 )   The corrosion of steels in liquid metal lead (Pb) and bismuth (Bi) is a critical challenge in the development of accelerator driven systems (ADS). Using a first-principles method with a slab model, we theoretically investigate the interaction between the Pb (Bi) atom and the iron (Fe) (100) surface to assess the fundamental corrosion properties. Our investigation demonstrates that both Pb and Bi atoms favorably adsorb on the (100) surface. Such an adsorption decreases the energy required for the dissociation of an Fe atom from the surface, enhancing the dissolution tendency significantly. The segregation of six common alloying elements (Cr, Al, Mn, Ni, Nb, and Si) to the surface and their impacts on the corrosion properties are also considered. The present results reveal that Si seems to have a relatively good performance to stabilize the surface and alleviate the dissolving trend caused by Pb and Bi.

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

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First-principles study of the influences of oxygen defects upon the electronic properties of Nb-doped TiO2 by GGA + U methods Song Chen-Lu (宋晨路), Yang Zhen-Hui (杨振辉), Su Ting (苏婷), Wang Kang-Kai (王慷慨), Wang Ju (王菊), Liu Yong (刘涌), Han Gao-Rong (韩高荣) Chin. Phys. B, 2014, 23 (5):  057101.  DOI: 10.1088/1674-1056/23/5/057101 Abstract ( 423 )   PDF (1827KB) ( 542 )   The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation (GGA)+U method. Four independent models (i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site (NbTi), an anatase cell with a Nb-dopant and an oxygen vacancy (NbTi+VO), and an anatase cell with a Nb-dopant and an interstitial oxygen (NbTi+Oi)) were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calculated. The results show that in the NbTi+VO cell both eg and t2g levels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies (VO) collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi+Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.

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4H-SiC Schottky barrier diodes with semi-insulating polycrystalline silicon field plate termination Yuan Hao (袁昊), Tang Xiao-Yan (汤晓燕), Zhang Yi-Men (张义门), Zhang Yu-Ming (张玉明), Song Qing-Wen (宋庆文), Yang Fei (杨霏), Wu Hao (吴昊) Chin. Phys. B, 2014, 23 (5):  057102.  DOI: 10.1088/1674-1056/23/5/057102 Abstract ( 618 )   PDF (437KB) ( 577 )   Based on the theoretical analysis of the 4H-SiC Schottky-barrier diodes (SBDs) with field plate termination, 4H-SiC SBD with semi-insulating polycrystalline silicon (SIPOS) FP termination has been fabricated. The relative dielectric constant of the SIPOS dielectric first used in 4H-SiC devices is 10.4, which is much higher than that of the SiO2 dielectric, leading to benefitting the performance of devices. The breakdown voltage of the fabricated SBD could reach 1200 V at leakage current 20 uA, about 70% of the theoretical breakdown voltage. Meanwhile, both of the simulation and experimental results show that the length of the SIPOS FP termination is an important factor for structure design.

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Rectifying and photovoltaic properties of ZnCo2O4/Si heterostructure grown by pulsed laser deposition Chen Zhao (陈钊), Wen Xiao-Li (温晓莉), Niu Li-Wei (牛利伟), Duan Meng-Meng (段萌萌), Zhang Yun-Jie (张云捷), Dong Xiang-Lei (董祥雷), Chen Chang-Le (陈长乐) Chin. Phys. B, 2014, 23 (5):  057103.  DOI: 10.1088/1674-1056/23/5/057103 Abstract ( 459 )   PDF (532KB) ( 339 )   ZnCo2O4/Si heterostructures have been fabricated by a pulsed laser deposition method, and their transport behaviors and photovoltaic properties have been characterized. The ZnCo2O4/Si heterostructures show a good rectifying behavior at five different temperatures ranging from 50 K to 290 K. The measurements of the photovoltaic response reveal that a photovoltage of 33 mV is generated when the heterostructures are illuminated by a 532 nm laser of 250 mW/cm2 and mechanically chopped at 2500 Hz. Both the photocurrent and the photovoltage clearly increase with the increase of the laser intensity at room temperature. However, the photovoltage peak of the heterostructures decreases with the increase of the temperature. This work may open new perspectives for ZnCo2O4/Si heterostructure-based devices.

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Electronic and optical properties of Au-doped Cu2O：A first principles investigation Jiang Zhong-Qian (姜中钱), Yao Gang (姚钢), An Xin-You (安辛友), Fu Ya-Jun (符亚军), Cao Lin-Hong (曹林洪), Wu Wei-Dong (吴卫东), Wang Xue-Min (王雪敏) Chin. Phys. B, 2014, 23 (5):  057104.  DOI: 10.1088/1674-1056/23/5/057104 Abstract ( 463 )   PDF (792KB) ( 717 )   The Cu2O and Au-doped Cu2O films are prepared on MgO (001) substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decreases by 1.6% after Au doping. The electronic and optical properties of pure and Au-doped cuprite Cu2O films are investigated by the first principles. The calculated results indicate that Cu2O is a direct band-gap semiconductor. The scissors operation of 1.64 eV has been carried out. After correcting, the band gaps for pure and Au doped Cu2O are about 2.17 eV and 2.02 eV, respectively, decreasing by 6.9%. All of the optical spectra are closely related to the dielectric function. The optical spectrum red shift corresponding to the decreasing of band gap, and the additional absorption are observed in the visible region for Au doped Cu2O film. The experimental results are generally in agreement with the calculated results. These results indicate that Au doping could become one of the important factors influencing the photovoltaic activity of Cu2O film.

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Detection of Majorana fermions in an Aharonov-Bohm interferometer Hot! Shang En-Ming (尚恩明), Pan Yi-Ming (潘义明), Shao Lu-Bing (邵陆兵), Wang Bai-Gen (王伯根) Chin. Phys. B, 2014, 23 (5):  057201.  DOI: 10.1088/1674-1056/23/5/057201 Abstract ( 634 )   PDF (456KB) ( 619 )   By using the non-equilibrium Green's function technique, we investigate the electronic transport properties in an Aharonov-Bohm interferometer coupling with Majorana fermions. We find a fixed unit conductance peak which is independent of the other factors when the topological superconductor is grounded. Especially, an additional phase appears when the topological superconductor is in the strong Coulomb regime, which induces a new conductance resonant peak compared with the structure of replacing the topological superconductor by a quantum dot, and the conductance oscillation with the magnetic flux reveals a 2π phase shift by raising (lowering) a charge on the capacitor.

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Effect of charge order transition on tunneling resistance in Pr0.6Ca0.4MnO3/Nb-doped SrTiO3 heterojunction Wang Deng-Jing (王登京), Ma Jun-Jie (马俊杰), Wang Mei (王妹), Wang Ru-Wu (汪汝武), Li Yun-Bao (李云宝) Chin. Phys. B, 2014, 23 (5):  057202.  DOI: 10.1088/1674-1056/23/5/057202 Abstract ( 666 )   PDF (378KB) ( 412 )   An oxide p-n heterojunction composed of Pr0.6Ca0.4MnO3 film, with a charge order (CO) transition, and 1wt% Nb-doped SrTiO3 substrate is fabricated, and the transport properties of the interface are experimentally studied. The rectifying behavior of the junction, well described by the Newman equation, is observed, indicating that tunneling is the dominant process by which the carriers pass through the interface. Above and below the CO transition temperature, satisfactory linear dependencies of junction resistance on temperature are observed, but the slopes of the two resistance-temperature relations are different. The CO process is believed to be relevant to this difference.

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Experimental and numerical analyses of high voltage 4H-SiC junction barrier Schottky rectifiers with linearly graded field limiting ring Wang Xiang-Dong (王向东), Deng Xiao-Chuan (邓小川), Wang Yong-Wei (王永维), Wang Yong (王勇), Wen Yi (文译), Zhang Bo (张波) Chin. Phys. B, 2014, 23 (5):  057203.  DOI: 10.1088/1674-1056/23/5/057203 Abstract ( 658 )   PDF (498KB) ( 559 )   This paper describes the successful fabrication of 4H-SiC junction barrier Schottky (JBS) rectifiers with a linearly graded field limiting ring (LG-FLR). Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2 (about 80% of the theoretical value). Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termination, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.

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High performance oscillator with 2-mW output power at 300 GHz Wu De-Qi (武德起), Ding Wu-Chang (丁武昌), Yang Shan-Shan (杨姗姗), Jia Rui (贾锐), Jin Zhi (金智), Liu Xin-Yu (刘新宇) Chin. Phys. B, 2014, 23 (5):  057204.  DOI: 10.1088/1674-1056/23/5/057204 Abstract ( 682 )   PDF (1002KB) ( 442 )   Material structures and device structures of a 100-GHz InP based transferred-electron device are designed in this paper. In order to successfully fabricate the Gunn devices operating at 100 GHz, the InP substrate was entirely removed by mechanical thinning and wet etching. The Gunn device was connected to a tripler link and a high RF (radio frequency) output with power of 2 mW working at 300 GHz was obtained, which is high enough for applications in current military electronic systems.

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Fabrication and electrochemical performance of graphene-ZnO nanocomposites Li Zhen-Peng (李振鹏), Men Chuan-Ling (门传玲), Wang Wan (王婉), Cao Jun (曹军) Chin. Phys. B, 2014, 23 (5):  057205.  DOI: 10.1088/1674-1056/23/5/057205 Abstract ( 562 )   PDF (1085KB) ( 481 )   Graphene-ZnO nanocomposites were synthesized successfully through a one-step solvothermal approach. The morphology, structure, and composition of the prepared nanocomposites were investigated by scanning electron microscopy (SEM), transmission electron microscope (TEM), laser micro Raman spectroscopy, and Fourier transform infra-red spectroscopy (FT-IR). The outcomes confirmed that this approach is comparatively steady, practicable, and operable compared with other reported methods. The electrochemical performance of the graphene-ZnO electrodes was analyzed through cyclic voltammetry, altering-current (AC) impedance, and chronopotentiometry tests. The graphene-ZnO electrodes exhibited an improved electrode performance with higher specific capacitance (115 F·g-1), higher electrochemical stability, and higher energy density than the graphene electrodes and most reported graphene-ZnO electrodes. Graphene-ZnO nanocomposites have a steady reversible charge/discharge behavior, which makes them promising candidates for electrochemical capacitors (ECs).

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Interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique Liao Xue-Yang (廖雪阳), Zhang Kai (张凯), Zeng Chang (曾畅), Zheng Xue-Feng (郑雪峰), En Yun-Fei (恩云飞), Lai Ping (来萍), Hao Yue (郝跃) Chin. Phys. B, 2014, 23 (5):  057301.  DOI: 10.1088/1674-1056/23/5/057301 Abstract ( 527 )   PDF (386KB) ( 897 )   Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) structures. Two types of device structures, namely, the recessed gate structure (RGS) and the normal gate structure (NGS), are studied in the experiment. Interface trap parameters including trap density Dit, trap time constant τit, and trap state energy ET in both devices have been determined. Furthermore, the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching (RIE).

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Phonon-dependent transport through a serially coupled double quantum dot system M. Bagheri Tagani, H. Rahimpour Soleimani Chin. Phys. B, 2014, 23 (5):  057302.  DOI: 10.1088/1674-1056/23/5/057302 Abstract ( 497 )   PDF (641KB) ( 472 )   Using Keldysh nonequilibrium Green function formalism and mapping a many-body electron-phonon interaction onto a one body problem, the electron transport through a serially coupled double quantum dot system is analyzed. The influence of the electron-phonon interaction, temperature, detuning, and interdot tunneling on the transmission coefficient and current is studied. Our results show that the electron-phonon interaction results in the appearance of the side peaks in the transmission coefficient, whose height is strongly dependent on the phonon temperature. We have also found that the inequality of the electron-phonon interaction strength in two dots gives rise to an asymmetry in the current-voltage characteristic. In addition, the temperature difference between the phonon and electron subsystems results in the reduction of the saturated current and the destruction of the step-like behavior of the current. It is also observed that the detuning can improve the magnitude of the current by compensating the mismatch of the quantum dots energy levels induced by the electron-phonon interaction.

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Effect of additional silicon on titanium/4H-SiC contacts properties Zhang Yong-Ping (张永平), Chen Zhi-Zhan (陈之战), Lu Wu-Yue (卢吴越), Tan Jia-Hui (谈嘉慧), Cheng Yue (程越), Shi Wang-Zhou (石旺舟) Chin. Phys. B, 2014, 23 (5):  057303.  DOI: 10.1088/1674-1056/23/5/057303 Abstract ( 509 )   PDF (1338KB) ( 389 )   The Ti electrode was deposited on the (0001 ) face of an n-type 4H-SiC substrate by magnetron sputtering. The effect of the electrode placement method during the annealing treatment on the contact property was carefully investigated. When the electrode was faced to the Si tray and annealed, it showed ohmic behavior, otherwise it showed a non-ohmic property. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to characterize the electrode phase, composition, thickness, and surface morphology. The additional silicon introduced from the Si tray played a key role in the formation of the ohmic contact on the Ti/4H-SiC contact.

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Flat-roof phenomenon of dynamic equilibrium phase in the negative bias temperature instability effect on a power MOSFET Zhang Yue (张月), Zhuo Qing-Qing (卓青青), Liu Hong-Xia (刘红侠), Ma Xiao-Hua (马晓华), Hao Yue (郝跃) Chin. Phys. B, 2014, 23 (5):  057304.  DOI: 10.1088/1674-1056/23/5/057304 Abstract ( 525 )   PDF (303KB) ( 387 )   The effect of the static negative bias temperature (NBT) stress on a p-channel power metal-oxide-semiconductor field-effect transistor (MOSFET) is investigated by experiment and simulation. The time evolution of the negative bias temperature instability (NBTI) degradation has the trend predicted by the reaction-diffusion (R-D) model but with an exaggerated time scale. The phenomena of the flat-roof section are observed under various stress conditions, which can be considered as the dynamic equilibrium phase in the R-D process. Based on the simulated results, the variation of the flat-roof section with the stress condition can be explained.

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Model of hot-carrier induced degradation in ultra-deep sub-micrometer nMOSFET Lei Xiao-Yi (雷晓艺), Liu Hong-Xia (刘红侠), Zhang Yue (张月), Ma Xiao-Hua (马晓华), Hao Yue (郝跃) Chin. Phys. B, 2014, 23 (5):  057305.  DOI: 10.1088/1674-1056/23/5/057305 Abstract ( 513 )   PDF (322KB) ( 597 )   The degradation produced by hot carrier (HC) in ultra-deep sub-micron n-channel metal oxide semiconductor field effect transistor (nMOSFET) has been analyzed in this paper. The generation of negatively charged interface states is the predominant mechanism for the ultra-deep sub-micron nMOSFET. According to our lifetime model of p-channel MOFET (pMOFET) that was reported in a previous publication, a lifetime prediction model for nMOSFET is presented and the parameters in the model are extracted. For the first time, the lifetime models of nMOFET and pMOSFET are unified. In addition, the model can precisely predict the lifetime of the ultra-deep sub-micron nMOSFET and pMOSFET.

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Parallel variable-density spiral imaging using nonlocal total variation reconstruction Fang Sheng (方晟), Guo Hua (郭华) Chin. Phys. B, 2014, 23 (5):  057401.  DOI: 10.1088/1674-1056/23/5/057401 Abstract ( 564 )   PDF (1530KB) ( 298 )   The relatively long scan time is still a bottleneck for both clinical applications and research of magnetic resonance imaging. To reduce the data acquisition time, we propose a novel fast magnetic resonance imaging method based on parallel variable-density spiral acquisition, which combines undersampling optimization and nonlocal total variation reconstruction. The undersampling optimization promotes the incoherence of resultant aliasing artifact via the “worst-case” residual error metric, and thus accelerates the data acquisition. Moreover, nonlocal total variation reconstruction is utilized to remove such an incoherent aliasing artifact and so improve image quality. The feasibility of the proposed method is demonstrated by both numerical phantom simulation and in vivo experiment. The experimental results show that the proposed method can achieve high acceleration factor and effectively remove an aliasing artifact from data undersampling with well-preserved image details. The image quality is better than that achieved with the total variation method.

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Josephson current versus potential strength of the interface in ferromagnetic superconductors Hamidreza Emamipour Chin. Phys. B, 2014, 23 (5):  057402.  DOI: 10.1088/1674-1056/23/5/057402 Abstract ( 604 )   PDF (220KB) ( 332 )   Based on the scattering theory, we calculate the Josephson current in a junction between two ferromagnetic superconductors as a function of the interface potential z. We consider the ferromagnetic superconductor (FS) in three different Cooper pairing states: spin singlet s-wave pairing (SWP) state, spin triplet opposite spin pairing (OSP) state, and spin triplet equal spin pairing (ESP) state. We find that the critical Josephson current as a function of z shows clear differences among the SWP, OSP, and ESP states. The obtained results can be used as a useful tool for determining the pair symmetry of the ferromagnetic superconductors.

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Magnetic property improvement of niobium doped with rare earth elements Jiang Tao (江涛), He Fei-Si (贺斐思), Jiao Fei (焦飞), He Fa (何法), Lu Xiang-Yang (鲁向阳), Zhao Kui (赵夔), Zhao Hong-Yun (赵红运), You Yu-Song (游雨松), Chen Lin (陈林) Chin. Phys. B, 2014, 23 (5):  057403.  DOI: 10.1088/1674-1056/23/5/057403 Abstract ( 754 )   PDF (480KB) ( 383 )   A new idea is proposed by the PKU group to improve the magnetic properties of the Type-Ⅱ superconductor niobium. Rare earth elements like scandium and yttrium are doped into ingot niobium during the smelting processes. A series of experiments have been done since 2010. The preliminary testing results show that the magnetic properties of niobium materials have changed with different doping elements and proportions while the superconductive transition temperature does not change very much. This method may increase the superheating magnetic field of niobium so as to improve the performance of the niobium cavity, which is a key component of SRF accelerators. A Tesla-type single-cell cavity made of scandium-doped niobium is being fabricated.

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Monte Carlo study of the magnetic properties of spin liquid compound NiGa2S4 Zhang Kai-Cheng (张开成), Li Yong-Feng (李永峰), Liu Yong (刘永), Chi Feng (迟锋) Chin. Phys. B, 2014, 23 (5):  057501.  DOI: 10.1088/1674-1056/23/5/057501 Abstract ( 774 )   PDF (590KB) ( 354 )   The magnetic properties of two-dimensional antiferromagnet NiGa2S4 have attracted much attention and yet some problems are far from being solved. We investigate the magnetic properties of NiGa2S4 by Monte Carlo simulations. A new spin-interacting model is proposed to describe the system, and the specific heat together with the doping effect of nonmagnetic impurity is studied by simulations. The double peaks of the specific heat as well as other behaviors are well reproduced. We also compare our results with those of other models, and the underlying physics is discussed.

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Dielectric behavior of Cu-Zn ferrites with Si additive Uzma G Chin. Phys. B, 2014, 23 (5):  057502.  DOI: 10.1088/1674-1056/23/5/057502 Abstract ( 417 )   PDF (407KB) ( 338 )   Since ferrites are highly sensitive to the additives present in or added to them, extensive work, to improve the properties of basic ferrites, has been carried out on these aspects. The present paper reports the effects of composition, frequency, and temperature on the dielectric behavior of a series of CuxZn1-xFe2O4 ferrite samples prepared by the usual ceramic technique. In order to improve the properties of the samples, low cost Fe2O3 having 0.5 wt.% Si as an additive is selected to introduce into the system. The dielectric constant increases by increasing the Cu content, as the electron exchange of Cu2+<=>Cu+ is responsible for the conduction and the polarization. However, the addition of Si could decrease the dielectric constant as it suppresses the ceramic grain growth and promotes the quality factor at higher frequencies. Dielectric constant ε' and loss tangent tanδ of the mixed Cu-Zn ferrite decrease with increasing frequency, attributed to the Maxwell-Wagner polarization, which increases as the temperature increases.

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High sum-frequency generation in dielectric/antiferromagnet/Ag sandwich structures Fu Shu-Fang (付淑芳), Liang Hong (梁红), Zhou Sheng (周胜), Wang Xuan-Zhang (王选章) Chin. Phys. B, 2014, 23 (5):  057503.  DOI: 10.1088/1674-1056/23/5/057503 Abstract ( 643 )   PDF (1840KB) ( 603 )   We present a method to increase the sum-frequency (SF) outputs in dielectric/antiferromagnet(AF)/Ag sandwich structures for a fixed input power. Two incident waves simultaneously illuminate the upper surface, one is oblique and the other is normal to it. Numerical calculations based on the SiO2/MnF2/Ag and ZnF2/MnF2/Ag structures show that the SF outputs on the upper film increase a few times as compared to those of a single AF film when the thickness of the AF film is one-quarter of the vacuum wavelength. Moreover, the SF outputs generated near the higher resonant frequency will be higher than those obtained near the lower resonant frequency. An optimum AF film thickness is achieved through investigating its effect on the SF outputs in the two different dielectric sandwich structures.

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A new aluminum iron oxide Schottky photodiode designed via sol-gel coating method A. Tataroğlu, A. A. Hendi, R. H. Alorainy, F. Yakuphanoğlu Chin. Phys. B, 2014, 23 (5):  057504.  DOI: 10.1088/1674-1056/23/5/057504 Abstract ( 648 )   PDF (719KB) ( 725 )   A novel aluminum iron oxide (Al/AlFe2O4/p-Si) Schottky photodiode was successfully fabricated via the sol-gel coating process. The microstructure of the spinel ferrite (AlFe2O4) was examined by atomic force microscopy. The current-voltage characteristics of the fabricated photodiode were studied under dark and different illumination conditions at room temperature. By using the thermionic emission theory, the forward bias I-V characteristics of the photodiode are analyzed to determine the main electrical parameters such as the ideality factor (n) and barrier height (ΦB0) of the photodiode. The values of n and ΦB0 for all conditions are found to be about 7.00 and 0.76 eV, respectively. In addition, the values of series resistance (Rs) are determined using Cheung's method and Ohm's law. The values of Rs and shunt resistance (Rsh) are decreased with the increase of illumination intensity. These new spinel ferrites will open a new avenue to other spinel structure materials for optoelectronic devices in the near future.

TOPICAL REVIEW—Magnetism, magnetic materials, and interdisciplinary research

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Nanomagnetism：Principles, nanostructures, and biomedical applications Yang Ce (杨策), Hou Yang-Long (侯仰龙), Gao Song (高松) Chin. Phys. B, 2014, 23 (5):  057505.  DOI: 10.1088/1674-1056/23/5/057505 Abstract ( 642 )   PDF (1433KB) ( 1751 )   Nanomagnetism is the origin of many unique properties in magnetic nanomaterials that can be used as building blocks in information technology, spintronics, and biomedicine. Progresses in nanomagnetic principles, distinct magnetic nanostructures, and the biomedical applications of nanomagnetism are summarized.

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

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Photoluminescence properties and energy transfer in Y2O3：Eu3+ nanophosphors Cui Hang (崔航), Zhu Pei-Fen (朱培芬), Zhu Hong-Yang (祝洪洋), Li Hong-Dong (李红东), Cui Qi-Liang (崔啟良) Chin. Phys. B, 2014, 23 (5):  057801.  DOI: 10.1088/1674-1056/23/5/057801 Abstract ( 839 )   PDF (2800KB) ( 976 )   The photoluminescence (PL) properties of Y2O3:Eu3+ nanophosphors were systematically investigated with the goal of improving the color quality and quantum efficiency of Y2O3:Eu3+ nanophosphors for potential applications in nano-scale devices. The emission spectra, excitation spectra and fluorescence decay curves were employed to trace the energy transfer process from Eu3+ at C3i site to Eu3+ at C2 site. The experimental results show that the energy transfer process becomes more and more efficient with the increase in the Eu3+ concentration. The emission of Eu3+ at C2 site is favorable as it has high radiative efficiency and better color quality. The successful suppress of the emission Eu3+ at C3i is especially important for its applications in general illumination or display technology. The quantum efficiency and color quality of Y2O3:Eu3+ can be improved by controlling the energy transfer between the Eu3+ at S6 site and Eu3+ at C2 site.

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Up-conversion luminescence properties and energy transfer of Er3+/Yb3+ co-doped oxyfluoride glass ceramic containing CaF2 nano-crystals Ma Chen-Shuo (马辰硕), Jiao Qing (焦清), Li Long-Ji (李龙基), Zhou Da-Cheng (周大成), Yang Zheng-Wen (杨正文), Song Zhi-Guo (宋志国), Qiu Jian-Bei (邱建备) Chin. Phys. B, 2014, 23 (5):  057802.  DOI: 10.1088/1674-1056/23/5/057802 Abstract ( 596 )   PDF (1277KB) ( 556 )   The Er3+/Yb3+ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy (TEM) images showed that CaF2 nano-crystals of 20-30 nm in diameter precipitated uniformly in the glass matrix. Comparing with the host glass, high efficiency upconversion luminescence of Er3+ at 540 nm and 658 nm was observed in the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er3+ and Yb3+ was convinced and the possible mechanism of Er3+ up-conversion was discussed.

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Effects of thermal annealing on the properties of N-implanted ZnS films Xue Shu-Wen (薛书文), Zhang Jun (张军), Quan Jun (全军) Chin. Phys. B, 2014, 23 (5):  057803.  DOI: 10.1088/1674-1056/23/5/057803 Abstract ( 519 )   PDF (286KB) ( 398 )   N-ion-implantation to a fluence of 1× 1015 ions/cm2 was performed on ZnS thin films deposited on glass substrates by using the vacuum evaporation method. The films were annealed in flowing nitrogen at 400 ℃-500 ℃ after N-ion-implantation to repair the ion-beam-induced structural destruction and electrically activate the dopants. Effects of ion-implantation and post-thermal annealing on ZnS films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance, and electrical measurements. Results showed that the diffraction peaks and PL intensities were decreased by N-ion-implantation, but fully recovered by further annealing at 500 ℃. In this experiment, all films exhibited high resistivity due to the partial dopant activation under 500 ℃.

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Effects of oblique incidence on terahertz responses of planar split-ring resonators Pan Xue-Cong (潘学聪), Xia Xiao-Xiang (夏晓翔), Wang Li (汪力) Chin. Phys. B, 2014, 23 (5):  057804.  DOI: 10.1088/1674-1056/23/5/057804 Abstract ( 538 )   PDF (476KB) ( 567 )   Effects of oblique incidence of terahertz waves on the response of planar split-ring resonators are investigated, both experimentally and by simulation. It is found that the incident angle dependent phase delay and coupling conditions of neighboring split-ring resonator (SRR) units play important roles and greatly change both the transmission and reflection spectra for the resonant feature of linear charge oscillations. Our results show that the SRR structure-supported magnetoelectric couplings at oblique excitation are trivial and can be ignored. A highly symmetric response is found in the cross-polarization effects, which may manifest the bianisotropic properties of the SRR system but this needs further study.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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GaN hexagonal pyramids formed by a photo-assisted chemical etching method Zhang Shi-Ying (张士英), Xiu Xiang-Qian (修向前), Hua Xue-Mei (华雪梅), Xie Zi-Li (谢自力), Liu Bin (刘斌), Chen Peng (陈鹏), Han Ping (韩平), Lu Hai (陆海), Zhang Rong (张荣), Zheng You-Dou (郑有炓) Chin. Phys. B, 2014, 23 (5):  058101.  DOI: 10.1088/1674-1056/23/5/058101 Abstract ( 569 )   PDF (794KB) ( 466 )   A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a convenient photo-assisted chemical (PAC) etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed analysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.

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Dual-band and polarization-insensitive terahertz absorber based on fractal Koch curves Ma Yan-Bing (马岩冰), Zhang Huai-Wu (张怀武), Li Yuan-Xun (李元勋), Wang Yi-Cheng (王艺程), Lai Wei-En (赖伟恩), Li Jie (李颉) Chin. Phys. B, 2014, 23 (5):  058102.  DOI: 10.1088/1674-1056/23/5/058102 Abstract ( 632 )   PDF (1406KB) ( 592 )   We report the design, fabrication, and characterization of a dual-band and polarization-insensitive metamaterial absorber (MA), which consists of periodically arranged fractal Koch curves acting as the top resonator array and a metallic ground plane separated by a dielectric spacer. Compared with conventional MAs, a more compact size and multi-frequency operation are achieved by using fractal geometry as the unit cell of the MA. Both the effective medium theory and the multi-reflection interference theory are employed to investigate the underlying physical mechanism of the proposed terahertz MA, and results indicate that the latter theory is not suitable for explaining the absorption mechanism in our investigated structure. Two absorption peaks are observed at 0.226 THz and 0.622 THz with absorptivities of 91.3% and 95.6% respectively and good agreements between the full-wave simulation and experimental results are achieved.

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Synthesis and room-temperature NO2 gas sensing properties of a WO3 nanowires/porous silicon hybrid structure Zeng Peng (曾鹏), Zhang Ping (张平), Hu Ming (胡明), Ma Shuang-Yun (马双云), Yan Wen-Jun (闫文君) Chin. Phys. B, 2014, 23 (5):  058103.  DOI: 10.1088/1674-1056/23/5/058103 Abstract ( 517 )   PDF (2449KB) ( 618 )   We report on the fabrication and performance of a room-temperature NO2 gas sensor based on a WO3 nanowires/porous silicon hybrid structure. The W18O49 nanowires are synthesized directly from a sputtered tungsten film on a porous silicon (PS) layer under heating in an argon atmosphere. After a carefully controlled annealing treatment, WO3 nanowires are obtained on the PS layer without losing the morphology. The morphology, phase structure, and crystallinity of the nanowires are investigated by using field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), and high-resolution transmission electron microscopy (HRTEM). Comparative gas sensing results indicate that the sensor based on the WO3 nanowires exhibits a much higher sensitivity than that based on the PS and pure WO3 nanowires in detecting NO2 gas at room temperature. The mechanism of the WO3 nanowires/PS hybrid structure in the NO2 sensing is explained in detail.

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Structural and photoluminescence properties of terbium-doped zinc oxide nanoparticles Ningthoujam Surajkumar Singh, Shougaijam Dorendrajit Singh, Sanoujam Dhiren Meetei Chin. Phys. B, 2014, 23 (5):  058104.  DOI: 10.1088/1674-1056/23/5/058104 Abstract ( 786 )   PDF (949KB) ( 813 )   We present in this paper a study of the structural and photoluminescence (PL) properties of terbium (Tb) doped zinc oxide (ZnO) nanoparticles synthesized by a simple low temperature chemical precipitation method, using zinc acetate and terbium nitrate in an isopropanol medium with diethanolamine (DEA) as the capping agent at 60 ℃. The as-prepared samples were heat treated and the PL of the annealed samples were studied. The prepared nanoparticles were characterized with X-ray diffraction (XRD). The XRD patterns show the pattern of typical ZnO nanoparticles and correspond with the standard XRD pattern given by JCPDS card No. 36-1451, showing the hexagonal phase structure. The PL intensity was enhanced due to Tb3+ doping, and it decreased at higher concentrations of Tb3+ doping after reaching a certain optimum concentration. The PL spectra of Tb3+ doped samples exhibited blue, bluish green, and green emissions at 460 nm (5D3 - 7F3), 484 nm (5D4 - 7F6), and 530 nm (5D4 - 7F5), respectively, which were more intense than the emissions for the undoped ZnO sample. Based on the results, an energy level schematic diagram was proposed to explain the possible electron transition processes.

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Structural and electrical characterization of annealed Si1-xCx/SiC thin film prepared by magnetron sputtering Huang Shi-Hua (黄仕华), Liu Jian (刘剑) Chin. Phys. B, 2014, 23 (5):  058105.  DOI: 10.1088/1674-1056/23/5/058105 Abstract ( 596 )   PDF (341KB) ( 385 )   Si-rich Si1-xCx/SiC multilayer thin films are prepared using magnetron sputtering, subsequently followed by thermal annealing in the range of 800-1200 ℃. The influences of annealing temperature (Ta) on the formation of Si and/or SiC nanocrystals (NCs) and on the electrical characteristics of the multilayer film are investigated by using a variety of analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectrometry (FT-IR), current-voltage (I-V) technique, and capacitance-voltage (C-V) technique. XRD and Raman analyses indicate that Si NCs begin to form in samples for Ta ≥ 800 ℃. At annealing temperatures of 1000 ℃ or higher, the formation of Si NCs is accompanied by the formation of SiC NCs. With the increase in the annealing temperature, the shift of FT-IR Si-C bond absorption spectra toward a higher wave number along with the change of band shape can be explained by a Si-C transitional phase between the loss of substitutional carbon and the formation of SiC precipitates and a precursor for the growth of SiC crystalline. The C-V and I-V results indicate that the interface quality of Si1-xCx/SiC multilayer film is improved significantly and the leakage current is reduced rapidly for Ta ≥ 1000 ℃, which can be ascribed to the formation of Si and SiC NCs.

TOPICAL REVIEW—Magnetism, magnetic materials, and interdisciplinary research

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Progress in organic spintronics Yang Fu-Jiang (杨福江), Han Shi-Xuan (韩士轩), Xie Shi-Jie (解士杰) Chin. Phys. B, 2014, 23 (5):  058106.  DOI: 10.1088/1674-1056/23/5/058106 Abstract ( 425 )   PDF (1291KB) ( 896 )   Recent progress in organic spintronics is given an informative overview, covering spin injection, detection, and transport in organic spin valve devices, and the magnetic field effect in organic semiconductors (OSCs). In particular, we focus on our own recent work in spin injection and the organic magnetic field effect (OMFE).

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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A voltage-controlled chaotic oscillator based on carbon nanotube field-effect transistor for low-power embedded systems Van Ha Nguyen, Wonkyeong Park, Namtae Kim, Hanjung Song Chin. Phys. B, 2014, 23 (5):  058201.  DOI: 10.1088/1674-1056/23/5/058201 Abstract ( 722 )   PDF (1121KB) ( 596 )   This paper presents a compact and low-power-based discrete-time chaotic oscillator based on a carbon nanotube field-effect transistor implemented using Wong and Deng's well-known model. The chaotic circuit is composed of a nonlinear circuit that creates an adjustable chaos map, two sample and hold cells for capture and delay functions, and a voltage shifter that works as a buffer and adjusts the output voltage for feedback. The operation of the chaotic circuit is verified with the SPICE software package, which uses a supply voltage of 0.9 V at a frequency of 20 kHz. The time series, frequency spectra, transitions in phase space, sensitivity with the initial condition diagrams, and bifurcation phenomena are presented. The main advantage of this circuit is that its chaotic signal can be generated while dissipating approximately 7.8u W of power, making it suitable for embedded systems where many chaos-signal generators are required on a single chip.

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Multi-polar resistance switching and memory effect in copper phthalocyanine junctions Qiao Shi-Zhu (乔士柱), Kang Shi-Shou (康仕寿), Qin Yu-Feng (秦羽丰), Li Qiang (李强), Zhong Hai (钟海), Kang Yun (康韵), Yu Shu-Yun (于淑云), Han Guang-Bing (韩广兵), Yan Shi-Shen (颜世申), Mei Liang-Mo (梅良模) Chin. Phys. B, 2014, 23 (5):  058501.  DOI: 10.1088/1674-1056/23/5/058501 Abstract ( 567 )   PDF (1657KB) ( 531 )   Copper phthalocyanine junctions, fabricated by magnetron sputtering and evaporating methods, show multi-polar (unipolar and bipolar) resistance switching and the memory effect. The multi-polar resistance switching has not been observed simultaneously in one organic material before. With both electrodes being cobalt, the unipolar resistance switching is universal. The high resistance state is switched to the low resistance state when the bias reaches the set voltage. Generally, the set voltage increases with the thickness of copper phthalocyanine and decreases with increasing dwell time of bias. Moreover, the low resistance state could be switched to the high resistance state by absorbing the phonon energy. The stability of the low resistance state could be tuned by different electrodes. In Au/copper phthalocyanine/Co system, the low resistance state is far more stable, and the bipolar resistance switching is found. Temperature dependence of electrical transport measurements demonstrates that there are no obvious differences in the electrical transport mechanism before and after the resistance switching. They fit quite well with Mott variable range hopping theory. The effect of Al2O3 on the resistance switching is excluded by control experiments. The holes trapping and detrapping in copper phthalocyanine layer are responsible for the resistance switching, and the interfacial effect between electrodes and copper phthalocyanine layer affects the memory effect.

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Enhanced performance of GaN-based light-emitting diodes with InGaN/GaN superlattice barriers Cai Jin-Xin (蔡金鑫), Sun Hui-Qing (孙慧卿), Zheng Huan (郑欢), Zhang Pan-Jun (张盼君), Guo Zhi-You (郭志友) Chin. Phys. B, 2014, 23 (5):  058502.  DOI: 10.1088/1674-1056/23/5/058502 Abstract ( 523 )   PDF (433KB) ( 478 )   GaN-based multiple quantum well light-emitting diodes (LEDs) with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers can effectively enhance performances of the GaN-Based LEDs, mainly owing to the improvement of hole injection and transport among the MQW active region. Meanwhile, the improved electron capture decreases the electron leakage and alleviates the efficiency droop. The weak polarization field induced by the superlattice structure strengthens the intensity of the emission spectrum and leads to a blue-shift relative to the conventional one.

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High-power terahertz pulse sensor with overmoded structure Wang Xue-Feng (王雪锋), Wang Jian-Guo (王建国), Wang Guang-Qiang (王光强), Li Shuang (李爽), Xiong Zheng-Feng (熊正锋) Chin. Phys. B, 2014, 23 (5):  058701.  DOI: 10.1088/1674-1056/23/5/058701 Abstract ( 607 )   PDF (478KB) ( 401 )   Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investigated. The distribution of electromagnetic field components, voltage standing wave ratio (VSWR), and the average electric field in the silicon block are obtained by using the three-dimensional finite-difference time-domain (FDTD) method. By adjusting several factors (such as the length, width, height and specific resistance of the silicon block) a novel sensor with optimal structural parameters that can be used as a power measurement device for high power terahertz pulse directly is proposed. The results show that the sensor has a relative sensitivity of about 0.24 kW-1, with a fluctuation of relative sensitivity of no more than ± 22%, and the maximum of VSWR is 2.74 for 0.3-0.4 THz band.

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A conditioned level-set method with block-division strategy to flame front extraction based on OH-PLIF measurements Han Yue (韩乐), Cai Guo-Biao (蔡国飙), Xu Xu (徐旭), Renou Bruno, Boukhalfa Abdelkrim Chin. Phys. B, 2014, 23 (5):  058901.  DOI: 10.1088/1674-1056/23/5/058901 Abstract ( 634 )   PDF (1948KB) ( 377 )   A novel approach to extract flame fronts, which is called the conditioned level-set method with block division (CLSB), has been developed. Based on a two-phase level-set formulation, the conditioned initialization and region-lock optimization appear to be beneficial to improve the efficiency and accuracy of the flame contour identification. The original block-division strategy enables the approach to be unsupervised by calculating local self-adaptive threshold values autonomously before binarization. The CLSB approach has been applied to deal with a large set of experimental data involving swirl-stabilized premixed combustion in diluted regimes operating at atmospheric pressures. The OH-PLIF measurements have been carried out in this framework. The resulting images are, thus, featured by lower signal-to-noise ratios (SNRs) than the ideal image; relatively complex flame structures lead to significant non-uniformity in the OH signal intensity; and, the magnitude of the maximum OH gradient observed along the flame front can also vary depending on flow or local stoichiometry. Compared with other conventional edge detection operators, the CLSB method demonstrates a good ability to deal with the OH-PLIF images at low SNR and with the presence of a multiple scales of both OH intensity and OH gradient. The robustness to noise sensitivity and intensity inhomogeneity has been evaluated throughout a range of experimental images of diluted flames, as well as against a circle test as Ground Truth (GT).

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Biham-Middleton-Levine model in consideration of cooperative willingness Pan Wei (盘薇), Xue Yu (薛郁), Zhao Rui (赵瑞), Lu Wei-Zhen (卢伟真) Chin. Phys. B, 2014, 23 (5):  058902.  DOI: 10.1088/1674-1056/23/5/058902 Abstract ( 686 )   PDF (3854KB) ( 456 )   In this paper, the Biham-Middleton-Levine (BML) model with consideration of cooperative willingness has been proposed to study the traffic flow in urban networks. An evolutionary game with a cooperative willingness profile is introduced to deal with conflicts between disturbing neighbors. Simulation results suggest that imitating cooperative willingness can ease the effect of premature seizure on traffic flow due to the introduction of evolutionary games. Phase diagrams with a strategy profile and cooperative willingness profile have been investigated in detail. Our findings also prove that by imitating the more successful, cooperative willingness instead of simply the more successful strategies, the evolution of cooperation is significantly promoted, hence improving the order of cooperation and relieving the pressure of traffic networks.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Improved method for analyzing quasi-optical launchers Wu Ze-Wei (吴泽威), Li Hao (李浩), Xu Jian-Hua (徐建华), Li Tian-Ming (李天明), Li Jia-Yin (李家胤) Chin. Phys. B, 2014, 23 (5):  059201.  DOI: 10.1088/1674-1056/23/5/059201 Abstract ( 555 )   PDF (1799KB) ( 489 )   An improved method for analyzing the radiation characteristic of the quasi-optical launcher is presented. The launcher is decomposed into an open-ended waveguide and a helical cut according to the proposed method. The radiation from the open-ended waveguide is obtained by using the Stratton-Chu formulation. The helical cut's radiation is calculated based on its current distribution, gained by several iterative computations, which helps to improve the calculation accuracy since the diffraction effect introduced by the helical cut is considered during the calculation. The proposed method is used to study different launches, and the results are compared with the existing results. Good agreement is achieved between the results obtained from our proposed method and the reported results. The present results provide an alternative for analysis and synthesis of the optical-mode converter.

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Predicting extreme rainfall over eastern Asia by using complex networks He Su-Hong (何苏红), Feng Tai-Chen (封泰晨), Gong Yan-Chun (龚艳春), Huang Yan-Hua (黄雁华), Wu Cheng-Guo (吴成国), Gong Zhi-Qiang (龚志强) Chin. Phys. B, 2014, 23 (5):  059202.  DOI: 10.1088/1674-1056/23/5/059202 Abstract ( 540 )   PDF (410KB) ( 391 )   A climate network of extreme rainfall over eastern Asia is constructed for the period of 1971-2000, employing the tools of complex networks and a measure of nonlinear correlation called event synchronization (ES). Using this network, we predict the extreme rainfall for several cases without delay and with n-day delay (1 ≤ n ≤ 10). The prediction accuracy can reach 58% without delay, 21% with 1-day delay, and 12% with n-day delay (2 ≤ n ≤ 10). The results reveal that the prediction accuracy is low in years of a weak east Asia summer monsoon (EASM) or 1 year later and high in years of a strong EASM or 1 year later. Furthermore, the prediction accuracy is higher due to the many more links that represent correlations between different grid points and a higher extreme rainfall rate during strong EASM years.