中国物理B

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Applications of the first integral method to nonlinear evolution equations

Filiz Ta, scan, Ahmet Bekir

2010 (8): 80201-080201. doi: 10.1088/1674-1056/19/8/080201

摘要 ( 1945 )

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In this paper, we establish travelling wave solutions for some nonlinear evolution equations. The first integral method is used to construct the travelling wave solutions of the modified Benjamin-Bona{Mahony and the coupled Klein-Gordon equations. The obtained results include periodic and solitary wave solutions. The rst integral method presents a wider applicability to handling nonlinear wave equations.

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Approximate homotopy similarity reduction for the generalized Kawahara equation via Lie symmetry method and direct method

刘希忠

2010 (8): 80202-080202. doi: 10.1088/1674-1056/19/8/080202

摘要 ( 1718 )

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This paper studies the generalized Kawahara equation in terms of the approximate homotopy symmetry method and the approximate homotopy direct method. Using both methods it obtains the similarity reduction solutions and similarity reduction equations of different orders, showing that the approximate homotopy direct method yields more general approximate similarity reductions than the approximate homotopy symmetry method. The homotopy series solutions to the generalized Kawahara equation are consequently derived.

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Symmetry analysis and explicit solutions of the (3+1)-dimensional baroclinic potential vorticity equation

胡晓瑞, 陈勇, 黄菲

2010 (8): 80203-080203. doi: 10.1088/1674-1056/19/8/080203

摘要 ( 1789 )

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This paper investigates an important high-dimensional model in the atmospheric and oceanic dynamics-(3+1)-dimensional nonlinear baroclinic potential vorticity equation by the classical Lie group method. Its symmetry algebra, symmetry group and group-invariant solutions are analysed. Otherwise, some exact explicit solutions are obtained from the corresponding (2+1)-dimensional equation, the inviscid barotropic nondivergent vorticy equation. To show the properties and characters of these solutions, some plots as well as their possible physical meanings of the atmospheric circulation are given.

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Approximate analytic solutions for a generalized Hirota–Satsuma coupled KdV equation and a coupled mKdV equation

赵国忠, 蔚喜军, 徐云, 朱江, 吴迪

2010 (8): 80204-080204. doi: 10.1088/1674-1056/19/8/080204

摘要 ( 1684 )

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This paper applies the variational iteration method to obtain approximate analytic solutions of a generalized Hirota–Satsuma coupled Korteweg-de Vries (KdV) equation and a coupled modified Korteweg-de Vries (mKdV) equation. This method provides a sequence of functions which converges to the exact solution of the problem and is based on the use of the Lagrange multiplier for the identification of optimal values of parameters in a functional. Some examples are given to demonstrate the reliability and convenience of the method and comparisons are made with the exact solutions.

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Long-range correlation analysis of urban traffic data

盛鹏, 王俊峰, 唐铁桥, 赵树龙

2010 (8): 80205-080205. doi: 10.1088/1674-1056/19/8/080205

摘要 ( 1894 )

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This paper investigates urban traffic data by analysing the long-range correlation with detrended fluctuation analysis. Through a large number of real data collected by the travel time detection system in Beijing, the variation of flow in different time periods and intersections is studied. According to the long-range correlation in different time scales, it mainly discusses the effect of intersection location in road net, people activity customs and special traffic controls on urban traffic flow. As demonstrated by the obtained results, the urban traffic flow represents three-phase characters similar to highway traffic. Moreover, compared by the two groups of data obtained before and after the special traffic restrictions (vehicles with special numbered plates only run in a special workday) enforcement, it indicates that the rules not only reduce the flow but also avoid irregular fluctuation.

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Model for cascading failures with adaptive defense in complex networks

胡柯, 胡涛, 唐翌

2010 (8): 80206-080206. doi: 10.1088/1674-1056/19/8/080206

摘要 ( 1699 )

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This paper investigates cascading failures in networks by considering interplay between the flow dynamic and the network topology, where the fluxes exchanged between a pair of nodes can be adaptively adjusted depending on the changes of the shortest path lengths between them. The simulations on both an artificially created scale-free network and the real network structure of the power grid reveal that the adaptive adjustment of the fluxes can drastically enhance the robustness of complex networks against cascading failures. Particularly, there exists an optimal region where the propagation of the cascade is significantly suppressed and the fluxes supported by the network are maximal. With this understanding, a costless strategy of defense for preventing cascade breakdown is proposed. It is shown to be more effective for suppressing the propagation of the cascade than the recent proposed strategy of defense based on the intentional removal of nodes.

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Enhancing synchronizability by rewiring networks

王立夫, 王庆利, 孔芝, 井元伟

2010 (8): 80207-080207. doi: 10.1088/1674-1056/19/8/080207

摘要 ( 1801 )

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According to different forms of synchronized region, complex networks are divided into type I (unbounded synchronization region) and type II (bounded synchronization region) networks. This paper presents a rewiring algorithm to enhance the synchronizability of type I and type II networks. By utilizing the algorithm for an unweighted and undirected network, a better synchronizability of network with the same number of nodes and edges can be obtained. Numerical simulations on several different network models are used to support the proposed procedure. The relationship between different topological properties of the networks and the number of rewirings are shown. It finds that the final optimized network is independent of the initial network, and becomes homogeneous. In addition the optimized networks have similar structural properties in the sense of degree, and node and edge betweenness centralities. However, they do not have similar cluster coefficients for type II networks. The research may be useful for designing more synchronizable networks and understanding the synchronization behaviour of networks.

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Poisson theory and integration method of Birkhoffian systems in the event space

张毅

2010 (8): 80301-080301. doi: 10.1088/1674-1056/19/8/080301

摘要 ( 1664 )

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This paper focuses on studying the Poisson theory and the integration method of a Birkhoffian system in the event space. The Birkhoff's equations in the event space are given. The Poisson theory of the Birkhoffian system in the event space is established. The definition of the Jacobi last multiplier of the system is given, and the relation between the Jacobi last multiplier and the first integrals of the system is discussed. The researches show that for a Birkhoffian system in the event space, whose configuration is determined by (2n+1) Birkhoff's variables, the solution of the system can be found by the Jacobi last multiplier if 2n first integrals are known. An example is given to illustrate the application of the results.

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Stability for manifolds of equilibrium states of generalized Birkhoff system

李彦敏, 梅凤翔

2010 (8): 80302-080302. doi: 10.1088/1674-1056/19/8/080302

摘要 ( 1664 )

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Stability for the manifolds of equilibrium states of a generalized Birkhoff system is studied. A theorem for the stability of the manifolds of equilibrium states of the general autonomous system is used to the generalized Birkhoffian system and two propositions on the stability of the manifolds of equilibrium states of the system are obtained. An example is given to illustrate the application of the results.

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New application to Riccati equation

套格图桑, 斯仁道尔吉, 李姝敏

2010 (8): 80303-080303. doi: 10.1088/1674-1056/19/8/080303

摘要 ( 1899 )

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To seek new infinite sequence of exact solutions to nonlinear evolution equations, this paper gives the formula of nonlinear superposition of the solutions and Bäcklund transformation of Riccati equation. Based on the tanh-function expansion method and homogenous balance method, new infinite sequence of exact solutions to Zakharov–Kuznetsov equation, Karamoto–Sivashinsky equation and the set of (2+1)-dimensional asymmetric Nizhnik–Novikov–Veselov equations are obtained with the aid of symbolic computation system Mathematica. The method is of significance to construct infinite sequence exact solutions to other nonlinear evolution equations.

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Interactions between defects and propagating hydrodynamic solitons

潘军廷, 陈伟中, 郑鹭杰

2010 (8): 80304-080304. doi: 10.1088/1674-1056/19/8/080304

摘要 ( 1557 )

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This paper studies the hydrodynamic solitons propagating along a long trough with a defective bed. The slight deviation from the plane in the bed serves as the depth defects. Based on the perturbation method, it finds that the free surface wave is governed by a Korteweg-de Vries (KdV) equation with a defect term (KdVD). The numerical calculations show that, for a single-convexity localized defect, the propagating soliton is decelerated as it comes into the defect region, and it is accelerated back to its initial velocity as it leaves, which has a dipole effect. As a result, its displacement is lagged in contrast to the uninfluenced one. And an up-step defect makes the propagating soliton decelerate simply. The opposite influence will occur for a single-concavity localized defect and a down-step one. The defect-induced influence on propagating hydrodynamic solitons depends on the polarity of defects, which agrees with that on non-propagating ones. However, the involved dipole effect of the single localized defect is not displayed in non-propagating cases.

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Unconventional geometric logic gate in a strong-driving-assisted multi-mode cavity

潘长宁, 杨迪武, 赵学辉, 方卯发

2010 (8): 80305-080305. doi: 10.1088/1674-1056/19/8/080305

摘要 ( 1567 )

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We propose a scheme to implement an unconventional geometric logic gate separately in a two-mode cavity and a multi-mode cavity assisted by a strong classical driving field. The effect of the cavity decay is included in the investigation. The numerical calculation is carried out, and the result shows that our scheme is more tolerant to cavity decay than the previous one because the time consumed for finishing the logic gate is doubly reduced.

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Knotted picture of the whole complete quantum measurement process of quantum teleportation

顾之雨, 钱尚武

2010 (8): 80306-080306. doi: 10.1088/1674-1056/19/8/080306

摘要 ( 1648 )

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Based on the previous work about the knotted pictures of quantum states, quantum logic gates and unitary transformations, this paper further gives the whole complete quantum measurement process of quantum teleportation from the viewpoint of knot theory.

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Jointly-check iterative decoding algorithm for quantum sparse graph codes

邵军虎, 白宝明, 林伟, 周林

2010 (8): 80307-080307. doi: 10.1088/1674-1056/19/8/080307

摘要 ( 1486 )

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For quantum sparse graph codes with stabilizer formalism, the unavoidable girth-four cycles in their Tanner graphs greatly degrade the iterative decoding performance with a standard belief-propagation (BP) algorithm. In this paper, we present a jointly-check iterative algorithm suitable for decoding quantum sparse graph codes efficiently. Numerical simulations show that this modified method outperforms the standard BP algorithm with an obvious performance improvement.

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Internal cancellation of spikes using two avalanche photodiodes in series for single photon detection

刘云, 吴青林, 韩正甫, 戴逸民, 郭光灿

2010 (8): 80308-080308. doi: 10.1088/1674-1056/19/8/080308

摘要 ( 1621 )

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We propose a method of improving the performance of InGaAs/InP avalanche photodiodes by using two avalanche photodiodes in series as single photon detectors for 1550-nm wavelength. In this method, the raw single photon avalanche signals are not attenuated, thus a high signal-to-noise ratio can be obtained compared with the existing results. The performance of the scheme is investigated and the ratio of the dark count rate to the detection efficiency is obtained to be 1.3×10^-4 at 213 K.

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Scheme to implement optimal asymmetric economical 1→3 phase-covariant telecloning via cavity QED

宋庆敏, 叶柳

2010 (8): 80309-080309. doi: 10.1088/1674-1056/19/8/080309

摘要 ( 1656 )

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We propose an experimentally feasible scheme to implement the optimal asymmetric economical 1→3 phase-covariant telecloning protocol, which works without ancilla, based on cavity quantum electrodynamics (QED). The scheme is insensitive to the cavity field states and the cavity decay. In the telecloning process, the cavity is only virtually excited, it greatly prolongs the efficient decoherent time. Therefore, the scheme may be experimentally realized in the field of current cavity QED techniques.

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Probabilistic joint remote preparation of a high-dimensional equatorial quantum state

詹佑邦, 张群永, 施锦

2010 (8): 80310-080310. doi: 10.1088/1674-1056/19/8/080310

摘要 ( 1579 )

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This paper proposes a scheme for probabilistic joint remote preparation of an arbitrary high-dimensional equatorial quantum state by using high-dimensional single-particle orthogonal projective measurement and appropriate unitary operation. As a special case, a scheme of joint remote preparation of a single-qutrit equatorial state is presented in detail. The scheme is also generalized to the multi-party high-dimensional case. It shows that, only if when all the senders collaborate with each other, the receiver can reconstruct the original state with a certain probability.

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Formation of combined solitons in two-component Bose–Einstein condensates

李秋艳, 李再东, 姚淑芳, 李禄, 傅广生

2010 (8): 80501-080501. doi: 10.1088/1674-1056/19/8/080501

摘要 ( 1235 )

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We investigate the combined soliton solutions of two-component Bose--Einstein condensates with external potential. The ``phase diagram'' is obtained for the formation regions of different combined solitons. Our results show that the intraspecies (interspecies) interaction strengths and the external trapped potential clearly affect the formation of dark--dark, bright--bright, and dark--bright soliton solutions in different regions. Especially, we find that the bright--bright (dark--dark) soliton can exist in the case of both repulsive (attractive) intraspecies interaction strengths in the presence of external potential. This novel phenomenon is completely different from the formation of soliton solution of one-component Bose--Einstein condensates without external potential, and it will be useful for the study of two-component Bose--Einstein condensates.

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Stochastic resonance in a stochastic bistable system with additive noises and square-wave signal

郭锋, 罗向东, 李少甫, 周玉荣

2010 (8): 80502-080502. doi: 10.1088/1674-1056/19/8/080502

摘要 ( 1417 )

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This paper considers the stochastic resonance in a stochastic bistable system driven by a periodic square-wave signal and a static force as well as by additive white noise and dichotomous noise from the viewpoint of signal-to-noise ratio. It finds that the signal-to-noise ratio appears as stochastic resonance behaviour when it is plotted as a function of the noise strength of the white noise and dichotomous noise, as a function of the system parameters, or as a function of the static force. Moreover, the influence of the strength of the stochastic potential force and the correlation rate of the dichotomous noise on the signal-to-noise ratio is investigated.

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Simulation study of the effects of time delay on the correlation function of a bistable system with correlated noises

杜鲁春, 戴祖诚, 梅冬成

2010 (8): 80503-080503. doi: 10.1088/1674-1056/19/8/080503

摘要 ( 1998 )

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The effects of time delay on the fluctuation properties of a bistable system are investigated by simulating its normalised correlation function C(s). Three cases including linear delay, cubic delay and global delay in the system are considered respectively. The simulation results indicate that the linear delay enhances the fluctuation of the system (reduces the stability of the system) while the cubic delay and global delay weaken it (enforce the stability of the system), and the effect of cubic delay is more pronounced than the linear delay and global delay.

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Stochastic resonance in a monostable system driven by square-wave signal and dichotomous noise

郭锋, 罗向东, 李少甫, 周玉荣

2010 (8): 80504-080504. doi: 10.1088/1674-1056/19/8/080504

摘要 ( 1822 )

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This paper investigates the stochastic resonance in a monostable system driven by square-wave signal, asymmetric dichotomous noise as well as by multiplicative and additive white noise. By the use of the properties of the dichotomous noise, it obtains the expressions of the signal-to-noise ratio under the adiabatic approximation condition. It finds that the signal-to-noise ratio is a non-monotonic function of the asymmetry of the dichotomous noise, and which varies non-monotonously with the intensity of the multiplicative and additive noise as well as the system parameters. Moreover, the signal-to-noise ratio depends on the correlation rate and intensity of the dichotomous noise.

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Security analysis of a multiple pseudorandom-bit generator based on a spatiotemporal chaotic map

王世红, 李达

2010 (8): 80505-080505. doi: 10.1088/1674-1056/19/8/080505

摘要 ( 1592 )

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In this paper we analyse the security of a multiple pseudorandom-bit generator based on the coupled map lattice and suggest an improved model. Utilizing the error function attack, the multiple pseudorandom-bit generators which can be realized by the three digitization methods are analysed and the effective key spaces are estimated. We suggest an improved multiple pseudorandom-bit generator with 128-bit secret key, and analyse the key sensitivity and statistical properties of the system.

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Projective synchronization of spatiotemporal chaos in a weighted complex network

吕翎, 柴元, 栾玲

2010 (8): 80506-080506. doi: 10.1088/1674-1056/19/8/080506

摘要 ( 1743 )

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Projective synchronization of a weighted complex network is studied in which nodes are spatiotemporal chaos systems and all nodes are coupled not with the nonlinear terms of the system but through a weighted connection. The range of the linear coefficient matrix of separated configuration，when the synchronization is implemented, is determined according to Lyapunov stability theory. It is found that projective synchronization can be realized for unidirectional star-connection even if the coupling strength between the nodes is a given arbitrary weight value. The Gray–Scott models having spatiotemporal chaos behaviours are taken as nodes in the weighted complex network, and simulation results of spatiotemporal synchronization show the effectiveness of the method.

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Generalized chaos synchronization of a weighted complex network with different nodes

吕翎, 李钢, 郭丽, 孟乐, 邹家蕊, 杨明

2010 (8): 80507-080507. doi: 10.1088/1674-1056/19/8/080507

摘要 ( 1827 )

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This paper proposes a method of realizing generalized chaos synchronization of a weighted complex network with different nodes. Chaotic systems with diverse structures are taken as the nodes of the complex dynamical network, the nonlinear terms of the systems are taken as coupling functions, and the relations among the nodes are built through weighted connections. The structure of the coupling functions between the connected nodes is obtained based on Lyapunov stability theory. A complex network with nodes of Lorenz system, Coullet system, Rõssler system and the New system is taken as an example for simulation study and the results show that generalized chaos synchronization exists in the whole weighted complex network with different nodes when the coupling strength among the nodes is given with any weight value. The method can be used in realizing generalized chaos synchronization of a weighted complex network with different nodes. Furthermore, both the weight value of the coupling strength among the nodes and the number of the nodes have no effect on the stability of synchronization in the whole complex network.

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Robust adaptive synchronization of uncertain and delayed dynamical complex networks with faulty network

金小峥, 杨光红

2010 (8): 80508-080508. doi: 10.1088/1674-1056/19/8/080508

摘要 ( 1889 )

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This paper presents a new robust adaptive synchronization method for a class of uncertain dynamical complex networks with network failures and coupling time-varying delays. Adaptive schemes are proposed to adjust controller parameters for the faulty network compensations, as well as to estimate the upper and lower bounds of delayed state errors and perturbations to compensate the effects of delay and perturbation on-line without assuming symmetry or irreducibility of networks. It is shown that, through Lyapunov stability theory, distributed adaptive controllers constructed by the adaptive schemes are successful in ensuring the achievement of asymptotic synchronization of networks in the present of faulty and delayed networks, and perturbation inputs. A Chua's circuit network example is finally given to show the effectiveness of the proposed synchronization criteria.

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Robust H_∞ control of piecewise-linear chaotic systems with random data loss

张洪斌, 于永斌, 张健

2010 (8): 80509-080509. doi: 10.1088/1674-1056/19/8/080509

摘要 ( 1566 )

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This paper studies the problem of robust H_∞ control of piecewise-linear chaotic systems with random data loss. The communication links between the plant and the controller are assumed to be imperfect (that is, data loss occurs intermittently, which appears typically in a network environmen20). The data loss is modelled as a random process which obeys a Bernoulli distribution. In the face of random data loss, a piecewise controller is designed to robustly stabilize the networked system in the sense of mean square and also achieve a prescribed H_∞ disturbance attenuation performance based on a piecewise-quadratic Lyapunov function. The required H_∞ controllers can be designed by solving a set of linear matrix inequalities (LMI19). Chua's system is provided to illustrate the usefulness and applicability of the developed theoretical results.

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Symmetric bursting behaviour in non-smooth Chua's circuit

季颖, 毕勤胜

2010 (8): 80510-080510. doi: 10.1088/1674-1056/19/8/080510

摘要 ( 1681 )

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The dynamics of a non-smooth electric circuit with an order gap between its parameters is investigated in this paper. Different types of symmetric bursting phenomena can be observed in numerical simulations. Their dynamical behaviours are discussed by means of slow-fast analysis. Furthermore, the generalized Jacobian matrix at the non-smooth boundaries is introduced to explore the bifurcation mechanism for the bursting solutions, which can also be used to account for the evolution of the complicated structures of the phase portraits. With the variation of the parameter, the periodic symmetric bursting can evolve into chaotic symmetric bursting via period-doubling bifurcation.

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Intermittency and bifurcation in SEPICs under voltage-mode control

刘芳

2010 (8): 80511-080511. doi: 10.1088/1674-1056/19/8/080511

摘要 ( 1741 )

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A stroboscopic map for voltage-controlled single ended primary inductor converter (SEPIC) with pulse width modulation (PWM) is presented, where low-frequency oscillating phenomena such as quasi-periodic and intermittent quasi-periodic bifurcations occurring in the system are captured by numerical and experimental methods. According to bifurcation diagrams and nonlinear dynamical theory, the characteristics of the low-frequency oscillation and the mechanism for the appearance of the low-frequency oscillation are investigated. It is shown that as the controller parameter varies, the change in the conduction mode takes place from the continuous conduction mode (CCM) under the originally stable period one and high periodic orbits to the intermittent changes between CCM and discontinuous conduction mode (DCM), which may be related to the losing stability of the system and brought the system to exhibiting low-frequency oscillating behaviour in the time domain. Moreover, the occurrence of the intermittent quasi-periodic oscillation reflects that the system undergoes a Neimark--Sacker bifurcation.

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Properties of pulsating solitons in dissipative systems

吴亮, 郭志婕, 宋丽军

2010 (8): 80512-080512. doi: 10.1088/1674-1056/19/8/080512

摘要 ( 1578 )

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In this paper, a set of detailed numerical simulations of pulsating solitons in certain regions, where the pulsating solitons exist, have been carried out. The results show that the transformation between pulsating soliton and fronts can be realised through a series of period-doubling bifurcations, while there exist many kinds of special solutions. The complete transformation diagram has been obtained when the value of nonlinear gain varies within a definite range. The detailed analysis of the diagram reveals that the pulsating soliton experiences period-doubling bifurcations for smaller values of the nonlinear gain. For larger values of it, the pulsating solitons show chaotic behaviour and complex pulse splitting except for some special bifurcations. With the value of nonlinear gain increasing further, the pulse profiles resume pulsating, but the pulse energy is much higher than before and the pulse centre may move along the propagation direction.

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Interpreting a period-adding bifurcation scenario in neural bursting patterns using border-collision bifurcation in a discontinuous map of a slow control variable

莫娟, 李玉叶, 魏春玲, 杨明浩, 古华光, 屈世显, 任维

2010 (8): 80513-080513. doi: 10.1088/1674-1056/19/8/080513

摘要 ( 1843 )

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To further identify the dynamics of the period-adding bifurcation scenarios observed in both biological experiment and simulations with the differential Chay model, this paper fits a discontinuous map of a slow control variable of the Chay model based on simulation results. The procedure of period adding bifurcation scenario from period k to period k+1 bursting (k=1, 2, 3, 4) involved in the period-adding cascades and the stochastic effect of noise near each bifurcation point is also reproduced in the discontinuous map. Moreover, dynamics of the border-collision bifurcation are identified in the discontinuous map, which is employed to understand the experimentally observed period increment sequence. The simple discontinuous map is of practical importance in the modeling of collective behaviours of neural populations like synchronization in large neural circuits.

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A traffic flow lattice model considering relative current influence and its numerical simulation

孙棣华, 田川, 刘卫宁

2010 (8): 80514-080514. doi: 10.1088/1674-1056/19/8/080514

摘要 ( 1805 )

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Based on Xue's lattice model, an extended lattice model is proposed by considering the relative current information about next-nearest-neighbour sites ahead. The linear stability condition of the presented model is obtained by employing the linear stability theory. The density wave is investigated analytically with the perturbation method. The results show that the occurrence of traffic jamming transitions can be described by the kink–antikink solution of the modified Korteweg-de Vries (mKdV) equation. The simulation results are in good agreement with the analytical results, showing that the stability of traffic flow can be enhanced when the relative current of next-nearest-neighbour sites ahead is considered.

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Efficiency promotion for an on-ramp system based on intelligent transportation system information

谢东繁, 高自友, 赵小梅

2010 (8): 80515-080515. doi: 10.1088/1674-1056/19/8/080515

摘要 ( 1659 )

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The effect of cars with intelligent transportation systems (ITSs) on traffic flow near an on-ramp is investigated by car-following simulations. By numerical simulations, the dependences of flux on the inflow rate are investigated for various proportions of cars with ITSs. The phase diagrams as well as the spatiotemporal diagrams are presented to show different traffic flow states on the main road and the on-ramp. The results show that the saturated flux on the main road increases and the free flow region is enlarged with the increase of the proportion of cars with ITS. Interestingly, the congested regions of the main road disappear completely when the proportion is larger than a critical value. Further investigation shows that the capacity of the on-ramp system can be promoted by 13% by using the ITS information, and the saturated flux on the on-ramp can be kept at an appropriate value by adjusting the proportion of cars with ITS.

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Relaxation theory of spin-3/2 Ising system near phase transition temperatures

Osman Canko, Mustafa Keskin

2010 (8): 80516-080516. doi: 10.1088/1674-1056/19/8/080516

摘要 ( 1668 )

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Dynamics of a spin-3/2 Ising system Hamiltonian with bilinear and biquadratic nearest-neighbour exchange interactions is studied by a simple method in which the statistical equilibrium theory is combined with the Onsager's theory of irreversible thermodynamics. First, the equilibrium behaviour of the model in the molecular-field approximation is given briefly in order to obtain the phase transition temperatures, i.e. the first- and second-order and the tricritical points. Then, the Onsager theory is applied to the model and the kinetic or rate equations are obtained. By solving these equations three relaxation times are calculated and their behaviours are examined for temperatures near the phase transition points. Moreover, the z dynamic critical exponent is calculated and compared with the z values obtained for different systems experimentally and theoretically, and they are found to be in good agrement.

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Atomic force microscopy investigation of growth process of organic TCNQ aggregates on SiO₂ and mica substrates

郇庆, 胡昊, 潘理达, 肖江, 杜世萱, 高鸿钧

2010 (8): 80517-080517. doi: 10.1088/1674-1056/19/8/080517

摘要 ( 1613 )

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Deposition patterns of tetracyanoquinodimethane (TCNQ) molecules on different surfaces are investigated by atomic force microscopy. A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system, we investigate TCNQ thin film growth on both SiO₂ and mica surfaces. It is found that dense island patterns form at a high deposition rate, and a unique seahorse-like pattern forms at a low deposition rate. Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule–molecule interaction. Finally, a phenomenal "two-branch" model is proposed to simulate the growth process of the seahorse pattern.

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The forward and inverse problem of cardiac magnetic fields based on concentric ellipsoid torso-heart model

王倩, 华宁, 唐雪正, 陆宏, 马平, 唐发宽

2010 (8): 80601-080601. doi: 10.1088/1674-1056/19/8/080601

摘要 ( 1685 )

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This paper constructs a concentric ellipsoid torso-heart model by boundary element method and investigates the impacts of model structures on the cardiac magnetic fields generated by both equivalent primary source—a current dipole and volume currents. Then by using the simulated magnetic fields based on the torso-heart model as input, the cardiac current sources—an array of current dipoles by optimal constrained linear inverse method are constructed. Next, the current dipole array reconstruction considering boundaries are compared with that in an unbounded homogeneous medium. Furthermore, the influence of random noise on reconstruction is also considered and the reconstructing effect is judged by several reconstructing parameters.

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Laser pulse design for coherent control of Rydberg lithium atoms

张现周, 伍素玲, 蒋利娟, 马欢强, 贾光瑞

2010 (8): 83101-083101. doi: 10.1088/1674-1056/19/8/083101

摘要 ( 1924 )

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Using the time-dependent multilevel approach (TDML), this paper studies the dynamics of coherent control of Rydberg lithium atoms and demonstrates that Rydberg lithium atoms can be transferred to states of higher principal quantum number by exposing them to specially designed frequency-chirped laser pulses. The population transfer from n=70 to n=75 states of lithium atoms with efficiency of more than 90% is achieved by means of the sequential adiabatic rapid passages. The results agree well with the experimental ones and show that the coherent control of the population transfer from the lower n to the higher n states can be accomplished by the optimization of the chirping parameters and the intensity of laser field.

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The theoretical studies on the two-photon absorption properties of symmetric 1,4-bis{2-[4-(2-aryl)phenyl]vinyl}-2,5-bisdialkoxybenzenes

孙元红, 李龙禾, 李晶, 王传奎

2010 (8): 83102-083102. doi: 10.1088/1674-1056/19/8/083102

摘要 ( 1711 )

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On the level of the time-dependent hybrid density functional theory, the one- and two-photon absorption properties of a series of symmetric 4-bis 2-[4-(2-ary12) phenyl]vinyl-2,5-bisdialkoxybenzenes are studied respectively utilizing the analytic response theory and the few-state model methods. The calculated results show that the planarity of the geometrical structure plays a great role in enhancing the linear and nonlinear optical abilities of the molecule. However the effect of the length of the chain linked to the π-centre on the optical property is very little. For the investigated compounds, the A–π–A type charge-transfer molecules display more superior one- and two-photon absorption characteristics than the D–π–D type ones. Furthermore, the two-photon absorption results by use of few-state model are generally consistent with those by analytic response theory, demonstrating the reliability of the few-state model for evaluating the two-photon absorption cross section. The numerical simulations are in good agreement in tendency with the available experimental measurements.

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Effect of atomic initial phase difference on spontaneous emission of an atom embedded in photonic crystal

张冰, 孙秀冬, 姜向前

2010 (8): 83201-083201. doi: 10.1088/1674-1056/19/8/083201

摘要 ( 1609 )

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We investigate the effect of initial phase difference between the two excited states of a V-type three-level atom on its steady state behaviour of spontaneous emission. A modified density of modes is introduced to calculate the spontaneous emission spectra in photonic crystal. Spectra in free space are also shown to compare with that in photonic crystal with different relative positions of the excited levels from upper band-edge frequency. It is found that the initial phase difference plays an important role in the quantum interference property between the two decay channels. For a zero initial phase, destructive property is presented in the spectra. With the increase of initial phase difference, quantum interference between the two decay channels from upper levels to ground level turns to be constructive. Furthermore, we give an interpretation for the property of these spectra.

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Photon counting statistics in single multi-level quantum system

王东升, 郑雨军

2010 (8): 83202-083202. doi: 10.1088/1674-1056/19/8/083202

摘要 ( 1649 )

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We theoretically study the statistics of photon emission of a single multi-level quantum system by employing the generating functions approach developed recently. The generalized decay constants are included in a single multi-level quantum system with quasi-degenerated levels in this work although they are normally neglected in the absence of (quasi-)degeneracies in a multi-level quantum system within the rotating wave approximation. The quantum beats, the line shapes and the Mandel's Q parameters, etc. are studied.

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Attosecond manipulation of ionization and efficient broadband supercontinuum generation in stretched molecules

王少义, 洪伟毅, 张庆斌, 李钱光, 陆培祥

2010 (8): 83203-083203. doi: 10.1088/1674-1056/19/8/083203

摘要 ( 1549 )

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We theoretically investigate the high-order harmonic generation from stretched molecules in a linearly polarized intense field. By adopting an infrared pulse combined with an ultraviolet (UV) attosecond pulse, the ionization process can be controlled effectively. In this excitation scheme, the harmonic spectrum beyond I_p + 3.17U_p is significantly enhanced by two orders, where I_p and U_p = e²E_0² /(4m_eω²) are the ionization and ponderomotive potential, then smooth broadband supercontinuum with the bandwidth of about 120 eV is obtained, which leads to an isolated sub-60-as attosecond pulse with a high signal-noise ratio. Moreover, the bandwidth of the supercontinuum is weakly dependent on the location and pulse duration of the UV pulse.

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Propagation properties of electromagnetic fields in elliptic dielectric hollow fibres and their applications

李会容, 印建平

2010 (8): 83204-083204. doi: 10.1088/1674-1056/19/8/083204

摘要 ( 1622 )

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We numerically calculate and analyse the electromagnetic fields, optical intensity distributions, polarization states and orbital angular momentum of some elliptic hollow modes in an elliptic dielectric hollow fiber (EDHF) by using Mathieu functions, and also calculate the optical potential of the blue-detuned _eHE₁₁ mode evanescent-light wave for ⁸⁵Rb atoms, including the position-dependent van der Waals potential, and discuss briefly some potential applications of our EDHF in atom and molecule optics, etc. Our study shows that the vector electric field distributions of the odd modes in the cross section of the EDHF are the same as that of the even modes and with different boundary ellipses by rotating an angle of π/2, and the orbital angular momentum (OAM) of single HE (EH) mode is exactly equal to zero, while that of dual-mode in the EDHF is fractional in h, and has a sinusoidal oscillation as z varies. The EDHF can be used to produce various elliptic hollow beams, even to generate and study various atomic vortices with a fractional charge and its fractional quantum Hall effect in atomic Bose--Einstein condensate, and so on.

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Single layer atom chip for magnetically trapping one-dimensional array of ultracold atoms

程峰, 颜波, 柯敏, 王育竹

2010 (8): 83205-083205. doi: 10.1088/1674-1056/19/8/083205

摘要 ( 1571 )

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We propose a wire configuration to create a one-dimensional (1D) array of magnetic microtraps for trapping ultracold atoms. The configuration is formed by replacing the central part of the Z-wire pattern with a zigzag wire. We simulate the performance of this pattern by the finite element method which can take both the width and depth of the wire into consideration. The result of simulation shows that this configuration can create magnetic microtraps which can be separated and combined by changing the bias magnetic field. We manage to split the Z-wire trap and prove that a similar result can occur for the new wire configuration. The fabrication processes of the atom chip are also introduced. Finally we discuss the loading method.

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Ion-induced kinetic electron emission from ⁶LiF,⁷LiF and MgF₂ thin films

S. Ullah, A. H. Dogar, M. Ashraf, A. Qayyum

2010 (8): 83401-083401. doi: 10.1088/1674-1056/19/8/083401

摘要 ( 1509 )

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Secondary electron yields for Ar⁺ impact on ⁶LiF,⁷LiF and MgF₂ thin films grown on aluminum substrates are measured each as a function of target temperature and projectile energy. Remarkably different behaviours of the electron yields for LiF and MgF₂ films are observed in a temperature range from 25o to 300o. The electron yield of LiF is found to sharply increase with target temperature and to be saturated at about 175o. But the target temperature has no effect on the electron yield of MgF₂. It is also found that for the ion energies greater than 4keV, the electron yield of ⁶LiF is consistently high as compared with that of ⁷LiF that may be due to the enhanced contribution of recoiling ⁶Li atoms to the secondary electron generation. A comparison between the electron yields of MgF₂ and LiF reveales that above a certain ion energy the electron yield of MgF₂ is considerably low as compared with that of LiF. We suggest that the short inelastic mean free path of electrons in MgF₂ can be one of the reasons for its low electron yield.

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Theoretical study of stereodynamics for reaction O(³P)+HCl

朱通, 扈国栋, 陈建中, 刘新国, 张庆刚

2010 (8): 83402-083402. doi: 10.1088/1674-1056/19/8/083402

摘要 ( 1611 )

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The vector correlation between products and reagents for reaction O(³P)+HCl→OH+Cl is studied using a quasi-classical trajectory (QCT) method on the benchmark potential energy surface of the ground ³A'' state [Ramachandran and Peterson, J. Chem. Phys. 119 (2003) 9550]. The generalised differential cross section (2π/σ)(dσ₀₀/dω_t) is presented in the centre of mass frame. The distribution of dihedral angles, P(φ_r), and the distribution of angles between k and j', P(?_r), are calculated. The influence of the collision energy and the influence of the reagent rotation and vibration on the product polarization are studied in the present work. The calculated results indicate that the rotational polarization of the product molecule is almost independent of collision energy but sensitive to the reagent rotation and vibration.

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The relativistic density functional investigations on geometries, electronic and magnetic properties of Ir_n (n=1–13) clusters

郭平, 郑继明, 赵佩, 郑琳琳, 任兆玉

2010 (8): 83601-083601. doi: 10.1088/1674-1056/19/8/083601

摘要 ( 1508 )

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The Ir_n (n=1--13) clusters are studied using the relativistic density functional method with generalized gradient approximation. A series of low-lying structures with different spin multiplicities have been considered. It is found that all the lowest-energy Ir_n (n=4--13) geometries prefer non-compact structures rather than compact structure growth pattern. And the cube structure is a very stable cell for the lowest-energy Ir_n (n > 8) clusters. The second-order difference of energy, the vertical ionization potentials, the electron affinities and the atomic average magnetic moments for the lowest-energy Ir_n geometries all show odd--even alternative behaviours.

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Geometrical, energetic and electronic properties of Au_n–(C₃H₆O)_m complexes (n=3,5, m ≤ n): A density functional theory study

李迎春, 杨传路, 孙美玉, 李晓霞, 安义鹏, 王美山

2010 (8): 83602-083602. doi: 10.1088/1674-1056/19/8/083602

摘要 ( 1657 )

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The interactions of acetone molecules with clusters of Au₃ and Au₅ are investigated by using a density functional theory (DFT) within a generalized gradient approximation (GGA). The geometries, adsorption energies and deformation electron density distributions are used to analyse these interactions. The present calculations show that more than one acetone molecule can be adsorbed onto small gold clusters, and this adsorption is different from that of single molecule absorption. The coordination number of the adsorption site on the gold cluster is the dominant factor responsible for the strength of the interactions. The effects of the Au–O bond lengths in the complexes on adsorption energies between Au clusters and acetone molecules are also examined.

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Finite-difference time-domain studies of low-frequency stop band in superconductor-dielectric superlattice

王身云, 刘少斌, Le-Wei Joshua Li

2010 (8): 84101-084101. doi: 10.1088/1674-1056/19/8/084101

摘要 ( 1713 )

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The transmission coefficients of electromagnetic (EM) waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain (SO-FDTD) method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.

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Analysis of multiple scattering from two-dimensional dielectric sea surface with iterative Kirchhoff approximation

罗伟, 张民, 周平, 殷红成

2010 (8): 84102-084102. doi: 10.1088/1674-1056/19/8/084102

摘要 ( 1666 )

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An iterative method in the Kirchhoff approximation is proposed for high frequency multiple electromagnetic scattering from two-dimensional dielectric sea surface. The multiple interaction of the scattering field is characterized with the corrected electromagnetic currents of the wind-driven sea surface. The actual surface currents are approximated with the iterative solution of the corrected currents. A newly developed sea spectrum, Elfouhaily spectrum, is utilized to build the sea surface model. The shadowing correction is improved by the Depth–Buffer algorithm. The validity of the iterative Kirchhoff approximation is verified by the agreement of backscattering coefficients with the measured data.

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Microwave Doppler spectra of sea return at small incidence angles: specular point scattering contribution

张彦敏, 王运华, 赵朝方

2010 (8): 84103-084103. doi: 10.1088/1674-1056/19/8/084103

摘要 ( 1704 )

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It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller (≤20o). Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method (TSM) and the method of moment (MOM) are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.

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Scattering of scalar light wave from a Gaussianben–Schell model medium

王涛, 赵道木

2010 (8): 84201-084201. doi: 10.1088/1674-1056/19/8/084201

摘要 ( 1885 )

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The scattering of scalar light wave from a random medium with a correlation function of Gaussian–Schell model distribution is studied. It is shown that the properties of the scattered field, i.e., the spectral density and the spectral degree of coherence of the scattered field, are closely related to the properties of the scattering medium, including the scaled effective radius and the scaled correlation length of the correlation function.

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A novel orthogonally linearly polarized Nd:YVO₄ laser

闫兴鹏, 柳强, 陈海龙, 付星, 巩马理, 王东生

2010 (8): 84202-084202. doi: 10.1088/1674-1056/19/8/084202

摘要 ( 1684 )

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We presented a novel orthogonally linearly polarized Nd:YVO₄ laser. Two pieces of a-cut grown-together composite YVO₄/Nd:YVO₄ crystals were placed in the resonant cavity with the c-axis of the two crystals orthogonally. The polarization and power performance of the orthogonally polarized laser were investigated. A 26.2-W orthogonally linearly polarized laser was obtained. The power ratio between the two orthogonally polarized lasers was varied with the pump power caused by the polarized mode coupling. The longitudinal modes competition and the corresponding variable optical beats were also observed from the orthogonally polarized laser. We also adjusted the crystals with their c-axis parallele to each other, and a 40.7-W linearly polarized TEM₀₀ laser was obtained, and the beam quality factors were M²_x=1.37 and M²_y=1.25.

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Study on UV-light-induced absorption in LiNbO₃:Fe, Co crystal

陈洪建, 师丽红, 阎文博, 陈贵锋, 沈俊, 申绪男, 李养贤

2010 (8): 84203-084203. doi: 10.1088/1674-1056/19/8/084203

摘要 ( 1642 )

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In this paper, the temporary UV-light-induced absorption in LiNbO₃:Fe, Co crystal is investigated for different UV intensities. It is found that the sensitizing process in LiNbO₃:Fe, Co can be considered as a combination of two sub-processes with different time constants. Based on the lattice structure and the photochromic mechanism of the material, the two sub-processes are suggested to arise from electron transfer from O^{2 -} to Fe^{3 +} through two paths with different distances. The two-colour recording experiment in LiNbO₃:Fe, Co is also preformed by using UV and green light as gating and writing beams respectively. High sensitivity is obtained in the recording, which is considered as the consequence of direct charge transfer from O^{2 -} to Fe^{3 +}.

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Quantum coherence in Λ-three-level system driven by bichromatic coupling field

杨丽君, 赵敏, 张连水, 冯晓敏, 李晓莉, 尉长江

2010 (8): 84204-084204. doi: 10.1088/1674-1056/19/8/084204

摘要 ( 1595 )

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We present a theoretical study of quantum coherent effects in a λ-three-level system with a strong bichromatic coupling field and a weak probe field. When one component of the strong bichromatic coupling field is resonant with a corresponding transition and the other is detuning with an integer fraction of the Rabi frequency of the resonant field, the absorption spectrum exhibits a series of symmetrical doublets. While two frequencies of the strong bichromatic coupling field are symmetrically detuned from the transition, the position and the relative intensity of the absorption peak are both affected by the coupling field intensity and detuning. An explanation of the spectrum is given in term of the dressed-state formalism.

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Degree of fourth-order coherence by double Hanbury Brown–Twiss detections

张玉驰, 李园, 郭龑强, 李刚, 王军民, 张天才

2010 (8): 84205-084205. doi: 10.1088/1674-1056/19/8/084205

摘要 ( 1591 )

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Photon quantum statistics of light can be shown by the high-order coherence. The fourth-order coherences of various quantum states including Fock states, coherent states, thermal states and squeezed vacuum states are investigated based on a double Hanbury Brown–Twiss (HBT) scheme. The analytical results are obtained by taking the overall efficiency and background into account.

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Stimulated supercontinuum-radiation generation of carbon disulfide by all-trans-β-carotene fluorescence enhancement effect in liquid core optical fibre

门志伟, 房文汇, 里佐威, 曲冠男, 高淑琴, 陆国会, 杨健戈, 孙成林

2010 (8): 84206-084206. doi: 10.1088/1674-1056/19/8/084206

摘要 ( 1673 )

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We demonstrate stimulated supercontinuum-radiation of carbon disulfide (CS₂) influenced by biological molecules all-trans-β -carotene in liquid core optical fibre (LCOF). By virtue of the broad fluorescence characteristics and large third-order optical nonlinearities of all-{trans}-β-carotene,the high-order Stokes lines of stimulated Raman scattering (SRS) and the multi-order Stokes lines of stimulated Brillouin scattering (SBS) excitated by SRS are observed at low input-laser energies. The results indicate that the fluorescence not only enhances the SRS, but also the SBS. These Stokes lines generate the SRS--SBS supercontinuum radiation (RBSR). A flat-amplitude bandwidth of 110 nm from 515nm to 625nm is observed when a frequency-doubled Nd:YAG laser at 532nm with an energy of 0.86mJ is used. This result is expected to be useful for the multi-wavelength fibre laser.

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One-dimensional nonparaxial bright solitons and their coherent interactions in Kerr media

王红成, 朱德海, 凌东雄

2010 (8): 84207-084207. doi: 10.1088/1674-1056/19/8/084207

摘要 ( 1513 )

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The existence of one-dimensional bright Kerr solitons is investigated in Kerr media beyond the paraxial approximation. It is found that a nonparaxial soliton with no less than a minimum dimensionless width of about 0.76 can exist, which corresponds to the real width about a wavelength. Besides, the coherent interactions between two nonparaxial bright solitons in Kerr media are also investigated in detail. It is found that their separation and intensity ratio have great influence on the coherent interaction between these two solitons. Furthermore, the effect of the relative phase difference on the nonparaxial interaction is quite different from that on the paraxial interaction. Periodical breath, merging, repulsion, and energy transferring can be realized separately by choosing an appropriate initial relative phase between the coherent solitons.

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Enhancement of modulation depth of an all-optical switch using an azo dye-ethyl red film

陆文强, 陈桂英, 郝召锋, 许京军, 田建国, 张春平

2010 (8): 84208-084208. doi: 10.1088/1674-1056/19/8/084208

摘要 ( 1611 )

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The polymethyl methacrylate (PMMA) film doped with an azo dye ethyl-red (ER) film is employed to demonstrate the properties of an all-optical switch by its photoinduced dichroism and birefringence. We show how to enhance remarkably the modulation depth of all-optical switches almost to 100% by using two linear polarization beams: one beam is inclined at 45o with respect to the probing beam and serves as a pumping beam, and the other beam is perpendicular to the probing beam and used as an erasing beam. Furthermore, a maximum-to-minimum output intensity ratio of 2000:1 is achieved in experiment, which is very useful and important for optical storages and image displays.

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A novel method of rapidly modeling optical properties of actual photonic crystal fibres

王立文, 娄淑琴, 陈卫国, 李宏雷

2010 (8): 84209-084209. doi: 10.1088/1674-1056/19/8/084209

摘要 ( 1783 )

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The flexible structure of photonic crystal fibre not only offers novel optical properties but also brings some difficulties in keeping the fibre structure in the fabrication process which inevitably cause the optical properties of the resulting fibre to deviate from the designed properties. Therefore, a method of evaluating the optical properties of the actual fibre is necessary for the purpose of application. Up to now, the methods employed to measure the properties of the actual photonic crystal fibre often require long fibre samples or complex expensive equipments. To our knowledge, there are few studies of modeling an actual photonic crystal fibre and evaluating its properties rapidly. In this paper, a novel method, based on the combination model of digital image processing and the finite element method, is proposed to rapidly model the optical properties of the actual photonic crystal fibre. Two kinds of photonic crystal fibres made by Crystal Fiber A/S are modeled. It is confirmed from numerical results that the proposed method is simple, rapid and accurate for evaluating the optical properties of the actual photonic crystal fibre without requiring complex equipment.

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Sub-nanosecond optical switch based on silicon racetrack resonator

徐海华, 黄庆忠, 李运涛, 俞育德, 余金中

2010 (8): 84210-084210. doi: 10.1088/1674-1056/19/8/084210

摘要 ( 1913 )

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We experimentally demonstrate a small-size and high-speed silicon optical switch based on the free carrier plasma dispersion in silicon. Using an embedded racetrack resonator with a quality factor of 7400, the optical switch shows an extinction ratio exceeding 13 dB with a footprint of only 2.2×10^-3 mm². Moreover, a novel pre-emphasis technique is introduced to improve the optical response performance and the rise and the fall times are reduced down to 0.24 ns and 0.42 ns respectively, which are 25% and 44% lower than those without the pre-emphasis.

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Borehole guided waves in a non-Newtonian (Maxwell) fluid-saturated porous medium

崔志文, 刘金霞, 姚桂锦, 王克协

2010 (8): 84301-084301. doi: 10.1088/1674-1056/19/8/084301

摘要 ( 1603 )

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The property of acoustic guided waves generated in a fluid-filled borehole surrounded by a non-Newtonian (Maxwell) fluid-saturated porous formation with a permeable wall is investigated. The influence of non-Newtonian effects on acoustic guided waves such as Stoneley waves, pseudo-Rayleigh waves, flexural waves, and screw waves propagations in a fluid-filled borehole is demonstrated based on the generalized Biot–Tsiklauri model by calculating their velocity dispersion and attenuation coefficients. The corresponding acoustic waveforms illustrate their properties in time domain. The results are also compared with those based on generalized Biot's theory. The results show that the influence of non-Newtonian effect on acoustic guided wave, especially on the attenuation coefficient of guided wave propagation in borehole is noticeable.

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Quantitative measurement of local elasticity of SiO_x film by atomic force acoustic microscopy

何存富, 张改梅, 吴斌

2010 (8): 84302-084302. doi: 10.1088/1674-1056/19/8/084302

摘要 ( 1535 )

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In this paper the elastic properties of SiO_x film are investigated quantitatively for local fixed point and qualitatively for overall area by atomic force acoustic microscopy (AFAM) in which the sample is vibrated at the ultrasonic frequency while the sample surface is touched and scanned with the tip contacting the sample respectively for fixed point and continuous measurements. The SiO_x films on the silicon wafers are prepared by the plasma enhanced chemical vapour deposition (PECVD). The local contact stiffness of the tip-SiO_x film is calculated from the contact resonance spectrum measured with the atomic force acoustic microscopy. Using the reference approach, indentation modulus of SiO_x film for fixed point is obtained. The images of cantilever amplitude are also visualized and analysed when the SiO_x surface is excited at a fixed frequency. The results show that the acoustic amplitude images can reflect the elastic properties of the sample.

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Experimental studies of plasma sheath near meshes of different transmissivity

李毅人, 马锦秀, 郑尧邦, 张文贵

2010 (8): 85201-085201. doi: 10.1088/1674-1056/19/8/085201

摘要 ( 1636 )

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The measurements of the potential distributions in the boundary layer near meshes with different mesh spacing were conducted in weakly collisional plasmas using a fine-structured emissive probe and the results of the sheath thickness and electric field at the sheath-presheath edge were compared with theoretical models of collisional presheath and collisionless sheath. It was shown that, because the meshes are partially transparent to ions, the sheath is thinner and the electric field is stronger for the mesh of higher transmissivity, owing to the increased ion density in the sheath contributed from the ions transmitted from the other side of the mesh. However, the potential profiles in the presheath remain almost the same for different meshes except for the shift of the sheath-presheath edge. The thickness of the sheath decreases while the electric field at the edge increases with the increase of the neutral gas pressure. Furthermore, depending on the pressure, the measured electric fields at the edge are close to that from the models of a transition region.

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Characteristics of sealed plasma electrolytic oxidation coatings with electrochemical impedance spectroscopy

吕国华, 陈睆, 王兴权, 庞华, 张谷令, 邹斌, Lee Heon-Ju, 杨思泽

2010 (8): 85202-085202. doi: 10.1088/1674-1056/19/8/085202

摘要 ( 1594 )

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Plasma electrolytic oxidation (PEO) coatings are prepared on aluminium with graphite powders added into the electrolyte. The scanning electron microscopy (SEM) coupled with an energy dispersive x-ray analysis system (EDX) is used to characterize the surface and the cross-section morphologies of the coatings. The electrochemical impedance spectroscopy (EIS) is used not only to evaluate the corrosion resistance but also to analyse the structure of the coating. Results show that graphite powders are embedded in the PEO coating. The corrosion resistances of both the inner barrier and the outer porous layer are greatly improved, and the EIS could give some valuable detailed information about the coating structure.

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Structural and physical properties of undoped and nickel-doped BaFe_2-xNi_xAs₂(x=0, 0.04) single crystals

李正才, 陆伟, 董晓莉, 周放, 赵忠贤

2010 (8): 86101-086101. doi: 10.1088/1674-1056/19/8/086101

摘要 ( 1640 )

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Single crystals of undoped and nickel-doped BaFe_2-xNi_xAs₂ (x=0, 0.04) have been grown by FeAs self-flux method. The maximum dimension of the crystal is as large as ～ 1 cm along the ab plane. The crystalline topography of a cleaved crystal surface is examined by scanning electron microscope (SEM). By x-ray powder diffraction (XRD) experiments using pure silicon as an internal standard, precise unit cell parameters (tetragonal at room temperature) are determined: a=3.9606(4) ${\AA}$ (1 ${\AA}$ = 0.1 nm), c=13.015(2) ${\AA}$ for BaFe_1.96Ni_0.04As₂ and a =3.9590(5) ${\AA}$, c = 13.024(1) ${\AA}$ for BaFe₂As₂. DC magnetization and transport measurements are performed to check superconducting transition (T_c= 15 K for x = 0.04) and other subtle anomalies. For BaFe_1.96Ni_0.04As₂ crystal, the resistance curve at normal state shows two distinct anomalies associated with spin and structure transitions, and its magnetization data above ～ 91 K exhibit a linear temperature dependence due to spin density wave (SDW) instability.

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New expression of bimodal phase distributions in direct-method phasing of protein single-wavelength anomalous diffraction data

张涛, 古元新, 郑朝德, 范海福

2010 (8): 86102-086102. doi: 10.1088/1674-1056/19/8/086102

摘要 ( 1913 )

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One of the essential points of the direct-method single-wavelength anomalous diffraction (SAD) phasing for proteins is to express the bimodal SAD phase distribution by the sum of two Gaussian functions peaked respectively at φ"_h + |Δφ_h| and φ"_h - |Δφ_h|. The probability for Δφ_h being positive (P₊) can be derived based on the Cochran distribution in direct methods. Hence the SAD phase ambiguity can be resolved by multiplying the Gaussian function peaked at φ"_h + |Δφ_h| with P₊ and multiplying the Gaussian function peaked at φ"_h - |Δφ_h| with P_- (=1-P₊).The direct-method SAD phasing has been proved powerful in breaking SAD phase ambiguities, in particular when anomalous-scattering signals are weak.However, the approximation of bimodal phase distributions by the sum of two Gaussian functions introduces considerable errors. In this paper we show that a much better approximation can be achieved by replacing the two Gaussian functions with two von Mises distributions. Test results showed that this leads to significant improvement on the efficiency of direct-method SAD-phasing.

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OASIS4.0—a new version of the program OASIS for phasing protein diffraction data

张涛, 古元新, 郑朝德, 范海福

2010 (8): 86103-086103. doi: 10.1088/1674-1056/19/8/086103

摘要 ( 1649 )

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The program OASIS4.0 has been released. Apart from the improved single-wavelength anomalous diffraction (SAD) phasing algorithm described in a separate paper, an important new feature in this version is the automation of the iterative phasing and model-building process in solving protein structures. A new graphical user's interface (GUI) is provided for controlling and real-time monitoring the dual-space iterative process. The GUI is discussed in detail in the present paper.

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Diffusion activation energy versus the favourable energy in two-order-parameter model：A molecular dynamics study of liquid Al

李宜德, 郝清海, 曹启龙, 刘长松

2010 (8): 86104-086104. doi: 10.1088/1674-1056/19/8/086104

摘要 ( 1744 )

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In the present work, we find that both diffusion activation energy E_a(D) and E_a(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure dependence of excess entropy is well fitted by the expression -S^ex(T,P)/k_B=a(P)+b(P)T+c(P)exp(E_f/k_BT), which together with the small ratio of E_f/k_BT leads to the relationship of excess entropy to temperature and pressure, i.e. S^ex≈-cE_f/T, where c is about 12 and E_f (=Δ E-PΔV) is the favourable energy. Therefore, there exists a simple relation between E_a(S^ex) and E_f, i.e. E_a(S^ex)≈cE_f.

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Strain effect on transport properties of hexagonal boron–nitride nanoribbons

陈风, 陈元平, 张迷, 钟建新

2010 (8): 86105-086105. doi: 10.1088/1674-1056/19/8/086105

摘要 ( 1673 )

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The transport properties of hexagonal boron--nitride nanoribbons under the uniaxial strain are investigated by the Green's function method. We find that the transport properties of armchair boron--nitride nanoribbon strongly depend on the strain. In particular, the features of the conductance steps such as position and width are significantly changed by strain. As a strong tensile strain is exerted on the nanoribbon, the highest conductance step disappears and subsequently a dip emerges instead. The energy band structure and the local current density of armchair boron--nitride nanoribbon under strain are calculated and analysed in detail to explain these characteristics. In addition, the effect of strain on the conductance of zigzag boron--nitride nanoribbon is weaker than that of armchair boron nitride nanoribbon.

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Effect of high temperature annealing on strain and band gap of GaN nanoparticles

肖洪地, 毛宏志, 林兆军, 马洪磊

2010 (8): 86106-086106. doi: 10.1088/1674-1056/19/8/086106

摘要 ( 1604 )

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Black-coloured GaN nanoparticles with an average grain size of 50 nm have been obtained by annealing GaN nanoparticles under flowing nitrogen at 1200 oC for 30 min. XRD measurement result indicates an increase in the lattice parameter of the GaN nanoparticles annealed at 1200 oC, and HRTEM image shows that the increase cannot be ascribed to other ions in the interstitial positions. If the as-synthesised GaN nanoparticles at 950 oC are regarded as standard, the thermal expansion changes nonlinearly with temperature and is anisotropic; the expansion below 1000oC is smaller than that above 1000 oC. This study provides an experimental demonstration for selecting the proper annealing temperature of GaN. In addition, a large blueshift in optical bandgap of the annealed GaN nanoparticles at 1200 oC is observed, which can be ascribed to the dominant transitions from the C(Γ₇) with the peak energy at 3.532 eV.

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The equilibrium composition in Ge_xSi_1-x/Si self-assembled alloy quantum dot

王东林, 俞重远, 刘玉敏, 叶寒, 芦鹏飞, 赵龙, 郭晓涛

2010 (8): 86801-086801. doi: 10.1088/1674-1056/19/8/086801

摘要 ( 1679 )

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The equilibrium composition in strained quantum dot is the result of both elastic relaxation and chemical mixing effects, which have a direct relationship to the optical and electronic properties of the quantum-dot-based device. Using the method of moving asymptotes and finite element tools, an efficient technique has been developed to compute the composition profile by minimising the Gibbs free energy in self-assembled alloy quantum dot. In this paper, the composition of dome-shaped Ge_xSi_1-x/Si quantum dot is optimised, and the contribution of the different energy to equilibrium composition is discussed. The effect of composition on the critical size for shape transition of pyramid-shaped GeSi quantum dot is also studied.

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Thickness dependence of grain size and surface roughness for dc magnetron sputtered Au films

张鑫, 宋小会, 张殿琳

2010 (8): 86802-086802. doi: 10.1088/1674-1056/19/8/086802

摘要 ( 1768 )

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The grain size and surface morphology of sputtered Au films are studied by x-ray diffraction and atomic force microscope. For as-deposited samples the grain growth mechanism is consistent with the two-dimensional (2D) theory, which gives relatively low diffusion coefficient during deposition. The annealing process demonstrates the secondary grain growth mechanism in which the thickness dependence of grain boundary energy plays a key role. The surface roughness increases with the increase of grain size.

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First-principles research on influence of C dopants on magnetic and electric properties of rocksalt MgS

刘俊, 陈立, 董健, 李丽, 董会宁, 郑瑞伦

2010 (8): 87101-087101. doi: 10.1088/1674-1056/19/8/087101

摘要 ( 1545 )

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The 2×2×1 rocksalt C-doped MgS supercells are optimized and their magnetic and electric properties, including the half-metallicity, the conductivity and the supercell magnetic moments, are calculated or analysed by the first-principles researches based on the density functional theory. Results show that the concentration of C-dopants may cause important influence on the magnetic and the electric properties of rocksalt MgS. C dopants are inclined to have a scattering distribution. MgC_0.0625S_0.9375, ^aMgC_0.1250S_0.8750 and MgC_0.1875S_0.8125 have evident half-metallicity. They have wide spin energy gaps, thus high Curie temperature possibly. Their supercell magnetic moments are near to integral numbers 2.0, 4.0 and 6.0 μ_B. The main reason for spin polarization and half-metallicity of C-doped MgS is that there are sp hybridized orbitals in ligand compound ML₆ caused by covalent interaction between C-ions and Mg-ions.

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Structural, electronic and magnetic properties of the Mn–Ni(110) c(2×2) surface alloy

李登峰, 肖海燕, 祖小涛, 董会宁, 高飞

2010 (8): 87102-087102. doi: 10.1088/1674-1056/19/8/087102

摘要 ( 1565 )

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Using first-principles total energy method, we study the structural, the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy. Paramagnetic, ferromagnetic, and antiferromagnetic surfaces in the top layer and the second layer are considered. It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases. The buckling of the Mn–Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26á(1á=0.1 n13) and the weak rippling is 0.038 AA in the third layer, in excellent agreement with experimental results. It is proved that the magnetism of Mn can stabilize this surface alloy. Electronic structures show a large magnetic splitting for the Mn atom, which is slightly higher than that of Mn–Ni(100) c(2×2) surface alloy (3.41 eV) due to the higher magnetic moment. A large magnetic moment for the Mn atom is predicted to be 3.81 μ_B. We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate, which confirms the experimental results. The magnetism of Mn is identified as the driving force of the large buckling and the work-function change. The comparison with the other magnetic surface alloys is also presented and some trends are predicted.

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First-principles study on anatase TiO₂ codoped with nitrogen and praseodymium

高攀, 吴晶, 柳清菊, 周文芳

2010 (8): 87103-087103. doi: 10.1088/1674-1056/19/8/087103

摘要 ( 1658 )

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The crystal structures, electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO₂ were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory. Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO₂ nanocrystal photocatalyst were synthesized by a microwave chemical method. The calculated results show that the photocatalytic activity of TiO₂ can be enhanced by N doping or Pr doping, and can be further enhanced by N+Pr codoping. The band gap change of the codoping TiO₂ is more obvious than that of the single ion doping, which results in the red shift of the optical absorption edges. The results are of great significance for the understanding and further development of visible-light response high activity modified TiO₂ photocatalyst. The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light. The experimental results show that the codoping TiO₂ photocatalytic activity is obviously higher than that of the single ion doping. The experimental results accord with the calculated results.

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Fast impurity solver for dynamical mean field theory based on second order perturbation around the atomic limit

庄嘉宁, 刘青梅, 方忠, 戴希

2010 (8): 87104-087104. doi: 10.1088/1674-1056/19/8/087104

摘要 ( 1672 )

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This paper proposes an impurity solver for the dynamical mean field theory (DMFT) study of the Mott insulators, which is based on the second order perturbation of the hybridization function. After careful benchmarking with quantum Monte Carlo results on the anti-ferromagnetic phase of the Hubbard model, it concludes that this impurity solver can capture the main physical features in the strong coupling regime and can be a very useful tool for the LDA (local density approximation) +,DMFT studies of the Mott insulators with long range order.

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Origin of the metallic to insulating transition of an epitaxial Bi(111) film grown on Si(111)

庞斐, 梁学锦, 廖昭亮, 尹树力, 陈东敏

2010 (8): 87201-087201. doi: 10.1088/1674-1056/19/8/087201

摘要 ( 2138 )

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Transport characteristics of single crystal bismuth films on Si(111)-7×7 are found to be metallic or insulating at temperatures below or above T_C, respectively. The transition temperature T_C decreases as the film thickness increases. By combining thickness dependence of the films resistivity, we find the insulating behaviour results from the states inside film, while the metallic behaviour originates from the interface states. We show that quantum size effect in a Bi film, such as the semimetal-to-semiconductor transition, is only observable at a temperature higher than T_C.

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Study of a double epi-layers SiC junction barrier Schottky rectifiers embedded P layer in the drift region

宋庆文, 张玉明, 张义门, 张倩, 吕红亮

2010 (8): 87202-087202. doi: 10.1088/1674-1056/19/8/087202

摘要 ( 1827 )

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This paper proposes a double epi-layers 4H–SiC junction barrier Schottky rectifier (JBSR) with embedded P layer (EPL) in the drift region. The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process. The electric field and potential distribution are changed due to the buried P-layer, resulting in a high breakdown voltage (BV) and low specific on-resistance (R_on,sp). The influences of device parameters, such as the depth of the embedded P+ regions, the space between them and the doping concentration of the drift region, etc., on BV and R_on,sp are investigated by simulations, which provides a particularly useful guideline for the optimal design of the device. The results indicate that BV is increased by 48.5% and Baliga's figure of merit (BFOM) is increased by 67.9% compared to a conventional 4H–SiC JBSR.

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Coexistence of ferromagnetism and superconductivity in normal mental/superconductor/ferromagnet structures

郁华玲, 彭菊, 金本喜

2010 (8): 87203-087203. doi: 10.1088/1674-1056/19/8/087203

摘要 ( 1740 )

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We extend the Blonder, Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures. In the superconducting film, there are the gapless superconductivity and the spin-dependent density of states both within and without the energy gap. It indicates an appearance of the inverse-proximity-effect-induced ferromagnetism and a coexistence of ferromagnetism and superconductivity near the interface. The influence of exchange energy in the ferromagnet and barrier strength at the superconductor/ferromagnet interface on the inverse proximity effects is discussed.

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Angle-sensitive and fast photovoltage of silver nanocluster embeded ZnO thin films induced by 1.064-μm pulsed laser

赵嵩卿, 杨立敏, 刘闻炜, 赵昆, 周岳亮, 周庆莉

2010 (8): 87204-087204. doi: 10.1088/1674-1056/19/8/087204

摘要 ( 1825 )

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Silver nanocluster embedded ZnO composite thin film was observed to have an angle-sensitive and fast photovoltaic effect in the angle range from –90o to 90o, its peak value and the polarity varied regularly with the angle of incidence of the 1.064-μ m pulsed Nd:YAG laser radiation onto the ZnO surface. Meanwhile, for each photovoltaic signal, its rising time reached ～2 ns with an open-circuit photovoltage of ～2 ns full width at half-maximum. This angle-sensitive fast photovoltaic effect is expected to put this composite film a candidate for angle-sensitive and fast photodetector.

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Study of depth-dependent tetragonal distortion of quaternary AlInGaN epilayer by Rutherford backscattering/channeling

G. Husnain, 陈田祥, 法涛, 姚淑德

2010 (8): 87205-087205. doi: 10.1088/1674-1056/19/8/087205

摘要 ( 1550 )

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A 240-nm thick Al_0.4In_0.02Ga_0.58N layer is grown by metal organic chemical vapour deposition, with an over 1-μ m thick GaN layer used as a buffer layer on a substrate of sapphire (0001). Rutherford backscattering and channeling are used to characterize the microstructure of AlInGaN. The results show a good crystalline quality of AlInGaN (χ_min=1.5%) with GaN buffer layer. The channeling angular scan around an off-normal <12^{-13> axis in the {101^-0} plane of the AlInGaN layer is used to determine tetragonal distortion e_T, which is caused by the elastic strain in the AlInGaN. The resulting AlInGaN is subjected to an elastic strain at interfacial layer, and the strain decreases gradually towards the near-surface layer. It is expected that an epitaxial AlInGaN thin film with a thickness of 850 nm will be fully relaxed (e_T = 0).}

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The study of amorphous incubation layers during the growth of microcrystalline silicon films under different deposition conditions

陈永生, 徐艳华, 谷锦华, 卢景霄, 杨仕娥, 郜小勇

2010 (8): 87206-087206. doi: 10.1088/1674-1056/19/8/087206

摘要 ( 1769 )

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The structural un-uniformity of μc-Si:H films prepared using a very high frequency plasma-enhanced chemical vapour deposition method has been investigated by Raman spectroscopy, spectroscopic ellipsometer and atomic force microscopy. It was found that the formation of amorphous incubation layer was caused by the back diffusion of SiH₄ and the amorphous induction of glass surface during the initial ignition process, and growth of the incubation layer can be suppressed and uniform μc-Si:H phase is generated by the application of delayed initial SiH₄ density and silane profiling methods.

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The Sr content influence on the positive magnetoresistance in La_1-xSr_xMnO₃/Si heterojunctions

杨芳, 金奎娟, 黄延红, 何萌, 吕惠宾, 杨国桢

2010 (8): 87301-087301. doi: 10.1088/1674-1056/19/8/087301

摘要 ( 1788 )

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We fabricated La_1-xSr_xMnO₃/Si (LSMO/Si) heterojunctions with different Sr doping concentrations (x = 0.1, 0.2, 0.3) in LSMO and studied the Sr content influence on magnetoresistance (MR) ratio. The heterojunctions show positive MR and high sensitivity of MR ratio in a low applied magnetic field. The MR ratio is dependent on Sr content and the low Sr doping in LSMO causes a large positive MR in LSMO/Si junctions. The MR ratio for 0.1 Sr doping in the LSMO/Si heterostructure is 116% in 100 Oe (1 Oe=79.5775 A/m) at 210 K. The mechanism for the positive MR dependence on the doping density is considered to be the competition between the tunneling rate of electrons in e_g¹ ↑ to t_2g ↓ band and that to e_g² ↑ band at the interface region of LSMO. The experimental results are in agreement with those observed in La_0.9Sr_0.1MnO₃/SrNb_0.01Ti_0.99O₃ p-n junction. The results indicate that choosing low doping concentration to improve the low field sensitivity of the heterojunction deveces is a very efficacious method.

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Anisotropy of p-wave Josephson junction

王振彦, 沈瑞

2010 (8): 87401-087401. doi: 10.1088/1674-1056/19/8/087401

摘要 ( 1577 )

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The anisotropy of the dc Josephson current in the superconducting junctions of the p-wave equal spin pairing symmetry is theoretically investigated by the Furusaki–Tsukada-like formula. The current phase relations exhibit different oscillation periods and different phase shifts for the current along different directions, respectively.

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Tunneling spectra of underdoped Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ intrinsic Josephson junctions

袁涛, 王新强, 任建坤, 林德华, 田野, 任育峰, 赵士平

2010 (8): 87402-087402. doi: 10.1088/1674-1056/19/8/087402

摘要 ( 1623 )

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Project supported by the National Natural Science Foundation of China (Grant No. 10974242).

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Observation of lateral long range order in superconducting FeTe thin films

李位勇, 韩烨, 王焕华, 曹立新, 贾全杰, 陈雨, 姜晓明, 董成, 许波, 赵柏儒

2010 (8): 87403-087403. doi: 10.1088/1674-1056/19/8/087403

摘要 ( 1711 )

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We find that the superconductivity in the thin films of the formerly believed non-superconducting parent compound FeTe is accompanied by an emergence of second order with a correlation length of 742 nm and 258 nm at 10 K and 300 K, respectively. The structural phase transition found in iron pnictide superconductors, in non-superconducting FeTe bulk samples, and in FeSe superconducting thin films is not observed in the superconducting FeTe thin films. The interplay between superconductivity and long range order may suggest the crucial role of competition between electronic localization and itinerancy which leads to strong quantum fluctuations in the FeTe system.

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Method for fitting crystal field parameters and the energy level fitting for Yb³⁺ in crystal Sc₂O₃

张庆礼, 宁凯杰, 肖进, 丁丽华, 周文龙, 刘文鹏, 殷绍唐, 江海河

2010 (8): 87501-087501. doi: 10.1088/1674-1056/19/8/087501

摘要 ( 1448 )

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A method to compute the numerical derivative of eigenvalues of parameterized crystal field Hamiltonian matrix is given, based on the numerical derivatives the general iteration methods such as Levenberg–Marquardt, Newton method, and so on, can be used to solve crystal field parameters by fitting to experimental energy levels. With the numerical eigenvalue derivative, a detailed iteration algorithm to compute crystal field parameters by fitting experimental energy levels has also been described. This method is used to compute the crystal parameters of Yb³⁺ in Sc₂O₃ crystal, which is prepared by a co-precipitation method and whose structure was refined by Rietveld method. By fitting on the parameters of a simple overlap model of crystal field, the results show that the new method can fit the crystal field energy splitting with fast convergence and good stability.

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Micromagnetic simulation on the dynamic susceptibility spectra of cobalt nanowires arrays: the effect of magnetostatic interaction

陈文兵, 韩满贵, 周浩, 欧雨, 邓龙江

2010 (8): 87502-087502. doi: 10.1088/1674-1056/19/8/087502

摘要 ( 1594 )

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Micromagnetic simulations have been performed to obtain the dynamic susceptibility spectra of 4×4 cobalt nanowire arrays with different spatial configurations and geometries. The susceptibility spectra of isolated wires have also been simulated for comparison purposes. It is found that the susceptibility spectrum of nanowire array bears a lot of similarities to that of an isolated wire, such as the occurrences of the edge mode and the bulk resonance mode. The simulation results also reveal that the susceptibility spectrum of nanowire array behaves like that of single isolated wire as the interwire distance grows to an extent, which is believed due to the decrease of magnetostatic interaction among nanowires, and can be further confirmed by the static magnetic hysteresis simulations. In comparison with single nanowire, magnetostatic interaction may increase or decrease the resonance frequencies of nanowire arrays assuming a certain interwire distance when the length of array increases. Our simulation results are also analysed by employing the Kittel equation and recent theoretical studies.

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Lateral field excitation properties of langasite single crystal

马廷锋, 张超, 冯冠平, 江小宁

2010 (8): 87701-087701. doi: 10.1088/1674-1056/19/8/087701

摘要 ( 1587 )

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In this work, bulk acoustic wave propagation properties of langasite single crystal excited by lateral electric field have been investigated. Three important crystal cuts have been identified for different operational modes of lateral field excitation (LFE) on langasite substrate, namely the (yxl)65o (pure-LFE mode), (yxl)45o (quasi-LFE mode), and (yxl)0o (pseudo-LFE mode). Devices on langasite substrate with the above cuts were fabricated and tested, and the experimental results agree well with the theoretical analysis. It is found that a pure thickness shear mode exists in the (yxl)65o langasite LFE device with the bare side facing liquid, and no spurious mode is found due to its moderately large piezoelectric coupling factor. In addition, (yxl)0o langasite LFE device is also found suitable for liquid phase sensing applications.

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Influences of KrF laser irradiation on the structure and luminescence of ZnO single crystal

刘洁, 赵艳, 蒋毅坚, 刘玉龙

2010 (8): 87801-087801. doi: 10.1088/1674-1056/19/8/087801

摘要 ( 1616 )

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In this paper, we investigate the laser irradiation of ZnO single crystals and its influence on photoluminescence. Our study shows that the photoluminescence of ZnO single crystals strongly depends on surface morphologies. The ultraviolet emissions of laser treated-ZnO under 200 mJ/cm² become stronger, whereas for those deteriorated by irradiation above 200 mJ/cm², the green emissions centred at 2.53 eV are significantly enhanced with a red-shift to 2.19 eV, probably due to the changes in the charge states of the defects. Enhanced yellow-green emissions are well resolved into four peaks at around 1.98, 2.19, 2.36, and 2.53 eV due to a shallow irradiation depth. Possible origins are proposed and discussed.

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Scattering correction method for panel detector based cone beam computed tomography system

贾鹏翔, 张峰, 闫镔, 包尚联

2010 (8): 87802-087802. doi: 10.1088/1674-1056/19/8/087802

摘要 ( 1635 )

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A scattering correction method for a panel detector based cone beam computed tomography system is presented. First, the x-ray spectrum of the system is acquired by using the Monte Carlo simulation method. Secondly, scattered photon distribution is calculated and stored as correction matrixes by using the Monte Carlo simulation method according to scanned objects and computed tomography system specialties. Thirdly, scattered photons are removed from projection data by correction matrixes. A comparison of reconstruction image between before and after scattering correction demonstrates that the scattering correction method is effective for the panel detector based cone beam computed tomography system.

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Multi-wafer 3C–SiC heteroepitaxial growth on Si(100) substrates

孙国胜, 刘兴昉, 王雷, 赵万顺, 杨挺, 吴海雷, 闫果果, 赵永梅, 宁瑾, 曾一平, 李晋闽

2010 (8): 88101-088101. doi: 10.1088/1674-1056/19/8/088101

摘要 ( 1396 )

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Epitaxial growth of semiconductor films in multiple-wafer mode is under vigorous development in order to improve yield output to meet the industry increasing demands. Here we report on results of the heteroepitaxial growth of multi-wafer 3C–SiC films on Si(100) substrates by employing a home-made horizontal hot wall low pressure chemical vapour deposition (HWLPCVD) system which was designed to be have a high-throughput, multi-wafer (3×2-inch) capacity. 3C–SiC film properties of the intra-wafer and the wafer-to-wafer including crystalline morphologies, structures and electronics are characterized systematically. The undoped and the moderate NH₃ doped n-type 3C–SiC films with specular surface are grown in the HWLPCVD, thereafter uniformities of intra-wafer thickness and sheet resistance of the 3C–SiC films are obtained to be 6%～7% and 6.7%～8%, respectively, and within a run, the deviations of wafer-to-wafer thickness and sheet resistance are less than 1% and 0.8%, respectively.

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Impact of symmetrized and Burt–Foreman Hamiltonians on spurious solutions and energy levels of InAs/GaAs quantum dots

谷永先, 杨涛, 季海铭, 徐鹏飞, 王占国

2010 (8): 88102-088102. doi: 10.1088/1674-1056/19/8/088102

摘要 ( 1525 )

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We present a systematic investigation of calculating quantum dots (QDs) energy levels using the finite element method in the frame of the eight-band bm kcdot bm p method. Numerical results including piezoelectricity, electron and hole levels, as well as wave functions are achieved. In the calculation of energy levels, we do observe spurious solutions (SSs) no matter Burt–Foreman or symmetrized Hamiltonians are used. Different theories are used to analyse the SSs, we find that the ellipticity theory can give a better explanation for the origin of SSs and symmetrized Hamiltonian is easier to lead to SSs. The energy levels simulated with the two Hamiltonians are compared to each other after eliminating SSs, different Hamiltonians cause a larger difference on electron energy levels than that on hole energy levels and this difference decreases with the increase of QD size.

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Magnetic properties of DNA-templated Co/Cu naonoparticle chains

高有辉, 卫玲, 高春蕾, 夏卫星, 進藤大輔

2010 (8): 88103-088103. doi: 10.1088/1674-1056/19/8/088103

摘要 ( 1598 )

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According to ultraviolet (UV)-vis absorption spectra recorded in the DNA metallization process, DNA-templated Co/Cu binary nanoparticle chains are fabricated by incubating genome DNA of paralichthys olivaceus muscle in CoCl₂ and CuCl₂ mixture solution for 20 hours and reducing the complex for 2 hours. Transmission electron microscopy observation indicates that Co and Cu nanoparticles with 20 nm in diameter were randomly dispersed on the DNA template. The superconducting quantum interference device (SQUID) measurements display that the magnetic interaction between cobalt particles is greatly decreased by the copper particle. With increasing copper content, the coercivity of the systems enhance from 9 Oe to 100 Oe (1 Oe=79.5775 A/13).

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A general surface-treatment-free approach to fabrication of alignment layers using a super-aligned carbon nanotube film template

付伟琦, 魏洋, 朱峰, 刘亮, 李群庆, 范守善

2010 (8): 88104-088104. doi: 10.1088/1674-1056/19/8/088104

摘要 ( 1335 )

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We develop a general approach to the fabrication of films with unidirectional grooves, such as silicon nitride, silicon dioxide and aluminium oxide, in which the surface is not required to be treated. Super-aligned carbon nanotube (SACNT) film may be used as a template and as sacrificial layer, which is subsequently removed by heating in an atmosphere of air. The unidirectional morphology of the SACNT film turns into a desired film, which is found to possess the ability to align liquid crystal molecules. This approach also features high efficiency, low cost and easy scaling-up for mass production.

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Electrical resistance response of polyaniline films to water, ethanol, and nitric acid solution

尹红星, 李蒙蒙, 杨贺, 龙云泽

2010 (8): 88105-088105. doi: 10.1088/1674-1056/19/8/088105

摘要 ( 1474 )

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This paper reports on electrical resistance vs. aging time for the response of polyaniline films under exposure to water, ethanol and nitric acid (HNO₃) solution. Camphor sulfonic acid-doped polyaniline films were prepared by a "doping-dedoping-redoping" method, the morphology and microstructures of the films were characterized by a scanning electron microscope and an x-ray diffractometer, the electrical resistance was measured by a four-probe method. It was found that a lower amount of water molecules infiltrating the film can decrease the film's resistance possibly due to an enhancement of charge carrier transfer between polyaniline chains, whereas excessive water molecules can swell inter-chain distances and result in a quick increase of resistance. The resistance of the film under exposure to ethanol increases and becomes much larger than the original value. However, HNO₃ solution can decrease the film's resistance sharply possibly owing to doping effect of protonic acid. These results can help to understand the conduction mechanism in polyaniline films, and also indicate that the films have potential application in chemical sensors.

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An algorithm for computed tomography image reconstruction from limited-view projections

王林元, 李磊, 闫镔, 江成顺, 王浩宇, 包尚联

2010 (8): 88106-088106. doi: 10.1088/1674-1056/19/8/088106

摘要 ( 1512 )

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With the development of the compressive sensing theory, the image reconstruction from the projections viewed in limited angles is one of the hot problems in the research of computed tomography technology. This paper develops an iterative algorithm for image reconstruction, which can fit most cases. This method gives an image reconstruction flow with the difference image vector, which is based on the concept that the difference image vector between the reconstructed and the reference image is sparse enough. Then the l₁-norm minimization method is used to reconstruct the difference vector to recover the image for flat subjects in limited angles. The algorithm has been tested with a thin planar phantom and a real object in limited-view projection data. Moreover, all the studies showed the satisfactory results in accuracy at a rather high reconstruction speed.

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Effect of electrolyte concentration on DNA A–B conformational transition：An unrestrained molecular dynamics simulation study

藤本晋太郎, 于养信

2010 (8): 88701-088701. doi: 10.1088/1674-1056/19/8/088701

摘要 ( 1523 )

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The DNA conformational transition depends on both the DNA sequences and environment such as solvent as well as electrolyte in the solution. This paper uses the AMBER8 package to investigate the electrolyte concentration influence on the dynamics of the A→B conformational transition of DNA duplex d(CGCGAATTCGCG)₂. The results from the restrained molecular dynamics (MD) simulations indicate that the total energies of the systems for A--DNA are always higher than those for B--DNA, and that the A→B conformational transition in aqueous NaCl solution is a downhill process. The results from the unrestrained MD simulations, as judged by the average distance between the C5' atoms (average helical rise per ten base pair), show that the concentrated NaCl solution slows down the A→B conformational transition. This observation can be well understood by analyses of the difference between the counterion distributions around A--DNA and B--DNA.

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Propagation of cylindrical vector beams in a turbulent atmosphere

蒲继雄, 王涛, 林惠川, 李成良

2010 (8): 89201-089201. doi: 10.1088/1674-1056/19/8/089201

摘要 ( 1820 )

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Based on the extended Huygens–Fresnel principle, the propagation of cylindrical vector beams in a turbulent atmosphere is investigated. The intensity distribution and the polarization degree of beams on propagation are studied. It is found that the beam profile has a Gaussian shape under the influence of the atmospheric turbulence, and the polarization distribution shows a dip in the cross section as the beam propagates in the turbulent atmosphere. It is also found that the beam profile and the polarization distribution are closely related to beam parameter and atmospheric turbulence.

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