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CN 11-5639/O4
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  • Experimental demonstration of passive decoy state quantum key distribution

    Zhang Yang, Wang Shuang, Yin Zhen-Qiang, Chen Wei, Liang Wen-Ye, Li Hong-Wei, Guo Guang-Can, Han Zheng-Fu
    Chin. Phys. B 2012, 21 (10): 100307
    Passive decoy state quantum key distribution (PDS-QKD) has advantages in high-speed scenarios. We propose a modified model to simulate the PDS-QKD with a weak coherent light source based on Curty's theory [Opt. Lett.34 3238 (2009)]. The modified model can provide better performance in a practical PD...

  • Synthesis and thermoelectric properties of Mn-doped AgSbTe2 compounds

    Zhang He, Luo Jun, Zhu Hang-Tian, Liu Quan-Lin, Liang Jing-Kui, Li Jing-Bo, Liu Guang-Yao
    Chin. Phys. B 2012, 21 (10): 106101
    Polycrystalline p-type Ag0.9Sb1.1-xMnxTe2.05(x=0.05, 0.10, and 0.20) compounds have been prepared by a combined process of melt-quenching and spark plasma sintering. The sample composition of Ag0.9Sb1.1-xMnxTe2.05 has been specially designed in order to achieve the doping effect by replacing part of...

  • Influence of the Jahn–Teller distortion on magnetic ordering in TbMn1-xFexO3

    Jin Jin-Ling, Zhang Xiang-Qun, Li Guo-Ke, Cheng Zhao-Hua
    Chin. Phys. B 2012, 21 (10): 107501
    The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites. In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3 (x=0, 0.02, 0.05, 0.10, and 0.20) single crystals in the basal MnO2 plane....

Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.10
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Simulation of the relationship between porosity and tortuosity in porous media with cubic particles

Tang Xiao-Wu, Sun Zu-Feng, Cheng Guan-Chu
Chin. Phys. B, 2012, 21 (10): 100201 doi: 10.1088/1674-1056/21/10/100201
Full Text: [PDF 767 KB] (Downloads:1268)
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Tortuosity is an important parameter used in areas such as vascular medicine, neurobiology, and the field of soil permeability and diffusion to express the mass transport in porous media. It is a function of the porosity and the shape and distribution of particles. In this paper, the tortuosity of cubic particles is calculated. With the assumption that the porous medium is homogeneous, the problem is converted to the micro-level over a unit cell, and geometry models of flow paths are proposed. In three-dimensional (3D) cells, the flow paths are too complicated to define. Hence, the 3D models are converted to two-dimensional (2D) models to simplify the calculation process. It is noticed that the path in the 2D model is shorter than that in the 3D model. As a result, triangular particles and the interaction are also taken into consideration to account for the longer distance respectively. We have proposed quadrate particle and interaction (QI) and quadrate and triangular particle (QT) models with cubic particles. Both models have shown good agreement with the experimental data. It is also found that they can predict the toruosities of some kinds of porous media, like freshwater sediment and Negev chalk.

Hamilton formalism and Noether symmetry for mechanico–electrical systems with fractional derivatives

Zhang Shi-Hua, Chen Ben-Yong, Fu Jing-Li
Chin. Phys. B, 2012, 21 (10): 100202 doi: 10.1088/1674-1056/21/10/100202
Full Text: [PDF 112 KB] (Downloads:734)
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This paper presents extensions to the traditional calculus of variations for mechanico-electrical systems containing fractional derivatives. The Euler-Lagrange equations and the Hamilton formalism of the mechanico-electrical systems with fractional derivatives are established. The definition and the criteria for the fractional generalized Noether quasi-symmetry are presented. Furthermore, the fractional Noether theorem and conseved quantities of the systems are obtained by virtue of the invariance of the Hamiltonian action under the infinitesimal transformations. An example is presented to illustrate the application of the results.

Mei symmetry and Mei conserved quantity of Appell equations for a variable mass holonomic system of relative motion

Zhang Mei-Ling, Wang Xiao-Xiao, Han Yue-Lin, Jia Li-Qun
Chin. Phys. B, 2012, 21 (10): 100203 doi: 10.1088/1674-1056/21/10/100203
Full Text: [PDF 94 KB] (Downloads:536)
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Mei symmetry and Mei conserved quantity of Appell equations for a variable mass holonomic system of relative motion are studied. The definition and criterion of the Mei symmetry of Appell equations for a variable mass holonomic system of relative motion under the infinitesimal transformations of groups are given. The structural equation of Mei symmetry of Appell equations and the expression of Mei conserved quantity deduced directly from Mei symmetry for a variable mass holonomic system of relative motion are gained. Finally, an example is given to illustrate the application of the results.

Nonlinear integrable couplings of a nonlinear Schrödinger–modified Korteweg de Vries hierarchy with self-consistent sources

Yang Hong-Wei, Dong Huan-He, Yin Bao-Shu
Chin. Phys. B, 2012, 21 (10): 100204 doi: 10.1088/1674-1056/21/10/100204
Full Text: [PDF 105 KB] (Downloads:507)
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By means of the Lie algebra B2, a new extended Lie algebra F is constructed. Based on the Lie algebras B2 and F, the nonlinear Schrödinger-modified Korteweg de Vries (NLS-mKdV) hierarchy with self-consistent sources as well as its nonlinear integrable couplings are derived. With the help of the variational identity, their Hamiltonian structures are generated.

State estimation for neural neutral-type networks with mixed time-varying delays and Markovian jumping parameters

S. Lakshmanan, Ju H. Park, H. Y. Jung, P. Balasubramaniam
Chin. Phys. B, 2012, 21 (10): 100205 doi: 10.1088/1674-1056/21/10/100205
Full Text: [PDF 133 KB] (Downloads:690)
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This paper is concerned with a delay-dependent state estimator for neutral-type neural networks with mixed time-varying delays and Markovian jumping parameters. The addressed neural networks have a finite number of modes, and the modes may jump from one to another according to a Markov process. By construction of a suitable Lyapunov-Krasovskii functional, a delay-dependent condition is developed to estimate the neuron states through available output measurements such that the estimation error system is globally asymptotically stable in a mean square. The criterion is formulated in terms of a set of linear matrix inequalities (LMIs), which can be checked efficiently by use of some standard numerical packages.

Analytical investigation of the boundary-triggered phase transition dynamics in a cellular automata model with a slow-to-start rule

Jia Ning, Ma Shou-Feng, Zhong Shi-Quan
Chin. Phys. B, 2012, 21 (10): 100206 doi: 10.1088/1674-1056/21/10/100206
Full Text: [PDF 2381 KB] (Downloads:815)
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Previous studies suggest that there are three different jam phases in the cellular automata automaton model with a slow-to-start rule under open boundaries. In the present paper, the dynamics of each free-flow-jam phase transition is studied. By analysing the microscopic behaviour of the traffic flow, we obtain analytical results on the phase transition dynamics. Our results can describe the detailed time evolution of the system during phase transition, while they provide good approximation for the numerical simulation data. These findings can perfectly explain the microscopic mechanism and details of the boundary-triggered phase transition dynamics.

Epidemic spreading on a scale-free network with awareness

Lu Yan-Ling, Jiang Guo-Ping, Song Yu-Rong
Chin. Phys. B, 2012, 21 (10): 100207 doi: 10.1088/1674-1056/21/10/100207
Full Text: [PDF 182 KB] (Downloads:949)
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This paper presents a modified susceptible-infected-recovered (SIR) model with the effects of awareness and vaccination to study the epidemic spreading on scale-free networks based on the mean-field theory. In this model, when susceptible individuals receive awareness from their infected neighbor nodes, they will take vaccination measures. The theoretical analysis and the numerical simulations show that the existence of awareness and vaccination can significantly improve the epidemic threshold and reduce the risk of virus outbreaks. In addition, regardless of the existence of vaccination, the awareness can increase the spreading threshold and slow the spreading speed effectively. For a given awareness and a certain spreading rate, the total number of infections reduces with the increasing vaccination rate.

The complex variable meshless local Petrov–Galerkin method of solving two-dimensional potential problems

Yang Xiu-Li, Dai Bao-Dong, Zhang Wei-Wei
Chin. Phys. B, 2012, 21 (10): 100208 doi: 10.1088/1674-1056/21/10/100208
Full Text: [PDF 211 KB] (Downloads:610)
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Based on the complex variable moving least-square (CVMLS) approximation and a local symmetric weak form, the complex variable meshless local Petrov-Galerkin (CVMLPG) method of solving two-dimensional potential problems is presented in this paper. In the present formulation, the trial function of a two-dimensional problem is formed with a one-dimensional basis function. The number of unknown coefficients in the trial function of the CVMLS approximation is less than that in the trial function of the moving least-square (MLS) approximation. The essential boundary conditions are imposed by the penalty method. The main advantage of this approach over the conventional meshless local Petrov-Galerkin (MLPG) method is its computational efficiency. Several numerical examples are presented to illustrate the implementation and performance of the present CVMLPG method.

Analysis of the equal width wave equation with the mesh-free reproducing kernel particle Ritz method

Cheng Rong-Jun, Ge Hong-Xia
Chin. Phys. B, 2012, 21 (10): 100209 doi: 10.1088/1674-1056/21/10/100209
Full Text: [PDF 148 KB] (Downloads:706)
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In this paper, we analyse the equal width (EW) wave equation by using the mesh-free reproducing kernel particle Ritz (kp-Ritz) method. The mesh-free kernel particle estimate is employed to approximate the displacement field. A system of discrete equations is obtained through the application of the Ritz minimization procedure to the energy expressions. The effectiveness of the kp-Ritz method for the EW wave equation is investigated by numerical examples in this paper.

A realizable multi-bit dense coding scheme with an Einstein–Podolsky–Rosen channel

Guo Qi, Cheng Liu-Yong, Wang Hong-Fu, Zhang Shou, Yeon Kyu-Hwang
Chin. Phys. B, 2012, 21 (10): 100301 doi: 10.1088/1674-1056/21/10/100301
Full Text: [PDF 111 KB] (Downloads:543)
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We propose a multi-bit dense coding scheme by using only an Einstein-Podolsky-Rosen (EPR) channel and assistant qubits. It is shown that no matter how many classical bits there are, the quantum channel is always a Bell state. The present dense coding process can also prepare non-local multi-particle Greenberger-Horne-Zeilinger (GHZ) states at one of the participants. The quantum circuits for this dense coding process are constructed, the deterministic implementation method in an optical system based on the cross-Kerr nonlinearities is shown.

The Fresnel–Weyl complementary transformation

Xie Chuan-Mei, Fan Hong-Yi
Chin. Phys. B, 2012, 21 (10): 100302 doi: 10.1088/1674-1056/21/10/100302
Full Text: [PDF 85 KB] (Downloads:464)
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Based on the newly developed coherent-entangled state representation, we propose the so-called Fresnel-Weyl complementary transformation operator. The new operator plays the roles of both Fresnel transformation (for (a1-a2)√2 and the Weyl transformation (for (a1+a2)√2. Physically, (a1-a2)√2 and (a1+a2)√2 could be a symmetric beamsplitter's two output fields for the incoming fields a1 and a2. We show that the two transformations are concisely expressed in the coherent-entangled state representation as a projective operator in the integration form.

The rotating Morse potential energy eigenvalues solved by using the analytical transfer matrix method

He Ying, Tao Qiu-Gong, Yang Yan-Fang
Chin. Phys. B, 2012, 21 (10): 100303 doi: 10.1088/1674-1056/21/10/100303
Full Text: [PDF 152 KB] (Downloads:1137)
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We study the eigenvalues of the rotating Morse potential by using the quantization condition from the analytical transfer matrix (ATM) method. A hierarchy of supersymmetric partner potentials is obtained with Pekeris approximation, which can be used to calculate the energies of higher rotational states from the energies of lower states. The energies of rotational states of the hydrogen molecule are calculated by the ATM condition, and comparison of the results with those from the hypervirial perturbation method reveals that the accuracy of the approximate expression of Pekeris for the eigenvalues of the rotating Morse potential can be improved substantially in the framework of supersymmetric quantum mechanics.

Decoherence from a spin chain with Dzyaloshinskii–Moriya interaction

Yan Yi-Ying, Qin Li-Guo, Tian Li-Jun
Chin. Phys. B, 2012, 21 (10): 100304 doi: 10.1088/1674-1056/21/10/100304
Full Text: [PDF 599 KB] (Downloads:685)
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We study the dynamics of quantum discord and entanglement for two spin qubits coupled to a spin chain with Dzyaloshinsky-Moriya interaction. In the case of a two-qubit with an initial pure state, quantum correlations decay to zero at the critical point of the environment in a very short time. In the case of a two-qubit with initial mixed state, it is found that quantum discord may get maximized due to the quantum critical behavior of the environment, while entanglement vanishes under the same condition. Besides, we observed a sudden transition between classical and quantum decoherence when only a single qubit interacts with the environment. The effects of Dzyaloshinsky-Moriya interaction on quantum correlations are considered in the two cases. The decay of quantum correlations is always strengthened by Dzyaloshinsky-Moriya interaction.

A new bipartite entangled state describing the parametric down-conversion process and its applications in quantum optics

Meng Xiang-Guo, Wang Ji-Suo, Zhang Xiao-Yan
Chin. Phys. B, 2012, 21 (10): 100305 doi: 10.1088/1674-1056/21/10/100305
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We construct a new bipartite entangled state (NBES), which describes both the squeezing and the entanglement involved in the parametric down-conversion process and can be produced using a symmetric beam splitter. Constructing asymmetric ket-bra integrations based on the NBES leads to some new squeezing operators, which clearly exhibit the relationships between squeezing and entangled state transformations. Moreover, an entangled Wigner operator with a definite physical meaning is also presented.

Improved frequency standard via weighted graph states

Xue Peng
Chin. Phys. B, 2012, 21 (10): 100306 doi: 10.1088/1674-1056/21/10/100306
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We study the spin squeezing property of weighted graph states, which can be used to improve sensitivity in interferometry. We study the time evolution of spin squeezing under local decoherence acting independently on each qubit. Based on the analysis, the spin squeezing of the weighted graph states is somehow robust in the presence of decoherence and the decoherence limit in the improvement of the interferometric sensitivity is still achievable. Furthermore, one can obtain the optimal improvement of sensitivity by tuning the weighted of each edges of the weighted graph state.

Experimental demonstration of passive decoy state quantum key distribution Hot!

Zhang Yang, Wang Shuang, Yin Zhen-Qiang, Chen Wei, Liang Wen-Ye, Li Hong-Wei, Guo Guang-Can, Han Zheng-Fu
Chin. Phys. B, 2012, 21 (10): 100307 doi: 10.1088/1674-1056/21/10/100307
Full Text: [PDF 1477 KB] (Downloads:671)
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Passive decoy state quantum key distribution (PDS-QKD) has advantages in high-speed scenarios. We propose a modified model to simulate the PDS-QKD with a weak coherent light source based on Curty's theory [Opt. Lett.34 3238 (2009)]. The modified model can provide better performance in a practical PDS-QKD system. Moreover, we report an experimental demonstration of the PDS-QKD of over 22.0-dB channel loss.

Fault tolerant quantum secure direct communication with quantum encryption against collective noise

Huang Wei, Wen Qiao-Yan, Jia Heng-Yue, Qin Su-Juan, Gao Fei
Chin. Phys. B, 2012, 21 (10): 100308 doi: 10.1088/1674-1056/21/10/100308
Full Text: [PDF 117 KB] (Downloads:726)
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We present two novel quantum secure direct communication (QSDC) protocols over different collective-noise channels. Different from the previous QSDC schemes over collective-noise channels, which are all source-encrypting protocols, our two protocols are based on channel-encryption. In both schemes, two authorized users first share a sequence of EPR pairs as their reusable quantum key. Then they use their quantum key to encrypt and decrypt the secret message carried by the decoherence-free states over the collective-noise channel. In theory, the intrinsic efficiencies of both protocols are high since there is no need to consume any entangled states including both the quantum key and the information carriers except the ones used for eavesdropping checks. For checking eavesdropping, the two parties only need to perform two-particle measurements on the decoy states during each round. Finally, we make a security analysis of our two protocols and demonstrate that they are secure.

Iterative quantum algorithm for distributed clock synchronization

Wang Hong-Fu, Zhang Shou
Chin. Phys. B, 2012, 21 (10): 100309 doi: 10.1088/1674-1056/21/10/100309
Full Text: [PDF 413 KB] (Downloads:741)
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Clock synchronization is a well-studied problem with many practical and scientific applications. We propose an arbitrary accuracy iterative quantum algorithm for distributed clock synchronization using only three qubits. The n bits of the time difference Δ between two spatially separated clocks can be deterministically extracted by communicating only O(n) messages and executing the quantum iteration process n times based on the classical feedback and measurement operations. Finally, we also give the algorithm using only two qubits and discuss the success probability of the algorithm.

Control of purity and entanglement for two spatially two-separated qubits via phase damping

A. S. F. Obada, H. A. Hessian, A. B. A. Mohamed, M. Hashem
Chin. Phys. B, 2012, 21 (10): 100310 doi: 10.1088/1674-1056/21/10/100310
Full Text: [PDF 466 KB] (Downloads:1037)
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Control of purity and entanglement of two two-qubits dispersively coupled to a field with a reservoir are investigated. Initially the qubits are entangled, while the field is either in a coherent state or a statistical mixture of two coherent states. For an alternative entanglement measure we calculate the negativity of the eigenvalues of the partially transposed density matrix. A measure related to the mutual entropy, namely the index of entropy, is employed to measure the entanglement. Its results agree well with the negativity. It is found that the entanglement and purity have strong sensitivity to phase damping. The asymptotic behaviour of the states of the field, the two two-qubits, and the total system fall into mixed states.

Cosmological application on five-dimensional teleparallel theory equivalent to general relativity

Gamal G. L. Nashed
Chin. Phys. B, 2012, 21 (10): 100401 doi: 10.1088/1674-1056/21/10/100401
Full Text: [PDF 382 KB] (Downloads:512)
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A theory of (4+1)-dimensional gravity has been developed on the basis of which equivalent to the theory of general relativity by teleparallel. The fundamental gravitational field variables are the 5-dimensional (5D) vector fields (pentad), defined globally on a manifold M, and gravity is attributed to the torsion. The Lagrangian density is quadratic in the torsion tensor. We then apply the field equations to two different homogenous and isotropic geometric structures which give the same line element, i.e., FRW in five dimensions. The cosmological parameters are calculated and some cosmological problems are discussed.

Dynamical behaviors of a system with switches between the Rössler oscillator and Chua circuits

Zhang Chun, Yu Yue, Han Xiu-Jing, Bi Qin-Sheng
Chin. Phys. B, 2012, 21 (10): 100501 doi: 10.1088/1674-1056/21/10/100501
Full Text: [PDF 4811 KB] (Downloads:688)
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The behaviors of a system that alternates between the Rössler oscillator and Chua's circuit is investigated to explore the influence of the switches on the dynamical evolution. Switches related to the state variables are introduced, upon which a typical switching dynamical model is established. Bifurcation sets of the subsystems are derived via analysis of the related equilibrium points, which divide the parameters into several regions corresponding to different types of attractors. The dynamics behave typically in period orbits with the variation of the parameters. The focus/cycle periodic switching phenomenon is explored in detail to present the mechanism of the movement. The period-doubling bifurcation to chaos can be observed via the doubling increase of the turning points related to the switches. Furthermore, period-decreasing sequences have been obtained, which can be explained by the variation of the eigenvalues associated with the equilibrium points of the subsystems.

Chaotic behavior learning of Chua's circuit

Sun Jian-Cheng
Chin. Phys. B, 2012, 21 (10): 100502 doi: 10.1088/1674-1056/21/10/100502
Full Text: [PDF 802 KB] (Downloads:811)
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Least-square support vector machines (LS-SVM) are applied for learning the chaotic behavior of Chua's circuit. The system is divided into three multiple-input single-output (MISO) structures and the LS-SVM are trained individually. Comparing with classical approaches, the proposed one reduces the structural complexity and the selection of parameters is avoided. Some parameters of the attractor are used to compare the chaotic behavior of the reconstructed and the original systems for model validation. Results show that the LS-SVM combined with the MISO can be trained to identify the underlying link among Chua's circuit state variables, and exhibit the chaotic attractors under the autonomous working mode.

Symmetry breaking in the opinion dynamics of a multi-group project organization

Zhu Zhen-Tao, Zhou Jing, Li Ping, Chen Xing-Guang
Chin. Phys. B, 2012, 21 (10): 100503 doi: 10.1088/1674-1056/21/10/100503
Full Text: [PDF 260 KB] (Downloads:632)
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A bounded confidence model of opinion dynamics in multi-group projects is presented in which each group's opinion evolution is driven by two types of forces: (i) the group's cohesive force which tends to restore the opinion back towards the initial status because of its company culture; and (ii) nonlinear coupling forces with other groups which attempt to bring opinions closer due to collaboration willingness. Bifurcation analysis for the case of a two-group project shows a cusp catastrophe phenomenon and three distinctive evolutionary regimes, i.e., a deadlock regime, a convergence regime, and a bifurcation regime in opinion dynamics. The critical value of initial discord between the two groups is derived to discriminate which regime the opinion evolution belongs to. In the case of a three-group project with a symmetric social network, both bifurcation analysis and simulation results demonstrate that if each pair has a high initial discord, instead of symmetrically converging to consensus with the increase of coupling scale as expected by Gabbay's result (Physica A 378 (2007) p. 125 Fig. 5), project organization (PO) may be split into two distinct clusters because of the symmetry breaking phenomenon caused by pitchfork bifurcations, which urges that apart from divergence in participants' interests, nonlinear interaction can also make conflict inevitable in the PO. The effects of two asymmetric level parameters are tested in order to explore the ways of inducing dominant opinion in the whole PO. It is found that the strong influence imposed by a leader group with firm faith on the flexible and open minded follower groups can promote the formation of a positive dominant opinion in the PO.

Experimental investigation on chaos generation in erbium-doped fiber single-ring lasers

Chang Feng, Feng Yu-Ling, Yao Zhi-Hai, Fan Jian, Song Yuan-Chao, Zhao Yu-Zhu
Chin. Phys. B, 2012, 21 (10): 100504 doi: 10.1088/1674-1056/21/10/100504
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In this paper, the chaotic behaviors in an erbium-doped fiber (EDF) single-ring laser (EDFSRL) are investigated experimentally by using the loss modulation method. An electro-optic modulator (EOM) made of LiNbO3 crystal is added to the system. Thus, by changing the modulation voltage and the modulation frequency of the EOM, the freedom of the EDFSRL system is increased. The chaotic characteristics of the system are studied by observing the time series and the power spectra. The experimental results indicate that the erbium-doped fiber single-ring laser system can enter into chaos states through period-doubling bifurcation and intermittency routes.

Chaos in a fractional-order micro-electro-mechanical resonator and its suppression

Mohammad Pourmahmood Aghababa
Chin. Phys. B, 2012, 21 (10): 100505 doi: 10.1088/1674-1056/21/10/100505
Full Text: [PDF 466 KB] (Downloads:840)
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The present paper investigates the existence of chaos in a non-autonomous fractional-order micro-electro-mechanical resonator system (FOMEMRS). Using the maximal Lyapunov exponent criterion, we show that the FOMEMRS exhibits chaos. Strange attractors of the system are plotted to validate its chaotic behavior. Afterward, a novel fractional finite-time controller is introduced to suppress the chaos of the FOMEMRS with model uncertainties and external disturbances in a given finite time. Using the latest version of the fractional Lyapunov theory, the finite time stability and robustness of the proposed scheme are proved. Finally, we present some computer simulations to illustrate the usefulness and applicability of the proposed method.

Fractional-order permanent magnet synchronous motor and its adaptive chaotic control

Li Chun-Lai, Yu Si-Min, Luo Xiao-Shu
Chin. Phys. B, 2012, 21 (10): 100506 doi: 10.1088/1674-1056/21/10/100506
Full Text: [PDF 1272 KB] (Downloads:1226)
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In this paper we investigate the chaotic behaviors of the fractional-order permanent magnet synchronous motor (PMSM). The necessary condition for the existence of chaos in the fractional-order PMSM is deduced. And an adaptive-feedback controller is developed based on the stability theory for fractional systems. The presented control scheme, which contains only one single state variable, is simple and flexible, and it is suitable both for design and for implementation in practice. Simulation is carried out to verify that the obtained scheme is efficient and robust against external interference for controlling the fractional-order PMSM system.

Spatiotemporal chaos synchronization of an uncertain network based on sliding mode control

Lü Ling, Yu Miao, Wei Lin-Ling, Wei Lin-Ling, Li Yu-Shan
Chin. Phys. B, 2012, 21 (10): 100507 doi: 10.1088/1674-1056/21/10/100507
Full Text: [PDF 1034 KB] (Downloads:658)
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The sliding mode control method is used to study spatiotemporal chaos synchronization of an uncertain network. The method is extended from synchronization between two chaotic systems to the synchronization of complex network composed of N spatiotemporal chaotic systems. The sliding surface of the network and the control input are designed. Furthermore, the effectiveness of the method is analysed based on the stability theory. The Burgers equation with spatiotemporal chaos behavior is taken as an example to simulate the experiment. It is found that the synchronization performance of the network is very stable.

Novel stability criteria for fuzzy Hopfield neural networks based on an improved homogeneous matrix polynomials technique

Feng Yi-Fu, Zhang Qing-Ling, Feng De-Zhi
Chin. Phys. B, 2012, 21 (10): 100701 doi: 10.1088/1674-1056/21/10/100701
Full Text: [PDF 215 KB] (Downloads:588)
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The global stability problem of Takagi-Sugeno (T-S) fuzzy Hopfield neural networks (FHNNs) with time delays is investigated. Novel LMI-based stability criteria are obtained by using Lyapunov functional theory to guarantee the asymptotic stability of the FHNNs with less conservatism. Firstly, using both Finsler's lemma and an improved homogeneous matrix polynomial technique, and applying an affine parameter-dependent Lyapunov-Krasovskii functional, we obtain the convergent LMI-based stability criteria. Algebraic properties of the fuzzy membership functions in the unit simplex are considered in the process of stability analysis via the homogeneous matrix polynomials technique. Secondly, to further reduce the conservatism, a new right-hand-side slack variables introducing technique is also proposed in terms of LMIs, which is suitable to the homogeneous matrix polynomials setting. Finally, two illustrative examples are given to show the efficiency of the proposed approaches.

Improvement of fabrication and characterization methods for micromechanical disk resonators

Zhao Hui, Luo Wei, Zheng Hai-Yang, Yang Jin-Ling, Yang Fu-Hua
Chin. Phys. B, 2012, 21 (10): 100702 doi: 10.1088/1674-1056/21/10/100702
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In this paper we present a novel method to fabricate reliable micro-electro-mechanical system (MEMS) disk resonators with high yield and good performance. The key breakthrough in the fabrication process is a novel approach to effectively restraining electro-chemical corrosion of polycrystalline silicon (polysilicon) electrically coupled with noble metals of MEMS devices by hydrofluoric acid (HF)-based solutions. In addition, a measurement architecture based on a differential readout topology is demonstrated. The differential circuit proposed here can effectively suppress noise and feed-through current by common-mode rejection of the differential amplifier. This differential amplifier circuit configuration is also used to build up a notch filter. The preliminary result about the temperature dependence of the resonance frequency is discussed, and the device failure is analysed.

Effects of the structural order of canthaxanthin on the Raman scattering cross section in various solvents: A study by Raman spectroscopy and ab initio calculation

Wu Nan-Nan, Li Zuo-Wei, Liu Jing-Yao, Ou Yang Shun-Li
Chin. Phys. B, 2012, 21 (10): 103101 doi: 10.1088/1674-1056/21/10/103101
Full Text: [PDF 853 KB] (Downloads:673)
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In this work, we measure the Raman scattering cross sections (RSCSs) of the carbon-carbon (CC) stretching vibrational modes of canthaxanthin in benzene, acetone, n-heptane, cyclohexane, and m-xylene. It is found that the absolute RSCS of CC stretching mode of canthaxanthin reaches a value of 10-24 cm2·molecule-1·sr-1 at 8×10-5 M, which is 6 orders of magnitude larger than general RSCS (10-30 cm2·molecule-1·sr-1), and the RSCSs of canthaxanthin in various solvents are very different due to the hydrogen bond. A theoretical interpretation of the magnetic experimental results is given, which is introduced in a qualitative nonlinear model of coherent weakly damped electron-lattice vibration in the structural order of polyene chains. In addition, the optimal structure and the bond length alternation (BLA) parameter of canthaxanthin are calculated using quantum chemistry calculation (at the b3lyp/6-31g (d, p) level of theory). The theoretical calculations are in good agreement with the experimental results. Furthermore, the combination of Raman spectroscopy and the quantum chemistry calculation study would be a quite suitable method of studying the structures and the properties of the π -conjugated systems.

The 13-atom encapsulated gold cage clusters

Zhang Chuan-Hui, Cui Hang, Shen Jiang
Chin. Phys. B, 2012, 21 (10): 103102 doi: 10.1088/1674-1056/21/10/103102
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The structure and the magnetic moment of transition metal encapsulated in a Au12 cage cluster have been studied by using the density functional theory. The results show that all of the transition metal atoms (TMA) can embed into the Au12 cage and increase the stability of the clusters except Mn. Half of them have the Ih or Oh symmetry. The curves of binding energy have oscillation characteristics when the extra-nuclear electrons increase; the reason for this may be the interaction between parity changes of extra-nuclear electrons and Au atoms. The curves of highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap also have oscillation characteristics when the extra-nuclear electrons increase. The binding energies of many M@Au12 clusters are much larger than that of the pure Au13 cluster, while the gaps of some of them are less than that of Au13, so maybe Cr@Au12, Nb@Au12, and W@Au12 clusters are most stable in fact. For magnetic calculations, some clusters are quenched totally, but the Au13 cluster has the largest magnetic moment of 5 μ B. When the number of extra-nuclear electrons of the encapsulated TMA is even, the magnetic moment of relevant M@Au12 cluster is even, and so are the odd ones.

Variational-integral perturbation corrections of some lower excited states for hydrogen atoms in magnetic fields

Yuan Lin, Zhao Yun-Hui, Xu Jun, Zhou Ben-Hu, Hai Wen-Hua
Chin. Phys. B, 2012, 21 (10): 103103 doi: 10.1088/1674-1056/21/10/103103
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A variational-integral perturbation method (VIPM) is established by combining the variational perturbation with the integral perturbation. The first-order corrected wave functions are constructed, and the second-order energy corrections for the ground state and several lower excited states are calculated by applying the VIPM to the hydrogen atom in a strong uniform magnetic field. Our calculations demonstrated that the energy calculated by the VIPM only shows a negative value, which indicates that the VIPM method is more accurate than the other methods. Our study indicated that the VIPM can not only increase the accuracy of the results but also keep the convergence of the wave functions.

Vibrational spectra and intramolecular vibrational redistribution in methane and its isotopomers

Hou Xi-Wen, Wan Ming-Fang, Ma Zhong-Qi
Chin. Phys. B, 2012, 21 (10): 103301 doi: 10.1088/1674-1056/21/10/103301
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An improved U(2) algebraic model is introduced to study the stretching and bending vibrational spectra of methane and its isotopomers. The algebraic model with fewer parameters reproduces the experimental spectra with good precision. Moreover, the obtained parameters describe well the correct behavior of isotopic substitution. It is shown that the Fermi resonance leads to a very fast intramolecular vibrational redistribution among stretches and bends.

Dielectronic recombination and resonant transfer excitation processes for helium-like krypton

Hu Xiao-Li, Qu Yi-Zhi, Zhang Song-Bin, Zhang Yu
Chin. Phys. B, 2012, 21 (10): 103401 doi: 10.1088/1674-1056/21/10/103401
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The relativistic configuration interaction method is employed to calculate the dielectronic recombination (DR) cross sections of helium-like krypton via the 1s2lnl' (n=2,3,...,15) resonances. Then, the resonant transfer excitation (RTE) processes of Kr34+ colliding with H, He, H2, and CHx (x=0-4) targets are investigated under the impulse approximation. The needed Compton profiles of targets are obtained from the Hartree-Fock wave functions. The RTE cross sections are strongly dependent on DR resonant energies and strengths, and the electron momentum distributions of the target. For H2 and H targets, the ratio of their RTE cross sections changes from 1.85 for the 1s2l2l' to 1.88 for other resonances, which demonstrates the weak molecular effects on the Compton profiles of H2. For CHx (x=0-4) targets, the main contribution to the RTE cross section comes from the carbon atom since carbon carries 6 electrons; as the number of hydrogen increases in CHx, the RTE cross section almost increases by the same value, displaying the strong separate atom character for the hydrogen. However, further comparison of the individual orbital contributions of C(2p, 2s, 1s) and CH4(1t2, 2a1, 1a1) to the RTE cross sections shows that the molecular effects induce differences of about 25.1%, 19.9%, and 0.2% between 2p-1t2, 2s-2a1, and 1s-1a1 orbitals, respectively.

Atom-loss-induced quantum optical bi-stability switch

Wu Bao-Jun, Cui Fu-Cheng
Chin. Phys. B, 2012, 21 (10): 103701 doi: 10.1088/1674-1056/21/10/103701
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We investigate the nonlinear dynamics of a system composed of a cigar-shaped Bose-Einstein condensate and an optical cavity with the two sides coupled dispersively. By adopting discrete-mode approximation for the condensate, taking atom loss as a necessary part of the model to analyze the evolution of the system, while using trial and error method to find out steady states of the system as a reference, numerical simulation demonstrates that with a constant pump, atom loss will trigger a quantum optical bi-stability switch, which predicts a new interesting phenomenon for experiments to verify.

Finger capacitance of a terahertz photomixer in low-temperature-grown GaAs using the finite element method

Chen Long-Chao, Fan Wen-Hui
Chin. Phys. B, 2012, 21 (10): 104101 doi: 10.1088/1674-1056/21/10/104101
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Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method. For the frequently used electrode width (0.2 μm) and gap width (1.8 μm), the finger capacitance increases quasi-quadratically with the number of electrodes increasing. The quasi-quadratic dependence can be explained by a sequence of lumped capacitors connected in parallel. For a photomixer composed of 10 electrodes and 9 photoconductive gaps, the finger capacitance increases as the gap width increases at a small electrode width, and follows the reverse trend at a large electrode width. For a constant electrode width, the finger capacitance first decreases and then slightly increases as the gap broadens until the smallest finger capacitance is formed. We also investigate the finger capacitances at different electrode and gap configurations with the 8 μm ×8 μm photomixer commonly used in previous studies. These calculations lead to a better understanding of the finger capacitance affected by the finger parameters, and should lead to terahertz photomixer optimization.

Enhancement of Smith–Purcell radiation with surface-plasmon excitation

Zhang Ping, Zhang Ya-Xin, Zhou Jun, Liu Wei-Hao, Zhong Ren-Bin, Liu Sheng-Gang
Chin. Phys. B, 2012, 21 (10): 104102 doi: 10.1088/1674-1056/21/10/104102
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With the aid of a three-dimensional particle-in-cell code simulation, the enhancement of Smith-Purcell radiation with a surface-plasmon mode excited by a single electron bunch and by a premodulated electron beam is considered in the paper. In the simulation, the model is a grating covered by Ag film. The results demonstrate that when the surface-plasmon mode is excited by a single electron bunch, the maximum radiation occurs at an observation angle depending on the surface-plasmon frequency, and the radiation power can be enhanced more than ten times. And for pre-bunched electron beam excitation, when one of the harmonics of the bunching frequency is resonant with that of the surface-plasmon mode, the radiation power is twenty times more than that from a perfectly conducting grating excited by the same premodulated electron beam.

Linear theory of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam

Chen Ye, Zhao Ding, Liu Wen-Xin, Wang Yong, Wan Xiao-Sheng
Chin. Phys. B, 2012, 21 (10): 104103 doi: 10.1088/1674-1056/21/10/104103
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A three-dimensional model of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam for the beam-wave interaction is proposed. Based on this model, the hybrid-mode dispersion equation is derived with the Borgnis potential function by using the field-matching method. Its approximate solution is obtained under the assumption of a dilute electron beam. By using the Ansoft high frequency structural simulator (HFSS) code, the electromagnetic field distribution in the interaction structure is given. Through numerical calculations, the effects of beam thickness, beam and dielectric-layer gap distance, beam voltage, and current density on the resonant growth rate are analysed in detail.

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

S. Saviz, E. Lashani, Farzin M. Aghamir
Chin. Phys. B, 2012, 21 (10): 104104 doi: 10.1088/1674-1056/21/10/104104
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A theory for the two-stream free-electron laser (TSFEL) with a helical wiggler and an axial guide magnetic field is developed. In the analysis, the effects of self-fields are taken into account. An analysis of the two-stream steady-state electron trajectories is given by solving the equation of motion. Numerical calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of self-fields. The stability of the trajectories is studied numerically.

Optical nonlinearity measurement of 4-(N-methyl, N-hydroxyethl)amino, 4'-nitroazobenzene using a transmittance technique with a phase object (T-PO) with top-hat beams at 600-nm wavelength

Jin Xiao, Li Zhong-Guo, Zhang Xue-Ru, Yang Kun, Wang Yu-Xiao, Song Ying-Lin
Chin. Phys. B, 2012, 21 (10): 104201 doi: 10.1088/1674-1056/21/10/104201
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The transmittance technique with a phase object (T-PO), for measuring optical nonlinear coefficients is proposed with a top-hat beam. The sensitivity of the T-PO with a top-hat beam is a factor of 4 greater than that with a Gaussian beam. The validity of this method is verified by measuring the nonlinearity of a well-characterized liquid, CS2 at 532-nm wavelength. The ease of use of this method has been proved by measuring a new compound 4-(N-methyl, N-hydroxyethyl)amino, 4'-nitroazobenzene(ANAB) at 600-nm wavelength, indicating that this method can be extended to the measurement of optical nonlinearities in a wide-band spectrum.

Reconstructing a complex field from a series of its near-field diffraction patterns

Hong You-Li, Zhang Kai, Wang Zhi-Li, Zhu Zhong-Zhu, Zhao Xue-Jiao, Huang Wan-Xia, Yuan Qing-Xi, Zhu Pei-Ping, Wu Zi-Yu
Chin. Phys. B, 2012, 21 (10): 104202 doi: 10.1088/1674-1056/21/10/104202
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We propose a method for reconstructing a complex field from a series of its near-field diffraction patterns. This method is based on the paraxial Fresnel diffraction equation without making further approximations. Numerical simulations are presented showing that a complex field can even be reconstructed with moderate qualities from its two near-field diffraction patterns and almost exact reconstructions can be obtained when three or more diffraction patterns are used. We also show by numerical simulation that the correct diffraction distances can be recovered in case only coarsely measured values are available. This method may be applied to phase imaging of weak-absorption objects.

Dispersion compensation for an ultrathin metal film using LCD–CCD system

Dai Yu, Zhang Jian-Xu
Chin. Phys. B, 2012, 21 (10): 104203 doi: 10.1088/1674-1056/21/10/104203
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A dispersion compensation method is introduced to correct the distorted image passing through an ultrathin metal film. An LCD-CCD system is modeled by the back propagation network and used to evaluate the transmittance of the ultrathin metal film. Training samples for the network come from 729 images captured by shooting test patches, in which the RGB values are uniformity distributed between 0 and 255. The RGB value of the original image that will be distorted by the dispersion is first transformed by mapping from the LCD to the CCD, multiplied by the inverse matrix of the transmittance matrix, and finally transformed by mapping from the CCD to the LCD, then the corrected image is obtained. In order to verify the effectiveness of the proposed method, ultrathin aluminum films with different thicknesses are evaporated on glass substrates and laid between the CCD and LCD. Experimental results show that the proposed method compensates for the dispersion successfully.

Generation of a squeezed state at 1.55 μ with periodically poled LiNbO3

Liu Qin, Feng Jin-Xia, Li Hong, Jiao Yue-Chun, Zhang Kuan-Shou
Chin. Phys. B, 2012, 21 (10): 104204 doi: 10.1088/1674-1056/21/10/104204
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We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO3. Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm, the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained. This system is compatible with standard telecommunication optical fibers, and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.

Controlling group velocity in a superconductive quantum circuit

Qiu Tian-Hui, Yang Guo-Jian
Chin. Phys. B, 2012, 21 (10): 104205 doi: 10.1088/1674-1056/21/10/104205
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We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit (SQC) pumped by microwave fields, and the use of such a SQC function as an artificial Λ-type three-level atom. The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity, and the superluminal state is usually realized with a lower absorption. This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band.

Rotational motions of optically trapped microscopic particles by a vortex femtosecond laser

Ran Ling-Ling, Guo Zhong-Yi, Qu Shi-Liang
Chin. Phys. B, 2012, 21 (10): 104206 doi: 10.1088/1674-1056/21/10/104206
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The rotational motions of the optically trapped microscopic particles by the vortex femtosecond laser beam are investigated in this paper. Black particles can be trapped and rotated by a vortex femtosecond laser beam very effectively because the vortex beam carries orbital angular momentum due to the helical wave-front structure in assoication with the central phase singularity. Trapped black particles rotate in the vortex beam due to the absorption of the angular momentum transferred from the vortex beam. The rotating directions of the trapped particles can be modulated by reversing the topological charge of the optical vortex in the vortex femtosecond beam. And the rotating speeds of the trapped microscopic particles greatly depend on the topological charges of the vortex tweezer and the used pulse energies.

Modeling of resistance characteristics of a continuously-graded distributed Bragg reflector in a 980-nm vertical-cavity surface-emitting laser

Huang Meng, Wu Jian, Cui Huai-Yang, Qian Jian-Qiang, Ning Yong-Qiang
Chin. Phys. B, 2012, 21 (10): 104207 doi: 10.1088/1674-1056/21/10/104207
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The resistance characteristics of a continuously-graded distributed Bragg reflector (DBR) in a 980-nm vertical-cavity surface-emitting laser (VCSEL) are modeled in detail. The junction resistances between the layers of both the p- and n-DBR mirrors are analysed by combining the thermionic emission model and the finite difference method. In the meantime, the intrinsic resistance of the DBR material system is calculated to make a comparison with the junction resistance. The minimal values of series resistances of the graded p- and n-type DBR mirrors and the lateral temperature-dependent resistance variation are calculated and discussed. The result indicates the potential to optimize the design of the DBR reflectors of the 980-nm VCSELs.

A tunable corner-pumped Nd:YAG/YAG composite slab CW laser

Liu Huan, Gong Ma-Li
Chin. Phys. B, 2012, 21 (10): 104208 doi: 10.1088/1674-1056/21/10/104208
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A corner-pumped Nd:YAG/YAG composite slab continuous-wave laser operating at 1064 nm, 1074 nm, 1112 nm, 1116 nm, and 1123 nm simultaneously and a laser that is tunable at these wavelengths are reported for the first time. The maximum output power of the five-wavelength laser is 5.66 W with an optical-to-optical conversion efficiency of 11.3%. After a birefringent filter is inserted in the cavity, the five wavelengths can be separated successfully by rotating the filter. The maximum output powers of the 1064 nm, 1074 nm, 1112 nm, 1116 nm, and 1123 nm lasers are 1.51 W, 1.3 W, 1.27 W, 0.86 W, and 0.72 W, respectively.

Removing paint from a metal substrate using a flattened top laser

Shi Shu-Dong, Li Wei, Du Peng, Wang Meng, Song Feng, Liu Shu-Jing, Chen Nian-Jiang, Zhao Hong, Yang Wen-Shi
Chin. Phys. B, 2012, 21 (10): 104209 doi: 10.1088/1674-1056/21/10/104209
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In this paper, we investigate laser cleaning using a flattened top laser to remove paint coating from a metal substrate. Under the irradiation of a flattened top laser, the coating paint of the metal substrate can be removed efficiently by laser induced ablation, stress, and displacement force. The temperature distribution, stress, and displacement are calculated in the coating layer and substrate using finite element analysis. The effects of a Gaussian laser and a flattened top laser and the results of different diameters of laser spot are compared. The investigation shows that the flattened top laser can reduce the substrate damage and enhance the cleaning efficiency. This method meets the need of large area industrial cleaning applications by optimizing the flattened top laser parameters.

Optical properties of the two-port resonant tunneling filters in two-dimensional photonic crystal slabs

Ren Cheng, Cheng Li-Feng, Kang Feng, Gan Lin, Zhang Dao-Zhong, Li Zhi-Yuan
Chin. Phys. B, 2012, 21 (10): 104210 doi: 10.1088/1674-1056/21/10/104210
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We have designed and fabricated two types of two-port resonant tunneling filters with a triangular air-hole lattice in two-dimensional photonic crystal slabs. In order to improve the filtering efficiency, a feedback method is introduced by closing the waveguide. It is found that the relative position between the closed waveguide boundary and the resonator has an important impact on the dropping efficiency. Based on our analyses, two different types of filters are designed. The transmission spectra and scattering-light far-field patterns are measured, which agree well with theoretical prediction. In addition, the resonant filters are highly sensitive to the size of the resonant cavities, which are useful for practical applications.

Incident particle range dependence of radiation damage in a power bipolar junction transistor

Liu Chao-Ming, Li Xing-Ji, Geng Hong-Bin, Rui Er-Ming, Guo Li-Xin, Yang Jian-Qun
Chin. Phys. B, 2012, 21 (10): 104211 doi: 10.1088/1674-1056/21/10/104211
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The characteristic degradations in silicon NPN bipolar junction transistors (BJTs) of type 3DD155 are examined under the irradiations of 25-MeV carbon (C), 40-MeV silicon (Si), and 40-MeV chlorine (Cl) ions respectively. Different electrical parameters are measured in-situ during the exposure of heavy ions. The experimental data shows that the changes in the reciprocal of the gain variation (Δ (1/β )) of 3DD155 transistors irradiated respectively by 25-MeV C, 40-MeV Si, and 40-MeV Cl ions each present a nonlinear behaviour at a low fluence and a linear response at a high fluence. The Δ (1/β) of 3DD155 BJT irradiated by 25-MeV C ions is greatest at a given fluence, a little smaller when the device is irradiated by 40-MeV Si ions, and smallest in the case of the 40-MeV Cl ions irradiation. The measured and calculated results clearly show that the range of heavy ions in the base region of BJT affects the level of radiation damage.

Fabricating a reactive surface on the fibroin film by a room-temperature plasma jet array for biomolecule immobilization

Chen Guang-Liang, Zheng Xu, Lü Guo-Hua, Zhang Zhao-Xia, Sylvain Massey, Wilson Smith, Michael Tatoulian, Yang Si-Ze
Chin. Phys. B, 2012, 21 (10): 105201 doi: 10.1088/1674-1056/21/10/105201
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A simple dielectric barrier discharge (DBD) jet array was designed with a liquid electrode and helium gas. The characteristics of the jet array discharge and the preliminary polymerization with acrylic acid (AA) monomer were presented. The plasma reactor can produce a cold jet array with a gas temperature lower than 315 K, using an applied discharge power between 6 W and 30 W (Vdis×Idis). A silk fibroin film (SFF) was modified using the jet array and AA monomer, and the treated SFF samples were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle (CA). The deposition rate of the poly acrylic acid (PAA) was able to reach 300 nm/min, and the surface roughness and energy increased with the AA flow rate. The FTIR results indicate that the modified SFF had more carboxyl groups (-COOH) than the original SFF. This latter characteristic allowed the modified SFF to immobilize more quantities of antimicrobial peptide (AP, LL-37) which inhibited the Escherichia coli (E. Coli) effectively.

Synthesis and thermoelectric properties of Mn-doped AgSbTe2 compounds Hot!

Zhang He, Luo Jun, Zhu Hang-Tian, Liu Quan-Lin, Liang Jing-Kui, Li Jing-Bo, Liu Guang-Yao
Chin. Phys. B, 2012, 21 (10): 106101 doi: 10.1088/1674-1056/21/10/106101
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Polycrystalline p-type Ag0.9Sb1.1-xMnxTe2.05(x=0.05, 0.10, and 0.20) compounds have been prepared by a combined process of melt-quenching and spark plasma sintering. The sample composition of Ag0.9Sb1.1-xMnxTe2.05 has been specially designed in order to achieve the doping effect by replacing part of Sb with Mn and to present the uniformly dispersed Ag2Te phase in the matrix by adding insufficient Te, which is beneficial for optimizing the electrical transport properties and enhancing the phonon scattering effect. All the samples have the NaCl-type structure according to our X-ray powder diffraction analysis. After the treatment of spark plasma sintering, only the sample with x = 0.20 has a small amount of MnTe2 impurities. The thermal analysis indicates that a tiny amount of Ag2Te phase exists in all these samples. The presence of the MnTe2 impurity with high resistance and high thermal conductivity leads to the deteriorative thermoelectric performance of the sample with x=0.20 due to the decreased electrical transport properties and the increased thermal conductivity. In contrast, the sample with x=0.10 exhibits enhanced thermoeletric properties due to the Mn-doping effect. A dimensionless thermoelectric figure of merit of 1.2 is attained for the sample with x=0.10 at 573 K, showing promising thermoelectric properties in the medium temperature range.

Structure, stability, and motion of dislocations in double-wall carbon nanotubes

Zhang Kai-Wang, Li Zhong-Qiu, Wu Jian, Peng Xiang-Yang, Tan Xin-Jun, Sun Li-Zhong, Zhong Jian-Xin
Chin. Phys. B, 2012, 21 (10): 106102 doi: 10.1088/1674-1056/21/10/106102
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In this paper, a novel double-wall carbon nanotube (DWCNT) with both edge and screw dislocations is studied by using the molecular dynamics (MD) method. The differences between two adjacent tubule indexes of armchair and zigzag nanotubes are determined to be 5 and 9, respectively, by taking into account the symmetry, integrality, and thermal stability of the composite structures. It is found that melting first occurs near the dislocations, and the melting temperatures of the dislocated armchair and zigzag DWCNTs are around 2600 K-2700 K. At the pre-melting temperatures, the shrink of the dislocation loop, which is comprised of edge and screw dislocations, implies that the composite dislocation in DWCNTs has self-healing ability. The dislocated DWCNTs first fracture at the edge dislocations, which induces the entire break in axial tensile test. The dislocated DWCNTs have a smaller fracture strength compared to the perfect DWCNTs. Our results not only match with the dislocation glide of carbon nanotubes (CNTs) in experiments, but also can free from the electron beam radiation under experimental conditions observed by the high resolution transmission electron microscope (HRTEM), which is deemed to cause the motion of dislocation loop.

Structural analysis and crystal-field calculations of Nd3+ in GdxLu1-xTaO4 (x=0.85) polycrytalline

Gao Jin-Yun, Zhang Qing-Li, Yang Hua-Jun, Zhou Peng-Yu, Sun Dun-Lu, Yin Shao-Tang, He Ye
Chin. Phys. B, 2012, 21 (10): 106103 doi: 10.1088/1674-1056/21/10/106103
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The crystal structural parameters of Nd3+-doped rare earth orthotantalate GdxLu1-xTaO4 (x=0.85) are determined by applying the Rietveld refinement to its X-ray diffraction, and its emission and excitation spectra at 77 K are analysed. The relativistic model of ab-initio self-consistent DV-Xα method, which is applied to the cluster NdO8 in GdxLu1-xTaO4, and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters. The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm-1. According to the crystal-field calculations, 96 levels of Nd3+ are assigned. Finally, the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd3+:YAlO3. The results indicate that the free-ion parameters are similar to those of the Nd3+ in GdxLu1-xTaO4 and YAlO3 hosts, and the crystal-field interaction of Nd3+ in GdxLu1-xTaO4 is stronger than that in YAlO3.

Static strength of gold compressed up to 127 GPa

Jing Qiu-Min, Wu Qiang, Liu Lei, Bi Yan, Zhang Yi, Liu Sheng-Gang, Xu Ji-An
Chin. Phys. B, 2012, 21 (10): 106201 doi: 10.1088/1674-1056/21/10/106201
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Gold powder is compressed non-hydrostatically up to 127 GPa in a diamond anvil cell (DAC), and its angle dispersive X-ray diffraction patterns are recorded. The compressive strength of gold is investigated in a framework of the lattice strain theory by the line shift analysis. The result shows that the compressive strength of gold increases continuously with the pressure up to 106 GPa and reaches 2.8 GPa at the highest experimental pressure (127 GPa) achieved in our study. This result is in good agreement with our previous experimental result in a relevant pressure range. The compressive strength of gold may be the major source of the error in the equation-of-state measurement in various pressure environments.

Effects of twin and stacking faults on the deformation behaviors of Al nanowires under tension loading

An Min-Rong, Song Hai-Yang, Su Jin-Fang
Chin. Phys. B, 2012, 21 (10): 106202 doi: 10.1088/1674-1056/21/10/106202
Full Text: [PDF 2776 KB] (Downloads:1014)
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The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic (MD) simulation method. The result shows that the yield strength of nanotwinned Al decreases with the increase of twin spacing, which is related to the repulsive force between twin boundary and the dislocation. The result also shows that there is no strain-hardening at the yield point. On the contrary, the stress is raised by strain hardening in the plastic stage. In addition, we also investigate the effects of stacking fault thickness and temperature on the yield strength of the Al nanowire. The simulation results indicate that the stacking fault may strengthen the Al nanowire when the thickness of the stacking fault is below a critical value.

Lattice dynamical and thermodynamical properties of ReB2, RuB2, and OsB2 compounds in the ReB2 structure

E. Deligoz, K. Colakoglu, Y. O. Ciftci
Chin. Phys. B, 2012, 21 (10): 106301 doi: 10.1088/1674-1056/21/10/106301
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Structural and lattice dynamical properties of ReB2, RuB2, and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation. The present results show that these compounds are dynamically stable for the considered structure. The temperature-dependent behaviors of thermodynamical properties such as internal energy, free energy, entropy, and heat capacity are also presented. The obtained results are in good agreement with the available experimental and theoretical data.

First-principles study and electronic structures of Mn-doped ultrathin ZnO nanofilms

E. Salmani, A. Benyoussef, H. Ez-Zahraouy, E. H. Saidi, O. Mounkachi
Chin. Phys. B, 2012, 21 (10): 106601 doi: 10.1088/1674-1056/21/10/106601
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The first-principles density functional calculation is used to investigate the electronic structures and magnetic properties of Mn-doped and N-co-doped ZnO nanofilms. The band structure calculation shows that the band gaps of ZnO films with 2, 4, and 6 layers are larger than the band gap of the bulk with wurtzite structure and decrease with the increase of film thickness. However, the four-layer ZnO nanofilms exhibit ferromagnetic phases for Mn concentrations less than 24% and 12% for Mn-doping performed in the whole layers and two layers of the film respectively, while they exhibit spin glass phases for higher Mn concentrations. It is also found, on the one hand, that the spin glass phase turns into the ferromagnetic one, with the substitution of nitrogen atoms for oxygen atoms, for nitrogen concentrations higher than 16% and 5% for Mn-doping performed in the whole layers and two layers of the film respectively. On the other hand, the spin-glass state is more stable for ZnO bulk containing 5% of Mn impurities, while the ferromagnetic phase is stable by introducing the p-type carriers into the bulk system. Moreover, it is shown that using the effective field theory for ferromagnetic system, the Curie temperature is close to the room temperature for the undamped Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction.

Tunable Ba0.5Sr0.5TiO3 film bulk acoustic resonators using SiO2/Mo Bragg reflectors

Yang Tian-Ying, Jiang Shu-Wen, Li Ru-Guan, Jiang Bin
Chin. Phys. B, 2012, 21 (10): 106801 doi: 10.1088/1674-1056/21/10/106801
Full Text: [PDF 2419 KB] (Downloads:789)
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Tunable and switchable Ba0.5Sr0.5TiO3 film bulk acoustic resonators (FBARs) based on SiO2/Mo Bragg reflectors are explored, which can withstand high temperature for the deposition of BaxSr1-xTiO3 (BST) films at 800 ℃. The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect. The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing, while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias (< 45 V) while downwards at higher dc bias. The calculated relative tunability of shifts at series resonance frequency is around -2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias, which can be comparable to AlN FBARs. This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum (Mo) as the high acoustic impedance layer in a Bragg reflector, which not only provides excellent acoustic isolation from the substrate, but also improves the crystallinity of BST films withstanding higher deposition temperature.

Interfacial evolution of a spherical particle in a uniaximal straining flow

Chen Ming-Wen, He Guo-Wei, Chen Xiu-Yue, Wang Zi-Dong
Chin. Phys. B, 2012, 21 (10): 106802 doi: 10.1088/1674-1056/21/10/106802
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The growth behavior of a spherical particle in undercooled melt, affected by uniaxial straining flows, is studied. The analytical solution obtained by the matched asymptotic expansion method shows that the uniaxial straining flow effect results in higher local growth rate near the surface where the flow comes in and lower local growth rate near the surface where the flow goes out, and that the uniaxial straining flow causes an initially spherical particle to evolve into an oblate spheroid.

Structure and electronic structure of S-doped graphitic C3N4 investigated by density functional theory

Chen Gang, Gao Shang-Peng
Chin. Phys. B, 2012, 21 (10): 107101 doi: 10.1088/1674-1056/21/10/107101
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The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers. The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4. The S doptant is prone to substitute the N atom bonded with only two nearest C atoms. The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.

Optical absorption and electromagnetically induced transparency in semiconductor quantum well driven by intense terahertz field

Wu Hong-Wei, Mi Xian-Wu
Chin. Phys. B, 2012, 21 (10): 107102 doi: 10.1088/1674-1056/21/10/107102
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An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented. The formalism relies on the stationary single-photon Schrödinger equation in the full quantum mechanical framework. The optical absorption dynamics in both weak and strong couplings are discussed and compared. The excitonic absorption spectra show the Autler-Townes doublets for the resonance terahertz field, a replica peak for the non-resonance terahertz field, and the electromagnetically induced transparency phenomenon for modulating the decay rate of the second electron state in the weak coupling. In particular, the electromagnetically induced transparency phenomenon window range is discussed. In the strong coupling region,the multi-order energy level resonance splitting due to the strong optical field is found. There are three (non-resonance terahertz field) or four (resonance terahertz field) peaks in the optical absorption spectra. This work provides a simple and convenient approach to deal with the optical absorption in the exciton system.

Built-in electric field effect on cyclotron mass of magnetopolarons in a wurtzite InxGa1-xN/GaN quantum well

Zhao Feng-Qi, Yong Mei
Chin. Phys. B, 2012, 21 (10): 107103 doi: 10.1088/1674-1056/21/10/107103
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The cyclotron mass of magnetopolarons in wurtzite InxGa1-xN/GaN quantum well is studied in the presence of an external magnetic field by using the Larsen perturbation method. The effects of the built-in electric field and different phonon modes including interface, confined and half-space phonon modes are considered in our calculation. The results for a zinc-blende quantum well are also given for comparison. It is found that the main contribution to the transition energy comes from half-space and interface phonon modes when the well width is very small while the confined modes play a more important role in a wider well due to the location of the electron wave function. As the well width increases, the cyclotron mass of magnetopolarons first increases to a maximum and then decreases either with or without the built-in electric field in the wurtzite structure and the built-in electric field slightly reduces the cyclotron mass. The variation of cyclotron mass in a zinc-blende structure is similar to that in a wurtzite structure. With the increase of external magnetic field, the cyclotron mass of polarons almost linearly increases. The cyclotron frequency of magnetopolarons is also discussed.

Ferromagnetism, variable range hopping and anomalous Hall effect in epitaxial Co:ZnO thin film

Bai Hong-Liang, He Shu-Min, Xu Tong-Shuai, Liu Guo-Lei, Yan Shi-Shen, Zhu Da-Peng, Dai Zheng-Kun, Yang Feng-Fan, Dai You-Yong, Chen Yan-Xue, Mei Liang-Mo
Chin. Phys. B, 2012, 21 (10): 107201 doi: 10.1088/1674-1056/21/10/107201
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A series of high quality single crystalline epitaxial Zn0.95Co0.05O thin films is prepared by molecular beam epitaxy. Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 1018 cm-3-1020 cm-3 by changing the oxygen partial pressure during film growth. The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature. The ferromagnetism can be maintained up to room temperature. However, the anomalous Hall effect is observed only at low temperature and disappears above 160 K. This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures.

Spin-polarized transport in graphene nanoribbon superlattices

Yu Xin-Xin, Xie Yue-E, Yang Tao, Chen Yuan-Ping
Chin. Phys. B, 2012, 21 (10): 107202 doi: 10.1088/1674-1056/21/10/107202
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By the Green's function method, we investigate spin transport properties of a zigzag graphene nanoribbon superlattice (ZGNS) under a ferromagnetic insulator and edge effect. The exchange splitting induced by the ferromagnetic insulator eliminates the spin degeneracy, which leads to spin-polarized transport in structure. Spin-dependent minibands and minigaps are exhibited in the conductance profile near the Fermi energy. The location and width of the miniband are associated with the geometry of the ZGNS. In the optimal structure, the spin-up and spin-down minibands can be separated completely near the Fermi energy. Therefore, a wide, perfect spin polarization with clear stepwise pattern is observed, i.e., the perfect spin-polarized transport can be tuned from spin up to spin down by varying the electron energy.

Renormalization of the chemical potential due to multiphonon effects at the surface of metals

Ma Lei, Kang Guang-Zhen, Li Jun
Chin. Phys. B, 2012, 21 (10): 107301 doi: 10.1088/1674-1056/21/10/107301
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We study the relation between renormalization of the chemical potential due to multiphonon effects at the surface of Be(0001) and doping by solving the strong-coupling self-consistent equations of a two-dimensional (2D) electron-phonon interaction system. We present the quasiparticle dispersions and inverse lifetimes of a 2D electron system interacting with Einstein phonons under the different dopings (corresponding to chemical potentials). We find that the effect of electron-phonon interaction on electron structure is strongest at the half filling, but it has no effect on the chemical potential. However, the chemical potential shows distinct renormalization effects away from half filling due to the electron-phonon interaction.

A functional probe with bowtie aperture and bull's eye structure for nanolithograph

Wang Shuo, Li Xu-Feng, Wang Qiao, Guo Ying-Yan, Pan Shi
Chin. Phys. B, 2012, 21 (10): 107302 doi: 10.1088/1674-1056/21/10/107302
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The bowtie aperture surrounded by concentric gratings (the bull's eye structure) integrated on the near-field scanning optical microscopy (NSOM) probe (aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain (FDTD) method. By modifying the parameters of the bowtie aperture and the concentric gratings, a maximal field enhancement factor of 391.69 has been achieved, which is 18 times larger than that obtained from the single bowtie aperture. Additionally, the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength. The superiority of the combination of the bowtie aperture and the bull's eye structure is confirmed, and the mechanism for the electric field enhancement in this derived structure is analyzed.

Gain-assisted indented plasmonic waveguide for low-threshold nanolaser applications

Liu Jie-Tao, Xu Bin-Zong, Zhang Jing, Cai Li-Kang, Song Guo-Feng
Chin. Phys. B, 2012, 21 (10): 107303 doi: 10.1088/1674-1056/21/10/107303
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A subwavelength plasmonic indented waveguide with an active InGaAsP core is proposed. The characteristics of the gap plasmon mode and gain required for lossless propagation are investigated and analyzed by the finite element method. We numerically calculate the normalized mode areas and percentages of energy confined in InGaAsP and metal for plasmonic nanolaser applications. It is shown that the indentation of the sidewalls has an optimal value for which the lasing threshold gain is minimal. The structure could enable low-threshold subwavelength lasing and applications for optoelectronic integrated circuits.

Interface-related switching behaviors of amorphous Pr0.67Sr0.33MnO3-based memory cells

Zhang Ting, Bai Ying, Jia Cai-Hong, Zhang Wei-Feng
Chin. Phys. B, 2012, 21 (10): 107304 doi: 10.1088/1674-1056/21/10/107304
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The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated. Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33MnO3/F:SnO2 junctions are obtained at room temperature. Dramatically, the coexistence of two switching polarities could be reversibly adjusted by an applied voltage range. The results allocated those two switching types to areas of different defect densities beneath the same electrode. The migration of oxygen vacancies and the trapping effect of electrons under an applied electric field play an important role. An interface-effect-related resistance switching is proposed in an amorphous Pr0.67Sr0.33MnO3-based memory cell.

Spacer layer thickness fluctuation scattering in a modulation-doped AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well

Gu Cheng-Yan, Liu Gui-Peng, Shi Kai, Song Ya-Feng, Li Cheng-Ming, Liu Xiang-Lin, Yang Shao-Yan, Zhu Qin-Sheng, Wang Zhan-Guo
Chin. Phys. B, 2012, 21 (10): 107305 doi: 10.1088/1674-1056/21/10/107305
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We theoretically study the influence of spacer layer thickness fluctuation (SLTF) on the mobility of a two-dimensional electron gas (2DEG) in the modulation-doped AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well. The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained. The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.

A two-dimensional threshold voltage analytical model for metal-gate/high-k/SiO2/Si stacked MOSFETs

Ma Fei, Liu Hong-Xia, Fan Ji-Bin, Wang Shu-Long
Chin. Phys. B, 2012, 21 (10): 107306 doi: 10.1088/1674-1056/21/10/107306
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In this paper the influences of the metal-gate and high-k/SiO2/Si stacked structure on the metal-oxide-semiconductor field-effect transistor (MOSFET) are investigated. The flat-band voltage is revised by considering the influences of stacked structure and metal-semiconductor work function fluctuation. The two-dimensional Poisson's equation of potential distribution is presented. A threshold voltage analytical model for metal-gate/high-k/SiO2/Si stacked MOSFETs is developed by solving these Poisson's equations using the boundary conditions. The model is verified by a two-dimensional device simulator, which provides the basic design guidance for metal-gate/high-k/SiO2/Si stacked MOSFETs.

Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

Li Xiao-Qi, Xu Xiao-Guang, Wang Sheng, Wu Yong, Zhang De-Lin, Miao Jun, Jiang Yong
Chin. Phys. B, 2012, 21 (10): 107307 doi: 10.1088/1674-1056/21/10/107307
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Microstructures and magnetic properties of Ta/Pt/Co2FeAl (CFA)/MgO multilayers are studied to understand perpendicular magnetic anisotropy (PMA) of half-metallic full-Heusler alloy films. PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope. It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA. The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature. At the intersection points, the decreasing slope of the saturation magnetization (Ms) changes because of the conversions. The dependence of Ms on the annealing temperature and MgO thickness is also studied.

Influence of the Jahn–Teller distortion on magnetic ordering in TbMn1-xFexO3 Hot!

Jin Jin-Ling, Zhang Xiang-Qun, Li Guo-Ke, Cheng Zhao-Hua
Chin. Phys. B, 2012, 21 (10): 107501 doi: 10.1088/1674-1056/21/10/107501
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The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites. In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3 (x=0, 0.02, 0.05, 0.10, and 0.20) single crystals in the basal MnO2 plane. The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion, which makes the nearest neighboring (NN) FM interaction dominant over the next nearest neighbor (NNN) AFM interaction. This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering, which collapses when x≥0.05. The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.

Multiferroic phase transitions in manganites RMnO3: A two-orbital double exchange simulation

Tao Yong-Mei, Lin Lin, Dong Shuai, Liu Jun-Ming
Chin. Phys. B, 2012, 21 (10): 107502 doi: 10.1088/1674-1056/21/10/107502
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The semi-quantum two-orbital exchange model is used to investigate the effect of small rare-earth ion substitution on orthorhombic RMnO3 with A-type antiferromagnetic order, using the Monte Carlo algorithm, exact diagonalization, and zero-temperature optimization approaches. It is revealed that the substitution results in a rich multiferroic phase diagram where the coexisting A-type antiferromagnetic phase and spiral spin phase, pure spiral spin phase, coexisting spiral spin phase, the E-type antiferromagnetic phase, and the pure E-type antiferromagnetic phase emerge in sequence. The multiferroic phase transitions modulate substantially the electric polarization, which is consistent qualitatively with recent experiments.

Improved multiferroic properties of La-doped 0.6BiFeO3–0.4SrTiO3 solid solution ceramics

Ma Zheng-Zheng, Li Jian-Qing, Tian Zhao-Ming, Qiu Yang, Yuan Song-Liu
Chin. Phys. B, 2012, 21 (10): 107503 doi: 10.1088/1674-1056/21/10/107503
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The 0.6(Bi1-xLax)FeO3-0.4SrTiO3 (x=0, 0.1) multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO3 and La in BiFeO3. The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure. The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO3 and substitution of La. The values of the dielectric constant εr and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature. The La-doped 0.6BiFeO3-0.4SrTiO3 ceramics exhibit improved dielectric and ferroelectric properties, with higher dielectric constant enhanced remnant polarization (Pr) and lower leakage current at room temperature. Compared with a anti-ferromagnetic BiFeO3 compound, the 0.6(Bi0.9La0.1)FeO3-0.4SrTiO3 sample shows the optimal ferromagnetism with remnant magnetization Mr~0.135 emμ/g and ferroelectricity with Pr~5.94 μC/cm2 at room temperature.

Investigation of ultrafast dynamics of CdTe quantum dots by femtosecond fluorescence up-conversion spectroscopy

Yao Guan-Xin, L¨u Liang-Hong, Gui Mei-Fang, Zhang Xian-Yi, Zheng Xian-Feng, Ji Xue-Han, Zhang Hong, Cui Zhi-Feng
Chin. Phys. B, 2012, 21 (10): 107801 doi: 10.1088/1674-1056/21/10/107801
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The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence up-conversion spectroscopy. Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ~ 1.6 ps with exciting at 400 nm, depending on the state of the photo-excited hole. The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots. In addition, Auger relaxation of trapped carriers is observed to occur with a time constant of ~ 5 ps. A schematic model of photodynamics is established based on the results of the spectroscopy studies. Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.

Structural and band tail state photoluminescence properties of amorphous SiC films with different amounts of carbon

Fu Guang-Sheng, Wang Xin-Zhan, Lu Wan-Bing, Dai Wan-Lei, Li Xing-Kuo, Yu Wei
Chin. Phys. B, 2012, 21 (10): 107802 doi: 10.1088/1674-1056/21/10/107802
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Amorphous silicon carbide films are deposited by the plasma enhanced chemical vapour deposition technique, and optical emissions from the near-infrared to the visible are obtained. The optical band gap of the films increases from 1.91 eV to 2.92 eV by increasing the carbon content, and the photoluminescence (PL) peak shifts from 1.51 eV to 2.16 eV. The band tail state PL mechanism is confirmed by analysing the optical band gap, PL intensity, the Stocks shift of the PL, and the Urbach energy of the film. The PL decay times of the samples are in the nanosecond scale, and the dependence of the PL lifetime on the emission energy also supports that the optical emission is related to the radiative recombination in the band tail state.

Investigation of the free volume and ionic conducting mechanism of poly(ethylene oxide)-LiClO4 polymeric electrolyte by positron annihilating lifetime spectroscopy

Gong Jing, Gong Zhen-Li, Yan Xiao-Li, Gao Shu, Zhang Zhong-Liang, Wang Bo
Chin. Phys. B, 2012, 21 (10): 107803 doi: 10.1088/1674-1056/21/10/107803
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The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite (OREC) content and temperature in a range from 160 K to 300 K. According to the variation of ortho-positronium (o-Ps) lifetime with temperature, the glassy transition temperature is determined. The continuous maximum entropy lifetime (MELT) analysis clearly shows that the OREC and temperature have important effects on o-Ps lifetime and free volume distribution. The experimental results show that the temperature dependence of ionic conductivity obeys the Vogel-Tammann-Fulcher (VTF) and Williams-Landel-Ferry (WLF) equations, implying a free-volume transport mechanism. A linear least-squares procedure is used to evaluate the apparent activation energy related to the ionic transport in the VTF equation and several important parameters in the WLF equation. It is worthwhile to notice that a direct linear relationship between the ionic conductivity and free volume fraction is established using the WLF equation based on the free volume theory for nanocomposite electrolyte, which indicates that the segmental chain migration and ionic migration and diffusion could be explained by the free volume theory.

Quantum dots-templated growth of strain-relaxed GaN on a c-plane sapphire by radio-frequency molecular beam epitaxy

Guo Hao-Min, Wen Long, Zhao Zhi-Fei, Bu Shao-Jiang, Li Xin-Hua, Wang Yu-Qi
Chin. Phys. B, 2012, 21 (10): 108101 doi: 10.1088/1674-1056/21/10/108101
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We investigated the quantum dots-templated growth of a (0001) GaN film on a c-plane sapphire substrate. The growth was carried out in a radio-frequency molecular beam epitaxy system. The enlargement and coalescence of grains on the GaN quantum dots template was observed in the atom force microscopy images, as well as the more ideal surface morphology of the GaN epitaxial film on the quantum dots template compared with the one on the AlN buffer. The Ga polarity was confirmed by the reflected high energy electron diffraction patterns and the Raman spectra. The significant strain relaxation in the quantum dots-templated GaN film was calculated based on the Raman spectra and the X-ray rocking curves. Meanwhile, the threading dislocation density in the quantum dots-templated film was estimated to be 7.1×107 cm-2, which was significantly suppressed compared with that of the AlN-buffered GaN film. The room-temperature Hall measurement showed an electron mobility of up to 1860 cm2/V·s in the two-dimensional electron gas at the interface of the Al0.25Ga0.75N/GaN heterojunction.

Influence of annealing treatment on as-grown Ib-type diamond crystal at a high temperature and high pressure

Huang Guo-Feng, Yin Ji-Wen, Bai Hong-Bo, HuYi-Ga, Kai Li, Jing Jing, Ma Hong-An, Jia Xiao-Peng
Chin. Phys. B, 2012, 21 (10): 108102 doi: 10.1088/1674-1056/21/10/108102
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In this paper, we report on the influence of annealing treatment on as-grown Ib-type diamond crystal under high pressure and high temperature in a china-type cubic anvil high-pressure apparatus. Experiments are carried out at a pressure of 7.0 GPa and temperatures ranging from 1700 ℃ to 1900 ℃ for 1 h. Annealing treatment of the diamond crystal shows that the aggregation rate constant of nitrogen atoms in the as-grown Ib-type diamond crystal strongly depends on diamond morphology and annealing temperature. The aggregation rate constant of nitrogen remarkably increases with the increase of annealing temperature and its value in octahedral diamond is much higher than that in cubic diamond annealed at the same temperature. The colour of octahedral diamond crystal is obviously reduced from yellow to nearly colorless after annealing treatment for 1 h at 1900 ℃, which is induced by nitrogen aggregation in a diamond lattice. The extent of nitrogen aggregation in an annealed diamond could approach approximately 98% indicated from the infrared absorption spectra. The micro-Raman spectrum reveals that the annealing treatment can improve the crystalline quality of Ib-type diamond characterized by a half width at full maximum at first order Raman peak, and therefore the annealed diamond crystals exhibit nearly the same properties as the natural IaA-type diamond stones of high quality in the Raman measurements.

Implementation of an analogue model of a memristor based on a light-dependent resistor

Wang Xiao-Yuan, Andrew L. Fitch, Herbert H. C. Iu, Victor Sreeram, Qi Wei-Gui
Chin. Phys. B, 2012, 21 (10): 108501 doi: 10.1088/1674-1056/21/10/108501
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In this paper, an analogue model of a memristor using a light-dependent resistor (LDR) is presented. This model can be simplified into two parts: a control circuit and a variable resistor. It can be used to easily verify theoretical presumptions about the switching properties of memristors. This LDR-based memristor model can also be used in both simulations and experiments for future research into memristor applications. The paper includes mathematical models, simulations, and experimental results.

Breakdown voltage model and structure realization of a thin silicon layer with linear variable doping on a silicon on insulator high voltage device with multiple step field plates

Qiao Ming, Zhuang Xiang, Wu Li-Juan, Zhang Wen-Tong, Wen Heng-Juan, Zhang Bo, Li Zhao-Ji
Chin. Phys. B, 2012, 21 (10): 108502 doi: 10.1088/1674-1056/21/10/108502
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Based on the theoretical and experimental investigation of a thin silicon layer (TSL) with linear variable doping (LVD) and further research on the TSL LVD with a multiple step field plate (MSFP), a breakdown voltage (BV) model is proposed and experimentally verified in this paper. With the two-dimensional Poisson equation of the silicon on insulator (SOI) device, the lateral electric field in drift region of the thin silicon layer is assumed to be constant. For the SOI device with LVD in the thin silicon layer, the dependence of the BV on impurity concentration under the drain is investigated by an enhanced dielectric layer field (ENDIF), from which the reduced surface field (RESURF) condition is deduced. The drain in the centre of the device has a good self-isolation effect, but the problem of the high voltage interconnection (HVI) line will become serious. The two step field plates including the source field plate and gate field plate can be adopted to shield the HVI adverse effect on the device. Based on this model, the TSL LVD SOI n-channel lateral double-diffused MOSFET (nLDMOS) with MSFP is realized. The experimental breakdown voltage (BV) and specific on-resistance (Ron, sp) of the TSL LVD SOI device are 694 V and 21.3 Ω · mm2 with a drift region length of 60 μm, buried oxide layer of 3 μm, and silicon layer of 0.15 μm, respectively.

High-field-induced electron detrapping in An AlGaN/GaN high electron mobility transistor

Fu Li-Hua, Lu Hai, Chen Dun-Jun, Zhang Rongm, Zheng You-Dou, Wei Ke, Liu Xin-Yu
Chin. Phys. B, 2012, 21 (10): 108503 doi: 10.1088/1674-1056/21/10/108503
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A step stress test is carried out to study the reliability characteristics of an AlGaN/GaN high electron mobility transistor (HEMT). An anomalous critical drain-to-gate voltage with a negative temperature coefficient is observed in the stress sequence, beyond which the HEMT device starts to recover from degradation induced by early lower voltage stress. While the performance degradation featuring the drain current slump stems from electron trapping in the surface or bulk states during low-to-medium bias stress, the recovery is attributed to high field induced electron detrapping. The carrier detrapping mechanism could be helpful for lessening the trapping-related performance degradation of a GaN-based HEMT.

Enhancement of terahertz coupling efficiency by improved antenna design in GaN/AlGaN high electron mobility transistor detectors

Sun Yun-Fei, Sun Jan-Dong, Zhang Xiao-Yu, Qin Hua, Zhang Bao-Shun, Wu Dong-Min
Chin. Phys. B, 2012, 21 (10): 108504 doi: 10.1088/1674-1056/21/10/108504
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An optimized micro-gated terahertz detector with novel triple resonant antenna is presented. The novel resonant antenna operates at room temperature and shows more than a 700% increase in photocurrent response compared to the conventional bowtie antenna. In finite-difference-time-domain simulations, we found the performance of the self-mixing GaN/AlGaN high electron mobility transistor detector is mainly dependent on the parameters Lgs (the gap between the gate and the source/drain antenna) and Lw (the gap between the source and drain antenna). With the improved triple resonant antenna, an optimized micrometer-sized AlGaN/GaN high electron mobility transistor detector can achieve a high responsivity of 9.45×102 V/W at a frequency of 903 GHz at room temperature.

Efficiency droop alleviation in blue light emitting diodes using the InGaN/GaN triangular-shaped quantum well

Chen Zhao, Yang Wei, Liu Lei, Wan Cheng-Hao, Li Lei, He Yong-Fa, Liu Ning-Yang, Wang Lei, Li Din, Chen Wei-Hua, Hu Xiao-Dong
Chin. Phys. B, 2012, 21 (10): 108505 doi: 10.1088/1674-1056/21/10/108505
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The InGaN/GaN blue light emitting diode (LED) is numerically investigated using a triangular-shaped quantum well model, which involves analysis on its energy band, carrier concentration, overlap of electron and hole wave functions, radiative recombination rate, and internal quantum efficiency. The simulation results reveal that the InGaN/GaN blue light emitting diode with triangular quantum wells exhibits a higher radiative recombination rate than the conventional light emitting diode with rectangular quantum wells due to the enhanced overlap of electron and hole wave functions (above 90%) under the polarization field. Consequently, the efficiency droop is only 18% in the light emitting diode with triangular-shaped quantum wells, which is three times lower than that in a conventional LED.

High-contrast top-emitting organic light-emitting devices

Chen Shu-Fen, Chen Chun-Yan, Yang Yang, Xie Jun, Huang Wei, Shi Hong-Ying, Cheng Fan
Chin. Phys. B, 2012, 21 (10): 108506 doi: 10.1088/1674-1056/21/10/108506
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In this paper we report on a high-contrast top-emitting organic light-emitting device utilizing a moderate-reflection contrast-enhancement stack and a high refractive index anti-reflection layer. The contrast-enhancement stack consists of a thin metal anode layer, a dielectric bilayer, and a thick metal underlayer. The resulting device, with the optimized contrast-enhancement stack thicknesses of Ni (30 nm)/MgF2 (62 nm)/ZnS (16 nm)/Ni (20 nm) and the 25-nm-thick ZnS anti-reflection layer, achieves a luminous reflectance of 4.01% in the visible region and a maximum current efficiency of 0.99 cd/A (at 62.3 mA/cm2) together with a very stable chromaticity. The contrast ratio reaches 561:1 at an on-state brightness of 1000 cd/m2 under an ambient illumination of 140 lx. In addition, the anti-reflection layer can also enhance the transmissivity of the cathode and improve light out-coupling by the effective restraint of microcavity effects.

Efficient top-emitting white organic light emitting device with an extremely stable chromaticity and viewing-angle

Shao Ming, Guo Xu, Chen Shu-Fen, Fan Qu-Li, Huang Wei
Chin. Phys. B, 2012, 21 (10): 108507 doi: 10.1088/1674-1056/21/10/108507
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In this paper, we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic light-emitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer. With a 24-nm out-coupling layer, the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area. By introducing an efficient electron blocking layer tris(1-phenylpyrazolato,N,C2')iridium(III) (Ir(ppz)3) to confine the exciton recombination area, the current efficiency and the colour stability of the device are effectively improved. A white emission with the Ir(ppz)3 layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V, and the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates are almost constant during a large voltage change of 6 V-11 V. There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45°, with a CIEx,y coordinate variation of only (±0.0025, ±0.0008). Even at a large viewing angle (75°), the CIEx,y coordinate change is as small as (±0.0087, ±0.0013).

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic (FM/OSC/FM) system

Wang Yu-Mei, Ren Jun-Feng, Yuan Xiao-Bo, Dou Zhao-Tao, Hu Gui-Chao
Chin. Phys. B, 2012, 21 (10): 108508 doi: 10.1088/1674-1056/21/10/108508
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From experimental results of spin polarized injection and transport in organic semiconductors (OSCs), we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic (FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm's law. From the calculations, it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC. Furthermore, the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

Spiking sychronization regulated by noise in three types of Hodgkin–Huxley neuronal networks

Zhang Zheng-Zhen, Zeng Shang-You, Tang Wen-Yan, Hu Jin-Lin, Zeng Shao-Wen, Ning Wei-Lian, Qiu Yi, Wu Hui-Si
Chin. Phys. B, 2012, 21 (10): 108701 doi: 10.1088/1674-1056/21/10/108701
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In this paper, we study spiking synchronization in three different types of Hodgkin-Huxley neuronal networks, which are the small-world, regular, and random neuronal networks. All the neurons are subjected to subthreshold stimulus and external noise. It is found that in each of all the neuronal networks there is an optimal strength of noise to induce the maximal spiking synchronization. We further demonstrate that in each of the neuronal networks there is a range of synaptic conductance to induce the effect that an optimal strength of noise maximizes the spiking synchronization. Only when the magnitude of the synaptic conductance is moderate, will the effect be considerable. However, if the synaptic conductance is small or large, the effect vanishes. As the connections between neurons increase, the synaptic conductance to maximize the effect decreases. Therefore, we show quantitatively that the noise-induced maximal synchronization in the Hodgkin-Huxley neuronal network is a general effect, regardless of the specific type of neuronal network.

A 2-stage strategy updating rule promotes cooperation in the prisoner's dilemma game

Fang Xiang-Sheng, Zhu Ping, Liu Run-Ran, Liu En-Yu, Wei Gui-Yi
Chin. Phys. B, 2012, 21 (10): 108702 doi: 10.1088/1674-1056/21/10/108702
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In this study, we propose a spatial prisoner's dilemma game model with a 2-stage strategy updating rule, and focus on the cooperation behavior of the system. In the first stage, i.e., the pre-learning stage, a focal player decides whether to update his strategy according to the pre-learning factor β and the payoff difference between himself and the average of his neighbors. If the player makes up his mind to update, he enters into the second stage, i.e., the learning stage, and adopts a strategy of a randomly selected neighbor according to the standard Fermi updating rule. The simulation results show that the cooperation level has a non-trivial dependence on the pre-learning factor. Generally, the cooperation frequency decreases as the pre-learning factor increases; but a high cooperation level can be obtained in the intermediate region of -3<β<-1. We then give some explanations via studying the co-action of pre-learning and learning. Our results may sharpen the understanding of the influence of the strategy updating rule on evolutionary games.

A Compton scattering image reconstruction algorithm based on total variation minimization

Li Shou-Peng, Wang Lin-Yuan, Yan Bin, Li Lei, Liu Yong-Jun
Chin. Phys. B, 2012, 21 (10): 108703 doi: 10.1088/1674-1056/21/10/108703
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Compton scattering imaging is a novel radiation imaging method using scattered photons. Its main characteristics are detectors that do not have to be on the opposite side of the source, so avoiding the rotation process. The reconstruction problem of Compton scattering imaging is the inverse problem to solve electron densities from nonlinear equations, which is ill-posed. This means the solution exhibits instability and sensitivity to noise or erroneous measurements. Using the theory for reconstruction of sparse images, a reconstruction algorithm based on total variation minimization is proposed. The reconstruction problem is described as an optimization problem with nonlinear data-consistency constraint. The simulated results show that the proposed algorithm could reduce reconstruction error and improve image quality, especially when there are not enough measurements.

Self-organized phenomena of pedestrian counter flow in a channel under periodic boundary conditions

Li Xiang, Duan Xiao-Yin, Dong Li-Yun
Chin. Phys. B, 2012, 21 (10): 108901 doi: 10.1088/1674-1056/21/10/108901
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In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel. The lattice gas model is extended to take the effect of walkers in the opposite direction into account simultaneously when they are in the view field of a walker, i.e., walkers tend to follow the leaders in the same direction and avoid conflicts with those walking towards them. The improved model is then used to mimic pedestrian counter flow in a channel under periodic boundary conditions. Numerical simulations show that lane formation is well reproduced, and this process is rather rapid which coincides with real pedestrian traffic. The average velocity and critical density are found to increase to some degree with the consideration of view field.

A contrastive study on the influences of radial and three-dimensional satellite gravity gradiometry on the accuracy of the Earth's gravitational field recovery

Zheng Wei, Hsu Hou-Tse, Zhong Min, Yun Mei-Juan
Chin. Phys. B, 2012, 21 (10): 109101 doi: 10.1088/1674-1056/21/10/109101
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The accuracy of the Earth's gravitational field measured from the gravity field and steady-state ocean circulation explorer (GOCE), up to 250 degrees, influenced by the radial gravity gradient Vzz and three-dimensional gravity gradient Vij from the satellite gravity gradiometry (SGG) are contrastively demonstrated based on the analytical error model and numerical simulation, respectively. Firstly, the new analytical error model of the cumulative geoid height, influenced by the radial gravity gradient Vzz and three-dimensional gravity gradient Vij are established, respectively. In 250 degrees, the GOCE cumulative geoid height error measured by the radial gravity gradient Vzz is about 21/2 times higher than that measured by the three-dimensional gravity gradient Vij. Secondly, the Earth's gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient Vzz and three-dimensional gravity gradient Vij by numerical simulation, respectively. The study results show that when the measurement error of the gravity gradient is 3×10-12/s2, the cumulative geoid height errors using the radial gravity gradient Vzz and three-dimensional gravity gradient Vij are 12.319 cm and 9.295 cm at 250 degrees, respectively. The accuracy of the cumulative geoid height using the three-dimensional gravity gradient Vij is improved by 30%-40% on average compared with that using the radial gravity gradient Vzz in 250 degrees. Finally, by mutual verification of the analytical error model and numerical simulation, the orders of magnitude from the accuracies of the Earth's gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients, respectively. Therefore, it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10-13/s2-10-15/s2 for precisely producing the next-generation GOCE Follow-On Earth gravity field model with a high spatial resolution.

First principles calculations of alloying element diffusion coefficients in Ni using the five-frequency model

Wu Qiong, Li Shu-Suo, Ma Yue, Gong Sheng-Kai
Chin. Phys. B, 2012, 21 (10): 109102 doi: 10.1088/1674-1056/21/10/109102
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The diffusion coefficients of several alloying elements (Al, Mo, Co, Ta, Ru, W, Cr, Re) in Ni are directly calculated using the five-frequency model and the first principles density functional theory. The correlation factors provided by the five-frequency model are explicitly calculated. The calculated diffusion coefficients show their excellent agreement with the available experimental data. Both the diffusion pre-factor (D0) and the activation energy (Q) of impurity diffusion are obtained. The diffusion coefficients above 700 K are sorted in the following order: DAl>DCr>DCo>DTa>DMo>DRu>DW>DRe. It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair (E1). The value of E2-E1 (E2 is the solute diffusion energy) and the correlation factor each also show a positive correlation. The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.

Effect of oceanic current on typhoon-wave modeling in the East China Sea

Cui Hong, He Hai-Lun, Liu Xiao-Hui, Li Yi
Chin. Phys. B, 2012, 21 (10): 109201 doi: 10.1088/1674-1056/21/10/109201
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We use the WAVEWATCH-III model to quantify the effect of oceanic current on typhoon-wave modeling in the East-China-Sea (ECS). Typhoons Jelawat and Saomai in the autumn of 2000 are hindcasted. The oceanic currents in the ECS are mainly constituted of Kuroshio and typhoon-generated currents. The results show distinguishable differences in wave height and wave period under the typhoon conditions. The oceanic current causes the maximum differences, of up to a 0.5 m significant wave height and a 1 s mean wave period. Comparisons between typhoons Jelawat and Saomai show the dependence of the current effect on the typhoon characteristics.

Propagation modeling of ocean-scattered low-elevation GPS signals for maritime tropospheric duct inversion

Zhang Jin-Peng, Wu Zhen-Sen, Zhao Zhen-Wei, Zhang Yu-Sheng, Wang Bo
Chin. Phys. B, 2012, 21 (10): 109202 doi: 10.1088/1674-1056/21/10/109202
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The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface, and it can significantly affect the performance of many shore-based/shipboard radar and communication systems. We propose the idea that maritime tropospheric ducts can be retrieved from ocean forward-scattered low-elevation global positioning system (GPS) signals. Retrieval is accomplished by matching the measured power patterns of the signals to those predicted by the forward propagation model as a function of the modified refractivity profile. On the basis of a parabolic equation method and bistatic radar equation, we develop such a forward model for computing the trapped propagation characteristics of an ocean forward-scattered GPS signal within a tropospheric duct. A new GPS scattering initial field is defined for this model to start the propagation modeling. A preliminary test on the performance of this model is conducted using measured data obtained from a 2009-experiment in the South China Sea. Results demonstrate that this model can predict GPS propagation characteristics within maritime tropospheric ducts and serve as a forward model for duct inversion.

Characteristics of the spatiotemporal distribution of daily extreme temperature events in China: Minimum temperature records in different climate states against the background of the most probable temperature

Qian Zhong-Hua, Hu Jing-Guo, Feng Guo-Lin, Cao Yong-Zhong
Chin. Phys. B, 2012, 21 (10): 109203 doi: 10.1088/1674-1056/21/10/109203
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Based on the skewed function, the most probable temperature is defined and the spatiotemporal distributions of the frequencies and strengths of extreme temperature events in different climate states over China are investigated, where the climate states are referred to as State I, State II and State III, i.e., the daily minimum temperature records of 1961-1990, 1971-2000, and 1981-2009. The results show that in space the frequency of high temperature events in summer decreases clearly in the lower and middle reaches of the Yellow River in State I and that low temperature events decrease in northern China in State II. In the present state, the frequency of high temperature events increases significantly in most areas over China except the north east, while the frequency of low temperature events decreases mainly in north China and the regions between the Yangtze River and the Yellow River. The distributions of frequencies and strengths of extreme temperature events are consistent in space. The analysis of time evolution of extreme events shows that the occurrence of high temperature events become higher with the change in state, while that of low temperature events decreases. High temperature events are becoming stronger as well and deserve to be paid special attention.
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