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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.7
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GENERAL

Knotted pictures of the GHZ states on the surface of trivial torus

Gu Zhi-Yu, Qian Shang-Wu
Chin. Phys. B, 2012, 21 (7): 070201 doi: 10.1088/1674-1056/21/7/070201
Full Text: [PDF 3756 KB] (Downloads:846)
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By means of the method of torus knot theory, this paper presents the complete process of obtaining the knotted pictures of eight GHZ states on the surface of trivial torus from the knotted pictures of eight basic three-qubit states on the surface of trivial torus. Thus, we obtain eight knotted pictures 121 linkage on the ordinary plane.

Noether conserved quantities and Lie point symmetries for difference nonholonomic Hamiltonian systems in irregular lattices

Xia Li-Li, Chen Li-Qun
Chin. Phys. B, 2012, 21 (7): 070202 doi: 10.1088/1674-1056/21/7/070202
Full Text: [PDF 124 KB] (Downloads:557)
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The Noether conserved quantities and the Lie point symmetries for difference nonholonomic Hamiltonian systems in irregular lattices are studied. The generalized Hamiltonian equations of the systems are given on the basis of the transformation operators in the space of discrete Hamiltonians. The Lie transformations acting on the lattice, as well as the equations and the determining equations of the Lie symmetries are obtained for the nonholonomic Hamiltonian systems. The discrete analogue of the Noether conserved quantity is constructed by using the Lie point symmetries. An example is discussed to illustrate the results.

Mei symmetry and conserved quantities in Kirchhoff thin elastic rod statics

Wang Peng, Xue Yun, Liu Yu-Lu
Chin. Phys. B, 2012, 21 (7): 070203 doi: 10.1088/1674-1056/21/7/070203
Full Text: [PDF 100 KB] (Downloads:635)
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We investigate the application of the Mei symmetry analysis in finding conserved quantities for the thin elastic rod statics. By using the Mei symmetry analysis, we have obtained the Jacobi integral and the cyclic integrals for a thin elastic rod with the intrinsic twisting for both the cases of circular and non-circular cross sections. Our results can be easily reduced to the results without the intrinsic twisting that have been reported. Through calculation, we find that the Noether symmetry can be more directly and easily used than the Mei symmetry in finding the first integrals for the thin elastic rod. These first integrals will be helpful in the studying of exact solutions and the stability as well as the numerical simulation of the elastic rod model for DNA.

Form invariance and approximate conserved quantity of Appell equations for a weakly nonholonomic system

Jia Li-Qun, Zhang Mei-Ling, Wang Xiao-Xiao, Han Yue-Lin
Chin. Phys. B, 2012, 21 (7): 070204 doi: 10.1088/1674-1056/21/7/070204
Full Text: [PDF 86 KB] (Downloads:625)
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A weakly nonholonomic system is a nonholonomic system whose constraint equations contain a small parameter. The form invariance and the approximate conserved quantity of the Appell equations for a weakly nonholonomic system are studied. The Appell equations for the weakly nonholonomic system are established, and the definition and the criterion of form invariance of the system are given. The structure equation of form invariance for the weakly nonholonomic system and the approximate conserved quantity deduced from the form invariance of the system are obtained. Finally, an example is given to illustrate the application of the results.

An extension of the modified Sawada–Kotera equation and conservation laws

He Guo-Liang, Geng Xian-Guo
Chin. Phys. B, 2012, 21 (7): 070205 doi: 10.1088/1674-1056/21/7/070205
Full Text: [PDF 95 KB] (Downloads:796)
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Based on the modified Sawada--Kotera equation, we introduce a 3?3 matrix spectral problem with two potentials and derive a hierarchy of new nonlinear evolution equations. The second member in the hierarchy is a generalization of the modified Sawada--Kotera equation, by which a Lax pair of the modified Sawada--Kotera equation is obtained. With the help of the Miura transformation, explicit solutions of the Sawada--Kotera equation, the Kaup--Kupershmidt equation, and the modified Sawada--Kotera equation are given. Moreover, infinite sequences of conserved quantities of the first two nonlinear evolution equations in the hierarchy and the modified Sawada--Kotera equation are constructed with the aid of their Lax pairs.

Explicit multi-symplectic method for the Zakharov–Kuznetsov equation

Qian Xu, Song Song-He, Gao Er, Li Wei-Bin
Chin. Phys. B, 2012, 21 (7): 070206 doi: 10.1088/1674-1056/21/7/070206
Full Text: [PDF 1115 KB] (Downloads:814)
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We propose an explicit multi-symplectic method to solve the two-dimensional Zakharov--Kuznetsov equation. The method is is to combine the multi-symplectic Fourier pseudospectral method for spatial discretization and the Euler method for temporal discretization. It is verified that the proposed method has corresponding discrete multi-symplectic conservation laws. Numerical simulations indicate that the proposed scheme is characterized by excellent conservation.

Novel delay dependent stability analysis of Takagi–Sugeno fuzzy uncertain neural networks with time varying delays

M. Syed Ali
Chin. Phys. B, 2012, 21 (7): 070207 doi: 10.1088/1674-1056/21/7/070207
Full Text: [PDF 122 KB] (Downloads:604)
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This paper presents the stability analysis for a class of neural networks with time varying delays that are represented by the Takagi--Sugeno (T--S) model. The main results given here focus on the stability criteria using a new Lyapunov functional. New relaxed conditions and new linear matrix inequality-based designs are proposed that outperform the previous results found in the literature. Numerical examples are provided to show that the achieved conditions are less conservative than the existing ones in the literature.

Symmetry of Lagrangians of holonomic nonconservative system in event space

Zhang Bin, Fang Jian-Hui, Zhang Wei-Wei
Chin. Phys. B, 2012, 21 (7): 070208 doi: 10.1088/1674-1056/21/7/070208
Full Text: [PDF 85 KB] (Downloads:474)
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This paper analyzes the symmetry of Lagrangians and the conserved quantity for the holonomic non-conservative system in the event space. The criterion and the definition of the symmetry are proposed first, then a quantity caused by the symmetry and its existence condition are given. An example is shown to illustrate the application of the result in the end.

Visitor flow pattern of Expo 2010

Fan Chao, Guo Jin-Li
Chin. Phys. B, 2012, 21 (7): 070209 doi: 10.1088/1674-1056/21/7/070209
Full Text: [PDF 4124 KB] (Downloads:764)
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Expo 2010 Shanghai China was a successful, splendid, and unforgettable event, remaining us with valuable experiences. The visitor flow pattern of the Expo is investigated in this paper. The Hurst exponent, the mean value, and the standard deviation of visitor volume indicate that the visitor flow is fractal with long-term stability and correlation as well as obvious fluctuation in short period. Then the time series of visitor volume is converted into a complex network by using the visibility algorithm. It can be inferred from the topological properties of the visibility graph that the network is scale-free, small-world, and hierarchically constructed, confirming that the time series are fractal and a close relationship exists among the visitor volumes on different days. Furthermore, it is inevitable to have some extreme visitor volumes in the original visitor flow, and these extreme points may appear in group to a great extent. All these properties are closely related to the feature of the complex network. Finally, the revised linear regression is performed to forecast the next-day visitor volume based on the previous 10-day data.

Effects of information asymmetry on cooperation in the prisoners’ dilemma game

Wang Xi-Peng, Jiang Luo-Luo, Wang Bing-Hong
Chin. Phys. B, 2012, 21 (7): 070210 doi: 10.1088/1674-1056/21/7/070210
Full Text: [PDF 222 KB] (Downloads:674)
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Effects of information asymmetry on cooperation in the dilemma game of prisoners are investigated. The amplitude A is introduced to describe the degree of information asymmetry. It is found that there exists an optimal value of amplitude Aopt at which the fraction of cooperation reaches its maximal value. The reason lies in that cooperators on the two-dimensional grid form large clusters at Aopt. In addition, the theoretical analysis in terms of the mean-field theory is used to understand this kind of phenomenon. It is confirmed that the information asymmetry plays an important role in the dynamics of dilemma games of spatial prisoners.

Monte Carlo study of the universal area distribution of clusters in honeycomb O(n) loop model

Xu Ya-Dong, Liu Qing-Quan, Deng You-Jin
Chin. Phys. B, 2012, 21 (7): 070211 doi: 10.1088/1674-1056/21/7/070211
Full Text: [PDF 136 KB] (Downloads:460)
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We investigate the area distribution of clusters (loops) for the honeycomb O(n) loop model by means of worm algorithm with n=0.5, 1, 1.5, and 2. At the critical point, the number of clusters, whose enclosed area is greater than A, is proportional to A-1 with a proportionality constant C. We confirm numerically that C is universal, and its value agrees well with the predictions based on the Coulomb gas method.

Grammian and Pfaffian solutions as well as Pfaffianization for a (3+1)-dimensional generalized shallow water equation

Tang Ya-Ning, Ma Wen-Xiu, Xu Wei
Chin. Phys. B, 2012, 21 (7): 070212 doi: 10.1088/1674-1056/21/7/070212
Full Text: [PDF 98 KB] (Downloads:792)
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Based on the Grammian and Pfaffian derivative formulae, Grammian and Pfaffian solutions are obtained for a (3+1)-dimensional generalized shallow water equation in the Hirota bilinear form. Moreover, a Pfaffian extension is made for the equation by means of the Pfaffianization procedure, the Wronski-type and Gramm-type Pfaffian solutions of the resulting coupled system are presented.

A new type of photon-added squeezed coherent state and its statistical properties

Zhou Jun, Fan Hong-Yi, Song Jun
Chin. Phys. B, 2012, 21 (7): 070301 doi: 10.1088/1674-1056/21/7/070301
Full Text: [PDF 4410 KB] (Downloads:811)
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We construct a new type of photon-added squeezed coherent state generated by repeatedly operating the bosonic creation operator on a new type of squeezed coherent state [Fan H Y and Xiao M 1996 Phys. Lett. A 220 81]. We find that its normalization factor is related to single-variable Hermite polynomials. Furthermore, we investigate its statistical properties, such as Mandel's Q parameter, photon-number distribution, and Wigner function. The nonclassicality is displayed in terms of the intense oscillation of photon-number distribution and the negativity of the Wigner function.

Dynamical time versus system's time in quantum mechanics

Dušan Arsenović, Nikola Burić, Dragomir Davidović, Slobodan Prvanović
Chin. Phys. B, 2012, 21 (7): 070302 doi: 10.1088/1674-1056/21/7/070302
Full Text: [PDF 107 KB] (Downloads:616)
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Properties of an operator representing the dynamical time in the extended parameterization invariant formulation of quantum mechanics are studied. It is shown that this time operator is given by a positive operator measure analogously to the quantities that are known to represent various measurable time operators. The relation between the dynamical time of the extended formulation and the best known example of the system's time operator, i.e., for the free one-dimensional particle, is obtained.

Exact solutions of the Klein–Gordon equation with ring-shaped oscillator potential by using the Laplace integral transform

Sami Ortakaya
Chin. Phys. B, 2012, 21 (7): 070303 doi: 10.1088/1674-1056/21/7/070303
Full Text: [PDF 95 KB] (Downloads:1523)
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We present exact solutions for the Klein--Gordon equation with a ring-shaped oscillator potential. The energy eigenvalues and the normalized wave functions are obtained for a particle in the presence of non-central oscillator potential. The angular functions are expressed in terms of the hypergeometric functions. The radial eigenfunctions have been obtained by using the Laplace integral transform. By means of the Laplace transform method, which is efficient and simple, the radial Klein--Gordon equation is reduced to a first-order differential equation.

Exact solutions and localized excitations of (3+1)-dimensional Gross–Pitaevskii system

Fei Jin-Xi, Zheng Chun-Long
Chin. Phys. B, 2012, 21 (7): 070304 doi: 10.1088/1674-1056/21/7/070304
Full Text: [PDF 330 KB] (Downloads:586)
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Periodic wave solutions and solitary wave solutions to a generalized (3+1)-dimensional Gross--Pitaevskii equation with time-modulated dispersion, nonlinearity, and potential are derived in terms of an improved homogeneous balance principle and a mapping approach. These exact solutions exist under certain conditions via imposing suitable constraints on the functions describing dispersion, nonlinearity, and potential. The dynamics of the derived solutions can be manipulated by prescribing specific time-modulated dispersions, nonlinearities, and potentials. The results show that the periodic waves and solitary waves with novel behaviors are similar to similaritons reported in other nonlinear systems.

Exact projective solutions of generalized nonlinear Schrödinger system with variable parameters

Zheng Chun-Long, Li Yin
Chin. Phys. B, 2012, 21 (7): 070305 doi: 10.1088/1674-1056/21/7/070305
Full Text: [PDF 93 KB] (Downloads:596)
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A direct self-similarity mapping approach is successfully applied to a generalized nonlinear Schrödinger (NLS) system. Based on the known exact solutions of a self-similarity mapping equation, a few types of significant localized excitation with novel properties are obtained by selecting appropriate system parameters. The integrable constraint condition for the generalized NLS system derived naturally here is consistent with the known compatibility condition generated via the Painlev? analysis.

On the role of the uncertainty principle in superconductivity and superfluidity

Roberto Onofrio
Chin. Phys. B, 2012, 21 (7): 070306 doi: 10.1088/1674-1056/21/7/070306
Full Text: [PDF 212 KB] (Downloads:881)
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We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment, which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers. In the case of superconductors, this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field, and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time. In the case of ultracold atomic Fermi gases, this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity. Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors, and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.

A protocol to transform Svetlichny's genuine multipartite correlations into standard isotropic form

Xiang Yang, Ren Xi-Jun
Chin. Phys. B, 2012, 21 (7): 070307 doi: 10.1088/1674-1056/21/7/070307
Full Text: [PDF 90 KB] (Downloads:451)
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The standard isotropic correlations are widely used in the research of no-locality of quantum physics. We prove that any multipartite no-signaling correlation can be transformed into standard isotropic form through a randomization procedure which do not change Svetlichny's genuine multipartite correlation. For the tripartite correlations, every part with two-input and two-outcome, we explicitly give the protocol and the proof of its validity. We then generalize the protocol to deal with the case of N-partite.

Influence of pumping laser bandwidth on the quantum fluctuation chracteristic of non-degenerate optical parametric amplifier

Zhao Chao-Ying, Ye Xing-Zhen, Yang Cheng-Feng, Chen Li-Ya
Chin. Phys. B, 2012, 21 (7): 070308 doi: 10.1088/1674-1056/21/7/070308
Full Text: [PDF 139 KB] (Downloads:480)
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Usually the quantum fluctuation characteristic of the non-degenerate optical parametric amplifier is analysed under the assumption of monochromatic pumping. However, in experiments, the driving beam with finite bandwidth is used to obtain the non-degenerate signal and idler beam amplifications. On account of that, we derive an analytical solution for the non-degenerate optical parametric amplification system with finite bandwidth laser pumping, and evaluate the associated quantum fluctuation. Finally, the application of the V1 criterion to the bipartite entanglement is discussed.

Two methods to deal with inhomogenous Rabi frequency in microwave transition

Cheng Feng, Wang Yu-Zhu
Chin. Phys. B, 2012, 21 (7): 070309 doi: 10.1088/1674-1056/21/7/070309
Full Text: [PDF 947 KB] (Downloads:655)
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We analysed the influence of inhomogenous microwave field on the coherence of atom ensembles. Two methods were proposed to suppress the dephasing generated by the inhomogenous Rabi frequency. One of them was realized by spin echo, and the other one was based on the identical spin rotation effect. The results of calculation showed that the contrast of signal acquired in experiment can be improved by the two methods. Their advantages and drawbacks were discussed. We hope they could be used to improve the contrast of experimental signal in the situation that the microwave fields are very inhomogenous. Finally, we discussed the case of continuous working microwave field and showed that the dipole force raised with the inhomogeneity can be eased by spin flip.

Aharonov–Anandan phase gate in sub Hilbert space of a coupling flux qubits system

Zheng Guo-Lin, Deng Hui, Wu Yu-Lin, Wang Xin-Qiang, Chen Ying-Fei, Zheng Dong-Ning
Chin. Phys. B, 2012, 21 (7): 070310 doi: 10.1088/1674-1056/21/7/070310
Full Text: [PDF 2696 KB] (Downloads:776)
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We study two flux qubits with a parameter coupling scenario. Under the rotating wave approximation, we truncate the 4-dimension Hilbert space of a coupling flux qubits system to a 2-dimension subspace spanned by two dressed states |01> and |10>. In this subspace, we illustrate how to generate an Aharnov--Anandan phase, based on which, we can construct a NOT gate (as effective as a C-NOT gate) in this coupling flux qubits system. Finally, the fidelity of the NOT gate is also calculated in the presence of the simulated classical noise.

Area and entropy spectra of black holes via an adiabatic invariant

Liu Cheng-Zhou
Chin. Phys. B, 2012, 21 (7): 070401 doi: 10.1088/1674-1056/21/7/070401
Full Text: [PDF 96 KB] (Downloads:516)
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By considering an adiabatic invariant for black holes, the area and entropy spectra of static spherically-symmetric black holes are investigated. Without using quasi-normal modes of black holes, equally-spaced area and entropy spectra are derived by only utilizing the adiabatic invariant. The spectra for non-charged and charged black holes are calculated, respectively. All these results are consistent with the original Bekenstein spectra.

Discussion on the event horizon and quantum ergosphere of dynamic rotating black holes in a tunneling framework

Liu Bai-Sheng, Zhang Jing-Yi
Chin. Phys. B, 2012, 21 (7): 070402 doi: 10.1088/1674-1056/21/7/070402
Full Text: [PDF 100 KB] (Downloads:574)
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According to the Parikh--Wilczek tunneling framework, the locations of the local horizons of dynamic rotating black holes can be worked out. The calculations show that the quantum ergosphere of the black hole is identical with the tunneling potential barrier set by particle's tunneling across the relevant horizon. Then, some discussions on the origin of the Hawking radiation will be shown.

Fractional charges and fractional spins for composite fermions in quantum electrodynamics

Wang Yong-Long, Lu Wei-Tao, Jiang Hua, Xu Chang-Tan, Pan Hong-Zhe
Chin. Phys. B, 2012, 21 (7): 070501 doi: 10.1088/1674-1056/21/7/070501
Full Text: [PDF 118 KB] (Downloads:550)
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By using the Faddeev--Senjanovic path integral quantization method, we quantize the composite fermions in quantum electrodynamics (QED). In the sense of Dirac's conjecture, we deduce all the constraints and give Dirac's gauge transformations (DGT). According to that the effective action is invariant under the DGT, we obtain the Noether theorem at the quantum level, which shows the fractional charges for the composite fermions in QED. This result is better than the one deduced from the equations of motion for the statistical potentials, because this result contains both odd and even fractional numbers. Furthermore, we deduce the Noether theorem from the invariance of the effective action under the rotational transformations in 2-dimensional (x,y) plane. The result shows that the composite fermions have fractional spins and fractional statistics. These anomalous properties are given by the constraints for the statistical gauge potential.

Properties of train traffic flow in moving block system

Wang Min, Zeng Jun-Wei, Qian Yong-Sheng, Li Wen-Jun, Yang Fang, Jia Xin-Xin
Chin. Phys. B, 2012, 21 (7): 070502 doi: 10.1088/1674-1056/21/7/070502
Full Text: [PDF 358 KB] (Downloads:890)
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The development direction of railway is to improve the capacity and the service quality, where the service quality includes safety, schedule, high speed, and comfort. In light of the existing cellular automaton models, in this paper, we develop a model to analyze the mixed running processes of trains with maximal speeds of 500 km/h and 350 km/h respectively in the moving block system. In the proposed model, we establish some sound rules to control the running process of train, where the rules include the departure rules in the intermediate stations, the overtaking rules, and the conditions of speed limitation for train stopping at a station or passing through a station. With the consideration of the mixed ratio and the distance between two adjacent stations, the properties of the train traffic flow (including capacity and average speed) are simulated. The numerical results show that the interactions among different trains will affect the capacity, and a proper increasing of the spatial distance between two adjacent stations can enhance the capacity and the average speed under the moving block.

Dynamics of vibrational chaos and entanglement in triatomic molecules: Lie algebraic model

Zhai Liang-Jun, Zheng Yu-Jun, Ding Shi-Liang
Chin. Phys. B, 2012, 21 (7): 070503 doi: 10.1088/1674-1056/21/7/070503
Full Text: [PDF 5685 KB] (Downloads:889)
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In this paper, the dynamics of chaos and the entanglement in triatomic molecular vibrations are investigated. On the classical aspect, we study the chaotic trajectories in the phase space. We employ the linear entropy to examine the dynamical entanglement of the two bonds on the quantum aspect. The correspondence between the classical chaos and the quantum dynamical entanglement is also investigated. As an example, we apply our algebraic model to molecule H2O.

Matter-wave solutions of Bose–Einstein condensates with three-body interaction in linear magnetic and time-dependent laser fields

Etienne Wamba, Timoléon C. Kofané, Alidou Mohamadou
Chin. Phys. B, 2012, 21 (7): 070504 doi: 10.1088/1674-1056/21/7/070504
Full Text: [PDF 7937 KB] (Downloads:657)
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We construct, through a further extension of the tanh-function method, the matter-wave solutions of Bose--Einstein condensates (BECs) with a three-body interaction. The BECs are trapped in a potential comprising the linear magnetic and the time-dependent laser fields. The exact solutions obtained include soliton solutions, such as kink and antikink as well as bright, dark, multisolitonic modulated waves. We realize that the motion and the shape of the solitary wave can be manipulated by controlling the strengths of the fields.

A lattice hydrodynamical model considering turning capability

Tian Huan-Huan, Xue Yu
Chin. Phys. B, 2012, 21 (7): 070505 doi: 10.1088/1674-1056/21/7/070505
Full Text: [PDF 3163 KB] (Downloads:467)
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A new two-dimensional lattice hydrodynamic model considering the turning capability of cars is proposed. Based on this model, the stability condition for this new model is obtained by using linear stability analysis. Near the critical point, the modified KdV equation is deduced by using the nonlinear theory. The results of numerical simulation indicate that the critical point ac increases with the increase of the fraction p of northbound cars which continue to move along the positive y direction for c=0.3, but decreases with the increase of p for c=0.7. The results also indicate that the cars moving along only one direction (eastbound or northbound) are most stable.

Effects of anisotropy and magnetic fields on the specific heat of a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot

Zhai Zhi-Yuan, Li Yu-Qi, Pan Xiao-Yin
Chin. Phys. B, 2012, 21 (7): 070506 doi: 10.1088/1674-1056/21/7/070506
Full Text: [PDF 265 KB] (Downloads:541)
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We investigate the effects due to anisotropy and magnetic field interaction for a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot. The specific heat is studied with varying temperature, anisotropy, and magnetic field strength. The cases without and with the inclusion of the spin Zeeman interaction are considered.

Flow difference effect in the two-lane lattice hydrodynamic model

Wang Tao, Gao Zi-You, Zhao Xiao-Mei, Tian Jun-Fang, Zhang Wen-Yi
Chin. Phys. B, 2012, 21 (7): 070507 doi: 10.1088/1674-1056/21/7/070507
Full Text: [PDF 407 KB] (Downloads:1025)
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By introducing a flow difference effect, a modified lattice two-lane traffic flow model is proposed, which is proved to be capable of improving the stability of traffic flow. Both the linear stability condition and the kink--antikink solution derived from the modified Korteweg--de Vries (mKdV) equation are analyzed. Numerical simulations verify the theoretical analysis. Furthermore, the evolution laws under different disturbances in the metastable region is studied.

Stability and attractive basins of multiple equilibria in delayed two-neuron networks

Huang Yu-Jiao, Zhang Hua-Guang, Wang Zhan-Shan
Chin. Phys. B, 2012, 21 (7): 070701 doi: 10.1088/1674-1056/21/7/070701
Full Text: [PDF 617 KB] (Downloads:568)
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Multiple stability for two-dimensional delayed recurrent neural networks with piecewise linear activation functions of 2r (r≥q1) corner points is studied. Sufficient conditions are established for checking the existence of (2r+1)2 equilibria in delayed recurrent neural networks. Under these conditions, (r+1)2 equilibria are locally exponentially stable, and (2r+1)2-(r+1)2-r2 equilibria are unstable. Attractive basins of stable equilibria are estimated, which are larger than invariant sets derived by decomposing state space. One example is provided to illustrate the effectiveness of our results.
RAPID COMMUNICATION

Evolution of the 251 cm-1 infrared phonon mode with temperature in Ba0.6K0.4Fe2As2 Hot!

Dai Yao-Min, Xu Bing, Shen Bing, Xiao Hong, Lobo R. P. S. M, Qiu Xiang-Gang
Chin. Phys. B, 2012, 21 (7): 077403 doi: 10.1088/1674-1056/21/7/077403
Full Text: [PDF 141 KB] (Downloads:839)
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The far-infrared optical reflectivity of optimally doped Ba1-xKxFe2As2 (x = 0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1. This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by the chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound.

Magnetic anisotropy and magnetization reversal of ultrathin iron films with in-plane magnetization on Si(111) substrates

Liu Hao-Liang, He Wei, Du Hai-Feng, Fang Ya-Peng, Wu Qiong, Zhang Xiang-Qun, Yang Hai-Tao, Cheng Zhao-Hua
Chin. Phys. B, 2012, 21 (7): 077503 doi: 10.1088/1674-1056/21/7/077503
Full Text: [PDF 3113 KB] (Downloads:1347)
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The magnetic anisotropy and magnetization reversal of single crystal Fe films with thickness of 45 monolayer (ML) grown on Si(111) have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM). Owing to the significant modification of the energy surface in remanent state by slight misorientation from (111) plane and a uniaxial magnetic anisotropy, the azimuthal angular dependence of in-plane resonance field shows a six-fold symmetry with a weak uniaxial contribution, while the remanence of hysteresis loops displays a two-fold one. The competition between the first and second magnetocrystalline anisotropies may result in the switching of in-plane easy axis of the system. Combining the FMR and VSM measurements, the magnetization reversal mechanism has also been determined.
ATOMIC AND MOLECULAR PHYSICS

Population coherent control of Rydberg sodium atom in microwave field

Jiang Li-Juan, Zhang Xian-Zhou, Jia Guang-Rui, Zhang Yong-Hui, Xia Li-Hua
Chin. Phys. B, 2012, 21 (7): 073101 doi: 10.1088/1674-1056/21/7/073101
Full Text: [PDF 595 KB] (Downloads:563)
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The B-spline expansion technique and the time-dependent multilevel approach (TDMA) are used to study the interaction between microwave field and sodium atoms. The Rydberg sodium atom energy levels of p states in zero field are calculated, and the results are in good agreement with the other theoretical ones. The time evolutions during the population transfers of the five states from n=75 to n=79 in different microwave fields are obtained. The results show that the coherent control of the population transfer from the lower states to the higher ones can be accomplished by optimizing the microwave pulse parameters.

Charge density at the nucleus and radial behavior of ground state for lithium-like ions with Z = 21 to 30

Yu Wei-Wei, Wang Zhi-Wen, Chen Chao, Cai Juan, Zhang Nan
Chin. Phys. B, 2012, 21 (7): 073102 doi: 10.1088/1674-1056/21/7/073102
Full Text: [PDF 128 KB] (Downloads:795)
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By using the full core plus correlation (FCPC) type wave functions, the accurate charge densities ρ (0) at the nucleus and the radial expectation values of the ground states for the lithium-like systems with Z=21 to 30 are obtained. The determinantal conditions and the electron-nucleus cusp condition are used to calculate the inequalities of the upper and the lower bounds to ρ (0) with two or more expectation values. These inequalities derived by Angulo and Dehesa [Phys. Rev. A 44 1516 (1991)] are verified to be valid too for these ions with higher nuclear charge. The present results show that the wave functions used in this paper are satisfactory in the whole configuration space for these ions with higher nuclear charge.

Methyl orbital signatures in 2-amino-1-propanol

Wang Ke-Dong, Duan Kun-Jie, Liu Yu-Fang
Chin. Phys. B, 2012, 21 (7): 073103 doi: 10.1088/1674-1056/21/7/073103
Full Text: [PDF 2940 KB] (Downloads:628)
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Electron density distributions of 2-aminoethanol (2AE) and 2-amino-1-propanol (2AP) are calculated in both the coordinate and the momentum spaces using the B3LYP/TZVP method. Using the dual space analysis, molecular orbital signatures of methyl substituent in 2AP are identified with respect to 2AE. Relaxations of the geometry and the valence orbital in 2AP are found to be due to the insertion of the methyl group. Five orbitals, not four orbitals, are identified as the methyl signatures. They are orbital 5a in the core shell, orbitals 9a and 10a in the inner valence shell, and orbitals 15a and 16a in the outer valence. In the inner valence shell, the attachment of methyl to 2AE causes a splitting of its orbital 8a into orbitals 9a and 10a of 2AP, whereas in the outer valence shell, the methyl group results in the insertion of an additional orbital pair of 15a and 16a. The frontier molecular orbitals 21a, 20a, and 19a are found to have no significant role in the methylation of 2AE.

Surface effect of nanocrystals doped with rare earth ions enriched on surface and its application in upconversion luminescence

He En-Jie, Liu Ning, Zhang Mao-Lian, Qin Yan-Fu, Guan Bang-Gui, Li Yong, Guo Ming-Lei
Chin. Phys. B, 2012, 21 (7): 073201 doi: 10.1088/1674-1056/21/7/073201
Full Text: [PDF 29051 KB] (Downloads:388)
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By employing a certain proportion of hydrogen peroxide, ammonia, ammonium fluoride and ethylene diamine tetraacetic acid (EDTA) as precipitator, well-crystallized LaOF:Eu3+ and LaOF:Yb3+, Er3+ nanocrystals are synthesized with chemical co-precipitation method. The structural properties of these samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) spectra. The results show that all the samples have an average size below 70 nm and decreases gradually with the increase of the EDTA content, and a certain number of EDTA molecules are coupled with doped ions on the surfaces of nanocrystals. Most of the doped ions are proved to be enriched on the surfaces of nanocrystals and surrounded by the high energy vibration groups and bonds in EDTA molecules. The observed differences in upconversion emission spectrum among the different LaOF:Yb3+, Er3+ nanocrystals are explained by the different two-photon upconversion mechanisms. Especially, in the LaOF:Yb3+, Er3+ nanocrystals with EDTA, the two-photon processes that contain several special cross relaxation processes are introduced to analyse the corresponding upconversion mechanisms.

Photodetachment microscopy of the hydrogen negative ion in electric field near a metal surface

Tang Tian-Tian, Wang De-Hua, Wang Shan-Shan
Chin. Phys. B, 2012, 21 (7): 073202 doi: 10.1088/1674-1056/21/7/073202
Full Text: [PDF 371 KB] (Downloads:596)
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According to the semi-classical theory, we study the photodetachment microscopy of H- in the electric field near a metal surface. During the photodetachment, the electron is photo-detached by a laser and the electron is drawn toward a position-sensitive detector. The electron flux distribution is measured as a function of position. Two classical paths lead the ion to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If the metal surface perpendicular to the electric field is added, we find that the interference pattern is related not only to the electron energy and the electric-field strength, but also to the ion--surface distance. Besides, the laser polarization also has a great influence on the electron flux distribution. We present calculations predicting the interference pattern that may be seen in experiment. We hope that our study can provide a new understanding of the electron flux distribution of negative ions in external field and surface, and can guide the future experimental research on the negative ion photo-detachment microscopy.

Suppressing the weakly bound states in the photoassociation dynamics by a frequency cut-off laser pulse

Lin Feng, Zhang Wei, Zhao Ze-Yu, Cong Shu-Lin
Chin. Phys. B, 2012, 21 (7): 073203 doi: 10.1088/1674-1056/21/7/073203
Full Text: [PDF 212 KB] (Downloads:649)
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The photoassociation dynamics of ultracold lithium atoms controlled by a cut-off pulse has been investigated theoretically by solving numerically the time-dependent Schrödinger equation using the mapped Fourier grid method. The frequency components of the laser pulse close to the atomic resonance are partly cut off. Compared with the typical Gauss-type pulses, the cut-off pulse is helpful to suppress efficiently the weakly bound states and prepare the associated molecules in the lower vibrational states. Especially, the dependence of photoassociation probability on the cut-off position of the laser pulse is explored.

Calculations of the vibrational frequency and isotopic shift of UF6 and U2F6

Zhang Yun-Guang, Zha Xin-Wei
Chin. Phys. B, 2012, 21 (7): 073301 doi: 10.1088/1674-1056/21/7/073301
Full Text: [PDF 973 KB] (Downloads:896)
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Molecular structure, vibrational frequency and infrared intensity of UF6 are investigated by using revised Perdew--Burke--Enzerhof function with triple-zeta polarized basis set. The calculation results are in good agreement with the experimental values and indicate the existence of stable U2F6 molecule with a multiply bonded U2 unit. The calculation results also predict that the D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies, and infrared intensities are also reported for U2F6 molecules in D3d symmetry. In addition, the isotopic shift of vibrational frequencies of the two molecules under isotopic substitution of uranium atom are also investigated with the same method. The U2F6 molecule is predicted to be better than UF6 for laser uranic isotope separation.

Isotope effect on the stereodynamics for the collision reaction H+LiF(v = 0, j = 0)→ HF+Li

Yue Xian-Fang
Chin. Phys. B, 2012, 21 (7): 073401 doi: 10.1088/1674-1056/21/7/073401
Full Text: [PDF 2143 KB] (Downloads:1253)
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Stereodynamics for the reaction H+LiF(v = 0, j = 0)!HF+Li and its isotopic variants on the ground-state (1XXA′) potential energy surface (PES) are studied by employing the quasi-classical trajectory (QCT) method. At a collision energy of 1.0 eV, product rotational angular momentum distributions P(θr), P(?r), and P(θr, ?r), are calculated in the center-of-mass (CM) frame. The results demonstrate that the product rotational angular momentum j′ is not only aligned along the direction perpendicular to the reagent relative velocity vector k, but also oriented along the negative y axis. The four generalized polarization-dependent differential cross sections (PDDCSs) are also computed. The PDDCS00 distribution shows a preferential forward scattering for the product angular distribution in each of the three isotopic reactions, which indicates that the title collision reaction is a direct reaction mechanism. Isotope effect on the stereodynamics is revealed and discussed in detail.

Effect of initial-state target polarization on single ionization of helium by 1-keV electron impact

Sun Shi-Yan, Ma Xiao-Yan, Li Xia, Miao Xiang-Yang, Jia Xiang-Fu
Chin. Phys. B, 2012, 21 (7): 073402 doi: 10.1088/1674-1056/21/7/073402
Full Text: [PDF 274 KB] (Downloads:501)
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We report new results of triple differential cross sections for the single ionization of helium by 1-KeV electron impact at the ejection energy of 10 eV. Investigations have been made for both the perpendicular plane and the plane perpendicular to the momentum transfer geometries. The present calculation is based on the three-Coulomb wave function. Here we have also incorporated the effect of target polarization in the initial state. A comparison is made between the present calculation with the results of other theoretical methods and a recent experiment [D黵r M, Dimopoulou C, Najjari B, Dorn A, Bartschat K, Bray I, Fursa D V, Chen Z, Madison D H and Ullrich J 2008 Phys. Rev. A 77 032717]. At an impact energy of 1 KeV, the target polarization is found to induce a substantial change of the cross section for the ionization process. We observe that the effect of target polarization plays a dominant role in deciding the shape of triple differential cross sections.

Post collision interactions and polarization effect in (e, 2e) collisions of helium

Zang Shuang-Shuang, Ge Zi-Ming
Chin. Phys. B, 2012, 21 (7): 073403 doi: 10.1088/1674-1056/21/7/073403
Full Text: [PDF 130 KB] (Downloads:484)
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A modified distorted-wave Born approximation (DWBA) method is used to calculate the triple differential cross sections (TDCSs) in a coplanar asymmetric geometry for the electron impact single ionization of a He (1s2) atom at intermediate and lower energies. The post-collision interaction and the polarization effect in (e, 2e) collisions of helium are considered in the calculations. The polarization potentials from the damping method and density functional theory (DFT) are compared. Theoretical results are compared with the recent experimental data.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Demonstrating additional law of relativistic velocities based on squeezed light

Yang Da-Bao, Li Yan, Zhang Fu-Lin, Chen Jing-Ling
Chin. Phys. B, 2012, 21 (7): 074201 doi: 10.1088/1674-1056/21/7/074201
Full Text: [PDF 105 KB] (Downloads:776)
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The special relativity is the foundation for many branches of modern physics, of which the theoretical results are far beyond our daily experience and hard to realized in kinematic experiments. However, its outcomes could be demonstrated by making use of the convenient substitute, i.e., the squeezed light in the present paper. The squeezed light is very important in the field of quantum optics, and the corresponding transformation can be regarded as the coherent state of SU(1,1). In this paper, the connection between the squeezed operator and the Lorentz boost is built under certain conditions. Furthermore, the additional law of relativistic velocities and the angle of the Wigner rotation are deduced as well.

Design of a reentrant double staggered ladder circuit for V-band coupled-cavity traveling-wave tube

Liu Yang, Xu Jin, Lai Jian-Qiang, Xu Xiong, Shen Fei, Wei Yan-Yu, Huang Min-Zhi, Tang Tao, Gong Yu-Bin
Chin. Phys. B, 2012, 21 (7): 074202 doi: 10.1088/1674-1056/21/7/074202
Full Text: [PDF 1776 KB] (Downloads:869)
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The reentrant double staggered ladder slow-wave structure is employed in a high-power V-band coupled-cavity traveling-wave tube. This structure has a wide bandwidth, a moderate interaction impedance, and excellent thermal dissipation properties, besides the easy fabrication. A well-matched waveguide coupler is proposed for the structure. Combining the design of attenuators, a full-scale three-dimensional circuit model for the V-band coupled-cavity traveling-wave tube is constructed. The electromagnetic characteristics and the beam--wave interaction of this structure are investigated. The beam current is set to be 100 mA, and the cathode voltage is tuned from 16.8 kV to 15.8 kV. The calculation results show that this tube can produce a saturated average output power over 100 W with an instantaneous bandwidth greater than 1.25 GHz in the frequency ranging from 58 GHz to 62 GHz. The corresponding gain and electronic efficiency can reach over 32 dB and 6.5%, respectively.

Modeling and analysis of silicon-on-insulator elliptical microring resonators for future high-density integrated photonic circuits

Xiong Kang, Xiao Xi, Hu Ying-Tao, Li Zhi-Yong, Chu Tao, Yu Yu-De, Yu Jin-Zhong
Chin. Phys. B, 2012, 21 (7): 074203 doi: 10.1088/1674-1056/21/7/074203
Full Text: [PDF 2333 KB] (Downloads:1038)
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We propose a novel resonator containing an elliptical microring based on silicon-on-insulator platform. Simulations using the three-dimensional finite-difference time-domain method show that the novel elliptical microring can efficiently enhance the mode coupling between straight bus waveguides and resonator waveguides or between adjacent resonators while preserving relatively high intrinsic quality factors with large free spectral range. The proposed resonator would be an alternative choice for future high-density integrated photonic circuits.

The high dependence of polarization resolved laser-induced breakdown spectroscopy on experimental conditions

Nakimana Agnes, Hao Zuo-Qiang, Liu Jia, Tao Hai-Yan, Gao Xun, Sun Chang-Kai, Lin Jing-Quan
Chin. Phys. B, 2012, 21 (7): 074204 doi: 10.1088/1674-1056/21/7/074204
Full Text: [PDF 804 KB] (Downloads:742)
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It is shown that the continuum emission produced by the Al alloy ablated by femtosecond laser pulses is much more polarized than the characteristic lines of elements. A Glan--Thomson polarizer is used in the laser-induced breakdown spectroscopy experiment to investigate the polarization effect. The use of polarizer at its minimal transmission increases the signal-to-noise ratio. The effects of angle of detection, focal position, and pulse energy on the signal-to-noise ratio are also studied.

A new method for measuring the threshold of stimulated Brillouin scattering

Zhu Xue-Hua, Lü Zhi-Wei, Wang Yu-Lei
Chin. Phys. B, 2012, 21 (7): 074205 doi: 10.1088/1674-1056/21/7/074205
Full Text: [PDF 172 KB] (Downloads:778)
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A new method for measuring the threshold of stimulated Brillouin scattering (SBS) based on the generation location of Stokes beam is proposed for the first time to our knowledge. The length of the medium cell is selected to be longer than the free gain length of pump pulses in the Brillouin medium. The reflected light from a certain mirror in front of the medium cell is chosen as the reference beam, and the SBS threshold is measured by the ''jump'' of the delay between the Stokes beam and the reference beam. An 8-ns Q-switched single-longitudinal-mode pulse is used as the pump and the typical SBS medium FC-72 is selected as the nonlinear medium in our experiment. The SBS threshold intensity is measured to be 173--178 mW/cm2, which is consistent with existing results measured with the transmitted energy limiting method.

Surface defect gap solitons in two-dimensional optical lattices

Meng Yun-Ji, Liu You-Wen, Tang Yu-Huang
Chin. Phys. B, 2012, 21 (7): 074206 doi: 10.1088/1674-1056/21/7/074206
Full Text: [PDF 320 KB] (Downloads:752)
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We investigate the existence and stability of surface defect gap solitons at an interface between a defect of two-dimensional optical lattice and uniform saturable Kerr nonlinear medium. The surface defect embedded in the two-dimensional optical lattice gives rise to some unique properties. It is interestingly found that for the negative defect, stable surface defect gap solitons can exist both in the semi-infinite gap and in the first gap. The deeper the negative defect, the narrower the stable region in the semi-infinite gap will be. For a positive defect, the surface defect gap solitons exist only in the semi-infinite gap and the stable region localizes in a low power region.

Analytical model of signal amplification in silicon waveguides

Meng Fan, Yu Chong-Xiu, Yuan Jin-Hui
Chin. Phys. B, 2012, 21 (7): 074207 doi: 10.1088/1674-1056/21/7/074207
Full Text: [PDF 216 KB] (Downloads:537)
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In this paper, an analytical model to investigate the parametric amplification (PA) and the PA + stimulated Raman scattering (SRS) in silicon waveguides is put forward. When two pump signals are employed, the PA bandwidth of the probe signal is so large that the Raman contribution has to be considered. When Raman contribution fraction f is set to be 0, only the PA occurs to amplify the probe signal, and when f is set to be 0.043, the PA and the SRS amplify the probe signal at the same time. The signal amplifications of both single and dual pump schemes are investigated by using this model. With this model, three main affecting factors, i.e., zero dispersion wavelength (ZDWL), third-order dispersion (TOD), and fourth-order dispersion (FOD), are discussed in detail.

Sorption and permeation of gaseous molecules in amorphous and crystalline PPX C membranes: molecular dynamics and grand canonical Monte Carlo simulation studies

Bian Liang, Shu Yuan-Jie, Wang Xin-Feng
Chin. Phys. B, 2012, 21 (7): 074208 doi: 10.1088/1674-1056/21/7/074208
Full Text: [PDF 6339 KB] (Downloads:593)
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Amorphous and crystalline poly (chloro-p-xylylene) (PPX C) membranes are constructed by using a novel computational technique, that is, a combined method of NVT+NPT-molecular dynamics (MD) and gradually reducing the size (GRS) methods. The related free volumes are defined as homology clusters. Then the sorption and the permeation of gases in PPX C polymers are studied using grand canonical Monte Carlo (GCMC) and NVT-MD methods. The results show that the crystalline PPX C membranes provide smaller free volumes for absorbing or transferring gases relative to the amorphous PPX C area. The gas sorption in PPX C membranes mainly belongs to the physical one, and H bonds can appear obviously in the amorphous area. By cluster analyzing on the mean square displacement of gases, we find that gases walk along the x axis in the crystalline area and walk randomly in the amorphous area. The calculated permeability coefficients are close to the experimental data.

Ultra-violet and mid-infrared continuum generation by cross-phase modulation between red-shifted solitons and blue-shifted dispersive waves in a photonic crystal fiber

Shen Xiang-Wei, Yuan Jin-Hui, Sang Xin-Zhu, Yu Chong-Xiu, Rao Lan, Xin Xiang-Jun, Xia Min, Han Ying, Xia Chang-Ming, Hou Lan-Tian
Chin. Phys. B, 2012, 21 (7): 074209 doi: 10.1088/1674-1056/21/7/074209
Full Text: [PDF 486 KB] (Downloads:782)
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Using the photonic crystal fiber with the zero dispersion wavelength of the fundamental mode at 780 nm designed and fabricated in our lab, the ultra-violet and mid-infrared continua are generated by cross-phase modulation between red-shift solitons and blue-shift dispersive waves. The dependences of continuum on the pump power and wavelength are investigated. With the pump working at 820 nm, when the pump power increases from 300 to 500 mW, the bandwidths of ultra-violet and mid-infrared continua change from 80 to 140 nm and 100 to 200 nm, respectively. The wavelength of ultra-violet continuum is below 246 nm, and the wavelength of mid-infrared continuum exceeds 2500 nm. Moreover, the influences of pump power on wavelength and conversion efficiency of different parts of continua are also demonstrated.

Effect of single point defect on the confinement losses of air-guiding photonic bandgap fibers

Shi Wei-Hua, Zhao Yan, Qian Li-Guo, Chen He-Ming
Chin. Phys. B, 2012, 21 (7): 074210 doi: 10.1088/1674-1056/21/7/074210
Full Text: [PDF 524 KB] (Downloads:534)
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The confinement losses in air-guiding photonic bandgap fibers (PBGFs) with air hole missing are studied with full-vector finite-element method. It is confirmed that there are two loss peaks (1.555 and 1.598 μm), if there is a hole missing in the cladding far from the core. The closer to the core the hole missing is, the larger the confinement losses are, even no mode could propagate in the core. The main power of the fundamental mode leaks from the core to the cladding defect. The quality of PBGFs can be improved through controlling the number and position of defects.

Optical planar waveguides in Yb3+-doped phosphate glasses produced by He+ ion implantation

Liu Chun-Xiao, Li Wei-Nan, Wei Wei, Peng Bo
Chin. Phys. B, 2012, 21 (7): 074211 doi: 10.1088/1674-1056/21/7/074211
Full Text: [PDF 604 KB] (Downloads:800)
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Optical planar waveguides in Yb3+-doped phosphate glasses are fabricated by implanting triple-energy helium ions. The guiding modes and the near-field intensity distribution are measured by using the prism-coupling method and the end-face coupling setup with a He--Ne laser at 633 nm, respectively. The intensity calculation method (ICM) is used to reconstruct the refractive index profile of the waveguide. The absorption and the fluorescence investigations reveal that the glass bulk features are well preserved in the active volumes of the waveguides, suggesting the fabricated structures for possible applications as waveguide lasers.

In vivo hyperthermia effect induced by high-intensity pulsed ultrasound

Cui Wei-Cheng, Tu Juan, Hwang Joo-Ha, Li Qian, Fan Ting-Bo, Zhang Dong, Chen Jing-Hai, Chen Wei-Zhong
Chin. Phys. B, 2012, 21 (7): 074301 doi: 10.1088/1674-1056/21/7/074301
Full Text: [PDF 594 KB] (Downloads:553)
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Hyperthermia effects (39--44 ℃) induced by pulsed high-intensity focused ultrasound (HIFU) have been regarded as a promising therapeutic tool for boosting immune responses or enhancing drug delivery into solid tumor. However, previous studies also reported that the cell death occurs when cells are maintained at 43 ℃ for more than 20 minutes. The aim of this study is to investigate thermal responses inside in vivo rabbit auricular veins exposed to pulsed HIFU (1.17 MHz, 5300 W/cm2, with relatively low-duty ratios (0.2%--4.3%). The results show that: (1) with constant pulse repetition frequency (PRF) (e.g., 1 Hz), the thermal responses inside the vessel will increase with the increasing duty ratio; (2) a temperature elevation to 43 ℃ can be identified at the duty ratio of 4.3%; (3) with constant duty ratios, the change of PRF will not significantly affect the temperature measurement in the vessel; (4) as the duty ratios lower than 4.3%, the presence of microbubbles will not significantly enhance the thermal responses in the vessel, but will facilitate HIFU-induced inertial cavitation events.

The dynamic characteristics of a valve-less micropump

Jiang Dan, Li Song-Jing
Chin. Phys. B, 2012, 21 (7): 074701 doi: 10.1088/1674-1056/21/7/074701
Full Text: [PDF 9855 KB] (Downloads:1263)
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The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathematical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim software are developed. By using the finite-element analysis method, the static analysis of the diaphragm is carried out to obtain the maximum deflection and volumetric displacement. Dynamic characteristics of the valve-less micropump under different excitation voltages and frequencies are simulated and tested. Because of the discrepancy between simulation results and experimental data at frequencies other than the natural frequency, the revised model for the diaphragm maximum volumetric displacement is presented. Comparison between the simulation results based on the revised model and experimental data shows that the dynamic mathematical model based on the hydraulic analogue system is capable of predicting dynamic characteristics of the valve-less micropump at any excitation voltage and frequency.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Numerical simulation and experimental validation of direct current air corona discharge under atmospheric pressure

Liu Xing-Hua, He Wei, Yang Fan, Wang Hong-Yu, Liao Rui-Jin, Xiao Han-Guang
Chin. Phys. B, 2012, 21 (7): 075201 doi: 10.1088/1674-1056/21/7/075201
Full Text: [PDF 5505 KB] (Downloads:2849)
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Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage– current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.

Numerical study on characteristics of nitrogen discharge at high pressure with induced plasma

Wang Yi-Nan, Liu Yue, Zheng Shu, Lin Guo-Qiang
Chin. Phys. B, 2012, 21 (7): 075202 doi: 10.1088/1674-1056/21/7/075202
Full Text: [PDF 343 KB] (Downloads:1054)
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Based on the fluid theory of plasma, a model is built to study the characteristics of nitrogen discharge at high pressure with induced argon plasma. In the model, the spices such as electron, N2+, N4+, Ar+, and two metastable states (N2 (A3u+), N2 (a1u-)) are taken into account. The model includes particle's continuity equations, electron's energy balance equation, and Poisson equation. The model is solved with a finite difference method. The numerical results are obtained and used to investigate the effect of time taken to add nitrogen gas and initially-induced argon plasma pressure. It is found that lower speeds of adding the nitrogen gas and varying the gas pressure can induce higher plasma density, and inversely lower electron temperature. At high-pressure discharge, the electron density increases when the proportion of nitrogen component is below 40%, while the electron density will keep constant as the nitrogen component further increases. It is also shown that with the increase of initially-induced argon plasma pressure, the density of charged particles increases, and the electron temperature as well as the electric field decrease.

Spatial variation behaviors of argon inductively coupled plasma during discharge mode transition

Gao Fei, Li Xue-Chun, Zhao Shu-Xia, Wang You-Nian
Chin. Phys. B, 2012, 21 (7): 075203 doi: 10.1088/1674-1056/21/7/075203
Full Text: [PDF 1988 KB] (Downloads:911)
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A Langmuir probe and an ICCD are employed to study the discharge mode transition in an Ar inductively coupled plasma. Electron density and plasma emission intensity are measured during the E (capacitive discharge) to H (inductive discharge) mode transitions at different pressures. It is found that plasma exists with a low electron density and a weak emission intensity in the E mode, while it has a high electron density and a strong emission intensity in the H mode. Meanwhile, the plasma emission intensity spatial (2D image) profile is symmetrical in the H mode, but the 2D image is an asymmetric profile in the E mode. Moreover, the electron density and emission intensity jump up discontinuously at high pressure, but increase almost continuously at the E to H mode transition under low pressure.

Simulation of transition from Townsend mode to glow discharge mode in a helium dielectric barrier discharge at atmospheric pressure

Li Xue-Chen, Niu Dong-Ying, Xu Long-Fei, Jia Peng-Ying, Chang Yuan-Yuan
Chin. Phys. B, 2012, 21 (7): 075204 doi: 10.1088/1674-1056/21/7/075204
Full Text: [PDF 221 KB] (Downloads:768)
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The dielectric barrier discharge characteristics in helium at atmospheric pressure are simulated based on a one-dimensional fluid model. Under some discharge conditions, the results show that one discharge pulse per half voltage cycle usually appears when the amplitude of external voltage is low, while glow-like discharge occurs at high voltage. For the one discharge pulse per half voltage cycle, the maximum of electron density appears near the anode at the beginning of the discharge, which corresponds to a Townsend discharge mode. The maxima of the electron density and the intensity of electric field appear in the vicinity of the cathode when the discharge current increases to some extent, which indicates the formation of a cathode-fall region. Therefore, the discharge has a transition from Townsend mode to glow discharge mode during one discharge pulse, which is consistent with previous experimental results.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Fabrication processing effects on microstructure and morphology of erbium film

Shen Hua-Hai, Peng Shu-Ming, Long Xing-Gui, Zhou Xiao-Song, Yang Li, Liu Jin-Hua, Sun Qing-Qiang, Zu Xiao-Tao
Chin. Phys. B, 2012, 21 (7): 076101 doi: 10.1088/1674-1056/21/7/076101
Full Text: [PDF 7142 KB] (Downloads:964)
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The effects of substrate temperature on the microstructure and the morphology of erbium film are systematically investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the erbium films are grown by the electron-beam vapor deposition (EBVD). A novel preparation method for observing the cross-section morphology of the erbium film is developed. The films deposited at 200 ℃ have (002) preferred orientation, and the films deposited at 450 ℃ have mixed (100) and (101) texture, which are due to the different growth mechanisms of surface energy minimization and recrystallization, respectively. The peak positions and the full widths at half maximum (FWHMs) of erbium diffraction lines (100), (002), and (101) shift towards higher angles and decrease with the increasing substrate temperature in a largely uniform manner, respectively. Also, the lattice constants decrease with the increasing temperature. The transition in the film stresses can be used to interpret the changes in peak positions, FWHMs, and lattice constants. The stress is compressive for the as-growth films, and is counteracted by the tensile stress formed during the process of temperature cooling down to room temperature. The tensile stress mainly originates from the difference in the coefficients of thermal expansion of substrate--film couple.

Using a water-confined carbon nanotube to probe electricity of sequential charged segments of macromolecules Hot!

Wang Yu, Zhao Yan-Jiao, Huang Ji-Ping
Chin. Phys. B, 2012, 21 (7): 076102 doi: 10.1088/1674-1056/21/7/076102
Full Text: [PDF 897 KB] (Downloads:467)
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The detection of macromolecular conformation is particularly important in many physical and biological applications. Here we theoretically explore a method for achieving this detection by probing the electricity of sequential charged segments of macromolecules. Our analysis is based on molecular dynamics simulations, and we investigate a single file of water molecules confined in a half-capped single-walled carbon nanotube (SWCNT) with an external electric charge of +e or ?e (e is the elementary charge). The charge is located in the vicinity of the cap of the SWCNT and along the centerline of the SWCNT. We reveal the picosecond timescale for the re-orientation (namely, from one unidirectional direction to the other) of the water molecules in response to a switch in the charge signal, ?e → +e or +e → ?e. Our results are well understood by taking into account the electrical interactions between the water molecules and between the water molecules and the external charge. Because such signals of re-orientations can be magnified and transported according to Tu et al. [2009 Proc. Natl. Acad. Sci. USA 106 18120], it becomes possible to record fingerprints of electric signals arising from sequential charged segments of a macromolecule, which are expected to be useful for recognizing the conformations of some particular macromolecules.

The ground-state structure and physical properties of RuC: first-principles calculations

Zhang Mei-Guang, Yan Hai-Yan, Zhang Gang-Tai, Wang Hui
Chin. Phys. B, 2012, 21 (7): 076103 doi: 10.1088/1674-1056/21/7/076103
Full Text: [PDF 361 KB] (Downloads:854)
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We have extensively explored the ground-state structure of RuC using the particle swarm optimization algorithm for crystal structural prediction. A hexagonal R-3m structure has been proposed as the best candidate, which is energetically more favorable than the previously proposed zinc blend structure. The R-3m-RuC possesses alternative stacking of double hexagonal close-packed Ru atom layers and C atom layers, and it is dynamically stable evidenced by the calculation of phonon dispersion. The calculated large bulk modulus, shear modulus, and elastic constant C44 reveal that it is an ultra-incompressible and hard material. The evidence of strong covalent bonding of Ru--C, which plays an important role to form a hard material, is manifested by the partial densities of states analysis.

A nano-metallic-particles-based CMOS image sensor for DNA detection

He Jin, Su Yan-Mei, Ma Yu-Tao, Chen Qin, Wang Ruo-Nan, Ye Yun, Ma Yong, Liang Hai-Lang
Chin. Phys. B, 2012, 21 (7): 076104 doi: 10.1088/1674-1056/21/7/076104
Full Text: [PDF 4571 KB] (Downloads:1293)
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In this paper we report on a study of the CMOS image sensor detection of the DNA based on the self-assembled nano-metallic particles, which are selectively deposited on the surface of passive image sensor. The nano-metallic particles block the optical radiation in the visible spectrum of ordinary light source effectively. When such a technical method is applied to the DNA detection, the requirement for special UV light source in the most popular fluorescence is eliminated. The DNA detection methodology is tested on a CMOS sensor chip fabricated using a standard 0.5 μm CMOS process. It is demonstrated that the approach is highly selective to detecting even signal-base mismatched DNA target with extremely-low-concentration DNA sample down to 10 pM under ordinary light source.

Temperature dependence of Cu2O orientations in oxidation of Cu (111)/ZnO (0001) by oxygen plasma

Li Jun-Qiang, Mei Zeng-Xia, Ye Da-Qian, Hou Yao-Nan, Liu Yao-Ping, A. Yu. Kuznetsov, Du Xiao-Long
Chin. Phys. B, 2012, 21 (7): 076401 doi: 10.1088/1674-1056/21/7/076401
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The role of temperature on the oxidation dynamics of Cu2O on ZnO (0001) was investigated during the oxidation of Cu (111)/ZnO (0001) by using the oxygen plasma as oxidant. A transition from single crystalline Cu2O (111) orientation to micro-zone phase separation with multiple orientations was revealed when the oxidation temperature increased from 300 ℃ to higher. The experimental results clearly showed the effect of oxidation temperature with the assistance of oxygen plasma on changing the morphology of Cu (111) film and enhancing the lateral nucleation and migration abilities of cuprous oxides. A vertical top-down oxidation mode and a lateral migration model were proposed to explain the different nucleation and growth dynamics of the temperature-dependent oxidation process in the oxidation of Cu (111)/ZnO (0001).

Thermal properties of high-k Hf1-xSixO2

Si Feng-Juan, Lu Wen-Jiang, Tang Fu-Ling
Chin. Phys. B, 2012, 21 (7): 076501 doi: 10.1088/1674-1056/21/7/076501
Full Text: [PDF 436 KB] (Downloads:1084)
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Classical atomistic simulations based on lattice dynamics theory and Born core-shell model are performed to systematically study the crystal structure and thermal properties of high-k Hf1-xSixO2. The coefficients of thermal expansion, specific heats, Gr黱eisen parameters, phonon densities of states, and Debye temperatures, are calculated at different temperatures and for different Si-doping concentrations. With the increase of Si-doping concentration, the lattice constant decreases. At the same time, both the coefficient of thermal expansion and the specific heat at constant volume of Hf1-xSixO2 also decrease. Gr黱eisen parameter is about 0.95 at temperature less than 100 K. Compared with Si-doped HfO2, pure HfO2 has higher Debye temperature when temperature is less than 25 K, while it has lower Debye temperature when temperature is larger than 50 K. Some simulation results accord well with experimental data. We expect that our results will be helpful for understanding the local lattice structure and thermal properties of Hf1-xSixO2.

A theoretical study of the oxygen K-edge near-edge X-ray absorption ne structure of N2O/Ir(110)

Wu Tai-Quan, Zhu Ping, Wang Xin-Yan, Luo Hong-Lei
Chin. Phys. B, 2012, 21 (7): 076801 doi: 10.1088/1674-1056/21/7/076801
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A multiple-scattering cluster method is employed to calculate the oxygen K-edge near-edge X-ray absorption fine structure of N2O/Ir(110) and its monolayer. Two peaks and one weak resonance appear in both cases. The selfconsistent field DV-X calculations of the peaks and resonance show that the physical origin of the pre-edge peak x is different from those of the main peak 1 and the other weak resonance σ1. This setup is intrinsic to the N2O monolayer, owing to the interaction between the neighbouring molecular chains in the monolayer and partly to the adsorbed atomic oxygen, according to both the theoretical and experimental data.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Novel high-voltage power lateral MOSFET with adaptive buried electrodes

Zhang Wen-Tong, Wu Li-Juan, Qiao Ming, Luo Xiao-Rong, Zhang Bo, Li Zhao-Ji
Chin. Phys. B, 2012, 21 (7): 077101 doi: 10.1088/1674-1056/21/7/077101
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A new high-voltage and low-specific on-resistance (Ron,sp) adaptive buried electrode (ABE) silicon-on-insulator (SOI) power lateral MOSFET and its analytical model of the electric fields are proposed. The MOSFET features are that the electrodes are buried in the buried oxide (BOX) layer, the negative drain voltage Vd is divided into many partial voltages and output to the electrodes in the buried oxide layer, the potentials on the electrodes change linearly from the drain to the source. Because the interface silicon layer potentials are lower than the neighboring electrode potentials, the electronic potential wells are formed above the electrode regions, and the hole potential wells are formed in the spacings of two neighbouring electrode regions. The interface hole concentration is much higher than the electron concentration through designing the buried layer electrode potentials. Based on the interface charge enhanced dielectric layer field theory, the electric field strength in the buried layer is enhanced. The vertical electric field EI and the breakdown voltage (BV) of ABE SOI are 545 V/μm and -587 V in 50 μm long drift region and 1 μm thick dielectric layer, and a low Ron,sp is obtained. Furthermore, the structure also alleviates the self-heating effect (SHE). The analytical model matches well with the simulation result.

Structural, elastic, phonon, and electronic properties of MnPd alloy

Wang Jun-Fei, Chen Wen-Zhou, Jiang Zhen-Yi, Zhang Xiao-Dong, Si Liang
Chin. Phys. B, 2012, 21 (7): 077102 doi: 10.1088/1674-1056/21/7/077102
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The structural, elastic, phonon, and electronic properties of MnPd alloy have been investigated by using the first-principles calculations. The calculated lattice constants and electronic structure are in good agreement with the experimental results. The microscopic mechanism of the diffusionless martensitic transition from the paramagnetic B2 (PM-B2) phase to the antiferromagnetic L10 (AFM-L10) phase through the intermediate paramagnetic L10 (PM-L10) phase has been explored theoretically. The obtained negative shear modulus C′= (C11-C12)/2 of the PM-B2 phase is closely related to the instability of the cubic B2 phase with respect to the tetragonal distortions. The calculated phonon dispersions for PM-L10 and AFM-L10 phases indicate that they are dynamically stable. However, the AFM-L10 phase is energetically most favorable according to the calculated total energy order, so the PM-L10 !AFM-L10 transition is caused by the magnetism rather than the electron–phonon interaction. Additionally, the AFM-L10 state is stabilized through the formation of a pseudo gap located at the Fermi level. The calculated results show that the CuAu-I type structure in the collinear antiferromagnetic state is dynamically and mechanical stable, thus is the low temperature phase.

Effect of Si doping in wells of AlGaN/GaN superlattice on the characteristics of epitaxial layer

Zhang Wei, Xue Jun-Shuai, Zhou Xiao-Wei, Zhang Yue, Liu Zi-Yang, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B, 2012, 21 (7): 077103 doi: 10.1088/1674-1056/21/7/077103
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AlGaN/GaN superlattice grown on the top of GaN buffer induces the broadening of the full width at half maximum of (102) and (002) x-ray diffraction rocking curves. With the increase of Si-doped concentration in GaN wells, the full width at half maximum of the (102) rocking curves decreases, while that of the (002) rocking curves increases. Significant increase of the full width at half maximum of the (002) rocking curves when the doping concentration reaches 2.5?1019 cm-3 indicates the substantial increase of the inclined threading dislocation. High level doping in the AlGaN/GaN superlattice can greatly reduce the biaxial stress and optimize the surface roughness of the structures grown on the top of it.

A spin switch device based on a triple quantum dots superlattice using the Dicke effect

An Xing-Tao, Mu Hui-Ying, Xian Li-Fen, Liu Jian-Jun
Chin. Phys. B, 2012, 21 (7): 077201 doi: 10.1088/1674-1056/21/7/077201
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Spin-dependent transport in a triple quantum dots superlattice system with a bridge coupling to two leads is studied. There exists an odd–even parity oscillation of spin polarization at the central dot level εc = 0 due to the spin-dependent Fano and Dicke effects induced by the quantum interference and the Rashba spin–orbit interaction. In the case of even numbers of triple quantum dots, the device can be used as a spin switch by tuning the energy difference h between the energies of the central and the lateral dots. These results may be helpful to design and fabricate practical spintronic devices.

Generating and reversing spin accumulation by temperature gradient in a quantum dot attached to ferromagnetic leads

Bai Xu-Fang, Chi Feng, Zheng Jun, Li Yi-Nan
Chin. Phys. B, 2012, 21 (7): 077301 doi: 10.1088/1674-1056/21/7/077301
Full Text: [PDF 179 KB] (Downloads:549)
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We propose to generate and reverse the spin accumulation in a quantum dot (QD) by using the temperature difference between the two ferromagnetic leads connected to the dot. The electrons are driven purely by the temperature gradient in the absence of electric bias and magnetic field. In the Coulomb blockade regime, we find two ways to reverse the spin accumulation. One is by adjusting the QD energy level with a fixed temperature gradient, and the other is by reversing the temperature gradient direction for a fixed value of the dot level. The spin accumulation in the QD can be enhanced by the magnitudes of both the leads' spin polarization and the asymmetry of the dot--lead coupling strengths. The present device is quite simple, and the obtained results may have practical usage in spintronics or quantum information processing.

Nonadiabatic dynamics of electron injection into organic molecules

Zhu Li-Ping, Qiu Yu, Tong Guo-Ping
Chin. Phys. B, 2012, 21 (7): 077302 doi: 10.1088/1674-1056/21/7/077302
Full Text: [PDF 248 KB] (Downloads:453)
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We numerically investigate the injection process of electrons from metal electrodes to one-dimensional organic molecules by combining the extended Su--Schrieffer--Heeger (SSH) model with a nonadiabatic dynamics method. It is found that match between the Fermi level of electrodes and the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) of organic molecules can be greatly affected by the length of organic chains, which has great impact on electron injection. The correlation between oligomers and electrodes is found to open more efficient channels for electron injection as compared with that in polymer/electrode structures. For oligomer/electrode structures, we show that the Schottky barrier essentially does not affect the electron injection as the electrode work function is smaller than a critical value. This means that the Schottky barrier is pinned for small work-function electrode. For polymer/electrode structures, we find that it is possible for the Fermi level of electrodes to be pinned to the polaronic level. The condition under which the Fermi level of electrodes exceeds the polaronic level of polymers is shown not always to lead to spontaneous electron transfer from electrodes to polymers.

Quantum spin Hall effect in a square-lattice model under a uniform magnetic field

Guo Huai-Ming, Feng Shi-Ping
Chin. Phys. B, 2012, 21 (7): 077303 doi: 10.1088/1674-1056/21/7/077303
Full Text: [PDF 517 KB] (Downloads:951)
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We study a toy square-lattice model under a uniform magnetic field. Using the Landauer--B黷tiker formula, we calculate the transport properties of the system on a two-terminal, a four-terminal, and a six-terminal device. We find that the quantum spin Hall (QSH) effect appears in energy ranges where the spin-up and spin-down subsystems have different filling factors. We also study the robustness of the resulting QSH effect and find that it is robust when the Fermi levels of both spin subsystems are far away from the energy plateaus but is fragile when the Fermi level of any spin subsystem is near the energy plateaus. These results provide an example of QSH effect with the physical origin other than time-reversal (TR) preserving spin-orbit coupling (SOC).

Channel temperature determination of multifinger AlGaN/GaN high electron mobility transistor using micro-Raman technique

Yang Li-Yuan, Xue Xiao-Yong, Zhang Kai, Zheng Xue-Feng, Ma Xiao-Hua, Hao Yue
Chin. Phys. B, 2012, 21 (7): 077304 doi: 10.1088/1674-1056/21/7/077304
Full Text: [PDF 288 KB] (Downloads:1099)
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Self-heating in multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of AlGaN/GaN HEMT is estimated from the calibration curve of passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1 ℃ is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.

Abnormal magnetoresistance behavior in Nb thin film with rectangular arrays of antidots

Zhang Wei-Jun, He Shi-Kun, Li Bo-Hong, Cheng Fei, Xu Bing, Wen Zhen-Chao, Cao Wen-Hui, Xiao Hong, Han Xiu-Feng, Zhao Shi-Ping, Qiu Xiang-Gang
Chin. Phys. B, 2012, 21 (7): 077401 doi: 10.1088/1674-1056/21/7/077401
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Magnetoresistance in superconducting Nb films perforated with rectangular arrays of antidots (holes) is investigated at various temperatures and currents. Normally, the magnetoresistance increases with the increasing magnetic field. In this paper, we report a reverse behavior in a certain range of high fields after vortex reconfiguration transition, where the resistances at non-matching fields are smaller than those in the low field regime. This phenomenon is due to a strong caging effect, in which the interstitial vortices are trapped among the pinned multiquanta vortices. This effect is temperature and current dependent.

Substrate-induced stress in silicon nanocrystal/SiO2 multilayer structure

Tao Ye-Liao, Zuo Yu-Hua, Zheng Jun, Xue Chun-Lai, Cheng Bu-Wen, Wang Qi-Ming, Xu Jun
Chin. Phys. B, 2012, 21 (7): 077402 doi: 10.1088/1674-1056/21/7/077402
Full Text: [PDF 2265 KB] (Downloads:571)
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A Raman frequency upshift of nc-Si phonon mode is observed at room temperature, which is attributed to a strong compressive stress in Si nanocrystals. The 10-period amorphous-Si(3 nm)/amorphous-SiO2 (3 nm) layers are deposited by high vacuum radio-frequency magnetron sputtering on quartz and sapphire substrates at different temperatures. The samples are then annealed in N2 atmosphere at 1100 ℃ for 1 h for Si crystallization. It is demonstrated that the presence of a supporting substrate at the high grown temperature can induce different types of stresses in the Si nanocrystal layers. The strain is attributed to the difference in thermal expansion coefficient between the substrate and the Si/SiO2 SL film. Such a substrate-induced stress indicates a new method to tune the optical and the electronic properties of Si nanocrystals for strained engineering.

Lattice distortion in disordered antiferromagnetic XY models

Li Peng-Fei, Cao Hai-Jing
Chin. Phys. B, 2012, 21 (7): 077501 doi: 10.1088/1674-1056/21/7/077501
Full Text: [PDF 115 KB] (Downloads:481)
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The behavior of lattice distortion in the spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin--phonon coupling in the adiabatic limit. It is found that the lattice distortion relies on the strength of the random modulation. For strong or weak enough spin--phonon couplings, the average lattice distortion may decrease or increase as the random modulation is strengthened. This may be the results of the competition between the random magnetic modulation and the spin--phonon coupling.

Exchange coupling and helical spin order in the triangular lattice antiferromagnet CuCrO2 using first principles

Jiang Xue-Fan, Liu Xian-Feng, Wu Yin-Zhong, Han Jiu-Rong
Chin. Phys. B, 2012, 21 (7): 077502 doi: 10.1088/1674-1056/21/7/077502
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The magnetic and the electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first-principles through density functional theory calculations within generalized gradient approximations (GGA)+U scheme. The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and the spin frustration. It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction. Using Monte--Carlo simulation, we obtain the N閑l temperature to be 29.9 K, which accords well with the experimental value 24 K. Based on the non-collinear magnetic structure calculations, we verify that the incommensurate spiral-spin structure with (110) spiral plane is believable for the magnetic ground state, which is consistent with the experimental observations. Due to the intra-layer geometric spin frustration, parallel helical-spin chains arise along the a, b, or a+b directions each with a screw-rotation angle of about 120?. Our calculations of the density of states show that the spin frustration plays an important role in the change of d--p hybridization, while the spin-orbit coupling has very limited influence on the electronic structure.

Permittivity and its temperature dependence in hexagonal structure BN dominated by the local electric field

Zhang Ting, Wu Meng-Qiang, Zhang Shu-Ren, Xiong Jie, Wang Jin-Ming, Zhang Da-Hai, He Feng-Mei, Li Zhong-Ping
Chin. Phys. B, 2012, 21 (7): 077701 doi: 10.1088/1674-1056/21/7/077701
Full Text: [PDF 135 KB] (Downloads:1098)
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This paper presents an analysis of the local electric field in the hexagonal boron nitride (h-BN) by introducing a modified parameter. Based on the determination of the modified parameter of h-BN, the revised Lorenz equation is developed. Then, the permittivity at high temperature and in the microwave frequency is investigated. In addition, this equation is derived for evaluating the temperature coefficient of the permittivity of h-BN. The analyses show that the permittivity increases with the increasing temperature, which is mainly attributed to the positive temperature coefficient of the ionic polarizability.

The properties of GaMnN lms grown by metalorganic chemical vapour deposition using Raman spectroscopy

Xing Hai-Ying, Niu Ping-Juan, Xie Yu-Xin
Chin. Phys. B, 2012, 21 (7): 077801 doi: 10.1088/1674-1056/21/7/077801
Full Text: [PDF 213 KB] (Downloads:456)
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An investigation of room-temperature Raman scattering is carried out on ferromagnetic semiconductor GaMnN films grown by metalorganic chemical vapour deposition with different Mn content values. New bands around 300 and 669 cm-1, that are not observed in undoped GaN, are found. They are assigned to disorder-activated mode and local vibration mode (LVM), respectively. After annealing, the intensity ratio between the LVM and E2(high) mode, i.e., ILVM=IE2(high), increases. The LO phonon-plasmon coupled (LOPC) mode is found in GaMnN, and the frequency of the LOPC mode of GaMnN shifting toward higher side is observed with the increase in the Mn doping in GaN. The ferromagnetic character and the carrier density of our GaMnN sample are discussed.

The crystal structure and luminescent properties of nitrogen-rich Ca-α-sialon:Eu with saturated calcium solubility fabricated by the alloy-nitridation method

Yang Jian-Jun, Chen Guo-Dong, Du Fei-Fei, Liu Quan-Lin
Chin. Phys. B, 2012, 21 (7): 077802 doi: 10.1088/1674-1056/21/7/077802
Full Text: [PDF 191 KB] (Downloads:1044)
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Nitrogen-rich Ca- -sialon: Eu2+ phosphors with saturated calcium solubility are synthesized through a solidstate reaction (SSR) at 2173 K with stable alloy and nitride as the starting materials. The Ca1.83-1.5xSi8.34 Al3.66OxN16-x: xEu phosphors have intensive orange emissions, whose peaks are located at approximately 585–600 nm, and the emission wavelengths tend to shift toward the red region when the Eu concentrations increase from 0.5% to 18% (mole percentage). When the Eu concentration is equal to 9%, the phosphors suffer from concentration quenching. The low-temperature photoluminescence properties indicate that Ca1.83-1.5xSi8.34Al3.66OxN16-x: xEu phosphors show excellent thermal quenching. The crystal structures of Ca1.83-1.5xSi8.34Al3.66OOxN16-x: xEu are also investigated, and are found to have nitrogen-rich compositions with saturated calcium cations at the interstitial sites of the α-sialons. In addition, the influencing factors of -sialons with different compositions on the crystal lattice are discussed in detail.

Influence of polarization direction, incidence angle, and geometry on near-field enhancement in two-layered gold nanowires Hot!

Wu Da-Jian, Jiang Shu-Min, Liu Xiao-Jun
Chin. Phys. B, 2012, 21 (7): 077803 doi: 10.1088/1674-1056/21/7/077803
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The influences of polarization direction, incidence angle, and geometry on the near-field enhancements in two-layered gold nanowires (TGNWs) have been investigated by using the vector wave function method. When the polarization direction is perpendicular to the incidence plane, the local field factor (LFF) in TGNW decreases first and then increases with the increase of the incidence angle. The minimum LFF is observed at the incidence angle of 41?. It is found that the increase of the dielectric constant of the inner core leads to the decrease of LFF. With the increase of the inner core radius, the LFF in TGNW increases first and then decreases, and the maximum LFF is observed at the inner core radius of 27 nm. On the other hand, when the polarization direction is parallel to the incidence plane, the collective motions of the induced electrons are enhanced gradually with the decrease of the incidence angle, and hence the near-field enhancement is increased.

The effect of laser beam size on laser-induced damage performance

Han Wei, Wang Fang, Zhou Li-Dan, Feng Bin, Jia Huai-Ting, Li Ke-Yu, Xiang Yong, Zheng Wan-Guo
Chin. Phys. B, 2012, 21 (7): 077901 doi: 10.1088/1674-1056/21/7/077901
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The influence of laser beam size on laser-induced damage performance, especially damage probability and laser-induced damage threshold (LIDT), is investigated. It is found that the damage probability is dependent on the beam size when various damage precursors with different potential behaviors are involved. This causes the damage probability and the LIDT to be different between the cases under a large-aperture beam and under a small-aperture beam. Moreover, the fluence fluctuation of large-aperture laser beam brings out hot spots, which move randomly across the beam from shot to shot. Thus it leads the most probable maximum fluence after many shots at any location on the optical component to be several times the average beam fluence. These two effects result in the difference in damage performance of the optical component between the cases under a large-aperture laser and under a small-aperture laser.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The synthesis and exchange bias effect of monodisperse NiO nanocrystals

Duan Han-Ning, Yuan Song-Liu, Zheng Xian-Feng, Tian Zhao-Ming
Chin. Phys. B, 2012, 21 (7): 078101 doi: 10.1088/1674-1056/21/7/078101
Full Text: [PDF 817 KB] (Downloads:1009)
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Monodisperse NiO nanocrystals with an average particle size of 3? 0.4 nm are successfully synthesized by the thermal decomposition of Ni-oleylamine complex in an organic solvent under a continuous O2 flux. The crystalline structure and the morphology of the product are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscope. Magnetization and alternating-current (ac) susceptibility measurements indicate that the structure of the particles can be considered as consisting of an antiferromagnetically ordered core and a spin-glass like surface shell. In addition, both the exchange bias field and the vertical magnetization shift can be observed in this system at 10 K after the field cooling. This observed exchange bias effect is explained in terms of the exchange interaction between the antiferromagnetic core and the spin-glass like shell.

The effects of static magnetic field on microwave absorption of hydrogen plasma in carbon nanotubes: A numerical study

Peng Zhi-Hua, Gong Xue-Yu, Peng Yan-Feng, Guo Yan-Chun, Ning Yan-Tao
Chin. Phys. B, 2012, 21 (7): 078102 doi: 10.1088/1674-1056/21/7/078102
Full Text: [PDF 123 KB] (Downloads:986)
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We theoretically investigate the microwave absorption properties of hydrogen plasma in iron-catalyzed highpressure disproportionation-grown carbon nanotubes under an external static magnetic field in the frequency range 0.3 GHz to 30 GHz, using the Maxwell equations in conjunction with a general expression for the effective complex permittivity of magnetized plasma known as the Appleton–Hartree formula. The effects of the external static magnetic field intensity and the incident microwave propagation direction on the microwave absorption of hydrogen plasma in CNTs are studied in detail. The numerical results indicate that the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes can be obviously improved when the external static magnetic field is applied to the material. It is found that the specified frequency microwave can be strongly absorbed by the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes over a wide range of incidence angles by adjusting the external magnetic field intensity and the parameters of the hydrogen plasma.

A colloidal crystal double-heterostructure fabricated with the angle controlled inclined deposition method

Chen Ze-Feng, Xiong Yu-Ying, Han Peng, Chen Yi-Hang, Xiao Hua
Chin. Phys. B, 2012, 21 (7): 078103 doi: 10.1088/1674-1056/21/7/078103
Full Text: [PDF 2077 KB] (Downloads:824)
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A self-assembly method, named angle controlled inclined deposition method, is developed for fabricating well-ordered silica and polystyrene colloidal crystal. A high quality colloidal crystal with flat and uniform surface over a large area can be produced rapidly using a minute quantity of suspension and without any additional equipment. By controlling the inclined angle, we can fabricate colloidal crystals with diverse numbers of layers. A colloidal crystal double-heterostructure (composed of three different colloidal photonic crystals) is rapidly fabricated with this method. Both experimental and simulation results show that the photonic band gap of the double-heterostructure is not a simple superposition of those of the compositional colloidal crystals along the stacking direction.

Effect of post thermal annealing on the structural and optical properties of ZnO thin films prepared from polymer precursor

Jijoy. P. Mathew, George Varghese, Jacob Mathew
Chin. Phys. B, 2012, 21 (7): 078104 doi: 10.1088/1674-1056/21/7/078104
Full Text: [PDF 227 KB] (Downloads:1646)
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ZnO thin films were synthesised by a new method which uses polyvinyl alcohol (PVA) as polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and annealing time. All the films possess tensile strain which relaxes as the annealing temperature and the annealing time increases. The photoluminescence (PL) spectra contain only ultraviolet (UV) peaks at low temperature, but as the annealing temperature and time increase we observe peaks at blue and green regions with variation of the intensities of these peaks with annealing temperature and annealing time.

Characteristics and properties of metal aluminum thin film prepared by electron cyclotron resonance plasma-assisted atomic layer deposition technology

Xiong Yu-Qing, Li Xing-Cun, Chen Qiang, Lei Wen-Wen, Zhao Qiao, Sang Li-Jun, Liu Zhong-Wei, Wang Zheng-Duo, Yang Li-Zhen
Chin. Phys. B, 2012, 21 (7): 078105 doi: 10.1088/1674-1056/21/7/078105
Full Text: [PDF 3826 KB] (Downloads:3078)
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Metal aluminum (Al) thin films are prepared by 2450-MHz electron cyclotron resonance plasma-assisted atomic layer deposition on glass and p-Si substrates using trimethylaluminum as the precursor and hydrogen as the reductive gas. We focus our attention on the plasma source for thin-film preparation and annealing of as-deposited films related to the surface square resistivity. The square resistivity of as-deposited Al film is greatly reduced after annealing and almost reaches the value of bulk metal. Through chemical and structure analysis we conclude that the square resistivity is determined by neither contaminant concentration nor surface morphology, but by both crystallinity and crystal size in this process.

Simulation of ball motion and energy transfer in a planetary ball mill

Lu Sheng-Yong, Mao Qiong-Jing, Peng Zheng, Li Xiao-Dong, Yan Jian-Hua
Chin. Phys. B, 2012, 21 (7): 078201 doi: 10.1088/1674-1056/21/7/078201
Full Text: [PDF 946 KB] (Downloads:3804)
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A kinetic model is proposed for simulating the trajectory of a single milling ball in a planetary ball mill, and a model is also proposed for simulating the local energy transfer during the ball milling process under no-slip condition. Based on the kinematics of ball motion, the collision frequency and power are described and the normal impact forces and effective power are derived from analyses of collision geometry. The Hertzian impact theory is applied to formulate these models, after having established some relationships among geometric, dynamic, and thermophysical parameters. Simulation is carried out based on two models, and the effects of the rotation velocity of the planetary disk Ω and the vial-to-disk speed ratio ω/ Ω on other kinetic parameters have been investigated. As a result, the optimal ratio ω/Ω to obtain high impact energy in the standard operating condition at Ω =800 rpm is estimated, which is equal to 1.15.

Theoretical study of structure and analytic potential energy function for the ground state of PO2 molecule

Zeng Hui, Zhao Jun
Chin. Phys. B, 2012, 21 (7): 078202 doi: 10.1088/1674-1056/21/7/078202
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In this paper, the energy, the equilibrium geometry, and the harmonic frequency of the ground electronic state of PO2 are computed using B3LYP, B3P86, CCSD(T), and QCISD(T) methods in conjunction with 6-311++G(3df, 3pd) and cc-pVTZ basis sets. A comparison between the computational results and the experimental values indicates that the B3P86/6-311++G(3df, 3pd) method can give better energy calculation results for the PO2 molecule. It is shown that the ground state of the PO2 molecule has C2v symmetry and its ground electronic state is X2A1. The equilibrium parameters of the structure are RP-O=0.1465 nm, d=19.218 eV. The bent vibrational frequency ν1=386 cm-1, the symmetric stretching frequency ν2=1095 cm-1, and the asymmetric stretching frequency ν3=1333 cm-1 are obtained. On the basis of atomic and molecular reaction statics, the reasonable dissociation limit for the ground state of the PO2 molecule is determined. Then the analytic potential energy function of the PO2 molecule is first derived by using the many-body expansion theory. The potential curves correctly reproduce the configurations and the dissociation energy for the PO2 molecule.

Improving performance of polymer solar cell by adjusting crystallinity and nanoscale phase separation

Chen Wei-Bing, Xu Zong-Xiang, Li Kai, Chui Stephen Sin-Yin, Roy V. A. L., Lai Pui-To, Che Chi-Ming
Chin. Phys. B, 2012, 21 (7): 078401 doi: 10.1088/1674-1056/21/7/078401
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In this paper, we report a high-performance P3HT/PCBM bulk-heterojunction solar cell with a power conversion efficiency of 4.85% fabricated by adjusting polymer crystallinity and nanoscale phase separation using an ultrasonic irradiation mixing approach of the polymer. The results of grazing incidence X-ray diffraction, UV/Vis spectroscopic, and atomic force microscopic measurements of the P3HT/PCBM blend films reveal that the P3HT/PCBM film fabricated by ultrasonic irradiation mixing P3HT and PCBM solutions for 10 min has higher degree of crystallinity, higher absorption efficiency, and better phase separation, which altogether account for the higher charge transport properties and photovoltaic cell performance.

The influence of thermally assisted tunneling on the performance of charge trapping memory

Peng Ya-Hua, Liu Xiao-Yan, Du Gang, Liu Fei, Jin Rui, Kang Jin-Feng
Chin. Phys. B, 2012, 21 (7): 078501 doi: 10.1088/1674-1056/21/7/078501
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We evaluate the influence of thermally assisted tunneling (ThAT) mechanism on charge trapping memory (CTM) cell performance by numerical simulation, and comprehensively analyse the effects of temperature, trap depth, distribution of trapped charge, gate voltage and parameters of ThAT on erasing/programming speed and retention performance. The ThAT is an indispensable mechanism in CTM. This mechanism can increase the detrapping probability of trapped charge. Our results reveal that the ThAT effect causes the sensitivity of the cell performance to temperature and it could affect the operational speed, especially for the erasing operation. The retention performance degrades compared with the results when the ThAT mechanism is ignored.

A new analytical model for the surface electric field distribution and breakdown voltage of the SOI trench LDMOS

Hu Xia-Rong, Zhang Bo, Luo Xiao-Rong, Wang Yuan-Gang, Lei Tian-Fei, Li Zhao-Ji
Chin. Phys. B, 2012, 21 (7): 078502 doi: 10.1088/1674-1056/21/7/078502
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A new analytical model for the surface electric field distribution and breakdown voltage of the silicon on insulator (SOI) trench lateral double-diffused metal-oxide-semiconductor (LDMOS) is presented. Based on the two-dimensional Laplace solution and Poisson solution, the model considers the influence of structure parameters, such as the doping concentration of the drift region and the depth and width of the trench, on the surface electric field. Further, a simple analytical expression of the breakdown voltage is obtained, which offers an effective way to gain an optimal high voltage. All analytical results are in good agreement with the simulation results.

The effects of 60Co γ-ray irradiation on the DC characteristics of enhancement-mode AlGaN/GaN high-electron-mobility transistors

Chen Chao, Tian Ben-Lang, Liu Xing-Zhao, Dai Li-Ping, Deng Xin-Wu, Chen Yuan-Fu
Chin. Phys. B, 2012, 21 (7): 078503 doi: 10.1088/1674-1056/21/7/078503
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The effects of 60Co γ-ray irradiation on the DC characteristics of AlGaN/GaN enhancement-mode high-electronmobility transistors (E-mode HEMTs) are investigated. The results show that having been irradiated by 60Co γ-rays at a dose of 3 Mrad (Si), the E-mode HEMT reduces its saturation drain current and maximal transconductance by 6% and 5%, respectively, and significantly increases both forward and reverse gate currents, while its threshold voltage is affected only slightly. The obvious performance degradation of E-mode AlGaN/GaN HEMTs is consistent with the creation of electronegative surface state charges in the source-gate spacer and gate-drain spacer after being irradiated.

A feedback controlled Brownian ratchet operated by temperature switch

Zhang Hong-Wei, Wen Shu-Tang, Zhang Hai-Tao, Li Yu-Xiao, Chen Gai-Rong
Chin. Phys. B, 2012, 21 (7): 078701 doi: 10.1088/1674-1056/21/7/078701
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In this paper, we present a model of the Brownian motor in a feedback controlled ratchet, in which the application of the flashing potential depends on the state of the particle to be controlled. We derive an analytical expression for the velocity induced by the feedback ratchet, which is a function of several parameters, including the ratio of the two switching temperatures and the asymmetry parameter of the potential field. The motor shows a current inversion when either parameter is varied.

Self-sustained firing activities of the cortical network with plastic rules in weak AC electrical fields

Qin Ying-Mei, Wang Jiang, Men Cong, Zhao Jia, Wei Xi-Le, Deng Bin
Chin. Phys. B, 2012, 21 (7): 078702 doi: 10.1088/1674-1056/21/7/078702
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Both external and endogenous electrical fields widely exist in the environment of cortical neurons. The effects of weak alternating current (AC) field on a neural network model with synaptic plasticity are studied. It is found that self-sustained rhythmic firing patterns, which are closely correlated with the cognitive functions, are significantly modified due to the self-organizing of the network in the weak AC field. The activities of the neural networks are affected by the synaptic connection strength, the external stimuli, and so on. In the presence of learning rules, the synaptic connections can be modulated by the external stimuli, which will further enhance the sensitivity of the network to the external signal. The properties of the external AC stimuli can serve as control parameters in modulating the evolution of the neural network.

Variations of the epidemic distribution with some characteristic parameters

Liu Zhen-Zhen, Wang Xing-Yuan, Wang Mao-Ji
Chin. Phys. B, 2012, 21 (7): 078901 doi: 10.1088/1674-1056/21/7/078901
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Considering the epidemic spread among a population of mobile agents which can get infected and maintain the infection for a period, we investigate the variation of the homogeneity of the epidemic distribution with the remaining time of infection τ, the velocity modulus of the agent v, and the infection rate α. We find that the distribution of the infected cluster size is always exponential. By analyzing the variation of the characteristic infected cluster size coefficient, we show that, the inhomogeneity of the epidemic distribution increases with the increase of τ for very low v, while decreases with the increase of τ for moderate v. And the epidemic distribution tends to a homogeneous state as both v and α increase.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Spontaneous symmetry breaking vacuum energy in cosmology

Zhou Kang, Yue Rui-Hong, Yang Zhan-Ying, Zou De-Cheng
Chin. Phys. B, 2012, 21 (7): 079801 doi: 10.1088/1674-1056/21/7/079801
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The gravitational effect of spontaneous symmetry breaking vacuum energy density is investigated by subtracting the flat space–time contribution from the energy in the curved space–time. We find that the remaining effective energy– momentum tensor is too small to cause the acceleration of the universe, although it satisfies the characteristics of dark energy. However, it could provide a promising explanation to the puzzle of why the gravitational effect produced by the huge symmetry breaking vacuum energy in the electroweak theory has not been observed, as it has a sufficiently small value (smaller than the observed cosmic energy density by a factor of 1032).

Erratum to “Spinel lithium titanate (Li4Ti5O12) as novel anode material for room-temperature sodium-ion battery”

Zhao Liang, Pan Hui-Lin, Hu Yong-Sheng, Li Hong, Chen Li-Quan
Chin. Phys. B, 2012, 21 (7): 079901 doi: 10.1088/1674-1056/21/7/079901
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