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  • Significant effect of electron transfer between current collector and active material on high rate performance of Li4Ti5O12

    Pan Hui-Lin, Hu Yong-Sheng, Li Hong, Chen Li-Quan
    Chin. Phys. B 2011, 20 (11): 118202
    The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode ...

  • Valence orbitals of W(CO)6 using electron momentum spectroscopy

    Shi Le-Lei, Liu Kun, Luo Zhi-Hong, Ning Chuan-Gang, Deng Jing-Kang
    Chin. Phys. B 2011, 20 (11): 113403
    The binding energy spectra and the momentum distributions of the outer valence orbitals of W(CO)6 have been studied by using electron momentum spectroscopy as well as non-relativistic, scalar relativistic and spin-orbital relativistic DFT-B3LYP calculations. The experimental momentum profiles of the...

  • Intrinsic tunneling study of underdoped Bi2Sr2-xLaxCuO6+δ superconductors

    Ren Jian-Kun, Ren Yu-Feng, Tian Ye, Yu Hai-Feng, Zheng Dong-Ning, Zhao Shi-Ping, Lin Cheng-Tian
    Chin. Phys. B 2011, 20 (11): 117401
    We report on a tunneling study of underdoped submicron Bi2Sr2-xLaxCuO6+δ (La-Bi2201) intrinsic Josephson junctions (IJJs), whose self-heating is sufficiently suppressed. The tunneling spectra are measured from 4.2 K up to the pseudogap opening temperature of T* = 260 K. The gap value found from the ...

Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.11
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Mueller matrix analysis for all optical fiber co-existence of birefringence-polarization dependent gain-mode coupling at a single wavelength

Shang Chao, Wu Chong-Qing, Li Zheng-Yong, Yang Shuang-Shou, Gao Kai-Qiang, Yu Kuang-Lu, Feng Zhen
Chin. Phys. B, 2011, 20 (11): 110201 doi: 10.1088/1674-1056/20/11/110201
Full Text: [PDF 1113 KB] (Downloads:676)
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Birefringence (polarization-related phase-shift), polarization dependent gain (PDG) and mode coupling are three factors that may synchronously influence the transmission of single-wavelength polarized light in optical fibers. This paper obtains a new Mueller matrix analysis, which can be used under conditions that all these three factors are existing and changing. According to our transmission model, the state of polarization (SOP) changes along an optical microstructure fiber with co-existence of birefringence-PDG-mode coupling were simulated. The simulated results, which show the phenomena of SOP constringency, are in good agreement with previous theoretical analyses.

Lie symmetry and the generalized Hojman conserved quantity of Nielsen equations for a variable mass holonomic system of relative motion

Zhang Mei-Ling, Sun Xian-Ting, Wang Xiao-Xiao, Xie Yin-Li, Jia Li-Qun
Chin. Phys. B, 2011, 20 (11): 110202 doi: 10.1088/1674-1056/20/11/110202
Full Text: [PDF 97 KB] (Downloads:651)
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Lie symmetry and the generalized Hojman conserved quantity of Nielsen equations for a variable mass holonomic system of relative motion are studied. The determining equation of Lie symmetry of Nielsen equations for a variable mass holonomic system of relative motion under the infinitesimal transformations of groups is given. The expression of generalized Hojman conserved quantity deduced directly from Lie symmetry for a variable mass holonomic system of relative motion is obtained. An example is given to illustrate the application of the results.

Constructing infinite sequence exact solutions of nonlinear evolution equations

Taogetusang, Narenmandula
Chin. Phys. B, 2011, 20 (11): 110203 doi: 10.1088/1674-1056/20/11/110203
Full Text: [PDF 136 KB] (Downloads:609)
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To construct the infinite sequence new exact solutions of nonlinear evolution equations and study the first kind of elliptic function, new solutions and the corresponding Bäcklund transformation of the equation are presented. Based on this, the generalized pentavalent KdV equation and the breaking soliton equation are chosen as applicable examples and infinite sequence smooth soliton solutions, infinite sequence peak solitary wave solutions and infinite sequence compact soliton solutions are obtained with the help of symbolic computation system Mathematica. The method is of significance to search for infinite sequence new exact solutions to other nonlinear evolution equations.

Binary Bell polynomial application in generalized (2+1)-dimensional KdV equation with variable coefficients

Zhang Yi, Wei Wei-Wei, Cheng Teng-Fei, Song Yang
Chin. Phys. B, 2011, 20 (11): 110204 doi: 10.1088/1674-1056/20/11/110204
Full Text: [PDF 123 KB] (Downloads:916)
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In this paper, we apply the binary Bell polynomial approach to high-dimensional variable-coefficient nonlinear evolution equations. Taking the generalized (2+1)-dimensional KdV equation with variable coefficients as an illustrative example, the bilinear formulism, the bilinear Bäcklund transformation and the Lax pair are obtained in a quick and natural manner. Moreover, the infinite conservation laws are also derived.

Local discontinuous Galerkin method for solving Burgers and coupled Burgers equations

Zhang Rong-Pei, Yu Xi-Jun, Zhao Guo-Zhong
Chin. Phys. B, 2011, 20 (11): 110205 doi: 10.1088/1674-1056/20/11/110205
Full Text: [PDF 157 KB] (Downloads:860)
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In the current work, we extend the local discontinuous Galerkin method to a more general application system. The Burgers and coupled Burgers equations are solved by the local discontinuous Galerkin method. Numerical experiments are given to verify the efficiency and accuracy of our method. Moreover the numerical results show that the method can approximate sharp fronts accurately with minimal oscillation.

Distribution of non-Markovian intervals for open qubit systems

Zheng Yan-Ping, Tang Ning, rm Wang Guo-You, Zeng Hao-Sheng
Chin. Phys. B, 2011, 20 (11): 110301 doi: 10.1088/1674-1056/20/11/110301
Full Text: [PDF 180 KB] (Downloads:567)
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We study the non-Markovianity of open qubit systems using the measure N proposed by Breuer, Laine and Piilo [Phys. Rev. Lett. 103 210401 (2009)]. We find that for the three types of quantum noises, amplitude-damping, dephasing and depolarizing noises, there exist some non-Markovian time intervals whose distribution is independent of the selection of the pair of initial states. Therefore, the maximization in the definition of measure N can be actually removed without influencing the detection of non-Markovianity.

Controlling transfer of quantum correlations among bi-partitions of a composite quantum system by combining different noisy environments

Zhang Xiu-Xing, Li Fu-Li
Chin. Phys. B, 2011, 20 (11): 110302 doi: 10.1088/1674-1056/20/11/110302
Full Text: [PDF 409 KB] (Downloads:625)
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The correlation dynamics are investigated for various bi-partitions of a composite quantum system consisting of two qubits and two independent and non-identical noisy environments. The two qubits have no direct interaction with each other and locally interact with their environments. Classical and quantum correlations including the entanglement are initially prepared only between the two qubits. We find that contrary to the identical noisy environment case, the quantum correlation transfer direction can be controlled by combining different noisy environments. The amplitude-damping environment determines whether there exists the entanglement transfer among bi-partitions of the system. When one qubit is coupled to an amplitude-damping environment and the other one to a bit-flip one, we find a very interesting result that all the quantum and the classical correlations, and even the entanglement, originally existing between the qubits, can be completely transferred without any loss to the qubit coupled to the bit-flit environment and the amplitude-damping environment. We also notice that it is possible to distinguish the quantum correlation from the classical correlation and the entanglement by combining different noisy environments.

Dynamics of a multi-mode maximum entangled coherent state over an amplitude damping channel

A. El Allati, Y. Hassouni, N. Metwally
Chin. Phys. B, 2011, 20 (11): 110303 doi: 10.1088/1674-1056/20/11/110303
Full Text: [PDF 951 KB] (Downloads:694)
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The dynamics of the maximum entangled coherent state traveling through an amplitude damping channel is investigated. For small values of the transmissivity rate, the traveling state is very fragile to this noise channel, which suffers from the phase flip error with high probability. The entanglement decays smoothly for larger values of the transmissivity rate and speedily for smaller values of this rate. As the number of modes increases, the traveling state over this noise channel quickly loses its entanglement. The odd and even states vanish at the same value of field intensity.

Transfer of entangled state, entanglement swapping and quantum information processing via the Rydberg blockade

Deng Li, Chen Ai-Xi, Zhang Jian-Song
Chin. Phys. B, 2011, 20 (11): 110304 doi: 10.1088/1674-1056/20/11/110304
Full Text: [PDF 128 KB] (Downloads:572)
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We provide a scheme with which the transfer of the entangled state and the entanglement swapping can be realized in a system of neutral atoms via the Rydberg blockade. Our idea can be extended to teleport an unknown atomic state. According to the latest theoretical research of the Rydberg excitation and experimental reports of the Rydberg blockade effect in quantum information processing, we discuss the experimental feasibility of our scheme.

Controlled phase gates based on two nonidentical quantum dots trapped in separate cavities

Wang Xiao-Xia, Zhang Jian-Qi, Yu Ya-Fei, Zhang Zhi-Ming
Chin. Phys. B, 2011, 20 (11): 110306 doi: 10.1088/1674-1056/20/11/110306
Full Text: [PDF 239 KB] (Downloads:566)
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We propose a scheme for realizing two-qubit controlled phase gates on two nonidentical quantum dots trapped in separate cavities. In our scheme, each dot simultaneously interacts with one highly detuned cavity mode and two strong driven classical fields. During the gate operation, the quantum dots undergo no transition, while the system can acquire different phases conditional on different states of the quantum dots. With the application of the single-qubit operations, two-qubit controlled phase gates can be realized.

Combined periodic wave and solitary wave solutions in two-component Bose–Einstein condensates

Yao Shu-Fang, Li Qiu-Yan, Li Zai-Dong
Chin. Phys. B, 2011, 20 (11): 110307 doi: 10.1088/1674-1056/20/11/110307
Full Text: [PDF 129 KB] (Downloads:585)
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In this paper, the Jacobi elliptic function expansion method provides an effective approach to obtain the exact periodic wave solutions of two-component Bose-Einstein condensates. Exact combined bright-bright and dark-dark soliton wave solutions can be achieved in their limit conditions. We also obtain the different formation regions of combined solitons. Our results show that the intraspecies (interspecies) interaction strengths clearly affect the formation of dark-dark, bright-bright and dark-bright soliton solutions in different regions.

Energy and spatial momentum of charged rotating frames in tetrad gravity

Gamal G.L. Nashed
Chin. Phys. B, 2011, 20 (11): 110401 doi: 10.1088/1674-1056/20/11/110401
Full Text: [PDF 147 KB] (Downloads:463)
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We compute the total energy and the spatial momentum of four charged rotating (Kerr-Newman) frames by using the gravitational energy-momentum 3-form within the framework of the tetrad formulation of the general relativity theory. We show how the effect of the inertial always makes the total energy divergent. We use a natural regularization method, which yields the physical value for the total energy of the system. We show how the regularization method works on a number of different rotating frames that are related to each other by the local Lorentz transformation. We also show that the inertial has no effect on the spatial momentum components.

Five-dimensional teleparallel theory equivalent to general relativity, the axially symmetric solution, energy and spatial momentum

Gamal G.L. Nashed
Chin. Phys. B, 2011, 20 (11): 110402 doi: 10.1088/1674-1056/20/11/110402
Full Text: [PDF 127 KB] (Downloads:664)
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A theory of (4+1)-dimensional gravity is developed on the basis of the teleparallel theory equivalent to general relativity. The fundamental gravitational field variables are the five-dimensional vector fields (pentad), defined globally on a manifold M, and gravity is attributed to the torsion. The Lagrangian density is quadratic in the torsion tensor. We then give the exact five-dimensional solution. The solution is a generalization of the familiar Schwarzschild and Kerr solutions of the four-dimensional teleparallel equivalent of general relativity. We also use the definition of the gravitational energy to calculate the energy and the spatial momentum.

A simpler method for researching fermions tunneling from black holes

Lin Kai, Yang Shu-Zheng
Chin. Phys. B, 2011, 20 (11): 110403 doi: 10.1088/1674-1056/20/11/110403
Full Text: [PDF 119 KB] (Downloads:610)
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A new simpler mathematic method is proposed to study fermions tunneling from black holes. According to this method, by using semiclassical approximation theory, it simplifies the Dirac equation of curved spacetime and then the relationship of the gamma matrix and the component of contravariant metric is considered in order to transform the set of difficult quantum equations into a simple equation. Finally, the fermion tunneling and Hawking radiation of black holes are obtained. The method is very effective and simple, and we will take the Schwarzschild black hole with global monopole and the higher-dimensional Reissner-Nordstrom de Sitter black hole as two examples to show the fact.

Thermodynamic and geometric framework of a (2+1)-dimensional black hole with non-linear electrodynamics

Chen Gang, Liu Zhan-Fang, Lan Ming-Jian
Chin. Phys. B, 2011, 20 (11): 110404 doi: 10.1088/1674-1056/20/11/110404
Full Text: [PDF 113 KB] (Downloads:628)
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The thermodynamic properties of a (2 + 1)-dimensional black hole with non-linear electrodynamics from the viewpoint of geometry is studied and some kinds of temperatures of the black hole have been obtained. Weinhold curvature and Ruppeiner curvature are explored as information geometry. Moreover, based on Quevedo's theory, the Legendre invariant geometry is investigated for the black hole. We also study the relationship between the scalar curvatures of the above several metrics and the phase transitions produced from the heat capacity.

Effect of time delay on the upper bound of the time derivative of information entropy in a stochastic dynamical system

Zhang Min-Min, Wang Can-Jun, Mei Dong-Cheng
Chin. Phys. B, 2011, 20 (11): 110501 doi: 10.1088/1674-1056/20/11/110501
Full Text: [PDF 161 KB] (Downloads:526)
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The effects of the time delay on the upper bound of the time derivative of information entropy are investigated in a time-delayed dynamical system driven by correlated noise. Using the Markov approximation of the stochastic delay differential equations and the Schwartz inequality principle, we obtain an analytical expression for the upper bound UB(t) of the time derivative of the information entropy. The results show that there is a critical value of τ (delay time), and UB(t) presents opposite behaviours on difference sides of the critical value. For the case of the weak additive noise, τ can induce a reentrance transition. Delay time τ also causes a reversal behaviour in UB(t)-λ plot, where λ denotes the degree of the correlation between the two noises.

Optimization-based topology identification of complex networks

Tang Sheng-Xue, Chen Li, He Yi-Gang
Chin. Phys. B, 2011, 20 (11): 110502 doi: 10.1088/1674-1056/20/11/110502
Full Text: [PDF 186 KB] (Downloads:673)
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In many cases, the topological structures of a complex network are unknown or uncertain, and it is of significance to identify the exact topological structure. An optimization-based method of identifying the topological structure of a complex network is proposed in this paper. Identification of the exact network topological structure is converted into a minimal optimization problem by using the estimated network. Then, an improved quantum-behaved particle swarm optimization algorithm is used to solve the optimization problem. Compared with the previous adaptive synchronization-based method, the proposed method is simple and effective and is particularly valid to identify the topological structure of synchronization complex networks. In some cases where the states of a complex network are only partially observable, the exact topological structure of a network can also be identified by using the proposed method. Finally, numerical simulations are provided to show the effectiveness of the proposed method.

Amplitude wave in one-dimensional complex Ginzburg–Landau equation

Xie Ling-Ling, Gao Jia-Zhen, Xie Wei-Miao, Gao Ji-Hua
Chin. Phys. B, 2011, 20 (11): 110503 doi: 10.1088/1674-1056/20/11/110503
Full Text: [PDF 426 KB] (Downloads:567)
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The wave propagation in the one-dimensional complex Ginzburg-Landau equation (CGLE) is studied by considering a wave source at the system boundary. A special propagation region, which is an island-shaped zone surrounded by the defect turbulence in the system parameter space, is observed in our numerical experiment. The wave signal spreads in the whole space with a novel amplitude wave pattern in the area. The relevant factors of the pattern formation, such as the wave speed, the maximum propagating distance and the oscillatory frequency, are studied in detail. The stability and the generality of the region are testified by adopting various initial conditions. This finding of the amplitude pattern extends the wave propagation region in the parameter space and presents a new signal transmission mode, and is therefore expected to be of much importance.

Synchronization criteria for coupled Hopfield neural networks with time-varying delays

M.J. Park, O.M. Kwon, Ju H. Park, S.M. Lee, E.J. Cha
Chin. Phys. B, 2011, 20 (11): 110504 doi: 10.1088/1674-1056/20/11/110504
Full Text: [PDF 3411 KB] (Downloads:983)
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This paper proposes new delay-dependent synchronization criteria for coupled Hopfield neural networks with time-varying delays. By construction of a suitable Lyapunov-Krasovskii's functional and use of Finsler's lemma, novel synchronization criteria for the networks are established in terms of linear matrix inequalities (LMIs) which can be easily solved by various effective optimization algorithms. Two numerical examples are given to illustrate the effectiveness of the proposed methods.

Novel four-dimensional autonomous chaotic system generating one-, two-, three- and four-wing attractors

Yu Fei, Wang Chun-Hua, Yin Jin-Wen, Xu Hao
Chin. Phys. B, 2011, 20 (11): 110505 doi: 10.1088/1674-1056/20/11/110505
Full Text: [PDF 555 KB] (Downloads:1060)
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In this paper, we propose a novel four-dimensional autonomous chaotic system. Of particular interest is that this novel system can generate one-, two, three- and four-wing chaotic attractors with the variation of a single parameter, and the multi-wing type of the chaotic attractors can be displayed in all directions. The system is simple with a large positive Lyapunov exponent and can exhibit some interesting and complicated dynamical behaviours. Basic dynamical properties of the four-dimensional chaotic system, such as equilibrium points, the Poincaré map, the bifurcation diagram and the Lyapunov exponents are investigated by using either theoretical analysis or numerical method. Finally, a circuit is designed for the implementation of the multi-wing chaotic attractors. The electronic workbench observations are in good agreement with the numerical simulation results.

Adaptive stabilization of an incommensurate fractional order chaotic system via a single state controller

Zhang Ruo-Xun, Yang Shi-Ping
Chin. Phys. B, 2011, 20 (11): 110506 doi: 10.1088/1674-1056/20/11/110506
Full Text: [PDF 415 KB] (Downloads:1071)
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In this paper, we investigate the stabilization of an incommensurate fractional order chaotic systems and propose a modified adaptive-feedback controller for the incommensurate fractional order chaos control based on the Lyapunov stability theory, the fractional order differential inequality and the adaptive control theory. The present controller, which only contains a single state variable, is simple both in design and in implementation. The simulation results for several fractional order chaotic systems are provided to illustrate the effectiveness of the proposed scheme.

Transient transport processes in deformable porous media

Cs. Mészáros, Á. Bálint
Chin. Phys. B, 2011, 20 (11): 110507 doi: 10.1088/1674-1056/20/11/110507
Full Text: [PDF 237 KB] (Downloads:527)
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The basic partial differential equations relevant for convection-diffusion and convection-diffusion-wave phenomena are presented and solved analytically by using the MAPLE symbolic computer algebra system. The possible general nonlinear character of the constitutive equation of the convection-discussion process is replaced by a direct posteriori stochastic refinement of its solution represented for Dirichlet-type boundary conditions. A thermodynamic analysis is performed for connecting the relaxation time constants and Jacobi-determinants of deformations at transient transport processes. Finally, a new procedure for general description of coupled transport processes on the basis of the formalism originally developed for convection-free phenomena is presented by matrix analysis methods in the Fourier space.

Long-distance quantum state transfer through cavity-assisted interaction

Li Yu-Ning, Mei Feng, Yu Ya-Fei, Zhang Zhi-Ming
Chin. Phys. B, 2011, 20 (11): 110305 doi: 10.1088/1674-1056/20/11/110305
Full Text: [PDF 152 KB] (Downloads:745)
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We propose a scheme for long-distance quantum state transfer between different atoms based on cavity-assisted interactions. In our scheme, a coherent optical pulse sequentially interacts with two distant atoms trapped in separated cavities. Through the measurement of the state of the first atom and the homodyne detection of the final output coherent light, the quantum state can be transferred into the second atom with a success probability of unity and a fidelity of unity. In addition, our scheme neither requires the high-Q cavity working in the strong coupling regime nor employs the single-photon quantum channel, which greatly relaxes the experimental requirements.

A new quantum mechanical photon counting distribution formula

Yuan Hong-Chun, Fan Hong-Yi, Hu Li-Yun
Chin. Phys. B, 2011, 20 (11): 114204 doi: 10.1088/1674-1056/20/11/114204
Full Text: [PDF 113 KB] (Downloads:642)
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By virtue of the density operator's P-representation in the coherent state representation, we derive a new quantum mechanical photon counting distribution formula. As its application, we calculate photon counting distributions for some given light fields. It is found that the pure squeezed state's photon counting distribution is related to the Legendre function, which is a new result.

Significant effect of electron transfer between current collector and active material on high rate performance of Li4Ti5O12 Hot!

Pan Hui-Lin, Hu Yong-Sheng, Li Hong, Chen Li-Quan
Chin. Phys. B, 2011, 20 (11): 118202 doi: 10.1088/1674-1056/20/11/118202
Full Text: [PDF 182 KB] (Downloads:922)
Show Abstract
The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li4Ti5O12, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li4Ti5O12 pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on Al current collector. For Li4Ti5O12, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.

Electric and magnetic dipole couplings in split ring resonator metamaterials

Fan Jing, Sun Guang-Yong, Zhu Wei-Ren
Chin. Phys. B, 2011, 20 (11): 114101 doi: 10.1088/1674-1056/20/11/114101
Full Text: [PDF 237 KB] (Downloads:1934)
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In this paper, the electric and the magnetic dipole couplings between the outer and the inner rings of a single split ring resonator (SRR) are investigated. We numerically demonstrate that the magnetic resonance frequency can be substantially modified by changing the couplings of the electric and magnetic dipoles, and give a theoretical expression of the magnetic resonance frequency. The results in this work are expected to be conducive to a deeper understanding of the SRR and other similar metamaterials, and provide new guidance for complex metamaterials design with a tailored electromagnetic response.

Femtosecond electron pulse compression by using the time focusing technique in ultrafast electron diffraction

Wen Wen-Long, Lei Xiao-Hong, Hu Xin, Xu Xiang-Yan, Wang Jun-Feng, Cao Xi-Bin, Liu Hu-Lin, Wang Chao, Dang Li-Hong, Tian Jin-Shou
Chin. Phys. B, 2011, 20 (11): 114102 doi: 10.1088/1674-1056/20/11/114102
Full Text: [PDF 175 KB] (Downloads:753)
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We present a new model of an electron gun for generating subrelativistic femtosecond (fs) electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing electrode generates an electron energy chirp for bunching at the target. Without considering the space charge effects, simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode. Tracing and simulating large numbers of photoelectrons through Monte-Carlo and finite difference methods, the electron pulses with 1 ps can be compressed to 55 fs, which will allow significant advances in the field of ultrafast diagnosis.

Kurtosis parameters of super Lorentz–Gauss beams through a paraxial and real ABCD optical system

Zhou Guo-Quan
Chin. Phys. B, 2011, 20 (11): 114103 doi: 10.1088/1674-1056/20/11/114103
Full Text: [PDF 407 KB] (Downloads:741)
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Based on the propagation equation of higher-order intensity moments, analytical propagation expressions for the kurtosis parameters of a super Lorentz-Gauss (SLG) SLG01 beam through a paraxial and real ABCD optical system are derived. By replacing the parameters in the expressions of the kurtosis parameters of the SLG01 beam, the kurtosis parameters of the SLG10 and SLG11 beams through a paraxial and real ABCD optical system can be easily obtained. The kurtosis parameters of an SLG01 beam through a paraxial and real ABCD optical system depend on two ratios. One is the ratio of the transfer matrix element B to the product of the transfer matrix element A and the diffraction-free range of the super-Lorentzian part. The other is the ratio of the width parameter of the super-Lorentzian part to the waist of the Gaussian part. As a numerical example, the properties of the kurtosis parameters of an SLG01 beam propagating in free space are illustrated. The influences of different parameters on the kurtosis parameters of an SLG01 beam are analysed in detail.

Polarization mode dispersion compensation in a novel dual polarization differential quadrature phase shift keying system

Qin Jiang-Xing, Xi Li-Xia, Zhang Xiao-Guang, Tian Feng
Chin. Phys. B, 2011, 20 (11): 114201 doi: 10.1088/1674-1056/20/11/114201
Full Text: [PDF 369 KB] (Downloads:1383)
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A novel dual polarization differential quadrature phase shift keying (DP-DQPSK) system is proposed, whose receiver is the same as the single polarization DQPSK system, while it does not need polarization de-multiplexing like the conventional polarization division multiplexing QPSK (PDM-QPSK). Polarization mode dispersion (PMD) is mainly considered and PMD compensation for the DP-DQPSK system is studied. As the feedback signal for PMD compensation, the degree of polarization of the signals is discussed in detail. The results show that PMD tolerance can be improved by 89 ps within 1 dB optical signal noise ratio penalty after PMD compensation for the DP-DQPSK system.

Tight focusing of partially polarized vortex beams by binary phase Fresnel zone plates

Shu Jian-Hua, Chen Zi-Yang, Pu Ji-Xiong, Liu Yong-Xin
Chin. Phys. B, 2011, 20 (11): 114202 doi: 10.1088/1674-1056/20/11/114202
Full Text: [PDF 313 KB] (Downloads:767)
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Based on vectorial Debye theory, the focusing properties of partially polarized vortex beam by high numerical aperture Fresnel zone plate are investigated. The effects of the numerical apertures of and the phase difference of binary phase Fresnel zone plates, the topological charge of vortex beam and the degree of polarization of incident beam on the intensity distribution and degree of coherence in the focal plane are investigated in detail. It is shown that elliptical light spots and the flat top beam can be obtained by selecting certain parameters. Studies of degree of coherence reveal that the degree of coherence between x and y components of the electric field, which is zero in the source plane, is improved in the focal plane for vortex beam, but it is hardly changed for the nonvortex beam. It is also proved that any two of the three electric field components Ex, Ey and Ez are completely coherent everywhere in the focal region if the incident light beam is linearly polarized.

The 260-W coherent beam combining of two compact fibre amplifier chains

Wang Xiao-Lin, Ma Yan-Xing, Zhou Pu, He Bing, Xue Yu-Hao, Liu Chi, Li Zhen, Xiao Hu, Xu Xiao-Jun, Zhou Jun, Liu Ze-Jin, Zhao Yi-Jun
Chin. Phys. B, 2011, 20 (11): 114203 doi: 10.1088/1674-1056/20/11/114203
Full Text: [PDF 311 KB] (Downloads:633)
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Coherent beam combining of two fibre amplifier chains with a total power of 260 W in a compact system using the stochastic parallel gradient descent (SPGD) algorithm is demonstrated. A 150 MHz linewidth fibre laser is built and introduced for high-power amplification to mitigate stimulated Brillouin scattering (SBS). Compact high-power amplifier chains are built with low power all-fibre system and high-power bulk free-optics fibre amplifiers. When the total power is about 260 W, active phase-locking of two high-power amplifiers is demonstrated using the SPGD algorithm. In closed-loop, the power in the main lobe increases 1.68 times, the visibility is increased from 0 to 0.62, and the phase residual error is less than λ/10.

Sideband entanglement in collective resonance fluorescence

Zhang Xue-Hua, Hu Xiang-Ming
Chin. Phys. B, 2011, 20 (11): 114205 doi: 10.1088/1674-1056/20/11/114205
Full Text: [PDF 131 KB] (Downloads:554)
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We examine the quantum correlation between the Mollow sidebands in the collective resonance fluorescence from a strongly driven ensemble of two-level atoms. By using the criterion proposed by Shchukin and Vogel, we show that non-Gaussian entanglement exists between the two separated sidebands. The responsible mechanism is traced to the spontaneous parametric process, in which the nonclassical correlation is established. This suggests that the collective resonance fluorescence provides a continuous source for the non-Gaussian entangled light and thus has great potentials for various applications in quantum information and quantum computation.

Adjusting the properties of the photon generated via an optical parametric oscillator by using a pulse pumped laser

Chen Song, Shi Bao-Sen, Guo Guang-Can
Chin. Phys. B, 2011, 20 (11): 114206 doi: 10.1088/1674-1056/20/11/114206
Full Text: [PDF 1399 KB] (Downloads:721)
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The cavity-enhanced spontaneous parametric down-conversion far below threshold can be used to generate a narrow-band photon pair efficiently. Previous experiments on the cavity-enhanced spontaneous parametric down-conversion almost always utilize continuous wave pump light, but the pulse pumped case is rarely reported. One disadvantage of the continuous wave case is that the photon pair is produced randomly within the coherence time of the pump, which limits its application in the quantum information realm. However, a pulse pump can help to solve this problem. In this paper, we theoretically analyze pulse pumped cavity-enhanced spontaneous parametric down-conversion in detail and show how the pump pulse affects the multi-photon interference visibility, two-photon waveform, joint spectrum and spectral brightness.

Stationary properties of a single-mode laser system with non-Gaussian and Gaussian noise

Wang Bing, Wu Xiu-Qing
Chin. Phys. B, 2011, 20 (11): 114207 doi: 10.1088/1674-1056/20/11/114207
Full Text: [PDF 138 KB] (Downloads:738)
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A single-mode laser system with non-Gaussian and Gaussian noise is investigated. The stationary mean value and the normalized variance of the laser intensity are numerically calculated under the condition that the stationary probability distribution function (SPDF) is derived. The SPDF as a function of the laser intensity exhibits a maximum. The maximum becomes smaller with the increase of the correlation intensity or the non-Gaussian parameter, where the later is a measure of the deviation from the Gaussian characteristic. The maximum becomes larger as the correlation time increases. The laser intensity stationary mean value decreases with the increase of the correlation intensity or the non-Gaussian parameter while increases with the correlation time increasing. The laser intensity normalized variance increases with the increase of the correlation intensity or the non-Gaussian parameter while decreases as the correlation time increases.

High power tandem pumping fibre amplifier

Xiao Hu, Wu Wu-Ming, Xu Jiang-Ming, Zhou Pu, Xu Xiao-Jun
Chin. Phys. B, 2011, 20 (11): 114208 doi: 10.1088/1674-1056/20/11/114208
Full Text: [PDF 123 KB] (Downloads:1100)
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We demonstrate a high efficiency 1083 nm fibre amplifier tandem pumped by a 1030 nm fibre laser. The 1030 nm fibre laser is coupled into a 25 m long single clad ytterbium doped fibre via a high power wave division multiplexer to core pump the 1083 nm signal laser. An output power of 4.5 W and a power conversion efficiency of 76.6% are achieved without power-roll. The performance of the amplifier can be improved by optimizing the gain fibre length.

Dual-wavelength dissipative soliton operation of an erbium-doped fibre laser using a nonlinear polarization rotation technique

Cao Wen-Jun, Xu Wen-Cheng, Luo Zhi-Chao, Wang Lu-Yan, Wang Hui-Yi, Dong Jiang-Li, Luo Ai-Ping
Chin. Phys. B, 2011, 20 (11): 114209 doi: 10.1088/1674-1056/20/11/114209
Full Text: [PDF 312 KB] (Downloads:768)
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We report on the generation of dual-wavelength dissipative solitons in a passively mode-locked fibre laser with a net normal dispersion using the nonlinear polarization rotation (NPR) technique. Taking the intrinsic advantage of the intracavity birefringence-induced spectral filtering effect in the NPR-based ring laser cavity, the dual-wavelength dissipative solitons are obtained. In addition, the wavelength separation and the lasing location of the dual-wavelength solitons can be flexibly tuned by changing the orientation of the polarization controller.

Dependence of curvature type of thermal lensing on number of bounces in a zigzag slab laser: numerical modeling

Fu Xing, Liu Qiang, Yan Xing-Peng, Gong Ma-Li
Chin. Phys. B, 2011, 20 (11): 114210 doi: 10.1088/1674-1056/20/11/114210
Full Text: [PDF 922 KB] (Downloads:772)
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The curvature type of the thermal lens generated in a zigzag slab laser is numerically analysed. It is found that the curvature type of the thermal lens varies alternatively between the convex and the concave lenses with the number of bounces of light within the slab, which can be well explained by the trace of the zigzag propagation. In addition, we conclude that the beamlet with a larger number of bounces experiences weaker thermal lensing but more serious wavefront deformation due to the large side lobe portion in the curve of optical path difference.

Tight focus of a radially polarized and amplitude- modulated annular multi-Gaussian beam

Chen Jian-Nong, Xu Qin-Feng, Wang Gang
Chin. Phys. B, 2011, 20 (11): 114211 doi: 10.1088/1674-1056/20/11/114211
Full Text: [PDF 1514 KB] (Downloads:1031)
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The focusing of a radially polarized beam without annular apodization ora phase filter at the entrance pupil of the objective results in a wide focus and low purity of the longitudinally polarized component. However, the presence of a physical annular apodization or phase filter makes some applications more difficult or even impossible. We propose a radially polarized and amplitude-modulated annular multi-Gaussian beam mode. Numerical simulation shows that it can be focused into a sharper focal spot of 0.125λ2 without additional apodizations or filters. The beam quality describing the purity of longitudinally polarized component is up to 86%.

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

Qiao Yao-Jun, Liu Xue-Jun, Ji Yue-Feng
Chin. Phys. B, 2011, 20 (11): 114212 doi: 10.1088/1674-1056/20/11/114212
Full Text: [PDF 262 KB] (Downloads:1165)
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This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk-off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high-dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20×80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold (for Q > 10 dB) about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/(nm·km) dispersion coefficients.

Describing spatiotemporal couplings in ultrashort pulses using coupling coefficients

Zeng Shu-Guang, Dan You-Quan, Zhang Bin, Sun Nian-Chun, Sui Zhan
Chin. Phys. B, 2011, 20 (11): 114213 doi: 10.1088/1674-1056/20/11/114213
Full Text: [PDF 201 KB] (Downloads:573)
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Three coupling coefficients are defined to describe spatiotemporal coupling in ultrashort pulses. With these coupling coefficients, the first-order spatiotemporal couplings of Gaussian pulse and beam are described analytically. Also, the first-order and the second-order spatiotemporal couplings caused by angular dispersion elements are studied using these coupling coefficients. It can be shown that these coupling coefficients are dimensionless and normalized, and readily indicate the severity of spatiotemporal coupling.

Self-similar spatiotemporal solitary waves in Bessel–Hermite optical lattices

Xu Si-Liu, Liang Jian-Chu, Li Zhong-Ming
Chin. Phys. B, 2011, 20 (11): 114214 doi: 10.1088/1674-1056/20/11/114214
Full Text: [PDF 1749 KB] (Downloads:980)
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An exact self-similar solution to a (3+1)-dimensional nonlinear Schrödinger equation with gain in the Bessel-Hermite lattice is obtained analytically. The stability of the analytical solution is confirmed by using numerical simulation. It is shown that the light bullet has a stable ellipsoid or vortex profile and a linear spatiotemporal chirp.

Low noise, continuous-wave single-frequency 1.5-μm laser generated by a singly resonant optical parametric oscillator

Liu Jian-Li, Liu Qin, Li Hong, Li Peng, Zhang Kuan-Shou
Chin. Phys. B, 2011, 20 (11): 114215 doi: 10.1088/1674-1056/20/11/114215
Full Text: [PDF 978 KB] (Downloads:710)
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We report a low noise continuous-wave (CW) single-frequency 1.5-μm laser source obtained by a singly resonant optical parametric oscillator (SRO) based on periodically poled lithium niobate (PPLN). The SRO was pumped by a CW single-frequency Nd:YVO4 laser at 1.06 μm. The 1.02 W of CW single-frequency signal laser at 1.5 μm was obtained at pump power of 6 W. At the output power of around 0.75 W, the power stability was better than ±1.5% and no mode-hopping was observed in 30 min and frequency stability was better than 8.5 MHz in 1 min. The signal wavelength could be tuned from 1.57 to 1.59 μm by varying the PPLN temperature. The 1.5-μm laser exhibits low noise characteristics, the intensity noise of the laser reaches the shot noise limit (SNL) at an analysis frequency of 4 MHz and the phase noise is less than 1 dB above the SNL at analysis frequencies above 10 MHz.

Programmable agile beam steering based on a liquid crystal prism

Xu Lin, Huang Zi-Qiang, Yang Ruo-Fu
Chin. Phys. B, 2011, 20 (11): 114216 doi: 10.1088/1674-1056/20/11/114216
Full Text: [PDF 1466 KB] (Downloads:835)
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To meet the application need for agile precision beam steering, a novel liquid crystal prism device with a simple structure, convenient control, low cost and applicable performance is presented, and analysed theoretically and experimentally. The relationships between the optical path and the thickness of the liquid crystal cell under different voltages are investigated quantitatively by using a theoretical model. Analysis results show that the optical path profile of the liquid crystal prism has a quasi-linear slope and the standard deviation of the linear slope is less than 16 nm. The slope ratio can be changed by a voltage, which achieves the programmable beam steering and control. Practical liquid crystal prism devices are fabricated. Their deflection angles and wavefront profiles with different voltages are experimentally tested. The results are in good agreement with the simulated results. The results imply that the agile beam steering in a scope of 100 μrad with a micro-rad resolution is substantiated in the device. The two-dimensional beam steering is also achieved by cascading two liquid crystal prism devices.

Dark diffusional enhancement of holographic multiplexed gratings in phenanthrenequinone doped poly(methyl methacrylate) photopolymer

Yu Dan, Wang Heng, Liu Hong-Peng, Wang Jian, Jiang Yong-Yuan, Sun Xiu-Dong
Chin. Phys. B, 2011, 20 (11): 114217 doi: 10.1088/1674-1056/20/11/114217
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In this paper, we experimentally investigate the dark diffusional enhancement of the optimized multiplexed grating in the phenanthrenequinone doped poly (methyl methacrylate) (PQ-PMMA) photopolymer. The possibility of improving the holographic characteristics of the material through the dark enhancement is demonstrated. The optimal preillumination exposure and the optimal time interval between exposures are extracted to obtain the optimized diffraction efficiency, and their values are 3.4×103 mJ/cm2 and 2 min, respectively. The dark enhancement of the multiplexed grating is presented as an effective method to improve the response region and the dynamic range and to prevent saturation of the material. The dependence of the phenanthrenequinone concentration on the increment of the refractive index modulation is quantitatively studied, which provides a significant basis for improving the homogeneity in the multiplexed gratings using a quantitative strategy. Finally, a simple experimental procedure using the dark enhancement is introduced to improve the homogeneity of the diffraction efficiency and to avoid the complex schedule exposure.

Numerical simulation of a gradient-index fibre probe and its properties of light propagation

Wang Chi, Mao You-Xin, Tang Zhi, Fang Chen, Yu Ying-Jie, Qi Bo
Chin. Phys. B, 2011, 20 (11): 114218 doi: 10.1088/1674-1056/20/11/114218
Full Text: [PDF 745 KB] (Downloads:1175)
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In order to verify the properties of the light propagating through a gradient-index (GRIN) fibre probe for optical coherence tomography (OCT), numerical simulation using the optical software GLAD is carried out. Firstly, the model of the GRIN fibre probe is presented, which is consisted of a single mode fibre (SMF), a no-core fibre (NCF), a GRIN fibre lens and an air path. Then, the software GLAD is adopted to numerically investigate how the lengths of the NCF and the GRIN fibre lens influence the performance of the Gaussian beam focusing through the GRIN fibre probe. The simulation results are well consistent with the experimental ones, showing that the GLAD based numerical simulation technique is an intuitive and effective tool for the verification of the properties of the light propagation. In this paper, we find that on the conditions of a constant GRIN fibre lens length of 0.1 mm and an NCF length of 0.36 mm, the working distance of the probe will be 0.75 mm and the focus spot size is 32 μm.

Dynamics of solitons of the generalized (3+1)-dimensional nonlinear Schrödinger equation with distributed coefficients

Liu Xiao-Bei, Li Biao
Chin. Phys. B, 2011, 20 (11): 114219 doi: 10.1088/1674-1056/20/11/114219
Full Text: [PDF 362 KB] (Downloads:932)
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We present three families of soliton solutions to the generalized (3+1)-dimensional nonlinear Schrödinger equation with distributed coefficients. We investigate the dynamics of these solitons in nonlinear optics with some selected parameters. Different shapes of bright solitons, a train of bright solitons and dark solitons are observed. The obtained results may raise the possibilities of relevant experiments and potential applications.

Suppressing the hot carrier injection degradation rate in total ionizing dose effect hardened nMOSFETs

Chen Jian-Jun, Chen Shu-Ming, Liang Bin, He Yi-Bai, Chi Ya-Qing, Deng Ke-Feng
Chin. Phys. B, 2011, 20 (11): 114220 doi: 10.1088/1674-1056/20/11/114220
Full Text: [PDF 3380 KB] (Downloads:658)
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Annular gate nMOSFETs are frequently used in spaceborne integrated circuits due to their intrinsic good capability of resisting total ionizing dose (TID) effect. However, their capability of resisting the hot carrier effect (HCE) has also been proven to be very weak. In this paper, the reason why the annular gate nMOSFETs have good TID but bad HCE resistance is discussed in detail, and an improved design to locate the source contacts only along one side of the annular gate is used to weaken the HCE degradation. The good TID and HCE hardened capability of the design are verified by the experiments for I/O and core nMOSFETs in a 0.18 μm bulk CMOS technology. In addition, the shortcoming of this design is also discussed and the TID and the HCE characteristics of the replacers (the annular source nMOSFETs) are also studied to provide a possible alternative for the designers.

Acoustic carpet invisibility cloak with two open windows using multilayered homogeneous isotropic material

Ren Chun-Yu, Xiang Zhi-Hai, Cen Zhang-Zhi
Chin. Phys. B, 2011, 20 (11): 114301 doi: 10.1088/1674-1056/20/11/114301
Full Text: [PDF 1371 KB] (Downloads:922)
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We present a method for designing an open acoustic cloak that can conceal a perturbation on flat ground and simultaneously meet the requirement of communication and matter interchange between the inside and the outside of the cloak. This cloak can be constructed with a multilayered structure and each layer is an isotropic and homogeneous medium. The design scheme consists of two steps: firstly, we apply a conformal coordinate transformation to obtain a quasi-perfect cloak with heterogeneous isotropic material; then, according to the profile of the material distribution, we degenerate this cloak into a multilayered-homogeneous isotropic cloak, which has two open windows with negligible disturbance on its invisibility performance. This may greatly facilitate the fabrication and enhance the applicability of such a carpet-type cloak.

Effect of secondary radiation force on aggregation between encapsulated microbubbles

Zhang Yan-Li, Zheng Hai-Rong, Tang Meng-Xing, Zhang Dong
Chin. Phys. B, 2011, 20 (11): 114302 doi: 10.1088/1674-1056/20/11/114302
Full Text: [PDF 562 KB] (Downloads:748)
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Secondary radiation force can be an attractive force causing aggregates of encapsulated microbubbles in ultrasonic molecular imaging. The influence of the secondary radiation force on aggregation between two coated bubbles is investigated in this study. Numerical calculations are performed based on four simultaneous differential equations of radial and translational motions. Results show that the secondary force can change from attraction to repulsion during approach, and stable microbubble pairs can be formed in the vicinity of resonant regions; the possibility of microbubble aggregations can be reduced by using low exciting amplitude, ultrasonic frequencies deviating from the resonant frequencies or microbubbles with small compressibility.

Perfect plane-wave source for a high-order symplectic finite-difference time-domain scheme

Wang Hui, Huang Zhi-Xiang, Wu Xian-Liang, Ren Xin-Gang
Chin. Phys. B, 2011, 20 (11): 114701 doi: 10.1088/1674-1056/20/11/114701
Full Text: [PDF 222 KB] (Downloads:6097)
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The method of splitting a plane-wave finite-difference time-domain (SP-FDTD) algorithm is presented for the initiation of plane-wave source in the total-field / scattered-field (TF/SF) formulation of high-order symplectic finite-difference time-domain (SFDTD) scheme for the first time. By splitting the fields on one-dimensional grid and using the nature of numerical plane-wave in finite-difference time-domain (FDTD), the identical dispersion relation can be obtained and proved between the one-dimensional and three-dimensional grids. An efficient plane-wave source is simulated on one-dimensional grid and a perfect match can be achieved for a plane-wave propagating at any angle forming an integer grid cell ratio. Numerical simulations show that the method is valid for SFDTD and the residual field in SF region is shrinked down to -300 dB.

Entropy and weak solutions in the lattice Bhatnagar–Gross–Krook model

Ran Zheng, Xu Yu-Peng
Chin. Phys. B, 2011, 20 (11): 114702 doi: 10.1088/1674-1056/20/11/114702
Full Text: [PDF 115 KB] (Downloads:497)
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We derive the entropy functions whose local equilibria are suitable to recover the Euler-like equations in the framework of the lattice Boltzmann method. Numerical examples are also given, which are consistent with the above theoretical arguments. In all cases, we observe a negative entropy range existing near the shock, while numerical oscillations are captured.

Density functional study of Agn-1Y (n=2–10) clusters

Liu Xiao-Yong, Zhu Zheng-He, Sheng Yong
Chin. Phys. B, 2011, 20 (11): 113101 doi: 10.1088/1674-1056/20/11/113101
Full Text: [PDF 243 KB] (Downloads:819)
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Employing the density functional theory, we investigate the lowest-energy geometric, the stable and the electronic properties of Agn-1Y (n=2-10) clusters in this paper. The structural optimization and the frequency analysis are performed at the B3LYP/LANL2DZ level. Meanwhile, the differences in geometry, stability and electronic properties between Agn and Agn-1Y (n=2-10) clusters are also studied. The results show that for the doping of the yttrium atoms, the structures and the average binding lengths of the Agn clusters are greatly changed. In addition, the thermodynamic stabilities of the Agn clusters are enhanced generally with the doping of the Y atoms. In addition, the chemical stabilities of the Agn-1Y clusters are still improved compared with that of the three-dimensional Agn clusters.

Two-dimensional photoelectron momentum distribution of hydrogen in intense laser field

Sun Chang-Ping, Zhao Song-Feng, Chen Jian-Hong, Zhou Xiao-Xin
Chin. Phys. B, 2011, 20 (11): 113201 doi: 10.1088/1674-1056/20/11/113201
Full Text: [PDF 477 KB] (Downloads:795)
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Two-dimensional (2D) electron momentum distributions and energy spectra of a hydrogen in an intense laser field are calculated by solving the time-dependent Schrödinger equation combined with the window-operator technique. Compared with the standard projection technique, the window-operator technique has the advantage that the continuum states of atoms can be avoided in the calculation. We show that the 2D electron momentum distributions and the energy spectra from those two techniques accord quite well with each other if an appropriate energy width is used in the window operator.

Highly dispersed Pd nanoparticles on chemically modified graphene with aminophenyl groups for formic acid oxidation

Yang Su-Dong, Shen Cheng-Min, Tong Hao, He Wei, Zhang Xiao-Gang, Gao Hong-Jun
Chin. Phys. B, 2011, 20 (11): 113301 doi: 10.1088/1674-1056/20/11/113301
Full Text: [PDF 417 KB] (Downloads:596)
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A novel electrode material based on chemically modified graphene (CMG) with aminophenyl groups is covalently functionalized by a nucleophilic ring-opening reaction between the epoxy groups of graphene oxide and the aminophenyl groups of p-phenylenediamine. Palladium nanoparticles with an average diameter of 4.2 nm are deposited on the CMG by a liquid-phase borohydride reduction. The electrocatalytic activity and stability of the Pd/CMG composite towards formic acid oxidation are found to be higher than those of reduced graphene oxide and commercial carbon materials such as Vulcan XC-72 supported Pd electrocatalysts.

Rotational relaxation in ultracold He+BH collisions

Gong Ming-Yan, Xu Xiao-Tao, Feng Er-Yin
Chin. Phys. B, 2011, 20 (11): 113401 doi: 10.1088/1674-1056/20/11/113401
Full Text: [PDF 164 KB] (Downloads:453)
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Collisions of cold and ultracold BH in the v=0 level with the He atom are investigated using the quantum mechanical scattering formulation. The elastic and the inelastic cross sections are calculated using the two-dimensional ab initio potential energy surface. It is shown that the elastic cross section is larger than the inelastic one. When the collision energy is very low, the elastic cross section follows the Wigner threshold law and is one order of magnitude larger than that of He-O2, while it is much smaller than that of He-H2. The efficiency of the rotationally quenching state is given. The Δj=-1 transition is most efficient. The resonances are also found to occur at about the same translational energy (0.1-1 cm-1), which gives rise to steps in the rate coefficient at temperatures around 0.1-1 K.

Single electron capture in collisions of Nq+ (q=5, 6, 7) ions with helium

Wang Fei, Wang Miao-Miao
Chin. Phys. B, 2011, 20 (11): 113402 doi: 10.1088/1674-1056/20/11/113402
Full Text: [PDF 248 KB] (Downloads:568)
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Close-coupling calculations are carried out for cross sections of the single electron capture in collisions of Nq+ (q = 5, 6, 7) ions with helium atoms in the collision velocity range from 0.3 a.u. to 1.8 a.u. The relative importances of the single ionization (SI) to the single capture (SC) are investigated for the Nq+ (q = 5, 6, 7) projectiles, respectively. The SI/SC cross section ratio for the N7+ projectile obtained from our calculations is in excellent agreement with the experimental data. The ratio curves also show us distinct behaviours when the charge of the projectile is different. The partial electron capture cross sections for different projectiles indicate that the electron on the target He atom tends to be captured by the projectile into its lower orbital of the outer shell with the decreasing projectile charge.

Valence orbitals of W(CO)6 using electron momentum spectroscopy Hot!

Shi Le-Lei, Liu Kun, Luo Zhi-Hong, Ning Chuan-Gang, Deng Jing-Kang
Chin. Phys. B, 2011, 20 (11): 113403 doi: 10.1088/1674-1056/20/11/113403
Full Text: [PDF 612 KB] (Downloads:865)
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The binding energy spectra and the momentum distributions of the outer valence orbitals of W(CO)6 have been studied by using electron momentum spectroscopy as well as non-relativistic, scalar relativistic and spin-orbital relativistic DFT-B3LYP calculations. The experimental momentum profiles of the outer valence orbitals obtained with the impact energies of 1200 eV and 2400 eV were compared with various theoretical calculation results. The relativistic calculations could provide better descriptions for the experimental momentum distributions than the non-relativistic ones. Moreover, a new ordering of orbitals 10t1u, 3t2g, and 7eg, i.e., 10t1u < 3t2g < 7eg < 10a1g, is established in this work.

Structural and spectroscopic properties of small Pun (n=2–5) molecules

Jia Ting-Ting, Gao Tao, Zhang Yun-Guang, Lei Qiang-Hua, Luo De-Li
Chin. Phys. B, 2011, 20 (11): 113601 doi: 10.1088/1674-1056/20/11/113601
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The equilibrium structures and the electronic, spectroscopic and thermodynamic properties of small Pun (n=2-5) molecules are systematically investigated using the methods of general gradient approximation (GGA) of density functional theory (DFT). The results show that the bond length of the lowest-energy structure of Pu2 is 2.578 AA. The ground state structure of Pu3 is a triangle with D3h symmetry, whereas for Pu4, the ground state structure is a square (D4h) and the spin polarization of 16 for molecule Pu5 with square geometry (D4h) is the most stable structure. For the ground state structures, the vibrational spectra as well as thermodynamic parameters are worked out. In addition, the values for the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) along with the energy gap of all the Pu2-5 structures are presented. The relevant structural and chemical stabilities are predicted.

Linear and nonlinear excitations in complex plasmas with nonadiabatic dust charge fluctuation and dust size distribution

Zhang Li-Ping, Xue Ju-Kui, Li Yan-Long
Chin. Phys. B, 2011, 20 (11): 115201 doi: 10.1088/1674-1056/20/11/115201
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Both linear and nonlinear excitation in dusty plasmas have been investigated including the nonadiabatic dust charge fluctuation and Gaussian size distribution dust particles. A linear dispersion relation and a Korteweg-de Vries-Burgers equation governing the dust acoustic shock waves are obtained. The relevance of the instability of wave and the wave evolution to the dust size distribution and nonadiabatic dust charge fluctuation is illustrated both analytically and numerically. The numerical results show that the Gaussian size distribution of dust particles and the nonadiabatic dust charge fluctuation have strong common influence on the propagation of both linear and nonlinear excitations.

Band alignment of Ga2O3/6H-SiC heterojunction

Chang Shao-Hui, Chen Zhi-Zhan, Huang Wei, Liu Xue-Chao, Chen Bo-Yuan, Li Zheng-Zheng, Shi Er-Wei
Chin. Phys. B, 2011, 20 (11): 116101 doi: 10.1088/1674-1056/20/11/116101
Full Text: [PDF 650 KB] (Downloads:849)
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A high-quality Ga2O3 thin film is deposited on an SiC substrate to form a heterojunction structure. The band alignment of the Ga2O3/6H-SiC heterojunction is studied by using synchrotron radiation photoelectron spectroscopy. The energy band diagram of the Ga2O3/6H-SiC heterojunction is obtained by analysing the binding energies of Ga 3d and Si 2p at the surface and the interface of the heterojunction. The valence band offset is experimentally determined to be 2.8 eV and the conduction band offset is calculated to be 0.89 eV, which indicate a type-II band alignment. This provides useful guidance for the application of Ga2O3/6H-SiC electronic devices.

Optimizing the top profile of a nanowire for maximum forward emission

Wang Dong-Lin, Yu Zhong-Yuan, Liu Yu-Min, Guo Xiao-Tao, Cao Gui, Feng Hao
Chin. Phys. B, 2011, 20 (11): 116102 doi: 10.1088/1674-1056/20/11/116102
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The optimal top structure of a nanowire quantum emitter single photon source is significant in improving performance. Based on the axial symmetry of a cylindrical nanowire, this paper optimizes the top profile of a nanowire for the maximum forward emission by combining the geometry projection method and the finite element method. The results indicate that the nanowire with a cambered top has the stronger emission in the forward direction, which is helpful to improve the photon collection efficiency.

Si nanopillar arrays with nanocrystals produced by template-induced growth at room temperature

Bai An-Qi, Zheng Jun, Tao Ye-Liao, Zuo Yu-Hua, Xue Chun-Lai, Cheng Bu-Wen, Wang Qi-Ming
Chin. Phys. B, 2011, 20 (11): 116103 doi: 10.1088/1674-1056/20/11/116103
Full Text: [PDF 302 KB] (Downloads:689)
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Well-aligned and closely-packed silicon nanopillar (SNP) arrays are fabricated by using a simple method with magnetron sputtering of Si on a porous anodic alumina (PAA) template at room temperature. The SNPs are formed by selective growth on the top of the PAA pore walls. The growth mechanism analysis indicates that the structure of the SNPs can be modulated by the pore spacing of the PAA and the sputtering process and is independent of the wall width of the PAA. Moreover, nanocrystals are identified by using transmission electron microscopy in the as-deposited SNP samples, which are related to the heat isolation structure of the SNPs. The Raman focus depth profile reveals a high crystallization ratio on the surface.

Effect of annealing on structural and optical properties of lead tungstate microcrystals

Pang Hua-Feng, Li Zhi-Jie, Xiang Xia, Zhang Chun-Lai, Fu Yong-Qing, Zu Xiao-Tao
Chin. Phys. B, 2011, 20 (11): 116104 doi: 10.1088/1674-1056/20/11/116104
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Shuttle-like lead tungstate (PbWO4) microcrystals are synthesized at room temperature using the precipitation method with the cetyltrimethyl ammonium bromide. Results from both the X-ray diffraction and the scanning electron microscopy show that the lattice distortions of the PbWO4 microcrystals are reduced significantly when the annealing temperature is increased to 873 K. The result from the ultraviolet-visible diffuse reflectance spectroscopy shows that the exciton absorption appears in the sample annealed at 673 K. The self-trapped exciton luminescence due to the Jahn-Teller effect is also observed in the blue band. The interstitial oxygen ions in the WO42- groups are mainly resposible for the enhancement effect of the green luminescence of the annealed samples. The above results are supported by the spectrum analysis of the as-grown and the post-annealed samples using the X-ray photoelectron spectroscopy.

Analytic solutions to a finite width strip with a single edge crack of two-dimensional quasicrystals

Li Wu
Chin. Phys. B, 2011, 20 (11): 116201 doi: 10.1088/1674-1056/20/11/116201
Full Text: [PDF 109 KB] (Downloads:564)
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In this paper, we investigate the well-known problem of a finite width strip with a single edge crack, which is useful in basic engineering and material science. By extending the configuration to a two-dimensional decagonal quasicrystal, we obtain the analytic solutions of modes I and II using the transcendental function conformal mapping technique. Our calculation results provide an accurate estimate of the stress intensity factors KI and KII, which can be expressed in a quite simple form and are essential in the fracture theory of quasicrystals. Meanwhile, we suggest a generalized cohesive force model for the configuration to a two-dimensional decagonal quasicrystal. The results may provide theoretical guidance for the fracture theory of two-dimensional decagonal quasicrystals.

Acoustic band pinning in the phononic crystal plates of anti-symmetric structure

Cai Chen, Zhu Xue-Feng, Chen Qian, Yuan Ying, Liang Bin, Cheng Jian-Chun
Chin. Phys. B, 2011, 20 (11): 116301 doi: 10.1088/1674-1056/20/11/116301
Full Text: [PDF 2190 KB] (Downloads:732)
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Acoustic bands are studied numerically for a Lamb wave propagating in an anti-symmetric structure of a one-dimensional periodic plate by using the method of supercell plane-wave expansion. The results show that all the bands are pinned in pairs at the Brillouin zone boundary as long as the anti-symmetry remains and acoustic band gaps (ABGs) only appear between certain bands. In order to reveal the relationship between the band pinning and the anti-symmetry, the method of eigenmode analysis is introduced to calculate the displacement fields of different plate structures. Further, the method of harmony response analysis is employed to calculate the reference spectra to verify the accuracy of numerical calculations of acoustic band map, and both the locations and widths of ABGs in the acoustic band map are in good agreement with those of the reference spectra. The investigations show that the pinning effect is very sensitive to the anti-symmetry of periodic plates, and by introducing different types of breakages, more ABGs or narrow pass bands will appear, which is meaningful in band gap engineering.

Growth and properties of wide spectral white light emitting diodes

Xie Zi-Li, Zhang Rong, Fu De-Yi, Liu Bin, Xiu Xiang-Qian, Hua Xue-Mei, Zhao Hong, Chen Peng, Han Ping, Shi Yi, Zheng You-Dou
Chin. Phys. B, 2011, 20 (11): 116801 doi: 10.1088/1674-1056/20/11/116801
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Wide spectral white light emitting diodes have been designed and grown on a sapphire substrate by using a metal-organic chemical vapor deposition system. Three quantum wells with blue-light-emitting, green-light-emitting and red-light-emitting structures were grown according to the design. The surface morphology of the film was observed by using atomic force microscopy. The films were characterized by their photoluminescence measurements. X-ray diffraction θ/2θ scan spectroscopy was carried out on the multi-quantum wells. The secondary fringes of the symmetric ω/2θ X-ray diffraction scan peaks indicate that the thicknesses and the alloy compositions of the individual quantum wells are repeatable throughout the active region. The room temperature photoluminescence spectra of the structures indicate that the white light emission of the multi-quantum wells is obtained. The light spectrum covers 400-700 nm, which is almost the whole visible light spectrum.

Dynamic scaling and optical properties of Zn(S, O, OH) thin film grown by chemical bath deposition

Zhang Yi, Li Bo-Yan, Dang Xiang-Yu, Wu Li, Jin Jing, Li Feng-Yan, Ao Jian-Ping, Sun Yun
Chin. Phys. B, 2011, 20 (11): 116802 doi: 10.1088/1674-1056/20/11/116802
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The scaling behavior and optical properties of Zn(S, O and OH) thin films deposited on soda-lime glass substrates by chemical bath deposition method were studied by combined roughness measurements, scanning electron microscopy and optical properties measurement. From the scaling behaviour, the value of growth scaling exponent β , 0.38±0.06, was determined. This value indicated that the Zn(S, O, OH) film growth in the heterogeneous process was influenced by the surface diffusion and shadowing effect. Results of the optical properties measurements disclosed that the transmittance of the film was in the region of 70%-88% and the optical properties of the film grown for 40 min were better than those grown under other conditions. The energy band gap of the film deposited with 40 min was around 3.63 eV.

Modeling of polycrystalline ZnO thin-film transistors with a consideration of the deep and tail states

Gao Hai-Xia, Hu Rong, Yang Yin-Tang
Chin. Phys. B, 2011, 20 (11): 116803 doi: 10.1088/1674-1056/20/11/116803
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We report a model of the carrier transport and the subgap density of states in a polycrystalline ZnO film for simulating a polycrystalline ZnO thin film transistor. This simple model considering the deep and the band tail states reproduces well the characteristics of polycrystalline ZnO thin film transistors. Furthermore, using the developed model, we study the effects of defect parameters on the electrical performances of the polycrystalline ZnO thin film transistors.

Superexchange interaction enhancement of the quantum transport in a DNA-type molecule

Wang Rui, Zhang Cun-Xi, Zhou Yun-Qing, Kong Ling-Min
Chin. Phys. B, 2011, 20 (11): 117201 doi: 10.1088/1674-1056/20/11/117201
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We use the transfer matrix method and the Green function technique to theoretically study the quantum tunnelling through a DNA-type molecule. Ferromagnetic electrodes are used to produce the spin-polarized transmission probability and therefore the spin current. The distance-dependent crossover comes from the topological variation from the one-dimensional to the two-dimensional model transform as we switch on the interstrand coupling; a new base pair will present N-1 extrachannels for the charge and spin as N being the total base pairs. This will restrain the decay of the transmission and improve the stability of the quantum transport. The spin and charge transfer through the DNA-type molecule is consistent with the quantum tunneling barrier.

A novel thin drift region device with field limiting rings in substrate

Li Qi, Zhu Jin-Luan, Wang Wei-Dong, Wei Xue-Ming
Chin. Phys. B, 2011, 20 (11): 117202 doi: 10.1088/1674-1056/20/11/117202
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A novel thin drift region device with heavily doped N+ rings embedded in the substrate is reported, which is called the field limiting rings in substrate lateral double-diffused MOS transistor (SFLR LDMOS). In the SFLR LDMOS, the peak of the electric field at the main junction is reduced due to the transfer of the voltage from the main junction to other field limiting ring junctions, so the vertical electric field is improved significantly. A model of the breakdown voltage is developed, from which optimal spacing is obtained. The numerical results indicate that the breakdown voltage of the device proposed is increased by 76% in comparison to that of the conventional LDMOS.

Injection and transport of electric charge in a metal/copolymer structure

Li Dong-Mei, Yuan Xiao-Juan, Ma Jia-Sai, Liu De-Sheng
Chin. Phys. B, 2011, 20 (11): 117203 doi: 10.1088/1674-1056/20/11/117203
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The dynamical processes of the electric charge injection and transport from a metal electrode to the copolymer are investigated by using a nonadiabatic dynamic approach. The simulations are performed within the framework of an extended version of the one-dimensional Su-Schrieffer-Heeger (SSH) tight-binding model. It is found that the electric charge can be injected into the copolymer by increasing the applied voltage. For different structures of the copolymer, the critical voltage biases are different and the motion of the injected electric charge in the copolymer varies obviously. For the copolymer with a barrier-well-barrier configuration, the injected electric charge forms a wave packet due to the strong electron-lattice interaction in the barrier, then comes into the well and will be confined in it under a weak electric field. Under a medium electric field, the electric charge can go across the interface of two homopolymers and enter into the other potential barrier. For the copolymer with a well-barrier-well configuration, only under strong enough electric field can the electric charge transfer from the potential well into the barrier and ultimately reach a dynamic balance.

Edge termination study and fabrication of a 4H–SiC junction barrier Schottky diode

Chen Feng-Ping, Zhang Yu-Ming, Zhang Yi-Men, Tang Xiao-Yan, Wang Yue-Hu, Chen Wen-Hao
Chin. Phys. B, 2011, 20 (11): 117301 doi: 10.1088/1674-1056/20/11/117301
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The 4H-SiC junction barrier Schottky (JBS) diodes terminated by field guard rings and offset field plate are designed, fabricated and characterized. It is shown experimentally that a 3-μm P-type implantation window spacing gives an optimum trade-off between forward drop voltage and leakage current density for these diodes, yielding a specific on-resistance of 8.3 mΩ·cm2. A JBS diode with a turn-on voltage of 0.65 V and a reverse current density less than 1 A/cm2 under 500 V is fabricated, and the reverse recovery time is tested to be 80 ns, and the peak reverse current is 28.1 mA. Temperature-dependent characteristics are also studied in a temperature range of 75 ℃-200 ℃. The diode shows a stable Schottky barrier height of up to 200 ℃ and a stable operation under a continuous forward current of 100 A/cm2.

High temperature characteristics of AlGaN/GaN high electron mobility transistors

Yang Li-Yuan, Hao Yue, Ma Xiao-Hua, Zhang Jin-Cheng, Pan Cai-Yuan, Ma Ji-Gang, Zhang Kai, Ma Ping
Chin. Phys. B, 2011, 20 (11): 117302 doi: 10.1088/1674-1056/20/11/117302
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Direct current (DC) and pulsed measurements are performed to determine the degradation mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas (2DEG). The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.

Fano effect of a parallel-coupled triple Rashba quantum dot system

He Ze-Long, Lü Tian-Quan, Cui Lian, Xue Hui-Jie, Li Lin-Jun, Yin Hai-Tao
Chin. Phys. B, 2011, 20 (11): 117303 doi: 10.1088/1674-1056/20/11/117303
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Using the nonequilibrium Keldysh Green's function technique, the Fano effect of a parallel-coupled triple Rashba quantum dot system is investigated. The conductance as a function of electron energy is numerically calculated. Compared with the case of a parallel-coupled double quantum dot system, two additional Fano resonance peaks occur in the conductance spectrum. By adjusting the structural parameters, the two Fano resonance peaks may change into the resonance peaks. In addition, the influence of Rashba spin-orbit interaction on the conductance is studied.

Effects of B and N dopings and H2O adsorption on structural stability and field emission properties of cone-capped carbon nanotubes

Wang Yi-Jun, Wang Liu-Ding, Yang Min, Yan Cheng
Chin. Phys. B, 2011, 20 (11): 117304 doi: 10.1088/1674-1056/20/11/117304
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The effects of B and N dopings and H2O adsorption on the structural stability and the field emission properties of cone-capped carbon nanotubes (CCCNTs) were investigated by using the density-functional theoretical calculation. The adsorption of H2O can increase the structural stability and decrease the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO gap) of the CCCNTs. The strength of total electric field on the top of the H2O-adsorbed CCCNTs is larger than that of the B-doped and the N-doped CCCNTs, electrons will be emitted primarily from the H2O-adsorbed CCCNTs at the same applied voltage. Therefore, the H2O adsorption can lower the threshold voltage for the CCCNTs. While the B and the N dopings produce opposite effects. The HOMO-LUMO gap of the N-doped CCCNTs is the widest among all the gaps of the CCCNTs.

Intrinsic tunneling study of underdoped Bi2Sr2-xLaxCuO6+δ superconductors Hot!

Ren Jian-Kun, Ren Yu-Feng, Tian Ye, Yu Hai-Feng, Zheng Dong-Ning, Zhao Shi-Ping, Lin Cheng-Tian
Chin. Phys. B, 2011, 20 (11): 117401 doi: 10.1088/1674-1056/20/11/117401
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We report on a tunneling study of underdoped submicron Bi2Sr2-xLaxCuO6+δ (La-Bi2201) intrinsic Josephson junctions (IJJs), whose self-heating is sufficiently suppressed. The tunneling spectra are measured from 4.2 K up to the pseudogap opening temperature of T* = 260 K. The gap value found from the spectral peak position is about 35 meV and has a weak temperature dependence both below and above the superconducting transition temperature of Tc = 29 K. Since the superconducting gap should have a value of 10-15 meV, our results indicate that the pseudogap (~35 meV) plays an important role in the underdoped La-Bi2201 intrinsic tunneling spectroscopy down to the lowest temperature of 4.2 K. However, the contribution of the superconducting gap can be separated by normalizing the spectra to the one near and above Tc, which shows that the IJJs can be a useful tool for the study of the electronic properties of the La-Bi2201 cuprate superconductors.

Superconductivities and structural properties of ternary Ti–Zr–Ta alloys

Wang Zhi-Wei, Jia Li, Yang Huai-Xin, Tian Huan-Fang, Shi Hong-Long, Wang Zhen, Li Jian-Qi
Chin. Phys. B, 2011, 20 (11): 117402 doi: 10.1088/1674-1056/20/11/117402
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Superconductivities and structural properties of Ti-Zr-Ta ternary alloys are extensively investigated. The TiZrTa sample has a cubic structure (β -phase) and shows a sharp superconducting transition at a critical temperature (Tc) of about 7.3 K. In addition, two series of Ti-Zr-Ta alloys, with nominal compositions of Ti65-xZr35Tax and TixZr65-xTa35 respectively, are prepared, and their superconductivities and crystal structures change regularly with the chemical composition. Our experimental study also indicates that the annealing processing of this kind of material can cause the transition temperature to increase and the highest Tc is observed to be about 8.3 K in annealed samples.

Translation invariant tensor product states in a finite lattice system

Cai Jian-Wei, Chen Qiao-Ni, Zhao Hui-Hai, Xie Zhi-Yuan, Qin Ming-Pu, Wei Zhong-Chao, Xiang Tao
Chin. Phys. B, 2011, 20 (11): 117501 doi: 10.1088/1674-1056/20/11/117501
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We show that the matrix (or more generally tensor) product states in a finite translation invariant system can be accurately constructed from a same set of local matrices (or tensors) that are determined from an infinite lattice system in one or higher dimensions. This provides an efficient approach for studying translation invariant tensor product states in finite lattice systems. Two methods are introduced to determine the size-independent local tensors.

Effects of Fe doping on ac susceptibility of Pr0.75Na0.25MnO3

Li Yu, Cheng Qian, Qi Da-Wei, Wang Ji-Liang, Zhang Jing, Wang Shuang, Guan Jing
Chin. Phys. B, 2011, 20 (11): 117502 doi: 10.1088/1674-1056/20/11/117502
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Ac susceptibility at low temperatures of Pr0.75Na0.25Mn1-xFexO3 (0 ≤ x ≤ 0.30) is investigated. The peak value of the real component of ac susceptibility χ' at the freezing temperature Tf is suppressed with the increasing frequency. The peak value of χ' shows a linear relation between Tf and the logarithm of the frequency ω. The normalized slope P = ΔTf/TfΔlgω, which is much lower than canonical insulating spin glass systems in which 0.06 ≤ P ≤ 0.08. The peak value of the imaginary component of the ac susceptibility χ'' at Tf for the x = 0, 0.02, 0.30 samples increases with increasing frequency, suggesting a cluster glass ground state with a coexistence of charge-ordered phase and correlated ferromagnetic clusters in spin glass matrix. The peak value of χ'' at Tf for the x = 0.10 sample decreases with increasing frequency, suggesting a phase separation ground state. The peak value of χ'' at Tf for the x = 0.05 sample decreases with increasing frequency for ω ≤ 52 Hz and increases subsequently till 701 Hz, and then decreases with further increasing frequency for ω ≥ 1501 Hz. This complex behaviour is ascribed to the competition between the effects of large and little ferromagnetic clusters in the sample. The ground state of x = 0.05 sample is a transition state from cluster glass to phase separation.

Local leakage current behaviours of BiFeO3 films

Zou Cheng, Chen Bin, Zhu Xiao-Jian, Zuo Zheng-Hu, Liu Yi-Wei, Chen Yuan-Fu, Zhan Qing-Feng, Li Run-Wei
Chin. Phys. B, 2011, 20 (11): 117701 doi: 10.1088/1674-1056/20/11/117701
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The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeO3 films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films.

Nuclear spin induced collapse and revival shape of Rabi oscillations of a single electron spin in diamond

Hu Xin, Liu Dong-Qi, Pan Xin-Yu
Chin. Phys. B, 2011, 20 (11): 117801 doi: 10.1088/1674-1056/20/11/117801
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A collapse and revival shape of Rabi oscillations in an electron spin of a single nitrogen-vacancy centre has been observed in diamond at room temperature. Because of hyperfine interaction between the host 14N nuclear spin and the nitrogen-vacancy centre electron spin, different orientations of the 14N nuclear spins lead to a triplet splitting of the transition between ground state (ms =0) and excited state (ms =1). The manipulation of the single electron spin of nitrogen-vacancy centre is achieved by using a combination of selective microwave excitation and optical pumping at 532 nm. Microwaves can excite three transitions equally to induce three independent nutations and the shape of Rabi oscillations is a combination of the three nutations.

Focusing a beam beyond the diffraction limit using a hyperlens-based device

Zheng Guo-Xing, Zhang Rui-Ying, Li Song, He Ping-An, Zhou Hui
Chin. Phys. B, 2011, 20 (11): 117802 doi: 10.1088/1674-1056/20/11/117802
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A super-focusing device composed of a focusing objective and a hyperlens is proposed to focus an incident plane wave into the deep subwavelength dimension. In the device, the objective converts the incident plane wave into a convergent one. The half cylindrical hyperlens can support high wave vector k modes propagating towards its core. So the convergent wave can be focused into an ultrasmall spot beyond the diffraction limit. The layout is proposed for the super-focusing device and its characteristics are investigated theoretically. Numerical simulations verify that the focused beams are confined in a spot with a diameter of 16.3 nm in the focal plane of the focusing objective with a numerical aperture of 0.6, which corresponds to a super-resolution spot of λ0/23 (λ0 is the wavelength in vacuum). The simulations confirm the effectiveness of the proposed device.

Stability, defect and electronic properties of graphane-like carbon-halogen compounds

Lu Di, Yang Yu-Rong, Xiao Yang, Zhang Xiao-Yu
Chin. Phys. B, 2011, 20 (11): 118101 doi: 10.1088/1674-1056/20/11/118101
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We perform first-principles total energy calculations to investigate the stabilities and the electronic structures of graphane-like structures of carbon-halogen compounds, where the hydrogen atoms in the graphane are substituted by halogen atoms. Three halogen elements, fluorine (F), chlorine (Cl) and bromine (Br), are considered, and the graphane-like structures are named as CF, CCl and CBr, respectively. It is found that for the single-atom adsorption, only the F adatom can be chemically adsorbed on the graphene. However, the stable graphane-like structures of CF, CCl and CBr can form due to the interaction between the halogen atoms. The carbon atoms in the stable CF, CCl and CBr compounds are in the sp3 hybridization, forming a hexagonal network similar to the graphane. The electronic band calculations show that CF and CCl are semiconductors with band gaps of 3.28 eV and 1.66 eV, respectively, while CBr is a metal. Moreover, the molecular dynamics simulation is employed to clarify the stabilities of CF and CCl. Those two compounds are stable at room temperature. A high temperature (≥1200 K) is needed to damage CF, while CCl is destroyed at 700 K. Furthermore, the effects of a vacancy on the structure and the electronic property of CF are discussed.

Fabrication and photoluminescence characteristics of In2O3 nanohillocks

Wei He-Lin, Zhang Lei, Liu Zu-Li, Yao Kai-Lun
Chin. Phys. B, 2011, 20 (11): 118102 doi: 10.1088/1674-1056/20/11/118102
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Uniformly distributed polycrystalline indium nanohillocks are synthesized on silicon substrates with Au catalyst by using the radio frequency magnetic sputtering technique. The results show that the Au catalyst plays a key role in the formation of indium nanohillocks. After thermally oxidizing the indium nanohillocks at 500 ℃ in air for 5 h, the indium nanohillocks totally transform into In2O3 nanohillocks. The energy-dispersive X-ray spectroscopy result indicates that many oxygen vacancies and oxygen-indium vacancy pairs exist in the In2O3 nanohillocks. Photoluminescence spectra under an Ne laser excitation at 280 nm show broad emissions at 420 nm and 470 nm with a shoulder at 450 nm related to oxygen vacancies and oxygen-indium vacancies at room temperature.

A new solvent suppression method via radiation damping effect

Cui Xiao-Hong, Peng Ling, Zhang Zhen-Min, Cai Shu-Hui, Chen Zhong
Chin. Phys. B, 2011, 20 (11): 118201 doi: 10.1088/1674-1056/20/11/118201
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Radiation damping effects induced by the dominated solvent in a solution sample can be applied to suppress the solvent signal. The precession pathway and rate back to equilibrium state between solute and solvent spins are different under radiation damping. In this paper, a series of pulse sequences using radiation damping were designed for the solvent suppression in nuclear magnetic resonance (NMR) spectroscopy. Compared to the WATERGATE method, the solute signals adjacent to the solvent would not be influenced by using the radiation damping method. The one-dimensional (1D) 1H NMR, two-dimensional (2D) gCOSY, and J-resolved experimental results show the practicability of solvent suppression via radiation damping effects in 1D and 2D NMR spectroscopy.

Simulation study of a mixed terminal structure for 4H-SiC merged PiN/Schottky diode

Huang Jian-Hua, Lü Hong-Liang, Zhang Yu-Ming, Zhang Yi-Men, Tang Xiao-Yan, Chen Feng-Ping, Song Qing-Wen
Chin. Phys. B, 2011, 20 (11): 118401 doi: 10.1088/1674-1056/20/11/118401
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In this paper, a mixed terminal structure for the 4H-SiC merged PiN/Schottky diode (MPS) is investigated, which is a combination of a field plate, a junction termination extension and floating limiting rings. Optimization is performed on the terminal structure by using the ISE-TCAD. Further analysis shows that this structure can greatly reduce the sensitivity of the breakdown voltage to the doping concentration and can effectively suppress the effect of the interface charge compared with the structure of the junction termination extension. At the same time, the 4H-SiC MPS with this termination structure can reach a high and stable breakdown voltage.

Improvement of photoemission performance of a gradient-doping transmission-mode GaAs photocathode

Zhang Yi-Jun, Niu Jun, Zhao Jing, Xiong Ya-Juan, Ren Ling, Chang Ben-Kang, Qian Yun-Sheng
Chin. Phys. B, 2011, 20 (11): 118501 doi: 10.1088/1674-1056/20/11/118501
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Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response, one has a gradient-doping structure and the other has a uniform-doping structure. The experimental results show that the gradient-doping photocathode can obtain a higher photoemission capability than the uniform-doping one. As a result of the downward graded band-bending structure, the cathode performance parameters, such as the electron average diffusion length and the surface electron escape probability obtained by fitting quantum yield curves, are greater for the gradient-doping photocathode. The electron diffusion length is within a range of from 2.0 to 5.4 μm for doping concentration varying from 1019 to 1018 cm-3 and the electron average diffusion length of the gradient-doping photocathode achieves 3.2 μm.

Statistical distribution of Chinese names

Guo Jin-Zhong, Chen Qing-Hua, Wang You-Gui
Chin. Phys. B, 2011, 20 (11): 118901 doi: 10.1088/1674-1056/20/11/118901
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This paper studies the statistical characteristics of Chinese surnames, first names and full names based on a credible sample. The distribution of Chinese surnames, unlike that in any other countries, shows an exponential pattern in the top part and a power-law pattern in the tail part. The distributions of Chinese first names and full names have the characteristics of a power law with different exponents. Finally, the interrelation of the first name and the surname is demonstrated by using a computer simulation and an exhibition of the name network. Chinese people take the surname into account when they choose a first name for somebody.

Mobile user forecast and power-law acceleration invariance of scale-free networks

Guo Jin-Li, Guo Zhao-Hua, Liu Xue-Jiao
Chin. Phys. B, 2011, 20 (11): 118902 doi: 10.1088/1674-1056/20/11/118902
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This paper studies and predicts the number growth of China's mobile users by using the power-law regression. We find that the number growth of the mobile users follows a power law. Motivated by the data on the evolution of the mobile users, we consider scenarios of self-organization of accelerating growth networks into scale-free structures and propose a directed network model, in which the nodes grow following a power-law acceleration. The expressions for the transient and the stationary average degree distributions are obtained by using the Poisson process. This result shows that the model generates appropriate power-law connectivity distributions. Therefore, we find a power-law acceleration invariance of the scale-free networks. The numerical simulations of the models agree with the analytical results well.

Betweenness-based algorithm for a partition scale-free graph

Zhang Bai-Da, Wu Jun-Jie, Tang Yu-Hua, Zhou Jing
Chin. Phys. B, 2011, 20 (11): 118903 doi: 10.1088/1674-1056/20/11/118903
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Many real-world networks are found to be scale-free. However, graph partition technology, as a technology capable of parallel computing, performs poorly when scale-free graphs are provided. The reason for this is that traditional partitioning algorithms are designed for random networks and regular networks, rather than for scale-free networks. Multilevel graph-partitioning algorithms are currently considered to be the state of the art and are used extensively. In this paper, we analyse the reasons why traditional multilevel graph-partitioning algorithms perform poorly and present a new multilevel graph-partitioning paradigm, top down partitioning, which derives its name from the comparison with the traditional bottom-up partitioning. A new multilevel partitioning algorithm, named betweenness-based partitioning algorithm, is also presented as an implementation of top-down partitioning paradigm. An experimental evaluation of seven different real-world scale-free networks shows that the betweenness-based partitioning algorithm significantly outperforms the existing state-of-the-art approaches.

Variational assimilation in combination with the regularization method for sea level pressure retrieval from QuikSCAT scatterometer data I: Theoretical frame construction

Zhang Liang, Huang Si-Xun, Shen Chun, Shi Wei-Lai
Chin. Phys. B, 2011, 20 (11): 119201 doi: 10.1088/1674-1056/20/11/119201
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A new method of constructing a sea level pressure field from satellite microwave scatterometer measurements is presented. It is based on variational assimilation in combination with a regularization method using geostrophic vorticity to construct a sea level pressure field from scatterometer data that are given in this paper, which offers a new idea for the application of scatterometer measurements. Firstly, the geostrophic vorticity from the scatterometer data is computed to construct the observation field, and the vorticity field in an area and the sea level pressure on the borders are assimilated. Secondly, the gradient of sea level pressure (semi-norm) is used as the stable functional to educe the adjoint system, the adjoint boundary condition and the gradient of the cost functional in which a weight parameter is introduced for the harmony of the system and the Tikhonov regularization techniques in inverse problem are used to overcome the ill-posedness of the assimilation. Finally, the iteration method of the sea level pressure field is developed.
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