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CN 11-5639/O4
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  • Fermion tunneling from squashed black holes in the Gödel universe and charged Kaluza–Klein space–time

    Li Hui-Ling
    Chin. Phys. B 2011, 20 (3): 030402
    This paper is devoted to the investigation the fermion tunneling radiation of squashed black holes in the Gödel universe and charged Kaluza–Klein space–time. For black holes with different dimensions, establishing a set of appropriate matrices γμ for the general covariant D...

     
  • Determination of the transport properties in 4H-SiC wafers by Raman scattering measurement

    Sun Guo-Sheng, Liu Xing-Fang, Wu Hai-Lei, Yan Guo-Guo, Dong Lin, Zheng Liu, Zhao Wan-Shun, Wang Lei, Zeng Yi-Ping, Li Xi-Guang, Wang Zhan-Guo
    Chin. Phys. B 2011, 20 (3): 033301
    The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phonon–plasmon coupled (LOPC) modes, and compared with those determined by Hall-effect measurement and that p...

     
  • Magnetic field measurement based on a stimulated two-photon Raman transition

    Zhou Zi-Chao, Wei Rong, Shi Chun-Yan, Li Tang, Wang Yu-Zhu
    Chin. Phys. B 2011, 20 (3): 034206
    The magnetic field in the microwave interaction zone of the fountain atomic clock was measured by stimulated Raman transitions. By measuring the two-photon transition frequency between the Zeeman levels of the two ground states, we achieved a magnetic field measurement accuracy of the order of 0.28 ...

     
Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.3
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GENERAL

Conformal invariance and a kind of Hojman conserved quantity of the Nambu system

Li Yan, Fang Jian-Hui, Zhang Ke-Jun
Chin. Phys. B, 2011, 20 (3): 030201 doi: 10.1088/1674-1056/20/3/030201
Full Text: [PDF 150 KB] (Downloads:868)
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Conformal invariance and a kind of Hojman conserved quantity of the Nambu system under infinitesimal transformations are studied. The definition and the determining equation of conformal invariance of the system are presented. The necessary and sufficient condition under which the conformal invariance of the system would have Lie symmetry under infinitesimal transformations is derived. Then, the condition of existence and a kind of Hojman conserved quantity are obtained. Finally, an example is given to illustrate the application of the results.

Mei symmetries and Mei conserved quantities for higher-order nonholonomic constraint systems

Jiang Wen-An, Li Zhuang-Jun, Luo Shao-Kai
Chin. Phys. B, 2011, 20 (3): 030202 doi: 10.1088/1674-1056/20/3/030202
Full Text: [PDF 197 KB] (Downloads:900)
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This paper presents the Mei symmetries and new types of non-Noether conserved quantities for a higher-order nonholonomic constraint mechanical system. On the basis of the form invariance of differential equations of motion for dynamical functions under general infinitesimal transformation, the determining equations, the constraint restriction equations and the additional restriction equations of Mei symmetries of the system are constructed. The criterions of Mei symmetries, weak Mei symmetries and strong Mei symmetries of the system are given. New types of conserved quantities, i.e. the Mei symmetrical conserved quantities, the weak Mei symmetrical conserved quantities and the strong Mei symmetrical conserved quantities of a higher-order nonholonomic system, are obtained. Then, a deduction of the first-order nonholonomic system is discussed. Finally, two examples are given to illustrate the application of the method and then the results.

Evolutionary games in a generalized Moran process with arbitrary selection strength and mutation

Quan Ji, Wang Xian-Jia
Chin. Phys. B, 2011, 20 (3): 030203 doi: 10.1088/1674-1056/20/3/030203
Full Text: [PDF 303 KB] (Downloads:682)
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By using a generalized fitness-dependent Moran process, an evolutionary model for symmetric 2×2 games in a well-mixed population with a finite size is investigated. In the model, the individuals' payoff accumulating from games is mapped into fitness using an exponent function. Both selection strength β and mutation rate ε are considered. The process is an ergodic birth-death process. Based on the limit distribution of the process, we give the analysis results for which strategy will be favoured when ε is small enough. The results depend on not only the payoff matrix of the game, but also on the population size. Especially, we prove that natural selection favours the strategy which is risk-dominant when the population size is large enough. For arbitrary β and ε values, the 'Hawk–Dove' game and the 'Coordinate' game are used to illustrate our model. We give the evolutionary stable strategy (ESS) of the games and compare the results with those of the replicator dynamics in the infinite population. The results are determined by simulation experiments.

A new finite difference scheme for a dissipative cubic nonlinear Schr"odinger equation

Zhang Rong-Pei, Yu Xi-Jun, Zhao Guo-Zhong
Chin. Phys. B, 2011, 20 (3): 030204 doi: 10.1088/1674-1056/20/3/030204
Full Text: [PDF 236 KB] (Downloads:746)
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This paper considers the one-dimensional dissipative cubic nonlinear Schrödinger equation with zero Dirichlet boundary conditions on a bounded domain. The equation is discretized in time by a linear implicit three-level central difference scheme, which has analogous discrete conservation laws of charge and energy. The convergence with two orders and the stability of the scheme are analysed using a priori estimates. Numerical tests show that the three-level scheme is more efficient.

Comment on 'The scale-transformation of electromagnetic theory and its applications', 'Distribution characteristic of scattering field for an ellipsoidal target irradiated by an electromagnetic wave from an arbitrary direction' and 'Electric fields inside and outside an anisotropic dielectric sphere'

Zhao Shi-Hua, Li Ying-Jun
Chin. Phys. B, 2011, 20 (3): 030205 doi: 10.1088/1674-1056/20/3/030205
Full Text: [PDF 160 KB] (Downloads:784)
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It is shown that the 'scale-transformation' method proposed by Li Ying-Le et al. is not applicable to the Maxwell theory.

A meshless method for the nonlinear generalized regularized long wave equation

Wang Ju-Feng, Bai Fu-Nong, Cheng Yu-Min
Chin. Phys. B, 2011, 20 (3): 030206 doi: 10.1088/1674-1056/20/3/030206
Full Text: [PDF 314 KB] (Downloads:982)
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This paper presents a meshless method for the nonlinear generalized regularized long wave (GRLW) equation based on the moving least-squares approximation. The nonlinear discrete scheme of the GRLW equation is obtained and is solved using the iteration method. A theorem on the convergence of the iterative process is presented and proved using theorems of the infinity norm. Compared with numerical methods based on mesh, the meshless method for the GRLW equation only requires the scattered nodes instead of meshing the domain of the problem. Some examples, such as the propagation of single soliton and the interaction of two solitary waves, are given to show the effectiveness of the meshless method.

Influence of selective atomic measurement on the entanglement properties of a two-atom outside cavity

Lu Dao-Ming
Chin. Phys. B, 2011, 20 (3): 030301 doi: 10.1088/1674-1056/20/3/030301
Full Text: [PDF 392 KB] (Downloads:591)
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Considering three two-level atoms initially in the W or Greenberger–Horne–Zeilinger (GHZ) state, one of the three atoms is put into an initially coherent light cavity and made to resonantly interact with the cavity. The two-atom entanglement evolution outside the cavity is investigated. The influences of state-selective measurement of the atom inside the cavity and strength of the light field on the two-atom entanglement evolution outside the cavity are discussed. The results obtained from the numerical method show that the two-atom entanglement outside the cavity is strengthened through state-selective measurement of the atom inside the cavity. In addition, the strength of the light field also influences the two-atom entanglement properties.

Complex frequencies of a massless scalar field in loop quantum black hole spacetime

Chen Ju-Hua, Wang Yong-Jiu
Chin. Phys. B, 2011, 20 (3): 030401 doi: 10.1088/1674-1056/20/3/030401
Full Text: [PDF 314 KB] (Downloads:612)
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Recently, considerable progress has been made in understanding the early universe by loop quantum cosmology. Modesto et al. investigated the loop quantum black hole (LQBH)using improved semiclassical analysis and they found that the LQBH has two horizons, an event horizon and a Cauchy horizon, just like the Reissner--Nordström black hole. This paper focuses on the dynamical evolution of a massless scalar wave in the LQBH background. By investigating the relation between the complex frequencies of the massless scalar field and the LQBH parameters using the numerical method, we find that the polymeric parameter P makes the massless scalar field decay more quickly and makes the ground scalar wave oscillate slowly. However, the polymeric parameter P causes the frequency of the high harmonic massless scalar wave to shift according to its value. We also find that the loop quantum gravity area gap parameter a0 causes the massless scalar field to decay more slowly and makes the period of the massless scalar field wave become longer. In the complex ω plane, the frequency curves move counterclockwise when the polymeric parameter P increases and this spiral effect is more obvious for a higher harmonic scalar wave.

Fermion tunneling from squashed black holes in the Gödel universe and charged Kaluza–Klein space–time Hot!

Li Hui-Ling
Chin. Phys. B, 2011, 20 (3): 030402 doi: 10.1088/1674-1056/20/3/030402
Full Text: [PDF 164 KB] (Downloads:683)
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This paper is devoted to the investigation the fermion tunneling radiation of squashed black holes in the Gödel universe and charged Kaluza–Klein space–time. For black holes with different dimensions, establishing a set of appropriate matrices γμ for the general covariant Dirac equation plays an important role in the semi-classical tunneling method. By constructing two sets of γμ matrices, we have successfully derived the tunneling probability and Hawking temperature of the black holes.

The Stochastic stability of a Logistic model with Poisson white noise

Duan Dong-Hai, Xu Wei, Su Jun, Zhou Bing-Chang
Chin. Phys. B, 2011, 20 (3): 030501 doi: 10.1088/1674-1056/20/3/030501
Full Text: [PDF 360 KB] (Downloads:1142)
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The stochastic stability of a logistic model subjected to the effect of a random natural environment, modeled as Poisson white noise process, is investigated. The properties of the stochastic response are discussed for calculating the Lyapunov exponent, which had proven to be the most useful diagnostic tool for the stability of dynamical systems. The generalised It? differentiation formula is used to analyse the stochastic stability of the response. The results indicate that the stability of the response is related to the intensity and amplitude distribution of the environment noise and the growth rate of the species.

Corrigendum: Stochastic resonance in a parallel array of linear elements

Dong Xiao-Juan
Chin. Phys. B, 2011, 20 (3): 030502 doi: 10.1088/1674-1056/20/3/030502
Full Text: [PDF 147 KB] (Downloads:547)
Show Abstract
In this paper, we point out the errors occurring in the paper (Dong X J 2009 Chin. Phys. B 18 70) and present a correct conclusion.

Effects of an electromagnetic field on intracellular calcium oscillations in a cell with external noise

Duan Wei-Long, Yang Lin-Jing, Mei Dong-Cheng
Chin. Phys. B, 2011, 20 (3): 030503 doi: 10.1088/1674-1056/20/3/030503
Full Text: [PDF 382 KB] (Downloads:713)
Show Abstract
Intracellular calcium ion concentration oscillation in a cell subjected to external noise and irradiated by an electromagnetic field is considered. The effects of the intensity E0, the polar angle θ and the frequency omega of the external electric field on steady-state probability distribution and the mean Ca2+ concentration, respectively, are investigated by a numerical calculation method. The results indicate that (i) variation of ω cannot affect the intracellular calcium oscillation; (ii) the steady-state probability distribution presents a meaningful modification due to the variations of E0 and θ, while variation of θ does not affect the steady-state probability distribution under the condition of a small E0, and E0 cannot affect the steady-state probability distribution either when θ = π/2; (iii) the mean Ca2+ concentration increases as E0 increases when θ < π/2 and, as θ increases, it first increases and then decreases. However, it does not vary with E0 increasing when θ = π/2, but it increases with θ increasing when E0 is small.

Global synchronization of general delayed complex networks with stochastic disturbances

Tu Li-Lan
Chin. Phys. B, 2011, 20 (3): 030504 doi: 10.1088/1674-1056/20/3/030504
Full Text: [PDF 217 KB] (Downloads:864)
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In this paper, global synchronization of general delayed complex networks with stochastic disturbances, which is a zero-mean real scalar Wiener process, is investigated. The networks under consideration are continuous-time networks with time-varying delay. Based on the stochastic Lyapunov stability theory, ItÔ's differential rule and the linear matrix inequality (LMI) optimization technique, several delay-dependent synchronous criteria are established, which guarantee the asymptotical mean-square synchronization of drive networks and response networks with stochastic disturbances. The criteria are expressed in terms of LMI, which can be easily solved using the Matlab LMI Control Toolbox. Finally, two examples show the effectiveness and feasibility of the proposed synchronous conditions.

Synchronizing spiral waves in a coupled Rössler system

Gao Jia-Zhen, Yang Shu-Xin, Xie Ling-Ling, Gao Ji-Hua
Chin. Phys. B, 2011, 20 (3): 030505 doi: 10.1088/1674-1056/20/3/030505
Full Text: [PDF 351 KB] (Downloads:771)
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The synchronisation of spiral patterns in a drive-response Rössler system is studied. The existence of three types of synchronisation is revealed by inspecting the coupling parameter space. Two transient stages of phase synchronisation and partial synchronisation are observed in a comparatively weak feedback coupling parameter regime, whilst complete synchronisation of spirals is found with strong negative couplings. Detailed observations of the synchronous process, such as oscillatory frequencies, parameters mismatches and amplitude variations, etc, are investigated via numerical simulations.

Impulsive synchronisation of a class of fractional-order hyperchaotic systems

Wang Xing-Yuan, Zhang Yong-Lei, Lin Da, Zhang Na
Chin. Phys. B, 2011, 20 (3): 030506 doi: 10.1088/1674-1056/20/3/030506
Full Text: [PDF 330 KB] (Downloads:919)
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In this paper, an impulsive synchronisation scheme for a class of fractional-order hyperchaotic systems is proposed. The sufficient conditions of a class of integral-order hyperchaotic systems' impulsive synchronisation are illustrated. Furthermore, we apply the sufficient conditions to a class of fractional-order hyperchaotic systems and well achieve impulsive synchronisation of these fractional-order hyperchaotic systems, thereby extending the applicable scope of impulsive synchronisation. Numerical simulations further demonstrate the feasibility and effectiveness of the proposed scheme.

Electronic band structure of a type-II 'W' quantum well calculated by an eight-band k·p model

Yu Xiu, Gu Yong-Xian, Wang Qing, Wei Xin, Chen Liang-Hui
Chin. Phys. B, 2011, 20 (3): 030507 doi: 10.1088/1674-1056/20/3/030507
Full Text: [PDF 272 KB] (Downloads:655)
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In this paper, we present an investigation of type-II 'W' quantum wells for the InAs/Ga1-xInxSb/AlSb family, where 'W' denotes the conduction profile of the material. We focus our attention on using the eight-band k·p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period–AlSb/InAs/Ga1-xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1-xInxSb layer and the alloy composition in Ga1-xInxSb separately. In the last part, in order to compare the eight-band k·p model, we recalculate the conduction bands of the 'W' structure using the one-band k·p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained.

Phase transition, structural and thermodynamic properties of Mg2Si polymorphs

Yu Ben-Hai, Chen Dong
Chin. Phys. B, 2011, 20 (3): 030508 doi: 10.1088/1674-1056/20/3/030508
Full Text: [PDF 425 KB] (Downloads:3097)
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The plane-wave pseudo-potential method within the framework of first principles is used to investigate the structural and elastic properties of Mg2Si in its intermediate pressure (Pnma) and high pressure phases (P63/mmc). The lattice constants, the band structures. The bulk moduli of the Mg2Si polymorphs are presented and discussed. The phase transition from anti-cotunnite to Ni2In-type Mg2Si is successfully reproduced using a vibrational Debye-like model. The phase boundary can be described as P=24.02994+3.93×10-3T-4.66816×10-5T2-2.2501×10-9T3+2.33786×1011T4. To complete the fundamental characteristics of these polymorphs we have analysed thermodynamic properties, such as thermal expansion and heat capacity, in a pressure range of 0--40 GPa and a temperature range of 0--1300 K. The obtained results tend to support the available experimental data and other theoretical results. Therefore, the present results indicate that the combination of first principles and a vibrational Debye-like model is an efficient scheme to simulate the high temperature behaviours of Mg2Si.

Performance optimization analysis of a thermoelectric refrigerator with two resonances

Luo Xiao-Guang, He Ji-Zhou
Chin. Phys. B, 2011, 20 (3): 030509 doi: 10.1088/1674-1056/20/3/030509
Full Text: [PDF 288 KB] (Downloads:1021)
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Based on electron transport theory, the performance of kx and kr filtered thermoelectric refrigerators with two resonances are studied in this paper. The performance characteristic curves between the cooling rate and the coefficient of performance are plotted by numerical calculation. It is shown that the maximum cooling rate of the thermoelectric refrigerator with two resonances increases but the maximum coefficient of performance decreases compared with those with one resonance. No matter which resonance mechanism is used (kx or kr filtered), the cooling rate and the performance coefficient of the kr filtered refrigerator are much better than those of the kx filtered one.

Global exponential stability of reaction–diffusion neural networks with discrete and distributed time-varying delays

Zhang Wei-Yuan, Li Jun-Min
Chin. Phys. B, 2011, 20 (3): 030701 doi: 10.1088/1674-1056/20/3/030701
Full Text: [PDF 232 KB] (Downloads:772)
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This paper investigates the global exponential stability of reaction–diffusion neural networks with discrete and distributed time-varying delays. By constructing a more general type of Lyapunov–Krasovskii functional combined with a free-weighting matrix approach and analysis techniques, delay-dependent exponential stability criteria are derived in the form of linear matrix inequalities. The obtained results are dependent on the size of the time-varying delays and the measure of the space, which are usually less conservative than delay-independent and space-independent ones. These results are easy to check, and improve upon the existing stability results. Some remarks are given to show the advantages of the obtained results over the previous results. A numerical example has been presented to show the usefulness of the derived linear matrix inequality (LMI)-based stability conditions.

Simulation study of a magnetocardiogram based on a virtual heart model: effect of a cardiac equivalent source and a volume conductor

Shou Guo-Fa, Xia Ling, Ma Ping, Tang Fa-Kuan, Dai Ling
Chin. Phys. B, 2011, 20 (3): 030702 doi: 10.1088/1674-1056/20/3/030702
Full Text: [PDF 650 KB] (Downloads:782)
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In this paper, we present a magnetocardiogram (MCG) simulation study using the boundary element method (BEM) and based on the virtual heart model and the realistic human volume conductor model. The different contributions of cardiac equivalent source models and volume conductor models to the MCG are deeply and comprehensively investigated. The single dipole source model, the multiple dipoles source model and the equivalent double layer (EDL) source model are analysed and compared with the cardiac equivalent source models. Meanwhile, the effect of the volume conductor model on the MCG combined with these cardiac equivalent sources is investigated. The simulation results demonstrate that the cardiac electrophysiological information will be partly missed when only the single dipole source is taken, while the EDL source is a good option for MCG simulation and the effect of the volume conductor is smallest for the EDL source. Therefore, the EDL source is suitable for the study of MCG forward and inverse problems, and more attention should be paid to it in future MCG studies.

Dispersion characteristics of a slow wave structure with a modified photonic band gap

Gao Xi, Yang Zi-Qiang, Cao Wei-Ping, Jiang Yan-Nan
Chin. Phys. B, 2011, 20 (3): 030703 doi: 10.1088/1674-1056/20/3/030703
Full Text: [PDF 359 KB] (Downloads:1301)
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This paper studies the dispersion characteristics of a modified photonic band-gap slow-wave structure with an open boundary by simulation and experiment. A mode launcher with a wheel radiator and a coupling probe is presented to excite a pure TM01-like mode. The cold test and simulation results show that the TM01-like mode is effectively excited and no parasitic modes appear. The dispersion characteristics obtained from the cold test are in good agreement with the calculated results.
RAPID COMMUNICATION

Simultaneous low extinction and high local field enhancement in Ag nanocubes

Zhou Fei, Liu Ye, Li Zhi-Yuan
Chin. Phys. B, 2011, 20 (3): 037303 doi: 10.1088/1674-1056/20/3/037303
Full Text: [PDF 2101 KB] (Downloads:1141)
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We theoretically investigate surface plasmon resonance properties in Au and Ag cubic nanoparticles and find a novel plasmonic mode that exhibits simultaneous low extinction and high local field enhancement properties. We analyse this mode from different aspects by looking at the distribution patterns of local field intensity, energy flux, absorption and charge density. We find that in the mode the polarized charge is highly densified in a very limited volume around the corner of the nanocube and results in very strong local field enhancement. Perturbations of the incident energy flux and light absorption are also strongly localized in this small volume of the corner region, leading to both low absorption and low scattering cross section. As a result, the extinction is low for the mode. Metal nanoparticles involving such peculiar modes may be useful for constructing nonlinear compound materials with low linear absorption and high nonlinearity.
CLASSICAL AREAS OF PHENOMENOLOGY

A planar left-handed metamaterial based on electric resonators

Chen Chun-Hui, Qu Shao-Bo, Wang Jia-Fu, Ma Hua, Wang Xin-Hua, Xu Zhuo
Chin. Phys. B, 2011, 20 (3): 034101 doi: 10.1088/1674-1056/20/3/034101
Full Text: [PDF 386 KB] (Downloads:949)
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A planar left-handed metamaterial(LHM) composed of electric resonator pairs is presented in this paper. Theoretical analysis, an equivalent circuit model and simulated results of a wedge sample show that this material exhibits a negative refraction pass-band around 9.6GHz under normal-incidence and is insensitive to a change in incidence angle. Furthermore, as the angle between the arm of the electric resonators and the strip connecting the arms increases, the frequency range of the pass-band shifts downwards. Consequently, this LHM guarantees a relatively stable torlerence of errors when it is practically fabricated. Moreover, it is a candidate for designing multi-band LHM through combining the resonator pairs with different angles.

Absorption characteristic of arc plasma in the infrared region

Chen Yun-Yun, Song Yang, Li Zhen-Hua, He An-Zhi
Chin. Phys. B, 2011, 20 (3): 034201 doi: 10.1088/1674-1056/20/3/034201
Full Text: [PDF 347 KB] (Downloads:691)
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In this paper, argon arc plasma is chosen as an example to study the absorption characteristics of arc plasma in the infrared region. Firstly, the phase and the attenuation constants are deduced for the given temperature, pressure and probe wavelength regions. Based on those constants, the dependence of the attenuation constant on the temperature and pressure in the vicinity of a certain probe wavelength is found. Then, theoretical analysis and discussion are conducted. Maximal absorption occurs at the position where the contributions of neutral particles and electrons come to a balance in a physical point of view, which may provide some measures to take for decreasing or controlling the plasma absorption of electromagnetic waves.

Approximate analytical expressions of apertured broadband beams in the far field

Lu Shi-Zhuan, You Kai-Ming, Chen Lie-Zun, Wang You-Wen
Chin. Phys. B, 2011, 20 (3): 034202 doi: 10.1088/1674-1056/20/3/034202
Full Text: [PDF 338 KB] (Downloads:870)
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The approximate analytical expressions of the apertured broadband beams in the far field with Gaussian and Laguerre–Gaussian spatial modes are presented. For the radially polarized Laguerre–Gaussian beam, the result reveals that the electromagnetic field in the far field is transverse magnetic. The influences of bandwidth (Γ) and truncation parameter (C0) on the transverse intensity distribution of the Gaussian beam and on the energy flux distribution of radially polarized Laguerre–Gaussian beam are analysed.

Controllable cross-Kerr interaction between microwave photons in circuit quantum electrodynamics

Wu Qin-Qin, Liao Jie-Qiao, Kuang Le-Man
Chin. Phys. B, 2011, 20 (3): 034203 doi: 10.1088/1674-1056/20/3/034203
Full Text: [PDF 629 KB] (Downloads:933)
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We propose a scheme to enable a controllable cross-Kerr interaction between microwave photons in a circuit quantum electrodynamics (QED) system. In this scheme we use two transmission-line resonators (TLRs) and one superconducting quantum interference device (SQUID) type charge qubit, which acts as an artificial atom. It is shown that in the dispersive regime of the circuit-QED system, a controllable cross-Kerr interaction can be obtained by properly preparing the initial state of the qubit, and a large cross-phase shift between two microwave fields in the two TLRs can then be reached. Based on this cross-Kerr interaction, we show how to create a macroscopic entangled state between the two TLRs.

Modeling the pulse shape of Q-switched lasers to account for terminal-level relaxation

Zeng Qin-Yong, Wan Yong, Xiong Ji-Chuan, Zhu Da-Yong
Chin. Phys. B, 2011, 20 (3): 034204 doi: 10.1088/1674-1056/20/3/034204
Full Text: [PDF 253 KB] (Downloads:2161)
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To account for the effect of lower-level relaxation, we have derived a characteristic equation for describing the laser pulse from the modified rate equations for Q-switched lasers. The pulse temporal profile is related to the ratio of the lower-level lifetime to the cavity lifetime and the number of times the population inversion density is above the threshold. By solving the coupled rate equations numerically, the effect of terminal-level lifetime on pulse temporal behaviour is analysed. The mode is applied to the case of a diode-pumped Nd:YAG laser that is passively Q-switched by a Cr4+:YAG absorber. Theoretical results show good agreement with the experiments.

Theoretical study and optimization of a high power mid-infrared erbium-doped ZBLAN fibre laser

Li Jian-Feng, Stuart D. Jackson
Chin. Phys. B, 2011, 20 (3): 034205 doi: 10.1088/1674-1056/20/3/034205
Full Text: [PDF 431 KB] (Downloads:1161)
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Based on the rate equations describing the erbium-doped fluoride glass (ZBLAN) fibre lasers with different pumping configurations being taken into account, this paper presents theoretical calculations related to the dynamic population density and the operation performance of a high power mid-infrared all-fibre erbium-doped ZBLAN fibre laser. It shows that the ground-state absorption, excited-state absorption and energy-transfer-upconversion processes co-exist and produce a population balance, causing the laser to operate stably at a continuous wave state. A good agreement between the theoretical results and recent experimental measurement is obtained. Furthermore, the laser structure parameters including fibre length, reflectance of output fibre Bragg grating and pumping configurations are quantitatively optimised to achieve the best performance. The results show, as expected, that the slope efficiency of the fibre laser can be improved significantly through optimisation, which then provides an important guide for the design of high-performance mid-infrared erbium-doped ZBLAN fibre lasers.

Magnetic field measurement based on a stimulated two-photon Raman transition Hot!

Zhou Zi-Chao, Wei Rong, Shi Chun-Yan, Li Tang, Wang Yu-Zhu
Chin. Phys. B, 2011, 20 (3): 034206 doi: 10.1088/1674-1056/20/3/034206
Full Text: [PDF 387 KB] (Downloads:896)
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The magnetic field in the microwave interaction zone of the fountain atomic clock was measured by stimulated Raman transitions. By measuring the two-photon transition frequency between the Zeeman levels of the two ground states, we achieved a magnetic field measurement accuracy of the order of 0.28 nT. This method is immune to the Doppler shift and the AC Stark shift. The second order Zeeman shift of the fountain clock is 170.7×10-15, with the uncertainty of 7.2×10-16.

Noise-free frequency conversion of quantum states

Bai Yun-Fei, Zhai Shu-Qin, Gao Jiang-Rui, Zhang Jun-Xiang
Chin. Phys. B, 2011, 20 (3): 034207 doi: 10.1088/1674-1056/20/3/034207
Full Text: [PDF 218 KB] (Downloads:674)
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In this paper, the frequency conversion of quantum states based on the intracavity nonlinear interaction is proposed. The fidelity of an input state after frequency conversion is calculated, and it is shown the noise-free frequency conversion of a quantum state can be achieved by injecting a strong signal field. The dependences of conversion efficiency on the pump parameter, extra losses and input state amplitude are also analysed.

Spatial solitons in photonic lattices with large-scale defects

Yang Xiao-Yu, Zheng Jiang-Bo, Dong Liang-Wei
Chin. Phys. B, 2011, 20 (3): 034208 doi: 10.1088/1674-1056/20/3/034208
Full Text: [PDF 370 KB] (Downloads:704)
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We address the existence, stability and propagation dynamics of solitons supported by large-scale defects surrounded by the harmonic photonic lattices imprinted in the defocusing saturable nonlinear medium. Several families of soliton solutions, including flat-topped, dipole-like, and multipole-like solitons, can be supported by the defected lattices with different heights of defects. The width of existence domain of solitons is determined solely by the saturable parameter. The existence domains of various types of solitons can be shifted by the variations of defect size, lattice depth and soliton order. Solitons in the model are stable in a wide parameter window, provided that the propagation constant exceeds a critical value, which is in sharp contrast to the case where the soliton trains is supported by periodic lattices imprinted in defocusing saturable nonlinear medium. We also find stable solitons in the semi-infinite gap which rarely occur in the defocusing media.

Investigation of the influence of extra noises in seed beams on continuous-variable entanglement generation

Shang Ya-Na, Yan Zhi-Hui, Jia Xiao-Jun, Su Xiao-Long, Xie Chang-De
Chin. Phys. B, 2011, 20 (3): 034209 doi: 10.1088/1674-1056/20/3/034209
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The influence of the extra classical noises in seed beams on the entanglement between the signal and the idler modes of the output fields generated by a non-degenerate optical parametric amplifier operating at deamplification is investigated theoretically and experimentally. With the increase of the extra classical noises in the seed beams, the correlation degree of the output entangled optical fields, which is scaled by the quantum noise limit, decreases rapidly. The experimental results are in good agreement with the theoretical calculations.

Numerical investigation of slow solitons in Bragg gratings with a hyperbolic tangent apodization

Wang Kui-Ru, Cheng Jie-Lin, Sang Xin-Zhu, Chen Gong
Chin. Phys. B, 2011, 20 (3): 034210 doi: 10.1088/1674-1056/20/3/034210
Full Text: [PDF 371 KB] (Downloads:900)
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This paper numerically and analytically investigates the formation and propagation motion of optical soliton in the Bragg grating. We choose the fibre Bragg grating with hyperbolic tangent apodization in the middle section in order to obtain slower solitons. Optical fibre soliton but not Bragg grating soliton is used as input pulse in the discussion, which is much more approximate to the light source for the practical purpose. We discuss in detail the effects of the soliton's velocity with some parameters in the process of transmission. The results show that by choosing special parameters, one can make the soliton slow-down with a little distortion and energy decay and obtain tunable time-delay on a small scale.

Application of the Tikhonov regularization method to wind retrieval from scatterometer data I. Sensitivity analysis and simulation experiments

Zhong Jian, Huang Si-Xun, Du Hua-Dong, Zhang Liang
Chin. Phys. B, 2011, 20 (3): 034301 doi: 10.1088/1674-1056/20/3/034301
Full Text: [PDF 304 KB] (Downloads:761)
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Scatterometer is an instrument which provides all-day and large-scale wind field information, and its application especially to wind retrieval always attracts meteorologists. Certain reasons cause large direction error, so it is important to find where the error mainly comes. Does it mainly result from the background field, the normalized radar cross-section (NRCS) or the method of wind retrieval? It is valuable to research. First, depending on SDP2.0, the simulated 'true' NRCS is calculated from the simulated 'true' wind through the geophysical model function NSCAT2. The simulated background field is configured by adding a noise to the simulated 'true' wind with the non-divergence constraint. Also, the simulated 'measured' NRCS is formed by adding a noise to the simulated 'true' NRCS. Then, the sensitivity experiments are taken, and the new method of regularization is used to improve the ambiguity removal with simulation experiments. The results show that the accuracy of wind retrieval is more sensitive to the noise in the background than in the measured NRCS; compared with the two-dimensional variational (2DVAR) ambiguity removal method, the accuracy of wind retrieval can be improved with the new method of Tikhonov regularization through choosing an appropriate regularization parameter, especially for the case of large error in the background. The work will provide important information and a new method for the wind retrieval with real data.

Geometric formulations and variational integrators of discrete autonomous Birkhoff systems

Liu Shi-Xing, Liu Chang, Guo Yong-Xin
Chin. Phys. B, 2011, 20 (3): 034501 doi: 10.1088/1674-1056/20/3/034501
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The variational integrators of autonomous Birkhoff systems are obtained by the discrete variational principle. The geometric structure of the discrete autonomous Birkhoff system is formulated. The discretization of mathematical pendulum shows that the discrete variational method is as effective as symplectic scheme for the autonomous Birkhoff systems.

Symmetry of Hamiltonian and conserved quantity for a system of generalized classical mechanics

Zhang Yi
Chin. Phys. B, 2011, 20 (3): 034502 doi: 10.1088/1674-1056/20/3/034502
Full Text: [PDF 151 KB] (Downloads:875)
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This paper focuses on a new symmetry of Hamiltonian and its conserved quantity for a system of generalized classical mechanics. The differential equations of motion of the system are established. The definition and the criterion of the symmetry of Hamiltonian of the system are given. A conserved quantity directly derived from the symmetry of Hamiltonian of the generalized classical mechanical system is given. Since a Hamilton system is a special case of the generalized classical mechanics, the results above are equally applicable to the Hamilton system. The results of the paper are the generalization of a theorem known for the existing nonsingular equivalent Lagrangian. Finally, two examples are given to illustrate the application of the results.

A fast computing method to distinguish the hyperbolic trajectory of an non-autonomous system

Jia Meng, Fan Yang-Yu, Tian Wei-Jian
Chin. Phys. B, 2011, 20 (3): 034701 doi: 10.1088/1674-1056/20/3/034701
Full Text: [PDF 314 KB] (Downloads:587)
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Attempting to find a fast computing method to DHT (distinguished hyperbolic trajectory), this study first proves that the errors of the stable DHT can be ignored in normal direction when they are computed as the trajectories extend. This conclusion means that the stable flow with perturbation will approach to the real trajectory as it extends over time. Based on this theory and combined with the improved DHT computing method, this paper reports a new fast computing method to DHT, which magnifies the DHT computing speed without decreasing its accuracy.

Pattern selection in a predation model with self and cross diffusion

Wang Wei-Ming, Wang Wen-Juan, Lin Ye-Zhi, Tan Yong-Ji
Chin. Phys. B, 2011, 20 (3): 034702 doi: 10.1088/1674-1056/20/3/034702
Full Text: [PDF 302 KB] (Downloads:901)
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In this paper, we present the amplitude equations for the excited modes in a cross-diffusive predator--prey model with zero-flux boundary conditions. From these equations, the stability of patterns towards uniform and inhomogenous perturbations is determined. Furthermore, we present novel numerical evidence of six typical turing patterns, and find that the model dynamics exhibits complex pattern replications: for μ1<μμ2, the steady state is the only stable solution of the model; for μ2<μμ4, by increasing the control parameter μ, the sequence Hπ-hexagons → H0-hexagon-stripe mixtures rightarrow stripes → Hπ-hexagon-stripe mixtures → H0-hexagons is observed; for μ>μ4, the stripe pattern emerges. This may enrich the pattern formation in the cross-diffusive predator–prey model.
ATOMIC AND MOLECULAR PHYSICS

Density functional theory study of neutral AlSn(n=,2–9) clusters

Li Ting-Xin, Wang Lin, Wang Fei, Chen Jun, Jiang Zhen-Yi, Li Li-Sha
Chin. Phys. B, 2011, 20 (3): 033101 doi: 10.1088/1674-1056/20/3/033101
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This paper investigates the geometrical structures and relative stabilities of neutral AlSn(n=,2–9) using the density functional theory. Structural optimisation and frequency analysis are performed at the B3LYP/6-311G(d) level. The ground state structures of the AlSn show that the sulfur atoms prefer not only to evenly distribute on both sides of the aluminum atom but also to form stable structures in AlSn clusters. The structures of pure Sn are fundamentally changed due to the doping of the Al atom. The fragmentation energies and the second-order energy differences are calculated and discussed. Among neutral AlSn(n=,2–9) clusters, AlS4 and AlS6 are the most stable.

Conformation effects on the molecular orbitals of serine

Wang Ke-Dong, Ma Peng-Fei, Shan Xu
Chin. Phys. B, 2011, 20 (3): 033102 doi: 10.1088/1674-1056/20/3/033102
Full Text: [PDF 292 KB] (Downloads:718)
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This paper calculates the five most stable conformers of serine with Hartree–Fock theory, density functional theory (B3LYP), Møller–Plesset perturbation theory (MP4(SDQ)) and electron propagation theory with the 6-311++G(2d,2p) basis set. The calculated vertical ionization energies for the valence molecular orbitals of each conformer are in agreement with the experimental data, indicating that a range of molecular conformations would coexist in an equilibrium sample. Information of the five outer valence molecular orbitals for each conformer is explored in coordinate and momentum spaces using dual space analysis to investigate the conformational processes, which are generated from the global minimum conformer Ser1 by rotation of C2–C3 (Ser4), C1–C2 (Ser5) and C1–O2 (Ser2 and Ser3). Orbitals 28a, 27a and 26a are identified as the fingerprint orbitals for all the conformational processes.

Relativistic calculations of 3s2 1S0–3s3p 1P1 and 3s2 1S0–3s3p 3P1,2 transition probabilities in the Mg isoelectronic sequence

Cheng Cheng, Gao Xiang, Qing Bo, Zhang Xiao-Le, Li Jia-Ming
Chin. Phys. B, 2011, 20 (3): 033103 doi: 10.1088/1674-1056/20/3/033103
Full Text: [PDF 224 KB] (Downloads:733)
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Using the multi-configuration Dirac–Fock self-consistent field method and the relativistic configuration-interaction method, calculations of transition energies, oscillator strengths and rates are performed for the 3s2 1S0–3s3p 1P1 spin-allowed transition, 3s2 1S0–3s3p 3P1,2 intercombination and magnetic quadrupole transition in the Mg isoelectronic sequence (Mg I, Al II, Si III, P IV and S V). Electron correlations are treated adequately, including intravalence electron correlations. The influence of the Breit interaction on oscillator strengths and transition energies are investigated. Quantum electrodynamics corrections are added as corrections. The calculation results are found to be in good agreement with the experimental data and other theoretical calculations.

Photodetachment of H- near an elastic surface in a magnetic field

Wang Lei, Yang Hai-Feng, Liu Xiao-Jun, Liu Hong-Ping
Chin. Phys. B, 2011, 20 (3): 033104 doi: 10.1088/1674-1056/20/3/033104
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This paper investigates the photodetachment of the negative hydrogen ion H- near an elastic wall in a magnetic field. The magnetic field confines the perpendicular motion of the electron, which results in a real three-dimensional well for the detached electron. The analytical formulas for the cross section of the photodetachment in the three-dimensional quantum well are derived based on both the quantum approach and closed-orbit theory. The magnetic field and the elastic surface lead to two completely different modulations to the cross section of the photodetachment. The oscillation amplitude depends on the strength of the magnetic field, the ion-wall distance and the photon polarization as well. Specially, for the circularly polarized photon-induced photodetachment, the cross sections display a suppressed (EEth)-1/2 threshold law with energy E in the vicinity above Landau energy Eth, contrasting with the (EEth)-1/2 threshold law in the presence of only the magnetic field. The semiclassical calculation fits the quantum result quite well, although there are still small deviations. The difference is attributed to the failure of semiclassical mechanics.

Isomers of the Cu5 cluster: a density function theory study

Gong Heng-Feng, Li Gong-Ping, Jia Yan-Hui
Chin. Phys. B, 2011, 20 (3): 033105 doi: 10.1088/1674-1056/20/3/033105
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In this work, a systematic study of some possible isomer structures of the Cu5 cluster obtained from density functional theory methods is presented. The polarisation and pseudopotential basis sets are employed in the calculations. The results show that the binding energies, frequencies, coordination numbers and average bond lengths are in reasonable agreement with reported experimental data. Moreover, four isomers of the Cu5 cluster are obtained according to calculations, in which the most stable configuration is the planar structure. Meanwhile, two three-dimensional structures of the Cu5 cluster are obtained in this work, which might be valuable for further theoretical and experimental studies. In addition, our study proves the possibility of the isomer structures of the Cu5 cluster.

Accurate potential energy function and spectroscopic study of the X2Σ+, A2П and B2Σ+ states of the CP radical

Liu Yu-Fang, Jia Yi
Chin. Phys. B, 2011, 20 (3): 033106 doi: 10.1088/1674-1056/20/3/033106
Full Text: [PDF 188 KB] (Downloads:671)
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This paper calculates the equilibrium internuclear separations, the harmonic frequencies and the potential energy curves of the X2Σ+, A2П and B2Σ+ states of the CP radical by the highly accurate valence internally contracted multireference configuration interaction method with correlation-consistent basis sets (aug-cc-pV6Z for C atom and aug-cc-pVQZ for P atom). The potential energy curves are all fitted with the analytic potential energy function by the least-square fitting. Employing the analytic potential energy function, we determine the spectroscopic constants (Be, αe and ωeχe) of these states. For the X2Σ+ state, the obtained values of De, Be, αe, ωeχe, Re and ωe are 5.4831 eV, 0.792119 cm-1, 0.005521 cm-1, 6.89653 cm-1, 0.15683 nm, 12535.11 cm-1, respectively. For the A2П state, the present values of De, Be, αe, ωeχe, Re and ωe are 4.586 eV, 0.703333 cm-1, 0.005458 cm-1, 6.03398 cm-1, 0.16613 nm, 1057.89 cm-1, respectively. For the B2Σ+ state, the present values of De, Be, αe, ωeχe, Re and ωe are 3.506 eV, 0.677561 cm-1, 0.00603298 cm-1, 5.68809 cm-1, 0.1696 nm, 822.554 cm-1, respectively. For these states, the vibrational states with the rotational quantum number J equals zero (J = 0) are studied by solving the radial nuclear Schr"odinger equation using the Numerov method. For each vibrational state, the vibrational level, the classical turning points, the rotational inertial and the centrifugal distortion constants are calculated. Comparison is made with recent theoretical and experimental results.

An ab initio study of the Ne–CO complex

Wang Zhong-Quan, Zhang Chun-Zao, Yu Hai-Jun, Du Jian-Ming, Ma Jian-Guo
Chin. Phys. B, 2011, 20 (3): 033107 doi: 10.1088/1674-1056/20/3/033107
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A new ab initio potential energy surface of the Ne–CO complex is developed using single and double excitation coupled-cluster theory with noniterative treatment of triple excitations [CCSD(T)]. The potential has a minimum value of -49.396 cm-1 at Re=6.40a0 with approximately T-shaped geometry (θe =82.5o ). Bound state energies are calculated up to J=12. The theoretically predicted transition frequencies and spectroscopic constants are in good agreement with the available experimental results.

Determination of the transport properties in 4H-SiC wafers by Raman scattering measurement Hot!

Sun Guo-Sheng, Liu Xing-Fang, Wu Hai-Lei, Yan Guo-Guo, Dong Lin, Zheng Liu, Zhao Wan-Shun, Wang Lei, Zeng Yi-Ping, Li Xi-Guang, Wang Zhan-Guo
Chin. Phys. B, 2011, 20 (3): 033301 doi: 10.1088/1674-1056/20/3/033301
Full Text: [PDF 252 KB] (Downloads:1159)
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The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phonon–plasmon coupled (LOPC) modes, and compared with those determined by Hall-effect measurement and that provided by the vendors. The transport properties of thick and thin 4H-SiC epilayers grown in both vertical and horizontal reactors were also studied. The free carrier density ranges between 2×1018 cm-3 and 8×1018 cm-3 with a carrier mobility of 30–55 cm2/(V·s) for n-type 4H-SiC substrates and 1×1016–3×1016 cm-3 with mobility of 290–490 cm2/(V·s) for both thick and thin 4H-SiC epilayers grown in a horizontal reactor, while thick 4H-SiC epilayers grown in vertical reactor have a slightly higher carrier concentration of around 8.1×1016 cm-3 with mobility of 380 cm2/(V·s). It was shown that Raman spectroscopy is a potential technique for determining the transport properties of 4H-SiC wafers with the advantage of being able to probe very small volumes and also being non-destructive. This is especially useful for future mass production of 4H-SiC epi-wafers.

The dynamical properties of a Rydberg hydrogen atom between two parallel metal surfaces

Liu Wei, Li Hong-Yun, Yang Shan-Ying, Lin Sheng-Lu
Chin. Phys. B, 2011, 20 (3): 033401 doi: 10.1088/1674-1056/20/3/033401
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This paper presents the dynamical properties of a Rydberg hydrogen atom between two metal surfaces using phase space analysis methods. The dynamical behaviour of the excited hydrogen atom depends sensitively on the atom–surface distance d. There exists a critical atom–surface distance dc = 1586 a.u. When the atom–surface distance d is larger than the critical distance dc, the image charge potential is less important than the Coulomb potential, the system is near-integrable and the electron motion is regular. As the distance d decreases, the system will tend to be non-integrable and unstable, and the electron might be captured by the metal surfaces.

Cross sections of Oq+(q=1 - 4) electron loss in collisions with He, Ne and Ar

Lu Yan-Xia, Lu Xing-Qiang, Song Xiang, Zhang Bo-Li
Chin. Phys. B, 2011, 20 (3): 033402 doi: 10.1088/1674-1056/20/3/033402
Full Text: [PDF 218 KB] (Downloads:700)
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Electron-loss cross sections of Oq+ (q=1-4) colliding with He, Ne and Ar atoms are measured in the intermediate velocity regime. The ratios of the cross sections of two-electron loss to that of one-electron loss R21 are presented. It is shown that single-channel analysis is not sufficient to explain the results, but that projectile electron loss, electron capture by the projectile and target ionization must be considered together to interpret the experimental data. The screening and antiscreening effects can account for the threshold velocity results, but cannot explain the dependence of the ratio R21 on velocity quantitatively. In general, the effective charge of the target atom increases with velocity increasing because the high-speed projectile ion can penetrate into the inner electronic shell of target atom. Ne and Ar atoms have similar effective charges in this velocity regime, but He atoms have smaller ones at the same velocities due to its smaller nuclear charge.

Dynamical effects of the four-wave mixing enhancement induced by constructive quantum interference

Xue Yan, Wang Gang, Wu Jin-Hui, Zhang Bing, Gao Jin-Yue
Chin. Phys. B, 2011, 20 (3): 033403 doi: 10.1088/1674-1056/20/3/033403
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In a four-level system of ultracold 87Rb atoms, through analytical and numerical calculations we propose an efficient scheme to achieve the enhanced four-wave mixing process and demonstrate its dynamical control by various parameters such as the travel distance z, probe detuning δ and the probe pulse width τ. In particular, we find that the maximal intensity of the nonlinearly generated signal pulse can be about 80% of the initial input probe under the optimal condition. This greatly enhanced conversion efficiency occurs due to the constructive quantum interference between two different components of the generated signal pulse.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Plastic analysis of the crack problem in two-dimensional decagonal Al-Ni-Co quasicrystalline materials of point group 10,10

Li Wu, Fan Tian-You
Chin. Phys. B, 2011, 20 (3): 036101 doi: 10.1088/1674-1056/20/3/036101
Full Text: [PDF 220 KB] (Downloads:597)
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The fundamental plastic nature of the quasicrystalline materials remains an open problem due to its essential complicacy. By developing the proposed generalized cohesive force model, the plastic deformation of crack in point group 10,10 decagonal quasicrystals is analysed strictly and systematically. The crack tip opening displacement (CTOD) and the size of the plastic zone around the crack tip are determined exactly. The quantity of the crack tip opening displacement can be used as a parameter of nonlinear fracture mechanics of quasicrystalline material. In addition, the present work may provide a way for the plastic analysis of quasicrystals.

The relation between the generalised Eshelby integral and the generalised BCS and DB modelsvspace1mm

Fan Tian-You, Fan Lei
Chin. Phys. B, 2011, 20 (3): 036102 doi: 10.1088/1674-1056/20/3/036102
Full Text: [PDF 224 KB] (Downloads:800)
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The generalised BCS dislocation group model and the generalised DB atomic cohesive force zone model have obtained the same results on nonlinear fracture study of some one-, two- and three-dimensional quasicrystals. This work reveals some inherent connection between the two models, and finds that their common basis is the generalised Eshelby integral based on the generalised Eshelby energy--momentum tensor for quasicrystals. Further applications of the theory in solving nonlinear fracture problems of the materials are also discussed.

Hydrothermal synthesis and chromic properties of hexagonal WO3 nanowires

Yuan Hua-Jun, Chen Ya-Qi, Yu Fang, Peng Yue-Hua, He Xiong-Wu, Zhao Ding, Tang Dong-Sheng
Chin. Phys. B, 2011, 20 (3): 036103 doi: 10.1088/1674-1056/20/3/036103
Full Text: [PDF 333 KB] (Downloads:3196)
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This paper reports that highly purified hexagonal WO3 nanowires are synthesized by a simple hydrothermal method. The as-synthesized WO3 nanowires are investigated in detail by ultraviolet–visible–near infrared spectroscopy and electrical transport measurements under different conditions. It finds that the optical band gap and the diffuse reflection coefficient in the wavelength region above 450 nm of WO3 nanowires decrease observably upon exposure to ultraviolet light or NH3 gas. It is also found that there are electrons being trapped or released in individual WO3 nanowires when scanning bias voltage in different directions upon exposure to ultraviolet and NH3 gas. The experimental results suggest that the chromic properties might be attributed to the injection/extraction of hydrogen ions induced by ultraviolet light irradiation in air or creation/annihilation of oxygen vacancies induced by NH3 gas exposure, which serve as colour centres and trap electrons as polarons. The experimental results also suggest that the hexagonal WO3 nanowires will be a good candidate for sensing reduced gas such as NH3.

Be-composition effect on structure, electronic and optical properties of BexZn1-xO alloys

Lü Bing, Zhou Xun, Linghu Rong-Feng, Wang Xiao-Lu, Yang Xiang-Dong
Chin. Phys. B, 2011, 20 (3): 036104 doi: 10.1088/1674-1056/20/3/036104
Full Text: [PDF 470 KB] (Downloads:914)
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This paper carries out first principles calculation of the structure, electronic and optical properties of BexZn1-xO alloys based on the density-functional theory for the compositions x=0.0, 0.25, 0.5, 0.75, 1.0. The lattice constants deviations of alloys obey Vegard's law well. The BexZn1-xO alloys have the direct band gap (ΓΓ) character, and the bowing coefficients are less than the available theoretical values. Moreover, it investigates in detail the optical properties (dielectric functions, absorption spectrum and refractive index) of these ternary mixed crystals. The obtained results agree well with the available theoretical and experimental values.

Molecular dynamics study of helium bubble pressure in titanium

Zhang Bao-Ling, Wang Jun, Hou Qing
Chin. Phys. B, 2011, 20 (3): 036105 doi: 10.1088/1674-1056/20/3/036105
Full Text: [PDF 371 KB] (Downloads:1391)
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In this paper, the pressure state of the helium bubble in titanium is simulated by a molecular dynamics (MD) method. First, the possible helium/vacancy ratio is determined according to therelation between the bubble pressure and helium/vacancy ratio; then the dependences of the helium bubble pressure on the bubble radius at different temperatures are studied. It is shown that the product of the bubble pressure and the radius is approximately a constant, a result justifying the pressure-radius relation predicted by thermodynamics-based theory for gas bubble. Furthermore, a state equation of the helium bubble is established based on the MD calculations. Comparison between the results obtained by the state equation and corresponding experimental data shows that the state equation can describe reasonably the state of helium bubble and thus could be used for Monte Carlo simulations of the evolution of helium bubble in metals.

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

Cheng Zhi-Qun, Hu Sha, Liu Jun
Chin. Phys. B, 2011, 20 (3): 036106 doi: 10.1088/1674-1056/20/3/036106
Full Text: [PDF 316 KB] (Downloads:1276)
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In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor (HEMT) with an artificial neural network (ANN). The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping (neuro-SM) technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model.

Control of random Boolean networks via average sensitivity of Boolean functions

Chen Shi-Jian, Hong Yi-Guang
Chin. Phys. B, 2011, 20 (3): 036401 doi: 10.1088/1674-1056/20/3/036401
Full Text: [PDF 418 KB] (Downloads:576)
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In this paper, we discuss how to transform the disordered phase into an ordered phase in random Boolean networks. To increase the effectiveness, a control scheme is proposed, which periodically freezes a fraction of the network based on the average sensitivity of Boolean functions of the nodes. Theoretical analysis is carried out to estimate the expected critical value of the fraction, and shows that the critical value is reduced using this scheme compared to that of randomly freezing a fraction of the nodes. Finally, the simulation is given for illustrating the effectiveness of the proposed method.

Evidence for the anomalous scaling behaviour of the molecular-beam epitaxy growth equation

Tang Gang, Xia Hui, Hao Da-Peng, Xun Zhi-Peng, Wen Rong-Ji, Chen Yu-Ling
Chin. Phys. B, 2011, 20 (3): 036402 doi: 10.1088/1674-1056/20/3/036402
Full Text: [PDF 256 KB] (Downloads:546)
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According to the scaling idea of local slope, we investigate numerically and analytically anomalous dynamic scaling behaviour of (1+1)-dimensional growth equation for molecular-beam epitaxy. The growth model includes the linear molecular-beam epitaxy (LMBE) and the nonlinear Lai–Das Sarma–Villain (LDV) equations. The anomalous scaling exponents in both the LMBE and the LDV equations are obtained, respectively. Numerical results are consistent with the corresponding analytical predictions.

CO adsorption on small Aun(n=1–7) clusters supported on a reduced rutile TiO2(110) surface: a first-principles study

Wang Yun-Jiang, Wang Chong-Yu, Wang Shan-Ying
Chin. Phys. B, 2011, 20 (3): 036801 doi: 10.1088/1674-1056/20/3/036801
Full Text: [PDF 374 KB] (Downloads:800)
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CO adsorption on small Aun(n=1–7) clusters which are supported by a partially reduced rutile TiO2(110) surface has been investigated by the first-principles method. The low coordinated sites of Au clusters are favorable for CO adsorption. CO–Aun–TiO2 system displays surface magnetism. There is a strong interaction between the adsorbed CO molecule and the supported Au clusters.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

First-principles study of electronic properties and stability of Nb5SiB2 (001) surface

Xu Yu-Jiang-Zi, Shang Jia-Xiang, Wang Fu-He
Chin. Phys. B, 2011, 20 (3): 037101 doi: 10.1088/1674-1056/20/3/037101
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The density functional calculations are performed to study the electronic structure and stability of Nb5SiB2 (001) surface with different terminations. The calculated cleavage energies along the (001) planes in Nb5SiB2 are 5.015 ·m-2 and 6.593 J·m-2 with the break of Nb–Si and Nb–NbB bonds, respectively. There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy: the larger the cleavage energy, the larger the surface relaxation. Moreover, the surface stability of the Nb5SiB2 (001) with different terminations has been investigated by the chemical potential phase diagram. From a thermodynamics point of view, the four terminations can be stabilized under different conditions. In chemical potential space, NbB (Nb) and Nb (Si) terminations are just stable in a small area, whereas Si (Nb) and Nb (NbB) terminations are stable in a large area (the letters in brackets represent the subsurface atoms).

A new perspective on optoelectric conversion in conjugated polymers

Liu Wen, Zhang Ming-Hua, Li Hai-Hong, Wang Yong-Juan, Liu De-Sheng
Chin. Phys. B, 2011, 20 (3): 037102 doi: 10.1088/1674-1056/20/3/037102
Full Text: [PDF 281 KB] (Downloads:676)
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Photoexcitation of a neutral soliton will create a polaron and a charged soliton. According to a tight-binding model and a nonadiabatic method, we investigate the dynamical process of these two photogenerated charge carriers in an external electric field. It is found that the polaron and the soliton can pass through each other, which excludes the possibility of carrier recombination that usually occurs in existing organic solar cells. The results indicate a more efficient way to realize the optoelectric conversion by photoexciting polymer materials with soliton defects. On the other hand, it is found that solitons take on greater stability than polarons during collision.

Electronic properties and deep level transient spectroscopy of CdS/CdTe thin film solar cells

Li Bing, Feng Liang-Huan, Wang Zhao, Zheng Xu, Zheng Jia-Gui, Cai Ya-Ping, Zhang Jing-Quan, Li Wei, Wu Li-Li, Lei Zhi, Zeng Guang-Gen
Chin. Phys. B, 2011, 20 (3): 037103 doi: 10.1088/1674-1056/20/3/037103
Full Text: [PDF 197 KB] (Downloads:1379)
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It is well known that preparing temperatures and defects are highly related to deep-level impurities. In our studies, the CdTe polycrystalline films have been prepared at various temperatures by close spaced sublimation (CSS). The different preparing temperature effects on CdS/CdTe solar cells and deep-level impurities have been investigated by IV and CV measurements and deep level transient spectroscopy (DLTS). By comparison, less dark saturated current density, higher carrier concentration, and better photovoltaic performance are demonstrated in a 580oC sample. Also there is less deep-level impurity recombination, because the lower hole trap concentration is present in this sample. In addition, three deep levels, Ev+0.341 eV(H4), Ev+0.226 eV(H5) and EC–0.147 eV(E3), are found in the 580oC sample, and the possible source of deep levels is analysed and discussed.

Renormalization of spin polarised itinerant electron bands in the normal state of a model ferromagnetic superconductor

Ma Lei, Huang Ai-Qun, Li Jun
Chin. Phys. B, 2011, 20 (3): 037104 doi: 10.1088/1674-1056/20/3/037104
Full Text: [PDF 246 KB] (Downloads:640)
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This paper studies the normal state properties of itinerant electrons in a toy model, which is constructed according to the model for coexisting ferromagnetism and superconductivity proposed by Suhl [Suhl H 2001 Phys. Rev. Lett. 87 167007]. In this theory with ferromagnetic ordering based on localized spins, the exchange interaction J between conduction electrons and localized spin is taken as the pairing glue for s-wave superconductivity. It shows that this J term will first renormalize the normal state single conduction electron structures substantially. It finds dramatically enhanced or suppressed magnetization of itinerant electrons for positive or negative J. Singlet Cooper pairing can be ruled out due to strong spin polarisation in the J > 0 case while a narrow window for s-wave superconductivity is opened around some ferromagnetic J.

Impurity-related electronic properties in quantum dots under electric and magnetic fields

Zhang Hong, Zhai Li-Xue, Wang Xue, Zhang Chun-Yuan, Liu Jian-Jun
Chin. Phys. B, 2011, 20 (3): 037301 doi: 10.1088/1674-1056/20/3/037301
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This paper presents a systematic study of the ground-state binding energies of a hydrogenic impurity in quantum dots subjected to external electric and magnetic fields. The quantum dot is modeled by superposing a lateral parabolic potential, a Gaussian potential and the energies are calculated via the finite-difference method within the effective-mass approximation. The variation of the binding energy with the lateral confinement, external field, position of the impurity, and quantum-size is studied in detail. All these factors lead to complicated binding energies of the donor, and the following results are found: (1) the binding energies of the donor increase with the increasing magnetic strength and lateral confinement, and reduce with the increasing electric strength and the dot size; (2) there is a maximum value of the binding energies as the impurity placed in different positions along the z direction; (3) the electric field destroys the symmetric behaviour of the donor binding energies as the position of the impurity.

The surface plasmon polariton dispersion relations in a nonlinear-metal-nonlinear dielectric structure of arbitrary nonlinearity

Liu Bing-Can, Yu Li, Lu Zhi-Xin
Chin. Phys. B, 2011, 20 (3): 037302 doi: 10.1088/1674-1056/20/3/037302
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The analytic surface plasmon polaritons (SPPs) dispersion relation is studied in a system consisting of a thin metallic film bounded by two sides media of nonlinear dielectric of arbitrary nonlinearity is studied by applying a generalised first integral approach. We consider both asymmetric and symmetric structures. Especially, in the symmetric system, two possible modes can exist: the odd mode and the even mode. The dispersion relations of the two modes are obtained. Due to the nonlinear dielectric, the magnitude of the electric field at the interface appears and alters the dispersion relations. The changes in SPPs dispersion relations depending on film thicknesses and nonlinearity are studied.

Photoelectric property of LaAlO3-δ/Si heterojunctions with different oxygen contents

Xing Jie, Guo Er-Jia, Wen Juan
Chin. Phys. B, 2011, 20 (3): 037304 doi: 10.1088/1674-1056/20/3/037304
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Three oxide heterojunctions made of LaAlO3-δ/Si are fabricated under various oxygen pressures by laser molecular-beam epitaxy. They all show nonlinear and rectifying current–voltage characteristics, and the distinct difference in rectification behaviour among them. Their photoelectric properties are examined by a visible HeNe laser and an ultraviolet Hg lamp. We find that their photovoltaic responses are closely related to the oxygen contents in the LaAlO3-δ films. The junction fabricated under the lower oxygen pressure has a higher photovoltaic sensitivity. The possible mechanism is suggested based on the band structure of the p–n heterojunction.

Hot carrier injection degradation under dynamic stress

Ma Xiao-Hua, Cao Yan-Rong, Hao Yue, Zhang Yue
Chin. Phys. B, 2011, 20 (3): 037305 doi: 10.1088/1674-1056/20/3/037305
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In this paper, we have studied hot carrier injection (HCI) under alternant stress. Under different stress modes, different degradations are obtained from the experiment results. The different alternate stresses can reduce or enhance the HC effect, which mainly depends on the latter condition of the stress cycle. In the stress mode A (DC stress with electron injection), the degradation keeps increasing. In the stress modes B (DC stress and then stress with the smallest gate injection) and C (DC stress and then stress with hole injection under Vg=0 V and Vg=1.8 V), recovery appears in the second stress period. And in the stress mode D (DC stress and then stress with hole injection under Vg=-1.8 V and Vd=1.8 V), as the traps filled in by holes can be smaller or greater than the generated interface states, the continued degradation or recovery in different stress periods can be obtained.

Double-layer indium doped zinc oxide for silicon thin-film solar cell prepared by ultrasonic spray pyrolysis

Jiao Bao-Chen, Zhang Xiao-Dan, Wei Chang-Chun, Sun Jian, Ni Jian, Zhao Ying
Chin. Phys. B, 2011, 20 (3): 037306 doi: 10.1088/1674-1056/20/3/037306
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Indium doped zinc oxide (ZnO:In) thin films were prepared by ultrasonic spray pyrolysis on corning eagle 2000 glass substrate. 1 and 2 at.% indium doped single-layer ZnO:In thin films with different amounts of acetic acid added in the initial solution were fabricated. The 1 at.% indium doped single-layers have triangle grains. The 2 at.% indium doped single-layer with 0.18 acetic acid adding has the resistivity of 6.82×10-3Ω·cm and particle grains. The double-layers structure is designed to fabricate the ZnO:In thin film with low resistivity (2.58×10-3Ω·cm ) and good surface morphology. It is found that the surface morphology of the double-layer ZnO:In film strongly depends on the substrate-layer, and the second-layer plays a large part in the resistivity of the double-layer ZnO:In thin film. Both total and direct transmittances of the double-layer ZnO:In film are above 80% in the visible light region. Single junction a-Si:H solar cell based on the double-layer ZnO:In as front electrode is also investigated.

Optoelectronic characterisation of an individual ZnO nanowire in contact with a micro-grid template

Jiang Wei, Gao Hong, Xu Ling-Ling, Ma Jia-Ning, Zhang E, Wei Ping, Lin Jia-Qi
Chin. Phys. B, 2011, 20 (3): 037307 doi: 10.1088/1674-1056/20/3/037307
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Optoelectronic characterisation of an individual ZnO nanowire in contact with a micro-grid template has been studied. The low-cost micro-grid template made by photolithography is used to fabricate the ohmic contact metal electrodes. The current increases linearly with the bias, indicating good ohmic contacts between the nanowire and the electrodes. The resistivity of the ZnO nanowire is calculated to be 3.8 Ω·cm. We investigate the photoresponses of an individual ZnO nanowire under different light illumination using light emitting diodes (λ=505 nm, 460 nm, 375 nm) as excitation sources in atmosphere. When individual ZnO nanowire is exposured to different light irradiation, we find that it is extremely sensitive to UV illumination; the conductance is much larger upon UV illumination than that in the dark at room temperature. This phenomenon may be related to the surface oxygen molecule adsorbtion, which indicates their potential application to the optoelectronic switching device.

Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films

Liu Xue-Chao, Chen Zhi-Zhan, Shi Er-Wei, Liao Da-Qian, Zhou Ke-Jin
Chin. Phys. B, 2011, 20 (3): 037501 doi: 10.1088/1674-1056/20/3/037501
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This paper reports that the (Ga, Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition. Room-temperature ferromagnetism is observed for the as-grown thin films. The x-ray absorption fine structure characterization reveals that Co2+ and Ga3+ ions substitute for Zn2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin. The ferromagnetic (Ga, Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature. The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.

A hybrid model for the charging process of the amorphous SiO2 film in radio frequency microelectromechanical system capacitive switches

Wang Li-Feng, Huang Qing-An, Tang Jie-Ying, Liao Xiao-Ping
Chin. Phys. B, 2011, 20 (3): 037701 doi: 10.1088/1674-1056/20/3/037701
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Charging is one of the most important reliability issues in radio frequency microelectro- mechanical systems (RF MEMS) capacitive switches since it makes the actuation voltage unstable. This paper proposes a hybrid model to describe the transient dielectric charging and discharging process in the defect-rich amorphous SiO2 RF MEMS capacitive switches and verifies experimentally. The hybrid model contains two parts according to two different charging mechanisms of the amorphous SiO2, which are the polarisation and charge injection. The models for polarisation and for charge injection are established, respectively. Analysis and experimental results show that polarisation is always effective, while the charge injection has a threshold electric field to the amorphous SiO2 film. Under different control voltage conditions, the hybrid model can accurately describe the experimental data.

A metamaterial absorber with direction-selective and polarisation-insensitive properties

Gu Chao, Qu Shao-Bo, Pei Zhi-Bin, Xu Zhuo
Chin. Phys. B, 2011, 20 (3): 037801 doi: 10.1088/1674-1056/20/3/037801
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This paper reports the design of a metamaterial absorber with direction-selective and polarisation-insensitive property. Both theoretical and simulated results reveal that the absorber has a distinct absorption point with direction selectivity at 7.48 GHz, which is related to the resonance of the metamaterial and is not influenced by the polarisation. The retrieved impedance indicates that the impedance of the absorber can be tuned to approximatively match the impedance of the free space on one side and not to match the impedance of the free space on the other side. This design can result in the minimal reflectance, the minimal transmission and the highest absorbance at the absorption frequency. The distribution of the power loss indicates that the absorber is an excellent electromagnetic wave collector: the wave is first trapped and reinforced in certain specific locations, and then mostly consumed. The distribution of the surface current is consistent with the design, the retrieved impedance and the distribution of the power loss. This absorber may have applications in many scientific and technological areas.

Electric field-induced stress–birefringence in layered composites PbZr1-xTixO3/Polycarbonate

Li Xiang-Yang, Zhang Ning, Luo Xiao-Bin, Wang Wei, Wu Dong, Gao Jian-Sen
Chin. Phys. B, 2011, 20 (3): 037802 doi: 10.1088/1674-1056/20/3/037802
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Electro–optical composites based on the product of electro--strictive and elasto--optical effects are developed. Layered composites of PbZr1-xTixO3 and polycarbonate are synthesised. Their electro–optical properties are studied. The nominal transverse electro–optical coefficient of the composite is observed to be about 3.6 times larger than that of LiNbO3. Experiments and theoretical analyses show that the electro–optical effect of the composite has a strong 'size effect'. With the ratio of thickness/length decreasing or the width of elasto–optical phase increasing, the half-wave electric field intensity increases but the transverse electro–optical coefficient decreases for the layered composite.

Influence of the ordered structure of short-chain polymer molecule all-trans-β-carotene on Raman scattering cross section in liquid

Qu Guan-Nan, OuYang Shun-Li, Wang Wei-Wei, Li Zuo-Wei, Sun Cheng-Lin, Men Zhi-Wei
Chin. Phys. B, 2011, 20 (3): 037803 doi: 10.1088/1674-1056/20/3/037803
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We measured the resonant Raman spectra of all-trans-β-carotene in solvents with different densities and concentrations at different temperatures. The results demonstrated that the Raman scattering cross section (RSCS) of short-chain polymer all-trans-β-carotene is extremely high in liquid. Resonance and strong coherent weakly damped CC bond vibrating properties play important roles under these conditions. Coherent weakly damped CC bond vibration strength is associated with molecular ordered structure. All-trans-β-carotene has highly ordered structure and strong coherent weakly damped CC bond vibrating properties, which lead to large RSCS in the solvent with large density and low concentration at low temperature.

Influence of Si4+ substitution on the temperature-dependent characteristics of Y3Al5O12:Ce

Xu Sheng-Yan, Zhang Xiao-Song, Zhou Yong-Liang, Xi Qun, Li Lan
Chin. Phys. B, 2011, 20 (3): 037804 doi: 10.1088/1674-1056/20/3/037804
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A series of Y3Al5O12:Ce (YAG:Ce) phosphors doped with different Si4+ concentrations is prepared by solid-state reaction. The temperature dependent characteristics of luminescent spectrum and decay time of Ce3+ are investigated. With Si4+ doped, the emission spectrum shows a blue shift due to a decrease of the splitting of 5d levels of Ce3+ ion. The thermal stability is greatly improved by adding Si4+ because the activation energy ΔE increases from 0.1836 eV to 0.2401 eV. The study of the decay times against temperature for various doping concentrations of Si4+ shows that the calculated nonradiative decay rate is affected by Si4+ substitution. The results are explained by the configurational coordinate diagram.

Investigation of yellow luminescence intensity of N-polar unintentionally doped GaN

Du Da-Chao, Zhang Jin-Cheng, Ou Xin-Xiu, Wang Hao, Chen Ke, Xue Jun-Shuai, Xu Sheng-Rui, Hao Yue
Chin. Phys. B, 2011, 20 (3): 037805 doi: 10.1088/1674-1056/20/3/037805
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This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity, and reduces drastically in the N-polar unintentionally-doped GaN after etching in KOH solution. The ratio of yellow luminescence intensity to band-edge emission intensity decreases sharply with the etching time. The full width at half maximum of x-ray diffraction of (10-12) plane falls sharply after etching, and the surface morphology characterized by scanning electron microscope shows a rough surface that changes with the etching time. The mechanism for the generation of the yellow luminescence are explained in details.

Systematic study on visible light collimation by nanostructured slits in the metal surface

Fu Jin-Xin, Hua Yi-Lei, Chen Yu-Hui, Liu Rong-Juan, Li Jia-Fang, Li Zhi-Yuan
Chin. Phys. B, 2011, 20 (3): 037806 doi: 10.1088/1674-1056/20/3/037806
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We present a systematic experimental investigation on visible light collimation by a nanostructured slit flanked with a pair of periodic array of grooves in gold thin film. A wide variety of aspects are considered, such as the polarization state, the transport path of incident light, the groove–groove spacing, the groove width and depth. Our results clearly show that the relationship between the collimation wavelength and the periodicity of the slit-groove structure accords well with the surface plasmon dispersion model proposed by previous researchers. Furthermore, the surface plasmon wave phase retardation effect induced by the surface structure is also verified via the measurement for samples with different groove widths and depths. These results indicate that the detailed geometry of the groove structure has obvious impacts on the collimation effect and the angular distribution of the diffraction light in the subwavelength plasmonic system.

Optimization of a GaN-based irregular multiple quantum well structure for a dichromatic white LED

Lu Hui-Min, Chen Gen-Xiang
Chin. Phys. B, 2011, 20 (3): 037807 doi: 10.1088/1674-1056/20/3/037807
Full Text: [PDF 377 KB] (Downloads:679)
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GaN-based irregular multiple quantum well (IMQW) structures assembled two different types of QWs emitting complementary wavelengths for dichromatic white light-emitting diodes (LEDs) are optimized in order to obtain near white light emissions. The hole distributions and spontaneous emission spectra of the IMQW structures are analysed in detail by fully considering the effects of strain, well-coupling, valence band-mixing and polarization effect through employing a newly developed theoretical model from the k·p theory. Several structure parameters such as well material component, well width, layout of the wells and the thickness of barrier between different types of QWs are employed to analyse how these parameters together with the polarization effect influence the electronic and the optical properties of IMQW structure. Numerical results show that uniform hole distributions in different types of QWs are obtained when the number of the QWs emitting blue light is two, the number of the QWs emitting yellow light is one and the barrier between different types of QWs is 8nm in thickness. The near white light emission is realized using GaN-based IMQW structure with appropriate design parameters and injection level.

The charging stability of different silica glasses studied by measuring the secondary electron emission yield

Zhao Su-Ling, Bertrand Poumellec
Chin. Phys. B, 2011, 20 (3): 037901 doi: 10.1088/1674-1056/20/3/037901
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This paper reports that the charging properties of lead silica, Suprasil silica and Infrasil silica are investigated by measuring the secondary electron emission (SEE) yield. At a primary electron beam energy of 25 keV, the intrinsic SEE yields measured at very low injection dose are 0.54, 0.29 and 0.35, respectively for lead silica, Suprasil and Infrasil silica glass. During the first e-beam irradiation at a high injection current density, the SEE yields of lead silica and Suprasil increase continuously and slowly from their initial values to a steady state. At the steady state, the SEE yields of lead silica and Suprasil are 0.94 and 0.93, respectively. In Infrasil, several charging and discharging processes are observed during the experiment. This shows that Infrasil does not reach its steady state. Two hours later, all samples are irradiated again in the same place as the first irradiation at a low current density and low dose. The SEE yields of lead silica, Suprasil and Infrasil are 0.69, 0.76 and 0.55, respectively. Twenty hours later, the values are 0.62, 0.64 and 0.33, respectively, for lead silica, Suprasil and Infrasil. These results show that Infrasil has poor charging stability. Comparatively, the charging stability of lead silica is better, and Suprasil has the best characteristics.

Photoemission of graded-doping GaN photocathode

Fu Xiao-Qian, Chang Ben-Kang, Wang Xiao-Hui, Li Biao, Du Yu-Jie, Zhang Jun-Ju
Chin. Phys. B, 2011, 20 (3): 037902 doi: 10.1088/1674-1056/20/3/037902
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We study the photoemission process of graded-doping GaN photocathode and find that the built-in electric fields can increase the escape probability and the effective diffusion length of photo-generated electrons, which results in the enhancement of quantum efficiency. The intervalley scattering mechanism and the lattice scattering mechanism in high electric fields are also investigated. To prevent negative differential mobility from appearing, the surface doping concentration needs to be optimized, and it is calculated to be 3.19×1017 cm-3. The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile.

Tuning field emission properties of boron nanocones with catalyst concentration

Li Chen, Tian Yuan, Wang Deng-Ke, Shi Xue-Zhao, Hui Chao, Shen Cheng-Min, Gao Hong-Jun
Chin. Phys. B, 2011, 20 (3): 037903 doi: 10.1088/1674-1056/20/3/037903
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Single crystalline boron nanocones are prepared by using a simple spin spread method in which Fe3O4 nanoparticles are pre-manipulated on Si(111) to form catalyst patterns of different densities. The density of boron nanocones can be tuned by changing the concentration of catalyst nanoparticles. High-resolution transmission electron microscopy analysis shows that the boron nanocone has a β-tetragonal structure with good crystallization. The field emission behaviour is optimal when the spacing distance is close to the nanocone length, which indicates that this simple spin spread method has great potential applications in electron emission nanodevices.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Target voltage behaviour of a vanadium-oxide thin film during reactive magnetron sputtering

Wang Tao, Jiang Ya-Dong, Yu He, Wu Zhi-Ming, Zhao He-Nan
Chin. Phys. B, 2011, 20 (3): 038101 doi: 10.1088/1674-1056/20/3/038101
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This paper simulates reactive magnetron-sputtering in constant current mode in a Vanadium-O2/Ar system equipped with a DC power supply by adopting both kinetics model and Berg's model. The target voltage during the reactive sputtering has been investigated as a function of reactive gas flow. Both experiments and simulations demonstrate a hysteresis curve with respect to the oxygen supply. The time-dependent variation of the target mode is studied by measuring the target voltage for various reactive oxygen gas flows and pre-sputtering times. The pre-sputtering time increases with the increased initial target voltage. Furthermore, a corresponding time-dependent model simulating target voltage changes is also proposed. Based on these simulations, we find some relationships between the discharge voltage behaviour and the properties of the formed oxide. In this way, a better understanding of the target voltage changes during reactive sputtering can be achieved. We conclude that the presented theoretical models for parameter-dependent case and time-dependent case are in qualitative agreement with the experimental results and can be used to comprehend the target voltage behaviour in the deposition of vanadium oxide thin films.

Origin of high oxide to nitride polishing selectivity of ceria-based slurry in the presence of picolinic acid

Wang Liang-Yong, Liu Bo, Song Zhi-Tang, Liu Wei-Li, Feng Song-Lin, David Huang, S.V Babu
Chin. Phys. B, 2011, 20 (3): 038102 doi: 10.1088/1674-1056/20/3/038102
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We report on the investigation of the origin of high oxide to nitride polishing selectivity of ceria-based slurry in the presence of picolinic acid. The oxide to nitride removal selectivity of the ceria slurry with picolinic acid is as high as 76.6 in the chemical mechanical polishing. By using zeta potential analyzer, particle size analyzer, horizon profilometer, thermogravimetric analysis and Fourier transform infrared spectroscopy, the pre- and the post-polished wafer surfaces as well as the pre- and the post-used ceria-based slurries are compared. Possible mechanism of high oxide to nitride selectivity with using ceria-based slurry with picolinic acid is discussed.

Solar cells based on the poly(N-vinylcarbazole):porphyrin: tris(8-hydroxyquinolinato) aluminium blend system

Zhang Tian-Hui, Zhao Su-Ling, Piao Ling-Yu, Xu Zheng, Ju Si-Ting, Liu Xiao-Dong, Kong Chao, Xu Xu-Rong
Chin. Phys. B, 2011, 20 (3): 038401 doi: 10.1088/1674-1056/20/3/038401
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Organic solar cells based on poly(N-vinylcarbazole) (PVK): porphyrin: tris (8-hydroxyquinolinato) aluminium (Alq3) blend p-n junction systems have been fabricated in this work. The roles of the different components in the blend system and of the amount of porphyrin have been investigated. The 5, 10, 15, 20--tetraphenylporphyrin (TPP) and 5, 10, 15, 20-tetra(o-chloro)phenylporphyrinato-copper (CuTClPP) are used in the solar cells. The results show that TPP is better than CuTClPP in enhancing the performance of PVK:Alq3 solar cells. When the weight ratio of PVK:TPP:Alq3 is 1:1.5:1, the best performance of solar cell is obtained. The open circuit voltage (Voc) is 0.87 V, and the short circuit current (Jsc) is 17.5 μA·cm - 2. In the ternary bulk hereojunction system, the device may be regarded as a cascade of three devices of PVK:TPP, TPP:Alq3 and PVK:Alq3. PVK, TPP and Alq3 can improve the hole mobility, light absorption intensity and electron mobility of the ternary bulk hereojunction system, respectively.

Analysis of a phase synchronized functional network based on the rhythm of brain activities

Li Ling, Jin Zhen-Lan, Li Bin
Chin. Phys. B, 2011, 20 (3): 038701 doi: 10.1088/1674-1056/20/3/038701
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Rhythm of brain activities represents oscillations of postsynaptic potentials in neocortex, therefore it can serve as an indicator of the brain activity state. In order to check the connectivity of brain rhythm, this paper develops a new method of constructing functional network based on phase synchronization. Electroencephalogram (EEG) data were collected while subjects looking at a green cross in two states, performing an attention task and relaxing with eyes-open. The EEG from these two states was filtered by three band-pass filters to obtain signals of theta (4–7 Hz), alpha (8–13 Hz) and beta (14–30 Hz) bands. Mean resultant length was used to estimate strength of phase synchronization in three bands to construct networks of both states, and mean degree K and cluster coefficient C of networks were calculated as a function of threshold. The result shows higher cluster coefficient in the attention state than in the eyes-open state in all three bands, suggesting that cluster coefficient reflects brain state. In addition, an obvious fronto-parietal network is found in the attention state, which is a well-known attention network. These results indicate that attention modulates the fronto-parietal connectivity in different modes as compared with the eyes-open state. Taken together this method is an objective and important tool to study the properties of neural networks of brain rhythm.

The role of vacancy, impurity, impurity–vacancy complex in the kinetics of LiNH2 complex hydrides: a first-principles study

Liu Gui-Li, Zhang Guo-Ying, Zhang Hui, Zhu Sheng-Long
Chin. Phys. B, 2011, 20 (3): 038801 doi: 10.1088/1674-1056/20/3/038801
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This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity–vacancy complex in LiNH2, a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity–vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH2 by Ti catalysts and Mg substitution is due to the weak bonding of N–H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity–vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH2.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Effects of σ* and Φ mesons on the surface redshift of a neutron star

Zhao Xian-Feng
Chin. Phys. B, 2011, 20 (3): 039701 doi: 10.1088/1674-1056/20/3/039701
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The effects of σ* and Φ mesons on the surface redshift of a neutron star have been investigated within the framework of relativistic mean field theory for the baryon octet {n,p,Λ,Σ-0+-0} system. It is found that compared with those without considering the contributions of σ* and Φ mesons, the surface redshift decreases and that corresponding to the maximum value of the mass also decreases from 0.2540 to 0.2236, about by 12%. Meanwhile, it is also found that including σ* and Φ mesons, the M/R and that corresponding to the maximum mass decrease.
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