中国物理B

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Multi-component Harry--Dym hierarchy and its integrable couplings as well as their Hamiltonian structures

杨红卫, 董焕河

2009 (3): 845-849. doi: 10.1088/1674-1056/18/3/001

摘要 ( 1042 )

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This paper obtains the multi-component Harry--Dym (H--D) hierarchy and its integrable couplings by using two kinds of vector loop algebras \widetilde{G}₃ and \widetilde{G}₆. The Hamiltonian structures of the above system are given by the quadratic-form identity. The method can be used to produce the Hamiltonian structures of the other integrable couplings or multi-component hierarchies.

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Discrete integrable system and its integrable coupling

李柱

2009 (3): 850-855. doi: 10.1088/1674-1056/18/3/002

摘要 ( 1085 )

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This paper derives new discrete integrable system based on discrete isospectral problem. It shows that the hierarchy is completely integrable in the Liouville sense and possesses bi-Hamiltonian structure. Finally, integrable couplings of the obtained system is given by means of semi-direct sums of Lie algebras.

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Conformal invariance and Hojman conserved quantities of canonical Hamilton systems

刘畅, 刘世兴, 梅凤翔, 郭永新

2009 (3): 856-860. doi: 10.1088/1674-1056/18/3/003

摘要 ( 1112 )

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This paper discusses the conformal invariance by infinitesimal transformations of canonical Hamilton systems. The necessary and sufficient conditions of conformal invariance being Lie symmetrical simultaneously by the action of infinitesimal transformations are given. The determining equations of the conformal invariance are gained. Then the Hojman conserved quantities of conformal invariance by special infinitesimal transformations are obtained. Finally an illustrative example is given to verify the results.

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A third-order asymptotic solution of nonlinear standing water waves in Lagrangian coordinates

陈阳益, 许弘莒

2009 (3): 861-871. doi: 10.1088/1674-1056/18/3/004

摘要 ( 955 )

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Asymptotic solutions up to third-order which describe irrotational finite amplitude standing waves are derived in Lagrangian coordinates. The analytical Lagrangian solution that is uniformly valid for large times satisfies the irrotational condition and the pressure p=0 at the free surface, which is in contrast with the Eulerian solution existing under a residual pressure at the free surface due to Taylor's series expansion. In the third-order Lagrangian approximation, the explicit parametric equation and the Lagrangian wave frequency of water particles could be obtained. In particular, the Lagrangian mean level of a particle motion that is a function of vertical label is found as a part of the solution which is different from that in an Eulerian description. The dynamic properties of nonlinear standing waves in water of a finite depth, including particle trajectory, surface profile and wave pressure are investigated. It is also shown that the Lagrangian solution is superior to an Eulerian solution of the same order for describing the wave shape and the kinematics above the mean water level.

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Spatiotemporal multiple coherence resonances and calcium waves in a coupled hepatocyte system

王宝华, 陆启韶, 吕淑娟, 郎秀锋

2009 (3): 872-880. doi: 10.1088/1674-1056/18/3/005

摘要 ( 1097 )

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Spatiotemporal multiple coherence resonances for calcium activities induced by weak Gaussian white noise in coupled hepatocytes are studied. It is shown that bi-resonances in hepatocytes are induced by the interplay and competition between noise and coupling of cells, in other words, the cell in network can be excited either by noise or by its neighbour via gap junction which can transfer calcium ions between cells. Furthermore, the intercellular annular calcium waves induced by noise are observed, in which the wave length decreases with noise intensity augmenting but increases monotonically with coupling strength increasing. And for a fixed noise level, there is an optimal coupling strength that makes the coherence resonance reach maximum.

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The strain relaxation of InAs/GaAs self-organized quantum dot

刘玉敏, 俞重远, 任晓敏

2009 (3): 881-887. doi: 10.1088/1674-1056/18/3/006

摘要 ( 1308 )

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This paper presents a detailed analysis of the dependence of degree of strain relaxation of the self-organized InAs/GaAs quantum dot on the geometrical parameters. Differently shaped quantum dots arranged with different transverse periods are simulated in this analysis. It investigates the total residual strain energy that stored in the quantum dot and the substrate for all kinds of quantum dots with the same volume, as well as the dependence on both the aspect ratio and transverse period. The calculated results show that when the transverse period is larger than two times the base of the quantum dots, the influence of transverse periods can be ignored. The larger aspect ratio will lead more efficient strain relaxation. The larger angle between the faces and the substrate will lead more efficient strain relaxation. The obtained results can help to understand the shape transition mechanism during the epitaxial growth from the viewpoint of energy, because the strain relaxation is the main driving force of the quantum dot's self-organization.

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The influences of dipole--dipole interaction and detuning on the sudden death of entanglement between two atoms in the Tavis--Cummings model

陈丽, 邵晓强, 张寿

2009 (3): 888-893. doi: 10.1088/1674-1056/18/3/007

摘要 ( 3431 )

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The influences of dipole--dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis--Cummings model have been investigated by means of Wootters' concurrence, respectively. The results show that the entanglement between the two atoms can be enhanced via appropriately tuning the strength of dipole--dipole interaction of two atoms or the detunings between atom and cavity, and the so-called sudden death effect can be weakened simultaneously.

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A scheme for implementing quantum game in cavity QED

曹帅, 方卯发, 刘建斌, 汪新文, 郑小娟

2009 (3): 894-897. doi: 10.1088/1674-1056/18/3/008

摘要 ( 1166 )

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In this paper, we propose a scheme for implementing quantum game (QG) in cavity quantum electrodynamics(QED). In the scheme, the cavity is only virtually excited and thus the proposal is insensitive to the cavity fields states and cavity decay. So our proposal can be experimentally realized in the range of current cavity QED techniques.

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Theoretical analysis of quantum game in cavity QED

曹帅, 方卯发, 刘建斌, 汪新文, 郑小娟, 李海

2009 (3): 898-901. doi: 10.1088/1674-1056/18/3/009

摘要 ( 1153 )

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Recent years, several ways of implementing quantum games in different physical systems have been presented. In this paper, we perform a theoretical analysis of an experimentally feasible way to implement a two player quantum game in cavity quantum electrodynamic(QED). In the scheme, the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a classical field. So the scheme is insensitive to the influence from the cavity decay and the thermal field, and it does not require the cavity to remain in the vacuum state throughout the procedure.

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Wigner function of the thermo number states

胡利云, 范洪义

2009 (3): 902-909. doi: 10.1088/1674-1056/18/3/010

摘要 ( 1267 )

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Based on thermo field dynamics (TFD) and using the thermo Wigner operator in the thermo entangled state representation we derive the Wigner function of number states at finite temperature (named thermo number states). The figure of Wigner function shows that its shape gets smoothed as the temperature rises, implying that the quantum noise becomes larger.

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Scheme for realizing quantum computation and quantum information transfer with superconducting qubits coupling to a 1D transmission line resonator

施振刚, 谌雄文, 朱喜香, 宋克慧

2009 (3): 910-914. doi: 10.1088/1674-1056/18/3/011

摘要 ( 1186 )

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This paper proposes a simple scheme for realizing one-qubit and two-qubit quantum gates as well as multiqubit entanglement based on dc-SQUID charge qubits through the control of their coupling to a 1D transmission line resonator (TLR). The TLR behaves effectively as a quantum data-bus mode of a harmonic oscillator, which has several practical advantages including strong coupling strength, reproducibility, immunity to 1/f noise, and suppressed spontaneous emission. In this protocol, the data-bus does not need to stay adiabatically in its ground state, which results in not only fast quantum operation, but also high-fidelity quantum information processing. Also, it elaborates the transfer process with the 1D transmission line.

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Analysis of the differential-phase-shift-keying protocol in the quantum-key-distribution system

焦荣珍, 冯晨旭, 马海强

2009 (3): 915-917. doi: 10.1088/1674-1056/18/3/012

摘要 ( 1226 )

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The analysis is based on the error rate and the secure communication rate as functions of distance for three quantum-key-distribution (QKD) protocols: the Bennett--Brassard 1984, the Bennett--Brassard--Mermin 1992, and the coherent differential-phase-shift keying (DPSK) protocols. We consider the secure communication rate of the DPSK protocol against an arbitrary individual attack, including the most commonly considered intercept-resend and photon-number splitting attacks, and concluded that the simple and efficient differential-phase-shift-keying protocol allows for more than 200 km of secure communication distance with high communication rates.

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New approach for analysing master equations of generalized phase diffusion models in the entangled state representation

徐兴磊, 李洪奇, 范洪义

2009 (3): 918-921. doi: 10.1088/1674-1056/18/3/013

摘要 ( 1209 )

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By virtue of the well-behaved properties of the bipartite entangled states representation, this paper analyse and solves some master equations for generalized phase diffusion models, which seems concise and effective. This method can also be applied to solve other master equations.

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Noise in a coupling electromagnetic detecting system for high frequency gravitational waves

李瑾, 李芳昱, 仲元红

2009 (3): 922-926. doi: 10.1088/1674-1056/18/3/014

摘要 ( 1137 )

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This paper discusses the basic categories of noise in detecting high frequency gravitational waves in the microwave band (～0.1--10 GHz), which contain shot noise from the laser and the thermal radiation photons, thermal noise from statistical fluctuation of the thermal photons and fluctuation of the temperature, radiation press noise on the fractal membrane, the noise caused by the scattering of the Gaussian Beam (GB) in the detecting tube and noise in the microwave radiometers. The analysis shows that a reasonable signal-to-noise ratio may be achieved for a detecting device with the fixed power of GB (10⁵ W), only when the temperature of the environment is no more than T=1 K, and the optimal length of the microwave radiometers is about 0.3 m.

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Reversible Carnot cycle outside a black hole

邓熙浩, 高思杰

2009 (3): 927-932. doi: 10.1088/1674-1056/18/3/015

摘要 ( 1158 )

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A Carnot cycle outside a Schwarzschild black hole is investigated in detail. We propose a reversible Carnot cycle with a black hole being the cold reservoir. In our model, a Carnot engine operates between a hot reservoir with temperature T₁ and a black hole with Hawking temperature T_H. By naturally extending the ordinary Carnot cycle to the black hole system, we show that the thermal efficiency for a reversible process can reach the maximal efficiency 1-T_H/T₁. Consequently, black holes can be used to determine the thermodynamic temperature by means of the Carnot cycle. The role of the atmosphere around the black hole is discussed. We show that the thermal atmosphere provides a necessary mechanism to make the process reversible.

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Generating weighted community networks based on local events

徐琪欣, 许新建

2009 (3): 933-938. doi: 10.1088/1674-1056/18/3/016

摘要 ( 1085 )

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Many realistic networks have community structures, namely, a network consists of groups of nodes within which links are dense but among which links are sparse. This paper proposes a growing network model based on local processes, the addition of new nodes intra-community and new links intra- or inter-community. Also, it utilizes the preferential attachment for building connections determined by nodes' strengths, which evolves dynamically during the growth of the system. The resulting network reflects the intrinsic community structure with generalized power-law distributions of nodes' degrees and strengths.

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Controlling the motion of solitons in BEC by a weakly periodic potential

奚玉东, 王登龙, 何章明, 丁建文

2009 (3): 939-945. doi: 10.1088/1674-1056/18/3/017

摘要 ( 1200 )

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By developing multiple-scale method combined with Wentzel--Kramer--Brillouin expansion, this paper analytically studies the modulating effect of weakly periodic potential on the dynamical properties of the Bose--Einstein condensates (BEC) trapped in harmonic magnetic traps. A black--grey soliton transition is observed in the BEC trapped in harmonic magnetic potential, due to the weakly periodic potential modulating effect. Meanwhile, it finds that with the slight increase of the weakly periodic potential strength, the velocity of the soliton decreases, while its width firstly decreases then increases, a minimum exists there. These results show that the amplitude, velocity, and width of matter solitons can be effectively managed by means of a weakly periodic potential.

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Effects of time delay on stochastic resonance of a periodically driven linear system with multiplicative and periodically modulated additive white noises

杜鲁春, 梅冬成

2009 (3): 946-951. doi: 10.1088/1674-1056/18/3/018

摘要 ( 1373 )

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Stochastic resonance (SR) of a periodically driven time-delayed linear system with multiplicative white noise and periodically modulated additive white noise is investigated. In the condition of small delay time, an approximate analytical expression of output signal-to-noise ratio (SNR) is obtained. The analytical results indicate that (1) there exists a resonance peak in the curve for SNR versus time delay; (2) the time delay will suspend the SR dramatically for SNR versus other parameters of the system, such as noise intensity, correlation intensity, and signal frequency, once a certain value is reached, the SR phenomenon disappears.

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Stochastic resonance in a single-mode laser driven by frequency modulated signal and coloured noises

金国祥, 张良英, 曹力

2009 (3): 952-957. doi: 10.1088/1674-1056/18/3/019

摘要 ( 1173 )

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By adding frequency modulated signals to the intensity equation of gain--noise model of the single-mode laser driven by two coloured noises which are correlated, this paper uses the linear approximation method to calculate the power spectrum and signal-to-noise ratio (SNR) of the laser intensity. The results show that the SNR appears typical stochastic resonance with the variation of intensity of the pump noise and quantum noise. As the amplitude of a modulated signal has effects on the SNR, it shows suppression, monotone increasing, stochastic resonance, and multiple stochastic resonance with the variation of the frequency of a carrier signal and modulated signal.

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Regular nonlinear response of the driven Duffing oscillator to chaotic time series

袁野, 李月, Danilo P. Mandic, 杨宝俊

2009 (3): 958-968. doi: 10.1088/1674-1056/18/3/020

摘要 ( 3484 )

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Nonlinear response of the driven Duffing oscillator to periodic or quasi-periodic signals has been well studied. In this paper, we investigate the nonlinear response of the driven Duffing oscillator to non-periodic, more specifically, chaotic time series. Through numerical simulations, we find that the driven Duffing oscillator can also show regular nonlinear response to the chaotic time series with different degree of chaos as generated by the same chaotic series generating model, and there exists a relationship between the state of the driven Duffing oscillator and the chaoticity of the input signal of the driven Duffing oscillator. One real-world and two artificial chaotic time series are used to verify the new feature of Duffing oscillator. A potential application of the new feature of Duffing oscillator is also indicated.

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An improved impulsive control approach to nonlinear systems with time-varying delays

张化光, 浮洁, 马铁东, 佟绍成

2009 (3): 969-974. doi: 10.1088/1674-1056/18/3/021

摘要 ( 1151 )

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A scheme for the impulsive control of nonlinear systems with time-varying delays is investigated in this paper. Based on the Lyapunov-like stability theorem for impulsive functional differential equations (FDEs), some sufficient conditions are presented to guarantee the uniform asymptotic stability of impulsively controlled nonlinear systems with time-varying delays. These conditions are more effective and less conservative than those obtained. Finally, two numerical examples are provided to demonstrate the effectiveness of the proposed method.

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A new car-following model with consideration of the traffic interruption probability

唐铁桥, 黄海军, 黄仕进, 姜锐

2009 (3): 975-983. doi: 10.1088/1674-1056/18/3/022

摘要 ( 1362 )

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In this paper, we present a new car-following model by taking into account the effects of the traffic interruption probability on the car-following behaviour of the following vehicle. The stability condition of the model is obtained by using the linear stability theory. The modified Korteweg--de Vries (KdV) equation is constructed and solved, and three types of traffic flows in the headway sensitivity space---stable, metastable, and unstable---are classified. Both the analytical and simulation results show that the traffic interruption probability indeed has an influence on driving behaviour, and the consideration of traffic interruption probability in the car-following model could stabilize traffic flow.

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Performance characteristics of an energy selective electron refrigerator with double resonances

王小敏, 何济洲, 唐威

2009 (3): 984-991. doi: 10.1088/1674-1056/18/3/023

摘要 ( 1012 )

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This paper establishes the energy selective electron (ESE) engine with double resonances as a refrigerator in one dimensional (1D) system. It consists of two infinitely large electron reservoirs with different temperatures and chemical potentials, and they are perfectly thermally insulated from each other and interaction only via a double `idealized energy filter' whose widths are all finite. Taking advantage of the density of state and Fermi distribution in the 1D system, the heat flux into each reservoir may then be calculated. Moreover, the coefficient of performance may be derived from the expressions for the heat flux into the hot and cold reservoirs. The performance characteristic curves are plotted by numerical analysis. The influences of the resonances widths, the energy position of resonance and the space of two resonances on performance of the ESE refrigerator are discussed. The results obtained here have theoretical significance for the understanding of thermodynamic performance of the micro--nano devices.

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Tolerance of edge cascades with coupled map lattices methods

崔迪, 高自友, 郑建风

2009 (3): 992-996. doi: 10.1088/1674-1056/18/3/024

摘要 ( 1036 )

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This paper studies the cascading failure on random networks and scale-free networks by introducing the tolerance parameter of edge based on the coupled map lattices methods. The whole work focuses on investigating some indices including the number of failed edges, dynamic edge tolerance capacity and the perturbation of edge. In general, it assumes that the perturbation is attributed to the normal distribution in adopted simulations. By investigating the effectiveness of edge tolerance in scale-free and random networks, it finds that the larger tolerance parameter λ can more efficiently delay the cascading failure process for scale-free networks than random networks. These results indicate that the cascading failure process can be effectively controlled by increasing the tolerance parameter λ. Moreover, the simulations also show that, larger variance of perturbation can easily trigger the cascading failures than the smaller one. This study may be useful for evaluating efficiency of whole traffic systems, and for alleviating cascading failure in such systems.

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Fabrication of grating-like polystyrene latex monolayer structure as three-dimensional calibration standards for scanning probe microscope

朱国栋, 曾志刚, 国璋, 杜强国, 严学俭

2009 (3): 997-1001. doi: 10.1088/1674-1056/18/3/025

摘要 ( 873 )

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This paper illuminates the preparation of grating-like polystyrene latex monolayer structure, which can minimize the effects of the size deviation of spheres and the defect transfer on the accuracy as calibration samples for microscopes. The latex films are grown on freshly cleaved mica substrates by vertical deposition method. The concentration dependence of the structure and the topography of latex films is characterized by optical microscope, ultraviolet--visible transmission spectrum and scanning probe microscope. The origination of such a grating-like structure is also discussed.

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Topological aspect of disclinations in two-dimensional crystals

齐维开, 朱涛, 陈勇, 任继荣

2009 (3): 1002-1008. doi: 10.1088/1674-1056/18/3/026

摘要 ( 1183 )

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By using topological current theory, this paper studies the inner topological structure of disclinations during the melting of two-dimensional systems. From two-dimensional elasticity theory, it finds that there are topological currents for topological defects in homogeneous equation. The evolution of disclinations is studied, and the branch conditions for generating, annihilating, crossing, splitting and merging of disclinations are given.

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Judd--Oflet analysis of spectrum and laser performance of Ho:YAP crystal end-pumped by 1.91-μm Tm:YLF laser

姚宝权, 郑亮亮, 杨晓涛, 王天衡, 段小明, 赵广军, 董勤

2009 (3): 1009-1013. doi: 10.1088/1674-1056/18/3/027

摘要 ( 1389 )

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The Ho:YAP crystal is grown by the Czochralski technique. The room-temperature polarized absorption spectra of Ho:YAP crystal was measured on a c-cut sample with 1 at% holmium. According to the obtained Judd--Ofelt intensity parameters Ω₂=1.42× 10²⁰ cm², Ω₄=2.92× 10²⁰ cm², and Ω ₆=1.71× 10²⁰ cm², this paper calculated the fluorescence lifetime to be 6 ms for ⁵I₇→⁵I₈ transition, and the integrated emission cross section to be 2.24× 10^-18 cm². It investigates the room-temperature Ho:YAP laser end-pumped by a 1.91-μm Tm:YLF laser. The maximum output power was 4.1 W when the incident 1.91-μm pump power was 14.4 W. The slope efficiency is 40.8%, corresponding to an optical-to-optical conversion efficiency of 28.4%. The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.

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Intensity-dependent asymmetric photoionization in few-cycle laser pulses

张晓明, 张敬涛, 龚旗煌, 徐至展

2009 (3): 1014-1018. doi: 10.1088/1674-1056/18/3/028

摘要 ( 1255 )

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The asymmetric photoionization of atoms irradiated by intense, few-cycle laser pulses is studied numerically. The results show that the pulse intensity affects the asymmetric photoionization in three aspects. First, at higher intensities, the asymmetry becomes distinctive for few-cycle pulses of longer durations. Second, as the laser intensity increases, the maximal asymmetry first decreases then increases after it has reached a minimal value. Last, the value of the carrier-envelope phase corresponding to the maximal asymmetry varies with the pulse intensity. This study reveals that the increasing of pulse intensity is helpful for observing the asymmetric photoionization.

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Scattering properties of the ultracold ¹³³Cs₂ triplet state

孙金锋, 杜丙阁, 张计才, 李伟, 朱遵略

2009 (3): 1019-1024. doi: 10.1088/1674-1056/18/3/029

摘要 ( 1085 )

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The elastic scattering properties of ultracold ^{133}Cs₂ triplet state are investigated in detail. We construct a potential curve of the ¹³³Cs₂ triplet state, based on the latest ab initio molecular potential data and show how the scattering parameters are obtained by using three methods: the Numerov method, the semiclassical method and the variable phase method, where the scattering lengths of the ¹³³Cs₂ triplet state, i.e. 301.79a₀, 300.67a₀ and 310.81a₀ are obtained respectively, with a₀ being the Bohr radius. We also calculate the effective range and the number of bound states for the ¹³³Cs₂ triplet state. Our results are in agreement with the recent experimental data and the theoretical calculations. This confirms that the results of the scattering properties of the ultracold ^{133}Cs₂ triplet state, calculated by using these three methods, are reliable.

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The design of metamaterial cloaks embedded in anisotropic medium

马华, 屈绍波, 徐卓, 张介秋, 王甲富

2009 (3): 1025-1028. doi: 10.1088/1674-1056/18/3/030

摘要 ( 1390 )

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By using coordinate transformation method, this paper obtains an useful equation of designing meta-material cloaks embedded in anisotropic medium. This equation is the generalization of what was introduced early by Pendry et al (2006 \textit{Science} {312 1780) and can be more widely used. As an example of its applications, this paper deduces the material parameter equation for cylinder cloaks embedded in anisotropic medium, and then offers the numerical simulation. The results show that such a cylinder cloak has perfect cloaking performance and therefore verifies the method proposed in this paper.

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Surface plasmon resonance transmission filters at 1053nm based on metallic grating with narrow slit

麻健勇, 许程, 刘世杰, 张大伟, 晋云霞, 范正修, 邵建达

2009 (3): 1029-1032. doi: 10.1088/1674-1056/18/3/031

摘要 ( 1171 )

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Metallic gratings with narrow slits can lead to special optical properties such as strongly enhancing the transmission and considerably strengthening the polarized effect. A narrow-band filter suitable for application in optical communication is designed by sandwiching a metallic grating between two identical dielectric films. The maximum transmission can reach 96% after optimizing the parameters of films and grating at a central wavelength of 1053 nm. It is the first time, to our knowledge, that such high transmission has been reported since the discovery of the extraordinarily high transmission through periodic holes or slits; moreover, the extremely polarized effect is also found in P mode of this symmetric grating.

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Propagation of Gauss--Bessel beams in turbulent atmosphere

陈宝算, 蒲继雄

2009 (3): 1033-1039. doi: 10.1088/1674-1056/18/3/032

摘要 ( 1218 )

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This paper studies the propagation properties of Gauss--Bessel beams in a turbulent atmosphere. Based on the extended Huygens--Fresnel principle, it derives the intensity distribution expression for such beams propagating in a turbulent atmosphere. Then the influence of turbulence and source beam parameters on the beam propagation is studied in great detail. It finds that the intensity distribution of Gauss--Bessel beams will change into Gaussian profile in a turbulent atmosphere, and that stronger turbulence and smaller topological charges will lead to a faster changing.

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Light scattering by a spherical particle with multiple densely packed inclusions

孙贤明, 王海华, 刘万强, 申晋

2009 (3): 1040-1044. doi: 10.1088/1674-1056/18/3/033

摘要 ( 1255 )

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This paper calculates light scattering by a spherical water particle containing densely packed inclusions at a visible wavelength 0.55 \mum by a combination of ray-tracing and Monte Carlo techniques. While the individual reflection and refraction events at the outer boundary of a sphere particle are considered by a ray-tracing program, the Monte Carlo routine simulates internal scattering processes. The main advantage of this method is that the shape of the particle can be arbitrary, and multiple scattering can be considered in the internal scattering processes. A dense-medium light-scattering theory based on the introduction of the static structure factor is used to calculate the phase function and asymmetry parameters for densely packed inclusions. Numerical results of the single scattering characteristics for a sphere containing multiple densely packed inclusions are given.

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Deterministic generation of entangled coherent states for two atomic samples

卢道明, 郑仕标

2009 (3): 1045-1048. doi: 10.1088/1674-1056/18/3/034

摘要 ( 1149 )

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This paper proposes an efficient scheme for deterministic generation of entangled coherent states for two atomic samples. In the scheme two collections of atoms are trapped in an optical cavity and driven by a classical field. Under certain conditions the two atomic samples evolve from an coherent state to an entangled coherent state. During the interaction the cavity mode is always in the vacuum state and the atoms have no probability of being populated in the excited state. Thus, the scheme is insensitive to both the cavity decay and atomic spontaneous emission.

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Generation of Schr?dinger cat state of a single trapped cold ion

张淼, 贾焕玉, 姬晓辉, 司坤

2009 (3): 1049-1053. doi: 10.1088/1674-1056/18/3/035

摘要 ( 995 )

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The fidelity of the generated Schr?dinger Cat state (SCS) of a single trapped ion in the Lamb--Dicke approximation is discussed. The results show that the fidelity significantly decreases with the values of Lamb--Dicke parameter η and coherent state amplitude α increasing. For η= 0.20 and α= 3, the typical values of experimental parameters, the fidelity is rather low (30%). A scheme for generating the SCS is proposed without making the Lamb--Dike approximation in laser--ion interaction, and the fidelity of the generated SCS is about 99% for the typical values of experimental Lamb--Dicke parameters.

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Effects of relative phase on transient evolution in an open resonant ladder-type atomic system

杨艳玲, 刘中波, 王蕾, 仝殿民, 樊锡君

2009 (3): 1054-1060. doi: 10.1088/1674-1056/18/3/036

摘要 ( 1090 )

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In an open ladder-type resonant atomic system, variation in relative phase between probe and driving fields does not affect the transient evolution of populations, but it has remarkable effects on gain and dispersion of the probe field. No matter whether an incoherent pump is present or absent, transient and stationary gains without inversion (GWI) always can be obtained by choosing an appropriate value of the relative phase. When the incoherent pump is absent，the values of transient and stationary GWIs are much larger and the time interval required to reach the stationary value is longer than those when the incoherent pump is present. Varying the exit rate and the ratio between injection rates can obviously change the phase-dependent GWI. In addition, in the transient evolution process, the phenomenon of high dispersion (refractive index) without absorption occurs at some values of relative phase. In the corresponding closed system, the stationary GWI can be obtained by choosing an appropriate value of relative phase only when incoherent pump exists, moreover the gain is smaller than that in the open system.

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New approach for deriving density operator for describing continuum photodetection process

范洪义, 胡利云

2009 (3): 1061-1064. doi: 10.1088/1674-1056/18/3/037

摘要 ( 1206 )

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By introducing the two-mode entangled state representation <η| whose one mode is a fictitious one accompanying the system mode, this paper presents a new approach for deriving density operator for describing continuum photodetection process.

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Four-mode continuous-variables entangled state: generation from beam splitter, a parametric down-conversion and a polarizer

匡买花, 马善钧, 刘冬梅, 王淑静

2009 (3): 1065-1071. doi: 10.1088/1674-1056/18/3/038

摘要 ( 1131 )

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We introduce a new kind of four-mode continuous variable entangled state in Fock space. The completeness relation and the partly nonorthonormal property of such a state are proven. The scheme to generate this state is presented by combining a symmetrical beamsplitter, a parametric down-conversion and a polarizer. After making a single-mode quadrature amplitude measurement, the remaining three modes are kept in entanglement. And its applications are also discussed.

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Optical bistability and multistability in a three-level Δ-type atomic system under the nonresonant condition

陈爱喜, 王志平, 陈德海, 徐彦秋

2009 (3): 1072-1076. doi: 10.1088/1674-1056/18/3/039

摘要 ( 1239 )

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Under a nonresonant condition, we theoretically investigate hybrid absorptive-dispersive optical bistability and multistability behaviours in a three-level Δ-type system by using a microwave field to drive a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the optical bistability and multistability behaviours can be controlled by adjusting the intensity of the microwave field or the intensity of the coherent coupling field. Furthermore, our studies show an interesting phenomenon of the transition from the optical bistability to the optical multistability only by changing the negative detuning of the coupling field into the positive detuning of the coupling field.

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Simultaneous all-solid-state multi-wavelength lasers --- a promising pump source for generating highly coherent terahertz waves

刘欢, 徐德刚, 姚建铨

2009 (3): 1077-1084. doi: 10.1088/1674-1056/18/3/040

摘要 ( 1428 )

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A diode-end-pumped Nd:YAG dual-wavelength laser operating at 1319 and 1338 nm is demonstrated. The maximum average output power of the quasi-continuous wave linearly polarized dual-wavelength laser is obtained to be 2.1 W at a repetition rate of 50 kHz with an output power instability of less than 0.38% and beam quality factor M² of 1.45. Using the two lines, the highly coherent and narrow linewidth terahertz radiation of 3.23 THz can be generated in an organic 4-N, N-dimethylamino--methyl-stilbazolium tosylate (DAST) crystal. Meanwhile, the multi-wavelength red laser at 659.5, 664 and 669 nm is generated by frequency doubling and sum frequency processes in a lithium triborate (LBO) crystal. The average red laser output power is enhanced up to 1.625 W at a repetition rate of 15 kHz with an output power instability of better than 0.53% and beam quality factor M² of 6.05. Using the three lines, it is possible to generate the multi-wavelength THz radiation of 3.3, 3.43 and 6.73 THz in an appropriate difference frequency crystal.

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Simulation study on terahertz vibrational absorption in liquid crystal compounds

马恒, 施德恒, 赫君, 彭玉峰

2009 (3): 1085-1088. doi: 10.1088/1674-1056/18/3/041

摘要 ( 1142 )

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The terahertz (THz) spectrum absorptions of nematic liquid crystal (LC) material, i.e. N-(p-methoxybenzylidene)-p-butylaniline (MBBA), and its relevant compounds are simulated in this paper by using the density functional theory (DFT) method. A strong absorptive frequency is located at 3.65 THz for the MBBA, which is in agreement with experimental data found in the literature. The result suggests that the DFT method is effective for dealing with the anisotropic nematic LC compounds.

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Thermal stability test and analysis of a 20-actuator bimorph deformable mirror

宁禹, 周虹, 余浩, 饶长辉, 姜文汉

2009 (3): 1089-1095. doi: 10.1088/1674-1056/18/3/042

摘要 ( 1467 )

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One of the important characteristic of adaptive mirrors is the thermal stability of surface flatness. In this paper, the thermal stability from 13℃ to 25℃ of a 20-actuator bimorph deformable mirror is tested by a Shack--Hartmann wavefront sensor. Experimental results show that, the surface P--V of bimorph increases nearly linearly with ambient temperature. The ratio is 0.11μm/℃ and the major component of surface displacement is defocused, compared with which, astigmatism, coma and spherical aberration contribute very small. Besides, a finite element model is built up to analyse the influence of thickness, thermal expansion coefficient and Young's modulus of materials on thermal stability. Calculated results show that bimorph has the best thermal stability when the materials have the same thermal expansion coefficient. And when the thickness ratio of glass to PZT is 3 and Young's modulus ratio is approximately 0.4, the surface instability behaviour of the bimorph manifests itself most severely.

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Modeling of graded index waveguide fabricated by ion exchange on Er³⁺ doped glass

邵公望, 金国良

2009 (3): 1096-1104. doi: 10.1088/1674-1056/18/3/043

摘要 ( 1113 )

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A general numerical tool, based on thermal diffusion equation and full-vectorial eigen-mode equation, has been presented for the systematic analysis of graded index channel waveguide fabricated by ion exchange on Er³⁺ doped glass. Finite difference method with full-vectorial formulation (FV-FDM) is applied to solving the full-vectorial modes of graded index channel waveguide for the first time. The coupled difference equations based on magnetic fields in FV-FDM are derived from the Taylor series expansion and accurate formulation of boundary conditions. Hybrid nature of vectorial guided modes for both pump (980 nm) and signal light (1550 nm) are demonstrated by the simulation. Results show that the fabrication parameters of ion exchange, such as channel opening width and time ratio of second step to first step in ion exchange, have large influence on the properties of waveguide. By optimizing the fabrication parameters, maintenance of monomode for signal light and improvement of the gain dynamics can be achieved in Er³⁺ doped waveguide amplifier (EDWA) fabricated by ion exchange technique. This theoretical model is significant for the design and fabrication of EDWA with ion exchange technique. Furthermore, a single polarization EDWA, which operates at wavelength from 1528 nm to 1541 nm for HE polarization, is numerically designed.

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Generation of 10fs Ti:sapphire laser at repetition rate of 525MHz and measurement of carrier-envelope phase frequency

张炜, 韩海年, 滕浩, 魏志义

2009 (3): 1105-1108. doi: 10.1088/1674-1056/18/3/044

摘要 ( 1197 )

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This paper presents a Kerr-lens mode-locked Ti:sapphire laser at the repetition rate of 525 MHz, stable laser pulse as short as 10 fs with average output power of 480 mW is obtained. By injecting the pulse into photonics crystal fibre, octave-spanning spectrum covered from 500 to 1050 nm is generated, carrier-envelope phase frequency with signal-to-noise ratio of 31dB is measured, which paves the way for the generation of a compact frequency comb.

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Lateral stress-induced propagation characteristics in photonic crystal fibres

田宏达, 俞重远, 韩利红, 刘玉敏

2009 (3): 1109-1115. doi: 10.1088/1674-1056/18/3/045

摘要 ( 1116 )

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Using the finite element method, this paper investigates lateral stress-induced propagation characteristics in a photonic crystal fibre of hexagonal symmetry. The results of simulation show the strong stress dependence of effective index of the fundamental guided mode, phase modal birefringence and confinement loss. It also finds that the contribution of the geometrical effect that is related only to deformation of the photonic crystal fibre and the stress-related contribution to phase modal birefringence and confinement loss are entirely different. Furthermore, polarization-dependent stress sensitivity of confinement loss is proposed in this paper.

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Zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres

张虎, 杨伯君, 刘玉敏, 王秋国, 于丽, 张晓光

2009 (3): 1116-1122. doi: 10.1088/1674-1056/18/3/046

摘要 ( 1250 )

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This paper investigates the zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres (PBGFs) by using a full-vector finite element method. By simulation we found that theoretically the zero dispersion wavelength can be tailored by respectively changing the rounded diameter of air holes, pitch, refractive index, normalized thickness of core rings, and hole diameter to pitch ratio. At the same time the tailoring of dispersion slope can also be realized by changing the rounded diameter of air holes or pitch or normalized thickness of core rings. To illustrate the reasonability of fibre designs, this paper also gives the variance of normalized interface field intensity which measures the scattering loss relatively versus wavelength for different designs. From the viewpoint of loss, varying the rounded diameter and the thickness of core ring could shift zero wavelength but it is difficult to get the required parameters within so tiny range in practical drawing of PBGFs, on the other hand, it is possible in practice to respectively alter the pitch and refractive index to shift zero wavelength. But varying hole diameter to pitch ratio is not worthwhile because they each induce large increase of loss and narrowness of transmission bandwidth. The zero dispersion wavelength can be engineered by respectively varying the rounded diameter of air holes, pitch, refractive index, and normalized thickness of core rings without incurring large loss penalties.

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Acoustic elliptical cylindrical cloaks

马华, 屈绍波, 徐卓, 王甲富

2009 (3): 1123-1126. doi: 10.1088/1674-1056/18/3/047

摘要 ( 1213 )

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By making a comparison between the acoustic equations and the 2-dimensional (2D) Maxwell equations, we obtain the material parameter equations (MPE) for acoustic elliptical cylindrical cloaks. Both the theoretical results and the numerical results indicate that an elliptical cylindrical cloak can realize perfect acoustic invisibility when the spatial distributions of mass density and bulk modulus are exactly configured according to the proposed equations. The present work is the meaningful exploration of designing acoustic cloaks that are neither sphere nor circular cylinder in shape, and opens up possibilities for making complex and multiplex acoustic cloaks with simple models such as spheres, circular or elliptic cylinders.

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The numerical study of shock-induced hydrodynamic instability and mixing

王涛, 柏劲松, 李平, 钟敏

2009 (3): 1127-1135. doi: 10.1088/1674-1056/18/3/048

摘要 ( 1132 )

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Based on multi-fluid volume fraction and piecewise parabolic method (PPM), a multi-viscosity-fluid hydrodynamic code MVPPM (Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and applied to the problems of shock-induced hydrodynamic interfacial instability and mixing. Simulations of gas/liquid interface instability show that the influences of initial perturbations on the fluid mixing zone (FMZ) growth are significant, especially at the late stages, while grids have only a slight effect on the FMZ width, when the interface is impulsively accelerated by a shock wave passing through it. A numerical study of the hydrodynamic interfacial instability and mixing of gaseous flows impacted by re-shocks is presented. It reveals that the numerical results are in good agreement with the experimental results and the mixing growth rate strongly depends on initial conditions. Ultimately, the jelly layer experiment relevant to the instability impacted by exploding is simulated. The shape of jelly interface, position of front face of jelly layer, crest and trough of perturbation versus time are given; their simulated results are in good agreement with experimental results.

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Triggering and guiding of high voltage discharge by using femtosecond laser filaments with different parameters

张喆, 鲁欣, 梁文锡, 郝作强, 周木林, 王兆华, 张杰

2009 (3): 1136-1140. doi: 10.1088/1674-1056/18/3/049

摘要 ( 1358 )

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This paper demonstrates the triggering and guiding of the stationary high voltage (HV) discharges at 5--40 kV by using plasma filaments generated by femtosecond laser pulses in air. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser filamentation is observed. The discharge experiments are performed by using laser pulses with different energy from 15--60 mJ. The electron density of filaments is detected by sonography method. The influence of the electron density of laser filaments on the triggering and guiding HV discharge is experimentally investigated. The results have shown that the behaviour of plasma filaments can strongly affect the efficiency of triggering and guiding HV discharge.

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Anisotropic optical feedback of single frequency intra-cavity He--Ne laser

周鲁飞, 张斌, 张书练, 谈宜东, 刘维新

2009 (3): 1141-1146. doi: 10.1088/1674-1056/18/3/050

摘要 ( 1225 )

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This paper presents the anisotropic optical feedback of a single frequency intra-cavity He--Ne laser. A novel phenomenon was discovered that the laser output an elliptical polarized frequency instead of the initial linear polarized one. Two intensities with a phase difference were detected, both of which were modulated in the form of cosine wave and a fringe shift corresponds to a λ/2 movement of the feedback mirror. The phase difference can be continuously modulated by the wave plate in the external cavity. Frequency stabilization was used to stabilize the laser frequency so as to enlarge the measuring range and improve the measurement precision. This anisotropic optical feedback system offers a potential displacement measurement technology with the function of subdivision of λ/2 and in-time direction judgment. The three-mirror Fabry--Perot cavity model is used to present the experimental results. Given the lack of need of lasing adjustment, this full intra-cavity laser can significantly improve the simplicity and stability of the optical feedback system.

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The propagation and deposition of fast muons in dense DT mixture

李雪梅, 沈百飞, 张晓梅, 金张英, 王凤超

2009 (3): 1147-1152. doi: 10.1088/1674-1056/18/3/051

摘要 ( 1099 )

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The propagation of the fast muon population mainly due to collisional effect in a dense deuterium--tritium (DT for short) mixture is investigated and analysed within the framework of the relativistic Fokker--Planck equation. Without the approximation that the muons propagate straightly in the DT mixture, the muon penetration length, the straggling length, and the mean transverse dispersion radius are calculated for different initial energies, and especially for different densities of the densely compressed DT mixture in our suggested muon-driven fast ignition (FI). Unlike laser-driven FI requiring super-high temperature, muons can catalyze DT fusion at lower temperatures and may generate an ignition sparkle before the self-heating fusion follows. Our calculation is important for the feasibility and the experimental study of muon-driven FI.

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Electron temperature fluctuation in the HT-7 Tokamak plasma observed by electron cyclotron emission imaging

徐小圆, 王俊, 余弈, 闻一之, 俞昌旋, 刘万东, 万宝年, 高翔, N. C. Luhmann, C. W. Domier, 王剑, 夏正刚, 申作玮

2009 (3): 1153-1160. doi: 10.1088/1674-1056/18/3/052

摘要 ( 1121 )

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The fluctuation of the electron temperature has been measured by using the electron cyclotron emission imaging in the Hefei Tokamak-7 (HT-7) plasma. The electron temperature fluctuation with a broadband spectrum shows that it propagates in the electron diamagnetic drift direction, and the mean poloidal wave-number $\bar{k}_{\theta}$ is calculated to be about 1.58 cm^-1, or \bar{k}_θ ρ_s≈ 0.34. It indicates that the fluctuation should come from the electron drift wave turbulence. The linear global scaling of the electron temperature fluctuation with the gradient of electron temperature is consistent with the mixing length scale qualitatively. Evolution of spectrum of the fluctuation during the sawtooth oscillation phases is investigated, and the fluctuation is found to increase with the gradient of electron temperature increasing during most phases of the sawtooth oscillation. The results indicate that the electron temperature gradient is probably the driver of the fluctuation enhancement. The steady heat flux driven by electron temperature fluctuation is estimated and compared with the results from power balance estimation.

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Painleve properties and exact solutions for the high-dimensional Schwartz Boussinesq equation

任博, 林机

2009 (3): 1161-1167. doi: 10.1088/1674-1056/18/3/053

摘要 ( 1106 )

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The usual (1+1)-dimensional Schwartz Boussinesq equation is extended to the (1+1)-dimensional space--time symmetric form and the general (n+1)-dimensional space--time symmetric form. These extensions are Painlevé integrable in the sense that they possess the Painlevé property. The single soliton solutions and the periodic travelling wave solutions for arbitrary dimensional space--time symmetric form are obtained by the Painlevé—B?acklund transformation.

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Collision induced splitting of bright soliton in Bose--Einstein condensate

王悦悦, 张解放

2009 (3): 1168-1171. doi: 10.1088/1674-1056/18/3/054

摘要 ( 1344 )

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This paper studies the collision dynamics of bright soliton in Bose--Einstein condensate with trapezoid potential. It is found that besides the total reflection and total transmission, one bright soliton can be divided into two bright solitons with different amplitudes in a controllable manner.

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Observation of poloidal current flowed to the vessel after failure of vertical position feedback control in EAST Tokamak

钱金平, 万宝年, 沈飙, L. L. Lao, 肖炳甲, 李建刚, 林士耀, 罗正平

2009 (3): 1172-1176. doi: 10.1088/1674-1056/18/3/055

摘要 ( 1085 )

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Plasmas with vertically elongated cross-sections tend to be unstable to an axis-symmetric instability. This paper studies the magnetohydrodynamic equilibria in elongated plasmas after failure of vertical feedback control by using magnetic data for EAST device. Vertical forces on the vessel due to the induced polodial and toroidal currents are evaluated. The maximum force of the Fz_pol in vertical displacement events for EAST designed parameters is given.

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Numerical simulation of super-short pulsed discharge in Helium with particle-in-cell Monte--Carlo collisions technique

石锋, 张莉丽, 王德真

2009 (3): 1177-1180. doi: 10.1088/1674-1056/18/3/056

摘要 ( 1091 )

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This paper reports that a simulation of glow discharge in pure helium gas at the pressure of 1.333×10³ Pa under a high-voltage nanosecond pulse is performed by using a one-dimensional particle-in-cell Monte Carlo collisions (PIC--MCC) model. Numerical modelling results show that the cathode sheath is much thicker than that of anode during the pulse discharge, and that there exists the phenomenon of field reversal at relative high pressures near the end of the pulse, which results from the cumulative positive charges due to their finite mobility during the cathode sheath expansion. Moreover, electron energy distribution function (EEDF) and ion energy distribution function (IEDF) have been also observed. In the early stage of the pulse, a large amount of electrons can be accelerated above the ionization threshold energy. However, in the second half of the pulse, as the field in bulk plasma decreases and thereafter the reverse field forms due to the excessive charges in cathode sheath, although the plasma density grows, the high energy part of EEDF decreases. It concludes that the large volume non-equilibrium plasmas can be obtained with high-voltage nanosecond pulse discharges.

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Structure and bonding properties of Y doped ∑37 grain boundary in alumina

王亚斌, 张刚, 刘明杰, 陈湘陇, 陈军

2009 (3): 1181-1187. doi: 10.1088/1674-1056/18/3/057

摘要 ( 1099 )

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The microscopic structures and the bonding properties of Y-doped and undoped (01\bar {1}8)/[04\bar {4}1]/180° (∑37) grain boundaries in alumina are investigated by using \textit{ab initio} method. The formation energy of grain boundary and the segregation energy of Y to grain boundary are acquired. Electronic structures, potential distributions, bond orders and effective charges of Y-doped and undoped ∑37 GB systems are calculated. Our results reveal that the higher strength Y--O bond than Al--O bond is ascribed to the hybridization of Y(4p, 3d) with O(2s). Meanwhile, dopant Y also causes a change in potential distribution in the grain boundary region, thereby further affecting the transport property of ceramic alumina.

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A novel interconnect-optimal repeater insertion model with target delay constraint in 65nm CMOS

朱樟明, 钱利波, 杨银堂

2009 (3): 1188-1193. doi: 10.1088/1674-1056/18/3/058

摘要 ( 1390 )

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Repeater optimization is the key for SOC (System on Chip) interconnect delay design. This paper proposes a novel optimal model for minimizing power and area overhead of repeaters while meeting the target performance of on-chip interconnect lines. It also presents Lagrangian function to find the number of repeaters and their sizes required for minimizing area and power overhead with target delay constraint. Based on the 65 nanometre CMOS technology, the computed results of the intermediate and global lines show that the proposed model can significantly reduce area and power of interconnected lines, and the better performance will be achieved with the longer line. The results compared with the reference paper demonstrate the validity of this model. It can be integrated into repeater design methodology and CAD (computer aided design) tool for interconnect planning in nanometre SOC.

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First-principles study of the (001) surface of cubic PbHfO₃ and BaHfO₃

倪广鑫, 王渊旭

2009 (3): 1194-1200. doi: 10.1088/1674-1056/18/3/059

摘要 ( 1127 )

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Using first-principles techniques, we investigate the (001) surfaces of cubic PbHfO₃ (PHO) and BaHfO₃ (BHO) terminated with both AO (A=Pb and Ba) and HfO₂. Surface structure, partial density of states, band structure, and surface energy are obtained. The BaO surface is found to be similar to its counterpart in BHO. For the HfO₂-terminated surface of cubic PHO, the largest relaxation appears on the second-layer atoms but not on the first-layer ones. The analysis of the structure relaxation parameters reveals that the rumpling of the (001) surface for PHO is stronger than that for BHO. The surface thermodynamic stability is explored, and it is found that both the PbO- and the BaO-terminated surfaces are more stable than the HfO₂-terminated surfaces for PHO and BHO, respectively. The surface energy calculations show that the (001) surface of PHO is more easily constructed than that of BHO.

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Spin--polarized electronic properties of NiHe_0.25 under pressures

伞晓娇, 刘志明, 马琰铭, 崔田, 刘冰冰, 邹广田

2009 (3): 1201-1206. doi: 10.1088/1674-1056/18/3/060

摘要 ( 1172 )

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This paper studies the effects of He atom on the spin-polarized electronic properties of nickel under pressures using {\it ab initio} pseudopotential plan-wave method. Under high pressures, the compound of NiHe_0.25 can exist and helium-bubble can not create in Ni. A pressure-induced ferromagnetic to paramagnetic phase transition has been predicted in NiHe_0.25 at about 218 GPa. It is found that under pressures, the magnetic property of Ni atoms is more strongly affected by He atom than by H atom and that the behaviour of He atom in Ni are completely different from that of H atom, like the bonding characteristics and the electron transfer.

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Structural, thermodynamic and electronic properties of zinc-blende AlN from first-principles calculations

张伟, 程艳, 朱俊, 陈向荣

2009 (3): 1207-1213. doi: 10.1088/1674-1056/18/3/061

摘要 ( 1264 )

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Structural, thermodynamic and electronic properties of zinc-blende AlN under pressure are investigated by first-principles calculations based on the plane-wave basis set. Through the analysis of enthalpy variation of AlN in the zinc-blende (ZB) and the rock-salt (RS) structures with pressure, we find the phase transition of AlN from ZB to RS structure occurs at 6.7 GPa. By using the quasi-harmonic Debye model, we obtain the heat capacity C_V, Debye temperature Θ_D, Grüneisen parameter γ and thermal expansion coefficient α. The electronic properties including fundamental energy gaps and hydrostatic deformation potentials are investigated and the dependence of energy gaps on pressure is analysed.

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State vector evolution localized over the edges of a square tight-binding lattice

何良明, 石端文

2009 (3): 1214-1220. doi: 10.1088/1674-1056/18/3/062

摘要 ( 1243 )

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We study the time evolution of a state vector in a square tight-binding lattice, focusing on its evolution localized over the system surfaces. In this tight-binding lattice, the energy of atomic orbital centred at surface site is different from that at the interior (bulky) site by an energy shift U. It is shown that for the state vector initially localized on a surface, there exists an exponential law (y=a\e^x/b+y₀) determined by the absolute value of the energy shift, |U|, which describes the transition of the state evolving on the square tight-binding lattice, from delocalized over the whole lattice to localized over the surfaces.

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Electrical, dielectric and surface wetting properties of multi-walled carbon nanotubes/nylon-6 nanocomposites

龙云泽, 李蒙蒙, 隋万美, 孔庆山, 张磊

2009 (3): 1221-1226. doi: 10.1088/1674-1056/18/3/063

摘要 ( 1341 )

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This paper reports that the multi-walled carbon nanotubes (MWCNT)/nylon-6 (PA6) nanocomposites with different MWCNT loadings have been prepared by a simple melt-compounding method. The electrical, dielectric, and surface wetting properties of the CNT/PA6 composites have been studied. The temperature dependence of the conductivity of the CNT/PA6 composite with 10.0 wt{\%} CNT loading ($\sigma _{\rm RT} \sim 10^{-4}$ S/cm) are measured, and afterwards a charge-energy-limited tunnelling model (ln $\sigma (T) \sim T^{-1/2})$ is found. With increasing CNT weight percentage from 0.0 to 10.0 wt%, the dielectric constant of the CNT/PA6 composites enhances and the dielectric loss tangent increases two orders of magnitude. In addition, water contact angles of the CNT/PA6 composites increase and the composites with CNT loading larger than 2.0 wt%even become hydrophobic. The obtained results indicate that the electrical and surface properties of the composites have been significantly enhanced by the embedded carbon nanotubes.

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Frequency selective surface with better polarization-independency for arbitrary incident angle

贾宏燕, 高劲松, 冯晓国

2009 (3): 1227-1230. doi: 10.1088/1674-1056/18/3/064

摘要 ( 1080 )

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This paper investigates the frequency-selective property of a planar layer consisting of period arrays both theoretically and experimentally for different polarizations at arbitrary incident angle. The novel element is designed by loading the rectangular microstrip element with L-shaped conducting patch at its two ends. Based on the spectral-domain method, the frequency response including angle effect and polarization effect of the frequency selective surface (FSS) structure are analysed and the plots of the frequency versus transmission coefficient are obtained. As a result of the numerical analysis, it is shown that if the source polarization is changed, polarization-independence of previous FSS design can be achieved only for normal incidence, which limits most FSS applications. But in our proposed structure, the better polarization-independency for arbitrary incident angle can be achieved. It is observed that the simulated result comes very close to the experimental result.

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An oxide filled extended trench gate super junction MOSFET structure

王彩琳, 孙军

2009 (3): 1231-1236. doi: 10.1088/1674-1056/18/3/065

摘要 ( 1300 )

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This paper proposes an oxide filled extended trench gate super junction (SJ) MOSFET structure to meet the need of higher frequency power switches application. Compared with the conventional trench gate SJ MOSFET, new structure has the smaller input and output capacitances, and the remarkable improvements in the breakdown voltage, on-resistance and switching speed. Furthermore, the SJ in the new structure can be realized by the existing trench etching and shallow angle implantation, which offers more freedom to SJ MOSFET device design and fabrication.

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Solution-based metal induced crystallization of a-Si

吴春亚, 李学冬, 赵淑云, 李娟, 孟志国, 熊绍珍, 张芳

2009 (3): 1237-1241. doi: 10.1088/1674-1056/18/3/066

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This paper investigates a simplified metal induced crystallization (MIC) of a-Si, named solution-based MIC (S-MIC). The nickel inducing source was formed on a-Si from salt solution dissolved in de-ionized water or ethanol. a-Si thin film was deposited with low pressure chemical vapour deposition or plasma enhanced chemical vapour deposition as precursor material for MIC. It finds that the content of nickel source formed on a-Si can be controlled by solution concentration and dipping time. The dependence of crystallization rate of a-Si on annealing time illustrated that the linear density of nickel source was another critical factor that affects the crystallization of a-Si, besides the diffusion of nickel disilicide. The highest electron Hall mobility of thus prepared S-MIC poly-Si is 45.6cm²/(V.s). By using this S-MIC poly-Si, thin film transistors and display scan drivers were made, and their characteristics are presented.

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A novel micro accelerometer with adjustable sensitivity based on resonant tunneling diodes

熊继军, 毛海央, 张文栋, 王楷群

2009 (3): 1242-1247. doi: 10.1088/1674-1056/18/3/067

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Resonant tunnelling diodes (RTDs) have negative differential resistance effect, and the current--voltage characteristics change as a function of external stress, which is regarded as meso-piezoresistance effect of RTDs. In this paper, a novel micro-accelerometer based on AlAs/GaAs/In_0.1Ga_0.9As/GaAs/AlAs RTDs is designed and fabricated to be a four-beam-mass structure, and an RTD-Wheatstone bridge measurement system is established to test the basic properties of this novel accelerometer. According to the experimental results, the sensitivity of the RTD based micro-accelerometer is adjustable within a range of 3 orders when the bias voltage of the sensor changes. The largest sensitivity of this RTD based micro-accelerometer is 560.2025 mV/g which is about 10 times larger than that of silicon based micro piezoresistive accelerometer, while the smallest one is 1.49135 mV/g.

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First principle study on the elastic and thermodynamic properties of TiB₂ crystal under high temperature

王春雷, 余本海, 霍海亮, 陈东, 孙海斌

2009 (3): 1248-1252. doi: 10.1088/1674-1056/18/3/068

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This paper predicts the elastic and thermodynamic characteristics of TiB₂ crystal through the method of density functional theory within the generalized gradient approximation (GGA). The five independent elastic constants (C_ij), the bulk modulus (B₀), the dependence of bulk modulus (B₀) on temperature T and pressure P and the coefficient of thermal expansion (α_L) at various temperatures have been evaluated and discussed. According to calculation, the bulk modulus will increase with increasing pressure while decrease with the increasing temperature. The coefficient of thermal expansion is consistent with the famous Grüneisen's law when the temperature is not too high. The obtained results agree well with the experimental and other theoretical results.

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Local structure distortion and spin Hamiltonian parameters of oxide-diluted magnetic semiconductor Mn-doped ZnO

杨子元

2009 (3): 1253-1260. doi: 10.1088/1674-1056/18/3/069

摘要 ( 1043 )

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The local structure distortion, the spin Hamiltonian (SH) parameters, and the electric fine structure of the ground state for Mn²⁺(3d⁵) ion in ZnO crystals are systematically investigated, where spin--spin (SS), spin--other--orbit (SOO) and orbit--orbit (OO) magnetic interactions, besides the well-known spin--orbit (SO) coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zero-field splitting (ZFS) parameter D, the fourth-order ZFS parameter (a-F), the Zeeman g-factors: g_// and g_⊥, and the energy differences of the ground state: \delta₁ and \delta₂ for Mn²⁺ in Mn²⁺: ZnO are in good agreement with experimental measurements when the three O^2- ions below the Mn²⁺ ion rotate by 1.085^o away from the [111]-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn²⁺ ions in Mn²⁺: ZnO crystals. It is found for Mn²⁺ ions in Mn²⁺: ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO～SS～SOO～OO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.

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Annealing effects on the microwave permittivity and permeability properties of Fe₇₉Si₁₆B₅ microwires and their micowave absorption performances

韩满贵, 欧雨, 梁迪飞, 邓龙江

2009 (3): 1261-1265. doi: 10.1088/1674-1056/18/3/070

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This paper reports that amorphous magnetic microwires (Fe₇₉Si₁₆B₅) have been fabricated by a melt-extraction technique and have been annealed at 600℃ and 750℃ respectively. Differential scanning calorimeter measurements show that nanocrystalline magnetic phase (α-Fe) has been formed in the amorphous matrix when it was annealed at 600℃. Hard magnetic phase (Fe₂B) was formed in the microwires annealed at 750℃, which increases the magnetic coercivity. Microwave permittivity and permeability are found to be dependent on the microstructures. The permittivity fitting results show that multi Lorentzian dispersion processes exist. For microwires annealed at 750℃, their resonance peaks due to the domain wall movements and natural resonance are found higher than those of microwires annealed at 600℃. The microwave absorption performance of microwires annealed at 600℃ is found better than microwires annealed at 750℃.

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Effect of growth temperature on morphology, structure and luminescence of Tb-doped BN thin films

刘泉林, 于广华, 姜勇

2009 (3): 1266-1269. doi: 10.1088/1674-1056/18/3/071

摘要 ( 1202 )

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This paper investigates the effect of growth temperature on morphology, structure and photoluminescence (PL) of Tb-doped boron nitride (BN) films grown by magnetron sputtering, and the relationships of growth-temperature-structure-PL by scanning electron microscopy, transmission electron microscopy and PL. The characteristic emission lines of the Tb³⁺ were observed in the PL spectra at room temperature. The 473-K-grown film is mainly consisted of amorphous BN particles. With the growth temperature increasing up to 1273 K, the amount of amorphous BN decreases, while the amount of turbostratic BN increases. Correspondingly, the PL intensities from the Tb³⁺ ions increase with the increase of temperature in the range of 473--1273 K.

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Analysis of space harmonic selectivity of period-varying folded waveguide

徐翱, 王文祥, 魏彦玉, 宫玉彬

2009 (3): 1270-1275. doi: 10.1088/1674-1056/18/3/072

摘要 ( 1000 )

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A period-varying folded waveguide is formed by varying the period of a folded waveguide. It has the advantages of the space harmonic selectivity and the wide bandwidth. However, the regularities of the variety of these period-varying folded waveguides are unavailable from the published papers. In order to solve this problem, the principle of the space harmonic selectivity of a period-varying folded waveguide is analysed, and the conditions to select the space harmonic for this slow wave system are obtained. In addition, the space harmonic selectivities for a linear period-varying folded waveguide and a hyperbolic sine-varying period folded waveguide are also analysed as examples.

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Amine-containing film deposited in pulsed dielectric barrier discharge at a high pressure and its cell adsorption behaviours

胡文娟, 谢芬艳, 陈强, 翁静

2009 (3): 1276-1282. doi: 10.1088/1674-1056/18/3/073

摘要 ( 928 )

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With monomer allylamine, amine-containing functional films were prepared in alternative current pulsed dielectric barrier discharge (DBD) at a high pressure. This paper analyses in detail the film properties and structures, such as hydrophilicity, compounds and microstructures as well as amine density by the water contact angle, Fourier transform infrared spectroscopy, atomic force microscopy, and ultraviolet--visible measurement. The influence of discharge parameters, in particular applied power, on amine density was investigated. As an application the cell adsorption behaviours on plasma polymerization films was performed in-vitro. The results show that at a high pressure pulsed DBD plasma can polymerize films with sufficient amine group on surface, through which the very efficient cell adsorption behaviours was demonstrated, and the high rate of cell proliferation was visualized.

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Fatigue life of metal treated by magnetic field

刘兆龙, 胡海云, 范天佑, 邢修三

2009 (3): 1283-1286. doi: 10.1088/1674-1056/18/3/074

摘要 ( 804 )

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This paper investigates theoretically the influence of magnetization on fatigue life by using non-equilibrium statistical theory of fatigue fracture for metals. The fatigue microcrack growth rate is obtained from the dynamic equation of microcrack growth, where the influence of magnetization is described by an additional term in the potential energy of microcrack. The statistical value of fatigue life of metal under magnetic field is derived, which is expressed in terms of magnetic field and macrophysical as well as microphysical quantities. The fatigue life of AISI 4140 steel in static magnetic field from this theory is basically consistent with the experimental data.

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Effects of electrostatic interactions and geometrical confinements on depletion interactions in charged colloidal system

黄立新, 肖长明, 胡苹, 高海峡

2009 (3): 1287-1293. doi: 10.1088/1674-1056/18/3/075

摘要 ( 738 )

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In a charged colloidal system, the influence on depletion interaction between two like-charged macro-ions is studied through Monte Carlo simulation in this paper. The numerical results show that this depletion force is affected by both the electrostatic interactions between charged spheres and charged plates and by the geometrical factor of the two charged plates, and they further indicate that the influence of geometrical confinement on the depletion interaction is larger than that of electrostatic potential.

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Modeling of intercellular synchronization in the Drosophila circadian clock

王军威, 陈爱敏, 张家军, 苑占江, 周天寿

2009 (3): 1294-1300. doi: 10.1088/1674-1056/18/3/076

摘要 ( 1006 )

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In circadian rhythm generation, intercellular signaling factors are shown to play a crucial role in both sustaining intrinsic cellular rhythmicity and acquiring collective behaviours across a population of circadian neurons. However, the physical mechanism behind their role remains to be fully understood. In this paper, we propose an indirectly coupled multicellular model for the synchronization of Drosophila circadian oscillators combining both intracellular and intercellular dynamics. By simulating different experimental conditions, we find that such an indirect coupling way can synchronize both heterogeneous self-sustained circadian neurons and heterogeneous mutational damped circadian neurons. Moreover, they can also be entrained to ambient light--dark (LD) cycles depending on intercellular signaling.

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