中国物理B

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A new local-world evolving network model

覃森, 戴冠中

2009 (2): 383-390. doi: 10.1088/1674-1056/18/2/001

摘要 ( 1258 )

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In some real complex networks, only a few nodes can obtain the global information about the entire networks, but most of the nodes own only local connections therefore own only local information of the networks. A new local-world evolving network model is proposed in this paper. In the model, not all the nodes obtain local network information, which is different from the local world network model proposed by Li and Chen (LC model). In the LC model, each node has only the local connections therefore owns only local information about the entire networks. Theoretical analysis and numerical simulation show that adjusting the ratio of the number of nodes obtaining the global information of the network to the total number of nodes can effectively control the valuing range for the power-law exponent of the new network. Therefore, if the topological structure of a complex network, especially its exponent of power-law degree distribution, needs controlling, we just add or take away a few nodes which own the global information of the network.

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Direct perturbation method for perturbed complex Burgers equation

程雪苹, 林机, 姚建明

2009 (2): 391-394. doi: 10.1088/1674-1056/18/2/002

摘要 ( 1297 )

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So far, Lou's direct perturbation method has been applied successfully to solve the nonlinear Schr?dinger equation(NLSE) hierarchy, such as the NLSE, the coupled NLSE, the critical NLSE, and the derivative NLSE. But to our knowledge, this method for other types of perturbed nonlinear evolution equations has still been lacking. In this paper, Lou's direct perturbation method is applied to the study of perturbed complex Burgers equation. By this method, we calculate not only the zero-order adiabatic solution, but also the first order modification.

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Conformal invariance and conserved quantities of non-conservative Lagrange systems by point transformations

刘畅, 梅凤翔, 郭永新

2009 (2): 395-399. doi: 10.1088/1674-1056/18/2/003

摘要 ( 1141 )

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This paper studies the conformal invariance by infinitesimal point transformations of non-conservative Lagrange systems. It gives the necessary and sufficient conditions of conformal invariance by the action of infinitesimal point transformations being Lie symmetric simultaneously. Then the Noether conserved quantities of conformal invariance are obtained. Finally an illustrative example is given to verify the results.

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The (ω/g)-expansion method and its application to Vakhnenko equation

李文安, 陈浩, 张国才

2009 (2): 400-404. doi: 10.1088/1674-1056/18/2/004

摘要 ( 1085 )

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This paper presents a new function expansion method for finding travelling wave solutions of a nonlinear evolution equation and calls it the (ω/g)-expansion method, which can be thought of as the generalization of (G'/G)-expansion given by Wang et al recently. As an application of this new method, we study the well-known Vakhnenko equation which describes the propagation of high-frequency waves in a relaxing medium. With two new expansions, general types of soliton solutions and periodic solutions for Vakhnenko equation are obtained.

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The constructive technique and its application in solving a nonlinear reaction diffusion equation

赖绍永, 郭云喜, 青音, 吴永宏

2009 (2): 405-410. doi: 10.1088/1674-1056/18/2/005

摘要 ( 1286 )

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A mathematical technique based on the consideration of a nonlinear partial differential equation together with an additional condition in the form of an ordinary differential equation is employed to study a nonlinear reaction diffusion equation which describes a real process in physics and in chemistry. Several exact solutions for the equation are acquired under certain circumstances.

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Effects of Dzyaloshinski--Moriya interaction and intrinsic decoherence on teleportation via a two-qubit Heisenberg XYZ model

胡小勉, 刘金明

2009 (2): 411-417. doi: 10.1088/1674-1056/18/2/006

摘要 ( 1200 )

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Quantum teleportation via the entangled channel composed of a two-qubit Heisenberg XYZ model with Dzyaloshinski--Moriya (DM) interaction in the presence of intrinsic decoherence has been investigated. We find that the initial state of the channel plays an important role in the teleported state and the average fidelity of teleportation. When the initial channel is in the state |ψ ₁(0)>=a|00> +b|11>, the average fidelity is equal to 1/3 constantly, which is independent of the DM interaction and the intrinsic decoherence effect. But when the channel is initially in the state |ψ ₂(0)> =c|01> +d|10>, the average fidelity is always larger than 2/3. Moreover, under a certain condition, the average fidelity can be enhanced by adjusting the DM interaction, and the intrinsic decoherence leads to a suppression of the fluctuation of the average fidelity.

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Quantum entanglement and nonlocality properties of two-mode Gaussian squeezed states

向少华, 邵彬, 宋克慧

2009 (2): 418-425. doi: 10.1088/1674-1056/18/2/007

摘要 ( 1210 )

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Quantum entanglement and nonlocality properties of a family of two-mode Gaussian pure states have been investigated. The results show that the entanglement of these states is determined by both the two-mode squeezing parameter and the difference of the two single-mode squeezing parameters. For the same two-mode squeezing parameter, these states show larger entanglement than the usual two-mode squeezed vacuum state. The violation of Bell inequality depends strongly on all the squeezing parameters of these states and disappears completely in the limit of large squeezing. In particular, these states can exhibit much stronger violation of local realism than two-mode squeezed vacuum state in the range of experimentally available squeezing values.

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A quantum network for implementation of the optimal quantum cloning

戴结林, 张文海

2009 (2): 426-429. doi: 10.1088/1674-1056/18/2/008

摘要 ( 1203 )

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This paper presents a quantum network to implement the optimal 1→2 quantum cloning in 2 dimensions, including the optimal asymmetric universal, the optimal symmetric phase-covariant, and the asymmetric real state cloning. By only choosing different angles of the single-qubit rotations, the quantum network can implement three optimal quantum cloning.

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Decoherence of qubits: results beyond Markovian approximation

李铁夫, 游建强, 刘建设, 李志坚

2009 (2): 430-434. doi: 10.1088/1674-1056/18/2/009

摘要 ( 1230 )

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In this paper the master equation method is used to calculate the relaxation and decoherence times of a qubit. The results are beyond Markovian approximation, where the noise spectrum is assumed to be wide-band, so that they are valid for not only the wide- but also the narrow-band noises, which may be the main decoherence source in solid-state qubits. Moreover, for some special cases, analytical results can be achieved, which are consistent with those derived by others.

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Quantum secure direct communication with Greenberger--Horne--Zeilinger-type state (GHZ state) over noisy channels

张小龙, 张月霞, 魏华

2009 (2): 435-439. doi: 10.1088/1674-1056/18/2/010

摘要 ( 1390 )

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We propose a quantum error-rejection scheme for direct communication with three-qubit quantum codes based on the direct communication of secret messages without any secret key shared in advance. Given the symmetric and independent errors of the transmitted qubits, our scheme can tolerate a bit of error rate up to 33.1%, thus the protocol is deterministically secure against any eavesdropping attack even in a noisy channel.

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Two simple schemes for implementing Toffoli gate via atom--cavity field interaction in cavity quantum electrodynamics

邵晓强, 陈丽, 张寿

2009 (2): 440-445. doi: 10.1088/1674-1056/18/2/011

摘要 ( 1215 )

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This paper proposes two schemes for implementing three-qubit Toffoli gate with an atom (as target qubit) sent through a two-mode cavity (as control qubits). The first scheme is based on the large-detuning atom--cavity field interaction and the second scheme is based on the resonant atom-field interaction. Both the situations with and without cavity decay and atomic spontaneous emission are considered. The advantages and the experimental feasibility of these two schemes are discussed.

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The influence of electric field on a parabolic quantum dot qubit

尹辑文, 肖景林, 于毅夫, 王子武

2009 (2): 446-450. doi: 10.1088/1674-1056/18/2/012

摘要 ( 1324 )

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This paper calculates the time evolution of the quantum mechanical state of an electron by using variational method of Pekar type on the condition of electric--LO-phonon strong coupling in a parabolic quantum dot. It obtains the eigenenergies of the ground state and the first-excited state, the eigenfunctions of the ground state and the first-excited state This system in a quantum dot may be employed as a two-level quantum system qubit. The superposition state electron density oscillates in the quantum dot with a period when the electron is in the superposition state of the ground and the first-excited state. It studies the influence of the electric field on the eigenenergies of the ground state, the first-excited state and the period of oscillation at the different electron--LO-phonon coupling constant and the different confinement length.

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Information entropy for static spherically symmetric black holes

蒋继建, 李传安

2009 (2): 451-456. doi: 10.1088/1674-1056/18/2/013

摘要 ( 1240 )

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By using the new equation of state density derived from the generalized uncertainty relation, the number of the quantum states near event horizon is obtained, with which then the information entropy of static spherically symmetric black holes has been discussed. It is found that the divergent integral of quantum states near the event horizon can be naturally avoided if using the new equation of state density without introducing the ultraviolet cut-off. The information entropy of black holes can be obtained precisely by the residue theorem, which is shown to be proportional to the horizon area. The information entropy of black holes obtained agrees with the Bechenstein--Hawking entropy when the suitable cutoff factor is adopted.

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The generalized Stefan--Boltzmann law of a rectilinear non-uniformly accelerating Kinnersley black hole

蒋继建, 孟庆苗, 王帅

2009 (2): 457-461. doi: 10.1088/1674-1056/18/2/014

摘要 ( 1120 )

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Using entropy density of Dirac field near the event horizon of a rectilinear non-uniformly accelerating Kinnersley black hole, the law for the thermal radiation of black hole is studied and the instantaneous radiation energy density is obtained. It is found that the instantaneous radiation energy density of a black hole is always proportional to the quartic of the temperature on event horizon in the same direction. That is to say, the thermal radiation of a black hole always satisfies the generalized Stefan--Boltzmann law. In addition, the derived generalized Stefan--Boltzmann coefficient is no longer a constant, but a dynamic coefficient related to the space--time metric near the event horizon and the changing rate of the event horizon in black holes.

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Hawking radiation from the charged and magnetized BTZ black hole via covariant anomaly

曾晓雄, 杨树政

2009 (2): 462-467. doi: 10.1088/1674-1056/18/2/015

摘要 ( 1208 )

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This paper discusses Hawking radiation from the charged and magnetized Ba?ados--Teitelboim--Zanelli (BTZ) black hole from the viewpoint of anomaly, initiated by Robinson and Wilczek recently. It reconstructs the electromagnetic field tensor and the Lagrangian of the field corresponding to the source with electric and magnetic charges to redefine an equivalent charge and gauge potential. It employs the covariant anomaly cancellation method to determine the compensating fluxes of charge flow and energy-momentum tensor, which are shown to match with those of the 2-dimensional blackbody radiation at the Hawking temperature exactly.

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A new traffic model with the consideration of coupling effect with two lanes

彭光含, 孙棣华, 何恒攀

2009 (2): 468-474. doi: 10.1088/1674-1056/18/2/016

摘要 ( 1238 )

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This paper introduces a new two-lane high-order continuum model by embedding the two delay time scales continuum traffic model presented by Xue (2003 Phys. Rev. E 68 066123) into the multi-lane model proposed by Daganzo (1997 Transpn. Res. B 31 83) with the consideration of the coupling effect between the vehicles of two lanes in instantaneous traffic situation and lane-change effect. In the novel model, the coupling effect of two lanes and phenomena of lane change, which were not discussed in Daganzo's model and Xue's model, are taken into account. Numerical simulation shows that it is in accordance with real traffic flow. This obviously indicates that the new phenomenon and behaviour are analogous results as single lane presented by Xue, and the proposed model is more reasonable on two lanes. Furthermore, the generation rate between two lanes is also investigated. The results show that the formation and diffusion of traffic shock wave can be better simulated on two lanes.

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Some new solutions derived from the nonlinear (2+1)-dimensional Toda equation---an efficient method of creating solutions

白成林, 张霞, 张立华

2009 (2): 475-481. doi: 10.1088/1674-1056/18/2/017

摘要 ( 1189 )

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This paper presents a new and efficient approach for constructing exact solutions to nonlinear differential--difference equations (NLDDEs) and lattice equation. By using this method via symbolic computation system MAPLE, we obtained abundant soliton-like and/or period-form solutions to the (2+1)-dimensional Toda equation. It seems that solitary wave solutions are merely special cases in one family. Furthermore, the method can also be applied to other nonlinear differential--difference equations.

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Complete and phase synchronization in a heterogeneous small-world neuronal network

韩芳, 陆启韶, Wiercigroch Marian, 季全宝

2009 (2): 482-488. doi: 10.1088/1674-1056/18/2/018

摘要 ( 1354 )

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Synchronous firing of neurons is thought to be important for information communication in neuronal networks. This paper investigates the complete and phase synchronization in a heterogeneous small-world chaotic Hindmarsh--Rose neuronal network. The effects of various network parameters on synchronization behaviour are discussed with some biological explanations. Complete synchronization of small-world neuronal networks is studied theoretically by the master stability function method. It is shown that the coupling strength necessary for complete or phase synchronization decreases with the neuron number, the node degree and the connection density are increased. The effect of heterogeneity of neuronal networks is also considered and it is found that the network heterogeneity has an adverse effect on synchrony.

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Phase transitions in cellular automata models of spatial susceptible--infected--resistant--susceptible epidemics

郑智贞, 王爱玲

2009 (2): 489-500. doi: 10.1088/1674-1056/18/2/019

摘要 ( 1204 )

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Spatially explicit models have become widely used in today's mathematical ecology and epidemiology to study the persistence of populations. For simplicity, population dynamics is often analysed by using ordinary differential equations (ODEs) or partial differential equations (PDEs) in the one-dimensional (1D) space. An important question is to predict species extinction or persistence rate by mean of computer simulation based on the spatial model. Recently, it has been reported that stable turbulent and regular waves are persistent based on the spatial susceptible--infected--resistant--susceptible (SIRS) model by using the cellular automata (CA) method in the two-dimensional (2D) space [Proc. Natl. Acad. Sci. USA 101, 18246 (2004)]. In this paper, we address other important issues relevant to phase transitions of epidemic persistence. We are interested in assessing the significance of the risk of extinction in 1D space. Our results show that the 2D space can considerably increase the possibility of persistence of spread of epidemics when the degree distribution of the individuals is uniform, i.e. the pattern of 2D spatial persistence corresponding to extinction in a 1D system with the same parameters. The trade-offs of extinction and persistence between the infection period and infection rate are observed in the 1D case. Moreover, near the trade-off (phase transition) line, an independent estimation of the dynamic exponent can be performed, and it is in excellent agreement with the result obtained by using the conjectured relationship of directed percolation. We find that the introduction of a short-range diffusion and a long-range diffusion among the neighbourhoods can enhance the persistence and global disease spread in the space.

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Electronic transmission of three-terminal pyrene molecular bridge

王利光, 张秀梅, Terence Kin Shun Wong, Katsunori Tagami, Masaru Tsukada

2009 (2): 501-505. doi: 10.1088/1674-1056/18/2/020

摘要 ( 1000 )

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This paper investigates theoretically the electronic transmission spectra of the three terminal pyrene molecular bridge and the quantum current distribution on each bond by the tight-binding model based on nonequilibrium Green's function and the quantum current density approach, in which one π molecular orbital is taken into account per carbon atom when the energy levels and HOMO-LUMO gap are obtained. The transmission spectra show that the electronic transmission of the three terminal pyrene molecular bridge depends obviously on the incident electronic energy and the pyrene eigenenergy. The symmetrical and oscillation properties of the transmission spectra are illustrated. A novel plus-minus energy switching function is found. The quantum current distribution shows that the loop currents inside the pyrene are induced, and some bond currents are much larger than the input and the output currents. The reasons why the loop currents and the larger bond currents are induced are the phase difference of the atomic orbits and the degeneracy of the molecular orbits. The calculations illustrate that the quantum current distributions are in good agreement with Kirchhoff quantum current conservation law.

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Emergence of spatiotemporal chaos arising from far-field breakup of spiral waves in the plankton ecological systems

刘权兴, 孙桂全, 靳祯, 李百炼

2009 (2): 506-515. doi: 10.1088/1674-1056/18/2/021

摘要 ( 1217 )

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It has been reported that the minimal spatially extended phytoplankton--zooplankton system exhibits both temporal regular/chaotic behaviour, and spatiotemporal chaos in a patchy environment. As a further investigation by means of computer simulations and theoretical analysis, in this paper we observe that the spiral waves may exist and the spatiotemporal chaos emerge when the parameters are within the mixed Turing--Hopf bifurcation region, which arises from the far-field breakup of the spiral waves over a large range of diffusion coefficients of phytoplankton and zooplankton. Moreover, the spatiotemporal chaos arising from the far-field breakup of spiral waves does not gradually invade the whole space of that region. Our results are confirmed by nonlinear bifurcation of wave trains. We also discuss ecological implications of these spatially structured patterns.

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Properties of asymmetrically evolved community networks

崔迪, 高自友, 郑建风

2009 (2): 516-521. doi: 10.1088/1674-1056/18/2/022

摘要 ( 969 )

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This paper studies a simple asymmetrically evolved community network with a combination of preferential attachment and random properties. An important issue about community networks is to discover the different utility increments of two nodes, where the utility is introduced to investigate the asymmetrical effect of connecting two nodes. On the other hand, the connection of two nodes in community networks can be classified as two nodes belonging to the same or to different communities. The simulation results show that the model can reproduce a power-law utility distribution P(u)～u^-σ, σ = 2 + 1/p, which can be obtained by using mean-field approximation methods. Furthermore, the model exhibits exponential behaviour with respect to small values of a parameter denoting the random effect in our model at the low-utility region and a power-law feature with respect to big values of this parameter at the high-utility region, which is in good agreement with theoretical analysis. This kind of community network can reproduce a unique utility distribution by theoretical and numerical analysis.

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Evidence of self-affine multiplicity fluctuation of particle production in ⁸⁴Kr--emulsion interactions at 1.7 A GeV

张东海, 李惠玲

2009 (2): 522-530. doi: 10.1088/1674-1056/18/2/023

摘要 ( 1147 )

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Self-affine multiplicity fluctuation is investigated by using the two-dimensional factorial moment methodology and the concept of the Hurst exponent (H). Investigation on the experimental data of compound particles and target fragments emitted in ⁸⁴Kr--AgBr interactions at 1.7 A GeV reveals that the best power law behaviours are exhibited at H=0.7 and 0.6 respectively, and the data for shower particles produced in ⁸⁴Kr--emulsion interactions at 1.7 A GeV indicate that the best power law behaviour occurs at H=0.6, all of which show the self-affine multiplicity fluctuation patterns. The multifractality and the non-thermal phase transition occurring during producing the compound particles, the target fragments, and the shower particles in the ⁸⁴Kr--AgBr interaction and the ⁸⁴Kr--emulsion interaction are also discussed. The multifractality is observed during producing compound particles, target fragments, and shower particles. In the target fragment production, an evidence of non-thermal phase transition is observed, but in the shower particle production and the compound particle production, no evidence of non-thermal phase transition is observed.

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Helium production from ⁸⁴Kr-- and ¹⁹⁷Au--emulsion interactions at high energies

张东海, 程锦霞, 成宾, 王芳, 王琦, 张海青, 许蓉, 贾会明, 李雪琴

2009 (2): 531-536. doi: 10.1088/1674-1056/18/2/024

摘要 ( 1822 )

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The properties of the relativistic helium fragments produced in interactions of ⁸⁴Kr at 1.8 A GeV and ¹⁹⁷Au at 10.7 A GeV in emulsion are investigated. The experimental results are compared with those obtained from various projectiles with emulsion collisions at different energies. It is found that the multiplicity distribution of helium projectile fragments (HPFs) is well described by the Koba--Nielsen--Olesen (KNO) scaling presentation. The second Mueller moment f₂ of the HPF multiplicity distribution is independent of the projectile energy for the same projectile, but it is dependent on the projectile mass number. The value of f₂ increases with the increase of projectile mass number A_p. The negative value of f₂, when A_p<69, means that the emission of HPFs is anticorrelated, but positive value of f₂, when A_p>69, refers to that the emission of HPFs is correlated. The non-zero f₂ moment in this experiment implies the strong correlation existing between the HPFs.

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Nuclear fusion from Coulomb explosions of deuterated methane clusters subjected to ultraintense femtosecond laser pulses

卢海洋, 王成, 陈光龙, Kim Cheol-Jung, 刘建胜, 倪国权, 李儒新, 徐至展

2009 (2): 537-541. doi: 10.1088/1674-1056/18/2/025

摘要 ( 1290 )

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This paper reports that Coulomb explosions taken place in the experiment of heteronuclear deuterated methane clusters ((CD₄)₂) in a gas jet subjected to intense femtosecond laser pulses (170mJ, 70fs) have led to table-top laser driven DD nuclear fusion. The clusters produced in supersonic expansion had an average size of about 5nm in radius and the laser intensity used was 3×10¹⁷W/cm².The measured maximum and average energies of deuterons produced in the laser--cluster interaction were 60 and 13.5keV, respectively. From DD collisions of energetic deuterons, a yield of 2.5(±0.4)×10⁴ fusion neutrons of 2.45MeV per shot was realized, giving rise to a neutron production efficiency of about 1.5×10⁵ per joule of incident laser pulse energy. Theoretical calculations were performed and a fairly good agreement of the calculated neutron yield with that obtained from the present experiment was found.

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A generic procedure for determining atomic LS spectral terms and their LS eigenfunctions

熊庄, Bacalis N C

2009 (2): 542-548. doi: 10.1088/1674-1056/18/2/026

摘要 ( 1061 )

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This paper develops a Fortran code which is capable to construct the simplest LS eigenfunctions for desired symmetry and determine all permitted atomic LS spectral terms under a given orbital occupancy by implementing and extending the Schaefer and Harris method. Examples (in some cases the most complete set to date) of multiple spectroscopic terms of LS coupling of atomic states for both non-equivalent and equivalent electronic configurations are given. It also corrects a few observed errors from the recent literature.

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The theoretical character of the X¹∑⁺ and A¹∑⁺ states of ScN

白凤娟, 杨传路, 钱琪, 张玲

2009 (2): 549-552. doi: 10.1088/1674-1056/18/2/027

摘要 ( 1364 )

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This paper calculates the potential energy curves (PECs) of the ground state (X¹∑⁺) and excited state (A¹∑⁺) of ScN molecule by multireference configuration interaction method. The correct character of the PECs has been gripped while they had been improperly reported in the literature. Based on the PECs, the spectroscopic parameters and vibrational energy levels are determined, and compared with experimental data and other theoretical works available at the present.

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Calculated cross sections for the single ionization of atoms (N, Cu, As, Se, Sn, Sb, Te, I, Pb) by electron impact

侯育君, 程新路, 陈恒杰

2009 (2): 553-557. doi: 10.1088/1674-1056/18/2/028

摘要 ( 1367 )

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By correcting some primary parameters in the semi-classical Deutsch--M?rk (DM) formula, this paper calculates the absolute single electron-impact ionization cross sections of atoms N, Cu, As, Se, Sn, Sb, Te, I and Pb from threshold to 10000eV. The calculated cross sections are compared with available experimental data and other theoretical results. An excellent agreement was achieved between the calculated and measured cross sections for these atoms over a wide range of impact energies.

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Investigations on analytic potential energy function, spectroscopic parameters and vibrational manifolds (J=0) of the SD⁺X³∑^- ion

张金平, 施德恒, 孙金锋, 刘玉芳, 朱遵略, 马恒

2009 (2): 558-564. doi: 10.1088/1674-1056/18/2/029

摘要 ( 1163 )

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This paper investigates the spectroscopic properties of the SD⁺X³∑^- ion by employing the coupled-cluster singles-doubles-approximate-triples [CCSD(T)] theory combining with the quintuple correlation-consistent basis set augmented with diffuse functions (aug-cc-pV5Z) of Dunning and co-workers. The accurate adiabatic potential energy function is obtained by the least-squares fitting method with the 100 ab initio points, which are calculated at the unrestricted CCSD(T)/aug-cc-pV5Z level of theory over the internuclear separation range from 0.09 to 2.46nm. Using the potential, it accurately determines the spectroscopic parameters (D_e, ω_eХ_e, α_e and B_e. The present D_e, R_e, ω_e, ω_eХ_e, α_e and B_e results are of 3.69119eV, 0.13644nm, 1834.949 cm^-1, 25.6208cm^-1, 0.1068cm^-1 and 4.7778cm^-1, respectively, which are in remarkably good agreement with the experimental findings. A total of 29 vibrational states has been predicted by numerically solving the radial Schr?dinger equation of nuclear motion when the rotational quantum number J equals zero. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reported when J=0 for the first time, which are in good accord with the measurements wherever available.

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Conformal optical design with combination of static and dynamic aberration corrections

李岩, 李林, 黄一帆, 刘家国

2009 (2): 565-570. doi: 10.1088/1674-1056/18/2/030

摘要 ( 1326 )

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Conformal domes that are shaped to meet aerodynamic requirements can increase range and speed for the host platform. Because these domes typically deviate greatly from spherical surface descriptions, a variety of aberrations are induced which vary with the field-of-regard (FOR) angle. A system for correcting optical aberrations created by a conformal dome has an outer surface and an inner surface. Optimizing the inner surface is regard as static aberration correction. A deformable mirror is placed at the position of the secondary mirror in the two-mirror all reflective imaging system, which is the dynamic aberration correction. An ellipsoidal MgF2 conformal dome with a fineness ratio of 1.0 is designed as an example. The FOR angle is 0°--30°, and the design wavelength is 4μm. After the optimization at 7 zoom positions by using the design tools Code V, the root-mean-square (RMS) spot size is reduced to approximately 0.99 to 1.48 times the diffraction limit. The design results show that the performances of the conformal optical systems can be greatly improved by the combination of the static correction and the dynamic correction.

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Propagation of the off-axis superposition of partially coherent beams through atmospheric turbulence

张恩涛, 季小玲, 吕百达

2009 (2): 571-580. doi: 10.1088/1674-1056/18/2/031

摘要 ( 1260 )

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The propagation properties of the off-axis superposition of partially coherent beams through atmospheric turbulence and their beam quality in terms of the mean-squared beam width w(z) and the power in the bucket (PIB) are studied in detail, where the effects of partial coherence, off-axis beam superposition and atmospheric turbulence are considered. The analytical expressions for the intensity, the beam width and the PIB are derived, and illustrative examples are given numerically. It is shown that the maximum intensity I_max and the PIB decrease and w(z) increases as the refraction index structure constant C_n² increases. Therefore, the turbulence results in a degradation of the beam quality. However, the resulting partially coherent beam with a smaller value of spatial correlation parameter γ and larger values of separate distance x_d and beam number M is less affected by the turbulence than that with a larger value of γ and smaller values of x_d and M. The main results obtained in this paper are explained physically.

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Scintillation index of optical wave propagating in turbulent atmosphere

饶瑞中

2009 (2): 581-587. doi: 10.1088/1674-1056/18/2/032

摘要 ( 1423 )

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A concise expression of the scintillation index is proposed for a plane optical wave and a spherical optical wave both propagating in a turbulent atmosphere with a zero inner scale and a finite inner scale under an arbitrary fluctuation condition. The expression is based on both the results in the Rytov approximation under a weak fluctuation condition and the numerical results in a strong fluctuation regime. The maximum value of the scintillation index and its corresponding Rytov index are evaluated. These quantities are affected by the ratio of the turbulence inner scale to the Fresnel size.

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Robust generation of high-fidelity entangled states for multiple atoms

林丽华

2009 (2): 588-592. doi: 10.1088/1674-1056/18/2/033

摘要 ( 1309 )

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A scheme is presented for generating entangled states of multiple atoms in a cavity. In the scheme the atoms simultaneously interact with a cavity mode, with the first atom driven by two classical fields and the other atoms driven by a classical field. Our scheme is valid even if the cavity decay rate is larger than the effective coupling strength, which is important for experiment. The generation of entangled states is conditional on the detection of a photon decaying from the cavity and thus the fidelity of the entangled state is insensitive to the detection inefficiency. Furthermore, the scheme can be applied to the case with any number of atoms in principle.

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Generation of entanglement molecules via weak coherent field in cavity QED

苏万钧, 杨贞标, 吴怀志

2009 (2): 593-596. doi: 10.1088/1674-1056/18/2/034

摘要 ( 1090 )

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This paper presents a method for generating entanglement molecules, which is introduced by Dur (2001 Phys. Rev. A). In this scheme, N ladder-type three-level atoms are sent through a resonant weak coherent cavity field, then the system states are measured. And the system field may collapse onto some possible types of entanglement molecules. Meanwhile it discusses about the interaction time from the experimental point of view, and compare the result with the previous scheme proposed by Huang (2004 J. Phys. B: At. Mol. Opt. Phys.).

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Decoherence of two-qubit system in a non-Markovian squeezed reservoir

王发强, 张智明, 梁瑞生

2009 (2): 597-603. doi: 10.1088/1674-1056/18/2/035

摘要 ( 1177 )

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The decoherence of two initially entangled qubits coupled with a squeezed vacuum cavity separately is investigated exactly. The results show that, first, in principle, the disentanglement time decreases with the increase of squeeze parameter r, due to the augmenting of average photon number of every mode in the squeezed vacuum cavity. Second, there appear entanglement revivals after the complete disentanglement for the case of even parity initial Bell state, while there occur the entanglement decrease and the entanglement revival before the complete disentanglement for the case of odd parity initial Bell state. The results are quite different from those for the case of qubits in a vacuum cavity.

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Wigner functions and tomograms of the even and odd binomial states

张晓燕, 王继锁, 孟祥国, 苏杰

2009 (2): 604-610. doi: 10.1088/1674-1056/18/2/036

摘要 ( 1167 )

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Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, the Wigner functions of the even and odd binomial states (EOBSs) are obtained. The physical meaning of the Wigner functions for the EOBSs is given by means of their marginal distributions. Moreover, the tomograms of the EOBSs are calculated by virtue of intermediate coordinate-momentum representation in quantum optics.

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Relation between Fresnel transform of input light field and the two-parameter Radon transform of Wigner function of the field

范洪义, 胡利云

2009 (2): 611-615. doi: 10.1088/1674-1056/18/2/037

摘要 ( 1298 )

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This paper proves a new theorem on the relationship between optical field Wigner function's two-parameter Radon transform and optical Fresnel transform of the field, i.e., when an input field ψ( x') propagates through an optical [ D( -B) ( -C) A] system, the energy density of the output field is equal to the Radon transform of the Wigner function of the input field, where the Radon transform parameters are D,B. It prove this theorem in both spatial-domain and frequency-domain, in the latter case the Radon transform parameters are A,C.

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Solitons in optical lattices with nonlocal nonlinearity

葛丽娟, 王奇, 申明, 施解龙, 孔茜, 侯鹏

2009 (2): 616-623. doi: 10.1088/1674-1056/18/2/038

摘要 ( 1137 )

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The propagation of spatial solitons is systematically investigated in nonlocal nonlinear media with an imprinted transverse periodic modulation of the refractive index. Based on the variational principle and the infinitesimal approximation of Maclaurin series expansion, we obtain an analytical solution of such nonlocal spatial solitons and an interesting result that the critical power for such solitons propagation is smaller than that in uniform nonlocal self-focusing media. It is found that there exist thresholds in modulation period and lattice depth for such solitons. A stable spatial soliton propagation is maintained with proper adjustment of the modulation period and the lattice depth.

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Generation of time-dependent ultra-short optical pulse trains in the presence of self-steepening effect

钟先琼, 向安平

2009 (2): 624-629. doi: 10.1088/1674-1056/18/2/039

摘要 ( 1294 )

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Starting from the extended nonlinear Schr?dinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time related ultra-short optical pulse trains in an optical fibre are numerically simulated by adopting the split-step Fourier algorithm. The results show that the self-steepening effect can cause the characteristic of the pulse trains to vary with time, which is different from the self-steepening-free case where the generated pulse trains consist of single pulses which are identical in width, intensity, and interval, namely when pulses move a certain distance, they turn into the pulse trains within a certain time range. Moreover, each single pulse may split into several sub-pulses. And as time goes on, the number of the sub-pulses will decrease gradually and the pulse width and the pulse intensity will change too. With the increase of the self-steepening parameter, the distance needed to generate time-dependent pulse trains will shorten. In addition, for a large self-steepening parameter and at the distance where more sub-pulses appear, the corresponding frequency spectra of pulse trains are also wider.

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Effect of interstitial air holes on Bragg gratings in photonic crystal fibre with a Ge-doped core

张慧嘉, 李曙光, 侯蓝田

2009 (2): 630-635. doi: 10.1088/1674-1056/18/2/040

摘要 ( 1234 )

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The effect of interstitial air holes on Bragg gratings in photonic crystal fibre (PCF) with a Ge-doped core is numerically investigated by using the beam propagation method (BPM). It is shown that the interstitial air holes (IAHs) can make Bragg resonance wavelength λ_B shift a little towards short wavelengths and increase λ_B-λ₁ (the wavelength spacing between the main peak with Bragg resonance wavelength λ_B and the first side peak with wavelength λ₁ and the coupling coefficient к of Bragg resonance. Moreover, when the ratio of air hole diameter (d) to pitch (Λ), d/Λ, is small, IAHs can suppress the cladding mode resonance. When d/Λ is large, IAHs increase the number of mode that could strongly interact with the fundamental mode. By comparing the transmission spectral characteristics of PCF-based fibre Bragg grating (FBG) with IAHs with those without IAHs at the same air-filling fraction, it is clarified that the change of transmission spectral characteristics of PCF-based FBG with IAHs is not due to a simple change in air-filling fraction. It is also closely related to the distribution of interstitial air holes.

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Study on random and coherence states using a family of CML models

刘兆存

2009 (2): 636-645. doi: 10.1088/1674-1056/18/2/041

摘要 ( 1293 )

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A family of coupled map lattice (CML) models has been developed to simulate the interaction of convection, diffusion and dispersion in both weakly and strongly coupled cases. With variation of parameters, the models can simulate those systems of convection dominating, diffusion dominating, and dispersion dominating states. Not only coherent and turbulent properties as well as their interrelations, but also the transitional state between any modes with local coupling and global coupling are analysed to demonstrate the essential characteristics of any state. Numerical results show that the models are capable of simulating both layered coupling and stochastic mechanism, and thus can be conveniently used to analyse an initiative and driven coupled system. Results of numerical simulation also lead us to understand whether or not turbulence coherent structure is formed by modulation of wave packet. Finally, the duality of wave and particle characters of turbulence is illustrated in the numerical simulation.

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Characterizing uniform discharge in atmospheric helium by numerical modelling

吕博, 王新新, 罗海云, 梁卓

2009 (2): 646-651. doi: 10.1088/1674-1056/18/2/042

摘要 ( 1371 )

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One-dimensional fluid model of dielectric barrier discharge (DBD) in helium at atmospheric pressure was established and the discharge was numerically simulated. It was found that not only the spatial distributions of the internal parameters such as the electric field, the electron density and ion density are similar to those in a low-pressure glow discharge, but also the visually apparent attribute (light emission) is exactly the same as the observable feature of a low-pressure glow discharge. This confirms that the uniform DBD in atmospheric helium is a glow type discharge. The fact that the thickness of the cathode fall layer is about 0.5mm, much longer than that of a normal glow discharge in helium at atmospheric pressure, indicates the discharge being a sub-normal glow discharge close to normal one. The multipulse phenomenon was reproduced in the simulation and a much less complicated explanation for this phenomenon was given.

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Enhanced piezoresistivity in Ni--silicone rubber composites

常方高, 杨枫, 王少祥, 张娜, 宋桂林

2009 (2): 652-657. doi: 10.1088/1674-1056/18/2/043

摘要 ( 1029 )

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This paper reports that the nickel--silicone rubber composites with enhanced piezoresistivity were synthesized with much reduced nickel concentration. A large piezosensitivity of 0.716/kPa and a gauge factor of 600 have been obtained for a composite sample with filler-polymer ratio of 2.7:1 by weight. Measurements of resistance as a function of uniaxial force reveal that the piezoresistance arises predominantly from the internal heterogeneity of the material and the effect of geometrical changes of samples under pressure is neglectably small. The nonlinear current--voltage characteristic of the composite depends strongly on the filler content, the initial compression and the electrical current flowing in the sample. Ohmic behaviour has been observed only in the highly compressed samples. The breakdown strength decreases with increasing filler content of the composite. Both I-V and R-f characteristics indicates that the resistivity of the composites decreases with electrical field, suggesting that the composite may also be used to make voltage sensitive resistors for protecting circuits. All the experimental results favour a quantum tunnelling mechanism of conductivity. It finds that the concept `negative resistance', often used to describe the phenomena that current decreases with increasing voltage, is not appropriate and should be avoided.

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Pair interaction of bilayer-coated nanoscopic particles

张启义

2009 (2): 658-663. doi: 10.1088/1674-1056/18/2/044

摘要 ( 1201 )

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The pair interaction between bilayer membrane-coated nanosized particles has been explored by using the self-consistent field (SCF) theory. The bilayer membranes are composed of amphiphilic polymers. For different system parameters, the pair-interaction free energies are obtained. Particular emphasis is placed on the analysis of a sequence of structural transformations of bilayers on spherical particles, which occur during their approaching processes. For different head fractions of amphiphiles, the asymmetrical morphologies between bilayers on two particles and the inverted micellar intermediates have been found in the membrane fusion pathway. These results can benefit the fabrication of vesicles as encapsulation vectors for drug and gene delivery.

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Fast pore etching on high resistivity n-type silicon via photoelectrochemistry

包晓清, 葛道晗, 张圣, 李金鹏, 周萍, 焦继伟, 王跃林

2009 (2): 664-670. doi: 10.1088/1674-1056/18/2/045

摘要 ( 1094 )

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In this paper, five factors, namely the HF (hydrofluoric acid) concentration, field strength, illumination intensity as well as the oxidizing-power and conductivity of electrolytes were found to strongly affect the fast pore etching. The oxidizing power of aqueous HF electrolyte of different concentrations was especially measured and analysed. A positive correlation between optimal bias and HF concentration was generally observed and the relationship was semi-quantitatively interpreted. Pore density notably increased with enhanced HF-concentration or bias even on patterned substrates where 2D (two-dimensional) nuclei were densely pre-textured. The etch rate can reach 400μm/h and the aspect ratio of pores can be readily driven up to 250.

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Three-dimensional interfacial wave theory of dendritic growth: (I). multiple variables expansion solutions

陈永强, 唐熊忻, 徐鉴君

2009 (2): 671-685. doi: 10.1088/1674-1056/18/2/046

摘要 ( 1367 )

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Dendritic pattern formation at the interface between liquid and solid is a commonly observed phenomenon in crystal growth and solidification process. The theoretical investigation of dendritic growth is one of the most profound and highly challenging subjects in the broad areas of interfacial pattern formation, condensed matter physics and materials science, preoccupying many researchers from various areas. Some longstanding key issues on this subject finally gained a breakthrough in the late of last century, via the `{Interfacial Wave} (IFW) Theory' on the ground of systematical global stability analysis of the basic state of dendritic growth. The original form of the IFW theory mainly focus on the investigation of various axi-symmetric unsteady perturbed modes solutions around the axi-symmetric basic state of system of dendritic growth. In reality, the system may allow various non-axi-symmetric, unsteady perturbed states. Whether or not the system of dendritic growth allows some growing non-axi-symmetric modes? Will the stationary dendritic pattern be destroyed by some of such non-axi-symmetric modes? Or, in one word, what is the stability property of the system, once the non-axi-symmetric modes can be evoked? The answers for these questions are important for the solid foundation of IFW theory. The present work attempts to settle down these issues and develop a three-dimensional (3D) interfacial wave theory of dendritic growth. Our investigations verify that dendritic growth indeed allows a discrete set of non-axi-symmetric unstable global wave modes, which gives rise to a set of multiple arms spiral waves propagating along the Ivantsov's paraboloid.

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Three-dimensional interfacial wave theory of dendritic growth: (II). non-axi-symmetric global wave modes and selection criterion of pattern formation

陈永强, 唐熊忻, 徐鉴君

2009 (2): 686-698. doi: 10.1088/1674-1056/18/2/047

摘要 ( 1210 )

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This paper is the continuation of part (I), which completes the derivations of the 3D global wave modes solutions, yields the stability criterion and, on the basis of the results obtained, demonstrates the selection criterion of pattern formation.

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Solute distribution in KNbO₃ melt-solution and its effect on dendrite growth during rapid solidification

潘秀红, 金蔚青, 刘岩, 艾飞

2009 (2): 699-703. doi: 10.1088/1674-1056/18/2/048

摘要 ( 1126 )

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This paper reports that the rapid solidification of mixed Li₂B₄O₇ and KNbO₃ melted in a Pt loop heater has been performed experimentally by the method of quenching, and various morphologies of KNbO₃ crystals have been observed in different regions of the quenched melt-solution. Dendrites were formed in the central region where mass transfer is performed by diffusion, whereas polygonal crystals with smooth surface grew in the marginal region where convection dominates mass transport. Based on measurement of KNbO₃ concentration along crystal interface by electronic probe analysis, it finds the variety of crystal morphologies, which is the result of different solute distributions: in the central region the inhomogeneity of solute concentration is much sharper and morphological instability is easier to take place; nevertheless in the marginal region the concentration homogeneity has been greatly enhanced by convection which prevents the occurrence of morphological instability. Additional solute distribution in the melt along the primary dendrite trunk axis as well as that in mushy zones has also been determined. Results show that the solute concentration in the liquid increases linearly with distance from the trunk tip and more solutes were found to be concentrated in mushy zones. The closer the mushy zone is to trunk tip, the lower the solute concentration will be there.

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Specific heat of the non-centrosymmetric superconductor Re₃W

闫静, 单磊, 罗强, 汪卫华, 闻海虎

2009 (2): 704-708. doi: 10.1088/1674-1056/18/2/049

摘要 ( 1257 )

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The alloys of non-centrosymmetric superconductor, Re₃W, which were reported to have an α-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. 8, 265 (1959)] with T_c=9K, are prepared by arc melting. The values of ac susceptibility and the low-temperature specific heat of these alloys are measured. It is found that there are two superconducting phases coexisting in the samples with T_c1≈9K and T_c2≈7K, which are both non-centrosymmetric in structure as reported previously. By analysing the specific heat data measured in various magnetic fields down to a temperature of 1.8K, we find that the absence of the inversion symmetry does not lead to an obvious deviation from an s$-wave pairing symmetry in Re₃W.

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Dynamic behaviour of the icosahedral Al--Pd--Mn quasicrystal with a Griffith crack

王晓芳, 范天佑, 祝爱玉

2009 (2): 709-714. doi: 10.1088/1674-1056/18/2/050

摘要 ( 1166 )

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The dynamic response of an icosahedral Al--Pd--Mn quasicrystal with a Griffith crack to impact loading is investigated in this paper. The elastohydrodynamic model for the wave propagation and diffusion together with their interaction is adopted. Numerical results of stress, displacement and dynamic stress intensity factors are obtained by using the finite difference method. The effects of wave propagation, diffusion and phonon--phason coupling on the quasicrystal in the dynamic process are discussed in detail, where the phason dynamics is explored particularly.

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The quantum pressure correction to the excitation spectrum of the trapped superfluid Fermi gases in a BEC-BCS crossover

董行, 马永利

2009 (2): 715-725. doi: 10.1088/1674-1056/18/2/051

摘要 ( 1238 )

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Using quantum hydrodynamic approaches, we study the quantum pressure correction to the collective excitation spectrum of the interacting trapped superfluid Fermi gases in the BEC-BCS crossover. Based on a phenomenological equation of state, we derive hydrodynamic equations of the system in the whole BEC-BCS crossover regime. Beyond the Thomas--Fermi approximation, expressions of the frequency corrections of collective modes for both spherical and axial symmetric traps excited in the BEC-BCS crossover are given explicitly. The corrections of the eigenfrequencies due to the quantum pressure and their dependence on the inverse interaction strength, anisotropic parameter and particle numbers of the condensate are discussed in detail.

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A study on strain affecting electronic structures and optical properties of wurtzite Mg_0.25 Zn_0.75O by first-principles

史力斌, 李明标, 任骏原, 王立锦, 徐翠艳

2009 (2): 726-733. doi: 10.1088/1674-1056/18/2/052

摘要 ( 1229 )

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We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg_0.25Zn_0.75O. The calculation is carried out in a-axis and c-axis strain changing in the range from 0.3 to --0.2 in intervals of 0.1. The results calculated from density of states show that the bottom of conduction band is always dominated by Zn 4s and the top of valence band is always dominated by O 2p in a-axis and c-axis strain. Zn 4s will shift to higher energy range when a-axis strain changes in the range from 0.3 to 0, and then shift to lower energy range when a-axis strain changes in the range from 0 to --0.2. But Zn 4s will always shift to higher energy range when c-axis strain changes in the range from 0.3 to --0.2. The variations of band gap calculated from band structure and absorption spectra are also investigated, which are consistent with the results obtained from density of states. In addition, we analyse and discuss the imaginary part of the dielectric function ε₂.

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Structural feature and electronic property of an (8, 0) carbon--silicon carbide nanotube heterojunction

刘红霞, 张鹤鸣, 胡辉勇, 宋久旭

2009 (2): 734-737. doi: 10.1088/1674-1056/18/2/053

摘要 ( 1241 )

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A supercell of a nanotube heterojunction formed by an (8, 0) carbon nanotube (CNT) and an (8, 0) silicon carbide nanotube (SiCNT) is established, in which 96 C atoms and 32 Si atoms are included. The geometry optimization and the electronic property of the heterojunction are implemented through the first-principles calculation based on the density functional theory (DFT). The results indicate that the structural rearrangement takes place mainly on the interface and the energy gap of the heterojunction is 0.31eV, which is narrower than those of the isolated CNT and the isolated SiCNT. By using the average bond energy method, the valence band offset and the conduction band offset are obtained as 0.71 and --0.03eV, respectively.

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First-principles calculations of elasticity and thermodynamic properties of LaNi₅ crystal under pressure

陈东, 陈敬东, 赵丽华, 王春雷, 余本海, 施德恒

2009 (2): 738-743. doi: 10.1088/1674-1056/18/2/054

摘要 ( 1186 )

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This paper investigates the equilibrium lattice parameters, heat capacity, thermal expansion coefficient, bulk modulus and its pressure derivative of LaNi₅ crystal by using the first-principles plane-wave pseudopotential method in the GGA-PBE generalized gradient approximation as well as the quasi-harmonic Debye model. The dependences of bulk modulus on temperature and on pressure are investigated. For the first time it analyses the relationships between bulk modulus B and temperature T up to 1000K, the relationship between bulk modulus B and pressure at different temperatures are worked out. The pressure dependences of heat capacity C_v and thermal expansion α at various temperatures are also analysed. Finally, the Debye temperatures of LaNi₅ at different pressures are successfully obtained. The calculated results are in excellent agreement with the experimental data.

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First-principles calculation of elastic and thermodynamic properties of Ni₂MnGa Heusler alloy

徐国亮, 马建忠, 陈敬东, 陈东, 余本海, 施德恒

2009 (2): 744-748. doi: 10.1088/1674-1056/18/2/055

摘要 ( 1465 )

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The equilibrium lattice parameter, heat capacity, thermal expansion coefficient and bulk modulus of Ni₂MnGa Heusler alloy are successfully obtained using the first-principles plane-wave pseudopotential (PW-PP) method as well as the quasi-harmonic Debye model. We analyse the relationship between bulk modulus B and temperature T up to 800 K and obtain the relationship between bulk modulus B and pressure at different temperatures. It is found that the bulk modulus B increases monotonically with increasing pressure and decreases with increasing temperature. The pressure dependence of heat capacity C_v and thermal expansion α at various temperatures are also analysed. Finally, the Debye temperature of Ni₂MnGa is determined from the non-equilibrium Gibbs function. Our calculated results are in excellent agreement with the experimental data.

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The influence of the Dresselhaus spin--orbit coupling on the tunnelling magnetoresistance in ferromagnet/ insulator /semiconductor/ insulator /ferromagnet tunnel junctions

王晓华, 安兴涛, 刘建军

2009 (2): 749-756. doi: 10.1088/1674-1056/18/2/056

摘要 ( 1224 )

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This paper investigates the effect of Dresselhaus spin--orbit coupling on the spin-transport properties of ferromagnet/insulator/semiconductor/insulator/ferromagnet double-barrier structures. The influence of the thickness of the insulator between the ferromagnet and the semiconductor on the polarization is also considered. The obtained results indicate that (i) the polarization can be enhanced by reducing the insulator layers at zero temperature, and (ii) the tunnelling magnetoresistance inversion can be illustrated by the influence of the Dresselhaus spin--orbit coupling effect in the double-barrier structure. Due to the Dresselhaus spin--orbit coupling effect, the tunnelling magnetoresistance inversion occurs when the energy of a localized state in the barrier matches the Fermi energy E_F of the ferromagnetic electrodes.

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Effective response of nonlinear cylindrical coated composites under external AC and DC electric field

沈玉艳, 陈小刚, 崔巍, 郝艳华, 李倩倩

2009 (2): 757-762. doi: 10.1088/1674-1056/18/2/057

摘要 ( 1190 )

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This paper uses the perturbation method to study effective response of nonlinear cylindrical coated composites. Under the external AC and DC electric field E_a(1 + sinωt), the local potentials of composites at all harmonic frequencies are induced. An effective nonlinear response to composite is given for the cylindrical coated inclusions in the dilute limit.

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Thermal analytic model of current gain for bipolar junction transistor-bipolar static induction transistor compound device

张有润, 张波, 李泽宏, 赖昌菁, 李肇基

2009 (2): 763-767. doi: 10.1088/1674-1056/18/2/058

摘要 ( 1182 )

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This paper proposes a thermal analytical model of current gain for bipolar junction transistor-bipolar static induction transistor (BJT-BSIT) compound device in the low current operation. It also proposes a best thermal compensating factor to the compound device that indicates the relationship between the thermal variation rate of current gain and device structure. This is important for the design of compound device to be optimized. Finally, the analytical model is found to be in good agreement with numerical simulation and experimental results. The test results demonstrate that thermal variation rate of current gain is below 10% in 25℃--85℃ and 20{\%} in -55℃--25℃.

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Characteristics of high-quality HfSiON gate dielectric prepared by physical vapour deposition

许高博, 徐秋霞

2009 (2): 768-772. doi: 10.1088/1674-1056/18/2/059

摘要 ( 1422 )

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This paper presents a method using simple physical vapour deposition to form high-quality hafnium silicon oxynitride (HfSiON) on ultrathin SiO₂ buffer layer. The gate dielectric with 10? (1?= 0.1 nm) equivalent oxide thickness is obtained. The experimental results indicate that the prepared HfSiON gate dielectric exhibits good physical and electrical characteristics, including very good thermal stability up to 1000℃, excellent interface properties, high dielectric constant (k=14) and low gate-leakage current (I_g=1.9×10^-3A/cm² @V_g=V_fb-1V for EOT of 10?). TaN metal gate electrode is integrated with the HfSiON gate dielectric.The effective work function of TaN on HfSiON is 4.3eV, meeting the requirements of NMOS for the metal gate. And, the impacts of sputtering ambient and annealing temperature on the electrical properties of HfSiON gate dielectric are investigated.

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Columnar growth of crystalline silicon films on aluminium-coated glass by inductively coupled plasma CVD at room temperature

王金晓, 秦艳丽, 闫恒庆, 高平奇, 栗军帅, 尹旻, 贺德衍

2009 (2): 773-777. doi: 10.1088/1674-1056/18/2/060

摘要 ( 1229 )

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Silicon films were grown on aluminium-coated glass by inductively coupled plasma CVD at room temperature using a mixture of SiH₄ and H₂ as the source gas. The microstructure of the films was evaluated using Raman spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the films are composed of columnar grains and their surfaces show a random and uniform distribution of silicon nanocones. Such a microstructure is highly advantageous to the application of the films in solar cells and electron emission devices. Field electron emission measurement of the films demonstrated that the threshold field strength is as low as ～9.8V/μm and the electron emission characteristic is reproducible. In addition, a mechanism is suggested for the columnar growth of crystalline silicon films on aluminium-coated glass at room temperature.

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Effect of hydrogenation time on magnetic and electrical properties of polycrystalline Si_0.956Mn_0.044:B thin films

刘兴翀, 陆智海, 林应斌, 王剑峰, 路忠林, 吕丽娅, 张凤鸣, 都有为

2009 (2): 778-782. doi: 10.1088/1674-1056/18/2/061

摘要 ( 1145 )

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This paper reports that polycrystalline Si_0.956Mn_0.044:B films have been prepared by cosputtering deposition followed by rapid thermal annealing for crystallization. The polycrystalline thin films were treated by hydrogen plasma excited with approach of radio-frequency plasma enhanced chemical vapour deposition for different time of 10 minutes, 15 minutes and 40 minutes. After hydrogenation, the structural properties of the films do not show any change, while both the saturation magnetization and the hole concentration in the films increase at first, then decrease with the increase of hydrogenation time. The obvious correlation between the magnetic properties and the transport properties of the polycrystalline Si_0.956Mn_0.044:B films suggests that a mechanism of hole-mediated ferromagnetism is believed to exist in Si-based diluted magnetic semiconductors.

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Fano--Kondo effect in the T-shaped double quantum dots coupled to ferromagnetic leads

侯涛, 吴绍全, 毕爱华, 羊富彬, 陈嘉峰, 樊梦

2009 (2): 783-789. doi: 10.1088/1674-1056/18/2/062

摘要 ( 1424 )

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Using an equation-of-motion technique, we theoretically study the Fano--Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of states in this system with both parallel and antiparallel lead-polarization alignments, and our results reveal that the interdot coupling, the spin-polarized strength and the energy level of the side coupled quantum dot greatly influence the density of states of the central quantum dot. This system is a possible candidate for spin valve transistors and may have potential applications in the spintronics.

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Thermally activated magnetization reversal in magnetic tunnel junctions

周广宏, 王寅岗, 祁先进, 李子全, 陈建康

2009 (2): 790-794. doi: 10.1088/1674-1056/18/2/063

摘要 ( 1257 )

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In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.

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Lateral-field-excitation properties of LiNbO₃ single crystal

王文炎, 张超, 张志甜, 刘岩, 冯冠平

2009 (2): 795-802. doi: 10.1088/1674-1056/18/2/064

摘要 ( 1049 )

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LiNbO₃ has been found attractive for lateral field excitation (LFE) applications due to its high piezoelectric coupling. In this paper, bulk acoustic wave propagation properties for LiNbO₃ single crystal excited by a lateral electric field have been investigated using the extended Christoffel--Bechmann method. It is found that the LFE piezoelectric coupling factor for c mode reaches its maximum value of 95.46% when ψ = 0° for both (yxl)-58° and (yxwl)± 60°/58° LiNbO₃. The acoustic wave phase velocity of c mode TSM (thickness shear mode) changes from 3456m/s to 3983 m/s as a function of ψ. Here ψ represents the angle between the lateral electric field and the crystallographic X-axis in the substrate major surface. A 5MHz LFE device of (yxl)-58° LiNbO₃ with ψ=0° was designed and tested in air. A major resonance peak was observed with the motional resistance as low as 17Ω and the Q-factor value up to 10353. The test result is well in agreement with the theoretical analysis, and suggests that the LFE LiNbO₃ device can be a good platform for high performance resonator or sensor applications.

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Structure, ferroelectric and dielectric properties of Bi₂WO₆ with different bismuth content

王晓娟, 龚志强, 朱骏, 陈小兵

2009 (2): 803-809. doi: 10.1088/1674-1056/18/2/065

摘要 ( 1161 )

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This paper reports that the Bi₂WO₆ ferroelectric ceramics with excess Bi₂O₃ of 0.0, 2.0, 3.5 and 5.0wt.% of the stoichiometric composition are prepared by the conventional solid-state reaction method. Their microstructure, ferroelectric properties, the concentration and mobility of the defects have been analysed systematically. With increasing Bi content, the remnant polarization decreases, and the broken-down voltage increases. The optimum Bi excess, 3.5, lowers the oxygen vacancy concentration, while further Bi-addition brings about more defects. The activation energies fitted from cole-cole plots are 0.97eV, 1.07eV, 1.18eV, and 1.33eV, respectively. This suggests that the mobility of the defects is weakened by Bi-addition, which may be due to the increase of the ratio of the number of Bi₂O₂ layers to that of the perovskite blocks.

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The study of synchronization in the periodic nonuniform folded waveguide

徐翱, 王文祥, 魏彦玉, 宫玉彬

2009 (2): 810-814. doi: 10.1088/1674-1056/18/2/066

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The periodic nonuniform folded waveguides are special structures, the physical dimension of which is between the periodic folded waveguide and the tapering period folded waveguide. Therefore, the synchronization between the microwave and the electron beam can be maintained in the whole interaction process and the periods are not tapered. In comparison with the tapering period folded waveguide, the theoretical analysis and the technological requirements for this structure are more convenient. In order to study this structure, the space harmonics are analysed, the conditions to make the m-th space harmonic synchronizing with the electron beam in the whole interaction process are present, and the dispersion curve and the coupling impedance curve are obtained by the simulation software HFSS.

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Grain size reduction of copper subjected to repetitive uniaxial compression combined with accumulative fold

邹永涛, 雷力, 王赵, 王江华, 张伟, 贺端威

2009 (2): 815-820. doi: 10.1088/1674-1056/18/2/067

摘要 ( 974 )

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This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction (XRD), respectively. Our results show that the average grain size of samples decreases from about 830nm to 127nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.

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Effective first law of thermodynamics of black holes with two horizons

魏益焕

2009 (2): 821-824. doi: 10.1088/1674-1056/18/2/068

摘要 ( 1117 )

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For a black hole with two horizons, the effective entropy is assumed to be a linear combination of the two entropies of the outer and inner horizons. In terms of the effective thermodynamic quantities the effective Bekenstein-Smarr formula and the effective first law of thermodynamics are derived.

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Development of the spectrum of gamma-ray burst pulses influenced by the intrinsic spectral evolution and the curvature effect

覃一平

2009 (2): 825-844. doi: 10.1088/1674-1056/18/2/069

摘要 ( 1115 )

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The spectral evolution of gamma-ray burst pulses assumed to arise from the emission of fireballs is explored. It is found that due to the curvature effect, the integrated flux is well related to peak energy by a power law in the decaying phase of pulses, where the index is about 3, which does not depend on intrinsic emission and the Lorentz factor. The spectra of pulses in the decaying phase are slightly different from each other when different intrinsic spectral evolution patterns are considered, indicating that it is dominated by the curvature effect. In the rising phase, the integrated flux keeps increasing whilst the peak energy remains unchanged when the intrinsic emission bears an unchanged spectrum. Within this phase, the flux decreases with the increase of the peak energy for a hard-to-soft intrinsic spectrum, and for a soft-to-hard-to-soft intrinsic spectrum, the flux generally increases with the increase of the peak energy. An intrinsic soft-to-hard-to-soft spectral evolution within a co-moving pulse would give rise to a pulse-like evolutionary curve for the peak energy.

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