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    2004年, 第13卷, 第10期 刊出日期:2004-10-20 上一期    下一期
    GENERAL
    Reduced-order observer of singular system with unknown inputs
    吴健荣
    2004 (10):  1591-1596.  doi: 10.1088/1009-1963/13/10/001
    摘要 ( 1097 )   PDF(148KB) ( 627 )  
    For the general discrete singular system with unknown inputs, a new reduced-order observer is designed. A numerical example is presented to illustrate the design algorithms.
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    Electron behaviour in CH4/H2 gas mixture in electron-assisted chemical vapour deposition
    董丽芳, 马博琴, 王志军
    2004 (10):  1597-1600.  doi: 10.1088/1009-1963/13/10/002
    摘要 ( 1109 )   PDF(187KB) ( 415 )  
    The behaviour of electrons in CH$_{4}$/H$_{2}$ gas mixture in electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron drift velocity in gas mixture is obtained over a wide range of E/P (the ratio of the electric field to gas pressure) from 1500 to 300000 (V/m kPa$^{-1}$). The electron energy distribution and average energy under different gas pressure (0.1-20kPa) and CH_{4} concentration (0.5%-10.0%) are calculated. Their effects on the diamond growth are also discussed. It is believed that these results will be helpful to the selection of optimum experimental conditions for high quality diamond film deposition.
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    Phase shift of the population oscillation and population trapping
    张现周, 江红民, 饶建国, 李白文
    2004 (10):  1601-1605.  doi: 10.1088/1009-1963/13/10/003
    摘要 ( 1423 )   PDF(215KB) ( 389 )  
    Using our recently developed time-dependent multilevel approach, we have calculated the phase shift of the population oscillation of the excited potassium atom in frequency-modulated fields when the modulation amplitude is suddenly changed. The numerical results are in good agreement with the measurements. A new way of realizing population trapping is suggested.
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    The novel multi-solitary wave solution to the fifth-order KdV equation
    张翼, 陈登远
    2004 (10):  1606-1610.  doi: 10.1088/1009-1963/13/10/004
    摘要 ( 1230 )   PDF(164KB) ( 499 )  
    By using Hirota's method, the novel multi-solitary wave solutions to the fifth-order KdV equation are obtained. Furthermore, various new solitary wave solutions are also derived by a reconstructed bilinear B?cklund transformation.
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    Lie symmetries and non-Noether conserved quantities for Hamiltonian canonical equations
    傅景礼, 陈立群, 谢凤萍
    2004 (10):  1611-1614.  doi: 10.1088/1009-1963/13/10/005
    摘要 ( 1209 )   PDF(157KB) ( 519 )  
    This paper focuses on studying Lie symmetries and non-Noether conserved quantities of Hamiltonian dynamical systems in phase space. Based on the infinitesimal transformations with respect to the generalized coordinates and generalized momenta, we obtain the determining equations and structure equation of the Lie symmetry for Hamiltonian dynamical systems. This work extends the research of non-Noether conserved quantity for Hamilton canonical equations, and leads directly to a new type of non-Noether conserved quantities of the systems. Finally, an example is given to illustrate these results.
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    Lie symmetries and invariants of constrained Hamiltonian systems
    刘荣万, 陈立群
    2004 (10):  1615-1619.  doi: 10.1088/1009-1963/13/10/006
    摘要 ( 1343 )   PDF(151KB) ( 623 )  
    According to the theory of the invariance of ordinary differential equations under the infinitesimal transformations of group, the relations between Lie symmetries and invariants of the mechanical system with a singular Lagrangian are investigated in phase space. New dynamical equations of the system are given in canonical form and the determining equations of Lie symmetry transformations are derived. The proposition about the Lie symmetries and invariants are presented. An example is given to illustrate the application of the result in this paper.
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    The Lie symmetrical non-Noether conserved quantity of holonomic Hamiltonian system
    方建会, 廖永潘, 彭勇
    2004 (10):  1620-1622.  doi: 10.1088/1009-1963/13/10/007
    摘要 ( 1231 )   PDF(135KB) ( 976 )  
    In this paper, we study the Lie symmetrical non-Noether conserved quantity of a holonomic Hamiltonian system under the general infinitesimal transformations of groups. Firstly, we establish the determining equations of Lie symmetry of the system. Secondly, the Lie symmetrical non-Noether conserved quantity of the system is deduced. Finally, an example is given to illustrate the application of the result.
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    Surface waves in a vertically excited circular cylindrical container
    菅永军, 鄂学全, 张杰, 孟俊敏
    2004 (10):  1623-1630.  doi: 10.1088/1009-1963/13/10/008
    摘要 ( 1139 )   PDF(2647KB) ( 407 )  
    The nonlinear free surface amplitude equation, which has been derived from the inviscid fluid by solving the potential equation of water waves with a singular perturbation theory in a vertically oscillating rigid circular cylinder, is investigated successively in the fourth-order Runge-Kutta approach with an equivalent time-step. Computational results include the evolution of the amplitude with time, the characteristics of phase plane determined by the real and imaginary parts of the amplitude, the single-mode selection rules of the surface waves in different forced frequencies, contours of free surface displacement and corresponding three-dimensional evolution of surface waves, etc. In addition, the comparison of the surface wave modes is made between theoretical calculations and experimental measurements, and the results are reasonable although there are some differences in the forced frequency.
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    Instability of the vertically forced surface wave in a circular cylindrical container
    菅永军, 鄂学全
    2004 (10):  1631-1638.  doi: 10.1088/1009-1963/13/10/009
    摘要 ( 1406 )   PDF(448KB) ( 456 )  
    The nonlinear amplitude equation, which was derived by Jian Yongjun employing expansion of two-time scales in inviscid fluids in a vertically oscillating circular cylindrical vessel, is modified by introducing a damping term due to the viscous dissipation of this system. Instability of the surface wave is analysed and properties of the solutions of the modified equation are determined together with phase-plane trajectories. A necessary condition of forming a stable surface wave is obtained and unstable regions are illustrated. Research results show that the stable pattern of surface wave will not lose its stability to an infinitesimal disturbance.
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    GENERAL
    Using symbolic computation to construct travelling wave solutions to nonlinear partial differential equations
    李伟, 谢福鼎
    2004 (10):  1639-1643.  doi: 10.1088/1009-1963/13/10/010
    摘要 ( 1345 )   PDF(159KB) ( 645 )  
    Based upon the symbolic computation and the coupled projective Riccati equation, the tanh function method is further improved. As its applications, Wu-Zhang equation (which describes a (2+1)-dimensional dispersive long wave) and the (1+1)-dimensional dispersive long wave equation obtained from Wu-Zhang equation by scaling transformation and symmetry reduction are chosen to illustrate the validity of the proposed approach.
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    Preparation of arbitrary n-particle d-dimensional superposition states using only single qubit operations and CNOT gates
    王艳辉, 方卯发
    2004 (10):  1644-1648.  doi: 10.1088/1009-1963/13/10/011
    摘要 ( 1093 )   PDF(169KB) ( 424 )  
    In this article, using only single qubit operation and a CNOT gate, we propose a scheme for creating arbitrary n-particle d-dimensional superposition states including entangled states and give the relevant circuits for realizing this scheme.
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    GENERAL
    Coherent Landau states with gauge invariance
    田旭, 赵中云, 黎明发
    2004 (10):  1649-1651.  doi: 10.1088/1009-1963/13/10/012
    摘要 ( 1245 )   PDF(126KB) ( 356 )  
    Coherent states for the Landau system (planar charged particle moving in a uniform magnetic field) are developed. It is convenient to use these states to describe the circular motion of the charged particle. The results obtained do not depend on gauges.
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    A M?ssbauer study of the magnetic coupling in iron phosphorous trisulfides
    戴耀东, 王林, 杨亚新, 何云, 黄红波, 夏元复
    2004 (10):  1652-1656.  doi: 10.1088/1009-1963/13/10/013
    摘要 ( 1029 )   PDF(206KB) ( 562 )  
    The polycrystalline sample of layered compound FePS_3 has been investigated by using M?ssbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below T_N=120.5±1K. The M?ssbauer spectra below T_N indicate that the magnetization axis is perpendicular to the layer of FePS_3, and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Néel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model, and it can be interpreted on the basis of a crystal-field effect.
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    NUCLEAR PHYSICS
    Lattice-Boltzmann simulation of particle-laden flow over a backward-facing step
    陈胜, 施保昌, 柳朝晖, 贺铸, 郭照立, 郑楚光
    2004 (10):  1657-1664.  doi: 10.1088/1009-1963/13/10/014
    摘要 ( 1151 )   PDF(298KB) ( 557 )  
    This paper deals with the numerical simulation of gas-solid two-phase flows in an Eulerian-Lagrangian scheme. The particle tracks are calculated using a recently developed exponential Lagrangian scheme, and the approach presently used for the computation of fluid phase is based on a modified Lattice-BGK model. Different from earlier publications, the present study employs a two-way coupling mechanism to handle the interactions between carrier phase and dispersed phase in the model. This new model is applicable to simulating gas-solid two-phase flows. For example, based on the scheme, we have recaptured some phenomena of planar laminar particle-laden flow over a backward-facing step in this research, and found a new interesting phenomenon.
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    Lie algebraic analysis for the nonlinear transportof intense pulsed beams in electrostatics lenses
    吕建钦, 李金海
    2004 (10):  1665-1668.  doi: 10.1088/1009-1963/13/10/015
    摘要 ( 1116 )   PDF(157KB) ( 388 )  
    The Lie algebraic method is applied to the analysis of the nonlinear transport of an intense pulsed beam in cylindrically symmetrical electrostatic lenses, and particle orbits in a six-dimensional phase space (x, p_x, y, p_y, τ, p_τ) are obtained in the second order approximation. They can also be acquired in the third or higher order approximation if needed. In the analysis, we divide the electrostatic lenses into several segments. Each segment is considered as a uniform accelerating field, and each dividing point is treated as a thin lens. The particle distribution in a three-dimensional ellipsoid is of Gaussian type.
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    Absorption spectroscopy of cold caesium atoms confined in a magneto-optical trap
    闫树斌, 刘涛, 耿涛, 张天才, 彭堃墀, 王军民
    2004 (10):  1669-1673.  doi: 10.1088/1009-1963/13/10/016
    摘要 ( 1863 )   PDF(202KB) ( 549 )  
    Absorption spectra of cold caesium atoms confined in a magneto-optical trap are measured around D_2 line at 852nm with a weak probe beam. Absorption reduction dip due to electromagnetically induced transparency (EIT) effect induced by the cooling/trapping field in a V-type three-level system and a gain peak near the cycling transition are clearly observed. Several mechanisms mixed with EIT effect in a normal V-type three-level system are briefly discussed. A simple theoretical analysis based on a dressed-state model is presented for interpretation of the absorption spectra.
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    Preparation and spectral characterization of new Er3+-doped TeO2-B2O3-WO3-ZnO-ZnS glasses
    汪国年, 张军杰, 徐时清, 戴世勋, 胡丽丽, 姜中宏
    2004 (10):  1674-1678.  doi: 10.1088/1009-1963/13/10/017
    摘要 ( 1458 )   PDF(222KB) ( 532 )  
    Erbium-doped TeO_2-based oxysulfide glasses have been prepared in argon atmosphere in graphite crucibles. The results of thermal analysis and spectroscopic properties of Er^{3+} have been studied in terms of sulfide influence. As a function of composition, we have measured principally the optical absorption, spontaneous emission, and lifetime of the materials. Judd-Ofelt theory was introduced to calculate bandwidth and emission cross-section of Er^{3+}. The results demonstrate that addition of sulfide in tellurite glasses results in broad emission spectra, with high emission cross-section, slightly low emission lifetime and a comparatively high thermal stability as pure oxide glasses.
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    Transfer ionization of the isocharge sequence ion and Ar collisions
    蔡晓红, 于得洋, 曹柱荣, 卢荣春, 杨威, 邵曹杰, 陈熙萌
    2004 (10):  1679-1683.  doi: 10.1088/1009-1963/13/10/018
    摘要 ( 1235 )   PDF(176KB) ( 515 )  
    The ratios of transfer ionization to single capture for isocharge C^{q+}, N^{q+}, O^{q+}, Ne^{q+} ions on Ar atoms are measured by using position-sensitive and time-of-flight techniques. It is found that the ratio R_{1} increases with nuclear charge Z in a q=4 sequence, and the ratio R_{1} sequences have the minimum values at Z=7 and Z=8 in q=5 and q=6 sequences, respectively, and the ratio R_{1} decreases with the increase in the nuclear charge Z in a q=7 sequence. The results may be explained within the frame of the statistical model. It may be concluded that the transfer ionization depends remarkably upon the electronic structure of the projectile. The projectiles used in this study have the same charge state and velocity, but different electronic structures. The dependence of the ratio R_{1} on q is studied for Ne^{q+}-Ar collisions. The ratio R_{1} is found to increase as q increases for Ne^{q+}-Ar collisions. The measured dependence of the ratio R_{1} on q is compared with the calculation using the molecular Coulomb over-barrier model.
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    Electron impact ionization of large krypton clusters
    李邵辉, 李儒新, 倪国权, 徐至展
    2004 (10):  1684-1688.  doi: 10.1088/1009-1963/13/10/019
    摘要 ( 1323 )   PDF(201KB) ( 426 )  
    We show that the detection of ionization of very large van der Waals clusters in a pulsed jet or a beam can be realized by using a fast ion gauge. Rapid positive feedback electron impact ionization and fragmentation processes, which are initially ignited by electron impact ionization of the krypton clusters with the electron current of the ion gauge, result in the appearance of a progressional oscillation-like ion spectrum, or just of a single fast event under critical conditions. Each line in the spectrum represents a correlated explosion or avalanche ionization of the clusters. The phenomena have been analysed qualitatively along with a Rayleigh scattering experiment of the corresponding cluster jet.
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    Oscillation conditions of cw simultaneous dual-wavelength Nd:YAG laser for transitions 4F3/2-4I9/2 and 4F3/2-4I11/2
    李平雪, 李德华, 李春勇, 张治国
    2004 (10):  1689-1693.  doi: 10.1088/1009-1963/13/10/020
    摘要 ( 1220 )   PDF(186KB) ( 457 )  
    The operating condition of a cw simultaneous dual-wavelength Nd:YAG laser for both {}^4F_{3/2}-{}^4I_{9/2} (quasi-three-level system) and {}^4F_{3/2}-{}^4I_{11/2}(four-level system) transitions is studied. According to this condition, the cw simultaneous dual-wavelength at 1.06μm and 946 nm in Nd:YAG crystal has been realized experimentally through an adaptive coating design of the cavity mirrors. A total power output of 2.5W of the dual-wavelength at 946nm and 1.06μm has been achieved with an optical conversion efficiency 14.3%. The experimental results are in good agreement with the theoretical analysis.
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    CLASSICAL AREAS OF PHENOMENOLOGY
    Nonlinear cascade-configuration multi-wave mixing scheme based on electromagnetically induced transparency
    李家华, 杨文星, 彭菊村
    2004 (10):  1694-1699.  doi: 10.1088/1009-1963/13/10/021
    摘要 ( 1234 )   PDF(229KB) ( 449 )  
    A nonlinear optical cascade-configuration multi-wave mixing (CCMWM) scheme is presented and analysed for the generation of coherent light in a six-level atomic system in the context of electromagnetically induced transparency (EIT). A detailed semi-classical study of the propagation of the generated mixing and probe fields is demonstrated. We show by numerical simulations that EIT is capable of suppressing linear and nonlinear photon absorption. The analytical dependence of the generated mixing field on the probe field and the respective detuning is also predicted. Such a nonlinear optical process can be used for generating coherent short-wavelength radiation.
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    Preparation of multicomponent motional coherent and squeezed coherent states of a trapped ion
    李家华, 杨文星, 彭菊村
    2004 (10):  1700-1706.  doi: 10.1088/1009-1963/13/10/022
    摘要 ( 1190 )   PDF(188KB) ( 364 )  
    In this paper, we present a scheme for preparation of multicomponent motional coherent and squeezed coherent states of the quantized centre of mass of an ion trapped in a one-dimensional harmonic potential and driven by two travelling-wave laser beams tuned to the nth red and blue vibrational sidebands, respectively. In addition, our scheme also provides experimental possibility for quantum state engineering.
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    Measurement of the decoherence of a mesoscopic superposition of motional states of a trapped ion
    郑仕标
    2004 (10):  1707-1710.  doi: 10.1088/1009-1963/13/10/023
    摘要 ( 1168 )   PDF(138KB) ( 439 )  
    We propose a scheme to observe the decoherence of a mesoscopic superposition of two coherent states in the motion of a trapped ion. In the scheme the ion is excited by two perpendicular lasers tuned to the ion transition. The decoherence is revealed by the decrease of the correlation between two successive measurements of the internal state of the ion after relevant laser-ion interaction.
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    Effect of relaxation rate on population distribution, EIT and refraction in Λ and V systems
    孙庆青, 古英, 龚旗煌
    2004 (10):  1711-1716.  doi: 10.1088/1009-1963/13/10/024
    摘要 ( 1454 )   PDF(237KB) ( 464 )  
    In the three-level Λ-type and V-type systems, we find that the same pump-effect parameter R\left(=\dfrac{2|V_{c}|^{2}γ}{(ω_{ac}-ω_{c})^{2}+γ^{2}}\right) determines the population distributions, while the probe field leads to population fluctuations near the absorption peaks. With the increasing of the relaxation rate γ, the population distributions are shifted and their fluctuation amplitudes decrease. At the same time the electromagnetically induced transparency window becomes a broadened absorption peak, and the dispersion at the zero probe detuning changes from positive to negative. Large population fluctuation and non-fluctuation observed in different systems are attributed to the different relaxation rates.
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    Output power spectrum of a single-mode laser driven by coloured pump and quantum noises with coloured correlation
    韩立波, 曹力, 吴大进
    2004 (10):  1717-1721.  doi: 10.1088/1009-1963/13/10/025
    摘要 ( 1074 )   PDF(371KB) ( 424 )  
    By using the linear approximation method, the output power spectrum is calculated for a single-mode laser driven by coloured pump and quantum noises with coloured correlation. We have observed that the configuration of the output power spectrum is complicated: that is, it can be of single peak, two peaks or three peaks. The configurations of the power spectrum can be transformed from one into another by changing the cross-correlation time, the cross-correlation coefficient between the two noises, and pump noise intensity.
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    Quantum interference effects on the probe amplification without and with inversion in a four-level system
    张冰, 徐卫华, 张惠芳, 高锦岳
    2004 (10):  1722-1727.  doi: 10.1088/1009-1963/13/10/026
    摘要 ( 1049 )   PDF(222KB) ( 424 )  
    A four-level system driven by two coherent fields is considered. It is shown that in the presence of an incoherent pump, the probe gain at a short wavelength can be achieved due to the quantum interference. Our density matrix calculation provides the conditions for probe amplification from different origins, including gain without population inversion on any state basis, gain with population inversion on the dressed-state basis, and gain with population inversion on the bare-state basis. Also, by controlling the Rabi frequency of the coupling field a total change from non-inversion to inversion can be achieved which does not depend on the intensity of the incoherent pump.
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    Analysis of the laser performance of Tm3+: ZBLAN glass at 1.47μm wavelength
    黄莉蕾, 曹国熹, 张伦, 罗宏雷
    2004 (10):  1728-1732.  doi: 10.1088/1009-1963/13/10/027
    摘要 ( 1300 )   PDF(143KB) ( 420 )  
    A formula for the threshold energy of a four-level-system laser in Tm^{3+} doped fluoride glass is derived. The formula contains the parameters of the interaction between the ions and the up-conversion rate of the pump-light. It is discussed that the Tb^{3+} ions and the up-conversion pump-light have an influence on the laser performance of Tm^{3+} ions around 1.47μm wavelength. We draw the following two conclusions. (1) The laser threshold descends obviously due to the doping of Tb^{3+} ions, but the descending gradually flattens out with the increase of the content of Tb^{3+} ions. Its suitable content is (1-2)×10^{20}cm^{-3}. (2) When pump-lights both from the up-conversion and from the ground state excite simultaneously the single-doped Tm^{3+} ions, the threshold energy can reduce and the output energy can increase. In this paper, the energy conversion efficiency from the up-conversion pump-light to the output energy of laser is estimated.
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    Investigation of stimulated Brillouin scattering for broadband KrF laser
    王晓慧, 吕志伟, 林殿阳, 王超, 赵晓彦, 汤秀章, 张海峰, 单玉生
    2004 (10):  1733-1737.  doi: 10.1088/1009-1963/13/10/028
    摘要 ( 1207 )   PDF(208KB) ( 544 )  
    Stimulated Brillouin scattering (SBS) numerical mode for broadband multimode KrF laser pump with optical breakdown has been built up in this paper. The basic premises of the model are that KrF spectrum is composed of a number of lines and SBS arises from these lines with coupling to some extent. The broadband SBS threshold strongly depends on pump bandwidth. SBS and optical breakdown occur nearly simultaneously when broadband SBS and breakdown have the same threshold. The decrease of saturation reflectivity for broadband pump radiation is explained with this model. Experimental results agree well with the model.
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    CLASSICAL AREAS OF PHENOMENOLOGY
    Grey-grey incoherently coupled spatial soliton pairs in guest-host photorefractive polymers
    侯春风, 姚凤凤, 周忠祥, 裴延波, 孙秀冬
    2004 (10):  1738-1741.  doi: 10.1088/1009-1963/13/10/029
    摘要 ( 1035 )   PDF(173KB) ( 492 )  
    We show that incoherently coupled grey-grey spatial soliton pairs can be established in guest-host photorefractive polymers under steady-state conditions, provided that their carrier beams have the same polarization, wavelength, and are mutually incoherent. The properties of these soliton pairs, such as their width and polarization, are discussed in detail.
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    Study of the surface and far fields of terahertz radiation generated by large-aperture photoconductive antennas
    张同意, 曹俊成
    2004 (10):  1742-1746.  doi: 10.1088/1009-1963/13/10/030
    摘要 ( 1182 )   PDF(219KB) ( 653 )  
    We have studied analytically the temporal characteristics of terahertz radiation emitted from a biased large-aperture photoconductive antenna triggered by an ultrashort optical pulse. We have included the effects of the finite lifetime and transient mobility dynamics of photogenerated carriers in the analysis. Succinct explicit expressions are obtained for the emitted radiation in the surface field and in the far field. The dependence of the waveforms of the radiated field on the fluence and duration of triggering optical pulse, carrier relaxation time and carrier lifetime are discussed in detail using the obtained expressions.
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    RT instability in cylindrical implosion of jelly ring
    杨礼兵, 廖海东, 孙承纬, 欧阳凯, 李军, 黄显宾
    2004 (10):  1747-1752.  doi: 10.1088/1009-1963/13/10/031
    摘要 ( 1213 )   PDF(1690KB) ( 458 )  
    The interfacial RT instability experiments on imploding jelly liners in cylindrically convergent geometry have been performed. The liner's instability growth was observed clearly with a high-speed framing camera. Jelly liners have different initial perturbation forms on their inner and outer interfaces, being either smooth or sinusoidal. The initial perturbations also have different magnitudes and spatial frequencies (for example, mode n=5, 10, 20). The experimental results show that the growth and coupling of perturbations on inner and outer surfaces are remarkably different. Meanwhile, the relevant 2-D numerical simulation of hydrodynamics combined with Level Set method has been performed. Using the numerical code, we can design the parameters of imploding jelly liner, and predict the experimental results. The results of simulation are demonstrated to be in good agreement with the measured data in a series of experiments.
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    CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
    Raman spectra of ZnSe nanoparticles synthesized by thermal evaporation method
    安辉芝, 赵清, 杜为民
    2004 (10):  1753-1757.  doi: 10.1088/1009-1963/13/10/032
    摘要 ( 1791 )   PDF(269KB) ( 538 )  
    ZnSe nanoparticles were synthesized by using a thermal evaporation method for a vapour phase reaction of zinc and selenium sources. The sample was characterized by XRD, TEM, HRTEM and Raman spectroscopy. Raman spectra of longitudinal-optical (LO) like mode was analysed by a macroscopic continuum dielectric model. Large broadening of LO-mode is homogeneous and comes from the relaxation of the phonons at the interface and contribution of defects. Surface modes give the main contribution to the asymmetry of the lineshape.
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    Thermalization time of thin metal film heated by short pulse laser
    徐红玉, 张元冲, 宋亚勤, 陈殿云
    2004 (10):  1758-1765.  doi: 10.1088/1009-1963/13/10/033
    摘要 ( 1235 )   PDF(357KB) ( 521 )  
    Based on the hyperbolic two-step heat conduction model, using the Laplace transform and numerical inverse transform method (Riemann-sum approximation method), the thermal behaviour of thin metal films has been studied during femtosecond pulse laser heating. Also the thermalization time, which is the time for the electron gas and solid lattice to reach thermal balance, has been studied in detail. The values of thermalization time for silver (Ag), gold (Au), copper (Cu) and lead (Pb) are obtained. The effects of material parameters of the thin metal film on the thermalization time are considered for the four kinds of metals by changing one of the parameters and regarding the other parameters as constant. For a typical metal material, the order of the thermalization time is of the order of hundreds of picoseconds. The thermalization time decays exponentially with the increase of phonon-electron coupling factor or electron gas thermal conductivity, and it increases linearly with the increase of the ratio of lattice heat capacity to electron gas heat capacity. However, the relaxation time of the electron gas has very little effect on the thermalization time.
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    Quantum fluctuation of mesoscopic distributed parameter circuits
    罗海梅, 刘刚, 徐林, 嵇英华
    2004 (10):  1766-1769.  doi: 10.1088/1009-1963/13/10/034
    摘要 ( 1134 )   PDF(151KB) ( 346 )  
    Under the Born-von-Karmann periodic boundary condition, we propose a quantization scheme for a non-dissipative distributed parameter circuit (a uniform transmission line). Quantum fluctuations of charge and current in the vacuum state are investigated by adopting the canonical transformation and unitary transformation method. Our results indicate that in distributed parameter circuits, quantum fluctuations, which also have distributed properties, are related to both the circuit parameters and the positions and the mode of signals.
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    Numerical solution of Helmholtz equation of barotropic atmosphere using wavelets
    汪萍, 戴新刚
    2004 (10):  1770-1776.  doi: 10.1088/1009-1963/13/10/035
    摘要 ( 1068 )   PDF(366KB) ( 409 )  
    The numerical solution of the Helmholtz equation for barotropic atmosphere is estimated by use of the wavelet-Galerkin method. The solution involves the decomposition of a circulant matrix consisting up of 2-term connection coefficients of wavelet scaling functions. Three matrix decompositions, i.e. fast Fourier transformation (FFT), Jacobian and QR decomposition methods, are tested numerically. The Jacobian method has the smallest matrix-reconstruction error with the best orthogonality while the FFT method causes the biggest errors. Numerical result reveals that the numerical solution of the equation is very sensitive to the decomposition methods, and the QR and Jacobian decomposition methods, whose errors are of the order of 10^{-3}, much smaller than that with the FFT method, are more suitable to the numerical solution of the equation. With the two methods the solutions are also proved to have much higher accuracy than the iteration solution with the finite difference approximation. In addition, the wavelet numerical method is very useful for the solution of a climate model in low resolution. The solution accuracy of the equation may significantly increase with the order of Daubechies wavelet.
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