Table of contents

20 January 2006, Volume 15 Issue 1 Previous issue    Next issue

GENERAL

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Variable separation solutions and new solitary wave structures to the (1+1)-dimensional Ito system Xu Chang-Zhi (徐昌智), He Bao-Gang (何宝钢), Zhang Jie-Fang (张解放) Chinese Physics, 2006, 15 (1):  1-7.  DOI: 10.1088/1009-1963/15/1/001 Abstract ( 2014 )   PDF (228KB) ( 1058 )   A variable separation approach is proposed and extended to the (1+1)-dimensional physics system. The variable separation solution of (1+1)-dimensional Ito system is obtained. Some special types of solutions such as non-propagating solitary wave solution, propagating solitary wave solution and looped soliton solution are found by selecting the arbitrary function appropriately.

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Momentum-dependent symmetries and non-Noether conserved quantities for nonholonomic nonconservative Hamilton canonical systems Fu Jing-Li (傅景礼), Chen Li-Qun (陈立群), Chen Xiang-Wei (陈向炜) Chinese Physics, 2006, 15 (1):  8-12.  DOI: 10.1088/1009-1963/15/1/002 Abstract ( 1444 )   PDF (218KB) ( 602 )   This paper investigates the momentum-dependent symmetries for nonholonomic nonconservative Hamilton canonical systems. The definition and determining equations of the momentum-dependent symmetries are presented, based on the invariance of differential equations under infinitesimal transformations with respect to the generalized coordinates and generalized momentums. The structure equation and the non-Noether conserved quantities of the systems are obtained. The inverse issues associated with the momentum-dependent symmetries are discussed. Finally, an example is discussed to further illustrate the applications.

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A geometric framework for time-dependent mechanical systems with unilateral constraints Zhang Yi (张毅), Mei Feng-Xiang (梅凤翔) Chinese Physics, 2006, 15 (1):  13-18.  DOI: 10.1088/1009-1963/15/1/003 Abstract ( 1633 )   PDF (235KB) ( 675 )   The description of modern differential geometry for time-dependent Chetaev nonholonomic mechanical systems with unilateral constraints is studied. By using the structure of exact contact manifold, the geometric framework of time-dependent nonholonomic mechanical systems subject to unilateral nonholonomic constraints and unilateral holonomic constraints respectively is presented.

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Lie symmetry and conserved quantity of a system of first-order differential equations Xu Xue-Jun (许学军), Mei Feng-Xiang (梅凤翔), Zhang Yong-Fa (张永发) Chinese Physics, 2006, 15 (1):  19-21.  DOI: 10.1088/1009-1963/15/1/004 Abstract ( 1743 )   PDF (194KB) ( 679 )   This paper focuses on studying the Lie symmetry and a conserved quantity of a system of first-order differential equations. The determining equations of the Lie symmetry for a system of first-order differential equations, from which a kind of conserved quantity is deduced, are presented. And their general conclusion is applied to a Hamilton system, a Birkhoff system and a generalized Hamilton system. Two examples are given to illustrate the application of the results.

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Numerical method of the Riemann problem for two-dimensional multi-fluid flows with general equation of state Bai Jing-Song (柏劲松), Zhang Zhan-Ji (张展冀), Li Ping (李平), Zhong Min (钟敏) Chinese Physics, 2006, 15 (1):  22-34.  DOI: 10.1088/1009-1963/15/1/005 Abstract ( 1691 )   PDF (397KB) ( 672 )   Based on the classical Roe method, we develop an interface capture method according to the general equation of state, and extend the single-fluid Roe method to the two-dimensional (2D) multi-fluid flows, as well as construct the continuous Roe matrix for the whole flow field. The interface capture equations and fluid dynamic conservative equations are coupled together and solved by using any high-resolution schemes that usually suit for the single-fluid flows. Some numerical examples are given to illustrate the solution of 1D and 2D multi-fluid Riemann problems.

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New exact solutions of nonlinear Klein--Gordon equation Zheng Qiang (郑强), Yue Ping (岳萍), Gong Lun-Xun (龚伦训) Chinese Physics, 2006, 15 (1):  35-38.  DOI: 10.1088/1009-1963/15/1/006 Abstract ( 1983 )   PDF (229KB) ( 784 )   New exact solutions, expressed in terms of the Jacobi elliptic functions, to the nonlinear Klein--Gordon equation are obtained by using a modified mapping method. The solutions include the conditions for equation's parameters and travelling wave transformation parameters. Some figures for a specific kind of solution are also presented.

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Solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain Li De-Jun (李德俊), Mi Xian-Wu (米贤武), Deng Ke (邓科), Tang Yi (唐翌) Chinese Physics, 2006, 15 (1):  39-44.  DOI: 10.1088/1009-1963/15/1/007 Abstract ( 1893 )   PDF (226KB) ( 610 )   By use of the Hartree approximation and the method of multiple scales, we investigate quantum solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain. It is shown that there exist solitons of two different quantum frequency bands: i.e., magnetic optical solitons and acoustic solitons. At the boundary of the Brillouin zone, these solitons become quantum intrinsic localized modes: their quantum eigenfrequencies are below the bottom of the harmonic optical frequency band and above the top of the harmonic acoustic frequency band.

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Two classes of fractal structures for the (2+1)-dimensional dispersive long wave equation Ma Zheng-Yi (马正义), Zheng Chun-Long (郑春龙) Chinese Physics, 2006, 15 (1):  45-52.  DOI: 10.1088/1009-1963/15/1/008 Abstract ( 1663 )   PDF (577KB) ( 634 )   Using the mapping approach via a Riccati equation, a series of variable separation excitations with three arbitrary functions for the (2+1)-dimensional dispersive long wave (DLW) equation are derived. In addition to the usual localized coherent soliton excitations like dromions, rings, peakons and compactions, etc, some new types of excitations that possess fractal behaviour are obtained by introducing appropriate lower-dimensional localized patterns and Jacobian elliptic functions.

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Performance of an irreversible quantum refrigeration cycle He Ji-Zhou (何济洲), Ouyang Wei-Pin (欧阳微频), Wu Xin (伍歆) Chinese Physics, 2006, 15 (1):  53-59.  DOI: 10.1088/1009-1963/15/1/009 Abstract ( 1715 )   PDF (260KB) ( 734 )   A new model of a quantum refrigeration cycle composed of two adiabatic and two isomagnetic field processes is established. The working substance in the cycle consists of many non-interacting spin-1/2 systems. The performance of the cycle is investigated, based on the quantum master equation and semi-group approach. The general expressions of several important performance parameters, such as the coefficient of performance, cooling rate, and power input, are given. It is found that the coefficient of performance of this cycle is in the closest analogy to that of the classical Carnot cycle. Furthermore, at high temperatures the optimal relations of the cooling rate and the maximum cooling rate are analysed in detail. Some performance characteristic curves of the cycle are plotted, such as the cooling rate versus the maximum ratio between high and low ``temperatures'' of the working substances, the maximum cooling rate versus the ratio between high and low ``magnetic fields'' and the ``temperature'' ratio between high and low reservoirs. The obtained results are further generalized and discussed, so that they may be directly applied to describing the performance of the quantum refrigerator using spin-$J$ systems as the working substance. Finally, the optimum characteristics of the quantum Carnot and Ericsson refrigeration cycles are derived by analogy.

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The effect of quantum noise on the restricted quantum game Cao Shuai (曹帅), Fang Mao-Fa (方卯发) Chinese Physics, 2006, 15 (1):  60-65.  DOI: 10.1088/1009-1963/15/1/010 Abstract ( 1671 )   PDF (247KB) ( 629 )   It has recently been established that quantum strategies have great advantage over classical ones in quantum games. However, quantum states are easily affected by the quantum noise resulting in decoherence. In this paper, we investigate the effect of quantum noise on the restricted quantum game in which one player is restricted in classical strategic space, another in quantum strategic space and only the quantum player is affected by the quantum noise. Our results show that in the maximally entangled state, no Nash equilibria exist in the range of 0<p ?0.422 (p is the quantum noise parameter), while two special Nash equilibria appear in the range of 0.422<p<1. The advantage that the quantum player diminished only in the limit of maximum quantum noise. Increasing the amount of quantum noise leads to the increase of the classical player's payoff and the reduction of the quantum player's payoff, but is helpful in forming two Nash equilibria.

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New infinite-dimensional symmetry groups for the stationary axisymmetric Einstein--Maxwell equations with multiple Abelian gauge fields Gao Ya-Jun (高亚军) Chinese Physics, 2006, 15 (1):  66-76.  DOI: 10.1088/1009-1963/15/1/011 Abstract ( 1130 )   PDF (288KB) ( 537 )   The so-called extended hyperbolic complex (EHC) function method is used to study further the stationary axisymmetric Einstein--Maxwell theory with $p$ Abelian gauge fields (EM-$p$ theory, for short). Two EHC structural Riemann--Hilbert (RH) transformations are constructed and are then shown to give an infinite-dimensional symmetry group of the EM-$p$ theory. This symmetry group is verified to have the structure of semidirect product of Kac--Moody group $\widehat{SU(p+1,1)}$ and Virasoro group. Moreover, the infinitesimal forms of these two RH transformations are calculated and found to give exactly the same infinitesimal transformations as in previous author's paper by a different scheme. This demonstrates that the results obtained in the present paper provide some exponentiations of all the infinitesimal symmetry transformations obtained before.

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Quasinormal modes of a stationary axisymmetric EMDA black hole Pan Qi-Yuan (潘启沅), Jing Ji-Liang (荆继良) Chinese Physics, 2006, 15 (1):  77-82.  DOI: 10.1088/1009-1963/15/1/012 Abstract ( 1496 )   PDF (244KB) ( 560 )   The massless scalar quasinormal modes (QNMs) of a stationary axisymmetric Einstein--Maxwell dilaton--axion (EMDA) black hole are calculated numerically using the continued fraction method first proposed by Leaver. The fundamental quasinormal frequencies (slowly damped QNMs) are obtained and the peculiar behaviours of them are studied. It is shown that these frequencies depend on the dilaton parameter $D$, the rotational parameter $a$, the multiple moment $l$ and the azimuthal number $m$, and have the same values with other authors at the Schwarzschild and Kerr limit.

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A new output feedback synchronization theorem for a class of chaotic systems with a scalar transmitted signal Lu Jun-Guo (卢俊国) Chinese Physics, 2006, 15 (1):  83-88.  DOI: 10.1088/1009-1963/15/1/013 Abstract ( 1554 )   PDF (238KB) ( 619 )   This paper proposes a new, simple and yet applicable output feedback synchronization theorem for a large class of chaotic systems. We take a linear combination of drive system state variables as a scale-driving signal. It is proved that synchronization between the drive and the response systems can be obtained via a simple linear output error feedback control. The linear feedback gain is a function of a free parameter. The approach is illustrated using the R?ssler hyperchaotic systems and Chua's chaotic oscillators.

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Robust fuzzy control for chaotic dynamics in Lorenz systems with uncertainties Wang Yao-Nan (王耀南), Tan Wen (谭文), Duan Feng (段峰) Chinese Physics, 2006, 15 (1):  89-94.  DOI: 10.1088/1009-1963/15/1/014 Abstract ( 1724 )   PDF (247KB) ( 666 )   This paper deals with the robust fuzzy control for chaotic systems in the presence of parametric uncertainties. An uncertain Takagi--Sugeno fuzzy model for a Lorenz chaotic system is first constructed. Then a robust fuzzy state feedback control scheme ensures the control for stable operations under bounded parametric uncertainties. For a chaotic system with known uncertainty bounds, a robust fuzzy regulator is designed by choosing the control parameters satisfying the linear matrix inequality. To verify the validity and effectiveness of the proposed controller design method, an analysis technique is suggested and applied to the control of an uncertain Lorenz chaotic system.

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La Shalle's invariant-set-theory based asymptotic synchronization of duffing system with unknown parameters Yu Dong-Chuan (禹东川), Wu Ai-Guo (吴爱国) Chinese Physics, 2006, 15 (1):  95-99.  DOI: 10.1088/1009-1963/15/1/015 Abstract ( 1866 )   PDF (238KB) ( 540 )   A novel La Shalle's invariant set theory (LSIST) based adaptive asymptotic synchronization (LSISAAS) method is proposed to asymptotically synchronize Duffing system with unknown parameters which also are considered as system states. The LSISASS strategy depends on the only information, i.e. one state of the master system. According to the LSIST, the LSISASS method can asymptotically synchronize fully the states of the master system and the unknown system parameters as well. Simulation results also validate that the LSISAAS approach can obtain asymptotic synchronization.

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A digital filtering scheme for SQUID based magnetocardiography Zhu Xue-Min (朱学敏), Ren Yu-Feng (任育峰), Yu Hong-Wei (于洪伟), Zhao Shi-Ping (赵士平), Chen Geng-Hua (陈赓华), Zhang Li-Hua (张利华), Yang Qian-Sheng (杨乾声) Chinese Physics, 2006, 15 (1):  100-103.  DOI: 10.1088/1009-1963/15/1/016 Abstract ( 1556 )   PDF (226KB) ( 604 )   Considering the properties of slow change and quasi-periodicity of magnetocardiography (MCG) signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by high $T_{\rm c}$ SQUIDs. The adaptive filter in the time domain is based on a noise feedback normalized least-mean-square (NLMS) algorithm, and the low-pass filter with a cutoff at 100Hz in the frequency domain characterized by Gaussian functions is combined with a notch at the power line frequency. In this way, both relevant and irrelevant noises in original MCG data are largely eliminated. The method may also be useful for other slowly varying quasi-periodical signals.

NUCLEAR PHYSICS

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Direct neutron decay of analogue resonances in 105Rh Hu Bi-Tao (胡碧涛), Zarubin P.P., Juravlev U.U. Chinese Physics, 2006, 15 (1):  104-107.  DOI: 10.1088/1009-1963/15/1/017 Abstract ( 1489 )   PDF (205KB) ( 391 )   A new method, while takes into account the contribution of direct neutron decay of analogue resonances to the isomeric ratio resulting from (p,n) reaction, is used to analyse the published experimental data for the reaction $^{104}$Ru(p,n)$^{104}$Rh and also estimate a minimum probability of direct decay.

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GEANT4 simulation of gamma ray in a double-gap resistive plate chamber J. T. Rhee, M. Jamil, Steve Hall, Y. J. Jeon Chinese Physics, 2006, 15 (1):  108-115.  DOI: 10.1088/1009-1963/15/1/018 Abstract ( 1686 )   PDF (261KB) ( 713 )   For more than 20 years nuclear physicists have used the GEANT code to simulate particle-matter interaction. In most recent version, GEANT4 is a toolkit for simulating the passage of particles though matter, which contains a complete range of functionality including tracking, geometry, physics models, and hits. In this article, an attempt to use GEANT4 to model a double-gap resistive plate chamber (RPC) with its improved efficiency is presented. The efficiencies of the double-gap RPC have been evaluated as a function of gamma energy range 0.005--1000MeV. A comparison to available previous simulation package GEANT3 data is also performed.

ATOMIC AND MOLECULAR PHYSICS

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Diffracted field distribution from a knife-edge truncated semi-Gaussian beam as an atomic (molecular) mirror Zheng Ping (郑萍), Gao Wei-Jian (高伟建), Yin Jian-Ping (印建平) Chinese Physics, 2006, 15 (1):  116-125.  DOI: 10.1088/1009-1963/15/1/019 Abstract ( 1545 )   PDF (368KB) ( 911 )   We investigate the diffraction characteristics of an incident Gaussian beam cut by a straight edge bounding a semi-infinite opaque plane using Kirchhoff scalar wave theory in the Fresnel limit, and propose a new and simple mirror scheme to reflect atoms by using the intensity gradient induced by a blue-detuned semi-Gaussian laser beam. The optical potential of the diffracted light of the knife-cut semi-Gaussian beam for $^{85}$Rb atom and its spontaneous emission probability are calculated and compared with the performance of the evanescent-wave mirror. Our study shows that the optical potential of the diffracted light of the semi-Gaussian beam is far higher than that of the evanescent light wave, and the maximum normal velocity of the incident atoms can be far greater than that of the evanescent light wave under the same parameters, so the blue-detuned semi-Gaussian beam, as a novel atomic mirror, can be used to efficiently reflect cold atoms with a normal velocity of greater than 1 m/s. However, the intensity gradient (force) of the diffracted light of the semi-Gaussian-beam is much smaller than that of the evanescent light wave, so its spontaneous emission probability is greater than that from the evanescent-wave when the normal velocity of incident atoms is greater.

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Surface-enhanced resonance Raman scattering spectroscopy of single R6G molecules Zhou Zeng-Hui (周增会), Liu Li (刘力), Wang Gui-Ying (王桂英), Xu Zhi-Zhan (徐至展) Chinese Physics, 2006, 15 (1):  126-131.  DOI: 10.1088/1009-1963/15/1/020 Abstract ( 1731 )   PDF (254KB) ( 990 )   Surface-enhanced resonance Raman scattering (SERRS) of Rhodamine 6G (R6G) adsorbed on colloidal silver clusters has been studied. Based on the great enhancement of the Raman signal and the quench of the fluorescence, the SERRS spectra of R6G were recorded for the samples of dye colloidal solution with different concentrations. Spectral inhomogeneity behaviours from single molecules in the dried sample films were observed with complementary evidences, such as spectral polarization, spectral diffusion, intensity fluctuation of vibrational lines and even ``breathing'' of the molecules. Sequential spectra observed from a liquid sample with an average of 0.3 dye molecules in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1 or 2 molecules. Difference between the SERRS spectra of R6G excited by linearly and circularly polarized light were experimentally measured.

CLASSICAL AREAS OF PHENOMENOLOGY

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Efficient three-wave mixing in a three-level atomic medium with an assisting microwave driven field Li Jia-Hua (李家华), Luo Jin-Ming (罗进明), Yang Wen-Xing (杨文星), Zhan Zhi-Ming (詹志明) Chinese Physics, 2006, 15 (1):  132-137.  DOI: 10.1088/1009-1963/15/1/021 Abstract ( 1369 )   PDF (275KB) ( 658 )   The potential for nonlinear conversion between two laser pulses in a three-level V-type medium with assistance of an auxiliary microwave resonant radiation is studied. The results show that microwave driven field can lead to the parametric generation of a new laser pulse with high conversion efficiency when a weak pump laser pulse is applied.

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Autler--Townes doublet in novel sub-Doppler spectra with caesium vapour cell Wang Yan-Hua (王彦华), Yang Hai-Jing (杨海菁), Du Zhi-Jing (杜志静), Zhang Tian-Cai (张天才), Wang Jun-Min (王军民) Chinese Physics, 2006, 15 (1):  138-142.  DOI: 10.1088/1009-1963/15/1/022 Abstract ( 1552 )   PDF (221KB) ( 579 )   With a coupling laser locked to caesium 6S$_{1 / 2}$ $F_{\rm g}$=4--6P$_{3 / 2}$ $F_{\rm e}$=5 cycling transition and a co-propagating probe laser scanned across 6S$_{1 / 2}$ $F_{\rm g}$=4--6P$_{3 / 2}$ $F_{\rm e}$=3, 4 and 5 transitions, a novel scheme for sub-Doppler spectra in Doppler-broadened V-type three-level system is demonstrated by detecting the transmission of the coupling laser through a caesium vapour cell. The Autler--Townes doublet in the sub-Doppler spectra of the coupling laser is clearly observed. The effects of coupling laser intensity on the splitting and linewidth of the Autler--Townes doublet are experimentally investigated and the results agree well with theoretical predictions. Taking the multiple hyperfine levels of caesium atom into account, a brief analysis is presented.

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Full-vectorial analysis of optical waveguides by the finite difference method based on polynomial interpolation Xiao Jin-Biao (肖金标), Zhang Ming-De (张明德), Sun Xiao-Han (孙小菡) Chinese Physics, 2006, 15 (1):  143-148.  DOI: 10.1088/1009-1963/15/1/023 Abstract ( 1485 )   PDF (338KB) ( 1367 )   Based on the polynomial interpolation, a new finite difference (FD) method in solving the full-vectorial guided-modes for step-index optical waveguides is proposed. The discontinuities of the normal components of the electric field across abrupt dielectric interfaces are considered in the absence of the limitations of scalar and semivectorial approximation, and the present FD scheme can be applied to both uniform and non-uniform mesh grids. The modal propagation constants and field distributions for buried rectangular waveguides and optical rib waveguides are presented. The hybrid nature of the vectorial modes is demonstrated and the singular behaviours of the minor field components in the corners are observed. Moreover, solutions are in good agreement with those published early, which tests the validity of the present approach.

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Numerical simulation of the flow within and over an intersection model with Reynolds-averaged Navier--Stokes method Li Lei (李磊), Hu Fei (胡非), Cheng Xue-Ling (程雪玲), Jiang Jin-Hua (姜金华), Ma Xiao-Guang (马晓光) Chinese Physics, 2006, 15 (1):  149-155.  DOI: 10.1088/1009-1963/15/1/024 Abstract ( 1442 )   PDF (354KB) ( 619 )   In this study, the Reynolds-averaged Navier--Stokes (RANS) method is employed to simulate the flow within and over an intersection model with three kinds of $k$--$\varepsilon$ turbulence closure schemes, namely, standard model, renormalization group (RNG) model and realizable $k$--$\varepsilon$ model. The comparison between the simulated and observed flow fields shows that the RANS simulation with all the three turbulence models cannot completely and accurately reproduce the observed flow field in all details. A detailed comparison between the predicted profiles of wind velocities and the measured data shows that the realizable $k$--$\varepsilon$ model is the best one among the three turbulence closure models in general. However, the extent to which the improvement is achieved by the realizable $k$--$\varepsilon$ model is still not enough to completely and accurately describe the turbulent flow in a relatively complex environment.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Two-dimensional relativistic electromagnetic dromion-like soliton in a cold transparent plasma Wang Yun-Liang (王云良), Zhou Zhong-Xiang (周忠祥), Yuan Cheng-Xun (袁承勋), Jiang Xiang-Qian (姜向前), Qin Ru-Hu (秦汝虎) Chinese Physics, 2006, 15 (1):  156-162.  DOI: 10.1088/1009-1963/15/1/025 Abstract ( 1555 )   PDF (274KB) ( 736 )   By using a standard multiple scale method, a Davey--Stewartson (DS) equation has been derived and also applied to a multi-dimensional analytical investigation on the interaction of an ultra-intense laser pulse with a cold unmagnetized transparent electron-ion plasma. The regions of instability are found by considering the modulation instability of a plane wave solution of the DS equation. The DS equation is just of the Davey--Stewartson 1 (DS1) type and admits a dromion solution, i.e. a two-dimensional (2D) dromion soliton decaying exponentially in all spatial directions. A 2D relativistic electromagnetic dromion-like soliton (2D REDLS) is derived for a vector potential.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems Liu Jian-Jun (刘建军), Shen Man (沈曼), Liu Xiao-Jing (刘晓静), Yang Guo-Chen (杨国琛) Chinese Physics, 2006, 15 (1):  163-171.  DOI: 10.1088/1009-1963/15/1/026 Abstract ( 1362 )   PDF (294KB) ( 659 )   We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein--Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals.

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Effects of dispersion forces in the instability of polymer films Zhao He-Ping (赵鹤平), Tsui Ophelia K. C., Liu Zheng-You (刘正猷) Chinese Physics, 2006, 15 (1):  172-176.  DOI: 10.1088/1009-1963/15/1/027 Abstract ( 1332 )   PDF (218KB) ( 797 )   Spontaneous rupture of some polymer films upon heating is commonplace. The very criterion for this instability is the system free energy possessing a negative curvature. Within the framework of full frequency-dependent theory of dispersion forces, we have derived the excess free energy of a typical system---polystyrene film deposited on the silicon substrate. The excess free energy, wavelengths and growth rates are calculate and a comparison is made between the accurate results and the approximate results. It is found that the stability of the film can be tuned by the variation of the thickness of the coating and the retardation effects can be significant sometimes.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Quantum Boltzmann equation solved by Monte Carlo method for nano-scale semiconductor devices simulation Du Gang (杜刚), Liu Xiao-Yan (刘晓彦), Han Ru-Qi (韩汝琦) Chinese Physics, 2006, 15 (1):  177-181.  DOI: 10.1088/1009-1963/15/1/028 Abstract ( 1615 )   PDF (271KB) ( 765 )   A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC) method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to extend the MC method to the study of nano-scale semiconductor devices with obvious quantum mechanical (QM) effects. The quantum effects both in real space and momentum space in nano-scale semiconductor devices can be simulated. The effective mobility in the inversion layer of n and p channel MOSFET is simulated and compared with experimental data to verify this method. With this method 50nm ultra thin body silicon on insulator MOSFET are simulated. Results indicate that this method can be used to simulate the 2D QM effects in semiconductor devices including tunnelling effect.

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Dielectric responses of graded composites having generalized gradation profiles Wei En-Bo (魏恩泊), Gu Guo-Qing (顾国庆), Yu Kin-Wah (余建华) Chinese Physics, 2006, 15 (1):  182-189.  DOI: 10.1088/1009-1963/15/1/029 Abstract ( 1330 )   PDF (282KB) ( 440 )   Under an external uniform electric field, the dielectric response of graded cylindrical composites having generalized dielectric profile inclusions is investigated. The generalized dielectric profile of graded cylindrical inclusion is expressed in the form, $\varepsilon _i (r)=c(b+ r)^k{\rm e}^{\beta r}$ where $r$ is the radial variable of the cylindrical inclusions and $c$, $b$, $k$ and $\beta $ are parameters. The local potential solution of generalized dielectric profile graded composites is derived by means of the power series method and the effective dielectric response is predicted in the dilute limit. Moreover, from the result of generalized profile, the analytical solutions of local potentials and the effective responses of graded composites having three cases of dielectric profiles, i.e., the exponential profile $\varepsilon(r)_{\rm i}=c{\rm e}^{\beta r}$, the general power law profile $\varepsilon_{\rm i}(r)=c(b+r)^k$ and the profile $\varepsilon_{\rm i}(r)=cr^k{\rm e}^{\beta r}$, are sorted out, respectively. In the dilute limit, our exact results are used to test the validity of differential effective dipole approximation (DEDA) for estimating the effective response of graded cylindrical composites, and it is shown that the DEDA is in excellent agreement with the exact result.

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Direct current hopping conductance in one-dimensional diagonal disordered systems Ma Song-Shan (马松山), Xu Hui (徐慧), Liu Xiao-Liang (刘小良), Xiao Jian-Rong (肖剑荣) Chinese Physics, 2006, 15 (1):  190-194.  DOI: 10.1088/1009-1963/15/1/030 Abstract ( 1580 )   PDF (220KB) ( 664 )   Based on a tight-binding disordered model describing a single electron band, we establish a direct current (dc) electronic hopping transport conductance model of one-dimensional diagonal disordered systems, and also derive a dc conductance formula. By calculating the dc conductivity, the relationships between electric field and conductivity and between temperature and conductivity are analysed, and the role played by the degree of disorder in electronic transport is studied. The results indicate the conductivity of systems decreasing with the increase of the degree of disorder, characteristics of negative differential dependence of resistance on temperature at low temperatures in diagonal disordered systems, and the conductivity of systems decreasing with the increase of electric field, featuring the non-Ohm's law conductivity.

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Fabrication and characterization of groove-gate MOSFETs based on a self-aligned CMOS process Ma Xiao-Hua (马晓华), Hao Yue (郝跃), Sun Bao-Gang (孙宝刚), Gao Hai-Xia (高海霞), Ren Hong-Xia (任红霞), Zhang Jin-Cheng (张进城), Zhang Jin-Feng (张金凤), Zhang Xiao-Ju (张晓菊), Zhang Wei-Dong (张卫东) Chinese Physics, 2006, 15 (1):  195-198.  DOI: 10.1088/1009-1963/15/1/031 Abstract ( 1483 )   PDF (270KB) ( 961 )   N and P-channel groove-gate MOSFETs based on a self-aligned CMOS process have been fabricated and characterized. For the devices with channel length of 140nm, the measured drain induced barrier lowering (DIBL) was 66mV/V for n-MOSFETs and 82mV/V for p-MOSFETs. The substrate current of a groove-gate n-MOSFET was 150 times less than that of a conventional planar n-MOSFET. These results demonstrate that groove-gate MOSFETs have excellent capabilities in suppressing short-channel effects. It is worth emphasizing that our groove-gate MOSFET devices are fabricated by using a simple process flow, with the potential of fabricating devices in the sub-100nm range.

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Growth of n-type ZnO thin films by using mixture gas of hydrogen and argon Zhou Xin (周新), Wang Shi-Qi (王世奇), Lian Gui-Jun (连贵君), Xiong Guang-Cheng (熊光成) Chinese Physics, 2006, 15 (1):  199-202.  DOI: 10.1088/1009-1963/15/1/032 Abstract ( 1823 )   PDF (291KB) ( 756 )   High-quality oxide semiconductor ZnO thin films were prepared on single-crystal sapphire and LaAlO$_{3}$ substrates by pulsed laser deposition (PLD) in the mixture gas of hydrogen and argon. Low resistivity n-type ZnO thin films with smoother surface were achieved by deposition at 600$^\circ$C in 1Pa of the mixture gas. In addition, ferromagnetism was observed in Co-doped ZnO thin films and rectification $I-V$ curves were found in p-GaN/n-ZnO and p-CdTe/n-ZnO heterostructure junctions. The results indicated that using mixture gas of hydrogen and argon in PLD technique was a flexible method for depositing high-quality n-type oxide semiconductor films, especially for the multilayer thin film devices.

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Binding energies of an exciton in a Gaussian potential quantum dot Xie Wen-Fang (解文方) Chinese Physics, 2006, 15 (1):  203-208.  DOI: 10.1088/1009-1963/15/1/033 Abstract ( 1504 )   PDF (227KB) ( 787 )   In this paper, an exciton trapped by a Gaussian confining potential quantum dot has been investigated. Calculations are made by using the method of numerical diagonalization of Hamiltonian in the effective-mass approximation. The dependences of binding energies of the ground state and the first excited state on the size of the confining potential and the strength of the magnetic field are analysed explicitly.

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Upconversion luminescence of Tm3+/Yb3+codoped oxyfluoride glasses Duan Zhong-Chao (段忠超), Zhang Jun-Jie (张军杰), He Dong-Bing (何冬兵), Dai Shi-Xun (戴世勋), Hu Li-Li (胡丽丽) Chinese Physics, 2006, 15 (1):  209-212.  DOI: 10.1088/1009-1963/15/1/034 Abstract ( 1284 )   PDF (222KB) ( 534 )   Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3-xYbF3-(4.9-x) AlF3(x=0, 0.5, 1.0, 1.5, 2.0) in mol fraction. Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm3: 1D2 $\to$ 3F4, 1G4 $\to$ 3H6, 1G4 $\to$ 3F4, and 3H4 $\to$3H6, respectively, are observed. Due to the sensitization of Yb3+ ions, all the upconversion luminescence intensities are enhanced considerably with Yb3+ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Effect of substrate temperature on the growth and properties of boron-doped microcrystalline silicon films Lei Qing-Song (雷青松), Wu Zhi-Meng (吴志猛), Geng Xin-Hua (耿新华), Zhao Ying (赵颖), Sun Jian (孙健), Xi Jian-Ping (奚建平) Chinese Physics, 2006, 15 (1):  213-218.  DOI: 10.1088/1009-1963/15/1/035 Abstract ( 1293 )   PDF (273KB) ( 557 )   Highly conductive boron-doped hydrogenated microcrystalline silicon ($\mu$ c-Si:H) films are prepared by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at the substrate temperatures $T_{\rm S})$ ranging from 90$^\circ$C to 270$^\circ$C. The effects of $T_{\rm S}$ on the growth and properties of the films are investigated. Results indicate that the growth rate, the electrical (dark conductivity, carrier concentration and Hall mobility) and structural (crystallinity and grain size) properties are all strongly dependent on $T_{\rm S}$. As $T_{\rm S}$ increases, it is observed that 1) the growth rate initially increases and then arrives at a maximum value of 13.3 nm/min at $T_{\rm S}$=210$^\circ$C, 2) the crystalline volume fraction ($X_{\rm c})$ and the grain size increase initially, then reach their maximum values at $T_{\rm S}$=140$^\circ$C, and finally decrease, 3) the dark conductivity ($\sigma _{\rm d})$, carrier concentration and Hall mobility have a similar dependence on $T_{\rm S}$ and arrive at their maximum values at $T_{\rm S}$=190$^\circ$C. In addition, it is also observed that at a lower substrate temperature $T_{\rm S}$, a higher dopant concentration is required in order to obtain a maximum $\sigma _{\rm d}$.

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Anisotropic growth of multigrain in equiaxial solidification simulated with the phase field method Li Mei-E (李梅娥), Xiao Zhi-Ying (肖志英), Yang Gen-Cang (杨根仓), Zhou Yao-He (周尧和) Chinese Physics, 2006, 15 (1):  219-223.  DOI: 10.1088/1009-1963/15/1/036 Abstract ( 1485 )   PDF (417KB) ( 544 )   The phase field method has been mainly used to simulate the growth of a single crystal in the past. But polycrystalline materials predominate in engineering. In this work, a phase field model for multigrain solidification is developed, which takes into account the random crystallographic orientations of crystallites and preserves the rotational invariance of the free energy. The morphological evolution of equiaxial multigrain solidification is predicted and the effect of composition on transformation kinetics is studied. The numerical results indicate that due to the soft impingement of grains the Avrami exponent varies with the initial melt composition and the solidification fraction.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Molecular dynamics of MgSiO3 perovskite melting Liu Zi-Jiang (刘子江), Cheng Xin-Lu (程新路), Yang Xiang-Dong (杨向东), Zhang Hong (张红), Cai Ling-Cang (蔡灵仓) Chinese Physics, 2006, 15 (1):  224-228.  DOI: 10.1088/1009-1963/15/1/037 Abstract ( 1544 )   PDF (242KB) ( 688 )   The melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments.

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Mass neutrino oscillations in Robertson--Walker space--time Huang Xiu-Ju (黄秀菊), Li Ze-Jun (李泽军), Wang Yong-Jiu (王永久) Chinese Physics, 2006, 15 (1):  229-231.  DOI: 10.1088/1009-1963/15/1/038 Abstract ( 1299 )   PDF (179KB) ( 615 )   Along the geodesic we calculate the interference phase of the mass neutrinos propagating in the radial direction in Robertson--Walker space--time. Since our universe is expanding, the phase factor $\varPhi$ is increasing under the condition of the same proper physical distance l. Different values of curvature parameter k in Robertson--Walker metric represent different cosmological models, correspondingly, we obtain the different interference phases.

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Frame dragging in the field of Kerr family He Tang-Mei (何唐梅), Wang Yong-Jiu (王永久) Chinese Physics, 2006, 15 (1):  232-234.  DOI: 10.1088/1009-1963/15/1/039 Abstract ( 1747 )   PDF (177KB) ( 631 )   The interesting phenomenon of frame dragging which is associated with the rotation of the source in the field of Kerr family is discussed, and the angular velocity of an uncharged test particle is obtained with a straightforward mathematical method.

RAPID COMMUNICATION

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Single-mode quadrature-amplitude measurement for generalized two-mode squeezed states studied by virtue of the entangled state representation Xu Xue-Fen (许雪芬) Chinese Physics, 2006, 15 (1):  235-241.  DOI: 10.1088/1009-1963/15/1/040 Abstract ( 1645 )   PDF (237KB) ( 677 )   The result of one-mode quadrature-amplitude measurement for some generalized two-mode squeezed states has been studied by virtue of the entangled state representation of the corresponding two-mode squeezing operators. We find that the remaining field-mode simultaneously collapses to the single-mode squeezed state with more stronger squeezing. The measurement result caused by a single-mode squeezed state projector is also calculated, which indicates quantum entanglement in squeezing.