Table of contents

15 July 2001, Volume 10 Issue 7 Previous issue    Next issue

GENERAL

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SOME PROGRESS IN THE LATTICE BOLTZMANN MODEL Feng Shi-de (冯士德), Tsutahara Michihisa, Ji Zhong-zhen (季仲贞) Chinese Physics, 2001, 10 (7):  587-593.  DOI: 10.1088/1009-1963/10/7/301 Abstract ( 1026 )   PDF (260KB) ( 533 )   A lattice Boltzmann equation model has been developed by using the equilibrium distribution function of the Maxwell－Boltzmann-like form, which is third order in fluid velocity $u_\alpha$. The criteria of energy conservation between the macroscopic physical quantities and the microscopic particles are introduced into the model, thus the thermal hydrodynamic equations containing the effect of buoyancy force can be recovered in terms of the Taylor and Chapman－Enskog asymptotic expansion methods. The two-dimensional thermal convection phenomena in a square cavity and between two concentric cylinders have been calculated by implementing a heat flux boundary condition. Both numerical results are in good agreement with the conventional numerical results.

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DIRECT APPROACH FOR SOLITON PERTURBATIONS BASED ON THE GREEN'S FUNCTION Pan Liu-xian (潘留仙), Yan Jia-ren (颜家壬), Zhou Guang-hui (周光辉) Chinese Physics, 2001, 10 (7):  594-598.  DOI: 10.1088/1009-1963/10/7/302 Abstract ( 1152 )   PDF (232KB) ( 517 )   A direct approach has been developed for soliton perturbations based on the Green's function. We first linearized the soliton equation, and then derived the Green's function corresponding to approximation equations of different orders. Finally, we obtained the effects of perturbation on a soliton, namely both the slow time dependence of the soliton parameters and the corrections up to the second-order approximation. The higher-order effects can also be obtained in the same way.

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ADDING ONE BIFURCATION IN A ROTOR SYSTEM WITH CLEARANCES Sun Zheng-ce (孙政策), Xu Jian-xue (徐健学) Chinese Physics, 2001, 10 (7):  599-605.  DOI: 10.1088/1009-1963/10/7/303 Abstract ( 990 )   PDF (194KB) ( 494 )   A mathematical model of a rotor system with clearances is analysed by the application of modern nonlinear dynamic theory. From the bifurcation diagrams, it is discovered that the rotor system alternates between periodic and chaotic motions at a supercritical rotational speed, and after undergoing a chaotic region the periodic number of the motion will increase by one. At the same time, the periodic number is equal correspondingly to the integral multiple of the critical rotational speed. At the subcritical rotational speed, it is discovered that the chaotic bands among successive orders of superharmonic responses return to the period one through a reversed period-doubling bifurcation, as a result of a period-doubling bifurcation. It is shown that the increase of damping may reduce the width of the chaotic bands and the amplitude of the periodic response; the increase of nonlinear degree also leads to the reduction of chaotic bandwidth, but makes the amplitude of the subharmonic response increase. So it is suggested that proper damping and correct material selection by considering the dynamic characteristics of the rotor system may reduce the proportion of faults and enhance the dynamic characteristics when designing the rotor system. The working speed should not be selected at N times its natural frequency and should not be set in the chaotic bands among the successive orders of periodic motion for the same purpose.

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SYNCHRONIZATION FOR A CLASS OF CHAOTIC SYSTEMS BASED UPON OBSERVER THEORY Liu Feng (刘锋), Ren Yong (任勇), Shan Xiu-ming (山秀明), Qiu Zu-lian (邱祖廉) Chinese Physics, 2001, 10 (7):  606-610.  DOI: 10.1088/1009-1963/10/7/304 Abstract ( 1219 )   PDF (111KB) ( 425 )   A new synchronization theorem for a class of chaotic systems is presented based on nonlinear observer theory. We take the first state variable of the drive system as the driving scalar signal. Its linear feedback gain is a function of a free parameter. It is proven that global synchronization can be attained through simple linear output error feedback. This approach is illustrated by the WGY hyperchaotic system and Chua's oscillator.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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NEW MESON MASS RELATION AND LOWEST PSEUDOSCALAR GLUEBALL MASS Wu Ning (吴宁), Ruan Tu-nan (阮图南), Zheng Zhi-peng (郑志鹏) Chinese Physics, 2001, 10 (7):  611-612.  DOI: 10.1088/1009-1963/10/7/305 Abstract ( 1137 )   PDF (176KB) ( 472 )   After considering its mixing with the glueball, we give a new mass relation for the meson nonet. According to this mass relation and the predicted mass of the pseudoscalar glueball given by lattice calculations and the effective Hamiltonian, the expected mass of the mixed pseudoscalar glueball is about 1.7 GeV. This result is helpful in the experimental search for the mixed isoscalar pseudoscalar glueball. $\eta$(1760) is discussed as a possible candidate for this type of particle.

CLASSICAL AREAS OF PHENOMENOLOGY

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A NONLINEAR ANALYTICAL AND NUMERICAL STUDY FOR AN OPEN SYSTEM WITH COHERENT OFF-RESONANCE FIELDS Fan Xi-jun (樊锡君), Li Ping (李萍), Tian Shu-fen (田淑芬), Zhang Jun-liang (张郡亮), Liu Cheng-pu (刘呈普) Chinese Physics, 2001, 10 (7):  613-620.  DOI: 10.1088/1009-1963/10/7/306 Abstract ( 1431 )   PDF (193KB) ( 394 )   An exact nonlinear analytical solution of an open V-type inversionless lasing system with two incoherent pump fields, off-resonant driving and probe fields is given. Through qualitative and quantitative comparison of the gain, dispersion and population differences of the linear and nonlinear cases, some conclusions concerning the Rabi frequencies of the driving and the probe fields are drawn and discussed in detail.

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DESIGN OF A 532nm Nd:YVO4/KTP SINGLE-FREQUENCY LASER Xu Chun-lin (徐春林), Shen Nai-cheng (沈乃澂), Zang Er-jun (臧二军), Sun Yi-min (孙义民), Lu Hai-ning (鲁海宁), Zhao Kun (赵昆), Zhang Xue-bin (张学斌) Chinese Physics, 2001, 10 (7):  621-625.  DOI: 10.1088/1009-1963/10/7/307 Abstract ( 1452 )   PDF (306KB) ( 1079 )   A model of the laser-diode pumped solid-state laser is developed to deduce the minimum average radii of the pump beam in the solid medium, since the smaller the cavity waist, the higher the laser output power is expected to be. With an appropriate coupling system consisting of the collimating lens, prism pair and focusing lens, a diode-pumped single-frequency Nd:YVO4/KTP intracavity frequency-doubling cw laser has been demonstrated through the precise temperature control of the Nd:YVO4 crystal, the KTP crystal and the diode laser. The 532nm single-frequency output power of 40.4mW (in fact 55mW if the reflection loss of the triangular prism is taken into account) is obtained for an incident power of 515mW. It is derived theoretically and is verified in experiment that the frequency drift of the free-running laser can be reduced by increasing the cavity length.

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NONLINEAR PULSE PROPAGATION IN TWIN-CORE FIBRES WITH BIREFRINGENCE Li Hong (李宏), Huang De-xiu (黄德修) Chinese Physics, 2001, 10 (7):  626-630.  DOI: 10.1088/1009-1963/10/7/308 Abstract ( 1011 )   PDF (211KB) ( 423 )   An equation describing the nonlinear pulse propagation in twin-core fibres with birefringence is derived. Particularly, the properties of the nonlinear coupling equation are analysed, and modulational instability is discussed in detail.

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FABRICATION AND APPLICATION OF NEAR-FIELD OPTICAL FIBRE PROBE Sun Jia-lin (孙家林), Xu Jian-hua (徐建华), Tian Guang-yan (田广彦), Guo Ji-hua (郭继华), Zhao Jun (赵钧), Xie Ai-fang (谢爱芳), Zhang Ze-bo (张泽渤) Chinese Physics, 2001, 10 (7):  631-635.  DOI: 10.1088/1009-1963/10/7/309 Abstract ( 1214 )   PDF (851KB) ( 443 )   In this paper, the fabrication of a large cone angle near-field optical fibre probe, using the two-step chemical etching method and bent probe, is introduced, and the controlling parameters of the coated Cr－Al film at the probe tip are presented. The scanning electron microscopy images display that the tip diameter of the uncoated large cone angle fibre probe obtained is less than 50nm, the cone angle over 90°, and the diameter of light aperture at the coated probe tip is less than 100nm. The measured results of the optical transmission efficiency for various probe tips show that the uncoated straight optical fibre probe, film-coated straight probe and film-coated bent probe are 3×10-1, 2×10-3, and 1×10-4 times that of the flat fibre probe, respectively. In addition, the force images and near-field optical images of a standard sample are acquired using a large cone angle and film-coated bent probe.

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TO ENHANCE THE INTENSITY OF SONOLUMINESCENCE Qian Zu-wen (钱祖文) Chinese Physics, 2001, 10 (7):  636-638.  DOI: 10.1088/1009-1963/10/7/310 Abstract ( 1015 )   PDF (179KB) ( 538 )   The transient resonance of a sonoluminescence bubble has been analysed. When the bubble performs its transient resonance at the nth order harmonics of the standing waves in the liquid, the light intensity strongly depends on the amplitude of the driving pressure (proportional to its 2n power, with $n=f_r/f$, where $f_r$ is Minnaert's linear resonant frequency of the bubble and f is the frequency of driving sound). The kinetic energy of a vibrating bubble becomes maximum approximately when it is in its equilibrium size. For example, when the ambient temperature of a bubble decreases from 34℃ to 4℃, a huge increase of the light intensity emitted by it can be explained. A suggestion was made that, within the limits permitted by the phase diagrams, as high an increase in driving pressure as possible could enhance the light intensity of sonoluminescence up to four orders of magnitude.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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ELECTRON TRANSPORT BEHAVIOURS IN THE NITROGEN DIRECT CURRENT GLOW DISCHARGE Zhang Lian-zhu (张连珠), Yu Wei (于威), Wang Jiu-li (王久丽), Han Li (韩理), Fu Guang-sheng (傅广生) Chinese Physics, 2001, 10 (7):  639-644.  DOI: 10.1088/1009-1963/10/7/311 Abstract ( 1055 )   PDF (147KB) ( 545 )   A Monte Carlo simulation is presented to describe the electron transport behaviours in the nitrogen direct current glow discharge. The energy and angular distributions of the electrons at different positions of the cathode dark space are calculated; their energy and density distribution features throughout the entire discharge are discussed. The influence of molecular vibrational excitation, typical for electron－molecule collisions, has been studied and the elementary process of active species generation has been illustrated. The simulated results reveal that, in the cathode dark space, the high-energy electrons are mainly forward scattering and behave as a high-energy ‘electron beam'. The sharp increase of the number of secondary electrons plays an important role in producing active species at the interface between the cathode dark space and the negative glow region. The vibrational excitation enhances the energy loss of electrons in the negative glow region.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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ON THE SATURATION BEHAVIOUR OF TWISTED NEMATIC LIQUID CRYSTAL CELLS WITH A NONZERO PRETILT ANGLE Zhang Zhi-dong (张志东), Yu Hui (于慧), Li Li (李丽) Chinese Physics, 2001, 10 (7):  645-649.  DOI: 10.1088/1009-1963/10/7/312 Abstract ( 1186 )   PDF (122KB) ( 483 )   Equations are obtained for the surface tilt angle and the twist angle of the director in a twisted nematic liquid crystal cell under a high magnetic field. Under a zero pretilt angle, the two equations reduce to those obtained by Sugimura et al.[2,3] This fact has also been demonstrated numerically. With finite field strength and nonzero pretilt angle, no saturation transition exists.

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INFRARED EMISSION FROM Si IMPLANTED WITH HIGH Er CONCENTRATION Xiao Zhi-song (肖志松), Xu Fei (徐飞), Zhang Tong-he (张通和), Cheng Guo-an (程国安), Xie Da-tao (谢大韬), Gu Lan-lan (顾岚岚) Chinese Physics, 2001, 10 (7):  650-654.  DOI: 10.1088/1009-1963/10/7/313 Abstract ( 1249 )   PDF (390KB) ( 521 )   Erbium-doped silicon has been fabricated by ion implantation performed on a metal vapour vacuum arc ion source. After rapid thermal annealing (RTA), 1.54μm photoluminescence was observed at 77K. Rutherford backscattering spectrum indicated that Er ions are mainly distributed near the surface of the samples, and Er concentration exceeded 1021cm-3. Needle nanometre crystalline silicon (nc-Si) was formed on the substrate surface. Band edge emission spectrum at 10K verified that the minority carrier lifetime increased upon RTA. The photocarrier mediated processes enabled energy transferring from nc-Si (or c-Si) to the Er3+ ions and resulted in light emission of 1.54μm.

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

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EXCITON ENERGY OF THE InAs/GaAs SELF-ASSEMBLED QUANTUM DOT IN A SEMICONDUCTOR MICROCAVITY Pan Liu-xian (潘留仙), Li Shu-shen (李树深), Xia Jian-bai (夏建白) Chinese Physics, 2001, 10 (7):  655-657.  DOI: 10.1088/1009-1963/10/7/314 Abstract ( 1216 )   PDF (107KB) ( 482 )   We report on the theoretical study of the interaction of the quantum dot (QD) exciton with the photon waveguide models in a semiconductor microcavity. The InAs/GaAs self-assembled QD exciton energies are calculated in a microcavity. The calculated results reveal that the electromagnetic field reduces the exciton energies in a semiconductor microcavity. The effect of the electromagnetic field decreases as the radius of the QD increases. Our calculated results are useful for designing and fabricating photoelectron devices.

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A FORMULA FOR CALCULATING THE ERRORS OF SUPERCONDUCTING MAGNETIZATION CURVE Guo Shu-quan (郭树权), Liu Meng-lin (刘梦林), Zheng Dong-ning (郑东宁), Zhao Bai-ru (赵柏儒) Chinese Physics, 2001, 10 (7):  658-661.  DOI: 10.1088/1009-1963/10/7/315 Abstract ( 1147 )   PDF (121KB) ( 485 )   Because of field inhomogeneity in the magnetization measurement system, large errors may exist in the decreasing field superconducting magnetization curves, but not in the increasing field curves. The physical origin of the large errors is proposed here. A simple formula for calculating the errors is given. This formula is consistent with the experimental data.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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GAMMA-RAY LIGHT CURVE AND PHASE-RESOLVED SPECTRA FROM GEMINGA PULSAR Zhang Li (张力), Bian Xia (边霞), Mei Dong-cheng (梅冬成) Chinese Physics, 2001, 10 (7):  662-665.  DOI: 10.1088/1009-1963/10/7/316 Abstract ( 1053 )   PDF (138KB) ( 470 )   We calculate the light curve and phase-resolved spectra of Geminga in a three-dimensional pulsar magnetosphere model. The light curve of gamma-rays is consistent with that observed if the magnetic inclination and viewing angle are ～50° and ～86° respectively. We also model the phase-resolved spectra of the Geminga pulsar.