Table of contents

16 April 2003, Volume 12 Issue 4 Previous issue    Next issue

GENERAL

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Stability for the equilibrium state manifold of relativistic Birkhoffian systems Fu Jing-Li (傅景礼), Chen Li-Qun (陈立群), Luo Yi (骆毅), Luo Shao-Kai (罗绍凯) Chinese Physics, 2003, 12 (4):  351-356.  DOI: 10.1088/1009-1963/12/4/301 Abstract ( 1296 )   PDF (237KB) ( 446 )   In this paper, the stability of equilibrium state manifold for relativistic Birkhoffian systems is studied. The equilibrium state equations, the disturbance equations and their first approximation are presented. The criteria of stability for the equilibrium state manifold are obtained. The relationship between the stability of the equilibrium-state manifold of relativistic Birkhoffian systems and that of classical Birkhoffian systems is discussed. An example is given to illustrate the results.

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A set of the Lie symmetrical conservation laws for the rotational relativistic Birkhoffian system Luo Shao-Kai (罗绍凯), Cai Jian-Le (蔡建乐) Chinese Physics, 2003, 12 (4):  357-360.  DOI: 10.1088/1009-1963/12/4/302 Abstract ( 1238 )   PDF (206KB) ( 540 )   For a rotational relativistic Birkhoffian system, a set of the Lie symmetries and conservation laws is given under infinitesimal transformations. On the basis of the invariance of rotational relativistic Birkhoffian equations under infinitesimal transformations, Lie symmetrical transformations of the system are constructed, which only depend on the Birkhoffian variables. The determining equations of Lie symmetries are given, and a new type of non-noether conserved quantities are directly obtained from Lie symmetries of the system. An example is given to illustrate the application of the results.

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Explicit and exact travelling plane wave solutions of the (2+1)-dimensional Boussinesq equation Huang Wen-Hua (黄文华), Jin Mei-Zhen (金美贞) Chinese Physics, 2003, 12 (4):  361-364.  DOI: 10.1088/1009-1963/12/4/303 Abstract ( 1202 )   PDF (195KB) ( 604 )   The deformation mapping method is applied to solve a system of (2+1)-dimensional Boussinesq equations. Many types of explicit and exact travelling plane wave solutions, which contain solitary wave solutions,periodic wave solutions,Jacobian elliptic function solutions and others exact solutions, are obtained by a simple algebraic transformation relation between the (2+1)-dimensional Boussinesq equation and the cubic nonlinear Klein－Gordon equation.

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Sodium atom in strong magnetic fields: a pseudospectral approach Zou Yuan-Chuan (邹远川), Zhang Zhan-Jun (张战军), Qiao Hao-Xue (乔豪学) Chinese Physics, 2003, 12 (4):  365-370.  DOI: 10.1088/1009-1963/12/4/304 Abstract ( 1203 )   PDF (248KB) ( 379 )   Energies and wavefunctions of low-lying states and Rydberg states for the sodium atom in uniform magnetic fields varying from 0 to 105T are calculated using a pseudospectral approach with a model potential in spherical coordinates. The energies are comparable with experimental results as well as those obtained by other calculations. The spectra of oscillator strength are worked out. The evolution of them with the magnetic field is shown.

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Quantization of the space－time with topological defect Gao Chang-Jun (高长军), Shen You-Gen (沈有根) Chinese Physics, 2003, 12 (4):  371-376.  DOI: 10.1088/1009-1963/12/4/305 Abstract ( 1153 )   PDF (232KB) ( 405 )   We present the classical solution of Lagrange equations for the black hole with a global monopole or with a cosmic string. Then we obtain the wavefunction of the space－time by solving the Wheeler－De Witt equation. De Broglie－Bohm interpretation applied to the wavefunction gives the quantum solution of the space－time. In the end, the quantum effect on Hawking radiation is studied.

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Stochastic resonance in parabolic-bistable potential system with an additive colour noise Liang Gui-Yun (梁贵云) Chinese Physics, 2003, 12 (4):  377-380.  DOI: 10.1088/1009-1963/12/4/306 Abstract ( 1051 )   PDF (347KB) ( 479 )   We propose a new model (parabolic bistable system) with a colour noise source. In the presence of periodic input signal, we investigate the output signal to-noise ratio and the power spectral density of output signal, in which the self-correlation time may be an arbitrary value with no restriction. We find that the curves of signal-to-noise ratio versus the noise intensity D exhibits a bell-shape behaviour. The peak height increases with the increasing value of amplitude A0 of the input signal. However, the position of peak does not shift. Moreover, the signal-to-noise ratio is insensitive to the modulation frequency $\varOmega$, which completely differs from result of Ref.[6]. The power spectral density also has similar behaviour.

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Synchronization of the time-varying parameter chaotic system and its application to secure communication Mu Jing (牟静), Tao Chao (陶超), Du Gong-Huan (杜功焕) Chinese Physics, 2003, 12 (4):  381-388.  DOI: 10.1088/1009-1963/12/4/307 Abstract ( 1154 )   PDF (288KB) ( 447 )   In this paper we propose and investigate the synchronization of a new chaotic model with time-varying parameters and apply it to improve the security of chaotic communication. In this model, the chaotic system is modulated by both the message and the varying parameters. The varying parameters distort the phase space so heavily that they prevent the carrier from being broken by nonlinear dynamic forecasting method. Theory and simulation experiments with speech signal communication indicate that the receiver can gain a perfect synchronization with the transmitter, and the intruder cannot break down this communication system. We also discuss the robustness of the new communication system.

NUCLEAR PHYSICS

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Low frequency effects of surface states on 4H-SiC metal-semiconductor field effect transistor Yang Lin-An (杨林安), Yu Chun-Li (于春利), Zhang Yi-Men (张义门), Zhang Yu-Ming (张玉明) Chinese Physics, 2003, 12 (4):  389-393.  DOI: 10.1088/1009-1963/12/4/308 Abstract ( 1149 )   PDF (233KB) ( 515 )   The process-related surface state effect is investigated the fabrication of SiC devices, and a nonlinear model for 4H-SiC power metal-semiconductor field effect transistor (MESFET) is proposed, which takes into account the surface-related parameters. The frequency- and temperature- dependent transconductance dispersion is readily demonstrated in terms of the improved model. Simulation results show that larger dispersion and higher transition frequency occur in 4H-SiC MESFET than in GaAs MESFET. The advantage of this analytical model over the two-dimensional numerical simulation is the simplicity of calculations, therefore it is suitable for the processing improvement of SiC devices.

ATOMIC AND MOLECULAR PHYSICS

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Nonlinear interaction of resonator photons with parametric magnon pairs Shi Qing-Fan (史庆藩), Yan Xue-Qun (闫学群), Liu Xue-Guan (刘学观) Chinese Physics, 2003, 12 (4):  394-398.  DOI: 10.1088/1009-1963/12/4/309 Abstract ( 1017 )   PDF (222KB) ( 346 )   We consider the process of parametric resonance of magnons in magneto-ordered crystals in a microwave resonator. The nonlinear interaction of the resonator photons with the parametric magnon pairs is analysed theoretically, and the result expressed by the deviation frequencies relative to the pump frequency further demonstrates that the dynamics of resonator modes plays an important role once the pump power exceeds the threshold of parallel pumping.

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Transmission spectroscopy in a thin vapour layer and its derivative properties Zhao Yan-Ting (赵延霆), Zhao Jian-Ming (赵建明), Xiao Lian-Tuan (肖连团), Jia Suo-Tang (贾锁堂) Chinese Physics, 2003, 12 (4):  399-402.  DOI: 10.1088/1009-1963/12/4/310 Abstract ( 1067 )   PDF (223KB) ( 320 )   A novel method of high-resolution spectroscopy of gases is proposed. The method is based on observing the optical behaviour of thin vapour layer when the particles cross the light beam or collide with the cell walls. The atomic motion and electronic quenching on gas-solid interfaces are explored by numerical analysis. The periodicity of peak values of transmission spectra and its derivative spectra demonstrates a sub-Doppler structure corresponding to the resonant transitions.

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Light-induced nonlinear effects on dispersion relation of ultracold Bose gas Hu Zheng-Feng (胡正峰), Du Chun-Guang (杜春光), Li Shi-Qun (李师群) Chinese Physics, 2003, 12 (4):  403-407.  DOI: 10.1088/1009-1963/12/4/311 Abstract ( 1109 )   PDF (224KB) ( 396 )   We have investigated the optical properties of $\Lambda$-configuration ultracold dense Bose gas interacting with two laser pulses, which usually result in electromagnetically induced transparency. With the nonrelativistic quantum electrodynamics and taking into account the atomic dipole－dipole interaction and local field effect, we have derived the Maxwell－Bloch equations of the system. The dispersion relation of an ultracold Bose gas has been obtained and the light-induced nonlinear effects have been analysed. The light-induced nonlinear effects are different from the effects induced by two-body collision of Bose－Einstein condensation atoms which have a frequency shift of transparent window.

CLASSICAL AREAS OF PHENOMENOLOGY

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Non-conservation of energy arising from atomic dipole interactions and its effects on light field and coupled atoms Dong Chuan-Hua (董传华) Chinese Physics, 2003, 12 (4):  408-414.  DOI: 10.1088/1009-1963/12/4/312 Abstract ( 1210 )   PDF (316KB) ( 355 )   The interactions between coupled atoms and a single mode of a quantized electromagnetic field, which involve the terms originating from the dipole interactions, are discussed. In the usual Jaynes－Cummings model for coupled atoms, the terms of non-conservation of energy originating from dipole interactions are neglected, however, we take them into consideration in this paper. The effects of these terms on the evolutions of quantum statistic properties and squeezing of the field, the squeezing of atomic dipole moments and atomic population inversion are investigated. It has been shown that the coupling between atoms modulates these evolutions of fields and atoms. The terms of non-conservation of energy affect these evolutions of fields and atoms slightly. They also have effects on the squeezing of the field, the squeezing of atomic dipole and atomic population inversions. The initial states of atoms also affect these properties.

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Influence of group-velocity mismatch on soliton switching in a nonlinear fibre coupler Li Hong (李宏), Huang De-Xiu (黄德修), Wang Dong-Ning (王东宁) Chinese Physics, 2003, 12 (4):  415-418.  DOI: 10.1088/1009-1963/12/4/313 Abstract ( 1191 )   PDF (209KB) ( 471 )   In this work, the influence of group-velocity mismatch on soliton self-routing pulse switching in a nonlinear fibre coupler is discussed in detail by the use of both variational approach and numerical simulation. The results obtained show that the group-velocity mismatch leads to the relative displacement between the two orthogonal polarization modes, increase of the critical power, and reduction of the elimination-light ratio. For sub-ps pulse, the influence cannot be neglected.

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

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Inspection of the number of electrons in the ring of a quantum dot Huang Gang-Ming (黄钢明), Bao Cheng-Guang (鲍诚光) Chinese Physics, 2003, 12 (4):  419-425.  DOI: 10.1088/1009-1963/12/4/314 Abstract ( 934 )   PDF (554KB) ( 478 )   On the electronic structures of quantum dots, there is a new viewpoint saying that, in some specific states, a few electrons might behave as valence electrons moving outside surrounding a core. To clarify the validity of this viewpoint, a numerical calculation was performed in this paper. The results are against this viewpoint.

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Effect of crystalline microstructure on the photophysical performance of polymer/perylene composite films Feng Wei (封伟), Xu You-Long (徐友龙), Yi Wen-Hui (易文辉), Zhou Feng (周峰), Wang Xiao-Gong (王晓工), Yoshino Katsumi (吉野勝美) Chinese Physics, 2003, 12 (4):  426-432.  DOI: 10.1088/1009-1963/12/4/315 Abstract ( 1119 )   PDF (284KB) ( 497 )   To obtain high carrier mobility, better charge injection capability, and high photovoltaic device conversion efficiency, a powerful strategy is to improve the morphology of the polymer/dye composite films. Conjugated conducting polymer (CP) thin films doped with perylene derivative (PV) of various concentrations were prepared by spin-casting method, and their morphology and photovoltaic characteristics were examined. The change in morphology and molecular reorientation occurring in CP-PV composite films upon annealing at different temperatures was investigated using scanning electron microscopy, x-ray diffraction, Fourier transform infrared and UV-vis absorption. By changing the annealing temperature, PV microcrystallines of 8－10μm in size lying parallel to the substrate surface can be obtained. Annealing effect improved the photovoltaic performance of ITO/CP-PV/Al Schottky-type solar cells, which can be attributed to the formation of an electron conducting PV crystal network. Preliminary studies indicate that the morphological structure in CP-PV composite films has an important influence to their photovoltaic properties.

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Composites of nanotubular polyaniline containing Fe3O4 nanoparticles Long Yun-Ze (龙云泽), Chen Zhao-Jia (陈兆甲), Liu Zhen-Xing (刘振兴), Zhang Zhi-Ming (张志明), Wan Mei-Xiang (万梅香), Wang Nan-Lin (王楠林) Chinese Physics, 2003, 12 (4):  433-437.  DOI: 10.1088/1009-1963/12/4/316 Abstract ( 1376 )   PDF (390KB) ( 502 )   Results of charge-transport and magnetic measurements of nanotubular polyaniline (PANI) composites containing Fe3O4 nanoparticles (～10nm) synthesized by a "template-free" method are reported. The T -1/2 resistivity has been observed, and dc magnetic susceptibility data are fitted to an equation $\chi=\chi_P^*+C/T$. With increasing weight ratio of Fe3O4, the electrical conductivity and temperature- independent susceptibility $\chi_P^*$ increase, and the Curie-type susceptibility is suppressed at low temperatures. Further discussions have been given. The PANI-H3PO4/Fe3O4 composite containing 27wt% of Fe3O4 nanoparticles is superparamagnetic, exhibiting very little hysteresis even at 5K.

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Role of amorphous silicon domains on Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide film Chen Chang-Yong (陈长勇), Chen Wei-De (陈维德), Li Guo-Hua (李国华), Song Shu-Fang (宋淑芳), Ding Kun (丁琨), Xu Zhen-Jia (许振嘉) Chinese Physics, 2003, 12 (4):  438-442.  DOI: 10.1088/1009-1963/12/4/317 Abstract ( 1036 )   PDF (345KB) ( 445 )   An investigation on the correlation between amorphous Si (a-Si) domains and Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H<Er>) film is presented. On one hand, a-Si domains provide sufficient carriers for Er3+ carrier-mediated excitation which has been proved to be the highest excitation path for Er3+ ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiOx) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er3+ ions. This study provides a better understanding of the role of a-Si domains on Er3+ emission in a-Si:O:Hfilms.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Kinetic behaviour of two-species-group aggregation process with complete annihilation Ke Jian-Hong (柯见洪), Lin Zhen-Quan (林振权), Wang Xiang-Hong (王向红) Chinese Physics, 2003, 12 (4):  443-451.  DOI: 10.1088/1009-1963/12/4/318 Abstract ( 715 )   PDF (253KB) ( 332 )   We propose a two-species-group aggregation-annihilation model in which an irreversible aggregation reaction occurs between any two clusters of the same species, and an irreversible joint annihilation reaction occurs between two distinct species groups. Based on the mean-field theory, we have investigated the rate equations of the process with constant reaction rates to obtain the asymptotic descriptions of the cluster-mass distributions. The results indicate that for the symmetrical initial cases the kinetic behaviour of the system depends crucially on the ratio of the equivalent aggregation rate to the annihilation rate. The cluster-mass distribution of each species always obeys a conventional or modified scaling law in each individual case. Moreover, all the species cannot finally survive except for the cases in which at least one equivalent aggregation rate is less than twice the annihilation rate.