Table of contents

12 November 2002, Volume 11 Issue 11 Previous issue    Next issue

GENERAL

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Generalized energy integral and reduction of rotational relativistic Birkhoffian system Luo Shao-Kai (罗绍凯) Chinese Physics, 2002, 11 (11):  1097-1100.  DOI: 10.1088/1009-1963/11/11/301 Abstract ( 1135 )   PDF (197KB) ( 504 )   We study the order reduction method of the rotational relativistic Birkhoffian equations. For a rotational relativistic autonomous Birkhoffian system, if the conservative law of the Birkhoffian holds, the conservative quantity can be called the generalized energy integral. Through the generalized energy integral, the order of the system can be reduced. If the rotational relativistic Birkhoffian system has a generalized energy integral, then the Birkhoffian equations can be reduced by at least two degrees and the Birkhoffian form can be kept. An example is given to illustrate the application of the result.

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Coherent soliton structures of the (2+1)-dimensional long-wave－short-wave resonance interaction equation Huang Wen-Hua (黄文华), Zhang Jie-Fang (张解放), Sheng Zheng-Mao (盛正卯), Chinese Physics, 2002, 11 (11):  1101-1105.  DOI: 10.1088/1009-1963/11/11/302 Abstract ( 1184 )   PDF (303KB) ( 638 )   The variable separation approach is used to find exact solutions of the (2+1)-dimensional long-wave－short-wave resonance interaction equation. The abundance of the coherent soliton structures of this model is introduced by the entrance of an arbitrary function of the seed solutions. For some special selections of the arbitrary function, it is shown that the coherent soliton structures may be dromions, solitoffs, etc.

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Stochastic resonance in a financial model Mao Xiao-Ming (毛晓明), Sun Kai (孙锴), Ouyang Qi (欧阳颀) Chinese Physics, 2002, 11 (11):  1106-1110.  DOI: 10.1088/1009-1963/11/11/303 Abstract ( 1541 )   PDF (224KB) ( 657 )   We report on our model study of stochastic resonance in the stock market using numerical simulation and analysis. In the model, we take the interest rate as the external signal, the randomness of traders' behaviour as the noise, and the stock price as the output. With computer simulations, we find that the system demonstrates a characteristic of stochastic resonance as noise intensity varies. An analytical explanation is proposed.

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Mapping deformation method and its application to nonlinear equations Li Hua-Mei (李画眉) Chinese Physics, 2002, 11 (11):  1111-1114.  DOI: 10.1088/1009-1963/11/11/304 Abstract ( 1407 )   PDF (191KB) ( 546 )   An extended mapping deformation method is proposed for finding new exact travelling wave solutions of nonlinear partial differential equations (PDEs). The key idea of this method is to take full advantage of the simple algebraic mapping relation between the solutions of the PDEs and those of the cubic nonlinear Klein－Gordon equation. This is applied to solve a system of variant Boussinesq equations. As a result, many explicit and exact solutions are obtained, including solitary wave solutions, periodic wave solutions, Jacobian elliptic function solutions and other exact solutions.

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Study of the Wada fractal boundary and indeterminate crisis Hong Ling (洪灵), Xu Jian-Xue (徐健学) Chinese Physics, 2002, 11 (11):  1115-1123.  DOI: 10.1088/1009-1963/11/11/305 Abstract ( 1244 )   PDF (452KB) ( 505 )   By using the generalized cell mapping digraph (GCMD) method, we study bifurcations governing the escape of periodically forced oscillators in a potential well, in which a chaotic saddle plays an extremely important role. In this paper, we find the chaotic saddle, and we demonstrate that the chaotic saddle is embedded in a strange fractal boundary which has the Wada property, that any point on the boundary of that basin is also simultaneously on the boundary of at least two other basins. The chaotic saddle in the Wada fractal boundary, by colliding with a chaotic attractor, leads to a chaotic boundary crisis with a global indeterminate outcome which presents an extreme form of indeterminacy in a dynamical system. We also investigate the origin and evolution of the chaotic saddle in the Wada fractal boundary, particularly concentrating on its discontinuous bifurcations (metamorphoses). We demonstrate that the chaotic saddle in the Wada fractal boundary is created by the collision between two chaotic saddles in different fractal boundaries. After a final escape bifurcation, there only exists the attractor at infinity; a chaotic saddle with a beautiful pattern is left behind in phase space.

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A secure communication method for a high-power information signal based on chaotic masking Li Jian-Fen (李建芬), Li Nong (李农) Chinese Physics, 2002, 11 (11):  1124-1127.  DOI: 10.1088/1009-1963/11/11/306 Abstract ( 1269 )   PDF (216KB) ( 462 )   In this paper, we present a secure communication method for a high-power information signal based on chaotic masking. In the transmitter, an adaptive controller is adopted to pick up the change of the information signal, and to inject the controller's error into the transmitting system. At the same time, the information is directly added to the chaotic signal in transmission to drive the receiving system. In the receiver, another adaptive controller is used to maintain chaotic synchronization of the transmitting and receiving systems and to recover the information signal. Since the synchronization error is independent from the information signal, the power of the information signal can be equivalent to that of the chaotic signal, and the frequency of the information signal can be set within the range of the principal frequencies of the chaotic signal. The results of theoretical analysis and numerical simulation show that the presented method not only enhances the degree of security of low-dimensional chaotic systems but also significantly improves the signal-to-noise ratio at the receiving end.

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Analysis of the stability and density waves for traffic flow Xue Yu (薛郁) Chinese Physics, 2002, 11 (11):  1128-1134.  DOI: 10.1088/1009-1963/11/11/307 Abstract ( 1487 )   PDF (297KB) ( 993 )   In this paper, the optimal velocity model of traffic is extended to take into account the relative velocity. The stability and density waves for traffic flow are investigated analytically with the perturbation method. The stability criterion is derived by the linear stability analysis. It is shown that the triangular shock wave, soliton wave and kink wave appear respectively in our model for density waves in the three regions: stable, metastable and unstable regions. These correspond to the solutions of the Burgers equation, Korteweg－de Vries equation and modified Korteweg－de Vries equation. The analytical results are confirmed to be in good agreement with those of numerical simulation. All the results indicate that the interaction of a car with relative velocity can affect the stability of the traffic flow and raise critical density.

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A scanning superconducting quantum interference device microscope for room temperature samples Ding Hong-Sheng (丁红胜), Zhang Feng-Hui (张峰会), Yan Xiao-Ming (颜晓明), Han Shi-Ji (韩士吉), Dong Shi-Ying (董世迎), Yu Hong-Wei (于洪伟), Chen Geng-Hua (陈赓华), He Yu-Sheng (何豫生) Chinese Physics, 2002, 11 (11):  1135-1139.  DOI: 10.1088/1009-1963/11/11/308 Abstract ( 1238 )   PDF (400KB) ( 561 )   We have constructed a scanning low-Tc superconducting quantum interference device (SQUID) microscope, in which the SQUID is mounted on the lower end of a copper rod and cooled to liquid helium temperature. There is a 65μm thick sapphire window under the SQUID. The sample at room temperature underneath the window can be scanned to produce magnetic images. The microscope has a spatial resolution of 100－150μm and a magnetic field sensitivity of 3－60pT/$\sqrt{Hz}$ in a magnetically unshielded environment. We have used this scanning SQUID microscope to measure various room temperature samples.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Heavy meson spectra for heavy quark potential in quantum chromodynamics with dilaton Chen Hong (陈洪), Yang Xing-Hua (杨兴华), Jiang Huan-Qing (姜焕清) Chinese Physics, 2002, 11 (11):  1140-1144.  DOI: 10.1088/1009-1963/11/11/309 Abstract ( 999 )   PDF (233KB) ( 362 )   For heavy meson systems, we study the heavy quark potential, which emerges from the effective dilaton－gluon coupling inspired from the superstring theory. We put emphasis on the new confinement generating mechanism of this potential through the investigation of the spin-averaged energy levels of the heavy meson systems. By using a unified approach to the solutions of the Schr?dinger and the spinless Salpeter equations, we can examine in a realistic way the effects of using a relativistic kinetic energy. The obtained results agree favourably with other predictions, and the relativistic equation can better account for the observed energy levels.

NUCLEAR PHYSICS

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A method of detecting capture $\gamma$-rays in a strong pulsed radiation field Xu Rong-Kun (徐荣昆), Tang Zheng-Yuan (唐正元), He Xi-Jun (何锡钧) Chinese Physics, 2002, 11 (11):  1145-1148.  DOI: 10.1088/1009-1963/11/11/310 Abstract ( 1088 )   PDF (224KB) ( 443 )   We present a technology for diagnosing the D－T fusion process by detecting capture $\gamma$-rays. This technology provides an alternative route to diagnosing the D－T reaction process when a great deal of heavy Z materials surrounds the D－T region. A very important aspect of this paper is to focus on the methods of shielding low-energy $\gamma$-rays whose radiation intensity is 106 times higher than that of the capture $\gamma$-rays. Another aspect is about how to distinguish signal from noise. The result of a 50/1 signal-to-noise ratio indicates that the designed double-magnetic spectrograph is very successful for diagnosing the D－T fusion reaction process.

ATOMIC AND MOLECULAR PHYSICS

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Experimental and theoretical investigations of absolute optical oscillator strengths for valence excitations of nitric oxide Zhu Lin-Fan (朱林繁), Zhong Zhi-Ping (钟志萍), Yuan Zhen-Sheng (苑震生), Zhang Wei-Hua (张卫华), Liu Xiao-Jing (刘小井), Jiang Xi-Man (江锡满), Xu Ke-Zun (徐克尊), Li Jia-Ming (李家明) Chinese Physics, 2002, 11 (11):  1149-1156.  DOI: 10.1088/1009-1963/11/11/311 Abstract ( 1117 )   PDF (284KB) ( 459 )   The absolute optical oscillator strength density spectra of nitric oxide in the energy region of 5.0－22.0 eV have been measured by a high-resolution fast-electron energy loss spectrometer. With the calculated results obtained by the multiscattering self-consistent-field method and channel characteristics, the strongly overlapped spectra in the energy region of 7.5－9.3 eV have been analysed and the corresponding partially vibrationally resolved optical oscillator strengths have been estimated from the experimental spectra.

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Generations of dark hollow beams and their applications in laser cooling of atoms and all optical-type Bose－Einstein condensation Yin Jian-Ping (印建平), Gao Wei-Jian (高伟建), Wang Hai-Feng (王海峰), Long Quan (龙全), Wang Yu-Zhu (王育竹) Chinese Physics, 2002, 11 (11):  1157-1169.  DOI: 10.1088/1009-1963/11/11/312 Abstract ( 1719 )   PDF (524KB) ( 900 )   We report on a new experimental result to generate dark hollow beams by using a geometric optical method. We propose two new methods to produce focused and localized hollow laser beams by using $\pi$-phase plates. Using Monte-Carlo simulations, we have studied the Sisyphus cooling of alkali atoms in pyramidal hollow beam gravito-optical traps. We discuss some potential applications of the dark hollow beams in atom optics and the preparation of an all optically-cooled and optically-trapped atomic Bose－Einstein condensation (BEC). Our research shows that an ultracold atomic sample with a temperature of ～ 2μK can be obtained in the pyramidal hollow beam dipole trap and an all optical-type BEC may be realized in a far blue-detuned, hollow beam trap.

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Analysis of far-infrared laser magnetic resonance spectra of CH2Br at 447.3 and 671.1μm Liu Yu-Yan (刘煜炎), Huang Guang-Ming (黄光明), Duan Chuan-Xi (段传喜), Shi Li-Hua (石丽华), Cai Xin (蔡欣) Chinese Physics, 2002, 11 (11):  1170-1174.  DOI: 10.1088/1009-1963/11/11/313 Abstract ( 1334 )   PDF (264KB) ( 391 )   A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical.

CLASSICAL AREAS OF PHENOMENOLOGY

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Dispersive properties of tunnelling-induced transparency in an asymmetric double quantum well Su Xue-Mei (苏雪梅), Zhuo Zhong-Chang (卓仲畅), Wang Li-Jun (王立军), Gao Jin-Yue (高锦岳) Chinese Physics, 2002, 11 (11):  1175-1178.  DOI: 10.1088/1009-1963/11/11/314 Abstract ( 1354 )   PDF (209KB) ( 551 )   We have investigated the dispersive properties of tunnelling-induced transparency in asymmetric double quantum well structures where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. The intersubband transitions exhibit high dispersion at zero absorption, which leads to the slow light velocity in this medium as compared with that in vacuum (c=3×108). The group velocity in a specific GaAs/AlGaAs sample is calculated to be vg=c/4.30. This structure can be used to compensate for the dispersion and energy loss in fibre optical communications.

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Lasing features of dye-doped pendant drops added with polymer particles: spectral blueshift and intensity enhancement Pu Xiao-Yun (普小云), Zhang Shu (张曙), Chan Chiu-Wah (陈超华), Lee Wing-Kee (李荣基) Chinese Physics, 2002, 11 (11):  1179-1183.  DOI: 10.1088/1009-1963/11/11/315 Abstract ( 990 )   PDF (237KB) ( 517 )   When micrometre-sized polymer particles were added into a dye-doped pendant drop that acted as a quasi-two-dimensional circular resonator, we found a blueshift of the peak wavelength of its lasing spectrum. The lasing output was also enhanced by the particles. The spectral blueshift was explained by a model of dye lasing in a circular cavity. The model includes losses of the scattering particles, medium absorption, and radiation leakage. An optimum particle density for maximum lasing output was deduced. The results are consistent with our experimental findings.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Modulational instability of ion-acoustic waves in a warm plasma Xue Ju-Kui (薛具奎), Duan Wen-Shan (段文山), Lang He (郎和) Chinese Physics, 2002, 11 (11):  1184-1187.  DOI: 10.1088/1009-1963/11/11/316 Abstract ( 1493 )   PDF (218KB) ( 1156 )   Using the standard reductive perturbation technique, a nonlinear Schr?dinger equation is derived to study the modulational instability of finite-amplitude ion-acoustic waves in a non-magnetized warm plasma. It is found that the inclusion of ion temperature in the equation modifies the nature of the ion-acoustic wave stability and the soliton structures. The effects of ion plasma temperature on the modulational stability and ion-acoustic wave properties are investigated in detail.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Bulk sound velocity of porous materials at high pressures Geng Hua-Yun (耿华运), Wu Qiang (吴强), Tan Hua (谭华), Cai Ling-Cang (蔡灵仓), Jing Fu-Qian (经福谦) Chinese Physics, 2002, 11 (11):  1188-1192.  DOI: 10.1088/1009-1963/11/11/317 Abstract ( 1443 )   PDF (248KB) ( 828 )   A correction of Walsh's method for bulk sound velocity calculation for shocked porous materials is accomplished based on the Wu－Jing thermodynamic equation of state. The corrected bulk velocities for solid and porous samples with low porosities are in good agreement with the corresponding experimental data published previously. On the basis of this corrected equation, the influence of thermoelectrons on the bulk velocity of shocked materials is discussed in detail at pressures of 50, 70 and 200 GPa. Some interesting phenomena are revealed, which seem to be the unique features of a dynamic-pressure-loading process and could not be found in static experiments.

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The virial theorem in refined Thomas－Fermi－Dirac theory for the interior of atoms in a solid Zhu Ru-Zeng (朱如曾), Wen Yu-Hua (文玉华), Qian Jin (钱劲) Chinese Physics, 2002, 11 (11):  1193-1195.  DOI: 10.1088/1009-1963/11/11/318 Abstract ( 982 )   PDF (145KB) ( 577 )   The virial theorem in refined Thomas－Fermi－Dirac theory for the interior of atoms in a solid is given and proven.

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

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Reversible, electrical and optical switching on silver 3-phenyl-1-ureidonitrile complex thin films Zhang Hao-Xu (张昊旭), Shi Dong-Xia (时东霞), Song Yan-Lin (宋延林), Liu Hong-Wen (刘虹雯), Hou Shi-Min (侯士敏), Xue Zeng-Quan (薛增泉), Gao Hong-Jun (高鸿钧), Chinese Physics, 2002, 11 (11):  1196-1199.  DOI: 10.1088/1009-1963/11/11/319 Abstract ( 1145 )   PDF (238KB) ( 526 )   We report on the reversible, electrical and optical switching on silver 3-phenyl-1-ureidonitrile complex thin films. The films can switch from a high impedance state to a low impedance state with an applied electric field at the threshold of 3.5×107V/m. Furthermore, the films can be switched back to the original state by treating the samples at about 80℃. The optical recording is fulfilled using a semiconductor laser with a wavelength of 780 nm. Erasure can be accomplished by bulk heating or by the laser working with the power beneath the threshold. No loss of the organic was found in the experiments. This material may have a potential application in ultrahigh data density storage.

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Dynamic behaviour of a single-Cooper-pair box in a single-mode quantized field with dissipation Yao Yan-Sun (姚延荪), Zou Jian (邹健), Shao Bin (邵彬) Chinese Physics, 2002, 11 (11):  1200-1204.  DOI: 10.1088/1009-1963/11/11/320 Abstract ( 974 )   PDF (218KB) ( 480 )   We study the quantum dynamics of a single-Cooper-pair box biased by a classical voltage and also irradiated by a single-mode quantized field. We demonstrate that under the weak damping, the collapse-revival phenomena can exist in this system. We also demonstrate that the revivals of oscillations are sensitive to the initial coherent field and the damping rate of the single-mode quantized field.