Table of contents

16 September 2003, Volume 12 Issue 9 Previous issue    Next issue

GENERAL

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Sub-strategy updating evolution in minority game Yang Wei-Song (杨伟松), Wang Bing-Hong (汪秉宏), He Peng (贺鹏), Wang Wei-Ning (王卫宁), Quan Hong-Jun (全宏俊), Xie Yan-Bo (谢彦波) Chinese Physics, 2003, 12 (9):  931-935.  DOI: 10.1088/1009-1963/12/9/301 Abstract ( 925 )   PDF (220KB) ( 445 )   In this paper, we propose and study a new evolution model of minority game. Any strategy in minority game can be regarded as composed of sub-strategies corresponding to different histories. Based on the evolution model proposed by Li－Riolo－Savit, in which those agents that perform poorly may update their strategies randomly. This paper presents a new evolution model in which poor agents update their strategies by changing only a part of sub-strategy sets with low success rate. Simulation result shows that the new model with sub-strategy-set updating evolution mechanism may approach its steady state more quickly than the Li－Riolo－Savit model. In the steady state of the new model, stronger adaptive cooperation among agents will appear, implying that the social resource can be allocated more rationally and utilized more effectively compared with the Li－Riolo－Savit model.

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Exact invariants and adiabatic invariants of the singular Lagrange system Chen Xiang-Wei (陈向炜), Li Yan-Min (李彦敏) Chinese Physics, 2003, 12 (9):  936-939.  DOI: 10.1088/1009-1963/12/9/302 Abstract ( 1092 )   PDF (197KB) ( 513 )   Based on the theory of symmetries and conserved quantities of the singular Lagrange system, the perturbations to the symmetries and adiabatic invariants of the singular Lagrange systems are discussed. Firstly, the concept of higher-order adiabatic invariants of the singular Lagrange system is proposed. Then, the conditions for the existence of the exact invariants and adiabatic invariants are proved, and their forms are given. Finally, an example is presented to illustrate these results.

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Generalized Riccati equation expansion method and its application to the Bogoyavlenskii's generalized breaking soliton equation Chen Yong (陈勇), Li Biao (李彪), Zhang Hong-Qing (张鸿庆) Chinese Physics, 2003, 12 (9):  940-945.  DOI: 10.1088/1009-1963/12/9/303 Abstract ( 1085 )   PDF (226KB) ( 749 )   Based on the computerized symbolic system Maple and a Riccati equation, a Riccati equation expansion method is presented by a general ansatz. Compared with most of the existing tanh methods, the extended tanh-function method, the modified extended tanh-function method and generalized hyperbolic-function method, the proposed method is more powerful. By use of the method, we not only can successfully recover the previously known formal solutions but also construct new and more general formal solutions for some nonlinear differential equations. Making use of the method, we study the Bogoyavlenskii's generalized breaking soliton equation and obtain rich new families of the exact solutions, including the non-travelling wave and coefficient functions' soliton-like solutions, singular soliton-like solutions, periodic form solutions.

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Effect of signal modulating noise in bistable stochastic dynamical systems Xiao Fang-Hong (肖方红), Yan Gui-Rong (闫桂荣), Zhang Xin-Wu (张新武) Chinese Physics, 2003, 12 (9):  946-950.  DOI: 10.1088/1009-1963/12/9/304 Abstract ( 1153 )   PDF (220KB) ( 462 )   The effect of signal modulating noise in bistable stochastic dynamical systems is studied. The concept of instantaneous steady state is proposed for bistable dynamical systems. By making a dynamical analysis of bistable stochastic systems, we find that global and local effect of signal modulating noise as well as stochastic resonance can occur in bistable dynamical systems on which both a weak sinusoidal signal and noise are forced. The effect is demonstrated by numerical simulation.

ATOMIC AND MOLECULAR PHYSICS

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Energies and Auger widths of the triply excited states of He- Gou Bing-Cong (芶秉聪), Yu Kai-Zhi (俞开智), Wang Fei (王菲), Wu Xiao-Li (吴晓丽) Chinese Physics, 2003, 12 (9):  951-954.  DOI: 10.1088/1009-1963/12/9/305 Abstract ( 973 )   PDF (194KB) ( 364 )   Some triply excited states of He$^-$ ion are studied using the saddle-point complex-rotation method. The energies and Auger widths of these resonances are calculated with the relativistic corrections and mass polarization taken into account. The total Auger width is obtained by coupling the important open channels and summing over the other channels. These results are in good agreement with other theoretical and experimental data in the literature.

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Magnetic guide of cold atoms using a U-shaped current-carrying conductor Liu Nan-Chun (刘南春), Yin Jian-Ping (印建平) Chinese Physics, 2003, 12 (9):  955-963.  DOI: 10.1088/1009-1963/12/9/306 Abstract ( 1112 )   PDF (387KB) ( 462 )   We propose a new scheme to magnetically guide cold neutral atoms using a U-shaped current carrying conductor. The spatial magnetic field distribution from the U-shaped current-carrying conductor and the relationship between the magnetic field and parameters of the U-shaped conductor are analysed. Our study shows that U-shaped current-carrying conductor can be used to realize single- or double-channel magnetic guiding of cold atoms in weak-field-seeking states and to construct various atom-optical elements. By using Monte Carlo simulations, the dynamic process of the guided atomic-beam splitting in an atomic-beam splitter composed by the U-shaped current-carrying conductor is studied, and some results are presented.

CLASSICAL AREAS OF PHENOMENOLOGY

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Effect of concentration of Er3+ ions on ultra-large index of refraction via atomic coherence in Er3+: YAG crystal Zhang Hui-Fang (张惠芳), Dai Zhen-Wen (戴振文), Zhang Bing (张冰), Wu Jin-Hui (吴金辉), Gao Jin-Yue (高锦岳) Chinese Physics, 2003, 12 (9):  964-970.  DOI: 10.1088/1009-1963/12/9/307 Abstract ( 1121 )   PDF (268KB) ( 432 )   A four-level system is proposed to produce large index of refraction accompanied by vanishing absorption in the Er$^{3+}$-doped yttrium aluminium garnet (YAG) crystal. It is found that the high index of refraction with zero absorption can be provided by adjusting the incoherent pumping, the coherent field, as well as the concentration of Er$^{3+}$ ions in the crystal. Furthermore, the value of the incoherent pump to achieve the high index of refraction with zero absorption is greatly changed with increasing the concentration of Er$^{3+}$ ions in the crystal. This indicates that the effect of concentration on the high index of refraction with zero absorption cannot be neglected.

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Entangled states in the two-mode coherent fields interacting with a two-level atom Liu Xiao-Juan (刘小娟), Fang Mao-Fa (方卯发) Chinese Physics, 2003, 12 (9):  971-976.  DOI: 10.1088/1009-1963/12/9/308 Abstract ( 1140 )   PDF (241KB) ( 607 )   We investigate the entanglement properties of the two-mode coherent fields interacting with a two-level atom via the two-photon transition. We discuss the quantum entanglement between the two-mode coherent fields and the two-level atom by using the quantum reduced entropy and that between the two-mode coherent fields by using the quantum relative entropy. We also examine the influences of the initial states of the atom and the two-mode coherent fields on the quantum entanglement of the system. Our results show that three types of entangled states can be prepared via the two-mode coherent fields interacting with a two-level atom and choosing appropriately the initial-state parameters of the system.

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Efficient scheme for the preparation of arbitrary anticorrelated states of a two-mode field Zheng Shi-Biao (郑仕标) Chinese Physics, 2003, 12 (9):  977-980.  DOI: 10.1088/1009-1963/12/9/309 Abstract ( 1314 )   PDF (194KB) ( 404 )   A scheme is presented for generating any anticorrelated state of a two-mode field. In the scheme a sequence of suitably prepared three-level V-type atoms are sent across a two-mode cavity initially in the vacuum state. The detection of all the atoms in the ground state collapses the two-mode field to the desired state.

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Mode correlation and coherent-mode decomposition of laser beams Zhang Bin (张彬), Wen Qiao (文侨), Chu Xiao-Liang (楚晓亮) Chinese Physics, 2003, 12 (9):  981-985.  DOI: 10.1088/1009-1963/12/9/310 Abstract ( 993 )   PDF (216KB) ( 519 )   Theory of the coherent-mode decomposition of laser beams is proposed. The new model for the flat-topped beams proposed by Li recently is taken as an example. The analytical expressions for the $M^2$-factor and mode coherence coefficients of flat-topped beams have been derived in the rectangular coordinate system, by means of which the mode correlation, mode structure, and coherent-mode decomposition of flat-topped beams can be analysed.

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Experimental study on the chirped structure of the white-light continuum generation by femtosecond laser spectroscopy Quan Dong-Hui (全冬晖), Liu Shi-Lin (刘世林), Zhang Lei (张蕾), Yang Jian (杨健), Wang Li (汪力), Yang Guo-Zhen (杨国桢), Weng Yu-Xiang (翁羽翔) Chinese Physics, 2003, 12 (9):  986-991.  DOI: 10.1088/1009-1963/12/9/311 Abstract ( 1295 )   PDF (234KB) ( 514 )   The chirped structure of the white-light continuum generation (WLCG) pulse produced by focusing 800nm laser pulse with a pulse duration of 150fs (FWHM: full-width-at-half-maximum) onto a 2.4 mm thick sapphire plate was investigated by the optical Kerr gate technique with normal hexane as the optical Kerr gate medium. The observed WLCG was positively chirped, the measured anti-Stokes spectrum of WLCG ranges from 449 to 580nm with a temporal span of 2.56ps. When using metal reflecting mirrors to eliminate the group velocity dispersion (GVD) effect, we found that a span of 1.3ps still remained, indicating that the chirped pulse cannot be accounted for simply by GVD of the pulse propagation in the dispersive media. Our results suggest that the light-induced refractive index change due to the third-order nonlinear optical effect leads to an additional positive group velocity dispersion, which contributes to an important portion of the observed temporal broadening of the chirped WLCG. In addition to using reflective optical elements instead of dispersive optical elements, an effective way of reducing the chirp is to minimize the optical path length of the WLCG medium.

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Theoretical study of enhancement and suppression of the fluorescent spectra of dye molecules in a photonic crystal with a pseudogap Liu Xiao-Dong (刘晓东), Xu Xing-Sheng (许兴胜), Wang Yi-Quan (王义全), Zhang Dao-Zhong (张道中), Cheng Bing-Ying (程丙英) Chinese Physics, 2003, 12 (9):  992-996.  DOI: 10.1088/1009-1963/12/9/312 Abstract ( 1288 )   PDF (239KB) ( 513 )   We have investigated the analytical forms of the photonic density of states (DOS) in a photonic crystal in the interested frequency regime according to the rule of state conservation in a photonic crystal with pseudogaps, which states that, if a valley of the DOS appears in some range of frequencies, it must be compensated for by increasing over some other ranges. By using a model DOS with a state-conservative photonic pseudogap, we have also investigated the enhancement and suppression of spontaneous emission of two-level atoms with different frequency positions and widths of emission spectra in a state-conservative electromagnetic reservoir; and the DOS-induced suppression, enhancement, narrowing and redshifting or blueshifting of spontaneous emission spectra are naturally obtained.

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Spectral properties of erbium-doped heavy metal oxyfluoride silicate glasses for broadband amplification Xu Shi-Qing (徐时清), Yang Zhong-Min (杨中民), Dai Shi-Xun (戴世勋), Yang Jian-Hu (杨建虎), Dai Neng-Li (戴能利), Lin Ao-Xiang (林傲翔), Hu Li-Li (胡丽丽), Jiang Zhong-Hong (姜中宏) Chinese Physics, 2003, 12 (9):  997-1000.  DOI: 10.1088/1009-1963/12/9/313 Abstract ( 1111 )   PDF (220KB) ( 597 )   Erbium-doped glasses showing a wide 1.55μm emission band are reported in a novel heavy metal oxyfluoride glass system SiO$_2$－PbO－PbF$_2$ and their optical properties such as emission spectra, fluorescence lifetime and the refractive index have been investigated. The broad and flat ${}^4$I$_{13/2}$→${}^4$I$_{15/2}$ emission of Er$^{3+}$ ions around 1.55μm can be used as host materials for potential optical amplifiers in wavelength-division-multiplexing network system. We find that with increasing PbF$_2$ content in the glass composition, the fluorescence full width at half maximum and fluorescence lifetime of the ${}^4$I$_{13/2}$ level of Er$^{3+}$ increase, while refractive index and density decrease.

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Study of the behaviour of the fibre Bragg grating fabricated with cladding mode suppression fibre Xu Xin-Hua (徐新华), Lü Chang-Gui (吕昌贵), Cui Yi-Ping (崔一平) Chinese Physics, 2003, 12 (9):  1001-1006.  DOI: 10.1088/1009-1963/12/9/314 Abstract ( 1150 )   PDF (251KB) ( 494 )   One effective method for suppression of coupling from guided optical modes into cladding modes in an optical fibre Bragg grating is to use cladding mode suppression fibre. In this specially engineered fibre, the grating is written into the core and the inner cladding, both of which are photosensitive. A theory is presented in this paper to analyse the spectral characteristics of this kind of gratings. A fibre Bragg grating was experimentally fabricated with this kind of photosensitive fibre (PS-RMS-50 from StockerYale). It is shown both theoretically and experimentally that such gratings exhibit strong suppression of the coupling between core mode and cladding mode. The experimental result is in good agreement with the theoretical analysis.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Effect of temperature on deformation of carbon nanotube under compression Wang Yu (王宇), Ni Xiang-Gui (倪向贵), Wang Xiu-Xi (王秀喜), Wu Heng-An (吴恒安) Chinese Physics, 2003, 12 (9):  1007-1010.  DOI: 10.1088/1009-1963/12/9/315 Abstract ( 1040 )   PDF (248KB) ( 600 )   The mechanical behaviour of carbon nanotubes is one of the basic research fields on the nanotube composites and nano machinery. Molecular dynamics is an effective way for investigating the behaviour of nano structure. The compression deformation of carbon nanotubes (CNTs) under different temperature is simulated, by using the Tersoff－Brenner potential to describe the interactions in CNTs. The results show that thermal fluctuations may induce the strained CNT to overcome the local energy barrier and develop the plastic deformation.

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

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Calculation of scanning tunnelling microscopy images for Kr/graphite system Zhou Xiao-Lin (周晓林), Chen Xiang-Rong (陈向荣), Yang Xiang-Dong (杨向东), Gou Qing-Quan (芶清泉) Chinese Physics, 2003, 12 (9):  1011-1015.  DOI: 10.1088/1009-1963/12/9/316 Abstract ( 1133 )   PDF (286KB) ( 452 )   The scanning-tunnelling-microscopy (STM) images of Kr atoms adsorbed on a monolayer graphite sheet (Kr/graphite system) are calculated using the first-principle total-energy electronic structure calculations within the density functional theory in the local density approximation. The results obtained agree well with the observations. It is found that the optimal site of the adsorbed Kr atom is at the top of the centre of the carbon hexagon, and its equilibrium distance from monolayer graphite surface is about 0.335nm. It is shown that the hybridization of C 2p electronic states ($\pi$-electronic states) and Kr 4p and 5s electronic states is the main origin of the Fermi-level local density of state.

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Electronic structure and optical properties of zinc-blende GaN quantum dots Feng Dong-Hai (冯东海), Jia Tian-Qing (贾天卿), Xu Zhi-Zhan (徐至展) Chinese Physics, 2003, 12 (9):  1016-1020.  DOI: 10.1088/1009-1963/12/9/317 Abstract ( 1101 )   PDF (250KB) ( 530 )   The energy levels of zinc-blende GaN quantum dots (QDs) are studied within the framework of the effective-mass envelope-function approximation. The dependence of the energy of electron and hole states on the quantum dot (QD) size is presented. The selection rules for optical transitions are given and the oscillator strengths of the dipole-allowed transitions for various QD radii are calculated with the wavefunctions of quantized energy levels. The theoretical absorption spectrum of GaN QDs is in good agreement with the existing experimental result.

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Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm Xu Ben (徐贲), Yue Gu-Ming (岳古明), Zhang Yin-Chao (张寅超), Hu Huan-Ling (胡欢陵), Zhou Jun (周军), Hu Shun-Xing (胡顺星) Chinese Physics, 2003, 12 (9):  1021-1025.  DOI: 10.1088/1009-1963/12/9/318 Abstract ( 1172 )   PDF (233KB) ( 486 )   A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D$_2$, D$_2$/Ar and D$_2$/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S$_1$, 396.796nm) reaches 33.33% in D$_2$/Ar and the stability of S$_1$ in pure D$_2$ is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO$_2$ concentration profiles.

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Study of far-infrared reflection and Raman scattering spectra in reactive ion, etched ZnTe Wu Sen (吴森), Shen Wen-Zhong (沈文忠), Ogawa Hiroshi (小川博司), Guo Qi-Xin (郭其新) Chinese Physics, 2003, 12 (9):  1026-1032.  DOI: 10.1088/1009-1963/12/9/319 Abstract ( 1103 )   PDF (284KB) ( 456 )   Far-infrared reflection and Raman scattering measurements have been carried out on reactive ion, etched p-ZnTe samples. The averaged thickness of the surface damaged layer is found to be in the range of 1.0－1.5μm, and the, etch-induced defect density is in the order of $10^{18}$cm$^{-3}$. The Raman intensity ratio between the second-order Raman peaks and the first-order longitudinal optical phonons reveals an increase trend with the radio frequency (rf) power. With the aid of related theories, we discuss the effects of the rf plasma power and the concentration of CH$_4$/H$_2$ on the damage, disorder, and the second-order Raman structures in p-ZnTe samples.