Table of contents

16 August 2003, Volume 12 Issue 8 Previous issue    Next issue

GENERAL

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The periodic wave solutions for the generalized Nizhnik－Novikov－Veselov equation Zhang Jin-Liang (张金良), Ren Dong-Feng (任东锋), Wang Ming-Liang (王明亮), Wang Yue-Ming (王跃明), Fang Zong-De (方宗德) Chinese Physics, 2003, 12 (8):  825-830.  DOI: 10.1088/1009-1963/12/8/301 Abstract ( 1328 )   PDF (228KB) ( 864 )   The periodic wave solutions expressed by Jacobi elliptic functions for the generalized Nizhnik－Novikov－Veselov equation are obtained using the F-expansion method proposed recently. In the limiting cases, the solitary wave solutions and other types of travelling wave solutions for the system are obtained.

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The calculating formula for radial matrix elements of a relativistic harmonic oscillator Qiang Wen-Chao (强稳朝) Chinese Physics, 2003, 12 (8):  831-835.  DOI: 10.1088/1009-1963/12/8/302 Abstract ( 1221 )   PDF (214KB) ( 656 )   A universal practical formula is given for calculating an integral which includes two confluent hypergeometric functions, power and exponential functions; then by means of this formula, the expressions of the radial matrix elements for a relativistic harmonic oscillator are given.

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Chaos in a gravitational field with dipoles Chen Ju-Hua (陈菊华), Wang Yong-Jiu (王永久) Chinese Physics, 2003, 12 (8):  836-840.  DOI: 10.1088/1009-1963/12/8/303 Abstract ( 1248 )   PDF (222KB) ( 482 )   In this paper we investigate the dynamics of a test particle in the gravitational field with dipoles. At first we study the gravitational potential by numerical simulations, we find that, for appropriate parameters, there are two different cases in the potential curve: one is the one-well case with a stable critical point, and the other is the three-well case with three stable critical points and two unstable critical points. By performing Poincaré sections for different values of the parameters and initial conditions, we find a regular motion and a chaotic motion. From these Poincaré sections, we further confirm that the chaotic motion of the test particle originates mainly from the dipoles.

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A set of Lie symmetrical non-Noether conserved quantity for the relativistic Hamiltonian systems Cai Jian-Le (罗绍凯), Jia Li-Qun (贾利群), Luo Shao-Kai (蔡建乐) Chinese Physics, 2003, 12 (8):  841-845.  DOI: 10.1088/1009-1963/12/8/304 Abstract ( 1517 )   PDF (217KB) ( 509 )   For the relativistic Hamiltonian system, a new type of Lie symmetrical non-Noether conserved quantities are given. On the basis of the theory of invariance of differential equations under infinitesimal transformations, and introducing special infinitesimal transformations for $q_s$ and $p_s$, we construct the determining equations of Lie symmetrical transformations of the system, which only depend on the canonical variables. A set of non-Noether conserved quantities are directly obtained from the Lie symmetries of the system. An example is given to illustrate the application of the results.

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Directed transport of coupled systems in symmetric periodic potentials Zheng Zhi-Gang (郑志刚), Liu Feng-Zhi (刘凤芝), Gao Jian (高建) Chinese Physics, 2003, 12 (8):  846-850.  DOI: 10.1088/1009-1963/12/8/305 Abstract ( 1367 )   PDF (219KB) ( 433 )   In this paper, we discuss the damped unidirectional motions of a coupled lattice in a periodic potential. Each particle in the lattice is subject to a time-periodic ac force. Our studies reveal that a directed transport process can be observed when the ac forces acting on the coupled lattice have a phase shift (mismatch). This directed motion is a collaboration of the coupling, the substrate potential, and the periodic force, which are all symmetric. The absence of any one of these three factors will not give rise to a directed current. We discuss the complex relations between the directed current and parameters in the system. Results in this paper can be accomplished in experiments. Moreover, our results can be generalized to the studies of directed transport processes in more complicated spatially extended systems.

ATOMIC AND MOLECULAR PHYSICS

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Laser spectroscopy of jet-cooled CuF in visible region Zhang Xiao-Peng (张霄鹏), Guo Jing-Ru (郭静茹), Wang Ting-Ting (王婷婷), Pei Lin-Sen (裴林森), Chen Cong-Xiang (陈从香), Chen Yang (陈旸) Chinese Physics, 2003, 12 (8):  851-855.  DOI: 10.1088/1009-1963/12/8/306 Abstract ( 1219 )   PDF (239KB) ( 384 )   The laser-induced fluorescence excitation spectra of jet-cooled CuF have been recorded in the range of 19000－21470cm$^{-1}$, in which the CuF radicals were produced by the reaction of SF$_6$ with copper atoms from a dc discharge-sputtering source under supersonic jet conditions. Eight observed vibronic transition bands have been assigned as the transition from the ground state $X(^1\Sigma^+$) to $B(^1\Sigma^+$), $C(^1\Pi$) and an unreported upper state. The rotational structure of all observed bands has been analysed at the estimated rotational temperature 80K. We determined the newly observed band to be the ($^1\Pi, v=1)－X(^1\Sigma^+v=0$) transition according to the character of the rotational structure and the isotopic shift analysis. In addition, the lifetimes of the states involved in these bands were measured.

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Investigation of the time characteristics of a pulsed flow of large rare gas clusters Li Shao-Hui (李邵辉), Liu Bing-Chen (刘丙辰), Ni Guo-Quan (倪国权), Xu Zhi-Zhan (徐至展) Chinese Physics, 2003, 12 (8):  856-860.  DOI: 10.1088/1009-1963/12/8/307 Abstract ( 1134 )   PDF (228KB) ( 453 )   The time characteristics of a flow of large rare gas atomic clusters formed by supersonic expansion of a gas into vacuum through conic nozzles are studied using the time resolving Rayleigh scattering method. The results show a two-region structure of the time resolved spectrum of the scattered light from the clusters. The average cluster size in the second region is much, even orders of magnitude, larger than that in the first one. Three designs of the valve-nozzle assembly have been used to investigate the origin of this finding. Finally, the potential application of the observation is proposed.

CLASSICAL AREAS OF PHENOMENOLOGY

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Quantum teleportation of one- and two-photon superposition states Li Ying (李英), Zhang Tian-Cai (张天才), Zhang Jun-Xiang (张俊香), Xie Chang-De (谢常德) Chinese Physics, 2003, 12 (8):  861-865.  DOI: 10.1088/1009-1963/12/8/308 Abstract ( 1068 )   PDF (240KB) ( 492 )   Quantum teleportation of one- and two-photon superposition states based on EPR entanglement of continuous-wave two-mode squeezed state is discussed. The fidelities of teleportation are deduced for two different input quantum states. The dependence of the fidelity on the parameters of EPR entanglement and the gain of the classical channels are shown numerically. Comparing with the teleportation of Fock state and coherent state, it is pointed out that for given EPR entanglement and classical gain, the higher the nonclassicality of the input state, the lower the accessible fidelity of teleportation.

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Linear entropy dynamics of the field in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation Li Chun-Xian (李春先), Fang Mao-Fa (方卯发) Chinese Physics, 2003, 12 (8):  866-871.  DOI: 10.1088/1009-1963/12/8/309 Abstract ( 1269 )   PDF (240KB) ( 543 )   We present the linear entropy dynamics of the field state in the dispersive cavity in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation, and investigate the influence of dissipation on entanglement between the field and the atoms. We show that the coherence properties of the field are also affected by the cavity when the nonlinear process of the field interacting with the atoms with an intensity-dependent coupling is involved, and find that the dissipation constant, the intensity of the field and the atomic distribution angle have different influence on the coherence properties of the field.

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Atomic emission and cavity field spectra of the Jaynes－Cummings model Li Fu-Li (李福利), Gao Shao-Yan (高韶燕), Zhao Yong-Tao (赵永涛) Chinese Physics, 2003, 12 (8):  872-878.  DOI: 10.1088/1009-1963/12/8/310 Abstract ( 1306 )   PDF (251KB) ( 518 )   Atomic emission and cavity field spectra of the Jaynes－Cummings model are analytically compared. We show that the two spectra are in general different, except for the special case where the interaction is resonant, the cavity is initially empty and the retarded time of one-photon emission is considered in calculations of the spectra. In this case, the two spectra are the same. We also show that this result comes from the fact that the two-time autocorrelation function of the cavity field is not directly proportional to that of the atom.

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Propagation of ultrashort pulsed beams in dispersive media Liu Zhi-Jun (刘志军), Lü Bai-Da (吕百达) Chinese Physics, 2003, 12 (8):  879-885.  DOI: 10.1088/1009-1963/12/8/311 Abstract ( 1154 )   PDF (250KB) ( 461 )   Starting from the Rayleigh diffraction integral, the propagation equation of ultrashort pulsed beams in dispersive media is derived without making the paraxial approximation and slowly varying envelope approximation (SVEA). The spatiotemporal properties of ultrashort pulsed beams in dispersive media, such as spectrum redshifting, narrowing and pulse distortion are illustrated with pulsed Gaussian beams. It is stressed that the "antibeam" behaviour of ultrashort pulsed beams can be avoided, if a suitable truncation function is chosen.

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Passive mode locking of a Nd:YAG laser with co-doped Nd, Cr:YAG as saturable absorber Yang Lin (杨林), Feng Bao-Hua (冯宝华), Zhang Zhi-Guo (张治国), Gaebler Volker, Liu Bai-Ning (刘百宁), Eichler Hans Chinese Physics, 2003, 12 (8):  886-889.  DOI: 10.1088/1009-1963/12/8/312 Abstract ( 1364 )   PDF (215KB) ( 471 )   We demonstrate the characteristics of relatively low saturation intensity using co-doped Nd, Cr:YAG as saturable absorber for passively mode locking the Nd:YAG laser. The difference of the saturation intensity between Q-switched and mode-locked operation in co-doped Nd, Cr:YAG was only one to two orders of magnitude, while Cr:YAG was generally reported at a difference of five orders of magnitude. More than 80% mode locking modulation depth was achieved at an incident pump power of 4.4W, corresponding to an intracavity intensity of $6×10^4$W/cm$^2$, using a 68cm long plano-concave cavity.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Phasing of lysozyme using one-wavelength anomalous scattering of sulphur atoms through the combination of direct methods and density modification Jiang Fan (江凡), Gu Yuan-Xin (古元新), Zheng Chao-De (郑朝德), Fan Hai-Fu (范海福) Chinese Physics, 2003, 12 (8):  890-894.  DOI: 10.1088/1009-1963/12/8/313 Abstract ( 1072 )   PDF (231KB) ( 405 )   A new method of combining one-wavelength anomalous scattering (OAS) phasing and density modification has been described, in which the improved phases from density modification are re-introduced into OAS phasing. In this way, the phases could be improved iteratively until convergence. The OAS phasing method is based on the previously established sign-probability formula, which breaks the phase ambiguity in the OAS phasing. The implementation of this method has been available in CCP4 as OASIS. This method, although based on direct-methods, could also incorporate known phases and figures of merit into its sign-probability formula. In the implementation of OASIS, the known phases are from the positions of the anomalous scatters. In the current method, the known phases are from the density modification. The current method was tested on phasing a lysozyme crystal using anomalous scattering of sulphur atoms with diffraction data collected on an in-house x-ray source. The resulting map was well connected for the backbone atoms and clearly traceable, with an average map correlation coefficient of 0.6622 for the backbone atoms.

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

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Numerical modelling of anisotropy in 4H-SiC MESFET's Lü Hong-Liang (吕红亮), Zhang Yi-Men (张义门), Zhang Yu-Ming (张玉明) Chinese Physics, 2003, 12 (8):  895-898.  DOI: 10.1088/1009-1963/12/8/314 Abstract ( 1409 )   PDF (212KB) ( 489 )   A numerical model for 4H-SiC MESFET anisotropy is presented in this paper and the device performances, such as breakdown, temperature and transient characteristics, are demonstrated. The simulation results show obvious effects of the anisotropy for 4H-SiC and are in better accordance with the experimental results. The anisotropy for 4H-SiC should be involved in the device design to acquire better performances.

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Dynamical properties of two-band superlattices with strong interband coupling in real space under the action of ac and dc－ac fields Duan Su-Qing (段素青), Wang Zhi-Gang (王志刚), Zhao Xian-Geng (赵宪庚) Chinese Physics, 2003, 12 (8):  899-904.  DOI: 10.1088/1009-1963/12/8/315 Abstract ( 1099 )   PDF (271KB) ( 470 )   Within a two-band tight-binding model driven by ac and dc－ac electric fields, using numerical methods, we investigate the dynamics of electrons and the quasi-energy spectrum of the system with strong interband coupling in real space. We find that when the bandwidth is suppressed to a value much smaller than the field frequency, the dynamical localization can exist in the system. The corresponding regions are found for the occurrence of dynamical localization in the parameter space.

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Bifurcation of a periodic instanton and quantum-classical transition in the biaxial nano-ferromagnet with a magnetic field along hard axis Nie Yi-Hang (聂一行), Li Zhi-Jian (李志坚), Liang Jiu-Qing (梁九卿), Yan Qi-Wei (严启伟) Chinese Physics, 2003, 12 (8):  905-910.  DOI: 10.1088/1009-1963/12/8/316 Abstract ( 1147 )   PDF (255KB) ( 377 )   Crossover from classical to quantum regimes of the barrier transition rate in a biaxial ferromagnetic magnet with a magnetic field applied along hard anisotropy axis is investigated. We show that the type of action-temperature diagrams can be determined by counting the number of bifurcation points. The model possesses not only the known type I and II, but also the interesting type III and IV of transition which do not occur in general.

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Large magnetic entropy change and magnetic properties in La(Fe1-xMnx)11.7Si1.3Hy compounds Wang Fang (王芳), Chen Yuan-Fu (陈远富), Wang Guang-Jun (王光军), Sun Ji-Rong (孙继荣), Shen Bao-Gen (沈保根) Chinese Physics, 2003, 12 (8):  911-914.  DOI: 10.1088/1009-1963/12/8/317 Abstract ( 1055 )   PDF (244KB) ( 471 )   Magnetic properties and magnetic entropy change in La(Fe$_{1-x}$Mn$_x$)$_{11.7}$Si$_{1.3}$H$_y$ compounds have been investigated. A significant increase of the Curie temperature $T_{\rm C}$ and a small increase of the saturation magnetizations $\mu_{\rm S}$ have been observed after the introduction of interstitial H, which caused a slight volume expansion. The first-order field-induced itinerant-electron metamagnetic (IEM) transition remains and brings about a large magnetic entropy change around room temperatures for the compounds. The maximal magnetic entropy change is about 23.4, 17.7 and 15.9J/kg·K under a magnetic field change from 0 to 5T for x=0.01, 0.02 and 0.03, respectively. Therefore, the compounds appear to be potential candidates for magnetic refrigerants around room temperatures.