Current Issue

Volume 15 Issue 12
Online Date:
Previous Issue    Next Issue
Original Articles
Interaction Mechanism of the Parametrically Excited Solitons
WANG Xin-long
Chin. Phys. Lett. 1998, 15 (12): 859-861 .  
Abstract   PDF(pc) (267KB) ( 624 )
The parametrically excited solitons manifest themselves with many distinct particle-like behaviors. Here the internal dynamics of the soliton-soliton interactions is explored both analytically and numerically. The results confirm the attraction between polarity-like solitons and the repulsion between opposite polarity ones. The attraction can make a pair of like polarity solitons form a standing (or oscillating) bound state. Therefore, multisolitons in an unbounded waveguide would asymptotically develop into an array of mutually independent standing soliton(s) or/and the bound state(s). It is shown that the bound state has two unidirectional momenta flowing toward the symmetric center, and thus the solitons do not perform the collisions in the classical sense. It is further demonstrated that the observed periodic “collisions” are actually due to the dissipative-induced collapses and the parametric recreations of solitons.
Dwell Time of Particles in Tunneling Barriers of Arbitrary Shape
BAI Er-juan, SHU Qi-qing
Chin. Phys. Lett. 1998, 15 (12): 862-864 .  
Abstract   PDF(pc) (237KB) ( 424 )
For a one-dimensional barrier of arbitrary shape, an expression of the dwell time of tunneling particles has been obtained by subdividing it into infinitesimal rectangular barrier elements and then summing the dwell times spent by particles inside the barrier elements, and the dwell times in a parabolic potential barrier were calculated. The results show that the dwell times are almost independent of the barrier width as it is greater than a characteristic width Wc. This can be ascribed that in the width range beyond Wc, the tunneling probabilities through the barrier elements are very small, thus the times taken to tunnel through them make little contribution to the summation of the dwell times in all the barrier elements.
Estimates of SU(2) Glueballs on a Coarse, Anisotropic Lattice
ZHANG Jian-bo, JIN Min, JI Da-ren
Chin. Phys. Lett. 1998, 15 (12): 865-867 .  
Abstract   PDF(pc) (248KB) ( 399 )
Using Tadpole-improved lattice action, the low-lying glueball spectrum of the pure-gauge SU(2) theory is calculated on an anisotropic lattice. The results of m(0+), m(2+), and m(0-) are consistent with that for the Wilson action on much larger lattices. This shows the advantage of using the coarse, anisotropic lattice to calculate the glueball masses.
Extraction of the Structure Functions in τ→3πv Decay Using Li Model
XIONG Zhao-hua, CHEN Guo-ming, CHEN He-sheng
Chin. Phys. Lett. 1998, 15 (12): 868-870 .  
Abstract   PDF(pc) (221KB) ( 360 )
The structure functions in the τ→3πv decay are extracted using the model proposed by Li. The predictions of Li model are compared with KS ones and the data from OPAL experiment. It is found that predictions by the model for ωA (Q2) are consistent with the data except for in the high energy region (Q2 > 1.2 GeV2 ) , and ωC, ωD, ωE normalized to ωA are in reasonable agreement with the experimental results. Correction factors to the Breit-Wigner distribution of a1 and the Lagrangian of this decay are proposed to the model.
Leptonic Decay of J/ψ 
LIU Bo, SHEN Peng-nian, JIANG Huan-qing
Chin. Phys. Lett. 1998, 15 (12): 871-873 .  
Abstract   PDF(pc) (240KB) ( 327 )
A more realistic non-relativistic quark-quark potential in the thermal and dense medium is proposed and used to study the laptonic decay of J/ψ . The laptonic decay property of J/ψ in the hot and dense matter depends on the form of the binding potential. The decay width in the potential case is much sensitive to the temperature than that in the Karsch’s potential case, especially in the lower temperature region. In both cases, the decay widths decreased with the increasing temperature and density. The resultant critical temperature of 200 MeV is consistent with the lattice quantum chromodynamics finding.
Energy Loss and J/ψ Suppression in Relativistic pA and AA Collisions
TAI An, CHAO Wei-qin, YAO Xia-xia,
Chin. Phys. Lett. 1998, 15 (12): 874-876 .  
Abstract   PDF(pc) (242KB) ( 353 )
When the cross section of J/ψ production is considered as varying with the energy of the nucleon-nucleon interaction, the production of J/ψ in pA and A A collisions has been studied by using FRITIOF Model. The calculation shows that the cross section of J/ψ production “per nucleon-nucleon collision” decreases with the increasing mass number and centrality as a consequence of continuous energy loss of the projectile nucleons to the target nucleons in their successive binary nucleon-nucleon collisions. The model predictions have been compared with the experimental data of J/ψ production.
Calculation of Differential Cross-Section of Elastic and 41S -41P Excitation of Calcium by Electron Impact
ZHOU Ya-jun, ZHONG Zheng, HE Xun, PAN Shou-fu
Chin. Phys. Lett. 1998, 15 (12): 877-879 .  
Abstract   PDF(pc) (211KB) ( 576 )
Differential cross-sections of elastic and 41S -41P excitation for electron scattering by calcium at intermediate energies have been calculated and compared with experiment. The method used is the momentum space coupled channels optical method with the complex equivalent-local polarization potentials, which takes all channels into account. Discrete channels are included in a coupled equation and the optical potential is added that describes effects of target continuum.
Squeezed Quantum-Beat Laser Without Inversion
HU Xiang-ming, PENG Jin-sheng
Chin. Phys. Lett. 1998, 15 (12): 880-882 .  
Abstract   PDF(pc) (250KB) ( 560 )
A quantum-beat laser without inversion is proposed for producing two-mode suqeezing. Using the dressed-atom-dressed-mode approach, the master equation is derived and the variances in the sum mode intensity and in the relative amplitude and phase are calculated. When the laser is operated well above threshold, the intensity fluctuations in the sum mode are reduced below the shot noise limit with an optimum Mandel parameter of -0.5. At the same time, the fluctuations in the relative amplitude and phase are retained at their vaccum noise levels.
Cr4+:YAG as a Passive Q-Switch in a Diode-Pumped cw Nd:YVO4 Laser
HE Jing-liang, HOU Wei, ZHANG Heng-li, WU Ling-an, XU Zu-yan, YANG Guo-zhen, DENG Pei-zhen, XU Jun, QIAO Jing-wen
Chin. Phys. Lett. 1998, 15 (12): 883-885 .  
Abstract   PDF(pc) (203KB) ( 451 )
The performance of a passively Q-switched all-solid-state Nd:YVO4 laser using Cr4+:YAG as saturable absorber is reported. Optimum coupling operation at 1064nm resulted in 70ns pulses at 40kHz repetition rates with average output power of 2.1 W. A quantitative theoretical description agrees well with the experimental results.
Hydrogen Concentration Dependence of Bragg Wavelength of UV-Written Fiber Grating
FU Li-bin, TAN Gu, XU Wan-jin, LIN Xiang-zhi, LIU Hong-du
Chin. Phys. Lett. 1998, 15 (12): 886-888 .  
Abstract   PDF(pc) (192KB) ( 402 )
Hydrogen loading provides highly enhanced photosensitivity in Ge-doped fiber. But the Bragg wavelength of UV-written fiber grating will shift from its initial value as the remaining hydrogen diffuses out of such fiber. A simple model to calculate the index change of hydrogenated fibers is presented. The theoretical model is in good agreement with experimental results and it can well predict the final wavelength position of UV-written weak fiber grating.
Analyzing Characters of Plasma Wake with Method of Chaos Dynamics
CAO Jin-xiang, FANG Jian-dong, ZHAO Hong-bo, LIN Yi-jun, ZHANG Jia-xiang, WANG Jie-xia, DONG Yong-hui
Chin. Phys. Lett. 1998, 15 (12): 889-891 .  
Abstract   PDF(pc) (258KB) ( 418 )
In this paper, analyzing the experiment data of multiple scanning probes in the arc wind-driven hypersonic plasma flows with the chaos dynamics method, we have obtained the power spectrum, the frequency wavenumber spectral density, the correlation dimension and Kolmogorov entropy of the flows, respectively. The distribution of correlation dimension and Kolmogorov entropy of the blunt cone wakes along the axis and the radius of the flows are presented successfully in the flows. The distributions clearly show the structure of turbulence and lamination in blunt cone wakes. Using the method of minimum Kolmogorov entropy, we observed the structure of the bow shock at far wake region in the blunt cone wakes.
Modified Dust-Acoustic Solitons by Adiabatic Variation of Dust Charges
XIE Bai-song, HE Kai-fen, HUANG Zu-qia
Chin. Phys. Lett. 1998, 15 (12): 892-894 .  
Abstract   PDF(pc) (220KB) ( 388 )
By the multi-scale expansion method an effect of adiabatic variation of dust charges on dust-acoustic soliton is investigated. It is found that the amplitude of the soliton decreases while its width narrows in comparison with the case of constant dust charges.
Particle Simulations for Electron Beam-Plasma Interactions
ZHOU Guo-cheng, LI Yang, CAO Jin-bin, WANG Xue-yi
Chin. Phys. Lett. 1998, 15 (12): 895-897 .  
Abstract   PDF(pc) (239KB) ( 437 )
The computer simulations of high-frequency instabilities excited by the high density electron beam and their nonlinear effect are presented. One-dimensional electromagnetic particle simulations are performed with different values of the electron beam-to-plasma density ratio. The results show that for the high electron beam-to-background plasma density ratio, all the Langmuir waves and two electromagnetic waves with left-hand and right-hand circular polarizations (i.e., the “L-O mode” and the “R-X mode”) propagating parallel to the magnetic field can be generated and the maximum values of wave electric fields are nearly the same. The electron beam and background plasma are diffused and a part of energetic background electrons are obviously accelerated by the wave-particle interactions. The heating of the beam and background plasma is mainly due to the electrostatic (Langmuir) wave-particle interactions, but the accelerations of a part of energetic background electrons may be mainly due to the electromagnetic wave-particle interactions.
Radiation of a Magnetic Dipole in an Infinite Anisotropic Plasma Medium
LI Kai
Chin. Phys. Lett. 1998, 15 (12): 898-900 .  
Abstract   PDF(pc) (202KB) ( 434 )
The radiation of a magnetic dipole in an infinite anisotropic plasma medium is analyzed. A three-dimensional Fourier transform is employed to compute the field which is represented by using a dyadic formulation and it is shown that the far field can be expressed as a sum of two separate spherical waves. As an example, radiation patterns of the dipole parallel to the geomagnetic field in two different frequency regions are calculated.

Crystallization of Ternary Amorphous Ni-Y-AI Films Observed by Scanning Tunneling Microscopy
WANG De-liang, U. Geyer, S. Schneider
Chin. Phys. Lett. 1998, 15 (12): 901-903 .  
Abstract   PDF(pc) (619KB) ( 337 )
Ternary thin Ni90-xYxAl10 films have been prepared by using cocondensation method under ultrahigh vacuum condition. Films with a wide concentration range between Ni80Y10Al10 and Ni20Y70AI10 were found to be amorphous. With an addition of 10at.% AI the thermal stability of binary amorphous NiY has been enhanced. This is caused by a more closely packed structure and the bondings between AI and Ni, Y may also play an important role. The surface investigation by scanning tunneling microscopy suggests that the atom redistribution and the crystallization have been limited in the clusters with a size of about 10.5nm. The nanosized amorphous clusters of Ni80Y10Al10 film have changed to nanosized crystalline with the same size of about 12.3nm when crystallization occurred.
Pulsed Laser Deposition of VO2 Single Crystal Thin Films on Sapphire Substrates
ZHU Pei-ran, S. Yamamoto, A. Miyashita, H. Naramoto
Chin. Phys. Lett. 1998, 15 (12): 904-906 .  
Abstract   PDF(pc) (233KB) ( 449 )
Thin films of VO2 single-crystalline on (0001) sapphire substrates have been prepared by visible pulsed laser ablation technique. The crystal quality and properties of the films are evaluated through electrical resistance measurement, x-ray diffraction (XRD), and Rutherford- backscattering spectroscopy/channeling (RBS/C) analysis. The dependence of the surface electrical resistance of the films on the temperature shows semiconductor-to-metal transitions with the resistance change of 7x103-2 x 104. The hysteresis widths are from less than 1 to 3 K . XRD and RBS/C data reveal that the films prepared in particular conditions are single-crystalline VO2 with the (010) planes parallel to the surface of the sapphire substrate.
High-Resolution Electron Energy Loss Spectroscopy of Cs Vibration on the Ru (0001) Surface
HE Pei-mo, Karl Jacobi
Chin. Phys. Lett. 1998, 15 (12): 907-909 .  
Abstract   PDF(pc) (276KB) ( 450 )
By using a newly implemented high-resolution electron energy loss spectrometer with better resolution, a new loss at a energy near to double energy of the Cs-Ru stretching vibration, and its dependence on Cs coverage for Cs overlayer on Ru (0001) were observed. Since the energy is slightly smaller than the double energy of the Cs-Ru vibration (intrinsic loss), overtone excitation must be responsible for this new loss observed, but two-phonon process is not excluded.

Reaction Processes at the Initial Stage of Diamond Nucleation on the Surface of Si(111)
XIE Fang-qing, ZHANG Qing-zhe, LIN Zhang-da
Chin. Phys. Lett. 1998, 15 (12): 910-912 .  
Abstract   PDF(pc) (285KB) ( 437 )
The thermal behavior of CHx (x=2,3) radicals and H atoms adsorbed on Si (111) surface was investigated by high-resolution electron-energy-loss spectroscopy, quadrupole mass spectrometry, and low-energy electron diffraction. Based on the analysis of thermal desorption mass spectrometry, the initial stage of diamond nucleation on Si is speculated. Compared with the result reported by Lee for diamond, it is concluded that low stability of hydrocarbon species on Si is the basic reason which results in the difficulty of diamond nucleation on perfect Si surface.

Plasma Enhanced Chemical Vapor Deposition Synthesizing Carbon Nitride Hard Thin Films
ZHANG Zhi-hong, GUO Huai-xi, MENG Xian-quan, YE Ming-sheng, ZHANG Wei, FAN Xiang-jun
Chin. Phys. Lett. 1998, 15 (12): 913-915 .  
Abstract   PDF(pc) (209KB) ( 472 )
Using plasma enhanced chemical vapor deposition and SiC and carbon buffer layers, we have obtained carbon nitride thin films on Si(100) and Si(111). The x-ray diffraction and x-ray photoelectron spectroscopy are used to characterize the thin films. The Vickers hardness of the carbon nitride thin films is more than 5100kgf/mm2 and comparable to that of diamond.
Nonlinear Behavior of Multiple Cluster Growth Simulated by Monte Carlo Method
WU Feng-min, ZHU Qi-peng, WANG Xiao-ping, WU Zi-qin
Chin. Phys. Lett. 1998, 15 (12): 916-918 .  
Abstract   PDF(pc) (255KB) ( 440 )
Monte Carlo simulations have been carried out to investigate the kinetic growth process of ultrathinfilm. It is found that the area of cluster S(t) grows with time t as tk , where growth exponent k is less than 1 when averaged from all clusters. The further results indicate that the cluster growth is nonlinear, i.e., the bigger the cluster area S is, the faster it grows (the larger the k). Similar results also show the fractal dimension D increases with the increasing S. Both the slope a of lgk-lgS and the slope δ of 1gD-lgS are positive and related to the nucleation and growth kinetics.
Quantum XY Spin Glass with Ferromagnetic Coupling in External Field
SHANG Yu-min, YAO Kai-lun
Chin. Phys. Lett. 1998, 15 (12): 919-921 .  
Abstract   PDF(pc) (195KB) ( 524 )
The quantum XY spin glass model with ferromagnetic coupling in an external field is investigated numerically. The susceptibility exhibits the typical spin glass feature, the cusp of the transverse susceptibility corresponding to the phase transition is shifted to lower temperature by increasing field. In addition to the crossover feature observed in CuMn, the specific heat exhibits the 2-dimensional Ising model-like feature.
Structural and Magnetic Properties of Tb(Fel-xNix)11.3Nb0.7 Compounds
WANG Jian-li, YANG Fu-ming, BAO Fu-quan, TANG Ning, HAN Xiu-feng, YANG Dong, ZHANG Cheng, F. R. de Boer
Chin. Phys. Lett. 1998, 15 (12): 922-924 .  
Abstract   PDF(pc) (268KB) ( 371 )
Structural and magnetic properties of Tb(Fel-xNix)11.3Nb0.7 compounds have been investigated. The x-ray diffraction patterns show that all compounds crystallize in the ThMn12-type structure and that all samples are almost of single phase. The lattice constants monotonously decrease with increasing Ni content. The Curie temperature Tc clearly increases and the saturation moment Ms monotonously decreases with increasing Ni content. X-ray diffraction patterns of aligned samples at room temperature show that for x ≤ 0.2 the easy magnetization direction is in the plane while for the x = 0.25 compound the easy magnetization direction is along the c-axis. In the compounds with x ≤ 0.20 spin reorientation occurs above room temperature whereas in the compounds with x > 0.2 there is a spin reorientation below room temperature. It has been found that Ni contributes positively to the T-sublattice moment MT.
Local Structure Distortion and Quadrupole Splitting of Fe Ions in Bal+xNdl-xFeTiO6
LI Li-ping, LI Guang-she, SONG Xiao-yu, MIA0 Ji-peng, ZHOU Xian-feng, SU Wen-hui,
Chin. Phys. Lett. 1998, 15 (12): 925-927 .  
Abstract   PDF(pc) (212KB) ( 517 )
A series of samples Bal+xNdl-xFeTiO6(x = 0.0-0.5) were prepared by solid state reactions and characterized by x-ray diffraction and Mössbauer spectroscopy. All samples crystallized in cubic structure. A random distribution of Fe and Ti ions at octahedral sites was shown. 57Fe Mössbauer spectra of the samples consisted of a quadrupole doublet. The quadrupole splittings obtained by fitting the experimental data were larger than 0.5mm/s, indicating local structure distortions in these cubic phases. The relationship between quadrupole splitting and dopant content x of Bal+xNdl-xFeTiO6is discussed.
Preparation and Surface Layer Modification of Silicon Nanoparticles Dispersed in 2-Propanol
ZHU Yong, S. Iwasaki, K. Kimura, ZHANG Li-de
Chin. Phys. Lett. 1998, 15 (12): 928-930 .  
Abstract   PDF(pc) (315KB) ( 423 )
Silicon nanoparticles dispersed in 2-propanol were prepared by using an arc plasma with gas flow method in a new designed home-made apparatus. The particles are composed of silicon crystal core covered by oxidized amorphous silicon shell. The composition of the particle surface layer can be modified by preparing the sample in different atmosphere. The particles can be also obtained with different core composition and different size which we need.
Hydrodynamical Basis for Interpreting the Features of a Kind of Ocean Objects on Synthetic Aperture Radar Images
YU Wei-dong, HUA Feng, JIN Mei-bing, PAN Zeng-di, YUAN Ye-li
Chin. Phys. Lett. 1998, 15 (12): 931-933 .  
Abstract   PDF(pc) (250KB) ( 408 )
A new hydrodynamical model interpreting the synthetic aperture radar (SAR) imaging of a kind of ocean objects is proposed. It is based on the perturbation analysis of the wave height spectrum balance equation. An appropriate form of equilibrium wave height spectrum is deduced and then used to obtain the relative variation rate of the spectrum perturbation to its equilibrium state. Such variation rate reflects directly the features of a kind of ocean objects on the SAR images.
Bare Strange Stars Might Not Be Bare
XU Ren-xin, QIAO Guo-jun
Chin. Phys. Lett. 1998, 15 (12): 934-936 .  
Abstract   PDF(pc) (306KB) ( 430 )
It is proposed that the bare strange matter stars might not be bare, and the observed pulsars might be in fact the bare strange stars. As intensely magnetized strange matter stars rotate, the induced unipolar electric fields would be large enough to construct magnetospheres. This situation is very similar to that discussed by many authors for rotating neutron stars. Also, the strange stars with accretion crusts in binaries could act as x-ray pulsars or x-ray bursters. There are some advantages if pulsars are bare strange stars.
26 articles