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Volume 16 Issue 12
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Original Articles
An Oscillatory Solution for Damping Sine-Gordon Equation
HE Wei-zhong, XU Liu-su, HU Zhao-hui, ZOU Feng-wu
Chin. Phys. Lett. 1999, 16 (12): 859-860 .  
Abstract   PDF(pc) (162KB) ( 320 )
Using the perturbation method and by means of a general mathematics technique similar to the variation of constant, we present mainly some relative oscillation solution for the damping Sine-Gordon equation under certain conditions. And at the end of this paper, we give two so-called critical speeds of traveling wave. There is an interesting relationship about value and ordering of the two critical speeds.
A Unified Algebraic Dynamical Solution to General Two-Photon Algebra Systems
YING Zu-jian, WANG Shun-jin,
Chin. Phys. Lett. 1999, 16 (12): 861-863 .  
Abstract   PDF(pc) (143KB) ( 438 )
We use squeezing and displacement operators and apply algebraic dynamics to develop a unified solution of general time-dependent two-photon algebra systems. A set of orthogonal-and-normalized solutions are derived with the ground state being the conventional squeezed state. Landau system is given as an example.
Interference of Independent Inhomogeneous Bose Condensates via Continuous Measurement
LI Chuan-feng, GUO Guang-can
Chin. Phys. Lett. 1999, 16 (12): 864-866 .  
Abstract   PDF(pc) (211KB) ( 361 )
Continuous measurement theory is generalized to inhomogeneous case via the Wigner function. Applying it to two independent condensates shows that a relative phase builds up via the measurement at the expense of a decrease of the interference pattern visibility. A general pattern depending on the wave functions of the condensates is provided which can be applied to other nonlocal quantum system.
Determination of the Unperturbed Period of a Torsion Pendulum in the Time-of-Swing Method
LUO Jun, HU Zhong-kun, LUO Xu-jun, WU Zi-gang
Chin. Phys. Lett. 1999, 16 (12): 867-869 .  
Abstract   PDF(pc) (260KB) ( 493 )
A symmetric disc-shaped torsion pendulum was designed to study the nonlinear effects of the torsion fiber. It was showed that the period of the pendulum decreases with the amplitude of the oscillation. Determination of the unperturbed period through a fit to measured data of the period variation with amplitude shows that this systematic error in the measurement of Newtonian gravitational constant G by the time-of-swing method can be reduced by an order of the magnitude at least.
Comprehensive Evidence of Octupole Vibration in 158Gd
LONG Gui-lu, , JI Hua-ying, ZHAO En-guang,
Chin. Phys. Lett. 1999, 16 (12): 870-872 .  
Abstract   PDF(pc) (224KB) ( 338 )
Comprehensive evidence of the SU(3) octupole vibration limit in the spdf interacting boson model is found in the spectrum, E2 and El transition rates, and relative intensities in 158Gd. This is a good example of a rotational nucleus with octupole vibration in the rare-earth region.
Angular Distribution for 7Be(d, n)8B Reaction at Ec.m. = 8.3MeV and the Astrophysical Sl7(0) Factor for 7Be(p, γ)8B Reaction
WANG You-bao, LIU Wei-ping, BAI Xi-xiang, LI Zhi-chang, LI An-li, ZHOU Shu-hua, ZHU Xiao-feng, LI Xiao-mei, HE Gao-kui, GUO Gang, LIAN Gang, TANG Xiao-dong
Chin. Phys. Lett. 1999, 16 (12): 873-875 .  
Abstract   PDF(pc) (208KB) ( 383 )
The differential cross section for 7Be(d, n)8B reaction at Ec.m. = 8.3 MeV has been measured by using a 7Be radioactive beam. The reaction cross section was determined to be 28 ± 3mb. The astrophysical Sl7(0) factor for the 7Be(p, γ)8B reaction was derived to be 24 ± 5 eV b through the asymptotic normalization constant of )8B extracted from the experimental data. This result is found to be consistent with a previous value obtained from the same reaction at Ec.m. = 5.8 MeV, implying the energy independence of this indirect method within the uncertainty.

Non-equilibrium Statistic Features in Dissipative Heavy Ion Collision 27Al+27Al
WANG Qi, LI Song-lin, TIAN Wen-dong, HU Peng-yun, LU Jun, F. Amorini, M. Cabibb, G. Cardellas, P. Figuere, A. Musumarra, M. Papa, G. pappalardo, F.Rizzo, S. Romano, S.Tudisco, B.Heusch
Chin. Phys. Lett. 1999, 16 (12): 876-878 .  
Abstract   PDF(pc) (246KB) ( 329 )
The excitation functions of dissipative products have been measured in the reaction 27Al+27Al at incident energies from 114 to 127MeV in steps of 200keV. Detection angles vary continuously from 10.4° to 57.4° in laboratory system. An angular coherent width more than 40° in center of mass is obtained. The results from the analysis of excitation functions with nonself-averaging are characterized by a quasi-periodic long-range energy structure embedded in the disorder Ericson fluctuation.

Dilepton Production in an Expanding Hot Baryon-Rich Quark-Gluon Matter
JIANG Wei-zhou, HE Ze-jun, ZHU Zhi-yuan, ZHANG Jia-ju
Chin. Phys. Lett. 1999, 16 (12): 879-881 .  
Abstract   PDF(pc) (284KB) ( 332 )
Under thermodynamic equilibrium, the initial values of the quark-gluon system from relativistic nucleus-nucleus collisions are obtained. From these initial values we have studied the dilepton production on the basis of the relativistic hydrodynamic model, and found that with increasing incident energy a characteristic plateau indicating the formation of the quark-gluon plasma appears in the total yield.
Optical Oscillator Strengths for 32S → 42P and 32S → 52P Excitations of Na
ZHANG Xiao-jun, ZHU Lin-fan, WANG Ying-xue, LIU Xiao-jing, FENG Ren-fei, XU Ke-zun, ZHONG Zhi-ping, YAN Jun
Chin. Phys. Lett. 1999, 16 (12): 882-884 .  
Abstract   PDF(pc) (231KB) ( 451 )
The electron-energy-loss-spectrum of sodium has been measured in discrete region at a 1.5 keV impact energy and a mean scattering angle of 0°. The relative optical oscillator strength density spectrum of the valence shell of sodium was established by using the dipole (e, e) method and then normalized to the theoretical optical oscillator strength of the 32s + 32P excitation. The optical oscillator strengths of the 32S → 42P and 32S → 52P excitations obtained in the present work are 0.014 ± 0.002 and 0.0026 ± 0.0004, respectively. Theoretical values of optical oscillator strengths for 32S → n2P (n = 3 - 5 ) excitations of sodium were obtained by using the relativistic configuration interaction method, which are 0.97, 0.012, and 0.0025, respectively.

Electron Interaction with Lithium Atoms and Electron Impact Broadening of the Lithium Resonance Line
ZHAO Zeng-xiu, YUAN Jian-min, SUN Yong-sheng
Chin. Phys. Lett. 1999, 16 (12): 885-887 .  
Abstract   PDF(pc) (227KB) ( 388 )
Electron collision with lithium atoms is calculated by using R-matrix method. The scattering parameters are applied in the determination of the electron impact broadening and shift of the lithium resonance line 2s2S-2p2P. The width and shift are obtained based on the impact approximation. A largest discrepancy of 30 percent for the broadening width is found from a semiclassical calculation.
Quantum Electrodynamic Perspective on Multiphoton Ionization
CHEN Jing, CHEN Shi-gang, LIU Jie
Chin. Phys. Lett. 1999, 16 (12): 888-890 .  
Abstract   PDF(pc) (228KB) ( 477 )
A fully quantum nonperturbative method is developed to describe multiphoton ionization in intense fields. It is shown that, treating the radiation field with quantum electrodynamic(QED) theory enables u s to obtain the above-threshold ionization energy distribution spectrum in analytical form firstly. Moreover, in addition to the well-known semiclassical theory, the framework presented here, derived from a QED perspective, provides a new picture of the multiphoton ionization.
Ground Rotation Band of a 6-Boson System
BAO Cheng-guang, HUI Ping, HE Yan-zhang
Chin. Phys. Lett. 1999, 16 (12): 891-893 .  
Abstract   PDF(pc) (262KB) ( 301 )
A 6-boson system has been qualitatively studied based on symmetry consideration. Emphasis is placed on the ground rotation band based on the octahedron structure. In this band the L = 1 , 2, and 3 states are found to be prohibited by symmetry. Therefore there is a gap to hinder the rotational excitation of the ground state.
Effective Curvature Matrices and Mixed Moments of General Pulsed Paraxial Beams
YANG Jun, FAN Dian-yuan
Chin. Phys. Lett. 1999, 16 (12): 894-895 .  
Abstract   PDF(pc) (183KB) ( 349 )
On the basis of the space-time Wigner distribution function, we use the least-squares fitting method to derive the relationship between effective wavefront curvature matrices and second-order mixed moments of quasimonochromatic and polychromatic pulsed paraxial beams. The expressions here are valid for both completely coherent and partially coherent light in the three-dimensional space. Finally, the fitting method is extended to the higher-order situation; from this, a novel technique for characterizing the beam phase from the moments and their derivatives is presented.
Collapse and Revival in the Damped Jaynes-Cummings Model
TAN Wei-han, YAN Ke-zhu
Chin. Phys. Lett. 1999, 16 (12): 896-898 .  
Abstract   PDF(pc) (191KB) ( 909 )
We present the first results for the analytic solution of the dissipative Jaynes-Cummings model and its application to the collapse and revival of atomic inversion. We find that the atomic inversion oscillates more and more slowly with decreasing Rabi frequency due to the cavity losses. At the same time, long drawn-out revivals after collapse are observed.
Photorefractive Mutually-Pumped Phase Conjugation with Coherent Beams: Sensitivity to Small Perturbations
SHEN Jing-ling, DAI Jian-hua, ZHANG Hong-jun
Chin. Phys. Lett. 1999, 16 (12): 899-901 .  
Abstract   PDF(pc) (286KB) ( 356 )
Mutually-pumped phase conjugation in BaTiO3 crystal with two coherent incident beams has been studied experimentally for the bridge configuration. We observed that when the two pump beams are blocked individually, the transient behavior of the phase conjugation reflectivity with coherent beams was greatly different from that with incoherent beams. The phase conjugate reflectivity was sensitive to small perturbations such as vibration, exhibiting a change of as much as a factor of 10. The response time to the vibration was measured to be about 0.3s.
New Method to Obtain Strain Gradient Chirped Fiber Bragg Gratings
WANG Ling, FU Li-bin, XU Wan-jin, AN Hong-lin, LIN Xiang-zhi, LIU Hong-du
Chin. Phys. Lett. 1999, 16 (12): 902-904 .  
Abstract   PDF(pc) (207KB) ( 544 )
We describe a new method for applying a strain gradient with different profiles to convert uniform fiber Bragg gratings into linear or non-linear chirped ones. The chirping profile and the chirp rate of the fiber gratings can be controlled by simply varying the tension applied. Both the theory and experimental results are presented.
A Numerical Approach to the Frequencies and Damping Rates of Ion-Acoustic Waves in Ion-Collisional Plasmas
ZHENG Jian, YU Chang-xuan
Chin. Phys. Lett. 1999, 16 (12): 905-907 .  
Abstract   PDF(pc) (215KB) ( 613 )
A numerical solution to the linearized ion Fokker-Planck equation is presented for large ionization-temperature ratio ZTe/Ti ( ≥32). By reducing the equation to an eigenvalue problem through the moment approach, the frequencies and damping rates of ion-acoustic waves in ion-collisional plasmas are calculated as well as the specific heat ratios. Comparing our results with those calculated by Tracy et al. [Phys. Fluids, B5 (1993) 1430] shows that our method is accurate enough in large ZTe/Ti plasmas.
Acceleration of Ionospheric Out-Flowing Ions in the Substorm in Geo-magnetotail
SHI Jian-kui, LIU Zhen-Xing, T. L. Zhang, K. Torkar
Chin. Phys. Lett. 1999, 16 (12): 908-910 .  
Abstract   PDF(pc) (192KB) ( 377 )
Using dynamics equation, acceleration of out-flowing ion during dipolarization in a substorm in the magneto-tail is simulated. The main results show that: (1) The ion distribution function that is initially exponentially decreasing with increasing speed is turned into a single peak distribution, and with time the peak moves towards higher speed. (2) The peak moves along V faster than that along V||, and the ion acceleration mainly occurs in the middle of the dipolarization. (3) The higher the initial energy, the faster the peak moves, and the more energy is obtained by the ions. The ion energy theoretically calculated is as high as about 102 keV, this is consistent with the observation.
Preparation of the Bilayer Film Electret of SiO2 Matrix Amorphous Composite
HUANG Zhi-qiang, XU Zheng
Chin. Phys. Lett. 1999, 16 (12): 911-913 .  
Abstract   PDF(pc) (274KB) ( 440 )
Through the fusing and the thermal oxidation technology, the bilayer compound film (SiO2-PbO-Al2O3)/SiO2 electret was successfully prepared on the single crystalline silicon substrate. Experiments indicated that this co-mixture laminated-layer compound film possessed unique excellent electret properties. Without any chemical modification, the surface electric potential of the sample could get the equal value of the grid voltage after corona charging and decayed no more than 5% in 270d. Moreover, not only did the samples have the excellent capability of negative charges injection and storage, but also did they have the outstanding positive ones. Thermally stimulated discharge current spectra showed that the compound film had unique, single but stable charge-trapped mechanism corresponding to T = 290°C positive/negative discharge current peak, which could be attributed to its special inner microstructure.
Application of a Simple Semi-empirical Interatomic Potential Model to Phonon Density of States of Fe3Al
LIU Shao-jun, CAI Jun, DUAN Su-qing, MA Ben-kun
Chin. Phys. Lett. 1999, 16 (12): 914-916 .  
Abstract   PDF(pc) (244KB) ( 443 )
We proposed a simple analytical interatomic potential model by extending the framework of embedded-atom model to include the non-central three-body potentials. This model can be easily applied to treat transition metals and their alloys based on the very recently developed lattice inversion method. We used the model to calculate the phonon density of states and entropy of Fe3AI, and the results were in agreement with the experimental data.
Oscillation Period of Two-Level Systems Driven by Time-Dependent Fields
ZHAO Xian-geng
Chin. Phys. Lett. 1999, 16 (12): 917-918 .  
Abstract   PDF(pc) (184KB) ( 326 )
We study the dynamics of two-level systems under the influence of time-dependent external fields. An oscillation period describing the transition between two states is obtained analytically by the use of perturbation theory, from which the results for any special case can be derived. We illustrate two examples to show the advantage of our theory, in which the phenomenon of localization/delocalization can be addressed uniformly by oscillation period.
Asymmetrical Spin-Polarized Tunneling in a Composed-Barrier Magnetic Tunnel Junctions Under the Forward and Reverse Biases
XU Hui-ying, YU Wen-xue, KANG Jian, MAI Zhen-hong
Chin. Phys. Lett. 1999, 16 (12): 919-921 .  
Abstract   PDF(pc) (259KB) ( 374 )
Based on the two-band model and nearly-free-electron approximation, the tunnel current, conductance and mag-netoresistance of the composed-barrier magnetic tunnel junctions ( MTJ ) under the forward and reverse biases are discussed, respectively, and the numerical results are compared with the experimental results of the single-barrier MTJ . We find that there exists an asymmetrical spin-polarized tunneling in this structure under the forward and reverse biases. It suggests that this type of MTJ will provide novel functions to the potential applications of traditional types of MTJ.

Characteristics of the Organic Single-Quantum-Well Devices Fabricated by the Doping Method
HUANG Jing-song, XIE Zhi-yuan, YANG Kai-xia, LI Chuan-nan, ZHAO Yi, LIU Shi-yong
Chin. Phys. Lett. 1999, 16 (12): 922-924 .  
Abstract   PDF(pc) (231KB) ( 607 )
A doping technique to fabricate an organic quantum-well electroluminescent device is demonstrated. The fabricated single-quantum-well device consists of the following structure: an N,N’-Bis(3-methyphenyl)-N,N’-diphenyl benzidine layer for hole transportation, an 8- (quino1inoJate)-aluminum (AJq) layer for electron transportation and a light emitting layer of Alq doped with 5,6,11,12-tetraphenylnaphthacene(rubrene). The dopant rubrene serves as a potential well, whereas the undoped Alq layer serves as a barrier layer. The efficiency and luminance of the device have been significantly improved. The observed phenomena of the spectral narrowing and the emission peak energy blue-shift are a result of the recombination of carriers from the quantized energy states.
Infrared Absorption Cut-Off of Molecular Nonlinear Optical Crystals: Theoretical Studies on Vibrational Spectra of MDNB, Urea and MNA Molecules
WU Ke-chen, LI Jun,
Chin. Phys. Lett. 1999, 16 (12): 925-927 .  
Abstract   PDF(pc) (217KB) ( 380 )
A theoretical model has been set up for evaluating the infrared absorption cut-off (λIR) of molecular nonlinear optical (NLO) crystals on the basis of calculated molecular infrared vibrational spectra. This model is applied to meta-dinitrobenzene (MDNB), urea, and 2-methyl-4-nitroaniline (MNA) crystals. The λIR values for MDNB and urea crystals are predicted to be 2.0 and 1.37μm, respectivelx which are in good agreement with experimental measurements. Although the λIR of MNA is experimentally unknown yet, we predict it to be 1.50μm. The theoretical analysis indicates that, while the λIR of MDNB arises from asymmetric torsion of N-O in the molecule, those of urea and MNA arise from symmetric N-H stretch and C-H stretch, respectively. These results should be helpful for the molecular design of novel infrared NLO crystals.
Electron-Spectroscopy Study of Amorphous CN:Ti Films
CAO Ze-xian, GUO Jian-dong, WANG En-ge, LIU Feng-qin
Chin. Phys. Lett. 1999, 16 (12): 928-930 .  
Abstract   PDF(pc) (269KB) ( 312 )
Amorphous CN:Ti films deposited by using the reactive magnetron sputtering method were annealed in vacuum under 200 to 600°C. Incorporation of Ti (less than 3at.%) has brought some new perspectives to the material. Electron-energy-loss spectrum indicates improved conductivity in CN:Ti films as in the insulating CN films. The high-resolution core-level x-ray photoelectron spectroscopy (XPS) studies show that most carbon atoms form homeopolar bonding in as-deposited CN:Ti film. While the N Is line always shrinks with increasing annealing temperature, the total full width at half maximum of C Is line decreases only at annealing temperature over 300°C when the broadening due to heterobonding formation is outdone by the effect of increasing order. An enhanced π-band feature in the valence-XPS spectra at high annealing temperatures confirms the graphitization tendency of this material.
Disk Stability of the Milky Way Near the Sun
LUO Xin-lian, PENG Qiu-he,
Chin. Phys. Lett. 1999, 16 (12): 931-933 .  
Abstract   PDF(pc) (206KB) ( 329 )
By solving Poisson's equation for logarithmic density disturbance in three-dimensional (3D) spiral galaxies, the disturbed potential can be given on the disk. Combining it with the corresponding dispersion relation, the local gravitational stability of our galaxy is discussed here. We have generalized the Toomre's stability criterion to the more realistic 3D galaxy models. The generalized Toomre's parameter Q near the sun is 2.08 or 2.20 for two or four armed spiral galaxy models, respectively.

Determining the Cosmic Equation of State from Gravitational Lensing
ZHU Zong-hong, CAO Li
Chin. Phys. Lett. 1999, 16 (12): 934-937 .  
Abstract   PDF(pc) (233KB) ( 322 )
An independent method is proposed to determine the equation of state, ωx ≡ pxx, for the dark energy component in the universe. This method is based on gravitational lensing statistics. An analytically simple expression for the optical depth of gravitational lensing in general Friedmann-Robertson- Walker cosmologies with dark energy component is derived. It is shown that for a flat universe the optical depth depends sensitively on the redshift to the source zs and the equation of state ωx which makes the method proposed here efficient and robust.
27 articles