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Volume 16 Issue 2
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Original Articles
First-Order Correction of the Perturbed sine-Gordon Equation
YAN Jia-ren, TANG Yi, ZHOU Guang-hui
Chin. Phys. Lett. 1999, 16 (2): 79-81 .  
Abstract   PDF(pc) (165KB) ( 364 )
A new direct approach based on the Fourier transformation is developed and applied to study the perturbed sine-Gordon equation. Since a new basis for perturbation expansion is introduced, the first-order correction is expressed in terms of Bessell functions.
Topological Approach to the Study of Global Stationary Property of Quantum Systems
XU Gong-ou, XING Yong-zhong, YANG Ya-tian
Chin. Phys. Lett. 1999, 16 (2): 82-84 .  
Abstract   PDF(pc) (247KB) ( 601 )
A topological approach to the study of global stationary property of quantum systems is carefully formulated. Particular attentions are paid to basic notions such as homeomorphic map, topological-structure-preserving (TSP) map, and bifurcation due to local destruction of the TSP condition.
Wormhole Solution in Lovelock Gravity Theory
SHANG Yan-wen, XU Jian-jun
Chin. Phys. Lett. 1999, 16 (2): 85-87 .  
Abstract   PDF(pc) (169KB) ( 911 )
In this work, we confirm the existence of wormhole solution in general form of Lovelock gravity theory, and present some diagrams from the numerical calculation with special coupling constants as support to our conclusion. Besides, we also find out that whether the cosmology constant is actually zero is also critical to the behavior of the solution as it is in general relativity.
Rare Decays B→ Xs,d vv and Bs,d →1+1- in the Multiscale Walking Technicolor Model
XIAO Zhen-jun, LU Lin-xia, GUO Hong-kai, LU Gong-ru
Chin. Phys. Lett. 1999, 16 (2): 88-90 .  
Abstract   PDF(pc) (229KB) ( 773 )
We calculate the contributions to the rare B-decays, B→Xs,d vv and Bs,d →l+l- from the unit-charged technipions. Within the considered parameter space we find that: (a) the enhancements to the branching ratios in question can be as large as three orders of magnitude; (b) the ALEPH data of B→ Xsvv lead to strong mass bounds on mpl and mp8: mp8 ≥ 620,475 GeV for FQ = 40 GeV and mpl = 100,400 GeV, respectively; (c) the CDF data of Bs→μμ lead to a relatively weak limit: mp8 ≥ 320 GeV for FQ = 40 GeV and mpl = 200 GeV.
Analysis of Multiplicity Fluctuations in pp Collisions at 400 GeV/c by Bunching Parameters
WANG Shao-shun, LIU Ran, WANG Zhao-min
Chin. Phys. Lett. 1999, 16 (2): 91-92 .  
Abstract   PDF(pc) (175KB) ( 294 )
The multiplicity fluctuations of charged particles produced in pp collisions at 400 GeV/c have been studied by means of the bunching parameters (BPs). The results show that the values of BPs ŋ2(M) and ŋ3(M) depend not only on the width of multiplicity distribution, but also on the phase space correlations. The BPs: ŋ2( M ) and ŋ3(M) follow the same power-law behavior, which indicates that the multifractal structure in pp collisions at 400 GeV/c is observed.
Microscopic Treatment for the Degree of Freedom Beyond the S-D Model Space
LU Da-hai, YANG Li-ming
Chin. Phys. Lett. 1999, 16 (2): 93-94 .  
Abstract   PDF(pc) (148KB) ( 308 )
A microscopic treatment of the collective degrees of freedom of nuclei beyond the S-D model space in interacting boson model is given. Following a similar line as in the case of defining the seniority particle operator, independent of the S degree of freedom in single j-shell, a modified S , D pairs and generalized OBT (operatorized Bogoliubov transformation) are introduced to separate both the S and D degrees of freedom from the rest in the model space of the nucleus spanned by a set of nucleon creation operators cjm (j = j1,j2,. . .).
Angular Distributions of Intermediate Mass Fragments Emitted in 30 MeV/u 40Ar Induced Reactions
GOU Quan-bu, ZHU Yong-tai, XU Hu-shan, WEI Zhi-yong, LU Jun, ZHANG Yu-hu, WANG Qi, LI Song-lin, WU Zhong-li
Chin. Phys. Lett. 1999, 16 (2): 95-97 .  
Abstract   PDF(pc) (268KB) ( 461 )
The angular distributions of intermediate mass fragments with charge numbers from 3 to 24 emitted in 30 MeV/u 40Ar +58,64Ni and 115In reactions over an angular range of 5o- 140ohave been measured. In different angular region an exponential distribution function dσ/dΩ = N exp(-θ/α) was used to fit the measured angular distributions. The decay factor a which can be connected with the interaction time T and the factor N which is related to the intensity of the emission sources have been extracted. The relationship of α(Z) and N(Z) with Z for different reaction systems and different angular regions has been discussed. The different behavior of dσ/dΩ, α(Z) , and N(Z) for the three studied reaction systems exists mainly in the middle and backward angular regions. The dependencies of angular distributions on isospin and the size of reaction systems have also been discussed.

Correlation Between Transverse Polarization and Rapidity of Λ Produced in S+Pb Collisions at 200GeV/c Per Nucleon
YE Yun-xiu, HUANG Qi-lin, LÜ, Hai-jiang, WANG Jian
Chin. Phys. Lett. 1999, 16 (2): 98-100 .  
Abstract   PDF(pc) (233KB) ( 413 )
The dependence of transverse polarization on rapidity of Λ produced in S+Pb collisions at 200 GeV/c per nucleon has been studied. The original experimental data are from NA36 Collaboration at SPS of CERN. The precession effect of Λ spin, owing to the interactions between spin moment of Λ and the magnetic field on the path which Λ passes through, on the polarization has been taken into account. The results show that there are slight differences for the transverse polarization in different rapidity-region. The origins for these results have been analysed and discussed.

Calculation of the Ground States of H- Ion and He Atom in Magnetic Field with a Modified Configuration Interaction Method
QIAO Hao-xue, RAO Jian-guo, LI Bai-wen
Chin. Phys. Lett. 1999, 16 (2): 101-103 .  
Abstract   PDF(pc) (251KB) ( 466 )
The modified configuration interaction method is extended to double electronic systems in magnetic fields. Eigen-values and binding energies of ground state of H- ion and He atom in uniform magnetic fields are calculated. In a range running from low to intermediate magnetic fields, the best results with relative errors of 1.0 X10-5 and 1.4x10-6 for H- and He, respectively, are obtained. The accuracy of our results are almost 2 orders of magnitude better than those obtained by the other methods.
Experimental and Theoretical Investigation of the Valence Orbital Binding Energy Spectra and Momentum Distributions of C4H10 Molecule
PANG Wen-ning, GAO Jun-fang, RUAN Cun-jun, GAO Nai-fei, SHANG Ren-cheng
Chin. Phys. Lett. 1999, 16 (2): 104-106 .  
Abstract   PDF(pc) (277KB) ( 335 )
The C4H10 molecule has been studied by high resolution (e,2e) spectrometer at a total energy of 1200eV and using symmetric non-coplanar kinematics. The binding energy spectra ranging up to 32eV are measured at out-of-plane azimuthal angles from 0o to 22o corresponding to target electron momentum from about 0.1 to 1.8 a.u. The binding energy spectra and electron momentum distributions obtained for the valence orbitals are compared with the theoretical result calculated by using restricted Hartree-Fock and density functional theory methods. The agreement between theory and experiment of orbital electron momentum distributions is generally good.

Structure and Heat Capacity of Wurtzite GaN from 113 to 1073K
CHEN Xiao-long, LAN Yu-cheng, LIANG Jing-kui, CHENG Xiang-rong, XU Yan-ping, XU Tao, JIANG Pei-zhi, LU Kun-quan
Chin. Phys. Lett. 1999, 16 (2): 107-108 .  
Abstract   PDF(pc) (163KB) ( 457 )
High pure wurtzite structure GaN has been synthesized by gas reaction method. Its structure was determined by powder x-ray diffraction using the Rietveld technique. The heat capacity Cp was measured from 113 to 1073 K , which can be represented by Cp = 0.362 + 3.010 x l0-4T - 3.411 x 103T-2 - 7.791 x 10-8T2. No measurable phase transition was observed in this temperature range.

Recovery of the Solitons Using a Lattice Boltzmann Model
YAN Guang-wu, SONG Min
Chin. Phys. Lett. 1999, 16 (2): 109-110 .  
Abstract   PDF(pc) (125KB) ( 274 )
We formulate a lattice Boltzmann model which simulates Korteweg-de Vries equation by using a method of higher moments of lattice Boltzmann equation. Using a series of lattice Boltzmann equations in different time scales and the conservation law in time scale t0, we obtain equilibrium distribution function. The numerical examples show that the method can be used to simulate soliton.

Exact Solution with Shock-Like Structure for Nonlinear Kinetic Alfvéh Waves and Electron Acceleration
WU De-jin
Chin. Phys. Lett. 1999, 16 (2): 111-113 .  
Abstract   PDF(pc) (230KB) ( 415 )
An analytical solution with shock-like structure for nonlinear kinetic Alfvén waves in a low-β (β << me /mi << 1) plasma is presented. It is showed that the oblique propagating nonlinear kinetic Alfvén wave can rarefy the plasma and lead to a local density jump over a characteristic width of 10λe at the wave front, in particular, these new shock-like structure of nonlinear kinetic Alfvén waves possess a net field-aligned electric potential drop with a typical order of (2me /miβ)Te / e >> Te / e , as a consequence, they can effectively accelerate field-aligned electrons to velocities of order of the Alfvén velocity.

Reconstruction of Current Profiles and q Profiles on the HL-1M Tokamak
XU Wen-bin, YANG Qing-wei, WANG En-yao, LI Guang-sheng, GUO Gan-cheng, LIU Li, LI Fang-zhu, DONG Jia-qi, DENG Hui-chen, YE Gao-ying, LIN Hao-shu
Chin. Phys. Lett. 1999, 16 (2): 114-116 .  
Abstract   PDF(pc) (214KB) ( 563 )
The algorithm for reconstructing plasma current and safety factor profiles on a tokamak with an iron core transformer is given and applied to the analysis of experimental data. It is shown that a central negative magnetic shear region is realized througth ajusting the ramp-up rate of plasma current in ohmic discharges and through lower hybrid current drive on HL-1M tokamak.
A Simple Method to Make Field Emitter Using Ropes of Single-Walled Carbon Nanotubes
DING Yu, HANG Qing-ling, ZHANG Hong-zhou, FENG Sun-qi, BAI Zhi-gang, YU Da-peng, ZHANG Zhao-xiang, XUE Zeng-quan, SHI Zu-jin, LIAN Yong-fu, GU Zhen-nan
Chin. Phys. Lett. 1999, 16 (2): 117-119 .  
Abstract   PDF(pc) (381KB) ( 590 )
Field emission characteristics of single-walled carbon nanotubes were studied by using a simple method in a field emission microscope. The nanotube emission gun works effectively at the room temperature under a threshold field as low as 3.9mV/μm. A typical I-V relationship of field emission was obtained with a high current density. The observed stable bright spots on the fluorescent screen originate from an ensemble emission from micro-ropes of the single-walled carbon nanotubes.
Auger Electron Spectroscopy and Rut herford Backscattering-Channeling Study of Silicon Nitride Formation by Low Energy N+2 Ion Implantation
CHAI Jian-wei, YANG Guo-hua, PAN Hao-chang, CAO Jian-qing, ZHU De-zhang, XU Hong-jie
Chin. Phys. Lett. 1999, 16 (2): 120-122 .  
Abstract   PDF(pc) (285KB) ( 722 )
Direct nitridation of Si (100) surface by low energy N+2 ion beam implantation at room temperature for differention doses and angles of incidence has been investigated by in-situ Auger electron spectroscopy and glancing Rutherford backscattering-channeling (RBS-C) measurements. The results show that with increase of N+2 ion dose the N concentration in the Si surface increases and reaches to a surface stoichiometry close to that of Si3N4. The saturation dose and the thickness of the silicon nitride layer are related to the N+2 ion energy. Complete nitride layer can be formed at incident angles of 0o - 30o. At larger angles the degree of nitridation decreases and no nitride layer could be found at incident angles larger than 54o. The RBS-C results also suggest that a heavy damaged layer beneath the surface nitride layer can be formed due to ion beam implantation.

Proton Transmitting Energy Spectra and Transmission Electron Microscope Examinations of Biological Samples
TAN Chun-yu, XIA Yue-yuan, ZHANG Jian-hua, MU Yu-guang, WANG Rui-jin, LIU Ji-tian, LIU Xiang-dong, YU Zeng-liang
Chin. Phys. Lett. 1999, 16 (2): 123-125 .  
Abstract   PDF(pc) (491KB) ( 433 )
Transmission energy spectra of 530 keV H+ ion penetrating 140μm thick seed coat of maize and fruit peel of grape with thickness of 100μm were measured. The result indicates that these thick biological targets, as seen by the penetrating ions, are inhomogeneous, and there are open “channel like” paths along which the incidentions can transmit the targets easily. While most of the incident ions are stopped in the targets, some of the transmitting ions only lose a small fraction of their initial incident energy. The transmission energy spectra show a pure electronic stopping feature. Transmission electron microscope (TEM) micrographes taken from the samples of seed coat of maize and fruit peel of tomato with thickness of 60μm indicate that 150keV electron beam from the TEM can penetrate the thick samples to give very good images with clear contrasts.

Fabrication and Optical Property of Copper Nanowires in Nuclear Track Membranes
PENG Liang-qiang, JU Xin, WANG Shi-cheng, XIAN Ding-chang, CHEN Hong, HE Yuan-Jin
Chin. Phys. Lett. 1999, 16 (2): 126-128 .  
Abstract   PDF(pc) (417KB) ( 967 )
The electrochemical growth of nanowires in nuclear track membranes has been studied and a strong plasma absorption of copper nanowires in the visible region of the electromagnetic spectrum is observed. The result of the plasma absorption is qualitatively in agreement with the prediction of the appropriate formulation of effective medium theory.
Variational Approach to One-Dimensional Electrons Non- Adiabatically Coupled to Phonons
PANG Xiao-feng
Chin. Phys. Lett. 1999, 16 (2): 129-131 .  
Abstract   PDF(pc) (218KB) ( 383 )
The effects of the nonadiabatic phonon behaviours on the ground state of the system and the quantum modifications of the polaron characteristics and the modification form of the uncertainty relation between the phonon coordinate and momentum due to fluctuations of the electron density in the coupled electron-phonon systems have been studied by using a new variational ansatz for coherent phonons with correlated displacement and squeezing including internations with electrons. The correlated effect results in the following effect: (1) the energy of the ground state of the system is found to be lower than that for the phonons with uncorrelated displacement and squeezing; (2) the binding energy of the polaron was found to be increased; (3) the nonadiabatic coupling with electrons enhances the quantum uncertainty for the phonon coordinate and momentum when compared with the adiabatic and uncorrelated case.

Localized and Delocalized States at the Band Gap in Heteroepitaxial GaAs Grown on Si
LIANG Jia-chang, XU Zhou, LE Xiao-yun
Chin. Phys. Lett. 1999, 16 (2): 132-133 .  
Abstract   PDF(pc) (158KB) ( 604 )
There exist the interfacial mismatch strains and high density structural defects in heteroepitaxial GaAs grown on Si (GaAs/Si) because of a large misfit of the lattice constants and a large difference in linear thermal expansion coefficient between GaAs and Si materials. Our experiments show that the disordering in GaAs/Si epilayers strongly depends on their growth condition, especially on the concentration ratio [As]/[Ga] and demonstrate that at [As]/[Ga]=20 to 40 the relationship of temperature versus intensities of the dominant photoluminescence (PL) peaks, related to the delocalized states at the band gap of GaAs/Si, satisfies an Arrhenius equation to determine the thermal activation energies of delocalized states and at [As]/[Ga] ≥ 50 the relationship of temperature versus intensities of the dominant PL peaks, related to the localized states, satisfies an equation valid for amorphous semiconductors to determine the characteristic temperatures of localized states reflecting the disorder degree in GaAs/Si epilayers.

Enhancement of Electron Mobility by an Intense High-Frequency Irradiation in GaAs-Based Two-Dimensional Systems
CHEN Yi-qiao, LEI Xiao-lin
Chin. Phys. Lett. 1999, 16 (2): 134-136 .  
Abstract   PDF(pc) (233KB) ( 710 )
A theoretical examination of the electron transport in GaAs-based quantum wells was carried out under the influence of an intense electromagnetic irradiation in the frequency range from 0.1 to 1 THz, based on the tirne-dependent, nonlinear steady-state response to the applied electric field. It is found that although at low temperature (T = 10 K ) the dc mobility of the systems is suppressed by the intense radiation field, in agreement with the available experimental observation, the effect can be reversed at elevated temperature. At T = 77 and 300 K, the dc mobility of the GaAs system turns out to be enhanced with the increasing strength of the ac field when its amplitude is large than a threshold value.
Photoinduced Light Scattering in Co- and Cr-Doped Lithium Niobate
CHEN Kan, ZHANG Ming-sheng, CHEN Wan-chun
Chin. Phys. Lett. 1999, 16 (2): 137-139 .  
Abstract   PDF(pc) (273KB) ( 389 )
Photoinduced light scattering of Co- and Cr-doped lithium niobate crystals is examined. The light climbing effect is observed in the Co- and Cr-doped lithium niobate crystals. The influences of the incident light wavelength, laser power, sample thickness and doping effects on the light climbing effect are studied. Higher photodamage threshold and quicker light climbing are found in the Cr- and Co-doped lithium niobate, which are attributed to the higher space electrical charge field and both different valence and occupation of the doping ions, respectively.

Manifestation of Quantum Chaos in the Spectra of Quantum Well with Tilted Magnetic Field
LIU Bo, DAI Jian-hua, ZHANG Guang-cai, ZHANG Hong-jun
Chin. Phys. Lett. 1999, 16 (2): 140-142 .  
Abstract   PDF(pc) (231KB) ( 350 )
Two statistical properties, the nearest neighbor energy level spacing distribution P( s ) and the spectral rigidity Δ3( L ), are reported for energy level of a quantum well in a tilted magnetic field. Time-reversal ( T ) symmetry is broken in the system. The system is invariant under the anti-unitary combination of symmetric operations which include T, leading to what is called false T-violation. With the increasing magnetic field, P(s) and Δ3( L ) change from Brody type-like distribution to the Gaussian orthogonal ensemble (GOE) distribution. This result is a clear manifestation of quantum chaos in the system and is in agreement with the prediction of which the false T-violation suffices to give the energy spectra the properties of the GOE, instead of the Gaussian unitary ensemble (GUE). The result indicates that the system translates from mixed-type state to quantum chaotic state. However, the spectral rigidity Δ3( L ) turns into GUE with the magnetic field increasing. The different demonstration of P( s ) and the Δ3(L) is due to the counting of only finite semi-classical orbits.

Suppression of Self-sustained Field Domain Oscillation in GaAs/AlAs Superlattice by Hydrostatic Pressure at Room Temperature
WU Jian-qing, LIU Zhen-xing, JIANG De-sheng, SUN Bao-quan
Chin. Phys. Lett. 1999, 16 (2): 143-145 .  
Abstract   PDF(pc) (281KB) ( 401 )
The behavior of room temperature self-sustained current oscillations resulting from sequential resonance tunneling in a doped weakly-coupled GaAs/AlAs superlattice (SL) is investigated under hydrostatic pressure. From atmosphere pressure to 6.5 kbar, oscillations exist in the whole plateau of the I-V curve and oscillating characteristics are affected by the pressure. When hydrostatic pressure is higher than 6.5 kbar, the current oscillations are completely suppressed although a current plateau still can be seen in the 1-V curve. The plateau disappears when the pressure is close to 13.5kbar. As the main effect of hydrostatic pressure is to lower the X point valley with respect to Г point valley, the disappearance of oscillation and the plateau shrinkage before Г - X resonance takes place are attributed to the increases of thermoionic emission and nonresonant tunneling components determined by the lowest Г - X barrier height in GaAs/AlAs SL structure.

Ultraviolet Super-Radiation Luminescence of Sputtering ZnO Film Under Cathode-Ray Excitation at Room Temperature
GUO Chang-xin, FU Zhu-xi, SHI Chao-shu
Chin. Phys. Lett. 1999, 16 (2): 146-148 .  
Abstract   PDF(pc) (325KB) ( 867 )
We report the observation of the cathode-ray (CR) pumped ultraviolet (UV) super-radiation luminescence in ZnO thin film at room temperature (RT). The dependence of UV (peak at about 390nm) and green (peak at about 520nm) luminescent peaks in ZnO thin film under CR excitation on excitation electron beam current has been investigated. With the increase of the density of excitation electron beam current, green peak relatively decreases and UV peak increases, resulting in a change of the luminescent color from green to blue-purple. The green peak intensity increases sublinearly with the increase of the electron beam current density and saturates at a relatively low density of electron beam current. But the intensity of 390nm UV peak increases superlinearly with the increase of the electron beam current density. This is a UV super-radiation luminescence of exciton in ZnO under high density pump. In this paper, three-dimensional atomic force microscope images of the surface of unannealled and annealled ZnO films are given.
High Efficient Green Emission from Organic Multi-quantum Wells Structure
XIE Zhi-yuan, HUANG Jing-song, LI Chuan-nan, CHEN Bai-jun, LIU Shi-yong, LI Yan-qin, WANG Yue, SHEN Jia-cong
Chin. Phys. Lett. 1999, 16 (2): 149-151 .  
Abstract   PDF(pc) (251KB) ( 444 )
Organic green light emitting devices (LEDs) with multi-quantum wells (MQWs) structure were fabricated. Aromatic diamine was used as hole-transporting layer and potential barrier layer; tris (8-hydroxyquinoline) aluminum acted as electron transporting layer and MQWs green emitting layer. The influence of the barrier layer thickness and quantum well number to the device performance was also investigated. The barrier thickness must be thin (such as 4nm) enough to tunnel through and distribute charge carriers uniformly in different wells (mainly electrons). The organic MQWs LEDs showed enhanced electroluminescent efficiencies. Maximum luminous efficiency and external quantum efficiency were 1.241m/W and 1.04%, respectively.

Electron Field Emission from Different sp3 Content Diamond-Like Carbon Films
MAO Dong-sheng, ZHAO Jun, LI Wei, WANG Xi, LIU Xiang-huai, ZHU Yu-kun, ZHOU Jiang-yun, FAN Zhong, LI Qiong, XU Jing-fang
Chin. Phys. Lett. 1999, 16 (2): 152-154 .  
Abstract   PDF(pc) (201KB) ( 492 )
Different sp3 content diamond-like carbon films are deposited on to highly n-doped Si (111) substrates by a new plasma deposition technique-filtered arc deposition. Their electron field emission properties are studied by using a simple diode structure. It is showed that the turn-on field is decreased and field emission current density is increased with the increasing sp3 content (75-80%, 80-83%,and 88-90%) of the films. Field emission current of 0.1μA from the three samples was detected under the electric field of 10.1, 5.6, and 2.9 V/μm and emission current density of 4.4, 15.2, and 43.2μA/cm2, respectively, under 14.3 V/μm. Fowler-Nordheim (F-N) plots of the three samples nearly show of lineaity indicating that electron field emission obeys F-N theory.

Cubic Boron Nitride Films with Low Stress
ZHAO Yong-nian, ZOU Guang-tian, HE Zhi, ZHU Pin-wen, WANG Xue-jin, ZHAO Bing
Chin. Phys. Lett. 1999, 16 (2): 155-156 .  
Abstract   PDF(pc) (213KB) ( 367 )
We report a cubic boron nitride (c-BN) film with low stress. Infrared (IR) peak position of c-BN at 1006.3cm-1measured by IR spectroscopy shows that the c-BN film has very low internal stress which leads to an excellent adhesion. Transmission electron microscope micrograph indicates the only BN phase on the surface of the film is c-BN phase. It is clearly seen from IR spectra that the intermediate layer between the substrate and the c-BN layer is of the molecular crystal explosion boron nitride, hexagonal boron nitride, and wurtzic boron nitride.

28 articles