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Volume 17 Issue 4
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Original Articles
A Unisonant r-Matrix Structure of Integrable Systems and Its Reductions
QIAO Zhi-Jun, Walter STRAMPP
Chin. Phys. Lett. 2000, 17 (4): 235-237 .  
Abstract   PDF(pc) (193KB) ( 345 )
A new method is presented to generate finite dimensional integrable systems. Our starting point is a generalized Lax matrix instead of usual Lax pair. Then a unisonant r-matrix structure and a set of generalized Hamiltonian functions are constructed. It can be clearly seen that various constrained integrable flows by nonlinearization method, such as the c-AKNS, c-MKdV, c-Toda, etc., are derived from the reduction of this structure. Furthermore, some new integrable flows are produced.
Minimum Uncertainty States for Number-Difference-Phase Uncertainty Relation in NFM Operational Phase Description
FAN Hong-Yi, SUN Zhi-Hu
Chin. Phys. Lett. 2000, 17 (4): 238-240 .  
Abstract   PDF(pc) (176KB) ( 516 )
For the Noh, Fougères and Mandel (NFM) operational quantum phase description, which is based on an eight-port homodyne-detection, we derive the minimum uncertainty states for the number-difference-phase uncertainty relation. The derivation makes full use of the newly constructed |q,r> representation which is the common eigenvector of the two-mode photon number-difference aa - bb and (a+b)(a+ b).

Exact Solution for a Chain of Coupled Oscillators with Two Types of Atom
LIU Ke-Jia, LU Huai-Xin, ZHANG Yong-De
Chin. Phys. Lett. 2000, 17 (4): 241-242 .  
Abstract   PDF(pc) (124KB) ( 1630 )
A quantum transformation that can diagonalize the Hamiltonian of a ring of N coupled diatomic oscillators is found. By means of the transformation, the dispersion relation of the atomic system is obtained. For large N it turns out that the dispersion relation resembles to the phonon spectrum of the lattice vibration derived by Newton's equation of motion.
Note on Entanglement of an Arbitrary State of Two Qubits
Chin. Phys. Lett. 2000, 17 (4): 243-245 .  
Abstract   PDF(pc) (289KB) ( 555 )
It is shown that the norm of the polarization vector of the reduced density matrix can characterize the entanglement of two qubits and so it is defined as a simple measure of entanglement. It is then extended to the generalized entanglement of polarization vector. It is proved that the entanglement of formation belongs to the generalized entanglement of polarization vector. Under the local general measurement and classical communication how this generalized entanglement of polarization vector changes is proved strictly and so the first and second laws of quantum information processing are verified clearly.

Complex Normal-mode Frequencies of External Perturbations in Generalized Schwarzschild Geometry
YUAN Ning-Yi, LI Xin-Zhou
Chin. Phys. Lett. 2000, 17 (4): 246-248 .  
Abstract   PDF(pc) (206KB) ( 473 )
A modified Wentzel-Kramers-Brillouin approach is used to determine the complex normal-mode frequencies of external perturbations in generalized Schwarzschild geometry. In the λ = 1 case (Schwarzschild geometry), the agreement with other methods is excellent for the low-lying modes. On the contrary, the λ ≠ 1 case of this geometry is unstable against external perturbations.
Stochastic Resonance on a Circle Without Periodic Excitation
QIAN Min, WANG Guan-Xiang
Chin. Phys. Lett. 2000, 17 (4): 249-251 .  
Abstract   PDF(pc) (219KB) ( 439 )
We analyse the appearance of coherent motion in the dynamics of the Langevin equation in the subtle case of I < 1, and show that stochastic resonance does exist even in the non-critical case I < 1. Moreover, we show the monotonicity of the rotation number and discuss the relationship between the center frequency of the power spectrum peak and the rotation number.
Star Products of Quartic Maps with Two Equally High Peaks
ZHOU Zhong, PENG Shou-Li,
Chin. Phys. Lett. 2000, 17 (4): 252-254 .  
Abstract   PDF(pc) (217KB) ( 442 )
The double-well potential systems and a hybrid optical bistability device with liquid crystal have a relation to quartic maps with two equally high peaks. The star products for all doubly superstable kneading sequences in the kneading plane are presented, the generalized Feigenbaum's metric universalities such as scaling factors {αc, α,D, αE} and convergent rates {δaηα,η} are obtained.

Phase Diagrams of One-Dimensional Commensurate-Incommensurate Transition Model with Triple-Well Interactions
XU Hai-Bo, XU Ai-Guo, WANG Guang-Rui, CHEN Shi-Gang
Chin. Phys. Lett. 2000, 17 (4): 255-257 .  
Abstract   PDF(pc) (228KB) ( 431 )
We generalize the Frenkel-Kontorov model to the Frenkel-Kontorova-Devonshire model in which the interaction is the triple-well potential. By use of the effective potential method, numerical solutions of eigenvalue problem are used to work out the exact phase diagrams of a triple-well potential W and a piecewise parabolic potential V. According to the winding number ω and the rotation number Ω, we analyze the periodicity of the phase diagram and find some complex but regular phase structures. The properties of the phase structures are closely related to the period of the external potential D.

Single W Boson Production at √s = 189 GeV
YANG Hai-Jun, CHEN Guo-Ming, YANG Min, XIONG Zhao-Hua, LU Liang, LU Yu-Sheng, CHEN He-Sheng, TANG Xiao-Wei, Martin Pohl*, JIN Bing-Nian*
Chin. Phys. Lett. 2000, 17 (4): 258-260 .  
Abstract   PDF(pc) (239KB) ( 400 )
Single W boson production is analyzed in a data sample collected by L3 detector at Large Electron Positron Collider in 1998. The integrated luminosity is 176.4pb-1 with center-of-mass energy at √s = 189GeV. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The total cross section of single W production is measured to be 0.58 ± 0.13 ± 0.04pb, in good agreement with standard nmodel prediction. From this measurement, the limits on the anomalous γWW triplegauge-boson couplings are derived at 95% confidence level: -0.48<Δκγ< 0.38 and -0.50 < λγ< 0.41 .

Hyperbolic Dependence of Moment of Inertia on ω2 in Bands Involving vi13/2 Orbital and its Application in Configuration Identification
LU Jing-Bin, LIU Yun-Zuo, ZHANG Fan
Chin. Phys. Lett. 2000, 17 (4): 261-263 .  
Abstract   PDF(pc) (284KB) ( 500 )
The so-called hyperbolic dependence of apparent moment of inertia on square of rotational frequency is developed to the bands involving vi13/2quasineutron around A~160 lighter rare-earth region. This can be explained as a characteristic of strongly Coriolis mixing in the high-j unique-parity bands. As applications of such an effect, the previously proposed assignments of band x of 160Ho, π1/2-[541]O vi13/2 band of 170Ta, as well as band B of 168Lu have been reviewed respectively.

Weak Coupling in 143Nd
ZHOU Xiao-Hong*, E. Ideguchi, T. Kishida, M. Ishihara, H. Tsuchida, Y. Gono, T. Morikawa, M. Shibata, H. Watanabe, M. Miyake, T. Tsutsumi, S. Motomura, S. Mitarai
Chin. Phys. Lett. 2000, 17 (4): 264-266 .  
Abstract   PDF(pc) (240KB) ( 415 )
The high-spin states of 143Nd have been studied in the 130Te(18O, 5n)143Nd reaction at a beam energy of 80 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ -γ- t coincidences, γ-ray angular distributions, and γ-ray linearpolarizations were performed. A level scheme of 143Nd with spin and parity assignments up to 53/2+ is proposed. While a weak coupling model can explain the level structure up to the Jπ=39/2-state, this model can not reproduce the higher-lying states. Additionally, a new low-lying non-yrast level sequence in 143Nd was observed in the present work, which can be well described by the weak coupling of an i13/2 neutron to the 142Nd core nucleus.

Isospin Effect of Fragmentation Reaction on the Isotopic Distribution Produced in Intermediate Energy Heavy Ion Collisions
FANG De-Qing, SHEN Wen-Qing, FENG Jun, CAI Xiang-Zhou, WANG Jian-Song, SU Qian-Min, MA Yu-Gang, ZHU Yong-Tai, LI Song-Lin, WU He-Yu, GOU Quan-Bu, JIN Gen-Ming, ZHAN Wen-Long, GUO Zhong-Yan, XIAO Guo-Qing
Chin. Phys. Lett. 2000, 17 (4): 267-269 .  
Abstract   PDF(pc) (262KB) ( 512 )
Fragments produced in the reaction of 60 MeV/n 18O on Be have been measured experimentally. The isotopic distribution of fragmentation reaction is well reproduced by a modified statistical abrasion-ablation model. It is predicted that the isotopic distribution shifts toward the neutron rich side for neutron rich projectile, but this isospin effect decreases with the increase of the atomic number difference Z - ZA and disappears at last, where Z and ZA are atomic numbers of the isotopic distribution and the projectile respectively.

Emission Spectra of a Moving Atom in an Electromagnetic Field
ZHANG Jing-Tao, FENG Xun-Li, XU Zhi-Zhan
Chin. Phys. Lett. 2000, 17 (4): 270-271 .  
Abstract   PDF(pc) (149KB) ( 366 )
The emission spectra of a two-level atom moving in an electromagnetic field are studied. We find that there is a shift in the peak position and that each peak splits into double peaks. The shift is due to the detuning induced by the atomic motion, and the splitting is caused by the atomic energy change due to the exchange of photons.
A Theoretical Distinction Between Time-Resolved Resonance Raman and Resonance Fluorescence
LU Jing, DU Si-De, FAN Kang-Nian, Lee Soo-Ying
Chin. Phys. Lett. 2000, 17 (4): 272-274 .  
Abstract   PDF(pc) (202KB) ( 424 )
Based on the time-dependent theory, an analysis of the distinction between resonance Raman (RR) and resonance fluorescence (RF) with pulse excitation was presented. The real population of the intermediate state gives two optical components-the independent time evolution of intermediate ket and bra states generates RR while RF originates from the phase coherent between ket and bra states. In cw limit, the transition probability of spontaneous emission with pulse excitation can be reduced to the classical theory.
Nondegenerate Four Wave Mixing in Rare-Earth Doped Fiber Under the Influence of Coherent Population Trapping
GUO Yang, MING Hai, LIU Fang-Xin, XU Li-Xin,
Chin. Phys. Lett. 2000, 17 (4): 275-276 .  
Abstract   PDF(pc) (164KB) ( 413 )
By applying a strong coupling field between a lower state and the upper state of an allowed transition to ground, an enhancement of nondegenerate four wave mixing (NDFWM) with a resonantly enhanced third-order nonlinear susceptibility in a rare-earth doped fiber can be obtained. We have derived an expression for the third-order non-linear susceptibility using quantum theory and discussed the conversion efficiency for NDFWM. The theoretical result shows that the conversion efficiency has a maximum value while the third-order nonlinear susceptibility shows constructive interference at the Rabi frequency Ω23 =±√Г2Г3. On account of phase-mismatch, the frequency conversion efficiency has a maximum value over a certain small range of frequency separation (such as 0 < Δf < 30 GHz at the wavelength λc = 1.55 μm), and the frequency conversion range increases with increase of the third-order nonlinear susceptibility.

A Spring Model for a Cylindrical Interface Layer with Hexagonal Symmetry Between Two Solids
LIU Sheng-Xing, WANG Yao-Jun
Chin. Phys. Lett. 2000, 17 (4): 277-278 .  
Abstract   PDF(pc) (174KB) ( 398 )
A unique spring model is established to describe a cylindrical interface layer with hexagonal (or transversely isotropic) symmetry between two solids, which is realized by asymptotically expanding the transfer matrix for the anisotropic layer. The accuracy of the model is evaluated based on a comparison between the exact and the approximate solutions of the scattering cross sections of an obliquely incident ultrasonic wave from an interface layer with different thickness.
A Molecular Dynamics Simulation of CaSiO3 Melt Under an Electric Field
HUANG Shi-Ping, YOU Jing-Pin, JIANG Guo-Chang, F. Yoshida, XU Kuang-Di
Chin. Phys. Lett. 2000, 17 (4): 279-281 .  
Abstract   PDF(pc) (254KB) ( 621 )
The results of a molecular dynamics (MD) simulation are presented for CaSiO3 melt under an electric field. The two-body interaction potential is adopted in the simulation, with parameters chosen so that the calculated static structure is consistent with results of high temperature x-ray experiments. It is found that the MD results for the heat capacity at constant volume, the self-diffusion coefficient and the electrical conductivity change greatly when the electric field is over 500 MV/m. Discussion is given on these results, together with the frequency-dependent electrical conductivity.

New Low-Frequency Relaxation Process in La2CuO4+δ by Internal Friction Experiments
WANG Shi-Xing, LIU Wei, LIU Yun-Long, ZHANG Li-De
Chin. Phys. Lett. 2000, 17 (4): 282-284 .  
Abstract   PDF(pc) (250KB) ( 424 )
The low-frequency relaxation internal friction spectrum of La2CuO4+δhas been measured from -170 to 200°C in an automatic torsion apparatus at frequencies between 0.1 and 5.0Hz. Three new relaxation processes are found with maxima, which are attributed to thermally activated diffusive jumps of oxygen atoms or vacancies in the oxygen sublattice, according to various activation enthalpies of three experimental runs. It is shown that the content of oxygen defect have important influences on the physical properties of La2CuO4+δ.

Dynamic Scaling of Surface Growth in the Influence of Small Clusters Mobility
Chin. Phys. Lett. 2000, 17 (4): 285-287 .  
Abstract   PDF(pc) (270KB) ( 334 )
The deposition, diffusion and coalescence processes appeared in the surface growth of compact or liquid-like clusters system are studied. By introducing a critical cluster size ic, such that clusters of size s≤ ic, are mobile while clusters of the size s > ic are immobile, the effects of mobility of small clusters on cluster size distribution are simulated. As ic increases, the exponent γ which relates the maximum cluster density to the normalized deposition rate is increased. Numerical simulation results indicate that the scaled cluster-size distributions are independent of the deposition rate, but closely associated with the small clusters mobility. As ic increases, it is found that the distributions become narrow.

Energy Levels of Valence Subbands in Si/Sil-xGex Quantum Well by Admittance Spectroscopy
LIN Feng, GONG Da-Wei, KE Lian, ZHANG Sheng-Kun, SHENG Chi
Chin. Phys. Lett. 2000, 17 (4): 288-290 .  
Abstract   PDF(pc) (209KB) ( 484 )
Using the admittance spectroscopy technique, energy levels of subbands in SiGe/Si quantum well are studied. The value of activation energy increases with increasing well width, in accordance with the quantum confinement effect. Two conductance peaks due to hole emission from heavy hole ground state and light hole ground state were observed. It was found that the value of activation energy increased with annealing time at the temperature of 800oC, while the activation energy decreases with the annealing time at 900oC.
Magnetic Effects on Resonant Tunneling Through Quantum-Wire Arrays
ZENG Zhao-Yang, ZHANG Li-De
Chin. Phys. Lett. 2000, 17 (4): 291-293 .  
Abstract   PDF(pc) (232KB) ( 480 )
We investigated the influences of a uniform and a nanoscaled periodic magnetic field on electron's resonant tunneling through quantum-wire arrays (QWA). It is shown that, due to the magnetic quantum-size effect and additional destructive interference induced by the nanoscaled periodic magnetic field, ballistic conductance spectrum for electron tunneling through the QWA is strongly modified; while for uniform magnetic modulation, it cannot modify the resonant structure of ballistic conductance.
Effect of Surface Hydrogen Coverage on Field Emission Properties of Diamond Films Investigated by High-Resolution Electron Energy Loss Spectroscopy
WANG Yu-Guang, GU Chang-Zhi, JIN Zeng-Sun, XIONG Yan-Yun, LIN Zhang-Da, FENG Ke-An
Chin. Phys. Lett. 2000, 17 (4): 294-295 .  
Abstract   PDF(pc) (210KB) ( 457 )
The influence of surface hydrogen coverage on the electron field emission of diamond films was investigated by high-resolution electron energy loss spectroscopy. It was found that hydrogen plasma treatment increased the surface hydrogen coverage while annealing caused hydrogen desorption and induced surface reconstruction. Field electron emission measurements manifested that increase of surface hydrogen coverage could improve the field emission properties, due to the decrease of electron affinity of the diamond surface by hydrogen adsorption.

Preparation and Properties of the Ni2MnGa Magnetic Shape Memory Alloy
LIANG Ting, XU Hui-Bin, JIANG Cheng-Bao, GONG Sheng-Kai
Chin. Phys. Lett. 2000, 17 (4): 296-297 .  
Abstract   PDF(pc) (184KB) ( 482 )
The polycrystalline Ni48.2Mn22.4Ga29.4 alloys were prepared by means of melting in argon arc furnace. X-ray diffraction pattern indicates a fcc cubic structure with a lattice parameter of 0.5822nm at room temperature. The phase transformation temperatures were: 1°C for martensite start temperature, -11°C for martensite finish temperature, 3°C for austenite start temperature and 11°C for austenite start temperature, respectively. The results showed that the effect of magnetic field on the strains increases with the decrease of temperature. A strain of 2.1 x10-4 was obtained with an applied magnetic field of 5kOe at -66°C.

Characteristics of Electrorheological Fluid Flow Between Two Concentric Cylinders
PENG Jie, ZHU Ke-Qin, XI Bao-Shu
Chin. Phys. Lett. 2000, 17 (4): 298-300 .  
Abstract   PDF(pc) (180KB) ( 440 )
The characteristics of Couette flow of electrorheological fluid (ERF) between concentric cylinders is dependent on the parameter β, which is in the yield stress formula of ERF. In the case of β > 2, the yield region locates between the yield surface and the outer cylinder. In the case of β< 2, the yield region locates between the yield surface and the inner cylinder. When β= 2, there is no yield surface. Steady and time dependent numerical results in relation to different β are presented and discussed.

Light-Induced Charge Separation and Transfer in Bacteriorhodopsin
HUANG Yu-Hua, ZHAO You-Yuan, ZHANG Zhong-Bin, OU-YANG Xiao-Ping, GONG Qin-Gan, CHEN Ling-Bing, LI Fu-Ming, LIU Jian, DING Jian-Dong, LI Qing-Guo
Chin. Phys. Lett. 2000, 17 (4): 301-303 .  
Abstract   PDF(pc) (256KB) ( 863 )
The photo-voltage signals in bacteriorhodopsin(bR) excited by 1064 nm pulse laser are different from those by 532 or 355nm. It shows that the positive and negative photoelectric signals are produced by the motion of the positive and negative charges, respectively, and more energy is needed for producing the positive charges than the negative. The mechanism of light-induced charge generation and charge transfer in bR was studied and analyzed by measuring the photoelectric signals with different impedance of measuring circuit and different pulse-width of 532nm laser as pump light.
Newly Discovered Herbig-Haro Objects near Haro 4-255
WANG Min, ZHAO Bing, YANG Ji, DENG Li-Cai, CHEN Jian-Sheng,
Chin. Phys. Lett. 2000, 17 (4): 304-306 .  
Abstract   PDF(pc) (449KB) ( 556 )
We have performed CCD (charge coupled device) imaging toward the region near Haro 4-255 with a narrow band [SII] filter and an intermediate band [BATC10] filter (BATC: the“Beijing-Arizona-Taiwan-Connecticut”multi-color sky survey project) and have discovered two Herbig-Haro (HH) objects, HH469 and HH470. They are identified to be driven by the Haro 4-255 (far-infrared) source and the T Tauri star Haro 4-255, respectively.

Detection of Proper Motion in OQ208?
LIU Xiang, C. Stanghellini, D. Dallacasa, M. Bondi
Chin. Phys. Lett. 2000, 17 (4): 307-309 .  
Abstract   PDF(pc) (215KB) ( 483 )
We report on an ongoing work aimed to detect the separation speed of the two hot-spots of the compact symmetric object OQ208. Comparing images at 8.4 GHz taken in 6 epoches between 1994 and 1997 we obtain an estimate of 0.058±0.038 mas/year as the relative motions between two components of the radio source. At the red-shift of OQ208 1 mas correspond to 1 pc, thus we obtain a projected jet speed of 0.095±0.062c. With an inclination of 45o between the jets and the line of sight, we have an actual jet velocity of 0.134±0.088c and therefore the kinematic age of the source is so young of 320±210 years.

Cosmology with Two Compactification Scales
A. G. Agnese, M. La Camera
Chin. Phys. Lett. 2000, 17 (4): 310-312 .  
Abstract   PDF(pc) (233KB) ( 563 )
We consider a (4 + d)-dimensional spacetime broken up into a (4 - n)-dimensional Minkowski spacetime (where n goes from 1 to 3) and a compact (n + d)-dimensional manifold. At the present time the n compactification radii are of the order of the Universe size, while the other d compactification radii are of the order of the Planck length.
28 articles