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Volume 16 Issue 4
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Original Articles
Molecular Dynamics Simulation Study of MgO Crystal
ZHANG Yong-hong, HUANG Shi-ping
Chin. Phys. Lett. 1999, 16 (4): 235-237 .  
Abstract   PDF(pc) (215KB) ( 415 )
Molecular dynamics simulation of MgO crystal at different temperature and pressure was carried out by using the shell model of ionic polarizability. The prediction of thermal expansion is in good agreement with the experiment. The heat capacity has been calculated with a semi-classical approximate method. The calculated values are less than the experimental data because the anharmonic effect and quantum correlation were not taken into account. The changes of transverse-optic and longitudinal-optic modes with the compression ration are also calculated.
One-Dimensional Chain of n-Level Atoms and Discrete Nonlinear Schrödinger Equation
LIU Xiao-juan, XIAO Yi, HAI Wen-hua
Chin. Phys. Lett. 1999, 16 (4): 238-240 .  
Abstract   PDF(pc) (174KB) ( 471 )
The Hamiltonian of one-dimensional chain of n-level atoms is represented in terms of Boson operators by using the Dyson-Maleev transformation and it is shown that the finite-ladder effect disappears when n tends toward infinity. In this way, it is found that the Heisenberg equation of motion of this system is exactly described in the coherent state representation by the dark discrete nonlinear Schrödinger (DNLS) equation. It is also briefly shown that the DNLS equation has some general soliton solutions. This indicates that this simple system has richness of nonlinear waves.
Geometric Phase in Path Integral and Quantisation Rule
WANG Zheng-chuan, LI Bo-zang
Chin. Phys. Lett. 1999, 16 (4): 241-243 .  
Abstract   PDF(pc) (212KB) ( 647 )
A description of geometric phase in terms of path integral formalism is presented. It is proved that this adiabatic phase can appear in the propagator or Green function of an adiabatic system. In the semiclassical approximation, following the Green function expression of the electronic density of states, the corresponding generalized Bohr-Sommerfeld quantisation rule can thus be obtained. It is shown that this rule has been corrected by the geometric phase.
Entanglement Swapping and Preparing Nonclassical Field Jaynes-Cummings Model with an Entangled State of by Nonlinear Atoms
YE Liu
Chin. Phys. Lett. 1999, 16 (4): 244-246 .  
Abstract   PDF(pc) (159KB) ( 450 )
The interaction of a cavity field with an entangled state of atoms is studied according to the nonlinear Jaynes-Cummings model. It is shown that the properties of the cavity field depend on not only the interaction time but also the nonlinear constant. After detecting an atom of the entangled state, the cavity field will be entangled with another atom even it is far away from the cavity. It is proved that the nonclassical properties of the field state are dramatically different from those in the case of no selective measurement.
Spherically Symmetric Cosmological Solutions of Einstein’s Equations
Mohammed Ashraful Islam
Chin. Phys. Lett. 1999, 16 (4): 247-248 .  
Abstract   PDF(pc) (97KB) ( 473 )
Two sets of solution of the Einstein’s equations of general theory of relativity which is spherically-symmetric and nonstatic homogeneous isotropic universe for perfect fluid are obtained. The first solution is the Einstein de-Sitter type containing a scale factor ( √6πкGt + a)4/3 and an arbitrary function f (R) of radial space coordinates. The second solution is for stiff equation of state p = ρc2, which also has a scale factor [3 √8πaG∫t0ξ(t)dt]2/3 and an arbitrary function h(R) of radial space coordinates.
Dispersive Property of Mode Grüneisen Parameter: Corundum and α-Quartz as Examples
XU Ji-an
Chin. Phys. Lett. 1999, 16 (4): 249-250 .  
Abstract   PDF(pc) (148KB) ( 341 )
The dispersive property of the mode Grüneisen parameter in solids is found theoretically. Such a property should appear in a reciprocal relationship to the mode frequency. This phenomenon is also confirmed experimentally in the cases of corundum and α-quartz.
Evidence for Heavy Ion Emission of 230U
PAN Qiang-yan, YANG Wei-fan, YUAN Shuang-gui, LI Zong-wei, MA Tao-tao, GUO Jun-sheng, LIU Ming-yi, LIU Hong-ye, XU Shu-wei, GAN Zai-guo, KONG Deng-ming, QIAO Ji-min, LUO Zi-hua, ZHANG Mu-tian, WANG Shu-hong
Chin. Phys. Lett. 1999, 16 (4): 251-252 .  
Abstract   PDF(pc) (357KB) ( 287 )
Radioisotope of 230Pa was synthesized by proton irradiation of ThO2 powder targets with thickness of about 2g/cm2. Pure 230Pa was extracted and deep purified from thorium and fission products by the radiochemical method. Thin 230Pa→230U sources were prepared for measuring the cluster decay of 230U. Two cases of decay via heavy ion emission, which were most probably for the neon decays of 230U, were detected by using solid-state track registration detectors. The preliminary branching ratio relative to a-decay comes out to be ( 1.3 ±0.8 ) 10-14.
On Multiplicity Difference Correlators in Second-Order Quark-Gluon Plasma Phase Transition
YAN Wen-biao, YANG Chun-bin, CAI Xu,
Chin. Phys. Lett. 1999, 16 (4): 253-255 .  
Abstract   PDF(pc) (226KB) ( 365 )
The multiplicity difference correlators between two well-separated bins are studied in second-order quark-gluon plasma (QGP) phase transition within the Ginzburg-Landau model. For the case with very low mean multiplicities, an exponent γ is found, which has very weak dependence on the parameters of the model and can be used as a signal for the formation of QGP in ultra-relativistic heavy-ion collisions.

Isospin Effects of Critical Behavior in Lattice Gas Model
MA Yu-gang, , SU Qian-min, SHEN Wen-qing, WANG Jian-song, CAI Xiang-zhou, FANG De-qing
Chin. Phys. Lett. 1999, 16 (4): 256-258 .  
Abstract   PDF(pc) (240KB) ( 352 )
Isospin effects of the critical phenomena were studied via Xe isotopes in the frame of the lattice gas model. All the critical temperatures for four Xe isotopes are close to 5.5 MeV at the same freeze-out density of about 0.39 ρ0. The critical values of power law parameter of mass distribution, mean multiplicity of intermediate mass fragments, information entropy and Campi's second moment show minor dependence on the isospin at the critical point.
Dilepton Production in an Expanding Hot Baryon-Rich Quark-Gluon Matter
He Ze-jun, ZHANG Jia-ju, JIANG Wei-Zhou, QIU Xi-jun, LIU Bo,
Chin. Phys. Lett. 1999, 16 (4): 259-261 .  
Abstract   PDF(pc) (221KB) ( 309 )
From the full stopping scenario, a relativistic hydrodynamic model describing the evolution of the baryon-rich quark-gluon matter fire-cylinder has been established. Based on it, the rapidity Distribution of dileptons with intermediate invariant masses has been studied. It is found that the quark phase gives the dominant contribution to the dilepton spectrum due to the influence of the phase boundary on the evolution of the system, especially the dilepton yield is strongly suppressed with the increasing rapidity.
Theoretical Study of Na Clusters by First Principle Molecular Dynamics Calculations
SU Chang-rong, ZHU Jie, LI Jia-ming, YANG Jin-long
Chin. Phys. Lett. 1999, 16 (4): 262-263 .  
Abstract   PDF(pc) (181KB) ( 346 )
Based on molecular dynamics simulations with first-principle forces, we have studied the Na clusters. Comparing with available high-precision experimental data (e.g., geometric structure of Na3), we then can assess validity of various first-principle theoretical methods. The first-principle molecular dynamics method is a powerful tool to study properties of clusters. Therefore, we can elucidate evolution of growth of Na clusters.
Enhanced Ionization of Linear Polyatomic Molecular Ions in Ultrashort Laser Fields
LEI An-le, NI Guo-quan, LI Zhong, ZHAI Hua-jin, XU Zhi-zhan
Chin. Phys. Lett. 1999, 16 (4): 264-266 .  
Abstract   PDF(pc) (207KB) ( 402 )
The ionization behavior of linear polyatomic molecular ions in ultrashort, intense laser fields was investigated with the time-dependent Schrödinger equation solved by the standard split-operator algorithm. The enhanced ionization effect was found as a general feature in the ions when the internuclear separation was in a critical distance range and can be explained in terms of the field-induced over-barrier ionization mechanism. In addition, the ionization energy does not influence the ionization probability significantly.


Existence of Two Higher L=0 Bound States of the Dipositroniums
BAO Cheng-guang, SHI Ting-yun
Chin. Phys. Lett. 1999, 16 (4): 267-268 .  
Abstract   PDF(pc) (159KB) ( 319 )
Symmetry has imposed very strong constraints on the internal structure of quantum mechanical system. In particular, whether a state can access a given outgoing channel is constrained by symmetry. For the dipositroniums, the most important channel is the Ps-Ps channel. However, based on symmetry consideration it was found that only a few excited states are allowed to access the Ps-Ps channel, thereby at least the existence of two higher L = 0 bound states (higher than the Ps-Ps threshold) has been affirmed.
Enhanced Self-pumped Phase Conjugation from 45o-Cut Rh:BaTiO3
ZHANG Dao-fan, YANG Chang-xi, NIU Xiao-juan, LIU Hong-bin, WU Xing, ZHU Yong
Chin. Phys. Lett. 1999, 16 (4): 269-270 .  
Abstract   PDF(pc) (179KB) ( 428 )
High efficiency self-pumped phase conjugation (SPPC) has been obtained in 45o-cut Rh:BaTiO3crystal using a Ti:AI2O3 laser. Stable SPPC reflectivities as high as 90% are measured in a region of incident angle between 45o and 67o. The SPPC buildup time is 5-7 times as fast as 0o-cut Rh: BaTiO3 crystal. Reflectivity as a function of wavelength is also obtained. The reflectivity remains essentially constant at 9±3% from 708 to 858nm. The photorefractive performance of this special 45o-cut Rh:BaTiO3is characterized and compared with the 0o-cut Rh: BaTiO3.

A New Lattice Boltzmann Model for Two-Phase Fluid
YU Hui-dan, ZHAO Kai-hua
Chin. Phys. Lett. 1999, 16 (4): 271-272 .  
Abstract   PDF(pc) (297KB) ( 400 )
On the basis of single phase lattice Boltzmann model(LBM), we construct a new LBM, which is more physical and computationally efficient, by introducing an effective attraction between particles with the same color in the equilibrium function to simulate immiscible two-phase flow. The separating simulation of two fluids illustrates its value.
Folded Waveguide: a New Kind of Radio-Frequency Antenna
YE Wei-wei, LI Jian-gang, CUI Ning-zhou, ZHAO Yan-ping
Chin. Phys. Lett. 1999, 16 (4): 273-275 .  
Abstract   PDF(pc) (254KB) ( 372 )
The properties of folded waveguide (FWG) couplers are researched. Firstly, the electromagnetic fields inside and outside of the FWG are analyzed theoretically. After substituting the relevant data, numerical results and corresponding two-dimensional and three-dimensional wave field figures are achieved. Secondly, in our scale model, series of experiments are carried out. The coupling and matching between the antenna and the coaxial line are examined. The experimental results demonstrate that FWG antenna can be used in ion cyclotron range of frequencies heating in tokamak with high power coupling efficiency.
Calculation of First Sound Speed in Liquid Helium
PAO Lu, Joseph P.Foy
Chin. Phys. Lett. 1999, 16 (4): 276-278 .  
Abstract   PDF(pc) (223KB) ( 384 )
The speed of first sound in liquid helium II is calculated quantum mechanically. The calculation is made by using a modified version of Brueckner and Sawada’s method [Phys. Rev. 106 (1959) 1128] and is based on the postulate that the hard core length is directly proportional to the negative of the pressure.
Computer Simulation of Early Stage in Thin-Film Growth
WU Feng-min, LI Qiao-wen, ZHU Qi-peng, WU Zi-qin
Chin. Phys. Lett. 1999, 16 (4): 279-281 .  
Abstract   PDF(pc) (245KB) ( 373 )
Nucleation and growth process has been studied on atomic scale for the early stage of thin-film growth by means of computer simulation. The island number and its shape vary with a set of control conditions, such as deposition flux R, surface diffusion rate W and coverage. The kinetic parameters p and q obtained from simulation are positive and dependent on the growth process. The transition from the initial steps of nucleation to growth is also explored. The simulation results are consistent with the experiments and the rate equations from nucleation theory.
Buried CoSi2 Layers in Silicon on Insulator Formed by Wafer Bonding
ZHU Shi-yang, HUANG Yi-ping, RU Guo-ping
Chin. Phys. Lett. 1999, 16 (4): 282-284 .  
Abstract   PDF(pc) (373KB) ( 337 )
A novel single-crystalline Si/poly-CoSi2/SiO2/Sub-Si structure has been successfully formed by silicon wafer bonding technique. The surface energy of the as-bonded wafers at room temperature is about 70erg/cm2. Annealing at 800°C for 30min does not only strengthen the bond to about 1100erg/cm2, but also employs solid phase reaction of sputtered cobalt to form a buried poly-crystalline CoSi2 layer with a resistivity of approximately 160μΩ.cm. Two bond processes has been compared. The quality of the sputtered Si-SiO2 bonding is better than that of the sputtered Si-Si bonding.
New Modified M-type Ferrite Nanoparticles with Spinel Phase Epitaxial Overlayer
FANG Qing-qing, ZHONG Wei, DU You-wei
Chin. Phys. Lett. 1999, 16 (4): 285-287 .  
Abstract   PDF(pc) (266KB) ( 479 )
New modified Fe3O4-Ba(or Sr)Fe12O19 nanoparticles were prepared by using an epitaxial technique for high density magnetic recording. Coercive force reduced from 6.5kOe of M-type ferrite particles to minimal about 0.2kOe of modified particles, and saturation magnetization increased from 62.2 to 82.6emu/g at the same time. These parameters, Hc σs, and particle size d, can be easily controlled by changing the content of coating material. The magnetic measurements have shown that the modified particles have an interface coupling between epitaxial layer and core particle. As a result of x-ray diffraction measurements, the reflection intensity of spinel phase increases and that of hexagonal magnetoplumbite phase decreases with the increasing number of Fe2+ ions. The shape of modified particles gradually changes from hexagonal platelike of M-type ferrite particles to square platelike of modified particles. The analysis shows that the Fe2+ ions in suspension directly combined with Fe3+ ions from R-block of core particle to form Fe3O4 layer.
Noncollinear Interaction of Guided Optical Waves and Magnetostatic Forward Volume Waves Under Inclined Bias Magnetic Field
WU Bao-jian, LIU Gong-qiang
Chin. Phys. Lett. 1999, 16 (4): 288-289 .  
Abstract   PDF(pc) (172KB) ( 360 )
Coupled-mode equations for Stokes and anti-Stokes interactions of guided optical waves with magnetostatic forward volume waves under inclined magnetic field are given. Calculation results indicate that, only at normal magnetization, the diffraction efficiency (DE) is equal to the mode-conversion efficiency (MCE) in magnitude; by comparison to the case of normal magnetization, the DE and the MCE can be increased greatly under appropriate inclined magnetic field. For the YIG waveguide used, the DE for the Stokes interaction is much greater than that for the anti-Stokes interaction when the inclined angle |θ| < 25o and the MCE is symmetrical about θ. For the Bi-doped YIG film, the MCE presents a rapid oscillation with θ. The obtained results tally with the experiments.
Light Scattering Properties of Biotissue Versus Equivalent Particle Size Distribution
LI Hui, LU Zu-kang, LIN Lei, XIE Shu-sen
Chin. Phys. Lett. 1999, 16 (4): 290-292 .  
Abstract   PDF(pc) (234KB) ( 412 )
An equivalent particle size distribution function n(r) is applied to describe optical scattering property of tissue. Under the Fraunhofer diffraction approximation, both the scattering coefficient μs and the scattering phase function S(θ) are educible from n(r). Moreover, such a scheme provides a new feasible method based on the light scattering techniques for particle size analysis to measure the optical properties of tissue. Experimental results of the whole human blood and a thin porcine muscle sample are also provided and so is a calculation resulting from an optical phantom of tissue. The light scattering equivalency between the practical tissue and the corresponding equivalent particles has been verified.
Structural and Photoluminescence Characterization of GaN Film Grown on Si(111)Substrate
YE Zhi-zhen, ZHANG Hao-xiang, LU Huan-ming, ZHAO Bing-hui
Chin. Phys. Lett. 1999, 16 (4): 293-294 .  
Abstract   PDF(pc) (222KB) ( 386 )
GaN epilayer grown on Si(111)substrate by a novel vacuum reaction method rather than metal organic chemical vapor deposition or molecule beam epitaxy is reported. Scanning electron micrograph shows that surface of GaN film is flat and crack-free. A pronounced GaN (0002) peak appears in the x-ray diffraction pattern. The full width at half-maximum (FWHM) of the double-crystal x-ray rocking curve for (0002) diffraction from the GaN epilayer is 30arcmin. The photoluminescence spectrum shows that the GaN epilayer emits light at the wavelength of 365nm with an FWHM of 8nm (74.6meV).
Photoluminescence from Porous-Like SiC and Its Light-Induced Enhancement
CHEN Zhi-ming, YU Ming-bin, WANG Jian-nong, HU Bao-hong
Chin. Phys. Lett. 1999, 16 (4): 295-297 .  
Abstract   PDF(pc) (375KB) ( 527 )
Intense photoluminescence (PL) from porous-like SiC has been observed at room temperature. The samples were prepared by electrochemical anodization from nanocrystalline SiC thin films grown on Si (100) substrates in hot filament chemical vapor deposition. It has been found that a light-induced enhancement of the PL intensity will take place if the incident light beam from an He-Cd laser (325nm, 10mW) is employed for the excitation. Blue-shift of the PL peak energy from about 1.9eV of as-anodized samples to about 2.1 eV and an accompanied spectral widening have also been observed for a long enough irradiation time. However, the novel effects have not been observed at low temperature. Origin of the light-induced change is suggested to be related to some light-induced metastable defects.


Red Luminesecnce from Self-Assembled InAlAs/AlGaAs Quantum Dots with Bimodal Size Distribution
ZHOU Wei, XU Bo, XU Huai-zhe, LIU Feng-qi, GONG Qian, JIANG Wei-hong, SUN Zhong-zhe, DING Ding, LIANG Ji-bei, WANG Zhan-guo, ZHU Zuo-ming, LI Guo-hua
Chin. Phys. Lett. 1999, 16 (4): 298-300 .  
Abstract   PDF(pc) (321KB) ( 475 )
Red-emitting at about 640nm from self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy are demonstrated. A doublepeak structure of photoluminescence (PL) spectra from quantum dots was observed, and a bimodal distribution of dot sizes was also confirmed by an atomic force micrograph (AFM) image for uncapped sample. From the temperature and excitation intensity dependence of PL spectra, it is found that the double-peak structure of PL spectra from quantum dots is strongly correlated to the two predominant quantum dot families. Taking into account the quantum-size effect on the peak energy, it is proposed that the high (low) energy peak results from a smaller (larger) dot family, and this result is identical to the statistical distribution of dot lateral size from the AFM image.
On the Scaling Law for Af Type Free Radical Homopolymerization
WANG Hai-jun, BA Xin-wu, ZHAO Min, LI Ze-sheng
Chin. Phys. Lett. 1999, 16 (4): 301-303 .  
Abstract   PDF(pc) (186KB) ( 368 )
From the equilibrium number fraction distribution for Af type free radical homopolymerization, the asymptotic distribution and polymer moments near the gel point are deduced. As a direct result of scaling transformation, ageneralized scaling law which characterizes the sol-gel transition is obtained. This reveals that the curing of this type is in essence a phase transition process.
Mechanical Properties of an Ideal Electrorheological Fluid: Metal-Particle/Insulating Oil System
ZHAO He-ping, LIU Zheng-you, SHEN Jia-rui, LIU You-yan,
Chin. Phys. Lett. 1999, 16 (4): 304-306 .  
Abstract   PDF(pc) (230KB) ( 366 )
The electrorheological properties of a model system consisting of metal particles with insulating coating in a dielectric oil are analyzed by extending Rayleigh identity based on a multipole expansion theory. Evaluation of the effective dielectric constant is emphasized. The dependence of the shear stress т on the shear strain θ and the shear modulus G for the electrorheological solid is presented. It is found that the model system shows much higher electrorheological performance than the traditional suspensions.

Geometry Asymmetry of Mean Pulse Profile of Pulsar
PAN Jun, WU Xin-ji
Chin. Phys. Lett. 1999, 16 (4): 307-309 .  
Abstract   PDF(pc) (214KB) ( 420 )
The effects of aberration, retardation and magnetic field sweep back, which are caused directly or indirectly by pulsar’s rapid rotation, are estimated in order to examine their influences on the geometry asymmetry of the mean pulse profile. The geometric asymmetry exhibits different behaviors at different cases. The millisecond pulsars incline to develop mean pulse profiles with asymmetric contrary to the normal pulsars. The pulsar J0437-4715 is analyzed as an example.
Locations of Sonic Points in Advection Dominated Accretion Flows Around Black Holes
YUAN Feng, HUANG Ke-liang
Chin. Phys. Lett. 1999, 16 (4): 310-312 .  
Abstract   PDF(pc) (251KB) ( 389 )
The global transonic solutions describing advection dominated accretion flows around black holes are obtained by directly integrating the set of differential equations from the sonic point inward to the horizon and outward. The results show that the sonic points can locate themselves at almost any radius, regardless of the viscous parameter a and polytropic index γ. This result is greatly different with previous ones. Example solutions with very different values of Rs from 4.3 to 300Rg and with γ = 1.5,5/3 are given explicitly. The consistency between this result and that in inviscid flows is emphasized.
29 articles