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Volume 23 Issue 3
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Original Articles
Approximate Generalized Conditional Symmetries for the Perturbed Nonlinear Diffusion--Convection Equations
ZHANG Shun-Li, , QU Chang-Zheng
Chin. Phys. Lett. 2006, 23 (3): 527-530 .  
Abstract   PDF(pc) (228KB) ( 804 )
The concept of approximate generalized conditional symmetry (AGCS) as a generalization to both approximate Lie point symmetry and generalized conditional symmetry is introduced, and it is applied to study the perturbed nonlinear diffusion-convection equations. Complete classification of those perturbed equations which admit certain types of AGCSs is derived. Some approximate solutions to the resulting equations can be obtained via the AGCS and the corresponding unperturbed equations.
Prisoner’s Dilemma Game with Heterogeneous Influential Effect on Regular Small-World Networks
WU Zhi-Xi, XU Xin-Jian, WANG Ying-Hai
Chin. Phys. Lett. 2006, 23 (3): 531-534 .  
Abstract   PDF(pc) (258KB) ( 903 )
The effect of heterogeneous influence of different individuals on the maintenance of co-operative behaviour is studied in an evolutionary Prisoner’s Dilemma game with players located on the sites of regular small-world networks. The players interacting with their neighbours can either co-operate or defect and update their states by choosing one of the neighbours and adopting its strategy with a probability depending on the payoff difference. The selection of the neighbour obeys a preferential rule: the more influential a neighbour, the larger the probability it is picked. It is found that this simple preferential selection rule can promote continuously the co-operation of the whole population with the strengthening of the disorder of the underlying network.
Exact Solution to Rate Equation with Time-Dependent Coefficients: Its Application in InGaAsP Lasers
WANG Gang, LUO Bin, PAN Wei, WU Shao-Quan, HOU Bang-Pin
Chin. Phys. Lett. 2006, 23 (3): 535-538 .  
Abstract   PDF(pc) (210KB) ( 1275 )
By using the algebraic dynamics method, we obtain exact analytical solutions of rate equations with time-dependent coefficients, which might present an effective description of the physical mechanism of the practical semiconductor lasers. Based on the exact solutions, we investigate the dynamic behaviour and the emitted properties of the InGaAsP laser, which has been commonly used in long wavelength optical communication systems. It is found that when the cavity length varies with time exponentially, the output power of the laser will drop and approach its asymptote. When the cavity length is a sinusoid function of time, the intensity of the emitted optical pulses can be controlled by the amplitude of this function.
Bound States of the S-Wave Equation with Equal Scalar and Vector Standard Eckart Potential
Eser Olgar, Ramazan Koc, Hayriye Tütüncüler
Chin. Phys. Lett. 2006, 23 (3): 539-541 .  
Abstract   PDF(pc) (167KB) ( 552 )
A supersymmetric technique for the bound-state solutions of the s-wave Klein--Gordon equation with equal scalar and vector standard Eckart-type potential is proposed. Its exact solutions are obtained. Possible generalization of our approach is outlined.
Concurrence and Wigner--Yanase Skew Information
TANG Li, , CHEN Ze-Qian
Chin. Phys. Lett. 2006, 23 (3): 542-544 .  
Abstract   PDF(pc) (194KB) ( 670 )
A measure of entanglement on n qubits is defined in terms of Wigner--Yanase skew information. It is shown that the measure coincides essentially with the concurrence on two qubits. This uncovers the information-theoretic meaning of the concurrence of entangled states.
Quantum Remote Control of Unitary Operations on a Qubit of Pure Entangled States
YAO Chun-Mei
Chin. Phys. Lett. 2006, 23 (3): 545-547 .  
Abstract   PDF(pc) (170KB) ( 736 )
We consider the remote implementation of an arbitrary unitary operation on one qubit of a pure two-qubit entangled state with 100% efficiency via entanglement swapping in detail, then directly generalize this protocol from two-qubit to N-qubit entangled states. The overall classical information and distributed entanglement cost required for this quantum remote control protocol is less than the bi-directional quantum state teleportation method.
Remote State Preparation Using Non-Maximally Entangled State: Universality and Necessary Amount of Quantum Channels
MEI Yu-Xue, CHEN Lin, CHEN Yi-Xin
Chin. Phys. Lett. 2006, 23 (3): 548-551 .  
Abstract   PDF(pc) (229KB) ( 798 )
In a process of remote state preparation, the universality of quantum channel is an essential ingredient. That is, one quantum channel should be feasible to remotely prepare any given qubit state. This problem appears in a process where one uses non-maximally entangled state as the passage. We present a scheme in which any given qubit |Ф>=cosθ|0>+sinθe|1> could be remotely prepared by using minimum classical bits and the previously shared non-maximally entangled state with a high fidelity, under the condition that the receiver holds the knowledge of $\theta$. This condition is helpful to reduce the necessary amount of quantum channels, which is proven to be a low quantity to realize the universality. We also give several methods to investigate the trade-off between this amount and the achievable fidelity of the protocol.

Engineering of Multi-Dimensional Entangled States of Photon Pairs Using Hyper-Entanglement
REN Xi-Feng, GUO Guo-Ping, LI Jian, LI Chuan-Feng, GUO Guang-Can
Chin. Phys. Lett. 2006, 23 (3): 552-555 .  
Abstract   PDF(pc) (216KB) ( 891 )
Multi-dimensional entangled states have been proven to be more powerful in some quantum information processes. Down-converted photons from spontaneous parametric down-conversion are used to engineer multi-dimensional entangled states. A kind of multi-degree multi-dimensional Greenberger--Horne--Zeilinger states can also be generated. The hyper-entangled photons are entangled in energy-time, polarization and orbital angular momentum, which is proven to be useful to increase the dimension of systems and to investigate higher-dimensional entangled states.
Bloch Oscillations of Two-Component Bose--Einstein Condensates in Optical Lattices
GU Huai-Qiang, WANG Zhi-Cheng, JIN Kang, TAN Lei
Chin. Phys. Lett. 2006, 23 (3): 556-559 .  
Abstract   PDF(pc) (261KB) ( 531 )
We study the Bloch oscillations of two-component Bose--Einstein condensates trapped in spin-dependent optical lattices. The influence of the intercomponent atom interaction on the system is discussed in detail. Accelerated breakdown of the Bloch oscillations and revival phenomena are found respectively for the repulsive and attractive case. For both the cases, the system will finally be set in a quantum self-trapping state due to dynamical instability.
Information Transmission in Phase Synchronous Chaotic Arrays
M. S. Baptista, C. Zhou, J. Kurths
Chin. Phys. Lett. 2006, 23 (3): 560-563 .  
Abstract   PDF(pc) (267KB) ( 555 )
We show many versatile phase synchronous configurations that emerge in an array of coupled chaotic elements due to the presence of a periodic stimulus. Then, we explain the relevance of these configurations to the understanding of how information about such a stimulus is transmitted from one side to the other in this array. The stimulus actively creates the ways to be transmitted, by making the chaotic elements to phase synchronize.
Possible Instability of the Ground State of Two-Flavour Colour Superconductor Induced by Colour Neutrality
HE Lian-Yi, JIN Meng, ZHUANG Peng-Fei
Chin. Phys. Lett. 2006, 23 (3): 564-567 .  
Abstract   PDF(pc) (233KB) ( 429 )
The diquark condensate susceptibility in neutral colour superconductor at moderate baryon density is calculated in the frame of the two-flavour Nambu--Jona--Lasinio model with the mean field approximation. When colour chemical potential is introduced to keep charge neutrality, the diquark condensate susceptibility
is negative in the directions without diquark condensate in colour space, which may be regarded as a signal of the instability of the conventional ground state with only diquark condensate in the colour-3 direction.
Tetraquarks Production in Quark--Gluon Plasma with Diquarks
MA Zhong-Biao, , GAO Chong-Shou
Chin. Phys. Lett. 2006, 23 (3): 568-571 .  
Abstract   PDF(pc) (230KB) ( 695 )
We present a way to calculate tetraquarks ratios for quark--gluon plasma with diquarks. The ratios of tetraquarks over baryons produced from quark matter are high than hadronic gas model limits. It is a better way to search for four-quark states in relativistic heavy ion collisions. It may become a criterion to judge whether quark--gluon plasma has formed to search for four-quark states in relativistic heavy ion collisions.
Cross Section of Heavy Ion Reaction (14.5MeV/u) 132Xe + Bi
G. Sher, M. I. Shahzad, M. Hussain, M. A. Rana, E. U. Khan
Chin. Phys. Lett. 2006, 23 (3): 572-575 .  
Abstract   PDF(pc) (235KB) ( 815 )
We investigate the cross section of the heavy ion reaction (14.5MeV/u) 132Xe + Bi by using a CR-39 plastic track detector. The target-detector assembly is exposed at UNILAC beam facility of GSI, Germany. After etching under appropriate etching conditions, the detector is scanned for multipronged events produced as a result of interactions of projectile ions with target atoms. The elastic events are separated from binary events and used for the determination of the quarter-point angle. The quarter-point angle obtained is used to determine the total reaction cross section. The total experimental reaction cross section is determined by using statistics of inelastic events of two-pronged and higher multiplicity events. The experimental reaction cross sections determined by using elastic and inelastic data observed in the reaction under study are found to be in good agreement with the theoretically calculated value of reaction cross section using a sharp cutoff model.
Imaging Internuclear Separation of H2+ in Configuration Space: Reduced Dimensionality Model
ZHANG Zhe, ZHANG Zhong-Qing, ZHANG Gui-Zhong, XIANG Wang-Hua, W. T. Hill III
Chin. Phys. Lett. 2006, 23 (3): 576-578 .  
Abstract   PDF(pc) (195KB) ( 467 )
We present a method for obtaining the internuclear separation of diatomic molecular ion H2+ irradiated by attosecond-duration laser pulse, by computing the probability flux of wavefunction pattern of photoelectron in configuration space. In contrast to earlier means of attosecond-scale time-gating or taking ratio of image data in momentum space, our alternative is characterized by experimental feasibility. The numerical results of a reduced-dimensionality model on hydrogenic ions corroborated our method are obtained and can be generalized to more complex molecular systems for inferring bond length or bond angle information.
Recombination Process of Hydrogen Molecular Ions: An Application of Time-Dependent Wave Packet Dynamics Method
WANG Xiao-Lu, CHEN Shao-Hao, HE Chun-Long, LI Jia-Ming,
Chin. Phys. Lett. 2006, 23 (3): 579-582 .  
Abstract   PDF(pc) (221KB) ( 444 )
We present our studies of recombination processes of H2+, HD+ and D2+ with high-energy electrons based on a time-dependent wave packet dynamics method. The final vibrational distributions of the products (H2, HD and D2) have been studied. The isotope effects of the final vibrational distributions and their dependence on initial states are elucidated. The study of the final vibrational distributions is relevant to the infrared gas laser researches.
Highest Occupied Molecular Orbital of Cyclopentanone by Binary (e, 2e) Spectroscopy
ZHANG Shu-Feng, NING Chuan-Gang, DENG Jing-Kang, REN Xue-Guang, SU Guo-Lin, YANG Tie-Cheng, HUANG Yan-Ru
Chin. Phys. Lett. 2006, 23 (3): 583-596 .  
Abstract   PDF(pc) (247KB) ( 648 )
We report the first measurements of the momentum profiles of highest occupied molecular orbital (HOMO) and the complete valence shell binding energy spectra of cyclopentanone with impact energies of 600 and 1200eV by a binary (e, 2e) spectrometer. The experimental momentum profiles of the HOMO orbital are compared with the theoretical momentum distribution calculated using the Hartree--Fock and density functional theory methods with various basis sets. However, none of these calculations gives a completely satisfactory description of the momentum distributions of the HOMO 7b2. The inadequacy of the calculations could result in the intensity difference of the second maximum at p~1.2a.u. between the experiment and the theory. The discrepancy between experimental and theoretical data in the low-momentum region is explained with the distorted wave effect.
State-Selective Electron Capture for keV He2+ Ions on Helium Collisions Studied by Recoil Momentum Spectroscopy
ZHU Xiao-Long, MA Xin-Wen, LI Bin, LIU Hui-Ping, CHEN Lan-Fang, ZHANG Shao-Feng, QIAN Dong-Bin, FENG Wen-Tian, CAO Shi-Ping, SHA Shan, ZHANG Da-Cheng,
Chin. Phys. Lett. 2006, 23 (3): 587-590 .  
Abstract   PDF(pc) (233KB) ( 741 )
State-selective single electron capture cross sections are measured by recoil ion momentum spectroscopy technique for He2+ on He at 30keV incident energy. The cross sections for capture into ground and excited states are obtained and compared to classical model calculations as well as to the quantum mechanical calculations. The experimental results are in good agreement with quantum mechanical results.
Analysis of Three Coupled Defects in One-Dimensional Photonic Bandgap Structure
LIU Dan-Dong, CHEN Guang-De, XU Zhong-Feng
Chin. Phys. Lett. 2006, 23 (3): 591-594 .  
Abstract   PDF(pc) (219KB) ( 478 )
The mutual interaction of three different defects in photonic crystals is studied theoretically. A theoretical model based on the classical wave analogue of the tight-binding (TB) picture is applied to the structure. We obtain analytic expressions for the eigenfrequencies and eigenmodes, from which the transmissions at resonance are derived. Based on this, a new type of the photonic quantum-well structure is investigated and its possible application is discussed. The TB predictions are compared with the transfer matrix method simulation results.

Solution of Electromagnetic Wave in Time-Varying Media in Two-Dimensional Space
CHEN Bing-Kang, ZHANG-Ying, GAO Ben-Qing
Chin. Phys. Lett. 2006, 23 (3): 595-598 .  
Abstract   PDF(pc) (205KB) ( 414 )
The analytical solution of gradual change media in two-dimensional free space is studied. Using separation of variables, the solution of electromagnetic wave in time-varying media, which is an exponential function of time, is derived in two-dimensional space. The rationality of the solution is verified indirectly. According to the solution, the figures of the wave are depicted. Based on these figures, the character of the wave in time-varying media is obtained, which shows frequency shift and changes of phase velocity and amplitude.
High-Order Temporal Corrected Fields of Ultra-Short Laser Pulses and Laser-Driven Acceleration
XIE Yong-Jie, HUO Yu-Kun, KONG Qing, WANG Ping-Xiao, CHEN Zhao, LIU Jing-Ru
Chin. Phys. Lett. 2006, 23 (3): 599-602 .  
Abstract   PDF(pc) (264KB) ( 693 )
Up to third-order temporal correction in terms of a small dimensionless temporal parameter ε =1/(ω0 t0) (ω0 = ck0 the central oscillatory frequency, t0 the pulse duration of half period), the field expressions of ultra-short focused laser pulses are explicitly presented. To evaluate the correction efficacy, electric amplitudes of zeroth-order and higher-order corrected fields are compared for different pulse durations. Furthermore, electron interaction with ultra-short laser pulses is simulated using both the zeroth-order and higher-order corrected field equations. Our simulation results show that the third-order correction terms should be considered for investigating the interaction if the laser pulse duration decreases to a few optical periods.
Optical Image Addition and Encryption by Multi-Exposure Based on Fractional Fourier Transform Hologram
CHEN Lin-Fei, ZHAO Dao-Mu
Chin. Phys. Lett. 2006, 23 (3): 603-606 .  
Abstract   PDF(pc) (376KB) ( 688 )
We propose a new method to add different images together by optical implementation that is realized by the multi-exposure based on fractional Fourier transform hologram. Partial image fusion is proposed and realized by this method. Multiple images encryption can also be implemented by the multi-exposure of the hologram based on fractional Fourier transform. Computer simulations prove that this method is valid.
Wave-Front Aberrations of Cornea and Crystalline Lens
WANG Wei, WANG Zhao-Qi, WANG Yan, ZUO Tong, FAN Hai-Ying
Chin. Phys. Lett. 2006, 23 (3): 607-609 .  
Abstract   PDF(pc) (178KB) ( 989 )
The aberrations for anterior corneal surface, posterior corneal surface and complete eyes are measured and calculated. The aberrations for the crystalline lens are obtained by subtracting the aberrations in cornea from that in complete eyes. It is shown that the combination between the crystalline lens and the cornea can be either a compensatory or an additive process. The combination between the anterior and the posterior corneal surfaces on the aberrations is complicated, compensatory or additive. The anterior corneal surface contributes mainly lower-order aberrations (astigmatism) of images, while the posterior corneal surface and the crystalline lens contribute mainly higher-order aberrations.
Production of Three-Dimensional Maximal Entanglement for Two Cavity Modes
ZHENG Shi-Biao
Chin. Phys. Lett. 2006, 23 (3): 610-611 .  
Abstract   PDF(pc) (153KB) ( 610 )
A scheme is proposed for generating maximally entangled states for two cavity modes, with each containing no more than two photons. In the scheme a single atom is sent through two resonant single-mode cavities. Based on the presently available techniques, our scheme might be experimentally realizable.
Probe Amplification with or without Population Inversion in a Five-Level Atomic System with Double-Dark Resonances
LI Jia-Hua, XIE Xiao-Tao, LUO Jin-Ming, LIU Ji-Bing
Chin. Phys. Lett. 2006, 23 (3): 612-615 .  
Abstract   PDF(pc) (221KB) ( 652 )
We theoretically investigate the response of the probe amplification in a five-level atomic system in the presence of interacting double-dark resonances disturbed by introducing an additional signal field. It is found that a large enhancement of the probe amplification with or without population inversion can be achieved by properly adjusting the strengths of the microwave driving field and the signal laser field. From viewpoint of physics, we qualitatively explain these results in terms of quantum interference and dressed states.
Comparison between Two Kinds of Semiconductor Absorbers for Mode-Locking in Nd:YVO4 Laser
WANG Cui-Luan, WANG Yong-Gang, MA Xiao-Yu, LIU Yang, SUN Li-Qun, TIAN Qian, ZANG Zhi-Gang, WANG Qin-Yue
Chin. Phys. Lett. 2006, 23 (3): 616-618 .  
Abstract   PDF(pc) (222KB) ( 422 )
We have demonstrated passive mode-locking in a diode-end-pumped Nd:YVO4 laser using two kinds of semiconductor absorbers whose relaxation region comes from In0.25Ga0.75As grown at low temperature (LT) and GaAs/air interface respectively. Mode-locking, using absorbers of the GaAs/air interface relaxation region, has the characteristics of less Q-switching tendency and higher average output power than that using absorbers of LT In0.25Ga0.75As relaxation region, but is not as stable as the latter.

Diode-Pumped Passive Q-Switched 946nm Nd:YAG Laser with a GaAs Saturable Absorber
WANG Su-Mei, ZHANG Qiu-Lin, ZHANG Ling, ZHANG Chun-Yu, ZHANG Dong-Xiang, FENG Bao-Hua, ZHANG Zhi-Guo
Chin. Phys. Lett. 2006, 23 (3): 619-621 .  
Abstract   PDF(pc) (193KB) ( 1014 )
We report, for the first time to our knowledge, a diode-pumped passive Q-switched 946nm Nd:YAG laser by using a GaAs as saturable absorber. The maximum average output power is 1.24W at an incident pump power of 15W, corresponding to a slope efficiency of 10%. Laser pulses with pulse duration of 70ns and repetition rate of 330kHz are generated.
Nonlinear Optical Properties of Indium Phthalocyanine Axially Grafted Polystyrene Thin Film
ZHU Rong-Yi, QIU Xue-Qiong, CHEN Yu, QIAN Shi-Xiong
Chin. Phys. Lett. 2006, 23 (3): 622-624 .  
Abstract   PDF(pc) (208KB) ( 730 )
Ultrafast dynamics and third-order nonlinearity of thin films of tert-butyl peripherally-substituted indium phthalocyanine axially grafted polystyrene (tBu4PcIn--PS) are investigated by femtosecond optical-Kerr-effect (OKE) and z-scan experiments. The fastest component (< 200 fs) in the OKE traces of the film is related to the electron cloud distortion, where the phthalocyanine-polymer interaction may enhance this contribution. The z-scan measurement also indicates that this interaction might enhance the third-order optical nonlinearity. The measurements shows that the magnitudes of X3 of these films are in order of 10-11esu.
Control of Polarization Interference in Doppler Broadened Two-Photon Resonant Four-Wave Mixing System
ZUO Zhan-Chun, LIU Xia, SUN Jiang, WU Ling-An, FU Pan-Ming
Chin. Phys. Lett. 2006, 23 (3): 625-628 .  
Abstract   PDF(pc) (236KB) ( 456 )
We study two-photon resonant nondegenerate four-wave mixing (NFWM) in a Doppler broadened system. It is found that because the induced polarization is sensitive to the atomic velocity, there exists interference between polarizations of atoms with different velocities, leading to significant modification of the NFWM spectra. This polarization interference can be controlled through applying an additional coupling field.
Effect of Distribution Pattern of Molecular Dipoles on Microscopic Second-Harmonic Generation
DENG Xiao-Yuan, WANG Xian-Ju, LIU Han-Ping, ZHUANG Zheng-Fei, GUO Zhou-Yi
Chin. Phys. Lett. 2006, 23 (3): 629-632 .  
Abstract   PDF(pc) (1140KB) ( 769 )
We set up a model for dealing with the second-harmonic generation (SHG) from molecular dipoles in a line alignment pattern rather than a planar distribution under a microscope. Because of this model, it is possible to perform a flexibly quantitative investigation of SHG from collagen fibres at a molecular level. The line alignment pattern induces more significant modifications in both the angular dipole distribution structure A(θ,ψ) and the second-harmonic power structure θy (θ,ψ), compared to a planar distribution. Also, the line alignment angle t has strong effect on A(θ,ψ) and θy(θ,ψ), resulting in an irregular SHG angular power distribution. That is to say, it is unnecessary for SHG emission to present two well-defined off-axis lobes. The total SHG power shows two symmetrical peaks at angles of t=50° and t =130° while a drop at t=90°. The weakest SHG signals can be measured at t=0° and t=180°.
Gain Characteristics of Er3+-Doped Phosphate Glass Fibres
XU Shan-Hui, YANG Zhong-Min, ZHANG Qin-Yuan, DENG Zai-De, JIANG Zhong-Hong,
Chin. Phys. Lett. 2006, 23 (3): 633-634 .  
Abstract   PDF(pc) (191KB) ( 604 )
An erbium-doped phosphate glass fibre has been drawn by the rod-in-tube technique in our laboratory. The gain for the Er3+-doped phosphate glass fibre with different pump powers and with different input signal wavelengths is investigated. The 2.2-cm-long fibre, pumped by a single-mode 980-nm fibre-pigtailed laser diode, can provide a net gain per unit length greater than 1.8dBcm. The pump threshold is about 50mW at the wavelength of 1534nm, and below 70mW at 1550nm. The gain linewidth of the Er3+-doped phosphate glass fibre is greater than 34nm and can cover the C band in optical communication networks.
Anisotropy in Third-Order Nonlinear Optical Susceptibility of a Squarylium Dye in a Nematic Liquid Crystal
JIN Zhao-Hui, LI Zhong-Yu, KASATANI Kazuo, OKAMOTO Hiroaki
Chin. Phys. Lett. 2006, 23 (3): 635-638 .  
Abstract   PDF(pc) (218KB) ( 542 )
A squarylium dye is dissolved in 4-cyano-4’-pentylbiphenyl (5CB) and oriented by sandwiching mixtures between two pieces of rubbed glass plates. The optical absorption spectra of the oriented squarylium dye-5CB layers exhibit high anisotropy. The third-order nonlinear optical responses and susceptibilities X3e of squarylium dye in 5CB are measured with light polarizations parallel and perpendicular to the orientational direction by the resonant femtosecond degenerate four-wave mixing (DFWM) technique. Temporal profiles of the DFWM signal of the oriented squarylium dye-5CB layers with light polarizations parallel and perpendicular to the orientational direction are measured with a time resolution of 0.3ps (FWHM), and are found to consist of two components, i.e., the coherent instantaneous nonlinear response and slow response due to the formation of excited molecules. A high anisotropic ratio of X3e, 10.8±1.2, is observed for the oriented layers.
Enlargement of Photonic Band Gaps and Physical Picture of Photonic Band Structures
ZHANG Yan, SHI Jun-Jie
Chin. Phys. Lett. 2006, 23 (3): 639-642 .  
Abstract   PDF(pc) (231KB) ( 605 )
Light propagation in a one-dimensional photonic crystal (PC), consisting of alternative slabs with refractive indices (layer thicknesses) n1 (a) and n2 (b), is investigated. An important optimal parameter matching condition, n1a approx n2b, is obtained for the largest photonic band gap (PBG). Moreover, we find that the exact analytical solutions for the electric/magnetic field eigenmodes at the band edges are standing waves with odd or even symmetry about the centre of each layer. The electric/magnetic field eigenfunctions at the top and bottom of the nth band have n and n-1 nodes in one period of PC, respectively. The PBG arises from the symmetric differences of the field eigenfunctions at the band edges.
Polarization-Insensitive Narrow Band Filter with a Symmetrical Metal-Cladding Optical Waveguide
LI Hong-Gen, CAO Zhuang-Qi, LU Hai-Feng, SHEN Qi-Shun
Chin. Phys. Lett. 2006, 23 (3): 643-644 .  
Abstract   PDF(pc) (174KB) ( 536 )
We demonstrate the promising configurations that permit very narrow spectral filtering. The waveguide filter consists of a glass slab with an anomalous thickness of about 500μm, which is sandwiched between two pre-coated metal films. By using the free-space coupling technique, a polarization-insensitive and tunable notch filter with a spectral bandwidth as narrow as 0.08nm has been obtained due to the excitation of ultrahigh-order modes of the symmetrical metal-cladding optical waveguide.
Isolation of Integrated Optical Acousto-Optic Switch
XIAO Li-Feng, LIU Ying, WANG Wei-Peng, GENG Fan,
Chin. Phys. Lett. 2006, 23 (3): 645-648 .  
Abstract   PDF(pc) (207KB) ( 484 )
Isolation of a new structured acousto-optic switch based on an integrated optical polarization-independent quasi-collinear acousto-optic tunable filter is studied in detail. The factors that influence the isolation of the optical switch are analysed, the expressions of the isolation are educed, and the isolation of the device is measured in experiment. It is found that the isolation mainly depends on the TE/TM mode intensity ratio, the mode-splitter extinction rate, and the conversion efficiency.
Theoretical Prediction of the Acoustical Nonlinear Field Radiated from a Concave Focusing Source with a Wide Aperture Angle
SUN Min, ZHANG Dong, GONG Xiu-Fen
Chin. Phys. Lett. 2006, 23 (3): 649-651 .  
Abstract   PDF(pc) (220KB) ( 574 )
We propose a time-domain theoretical approach to predict the acoustic nonlinear field radiated from a concave focusing spherical source with a wide aperture angle. The nonlinear sound propagation is theoretically described by an accurate mathematical model including the continuity and momentum equations. Numerical calculation is implemented by using the finite difference time domain algorithm in the oblate spheroidal coordinate system. To examine the validity of the theoretical model, we calculate the sound fields
radiated from concave spherical focusing transducers with aperture angles 30° and 40° and the results are compared with those obtained by the SBE solution.
Double-Humped Transverse Density Profile in Two-Dimensional Chute Flow with Rough Sidewalls
HU Guo-Qi, ZHANG Xun-Sheng, BAO De-Song, TANG Xiao-Wei
Chin. Phys. Lett. 2006, 23 (3): 652-655 .  
Abstract   PDF(pc) (380KB) ( 452 )
We study a two-dimensional granular rapid flow with rough sidewalls stuck with the same size discs by molecular dynamics simulation. A transient state of the double-humped density profile in the flowing process has been found, which appears and moves as travelling wave and is the same as the phenomena in the recent experiments [Acta Phys. Sin. 53 (2004) 3389 (in Chinese)]. Our simulation shows that the rough sidewalls play an important role in the converting momentum of boundary discs from the vertical direction to the horizontal one through particle collisions to form this profile and the good elasticity of discs ensures this effect. The appearance of the double-humped profile may be a precursor, which determines if the whole flow will be far repulsed from the boundary and become dilute eventually.
A Novel Lattice Boltzmann Model For Reactive Flows with Fast Chemistry
CHEN Sheng, LIU Zhao-Hui, HE Zhu, ZHANG Chao, TIAN Zhi-Wei, SHI Bao-Chang, ZHENG Chu-Guang
Chin. Phys. Lett. 2006, 23 (3): 656-659 .  
Abstract   PDF(pc) (243KB) ( 591 )
A novel lattice Boltzmann model, in which we take the ratio of temperature difference in the temperature field to the environment one to be more than one order of magnitude than before, is developed to simulate two-dimensional reactive flows with fast chemistry. Different from the hybrid scheme for reactive flows [Comput. Phys. Commun. 129(2000)267], this scheme is strictly in a pure lattice Boltzmann style (i.e., we solve the flow, temperature, and concentration fields using the lattice Boltzmann method only). Different from the recent non-coupled lattice Boltzmann scheme [Int. J. Mod. Phys. B 17(2003)197], the fluid density in our model is coupled directly with the temperature. Excellent agreement between the present results and other numerical data shows that this scheme is an efficient numerical method for practical reactive flows with fast chemistry.
Detailed Radiative Opacity Studies of a High-Temperature Gold Plasma
ZENG Jiao-Long, ZHAO Gang, YUAN Jian-Min,
Chin. Phys. Lett. 2006, 23 (3): 660-663 .  
Abstract   PDF(pc) (238KB) ( 632 )
The radiative opacity of a gold plasma at a temperature of 360eV and a density of 0.01g/cm3 has been studied using a detailed level accounting (DLA) method. Under this plasma condition, the average ionization degree is 50.2. Dominant ion types in the plasma are Au+49, Au+50 and Au+51, which account for 18.3%, 33.1% and 32.6%, respectively. The spectrally resolved opacity shows complex fine structures. The result obtained by the DLA method is compared with that of the average atom model. Detailed analyses are carried out to study the strongest absorption peaks caused by 3d-4f transitions near the photon energy of 2600eV. To better understand the value of the Rosseland mean opacity, the radiative opacity around the energy region of the maximal Rosseland weighting function is also discussed in detail.

Relativistic Electromagnetic Solitary Wave in a Cylindrical Magnetized Plasma
WANG Yun-Liang, ZHOU Zhong-Xiang, JIANG Xiang-Qian, YUAN Cheng-Xun, WANG Hai-Feng, ZHANG Hai-Feng, HOU Chun-Feng, JIANG Yong-Yuan, SUN Xiu-Dong, QIN Ru-Hu
Chin. Phys. Lett. 2006, 23 (3): 664-667 .  
Abstract   PDF(pc) (244KB) ( 623 )
In the presence of an applied static and uniform magnetic field, a cylindrical Kadomtsev--Petviashivili equation is derived for a relativistic electromagnetic solitary wave propagating in collisionless plasma consisting electrons, positrons, and ions in the case of weak relativistic limit. This equation is solved in a stationary frame to obtain explicit expression for the velocity, amplitude and width of solitons. The amplitude of the solitary wave has a maximum value at a critical αc of the ratio of the ion equilibrium density to the electron one, and it increases as the applied magnetic field becomes larger.
Investigation of Dual Radio-Frequency Driven Sheaths and Ion Energy Distributions Bombarding an Insulating Substrate
WANG Li-Hong, DAI Zhong-Ling, WANG You-Nian
Chin. Phys. Lett. 2006, 23 (3): 668-671 .  
Abstract   PDF(pc) (234KB) ( 570 )
Dual radio-frequency (rf) sources at widely different frequencies are often simultaneously used to separately optimize the plasma parameters and ion energy distributions (IEDs) incident onto a substrate. Characteristics of collisionless dual rf biased-sheaths and IEDs impinging on an insulating substrate are studied with a self-consistent one-dimensional fluid model. In order to describe the sheath dynamics over a wide range of frequency, the model includes all the time-dependent terms in the ion fluid equation. Meanwhile, an equivalent circuit model is used to self-consistently determine the relationship among the instantaneous voltage on the insulating substrate, the instantaneous sheath thickness, and the dual currents applied to the electrode. The numerical results show that some parameters such as the bias frequency and bias power of the lower frequency source are crucial for determining the parameters of dual rf biased-sheaths and IEDs arriving at the insulating substrate.

Glass Formation Ability and Kinetics of the Gd55Al20Ni25 Bulk Metallic Glass
JO Chol-Lyong, XIA Lei, DING Ding, DONG Yuan-Da
Chin. Phys. Lett. 2006, 23 (3): 672-674 .  
Abstract   PDF(pc) (208KB) ( 510 )
We report a new bulk glass-forming alloy Gd55Al20Ni25. The bulk sample of the alloy is prepared in the shape of rods in diameter 2mm by suction casting. The rod exhibits typical amorphous characteristics in the x-ray diffraction pattern, paramagnetic property at 300K, distinct glass transition and multi-step crystallization behaviour in differential scanning calorimetry traces. The glass formation ability of the alloy is investigated by using the reduced glass transition temperature Trg and the parameter γ. Kinetics of glass transition and primary crystallization is also studied. The fragility parameter m obtained from the Vogel--Fulcher--Tammann dependence of glass transition temperature Tg on lnФ (Ф is the heating rate) classifies the bulk metallic glasses into the intermediate category according to Angell's classification.
Energy Variable Slow Positron Beam Study of Li+-Implantation-Induced Defects in ZnO
CHEN Zhi-Quan, M. Maekawa, A. Kawasuso
Chin. Phys. Lett. 2006, 23 (3): 675-677 .  
Abstract   PDF(pc) (200KB) ( 598 )
ZnO films grown on sapphire substrates are implanted with 100-keV Li ions up to a total dose of 1×10-16 cm-2. Vacancy-type defects, mostly vacancy clusters, are observed by positron annihilation measurements after implantation. Upon annealing, they first have an agglomeration process which leads to the growth in the vacancy size. After annealing at about 500°C, vacancy clusters grow into microvoids, which is indicated by the positronium formation. With annealing temperature increases to above 500°C, the microvoids begin to recover, and finally all the implantation-induced vacancy defects are removed at 1000°C. No Li nanoclusters can be observed after Li+ implantation.
NiSi Film Synthesized by Isochronal Annealing in a Magnetron Sputtering System
YUE Shuang-Lin, LUO Qiang, SHI Cheng-Ying, YANG Hong-Xin, WANG Qiang, XU Peng, GU Chang-Zhi
Chin. Phys. Lett. 2006, 23 (3): 678-681 .  
Abstract   PDF(pc) (270KB) ( 486 )
By repeatedly pre-cleaning the sputtering chamber with Ar gas and in-situ isochronal annealing samples, NiSi films are successfully prepared on Si (100) substrates in a radio-frequency magnetron sputtering system. A comparison between the obtained NiSi and excess oxygen-contaminated Ni/Si films has been performed by EDX analysis of oxygen atomic content in both the films. Focused ion beam milling technology is employed to make the cross-sections of the samples for characterizing the NiSi film thickness and NiSi/Si interface roughness. The influences of nickel film thickness on the NiSi-film morphology and on the NiSi/Si interface roughness are studied.

Compositional and Structural Properties of TiO2-xNx Thin Films Deposited by Radio-Frequency Magnetron Sputtering
JING Shi-Wei, LIU Yi-Chun, LIANG Yu, MA Jian-Gang, LU You-Ming, SHEN De-Zhen, ZHANG Ji-Ying, FAN Xi-Wu, MU Ri-Xiang
Chin. Phys. Lett. 2006, 23 (3): 682-685 .  
Abstract   PDF(pc) (231KB) ( 664 )
TiO2-xNx thin films are deposited onto Si(100) and quartz substrates by a rf magnetron sputtering method using a titanium metal disc as a target in Ar, N2, and O2 atmospheres. The substrate temperature is kept at 300°C. The O2 and Ar gas flow rates are kept to be constants and the N gas flow rate is varied. TiO2-xNx films with different N contents are characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The results indicate that the TiO2-xNx thin films can be obtained at 13% N and 15% N contents in the film, and the films with mixed TiO2 and TiN crystal can be obtained at 13% N and 15% N contents in the film. In terms of the results of x-ray photoelectron spectroscopy, N 1s of β-N (396eV) is the main component in the TiO2-xNx thin films. Because the energy level of β-N is positioned above the valence-band maximum of TiO2, an effective optical-energy gap decreases from 2.8eV (for pure TiO2 film deposited by the same rf sputtering system) to 2.3eV, which is verified by the optical-absorption spectra.
Fabrication of Syringe-Shaped GaN Nanorods
XUE Cheng-Shan, WU Yu-Xin, ZHUANG Hui-Zhao, TIAN De-Heng, LIU Yi-An, HE Jian-Ting, AI Yu-Jie, SUN Li-Li, WANG Fu-Xue, CAO Yu-Ping
Chin. Phys. Lett. 2006, 23 (3): 686-688 .  
Abstract   PDF(pc) (274KB) ( 472 )
Syringe-shaped GaN nanorods are synthesized on Si(111) substrates by annealing sputtered Ga2O3/BN films under flowing ammonia at temperature of 950°C. Most of the nanorods consist of a main rod and a top needle, looking like a syringe. X-ray diffraction and selected-area electron diffraction confirm that the syringe-shaped nanorods are hexagonal wurtzite GaN. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that these nanorods are as long as several micrometres, with diameters ranging from 100 to 300nm. In addition to the BN intermediate layer, the proper annealing temperature has been demonstrated to be a crucial factor for the growth of syringe-shaped nanorods by this method.
An ab initio Non-Equilibrium Green Function Approach to Charge Transport: Dithiolethine
Alexander Schnurpfeil, SONG Bo, Martin Albrecht
Chin. Phys. Lett. 2006, 23 (3): 689-692 .  
Abstract   PDF(pc) (233KB) ( 557 )
We present a novel ab initio non-equilibrium approach to calculate the current across a molecular junction. The method rests on a wavefunction-based full ab initio description of the central region of the junction combined with a tight binding approximation for the electrodes in the frame of the Keldysh Green function formalism. Our procedure is demonstrated for a dithiolethine molecule located between silver electrodes. The main conducting channel is identified and the full current--voltage characteristic is calculated.
Photoconductive Properties of MEH-PPV/CuS-Nanoparticle Composites
JIN Hui, HOU Yan-Bing, TANG Ai-Wei, MENG Xian-Guo, TENG Feng
Chin. Phys. Lett. 2006, 23 (3): 693-696 .  
Abstract   PDF(pc) (249KB) ( 826 )
Photoconductive properties of photodiodes based on composites of CuS nanoparticles and Poly[2-methoxy,5-(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) are investigated. By comparing composite devices with different MEH-PPV:CuS weight ratios of 1:1 (D2-1), 1:1.25 (D2-2), 1:2.5 (D2-3) and 1:5 (D2-4), it is found that the device D2-3 exhibited the best performance: the short-circuit current density of 17μA/cm2 with the light intensity of 16.7 mW/cm2, the highest open-circuit voltage of 0.83V, and the photosensitivity of 132 at reverse bias of -1 V. The photosensitivity is improved by a factor of 5 compared with the undoped MEH-PPV device.

Resonant Tunnelling Diodes and High Electron Mobility Transistors Integrated on GaAs Substrates
HUANG Ying-Long, MA Long, YANG Fu-Hua, WANG Liang-Chen, ZENG Yi-Ping
Chin. Phys. Lett. 2006, 23 (3): 697-700 .  
Abstract   PDF(pc) (227KB) ( 575 )
AlGaAs/InGaAs high electron mobility transistors (HEMTs) and AlAs/GaAs resonant tunnelling diodes (RTDs) are integrated on GaAs substrates. Molecular beam epitaxy is used to grow the RTD on the HEMT structure. The current--voltage characteristics of the RTD and HEMT are obtained on a two-inch wafer. At room temperature, the peak-valley current ratio and the peak voltage are about 4.8 and 0.44V, respectively. The HEMT is characterized by a gate length of 1μm, a maximum transconductance of 125mS/mm, and a threshold voltage of -1.0V. The current--voltage characteristics of the series-connected RTDs are presented. The current--voltage curves of the parallel connection of one RTD and one HEMT are also presented.
Improvements of the Analytical Model of Monte Carlo
HE Qing-Fang, XU Zheng, TENG Feng, LIU De-Ang, XU Xu-Rong
Chin. Phys. Lett. 2006, 23 (3): 701-704 .  
Abstract   PDF(pc) (212KB) ( 430 )
By extending the conduction band structure, we set up a new analytical model in ZnS. Compared the results with both the old analytical model and the full band model, it is found that they are possibly in reasonable agreement with the full band method and we can improve the calculation precision. Another important work is to reduce the programme computation time using the method of data fitting scattering rate curves.

Aharonov--Bohm Oscillations and Fano Resonance of a Coupled Dot-Ring System
XIONG Yong-Jian
Chin. Phys. Lett. 2006, 23 (3): 705-707 .  
Abstract   PDF(pc) (204KB) ( 448 )
We derive an exact expression for the transmission coefficient through an Aharonov--Bohm ring with a side-coupled quantum dot using the scattering-matrix approach. We show a sudden AB phase change by π as the quantum dot is tuned across the resonance. The Aharonov--Bohm oscillation amplitude can be modulated effectively by tuning the quantum dot level. The transmission coefficient has an expression of the generalized Fano form with a complex Fano parameter q in the presence of the Aharonov--Bohm flux.
Stationary Entanglement of Two Charge Qubits Induced by a Damped and Driven Cavity
LI Jun-Gang, ZOU Jian, CAI Jin-Fang, SHAO Bin
Chin. Phys. Lett. 2006, 23 (3): 708-711 .  
Abstract   PDF(pc) (271KB) ( 488 )
Two charge qubits located inside a damped driven cavity is considered. The dynamical evolution of the entanglement between the two qubits is demonstrated analytically or numerically. It is found that with the cavity dissipation, the steady entanglement between the two qubits is sensitive to the initial state of the qubits, but independent of the cavity field's initial state. The two qubits initially in the separable and most mixed state can be more easily entangled. The external field can be used to enhance the steady entanglement between the two charge qubits.

Anisotropic Effects on Magnetoelastic Transition in Magnetic Molecular Rings
LI Peng-Fei, CHEN Yu-Guang, CHEN Hong
Chin. Phys. Lett. 2006, 23 (3): 712-715 .  
Abstract   PDF(pc) (206KB) ( 492 )
We numerically study the anisotropic effects on the magnetoelastic transition in an S=1/2 XXZ model with a finite lattice number. It is found that the order of the magnetoelastic transition is strongly affected by the anisotropy parameter λ and there may exist a critical λc dividing the first-order transition and the continuous transition.
Fabrication and Characterization of Well-Aligned Zn1-xMnxO Nanorods
CHANG Yong-Qin, ZHANG Hong-Zhou, LONG Yi, YE Rong-Chang
Chin. Phys. Lett. 2006, 23 (3): 716-719 .  
Abstract   PDF(pc) (1178KB) ( 488 )
Well-aligned Zn1-xMnxO nanorods have been synthesized successfully on bare silicon substrates by a simple evaporation method without using any catalyst. X-ray diffraction and electron microscopy studies demonstrate that the as-grown nanorods are of single wurtzite phase with a preferential growth direction along their c-axes. Quantitative energy-dispersive spectrum analysis reveals that the concentration of manganese is around 4 at.%. Magnetic measurements show the single-phase Zn1-xMnxO nanorod arrays exhibiting the paramagnetic behaviour. Photoluminescence spectra demonstrate that the Zn1-xMnxO nanorods preserve ultraviolet emission at room temperature.

Pregelation Behaviour of Coagulation Processes with the Constant-Reaction-Number Kernel
KE Jian-Hong, LIN Zhen-Quan, CHEN Xiao-Shuang
Chin. Phys. Lett. 2006, 23 (3): 720-723 .  
Abstract   PDF(pc) (227KB) ( 434 )
We propose an irreversible binary coagulation model with a constant-reaction-number kernel, in which, among all the possible binary coagulation reactions, only p reactions are permitted to take place at every time. By means of the generalized rate equation we investigate the kinetic behaviour of the system with the reaction rate kernel K(i;j)=(ij)ω (0≤ ω <1/2), at which an i-mer and a j-mer coagulate together to form a large one. It is found that for such a system there always exists a gelation transition at a finite time tc, which is in contrast to the ordinary binary coagulation with the same rate kernel. Moreover, the pre-gelation behaviour of the cluster size distribution near the gelation point falls in a scaling regime and the typical cluster size grows as (tc-t)-1/(1-2ω). On the other hand, our model can also provide some predictions for the evolution of the cluster distribution in multicomponent complex networks.
Investigation of Mechanisms of Enhanced Open-Circuit Photovoltage of Dye-Sensitized Solar Cells Based the Electrolyte Containing 1-Hexyl-3-Methylimidazolium Iodide
WANG Miao, ZHANG Qing-Li, WENG Yu-Xiang, LIN Yuan, XIAO Xu-Rui
Chin. Phys. Lett. 2006, 23 (3): 724-727 .  
Abstract   PDF(pc) (212KB) ( 674 )
The open-circuit photovoltage is improved by adding 1-hexyl-3-methylimidazolium iodide (HMImI) into the electrolyte. To investigate the mechanisms of the increase of the open-circuit photovoltage, we take the Mott--Schottky analysis and time-resolved mid-infrared absorption spectroscopy to study the band edge movement of TiO2 and the rate of back electron transfer, respectively. The results indicate that the negative shift of the conduction band of TiO2 is a predominant factor to increase the open-circuit photovoltage for the electrolyte containing HMImI.
Nonlinear Electrical Characteristics of Antimony and Copper Doped Tin Oxide Based Varistor Ceramics
WANG Chun-Ming, WANG Jin-Feng, SU Wen-Bin
Chin. Phys. Lett. 2006, 23 (3): 728-731 .  
Abstract   PDF(pc) (269KB) ( 838 )
The novel CuO-doped dense tin oxide varistor ceramics are investigated. The densification of tin oxide varistor ceramics could be greatly improved by doping copper oxide additives. The introduction of antimony additives into a SnO2.CuO ceramic system would make it possess excellent nonlinearity. The sample doped with 0.05mol% Sb2O3 possesses the highest nonlinearity coefficient (α=17.9) and the lowest leakage current density (JL=52μA cm-2) among all the samples. A modified defect barrier model is introduced to explain the formation of the grain-boundary barrier. The nonlinear behaviour of (Cu, Sb)-doped SnO2 varistor system could be explained by the barrier model.

A MEMS-Based Piezoelectric Power Generator for Low Frequency Vibration Energy Harvesting
FANG Hua-Bin, LIU Jing-Quan, XU Zheng-Yi, DONG Lu, CHEN Di, CAI Bing-Chu, LIU Yue
Chin. Phys. Lett. 2006, 23 (3): 732-734 .  
Abstract   PDF(pc) (222KB) ( 701 )
A novel power generator has been achieved to convert vibration to electrical energy via the piezoelectric effect. The generator obtained by micro fabrication process mainly consists of silicon based frame and composite cantilever. The prototype tested at resonant vibration generates 1.15μW of effective power to a 20.4-kΩ resistance load. The potential of this work is to offer miniaturization solutions for power generators, and with the proposed method the ambient ubiquitous vibration can be harvested effectively as endless energy source to form an integrated self-powering system.
Fabrication of Ge Nano-Dot Heterojunction Phototransistors for Improved Light Detection at 1.55μm
SHI Wen-Hua, MAO Rong-Wei, ZHAO Lei, LUO Li-Ping, WANG Qi-Ming
Chin. Phys. Lett. 2006, 23 (3): 735-737 .  
Abstract   PDF(pc) (207KB) ( 551 )
Heterojunction phototransistors (HPTs) with several Ge/Si nano-dot layers as the absorption region are fabricated to obtain improved light detectivity at 1.55μm. The HPT detectors are of n-p-n type with ten layers of Ge(8ML)/Si(45nm) incorporated in the base-collector junction and are grown by an ultrahigh-vacuum chemical-vapor-deposition system. The detectors are operated with normal incidence. Because of the good quality of the grown material and fabrication process, the dark current is only 0.71pA/μm2 under 5V bias and the breakdown voltage is over 20V. Compared to the positive-intrinsic-negative (PIN) reference detector with the same absorption layer, the responsivity is improved over 17 times for normal incidence at 1.55μm.
Lattice BGK Simulations of the Blood Flow in Elastic Vessels
LU Xiao-Yang, YI Hou-Hui, CHEN Ji-Yao, FANG Hai-Ping
Chin. Phys. Lett. 2006, 23 (3): 738-741 .  
Abstract   PDF(pc) (235KB) ( 602 )
The lattice Boltzmann method is applied to study the flow in elastic blood vessels. The volume--flow rate increases considerably when the compliance constant of the blood vessel is below a critical value. There is a region of the compliance constant in which the average volume--flow rate is dramatically enhanced. A harmonic perturbation of the pressure does not change the behaviour of the average volume--flow rate while the harmonic wave attenuates very quickly along the tube when the resonant period is close to that of the input wave. The model, together with the simulation results, is expected to be helpful to understand the mechanism of the blood volume--flow rate related to the compliance constant of the blood vessel, especially on the dependence of the flux of human blood vessel under weather changes, which has medical significance.
Correlated Noises in a Prey--Predator Ecosystem
ZHONG Wei-Rong, SHAO Yuan-Zhi, HE Zhen-Hui
Chin. Phys. Lett. 2006, 23 (3): 742-745 .  
Abstract   PDF(pc) (259KB) ( 648 )
We investigate a Volterra ecosystem driven by correlated noises. The fluctuation in the death rate of the predator induces an increase of population density of the predators. The fluctuation in the growth rate of the prey, however, leads the predators to decay. It is reported that the predators undergo sensitivity to a random environment, whereas the preys exhibit a surprising endurance to the same stochastic factor. The predators are of better stability under strong correlation of noises.
Multistage Random Growing Small-World Networks with Power-Law Degree Distribution
LIU Jian-Guo, DANG Yan-Zhong, WANG Zhong-Tuo
Chin. Phys. Lett. 2006, 23 (3): 746-749 .  
Abstract   PDF(pc) (237KB) ( 609 )
We present a simple rule which could generate scale-free networks with very large clustering coefficient and very small average distance. These networks, called the multistage random growing networks (MRGNs), are constructed by a two-stage adding process for each new node. The analytic results of the power-law exponent γ=3 and the clustering coefficient C=0.81 are obtained, which agree with the simulation results approximately. In addition, we find that the average distance of the networks increases logarithmically with the network size, which is consistent with the theoretical predictions. Since many real-world networks are both scale-free and small-world, the MRGNs may perform well in mimicking reality.
Growing Small-World Networks Based on a Modified BA Model
XU Xin-Ping, LIU Feng, LI Wei
Chin. Phys. Lett. 2006, 23 (3): 750-753 .  
Abstract   PDF(pc) (217KB) ( 769 )
We modify the (Barabási--Albert) BA model for the evolution of small-world networks. It is introduced as a modified BA model in which all the edges connected to the new node are made locally to the old node and its nearest neighbours. It is found that this model can produce small-world networks with power-law degree distributions. Properties of our model, including the degree distribution, clustering, average path length and degree correlation coefficient are compared with that of the BA model. Since most real networks are both scale-free and small-world networks, our model may provide a satisfactory description for empirical characteristics of real networks.
Empirical Study on the Volatility of the Hang-Seng Index
CAI Shi-Min, ZHOU Pei-Ling, YANG Hui-Jie, YANG Chun-Xia, WANG Bing-Hong, ZHOU Tao,
Chin. Phys. Lett. 2006, 23 (3): 754-757 .  
Abstract   PDF(pc) (266KB) ( 686 )
We study the statistical properties of volatility of price fluctuation for the Hang-Seng index in the Hong Kong stock market, they are measured by locally averaging over a time window T, the absolute value of price change over a short time interval Δt. The data include minute-by-minute records of the Hang-Seng index from 3 January 1994 to 28 May 1997. We find that the cumulative distribution of the volatility is consistent with the asymptotic power-law behaviour, characterized by the power exponent μ=2.12 ± 0.04, different from that found in the previous studies as μ approx 3. The volatility distribution remains the same asymptotic power-law behaviour for the time scales from T=10 min to T=80 min. Furthermore, we investigate the volatility correlations by using the power spectrum analysis and detrended fluctuation analysis. Both the methods show a long-range power-law decay with the exponent α=0.636±0.002.
Applications of the Junction Conditions Connecting the Robertson--Walker Metric and the Metric of a Local System on Our Universe
QIN Yi-Ping
Chin. Phys. Lett. 2006, 23 (3): 758-761 .  
Abstract   PDF(pc) (206KB) ( 607 )
We investigate how the local and global metrics are connected in an ideal model of spacetime where the local system is assumed to be highly symmetric and the cosmological matter is kept away from the local system and does not disturbed by the local system. A boundary condition arising from the junction conditions is obtained and its implication in our universe is studied. We know that the total mass of a sufficiently large system must be that of the cosmological matter within the region of that size. This requirement is satisfied since it is just a consequence of the boundary condition. The analysis shows that at the very late epoch of the universe, there exists a particular time when the largest symmetric local systems stop growing and the observation of this time can be used to check the cosmological parameters. Adopting the popular values (ΩMΛ)=(0.28,0.72), we find that particular time would be associated with z=0.726, the effect of dark matter on the clustering of objects would be insignificant, and the Virgo cluster would be gravitationally bound even if dark matter is ignored.
Development of the Model of the Generalized Quintom Dark Energy
WANG Wei, GUI Yuan-Xing, SHAO Ying
Chin. Phys. Lett. 2006, 23 (3): 762-764 .  
Abstract   PDF(pc) (184KB) ( 707 )
We consider a generalized quintom (GQ) dark energy model for changing the equal weight of the negative-kinetic scalar field (phantom) and the normal scalar field (quintessence) in quintom dark energy. Though the phantom-dominated scaling solution is a stable late-time attractor, the early evolution of GQ is different from that of the quintom model and the adjustability of the dark energy state equation in the model is improved.
65 articles