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Volume 22 Issue 11
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Original Articles
Functional Variable Separation for Extended (1+2)-Dimensional Nonlinear Wave Equations
ZHANG Shun-Li, , LOU Sen-Yue, QU Chang-Zheng
Chin. Phys. Lett. 2005, 22 (11): 2731-2734 .  
Abstract   PDF(pc) (218KB) ( 588 )
The functional variable separation approach is applied to study extended (1+2)-dimensional nonlinear wave equations. Complete classification for those equations admitting the functional separable solutions and some exact separable solutions are obtained.
Completely Integrable Hamiltonian Systems Generated by Poisson
LEI De-Chao, ZHANG Xiang
Chin. Phys. Lett. 2005, 22 (11): 2735-2737 .  
Abstract   PDF(pc) (195KB) ( 423 )
The completely integrable Hamiltonian systems have been applied to physics and mechanics intensively. We generate a family of completely integrable Hamiltonian systems from some kinds of exact Poisson structures in R3 by the realization of the Poisson algebra. Moreover, we prove that there is a Poisson algebra which cannot be realized by an exact Poisson structure.
A Continuation Method of Parameter Inversion for Non-Equilibrium Convection--Dispersion Equation
CUI Kai, YANG Guo-Wei
Chin. Phys. Lett. 2005, 22 (11): 2738-2741 .  
Abstract   PDF(pc) (214KB) ( 486 )
Based on the homotopy mapping, a globally convergent method of parameter inversion for non-equilibrium convection-dispersion equations (CDEs) is developed. Moreover, in order to further improve the computational efficiency of the algorithm, a properly smooth function, which is derived from the sigmoid function, is employed to update the homotopy parameter during iteration. Numerical results show the feature of global convergence and high performance of this method. In addition, even the measurement quantities are heavily contaminated by noises, and a good solution can be found.
Remarks on Exact Solvability of Quantum Systems with Spatially Varying Effective Mass
B. Gö, nül, M. Kocak
Chin. Phys. Lett. 2005, 22 (11): 2742-2745 .  
Abstract   PDF(pc) (184KB) ( 508 )
Within the frame of a novel treatment we make a complete mathematical analysis of exactly solvable one-dimensional quantum systems with non-constant mass, involving their ordering ambiguities. This work extends the results recently reported in the literature and clarifies the relation between physically acceptable effective mass Hamiltonians.
Accurate Bound-State Spectra for Hydrogenic Donors in GaAs--(Ga, Al)As Quantum Dots
XU Tian, CAO Zhuang-Qi, OU Yong-Cheng, ZHU Guo-Long
Chin. Phys. Lett. 2005, 22 (11): 2746-2747 .  
Abstract   PDF(pc) (185KB) ( 449 )
We extend the analytical transfer matrix method (ATMM) to study the bound-state spectra for hydrogenic donors in GaAs--(Ga, Al)As quantum dots. Comparison of the energy eigenvalues from ATMM with those from the wavefunction method reveals wavefunction results show large deviation from the exact ones when the radius of quantum dots r0 become large, whereas ATMM is better accuracy.
An Eavesdropping Detecting Approach Based on Mode--Mode Correlation
XIONG Jin, ZENG Gui-Hua, ZHOU Nan-Run
Chin. Phys. Lett. 2005, 22 (11): 2748-2750 .  
Abstract   PDF(pc) (201KB) ( 764 )
We find that second-order coherence as well as a Hanbury--Brown--Twiss intensity interferometer may provide an optimal approach for eavesdropping detection in the quantum key distribution based on two-mode squeezed vacuum states. With this approach, eavesdropping can be easily detected without sacrificing extra secret bits as the test key. In addition, the efficiency of the quantum key distribution protocol is enhanced greatly.
Quantum State Sharing by Using Two-Mode and Single-Mode Squeezed State Lights
ZHANG Jun-Xiang, JING Jie-Tai, XIE Chang-De, PENG Kun-Chi
Chin. Phys. Lett. 2005, 22 (11): 2751-2754 .  
Abstract   PDF(pc) (214KB) ( 471 )
We propose a quantum state sharing scheme for continuous variables using bright two-mode squeezed state and single-mode squeezed state light. The squeezing of a single-mode state is applied to enhance the security of information in quantum teleportation network. The signal-to-noise ratio of communication and the fidelity between the secret and reconstruction state are analysed. It is shown that both the receivers of Bob and Charlie cannot extract information with a high signal-to-noise ratio because of the large noise come from the other quadrature component of single mode squeezed state. Anyone of Bob and Charlie can retrieve the quantum state with a high signal-to-noise ratio if and only if the other one cooperates with the measurement.

Relative Entropy of Entanglement of a Kind of Two-Qubit Entangled States
CHEN Xiao-Yu, MENG Li-Min, JIANG Li-Zhen, LI Xiang-Jun
Chin. Phys. Lett. 2005, 22 (11): 2755-2758 .  
Abstract   PDF(pc) (196KB) ( 448 )
We strictly prove that some block diagonalizable two-qubit entangled state with six non-zero elements reaches its quantum relative entropy entanglement by a separable state having the same matrix structure. The entangled state comprises local filtering result state as a special case.
Von Neumann Entropy of an Electron in One-Dimensional Determined Potentials
GONG Long-Yan, TONG Pei-Qing
Chin. Phys. Lett. 2005, 22 (11): 2759-2762 .  
Abstract   PDF(pc) (244KB) ( 712 )
By using the measure of von Neumann entropy, we numerically investigate quantum entanglement of an electron moving in the one-dimensional Harper model and in the one-dimensional slowly varying potential model. The delocalized and localized eigenstates can be distinguished by von Neumann entropy of the individual eigenstates. There are drastic decreases in von Neumann entropy of the individual eigenstates at mobility edges. In the curve of the spectrum averaged von Neumann entropy as a function of potential parameter λ, a sharp transition exists at the metal--insulator transition point λc=2. It is found that the von Neumann entropy is a good quantity to reflect localization and metal--insulator transition.

Object Picture of Quasinormal Modes for Stringy Black Holes
XI Ping, LI Xin-Zhou
Chin. Phys. Lett. 2005, 22 (11): 2763-2765 .  
Abstract   PDF(pc) (222KB) ( 530 )
We study the quasinormal modes (QNMs) for stringy black holes. By using numerical calculation, the relations between the QNMs and the parameters of black holes are minutely shown. For (1+1)-dimensional stringy black hole, the real part of the quasinormal frequency increases and the imaginary part of the quasinormal frequency decreases as the mass of the black hole increases. Furthermore, the dependence of the QNMs on the charge of the black hole and the flatness parameter is also illustrated. For (1+3)-dimensional stringy black hole, increasing either the event horizon or the multipole index, the real part of the quasinormal frequency decreases. The imaginary part of the quasinormal frequency increases no matter whether the event horizon is increased or the multipole index is decreased.
Quantum Spectrum of Stationary Axisymmetric Einstein--Maxwell Dilaton--Axion Black Hole
WANG Jin, JING Ji-Liang
Chin. Phys. Lett. 2005, 22 (11): 2766-2768 .  
Abstract   PDF(pc) (196KB) ( 534 )
The horizon area spectrum of a stationary axisymmetric Einstein--Maxwell Dilaton--Axion (EMDA) black hole is studied by using Gour--Medved’s method. It is found that the quantized area operator can be expressed in terms of two quantum numbers, i.e. A=8πħ(1/2+n+l), where n and l are strictly non-negative integers and related respectively to the mass and angular momentum. The result shows that there is qualitatively a property difference between the quantum spectrum of the EMDA black hole which obtained from string theory and the one of the Kerr--Newman black hole which obtained from general relativity, although both they are characterized by mass, angular momentum and charge.
Quantum Tunnelling and Hawking Radiation of Schwarzchild--Anti-de Sitter Black Hole with Topological Defect
HAN Yi-Wen, YANG Shu-Zheng
Chin. Phys. Lett. 2005, 22 (11): 2769-2771 .  
Abstract   PDF(pc) (182KB) ( 516 )
We extend Parikh’s recent work to Schwarzchild--anti-de Sitter black hole with topological defect whose Arnowitt--Deser--Misner (ADM) mass is no longer identical to its mass parameter. We view the Hawking radiation as a tunnelling process across the event horizon and the cosmological horizon. From the tunnelling probability, we find a leading correction to the semi-classical emission rate. The result employs an underlying unitary theory.
Current Inversion in a Temperature Ratchet with Asymmetric Unbiased External Forces
AI Bao-Quan, XIE Hui-Zhang, LIU Liang-Gang
Chin. Phys. Lett. 2005, 22 (11): 2772-2775 .  
Abstract   PDF(pc) (215KB) ( 542 )
Transport of a Brownian particle moving in a symmetric potential is investigated in the presence of an asymmetric unbiased external force. The viscous medium is alternately in contact with the two heat reservoirs. We present the analytical expression of the net current at the quasi-steady state limit. It is found that the competition of the temporal asymmetric parameter of the driving force with the temperature difference leads to current reversals. The competition between the two opposite driving factors is a necessary but not a sufficient condition for current reversals.
Local Prediction of Chaotic Time Series Based on Support Vector Machine
LI Heng-Chao, ZHANG Jia-Shu
Chin. Phys. Lett. 2005, 22 (11): 2776-2779 .  
Abstract   PDF(pc) (223KB) ( 561 )
Based on phase space delay-coordinate reconstruction of a chaotic dynamics system, we propose a local prediction of chaotic time series using a support vector machine (SVM) to overcome the shortcomings of traditional local prediction methods. The simulation results show that the performance of this proposed predictor for making one-step and multi-step prediction is superior to that of the traditional local linear prediction method and global SVM method. In addition, it is significant that its prediction performance is insensitive to the selection of embedding dimension and the number of nearest neighbours, so the satisfying results can be achieved even if we do not know the optimal embedding dimension and how to select the number of nearest neighbours.
Limit Cycles near Stationary Points in the Lorenz System
YANG Shi-Pu, ZHU Ke-Qin, ZHOU Xiao-Zhou
Chin. Phys. Lett. 2005, 22 (11): 2780-2783 .  
Abstract   PDF(pc) (194KB) ( 1102 )
The limit cycles in the Lorenz system near the stationary points are analysed numerically. A plane in phase space of the linear Lorenz system is used to locate suitable initial points of trajectories near the limit cycles. The numerical results show a stable and an unstable limit cycle near the stationary point. The stable limit cycle is smaller than the unstable one and has not been previously reported in the literature. In addition, all the limit cycles in the Lorenz system are theoretically proven not to be planar.


Diquark Structure of Pentaquark in the Quark Delocalization Colour Screening Model
HUANG Hong-Xia, GONG Li-Ying, PING Jia-Lun,
Chin. Phys. Lett. 2005, 22 (11): 2784-2787 .  
Abstract   PDF(pc) (242KB) ( 405 )
In the framework of quark-delocalization, colour-screening model, the diquark structure of pentaquark θ+ is studied in detail under the adiabatic approximation. The calculation is carried out by using the fractional parentage expansion technique, which greatly simplify the calculation of the matrix elements of Hamiltonian. The results show that the ground state of the pentaquark has negative parity rather than positive parity, which was proposed by Jaffe--Wilczek. However the mass obtained is about 1651MeV which is still higher than the observed mass 1540MeV.
Observation of High-j Two-Quasiparticle Bands in Odd--Odd
ZHANG Yu-Hu, GUO Song, ZHOU Xiao-Hong, MA Long, Oshima M., Toh Y., Koizumi M., Osa A., Kimura A., Hatsukawa Y., Sugawara M., Kusakari H.
Chin. Phys. Lett. 2005, 22 (11): 2788-2791 .  
Abstract   PDF(pc) (239KB) ( 501 )
High spin states in 174Re have been investigated via the 152Sm (27Al, 5nγ)174Re reaction. Gamma-ray excitation functions, x-γ and γ-γ coincidences have been measured. Two rotational bands built on the π h9/2 otimes vi13/2 and π h11/2 otimes vi13/2 configurations have been identified and extended up to high-spin states. The relative spin and parity of the band levels have been unambiguously fixed due to observations of several inter-band transitions. Both the bands show the low-spin signature inversion, which is consistent with systematic expectations for the high-j two-quasiparticle bands in the A=170 mass region.
Simultaneous Elastic Recoil Detection Analysis of H and Other Elements in Foils
LU Xiu-Qin, ZHOU Ping, GUO Ji-Yu, ZHANG Xin, ZHAO Kui, NI Mei-Nan, SUI Li, MEI Jun-Ping, LIU Jian-Cheng
Chin. Phys. Lett. 2005, 22 (11): 2792-2794 .  
Abstract   PDF(pc) (214KB) ( 455 )
Hydrogen and other elements in SixNyHz foils have been simultaneously measured by using a single E(gas)-E(PSD) telescope and heavy 127I ion beam in elastic recoil detection analysis (ERDA). Hydrogen is measured in the non-coincidence spectrum of E(PSD), and other elements from the Δ E-E coincidence spectrum. The composition and depth profiling of the foils are obtained from the simulated spectra.
Ab Initio Calculations for the Polarizabilities of Small Sulfur Clusters
BAI Yu-Lin, CHEN Xiang-Rong, CHENG Xiao-Hong, YANG Xiang-Dong,
Chin. Phys. Lett. 2005, 22 (11): 2795-2797 .  
Abstract   PDF(pc) (206KB) ( 744 )
Polarizabilities of small Sn (n=2--8) clusters are calculated by using the higher-order finite- difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters are considered to be higher than the value estimated from the ``hard sphere'' model using the bulk static dielectric constant. The computed polarizabilities per atom tend to decrease with the increasing cluster size. The polarizabilities are closely related to the HOMO-LUMO gaps and the geometrical configurations.
Radiative Lifetimes of Doubly Ionized Terbium
XU Huai-Liang, JIANG Zhan-Kui,
Chin. Phys. Lett. 2005, 22 (11): 2798-2800 .  
Abstract   PDF(pc) (197KB) ( 560 )
Radiative lifetimes of two short-lived levels (i.e. 4f8 (7F6)6p1/2 (6,1/2)11/2,13/2) in Tb III are measured by time-resolved laser-induced fluorescence (LIF) technique with a two-step excitation process. Free Tb III ions are produced in a laser-induced plasma. Lifetime values are evaluated with a deconvolution procedure of the time-resolved fluorescence signal with the temporal shape of second-step excitation pulse (about 1ns). The lifetimes of the 4f8 (7F6)6p1/2 (6,1/2)11/2 and 4f8 (7F6)6p1/2 (6,1/2)13/2 levels are determined to be 1.9 (2) and 2.0 (2)ns, respectively.
An Empirical Formula Approach to Total Cross Sections for Electron Scattering on Polyatomic Molecules
DU Chao-Ling, SUN Jin-Feng, LIU Yu-Fang, CHENG Guang-Xu, CHEN Yan-Feng
Chin. Phys. Lett. 2005, 22 (11): 2801-2804 .  
Abstract   PDF(pc) (201KB) ( 750 )
Considering the real experimental process of e-molecule scattering a new empirical formula has been developed to calculate the total cross sections (TCSs) for electron scattering on polyatomic molecules (CH4, C2H2, CH3OH and CH3F). The present results are compared with other available theoretical results and experimental data. The new formula incorporates an energy factor f(E) to represent the elastic and inelastic changing process during experiments. It depends on no adjustable parameters and has also extended the validity of the empirical approaches to lower energy range further.
Arc Root Attachment on the Anode Surface of Arc Plasma Torch Observed with a Novel Method
PAN Wen-Xia, LI Teng, MENG Xian, CHEN Xi, WU Cheng-Kang
Chin. Phys. Lett. 2005, 22 (11): 2805-2898 .  
Abstract   PDF(pc) (199KB) ( 842 )
The arc-root attachment on the anode surface of a dc non-transferred arc plasma torch has been successfully observed using a novel approach. A specially designed copper mirror with a boron nitride film coated on its surface central-region is employed to avoid the effect of intensive light emitted from the arc column upon the observation of weakly luminous arc root. It is found that the arc-root attachment is diffusive on the anode surface of the argon plasma torch, while constricted arc roots often occur when hydrogen or nitrogen is added into argon as the plasma-forming gas.

Energy-Pooling Collisions in Rubidium: 5P3/2+53/2 → 5S +(nl=5D, 7S)
SHEN Yi-Fan, DAI Kang, MU Bao-Xia, WANG Shu-Ying, CUI Xiu-Hua
Chin. Phys. Lett. 2005, 22 (11): 2805-2807 .  
Abstract   PDF(pc) (228KB) ( 640 )
We experimentally study rubidium energy pooling collisions of Rb(5P3/2)+Rb(5P3/2) → Rb(5S1/2)+Rb(nlJ=5DJ, 7 S1/2 at low densities in a cell using diode laser excitation. The excited-atom density and spatial distribution are mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam, tuned to the 5P3/2 → 7 S1/2 transition, which could be translated parallel to the pump beam. The excited atom densities are combined with measured fluorescence ratios to determine cross sections for the rubidium energy pooling process. The cross sections for nlJ being 5 D5/2, 5D3/2, and 7 S1/2 are (1.32±0.59)×10-14, (1.18±0.53)×10-14 and (3.21±1.44)×10-15,cm2, respectively.
Modified Two-Scale Model for Electromagnetic Scattering from the Non-Gaussian Oceanic Surface
WANG Yun-Hua, GUO Li-Xin, WU Zhen-Sen
Chin. Phys. Lett. 2005, 22 (11): 2808-2811 .  
Abstract   PDF(pc) (258KB) ( 460 )
Based on the skewness of sea waves, a modified two-scale model is developed for the non-Gaussian sea surface scattering. In this new model, a complementary term is added to the first-order scattering coefficient of the classical small perturbation method (SPM), the additional part is proportional to the surface bispectrum and it is the critical part in explaining the scattering difference between upwind and downwind observations. Meanwhile, the effects of the shadowing function of the anisotropic surface, the curvature of the surface are also taken into account. The numerical results show the theoretical estimates obtained are consistent with the experimental result, and the influence of the wind speed, the trend and the incident frequency on the backscattering coefficients from the non-Gaussian oceanic surface is discussed in detail.
Two-Photon Micromaser with Initial Atomic Coherence
SUN Wei-Hui, DU Si-De, CHEN Xiao-Shuang
Chin. Phys. Lett. 2005, 22 (11): 2812-2815 .  
Abstract   PDF(pc) (228KB) ( 461 )
We investigate the quantum dynamics of a two-photon micromaser pumped by atoms injected in the superposition state of the upper and intermediate levels. We simulate a master equation governing the system by the Monte Carlo wavefunction approach and analyse the steady-state behaviour as a function of the atomic transit time. The atomic coherence can effectively enhance the intensity and sub-Poissonian of the cavity field as compared with the atomic mixture. It is also discovered that the phase of the cavity field can be shifted by adjusting the detuning between the atom and field. This result shows that it is possible to manipulate the phase of the cavity field by detuning, due to atomic coherence.
Matched Ultra Slow Optical Solitons in Double-λ Media
YANG Xiao-Xue, WU Xuan, WU Ying
Chin. Phys. Lett. 2005, 22 (11): 2816-2819 .  
Abstract   PDF(pc) (242KB) ( 544 )
We study the four-wave mixing (FWM) in a double-λ atomic system where two strong continuous-wave pump lasers and a weak pulsed probe laser produce an FWM generated pulse. We show that both the probe and FWM generated fields may evolve into bright and dark solitons with the same shape and the same ultraslow group velocity.
Vacuum-Induced Quantum Interference in a Trapped Λ-Configuration Three-Level System
WANG Zheng-Ling, YIN Jian-Ping
Chin. Phys. Lett. 2005, 22 (11): 2820-2823 .  
Abstract   PDF(pc) (224KB) ( 531 )
In consideration of quantization of centre-of-mass motion, we derive the second-order solution of the dynamic equation of a Λ-configuration three-level atom confined in an approximately harmonic trap by using the time-dependent perturbation theory. It is found that there are a series of dark lines in the second-order probability spectrum with multi-peak structures, which is the result of the quantum interference from the same vacuum mode in the spontaneous decay process of the trapped atom from the upper level to the two nearby lower levels. Our study shows that the second-order spectrum may be modified by the oscillation frequency Ω of the trap and the frequency difference Δ between two lower levels of the three-level atom, and the depth of the dark lines from the vacuum-induced quantum interference effect is strongly dependent on the above two parameters (Ω and Δ).
Super-Resolution of Interference Pattern with Independent Laser Beams
XIONG Jun, HUANG Feng, CAO De-Zhong, LI Hong-Guo, SUN Xu-Juan, WANG Kai-Ge
Chin. Phys. Lett. 2005, 22 (11): 2824-2826 .  
Abstract   PDF(pc) (200KB) ( 709 )
We propose a scheme to achieve super-resolution of interference pattern with independent laser beams. We perform an experimental observation of a double-slit interference with two orthogonally polarized laser beams. The resolution of the interference pattern measured by a two-photon detection is doubled provided the two beams illuminate the double-slit with certain incident angles. The scheme is simple and can favour both high intensity and perfect visibility.
Effect of Pump Area on Lasing Modes in Active Random Media
XIE Ying-Mao, LIU Zheng-Dong,
Chin. Phys. Lett. 2005, 22 (11): 2827-2830 .  
Abstract   PDF(pc) (207KB) ( 639 )
We investigate the effect of pump area on lasing modes in an active random medium. Considering the structure characteristics in a real experimental system, the random medium is divided into two regions, i.e. pump and non-pump areas. The dependence of lasing modes on the pump area is qualitatively explained by means of the model in which the lasing is ascribed to the interaction of the complex localized modes in the active random medium with local aperiodic quasi-structure with appropriate pump light. There exist different pump sizes for lasing with different modes. As the pump size decreases in this random system, the pump threshold of the lasing modes increases. There are different lasing modes in different excitation regions in this random system. This gives us some information about the dependence of lasing modes on pump areas in active random media.
Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3:Fe,Mg Crystal
WANG Zhen-Hua, ZHANG Xin-Zheng, XU Jing-Jun, WU Qiang, QIAO Hai-Jun, TANG Bai-Quan, RUPP Romano, KONG Yong-Fa, CHEN Shao-Lin, HUANG Zi-Heng, LI Bing, LIU Shi-Guo, ZHANG Ling
Chin. Phys. Lett. 2005, 22 (11): 2831-2833 .  
Abstract   PDF(pc) (242KB) ( 513 )
Forward degenerate four-wave mixing (DFWM) processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron (LiNbO3:Fe,Mg). The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility x(3) in the material is evaluated to be 4.96×10-13esu. The time-resolved DFWM process shows a response time of x(3) shorter than 100fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast x(3) optical nonlinearity.
Third-Order Optical Nonlinearity of a Novel Material: (Tetramethylammonium)bis(1,3-dithiole-2-thione-4,5-dithiolato) Copper
FENG Lin, WANG Yan-Ling, REN Quan, ZHGNG Guang-Hui, YANG Hong-Liang, SUN Xiang-Bing
Chin. Phys. Lett. 2005, 22 (11): 2834-2836 .  
Abstract   PDF(pc) (202KB) ( 427 )
A novel dmit2- salt: (tetramethylammonium)bis(1,3-dithiole-2-thione-4,5-dithiolato) copper, abbreviated as MECu, is synthesized and its third-order optical nonlinearity is characterized by Z-scan technique at a wavelength of 1064nm with laser duration of 30ps. Z-scan curves reveal a negative Kerr coefficient at 1064nm and no nonlinear absorption is observed. The nonlinear refraction coefficient n2 and the second hyperpolarizability γ have been determined to be as large as 2.15×10-11esu and 3.23×10-31esu, respectively, suggesting MECu is a potential material for optical device applications.
Vector Lattice Vortex Solitons
WANG Jian-Dong, YE Fang-Wei, DONG Liang-Wei, LI Yong-Ping
Chin. Phys. Lett. 2005, 22 (11): 2837-2839 .  
Abstract   PDF(pc) (195KB) ( 438 )
Two-dimensional vector vortex solitons in harmonic optical lattices are investigated. The stability properties of such solitons are closely connected to the lattice depth V0. For small V0, vector vortex solitons with the total zero-angular momentum are more stable than those with the total nonzero-angular momentum, while for large V0, this case is inversed. If V0 is large enough, both the types of such solitons are stable.
High and Stable Conversion Efficiency Obtaining in Single-Stage Multi-Crystal Optical Parametric Chirped Pulse Amplification System
JIANG Yong-Liang, LENG Yu-Xin, ZHAO Bao-Zhen, WANG Cheng, LIANG Xiao-Yan, LU Hai-He, XU Zhi-Zhan
Chin. Phys. Lett. 2005, 22 (11): 2840-2842 .  
Abstract   PDF(pc) (193KB) ( 572 )
An optical parametric chirped-pulse amplification system is demonstrated to provide 32.9% pump-to-signal conversion efficiency. Special techniques are used to make the signal and pump pulses match with each other in both spectral and temporal domains. The broadband 9.5-mJ pulses are produced at the repetition rate of 1Hz with the gain of over 1.9×108. The output energy fluctuation of 7.8% is achieved for the saturated amplification process against the pump fluctuation of 10%.
Riboflavin Sensitized Photopolymer Materials for Holographic Storage
ZHAI Feng-Xiao, WANG Ai-Rong, YIN Qiong, LIU Jun-Hui, HUANG Ming-Ju,
Chin. Phys. Lett. 2005, 22 (11): 2843-2846 .  
Abstract   PDF(pc) (229KB) ( 473 )
Riboflavin is employed as the photosensitizer of a novel photopolymer material for holographic recording. This material has a broad absorption spectrum range (more than 200nm) due to the addition of this dye. The experimental results show that our material has high diffraction efficiency and large refractive index modulation. The maximum diffraction efficiency of the photopolymer is about 56%. The digital data pages are stored in this medium and the reconstructed data page has a good fidelity, with the bit-error-ratio of about 1.8×10-4. It is found that the photopolymer material is suitable for high-density volume holographic digital storage.
Unidirectional Transmission in Asymmetrically Confined Photonic Crystal Defects with Kerr Nonlinearity
LIN Xu-Sheng, LAN Sheng
Chin. Phys. Lett. 2005, 22 (11): 2847-2850 .  
Abstract   PDF(pc) (226KB) ( 452 )
We investigate the unidirectional transmission behaviour of an asymmetrically confined photonic crystal (PC) defect with Kerr nonlinearity. Basically, the unidirectional transmission originates from the strong dependence of the threshold input power for the sharp increase of transmission on the launch direction of the input wave. This can be well explained in the framework of the coupled mode theory. Our theoretical analysis reveals the existence of an upper limit for the transmission contrast when such a single PC defect is employed. This is supported by the simulation results based on the nonlinear finite-difference time-domain technique.
Focusing Properties of Fractal Zone Plates with Variable Lacunarity: Experimental Studies Based on Liquid Crystal on Silicon
DAI Hai-Tao, WANG Xin, XU Ke-Shu
Chin. Phys. Lett. 2005, 22 (11): 2851-2854 .  
Abstract   PDF(pc) (233KB) ( 536 )
The focusing properties of fractal zone plates (FZPs) with different structure parameters are studied experimentally. The axial irradiance of FZPs is deduced at n=4. The experimental results are in good agreement with the theoretical prediction. A method to fabricate FZPs with variable structure parameters is mentioned, and the liquid-crystal-on-silicon device is used to implement this experiment. The experimental results indicate that the focal depth of lower order FZPs is larger than that of higher order FZPs.
A Kind of Low Loss Birefringent Photonic Crystal Fibre with Increasing-Diameter Air-Holes
LI Shu-Guang, LIU Xiao-Dong, ZHOU Gui-Yao, HOU Lan-Tian
Chin. Phys. Lett. 2005, 22 (11): 2855-2857 .  
Abstract   PDF(pc) (210KB) ( 493 )
We report the results of our investigation on the loss property of a birefringent photonic crystal fibre (PCF) based on a particular periodic arrangement of air-holes and pure silica. The structure of the birefringent PCF, whose air-hole diameter in one ring is always larger than the next inner ring, presents an obviously low confinement loss than the one whose air-hole (except those on the horizontal line) diameter is constant. It is shown from numerical results that a four-ring PCF with birefringence B=5×10-4 and fast axis confinement loss of 4.5×10-3dB/km at wavelength of 1.55μm can be designed.
Simulations of Effect of High-Index Materials on Highly Birefringent Photonic Crystal Fibres
ZHANG Chun-Shu, KAI Gui-Yun, WANG Zhi, LIU Yan-Ge, SUN Ting-Ting, LIU Jian-Guo, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2005, 22 (11): 2858-2861 .  
Abstract   PDF(pc) (232KB) ( 750 )
Novel highly birefringent photonic bandgap fibres (PBGFs) are obtained by filling of a high index material in the air holes of total internal reflection birefringent photonic crystal fibres. The effect of the filling high index material on the transmission characteristics has been theoretically investigated. The photonic bandgap has been achieved by using plane-wave method. Moreover, the phase and group modal birefringence have been studied by a full-vector finite-element method. Numerical results show that very high group and phase modal birefringence with magnitude of order of 10-2 and 10-3 has been respectively acquired, which is much higher than those of the non-filled fibres. Furthermore, strong coupling between surface modes and the fundamental modes has been found in the bandgap of the birefringent PBGFs, whose effect on the birefringence and confinement loss has also been discussed.
Gain and Noise Figure of a Double-Pass Waveguide Amplifier Based on Er/Yb-Doped Phosphate Glass
JIN Guo-Liang, SHAO Gong-Wang, Mu Huan, HU Li-Li, LI Qu
Chin. Phys. Lett. 2005, 22 (11): 2862-2864 .  
Abstract   PDF(pc) (200KB) ( 456 )
A waveguide amplifier is fabricated by Ag+--Na+ two-step ion exchange on Er/Yb-doped phosphate glass. The spectroscopic performance of glass and the properties of channel waveguide are characterized. A double-pass configuration is adopted to measure the gain and noise figure (NF) of the waveguide amplifier, and the comparison of gain and NF for the single and double-pass configuration of the waveguide amplifier is presented. The results show that the double-pass configuration can make the gain increase from 8.8dB (net gain 2.2dB/cm) of the single-pass one to 14.6dB (net gain 3.65dB/cm) for small input power at 1534nm, and the NF are all lower than 5.5dB for both the configurations.
A Novel Design of Grating Couplers for Efficient Broadband Coupling between Silicon-on-Insulator Nanophotonic Waveguides and Fibres
YU He-Jun, YU Jin-Zhong
Chin. Phys. Lett. 2005, 22 (11): 2865-2868 .  
Abstract   PDF(pc) (220KB) ( 555 )
A novel design of out-of-plane grating couplers is proposed for coupling between silicon-on-insulator nanophotonic waveguides and single-mode fibres. The coupler with the first-order diffraction coupling to the optical fibre is actually a second-order reflected grating with two times of period of the first-order grating. To enhance outcoupled power, a back hole is designed to form in the silicon substrate and a kind of metals is placed on the top acting as a reflection layer. The coupler is optimized using coupled-mode-based simulations, showing that the coupling efficiency to and from tapered optical fibre can be as high as 85% with 1dB bandwidth about 23nm.
An Analytical Method for Calculating P-SV Acoustical Field Excited by a Piezoelectric Strip with Finite Width and Thickness
ZHANG Bi-Xing, WANG Cheng-Hao, Anders Boströ, m
Chin. Phys. Lett. 2005, 22 (11): 2869-2872 .  
Abstract   PDF(pc) (231KB) ( 408 )
A piezoelectric strip with finite width and thickness is placed on top of an isotropic elastic half-space. Acoustical field can be excited when a voltage is across the piezoelectric strip. An analytical method is presented to calculate the acoustical field by the dynamics characteristics of the piezoelectric strip. Considering the piezoelectric strip as an anisotropic material of the 6mm-type crystal system, we study the two-dimensional P-SV acoustical fields inside the piezoelectric strip and the isotropic half-space. The displacement and stress distributions are analysed thoroughly. The effects of the width and thickness of the piezoelectric strip and other parameters on the acoustical field are also analysed.
Simulation of Blood Flow at Vessel Bifurcation by Lattice Boltzmann Method
KANG Xiu-Ying, LIU Da-He, ZHOU Jing, JIN Yong-Juan
Chin. Phys. Lett. 2005, 22 (11): 2873-2876 .  
Abstract   PDF(pc) (257KB) ( 715 )
The application of the lattice Boltzmann method to the large vessel bifurcation blood flow is investigated in a wide range of Reynolds numbers. The velocity, shear stress and pressure distributions at the bifurcation are presented in detail. The flow separation zones revealed with increase of Reynolds number are located in the areas of the daughter branches distal to the outer corners of the bifurcation where some deposition of particular blood components might occur to form arteriosclerosis. The results also demonstrate that the lattice Boltzmann method is adaptive to simulating the flow in larger vessels under a high Reynolds number.
Multi-Scale Analysis of Energy Transfer in Scalar Turbulence
FANG Le, CUI Gui-Xiang, XU Chun-Xiao, ZHANG Zhao-Shun
Chin. Phys. Lett. 2005, 22 (11): 2877-2880 .  
Abstract   PDF(pc) (217KB) ( 456 )
The energy transfer of homogeneous scalar turbulence is studied numerically by triad interaction in spectral space. The different transfer properties between turbulent kinetic energy and turbulent scalar energy reveal that non-local energy transfer exists as important as the local energy transfer in scalar turbulence. The non-local energy transfer of scalar turbulence results from non-local triad interaction. As a result there will be longer inertia-convective range in scalar turbulence than the inertial subrange in turbulent kinetic transfer at Reλ= Peλ. The non-local transfer of turbulent scalar energy generates more energy transfer into dissipation range. The discovery of non-local transfer of turbulent scalar energy indicates that this phenomenon should be concerned carefully in numerical scheme and subgrid modelling of direct numerical simulation or large eddy simulation scalar turbulence.
Dynamic Bubble Behaviour during Microscale Subcooled Boiling
WANG Hao, PENG Xiao-Feng, David M. Christopher
Chin. Phys. Lett. 2005, 22 (11): 2881-2884 .  
Abstract   PDF(pc) (211KB) ( 469 )
Bubble cycles, including initiation, growth and departure, are the physical basis of nucleate boiling. The present investigation, however, reveals unusual bubble motions during subcooled nucleate boiling on microwires 25 or 100μm in diameter. Two types of bubble motions, bubble sweeping and bubble return, are observed in the experiments. Bubble sweeping describes a bubble moving back and forth along the wire, which is motion parallel to the wire. Bubble return is the bubble moving back to the wire after it has detached or leaping above the wire. Theoretical analyses and numerical simulations are conducted to investigate the driving mechanisms for both bubble sweeping and return. Marangoni flow from warm to cool regions along the bubble interface is found to produce the shear stresses needed to drive these unusual bubble movements.
Reduce of Threshold of Laser Inducing Breakdown in Atmosphere by Introducing an Electric Spark
ZHANG Xian-Bin, SHI Wei, LI Hua
Chin. Phys. Lett. 2005, 22 (11): 2885-2887 .  
Abstract   PDF(pc) (191KB) ( 483 )
We report laser-generated plasmas in atmosphere with electrical spark generated by a synchronization circuit. The breakdown thresholds under the conditions that the electrical spark is used and not used are compared. The breakdown threshold has a distinct decrease after the electrical spark is used. Breakdown thresholds as a function of atmosphere pressure have also been measured at laser wavelengths 532nm and 1064nm for the laser pulse width of 15ns. We also discuss the principle and performances of the ionized atmosphere by Nd:YAG laser under the condition of electrical spark introduction. Multiphoton ionization and cascade ionization play important roles in the whole process of atmosphere ionization. The free electron induced by electrical spark can supply the initialization free electron number for multiphoton ionization and cascade ionization. A model for breakdown in atmosphere, which is in good agreement with the experimental results, is described.
Simulation of Chemical Processes in Repetitively Pulsed Atmospheric Plasmas
FANG Tong-Zhen, OUYANG Jian-Ming, WANG Long
Chin. Phys. Lett. 2005, 22 (11): 2888-2891 .  
Abstract   PDF(pc) (211KB) ( 515 )
We numerically simulate the temporal evolutions of the densities of charged and neutral species in a plasma generated with repetitively pulsed discharge in atmospheric environment at 60km altitude. The particles are divided into three categories according to their temporal behaviour. All charged particles exhibit oscillations with the same frequency as the driven power. Densities of elements O, N and H increase in a long-time scale. Densities of O3 and NO increase firstly and then decrease at t=0.65s; in particular, they have very similar density evolution profiles to each other.
Striations in Plasma Display Panel
OUYANG Ji-Ting, CAO Jing, MIAO Jin-Song
Chin. Phys. Lett. 2005, 22 (11): 2892-2894 .  
Abstract   PDF(pc) (190KB) ( 515 )
The phenomenon of striation has been investigated experimentally in a macroscopic ac-plasma display panel (PDP). The relationship between the characteristics of striation and the operation conditions including voltage, frequency, rib, and electrode configuration, etc is obtained experimentally. The origin of the striations is considered to be the ionization waves in the transient positive column near the dielectric surface in the anode area during the discharge, and the perturbation is caused by resonance kinetic effects in inert gas.

Reduction of Ordering Temperature of FePt--Al2O3 Thin Films by N2 Addition During Sputtering
CAO Jiang-Wei, N. Katayama, YANG Zheng, WEI Fu-Lin, M. Matsumoto, A. Morisako, LIU Xiao-Xi, S. Takei
Chin. Phys. Lett. 2005, 22 (11): 2899-2902 .  
Abstract   PDF(pc) (242KB) ( 518 )
We investigate the effect of N2 addition during sputtering on the microstructure and magnetic properties of FePt--Al2O3 thin films. The texture of FePt phase in FePt--Al2O3 thin films changes from (111) to a more random orientation by N2 addition during sputtering. The ordering temperature of FePt phase reduces about 100°C with appropriate N2 partial pressure. A larger coercivity of 6.0×105A/m is obtained with N2 partial pressure about 15%. Structural analysis reveals that a small quantity of Fe3N phase forms during sputtering and the release of N atoms during the post annealing induces a large number of vacancies in the films, which benefits to the transformation of FePt phase from fcc to fct.
Release Behaviour of Shock Loaded LY12 Aluminium Alloy
YAN Min, DAI Lan-Hong, SHEN Le-Tian
Chin. Phys. Lett. 2005, 22 (11): 2903-2905 .  
Abstract   PDF(pc) (207KB) ( 412 )
By making use of a light gas gun, a specially designed target is impacted by the LY12 flyer, and the pressure is taken in the range of 0.6--3GPa. Based on the stress profiles measured in the buffer materials by manganese gauges, the Hugoniot curve and release curves of LY12 aluminium alloy are obtained. Meanwhile, the release curves from different initial shocked states are described in both the pressure-particle velocity plane and the pressure-specific volume plane.
Probing Cu Diffusion Barrier Layers on Porous Low-Dielectric-Constant Films by Posireonium Annihilation Lifetime Spectroscopy
HU Yi-Fan, SUN Jia-Ning, Gidley D.W.
Chin. Phys. Lett. 2005, 22 (11): 2906-2909 .  
Abstract   PDF(pc) (210KB) ( 448 )
Two kinds of Cu diffusion barrier layers, sealed films and capped films, on nanoporous low-dielectric constant films are investigated by positronium annihilation lifetime spectroscopy (PALS). We have found that the minimum thickness of Ta to form an effective diffusion barrier is affected by the pore size. The films with large pores require thick barrier layers to form effective diffusion barriers. In addition, a possible ultra-thin diffusion barrier, i.e. a plasma-induced densification layer, has also been investigated. The PALS data confirm that a porous low-dielectric-constant thin film can be shrunk by exposure to plasma. This shrinkage is confined to a surface layer of collapsed pores and forms a dense layer. The dense layer tends to behave as Ps (positronium) diffusion barriers. Indeed, the controlled thin ``skin'' layer could prevent Cu diffusion into the underlying dielectrics.


Exchange Coupling and Stability of SmCo7-xHfx
ZHANG Chang-Wen, LI Hua, DONG Jian-Min, WANG Yong-Juan, PAN Feng-Chun, GUO Yong-Quan, LI Wei
Chin. Phys. Lett. 2005, 22 (11): 2910-2913 .  
Abstract   PDF(pc) (222KB) ( 545 )
Electronic structure of SmCo7-xHfx compound is calculated by using the multi-scattering Xα method. It is shown that a few of electrons can transfer to the Sm 5d orbital due to orbital hybridization between Sm and Co atoms. The 3d-5d coupling is stronger, which is the main reason to result in the long-range ferromagnetic order between Sm and Co atoms in SmCo7-xHfx. According to the Stoner criterion, the result of spin-unpolarized calculation for the Sm5Co32Hf2 cluster could lead to a better understanding of why the ferromagnetic SmCo7-xHfx is a stable phase. For the Sm5Co32Hf2 cluster the Fermi level is situated at the overall maximum of the density of states. Moreover the cluster wavefunctions at EF are antibonding and hence highly localized in real space, which would lead to a large value for the cluster Stoner integral. Thus a rationalization for the magnetic stability of SmCo7-xHfx has been obtained.
Two-Site Holstein Model: a Variational Wavefunction Analysis
REN Qing-Bao, CHEN Qing-Hu
Chin. Phys. Lett. 2005, 22 (11): 2914-2917 .  
Abstract   PDF(pc) (355KB) ( 604 )
A novel variational approach is proposed to calculate the ground-state (GS) properties of the two-site Holstein model. By the linear superposition of two coherent states, which simulate the behaviour of the weak and strong coupling limits, we can obtain very accurate GS energy for arbitrary electron--phonon coupling constant. Other GS properties are also discussed. Moreover, the present concise approach is hopefully generalized to many other Holstein models.
Persistent Current in a Mesoscopic Ring Side-Attached with a Quantum Dot
ZHOU Bo, CHEN Xiong-Wen, LI Tie, NIE Yu-Mei, WU Shao-Quan
Chin. Phys. Lett. 2005, 22 (11): 2918-2921 .  
Abstract   PDF(pc) (245KB) ( 507 )
We theoretically investigate properties of the ground state of a closed dot-ring system with a magnetic flux in the Kondo regime by means of a tight-banding Anderson Hamiltonian, using the Slave--Boson mean-field approach. The persistent current shows interesting dependences on the parity and on the size of the system. The signature of Kondo resonance at xik/L=0.15 is expected to be observed experimentally in the future. With the intensity of the coupling tD changes from weak to strong, the properties of the system changes largely, which are different from the in-line one because of the attached dot.
Resonant Photon-Assisted Structure of Conductance through a Quantum Wire
LIAO Wen-Hu, ZHOU Guang-Hui
Chin. Phys. Lett. 2005, 22 (11): 2922-2925 .  
Abstract   PDF(pc) (198KB) ( 565 )
We investigate theoretically the electron transport properties of a two-sublevel quantum wire irradiated by a strong laser field resonant with the quasiparticle transition at low temperatures. Using the method of the Keldysh equation of motion for nonequilibrium Green function, we examine the time-averaged conductance for the system with photon polarization parallel and perpendicular to the tunnelling current direction, respectively. We demonstrate that, by analysing some numerical examples, a feature of absolute negative conductance appears in the parallel case, while the conductance shows a symmetry distributed peaks in the perpendicular case.

Investigation on Nonradiative Decay of the Er3+ 4I13/24I15/2 Transition in Different Tellurite Glass Matrix
YU Chun-Lei, DAI Shi-Xun, ZHOU Gang, ZHANG Jun-Jie, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2005, 22 (11): 2926-2928 .  
Abstract   PDF(pc) (221KB) ( 446 )
Three kinds of Er3-doped tellurite glasses with different hydroxyl groups are prepared by the conventional melt-quenching method. Infrared spectra are measured to estimate the exact content of OH- groups in samples. The maximum phonon energy in glasses are obtained by measuring the Raman scattering spectra. The strength parameters Ω5 (t=2,4,6) for all the samples are calculated and compared. The nonradiative decay rate of the Er3+ 4I13/24I15/2 transition are calculated for the glass samples with different phonon energy and OH- group contents. Finally, the effect of OH- groups on fluorescence decay rate of Er3+ is analysed, the constant KOH-Er of TWN, TZPL and TZL glasses are calculated to be 9.2×10-19cm4s-1, 5.9×10-19cm4s-1, and 3.5×10-19cm4s-1, respectively.
Characteristics of Sn-Doped Ge2Sb2Te5 Films Used for Phase-Change Memory
XU Cheng, LIU Bo, SONG Zhi-Tang, FENG Song-Lin, CHEN Bomy
Chin. Phys. Lett. 2005, 22 (11): 2929-2932 .  
Abstract   PDF(pc) (217KB) ( 668 )
Sn-doped Ge2Sb2Te5 thin films deposited on Si(100)/SiO2 substrates by rf magnetron sputtering are investigated by a differential scanning calorimeter, x-ray diffraction and sheet resistance measurement. The crystallization temperatures of the 3.58 at.%, 6.92 at.% and 10.04 at.% Sn-doped Ge2Sb2Te5 thin films have decreases of 5.3, 6.1 and 0.9 °C, respectively, which is beneficial to reduce the switching current for the amorphous-to-crystalline phase transition. Due to Sn-doping, the sheet resistance of crystalline Ge2Sb2Te5 thin films increases about 2--10 times, which may be useful to reduce the switching current for the amorphous-to-crystalline phase change. In addition, an obvious decreasing dispersibility for the sheet resistance of Sn-doped Ge2Sb2Te5 thin films in the crystalline state has been observed, which can play an important role in minimizing resistance difference for the phase-change memory cell element arrays.
Heat and Mass Transfer Investigation of Hydrocarbon Droplet Evaporation under Rotatory Movement
J. Dgheim, B. Zeghmati
Chin. Phys. Lett. 2005, 22 (11): 2933-2935 .  
Abstract   PDF(pc) (199KB) ( 525 )
The steady-state boundary layer equations of a rotatory movement around hydrocarbon droplets saturated of pure fuel are numerically solved. The transfer equations are schemed by using an implicit finite difference method. The system of algebraic equations is solved by using the Thomas algorithm. The model is compared to the Kreith one and a good agreement is observed between both models. The dimensionless physical parameters of the evaporation phenomena of droplet in rotation are calculated and presented under the effect of the convection.
Current-Induced Resistive Effect in Cu/MgO/La0.9Sr0.1 MnO3 Trilayers on SrTiO3 (001) Substrates
FENG Jia-Feng, ZHAO Kun, HUANG Yan-Hong, ZHAO Jian-Gao, Lü Hui-Bin, HE Meng, HAN Xiu-Feng, ZHAN Wen-Shan
Chin. Phys. Lett. 2005, 22 (11): 2936-2939 .  
Abstract   PDF(pc) (246KB) ( 385 )
Cu/MgO/La0.9Sr0.1MnO3 pillars are fabricated on SrTiO3 (001) substrates by the micro-fabrication patterning processes. Their electric transport properties have been measured in the temperature range from the temperature smaller than the Curie one to 300K. At 125K there emerges abrupt breaks of output voltage in voltage--current (V--I) curves, corresponding to switching in resistance to metastable states, and finally two closed loops are formed with double threshold biases. Around room temperature the V--I characteristics are non-ohmic and show some gradual hysteresis when sweeping the current in a round-trip scan. A large current-induced resistive change ΔR/R0, ~ -63.2%, is obtained under a current density of 1.0×104 Acm-2. Especially, ΔR0depends linearly on the applied current and is independent of the applied magnetic field. The current-induced resistive effect should be of interest for various applications such as switching and field effect devices.

Intergranular Tunnelling and Field-Induced Percolation Fluctuation of Granular Composites (La1-zAgzMnO3)/(MnO2/Mn2O3)
ZHANG Ning, BAO Jian-Chun, LI Gang, GENG Tao, CHEN Ji-Kang
Chin. Phys. Lett. 2005, 22 (11): 2940-2943 .  
Abstract   PDF(pc) (245KB) ( 508 )
We investigate the giant magnetoresistance of composites (La1-zAgzMnO3)1-y(MnO2/Mn2O3)y. The magnetoresistive property of the composites shows the characteristics of intergranular tunnelling. A conductivity leap has been observed around y=0.7. The composite (La0.926Ag0.074MnO3)0.698(MnO2/Mn2O3)0.302 has been found to show the greatest magnetoresistance in the samples. Its room-temperature MR ratio reaches 24% under a field of 1.8T. These phenomena suggest a percolation transformation and a kind of field-induced fluctuation in percolation in the samples investigated.
Hydrodynamic Properties of Fe3O4 Kerosene-Based Ferrofluids with Narrow Particle Size Distribution
ZHANG Jian-Hui, XU Xue-Fei, SI Ming-Su, ZHOU You-He, XUE De-Sheng
Chin. Phys. Lett. 2005, 22 (11): 2944-2946 .  
Abstract   PDF(pc) (215KB) ( 920 )
We investigate the hydrodynamic properties of Fe3O4 kerosene-based ferrofluids with narrow particle size distribution. The ferrofluids are synthesized by improving chemical coprecipitation technique. A narrow distribution of 8.6--10.8nm particle sizes is obtained from the magnetization curve with the free-form model based on the Bayesian inference theory. The fitting result is consistent with average particle size obtained from x-ray diffraction. With the increase of applied magnetic field and magnetic particle concentration, apparent viscosity of ferrofluids increases. At concentration 4.04%, the type of flow for the ferrofluid transforms from Newtonian to Bingham plastic fluid as the applied magnetic field increases.
Dielectric Properties of Multilayered Ba0.5Sr0.5TiO3 Thin Films Deposited on ITO-Coated Corning 1737 Glass by rf Magnetron Sputtering
LIN Ming-Tong, CHEN Guo-Rong, YANG Yun-Xia, XIAO Tian, XU Yi, LOU Jun-Hui, CHEN Chen-Xi
Chin. Phys. Lett. 2005, 22 (11): 2947-2949 .  
Abstract   PDF(pc) (203KB) ( 571 )
A new stacking method via variation of substrate temperature in rf magnetron sputter is used to fabricate polycrystalline/polycrystalline Ba0.5Sr0.5TiO3 thin films with higher dielectric constant, higher breakdown strength and lower leakage current densities than those prepared by a conventional deposition method. The improved figure of merit G (ε0εrEb) of the Ba0.5Sr0.5TiO3 thin films implies that they are a feasible insulation layer for thin film electroluminescent devices.
Laser Molecular Beam Epitaxy Growth of BaTiO3 in Seven Thousands of Unit-Cell Layers
HUANG Yan-Hong, HE Meng, ZHAO Kun, TIAN Huan-Fang, Lü Hui-Bin, JIN Kui-Juan, CHEN Zheng-Hao, ZHOU Yue-Liang, LI Jian-Qi, YANG Guo-Zhen
Chin. Phys. Lett. 2005, 22 (11): 2950-2951 .  
Abstract   PDF(pc) (217KB) ( 455 )
BaTiO3 thin films in seven thousands of unit-cell layers hav been successfully fabricated on SrTiO3 (001) substrates by laser molecular beam epitaxy. The fine streak pattern and the undamping intensity oscillation of reflection high-energy electron diffraction indicate that the BaTiO3 film was layer-by-layer epitaxial growth. The measurements of scanning electron microscopy and atomic force microscopy show that surfaces of the BaTiO3 thin film are atomically smooth. The measurements of x-ray diffraction and transmission electron microscopy, as well as selected-area electron diffraction reveal that the BaTiO3 thin film is a c-oriented epitaxial crystalline structure.
Electron--Phonon Interactions on the Optical Kerr Effect in a Quantum Disc
GUO Kang-Xian
Chin. Phys. Lett. 2005, 22 (11): 2953-2956 .  
Abstract   PDF(pc) (227KB) ( 627 )
The optical Kerr effect in a quantum disc is investigated with the density-matrix approach, most emphasis is devoted to the electron--phonon interactions on the optical Kerr effect. The numerical results are presented with characteristic parameters of a GaAs quantum disc. It is shown that the optical Kerr effect increases as the disc thickness D decreases. LO-phonons impose greater influence on the optical Kerr effect than SO-phonons. The smaller the disc thickness D, the sharper the peak, and the larger the peak intensity. When the disc thickness is greater than 30, the peak will disappear gradually.
Direct Observation of NN Pairs Transfer in GaP1-xNx (x =0.12%)
LU Yi-Jun, GAO Yu-Lin, ZHENG Jian-Sheng, ZHANG Yong, MASCARENHAS A., XIN H.P., TU C. W.
Chin. Phys. Lett. 2005, 22 (11): 2957-2959 .  
Abstract   PDF(pc) (216KB) ( 350 )
Time-resolved photoluminescence (TRPL) was applied to investigate the transient process in GaP1-xNx (x=0.12%) alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The NN4 pair, either not present or only a small obscure peak under a proper excitation condition in the steady-state photoluminescence spectrum, is well resolved by TRPL.
Second-Order Correlation Function of the Photon Emission from a Single Quantum Dot
LI Yao-Yi, CHENG Mu-Tian, ZHOU Hui-Jun, LIU Shao-Ding, WANG Qu-Quan
Chin. Phys. Lett. 2005, 22 (11): 2960-2962 .  
Abstract   PDF(pc) (215KB) ( 2051 )
The photon correlation of photon emission from a single quantum dot with cw excitation and pulsed excitation is investigated in details. To calculate the second-order correlation function for optical pumping, we deduce rate equations with a simplified two-level model under cw excitation and present the master equation approach in the interaction picture to the study of evolution of a three-level system under pulsed excitation. In addition, we report photon correlation measurements on a single self-assembled In0.5Ga0.5As quantum dot, which show strong antibunching behaviour under both the conditions of cw and pulsed excitations. The calculated results are in agreement with the experimental measurements.
Exciton and Biexciton Binding Energies in Rectangular Quantum Dots
LIU Yong-Hui, KONG Xiao-Jun
Chin. Phys. Lett. 2005, 22 (11): 2963-2965 .  
Abstract   PDF(pc) (200KB) ( 521 )
In the effective mass approximation, using the variational technology and a method of expanding the wavefunctions of exciton in terms of the eigenfunctions of the noninteracting electron-hole system, we calculate the exciton and biexciton ground state binding energies for rectangular quantum dots (QDs). In the calculation, a three-dimensional Fourier expansion of Coulomb potential is used to remove the numerical difficulty with the 1/r singularity, and it considerably reduces the computational effort. Our results agree fairly well with the previous results. It is found that the binding energies are highly correlated to the size of QDs. The quantum confinement effect of spherical QDs about biexciton is obviously larger than that of rectangular QDs when the well width is narrower than 2.0αB.
In Situ Observation of Cell-to-Dendrite Transition
PAN Xiu-Hong, HONG Yong, JIN Wei-Qing
Chin. Phys. Lett. 2005, 22 (11): 2966-2968 .  
Abstract   PDF(pc) (210KB) ( 873 )
The cell-to-dendrite transition of succinonitrile melt suspended on a loop-shaped Pt heater is observed in real time by a differential interference microscope coupled with Schlieren technique. The transition is divided into two parts: a dendrite coalition process and a subsequent dendrite elimination process. Firstly the dendrites from the same cell are united into a single dendrite. Secondly the competitive growth of dendrites from different cells leads to the elimination of dendrites. The two processes can be understood when involving crystallographic orientation. In addition, the tip velocity and primary spacing of a cell/dendrite are also measured. It turns out that the primary spacing has a significant jump, whereas the growth velocity has no abrupt change during the cell-to-dendrite transition.
Effect of Gas Pressure on Nanocrystalline Diamond Films Prepared by Electron-Assisted Chemical Vapour Deposition
WU Nan-Chun, XIA Yi-Ben, TAN Shou-Hong, WANG Lin-Jun
Chin. Phys. Lett. 2005, 22 (11): 2969-2972 .  
Abstract   PDF(pc) (227KB) ( 524 )
With use of electron-assisted chemical vapour deposition (EACVD) technology, nanocrystalline diamond films are successfully deposited on an α-SiC single phase ceramics substrate by means of reduction of the reactive gas pressure. The structure and surface morphology of the deposited films are characterized by Raman spectroscopy, x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The results examined by FE-SEM and AFM show that when the gas pressure was reduced to 0.5--1kPa, the surface grain size and surface roughness of the diamond film are decreased greatly to 18--32nm and 34--58nm respectively. The grain sizes estimated from full with at half maximum of (111) XRD peak by the Scherrer formula are 6--28nm. However, too high secondary nucleation rate may result in pores and defects in the deposited films. Only at suitable gas pressure (1 kPa) to deposit films can we obtain densification and better quality nanocrystalline films.

Structure and Photoluminescence of Polycrystalline MgxZn1-xO Films
ZHAO Yi-Kun, LIAN Jie, WANG Qing-Pu, ZHANG Xi-Jian, ZHANG Sa-Sa, WANG Gong-Tang
Chin. Phys. Lett. 2005, 22 (11): 2973-2976 .  
Abstract   PDF(pc) (222KB) ( 609 )
Different photoluminescence (PL) spectra are observed for rf magnetron sputtered polycrystalline Mg0.25Zn0.75O and Mg0.37Zn0.63O films on silicon substrates when excited by different wavelengths. When the excitation wavelength is 280nm, a UV emission peak at 370nm and a blue peak at 462nm are generated for the Mg0.25Zn0.75O film, and those two peaks for the Mg0.37Zn0.63O film shift to 366nm and 466nm, respectively. The wavelengths of the PL peaks are related to the excitation wavelength. The stronger peak is obtained in the blue band due to a large number of oxygen vacancies caused by excess Zn and Mg atoms, while the weaker peak is obtained in the ultraviolet band.
Growth and Characterization of Cu2O Films Made by Rapid Thermal Oxidation Technique
Raid A. Ismail, Ibrahim Ramadhan, Aseel Mustafa
Chin. Phys. Lett. 2005, 22 (11): 2977-2979 .  
Abstract   PDF(pc) (188KB) ( 2792 )
Cu2O thin films with (111) preferred orientation have been grown on glass and Cu substrates by rapid thermal oxidation of Cu at 500°C for 45s. The optical band gap energy was determined by spectral data of transmittance and absorbance to be 2.04eV. The electrical conductivity of grown films was measured around (1.1×10-5Ω-1cm-1) at 300K. Thermoelectric power measurements of the film were carried out. Furthermore, the properties of these films are compared with properties of Cu2O obtained by other methods.
Monte Carlo Simulation of Kinesin Movement with a Lattice Model
WANG Hong, DOU Shuo-Xing, WANG Peng-Ye
Chin. Phys. Lett. 2005, 22 (11): 2980-2982 .  
Abstract   PDF(pc) (470KB) ( 924 )
Kinesin is a processive double-headed molecular motor that moves along a microtubule by taking about 8nm steps. It generally hydrolyzes one ATP molecule for taking each forward step. The processive movement of the kinesin molecular motors is numerically simulated with a lattice model. The motors are considered as Brownian particles and the ATPase processes of both heads are taken into account. The Monte Carlo simulation results agree well with recent experimental observations, especially on the relation of velocity versus ATP and ADP concentrations.
Detectivity of Fe Kα Lines in Gamma-Ray Bursts by Cerenkov Line Mechanism
SU Jie, JIN Sheng-Zhen
Chin. Phys. Lett. 2005, 22 (11): 2983-2986 .  
Abstract   PDF(pc) (236KB) ( 989 )
The Fe Kα lines in gamma-ray bursts (GRBs) produced with the Cerenkov line mechanism are studied. We theoretically predict the Fe Kα line luminosities in both the early (before 1 hour) and late (~ 1day) afterglows. Assuming about 200GRBs could be detected by Swift per year, we sampled the redshift of these GRBs using the Monte Carlo method according to the GRB formation rate derived from the statistical correlation between the spectral peak energy and the peak luminosity of GRBs. Then we obtain the Fe Kα line flux distributions of the simulated GRB sample in the early and late phases. The simulated results show that the iron line flux is relatively low, so the line detection would be still a rare event at present. In addition, our results suggest that the iron lines from GRBs could be detected in the high redshift: z~3 for the early phase and z~6 for the late phase. Therefore, it is possible that the identification of Fe Kα lines in GRBs provides a tool to directly measure redshift and to study the high-redshift GRBs in the Swift era.
72 articles