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Volume 24 Issue 1
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Original Articles
New Doubly Periodic Waves of the (2+1)-Dimensional Double Sine-Gordon Equation
HU Heng-Chun, ZHU Hai-Dong
Chin. Phys. Lett. 2007, 24 (1): 1-4 .  
Abstract   PDF(pc) (394KB) ( 1346 )
New exact solutions of the (2+1)-dimensional double sine-Gordon equation are studied by introducing the modified mapping relations between the cubic nonlinear Klein--Gordon system and double sine-Gordon equation. Two arbitrary functions are included into the Jacobi elliptic function solutions. New doubly periodic wave solutions are obtained and displayed graphically by proper selections of the arbitrary functions.
He--McKellar--Wilkens Effect in Noncommutative Space
WANG Jian-Hua, LI Kang,
Chin. Phys. Lett. 2007, 24 (1): 5-7 .  
Abstract   PDF(pc) (198KB) ( 690 )
The He--McKellar--Wilkens (HMW) effect in non-commutative (NC) space is studied. By solving the Dirac equations on NC space, we obtain topological HMW phase in NC space where the additional terms related to the space non-commutativity are given explicitly.
Entanglement in the Ground State of an Isotropic Three-Qubit Transverse XY Chain with Energy Current
LIU Dan, ZHANG Yong, LIU Yang, LONG Gui-Lu,
Chin. Phys. Lett. 2007, 24 (1): 8-10 .  
Abstract   PDF(pc) (206KB) ( 744 )
The ground state entanglement in an isotropic three-qubit transverse XY chain with energy current is analysed. A quantum phase transition from a no-energy-current phase to energy-current phase is found when the magnetic field changes. It has also been found that the ground state changes in company with the quantum phase transition.

Dense Coding with Multi-Atom Entanglement Channel in Cavity QED
WANG Xin-Wen, LIU Xiang, WANG Zhi-Yong
Chin. Phys. Lett. 2007, 24 (1): 11-14 .  
Abstract   PDF(pc) (244KB) ( 785 )
Dense coding of multi-atom entangled states in cavity QED is studied. If the quantum channel is generalized GHZ states, dense coding can be directly realized in a simply way. As for the partially entangled pure states, we propose a feasible protocol for entanglement concentration, and the efficiency of information transmitted is calculated. The schemes are insensitive to the cavity decay and the field state, due to the fact that the interaction here is a large-detuned one between atoms and the cavity.
Improvement of Security of Three-Party Quantum Secure Direct Communication Based on GHZ States
MAN Zhong-Xiao, XIA Yun-Jie
Chin. Phys. Lett. 2007, 24 (1): 15-18 .  
Abstract   PDF(pc) (209KB) ( 680 )
A protocol for three-party quantum secure direct communication based on Greenberger--Horne--Zeilinger (GHZ) states was recently proposed by Jin it et al. [Phys. Lett. A 354(2006)67] By analysing the protocol we find some security loopholes, e.g. one bit of secret messages of a party (Alice in the original paper) can always be leaked straight to the public without any eavesdropping. These problems suggested previously are discussed and possible solutions are presented to improve the security of the original protocol.
Quantum Bidirectional Secure Direct Communication via Entanglement Swapping
CHEN Yan, MAN Zhong-Xiao, XIA Yun-Jie
Chin. Phys. Lett. 2007, 24 (1): 19-22 .  
Abstract   PDF(pc) (213KB) ( 586 )
In light of a quantum secure direct communication (QSDC) scheme using entanglement swapping [Chin. Phys. Lett. 22(2005)18], by introducing additional local operations for encoding, we propose a bidirectional QSDC (BQSDC) protocol, in which two legitimate users can simultaneously exchange their respective messages. The rule for the users to retrieve his/her partner’s messages is derived explicitly in the most general case. Eve’s commonly used attack method has been discussed and can be detected with the security checking process.
Multiparty Quantum Remote Secret Conference
LI Xi-Han, LI Chun-Yan, DENG Fu-Guo, , ZHOU Ping, LIANG Yu-Jie, ZHOU Hong-Yu,
Chin. Phys. Lett. 2007, 24 (1): 23-26 .  
Abstract   PDF(pc) (224KB) ( 503 )
We present two schemes for multiparty quantum remote secret conference in which each legitimate conferee can read out securely the secret message announced by another, but a vicious eavesdropper can get nothing about it. The first one is based on the same key shared efficiently and securely by all the parties with reenberger--Horne--Zeilinger (GHZ) states, and each conferee sends his secret message to the others with one-time pad crypto-system. The other one is based on quantum encryption with a quantum key, a sequence of GHZ states shared among all the conferees and used repeatedly after confirming their security. Both these schemes are optimal as their intrinsic efficiency for qubits approaches the maximal value.
Demonstration of a Sagnac-Type Cold Atom Interferometer with Stimulated Raman Transitions
WANG Ping, , LI Run-Bing, , YAN Hui, , WANG Jin, ZHAN Ming-Sheng,
Chin. Phys. Lett. 2007, 24 (1): 27-30 .  
Abstract   PDF(pc) (250KB) ( 639 )
Cold-matter-wave Sagnac interferometers possess many advantages over their thermal atomic beam counterparts when they are used as precise inertial sensors. We report a realization of a Sagnac-type interferometer with cold atoms. Cold rubidium atoms are prepared in a magneto-optical trap and are pushed by resonant laser pulse to form slow atomic beam. In the interference region, atomic wave packets are coherently manipulated using π/2-π-π/2 Raman pulse sequences. Interference fringes with maximum contrast of 37% are observed experimentally.
Hyperbolic Bending of Vortex Lines with Finite Number and Length in Rotating Trapped Bose--Einstein Condensates
DU Guo-Dong, MA Yong-Li
Chin. Phys. Lett. 2007, 24 (1): 31-34 .  
Abstract   PDF(pc) (247KB) ( 425 )
The minimal energy configurations of hyperbolic bending vortex lines in the rotating trapped Bose--Einstein condensates are investigated by using a variational ansatz and numerical simulation. The theoretical calculation of the energy of the vortex lines as a function of the rotation frequency gives self-consistently vortex number, curvature and configuration. The numerical results show that bending is more stable than straight vortex line along the z-axis, and the vortex configuration in the xy-plane has a little expansion by increasing z.
Motion of a Bose--Einstein Condensate Bright Soliton Incident on a Step-Like Potential
CHENG Yong-Shan, GONG Rong-Zhou, LI Hong
Chin. Phys. Lett. 2007, 24 (1): 35-38 .  
Abstract   PDF(pc) (290KB) ( 451 )
The motion characteristics of a Bose--Einstein condensate bright soliton incident on a local step-like potential barrier are investigated analytically by means of the variational approach. The dynamics of the soliton-potential interaction is studied as well. Then the results are verified by direct numerical simulations of the Gross--Pitaevskii equation. It is found that a moving bright soliton can be reflected from or pass over a step-like potential in a controllable fashion, the critical velocity depends on the width of the soliton and the parameters of the step, and the motion trajectory of the soliton does not depend on its phase. The atom density envelope of the soliton is changed as the result of the interaction between the soliton and the step-like potential.
A New Method to Study Hawking Radiation of Charged Particle from Stationary Axisymmetric Sen Black Hole
YANG Shu-Zheng, CHEN De-You
Chin. Phys. Lett. 2007, 24 (1): 39-41 .  
Abstract   PDF(pc) (199KB) ( 557 )
Taking the self-gravitation interaction and energy conservation, charge conservation and angular momentum conservation into account, we discuss the tunnelling characteristics of the charged particle from Sen black hole by the Hamilton--Jacobi method. The result shows that the tunnelling probability is related to the change of Bekenstein--Hawking entropy, and the actual radiation spectrum deviates from the pure thermal one, which is consistent with the result of Parikh and Wilczek and gives a new method to correct the Hawking pure thermal spectrum of Sen black hole.
Multi-Scale Gaussian Processes: a Novel Model for Chaotic Time Series Prediction
ZHOU Ya-Tong, ZHANG Tai-Yi, SUN Jian-Cheng
Chin. Phys. Lett. 2007, 24 (1): 42-45 .  
Abstract   PDF(pc) (310KB) ( 447 )
Based on the classical Gaussian process (GP) model, we propose a multi-scale Gaussian process (MGP) model to predict the existence of chaotic time series. The MGP employs a covariance function that is constructed by a scaling function with its different dilations and translations, ensuring that the optimal hyperparameter is easy to determine. Moreover, the scaling function with its different dilations and translations can form a set of complete bases, resulting in the fact that the MGP can acquire better prediction performance than the GP. The experiments can lead to the following conclusions: (i) The MGP gives a relatively better prediction performance in comparison with the classical GP model. (ii) The prediction performance of the MGP is competitive with support vector machine (SVM). They give better performance as compared to the radial basis function networks.

Noise-Mediated Generalized Synchronization
CHEN Yue-Hua, WU Zhi-Yuan, YANG Jun-Zhong
Chin. Phys. Lett. 2007, 24 (1): 46-49 .  
Abstract   PDF(pc) (253KB) ( 554 )
We investigate a drive-response system by considering the impacts of noise on generalized synchronization (GS). It is found that a small amount of noise can turn the system from desynchronization to the GS state in the resonant case no matter how noise is injected into the system. In the non-resonant case, noise with intensity in a certain range is helpful in building GS only when the noise is injected to the driving system. The mechanism behind the observed phenomena is discussed.
Different Types of Synchronization in Time-Delayed Systems
FENG Cun-Fang, ZHANG Yan, WANG Ying-Hai
Chin. Phys. Lett. 2007, 24 (1): 50-53 .  
Abstract   PDF(pc) (228KB) ( 687 )
We investigate different types of synchronization between two unidirectionally nonlinearly coupled identical delay-differential systems related to optical bistable or hybrid optical bistable devices. This system can represent some kinds of delay-differential models, i.e. Ikeda model, Vallée model, sine-square model, Mackey--Glass model, and so on. We find existence and sufficient stability conditions by theoretical analysis and test the correctness by numerical simulations. Lag, complete and anticipating synchronization are bserved, respectively. It is found that the time-delay system can be divided into two parts, one is the instant term and the other is the delay term. Synchronization between two identical chaotic systems can be derived by adding a coupled term to the delay term in the driven system.
Phase Transition of FeS in Terms of In-Situ Resistance Measurement
LI Ming, GAO Chun-Xiao, ZHANG Dong-Mei, HE Chun-Yuan, HAO Ai-Min, HUANG Xiao-Wei, YU Cui-Ling, LI Yan-Chun, LI Xiao-Dong, LIU Jing, ZOU Guang-Tian
Chin. Phys. Lett. 2007, 24 (1): 54-56 .  
Abstract   PDF(pc) (240KB) ( 704 )
Electrical properties of stoichiometric iron sulfide (FeS) are investigated under high pressure with a designed diamond anvil cell. The process of phase transition is reflected by changing the electrical conductivity under high pressure, and the conductivity of FeS with the NiAs structure is found to be much smaller than other phases. Two new phase transitions without structural change are observed at 34.7GPa and 61.3GPa. The temperature dependence of the conductivity is found to be similar to that of a semiconductor when the pressure is higher than 35GPa
Single Production of Vector-Like Top Quark in the Littlest Higgs Model at TeV Energy e-γ Colliders
LIU Yao-Bei, WANG Xue-Lei, CAO Yong-Hua
Chin. Phys. Lett. 2007, 24 (1): 57-60 .  
Abstract   PDF(pc) (249KB) ( 398 )
The existence of a new coloured vector-like heavy fermion T is a crucial prediction in little Higgs models, which play a key role in breaking the electroweak symmetry. The littlest Higgs model is the most economical one among various little Higgs models. In the context of the littlest Higgs model, we study single production of the new heavy vector-like quark and discuss the possibility of detecting this new particle in the future LC experiment. It is found that the production cross section is in the range of 1.7×10-3-30fb at TeV energy electron--photon collider with √s=3TeV and a yearly integrated luminosity of £=500fb-1.
Factors in Light-Cone Sum Rules and the D-Meson Distribution Amplitude
Chin. Phys. Lett. 2007, 24 (1): 61-64 .  
Abstract   PDF(pc) (269KB) ( 337 )
We calculate the weak form factors of the decays Bc(B)\to Dlύ by using the chiral current orrelator within the framework of the QCD light-cone sum rules (LCSRs). The expressions of the form factors only depend on the leading twist distribution amplitude (DA) of the D meson. Three models of the D-meson distribution amplitude are employed. Our prediction, by using the D-meson distribution amplitude with the exponential suppression at the end points, favours the three-points sum rule (3PSR) approach with the Coulomb corrections included, and is compatible with other approaches.
Determination of Astrophysical 13N(p,γ)14O S-factors from the Asymptotic Normalization Coefficient of )14C → 13C + n
GUO Bing, LI Zhi-Hong
Chin. Phys. Lett. 2007, 24 (1): 65-69 .  
Abstract   PDF(pc) (258KB) ( 532 )
The angular distribution of the 13C(d,p)14C reaction is reanalysed using the Johnson--Soper approach. The squared asymptotic normalization coefficient (ANC) of virtual decay 14C →13C + n is then derived to be 21.4 ± 5.0fm-1. The squared ANC and spectroscopic factor (SF) of 14O → 13N + p are extracted to be 30.4 ± 7.1fm-1 and 1.94 ± 0.45, respectively. The astrophysical S-factors and reaction rates of 13N(pγ)14O are determined from the ANC of 14O → 13N + p using the R-matrix approach.
Influence of D-state in 4He on S Factor for the 2H(d,γ)4He Reaction
MA Yin-Qun, TIAN Yuan, MA Zhong-Yu,
Chin. Phys. Lett. 2007, 24 (1): 69-71 .  
Abstract   PDF(pc) (249KB) ( 463 )
We employ a direct capture method to study the influence of D-state in 4He on S factor for the 2H(d,γ)4He reaction, in which the D-state component of the colliding deuterons and D-state component in 4He ground state are considered. The parameters of Woods--Saxon (WS) potentials are obtained by reproducing the binding energy of d--d (i.e. 2H--2H) system, and d--d elastic scattering phase shifts calculated by the resonating group method. The theoretical results are in good agreement with the experimental data at Ec.m < 3MeV. The impact of the D state probability in 4He on the extrapolated value of the astrophysical S factor for 2H(d,γ)4He reaction is discussed.
Mechanism of Proton-Induced Reactions on Targets 16O, 27Al, 56Fe, 112Cd, 184W and 208Pb At Ep = 800MeV
OU Li, ZHANG Ying-Xun, LI Zhu-Xia,
Chin. Phys. Lett. 2007, 24 (1): 72-75 .  
Abstract   PDF(pc) (319KB) ( 636 )
We investigate the 800MeV proton-induced spallation reactions on various targets by the improved quantum molecular dynamics (ImQMD05) model incorporated with a statistical decay model (SDM). The influence of the nucleon--nucleon effective interaction on proton induced spallation reactions is studied by using different Skyrme interactions. It is found that the low energy part of the neutron double differential cross sections (DDCS), which is mainly contributed from the decay of the excited residue, is influenced by the effective nucleon--nucleon interaction strongly, while the high energy part of neutron DDCS is influenced weakly. Among the Skyrme interactions used in the calculations, the calculation results with SkP give the best agreement with the experimental data.
Probing Balance Energy Using Momentum- and Isospin-Dependent Potential
CHEN Ji-Yan, ZUO Wei, MA Lei, ZHANG Fang, LI Bao-An
Chin. Phys. Lett. 2007, 24 (1): 76-79 .  
Abstract   PDF(pc) (233KB) ( 425 )
Using the momentum- and isospin-dependent Boltmann--Uehling--Uhlenbeck (BUU) model, we investigate the transverse flow and balance energy in two isotopic colliding systems 48Ca+58Fe and 48Cr+58Ni by adopting different symmetry potentials. By comparing the results between the two colliding systems, we find that the difference between the balance energies of two isotopic systems can be considered as a sensitive probe to the density dependence of symmetry energy.
Optimization on Synchrotron Radiation Lattice of BEPCII
SUN Yi-Peng, GAO Jie, GUO Zhi-Yu
Chin. Phys. Lett. 2007, 24 (1): 80-82 .  
Abstract   PDF(pc) (357KB) ( 513 )
The Beijing Electron and Positron Collider II (BEPCII) is a double ring electron--positron collider, which can also be used as a synchrotron radiation (SR) light source. Since the BEPCII will start commissioning with SR mode in November 2006, it is essential to have a satisfying SR lattice. Here we first perform frequency map analysis on the original BEPCII SR lattice. The result shows that the resonance is really severe in the lattice and the transverse motion of particles is unstable. Then a new SR lattice is designed to obtain a arge dynamic aperture and much more stable transverse motion. The dynamic aperture of the new lattice including nonlinear wiggler effect is calculated to be very good. This new SR lattice can be used in the commissioning stage of the BEPCII.
Resonance Energies, Absorption Oscillator Strengths and Ionization Potentials for the Element Hassium
LI Ji-Guang, DONG Chen-Zhong, DING Xiao-Bin
Chin. Phys. Lett. 2007, 24 (1): 83-85 .  
Abstract   PDF(pc) (209KB) ( 554 )
On the basis of successfully predicting low-lying energy levels for the element fermium (Z=100), we calculate the resonance energies, absorption oscillator strengths and the first ionization potential of the element hassium (Z=108) by taking important relativistic and improved electron correlation effects into account using the multiconfiguration Dirac--Fock method. These calculations are carried out with the aim of assisting experimental investigations of hassium.
Single X-Ray Attosecond Pulse Generation by Using Combined Pulses Irradiating on a United Two-Atom System
CHEN Ji-Gen, LI Chen, CHI Fang-Ping, YANG Yu-Jun,
Chin. Phys. Lett. 2007, 24 (1): 86-89 .  
Abstract   PDF(pc) (252KB) ( 458 )
A scheme of a single x-ray attosecond pulse generation from a two-atom system exposed to the combined laser pulses is proposed. Our numerical results show that a single x-ray attosecond pulse rather than a train one can be produced by modulation of ionization. Furthermore, when we change the peak intensity Ih of the high-frequency pulse and keep the intensity of the low-frequency pulse constant, we can find that a range of Ih where the intensity of the attosecond pulse is optimal is available, and a explanation by the stimulated property of the recombination is also presented.
Analysis of (1, 2) (1, 3) and (2, 3) Bands in the c3IIu-b3IIg System of P2
WU Ling, ZHENG Li-Juan, KANIKI Kakule, CHEN Yang-Qin, YANG Xiao-Hua
Chin. Phys. Lett. 2007, 24 (1): 90-93 .  
Abstract   PDF(pc) (227KB) ( 371 )
We investigate the high resolution absorption spectroscopy of P2 radical, generated in ac glow discharge of PCl3 buffered with helium, using optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the visible region. The (1, 2), (1, 3) and (2, 3) bands of c3IIu-b3IIg in the range 16620--17860cm-1 are observed and their 3II2-3II2 subbands are rotationally analysed. A set of effective molecular constants for the Ω=2 component of the states involved are determined.
Double Electron Processes in Collisions of Partially Stripped Ions Cq+(q=1-4) with Helium
DING Bao-Wei, CHEN Xi-Meng, YU De-Yang, FU Hong-Bin, LIU Zhao-Yuan, SUN Guang-Zhi, LIU Yu-Wen, LU Yan-Xia, XIE Jiang-Shan, DU Juan, GAO Zhi-Min, CHEN Lin, CUI Ying, SHAO Jian-Xiong, HE Zi-Feng, CAI Xiao-Hong
Chin. Phys. Lett. 2007, 24 (1): 94-96 .  
Abstract   PDF(pc) (238KB) ( 426 )
The multi-electron processes are investigated for 17.9--120keV/u C1+, 30--323keV/u C2+, 120--438keV/u C3+, 287--480keV/u C4+ incident on a helium target. The cross-section ratios of double electron (DE) process to the total of the single electron (SE) and the double electron process (i.e. SE+DE), the direct double electron (DDI) to the direct single ionization (DSI) as well as the contributions of DDI to DE and of TI to DE are measured using coincidence techniques. The energy and charge state dependences of the measured cross-section ratios are studied and discussed.
Scattering from Alpha-Stable Non-Gaussian Distributed Surfaces
REN Yu-Chao, GUO Li-Xin, WU Zhen-Sen
Chin. Phys. Lett. 2007, 24 (1): 97-100 .  
Abstract   PDF(pc) (285KB) ( 476 )
The scattering problem of alpha-stable non-Gaussian distributed rough surfaces is studied. The alpha-stable non-Gaussian distribution is used to describe the surfaces that exhibit sharp and sparse peaks, not usually seen in Gaussian distributed surfaces. Then a magnetic field integral equation is formulated to calculate the scattered field and the scattering coefficient. Numerical simulations show that the magnitude distribution of the scattered field is affected significantly by the probability distribution of the surface when the height of the surface changes in a random way. In addition, simulation results are presented as bistatic scattering coefficient for alpha-stable distributed surfaces.
A Novel Method to Calculate the Initial Phase Difference between the Two Fibre Arms of Laser Homodyne Interferometer
LUO Hong-E, TIAN Xiao-Jian, GAO Bo, LI Liang, WU Ge, CAO Liang
Chin. Phys. Lett. 2007, 24 (1): 101-103 .  
Abstract   PDF(pc) (186KB) ( 399 )
We suggest a novel method to calculate the initial phase difference between two fibre arms of a laser homodyne interferometer. Put the two fibre arms in a temperature controller, whose short term stability is 0.02°C (measured in an hour), then measure the interference photocurrent and the photocurrents from the two fibre arms at a fixed temperature. With these three photocurrents we can calculate the value of the initial phase difference. We set up a simple laser homodyne interferometer to test the theory. The experimental results are repeatable and the measurement precision is about 0.04°. It is theoretically and experimentally proven that this method is potentially easy and practical.
Preparation of Cluster States with Trapped Ions in Thermal Motion
YANG Wen-Xing
Chin. Phys. Lett. 2007, 24 (1): 104-107 .  
Abstract   PDF(pc) (198KB) ( 642 )
A potential scheme is proposed for generating cluster states of many trapped ions in thermal motion, in which the effective Hamiltonian does not involve the external degree of freedom and thus the scheme is insensitive to the external state, allowing it to be thermal state. The required experimental techniques of the schemes are within the scope that can be obtained in the ion-trap setup.
Controllable Optical Bistability and Multistability in a Four-Level Atomic System with Closed-Loop Configuration
Lü Xin-You, LI Jia-Hua, LIU Ji-Bing
Chin. Phys. Lett. 2007, 24 (1): 108-111 .  
Abstract   PDF(pc) (247KB) ( 506 )
We theoretically investigate optical bistability (OB) and multistability (OM) behaviour of a closed-loop configuration atomic system driven by a degenerate coupling field and a degenerate probe field inside a unidirectional ring cavity. It is found that the OB and OM behaviour can be controlled by adjusting the intensity and the frequency detuning of the coupling field, respectively. Interestingly, our numerical results show that it is easy to realize the transition from OB to OM or vice versa by adjusting the intensity of the coupling field under a appropriate frequency detuning. The effect of the atomic cooperation parameter on the OB behaviour is also discussed.
Diode End-Pumped Passively Q-Switched Nd3+:GdVO4 Self-Raman Laser at 1176nm
WANG Bao-Shan, PENG Ji-Ying, MIAO Jie-Guang, LI Yi-Min, HAO Er-Juan, ZHNG Zhe, GAO Lan-Lan, TAN Hui-Ming
Chin. Phys. Lett. 2007, 24 (1): 112-114 .  
Abstract   PDF(pc) (238KB) ( 678 )
A compact diode-end-pumped passively Q-switched Nd3+:GdVO4/Cr4+:YAG self-Raman laser at 1176nm is demonstrated. When the T0=80% Cr4+:YAG saturable absorber is inserted into the cavity, the maximum Raman laser output reaches 175mW with 3.8W incident pump power. The optical conversion from incident to the Raman laser is 4.6% and the slope efficiency is 6.5%. The pulse energy, duration, and repetition frequency of the first stokes laser are 4.5μJ, 1.8,ns, and 38.5kHz, respectively. There is trong blue emission (about 350--400nm) can be observed in the d3+:GdVO4 crystal when the process of stimulated Raman scattering occurs, which is induced by the upconversion of the d3+ ions.
Highly Efficient and Stable Ring Regenerative Amplifier for Chirped-Pulse Amplification at Repetition Rate 1kHz
ZHAO Huan, WANG Peng, WEI Zhi-Yi, TIAN Jin-Rong, LI De-Hua, WANG Zhao-Hua, ZHANG Jie
Chin. Phys. Lett. 2007, 24 (1): 115-118 .  
Abstract   PDF(pc) (234KB) ( 521 )
A highly efficient and stable ring-cavity regenerative amplifier for chirped-pulse amplification at a 1kHz repetition rate, with slope efficiency up to 40% and output pulse-to-pulse energy-jitter less than 1.25%, is demonstrated. The pulse energy as high as 2.4mJ is obtained.
High Efficient C6H12 Raman Laser Enhanced by DCM Fluorescence
WANG Hong-Bo, LIANG Hui-Min, WANG Zhi-Hua, LUO Shi-Rong, YANG Jing-Guo, ZHENG Wan-Guo, WEI Xiao-Feng, HE Shao-Bo, CHEN Yuan-Bin
Chin. Phys. Lett. 2007, 24 (1): 119-122 .  
Abstract   PDF(pc) (239KB) ( 468 )
We report the first-order Stokes output (wavelength of 627.6nm) from C6H12 enhanced by DCM dye fluorescence with high energy conversion efficiency of 47.9%, quantum conversion efficiency of 56.5%. To our knowledge, it is the highest conversion efficiency of stimulated Raman scattering obtained from liquid Raman laser. A 532nm frequency doubled Nd:YAG laser with 8Hz repetition rate is employed as the pump source, and the enhancement medium is DCM dye solution in ethanol. The conversion efficiencies at various pump energies and various pump repetition rates are measured and analysed. The enhancement mechanism of SRS together with its potential application is discussed.
Influence of Spectral Filtering and Nonlinear Gain on an Optical Soliton
LIU Ling-Hong, YAN Jia-Ren, TANG Zheng-Hua
Chin. Phys. Lett. 2007, 24 (1): 123-126 .  
Abstract   PDF(pc) (220KB) ( 654 )
Using the direct soliton perturbation theory, we investigate the evolution of soliton parameters and the first-order correction of bright soliton in a system with linear and nonlinear gain (or loss) and spectral filtering in a comprehensive way. The results obtained by means of our analytic method are consistent with numerical simulations. It is also found that the stable soliton propagation which has been investigated in a previous report by others is the limit case of our results.
Photonic Crystal Waveguide Intersection Based on Self-Imaging of Multi-Mode Interference
DING Wei-Qiang, TANG Dong-Hua, CHEN Li-Xue, ZHAO Yuan, LIU Yan
Chin. Phys. Lett. 2007, 24 (1): 127-130 .  
Abstract   PDF(pc) (359KB) ( 604 )
A new mechanism of intersection formed by two line defect photonic crystal (PC) waveguides are numerically investigated using the finite-difference time-domain method. The results show that the normalized crosstalk is smaller than 10-4; the reflection is smaller than 10-3, and the transmission is larger than 0.999. The authors analyse the physical origins and find that a modified self-imaging process in the intersected multi-mode region is the main reason of the excellent performance. This kind of multi-mode interference based intersection may find potential applications in PC optical circuits.
A Simple Model for Nonlinear Confocal Ultrasonic Beams
ZHANG Dong, ZHOU Lin, SI Li-Sheng, GONG Xiu-Fen
Chin. Phys. Lett. 2007, 24 (1): 131-134 .  
Abstract   PDF(pc) (227KB) ( 450 )
A confocally and coaxially arranged pair of focused transmitter and receiver represents one of the best geometries for medical ultrasonic imaging and non-invasive detection. We develop a simple theoretical model for describing the nonlinear propagation of a confocal ultrasonic beam in biological tissues. On the basis of the parabolic approximation and quasi-linear approximation, the nonlinear Khokhlov--Zabolotskaya--Kuznetsov (KZK) equation is solved by using the angular spectrum approach. Gaussian superposition technique is applied to simplify the solution, and an analytical solution for the second harmonics in the confocal ultrasonic beam is presented. Measurements are performed to examine the validity of the theoretical model. This model provides a preliminary model for acoustic nonlinear microscopy.

Resonance Shift of Single-Axis Acoustic Levitation
XIE Wen-Jun, WEI Bing-Bo
Chin. Phys. Lett. 2007, 24 (1): 135-138 .  
Abstract   PDF(pc) (251KB) ( 425 )
The resonance shift due to the presence and movement of a rigid spherical sample in a single-axis acoustic levitator is studied with the boundary element method on the basis of a two-cylinder model of the levitator. The introduction of a sample into the sound pressure nodes, where it is usually levitated, reduces the resonant interval Hn (n is the mode number) between the reflector and emitter. The larger the sample radius, the greater the resonance shift. When the sample moves along the symmetric axis, the resonance interval Hn varies in an approximately periodical manner, which reaches the minima near the pressure nodes and the maxima near the pressure antinodes. This suggests a resonance interval oscillation around its minimum if the stably levitated sample is slightly perturbed. The dependence of the resonance shift on the sample radius R and position h for the single-axis acoustic levitator is compared with Leung’s theory for a closed rectangular chamber, which shows a good agreement.
Series Solution for Unsteady Boundary-Layer Flows Due to Impulsively Stretching Plate
Seripah Awang Kechil, Ishak Hashim
Chin. Phys. Lett. 2007, 24 (1): 139-142 .  
Abstract   PDF(pc) (221KB) ( 557 )
The third-order nonlinear partial differential equation modelling the unsteady boundary-layer flows caused by an impulsively stretching flat plate is solved by using the Adomian decomposition method (ADM). The ADM yields analytic solution in the form of a rapidly convergent infinite series with easily computable terms. The series solution using the ADM for the unsteady flows is presented for the first time.

From Discreteness to Continuity: Dislocation Equation for Two-Dimensional Triangular Lattice
WANG Shao-Feng
Chin. Phys. Lett. 2007, 24 (1): 143-146 .  
Abstract   PDF(pc) (181KB) ( 960 )
A systematic method from the discreteness to the continuity is presented for the dislocation equation of the triangular lattice. A modification of the Peierls equation has been derived strictly. The modified equation includes the higher order corrections of the discrete effect which are important for the core structure of dislocation. It is observed that the modified equation possesses a universal form which is model-independent except the factors. The factors, which depend on the detail of the model, are related to the derivatives of the kernel at its zero point in the wave-vector space. The results open a way to deal with the complicated models because what one needs to do is to investigate the behaviour near the zero point of the kernel in the wave-vector space instead of calculating the kernel completely.
Coherent Structures in Transition of a Flat-Plate Boundary Layer at Ma =0.7
ZHOU Ying, LI Xin-Liang, FU De-Xun, MA Yan-Wen
Chin. Phys. Lett. 2007, 24 (1): 147-150 .  
Abstract   PDF(pc) (362KB) ( 499 )
Direct numerical simulation (DNS) of a spatially evolving flat-plate boundary layer transition process at free stream Mach number 0.7 is performed. Tollmien--Schlichting (T-S) waves are added on the inlet boundary as the disturbances before transition. Typical coherent structures in the transition process are investigated based on the second invariant of velocity gradient tensor. The instantaneous shear stress and the mean velocity profile in the transition region are studied. In our view, the fact that the peak value of shear stress in the stress concentration area increases and exceeds a threshold value during the later stage of the transition process plays an important role in the laminar breakdown process.
Propagation of Ion-Acoustic Wave in an Inhomogeneous Dusty Plasma with Dust Charge Fluctuation
LI Jing-Ju, XIAO De-Long, LI Yang-Fang, MA Jin-Xiu
Chin. Phys. Lett. 2007, 24 (1): 151-154 .  
Abstract   PDF(pc) (203KB) ( 521 )
The propagation of dust ion-acoustic wave in an inhomogeneous dusty plasma is studied by taking the dust charge fluctuation and collisions into account. It is shown that the dust charge fluctuation brings a phase shift to the wave. Furthermore, because of the presence of dust charge fluctuation, a new damping term rises, which makes the damping more sharply.
New Mechanism for Enhancing Ash Removal Efficiency and Reducing Tritium Inventory
LI Cheng-Yue, DENG Bai-Quan, YAN Jian-Cheng
Chin. Phys. Lett. 2007, 24 (1): 155-157 .  
Abstract   PDF(pc) (228KB) ( 744 )
A new mechanism is suggested to suppress ash particle back streams in the divertor region of our fusion experimental breeder (FEB) reactor for enhancing the ash removal efficiency and reducing the tritium inventory by applications of the nonlinear effect of high power rf ponderomotive force potential which reflects the plate-released and re-ionized He+ back to the plate. Meanwhile, the potential does not hinder α particles, which are coming from scraping of the layer, flowing to the target plate. However, it does stop tritium ions flowing to the target. Based on the FEB design parameters, our calculations have shown that the ash removal efficiency can be improved by as much as 40% if the parallel component of rf field 150--200V/cm is applied to the location at a perpendicular distance L=20cm apart from the plate and the plate-recycling neutral helium atom energy is about 0.75eV, at the same time, the tritium inventory can be reduced to some extent.

Structural Transition of Gd2O3:Eu Induced by High Pressure
CHEN Hai-Yong, HE Chun-Yuan, GAO Chun-Xiao, ZHANG Jia-Hua, GAO Shi-Yong, LU Hong-Liang, NIE Yan-Guang, LI Dong-Mei, KAN Shi-Hai, ZOU Guang-Tian
Chin. Phys. Lett. 2007, 24 (1): 158-160 .  
Abstract   PDF(pc) (270KB) ( 900 )
The structural transition of bulk and nano-size Gd2O3:Eu are studied by high pressure energy disperse x-ray diffraction (XRD) and high pressure photoluminescence. Our results show that in spite of different size of Gd2O3 particles, the cubic structure turns into a possible hexagonal one above 13.4GPa. When the pressure is released, the sample reverses to the monoclinic structure. No cubic structure presents in the released samples. That is to say, the compression and relaxation of the sample leads to the cubic Gd2O3:Eu then turns into the monoclinic one.
Bridging Atomistic/Continuum Scales in Solids with Moving Dislocations
TANG Shao-Qiang, LIU Wing K., KARPOV Eduard G., HOU Thomas Y.
Chin. Phys. Lett. 2007, 24 (1): 161-164 .  
Abstract   PDF(pc) (326KB) ( 305 )
We propose a multiscale method for simulating solids with moving dislocations. Away from atomistic ubdomains where the atomistic dynamics are fully resolved, a dislocation is represented by a localized jump profile, superposed on a defect-free field. We assign a thin relay zone around an atomistic subdomain to detect the dislocation profile and its propagation speed at a selected relay time. The detection technique utilizes a lattice time history integral treatment. After the relay, an atomistic computation is performed only for the defect-free field. The method allows one to effectively absorb the fine scale fluctuations and the dynamic dislocations at the interface between the atomistic and continuum domains. In the surrounding region, a coarse grid computation is adequate.

Atomistic Failure Mechanism of Single Wall Carbon Nanotubes with Small Diameters
JI Dong, GAO Xiang, KONG Xiang-Yang, LI Jia-Ming,
Chin. Phys. Lett. 2007, 24 (1): 165-168 .  
Abstract   PDF(pc) (276KB) ( 637 )
Single wall carbon nanotubes with small diameters (<5.0Å) subjected to bending deformation are simulated by orthogonal tight-binding molecular dynamics approach. Based on the calculations of C--C bond stretching and breaking in the bending nanotubes, we elucidate the atomistic failure mechanisms of nanotube with small diameters. In the folding zone of bending nanotube, a large elongation of C--C bonds occurs, accounting for the superelastic behaviour. The C--C bonds parallel to the axis direction of nanotube are broken firstly due to the sustained longitudinal stretching strain, giving rising to forming one-notch or two-notch bond-breaking mode depending on nanotube chiralities. The direct bond-breaking mechanism is responsible for the brittle fracture behaviour of nanotubes with small diameters.
A Reflected Terahertz-Emission Microscopy
YANG Yu-Ping, YAN Wei, WANG Li
Chin. Phys. Lett. 2007, 24 (1): 169-171 .  
Abstract   PDF(pc) (249KB) ( 410 )
A novel reflected terahertz-emission microscopy is proposed and developed for improving the spatial resolution of THz imaging. When attaching a bow-tie antenna directly onto a thin generation crystal, the reflected THz waves can be collected and detected by a photoconductive antenna, and the spatial resolution is decided by the diameter of focused pump beam. In this way, the detected resolution can be largely improved and tunable. The configuration and characteristics of this microscopy are described in detail.
Structural Stabilities of Ordered Nb4 Clusters on the Cu(111) and Cu(100) Surfaces
WANG Xiao-Chun, ZHU Zi-Zhong
Chin. Phys. Lett. 2007, 24 (1): 172-175 .  
Abstract   PDF(pc) (359KB) ( 455 )
Based on first-principles calculations, we show that very high-density periodic arrays of Nb4 clusters with both the tetrahedron and quadrangle configurations can be stably absorbed on the Cu(111) and Cu(100) surfaces, with the quadrangle configurations more stable than the tetrahedron ones. The strong covalent bonding between atoms within the Nb4 clusters contributes to the stability of Nb4 adsorptions on the Cu surfaces. The energy barriers for the tetrahedron to the quadrangle-Nb4 on Cu(111) and (100) are around 1.21eV and 0.94eV/cluster, respectively. The stable adsorption of high-density Nb4 on these surfaces should have important applications.
Four Electrons in a Coupled Three-Layer Quantum Dot
XIE Wen-Fang
Chin. Phys. Lett. 2007, 24 (1): 176-179 .  
Abstract   PDF(pc) (233KB) ( 450 )
We investigate four electrons confined in a coupled three-layer quantum dot, by the exact diagonalization method. A vertical magnetic field to the confinement plane is considered. The ground-state electronic structures and angular momentum transitions are investigated. We find that for four-electron QDs, the series of the magic numbers in three-layer QDs are different from those in one-, and two-layer QDs. These are connected to the exchange and rotational symmetries of the systems.
First-Principles Study of Structural and Electronic Properties of Layered B2CN Crystals
WU Qing-Hua, HU Qian-Ku, LUO Xiao-Guang, YU Dong-Li, LI Dong-Chun, HE Ju-Long
Chin. Phys. Lett. 2007, 24 (1): 180-183 .  
Abstract   PDF(pc) (292KB) ( 673 )
Based on the hexagonal BN structure, six possible layered B2CN structures are constructed. Their total energies, lattice constants as well as electronic properties are calculated using the ab initio pseudopotential density functional method within the local density approximation. The calculated results show that the B2CN-V configuration with AA stacking sequence is the most stable among the six B2CN layered structures. The characteristics of electronic structures indicate that the B2CN-V shows metallicity, which mainly comes from -B1--C--B1--C- chains.
Ground State Property of LiV2O4
XU Ying, ZENG Zhi
Chin. Phys. Lett. 2007, 24 (1): 184-186 .  
Abstract   PDF(pc) (201KB) ( 734 )
The spinel structure LiV2O4 is studied by local density approximation (LDA) as well as including strong correlation correction potential, i.e. the LDA+U scheme, which concerns the strongly correlated interaction. With LDA, the orbitals of V 3d and O 2p are well separated so that it presents purely metallic heavy fermion behaviour. The total energy of ferromagnetic phase is slightly lower than that of paramagnetic phase within the LDA approach. This implies that the ferromagnetic instability as a consequence of spin frustrated magnetism can be observed in experiments. The strong correlation interaction by using LDA+U enhances the exchange splitting. The heavy-fermion feature can be derived from the sharp peak around the Fermi level from the density of states.
Measurement of Electrical Conductivity of Porous Titanium and Ti6Al4V Prepared by the Powder Metallurgy Method
ZHU Ke, LI Cheng-Feng, ZHU Zhen-Gang
Chin. Phys. Lett. 2007, 24 (1): 187-190 .  
Abstract   PDF(pc) (285KB) ( 3874 )
Porous titanium and Ti6Al4V are produced by the powder metallurgy method. Dependence of the electrical conductivity on the porosity and pore size is investigated and the experimental results are correlative and compared with several earlier models. A newly modified Mori--Tanaka relationship based on the effective field method is proposed, which is successfully applied to describe the dependence of the electrical conductivity of porous titanium and Ti6Al4V on the porosity. The pore size has a minor effect on the electrical onductivity of both samples.
Photon-Assisted Conductance Structure for a Quantum Dot
LIAO Wen-Hu, GAO Qin-Xiang, ZHOU Guang-Hui,
Chin. Phys. Lett. 2007, 24 (1): 191-194 .  
Abstract   PDF(pc) (220KB) ( 827 )
We investigate theoretically the electron transport of a two-level quantum dot irradiated under a weak laser field at low temperatures in the rotating wave approximation. Using the method of the Keldysh equation of motion for nonequilibrium Green function, we examine the conductance for the system with photon polarization perpendicular to the tunnelling current direction. It is demonstrated that by analytic analysing and numerical examples, a feature of conductance peak splitting appears, and the dependence of conductance on the incident laser frequency and self-energy are discussed.
Current and Shot Noise in a Quantum Dot Coupled to Ferromagnetic Leads in the Kondo Regime
LÜ, Rong, LIU Zhi-Rong
Chin. Phys. Lett. 2007, 24 (1): 195-198 .  
Abstract   PDF(pc) (260KB) ( 690 )
Using the Keldysh nonequilibrium Green function technique, we study the current and shot noise spectroscopy of an interacting quantum dot coupled to two ferromagnetic leads with different polarizations in the Kondo regime. General formulas of current and shot noise are obtained, which can be applied in both the parallel (P) and antiparallel (AP) alignment cases. For large polarization values, it is revealed that the behaviour of differential conductance and shot noise are completely different for spin up and spin down configurations in the P alignment case. However, the differential conductance and shot noise have similar properties for different spin configurations in the P alignment case with the small polarization value and in the AP alignment case with any polarization value.
Magnetic-Field-Induced Semimetal-Insulator-like Transition in Highly Oriented Pyrolitic Graphite
WANG Zhi-Ming, XING Ding-Yu, ZHANG Shi-Yuan, XU Qing-Yu, Margriet VanBael, DU You-Wei
Chin. Phys. Lett. 2007, 24 (1): 199-202 .  
Abstract   PDF(pc) (260KB) ( 687 )
We report the extraordinarily large positive magnetoresistances (MR, 69400% at 4.5K under a magnetic field of 8.15T), de Hass--van Alphen oscillations effect at 10K and the semimetal-insulator-like transition in a wide range of temperature in highly oriented pyrolitic graphite (HOPG). Besides a dominating ordinary MR (OMR) mechanism in the free-electron mode, it is realized from qualitative analysis that the Coulomb interacting quasiparticles within graphite layers play some roles. However it is difficult to associate the transition with thesimple OMR theory. In order to investigate the possible origins of the transition, further analysis is carried out. It is revealed that the magnetic-field-induced behaviour is responsible for the semimetal-insulator-like transitions in HOPG.
Creep Motion in Two-Dimensional Fully Frustrated Coulomb Gas Model
REN Qing-Bao, ZHOU Zhen-Chun, CHEN Ju, LUO Meng-Bo
Chin. Phys. Lett. 2007, 24 (1): 203-206 .  
Abstract   PDF(pc) (268KB) ( 377 )
The creep motion in a two-dimensional fully frustrated square lattice Coulomb gas model with disorders is studied by using the Monte Carlo technique. The dependence of charge current density J on electric field E is investigated at low temperature T and at low E. The results show that the creep obeys the Arrhenius law J ~ C(T) exp [-U(E)/T]. The prefactor C(T) increases with the temperature in a power law relation with an exponent about 3.0. The energy barrier U(E) increases logarithmically with Ec/E as U(E) ~ U0ln (Ec/E) with Ec being the critical field at zero temperature.
Magnetism of Rare-Earth Compounds with Non-Magnetic Crystal-Field Ground Levels
LIU Zhao-Sen
Chin. Phys. Lett. 2007, 24 (1): 207-209 .  
Abstract   PDF(pc) (177KB) ( 378 )
Among rare-earth compounds, there are many materials having non-magnetic crystal-field (CF) ground levels. To understand their magnetic behaviour at low temperatures, we study the effects of the CF levels and the Heisenberg-like coupling on the magnetic process of such a crystalline with mean-field and CF theory. It is found that the material can be magnetically ordered if the Heisenberg exchange is sufficiently strong. Additionally we obtain a condition for initial magnetic ordering, and derive a formula for estimating the Curie temperature if the ordering occurs.
In-Situ Alignment of MnBi Crystals Induced by High Magnetic Field above Curie Temperature
LIU Yong-Sheng, ZHANG Jin-Cang, REN Zhong-Ming, CAO Shi-Xun
Chin. Phys. Lett. 2007, 24 (1): 210-213 .  
Abstract   PDF(pc) (289KB) ( 653 )
Above Curie temperature, MnBi crystals are aligned in situ along the c-axis in a Bi matrix by a high fabrication magnetic field Hf of 10T. Magnetic testing shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from the alignment. The successful alignment may result from the fact that the easy magnetization direction is along the c-axis of MnBi and the high fabrication field of 10T is large enough to rotate the MnBi crystal to this direction even though the temperature is above the Curie temperature.
Variations from Zn1-xCoxO Magnetic Semiconductor to Co--ZnCoO Granular Composite
CHEN Yan-Xue, YAN Shi-Shen, LIU Guo-Lei, MEI Liang-Mo, REN Miao-Juan
Chin. Phys. Lett. 2007, 24 (1): 214-217 .  
Abstract   PDF(pc) (258KB) ( 509 )
We investigate the variations from as-deposited Zn1-xCoxO magnetic semiconductors to the post-annealed Co--ZnCoO granular composite. The as-deposited Zn1-xCoxO magnetic semiconductor deposited under thermal non-equilibrium conditions is composed of Zn1-xCoxO nanograins of high Co concentration. The room-temperature ferromagnetism with high magnetization and large negative magnetoresistance are found in the as-deposited samples. By annealing, the samples become of granular composite consisting of the Co metal grains and the remanent Zn1-xCoxO matrix. Although the magnetization is enhanced after annealing, the spin-dependent negative magnetoresistance disappears at room temperature. The magnetoresistance observed in the annealed samples in the high field region has no relation with the ferromagnetism, which in turn indicates that the room-temperature ferromagnetism and large negative magnetoresistance observed in the as-deposited are the intrinsic properties of the Zn1-xCoxO magnetic semiconductor.
Room-Temperature Ferromagnetism of Co-Doped CeO2 Thin Films on Si(111) substrates
SONG Yuan-Qiang, ZHANG Huai-Wu, WEN Qi-Ye, LI Yuan-Xun, John Q. Xiao
Chin. Phys. Lett. 2007, 24 (1): 218-221 .  
Abstract   PDF(pc) (307KB) ( 851 )
Using Co2O3 as the Co source, doped cerium oxide thin films with the composition of Ce0.97Co0.03O2-δ (CCO) are deposited on Si(111) and glass substrates by pulse laser deposition technique. X-ray diffraction reveals that CCO films with (111) preferential orientation are grown on Si, while the film on glass is polycrystalline with nanocrystal. X-ray photoelectron spectroscopy shows that the Co displaces the Ce atom and exists in high spin state rather than low spin state, which contributes to the room-temperature ferromagnetism confirmed by vibration sample magnetometer. Films on Si and glass are different in ferromagnetism, which is believed to be induced by different film microstructures. Based on these results, the possible ferromagnetism in this insulating film is discussed. Anyway, successful fabrication of CCO films with room-temperature ferromagnetism on Si substrates is of great importance in both technological and theoretical aspects.
Magnetic Force Microscopy Study of Alternate Sputtered (001) Oriented L10 Phase FePt Films
XIA Ai-Lin, CAO Jiang-Wei, TONG Liu-Niu, WEI Fu-Lin, YANG Zheng, HAN Bao-Shan
Chin. Phys. Lett. 2007, 24 (1): 222-225 .  
Abstract   PDF(pc) (376KB) ( 428 )
We present a magnetic force microscopy study of alternate sputtered (001) oriented L10 phase FePt films. It is found that the root-mean-square value of phase shift of magnetic force images, (ΔФ)rms, can be used to characterize the perpendicular anisotropy for a series of specimens. Therefore, the considerable improvement of the perpendicular anisotropy after post-annealing can be characterized. In addition, the magnetic properties, magnetic and crystalline microstructures before and after post-annealing are compared for the typical [Fe5nmPt5nm]10 film with substrate temperature Ts=500°C, single layer thickness d=5nm and total layer thickness D=100nm to confirm the effect of post-annealing on improving the perpendicular anisotropy for Fe--Pt films.
Magnetic Properties of Exchange-Coupled Dual-Layer SmTbCo Thin Films
HUANG Zhi-Xin, GAO Jian-Ming, DING Xiao-Xia, ZHANG Ping, WANG Xiang, LI Zuo-Yi
Chin. Phys. Lett. 2007, 24 (1): 226-228 .  
Abstract   PDF(pc) (224KB) ( 523 )
Exchange-coupled SmTbCo dual-layer media are prepared by an r.f magnetron sputtering system and their magnetic properties are investigated. The prepared SmTbCo dual layer is composed of a 340emu/cm3 TM-rich readout layer and a 5.80 kOe RE-rich memory layer, meeting the requirements of high saturation magnetization and large coercivity for hybrid recording. Through exchange coupling, the coercivity of the high-saturation-magnetization SmTbCo layer is greatly enhanced from 1.85 to 5.96kOe. The calculated interface wall energy for Sm6.65Tb12.35Co81 (20nm)/Sm1.22Tb42.16Co56.62 (20nm) is about 3.85erg/cm2. The reversal magnetization of the SmTbCo exchange-coupling dual-layer films is analysed based on a micro-magnetic model.
Imaging Properties of a Rectangular-Lattice Metallic Photonic-Crystal Slab
FENG Shuai, WANG Yi-Quan, LI Zhi-Yuan, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2007, 24 (1): 229-232 .  
Abstract   PDF(pc) (320KB) ( 594 )
We report the imaging properties of a two-dimensional rectangular-lattice photonic crystal (PC) slab consisting of rectangular metallic rods immersed in a dielectric background. By simulating the electromagnetic wave propagation through such a PC slab with the finite-difference time-domain method, we find that a point source placed in the vicinity of the PC slab can form a good-quality image through the slab. The frequency region where a good-quality image is formed can be controlled by choosing the direction along which the PC slab surface normal is placed.
Field Emission Enhancement of Carbon Nanotubes by Surface Modification
YONG Zhen-Zhong, GONG Jin-Long, WANG Zhen-Xia, ZHU Zhi-Yuan, HU Jian-Gang, PAN Qiang-Yan
Chin. Phys. Lett. 2007, 24 (1): 233-235 .  
Abstract   PDF(pc) (287KB) ( 728 )
By employing a multi-walled carbon nanotube (MWCNT) film as the substrate, we obtain Fe tipped carbon nanorods or carbon nanoparticles grown on the outer walls of MWCNTs by combining sputtering deposition of Fe films and rf plasma enhanced chemical vapour deposition at high temperature. Scanning electron microscopy and high-resolution transmission electron microscopy are used to examine the structure of carbon nanorods and carbon nanoparticles. In addition, the formation mechanism is discussed briefly. The electron field emission tests indicate that the turn-on field (at 10μA/cm2) of the treated MWCNT films decreases from 2.4V/μm to 0.79V/μm and the field emission current is relatively stable. The enhanced field enhancement factor, increasing emission densities coming from the grown nanorods and nanoparticles, and H terminated by H plasma all are responsible for the enhancement of the field enhancement factor.
Growth and Characterization of Trumpet-Shaped ZnO Microtube Arrays on Si Substrates
LI Meng-Ke, WANG De-Zhen, SHI Feng, DING Sheng, JIN Hong
Chin. Phys. Lett. 2007, 24 (1): 236-239 .  
Abstract   PDF(pc) (316KB) ( 681 )
Aligned trumpet-shaped zinc oxide microtube arrays have been successfully prepared on silicon (100) substrates via the chemical vapour deposition method with a mixture of ZnO and active carbon powders as reactants. The results show that two types of trumpet-shaped ZnO microtubes can be obtained. A plausible growth mechanism based on the studies of scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and room-temperature photoluminescence spectroscopy is proposed and discussed. The initial metastable zinc-rich ZnOx embryos play a key role in the formation of trumpet-shaped ZnO microtubes. On the different surfaces of metastable zinc-rich ZnOx (x<1), embryos exhibit different stabilities and resistivities to oxidation; these tiny embryos are gradually extended with different growing rates along the directions of its long axis and circular boundary around its oxide shell. Just this special reason creates the formation of trumpet-shaped microtubes and results in the inerratic and imperfect hexagonshaped cross section that appears. Moreover, the analytical results also show that the as-synthesized ZnO microtube arrays can exhibit better room-temperature photoluminescence behaviour.
Effect of III/V Ratio of HT-AlN Buffer Layer on Polarity Selection and Electrical Quality of GaN Films Grown by Radio Frequency Molecular Beam Epitaxy
ZHONG Fei, QIU Kai, LI Xin-Hua, YIN Zhi-Jun, XIE Xin-Jian, WANG Yang, JI Chang-Jian, CAO Xian-Cun, HAN Qi-Feng, CHEN Jia-Rong, WANG Yu-Qi
Chin. Phys. Lett. 2007, 24 (1): 240-243 .  
Abstract   PDF(pc) (317KB) ( 840 )
We investigate the effect of Al/N ratio of the high temperature (HT) AlN buffer layer on polarity selection and electrical quality of GaN films grown by radio frequency molecular beam epitaxy. The results show that low Al/N ratio results in N-polarity GaN films and intermediate Al/N ratio leads to mixed-polarity GaN films with poor electrical quality. GaN films tend to grow with Ga polarity on Al-rich AlN buffer layers. GaN films with different polarities are confirmed by in-situ reflection high-energy electron diffraction during the growth process. Wet chemical etching, together with atomic force microscopy, also proves the polarity assignments. The optimum value for room-temperature Hall mobility of the Ga-polarity GaN film is 703cm2/V.s, which is superior to the N-polarity and mixed-polarity GaN films.
Effect of Annealing on Ferroelectric Properties of Nanometre BaTiO3 Ceramics Prepared by High Pressure Sintering Method
LI Peng-Fei, JIN Chang-Qing, XIAO Chang-Jiang, WANG Feng-Ping, WANG Xiao-Hui, LI Long-Tu
Chin. Phys. Lett. 2007, 24 (1): 244-247 .  
Abstract   PDF(pc) (242KB) ( 424 )
Dense nanocrystalline BaTiO3 ceramics with a grain size of 50nm are prepared under 6GPa at 1273K using a high pressure sintering method. The sintered bulk is uniform and the relative density is above 97%. We anneal the ceramic samples in oxygen with various temperatures and for different times without apparent grain growth. After the annealing, several broadened peaks can be observed at about 378K by dielectric measurements. However, these peaks are very different from those of coarser-grained ceramics. It is indicated that both the elimination of oxygen vacancies and the release of residual stresses caused by high pressure greatly improve the overall ferroelectric properties of BaTiO3 ceramics. The observation of nearly linear polarization hysteresis loop after anneal provides the solid evidence of ferroelectricity in these nano-sized BaTiO3 ceramics. It is believed that the absence of 90° domains and the existence of poor-permittivity nonferroelectric grain boundaries contribute to the slim loop.
Effects of Radius and Orientation of Single-Walled Carbon Nanotubes on Their Nonlinear Tensile Deformation Behaviour
WANG Yu, FANG Dai-Ning, SOH Ai-Kah, LIU Bin
Chin. Phys. Lett. 2007, 24 (1): 248-251 .  
Abstract   PDF(pc) (257KB) ( 476 )
By capturing the atomic information and reflecting the behaviour governed by a nonlinear potential function, an analytical molecular mechanics approach is applied to establish the constitutive relation for single-walled carbon nanotubes (SWCNTs). The nonlinear tensile deformation curves of zigzag and armchair nanotubes with different radii are predicted, and the elastic properties of these SWCNTs are obtained. A conclusion is made that the nanotube radius has little effect on the mechanical behaviour of SWCNTs subject to simple tension, while the nanotube orientation has larger influence.

Chiral Symmetry Breaking During Growing Process of NaClO3 Crystal under Direct-Current Electric Field
CHEN Wan-Chun, CHEN Xiao-Long
Chin. Phys. Lett. 2007, 24 (1): 252-255 .  
Abstract   PDF(pc) (428KB) ( 699 )
We investigate the influence of dc electric field on chiral symmetry breaking during the growing process of NaClO3 crystal. Nucleation and growth of NaClO3 are completed from an aqueous solution by a fast cooling temperature technology. A pair of polarization microscopes are used to identify a distribution of chiral crystals. Experimental results indicate that the dc electric field has an effect on distribution of chirality, but the direction of the dc electric field is not sensitive to the chiral autocatalysis and selectivity, i.e. the nature convection driving by the gravity does not play an important role on a thin layer of NaClO3 solution. The experimental phenomena may be elucidated by the ECSN mechanism.
Photocatalytic Properties of TiO2/Si-NPA Nano Composite Systems
SUN Meng, HAO Wei-Chang, WANG Chun-Zhong, LI Xin-Jian, WANG Tian-Min
Chin. Phys. Lett. 2007, 24 (1): 256-258 .  
Abstract   PDF(pc) (247KB) ( 618 )
A new composite system is fabricated by depositing the TiO2 film on a silicon nanoporous pillar array (Si-NPA) and annealing at 500°C using the spin coating method. Such a composite system exhibits a uniform morphology with the micron-dimension pillar array. Photocatalytic properties are investigated based on the degradation of methyl orange dye solution, and the results show that the photocatalytic efficiency of such a nano-composite system is 1.7 times that of the TiO2/glass system. The enhancement of hotocatalytic efficiency is attributed to the large surface area of the TiO2/Si-NPA system.
Effect of Chemicals on Chemical Mechanical Polishing of Glass Substrates
WANG Liang-Yong, ZHANG Kai-Liang, SONG Zhi-Tang, FENG Song-Lin
Chin. Phys. Lett. 2007, 24 (1): 259-261 .  
Abstract   PDF(pc) (251KB) ( 1067 )
We investigate the effect of chemicals on chemical mechanical polishing (CMP) of glass substrates. Ceria slurry in an ultra-low concentration of 0.25wt.% is used and characterized by scanning electron microscopy. Three typical molecules, i.e. acetic acid, citric acid and sodium acrylic polymer, are adopted to investigate the effect on CMP performance in terms of material removal rate (MRR) and surface quality. The addition of sodium acrylic polymer shows the highest MRR as well as the best surface by atomic force microscopy after CMP, while the addition of citric acid shows the worst performance. These results reveal a mechanism that a long-chain molecule without any branches rather than small molecules and common molecules with ramose abundant-electron groups is better for the dispersion of the slurry and thus better for the CMP process.
Contrast Adaptation Decreases Complexity in Retinal Ganglion Cell Spike Train
WANG Guang-Li, HUANG Shi-Yong, ZHANG Ying-Ying, LIANG Pei-Ji
Chin. Phys. Lett. 2007, 24 (1): 261-274 .  
Abstract   PDF(pc) (213KB) ( 470 )
The difference in temporal structures of retinal ganglion cell spike trains between spontaneous activity and firing activity after contrast adaptation is investigated. The Lempel--Ziv complexity analysis reveals that the complexity of the neural spike train decreases after contrast adaptation. This implies that the behaviour of the neuron becomes ordered, which may carry relevant information about the external stimulus. Thus, during the neuron activity after contrast adaptation, external information could be encoded in forms of some certain patterns in the temporal structure of spike train that is significantly different, compared to that of the spike train during spontaneous activity, although the firing rates in spontaneous activity and firing activity after contrast adaptation are sometime similar.
Chalcogenide Random Access Memory Cell with Structure of W Sub-Microtube Heater Electrode
LIU Bo, FENG Gao-Ming, WU Liang-Cai, SONG Zhi-Tang, LIU Qi-Bin, FENG Song-Lin, CHEN Bomy
Chin. Phys. Lett. 2007, 24 (1): 262-264 .  
Abstract   PDF(pc) (255KB) ( 809 )
In order to reduce the reset current of chalcogenide random access memory, a W sub-microtube heater electrode with outer/inner diameter of 260/100nm, which was fabricated with standard 0.18-μm echnology, is proposed for the first time to achieve a reset current of about 0.5mA. The reasons may be that sub-microtube increases the number of electrode edge and thermal efficiency is improved greatly because the thermal density on the edge of sub-microtube electrode is generally the highest.
Silicon Light Emitting Devices in CMOS Technology
CHEN Hong-Da, LIU Hai-Jun, LIU Jin-Bin, GU Ming, HUANG Bei-Ju
Chin. Phys. Lett. 2007, 24 (1): 265-267 .  
Abstract   PDF(pc) (241KB) ( 459 )
Two silicon light emitting devices with different structures are realized in standard 0.35μm complementary metal-oxide-semiconductor (CMOS) technology. They operate in reverse breakdown mode and can be turned on at 8.3V. Output optical powers of 13.6nW and 12.1nW are measured at 10V and 100mA, respectively, and both the calculated light emission intensities are more than 1mW/cm2. The optical spectra of the two devices are between 600--790nm with a clear peak near 760nm.

Flip-Chip GaN-Based Light-Emitting Diodes with Mesh-Contact Electrodes
ZHU Yan-Xu, XU Chen, HAN Jun, SHEN Guang-Di
Chin. Phys. Lett. 2007, 24 (1): 268-270 .  
Abstract   PDF(pc) (236KB) ( 639 )
GaN-based light-emitting diodes (LEDs) with mesh-contact electrodes have been developed. The p-type ohmic contact layer is composed of oxidized Ni/Au mesh and NiO overlay (20Å). An Ag (3000Å) omni-directional reflector covers the p-type contact. The n-type contact is a Ti/Al planar film with a 10-μm-width Ti/Al stripe. The Ti/Al stripe surrounds the centre of LED mesa. With a 20-mA current injection, the light output power of GaN-based LEDs with mesh-contact electrodes is 23% higher than that of the conventional LEDs.
Suprathreshold Stochastic Resonance in a Single Comparator
WANG Ren-Guo, LONG Zhang-Cai
Chin. Phys. Lett. 2007, 24 (1): 275-278 .  
Abstract   PDF(pc) (233KB) ( 360 )
Stochastic resonance usually appears when stimulus is too weak to overcome barriers in a nonlinear system. Unusually, we demonstrate that in a simple comparator as a prototype model, stochastic resonance can still occur when the stimulus is predominantly suprathreshold. This result provides new knowledge for understanding of mechanism underlying information process in biological systems and also finds applications in signal processing.
Sensitivity of Exponents of Three-Power Laws to Hybrid Ratio in Weighted HUHPM
FANG Jin-Qing, BI Qiao, LI Yong, LU Xin-Biao, LIU Qiang
Chin. Phys. Lett. 2007, 24 (1): 279-282 .  
Abstract   PDF(pc) (275KB) ( 457 )
The sensitivity of exponents of three-power laws for node degree, node strength and edged weight to hybrid ratio are studied analytically and numerically in the weighted harmonious unifying hybrid preferential model (HUHPM), which is extended from un-weighted hybrid preferential attachment model we proposed previously [Chin. Phys. Lett. 22(2005)719]. Our weighted HUHPMs plus the Barrat--Barthelemy--Vespignani model and the traffic-driven evolution model, respectively, are taken as two typical examples for demonstration and application of the HUHPM.
Topological Effects on the Performance of Transportation Networks
ZHAO Xiao-Mei, GAO Zi-You
Chin. Phys. Lett. 2007, 24 (1): 283-286 .  
Abstract   PDF(pc) (249KB) ( 633 )
We investigate the influence of the network topology on the performance (characterized by the total system cost and maximal traffic volume) of transportation networks, where the weights are not static (constant), but dynamic (a function of the flow on the link). Four classes of networks are used in the simulation, including regular networks, random networks, small-world networks and scale-free networks. The initial simulation results show that topologies play important roles on the performance of transportation networks, and random networks have better performance than other networks. Also, we find that there are distinct difference of the link flow distribution for various networks in both the distribution function form and the span between the minimum and the maximum of the link flow, explaining the difference of the performance among distinct networks. These findings will be useful in network design problems of transportation systems.
Phase Transition and EOS of Marmatite (Zn0.76Fe0.23S) up to 623K and 17GPa
JIANG Xi, ZHOU Wen-Ge, XIE Hong-Sen, LIU Yong-Gang, FAN Da-Wei, LIU Jing, LI Yan-Chun, LUO Chong-Ju, MA Mai-Ning
Chin. Phys. Lett. 2007, 24 (1): 287-290 .  
Abstract   PDF(pc) (262KB) ( 416 )
In situ energy dispersive x-ray diffraction for natural marmatite (Zn0.76Fe0.23S) is performed up to 17.7GPa and 623K. It is fitted by the Birch--Murnaghan equation of state (EOS) that K0 and α0 for marmatite are 85(3)GPa and 0.79(16)×10-4K-1, respectively. Fe2+ isomorphic replacing to Zn2+ in natural crystal is responsible for high bulk modulus and thermal expansivity of marmatite. Temperature derivative of bulk modulus (∂K/∂T)P for marmatite is fitted to be -0.044(23)GPaK-1. The unambiguous B3--B1 phase boundaries for marmatite are determined to be Pupper(GPa)=15.50-0.016 T(°C) and Plower (GPa)=9.94--0.012T(°C) at 300--623K.
Construction of a Quadratic Model for Predicted and Measured Global Solar Radiation in Chile
Ercan YILMAZ, Beatriz CANCINO, Edmundo LOPEZ
Chin. Phys. Lett. 2007, 24 (1): 291-293 .  
Abstract   PDF(pc) (184KB) ( 515 )
Global solar radiation data for sites in Chile are analysed and presented in a form suitable for their use in engineering. A new model for monthly average data is developed to predict monthly average global radiation with acceptable accuracy by using actinographic data due to scarcing of pyranometer data. Use of the new quadratic model is proposed because of its relatively wider spectrum of values for Å ngstrom coefficients a0, a1, and a2.
Bounce-Averaged Acceleration of Energetic Electrons by Whistler Mode Chorus in the Magnetosphere
XIAO Fu-Liang, CHEN Liang-Xu, ZHOU Qing-Hua, HE Hui-Yong, WEN Yong-Jun
Chin. Phys. Lett. 2007, 24 (1): 294-297 .  
Abstract   PDF(pc) (290KB) ( 418 )
We construct the bounce-averaged diffusion coefficients and study the bounce-averaged acceleration for energetic electrons in gyroresonance with whistler mode chorus. Numerical calculations have been performed for a band of chorus frequency distributed over a standard Gaussian spectrum specifically in the region near L=4.5, where peaks of the electron phase space density occur. It is found that whistler mode chorus can efficiently accelerate electrons and can increase the phase space density at energies of about 1MeV by more than one order of magnitude about one day, in agreement with the satellite observations during the recovery phase of magnetic storms.
Theoretical Study on Ion Escape in Martian Atmosphere
SHI Jian-Kui, LIU Zhen-Xing, Klaus TORKAR, Tielong ZHANG
Chin. Phys. Lett. 2007, 24 (1): 298-301 .  
Abstract   PDF(pc) (215KB) ( 643 )
Based on the observation that Martian magnetic moment is gradually reducing from the ancient to the present, we investigate the O+ ion flux distribution along magnetic field lines and the ion escaping flux in Martian tail with different assumed Martian magnetic moments. The results show that the O+ ion flux along magnetic field lines decreases with distance from Mars; the ion flux along the field line decreases more quickly if the magnetic moment is larger; the larger the magnetic moment, the smaller the ion escaping flux in the Martian tail. The ion escaping flux depends on Z-coordinate in the Martian tail. With decrease of the magnetic moment, the ion escaping flux in the Martian tail increases. The results are significant for studying the water loss from Mars surface.
Evolution of Variable Generalized Chaplygin Gas
YANG Xiu-Yi, WU Ya-Bo, LÜ, Jian-Bo, LI Song
Chin. Phys. Lett. 2007, 24 (1): 302-304 .  
Abstract   PDF(pc) (220KB) ( 451 )
We consider the variable Generalized Chaplygin gas (VGCG) proposal for unification of dark matter and dark energy with p=pde and ρ=ρdede. The equation of state of the VGCG is given by p=-A0 a-nα, where a is the scale factor. Some cosmological quantities such as the fractional contributions of different components of the universe Ωi (i respectively denotes baryons, dark matter and dark energy) to the critical density, the deceleration parameter q are all obtained. The transition from deceleration to acceleration is described in this model. In addition, we find the behaviour of variable Generalized Chaplgin gas is similar to dust-like matter at early times and will be quiessence or phantom at late stage.
82 articles