#### Current Issue

Volume 22 Issue 5
Online Date:
Original Articles
 Select Functional Variable Separation for Generalized (1+2)-Dimensional Nonlinear Diffusion Equations ZHANG Shun-Li, LOU Sen-Yue, QU Chang-Zheng Chin. Phys. Lett. 2005, 22 (5): 1029-1032 .   Abstract   PDF(pc) (226KB) ( 574 ) The functional variable separation approach is applied to study the generalized (1+2)-dimensional nonlinear diffusion equations. Complete classification for those equations admitting the functional separable solutions and some such exact solutions are obtained. Consequently, the results reported previously are widely extended.
 Select Quantum Games of Continuous Distributed Incomplete Information CHEN Xi, QIN Gan, ZHOU Xian-Yi, DU Jiang-Feng, sup> Chin. Phys. Lett. 2005, 22 (5): 1033-1036 .   Abstract   PDF(pc) (412KB) ( 605 ) We study two-player quantum games of incomplete information in which both the sides have partial information. The previous results of Du et al. [Phys. Rev. E 68(2003)016124] are incorporated in our more general formalism. Because of different roles played by the total information uncertainty and the information asymmetry, the game exhibits many interesting features.
 Select Exact Solution to Helmholtz Equation for Inhomogeneous Medium: Its Application in Optical Communication WANG Gang, WU Shao-Quan, HOU Bang-Pin Chin. Phys. Lett. 2005, 22 (5): 1037-1040 .   Abstract   PDF(pc) (322KB) ( 500 ) In order to study the capability of amplifying the input optical signal of certain materials, we investigate the Helmholtz equation which describes a system of inhomogeneous media. After exploring its SU(1,1) algebraic structure, we obtain the exact solutions of this Helmholtz equation by means of the algebraic dynamical method. Based on the exact solutions, we analyse the capability of optical amplifiers, which is an important issue in modern optical communication. We take the wave number k0(z) and the expansion coefficient k2(z) to be the trigonometric functions, exponential functions and power functions of variable z, respectively. It is found that the material following the exponential functions is the best one for optical amplifiers.
 Select Indirect Relativistic Effect in Electron--Alkali-Atom Collision LIU Yi-Bao, PANG Wen-Ning, DING Hai-Bing, SHANG Ren-Cheng Chin. Phys. Lett. 2005, 22 (5): 1041-1044 .   Abstract   PDF(pc) (462KB) ( 561 ) We present detailed studies on the differential cross section (DCS) and total cross section (TCS) in electron--alkali-atom collision processes by using two types of distorted wave methods, the ordinary distorted wave method and the indirect-relativistic distorted wave method. We find that the indirect relativistic effect in the target atom can be neglected in the TCS calculation in the processes; however, with an increase of the atomic number, this effect becomes significant in the DCS calculation. Then, based on the density matrix theory, the orientation and alignment parameters of excited caesium P states scattered by electrons at low incident energy are calculated, and comparisons are made for the two series between the two methods. The results show that accordance is reached at scattering angles smaller than 45°, but considerable difference appears at angles larger than 45° due to the relativistic effect.
 Select Effect of Connected Multi-Ring Impurity Scattering on Quantum Transport GAO Ying-Fang, ZHANG Yong-Ping Chin. Phys. Lett. 2005, 22 (5): 1045-1048 .   Abstract   PDF(pc) (518KB) ( 969 ) We investigate the quantum transmission properties of connected multi-rings with impurities and analyse the effect of the impurities on the band formation in these geometric structures. It is shown that energy bands and band gaps are formed clearly while there is not any fixed band structure for the case of the single ring. The number of resonant peaks in conductance bands increases with the number of rings. Some essential differences are pointed out and magnetic properties of loop configurations in the presence of Aharonov--Bohm flux are explored as well.
 Select Secure Quantum Key Distribution Network with Bell States and Local Unitary Operations LI Chun-Yan, ZHOU Hong-Yu, , WANG Yan, DENG Fu-Guo, Chin. Phys. Lett. 2005, 22 (5): 1049-1052 .   Abstract   PDF(pc) (282KB) ( 984 ) We propose a theoretical scheme for secure quantum key distribution network following the ideas in quantum dense coding. In this scheme, the server of the network provides the service for preparing and measuring the Bell states, and the users encode the states with local unitary operations. For preventing the server from eavesdropping, we design a decoy when the particle is transmitted between the users. The scheme has high capacity as one particle carries two bits of information and its efficiency for qubits approaches 100%. Moreover, it is unnecessary for the users to store the quantum states, which makes this scheme more convenient in applications than others.
 Select General Probabilistic Dense Coding Scheme WANG Mei-Yu, YANG Lin-Guang, YAN Feng-Li, Chin. Phys. Lett. 2005, 22 (5): 1053-1056 .   Abstract   PDF(pc) (192KB) ( 527 ) We present a scheme of probabilistic dense coding using a quantum channel of general pure entangled states. Furthermore, the efficiency of information transmitted in this scheme is calculated.
 Select Superadditivity with Mixed States Ensemble LIN Qing, LI Jian, GUO Guang-Can Chin. Phys. Lett. 2005, 22 (5): 1057-1060 .   Abstract   PDF(pc) (351KB) ( 465 ) Superadditivity is a special property in quantum communication theory. We present the optimal measurement for a mixed-state ensemble and calculate the amount of one-shot capacity, which is connected to the intensity of noise of the channel. Then the property of superadditivity is preserved when the mixed-state ensemble is used to transmit information.
 Select Stochastic Resonance in an Asymmetric Bistable System Subject to Frequency Mixing Periodic Force and Noise JIN Yan-Fei, XU Wei, XU Meng Chin. Phys. Lett. 2005, 22 (5): 1061-1064 .   Abstract   PDF(pc) (333KB) ( 511 ) The phenomenon of stochastic resonance (SR) in an asymmetric bistable system subject to the multiplicative and additive white noises and two periodic fields is investigated. Using the two-state theory, analytic expressions of the signal-to-noise ratio (SNR) for fundamental harmonics and higher harmonics are derived. It is found that SR appears at both fundamental harmonics and mixed harmonics (of second- and third-order approximation). Moreover, the higher the order of mixed harmonics is, the larger the SNR values are. The effects of static asymmetry on the SNR (of second- and third-order approximation) are different, and the noise intensity ratio can enhance the SNR for higher harmonics.
 Select An Anti-Control Scheme for Spiral under Lorenz Chaotic Signals MA Jun, YING He-Ping, PU Zhong-Sheng Chin. Phys. Lett. 2005, 22 (5): 1065-1068 .   Abstract   PDF(pc) (367KB) ( 579 ) The Fitzhugh--Nagumo (FHN) equation is used to generate spiral and spatiotemporal chaos. The weak Lorenz chaotic signal is imposed on the system locally and globally. It is found that for the right chaotic driving signal, spiral and spatiotemporal chaos can be suppressed. The simulation results also show that this anti-control scheme is effective so that the system emerges into the stable states quickly after a short duration of chaotic driving (about 50 time units) and the continuous driving keeps the system in a homogeneous state.
 Select Adaptive Control on a Class of Uncertain Chaotic Systems LIU Guo-Gang, ZHAO Yi Chin. Phys. Lett. 2005, 22 (5): 1069-1071 .   Abstract   PDF(pc) (384KB) ( 836 ) By using a simple combination of feedback entrainment control (with an updating feedback strength) and adaptive scheme, for a large class of chaotic systems, it is proven rigorously by using the invariance principle of differential equations that all unknown model parameters can be estimated dynamically and the uncertain system can be controlled to an arbitrary desired smooth orbit. The illustration of the Lorenz system and the corresponding numerical results on the effect of noise are given.
 Select Catastrophes in Scale-Free Networks ZHOU Tao, WANG Bing-Hong Chin. Phys. Lett. 2005, 22 (5): 1072-1075 .   Abstract   PDF(pc) (385KB) ( 1063 ) An alternative model about cascading occurrences caused by perturbation is established to search the mechanism because catastrophes in networks occur. We investigate the avalanche dynamics of our model on two-dimensional Euclidean lattices and scale-free networks and find that the avalanche dynamic behaviour is sensitive to the topological structure of networks. The simulation results show that the catastrophes occur much more frequently in scale-free networks than those in Euclidean lattices, and the greatest catastrophe in scale-free networks is much more serious than that in Euclidean lattices. Furthermore, we have studied how to reduce the catastrophes' degree, and have schemed out an effective strategy, called the targeted safeguard strategy for scale-free networks.
 Select On Noncommutative Sinh--Gordon Equation U. Saleem, M. Siddiq, M. Hassan Chin. Phys. Lett. 2005, 22 (5): 1076-1078 .   Abstract   PDF(pc) (163KB) ( 473 ) We give a noncommutative extension of a sinh--Gordon equation. We generalize a linear system and Lax representation of the sinh--Gordon equation in noncommutative space. This generalization gives a noncommutative version of the sinh--Gordon equation with extra constraints, which can be expressed as global conserved currents.
 Select The Topological Inner Structure of Chern--Simons Tensor Current and the World-Sheet of Strings DUAN Yi-Shi, YANG Jie Chin. Phys. Lett. 2005, 22 (5): 1079-1082 .   Abstract   PDF(pc) (208KB) ( 419 ) Using the decomposition theory of U(1) gauge potential and Ф-mapping topological current theory, we investigate the topological inner structure of Chern--Simons tensor current. It is proven that the U(1) Chern--Simons tensor current in four-dimensional manifold is just the topological current of creating the string world-sheets.
 Select Searching for the Vector-Like Top Quark T at the Future Linac-Ring-Type ep Collider YUE Chong-Xing, ZHANG Feng, WANG Wei Chin. Phys. Lett. 2005, 22 (5): 1083-1086 .   Abstract   PDF(pc) (269KB) ( 452 ) The little-Higgs models typically contain a new vector-like top quark T, which plays a key role in breaking the electroweak symmetry. In the context of the littlest Higgs (LH) model, we study single production of this kind of new particles via the process ep→eb→veT in the future linac-ring-type ep collider (LC⊕LHC). We find that the production cross section is in the range of 1.2×10-4-0.48pb at the LC⊕LHC with √s=3.7TeV.
 Select Theoretical Analysis of the Exotic Structure of 17F LIANG Yu-Jie, , LI Xi-Han, , ZHOU Hong-Yu, , LIU Zu-Hua, DENG Fu-Guo, Chin. Phys. Lett. 2005, 22 (5): 1086-1088 .   Abstract   PDF(pc) (292KB) ( 483 ) The first excited state and the ground state of 7F are studied with the asymptotic normalization coefficient method. The results show that the probabilities of the last proton being out of the binding potential in both the states are P=59.71% and P=27.61%, respectively. This means that the last nucleon in both the states of 17F is far-extended beyond the range of nuclear force, especially in the first excited state. This result is also verified by the calculation of the density distributions of the last proton in 17F. It is quantitatively confirmed that the first excited state of 17F is a nuclear halo state and its ground state is a proton skin state.
 Select Excitation Energies of 1s2 ns (6≤n≤9) States for Lithium-Like Systems from Z=11 to 20 HU Mu-Hong, WANG Zhi-Wen Chin. Phys. Lett. 2005, 22 (5): 1089-1092 .   Abstract   PDF(pc) (229KB) ( 551 ) The non-relativistic energies of 1s2 ns (6≤n≤9) states for the lithium-like systems from $Z = 11$ to 20 are calculated by using a full-core-plus-correlation (FCPC) method. The relativistic and mass-polarization effects on the energy are calculated by the first-order perturbation corrections. The correction from the quantum-electrodynamics effect is also included using effective nuclear charge. Based on these results and the quantum defect theory, the quantum defects of 1s2 ns series for these ions, as a function of energy, are determined. The comparisons between the ionization potentials for 1s2 ns states (6≤n≤9) obtained by the FCPC method and the semi-empirical method are carried out. The results show that their agreement is very well and the energies of all discrete states (n≥10) below the ionization threshold of this series for the ions can be predicted by using their quantum defects.
 Select Stereodynamics and Rovibrational Effect for H+NH3→H2+NH2 Reaction LI Hao, LIU Xin-Guo, ZHANG Qing-Gang Chin. Phys. Lett. 2005, 22 (5): 1093-1096 .   Abstract   PDF(pc) (413KB) ( 562 ) We employ the semirigid vibrating rotor target (SVRT) model to study the influence of rotational and vibrational excitation of the reagent on reactivity for the reaction H+NH3. The excitation of the pseudo H--NH2 stretching vibration of the SVRT model gives significant enhancement of reaction probability. Detailed study of the influence of initial rotational states on reaction probability shows strong steric effect. The steric effect of polyatomic reactions, treated by the SVRT model, is more complex and richer than theoretical calculations involving linear molecular models.
 Select An Alternative Approach for Determining Photoionization Rate in H2+: Numerical Results ZHOU Yu, ZHANG Gui-Zhong, XIANG Wang-Hua, W. T. Hill III Chin. Phys. Lett. 2005, 22 (5): 1097-1098 .   Abstract   PDF(pc) (244KB) ( 486 ) We present an alternative approach for determining the photoionization rate of hydrogen molecules under the interaction of intense light, by calculating the spatial overlap integral between the potential function and the time-dependent wavefunction. The suggested method was applied to varying excitation pulse shapes: square envelope and chirped hyperbolic secant envelope. The computed results confirmed that our method was robust and could be extended to general molecular dynamics calculations.
 Select Oscillator Strength for n=2 Transitions in Highly Ionized Sulfur YANG Zhi-Hu, DU Shu-Bin, CHANG Hong-Wei, ZHANG Xiao-An, SU Hong, ZHANG Yan-Ping, SONG Zhang-Yong Chin. Phys. Lett. 2005, 22 (5): 1099-1101 .   Abstract   PDF(pc) (253KB) ( 539 ) Oscillator strength f-values for L-shell transitions in highly ionized sulfur are studied by the beam--foil technique at the HI-13 tandem accelerator in China Institute of Atomic Energy. The lifetimes of the upper levels 2s2p1P01, 2p2 1S0, 2p2 3P1, 2p2 3 P2, 2 p2 3P0 of Be-like sulfur are measured to be 129±4, 81±5, 165±7, 159±8, 176±11ps. By using the measured lifetimes, the f-values are calculated to be 0.074, 0.082, 0.060, 0.066, 0.229, 0.056, 0.083, 0.089, 0.028 for the transitions 2s22p2 3P1－2s2p3 3P01, 2s22p 2P03/2-2s2p2 2P1/2, 2s2p2 4P3/2-2p3 4S03/2, 2s22p 2P01/2-2s2p2 2D3/2, 2s2 1S0-2s2p 1P01, 2s2p1P01-2p2 1S0, 2s2p3P00-2p2 3P1, 2s2p 3P022p2 3P2 and 2s2p 3P01-2p2 3P0. Most of the experimental results are in agreement with theoretical studies, but differ slightly from the previous experimental data.
 Select A Novel Atomic Guiding Using a Blue-Detuned TE01 Mode in Hollow Metallic Waveguides AI Meng, YIN Jian-Ping Chin. Phys. Lett. 2005, 22 (5): 1102-1105 .   Abstract   PDF(pc) (349KB) ( 448 ) We propose a novel scheme to guide cold atoms using a blue-detuned TE01 doughnut mode in a hollow metallic waveguide, calculate the electromagnetic field distribution of the TE01 mode in the hollow metallic waveguide, and compare the attenuation characters of the EH11 and TE01 mode in the hollow metallic waveguide. We also calculate the optical potential of the TE01 doughnut mode for two-level 85Rb atoms and estimate the photon scattering rate. It is found that when the detuning δ= 300GHz, the photon scattering induced heating can be neglected, and the optical potential (Umax about 570mK) of the TE01 mode is high enough to load cold atoms (120μK) from a standard magneto-optical trap and to guide them in the hollow metallic waveguide, which is a desirable scheme to realize a computer-controlled atom lithography with an arbitrary pattern.
 Select Observation of F=2 Spinor Bose--Einstein Condensation in a Magnetic Field MA Xiu-Quan, CHEN Shuai, YANG Fan, XIA Lin, ZHOU Xiao-Ji, WANG Yi-Qiu, CHEN Xu-Zong, Chin. Phys. Lett. 2005, 22 (5): 1106-1109 .   Abstract   PDF(pc) (516KB) ( 543 ) Multiple-component Bose-Einstein condensation has been observed in a magnetic field generated by a controllable magnetic quadrupole-Ioffe-configuration trap. Different distributions of atoms in spinor Bose--Einstein condensates are created by changing the time difference of switching-off current in quadrupole-Ioffe-configuration coils and bias coils of the magnetic trap. A simple analysis is carried out to explain some phenomena of the experiment.
 Select Near-Threshold Low Rydberg Depletion Spectroscopy of H2, D2, and HD ZHANG Yan-Peng, GAN Chen-Li, SONG Jian-Ping, YU Xiao-Jun, GE Hao, MA Rui-Qiong, LI Chuang-She, LU Ke-Qing, E. E. Eyler Chin. Phys. Lett. 2005, 22 (5): 1110-1113 .   Abstract   PDF(pc) (393KB) ( 418 ) Using high-resolution depletion spectroscopy, we have experimentally studied the physics of near-threshold low Rydberg states of all three stable isotopic variants of molecular hydrogen. The experiments were required to calibrate the absolute wavelength, including several transitions from the EF (v=0) and EF (v=6 or v=9) to the same low-n Rydberg states. The measurements have been performed for several initial rotational levels in all three stable isotopic variants. Transitions to very high vibrational levels of the B, B', and C states have been measured with accuracy 0.002cm1. The pulsed amplifier perturbations were also measured by optical heterodyne methods.
 Select Continuum Structures at the Second Dissociation Limit of Hydrogen Molecules ZHANG Yan-Peng, GAN Chen-Li, SONG Jian-Ping, YU Xiao-Jun, MA Rui-Qiong, GE Hao, JIANG Tong, LU Ke-Qing, E. E. Eyler Chin. Phys. Lett. 2005, 22 (5): 1114-1117 .   Abstract   PDF(pc) (545KB) ( 490 ) We describe near-threshold high-resolution spectra and continuum resonance dynamical behaviour of all three stable hydrogen isotopic variants, and finally obtain improved values for the dissociation energies of hydrogen molecule and its ion. The second dissociation limit is determined by analysing the onset of the vibrational continuum.
 Select X-Ray Emission from Zr, Mo, In and Pb Targets Bombarded by Slow Highly Charged Arq+(q =13, 14, 15, 16) Ions CAI Xiao-Hong, YU De-Yang, LU Rong-Chun, SHAO Cao-Jie, Lu Jun, RUAN Fang-Fang, YANG Zhi-Hu, DING Bao-Wei, ZHANG Hong-Qiang, SHAO Jian-Xiong, CUI Ying, XU Xu, CHEN Xi-Meng Chin. Phys. Lett. 2005, 22 (5): 1118-1120 .   Abstract   PDF(pc) (408KB) ( 524 ) We study the L x-ray emission from Zr, Mo and In targets and M x-ray emission from Pb target under bombardment of low energy Arq+ (q=13,14,15,16) ions. The relative x-ray yields were measured in the projectile kinetic energy range 210--360keV. It is found that the relative x-ray yields from Zr, Mo and Pb targets increase with the increasing projectile kinetic energy for Ar14+ and Ar16 projectiles and depend on the potential energy of the projectile remarkably.
 Select Optical Image Contrast Reversal Using Bacteriorhodopsin Films WANG Ying-Li, YAO Bao-Li, MENKE Neimule, ZHENG Yuan, LEI Ming, CHEN Guo-Fu Chin. Phys. Lett. 2005, 22 (5): 1121-1123 .   Abstract   PDF(pc) (296KB) ( 581 ) The implementation of image contrast reversal by using a photochromic material of Bacteriorhodopsin (BR) films is demonstrated with two methods based on the optical properties of BR. One is based on the absorption difference between the B and M states. Images recorded by green light can be contrast reversed readout by violet light. The other is based on the photoinduced anisotropy of BR when it is excited by linear polarization light. By placing the BR film between two crossed polarizers (i.e. a polarizer and an analyser), the difference of polarization states of the recorded area and the unrecorded area can be detected, and thus different contrast images can be obtained by rotating the polarization axis of the analyser.
 Select Optical Wavelet Packet Transform CAI De, YAN Ying-Bai, HUANG Huan, JIN Guo-Fan Chin. Phys. Lett. 2005, 22 (5): 1124-1126 .   Abstract   PDF(pc) (252KB) ( 821 ) We employ optical wavelet packet transform (OWPT) to propose an opto-electronic system based on volume holography to select the best bases of image banks for image compression, because of the superior processing ability to optical wavelet transform and the potentiality in new application fields. The simulation results show that the best bases chosen are the same as the bases selected by discrete wavelet packet transform (DWPT). Because DWPT is time consuming, especially when the volume of image bank is very large, processing time can be greatly shortened by OWPT.
 Select Sensitivity Improvement by UV-Light Recording in LiNbO3:Ce:Cu Crystals DAI Cui-Xia, LIU Li-Ren, LIU De-An, CHAI Zhi-Fang Chin. Phys. Lett. 2005, 22 (5): 1127-1130 .   Abstract   PDF(pc) (381KB) ( 514 ) Modulated UV light is used to increase the sensitivity of the two-centre holographic recording. Inherent mechanisms of nonvolatile holographic recording in oxidized and reduced crystals are numerically analysed based on solving the two-centre material equations modified for UV-light recording. Experiments verification is performed with an oxidized crystal and a reduced crystal, and the role of UV intensity on the sensitivity is presented.
 Select Multi-Partite EPR Entangled State Representation for Continuous Variables and Its Application in Squeezing Theory JIANG Nian-Quan Chin. Phys. Lett. 2005, 22 (5): 1131-1134 .   Abstract   PDF(pc) (190KB) ( 615 ) By extending the Einstein--Podolsky--Rosen (EPR) bipartite entanglement to an n-partite case, we construct the common eigenstate of the n-partite total coordinate and relative momenta for the continuous variables. The entanglement property of the state is shown. The classical dilation transform of variables in such a state induces a new n-mode squeezing operator related to an n-mode bosonic operator realization of SU(1,1) Lie algebra.
 Select Analytical Expression of Efficiency for an Ultraslow Light Four-Wave Mixing Scheme YANG Xiao-Xue, WEI Hua, WU Ying, Chin. Phys. Lett. 2005, 22 (5): 1134-1136 .   Abstract   PDF(pc) (320KB) ( 583 ) We derive an explicit analytical expression of the efficiency for a scheme of four-wave mixing (FWM) in a ladder-type lifetime broadened four-level atomic system and show that this scheme can achieve an FWM efficiency higher than the previous ultraslow light FWM schemes.
 Select High Power One- and Two-Order Cascaded Raman Lasers Based on Home-Made Phosphosilicate Fibre FENG Ming, LI Yi-Gang, LI Jia-Fang, LI Jing, ZHANG Xiao-Guang, LU Ke-Cheng, WANG Hong-Jie Chin. Phys. Lett. 2005, 22 (5): 1137-1143 .   Abstract   PDF(pc) (416KB) ( 942 ) One- and two-order cascaded Raman fibre lasers are demonstrated by using home-made P-doped Raman fibres. An output power of 2.8W at 1245nm with a slope efficiency of 33.4% and an output power of 2.0W at 1495nm with a slope efficiency of 23.5% are obtained with the pump source at 1069.7nm.
 Select Blue Up-Conversion Fibre Laser Pumped by a 1120-nm Raman Fibre Laser QIN Guan-Shi, HUANG Sheng-Hong, FENG Yan, SHIRAKAWA A., MUSHA M., UEDA Ken-ichi Chin. Phys. Lett. 2005, 22 (5): 1140-1143 .   Abstract   PDF(pc) (425KB) ( 570 ) A Tm3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibre up-conversion laser pumped by a 1120-nm Raman fibre laser is demonstrated with blue output power levels up to 116mW. For the output mirror with 80% reflectivity, the slope efficiency is about 15%, the optical-to-optical conversion efficiency is 11%, and the maximum un-saturated output power is 116mW. For 60% reflectivity, the slope efficiency is about 18% and the optical-to-optical conversion efficiency is 12%, whilst the maximum saturated output power is about 80mW due to the existence of photo-degradation effect in Tm3+ doped ZBLAN glass fibre.
 Select A High-Power Continuous-Wave Laser-Diode End-Pumped Nd:YVO Laser of Single-Frequency Operation XI Wen-Qiang, ZHAO Jing-Yun, ZHANG Kuan-Shou Chin. Phys. Lett. 2005, 22 (5): 1144-1147 .   Abstract   PDF(pc) (424KB) ( 975 ) We design and build a cw high quality and high power Nd:YVO4 laser of single frequency operation with a laser-diode dual-end-pumped geometry. The influence of the Nd3+-doping concentration in the Nd:YVO4 crystal on the output performance of laser is theoretically and experimentally studied. With a Nd:YVO4 crystal of the Nd3-doping concentration 0.3at.% and at pump power of 45W, the output power of the single frequency laser is 18W, and the slope efficiency is 48%.
 Select A Novel Method for Multi-Pumped Fibre Raman Amplifier Gain Adjustment HAN Qun, NING Ji-Ping, CHEN Zhi-Qiang, SHANG Lian-Ju Chin. Phys. Lett. 2005, 22 (5): 1148-1151 .   Abstract   PDF(pc) (535KB) ( 467 ) A novel method for gain adjustment of multi-pumped fibre Raman amplifiers is proposed and numerically demonstrated. The method uses the areas under the curves of the pump power evolution along the gain fibre and the Newton--Raphson method to find an appropriate power combination of the pumps to realize the desired gain profile. Compared with the previously proposed methods, our method has two advantages: first, it can maintain the gain profile while changing the gain magnitude to the desired value; second, it is independent of the actual pumping scheme of the amplifier, i.e. it can be used for fibre Raman amplifiers with all kinds of pumping schemes including co-, counter-, or bi-directional pumping. Numerical simulations are provided to verify the proposed method and to demonstrate its effectiveness.
 Select Four-Photon Process Induced Upconversion Lasing FAN Hai-Hua, WANG He-Zhou, TIAN Yu-Peng Chin. Phys. Lett. 2005, 22 (5): 1152-1154 .   Abstract   PDF(pc) (322KB) ( 588 ) It is measured that upconversion fluorescent intensity of a new molecule is proportional to the quartic of excitation density. This demonstrates that it is a four-photon absorption process. Furthermore, at high-density ultrashort pulse laser pumping, an emission appears to satisfy four criteria of lasing, including the highly directional emission, the short emission duration, the spectral narrowing, and changing to linear output/input relationship above a threshold. The experimental results demonstrate that the four-photon-process-induced amplified spontaneous emission occurs.
 Select Preparation of TiO2 Inverse Opal via a Modified Filling Process ZHOU Qian, DONG Peng, YI Gui-Yun, LIU Li-Xia, CHENG Bing-Ying Chin. Phys. Lett. 2005, 22 (5): 1155-1158 .   Abstract   PDF(pc) (424KB) ( 1150 ) By applying polystyrene opals made by a vertical deposition method as the templates, a modified filling method and a well-controlled calcination process, we have successfully obtained a large-area ordered TiO2 inverse opal with a higher volume fraction (14.5%) and a visible photonic bandgap. The influences of the filling process and calcination conditions on the fabrication of the TiO2 inverse opal are investigated.
 Select Polarization-Independent All-Fibre Comb Filter with Dynamically Halved Channel Spacing MA Xiu-Rong, KAI Gui-Yun, WU Zhi-Fang, GUO Hong-Lei, ZHANG Hao, LIU Yan-Ge, YUAN Shu-Zhong, DONG Xiao-Yi Chin. Phys. Lett. 2005, 22 (5): 1159-1161 .   Abstract   PDF(pc) (438KB) ( 612 ) A polarization-independent all-fibre comb filter with dynamically halved channel spacing is proposed. The filter is based on high-birefringent fibre Sagnac interferometers and its channel spacing can be dynamically halved by turning on an optical switch. A good agreement between the numerical simulation and the experimental results is achieved.
 Select Mathematical Model for Fabrication of Micro-Structure Fibres ZHOU Gui-Yao, HOU Zhi-Yun, LI Shu-Guang, HOU Lan-Tian Chin. Phys. Lett. 2005, 22 (5): 1162-1165 .   Abstract   PDF(pc) (356KB) ( 734 ) Using the classic principles of mechanics, we discuss the shape transformation of the micro-structure fibre preform under high temperature of the fibre drawing process, which leads to the theoretical relations among the structural diameter of the micro-structure fibre, the drawing technical parameter, and the physical constant of the micro-structure fibre material. The theoretic values are basically in agreement with the experimental results.
 Select Spatial Characteristics of Head-Related Transfer Function ZHONG Xiao-Li, XIE Bo-Sun Chin. Phys. Lett. 2005, 22 (5): 1166-1169 .   Abstract   PDF(pc) (407KB) ( 700 ) The spatial characteristics of head-related transfer functions (HRTFs) are studied by a spatial Fourier analysis. A law of the HRTF spatial sampling in different elevation planes is obtained, and the corresponding spatial interpolating method used to recover the continuous HRTF is proposed. The method is valid, for the average error between the measured and interpolated HRTFs in the horizontal plane is about 0.5%. These results provide guidance for the discrete spatial measurement of HRTFs.
 Select Electron Temperature Gradient Driven Instability in High Beta Plasmas of a Sheared Slab LIU Feng, DONG Jia-Qi, GAO Zhe Chin. Phys. Lett. 2005, 22 (5): 1170-1173 .   Abstract   PDF(pc) (418KB) ( 638 ) Neglecting the magnetic gradient drift effects, we derive a simplified version of the integral eigenvalue equations for perturbations of electrostatic potential, and the perpendicular and parallel components of magnetic vector potential in plasmas of sheared slab geometry. The electron temperature gradient (ETG) instability in high beta plasmas is studied with the equations and the corresponding computer code. The preliminary results indicate that the coupling to perturbation of the perpendicular component of the magnetic vector potential has strong destabilization effects on ETG instabilities in contrast to the stabilization effects from the coupling to that of the parallel component when the magnetic gradient drift is not taken into account.
 Select High-Energy Ion Emission from Cooled Deuterium Clusters in 20TW Laser Fields LIU Hong-Jie, GU Yu-Qiu, WANG Hong-Bin, ZHENG Zhi-Jian, GE Fang-Fang, WEN Xian-Lun, JIAO Chun-Ye, HE Ying-Ling, WEN Tian-Shu, HUANG Wen-Zhong, WANG Guang-Chang, ZHOU Wei-Min, ZHANG Shuang-Gen, WANG Xiang-Xian, ZHOU Kai-Nan, WANG Xiao-Dong, HUANG Xiao-Jun, NI Guo-Quan Chin. Phys. Lett. 2005, 22 (5): 1174-1175 .   Abstract   PDF(pc) (250KB) ( 562 ) High-energy ion emission from intense-ultrashort (30fs) laser-pulse-cooled deuterium-cluster (80K) interaction is measured. The deuterium ions have an average energy 20keV, which greatly exceeds Zweiback's expectation [Phys. Rev. Lett. 84 (2000) 2634]. These fast deuterium ions can be used to drive fusion and have a broad prospect.
 Select Dependence of the Average Lorentz Factor on Temperature in Relativistic Plasmas AN Wei-Ke, QIU Xi-Jun, SHI Chun-Hua, ZHU Zhi-Yuan Chin. Phys. Lett. 2005, 22 (5): 1176-1178 .   Abstract   PDF(pc) (241KB) ( 478 ) For the relativistic plasma, how to fix the Lorentz factors of the particles is an important but difficult problem. We resolve this problem by demonstrating the exact relation between the average Lorentz factor and temperature in relativistic plasmas. A rather simple relation is also obtained for the ultra-relativistic case.
 Select Geodesic Acoustic Mode in Toroidally Axisymmetric Plasmas with Non-Circular Cross Sections SHI Bing-Ren, LI Ji-Quan, DONG Jia-Qi Chin. Phys. Lett. 2005, 22 (5): 1179-1182 .   Abstract   PDF(pc) (349KB) ( 458 ) The geodesic acoustic mode in general toroidally axisymmetric plasmas such as Tokamak and spherical torus is studied in detail. The mode structure is found and the dispersion equation is derived and solved for arbitrary toroidally axi-symmetric plasmas. Besides the finite aspect ratio, effects of elongation and triangularity on this mode are clarified.
 Select Coronal and Local Thermodynamic Equilibriums in a Hollow Cathode Discharge ZHENG Xu-Tao, Chin. Phys. Lett. 2005, 22 (5): 1183-1186 .   Abstract   PDF(pc) (360KB) ( 450 ) A characteristic two-section profile of excited-state populations is observed in a hollow cathode discharge and is explained by coexistence of the coronal equilibrium (CE) and the local thermodynamic equilibrium (LTE). At helium pressure 0.1Torr and cathode current 200--300mA, vacuum ultraviolet radiations from He I 1snp 1 (n= 2-16) and He II np2P (n= 2-14) are resolved with a 2.2-M McPherson spectrometer. Relative populations of these states are deduced from the discrete line intensities and are plotted against energy levels. For both the He I and He II series, as energy level increases, populations of high-n (n>10) states are found to decrease much more quickly than low-n (n< 7) populations. While low-n populations are described with the CE dominated by direct electron-impact excitations, high-n populations are fitted with the LTE to calculate the population temperatures of gas atoms and ions.Validities of the CE and LTE in different n-ranges are considered on the competition between radiative decays of the excited states and their collisions with gas atoms.
 Select A Two-Flux Radiation Model for Helical Instability of Arcs GONG Ye, ZHENG Shu, XU Xiang, ZOU Xiu, LIU Jin-Yuan, LIU Yue, WANG Xiao-Gang Chin. Phys. Lett. 2005, 22 (5): 1187-1190 .   Abstract   PDF(pc) (365KB) ( 527 ) A two-flux radiation model of the helical instability of arcs in axial magnetic field is presented. The temperature (and electrical conductivity) is approximated in a more realistic way (parabolic instead of flat profile) and a simplified term of radiation losses is included in the energy equation. The magnetohydrodynamic equations in an electrostatic approximation serve as the starting point of the theory. Using a linear time-dependent perturbation theory, the corresponding equations and an explicit analytic expression that corresponds to the term of radiation losses are derived in the presence of the radiation transfer energy, from which the marginal Maecker number and the growth rate of the helical instability can be given. It is found that, in comparison with the results without radiation, the arc stable area is reduced.
 Select Growth and Characterization of GaAs/AlGaAs Thue--Morse Quasicrystal Photonic Bandgap Structures ZHANG Yong-Gang, JIANG Xun-Ya, ZHU Cheng, GU Yi, LI Ai-Zhen, QI Ming, FENG Song-Lin Chin. Phys. Lett. 2005, 22 (5): 1191-1194 .   Abstract   PDF(pc) (0KB) ( 441 ) One-dimensional quasicrystal structures composed of III-V semiconductor GaAs/AlGaAs multilayers in deterministic Thue--Morse (TM) sequences have been grown by using gas-source molecular beam epitaxy to investigate both the structural and the photonic bandgap properties. The x-ray measurements show that this aperiodic system exhibits obvious periodic spatial correlations, from which the precise thickness of the constitutive layers could be determined. Transmission and reflection measurements experimentally demonstrated plenty of photonic bandgaps with traditional or fractal features existing in those quasicrystal structures, which are in good agreement with the transfer matrix simulations. The diversity of this TM system makes it a good candidate for photonic device applications.
 Select Electronic and Elastic Properties of Helical Nickel Nanowires WANG Bao-Lin, , ZHAO Ji-Jun, SHI Da-Ning, JIA Jian-Min, WANG Guang-Hou Chin. Phys. Lett. 2005, 22 (5): 1195-1198 .   Abstract   PDF(pc) (364KB) ( 683 ) The structural and elastic properties of ultrathin nickel nanowires are investigated by using molecular dynamics simulation with a Sutton--Chen potential. Helical multi-shell structures are obtained as the most stable structures for Ni nanowires with diameters of about 1nm. The electronic states of these nanowires are computed and compared with that of Ni solid. The mechanical responses of the helical nanowires under tensile forces are simulated. We observe elastic deformation of nanowires characterized by periodic oscillations of the nanowire length under constant force. Within an elastic limit, both the atomic structures and the electronic structures remain stable under external tensile loading.
 Select Isostructural Phase Transition of TiN under High Pressure ZHAO Jing-Geng, YANG Liu-Xiang, YU Yong, YOU Shu-Jie, YU Ri-Cheng, LI Feng-Ying, CHEN Liang-Chen, JIN Chang-Qing, LI Xiao-Dong, LI Yan-Chun, LIU Jing Chin. Phys. Lett. 2005, 22 (5): 1199-1201 .   Abstract   PDF(pc) (375KB) ( 672 ) In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaCl-type structure have been conducted with the pressure up to 30.1GPa by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The experimental results suggest that an isostructural phase transition might exist at about 7GPa as revealed by the discontinuity of V/V0 with pressure.
 Select Phase Structural Characteristics of ZrV2 Thin Film Prepared by Magnetron Sputtering XU Shi-Lin, SHI Li-Qun Chin. Phys. Lett. 2005, 22 (5): 1202-1204 .   Abstract   PDF(pc) (454KB) ( 554 ) The thin film metal hydride has become an emerging field of research in metal hydride batteries for its good mechanical and hydrogenation properties. ZrV2 thin films have been prepared using a dc magnetron sputtering method, and the phase structure is investigated. Only amorphous or crystalline Zr and V mixture phases are achieved when substrates are heated during either to 400°C or to 550°C. The annealing causes segregation of Zr and V in the film induced by strain-driven diffusion and interdiffusion between substrate Mo and film elements at high temperature, which results in the formation of mixture phases of C14, C15, Zr and V, but the content of C15 phase is not higher compared with that in the bulk material.
 Select A New Method to Prepare Boron Nitride Thin Films LIU Li-Hua, LI Ying-Ai, FENG Wei, LI Wei-Qing, ZHAO Chun-Hong, WANG Yu-Xin, ZHAO Yong-Nian Chin. Phys. Lett. 2005, 22 (5): 1205-1209 .   Abstract   PDF(pc) (314KB) ( 538 ) We report a new method to prepare boron nitride (BN) thin films on Si (100) substrates in an Ar-N2-BCl3-H2 gas system by magnetron arc enhanced plasma chemical vapour deposition. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize the films. The FTIR spectra show that the deposited boron nitride films experienced a transition from pure h-BN phase to a cubic-containing phase with the variation of arc current ranging from 10A to 18A. The BN film with 42% c-BN was obtained without substrate bias voltage. In the gas system of Ar--N2-BCl2-H2, h-BN can be preferentially etched by chlorine. The chemical etching effect of chlorine allows the formation of c-BN without substrate bias voltage, which may develop a new perspective for the deposition of high quality c-BN film with low stress.
 Select One-Dimensional Anyon Lattice and slq(2) Algebra Realization Z. Bentalha, M. Tahiri, B. Liani Chin. Phys. Lett. 2005, 22 (5): 1207-1209 .   Abstract   PDF(pc) (205KB) ( 736 ) We discuss the connection between anyons (particles with fractional statistics) living on a one-dimensional lattice and slq(2) algebra. We assign to each site-anyon field, then we demand the anyonic fields to be noncommuting objects in agreement with the Chern--Simons picture of anyons. We show how the anyonic algebra can emerge from these noncommuting objects. Starting from the emerged algebra we build the slq(2) algebra at q roots of unity.
 Select The Second Threshold Field of Charge-Density-Wave Conductor Rb0.3MoO3 in High Temperature Range LI Da-Hua, XIONG Rui, WANG Jun-Feng, LI Chang-Zhen, YIN Di, YI Fan, TANG Wu-Feng, SHI Jing, Chin. Phys. Lett. 2005, 22 (5): 1210-1213 .   Abstract   PDF(pc) (523KB) ( 480 ) The switching and threshold properties of quasi-one-dimensional charge-density-wave conductor rubidium blue bronze Rb0.33MoO3 single crystals are investigated in a comparative high and large temperature range. Beyond the limit temperature 50K of Littlewood's theory, even up to about 100K, typical sharp switching to negative or zero differential resistance is observed in E-I characteristic curves. Correspondingly, an obvious switching between two conducting states, from a lowly conducting state to a highly conducting state, is observed in the I-E characteristic curves in the same temperature range. Temperature dependence of the second threshold field ET2 accompanied by this kind of high field switching behaviour is firstly obtained. These new observations are discussed in the mechanism of the current inhomogeneity and redistribution due to the existence of transverse energy barriers suggested by Zhang et al. [Solid State Commun. 85 (1993) 121]
 Select Variable Energy Positron Annihilation Spectroscopy of GaN Grown on Sapphire Substrates with MOCVD HU Yi-Fan, C. D. Beling, S. Fung Chin. Phys. Lett. 2005, 22 (5): 1214-1217 .   Abstract   PDF(pc) (378KB) ( 630 ) Depth profiled Doppler broadening of positron annihilation spectroscopy (DBPAS), which is also called the variable energy positron annihilation spectroscopy (VEPAS), is used in characterization of GaN grown on sapphire substrates with metal-organic chemical vapour deposition (MOCVD). The GaN film and the film/substrate interface are investigated. The VEPFIT (variable energy positron fit) software was used for analysing the data, and the positron diffusion length of the sapphire is obtained. The results suggest that there is a highly defected region near the GaN/sapphire interface. This thin dislocated region is generated at the film/substrate interface to relieve the strain. Effects of implantation dose on defect formation, for the GaN/Sapphire samples, which implanted by Al+ ions, are also investigated. Studies on Al+ implanted GaN films (not including the interface and sapphire) have revealed that there are two different regions of implantation damage. For the low Al+ implantation dose samples, in the region close to the surface, defects are mainly composed of vacancy pairs with small amount of vacancy clusters, and in the interior region of the film the positron traps are vacancy clusters without micro-voids. For the highest dose sample, however, some positron trap centres are in the form of micro-voids in the second region.
 Select Temperature-Dependent Galvanomagnetic Measurements on Doped InSb and InAs Grown by Liquid Encapsulated Czochralski M. Kasap, S. Acar, S. Ö, celik, S. Karadeniz, N. Tugluoglu Chin. Phys. Lett. 2005, 22 (5): 1218-1221 .   Abstract   PDF(pc) (597KB) ( 710 ) Resistivity, magnetoresistivity and Hall effect measurements in n-type Te-doped InSb and S-doped InAs samples grown by the liquid encapsulated Czochralski technique were carried out as a function of temperature (14-350K) and magnetic field (0-1.35T). In Te-doped InSb, an impurity level with energy E1 = 3meV and the activation energy E0= 0.26eV, which is the band gap energy, are obtained from the resistivity and Hall carrier concentration analysis. In S-doped InAs, both the linear and power law models are used in explaining the temperature-dependent resistivity. The effects of impurities on the electron and magnetic transportation properties of InAs and InSb have also been discussed.
 Select A New Type of Photoelectric Response in a Double Barrier Structure with a Wide Quantum Well ZHOU Xia, ZHENG Hou-Zhi Chin. Phys. Lett. 2005, 22 (5): 1222-1224 .   Abstract   PDF(pc) (299KB) ( 505 ) We have calculated the photoelectric response in a specially designed double barrier structure. It has been verified that a transfer of the internal photovoltaic effect in the quantum well to the tunnelling transport through above-barrier quasibound states of the emitter barrier may give rise to a remarkable photocurrent.
 Select Photoluminescence of Eu (III)-Doped ZnO Nanopowder and Energy Transfer from ZnO to Eu(III) Ions ZHANG Lin-Li, GUO Chang-Xin, ZHAO Jun-Jing, HU Jun-Tao Chin. Phys. Lett. 2005, 22 (5): 1225-1227 .   Abstract   PDF(pc) (488KB) ( 903 ) An europium(III)-doped ZnO (ZnO:Eu3+) nanopowder has been directly synthesized by a high-temperature calcination method. Under the typical UV ZnO excitation, Eu3+-doped samples exhibit strong red luminescence from Eu3+ ions with complete quenching broad emission. An energy transfer from ZnO host to Eu3+ ions can be observed.
 Select Substrate Dependence of Properties of Sputtered ITO Films GAO Mei-Zhen, SHI Hui-Gang, Job R., LI Fa-Shen, Fahrner W. R. Chin. Phys. Lett. 2005, 22 (5): 1228-1231 .   Abstract   PDF(pc) (576KB) ( 541 ) High-quality indium-tin-oxide (ITO) films are deposited on p-type Czochralski silicon and 7059 Corning glass by direct-current magnetron sputtering at various temperatures. The structural, electrical and optical properties of the ITO films are investigated as functions of the substrate temperature. A comparison between the characteristics of the ITO films on silicon and Corning glass is presented. The results show that for the ITO film on silicon, the nucleation begins from room temperature; the resistivity reaches a maximum value at 75°C; the reflectivity increases with increasing temperature; when temperature is above 125°C, the ITO grows in a three-dimensional manner and forms a granular structure. However, for the ITO film on glass, it is still in an amorphous state at 75°C. Moreover, both the resistivity and the reflectivity decrease with increasing temperature. Above 125°C, the ITO grows in a two-dimensional manner and forms a domain structure.
 Select First-Principles Study of Structural and Magnetic Properties for Ultrathin Cr Films on W(100) and W(110) WEI Xin, JIANG Ping, CHE Jing-Guang Chin. Phys. Lett. 2005, 22 (5): 1232-1235 .   Abstract   PDF(pc) (330KB) ( 707 ) The stability, atomic structural and magnetic properties of ultrathin Cr films on W(100) and W(110) substrates are studied by using ab-initio total energy calculations. It is demonstrated that the overlayer structures of monolayer (ML) Cr on W(100) or W(110) substrates are stable against the interdiffusion. Large top-layer downward relaxations are found for both the systems. The relationship between relaxation and magnetic configuration is also analysed. The magnetic ground state is found to be p(1×1) ferromagnetic and c(2×2) antiferromagnetic with enhanced magnetic moments of 2.47μB and 2.55vB for 1ML Cr on W(100) and W(110) substrates, respectively.
 Select Reorientation of Defect Dipoles in Ferroelectric Ceramics LI Bao-Shan, LI Guo-Rong, ZHAO Su-Chuan, ZHU Zhi-Gang, DING Ai-Li Chin. Phys. Lett. 2005, 22 (5): 1236-1238 .   Abstract   PDF(pc) (473KB) ( 1316 ) We investigate the frequency, temperature, tetragonality and quenched temperature dependences of the hysteresis loops in Pb[(Zr0.52Ti0.48)0.95(Mn1/3Nb2/3)0.05]O3 (PMnN-PZT) ceramics. It has been demonstrated that the polarization-field hysteresis curves show pinched'' shapes when tested at room temperature, higher frequency or using the large-tetragonality specimen. While normal square-like loops are observed at 200°C and 0.01Hz or using the small-tetragonality one. Meanwhile, close relations between the P-E loops and the applied frequency, temperature or tetragonality reveal that there exists a typical relaxation time corresponding to the reorientation of the defect dipoles. It can be seen further from the quenched temperature dependences of the loops that the reorientation of the defect dipoles may influence the pinching. Compared to the intrinsic depinning procedure induced by changes of the distribution of defect dipoles, we provide new evidence for extrinsic depinning mechanism of the defect dipoles in the ferroelectric ceramics.
 Select Water-Induced Degradation in Lead Zinc Niobate--Lead Zirconate Titanate Soft Piezoelectric Ceramics JIANG Xiang-Ping, CHEN Wan-Ping, PENG Zhi, ZENG Min, CHAN-WANG Li-Hua, YIN Qing-Rui Chin. Phys. Lett. 2005, 22 (5): 1239-1242 .   Abstract   PDF(pc) (392KB) ( 521 ) Water-induced degradation of lead zinc niobate--lead zirconate titanate (Pb(Zn1/3Nb2/3)O3-Pb(ZrTi)O3) soft piezoelectric ceramics is studied using electrochemical hydrogen charging, in which the silver electrodes of the piezoelectric ceramics constitute a cathode in 0.01-M NaOH solution to evolve hydrogen by electrolysis of water. It is found that with the increasing hydrogen charging time, the resonance impedance increases, the difference between the resonance frequency and the anti-resonance frequency decreases, the spontaneous polarization, the remanent polarization and the piezoelectric coefficient d33 decrease. The degradation behaviour of the soft piezoelectric ceramics can be explained to hydrogen incorporating into the lattice and forming hydroxy (OH-) bonds in the perovskite structure, which prevents the Ti ions from switching and increases the coercive field Ec. The degradation characteristics of the soft piezoelectric ceramics are quite different from that of lead zirconate titanate hard piezoelectric ceramics.
 Select Effects of Substrates with Different Dielectric Parameters on Left-Handed Frequency of Left-Handed Materials QUAN Bao-Gang, LI Chao, SUI Qiang, LI Jun-Jie, LIU Wu-Ming, LI Fang, GU Chang-Zhi Chin. Phys. Lett. 2005, 22 (5): 1243-1245 .   Abstract   PDF(pc) (396KB) ( 544 ) Wedge-shaped left-handed materials (LHMs) with split ring resonators and wires structures are fabricated by photolithography and lift-off techniques, and the variation of left-handed frequency induced by substrates with different dielectric parameters is investigated. The Snell refraction experiments of the LHM samples are carried out on an angular resoled microwave spectrometer, and the results indicate that the left-handed frequencies of the LHMs shifted downward from 10.57GHz to 9.74GHz when the dielectric parameters of the LHM substrates increase from 3.7 to 4.8. Moreover, the finite difference time domain method is used to simulate the microwave transmission properties of the left-handed materials with different substrates, and the experimental results are in agreement with the numerical simulation results. In addition, the reason for the shifting of the left-handed frequency of the LHMs is discussed theoretically.
 Select optical, Structural and Laser-Induced Damage Threshold Properties of HfO2 Thin Films Prepared by Electron Beam Evaporation ZHAN Mei-Qiong, Zhang Dong-Ping, TAN Tian-Ya, HE Hong-Bo, SHAO Jian-Da, FAN Zheng-Xiu Chin. Phys. Lett. 2005, 22 (5): 1246-1248 .   Abstract   PDF(pc) (535KB) ( 745 ) We prepare HfO2 thin films by electron beam evaporation technology. The samples are annealed in air after deposition. With increasing annealing temperature, it is found that the absorption of the samples decreases firstly and then increases. Also, the laser-induced damage threshold (LIDT) increases firstly and then decreases. When annealing temperature is 473K, the sample has the highest LIDT of 2.17J/cm2, and the lowest absorption of 18ppm. By investigating the optical and structural characteristics and their relations to LIDT, it is shown that the principal factor dominating the LIDT is absorption.
 Select Structural and Upconversion Fluorescence Properties of Er3+/Yb3+-Codoped Lead-Free Germanium-Bismuth Glass SUN Hong-Tao, ZHANG Li-Yan, DUAN Zhong-Chao, YU Chun-Lei, ZHANG Jun-Jie, Dai Shi-Xun, HU Li-Li, JIANG Zhong-Hong Chin. Phys. Lett. 2005, 22 (5): 1249-1252 .   Abstract   PDF(pc) (381KB) ( 537 ) We study the structural and infrared-to-visible upconversion fluorescence properties of Er3+/Yb3+-codoped lead-free germanium-bismuth glass. The structure of lead-free germanium-bismuth-lanthanum glass is investigated by peak-deconvolution of Raman spectroscopy. Intense green and red emissions centred at 525, 546, and 657nm, corresponding to the transitions 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2, respectively, are observed at room temperature. The quadratic dependence of the 525, 546, and 657nm emissions on excitation power indicates that a two-photon absorption process occurs under 975nm excitation.
 Select Conduction Current Characteristics and Carrier Mobility of Both Original and Corona-Resistant Polyimide Films ZHANG Pei-Hong, FAN Yong, WANG Fo-Chi, XIE Hua, LI Gang, LEI Qing-Quan Chin. Phys. Lett. 2005, 22 (5): 1253-1255 .   Abstract   PDF(pc) (424KB) ( 546 ) The electric conduction current characteristics of both Dupont original and corona-resistant polyimide films (100HN and 100CR) before and after corona-aging eight hours under electric field of 10kV/mm and 20kV/mm were measured. The results show that the conduction current of 100CR is about one order of magnitude larger than that of 100HN. Based on the space charge aging theory, the electric degradation threshold obtained from the space charge limit current plot is 40kV/mm for 100CR and 35kV/mm for 100HN, and decreases with the increasing corona-aged field. By measuring the depolarization current of the two films at 170°C, it is observed that the decay of depolarization current of 100CR is faster than that of 100HN. Based on the depolarization current curve, the apparent carrier mobility and trap depth of 1.2×1013,m3/Vs to 3×1014m2/Vs and 1.052eV to 1.105eV for 100CR, 1.12×1013m2/Vs to 8×10-14m2/Vs and 1.054eV to 1.069eV for 100HN were, respectively, calculated during depolarizing.
 Select Luminescence Kinetic Model for Long-Afterglow Phosphor (Sr0.5Ca1.5)MgSi2O7:Eu2+,Dy3+ LIU Bo, SHI Chao-Shu, TAO Ye, XIAO Zhi-Guo Chin. Phys. Lett. 2005, 22 (5): 1256-1259 .   Abstract   PDF(pc) (426KB) ( 707 ) A luminescence kinetic model for the green-emission long-afterglow phosphor (Sr0.5Ca1.5)MgSi2O7:Eu2+,Dy3+ is proposed based on the studies of the thermoluminescence and isothermal decay curves at different temperatures. The isothermal decay curves at different temperatures meet the hyperbolic law and show to be dependent on temperature. Combined with the decay curves and the thermoluminescence curves, it can be concluded that the long afterglow of this material originates from the traps with energy distribution rather than a single level trap. Upon illumination with ultra-violet or visible light, the trap filling can proceed via excitation of 4f electrons to the 5d level of Eu2+ ions. After excitation, 5d electrons can be transferred to the trap related to Dy3+ ions, and Eu3+ is left behind. Upon subsequent heating, the electron is released from this trap and recombines with Eu3+ to produce Eu2+ emission.
 Select Nanomorph Silicon Thin Films Prepared by Using an HW-MWECR CVD System HU Yue-Hui, CHEN Guang-Hua, ZHOU Jian-Er, RONG Yan-Dong, LI Ying, SONG Xue-Mei, ZHANG Wen-Li, DING Yi, GAO Zhuo, MA Zhan-Jie, ZHOU Huai-En, ZHU Xiu-Hong Chin. Phys. Lett. 2005, 22 (5): 1260-1263 .   Abstract   PDF(pc) (505KB) ( 468 ) We have prepared hydrogenated nano-amorph silicon (na-Si:H) films by using a hot-wire-assisted microwave electron-cyclotron-resonance (HW-MWECR) chemical vapour deposition (CVD) system. The films are deposited in two steps: in the first 9min, a hydrogenated amorphous silicon layer is deposited by using hydrogen-diluted silane with a concentration of SiH4/(SiH4+H2)=20%, and then a nanocrystalline silicon (nc-Si) layer is deposited by using various highly hydrogen-diluted silane. The Raman TO-like mode peak of the films was found in the range 497-508cm$^{-1}$. When the silane concentration used for preparation of the nc-Si layer is 14.3%, the film has a large crystalline volume fraction of 65.4%, a wide optical band gap of 1.89eV and a low hydrogen content of 9.5at.%. Moreover, the na-Si:H films rather than nc-Si possess high photosensitivity of about 105.
 Select Characterization of Defects in Chemical Vapour Deposited Diamonds ZHANG Ming-Long, XIA Yi-Ben, WANG Lin-Jun, GU Bei-Bei Chin. Phys. Lett. 2005, 22 (5): 1264-1266 .   Abstract   PDF(pc) (333KB) ( 513 ) Room-temperature Raman and PL spectra, photocurrent (PC) and thermally stimulated current (TSC) were measured to investigate the mid-gap defects in diamonds grown by using a hot-filament chemical vapour deposition (CVD) technique. The [Si-V]0 centres caused by the Si-C bonds in diamond grains and at grain boundaries are located at 1.68eV. We firstly detect the level 1.55eV by using PL and it is tentatively attributed to the zero-phonon luminescence line or vibronic band of the [Si-V]0 induced by the Si-O bonds. The 2.7-3.2eV and 1.9-2.1eV PC peaks were detected and discussed. The [N-V] complex may be attributed to these defect levels. Some shallow energy levels lower than 1.0eV were also observed in the CVD diamond.
 Select Effect of Geometrical Confinement on Depletion Interactions in Colloidal Suspensions GUO Ji-Yuan, LI Chun-Shu, XIAO Chang-Ming Chin. Phys. Lett. 2005, 22 (5): 1267-1269 .   Abstract   PDF(pc) (381KB) ( 553 ) The depletion effect between two big hard spheres in a sea of small spheres under a geometrical confinement is studied by Monte Carlo simulations. The numerical results show that both the depletion potential and depletion force are sensitive to the geometrical confinements.
 Select An Effective Three-Dimensional Micromagnetic Method and Its Application to Magnetic Tunnel Junctions LIU Yao-Wen, CHEN Yu-Guang, YANG Ya-Ping, CHEN Hong, Martins J. L. Chin. Phys. Lett. 2005, 22 (5): 1270-1273 .   Abstract   PDF(pc) (404KB) ( 577 ) An effective three-dimensional micromagnetic method for predicting equilibrium configuration of magnetization states is presented with conjugate-gradient technique to minimize the total energy, which has a much faster convergence rate than that of the quasi-Newton method. As an application, magnetic tunnel junctions with pinholes in the ultrathin barrier are simulated. The calculated coupling field Hf increases with the pinhole density increase, corresponding to the decrease of barrier thickness. The free layer domain configuration of tunnel junction during the switching process is also demonstrated.
 Select Scaling Behaviour of Conserved Sites in Protein Families LI Jie, WANG Jun, WANG Wei Chin. Phys. Lett. 2005, 22 (5): 1274-1277 .   Abstract   PDF(pc) (316KB) ( 435 ) Base on the database of families of structurally similar proteins, a statistical study is made on the scaling behaviour of occupying probabilities of conserved sites (Pc) in various protein families. A power-law decrease of Pc with the increasing protein-chain length Lf is found. This is related to the power-law scaling behaviour of the occurring probabilities of local contact interactions (Plocal) between residues. In addition, applying residue grouping, we find the same scaling behaviour when the number of residue types is more than 12, indicating that 12 residue types are enough to present the complexity of proteins.
 Select Measurement of Breaking Force of Fluorescence Labelled Microtubules with Optical Tweezers LIU Chun-Xiang, GUO Hong-Lian, XU Chun-Hua, YUAN Ming, LI Zhao-Lin, CHENG Bing-Ying, ZHANG Dao-Zhong Chin. Phys. Lett. 2005, 22 (5): 1278-1280 .   Abstract   PDF(pc) (315KB) ( 505 ) Under illumination of excitation light, the force that can make fluorescent dye-labelled microtubules break up is measured by using dual-beam optical tweezers. It is found that this force is about several piconewtons, which is two orders of magnitude smaller than that without fluorescence label. Microtubules can be elongated about 20% and the increase of the tensile force is nonlinear with the microtubule elongation. Some qualitative explanations are given for the mechanisms about the breakup and elongation of microtubules exposed to excitation light.
 Select Fermi--Dirac Statistics of Complex Networks SHEN Yi, ZHU Di-Ling, LIU Wei-Ming Chin. Phys. Lett. 2005, 22 (5): 1281-1284 .   Abstract   PDF(pc) (336KB) ( 616 ) We investigate phenomena of decline of complex networks by employing and analysing an illness model. Its intrinsic relation with the Fermi distribution is shown and a mapping to Fermi gas is established. The results of numerical simulations are obtained in two ways. We also compare the model with other models, including the dual relationship with the fitness model, and its difference from the Cayley tree model.
 Select Networks Emerging from the Competition of Pullulation and Decrepitude JIANG Pin-Qun, WANG Bing-Hong, ZHOU Tao, JIN Ying-Di, FU Zhong-Qian, ZHOU Pei-Ling, LUO Xiao-Shu Chin. Phys. Lett. 2005, 22 (5): 1285-1288 .   Abstract   PDF(pc) (595KB) ( 608 ) In real-world network evolution, the aging effect is universal. We propose a microscopic model for aging networks, which suggests that the activity of a vertex is the result of the competition of two factors: pullulation and decrepitude. By incorporating the pullulation factor into previous models of aging networks, both the global and individual aging effect curves in our model are single peaked, which agrees with the empirical data well. This model can generate networks with scale-free degree distribution, large clustering coefficient and small average distance when the decrepitude intensity is small and the network size not very large. The results of our model show that pullulation may be one of the most important factors affecting the structure and function of aging networks and should not be neglected at all.
 Select Effect of Gamma-Ray Beaming on the Fluxes of Gamma-Ray Pulsars JIANG Ze-Jun, ZHANG Li, Chin. Phys. Lett. 2005, 22 (5): 1289-1292 .   Abstract   PDF(pc) (388KB) ( 590 ) We study the effect of γ-ray beaming on γ-ray emission of the pulsars in a self-sustained outer gap model. In this model, averaged γ-ray flux is a function of period, magnetic field, magnetic inclination angle and solid angle of γ-ray beaming for a γ-ray pulsar. We generate a sample of γ-ray pulsars with their ages less than 106 years by using the Monte Carlo method, and then study the γ-ray beaming effect. The comparison of distributions of periods, magnetic fields, distances, γ-ray energy fluxes and period derivatives of the simulated γ-ray pulsars with those of observed γ-ray pulsars by the detector EGRET shows that γ-ray beaming has an important role on the detection of γ-ray pulsars. Furthermore, possible γ-ray pulsars observed by the detector GLAST are predicted.
 Select An Electromagnetic Model for Jet Power from an Advection Dominated Accretion Flow around a Rotating Black Hole GONG Xiao-Long, WANG Ding-Xiong Chin. Phys. Lett. 2005, 22 (5): 1293-1295 .   Abstract   PDF(pc) (341KB) ( 878 ) We discuss jet production from an advection dominated accretion flow (ADAF) around a rotating black hole (BH) in an electromagnetic regime. An analytical expression for the jet power is derived by using an equivalent circuit in the BH magnetosphere. It turns out that a large fraction of jet powers is contributed from the inner region of the ADAF, and the jet power depends sensitively on the degree to which the flow is advection-dominated. In addition, we use our model to fit the strong jet powers of several BL Lac objects, which cannot be explained by virtue of the BZ process.
 Select Exact Inflationary Solution to Nonminimally Coupled Scalar Field WANG Wen-Fu, YANG Shu-Zheng Chin. Phys. Lett. 2005, 22 (5): 1296-1299 .   Abstract   PDF(pc) (208KB) ( 522 ) We present a new exact inflationary solution to nonminimally coupled scalar field. The inflation is driven by the evolution of scalar field with inflation potential V(λ) =λ /4 ψ4 - 1/2m2 ψ 2 + V0. This includes the solution that behaves exponential inflation for ψ0 > ψ > ψend and then develops smoothly towards radiation-like evolution for ψ < ψend. The spectral index of the scalar density fluctuations, ns, is computed, and the result is consistent with the analysis of the Wilkinson-microwave anisotropy probe data. This model can lead to successful inflation with approx 10-7, rather than 10-13 reported previously.
 Select Topological String in Quantum-Chromodynamical Chiral Phase Transitions LI Yun-De Chin. Phys. Lett. 2005, 22 (5): 1300-1302 .   Abstract   PDF(pc) (193KB) ( 708 ) It is pointed out that if in heavy ion collision processes, the quark-gluon plasma SU(2) chiral phase transition really takes place and the phase transition is a second order. Then the topological string, i.e., the π string, will be formed. The main effect of this phenomenon is that there will be a number of pions produced by decay of the π string in the final state. The pions from the decay of the π string lead to the same effect of decreasing the Hanbury-Brown-Twiss peak in two-pion spectra which is just as that of the long-lived hadronic resonances. At relativistic heavy-ion collision and large hadron collision energies, it is expected that the factors are about α ～ 0.7-0.9 and α ～ 0.6-0.85, respectively.
77 articles