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Volume 20 Issue 12
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Original Articles
Simulation of Ab Initio Molecular Dynamics of Shock Wave on Copper
ZHANG Lin, CAI Ling-Cang, XIANG Shi-Kai, JING Fu-Qian, CHEN Dong-Quan
Chin. Phys. Lett. 2003, 20 (12): 2091-2093 .  
Abstract   PDF(pc) (268KB) ( 1087 )
The relation between particle velocity Up, up to 4 km/s, and shock wave velocity Us in copper has been simulated with ab-initio molecular dynamics. The simulated relationship without considering the correction of zero-point and finite temperature effects is Us = 4.23 + 1.53Up. After considering the correction the relation becomes Us = 4.08 + 1.53Up, which is consistent with the experimental result.
Quantum Logic Network for Probabilistic Teleportation of Two-Particle State in a General Form
GAO Ting, WANG Zhi-Xi, YAN Feng-Li,
Chin. Phys. Lett. 2003, 20 (12): 2094-2097 .  
Abstract   PDF(pc) (274KB) ( 470 )
A simplification scheme of probabilistic teleportation of two particle state in a general form is given. By means of the primitive operations consisting of single-qubit gates, two-qubit controlled-not gates, Von Neumann measurement and classically controlled operations, we construct an efficient quantum logical network for implementing the new scheme of probabilistic teleportation of a two-particle state in a general form.

Breathing Bright Solitons in a Bose-Einstein Condensate
CHONG Gui-Shu, HAI Wen-Hua, XIE Qiong-Tao
Chin. Phys. Lett. 2003, 20 (12): 2098-2101 .  
Abstract   PDF(pc) (439KB) ( 473 )
A Bose-Einstein condensate with time varying scattering length in time-dependent harmonic trap is analytically investigated and soliton-like solutions of the Gross-Pitaeviskii equation are obtained to describe single soliton, bisoliton and N-soliton properties of the matter-wave. The influences of the geometrical property and modulate frequency of trapping potential on soliton behaviour are discussed. When the trap potential has a very small trap aspect ratio or oscillates with a high frequency, the matter-wave preserves its shape nearly like a soliton train in propagation. While the breathing behaviour, which displays the periodic collapse and revival of the matter-wave, is found for a relatively large aspect ratio or slow varying potential. Meanwhile mass center of the matter-wave translates and/or oscillates for different trap aspect ratio and trap frequnces.
Coherent Photo-Association in Double-Well Bose-Einstein Condensates
JING Hui, GE Mo-Lin, WANG Yu-Zhu
Chin. Phys. Lett. 2003, 20 (12): 2102-2104 .  
Abstract   PDF(pc) (179KB) ( 393 )
We investigate the quantum dynamics and statistics of an interesting system of the double-well Bose-Einstein condensates in the presence of a coherent photo-association process occurring in one of the two wells. Through the analytical solutions of a simplified model of the atom-molecule condensate, our results show the important impact of initial state preparations on the atomic coherence, especially the different squeezing behaviour for the case of photo-association via left-well atoms tunnelling from initial right-well atomic condensate, which holds the promise to be observed in the present laboratory.
Quantum Inequality for Negative Energy Density States of Massive Dirac Field in Four-Dimensional Spacetime
SHU Wei-Xing, WU Pun-Xun, YU Hong-Wei
Chin. Phys. Lett. 2003, 20 (12): 2105-2106 .  
Abstract   PDF(pc) (169KB) ( 633 )
Negative energy density and the quantum inequality are examined for the Dirac field. A proof is given to the quantum inequality for negative energy densities in the massive Dirac field produced by the superposition of two single particle electron states.
Thermodynamic Properties of Hard-Sphere Fluid under Confined Condition Based on Bridge Density Function
ZHOU Shi-Qi
Chin. Phys. Lett. 2003, 20 (12): 2107-2109 .  
Abstract   PDF(pc) (203KB) ( 414 )
Based on the functional integral procedure, a recently proposed bridge density function [J. Chem. Phys. 112 (2000) 8079] is developed to calculate global thermodynamic properties of non-uniform fluids. The resulting surface tension of a hard wall-hard sphere interface as a function of the bulk hard sphere fluid density is in good agreement with the available simulation data. The proposed numerical procedure from the approximation of non-uniform first-order direct correlation function to a non-uniform system with excess Helmholtz free energy is of fundamental importance for phase behaviour under the confined condition due to the fact that many available simple approximations in classical density functional theory are for non-uniform first-order direct correlation function.
Controlling Halo-Chaos via Variable Structure Method
FANG Jin-Qing, YU Xing-Huo, CHEN Guan-Rong
Chin. Phys. Lett. 2003, 20 (12): 2110-2113 .  
Abstract   PDF(pc) (554KB) ( 376 )
We propose a variable structure control method which is another innovative technique for suppressing beam halo-chaos in the periodic focusing channels of high-current proton beam accelerator, which belongs to a high-tech field. The analysis and numerical results show that the method is effective for controlling beam halo-chaos. Physical implementation of such a kind of control strategy remains an important and open issue for further applications.
Construction of Generalized Synchronization for a Kind of Array Differential Equations and Applications
ZHANG Xiao-Dan, ZHANG Li-Li, MIN Le-Quan
Chin. Phys. Lett. 2003, 20 (12): 2114-2117 .  
Abstract   PDF(pc) (901KB) ( 413 )
Chaos synchronization, as a special complex phenomenon, has been studied for about a decade. Only recently, generalized chaotic synchronization phenomena have been realized to be general in the real world and have potential applications. We present two theorems for constructing a kind of array differential equations with generalized synchronization (GS) with respect to linear transformations. Two array differential equation systems with GS are introduced based on our theorems. Numerical simulations show that the two systems display periodic GS and chaotic GS, respectively.
Local Lyapunov Exponent for the Bak-Sneppen Model
MA Ke, YANG Chun-Bin, CAI Xu
Chin. Phys. Lett. 2003, 20 (12): 2118-2121 .  
Abstract   PDF(pc) (243KB) ( 390 )
The chaotic property of the Bak-Sneppen model is studied from the local Lyapunov exponent in the same way as for dynamical nonlinear systems. Similar behaviour is found for the one- and two-dimensional Bak-Sneppen models. The Lyapunov exponents for the two cases have the same order of magnitude and both decrease at early evolution but show a slow increasing saturation at late evolution.
Mechanisms of Avalanche Dynamics in a Stochastic Four-State Sandpile Model
ZHANG Duan-Ming, PAN Gui-Jun, LEI Ya-Jei
Chin. Phys. Lett. 2003, 20 (12): 2122-2125 .  
Abstract   PDF(pc) (389KB) ( 495 )
We study the stochastic four-state sandpile model on the square lattice. The static and dynamical properties of the model are investigated and compared with the deterministic sandpile model of Bak, Tang, and Wiesenfled [Phys. Rev. Lett. 59 (1987) 381 ]. The numerical results show that the stochastic model defines a new universality class with respect to the deterministic sandpile. We also find that the waves in an avalanche are uncorrelated in the stochastic model (in the BTW model, the waves in an avalanche are correlated). The physical origin of the critical behaviour of the stochastic model being different from that of the BTW model is ascribed to the ordering and deterministic property of the toppling law in the BTW model.
A Two-Photon Femtosecond Laser System for Three-Dimensional Microfabrication and Data Storage
JIANG Zhong-Wei, ZHOU Yong-Jun, YUAN Da-Jun, HUANG Wen-Hao, XIA An-Dong,
Chin. Phys. Lett. 2003, 20 (12): 2126-2129 .  
Abstract   PDF(pc) (486KB) ( 975 )
Utilizing the well-focused femtosecond laser with extreme high pulse intensity, we built a two-photon microfabrication and data storage system, which was introduced through several functional parts. Based on this homemade system, several three-dimensional microstructures were fabricated by two-photon polymerization, and three-dimensional data storage of six-layers was achieved by two-photon excitation with a photochromic material.
Uncooled Optically Readable Bimaterial Micro-Cantilever Infrared Imaging Device
DUAN Zhi-Hui, ZHANG Qing-Chuan, WU Xiao-Ping, PAN Liang, CHEN Da-Peng, WANG Wei-Bing, GUO Zhe-Ying
Chin. Phys. Lett. 2003, 20 (12): 2130-2132 .  
Abstract   PDF(pc) (394KB) ( 705 )
We develop an uncooled infrared imaging device that contains a SiN-Au bimaterial micro-cantilever arrays detector and an optical read-out section. The detector converts the incident infrared radiation to the cantilever inclination angles, and the optical read-out section converts these angles directly to a visible image through an optical filtering operation to the spectra of the cantilever arrays with a knife-edge filter. The present results with the 140 x 98 cantilever arrays and the 8-bit A/D quantizer suggest that the objects at the temperature of 250°C at the distance as far as 1m can be detected and the noise-equivalent temperature difference (NETD) of the device is about 10 K. The further improvement of NETD is expected to approach about 14 mK with the optimized cantilever design and 12-bit quantizer.


Cosmic Strings and Quintessence
DUAN Yi-Shi, REN Ji-Rong, YANG Jie
Chin. Phys. Lett. 2003, 20 (12): 2133-2136 .  
Abstract   PDF(pc) (215KB) ( 394 )
Using torsion two-form we present a new Lorentz gauge invariant U(1) topological field theory in Riemann-Cartan space-time manifold U4. By virtue of the decomposition theory of U(1) gauge potential and the Ф-mapping topological current theory, it is proven that the U(1) complex scalar field Ф can be looked upon as the order parameter field in our Universe, and a set of zero points of Ф(x) create the cosmic strings as the space-time defects in the early Universe. In the standard cosmology, this complex scalar order parameter field possesses negative pressure, provides an accelerating expansion of Universe, and be able to explain the inflation in the early Universe. Therefore this complex scalar field is not only the order parameter field created the cosmic strings in the early universe, but also reasonably behaves as the quintessence, the dark energy.
Structure of Nonlocal Vacuum Condensate of Quarks
ZHOU Li-Juan, MA Wei-Xing,
Chin. Phys. Lett. 2003, 20 (12): 2137-2139 .  
Abstract   PDF(pc) (220KB) ( 353 )
The Dyson-Schwinger formalism is used to derive a fully dressed quark propagator. By use of the derived form of the quark propagator, the structure of non-local quark vacuum condensate is studied, and the values of local quark vacuum condensate as well as quark gluon mixed condensate are calculated. The theoretical predictions are in good agreement with the empirical one used commonly in the literature.

Anomalous Signature Splitting of the πh11/2 vi13/2 Band in A ~ 160 Odd-Odd Nuclei
YANG Chun-Xiang, , ZHOU Hong-Yu,
Chin. Phys. Lett. 2003, 20 (12): 2140-2143 .  
Abstract   PDF(pc) (514KB) ( 352 )
Systematic features of anomalous signature splitting of the πh11/2 vi13/2 band in A ~ 160 odd-odd nuclei have been investigated. It is shown that the mechanism of anomalous signature splitting is similar to that of the normal signature splitting which is essentially caused by the Coriolis mixing of Ω = 1/2 components into the nuclear wave function and the anomalous splitting in signature is mainly caused by the definition. The extensively observed anomalous signature splitting in this band might be an indication that the interaction between the h11/2 proton and the i13/2 neutron can not be neglected. The new observation of high- and low-K bands based on the same πh11/2 vi13/2 configuration in 164Tm is also discussed.
Statistical Significance of Non-Reproducibility of Cross Sections in Dissipative Reactions
WANG Qi, DONG Yu-Chuan, LI Song-Lin, TIAN Wen-Dong, LI Zhi-Chang, LU Xiu-Qin, ZHAO Kui, FU Chang-Bo, LIU Jian-Cheng, JIANG Hua, HU Gui-Qing
Chin. Phys. Lett. 2003, 20 (12): 2144-2147 .  
Abstract   PDF(pc) (578KB) ( 452 )
Two independent excitation function measurements have been performed in the reaction system of 19F+93Nb using two target foils of the same nominal thickness. We measured the dissipative reaction products at incident energies of 102 through 108 MeV with a step of 250 keV. The variance of energy autocorrelation functions of the reaction products was found to be three times of that originated from the randomized counting rates. By analysing the probability distributions of the deviations in the measured cross sections, we found that about 20% of all the deviations exceeds three standard deviations. This indicates that the non-reproducibility of the cross sections in the two independent measurements is of a statistical significance but not originated from randomized fluctuation of counting rates.
Femtosecond Dynamics of Energy Transfer in Native B800-B850 and B800-Released LH2 Complexes of Rhodobacter Sphaeroides
LIU Wei-Min, ZHU Rong-Yi, XIA Chen-An, LIU Yuan, XU Chun-He, QIAN Shi-Xiong
Chin. Phys. Lett. 2003, 20 (12): 2148-2151 .  
Abstract   PDF(pc) (364KB) ( 432 )
Two kinds of antenna complexes LH2 of Rhodobacter sphaeroides, wild type RS601 and the removal of B800 pigments (B800 released), were used in our experiment. These two LH2 complexes show quite different behaviour in absorption and femtosecond dynamics. By using the femtosecond pump-probe technique, the energy transfer processes occurred in two complexes were studied. Because of removing the B800 pigment from the LH2 in B800-released LH2 complex, the energy transfer between the B800 to B850 pigment was completely eliminated, while the pure internal energy transfer within the exciton states of B850 pigment could be carefully investigated. The results show that, at B800 absorption band, B800-released LH2 obviously shows a dominated transient absorption different from the photobleaching observed in RS601; while at the B850 band, these two complexes show similar photobleaching behaviour.
Optical Oscillator Strengths of Hydrogen Chloride in the Energy Region of 5.5-20eV
LI Wen-Bin, ZHU Lin-Fan, LIU Xiao-Jing, YUAN Zhen-Sheng, SUN Jian-Min, CHENG Hua-Dong, Yasuhiro Sakai, XU Ke-Zun
Chin. Phys. Lett. 2003, 20 (12): 2152-2154 .  
Abstract   PDF(pc) (288KB) ( 684 )
Absolute optical oscillator strength density (OOSD) spectrum of HCl in the valence shell energy region of 5.5-20 eV has been determined by the high resolution fast electron energy loss spectrometer (EELS). The optical oscillator strengths for the broad A1 + 13Σ+ dissociation peak and the discrete transitions of b3(v' = 0), C1(v'= 0,1,2) and M1(v'= 0) are reported.

High-Order Bessel-Gaussian Beam and Its Propagation Properties
LU Xuan-Hui, CHEN Xu-Min, ZHANG Lei, XUE Da-Jian
Chin. Phys. Lett. 2003, 20 (12): 2155-2157 .  
Abstract   PDF(pc) (313KB) ( 800 )
A high-order Bessel-Gaussian mode is introduced to describe hollow beams. The results for high-order Bessel-Gaussian beams propagating through lens focusing system and free space are derived in terms of Collins integral formula. The diffraction patterns and profile for high-order Bessel-Gaussian beams propagating through the above-mentioned optical systems are illustrated.
An Improved Computing Method for Analysing the Spatial Resolved Reflectance from Biological Tissues
LAI Jian-Cheng, LI Zhen-Hua, HE An-Zhi
Chin. Phys. Lett. 2003, 20 (12): 2158-2160 .  
Abstract   PDF(pc) (329KB) ( 365 )
A mathematical expression of reflectance point-spread-function, which is defined as the spatial distribution of light diffuse-reflected from bio-tissues irradiated by an infinitely narrow photon beam, is derived from the diffusion approximation (DA) theory. With the introduction of reflectance point-spread-function to describe the reflectance characteristics of bio-tissues, the convolution method is used to calculate the spatial resolved reflectance from dense and thick tissues irradiated by different photon beams. This is called the DA based convolution method and is used to calculate the responses of the semi-infinite bio-tissues irradiated by a Gaussian beam and a flat beam with different beam radius. The calculation results show that the DA based convolution method has much higher computing efficiency compared to the Monte Carlo method.
A Novel Optical Filter for Removing Bright-Background Using an Enhanced Bacteriorhodopsin Thin Film
ZHANG Chun-Ping, GU Li-Qun, CHEN Gui-Ying, GUO Zong-Xia, FU Guang-Hua, ZHANG Guang-Yin, ZHANG Tian-Hao, LI Yu-Dong, Q. Wang SONG
Chin. Phys. Lett. 2003, 20 (12): 2161-2164 .  
Abstract   PDF(pc) (475KB) ( 380 )
We found that the bacteriorhodopsin (bR) film has a special property of complementary suppression modulated transmission (CSMT). The yellow and the blue beams can be suppressed mutually when both the beams illuminate the bR film simultaneously. When the blue beam carrying an image with a bright-background noise illuminates on the bR film and then a yellow beam with uniform intensity distribution illuminates the same area, the bright-background can be removed due to the CSMT. In our demonstration, the pattern model is letters “VLSI”with ground noise of small words and the ground noise is removed from the pattern by the new optical filter.
Ultrasound-Modulated Optical Tomography in Reflective and Coaxial Configuration
FU Hong-Bo, XING Da, ZENG Ya-Guang, WANG Yi, CHEN Qun
Chin. Phys. Lett. 2003, 20 (12): 2165-2168 .  
Abstract   PDF(pc) (479KB) ( 495 )
Ultrasound-modulated optical tomography affords a very promising noninvasive imaging method for biomedical diagnosis. With this technique, an ultrasound beam is focused into a scattering medium to provide an accurate localization and, simultaneously, a modulation of laser light inside the medium. Based on the high-sensitivity detection technique, we have developed a unique reflective configuration, which was more convenient and practical than other existing configurations. Furthermore, the configuration also introduced a new scheme to improve the spatial resolution in the imaging. A phantom was imaged to validate the fesibility of the proposed configuration.
Yb3+-Doped Double-Clad Fibre Laser Based on Fibre Bragg Grating
FAN Wan-De, FU Sheng-Gui, ZHANG Qiang, NING Ding, LI Li-Jun, WANG Zhi, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2003, 20 (12): 2169-2171 .  
Abstract   PDF(pc) (360KB) ( 634 )
A novel Yb3+-doped double-clad fibre laser based on a double-clad fibre Bragg grating is presented. The fibre Bragg grating, as the output mirror, has been formed in Yb3+-doped double-clad fibre with the phase-mask method. When the input pump power is 2.8 W, the maximum laser output power is 570 mW, with < 0.2 nm in line-width at the wavelength of 1.058 μm, over 40dB signal-to-noise ratio and 24% slope efficiency.
Spectral Shaping in Rapid Scanning Optical Delay Line of Optical Coherence Tomography
WU Ji-Gang, XUE Ping, SUN Shan, GUO Ji-Hua
Chin. Phys. Lett. 2003, 20 (12): 2172-2174 .  
Abstract   PDF(pc) (311KB) ( 600 )
A small spatial optical filter is put into the rapid-scanning optical delay line (RSOD) to shape the spectrum of the reference beam in optical coherence tomography (OCT). The experimental results show that the longitudinal resolution can be improved by a factor of 81% with this method, while at the same time, the signal-to-noise ratio of the OCT system is not much affected. This method can be used in OCT systems that use RSOD as the reference arm with a light source of superluminescent diodes, femtosecond lasers and crystal fibre as well.
Efficient Generation of Red and Blue Light in a Dual-Structure Periodically Poled LiTaO3 Crystal
HE Jing-Liang, HU Xiao-Peng, ZHU Shi-Ning, ZHU Yong-Yuan, MIN Nai-Ben
Chin. Phys. Lett. 2003, 20 (12): 2175-2177 .  
Abstract   PDF(pc) (337KB) ( 1066 )
We demonstrate the efficient generation of red light at 671 nm and blue light at 447 nm from a diode-pumped Q-switched 1342 nm Nd:YVO4 laser together with a periodically poled LiTaO3 (PPLT) crystal. The sample used in this experiment is a dual-structure PPLT crystal with the period of 14.9 μm for the second harmonic generation and that of 4.9 μm for the third harmonic generation. The red and blue light, with the respective average power of 752 mW and 153 mW were obtained in a single path under an average fundamental power of 1.74 W, corresponding to the conversion efficiencies of 43.2% and 8.8%, respectively. These results indicate that the dual-structure PPLT can be used to construct a compact and efficient all-solid-state red-and-blue dual-wavelength laser.
Green-Light Static Rewritable Optical Storage Properties of a Novel CuTCNQ Derivative Thin Film
HUANG Wu-Qiao, WU Yi-Qun, GU Dong-Hong, GAN Fu-Xi
Chin. Phys. Lett. 2003, 20 (12): 2178-2181 .  
Abstract   PDF(pc) (400KB) ( 645 )
A novel charge-transfer complex film: copper-(n-propyl ester 7,7,8,8- tetracyanoquinodimethane-2,5-ylene-(3-propionic acid)) (Cu-TCNQ(C2H4COOC3H7)2) was prepared by spin-coating. Absorption spectra, green-light (514.5 nm) static rewritable optical recording properties and rewritable mechanism of this film were studied. The results show that there are two strong absorption peaks at 388 nm and 675 nm, which can be assigned to electronic transitions in anion radical TCNQ(C2H4COOC3H7)-2. Green-light optical storage experimental results of this film were as follows: write-in power was 9 mW, pulse duration was 80 ns; erasing power was 4 mW, pulse duration was 500 ns; the reflectivity contrast C ≥15%; number of write-erase cycle N ≥ 100. It is found that the realization of rewritable optical storage of the Cu-TCNQ (C2H4COOC3H7)2 film is related to the reversible changes of the optical properties, which is caused by the reversible charge transfer between copper and n-propyl ester 7,7,8,8- tetracyanoquinodimethane-2,5-ylene-(3-propionic acid) in the complex through inducement of laser irradiation.
Experimental Demonstration of Two-Dimensional Multimode-Interference Optical Power Splitter
SUN Yi-Ling, JIANG Xiao-Qing, YANG Jian-Yi, TANG Yi, WANG Ming-Hua
Chin. Phys. Lett. 2003, 20 (12): 2182-2184 .  
Abstract   PDF(pc) (216KB) ( 816 )
A two-dimensional multimode-interference optical power splitter is designed and demonstrated. The new device can be used for the optical power splitting in two transverse directions. Silicon-on-insulator technology is utilized to fabricate the device. The performance of the device is tested.
Fabrication of Thermo-Optic Switch in Silicon-on-Insulator
WANG Zhang-Tao, XIA Jin-Song, FAN Zhong-Chao, CHEN Shao-Wu, YU Jin-Zhong
Chin. Phys. Lett. 2003, 20 (12): 2185-2187 .  
Abstract   PDF(pc) (305KB) ( 761 )
Silicon-on-insulator technology has been used to fabricate 2 x 2 thermo-optic switches. The switch shows crosstalk of -23.4 dB and extinction ratio of 18.1 dB in the bar-state. The switching speed is less than 30 μs and the power consumption is about 420 mW. The measured excess loss is 1.8 dB. These merits make the switch more attractive for applications in wavelength division multiplexing.
Stochastic Inversion of Seabottom Scattering Coefficients from Shallow-Water Reverberation
LIU Jian-Jun, LI Feng-Hua, PENG Zhao-Hui
Chin. Phys. Lett. 2003, 20 (12): 2188-2191 .  
Abstract   PDF(pc) (528KB) ( 394 )
A stochastic inverse method is presented to estimate the seabottom scattering coefficients on the base of shallow-water ray mode reverberation theory. The reverberation data measured in the Asian Sea International Acoustic Experiment (ASIAEX) in the East China Sea in 2001 are analysed. The seabottom scattering coefficients are estimated from the reverberation loss. The inverted results are then tested by comparing the experiment data with the predictions of the reverberation vertical correlation and the reverberation loss measured on the different sea states at the same site. The fact that the experimental data are in good agreement with the theoretical predictions indicates the validity of the estimates.
Phase Leading of Temperature Variations in Cavity Caused by Heat Conduction Between Air and Rock
WU Shu-Chao, CHEN Fan, FAN Shu-Hua, LUO Jun
Chin. Phys. Lett. 2003, 20 (12): 2192-2194 .  
Abstract   PDF(pc) (349KB) ( 435 )
It is well known that the terrestrial temperature varies with the period of 24 hours mainly due to the rotation of the earth in the field of the solar radiation. However, we observed the phenomenon that the semidiurnal (12-hour) temperature oscillation is dominant in our underground laboratory. By the spectrum analysis, the close correlation between the variations of temperature and atmospheric pressure was discovered, and the result of phase analysis showed that the phase of semidiurnal pressure lags behind that of the semidiurnal temperature. A model of heat conduction between air and rock is presented to explain the semidiurnal temperature oscillation observed in the underground laboratory.
Depicting Vortex Stretching and Vortex Relaxing Mechanisms
FU Song, LI Qi-Bing, WANG Ming-Hao
Chin. Phys. Lett. 2003, 20 (12): 2195-2198 .  
Abstract   PDF(pc) (687KB) ( 808 )
Different from many existing studies on the parameterization of vortices, we investigate the effectiveness of two new parameters for identifying the vortex stretching and vortex relaxing mechanisms. These parameters are invariants and identify three-dimensional flow structures only, i.e., they diminish in two-dimensional flows. This is also unlike the existing vortex identification approaches which deliver information in two-dimensional flows. The present proposals have been successfully applied to identify the stretching and relaxing vortices in compressible mixing layers and natural convection flows.
Application of BGK Scheme on Micro-Channel Gas Flow
SUN Xi-Ming, HE Feng, DING Ying-Tao
Chin. Phys. Lett. 2003, 20 (12): 2199-2202 .  
Abstract   PDF(pc) (589KB) ( 360 )
A modified gas kinetic Bhatnagar-Gross-Krook (BGK) scheme for microflow has been developed upon the simultaneous collision model. Based on experimental and numerical results, the sub-choked pressure ratios are investigated. The current numerical approach is validated to provide a practical solution for microchannel flow.
Instability of Longitudinal Wave in Magnetized Strongly Coupled Dusty Plasma
XIE Bai-Song
Chin. Phys. Lett. 2003, 20 (12): 2203-2205 .  
Abstract   PDF(pc) (191KB) ( 580 )
Instability of longitudinal wave in magnetized strongly coupled dusty plasmas is investigated. The dust charging relaxation is taken into account. It is found that there exists threshold of interdust distance for the instablity of wave, which is determined significantly by the dust charging relaxation, the coupling parameter of high correlation of dust as well the strength of magnetic field.
Opacity of Hot and Dense Stellar Material: Flexible for Changes in Composition and Abundance
WANG Fei-Lu, ZHAO Gang, YUAN Jian-Min,
Chin. Phys. Lett. 2003, 20 (12): 2206-2209 .  
Abstract   PDF(pc) (413KB) ( 424 )
Opacity of stellar materials with the composition and relative abundance specified according to sun has been calculated by using an average-atom scheme, which is designed to treat electronic structures of atoms and ions in a mixture. Different relative abundances of the metallic elements are considered. Comparisons between the present results and those of OPAL are made for the opacity to show that the difference is less than 10% for most cases and less than 30% for the largest point with the density of 1.0g/cm3 and temperatures from 50 to 6000 eV. In view of the simplicity of the present approach, it is quite flexible to apply the method to different models of the stellar materials with changes in composition as well as in relative abundance.
First Measurement of the Magnetic Turbulence Induced Reynolds Stress in a Tokamak
XU Guo-Sheng, WAN Bao-Nian, SONG-Mei
Chin. Phys. Lett. 2003, 20 (12): 2210-2213 .  
Abstract   PDF(pc) (507KB) ( 430 )
Reynolds stress component due to magnetic turbulence was first measured in the plasma edge region of the HT-7 superconducting tokamak using an insert-able magnetic probe. A radial gradient of magnetic Reynolds stress was observed to be close to the velocity shear layer location; however, in this experiment its contribution to driving the poloidal flows is small compared to the electrostatic component. The electron heat transport driven by magnetic turbulence is quite small and can not account for the total energy transport at the plasma edge.
Determination of Mean Inner Potential by Electron Holography Along with Electron Dynamic Simulation
WANG Yan-Guo, LIU Hong-Rong, YANG Qi-Bin, ZHANG Ze
Chin. Phys. Lett. 2003, 20 (12): 2214-2217 .  
Abstract   PDF(pc) (286KB) ( 1002 )
Off-axis electron holography in a field-emission-gun transmission electron microscope and electron dynamic simulation is used to determine the mean inner potential of copper. The phase shift of object wave versus specimen thickness is calculated up to 30 nm using electron dynamic formula, and the sample thickness is decided by match of the experimental and calculated phase shift. Based on the measured phase shift, the calculated mean inner potential of Cu is 21.2 V, which agrees with the reported values within the experimental error.
Langevin Simulation of Non-Uniform Granular Gases
ZHANG Duan-Ming, LEI Ya-Jie, PAN Gui-Jun, YU Bo-Ming
Chin. Phys. Lett. 2003, 20 (12): 2218-2221 .  
Abstract   PDF(pc) (379KB) ( 357 )
We present and study a fractal model of a non-uniform granular system for the first time, based on which we numerically solve the dynamics actions in the system successfully in one-dimensional case. The multi-mixture is composed of N different particles, whose granularity distribution has the fractal characteristic. The particles subject to inelastic mutual collisions and obey to Langevin equation between collisions. Far from the equilibrium, i.e., the given typical relaxation time τ of the driving Brownian process is much larger than the mean collision time τc, the results of simulation indicate that the degree of inhomogeneity in the granularity distribution signed by the fractal dimension D of size distribution has great influences on the dynamics actions of the system. The velocity distribution deviates obviously from the Gaussian distribution and the particles cluster more pronounced with the larger value of D in the system. The velocity distribution and spatial clusterization changing with D are presented.

Short-Time Resistively-Shunted Junction Dynamic Study on Two-Dimensional Fully Frustrated XY Model
YOU Yu, LUO Meng-Bo, YING He-Ping, CHEN Qing-Hu
Chin. Phys. Lett. 2003, 20 (12): 2222-2225 .  
Abstract   PDF(pc) (344KB) ( 419 )
Short-time dynamic behaviour of two-dimensional fully frustrated XY model near the Ising-like phase-transition temperature is studied with resistively shunted junction dynamics. The transition temperature Tc and the dynamic and static critical exponents z, 2β/v, and v are estimated under both a periodic boundary condition (PBC) and a fluctuating twist boundary condition (FTBC) using the short-time dynamic scaling analysis. The results show that Tc, 2β/v, and v are almost independent of the boundary conditions, whereas z depends on the boundary condition. The value of z = 2.18(5) of the PBC is roughly equal to that of the FFXY model with Monte Carlo dynamics under the PBC, while z = 2.05(4) of the FTBC is in agreement with that of the Coulomb gas model.
Analytic Solution for In-Plane Valence Subbands of Strained SiGe Superlattice
LU Yan-Wu, SUN Gregory
Chin. Phys. Lett. 2003, 20 (12): 2226-2228 .  
Abstract   PDF(pc) (245KB) ( 378 )
Effective mass theory is used to calculate the in-plane valence subbands of strained SiGe superlattice within the 6 x 6 Luttinger model and under a correct boundary condition. The envelope wavefunctions are given analytically as a linear combination of bulk wavefuctions. The boundary conditions imposed on the envelope functions yield a 24 x 24 matrix, and from the zeros of its determinant the inplane energy dispersion E is obtained as a function of inplane wavevector k||. We discuss the mixing among the heavy-hole, light-hole and spin-split-off states at finite k|| and the dependence of the dispersion on the spin-split-off band and strain.
Giant Quenching of Spin-Orbit Interaction of Ga1-xVxP Crystals
ZHAO Min-Guang
Chin. Phys. Lett. 2003, 20 (12): 2229-2230 .  
Abstract   PDF(pc) (182KB) ( 483 )
We prove the presence of a giant quenching of the spin-orbit coupling of V2+ ion in GaP on the basis of a trigonal crystal field model and a complete diagonalization procedure. The calculated result is in good agreement with the experimental data of the thermally detected electron paramagnetic resonance. It was also shown that the dynamical Jahn-Teller explanation can not be excluded.
Quantum Fluctuation of Mesoscopic Capacitance Coupled Circuit in a Thermal Vacuum State
ZHU Ai-Dong, ZHANG Shou, JIN Zh, ZHAO Yong-Fang, JING Xiao-Gong, QIAN Zheng-Nan, SU Wen-Hui
Chin. Phys. Lett. 2003, 20 (12): 2231-2234 .  
Abstract   PDF(pc) (225KB) ( 331 )
The quantum fluctuations of mesoscopic capacitance-coupled circuit in thermal vacuum state are investigated by using the theory of thermal field dynamics on the basis of quantization of the mesoscopic circuit. It is shown that under a definite temperature, the fluctuations of electric charges and currents change with temperature. The higher the temperature, the more quantum noise the coupled circuit exhibits.
Growth of ZnO Thin Films on Lattice-Matched Substrates by Pulsed-Laser Deposition
YU Qing-Xuan, XU Bo, WU Qi-Hong, LIAO Yuan, WANG Guan-Zhong, FANG Rong-Chuan
Chin. Phys. Lett. 2003, 20 (12): 2235-2238 .  
Abstract   PDF(pc) (360KB) ( 948 )
ZnO films were grown on GaN and sapphire substrates by pulse laser deposition, respectively. The effects of crystalline quality on the optical properties in ZnO epitaxial layers were investigated by x-ray rocking curve and photoluminescence. The x-ray rocking curve of the film deposited on the GaN substrate has the full half maximum (FWHM) of 0.45°, whereas the FWHM of the x-ray θ-rocking curve of the ZnO film deposited on a sapphire substrate was measured to be about 0.77°. In photoluminescence (PL) measurement, the intensity of UV photoluminescence for the ZnO film on the GaN substrate decreased by approximately two orders of magnitude in comparison with that of the ZnO film on sapphire. It is concluded that the UV luminescence intensity almost does not depend on the textured growth of the ZnO thin film.
Magnetic and Transport Properties of ZnO/Co Nanomultilayers
REN Miao-Juan, YAN Shi-Shen, JI Gang, CHEN Yan-Xue, SONG Hong-Qiang, MEI Liang-Mo
Chin. Phys. Lett. 2003, 20 (12): 2239-2241 .  
Abstract   PDF(pc) (382KB) ( 422 )
[ZnO(0.5 nm)/Co(0.6 nm)]60 multilayers were fabricated by magnetron sputtering. The magnetic, transport and optical properties were studied. The ferromagnetic state at low temperature was demonstrated. Most of the grains in the samples will be unblocked when temperature is below 50 K. The measured magneto-resistance at 4.8 K is higher than 30%. This value is larger than any other reported data. The transport mechanism may come down to a combination of tunneling conduction with the second-order hopping. Some small peaks on transmittance curves were found, the matter is still open.
Effects of Rapid Recurrent Thermal Annealing on Giant Magnetoresistance NiFe/Ag Multilayers
WEN Qi-Ye, ZHANG Huai-Wu, JIANG Xiang-Dong, TANG Xiao-Li, ZHANG Wan-Li
Chin. Phys. Lett. 2003, 20 (12): 2242-2245 .  
Abstract   PDF(pc) (357KB) ( 547 )
NiFe/Ag multilayers were prepared by dc sputtering onto glass-ceramic substrates directly at room temperature. The samples were thermally processed by rapid recurrent thermal anneal (RRTA). We studied the effects of RRTA on giant magnetoresistance (GMR) NiFe/Ag multilayer by controlling the anneal temperature as well as the rapid anneal cycle. The samples after three RRTA cycles have a similar annealing temperature dependence of GMR responses to the ordinary annealed samples. With the increasing anneal cycle, the GMR response improved at first and then reached an unexpected high value of 9% before descent rapidly. Microstructure study shows that this effect is ascribed to the transformation of continuous NiFe layer into discontinuous one, and then into a granular like film in a step-by-step way.
Giant Magnetoimpedance Effect in Surface Modified CoFeMoSiB Amorphous Ribbons
M. A. Cerdeira, G. V. Kurlyandskaya, A. Fernandez, M. Tejedor, H. Garcia-Miquel
Chin. Phys. Lett. 2003, 20 (12): 2246-2249 .  
Abstract   PDF(pc) (417KB) ( 371 )
Thin magnetic Fe layers in thickness of 10-240 nm were deposited onto a wheel surface of CoFeMoSiB amorphous ribbons to check our concept of a new type of heterogeneous magnetoimpedance materials formed by two different magnetic parts. The presence of an additional iron layer modifies the magnetoimpedance response of the composite material and leads to increase of the magnetoimpedance ratio from 330 to 345% at a frequency of 3.5 MHz. Two possible mechanisms are discussed for explanation to the observed behaviour. Modification of the surface properties of the amorphous ribbons may have certain potential for technological applications.

Effect of Lateral Pressure On The Non-Linear Behavior of PZT Ceramics
LI Fa-Xin, FANG Dai-Ning, FENG Xue
Chin. Phys. Lett. 2003, 20 (12): 2250-2251 .  
Abstract   PDF(pc) (395KB) ( 543 )
The non-linear behavior of PZT-5 ceramics under coupled electrical-mechanical loading (E3 and σ11) is experimentally studied. The effect of different levels of compressive stress on the electrical-mechanical response is examined. Withthe increase of compressive stress, shapes of the electric hysteresis loop and the butterfly curve are slightly changed, while the reversed butterfly curve (ε11 vs E3) varies significantly, and the value of the piezoelectric constant d31) decreases evidently. Based on these experimental results, a simple design is proposed to improve the sensitivity and reliability of the submarine detectors and sensors.
Peak Position of Photoluminescence of Si Nanocrystals versus Thickness of SiOx Thin Films
FANG Ying-Cui, LI Wei-Qing, QI Le-Jun, ZHANG Zhuang-Jian, LU Ming
Chin. Phys. Lett. 2003, 20 (12): 2252-2254 .  
Abstract   PDF(pc) (323KB) ( 701 )
Peak position of photoluminescence (PL) of Si nanocrystals was found to change in an exponential decay form with the increasing thickness of SiOx (0 < x < 2) thin films. The results were interpreted in terms of a model modified from the theory of Zacharias-Streitenberger [Phys. Rev. B 62 (2000) 8391] from an energetic viewpoint. It was inferred from our model that under certain conditions regarding the energies of interfaces between the substrate and Si clusters and between the matrix and the Si clusters, the farer the Si cluster away from the substrate, the larger the nc-Si size until saturation is reached. This conclusion explains our PL observations according to the quantum confinement effect.
Improved Performance by Modification of Cathode in Polymer Light-Emitting Diode Based on a Novel Se-Containing Electroluminescent Copolymer
TIAN Ren-Yu, YANG Ren-Qiang, PENG Jun-Biao, CAO Yong
Chin. Phys. Lett. 2003, 20 (12): 2255-2258 .  
Abstract   PDF(pc) (402KB) ( 530 )
The electroluminescent characteristics of polymer light-emitting diodes (PLEDs) with the structure ITO/PEDOT/ PFO-Selenophene copolymer/cathode were investigated. Various cathodes, such as Al, Li/Al, Ba/Al, LiF/Al and LiF/Ba/Al, were used for testing the device performances. The strongest light output (1112 cd/m2) and the highest quantum efficiency (0.74%) were achieved by using the LiF/Ba/Al cathode. A possible working mechanism for improving the PLED performance was discussed.














Spectroscopy and Optical Properties of Novel Metal(II)-Azo Complex Films in Blue-Violet Light Region
HUANG Fu-Xin, WU Yi-Qun, GU Dong-Hong, GAN Fu-Xi
Chin. Phys. Lett. 2003, 20 (12): 2259-2261 .  
Abstract   PDF(pc) (433KB) ( 437 )
A novel azo derivative, α-(2-azoxyisoxazole)-β-diketone derivative (ADD), and its copper (II) and nickel (II) complex (CuADD and NiADD) films have been prepared respectively by spin-coated method. The absorption spectra of the films on a K9 glass substrate in the 300-800 nm wavelength region have been measured. The optical constants (complex refractive index N = n+ik) and thickness of the complex films on a single-crystal silicon substrate in the 300-600 nm wavelength region have been investigated on an improved rotating analyzer-polarizer (RAP) type of scanning ellipsometer, and the dielectric constants ε (ε = ε1 + iε2), absorption coefficients α as well as reflectance R of the films were calculated. It is found that the absorption maxima of the ADD, CuADD and NiADD films are at 324 nm, 372 nm and 385 nm, respectively, and small absorption values and steep absorption band edges of the CuADD and NiADD films are observed at the 405 nm side, the CuADD and NiADD films give high n values of 2.08 and 1.98, and low k values of 0.2 and 0.28, respectively, at 405 nm, and their thicknesses in the range of 130-150 nm, the high reflectivity of 58.5% and 45.5% of the CuADD and NiADD films with Ag as a reflective layer were obtained at the film thicknesses of 70 nm and 80 nm respectively. These results show that the novel CuADD and NiADD films seem to be a very promising organic recording material for next generation of high density digital versatile disc-recordable (HD-DVD-R) systems that use a high numerical aperture of 0.85 at 405 nm wavelength.
Dynamic Phase Transition of Two-Dimensional Disordered Colloids
CHEN Jiang-Xing, CAO Yi-Gang, JIAO Zheng-Kuan
Chin. Phys. Lett. 2003, 20 (12): 2262-2264 .  
Abstract   PDF(pc) (481KB) ( 419 )
Using Langevin simulations, we numerically study the influence of temperature to the dynamics of driven two-dimensional colloids on a disordered substrate. With decreasing temperature, the result shows a dynamic phase transition from the moving liquid to the moving smectic at high driving forces. A peak appears in the dynamically-critical driving force across the transition, accompanied by a clear cross of the curves of velocity-force dependence.
A New High Efficiency Multiwave Cerenkov Generator Operating at Low Magnetic Field
ZHANG Jun, ZHONG Hui-Huang, SHU Ting, YANG Jian-Hua
Chin. Phys. Lett. 2003, 20 (12): 2265-2268 .  
Abstract   PDF(pc) (675KB) ( 420 )
With a resonant cavity inserted between the second slow-wave-structure section and the tapered waveguide, a new structure of the multiwave Cerenkov generator (MWCG) operating at low guiding magnetic field is proposed to produce high efficiency and high power microwave. Some features and potential advantages of the proposed device are analysed. The 2.5-dimensional particle-in-cell simulation is employed to verify the initial expectation. The results show that, with the use of an electron beam of 640 keV and 8.4 kA guided by the magnetic field of 0.6 T, a stable and monochromatic X-band microwave output of 4 GW in peak power is achieved, and the average efficiency is over 30%.
Inverse Optimizing Method of Bio-Temperature-Field Reconstruction in rf-Capacitive Hyperthermia
WAN Bai-Kun, ZHU Xin, CHENG Xiao-Man, LIN Shi-Yin
Chin. Phys. Lett. 2003, 20 (12): 2269-2272 .  
Abstract   PDF(pc) (420KB) ( 557 )
We propose an inverse optimizing method, used in rf-capacitive hyperthermia to obtain a certain target tumor temperature and to avoid the over-heating of normal tissues. Based on the finite-element-method solutions of the Laplace electric potential equation and Penne's bio-heat transfer equation, the heating conditions are modified by the genetic algorithms recursively to minimize the objective function for searching an optimum physical configuration. With a simplified human tissue model extracted from an x-ray computed tomography slice which has deep- and shallow-seated tumors, satisfied simulation results are obtained both on bi-plate and three-plate systems, e.g., the tumor temperature is higher than 43°C and the temperature of normal tissues is lower than 39°C. It is suggested that the proposed algorithm is suitable for both shallow and deep seated cancer oncology.

Fluxes and Death Lines of Gamma-Ray Pulsars
ZHANG Li, JIANG Ze-Jun
Chin. Phys. Lett. 2003, 20 (12): 2273-2276 .  
Abstract   PDF(pc) (481KB) ( 401 )
We study the fluxes and the death lines of γ-ray emission of the pulsars with outer gaps. In a self-sustained outer gap, we derive that the fractional size of the outer gap is a function of period, period derivative, radial distance and magnetic inclination angle for a pulsar. Our results indicate that (i) averaged typical γ-ray energy and γ-ray flux of a pulsar with an outer gap increase with the magnetic inclination angle. We estimate the averaged γ-ray fluxes for observed canonical pulsars with outer gaps and compare them with the sensitivities of AGILE and GLAST, and (ii) if the fractional size of the outer gap at the inner boundary of the outer gap is not greater than unity, then an outer gap exists, such a condition gives the death lines of the pulsars with outer gaps.
53 articles