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Volume 19 Issue 9
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Original Articles
Multi-player and Multi-choice Quantum Game
DU Jiang-Feng, LI Hui, XU Xiao-Dong, ZHOU Xian-Yi, HAN Rong-Dian,
Chin. Phys. Lett. 2002, 19 (9): 1221-1224 .  
Abstract   PDF(pc) (223KB) ( 462 )
We investigate a multi-player and multi-choice quantum game. We start from a two-player and two-choice game, and the result is better than its classical version. Then we extend this to N-player and N-choice cases. In the quantum domain, we provide a strategy with which players can always avoid the worst outcome. Also, by changing the value of the parameter of the initial state, the probabilities for players to obtain the best pay-off will be much higher that in its classical version.
Characteristic Manifold and Painlevé Integrability: Fifth-Order Schwarzian Korteweg-de Type Equation
TANG Xiao-Yan, HU Heng-Chun,
Chin. Phys. Lett. 2002, 19 (9): 1225-1227 .  
Abstract   PDF(pc) (185KB) ( 473 )
The single valued behaviour of the characteristic manifold is seldom considered when analysing the Painlevé property of a partial differential equation. Considering this, We take a simple example-the generalized fifth-order Schwarzian Korteweg-de Vries equation-to emphasize the usefulness to include the analysis of the single valued properties about the characteristic manifold in the Pianlevé test. The result shows that some types of Schwarzian equations may not be Painlevé integrable, though many of them may be.
An Automated Jacobi Elliptic Function Method for Finding Periodic Wave Solutions to Nonlinear Evolution Equations
LIU Yin-Ping, LI Zhi-Bin
Chin. Phys. Lett. 2002, 19 (9): 1228-1230 .  
Abstract   PDF(pc) (177KB) ( 524 )
We describe the Jacobi elliptic function method for finding exact periodic wave solutions to nonlinear evolution equations. We present a Maple packaged automated Jacobi elliptic function method which can entirely automatically output the exact periodic wave solutions. The effectiveness of the automated Jacobi elliptic function method is demonstrated using as examples the applications to a variety of equations with physical interest. Not only are the previously known solutions recovered but in some cases new solutions and more general form of solutions are obtained.
Weakly Two-Dimensional Solitary Waves on Coupled Nonlinear Transmission Lines
DUAN Wen-Shan, HONG Xue-Ren, SHI Yu-Ren, LU Ke-Pu, SUN Jian-An
Chin. Phys. Lett. 2002, 19 (9): 1231-1233 .  
Abstract   PDF(pc) (245KB) ( 402 )
We study the nonlinear solitary wave solution under the transverse perturbations for a system of coupled nonlinear electrical transmission lines. In the continuum limit and suitably scaled coordinates, the voltage on the system is described by a modified Zakharov-Kuznetsov equation. The cut-off frequency of the growth rate for the solitary waves under transverse perturbations has been analytically obtained. It is in agreement with the case p=1/2 and p=1 which has been studied previously.
Stimulated Raman Adiabatic Population Transfer of Two Bose-Einstein Condensates
HU Zheng-Feng, DU Chun-Guang, LI Dai-Jun, LI Shi-Qun
Chin. Phys. Lett. 2002, 19 (9): 1234-1237 .  
Abstract   PDF(pc) (369KB) ( 388 )
Considering all the ground-state atom interactions, we investigate the population transfer of two Bose-Einstein condensate (BECs) states, which are trapped in different potential wells, or two ground states of the BEC in the same trap using the stimulated Raman adiabatic process. With a proper choosing of pulsed geometric parameters, the dark state exists. By simply choosing ground-state detunings, the effects of the interatomic interaction can be suppressed and a high population transfer rate can be obtained.
Schrödinger Equation for an Open System
BI Qiao, , H. E. Ruda
Chin. Phys. Lett. 2002, 19 (9): 1238-1241 .  
Abstract   PDF(pc) (249KB) ( 339 )
We present a Schrödinger (Liouville) type of equation for a quantum open system. It has a correlated part, and various master equations may be its special cases. It also has significant applications to construct decoherence-free subspace for quantum computation. It is related to the original Schrödinger (Liouville) equation for the total system through a non-unitary similarity transformation. It is unnecessary for its correlated part to be self-adjoint, so there is a complex spectrum for the corresponding Hamiltonian (Liouvillian), which enables the time evolution of states to be asymetric. This shows just the correlation to produce evolution of world.

Entanglement Concentration for Higher-Dimensional Quantum Systems
YAO Chun-Mei, GU Yong-Jian, YE Liu, GUO Guang-Can
Chin. Phys. Lett. 2002, 19 (9): 1242-1244 .  
Abstract   PDF(pc) (181KB) ( 379 )
Using local operations and classical communication, We present two schemes for realizing entanglement concentration from pure entangled pairs of qutrits. These methods can be easily generalized to d-dimensional (d > 3) quantum systems.
Bose-Einstein Condensation in a Spherical Symmetric Harmonic Trap
YAN Jia-Ren, LU Jing, AO Sheng-Mei, CAO Dong-Bo
Chin. Phys. Lett. 2002, 19 (9): 1245-1247 .  
Abstract   PDF(pc) (252KB) ( 392 )
Using a perturbation theory approach, we derive an approximate analytical solution of the Gross-Pitaevskii equation in a spherical symmetric harmonic trap. This solution is consistent with that obtained numerically.
A Flashing Model for Transport of Brownian Motors
ZHAO Tong-Jun, ZHAN Yong, WU Jian-Hai, WANG Yong-Hong
Chin. Phys. Lett. 2002, 19 (9): 1248-1250 .  
Abstract   PDF(pc) (321KB) ( 329 )
A flashing colored noise model is proposed to describe the motion of a molecular motor. In this model, the overdamped Brownian particle moves in an asymmetric periodic potential with a flashing Ornstein-Ulenbeck colored noise. The relationship between the current and the parameters-such as the intensity, the correlation time of colored noise and the flip rate of the noise-is discussed using the Monte Carlo simulation method. Current reversal occurs with the change of the correlation time and the flip rate of colored noise, which may be related to the directed motion and the current reversal of molecular motors.
Impulsive Control for the Stabilization of Discrete Chaotic System
ZHENG Yong-Ai, NIAN Yi-Bei, LIU Zeng-Rong
Chin. Phys. Lett. 2002, 19 (9): 1251-1253 .  
Abstract   PDF(pc) (506KB) ( 303 )
We first give the theoretical result on stabilization of general discrete chaotic systems by using impulsive control. As an example and application of the theoretical result, we derive some sufficient conditions for the stabilization of the double rotor map via impulsive control. The computer simulation result is given to demonstrate the method.
Hyperbolic Structures and the Stickiness Effect
ZHOU Ji-Lin, ZHOU Li-Yong, SUN Yi-Sui
Chin. Phys. Lett. 2002, 19 (9): 1254-1256 .  
Abstract   PDF(pc) (648KB) ( 726 )
The stickiness effect of invariant tori in the phase space is widely studied and extended to the slow-down of orbital diffusion due to some other invariant sets, such as Cantori, island-chains and hyperbolic periodic orbits. We report two models in which hyperbolic periodic orbits show the stickiness effect. The generalized stickiness effects caused by different invariant sets are discussed. We believe that the main cause of the generalized stickiness effects is the hyperbolic structures in the phase space of the dynamical systems.
Synchronizing Chaotic Systems in Strict-Feedback Form Using a Single Controller
CHEN Shi-Hua, LIU Jie, FENG Jian-Wen, LÜ, Jin-Hu
Chin. Phys. Lett. 2002, 19 (9): 1257-1259 .  
Abstract   PDF(pc) (198KB) ( 431 )
A synchronization method is proposed for a class of chaotic systems which can be translated into the strict-feedback form. This approach needs only a single controller and turns out to be globally exponentially asymptotically stable. The effectiveness of this approach was demonstrated with the Rössler chaotic system.
Asymptotic Analysis of a Modified Lorenz System
LÜ, Jin-Hu, CHEN Guan-Rong, YU Yong-Guang
Chin. Phys. Lett. 2002, 19 (9): 1260-1263 .  
Abstract   PDF(pc) (656KB) ( 669 )
We investigate the dynamical behaviour of a modified Lorenz system. Some basic dynamical properties such as bifurcations, routes to chaos, periodic windows, and some Poincaré mappings of this system are studied, either analytically or numerically. Also, the compound structure of the butterfly-shaped attractor is explored.
Quantum Poincaré Section of a Two-Dimensional Hamiltonian in a Coherent State Representation
JIN Ying-Xin, HE Kai-Fen
Chin. Phys. Lett. 2002, 19 (9): 1264-1267 .  
Abstract   PDF(pc) (629KB) ( 385 )
We study the quantum behaviour of a quasi-integrable Hamiltonian. The unperturbed Hamiltonian displays degeneracies of energy levels, which become avoided-crossings under a nonintegrable perturbation. In this two-dimensional system, the quantum Poincaré section plot is constructed in the coherent state representation with the restriction that the centers of wavepackets are confined at the classical surface of constant energy. It is found that the quantum Poincaré section plot obtained in this way provides an evident counterpart of the classical system.
A Tapping-Mode Tuning Fork with a Short Fiber Probe Sensor for a Near-Field Scanning Optical Microscope
WANG Pei, LU Yong-Hua, ZHANG Jiang-Ying, MING Hai, XIE Jian-Ping, HUANG Chien-Wen, KAO Tsung-Sheng, TSAI Din-Ping
Chin. Phys. Lett. 2002, 19 (9): 1268-1270 .  
Abstract   PDF(pc) (370KB) ( 364 )
We report on a tapping-mode tuning fork with a short fibre probe sensing for a near-field scanning optical microscope. The method demonstrates how to fabricate the short fibre probe. This tapping-mode tuning fork with a short fibre probe can provide stable and high Q at the tapping frequency of the tuning fork, and give high-quality near-field scanning optical microscopic and atomic force microscopic images of samples. We present the results of using the tapping-mode tuning fork with a short fibre probe sensing for a near-field scanning optical microscope performed on an eight-channel silica waveguide.
Monte Carlo Analysis of the Lévy Stability and Multi-fractal Spectrum in e+e- Collisions
CHEN Gang, LIU Lian-Shou
Chin. Phys. Lett. 2002, 19 (9): 1271-1273 .  
Abstract   PDF(pc) (339KB) ( 347 )
The Lévy stability analysis is carried out for e+e- collisions at Z0 mass using the Monte Carlo method. The Lévy index μ is found to be μ = 1.701±0.043. The self-similar generalized dimensions D(q) and multi-fractal spectrum f(α) are presented. The Rényi dimension D(q) decreases with increasing q. The self-similar multi-fractal spectrum is a convex curve with a maximum at q = 0, α = 1.169±0.011. The right-hand side of the spectrum, corresponding to negative values of q, is obtained through analytical continuation.
Projected Shell Model Analysis of Multi-quasiparticle High-K Isomers in 174Hf
ZHOU Xian-Rong, SUN Yang, LONG Gui-Lu, ZHAO En-Guang,
Chin. Phys. Lett. 2002, 19 (9): 1274-1276 .  
Abstract   PDF(pc) (320KB) ( 450 )
Multi-quasiparticle high-K states in 174Hf are studied in the framework of the projected shell model. The calculation reproduces well the observed ground state band as well as most of the two- and four-quasiparticle rotational bands. Some yet-unobserved high-K isomeric states in 174Hf are predicted. Possible reasons for the existing discrepancies between calculation and experiment are discussed. It is suggested that the projected shell model may be a useful method for studying the multi-quasiparticle high-K isomers and the K-mixing phenomenon in heavy deformed nuclei.
Band (5, 0) in the Red System A2II1 - X2Σ+ of CN Studied by Optical Heterodyne Magnetic Rotation Enhanced Concentration Modulation Spectroscopy
XU Chao-Xiong, WU Ling, LIU Jin-Jun, WU Sheng-Hai, DUAN Chuan-Xi, CHEN Yang-Qin, LIU Yu-Yu,
Chin. Phys. Lett. 2002, 19 (9): 1277-1279 .  
Abstract   PDF(pc) (333KB) ( 775 )
We study the CN radical using optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the visible region. The radical has been produced in the ac glow discharge of acetonitrile with helium as the carrier gas. The (5, 0) band of the red system A2II1 - X2Σ+ in the range 17450--17830cm-1 has been observed and rotationally analysed. We determine a set of precise molecular constants for the v = 5 vibrational level of CN in the A2II1 state.
Assignment of Infrared and Far-Infrared Transitions of CH2CF2
LIU Yu-Yan, HUANG Guang-Ming, SHI Li-Hua, DUAN Chuan-Xi
Chin. Phys. Lett. 2002, 19 (9): 1280-1282 .  
Abstract   PDF(pc) (294KB) ( 492 )
Starting from the Watson A-reduced Hamitonian and considering the infrared transitions with ΔKa = 0, ΔKc = ±1 (A-type) or ΔKa = ±1, ΔKc = ±1 (B-type), and the far-infrared transitions with ΔKa = 0,±2 and ΔKc = ±1, we calculate all the possible infrared absorption and far-infrared emission transitions of the v4 and v9 bands of 1,1-difluoroethylene (CH2CF2) pumped by 10P10 and 10P12 CO2 laser lines, and assign four previously unassigned CH2CF2 far-infrared laser lines (291.3μm, 339.3μm, 349.5μm and 657.9μm), where Ka and Kc represent the quantum number K of the limiting prolate top and the limiting oblate top, respectively. The 291.3μm line is identified to be generated from the cascade transition. The assignment of the 288.5μm line by Lafferty et al. (J. Mol. Spectrosc. 87(1981)416) is also confirmed.
Measurement of Random Surface Parameters of Weak Scatterers using the Speckle Contrast Method
CHENG Chuan-Fu, LIU Chun-Xiang, TENG Shu-yun, ZHANG Ning-Yu, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2002, 19 (9): 1283-1286 .  
Abstract   PDF(pc) (407KB) ( 445 )
Theoretical analysis shows that the deviation roughness w and lateral correlation length ξ of a weak scattering object determine the different properties of the contrast of the speckles in the image plane of a 4f system. Experimentally, we have measured the data of the speckle contrast versus the radius R of the variable filtering aperture. By fitting the theoretical results to these data, the parameters w and ξ of the random surfaces with Gaussian correlation are extracted. This method can determine the two parameters simultaneously and independently, and pre-calibrations are not needed.
Propagation of Partially Coherent Twisted Anisotropic Gaussian-Schell Model Beams in Spatial-Frequency Domain
CAI Yang-Jian, LIN Qiang
Chin. Phys. Lett. 2002, 19 (9): 1287-1290 .  
Abstract   PDF(pc) (267KB) ( 651 )
The generalized Collins formula for partially coherent beams through axially non-symmetrical optical systems in the spatial-frequency domain is derived by means of the tensor method. Based on this formula, the tensor ABCD law in the spatial-frequency domain for partially coherent twisted anisotropic Gaussian-Schell model (GSM) beams is derived, which governs the transformation of the twisted anisotropic GSM beams in spatial-frequency domain. An application example is provided.
High Spatial Resolution of an Optical Addressing Spatial Light Modulator Made by Photorefractive Semi-insulting Multiple Quantum Wells
CHEN Jing, LI Chun-Yong, HAN Ying-Jun, GUO Li-Wei, HUANG Qi, ZHANG Zhi-Guo, TANG Jun-Xion, DUAN Ming-Hao
Chin. Phys. Lett. 2002, 19 (9): 1291-1292 .  
Abstract   PDF(pc) (288KB) ( 373 )
We use nondegenerate four-wave mixing to study the spatial resolution of photorefractive semi-insulating multiple quantum wells grown by molecular beam epitaxy. By optimizing the experimental conditions, we have demonstrated that our sample has spatial resolution up to 2.5μm, which approaches the theoretical limit. We also analyse the factors that affect the spatial resolution of multiple quantum wells.
High Efficient Laser Operation of the High-Doped Nd:YAG Crystal Grown by Temperature Gradient Technology
MAO Yan-Li, DENG Pei-Zhen, ZHANG Ying-Hua, GUO Ju-Pin, GAN Fu-Xi
Chin. Phys. Lett. 2002, 19 (9): 1293-1295 .  
Abstract   PDF(pc) (317KB) ( 1745 )
We investigate the optical properties of Nd:YAG crystals grown by temperature gradient technology with different Nd-doping levels. The Nd concentrations used are 1.0at.%, 1.5at.%, 2.0at.%, 2.5at.%, and 3.0at.%, respectively. It is found that the absorption coefficients of Nd:YAG crystals increase with the increasing Nd concentrations. The absorption coefficient of 3.0at.% Nd:YAG is up to 22.1cm-1. The laser performance of these Nd:YAG crystals is compared with that of the traditional Nd:YAG (1.1at.% Nd) grown by the Czochralski (CZ) method. Although concentration quenching exists in highly doped Nd:YAG, 2.0at.% Nd:YAG shows excellent performance with the slope efficiency of 46.7%, which is higher than that (39%) of 1.1at.% Nd:YAG grown by the CZ method.
Linear Cavity Erbium-Doped Fibre Laser with Tunable Wavelength Range of 112nm
DONG Xin-Yong, TAM Hwa-Yaw, GUAN Bai-Ou, KAI Gui-Yun, DONG Xiao-Yi
Chin. Phys. Lett. 2002, 19 (9): 1296-1297 .  
Abstract   PDF(pc) (290KB) ( 486 )
We report on a linear cavity erbium-doped fibre laser with a large tuning range of 1509--1621 nm. We obtain a 1 dB flat tuning range of 1538--1613 nm and a 3 dB tuning range of 1516--1621 nm. The threshold at 1580 nm is 6.1 mW, the slope efficiency is 0.193 and the output power is 18.2 mW, when 100 mW pump power at 1480 nm is provided. High signal-to-noise radios of better than 60 dB are achieved within all the tuning ranges.
Bright-Dark Vector Screening-Photovoltaic Spatial Solitons in Biased Photorefractive-Photovoltaic Crystals
LU Ke-Qing, QIAN Shi-Xiong, DOU Chun-Sheng, WU Zhen-Sen
Chin. Phys. Lett. 2002, 19 (9): 1298-1300 .  
Abstract   PDF(pc) (291KB) ( 379 )
We show that the vector beam evolution equations in properly
oriented biased photorefractive-photovoltaic crystals can exhibit bright-dark vector solitons, which result from both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. By adjusting the polarization of the incident beam to obtain the appropriate ratio of two orthogonal components, these vector solitons can be established. When the bulk photovoltaic effect is negligible, these vector solitons are bright-dark vector screening solitons. When the external field is absent, these vector solitons predict bright-dark vector photovoltaic solitons.
Fifth-Order Harmonic Generation using a Coherent Controlled Two-Pulsed Optical Field
LIU Ting-Ting, WANG Da-Wei, LU Wei-Xin, SUN Quan, YANG Hong, JIANG Hong-Bing, GONG Qi-Huang
Chin. Phys. Lett. 2002, 19 (9): 1301-1303 .  
Abstract   PDF(pc) (390KB) ( 447 )
We have experimentally studied the characteristic of fifth-order harmonic radiation produced by two coherent femtosecond laser pulses with a changeable relative phase. The intensities of harmonic generation are found to increase with the coherent degree. In one optical period, the temporal variation of harmonics exhibits an asymmetric characteristic, which is interpreted in terms of ionization theory and the deformation of the wave packets of fundamental field contribution to harmonic generation.
Optical Properties of ZnFe2O4-SiO2 Granular Films Prepared by rf Magnetron Sputtering
JIN Yun-Xia, LI Guang-Hai, ZHANG Yun-Xia, ZHANG Li-De
Chin. Phys. Lett. 2002, 19 (9): 1304-1306 .  
Abstract   PDF(pc) (431KB) ( 949 )
We report on the optical properties of ZnFe2O4-SiO2 granular films prepared on quartz substrates by the radio frequency magnetron sputtering method. Post-annealing was performed at different temperatures under flow oxygen atmosphere. The morphology and structures of ZnFe2O4 nanoparticles were characterized by x-ray diffraction, transmission electron microscopy, and optical absorption spectra. It has been found that there are two different line types in the optical absorption curves of ZnFe2O4-SiO2 granular films. The critical transition of line types occurs when ZnFe2O4 changes from amorphous to crystalline, and the transition temperature increases with increasing content of ZnFe2O4. There is an obvious blueshift of the optical absorption edge of the granular films with the decreasing annealing temperature.

A Novel Conventional/Long-Band Erbium-Doped Fibre Amplified Spontaneous Emission Source with 80 nm Bandwidth
HUANG Wen-Cai, TAM Hwa-Yaw, WAI P.K.A, DONG Xin-Yong, MING Hai, XIE Jin-Ping
Chin. Phys. Lett. 2002, 19 (9): 1307-1308 .  
Abstract   PDF(pc) (343KB) ( 462 )
We report on a one-stage erbium-doped fibre amplified spontaneous emission (ASE) source with 80 nm bandwidth and 13.5 dBm output power. The broad bandwidth erbium ASE source was realized in an erbium-doped fibre with 37 m length by a 1480 nm laser diode and a 980 nm laser diode as forward and backward pump sources, respectively. The total pump power is only 95.7 mW.
Rheological Properties of Electrorheological Fluids Beyond and in the Original Transition Zone
FAN Zhi-Kang, LIANG Shu-Hua, XUE Xu
Chin. Phys. Lett. 2002, 19 (9): 1309-1311 .  
Abstract   PDF(pc) (428KB) ( 439 )
We find a nonlinear relationship between the shear stress and shear rate of electrorheological (ER) fluids with aluminosilicate suspension in original zone corresponding with low shear rates. Beyond the original zone, the ER fluids behave like a Bingham plastic fluid, and their viscosity is nearly constants.
Effect of Magnetohydrodynamic Perturbations on the Orbit Loss of Alpha Particles in Tokamak Plasma
WU Liang-Neng, YU Guo-Yang
Chin. Phys. Lett. 2002, 19 (9): 1312-1315 .  
Abstract   PDF(pc) (704KB) ( 558 )
We investigate the orbit loss of alpha particles under helical magnetic perturbation in a tokamak. The results show that low-frequency and low-mode number magnetic perturbation can cause stochastic loss of alpha particles. This effect is significant for those particles close to the boundary between the transit zone and the trapped zone. The particle loss is sensitive to the phase of the magnetic perturbation, indicating the modulation of the particle loss with respect to magnetic perturbation. It is also found that the precession of the particle banana orbit can even further enhance the particle loss.
Observation of Lower Hybrid Current Drive Improved Confinement with a Graphite Probe at the Last Closed Flux Surface of the HT-7 Tokamak
XU Guo-Sheng, WAN Bao-Nian, SONG Mei, LING Bi-Li, KUANG Guang-Li, DING Bo-Jiang
Chin. Phys. Lett. 2002, 19 (9): 1316-1318 .  
Abstract   PDF(pc) (445KB) ( 1041 )
High time resolution measurements of the electrostatic fluctuations, radial electric field Er and turbulence-induced electron flux Γe have been performed across the transition of lower-hybrid-current-drive-improved confinement with a graphite Langmuir probe array at the last closed flux surface of HT-7 tokamak. The decrease of Γe is dominated by the suppression of fluctuation levels, which follows the change of Er. A reversion of the poloidal propagation direction of turbulence demonstrates that the poloidal propagation is dominated by Er x BФ drift. The enhancement of poloidal coherence accompanies the fluctuation suppression, which suggests the subtle variation of turbulence features.
A Calculation Approach to Elastic Constants of Crystallines at High Pressure and Finite Temperature
XIANG Shi-Kai, CAI Ling-Cang, ZHANG Lin, JING Fu-Qian,
Chin. Phys. Lett. 2002, 19 (9): 1319-1321 .  
Abstract   PDF(pc) (422KB) ( 453 )
Elastic constants of Na and Li metals are calculated successfully for temperature up to 350 K and pressure up to 30 GPa using a scheme without involving any adjustable parameter. Elastic constants are assumed to depend only on an effective pair potential that is only determined by the average interatomic distance. Temperature has an effect on elastic constants by way of charging the equilibrium. The elastic constants can be obtained by fitting the relationship between total energy and strain tensor using the new set of lattice parameters obtained by calculating displacement of atoms at the finite temperature and at a fixed pressure. The relationship between effective pair potential and the interatomic distance is fitted by using a series of data of cohesive energy corresponding to lattice parameters.
Functional Counterpart of Lagrangian Theorem and Perturbative Density Functional Theory: a Forgotten Idea
Chin. Phys. Lett. 2002, 19 (9): 1322-1325 .  
Abstract   PDF(pc) (347KB) ( 428 )
In this letter, we truncates the functional expansion of non-uniform first-order direct correlation function (DCF) around the bulk density at the lowest order. But the truncation is performed formally and exactly by making use of functional counterpart of the Lagrangian theorem of differential calculus. Consequently the expansion coefficient, i.e., the uniform second-order DCF, is replaced by its non-uniform counterpart whose density argument is appropriate mixture of calculated density distribution and the bulk density with a mixing parameter determined by a hard-wall sum rule. The non-uniform second-order DCF is then approximated by the uniform second-order DCF with an appropriate weighted density as its density argument. The present formally exact truncated functional expansion predicts the density distribution in good agreement with simulation data for hard sphere and Lennard-Jones fluid exerted by an external field.

Phase Transition and Temperature Dependence of the A1 Low-Frequency Exciton Band Parameters in Quaternary Compound Rb0.5Cs0.5Ag4I5 Thin Films
SUN Jia-Lin, TIAN Guang-Yan, CAO Yang, SHI Shuo, TAN Xiao-Jing, CHEN Tao
Chin. Phys. Lett. 2002, 19 (9): 1326-1328 .  
Abstract   PDF(pc) (354KB) ( 469 )
The absorption spectra of the A1 low-frequency exciton band in quaternary compound Rb0.5Cs0.5Ag4I5 thin films have been measured by an UV-2100 spectrophotometer at the temperature (T) range from 78 to 289 K. The measurements at intermediate temperatures are performed within an interval of photon energies from 3.44 to 3.70 eV. The spectra have been computer-processed to separate the A1 band from the interband absorption edges, and to determine their parameters: the spectral peak position (Em), the half-width (G) of the exciton band, and the Gaussian shape ratio in the spectrum. The results show that at T < 107 K, dEm/dT = -6.34 x 10-4 eV.K-1, dG/dT = 3.04 x 10-4 eV.K-1; at T > 107 K, dEm/dT = -3.01 x 10-4 eV.K-1, dG/dT = 5.47 x 10-4 eV.K-1. It is emphasized that the phase transition γ → β in this material is carried out at temperature 107 K.

A Novel Contactless Method for Characterization of Semiconductors: Surface Electron Beam Induced Voltage in Scanning Electron Microscopy
ZHU Shi-Qiu, E. I. RAU, YANG Fu-Hua, ZHENG Hou-Zhi
Chin. Phys. Lett. 2002, 19 (9): 1329-1332 .  
Abstract   PDF(pc) (322KB) ( 368 )
We present a novel contactless and nondestructive method called the surface electron beam induced voltage (SEBIV) method for characterizing semiconductor materials and devices. The SEBIV method is based on the detection of the surface potential induced by electron beams of scanning electron microscopy (SEM). The core part of the SEBIV detection setup is a circular metal detector placed above the sample surface. Capacitance between the circular detector and whole surface of the sample is estimated to be about 0.64 pf. It is large enough for the detection of the induced surface potential. The irradiation mode of electron beam (e-beam) influences the signal generation. When the e-beam irradiates on the surface of semiconductors continuously, a differential signal is obtained. The real distribution of surface potentials can be obtained when a pulsed e-beam with a fixed frequency is used for irradiation and a lock-in amplifier is employed for detection. The polarity of induced potential depends on the structure of potential barriers and surface states of samples. The contrast of SEBIV images in SEM changes with irradiation time and e-beam intensity.
Universal Quantum Fluctuations and Crossover Phenomena in Tunneling Through Small Coulomb Islands
YI Lin, WANG Jian-Sheng
Chin. Phys. Lett. 2002, 19 (9): 1333-1335 .  
Abstract   PDF(pc) (439KB) ( 518 )
Tunneling through small Coulomb islands is studied in the intermediate coupling regime based on a generalized multi-level Anderson-Wolff model. It is shown that conductance and magnetization as a function of voltage exhibit a type of the universal quantum fluctuations. We predict new crossover from the Coulomb blockade oscillations to the universal conductance fluctuations, and the Coulomb blockade oscillations assisted Kondo peaks.
Electronic Structural Properties and Superconductivity of Diborides in the MgB2 Structure
YANG Fan, HAN Ru-Shan, TONG Ning-Hua, GUO Wei
Chin. Phys. Lett. 2002, 19 (9): 1336-1339 .  
Abstract   PDF(pc) (330KB) ( 1059 )
We calculate the critical temperature Tc of a wide range of diborides which have the same crystal structure as MgB2. Their electronic structure is also calculated in the framework of the local density approximation method of density functional theory by using the psudopotential plane wave approach. The Hopfield factors η of these materials are calculated by the frozen phonon method. Our results show that most of these diborides have low η, and hence low or no Tc, which are consistent with experimental observations. The most important result of our calculation is that AgB2 and AuB2 have higher Tc than MgB2. The high Tc of these two material comes from the combination of high density of states and high deformation potential of the σ bands.
Experimental Study of the Plasma Fluorination of Y-Ba-Cu-O Thin Films
LI Qin, FU Ze-Lu, JI Zheng-Ming, FENG Yi-Jun, KANG Lin, YANG Sen-Zu, WU Pei-Heng, WANG Xiao-Shu, YE Yu-Da
Chin. Phys. Lett. 2002, 19 (9): 1340-1343 .  
Abstract   PDF(pc) (467KB) ( 423 )
We have experimentally studied the surface modifications of the
Y-Ba-Cu-O (YBCO) thin films by CF4 plasma. The intensity of the plasma fluorination was controlled by changing the biasing voltage and the time of the plasma treatment. Microstructure analyses reveal that the oxygen content of the YBCO thin films had been changed. Transport measurements of sufficient fluorinated YBCO films imply that the films had been changed totally into an oxygen-deficient semi-conducting state. From these experimental results we believe that the plasma fluorination is a quite useful method to form controllable thin barrier layer in fabricating interface engineered junctions and to form a stable narrow weak-link region in fabricating planar superconductor-normal-superconductor junctions.
Nonequilibrium Dynamical Phase Transition of a Three-Dimensional Kinetic Heisenberg Spin System
SHAO Yuan-Zhi, J. K. L. Lai, C. H. Shek, LIN Guang-Min, LAN Tu
Chin. Phys. Lett. 2002, 19 (9): 1344-1346 .  
Abstract   PDF(pc) (302KB) ( 658 )
We systematically investigate the dynamical response of a three-dimensional kinetic isotropic Heisenberg spin system (HSS) to an external driving field by Monte Carlo numerical simulation. The dynamical response of isotropic HSS differs obviously from those of the anisotropic Ising spin system in which no real stable ordered state and relevant dynamical phase transition were observed in the kinetic HSS. There is a threshold time after which the magnetization m(t) in the HSS driven by a symmetrical external field always tends asymptotically to a disorder state regardless of the initial state of the system. The threshold time depends on the reduced temperature T/TC of the investigated spin system, amplitude H0 and frequency of the external field, i.e., τ = C.ωα.H0.(T/TC). C is a constant equal to 0.0302 for a three-dimensional lattice and exponents α = 1.18±0.01, β = 1.81±0.01 and γ = 1.68±0.01.
Dead Layer in a Ta/Ni81Fe19/Ta Structure
YU Guang-Hua, REN Ting-Ting, LI Ming-Hua, ZHU Feng-Wu, JIANG Huang-Wei, LAI Wu-Yan
Chin. Phys. Lett. 2002, 19 (9): 1347-1349 .  
Abstract   PDF(pc) (320KB) ( 588 )
Effect of Ta seed layers and Ta cap layers on the effective magnetic thickness of ultrathin permalloy (Ni81Fe19) was experimentally investigated for magnetic random access memory applications. The films were deposited by magnetron sputtering. For a Ta/Ni81Fe19/Ta fundamental structure, Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6±0.2nm. In order to find the mechanism, the composition and chemical states at the interface regions of Ta/Ni81Fe19 and Ni81Fe19/Ta were studied using the x-ray photoelectron spectroscopy and peak decomposition technique. The results show that there are thermodynamically favorable reactions at the Ta/Ni81Fe19 and Ni81Fe19/Ta interfaces: 2Ta+Ni=NiTa2.
Structural Characterization and Photoluminescent Properties of Zn1-xMgxO Films on Silicon
ZOU Lu, YE Zhi-Zhen, HUANG Jing-Yun, ZHAO Bing-Hui
Chin. Phys. Lett. 2002, 19 (9): 1350-1352 .  
Abstract   PDF(pc) (309KB) ( 694 )
Zn1-xMgxO films have been grown on silicon at various substrate temperatures by pulsed laser deposition. The structural and photoluminescent properties of films as a function of substrate temperature were studied. The optimized substrate temperature is 650°C. The x-ray diffraction spectra indicate that the films are highly C-axis oriented, and no phase separation is observed. The crystal grain size of film is about 100 nm as examined by atomic force microscopy. The cross-sectional transmission electron microscopy verified C-axis orientation of the Zn1-xMgxO. These films showed ultraviolet photoluminescence at room temperature. The near-band-edge emission peak of the Zn1-xMgxO film deposited at 600°C has a blue shift (0.40 eV) larger than that of the film deposited at 500°C (0.33 eV). The ratio of the near-band-edge to defect level peak intensity is as large as 159.
Mid-infrared Photon Localization Using Two Kinds of Mid-infrared Materials as Random Scatterers
LIU Xiao-Dong, HOU Lan-Tian, WANG Hui-Tian, LI Shu-Guang, HUO Guang-Li
Chin. Phys. Lett. 2002, 19 (9): 1353-1355 .  
Abstract   PDF(pc) (523KB) ( 405 )
We report on some theoretical results of the photon localization parameter in the transparent matrix in which there are constant-high-refractive-index scatterers or anomalous dispersive dielectrics (ADD) scatterers in the mid-infrared region. Strong photon localization appears when the relative refractive index m is large, and predominant backscattering occurs when m > 3.1. The roles of the matrices on photon localization are found to be very different in two kinds of random media.
Energy and Charge Transfer from Guest to Host in Doped Organic Electroluminescent Devices
LI Hong-Jian, PENG Jing-Cui, XU Xue-Mei, QU Shu, LUO Xiao-Hua, ZHAO Chu-Jun
Chin. Phys. Lett. 2002, 19 (9): 1356-1358 .  
Abstract   PDF(pc) (267KB) ( 341 )
The luminescence properties of doped organic electroluminescent devices are explained by means of a Hamiltonian model. The results show that there is a corresponding relation between the amount of the transferred charge and the change of the energy originated from charge transfer, and the relation can be influenced by dopant concentration. As the amount of the transferred charge increases, the total energy decreases and the luminescence intensity increases. Therefore, we deduce that the energy transfer from guest to host may be derived from the charge transfer. For a given organic electroluminescent device, the maximum value of the conductivities can be observed in a specific dopant concentration. The calculated results show that the greater the transferred charges, the higher the conductivities in doped organic electroluminescent devices. The results agree basically with experimental results.
Novel Alternating Current Electroluminescent Devices with an Asymmetric Structure Based on a Polymer Heterojunction
TAN Hai-Shu, YAO Jian-Quan, WANG Xin, WANG Peng, XIE Hong-Quan
Chin. Phys. Lett. 2002, 19 (9): 1359-1361 .  
Abstract   PDF(pc) (384KB) ( 413 )
Novel alternating current electroluminescent devices with an
asymmetric structure are successfully fabricated by using a hole-type polymer, poly (2,5-bis (dodecyloxy)-phenylenevinylene) (PDDOPV) and an electron-type polymer, poly (phenyl quinoxaline) (PPQ). The performance of the polymer devices with heterojunction under ac operation is insensitive to thickness of the two polymer layers, compared to that under dc operation. This new advantage means an easy and cheap production facility on a large scale in the near future. Different emission spectra are obtained when our ac devices are operated in an ac mode, forward, or reverse bias. The emission spectrum at reverse bias includes two parts. One from PDDOPV and the other is from PPQ.

Doping in the Mixed Layer to Achieve High Brightness and Efficiency Organic Light Emitting Devices
GAO Wen-Bao, YANG Kai-Xia, LIU Hong-Yu, FENG Jing, LIU Shi-Yong
Chin. Phys. Lett. 2002, 19 (9): 1362-1364 .  
Abstract   PDF(pc) (408KB) ( 567 )
Doping in the mixed layer was introduced to fabricate high brightness and high efficiency organic light-emitting devices, in which a copper phthalocyanine (CuPc) film acts as the buffer layer, a naphthylphenybiphenyl amine (NPB) film as the hole-transport layer and a tris (8-hydroxyquinolinolate)aluminum (Alq3) film as the electron-transport layer. The luminescent layer consists of the mixture of NPB, Alq3 (to be called the mixed layer), and an emitting dopant 5,6,11,12-petraphenylnaphthacene (rubrene), where the concentration of NPB declined and the concentration of Alq3 was increased gradually in the deposition process. Adopting this doping mixed layer, the device exhibites the maximum emission of 49300cd/m2 at 35V and the maximum efficiency of 7.96cd/A at 10.5V, respectively, which have been improved by twice in comparison with the conventional doped devices. We attribute this improvement to the effective confinement of carriers in the mixed layer, which leads to the increase of the recombination efficiency of carriers.
Microstructure and Optical Absorption Properties of Cu-MgF2 Nanoparticle Cermet Film
SUN Zhao-Qi, , SUN Da-Ming, RUAN Tu-Nan,
Chin. Phys. Lett. 2002, 19 (9): 1365-1368 .  
Abstract   PDF(pc) (511KB) ( 442 )
The microstructure and optical absorption spectra of 10-30vol% Cu-MgF2 nanoparticle cermet films prepared by co-evaporation in vacuum are examined. The results show that the Cu-MgF2 cermet films are mainly composed of amorphous MgF2 matrix with embedded fcc-Cu nanoparticles of average size 12-24 nm. The results also show that the optical absorption of the films decreases as the wavelength increases in the range of 200-800 nm. The surface plasmon resonance absorption peaks of Cu nanoparticles in 10, 20, and 30vol% Cu-MgF2 films appear at 578, 588, and 606nm, respectively, and the interband transition absorption of Cu starts from 590 nm downwards. Based on the Maxwell-Garnett theory, the experimental optical absorption properties of the films have been quantitatively evaluated.

Near-Field Scanning Optical Spectroscopy: Localized Fluorescence Spectra of Clusters in Nd3+ Doped Polymer Optical Fibre
GUO Yang, BAI Ming, TANG Lin, MING Hai
Chin. Phys. Lett. 2002, 19 (9): 1369-1370 .  
Abstract   PDF(pc) (337KB) ( 620 )
The optical characteristics of fractal clusters in Nd3+ doped poly(methyl and methacrylate) (PMMA) are investigated. The localized fluorescence spectra of clusters in Nd3+ doped PMMA are detected with a near-field scanning optical microscope. The experimental results demonstrate that the fractal clusters are harmful to the polymer optical fibre laser and amplifier. The corresponding explanation shows that there are interactions between two adjacent Nd3+ ions.
Twins Diamond Crystals Grown at High Temperature and High Pressure from the Fe-Ni-C System
YIN Long-Wei, YUAN Quan, LI Mu-Sen, LIU Yu-Xian, XU Bin, HAO Zhao-Yin
Chin. Phys. Lett. 2002, 19 (9): 1371-1373 .  
Abstract   PDF(pc) (251KB) ( 789 )
Twin diamond crystals grown at high temperature and high pressure (HPHT) in the presence of FeNi catalyst have been xamined by transmission electron microscopy (TEM). Direct observation by TEM shows that there are a large amount of twins which lie on the {111} planes in the HPHT-grown diamonds. The twins in the diamond may be formed and may extend into the inner crystal from the twin nucleus formed in the nucleation process. The twins can be formed due to the carbon atoms falling mistakingly into positions where a twin crystal can form during diamond growth, or condensation of supersaturated vacancies on the {111} plane. Some hexagonal dislocation loops related to supersaturated vacancies are found on the twins. The Moiré fringe image reveals that stacking faults terminate on intersecting twin boundary. This suggests that, at the temperature that the HPHT diamond is grown, the bordering partial has propagated by gliding up to the twin interface, which can be described by the reaction of a Shockley partial dislocation with a twin on the {111} plane.

Synthesis of Thick Diamond Film by Direct Current Hot-Cathode Plasma Chemical Vapor Deposition
JIN Zeng-Sun, JIANG Zhi-Gang, BAI Yi-Zhen, LÜ, Xian-Yi
Chin. Phys. Lett. 2002, 19 (9): 1374-1376 .  
Abstract   PDF(pc) (271KB) ( 671 )
The method of direct current hot-cathode plasma chemical vapour deposition method is established. A long-time stable glow discharge at large discharge current and high gas pressure has been achieved by using a hot cathode in the temperature range from 1100°C to 1500°C and nonsymmetrical configuration of the poles, in which the diameter of cathode is larger than that of anode. High quality thick diamond films in diameter of 40-50 mm and thickness of 0.5-4.2 mm, have been synthesized by this method. Transparent thick diamond films were grown over a range of growth rates of 5-10μm/h. Most of the thick diamond films have thermal conductivities of 10-12W/ The thick diamond films with high thermal conductivity can be used as a heat sink of semiconducting laser diode array and used as a heat spreading and isolation substrate of multichip modules. The performance can be obviously improved.
Face-Centered-Cubic Artificial Opal Embedded with CdS Quantum Dots
XU Ling, LI Ming-Hai, ZHANG Yu, MA Yi, XU Jun, HUANG Xin-Fan, CHEN Kun-Ji
Chin. Phys. Lett. 2002, 19 (9): 1377-1379 .  
Abstract   PDF(pc) (289KB) ( 782 )
Highly monodispersed colloidal silica spheres in sub-micrometer size with distribution standard deviation less than 5% were synthesized by a chemical method. Using the self-crystallization of the silica spheres, we successfully obtained the three-dimensional close-packed fcc silica matrices and artificial opals. Then, a colloidal photonic crystal embedded with CdS quantum dots (QDs) was also chemically prepared by using artificial opals as a template. A reflection spectra study reveals that both artificial opals with and without CdS QDs possess (111) directional photonic bandgap features.
High-Tc Superconductor Detection Coils for a Magnetic Resonance System
KANG Lin, WU Pei-Heng, PAN Jun, CAI Wei-Xing, YANG Sen-Zu, CAO Chun-Hai
Chin. Phys. Lett. 2002, 19 (9): 1380-1381 .  
Abstract   PDF(pc) (363KB) ( 408 )
Considering that in a magnetic resonance system, if the detection coil contributes dominantly to the system noise, the performance of the whole system can certainly be improved by switching to a detection coil made of high-temperature superconductor, and using YBa2Cu3O7 thin films on 25 x 25mm2 LaAlO3 substrates, we have prepared two kinds of detection coils, i.e., single-coil and two-coil. Encouragingly, their quality factors are measured to be Q > 2500 for two-coil (at 22.566 MHz and 77 K) and Q > 5500 for single-coil (at 92.3 MHz and 77 K), respectively. Here, we describe the details of the design, fabrication and tests of the coils.
Influence of Monomer Types on Designability of a Protein-Model Chain
LIANG Hao-Jun, WANG Yuan-Yuan
Chin. Phys. Lett. 2002, 19 (9): 1382-1384 .  
Abstract   PDF(pc) (186KB) ( 350 )
In a three-dimensional off-lattice model, the method of Shakhnovich and Gutin for minimizing the Hamiltonian is applied to the design of a protein-model chain. The effect of the number of hydrophobic and hydrophilic monomer types on the designability of a protein-model chain is investigated. The simulation results reveal that the number of hydrophobic monomer types is a much more important factor than that of the polar monomer types in the design of a protein-model chain.
Single-Shot Magnetic Resonance Imaging of a Moving Object Based on the High-Speed Spiral-Scan Echo Planner Technique at 4.7T
LU Guang, LIU Mai-Li, LI Li-Yun, YE Chao-Hui
Chin. Phys. Lett. 2002, 19 (9): 1385-1388 .  
Abstract   PDF(pc) (600KB) ( 296 )
The single-shot spiral magnetic resonance imaging (MRI) technique was implemented and optimized on a Bruker Biospec47/30 scanner. The technique includes the pulse sequence for generation and detection of the k-space MRI signal (free induction decay (FID)), and PC based programs for the data grid and image reconstruction. The temporal resolution is 70 ms (14 images per second), which consists of a data acquisition time as short as 13.7 ms, spin-echo time of 13.6 ms and the a magnetization recovery time of 43 ms. This makes it possible to take real time images of moving objects. The technique is demonstrated using a pendulum (tube) filled with water.
Observation of the in-vivo Reporter of Green Fluorescent Protein in a Plant Root by Scanning Near-Field Optical Microscopy
SUN Jia-Lin, XU Jian-Hua, CHEN Tao, TAN Xiao-Jing, CAO Yang, LIU Jin-Yuan, XIE Ai-Fang, ZHANG Ze-Bo, GUO Ji-Hua
Chin. Phys. Lett. 2002, 19 (9): 1389-1391 .  
Abstract   PDF(pc) (341KB) ( 513 )
An in vivo reporter of green-fluorescent protein (GFP) in a living plant root has been imaged by scanning near-field optical microscope (SNOM) in the transmission mode. The exciting light is 488 nm wavelength of the argon ion laser and the bandpass filters (514±10) nm is put into the detecting optical pathway. The results indicate that in the living plant cells, the GFPs gather together and form an area of 2-4μm, rather than being individually distributed. The transmission coefficient of the eigenfunction is incorporated into Bethe's theoretical model modified by Grober, and the near-field excited light intensity along the fibre probe axis (z-axis) in the air medium and biological medium is calculated. Based on that, along the z-axis direction of the GFP detected in the sample, numerous GFPs locate near the epidermal cells wall (in the range of 0-38 nm) in the living root. The experiments show that SNOM has an advantage of optical nanometer-scale resolution along the z-axis.
Creation from Nothing: A New Model
LIU Liao, DAI Lu-Ru
Chin. Phys. Lett. 2002, 19 (9): 1392-1395 .  
Abstract   PDF(pc) (279KB) ( 426 )
We try to propose a new model of the creation of Universe: first, the de Sitter spacetime is created from nothing and then we obtain an anti-de Sitter spacetime which has closed time-like curves by analytical continuation. We know that the anti-de Sitter spacetime is classical instable, so it is easier to create an inflationary bubble universe as we live in.
Quintessence Cosmology with Coupled Real Scalar Field
GAO Chang-Jun, SHEN You-Gen, ,
Chin. Phys. Lett. 2002, 19 (9): 1396-1398 .  
Abstract   PDF(pc) (194KB) ( 325 )
In the light of the recent observations of type Ia supernovae (SNe Ia) suggesting an accelerating Universe, we show the possibility of a coupled real scalar field to be quintessence for the source of the accelerating Universe. We derive the main equations which govern the evolution of the Universe and rewrite them with the observable quantities. Finally we point out very briefly how future observations may determine the equation of state of quintessence.
56 articles