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Volume 22 Issue 2
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Original Articles
A New Lattice Bhatnagar--Gross--Krook Model for the Convection--Diffusion Equation with a Source Term
DENG Bin, SHI Bao-Chang, WANG Guang-Chao
Chin. Phys. Lett. 2005, 22 (2): 267-270 .  
Abstract   PDF(pc) (205KB) ( 522 )
A new lattice Bhatnagar--Gross--Krook (LBGK) model for the convection--diffusion equation with a source term is proposed. Unlike the models proposed previously, the present model does not require any additional assumption on the source term. Numerical results are found to be in excellent agreement with the analytical solutions. It is also found that the numerical accuracy of the model is much better than that of the existing models.
Spin Squeezing and Entanglement of Many-Particle Spin-Half States
YAN Dong, WANG Xiao-Guang, WU Ling-An
Chin. Phys. Lett. 2005, 22 (2): 271-274 .  
Abstract   PDF(pc) (247KB) ( 818 )
In many-particle spin-half systems with exchange symmetry, we find that the spin squeezing is related to two types of entanglement, the bipartite and the pairwise entanglement. A quantitative relationship is revealed for the spin squeezing parameter, the tangle, and the concurrence. We find that a class of states is spin squeezed if the pairwise entanglement is stronger than the bipartite entanglement.
Quantum Cryptography with Entangled QuNits
ENG Hong-Liang, FANG Xi-Ming
Chin. Phys. Lett. 2005, 22 (2): 275-278 .  
Abstract   PDF(pc) (262KB) ( 943 )
We propose an extension of quantum key distribution based on encoding the key into quNits, i.e. quantum states in an N-dimensional Hilbert space. In our protocol, we adopt asymmetric measurement scheme resulting in an efficiency higher than previous protocols and a generalized Bell inequality [Phys. Rev. Lett.92(2004)130404] is employed to detect the presence of an eavesdropper Eve. We also derive the information gained by a potential eavesdropper Eve applying a cloning-based attack and the maximal error rate which measures the robustness of the protocol. The result shows that the security of our scheme increases with the dimension N.
Experimental Creation of Entanglement Using Separable States
YANG Xiao-Dong, WANG An-Min, MA Xiao-San, XU Feng, YOU Hao, NIU Wan-Qing
Chin. Phys. Lett. 2005, 22 (2): 279-282 .  
Abstract   PDF(pc) (279KB) ( 549 )
We experimentally demonstrate that the entanglement can be created on two distant particles using separable states. We show that two working particles can share some entanglement, while one ancilla particle always remains separable from the two working particles during the experimental evolution of the system. Our experiment can be viewed as a benchmark to illustrate the idea that no prior entanglement is necessary to create entanglement.
Negative Resistance in a Two-Dimensional System with Entropic Barrier
ZHANG Xiao-Peng, BAO Jing-Dong
Chin. Phys. Lett. 2005, 22 (2): 283-286 .  
Abstract   PDF(pc) (585KB) ( 591 )
A phenomenon of negative resistance is found in two-dimensional bistable and periodic potentials via Langevin simulation, where output quantities for noise and signal driven system, such as the power-spectrum density modulus and the signal power amplification, can become minima at finite temperatures. In such a system, the curvature of the potential along non-transport degree of freedom at the barrier is larger than that at the local minima. The temperature-dependent effective barrier, i.e. entropic barrier, is introduced via integration over the non-transport variables. The system shows the negative resistance because of the competence between the signal and the entropic barrier.
Light-Gradient-Induced Spiral Wave Drifts in a Belousov--Zhabotinsky Reaction
ZHANG Hui-Jie, WANG Peng-Ye, ZHAO Ying-Ying
Chin. Phys. Lett. 2005, 22 (2): 287-290 .  
Abstract   PDF(pc) (406KB) ( 822 )
The dynamic behaviour of spiral tip in the light-sensitive Belousov--Zhabotinsky reaction under the influence of an externally applied light gradient was experimentally studied. The gradient causes different drifts for different spiral patterns. The centre of the spiral wave moved toward the region of lower light intensity. The direction of an additional perpendicular drift depended on the chirality of the spiral wave. The dependences of the drifting angle and the drifting velocity on light gradient have been measured.
Elimination of Spiral Waves and Competition between Travelling Wave Impulses and Spiral Waves
YUAN Guo-Yong, ZHANG Guang-Cai, WANG Guang-Rui, CHEN Shi-Gang, SUN Peng,
Chin. Phys. Lett. 2005, 22 (2): 291-294 .  
Abstract   PDF(pc) (512KB) ( 664 )
The interaction between travelling wave impulses and spiral waves is studied and the results of their competition are related to the exciting period. From the results, it is known that the formation and development of spiral waves in cardiac tissue depend on the period by which the travelling wave impulses are excited. A method is proposed to eliminate spiral waves, which is easily operated.
Adaptive Learning and Pruning Using Periodic Packet for Fast Invariance Extraction and Recognition
CHANG Sheng-Jiang, ZHANG Bian-Li, LIN Lie, XIONG Tao, SHEN Jin-Yuan
Chin. Phys. Lett. 2005, 22 (2): 295-297 .  
Abstract   PDF(pc) (369KB) ( 532 )
A new learning scheme using a periodic packet as the neuronal activation function is proposed for invariance extraction and recognition of handwritten digits. Simulation results show that the proposed network can extract the invariant feature effectively and improve both the convergence and the recognition rate.
Lambda Hypernuclei in a Chiral Hadronic Model
LIANG Yin-Hua, GUO Hua,
Chin. Phys. Lett. 2005, 22 (2): 298-301 .  
Abstract   PDF(pc) (426KB) ( 436 )
Nuclear matter calculations in a chiral hadronic model have been performed. It has been found that the scalar and the vector potentials and binding energies per nucleon in the chiral hadronic model are very close to those of the microscopic relativistic Brueckner--Hartree--Fock calculations. The good results for finite nuclei can be obtained in the mean field approximation only if scalar mass ms and coupling constant gs have been improved with the fixed values of cs2 ≡gs2 (M/ms)2 as those given by the original parameter sets of the chiral hadronic model. Then the chiral hadronic model is extended to lambda hypernuclei. Our results predicted by the chiral hadronic model are compared with those by the nonlinear Walecka model. It has been shown that the hadronic model can also be used to describe lambda hypernuclei successfully.
Deformed Potential Energy of Super Heavy Element Z=120 in a Generalized Liquid Drop Model
CHEN Bao-Qiu, MA Zhong-Yu, ZHU Zhi-Yuan, SONG Hong-Qiu, ZHAO Yao-Lin
Chin. Phys. Lett. 2005, 22 (2): 302-305 .  
Abstract   PDF(pc) (384KB) ( 724 )
The macroscopic deformed potential energy for super-heavy elements Z=120 is determined within a generalized liquid drop model (GLDM). The shell correction is calculated with the Strutinsky method and the microscopic single particle energies are derived from the shell model in an axially deformed Woods--Saxon potential with the same quasi-molecular shape. The total potential energy of a nucleus is calculated by the macro-microscopic method as the summation of the liquid-drop energy and the Strutinsky shell correction. The theory is adopted to describe the deformed potential energies in a set of cold reactions. The neck in the quasi-molecular shape is responsible to the deep valley of the fusion barrier due to shell corrections. In the cold fusion path, the double-hump fusion barrier is predicted by the shell correction and complete fusion events may occur. The results show that some of projectile--target combinations in the entrance channel, such as
50Ca+252Fm→302120* and 58Fe+244Pu→302120*, favour the fusion reaction, which can be considered as candidates for the synthesis of super heavy nuclei Z=120 and the former might be the best cold fusion reaction to produce the nucleus 302120 among them.



Isoscaling Behaviour in the Isospin-Dependent Quantum Molecular Dynamics Model
TIAN Wen-Dong, MA Yu-Gang, CAI Xiang-Zhou, CHEN Jin-Gen, CHEN Jin-Hui, FANG De-Qing, GUO Wei, MA Chun-Wang, MA Guo-Liang, SHEN Wen-Qing, WANG Kun, WEI Yi-Bin, YAN Ting-Zhi, ZHONG Chen, ZUO Jia-Xu
Chin. Phys. Lett. 2005, 22 (2): 306-309 .  
Abstract   PDF(pc) (466KB) ( 488 )
The isoscaling behaviour is investigated in a frame of isospin-dependent quantum molecular dynamics models. The isotopic yields ratio Y2/Y1 for reactions 48Ca+48Ca and 40Ca+40Ca at different entrance channels are simulated and presented, the relationship between the isoscaling parameter and the entrance channel is analysed, the results show that α and β reduce with the rise of incident energies and increase with the impact parameter b, which can be attributed to the temperature varying of the pre-fragments in different entrance channels. The relation of α and symmetry-term coefficient Csym reveals that the chemical potential difference Δμ is sensitive to the symmetry-term coefficient Csym, and raises with the increasing Csym.

Free or Quasi-Free Electronic Density of States in a Confined Atom
MENG Xu-Jun, ZHU Xi-Rui, TIAN Ming-Feng, JIANG Min-Hao, WANG Zhi-Gang
Chin. Phys. Lett. 2005, 22 (2): 310-313 .  
Abstract   PDF(pc) (251KB) ( 488 )
A new general formula, for energy normalization of radial wave-functions of free electron and of quasi-free electron in confined atom, is derived in central field approximation, which can flexibly be applied to the cases of relativity, non-relativity, and of free atom.
Vibrational Distribution of Hydrogen Molecular Ions in High-Energy Ionization Processes
CHEN Shao-Hao, HE Chun-Long, CHEN Chao, LI Jia-Ming,
Chin. Phys. Lett. 2005, 22 (2): 314-316 .  
Abstract   PDF(pc) (351KB) ( 354 )
A theoretical time-dependent wave-packet dynamics method is applied to calculate the distribution of vibrational states of hydrogen molecular ions produced in high-energy ionization processes of hydrogen molecules. The isotope effect is elucidated in agreement with the available experimental measurements. Our proposed method should be readily applied in other atomic and molecular processes considering great advances in electronic computation science and technology.
Detection of Fluorescence from Single Chlorophyll a Molecules Absorbed on Glass Surface
JI Dong-Mei, HUANG Zheng-Xi, XIA An-Dong
Chin. Phys. Lett. 2005, 22 (2): 317-320 .  
Abstract   PDF(pc) (500KB) ( 548 )
We investigate the single molecule spectroscopy of chlorophyll a molecules on glass surface in N2-saturated environment. The basic photodynamic parameters of chlorophyll a molecules, such as fluorescence lifetime, survival time before photobleaching, on-time, and off-time, are reported. A four-level model is employed to describe the possible dynamics and photobleaching of chlorophyll a upon excitation. Broad distributions in fluorescence lifetimes and survival times are mainly due to the heterogeneities of both molecular conformation and local environment.
Absolute Differential Cross Sections for Elastic Scattering of Electrons from CO at Intermediate and High Energies
SHI De-Heng, LIU Yu-Fang, SUN Jin-Feng, YANG Xiang-Dong, ZHU Zun-Lue,
Chin. Phys. Lett. 2005, 22 (2): 321-323 .  
Abstract   PDF(pc) (300KB) ( 534 )
The additivity rule model together with the complex optical model potential correlated by the concept of bonded atoms, which considers the overlapping effect of electron clouds between two atoms in a molecule, is firstly employed to calculate the absolute differential cross sections for electrons scattered by carbon monoxide at intermediate and high energies at the Hartree--Fock level. A comparison of elastic differential cross section results, obtained by using the correlated complex optical model potential, with the available experimental data, shows a significant improvement over the uncorrelated ones. The differential cross sections obtained by using the correlated complex optical model potential are in very good agreement with the experimental data. It is shown that the additivity rule model together with the correlated complex optical model potential is suitable for the calculations of the absolute differential cross sections of e-CO scattering.
Optical Guiding of Trapped Atoms by a Blue-Detuned Hollow Laser Beam in the Horizontal Direction
JIANG Kai-Jun, , LI Ke, , WANG Jin, ZHAN Ming-Sheng,
Chin. Phys. Lett. 2005, 22 (2): 323-327 .  
Abstract   PDF(pc) (422KB) ( 638 )
Optical guiding of 85Rb atoms in a magneto-optical trap (MOT) by a blue-detuned horizontal hollow laser beam is demonstrated experimentally. The guiding efficiency and the velocity distribution of the guided atoms are found to have strong dependence on the detuning of the guiding laser. In particular, the optimum guiding occurs when the blue detuning of the hollow laser beam is approximately equal to the hyperfine structure splitting of the 85Rb ground states, in good agreement with the theoretical analysis based on a three-level model.
New Technique for Mixed Potential Integral Equation Formulation in Multilayered Media and Its Application of Electrically Small Antennas Connected with Vertical Via-Holes
ZHANG Min, YUAN Tao, BAI Lu, LI Le-Wei, WU Zhen-Sen
Chin. Phys. Lett. 2005, 22 (2): 328-331 .  
Abstract   PDF(pc) (495KB) ( 426 )
We present an effective technique for mixed potential integral equation formulations in multilayered media. In terms of the dipole source method, the formulations of Green functions in spectral domain are restructured concisely, a proper integration path is chosen to straightforwardly apply the two-level discrete complex image method and the high order Sommerfeld identities yield very accurate results of Green functions in the spatial domain for general electric and magnetic sources in three-dimensional multilayered media. Finally, it is used to design a realistic low temperature co-fired ceramic aperture coupled antenna with vertical via-holes connected at the Ka band.
Influence of Complex Refractive Index on Diffuse Reflection of Biological Tissues
LAI Jian-Cheng, LI Zhen-Hua, HE An-Zhi
Chin. Phys. Lett. 2005, 22 (2): 332-334 .  
Abstract   PDF(pc) (500KB) ( 571 )
Complex refractive indices are introduced to solve various boundary questions at the interfaces when modelling light migration within heterogeneous tissues. Combined with the complex refractive index, Fresnel’s formulae are used to describe the reflection and transmission at the interfaces between two heterogeneous tissues layers. Using the Monte Carlo method, the influence of the complex refractive index on diffuse reflection of semi-infinite biological tissues is discussed. The results show that neglecting the imaginary part of the refractive index of tissues will bring a major deviation in the diffuse reflection of semi-infinite biological tissues when its emitting point is apart from the incident point.
A "Which Way" Experiment of Two-Photon Interference
WANG Qin, HUANG Yun-Feng, SUN Fang-Wen, ZHANG Yong-Sheng, GUO Guang-Can
Chin. Phys. Lett. 2005, 22 (2): 335-338 .  
Abstract   PDF(pc) (375KB) ( 428 )
It is well known that the indistinguishability of particles causes interference. We give a "which way" experiment of two-photon interference marked with polarization. The result shows that the greater the distinguishability of the path by which two-photon passes, the lower the fringe visibility will be, and this phenomenon will disappear when the path becomes completely distinguishable.
Investigation on Performance of High Repetition Diode-Pumped Heat-Capacity Nd:YAG Laser
SUN Zhi-Pei, LI Rui-Ning, BI Yong, BO Yong, YANG Xiao-Dong, CHEN Ya-Hui, GUO Lin, HOU Wei, ZHANG Hong-Bo, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2005, 22 (2): 339-342 .  
Abstract   PDF(pc) (432KB) ( 683 )
We demonstrate the improvements of both beam quality and thermal depolarization loss of an all-solid-state heat-capacity Nd:YAG laser with repetition rate of 50Hz, for the first time to our best knowledge, compared with the conventional steady-state laser. The beam quality of the heat-capacity laser has been improved three times higher than the conventional steady-state laser within the lasing periods of 60s. The depolarization loss caused by thermo-optical effects which is definitely considerable in steady-state Nd:YAG laser has almost not been observed under heat-capacity operation. Design and operations of the all-solid-state heat capacity Nd:YAG laser with average output power of 25W with repetition 50Hz are also studied with the optical-to-optical efficiency of 33.3%.
High-Power Er3+/Yb3+ Codoped Double-Cladding Fibre Amplifier with More Than 2W Output Power
LIU Yan-Ge, FENG Xin-Huan, LI Li-Jun, LI Yao, YUAN Shu-Zhong, KAI Gui-Yun, LI Yi-Gang, DONG Xiao-Yi
Chin. Phys. Lett. 2005, 22 (2): 343-345 .  
Abstract   PDF(pc) (302KB) ( 718 )
A high-power Er3+/Yb3+-codoped double-cladding all-fibre amplifier was successfully demonstrated and experimentally investigated. The amplifier could be operated with a maximum output power of 2.18W and 2.11W at 1541nm and 1550nm wavelengths, respectively, when the maximum pump power was 6.07W. The power conversion efficiency was up to 35.6% and 34.4% at the two wavelengths, respectively. The output power and the gain were greater than 2.00W and 20.0dB, respectively, in the wavelength range from 1539nm to 1565nm for 20.0mW input signal power. The gain fluctuation and the noise figure around 1550nm wavelength were less than 0.3dB and 6.0dB, respectively.
Laser Tracking and Pointing at a Target with Stimulated Brillouin Scattering
JU You-Lun, CHEN De-Ying, WANG Yue-Zhu
Chin. Phys. Lett. 2005, 22 (2): 346-348 .  
Abstract   PDF(pc) (330KB) ( 587 )
Laser tracking and pointing at a simulated moving target in atmosphere 1.27km away is realized experimentally, in which stimulated Brillouin scattering (SBS) phase conjugation technology and velocity compensation mirror are used. Only if the angle between the SBS phase conjugation laser and the illumination laser is smaller than the atmosphere isoplanatic angle ψ0 , is the wave-front aberration of laser beam produced by atmospheric turbulence compensated for in real time. This experiment was carried out with horizontal ranges 1.27km at 50m height above the ground, and Nd:YAG lasers are used. By changing the angle of a velocity compensation mirror reflecting the SBS phase conjugation laser to the simulated target, simulated targets with different moving velocities are tracked and pointed by the laser beam. The spot and energy distribution of illumination laser spot and SBS phase conjugation laser are recorded. The energy back to target is up to 75mJ. The SBS phase conjugation laser spot shows that it is focused at the simulated moving target within a small area.
Transfer Functions for Direct Temporal Structure Measurement of Femtosecond Soft X-Ray
GE Yu-Cheng
Chin. Phys. Lett. 2005, 22 (2): 349-352 .  
Abstract   PDF(pc) (619KB) ( 825 )
Under cross correlation between linearly polarized short duration laser and narrow bandwidth soft x-ray, the temporal structure of femtosecond soft x-ray can be directly reconstructed via the presented transfer functions from energy derivative of the excited photoelectron energy spectrum measured in the direction of or perpendicular to the laser polarization. The method has a broader temporal measurement range. The energy resolution of a photoelectron spectrometer and the size of energy bin are two important parameters for both measurement and calculation. The methods can be used for ultra-fast measurements and pump--probe detections on the femtosecond time scale.
Generation of 10GHz 2ps Short Laser Pulses Using an Electroabsorption Modulator and Two-Stage Compression
HUO Li, LOU Cai-Yun, GAO Yi-Zhi
Chin. Phys. Lett. 2005, 22 (2): 353-356 .  
Abstract   PDF(pc) (608KB) ( 385 )
A short pulse generator based on a commercially available bulk material electroabsorption modulator was experimentally demonstrated. By optimizing the length of the dispersion compensation fibre, nearly transform limited pulse was generated. There are a 2-ps-pulsed train with a timing jitter of 650fs and a repetition rate of 10GHz obtained with two-stage nonlinear compression. The quality of the pulse was further verified by 4×10Gbit/s optical time-division-multiplexed communication system experiment in which a low demultiplexing power penalty of 0.3dB was achieved.
Ultraslow Bright and Dark Solitons Using only a Pulsed Laser in a Cold Three-State Medium
LI Jia-Hua, YANG Wen-Xing, ZHAN Zhi-Ming, PENG Ju-Cun
Chin. Phys. Lett. 2005, 22 (2): 357-360 .  
Abstract   PDF(pc) (265KB) ( 512 )
We demonstrate the efficient generation of ultraslow bright and dark optical solitons in a lifetime-broadened three-level atomic medium by using only a low-intensity pulsed laser radiation. The proposed scheme may be useful, in principle, for the control technology of optical delay lines and optical buffers.
Numerical Solutions of Dissipative Holographic Solitons Under Large-Signal Conditions
LIU Jin-Song, ZHANG Hui-Lan, WANG Cheng, DU Zhe-Ming
Chin. Phys. Lett. 2005, 22 (2): 361-364 .  
Abstract   PDF(pc) (393KB) ( 410 )
It is numerically proven that dissipative holographic solitons, which are proposed for biased photorefractive materials when the self-trapping beam couples coherently with a pump beam via two-wave mixing, can exist when the intensity of the self-trapping beam is comparable with or stronger than that of the pump beam. Based on the mechanism of forming the soliton, an approach is established used to find the numerical solutions of the soliton. Such numerical solutions have been found for a broad range of system parameters. An experimental way to find such solitons is proposed.
Defect Modes in Multiple-Constituent One-Dimensional Photonic Crystals Examined by an Analytic Bloch-Mode Approach
SANG Hong-Yi, LI Zhi-Yuan, GU Ben-Yuan
Chin. Phys. Lett. 2005, 22 (2): 365-368 .  
Abstract   PDF(pc) (307KB) ( 416 )
Defect modes in one-dimensional photonic crystals (PCs) can be readily detected from the solution of the transmission spectra via the standard transfer-matrix method. We adopt an analytic Bloch-mode approach to examine this problem in terms of eigenmode solutions and investigate the dispersion behaviour of localized defect modes supported by a defect layer sandwiched within two symmetric semi-infinite PCs that are made from multiple constituents. The results show that the number of defect modes grows when the dielectric constant and width of the defect layer increase.
Fabrication of Compound Lattice by Holographic Lithography
ZHONG Yong-Chun, ZHU Shao-An, WANG He-Zhou
Chin. Phys. Lett. 2005, 22 (2): 369-372 .  
Abstract   PDF(pc) (266KB) ( 636 )
Some compound lattices in photonic crystals with large complete photonic band gaps, such as the diamond structure and the two-dimensional hexagonal compound structure, is desired for fabrication. A novel method for fabrication of compound lattices by holographic lithography is reported. The key point is phase modulation by photoelectrical control and multiple-exposure techniques. This technique introduces many advances: for instance, using the same coherent beams and without changing the position of the sample during multiple-exposure.

Fabrication of a Two-Dimensional Organic Photonic Crystal
HU Xiao-Yong, LI Yan, GONG Qi-Huang, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2005, 22 (2): 373-375 .  
Abstract   PDF(pc) (360KB) ( 503 )
A high-quality two-dimensional polystyrene photonic crystal is fabricated by the method of focused ion beam etching. The scanning electron microscopy (SEM) and the transmittance spectrum are used to characterize the properties of the photonic crystal. The measured transmittance spectrum is in agreement with the theoretical one. The influences of the disorders caused by the random perturbations in the diameter or the position of the air holes on the photonic band structure are analysed. It is found that the phtonic bandgap can tolerate less than 10% degree of disorder.
Frequency Dependence of Polarization Mode Dispersion in a Crystal-Based Polarization Mode Dispersion Compensator
LI Shi-Guang, YANG Chang-Xi, MIAO Hou-Xun, ZHANG Yang, ZHANG En-Yao, JIN Guo-Fan
Chin. Phys. Lett. 2005, 22 (2): 376-379 .  
Abstract   PDF(pc) (786KB) ( 390 )
We report the frequency dependence of polarization mode dispersion (PMD) in a PMD compensator based on six cascaded birefringent crystals separated by Faraday rotators. When all crystal axes are aligned, the device can compensate for the first-order PMD. However, if all crystal axes are coupled with arbitrary angles, it can compensate for high-order PMD. The variations of differential group delay and principal state of polarization with optical frequency are analysed. The PMD vector and Stokes components of the device versus wavelength are measured. The theoretical simulations agree well with the experimental results.
Spectral Broadening in a Polarization-Maintaining Photonic Crystal Fibre by Femtosecond Pulses from an Optical Parametric Amplifier
YU Yong-Qin, RUAN Shuang-Chen, CHENG Chao, DU Chen-Lin, LIU Cheng-Xiang, LIN Hao-Jia
Chin. Phys. Lett. 2005, 22 (2): 380-383 .  
Abstract   PDF(pc) (501KB) ( 546 )
The spectral broadening with the bandwidth of 83nm (1.2486--1.3318μm) in the 1.3μm region is achieved in a 0.2-m-long, polarization-maintaining photonic crystal fibre (PCF) with an average core radius of 1.8μm, pumped by optical pulses at the wavelength 1.269μm, with the duration 250fs and the repetition rate 250kHz from an optical parametric amplifier. The polarization characteristics of the output spectra are also investigated.
Supercontinuum Generation Using a Polarization-Maintaining Photonic Crystal Fibre by a Regeneratively Amplified Ti:Sapphire Laser
YU Yong-Qin, RUAN Shuang-Chen, DU Chen-Lin, YAO Jian-Quan
Chin. Phys. Lett. 2005, 22 (2): 384-387 .  
Abstract   PDF(pc) (437KB) ( 391 )
Supercontinuum with an ultra-broad bandwidth in the range from 380nm to 1750nm was generated by injecting 250kHz 200fs optical pulses produced by a regeneratively amplified Ti:sapphire laser into a 2.5-m-long polarization-maintaining photonic crystal fibre (PCF). It is indicated that the mechanism for the supercontinuum generation in the anomalous dispersion region of the PCF are directly related to the Raman effect, the fission of higher-order solitons, nonsolitonic radiation, and the coinstantaneous effect of four-wave mixing. The frequency components beyond 1.4μm were also observed. It is interpreted that the energy of solitons is shifted beyond the OH absorption with a higher input power.
Doped Silicate Glass Photonic Crystal Fibres
YANG Lu-Yun, CHEN Dan-Ping, XIA Jin-An, WANG Chen, JIANG Xiong-Wei, ZHU Cong-Shan, QIU Jian-Rong
Chin. Phys. Lett. 2005, 22 (2): 388-390 .  
Abstract   PDF(pc) (212KB) ( 464 )
We report on the fabrication of two kinds of large core area Nd3+ doped silicate glass photonic crystal fibres, and demonstration of the fibre waveguiding properties. The measured minimum loss of one kind of fibres is 2.5db/m at 660nm. The fibres sustain only a single mode at least over the wavelength range from 660nm to 980nm.
Passive Q-Switching Modelocked Yb3+-Doped Fibre Laser with GaAs Absorber Grown at Low Temperature
FENG Xiao-Ming, WANG Yong-Gang, LIU Yuan-Yuan, LAN Yong-Sheng, LIN Tao, WANG Jun, WANG Xiao-Wei, FANG Gao-Zhan, MA Xiao-Yu, WANG Yong-Gang, ZHANG Zhi-Gang
Chin. Phys. Lett. 2005, 22 (2): 391-393 .  
Abstract   PDF(pc) (436KB) ( 592 )
GaAs absorber was grown at low temperature (550°C) by metal organic chemical vapour deposition (MOCVD) and was used as an output coupler with which we realized Q-switching modelocked Yb3+-doped fibre laser. The shortest period of the envelope of the Q-switched modelocking is about 3μs. The modelocking threshold is 4.27W and the highest average output pulse power is 290mW. The modelocking frequency is 12MHz.
Non-Bragg Resonance of Standing Acoustic Wave in a Cylindrical Waveguide with Sinusoidally Perturbed Walls
TAO Zhi-Yong, XIAO Yu-Meng, WANG Xin-Long
Chin. Phys. Lett. 2005, 22 (2): 394-397 .  
Abstract   PDF(pc) (251KB) ( 462 )
A novel type of acoustic resonance different from the well-known Bragg resonance is predicted theoretically in an acoustic cylindrical waveguide with sinusoidally perturbed hard walls. The resonance is caused by the interaction between the standing acoustic waves, i.e. transverse modes in the waveguide. It results in the frequency spectrum splitting and the appearance of forbidden bands. For small-perturbed wall corrugation, it is found that the shifts of resonant frequencies and the width of the forbidden gap can be as small as the wall amplitude. The appearance of the non-Bragg resonance depends highly on the wall period. When the period is greater than 2.319 times the average cylinder radius, all the non-Bragg resonances cut off. The smaller the wall period, the greater the transverse mode involvement.
Multi-Phase Flow and Heat Transfer of a Micro-Pump Thermally Driven by a Multi-Output Pulse Laser
HUAI Xiu-Lan, TANG Zhi-Wei, WANG Guo-Xiang, WANG Wei-Wei
Chin. Phys. Lett. 2005, 22 (2): 398-401 .  
Abstract   PDF(pc) (364KB) ( 416 )
We present an experimental study of multi-phase flow and heat transfer in a micro-tube induced by a multi-output pulse laser. Extensive flow and heat transfer measurements and visualization experiments have been carried out to characterize the micro-pump behaviour under various conditions. The experiments reveal extremely unsteady and complex flow patterns in the micro tube with the flow closely related with generation and collapse of bubbles. It is found that the flow rates are controlled by the heating and condensation conditions within the tube. The laser pulse duration, pulse interval and output-power as well as the tube diameter all show a strong influence on the flow rate of the micro-pump. This study provides a basis for the design of thermally-driven micro-pump induced by a pulsed laser beam.

Marangoni--Bénard Instability with the Exchange of Evaporation at Liquid--Vapour Interface
LIU Rong, LIU Qiu-Sheng, HU Wen-Rui
Chin. Phys. Lett. 2005, 22 (2): 402-404 .  
Abstract   PDF(pc) (337KB) ( 476 )
A new two-sided model rather than the one-sided model in previous works is put forward. The linear instability analysis is performed on the Marangoni--Bénard convection in the two-layer system with an evaporation interface. We define a new evaporation Biot number which is different from that in the one-sided model, and obtain the curves of critical Marangoni number versus wavenumber. The influence of evaporation velocity and Biot number on the system is discussed and a new phenomenon uninterpreted before is now explained from our numerical results.
Dust Charging in Electronegative SiH4 Plasmas
DUAN Ping, WANG Zheng-Xiong, LIU Yue, LIU Jin-Yuan, WANG Xiao-Gang
Chin. Phys. Lett. 2005, 22 (2): 405-408 .  
Abstract   PDF(pc) (378KB) ( 683 )
We theoretically investigate the dust charging in electronegative silane (SiH4) plasmas, taking into account the effects of UV photodetachment. It is found that UV photodetachment could significantly lower the dust negative charge and even makes dust grains be positively charged under some special conditions. In addition, the other parameters, involving the negative ion and dust number densities, electron temperature and dust radius, have great effects upon the dust charging.
Electron Acceleration in Collisionless Magnetic Reconnection
GUO Jun, LU Quan-Ming, WANG Shui, FU Xiang-Rong
Chin. Phys. Lett. 2005, 22 (2): 409-412 .  
Abstract   PDF(pc) (907KB) ( 602 )
A 5/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the electron acceleration in collisionless magnetic reconnection. The results show that the electrons are accelerated in the diffusion region near the X point, and the acceleration process can be roughly divided into two procedures: firstly the electrons are accelerated in the z direction due to the electric field in the negative z direction. Then the electrons gyrate surrounding the magnetic field with the action of the Lorentz force, through this procedure the electrons reach higher velocity in the x direction and then flow out of the diffusion region. After being accelerated away from the diffusion region, part of electrons is trapped near the O point, and the other part of electrons flows into plasma sheet boundary layer along the magnetic field.
X-Ray Radiation Characteristics of Nested-Wire Array Implosion in Sino-Russian Joint Z-pinch Experiments on Angara-5-1
XU Rong-Kun, LI Zheng-Hong, NING Jia-Min, GUO Cun, XU Ze-Ping, YANG Jian-Lun, LI Lin-Bo, XIA Guang-Xin, HUA Xin-Sheng, DING Ning, LIU Qiang, GU Yuan-Chao, E. V. Grabovsky, G. M. Oleynic, S. L. Nedoseev, V. V. Alexandrov, K. N.Mitrofanov, M. V. Zurin, G. S. Volkov, I. A. Porofeev, I. N. Frolov, V. P. Smirnov
Chin. Phys. Lett. 2005, 22 (2): 413-415 .  
Abstract   PDF(pc) (363KB) ( 430 )
We report and discuss the results of x-ray radiation measurements in the Sino-Russian joint Z-Pinch experiments on Angara-5-1 facility with a load current of 2.5--3.6MA. The measurements were conducted by using an x-ray power meter (XRPM) and a time-resolved one-dimensional x-ray imaging system developed in China Academy of Engineering Physics. The experimental results indicate that an x-ray power-platform prior to a main peak and a less intensive sub-peak after the main peak in the waveform exist for the nested-wire array implosions, and the radiation process is relatively faster than that in the case of the single array. Laser shadowgraph of the imploding plasma suggests that the prior power-platform is a result of the collision of the inner-outer plasma layers. The faster radiation process of nested array implosion can be explained by analysing the corresponding result of the time-resolved one-dimensional imaging system, which demonstrates a better axial imploding uniformity and synchronization. In comparison with x-ray diode, the XRPM yields a higher height of x-ray power-platform due to its flat energy response. The sub-peak after the main peak is proposed to be a result of the later-time additional implosion of plasma.

Discharge Characteristics in Atmospheric Pressure Glow Surface Discharge in Helium Gas
LI Xue-Chen, WANG Long
Chin. Phys. Lett. 2005, 22 (2): 416-419 .  
Abstract   PDF(pc) (488KB) ( 489 )
Atmospheric pressure glow discharge is observed for the first time in a surface discharge generator in flowing helium. Electrical and optical methods are used to measure the characteristics of atmospheric pressure glow discharge for different voltages. The results show that discharge current waveforms are asymmetric for the different polarities of the applied voltage. A continuous discharge profile with a width of several microseconds appears for per half cycle of the applied voltage when the voltage is increased to a certain value. The short-pulsed discharge and the continuous current would result from the Townsend breakdown and glow discharge mechanisms respectively. The properties of surface discharge in stagnant helium are completely different from that in flowing helium.

Dissociative Chemisorption of an H2(v,j) Molecule on Rigid Ni (100) Surface: Dependence on Surface Topologies and Initial Rovibrational States of the Molecules
Meryem Evecen, Mustafa Bö, yükata, Mehmet Civi, Ziya B. Güvenc
Chin. Phys. Lett. 2005, 22 (2): 420-423 .  
Abstract   PDF(pc) (387KB) ( 653 )
The H2(v,j)+Ni(100) collision system has been studied to understand the effects of the surface sites and initial rovibrational states of the molecule on molecule-surface interactions, by a quasiclassical molecular dynamic simulation method. Dissociative adsorption of an H2 molecule on the rigid Ni(100) surface is investigated at topologically different three sites of the surface. Interaction between the molecule and Ni surface was described by a London--Eyring--Polani--Sato (LEPS) potential. Dissociative chemisorption probabilities of the H2(v, j) molecule on various sites of the surface are presented as a function of the translation energies between 0.001--1.0eV. The probabilities obtained at each collision site have unique behaviour. At lower collision energies, indirect processes enhance the reactivity, effects of the rotational excitations and impact sites on the reactivity are more pronounced. The results are compared with the available studies. The physical mechanisms underlying the results and quantum effects are discussed.
First-Principle-Based Calculations of the Hugoniot of Cu
XIANG Shi-Kai, CAI Ling-Cang, JING Fu-Qian, WANG Shun-Jin/sup>
Chin. Phys. Lett. 2005, 22 (2): 424-426 .  
Abstract   PDF(pc) (245KB) ( 525 )
The equation of state of face-centred-cubic (fcc) copper rystals at pressures up to 500GPa and relative volume to 0.55 ave been evaluated by using the full-potential linear muffin-tin rbital (FPLMTO) total-energy method combining with a mean-field odel of the vibrational partition function. The mean-field is onstructed from the sum of all the pair potentials between the eference atom and the others of the system. The alculated roperties are in good agreement with the available shock-wave xperimental measurements.

Dynamical Behaviour of Ag and Cu Double-Layer Islands on fcc (111) Surfaces
HU Biao, GONG Xiu-Fang, NING Xi-Jing
Chin. Phys. Lett. 2005, 22 (2): 427-430 .  
Abstract   PDF(pc) (356KB) ( 622 )
Molecular dynamics simulations are preformed to investigate the diffusion behaviour of Ag/Cu double-layer islands on Ag(111)/Cu(111) surfaces, showing that atoms of the top island usually diffuse into the lower island by exchange mechanism when they move to the verge of the lower island via a concerted motion. Compared to the Cu adatoms, the Ag adatoms can easily form a kind of stable compact cluster of hexagonal island during their diffusion processes, and this cluster make it possible that the decay rate of the top Ag island is considerably slower than that of the Cu island. In addition, we find that the exchange mechanism is predominant compared to the jumping process in the simple potential calculation. These simulation results are in agreement with previous experimental observations and theoretical calculations.
Nanostructuring of Si(100) by Normal-Incident Ar+ Ion Sputtering at Low Ion Flux
QI Le-Jun, LI Wei-Qing, YANG Xin-Ju, FANG Ying-Cui, LU Ming
Chin. Phys. Lett. 2005, 22 (2): 431-434 .  
Abstract   PDF(pc) (334KB) ( 499 )
We investigate Si(100) surface morphology evolution under normal-incident Ar+ ions sputtering with low ion flux of 20μA/cm2. The results indicate that under the low flux ion sputtering, the nanostructuring process of Si(100) is governed by the Ehrlich--Schwoebel (ES) mechanism, rather than by the Bradley--Harper (BH) one for the case of high flux (normally the order of 102 μA/cm2 or larger). This work reveals that the ion flux plays an important role in the surface morphology evolution under ion sputtering, and a usually accepted classification that the ES mechanism is related to metal single-crystals under ion sputtering, while the BH one is to amorphous, and semiconductor targets is questionable.
New Infrared Properties of the Tetragonal CaTiO3
YI Lin, DUAN Yi-Feng
Chin. Phys. Lett. 2005, 22 (2): 435-438 .  
Abstract   PDF(pc) (535KB) ( 947 )
First-principle calculations are performed to study the infrared optical and electronic properties of the tetragonal CaTiO3. We find that dielectric function and reflectivity exhibit a new single-peak infrared spectrum. It is shown that strong orbital hybridization can form the dipole distribution of covalent bonds (Ti-O1 and Ti-O2) and can result in anomalous optical behaviour. The tetragonal structure that determines the dipole configuration and leads to the optical dipole-dipole transition forbidden is therefore realized to be vital to cause such optical phenomena with the insulator feature.
Orbital Hybridization of the Ferroelectric Rb2Cd2 (SO4)3: Origin of Domain Walls
DUAN Yi-Feng, YI Lin
Chin. Phys. Lett. 2005, 22 (2): 439-441 .  
Abstract   PDF(pc) (385KB) ( 534 )
We perform first-principle calculations for the study of the orthorhombic Rb2Cd2 (SO4)3 structure. Electronic energy bands, total and partial densities of states are reported and analysed. It is found that oxygen atomic 2p electrons strongly hybridize with Rb/or Cd 4d and S 2p states, resulting in two-type ionic groups with weak couplings. It is shown that macroscopic domain walls originate from such weak-coupling ionic groups, arising at the cell boundaries. The asymmetric cation bonds (Rb--O and Cd--O) and the subsequent rotations of the SO4 tetrahedra can lead to the driving force of the ferroelectric behaviour. The predicted pyroelectric current effects are observed experimentally in the ferroelectric phase.
First-Principles Studies on the Electronic Structures and Optical Properties for the PbWO4 Crystal Containing VPb2-
LIU Ting-Yu, ZHANG Qi-Ren, ZHUANG Song-Lin
Chin. Phys. Lett. 2005, 22 (2): 442-445 .  
Abstract   PDF(pc) (559KB) ( 674 )
The electronic structures, dielectric functions, complex refractive indices and absorption spectra for a perfect PbWO4 (PWO) crystal and the PWO crystals containing lead vacancy VPb2- have been calculated using a full-potential (linearized) augmented plane-wave (LAPW) + local orbitals (LO) method with the lattice structure optimized. The peaks of the absorption spectra corresponding to the electronic transitions have been studied. The calculated results indicate that the absorption band of the perfect PWO crystal does not occur in the visible region. However, the PWO crystal containing VPb2- has two additional absorption bands in this region. The two bands can be well decomposed into four gaussian-shape bands peaking at 350nm, 405nm, 550nm and 670nm, respectively, which coincide well with the 350nm, 420nm, 550nm and 680nm absorption bands measured in PWO crystals. Therefore, it can be concluded that the 350nm, 420nm, 550nm and 680nm absorption bands are related to the existence of VPb2- in the PWO crystal.
Propagation of Cylindrical Waves in Media of Time-Dependent Permittivity
ZHANG Ying, GAO Ben-Qing
Chin. Phys. Lett. 2005, 22 (2): 446-449 .  
Abstract   PDF(pc) (381KB) ( 510 )
We present the propagation of cylindrical waves in the media whose permittivity varies with time abruptly or continuously. By the method of variable separation, we derive the general expression of electric field of TM-polarized waves in two-dimensional space with excitation of any point at any time. With this expression, the solution for a spatially and temporally distributed source can be obtained theoretically. The focusing of reflected waves in the cross section is shown when the media undergoes a sudden or continuous change. The wave propagation in time-invariant media can be considered as a special case of the media under exponential variance.
Electrical Resistance Measurement of an Individual Carbon Nanotube
LIU Jin-Ping, XIAO Cun-Ying, HUANG Xin-Tang
Chin. Phys. Lett. 2005, 22 (2): 450-453 .  
Abstract   PDF(pc) (347KB) ( 525 )
Aiming at the difficulty in the electrical resistance measurement, we develop a simple statistical model for the carbon nanotubes adequately dispersed in available insulated liquid and introduce the concept of "the most probability". Based on this model, we obtain the function between macroscopic resistance R and resistance of an individual nanotube, R0, from which one can calculate the resistance of an individual nanotube by measuring the macroscopic resistance. By computational simulation, we prove the reliability of the model. Then, we analyse the feasibility of the model when applied to experiment.
Investigation into the Energy Band Diagram and Charge Distribution in AlGaN/GaN Double Heterostructures by Self-Consistent Poisson--Schrödinger Calculations
JI Xiao-Li, CHEN Fan, JIANG Ruo-Lian, ZHOU Jian-Jun, WEN Bo, HAN Ping, XIE Zi-Li, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2005, 22 (2): 454-456 .  
Abstract   PDF(pc) (375KB) ( 572 )
The energy band diagram and charge distribution of the unintentional doped AlGaN/GaN/AlGaN/GaN double heterostructure were obtained by self-consistent Poisson--Schrödinger calculations. The severe band tilting and high two-dimensional electron gas (2DEG) density mainly attribute to the large internal polarization intensity, which is close to a linear function of Al composition. The influence of Al composition is investigated. The results show that band tilting enlarges and 2DEG gains with Al composition, and two-dimensional hole gas occurs when Al composition reaches a certain extent. The influence of Al composition and two-dimensional hole gas (2DHG) on devices is discussed.
Fluorescence Lifetime Increasing with F- Ions into Ytterbium-Doped Germanium--Lead--Tellurite Glasses
WANG Guo-Nian, DAI Shi-Xun, ZHANG Jun-Jie, XU Shi-Qing, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2005, 22 (2): 457-459 .  
Abstract   PDF(pc) (292KB) ( 535 )
The effects of F- ions in a germanium--lead--tellurite glass system on the spectral and potential laser properties of the Yb3+ are investigated. The absorption spectra, lifetimes, the emission cross-sections and the minimum pump intensities of the glass system with and without F- ions have been measured and calculated. The results show that the fluorescence lifetime and the minimum pump intensity of Yb3+ ions increase evidently, which indicates that germanium--lead--oxyfluoride tellurite glass is a promising laser host matrix for high power generation. FT-IR spectra were used to analyse the effect of F- ions on OH- groups in this glass system. Analysis demonstrates that addition of fluoride removes the OH- groups and results in improvement of fluorescence lifetime of Yb3+.
Hybridization and Magnetic Ground States in Heavy Fermion Compound CeRhIn5
XU Ying, WANG Jiang-Long, ZENG Zhi
Chin. Phys. Lett. 2005, 22 (2): 460-462 .  
Abstract   PDF(pc) (304KB) ( 781 )
The magnetic properties of CeRhIn5 are studied by first-principles calculation. Spin-orbit coupling is considered as well as different corrections including local density approximation plus on-site Coulomb interaction U (U=1, 1.5, 3eV) and orbital polarization. The results show the existence of only moderate correlation in CeRhIn5 and Ce-4f electrons are on the border of localization and itinerancy. The effect of pressure by changing the volume of the unit cell is also studied.
Magnetic and Transport Properties of Ferromagnetic Semiconductor GaDyN Thin Film
LI Xi-Jun, ZHOU YI-Kai, KIM M., KIMURA S., TERAGUCHI N., EMURA S., HASEGAWA S., ASAHI H.
Chin. Phys. Lett. 2005, 22 (2): 463-465 .  
Abstract   PDF(pc) (309KB) ( 537 )
Magnetic properties and temperature dependence of electrical transport properties of rare-earth-metal Dy-doped GaN thin film are experimentally studied with a superconducting quantum interference device magnetometer and van der Pauw method. It was found that this thin nitride film has both semiconductor properties and ferromagnetism from 10K to room temperature. The dopant-band (conducting band due to doping) electron conduction dominates the transport properties of this film at low temperatures. These results indicate that Dy-doped GaN is an n-type ferromagnetic semiconductor at room temperature.
Effect of Annealing on Structural and Magnetic Properties of a Thick (Ga,Mn)As Layer
DENG Jia-Jun, ZHAO Jian-Hua, JIANG Chun-Ping, ZHANG Yan, NIU Zhi-Chuan, YANG Fu-Hua, WU Xiao-Guang, ZHENG Hou-Zhi
Chin. Phys. Lett. 2005, 22 (2): 466-468 .  
Abstract   PDF(pc) (393KB) ( 460 )
We investigate effects of annealing on magnetic properties of a thick (Ga,Mn)As layer, and find a dramatic increase of the Curie temperature from 65 to 115K by postgrowth annealing for a 500-nm (Ga,Mn)As layer. Auger electron spectroscopy measurements suggest that the increase of the Curie temperature is mainly due to diffusion of Mn interstitial to the free surface. The double-crystal x-ray diffraction patterns show that the lattice constant of (Ga,Mn)As decreases with increasing annealing temperature. As a result, the annealing induced reduction of the lattice constant is mainly attributed to removal of Mn interstitial.
First Principles Study on Electronic Structure of PbFe0.5Nb0.5O3
WANG Yuan-Xu, , WANG Chun-Lei, ZHAO Ming-Lei, ZHANG Jia-Liang
Chin. Phys. Lett. 2005, 22 (2): 469-471 .  
Abstract   PDF(pc) (513KB) ( 833 )
The full potential linearized augmented plane wave (FLAPW) method is used to study the crystal structure and electronic structure properties of PbFe0.5Nb0.5O3 (PFN). The optimized crystal structure, density of states, band structure and electron density distribution have been obtained to understand the ferroelectric behaviour of PFN. The analysis result of the density of states shows there is an obvious change of Nbd states in the paraelectric-to-ferroelectric phase transition. The polarization result shows that the contribution to ferroelectricity of Nb atoms is larger than that of Fe atoms. In ferroelectric phase there is a hybridization of Fed--Op and Nbd--Op in ferroelectric PFN. This is consistent with the result of the electronic band structure. This hybridization is responsible for the tendency to its ferroelectricity.
Time-Resolved Photoluminescence Studies of Indium-Rich InGaN Alloys
CHEN Guang-De, ZHU You-Zhang, YAN Guo-Jun, YUAN Jin-She, K. H. Kim, J. Y. Lin, H. X. Jiang
Chin. Phys. Lett. 2005, 22 (2): 472-474 .  
Abstract   PDF(pc) (486KB) ( 661 )
Time-resolved photoluminescence (PL) spectroscopy has be used to investigate indium-rich InGaN alloys grown on sapphire substrates by metal organic chemical vapor deposition. Photoluminescence measurement indicates two dominant emission lines originating from phase-separated high- and low-indium-content regions. Temperature and excitation intensity dependence of the two main emission lines in these InGaN alloys have been measured. Temperature and energy dependence of PL decay lifetime show clearly different decay behaviour for the two main lines. Our results show that photo-excited carriers are deeply localized in the high indium regions while photo-excited carriers can be transferred within the low-indium-content regions as well as to
high-content regions.
Off-Resonant Third-Order Optical Nonlinearity of an Ag:TiO2 Composite Film
ZHANG Chun-Feng, YOU Guan-Jun, DONG Zhi-Wei, LIU Ye, MA Guo-Hong, QIAN Shi-Xiong
Chin. Phys. Lett. 2005, 22 (2): 475-477 .  
Abstract   PDF(pc) (326KB) ( 474 )
Using the femtosecond time-resolved optical Kerr effect technique, we investigate the off-resonant nonlinear optical response of an Ag:TiO2 composite film prepared by a vacuum magnetron sputtering method. The third-order nonlinear optical susceptibility of the composite film with silver nanoparticle size of about 30nm is estimated to be 1.9×10-10 esu at the incident laser wavelength of 800nm. When the photon energy of the incident beam is lower than that for surface plasmon or the interband transition of silver nanoparticles, the observed third-order optical nonlinearity is attributed to the intraband transition of the free electrons. Based on the linear limit of the electric field within micro-spherical model, we assign this large optical nonlinearity to the local field enhancement of the third-order nonlinearity.
Carbide Identification in Different Regions of a Thin Metal Film Covering on an HPHT As-Grown Diamond Single Crystal from Ni--Mn--C System
XU Bin, CUI Jian-Jun, LI Mu-Sen, LI Cheng-Mei, CHU Fu-Min, FENG Li-Ming
Chin. Phys. Lett. 2005, 22 (2): 478-481 .  
Abstract   PDF(pc) (473KB) ( 546 )
Diamond single crystals were synthesized in the presence of Ni--Mn catalyst under high temperature and high pressure (HPHT). A thin metal film covering on as-grown diamond formed during diamond growth was examined using transmission electron microscopy. It was shown that phase compositions of the region near the as-grown diamond are different from those of other regions in the film. We found γ-(Ni,Mn) solid solution, diamond, Ni3C and Mn23C6 in the region near the as-grown diamond, while graphite, Mn7C3 and γ-(Ni,Mn) could be found in other regions of the film. The relationship between the diamond growth and the carbides in the film was analysed briefly. It is suggested that the carbon source for diamond growth should be closely related to the decomposition of carbides in the region near the diamond single crystal at HPHT, not being directly from that of the graphite structure.
Direct Measurement of the Metastable Liquid Miscibility Gap in Fe--Co--Cu Ternary Alloy System
CAO Chong-De, Georg P. Gö, RLER
Chin. Phys. Lett. 2005, 22 (2): 482-484 .  
Abstract   PDF(pc) (370KB) ( 862 )
The metastable liquid--liquid phase separation in undercooled Fe--Co--Cu ternary alloy melts (XCu=0.10--0.84; XCo:XFe=1:3, 1:1 and 3:1) is investigated by differential thermal analysis in combination with glass fluxing technique. In almost every case, the undercooling of the homogeneous alloy melt was sufficient to reach the boundary line of the submerged miscibility gap. The differential-thermal-analysis signals indicate that this separation into a (Fe,Co)-rich liquid phase L1 and a Cu-rich liquid L2 is exothermic and proceeds until the rapid solidification of the L1 phase occurs. At a given Cu concentration and with the increase of Co content, the phase separation temperatures decrease monotonically between the corresponding values of the boundary systems Fe--Cu and Co--Cu. The boundary lines of the miscibility gap, which are determined for the three quasi-binary cross-sections of the (Fe,Co)--Cu alloy system, show remarkably flat domes. The occurrence of the liquid phase separation shows an evident influence on the subsequent γ-Fe(Co,Cu)→α-Fe(Co, Cu) solid phase transformation.

Microstructures in Strongly Interacting Dipolar Fluids
XU Chen, MA Yu-Qiang, HUI Pak-Ming, TONG Fu-Qiang
Chin. Phys. Lett. 2005, 22 (2): 485-488 .  
Abstract   PDF(pc) (424KB) ( 500 )
The formation of ring- and chain-like microstructures in ferrofluids consisting of interacting magnetic particles coated by a surfactant layer is studied by Monte Carlo simulations. For thin coating layers, it is found that ring- and chain-like structures coexist. The ring-like structures are suppressed by thicker coating layers. These observations are in agreement with recent experiments. Also, the ring-like structures are formed by dynamical aggregation of particles, instead of bending of linear chains. The latter process is forbidden by a substantial energy barrier. More generally, it is found that the ring structures exist when the parameter α=μ2 /[kBT (d+2δ)3] is higher than a critical value αc, where μ is the magnitude of magnetic moment, d is the diameter, and δ is the coating thickness of a particle. We find that when α<αc, the ring structures cannot be formed spontaneously, while the chain-like structures still exist. Furthermore, the critical value αc is almost independent of magnetic particle volume density in the low density range.
Temperature-Dependent Dynamic Properties of LixMn2O4 in Monte Carlo Simulations
OUYANG Chu-Ying, SHI Si-Qi, WANG Zhao-Xiang, LI Hong, HUANG Xue-Jie, CHEN Li-Quan
Chin. Phys. Lett. 2005, 22 (2): 489-492 .  
Abstract   PDF(pc) (453KB) ( 601 )
Monte Carlo (MC) simulations are used to simulate the voltage profile and the ionic conductivity s of Li ions in LixMn2O4 and its dependence on the lithium concentration x. The open circuit potential shows clearly the two plateaus in the charge/discharge curve, which agrees well with the experimental results. The two plateaus become more and more steep when the temperature is increased. The simulated ionic conductivity shows an M-shaped curve in the plot of ionic conductivity σ versus x when the simulation temperature is low. Interestingly, the minimum valley, which lies at the middle single-phase area near x = 0.5, disappears gradually when the temperature increases to 453K.
Influence of Particle Coordination Number in Nanoporous TiO2 Films on the Performance of Dye-Sensitized Solar Cell Modules
HU Lin-Hua, DAI Song-Yuan, WANG Kong-Jia
Chin. Phys. Lett. 2005, 22 (2): 493-495 .  
Abstract   PDF(pc) (248KB) ( 611 )
The average particle coordination number, one of the characters concerning the pore size distribution in the films, was introduced in dye-sensitized solar cell (DSC) modules with the size of 15cm × 20cm and the active area of 187.2cm2 to estimate the performance of a TiO2 nanoporous film, which is critical to the future DSC production. The current--voltage measurement of the DSC modules indicates that the average particle coordination number in the range of 4--5 typically appears in nanocrystalline TiO2 films used in the DSC modules and that the average coordination number could provide a very valuable way to evaluate the performance of nanoporous TiO2 films.
Ambipolar Thin-Film Field-Effect Transistor Based on Pentacene
WANG Wei, SHI Jia-Wei, LIANG Chang, ZHANG Hong-Mei, LIU Ming-Da, QUAN Bao-Fu, GUO Shu-Xu, FANG Jun-Feng, MA Dong-Ge
Chin. Phys. Lett. 2005, 22 (2): 496-498 .  
Abstract   PDF(pc) (333KB) ( 619 )
Organic thin film field-effect transistors based on pentacene have been fabricated by the method of fully-evaporation. The present device with a thin insulator layer can operate in low voltage, and shows ambipolar mode. In the case of the p-channel, the field-effect hole mobility was calculated to be 0.17cm2/Vs, whereas the field-effect electron mobility was about 0.02cm2/Vs for n-channel.
Electrostatic Interactions Between Glycosaminoglycan Molecules
SONG Fan, MOYNE Christian, BAI Yi-Long
Chin. Phys. Lett. 2005, 22 (2): 499-502 .  
Abstract   PDF(pc) (486KB) ( 465 )
The electrostatic interactions between nearest-neighbouring chondroitin sulfate glycosaminoglycan (CS-GAG) molecular chains are obtained on the bottle brush conformation of proteoglycan aggrecan based on an asymptotic solution of the Poisson-Boltzmann equation the CS-GAGs satisfy under the physiological conditions of articular cartilage. The present results show that the interactions are associated intimately with the minimum separation distance and mutual angle between the molecular chains themselves. Further analysis indicates that the electrostatic interactions are not only expressed to be purely exponential in separation distance and decrease with the increasing mutual angle but also dependent sensitively on the saline concentration in the electrolyte solution within the tissue, which is in agreement with the existed relevant conclusions.
Master Equation Approach to Molecular Motor’s Directed Motion
FENG Juan, ZHUO Yi-Zhong,
Chin. Phys. Lett. 2005, 22 (2): 503-506 .  
Abstract   PDF(pc) (408KB) ( 552 )
The master equation approach based on the periodic one-dimensional three-state hopping model is developed to study the molecular motor’s directed motion. An explicit solution Px(t) is obtained for the probability distribution as a function of the time for any initial distribution Px(0) with all the transients included. We introduce dj to represent the sub-step lengths, which can reflect how the external load affects the individual rate via load distribution factors θj+ and θj-. A wide variety of molecular motor behaviour under external load f can readily be obtained by the unequal-distance transition model with load-dependent transition rates. By comparison with the experiments, namely of the drift velocity v and the randomness parameter r versus adenosine triphosphate concentration and external load f, it is shown that the model presented here can rather satisfactorily explain the available data.
Phase Locking Phenomena and Electroencephalogram-Like Activities in Dynamic Neuronal Systems
XU Xin-Jian, WANG Sheng-Jun, TANG Wei, WANG Ying-Hai
Chin. Phys. Lett. 2005, 22 (2): 507-509 .  
Abstract   PDF(pc) (388KB) ( 461 )
We study signal detection and transduction of dynamic neuronal systems under the influence of external noise, white and coloured. Based on simulations, we show explicitly phase locking phenomena between the output and the input of a single neuron and Electroencephalogram-like activities on neural networks with small-world connectivity. The numerical results prove that the dynamic neuronal system can be adjusted to an optimal sensitive state for signal processing in the presence of additive noise.
Epidemic Spread in Weighted Scale-Free Networks
YAN Gang, ZHOU Tao, WANG Jie, FU Zhong-Qian, WANG Bing-Hong
Chin. Phys. Lett. 2005, 22 (2): 510-513 .  
Abstract   PDF(pc) (529KB) ( 1309 )
We investigate the detailed epidemic spreading process in scale-free networks with link weights that denote familiarity between two individuals. It is found that the spreading velocity reaches a peak quickly then decays in a power-law form. Numerical study exhibits that the nodes with larger strength is preferential to be infected, but the hierarchical dynamics are not clearly found, which is different from the well-known result in the unweighed network case. In addition, also by numerical study, we demonstrate that larger dispersion of weight of networks results in slower spreading, which indicates that epidemic spreads more quickly on unweighted scale-free networks than on weighted scale-free networks with the same condition.
The Grüneisen Parameter of NaCl at High Pressures and Temperatures: a Molecular Dynamics Study
CAI Ling-Cang, CHEN Qi-Feng, CUI Shou-Xin, JING Fu-Qian
Chin. Phys. Lett. 2005, 22 (2): 514-516 .  
Abstract   PDF(pc) (353KB) ( 636 )
The isotherms and Grüneisen parameters are calculated by using the molecular dynamics (MD) method with an improved Tosi--Fumi pair potential. The results show that the approximate power law dependence of the Grüneisen parameter on compression γ = γ 0 (V/V0)q, with q approximate 1.078, holds in the temperature range from 298 to 1073K and pressure range from 0 to 60GPa, and that the Grüneisen parameter for a given density of 2.16g/cm3 varies with temperature in a wind range from 300 to 10000K, expressed by γ = 1.052 + 0.582\exp( - T/4878.56).
Resonant Acceleration of Magnetospheric Electrons Driven by the R--X Mode
XIAO Fu-Liang, ZHENG Hui-Nan, WANG Shui
Chin. Phys. Lett. 2005, 22 (2): 517-520 .  
Abstract   PDF(pc) (525KB) ( 1114 )
An extended relativistic model is developed to evaluate the superluminous R--X-mode resonance especially the second-order and third-order resonances with electrons in the Earth’s magnetosphere. The potential for stochastic electron acceleration driven by the R--X mode is determined by the dispersive properties of the R--X mode and specifically the resonant harmonic N. In contrast to the limited acceleration at the first harmonic (1N=1) resonance, for the higher harmonic (N>1) resonances, the R--X mode is capable of accelerating electrons from ~10keV to ~ MeV energies, over a wide range of wave normal angles, in spatial regions extending from the auroral cavity to the latitude (>30°) outer radiation belt. This indicates that higher-order resonance is essentially important for the electron acceleration for the oblique wave propagation.
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