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Volume 25 Issue 8
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Original Articles
Interaction between Soliton and Periodic Wave
LI Yu-Qi
Chin. Phys. Lett. 2008, 25 (8): 2735-2738 .  
Abstract   PDF(pc) (940KB) ( 643 )
A truncation for the Laurent series in the Painlevé analysis of the KdV equation is restudied. When the truncation occurs the singular manifold satisfies two compatible fourth-order PDEs, which are homogeneous of degree 3. Both of the PDEs can be factored in the operator sense. The common factor is a third-order PDE, which is homogeneous of degree 2. The first few invariant manifolds of the third-order PDE are studied. We find that the invariant manifolds of the third-order PDE can be obtained by factoring the invariant manifolds of the KdV equation. A numerical solution of the third-order PDE is also presented. The solution reveals some interesting facts about the third-order PDE.
Periodic Wave Solution to the (3+1)-Dimensional Boussinesq Equation
WU Yong-Qi
Chin. Phys. Lett. 2008, 25 (8): 2739-2742 .  
Abstract   PDF(pc) (204KB) ( 689 )
One- and two-periodic wave solutions for (3+1)-dimensional Boussinesq equation are presented by means of Hirota's bilinear method and the Riemann theta function. The soliton solution can be obtained from the periodic wave solution in an appropriate limiting procedure.
Chaos Anti-synchronization between Two Novel Different Hyperchaotic Systems
M. Mossa Al-Sawalha, M. S. M. Noorani
Chin. Phys. Lett. 2008, 25 (8): 2743-2746 .  
Abstract   PDF(pc) (347KB) ( 960 )
We demonstrate that anti-synchronization can coexist in two different hyperchaotic systems of ratchets moving in different asymmetric potentials by active control method. By using rigorous mathematical theory, the sufficient condition is drawn for the stability of the error dynamics, where the controllers are designed by using the sum of the relevant variables in hyperchaotic systems. Numerical results are presented to justify the theoretical analysis strategy.
Temperature Dependence of Elastic Properties for Amorphous SiO2 by Molecular Dynamics Simulation
LIU Bin, WANG Jing-Yang, ZHOU Yan-Chun, LI Fang-Zhi,
Chin. Phys. Lett. 2008, 25 (8): 2747-2750 .  
Abstract   PDF(pc) (276KB) ( 1955 )
Large-scale and long-time molecular-dynamics simulations are used to investigate the temperature dependences of elastic properties for amorphous SiO2. The elastic moduli increase in a temperature range up to 1600 K and decrease thereafter. The anomalous behaviour in elasticity is explained by analysing the changes of atomic-scale structure with respect to increment of temperature. The mechanism originates predominantly from distortion of the SiO4 tetrahedra network in low-temperature ranges. At an elevated temperature range, thermal-induced Si--O bond stretching dominates the process and leads to normal temperature dependence of elastic properties.
From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality
WU Hong-Tu, HUANG Chao-Guang, GUO Han-Ying
Chin. Phys. Lett. 2008, 25 (8): 2751-2753 .  
Abstract   PDF(pc) (115KB) ( 484 )
By means of the Dirac procedure, we re-examine Yang's quantized space--time model, its relation to Snyder's model, the dS special relativity and their UV--IR duality. Starting from a dimensionless dS5-space in a (5+1)-dimensional Mink-space a complete Yang model at both classical and quantum level can be presented and there really exists Snyder's model, the dS special relativity and the duality.
Exact Solutions of Klein--Gordon Equation with Scalar and Vector Rosen--Morse-Type Potentials
A. Soylu, O. Bayrak, I. Boztosun
Chin. Phys. Lett. 2008, 25 (8): 2754-2757 .  
Abstract   PDF(pc) (98KB) ( 1131 )
We obtain an exact analytical solution of the Klein--Gordon equation for the equal vector and scalar Rosen--Morse and Eckart potentials as well as the parity-time (PT) symmetric version of the these potentials by using the asymptotic iteration method. Although these PT symmetric potentials are non-Hermitian, the corresponding eigenvalues are real as a result of the PT symmetry.
Time-Dependent Variational Approach to Ground-State Phase Transition and Phonon Dispersion Relation of the Quantum Double-Well Model
ZHONG Hong-Wei, XU Hai-Qing, HUANG Ping-Hua
Chin. Phys. Lett. 2008, 25 (8): 2758-2761 .  
Abstract   PDF(pc) (112KB) ( 548 )
The ground-state phase transition and the phonon dispersion relation of the quantum double-well model are studied by means of the time-dependent variational approach combined with a Hartree-type many-body trial wavefunction. The single-particle state is taken to be a frozen Jackiw--Kerman wavefunction. Under the condition of minimum uncertainty relation, we obtain an effective classical Hamiltonian for the system and equations of motion for the particle's expectation values. It is shown that the effective substrate potential transits from a symmetric double-well potential to a symmetric single-well potential, and the ground state exhibits a transition from a broken symmetry phase to a restored symmetry phase as increasing the strength of quantum fluctuations. We also obtain the phonon dispersion relations and the phonon gaps at the two phases.
Wigner Function of Thermo-Invariant Coherent State
XU Xue-Fen, ZHU Shi-Qun
Chin. Phys. Lett. 2008, 25 (8): 2762-2764 .  
Abstract   PDF(pc) (293KB) ( 541 )
By using the thermal Winger operator of thermo-field dynamics in the coherent thermal state |ξ> representation and the technique of integration within an ordered product of operators, the Wigner function of the thermo-invariant coherent state |z, N>is derived. The nonclassical properties of state |z, N> is discussed based on the negativity of the Wigner function.
Forcible-Measurement Attack on Quantum Secure Direct Communication Protocol with Cluster State
GAO Fei, GUO Fen-Zhuo, WEN Qiao-Yan, ZHU Fu-Chen
Chin. Phys. Lett. 2008, 25 (8): 2766-2769 .  
Abstract   PDF(pc) (107KB) ( 505 )
The security of the quantum secure direct communication (QSDC) protocol with cluster state is analysed. It is shown that the secret would be partially leaked out when an eavesdropper performs forcible measurements on the transmitted particles. With the help of the result in minimum error discrimination, an upper bound (i.e. 40%) of this leakage is obtained. Moreover, the particular measurements which makes the leakage reach this bound are given.
Symmetric Telecloning and Entanglement Distribution of Spin Quantum States
WANG Qiong, LI Ji-Xin, ZANG Hao-Sheng
Chin. Phys. Lett. 2008, 25 (8): 2770-2773 .  
Abstract   PDF(pc) (582KB) ( 591 )
We propose a physical realization of symmetric telecloning machine for spin quantum states. The concept of area average fidelity is introduced to describe the telecloning quality. It is indicated that for certain input states this quantity may come to an enough high level to satisfy the need of quantum information processing. We also study the properties of entanglement distribution via the spin chain for arbitrary two-qubit entangled pure states as inputs and find that the decay ratio of entanglement for the output states is only determined by the parameters of spin chain and waiting time, independent of the initial input states.
Research on Quantum Searching Algorithms Based on Phase Shifts
ZHONG Pu-Cha, BAO Wan-Su
Chin. Phys. Lett. 2008, 25 (8): 2774-2777 .  
Abstract   PDF(pc) (2163KB) ( 900 )
One iterative in Grover's original quantum search algorithm consists of two Hadamard--Walsh transformations, a selective amplitude inversion and a diffusion amplitude inversion. We concentrate on the relation among the probability of success of the algorithm, the phase shifts, the number of target items and the number of iterations via replacing the two amplitude inversions by phase shifts of an arbitrary Φ =φ(0≤Φ,φ≤2π). Then, according to the relation we find out the optimal phase shifts when the number of iterations is given. We present a new quantum search algorithm based on the optimal phase shifts of 1.018 after 0.5π/√ M/N iterations. The new algorithm can obtain either a single target item or multiple target items in the search space with the probability of success at least 93.43%.
Coupling between Collective Excitations of a Bose--Einstein Condensate and Modulated Interactions
Chin. Phys. Lett. 2008, 25 (8): 2778-2781 .  
Abstract   PDF(pc) (130KB) ( 413 )
We investigate collective excitations of a Bose--Einstein condensate in the presence of temporal modulation of repulsive interactions, and analytically demonstrate that the modulated interaction can drive the condensate to oscillate with the external modulation frequency, and that the interaction couples with the eigen modes of the condensate collective excitations, which was previously considered to be independent of interaction. When the external modulation frequency approaches or is far away from the eigen frequency of the density monopole mode, the condensate shows resonant or beating behaviour.
Quasi-Local Energy Distribution of the Modified Reissner--Nordström Black Hole
WEI Yi-Huan
Chin. Phys. Lett. 2008, 25 (8): 2782-2784 .  
Abstract   PDF(pc) (87KB) ( 576 )
We discuss the energy distribution of the modified Reissner--Nordström black hole. It is suggested that the quasi-local energy distribution from Einstein energy-momentum complex should be appropriate. For the Reissner-ordström spacetime, it can be seen that the energies of the outer and inner regions are exactly equivalent.
Accelerated D-Dimensional Compactified Universe in Gauss--Bonnet--Dilatonic Scalar Gravity from D-Brane/M-Theory
Chin. Phys. Lett. 2008, 25 (8): 2785-2788 .  
Abstract   PDF(pc) (115KB) ( 474 )
We discuss a particular d-dimensional Gauss--Bonnet--dilatonic universe compactified on S1 motivated from M-theory. We examine the time-evolution of the dynamical equations where many interesting consequences are revealed and discussed in some details. Under reasonable conditions, the discussed model can provide a mechanism to realize, in higher-dimensions (d>4), the accelerated expansion of the universe in the presence of dark energy, without the presence of phantom energy and without the contraction of some internal dimension.
Quantum de Sitter Spacetime and Energy Density Contributed from the Cosmological Constant
LIU Liao
Chin. Phys. Lett. 2008, 25 (8): 2789-2790 .  
Abstract   PDF(pc) (76KB) ( 539 )
Previously we introduce a new way to quantize the static Schwarzschild black hole (SSBH), there the SSBH was first treated as a single periodic Euclidean system and then the Bohr--Sommerfeld quantum condition of action was used to obtain a quantum theory of Schwarzschild black hole [Chin. Phys. Lett. (2004) 21 1887]. Here we try to extend the above method to quantize the static de Sitter (SDS) spacetime and establish a quantum theory of both SDS space and the energy density contributed from the cosmological constant.
Casimir Energy in Hartle--Hawking State
FANG Heng-Zhong, ZHU Jian-Yang
Chin. Phys. Lett. 2008, 25 (8): 2791-2794 .  
Abstract   PDF(pc) (108KB) ( 474 )
We calculate the Casimir effect at finite temperature in Minkowski spacetime by using statistical method, the approximate expressions of the Casimir effect in the low and high temperature limits are also discussed. Then employing some general properties of the renormalized stress tensor, we obtain the Casimir energy stress tensor in Hartle--Hawking state.
Synchronized Flow in a Cellular Automaton Model with Time Headway Dependent Randomization
CHEN Tao, JIA Bin, LI Xin-Gang, JIANG Rui, GAO Zi-You
Chin. Phys. Lett. 2008, 25 (8): 2795-2798 .  
Abstract   PDF(pc) (4852KB) ( 710 )
We propose another possible mechanism of synchronized flow, i.e. that a time headway dependent randomization can exhibit synchronized flow. Based on this assumption, we present a new cellular automaton (CA) model for traffic flow, in which randomization effect is enhanced with the decrease of time headway. We study fundamental diagram and spatial-temporal diagrams of the model and perform microscopic analysis of time series data, which shows the model could reproduce synchronized flow as expected. It is also shown that a spontaneous transition from synchronized flow to jam could be observed by incorporating slow-to-start effect into the model. We expect that our work could contribute to the understanding of the real origin of synchronized flow.
Two Different Bifurcation Scenarios in Neural Firing Rhythms Discovered in Biological Experiments by Adjusting Two Parameters
WU Xiao-Bo, MO Juan, YANG Ming-Hao, ZHENG Qiao-Hua, GU Hua-Guang, REN Wei
Chin. Phys. Lett. 2008, 25 (8): 2799-2802 .  
Abstract   PDF(pc) (201KB) ( 1100 )
Two different bifurcation scenarios, one is novel and the other is relatively simpler, in the transition procedures of neural firing patterns are studied in biological experiments on a neural pacemaker by adjusting two parameters. The experimental observations are simulated with a relevant theoretical model neuron. The deterministic non-periodic firing pattern lying within the novel bifurcation scenario is suggested to be a new case of chaos, which has not been observed in previous neurodynamical experiments.
A New High Performance Realization of Hyperchaotic Modified Canonical Chua Circuit Using JFETs
Prem Bhushan Mital, Umesh Kumar, R.S. Prasad
Chin. Phys. Lett. 2008, 25 (8): 2803-2805 .  
Abstract   PDF(pc) (103KB) ( 817 )
A new implementation of hyperchaotic modified canonical Chua circuit using junction field-effect transistors (JFETs) is proposed. The design is based on a source coupled JFET circuit to approximate a smooth cubic nonlinearity and a two-terminal negative resistance element containing a p-n-p silicon transistor and an n-channel JFET. The realization is supported by Orcad Pspice simulation and numerical MATLAB results. The hyperchaotic nature is confirmed by two positive Lyapunov exponents associated with the attractor which is a fractal with a Lyapunov dimension between 3 and 4.
Firing Patterns and Transitions in Coupled Neurons Controlled by a Pacemaker
LI Mei-Sheng, LU Qi-Shao, DUAN Li-Xia, WANG Qing-Yun
Chin. Phys. Lett. 2008, 25 (8): 2806-2808 .  
Abstract   PDF(pc) (155KB) ( 517 )
To reveal the dynamics of neuronal networks with pacemakers, the firing patterns and their transitions are investigated in a ring HR neuronal network with gap junctions under the control of a pacemaker. Compared with the situation without pacemaker, the neurons in the network can exhibit various firing patterns as the external current is applied or the coupling strength of pacemaker varies. The results are beneficial for understanding the complex cooperative behaviour of large neural assemblies with pacemaker control.
Insight into Phenomena of Symmetry Breaking Bifurcation
Chin. Phys. Lett. 2008, 25 (8): 2809-2811 .  
Abstract   PDF(pc) (142KB) ( 612 )
We show that symmetry-breaking (SB) bifurcation is just a transition of different forms of symmetry, while still preserving system's symmetry. SB bifurcation always associates with a periodic saddle-node bifurcation, identifiable by a zero maximum of the top Lyapunov exponent of the system. In addition, we show a significant phase portrait of a newly born periodic saddle and its stable and unstable invariant manifolds, together with their neighbouring flow pattern of Poincaré mapping points just after the periodic saddle-node bifurcation, thus gaining an insight into the mechanism of SB bifurcation.
Impulsive Control for Fractional-Order Chaotic Systems
ZHONG Qi-Shui, BAO Jing-Fu, YU Yong-Bin, LIAO Xiao-Feng
Chin. Phys. Lett. 2008, 25 (8): 2812-2815 .  
Abstract   PDF(pc) (135KB) ( 665 )
We propose an impulsive control scheme for fractional-order chaotic systems. Based on the Takagi--Sugeno (T-S) fuzzy model and linear matrix inequalities (LMIs), some sufficient conditions are given to stabilize the fractional-order chaotic system via impulsive control. Numerical simulation shows the effectiveness of this approach.
Projective Synchronization in Drive--Response Networks via Impulsive Control
GUO Liu-Xiao, XU Zhen-Yuan, HU Man-Feng,
Chin. Phys. Lett. 2008, 25 (8): 2816-2819 .  
Abstract   PDF(pc) (272KB) ( 591 )
Impulsive projective synchronization in 1+N coupled chaotic systems are investigated with the drive--response dynamical network (DRDN) model. Based on impulsive stability theory, some simple but less conservative criteria are achieved for projective synchronization in DRDNs. Furthermore, impulsive pinning scheme is also adopted to direct the scaling factor onto the desired value. Numerical simulations on generalized chaotic unified system are illustrated to verify the theoretical results.
A Super High Resolution Distance Measurement Method Based on Phase Comparison
LI Zhi-Qi, ZHOU Wei, MIAO Miao, ZHOU Hui, ZHENG Sheng-Feng
Chin. Phys. Lett. 2008, 25 (8): 2820-2822 .  
Abstract   PDF(pc) (94KB) ( 1813 )
Phase comparison method can enhance the measurement resolution to 10-13/τ in time domain. This method can also be used in distance measurement in the navigation and positioning. We propose a super high-resolution distance measurement based on linear phase comparison method. A high resolution scheme is put forward on the basis of the research of major factors concerning the phase comparison in the distance measurement. Conversion of a high-linearity phase difference to voltage and high-resolution voltage meter make it possible to obtain a very high phase measurement resolution. When the purpose is to measure distance, the phase noise of frequency source used in the measurement can be reduced partly. Thus this method is favourable for high resolution distance measurement. The precision of the distance measurement can reach 0.1c ps with c being the velocity of light in vacuum.
Calculation of Particle-Number Susceptibility of QED3 at Finite Temperature
HU Fei, JIANG Yu, FENG Hong-Tao, SUN Wei-Min, ZONG Hong-Shi,
Chin. Phys. Lett. 2008, 25 (8): 2823-2826 .  
Abstract   PDF(pc) (279KB) ( 518 )
Based on the external field approach and the differential form of Ward identity, we derive a more compact formula for the particle-number susceptibility in QED3 at finite temperature. Using the zero frequency approximation the numerical value of the particle-number susceptibility is calculated in the Dyson--Schwinger approach for the case that the number of fermion flavours equals one and two, respectively. An enhanced fluctuation of the particle-number density is observed across the transition temperature, which should be an essential characteristic of chiral phase transition in QED3.
B→ηK* and B→ΦKS Decays in the Two Higgs Doublet Model III
WANG Shuai-Wei, SONG Tai-Ping, LÜ, Lin-Xia
Chin. Phys. Lett. 2008, 25 (8): 2827-2830 .  
Abstract   PDF(pc) (147KB) ( 413 )
Using the QCD factorization approach, we investigate the large branching ratios of B→ηK* decays and the S KS anomaly of B→ΦKS decay in the two Higgs doublet model III. With the contributions of flavour-changing neutral current mediated by the neutral Higgs bosons H^0, h0 and A0 at the tree level, we provide a coherent resolution to these anomalies within the constrained parameter spaces, which are 120<|λbsλss|<136. This will be really interesting in searching for the signs of new physics.
Phenomenological Study of 3He Photodisintegration up to 150MeV
WANG Cheng-Bin, ZHU Zhi-Yuan
Chin. Phys. Lett. 2008, 25 (8): 2831-2833 .  
Abstract   PDF(pc) (261KB) ( 443 )
A parametrization of 3He(γ,p)2H cross section data at laboratory photon energies between 9 and 150MeV is carried out with a simple phenomenological function. The differential cross section data are normalized to the total cross-section values, which are consistent with the measurement from monochromatic photon beams. The obtained results give a good representation of the experimental points
Surface Diffuseness Anomaly in 16O+208Pb Quasi-elastic Scattering at Backward Angle
JIA Hui-Ming, LIN Cheng-Jian, ZHANG Huan-Qiao, LIU Zu-Hua, YANG Feng, JIAFei, ZHANG Chun-Lei, AN Guang-Peng, WU Zhen-Dong, XU Xin-Xing, BAI Chun-Lin, YU Ning
Chin. Phys. Lett. 2008, 25 (8): 2834-2836 .  
Abstract   PDF(pc) (142KB) ( 554 )
The quasi-elastic scattering excitation function of the doubly magic 16O+208Pb system at a backward angle is measured at sub-barrier energies with high precision. The diffuseness parameters extracted from both the single-channel and the coupled-channels calculations give almost the same value a = 0.76±0.04fm. The results show that the coupling effect is negligible for the spherical system. The obtained value is smaller than the extracted value from the fusion excitation function, but larger than the value of a = 0.63fm, which is from the systematic analysis of elastic scattering data.
Comparison of Properties of the Simplest Neutron Stars in Three RMF Models
WANG Guo-Hua, FU Wei-Jie and LIU Yu-Xin,
Chin. Phys. Lett. 2008, 25 (8): 2837-2840 .  
Abstract   PDF(pc) (347KB) ( 451 )
We study some properties of the simplest neutron stars (NSs) in the Glendenning–Moszkowski (GM) model, the hybrid derivative coupling (HD) model and the Zimanyi–Moszkowski (ZM) model in the framework of relativistic mean field (RMF) theory with and without the interaction by exchanging the δ-meson. We show that the maximal mass of the NSs becomes smaller, but the redshift becomes larger from the GM model to the HD model, then to the ZM model. The interaction with the δ-meson exchange enlarges the maximal mass of neutron stars, increases the relative population of charged particles (proton, electron and muon) and descends the relative population of neutron.
Application of Complete Orthonormal Sets of Ψα-Exponential-Type Orbitals to Accurate Ground and Excited States Calculations of One-Electron Diatomic Molecules Using Single-Zeta Approximation
I. Guseinov, R. Aydin, A. Bagci
Chin. Phys. Lett. 2008, 25 (8): 2841-2844 .  
Abstract   PDF(pc) (127KB) ( 545 )
The applicability of the complete orthonormal sets of Ψα-exponential-type orbitals introduced by one of the authors to the study of electronic structure of one electron diatomic molecules is demonstrated using single-zeta approximation. As an example of application, the calculations have been performed for σ, π and δ states of one electron homo- and hetero-nuclear diatomic molecules H2+ and HeH2+, respectively. The calculation results are presented. The values for these molecules obtained in eight-digit accuracy are close to the results of solution presented in literature.
Above-Threshold Dissociation of HD+ in Femtosecond Laser Field
BA Song-Yue, YUAN Kai-Jun, HAN Yong-Chang, CONG Shu-Lin
Chin. Phys. Lett. 2008, 25 (8): 2845-2848 .  
Abstract   PDF(pc) (222KB) ( 456 )
The above-threshold dissociation (ATD) of the HD+ molecular ion in femtosecond laser field is investigated theoretically. The energy-dependent distribution of the dissociated fragments is calculated using an asymptotic-flow expression in the momentum space. The calculations show that the ATD of HD+ is sensitive to the initial vibrational level of ground electronic state. Multiphoton ATDs can be observed in the dissociation processes. The dynamics phenomena are interpreted by using the concept of light-dressed potential.
Theoretical Investigation on Excitation, Ionization and Capture in H(1s,2s) +H(1s, 2s) Collisions
CHEN Lan-Fang, ZHU Xiao-Long, MA Xin-Wen, LIU Ling, HE Bin, WANG Jian-Guo, Ratko JANEV
Chin. Phys. Lett. 2008, 25 (8): 2849-2852 .  
Abstract   PDF(pc) (154KB) ( 445 )
Cross sections of electron-loss in H(1s)+ H(1s) collisions and total collisional destruction of H(2s) in H(1s) + H(2s) collisions are calculated by four-body classical-trajectory Monte Carlo (CTMC) method and compared with previous theoretical and experimental data over the energy range of 4--100keV. For the former a good agreement is obtained within different four-body CTMC calculations, and for the incident energy Ep>10keV, comparison with the experimental data shows a better agreement than the results calculated by the impact parameter approximation. For the latter, our theory predicts the correct experimental behaviour, and the discrepancies between our results and experimental ones are less than 30%. Based on the successive comparison with experiments, the cross sections for excitation to H(2p), single- and double-ionization and H- formation in H(2s)+H(2s) collisions are calculate in the energy range of 4--100keV for the first time, and compared with those in H(1s)+H(1s) and H(1s)+H(2s) collisions.
Translocation of Biopolymer Chain Through a Nanopore: Coil--Helix Transition
GU Fang, WANG Hai-Jun, HONG Xiao-Zhong, BA Xin-Wu
Chin. Phys. Lett. 2008, 25 (8): 2853-5856 .  
Abstract   PDF(pc) (134KB) ( 503 )
The translocation dynamics of a single biopolymer chain through a nanopore in a membrane is investigated by taking the coil--helix transition into account. Based on the changing of the free energy due to the coil--helix transition, the mean first passage time τ is obtained, and then the corresponding numerical simulations are presented under different conditions. It is shown that the coil--helix transition can significantly shorten the translocation time of the biopolymer chain. In addition, we also discuss the scaling behaviour for τ with the chain length N and some related problems.
Photopolymerization-Induced Two-Beam Coupling and Light-Induced Scattering in Polymethyl Methacrylate
LI Wei, ZHANG Xin-Zheng, SHI Yan-Li, XU Jing-Jun, QIAO Hai-Jun, WU Qiang, Romano A. Rupp, LOU Ci-Bo, WANG Zhen-Hua, GAO Feng, TANG Bai-Quan, Christian Pruner
Chin. Phys. Lett. 2008, 25 (8): 2857-2859 .  
Abstract   PDF(pc) (1131KB) ( 554 )
Light amplification due to two-beam coupling is realized in doped polymethyl methacrylate (PMMA) glasses. A coupling gain as large as 14cm-1 is obtained. The dynamic behaviour of absorption and light-induced scattering due to the process of photopolymerization are also studied. The results show that the amplification and its dynamic process enable possible applications of PMMA in optical devices.
Small-Pitch Kagome Hollow-Core Photonic Crystal Fibre
MENG Jia, HOU Lan-Tian, ZHOU Gui-Yao, WANG Kang, CHEN Chao
Chin. Phys. Lett. 2008, 25 (8): 2860-2862 .  
Abstract   PDF(pc) (1752KB) ( 651 )
A hollow-core photonic crystal fibre (HC-PCF) based on small-pitch kagome lattice cladding is designed and fabricated. The pitch of the fibre is only 2.45μm and it corresponds to a region of low normalized frequency which has never been investigated before. Both experiments and calculations show that this kagome HC-PCF has a broad optical transmission band from 400nm to 900nm, covering the whole visible and near infrared region of the spectrum. Additionally, the loss curve of the fibre is flat in the visible region and the minimum of the loss achieves 0.16dB/m, which is lower than the loss of the kagome HC-PCFs reported before. Furthermore, this fibre can well confine the modes in the air core. No surface modes can be detected in the surrounding silica of the hollow core.
Application of Cosine Zone Plates to Image Encryption
GE Fan, CHEN Lin-Fei, ZHAO Dao-Mu
Chin. Phys. Lett. 2008, 25 (8): 2863-2865 .  
Abstract   PDF(pc) (2102KB) ( 557 )
We analyse the diffraction result of optical field after Cosine zone plate, and theoretically deduce its transform matrix. Under some conditions, its diffraction distribution is a mixture of fractional Fourier spectra. Then we use Cosine zone plate and its diffraction result to image encryption. Possible optical image encryption and decryption implementations are proposed, and some numerical simulation results are also provided.
Crosstalk Noise Reduction in Shift-Multiplexed Holographic Storage System Using Multiple Point Sources
YI Tao, ZHANG Jia-Sen, ZHU Yi-Chao, GONG Qi-Huang
Chin. Phys. Lett. 2008, 25 (8): 2866-2869 .  
Abstract   PDF(pc) (145KB) ( 478 )
We propose and analyse a new method to reduce cross-talk noise in a shift multiplexed holographic storage system using multiple point sources. The normalized diffraction efficiency is given analytically with respect to the shift distance. The noise-to-signal ratio is defined and calculated to value the cross-talk of the system. The numerical results show that using multiple point sources can effectively decrease the cross-talk.
Design of Highly Directive Ni-Like Ag X-Ray Laser at 13.9nm
ZHAO Jing, DONG Quan-Li, WANG Shou-Jun, ZHANG Lei, ZHANG Jie,
Chin. Phys. Lett. 2008, 25 (8): 2870-2872 .  
Abstract   PDF(pc) (128KB) ( 416 )
We theoretically investigate a 13.9nm Ni-like Ag x-ray laser using a one-dimensional hydrodynamic code coupled with an atomic physics data package. The population inversion is transiently pumped by a grazing incident 0.5ps main pulse irradiating into an optimized plasma, which is generated by a normal incidence 300ps pulse and a subsequent grazing incidence 300ps pulse. The effect of the grazing-incidence angle on the source position of the output x-ray laser is investigated. Near zero deflecting angle is found for the peak output intensity of the Ni-like Ag x-ray lasers, with a small FWHM divergence of 5mrad. It is predicted that saturation can be achieved with a total pump energy of 165mJ.
Fibre-Format Photonic Source Based on Efficient Frequency Doubling of Continuous-Wave Erbium-Fibre Laser Amplifier
ZHANG Shuang-Gen, YAO Jiang-Hong, SHI Qing, LIU Yan-Ge, LI Yong-Nan, TU Cheng-Hou, GUO Wen-Gang, LU Fu-Yun
Chin. Phys. Lett. 2008, 25 (8): 2873-2875 .  
Abstract   PDF(pc) (183KB) ( 451 )
We demonstrate a compact photonic device based on efficient and wavelength-tunable doubling of an all fibre-format source. Quasi-phase-matched second-harmonic generation in periodically poled lithium niobate is used to generate 90.6mW at 775.9nm with a single-pass conversion efficiency of 14.7%. A tuning bandwidth of 2.1nm and a tuning temperature range of 150.6pm1.7°C can be achieved. The Er-doped seed fibre source is amplified by a clad-pumped Er3+/Yb3+-codoped fibre laser with a high output power up to 2.18W over a tunable wavelength range from 1535nm to 1570nm.
Broadly Tunable SOA-Based Active Mode-Locked Fibre Ring aser by Forward Injection Optical Pulse
YAN Shuang-Yi, ZHANG Jian Guo, ZHAO Wei, LU Hong-Qiang, WANG Wei-Qiang
Chin. Phys. Lett. 2008, 25 (8): 2876-2879 .  
Abstract   PDF(pc) (148KB) ( 623 )
We present a broadly tunable active mode-locked fibre ring laser based on a semiconductor optical amplifier (SOA), with forward injection optical pulses. The laser can generate pulse sequence with pulsewidth about 12ps and high output power up to 8.56dBm at 2.5GHz stably. Incorporated with a wavelength-tunable optical bandpass filter, the pulse laser can operate with a broad wavelength tunable span up to 37nm with almost constant pulsewidth. A detailed experimental analysis is also carried out to investigate the relationship between the power of the internal cavity and the pulsewidth of the output pulse sequence. The experimental configuration of the pulse laser is very simple and easy to setup with no polarization-sensitive components.
Numerical Modelling of QCW-Pumped Passively Q-Switched Nd:YAG Lasers with Cr4+:YAG as Saturable Absorber
WANG Yu-Ye, XU De-Gang, XIONG Jing-Ping, WANG Zhuo, WANG Peng, YAO Jian-Quan,
Chin. Phys. Lett. 2008, 25 (8): 2880-2883 .  
Abstract   PDF(pc) (794KB) ( 1040 )
Passively Q-switched quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser with Cr4+:YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.
Examination of Validity of Paraxial Approximation in Second Harmonic Generation Microscopy under Low Numerical Aperture
WANG Xiang-Hui, LIN Lie, CHANG Sheng-Jiang, ZHANG Hao, HAO Shu-Juan
Chin. Phys. Lett. 2008, 25 (8): 2884-2887 .  
Abstract   PDF(pc) (172KB) ( 593 )
By using a vectorial approach, the validity of paraxial approximation in second harmonic generation (SHG) microscopy under low numerical aperture (NA) is examined when the sample is a collagen fibril. Due to the larger value of dzzx and tensorial nature of SHG, the component Ez of the focused field may have strong effect on the radiation pattern of SHG. Numerical results indicate that when the value of NA exceeds 0.3, the effect of Ez can not be neglected, which results in the invalidation of paraxial approximation in SHG microscopy despite the fact that SHG microscopy is still under low NA focusing.
Numerical Simulation of Self-Pumped Phase Conjugate Plane--Curve Loop Mirror Based on Photorefractive Nonlinearity
Mehran Vahdani Moghaddam, Zeynab Chenari, Hamid Latifi, Vladimir Vladimirovich Shuvalov, Konestantin Valentinovich Rudenko
Chin. Phys. Lett. 2008, 25 (8): 2888-2891 .  
Abstract   PDF(pc) (790KB) ( 546 )
We deal with computer simulation of a transient process in a self-pumped phase conjugate plane--curve loop mirror based on BaTiO3. In optimal circumstances the nonlinear reflectivity and fidelity of such a mirror respectively achieve 0.80--0.90 and 0.95--0.98. The generation of conjugate wave-front occurs due to scattering from the dynamic hologram which is produced in the region of self-intersection of forward and backward beams. In such a model the scenario of passing to unstable generation regimes is similar to the self-pumped phase conjugate plane--plane loop mirror and substantially differs from a single-crystal double phase conjugate mirror.
Observation of Sub-femtosecond Polarization Beats Using Twin Noisy Driving Fields
LI Chuang-She, SHEN Lei-Jian, DU Yi-Gang, ZHENG Huai-Bin, NIE Zhi-Qiang, YANG Yong-Ming, ZHANG Wei-Feng, GAN Chen-Li, ZHANG Yan-Peng,
Chin. Phys. Lett. 2008, 25 (8): 2892-2895 .  
Abstract   PDF(pc) (191KB) ( 394 )
We study the phase-conjugate polarization interference in a V-type three-level system and obtain an analytic closed form for the second-order stochastic correlation of sum-frequency polarization beat. In our Na vapour atomic system pumped by laser pulse of nano-second timescale duration, we experimentally demonstrate an ultrafast modulation of the four-wave mixing signal intensity with a sub-femtosecond timescale period, corresponding to the sum-frequency of the resonant transitions from 3S1/2 to 3P1/2 and 3P3/2.
Scattering Noise Properties of Holographic Photopolymers by Means of Real-Time Transmittance Analysis
TAO Shi-Quan, WANG Huan-Yong, WAN Xiao-Jun, ZHAO Yu-Xia, ZHAI Qian-Li, LIU Peng-Fei, WU Fei-Peng
Chin. Phys. Lett. 2008, 25 (8): 2896-2899 .  
Abstract   PDF(pc) (979KB) ( 594 )
We propose a simplified model to analyse the temporary behaviour of transmittance for holographic photopolymers, based on the existing first-harmonic diffusion theory, with assumptions of constant polymerization coefficient and negligible diffusion effect for noise gratings. By applying this model to measure real-time transmittance of our novel blue-sensitized photopolymer, the bleaching time constant of dye and polymerization rate are extracted, and the effect of the material composite on the noise property is revealed. This provides a prompt method to assess the performances of holographic photopolymers.
High-Efficiency Bistable Switching Based on One-Dimensional Photonic Crystals with Single-Negative Materials
DU Gui-Qiang, JIANG Hai-tao, LI Hong-Qiang, ZHANG Ye-Wen, CHEN Hong
Chin. Phys. Lett. 2008, 25 (8): 2900-2903 .  
Abstract   PDF(pc) (173KB) ( 664 )
We study theoretically the nonlinear responses of one-dimensional photonic crystals (PCs) composed of alternating two kinds of single-negative (permittivity-negative and permeability-negative) materials embedded with a Kerr-type nonlinear defect layer. In conventional PCs, it is difficult to realize a bistable switching with both low threshold and quick response time. However, in PCs with single-negative materials, by changing the ratio of the thicknesses of the two types of layers, with the decreasing size of the structure, the switching response time is shortened and the threshold intensity decreases simultaneously.
Proposals for Fabrication of Long-Period Grating in LiNbO3 Strip Waveguides
ZHANG De-Long, YANG Qing-Zhong, E. Y. B. Pun
Chin. Phys. Lett. 2008, 25 (8): 2904-2907 .  
Abstract   PDF(pc) (302KB) ( 726 )
Spatial Light Modulator Based on Surface Plasmon Polaritons for Chromatic Display
WANG Jing-Quan, HUANG Peng, , DU Jing-Lei, GUO Yong-Kang, LUO Xian-Gang, DU Chun-Lei
Chin. Phys. Lett. 2008, 25 (8): 2908-2911 .  
Abstract   PDF(pc) (305KB) ( 551 )
A spatial light modulator (SLM) based on surface plasmon polaritons (SPPs) that can generate chromatic pattern is demonstrated. The device is composed of a waveguide with a thin silver film and an active material. The simulated results show that the SLM can modulate the intensity of three different wavelengths at the same time and combine a colour picture in the image surface. The SLM also owns the characteristics of high sensitivity, high contrast, fast time response etc. This means that the SLM is promising in the chromatic display.
Multimode-Waveguide-Based Optical Power Splitters in Glass
GAO Yang, GONG Zhao, BAI Ren, HAO Yin-Lei, LI Xi-Hua, JIANG Xiao-Qing, WANG Ming-Hua, PAN Jian-Xia, YANG Jian-Yi
Chin. Phys. Lett. 2008, 25 (8): 2912-2914 .  
Abstract   PDF(pc) (981KB) ( 649 )
Low-loss glass-based buried multimode waveguides are fabricated by using the field-assisted Ag+--Na+ ion-exchange technique, and multimode optical power splitters are investigated. The measured loss of the multimode waveguides is lower than 0.1dB/cm, and the additional loss of the multimode optical power splitters is lower than 1.3dB under the uniform splitting condition.
A Feasible Approach to Optical--Electrical Hybrid Data Storage Using Phase Change Material
SUN Hua-Jun, HOU Li-Song, WU Yi-Qun, ZHAI Feng-Xiao
Chin. Phys. Lett. 2008, 25 (8): 2915-2917 .  
Abstract   PDF(pc) (827KB) ( 489 )
We present our experimental results supporting optical--electrical hybrid data storage by optical recording and electrical reading using Ge2Sb2Te5as recording medium. The sheet resistance of laser-irradiated Ge2Sb2Te5 films exhibits an abrupt change of four orders of magnitude (from 107 to 103Ω/sq) with increasing laser power, current-voltage curves of the amorphous area and the laser-crystallized dots, measured by a conductive atomic force microscope (C-AFM), show that their resistivities are 2.725 and 3.375×10-3Ω, respectively, the surface current distribution in the films also shows high and low resistance states. All these results suggest that the laser-recorded bit can be read electrically by measuring the change of electrical resistivity, thus making optical--electrical hybrid data storage possible.
Modelling and Analysis of Modal Behaviour in SOI Slot Waveguides
LIU Yan, XU Xue-Jun, CHEN Shao-Wu, YU Jin-Zhong
Chin. Phys. Lett. 2008, 25 (8): 2918-2921 .  
Abstract   PDF(pc) (969KB) ( 739 )
Mode behaviour for SOI slot waveguides is modelled and analysed using a numerical full vectorial method based on the film mode matching method (MMM). Only the quasi-TE mode is investigated. Waveguide heights and slot widths, as well as silicon widths are properly chosen with respect to the single mode behaviour in the slot region. Comparison between the effective index method and our side loss method shows that our single mode condition is creditable. The optical power confinement in slot region for the quasi-TE mode is also studied and presented. We demonstrate that the maximum achievable optical power confinement Pslot and the maximum normalized average optical intensity Islot are 42% and 26μm-2, respectively.
Acoustic Band Gaps in Three-Dimensional NaCl-Type Acoustic Crystals
FANG Nong-Yu, WU Fu-Gen, ZHANG Xin
Chin. Phys. Lett. 2008, 25 (8): 2922-2925 .  
Abstract   PDF(pc) (344KB) ( 461 )
We present the acoustic band gaps (ABGs) for a geometry of three-dimensional complex acoustic crystals: the NaCl-type structure. By using the super cell method based on the plane-wave expansion method (PWE), we study the three configurations formed by water objects (either a sphere of different sizes or a cube) located at the vertices of simple cubic (SC) lattice and surrounded by mercury background. The numerical results show that ABGs larger than the original SC structure for all the three configurations can be obtained by adjusting the length-diameter ratio of adjacent objects but keeping the filling fraction (f=0.25) of the unit cell unchanged. We also compare our results with that of 3D solid composites and find that the ABGs in liquid composites are insensitive to the shapes as that in the solid composites. We further prove that the decrease of the translation group symmetry is more efficient in creating the ABGs in 3D water-mercury systems.
Effect of Sound Source Scattering on Measurement of Near-Field Head-Related Transfer Functions
YU Guang-Zheng, XIE Bo-Sun, RAO Dan,
Chin. Phys. Lett. 2008, 25 (8): 2926-2929 .  
Abstract   PDF(pc) (493KB) ( 487 )
A simple spherical head and pulsating spherical sound source model are proposed to investigate the effect of multiple scattering between the head and the sound source on near-field head-related transfer function (HRTF) measurement. Multipole expansion method is used to calculate HRTFs of the model, then the relationships among the magnitude error of HRTF with frequency, source direction, source size, and the distance between the head centre and the sound source are analysed. The results show that to ensure the magnitude error of HRTF within 1.0dB up to 20kHz, for source distance not less than 0.15m or 0.20m, the radius of the sound source should not exceed 0.03m or 0.05m, respectively. The conclusion suggests an appropriate size of sound source in near-field HRTF measurement.
Relativistic Magnetosonic Soliton in a Negative-Ion-Rich Magnetized Plasma
WANG Yun-Liang, ZHOU Zhong-Xiang, LU Yan-Zhen, NI Xiao-Dong, SHEN Jiang, ZHANG Yu
Chin. Phys. Lett. 2008, 25 (8): 2930-2933 .  
Abstract   PDF(pc) (837KB) ( 504 )
Two-dimensional (2D) relativistic magnetosonic solitons in the negative-ion-rich plasma consisting of positive ions Ar+, negative ions SF6- and electrons are investigated in the presence of an applied magnetic field B0 and can be described by a Kadomtsev--Petviashvili (KP) equation in the weakly relativistic limit. The ratio of positive ion density to negative ion density has a marked influence on the amplitude Φm and width W of the steady-state KP soliton. The interaction law of the nontrivial solitons with rich web structure is studied by the Wronskian determinant method.
Generation of Electric Field and Net Charge in Hall Reconnection
MA Zhi-Wei, FENG Shu-Ling
Chin. Phys. Lett. 2008, 25 (8): 2934-2937 .  
Abstract   PDF(pc) (809KB) ( 544 )
Generation of Hall electric field and net charge associated with magnetic reconnection is studied under different initial conditions of plasma density and magnetic field. With inclusion of the Hall effects, decoupling of the electron and ion motions leads to the formation of a narrow layer with strong electric field and large net charge density along the separatrix. The asymmetry of the plasma density or magnetic field or both across the current sheet will largely increase the magnitude of the electric field and net charge. The results indicate that the asymmetry of the magnetic field is more effective in producing larger electric field and charge density. The electric field and net charge are always much larger in the low density or/and high magnetic field side than those in the high density or/and low magnetic field side. Both the electric field and net charge density are linearly dependent on the ratios of the plasma density or the square of the magnetic field across the current sheet. For the case with both initial asymmetries of the magnetic field and density, rather large Hall electric field and charge density are generated.
Self-Injection and Acceleration of Monoenergetic Electron Beams from Laser Wakefield Accelerators in a Highly Relativistic Regime
H. Yoshitama, T. Kameshima, GU Yu-Qiu, GUO Yi, JIAO Chun-Ye, LIU Hong-Jie, PENG Han-Sheng, TANG Chuan-Ming, WANG Xiao-Dong, WEN Xian-Lun, WEN Tian-Shu, WU Yu-Chi, ZHANG Bao-Han, ZHU Qi-Hua, HUANG Xiao-Jun, AN Wei-Min, HUNG Wen-Hui, TANG Chuan-Xiang, LIN Yu-Zheng, WANG Xiao-Dong, CHEN Li-Ming, H.~Kotaki, M.~Kando, K.~Nakajima,
Chin. Phys. Lett. 2008, 25 (8): 2938-2941 .  
Abstract   PDF(pc) (2767KB) ( 737 )
Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100TW class, 27fs laser pulses. Quasi-monoenergetic multi-bunched beams with energies as high as multi-hundredMeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelling and self-injection of electrons into a plasma wake, referred to as a `bubble'. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5GeV/cm.
CHF3 Dual-Frequency Capacitively Coupled Plasma by Optical Emission Spectroscopy
XU Yi-Jun, YE Chao, HUANG Xiao-Jiang, YUAN Jing, XING Zhen-Yu, NINGZhao-Yuan
Chin. Phys. Lett. 2008, 25 (8): 2942-2945 .  
Abstract   PDF(pc) (195KB) ( 948 )
We investigate the intermediate gas phase in the CHF3 13.56MHz/2MHz dual-frequency capacitively couple plasma (CCP) for the SiCOH low dielectric constant (low-k) film etching, and the effect of 2MHz power on radicals concentration. The major dissociation reactions of CHF3 in 13.56MHz CCP are the low dissociation bond energy reactions, which lead to the low F and high CF2 concentrations. The addition of 2MHz power can raise the probability of high dissociation bond energy reactions and lead to the increase of F concentration while keeping the CF2 concentration almost a constant, which is of advantage to the SiCOH low-k films etching. The radical spatial uniformity is dependent on the power coupling of two sources. The increase of 2MHz power leads to a poor uniformity, however, the uniformity can be improved by increasing 13.56MHz power.
Molecular Dynamics Study of Mechanical Behaviour of Screw Dislocation during Cutting with Diamond Tip on Silicon
TANG Qi-Heng
Chin. Phys. Lett. 2008, 25 (8): 2946-2949 .  
Abstract   PDF(pc) (2497KB) ( 583 )

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are calculated. A screw dislocation is introduced into workpiece Si. It is found that motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocation is far below the yield strength of Si.

First-Principles Calculations of Elastic Properties of LaNi5 Compound
CHEN Dong, XU Guo-Liang, ZHANG Xin-Wei, ZHAO Ying-Lu, YU Ben-Hai, SHI De-Heng
Chin. Phys. Lett. 2008, 25 (8): 2950-2953 .  
Abstract   PDF(pc) (141KB) ( 532 )
The equilibrium lattice constants, temperature dependence of bulk modulus, the pressure dependence of the normalized volume V/V0, elastic constants Cij and bulk modulus of LaNi5 crystal are obtained using the first-principles plane-wave pseudopotential method in the GGA-PBE generalized gradient approximation as well as the quasi-harmonic Debye model. We analyse the relationship between bulk modulus and temperature up to 1000K and obtain the relationship between bulk modulus B and pressure at different temperatures. It is found that the bulk modulus B increases monotonously with increasing pressure. Moreover, the pressure dependences of Debye temperatures and the pressure derivatives of lattice constants are also successfully obtained. The calculated results are in agreement with the experimental data and the other theoretical results
Dynamic Response and Fracture Mechanism of a Novel Structural Radar Absorbing Material
CAO Mao-Sheng, ZHOU Wei, QU Gui-Min, RONG Ji-Li
Chin. Phys. Lett. 2008, 25 (8): 2954-2956 .  
Abstract   PDF(pc) (1230KB) ( 1066 )
A novel structural radar absorbing material (SRAM), which gives the normal resin-base composites new function, is prepared. The dynamic compressive tests of SRAM are carried out in both in-plane and normal directions of composites by means of the split Hopkinson pressure bar (SHPB). In the compressive test along in-plane direction, failure occurs at the interface between a fibre and the matrix. A fracture mode and mechanism was proposed to explain these results. The addition of absorbing particles results in the deterioration of the compressive properties. However, there is no obvious decrease on compressive strength of SRAM with the radar absorbing properties.
Fabrication of Two-Dimensional Arrays of Micron-Sized Gold Rings Based on Preferential Nucleation at Reentrant Sites
DONG Wen, GUO Xiang, WANG Si-Zhen, WANG Zhen-Lin, MINGNai-Ben
Chin. Phys. Lett. 2008, 25 (8): 2957-2960 .  
Abstract   PDF(pc) (3499KB) ( 566 )
A templating method for fabricating two-dimensional (2D) arrays of micron-sized gold rings is reported. The microstructures are formed by electroless plating in a through-porous polymer membrane on a silicon substrate obtained from a closed-packed silica colloidal crystal. Our results show that the sizes of gold rings can be altered by varying electroless plating conditions for the porous polystyrene membranes. Moreover, we explain the growth mechanism of gold rings using the classical crystal growth theory that is preferential nucleation at reentrant sites
Experimental Investigation of Energy Level Dynamics in luminium Blocks with Temperature Distribution
ZHANG Qin-Lei, YANG Guang-Can
Chin. Phys. Lett. 2008, 25 (8): 2961-2964 .  
Abstract   PDF(pc) (1960KB) ( 440 )
Using temperature distribution as an external parameter to change symmetry and measuring frequency spectrum of acoustic resonances in aluminium blocks, we investigate the statistics and dynamics of energy levels in the chaotic billiards. To extract the resonances accurately and eliminate the influence of noise, a filter-diagonalization method for harmonic inversion is used to overcome low resolution of conventional fast Fourier transform method for low quantity factor resonance systems. We present an improved and feasible simulation method to study chaotic characteristic of quantum systems experimentally.
Interaction of Shock Waves in Cement Mortar Plate Investigated by the Digital Speckle Correlation Method
LI Xu-Dong, LIU Kai-Xin, ZHANG Guang-Sheng, WEN Shang-Gang, TANFu-Li
Chin. Phys. Lett. 2008, 25 (8): 2965-2968 .  
Abstract   PDF(pc) (1612KB) ( 478 )
Interaction of shock waves in cement mortar plate is studied by digital speckle correlation method and digital high-speed photography technique. When the plates were destroyed by two detonators exploding at the same time, variation of shock wave field is obtained. Experimental results show that the interaction of shock waves will result in a nonlinear huge increase of local normal strain, leading to large deformation and serious destruction. However, the occurrence of this strongly nonlinear phenomenon sensitively depends on the interval between detonators, and it will only appear when the interval is smaller than the diameter of the region where shock waves exist
Melting Behaviour of Mo by Shock Wave Experiment
ZHANG Xiu-Lu, CAI Ling-Cang, CHEN Jun, XU Ji-An, JING Fu-Qian,
Chin. Phys. Lett. 2008, 25 (8): 2969-2972 .  
Abstract   PDF(pc) (175KB) ( 681 )
In order to clarify the apparent discrepancy in determinations of melting temperature Tm of Mo between diamond-anvil cell (DAC) measurements from 0 to about 100GPa and shock wave (SW) measurement at only one pressure of about 390GPa by comparison with visual extrapolation, we perform SW experiments to replenish more Tm data on purpose to make this comparison more directly and rationally as well. The techniques adopted consist of Hügoniot sound velocity measurement for porous Mo and shock-induced release Tm measurements for both solid and porous Mo. Totally five SW Tm data, which extends the measured pressure range from previous about 390GPa down to about 136GPa that is close to the highest pressure (about 100GPa) attained by previous DAC experiments, are therefore obtained. These measured Tm data, other than the extrapolated as mentioned above, exhibit a manner of continuous variation with pressure and can be fitted well with Lindemann melting description. More significantly, the measured Tm data at lowest pressure are still much higher than that of the DACs and the overall trend of these Tm data is against to the two-segment melting curve model, with a sudden change in dTm/dP at about 210GPa, previously proposed by Errandonea [Physica B 357 (2005) 356]. Though the problem of large discrepancy in Tm data measured between DAC and SW has not been completely explained, our knowledge on this matter achieves indubitable progress since it is of value to programme the next clarification. Some suggestions for further clarifying the issue of large discrepancy between DAC and SW measurements are also proposed.
Molecular Dynamics Simulation of Thermal Conductivity in Si--Ge Nanocomposites
HUANG Xiao-Peng, HUAI Xiu-Lan
Chin. Phys. Lett. 2008, 25 (8): 2973-2976 .  
Abstract   PDF(pc) (331KB) ( 708 )
Thermal conductivity of nanocomposites is calculated by molecular dynamics (MD) simulation. The effect of size on thermal conductivity of nanowire composites and the temperature profiles are studied. The results indicate that the thermal conductivity of nanowire composites could be much lower than alloy value; the thermal conductivity is slightly dependent on temperature except at very low temperature.
Bi- and Au-Induced Reconstructions on GaAs(001)-2×4 Surface
TANG Zhe, YANG Shen-Yuan, JIANG Ying, WANG Wen-Xin, JIA Jin-Feng, XUEQi-Kun, WANG En-Ge, WU Ke-Hui
Chin. Phys. Lett. 2008, 25 (8): 2977-2980 .  
Abstract   PDF(pc) (4979KB) ( 430 )
Submonolayer Bi and Au adsorptions on the GaAs(001)-2×4 surface are investigated by scanning tunnelling microscopy, low energy electron diffraction and first-principles calculations. The 1×4 and 3×4 reconstructed surface induced by Bi and Au, respectively, are revealed and their structural models are proposed based on experiments and first-principles calculations. Moreover, the validity of the recently proposed generalized electron counting (GEC) model [Phys. Rev. Lett. 97 (2006) 126103] is examined in detail by using the two surfaces. The GEC model perfectly explains the structural features, such as the characteristic short double-line structure in the Bi-1×4 surface and the 3× arrangement of four-atom Au clusters.
Interactions of a Charged Particle with Parallel Two-Dimensional Quantum Electron Gases
LI Chun-Zhi, SONG Yuan-Hong, WANG You-Nian
Chin. Phys. Lett. 2008, 25 (8): 2981-2984 .  
Abstract   PDF(pc) (495KB) ( 560 )
By using the linearized quantum hydrodynamic (QHD) theory, electronic excitations induced by a charged particle moving between or over two parallel two-dimensional quantum electron gases (2DQEG) are investigated. The calculation shows that the influence of the quantum effects on the interaction process should be taken into account. Including the quantum statistical and quantum diffraction effects, the general expressions of the induced potential and the stopping power are obtained. Our simulation results indicate that a V-shaped oscillatory wake potential exists in the electron gases during the test charge intrusion. Meanwhile, double peaks will occur in the stopping power when the distance of two surfaces is smaller and the test charge gets closer to any one of the two sheets.
Electron Orbital Magnetic Moments in the Armchair Carbon Nanotubes
CHEN Jing-Zhe, CHEN Xing, LIU Guang-Hua, HAN Ru-Shan
Chin. Phys. Lett. 2008, 25 (8): 2985-2988 .  
Abstract   PDF(pc) (1288KB) ( 510 )
Based on the density functional theory, we calculate the band structure of an armchair carbon nanotube in an axial magnetic field. The result shows that there are two kinds of magnetic moments with different symmetries. One is the Aharonov--Bohm-type magnetic moment which can be easily understood with classical picture, the other belonging to the valence, and conduction sub-bands should be explained by quantum mechanics. We use an effective mass model to analyse the magnetic moments and by comparing with the result of first-principle calculation, we conclude that the effective mass model is reasonable to estimate the change of the band gap in magnetic fields.
First Principles Study of Aluminium Vacancy in Wurtzite Aluminium Nitride
GAO Ting-Ge, YI Jue-Min, ZHOU Zi-Yao, HU Xiao-Dong
Chin. Phys. Lett. 2008, 25 (8): 2989-2992 .  
Abstract   PDF(pc) (169KB) ( 659 )
We report that the aluminium vacancy in wurtzite AlN brings about two impurity levels e and a2 in the band gap, not just one single t2 level. The aluminium vacancy carries a magnetic moment of 1μB in the ground state. The molecule orbit of the aluminium vacancy becomes e↑↑a2 rather than e↑↑a2. The calculation is carried out by using the CASTEP code. The intrinsic symmetry of wurtzite AlN is the driving force for this spin splitting. Finally the symmetry of wurtzite AlN results in an anti-ferromagnetic coupling between the aluminium vacancies, as is predicted. Our findings are helpful to gain a more through understanding of the structural and spin property of aluminium vacancy in wurtzite AlN.
Formation Mechanisms of Electrical Conductivity and Optical Properties of ZnO:N Film Produced by Annealing Treatment
WANG Xiang-Hu, YAO Bin, WEI Zhi-Peng, SHEN De-Zhen, ZHANG Zhen-Zhong, LU You-Ming, ZHANG Ji-Ying, FAN Xi-Wu
Chin. Phys. Lett. 2008, 25 (8): 2993-2996 .  
Abstract   PDF(pc) (293KB) ( 564 )

The effects of annealing on the chemical states of N dopant, electrical, and optical properties of N-doped ZnO film grown by molecular beam epitaxy (MBE) are investigated. Both the as-grown ZnO:N film and the film annealed in N2 are of n-type conductivity, whereas the conductivity converts into p-type conductivity for the film annealed in O2. We suggest that the transformation of conductivity is ascribed to the change in ratio of the N molecular number on O site (N2)O to the N atom number on O site (NO) in ZnO:N films under the various annealed atmosphere. For the ZnO:N film annealed in N2, the percentage content of (N2)O is larger than that of NO, i.e.the ratio >1, resulting in the n-type conductivity. However, in the case of the ZnO:N film annealed in O2, the percentage content of (N2)O is fewer than that of NO, i.e., the ratio <1, giving rise to the p-type conductivity. There is an obvious difference between low-temperature (80K) PL spectra of ZnO:N film annealed in N2 and that of ZnO:N film annealed in O2. An emission band located at 3.358eV is observed in the spectra of the ZnO:N film after annealed in N2, this emission band is due to donor-bound exciton (D0X). After annealed in O2, the PL of the donor-bound exciton disappeared, an emission band located at 3.348eV is observed, this emission band is assigned to acceptor-bound exciton (A0X).

First-Principles Study of Defects in CuGaO2
FANG Zhi-Jie, FANG Cheng, SHI Li-Jie, LIU Yong-Hui, HE Man-Chao
Chin. Phys. Lett. 2008, 25 (8): 2997-3000 .  
Abstract   PDF(pc) (132KB) ( 659 )
Using the first-principles methods, we study the electronic structure, intrinsic and extrinsic defects doping in transparent conducting oxides CuGaO2. Intrinsic defects, acceptor-type and donor-type extrinsic defects in their relevant charge state are considered. The calculation result show that copper vacancy and oxygen interstitial are the relevant defects in CuGaO2. In addition, copper vacancy is the most efficient acceptor. Substituting Be for Ga is the prominent acceptor, and substituting Ca for Cu is the prominent donors in CuGaO2. Our calculation results are expected to be a guide for preparing n-type and p-type materials in CuGaO2.
Spin Transport in the Presence of Rashba Interaction
WANG Jing, WU Chang-Qin
Chin. Phys. Lett. 2008, 25 (8): 3001-3004 .  
Abstract   PDF(pc) (543KB) ( 590 )
A Gaussian type spin-polarized electronic wave packet is constructed to investigate the spin transport behaviour in an infinite two-dimensional electron gas system with Rashba spin--orbit (SO) interaction by solving the Schrödinger equation exactly. In the presence of Rashba SO interaction, the spin-dependent force induces a momentum dependent splitting of the two spin directions, the average spin current indicates the corresponding spin accumulation clearly. Furthermore, the coherence of the injected spin-polarized wave packet, as well as the transverse force, decays during the motion in the Rashba SO regime.
Influence of Ring Oxidation-Induced Stack Faults on Efficiency in Silicon Solar Cells
ZHOU Chun-Lan, WANG Wen-Jing, LI Hai-Ling, ZHAO Lei, DIAO Hong-Wei, LI-Xu-Dong
Chin. Phys. Lett. 2008, 25 (8): 3005-3008 .  
Abstract   PDF(pc) (2049KB) ( 1832 )
We observe a strong correlation between the ring oxidation-induced stack faults (OISF) formed in the course of phosphor diffusion and the efficiency of Czochralski-grown silicon solar cells. The main reason for ring-OISF formation and growth in substrate is the silicon oxidation and phosphorus diffusion process induced silicon self-interstitial point defect during POCl3 diffusion. The decreasing of minority carrier diffusion length in crystal silicon solar cell induced by ring-OISF defects is identified to be one of the major causes of efficiency loss.
Charge Injection and Transport in Metal/Polymer Chains/Metal Sandwich Structure
LI Hai-Hong, LI Dong-Mei, LI Yuan, GAO Kun, LIU De-Sheng, XIE Shi-Jie
Chin. Phys. Lett. 2008, 25 (8): 3009-3012 .  
Abstract   PDF(pc) (154KB) ( 363 )
Using the tight-binding Su--Schrieffer--Heeger model and a nonadiabatic dynamic evolution method, we study the dynamic processes of the charge injection and transport in a metal/two coupled conjugated polymer chains/metal structure. It is found that the charge interchain transport is determined by the strength of the electric field and the magnitude of the voltage bias applied on the metal electrode. The stronger electric field and the larger voltage bias are both in favour of the charge interchain transport.
Photovoltaic Cells with TiO2 Nanocrystals and Conjugated Polymer Composites
YU Huang-Zhong, LIU Jin-Cheng, PENG Jun-Biao
Chin. Phys. Lett. 2008, 25 (8): 3013-3016 .  
Abstract   PDF(pc) (808KB) ( 675 )
Various compositional photovoltaic cells based on the blend of poly(3-hexylthiophene) (P3HT) as donors and TiO2 nanocrystals as acceptors are fabricated and investigated. It is demonstrated that the blend ratio of P3HT and TiO2 nanocrystals could greatly influence the performance of the photovoltaic cells. The maximum of 0.411% in power conversion efficiency under AM 1.5, 100mW/cm2, and 44.4% of fill factor are obtained in the solar cell with the blend weight ratio 1:1 of P3HT and TiO2 nanocrystals. The function of nanocrystal composition is discussed in terms of the results of photoluminescence spectroscopy, atomic force microscopy, transmission electron microscopy, and charge transport I-V curve.
External Electric Field Effect on Hydrogenic Donor Impurity in Zinc-Blende InGaN Quantum Dot
JIANG Li-Ming, WANG Hai-Long, WU Hui-Ting, GONG Qian, FENG Song-Lin
Chin. Phys. Lett. 2008, 25 (8): 3017-3020 .  
Abstract   PDF(pc) (159KB) ( 594 )
The binding energy of a hydrogenic donor impurity in zinc-blende (ZB) InGaN quantum dot (QD) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position, QD size and the external electric field. The symmetry of the electron probability distribution is broken and the maximum of the donor binding energy is shifted from the centre of QD in the presence of the external electric field. The degenerating energy levels for symmetrical positions with respect to the centre of QD are split. The splitting increases with the increase of QD height while the splitting increases up to a maximum value and then decreases with the increase of QD radius.
Effects of Electric Field on Electronic States in a GaAs/GaAlAs Quantum Dot with Different Confinements
A. John Peter, Vemuri Lakshminarayana
Chin. Phys. Lett. 2008, 25 (8): 3021-3024 .  
Abstract   PDF(pc) (132KB) ( 1005 )
Binding energies of shallow hydrogenic impurity in a GaAs/GaAlAs quantum dot with spherical confinement, parabolic confinement and rectangular confinement are calculated as a function of dot radius in the influence of electric field. The binding energy is calculated following a variational procedure within the effective mass approximation along with the spatial depended dielectric function. A finite confining potential well with depth is determined by the discontinuity of the band gap in the quantum dot and the cladding. It is found that the contribution of spatially dependent screening effects are small for a donor impurity and it is concluded that the rectangular confinement is better than the parabolic and spherical confinements. These results are compared with the existing literature.
Effect of CO on Characteristics of AlGaN/GaN Schottky Diode
FENG Chun, WANG Xiao-Liang, YANG Cui-Bai, XIAO Hong-Ling, ZHANG Ming-Lan, JIANG Li-Juan, TANG Jian, HU Guo-Xin, WANG Jun-Xi, WANG Zhan-Guo
Chin. Phys. Lett. 2008, 25 (8): 3025-3027 .  
Abstract   PDF(pc) (860KB) ( 428 )
Pt Schottky diode gas sensors for CO are fabricated using AlGaN/GaN high electron mobility transistor (HEMTs) structure. The diodes show a remarkable sensor signal (3mA, in N2; 2mA in air ambient) biased 2V after 1% CO is introduced at 50°C. The Schottky barrier heights decrease for 36meV and 27meV in the two cases respectively. The devices exhibit a slow recovery characteristic in air ambient but almost none in the background of pure N2, which reveals that oxygen molecules could accelerate the desorption of CO and offer restrictions to CO detection.
Fano--Kondo Effect in a Triple Quantum Dots Coupled to Ferromagnetic Leads
BI Ai-Hua, WU Shao-Quan, HOU Tao, SUN Wei-Li
Chin. Phys. Lett. 2008, 25 (8): 3028-3031 .  
Abstract   PDF(pc) (175KB) ( 608 )
Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we have qualitatively studied the spin-dependent transport of a triple-QD system in the Kondo regime. It is shown that the Kondo resonance and Fano interference coexist, and in this system the Fano--Kondo effect shows dip behaviours richer than that in the T-shaped QDs. The interdot coupling, the energy level of the side coupled QDs and the spin polarization strength greatly influence the DOS of the central quantum dot QD0. Either the increase of the coupling strength between the two QDs or that of the energy levels of the side coupled QDs enhances the Kondo resonance. Especially, the Kondo resonance is strengthened greatly when the side dot energy is fixed at the Fermi energy. Meanwhile, the Kondo resonance splits for the spin-up and spin-down configurations due to the polarization: the down-spin resonance is enhanced, and the up-spin resonance is suppressed.
Thermal Rectification Effect of an Interacting Quantum Dot
CHEN Xue-Ou, DONG Bing, LEI Xiao-Lin
Chin. Phys. Lett. 2008, 25 (8): 3032-3035 .  
Abstract   PDF(pc) (214KB) ( 752 )
We investigate the nonlinear thermal transport properties of a single interacting quantum dot with two energy levels tunnel-coupled to two electrodes using nonequilibrium Green function method and Hartree--Fock decoupling approximation. In the case of asymmetric tunnel-couplings to two electrodes, for example, when the upper level of the quantum dot is open for transport, whereas the lower level is blocked, our calculations predict a strong asymmetry for the heat (energy) current, which shows that the quantum dot system may act as a thermal rectifier in this specific situation.
Lattice Dynamics and Superconductivity of RuB2: A First-Principles Study
WANG Yue-Qin, YUAN Lan-Feng, YANG Jin-Long
Chin. Phys. Lett. 2008, 25 (8): 3036-3039 .  
Abstract   PDF(pc) (343KB) ( 602 )
We report the first-principles linear response calculations on lattice dynamics and electron-phonon coupling (EPC) of superhard material RuB2. Phonon frequencies and eigenvectors are obtained throughout the whole Brillouin zone. The calculated EPC parameters for the optical phonon modes at Γ indicate that the d electrons of transition metal play the most important role in deciding the superconducting behaviour, and there are sizeable contributions from B p electrons to EPC. Our calculated EPC constant is 0.41, and the estimated superconducting transition temperature Tc is 1.6K using the Coulomb pseudopotential μ*=0.12, in excellent agreement with the
Room Temperature Ferromagnetism and Optical Tunability in Cu Doped GaN Nanowires
WANG Peng-Wei, ZHANG Xue-Jin, WANG Bai-Qi, ZHANG Xin-Zheng, YU Da-Peng
Chin. Phys. Lett. 2008, 25 (8): 3040-3043 .  
Abstract   PDF(pc) (2991KB) ( 909 )
GaN nanowires doped with 2at.% and 6at.% Cu ions are synthesized by chemical vapour deposition method. Structural and compositional analyses demonstrate that the as-grown nanowires are of single crystal wurtzite GaN structure. Magnetic characterizations reveal that the doped GaN nanowires exhibit room temperature ferromagnetism. The measured saturation magnetic moments are 0.37μB and 0.47μB per Cu atom at 300K for Cu 2at.% and 6at.%, respectively. The photoluminescence spectra show that Cu dopant can tune the band gap of the GaN, which leads to a red shift of band-edge emission with increasing dopant concentration.
Dielectric and Pyroelectric Properties of (Pb0.50Sr0.50)TiO3 Ceramics
JIANG Yan-Ping, TANG Xin-Gui, LIU Qiu-Xiang, ZHOU Yi-Chun, CHAN-WONG Lai-Wa
Chin. Phys. Lett. 2008, 25 (8): 3044-3047 .  
Abstract   PDF(pc) (180KB) ( 467 )
Lead strontium titanate (Pb0.50Sr0.50)TiO3 (PST) ceramics are prepared by the traditional ceramic processing. The dielectric constants and dielectric loss have been investigated in a temperature range from 25°C to 300°C. The maximum dielectric constants for unpoled and poled samples are 9924 and 9683, respectively. The temperatures of phase transition for unpoled and poled samples are observed at 153°C and 157°C, respectively. The phase-transition temperatures for unpoled and poled samples are not equal, which results from the polarization state of the domains. The remnant polarization and the coercive electric field are 18μC/cm2 and 6kV/cm, respectively, from polarization-electric field (P-E) hysteresis loop. The temperature dependence of pyroelectric coefficients of the PST ceramics is measured by a dynamic technique. The dielectric constant and loss tan δ of the poled PST ceramics are 813 and 0.010, respectively. The pyroelectric coefficients and figure of merit are 294μC/cm2K and 13.6×10-6Pa-0.5, respectively, at room
temperature 25°C and frequency 100Hz.

A Novel Fully Depleted Air AlN Silicon-on-Insulator Metal--Oxide--Semiconductor Field Effect Transistor
YANG Yuan, GAO Yong, GONG Peng-Liang
Chin. Phys. Lett. 2008, 25 (8): 3048-3051 .  
Abstract   PDF(pc) (457KB) ( 504 )
A novel fully depleted air AlN silicon-on-insulator (SOI) metal--oxide--semiconductor field effect transistor (MOSFET) is presented, which can eliminate the self-heating effect and solve the problem that the off-state current of SOI MOSFETs increases and the threshold voltage characteristics become worse when employing a high thermal conductivity material as a buried layer. The simulation results reveal that the lattice temperature in normal SOI devices is 75K higher than the atmosphere temperature, while the lattice temperature is just 4K higher than the atmosphere temperature resulting in less severe self-heating effect in air AlN SOI MOSFETs and AlN SOI MOSFETs. The on-state current of air AlN SOI MOSFETs is similar to the AlN SOI structure, and improves 12.3% more than that of normal SOI MOSFETs. The off-state current of AlN SOI is 6.7 times of normal SOI MOSFETs, while the counterpart of air AlN SOI MOSFETs is lower than that of SOI MOSFETs by two orders of magnitude. The threshold voltage change of air AlN SOI MOSFETs with different drain voltage is much less than that of AlN SOI devices, when the drain voltage is biased at 0.8V, this difference is 28mV, so the threshold voltage change induced by employing high thermal conductivity material is cured.
A New Conducting Polymer Electrode for Organic Electroluminescence Devices
QU Shu, PENG Jing-Cui
Chin. Phys. Lett. 2008, 25 (8): 3052-3055 .  
Abstract   PDF(pc) (178KB) ( 558 )
Conducting polymer polydimethylsiloxane (PDMS) is studied for the high performance electrode of organic electroluminescence devices. A method to prepare the electrode consisting of a SiC thin film and PDMS is investigated. By using ultra thin SiC films with different thicknesses, the organic electroluminescence devices are obtained in an ultra vacuum system with the model device PDMS/SiC/PPV/Alq3, where PPV is poly para-phenylene vinylene and Alq3 is tris(8-hydroxyquinoline) aluminium. The capacitance--voltage (C-V), capacitance--frequency (C-F), current--voltage (I-V), radiation intensity--voltage (R-V) and luminance efficiency--voltage (E-V) measurements are systematically studied to investigate the conductivity, Fermi alignment and devices properties in organic semiconductors. Scanning Kelvin probe measurement shows that the work function of PDMS/SiC anode with a 2.5-nm SiC over layer can be increased by as much as 0.28eV, compared to the conventional ITO anode. The result is attributed to the charge transfer effect and ohmic contacts at the interface.
Growth Mechanism and Optimized Parameters to Synthesize Nafion-115 Nanowire Arrays with Anodic Aluminium Oxide Membranes as Templates
ZHANG Lu, PAN Cao-Feng, ZHU Jing
Chin. Phys. Lett. 2008, 25 (8): 3056-3058 .  
Abstract   PDF(pc) (3371KB) ( 592 )
Nafion-115 nanowire arrays are synthesized with an extrusion method using AAO membranes as templates. It is indicated that the vacuum treating of AAO templates before surface decoration plays an important role in obtaining high filling rate of the Nafion-115 nanowires in the AAO templates, while the concentration of Nafion-115 DMSO solutions does not affect the filling rate greatly. The optimized parameters to synthesize the Nafion-115 nanowire arrays are studied. The filling rate of the Nafion-115 nanowires in the AAO templates synthesized with the optimized parameters is about 95%. The growth mechanism of Nafion-115 nanowires is discussed to qualitatively explain the experimental results.
Broadening of Photoluminescence by Nonhomogeneous Size Distribution of Self-Assembled InAs Quantum Dots
YANG Xi-Feng, LIU Zhao-Lin, CHEN Ping-Ping, CHEN Xiao-Shuang, LI Tian-Xin, LU Wei
Chin. Phys. Lett. 2008, 25 (8): 3059-3062 .  
Abstract   PDF(pc) (529KB) ( 3147 )
The photoluminescence spectrum (PL) of InAs quantum dots (QDs) at 80K is studied by comparison between the theoretical calculation and experimental measurement. The Gaussian line shape is used to approximate the size distribution of QDs. Its mean volume and the standard size deviation are well correlated with the peak and full width at half maximum (FWHM) of the PL spectrum. The experimental PL spectrum is well reproduced by the theoretical model based on the effect mass approximation including the size distribution without any adjustable parameters. Compared with the standard size deviation value σs=9×10-2 determined by atomic force microscopic method a small value σs=7×10-2 is obtained by the best fitting process from the measured and calculated PL spectra
A Simple Route of Morphology Control and Structural and Optical Properties of ZnO Grown by Metal-Organic Chemical Vapour Deposition
FAN Hai-Bo, YANG Shao-Yan, ZHANG Pan-Feng, WEI Hong-Yuan, LIU Xiang-Lin, JIAO Chun-Mei, ZHU Qin-Sheng, CHEN Yong-Hai, WANG Zhan-Guo
Chin. Phys. Lett. 2008, 25 (8): 3063-3066 .  
Abstract   PDF(pc) (3252KB) ( 556 )
Employing the metal-organic chemical vapour deposition (MOCVD) technique, we prepare ZnO samples with different morphologies from the film to nanorods through conveniently changing the bubbled diethylzinc flux (BDF) and the carrier gas flux of oxygen (OCGF). The scanning electron microscope
images indicate that small BDF and OCGF induce two-dimensional growth while the large ones avail quasi-one-dimensional growth. X-ray diffraction (XRD) and Raman scattering analyses show that all of the morphology-dependent ZnO samples are of high crystal quality with a c-axis orientation. From the precise shifts of the 2θ locations of ZnO (002) face in the XRD patterns and the E2(high) locations in the Raman spectra, we deduce that the compressive stress forms in the ZnO samples and is strengthened with the increasing BDF and OCGF. Photoluminescence spectroscopy results show all the samples have a sharp ultraviolet luminescent band without any defects-related emission. Upon the experiments a possible growth mechanism is proposed.

Preparation of Aligned Polymer Micro/Nanofibres by Electrospinning
TAN Jin-Shan, LONG Yun-Ze, LI Meng-Meng
Chin. Phys. Lett. 2008, 25 (8): 3067-3070 .  
Abstract   PDF(pc) (1898KB) ( 480 )
Polymer micro/nanofibres are prepared by typical and modified methods of electrospinning. The morphologies and microstructures of the electrospun
micro/nanofibres are characterized by a scanning electron microscope (SEM). The micro/nanofibres prepared by the typical electrospinning are usually collected in the form of non-woven mats lacking of structural orientation. However, by modifying collector(s) of the electrospinning setup, the resulting polymer fibres show aligned structures to some extent. We analyse all the forces that the fibres experienced during electrospinning and find that the electrostatic force originating from the splitting electric field plays a key role in the alignment of the micro/nanofibres.
Measuring Electrospun Nanofibre Diameter: a Novel Approach
M. Ziabari, V. Mottaghitalab, S. T. McGovern A. K. Haghi
Chin. Phys. Lett. 2008, 25 (8): 3071-3074 .  
Abstract   PDF(pc) (1167KB) ( 1529 )
A new method based on image analysis for electrospun nanofibre diameter measurement is presented. First, the SEM micrograph of the nanofibre web obtained by electrospinning process is converted to binary image using local thresholding method. In the next step, skeleton and distance transformed image are generated. Then, the intersection points which bring about untrue measurements are identified and removed from the skeleton. Finally, the resulting skeleton and distance transformed image are used to determine fibre diameter. The method is evaluated by a simulated image with known characteristics generated by ?-randomness procedure. The results indicate that this approach is successful in making fast, accurate automated measurements of electrospun fibre diameters.
High Current Multi-finger InGaAs/InP Double Heterojunction Bipolar Transistor with the Maximum Oscillation Frequency 253GHz
JIN Zhi, SU Yong-Bo, CHENG Wei, LIU Xin-Yu, XU An-Huai, QI Ming
Chin. Phys. Lett. 2008, 25 (8): 3075-3078 .  
Abstract   PDF(pc) (803KB) ( 708 )
A four-finger InGaAs/InP double heterojunction bipolar transistor is designed and fabricated successfully by using planarization technology. The emitter area of each finger is 1×15μm2. The breakdown voltage is more than 7V, the maximum collector current could be more than 100mA. The current gain cutoff frequency is as high as 155GHz and the maximum oscillation frequency reaches 253GHz. The heterostructure bipolar transistor can offer more than 70mW class-A maximum output power at W band and the maximum power density can be as high as 1.2W/mm.
Viscoelastic BISQ Model for Low-Permeability Sandstone with Clay
NIE Jian-Xin, YANG Ding-Hui
Chin. Phys. Lett. 2008, 25 (8): 3079-3082 .  
Abstract   PDF(pc) (160KB) ( 670 )
A modified BISQ (Biot/Squirt) model for wave propagation in low-permeability sandstone is developed by introducing the viscoelastic mechanism of a porous skeleton into Dvorkin's model. The linear viscoelasticity of the Kelvin--Voigt constitutive law is employed to describe the stress-strain relation of a solid frame with clay while the ultrasonic waves propagate through the fluid-saturated sandstone. The phase velocity and attenuation of two p-waves are given based on the present BISQ model. The comparisons between numerical results and experimental data indicate that our viscoelastic model is more realistic and feasible for wave propagation in the low-permeability sandstone, especially with clay, than traditional BISQ models.
Spatial Distribution of Energetic Electrons during Magnetic Reconnection
WANG Rong-Sheng, LU Quan-Ming, GUO Jun, WANG Shui
Chin. Phys. Lett. 2008, 25 (8): 3083-3085 .  
Abstract   PDF(pc) (186KB) ( 518 )
Electron acceleration by the inductive electric field near the X point in magnetic reconnection is an important generation mechanism for energetic electrons. Particle simulations have revealed that most of energetic electrons reside in the magnetic field line pileup region, and a depletion of energetic electrons can be found near the centre of the diffusion region [Phys. Plasmas, 13 (2006) 012309]. We report direct measurement of energetic electron in and around the ion diffusion region in near-Earth tail by the cluster, and our observations confirm the above predictions: a depletion of the high-energy electron fluxes is detected near the centre of the diffusion region. At the same time, the plasma temperature has a similar profile in the diffusion region.
Constraints on Dark Energy Models from Weak Gravity Conjecture
CHEN Xi-Ming, LIU Jie, GONG Yun-Gui
Chin. Phys. Lett. 2008, 25 (8): 3086-3089 .  
Abstract   PDF(pc) (233KB) ( 457 )

We study the constraints on the dark energy model with constant equation of state parameter w=p/ρ and the holographic dark energy model by using the weak gravity conjecture. The combination of weak gravity conjecture and the observational data gives w<-0.7 at the 3σ confidence level. The holographic dark energy model realized by a scalar field is in swampland.

Bianchi Type-V Bulk Viscous Barotropic Fluid Cosmological Model with Variable G and Λ
Raj Bali, Seema Tinker
Chin. Phys. Lett. 2008, 25 (8): 3090-3093 .  
Abstract   PDF(pc) (105KB) ( 644 )
We investigate the Bianchi type-V bulk viscous barotropic fluid cosmological model with variable gravitational constant G and the cosmological constant Λ, assuming the condition on metric potential as A'/A=B'/B=C'/C=m/tn, where A, B, and C are functions of time t, while m and n are constants. To obtain the deterministic model, we also assume the relations P = p - 3ηH, p =γρ, η=η0ρs, where p is the isotropic pressure, η the bulk viscosity, 0≤γ≤1, H the Hubble constant, η0 and s are constants. Various physical aspects of the model are discussed. The case of n = 1 is also discussed to compare the results with the actual universe.
Withdrawal of Chin. Phys. Lett. 24(2007)1821 by M. Aygun et al.
Chin. Phys. Lett. 2008, 25 (8): 3094-3094 .  
Abstract   PDF(pc) (28KB) ( 394 )
Editorial Announcement: Withdrawal of Chin. Phys. Lett. 24(2007)355 by S. Aygun et al.
Chin. Phys. Lett. 2008, 25 (8): 3094-3094 .  
Abstract   PDF(pc) (28KB) ( 155 )
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