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Volume 24 Issue 11
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Original Articles
Lie Symmetrical Perturbation and Adiabatic Invariants of Generalized Hojman Type for Disturbed Nonholonomic Systems
LUO Shao-Kai
Chin. Phys. Lett. 2007, 24 (11): 3017-3020 .  
Abstract   PDF(pc) (206KB) ( 934 )
For a nonholonomic mechanics system with the action of small disturbance, the Lie symmetrical perturbation and adiabatic invariants of generalized Hojman type are studied under general infinitesimal transformations of groups in which the generalized coordinates and timeare variable. On the basis of the invariance of disturbed nonholonomic dynamical equations under general infinitesimal transformations, the determining equations, the constrained restriction equations and the additional restriction equations of Lie symmetries of the system are constructed, which only depend on the variables t, qs and .qs. Based on the definition of higher-order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for a
nonholonomic system with the action of small disturbance is investigated, and the Lie symmetrical adiabatic invariants, the weakly Lie symmetrical adiabatic invariants and the strongly Lie symmetrical adiabatic invariants of generalized Hojman type of disturbed nonholonomic systems are obtained. An example is given to illustrate applications of the results.
Conservation Laws and Lax Pair of the Variable Coefficient KdV Equation
Chin. Phys. Lett. 2007, 24 (11): 3021-3023 .  
Abstract   PDF(pc) (180KB) ( 707 )
A Search on Dirac Equation
M. Kocak, B. Gonül
Chin. Phys. Lett. 2007, 24 (11): 3024-3027 .  
Abstract   PDF(pc) (217KB) ( 390 )
The solutions, in terms of orthogonal polynomials, of Dirac equation with analytically solvable potentials are investigated within a novel formalism by transforming the relativistic equation into a Schrodinger-like one. Earlier results are discussed in a unified framework, and some solutions of a large class of potentials are given.
An Improvement of the Asymptotic Iteration Method for Exactly Solvable Eigenvalue Problems
I. Boztosun, M. Karakoc
Chin. Phys. Lett. 2007, 24 (11): 3028-3031 .  
Abstract   PDF(pc) (191KB) ( 522 )
We derive a formula that simplifies the original asymptotic iteration method formulation to find the energy eigenvalues for the analytically solvable cases. We then show that there is a connection between the asymptotic iteration and the Nikiforov--Uvarov methods, which both solve the second order linear ordinary differential equations analytically.
Direct Evaluation of Transition Amplitude Using Determinant of Wave Operator in One-Dimensional Potential Scattering System
Itsuki Banno, Kazumi Fujima
Chin. Phys. Lett. 2007, 24 (11): 3032-3035 .  
Abstract   PDF(pc) (233KB) ( 373 )
A determinantal formula is developed for direct evaluation of transition amplitude without solving the wave equation in a one-dimensional potential scattering system. Our formulation is based on the principle that a desired quantity can be extracted from the wave operator, which is the master operator maintaining all the information of the system. This principle is tested in a simplified system, i.e., in a one-dimensional potential scattering system. We are now developing a formula for direct evaluation of near-field amplitude to design a system, in which local field enhancement is desired.
Bell Theorem without Inequality for Some Generalized GHZ and W States
REN Chang-Liang, SHI Ming-Jun, DU Jiang-Feng,
Chin. Phys. Lett. 2007, 24 (11): 3036-3039 .  
Abstract   PDF(pc) (237KB) ( 387 )
Bell's theorem without inequalities is applied for some general Greenberger--Horn--Zeilinger (GHZ) states and W states and a wide range of such states can exhibit all-versus-nothing conflict between local realism and quantum theory. The case of standard GHZ state is contained in our proposal. For some generalized GHZ states more intensive violation on local realism is manifested.
Quantum Stackelberg Duopoly of Continuous Distributed Asymmetric Information
WANG Xia, YANG Xiao-Hua, MIAO Lin, ZHOU Xiang, HU Cheng-Zheng
Chin. Phys. Lett. 2007, 24 (11): 3040-3043 .  
Abstract   PDF(pc) (321KB) ( 616 )
The minimal quantization structure is employed to investigate the quantum version of the Stackelberg duopoly with continuous distributed asymmetric information, i.e. the first mover has incomplete information that obeys a continuous distribution while the second mover has complete information. It is found that the effects of the positive quantum entanglement on the outcomes exhibit many interesting features due to the information asymmetry. Moreover, although the first-mover advantage is counteracted by the information asymmetry, the positive quantum entanglement still enhances the first-mover advantage and improves the first-mover tolerance of the information asymmetry beyond the classical limit.
Quantum State Transfer in Trapped-Ion-Cavity Systems
GUO Yu, LIAO Jie-Qiao, KUANG Le-Man
Chin. Phys. Lett. 2007, 24 (11): 3044-3047 .  
Abstract   PDF(pc) (214KB) ( 491 )
We study the information transfer and entanglement transfer in a system consisting of single trapped ions in cavities by the three-mode cross-Kerr-like interaction among the cavity field (photons), the centre-of-mass motion (phonons) and the internal state of the trapped ion in the Lamb--Dicke and large detuning regime.
Universal Quantum Cloning Machines for Two Identical Mixed Qubits
YANG Shuai, ZHAO Mei-Sheng, LIU Nai-Le, CHEN Zeng-Bing
Chin. Phys. Lett. 2007, 24 (11): 3048-3050 .  
Abstract   PDF(pc) (199KB) ( 548 )
We present a series of universal quantum cloning machines for two identical mixed qubits. Every machine is optimal in the sense that it achieves the optimal bound of the single copy shrinking factor. Unlike in the case of pure state cloning, the single copy shrinking factor does not uniquely determine the cloning map in the case of mixed state cloning.
Quantum Cryptography in Spin Networks
DENG Hong-Liang, FANG Xi-Ming
Chin. Phys. Lett. 2007, 24 (11): 3051-3054 .  
Abstract   PDF(pc) (342KB) ( 448 )
In this paper we propose a new scheme of long-distance quantum cryptography based on spin networks with qubits stored in electron spins of quantum dots. By conditional Faraday rotation, single photon polarization measurement, and quantum state transfer, maximal-entangled Bell states for quantum cryptography between two long-distance parties are created. Meanwhile, efficient quantum state transfer over arbitrary distances is obtained in a spin chain by a proper choice of coupling strengths and using spin memory technique improved. We also analyse the security of the scheme
against the cloning-based attack which can be also implemented in spin network and discover that this spin network cloning coincides with the optimal fidelity achieved by an eavesdropper for entanglement-based cryptography.
Effective Scheme for Generating Cluster States in Cavity QED
WU Huai-Zhi, YANG Zhen-Biao, ZHENG Shi-Biao
Chin. Phys. Lett. 2007, 24 (11): 3055-3058 .  
Abstract   PDF(pc) (251KB) ( 524 )
We propose a scheme to prepare many two-mode cavities into one-dimensional cluster states in the context of cavity QED. The left-circularly polarized state and right-circularly polarized state of the cavity are encoded as the logic zero and one of the qubits. In the scheme, the atomic spontaneous emission is suppressed, and the fidelity is unaffected by the cavity decay on the assumption that the detection efficiencies of all the photondetectors are 1.
Regular Charged Solutions in Moller's Tetrad Theory of Gravitation
Gamal G. L. Nashed
Chin. Phys. Lett. 2007, 24 (11): 3059-3062 .  
Abstract   PDF(pc) (233KB) ( 414 )
We find the most general tetrads which give a regular charged spacetime in tetrad theory of gravitation. The metric is a static one and it includes the
Schwarzschild and Reissner Nordstrom black holes. The energy content contained in a sphere of radius R is calculated using the superpotential given by Moller in the context of Weitzenbock spacetime.
Geodetic Precession in Schwarzschild Spacetime Surrounded by Quintessence
CHEN Ju-Hua, WANG Yong-Jiu
Chin. Phys. Lett. 2007, 24 (11): 3063-3065 .  
Abstract   PDF(pc) (199KB) ( 466 )
We investigate the geodetic precession of light in the Schwarzschild spacetime surrounded by quintessence. With the analysis and numerical
methods, we find that the geodetic precession of light in the Schwarzschild spacetime surrounded by quintessence increases when the normalization factor c increases, and the geodetic precession decreases when the quintessential state parameter ωq increases.
Detection of Mechanism of Noise-Induced Synchronization between Two Identical Uncoupled Neurons
WU Ying, XU Jian-Xue, JIN Wu-Yin, HONG Ling
Chin. Phys. Lett. 2007, 24 (11): 3066-3069 .  
Abstract   PDF(pc) (341KB) ( 677 )
We investigate the noise-induced synchronization between two identical
uncoupled Hodgkin--Huxley neurons with sinusoidal stimulations. The numerical results confirm that the value of critical noise intensity for synchronizing two systems is much less than the magnitude of mean size of the attractor in the original system, and the deterministic feature of the attractor in the original system remains unchanged. This finding is significantly different from the previous work [Phys. Rev. E 67 (2003) 027201] in which the value of the critical noise intensity for synchronizing two systems was found to be roughly equal to the magnitude of mean size of the attractor in the original system, and at this intensity, the noise swamps the qualitative
structure of the attractor in the original deterministic systems to synchronize to their stochastic dynamics. Further investigation shows that the critical noise intensity for synchronizing two neurons induced by noise may be related to the structure of interspike intervals of the original systems.
Escape for System with Non-Fluctuating Potential Barrier Only Driven by Three-State Noise
LI Jing-Hui
Chin. Phys. Lett. 2007, 24 (11): 3070-3073 .  
Abstract   PDF(pc) (224KB) ( 429 )
We study the escape for the mean first passage time (MFPT) over a potential barrier for a system with non-fluctuating potential barrier and only driven by a three-state noise. It is shown that in some circumstances, the three-state noise can induce the resonant activation for the MFPT over the potential barrier; but in other circumstances, it can not. There are three resonant activations for the MFPT over the potential barrier, which are respectively as the functions of the transition rates of the three-state noise.
Effects of Time Delay on the Bistable System Subjected to Correlated Noises
NIE Lin-Ru, Mei Dong-Cheng
Chin. Phys. Lett. 2007, 24 (11): 3074-3077 .  
Abstract   PDF(pc) (216KB) ( 448 )
The time-delayed bistable system subjected to the multiplicative and additive noises is investigated. In the condition of small delay time, the stationary probability distribution function (SPDF) is derived, and under the condition of large delay time, the SPDF is stochastically simulated. The analytical and
simulative results indicate that: (i) For the case of λ=0 (λ denotes the strength of correlations between the multiplicative and additive noises), the time delay affects weakly the SPDF peak structure, and the symmetrical
property of the SPDF two-peak structure does not change with the increasing delay time. (ii) For the case of λ≠0, the two-peak structure changes with the increasing delay time, i.e. one peak goes up and the other go down simultaneously as the delay time increases and along with further increase of the delay time, the lower peak disappears gradually while the higher one goes up, i.e. the structure of the SPDF changes from a bimodal to a unimodal and the system becomes monostable.
Boundary-Dependent Chaotic Regions for a Bose--Einstein Condensate Interacting with Laser Field
ZHU Qian-Quan, HAI Wen-Hua, DENG Hai-Ming
Chin. Phys. Lett. 2007, 24 (11): 3077-3080 .  
Abstract   PDF(pc) (269KB) ( 463 )

Spatial chaos of a Bose--Einstein condensate perturbed by a weak laser
standing wave and a weak laser δ pulse is studied. By using the perturbed chaotic solution we investigate the new type of Melnikov chaotic regions, which depend on an integration constant c0 determined by the boundary conditions. It is shown that when the |c0| values are small, the chaotic region corresponds to small values of laser wave vector k, and the chaotic region for the larger k values is related to the large |c0| values. The result is confirmed
numerically by finding the chaotic and regular orbits on the Poincaré section for the two different parameter regions. Thus, for a fixed c0 the adjustment of k from a small value to large value can transform the chaotic region into the regular one or on the contrary, which suggests a feasible method for eliminating or generating Melnikov chaos.

Temperature Effects on Prism-Based Surface Plasmon Resonance Sensor
LIN Kai-Qun, WEI Lai-Ming, ZHANG Dou-Guo, ZHENG Rong-Sheng, WANG Pei, LU Yong-Hua, MING Hai
Chin. Phys. Lett. 2007, 24 (11): 3081-3084 .  
Abstract   PDF(pc) (320KB) ( 1241 )
We theoretically analyse the temperature effects on a surface plasmon resonance (SPR) sensor in Kretschmann configuration. The temperature effects include the thermo-optic effect and the dispersion of thermal-optic coefficient in the dielectric along with the thermal expansion effect, phonon--electron scattering and electron--electron scattering in the metal layer. We simulate the temperature dependence of the resonance position and the sensitivity of the SPR sensor under wavelength-interrogation and angular-interrogation mode of operation and the differences are pointed out in the two modes.
High-Pressure Phase Transition in CTAB-Micellar Solutions: A Raman Spectroscopic Study
LIN Ao-Lei, WANG Kai, ZHAO Yu, HAO Jian, ZOU Bo,
Chin. Phys. Lett. 2007, 24 (11): 3085-3087 .  
Abstract   PDF(pc) (229KB) ( 536 )
We use a diamond anvil cell for the first time to investigate the Raman spectra of an aqueous micellar solution of hexadecyltrimethylammonium bromide (CTAB) at pressures up to 3.85GPa. The pressure-induced phase transition between the micellar and coagel phases is found to occur at 0.64GPa and 60°C. This phase transition has a pressure hysteresis, and thus exhibits the first-order phase transition properties. Further experimental results show that although the structure of the coagel phase is similar to that of the CTAB crystal, the interchain distance is slightly larger in the coagel phase than that
in the CTAB crystal.
A Volt--Second Source for Calibration of Integrator in a Pulsed Field Magnetometer
LIN An-Li, HE Jian, ZHANG Yue, John Dudding, Michael Hall
Chin. Phys. Lett. 2007, 24 (11): 3088-3091 .  
Abstract   PDF(pc) (215KB) ( 566 )
A volt--second (Vs) source intended for absolutely calibrating the integrator in a pulsed field magnetometer (PFM) is designed and proven to be with accurate rising and falling edges and reasonable lower uncertainty. A comparison experiment shows that the difference between the magnetic fluxes generated respectively by the Vs source and the mutual inductor is within ±0.04%. The PFM is then calibrated in an absolute way of the Vs source. The calibrated PFM gives the measured results in good agreement with a static BH tracer supplied by National Institute of Metrology of China and provides a convenient way of studying the effect of mathematic process on the dynamic measuring curve of PFMs.
Flat Currents and Solutions of the Green--Schwarz Superstring on AdS5i×S5
ZHANG Li-Xia, WU Sheng, XIE Xiao-Ning, XIONG Chuan-Hua, YUE Rui-Hong, SHI Kang-Jie
Chin. Phys. Lett. 2007, 24 (11): 3092-3095 .  
Abstract   PDF(pc) (236KB) ( 431 )
We show that for the Green--Schwarz superstring on AdS5i×S5, the Cartan 1-forms associated with the flat currents given by Bena, Polchinski and Roiban [Phys. Rev. D 69(2004)046002] also satisfy equations of motion and the Virasoro constraint. Thus one can generate a series of classical solutions with a spectrum parameter from the existing one, and these solutions have the same infinite set of classically conserved quantities.
QCD Phase Transitions and Bag Constants at Finite Chemical Potential
YANG Shu, GUO Hua, ZHAO En-Guang, Lü Xiao-Fu,
Chin. Phys. Lett. 2007, 24 (11): 3096-3099 .  
Abstract   PDF(pc) (236KB) ( 443 )
The global colour model at finite temperature is further extended to study the systems at finite chemical potential. The deconfinement and chiral phase transition at finite chemical potential and at temperature T=0K are studied simultaneously. Meanwhile the evolution of the bag constants at finite chemical potential is calculated. The dependences of results on the model parameters are discussed in detail.
Assignment of Isodoublet of 23S1 Meson Nonet
FENG Xue-Chao, JIANG Feng-Chun
Chin. Phys. Lett. 2007, 24 (11): 3100-3102 .  
Abstract   PDF(pc) (209KB) ( 585 )
Inserting the masses of some states, which have been established in the
experiments or the theory of lattice QCD, we investigate the mass of the
isodoublet of the 23S1 meson nonet. The agreement results, 1567±22.6MeV and 1576.8MeV, are given by two different approaches. We suggest that the assignment of 23S1 meson nonet should be re-examined in future experiments.
Measurement of D(d,p) T Reaction Cross Sections in Sm Metal in Low Energy Region (10≤Ed≤20keV)
WANG Tie-Shan, YANG Zhen, H. Yunemura, A. Nakagawa, LV Hui-Yi, CHEN Jian-Yong, LIU Sheng-Jin, J. Kasagi
Chin. Phys. Lett. 2007, 24 (11): 3103-3106 .  
Abstract   PDF(pc) (268KB) ( 366 )

To study the screening effect of nuclear reactions in metallic environments, the thick target yields, the cross sections and the experimental S(E) factors of the D(d,p)T reaction have been measured on deuterons implanted in Sm metal at 133.2K for beam energies ranging from 10 to 20keV. The thick target yields of protons emitted in the D(d,p) T reaction are measured and compared with those data extrapolated from cross sections and stopping power data at higher energies. The screening potential in Sm metal at 133.2K is deduced to
be 520±56eV. As compared with the value achieved in the gas target, the
calculated screening potential values are much larger. This screening potential cannot be simply interpreted only by the electron screening. Energy dependences of the cross section σ(E) and the experimental S(E) factor for D(d,p)T reaction in Sm metal at 133.2K are obtained, respectively.

Etchability of Latent Fission Fragment Tracks in CR-39
Mukhtar Ahmed Rana
Chin. Phys. Lett. 2007, 24 (11): 3107-3110 .  
Abstract   PDF(pc) (397KB) ( 795 )
We report the chemical etching behaviour of the CR-39 polymer detector exposed to fission fragments of 252Cf describing etchability of latent tracks, which are like nanocylinders. The fission fragment exposed detectors were etched in 1--7N NaOH water solutions at temperatures 50--80°C for 45min in the case of track length and 180min in the case of track diameter measurements. The reduced etch rate S (called here etchability) is determined using experimental results for all etching conditions and the etching conditions with the highest reduced etch are obtained. Physics and energetics of bulk and track etching are discussed. Possible effects causing spurious changes in determination of activation energy of etching are investigated.
Field-Free Molecular Orientation Generated from Cyclic Rotational States by Using Two Trains of Half-Cycle Pulses
HUANG Yu-Xin, YANG Yu-Jun, ZHU Hong-Yu, WANG Li, WANG Hui, ZHU Qi-Ren
Chin. Phys. Lett. 2007, 24 (11): 3111-3114 .  
Abstract   PDF(pc) (286KB) ( 378 )
We show that two trains of half-cycle pulses (HCPs) with different amplitudes irradiating alternately on polar molecules can achieve a remarkable enhancement of field-free orientation compared with the case of an equal amplitude HCPs train for the same pulse separation. This kind of orientation enhancements is mainly due to an optimal adjustment of the population distribution on every field-free angular momentum eigenstate, in which the populations on the undesired states of high angular momenta are effectively suppressed, and the populations on the desired states of low angular momenta are correspondingly promoted.
Neutralization and Detachment in H+--H- Collisions
LIU Ling, WANG Jian-Guo
Chin. Phys. Lett. 2007, 24 (11): 3115-3118 .  
Abstract   PDF(pc) (264KB) ( 410 )
The cross sections for neutralization and detachment in H+--H- collisions in the energy range from 1.0 to 100keV/u are calculated using the two-centre atomic orbital close-coupling (TC-AOCC) method. The results are compared with the available experimental and theoretical data. It is found that the
neutralization cross section agrees well with the experimental data by Schon et al. [J. Phys. B 20 (1987) L759] and Melchert et al., [J. Phys. B 32 (1999) L139] especially at low energies. However, for the detachment process, our calculated cross section lies between the experimental data by Melchert et al. and by Peart et al. [J. Phys. B 9 (1976) 3047] for the energy below 15keV/u. Above this energy, our result is smaller than the two experimental data. It is worth pointing out that there exists a large difference between these two experimental data and it is difficult to judge which data is more accurate.
Therefore, a high-precision measurement for detachment cross sections is expected to resolve this discrepancy and to test the theoretical calculations.
Resonances in Positron--He Scattering
XIAO Dan, JIANG Ping-Hui, ZHOU Ya-Jun
Chin. Phys. Lett. 2007, 24 (11): 3119-3121 .  
Abstract   PDF(pc) (195KB) ( 410 )
We present the results for resonances in positron--He scattering at low impact energy (19.3--24.0eV) by using the momentum space coupled-channel optical (CCO) method. The S-partial wave resonance at 20.16eV is found for the first time.
Calculation of Total Cross Sections for Positron--Mg Collision
CHENG Cheng, ZHOU Ya-Jun
Chin. Phys. Lett. 2007, 24 (11): 3122-3124 .  
Abstract   PDF(pc) (194KB) ( 364 )
Total cross sections in positron--Mg collision are calculated in the range 2.0--60.0eV using the momentum space coupled channels optical potential approach. The target ionization continuum and the positronium formation are included in the optical potential. The present total cross sections are compared with the experiment data and the other theoretical results.
Polarization Properties of Quantum Cyclotron Radiation
CHEN Lei, YOU Jun-Han, LIU Dang-Bo
Chin. Phys. Lett. 2007, 24 (11): 3125-3128 .  
Abstract   PDF(pc) (199KB) ( 531 )
We present a simplified formulae system describing the polarization properties of the quantum cyclotron radiation by a nonrelativistic thermal electron in a very strong magnetic field. In this system, each of the derived quantities, including the Einstein coefficients, the absorption cross sections, and scattering cross sections, as well as the absorption coefficients by plasma, is divided into the perpendicularly and parallelly polarized components. The results, especially the absorption and scattering cross sections of resonant frequency photons, are potentially important in x-ray and gamma-ray astronomy, particularly in the study of gamma-ray bursts and pulsars.
Influence of Deviation on Optical Transmission through Aperiodic Superlattices
YIN Hai-Long, YANG Xiang-Bo, LAN Sheng, HU Wei
Chin. Phys. Lett. 2007, 24 (11): 3129-3132 .  
Abstract   PDF(pc) (231KB) ( 420 )
We propose a deviation model and study the influences of the relative error and sensitivity of a machine on the transmission coefficients (TCs) of Fibonacci superlattices. It is found that for a system with fewer layers, the influence of deviation can be ignored. When superlattices become more complicated, they may be fabricated by a machine with suitable relative error and possess the designed value of TC. However, when the number of system layers exceeds some critical value, superlattices should be manufactured only by precise machines. The influence of the sensitivity is also discussed.
A Simple Model for Measuring Refractive Index of a Liquid Based upon Fresnel Equations
ZHANG Zhi-Wei, WU Zhi-Fang, WEN Ting-Dun
Chin. Phys. Lett. 2007, 24 (11): 3133-3136 .  
Abstract   PDF(pc) (133KB) ( 1166 )
Due to many experimental data required and a lot of calculations involved, it is very complex and cumbersome to model prism-based liquid-refractive-index-measuring methods. We develop a new method of mathematical modelling for measuring refractive index of a liquid based upon the Fresnel formula and prism internal reflection at an incident angle less than the critical angle. With this method, only two different concentrations measurements for a kind of solution can lead to the determination of computational model. Measurements are performed to examine the validity of the theoretical model. Experimental results indicate the feasibility of the theoretical model with an error of 1%.
The method is also capable of measuring even smaller changes in the optical refractive index of the material on a metal surface by the surface plasma resonance sensing techniques.
Characteristics of Spontaneous Emission of Polarized Atoms in Metal--Dielectric Multiple Layer Structures
ZHAO Li-Ming, GU Ben-Yuan, ZHOU Yun-Song
Chin. Phys. Lett. 2007, 24 (11): 3137-3140 .  
Abstract   PDF(pc) (242KB) ( 465 )
The spontaneous emission (SE) progress of polarized atoms in a stratified structure of air--dielectric(D0)--metal(M)--dielectric(D1)--air can be controlled effectively by changing the thickness of the D1 layer and rotating the polarized direction of atoms. It is found that the normalized SE rate of atoms located inside the D0 layer crucially depends on the atomic position and the thickness of the D1 layer. When the atom is located near the D0--M interface, the normalized atomic SE rate as a function of the atomic position is abruptly onset for the thin D1 layer. However, with the increasing thickness of the D1 layer, the corresponding curve profile exhibits plateau and stays nearly unchanged. The substantial change of the SE rate stems from the excitation of the surface plasmon polaritons in metal-dielectric interface, and the feature crucially depends on the thickness of D1 layer. If atoms are positioned near the D0--air interface, the substantial variation of the normalized SE rate appears when rotating the polarized direction of atoms. These findings manifest that the atomic SE processes can be flexibly controlled by altering the thickness of the dielectric layer D1 or rotating the orientation of the polarization of atoms.
Precision Controlling of Frequency Difference for Elastic-Stress Birefringence He--Ne Dual-Frequency Lasers
ZHOU Lu-Fei, ZHANG Shu-Lian, GUO Hong, REN Zhou
Chin. Phys. Lett. 2007, 24 (11): 3141-3144 .  
Abstract   PDF(pc) (222KB) ( 556 )
Birefringence-Zeeman dual frequency lasers are capable of producing frequency difference from several kilohertz to hundreds of megahertz, but the precision of giving and stabilizing of the beat frequency still needs improvement to the range of ±200kHz. We design a new elastic force-exerting device comprised of the bottom part, two arms and two pieces of force-exerting sheets. The frequency difference smoothly tuning is realized with this device in a large range of 2MHz to 20MHz. Power-balance frequency stabilization system is used to investigate characters of the temperature, frequency difference and laser power. The precision of the frequency difference has reach up to ±100kHz after system temperature balance. Analyses of the laser frequency difference and power character are carried out.
Dual-Wavelength Erbium-Doped Fibre Ring Laser by Cascading Tunable Bandpass Filter with Bandstop Filter
CHEN Guo-Jie, HUANG De-Xiu, ZHANG Xin-Liang, CAO Hui
Chin. Phys. Lett. 2007, 24 (11): 3145-3148 .  
Abstract   PDF(pc) (233KB) ( 416 )
A novel fibre ring laser is proposed and successfully demonstrated. By cascading a tunable bandpass filter with a bandstop filter to construct the desired narrow dual-transmission-peak spectrum, and employing a segment of unpumped erbium-doped fibre as a saturable absorber, a stable fibre ring laser is achieved at room temperature. The proposed laser can operate in dual-wavelength with the wavelength spacing of 0.48nm and the extinction ratio more than 50dB or switch between the two wavelengths by adjusting a polarization controller. The stability is investigated experimentally and explained theoretically.
Green Output of 1.5W from a Diode-Pumped Intracavity Frequency-Doubled Self-Q-Switched and Mode-Locked Cr,Nd:YAG Laser
DU Shi-Feng, WANG Su-Mei, ZHANG Dong-Xiang, LI De-Hua, ZHANG Zhi-Guo, FENG Bao-Hua, ZHANG Shi-Wen
Chin. Phys. Lett. 2007, 24 (11): 3149-3152 .  
Abstract   PDF(pc) (293KB) ( 505 )
We report a diode-pumped intracavity frequency-doubled self-Q-switched and mode-locked Cr,Nd:YAG/KTP green laser with a Z-type cavity, which produces 1.5W of average power at 532nm with incident pump power 14.2W. The individual mode-locked green pulse duration is about 560ps with 149MHz repetition rate. Almost 100% modulation depth of the mode-locked green pulses is achieved at an incident pump power of 4.13W. The maximum energy of Q-switched green pulse is 19.8μJ. The experimental results of pulse duration and pulse energy of Q-switched green pulse agree well with the theoretical calculations.
Surface Emitting THz Wave Parametrical Oscillator Using MgO:LiNbO
ZHANG Xian-Bin, SHI Wei, T. Ikari, H. Ito
Chin. Phys. Lett. 2007, 24 (11): 3153-3156 .  
Abstract   PDF(pc) (259KB) ( 707 )
Room-temperature operation terahertz (THz) wave source is demonstrated using three MgO:LiNbO3 crystals which have a noncollinear arrangement. The experimental results show that the THz wave can be tunable from 0.8THz to 3.0THz, and the peak energy output is 103pJ/pulse at 1.5THz. The noncollinear cavity configuration makes the THz beam have Gaussian-like spatial distribution, small divergence angle, perpendicularly eradiated from the crystal surface. The beam quality factor M2 is measured to be Mx2=1.15,
Mz2=1.25 for characterizing the THz wave beam. Experiments also show that the THz beam can be focused by using a polyethylene lens, and the focal spot size is close to the diffraction limit.
Efficient Nanosecond Dual-Signal Optical Parametric Generator with a Periodically Phase Reversed PPMgLN
JI Feng, LI Xi-Fu, ZHANG Bai-Gang, ZHANG Tie-Li, WANG Peng, XU De-Gang, YAO Jian-Quan
Chin. Phys. Lett. 2007, 24 (11): 3157-3159 .  
Abstract   PDF(pc) (234KB) ( 506 )
We report an efficient nanosecond optical parametric generator (OPG) with a periodically-phase-reversed periodically poled MgO:LiNbO3(ppr-PPMgLN), which produces two pairs of signal and idler waves. The OPG is pumped by a 1.064μm Q-switched Nd:YVO4 laser. When the repetition rate is set at 10kHz, the maximum average total output power of 570mW is achieved, including 410mW of dual-signal radiations and 160mW of dual-idler radiations. The total
conversion efficiency is 32.5%. The tunable dual-signal wavelengths in the range of 1.474--1.518μm and 1.490--1.539μm and the dual-idler of 3.826--3.558μm and 3.726--3.451μm are obtained by changing the crystal temperature from 30°C to 200μC.
Fabrication of Two-Dimensional Photonic Crystals with Controlled Defects by Combination of Holographic Lithography and Two-Photon Polymerization
SHEN Xiao-Xia, YU Xiao-Qiang, YANG Xiu-Lun, CAI Lv-Zhong, WANG Yu-Rong, DONG Guo-Yan, MENG Xiang-Feng, XU Xian-Feng
Chin. Phys. Lett. 2007, 24 (11): 3160-3163 .  
Abstract   PDF(pc) (544KB) ( 460 )
A new ternary photopolymer system is used in fabricating photonic crystals (PhCs) with controlled defects by combination of single-photon and two-photon photopolymerization. The former process can produce PhCs in one-step recording with a low-power (tens mW) continuous-wave laser at 532nm, while the latter can create desired defects. The preparation of the material, the optical setup and the preliminary experimental results are given. Compared with other methods, this approach is much more accessible and convenient for use of visible light and has advantages of making PhCs in a large scale quickly and economically and introducing any defects exactly, especially for three-dimensional structures.
Rapid Fabrication of Three-Dimensional Woodpile Photonic Crystals by Means of Two-Photon Photopolymerization
ZHOU Ming, KONG Jun-Jie, YANG Hai-Feng, YAN Feng, CAI Lan
Chin. Phys. Lett. 2007, 24 (11): 3164-3167 .  
Abstract   PDF(pc) (864KB) ( 590 )
Two-photon photopolymerization (TPP) of femtosecond laser is a promising method to fabricate three-dimensional woodpile photonic crystals (PCs). We build micro-fabrication system based on the principle of TPP. Three-dimensional woodpile PCs consisting of in-plane rod distances ranging from 1000nm to 2000nm are fabricated by focusing femtosecond laser in photosensitive liquid resin ORMOCER. The properties of the PCs are also discussed, and fundamental photonic band gaps in middle-infrared range are measured, whose in-plane rod distances are 1500nm and 2000nm. Three-dimensional woodpile PC devices with desired defects, such as cross-waveguide and micro-laser structures, are introduced easily by TPP. We fabricate the three-dimensional woodpile PCs in the liquid resin at the fast scanning speed of 120μm/s.
Tunable Pair Transmission in One-Dimensional Photonic Crystals Consisting of Single-Negative Materials
DENG Xin-Hua, LIU Nian-Hua
Chin. Phys. Lett. 2007, 24 (11): 3168-3171 .  
Abstract   PDF(pc) (245KB) ( 407 )
We study the transmission of one-dimensional photonic crystals consisting of single-negative permittivity and single-negative permeability media by using transfer matrix method. A pair of transmission modes is found in the gap. The transmission modes are dependent only on the ratio of the thicknesses of the two alternating layers. The separation of a pair of transmission modes can be
tuned by varying the thickness of the defect layer or the ratio of thicknesses of the two alternating layers.
Mach--Zehnder Interferometer Based on Coupled Dielectric Pillars
GAO Ding-Shan, HAO Ran, ZHOU Zhi-Ping,
Chin. Phys. Lett. 2007, 24 (11): 3172-3174 .  
Abstract   PDF(pc) (350KB) ( 606 )
We propose a Mach--Zehnder interferometer (MZI) based on coupled dielectric pillars. It is composed of single-row pillar coupled waveguide modulating arms and three-row pillar waveguide 3dB couplers. The slow light property and transmission loss of the single-row pillar modulating arm are optimized by the plane wave expansion method. A short 3dB coupler is designed based on the modes transformation in three-row pillar waveguide. Finite difference time domain simulations prove the validity of this MZI and show that it has low insertion loss of <1.1dB and high extinction ratio of >12dB.
Pulse Evolution Characteristics in Self-Similar Mode-locked Fibre Laser
TU Cheng-Hou, LI Zhen, LEI Ting, LI Yong-Nan, GUO Wen-Gang, WEI Dai, ZHU Hui, ZHANG Shuang-Gen, LU Fu-Yun
Chin. Phys. Lett. 2007, 24 (11): 3175-3178 .  
Abstract   PDF(pc) (247KB) ( 1019 )
A self-similar mode locked fibre laser is studied based on a numerical model. By introducing a dimensionless factor k to characterize the pulse shape, the self-similar pulse evolution, formation and the temporal and spectral shape changes due to the elements in the cavity are investigated throughout the laser cavity. The results show that in the self-similar mode locked fibre laser, self-similar pulse is first formed in the single-mode fibre, which is then amplified in the gain fibre. Gain bandwidth has a small influence on pulse shape, so high energy self-similar pulse can be obtained after amplification. Because net cavity dispersion directly influences the pulse width as well as
peak power after compression by a pair of gratings, which can determine
the pulse self-similar evolution, it is very important to control the net cavity dispersion to a certain range to obtain self-similar pulses.
Perturbation Analysis on Guided Waves in a Fluid-Filled Borehole Surrounded by a Cubic Crystal Anisotropic Medium
Chin. Phys. Lett. 2007, 24 (11): 3179-3182 .  
Abstract   PDF(pc) (268KB) ( 448 )
The perturbation method is employed to analyse the guided waves in a borehole surrounded by a cubic crystal medium for the first time. The cubic crystal medium is regarded as a reference unperturbed isotropic state added to the perturbation. The dispersion characteristics of Stoneley wave, pseudo-Rayleigh wave, flexural wave, and screw wave are investigated in detail. It is found that dispersion of the guided waves excited by monopole and dipole sources does not depend on the azimuth of the source, whereas the dispersion of screw wave excited by quadrupole source is significantly related to the azimuth of the source. Screw waves propagated along different azimuth in the borehole can be split. This is different from screw waves in transversely isotropic media (hexagonal crystal), which have been widely studied.
New Evidence of Active Tuning in Cochlea
ZHAO Xiang-Hui, LONG Zhang-Cai
Chin. Phys. Lett. 2007, 24 (11): 3183-3186 .  
Abstract   PDF(pc) (251KB) ( 456 )
The wonderful performance of hearing systems is mainly attributed to the
tuning filtering of basilar membrane (BM). Although theory of the cochlear mechanism has been greatly developed since the 1970s and the amplification or sensitivity of the cochlea has been concluded due to the out hair cells, the mechanics underlying the sharp-tuning or frequency selectivity of cochlea remains a puzzle. We use the cochlear translation function derived from the data of an experiment of the BM in vivo to calculate basilar responses to tone bursts, and find that there are resonant peaks with the characteristic frequency at the corresponding place in the initial and terminal part of the responses. However, when the translation function is shallower, there will be no resonant peaks in the responses. The result indicates that the sharp tuning is due to existence of the active resonant tuning mechanism.
Determination of Thermal Conductivity of Liquids by a Multi-Point Laser Pump Method
MA Di, KUO Pao-Kuang, XU Xiao-Dong, ZHANG Shu-Yi
Chin. Phys. Lett. 2007, 24 (11): 3187-3190 .  
Abstract   PDF(pc) (483KB) ( 372 )
As an advanced optical method, a multi-point pump method is presented for measurements of thermo-physical properties of liquids. Meanwhile, based on the laser-induced thermal grating method, a new theory model is presented and used to analyse the thermal effects caused by the multi-point laser pump, by which the thermal conductivity of liquids can be obtained. The results of some typical liquids, such as water, ethanol and acetone, are presented and are consistent with those of acknowledged values, demonstrating that the multi-point method is simple and useful for characterizing thermal properties of liquids.
Edge Particle Flux with Temperature Fluctuation in the HL-2A Tokamak
CHENG Jun, YAN Long-Wen, HONG Wen-Yu, QIAN Jun, ZHAO Kai-Jun
Chin. Phys. Lett. 2007, 24 (11): 3191-3194 .  
Abstract   PDF(pc) (269KB) ( 565 )
Electron temperature, density, plasma potential and their fluctuation profiles at edge plasmas are measured simultaneously with a reciprocating probe system in HL-2A. The analysis results of four-tip data indicate that the temperature fluctuation has relative amplitude of 10--15%, gives more contribution to particle flux in lower (0--25kHz) and higher frequency (50--250kHz) ranges. The coherence between temperature fluctuations and density or potential fluctuations implies that their coupling will impact anomalous transport. The measured diffusion coefficient is about three times of the Bohm diffusion coefficient when considering the temperature fluctuation. The particle flux with temperature fluctuation is discussed in HL-2A for the first time.
Runaway Electron Beam Instability in Slide-Away Discharges in the HT-7 Tokamak
CHEN Zhong-Yong, WAN Bao-Nian, LING Bi-Li, GAO Xiang, DU Qin, TI Ang, LIN Shi-Yao, S. Sajjad, HT- Team
Chin. Phys. Lett. 2007, 24 (11): 3195-3198 .  
Abstract   PDF(pc) (247KB) ( 562 )

Slide-away discharges are achieved by decreasing the plasma density or ramping down the plasma current in runaway discharges in the HT-7 tokamak. In the case of plasma current ramp down, the ratio of the electron plasma frequency to the electron cyclotron frequency is higher than in the stationary pulses when the discharge goes into a slide-away regime. The instability regime is characterized by relaxations in the electron cyclotron emission due to relativistic anomalous Doppler effect which transfers energy from parallel to perpendicular motion. The triggering of relativistic anomalous Doppler effect at higher density by ramping down of plasma current may provide a alternative runaway energy control scenario.

Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection
GUO Jun, LU Quan-Ming
Chin. Phys. Lett. 2007, 24 (11): 3199-3202 .  
Abstract   PDF(pc) (1232KB) ( 573 )

A 2.5-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate electron behaviour in collisionless magnetic reconnection. The results show that the ion/electron mass ratio (mi/me) almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron
current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger.
Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.

Pressure Induced Metallization in the ε Phase of Solid Oxygen by ab initio Pseudopotential Plane-Wave Calculations
LIU Yan-Hui, LIU Zhi-Ming, MA Yan-Ming, HE Zhi, TIAN Fu-Bo, CUI Tian, LIU Bing-Bing, ZOU Guang-Tian
Chin. Phys. Lett. 2007, 24 (11): 3203-3205 .  
Abstract   PDF(pc) (642KB) ( 385 )
We perform an ab initio study on the electronic structure and charge density of the ε-oxygen under high pressure, which is obtained by powder x-ray diffraction experiment recently. Our results show that the hybridization among the σg*, πu and πg* bands in the ε-oxygen are not significant even at megabar pressure. Pressure-induced metallization occurs due to the band overlapping near the Fermi level at about 50GPa. A new network along the b-axis is formed and the O8 characteristic in the ε phase disappears above 50GPa even though the symmetry remains unchanged.
Indentation Load Effect on Young's Modulus and Hardness of Porous Sialon Ceramic by Depth Sensing Indentation Tests
Chin. Phys. Lett. 2007, 24 (11): 3206-3209 .  
Abstract   PDF(pc) (353KB) ( 1397 )
Depth sensing indentation (DSI) tests at the range of 200--1800mN are
performed on porous sialon ceramic to determine the indentation load on
Young's modulus and hardness values. The Young modulus and hardness
(Dynamic and Martens) values are deduced by analysing the unloading
segments of the DSI test load-displacement curves using the Oliver--Pharr method. It is found that Young's modulus Er, the dynamic hardness HD and the Martens hardness HM exhibit significant indentation load dependences. The values of Young's modulus and hardness decrease with the increasing indentation load, as a result of indentation load effect. The experimental hf/hm ratios lower than the critical value 0.7, with hm being the maximum penetration depth during loading and hf the final unloading depth, indicate that our sample shows the work hardening behaviour.
Directional Motion of Droplets in a Conical Tube or on a Conical Fibre
LIU Jian-Lin, XIA Re, LI Bing-Wei, FENG Xi-Qiao
Chin. Phys. Lett. 2007, 24 (11): 3210-3213 .  
Abstract   PDF(pc) (370KB) ( 818 )
Manipulating the directional movement of liquid droplets is of significance for design and fabrication of some microfluidic devices. An energy-based method is adopted to analyse the directional movement of a droplet deposited in a conical tube or on a conical fibre. We perform an experiment to investigate the directional motion of a droplet in an open conical tube. Our theoretical analysis and experimental observations both demonstrate that surface tension can drive the droplet to move in the conical tube. The critical condition
of the liquid moving in the conical tube is presented. We also analyse a droplet on a conical hydrophilic fibre, which can move from the thinner to the thicker end.
Growth of Cu Films on Si(111)-7×7 Surfaces at Low Temperature: A Scanning Tunnelling Microscopy Study
SHEN Quan-Tong, SUN Guo-Feng, LI Wen-Juan, DONG Guo-Cai, HAN Tie-Zhu, MA Da-Yan, SUN Yu-Jie, JIA Jin-Feng, XUE Qi-Kun,
Chin. Phys. Lett. 2007, 24 (11): 3214-3217 .  
Abstract   PDF(pc) (766KB) ( 923 )
Morphologies of Cu(111) films on Si(111)-7×7 surfaces prepared at low
temperature are investigated by scanning tunnelling microscopy (STM) and
reflection high-energy electron diffraction (RHEED). At the initial growth stage, Cu films are flat due to the formation of silicide at the interface that decreases the mismatch between Cu films and the Si substrate. Different from the usual multilayer growth of Cu/Cu(111), on the silicide layer a layer-by-layer growth is observed. The two dimensional (2D) growth is explained by the enhanced high island density at low deposition temperature. Increasing deposition rate
produces films with different morphologies, which is the result of Ostwald ripening.
First-Principles Study of Electronic Properties in PbS(100) with Vacancy Defect
DING Zong-Ling, XING Huai-Zhong, XU Sheng-Lan, HUANG Yan, CHENXiao-Shuang
Chin. Phys. Lett. 2007, 24 (11): 3218-3221 .  
Abstract   PDF(pc) (239KB) ( 679 )
Electronic properties of both Pb and S vacancy defects in PbS(100) have been studied using the first-principles density functional theory (DFT) calculations with the plane-wave pseudopotentials. It is found that the density of states (DOS) near the top of the valence band and the bottom of the conduction band is significantly modified by these defects. Our calculation indicates that in the case of S vacancy defects the Fermi energy shifts to the conduction band making it as an n-type PbS (donor). However, in the case of Pb vacancy, because of the appreciable change of the DOS, the system acts as a p-type PbS (accepter). In addition, the structural relaxation shows that the defect leads to outward relaxation of the nearest-neighbouring atoms and inward relaxation of the next-nearest neighbouring atoms.
Self-Trapping of Acoustic Polaron in One Dimension
HOU Jun-Hua, LIANG Xi-Xia
Chin. Phys. Lett. 2007, 24 (11): 3222-3224 .  
Abstract   PDF(pc) (211KB) ( 492 )
The ground-state energy and effective mass of an acoustic polaron in one
dimension are calculated by using an electron--longitudinal-acoustic-phonon interaction Hamiltonian derived here. The self-trapping of the acoustic polaron is discussed. It is found that the critical coupling constant shifts toward weaker electron--phonon interaction with the increasing cutoff wave vector and the products of the critical coupling constant by the cutoff wave vector
tend to a certain value. The self-trapping of acoustic polarons in one
dimension is easier to be realized than that in three- and two-dimensional systems. The self-trapping transition of acoustic polarons is expected to be observed in the one dimensional systems of alkali halides and wide-band-gap semiconductors.
Kondo Resonance versus Fano Interference in Double Quantum Dots Coupled to a Two-Lead One-Ring System
CHEN Xiong-Wen, SHI Zhen-Gang, CHEN Bao-Ju, SONG Ke-Hui
Chin. Phys. Lett. 2007, 24 (11): 3225-3228 .  
Abstract   PDF(pc) (328KB) ( 491 )
We analyse the transport properties of a coupled double quantum dot (DQD) device with one of the dots (QD1) coupled to metallic leads and the other (QD2) embedded in an Aharonov--Bhom (A-B) ring by means of the slave-boson mean-field theory. It is found that in this system, the Kondo resonance and the Fano interference exist simultaneously, the enhancing Kondo effect and the increasing hopping of the QD2-Ring destroy the localized electron state in the QD2 for the QD1-leads, and accordingly, the Fano interference between the DQD-leads and the QD1-leads are suppressed. Under some conditions, the Fano interference can be quenched fully and the single Kondo resonance of the QD1-leads comes into being. Moreover, when the magnetic flux of the A-B ring is zero, the influence of the parity of the A-B ring on the transport properties is very weak, but this influence becomes more obvious with non-zero magnetic flux. Thus this model may be a candidate for future
device applications.
Influence of Interface Structure of Co/Cu (100) Superlattices on Electronic Structure and Giant Magnetoresistance
LU Shuo, SHANG Jia-Xiang, ZHANG Yue
Chin. Phys. Lett. 2007, 24 (11): 3229-3232 .  
Abstract   PDF(pc) (502KB) ( 372 )
Electronic structures and magnetoresistance (MR) of Co3Cu5 and Co3Cu7 models as well as their interface atom exchange models Co2CuCoCu4 and
Co2CuCoCu6 are investigated by the first-principles pseudopotential plane-wave method based on density functional theory. Charge transfer, magnetic moment, density of states, spin asymmetry factor, and MR ratio are discussed. The results show that the values of charge transfer and spin asymmetry factor at the Fermi level of Co layers are closely related to the neighbouring background of the Co layer. The Co layer with two sides adjacent to the Cu layer would transfer more charge to the Cu layer than other neighbouring background and have the largest spin asymmetry factor at the Fermi level. The Co layer with two neighbouring Co layers (interior Co) would gain a little
charge and have the smallest spin asymmetry factor at the Fermi level. Two-current model is used to evaluate the MR ratio of Co2CuCoCu_4 (Co2CuCoCu6) to be larger than that of Co3Cu5 (Co3Cu7), which can be explained by the charge transfer and spin asymmetry factor.
Complex Modulation in Plasmon-Assisted Transmission Spectra of a Two-Slit Structure
LI Zhi, ZHANG Jia-Sen, YAN Hai-Feng, GONG Qi-Huang
Chin. Phys. Lett. 2007, 24 (11): 3233-3236 .  
Abstract   PDF(pc) (380KB) ( 539 )
We study the plasmon-assisted transmission of two kinds of slit structures in a 290-nm-thick silver film on a glass substrate. For the two-slit structure, the total transmission intensity spectra displays a complex modulation, which is attributed to different propagation constants of the surface plasmon polaritons (SPPs) on the silver-air and silver-glass interfaces. Replacing one of the two slits by a shallow corrugation results in a simple sinusoidal intensity modulation because of the only effective SPP excitation and propagation on the silver-air interface. These confirm the role of different SPP propagations and interference in the transmission properties of metal nanoslits.
Strain Compensated AlInGaAs/InGaAs/InAs Triangular Quantum Wells for Lasing Wavelength beyond 2μm
GU Yi, ZHANG Yong-Gang, LIU Sheng
Chin. Phys. Lett. 2007, 24 (11): 3237-3240 .  
Abstract   PDF(pc) (236KB) ( 370 )
The subband energy and lasing wavelength of compressively strained triangular In0.53Ga0.47As/InAs quantum well are calculated and compared with the conventional rectangular ones with the same strain contents. The strain compensation using Al0.33In0.36Ga0.31As barrier is introduced. The
results show that lasing wavelength can be extended dramatically to beyond 2.8μm by changing the energy band from the conventional rectangular shape to a triangular one, the realization of such a structure using molecular beam epitaxy technology is also discussed.
Cooper-Pair Number-Phase Quantization for a Mesoscopic LC Circuit Including a Josephson Junction
LIANG Bao-Long, WANG Ji-Suo, FAN Hong-Yi,
Chin. Phys. Lett. 2007, 24 (11): 3241-3244 .  
Abstract   PDF(pc) (243KB) ( 451 )
By introducing the entangled state representation and Feynman assumption that `electron pairs are bosons, ..., a bound pair acts as a Bose particle', we construct an operator Hamiltonian for a mesoscopic inductance-capacitance (LC) circuit including a Josephson junction, then we use the Heisenberg equation of motion to derive the current equation and the voltage equation across the inductance as well as across the Josephson junction. The result manifestly shows how the junction voltage is affected by the capacitance coupling. In this way the Cooper-pair number-phase quantization for this system is completed.
Electrical Characteristics of InGaN/AlGaN and InGaN/GaN MQW Near UV-LEDs
MU Sen, YU Tong-Jun, HUANG Liu-Bing, JIA Chuan-Yu, PAN Yao-Bo, YANG Zhi-Jian, CHEN Zhi-Zhong, QIN Zhi-Xin, ZHANG Guo-Yi
Chin. Phys. Lett. 2007, 24 (11): 3245-3248 .  
Abstract   PDF(pc) (258KB) ( 1589 )
Electrical characteristics of In0.05Ga0.95N/Al0.07Ga0.93N and In0.05Ga0.95N/GaN multiple quantum well (MQW) ultraviolet light-emitting diodes (UV-LEDs) at 400nm wavelength are measured. It is found that for InGaN/AlGaN MQW LEDs, both ideality factor and parallel resistance are similar to those of InGaN/GaN MQW LEDs, while series resistance is two times larger. It is suggested that the Al0.07Ga0.93N barrier layer did not change crystal quality and electrical characteristic of p-n junction either, but brought larger series resistance. As a result, InGaN/AlGaN MQW LEDs suffer more serious thermal dissipation problem although they show higher light output efficiency.
Magnetic Properties and Spin State Transition of Gallium Doped Perovskite Cobaltite Oxide
WU Zhi-Min, , WANG Xin-Qiang, WANG Fang-Wei
Chin. Phys. Lett. 2007, 24 (11): 3249-3252 .  
Abstract   PDF(pc) (241KB) ( 561 )
A series of Ga doping perovskite cobaltite La2/3Sr1/3(Co1-yGay)O3 (y=0, 0.1, 0.2, 0.3 and 0.4) are prepared by the standard solid-state reaction method. Their magnetic properties and Co ions spin state transitions are studied. Upon doping, no appreciable structure changes can be found. However, the corresponding Curie temperature sharply decreases and the magnetization is greatly reduced, indicating that Ga doping destroys the ferromagnetic interaction in the system. In addition, the high temperature magnetization data follow the Curie--Weiss law. At least one kind of Co ions (Co3+ or
Co4+) favours the mixed spin state, and most Co ions are at the lower spin state (low and intermediate state). With increasing Ga content, more Co ions transit to the higher spin state.
Electrical Properties of Nanostructured Magnetic Colloid and Influence of Magnetic Field
PU Sheng-Li, CHEN Xian-Feng, DI Zi-Yun, GENG Tao, XIA Yu-Xing
Chin. Phys. Lett. 2007, 24 (11): 3253-3256 .  
Abstract   PDF(pc) (340KB) ( 310 )
We investigate the electrical properties of the nanostructured magnetic colloid without and with magnetic field. The competition between the directional motion of the charged magnetic nanoparticles and other minor nonmagnetic impurities (also small amount of ions) under applied voltage and their random orientation due to thermal activation is implemented to elaborate the electrically conduction mechanism under zero magnetic field. Two equivalent electric circuits are employed for explaining the charging and discharging processes. The tunnelling conduction mechanism upon application of externally magnetic field may exist in the nanostructured magnetic colloid. The alternation of the two conduction mechanisms accounts for the current spikes when the magnetic field is switched on or off. This work presents the peculiar electrical phenomena of the magnetically colloidal system.
Properties of Co-Doped 0.92(Na0.5Bi0.5) TiO3-0.08BaTiO3 Lead-Free Ceramics
JIANG Xiang-Ping, ZHENG Yan-Yan, JIANG Fu-Lan, LIU Li-Hua, KWOK Kin-Wing, CHAN-WONG Lai-Wa
Chin. Phys. Lett. 2007, 24 (11): 3257-3259 .  
Abstract   PDF(pc) (301KB) ( 478 )
Lead-free piezoelectric ceramics 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3+xmol% Co3+ (BNBT-Co, x=0--8) are prepared by the solid state reaction method. Effects of the amount of Co3+ on the electrical properties and phase transition are studied. The results indicate that the addition of Co3+ enhances the mechanical quality factor Qm significantly, whereas the dissipation factor tan δ has a minimum value at x=3.5. Meanwhile, addition of Co3+ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3+3.5mol% Co3+ ceramics exhibit good performance with mechanical quality factor Qm=910, piezoelectric constant d33=106pC/N, planar electromechanical coupling kp=10% and dissipation factor tanδ=1.1% at 1kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of εT33 vs temperature for the pure BNBT ceramics. However, the first dielectric peak Td disappears after the addition of Co3+ which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.
Optimum Indium Concentration for Growth of 1.3μmInAs/InxGa1-xAs Quantum Dots in a Well
WANG Chong, LIU Zhao-Lin, CHEN Xue-Mei, XIA Chang-Sheng, ZHANGShu, YANG Yu, LU Wei
Chin. Phys. Lett. 2007, 24 (11): 3260-3263 .  
Abstract   PDF(pc) (470KB) ( 483 )
Five InAs/InxGa1-xAs quantum dots in a well (DWELL) with different indium concentration x are grown by solid source molecular beam epitaxy. The high quantum dot density is observed in the InAs/In0.3Ga0.7As DWELL. The photoluminescence (PL) experiments indicate that the ground state peaks of
InAs/In0.15Ga0.85As and InAs/In0.22Ga0.78As DWELLs shift to 1.31 and 1.33μm, respectively. The optical properties are investigated by using the PL and piezoreflectance spectroscope methods. An abnormal blue shift has been observed with the further increase of x from 0.22 to 0.30.
Dielectric Response and Broadband Microwave Absorption Properties of Three-Layer Graded ZnO Nanowhisker/Polyester Composites
ZHOU Yan, SHI Xiao-Ling, YUAN Jie, FANG Xiao-Yong, CAO Mao-Sheng
Chin. Phys. Lett. 2007, 24 (11): 3264-3267 .  
Abstract   PDF(pc) (475KB) ( 496 )
We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measured. Experimental results have shown that the graded dispersion with ZnO nanowhiskers contributes to broadband microwave absorption. In other words, the absorption band depends on the graded dispersion configuration of ZnO nanowhiskers in polyester matrix.
Depletion Interactions in a Cylindric Pipeline with a Small Shape Change
LI Chun-Shu, GAO Hai-Xia, XIAO Chang-Ming
Chin. Phys. Lett. 2007, 24 (11): 3268-3271 .  
Abstract   PDF(pc) (227KB) ( 390 )
Stressed by external forces, it is possible for a cylindric pipeline to change into an elliptic pipeline. To expose the effect of small shape change of the pipeline on the depletion interactions, both the depletion potentials and depletion forces in the hard sphere systems confined by a cylindric pipeline or by an elliptic pipeline are studied by Monte Carlo simulations. The numerical results show that the depletion interactions are strongly affected by the small change of the shape of the pipeline in a way. Furthermore, it is also found that the depletion interactions will be strengthened if the short axis of the elliptic pipeline is decreased.
Explanation of Effect of Added Water on Dye-Sensitized Nanocrystalline TiO2 Solar Cell: Correlation between Performance and Carrier Relaxation Kinetics
ZHAO Hui, YIN Xiong, LI Heng, LIN Yuan, WENG Yu-Xiang
Chin. Phys. Lett. 2007, 24 (11): 3272-3275 .  
Abstract   PDF(pc) (249KB) ( 472 )
Time-resolved mid-IR transient absorption spectroscopy is employed to explore the mechanism of improving the performance of dye-sensitized TiO2 solar cell (DSSC) when a certain amount of H2O is added into the electrolyte. The relaxation kinetics of dye-sensitized TiO2 nanocrystalline film and the corresponding DSSC performance are investigated under different conditions. It is found that the interfacial charge recombination is retarded and electron injection efficiency is increased in the water vapour and in the electrolyte when D2O is added. The values of open-circuit photovoltage Voc and the short-circuit photocurrent Jsc of the cells are linearly correlated to the product of the two decay time constants. We also observed that Voc well correlates with electron injection efficiency. It provides a preliminary microscopic account for the function of the added water in improving the performance of DSSCs.
Molecular Dynamics Simulation of Water Confined in Carbon Nanotubes
WANG Yan, YUAN Hong-Jun
Chin. Phys. Lett. 2007, 24 (11): 3276-3279 .  
Abstract   PDF(pc) (1110KB) ( 646 )
Molecular dynamics simulations are performed for water confined in carbon nanotubes with various diameters (11.0--13.8AA). The simulations under an isobaric pressure (one atmosphere) by lowering temperatures from 300K to 190K are carried out. Water molecules within variously sized tubes tend to transform from disorder to order with different configurations (four-water-molecule ring, six-water-molecule ring and seven-water-molecule ring) at phase transition temperatures, which may be lowered by the increasing tube radius. It is also found that the configurations of water in (10, 10) tube are not unique (seven-molecule ring and seven-molecule ring plus water chain).
Nonvolatile Memory Devices Based on Gold Nanoparticle and Poly (N-Vinylcarbazole) Composite
LIN Jian, LI Di, CHEN Jiang-Shan, LI Jing-Hong, MA Dong-Ge
Chin. Phys. Lett. 2007, 24 (11): 3280-3282 .  
Abstract   PDF(pc) (229KB) ( 514 )
A rewritable polymer memory device based on gold nanoparticle doped poly (N-vinylcarbazole) (PVK), which can be easily fabricated by simple spin coating, has been described. An electrical bistable phenomenon is observed in the current-voltage characteristics of this device, and it is found that the electrical bistability is repeatable by proper writing voltage and erasing voltage. The unique behaviour of the devices provides an interesting approach such that doping nanoparticles in polymer can be used to realize high performance nonvolatile polymer memory devices.
A New Resonant Tunnelling Structure of Integrated InGaAs/GaAs Very-Long-Wavelength Quantum-Well Infrared Photodetector
XIONG Da-Yuan, LI Ning, XU Wen-Lan, YIN Fei, LU Wei
Chin. Phys. Lett. 2007, 24 (11): 3283-3285 .  
Abstract   PDF(pc) (244KB) ( 365 )
We perform a theoretical study on a low dark current InGaAs/GaAs very-long-wavelength (>12μm) quantum well infrared photodetector (VLW-QWIP), based on a double barrier resonant tunnelling structure (DBRTS). The ground tunnelling state of the central quantum well (QW) of the DBRTS can resonate with the first excited bound state of the doped InGaAs QW by adjusting the structure parameters of the DBRTS. Investigation of the carrier transport performance of this device is carried out based on quantum wave transport theory. It has been shown that the dark current in this device can be significantly reduced by two orders compared to conventional InGaAs/GaAs VLW-QWIPs, while the photocurrent is almost the same as those in conventional VLW-QWIPs. This DBRTS integrated VLW-QWIP structure may stimulate the experimental investigation for VLW-QWIPs at high operation temperatures.
Quintessence Contribution to a Schwarzschild Black Hole Entropy
MA Chun-Rui, GUI Yuan-Xing, WANG Fu-Jun
Chin. Phys. Lett. 2007, 24 (11): 3286-3289 .  
Abstract   PDF(pc) (210KB) ( 460 )
The quintessence contribution to a Schwarzschild black hole entropy is thoroughly investigated by using the improved brick-wall model. It is found that due to the present of the quintessence, there are two horizons, one is the cosmological horizon, and the other is the black hole horizon. By regulating the cut-off factor ε and the thickness of the thin layer δ, we obtain that the entropy of the system is 1/4 of the sum of the areas of the two event horizons.
C-field Cosmology with Variable G in the Flat Friedmann--Robertson--Walker Model
Raj Bali, R. S.Tikekar
Chin. Phys. Lett. 2007, 24 (11): 3290-3292 .  
Abstract   PDF(pc) (191KB) ( 456 )

The C-field cosmological model based on the Hoyle--Narlikar theory with variable gravitational constant G is investigated. To obtain the deterministic value of C=dC/dt we present certain constant values for integration constants. The creation field is proportional to time. G and ρ (density) decrease with time and the universe represents an expanding universe. The creation field increases as time increases. We find C=√{1/(2πf)}t where
f>0. Thus C=1 when f=1/(2π)>0.

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