#### Current Issue

Volume 24 Issue 8
Online Date:
Original Articles
 Select Solutions of Two Kinds of Non-Isospectral Generalized Nonlinear Schrodinger Equation Related to Bose--Einstein Condensates HE Jing-Song, JI Mei, LI Yi-Shen Chin. Phys. Lett. 2007, 24 (8): 2157-2160 .   Abstract   PDF(pc) (441KB) ( 731 ) Two non-isospectral generalized nonlinear Schrodinger (GNLS) equations, which are two important models of nonlinear excitations of matter waves in Bose--Einstein condensates, are studied. Two novel transformations are constructed such that these two GNLS equations are transformed to the well-known nonlinear Schrodinger (NLS) equation, which is an isospectral equation. Therefore, once one solution of the NLS equation is provided, we can immediately obtain one solution for two GNLS equations by these transformations. Thus it is unnecessary to solve these two non-isospectral GNLS equations directly. Soliton solutions and periodic solutions are obtained for them by two transformations from the corresponding solutions of the NLS equation, which are generated by Darboux transformation.
 Select Spread and Quote-Update Frequency of the Limit-Order Driven Sergei Maslov Model QIU Tian, CHEN Guang Chin. Phys. Lett. 2007, 24 (8): 2161-2163 .   Abstract   PDF(pc) (201KB) ( 583 ) We perform numerical simulations of the limit-order driven Sergei Maslov (SM) model and investigate the probability distribution and autocorrelation function of the bid--ask spread S and the quote-update frequency U. For the probability distribution, the model successfully reproduces the power law decay of the spread and the exponential decay of the quote-update frequency. For the autocorrelation function, both the spread and the quote-update frequency of the model decay by a power law, which is consistentwith the empirical study. We obtain the power law exponent 0.54 for the spread, which is in good agreement with the real financial market.
 Select Mei Symmetry and New Conserved Quantity of Tzenoff Equations for Holonomic Systems ZHENG Shi-Wang, XIE Jia-Fang, ZHANG Qing-Hua Chin. Phys. Lett. 2007, 24 (8): 2164-2166 .   Abstract   PDF(pc) (191KB) ( 502 ) A new conserved quantity is deduced from Mei symmetry of Tzenoff equations for holonomic systems. The expression of this new conserved quantity is given, and the determining equation to induce this new conserved quantity is presented. The results exhibit that this new method is easier to find moreconserved quantities than the previously reported ones. Finally, applicationof this new result is presented by a practical example.
 Select General Properties of Thermal Entanglement in an Arbitrary-Length Heisenberg Spin Chain ZHANG Ting, WU Wei, CHEN Ping-Xing, LI Cheng-Zu Chin. Phys. Lett. 2007, 24 (8): 2167-2169 .   Abstract   PDF(pc) (214KB) ( 529 ) We investigate general properties of thermal entanglement in arbitrary-length 1D Heisenberg spin-1/2 chain based on classifications of its eigenstates. The influences of magnetic field and temperature on entanglement are qualitatively discussed and three features are presented. The conclusions hold for both bipartite and multipartite entanglement, and are in agreement with the results numerically proven by Arnesen et al. [Phys. Rev. Lett. 59(2001)017901].
 Select Berry Phase in an Entangled Spin Cluster with Five Particles YAN Xiao-Bo Chin. Phys. Lett. 2007, 24 (8): 2170-2172 .   Abstract   PDF(pc) (292KB) ( 605 ) The geometric phase, in particular the Berry phase, in an entangled state of five spin-1/2 particles is studied. A time-dependent magnetic field is applied to control the time evolution of the cluster. Using the method of algebraic dynamics, we calculate the non-adiabatic geometric phase or Berry phase and the degeneracy energy levels when the magnetic rotates around Z axis. Based on the exact analytical solutions, we show how the Berry phase of the entangled state of this cluster depends on the external magnetic field parameters ω (the angular velocity of the rotating magnetic field) and θ (the angle between the magnetic field and Z axis).
 Select Algebraic Treatment of the MIC-Kepler System in Spherical Coordinates M. T. Chefrour Chin. Phys. Lett. 2007, 24 (8): 2173-2176 .   Abstract   PDF(pc) (219KB) ( 518 ) The MIC-Kepler system is studied via the Milshtein--Strakhovenko variant of the so(2,1) Lie algebra. Green's function is constructed in spherical coordinates, with the help of the Kustaanheimo--Stiefel variables and the generators of the SO(2,1) group. The energy spectrum and the normalized wavefunctions of the bound states are obtained.
 Select Quantum Overloading Cryptography Using Single-Photon Nonlocality TAN Yong-Gang, CAI Qing-Yu, SHI Ting-Yun Chin. Phys. Lett. 2007, 24 (8): 2177-2180 .   Abstract   PDF(pc) (214KB) ( 538 ) Using the single-photon nonlocality, we propose a quantum novel overloading cryptography scheme, in which a single photon carries two bits information in one-way quantum channel. Two commutative modes of the single photon, the polarization mode and the spatial mode, are used to encode secret information. Strict time windows are set to detect the impersonation attack. The spatial mode which denotes the existence of photons is noncommutative with the phase of the photon, so that our scheme is secure against photon-number-splitting attack. Our protocol may be secure against individual attack.
 Select Efficient Three-Party Quantum Secret Sharing with Single Photons HOU Ping, LI Xi-Han, DENG Fu-Guo, , ZHOU Hong-Yu, Chin. Phys. Lett. 2007, 24 (8): 2181-2184 .   Abstract   PDF(pc) (218KB) ( 574 ) A scheme for three-party quantum secret sharing of a private key is presented with single photons. The agent Bob first prepares a sequence of single photons with two biased bases and then sends them to the boss Alice who checks the security of the transmission with measurements and produces some decoy photons by rearranging the orders of some sample photons. Alice encodes her bits with two unitary operations on the photonsand then sends them to the other agent. The security of this scheme is equivalent to that in the modified Bennett--Brassard 1984 quantum key distribution protocol. Moreover, each photon can carry one bit of the private key and the intrinsic efficiency for qubits and the total efficiency both approach the maximal value 100% when the number of the bits in the key is very large.
 Select Five-Dimensional Cosmological Model with Variable G and Λ H. Baysal, .I. Yilmaz Chin. Phys. Lett. 2007, 24 (8): 2185-2188 .   Abstract   PDF(pc) (209KB) ( 630 ) Einstein's field equations with G and Λ both varying with time are considered in the presence of a perfect fluid for five-dimensional cosmological model in a way which conserves the energy momentum tensor of the matter content. Several sets of explicit solutions in the five-dimensional Kaluza--Klein typecosmological models with variable G and Λ are obtained. The diminishment of extra dimension with the evolution of the universe for the five-dimensional model is exhibited. The physical properties of the models are examined.
 Select Statistical-Mechanical Entropies of Schwarzschild Black Hole due to Arbitrary Spin Fields in Different Coordinates DING Chi-Kun, JING Ji-Liang Chin. Phys. Lett. 2007, 24 (8): 2189-2192 .   Abstract   PDF(pc) (220KB) ( 687 ) The statistical-mechanical entropies of the Schwarzschild black hole arising from the scalar, Weyl neutrino, electromagnetic, Rarita--Schwinger and gravitational fields are investigated in the Painleve and Lemaitre coordinates. Although the metrics in the Painleve and the Lemaitre coordinates do not obviously possess the singularity as that in the Schwarzschild coordinate, we find that the entropies of the arbitrary spin fields in both the Painleve andLemaitre coordinates are exactly equivalent to that in the Schwarzschildcoordinate.
 Select Possible Approach to Improve Sensitivity of a Michelson Interferometer FU Jian, TANG Shao-Fang Chin. Phys. Lett. 2007, 24 (8): 2193-2196 .   Abstract   PDF(pc) (376KB) ( 554 ) We propose a possible approach to achieve a 1/N sensitivity of Michelson interferometer by using a properly designed random phase modulation. Different from other approaches, the sensitivity improvement does not depend on increasing optical powers or utilizing the quantum properties of light. Moreover the requirements for optical losses and the quantum efficiencies of photodetection systems may be lower than the quantum approaches and the sensitivity improvement is independent of frequency in all the detection bands.
 Select Existence and Stability of Compact-Like Discrete Breather in Discrete One-Dimensional Monatomic Chains XU Quan, TIAN Qiang Chin. Phys. Lett. 2007, 24 (8): 2197-2199 .   Abstract   PDF(pc) (198KB) ( 524 ) Compact-like discrete breathers in discrete one-dimensional monatomic chains are investigated by discussing a generalized discrete one-dimensional monatomic model. It is proven that compact-like discrete breathers exist not only in soft ψ4 potential but also in hard ψ4 potential and K4 chains. Themeasurements of compact-like discrete breathers' core in soft and hard ψ4 potential are determined by coupling parameter K4, while the measurements of compact-like discrete breathers' core in K4 chains are not related to coupling parameter K4. The stabilities of compact-like discrete breathers correlate closely to coupling parameter K4 and the boundary condition of lattice.
 Select Sandpile Dynamics Driven by Degree on Scale-Free Networks YIN Yan-Ping, ZHANG Duan-Ming, PAN Gui-Jun, HE Min-Hua Chin. Phys. Lett. 2007, 24 (8): 2200-2203 .   Abstract   PDF(pc) (229KB) ( 503 ) We introduce a sandpile model driven by degree on scale-free networks, where the perturbation is triggered at nodes with the same degree. We numerically investigate the avalanche behaviour of sandpile driven by different degrees on scale-free networks. It is observed that the avalanche area has the same behaviour with avalanche size. When the sandpile is driven at nodes with the minimal degree, the avalanches of our model behave similarly to those of the original Bak--Tang--Wiesenfeld (BTW) model on scale-free networks. As the degree of driven nodes increases from the minimalvalue to the maximal value, the avalanche distribution gradually changes from a clean power law, then a mixture of Poissonian and power laws, finally to a Poisson-like distribution. The average avalanche area is found to increase with the degree of driven nodes so that perturbation triggered on higher-degree nodes will result in broader spreading of avalanche propagation.
 Select In-Situ High Pressure Raman Spectrum and Electrical Property of PbMoO4 YU Cui-Ling, YU Qing-Jiang, GAO Chun-Xiao, LIU Bao, HAO Ai-Min, HE Chun-Yuan, HUANG Xiao-Wei, ZHANG Dong-Mei, CUI Xiao-Yan, LI Ming, LI Dong-Mei, Ma Yan-Zhang, ZOU Guang-Tian Chin. Phys. Lett. 2007, 24 (8): 2204-2207 .   Abstract   PDF(pc) (394KB) ( 646 ) In-situ high pressure Raman spectra and electrical conductivity measurements of scheelite-structure compound PbMoO4 are presented. The Raman spectrum of PbMoO4 is determined up to 26.5GPa on a powdered sample in a diamond anvil cell (DAC) under nonhydrostatic conditions. The PbMoO4 gradually experiences the transformation from the crystal to amorphous between 9.2 and 12.5GPa. The crystal to amorphous transition may be due to the mechanical deformation and the crystallographic transformation. Furthermore, the electrical conductivity of PbMoO4 is in situ measured accurately using a microcircuit fabricated on a DAC based on the van der Pauw method. The results show that the electrical conductivity of PbMoO4 increases with increases of pressure and temperature. At 26.5GPa, the electrical conductivity value of PbMoO4 at 295K is 1.93×10-4S/cm, while it raises by one order of magnitude at 430K and reached 3.33×10-3S/cm. However, at 430K, compared with the electrical conductivity value of PbMoO4 at 26.5GPa, itdrops by about two order magnitude at 7.4GPa and achieves 2.81×10-5S/cm. This indicates that the effect of pressure on the electrical conductivity of PbMoO4 is more obvious than that of temperature.
 Select Radial Excitations in the Global Colour Soliton Model WANG Bin, LIU Yu-Xin Chin. Phys. Lett. 2007, 24 (8): 2208-2211 .   Abstract   PDF(pc) (264KB) ( 431 ) With the Munczek--Nemirovsky model of the effective gluon propagator in the global colour model, we study the radially excited solitons in which one quark is excited and the other two are at the ground state. The obtained masses of the two radial excitations are comparable with the experimental data.
 Select Multi-Λ Hypernuclei in an Effective Hadronic Model LIANG Yin-Hua, GUO Hua, LIU Yu-Xin, Chin. Phys. Lett. 2007, 24 (8): 2212-2215 .   Abstract   PDF(pc) (278KB) ( 519 ) We extend the chiral hadronic model (FST) with an inclusion of Λhyperon to investigate the properties of multi-Λhypernuclei. With such an effectivehadronic model in the relativistic mean-field approximation, we accomplish the calculations with both the conventional strong Λ--Λ interaction and the weak Λ-- -->
 Select Measurement of Gamma-Rays from 11ΛB and 12ΛC FU Yuan-Yong, ZHOU Shu-Hua, T. Koike, S. Kinoshita, Y. Ma, Y. Miura, K. Miwa, Y. Miyagi, K. Shirotori, T. Suzuki, H. Tamura, K. Tsukada, M. Ukai, K. Futatsukawa, K. Hosomi, M. Kawai, M. Mimori, N. Terada, N. Maruyama, K. Aoki, H. Fujioka, Y. Kakiguchi, T. Nagae, D. Nakajima, H. Noumi, T. Takahashi, T.N. Takahashi, A. Toyota, M. Dairaku, T. Fukuda, S. Minami, W. Imoto, S. Ajimura, K. Tanida Chin. Phys. Lett. 2007, 24 (8): 2216-2218 .   Abstract   PDF(pc) (248KB) ( 551 ) From the 12C(π+, K+)12ΛC reaction, the γ-rays of 261.6±0.24keV (7/2+→to5/2+) and 1481.7±0.7keV (1/2+±5/2+) of 11ΛB, and 2667.3±2.8keV (12-→to 21-) of 12ΛC hypernuclei have been identified using a large germanium detector array Hyperball2 at K6 beam line of KEK. The observed energies of the transitions 1481.7keV and 261.6keV are significantly different from the values predicted by the shell model using the △ and SN parameters determined from the 7ΛLi data.
 Select Nuclear Potential and Fusion Cross Sections for Synthesizing Super-Heavy Elements in Di-nuclear Systems WANG Nan, LI Jun-Qing, ZHAO En-Guang, , FENG Zhao-Qing. Chin. Phys. Lett. 2007, 24 (8): 2219-2222 .   Abstract   PDF(pc) (271KB) ( 550 ) A double folding method with simplified Skyrme-type nucleon--nucleon interaction is used to calculate the nuclear interaction potential between two nuclei. The calculation is performed in tip-to-tip orientation of the two nuclei if they are deformed. Based on this method, the potential energy surfaces, the fusion probabilities and the evaporation residue cross sections for some cold fusion reactions leading to super-heavy elements within di-nuclear system model are evaluated. It is indicated that after the improvement, the exponential decreasing systematics of the fusion probability with increasing charge number of projectile on the Pb based target become better and theevaporation residue cross sections are in better agreement with theexperimental data.
 Select Dependence of Isoscaling Parameters on Nucleon--Nucleon Cross Section and Momentum-Dependent Interaction XING Yong-Zhong, HAO Huan-Feng, LIU Xiao-Bin, FANG Yu-Tian, LIU Bao-Yi Chin. Phys. Lett. 2007, 24 (8): 2223-2226 .   Abstract   PDF(pc) (255KB) ( 471 ) Influences of the isospin dependence of the in-medium nucleon--nucleon cross section and the momentum-dependent interaction (MDI) on the isotope scaling are investigated by using the isospin-dependent quantum molecular dynamics model (IQMD). The results show that both the isospin dependence of the in-medium nucleon--nucleon cross section and the momentum-dependent interaction affect the isoscaling parameters appreciably and independently. The influence caused by the isospin dependence of two-body collision is relatively larger than that from the MDI in the mean field. Aiming at exploring the implication of isoscaling behaviour, which the statistical equilibrium in the reaction is reached, the statistical properties in the mass distribution and the kinetic energy distribution of the fragments simulated by IQMD are presented.
 Select Gold Nanobelt Reorientation by Molecular Dynamics Simulation ZHANG Chun-Fang, WEI He-Lin, WANG Jian, LIU Zu-Li Chin. Phys. Lett. 2007, 24 (8): 2227-2229 .   Abstract   PDF(pc) (536KB) ( 607 ) The embedded atom method is used to study the structure stabilityof gold nanobelt. The Au nanobelts have a rectangular cross-section with<100> orientation along the x-, y- and z-axes. Free surfaces are used along the x- and y-directions, and periodic boundary condition is used along z-direction. The simulation is performed at different temperatures and cross-section sizes. Our results show that the structure stability of the Au nanobelts depends on the nanobelt size, initial orientation, boundary conditions and temperature. A critical temperature exists for Au nanobelts to transform from initial <100> nanobelt to final <110> nanobelt. The mechanism of the reorientation is the slip and spread of dislocation through the nanobelt under compressive stress caused by tensile surface-stress components.
 Select A Theoretical Study of Photoabsorption Cross Sections of Na2+ ZHANG Wei-Hua, GAO Xiang, HAN Xiao-Ying, LI Jia-Ming, Chin. Phys. Lett. 2007, 24 (8): 2230-2233 .   Abstract   PDF(pc) (227KB) ( 482 ) In the framework of quantum defect theory, we calculate photoabsorptioncross sections of Na2+. Based on our calculations, there is an absorption window in the photoabsorption cross sections of Na2+, and more than one bump above the absorption window. The calculated photoabsorption cross sections provide an explanation for the abnormal bump in the experimental measurements of Hudson, which is a long-standing experimental puzzle.
 Select Observation of Quantum Beat in Rb by Parametric Four-Wave Mixing ZHU Chang-Jun, HE Jun-Fang, XUE Bing, ZHAI Xue-Jun Chin. Phys. Lett. 2007, 24 (8): 2234-2237 .   Abstract   PDF(pc) (367KB) ( 470 ) Two coupled parametric four-wave-mixing processes in Rb atoms are studied using perturbation theory, which reveals clear evidence of the appearance of quantum beat at 608cm-1, corresponding to the energy difference of the 7s-5d states of Rb atoms, in the parametric four-wave-mixing signals. A pump--probe technique is utilized to observe the quantum beat. Time-varying characteristics of the quantum beat are investigated using time-dependent Fourier transform. The results show that the time-varying characteristics of the quantum beat not only offers a sensitive detecting method for observing the decay of atomic wave packets, but also provides a potential tool formonitoring the dissociation of molecules.
 Select Fresnel-Transform's Quantum Correspondence and Quantum Optical ABCD Law FAN Hong-Yi, HU Li-Yun Chin. Phys. Lett. 2007, 24 (8): 2238-2341 .   Abstract   PDF(pc) (221KB) ( 517 ) Corresponding to the Fresnel transform there exists a unitary operator in quantum optics theory, which could be known the Fresnel operator (FO). We show that the multiplication rule of the FO naturally leads to the quantum optical ABCD law. The canonical operator methods as mapping of ray-transferABCD matrix is explicitly shown by the normally ordered expansion of the FO through the coherent state representation and the technique of integration within an ordered product of operators. We show that time evolution of the damping oscillator embodies the quantum optical ABCD law.
 Select High-Power Diode-Side-Pumped Intracavity-Frequency-Doubled Continuous Wave 532nm Laser ZHANG Yu-Ping, ZHANG Hui-Yun, ZHONG Kai, LI Xi-Fu, WANG Peng, YAO Jian-Quan Chin. Phys. Lett. 2007, 24 (8): 2242-2244 .   Abstract   PDF(pc) (230KB) ( 675 ) An efficient and high-power diode-side-pumped cw 532nm green laser based on a V-shaped cavity geometry, and capable of generating 22.7W green radiation with optical conversion efficiency of 8.31%, has been demonstrated. The laser is operated with rms noise amplitude of less than 1% and with M2-parameter of about 6.45 at the top of the output power. This laser has the potential for scaling to much higher output power.
 Select Stimulated Raman Scattering in a Weakly Polar III-V Semiconductor: Effect of dc Magnetic Field and Free Carrier Concentration M. Singh, P. Aghamkar, P. K. Sen Chin. Phys. Lett. 2007, 24 (8): 2245-2248 .   Abstract   PDF(pc) (223KB) ( 589 ) Using the hydrodynamic model of semiconductor plasmas, we perform ananalytical investigation of stimulated Raman scattering (SRS) of an electromagnetic pump wave in a transversely magnetized weakly polarsemiconductor arising from electron-density perturbations and molecularvibrations of the medium both produced at the longitudinal optical phonon frequency. Assuming that the origin of SRS lies in the third-order susceptibility of the medium, we investigate the growth rate of Stokes mode. The dependence of stimulated Raman gain on the external dc magnetic field strength and free carrier concentration is reported. The possibility of the occurrence of optical phase conjugation via SRS is also studied. The steady-state Raman gain is found to be greatly enhanced by the presence of the strong external dc magnetic field.
 Select Evaluation of Optical Properties of Self-Frequency-Doubling Crystal Yb:GdYAl3(BO3)4 for Laser Applications LI Jing, LI Qiang, WANG Ji-Yang, ZHAO Hong-Yang Chin. Phys. Lett. 2007, 24 (8): 2249-2251 .   Abstract   PDF(pc) (232KB) ( 622 ) Yb:GdYAl3(BO3)4(Yb:GdYAB) is investigated as a new laser crystal for potential applications in self-frequency doubling. The emission and absorption properties of Yb:GdYAB crystal are studied, and the emission decay times of the upper laser level are measured. The emission cross sections are evaluated using the absorption cross section and principle of reciprocity. The other laser performance parameters, such as the minimum inversion fraction βmin, pump saturation intensity Isat and minimum pump intensity Imin, are also calculated. The results are discussed in the framework of requirements for an effective diode-pumped Yb3+ laser system. Yb:GdYAB is expected to exhibit the most useful laser properties and to be superior to Yb:YAB crystalthat has been excellent self-frequency-doubling crystal at present in many key spectroscopic parameter values.
 Select Modified Spontaneous Emission from Dye Molecules inside a Photonic Crystal Microcavity WANG Zhi-Bing, YE Yong-Hong, ZHANG Jia-Yu Chin. Phys. Lett. 2007, 24 (8): 2252-2254 .   Abstract   PDF(pc) (369KB) ( 752 ) We fabricate a photonic crystal microcavity containing Alq3 in a sandwiched structure by the self-assemble method. The angle-dependent photoluminescence (PL) spectra and the variation of the PL lifetime demonstrate the effect of the photonic band gap on the spontaneousemission of Alq3 in the photonic crystals.
 Select Design of Microstructured Optical Fibres with Elliptical Air Holes for Properties: Single-Polarization Single-Mode and Nearly Zero Ultra-Flattened Dispersion WANG Jian, LEI Nai-Guang, YU Chong-Xiu Chin. Phys. Lett. 2007, 24 (8): 2255-2258 .   Abstract   PDF(pc) (246KB) ( 662 ) By using the complex finite element method (FEM) under perfectly matched layer (PML) boundary conditions, dispersion properties of microstructured optical fibres (MOFs) with elliptical air holes are analysed by changing the pitch and sizes of air holes belonging to the inner three rings. Meanwhile, the confinement loss of the fundamental mode is engineered to achieve the single-polarization single-mode transmission. Based on this analysis, a novel design of MOFs for properties of the single-polarization single-mode and the nearly zero ultra-flattened dispersion between 1pskm-1nm-1 in the wavelength range of 1.2--1.6μm is presented for the first time.
 Select Properties of All-Solid Square-Lattice Photonic Bandgap Fibres SHI Qing, KAI Gui-Yun, WANG Zhi, YUE Yang, DU Jiang-Bing, FANG Qiang, LIUYan-Ge, LV Fu-Yun, YUAN Shu-Zhong, DONG Xiao-Yi Chin. Phys. Lett. 2007, 24 (8): 2259-2262 .   Abstract   PDF(pc) (298KB) ( 683 ) Properties of all-solid square-lattice photonic bandgap fibres are studied for the first time to the best of our knowledge. Using the plane-wave expansion method and finite element method, we investigate the mode, effective area, confinement loss and dispersion of such fibres. The simulation results demonstrate that the proposed effective mode area of all-solid square-lattice photonic bandgap fibres is 1.25 times larger than triangular-lattice ones and the confinement loss of the fibres is no more than 0.1dB/m within the bandgap.
 Select A Simple Method for Measuring Tensile Force with Piezoelectric Patch ZHANG Zhi-Wen, JIANG Zhong-Wei, Tetsuya Morisaki Chin. Phys. Lett. 2007, 24 (8): 2263-2266 .   Abstract   PDF(pc) (223KB) ( 585 ) We propose a simple method for monitoring the axial tensile and compressive force in a structure by using a piezoelectric patch with the piezoelectric impedance based measurement. A simple approximate equation for estimating the tensile force in two different conditions, which can be calculated easily if the natural frequencies in two different states are measured, is explained in detail. On another front, the natural frequency can be very easily measured by a piezoelectric element by bonding it on the measuring subject structure, because its electric impedance of piezoelement is related to the structural mechanical impedance. Furthermore, an experiment for measuring a tensile force in a simple supported beam is carried out for validating the proposed method. The results show a good accuracy in estimating the tensile force variation by the natural frequency change measured from the piezoelement.
 Select Nonlinear Effect on Focusing Gain of a Focusing Transducer with a Wide Aperture Angle LIU Ming-He, ZHANG Dong, GONG Xiu-Fen Chin. Phys. Lett. 2007, 24 (8): 2267-2271 .   Abstract   PDF(pc) (396KB) ( 531 ) Nonlinear effect on focusing gain of acoustic field radiated from a 1-MHz focusing transmitter with a wide aperture angle of 35° is theoretically and experimentally investigated. With the enhancement of nonlinearity, the focusing gains of both intensity and peak positive pressure show non-monotonic behaviour. There exist the same saturated levels at which the maximum outputs are reached and their spatial distributions are more localized. In contrast, the peak negative pressure always decreases monotonically and its spatial distribution is less localized.
 Select Effect of Temperature on the Void Growth in Pure Aluminium at High Strain-Rate Loading QI Mei-Lan, HE Hong-Liang, YAN Shi-Lin Chin. Phys. Lett. 2007, 24 (8): 2271-2273 .   Abstract   PDF(pc) (226KB) ( 492 ) With the environment temperature varying from 273K to 773K, the dynamicprocess of void growth in pure aluminium at high strain-rate loading iscalculated based on the dynamic growth equation of a void with internalpressure. The result shows that the effect of temperature on the growthof void should be emphasized. Because the initial pressure of void with gas will increase and the viscosity of materials will decrease with the rising of temperature, the growth of void is accelerated. Furthermore, material inertia restrains the growth of void evidently when the diameter exceeds 10μm. The effect of surface tension is very weak in the whole process of void growth.
 Select Boundary Layer on a Moving Wall with Suction and Injection Anuar Ishak, Roslinda Nazar, Ioan Pop Chin. Phys. Lett. 2007, 24 (8): 2274-2276 .   Abstract   PDF(pc) (188KB) ( 779 ) We investigate the boundary-layer flow on a moving permeable plate parallel to a moving stream. The governing equations are solved numerically by a finite-difference method. Dual solutions are found to exist when the plate and the free stream move in the opposite directions.
 Select Curvature Effect on Compressible Turbulent Flow over a Wavy Wall SUN Xiao-Bo, LU Xi-Yun Chin. Phys. Lett. 2007, 24 (8): 2277-2280 .   Abstract   PDF(pc) (608KB) ( 705 ) A fully developed compressible turbulent flow in a channel with a lower wavy wall and a upper plane wall is studied using large eddy simulation. We mainly attempt to deal with the curvature effect on compressible turbulent flow over the wavy wall. Some typical quantities including the mean turbulence statistics, dilatation and baroclinic terms in the enstrophy equation, turbulent kinetic energy budgets and the near-wall turbulent structures are analysed. The results obtained in this study provide physical insight into theunderstanding of the effects of curvature and compressibility on wall-bounded compressible turbulent flow.
 Select Theoretical Prediction of Asymmetrical Jet Formation in Two-Metallic-Flow Collision SHI Yi-Na, QIN Cheng-Sen Chin. Phys. Lett. 2007, 24 (8): 2281-2284 .   Abstract   PDF(pc) (326KB) ( 578 ) We develop a basic problem in ballistics and impact engineering, concerning the collision of two fluid streams with different widths. The geometrical theory of plane asymmetrical jet formation is presented and a closed form solution is given. The width and flow direction of the outgoing flows are predicted both analytically and numerically as a function of initial configuration of the incoming flows. The predictions are more accurate than the results of other analytic models and in agreement with the experimental data and numerical results over a wide range of flow widths ratio variation.
 Select Water Surface Wave in a Trough with Periodical Topographic Bottom WANG Qi, ZHANG Hua, MIAO Guo-Qing, WEI Rong-Jue Chin. Phys. Lett. 2007, 24 (8): 2285-2288 .   Abstract   PDF(pc) (410KB) ( 787 ) We present the theoretical and experimental results of water surface wave in a trough with periodical topographic bottom under parametric excitation. There are 19 steps of the same size periodically inserted into the trough. It is found that waveforms observed in the experiment are consistent with theoretical ones. Moreover, some complex and interesting phenomena arise in the experiment due to nonlinearity.
 Select Theoretical Study on the Capillary Force between an Atomic Force Microscope Tip and a Nanoparticle LI Zhao-Xia, ZHANG Li-Juan, YI Hou-Hui, FANG Hai-Ping Chin. Phys. Lett. 2007, 24 (8): 2289-2292 .   Abstract   PDF(pc) (234KB) ( 465 ) Considering that capillary force is one of the most important forces between nanoparticles and atomic force microscope (AFM) tips in ambient atmosphere, we develop an analytic approach on the capillary force between an AFM tip and a nanoparticle. The results show that the capillary forces are considerably affected by the geometry of the AFM tip, the humidity of the environment, the vertical distance between the AFM tip and the nanoparticle, as well as the contact angles of the meniscus with an AFM tip and a nanoparticle. It is found that the sharper the AFM tip, the smaller the capillary force. The analyses andresults are expected to be helpful for the quantitative imaging and manipulating of nanoparticles by AFMs.
 Select Two-Time Diffusion Process in the Porous Medium TU Tao, HAO Xiao-Jie, GUO Guo-Ping, GUO Guang-Can Chin. Phys. Lett. 2007, 24 (8): 2293-2296 .   Abstract   PDF(pc) (257KB) ( 453 ) We find that there are two time scales t and ε ln t in the asymptotic behaviour of diffusion process in the porous medium, which give us a new insight to the anomalous dimension in this problem. Further we construct an iterative method to calculate the anomalous dimension and obtain an improved result.
 Select Theoretical Computation for Non-Equilibrium Air Plasma Electrical Conductivity at Atmospheric Pressure HAN Dong, GUO Wen-Kang, XU Ping, LIANG Rong-Qing Chin. Phys. Lett. 2007, 24 (8): 2297-2300 .   Abstract   PDF(pc) (257KB) ( 498 ) Based on the Chapman--Enskog theory, we calculate the electrical conductivity of non-equilibrium air plasma in the two-temperature model. We consider different degrees of non-equilibrium, which is defined by the ratio of electronic temperature to heavy particles temperature. The method of computing the composition of air plasma is demonstrated. After calculating the electrical conductivity from electron temperature 1000K to 15000K, the present result is compared with Murphy's study [Plasma Chem. Plasma Process 15 (1994) 279] for equilibrium case. All the calculation is completed atatmospheric pressure. The present results may have potential applications in numerical calculation of non-equilibrium air plasma.
 Select Tunable Diode Laser Absorption Spectroscopy Detection of N2O at 2.1μm Using Antimonide Laser and InGaAs Photodiode ZHANG Yong-Gang, ZHANG Xiao-Jun, ZHU Xiang-Rong, LI Ai-Zhen, LIU Sheng Chin. Phys. Lett. 2007, 24 (8): 2301-2303 .   Abstract   PDF(pc) (251KB) ( 601 ) Tunable diode laser absorption spectroscopy detection of N2O around 2.1μm is demonstrated by using a homemade InGaAsSb/AlGaAsSb MQW laser diode and an InGaAs wavelength extended photodiode. Details of the devices and the detection system are described. In the system, the laser is driven by low frequency pulses with long duration to form a wavelength scan around 4741cm-1; the absorption information is obtained from the detected signal of the photodiode. By using a gas cell with 15cm path length, a detection limit is estimated to be smaller than 0.2Torr.
 Select Mechanism of Striation in Dielectric Barrier Discharge FENG Shuo, HE Feng, OUYANG Ji-Ting Chin. Phys. Lett. 2007, 24 (8): 2304-2307 .   Abstract   PDF(pc) (587KB) ( 598 ) The mechanism of striations in dielectric barrier discharge in pure neon is studied by a two-dimensional particle-in-cell/Monte Carlo collision (PIC-MCC) model. It is shown that the striations appear in the plasma background, and non-uniform electrical field resulting from ionization and the negative wall charge appear on the dielectric layer above the anode. The sustainment of striations is a non-local kinetic effect of electrons in a stratified field controlled by non-elastic impact with neutral gases. The striations in the transientdielectric barrier discharge are similar to those in dc positive column discharge.
 Select Compressible Rayleigh--Taylor Instability with Preheat in Inertial Confinement Fusion FAN Zheng-Feng, LUO Ji-Sheng, YE Wen-Hua Chin. Phys. Lett. 2007, 24 (8): 2308-2311 .   Abstract   PDF(pc) (232KB) ( 552 ) The compressible Rayleigh--Taylor instability of accelerated ablation front is analysed in consideration of the preheat effects, and the corresponding eigen-problem is solved numerically using the fourth-order accurate two-point compact difference scheme. Both the growth rate and perturbation profiles are obtained, and the obtained growth rate is close to the results of direct numerical simulation. Our results show that the growth rate is more reduced and the cutoff wave length becomes longer as preheat increases.
 Select Phase Shifts during Interaction between Two Solitons in Two-Dimensional Dusty Plasma LI Sheng-Chang, WU Li-Hua, LIN Mai-Mai, DUAN Wen-Shan Chin. Phys. Lett. 2007, 24 (8): 2312-2315 .   Abstract   PDF(pc) (263KB) ( 1003 ) The dust acoustic solitary waves propagating in two different directions in two-dimensional dusty plasma are investigated. In order to study thesoliton interactions in multi-dimensional systems, we extend the reductive perturbation method and obtain two Korteweg--de Vries equations for nonlinear waves in both the ξ and η directions, respectively. The phase shifts after collision of two solitons with arbitrary angle are given. Finally, the solution of nd up to O(ε4) order is obtained.
 Select Structures of Strong Shock Waves in Dense Plasmas JIANG Zhong-He, HE Yong, HU Xi-Wei, LV Jian-Hong, HU Ye-Min Chin. Phys. Lett. 2007, 24 (8): 2316-2318 .   Abstract   PDF(pc) (222KB) ( 635 ) Structures of strong shock waves in dense plasmas are investigated via the steady-state Navier--Stokes equations and Poisson equation. The structures from fluid simulation agree with the ones from kinetic simulation. The effects of the transport coefficients on the structures are analysed. The enhancements of the electronic heat conduction and ionic viscosity both will broaden the width of the shock fronts, and decrease the electric fields in the fronts.
 Select Formation of NiZr2 Binary Metallic Glass: Experimental and Molecular Dynamics Analyses WANG Li, ZHANG Yan-Ning, MAO Xiu-Ming, PENG Chuan-Xiao Chin. Phys. Lett. 2007, 24 (8): 2319-2322 .   Abstract   PDF(pc) (331KB) ( 533 ) The local atomic structure of an amorphous NiZr2 alloy is identified by using x-ray diffraction, transmission electron microscopy, and differential scanning calorimeter. Based on the experimental results, molecular dynamics simulation is performed to investigate the glass formation of liquid NiZr2 alloy. Somerelevant features of the pair correlation functions are in good agreement with those obtained by experiment. The pair analysis parameters are calculated, suggesting that there exist icosahedral ordering, four-fold symmetrical bipyramid and triangular-faced polyhedral units in the amorphous NiZr2 structure. The result is beneficial to open avenues toward the understanding of fundamental theoretical problems of glass formation of simple binary alloys.
 Select Compression Behaviour of Bulk Metallic Glasses and Binary Amorphous Alloy LI Gong, LIU Jing, LIU Ri-Ping Chin. Phys. Lett. 2007, 24 (8): 2323-2326 .   Abstract   PDF(pc) (240KB) ( 520 ) The compression properties of Zr41Ti14Cu12.5Ni10Be22.5, Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glasses and Ni77P23 binary amorphous alloy are investigated at room temperature up to 24GPa, 39GPa and 30.5GPa, respectively, using in-situ high pressure energy dispersive x-raydiffraction with a synchrotron radiation source. The pressure--volumerelationship of Ni77P23 amorphous alloy is consistent well with the second order Birch--Murnaghan (B-M) equation within the experimental pressure range. However, under higher pressure, the experimental data of Zr-based specimens deviate from the B-M equation. Compare to the binary amorphous alloy, less excess free volume existing in the bulk metallic glass and multi-component atomic configuration results in a two-stage relationship betweencompressibility and pressure.
 Select Evolution of Voronoi/Delaunay Characterized Micro Structure with Transition from Loose to Dense Sphere Packing AN Xi-Zhong Chin. Phys. Lett. 2007, 24 (8): 2327-2330 .   Abstract   PDF(pc) (255KB) ( 491 ) Micro structures of equal sphere packing (ranging from loose to densepacking) generated numerically by discrete element method under different vibration conditions are characterized using Voronoi/Delaunay tessellation, which is applied on a wide range of packing densities. The analysis on micro properties such as the total perimeter, surface area, and the face number distribution of each Voronoi polyhedron, and the pore size distribution in each Voronoi/Delaunay subunit is systematically carried out. The results show that with the increasing density of sphere packing, the Voronoi/Delaunay pore size distribution is narrowed. That indicates large pores to be gradually substituted by small uniformed ones during densification. Meanwhile, the distributions of face number, total perimeter, and surface area of Voronoi polyhedra at high packing densities tend to be narrower and higher, which is in good agreement with those in random loose packing.
 Select Plastic Deformation of Fine-Grained Al--Cu--Fe--(B) Icosahedral Poly-Quasicrystals at Elevated Temperature WANG Jian-Bo, MA Jia-Yan, LU Lu, XIONG Dong-Xia, ZHAO Dong-Shan, WANG Ren-Hui Chin. Phys. Lett. 2007, 24 (8): 2331-2334 .   Abstract   PDF(pc) (240KB) ( 577 ) Fine-grained Al--Cu--Fe--(B) icosahedral poly-quasicrystals (IQCs) as the main materials and fine-grained Al--Pd--Mn IQCs as the supplements, both prepared by powder metallurgy, are uniaxially deformed at various temperatures and strain rates. The systematic study shows the dependences of curves of the true stress versus true strain on several parameters, such as temperature, strain rate and grain size. For Al--Cu--Fe IQCs with grain sizes of about 10--30μm, QC-specific intra-granular softening drop appears in the deformation curves at lower temperatures and/or faster strain rates, but disappears in those curves at higher temperatures and/or slower strain rates, which suggests that the inter-granular effects such as grain-boundary slidingshould be taken into account to interpret the continuous hardening, similarly to conventional poly-crystals. For Al--Cu--Fe-B IQCs with smaller grain sizes of about 1μm and fine-grained Al--Pd--Mn IQCs with grain sizes of about 10μm, QC-specific intra-granular softening drop is absent for all the deformation curves at the possible lowest temperature and fastest strain rate. This implies that the smaller the grain size, the more the inter-granular contribution. At the same time, due to the rapid recovery caused by intense diffusion in small-sized grains, the intra-granular quasicrystal lattice reorders rapidly fromdisordering, which also inhibits the intra-granular softening drop to some extent.
 Select Enhanced Field Emission of Composite Au Nanostructured Network n Si Nanoporous Pillar Array FU Xiao-Nan, LI Xin-Jian Chin. Phys. Lett. 2007, 24 (8): 2335-2337 .   Abstract   PDF(pc) (466KB) ( 498 ) Nanocrystallites Au particles are deposited on a well-aligned silicon nanoporous pillar array (Si-NPA) surface through immersion plating to form an Au/Si-NPA composite system. It is found that a large number of Au nanoparticles are accumulated on the bottom of Si pillars to form a regular network structure. By studying the field emission properties of such an Au/Si-NPA composite system, we find that the Au/Si-NPA exhibits good field emission properties, with staring field about 2V/μm and emission current density 67μA/cm2 at 7.59V/μm. The enhanced field emission can be deduced from the unique morphology and structure of Au/Si-NPA.
 Select Measurement and Analysis of Spall Characteristics of High-Pure Aluminium at One-Dimensional Strain Loading QI Mei-Lan, HE Hong-Liang, YAN Shi-Lin Chin. Phys. Lett. 2007, 24 (8): 2338-2340 .   Abstract   PDF(pc) (228KB) ( 559 ) With an impact velocity varying from 196.9m/s to 317.9m/s and ratios of flyer/sample thickness of 2:4 and 3:6, the free-surface velocity profiles of the shock compressed high purity aluminium (HPA 99.999%) samples are measured with a velocity interferometer system for any reflector. Based on the vibrating features of the velocity profiles, the damage behaviour of HPA is analysed. The results indicate that the vibrating amplitude increases with increasing shock stress, and the subsequent reverberations describing the spall become more obvious. When the shock stress in the material is below a critical or smaller than the threshold level, the free-surface velocity profile replicates virtually the form of the compression pulse inside the sample. When the impact stress exceeds a critical value (1.4GPa), the micro damage wouldappear, and the free-surface velocity profile changes significantly, showing a series of short-duration reverberations in the profile. When the impact stress exceeds the threshold of damage, a compressive disturbance called the spall pulse'' appears in the free-surface velocity profile, and the subsequent reverberation becomes regular again. The measured spall strength of HPA is much higher than those of commercially pure aluminium reported in many references. In addition, the strength of HPA is similar to that of single-crystal aluminium.
 Select Shock Induced Emission from Sapphire in High-Pressure Phase of Rh2O3 (II) Structure ZHANG Dai-Yu, LIU Fu-Sheng, HAO Gao-Yu, SUN Yu-Huai Chin. Phys. Lett. 2007, 24 (8): 2341-2344 .   Abstract   PDF(pc) (253KB) ( 567 ) A distinct optical emission from the Rh2O3 (II) structural sapphire is observed under shock compression of 125, 132, and 143GPa. The emission intensity continuously increases with the thickness of shocked sapphire. The colour temperature is determined to be about 4000K, which is obviously smaller than the reported value of the alpha phase alumina at the pressures below 80GPa. The present results suggest that the structural transformation will cause anobvious change of optical property in sapphire.
 Select Relationship between Spreading Rate and Wetting Behaviour of Oil on Surface of Surfactant Solution YE Xi, CHENG Yang, HUANG Xue-Dong, MA Hong-Ru Chin. Phys. Lett. 2007, 24 (8): 2345-2348 .   Abstract   PDF(pc) (227KB) ( 663 ) We report a systematic investigation of the spreading of a polydimethylsiloxane oil layer on flat surfaces of solution containing anionic surfactant of sodium dodecylsulfate. The experiment reveals that different wetting behaviours of the oil follow different spreading rates. In the case of complete wetting, it obeys a 0.75 power law, while in the pseudopartial wetting it follows a non-power law. The results can well be explained by a new simple theory of spreading. The theory further predicts that for a complete wetting state there exists another spreading rate.
 Select Capillary Adhesion of Microbeams: Finite Deformation Analysis LIU Jian-Lin, FENG Xi-Qiao Chin. Phys. Lett. 2007, 24 (8): 2349-2352 .   Abstract   PDF(pc) (240KB) ( 582 ) Capillary force may cause adhesion of devices at micro- and nano-scales.Considering the fact that large deformation is often involved in adhesion of microbeams, we analysed the capillary adhesion of two beams using finite deformation elasticity theory. The critical adhesion condition can be obtained from the present method as a function of the bending stiffness, Young's contact angle, the spacing of the two beams as well as the surface tensions of the solid and liquid phases. The solution for the capillary adhesion of a beam with a rigid substrate is also given. The results from the finite deformation analysis are compared with that of infinitesimal deformation method in order to show the necessity of accounting for the nonlinear effect associated with large deflection. The method adopted in this study can also be used to solve other adhesion problems associated with van der Waals force or electrostatic force.
 Select Dislocation Reduction Mechanisms in Gallium Nitride Films Grown by Canti-Bridge Epitaxy Method XING Zhi-Gang, WANG Jing, PEI Xiao-Jiang, WAN Wei, CHEN Hong, ZHOU Jun-Ming Chin. Phys. Lett. 2007, 24 (8): 2353-2356 .   Abstract   PDF(pc) (859KB) ( 658 ) By using the special maskless V-grooved c-plane sapphire as the substrate, we previously developed a novel GaN LEO method, or the so-called canti-bridge epitaxy (CBE), and consequently wing-tilt-free GaN films were obtained with low dislocation densities, with which all the conventional difficulties can be overcome [J. Vacuum Sci. Technol. B 23 (2005) 2476]. Here the evolution manner of dislocations in the CBE GaN films is investigated using transmission electron microscopy. The mechanisms of dislocation reduction are discussed.Dislocation behaviour is found to be similar to that in the conventional LEO GaN films except the enhanced dislocation-combination at the coalescence boundary that is a major dislocation-reduction mechanism for the bent horizontal-propagating dislocations in the CBE GaN films. The enhancement of this dislocation-combination probability is believed to result from the inclined shape and the undulate morphology of the sidewalls, which can be readily obtained in a wide range of applicable film-growth conditions during the GaN CBE process. Further development of the GaN CBE method and better crystal-quality of the GaN film both are expected.
 Select Annealing Behaviour of Helium Bubbles in Titanium Films by Thermal Desorption Spectroscopy and Positron Beam Analysis LIU Chao-Zhuo, ZHOU Zhu-Ying, SHI Li-Qun, WANG Bao-Yi, HAOXiao-Peng, ZHAO Guo-Qing Chin. Phys. Lett. 2007, 24 (8): 2357-2360 .   Abstract   PDF(pc) (246KB) ( 826 ) Helium-containing Ti films are prepared using magnetron sputtering in the helium--argon atmosphere. Isochronal annealing at different temperatures for an hour is employed to reveal the behaviour of helium bubble growth. Ion beam analysis is used to measure the retained helium content. Helium can release largely when annealing above 970K. A thermal helium desorption spectroscopy system is constructed for assessment of the evolution of helium bubbles in the annealed samples by linear heating (0.4K/s) from room temperature to 1500K. Also, Doppler broadening measurements of positron annihilation radiation spectrum are performed by using changeable energy positron beam. Bubble coarsening evolves gradually below 680K, migration and coalescence of small bubbles dominates in the range of 680--970K, and the Ostwald ripening mechanism enlarges the bubbles with a massive elease above 970K.
 Select First-Principles Studies on Electronic Structures and Absorption Spectra of PbWO4 Crystals with Defect [VPb2---VO2+ --VPb2-]2- LIU Ting-Yu, ZHANG Qi-Ren, ZHUANG Song-Lin Chin. Phys. Lett. 2007, 24 (8): 2361-2364 .   Abstract   PDF(pc) (253KB) ( 386 ) Electronic structures and absorption spectra for perfect PbWO4 (PWO) crystals and the crystal containing aggregated defect[VPb2---VO2+--VPb2-]2-have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing the aggregated defect [VPb2---VO2+--VPb2-]2- exhibit two absorption bands peaking at 1.90eV (650nm) and 3.02eV(410nm). It is predicted that the 420 and 680nm absorption bands are related to the existence of the aggregated defect [VPb2---VO2+--VPb2-]2- in the PWOcrystal.
 Select Inelastic Electron Transport in Monoatomic Wires ZHANG Jin, CHEN Jing-Zhe, CHEN Qing, REN Shang-Fen, HAN Ru-Shan Chin. Phys. Lett. 2007, 24 (8): 2365-2368 .   Abstract   PDF(pc) (263KB) ( 574 ) Based on non-equilibrium Green's function theory and density functionaltheory, we investigate the vibrational property and electron--phonon (el--ph) interaction induced inelastic scattering in electron transport through metallic monoatomic wires.
 Select Design and First-principles Study of a Fullerene Molecular Device OUYANG Fang-Ping, XU Hui Chin. Phys. Lett. 2007, 24 (8): 2369-2372 .   Abstract   PDF(pc) (967KB) ( 774 ) By using open-ended armchair (6, 6) single-wall carbon nanotubes as electrodes, we investigate the electron transport properties of an all-carbon molecular junction based on the C82 molecule. We find the most stable system among different isomers by performing structural optimization calculations of the C82 isomers and the C82 extended molecules. Thecalculated results show that the C82--C2(3) isomer and the C82 extended molecule with C82--C2v isomer are most stable. For the all-carbon hybrid system consisting of C82--C2v extended molecules, it is shown that theLandauer conductance can be tuned over several orders of magnitude bothby changing the distance between two electrodes and by changing theorientation of the C82 molecule or rotating one of the tubes around the symmetry axis of the system at a fixed distance. Also, we find the most stable distance between two electrodes from the total energy curve. This fact could make this all-carbon molecular system a possible candidate for a nanoelectronic switch. Moreover, we interpret the conductance mechanism for such a molecular device.
 Select Temperature-Dependent Electron Transport in In0.5Ga0.5P/GaAs Grown by MOVPE S. Acar, A. Yildiz, M. Kasap, M. Bosi Chin. Phys. Lett. 2007, 24 (8): 2373-2375 .   Abstract   PDF(pc) (204KB) ( 540 ) Hall effect measurements in undoped In0.5Ga0.5P/GaAs alloy grown by metal organic vapour-phase epitaxy (MOVPE) have been carried out in the temperature range 15--350K. The experimental results are analysed using a two-band model including conduction band transport calculated using an iterative solution of the Boltzmann equation. A good agreement was obtained between theory and experiment. The impurity contents of In0.5Ga0.5P/GaAs alloy, such as donor density ND, acceptor density NA and donor activationenergy εD, were also determined.
 Select Linear and Nonlinear Intersubband Optical Absorptions and Refractive Index Changes in InGaN Strained Single Quantum Wells: Strong Built-in CHI Yue-Meng, SHI Jun-Jie Chin. Phys. Lett. 2007, 24 (8): 2376-2379 .   Abstract   PDF(pc) (261KB) ( 850 ) Considering the strong built-in electric field (BEF) effects due to the spontaneous and piezoelectric polarizations, the intersubband optical absorptions and refractive index changes for an InxGa1-xN/AlyGa1-yN strained single quantum well are studied theoretically within the framework of the density matrix method and effective-mass approximation. The linear, third-order nonlinear and total absorption coefficients and refractive indexchanges are calculated as a function of the incident optical intensity and photon energy. Our results show that both the incident optical intensity and the strong BEF have great influence on the total absorptions and refractive index changes. The results are significant for designing some important photodetectors and the photonic crystal devices with adjustable photonic band structures.
 Select Time-Resolved Photoluminescence Spectroscopy: A Novel Technique for Determination of Luminescence of Quantum Dots ZHENG Zhu-Hong, SHEN De-Zhen Chin. Phys. Lett. 2007, 24 (8): 2380-2382 .   Abstract   PDF(pc) (200KB) ( 637 ) The time-resolved photoluminescence (PL) spectroscopy measured by thegradually increasing start delay time is utilized as a tool for the determination of the luminescence of quantum dots (QDs). The luminescence evolution of self-assembled CdSe QDs during the luminescence decay is fully revealed in terms of the experiment technique. The characteristic narrow luminescence lines of self-assembled CdSe QDs are obtained with increasing start delay time.
 Select Coherent Tunnelling in Coupled Quantum Wells under a Uniform Magnetic Field GONG Jian, YANG Fu-Hua, FENG Song-Lin Chin. Phys. Lett. 2007, 24 (8): 2383-2386 .   Abstract   PDF(pc) (251KB) ( 541 ) Coherent tunnelling is studied in the framework of the effective mass approximation for an asymmetric coupled quantum well. The Hartree potential due to the electron--electron interaction is considered in our calculation. The effects of the longitudinal and transverse magnetic field on coherent tunnelling characteristics are discussed. It has been found that the external field plays an important role in modulating the electron states.
 Select Dielectric and Ferroelectric Properties of La-Doped SrBi2Nb2O9 Ceramics LIU Guo-Zhen, GU Hao-Shuang, WANG Chun-Chang, QIU Jie, LU Hui-Bin Chin. Phys. Lett. 2007, 24 (8): 2387-2389 .   Abstract   PDF(pc) (542KB) ( 530 ) Sr1-xLa2x/3Bi2Nb2O9 (0 ≤x≤ 0.2) ceramic samples are prepared by the solid-state reaction method. Their structure, dielectric and ferroelectric properties are investigated. The incorporation of La3+ improves the densification and decreases the grain size of the ceramics without changing the crystal structure. The remanent polarization 2Pr increases with increasing La content and reaches a maximum value of 22.8μC/cm2 at x=0.125, which is approximately 60% larger than that of pure SrBi2Nb2O9. The Curie temperature keeps almost unchanged at a value of about 440°C. The relationship between doping and the ferroelectric and dielectric properties are discussed.
 Select Electroluminescence of Si Nanocrystal-Doped SiO2 CHEN Dan, XIE Zhi-Qiang, WU Qian, ZHAO You-Yuan, LU Ming Chin. Phys. Lett. 2007, 24 (8): 2390-2393 .   Abstract   PDF(pc) (218KB) ( 503 ) We perform a comparative study on the electroluminescence (EL) andphotoluminescence (PL) of Si nanocrystal-doped SiO2 (nc-Si:SiO2) and SiO2, and clarify whether the contribution from Si nanocrystals in the EL of nc-Si:SiO2 truly exists. The results unambiguously indicate the presence of EL of Si nanocrystals. The difference of peak positions between the EL and PLspectra are discussed. It is found that the normal method of passivation to enhance the PL of Si nanocrystals is not equally effective for the EL, hence new methods need to be explored to promote the EL of Si nanocrystals.
 Select An Electroluminescence Delay Time Model of Bilayer Organic Light-Emitting Diodes LI Hong-Jian, ZHU Ru-Hui, LI Xue-Yong, YANG Bing-Chu Chin. Phys. Lett. 2007, 24 (8): 2394-2397 .   Abstract   PDF(pc) (264KB) ( 930 ) Based on the mechanism of injection, transport and recombination of the charge carriers, we develop a model to calculate the delay time of electroluminescence (EL) from bilayer organic light emitting diodes. The effect of injection, transport and recombination processes on the EL delay time is discussed, and the relationship between the internal interface barrier and the recombination time is revealed. The results show that the EL delay time is dominated by the recombination process at lower applied voltage and by the transport process at higher applied voltage. When the internal interface barrier varies from 0.15eV to 0.3eV, the recombination delay time increases rapidly, while the internal interface barrier exceeds about 0.3eV, the dependence of the recombination delay time on applied voltage is almostundiversified, which may serve as a guideline for designing of a high-speed EL response device.
 Select Luminescence with Local Distribution and Its Possible Mechanism in Zinc Oxide Micro-Crystallites SHI Yuan-Yuan, TIAN Ke, LIN Bi-Xia, FU Zhu-Xi Chin. Phys. Lett. 2007, 24 (8): 2398-2400 .   Abstract   PDF(pc) (674KB) ( 599 ) The spatial luminescence distribution in the ZnO micro-crystallite films deposited on silicon substrates by CVD at room temperature is investigated by the cathedoluminescence (CL) image. It has been observed that the CL image of the samples constitutes a certain pattern. The UV emission pattern projective to the (0001) face of ZnO grains consists of a series of lines nearby the grain boundaries .The included angles between any two adjacent lines are almost 120°. What is more, some luminescent lines form a close hexagon similar to ZnOcrystalline structure. Such a local distribution property shows that the UV emission on as-grown ZnO crystallite should be due to some localdefects congregated to {1010} facets of ZnO grain rather than free exciton recombination.
 Select Influence of Phase Transition of Starting Materials on Growth of GaN Nanomaterials by CVD ZHAO Mei, CHEN Xiao-Long, WANG Wen-Jun, ZHANG Zhi-Hua, XU Yan-Ping Chin. Phys. Lett. 2007, 24 (8): 2401-2404 .   Abstract   PDF(pc) (852KB) ( 676 ) Ground by mechanical ball milling under certain conditions, β-Ga2O3 powders can transit to ε-Ga2O3 ones. As starting materials, Ga2O3 powders treated bydifferent methods are used to prepare GaN nanomaterials. It is found that the morphologies of GaN nanomaterials are quite different due to the phase transition of Ga2O3 from β-Ga2O3 to ε-Ga2O3.
 Select Preparation and Visible Light Photocatalytic Activity for Photocatalyst of Permeable Glass Membrane/TiO2 Doped with Co HU Ke-Yan, CUI Ping, CHEN Xiao-Ming, ZHANG Min, LI Yong Chin. Phys. Lett. 2007, 24 (8): 2405-2407 .   Abstract   PDF(pc) (566KB) ( 474 ) The photocatalyst of permeable glass membrane/TiO2 doped with Co (permeable glass membrane/TiO2 doped with Co) is prepared by the sol-gel method. The morphology and phase of the samples are determined by the field emission scanning electron microscopy (FESEM) and x-ray diffraction experiment, respectively. The photocatalytic results show that the photocatalyst is sensitive to the visible light and exhibits excellent photocatalytic activity of photodegradation methylene blue. The photocatalytic mechanism is also discussed.
 Select Controlled Growth of Zn-Polar ZnO Films on Al-Terminated α-Al2O3(0001) Surface by Using Wurtzite MgO Buffer YUAN Hong-Tao, LIU Yu-Zi, WANG Xi-Na, LI Han-Dong, WANG Yong, ZENG Zhao-Quan, MEI Zeng-Xia, DU Xiao-Long, JIA Jin-Feng, XUE Qi-Kun, ZHANG Ze Chin. Phys. Lett. 2007, 24 (8): 2408-2411 .   Abstract   PDF(pc) (757KB) ( 426 ) The controlled growth of Zn-polar ZnO films on Al-terminated αAl2O3 (0001) substrates is investigated by the radio-frequency plasma-assisted molecular beam epitaxy method. Prior to the growth, αAl2O3 (0001) surface is modified by an ultrathin MgO layer, which serves as a uniform template for epitaxy ofZn-polar ZnO films. The microstructures of ZnO/MgO/Al2O3 interface are investigated by in-situ reflection high-energy electron diffraction observations and ex-situ high-resolution transmission electron microscopy characterization. It is found that under Mg-rich condition, the achievement of the wurtzite MgO ultrathin layer plays a key role in the subsequent growth of Zn-polar ZnO. Aninterfacial atomic model is proposed to explain the mechanism of polarity selection of both MgO and ZnO films.
 Select Cubic BN Sintered with Al under High Temperature and High Pressure ZHAO Yu-Cheng, WANG Ming-Zhi Chin. Phys. Lett. 2007, 24 (8): 2412-2414 .   Abstract   PDF(pc) (844KB) ( 719 ) Sintering of cubic boron nitride (cBN) with addition of Al is carried out in the temperature range 1300--1500°C and under the pressure 5.5GPa. When sintered at 1300°C, a weak diffractive peak of hexagonal BN (hBN) is observed in the Al-cBN sample, indicating the transformation from cBN to hBN. No nitrides or borides of Al are observed, which indicated that Al does not react with cBN obviously. When the sintering temperature is increased to 1400°C, the diffractive peak of hBN disappears and new phases of AlN and AlB2 are observed, due to reactions between Al and cBN. When the sinteringtemperature is further increased to 1500°C, the contents of AlN and AlB2 phases increase and the Al phase disappears completely.
 Select Controlling Spiral Dynamics in Excitable Media by a Weakly Localized Pacing LI Bing-Wei, SUN Li-Li, CHEN Bin, YING He-Ping Chin. Phys. Lett. 2007, 24 (8): 2415-2418 .   Abstract   PDF(pc) (388KB) ( 527 ) Spiral dynamics controlled by a weakly localized pacing around the spiral tip is investigated. Numerical simulations show two distinct characteristics when the pacing is applied with the weak amplitude for suitable frequencies: for a rigidly rotating spiral, a transition from rigid rotation to meandering motion is observed, and for unstable spiral waves, spiral breakup can be prevented.Successfully preventing spiral breakup is relevant to the modulation of the tip trajectory induced by a localized pacing.
 Select GaN MOS-HEMT Using Ultra-Thin Al2O3 Dielectric Grown by Atomic Layer Deposition YUE Yuan-Zheng, HAO Yue, FENG Qian, ZHANG Jin-Cheng, MA Xiao-Hua, NI Jin-Yu Chin. Phys. Lett. 2007, 24 (8): 2419-2422 .   Abstract   PDF(pc) (277KB) ( 1194 ) We report a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with atomic layer deposited (ALD) Al2O3 gate dielectric. Based on the previous work [Appl. Phys. Lett. 86 (2005) 063501] of Ye et al. by decreasing the thickness of the gate oxide to 3.5nm and optimizing the devicefabrication process, the device with maximum transconductance of 150mS/mm is produced and discussed in comparison with the result of 100mS/mm of Ye et al. The corresponding drain current density in the 0.8-μm-gate-length MOS-HEMT is 800mA/mm at the gate bias of 3.0V. The gate leakage is two orders of magnitude lower than that of the conventional AlGaN/GaN HEMT.The excellent characteristics of this novel MOS-HEMT device structure with ALD Al2O3 gate dielectric are presented.
 Select Stable Electron Field Emission from CeO2 Nanowires by Hydrothermal Method FU Xing-Qiu, FENG Ping, WANG Chong, WANG Tai-Hong Chin. Phys. Lett. 2007, 24 (8): 2423-2425 .   Abstract   PDF(pc) (447KB) ( 832 ) CeO2 nanowires are successful synthesized by hydrothermal method and their field emission (FE) properties are investigated. The turn-on electric field is 5.8V/μm at an emitter--anode spacing of 700μm. The FE current is stable and the current fluctuations are less than 3% over 5h. All the plotted Fowler--Nordheim curves yield straight lines, which are in agreement with the Fowler--Nordheim theory. The relationship between the field enhancement factor β and the emitter--anode spacing d follows a universal equation. Our resultsimply that the CeO2 nanowires are promising materials for fabricating FE cathodes.
 Select Protein Folding under Mediation of Ordering Water: an Off-Lattice Go--Like Model Study ZUO Guang-Hong, HU Jun, FANG Hai-Ping, Chin. Phys. Lett. 2007, 24 (8): 2426-2429 .   Abstract   PDF(pc) (313KB) ( 564 ) Water plays an important role in the structure and function of biomolecules. Water confined at the nanoscale usually exhibits phenomena not seen in bulk water, including the ice-like ordering structure on the surfaces of many substrates. We investigate the behaviour of protein folding in which the proteins are assumed in an environment with ordering water by using of anoff-lattice Go--like model. It is found that in the physiological temperature, both the folding rate and the thermodynamic stability of the protein are greatly promoted by the existence of ordering of water.
 Select Macro-Behaviour of Agents' Opinion under Influence of an External Field CHANG Yun-Feng, CAI Xu Chin. Phys. Lett. 2007, 24 (8): 2430-2433 .   Abstract   PDF(pc) (258KB) ( 587 ) We propose a model to study the evolution of opinion under the influence of an external field on small world network. The macro-behaviour of agents' opinion and the relative change rate as time elapses are studied. The external field is found to play an important role in making the opinion s(t) balance or increase, and without the influence of the external field, the relative change rate γ(t) shows nonlinear increasing behaviour as time runs. What is more, this nonlinear increasing behaviour is independent of the initial condition, the strength of the external field and the time that we cancel theexternal field. The results may reflect some phenomena in our society, such as the function of the macro-control in China or the mass media in our society.
 Select Power-Law Tail in the Chinese Wealth Distribution DING Ning, WANG You-Gui Chin. Phys. Lett. 2007, 24 (8): 2434-2436 .   Abstract   PDF(pc) (222KB) ( 786 ) We analyse the data from the recently published lists of the richest Chinese from the year 2003 to 2005. The results confirm that in these years the wealth is distributed according to a power law with exponents between 1.758 and 2.285 in the high end. The power distribution is found to be quite robust although the persons in the list change drastically and the wealth increases rapidly. The relation between the wealth and the absolute change of wealth rejects the notion that the wealth evolution is a multiplicative stochastic process.
 Select Improvement of Synchronizability of Scale-Free Networks GUO Qiang, LIU Jian-Guo, WANG Rui-Li, CHEN Xing-Wen, YAO Yu-Hua Chin. Phys. Lett. 2007, 24 (8): 2437-2440 .   Abstract   PDF(pc) (298KB) ( 616 ) We investigate the factors that affect synchronizability of coupled oscillators on scale-free networks. Using the memory Tabu search (MTS) algorithm, we improve the eigen-ratio Q of a coupling matrix by edge intercrossing. The numerical results show that the synchronization-improved scale-free networks should have distinctive both small average distance and larger clustering coefficient, which are consistent with some real-world networks. Moreover, the synchronizability-improved networks demonstrate the disassortative coefficient.
 Select Measuring Grüneisen Parameter of Lead by High Pressure-Jump Method HUANG Dai-Hui, LIU Xiu-Ru, SU Lei, HU Yun, LV Shi-Jie, LIU Hai-Long, HONG Shi-Ming Chin. Phys. Lett. 2007, 24 (8): 2441-2443 .   Abstract   PDF(pc) (228KB) ( 675 ) Using the technology of pressure jump, variations of temperature associated with pressure from 2.4GPa to 4.6GPa are measured for lead. The Grüneisen parameter is calculated from the thermodynamic relation γ= (Ks/T) (∂T/ ∂P)s, in which substitution of △T/△P for ∂T/∂P at median pressure is strictly justified. The correction of temperature change is carried out by analysing theexperimental data, which makes the process more approaching to anadiabatic condition. The calculated values of △T/△P and γ gradually decrease with the increasing pressure. The decrease trend is consistent with the previous work. The γ values in the range of 2--3GPa are averagely higher than the results of Ramakrishnan et al., indicating the effect of temperature correction. The improved method is promising for measurements of Grüneisen parameter to higher pressure range.
 Select Alternative Solutions to Bianchi Type-I Cosmology YI Ying, LI Fang-Yu Chin. Phys. Lett. 2007, 24 (8): 2444-2447 .   Abstract   PDF(pc) (184KB) ( 441 ) We present a class of new exact solutions in string cosmology theory, and the solutions describe a homogeneous but anisotropic plane-symmetric string universe within the framework of Bianchi type-I cosmology. Some solutions previously discussed are included in the class of exact solutions as the special cases. Our result may provide further quantitative description and theoretical basis for the string cosmology model.
 Select Dirac Particles' Hawking Radiation from a Schwarzschild Black Hole HE Xiao-Kai, LIU Wen-Biao Chin. Phys. Lett. 2007, 24 (8): 2448-2450 .   Abstract   PDF(pc) (212KB) ( 379 ) Considering energy conservation and the backreaction of particles to spacetime, we investigate the massless/massive Dirac particles' Hawkingradiation from a Schwarzschild black hole. The exact expression of the emission rate near the horizon is obtained and the result indicates that Hawking radiation spectrum is not purely thermal. The result obtained is consistent with the results obtained before. It satisfies the underlying unitary theory and offers a possible mechanism to explain the information loss paradox. Whereas the improved Damour--Ruffini method is more concise and understandable.
 Select Convection-Dominated Accretion Flows with Radiative Cooling LI Shuang-Liang, XUE Li, LU Ju-Fu Chin. Phys. Lett. 2007, 24 (8): 2451-2454 .   Abstract   PDF(pc) (248KB) ( 535 ) By numerically solving the set of basic equations describing black hole accretion flows with low accretion rates, we show that although the dynamical structure of these flows is essentially unaffected by radiative processes in comparison with the case in which the radiation is not considered, the radiative cooling can be more important than the advective cooling in the flow's convection-dominated zone, and this result may have implications to distinguish observationally convection-dominated accretion flows from advection-dominated accretion flows.
 Select Bianchi Type-I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in General Relativity BALI Raj, PAREEK Umesh Kumar, PRADHAN Anirudh Chin. Phys. Lett. 2007, 24 (8): 2455-2458 .   Abstract   PDF(pc) (212KB) ( 703 ) Bianchi type-I massive string cosmological model with magnetic field of barotropic perfect fluid distribution through the techniques used by Latelier and Stachel is investigated. To obtain the deterministic model of the universe, it is assumed that the universe is filled with barotropic perfect fluid distribution. The magnetic field is due to electric current produced along the x-axis with infinite electrical conductivity. The behaviour of the model in the presence and absence of magnetic field together with other physical aspects is further discussed.
 Select Cosmological Constant or Variable Dark Energy? XU Li-Xin, ZHANG Cheng-Wu, LIU Hong-Ya Chin. Phys. Lett. 2007, 24 (8): 2459-2462 .   Abstract   PDF(pc) (228KB) ( 500 ) Selection statics of the Akaike information criterion (AIC) model and the Bayesian information criterion (BIC) model are applied to the Λ-cold dark matter (ΛCDM) cosmological model, the constant equation of state of dark energy, w=constant, and the parametrized equation of state of dark energy, w(z)=w_0+w_1 z/(1+z), to determine which one is the better cosmological model to describe the evolution of the universe by combining the recentcosmic observational data including Sne Ia, the size of baryonic acoustic oscillation (BAO) peak from SDSS, the three-year WMAP CMB shift parameter. The results show that AIC, BIC and current datasets are not powerful enough to discriminate one model from the others, though odds suggest differences between them.
83 articles