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Volume 26 Issue 6
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GENERAL
 Select Clustering Effect on the Evolution of Cooperation in a Herding Snowdrift Game CHEN Guang, QIU Tian, WU Xiao-Run Chin. Phys. Lett. 2009, 26 (6): 060201 .   DOI: 10.1088/0256-307X/26/6/060201 Abstract   PDF(pc) (284KB) ( 599 ) We study the evolution of cooperation for two cluster breaking mechanisms in a herding snowdrift game. The cooperative behavior is observed to be related to the cluster size. A negative dependence of the payoff parameter r on cooperative behavior is discovered. For a low r, herding helps promote the cooperation, whereas for a high r, herding tends to prevent cooperative behavior.
 Select A Variational Iteration Solving Method for a Class of Generalized Boussinesq Equations MO Jia-Qi Chin. Phys. Lett. 2009, 26 (6): 060202 .   DOI: 10.1088/0256-307X/26/6/060202 Abstract   PDF(pc) (344KB) ( 1091 ) We study a generalized nonlinear Boussinesq equation by introducing a proper functional and constructing the variational iteration sequence with suitable initial approximation. The approximate solution is obtained for the solitary wave of the Boussinesq equation with the variational iteration method.
 Select Preparation of Entanglement of Atoms and of Photons via Cavity Input-Output Process ZHOU Yan-Li, YANG Li-Jia, DAI Hong-Yi, LI Cheng-Zu Chin. Phys. Lett. 2009, 26 (6): 060301 .   DOI: 10.1088/0256-307X/26/6/060301 Abstract   PDF(pc) (289KB) ( 487 ) We propose a method to prepare multipartite entangled states such as cluster states and graph states based on the cavity input-output process and single photon measurement. Two quantum gates, a controlled phase gate and a fusion gate between two atoms trapped in respective cavities, are proposed to prepare atomic cluster states and graph states with one and two dimensions. We also introduce a scheme that can generate an arbitrary multipartite photon cluster state which uses two coherent states as a qubit basis.
 Select Casimir Force of Piston Systems with Arbitrary Cross Sections under Different Boundary Conditions XIONG Ai-Min, CHEN Xiao-Song Chin. Phys. Lett. 2009, 26 (6): 060302 .   DOI: 10.1088/0256-307X/26/6/060302 Abstract   PDF(pc) (216KB) ( 421 ) We study the Casimir force between two pistons under different boundary conditions inside an infinite cylinder with arbitrary cross section. It is found that the attractive or repulsive character of the Casimir force for a scalar field is determined only by the boundary condition along the longitudinal direction and is independent of the cross section, transverse boundary conditions and the mass of the field. Under symmetric Dirichlet-Dirichlet, Neumann-Neumann and periodic longitudinal boundary conditions the Casimir force is alwaysattractive, but is repulsive under non-symmetric Dirichlet-Neumann and anti-periodic longitudinal boundary conditions. The Casimir force of the electromagnetic field in an ideal conductive piston is also investigated. This force is always attractive regardless of the shape of the cross section and the transverse boundary conditions.
 Select Locally Accessible Information from Multipartite Ensembles SONG Wei Chin. Phys. Lett. 2009, 26 (6): 060303 .   DOI: 10.1088/0256-307X/26/6/060303 Abstract   PDF(pc) (196KB) ( 423 ) We present a universal Holevo-like upper bound on the locally accessible information for arbitrary multipartite ensembles. This bound allows us to analyze the indistinguishability of a set of orthogonal states under local operations and classical communication. We also derive the upper bound for the capacity of distributed dense coding with multipartite senders and multipartite receivers.
 Select New Representation of Rotation Operator and Its Application WANG Shuai, JIANG Ji-Jian, LI Hong-Qi Chin. Phys. Lett. 2009, 26 (6): 060304 .   DOI: 10.1088/0256-307X/26/6/060304 Abstract   PDF(pc) (222KB) ( 550 ) By employing the technique of integration within an ordered product of operators, we derive natural representations of the rotation operator, the two-mode Fourier transform operator and the two-mode parity operator in entangled state representations. As an application, it is proved that the rotation operator constructed by the entangled state representation is a useful tool to solve the exact energy spectra of the two-mode harmonic oscillators with coordinate-momentum interaction.
 Select Partial Hermitian Conjugate Separability Criteria for Pure Quantum States ZHAO Xin, WU Hua, LI Yan-Song, LONG Gui-Lu, Chin. Phys. Lett. 2009, 26 (6): 060305 .   DOI: 10.1088/0256-307X/26/6/060305 Abstract   PDF(pc) (211KB) ( 698 ) We propose a criterion for the separability of quantum pure states using the concept of a partial Hermitian conjugate. It is equivalent to the usual positive partial transposition criteria, with a simple physical interpretation.
 Select A Lower Bound on Concurrence LIU Li-Guo, TIAN Cheng-Lin, CHEN Ping-Xing, YUAN Nai-Chang Chin. Phys. Lett. 2009, 26 (6): 060306 .   DOI: 10.1088/0256-307X/26/6/060306 Abstract   PDF(pc) (270KB) ( 456 ) We derive an analytical lower bound on the concurrence for bipartite quantum systems with an improved computable cross norm or realignment criterion and an improved positive partial transpose criterion respectively. Furthermore we demonstrate that our bound is better than that obtained from the local uncertainty relations criterion with optimal local orthogonal observables which is known as one of the best estimations of concurrence.
 Select Generalized Positive-Definite Operator in Quantum Phase Space Obtained by Virtue of the Weyl Quantization Rule HU Li-Yun, FAN Hong-Yi Chin. Phys. Lett. 2009, 26 (6): 060307 .   DOI: 10.1088/0256-307X/26/6/060307 Abstract   PDF(pc) (190KB) ( 384 ) We introduce a generalized positive-definite operator Δg(q,p) by smoothing out the Wigner operator Δw(q,p) and by averaging over the "coarse graining'' function. The function is then regarded as the classical Weyl correspondence of the operator Δg(q,p); in this way we can easily identify a quantum state |Φ> such that Δg(q,p)=|Φ><Φ|, and |Φ> turns out to be a new kind of squeezed coherent state. Correspondingly, the generalized distribution function for any state |φ> is <φ| Δg(q,p) |φ> =|<Φ|φ>|2 , which is obviously positive-definite and is a generalization of the Husimi function.
 Select Realization of a Multiqubit Conditional Phase Gate by Virtue of a Weak Coherent Light Field HUANG Xiu-Hua, CHEN Zhi-Hua, TANG Yao-Xiang, LIN Xiu-Min Chin. Phys. Lett. 2009, 26 (6): 060308 .   DOI: 10.1088/0256-307X/26/6/060308 Abstract   PDF(pc) (250KB) ( 504 ) We propose a scalable scheme to generate a multiqubit conditional phase gate by using a basic building block, i.e., a weak coherent optical pulse |α> reflected successively from a cavity with trapped atoms. In the scheme, we use a coherent state of light instead of a single photon source, homodyne measurement on a coherent light field instead of single photon detection, which reduces the complexity of the practical experiment. The outcomes of these measurements indicate either completion of the gate or the presence of the original qubits such that the operation can be repeated until it is successful.
 Select A New Solution to Einstein's Field Equations SHEN Ming Chin. Phys. Lett. 2009, 26 (6): 060401 .   DOI: 10.1088/0256-307X/26/6/060401 Abstract   PDF(pc) (163KB) ( 743 ) We construct a new exact solution to the vacuum Einstein field equations. This solution possesses a naked physical singularity. The norm of the Riemann curvature tensor of the solution takes infinity at some points and the solution does not have any event horizon around the singularity. A detailed analysis of this new singularity is also presented.
 Select Gauss-Bonnet and Lovelock Gravities and the Generalized Second Law of Thermodynamics M. Akbar, Asghar Qadir Chin. Phys. Lett. 2009, 26 (6): 060402 .   DOI: 10.1088/0256-307X/26/6/060402 Abstract   PDF(pc) (174KB) ( 633 ) It has been shown [Chin.Phys.Lett.25(2008)4199] that the generalized second law of thermodynamics holds in Einstein gravity. Here we extend this procedure for Gauss--Bonnet and Lovelock gravities. It is shown that by employing the general expression for temperature associated with the apparent horizon of a Friedman-Robertson-Walker (FRW) universe and assuming Tm=bTh, we are able to construct conditions for which the generalized second law holds in Gauss-Bonnet and Lovelock gravities, where Tm and Th are the temperatures of the source and the horizon respectively.
 Select Cosmological Models with Time Dependent G and Λ Coupling Scalars N. Ibotombi Singh, S. Kiranmla Chanu, S. Surendra Singh Chin. Phys. Lett. 2009, 26 (6): 060403 .   DOI: 10.1088/0256-307X/26/6/060403 Abstract   PDF(pc) (144KB) ( 524 ) A cosmological model in which the universe has its critical density and gravitational constants generalized as coupling scalars in Einstein's theory is considered. A general method of solving the field equations is given. An exact solution for matter distribution in cosmological models satisfying G=G0(R/R0)n is presented. Corresponding physical interpretations of the cosmological solutions are also discussed.
 Select Renormalization Group Method for Soliton Evolution in a Perturbed KdV Equation TU Tao, WANG Lin-Jun, HAO Xiao-Jie, GUO Guang-Can, GUO Guo-Ping Chin. Phys. Lett. 2009, 26 (6): 060501 .   DOI: 10.1088/0256-307X/26/6/060501 Abstract   PDF(pc) (220KB) ( 413 ) We show that the conventional renormalization group method can be used to give an analytic description of the evolution of a soliton in a perturbed KdV equation. The renormalization group equations describe the deformation of the soliton as the effect of perturbations. The method is concise and easy to understand and the results obtained agree with the results of other approaches.
 Select Multidimensional Z-Matrix with Control Parameters and Its Applications in Image Encryption ZHAO Liang, LIAO Xiao-Feng, XIANG Tao, XIAO Di Chin. Phys. Lett. 2009, 26 (6): 060502 .   DOI: 10.1088/0256-307X/26/6/060502 Abstract   PDF(pc) (902KB) ( 738 ) An n-dimensional Z-matrix with control parameters is presented, and its periodicity and chaos are testified. Experimental results show that the proposed Z-matrix has a long period and changeable periodicity with different dimensions. Some examples of image encryption with a Z-matrix of different dimensions are listed for demonstrating its applications
 Select Dynamical System Approach to a Coupled Dispersionless System: Localized and Periodic Traveling Waves Gambo Betchewe, Kuetche Kamgang Victor, Bouetou Bouetou Thomas, , Timoleon Crepin Kofane, Chin. Phys. Lett. 2009, 26 (6): 060503 .   DOI: 10.1088/0256-307X/26/6/060503 Abstract   PDF(pc) (281KB) ( 478 ) We investigate the dynamical behavior of a coupled dispersionless system describing a current-conducting string with infinite length within a magnetic field. Thus, following a dynamical system approach, we unwrap typical miscellaneous traveling waves including localized and periodic ones. Studying the relative stabilities of such structures through their energy densities, we find that under some boundary conditions, localized waves moving in positive directions are more stable than periodic waves which in contrast stand for the most stable traveling waves in another boundary condition situation.
 Select Resonant-Like Activation in a Bistable System with Noise and Time Delay NIE Lin-Ru, GONG Ai-Ling, MEI Dong-Cheng Chin. Phys. Lett. 2009, 26 (6): 060504 .   DOI: 10.1088/0256-307X/26/6/060504 Abstract   PDF(pc) (281KB) ( 878 ) A bistable system with noise and time delay is investigated. Theoretical analysis and stochastic simulation show that: (i) In the case of a system driven only by multiplicative Gaussian white noise, the mean first-passage time for a particle to reach the other stable state from one stable state exhibits a minimum with respect to delay time, i.e., a resonant-like activation (RA) phenomenon. (ii) In the action of additive and multiplicative noise, as the additive noise intensity increases, no matter whether a correlation between the two types of noise exists or not, the RA gradually disappears. (iii) The correlation strength between the two types of noise does not influence the existence of the RA.
 Select Adaptive Synchronization between Two Different Complex Networks with Time-Varying Delay Coupling CHEN Jian-Rui, JIAO Li-Cheng, WU Jian-She, WANG Xiao-Hua Chin. Phys. Lett. 2009, 26 (6): 060505 .   DOI: 10.1088/0256-307X/26/6/060505 Abstract   PDF(pc) (284KB) ( 627 ) A new general network model for two complex networks with time-varying delay coupling is presented. Then we investigate its synchronization phenomena. The two complex networks of the model differ in dynamic nodes, the number of nodes and the coupling connections. By using adaptive controllers, a synchronization criterion is derived. Numerical examples are given to demonstrate the effectiveness of the obtained synchronization criterion. This study may widen the application range of synchronization, such as in chaotic secure communication.
 Select Behavior of a Logistic Map Driven by White Noise YANG Zheng-Ling, GAO Yang, GAO Yong-Tao, ZHANG Jun Chin. Phys. Lett. 2009, 26 (6): 060506 .   DOI: 10.1088/0256-307X/26/6/060506 Abstract   PDF(pc) (386KB) ( 921 ) In the real world, every nonlinear system is inevitably affected by noise. As an example, a logistic map driven by white noise is studied. Unlike previous studies which focused on the behavior under local parameters to find analytical results, we investigate the whole driven logistic map. For a white noise driven logistic map, its non-divergent interval decreases with increasing white noise. The white noise does not change the equilibrium point and two-cycle intervals in statistics, if the driven logistic map is kept non-divergent. In particular, chaos can be excited by white noise only after the four-cycle bifurcation begins. The latest result is a necessary condition which has not been given in the literature [Int. J. Bifur. Chaos 18(2008)509], and it can be deduced from Sharkovsky's theorem. Numerical simulations prove these analytical results.
 Select Pattern Synchronization in a Two-Layer Neuronal Network SUN Xiao-Juan, LU Qi-Shao Chin. Phys. Lett. 2009, 26 (6): 060507 .   DOI: 10.1088/0256-307X/26/6/060507 Abstract   PDF(pc) (1352KB) ( 644 ) Pattern synchronization in a two-layer neuronal network is studied. For a single-layer network of Rulkov map neurons, there are three kinds of patterns induced by noise. Additive noise can induce ordered patterns at some intermediate noise intensities in a resonant way; however, for small and large noise intensities there exist excitable patterns and disorderedpatterns, respectively. For a neuronal network coupled by two single-layer networks with noise intensity differences between layers, we find that the two-layer network can achieve synchrony as the interlayer coupling strength increases. The synchronous states strongly depend on the interlayer coupling strength and the noise intensity difference between layers.
 Select Modeling of a Silicon Nanowire pH Sensor with Nanoscale Side Gate Voltage Alireza Kargar Chin. Phys. Lett. 2009, 26 (6): 060701 .   DOI: 10.1088/0256-307X/26/6/060701 Abstract   PDF(pc) (235KB) ( 637 ) A silicon nanowire (Si-NW) sensor for pH detection is presented. The conductance of the device is analytically obtained, demonstrating that the conductance increases with decreasing oxide thickness. To calculate the electrical conductance of the sensor, the diffusion-drift model and nonlinear Poisson-Boltzmann equation are applied. To improve the conductance and sensitivity, a Si-NW sensor with nanoscale side gate voltage is offered and its characteristics are theoretically achieved. It is revealed that the conductance and sensor sensitivity can be enhanced by adding appropriate side gate voltages. This effect is compared to a similar fabricated structure in the literature, which has a wire with a rectangular cross section. Finally, the effect of NW length on sensor performance is investigated and an inverse relation between sensor sensitivity and NW length is achieved.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
 Select Two-Photon-Exchange Correction to Elastic ep Scattering in the Forward Angle Limit ZHOU Hai-Qing Chin. Phys. Lett. 2009, 26 (6): 061201 .   DOI: 10.1088/0256-307X/26/6/061201 Abstract   PDF(pc) (168KB) ( 451 ) The two-photon-exchange (TPE) correction to elastic ep scattering in the forward angle region is discussed based on a simple hadronic model. It is found that the correction is exactly zero in the forward angle limit. This analytical result gives a good explanation of the previous numerical results and shows the clear power behavior of the TPE correction to elastic ep scattering in the forward angle region.
 Select Strangeness by Thermal Model Simulation at RHIC SHI Xing-Hua, MA Yu-Gang, CAI Xiang-Zhou, CHEN Jin-Hui, MA Guo-Liang, ZHONG Chen Chin. Phys. Lett. 2009, 26 (6): 061202 .   DOI: 10.1088/0256-307X/26/6/061202 Abstract   PDF(pc) (365KB) ( 400 ) The local temperature effect on strangeness enhancement in relativistic heavy ion collisions is discussed in the framework of the thermal model in which the K+/h+ ratio becomes smaller with increasing freeze-out temperature. Considering that most strangeness particles of final-state particles are from the kaon meson, the temperature effect may play a role in strangeness production in hot dense matter where a slightly different temperature distribution in different areas could be produced by jet energy loss. This phenomenon is predicted by thermal model calculation at RHIC energy. The Ξ-/Φ ratio in central Au+Au collisions at 200GeV from the thermal model depends on the freeze-out temperature obviously when γS is different. It should be one of the reasons why strangeness enhancements of Ξ and Φ are different though they include two strange quarks. These results indicate that thermodynamics is an important factor for strangeness production and the strangeness enhancement phenomenon.
 Select Direct Measurement of Branching Fraction for Inclusive Semimuonic Decay of Neutral D Mesons LIU Hui-Hui, ZHANG Xiao-Fei, CHEN Jiang-Chuan Chin. Phys. Lett. 2009, 26 (6): 061203 .   DOI: 10.1088/0256-307X/26/6/061203 Abstract   PDF(pc) (230KB) ( 411 ) Using a data sample of about 33pb-1 collected at and around √s=3.773GeV with the BES-II detector at the BEPC, we have directly measured the branching fraction for inclusive semimuonic decay of neutral D mesons to be BF(D0→μ+X) =(7.2±1.5±0.8)%.
NUCLEAR PHYSICS
 Select Branching Ratios of α Decay for Nuclei near Deformed Shell Closures WANG Yan-Zhao, ZHANG Hong-Fei, DONG Jian-Min, SU Xin-Ning, ZUO Wei, LI Jun-Qing Chin. Phys. Lett. 2009, 26 (6): 062101 .   DOI: 10.1088/0256-307X/26/6/062101 Abstract   PDF(pc) (338KB) ( 570 ) The generalized liquid drop model (GLDM) is extended to the region around deformed shell closure 270Hs by taking into account the excitation energy EI+ of the residual daughter nucleus and the centrifugal potential energy Vcen(r). The branching ratios of α decays from the ground state of a parent nucleus to the ground state 0+ of its deformed daughter nucleus and to the first excited state 2+ are calculated in the framework of the GLDM. The results support the proposal that a measurement of α spectroscopy is a feasible method to extract information on nuclear deformation of superheavy nuclei around the deformed nucleus 270Hs.
 Select Pion Production in Heavy-Ion Collisions in the 1 A GeV Region FENG Zhao-Qing, JIN Gen-Ming, Chin. Phys. Lett. 2009, 26 (6): 062501 .   DOI: 10.1088/0256-307X/26/6/062501 Abstract   PDF(pc) (399KB) ( 486 ) Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, pion emission in heavy-ion collisions in the region 1AGeV is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances ∆(1232) and N*(1440). The in-medium dependence and Coulomb effects of pion production are included in the calculation. Total pion multiplicity and π-/π+ yields are calculated for the reaction 197\Au+197\Au in central collisions for selected Skyrme parameters SkP, SLy6, Ska, SIII and compared with the measured data of the FOPI collaboration.
 Select Possible Mechanisms of Ternary Fission in the 197Au+197Au System at 15 A MeV TIAN Jun-Long, LI Xian, WU Xi-Zhen, LI Zhu-Xia, YAN Shi-Wei Chin. Phys. Lett. 2009, 26 (6): 062502 .   DOI: 10.1088/0256-307X/26/6/062502 Abstract   PDF(pc) (538KB) ( 490 ) Ternary fission in 197Au+197Au collisions at 15 A \ MeV is investigated by using the improved quantum molecular dynamical (ImQMD) model. The experimental mass distributions for each of the three fragments are reproduced for the first time without any freely adjusting parameters. The mechanisms of ternary fission in central and semi-central collisions are dynamically studied. In direct prolate ternary fission, two necks are found to be formed almost simultaneously and rupture sequentially in a very short time interval. Direct oblate ternary fission is a very rare fission event, in which three necks are formed and rupture simultaneously, forming three equally sized fragments along space-symmetric directions in the reaction plane. In sequential ternary fission a binary division is followed by another binary fission event after hundreds of fm/c.
 Select Properties of Dihadron Correlations for p+p Collisions at √sNN= 200 GeV XIN Ke-Feng, ZHANG Song, MA Yu-Gang, CAI Xiang-Zhou, MA Guo-Liang, ZHONG Chen Chin. Phys. Lett. 2009, 26 (6): 062503 .   DOI: 10.1088/0256-307X/26/6/062503 Abstract   PDF(pc) (501KB) ( 488 ) The dihadron azimuthal angular correlations for p+p collisions at√sNN=200 GeV are simulated by a multi-phase transport model. The dispersions of near-side and away-side peaks, indicated by the width of Gaussian fit functions and the rms width, decrease with the transverse momentum of associated particles. This trend is consistent with the experimental results. Conditional-yields are also calculated to obtain distributions of the associated particle transverse momentum for both away-side and near-side. Furthermore, the hadronic rescattering effects make the conditional-yield distributions softer.
ATOMIC AND MOLECULAR PHYSICS
 Select Stabilization and Shift of Frequency in an External Cavity Diode Laser with Solenoid-Assisted Saturated Absorption HAN Shun-Li, CHENG Bing, ZHANG Jing-Fang, XU Yun-Fei, WANG Zhao-Ying, LIN Qiang Chin. Phys. Lett. 2009, 26 (6): 063201 .   DOI: 10.1088/0256-307X/26/6/063201 Abstract   PDF(pc) (336KB) ( 648 ) A simple method to realize both stabilization and shift of the frequency in an external cavity diode laser (ECDL) is reported. Due to the Zeeman effect, the saturated absorption spectrum of Rb atoms in a magnetic field is shifted. This shift can be used to detune the frequency of the ECDL, which is locked to the saturated absorption spectrum. The frequency shift amount can be controlled by changing the magnetic field for a specific polarization state of the laser beam. The advantages of this tunable frequency lock include low laser power requirement, without additional power loss, cheapness, and so on.
 Select Theoretical Study on Inner Shell Electron Impact Excitation of Lithium YANG Ning-Xuan, DONG Chen-Zhong, JIANG Jun Chin. Phys. Lett. 2009, 26 (6): 063401 .   DOI: 10.1088/0256-307X/26/6/063401 Abstract   PDF(pc) (264KB) ( 434 ) Cross sections for electron impact excitation of lithium from the ground state 1s22s to the excited states 1s2s2, 1s2p2, 1s2snp (n=2-5), 1s2sns (n=3-5), 1s2pns (n=3-5), and 1s2pnp (n=3-5) are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500eV [Chin. Phys. Lett. 25(2008)3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57eV show two-peak structures.
 Select Guiding of Highly Charged Ions through PC Nanocapillaries LI De-Hui, WANG Yu-Yu, ZHAO Yong-Tao, XIAO Guo-Qing, ZHAO Di, XU Zhong-Feng, LI Fu-Li Chin. Phys. Lett. 2009, 26 (6): 063402 .   DOI: 10.1088/0256-307X/26/6/063402 Abstract   PDF(pc) (365KB) ( 410 ) Angular distribution and current dependence of the transmitted ion fraction are investigated for 40keV Xe7+ bombarding on polycarbonate (PC) nanocapillaries. By measuring the angular distribution of the transmitted ion fraction, a strong guiding effect is found in PC nanocapillaries. Furthermore, with increase of the incident current, a turning point of the transmitted ion fraction is found, which is explained qualitatively by the discharge capacity of the nanocapillaries.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
 Select Generation of Intense THz Pulsed Lasers Pumped Strongly by CO2 Pulsed Lasers QI Chun-Chao, CHENG Zu-Hai Chin. Phys. Lett. 2009, 26 (6): 064201 .   DOI: 10.1088/0256-307X/26/6/064201 Abstract   PDF(pc) (203KB) ( 469 ) A theoretical method dealing with two intense laser fields interacting with a three-level molecular system is proposed. A discussion is presented on the properties of the solutions for time-independent and time-dependent absorption coefficients and gain coefficient on resonance for strong laser fields, based on analytic evaluation of the rate equations for a homogeneously broadened, three-level molecular system. The pump intensity range can be estimated according to the analytic expression of pump saturation intensity. The effects of pulse width, gas pressure and path length on the energy absorbed from pump light are studied theoretically. The results can be applied to the analysis of pulsed, optically pumped terahertz lasers.
 Select Pulse Compression Based on Laser-Induced Optical Breakdown in Suspension HASI Wu-Li-Ji, FU Mei-Ling, LU Huan-Huan, GONG Sheng, LU Zhi-Wei, LIN Dian-Yang, HE Wei-Ming Chin. Phys. Lett. 2009, 26 (6): 064202 .   DOI: 10.1088/0256-307X/26/6/064202 Abstract   PDF(pc) (278KB) ( 486 ) Pulse compression based on laser-induced optical breakdown in suspension is investigated. The physical mechanism behind it is analyzed theoretically and validated in the Q-switched Nd:YAG laser system. A 12-ns pump pulse is suppressed to 5ns with good fidelity in the front edge and sharp steepness in the trailing edge. The HT-270, which has a small gain coefficient and absorption coefficient, is used as a solvent, and therefore the disturbance induced by stimulated Brillouin scattering and absorption are minimized and the transmittivity is enhanced.
 Select Optical Four-Wave Mixing Operator, Fresnel Operators and Three-Mode Entangled State Representation MA Shan-Jun Chin. Phys. Lett. 2009, 26 (6): 064203 .   DOI: 10.1088/0256-307X/26/6/064203 Abstract   PDF(pc) (182KB) ( 502 ) We analyse the optical four-wave mixing operator S and relate it to the two-mode Fresnel operator. It is shown that the direct product of the two-mode Fresnel operator and the single-mode Fresnel operator has a natural representation on the basis of a three-mode entangled state, which is constructed by S and a beam splitter transform.
 Select Generation of a Non-Classical Correlated Photon Pair via Spontaneous Four-Wave Mixing in a Cold Atomic Ensemble LU Xiao-Song, CHEN Qun-Feng, SHI Bao-Sen, GUO Guang-Can Chin. Phys. Lett. 2009, 26 (6): 064204 .   DOI: 10.1088/0256-307X/26/6/064204 Abstract   PDF(pc) (246KB) ( 793 ) Counter propagated write and read lasers can be used to generate non-classical correlated photon pairs in an atomic ensemble. We experimentally investigate how the detuning of the write laser affects the non-classical correlation function between the Stokes photon and the anti-Stokes photon, which are generated via a spontaneous four-wave mixing process using an off-axis configuration in a cold 85Rb atomic ensemble. The change of the time-resolved second-order correlated function between the Stokes and anti-Stokes photons is presented. The experimental result suggests that a suitable choice of detuning should be considered in such an experiment.
 Select Coexisting Raman- and Rayleigh-Enhanced Four-Wave Mixing in Femtosecond Polarization Beats NIE Zhi-Qiang, ZHAO Yan, ZHANG Yan-Peng, GAN Chen-Li, ZHENG Huai-Bin, LI Chang-Biao, LU Ke-Qing Chin. Phys. Lett. 2009, 26 (6): 064205 .   DOI: 10.1088/0256-307X/26/6/064205 Abstract   PDF(pc) (439KB) ( 601 ) Based on the polarization interference of Raman- and Rayleigh-enhanced four-wave mixing processes, heterodyne detection of the Raman, Rayleigh and coexisting Raman and Rayleigh femtosecond difference-frequency polarization beats is investigated in the cw and the three Markovian stochastic models, respectively. These two processes exhibit asymmetric and symmetric spectra, respectively, and the thermal effect in them can be suppressed by a field-correlation method. Such studies of coexisting Raman- and Rayleigh-enhanced four-wave mixing processes can have important applications in coherence quantum control, and quantum information processing.
 Select Two-Dimensional (2D) Polygonal Electromagnetic Cloaks LI Chao, YAO Kan, LI Fang Chin. Phys. Lett. 2009, 26 (6): 064206 .   DOI: 10.1088/0256-307X/26/6/064206 Abstract   PDF(pc) (807KB) ( 682 ) Transformation optics offers remarkable control over electromagnetic fields and opens an exciting gateway to design invisible cloak devices' recently. We present an important class of two-dimensional (2D) cloaks with polygon geometries. Explicit expressions of transformed medium parameters are derived with their unique properties investigated. It is found that the elements of diagonalized permittivity tensors are always positive within an irregular polygon cloak besides one element diverges to plus infinity and the other two become zero at the inner boundary. At most positions, the principle axes of permittivity tensors do not align with position vectors. An irregular polygon cloak is designed and its invisibility to external electromagnetic waves is numerically verified. Since polygon cloaks can be tailored to resemble any objects, the transformation is finally generalized to the realization of 2D cloaks with arbitrary geometries
 Select Thermal Analysis of InAs/AlSb Short Wavelength Mid-IR Quantum Cascade Lasers WEI Lin, LI Ai-Zhen, XU Gang-Yi Chin. Phys. Lett. 2009, 26 (6): 064207 .   DOI: 10.1088/0256-307X/26/6/064207 Abstract   PDF(pc) (524KB) ( 452 ) We present the effects of hetero-interfaces and major key parameters on the thermal behaviors and performance of short wavelength mid-IR InAs/AlSb quantum cascade lasers (QCLs). We use a finite element method (FEM) with commercial software, ANSYS, to simulate the heat dissipation in QCLs in cw operation mode with an epilayer-down mounting package. The thermal performance is characterized by the temperature increase Δ T (self-heating effect) between the active region of QCLs and the heatsink. Results show that (1) the self-heating effects of InAs/AlSb QCLs are much less than those in AlInAs/GaInAs QCLs, (2) narrower ridges lead to significantly cooler active regions of InAs/AlSb QCLs due to poor heat transport in the cross-plane direction (across interfaces) and that most of the heat flows out of the active region in the lateral direction, and (3) the cavity length of the laser has little influence on the self-heating effect of the device, but the long cavity reduces mirror loss and threshold current density.
 Select Switchable Multi-Wavelength Erbium-Doped Fiber Lasers based on a Mach-Zehnder Interferometer Using a Twin-Core Fiber FENG Su-Chun, XU Ou, LU Shao-Hua, JIAN Shui-Sheng Chin. Phys. Lett. 2009, 26 (6): 064208 .   DOI: 10.1088/0256-307X/26/6/064208 Abstract   PDF(pc) (366KB) ( 616 ) A switchable multi-wavelength erbium-doped fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer comb filter at room temperature is presented. The comb filter is formed by splicing a section of twin-core fiber between two single mode fibers. By adjusting the states of the polarization controller appropriately, the laser can be made to operate in stable single-, dual- and three-wavelength lasing states. The operation principle is based on spectral hole burning induced by the saturated effect and polarization hole burning.
 Select Long-Range Interactions between Nematicons CAO Long-Gui, ZHENG Ya-Jian, HU Wei, YANG Ping-Bao, GUO Qi Chin. Phys. Lett. 2009, 26 (6): 064209 .   DOI: 10.1088/0256-307X/26/6/064209 Abstract   PDF(pc) (532KB) ( 473 ) We theoretically and experimentally investigate the long-range interaction between nematicons. It is demonstrated that the interaction becomes strongest when the pretilt angle of liquid crystal molecules is nearly π/4 for a given single-beam input power P0, and that the interaction becomes stronger when the incident power P0 increases at a given pretilt angle. In this way, the interaction is still observed when the initial separation is 43 times of the soliton width, much larger than that implemented in lead glasses [Nature Phys. 2(2006)769].
 Select Efficient Compound-Cavity Eye-Safe KTP OPO at 1.57 μupm Pumped by an Electro-Optic Q-Switched Nd:YAG Laser ZHONG Kai, WANG Yu-Ye, XU De-Gang, GENG You-Fu, WANG Jing-Li, WANG Peng, YAO Jian-Quan, Chin. Phys. Lett. 2009, 26 (6): 064210 .   DOI: 10.1088/0256-307X/26/6/064210 Abstract   PDF(pc) (447KB) ( 871 ) An efficient high-energy eye-safe optical parametric oscillator (OPO) based on a type-II non-critically phase-matched KTP crystal is demonstrated. The KTP OPO is pumped by a quasi-cw diode side-pumped electro-optic Q-switched Nd:YAG laser in a compound-cavity configuration. The maximum output energy of the signal wavelength at 1.57 μm is 66.5mJ, corresponding to an electrical-to-optical conversion efficiency of 4.47% and an optical-to-optical conversion efficiency of 12.1%. The pulse width (FWHM) is about 3.6ns with a peak power of 18.5MW. The output energy is insensitive to repetition rate and demonstrates good stability.
 Select Electrically Pumped Room-Temperature Pulsed InGaAsP-Si Hybrid Lasers Based on Metal Bonding CHEN Ting, HONG Tao, PAN Jiao-Qing, CHEN Wei-Xi, CHENG Yuan-Bing, WANG Yang, MA Xiao-Bo, LIU Wei-Li, ZHAO Ling-Juan, RAN Guang-Zhao, WANG Wei, QIN Guo-Gang Chin. Phys. Lett. 2009, 26 (6): 064211 .   DOI: 10.1088/0256-307X/26/6/064211 Abstract   PDF(pc) (572KB) ( 435 ) A pulsed InGaAsP-Si hybrid laser is fabricated using metal bonding. A novel structure in which the optical coupling and metal bonding areas are transversely separated is employed to integrate the silicon waveguide with an InGaAsP multi-quantum well distributed feedback structure. When electrically pumped at room temperature, the laser operates with a threshold current density of 2.9kA/cm2 and a slope efficiency of 0.02W/A. The 1542nm laser output exits mainly from the Si waveguide.
 Select Non-uniform Influence of Prepulse Duration on a Nickel-Like Mo X-Ray Laser in XLIII CHENG Tao, LI Ying-Jun, MENG Li-Min, ZHANG Jie Chin. Phys. Lett. 2009, 26 (6): 064212 .   DOI: 10.1088/0256-307X/26/6/064212 Abstract   PDF(pc) (832KB) ( 563 ) An experiment on a transient nickel-like Mo x-ray laser in the extreme light III (XL III) laser facility is analyzed, based on the two-dimensional hydrodynamic evolutions of a plasma under a non-uniform incident laser. Influences of the pulse duration and intensity on plasma scale length, electron density, temperature, as well as their distributions are investigated, based on which the pre-pulse character and delay time are determined according to the parameters of laser line focus on XLIII. It is found that the optimal intensity of the pre-pulse is 1.0TW/cm2 with a duration of 500ps; a well modified pre-plasma can be obtained after 1.6ns under low quality line focus in the lab.
 Select Generation of Efficient Dispersive Waves in Photonic Crystal Fibers LEI Da-Jun, DONG Hui, YANG Hua, WEN Shuang-Chun, ZHANG Jing-Gui, XU Hui-Wen Chin. Phys. Lett. 2009, 26 (6): 064213 .   DOI: 10.1088/0256-307X/26/6/064213 Abstract   PDF(pc) (345KB) ( 487 ) Based on the generalized nonlinear Schrodinger equation, we investigate efficient dispersive wave (DW) generation in a photonic crystal fiber (PCF) by numerical simulation and discuss a way to control DW generation by using an initial input pulse chirp. It is shown that efficient red-shifted DW generation can be obtained in a PCF with negative dispersion slopes. The energy contained in the DWs is considerably decreased for both positively and negatively chirped pulses at the fiber output. This provides us with an opportunity to conveniently and efficiently manipulate the DW generation by controlling the pre-chirp of the soliton. Moreover, we also show that forth- and higher-order dispersion terms play little part in deciding the evolution of DWs.
 Select Demonstration of Mo Soft X-Ray Lasers with a Grazing Incidence Pumping Scheme in the XL-II Facility DONG Quan-Li, WANG Shou-Jun, WANG Zhao-Hua, ZHAO Jing, WEI Zhi-Yi, ZHANG Jie, Chin. Phys. Lett. 2009, 26 (6): 064214 .   DOI: 10.1088/0256-307X/26/6/064214 Abstract   PDF(pc) (413KB) ( 580 ) A Ni-like Mo soft x-ray laser (SXRLs) operating at 18.9nm has been demonstrated by employing a grazing incidence pumping scheme with 120mJ in the 200ps pre-pulse and 140mJ in the 200fs main pulse. The SXRL gain is estimated to be 1.5-3cm-1 when a grazing incidence angle of 14° is applied. Numerical simulations are also performed to investigate the dynamics of the ion distribution. It is found that a high intensity at 2.4×1014W/cm2 of the 200fs main pulse could heat the pre-plasma rapidly to an appropriate temperature for population inversion, and could compensate for the shortage of the total pump energy to a certain extent.
 Select High Power Er/Yb Codoped Double Clad Fiber Pulsed Amplifier Based on an All-Fiber Configuration ZHOU Lei, NING Ji-Ping, CHEN Cheng, HAN Qun, ZHANG Wei-Yi, WANG Jun-Tao Chin. Phys. Lett. 2009, 26 (6): 064215 .   DOI: 10.1088/0256-307X/26/6/064215 Abstract   PDF(pc) (543KB) ( 5016 ) We report an all-fiber two-stage high power pulsed amplifier, seeded with a 1550nm, 1kHz repetition rate rectangular pulse, and based on Er/Yb co-doped double clad fiber. All the characteristics are measured in the experiment. The maximal slope efficiency is 22.56%, which is the highest we know of at such a low repetition rate, and the maximal output signal power is 1W. The various factors that affect the pulsed amplifier performance are analyzed. A high output power while keeping high power conversion efficiency can be obtained with careful selection of the input power, pump power and repetition rate. The experimental results show that the crucial parameters should be optimized when designing all-fiber pulsed amplifiers.
 Select Intrinsic Bistability and Critical Slowing in Tm3+/Yb3+ Codoped Laser Crystal with the Photon Avalanche Mechanism LI Li, ZHANG Xin-Lu, CHEN Li-Xue Chin. Phys. Lett. 2009, 26 (6): 064216 .   DOI: 10.1088/0256-307X/26/6/064216 Abstract   PDF(pc) (271KB) ( 590 ) We present theoretically a novel intrinsic optical bistability (IOB) in the Tm3+/Yb3+ codoped system with a photon avalanche mechanism. Numerical simulations based on the rate equation model demonstrate distinct IOB hysteresis and critical slowing dynamics around the avalanche thresholds. Such an IOB characteristic in Tm3+/Yb3+ codoped crystal has potential applications in solid-state bistable optical displays and luminescence switchers in visible-infrared spectra.
 Select Numerical Calculation of SAW Propagation Properties at the x-Cut of Ferroelectric PMN-33%PT Single Crystals ZHANG Wei, LI Xiu-Ming, ZHANG Rui, HUANG Nai-Xing, CAO Wen-Wu, Chin. Phys. Lett. 2009, 26 (6): 064301 .   DOI: 10.1088/0256-307X/26/6/064301 Abstract   PDF(pc) (328KB) ( 570 ) Surface acoustic wave (SAW) properties at the x-cut of relaxor-based 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-33%PT) ferroelectric single crystals are analyzed theoretically when poled along the [001]c cubic direction. It can be found that PMN-33%PT single crystal is a kind of material with a low phase velocity and high electromechanical coupling coefficient, and the single crystal possesses some cuts with zero power flow angle. The results are based on the material parameters at room temperature. The conclusions provide device designers with a few ideal cuts of PMN-33%PT single crystals. Moreover, choosing an optimal cut will dramatically improve the performance of SAW devices, and corresponding results for crystal systems working at othertemperatures could also be figured out by employing the method.
 Select A Lattice Boltzmann Model for Fluid-Solid Coupling Heat Transfer in Fractal Porous Media CAI Jun, HUAI Xiu-Lan Chin. Phys. Lett. 2009, 26 (6): 064401 .   DOI: 10.1088/0256-307X/26/6/064401 Abstract   PDF(pc) (265KB) ( 719 ) We report a lattice Boltzmann model that can be used to simulate fluid-solid coupling heat transfer in fractal porous media. A numerical simulation is conducted to investigate the temperature evolution under different ratios of thermal conductivity of solid matrix of porous media to that of fluid. The accordance of our simulation results with the solutions from the conventional CFD method indicates the feasibility and the reliability for the developed lattice Boltzmann model to reveal the phenomena and rules of fluid-solid coupling heat transfer in complex porous structures.
 Select Scalar Statistics along Inertial Particle Trajectory in Isotropic Turbulence LIU Ya-Ming, LIU Zhao-Hui, HAN Hai-Feng, LI Jing, WANG Han-Feng, ZHENGChu-Guang Chin. Phys. Lett. 2009, 26 (6): 064402 .   DOI: 10.1088/0256-307X/26/6/064402 Abstract   PDF(pc) (288KB) ( 433 ) The statistics of a passive scalar along inertial particle trajectory in homogeneous isotropic turbulence with a mean scalar gradient is investigated by using direct numerical simulation. We are interested in the influence of particle inertia on such statistics, which is crucial for further understanding and development of models in non-isothermal gas-particle flows. The results show that the scalar variance along particle trajectory decreases with the increasing particle inertia firstly; when the particle's Stokes number St is less than 1.0, it reaches the minimal value when St is around 1.0, then it increases if St increases further. However, the scalardissipation rate along the particle trajectory shows completely contrasting behavior in comparison with the scalar variance. The mechanical-to-thermal time scale ratios averaged along particle, p, are approximately two times smaller than that computed in the Eulerian frame r, and stay at nearly 1.77 with a weak dependence on particle inertia. In addition, the correlations between scalar dissipation and flow structure characteristics along particle trajectories, such as strain and vorticity, are also computed, and they reach their maximum and minimum, 0.31 and 0.25, respectively, when St is around 1.0.
 Select A Particle Resistance Model for Flow through Porous Media WU Jin-Sui, YIN Shang-Xian, ZHAO Dong-Yu Chin. Phys. Lett. 2009, 26 (6): 064701 .   DOI: 10.1088/0256-307X/26/6/064701 Abstract   PDF(pc) (348KB) ( 555 ) A particle model for resistance of flow in isotropic porous media is developed based on the fractal geometry theory and on the drag force flowing around sphere. The proposed model is expressed as a function of porosity, fluid property, particle size, fluid velocity (or Reynolds number) and fractal characters Df of particles in porous media. The model predictions are in good agreement with the experimental data. The validity of the proposed model is thus verified.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
 Select Heat Diffusion across a Strong Stochastic Magnetic Field in Tokamak Plasmas GAO Hong, , YU Qing-Quan Chin. Phys. Lett. 2009, 26 (6): 065201 .   DOI: 10.1088/0256-307X/26/6/065201 Abstract   PDF(pc) (303KB) ( 628 ) We investigate heat diffusion across a local strong stochastic magnetic field by using eleven low-m perturbed magnetic islands. A maximum stochasticity of 38.82 between two neighboring rational surfaces is attained. The correlation between the effective radial heat conductivity χr and the ratio of the parallel heat diffusion coefficient to the perpendicular coefficient, χ||/χ⊥, is numerically studied and compared with earlier work.
 Select Attachment Instabilities of SF6 Inductively Coupled Plasmas under Different Coupling Intensities GAO Wei, SUN Bin, DING Zhen-Feng Chin. Phys. Lett. 2009, 26 (6): 065202 .   DOI: 10.1088/0256-307X/26/6/065202 Abstract   PDF(pc) (416KB) ( 661 ) Characteristics of attachment instabilities in SF6 inductively coupled plasmas are experimentally studied under different coupling intensities. Experimental results show that the instabilities only occur in H modes operating in positive feedback regions. Both the sudden mode transitions and the instabilities are influenced by the coupling intensities. With increasing absorbed power, weak and middle coupling discharges can sequently undergo sudden mode transitions and attachment instabilities. In strong coupling discharges, the sudden mode transitions disappear and only attachment instabilities exist. The strong and weak coupling discharges are the most stable and unstable, respectively.
 Select Ultra-Thin Silicon Carbon Nitride Film: a Promising Protective Coating for Read/Write Heads in Magnetic Storage Devices GAO Peng, XU Jun, DING Wan-Yu, DONG Chuang Chin. Phys. Lett. 2009, 26 (6): 065203 .   DOI: 10.1088/0256-307X/26/6/065203 Abstract   PDF(pc) (740KB) ( 749 ) Ultra-thin amorphous Si-C-N films, down to 2nm, have been synthesized by MW-ECR plasma enhanced unbalanced magnetron sputtering. The friction coefficient of the film is only 0.11, determined in dry friction tests against the GCr15 ball at a load of 400mN for 20min. The films exhibit good protection against corrosion when they are immersed in a more severe corrosion environment of 0.1mol/L oxalic acid for 12h compared to the usual conditions (0.05mol/L, 4min) used in current computer industries. These good properties can be attributed to the smooth, dense and pore free structure of the film. These indicate that the Si-C-N film synthesized by the present technique may be a promising protective coating for read/write heads and other magnetic storage devices.
 Select Laser-Induced Particle Jet and Its Ignition Application in Premixed Combustible Gases YANG Qian-Suo, LIU Chun, PENG Zhi-Min, ZHU Nai-Yi Chin. Phys. Lett. 2009, 26 (6): 065204 .   DOI: 10.1088/0256-307X/26/6/065204 Abstract   PDF(pc) (592KB) ( 402 ) A hot particle jet is induced as a laser pulse from a free oscillated Nd:YAG laser focused on a coal target. The particle jet successfully initiates combustion in a premixed combustible gas consisting of hydrogen, oxygen, and air. The experiment reveals that the ionization of the particle jet is enhanced during the laser pulse. This characteristic is attributed to the electron cascade process and the ionization of the particles or molecules of the target. The initial free electrons, which are ablated from the coal target, are accelerated by the laser pulse through the inverse Bremsstrahlung process and then collide with the neutrals in the jet, causing the latter to be ionized.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
 Select Antisite Defects of the L12 Structure Determined by the Phase Field Microelasticity Model ZHANG Jing, CHEN Zheng, LU Yan-Li, WANG Yong-Xin, ZHAO Yan Chin. Phys. Lett. 2009, 26 (6): 066101 .   DOI: 10.1088/0256-307X/26/6/066101 Abstract   PDF(pc) (325KB) ( 428 ) A phase field microelasticity simulation is performed to examine the antisite defect of L12-Ni3Al in Ni75Al5.3V19.7 ternary alloy. Combinimg strain energy with the phase field model leads to an atom configuration change as time proceeds. For the Ni sublattice, the antisite defect AlNi, the equilibrium occupancy probability (OP) of which declines, precedes NiNi and VNi in reaching equilibrium; subsequently, NiNi and VNi present a phenomenon of symmetrical rise and decline individually. Similarly, for the Al sublattice, the antisite defect NiAl, the OP of which eventually rises, takes fewer time steps than AlAl and VAl to attain equilibrium. Thereafter, AlAl rises while VAl declines symmetrically at the axes of the NiAl curve. Furthermore, the OP for the Al sublattice is much more sensitive to strain energy than that for the Ni sublattice.
 Select Modal Characterization of a Planar Waveguide in Bismuth Borate Crystal WANG Lei, LU Qing-Ming, MA Hong-Ji Chin. Phys. Lett. 2009, 26 (6): 066102 .   DOI: 10.1088/0256-307X/26/6/066102 Abstract   PDF(pc) (999KB) ( 605 ) We report on the fabrication and modal property studies of planar waveguide structure in x-cut bismuth borate biaxial crystal formed by He ion implantation with triple energies. The prism coupling method is used to measure the effective refractive indices of this waveguide. We reconstruct the refractive index distribution of this waveguide by the reflectivity calculation method. Our results indicate that a broadened optical barrier is produced by the multiple He ion implantations. The so-called tunneling effect of the non-stationary mode in this type of barrier waveguide is presented by the well-known finite difference beam propagation method.
 Select Molecular Dynamics Study of Stability of Solid Solutions and Amorphous Phase in the Cu-Al System YANG Bin, LAI Wen-Sheng Chin. Phys. Lett. 2009, 26 (6): 066103 .   DOI: 10.1088/0256-307X/26/6/066103 Abstract   PDF(pc) (344KB) ( 583 ) The relative stability of fcc and bcc solid solutions and amorphous phase with different compositions in the Cu-Al system is studied by molecular dynamics simulations with n-body potentials. For Cu1-xAlx alloys, the calculations show that the fcc solid solution has the lowest energies in the composition region with x <0.32 or x >0.72, while the bcc solid solution has the lowest energies in the central composition range, in agreement with the ball-milling experiments that a single bcc solid solution with 0.30< x<0.70 is obtained. The evolution of structures in solid solutions and amorphous phase is studied by the coordination number (CN) and bond-length analysis so as to unveil the underlying physics. It is found that the energy sequence among three phases is determined by the competition in energy change originating from the bond length and CNs (or the number of bonds).
 Select Optical Properties of Hexagonal and Cubic ZnS Nanoribbons: Experiment and Theory ZHANG Zhi-Hua, HE Ming, DUAN Xiao-Feng Chin. Phys. Lett. 2009, 26 (6): 066104 .   DOI: 10.1088/0256-307X/26/6/066104 Abstract   PDF(pc) (1103KB) ( 632 ) Optical properties of hexagonal and cubic ZnS nanoribbons are studied by using valence electron energy loss spectroscopy (VEELS) and ab initio band structure calculations. The peaks in VEELS are assigned to interband transitions by comparing the interband transition strengths with the calculated densities of states. The optical properties are deduced from the experimental VEELS, and the theoretical calculations give consistent results. This combination of experimental and theoretical approaches provides a comprehensive understanding of the optical properties of polytype ZnS.
 Select Effect of Yttrium Addition on Glass Forming Ability of ZrCuAlSi Alloy ZHANG Bao-Qing, ZHANG Xin-Yu, LI Gong, SUN Bao-Ru, FAN Chang-Zeng, ZHAN Zai-Ji, LIU Ri-Ping, WANG Wen-Kui Chin. Phys. Lett. 2009, 26 (6): 066105 .   DOI: 10.1088/0256-307X/26/6/066105 Abstract   PDF(pc) (848KB) ( 492 ) The effect of yttrium addition on glass formation of a ZrCuAlSi alloy is investigated. The maximum diameter 8mm of the glassy rods for (Zr46.3Cu43.3Al8.9Si1.5)100-xYx alloy with x=2.5 is obtained by copper mould casting. Apparent enhancement of the glass formation ability is found with addition of yttrium, mainly due to the purification of the alloy melt and the suppression of formation of the primary phases by yttrium.
 Select Size- and Temperature-Dependent Thermal Expansion Coefficient of a Nanofilm ZHOU Li-Jun, GUO Jian-Gang, ZHAO Ya-Pu Chin. Phys. Lett. 2009, 26 (6): 066201 .   DOI: 10.1088/0256-307X/26/6/066201 Abstract   PDF(pc) (246KB) ( 1143 ) The thermal expansion coefficient (TEC) of an ideal crystal is derived by using a method of Boltzmann statistics. The Morse potential energy function is adopted to show the dependence of the TEC on the temperature. By taking the effects of the surface relaxation and the surface energy into consideration, the dimensionless TEC of a nanofilm is derived. It is shown that with decreasing thickness, the TEC can increase or decrease, depending on the surface relaxation of the nanofilm.
 Select Dependence of Nanofluid Viscosity on Particle Size and pH Value ZHAO Jia-Fei, LUO Zhong-Yang, NI Ming-Jiang, CEN Ke-Fa Chin. Phys. Lett. 2009, 26 (6): 066202 .   DOI: 10.1088/0256-307X/26/6/066202 Abstract   PDF(pc) (286KB) ( 2350 ) We investigate the viscosity of silicon dioxide nanofluid at different particle sizes and pH values considering nanoparticle aggregation. The experimental and simulation results indicate that nanoparticle size is of crucial importance to the viscosity of the nanofluid due to aggregation. As the nanoparticle size decreases, the viscosity becomes much more dependent on the volume fraction. Moreover, when the nanoparticle diameter is smaller than 20nm, the viscosity is closely related to the pH of the nanofluid, and fluctuates with pH values from 5 and 7.
 Select Numerical Simulation of Wave Propagation and Phase Transition of Tin under Shock-Wave Loading SONG Hai-Feng, LIU Hai-Feng, ZHANG Guang-Cai, ZHAO Yan-Hong Chin. Phys. Lett. 2009, 26 (6): 066401 .   DOI: 10.1088/0256-307X/26/6/066401 Abstract   PDF(pc) (459KB) ( 934 ) We undertake a numerical simulation of shock experiments on tin reported in the literature, by using a multiphase equation of state (MEOS) and a multiphase Steinberg Guinan (MSG) constitutive model for tin in the β, γ and liquid phases. In the MSG model, the Bauschinger effect is considered to better describe the unloading behavior. The phase diagram and Hugoniot of tin are calculated by MEOS, and they agree well with the experimental data. Combined with the MEOS and MSG models, hydrodynamic computer simulations are successful in reproducing the measured velocity profile of the shock wave experiment. Moreover, by analyzing the mass fraction contour as well as stress and temperature profiles of each phase for tin, we further discuss the complex behavior of tin under shock-wave loading.
 Select Ductile Bulk Aluminum-Based Alloy with Good Glass-Forming Ability and High Strength ZHUO Long-Chao, PANG Shu-Jie, WANG Hui, ZHANG Tao Chin. Phys. Lett. 2009, 26 (6): 066402 .   DOI: 10.1088/0256-307X/26/6/066402 Abstract   PDF(pc) (1093KB) ( 671 ) Based on a new approach for designing glassy alloy compositions, bulk Al-based alloys with good glass-forming ability (GFA) are synthesized. The cast Al86Si0.5Ni4.06Co2.94Y6Sc0.5 rod with a diameter of 1 mm shows almost fully amorphous structure besides about 5% fcc-Al nucleated in the center of the rod. The bulk alloy with high Al concentration exhibits an ultrahigh yield strength of 1.18GPa and maximum strength of 1.27GPa as well as an obvious plastic strain of about 2.4% during compressive deformation. This light Al-based alloy with good GFA and mechanical properties is promising as a new high specific strength material with good deformability.
 Select Improvement of Field Emission Characteristics of Copper Nitride Films with Increasing Copper Content WANG Tao, LI Rui-Shan, PAN Xiao-Jun, ZHANG Pei-Zeng, ZHOU Ming, SONGXi, XIE Er-Qing Chin. Phys. Lett. 2009, 26 (6): 066801 .   DOI: 10.1088/0256-307X/26/6/066801 Abstract   PDF(pc) (518KB) ( 750 ) A copper nitride (Cu3N) thin film is deposited on a Si substrate by the reactive magnetron sputtering method. The XPS measurements of the composite film indicate that the Cu content in the film is increased to 80.82at.% and the value of the Cu/N ratio to 4.2:1 by introducing 4% H2 into the reactive gas. X-ray diffraction measurements show that the film is composed of Cu3N crystallites with an anti-ReO3 structure. The effects of the increase of copper content on the field emission characteristics of the Cu3N thin film are investigated. Significant improvement in emission current density and emission repeatability could be attributed to the geometric field enhancement, caused by numerous surface nanotips, and the decrease of resistivity of the film.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
 Select Modification of Band Gap of -SiC by N-Doping LIU Hong-Sheng, FANG Xiao-Yong, SONG Wei-Li, HOU Zhi-Ling, LU Ran, YUAN Jie, CAO Mao-Sheng Chin. Phys. Lett. 2009, 26 (6): 067101 .   DOI: 10.1088/0256-307X/26/6/067101 Abstract   PDF(pc) (577KB) ( 1046 ) The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1-xNx (x=0, 1/32, 1/16, 1/8, 1/4) with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity.
 Select Effect of In-Doping on Electronic Structure and Optical Properties of Sr2TiO4 YUN Jiang-Ni, ZHANG Zhi-Yong, YAN Jun-Feng, ZHANG Fu-Chun Chin. Phys. Lett. 2009, 26 (6): 067102 .   DOI: 10.1088/0256-307X/26/6/067102 Abstract   PDF(pc) (525KB) ( 564 ) The effect of In doping on the electronic structure and optical properties of Sr2TiO4 is investigated by a first-principles calculation of plane wave ultrasoft pseudopotentials based on density functional theory. The calculated results reveal that corner-shared TiO6 octahedra dominate the main electronic properties of Sr2TiO4 and the covalency of the Ti-O(1) bond in the ab plane is stronger than that of the Ti-O(2) bond along the c-axis. After In doping, there is a little lattice expansion in Sr2In0.125Ti0.875O4 and the interaction between the Ti-O bond near the impurity In atom is weakened. The binding energies of Sr2TiO4 and Sr2In0.125Ti0.875O4 estimated from the electronic structure calculations indicate that the crystal structure of Sr2In0.125Ti0.875O4 is still stable after doping, but its stability is lower than that of undoped Sr2TiO4. Moreover, the valence bands (VBs) of the Sr2In0.125Ti0.875O4 system consist of O 2p and In 4d states, and the mixing of O 2p and In 4d states makes the top VBs shift significantly to high energies, resulting in visible light absorption. The adsorption of visible light is of practical importance for the application of Sr2TiO4 as a photocatalyst.
 Select Screening of Local Magnetic Moment by Electrons of Disordered Graphene SHI Li-Peng, XIONG Shi-Jie Chin. Phys. Lett. 2009, 26 (6): 067103 .   DOI: 10.1088/0256-307X/26/6/067103 Abstract   PDF(pc) (3571KB) ( 697 ) Based on the Anderson impurity model and self-consistent approach, we investigate the condition for the screening of a local magnetic moment by electrons in graphene and the influence of the moment on electronic properties of the system. The results of numerical calculations carried out on a finite sheet of graphene show that when the Fermi energy is above the single occupancy energy and below the double occupancy energy of the local impurity, a magnetic state is possible. A phase diagram in a parameter space spanned by the Coulomb energy U and the Fermi energy is obtained to distinguish the parameter regions for the magnetic and nonmagnetic states of the impurity. We find that the combined effect of the impurity and finite size effect results in alarge charge density near the edges of the finite graphene sheet. The density of states exhibits a peak at the Dirac point which is caused by the appearance of the edge states localized at the zigzag edges of the sheet.
 Select A Peak in Density Dependence of Electron Spin Relaxation Time in n-Type Bulk GaAs in the Metallic Regime SHEN Ka Chin. Phys. Lett. 2009, 26 (6): 067201 .   DOI: 10.1088/0256-307X/26/6/067201 Abstract   PDF(pc) (193KB) ( 524 ) We demonstrate that the peak in the density dependence of electron spin relaxation time in n-type bulk GaAs in the metallic regime predicted by Jiang and Wu [Phys.Rev.B 79(2009)125206] has been realized experimentally in the latest work [arXiv:0902.0270] by Krauβ, et al.
 Select Electrical Characteristics of Co/n-Si Schottky Barrier Diodes Using I-V and C-V Measurements G. Güler, Ö, . Güllü, S. Karatas, Ö, . F. Bakkaloglu Chin. Phys. Lett. 2009, 26 (6): 067301 .   DOI: 10.1088/0256-307X/26/6/067301 Abstract   PDF(pc) (313KB) ( 1115 ) Electrical characteristics of Co/n-Si Schottky barrier diodes are analysed by current-voltage (I-V) and capacitance-voltage (C-V) techniques at room temperature. The electronic parameters such as ideality factor, barrier height and average series resistance are determined. The barrier height 0.76eV obtained from the C-V measurements is higher than that of the value 0.70eV obtained from the I-V measurements. The series resistance RS and the ideality factor n are determined from the d\ln(I)/dV plot and are found to be 193.62Ω and 1.34, respectively. The barrier height and the RS value are calculated from the H(I)-I plot and are found to be 0.71eV and 205.95Ω. Furthermore, the energy distribution of the interface state density is determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density Nss ranges from 6.484×1011cm-2eV-1 in (EC-0.446)eV to 2.801×1010cm-2eV-1 in (EC-0.631,eV, of the Co/n-Si Schottky barrier diode. The results show the presence of a thin interfacial layer between the metal and the semiconductor.
 Select The Magnetic Properties of TbNi2B2C Investigated with a Two-Sublattice Model LIU Zhao-Sen, Divis Martin, Sechovsky Vladimir Chin. Phys. Lett. 2009, 26 (6): 067501 .   DOI: 10.1088/0256-307X/26/6/067501 Abstract   PDF(pc) (340KB) ( 587 ) A two-sublattice model for rare-earth antiferromagnets is employed to study the magnetic properties of TbNi2B2C. The theoretical susceptibility and magnetization curves obtained with the model show reasonable agreement with the experimental results.
 Select GaAs-Based Metamorphic Long-Wavelength InAs Quantum Dots Grown by Molecular Beam Epitaxy WANG Peng-Fei, XIONG Yong-Hua, WANG Hai-Li, HUANG She-Song, NI Hai-Qiao, XU Ying-Qiang, HE Zhen-Hong, NIU Zhi-Chuan Chin. Phys. Lett. 2009, 26 (6): 067801 .   DOI: 10.1088/0256-307X/26/6/067801 Abstract   PDF(pc) (498KB) ( 506 ) A bilayer stacked InAs/GaAs quantum dot structure grown by molecular beam epitaxy on an In0.05Ga0.95As metamorphic buffer is investigated. By introducing a InGaAs:Sb cover layer on the upper InAs quantum dots (QDs) layers, the emission wavelength of the QDs is extended successfully to 1.533μm at room temperature, and the density of the QDs is in the range of 4×109-8×109cm-2. Strong photoluminescence (PL) intensity with a full width at half maximum of 28.6meV of the PL spectrum shows good optical quality of the bilayer QDs. The growth of bilayer QDs on metamorphic buffers offers a useful way to extend the wavelengths of GaAs-based materials for potential applications in optoelectronic and quantum functional devices.
 Select Resonant Modes of L-Shaped Gold Nanoparticles YANG Jing, ZHANG Jia-Sen, WU Xiao-Fei, GONG Qi-Huang Chin. Phys. Lett. 2009, 26 (6): 067802 .   DOI: 10.1088/0256-307X/26/6/067802 Abstract   PDF(pc) (418KB) ( 480 ) We analyze the electric field modes excited in resonant L-shaped gold nanoparticles using a finite-difference time domain method. Compared to a single gold nanorod, both the odd and even modes of the L-shaped nanoparticles can be excited due to the symmetry breaking. The nanoparticles with equal and unequal arms have different dependence of field enhancement and mode on the incident polarization.
 Select Hydrothermal Synthesis and Vacuum Ultraviolet-Excited Luminescence Properties of Novel Dy3+-doped GdPO4 White Light Phosphors HAN Guo-Cai, WANG Yu-Hua, WU Chun-Fang, ZHANG Jia-Chi, LU Yang-Hua Chin. Phys. Lett. 2009, 26 (6): 067803 .   DOI: 10.1088/0256-307X/26/6/067803 Abstract   PDF(pc) (347KB) ( 658 ) Novel Dy3+-doped GdPO4 white light phosphors with a monoclinic system are successfully synthesized by the hydrothermal method at 240°C. The strong absorption at around 147nm in the excitation spectrum is assigned to the host absorption. It is suggested that the vacuum ultraviolet excited energy is transferred from the host to the Dy3+ ions. The f-d transition of the Dy3+ ion is observed to be located at 182nm, which is consistent with the calculated value using Dorenbos's expression. Under 147nm excitation, Gd0.92PO4:0.08Dy3+ phosphor exhibits two emission bands located at 572nm (yellow) and 478nm (blue), which correspond to the hypersensitive transitions 4F9/2-6H13/2 and 4F9/2-6H15/2. The two emission bands lead to the white light. Because of the strong absorption at about 147nm, Gd0.92PO4:0.08Dy3+ under vacuum ultraviolet excitation is an effective white light phosphor, and has promising applications to mercury-free lamps.
 Select Absorption Related to Electrochromism in Cubic Boron Nitride Single Crystals REN Ce, CHEN Zhan-Guo, JIA Gang, LIU Xiu-Huan, ZHAO Jian-Xun, WANG Shuang Chin. Phys. Lett. 2009, 26 (6): 067804 .   DOI: 10.1088/0256-307X/26/6/067804 Abstract   PDF(pc) (355KB) ( 618 ) A unusual electrochromism is observed in amber cubic boron nitride (cBN) single crystals when breakdown possibly related to impurities and defects occurs. The electrochromism induces an abrupt increase in the absorption coefficient of the cBN crystals within the visible and infrared region. The change of the absorption coefficient of cBN crystal can be increased linearly by raising the current after the electrochromism occurs, whereas it is irrelevant to the polarization of the incident light. The absorption related to the electrochromism in the cBN single crystal has potential applications in designing and manufacturing electro-optical modulators, optical switches, and other optoelectric devices.
 Select Experimental Investigation on a Highly Sensitive Atomic Magnetometer LI Shu-Guang, XU Yun-Fei, WANG Zhao-Ying, LIU Yun-Xian, LIN Qiang Chin. Phys. Lett. 2009, 26 (6): 067805 .   DOI: 10.1088/0256-307X/26/6/067805 Abstract   PDF(pc) (355KB) ( 832 ) A highly sensitive all-optical atomic magnetometer based on the magnetooptical effect which uses the advanced technique of single laser beam detection is reported and demonstrated experimentally. A sensitivity of 0.5pT/Hz1/2 is obtained by analyzing the magnetic noise spectrum, which exceeds that of most traditional magnetometers. This kind of atomic magnetometer is very compact, has a low power consumption, and has a high theoretical sensitivity limit, which make it suitable for many applications.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
 Select Growth and Characteristics of Epitaxial AlxGa1-xN by MOCVD ZHANG Jie, GUO Li-Wei, CHEN Yao, XU Pei-Qiang, DING Guo-Jian, PENGMing-Zeng, JIA Hai-Qiang, ZHOU Jun-Ming, CHEN Hong Chin. Phys. Lett. 2009, 26 (6): 068101 .   DOI: 10.1088/0256-307X/26/6/068101 Abstract   PDF(pc) (1207KB) ( 1161 ) AlxGa1-xN epilayers with a wide Al composition range (0.2≤x≤ 0.68) were grown on AlN/sapphire templates by low-pressure metalorganic chemical vapour deposition (LP-MOCVD). X-ray diffraction results reveal that both the (0002) and (10-15) full widths at half-maximum (FWHM) of the AlxGa1-xN epilayer decrease with increasing Al composition due to the smaller lattice mismatch to the AlN template. However, the surface morphology becomes rougher with increasing Al composition due to the weak migration ability of Al atoms. Low temperature photoluminescence (PL) spectra show pronounced near band edge (NBE) emission and the NBE FWHM becomes broader with increasing Al composition mainly caused by alloy disorder. Meanwhile, possible causes of the low energy peaks in the PL spectra are discussed.
 Select Two Possible Configurations for Silver-C60-Silver Molecular Devices and Their Conductance Characteristics TIAN Guang-Jun, SU Wen-Yong Chin. Phys. Lett. 2009, 26 (6): 068501 .   DOI: 10.1088/0256-307X/26/6/068501 Abstract   PDF(pc) (672KB) ( 505 ) Coherent electronic transport properties of silver-C60-silver molecular junctions in different configurations are studied using hybrid density functiontheory. The experimentally measured current flows of C60 molecules adsorbed on the silver surface are well reproduced by theoretical calculations. It is found that the current-voltage characteristics of the molecular junctions depend strongly on the configurations of the junctions. Transmission spectra combined with density of states can help us to understand in depth the transport properties. Different kinds of electrode construction are also discussed. With the help of the calculation, two possibleconfigurations of silver-C60-silver molecular junctions are suggested.
 Select Manipulation of Nanoparticles Using Dark-Field-Illumination Optical Tweezers with Compensating Spherical Aberration ZHOU Jin-Hua, TAO Run-Zhe, HU Zhi-Bin, ZHONG Min-Cheng, WANG Zi-Qiang, CAI Jun, LI Yin-Mei, Chin. Phys. Lett. 2009, 26 (6): 068701 .   DOI: 10.1088/0256-307X/26/6/068701 Abstract   PDF(pc) (428KB) ( 627 ) Based on our previous investigation of optical tweezers with dark field illumination [Chin. Phys. Lett. 25(2008)329], nanoparticles at large trap depth are better viewed in wide field and real time for a long time, but with poor forces. Here we present the mismatched tube length to compensate for spherical aberration of an oil-immersion objective in a glass-water interface in an optical tweezers system for manipulating nanoparticles. In this way, the critical power of stable trapping particles is measured at different trap depths. It is found that trap depth is enlarged for trapping nanoparticles and trapping forces are enhanced at large trap depth. According to the measurement, 70-nm particles are manipulated in three dimensions and observed clearly at large appropriate depth. This will expand applications of optical tweezers in a nanometre-scale colloidal system.
 Select Gating of Water Flow Induced by Bending of a Carbon Nanotube WANG Shen, LU Hang-Jun, TU Yu-Song, WANG Chun-Lei, FANG Hai-Ping, Chin. Phys. Lett. 2009, 26 (6): 068702 .   DOI: 10.1088/0256-307X/26/6/068702 Abstract   PDF(pc) (430KB) ( 456 ) The ON-OFF state transition of the water transport induced by the structural bending of a carbon nanotube is studied by molecule dynamics simulation. The water permeation through a bent carbon nanotube shows excellent gating property with a threshold bending angle of about 14.6°. We also investigate the water density distribution inside the nanochannel to illustrate the mechanism.
 Select Modulated Wave Packets in DNA and Impact of Viscosity Conrad Bertrand Tabi, Alidou Mohamadou, Timoleon Crepin Kofané Chin. Phys. Lett. 2009, 26 (6): 068703 .   DOI: 10.1088/0256-307X/26/6/068703 Abstract   PDF(pc) (735KB) ( 724 ) We study the nonlinear dynamics of a DNA molecular system at physiological temperature in a viscous media by using the Peyrard-Bishop model. The nonlinear dynamics of the above system is shown to be governed by the discrete complex Ginzburg-Landau equation. In the non-viscous limit, the equation reduces to the nonlinear Schrödinger equation. Modulational instability criteria are derived for both the cases. On the basis of these criteria, numerical simulations are made, which confirm the analytical predictions. The planar wave solution used as the initial condition makes localized oscillations of base pairs and causes energy localization. The results also show that the viscosity of the solvent in the surrounding damps out the amplitude of wave patterns.
 Select An Efficient Control Strategy of Epidemic Spreading on Scale-Free Networks HANG Hai-Feng, LI Ke-Zan, FU Xin-Chu, WANG Bing-Hong, Chin. Phys. Lett. 2009, 26 (6): 068901 .   DOI: 10.1088/0256-307X/26/6/068901 Abstract   PDF(pc) (325KB) ( 667 ) We present a novel and effective method for controlling epidemic spreading on complex networks, especially on scale-free networks. The proposed strategy is performed by deleting edges according to their significances (thesignificance of an edge is defined as the product of the degrees of two nodes of this edge). In contrast to other methods, e.g., random immunization, proportional immunization, targeted immunization, acquaintance immunization and so on, which mainly focus on how to delete nodes to realize the control of epidemic spreading on complex networks, our method is more effective in realizing the control of epidemic spreading on complex networks, moreover, such a method can better retain the integrity of complex networks.
 Select Modelling Moran Process with Network Dynamics for the Evolution of Cooperation YANG Dong-Ping, LIN Hai, WU Chen-Xu, SHUAI Jian-Wei Chin. Phys. Lett. 2009, 26 (6): 068902 .   DOI: 10.1088/0256-307X/26/6/068902 Abstract   PDF(pc) (274KB) ( 495 ) We introduce a simple model based on the Moran process with network dynamics. Using pair approximation, the cooperation frequencies at equilibrium states are deduced for general interactions. Three usual social dilemmas are discussed in the framework of our model. It is found that they all have a phase transition at the same value of cost-to-benefit ratio. For the prisoner's dilemma game, notably it is exactly the simple rule reported in the literature [Nature 441(2006)502]. In our model, the simple rule results from the parent-offspring link. Thus the basic mechanism for cooperation enhancement in network reciprocity is in line with the Hamilton rule of kin selection. Our simulations verify the analysis obtained from pair approximation.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
 Select A Two-Field Dilaton Model of Dark Energy LIANG Nan, GAO Chang-Jun, ZHANG Shuang-Nan, Chin. Phys. Lett. 2009, 26 (6): 069501 .   DOI: 10.1088/0256-307X/26/6/069501 Abstract   PDF(pc) (254KB) ( 675 ) We investigate the cosmological evolution of a two-field model of dark energy, where one is a dilaton field with canonical kinetic energy and the other is a phantom field with a negative kinetic energy term. Phase-plane analysis shows that the `phantom''-dominated scaling solution is the stable late-time attractor of this type of model. We find that during the evolution of the universe, the equation of state w changes from w > -1 to w <-1, which is consistent with recent observations.
 Select Nightside Martian Ionosphere Produced by Electron Impact Ionization ZHANG Yi-Teng, LI Lei Chin. Phys. Lett. 2009, 26 (6): 069601 .   DOI: 10.1088/0256-307X/26/6/069601 Abstract   PDF(pc) (469KB) ( 873 ) Based on the Martian magnetic field model established by magnetohydrodynamics simulation, we determine the possible precipitation areas of the solar wind electron in the nightside Martian atmosphere, and analyze the electron impact ionization to estimate the height of the nightside Martian ionospheric peak and the electron density profile using the energy flux analysis method. The influences of the single electron energy, electron energy density and ionization efficiency on the altitude of the ionospheric peak and the electron density profile are also investigated. Our results show that the solar wind electron moves along the V-shaped solar wind magnetic field lines, to precipitate into the Martian atmosphere. Due to the crustal magnetic field, the precipitation regions on the nightside are quite narrow and unstable. The impact ionization happens at the altitude of 130-500km, and the height of the ionospheric peak is around 170km, with a peak electron density of 3.0×103cm-3. The simulation results are consistent with the results from Mars 4/5 and Viking occultation measurements.
Original Articles
 Select Dynamical Stability and Attractor of the Variable Generalized Chaplygin Gas Model FU Huan-Huan, WU Ya-Bo, CHENG Fang-Yuan Chin. Phys. Lett. 2009, 26 (6): 069801 .   DOI: 10.1088/0256-307X/26/6/069801 Abstract   PDF(pc) (296KB) ( 664 ) For the variable generalized Chaplygin gas (VGCG) as a dynamical system, its stability is analyzed and the related dynamical attractors are investigated. By analysis it is shown that there are two critical points corresponding to the matter-dominated phase and the VGCG dark energy-dominated phase, respectively. Moreover, when the parameters n, α and γ take some fixed values, the phase with ωVGCG= -0.92 is a dynamical attractor and the equation of state of VGCG reaches it from either ωVGCG > -1 or ωVGCG< -1, independent of the initial values of the dynamical system. This shows a satisfactory cosmological model: the early matter-dominated era, followed by the dark energy-dominated era. Meanwhile, the evolutions of density parameters Ωγ and ΩVGCG are quite different from each other. For different initial values of x and y,Ωγ decreases and ΩVGCG increases as the time grows, they will eventually approach Ωγ=0 and ΩVGCG= 1. Furthermore, since different values of n or α may lead to different equation-of-state parameters ΩVGCG, we also discuss the constraints on the parameters n and α by the observation data.
86 articles