Oct 2012, Volume 7 Issue 5

Cover illustration

  • Intensive investigations have been devoted to synthesizing and characterizing silver nanoparticles in recent years because of their rich optical properties raised by the surface plasmon resonances in the visible spectral range. Branched silver nanostructures have attracted people’s interests for their high surface to volume ratios and fancy shapes. These unique properties make them the promising candidates for both catalysts and substrates in surface-enhanced Raman scat [Detail] ...

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    XinChou Lou
    J. F. Chen, Shengwang Du

    In this article, we review on narrowband photon pairs producedin nonlinear crystals, and especially in atomic ensembles. In atomicensembles, “write-read” process in pulse mode andspontaneous four-wave mixing process (SFWM) in continuous mode aretwo popular photon pair generation schemes. We specifically discussthe experimental works with continuous SFWM scheme in cold atomicensembles. Photon pairs produced in these systems are characteristicof controllable long coherence time, and therefore are accessiblewith direct temporal modulation. We elaborate on the recent techniqueson modulation and waveform reshaping of narrow-band paired photons.

    Werner A. Hofer

    So far no mechanism is known, which could connect the two measurementsin an Aspect-type experiment. Here, we suggest such a mechanism, basedon the phase of a photon’s field during propagation. We showthat two polarization measurements are correlated, even if no signalpasses from one point of measurement to the other. The non-local connectionof a photon pair is the result of its origin at a common source, wherethe two fields acquire a well defined phase difference. Therefore,it is not actually a non-local effect in any conventional sense. Weexpect that the model and the detailed analysis it allows will havea major impact on quantum cryptography and quantum computation.

    Yun-Xia Dong, Xiao-Hua Cui

    Based on the quantization scheme of the radiation fields inthe dispersive and absorptive magnetic media, the normally orderedcorrelation functions of the outgoing field through a metamaterialplate are obtained. Then the relative photon-number densities of thetransmitted field, the reflected field and the absorbed field aregotten through the correlation functions. Furthermore, the contributionsof the relative permittivity and permeability of the metamaterialsto the transmission are analyzed. Our results show that the permittivity and permeability reinforce the transmission for frequencies that arebig compared with the magnetic resonance frequency.

    Liang-Jun Zhai(翟良君), Yu-Jun Zheng(郑雨军), Shi-Liang Ding(丁世良)

    Within Lie algebraic model, the vibrational chaotic dynamics in triatomic molecules are studied. The molecules of H2S, NO2, and O3 are sampled to explore the dynamical differences between the local and normal mode molecules. The comprehensive effects of the local and normal mode vibrations, resonances and chaos on the dynamical entanglement are studied. The results demonstrate that the resonances as well as chaos can promote the evolution of dynamical entanglement.

    Feng-Zi Cong, Hong Wei, Xiao-Rui Tian, Hong-Xing Xu

    We report a facile method of preparing novel branched silvernanowire structures such as Y-shaped, K-shaped and other multi-branchednanowires. These branched nanostructures are synthesized by reducingsilver nitrate (AgNO3) in polyethylene glycol(PEG) with polyvinglpyrrolidone (PVP) as capping agent. Statisticaldata indicate that for the “y” typed branched nanowire,the branches grow out from the side of the trunk nanowire in a preferentialorientation with an angle of 55? between the branch and the trunk.Transmission electron microscopy (TEM) studies indicate that the defectson silver nanowires could support the growth of branched nanowires.Conditions such as the molar ratio of PVP/AgNO3, the reaction temperature, and the degree of polymerization of reducingagent and PVP play important roles in determining the yield of thesilver branches. Due to the rough surface, these branched nanostructurescan be used as efficient substrates for surface-enhanced Raman scatteringapplications.

    Xing-Hai Zhao, Guang-Cun Shan, Chan-Hung Shek

    In this work, we present a schematic configuration and devicemodel for a graphene-nanoribbon (GNR)-array-based nanolaser, whichconsists of a three-variable rate equations that takes into accountcarrier capture and Pauli blocking in semiconductor GNR-array lasersto analyze the steadystate properties and dynamics in terms of therole of the capture rate and the gain coefficient in GNR array nanolasers.Furthermore, our GNR-array nanolaser device model can be determinedas two distinct two-variable reductions of the rate equations in thelimit of large capture rates, depending on their relative values.The first case leads to the rate equations for quantum well lasers,exhibiting relaxation oscillations dynamics. The second case correspondsto GNRs nearly saturated by the carriers and is characterized by theabsence of relaxation oscillations. Our results here demonstratedthat GNR-array as gain material embedded into a high finesse microcavitycan serve as an ultralow lasing threshold nanolaser with promisingapplications ranging widely from optical fiber communication withincreasing data processing speed to digital optical recording andbiology spectroscopy.

    Bo Feng, Mingxing Luo

    This article provides an introduction to on-shell recursionrelations for calculations of tree-level amplitudes. Starting withthe basics, such as spinor notations and color decompositions, weexpose analytic properties of gauge-boson amplitudes, BCFW-deformations,the large z-behavior of amplitudes, and on-shell recursion relationsof gluons. We discuss further developments of on-shell recursion relations,including generalization to other quantum field theories, supersymmetrictheories in particular, recursion relations for off-shell currents,recursion relation with nonzero boundary contributions, bonus relations,relations for rational parts of one-loop amplitudes, recursion relationsin 3D and a proof of CSW rules. Finally, we present samples of applications,including solutions of split helicity amplitudes and of N = 4 SYM theories, consequences of consistentconditions under recursion relation, Kleiss-Kuijf (KK) and Bern-Carrasco-Johansson(BCJ) relations for color-ordered gluon tree amplitudes, Kawai-Lewellen-Tye(KLT) relations.

    Eric W. Frey, Ashton A. Gooding, Sitara Wijeratne, Ching-Hwa Kiang

    Processes for decoding the genetic information in cells, includingtranscription, replication, recombination and repair, involve thedeformation of DNA from its equilibrium structures such as bending,stretching, twisting, and unzipping of the double helix. Single-moleculemanipulation techniques have made it possible to control DNA conformationand simultaneously detect the induced changes, revealing a rich varietyof mechanically-induced conformational changes and thermodynamic states.These single-molecule techniques helped us to reveal the physics ofDNA and the processes involved in the passing on of the genetic code.

    Ai-Guo Xu, Guang-Cai Zhang, Yan-Biao Gan, Feng Chen, Xi-Jun Yu

    In this mini-review we summarize the progress of Lattice Boltzmann(LB) modeling and simulating compressible flows in our group in recentyears. Main contents include (i) Single-Relaxation-Time (SRT) LB modelsupplemented by additional viscosity, (ii) Multiple-Relaxation-Time(MRT) LB model, and (iii) LB study on hydrodynamic instabilities.The former two belong to improvements of physical modeling and thethird belongs to simulation or application. The SRT-LB model supplementedby additional viscosity keeps the original framework of Lattice Bhatnagar–Gross–Krook(LBGK). So, it is easier and more convenient for previous SRT-LB users.The MRT-LB is a completely new framework for physical modeling. Itsignificantly extends the range of LB applications. The cost is longercomputational time. The developed SRT-LB and MRT-LB are complementaryfrom the sides of convenience and applicability.