Mar 2008, Volume 3 Issue 1

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  • LOU Ci-bo, TANG Li-qin, SONG Dao-hong, WANG Xiao-sheng, XU Jing-jun, CHEN Zhi-gang
    The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics, and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array, a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential applications in optical switching and navigation. In this review article, we present a brief overview on our experimental demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein condensates) propagating in periodic potentials.
  • DENG LÜ-bi
    In the preceding paper, we discussed eight configurations of particle Fraunhofer diffraction. In this paper, we consider nine configurations of particle Fresnel diffraction, and have derived the wave functions of particles in these configurations. Furthermore, the author presents a new inertial navigator principle. Its devised accuracy is not lower than that of the inertial navigator based on cold atom interferometer. The new inertial navigator is named as ABSE inertial navigator. ABSE is abbreviation for Aharonov-Bohm-Sagnac effect.
  • YUN Min, LIU Yang, DENG Lian-zhong, ZHOU Qi, YIN Jian-ping
    A new kind of continuous-wave (CW) cold molecular beam, methyl cyanide (CH3CN) beam, is generated by a bent electrostatic quadrupole guiding. The Stark shift of rotational energy levels of CH3CN molecule and its population distribution are calculated, and the dynamic processes of electrostatic guiding and energy filtering of CH3CN molecules from a gas source with room temperature (300 K) are simulated by Monte Carlo Method. The study showed that the longitudinal and transversal temperatures of output cold CH3CN beam could be about ∼ 2 K and ∼ 420 mK, and the corresponding guiding efficiency was about 10-5 as the guiding voltage was 3 kV. Furthermore, the temperature of the guided molecules and its guiding efficiency can be controlled by adjusting the guiding voltages applied on electrodes.
  • LI Bin, ZHAO Jin, FENG Min, ONDA Ken
    The femtosecond time-resolved two-photon photoemission (TR-2PP) and the ultra high vacuum (UHV) surface science techniques are integrated to investigate the elec- tronic structures and the interfacial electron transfer dynamics at the atomically ordered adsorbate overlayers on TiO2 single- crystalline surfaces. Our research into the CH3OH/TiO2 system exhibits complex dynamics, providing abundant informa- tion with regard to electron transport and solvation processes in the interfacial solvent structures. These represent the fundamentally physical, photochemical, and photocatalytic reactions of protic chemicals covered with metal-oxides.
  • HAN Yong, LIU Feng
    We discuss Coulomb effects on the coarsening of metal nanostructures on surfaces. We have proposed a new concept of a “Coulomb sink” [Phys. Rev. Lett., 2004, 93: 106102] to elucidate the effect of Coulomb charging on the coarsening of metal mesas grown on semiconductor surfaces. A charged mesa, due to its reduced chemical potential, acts as a Coulomb sink and grows at the expense of neighboring neutral mesas. The Coulomb sink provides a potentially useful method for the controlled fabrication of metal nanostructures. In this article, we will describe in detail the proposed physical models, which can explain qualitatively the most salient features of coarsening of charged Pb mesas on the Si(111) surface, as observed by scanning tunneling microscopy (STM). We will also describe a method of precisely fabricating large-scale nanocrystals with well-defined shape and size. By using the Coulomb sink effect, the artificial center-full-hollowed or half-hollowed nanowells can be created.
  • WANG Qin, JIANG Cheng, ZHENG Hang
    Using the spin-boson model with coupling to Ohmic bath, an analytical approach is developed to study the dynamics of the current correlation function in dissipative two-state systems with the view of understanding the effects of environment and tunneling on the coherent oscillation and the long-time decay of the current correlation function in these systems. An analytic expression of current correlation function is obtained and the results agree very well with that of numerical simulations.
  • LUO Ting, ZHANG Yi, ZHANG Yue-yang, FENG Qing-rong, LI Xing-guo, LIN Li
    Systematic studies of synthesizing behaviors of sol-gel YBa2Cu3O7-x samples in flowing oxygen atmosphere and their superconductivity have been performed. A set of high temperature ?-T curves has been obtained for the whole synthesizing process. After four rounds of synthesizing, the resistivity of the sample was around ? = 1.00 × 10-3 ?cm at room temperature. The ?-T curve of the fourth round shows that the orthorhombic to tetragonal phase transformation of the sample occurs around 600°C, which is lower than that of the YBa2Cu3O7-x sample prepared by conventional solid-state reaction method. Other measurements, such as X-ray diffraction, SEM measurement and low temperature R-T and M-T measurement, were also performed. And the R-T and M-T measurement results suggest that during the synthesizing process, there exist some state at which the sample has better superconductivity than the other states. Moreover, we found screw dislocations presenting on the sample broken surface from the SEM images. This will change the concept that the screw dislocations can only grow on the surface of the YBCO thin films and single crystals.
  • ZHOU Li-juan, MA Wei-xing, WU Qing
    Based on the Dyson-Schwinger Equations (DSEs) of QCD in the “rainbow” approximation, the fully dressed quark propagator Sf(p) is investigated, and then an algebraic parametrization form of the propagator is obtained as a solution of the equations. The dressed quark amplitudes Af and Bf which built up the fully dressed quark propagator, and the dynamical running masses Mf, which is defined by Af and Bf for light quarks u, d and s, are calculated, respectively. Using the predicted current masses mf, quark local vacuum condensates, and our predicted value of pion decay constant, the masses of Goldstone bosons K, ? and ? and their in-medium values are also evaluated. Our predictions fit to data and to many other different calculations quite well. The numerical results show that the mass of quark is dependent of its momentum p2. The fully dressed quark amplitudes Af and Bf have correct behaviors and can be used for many purposes in our future researches on non-perturbative QCD.
  • XIE Xiao-ning, YUE Rui-hong, SHI Kang-jie, WU Sheng, ZHANG Li-xia
    In this paper, we show that the Lax connections can yield new classical solutions with a spectral parameter of the hybrid formulism for the Type IIB superstring in an AdS2 × S2 background with Ramond-Ramond flux. This series of classical solutions have the same infinite set of classically conserved charges.
  • MAO You-dong, LUO Chun-xiong, OU-YANG Qi
    This paper summarizes our studies of DNA nanocompartement in recent years. Biological macromolecules have been used to fabricate many nanostructures, bio-devices, and biomimetics because of their physical and chemical properties. But dynamic nanostructure and bio-machinery that depend on collective behavior of biomolecules have not been demonstrated. Here, we report the design of DNA nanocompartment on surfaces that exhibit reversible changes in molecular mechanical properties. Such molecular nanocompar- tment is served to encage molecules, switched by the collective effect of Watson-Crick base- pairing interactions. This effect is used to investigate the dynamic process of nanocompartment switching and molecular thermosensing, as well as perform molecular recognition. Further, we found that ‘fuel’ strands with single-base variation cannot afford an efficient closing of nanocompartment, which allows highly sensitive label-free DNA array detection. Theoretical analysis and computer simulations confirm our experimental observations, which are discussed in this review paper. Our results suggest that DNA nanocompartment can be used as building blocks for complex biomaterials, because its core functions are independent of substrates and mediators.
  • NIESNER Raluca, GERICKE Karl-Heinz
    The biosciences require the development of methods that allow a non-invasive and rapid investigation of biological systems. In this aspect, high-end imaging techniques allow intravital microscopy in real-time, providing information on a molecular basis. Far-field fluorescence imaging techniques are some of the most adequate methods for such investigations. However, there are great differences between the common fluorescence imaging techniques, i.e., wide-field, confocal one-photon and two-photon microscopy, as far as their applicability in diverse bioscientific research areas is concerned. In the first part of this work, we briefly compare these techniques. Standard methods used in the biosciences, i.e., steady-state techniques based on the analysis of the total fluorescence signal originating from the sample, can successfully be employed in the study of cell, tissue and organ morphology as well as in monitoring the macroscopic tissue function. However, they are mostly inadequate for the quantitative investigation of the cellular function at the molecular level. The intrinsic disadvantages of steady-state techniques are countered by using time-resolved techniques. Among these fluorescence lifetime imaging (FLIM) is currently the most common. Different FLIM principles as well as applications of particular relevance for the biosciences, especially for fast intravital studies are discussed in this work.
  • YANG Kong-qing, YANG Lei, GONG Bai-hua, LIN Zhong-cai, HE Hong-sheng, HUANG Liang
    Complex networks describe a wide range of systems in nature and society. Since most real systems exist in certain physical space and the distance between the nodes has influence on the connections, it is helpful to study geographical complex networks and to investigate how the geographical constrains on the connections affect the network properties. In this paper, we briefly review our recent progress on geographical complex networks with respect of statistics, modelling, robustness, and synchronizability. It has been shown that the geographical constrains tend to make the network less robust and less synchronizable. Synchronization on random networks and clustered networks is also studied.