Chaotic rocking behavior of freestanding objects with sliding motion

This paper examines the influence of effects of sliding on the non-linear rocking response behavior of freestanding rigid objects (blocks) subjected to harmonic horizontal and vertical excitations. It is well known that the rocking responses depend strongly on the impact effect between object and the base, which takes place with abrupt reduction in kinetic energy. In this study, it is shown that the rocking behavior is significantly affected by the presence of the sliding motion. A parametric response analysis is carried out over a range of excitation amplitudes and frequencies. Chaotic responses are observed over a wide response region, particularly for the case of large vertical amplitude excitation with significant sliding motions. The chaotic characteristics are demonstrated using time histories, Poincaré sections, power spectral density and Lyapunov exponents of the rocking responses. The complex chaotic response behavior is illustrated by Poincaré section in the phase space. The distribution of various types of rocking responses and the effects of sliding motion are examined via bifurcation diagrams and examples of typical rocking responses.     

Design and fabrication of polarization-insensitive hybrid solgel arrayed waveguide gratings

We report on the successful design and fabrication of a polarization-insensitive arrayed waveguide grating (AWG), using solgel-derived silica glass films formed on fused-silica substrates. By controlling the waveguide width and making the propagation constants of the polarizations equal, we have found it possible to fabricate polarization-insensitive solgel-based AWGs. Polarization-insensitive design improves the cross talk by approximately 10 dB in the dynamic range.     

Photoluminescence behavior of pulsed laser deposited ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript> thin-film phosphors grown on various substrates

ZnGa₂O₄ thin-film phosphors have been grown on Si(100), Al₂O₃(0001) and MgO(100) substrates using pulsed laser deposition. The structural characterization was carried out on a series of ZnGa₂O₄ films grown on various substrates under various substrate temperatures and oxygen pressures. The films grown on these substrates not only have different crystallinity and surface morphology, but also different Zn/Ga composition ratio. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular the stoichiometry ratio of Zn/Ga and the kind of substrate. The variation of Zn/Ga in the films also depends on not only the oxygen pressure but also the substrate temperature during deposition. The PL properties of pulsed laser deposited ZnGa₂O₄ thin films have indicated that Al₂O₃(0001) and MgO(100) are promising substrates for the growth of high-quality ZnGa₂O₄ thin films and that the luminescence brightness depends on the substrate. The luminescence spectra show a broad band extending from 350 to 600 nm and peaking at 460 nm. Received: 11 July 2002 / Accepted: 31 July 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +82-51-6206356, E-mail: jhjeong@pknu.ac.kr     

Structural transformation of fluorinated carbon nanotubes induced by in situ electron-beam irradiation

We have investigated the structural transformation of fluorinated singlewalled nanotubes (SWNTs) induced by electron-beam irradiation during the transmission electron microscope observations. Heavily fluorinated SWNT bundles were systematically transformed into multiwall-like nanotubes by releasing fluorine atoms during electron-beam irradiation and even broken into two pieces of the capped graphitic structures. Such structural transformations at relatively low kinetic energy (< or = 300 keV) could be explained by the local strains induced by fluorination, where C-C bonds that were fluorine-attached became 1.53 A, a single bond similar to that of a diamond, from our density functional calculations. We propose a possible concerted pathway for the structural transformation of fluorinated SWNTs induced by electron-beam irradiation based on the experimental observations.     

Microbial transformation of terreusinone, an ultraviolet-A (UV-A) protecting dipyrroloquinone, by Streptomyces sp

Biotransformation study was conducted on the marine dipyrroloquinone, terreusinone (1) isolated from the marine-derived fungus Aspergillus terreus. Preparative-scale fermentation of terreusinone with Streptomyces sp. has resulted in the isolation of a new oxidized metabolite, terreusinol (2). The structure was elucidated as 2-[(1R)-1-hydroxyisobutyl]-6-[(1R)-1,2-dihydroxyisobutyl]-1H,5H-pyrrolo[2,3-b]indole-4,8-dione (2) on the basis of physicochemical evidence. Terreusinol (2) showed an ultraviolet-A (UV-A) (320-390 nm) protecting activity with ED(50) values of 150 microM, which is more active than oxybenzone (ED(50), 350 microM) currently being used as sunscreen.     

Humulene derivatives from Zingiber zerumbet with the inhibitory effects on lipopolysaccharide-induced nitric oxide production

A new humulene sesquiterpene, 5-hydroxyzerumbone (5-hydroxy-2E,6E,9E-humulatrien-8-one) (1) and a known compound, zerumboneoxide (2) were isolated from the rhizomes of Zingiber zerumbet (Zingiberaceae), and found to inhibit lipopolysaccharide-induced nitric oxide production in murine macrophage RAW 264.7 cells with IC50 values of 14.1 and 23.5 microM, respectively, by bioassay-guided fractionation (positive control: N(omega)-monomethyl-L-arginine, IC50=21.3 microM). The structure of 1 was determined by spectroscopic methods including 1D and 2D-NMR.     

Wigner Distribution Function for the Time-Dependent Quadratic-Hamiltonian Quantum System using the Lewis–Riesenfeld Invariant Operator

We investigate the Wigner distribution function of the general time-dependent quadratic-Hamiltonian quantum system with the Lewis–Riesenfeld invariant operator method. The Wigner distribution function of the system in Fock state, coherent state, squeezed state, and thermal state are derived. We apply our study to the one-dimensional motion of a Brownian particle and to the driven oscillator with strongly pulsating mass.PACS: 03.65.-w, 03.65.Ca     

Universality class of the fiber bundle model on complex networks

We investigate the failure characteristics of complex networks within the framework of the fiber bundle model subject to the local load sharing rule in which the load of the broken fiber is transferred only to its neighbor fibers. Although the load sharing is strictly local, it is found that the critical behavior belongs to the universality class of global load sharing where the load is transferred equally to all fibers in the system. From the numerical simulations and the analytical approach applied to the microscopic behavior, it is revealed that the emergence of a single dominant hub cluster of broken fibers causes the global load sharing effect in the failure process.     

Femtosecond laser pulses for surface-profile metrology

We discuss two ways to use femtosecond pulsed lasers as a new interferometric light source for enhanced precision surface-profile metrology. First, a train of ultrafast laser pulses yields repeated low temporal coherence, which allows unequal-path scanning interferometry, which is not feasible with white light, to be performed. Second, the high spatial coherence of femtosecond pulsed lasers enables large-sized optics to be tested in nonsymmetric configurations with relatively small-sized reference surfaces. These two advantages are verified experimentally with Fizeau and Twyman-Green type scanning interferometers.     

Multiport N x N multimode air-clad holey fiber coupler for high-power combiner and splitter

We report 2 x 2 and 4 x 4 multimode air-clad holey fiber couplers fabricated by a novel fusion and tapering technique. The devices showed excellent port-to-port coupling uniformity over a wide spectral range of 800-1650 nm. The 4 x 4 coupler showed a low insertion loss of 9.9 dB and excess loss of 3.9 dB at 1310 nm. Because of its unique air cladding and the high numerical aperture of the holey fiber structure, the device showed strong potential in high-power applications.