Symmetric Itinerary Sets

We consider a one parameter family of dynamical systems W :[0, 1] -> [0, 1] constructed from a pair of monotone increasing diffeomorphisms Wsub(i), such that Wsub(i)(inverse): [0, 1] -> [0, 1], (i = 0, 1). We characterise the set of symbolic itineraries of W using an attractor of an iterated closed relation,in the terminology of McGehee, and prove that there is a member of the family for which is symmetrical

Classical dynamics near the triple collision in a three-body Coulomb problem

We investigate the classical motion of three charged particles with both attractive and repulsive interaction.The triple collision is a main source of chaos in such three body Coulomb problems.By employing the McGehee scaling technique, we analyse here for the first time in detail the three-body dynamics near the triple collision in 3 degrees of freedom.We reveal surprisingly simple dynamical patterns in large parts of the chaotic phase space. The underlying degree of order in the form of approximate Markov partitions may help in understanding the global structures observed in quantum spectra of two-electron atoms.Comment: 4 pages, 3 figure

Multi-static, multi-frequency scattering from zooplankton

Abstract: Inversion of multi-frequency acoustic backscattering cm be used to estkate size-abundances of zooplankton, given a valid model for backscattering for the zooplankters. me physical properties of the scatterers, density and compressibility (or compressional-wave sound speed), are usually assigned fixed values in the scattering model.~ese properties wotid be of interest if they could be mew~~in~it~, e.g.to exm~e~hange$in liPid contents over seasons. Extension of currently-favored backscattering models to multi-static configurations looks promising as a method to directly measure these relevant physical properties simultaneously with size-abundance estimation

Relationship between photonic band structure and emission characteristics of a polymer distributed feedback laser

G. A. Turnbull, P. Andrew, M. J. Jory, William L. Barnes, and I. D. W. Samuel, Physical Review B, Vol. 64, article 125122 (2001). "Copyright © 2001 by the American Physical Society."We present an experimental study of the emission characteristics and photonic band structure of a distributed feedback polymer laser, based on the material poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. We use measurements of the photonic band dispersion to explain how the substrate microstructure modifies both spontaneous and stimulated emission. The lasing structure exhibits a one-dimensional photonic band gap around 610 nm, with lasing occurring at one of the two associated band edges. The band edge (frequency) selection mechanism is found to be a difference in the level of output coupling of the modes associated with the two band edges. This is a feature of the second-order distributed feedback mechanism we have employed and is clearly evident in the measured photonic band structur

M Dwarfs in SDSS Stripe 82: Photometric Light Curves and Flare Rate Analysis

We present a flare rate analysis of 50,130 M dwarf light curves in SDSS Stripe 82. We identified 271 flares using a customized variability index to search ~2.5 million photometric observations for flux increases in the u- and g-bands. Every image of a flaring observation was examined by eye and with a PSF-matching and image subtraction tool to guard against false positives. Flaring is found to be strongly correlated with the appearance of H-alpha in emission in the quiet spectrum. Of the 99 flare stars that have spectra, we classify 8 as relatively inactive. The flaring fraction is found to increase strongly in stars with redder colors during quiescence, which can be attributed to the increasing flare visibility and increasing active fraction for redder stars. The flaring fraction is strongly correlated with |Z| distance such that most stars that flare are within 300 pc of the Galactic plane. We derive flare u-band luminosities and find that the most luminous flares occur on the earlier-type M dwarfs. Our best estimate of the lower limit on the flaring rate (averaged over Stripe 82) for flares with \Delta u \ge 0.7 magnitudes on stars with u < 22 is 1.3 flares hour^-1 square degree^-1 but can vary significantly with the line-of-sight.Comment: 44 pages, 13 figure

On stochastic sea of the standard map

Consider a generic one-parameter unfolding of a homoclinic tangency of an area preserving surface diffeomorphism. We show that for many parameters (residual subset in an open set approaching the critical value) the corresponding diffeomorphism has a transitive invariant set $\Omega$ of full Hausdorff dimension. The set $\Omega$ is a topological limit of hyperbolic sets and is accumulated by elliptic islands. As an application we prove that stochastic sea of the standard map has full Hausdorff dimension for sufficiently large topologically generic parameters.Comment: 36 pages, 5 figure

Electrospun amplified fiber optics

A lot of research is focused on all-optical signal processing, aiming to obtain effective alternatives to existing data transmission platforms. Amplification of light in fiber optics, such as in Erbium-doped fiber amplifiers, is especially important for an efficient signal transmission. However, the complex fabrication methods, involving high-temperature processes performed in highly pure environment, slow down the fabrication and make amplified components expensive with respect to an ideal, high-throughput and room temperature production. Here, we report on near infrared polymer fiber amplifiers, working over a band of about 20 nm. The fibers are cheap, spun with a process entirely carried out at room temperature, and show amplified spontaneous emission with good gain coefficients as well as low optical losses (a few cm^-1). The amplification process is favoured by the high fiber quality and low self-absorption. The found performance metrics promise to be suitable for short-distance operation, and the large variety of commercially-available doping dyes might allow for effective multi-wavelength operation by electrospun amplified fiber optics.Comment: 27 pages, 8 figure

A First Look at White Dwarf - M Dwarf Pairs in the Sloan Digital Sky Survey (SDSS)

We have identified 109 White Dwarf (WD) - M dwarf pairs in the Sloan Digital Sky Survey (SDSS) with g < 20th magnitude. For each system we determined the temperature of the WD primary and the spectral type of the M dwarf secondary. Using H-alpha emission as a proxy for the chromospheric activity level of the M dwarf, we investigated correlations between the activity level and properties of the system. Compared with field M dwarfs (Hawley et al. 1996), we see a slightly higher active fraction of early-type stars, with activity levels similar to the field. We have conducted followup observations at the ARC 3.5m telescope to obtain radial velocity information and to search for short period binaries, which may be on the verge of interacting. We report on one system with a 4.1 hour period, and several additional systems with significant velocity variations.Comment: 23 pages with 10 figures. Accepted by AJ, to appear in May 2003 issu