Quantum Corrections to Fidelity Decay in Chaotic Systems

By considering correlations between classical orbits we derive semiclassical expressions for the decay of the quantum fidelity amplitude for classically chaotic quantum systems, as well as for its squared modulus, the fidelity or Loschmidt echo. Our semiclassical results for the fidelity amplitude agree with random matrix theory (RMT) and supersymmetry predictions in the universal Fermi golden rule regime. The calculated quantum corrections can be viewed as arising from a static random perturbation acting on nearly self-retracing interfering paths, and hence will be suppressed for time-varying perturbations. Moreover, using trajectory-based methods we show a relation, recently obtained in RMT, between the fidelity amplitude and the cross-form factor for parametric level correlations. Beyond RMT, we compute Ehrenfest-time effects on the fidelity amplitude. Furthermore our semiclassical approach allows for a unified treatment of the fidelity, both in the Fermi golden rule and Lyapunov regimes, demonstrating that quantum corrections are suppressed in the latter.Comment: 14 pages, 4 figure

A Digital Archive of HI 21 cm Line Spectra of Optically-targeted Galaxies

We present a homogeneous compilation of HI spectral parameters extracted from global 21 cm line spectra for some 9000 galaxies in the local universe (heliocentric velocity -200 < V_Sun < 28,000 km/s) obtained with a variety of large single dish radio telescopes but reanalyzed using a single set of parameter extraction algorithms. Corrections to the observed HI line flux for source extent and pointing offsets and to the HI line widths for instrumental broadening and smoothing are applied according to model estimates to produce a homogenous catalog of derived properties with quantitative error estimates. Where the redshift is available from optical studies, we also provide flux measurements for an additional 156 galaxies classified as marginal HI detections and rms noise limits for 494 galaxies classified as nondetections. Given the diverse nature of the observing programs contributing to it, the characteristics of the combined dataset are heterogeneous, and as such, the compilation is neither integrated HI line flux nor peak flux limited. However, because of the large statistical base and homogenous reprocessing, the spectra and spectral parameters of galaxies in this optically targeted sample can be used to complement data obtained at other wavelengths to characterize the properties of galaxies in the local universe and to explore the large scale structures in which they reside.Comment: 13 pages, 9 figures, 3 external online tables, accepted for publication in ApJ

Semiclassical Mechanism for the Quantum Decay in Open Chaotic Systems

We address the decay in open chaotic quantum systems and calculate semiclassical corrections to the classical exponential decay. We confirm random matrix predictions and, going beyond, calculate Ehrenfest time effects. To support our results we perform extensive numerical simulations. Within our approach we show that certain (previously unnoticed) pairs of interfering, correlated classical trajectories are of vital importance. They also provide the dynamical mechanism for related phenomena such as photo-ionization and -dissociation, for which we compute cross section correlations. Moreover, these orbits allow us to establish a semiclassical version of the continuity equation.Comment: 4 pages, 2 figure

Deep-scaled fish (Osteichthyes: Actinopterygii) from the lower Permian (Cisuralian) lacustrine deposits of the Parnaíba Basin, NE Brazil

The richly fossiliferous deposits of the Brazilian Pedra de Fogo Formation originated in an extensive aquatic system in tropical Pangaea, and grade from marginal lacustrine into marine deposits at the depocenter in the western part of the Parnaíba Basin. In addition to the well-known tetrapod and macrofloral records from these deposits, the Pedra de Fogo Formation yields extensive fish fossils indicating a diverse and abundant ichthyofauna. Among the actinopterygians, deep-bodied morphotypes are represented by whole fish as well as disarticulated dermal scales found at various localities in the states of Maranhão and Piauí. The gross morphology, ornamentation, and histology of some of these scales is highly distinctive, indicating the presence of a novel taxon (Piratata rogersmithii gen. et sp. nov.). The external surface of a Piratata scale is covered in multiple round-to-slightly elongated tubercles. The scale lacks a ganoin cover and is made up of cellular bone and odontocomplexes of orthodentine composing the tuberculated scale surface. The scale morphology and ornamentation most closely resemble that of Cleithrolepis granulatus from the Triassic of Australia and Cleithrolepis extoni from the Triassic Stormberg Beds of South Africa, but the new taxon differs from previously described species in several diagnostic morphological features. The use of scale characters in the taxonomy of ray-finned fishes and the palaeogeographic, palaeoenvironmental, and geochronological implications of the new taxon are discussed.Fil: Richter, Martha. British Museum (Natural History); Reino UnidoFil: Cisneros, Juan C.. Universidade Federal do Piaui; BrasilFil: Kammerer, Christian. North Carolina Museum Of Natural Sciences; Estados UnidosFil: Pardo, Jason. Field Museum of National History; Estados UnidosFil: Marsicano, Claudia Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Frobisch, Jorg. Staatliches Museum fur Naturkunde Stuttgart; AlemaniaFil: Angielczyk, Ken. Field Museum of National History; Estados Unido

A Photometric Method for Quantifying Asymmetries in Disk Galaxies

A photometric method for quantifying deviations from axisymmetry in optical images of disk galaxies is applied to a sample of 32 face-on and nearly face-on spirals. The method involves comparing the relative fluxes contained within trapezoidal sectors arranged symmetrically about the galaxy center of light, excluding the bulge and/or barred regions. Such a method has several advantages over others, especially when quantifying asymmetry in flocculent galaxies. Specifically, the averaging of large regions improves the signal-to-noise in the measurements; the method is not strongly affected by the presence of spiral arms; and it identifies the kinds of asymmetry that are likely to be dynamically important. Application of this "method of sectors" to R-band images of 32 disk galaxies indicates that about 30% of spirals show deviations from axisymmetry at the 5-sigma level.Comment: 17 pages, 2 tables and 6 figures, uses psfig and AAS LaTex; to appear in A

Semiclassical Theory for Decay and Fragmentation Processes in Chaotic Quantum Systems

We consider quantum decay and photofragmentation processes in open chaotic systems in the semiclassical limit. We devise a semiclassical approach which allows us to consistently calculate quantum corrections to the classical decay to high order in an expansion in the inverse Heisenberg time. We present results for systems with and without time reversal symmetry and also for the symplectic case, as well as extending recent results to non-localized initial states. We further analyze related photodissociation and photoionization phenomena and semiclassically compute cross-section correlations, including their Ehrenfest time dependence.Comment: 17 pages, 5 figure

Signatures of Galaxy-Cluster Interactions: Spiral Galaxy Rotation Curve Asymmetry, Shape, and Extent

The environmental dependencies of the characteristics of spiral galaxy rotation curves are studied in this work. We use our large, homogeneously collected sample of 510 cluster spiral galaxy rotation curves to test the claim that the shape of a galaxy's rotation curve strongly depends on its location within the cluster, and thus presumably on the strength of the local intracluster medium and on the frequency and strength of tidal interactions with the cluster and cluster galaxies. Our data do not corroborate such a scenario, consistent with the fact that Tully-Fisher residuals are independent of galaxy location within the cluster; while the average late-type spiral galaxy shows more rise in the outer parts of its rotation curve than does the typical early-type spiral galaxy, there is no apparent trend for either subset with cluster environment. We also investigate as a function of cluster environment rotation curve asymmetry and the radial distribution of H II region tracers within galactic disks. Mild trends with projected cluster-centric distance are observed: (i) the (normalized) radial extent of optical line emission averaged over all spiral galaxy types shows a 4%+/-2% increase per Mpc of galaxy-cluster core separation, and (ii) rotation curve asymmetry falls by a factor of two between the inner and outer cluster for early-type spirals (a negligible decrease is found for late-type spirals). Such trends are consistent with spiral disk perturbations or even the stripping of the diffuse, outermost gaseous regions within the disks as galaxies pass through the dense cluster cores.Comment: 17 pages; to appear in the April 2001 Astronomical Journa

A palaeobiologist's guide to 'virtual' micro-CT preparation

This paper provides a brief but comprehensive guide to creating, preparing and dissecting a 'virtual' fossil, using a worked example to demonstrate some standard data processing techniques. Computed tomography (CT) is a 3D imaging modality for producing 'virtual' models of an object on a computer. In the last decade, CT technology has greatly improved, allowing bigger and denser objects to be scanned increasingly rapidly. The technique has now reached a stage where systems can facilitate large-scale, non-destructive comparative studies of extinct fossils and their living relatives. Consequently the main limiting factor in CT-based analyses is no longer scanning, but the hurdles of data processing (see disclaimer). The latter comprises the techniques required to convert a 3D CT volume (stack of digital slices) into a virtual image of the fossil that can be prepared (separated) from the matrix and 'dissected' into its anatomical parts. This technique can be applied to specimens or part of specimens embedded in the rock matrix that until now have been otherwise impossible to visualise. This paper presents a suggested workflow explaining the steps required, using as example a fossil tooth of Sphenacanthus hybodoides (Egerton), a shark from the Late Carboniferous of England. The original NHMUK copyrighted CT slice stack can be downloaded for practice of the described techniques, which include segmentation, rendering, movie animation, stereo-anaglyphy, data storage and dissemination. Fragile, rare specimens and type materials in university and museum collections can therefore be virtually processed for a variety of purposes, including virtual loans, website illustrations, publications and digital collections. Micro-CT and other 3D imaging techniques are increasingly utilized to facilitate data sharing among scientists and on education and outreach projects. Hence there is the potential to usher in a new era of global scientific collaboration and public communication using specimens in museum collections

Cephalosporin-resistant Pneumococci and Sickle Cell Disease

Increasingly resistant bacteria in sickle cell disease patients indicate need to evaluate extendedspectrum cephalosporin therapy

Departures From Axisymmetric Morphology and Dynamics in Spiral Galaxies

New HI synthesis data have been obtained for six face-on galaxies with the Very Large Array. These data and reanalyses of three additional data sets make up a sample of nine face-on galaxies analyzed for deviations from axisymmetry in morphology and dynamics. This sample represents a subsample of galaxies already analyzed for morphological symmetry properties in the R-band. Four quantitative measures of dynamical nonaxisymmetry are compared to one another and to the quantitative measures of morphological asymmetry in HI and R-band to investigate the relationships between nonaxisymmetric morphology and dynamics. We find no significant relationship between asymmetric morphology and most of the dynamical measures in our sample. A possible relationship is found, however, between morphology and dynamical position angle differences between approaching and receding sides of the galaxy.Comment: 24 pages, 19 figures, AASTeX, accepted for publication in AJ, postscript figures available at ftp://culebra.tn.cornell.edu/pub/david/figures.tar.g