Aharonov-Bohm effect in the non-Abelian quantum Hall fluid

The nu=5/2 fractional quantum Hall effect state has attracted great interest recently, both as an arena to explore the physics of non-Abelian quasiparticle excitations, and as a possible architecture for topological quantum information processing. Here we use the conformal field theoretic description of the Moore-Read state to provide clear tunneling signatures of this state in an Aharonov-Bohm geometry. While not probing statistics directly, the measurements proposed here would provide a first, experimentally tractable step towards a full characterization of the 5/2 state.Comment: 5 pages, 3 figures, 2 tables, added one more figure and conductances formulae for the three channel

Transverse Galaxy Velocities from Multiple Topological Images

The study of the kinematics of galaxies within clusters or groups has the limitation that only one of the three velocity components and only two of the three spatial components of a galaxy position in six-dimensional phase space can normally be measured. However, if multiple topological images of a cluster exist, then the radial positions and sky plane mean velocities of galaxies in the cluster may also be measurable from photometry of the two cluster images. The vector arithmetic and principles of the analysis are presented. These are demonstrated by assuming the suggested topological identification of the clusters RX J1347.5-1145 and CL 09104+4109 to be correct and deducing the sky-plane relative velocity component along the axis common to both images of this would-be single cluster. Three out of four of the inferred transverse velocities are consistent with those expected in a rich cluster. A control sample of random `common' sky-plane axes, independent of the topological hypothesis, implies that this is not surprising. This shows that while galaxy kinematics are deducible from knowledge of cosmological topology, it is not easy to use them to refute a specific candidate manifold.Comment: 13 pages, 7 figures, accepted for MNRA

The creeping motion of a spherical particle normal to a deformable interface

Numerical results are presented for the approach of a rigid sphere normal to a deformable fluid-fluid interface in the velocity range for which inertial effects may be neglected. Both the case of a sphere moving with constant velocity, and that of a sphere moving under the action of a constant non-hydrodynamic body force are considered for several values of the viscosity ratio, density difference and interfacial tension between the two fluids. Two distinct modes of interface deformation are demonstrated: a film drainage mode in which fluid drains away in front of the sphere leaving an ever-thinning film, and a tailing mode where the sphere passes several radii beyond the plane of the initially undeformed interface, while remaining encapsulated by the original surrounding fluid which is connected with its main body by a thin thread-like tail behind the sphere. We consider the influence of the viscosity ratio, density difference, interfacial tension and starting position of the sphere in deter-mining which of these two modes of deformation will occur

An excess of damped Lyman alpha galaxies near QSOs

We present a sample of 33 damped Lyman alpha systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts (z_abs) are within 6000 km/s of the QSO's systemic redshift (z_sys). Our sample is based on 731 2.5 < z_sys < 4.5 non-broad-absorption-line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ~100 % complete for absorbers with N(HI) >= 2e20 cm^-2. The derived number density of DLAs per unit redshift, n(z), within v < 6000 km/s is higher (3.5 sigma significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening 'field' DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar.Comment: Accepted for publication in MNRAS (13 pages, 6 figures

Adaptive Density Estimation on the Circle by Nearly-Tight Frames

This work is concerned with the study of asymptotic properties of nonparametric density estimates in the framework of circular data. The estimation procedure here applied is based on wavelet thresholding methods: the wavelets used are the so-called Mexican needlets, which describe a nearly-tight frame on the circle. We study the asymptotic behaviour of the $L^{2}$-risk function for these estimates, in particular its adaptivity, proving that its rate of convergence is nearly optimal.Comment: 30 pages, 3 figure

Rethinking reactive halogen budgets in the midlatitude lower stratosphere

Current stratospheric models have difficulties in fully explaining the observed midlatitude ozone depletion in the lowermost stratosphere, particularly near the tropopause. Such models assume that only long-lived source gases provide significant contributions to the stratospheric halogen budget, while all the short-lived compounds are removed in the troposphere, the products being rained out. Here we show this assumption to be flawed. Using bromine species as an example, we show that in the lowermost stratosphere, where the observed midlatitude ozone trend maximizes, bromoform (CHBr3) alone likely contributes more inorganic bromine than all the conventional long-lived sources (halons and methyl bromide) combined. Copyright 1999 by the American Geophysical Union

Clustering of Galaxies in a Hierarchical Universe: I. Methods and Results at z=0

We introduce a new technique for following the formation and evolution of galaxies in cosmological N-body simulations. Dissipationless simulations are used to track the formation and merging of dark matter halos as a function of redshift. Simple prescriptions, taken directly from semi-analytic models of galaxy formation, are adopted for cooling, star formation, supernova feedback and the merging of galaxies within the halos. This scheme enables us to study the clustering properties of galaxies and to investigate how selection by type, colour or luminosity influences the results. In this paper, we study properties of the galaxy distribution at z=0. These include luminosity functions, colours, correlation functions, pairwise peculiar velocities, cluster M/L ratios and star formation rates. We focus on two variants of a CDM cosmology: a high- density model with Gamma=0.21 (TCDM) and a low-density model with Omega=0.3 and Lambda=0.7 (LCDM). Both are normalized to reproduce the I-band Tully-Fisher relation near a circular velocity of 220 km/s. Our results depend strongly both on this normalization and on the prescriptions for star formation and feedback. Very different assumptions are required to obtain an acceptable model in the two cases. For TCDM, efficient feedback is required to suppress the growth of galaxies low-mass field halos. Without it, there are too many galaxies and the correlation function turns over below 1 Mpc. For LCDM, feedback must be weak, otherwise too few L* galaxies are produced and the correlation function is too steep. Given the uncertainties in modelling some of the key physical processes, we conclude that it is not yet possible to draw conclusions about the values of cosmological parameters from studies of this kind. Further work on global star formation and feedback effects is required to narrow the range of possibilitiesComment: 43 pages, Latex, 16 figures included, 2 additional GIF format figures, submitted to MNRA