Prospects for Redshifted 21-cm observations of quasar HII regions

The introduction of low-frequency radio arrays over the coming decade is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21cm emission between a large HII region and the surrounding neutral IGM will be the simplest and most easily interpreted signature. We find that an instrument like the planned Mileura Widefield Array Low-Frequency Demonstrator (LFD) will be able to obtain good signal to noise on HII regions around the most luminous quasars, and determine some gross geometric properties, e.g. whether the HII region is spherical or conical. A hypothetical follow-up instrument with 10 times the collecting area of the LFD (MWA-5000) will be capable of mapping the detailed geometry of HII regions, while SKA will be capable of detecting very narrow spectral features as well as the sharpness of the HII region boundary. The MWA-5000 will discover serendipitous HII regions in widefield observations. We estimate the number of HII regions which are expected to be generated by quasars. Assuming a late reionization at z~6 we find that there should be several tens of quasar HII regions larger than 4Mpc at z~6-8 per field of view. Identification of HII regions in forthcoming 21cm surveys can guide a search for bright galaxies in the middle of these regions. Most of the discovered galaxies would be the massive hosts of dormant quasars that left behind fossil HII cavities that persisted long after the quasar emission ended, owing to the long recombination time of intergalactic hydrogen. A snap-shot survey of candidate HII regions selected in redshifted 21cm image cubes may prove to be the most efficient method for finding very high redshift quasars and galaxies.Comment: 14 pages, 8 figures. Submitted to Ap

Resolving velocity space dynamics in continuum gyrokinetics

Many plasmas of interest to the astrophysical and fusion communities are weakly collisional. In such plasmas, small scales can develop in the distribution of particle velocities, potentially affecting observable quantities such as turbulent fluxes. Consequently, it is necessary to monitor velocity space resolution in gyrokinetic simulations. In this paper, we present a set of computationally efficient diagnostics for measuring velocity space resolution in gyrokinetic simulations and apply them to a range of plasma physics phenomena using the continuum gyrokinetic code GS2. For the cases considered here, it is found that the use of a collisionality at or below experimental values allows for the resolution of plasma dynamics with relatively few velocity space grid points. Additionally, we describe implementation of an adaptive collision frequency which can be used to improve velocity space resolution in the collisionless regime, where results are expected to be independent of collision frequency.Comment: 20 pages, 11 figures, submitted to Phys. Plasma

Use of 2G coated conductors for efficient shielding of DC magnetic fields

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO) coated conductors. Since effective screening of the axial DC magnetic field requires the unimpeded flow of an azimuthal persistent current, we demonstrate a configuration of a screening shell made out of standard YBCO coated conductor capable to accomplish that. The screen allows the persistent current to flow in the predominantly azimuthal direction at a temperature of 77 K. The persistent screen, incorporating a single layer of superconducting film, can attenuate an external magnetic field of up to 5 mT by more than an order of magnitude. For comparison purposes, another type of screen which incorporates low critical temperature quasi-persistent joints was also built. The shielding technique we describe here appears to be especially promising for the realization of large scale high-Tc superconducting screens.Comment: 8 pages, 3 figure

From ‘other’ to involved: User involvement in research: An emerging paradigm

This article has been made available through the Brunel Open Access Publishing Fund. Copyright @ 2013 The Author(s). This is an Open Access article. Non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly attributed, cited, and is not altered, transformed, or built upon in any way, is permitted. The moral rights of the named author(s) have been asserted.This article explores the issue of ‘othering’ service users and the role that involving them, particularly in social policy and social work research may play in reducing this. It takes, as its starting point, the concept of ‘social exclusion’, which has developed in Europe and the marginal role that those who have been included in this construct have played in its development and the damaging effects this may have. The article explores service user involvement in research and is itself written from a service user perspective. It pays particular attention to the ideological, practical, theoretical, ethical and methodological issues that such user involvement may raise for research. It examines problems that both research and user involvement may give rise to and also considers developments internationally to involve service users/subjects of research, highlighting some of the possible implications and gains of engaging service user knowledge in research and the need for this to be evaluated

Measurement of Spin Transfer Observables in Antiproton-Proton -> Antilambda-Lambda at 1.637 GeV/c

Spin transfer observables for the strangeness-production reaction Antiproton-Proton -> Antilambda-Lambda have been measured by the PS185 collaboration using a transversely-polarized frozen-spin target with an antiproton beam momentum of 1.637 GeV/c at the Low Energy Antiproton Ring at CERN. This measurement investigates observables for which current models of the reaction near threshold make significantly differing predictions. Those models are in good agreement with existing measurements performed with unpolarized particles in the initial state. Theoretical attention has focused on the fact that these models produce conflicting predictions for the spin-transfer observables D_{nn} and K_{nn}, which are measurable only with polarized target or beam. Results presented here for D_{nn} and K_{nn} are found to be in disagreement with predictions from existing models. These results also underscore the importance of singlet-state production at backward angles, while current models predict complete or near-complete triplet-state dominance.Comment: 5 pages, 3 figure

Particle growing mechanisms in Ag-ZrO2 and Au-ZrO2 granular films obtained by pulsed laser deposition

Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO2 matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08<x(Ag)<0.28 and 0.08<x(Au)<0.52). High resolution transmission electron microscopy (TEM) showed regular distribution of spherical Au and Ag nanoparticles having very sharp interfaces with the amorphous matrix. Mean particle size determined from X-ray diffraction agreed with direct TEM observation. The silver mean diameter increases more abruptly with metal volume content than that corresponding to gold particles prepared under the same conditions. Two mechanisms of particle growing are observed: nucleation and particle coalescence, their relative significance being different in both granular systems, which yields very different values of the percolation threshold (xc(Ag)~0.28 and xc(Au)~0.52).Comment: 6 figure

On the Symmetries of the Edgar-Ludwig Metric

The conformal Killing equations for the most general (non-plane wave) conformally flat pure radiation field are solved to find the conformal Killing vectors. As expected fifteen independent conformal Killing vectors exist, but in general the metric admits no Killing or homothetic vectors. However for certain special cases a one-dimensional group of homotheties or motions may exist and in one very special case, overlooked by previous investigators, a two-dimensional homethety group exists. No higher dimensional groups of motions or homotheties are admitted by these metrics.Comment: Plain TeX, 7 pages, No figure

Characterizing Multi-planet Systems with Classical Secular Theory

Classical secular theory can be a powerful tool to describe the qualitative character of multi-planet systems and offer insight into their histories. The eigenmodes of the secular behavior, rather than current orbital elements, can help identify tidal effects, early planet-planet scattering, and dynamical coupling among the planets, for systems in which mean-motion resonances do not play a role. Although tidal damping can result in aligned major axes after all but one eigenmode have damped away, such alignment may simply be fortuitous. An example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where multiple eigenmodes remain undamped. Various solutions for 55 Cancri are compared, showing differing dynamical groupings, with implications for the coupling of eccentricities and for the partitioning of damping among the planets. Solutions for orbits that include expectations of past tidal evolution with observational data, must take into account which eigenmodes should be damped, rather than expecting particular eccentricities to be near zero. Classical secular theory is only accurate for low eccentricity values, but comparison with other results suggests that it can yield useful qualitative descriptions of behavior even for moderately large eccentricity values, and may have advantages for revealing underlying physical processes and, as large numbers of new systems are discovered, for triage to identify where more comprehensive dynamical studies should have priority.Comment: Published in Celestial Mechanics and Dynamical Astronomy, 25 pages, 10 figure