On the motion and radiation of charged particles in strong electromagnetic waves. 1 - Motion in plane and spherical waves

Motion and radiation of charged particles in strong electromagnetic waves in plane and spherical wave

A new method to simulate vertical and horizontal structure in galactic disks

We have modified the particles in an N-body treecode to have different softening lengths in the horizontal and vertical directions. This allows us to simultaneously have thin enough particles to resolve the vertical structure in galactic disks, and horizontally large enough particles to suppress the vertical heating due to two-body effects

A Catalog of Digital Images of 113 Nearby Galaxies

We present a digital catalog of images of 113 galaxies in this paper. These galaxies are all nearby, bright, large and well resolved. All images were recorded with charge coupled devices (CCDs) at the Palomar Observatory with the 1.5 meter telescope and at the Lowell Observatory with the 1.1 meter telescope. At Palomar we used the Thuan--Gunn g, r and i photometric bands to take 3 images each of 31 spiral galaxies; at Lowell we used the B_J and R bands (2 images per galaxy) of the photometric system by Gullixson et al. (1995) to observe 82 spirals and ellipticals. The galaxies were selected to span the Hubble classification classes. All data are photometrically calibrated with foreground stars removed. Important data on these galaxies published in the "Third Reference Catalog of Bright Galaxies" (RC3) are recorded in the FITS file headers. All files are available through anonymous FTP from ftp://astro.princeton.edu/, through WWW at http://astro.princeton.edu/~frei/galaxy_catalog.html, and Princeton University Press will soon publish the data on CD-ROM.Comment: uuencoded compressed tar archive of postscript files (paper + 2 tables + 7 figures) Accepted for publication in the Astronomical Journa

Evaluation of approaches to control of Maedi-Visna disease of sheep using a Markov chain simulation model for a range of typical British Flocks

An epidemiological model is described that closely mimicked results of a published serological study of natural transmission of Maedi-Visna virus in a low ground flock of sheep. We adjusted parameters in the model from this baseline to explore the possible implications for the control of Maedi-Visna virus in typical British flocks. On closed hill farms, low probability of effective contact was most critical for control. In open low ground flocks, purchasing accredited replacements eliminated disease spread, otherwise flock size was the most important factor governing flock prevalence. Results highlighted the need for more epidemiological information about Maedi-Visna, particularly whether hill farms act as a hidden reservoir of virus or reduce the impact of this disease on the industry by providing a source of clean replacementsLivestock Production/Industries, Maedi-Visna, Model, Markov Chain, Sheep, Control,

Color-Induced Displacement double stars in SDSS

We report the first successful application of the astrometric color-induced displacement technique (CID, the displacement of the photocenter between different bandpasses due to a varying contribution of differently colored components to the total light), originally proposed by Wielen (1996) for discovering unresolved binary stars. Using the Sloan Digital Sky Survey (SDSS) Data Release 1 with 2.5 million stars brighter than 21m in the u and g bands, we select 419 candidate binary stars with CID greater than 0.5 arcsec. The SDSS colors of the majority of these candidates are consistent with binary systems including a white dwarf and any main sequence star with spectral type later than ~K7. The astrometric CID method discussed here is complementary to the photometric selection of binary stars in SDSS discussed by Smolcic et al. (2004), but there is considerable overlap (15%) between the two samples of selected candidates. This overlap testifies both to the physical soundness of both methods, as well as to the astrometric and photometric quality of SDSS data.Comment: submitted to A&A, 13 pages, 6 figure

Unbound Universe

Astronom

Intra-group Stigma: Examining Peer Relationships Among Women in Recovery for Addictions

This grounded theory study explores how women with histories of addiction perceive stigma while in treatment. In-depth interviews were conducted with 30 women participating in a residential drug treatment centre. Previous research has found that support from peers during recovery can be critical to managing illnesses. In fact, researchers have postulated that peers can be a more effective form of support than even family. This study extends existing literature indicating that peer support systems can be supportive, however they can also can be perceived as negative support that impose stigmas. Findings reveal that women perceive stigmas due to how various types of drug use violate societal expectations and conflict with notions of deservingness. Specifically, the hard users\u27\u27 (i.e. women who use heroin or crack cocaine) perceive stigmas regarding how their drug use violates norms of womanhood. Moreover, the soft users\u27\u27 (i.e. those who use alcohol or marijuana) perceive stigmas that their drug use is considered undeserving of support. This article explores the factors that contribute to stigma amongst populations who potentially face marginalisation from larger society. Implications for treatment and group work are discussed

Issues for the Next Generation of Galaxy Surveys

I argue that the weight of the available evidence favours the conclusions that galaxies are unbiased tracers of mass, the mean mass density (excluding a cosmological constant or its equivalent) is less than the critical Einstein-de Sitter value, and an isocurvature model for structure formation offers a viable and arguably attractive model for the early assembly of galaxies. If valid these conclusions complicate our work of adding structure formation to the standard model for cosmology, but it seems sensible to pay attention to evidence.Comment: 14 pages, 3 postscript figures, uses rspublic.st

The Stellar Halos of Massive Elliptical Galaxies II: Detailed Abundance Ratios at Large Radius

We study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions sigma* > 150 km/s. We measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, the typical star at 2 R_e is old (~10 Gyr), relatively metal poor ([Fe/H] -0.5), and alpha-enhanced ([Mg/Fe]~0.3). The stars were made rapidly at z~1.5-2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid star formation timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to Milky Way thick disk stars. Our observations are thus consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose star formation is truncated early (z~1.5-2).Comment: ApJ in press, 12 pages, 6 figure