6,323 research outputs found
A Deep Survey of HI-Selected Galaxies: The Sample and the Data
In a 21 cm neutral hydrogen survey of approximately 55 sq deg out to a
redshift of cz=8340 km/s, we have identified 75 extragalactic HI sources. These
objects comprise a well-defined sample of extragalactic sources chosen by means
that are independent of optical surface brightness selection effects. In this
paper we describe the Arecibo survey procedures and HI data, follow-up VLA HI
observations made of several unusual sources, and Kitt Peak B-, R-, and I-band
photometry for nearly all of the galaxies. We have also gathered information
for some of the optically detected galaxies within the same search volume. We
examine how samples generated by different types of search techniques overlap
with selection by HI flux. Only the least massive HI object, which is among the
lowest mass HI sources previously found, does not have a clear optical
counterpart, but a nearby bright star may hide low surface brightness emission.
However the newly-detected systems do have unusual optical properties. Most of
the 40 galaxies that were not previously identified in magnitude-limited
catalogs appear to be gas-dominated systems, and several of these systems have
HI mass-to-light ratios among the largest values ever previously found. These
gas-dominated objects also tend to have very blue colors, low surface
brightnesses, and no central bulges, which correlate strongly with their
relative star-to-gas content.Comment: 48 pages, 10 figures, Figure 3 included as 3 separate JPG images. To
appear in Ap J Supplement
Spectral Decomposition of Broad-Line AGNs and Host Galaxies
Using an eigenspectrum decomposition technique, we separate the host galaxy
from the broad line active galactic nucleus (AGN) in a set of 4666 spectra from
the Sloan Digital Sky Survey (SDSS), from redshifts near zero up to about 0.75.
The decomposition technique uses separate sets of galaxy and quasar
eigenspectra to efficiently and reliably separate the AGN and host
spectroscopic components. The technique accurately reproduces the host galaxy
spectrum, its contributing fraction, and its classification. We show how the
accuracy of the decomposition depends upon S/N, host galaxy fraction, and the
galaxy class. Based on the eigencoefficients, the sample of SDSS broad-line AGN
host galaxies spans a wide range of spectral types, but the distribution
differs significantly from inactive galaxies. In particular, post-starburst
activity appears to be much more common among AGN host galaxies. The
luminosities of the hosts are much higher than expected for normal early-type
galaxies, and their colors become increasingly bluer than early-type galaxies
with increasing host luminosity. Most of the AGNs with detected hosts are
emitting at between 1% and 10% of their estimated Eddington luminosities, but
the sensitivity of the technique usually does not extend to the Eddington
limit. There are mild correlations among the AGN and host galaxy
eigencoefficients, possibly indicating a link between recent star formation and
the onset of AGN activity. The catalog of spectral reconstruction parameters is
available as an electronic table.Comment: 18 pages; accepted for publication in A
A Theater Intervention to Prevent Teen Dating Violence for Mexican-American Middle School Students
Purpose To test a theater intervention designed to raise awareness of the dynamics and consequences of teen dating violence (TDV) and to facilitate creation of nonviolent responses to TDV among Latino and Latina adolescents. The intervention was based on Theater of the Oppressed, which advocates the use of theater methods to explore social issues and to allow audiences to experiment with problem-solving, thereby promoting change. Methods This study used a pretest–posttest, no control group, mixed-measures design to study 66 Mexican-American adolescents (mean age, 13.4 ± 5 years). Two plays containing subtle and overt signs of control and abuse were written and performed. Scripts were based on data from prior studies of TDV among Latino and Latina adolescents. At baseline, we measured sociodemographics, personal safety, and ethnic identity. Pre–post instruments measured acceptance of TDV, confidence to resolve conflicts nonviolently, and intentions to use nonviolent strategies to resolve conflict. We collected qualitative data via essay. Results At posttest, participants had less acceptance of TDV (t = −2.08; p \u3c .05), increased confidence to resolve conflicts nonviolently (t = 3.82; p \u3c .001), and higher intentions to use nonviolent strategies (t = 3.35; p = .001). We analyzed 20 essays. Qualitative results provided context for understanding participants\u27 changes in attitude, confidence, and nonviolent behavioral intentions. Conclusions This adaptation of Theater of the Oppressed was an effective way to interact with Latino adolescents. In a safe setting, participants vicariously experienced TDV, which facilitated self-reflection and cognitive rehearsal strategies to respond nonviolently to TDV
Organizational boundaries of medical practice: the case of physician ownership of ancillary services
Physician ownership of in-office ancillary services (IOASs) has come under increasing scrutiny. Advocates of argue that IOASs allow physicians to supervise the quality and coordination of care. Critics have argued that IOASs create financial incentives for physicians to increase ancillary service volume. In this paper we develop a conceptual framework to evaluate the tradeoffs associated with physician ownership of IOASs. There is some evidence supporting the existence of scope and transaction economies in IOASs. Improvement in flow and continuity of care are likely to generate scope economies and improvements in quality monitoring and reductions in consumer transaction costs are likely to generate transaction economies. Other factors include the capture of upstream and downstream profits, but these incentives are likely to be small compared to scope and transaction economies. Policy debates on the merits of IOASs should include an explicit assessment of these tradeoffs. This research was supported in part by funding from the American Association of Orthopaedic Surgeons (AAOS)
Exoplanet Catalogues
One of the most exciting developments in the field of exoplanets has been the
progression from 'stamp-collecting' to demography, from discovery to
characterisation, from exoplanets to comparative exoplanetology. There is an
exhilaration when a prediction is confirmed, a trend is observed, or a new
population appears. This transition has been driven by the rise in the sheer
number of known exoplanets, which has been rising exponentially for two decades
(Mamajek 2016). However, the careful collection, scrutiny and organisation of
these exoplanets is necessary for drawing robust, scientific conclusions that
are sensitive to the biases and caveats that have gone into their discovery.
The purpose of this chapter is to discuss and demonstrate important
considerations to keep in mind when examining or constructing a catalogue of
exoplanets. First, we introduce the value of exoplanetary catalogues. There are
a handful of large, online databases that aggregate the available exoplanet
literature and render it digestible and navigable - an ever more complex task
with the growing number and diversity of exoplanet discoveries. We compare and
contrast three of the most up-to-date general catalogues, including the data
and tools that are available. We then describe exoplanet catalogues that were
constructed to address specific science questions or exoplanet discovery space.
Although we do not attempt to list or summarise all the published lists of
exoplanets in the literature in this chapter, we explore the case study of the
NASA Kepler mission planet catalogues in some detail. Finally, we lay out some
of the best practices to adopt when constructing or utilising an exoplanet
catalogue.Comment: 14 pages, 6 figures. Invited review chapter, to appear in "Handbook
of Exoplanets", edited by H.J. Deeg and J.A. Belmonte, section editor N.
Batalh
- …