1,130 research outputs found
A Radio Survey of Seven Southern X-ray Luminous Clusters of Galaxies
The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38
GHz to survey seven southern Abell clusters of galaxies with high X-ray
luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters
have also been surveyed at 0.843 GHz with the Molonglo Observatory Synthesis
Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio
sources within the Abell circles centred on their X-ray centroids. We compare
their identification fractions, emitted 1.38-GHz and optical powers, radio
spectral indices and radial variation in projected source density with those of
the radio-selected samples of Slee et al. (1998). We compare our fractional
radio luminosity function with that of the radio-selected samples of Ledlow and
Owen (1996) and Slee et al. (1998). Three significant differences are noted
between X-ray and radio-selected samples of clusters; (1) the X-ray sample has
an excess of flat-spectrum radio sources; (2) the fractional radio luminosity
function for the FR I sources in the X-ray selected sample is much steeper,
implying that fewer of their cluster galaxies become hosts for the stronger FR
I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray
selected sample. The average excess projected density of radio sources near our
cluster centres is approx. 5 times the background source density.Comment: 24 pages, 8 figures, plus 6 figures to be published online only;
accepted to appear in MNRA
The Origin of Radio Emission in Low-Luminosity Active Galactic Nuclei: Jets, Accretion Flows, or Both?
The low-luminosity active galactic nuclei in NGC 3147, NGC 4203, and NGC 4579
have been imaged at four frequencies with the Very Long Baseline Array. The
galaxies are unresolved at all frequencies, with size upper limits of
times the Schwarzschild radii of their central massive black holes.
The spectral indices between 1.7 and 5.0 GHz range from 0.2 to 0.4; one and
possibly two of the galaxies show spectral turnovers between 5.0 and 8.4 GHz.
The high brightness temperatures ( K) and relatively straight spectra
imply that free-free emission and/or absorption cannot account for the slightly
inverted spectra. Although the radio properties of the cores superficially
resemble predictions for advection-dominated accretion flows, the radio
luminosities are too high compared to the X-ray luminosities. We suggest that
the bulk of the radio emission is generated by a compact radio jet, which may
coexist with a low radiative efficiency accretion flow.Comment: To appear in ApJ (Letters). 4 page
Chandra Observations of the Disruption of the Cool Core in Abell 133
We present the analysis of a Chandra observation of the galaxy cluster Abell
133, which has a cooling flow core, a central radio source, and a diffuse,
filamentary radio source which has been classified as a radio relic.
The X-ray image shows that the core has a complex structure. The most
prominent feature is a "tongue" of emission which extends from the central cD
galaxy to the northwest and partly overlaps the radio relic. One possibility is
that this tongue is produced by Kelvin-Helmholtz (KH) instabilities through the
interaction between the cold gas around the cD galaxy and hot intracluster
medium. We estimate the critical velocity and time scale for the KH instability
to be effective for the cold core around the cD galaxy. We find that the KH
instability can disrupt the cold core if the relative velocity is >~400 km
s^-1. We compare the results with those of clusters in which sharp, undisrupted
cold fronts have been observed; in these clusters, the low temperature gas in
their central regions has a more regular distribution. In contrast to Abell
133, these cluster cores have longer timescales for the disruption of the core
by the KH instability when they are normalized to the timescale of the cD
galaxy motion. Thus, the other cores are less vulnerable to KH instability.
Another possible origin of the tongue is that it is gas which has been uplifted
by a buoyant bubble of nonthermal plasma that we identify with the observed
radio relic. From the position of the bubble and the radio estimate of the age
of the relic source, we estimate avelocity of ~700 km s^-1 for the bubble. The
structure of the bubble and this velocity are consistent with numerical models
for such buoyant bubbles. (abridged)Comment: 38 pages, 15 figures, accepted for publication in Ap
Diffuse radio sources in the cluster of galaxies Abell 548b
We report extensive VLA and ATCA observations of the two diffuse radio
sources in the cluster of galaxies Abell 548b, which confirm their
classification as relics. The two relics (named A and B) show similar flux
density, extent, shape, polarization and spectral index and are located at
projected distances of about 430 and 500 kpc from the cluster center, on the
same side of the cluster's X-ray peak. On the basis of spectral indices of
discrete radio sources embedded within the diffuse features, we have attempted
to distinguish emission peaks of the diffuse sources from unrelated sources. We
have found that both relics, in particular the B-relic, show possible fine
structure, when observed at high resolution. Another diffuse source (named C)
is detected close in projection to the cluster center. High-resolution images
show that it contains two discrete radio sources and a diffuse component, which
might be a candidate for a small relic source. The nature and properties of the
diffuse radio sources are discussed. We conclude that they are likely related
to the merger activity in the cluster.Comment: Accepted for publication in MNRAS. 11 pages, 7 figures. Some figures
are degraded to reduce their size. A version with high resolution images is
available at http://www.ira.inaf.it/~lferetti/OUTGOING/papA548b.ps.g
Skateboard Injuries in a Campus Community
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67018/2/10.1177_000992286700600421.pd
Systematic review of risk factors for eating psychopathology in athletes: A critique of an etiological model
Objective:
The theoretical model by Petrie and Greenleaf (2007, 2012) is an admirable attempt to collate the causal factors of disordered eating in athletes. The aims of this systematic review are (a) to provide an overview of the findings from the relevant literature, (b) to assess whether the model is supported by the existing research, (c) to evaluate the different designs, methods, and measures used to test the mediators in the model, and (d) to highlight areas for improvements and future research.
Method:
A systematic review of four major online databases identified 37 relevant papers on risk factors of disordered eating in athletes, which were reviewed and critically compared with the theoretical model.
Results:
There is a lack of longitudinal research with the relevant mediators in athlete populations, which makes it difficult to determine whether the potential mediators described by Petrie and Greenleaf are causal risk factors rather than simply correlates of disordered eating for athletes. Findings for all the potential mediators are inconsistent, and the range of measures used makes it problematic to draw conclusions.
Conclusions:
Future research needs to use gold standard measures and longitudinal designs in order to fully test and possibly update the model
The VLA Low-frequency Sky Survey
The Very Large Array (VLA) Low-frequency Sky Survey (VLSS) has imaged 95% of
the 3*pi sr of sky north of declination = -30 degrees at a frequency of 74 MHz
(4 meter wavelength). The resolution is 80" (FWHM) throughout, and the typical
RMS noise level is ~0.1 Jy/beam. The typical point-source detection limit is
0.7 Jy/beam and so far nearly 70,000 sources have been catalogued. This survey
used the 74 MHz system added to the VLA in 1998. It required new imaging
algorithms to remove the large ionospheric distortions at this very low
frequency throughout the entire ~11.9 degree field of view. This paper
describes the observation and data reduction methods used for the VLSS and
presents the survey images and source catalog. All of the calibrated images and
the source catalog are available online (http://lwa.nrl.navy.mil/VLSS) for use
by the astronomical community.Comment: 53 pages, including 3 tables and 15 figures. Has been accepted for
publication in the Astronomical Journa
Emergency Department Pain Management Following Implementation of a Geriatric Hip Fracture Program
Introduction: Over 300,000 patients in the United States sustain low-trauma fragility hip fractures annually. Multidisciplinary geriatric fracture programs (GFP) including early, multimodal pain management reduce morbidity and mortality. Our overall goal was to determine the effects of a GFP on the emergency department (ED) pain management of geriatric fragility hip fractures. Methods: We performed a retrospective study including patients age ≥65 years with fragility hip fractures two years before and two years after the implementation of the GFP. Outcomes were time to (any) first analgesic, use of acetaminophen and fascia iliaca compartment block (FICB) in the ED, and amount of opioid medication administered in the first 24 hours. We used permutation tests to evaluate differences in ED pain management following GFP implementation. Results: We studied 131 patients in the pre-GFP period and 177 patients in the post-GFP period. In the post-GFP period, more patients received FICB (6% vs. 60%; difference 54%, 95% confidence interval [CI] 45–63%; p<0.001) and acetaminophen (10% vs. 51%; difference 41%, 95% CI 32–51%; p<0.001) in the ED. Patients in the post-GFP period also had a shorter time to first analgesic (103 vs. 93 minutes; p=0.04) and received fewer morphine equivalents in the first 24 hours (15mg vs. 10mg, p<0.001) than patients in the pre-GFP period. Conclusion: Implementation of a GFP was associated with improved ED pain management for geriatric patients with fragility hip fractures. Future studies should evaluate the effects of these changes in pain management on longer-term outcomes
Four Extreme Relic Radio Sources in Clusters of Galaxies
(Abridged) We describe the results of the highest-resolution radio
observations yet made of four relic radio sources in the Abell clusters A13,
A85, A133 and A4038. Our VLA images at 1.4 GHz with 4" resolution show a
remarkable variety of fine structure in the form of spectacular arcs, wisps,
plumes and loops. Their integrated radio flux densities fall very rapidly with
frequency, with power-law slopes between 2.1 and 4.4 near 1.4 GHz The relics
possess linear polarization levels ranging between 2.3 % (A133) and 35 % (A85);
the higher polarization fractions imply a highly ordered magnetic field in the
fine structure and low differential Faraday rotation in the intervening cluster
gas. The optical identification of host galaxies remains problematic. In A85,
A133 and A4038 the travel times for the brightest cluster galaxies are
significantly longer than the modeled ages of the relics and nearby bright
ellipticals provide a better match. Excess X-ray emission in the 0.5 keV-to-2
keV band was found near the relics in A85 and A133. The surface brightness was
too high to be attributed to the inverse-Compton mechanism alone. We found
excellent fits to the broad-band radio spectra using the anisotropic (KGKP)
model of spectral ageing, and we have extended the model to include diffusion
of particles between regions of different field strength (the Murgia-JP, or
MJP, model). The steep radio spectra imply ages for the relics of ~ 10^8 yr, at
the start of which period their radio luminosities would have been ~ 10^25 W/Hz
at 1.4 GHz.Comment: 43 pages, 13 figures, AJ, Sep 2001 (accepted
Scaling Laws for Advection Dominated Flows: Applications to Low Luminosity Galactic Nuclei
We present analytical scaling laws for self-similar advection dominated
flows. The spectra from these systems range from 10 - 10 Hz, and
are determined by considering cooling of electrons through synchrotron,
bremsstrahlung, and Compton processes. We show that the spectra can be quite
accurately reproduced without detailed numerical calculations, and that there
is a strong testable correlation between the radio and X-ray fluxes from these
systems. We describe how different regions of the spectrum scale with the mass
of the accreting black hole, , the accretion rate of the gas, , and
the equilibrium temperature of the electrons, . We show that the universal
radio spectral index of 1/3 observed in most elliptical galaxies (Slee et al.
1994) is a natural consequence of self-absorbed synchrotron radiation from
these flows. We also give expressions for the total luminosity of these flows,
and the critical accretion rate, , above which the advection
solutions cease to exist. We find that for most cases of interest the
equilibrium electron temperature is fairly insensitive to , , and
parameters in the model. We apply these results to low luminosity black holes
in galactic nuclei. We show that the problem posed by Fabian & Canizares (1988)
of whether bright elliptical galaxies host dead quasars is resolved, as pointed
out recently by Fabian & Rees (1995), by considering advection-dominated flows.Comment: 30 pages, 5 postscript files. Accepted to ApJ. Also available
http://cfa-www.harvard.edu/~rohan/publications.htm
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