167 research outputs found
GMRT Observations of Microquasar V4641 Sgr
We report the GMRT observations of V4641 Sgr during the May 2002 outburst at
radio frequencies of 610 and 244 MHz. This is the lowest frequency radio
detection of this source. The present low frequency radio observations clearly
showed spectral evolution from the optically thick to thin state. This behavior
is broadly consistent with the expanding bubble model. However, the flux
densities observed at lower frequencies are much higher than predicted by this
model. In the conical jet model, this discrepancy could be reconciled.Comment: 5 pages, 3 figure
Mass and dust in the disk of a spiral lens galaxy
Gravitational lensing is a potentially important probe of spiral galaxy
structure, but only a few cases of lensing by spiral galaxies are known. We
present Hubble Space Telescope and Magellan observations of the two-image
quasar PMN J2004-1349, revealing that the lens galaxy is a spiral galaxy. One
of the quasar images passes through a spiral arm of the galaxy and suffers 3
magnitudes of V-band extinction. Using simple lens models, we show that the
mass quadrupole is well-aligned with the observed galaxy disk. A more detailed
model with components representing the bulge and disk gives a bulge-to-disk
mass ratio of 0.16 +/- 0.05. The addition of a spherical dark halo, tailored to
produce an overall flat rotation curve, does not change this conclusion.Comment: ApJ, in press [9pp, 7 figs
Probing The Dust-To-Gas Ratio of z > 0 Galaxies Through Gravitational Lenses
We report the detection of differential gas column densities in three
gravitational lenses, MG0414+0534, HE1104-1805, and PKS1830-211. Combined with
the previous differential column density measurements in B1600+434 and
Q2237+0305 and the differential extinction measurements of these lenses, we
probe the dust-to-gas ratio of a small sample of cosmologically distant normal
galaxies. We obtain an average dust-to-gas ratio of E(B-V)/NH =(1.4\pm0.5) e-22
mag cm^2/atoms with an estimated intrinsic dispersion in the ratio of ~40%.
This average dust-to-gas ratio is consistent with the average Galactic value of
1.7e-22 mag cm^2/atoms and the estimated intrinsic dispersion is also
consistent with the 30% observed in the Galaxy.Comment: 14 pages, 4 figures, Accepted by Ap
Low Frequency Radio Observations of GRS1915+105 with GMRT
We present the first detailed low frequency radio measurements of the
galactic microquasar GRS1915+105 with GMRT. Simultaneous observations were
carried out at 610 and 244 MHz. Our data does not show any signature of
spectral turn over even at low radio frequency of 244 MHz. We propose that
while the radio emission at high radio frequencies could predominantly come
from compact jets, the emission at lower frequency originates in the lobes at
the end of the jet which acts like a reservoir of low energy electrons.Comment: 7 pages, 3 figure
Optical and Radio observations of the bright GRB010222 afterglow: evidence for rapid synchrotron cooling?
We report photometric observations of the optical afterglow of GRB010222 in
V,R and I passbands carried out at UPSO, Naini Tal between 22-27 Feb 2001. We
determine CCD Johnson BV and Cousins RI photometric magnitudes for 31 stars in
the field of GRB010222 and use them to calibrate our measurements as well as
other published BVRI photometric magnitudes of GRB010222 afterglow. We
construct the light curve in V,R,I passbands and from a broken power-law fit
determine the decay indices of 0.74+/-0.05 and 1.35+/-0.04 before and after the
break at 0.7 days. Using reported X-ray flux measurements at 0.35 and 9.13 days
after the burst we determine X-ray to opt/IR spectral index of 0.61+/-0.02 and
0.75+/-0.02 on these two days. We also report upper limits to the radio flux
obtained from the RATAN-600 telescope and the GMRT, and millimeter-wave upper
limits obtained from the Plateau de Bure Millimeter interferometer. We argue
that the synchrotron cooling frequency is below the optical band for most of
the observing period. We also estimate an initial jet opening angle of about
2.0n^(1/8) degrees, where n is the number density of the ambient medium.Comment: 16 pages, 4 postscript figures, minor revisions according to
referee's comments, millimeter upper limit added, accepted for publication in
Bulletin of the Astronomical Society of Indi
PKS 1830-211: A Face-On Spiral Galaxy Lens
We present new Hubble Space Telescope images of the gravitational lens PKS
1830-211, which allow us to characterize the lens galaxy and update the
determination of the Hubble constant from this system. The I-band image shows
that the lens galaxy is a face-on spiral galaxy with clearly delineated spiral
arms. The southwestern image of the background quasar passes through one of the
spiral arms, explaining the previous detections of large quantities of
molecular gas and dust in front of this image. The lens galaxy photometry is
consistent with the Tully-Fisher relation, suggesting the lens galaxy is a
typical spiral galaxy for its redshift. The lens galaxy position, which was the
main source of uncertainty in previous attempts to determine H_0, is now known
precisely. Given the current time delay measurement and assuming the lens
galaxy has an isothermal mass distribution, we compute H_0 = 44 +/- 9 km/s/Mpc
for an Omega_m = 0.3 flat cosmological model. We describe some possible
systematic errors and how to reduce them. We also discuss the possibility
raised by Courbin et al. (2002), that what we have identified as a single lens
galaxy is actually a foreground star and two separate galaxies.Comment: 21 pp., 4 figs., accepted by ApJ, section added to discuss related
work by Courbin et al. (astro-ph/0202026
Quality indicators in surgical oncology: systematic review of measures used to compare quality across hospitals
Background: Measurement and reporting of quality indicators at the hospital level has been shown to improve outcomes and support patient choice. Although there are many studies validating individual quality indicators, there has been no systematic approach to understanding what quality indicators exist for surgical oncology and no standardization for their use. The aim of this study was to review quality indicators used to assess variation in quality in surgical oncology care across hospitals or regions. It also sought to describe the aims of these studies and what, if any, feedback was offered to the analysed groups. Methods: A literature search was performed to identify studies published between 1 January 2000 and 23 October 2023 that applied surgical quality indicators to detect variation in cancer care at the hospital or regional level. Results: A total of 89 studies assessed 91 unique quality indicators that fell into the following Donabedian domains: process indicators (58; 64%); outcome indicators (26; 29%); structure indicators (6; 7%); and structure and outcome indicators (1; 1%). Purposes of evaluating variation included: identifying outliers (43; 48%); comparing centres with a benchmark (14; 16%); and supplying evidence of practice variation (29; 33%). Only 23 studies (26%) reported providing the results of their analyses back to those supplying data. Conclusion: Comparisons of quality in surgical oncology within and among hospitals and regions have been undertaken in high-income countries. Quality indicators tended to be process measures and reporting focused on identifying outlying hospitals. Few studies offered feedback to data suppliers
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