3,744 research outputs found
Thermal photon production in high-energy nuclear collisions
We use a boost-invariant one-dimensional (cylindrically symmetric) fluid
dynamics code to calculate thermal photon production in the central rapidity
region of S+Au and Pb+Pb collisions at SPS energy ( GeV/nucleon).
We assume that the hot matter is in thermal equilibrium throughout the
expansion, but consider deviations from chemical equilibrium in the high
temperature (deconfined) phase. We use equations of state with a first-order
phase transition between a massless pion gas and quark gluon plasma, with
transition temperatures in the range MeV.Comment: revised, now includes a_1 contribution. revtex, 10 pages plus 4
figures (uuencoded postscript
Measuring hadron properties at finite temperature
We estimate the numbers and mass spectra of observed lepton and kaon pairs
produced from meson decays in the central rapidity region of an Au+Au
collision at lab energy 11.6 GeV/nucleon. The following effects are considered:
possible mass shifts, thermal broadening due to collisions with hadronic
resonances, and superheating of the resonance gas. Changes in the dilepton mass
spectrum may be seen, but changes in the dikaon spectrum are too small to be
detectable.Comment: 9 pages (revtex), 3 figures (uuencoded postscript
Tightly Correlated HI and FUV Emission in the Outskirts of M83
We compare sensitive HI data from The HI Nearby Galaxy Survey (THINGS) and
deep far UV (FUV) data from GALEX in the outer disk of M83. The FUV and HI maps
show a stunning spatial correlation out to almost 4 optical radii (r25),
roughly the extent of our maps. This underscores that HI traces the gas
reservoir for outer disk star formation and it implies that massive (at least
low level) star formation proceeds almost everywhere HI is observed. Whereas
the average FUV intensity decreases steadily with increasing radius before
leveling off at ~1.7 r25, the decline in HI surface density is more subtle. Low
HI columns (<2 M_solar/pc^2) contribute most of the mass in the outer disk,
which is not the case within r25. The time for star formation to consume the
available HI, inferred from the ratio of HI to FUV intensity, rises with
increasing radius before leveling off at ~100 Gyr, i.e., many Hubble times,
near ~1.7 r25. Assuming the relatively short H2 depletion times observed in the
inner parts of galaxies hold in outer disks, the conversion of HI into bound,
molecular clouds seems to limit star formation in outer galaxy disks. The long
consumption times suggest that most of the extended HI observed in M83 will not
be consumed by in situ star formation. However, even these low star formation
rates are enough to expect moderate chemical enrichment in a closed outer disk.Comment: Accepted for Publication in ApJ
The Starburst Nature of Lyman-Break Galaxies: Testing UV Extinction with X-rays
We derive the bolometric to X-ray correlation for a local sample of normal
and starburst galaxies and use it, in combination with several UV reddening
schemes, to predict the 2--8 keV X-ray luminosity for a sample of 24
Lyman-break galaxies in the HDF/CDF-N. We find that the mean X-ray luminosity,
as predicted from the Meurer UV reddening relation for starburst galaxies,
agrees extremely well with the Brandt stacking analysis. This provides
additional evidence that Lyman-break galaxies can be considered as scaled-up
local starbursts and that the locally derived starburst UV reddening relation
may be a reasonable tool for estimating the UV extinction at high redshift. Our
analysis shows that the Lyman-break sample can not have far-IR to far-UV flux
ratios similar to nearby ULIGs, as this would predict a mean X-ray luminosity
100 times larger than observed, as well as far-IR luminosities large enough to
be detected in the sub-mm. We calculate the UV reddening expected from the
Calzetti effective starburst attenuation curve and the radiative transfer
models of Witt & Gordon for low metallicity dust in a shell geometry with
homogeneous or clumpy dust distributions and find that all are consistent with
the observed X-ray emission. Finally, we show that the mean X-ray luminosity of
the sample would be under predicted by a factor of 6 if the the far-UV is
unattenuated by dust.Comment: 7 pages, 3 figures. Accepted for publication in A
GALEX and Optical Light Curves of EF Eridanus During a Low State: the Puzzling Source of UV Light
Low state optical photometry of EF Eri during an extended low accretion state
combined with GALEX near and far UV time-resolved photometry reveals a source
of UV flux that is much larger than the underlying 9500K white dwarf, and that
is highly modulated on the orbital period. The near UV and optical light curves
can be modeled with a 20,000K spot but no spot model can explain both the large
amplitude FUV variations and the SED. The limitations of limb darkening,
cyclotron and magnetic white dwarf models in explaining the observations are
discussed.Comment: 10 pages, 4 figures to be published in ApJ Letter
A Call for the Structured Physicist Report
Introduction:
The field of diagnostic radiology continues to struggle with the clinical adoption of the structured interpretive report, with many radiologists preferring a semistructured, free-text dictation style to a more rigid, highly structured approach that some professional leaders have promoted [1]. Although structured reporting compliance in the radiologist community has been difficult to achieve, diagnostic radiologists have been thinking about and discussing this important issue for many years; it is also a part of the ACR’s Imaging 3.0_ campaign [2]. In the breast imaging community, the well-established BI-RADS_ recommendations produce a very structured report, with a discussion of interpretive findings culminating in a numeric BI-RADS score ranging from 0 to 6 [3]. Unlike some interpretive radiology reports, which can be ambiguous in terms of the next course of action, the BI-RADS scale is not only a diagnostic scale but also prescriptive of what the necessary follow-up should be
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