9,004 research outputs found
An SZ/X-ray galaxy cluster model and the X-ray follow-up of the Planck clusters
Sunyaev-Zel'dovich (SZ) cluster surveys will become an important cosmological
tool over next few years, and it will be essential to relate these new surveys
to cluster surveys in other wavebands. We present an empirical model of cluster
SZ and X-ray observables constructed to address this question and to motivate,
dimension and guide X-ray follow-up of SZ surveys. As an example application of
the model, we discuss potential XMM-Newton follow-up of Planck clusters.Comment: 4 pages, 5 figures. To appear in the proceedings of the XXXXIIIrd
Rencontres de Morion
Fluorescence from a few electrons
Systems containing few Fermions (e.g., electrons) are of great current
interest. Fluorescence occurs when electrons drop from one level to another
without changing spin. Only electron gases in a state of equilibrium are
considered. When the system may exchange electrons with a large reservoir, the
electron-gas fluorescence is easily obtained from the well-known Fermi-Dirac
distribution. But this is not so when the number of electrons in the system is
prevented from varying, as is the case for isolated systems and for systems
that are in thermal contact with electrical insulators such as diamond. Our
accurate expressions rest on the assumption that single-electron energy levels
are evenly spaced, and that energy coupling and spin coupling between electrons
are small. These assumptions are shown to be realistic for many systems.
Fluorescence from short, nearly isolated, quantum wires is predicted to drop
abruptly in the visible, a result not predicted by the Fermi-Dirac
distribution. Our exact formulas are based on restricted and unrestricted
partitions of integers. The method is considerably simpler than the ones
proposed earlier, which are based on second quantization and contour
integration.Comment: 10 pages, 3 figures, RevTe
A Cloudy/Xspec Interface
We discuss new functionality of the spectral simulation code CLOUDY which
allows the user to calculate grids with one or more initial parameters varied
and formats the predicted spectra in the standard FITS format. These files can
then be imported into the x-ray spectral analysis software XSPEC and used as
theoretical models for observations. We present and verify a test case.
Finally, we consider a few observations and discuss our results.Comment: 13 pages, 1 table, 4 figures, accepted for publication in PAS
Extracting galactic binary signals from the first round of Mock LISA Data Challenges
We report on the performance of an end-to-end Bayesian analysis pipeline for
detecting and characterizing galactic binary signals in simulated LISA data.
Our principal analysis tool is the Blocked-Annealed Metropolis Hasting (BAM)
algorithm, which has been optimized to search for tens of thousands of
overlapping signals across the LISA band. The BAM algorithm employs Bayesian
model selection to determine the number of resolvable sources, and provides
posterior distribution functions for all the model parameters. The BAM
algorithm performed almost flawlessly on all the Round 1 Mock LISA Data
Challenge data sets, including those with many highly overlapping sources. The
only misses were later traced to a coding error that affected high frequency
sources. In addition to the BAM algorithm we also successfully tested a Genetic
Algorithm (GA), but only on data sets with isolated signals as the GA has yet
to be optimized to handle large numbers of overlapping signals.Comment: 13 pages, 4 figures, submitted to Proceedings of GWDAW-11 (Berlin,
Dec. '06
The Enrichment History of Hot Gas in Poor Galaxy Groups
We have analyzed the ASCA SIS and GIS data for seventeen groups and
determined the average temperature and abundance of the hot x-ray emitting gas.
For groups with gas temperatures less than 1.5 keV we find that the abundance
is correlated with the gas temperature and luminosity. We have also determined
the abundance of the alpha-elements and iron independently for those groups
with sufficient counts. We find that for the cool groups (i.e. kT <1.5 keV) the
ratio of alpha-elements to iron is ~1, about half that seen in clusters.
Spectral fits with the S, Si and Fe abundances allowed to vary separately
suggest the S/Fe ratio is similar to that seen in clusters while the Si/Fe
ratio in groups is half the value determined for richer systems. The mass of
metals per unit blue luminosity drops rapidly in groups as the temperature
drops. There are two possible explanations for this decrease. One is that the
star formation in groups is very different from that in rich clusters. The
other explanation is that groups lose much of their enriched material via winds
during the early evolution of ellipticals. If the latter is true, we find that
poor groups will have contributed significantly (roughly 1/3 of the metals) to
the enrichment of the intergalactic medium.Comment: 19 Pages with 2 figures, Accepted for publication in the
Astrophysical Journa
Metabolism of maltitol by conventional rats and mice and germ-free mice, and comparative digestibility between maltitol and sorbitol in germ-free mice
The metabolism of maltitol (4-α-D-glucosylsorbitol) was assessed in fasting conventional (C) rats, C mice and germ-free (GF) mice, using [U-14C]maltitol. The radiorespirometric patterns of 14CO2 collected for 48 h after the administration of labelled maltitol were characterized by a constant rate of 14CO2 production lasting 4 h for both C rats and mice. The pattern for the GF mice showed a peak at the second hour followed immediately by a slow decrease. The percentage recovery of 14CO2 was significantly lower for the GF mice (59%) compared with C animals (72-74%). Urine, faeces and intestinal contents after 48 h totalled 19% of the administered radioactivity in the C rats and mice and 39% in the GF mice. The digestibility of maltitol and the absorption of sorbitol in GF mice was also assessed. The caecum and small intestine of GF mice, 3 h after administration of equimolar quantities of maltitol (140 mg/kg body-weight) or sorbitol (70 mg/kg body-weight), contained 39 and 51 % of the ingested dose respectively, present mostly in the caecum as sorbitol. The α-glucosidase (maltase) (EC 3.2.1.20) activity of the small intestine was appreciably higher (1·5-1·7 times) in the GF mice than in the C mice. These results suggest that the enzymic activities in the small intestine of mice and rats are sufficient to hydrolyse maltitol extensively. Consequently, the slow absorption of sorbitol seems to be an important factor limiting the overall assimilation of maltitol in the small intestin
Numerical Simulations of Shock Wave-Driven Jets
We present the results of numerical simulations of shock wave-driven jets in
the solar atmosphere. The dependence of observable quantities like maximum
velocity and deceleration on parameters such as the period and amplitude of
initial disturbances and the inclination of the magnetic field is investigated.
Our simulations show excellent agreement with observations, and shed new light
on the correlation between velocity and deceleration and on the regional
differences found in observations.Comment: 7 pages, 11 figures, submitted to Ap
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