46,508 research outputs found
A Reverse Monte Carlo study of H+D Lyman alpha absorption from QSO spectra
A new method based on a Reverse Monte Carlo [RMC] technique and aimed at the
inverse problem in the analysis of interstellar (intergalactic) absorption
lines is presented. The line formation process in chaotic media with a finite
correlation length of the stochastic velocity field (mesoturbulence)
is considered. This generalizes the standard assumption of completely
uncorrelated bulk motions in the microturbulent approximation
which is used for the data analysis up-to-now. It is shown that the RMC method
allows to estimate from an observed spectrum the proper physical parameters of
the absorbing gas and simultaneously an appropriate structure of the velocity
field parallel to the line-of-sight. The application to the analysis of the H+D
Ly profile is demonstrated using Burles & Tytler [B&T] data for QSO
1009+2956 where the DI Ly line is seen at . The results
obtained favor a low D/H ratio in this absorption system, although our upper
limit for the hydrogen isotopic ratio of about is slightly
higher than that of B&T (D/H = ). We also
show that the D/H and N(HI) values are, in general, correlated, i.e. the
derived D-abundance may be badly dependent on the assumed hydrogen column
density. The corresponding confidence regions for an arbitrary and a fixed
stochastic velocity field distribution are calculated.Comment: 6 pages, LaTeX, 2 Postscript figures, to appear in "The Primordial
Nuclei and Their Galactic Evolution", eds. N. Prantzos, M. Tosi, R. von
Steiger (Kluwer: Dordrecht
Quantitative Analysis of Candida Cell Wall Components by Flow Cytometrywith Triple-Fluorescence Staining
This work was supported by the European Commission within the FP7 Framework Programme [Fungitect-Grant No 602125]. We also thank Thomas Sauer, Vienna Biocenter Campus (VBC), Austria, for technical support at the FACS facility of the MFPL, Karl Kuchler, MFPL-Department of Medical Biochemistry, Medical University of Vienna, Max F. Perutz Laboratories, Campus Vienna Biocenter, Vienna, Austria and Ernst Thuer, Centre for Genomic Regulation, Barcelona, Spain, for advice on statistical approaches. Neil Gow acknowledges the support of the Wellcome Trust and the MRC Centre for Medical MycologyPeer reviewedPublisher PD
The X-ray coronae of the two brightest galaxies in the Coma cluster
We use deep Chandra X-ray Observatory observations to examine the coronae of
the two brightest cluster galaxies in the Coma cluster of galaxies, NGC 4874
and NGC 4889. We find that NGC 4889 hosts a central depression in X-ray surface
brightness consistent with a cavity or pair of cavities of radius 0.6 kpc. If
the central cavity is associated with an AGN outburst and contains relativistic
material, its enthalpy should be around 5x10^55 erg. The implied heating power
of this cavity would be around an order of magnitude larger than the energy
lost by X-ray emission. It would be the smallest and youngest known cavity in a
brightest cluster galaxy and the lack of over pressuring implies heating is
still gentle. In contrast, NGC 4874 does not show any evidence for cavities,
although it hosts a well-known wide-angle-tail radio source which is visible
outside the region occupied by the X-ray corona. These two galaxies show that
AGN feedback can behave in varied ways in the same cluster environment.Comment: 11 pages, 11 figures, accepted by MNRA
Influence, originality and similarity in directed acyclic graphs
We introduce a framework for network analysis based on random walks on
directed acyclic graphs where the probability of passing through a given node
is the key ingredient. We illustrate its use in evaluating the mutual influence
of nodes and discovering seminal papers in a citation network. We further
introduce a new similarity metric and test it in a simple personalized
recommendation process. This metric's performance is comparable to that of
classical similarity metrics, thus further supporting the validity of our
framework.Comment: 6 pages, 4 figure
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