45,997 research outputs found

    A Reverse Monte Carlo study of H+D Lyman alpha absorption from QSO spectra

    Get PDF
    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 (l>0)(l > 0) of the stochastic velocity field (mesoturbulence) is considered. This generalizes the standard assumption of completely uncorrelated bulk motions (l≡0)(l \equiv 0) 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 Lyα\alpha profile is demonstrated using Burles & Tytler [B&T] data for QSO 1009+2956 where the DI Lyα\alpha line is seen at za=2.504z_a = 2.504. The results obtained favor a low D/H ratio in this absorption system, although our upper limit for the hydrogen isotopic ratio of about 4.5×10−54.5\times10^{-5} is slightly higher than that of B&T (D/H = 3.0−0.5+0.6×10−53.0^{+0.6}_{-0.5} \times 10^{-5}). 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

    Get PDF
    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

    Full text link
    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

    Get PDF
    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
    • 

    corecore