282 research outputs found
A combined deficiency of tissue factor and PAR-4 is associated with fatal pulmonary hemorrhage in mice
Mice with a complete absence of tissue factor (TF) die during embryonic development whereas mice with low levels of TF (Low-TF mice) survive to adulthood. Low-TF mice exhibit spontaneous hemorrhage in various organs, including the lung. In contrast, mice can survive without protease-activated receptor (PAR)-4, which is the major thrombin receptor on mouse platelets. We determined the effect of combining a deficiency PAR-4 (primary hemostasis) with a deficiency in TF (secondary hemostasis) on embryonic development and survival of adult mice
The multifrequency behaviour of the recurrent nova RS Ophiuchi
This review concentrates on the multifrequency behaviour of RS Ophiuchi and
in particular during its latest outburst. Confirmation of the 1945 outburst,
bipolar outflows and its possible fate as a Type Ia Supernova are discussed.Comment: 5 pages, 5 figures, in The Golden Age of Cataclysmic Variables and
Related Objects, F. Giovannelli & L. Sabau-Graziati (eds.), Mem. SAIt. 83 N.2
(in press
Theoretical investigation of variable infra-red emission by cosmic dust sources
Light travel time considerations are applied to the development of the infra-red flux from a cloud of dust grains surrounding a variable cosmic source of heating radiation. The properties of individual grains are explored, and the equation of radiative transfer is solved for the case of a spherically symmetric thermal source observed at a large distance. Models of specific novae are developed from the standpoint of grains existing prior to nova outburst. The situation in which a variable primary source is surrounded by a disc of dust grains is explored, as is that in which an expanding central cavity is formed by grain evaporation. In both cases qualitative comparisons are made with observations of cosmic sources of variable thermal emission from dust grains
Binding dynamics of a monomeric SSB protein to DNA : a single-molecule multi-process approach
People Programme of the European Union’s Seventh Framework Programme [REA 334496 to B.E.B.]; Leonardo da Vinci European Union Programme (to M.F.G.); Wellcome Trust [099149/Z/12/Z, 091825/Z/10/Z]. Funding for open access charge: Wellcome Trust; University of St Andrews.Single-stranded DNA binding proteins (SSBs) are ubiquitous across all organisms and are characterized by the presence of an OB (oligonucleotide/oligosaccharide/oligopeptide) binding motif to recognize single-stranded DNA (ssDNA). Despite their critical role in genome maintenance, our knowledge about SSB function is limited to proteins containing multiple OB-domains and little is known about single OB-folds interacting with ssDNA. Sulfolobus solfataricus SSB (SsoSSB) contains a single OB-fold and being the simplest representative of the SSB-family may serve as a model to understand fundamental aspects of SSB:DNA interactions. Here, we introduce a novel approach based on the competition between Förster resonance energy transfer (FRET), protein-induced fluorescence enhancement (PIFE) and quenching to dissect SsoSSB binding dynamics at single monomer resolution. We demonstrate that SsoSSB follows a monomer-by-monomer binding mechanism that involves a positive-cooperativity component between adjacent monomers. We found that SsoSSB dynamic behaviour is closer to that of Replication Protein A than to Escherichia coli SSB; a feature that might be inherited from the structural analogies of their DNA-binding domains. We hypothesize that SsoSSB has developed a balance between highdensity binding and a highly dynamic interaction with ssDNA to ensure efficient protection of the genome but still allow access to ssDNA during vital cellular processes.Publisher PDFPeer reviewe
The Radio Light Curve of the Gamma-Ray Nova in V407 Cyg: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from Within by the Nova Blast
We present multi-frequency radio observations of the 2010 nova event in the
symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array
and spanning 1-45 GHz and 17-770 days following discovery. This nova---the
first ever detected in gamma rays---shows a radio light curve dominated by the
wind of the Mira giant companion, rather than the nova ejecta themselves. The
radio luminosity grew as the wind became increasingly ionized by the nova
outburst, and faded as the wind was violently heated from within by the nova
shock. This study marks the first time that this physical mechanism has been
shown to dominate the radio light curve of an astrophysical transient. We do
not observe a thermal signature from the nova ejecta or synchrotron emission
from the shock, due to the fact that these components were hidden behind the
absorbing screen of the Mira wind.
We estimate a mass loss rate for the Mira wind of Mdot_w ~ 10^-6 M_sun/yr. We
also present the only radio detection of V407 Cyg before the 2010 nova, gleaned
from unpublished 1993 archival VLA data, which shows that the radio luminosity
of the Mira wind varies by a factor of >~20 even in quiescence. Although V407
Cyg likely hosts a massive accreting white dwarf, making it a candidate
progenitor system for a Type Ia supernova, the dense and radially continuous
circumbinary material surrounding V407 Cyg is inconsistent with observational
constraints on the environments of most Type Ia supernovae.Comment: Resubmitted to ApJ after incorporating referee's comment
Radio studies of novae: a current status report and highlights of new results
Novae, which are the sudden visual brightening triggered by runaway
thermonuclear burning on the surface of an accreting white dwarf, are fairly
common and bright events. Despite their astronomical significance as nearby
laboratories for the study of nuclear burning and accretion phenomena, many
aspects of these common stellar explosions are observationally not
well-constrained and remain poorly understood. Radio observations, modeling and
interpretation can potentially play a crucial role in addressing some of these
puzzling issues. In this review on radio studies of novae, we focus on the
possibility of testing and improving the nova models with radio observations,
and present a current status report on the progress in both the observational
front and theoretical developments. We specifically address the issues of
accurate estimation of ejecta mass, multi-phase and complex ejection phenomena,
and the effect of a dense environment around novae. With highlights of new
observational results, we illustrate how radio observations can shed light on
some of these long-standing puzzles.Comment: 19 pages, 4 figures. Review article published in the Bulletin of the
Astronomical Society of India (BASI) special issue on nova
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