1,326 research outputs found
Type IIP supernova light curves affected by the acceleration of red supergiant winds
We introduce the first synthetic light-curve model set of Type IIP supernovae
exploded within circumstellar media in which the acceleration of the red
supergiant winds is taken into account. Because wind acceleration makes the
wind velocities near the progenitors low, the density of the immediate vicinity
of the red supergiant supernova progenitors can be higher than that
extrapolated by using a constant terminal wind velocity. Therefore, even if the
mass-loss rate of the progenitor is relatively low, it can have a dense
circumstellar medium at the immediate stellar vicinity and the early light
curves of Type IIP supernovae are significantly affected by it. We adopt a
simple beta velocity law to formulate the wind acceleration. We provide
bolometric and multicolor light curves of Type IIP supernovae exploding within
such accelerated winds from the combinations of three progenitors, 12 - 16
Msun; five beta, 1-5; seven mass-loss rates, 1e-5 - 1e-2 Msun/yr; and four
explosion energies, 0.5e51 - 2e51 erg. All the light curve models are available
at https://goo.gl/o5phYb. When the circumstellar density is sufficiently high,
our models do not show a classical shock breakout as a consequence of the
interaction with the dense and optically-thick circumstellar media. Instead,
they show a delayed 'wind breakout', substantially affecting early light curves
of Type IIP supernovae. We find that the mass-loss rates of the progenitors
need to be 1e-3 - 1e-2 Msun/yr to explain typical rise times of 5 - 10 days in
Type IIP supernovae assuming a dense circumstellar radius of 1e15 cm.Comment: 12 pages, 9 figures, 2 tables, accepted by Monthly Notices of the
Royal Astronomical Societ
The role of the Public Employment Ser-vices related to ‘Flexicurity’ in the Euro-pean Labour Markets
INTEGRAL discovery of persistent hard X-ray emission from the Soft Gamma Ray Repeater SGR 1806-20
We report the discovery of persistent hard X-ray emission extending up to 150
keV from the soft gamma-ray repeater SGR 1806-20 using data obtained with the
INTEGRAL satellite in 2003-2004. Previous observations of hard X-rays from
objects of this class were limited to short duration bursts and rare transient
episodes of strongly enhanced luminosity (``flares''). The emission observed
with the IBIS instrument above 20 keV has a power law spectrum with photon
index in the range 1.5-1.9 and a flux of 3 milliCrabs, corresponding to a
20-100 keV luminosity of ~10^36 erg s^-1 (for a distance of 15 kpc). The
spectral hardness and the luminosity correlate with the level of source
activity as measured from the number of emitted bursts.Comment: 5 pages, 3 figures, Revised version accepted for publication in
Astronomy and Astrophysics Letter
Identifying biological mechanisms for favorable cancer prognosis using non-hypothesis-driven iterative survival analysis.
Survival analyses based on the Kaplan-Meier estimate have been pervasively used to support or validate the relevance of biological mechanisms in cancer research. Recently, with the appearance of gene expression high-throughput technologies, this kind of analysis has been applied to tumor transcriptomics data. In a 'bottom-up' approach, gene-expression profiles that are associated with a deregulated pathway hypothetically involved in cancer progression are first identified and then subsequently correlated with a survival effect, which statistically supports or requires the rejection of such a hypothesis. In this work, we propose a 'top-down' approach, in which the clinical outcome (survival) is the starting point that guides the identification of deregulated biological mechanisms in cancer by a non-hypothesis-driven iterative survival analysis. We show that the application of our novel method to a population of ~2,000 breast cancer patients of the METABRIC consortium allows the identification of several well-known cancer mechanisms, such as ERBB4, HNF3A and TGFB pathways, and the investigation of their paradoxical dual effect. In addition, several novel biological mechanisms are proposed as potentially involved in cancer progression. The proposed exploratory methodology can be considered both alternative and complementary to classical 'bottom-up' approaches for validation of biological hypotheses. We propose that our method may be used to better characterize cancer, and may therefore impact the future design of therapies that are truly molecularly tailored to individual patients. The method, named SURCOMED, was implemented as a web-based tool, which is publicly available at http://surcomed.vital-it.ch. R scripts are also available at http://surcomed.sourceforge.net)
Elevated plasma levels of endothelin are associated with the severity of sepsis and presence of shock in contrast to the levels of atrial natriuretic peptide
Immunoreactive endothelin (ETi) and atrial natriuretic peptide (ANPi) blood levels were measured by radioimmunoassay in patients with clinically defined sepsis. The interaction between these two peptides and their relation to circulatory shock and mortality were studied. All septic patients (n = 16) had significantly higher ETi (22.3 ± 11.1 pg/ml) and ANPi (398.3 ± 154.3 pg/ml) plasma concentrations compared to control subjects (ETi, 4.1 ± 1.2; ANPi, 59.1 ± 14.8 pg/ml; n = 13). ETi levels followed the severity of illness according to the APACHE II scoring system and were higher in patients who did not survive. ETi levels were significantly higher in the presence of shock and bacteraemia. Furthermore, ETi correlated well with plasma lactate (r = 0.83, p < 0.05), but not with renal function. ANPi levels did not show correlation with any of these determinants. Serial blood sampling, six consecutive days after admission, showed that ETi levels gradually decreased in normotensive patients in contrast to patients with septic shock. ANPi levels did not show systematic changes in time, and no relationship was observed between ETi and ANPi levels. These results suggest that plasma ETi levels are indicative for disease severity and might have prognostic significance. The role of ANPi during sepsis remains to be eludicated
Excitations in one-dimensional S=1/2 quantum antiferromagnets
The transition from dimerized to uniform phases is studied in terms of
spectral weights for spin chains using continuous unitary transformations
(CUTs). The spectral weights in the S=1 channel are computed perturbatively
around the limit of strong dimerization. We find that the spectral weight is
concentrated mainly in the subspaces with a small number of elementary triplets
(triplons), even for vanishing dimerization. So, besides spinons, triplons may
be used as elementary excitations in spin chains. We conclude that there is no
necessity to use fractional excitations in low-dimensional, undoped or doped
quantum antiferromagnets.Comment: 4 pages, 1 figure include
On Symmetry Enhancement in the psu(1,1|2) Sector of N=4 SYM
Strong evidence indicates that the spectrum of planar anomalous dimensions of
N=4 super Yang-Mills theory is given asymptotically by Bethe equations. A
curious observation is that the Bethe equations for the psu(1,1|2) subsector
lead to very large degeneracies of 2^M multiplets, which apparently do not
follow from conventional integrable structures. In this article, we explain
such degeneracies by constructing suitable conserved nonlocal generators acting
on the spin chain. We propose that they generate a subalgebra of the loop
algebra for the su(2) automorphism of psu(1,1|2). Then the degenerate
multiplets of size 2^M transform in irreducible tensor products of M
two-dimensional evaluation representations of the loop algebra.Comment: 35 pages, v2: references added, sign inconsistency resolved in
(5.5,5.6), v3: Section 3.4 on Hamiltonian added, minor improvements, to
appear in JHE
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A classical description of subnanometer resolution by atomic features in metallic structures
Recent experiments have evidenced sub-nanometer resolution in plasmonic-enhanced probe spectroscopy. Such a high resolution cannot be simply explained using the commonly considered radii of metallic nanoparticles on plasmonic probes. In this contribution the effects of defects as small as a single atom found on spherical plasmonic particles acting as probing tips are investigated in connection with the spatial resolution provided. The presence of abundant edge and corner sites with atomic scale dimensions in crystalline metallic nanoparticles is evident from transmission electron microscopy (TEM) images. Electrodynamic calculations based on the Finite Element Method (FEM) are implemented to reveal the impact of the presence of such atomic features in probing tips on the lateral spatial resolution and field localization. Our analysis is developed for three different configurations, and under resonant and non-resonant illumination conditions, respectively. Based on this analysis, the limits of field enhancement, lateral resolution and field confinement in plasmon-enhanced spectroscopy and microscopy are inferred, reaching values below 1 nanometer for reasonable atomic sizes
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