110 research outputs found
Cosmic radioactivities
Radionuclides with half-lives ranging from some years to billions of years
presumably synthesized outside of the solar system are now recorded in ``live''
or ``fossil'' form in various types of materials, like meteorites or the
galactic cosmic rays. They bring specific astrophysical messages the
deciphering of which is briefly reviewed here, with special emphasis on the
contribution of Dave Schramm and his collaborators to this exciting field of
research. Short-lived radionuclides are also present in the Universe today, as
directly testified by the gamma-ray lines emitted by the de-excitation of their
daughter products. A short review of recent developments in this field is also
presented.Comment: Invited Review to appear in New Astronomy, 16 pages, 2 figure
The survival of 205Pb in intermediate-mass AGB stars
The now extinct 205Pb is a pure s-process radionuclide (t_{1/2} = 1.5x10^7 y)
of possible substantial cosmochemical interest. As a necessary complement to
the detailed theoretical study of the nuclear physics and astrophysics aspects
of the 205Pb - 205Tl pair carried out by Yokoi et al. (1985), and to the recent
calculation of the 205Pb production in Wolf-Rayet stars by Arnould et al.
(1997), this paper addresses for the first time in some detail the question of
the survival of this radionuclide in thermally pulsing AGB stars. This problem
is made difficult by the high sensitivity to temperature and density of the
rates of the weak interaction processes that are able to produce or destroy
205Pb. In view of this sensitivity, a recourse to detailed stellar models is
mandatory. With the help of some simplifying assumptions concerning in
particular the third dredge-up characteristics, some of which (like its depth)
being considered as free parameters, predictions are made for the 205Pb
contamination of the stellar surface at the end of a pulse-interpulse cycle
following a series of a dozen of pulses in three different intermediate-mass
stars (M=3M_sun,Z=0.02; M=6M_sun,Z=0.02; M=3M_sun,Z=0.001). It is concluded
that the chances for a significant 205Pb surface enrichment are likely to
increase with M for a given Z, or to increase with decreasing Z for a given M.
More specifically, following the considered pulses at least, the enrichment
appears to be rather unlikely in the 3M_sun star with Z=0.02, while it seems to
be much more probable in the other two considered stars. It is also speculated
that the (3M_sun,Z=0.02) star could possibly experience some 205Pb enrichment
following later pulses than the ones considered in this paper.Comment: 10 pages, 10 figures, Latex A&A, ps file available at
ftp://obsftp.unige.ch/pub/mowlavi/pbtl.ps; accepted for publication in A&
NACRE II: an update of the NACRE compilation of charged-particle-induced thermonuclear reaction rates for nuclei with mass number
An update of the NACRE compilation [Angulo et al., Nucl. Phys. A 656 (1999)
3] is presented. This new compilation, referred to as NACRE II, reports
thermonuclear reaction rates for 34 charged-particle induced, two-body exoergic
reactions on nuclides with mass number , of which fifteen are
particle-transfer reactions and the rest radiative capture reactions. When
compared with NACRE, NACRE II features in particular (1) the addition to the
experimental data collected in NACRE of those reported later, preferentially in
the major journals of the field by early 2013, and (2) the adoption of
potential models as the primary tool for extrapolation to very low energies of
astrophysical -factors, with a systematic evaluation of uncertainties.
As in NACRE, the rates are presented in tabular form for temperatures in the
T K range. Along with the 'adopted'
rates, their low and high limits are provided. The new rates are available in
electronic form as part of the Brussels Library (BRUSLIB) of nuclear data. The
NACRE II rates also supersede the previous NACRE rates in the Nuclear Network
Generator (NETGEN) for astrophysics.
[http://www.astro.ulb.ac.be/databases.html.]Comment: 86 figure
Les argiles bleues du Cambrien inférieur de Saint-Pétersbourg et leur fissuration. Implications pour des stockages souterrains
A compilation of charged-particle induced thermonuclear reaction rates
Low-energy cross section data for 86 charged-particle induced reactions involving light (1 less than or equal to Z less than or equal to 14), mostly stable, nuclei are compiled. The corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 10(6) K to 10(10) K are calculated. These evaluations assume either that the target nuclei are in their ground state, or that the target states are thermally populated following a Maxwell-Boltzmann distribution, except in some cases involving isomeric states. Adopted values complemented with lower and upper limits of the rates are presented in tabular form. Analytical approximations to the adopted rates, as well as to the inverse/direct rate ratios, are provided. (C) 1999 Elsevier Science B.V. All rights reserved
Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples
Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts
Contribution à l'étude de la nucléosynthèse des éléments lourds du système solaire et lors des phases avancées de l'évolution stellaire
Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe
La physique des étoiles : un défi pluridisciplinaire
Arnould Marcel. La physique des étoiles : un défi pluridisciplinaire. In: Bulletin de la Classe des sciences, tome 17, n°7-12, 2006. pp. 207-208
Contribution à l'étude de la nucléosynthèse des éléments lourds du système solaire et lors des phases avancées de l'évolution stellaire
Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe
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