48 research outputs found
R-process enrichment from a single event in an ancient dwarf galaxy
Elements heavier than zinc are synthesized through the (r)apid and (s)low
neutron-capture processes. The main site of production of the r-process
elements (such as europium) has been debated for nearly 60 years. Initial
studies of chemical abundance trends in old Milky Way halo stars suggested
continual r-process production, in sites like core-collapse supernovae. But
evidence from the local Universe favors r-process production mainly during rare
events, such as neutron star mergers. The appearance of a europium abundance
plateau in some dwarf spheroidal galaxies has been suggested as evidence for
rare r-process enrichment in the early Universe, but only under the assumption
of no gas accretion into the dwarf galaxies. Cosmologically motivated gas
accretion favors continual r-process enrichment in these systems. Furthermore,
the universal r-process pattern has not been cleanly identified in dwarf
spheroidals. The smaller, chemically simpler, and more ancient ultra-faint
dwarf galaxies assembled shortly after the first stars formed, and are ideal
systems with which to study nucleosynthesis events such as the r-process.
Reticulum II is one such galaxy. The abundances of non-neutron-capture elements
in this galaxy (and others like it) are similar to those of other old stars.
Here, we report that seven of nine stars in Reticulum II observed with
high-resolution spectroscopy show strong enhancements in heavy neutron-capture
elements, with abundances that follow the universal r-process pattern above
barium. The enhancement in this "r-process galaxy" is 2-3 orders of magnitude
higher than that detected in any other ultra-faint dwarf galaxy. This implies
that a single rare event produced the r-process material in Reticulum II. The
r-process yield and event rate are incompatible with ordinary core-collapse
supernovae, but consistent with other possible sites, such as neutron star
mergers.Comment: Published in Nature, 21 Mar 2016:
http://dx.doi.org/10.1038/nature1742
Pleosporales
One hundred and five generic types of Pleosporales are described and illustrated. A brief introduction and detailed history with short notes on morphology, molecular phylogeny as well as a general conclusion of each genus are provided. For those genera where the type or a representative specimen is unavailable, a brief note is given. Altogether 174 genera of Pleosporales are treated. Phaeotrichaceae as well as Kriegeriella, Zeuctomorpha and Muroia are excluded from Pleosporales. Based on the multigene phylogenetic analysis, the suborder Massarineae is emended to accommodate five families, viz. Lentitheciaceae, Massarinaceae, Montagnulaceae, Morosphaeriaceae and Trematosphaeriaceae
Comparative proteome analysis of embryo and endosperm reveals central differential expression proteins involved in wheat seed germination
Preparing for the future: a review of tools and strategies to support autonomous goal setting for children and youth with autism spectrum disorders
Reviewing Research on the Self-Determined Learning Model of Instruction: Mapping the Terrain and Charting a Course to Promote Adoption and Use
Possible house-keeping and other draft proposals to clarify or enhance the naming of fungi within the International Code of Nomenclature for algae, fungi, and plants (ICN)
The 10th International Mycological Congress (IMC10), to be held in August 2014, will be the last before the 19th International Botanical Congress (IBC) scheduled for July 2017 at which changes in the ICN will be adopted. IMC10 will therefore be the last opportunity for mycologists as a whole to debate and propose clarifications and other changes they would like to see made in the ICN which was adopted in Melbourne in 2011. In order to stimulate debate, draft proposals are presented here on ten topics: terminology of the new lists; protection against unlisted names; priority for sexual morph typified names; removal of exemptions for lichen-forming fungi; extension of sanctioning to additional works; extending conservation to additional ranks; names with the same epithet; registration of typifications subsequent to valid publication; sequenced epitypes; and generic homonyms in other kingdoms. It is anticipated that the draft proposals presented here will be abandoned, refined, or supplemented by debates at the Genera and Genomes symposium in Amsterdam in April 2014 and during IMC10, and also by other comments received from individual mycologists or other bodies. Formal proposals will then be prepared for presentation and decision at the IBC in 2017
A Multivariate Analysis of the Self-Determination of Adolescents
Self-determination, Quality of life, Self-efficacy, Adolescents, Assertiveness,