Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Adipose tissue. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

Extensive water ice within Ceres’ aqueously altered regolith: Evidence from nuclear spectroscopy

Abstract: The surface elemental composition of dwarf planet Ceres constrains its regolith ice content, aqueous alteration processes, and interior evolution. Using nuclear spectroscopy data acquired by NASA’s Dawn mission, we determined the concentrations of elemental hydrogen, iron, and potassium on Ceres. The data show that surface materials were processed by the action of water within the interior. The non-icy portion of Ceres’ carbon-bearing regolith contains similar amounts of hydrogen to those present in aqueously altered carbonaceous chondrites; however, the concentration of iron on Ceres is lower than in the aforementioned chondrites. This allows for the possibility that Ceres experienced modest ice-rock fractionation, resulting in differences between surface and bulk composition. At mid-to-high latitudes, the regolith contains high concentrations of hydrogen, consistent with broad expanses of water ice, confirming theoretical predictions that ice can survive for billions of years just beneath the surface.

An Overview of Palladium Nanocatalysts: Surface and Molecular Reactivity

Abstract: The use of metallic nanoparticles in catalysis under homogeneous conditions leads to a discussion of their catalytic nature: whether the catalyst behaves as a molecular species or, on the contrary, the metallic surface is directly involved in the reactivity. This dilemma is intrinsically associated to the kinetic stability of the nanoclusters, favouring their agglomeration, and also to the formation of molecular species by reaction of the atoms placed at low-coordination positions at the metallic surface. In particular, for palladium-catalyzed processes, a large number of contributions have been reported in the last decade involving nanoparticles, but few of them analyze the mechanistic aspects. The present review aims to collect the more relevant research carried out in catalysis involving palladium nanoparticles in the liquid phase and addressing the nature of the catalytically active species. This kind of work is mainly focused on hydrogenation and C–C coupling processes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Light nuclei in galactic globular clusters: constraints on the self-enrichment scenario from nucleosynthesis

Abstract: Aims. Hydrogen-burning is the root cause of the star-to-star abundance variations of light nuclei in Galactic globular clusters (GC). In the present work we constrain the physical conditions that gave rise to the observed abundance patterns of Li, C, N, O, Na, Mg, Al, as well as Mg isotopes in the typical case of NGC 6752. Methods. We perform nucleosynthesis calculations at constant temperature, adopting realistic initial abundances for the proto-cluster gas. We use a detailed nuclear reaction network and state-of-the-art nuclear reaction rates. Results. Although simplistic, our analysis provides original results and new constraints on the self-enrichment scenario for GCs. Our parametric calculations allow us to determine a narrow range of temperature where the observed extreme abundances of all light elements and isotopes in NGC 6752 are nicely reproduced simultaneously. This agreement is obtained after mixing of the H-processed material with ∼30% of unprocessed gas. We show that the observed C-N, O-Na, Mg-Al, Li-Na and F-Na anticorrelations as well as the behaviour of the Mg isotopes can be recovered by assuming mixing with various dilution factors. Li production by the stars that build up the other abundance anomalies is not mandatory in the case of NGC 6752. Conclusions. Observations of O, Na, Mg and Al constrain the temperature range for H-burning; such temperatures are encountered in the two main candidate “polluters” proposed for GCs, namely massive AGBs and the most massive main-sequence stars. Furthermore, observations require dilution of H-burning processed material with pristine one. They provide no clue, however, as to the nature of the unprocessed material required for mixing. The complementary observations of the fragile Li and F clearly point to ISM origin for the mixed material.

Revealing the demographic histories of species using DNA sequences

Abstract: Various methodological approaches using molecular sequence data have been developed and applied across several fields, including phylogeography, conservation biology, virology and human evolution. The aim of these approaches is to obtain predictive estimates of population history from DNA sequence data that can then be used for hypothesis testing with empirical data. This recent work provides opportunities to evaluate hypotheses of constant population size through time, of population growth or decline, of the rate of growth or decline, and of migration and growth in subdivided populations. At the core of many of these approaches is the extraction of information from the structure of phylogenetic trees to infer the demographic history of a population, and underlying nearly all methods is coalescent theory. With the increasing availability of DNA sequence data, it is important to review the different ways in which information can be extracted from DNA sequence data to estimate demographic parameters.