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Accueil du site > Séminaires > A venir ...

A venir ...

 
Jeudi 04 Mai 2017
Marc Blanchard
Laboratoire Géosciences Environnement Toulouse (GET) - Observatoire Midi-Pyrénées (OMP) - Université Toulouse III, 14 avenue Edouard Belin, 31400 Toulouse, FRANCE
Theoretical investigation of equilibrium fractionation of stable isotopes: Mg isotopes in carbonate minerals
The analysis of the mechanisms controlling the stable isotope composition of natural compounds and the use of these isotopic compositions to elucidate natural processes is a central field of geochemistry. An essential basis for interpreting isotopic compositions is to know the equilibrium isotopic fractionation factors. Although thermodynamic equilibrium can be achieved between minerals at high temperature, many natural processes involve reactions between aqueous solutions and minerals. While for crystals, it is well established that equilibrium isotopic fractionation factors can be calculated using a statistical thermodynamic approach based on the vibrational properties, several theoretical methods are currently used to model ions in aqueous solution, such as finite-size molecular clusters or snapshots obtained from molecular dynamics simulations. In this talk, we will present a brief state of the art of this research field before focusing on the example of magnesium isotope fractionation between aqueous Mg2+ and carbonate minerals. Magnesium is a common impurity of calcium carbonate minerals and its isotopic composition could represent an important geochemical proxy of past oceans.

Vendredi 12 Mai 2017
Valentina Giordano
Institut Lumière Matière, Lyon
Unveiling the structural arrangements responsible for the atomic dynamics in metallic glasses during physical aging by synchrotron radiation
Understanding and controlling physical aging, i.e. the spontaneous temporal evolution of out-of- equilibrium systems, represents one of the greatest tasks in material science. Recent studies have revealed the existence of a complex atomic motion in metallic glasses, with di erent aging regimes in contrast with the typical continuous aging observed in macroscopic quantities. By combining dynamical and structural synchrotron techniques, for the rst time we directly connect previously identi ed microscopic structural mechanisms with the peculiar atomic motion, providing a broader unique view of their complexity. We show that the atomic scale is dominated by the interplay between two processes: rearrangements releasing residual stresses related to a cascade mechanism of relaxation, and medium range ordering processes, which do not a ect the local density, likely due to localized relaxations of liquid-like regions. As temperature increases, a surprising additional secondary relax- ation process sets in, together with a faster medium range ordering, likely precursors of crystallization.

Mercredi 17 Mai 2017
Anna KRIVOSHEEVA
Center of Nanoelectronics and Novel Materials (CNN), Belarusian State University of Informatics and Radioelectronics
State of the Art on DFT modelling and experimental synthesis of 2D dichalcogenides
The last achievements in the field of investigation of two-dimensional dichalcogenides over past few years are considered. The data of theoretical modeling and experimental methods for formation of the films and heterostructures based on them are presented. The possibility of creating of doped heterostructures based on 2D dichalcogenides is studied and the probability of occurrence of magnetic ordering and stable ferromagnetism in them is estimated. Results on calculations of electronic and related properties are summarized. Recommendations on the possible practical use of the investigated structures are presented.

Jeudi 29 Juin 2017
Juris Purans
Institut de Physique des Solides de Riga, Lettonie

Jeudi 12 Octobre 2017
Olivier Pouliquen
IUSTI, CNRS - Aix-Marseille Université