Influence of the cooling-rate on the glass transition temperature and the structural properties of glassy GeS2: an ab initio molecular dynamics study

Using density-functional molecular dynamics simulations we analyzed the cooling-rate effects on the physical properties of GeS$_2$ chalcogenide glasses. Liquid samples were cooled linearly in time according to $T(t) = T_0 - \gamma t$ where $\gamma$ is the cooling rate. We found that our model leads to a promising description of the glass transition temperature $T_g$ as a function of $\gamma$ and gives a correct $T_g$ for experimental cooling rates. We also investigated the dependence of the structural properties on the cooling rate. We show that, globally, the properties determined from our simulations are in good agreement with experimental values and this even for the highest cooling rates. In particular, our results confirm that, in the range of cooling rates studied here, homopolar bonds and extended charged regions are always present in the glassy phase. Nevertheless in order to reproduce the experimental intermediate range order of the glass, a maximum cooling rate should not be exceeded in numerical simulations.Comment: 12 pages, 6 figures. To appear in J. Phys.: C

Aerosol deposition and origin in French mountains estimated with soil inventories of 210Pb and artificial radionuclides

Radionuclide inventories were measured in soils from different French mountainous areas: Chaîne des Puys (Massif Central), Eastern Corsica, Jura, Montagne Noire, Savoie, Vosges and Rhine Valley. 210Pb soil inventories were used to estimate long-term (>75 yr) deposition of submicron aerosols. Whereas 210Pb total deposition is explained partly by wet deposition, as demonstrated by increase of 210Pb inventory with annual rainfall; a part of 210Pb in the soils of higher altitude is caused by orographic depositions. Using measurements of radionuclides coming from nuclear aerial weapon tests (137Cs and Pu isotopes), we were able to estimate the origin of aerosols deposited in high-altitude sites and to confirm the importance of occult deposition and feeder–seeder mechanism. Using a simple mass balance model, we estimate that occult deposition and feeder–seeder mechanisms account to more than 50% of total deposition of 210Pb and associated submicron aerosols in French altitude sites

Formation de NDMA par chloramination de micropolluants

International audienceL'utilisation des chloramines dans les procédés de production d'eau potable permet de limiter la formation de sous-produits de chloration tels que les trihalométhanes (THMs) et les acides haloacétiques (HAAs). Cependant, la chloramination entraîne la formation de N-nitrosamines, en particulier la N-nitrosodiméthylamine (NDMA), un sous-produit de désinfection non halogéné cancérigène pour l'homme. Les mécanismes de formation de la NDMA lors des traitements par chloramination ne sont que partiellement établis. L'étude montre que des composés azotés pouvant être rencontrés dans les eaux naturelles, par exemple des herbicides (diuron, isoproturon) ou des composés pharmaceutiques (ranitidine, mifépristone), peuvent être des précurseurs importants de NDMA. Il apparaît que les quantités importantes de NDMA formées à partir de ces composés (en particulier la ranitidine) ne peuvent pas être expliquées par les mécanismes de formation actuellement disponibles dans la littérature. De nouveaux mécanismes de formation impliquant les caractéristiques structurales des amines tertiaires doivent être envisagés

Deposition of artificial radionuclides from atmospheric Nuclear Weapon Tests estimated by soil inventories in French areas low-impacted by Chernobyl

Soil inventories of anthropogenic radionuclides were investigated in altitudinal transects in 2 French regions, Savoie and Montagne Noire. Rain was negligible in these 2 areas the days after the Chernobyl accident. Thus anthropogenic radionuclides are coming hypothetically only from Global Fallout following Atmospheric Nuclear Weapon Tests. This is confirmed by the isotopic signatures (238Pu/239þ240Pu; 137Cs/239þ240Pu; and 241Am/239þ240Pu) close to Global Fallout value. In Savoie, a peat core age-dated by 210Pbex confirmed that the main part of deposition of anthropogenic radionuclides occurred during the late sixties and the early seventies. In agreement with previous studies, the anthropogenic radionuclide inventories are well correlated with the annual precipitations. However, this is the first time that a study investigates such a large panel of annual precipitation and therefore of anthropogenic radionuclide deposition. It seems that at high-altitude sites, deposition of artificial radionuclides was higher possibly due to orographic precipitations

Analyse géométrique des données : une enquête sur le racisme

In this paper, we present the data analysis processing of a survey about racism. The methodology is that of the analysis of structured data, inspired by specific comparisons in ANOVA, and applied to geometric data (Euclidean clouds). Its realization is done by means of the Language for Interrogating Data (LID) implemented in the EyeLID software.Dans cet article, nous présentons une démarche d'analyse statistique d'un questionnaire appliquée à une enquête sur le racisme. La méthodologie suivie est celle de l'analyse des données structurées, inspirée des comparaisons spécifiques en analyse de variance, et appliquée à des données géométriques (nuage euclidien). La mise en Ïuvre est réalisée grâce au langage d'interrogation de données (LID) implanté dans le logiciel EyeLID

Influence of isothermal and cyclic oxidation on the apparent interfacial toughness in thermal barrier coating systems

In thermal barrier coatings (TBCs), the toughness relative to the interface lying either between the bond coat (BC) and the Thermal Grown Oxide (TGO) or between the TGO and the yttria stabilized zirconia topcoat (TP) is a critical parameter regarding TBCs durability. In this paper, the influence of aging conditions on the apparent interfacial toughness in Electron Beam-Physical Vapor Deposition (EB-PVD) TBCs is investigated using a specifically dedicated approach based on Interfacial Vickers Indentation (IVI), coupled with Scanning Electron Microscopy (SEM) observations to create interfacial cracks and measure the extent of crack propagation, respectively