Synthetic Smectite Colloids: Characterization of Nanoparticles after Co-Precipitation in the Presence of Lanthanides and Tetravalent Elements (Zr, Th)

The magnesian smectite hectorite is a corrosion product frequently detected in nuclear waste glass alteration experiments. The structural incorporation of a single trivalent lanthanide was previously demonstrated. Hectorite was presently synthesized, for the first time, in the presence of several lanthanides (La, Eu, Yb) following a multi-step synthesis protocol. The smallest-sized particles (nanoparticles, NPs) were isolated by centrifugation and analyzed by asymmetrical flow field-flow fractionation (AsFlFFF) coupled to ICP-MS, in order to obtain information on the elemental composition and distribution as a function of the size. Nanoparticles can be separated from the bulk smectite phase. The particles are able to accommodate even the larger-sized lanthanides such as La, however, with lower efficiency. We, therefore, assume that the incorporation proceeds by substitution for octahedral Mg accompanied by a concomitant lattice strain that increases with the size of the lanthanides. The presence of a mixture does not seem to affect the incorporation extent of any specific element. Furthermore, syntheses were performed where in addition the tetravalent zirconium or thorium elements were admixed, as this oxidation state may prevail for many actinide ions in a nuclear waste repository. The results show that they can be incorporated as well

Viticulture et viniculture dans le nord du bassin parisien d’après les données archéobotaniques

International audienceDespite the sparse traces of Roman viticulture in the north provinces documentation goes progressively increasing. Considered separately, pips discoveries don’t illustrate wine growing and producing technology in these areas but an extensive analysis of remains, such as marc residues and associated marks, give a new information concerning processes as well as ampelographic practices, revealed by morphometric analysis of the pips.Les traces d’une viticulture romaine dans les provinces du Nord sont certes dispersées, mais le dossier s’étoffe progressivement. Considérées de manière isolée, les découvertes de pépins de raisin ne constituent pas une illustration directe des procédés viticoles et vinicoles pratiqués dans ces régions, mais une analyse plus poussée des restes et des indices associés nous fournit des informations inédites, qu’il s’agisse de résidus de marc, ou que les pépins conservent, dans leur morphologie, la trace de pratiques ampélographiques mises en lumière par l’étude morphométrique

Montmorillonite colloids: I. Characterization and stability of dispersions with different size fractions

International audienceBentonite is planned to be used as a technical barrier in the final storage of spent nuclear fuel and high level vitrified waste. In contact with ground water of low ionic strength, montmorillonite colloids may be released from the bentonite buffer and thereby enhance the transport of radionuclides (RNs) sorbed. In the present case, clay colloids represent aggregates of several clay mineral layers. It is of major importance to determine RN sorption properties for different sizes of montmorillonite aggregates, since size fractionation may occur during particle transport in natural media. In this study, a protocol for size fractionation of clay aggregates is developed, by sequential and direct centrifugation, in the presence and absence of organic matter. Seven colloidal fractions of different mean aggregate sizes are obtained ranging, when considering the mean equivalent hydrodynamic sphere diameter (ESD), from ~ 960 nm down to ~ 85 nm. Applying mathematical treatments (Jennings and Parslow, 1988) and approximating the clay aggregates to regular disc-shaped stacks of clay mineral sheets result in mean surface diameters varying from ~ 1.5 μm down to ~ 190 nm. All these colloidal fractions are characterized by XRD, IC and ICP-OES where they are found to have the same chemical composition. The number of edge sites (aluminol and silanol) is estimated (in mol/kg) for each colloidal fraction according to (Tournassat et al., 2003). It is calculated from the mean particle sizes obtained from AsFlFFF and PCS measurements, where the clay aggregates are approximated to regular disc-shaped stacks of clay mineral sheets. The estimated number of edge sites varies significantly for the different clay dispersions. In addition, stability studies using the various clay colloidal fractions are performed by the addition of NaCl, CaCl2 or MgCl2, in the presence or absence of organic matter, where no difference in stability is found

Du Bronze final III au 1er âge du Fer. Premiers résultats des fouilles du site du Menhir à EYNE

International audienceEn Cerdagne, les habitats de plein air possédant une stratigraphie conservée sont rarissimes et, jusqu’à récemment, seul le site de Llo entrait dans l’inventaire. Le site du Menhir à Eyne, fouillé en 2010 et 2011, avec des séquences stratigraphiques datées par le 14C, offre une lecture de la transition âge du Bronze – âge du Fer tout à fait remarquable et entre à son tour dans le "club" très fermé des sites stratifiés. La chronologie de ce gisement nous montre un paysage tout en nuances d’une période à l’autre. La présence, dans les couches datées, du Bronze final III, de formes et décors de poterie nouveaux, trouveront leur apogée au 1er âge du Fer pour disparaître progressivement vers la fin de cette période

Deep learning<i>versus</i>geometric morphometrics for archaeobotanical domestication study and subspecific identification

Taxonomical identification of archaeological fruit and seed is of prime importance for any archaeobotanical studies. We compared the relative performance of deep learning and geometric morphometrics at identifying pairs of plant taxa. We used their seeds and fruit stones that are the most abundant recovered organs in archaeobotanical assemblages, and whose morphological identification, chiefly between wild and domesticated types, allow to document their domestication and biogeographical history. We used existing modern datasets of four plant taxa (date palm, barley, olive and grapevine) corresponding to photographs of two orthogonal views of their seeds that were analysed separately to offer a larger spectrum of shape diversity. On these eight datasets, we compared the performance of a deep learning approach, here convolutional neural networks (CNN), to that of a geometric morphometric approach, here outline analyses using elliptical Fourier transforms (EFT). Sample sizes were at minimum eight hundred seeds in each class, which is quite small when training deep learning models but of typical magnitude for archaeobotanical studies. Our objectives were twofold: i) to test whether deep learning can beat geometric morphometrics in taxonomic identification and if so, ii) to test which minimal sample size is required. We ran simulations on the full datasets and also on subsets, starting from 50 images in each binary class. For CNN networks, we deliberately used a candid approach relying on pre-parameterised VGG16 network. For EFT, we used a state-of-the art morphometrical pipeline. The main difference rests in the data used by each model: CNN used bare photographs where EFT used (x, y) outline coordinates. This "pre-distilled" geometrical description of seed outlines is often the most time-consuming part of morphometric studies. Results show that CNN beats EFT in most cases, even for very small datasets. We finally discuss the potential of CNN for archaeobotany, why outline analyses and morphometrics have not yet said their last word by providing quantitative descriptions, and how bioarchaeological studies could embrace both approaches, used in a complementary way, to better assess and understand the past history of species

La transition âge du bronze - âge du fer en Cerdagne. Programme collectif de recherche, rapport 2011

320 p