From diluted magnetic semiconductors to self-organized nanocolumns of GeMn in Germanium

While achieving high Curie temperatures (above room temperature) in diluted magnetic semiconductors remains a challenge in the case of well controlled homogeneous alloys, several systems characterized by a strongly inhomogeneous incorporation of the magnetic component appear as promising. Incorporation of manganese into germanium drastically alters the growth conditions, and in certain conditions of low temperature Molecular Beam Epitaxy it leads to the formation of well organized nanocolumns of a Mn-rich material, with a crystalline structure in epitaxial relationship with the Mn-poor germanium matrix. A strong interaction between the Mn atoms in these nanocolums is demonstrated by x-ray absorption spectroscopy, giving rise to a ferromagnetic character as observed through magnetometry and x-ray magnetic circular dichroism. Most interesting, intense magneto-transport features are observed on the whole structure, which strongly depend on the magnetic configuration of the nanocolumns.Comment: SPIE Optics & Photonics Symposium, San Diego : \'Etats-Unis d'Am\'erique (2008

High-Curie-temperature ferromagnetism in self-organized GeMn nanocolumns

International audienceThe emerging field of spintronics would be dramatically boosted if room-temperature ferromagnetism could be added to semiconductor nanostructures that are compatible with silicon technology. Here, we report a high-TC (>400 K) ferromagnetic phase of (Ge,Mn) epitaxial layer. The manganese content is 6%, and careful structural and chemical analyses show that the Mn distribution is strongly inhomogeneous: we observe eutectoid growth of well-defined Mn-rich nanocolumns surrounded by a Mn-poor matrix. The average diameter of these nanocolumns is 3 nm and their spacing is 10nm. Their composition is close to Ge2Mn, which corresponds to an unknown germanium-rich phase, and they have a uniaxially elongated diamond structure. Their Curie temperature is higher than 400 K. Magnetotransport reveals a pronounced anomalous Hall effect up to room temperature. A giant positive magnetoresistance is measured from 7,000% at 30K to 200% at 300K and 9 T, with no evidence of saturation

Le site préhistorique de la Roche-Cotard IV (Indre-et-Loire, France) : une séquence du Pléistocène moyen et supérieur, référence pour le Val de Loire tourangeau

International audienceThe prehistoric site of La Roche-Cotard (LRC) is located on the right bank slope of the Loire Valley, a little upstream of Langeais in Indre-et-Loire. The site was made accessible by extensive material collection in 1846. The main cave, LRC I, was exca-vated in 1912: it contained a middle Paleolithic industry and digital traces were discovered in 1975 and validated in 2008.The resumption of excavations on the site since 2008 has highlighted a powerful 11 meter section with 22 distinct layers, the lower part of which fills a shelter : locus LRC IV, very close to LRC I. The stratigraphy combines from the bottom to the top, karstic inputs, fluvial and eolian sands from the Loire valley and slope deposits. Indices of anthropic occupation (lithic industry, burned bones) attest to the occupation of this space. Numerous radiocarbon and OSL ages make it possible to chronologically constrains this filling between the limit of the isotopic stages 7 and 6 (layer 22 - 169 ka) and the end of stage 3 (layer 2 - 25 ka).The locus has given rise to a multidisciplinary study as complete as possible (sedimentology and micromorphology, small and large vertebrate faunas, lithic industry...). These data provide new information on the palaeoenvironmental evolution of the region, which is poorly known in this time range. The geometry and the age of the deposits lead to the hypothesis that the main cave LRC I was impenetrable by Homo sapiens at least starting from the beginning of the isotopic stage 3 (60 ka) and thus that the parietal productions with symbolic character of the cave are most likely to be attributed to Neanderthal man.Le site préhistorique de La Roche-Cotard (LRC) se trouve sur le versant de rive droite de la vallée de la Loire, un peu en amont de Langeais, en Indre-et-Loire. Le site a été rendu accessible grâce à un important prélèvement de matériaux en 1846. La grotte principale (LRC I) a été fouillée en 1912 : elle contenait une industrie du Paléolithique moyen et des tracés digitaux y ont été découverts en 1975 et validés en 2008.La reprise des fouilles sur le site à partir de 2008 (locus LRC IV très proche de LRC I) a permis de mettre en évidence une coupe puissante de 11 mètres comprenant 22 couches distinctes dont la partie inférieure comble un abri. La stratigraphie combine, de bas en haut, des apports karstiques de milieu souterrain, des sables fluviatiles et éoliens issus de la vallée de la Loire et gravitaires du versant. Des indices d’occupation anthropique (industrie lithique, os brûlés) attestent une occupation de cet espace. Les nombreuses datations des couches par radiocarbone et par OSL permettent de situer chronologiquement ce remplissage entre la limite des stades isotopiques marins 7 et 6 (couche 22 - 169 ka) et la limite des stades 3 et 2 (couche 2 - 25 ka).Le locus a donné lieu à une étude pluridisciplinaire aussi complète que possible (sédimentologie et micromorphologie, faunes de petits et grands vertébrés, industrie lithique). Ces données apportent des précisions nouvelles sur l’évolution paléoenvironnementale de la région, mal connue dans cette fourchette de temps. La géométrie et l’âge des dépôts conduisent à l’hypothèse selon laquelle la grotte (LRC I) a été impénétrable par Homo sapiens au moins à partir du début du stade isotopique marin 3 (60 ka) et donc que les productions pariétales à caractère symbolique de la grotte sont très probablement à attribuer à l’homme de Néandertal

Influence of islet transportation on pancreatic islet allotransplantation in type 1 diabetic patients within the Swiss-French GRAGIL network

The influence of islet transportation on pancreatic islet allotransplantation in type 1 diabetic patients was evaluated within the GRAGIL network

Logistics and transplant coordination activity in the GRAGIL Swiss-French multicenter network of islet transplantation

Since the Edmonton trial in 2000, increasing numbers of transplant centers have been implementing islet transplantation programs. Some institutions have elected to associate in multicenter networks, such as the Swiss-French GRAGIL (Groupe Rhin-Rhône-Alpes-Genève pour la Transplantation d'Ilots de Langerhans) consortium