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Search Results: 1 - 10 of 10905 matches for " Pierre Ferret "
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Auto-protective redox buffering systems in stimulated macrophages
Pierre-Jacques Ferret, Emmanuelle Soum, Olivier Negre, Didier Fradelizi
BMC Immunology , 2002, DOI: 10.1186/1471-2172-3-3
Abstract: We observed that survivors (10–50% depending on the experiments) had acquired a resistant phenotype being capable to survive when further exposed in vitro to an apoptosis inducing dose of the NO donor compound DETA-NO. These cells expressed an increased steady-state levels of Mn SOD, CuZn SOD and catalase mRNA (130–200%), together with an increased activity of the corresponding enzymes. Intracellular concentration of glutathione was also increased (× 3.5 fold at 6 hours, still maintained × 5.2 fold at 48 hours). Neither mRNA for glutathione peroxydase, γ-glutamylcysteine synthase and glutathione reductase, nor thioredoxine and thioredoxine reductase, were significantly modified. Additional experiments in which RAW 264.7 cells were stimulated with LPS and/or IFN-γ in the presence of relatively specific inhibitors of both Mn and Cu/Zn SOD, aminotriazol (ATZ) catalase inhibitor and buthionine sulfoximine (BSO) glutathione inhibitor, showed that inhibiting LPS-induced up-regulation of intracellular redox buffering systems also prevented acquisition of the resistant phenotype.Our data suggest a direct causal relationship between survival of a fraction of macrophages and a up-regulation of key sets of auto-protective intracellular redox buffering systems, occurring simultaneously with modulation of expression of apoptotic molecules of the Bcl2-Bcl-XL/Bax-Bad family.Macrophages, and their circulating form monocytes, are potent defenders of the integrity of our body by mediating crucial physiological and protective functions. Just to mention some : they are central actors in innate immunity and inflammatory reactions; they process and present foreign antigens either by themselves, or through their lineage descendents; they are also dead cells scavengers. Strikingly, their role as front line defense against myriad of potentially pathogenic infectious agents in the outside environment, is essential in many species from insects to humans. Macrophages use various sets of recept
MOCVD growth mechanisms of ZnO nanorods
Guillaume Perillat-Merceroz,Pierre-Henri Jouneau,Guy Feuillet,Robin Thierry,Milan Rosina,Pierre Ferret
Physics , 2011, DOI: 10.1088/1742-6596/209/1/012034
Abstract: ZnO is a promising material for the fabrication of light emitting devices. One approach to achieve this goal is to use ZnO nanorods because of their expected high crystalline and optical quality. Catalyst free growth of nanorods by metalorganic chemical vapour deposition (MOCVD) was carried out on (0001) sapphire substrates. Arrays of well-aligned, vertical nanorods were obtained with uniform lengths and diameters. A thin wetting layer in epitaxy with the sapphire substrate is formed first, followed by pyramids and nanorods. The nucleation of nanorods occurs either directly at the interface, or later on top of some of the pyramids, suggesting various nucleation mechanisms. It is shown that crystal polarity plays a critical role in the growth mechanism with nanorods of Zn polarity and their surrounding pyramids with O polarity. A growth mechanism is proposed to explain that most threading dislocations lie in the wetting layer, with only a few in the pyramids and none in the nanorods.
Structural recovery of ion implanted ZnO nanowires
Guillaume Perillat-Merceroz,Fabrice Donatini,Robin Thierry,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2012, DOI: 10.1063/1.4704697
Abstract: Ion implantation is an interesting method to dope semiconducting materials such as zinc oxide provided that the implantation-induced defects can be subsequently removed. Nitrogen implantation followed by anneals under O2 were carried out on zinc oxide nanowires in the same conditions as in a previous study on bulk ZnO [J. Appl.Phys. 109, 023513 (2011)], allowing a direct comparison of the defect recovery mechanisms. Transmission electron microscopy and cathodoluminescence were carried out to assess the effects of nitrogen implantation and of subsequent anneals on the structural and optical properties of ZnO nanowires. Defect recovery is shown to be more effective in nanowires compared with bulk material due to the proximity of free surfaces. Nevertheless, the optical emission of implanted and annealed nanowires deteriorated compared to as-grown nanowires, as also observed for unimplanted and annealed nanowires. This is tentatively attributed to the dissociation of excitons in the space charge region induced by O2 adsorption on the nanowire surface.
Strain relaxation by dislocation glide in ZnO/ZnMgO core-shell nanowires
Guillaume Perillat-Merceroz,Robin Thierry,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2012, DOI: 10.1063/1.4704927
Abstract: Plastic relaxation of the misfit stress in core-shell semi-conducting nanowires can lead to structural defects, detrimental to applications. Core-shell Zn{0.7}Mg{0.3}O/ZnO quantum well heterostructures were deposited on ZnO nanowires. Strain along the a and c axes of the wurtzite structure is relaxed through the glide of dislocation half-loops from the free surfaces, within pyramidal and prismatic planes. Some half-loops are closed up in the barriers to accommodate the misfit at two consecutive interfaces of the quantum well stack. Dislocations are also observed within the nanowire core: contrary to two-dimensional structures, both the core and the shell can be plastically relaxed.
Core-shell multi-quantum wells in ZnO / ZnMgO nanowires with high optical efficiency at room temperature
Robin Thierry,Guillaume Perillat-Merceroz,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2013, DOI: 10.1088/0957-4484/23/8/085705
Abstract: Nanowire-based light-emitting devices require multi-quantum well heterostructures with high room temperature optical efficiencies. We demonstrate that such efficiencies can be attained through the use of ZnO/Zn(1-x)MgxO core shell quantum well heterostructures grown by metal organic vapour phase epitaxy. Varying the barrier Mg concentration from x=0.15 to x=0.3 leads to the formation of misfit induced dislocations in the multi quantum wells. Correlatively, temperature dependant photoluminescence reveals that the radial well luminescence intensity decreases much less rapidly with increasing temperature for the lower Mg concentration. Indeed, about 54% of the 10K intensity is retained at room temperature with x=0.15, against 2% with x=0.30. Those results open the way to the realization of high optical efficiency nanowire-based light emitting diodes.
Compared growth mechanisms of Zn-polar ZnO nanowires on O-polar ZnO and on sapphire
Guillaume Perillat-Merceroz,Robin Thierry,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2013, DOI: 10.1088/0957-4484/23/12/125702
Abstract: Controlling the growth of zinc oxide nanowires is necessary to optimize the performances of nanowire-based devices such as photovoltaic solar cells, nano-generators, or light-emitting diodes. In this view, we investigate the nucleation and growth mechanisms of ZnO nanowires grown by metalorganic vapor phase epitaxy either on O-polar ZnO or on sapphire substrates. Whatever the substrate, ZnO nanowires are Zn-polar, as demonstrated by convergent beam electron diffraction. For growth on O-polar ZnO substrate, the nanowires are found to sit on O-polar pyramids. As growth proceeds, the inversion domain boundary moves up in order to remain at the top of the O-polar pyramids. For growth on sapphire substrates, the nanowires may also originate from the sapphire / ZnO interface. The presence of atomic steps and the non-polar character of sapphire could be the cause of the Zn-polar crystal nucleation on sapphire, whereas it is proposed that the segregation of aluminum impurities could account for the nucleation of inverted domains for growth on O-polar ZnO.
Metal organic vapour-phase epitaxy growth of GaN wires on Si (111) for light-emitting diode applications
Damien Salomon,, Amelie Dussaigne, Matthieu Lafossas, Christophe Durand, Catherine Bougerol, Pierre Ferret and Joel Eymery
Nanoscale Research Letters , 2013, DOI: 10.1186/1556-276X-8-61
Abstract: GaN wires are grown on a Si (111) substrate by metal organic vapour-phase epitaxy on a thin deposited AlN blanket and through a thin SiNx layer formed spontaneously at the AlN/Si interface. N-doped wires are used as templates for the growth of core-shell InGaN/GaN multiple quantum wells coated by a p-doped shell. Standing single-wire heterostructures are connected using a metallic tip and a Si substrate backside contact, and the electroluminescence at room temperature and forward bias is demonstrated at 420 nm. This result points out the feasibility of lower cost nitride-based wires for light-emitting diode applications.
Paroles édifiantes: les éloges d’Antoine-Leonard Thomas
Olivier Ferret
Cromohs (Firenze) , 2008,
Abstract: Treating the eulogies written by Thomas between 1759 and 1770, we show how the use of reported speech of the persons being eulogised is part of a memorial ceremony that brings the character to life. This theatrical process helps to blur the generic status of these texts, which are halfway between historical narration and rhetorical speech. The use of reported speech may be understood less as a means of individualising the person in question, however, than of promoting him as an exemplum embodying virtues in action. These virtues derive from Aristotle’s analysis of the aims and values of epideictic rhetoric, but the rhetorical design of Thomas’ eulogies shapes an underlying ideological discourse designed to make a pragmatic impact on the reader: transforming the genre from an academic exercise of scholarship into an engaged discourse, Thomas clearly sides with French ‘philosophes’, and his eulogies confirm the evolution of the genre described by Jean-Claude Bonnet: their purpose is at one to celebrate the past, to satirise the present and, perhaps, to influence the future.
Approches endogène et exogène pour améliorer la segmentation thématique de documents
Olivier Ferret
Traitement Automatique des Langues , 2007,
Abstract: Topic segmentation was addressed by a large amount of work from which it is not easy to draw conclusions, especially about the need for knowledge. In this article, we propose in the same framework two methods for improving the results of a topic segmenter based on lexical reiteration. The first one is endogenous and exploits the distributional similarity of the words of a document for discovering its topics. These topics are then used to facilitate the detection of topical similarity between discourse units. The second approach achieves the same goal by relying on an external resource, that is a network of lexical co-occurrences built from a large corpus. These two approaches are also combined. An evaluation of these approaches and their combination is performed in a reference framework and shows the interest of this combination.
Crise sociale, question nationale et violence urbaine. Retour sur la mystérieuse Kale Borroka en Espagne
Jér?me Ferret
Papeles del CEIC , 2012,
Abstract: Proponemos en este artículo regresar sobre el fenómenode la Kale Borroka presentando un nuevo régimen decomprensión de esta violencia callejera que se desarrolladesde principios de la década de los 90 en el PaísVasco. El razonamiento se desglosa en un juego de 5hipótesis que son otros tantos problemas sociológicosgenerales pudiendo servir de matriz de comparación conotras formas de violencia urbana vigentes particularmenteen Francia. / Nous proposons dans cet article de revenir sur le phénomènede la Kale Borroka en présentant un nouveaurégime de compréhension de cette violence de rue quis’exprime depuis le début des années 1990 au PaysBasque en Espagne. Le raisonnement se décompose enun jeu de 5 hypothèses qui sont autant de problèmessociologiques généraux pouvant servir de matrice decomparaison avec d’autres formes de violence urbaineà l’oeuvre en particulier en France.
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