Effect of temperature and time on properties of Spark Plasma Sintered NiCuZn: Co ferrite

3 pagesInternational audienceSpark Plasma Sintering is a powerfal method to produce fine grain dense ferrite at low temperature. However, the process, usually conducted in neutral atmosphere in a carbon die, yields carbon surface deposition and reduction of Fe3+ into Fe2+. It's shown that subsequent annealing in air can remove carbon and, under some conditions, produce complete oxidation of Fe2+ ions. Regular values of the resistivity and permittivity (resp. 1 M­m, 13 "0) are recovered for most samples annealed not higher than 750±C. Relatively high value of the permeability (up to 240) and high merit factor (μs × fr > 5 GHz) have been achieved

Etude du dopage dans les nanofils d'oxyde de zinc

The work presented in this thesis aims to study the p-doping of ZnO nanowires by two different methods: in-situ (during growth) and ex-situ by diffusion of impurities in the nanowires from a gas phase. ZnO nanowires were prepared by MOCVD and characterized by different techniques: SEM, TEM, EDX, XPS, nano-Auger, XRD, SIMS, atom probe tomography, Raman, PL and I (V). The ex-situ doping attempts have not allowed the dopants (arsenic, phosphorus and antimony) to be diffused and incorporated into the ZnO matrix. They still remained on the surface. However, this process has highlighted the importance of nanowire surface annealing treatment with zinc, in order to reduce i) the density of surface related defects, and ii) the density of residual impurities n-type. This is a precondition for the incorporation of electrically active p-type dopants. For in-situ doping of ZnO nanowires, the dopant (nitrogen) is incorporated more easily into the ZnO matrix, reaching a concentration of about 1020 at.cm-3. Analyses of μ-Raman and μ-PL show that nitrogen atoms are inhomogeneously incorporated along the nanowires. If optical measurements confirm the presence of acceptors in the material after doping, the electrical measurements show, however, that nitrogen doped nanowires remain n-type.Le travail présenté dans cette thèse a pour objectif d’étudier le dopage p des nanofils de ZnO par deux procédés différents : in-situ (durant la croissance) et ex-situ par diffusion des impuretés dans les nanofils à partir d’une phase gazeuse. Les nanofils de ZnO étudiés ont été élaborés par MOCVD et caractérisés par différentes techniques : MEB, MET, EDX, XPS, nano-Auger, DRX, SIMS, Sonde atomique tomographique, Raman, PL et I(V). Les tentatives de dopage ex-situ n’ont pas permis aux dopants (arsenic, phosphore et antimoine) de diffuser et de s’incorporer dans la matrice de ZnO. Ces derniers sont restés en surface. Néanmoins, ce procédé a mis en évidence l’importance du traitement de surface des nanofils, avec un recuit sous zinc, afin de réduire d'une part les défauts associés à la surface très réactive de ZnO, et d'autre part de diminuer la densité d’impuretés résiduelle de type n, condition préliminaire à l’incorporation de dopants de type p électriquement actifs. Concernant le dopage in-situ des nanofils de ZnO, le dopant (azote) s’incorpore plus facilement dans la matrice ZnO atteignant une concentration de l’ordre de 1020 at.cm-3. Les analyses de μ-Raman et de μ-PL montrent que l’azote est reparti de façon inhomogène le long des fils. Si les mesures optiques confirment la présence d'accepteurs dans le matériau après dopage, les mesures électriques révèlent toutefois que la conduction des fils dopés azote restent de type n

Une colite à CMV révélant un lupus érythémateux systémique

Le cytomégalovirus (CMV) est responsable d’infections souvent asymptomatiques chez les immunocompétents mais également d’infections graves chez les immunodéprimés notamment chez les patients lupiques. La réactivation du CMV au cours du lupus est une complication fréquente mais rarement inaugurale. Nous rapportons l’observation d’un patient ayant présenté une colite à CMV révélatrice d’un lupus érythémateux systémique. Le diagnostic a été retenu sur les données sérologiques, de la biopsie colique et la bonne évolution après un traitement par ganciclovir

Study of the first paramagnetic to ferromagnetic transition in as prepared samples of Mn-Fe-P-Si magnetocaloric compounds prepared by different synthesis routes

International audienceMagnetocaloric materials with composition of Mn 1.3 Fe 0.65 P 0.5 Si 0.5 have been prepared by ball milling and solid-state reaction methods and consolidated using powder annealing, and conventional and spark plasma sintering. Magnetic and calorimetric measurements show remarkable differences upon first cooling, and slight differences on second and further coolings between the samples prepared by different synthesis routes. Further measurements using Hall probe imaging in high magnetic field have been also carried out. As-prepared samples have been cooled down just above the critical temperature, and the first phase transition has been induced by application of a magnetic field. Bulk samples show staircase isothermal magnetization curves whereas powders show smoother transition curves

ANALYSE FRACTALE DE TEXTURE : APPLICATION A L’IMAGE IRM ET CT-SCAN DE L’OS TRABECULAIRE

Cet article porte sur l’analyse fractale de texture, et en particulier l’analyse de la dimension fractale qui est l’un des paramètres les plus importants permettant de quantifier la complexité des images. Pour ce faire, les approches de comptage de boites (Box counting) qui sert à la subdivision de l’image en boites de carrées égaux puis le calcul de la dimension fractale, et l’approche morphologique qui se base sur l’utilisation de la différence entre l’érosion et la dilatation de chacune des carrées de l’image pour calculé la dimension fractale; ces deux approches ont été appliquées pour quantifier l’irrégularité et la fragmentation des images de textures. Et comme application, nous avons utilisés la base de données d’INSERM U 703 Lille, qui est un ensemble des images IRM et CT-Scan de textures ROI (Region Of Interest) des os trabéculaire normales et pathologiques. This article focuses on the fractal analysis of texture, and in particular the analysis of fractal dimension is one of the most important parameters for quantifying the complexity of the images. To do so, box-counting approach that serves the subdivision of the image in square boxes of equal then the calculation of fractal dimension, and the morphological approach that relies on the use of difference between erosion and dilation of each square of the image to calculate the fractal dimension, these two approaches have been applied to quantify the irregularity and fragmentation of texture images. And as an application, we used the database of Lille INSERM U 703, which is a set of MRI images and CT-scan textures ROI (Region Of Interest) of the trabecular bone of normal and pathological

Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation

Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development. Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to ¿ 350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at.%. Nitrogen content increase induces a higher sp2 character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor.This work is produced with the financial support of the Future Program Lyon Saint-Etienne (PALSE) from the University of Lyon (ANR-11-IDEX-0007), under the “Investissements d'Avenir” program managed by the National Agency Research (ANR)

Naked singularities in Tolman-Bondi-de Sitter collapse

We study the formation of central naked singularities in spherical dust collapse with a cosmological constant. We find that the central curvature singularity is locally naked, Tipler strong, and generic, in the sense that it forms from a non-zero-measure set of regular initial data. We also find that the Weyl and Ricci curvature scalars diverge at the singularity, with the former dominating over the latter, thereby signaling the non-local origin of the singularity.Comment: 8 pages, RevTeX, 1 eps figure; accepted for publication in Phys. Rev.

Microglia maintain structural integrity during fetal brain morphogenesis

Microglia (MG), the brain-resident macrophages, play major roles in health and disease via a diversity of cellular states. While embryonic MG display a large heterogeneity of cellular distribution and transcriptomic states, their functions remain poorly characterized. Here, we uncovered a role for MG in the maintenance of structural integrity at two fetal cortical boundaries. At these boundaries between structures that grow in distinct directions, embryonic MG accumulate, display a state resembling post-natal axon-tract-associated microglia (ATM) and prevent the progression of microcavities into large cavitary lesions, in part via a mechanism involving the ATM-factor Spp1. MG and Spp1 furthermore contribute to the rapid repair of lesions, collectively highlighting protective functions that preserve the fetal brain from physiological morphogenetic stress and injury. Our study thus highlights key major roles for embryonic MG and Spp1 in maintaining structural integrity during morphogenesis, with major implications for our understanding of MG functions and brain development.</p