Characterization of aluminum nitride material under swift heavy ion irradiations

International audienceFor Generation IV reactors, and more particularly the Gas Fast Reactor, aluminum nitride is an interesting candidate for the application as fuel coating; actually, its great thermal conductivity should allow efficient thermal transfer between the fuel pellets and the coolant. Unfortunately, few data are available on its behavior under irradiation. In this study, we attempted to understand the effect of irradiation parameters on the defect creation thanks to thermally-stimulated luminescence and optical absorption spectrophotometry. Thus, we didn't note any new defect created by the irradiation and the fact that these techniques complement each other allowed to know the influence of each irradiation parameter on the defects concentration

Heavy ion induced damages in Ti3SiC2: study of the swelling

International audienceFor Generation IV reactors, and more particularly the Gas Fast Reactor, ternary carbide Ti3SiC2 is an interesting candidate for the application as fuel coating; actually, it has the advantage to combine some properties of metals with those generally attributed to ceramics. Unfortunately, few data are available on its behavior under irradiation. In this study, we attempted to measure and to understand the origin of the swelling induced by nuclear collisions. Thus, it seems that Ti3SiC2 irradiated at room temperature swell less than silicon carbide and that critical amorphization temperature is less than room temperature

Heavy ions induced damages in Ti3SiC2: effect of irradiation temperature

International audienceThanks to their refractoriness, carbides are sensed as fuel coating for the IVth generation of reactors. Among those studied, the Ti3SiC2 ternary compound can be distinguished for its noteworthy mechanical properties: the nanolamellar structure imparts to this material some softness as well as better toughness than other classical carbides such as SiC or TiC. However, under irradiation, its behaviour is still unknown. In order to understand this behaviour, specimens were irradiated with heavy ions of different energies, then characterised. The choice of energies used allowed separation of the effects of nuclear interactions from those of electronic ones. Thus, AFM, SEM and XRD techniques allowed to note an important spoiling due to nuclear collision whereas electronic interactions would induce the formation of hills and the expansion of the unit cell. Irradiations at higher temperatures allowed to study the effect of temperature on these results

Dommages d'irradiation dans Ti3SiC2 : Effets des interactions nucléaires et électroniques

Comme pour tout système nucléaire, le concept du combustible pour les réacteurs de IVème génération consiste en des pastilles de combustible conditionnées dans une matrice qui doit contenir les produits de fission. De par leur excellente réfractarité, les carbures sont pressentis pour constituer cette barrière de confinement. Parmi ceux étudiés, le ternaire Ti3SiC2 se distingue par ses propriétés mécaniques particulières : en effet, sa structure nanolamellaire lui confère une certaine plasticité ainsi qu'une ténacité supérieure aux carbures classiques tels que SiC ou TiC. Cependant, son comportement sous irradiation n'est pas connu. Afin d'appréhender ce comportement, des échantillons ont été irradiés aux ions lourds de différentes énergies puis caractérisés. Le panel d'énergies utilisé a permis de discriminer l'effet des interactions nucléaires – pulvérisation – des interactions électroniques – apparition de monticules et dilatation de la maille cristalline

Irradiation damages in Ti3SiC2: formation and characterisation of the oxide layer

International audienceThe concept of the fuel for the IVth generation reactors should consist of fuel pellets surrounded with a matrix that must contain fission products. Thanks to their interesting thermo-mechanical properties, carbides are sensed to become this matrix. Among the studied carbides, Ti3SiC2 can be distinguished; actually, its nano-laminated structure confers to it some softness as well as a better toughness than classical carbides like SiC or TiC. However, before to use this remarkable carbide, a study of its behaviour under irradiation must be led. Thus, some characterisations were performed on 75 MeV Kr irradiated specimens. They allowed to underline that TiO2 (formed on the surface of Ti3SiC2 during the surface preparation) seems to be sputtered by irradiation, and that the unit cell of Ti3SiC2 is dilated along c axis

Dommages d'irradiation dans Ti3SiC2

Les carbures, de par leurs propriétés remarquables, sont pressentis comme matériau de structure autour du combustible du réacteur de génération IV. Parmi ceux étudiés, Ti3SiC2 se distingue car il associe les propriétés des céramiques à celles des métaux. Cependant, son comportement sous irradiation n'est pas connu. Des caractérisations ont été réalisées sur des échantillons irradiés aux ions Kr à 75 MeV. Elles ont permis de mettre en exergue que TiO2 (formé en surface de Ti3SiC2) est pulvérisé par l'irradiation et que la maille cristalline de Ti3SiC2 se dilate suivant c

Damages induced by heavy ions in titanium silicon carbide: effects of nuclear and electronic interactions at room temperature

International audienceThanks to their refractoriness, carbides are sensed as fuel coating for the IVth generation of reactors. Among those studied, the Ti3SiC2 ternary compound can be distinguished for its noteworthy mechanical properties: the nanolamellar structure imparts to this material some softness as well as better toughness than other classical carbides such as SiC or TiC. However, under irradiation, its behaviour is still unknown. In order to understand this behaviour, specimens were irradiated with heavy ions of different energies, then characterised. The choice of energies used allowed separation of the effects of nuclear interactions from those of electronic ones

Microstructural changes induced by low energy heavy ion irradiation in titanium silicon carbide

International audienceLow energy ion irradiation was used to investigate the microstructural modifications induced in Ti3SiC2 by nuclear collisions. Characterization of the microstructure of the pristine sample by electron back-scatter diffraction (EBSD) shows a strong texturing of TiSi2, which is a common secondary phase present in Ti3SiC2. A methodology based on atomic force microscopy (AFM) was developed to measure the volume swelling induced by ion irradiation, and it was validated on irradiated silicon carbide. The swelling of Ti3SiC2 was estimated to 2.2 ± 0.8% for an irradiation dose of 4.3 dpa at room temperature. Results obtained by both EBSD and AFM analyses showed that nuclear collisions induce an anisotropic swelling in Ti3SiC2

L’information médico-économique entre décision stratégique et action publique : tout savoir pour peu pouvoir !

À partir d’une série de recherches-interventions menées depuis 1990, cet article critique les apports de la transparence de l’activité des hôpitaux publics sur leur pilotage. Paradoxalement, alors que les acteurs possèdent une connaissance quasi-exhaustive de la production hospitalière avec le Programme de médicalisation des systèmes d’information (PMSI), les autorités de régulation et les hôpitaux publics font face à la difficulté de mettre en œuvre les décisions découlant des usages sophistiqués de cette connaissance. En effet, la politique de régulation de l’offre sur un territoire s’oppose aux incitations concurrentielles de la Tarification à l’activité, tandis que la stratégie concurrentielle des établissements publics est limitée par leurs problèmes de recrutement de la ressource médicale et par la rigidité de leurs coûts de production. Les cliniques privées, du fait de leur plasticité, apparaissent en retour comme les principales bénéficiaires de ce système d’information.Based on action research accumulated since 1990, this paper analyzes the limited impact of the French medical information system [Program of medicalization of information system (PMSI)] on the strategic management capability of the public hospital sector. Whereas the PMSI provides nearly exhaustive knowledge of hospital activities, regulatory authorities and public hospital administrators are unable to act on this knowledge that is often highly sophisticated. Supply side regulation of regional markets contrasts with the competitive pressure arising from the prospective payment system. The competitive strategy of the public hospital is limited by the difficulties of recruiting medical resources and by the rigidity of their produc- tion costs. On the other hand, thanks to their malleability, private hospitals appear to be the main beneficiaries of this information system

The Polyketide Synthase Pks13 Catalyzes a Novel Mechanism of Lipid Transfer in Mycobacteria

SummaryMycolate-containing compounds constitute major strategic elements of the protective coat surrounding the tubercle bacillus. We have previously shown that FAAL32-Pks13 polyketide synthase catalyzes the condensation reaction, which produces α-alkyl β-ketoacids, direct precursors of mycolic acids. In contrast to the current biosynthesis model, we show here that Pks13 catalyzes itself the release of the neosynthesized products and demonstrate that this function is carried by its thioesterase-like domain. Most importantly, in agreement with the prediction of a trehalose-binding pocket in its catalytic site, this domain exhibits an acyltransferase activity and transfers Pks13’s products onto an acceptor molecule, mainly trehalose, leading to the formation of the trehalose monomycolate precursor. Thus, this work allows elucidation of the hinge step of the mycolate-containing compound biosynthesis pathway. Above all, it highlights a unique mechanism of transfer of polyketide synthase products in mycobacteria, which is distinct from the conventional intervention of the discrete polyketide-associated protein (Pap)-type acyltransferases