Mechanisms of deformation in gum metal TNTZ-O and TNTZ titanium alloys: A comparative study on the oxygen influence

International audienceIn this work, Ti-23Nb-0.7Ta-2Zr (TNTZ) and gum metal Ti-23Nb-0.7Ta-2Zr-1.2O (TNTZ-O) alloys were synthesized by cold crucible levitation melting with the objective of investigating the influence of oxygen on the deformation mechanisms. By tensile tests, electron backscatter diffraction, atomic force microscopy and transmission electron microscopy analyses, we showed that the deformation in the TNTZ-O alloy is only accommodated by dislocation slip. Thus, the addition of oxygen suppresses the formation of α″ martensite and prevents the twinning deformation mechanism, which were both observed in the TNTZ alloy. In addition, in situ tensile tests in a transmission electron microscope showed that conventional a/2〈1 1 1〉 dislocation slip occurs widely in the TNTZ-O alloy. Screw dislocations have a lower mobility than non-screw dislocations. Cross-slip is shown to be easy and multiplication of dislocations by a double cross-slip mechanism occurs extensively, leading to the formation of large slip bands

Dislocation mobility in gum metal β-titanium alloy studied via in situ transmission electron microscopy

International audienceIn situ tensile tests in a transmission electron microscope were carried out on a "Gum Metal" β titanium alloy. Conventional dislocation slip was observed to be the only mechanism occurring during the plastic deformation. The low mobility of screw dislocations was shown to be due to their core structure configuration. Nanometer-sized obstacles were also present but have a weaker effect of the dislocation mobility. The density of these obstacles and the variation in energy due to the core structure of screw dislocations were measured and compared to theoretical data of literature

L’autre réalité du programme Erasmus : affinité sélective entre établissements et reproduction sociale des étudiants

Le spectre des migrations étudiantes s’est élargi au cours de ces dernières années en Europe. Son étude révèle les logiques sociales et politiques transnationales qui les mettent en œuvre. Autrement dit, les qualités individuelles que l’on prête aux étudiants migrants sont fortement liées à leurs caractéristiques scolaires et sociales, lesquelles se traduisent par une diversification croissante des parcours étudiants. Cet article a pour objet d’étude le dispositif Erasmus, programme d’échanges entre étudiants au sein de la Communauté européenne. Il s’appuie sur une analyse comparative entre trois pays : la France, la Grande-Bretagne et l’Italie. Il entend souligner qu’en dépit d’un principe de réciprocité des échanges, les relations concrètes entre institutions universitaires se fondent sur des logiques d’« affinités sélectives » qui à la fois révèlent le caractère relativement élitiste du dispositif et renforcent les déséquilibres migratoires déjà existants entre les pays concernés.The spectrum of student migrations has broadened in Europe in recent years. A study of it reveals the transnational social and political logics which implement them. In other words, the individual capacities attributed to migrant students are closely linked to their educational and social characteristics, which are reflected in a growing diversification of student careers. This article considers the Erasmus system, an exchange programme between students within the European community. It is based on a comparative analysis between three countries: France, Great Britain and Italy. It aims to stress that despite a principle of reciprocal exchanges, the concrete relations between universities are based on logics of "selective affinities" which reveal the relatively elitist character of the programme and also reinforce the migratory imbalances already existing between the countries concerned.Das Spektrum studentischer Migration in Europa hat sich innerhalb der letzten Jahre immens erweitert. Eine Untersuchung dieser Mobilität macht deutlich, welche sozialen Logiken und transnationalen Politiken hier zum Zuge kommen. D.h., individuelle Qualitäten mobiler Studenten hängen von sozialen und schulischen Eigenschaften ab, die sich in einer zunehmenden Vielfalt studentischer Bildungswege niederschlagen. In diesem Beitrag wird das ERASMUS-Programm, das Aktionsprogramm der Europäischen Gemeinschaft zur Förderung der Mobilität von Hochschulstudenten, anhand einer vergleichenden Länderstudie zwischen Frankreich, Großbritannien und Italien untersucht. Obwohl der Austausch zwischen den Hochschuleinrichtungen auf Reziprozität beruhen soll, gestalten sich derartige Kontakte und Netzwerke eher je nach Affinität. Dadurch wird einerseits der elitäre Charakter dieses Instruments deutlich und andererseits der unausgewogene Studierendenaustausch zwischen diesen drei Ländern noch verstärkt.El espectro de las migraciones estudiantiles se amplió en el curso de los últimos años en Europa. Su estudio revela las lógicas sociales y políticas transnacionales que las implementan. En otras palabras, las cualidades individuales que se le asignan a los estudiantes migrantes están fuertemente vinculadas con sus características escolares y sociales, que se traducen en una diversificación creciente de los itinerarios estudiantiles. Este artículo tiene como objeto de estudio el dispositivo Erasmus, programa de intercambios entre estudiantes dentro de la comunidad europea. Se basa en un análisis comparativo entre tres países : Francia, Gran Bretaña e Italia. Busca destacar que, a pesar de un principio de reciprocidad de los intercambios, las relaciones concretas entre instituciones universitarias se basan en lógicas de « afinidades selectivas » que a la vez revelan el carácter relativamente elitista del dispositivo y refuerzan los desequilibrios migratorios ya existentes entre los países involucrados

L’autre réalité du programme Erasmus : affinité sélective entre établissements et reproduction sociale des étudiants

Le spectre des migrations étudiantes s’est élargi au cours de ces dernières années en Europe. Son étude révèle les logiques sociales et politiques transnationales qui les mettent en œuvre. Autrement dit, les qualités individuelles que l’on prête aux étudiants migrants sont fortement liées à leurs caractéristiques scolaires et sociales, lesquelles se traduisent par une diversification croissante des parcours étudiants. Cet article a pour objet d’étude le dispositif Erasmus, programme d’échanges entre étudiants au sein de la Communauté européenne. Il s’appuie sur une analyse comparative entre trois pays : la France, la Grande-Bretagne et l’Italie. Il entend souligner qu’en dépit d’un principe de réciprocité des échanges, les relations concrètes entre institutions universitaires se fondent sur des logiques d’« affinités sélectives » qui à la fois révèlent le caractère relativement élitiste du dispositif et renforcent les déséquilibres migratoires déjà existants entre les pays concernés.The spectrum of student migrations has broadened in Europe in recent years. A study of it reveals the transnational social and political logics which implement them. In other words, the individual capacities attributed to migrant students are closely linked to their educational and social characteristics, which are reflected in a growing diversification of student careers. This article considers the Erasmus system, an exchange programme between students within the European community. It is based on a comparative analysis between three countries: France, Great Britain and Italy. It aims to stress that despite a principle of reciprocal exchanges, the concrete relations between universities are based on logics of "selective affinities" which reveal the relatively elitist character of the programme and also reinforce the migratory imbalances already existing between the countries concerned.Das Spektrum studentischer Migration in Europa hat sich innerhalb der letzten Jahre immens erweitert. Eine Untersuchung dieser Mobilität macht deutlich, welche sozialen Logiken und transnationalen Politiken hier zum Zuge kommen. D.h., individuelle Qualitäten mobiler Studenten hängen von sozialen und schulischen Eigenschaften ab, die sich in einer zunehmenden Vielfalt studentischer Bildungswege niederschlagen. In diesem Beitrag wird das ERASMUS-Programm, das Aktionsprogramm der Europäischen Gemeinschaft zur Förderung der Mobilität von Hochschulstudenten, anhand einer vergleichenden Länderstudie zwischen Frankreich, Großbritannien und Italien untersucht. Obwohl der Austausch zwischen den Hochschuleinrichtungen auf Reziprozität beruhen soll, gestalten sich derartige Kontakte und Netzwerke eher je nach Affinität. Dadurch wird einerseits der elitäre Charakter dieses Instruments deutlich und andererseits der unausgewogene Studierendenaustausch zwischen diesen drei Ländern noch verstärkt.El espectro de las migraciones estudiantiles se amplió en el curso de los últimos años en Europa. Su estudio revela las lógicas sociales y políticas transnacionales que las implementan. En otras palabras, las cualidades individuales que se le asignan a los estudiantes migrantes están fuertemente vinculadas con sus características escolares y sociales, que se traducen en una diversificación creciente de los itinerarios estudiantiles. Este artículo tiene como objeto de estudio el dispositivo Erasmus, programa de intercambios entre estudiantes dentro de la comunidad europea. Se basa en un análisis comparativo entre tres países : Francia, Gran Bretaña e Italia. Busca destacar que, a pesar de un principio de reciprocidad de los intercambios, las relaciones concretas entre instituciones universitarias se basan en lógicas de « afinidades selectivas » que a la vez revelan el carácter relativamente elitista del dispositivo y refuerzan los desequilibrios migratorios ya existentes entre los países involucrados

Numerical and experimental study of Favre Waves with TELEMAC-3D and MASCARET

Water Qualit

Mechanical alterations of the bone-cartilage unit in a rabbit model of early osteoarthrosis

International audienc

Self-organized populations interacting under pursuit-evasion dynamics

International audienceWe discuss the modelling of interacting populations through pursuit-evasion ---- or attraction-repulsion ---- principles~: preys try to escape chasers, chasers are attracted by the presence of preys. We construct a hierarchy of models, ranging from ODEs systems with finite numbers of individuals of each population, to hydrodynamic systems. First order macroscopic models look like generalized ''two-species Keller-Segel equations''. But, due to cross--interactions, we can show that the system does not exhibit any blow up phenomena in finite time. We also obtain second order models, that have the form of systems of balance laws, derived from kinetic models. We bring out a few remarkable features of the models based either on mathematical analysis or numerical simulations

Asymptotic problems and numerical schemes for traffic flows with unilateral constraints describing the formation of jams

International audienceWe discuss numerical strategies to deal with PDE systems describing traffic flows, taking into account a density threshold, which restricts the vehicles density in the situation of congestion. These models are obtained through asymptotic arguments. Hence, we are interested in the simulation of approached models that contain stiff terms and large speeds of propagation. We design schemes intended to apply with relaxed stability conditions

Ultrastructure and distribution of kleptoplasts in benthic foraminifera from shallow-water (photic) habitats

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Marine Micropaleontology 138 (2018): 46-62, doi:10.1016/j.marmicro.2017.10.003.Assimilation, sequestration and maintenance of foreign chloroplasts inside an organism is termed “chloroplast sequestration” or “kleptoplasty”. This phenomenon is known in certain benthic foraminifera, in which such kleptoplasts can be found both intact and functional, but with different retention times depending on foraminiferal species. In the present study, seven species of benthic foraminifera (Haynesina germanica, Elphidium williamsoni, E. selseyense, E. oceanense, E. aff. E. crispum, Planoglabratella opercularis and Ammonia sp.) were collected from shallow-water benthic habitats and examined with transmission electron microscope (TEM) for cellular ultrastructure to ascertain attributes of kleptoplasts. Results indicate that all these foraminiferal taxa actively obtain kleptoplasts but organized them differently within their endoplasm. In some species, the kleptoplasts were evenly distributed throughout the endoplasm (e.g., H. germanica, E. oceanense, Ammonia sp.), whereas other species consistently had plastids distributed close to the external cell membrane (e.g., Elphidium williamsoni, E. selseyense, P. opercularis). Chloroplast degradation also seemed to differ between species, as many degraded plastids were found in Ammonia sp. and E. oceanense compared to other investigated species. Digestion ability, along with different feeding and sequestration strategies may explain the differences in retention time between taxa. Additionally, the organization of the sequestered plastids within the endoplasm may also suggest behavioral strategies to expose and/or protect the sequestered plastids to/from light and/or to favor gas and/or nutrient exchange with their surrounding habitats.TJ was funded by the “FRESCO” project, a project supported by the Region Pays de Loire and the University of Angers. This work was also supported by a grant no. 200021_149333 from the Swiss National Science Foundation and the French national program EC2CO-LEFE (project ForChlo).JMB acknowledges the Robert W. Morse Chair for Excellence in Oceanography and the Investment in Science Fund at WHOI. Also, KK acknowledges the Academy of Finland (Project numbers: 278827, 283453)