Étude des effets du mercaptoéthanol et du dithiodiglycol sur la division cellulaire chez les œfs d'Amphibiens

Les effets du β-mercaptoéthanol, substance contenant un groupe -SH et qui est très réductrice, ont été comparés à ceux de son produit d'oxydation, le dithiodiglycol. Ces deux substances inhibent la division cellulaire des œufs d'Amphibiens en voie de segmentation.Elles ont toutes deux une action défavorable sur l'appareil achromatique des œufs d'Amphibiens, mais elles agissent selon des modalités différentes: le mercaptoéthanol en accélérant la régression de l'appareil achromatique, le dithiodiglycol en s'y opposant.La signification de ces résultats est discutée.info:eu-repo/semantics/publishe

Dispersal and Metapopulation Viability in a Heterogeneous Landscape

International audienceConditions of persistence or extinction of a metapopulation of a colonizing annual species are studied in a heterogeneous landscape, a mixture of two elementary landscapes. An elementary landscape is a landscape whose age-structure is described by only one transition matrix, giving the probability for a site to be disturbed, or to follow the process of succession. We first provide an analytical study of the range of dispersal rates that allow metapopulation persistence in an elementary landscape. Second, conditions for metapopulation persistence in a heterogeneous landscape are derived from results obtained in each elementary landscape. Three cases are distinguished. If the two ranges of dispersal rates defined in each elementary landscape overlap, the metapopulation persists in any mixture of the elementary landscapes. If these two dispersal rates ranges are non-overlapping, either the metapopulation goes extinct for some values of the proportion of the elementary landscapes, or two discontinuous ranges of dispersal rates allow the metapopulation persistence. The consequences of these results are discussed in terms of landscape management. In particular, it is shown that under some conditions, a rapid change in environment (from one elementary landscape to another one) might less often lead to metapopulation extinction than a slower change

Hydromorpho : un modèle couplé pour les équations de Stokes/Exner et des résultats numériques avec Feel++

International audienceCEMRACS 2015 final presentation, Hydromorpho projectPrésentation finale du CEMRACS 2015, projet Hydromorph

High-temperature mechanical properties improvement on modified 9Cr–1Mo martensitic steel through thermomechanical treatments

International audienceIn the framework of the development of generation IV nuclear reactors and fusion nuclear reactors, materials with an improved high temperature (congruent with650 °C) mechanical strength are required for specific components. The 9–12%Cr martensitic steels are candidate for these applications. Thermomechanical treatments including normalisation at elevated temperature (1150 °C), followed by warm-rolling in metastable austenitic phase and tempering, have been applied on the commercial Grade 91 martensitic steel in order to refine its microstructure and to improve its precipitation state. The temperature of the warm-rolling was set at 600 °C, and those of the tempering heat-treatment at 650 °C and 700 °C thanks to MatCalc software calculations. Microstructural observations proved that the warm-rolling and the following tempering heat-treatment lead to a finer martensitic microstructure pinned with numerous small carbide and nitride particles. The hardness values of thermomechanically treated Grade 91 steel are higher than those of the as-received Grade 91. It is also shown that the yield stress and the ductility of the thermomechanically treated Grade 91 steel are significantly improved compared to the as-received material. Preliminary creep results showed that these thermomechanical treatments improve the creep lifetime by at least a factor 14

Les micropolluants sont-ils responsables des déformations observées chez les crevettes blanches de l'estuaire de la Gironde ? Description du phénomène et recherches en cours

National audiencePrésentation et analyse des déformations observées sur la crevette blanche dans l'estuaire de la Gironde

Système génétique, polymorphisme neutre et sélectionné: implications en biologie de la conservation

International audienceThe genetic system, selected genes and neutral polymorphism: implications for conservation biology. Neutral diversity is often viewed as a good indicator of the evolutionary potential of a population. This is to be attributed to the expected relationship between neutral and selected diversity, the latter being viewed as the major determinant of the evolutionary potential. However, recent publications using the coalescence theory show unambiguously that neutral diversity is only a record of the past demography of the population, including the demographic effects of background selection and balanced polymorphisms. Moreover, this demography is difficult to reconstruct. Other studies, especially the recent formalisation of the mutation-selection equilibrium by quantitative genetics, emphasise the role of slightly deleterious mutations, either polymorphic within a population or fixed. As a consequence, one needs to consider the genetic quality of a population as well as its polymorphism for selected genes in conservation biology programmes. Such a viewpoint illustrates the convergence implying population genetics and ecology that leads to a better understanding of the genetic bases of ecological interactions. This allows conservation biology to take into account basic mechanisms of evolution. A few possible applications are discussed