La conservation d'une espèce patrimoniale en déclin au sein d'un agrosystème. Le cas de la Guifette noire Chlidonias niger (Linnaeus, 1758) dans le Marais poitevin

National audienceThe Marais poitevin, the second largest wetland in France, has been progressively cultivated, and can be considered as an agrosystem. Humid grasslands (essentially submitted to cattle grazing), are considered as the last remaining wetlands of the area, and biodiversity conservation measures are now focusing on them. Among the patrimonial grassland species, we interested in the Black tern Chlidonias niger (Linnaeus, 1758). Several conservation measures (protected areas, environmental management) have been deployed in the area to conserve this threatened species. However, despite some positive effects of these measures, the species is still signifi cantly declining and is now concentrating in areas benefi ting from an environmental management. The example of such a wetland species living in an agrosystem raises the question of the conservation policies to adopt in the current context of large-scale land-use changes. Should we develop interventionist management measures or preferring the restoration of habitat functionalities to conserve threatened species?Le Marais poitevin, deuxième zone humide de France, a été progressivement mis en culture au point de devenir un agrosystème. Les prairies humides (pour l'essentiel pâturées), considérées comme des vestiges de l'ancienne zone humide, sont les espaces sur lesquels se concentrent les mesures de conservation de la biodiversité du marais. Parmi les espèces patrimoniales associées à ces milieux, nous présentons l'exemple de la Guifette noire Chlidonias niger (Linnaeus, 1758). Cette espèce menacée a été à l'origine de multiples mesures de conservation (aires protégées et aménagements lui étant spécialement consacrés) dans le marais. Cette étude révèle que de telles mesures, bien qu'ayant des effets positifs, ne parviennent toutefois pas à enrayer le déclin signifi catif de la population qui se concentre de plus en plus sur les espaces bénéfi ciant d'une gestion environnementale. L'exemple de cette espèce de zone humide, aujourd'hui présente au sein de milieux de substitution qu'offre un agrosystème, pose la question des choix de politiques conservatoires qui doivent être opérés dans un contexte de changement d'occupation du sol à large échelle. Doit-on encore développer des mesures de gestion interventionniste ou privilégier la restauration de la fonctionnalité de milieux pour conserver des espèces menacées

La conservation d’une espèce patrimoniale en déclin au sein d’un agrosystème. Le cas de la Guifette noire Chlidonias niger (Linnaeus, 1758) dans le Marais poitevin

Le Marais poitevin, deuxième zone humide de France, a été progressivement mis en culture au point de devenir un agrosystème. Les prairies humides (pour l’essentiel pâturées), considérées comme des vestiges de l’ancienne zone humide, sont les espaces sur lesquels se concentrent les mesures de conservation de la biodiversité du marais. Parmi les espèces patrimoniales associées à ces milieux, nous présentons l’exemple de la Guifette noire Chlidonias niger (Linnaeus, 1758). Cette espèce menacée a été à l’origine de multiples mesures de conservation (aires protégées et aménagements lui étant spécialement consacrés) dans le marais. Cette étude révèle que de telles mesures, bien qu’ayant des effets positifs, ne parviennent toutefois pas à enrayer le déclin significatif de la population qui se concentre de plus en plus sur les espaces bénéficiant d’une gestion environnementale. L’exemple de cette espèce de zone humide, aujourd’hui présente au sein de milieux de substitution qu’offre un agrosystème, pose la question des choix de politiques conservatoires qui doivent être opérés dans un contexte de changement d’occupation du sol à large échelle. Doit-on encore développer des mesures de gestion interventionniste ou privilégier la restauration de la fonctionnalité de milieux pour conserver des espèces menacées ?The Marais poitevin, the second largest wetland in France, has been progressively cultivated, and can be considered as an agrosystem. Humid grasslands (essentially submitted to cattle grazing), are considered as the last remaining wetlands of the area, and biodiversity conservation measures are now focusing on them. Among the patrimonial grassland species, we interested in the Black tern Chlidonias niger (Linnaeus, 1758). Several conservation measures (protected areas, environmental management) have been deployed in the area to conserve this threatened species. However, despite some positive effects of these measures, the species is still significantly declining and is now concentrating in areas benefiting from an environmental management. The example of such a wetland species living in an agrosystem raises the question of the conservation policies to adopt in the current context of large-scale land-use changes. Should we develop interventionist management measures or preferring the restoration of habitat functionalities to conserve threatened species

A Power Consumption Estimation Approach for Embedded Software Design using Trace Analysis

International audienceWith the explosion of advanced power control knobs such as dynamic voltage frequency scaling, mastering energy constraints in embedded systems is becoming challenging for software developers. Several power estimation techniques have been proposed over the past years, from electrical level to more abstract models such as SystemC/TLM. They offer various trade-offs between performance and accuracy, but suffer from a number of shortcomings. They are expensive and time-consuming, requiring intricate models of the architecture and finally, fail to be applied from the software developer perspective. In this paper, we propose a lightweight and cost-effective approach suitable for software developers. It relies on trace analysis and high-level modeling of architectures to perform quick and efficient power consumption estimations without loosing accuracy. This approach is fully supported by a tool and is validated using a simple thermal mitigation case study and checked against physical measurements. We show that, for our case study, the relative error between our tool and real values is 8% in average

Toward the understanding of the brittle to ductile transition at low size in silicon: Experiments and simulations

While bulk silicon is brittle at temperatures below 600-700K, the compression of nanopillars has shown that a decrease of the diameter below few hundreds of nanometers could change the silicon behavior from brittle to ductile [1,2]. This size effect cannot be explained by the initial defect density like in metals, because pristine silicon nano-objects do not contain residual defects. In these conditions the cracks and/or the dislocations nucleation should take origin at the surface. The identification of the parameters governing the brittle to ductile transition in size and the understanding of the mechanisms are the key points to further develop the MEMS and NEMS technology or to prevent the failure of microelectronic components based on the silicon strained technology. Nowadays the respective improvements in simulations and experiments allow to investigate the mechanical properties of objects of similar sizes, close to hundreds of nanometers. We have then used both approaches - experiments and simulations – to understand the mechanisms at the origin of cracks and dislocations nucleation in such nanopillars. Experimentally,nanopillars with diameters of 100 nm and heights of 300 nm are obtained by lithography. They are deformed in compression by a flat punch nano-indentor under controlled-displacement mode at room temperature, and analyzed by scanning electron microscopy and high resolution transmission electron microscopy. In simulation, nanopillars up to 44 nm in diameter and height are investigated under compression and tension in controlled-displacement too, with a temperature ranging from 1 to 600K. The atomic interactions in silicon are modeled by two different semi-empirical potentials, Stillinger Weber and a Modified Embedded-Atom-Method (MEAM), both fitted to better reproduce the ductile and brittle properties of bulk silicon. Under compressive load (Fig. 1), both approaches reveal a ductile behavior with similar stress-strain curves, and large shear bands of amorphous silicon along the slip plane. In addition the simulations enlighten the formation of stacking fault plane in the anti-twining shear stress direction at the onset of plasticity, not yet confirmed by experiments (work in progress). The simulations under tensile load (Fig. 2) show the nucleation of perfect dislocations from the surface that can lead to cavity opening when they interact [3]. We observe first that the height of the nanopillars must be higher than 20 nm to allow the cavity opening, and second that the brittle to ductile transition is controlled by the diameter of the nanopillars, as observed experimentally in compression. The deformation of pillars with large diameters operates by cavity expansion leading to the brittle fracture, while pillars with smaller diameters are deformed by dislocations gliding leading to ductile fracture. Finally, the simulations in temperature seem to corroborate the fact that the size of the brittle to ductile transition could increase with temperature, as presumed experimentally [2]

A new globular cluster black hole in NGC 4472

We discuss CXOU~1229410+075744, a new black hole candidate in a globular cluster in the elliptical galaxy NGC~4472. By comparing two Chandra observations of the galaxy, we find a source that varies by at least a factor of 4, and has a peak luminosity of at least $2\times10^{39}$ ergs/sec. As such, the source varies by significantly more than the Eddington luminosity for a single neutron star, and is a strong candidate for being a globular cluster black hole. The source's X-ray spectrum also evolves in a manner consistent with what would be expected from a single accreting stellar mass black hole. We consider the properties of the host cluster of this source and the six other strong black hole X-ray binary candidates, and find that there is suggestive evidence that black hole X-ray binary formation is favored in bright and metal rich clusters, just as is the case for bright X-ray sources in general.Comment: 6 pages, one 2-panel figure, 2 tables; accepted to MNRA

Usages des modèles spatiaux pour la prospective

International audienceCet article théorique a pour objectif de faire un état de l'art sur l'usage des modèles spatiaux pour la prospective. Dans un premier temps, il présente un bref historique de la convergence implicite entre prospective et géographie. Dans un second temps, il aborde la question du choix du modèle en présentant les critères à prendre en compte. Dans un troisième temps, il présente la validation des modèles comme un moyen d'améliorer la plausibilité des scénarios à travers la combinaison de méthodes d'évaluation. Enfin, si on constate un usage de plus en plus important de modèles spatiaux en prospective, les méthodes évoquées sont loin d'être exhaustives et replacent la géoprospective comme une simple communauté de pratiques et de méthodes ayant un objectif commun : mieux explorer les futurs pour éclairer l'action présente. Au final, il apporte un éclairage sur l'apport des modèles aux démarches prospectives et vise à aider les géographes, les modélisateurs et/ou les prospectivistes à choisir un modèle approprié à leur problématique et à leurs objectifs afin de tirer parti de tous les avantages qu'ils offrent. Il tente également de clarifier certaines confusions sémantiques qui existent autour de l'usage des modèles couplés à des scénarios

Exploring subtle land use and land cover changes: a framework for future landscape studies

UMR AMAP, équipe 3International audienceLand cover and land use changes can have a wide variety of ecological effects, including significant impacts on soils and water quality. In rural areas, even subtle changes in farming practices can affect landscape features and functions, and consequently the environment. Fine-scale analyses have to be performed to better understand the land cover change processes. At the same time, models of land cover change have to be developed in order to anticipate where changes are more likely to occur next. Such predictive information is essential to propose and implement sustainable and efficient environmental policies. Future landscape studies can provide a framework to forecast how land use and land cover changes is likely to react differently to subtle changes. This paper proposes a four step framework to forecast landscape futures at fine scales by coupling scenarios and landscape modelling approaches. This methodology has been tested on two contrasting agricultural landscapes located in the United States and France, to identify possible landscape changes based on forecasting and backcasting agriculture intensification scenarios. Both examples demonstrate that relatively subtle land cover and land use changes can have a large impact on future landscapes. Results highlight how such subtle changes have to be considered in term of quantity, location, and frequency of land use and land cover to appropriately assess environmental impacts on water pollution (France) and soil erosion (US). The results highlight opportunities for improvements in landscape modelling

Structural determinants of TAR RNA-DNA annealing in the absence and presence of HIV-1 nucleocapsid protein

Annealing of the TAR RNA hairpin to the cTAR DNA hairpin is required for the minus-strand transfer step of HIV-1 reverse transcription. HIV-1 nucleocapsid protein (NC) plays a crucial role by facilitating annealing of the complementary hairpins. To gain insight into the mechanism of NC-mediated TAR RNA–DNA annealing, we used structural probes (nucleases and potassium permanganate), gel retardation assays, fluorescence anisotropy and cTAR mutants under conditions allowing strand transfer. In the absence of NC, cTAR DNA-TAR RNA annealing depends on nucleation through the apical loops. We show that the annealing intermediate of the kissing pathway is a loop–loop kissing complex involving six base-pairs and that the apical stems are not destabilized by this loop–loop interaction. Our data support a dynamic structure of the cTAR hairpin in the absence of NC, involving equilibrium between both the closed conformation and the partially open ‘Y’ conformation. This study is the first to show that the apical and internal loops of cTAR are weak and strong binding sites for NC, respectively. NC slightly destabilizes the lower stem that is adjacent to the internal loop and shifts the equilibrium toward the ‘Y’ conformation exhibiting at least 12 unpaired nucleotides in its lower part