Translation on Graphs: An Isometric Shift Operator

International audienceIn this letter, we propose a new shift operator for graph signals, enforcing that our operator is isometric. Doing so, we ensure that as many properties of the time shift as possible get carried over. Finally, we show that our operator behaves reasonably for graph signals

Graphe de contacts et ondelettes

National audienceLes infections nosocomiales sont une source importante de mortalité lors d'un séjour hospitalier. En particulier, les bactéries multi-résistantes telles que les staphilocoques dorés présentent un problème sanitaire croissant puisque le nombre de traitements antibiotiques efficaces s'amenuise. Cette étude a pour but de comprendre le processus épidémique au sein d'un hôpital sur une durée de plusieurs mois. Pour cela, nous utilisons des outils inspirés du traitement du signal et appliqués aux graphes pour en déduire les différentes dimensions spatio-temporelles des données

Signaux stationnaires sur graphe : étude d'un cas réel

National audienceBased on a real geographical dataset, we apply the stationarity characterisation of a graph signal, through the analysis of its spectral decomposition. In the course, we identify possible sources of non-stationarity and we elaborate on the impact of the graph used to model the structural coherence of the data.Sur un jeu de données géographiques réelles, nous appliquons la caractérisation de la propriété de stationnarité d'un signal sur graphe via l'analyse de ses coefficients spectraux. Nous identifions différentes sources possibles de non-stationnarité et isolons l'influence qu'a le graphe sous-jacent sur la cohérence structurelle des données

Organic chemistry in the ionosphere of the early Earth

International audienceThe emergence of life on the Early Earth during the Archean has required a prior complex organic chemistry providing the prerequisite bricks of life. The origin of the organic matter and its evolution on the early Earth is far from being understood. Several hypotheses are investigated, possibly complementary, which can be divided in two main categories: the endogenous and the exogenous sources. In this work we have been interested in the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the early Earth. At these high altitudes, the VUV contribution of the young sun was important, involving an efficient production of reactive species. Here we address the issue whether this chemistry can lead to the production of larger molecules with a prebiotic interest in spite of the competitive lysing effect of the harsh irradiation at these altitudes

Traitement du Signal sur Graphe : Interprétation en termes de Filtre de l'Apprentissage Semi-Supervisé sur Graphe

National audienceNous montrons comment les outils de traitement du signal sur graphe peuvent dégager des notions de fréquences sur les graphes pour étudier des données portées par les nœud d'un graphe. Prenant l'exemple de l'apprentissage semi-supervisé, nous montrons alors qu'il peut s'interpréter comme le filtre d'un signal sur graphe

Extraction des paramètres électriques sur les transistors CMOS de technologies avancées

Session POSTER 3L'extraction des paramètres électriques est un point clef pour la compréhension des phénomènes physiques qui régissent le fonctionnement des transistors. La réduction des dimensions impose aujourd'hui d'adapter les méthodes d'extraction préexistantes aux nouvelles générations de dispositifs. Ainsi, nous montrons comment – à partir de courbe courant-tension ID(VG) et capacité-tension Cgc(VG) – il est possible d'extraire avec précision la mobilité à bas champ (μ0) et les résistances séries (RSD) sur des transistors ultra-courts

Nitrogen isotopic fractionation during abiotic synthesis of organic solid particles

The formation of organic compounds is generally assumed to result from abiotic processes in the Solar System, with the exception of biogenic organics on Earth. Nitrogen-bearing organics are of particular interest, notably for prebiotic perspectives but also for overall comprehension of organic formation in the young solar system and in planetary atmospheres. We have investigated abiotic synthesis of organics upon plasma discharge, with special attention to N isotope fractionation. Organic aerosols were synthesized from N2-CH4 and N2-CO gaseous mixtures using low-pressure plasma discharge experiments, aimed at simulating chemistry occurring in Titan s atmosphere and in the protosolar nebula, respectively. Nitrogen is efficiently incorporated into the synthesized solids, independently of the oxidation degree, of the N2 content of the starting gas mixture, and of the nitrogen speciation in the aerosols. The aerosols are depleted in 15N by 15-25 permil relative to the initial N2 gas, whatever the experimental setup is. Such an isotopic fractionation is attributed to mass-dependent kinetic effect(s). Nitrogen isotope fractionation upon electric discharge cannot account for the large N isotope variations observed among solar system objects and reservoirs. Extreme N isotope signatures in the solar system are more likely the result of self-shielding during N2 photodissociation, exotic effect during photodissociation of N2 and/or low temperature ion-molecule isotope exchange. Kinetic N isotope fractionation may play a significant role in the Titan s atmosphere. We also suggest that the low delta15N values of Archaean organic matter are partly the result of abiotic synthesis of organics that occurred at that time

Genetic association of stomatal traits and yield in wheat grown in low rainfall environments

Published: 4 July 2016Background: In wheat, grain filling is closely related to flag leaf characteristics and function. Stomata are specialized leaf epidermal cells which regulate photosynthetic CO2 uptake and water loss by transpiration. Understanding the mechanisms controlling stomatal size, and their opening under drought, is critical to reduce plant water loss and maintain a high photosynthetic rate which ultimately leads to elevated yield. We applied a leaf imprinting method for rapid and non-destructive phenotyping to explore genetic variation and identify quantitative traits loci (QTL) for stomatal traits in wheat grown under greenhouse and field conditions. Results: The genetics of stomatal traits on the adaxial surface of the flag leaf was investigated using 146 double haploid lines derived from a cross between two Australian lines of Triticum aestivum, RAC875 and Kukri. The drought tolerant line RAC875 showed numerous small stomata in contrast to Kukri. Significant differences between the lines were observed for stomatal densitity and size related traits. A negative correlation was found between stomatal size and density, reflecting a compensatory relationship between these traits to maintain total pore area per unit leaf surface area. QTL were identified for stomatal traits on chromosomes 1A, 1B, 2B, and 7A under field and controlled conditions. Most importantly some of these loci overlap with QTL on chromosome 7A that control kernel number per spike, normalized difference vegetation index, harvest index and yield in the same population. Conclusions: In this first study to decifer genetic relationships between wheat stomatal traits and yield in response to water deficit, no significant correlations were observed among yield and stomatal traits under field conditions. However we found some overlaps between QTL for stomatal traits and yield across environments. This suggested that stomatal traits could be an underlying mechanism increasing yield at specific loci and used as a proxy to track a target QTL in recombinant lines. This finding is a step-forward in understanding the function of these loci and identifying candidate genes to accelerate positional cloning of yield QTL in wheat under drought.Fahimeh Shahinnia, Julien Le Roy, Benjamin Laborde, Beata Sznajder, Priyanka Kalambettu, Saba Mahjourimajd, Joanne Tilbrook and Delphine Fleur

MOMAC: a SAXS/WAXS laboratory instrument dedicated to nanomaterials

International audienceThis article presents the technical characteristics of a newly built small-and wide-angle X-ray scattering (SAXS/WAXS) apparatus dedicated to structural characterization of a wide range of nanomaterials in the powder or dispersion form. The instrument is based on a high-flux rotating anode generator with a molybdenum target, enabling the assessment of highly absorbing samples containing heavy elements. The SAXS part is composed of a collimation system including a multilayer optic and scatterless slits, a motorized sample holder, a vacuum chamber, and a two-dimensional image-plate detector. All the control command is done through a TANGO interface. Normalization and data correction yield scattering patterns at the absolute scale automatically with a q range from 0.03 to 3.2 A ˚ À1. The WAXS part features a multilayer collimating optic and a two-dimensional image-plate detector with variable sample-to-detector distances. The accessible q range is 0.4–9 A ˚ À1 , ensuring a large overlap in q range between the two instruments. A few examples of applications are also presented, namely coupled SAXS/WAXS structure and symmetry determination of gold nanocrystals in solution and characterization of imogolite nanotubes and iron-filled carbon nanotube samples

Disrupted dispersal in logged tropical forest

Selective logging in tropical forests is restricted to a few species, the so-called commercial species. Among those commercial species, many produce fleshy fruits of large size. These tree species provide food to a large number of mammals and birds that often exclusively rely on these resources. These mammals and birds may also be vital for the demography of fleshy fruit trees because they act as dispersers towards more suitable place for seedling establishment (directed dispersal hypothesis or colonization hypothesis), or they increase seedling survival by avoiding conspecific high densities (escape hypothesis). Selective logging generally targets large trees, above the legal minimum cutting diameter, that also produce an important quantity of fruits to frugivores feeding in the canopy. Therefore, selective logging may impact frugivore populations in the long-term and in fine may disrupt the dispersal processes of logged species but not only. Indeed, selective logging of the largest - in terms of size and quantity -fleshy fruit producers may impact all fleshy fruit producers in decreasing the abundance of the resources hence creating local extinction of frugivores (the resource concentration hypothesis). Large frugivores feeding on the largest fruits may be more rapidly impacted. Until now studying the effect of logging is not an easy task because logging is generally correlated to hunting pressure. Based on a multispecies comparison using data from a replicated experimental logged forest with various intensities (and including control plots) at constant hunting pressure, we test the effect of selective logging on seed dispersal of tropical forest trees. Seed dispersal will be estimated as a cluster size using Ripley's K functions. In particular, we will test if dispersal distances of fleshy fruit species in logged plots decrease compared to control plots. We hypothesize that animal-dispersed species with larger seeds are dispersed less far away in treated vs control plots than smaller seeded and non animal-dispersed species. We propose to take into account tree species with different dispersal syndromes i.e. tree species with different seed size among animal-dispersed trees, and tree species with different dispersal mode such as wind-dispersed, mechanically dispersed trees or gravity dispersed trees. We also propose to link the difference in dispersal between disturbed and undisturbed forest with the structural properties of the interaction network. (Texte intégral