Étude et réalisation d'un générateur de chaos optoélectronique sur la phase optique pour les télécommunications cryptées haut-débit.

This work develops a theoretical and experimental demonstration for the generation of a wide spectrum chaotic signals. It consists of a new optoelectronics chaos generator, for which the dynamical variable is the optical phase. This chaotic modulation is produced using an electro-optic phase modulator combined to a fiber ring cavity, the latter performing at the same time a nonlinearity as well as a time delay. An optoelectronic feedback loop completes the system. Such a device can be modelled by a delay differential equation and can produce highly complex chaotic signals. The originality of the presented system lies in the fact that it can hide messages on a very large spectrum (several GHz). The manuscript consists of four parts. The first part introduces the theory of the Chaos and makes a state of the art in the field of delayed nonlinear dynamics. Then, we expose methods and tools helping to characterize the optical phase chaos generator. Finally, in the last two parts we give the theoretical modle, numerical and experimental results related to the system.Ce travail de thèse étudie la démonstration théorique et expérimentale de la génération de signaux chaotiques sur une très large bande de fréquences à partir d'un nouveau générateur de chaos opto-électronique dont la variable dynamique est la phase optique. Cette modulation chaotique est produite grâce à un modulateur de phase électro-optique qui, combiné à une cavité en anneau fibrée, réalise une fonction non-linéaire et un retard temporel. Une boucle de rétroaction opto-électronique complète le système. Un tel dispositif peut être modélisé par une équation différentielle à retard et est destiné à la génération de signaux chaotiques très complexes. La particularité du système présenté réside dans le fait qu'il est potentiellement capable de masquer des signaux sur un très large spectre (plusieurs GHz), dans un contexte de sécurisation des données à haut débit sur un canal optique. La première partie de ce manuscrit introduit la théorie du chaos et fait un état de l'art des dynamiques non-linéaires à retard. Ensuite, nous exposons les méthodes et les outils servant à la caractérisation du générateur de chaos en phase optique. Enfin, dans les deux dernières parties, nous donnons le modèle théorique ainsi que les résultats numériques et expérimentaux relatifs à ce système

Mapping hotspots of potential ecosystem fragility using commonly available spatial data

International audienc

Does epilepsy in multiplex autism pedigrees define a different subgroup in terms of clinical characteristics and genetic risk?

International audienceBACKGROUND: Autism spectrum disorders (ASD) and epilepsy frequently occur together. Prevalence rates are variable, and have been attributed to age, gender, comorbidity, subtype of pervasive developmental disorder (PDD) and risk factors. Recent studies have suggested disparate clinical and genetic settings depending on simplex or multiplex autism. The aim of this study was to assess: 1) the prevalence of epilepsy in multiplex autism and its association with genetic and non-genetic risk factors of major effect, intellectual disability and gender; and 2) whether autism and epilepsy cosegregate within multiplex autism families. METHODS: We extracted from the Autism Genetic Resource Exchange (AGRE) database (n = 3,818 children from 1,264 families) all families with relevant medical data (n = 664 children from 290 families). The sample included 478 children with ASD and 186 siblings without ASD. We analyzed the following variables: seizures, genetic and non-genetic risk factors, gender, and cognitive functioning as assessed by Raven's Colored Progressive Matrices (RCPM) and Vineland Adaptive Behavior Scales (VABS). RESULTS: The prevalence of epilepsy was 12.8% in cases with ASD and 2.2% in siblings without ASD (P <10-5). With each RCPM or VABS measure, the risk of epilepsy in multiplex autism was significantly associated with intellectual disability, but not with gender. Identified risk factors (genetic or non-genetic) of autism tended to be significantly associated with epilepsy (P = 0.052). When children with prematurity, pre- or perinatal insult, or cerebral palsy were excluded, a genetic risk factor was reported for 6/59 (10.2%) of children with epilepsy and 12/395 (3.0%) of children without epilepsy (P = 0.002). Finally, using a permutation test, there was significant evidence that the epilepsy phenotype co-segregated within families (P <10-4). CONCLUSIONS: Epilepsy in multiplex autism may define a different subgroup in terms of clinical characteristics and genetic risk

Identification and characterization of a novel antimicrobial peptide from the venom of the ant Tetramorium bicarinatum.

International audienceA novel antimicrobial peptide, named Bicarinalin, has been isolated from the venom of the ant Tetramorium bicarinatum. Its amino acid sequence has been determined by de novo sequencing using mass spectrometry and by Edman degradation. Bicarinalin contained 20 amino acid residues and was C-terminally amidated as the majority of antimicrobial peptides isolated to date from insect venoms. Interestingly, this peptide had a linear structure and exhibited no meaningful similarity with any known peptides. Antibacterial activities against Staphylococcus aureus and S. xylosus strains were evaluated using a synthetic replicate. Bicarinalin had a potent and broad antibacterial activity of the same magnitude as Melittin and other hymenopteran antimicrobial peptides such as Pilosulin or Defensin. Moreover, this antimicrobial peptide has a weak hemolytic activity compared to Melittin on erythrocytes, suggesting potential for development into an anti-infective agent for use against emerging antibiotic-resistant pathogens

A multi-scale evaluation of pack stock effects on subalpine meadow plant communities in the Sierra Nevada

We evaluated the influence of pack stock (i.e., horse and mule) use on meadow plant communities in Sequoia and Yosemite National Parks in the Sierra Nevada of California. Meadows were sampled to account for inherent variability across multiple scales by: 1) controlling for among-meadow variability by using remotely sensed hydro-climatic and geospatial data to pair stock use meadows with similar non-stock (reference) sites, 2) accounting for within-meadow variation in the local hydrology using in-situ soil moisture readings, and 3) incorporating variation in stock use intensity by sampling across the entire available gradient of pack stock use. Increased cover of bare ground was detected only within "dry" meadow areas at the two most heavily used pack stock meadows (maximum animals per night per hectare). There was no difference in plant community composition for any level of soil moisture or pack stock use. Increased local-scale spatial variability in plant community composition (species dispersion) was detected in "wet" meadow areas at the two most heavily used meadows. These results suggest that at the meadow scale, plant communities are generally resistant to the contemporary levels of recreational pack stock use. However, finer-scale within-meadow responses such as increased bare ground or spatial variability in the plant community can be a function of local-scale hydrological conditions. Wilderness managers can improve monitoring of disturbance in Sierra Nevada meadows by adopting multiple plant community indices while simultaneously considering local moisture regimes

A multi-scale evaluation of pack stock effects on subalpine meadow plant communities in the Sierra Nevada.

We evaluated the influence of pack stock (i.e., horse and mule) use on meadow plant communities in Sequoia and Yosemite National Parks in the Sierra Nevada of California. Meadows were sampled to account for inherent variability across multiple scales by: 1) controlling for among-meadow variability by using remotely sensed hydro-climatic and geospatial data to pair stock use meadows with similar non-stock (reference) sites, 2) accounting for within-meadow variation in the local hydrology using in-situ soil moisture readings, and 3) incorporating variation in stock use intensity by sampling across the entire available gradient of pack stock use. Increased cover of bare ground was detected only within "dry" meadow areas at the two most heavily used pack stock meadows (maximum animals per night per hectare). There was no difference in plant community composition for any level of soil moisture or pack stock use. Increased local-scale spatial variability in plant community composition (species dispersion) was detected in "wet" meadow areas at the two most heavily used meadows. These results suggest that at the meadow scale, plant communities are generally resistant to the contemporary levels of recreational pack stock use. However, finer-scale within-meadow responses such as increased bare ground or spatial variability in the plant community can be a function of local-scale hydrological conditions. Wilderness managers can improve monitoring of disturbance in Sierra Nevada meadows by adopting multiple plant community indices while simultaneously considering local moisture regimes

Environmental and biotic drivers of soil microbial β‐diversity across spatial and phylogenetic scales

International audienceSoil microbial communities play a key role in ecosystem functioning but still little is known about the processes that determine their turnover (β-diversity) along ecological gradients. Here, we characterize soil microbial β-diversity at two spatial scales and at multiple phylogenetic grains to ask how archaeal, bacterial and fungal communities are shaped by abiotic processes and biotic interactions with plants. We characterized microbial and plant communities using DNA metabarcoding of soil samples distributed across and within eighteen plots along an elevation gradient in the French Alps. The recovered taxa were placed onto phylogenies to estimate microbial and plant β-diversity at different phylogenetic grains (i.e. resolution). We then modeled microbial β-diversities with respect to plant β-diversities and environmental dissimilarities across plots (landscape scale) and with respect to plant β-diversities and spatial distances within plots (plot scale). At the landscape scale, fungal and archaeal β-diversities were mostly related to plant β-diversity, while bacterial β-diversities were mostly related to environmental dissimilarities. At the plot scale, we detected a modest covariation of bacterial and fungal β-diversities with plant β-diversity; as well as a distance-decay relationship that suggested the influence of ecological drift on microbial communities. In addition, the covariation between fungal and plant β-diversity at the plot scale was highest at fine or intermediate phylogenetic grains hinting that biotic interactions between those clades depends on early-evolved traits. Altogether, we show how multiple ecological processes determine soil microbial community assembly at different spatial scales and how the strength of these processes change among microbial clades. In addition, we emphasized the imprint of microbial and plant evolutionary history on today's microbial community structure

A multi-scale evaluation of pack stock effects on subalpine meadow plant communities in the Sierra Nevada

<div><p>We evaluated the influence of pack stock (i.e., horse and mule) use on meadow plant communities in Sequoia and Yosemite National Parks in the Sierra Nevada of California. Meadows were sampled to account for inherent variability across multiple scales by: 1) controlling for among-meadow variability by using remotely sensed hydro-climatic and geospatial data to pair stock use meadows with similar non-stock (reference) sites, 2) accounting for within-meadow variation in the local hydrology using in-situ soil moisture readings, and 3) incorporating variation in stock use intensity by sampling across the entire available gradient of pack stock use. Increased cover of bare ground was detected only within “dry” meadow areas at the two most heavily used pack stock meadows (maximum animals per night per hectare). There was no difference in plant community composition for any level of soil moisture or pack stock use. Increased local-scale spatial variability in plant community composition (species dispersion) was detected in “wet” meadow areas at the two most heavily used meadows. These results suggest that at the meadow scale, plant communities are generally resistant to the contemporary levels of recreational pack stock use. However, finer-scale within-meadow responses such as increased bare ground or spatial variability in the plant community can be a function of local-scale hydrological conditions. Wilderness managers can improve monitoring of disturbance in Sierra Nevada meadows by adopting multiple plant community indices while simultaneously considering local moisture regimes.</p></div

Twenty-seven geospatial, hydro-climatic, and vegetation variables derived from remote sensing used for multivariate matching of non-stock meadows to selected stock meadows in Yosemite (YOSE) and Sequoia (SEKI) National Parks.

<p>Twenty-seven geospatial, hydro-climatic, and vegetation variables derived from remote sensing used for multivariate matching of non-stock meadows to selected stock meadows in Yosemite (YOSE) and Sequoia (SEKI) National Parks.</p

Bootstrapped mean (with 95% confidence intervals) differences in percent bare ground cover for the Dry vegetation communities between matched meadows (N = 22) in Yosemite (YOSE) and Sequoia (SEKI) National Parks.

<p>The range of 1–5.7 (ln) maximum stock nights/ha corresponds to a range of 4–308 untransformed maximum stock nights/ha.</p