Development of a radar simulator for monitoring wake vortices in rainy weather

A simulator for the evaluation of the radar signature of raindrops within wake vortices is presented. Simulated Doppler spectrum of raindrops within vortices let to think that it could be a potential criterion for identifying wake vortex hazard in rainy weather

Modeling the Radar Signature of Raindrops in Aircraft Wake Vortices

The present work is dedicated to the modeling and evaluation of the radar signature of raindrops within wake vortices. This is achieved through the computation of the motion equation of raindrops within the wake vortex flow. Based on the inhomogeneous distribution of raindrops within wake vortices, the radar echo model is computed for raindrops in a given pulse resolution volume. Simulated Radar Doppler signature of raindrops within wake vortices is illustrated to be a potential criterion for identifying wake vortex hazard in air traffic control. The dependence of the radar signature on various parameters, including the radial resolution, antenna elevation angle, is also analyzed

Smart gateways for terabit/s satellite

To reach the terabit per second of throughput, telecommunication satellites cannot make use of frequency below Ka band only. Therefore, the use of broad portion of the spectrum available at Q/V (40/50 GHz) band is foreseen for the feeder link. This study presents the evaluation of performances of different macro-diversity schemes that may allow mitigating the deep fades experienced at Q/V bands by introducing cooperation and a limited redundancy between the different gateways of the system. Two different solutions are firstly described. The performances resulting from the use of those assumptions are derived in a second stage

Wave-mixing origin and optimization in single and compact aluminum nanoantennas

The outstanding optical properties for plasmon resonances in noble metal nanoparticles enable the observation of non-linear optical processes such as second-harmonic generation (SHG) at the nanoscale. Here, we investigate the SHG process in single rectangular aluminum nanoantennas and demonstrate that i) a doubly resonant regime can be achieved in very compact nanostructures, yielding a 7.5 enhancement compared to singly resonant structures and ii) the $\chi_{\perp\perp\perp}$ local surface and $\gamma_{bulk}$ nonlocal bulk contributions can be separated while imaging resonant nanostructures excited by a tightly focused beam, provided the $\chi_{\perp\parallel\parallel}$ local surface is assumed to be zero, as it is the case in all existing models for metals. Thanks to the quantitative agreement between experimental and simulated far-field SHG maps, taking into account the real experimental configuration (focusing and substrate), we identify the physical origin of the SHG in aluminum nanoantennas as arising mainly from $\chi_{\perp\perp\perp}$ local surface sources

A radar simulator for monitoring wake turbulence in rainy weather

Wake vortices are associated to the generation of lift when an aircraft is flying. During the take-off and landing phases, wake vortices are hazardous if encountered by other flying aircrafts. In order to ensure flight safety and increase airports capacity as a constraining minimum distance between successive aircrafts has been defined to avoid them, wake vortex monitoring in real time has emerged as one of the key challenge in air traffic management. In this paper, the potential use of an X band Doppler radar for detecting and monitoring wake vortices in rainy weather is assessed by simulation. The Doppler signature measured by an X band radar in presence of a wake vortex in rainy weather is simulated accounting for the backscattering of each individual raindrop in the volume surrounding wake vortices. Starting from a given DSD and a homogeneous repartition of the raindrops in still air, their trajectory is computed assuming a generic air flow induced vortex and a simple model of drag. The descent velocity of the vortex due to the local reduction of buoyancy in the vortices is also taken into consideration in the computation of the trajectory. A scheme for computing the radar signals from the raindrops within wake vortices is described. The X band radar signatures in scanning mode are computed for raindrops in each concerned radar cell. According to the simulation results, the Doppler spectrum width of the raindrops disturbed by wake vortices is extended, thus providing a mean to identify the potential location of wake vortices in the scanned area and therefore to localize the hazards. The potentiality of this tool for the design of inversion algorithms from wake vortices signatures will also be addressed

Dole – Place Nationale Charles-de-Gaulle

Les travaux municipaux de réfection et de mise en valeur de la Place Nationale Charles-de-Gaulle ont affecté un lieu de sociabilité dans l’espace urbain attesté depuis le xiiie s. par les sources d’archives. Le potentiel archéologique, mis en évidence lors du diagnostic de décembre 1997, est à l’origine d’un accompagnement des travaux de réseaux et de terrassement de la place dès le début de février. La découverte de vestiges très érodés de l’ancienne église Notre-Dame à la fin de ce mois mot..

Application of ToF-SIMS for sulfur isotopic fractionation in sulfide phases of iron corrosion layers: determination of bacterial impact on the formation of these phases

International audienceTo a better understanding of the iron corrosion mechanisms, it is crucial to elucidate the role of bacteria. Thus, in order to have a diagnosis of the action of bacteria in the iron corrosion, the objective of this study is to determine by ToF-SIMS the isotopic sulfur fractionation δ 34 S in iron sulfides of (sub)micrometric size located in the corrosion product layers of the ferrous objects corroded in anoxic soils and marine environment. These iron sulfides may have two origins: an abiotic origin resulting in the dissolution/reprecipitation of sulfides from the surrounding medium (for example from pyrite in a soil) or a biotic origin by the action of the sulfate-reducing bacteria that reduce sulfate ions into sulfides leading to the formation of iron sulfides with ferrous ions issued from the aqueous dissolution of metal iron. A difference in the isotopic sulfur fractionation δ 34 S in the sulfur phases according to the abiotic or biotic origin of these phases is reported in the literature. Thus in this study, the isotopic sulfur fractionation δ 34 S in the iron sulfides formed in the corrosion product layers of iron was determined to identify the formation origin of these phases and the role of bacteria in the iron corrosion. After characterization of the distribution of the different iron sulfides within the layers (optical microscopy, SEM-EDS, μRaman spectroscopy), the local isotopic fractionation of sulfur is measured by the imaging and spectroscopy ToF-SIMS technique. Some important results have been obtained. First of all, the reproducibility and the accuracy of the method were established by the choice and the validation of a hydrothermal pyrite sample calibrated relatively to the international sulfur isotopic standard Canon Diablo Troilite. Secondly, it was observed that there was no or little variation in the isotopic sulfur fractionation δ 34 S with the degree of oxidation of sulfur. Finally, a noticeable difference in the isotopic sulfur fractionation δ 34 S between iron sulfides formed in laboratory under abiotic or biotic conditions was evidenced: δ 34 S is close to 0 in abiotic conditions whereas in biotic conditions it is shifted from 0 with values up to up to some tens per mil. These first results being promising, the study is actually in progress to determine the formation origin (abiotic/biotic) of the Fe-S present in the corrosion product layers of natural systems of iron corrosion, from soils, subaquatic and marine environments

Simulation numérique et caractérisation de composants de puissance en diamant

International audienceCet article présente les avancées sur la simulation analytique et numérique de composants de puissance en diamant, ainsi que les problématiques de caractérisation associées. Les modèles spécifiques au diamant ont été implémentés et ont été calibrés en confrontant les résultats de simulation aux dernières données expérimentales existantes. Enfin, un soin particulier a été apporté sur la maîtrise de l'auto-échauffement et de la calibration de la température du composant diamant sous test.  </p

Control Architecture Concepts and Properties of an Ontology Devoted to Exchanges in Mobile Robotics

National audienceA specific ontology is proposed in the scope of the development of a platform devoted to exchanges between academics and industrials of the robotic domain. This paper presents the tools used for knowledge elicitation, the concepts and properties linked with control architecture, the use of the resulting ontology for description of some scenarios and the tracks for the development of a domain specific language grounded on the ontology. Knowledge elicitation is performed in web ontology language thanks to Protégé ontology editor. The ontology is structured as a set of modules organized around a kernel. Modules addressing systems, information, robot and mission include concepts and properties for control architecture description. The expressivity of the ontology is demonstrated describing architectures for a set of scenarios; urban robotic scenario, air-ground scenario, landmark search scenario and military unmanned aerial vehicles scenario. Finally some tracks for the use of the ontology for developing a domain specific language are given