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Investigation of drift velocity effects on the EDGE and SOL transport
No full textInternational audienceTo understand the mechanisms behind poloidal asymmetries of the transport in the edge and SOL plasma, it is important to take into account drift velocity in the transport model. We investigate the effects of an imposed radial electric field on the plasma equilibrium in the transport code SOLEDGE2D. In the edge, we show an important modification of the flow pattern due to poloidal E × B drift velocity. The drift velocity generates asymmetry of the density through the Pfirsch–Schluter flows which creates an important parallel rotation through the viscous balance. In comparison to heat load imbalance studies in the SOL of divertor tokamak, a strong link between the amplitude of the radial electric field and the heat load imbalance in the SOL of limiter tokamak has been highlighted using different amplitude of the imposed radial electric field
La gestion paradoxale des compétences de service
No full textThis paper focuses on service skills which are mobilized by front office agents when they are involved with customers. These skills are most of the time tacit. We consider that the way in which firms recognize these skills and contribute to their development is an important management issue. It is all the more important that a lot of jobs combine poor levels of qualification and highly situated skills.Cet article s’intéresse aux compétences de service mobilisées par les agents au contact de la clientèle et qui sont la plupart du temps tacites. À ce titre, s’interroger sur la reconnaissance de ces compétences et sur leur développement constitue un enjeu de gestion pour les organisations. C’est d’autant plus important que de nombreux métiers de service allient faible qualification et fortes compétences situées
Electron Rephasing in a Laser-Wakefield Accelerator
No full textInternational audienceAn important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%
Highly reproducible, hysteresis-free, flexible strain sensors by inkjet printing of carbon nanotubes
No full textIn order to build upon the exceptional interest for flexible sensors based on carbon nanotube networks (CNNs), the field requires high device-to-device reproducibility. Inkjet printing has provided outstanding results for flexible ohmic sensors in terms of reproducibility of their resistance. However, the reproducibility of the sensitivity, the most critical parameter for sensing application, has been only marginally assessed. In the present paper, CNN based resistive strain sensors fabricated by inkjet-printing on flexible Ethylene Tetrafluoroethylene (EFTE) sheets are presented. The variability on the device initial resistance is studied for 5 different batches of sensors from 3 to 72 devices each. The variability ranges between 8.4% and 43% depending on the size of the batches, with a 20% average. An 8-device batch with 15% variability on initial resistance is further studied for variability on the strain and thermal sensitivity. Standard deviation values are found to be as low as 16% on the strain sensitivity and 8% on the temperature sensitivity. Moreover, the devices are hysteresis free, a rare achievement for CNT strain sensors on plastics
Analysis of Some Qualitative Methods for Inverse Electromagnetic Scattering Problems
No full textInternational audienceThis chapter provides a comprehensive presentation of some qualitative methods associated with inverse 3D electromagnetic scattering problem from inhomogeneous and anisotropic media. We first discuss the problem in the framework of so-called Born approximation, that leads to a linearisation of the inverse problem. We second present and analyze the application of the Linear Sampling Method to the full non linear problem using multistatic data at a given frequency. We especially focus on a generalization of this method based on an exact characterization of the inclusion shape in terms of the available data. We then discuss the closely related interior transmission problem and associated transmission eigenvalues. We complement each chapter with some open challenging questions as well as references for further readings
Processus de formation et d'étalement des nuages sur l'île de la Réunion : caractérisation à partir de données issues d'observations satellite, sol et du modèle numérique de prévision AROME ; application à la prévision des énergies solaires.
No full textThe last decade has seen new methods to produce energy such as solar or wind power. They are more and more used in power production especially on Reunion island. In order to better take into account the solar power production, it is important to improve the storage capabilities as well as the integration of this intermittent energy. Furthermore, the solar forecasting must be improved to optimised cells uses. Different tools can be used: weather forecasting models, satellites imageries, meteorological ground stations. This thesis aims to study the spatial and temporal cloudiness over Reunion island as well as solar ressource. In the first part, we identified the physical processes and parameters which play key roles in cloud life cycle. To do so, we describe the global and local atmospheric physics especially in the tropic. In the second part, we discussed the evaluation of tool. The main tool correspond to the meso-scale numerical weather forecast model, AROME (Application de la recherche à l'opérationnelle à méso-échelle), developped by Météo-France. We validated it using meteorological ground stations and ERA-Interim reanalyses from ECMWF (European Centre for Medium-Range Weather Forecasts) in order to validate wind and temperature at different scales. Meteosat7 satellite data are used to estimate the solar forcasting and the shape and localisation of clouds. This study gave information of spatial and temporal variability of cloud to produce cloudy patterns.The last part is dedicated to the study of clouds life cycle divided into three parts: (1) the study of cloud formation during the night; (2) the study of cloud formation and evolution during the day in relation with the night clouds patterns; (3) the study of clouds spreading on two parts of the island, in the West and the North. To conclude, we discussed the uncertainties of solar forecast based on previous studies.La dernière décennie a vu un développement important de nouvelles méthodes de production d'énergie telles que l'énergie solaire ou éolienne. Elles occupent une part croissante dans la production d'électricité sur l'île de la Réunion. Afin d'améliorer l'intégration de l'énergie photovoltaïque (PV), il est important de coupler la production à des moyens de stockage pour limiter le caractère intermittent de cette source d'énergie. Pour optimiser l'utilisation de différentes sources d'énergie couplées à la gestion d'une batterie, il est nécessaire d'améliorer la prévision de production PV. Pour obtenir une prévision, il existe plusieurs outils: la prévision déterministe par un modèle numérique de prévision météorologique à méso-échelle, les images satellites, les données météorologiques sol. Les travaux de cette thèse se place dans ce contexte de prévision de l'énergie solaire face à la forte variabilité de l'ennuagement et donc de la ressource solaire sur l'île de la Réunion.Le début de la thèse est focalisé sur l'identification des processus et paramètres physiques à prendre en compte afin d'identifier le meilleur moyen d'expliquer et de prévoir le cycle de vie des nuages sur l'île de la Réunion. Pour cela, la première partie de la thèse présente les processus physiques aux échelles globales et locales régissant les mouvements de l'atmosphère autour et sur l'île de la Réunion. La deuxième partie de la thèse présente les outils utilisés et leur évaluation. L'outil principal est le modèle de prévision du temps opérationnel, AROME (Application de la recherche à l'opérationnelle à méso-échelle), développé par Météo-France. Une étude de validation du modèle AROME est présentée. Elle s'appuie sur des données des stations météorologiques sol et des réanalyses ERA-Interim d'ECMWF (European Centre for Medium-Range Weather Forecasts) permettant de valider les variables de vent et température aux échelles locale et synoptique. Afin de pouvoir valider et comparer l'ennuagement, les images satellites de Météosat7 seront utilisées pour évaluer le rayonnement solaire incident au sol mais également la localisation et la forme des nuages. Cette étude nous permettra d'étudier la variabilité spatiale et temporelle de l'ennuagement sur l'île de la Région et de déterminer des régimes d'ennuagement.La troisième partie de la thèse est dédiée à l'étude du cycle de vie des nuages sur l'île de la Réunion. Elle est organisée en trois études : (1) la première étude explore les processus synoptiques et locaux ayant un impact sur la formation de nuages durant la nuit; (2) la seconde étude présente les liens établis entre les scénarios d'ennuagement obtenus durant la nuit et la formation de nuages en journée et la variabilité observée; (3) la troisième étude se focalise sur les mécanismes d'étalement des nuages. Des étalements sont observés notamment sur deux côtés de l'île, à l'Ouest et au Nord. Ces deux étalements sont étudiés. La conclusion de la thèse présente une analyse des facteurs influençant les incertitudes de prévision du rayonnement solaire, s'appuyant sur les conclusions des trois parties précédentes
A conformal mapping algorithm for the Bernoulli free boundary value problem
No full textInternational audienceWe propose a new numerical method for the solution of Bernoulli's free boundary valueproblem for harmonic functions in a doubly connected domain in where an unknown free boundary is determined by prescribed Cauchy data on in addition to a Dirichlet condition on the known boundary .Our main idea is to involve the conformal mapping methodas proposed and analyzed by Akduman, Haddar and Kress~\cite{AkKr,HaKr05}for the solution of a related inverse boundary value problem. For this we interpret the free boundary as the unknown boundary in the inverse problem to construct from the Dirichlet condition on and Cauchy data on the known boundary . Our method for the Bernoulli problem iterates on the missing normal derivative on by alternating between the application of the conformal mapping method for the inverse problemand solving a mixed Dirichlet--Neumann boundary value problem in . We present the mathematicalfoundations of our algorithm and prove a convergence result. Some numerical examples will serve as proof of concept of our approach
Topic Detection and Compressed Classification in Twitter
No full textInternational audienceIn this paper we introduce a novel information propagation method in Twitter, while maintaining a low computational complexity. It exploits the power of Compressive Sensing in conjunction with a Kalman filter to update the states of a dynamical system. The proposed method first employs Joint Complexity, which is defined as the cardinality of a set of all distinct factors of a given string represented by suffix trees, to perform topic detection. Then based on the nature of the data, we apply the theory of Compressive Sensing to perform topic classification by recovering an indicator vector, while reducing significantly the amount of information from the tweets. We exploit datasets in various languages collected by using the Twitter streaming API and achieve better classification accuracy when compared with state-of-the-art methods
Systematic modulation of heavy precipitation in the region of Valencia (Spain) by Mistral-induced sea-surface cooling in the previous days
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Sources, transport and deposition of iron in the global atmosphere
No full textInternational audienceAtmospheric deposition of iron (Fe) plays an important role in controlling oceanic primary productivity. However, the sources of Fe in the atmosphere are not well understood. In particular, the combustion sources of Fe and the subsequent deposition to the oceans have been accounted for in only few ocean biogeochemical models of the carbon cycle. Here we used a mass-balance method to estimate the emissions of Fe from the combustion of fossil fuels and biomass by accounting for the Fe contents in fuel and the partitioning of Fe during combustion. The emissions of Fe attached to aerosols from combustion sources were estimated by particle size, and their uncertainties were quantified by a Monte Carlo simulation. The emissions of Fe from mineral sources were estimated using the latest soil mineralogical database to date. As a result, the total Fe emissions from combustion averaged for 1960–2007 were estimated to be 5.3 Tg yr−1 (90% confidence of 2.3 to 12.1). Of these emissions, 1, 27 and 72% were emitted in particles 10 μm (PM> 10), respectively, compared to a total Fe emission from mineral dust of 41.0 Tg yr−1 in a log-normal distribution with a mass median diameter of 2.5 μm and a geometric standard deviation of 2. For combustion sources, different temporal trends were found in fine and medium-to-coarse particles, with a notable increase in Fe emissions in PM1 since 2000 due to an increase in Fe emission from motor vehicles (from 0.008 to 0.0103 Tg yr−1 in 2000 and 2007, respectively). These emissions have been introduced in a global 3-D transport model run at a spatial resolution of 0.94° latitude by 1.28° longitude to evaluate our estimation of Fe emissions. The modelled Fe concentrations as monthly means were compared with the monthly (57 sites) or daily (768 sites) measured concentrations at a total of 825 sampling stations. The deviation between modelled and observed Fe concentrations attached to aerosols at the surface was within a factor of 2 at most sampling stations, and the deviation was within a factor of 1.5 at sampling stations dominated by combustion sources. We analysed the relative contribution of combustion sources to total Fe concentrations over different regions of the world. The new mineralogical database led to a modest improvement in the simulation relative to station data even in dust-dominated regions, but could provide useful information on the chemical forms of Fe in dust for coupling with ocean biota models. We estimated a total Fe deposition sink of 8.4 Tg yr−1 over global oceans, 7% of which originated from the combustion sources. Our central estimates of Fe emissions from fossil fuel combustion (mainly from coal) are generally higher than those in previous studies, although they are within the uncertainty range of our estimates. In particular, the higher than previously estimated Fe emission from coal combustion implies a larger atmospheric anthropogenic input of soluble Fe to the northern Atlantic and northern Pacific Oceans, which is expected to enhance the biological carbon pump in those regions