Some inverse problems around the tokamak Tore Supra

International audienceWe consider two inverse problems related to the tokamak \textsl{Tore Supra} through the study of the magnetostatic equation for the poloidal flux. The first one deals with the Cauchy issue of recovering in a two dimensional annular domain boundary magnetic values on the inner boundary, namely the limiter, from available overdetermined data on the outer boundary. Using tools from complex analysis and properties of genereralized Hardy spaces, we establish stability and existence properties. Secondly the inverse problem of recovering the shape of the plasma is addressed thank tools of shape optimization. Again results about existence and optimality are provided. They give rise to a fast algorithm of identification which is applied to several numerical simulations computing good results either for the classical harmonic case or for the data coming from \textsl{Tore Supra}

Evaluation of activated alginate-GO beads for removal of pharmaceuticals from water: bachelor's thesis : diploma 2016

The aim of this project was to produce calcium alginate beads with graphene oxide incorporated into the structure, in order to enhance the adsorption properties. The effects of initial concentration, adsorbent dose, pH, temperature, contact time were investigated. Adsorption kinetics and isotherms were evaluated with different models such as pseudo-first-order, pseudo-second-order, intraparticle diffusion, Langmuir and Freundlich models. In addition, thermodynamic and desorption studies were performed. Thus, CaOAlg2/GO beads were assessed as potential adsorbent for three micropollutants

Identification de paramètres magnétiques à l'intérieur d'un tokamak

We study the inverse Cauchy problem which consists in recovering magnetic data (the flux and its normal derivative) inside a tokamak, more precisely in the area located outside of the plasma, from their measurements on the outer boundary of the device. We propose an original approach which mostly relies on complex analysis tools so that the inverse problem is formulated as a best approximation one under constraint. A constructive resolution's method involving the use of toroidal harmonics basis is suggested.Nous étudions le problème inverse de Cauchy consistant à retrouver des données magnétiques (le flux ainsi que sa dérivée normale) à l'intérieur d'un tokamak, plus précisément dans la région située à l'extérieur du plasma, et ce uniquement à partir de quantités magnétiques mesurées sur la frontière extérieure de la machine. L'originalité de l'approche proposée réside dans l'utilisation d'outils d'analyse complexe permettant de voir le problème inverse comme un problème de meilleure approximation sous contrainte. Une méthode constructive de résolution s'appuyant sur l'utilisation de bases d'harmoniques toroïdales est présentée

On the assumption of mutual independence of jitter realizations in P-TRNG stochastic models

International audienceSecurity in true random number generation in cryptography is based on entropy per bit at the generator output. The entropy is evaluated using stochastic models. Several recent works propose stochastic models based on assumptions related to selected physical analog phenomena such as noise or jittery signal and on the knowledge of the principle of randomness extraction from the obtained analog signal. However, these assumptions simplify often considerably the underlying analog processes, which include several noise sources. In this paper, we present a new comprehensive multilevel approach, which enables to build the stochastic model based on detailed analysis of noise sources starting at transistor level and on conversion of the noise to the clock jitter exploited at the generator level. Using this approach, we can estimate proportion of the jitter coming only from the thermal noise, which is included in the total clock jitter

Micromechanisms of fracture propagation in glassy polymers

While most glassy polymers are nominally brittle at macroscopic scales, they are known to exhibit plastic deformation in indentation, scratching, and microcutting when the loaded region is sufficiently small. The same applies to the micrometer size process zone at the tip of a propagating crack. While the presence and approximate size of this microscale plastic zone is well described by the Dugdale model, the prediction of the toughness of these materials is not possible without accounting for the details of the local large strain field and the work hardening behaviour of these polymers, which can be inferred from their response to compressive tests. Strain localization mechanisms such as crazing or shear banding should also be taken into account to properly model toughness. Finally, viscoplastic creep plays a major role in determining the dependence of the toughness on crack propagation velocity, as well as the important difference between the initiation and propagation toughness, which is responsible for the occurrence of a characteristic stick-slip propagation under some loading conditions. Please click Additional Files below to see the full abstract

Fracture propagation in glassy polymers: From nanometer to centimeter

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Bounded extremal problems in Hardy spaces for the conjugate Beltrami equation in simply-connected domains

Techniques of constrained approximation are used to recover solutions to elliptic partial differential equations from incomplete and corrupted boundary data. The approach involves the use of generalized Hardy spaces of functions whose real and imaginary parts are related by formulae similar to the Cauchy--Riemann equations. A prime motivation for this is the modelling of plasma confinement in a tokamak reactor. Constructive and numerical aspects are also discussed

Antifragility in Climbing:Determining Optimal Stress Loads for Athletic Performance Training

In the past decades, much research has examined the negative effects of stressors on the performance of athletes. However, according to evolutionary biology, organisms may exhibit growth under stress, a phenomenon called antifragility. For both coaches and their athletes, a key question is how to design training conditions to help athletes develop the kinds of physical, physiological, and behavioral adaptations underlying antifragility. An answer to this important question requires a better understanding of how individual athletes respond to stress or loads in the context of relevant sports tasks. In order to contribute to such understanding, the present study leverages a theoretical and methodological approach to generate individualized load–response profiles in the context of a climbing task. Climbers (n = 37) were asked to complete different bouldering (climbing) routes with increasing loading (i.e. difficulty). We quantified the behavioral responses of each individual athlete by mathematically combining two measures obtained for each route: (a) maximal performance (i.e. the percentage of the route that was completed) and (b) number of attempts required to achieve maximal performance. We mapped this composite response variable as a function of route difficulty. This procedure resulted in load–response curves that captured each athlete’s adaptability to stress, termed phenotypic plasticity (PP), specifically operationalized as the area under the generated curves. The results indicate individual load–response profiles (and by extension PP) for athletes who perform at similar maximum levels. We discuss how these profiles might be used by coaches to systematically select stress loads that may be ideally featured in performance training