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Ingénierie d’interfaces électrode / électrolyte pour accroître les performances d’un électrolyseur à haute température
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Self-protective motion planning for mobile manipulators in a dynamic door-closing workspace
No full textInternational audiencePurpose Many work conditions require manipulators to open cabinet doors and then gain access to the desired workspace. However, after opening, the unlocked doors can easily close, interrupt a task and potentially break the operating end-effectors. This paper aims to address a manipulator's behavior planning problem for responding to a dynamic workspace released by door opening. Design/methodology/approach A dynamic model of the restricted workspace released by an unlocked door is established. As a whole system to treat, the interactions between the workspace and robot are analyzed by using a partially observable Markov decision process. A self-protective policy decision executed as a belief tree is proposed. To respond to the policy, this study has designed three types of actions: stay on guard in the workspace, using an elbow joint to defense the door and linear escape out of the workspace for self-protection by observing collision risk levels to trigger them. Finally, this study proposes self-protective motion controllers based on risk time optimization to act to the planned actions. Findings The elbow defense could balance robotic safety and work efficiency by interrupting the end-effector's work and using the elbow joint to prevent the door-closing in an active collision way. Compared with the stay and escape action, the advantage of the elbow defense is having a predictable performance to quick callback the interrupted work after the risk was relieved. Originality/value This work provides guidance for the safe operation of a class of robot operations and the upgrade of motion planning
Characterization and performance of the Apollon short-focal-area facility following its commissioning at 1 PW level
No full textInternational audienceWe present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility (located in Saclay, France), which was performed with the first available laser beam (F2), scaled to a nominal power of 1 PW. Under the conditions that were tested, this beam delivered on-target pulses of 10 J average energy and 24 fs duration. Several diagnostics were fielded to assess the performance of the facility. The on-target focal spot and its spatial stability, the temporal intensity profile prior to the main pulse, and the resulting density gradient formed at the irradiated side of solid targets have been thoroughly characterized, with the goal of helping users design future experiments. Emissions of energetic electrons, ions, and electromagnetic radiation were recorded, showing good laser-to-target coupling efficiency and an overall performance comparable to that of similar international facilities. This will be followed in 2022 by a further commissioning stage at the multi-petawatt level
Homogenization of Maxwell's equations and related scalar problems with sign-changing coefficients
No full textInternational audienceIn this work, we are interested in the homogenization of time-harmonic Maxwell's equations in a composite medium with periodically distributed small inclusions of a negative material. Here a negative material is a material modelled by negative permittivity and permeability. Due to the sign-changing coefficients in the equations, it is not straightforward to obtain uniform energy estimates to apply the usual homogenization techniques. The goal of this article is to explain how to proceed in this context. The analysis of Maxwell's equations is based on a precise study of two associated scalar problems: one involving the sign-changing permittivity with Dirichlet boundary conditions, another involving the sign-changing permeability with Neumann boundary conditions. For both problems, we obtain a criterion on the physical parameters ensuring uniform invertibility of the corresponding operators as the size of the inclusions tends to zero. In the process, we explain the link existing with the so-called Neumann-Poincaré operator, complementing the existing literature on this topic. Then we use the results obtained for the scalar problems to derive uniform energy estimates for Maxwell's system. At this stage, an additional difficulty comes from the fact that Maxwell's equations are also sign-indefinite due to the term involving the frequency. To cope with it, we establish some sort of uniform compactness result.Dans ce travail, nous nous intéressons à l’homogénéisation des équations de Maxwell harmoniques dans un milieu composite contenant une distribution périodique de petites inclusions de matériau négatif. On désigne ici par matériau négatif un matériau décrit par une permittivité et une perméabilité négatives. En raison du changement de signe des coefficients intervenant dans les équations, il n’est pas évident d’obtenir des estimations d’énergie uniformes et d’appliquer les techniques d’homogénéisation classiques. Le but de cet article est d’indiquer comment on peut néanmoins procéder dans ce contexte. L’analyse des équations de Maxwell est basée sur une étude précise de deux problèmes scalaires : l’un faisant intervenir la permittivité changeant de signe avec des conditions aux limites de Dirichlet, et l’autre la perméabilité changeant de signe avec des conditions aux limites de Neumann. Pour chacun de ces deux problèmes, on obtient un critère portant sur les paramètres physiques garantissant l’inversibilité uniforme des opérateurs associés lorsque la taille des inclusions tend vers zéro. Incidemment, nous expliquons le lien existant avec l’opérateur de Neumann–Poincaré, complétant la littérature existant sur le sujet. Les résultats obtenus pour les problèmes scalaires sont ensuite utilisés pour obtenir des estimations d’énergie uniforme pour le système de Maxwell. A ce stade, il faut contourner une difficulté supplémentaire liée au caractère indéfini induit par le terme fréquentiel. Ceci est réalisé en établissant un résultat de type compacité uniforme
Finalités, contenus et démarches pédagogiques des écoles d'ingénieurs en Algérie face aux enjeux environnementaux
No full textThe 21st century is marked by the depletion of natural resources, biodiversity, the increase in environmental problems and natural disasters. Algeria, in particular, is affected by global warming, mega fires, and water stress. Therefore, it is fundamental to change behaviours so as to attain sustainable development. This objective and its transmission to future generations requires the integration of this issue into engineering training with the purpose of preparing students to create and develop permanent materials that are based on a critical thinking, creative and an open-minded reasoning which can cope with all these changes. Engineering training is most notably concerned with this issue because future graduates will have face the major national challenges.The aim of this research is to understand how engineering schools integrate environmental issues into their curricula and whether those involved are caring to train engineers who will be able to handle environmental challenges.As part of a sociology if curriculum, a qualitative survey was conducted between 2018 and 2020. It comprises an analysis of the curricula of three Algerian engineering schools and also 24 interviews with professors and academic advisors. The analysis of the curricula reveals that some schools have been providing teaching units and specialities that deal with environmental and social issues over several years. Yet, training engineers about environmental issues and sustainable development was not a priority in the three schools, except for the specialities that directly tackle these issues. The interviews reveal that the interviewees are not all aware of the importance of integrating environmental issues into the curricula for the training of a responsible citizen engineer. Added to that, the analysis of institutional texts shows that the Ministry of the Environment is supposed to be involved in all trainings related to environmental issues. Our research reveals the limits of this involvement and the great autonomy of teachers in the initiatives they implement.Le XXIe siècle est marqué par la mise sous tension des ressources naturelles et de la biodiversité, et par la multiplication des problèmes environnementaux et des catastrophes naturelles. L’Algérie est particulièrement impactée par le réchauffement climatique, les méga feux et le stress hydrique. Le changement de nos comportements pour la réalisation d’un développement durable s’impose d’une manière cruciale. Un tel objectif et sa transmission aux générations futures requiert l’intégration de cet enjeu dans les formations d’ingénieurs afin de préparer les étudiants à créer et développer des outils durables avec une posture critique, créatrice, ouverte d’esprit et qui s’adapte aux changements. Les formations d’ingénieurs sont particulièrement concernées car les futurs diplômés auront à prendre en charge les grands défis sociotechniques nationaux.L’objectif de ce travail de recherche est de comprendre comment les écoles d’ingénieurs intègrent les enjeux environnementaux dans leurs offres curriculaires et si les différents acteurs se soucient de former des ingénieurs qui sauront faire face aux défis environnementaux.Dans le cadre d’une sociologie du curriculum, une enquête qualitative a été menée entre 2018 et 2020, constituée d’une part d’une analyse des offres de formation de trois écoles d’ingénieurs algériennes et d’autre part de 24 entretiens menés avec des enseignants et des responsables pédagogiques. L’analyse des programmes montre que certaines écoles proposent depuis plusieurs années des unités d’enseignement et des spécialités qui traitent des enjeux environnementaux et sociaux. Néanmoins, la priorité dans les trois écoles n’est pas de former les ingénieurs aux enjeux environnementaux et au développement durable, sauf pour les spécialités qui touchent directement à ces questions. Les entretiens révèlent que les interviewés ne sont pas tous sensibilisés et conscients de l’importance de l’intégration des problématiques environnementales dans les curricula. L’analyse des textes institutionnels montre que le Ministère de l’Environnement est censé être impliqué dans toutes les formations qui touchent aux questions environnementales. Nos recherches révèlent les limites de cette implication et la grande autonomie des enseignants dans les initiatives
Research on the impacts of wind turbine noise on humans: sound, perception, health (RIBEolH)
No full textInternational audienceWind energy is expanding rapidly in France as elsewhere in the world, but the population is worried about the health impacts of wind turbine noise and some people are more annoyed than the sound field measurements would suggest. The annoyance is often described as resulting from infrasounds (IS) whereas the acoustic pressures of IS emitted by wind turbines would be below the perception thresholds. However, the possible inaudibility of IS does not exclude their action on the inner ear or the central nervous system (CNS). In this context, we propose a Research project on the Impacts of wind turbine noise on humans, in terms of sound simulation/synthesis and perception, and its effects on human Health (“RIBEolH”). The objectives of RIBEolH project are: - To assess the health effects of audible noise, low-frequency sounds (LFS) particularly, and IS, emitted by wind turbines. - To better understand the auditory mechanisms associated with the perception of IS and LFS emitted by wind turbines. - To better understand the effects of IS on the inner ear or CNS. To address these objectives, RIBEolH is based on two complementary parts: an epidemiological study and a psychoacoustic and physiological study
Super résolution modale à partir d’une antenne linéaire horizontale
No full textThe objective of this thesis is to propose a method for reconstructing the wavenumbers associated with propagative modes over frequencies in the case of broadband sources emitting in a shallow environment. We first present the acoustic propagation governing our case study, in doing so we can describe the signal received by a sensor as the sum of a small number of modal components. As long as the acquisition of the signal is done regularly in the spatial domain, a classic Fourier analysis makes it possible to estimate these wavenumbers. However, the Fourier transform approach is subject to the provision of a large number of sensors, which results in the deployment of antennas several kilometers long. We will then see a new method of signal processing allowing to reconstruct a signal by having a smaller number of measurements than those necessary for the Fourier analysis. After a state of the art on the sparse reconstruction methods used in the context of wavenumber reconstruction, we will discuss the case of continuous approaches allowing to refine the detection of wavenumbers. Taking into account a physical relationship linking the wavenumbers of the same mode to two successive frequency indices in a continuous greedy type approach allows us to propose the CPOMP algorithm. We will submit our approach to a quantitative study conducted on two sets of synthetic data from two models: a Pekeris guide and a more generic guide because it is stratified. We also offer a qualitative analysis of our approach conducted on real datasets from the seismic campaign conducted in the North Sea as well as the SBCEX campaign.L’objectif de ces travaux de thèse est de proposer une méthode permettant de reconstruire les nombres d’onde associés à des modes propagatifs au fil des fréquences dans le cas de sources large-bande émettant dans un milieu petit fond. Nous présentons dans un premier temps la propagation acoustique régissant notre cas d’étude, ce faisant nous pourrons décrire le signal reçu par un capteur comme la somme d’un petit nombre de composantes modales. Tant que l’acquisition du signal se fait de façon régulière dans le domaine spatial, une analyse de Fourier classique permet d’estimer ces nombres d’onde.Toutefois l’approche par transformée de Fourier est sujet à la disposition d’un nombre important de capteurs ce qui résulte au déploiement d’antenne de plusieurs kilomètres de long.Nous verrons ensuite une nouvelle méthode de traitement de signal permettant de reconstruire un signal en disposant d’un plus petit nombre de mesures que celles nécessaires pour l’analyse de Fourier. Après un état de l’art sur les méthodes de reconstruction parcimonieuse utilisées dans le cadre de la reconstruction de nombre d’onde nous aborderons le cas des approches continues permettant d’affiner la détection des nombres d’onde. La prise en compte d’une relation physique liant les nombres d’onde d’un même mode à deux indices fréquentiels successifs dans une approche continue de type gloutonne nous permet de proposer l’algorithme CPOMP.Nous soumettrons notre approche à une étude quantitative mené sur deux jeux de données synthétiques issues de deux modèles : un guide de Pekeris et un guide plus générique car stratifié. Nous proposons de plus une analyse qualitative de notre approche menée sur des jeux de données réelles issus de la campagne sismique menée en Mer du Nord ainsi que de la campagne SBCEX
Using ab initio calculation to predict the thermochemical and safety properties of multicomponent systems
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