Mécanismes d'ionisation de systèmes libres en lumière extrême décrits par la théorie de la fonctionnelle de la densité dépendante du temps

Cette thèse présente des applications d'un modèle théorique basé sur la théorie de la fonctionnelle de la densité dépendante du temps, permettant de décrire la dynamique non-linéaire d'agrégats métalliques et de petites molécules organiques soumis à une excitation intense (irradiation par un laser femtoseconde, collision avec un ion multichargé). Nous avons choisi d'étudier, en particulier, le mécanisme dynamique de déplétion des niveaux électroniques d'agrégats de sodium, de la pyridine et de l'uracile. Nous avons observé que la distribution des électrons émis dépend sensiblement de la fréquence des photons. Les fréquences proches de la lumière visible excitent exclusivement les électrons à la surface de Fermi; alors que la lumière dans les hautes fréquences ultraviolettes, comme celles délivrées par les lasers à électrons libres, tend à extraire les électrons de tous les niveaux électroniques, avec une préférence pour les états de valence les plus liés. Nous avons aussi étudié le spectre de photoélectrons de petits agrégats de sodium et mis en évidence une corrélation avec la déplétion électronique en fonction de la fréquence du laser.This thesis presents a theoretical model, in the framework of time-dependent density functional theory, to describe the non-linear dynamics of metal clusters and small organic molecules exposed to an intense excitation (irradiation by a femtosecond laser, collision with multicharged ions). We have chosen to study, in particular, the dynamical mechanism of the depletion of the electronic levels for sodium clusters, pyridine and uracil. We observed that the distribution of emitted electrons sensitively depends on the photon frequency. Frequencies close to visible light only excite the electrons from the Fermi surface while the light in the ultraviolet high frequencies, like these delivered by free electron lasers, tends to remove the electrons from all electronic levels, with a preference for the deepest bounded valence states. We also studied photoelectron spectra of sodium clusters and we exhibited a correlation with the electronic depletion scheme

Colour-Difference Assessment for Driving Headlight Simulation

In high quality driving simulation applications, such as headlight simulation, colorimetric validity is essential. In virtual testing of headlight systems, it is important that the WYSIWYG (What You See Is What You Get) paradigm is respected for product quality headlight assessment. Indeed, if a slightly reddish orange colour is displayed instead of the typical orange of halogen lighting, the effect for driver comfort or traffic safety can be critical. The lighting specialist should accept a headlight which doesn't have the right colour. Previous studies have shown that there is a significant colour difference between virtual and real environments. Nevertheless, in virtual headlight testing the rendered colour fidelity has to fit industrial assessment. This study therefore deals with the colour-difference perceptibility that is the ability of an observer to detect a difference between two colours and, more precisely, on the acceptability of the perceived difference. We propose in this paper a psychophysical function for colour difference acceptability which fits well with the measured data. The colour acceptability function was implemented in a driving simulator for high validity headlight assessment. Driver acceptability experimentation was carried out using Renault's headlight driving simulation equipped with a fullcab and a 210° cylindrical display screen

Color-difference assessment and enhancement for driving headlight simulation

Real-time headlight simulation in driving conditions is used by most car manufacturers to assure the quality, cost, and delivery of headlight engineering design. An important parameter judged by the headlight assessment team is color restitution; indeed, this parameter has to meet the standard of “lamps for road vehicles.” Therefore, the goal of this study was the color assessment and enhancement of a driving headlight simulator. For this purpose, this study was conducted in two phases: the process of constructing two color acceptability scales that directly reflect the perception of two different populations (experts and “naive”), and the assessment of a method based on the chromatic adaptation transform (CAT) for reducing the color difference between real and virtual environments. In the first phase, we conducted two psychophysical experiments (i.e., one for each population), in which the observers had to report their degree of satisfaction about the color difference. These two experiments enabled the creation of two acceptability scales for headlight simulation. In the second phase, we compared the performance of different chromatic transformations; as a result of this comparison, we advise the use of the CAT02 transformation, in order to reduce the color difference for headlight assessment in driving simulation experiments.ANRT (Association Nationale de la Recherche et de la Technologie) and Renaul

Detection of seismic site effects: Development of experimental methods and application to the city of Nice

Les effets de site représentent un enjeu important pour la prévention parasismique, puisqu’ils peuvent aggraver considérablement les dommages lors d’un séisme. La connaissance de la réponse des sols aux séismes permet d’adapter la réglementation parasismique à ces contraintes lors de l’élaboration de microzonages et de Plan de Prévention des risques. Les méthodes expérimentales de détermination des effets de site visent à obtenir les paramètres de l’amplification sismique par la mesure de séismes ou de bruit de fond sismique. Cet article présente les principaux résultats obtenus jusqu’en 2005 par l’ERA « Risque sismique » dans la mise au point de ces techniques et leur application comparée sur la ville de Nice. Cette ville a effectivement constitué le principal chantier d’application grâce à de multiples campagnes d’enregistrements sismiques. De nombreux séismes ont d’abord été analysés par la méthode des fonctions de transfert. La méthode « H/V bruit de fond » a été appliquée sur plus de 600 points et les résultats interpolés spatialement. Un modèle géotechnique du sous-sol a ensuite permis de comparer les résultats obtenus avec la géologie et des simulations numériques de la propagation des ondes. La complémentarité des méthodes et leurs atouts respectifs sont mis en valeur sur ce territoire à fort enjeu.Site effects represent a critical challenge in the field of earthquake prevention since these effects are capable of seriously exacerbating damage whenever an earthquake strikes. Knowledge of the soil response to seismic activity allows adapting earthquake protection regulations to better incorporate these constraints during the process of defining microzones and producing the Risk Prevention Plan. The experimental methods employed to determine site effects seek to obtain seismic amplification parameters by means of measuring earthquakes or seismic background noise. This article presents the main set of results derived until 2005 by the “Seismic risk” ERA research team during development of these techniques as well as their comparative application to Nice, a city that has constituted the main field application site thanks to its hosting of multiple seismic recording campaigns. For starters, many earthquakes have been analyzed according to the transfer function method. The “Horizontal/Vertical background noise” method was in particular applied to over 600 points, with results being spatially interpolated. A geotechnical model of the subsoil then served to compare the results output with both the geology and numerical simulations of wave propagation. The complementarity of methods and their respective advantages are highlighted in this seismically-active setting

Éditorial

Le lien entre migrations, ville et confection se tisse aux premiers temps de la Révolution industrielle. En 1835, à l’occasion de son second voyage en Angleterre, Alexis de Tocqueville dresse un tableau effrayant des quartiers de Manchester où, dans des caves vétustes, s’entassent des Irlandais qui ont quitté leur île pour échapper à la misère. « Parmi les ouvriers, écrit-il, des hommes qui arrivent d’un pays où les besoins de l’homme se réduisent presque à ceux du sauvage, et qui travaillent..

Surrogate models to predict the adequacy and flexibility of large-scale power systems: case-study with the EU power system

editorial reviewedA new body of research has recently emerged in energy systems, focusing on the links between centralized and decentralized power generation, and on the interactions between different energy sectors. This research has brought new concepts such as « Smart Energy Systems », « Integrated Energy Systems » or « Virtual Power plants ». In smart energy systems, the focus is on the integration of the electricity, heating, cooling, gas and transport sectors, and on the use of the flexibility in demands and various short-term and longer-term storage. To enable this, the smart energy system must coordinate between a number of sectors, which includes electricity grids, district heating and cooling grids, gas grids and different fuel infrastructures. Modeling these different aspects in an integrated manner is a challenge: the high temporal and technical granularities required by the power system models can become uncompatible with the requirements of long-term energy planning involving all relevant energy sectors. Current solutions to this involve hard-linking or soft-linking between models, with their associated challenges such as computational traceability or numerical convergence. In this paper, an alternative approach is proposed to couple a power system model (the EU-wide Dispa-SET power system model) and a system dynamics model (the MEDEAS model). The methods relies on the creation of surrogate models that approximate the results of the power system optimizations. A multi-dimensional inputs space is created by varying key system characteristics: flexible capacity, no flexible capacity, short-term storage, long-term storage, grid infrastructure, renewable penetration. A latin hypercube sampling is then defined to run the model over this inputs space and Artificial Neural Networks are used to predict key system performance indicators (in this case curtailment and loss of load) as a function of the system features. Results indicate that ANN can predict with good accuracy the main power system constraints and outcomes. The generated surrogate models are therefore suitable to be integrated into a more general system-dynamics model of the energy systems, thus improving the representation of the power system operation and constraints

Éditorial

UID/ANT/04038/2013publishersversionpublishe

Colour-Difference Assessment for Driving Headlight Simulation

In high quality driving simulation applications, such as headlight simulation, colorimetric validity is essential. In virtual testing of headlight systems, it is important that the WYSIWYG (What You See Is What You Get) paradigm is respected for product quality headlight assessment. Indeed, if a slightly reddish orange colour is displayed instead of the typical orange of halogen lighting, the effect for driver comfort or traffic safety can be critical. The lighting specialist should accept a headlight which doesn't have the right colour. Previous studies have shown that there is a significant colour difference between virtual and real environments. Nevertheless, in virtual headlight testing the rendered colour fidelity has to fit industrial assessment. This study therefore deals with the colour-difference perceptibility that is the ability of an observer to detect a difference between two colours and, more precisely, on the acceptability of the perceived difference. We propose in this paper a psychophysical function for colour difference acceptability which fits well with the measured data. The colour acceptability function was implemented in a driving simulator for high validity headlight assessment. Driver acceptability experimentation was carried out using Renault's headlight driving simulation equipped with a fullcab and a 210° cylindrical display screen

Color-difference assessment and enhancement for driving headlight simulation

Real-time headlight simulation in driving conditions is used by most car manufacturers to assure the quality, cost, and delivery of headlight engineering design. An important parameter judged by the headlight assessment team is color restitution; indeed, this parameter has to meet the standard of “lamps for road vehicles.” Therefore, the goal of this study was the color assessment and enhancement of a driving headlight simulator. For this purpose, this study was conducted in two phases: the process of constructing two color acceptability scales that directly reflect the perception of two different populations (experts and “naive”), and the assessment of a method based on the chromatic adaptation transform (CAT) for reducing the color difference between real and virtual environments. In the first phase, we conducted two psychophysical experiments (i.e., one for each population), in which the observers had to report their degree of satisfaction about the color difference. These two experiments enabled the creation of two acceptability scales for headlight simulation. In the second phase, we compared the performance of different chromatic transformations; as a result of this comparison, we advise the use of the CAT02 transformation, in order to reduce the color difference for headlight assessment in driving simulation experiments.ANRT (Association Nationale de la Recherche et de la Technologie) and Renaul

Colorimétrie appliquée à la simulation de phare de voiture

Afin d’optimiser les temps de conception d’un système d’une voiture (phare, système de freinage, etc.), les industries utilisent de manière de plus en plus régulière des logiciels de simulation et de Conception Assistée par Ordinateur (CAO). Ces derniers permettent la visualisation en temps réel de ces systèmes sous diverses conditions (analyse de la résistance à la pression, à la chaleur, etc.). Le Centre de Réalité Virtuelle et de Simulation Immersive (CRVSI) de Renault dispose d’outils de conception et de maquettage virtuel (CAVE, simulateur dynamique, etc.). Ces derniers s’intègrent dans le cycle de la conception des véhicules en offrant aux utilisateurs la possibilité d’interagir, en temps réel, avec des maquettes virtuelles. Dans le cadre spécifique de la simulation des phares d’une voiture, il est important d’étudier la représentativité des couleurs affichées. Il est en effet primordial que, pour un outil de validation, la restitution des couleurs soit au plus proche de la réalité physique (phare halogène, LED, Xenon, etc.). La colorimétrie offre plusieurs outils permettant de calculer une différence colorimétrique. Nous avons ainsi étudié l’uniformité colorimétrique des métriques CIE76, CIE94 et CIEDE2000 afin d’une part, de proposer des coefficients de pondération pour la teinte et la chroma et, d’autre part, de comparer les résultats de chacune afin de déterminer celle qui uniformise le mieux l’espace CIELAB pour la simulation d’éclairage