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Jean-Jacques Rousseau. Les Consolations des misères de ma vie ou Recueil d'airs, romances et dos suivi de Canzoni da batello & Raccolta di Canzoni Veneziane et Toscane: Tome XIX C - 1744-1778
No full textInternational audienceDans le cadre des Oeuvres complètes de Jean-Jacques Rousseau, ce tome est une édition critique des oeuvres poétioco-musicales de compositeur philosophe
Experimental observation of mutual coupling in resonator array on thin-metal-film
No full textInternational audienceWe present the experimental observation of electromagnetic mutual coupling in an array of ring-shaped resonators (meta-atoms) fabricated on a free-standing thin metal film using a maskless direct laser ablation technique. The transmission spectra of various resonator configurations were measured via terahertz time-domain spectroscopy and a vector network analysis. Numerical modeling of periodically arranged resonators, employing multipole decomposition, revealed a clear dependence of inter-element coupling on the number of meta-atoms in the array. Theoretical analysis of electric and magnetic dipoles and quadrupoles elucidates the nature of resonance peak splitting and broadening, resulting in a reduction in the quality factor as the number of meta-atoms increases. We anticipate that observed inter-element coupling behavior along with multipole mode analysis could advance the development of multi-pixel emitters, 2D plasmonic THz sources, sensors, electro-optical modulators, and resonators for subwavelength photonic and plasmonic applications
Bi‐LORA : A Vision‐Language Approach for Synthetic Image Detection
No full textInternational audienceAdvancements in deep image synthesis techniques, such as generative adversarial networks (GANs) and diffusion models (DMs), have ushered in an era of generating highly realistic images. While this technological progress has captured significant interest, it has also raised concerns about the high challenge in distinguishing real images from their synthetic counterparts. This paper takes inspiration from the potent convergence capabilities between vision and language, coupled with the zero‐shot nature of vision‐language models (VLMs). We introduce an innovative method called Bi‐LORA that leverages VLMs, combined with low‐rank adaptation (LORA) tuning techniques, to enhance the precision of synthetic image detection for unseen model‐generated images. The pivotal conceptual shift in our methodology revolves around reframing binary classification as an image captioning task, leveraging the distinctive capabilities of cutting‐edge VLM, notably bootstrapping language image pre‐training (BLIP)2. Rigorous and comprehensive experiments are conducted to validate the effectiveness of our proposed approach, particularly in detecting unseen diffusion‐generated images from unknown diffusion‐based generative models during training, showcasing robustness to noise, and demonstrating generalisation capabilities to GANs. The experiments show that Bi‐LORA outperforms state of the art models in cross‐generator tasks because it leverages multi‐modal learning, open‐world visual knowledge, and benefits from robust, high‐level semantic understanding. By combining visual and textual knowledge, it can handle variations in the data distribution (such as those caused by different generators) and maintain strong performance across different domains. Its ability to transfer knowledge, robustly extract features and perform zero‐shot learning also contributes to its generalisation capabilities, making it more adaptable to new generators. The experimental results showcase an impressive average accuracy of 93.41% in synthetic image detection on unseen generation models. The code and models associated with this research can be publicly accessed at https://github.com/Mamadou‐Keita/VLM‐DETECT
Le caractère manifestement exagéré des primes ne s’apprécie pas par rapport à l’actif successoral laissé par le souscripteur
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Optimisation de procédés de fabrication pour le développement de transistors de puissance en technologie GaN
No full textThis thesis investigates the design and optimization of gallium nitride (GaN) power transistors, focusing on lateral high-electron-mobility transistors (HEMTs) and vertical trench MOSFETs (V-T-MOSFETs). The objective is to achieve robust and reliable operation in the 600–1200 V class while maintaining high efficiency and fast switching.As demand for electrical energy and power-conversion density continues to grow, conventional silicon devices are reaching their physical and performance limits. Wide bandgap semiconductors provide a path forward. Among them, GaN combines a high critical electric field and high electron mobility with device architectures that enable compact, high-frequency, and energy-efficient converters.Chapter 1 establishes the context by retracing the evolution of power transistors from BJTs and MOSFETs to IGBTs and wide bandgap devices, and by benchmarking the intrinsic properties of Si, SiC, and GaN. This analysis highlights GaN’s advantages in breakdown field, carrier mobility, and frequency capability, and reviews the state of the art in both lateral and vertical device families.Chapter 2 focuses on the optimization of lateral GaN HEMTs. Using a combination of TCAD simulations and prototype fabrication, the influence of key design parameters such as buffer carbon concentration and back-barrier composition is investigated. Particular emphasis is placed on GaN HEMTs on sapphire substrates, which are optimized in view of an innovative vertical integration pathway based on the exfoliation technique that is studied by simulation. Experimental characterization validates the simulated trends and provides design guidelines to mitigate trapping and improve dynamic performance.Chapter 3 addresses the development of vertical GaN architectures, presenting the design, fabrication, and characterization of GaN V-T-MOSFETs on silicon. Edge-termination techniques including fluorine implantation and p-GaN regrowth are evaluated through simulation. A complete fabrication flow for a vertical GaN-on-Si transistor is developed, and the resulting devices are electrically benchmarked to highlight both their potential and their current limitations.Chapter 4 explores future optimization strategies for vertical GaN devices, including low-damage trench etching, corner rounding, and gate-dielectric engineering to suppress electric-field crowding and interface trapping. Methods to improve device ruggedness, such as p-shielded gates and slanted p-body designs, are also discussed. These approaches point toward the requirements for reliable, high-voltage GaN transistors in automotive, renewable energy, and grid applications.Cette thèse porte sur la conception et l’optimisation de transistors de puissance en nitrure de gallium (GaN), en se concentrant sur les transistors à haute mobilité électronique latéraux (HEMTs) et les transistors MOSFETs verticaux à tranchée (V-T-MOSFETs). L’objectif est d’assurer un fonctionnement robuste et fiable dans la gamme de tension 600–1200 V, tout en maintenant une efficacité élevée et une commutation rapide.Avec la croissance continue de la demande en énergie électrique et en densité de conversion de puissance, les dispositifs en silicium conventionnels atteignent leurs limites physiques et de performance. Les semi-conducteurs à large bande interdite offrent une voie de progrès. Parmi eux, le GaN combine un champ électrique critique élevé et une forte mobilité électronique avec des architectures de dispositifs permettant des convertisseurs compacts, à haute fréquence et à haut rendement énergétique.Le chapitre 1 établit le contexte en retraçant l’évolution des transistors de puissance — des BJTs et MOSFETs aux IGBTs et dispositifs à large bande interdite — et en comparant les propriétés intrinsèques du Si, du SiC et du GaN. Cette analyse met en évidence les avantages du GaN en termes de champ de claquage, de mobilité des porteurs et de capacité fréquentielle, tout en présentant l’état de l’art des technologies latérales et verticales.Le chapitre 2 est consacré à l’optimisation des HEMTs GaN latéraux. À l’aide d’une combinaison de simulations TCAD et de fabrications de prototypes, l’influence de paramètres clés tels que la concentration en carbone du buffer et la composition du back-barrier est étudiée. Une attention particulière est portée aux HEMTs GaN sur substrats saphir, optimisés en vue d’une voie d’intégration verticale innovante basée sur la technique d’exfoliation, étudiée par simulation. La caractérisation expérimentale confirme les tendances simulées et fournit des lignes directrices de conception pour atténuer les phénomènes de piégeage et améliorer les performances dynamiques.Le chapitre 3 aborde le développement des architectures GaN verticales, en présentant la conception, la fabrication et la caractérisation de V-T-MOSFETs GaN sur silicium. Des techniques de terminaison de bord, telles que l’implantation de fluor et la recroissance de p-GaN, sont évaluées par simulation. Un procédé complet de fabrication d’un transistor vertical GaN-on-Si est développé, et les dispositifs réalisés sont caractérisés électriquement afin de mettre en évidence à la fois leur potentiel et leurs limitations actuelles.Le chapitre 4 explore des stratégies futures d’optimisation des dispositifs GaN verticaux, incluant la gravure de tranchées à faible dommage, l’arrondissement des coins et l’ingénierie du diélectrique de grille pour réduire les concentrations de champ électrique et les pièges d’interface. Des méthodes visant à renforcer la robustesse des dispositifs, telles que les grilles p-protégées et les conceptions à corps p incliné, sont également discutées. Ces approches ouvrent la voie à la réalisation de transistors GaN fiables et à haute tension pour les applications automobiles, les énergies renouvelables et les réseaux électriques
Territoires zéro chômeur de longue durée - Quelle hiérarchisation des justifications de la création d’activités ?
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Recent Advances in Sustainable and Green Chemistry for Polyurethane-Based High-Performance Supercapacitor Electrodes
No full textInternational audienceThe increasing demand for sustainable energy storage solutions has intensified the focus on high-performance supercapacitors, known for their rapid charge/discharge capabilities, high power density, and long cycle life. Polyurethane (PU)-based materials have gained attention as promising candidates for supercapacitor electrodes, due to their flexibility, mechanical robustness, and tunable properties. It is important to clarify that PU typically does not contribute directly to charge storage via adsorption or pseudocapacitive mechanisms. Instead, PU serves as a flexible scaffold, a binder, or a precursor for the preparation of heteroatom-doped carbon materials upon thermal treatment. Thus, the term 'PU-based' in this review refers to PU-supported or PU-derived composites, where PU enables structural or functional integration of active electrode Materials. Polyurethane composites incorporating graphene oxide have demonstrated a specific capacitance of 758.8 mF/cm 2 with capacitance retention of 92% over 5,000 cycles. Other PU-based electrodes have achieved energy densities up to 22.5 Wh/kg and power densities of 1472.7 W/kg, reflecting their potential for high-performance energy storage applications. Despite these advantages, challenges, such as low intrinsic conductivity and the environmental impact of traditional synthesis methods, limit their widespread adoption. Conventional PU composites often incorporate conductive additives like carbon materials, metal oxides, or conductive polymers to enhance their electrochemical performance, yet these approaches may involve non-renewable or toxic components. Developing green energy materials that adhere to sustainability and green chemistry principles is crucial to address these limitations. This includes using renewable resources, environmentally friendly processing techniques, and recyclable materials to reduce the ecological footprint and meet the growing need for sustainable energy storage technologies. This review highlights current trends in developing eco-friendly supercapacitor materials, addressing key challenges such as limited conductivity and complex processing. It uniquely integrates green chemistry principles with advances in polyurethane composites, emphasizing sustainable feedstocks, heteroatom doping, and functional nanomaterials. By combining these aspects, this review provides a comprehensive perspective not fully covered in existing literature
Design and fabrication of bioinspired selfsimilar and non-self-similar metamaterials
No full textMatériaux poreux et métamatériaux acoustiques; GABE - Acoustique du Bâtiment et de l'Environnement: GAPSUS - Acoustique Physique, Sous-Marine et Ultra-Sonore: GVB - Vibro acoustique et Contrôle du BruitNational audienceHierarchical structures with constituents organized across multiple length scales are commonly found in natural materials such as bones, shells, and spider silk. These materials exhibit remarkable quasi-static mechanical properties, including high specific strength, stiffness, and toughness. However, the impact of hierarchical organization on the dynamic behavior of metamaterials remains relatively under-explored compared to its static counterparts. This presentation examines the influence of bio-inspired hierarchical architectures-accounting for visco-elastic effects-on the wave attenuation properties of phononic crystals and elastic metamaterials. Both self-similar and non-self-similar unit cells with varying hierarchical levels and configurations are analyzed. Key findings highlight the advantages and trade-offs associated with structural hierarchy: Advantages: - Hierarchically induced band gaps emerge alongside those found in corresponding non-hierarchical structures, providing enhanced control over wave propagation. - Hierarchical designs enable the tuning of band-gap frequencies to lower ranges while significantly reducing overall structural weight. Trade-offs: - Due to the specific design approach (holes within a matrix), structural rigidity may be compromised. The results, supported by numerical simulations and experimental validation, emphasize the critical role of even small visco-elastic effects in shaping attenuation behavior, particularly between band gaps. These findings underscore the potential of hierarchical designs for advancing the dynamic performance of metamaterials
Lentille de Luneburg pour les ondes de gravité
No full textMatériaux poreux et métamatériaux acoustiques; GABE - Acoustique du Bâtiment et de l'Environnement: GAPSUS - Acoustique Physique, Sous-Marine et Ultra-Sonore: GVB - Vibro acoustique et Contrôle du BruitNational audienceDans cet exposé, la focalisation des ondes de surface à l'aide d'une lentille de Luneburg composée de piliers immergés de hauteur uniforme est étudiée numériquement. La conception de cette lentille repose sur la dérivation et la résolution numérique des équations 3D du potentiel de vitesse issues du cadre de Navier-Stokes. Cette approche permet de prendre en compte les effets de champ proche entre les piliers rapprochés, effets qui sont négligés dans le cadre des approximations des eaux peu profondes. La bathymétrie complexe de la lentille est conçue pour reproduire le profil théorique de l'indice de réfraction d'une lentille de Luneburg. Les résultats montrent que la lentille constituée de piliers immergés offre des performances de focalisation comparables à celles d'une lentille de Luneburg « idéale » avec une distribution continue de la hauteur. Cette étude met en lumière le potentiel des structures discrétisées pour reproduire avec une grande fidélité les propriétés optiques des conceptions théoriques
