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Stinging nettle (Urtica dioica L.) as reinforcement in short fibre-reinforced biobased composites for application in injection moulding -A possible use case for biomass from marginal land?
No full textInternational audienceStinging nettle (Urtica dioica L.) has been observed to grow spontaneously on metal-contaminated soils marginalised by heavy industrial use, thereby presenting an opportunity for the economic utilisation of such lands. This study explores the potential of nettle as a fibre crop by producing short fibre-reinforced polylactic acid (PLA) composites through compounding and injection moulding. Whole stem segments from three nettle clones (B13, L18, and Roville), along with separated fibre bundles from the L18 clone, were processed. The fibre bundles were separated using a roller breaker unit and a hammer mill. From separation with the hammer mill, not only cleaned fibre bundles but also the uncleaned fibre-shive mixture and the undersieve fraction were processed. The Young's modulus of all composites exceeded that of unreinforced PLA, with mean values ranging from 5.7 to 8.1 GPa. However, the tensile strength of most composites was lower than that of pure PLA, except for the two composites reinforced with cleaned fibre bundles. Of these two, the reinforcement with fibre bundles from separation with the hammer mill led to superior mechanical properties, with a higher Young's modulus (8.1 GPa) and tensile strength (61.8 MPa) compared to those separated using the breaking unit (7.2 GPa and 55.9 MPa). This enhancement is hypothesised to result from reduced fibre damage and lower fibre bundle thickness. The findings suggest that nettle cultivation on marginal lands could be a viable option for producing short-fibre composites, thereby offering a sustainable use of these otherwise underutilised areas
Mémoires collectifs de Master en ligne. Pourquoi ? Comment ?
No full textInternational audienceThis article presents the experiment that led to the development of the collective dissertation method, particularly for Masters students. The research approach was based on the action-research model of successive cycles. The current results are very encouraging, but require the dissertation supervisor to do a great deal of follow-up work on student behavior. This is why, at the end of this article, we propose to set up a research project on the use of Artificial Intelligence to assist the dissertation director in observing the behaviors and roles of each student involved in the research and writing of the collective dissertation.L'article proposé présente l'expérimentation qui a permis de mettre au point la méthode des mémoires collectifs, en particulier des Masters. La démarche de recherche s'est fondée sur le modèle de recherche-action par cycles successifs. Les résultats actuels sont très encourageants, mais impliquent un travail important de suivi des comportements des étudiants par le directeur de mémoire. C'est la raison pour laquelle, au terme de cet article, nous proposons de mettre en place un travail de recherche sur l'utilisation de l'Intelligence Artificielle pour assister le directeur de mémoire dans l'observation des comportements et des rôles de chaque étudiant participant à la recherche et à la rédaction du mémoire collectif.</div
Sciences archéologiques et statistiques: Questions, données, méthodes
No full textNational audienceLes statistiques sont partie intégrante du raisonnement archéologique, pour structurer des ensembles d’information archéologique, pour établir des ordres de grandeur ou encore mettre en relation différents processus afin de proposer des interprétations de phénomènes passés. Dans la pratique, l’approche statistique engage, de manière sous-jacente, des concepts archéologiques liés au questionnement, repose sur l’identification d’éléments empiriques correspondants, utilise des méthodes statistiques pour l’analyse. C’est donc un dialogue entre archéologie et statistiques auquel nous sommes conviés, qui ne peut pas être réduit à sa simple expression technique.Face à un enjeu de sensibilisation et de transmission des connaissances des pratiques statistiques pour l’archéologie, cet ouvrage offre une approche didactique interdisciplinaire accessible aux non-spécialistes. Réciproquement, il permettra aux statisticiens d’appréhender la manière dont les archéologues transcrivent une problématique plus ou moins complexe en un schéma d’analyse statistique. Dans une première partie, nous partons des questions que se posent les archéologues lorsqu’il s’agit de reconstituer des chronologies, de comprendre les dynamiques spatiales, de lire des informations anthropologiques. Des exemples d’études sont présentés sous l’angle de trois dimensions articulées autour des questions « Quand ? », « Où ? », « Qui/Quoi ? ». Dans une deuxième partie, nous invitons le lecteur à approcher les méthodes statistiques, des plus simples aux plus élaborées. En réunissant les contributions de spécialistes de la chronologie, de la culture matérielle, de la géographie du passé, de l’anthropologie biologique, de la paléontologie et de la statistique, cet ouvrage propose un panorama non exhaustif d’études de cas qui, à travers la diversité des objets empiriques et des approches statistiques mobilisés, éprouvent les méthodes et les conditions d’application des outils non sans aborder apports et limites interprétatifs.Cet ouvrage s’adresse aux apprenants comme aux praticiens, étudiants et scientifiques intéressés par la mobilisation de méthodes statistiques pour répondre à des problématiques archéologiques. Il a pour ambition de décloisonner les approches en offrant à chacun des pistes de réflexion quel que soit le niveau de lecture
Vers un laser superradiant : ensembles atomiques d’ytterbium et développements métrologiques pour des références de fréquence ultra-stables
No full textThis thesis presents the initial steps toward the realization of an ultra-stable superradiant oscillator. It explores the use of the quantum phenomenon of superradiance, which leverages the coherence and indistinguishability of an atomic ensemble to enhance coherent optical radiation. A superradiant laser consists of atoms collectively coupled to a Fabry-Perot cavity, operating in the bad-cavity regime to minimize sensitivity to cavity fluctuations.In this work, the first realization and characterization of a cold ytterbium atomic ensemble are demonstrated, laying the foundation for future superradiant operation. The experimental setup for atomic transport into the cavity has been planned, enabling sequential loading of atoms for quasi-continuous superradiant emission.To support the future characterization of the superradiant laser, a compensated optical fiber link for local ultra-stable frequency transfer has been implemented. This system features fully digital signal processing and a novel characterization method that does not require access to the remote fiber end. The achieved fractional frequency instability reaches the 10^{-18} range, demonstrating its suitability for high-precision frequency dissemination within an institute.Cette thèse présente les premières étapes vers la réalisation d’un oscillateur superradiant ultra-stable. Elle explore l’utilisation du phénomène quantique de superradiance, qui repose sur la cohérence et l’indistinguabilité d’un ensemble atomique pour produire une émission optique cohérente. Un laser superradiant est constitué d’atomes couplés collectivement à une cavité Fabry-Perot, fonctionnant dans le régime dit de ``mauvaise cavité'' afin de minimiser la sensibilité aux fluctuations de cavité.Dans ce travail, la première réalisation et caractérisation d’un ensemble atomique d’ytterbium refroidi sont démontrées, jetant les bases d’un futur fonctionnement superradiant. L’installation expérimentale pour le transport des atomes dans la cavité a été planifiée, permettant un chargement séquentiel des atomes pour une émission superradiant quasi-continue.Afin de soutenir la future caractérisation du laser superradiant, une liaison optique fibrée compensée a été mise en place pour le transfert local de fréquence ultra-stable. Ce système intègre un traitement du signal entièrement numérique et une méthode de caractérisation innovante ne nécessitant pas d’accès à l’extrémité distante de la fibre. L’instabilité relative de fréquence obtenue atteint l’ordre de 10^{-18}, démontrant ainsi son adéquation pour la dissémination de fréquence de haute précision au sein d’un institut
Acid/Base‐Responsive Circularly Polarized Luminescence Emitters with Configurationally Stable Nitrogen Stereogenic Centers
No full textInternational audienceA way to prevent the fast configurational interconversion of tertiary amines is to invoke Tröger's base analogs, which display methano‐ or ethano‐bridged diazocine cores fused to aromatic rings. These derivatives are configurationally stable, even in acidic media when their structures bear ethylene bridges. Here, a two‐ to three‐step synthesis is presented of methano‐ and ethano‐bridged Tröger's base analogs with two peripheral fluorophores, i.e., anthracene, pyrene, and 9,9‐dimethylfluorene units. These compounds, possessing two nitrogen stereogenic centers, exhibit good circularly polarized luminescence (CPL) dissymmetry factors (|glum| up to 1.2 × 10 −3 ) and brightnesses ( BCPL up to 26.3 M −1 cm −1 ), as well as excellent fluorescence quantum yields, demonstrating the Tröger´s base core to be a convenient scaffold to prepare CPL emitters upon functionalization with simple achiral fluorophores. Furthermore, the configurationally stable ethano‐bridged Tröger's base analogs are employed to modulate their CPL response, generating a CPL switch through their protonation/deprotonation by consecutive additions of acid and base. The reversibility of the switching process is demonstrated for two cycles without altering the CPL performance of the molecule. It is believed that this straightforward and efficient approach to building CPL emitters employing the Tröger's base core could lead to its incorporation in CPL‐based sensors and materials
Late Paleolithic whale bone tools reveal human and whale ecology in the Bay of Biscay
No full textVoir aussi l'Author Correction : Nature Communications, 2025, 16 (1):7795 ou ou hal-05299911International audienceReconstructing how prehistoric humans used the products obtained from large cetaceans is challenging, but key to understand the history of early human coastal adaptations. Here we report the multiproxy analysis (ZooMS, radiocarbon, stable isotopes) of worked objects made of whale bone, and unworked whale bone fragments, found at Upper Paleolithic sites (Magdalenian) around the Bay of Biscay. Taxonomic identification using ZooMS reveals at least five species of large whales, expanding the range of known taxa whose products were utilized by humans in this period. Radiocarbon places the use of whale products ca. 20–14 ka cal BP, with a maximum diffusion and diversity at 17.5–16 ka cal BP, making it the oldest evidence of whale-bone working to our knowledge. δ 13 C and δ 15 N stable isotope values reflect taxon-specific differences in foraging behavior. The diversity and chronology of these cetacean populations attest to the richness of the marine ecosystem of the Bay of Biscay in the late Paleolithic, broadening our understanding of coastal adaptations at that time
A Versatile Prognostics Approach for Batteries and Hydrogen Storage Systems Health Management
No full textInternational audienceThe degradation of energy storage systems, including batteries, proton exchange membrane fuel cells, and electrolyzers, presents a critical challenge to their long-term reliability and efficiency. This study addresses the prediction of Remaining Useful Life by selecting a robust state-of-health indicator tailored to each system. A novel data-driven prognostic approach is proposed, leveraging Long Short-Term Memory neural networks to capture temporal dependencies and nonlinear degradation trends. The recurrent neural network model demonstrates versatility, adapting to both electrochemical storage and hydrogen-based systems by effectively learning from diverse datasets. Results highlight the method's capability to generalize across technologies, enabling accurate degradation predictions and offering significant insights into performance management
Localized Forest Fire Risk Prediction: A Department-Aware Approach for Operational Decision Support
No full textInternational audienceForest fire prediction involves estimating the likelihood of fire ignition or related risk levels in a specific area over a defined time period. With climate change intensifying fire behavior and frequency, accurate prediction has become one of the most pressing challenges in Artificial Intelligence (AI). Traditionally, fire ignition is approached as a binary classification task in the literature. However, this formulation oversimplifies the problem, especially from the perspective of end-users such as firefighters. In general, as is the case in France, firefighting units are organized by department, each with its terrain, climate conditions, and historical experience with fire events. Consequently, fire risk should be modeled in a way that is sensitive to local conditions and does not assume uniform risk across all regions. This paper proposes a new approach that tailors fire risk assessment to departmental contexts, offering more actionable and region-specific predictions for operational use. With this, we present the first national-scale AI benchmark for metropolitan France using state-of-the-art AI models on a relatively unexplored dataset. Finally, we offer a summary of important future works that should be taken into account. Supplementary materials are available on Github
