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Absolute gravity measurements at Brest (France) between 1998 and 2022
No full textInternational audienceRepeated absolute gravity measurements, conducted once or twice per year, have proven valuable for quantifying slow vertical land motion with a precision better than 0.4 µGal yr−1 (1 µGal = 10−8 m s−2) after a decade or more. This precision is comparable to vertical velocity estimates derived from continuously operating space-based geodetic techniques such as the Global Navigation Satellite System (GNSS). Furthermore, absolute gravimeters are particularly well suited for long-term studies, as their measurements are based on fundamental length and time standards (laser and atomic clock) and remain independent of terrestrial reference frame realizations, unlike GNSS. Consequently, an absolute gravimeter can return years or even decades later and provide relevant measurements, provided the initial gravity data are well documented and the ground gravity marker remains undisturbed. Following this line of thinking, we have compiled and consistently reprocessed absolute gravity measurements collected between 1998 and 2022 in Brest, on the French Atlantic coast, near its century-long tide gauge station. The entire dataset has been reanalyzed in accordance with international recognized standards for instrumental and modelling corrections. This effort has yielded a 25-year time series of absolute gravity values, which we present and document for future studies, along with details on our reprocessing methodology. We assess the quality of this dataset and evaluate the extent to which the observed linear gravity trend agrees with vertical velocity estimates from the nearby GNSS station co-located with the tide gauge. The gravity data and metadata are made available via the French hydrographic agency Shom portal (https://doi.org/10.17183/DATASET_GRAVI_BREST; Lalancette et al., 2024)
Towards a better understanding of hydrogen embrittlement mechanisms in nickel-based alloys
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À propos des Hommes lents. Résister à la modernité (XVe-XXe siècle) [Paris, Flammarion, 2020]. Entretien avec Laurent Vidal.
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Tropical cyclone induced compound flooding in Madagascar: a coupled modeling approach
No full textInternational audienceCompound flooding occurs when multiple contributing factors, such as oceanic (storm surge, tide, and waves) and continental (heavy rainfall and river discharge), combine to exacerbate flood impacts. Tropical cyclone (TC)-induced compound flooding is a major hazard and societal concern, particularly in underdeveloped, highly exposed and vulnerable countries like Madagascar. Despite being repeatedly impacted by TCs, the region receives little attention from the scientific community, particularly in the modeling of TC-induced flooding and associated hazards. Here, we developed a high-resolution (30 m) compound flood model over Madagascar. The model is nested in a regional tide-surge-wave model purpose-built for this region. A dedicated topographic and bathymetric dataset was developed to accurately represent the whole land-ocean continuum. Using this framework, we modeled a recent intense TC Batsirai (2022) and assessed the resulting flooding. Our model shows good accuracy, achieving a hit ratio of 0.83 when matched with the remote sensing derived flood map. Our results demonstrate that the TC-induced flooding in this region is compound in nature, with flooding being significantly underestimated when continental factors (e.g. rainfall-runoff) are excluded. The impact of the ocean is primarily observed along the coastline, extending 5-10 km inland along the rivers. Additionally, we identified a non-linear interaction between oceanic and continental factors, which has important implications for the numerical modeling of such compound flood events. We estimate that at least 30% of the flooded area in our modeled domain comprises agricultural lands, highlighting the potential for significant societal impact. The developments and findings of this study pave the path forward for a national-scale compound flood modeling over Madagascar at a resolution suited for household-scale flood risk and impact assessments
Comfy’Pack : Assessing urban microclimate conditions and outdoor thermal comfort at pedestrian scale
No full textInternational audienceHow does urban space shape small-scale pedestrian thermal environments in the context of intense heat? To answer this research question, various mobile sensing techniques are proposed recently. However, the assessment of thermal environments at pedestrian level is complex because of physical urban heterogeneity, highly variable microclimate conditions and dynamically changing environmental factors. Therefore, high spatio-temporal resolution data is needed, which implies adapted sampling frequency, low sensor inertia and suitable data post processing methods.In this context, this work aims to present the portable meteorological measuring prototype, Comfy’PACK (Comfort Pedestrian Assessment of CitywalKs), to improve microclimate and pedestrian thermal comfort zoning in a dynamically changing physical urban environment. The wearable device consists of air temperature, humidity, solar radiation, wind speed and mean radiant temperature sensors, a GPS and a thermal camera. The experimental site is an identified future de-sealing site in the city of Nantes (France), aiming to improve local outdoor thermal comfort. After a detailed physical characterisation of pedestrian pathways on site, mobile measures are repeated over several days, investigating transitions between different thermal ambiances. In this work we present the prototypes’ performances and its first application to an urban case study, evaluating small scale microclimate and thermal comfort conditions for pedestrians in relation with urban heterogeneity. Thermal comfort indicators are calculated, questioning their pertinence within various thermal environmental contexts. Data mapping will allow establishing a more detailed microclimate comfort zone classification. As part of the French research project PERMEPOLIS the findings will support the methodological development of soil de-sealing strategies and identification of alternative cool walking path in the urban space
Sensing the Ocean through the Exquisite Corpse ArtScience method
No full textInternational audienceThe current interconnected crises of climate breakdown, biodiversity loss, and lack of justice and equity suggest that existing mainstream actions are inadequate and that different approaches are needed. Using a participatory action research approach, we aimed to demonstrate the potential of the asynchronous group-based "Exquisite Corpse" art process to catalyze meaningful relationships within an interdisciplinary group of ocean ArtScience practitioners. We conducted two action cycles and iterations of this process and a final action cycle of collective meaning-making. The first iteration took place in Fall 2021 with 7 participants focused on the topic of "ocean hypoxia"; the second focused on "extreme ocean events" with 10 participants in Spring 2022. The third action cycle in Spring 2023 resulted in the themes of "curiosity and connecting with people in a safe(r) space," "semi-ambiguous seed as a catalyst," "space for experimentation and creation," "sharing findings and experiences," "collective creation of connected artworks," "finding commons and common ground(s)," "giving, receiving and opening," "developing relationships," and "boundaries navigating fluidity." These themes describe the benefits that can arise from the Exquisite Corpse process on both individual and community levels of practice that could be extrapolated more widely and illustrate the potential contributions of ocean ArtScience on a systemic level. On an individual level, participants gained new scientific, artistic or personal insights, expanded their practices and deeply connected with other participants. At the community level, we argue that participatory exercises like the Exquisite Corpse process can increase relational trust, generating community-wide benefits. Additionally, activating pluralistic perspectives can help communities create more welcoming spaces for diverse participants. These emerging relationships have strengthened this budding community of practice, with further projects and opportunities growing from the endeavor. Our project also highlights how ArtScience approaches can help meet the challenges of the UN Decade of Ocean Science for Sustainable Development.</div
Analyse de l'efficacité énergétique d'applications basées sur des microservices
No full textThe environmental footprint of digital technologies has become a major concern, driven by the rapid growth of digital services and the increasing energy consumption of distributed infrastructures across the Cloud–Fog–Edge continuum. Modern applications such as social networks, streaming platforms, and messaging services rely increasingly on a microservice-based architecture. This model, which breaks down applications into small, independent services communicating over the Internet, enhances scalability and eases maintenance. However, it also intensifies network usage by multiplying data exchanges, often across long distances between servers. In this context, this thesis focuses on rethinking microservice placement across the Cloud–Fog–Edge continuum, aiming to reconcile application performance with energy efficiency. Optimizing their distribution within these distributed infrastructures is a key lever for reducing energy costs associated with inter- and intra-node communication, while still ensuring optimal service quality. Indeed, a poorly optimized placement can increase data travel distances, response times, and overall energy consumption. Conversely, an effective placement strategy can reduce long-distance communication, better leverage available resources, and ultimately lower the carbon footprint of digital services. Our approach uses a graph-based modeling of the placement problem, which serves as a foundation for proposing several placement strategies. This work leads to three main contributions. First, an in-depth review of the state of the art on service placement, including a classification of existing approaches, a critical analysis of their objectives (latency, cost, energy, etc.), and the identification of current gaps, particularly regarding energy-aware optimization. The second contribution introduces a global energy-efficient placement heuristic, grounded in community detection within microservice graphs. This method aims to group tightly connected services on nearby nodes, thereby minimizing communication distances and associated energy consumption. The third contribution presents a user-centric model capable of dynamically adapting placement based on demand, through a controlled replication and mutualization mechanism for microservices. These studies have provided deeper insights into the complex interactions between placement choices, microservice communication patterns, and energy constraints. In particular, we analyzed how network topology, user proximity, and functional dependencies between services influence overall system performance. To support this, we proposed a simple yet extensible model to better represent the complex impact of placement decisions on energy usage in distributed environments. This research enabled us to explore various trade-offs between performance, energy consumption, and resource allocation, progressively integrating real-world parameters such as user location and infrastructure constraints. The originality of our approach lies in its interdisciplinary nature, at the intersection of computer science, combinatorial optimization, communication networks, and ecological transition. It provides actionable solutions for more responsible deployment of digital services, taking into account both user needs and technical and environmental considerations.L’empreinte environnementale du numérique est devenue une préoccupation centrale, alimentée par l’essor rapide des usages numériques et la consommation énergétique croissante des infrastructures distribuées du continuum Cloud–Fog–Edge. Les applications modernes, telles que les réseaux sociaux, plateformes de streaming et services de messagerie, reposent de plus en plus sur une architecture microservices. Ce modèle, basé sur la division d’une application en petits services indépendants communiquant via Internet, favorise la scalabilité et simplifie la maintenance. Toutefois, il accroît aussi la sollicitation du réseau, en multipliant les échanges de données, parfois sur de longues distances entre serveurs. Dans ce contexte, cette thèse s’attache à repenser le placement des microservices dans le continuum Cloud–Fog–Edge, avec l’objectif de concilier performance applicative et sobriété énergétique. Optimiser leur répartition dans ces infrastructures distribuées devient un levier essentiel pour limiter les coûts énergétiques liés aux communications inter- et intra-nœuds, tout en garantissant une qualité de service optimale. En effet, une disposition inadaptée des services peut allonger les trajets des données, accroître les temps de réponse et engendrer une consommation énergétique inutilement élevée. À l’inverse, une stratégie de placement efficace permet de réduire les échanges longue distance, de mieux exploiter les ressources disponibles et, in fine, de diminuer l’empreinte carbone des communications. Notre démarche s’appuie sur une modélisation par graphes du problème, que nous avons exploitée pour proposer plusieurs stratégies de placement. Trois contributions principales en découlent. La première est une revue approfondie de l’état de l’art sur le problème de placement de services, incluant une classification des approches, une analyse critique des objectifs visés (latence, coût, énergie, etc.), ainsi qu’une identification des lacunes actuelles, notamment en matière d’optimisation énergétique. La seconde contribution consiste en une heuristique globale de placement écoénergétique, fondée sur la détection de communautés dans les graphes de microservices. Cette approche vise à regrouper les services fortement interconnectés sur des nœuds proches, réduisant les distances de communication et, par conséquent, l’énergie consommée. La dernière contribution introduit un modèle centré sur l’utilisateur, capable d’adapter dynamiquement le placement en fonction de la demande, grâce à un mécanisme de duplication contrôlée et de mutualisation des microservices. Ces travaux nous ont permis de mieux comprendre les interactions complexes entre les choix de placement, les structures de communication des microservices et les contraintes énergétiques. Nous avons notamment analysé l’influence de la structure du réseau, de la proximité entre les utilisateurs et des dépendances fonctionnelles entre services, sur les performances globales du système. À ce titre, nous avons proposé un modèle simple, mais extensible, pour mieux représenter la complexité de l’impact énergétique du placement dans un environnement distribué. Ces travaux ont été l’occasion d’évaluer différents compromis entre performances, consommation énergétique et allocation des ressources, en intégrant progressivement des paramètres réels comme la localisation des utilisateurs ou les contraintes d’infrastructure. L’originalité de notre approche réside dans sa dimension interdisciplinaire, à la croisée de l’informatique, de l’optimisation combinatoire, des réseaux de communication et de la transition écologique. Elle permet de proposer des solutions concrètes pour un déploiement plus responsable des services numériques, en tenant compte à la fois des utilisateurs et des aspects techniques et environnementaux
Stratégies d’hivernage et parcours de reproduction du Courlis cendré : Sélection de l’habitat et enjeux de conservation en Europe
No full textThe Eurasian curlew (Numenius arquata) is a migratory shorebird whose range extends from the Urals in Russia to the North-west of Africa and western Europe. The species typically spends the winter on the Atlantic and North Sea coasts, before to reach agricultural landscapes in temperate and boreal regions for breeding. Given the significant declines of the species across Europe, where breeds the entire subspecies N. a. arquata, the intensification of agricultural practices and the current degradation of coastal habitats through climate change and human activities raises severe conservation concerns. In order to ensure sufficient and suitable habitats and thus maintain the populations, a thorough understanding of the spatial and temporal ecology of the species during its entire annual cycle is urgently required. Hence, this thesis aims (1) to define the habitats used by the species during its wintering and breeding seasons in Europe, (2) to understand why birds select some habitats for feeding, nesting or resting and (3) to highlight some current and future threats that birds face or will face using these habitats for the purpose of better medium-term conservation of the species. We benefited from the GPS tracking data of more than 350 Eurasian curlews obtained through multiple research and conservation programs in Europe, allowing us to estimate the large-scale distribution of the species, its annual phenology and the coastal and agricultural habitats it depends to survive and successfully breed. In parallel, field monitoring and invertebrate sampling were carried out at nine breeding sites in France, whose populations range from only a few pairs to several hundred individuals, to better understand the contrasted dynamics observed.Overall, the tracked curlews wintered from Morocco to Scotland, using mainly intertidal and estuarine mudflats for feeding and saltmarshes for both feeding and resting. Despite different environments, the large batches of tagged individuals wintering in the Pertuis Charentais (France) and the Wadden Sea (Germany) displayed similar strategies of space use. In particular, birds exhibited an exploratory behaviour the first months of the season, spending a greater proportion of time on mudflat and selecting distinct foraging areas compared to later in the season, e.g., more seagrass beds. These individuals leaved their wintering site in March-April to reach northern breeding grounds in Russia and Finland, where most of the subspecies breeds. The northernmost individuals settled mainly in bogs, where they exhibited a higher hatching success than southern individuals breeding in exploited or abandoned farmlands. In France, breeders arrived earlier, i.e., in early February, because they did not need to match their arrival with snowmelt as in northern individuals. The two major populations nested and fed essentially in floodplain grasslands, which had the greatest availability of potential prey for chicks. Conversely, the smallest and drastically declining populations nested in moorlands, where the abundance and biomass of prey were comparatively very low, adults therefore selecting surrounding grasslands and crops to feed. Both partners shared the parental care, although males tended to have a longer incubation time than females, typically incubating overnight while females fed or rested with congeners. Hence, the results obtained underline the most suitable coastal and inland habitats to be preserved as a priority at the level of Europe, with a focus in France where the species has been little studied. Despite the inter-individual variability in space use, the high site fidelity shown by this near-threatened species raises concerns about its capacity to respond to environmental and anthropogenic modifications in coastal and agricultural landscapes.Le Courlis cendré (Numenius arquata) est un limicole migrateur dont l’aire de répartition s’étend de l’Oural en Russie au Nord-ouest de l’Afrique et de l’Europe. L’espèce hiverne généralement sur les côtes ouest de l’Europe, avant de partir se reproduire dans des paysages agricoles des régions tempérées et boréales. Étant donné les déclins importants de l’espèce à travers l’Europe, où niche la totalité de la sous-espèce N. a. arquata, l’intensification des pratiques agricoles et la dégradation actuelle des habitats côtiers soulèvent de graves préoccupations en termes de conservation. Afin d’assurer des habitats suffisants et durables et ainsi maintenir les populations, une meilleure compréhension de l’écologie spatiale et temporelle de l’espèce durant l’entièreté de son cycle annuel est requise. Cette thèse a donc pour but de (1) définir les habitats utilisés par l’espèce durant les périodes d’hivernage et de reproduction en Europe, (2) de comprendre pourquoi les oiseaux sélectionnent certains habitats pour s’alimenter, nicher ou se reposer et (3) pour mettre en évidence certaines menaces actuelles et futures dont font ou feront face les oiseaux en utilisant ces habitats, dans le but d’une meilleure conservation de l’espèce à moyen-terme. Nous bénéficions des données de suivi GPS de plus de 350 Courlis cendrés obtenues via plusieurs programmes en Europe, nous permettant d’estimer la distribution de l’espèce, sa phénologie et les habitats dont elle dépend pour survivre et se reproduire. En parallèle, un suivi sur le terrain et un échantillonnage d’invertébrés ont été réalisés au niveau de neuf sites de reproduction en France, dont les populations varient de quelques couples à plusieurs centaines d’individus, afin de mieux comprendre ces dynamiques contrastées.Dans l’ensemble, les courlis équipés hivernaient du Maroc à l’Ecosse, utilisant principalement les vasières intertidales pour s’alimenter et les prés salés pour s’alimenter et se reposer. Malgré des environnements différents, les gros noyaux de courlis hivernants équipés dans les Pertuis Charentais (France) et en Mer des Wadden (Allemagne) témoignaient de stratégies d’utilisation de l’espace similaires. Les oiseaux présentaient notamment un comportement exploratoire les premiers mois de l’hiver, passant plus de temps sur la vasière et sélectionnant des aires d’alimentation particulières, e.g. herbiers. Ces mêmes individus quittaient leur site d’hivernage en mars-avril pour rejoindre des aires de reproduction en Russie et en Finlande. Les individus nichaient principalement dans les tourbières au nord, présentant alors un meilleur succès à l’éclosion que les individus au sud nichant dans des terres agricoles exploitées ou abandonnées. En France, les couples arrivaient plus tard, i.e., dès février, pouvant s’affranchir de la fonte nivale. Les deux populations majeures nichaient et s’alimentaient principalement dans des prairies humides arborant une plus grande disponibilité en proies potentielles pour les poussins. A l’inverse, les plus petites populations en fort déclin nichaient dans des landes, où l’abondance et la biomasse en proies étaient en comparatif très faibles, les adultes sélectionnant alors les prairies et les cultures environnantes pour s’alimenter. Les partenaires partageaient les soins parentaux, bien que les mâles aient tendance à plus incuber que les femelles, restant généralement au nid toute la nuit tandis que ces dernières s’alimentaient ou rejoignaient un dortoir. Ainsi, les résultats obtenus mettent en évidence les habitats côtiers et intérieurs à préserver en priorité au niveau de l’Europe, avec un accent sur la France où l’espèce n’a été que très peu étudiée. Malgré la variabilité interindividuelle dans l’utilisation de l’espace, la grande fidélité au site manifestée par cette espèce quasi-menacée soulève des préoccupations quant à sa capacité à répondre aux modifications environnementales et anthropiques au sein des paysages littoraux et agricoles
Elephant seal dive behaviour responds consistently to changes in foraging success regardless of sex or ocean habitat
No full textInternational audienceUnderstanding how air-breathing diving animals moderate their dive behaviour when foraging successfully is foundational in the study of their foraging ecology. Yet, this fundamental relationship remains unresolved with previous research pointing to inconsistent relationships, differing nominally according to sex, habitat type and scale. Empirically testing the relationships between dive effort responses and foraging success is further hampered because of challenges obtaining concurrent measures of behavioural responses and foraging success at sea. We compiled a multi-decadal dive dataset from 609 southern elephant seals, including their dive responses (transit rate, and relative dive and surface recovery duration) and buoyancy-changes in which provide an indirect measure of body condition change and foraging success. Using this dataset, we tested how seal dive behaviour alters when foraging remotely at sea. We found that as foraging success increased, seals increased transit (ascent, descent) rates and decreased relative dive durations for a given depth, with no response in surface recovery. Our results were consistent across sexes and foraging habitats, and account for the general effects of buoyancy on dive behaviour. The homogeneity of these findings suggests that there is a general functional response in which elephant seals perform, on average, shorter, steeper dives during periods of successful foraging. Importantly, we can align these results with predictions from the marginal value theorem (MVT), that a forager should remain in a patch only until gains drop below the neighbourhood mean. Our findings have broad-based implications for how ecologists interpret dive responses of wild marine animals, demonstrating the value of seeking independent in situ information on foraging success.</div
La nature à ses justes valeurs
No full textÉdition bilingue anglais/françaisInternational audiencePartout dans le monde, l’effondrement de la biodiversité et la dégradation des écosystèmes nous confrontent à des défis majeurs. Pourtant, si les alertes scientifiques se multiplient, les réponses apportées restent souvent timides ou ambivalentes. Pourquoi cette inertie, voire, ces retours en arrière ? Ces situations paradoxales révèlent que la « crise écologique » touche aussi à nos manières d’être en relation avec la nature, c’est-à-dire aux valeurs que nous mobilisons pour la défendre ou la transformer. Ni figées ni universelles, ces valeurs sont plurielles, susceptibles d’entrer en tension les unes avec les autres, selon les intérêts qu’elles représentent.Il est donc crucial de saisir et de prendre en compte, à chaque arbitrage politique ou économique impactant la nature, la diversité des valeurs en jeu. Ce manifeste nous y invite en proposant un nouveau cadre de réflexion et d’action à même de nous permettre d’engager les transitions écologiques et les transformations sociales nécessaires à un avenir juste et durable