HAL-Université de Bretagne Occidentale
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Ageing of polyethylene terephthalate (PET) fibres in a marine environment: understanding changes in mechanical behaviour
No full textInternational audiencePolyethylene terephthalate (PET) fibres are widely used in marine environments, particularly in mooring and structural textiles, where they are exposed to long-term seawater immersion (about 25 years). In this study, PET fibres were immersed in renewed natural seawater at temperatures from 60 to 90°C in order to accelerate ageing for periods up to one year. Tensile properties were evaluated after ageing, and physico-chemical analyses were carried out to investigate microstructural changes. A significant loss of mechanical properties at break was observed, linked to hydrolytic chain scission and a strong decrease in number-average molar mass. Crystallinity increased slightly due to chemi-crystallisation. Time–temperature superposition based on molar mass decrease provided activation energy consistent with literature values. Results suggest that, even in fibre form and in marine conditions, PET undergoes hydrolysis-driven degradation, confirming that accelerated testing is essential for lifetime assessment in marine applications
Rares ou invisibles ? Les crabes durant la Préhistoire
No full textInternational audiencePrehistoric shell middens have been studied since the 19th century in archaeology along the European Atlantic façade. These sites correspond to refuses of daily activities of human populations living near the sea. Amongst these, food remains are numerous and correspond to the exploitation of the marine environments, such as seashells. In order to understand the place of crustaceans in the daily life of past populations, this article reviews crab remains found in prehistoric shell middens in Atlantic Europe, from the Palaeolithic to the Neolithic. Data from the Mesolithic and Neolithic periods come from the online European Atlantic Prehistoric Shell-middens database (EAPSM). In addition, a synthesis of previous publications on crab remains from Palaeolithic sites in Atlantic Europe is provided. The main objective is to assess the presence and role of crab in the diet of prehistoric populations from the Palaeolithic to the Neolithic. These topics will be addressed by examining the impact of the excavation methods used to detect them and also the preservation of coastal sites linked to variations of the sea level over time. Analysis of published data shows a very uneven representation of sites across periods and spaces, with for example a high concentration in the Mesolithic and in southern regions (Iberian Peninsula). This first result can be explained by a lower level of the sea during the Palaeolithic. Except for the high cliffs of Spain or Portugal, Palaeolithic shell middens are not preserved if they ever existed. For all periods, crab remains are generally underrepresented. This result seems to be largely due both to their fragmentary state and the lack of systematic identification protocols. These gaps limit our vision of how human populations exploited crab. The article recommends a reassessment of archaeological material when sieved sediment existed and the implementation of standardized methods on new ones for the study of crabs in coastal subsistence economies during prehistory.Les amas coquilliers préhistoriques ont été étudiés depuis le XIXe siècle en archéologie le long de la façade atlantique européenne. Ces sites correspondent aux déchets des activités quotidiennes des populations humaines vivant près de la mer. Parmi ceux-ci, les restes alimentaires sont nombreux et correspondent à l'exploitation des environnements marins, tels que les coquillages.Afin de comprendre la place des crustacés dans la vie quotidienne des populations passées, cet article examine les restes de crabes trouvés dans les amas coquilliers préhistoriques en Europe atlantique, du Paléolithique au Néolithique. Les données des périodes mésolithique et néolithique proviennent de la base de données en ligne European Atlantic Prehistoric Shell-middens (EAPSM). De plus, une synthèse des publications précédentes sur les restes de crabes provenant de sites paléolithiques en Europe atlantique est fournie.L'objectif principal est d'évaluer la présence et le rôle du crabe dans l'alimentation des populations préhistoriques du Paléolithique au Néolithique. Ces sujets seront abordés en examinant l'impact des méthodes de fouille utilisées pour les détecter ainsi que la préservation des sites côtiers liés aux variations du niveau marin au cours du temps.L'analyse des données publiées montre une représentation très inégale des sites à travers les périodes et les espaces, avec par exemple une forte concentration au Mésolithique et dans les régions méridionales (Péninsule Ibérique). Ce premier résultat peut s'expliquer par un niveau de la mer plus bas pendant le Paléolithique. À l'exception des hautes falaises d'Espagne ou du Portugal, les amas coquilliers paléolithiques ne sont pas conservés s'ils ont jamais existé. Pour toutes les périodes, les restes de crabes sont généralement sous-représentés. Ce résultat semble être largement dû à la fois à leur état fragmentaire et à l'absence de protocoles d'identification systématiques. Ces lacunes limitent notre vision de la manière dont les populations humaines exploitaient les crabes. L'article recommande une réévaluation du matériel archéologique lorsque des sédiments tamisés existaient et la mise en œuvre de méthodes standardisées sur de nouveaux pour l'étude des crabes dans les économies de subsistance côtières pendant la préhistoire
L'activité d'un agent public comme l'utilisation du matériel mis à sa disposition doivent être consacrées exclusivement à l'intérêt du service
No full textInternational audienceNote sous CAA Douai, 18 juin 2025, no 24DA01754, Cne d'Aulnoy-lez-Valencienne
Management Implications of Mesopelagic Forage Fisheries for Bigeye Tuna Stocks
No full textInternational audienceMany large marine predators forage on mesopelagic fish stocks, including commercially valuable tunas. The mesopelagic is under increasing interest for commercial exploitation, given its large biomass with potential to supply fishmeal for aquaculture feed or fish oil. However, the implications of large-scale mesopelagic fisheries on tunas and other predators may be substantial. Here, we adapt a bioeconomic model with a new predator-prey dynamic to evaluate the effects of potential commercial-scale mesopelagic fisheries on bigeye tuna (Thunnus obesus). Specifically, we use a novel diet share model term and the latest stable isotope food web data to operationalize predator-prey interactions. Model results highlight the importance of accounting for the predator-prey interactions in management of mesopelagic fisheries and demonstrate the sensitivity of equilibrium economic and ecological conditions for the tuna stock under different price and cost scenarios. Overall, this work suggests that a new mesopelagic fishery could be economically viable in and of itself, but may have significant negative impacts on existing tuna fisheries by reducing forage availability
The Politics of Counting Homelessness: The Case of Ireland
No full textInternational audienceHomelessness remains a critical social issue in Ireland, yet its true scale is systematically obscured by definitional limitations, methodological inconsistencies, and political interference in data collection. While official statistics reported 16,058 individuals relying on emergency accommodation as of July 2025 (a rise of +244% since July 2015), this figure excludes substantial populations: rough sleepers, domestic violence survivors, asylum seekers, and those experiencing hidden homelessness through enforced parental co-residence. This article examines the politics of homelessness enumeration through a critical analysis of seven data sources, policy documents spanning 2014–2025 and stakeholder interviews. The study reveals how Ireland’s measurement system exemplifies the political life of numbers. The analysis exposes five interconnected dimensions of measurement failure: fragmentation of sources and measurement approaches, methodological inconsistencies that undermine longitudinal analysis, systematic undercounting that renders substantial populations invisible, documented political manipulation and data integrity concerns, and structural barriers that impede comprehensive data collection and analysis. The findings demonstrate how apparently technical decisions about data collection and analysis become sites of political contestation. The research reveals the measurement politics in contemporary welfare states, demonstrating the need for inclusive frameworks, integrated systems, and transparent practices that prioritize social justice over administrative convenience
Firearm Violence in New York City, 2006-2024: A Time Series Analysis
No full textThis study analyzes 29,744 shooting incidents in New York City from 2006 to 2024 to identify temporal and spatial patterns. The temporal evolution reveals three distinct regimes: a sustained decline from 2006 to 2019, a dramatic 91.2% surge in 2020 coinciding with the COVID-19 pandemic, and post-2022 stabilization. Strong seasonal patterns emerge with summer months experiencing 2.3 times more incidents than winter months. Spatially, the top five precincts account for 22.7% of incidents despite representing only 7% of police precincts. Demographically, over 90% of both perpetrators and victims are male, with 81.7% of victims aged 18-44 and 71.9% identified as Black. Socioeconomic analysis reveals strong correlations between poverty rates and shooting incidents. Time series forecasting using SARIMA models captures temporal autocorrelation with reasonable out-of-sample accuracy, providing insights for future spatio-temporal modeling efforts to predict urban gun violence dynamics.</div
What if computers forget?
No full textInternational audienceComputing systems are designed to store data indefinitely, in contrast to human cognition where forgetting is an important and dynamic process. At scale, data forgetting could emerge as a disruptive sustainability-oriented optimization, enabling system-level efficiency gains while structurally reducing energy consumption and carbon footprint, rather than shifting impacts through rebound effects. This talk explores data forgetting as a system-level principle in which forgetting would be the default behavior. By relying on building mental models of data, progressive data degradation techniques, and data recovery mechanisms, data forgetting enables new optimization opportunities, improved storage efficiency, and better support for sustainability
L’impact économique de la crise sanitaire liée au Covid 19 sur les productions des pêches maritimes françaises en halles à marée.
No full textThe health crisis linked to Covid-19 has changed the situation of the seafish industry through market disruptions, both on the supply and demand sides. The main issue concerns the measurement of the impact of these disturbances on the fish auction markets considering the regional and local dimension. Fish auction markets form a regional system along each coastline. On a local scale, they are differentiated by the specialisation of the products offered on the fisrt market. The questions opened up by the measurement of the impacts of the health crisis concern the adaptation behaviour of fishermen on a regional and territorial scale. It is through the complementary nature of marketing channels that fishers must find solutions to future shocks.La crise sanitaire liée au Covid-19 a modifié la conjoncture de l’industrie des pêches maritimes par les perturbations des marchés, tant sur l’offre que sur la demande. La problématique de l’article porte sur la mesure de l’impact de ces perturbations dans les halles à marée tenant compte de la dimension régionale et locale. Les halles à marées s’inscrivent dans un ensemble régional par façade maritime. A l’échelle locale, elles se différencient par la spécialisation des produits mis en vente. Les questions ouvertes par la mesure des impacts de la crise sanitaire touchent aux comportements d’adaptation des pêcheurs à l’échelle régionale et territoriale. C’est par une complémentarité des circuits de commercialisation que les acteurs de la pêche doivent trouver des solutions aux chocs futurs
Remote Sensing Data Assimilation With a Chained Hydrologic‐Hydraulic Model for Flood Forecasting
No full textInternational audienceEffective flood risk management requires reliable forecasts with extended lead times to enable the implementation of cost‐effective and timely measures. In this study, we present a chained hydrologic‐hydraulic modeling framework designed for effective near‐real‐time flood forecasting. The system integrates runoff predictions from a large‐scale hydrologic model (ISBA‐CTRIP) as inputs into high‐resolution, local hydrodynamic models (TELEMAC‐2D) to forecast water levels and flood extents. To improve the forecast accuracy, an Ensemble Kalman Filter is employed to reduce uncertainties in hydrological forcing and friction parameters by jointly assimilating in situ water level measurements and satellite‐derived flood maps. Such a data assimilation framework operates in a real‐time forecasting configuration, consisting of a reanalysis phase having an assimilation window up to the current time, followed by a forecast phase from the current time to the expected lead time. Three forecasting strategies were evaluated: (a) using CTRIP‐predicted runoff for both reanalysis and forecast phases, (b) using observed discharge for reanalysis and CTRIP runoff for forecast, and (c) using observed discharge for reanalysis and keeping a constant discharge during the forecast. Results show that using observed discharge during reanalysis combined with CTRIP‐predicted runoff for forecasting yields the most consistent performance. However, for all three strategies, forecast accuracy declines with longer lead times, especially when errors in the CTRIP forcings are non‐stationary. This work highlights the potential for hydrologic model, despite their inherent imperfections, to serve as effective inputs for local hydraulic models, enabling near‐real‐time flood forecasting through the assimilation of in situ and remote sensing data
Analog-based ensembles to characterize turbulent dynamics from observed data
No full textInternational audienceWe present a methodology for the study of the dispersion of trajectories of stochastic processes in reconstructed phase spaces from observed data. The methodology allows to find ensembles of analog states, i.e. states that are close in the phase space. Once these states are found, we focus on the characterisation of their dispersion in function of 1) the time and 2) their initial separation. We study an experimental turbulent velocity measurement and two scale-invariant stochastic processes: a regularized fractional Brownian motion and a regularized multifractal random walk. Both stochastic processes are synthesized to have the same covariance structure as the experimental turbulent velocity, but only the regularized multifractal random walk mimics the intermittency of turbulent velocity. We illustrate that while the covariance structure of the processes governs the time dependence of the dispersion of the analog states, the intermittency phenomenon is responsible for the impact of the initial separation of the analogs on their dispersion