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Determination of discontinuous diffusion coefficients for the heat equation on a tree-shaped network
No full textInternational audienceIn this paper, we study the heat equation on a tree-shaped network with a piecewise regular diffusion coefficient. By developing new Carleman estimates, we establish stability results for the identification of the diffusion coefficient. These stability estimates are derived using either internal measurements or boundary observations, offering robust insights into the inverse problem for this class of equations
Corpus de synthèses bibliographiques : Le drone appliqué à la conservation des espèces et à l’inventaire des oiseaux marins
No full textSeabirds are fascinating not only for their adaptation to the marine environment and their diversity but also for the symbolism associated with them. In many cultures, seabirds represent freedom and travel. In our modern societies, they are also considered indicators of the health of the ecosystems they inhabit.In addition to infectious diseases, colonies are subject to anthropogenic pressures—such as disturbance, pollution, and degradation of breeding sites—which can impact their development and long-term survival. As part of monitoring efforts, various protocols are implemented and adapted based on the species and the nesting context. In recent years, protocols based on drone usage have been increasingly employed by various stakeholders.While this method is promising, there is now a clear need for a standardized framework that stakeholders can rely on to conduct efficient (both economically and temporally), high-quality, and ethical monitoring. It is within this context that the TRIDA project was launched. This project was born from a collaboration between non-profit organizations (GIS Oiseaux Marins, GON - Groupement Ornithologique et Naturaliste du Nord Pas-de-Calais) and private or institutional partners, including the LISIC (a research laboratory specializing in computer science and signal/image processing) and the French Biodiversity Agency (OFB).Les oiseaux marins ou oiseaux de mer fascinent tant par leur adaptation au milieu marin, leur diversité mais aussi par la symbolique qui leur est associée. Dans de nombreuses cultures, les oiseaux de mer sont les symboles de liberté et du voyage. Dans nos sociétés, ils peuvent être également considérés comme le reflet de la santé des écosystèmes qu’ils fréquentent. Outre les maladies infectieuses, les colonies sont également soumises à des pressions anthropiques (dérangement, pollution, dégradation des sites de reproduction) pouvant avoir des effets sur leur développement et leur persistance. Dans le cadre de cette surveillance, différents protocoles sont mis en place et adaptés selon les espèces et le contexte de nidification. Ces dernières années, des protocoles basés sur l’utilisation de drone ont été de plus en plus employés par différents acteurs. Si cette méthode est intéressante, nous ressentons aujourd’hui le besoin de mettre à disposition un socle sur lesquels ces acteurs pourraient s’appuyer, afin de réaliser des suivis efficaces (économiquement et temporellement), qualitatifs et éthiques. C’est dans ce contexte que le projet TRIDA a pris son essor. Ce projet est né de la collaboration entre des structures associatives (Groupement d’Intérêt Scientifique Oiseaux Marins, Groupement Ornithologique et Naturaliste du Nord Pas-de-Calais) et privées (Laboratoire de recherche spécialisé en informatique et dans le traitement du signal et de l’image (LISIC), et de l’Office Français de la Biodiversité
Typologie des usages du numérique dans les loisirs sportifs de nature
No full textInternational audienceL’entrée de nos sociétés dans une ère numérique a eu des effets sur différentes facettes de nos quotidiens (Sciadas, 2006), y compris dans les pratiques récréatives de nature (Mao et Obin, 2018), qu’elles soient sportives, de loisir et/ou touristiques (Axe 4) . Cela souligne plusieurs enjeux, que ce soit les effets de la numérisation sur les activités comme les usages potentiels des données produites par le recours aux objets connectés pour ces activités. Pour autant, il est préalablement nécessaire de mieux caractériser la nature de ce phénomène. En effet, l’utilisation du numérique dans les sports de nature semble étroitement liée à l’activité pratiquée : les concepteurs de produits et de services numériques développent des outils et applications spécifiquement adaptées à certaines activités ; les pratiquants ont tendance à faire communauté autour de leur pratique mais aussi autour d’un produit ou d’un service ; et une étude visant les sportifs de nature dans leur ensemble a révélé l’existence de liens entre les motifs et formes d’usage du numérique avec le sport de nature pratiqué (Lesné et al., 2024). Cependant, d’autres travaux ont mis en évidence des relations entre les formes d’utilisation des outils numériques dans les sports de nature et les caractéristiques des individus, telles que la fréquence de pratique, le type d’espace d’évolution, l’âge ou le genre (Ahtinen et al., 2008 ; Soulé et al., 2022 ; Vignal et al., 2022). Finalement, un travail a cherché à caractériser le recours au numérique et ses variations dans les sports de nature en général (Lesné et al., 2025), mais suivant une démarche exploratoire et à partir d’un échantillon restreint interrogé par entretiens. L’ambition de notre présentation est donc de proposer une nouvelle lecture de ce phénomène à partir d’un échantillon bien plus important.Une enquête par questionnaire diffusée en 2023 a permis de récolter les réponses de 2 721 sportifs de nature connectés renseignant 2 983 usages du numérique dans les sports de nature. Nous les analysons suivant une approche inductive « pragmatique » (Morgan, 2007) via une classification hiérarchique sur les composantes principales à partir d’une analyse des correspondances multiples. Nous identifions trois axes synthétiques de distinction dans l’échantillon, ces derniers se divisant en quatorze gradients thématiques, permettant de construire une typologique de six types d’usage du numérique dans les sports de nature. De plus, nous mettons en évidence des tendances significatives quant aux caractéristiques des individus liées à ces six types d’usage et, in fine, trois grandes tendances sociologiques : le lien entre l’engagement dans l’activité sportive de nature et l’engagement dans l’usage du numérique ; le lien entre l’univers sportif et culturel de l’activité pratiquée et la place accordée au numérique ; et l’effet des logiques de genre. Nous produisons ainsi une connaissance inédite du phénomène de la numérisation des sports de nature
Long-term changes in depth distribution and phenology of four North Atlantic plankton species
No full textInternational audiencePlankton are highly sensitive to climate change, and understanding their shifts in behaviour, physiology, phenology, and biogeography is important for anticipating changes in ecosystem services. This study used a recently developed ecological niche model to reanalyze data from the Continuous Plankton Recorder (CPR) survey using 8 environmental variables to build, for the first time, a CPR-based 4D data set (longitude × latitude × depth × day) of plankton abundance. First, we analyzed spatio-temporal changes in the abundance of 4 plankton species daily from 1958 to 2022: 2 diatoms ( Ephemera planamembranacea and Odontella sinensis ) and 2 calanoid copepods ( Calanus finmarchicus and C. helgolandicus ). We validated our new CPR-based 4D data set with existing in situ data and found that modeled spatio-temporal changes in abundance reproduced observations well. Then, we showed pronounced phenological and biogeographical shifts for the 4 species. Long-term latitudinal shifts in C. finmarchicus and E. planamembranacea were observed and correlated with the Atlantic subarctic gyre state, the North Atlantic Oscillation, and the Atlantic Multidecadal Oscillation. Our results also revealed a prominent positive influence of temperature on long-term changes in the abundance of E. planamembranacea , O. sinensis and C. helgolandicus , whereas they identified a negative influence of temperature on C. finmarchicus . Interestingly, our modeled data suggest a rise in the abundance of C. finmarchicus at greater depths during peak seasons, although this depth adjustment in response to changing conditions is unlikely to overcome the overall surface decline of the species
L’entrepreneuriat comme réalisation de l’imaginaire : l’exemple de la science-fiction institutionnelle
No full textInternational audienceEntrepreneurs have new creativity techniques to carry out their activities.Institutional science fiction (ISF) proposes to use science fiction to prototype and create performative strategic discourses. Thus, this article reflectson the imaginary dimension of management and entrepreneurship. To introduce this approach, an analysis of an anthology of ISF produced by Microsoftin 2015 is proposed, as well as a reflection on the notion of hyperreal entrepreneur,who like Elon Musk and Mark Zuckerberg, create science fiction. ISF produces a formof conservative utopianism, an oxymoron designating optimistic fictions justifying theexistence of the companies that create and finance them. If utopia is generally subversive, opposed to the dominant power, it can in the cases studied be put at the service of a techno-optimism source of innovation. Similarly, hyperreal entrepreneurs could findthemselves in the future in other sectors, realizing the many social and ecological utopias of science fiction.Les entrepreneurs disposent de nouvelles techniques de créativité pour mener à bien leur activité. La science-fiction institutionnelle (SFI) propose d’utiliser la science-fiction pour prototyper et créer des discours stratégiques performatifs. Ainsi, cet article réfléchit à la dimension imaginaire du management et de l’entrepreneuriat. Pour introduire cette approche, une analyse d’une anthologie de SFI produite par Microsoft en 2015 est proposée, ainsi qu’une réflexion sur la notion d’entrepreneur hyperréel, qui à l’instar d’Elon Musk et de Mark Zuckerberg, réalise la science-fiction. La SFI produit une forme d’utopisme conservateur, oxymore désignant des fictions optimistes justifiant l’existence des entreprises qui les créent et financent. Si l’utopie est généralement subversive, opposée au pouvoir dominant, elle peut dans les cas étudiés se mettre au service d’un techno-optimisme source d’innovation. De même, les entrepreneurs hyperréels pourraient se trouver à l’avenir dans d’autres secteurs en décidant de réaliser les nombreuses utopies sociales et écologiques de la science-fiction
High Electron Charge Carrier Mobility in the Nematic Phase of a Roof‐Shaped Nematogen with Optimum Molecular Biaxiality
No full textInternational audienceA roof‐shaped molecule forming exclusively a nematic liquid crystal phase is prepared based on a lead structure. The aspect ratio is designed to be almost optimum with respect to the molecular biaxiality. A broad nematic phase over more than 100 K is observed in which a weak, transient biaxial alignment can be induced under specific thermal and mechanical conditions. In sandwich cells, TOF electron mobilities of up to 2.2 × 10 −2 cm 2 V −1 s −1 are obtained, which are the highest found to date for nematic materials. The latter is attributed to the special self‐assembly of the biaxial, roof‐shaped mesogens, which favors the contacts between the aromatic units, which is confirmed by X‐ray scattering, modeling, and X‐ray scattering simulation. The material is responsive to the applied electric field, which results in the anomalous negative field dependence of the charge carrier mobilities
A novel multi-frequency ACVP adapted to dense sediment-laden openchannel flow studies: towards turbulence-resolved two-phase fluidparticle measurements
No full textInternational audienceSediment transport in rivers and coastal environments plays a major role in shaping aquatic habitats, regulating nutrient and pollutant fluxes, and maintaining the long-term stability of estuarine and deltaic systems. Accurate prediction of sediment fluxes, especially under climatic energetic flow conditions, requires experimental datasets for numerical model calibration and validation. However, the majority of existing sediment transport rate models rely on single-phase approaches assuming that particles follow the streamwise fluid velocity (except for the vertical settling velocity). Such approaches limit our understanding of key two-phase flow interactions—such as effects due to particle lag velocity on fluid turbulence modulation as discussed by Finn and Li (2016).To overcome these measurement limitations, this study presents the development and validation of a multi-frequency Acoustic Concentration and Velocity Profiler (ACVP), designed to simultaneously measure co-located velocity and concentration profiles at high spatial resolution (Hurther et al., 2011; Fromant et al, 2018). This instrument, based on the integration of ADVP and ABS technologies, operates at multiple ultrasound frequencies for potential discrimination between fluid and sediment induced scattering as originally proposed by Wilson and Hay (2015).An initial experimental campaign was conducted in the open-channel flume at LEGI (Grenoble), using microbubbles of air as fluid tracers in highly turbulent boundary layer open-channel flows over a range of Reynolds numbers (10⁴–10⁵) covering different dominant scattering regimes. Optical measurements (PIV/PTV) were used for comparison. Results show that ACVP-derived velocity profiles exhibit log-law behavior and agree well with PIV data for a given ultrasound frequency. Systematic discrepancies between measured fluid velocity at different acoustic frequencies were observed, with lower (higher) frequencies yielding higher (lower) mean streamwise velocities. An in-depth analysis of these differences is presented herein considering frequency-dependent -instrumentation effects (sensor directivity, sample-volume, and spectral pulse-broadening), turbulence-driven scattering effects induced by additive turbulent microstructures (TMS).To investigate these effects, concentration profiles were computed using an implicit inversion method based on acoustic backscatter intensity and calibrated against independent measurements provided by a laser diffraction granulometer (LISST). Deviations of up to a factor of two were found between ACVP and LISST measurements, suggesting that existing inversion models do not fully capture all scattering contributions—particularly those from TMS, as previously shown by Shen & Lemmin (1997).Additionally, to address velocity inconsistencies as a function of ultrasound frequency, geometric considerations of the ACVP measurement volume were revisited. Comparisons with a point-particle Lagrangian echo simulation model proposed by Fromant et al. (2024), demonstrate the need to include transducer’s beam directivities and sensor’s frequency responses for correction of systematic errors on both the geometrical transformation matrix and the Doppler frequencies. By integrating these corrections, ACVP provides reliable multifrequency velocity and particle concentration profiles in highly turbulent open-channel flows.Next steps will be devoted to sediment-laden open channel flow experiments with this novel multi-frequency ACVP technology for potential turbulence-resolved two-phase fluid-sediment velocity and sediment flux estimates
Radiolarian and Phaeodarian high-rank assemblage change through time in the Scotia Sea: A paleo-genomics approach (IODP Exp. 382)
No full textInternational audienceRadiolaria and Phaeodaria are single-celled eukaryotic zooplankton that inhabit diverse marine environments. While the sedimentary fossil record reveals their ancient origins and morphological diversity, recent advancements in metagenomics and sedimentary ancient DNA (sedaDNA) techniques have highlighted the significant contributions of rarely preserved taxa (e.g., those that are only lightly silicified or soft-bodied) to marine biodiversity and the carbon cycle. Using a paleo-genomic approach, we produced a sedaDNA-based time series of the Radiolarian and Phaeodarian community from the Scotia Sea covering the last 500 kyr. We compared the use of two reference databases, one Radiolarian-and Phaeodarian-specific (RPD) and one more comprehensive eukaryote database (PR 2 ), to assess the validity of a small, taxa-specific database. We determined that the two databases produced comparable results, showing that the overall assemblage changes at the glacial-interglacial scale were similar. At the Class level, Radiolarian and Phaeodarian assemblages appear to have experienced compositional changes during termination events and warm Interglacial periods. This study produced the first Radiolarian-and Phaeodarian-specific reference database. We showed that the Class-level changes that occurred over the last 500 kyr were associated with glacial-interglacial (G-I) cycles, and no permanent shifts away from the natural variation associated with the G-I cycles were found
Understanding the sustainability of the seafood sector : A social-ecological network approach applied to Europe's leading processing hub
No full textInternational audienceThe seafood sector can be understood as a set of interactions between social and environmental components, whether a social-ecological system promoting coastal community development within the sustainable Blue Economy. This sector, which significantly contributes to global food security by providing 15.3% of the animal protein consumed worldwide, faces many challenges, such as climate change, overfishing, and ecosystem degradation. In order to understand those interactions and support the sector sustainability, the study aims to build a social-ecological network of the seafood sector at Boulogne-sur-Mer (France), France's largest fishing port and Europe's leading seafood processing hub. Based on a transdisciplinary approach and stakeholders' participation, our method leads to identifying, categorizing, and interpreting the 227 nodes and 595 links forming the social-ecological network of the seafood sector at Boulogne-sur-Mer, from 'ocean to plate.' The network’s qualitative analysis shows the complexity of the relationships between the environmental, production, economic, and social components. It reminds us that the structure of social-ecological interactions in the seafood sector is not only based on aquatic resources exploitation but also on planning, regulations, lobbying, and innovation justified by multiple ethical frameworks. Results also underline the techno-scientific approach's prominence in promoting the blue economy's sustainability, to the detriment of social innovation and local and ecological knowledge. Our study highlights the need for a holistic understanding of the seafood sector, integrating the plurality of ethical approaches to social-ecological interactions to ensure the seafood sector's sustainability and the coastal community's resilience. This research opens the gate to new studies to understand the complexity and sustainability of the social-ecological system through metrics from network analysis and ecosystem modeling
L'impossibilité de devenir tous des entrepreneurs
No full textInternational audienceFrench public authorities facilitate business creation thanks to a specific legal framework, an enviable context and infrastructure. The reason is that the individual enrichment likely to result is likely to contribute to feeding the public treasury and social security. What does this sought-after enrichment consist of, and is it worth the effort? Perhaps we should consider salaries, dividends, contributions, taxes and duties. Moreover, the simple concern of reducing mass unemployment leads to convincing each job seeker to revise their career plan for employment or civil service, in favor of an employer activity; even as a self-employed entrepreneur.However, not everyone has a flair for business. Moreover, even a slight entrepreneurial appetite isn't always enough. Many French people don't yet have, or no longer have, the right to run, administer, or manage businesses. In what cases, and why ? The reader will find the answer to this question (and other related ones) in the chapter below, which first outlines the opportunities available to potential business creators.Les autorités publiques françaises facilitent la création d’entreprises grâce à un cadre juridique spécifique, un contexte et des infrastructures enviables. La raison est que l’enrichissement individuel susceptible de s’ensuivre est susceptible de contribuer à alimenter le Trésor public et la Sécurité sociale. En quoi consiste l’enrichissement ainsi recherché, et cette recherche vaut-elle la peine ? Peut-être faut-il songer aux salaires, aux dividendes, aux cotisations, aux impôts et aux taxes. Du reste, le simple souci de résorption du chômage de masse conduit à convaincre chacun des demandeurs d’emploi à réviser son projet professionnel de salariat ou de fonctionnariat, au profit d’une activité patronale ; serait-ce comme auto-entrepreneur. Néanmoins, tout le monde n’a pas la fibre des affaires. D’ailleurs l’éventuelle appétence entrepreneuriale ne suffit pas toujours. Car beaucoup de Français n’ont pas encore ou bien n’ont plus le droit de diriger, d’administrer ou de gérer des entreprises. Dans quels cas de figure ou pourquoi ? Le lecteur trouvera la réponse à cette question (et à d’autres connexes) dans le chapitre ci-dessous, lequel rappelle d’abord les facilités offertes aux potentiels créateurs d’entreprises