HAL-Université de Bretagne Occidentale
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Modeling Indian Ocean circulation to study marine debris dispersion: insights into high-resolution and wave forcing effects with Symphonie 3.6.6
No full textInternational audienceAbstract. The Indian Ocean basin faces significant anthropogenic pressure due to its connection to over 2.2 billion people through river basins. Indian Ocean dynamics are characterized by strong regional and seasonal variability driven by the monsoon system and intense eddy activity. To support future studies on land-sea transfers and marine debris dispersion in this complex ocean, we developed a new circulation modeling configuration using the hydrodynamic model SYMPHONIE. Our configuration introduces a unique telescopic grid covering the entire basin, enabling the study of sub-basin connectivity while resolving meso and submesoscale processes in the coastal region, from the Mozambique Channel to the Bay of Bengal, at a resolution of 1 to 3 km. Additionally, we integrate the recently released high-resolution GloFAS river discharge dataset to force the physical simulations with daily freshwater inputs. Three annual experiments are conducted, exploring the effects of wave forcing and spatial resolution. The reference simulation (IndOc.HR) uses high resolution without wave forcing, IndOc.HR-Sto uses the same resolution but includes wave forcing through both the Stokes-Coriolis force and the Stokes drift, and IndOc.12 is a lower-resolution simulation without wave forcing. Comparisons of temperature, salinity and sea level with in situ and satellite data show the good performance of the simulations and the ability of the high resolution model to accurately capture the spatial and temporal variability of surface dynamics and water masses over the Indian Ocean. We further analyze energy budgets and perform Lagrangian experiments to illustrate the critical role of resolution and waves in shaping the circulation and the resulting marine debris dispersion patterns. The effect of energy levels is particularly significant on trajectory statistics such as average travel distances and preferred spread direction. Notably, Stokes drift has a significant seasonal effect in the Arabian Sea during the southwest monsoon, while current field resolution strongly influences trajectories in the Mozambique Channel. Our results provide a robust modeling framework for studying Indian Ocean dynamics and exploring their effect on marine connectivity and the transport of matter, including pollutants, larvae or organic matter
Jet launching from the Kerr black hole magnetosphere: An electrogeodesic approach
No full textInternational audienceThe launch of relativistic jets of plasma on astrophysical to cosmological scales are observed in a variety of astrophysical sources, from active galactic nuclei to X-rays binaries. While these jets can be reproduced by the general relativistic magneto-hydrodynamic (GRMHD) and particle-in-cells (GRPIC) simulations of the dynamical Kerr magnetosphere, the development of analytic models to describe the physics of the jets has remained limited. A key challenge is to analytically describe the individual trajectories of accelerated charged particles which ultimately build up the jet and emit radiation. In this work, we provide a first simple but fully analytical model of jet launching from the Kerr magnetosphere based on the motion of charged particles. To that end, we use the integrability of electrogeodesic motion in the Kerr monopole magnetosphere to study the ejection of charged particles near the poles. This enables us to derive (i) a criterion for the rotation axis to constitute a stable latitunal equilibrium position, thereby representing an idealized jet, (ii) the expression for the magnetic frame-dragging effect, and (iii) the condition for an asymptotic observer to measure blueshifted particles emanating from the black hole surroundings. Our study reveals that particles can be accelerated only in a specific region whose maximal radius depends on the spin and magnetization of the black hole. Alongside these results, we provide a detailed review of the construction of test magnetospheres from (explicit and hidden) symmetries of the Kerr geometry and the condition for the separability of the electrogeodesic motion in a test magnetosphere, which serves as a basis for the model we study in this work
Petrographic and geochemical characterization of Eocene limestones from Thugga / Dougga (Tunisia) : implications for the provenance of stones used in construction and sculpture in the ancient town
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Gaussian process estimation of underwater acoustic fluctuations: Experimental validation on the Iceland–Faroe polar front
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Programmes provinciaux et traduction plastique de l’idéologie du principat : remarques sur les guirlandes du monument dédié aux Caesares par la cité des Rèmes
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A multi-omic resource for exploring microbial eukaryotes in the meromictic freshwater Lake Pavin
No full textInternational audienceAlthough recent advances in high-throughput sequencing have greatly expanded our understanding of microbial diversity and function in aquatic ecosystems, progress in studying freshwater microbial eukaryotes has been more limited, mainly due to their large genomes, immense diversity, and largely uncharacterised physiologies. In this work, we present a comprehensive multi-omic dataset, eukaryote-centred, including targeted-metagenomic (18S rDNA V4 and V9), metagenomic, metatranscriptomic and single amplified genomes (SAGs). Both the oxic and anoxic layers of Lake Pavin (France), a permanently stratified freshwater lake, were sampled at four distinct times throughout 2018, by day and night, targeting microbial eukaryotes of two size classes (0.65–10 µm and 10–50 µm). This dataset comprises 106 eukaryotic metagenome-assembled genomes (MAGs), over 9 million unigenes and 11 SAGs, encompassing several under-represented taxa in public databases ( e.g . Perkinsea, Chytridiomycota, Cryptista). Altogether, this dataset represents a resource for exploring the functional diversity and spatio-temporal dynamics of microbial eukaryotes
Un maire ne peut sacrifier le libre usage de la voie publique sur l'autel de la tranquillité publique
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Modelling the yield stress of cement pastes and mortars containing heterogeneous and unconventional aggregates like raw crushed wind turbine blade
No full textInternational audienceAbstract Determining the yield stress of cementitious materials is crucial for casting and concrete mix design. Fresh concrete possesses yield stress, behaving as a solid with viscoelastic properties below this threshold. When the yield stress is exceeded, concrete flows with a steady-state behavior commonly described by the Bingham or Herschel-Bulkley models. As the construction industry increasingly consumes more and more scarce raw materials, there is a growing need to develop and explore alternative construction materials to replace traditional ones while valorizing waste. Raw Crushed Wind Turbine Blade (RCWTB) has demonstrated interesting results when included in cementitious mixtures. However, a full characterization of rheology including the yield stress of mixtures containing RCWTB is still missing and would be of great practical interest. In this paper, the yield stress of cementitious pastes and mortars containing RCWTB with two different water/cement ratios is measured. Results demonstrate higher yield stress for higher RCWTB inclusion, this is mainly due to the bridge effect of the Glass Fiber Reinforced Polymer (GFRP) contained in the RCWTB. Finally, a physical model is applied for RCWTB to predict GFRP fibers maximum packing fraction based on their geometry, elastic properties, and the rheology of the surrounding cement-based material. This model is then validated with experimental yield stress of cement pastes and mortars
Segmentation en EEG néotanal — Apprentissage sur des représentations temps-fréquence
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Growth Rate and Energy Dissipation in Wind‐Forced Breaking Waves
No full textInternational audienceWe investigate the energy growth and dissipation of wind‐forced breaking waves at high wind speed using direct numerical simulations of the coupled air–water Navier–Stokes equations. A turbulent wind boundary layer drives the growth of a pre‐existing narrowband wave field until it breaks, transferring energy into the water column. Under sustained wind forcing, the wave field resumes growth. We separately analyze energy transfers during wave growth and breaking‐induced dissipation. Energy transfers are dominated by pressure input during growth and turbulent dissipation during breaking. Wind input during growth is balanced with dissipation during breaking over an entire growing‐breaking cycle. The wave growth rate scales with , modulated by the wave steepness due to sheltering, and the energy dissipation follows the inertial scaling with wave slope at breaking, confirming the universality of the process. Following breaking, near‐surface vertical turbulence dissipation profiles scale as , with their magnitude controlled by the breaking‐induced dissipation