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Unsupervised data-driven detection of exceptional atmospheric trajectories
No full textExtreme weather events in Europe are closely linked to the large-scale atmospheric circulation and often develop over several consecutive days. Most existing circulation-based approaches focus on identify extreme weather patterns as instantaneous atmospheric states and therefore do not explicitly account for the temporal evolution of the flow. In this study, we apply a data-driven and unsupervised methodology to identify rare atmospheric trajectories from reanalysis data. The method quantifies how isolated short segments of atmospheric evolution are within the space of all observed trajectories, using daily sea-level pressure fields over Europe. We apply the approach to several decades of reanalysis data and identify the most isolated trajectories for different trajectory lengths. The detected trajectories are characterised by large-scale circulation anomalies and strong pressure gradients. A comparison with independent databases of European extreme events shows a statistically significant overlap, particularly for windstorms. Increasing the trajectory length enhances the detection of multi-day events, indicating that the method captures persistent atmospheric evolutions rather than isolated states. In addition to windstorms, the detected trajectories correspond to cold spells and blocking-like circulation patterns, as well as events that are not systematically documented in existing pan-European databases. These results indicate that analysing rare atmospheric trajectories provides complementary information to state-based approaches and offers a general framework for the detection of extreme atmospheric evolutions in reanalysis datasets
Dislocation density evolution in hot‑compressed dual‑phase titanium alloys: A phase‑resolved EBSD–Taylor framework
No full textInternational audienceThis study proposes a generic phase-resolved framework to quantify dislocation density evolution during hot compression of dual-phase titanium alloys by integrating electron backscatter diffraction (EBSD) analysis with Taylor-based flow-stress modeling. Comparative tests were conducted on Ti–6Al–4V (α+β) and Ti–10V–2Fe–3Al (metastable β) in equiaxed and lamellar microstructures. Initial differences in dislocation density and flow stress, driven by morphology, diminish with strain as phase-resolved restoration mechanisms and α-texture development converge, underscoring the intrinsic contribution of both phases to flow softening. EBSD and Taylor approaches exhibit divergent dislocation density estimations with strain but provide complementary insights, as these trends are explained by phase-specific mechanisms. In the α phase, texture evolution involves c-axis rotation toward a soft configuration and increased low-angle grain boundary (LAGB) density, accommodating strain through progressive LAGB formation with limited high-angle grain boundary (HAGB) development near interfaces. Conversely, the β phase undergoes extensive continuous dynamic recrystallization (CDRX), stabilizing flow via new grain formation. Despite alloy-specific differences, phase-level mechanisms remain consistent under subtransus conditions, confirming the transferability of the framework. These findings advance understanding of microstructural restoration and texture evolution, offering a robust basis for predictive modeling and forging process optimization
Transmission des savoirs dans l’Inde ancienne et philologie indienne contemporaine.Le projet « L’Inde classique augmentée »
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Savoir-faire ou faire savoir ? Une transmission paradoxale face à l’inconnu de la transition démographique
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SWOT Sheds Light on Seiche Oscillations Within Atoll Islands
No full textInternational audienceAbstractThis study investigates the occurrence of surface elevation oscillations, known as seiches, at the atoll scale. We show that the innovative Ka-band Radar Interferometer (KaRIn) onboard the Surface Water Ocean Topography (SWOT) satellite makes it possible to visualize seiche-like structures within lagoons of French Polynesia. This ability to capture two-dimensional sea surface undulations of low amplitude (on the order of a few centimeters) in relatively small water bodies (less than 80 km in length) is unprecedented in satellite altimetry, and opens new avenues of research into these events and their contribution to coastal erosion and flooding. Our study combines sea surface height observations from SWOT with in situ measurements conducted in the Raroia lagoon and theoretical calculations based on an eigenvalue model. These three complementary approaches-satellite remote sensing, in situ data, and theoretical modeling-allow us to investigate both the spatial and spectral properties of seiches in atoll islands.Plain Language SummaryIn closed or semi-enclosed water bodies, a resonant phenomenon can happen in which the water surface performs standing oscillations. These oscillations, known as seiches, have well-defined periods and geometries at the basin scale. Here we investigate their presence in the lagoon of atoll islands using in situ measurements, modeling, and the Surface Water Ocean Topography (SWOT) mission, a new satellite that provides for the first time two-dimensional images of the ocean surface elevation with an unprecedented precision and resolution. We show that SWOT does capture seiche-like structures, and our in situ measurements confirm that such resonant modes do occur in the lagoon of Raroia. This is a first step toward understanding and assessing the importance of these modes in Pacific atoll islands, where they have received relatively little attention though they appear to play a role in sediment transport and submersion events
A Note on the Limiting Corner Angle of Liquid Drops in the Lubrication Approximation
No full textInternational audienceThe derivation of thin-film equations for liquid drops on an inclined plane is analyzed. It was found that the limiting corner angle of the contact line for such a drop should be close to 25 degrees, in accordance with observations. This is achieved by the method of Fuchsian reduction, which yields a more complete solution of the equation for the profile of drops than other methods
Les inscriptions araméennes christo-palestiniennes : géographie, épigraphie, paléographie, histoire
No full textInternational audienceAprès avoir observé la répartition géographique au Proche-Orient des inscriptions syriaques et des inscriptions araméennes christo-palestiniennes ainsi que les lieux connus de production de manuscrits christo-palestiniens, l’article présente les inscriptions christo-palestiniennes dans chacune des provinces byzantines des Palestines et de l’Arabie, dans leur contexte archéologique et en observant leur voisinage avec les inscriptions grecques. Il aboutit d’une part à une esquisse de comparaison paléographique des inscriptions christo-palestiniennes et d’autre part à une hypothèse sur leur histoire linguistique et sociale dans le Proche-Orient byzantin ; le christo-palestinien est lié à l’évangélisation de ces provinces sous l’impulsion du patriarcat melkite de Jérusalem
Le Grand Paris Express aux prises avec le calcul économique
No full textInternational audienceCet article propose une analyse de l’approche socio-économique développée par la Société du Grand Paris pour justifier de l’utilité du Grand Paris Express (GPE) lors des procédures d’enquête publique et de contre-expertise. Cette approche a en effet suscité une controverse mobilisant de nombreux acteurs académiques et associatifs ayant dénoncé une surévaluation de sa rentabilité au service d’un aménagement reposant sur l’idée d’« effets structurants » des réseaux de transport. Il montre comment, face à une rentabilité socio-économique initialement défavorable en raison des techniques d’évaluation en vigueur et de la morphologie du GPE, la SGP est parvenue à imposer une nouvelle méthode assise sur l’idée d’une meilleure intégration des interactions entre réseau et territoire dans le calcul économique. En étudiant les thèses et les modèles développés par les experts du service d’études économiques de la SGP ainsi que les controverses qu’elles ont suscitées dans différentes arènes, l’article propose ensuite une réflexion sur les problèmes de confiance posés par les modèles Land Use Transport Interaction (LUTI) et sur le type de vision du territoire que ce calcul économique incarne par sa méthode
Water Vapor Vertical Distribution on Mars After Six Yearsof TGO/NOMAD Solar Occultations: 2. Cross‐ValidationWithin TGO and Comparison With MPCM
No full textInternational audienceThis is the second part of an investigation of water vapor in the Martian atmosphere using solar occultation observations by the spectrometer NOMAD on board the ExoMars Trace Gas Orbiter. Following the analysis performed in the first part, hereafter named as Paper I, a cross-validation exercise between NOMAD and ACS results is presented, showing global as well as profile-by-profile comparisons. The results reveal an overall good agreement between different teams and instruments, taking into account the different retrieval methodologies. In order to compare with model predictions, we perform an exhaustive analysis of the water vapor simulated by Mars Planetary Climate Model (MPCM). It shows that the MPCM reproduces most of the water vapor climatological features observed in the atmosphere. However, several discrepancies between model and observations are noticed. Some of these are possibly related to the vertical distribution of dust and its effect on the global circulation and on the water vapor vertical transport. Other data-model differences found at 60 km seem to be related to discrepancies on the water ice cloud formation in the MPCM. In addition, we include a cluster analysis of Martian water vapor vertical profiles for the first time. This technique applied to MPCM and NOMAD water vapor retrievals reveal distinct groups of profiles being representative of specific seasons and latitudinal regions, similarly distributed in both model and observations. Moreover, it allows us to provide a simplified water vapor climatology, useful to detect out-of-season events and biases in the retrieval processes