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Exponential stability of a generalised Burgers equation in a n-dimensional torus
No full textWe study a generalized conservative Burgers equation on a n-dimensional torus. We first consider the associated linear system. By exploiting the Harnack inequality and the contraction property, we establish exponential stability. For the nonlinear problem, we derive a uniform-in-time estimate of the solution using the De Giorgi-Nash-Moser iteration method. Moreover, we show that the Hölder norm of the solution remains uniformly bounded and decays exponentially
Precipitating electron properties of Ganymede’s aurora retrieved from Juno/UVS observations during PJ34
No full textInternational audienceContext. Ganymede's UV aurorae, observed by HST and Juno/UVS, trace interactions between its atmosphere and Jupiter's magnetosphere. These emissions, dominated by O I lines at 130.4 and 135.6 nm, are driven by electron impact on species such as H 2 O, O, and O 2 , and yet the properties of the precipitating electrons remain poorly constrained. Aims. Our aim was to retrieve the energy and flux of precipitating electrons using UV observations from Juno/UVS during PJ34 and to assess the dominant atmospheric species producing the observed emissions. Methods. Using the TransPlanet electron transport model and a non-local thermodynamic equilibrium (non-LTE) radiative transfer module, we simulated O I emissions for 17 auroral subregions, testing both monoenergetic and kappa-type electron distributions. The I(135.6 nm)/I(130.4 nm) line ratio was used as a diagnostic, with values varying by target species. Results. Monoenergetic distributions fit most regions better, with mean energies of 17-300 eV and fluxes up to 2 mW m -2 . Kappa and Maxwellian distributions yielded higher fluxes, but poorer spectral fits. Poor fits in some regions reflect low S/N or non-ideal electron populations. Conclusions. Our results suggest that Ganymede's UV aurorae are mainly driven by low-to intermediate-energy electrons. Upcoming high-resolution observations and in situ data from Juice and Europa Clipper will be key to refining these diagnostics
An integrated multi-proxy approach to characterize the southern part of the Al Idrissi strike-slip fault system, Alboran sea
No full textInternational audienc
Modeling the formation of N2 and CH4 frost on the Pluto slopes
No full textInternational audienceContext . The equatorial region of Cthulhu as revealed by New Horizons appears to be generally dark and largely devoid of volatiles because its surface albedo is low. Localized bright patches, however, which are interpreted as CH4 frost, are observed on crater rims and slopes. Aims . Previous studies suggested that these frosts might result from the peculiar insolation driven by the geometry of these slopes, but this has never been tested quantitatively. We investigated the origin, stability, and potential role of these localized frost deposits in the volatile cycle of Pluto. Methods . We implemented a new subgrid-scale slope parameterization in the volatile transport model for Pluto, which accounts for the specific solar irradiation and the resulting surface and subsurface temperatures on sloped terrains. This parameterization also allows the condensation and sublimation of volatiles (either N2 or CH4 ) on slopes, including the effect of large-scale transport of these species. This is key to determining the amount of frost that forms or disappears. Results . Our simulations reproduce the observed CH4 frost on north-facing slopes as seasonal deposits that currently sublimate, predict perennial CH4 frost on south-facing slopes, and show that the slope microclimates are not expected to alter global volatile cycles. Conclusions . Seasonal and perennial N2 and CH4 frosts can form on the Pluto slopes, even in its darkest and warmest regions, because the locally sunlight received on inclined terrain is reduced. Despite the abundance of sloped surfaces on Pluto, the slope microclimates still only appear to have a minor effect on the global volatile cycles of the planet
Tectonic structures and stress state associated with seamount subduction in accretionary prism. Implications for slip behavior
No full textInternational audienceSeamounts on oceanic plates are thought to affect the dynamics of accretionary prism at subduction zones, particularly the slip behavior. Geophysical studies show that pore fluid overpressure is associated with the nucleation of shallow slow slip events (SSEs). We use numerical simulations in which the subducting plate bends in response to tectonic, gravitational collapse and surface processes to capture structural complexities arising from the subduction of buried seamounts and compute the resulting stress state. We show that tectonic slices of undeformed sediments develop on both sides of the seamount and that a basin forms atop the seaward slice. These structures, recognizable in seismic data, represent the long-term tectonic signature of seamount subduction.Gravitational collapse only occurs when a critical lengthscale, we quantified, of perturbed accretionary prism is reached. Seamounts that are small enough, instead get decapitated and do not perturb the prism over a sufficient lengthscale to trigger gravitational collapse.Stress analysis reveals that the seaward side of the seamount is under an extensional regime, whereas its landward side is in a compressive state. We thus propose that sustained pore fluid overpressure can only develop on the landward side. This mechanism supports observations along Hikurangi, where a highly reflective zone, interpreted as a zone of pore fluid overpressure, has been imaged downdip of the Papaku seamount. Since this zone coincides with the largest slip magnitudes of shallow SSEs, we propose that the landward slice of undeformed sediments presents favorable conditions for SSEs nucleation
Influence of uncertain bedrock seismic velocity structure on numerical simulation of earthquake ground motion (EGM): case study of the Le Teil earthquake (November 11, 2019, France)
No full textInternational audienceOn November 11, 2019 a very shallow magnitude Mw 4.9 earthquake shook Le Teil (Ardèche, France), some ten kilometres from two nuclear facilities. This earthquake, the strongest in metropolitan France in the last twenty years, occurred on a fault which was not identified as an active fault in the BDFA (Jomard et al., 2017) given its selection criteria, highlighting the importance of studying seismic hazard in low-seismicity areas. This earthquake occurred in a region with many assets, most of which are located in the Rhône valley and therefore subject to significant site effects due to a complex geology. The region has indeed been affected by a major erosion phase during the Messinian salinity crisis ca. 6 My ago, followed by the rapid flooding of the resulting canyon, thereby creating a basin filled with sediments of Pliocene to Quaternary ages embedded in a substratum composed of Secondary to Tertiary formations.In this study, we present our exploratory work in view to build a seismological model of this region. This will be done through the comparison between observed ground motions and physics-based numerical simulations accounting for uncertainties related to geological layers on the wave path. We want to explore these uncertainties to faithfully replicate the data when modelling the propagation of seismic waves for frequencies between 0.5 and 5 Hz, for scenarios of the Le Teil earthquake and its aftershocks.We focus particularly on the complexity of the pre-Messinian substratum and its impact on EGM outside the sedimentary basin. We propose a method for building geological interfaces bounding the velocity structure that can easily be parameterized, especially when multiple faults are present, facilitating the investigation of many potential structures.We were able to produce a first velocity model of the region incorporating faults and a velocity structure with non-planar interfaces, and to confront our numerical simulation of the November 23, 2019 aftershock to field data recorded by several seismic stations. We also identified model parameters subject to uncertainties (shear-wave velocities, layer interfaces, source depth…) and the associated uncertain spaces (approx. 1500-3500 m.s-1, up to 1.5 km variations, approx. 1-2 km depth). Following this work, a comprehensive sensitivity study including basin structure and source parameters will be conducted to understand which physical and structural parameters primarily control the prediction of EGM
Some aspects of students’ interpretation of double quantified statements
No full textInternational audienceDespite numerous research efforts, understanding how students interpret double quantifiedstatements has proven to be a challenging task since the pioneering work of Dubinsky andYiparaki (2000). While the shared finding puts forward the inefficiency of mathematical logicalsyntax (or conventions) in explaining how students interpret these statements, the severalaspects that influence such interpretations remain complex and intangible. This study deploysthe syntactic, semantic, and pragmatic perspectives to delve deeper into this issue. The mainresult highlights three aspects that may influence students' interpretive approaches todouble quantified statements: the kind of relation between the variables involved in thestatement, the mutual exclusion of prototypical relations, and the rejection of nonprototypicalrelations
Dynamiser l'enseignement des appareillages en spectroscopie : l'intégration d'un jeu sérieux - Spectrowave
No full textInternational audienceTo enhance learning and strengthen student interest, involvement, and motivation, a serious game was introduced at the L3 and M1 levels. This game enables students to develop knowledge of the components and functioning of the spectroscopy instruments most commonly used in analytical laboratories. In this article, we describe the evolution of the game, from its initial physical board format to its digital version, which can be played online and remotely. We also discuss improvements implemented over time, particularly the addition of interactions during sessions, which have proven essential for maintaining student engagement.Afin de faciliter l’apprentissage et accroître l’intérêt, l’implication et la motivation des étudiants, un jeu sérieux basé sur un jeu de plateau a été introduit en L3 et M1. Cet « edugame » permet aux étudiants d’acquérir des connaissances sur les composants et le fonctionnement des appareils de spectroscopie les plus couramment utilisés en laboratoire d’analyse. Dans cet article, nous présentons l’évolution de ce jeu, de sa version sur un plateau physique à une version numérique jouable en ligne et en distanciel. Enfin, nous discuterons des améliorations apportées, notamment l’ajout d’interactions en séance, qui se sont révélées essentielles pour maintenir l’engagement des étudiants
Érosion par sape et géomorphologie du Vexin (Bassin de Paris, France)
No full textInternational audienceThe Vexin is a natural and historical territory located in the northwest of the Paris Basin. It presents a series of landforms illustrating the process of seepage erosion, i.e., an inconspicuous but permanent erosion process linked to the emergence of groundwater. These landforms develop at different levels of the sedimentary pile, mainly above the transitions between clays and sands that crop out in the Ypresian and Rupelian levels. The resulting elementary geomorphological features are natural amphitheaters in steep-walled valley heads and residual hills or outliers. At a larger scale, typical dendritic hydrographic networks are observed. The timing of valley head retreat is addressed using archaeological data. The discussion focuses on the respective roles of seepage and runoff in the formation of landscapes and on the possible links between seepage and slope dynamics. We finally suggest that, thanks to its preserved natural heritage, the Vexin has all the resources to become a major spot for studying and teaching erosion processes.Le Vexin est un territoire naturel et historique situé au nord-ouest du Bassin de Paris. Il présente une série de morphologies illustrant le processus d'érosion par sape, c'est-à-dire un processus d'érosion discret mais permanent lié à l'émergence des eaux souterraines. Ces morphologies se développent à différents niveaux de la pile sédimentaire, principalement au-dessus des transitions entre argiles et sables qui affleurent dans les niveaux de l’Yprésien et du Rupélien. Les formes élémentaires qui en résultent sont des amphithéâtres naturels dans des fonds de vallée à versants abrupts et des buttes résiduelles (buttes-témoins). À plus large échelle, des réseaux hydrographiques dendritiques typiques sont observés. La chronologie du recul de tête de vallée est abordée à l'aide de données archéologiques. La discussion porte sur les rôles respectifs de la sape et du ruissellement dans la formation des paysages et sur les liens possibles entre sape et dynamique des versants. Nous suggérons enfin que, grâce à son patrimoine naturel préservé, le Vexin présente toutes les ressources pour devenir un laboratoire naturel d'étude et d'enseignement des processus d'érosion
