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A general machine learning model of aluminosilicate melt viscosity and its application to the surface properties of dry lava planets
No full textInternational audienceUltra-short-period exoplanets like K2-141 b likely have magma oceans on their dayside, which play a critical role in redistributing heat within the planet. This could lead to a warm nightside surface, measurable by the James Webb Space Telescope, offering insights into the planet's structure. Accurate models of properties like viscosity, which can vary by orders of magnitude, are essential for such studies. We present a new model for predicting molten magma viscosity, applicable in diverse scenarios, including magma oceans on lava planets. Using a database of 28,898 viscosity laboratory measurements on phospho-alumino-silicate melts, spanning superliquidus to undercooled temperatures and pressures up to 30 GPa, we trained a greybox artificial neural network, refined by a Gaussian process. This model achieves high predictive accuracy (RMSE ≈0.4log10 Paṡs) and can handle compositions from SiO2 to multicomponent magmatic and industrial glasses, accounting for pressure effects up to 30 GPa for compositions such as peridotite. Applying this model, we calculated the viscosity of K2-141 b's magma ocean under different compositions. Phase diagram calculations suggest that the dayside is fully molten, with extreme temperatures primarily controlling viscosity. Even in the absence of major volatiles (H, C, N), a tenuous rock-vapour atmosphere (0.1 bar) might exist around a 40° radius from the substellar point. At higher longitudes, atmospheric pressure drops, and by 90°, magma viscosity rapidly increases as solidification occurs. The nightside surface is likely solid, but previously estimated surface temperatures above 400 K imply a partly molten mantle, supporting geothermal flux through vertical convection
Glacial isostatic adjustment reveals Mars's interior viscosity structure
No full textInternational audienceInvestigating glacial isostatic adjustment has been the standard method to decipher Earth's interior viscosity structure1,2, but such an approach has been rarely applied to other planets because of a lack of observational data3,4. The north polar cap of Mars is the only millions-of-years-old surface feature that can induce measurable surface deformation on this planet, thereby holding clues to its present-day internal viscosity structure5,6. Here we investigate the emplacement of this ice cap by combining thermal evolution models7, viscoelastic deformation calculations8 and radar observations6. We show that downward motion of the northern regions is ongoing and can be constrained by analyses of the time-variable gravity field9 and NASA's InSight seismic moment rate10. Only models with present-day high viscosities (2–6 × 1022 Pa s for depths greater than 500 km), strong mantle depletion in radiogenic elements (more than 90%) and thick average crusts (thicker than 40 km) are consistent with the negligible flexure beneath the polar cap seen by radars. The northern lithosphere must deform at less than 0.13 mm per year and have a seismic efficiency less than 0.3 to satisfy gravity and seismic constraints, respectively. Our models show that the north polar cap formed over the last 1.7–12.0 Myr and that glacial isostatic adjustment can be further constrained by future gravity recovery missions to Mars11,12
Footwall Geology and Deformation at Flip-Flop Mid-Ocean Ridge Detachment Faults: 64°35'E Southwest Indian Ridge (SWIR)
No full textInternational audienceUsing bathymetry and ROV dives, we investigate two successive flip-flop detachment faults (D1 active, D2 older) in the near-amagmatic 64°35'E region of the SWIR. Kilometer-sized benches on the upper slopes of D1 footwall form the D1 degraded breakaway. Scarps at the top expose the D2 fault zone with deformed serpentinized peridotite, sigmoidal phacoids, planar fractures, and serpentinite microbreccia/gouge horizons. Two ROV sections of the D1 footwall show contrasting deformation styles, corresponding to distinct morphological domains, which relate to contrasting fault and footwall strength. One section documents corrugations, outcrops dominated by sigmoidal phacoids, and planar fractures with thin, discontinuous serpentinite microbreccia/gouge horizons. ROV dives in this corrugated domain show that NNE-trending km-spaced ridges and WNW-trending narrow benches in the shipboard bathymetry correspond, respectively, to broad undulations (mega-corrugations) of the D1 fault and to several antithetic minor normal faults (cumulated horizontal offset of ∼285 m). The other section, lacking corrugations, broad ridges, and antithetic fault, has thicker and more continuous serpentinite microbreccia/gouge horizons, indicating a weaker fault. The abundance of such weak gouges probably reflects hydrous fluid availability during deformation. We link mega-corrugations in the western domain and km-scale lobes of D1 emergence to a broad detachment damage zone with up to ∼600 m-thick mega-phacoids of less deformed serpentinized peridotite. Small antithetic normal faults in the corrugated domain are interpreted as due to bending forces in the D1 footwall. Our findings highlight the three-dimensional, non-planar structural and morphological variability of the exhumed D1 detachment fault zone along the ridge-axis
Time-averaged algorithm for solving the topology optimization problem for unsteady laminar, turbulent and anisothermal flows
No full textInternational audienceThis paper proposes a new algorithm to solve topology optimization problems for laminar unsteady or turbulent flows. Instead of computing the gradient of the cost function after solving the direct and adjoint (both unsteady) PDE on the full time interval, our algorithm uses averaged physical quantities on a smaller unspecified time interval to define a (steady) Reynolds-Averaged Method (RAM) model which is then used as constraint in an optimization problem to update the design variable. Another feature of the proposed method is that the RAM model can be defined whatever the initial model and CFD turbulence models initially chosen to compute the instantaneous physical quantities. The RAM model involves turbulent quantities such as turbulent kinetic viscosity and turbulent thermal diffusivity are estimated instead of using the concept of "frozen turbulence". In contrast with the classical methods built to solve unsteady topology optimization problems, the main advantage of the proposed algorithm is that it updates the design variable by solving an auxiliary steady topology optimization problem. Three configuration cases are studied to illustrate the ability of our algorithm to optimize pressure losses and heat transfer by adding material to smooth the laminar unsteady or turbulent flows. We also calculate the number of required design parameter updates to obtain an optimized design. Thus, our algorithm overcomes three major scientific challenges in solving optimization problems in turbulence, namely leveraging efficient temporal turbulence models or a Direct Numerical Simulation (DNS) model, computational cost and data storage requirements
Les évolutions de la formation initiale des enseignants en France, entre universitarisation et professionnalisation : regards des formateurs sur les transformations de leur activité. Symposium coordonné par F. M. Sarti, B. Wentzel et T. Perez-Roux « Trente ans d’universitarisation de la formation des enseignants : comparaisons internationales au regard de trois cas (Brésil, Québec, France) »
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Huntite [CaMg3(CO3)4], a rare carbonate phase formed during early diagenesis in modern microbialites.
No full textInternational audienceMicrobialites are sedimentary rocks formed under the influence of microbial communities and environmental factors, hence, particularly suited to look for traces of life and reconstruct palaeoenvironments. However, the mineral phases composing them and the signals they carry may be altered by secondary alteration during, e.g., early diagenesis. While the impact of early diagenesis has already been evidenced on some microbialites, some efforts are still needed for documenting its extent and its dependence on environmental conditions. Here, we analyzed early diagenetic transformations in shallow to deep modern microbialites formed in the seasonally stratified lake Alchichica, Mexico. We combined bulk analyses such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), with spatially resolved techniques, including petrographic microscopy, confocal laser scanning microscopy (CLSM), X-ray fluorescence (XRF) mapping, scanning electron microscopy (SEM), focused ion beam (FIB) milling and transmission electron microscopy (TEM). We showed the massive diagenetic formation of huntite (CaMg3(CO3)4), a rare carbonate, in microbialites developing at depths ≥20 m in the Lake Alchichica water column. Huntite replaced aragonite (CaCO3) and hydromagnesite (Mg5(CO3)4(OH)2·4H2O), the main primary phases forming Alchichica microbialites. The bulk isotope compositions of carbon and oxygen in carbonate phases also supported a diagenetic origin of huntite. We propose that specific conditions restricted to the pore water physicochemistry within the deep microbialites control the destabilization of the primary carbonates and the precipitation of huntite. Interestingly, thermodynamics predict that huntite instead of hydromagnesite and aragonite is the most stable phase under Lake Alchichica conditions. Yet the latter phases are dominant in most Alchichica microbialites. This suggests that the formation of huntite, similarly to that of dolomite in many surficial environments, is likely kinetically hindered and that the mineral assemblage composing microbialites does not necessarily follow thermodynamic predictions but is more controlled by kinetics. Last, the loss of luminescence in deep microbialites in comparison with shallow microbialites raises questions about the preservation of some mineralogical and biological signatures of microbialites over time
A Rotational Cultivation System for Indoor-Grown Lettuce: Feasibility in Terms of Yields, Resource Efficiency, Quality, and Postharvest Storage Capacity
No full textInternational audienceIndoor farming in plant factories with artificial lighting (PFAL) offers optimized growing conditions and higher water, light, and land surface use efficiencies compared to greenhouses or open field agriculture but faces challenges related to energy consumption. The objective of this work is to evaluate the feasibility of using a rotational cultivation system for indoor-grown lettuce production. We compare a rotational cultivation system to a horizontal control cultivation system in terms of yields, resource efficiency, quality at harvest, and postharvest storage capacity. No significant differences were observed in yields, water use efficiency, light use efficiency, or postharvest storage capacity between the systems. Energy and land surface use efficiencies were higher in the rotational cultivation system compared to the control and consistent with the literature. However, a slight trend toward lower fresh and dry weights throughout the cultivation period in the rotational system was noted, correlating with reduced net photosynthesis during the first two hours and at the end of the lighting period. This effect was attributed to decreased stomatal conductance and photosystem II efficiency. Furthermore, the rotational cultivation system modified the quality by modifying the global polyphenol profile of the lettuce compared to the control. Based on yields and efficiencies, we show the feasibility of using a rotational cultivation system for indoor lettuce production
Xdas: A Python Framework for Distributed Acoustic Sensing
No full textInternational audienceAbstract Xdas is a Python library designed to manipulate distributed acoustic sensing (DAS) data. It provides a unified abstraction for reading any DAS file format into a standardized Python object, streamlining data handling across different acquisition systems. To address the challenge of massive, multifile data sets, Xdas aggregates data chunks into virtually contiguous arrays organized by instrument and acquisition. This structure allows for efficient spatial and temporal slicing while minimizing overhead. To enable scalable offline processing of massive DAS data sets, Xdas processes data in manageable chunks. To ensure processing continuity, Xdas uses a stateful pipes-and-filters architecture. Most Xdas operations are multithreaded by default to take full advantage of multicore systems. This approach also enables real-time data processing. Its built-in network streaming capabilities allow Xdas to be deployed on DAS instruments for custom, real-time workflows at the point of data generation. At its core, Xdas uses a labeled ND (N-dimensional) array structure that encapsulates both data values and coordinate metadata and can be used to handle any kind of data set (not just time–space DAS records). This data model adheres to the established standards provided by the NetCDF4/HDF5 formats and the Climate and Forecast conventions. Designed to mirror the application programming interfaces (APIs) of popular libraries such as NumPy, SciPy, and Xarray, Xdas minimizes the learning curve for new users. Its modular and extensible design means that adding support for a new file format or integrating a processing function typically requires less than 10 lines of code
La mise en place ritualisée de gestes attentionnels, corporels et respiratoires : des bénéfices pour les apprentissages des élèves et la pratique des enseignants
No full textThis research project explored the effects of ritualizing attentional, physical, and breathing breaks on students’ sustained attention and the classroom climate as perceived by teachers, through a comparative study between two grade levels: preschool (moyenne section) and first grade (CP). The experiments, which combined observations, interviews, questionnaires, and practical classroom implementation, revealed that such breaks promote,better sustained attention, more stable posture, and more active listening among students. For teachers, they help establish a calmer working environment, thereby facilitating the learning process. These rituals appear to be effective tools for supporting student engagement, thus,enhancing the overall quality of the school environment. This research highlights a potential synergy between attentional breaks and academic performance, through a joint approach that addresses both student and teacher needs.Ce travail de recherche a permis d’explorer les effets de la ritualisation des pauses attentionnelles, corporelles et respiratoires sur le maintien de l’attention des élèves et le climat de classe perçu par les enseignants, au travers d’une étude comparative entre deux niveaux de classe : moyenne section et CP. Les expérimentations, articulées autour d’observations, d’entretiens, de questionnaires et d’une mise en œuvre pratique en classe, ont révélé que ces pauses favorisent un meilleur maintien de l’attention, une posture plus stable et une écoute plus active des élèves. Du côté des enseignants, elles contribuent à installer un climat de travail apaisé, facilitant ainsi la conduite des apprentissages. Ces rituels apparaissent comme des leviers efficients pour soutenir l’engagement des élèves, renforçant ainsi la qualité de l’environnement scolaire. Cette recherche met ainsi en lumière une synergie possible entre pauses attentionnelles et performance scolaire, à travers une approche conjointe des besoins des élèves et des enseignants