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L’informatique au cœur des limites de l’esprit
No full textInternational audienceLes concepts d’algorithmes et de programmes informatiques ont été utilisés par le logicien autrichien Kurt Gödel dans les années 1930, bien avant l’apparition du premier ordinateur afin de démontrer deux théorèmes d’une très grande profondeur, qui portent sur les limites de l’esprit et de la logique. Essayons de suivre son cheminement
Polygenic soils in the southern central Ecuadorian highlands as the result of long-lasting pedogenesis, geodynamic processes and climate change
No full textInternational audienc
On the size of stable minimal surfaces in
No full textInternational audienceThe Gauss map g of a surface ⌃ in R 4 takes its values in the Grassmannian of oriented 2-planes of R 4 : G + (2, 4). We give geometric criteria of stability for minimal surfaces in R 4 in terms of g. We show in particular that if the spherical area of the Gauss map |g(⌃)| of a minimal surface is smaller than 2⇡ then the surface is stable by deformations which fix the boundary of the surface. This answers the question of [BDC3] in R 4
Convex ordering for stochastic Volterra equations and their Euler schemes
No full textIn this paper, we are interested in comparing solutions to stochastic Volterra equations for the convex order on the space of continuous -valued paths and for the monotonic convex order when . Even if in general these solutions are neither semi-martingales nor Markov processes, we are able to exhibit conditions on their coefficients enabling the comparison. Our approach consists in first comparing their Euler schemes and then taking the limit as the time step vanishes. We consider two types of Euler schemes depending on the way the Volterra kernels are discretized. The conditions ensuring the comparison are slightly weaker for the first scheme than for the second one and this is the other way round for convergence. Moreover, we extend the integrability needed on the starting values in the existence and convergence results in the literature to be able to only assume finite first order moments, which is the natural framework for convex ordering
Systematic MRI in persistent post‐Covid‐19 olfactory dysfunction should be reassessed
No full textInternational audienceBackground: Magnetic resonance imaging (MRI) is the gold standard in the etiological assessment of a persistent olfactory dysfunction (OD). While the utility of imaging in COVID-19-related OD has yet to be established, MRI is recommended in all patients with persistent OD. The high prevalence of the latter after SARS-CoV-2 infection means evaluating this strategy is an important public health matter.Methods:The main objective was to examine the impact of systematic MRI on the management of patients with OD. All adult patients consulting for persistent OD (>2 months) after primary SARS-COV-2 infection (PCR) between March 2020 and December 2021 were included (n = 67). The secondary objective was to evaluate the relationship between the severity of the OD as measured by psychophysical testing (ETOC) and the volume of the olfactory bulb (OB) measured by MRI.Results: All patients underwent MRI, and none led to a change in diagnosis or treatment. Among them, 82% (55/67) were considered normal by the radiologist on initial interpretation. There were no significant differences (visual analysis or OB volume) between groups (mild, moderate, and severe hyposmia).Conclusion: Systematic MRI may be unnecessary in patients whose persistent OD began soon (a few days) after confirmed SARS-CoV-2 infection
Five Key Exoplanet Questions Answered via the Analysis of 25 Hot-Jupiter Atmospheres in Eclipse
No full textInternational audiencePopulation studies of exoplanets are key to unlocking their statistical properties. So far, the inferred properties have been mostly limited to planetary, orbital, and stellar parameters extracted from, e.g., Kepler, radial velocity, and Gaia data. More recently an increasing number of exoplanet atmospheres have been observed in detail from space and the ground. Generally, however, these atmospheric studies have focused on individual planets, with the exception of a couple of works that have detected the presence of water vapor and clouds in populations of gaseous planets via transmission spectroscopy. Here, using a suite of retrieval tools, we analyze spectroscopic and photometric data of 25 hot Jupiters, obtained with the Hubble and Spitzer Space Telescopes via the eclipse technique. By applying the tools uniformly across the entire set of 25 planets, we extract robust trends in the thermal structure and chemical properties of hot Jupiters not obtained in past studies. With the recent launch of the James Webb Space Telescope and the upcoming missions Twinkle and Ariel, population-based studies of exoplanet atmospheres, such as the one presented here, will be a key approach to understanding planet characteristics, formation, and evolution in our galaxy
Who Lives Where in the City? Amenities, Commuting and Income Sorting
No full textInternational audienceWe develop a new model of a "featureful" city in which locations are di¤erentiated by two attributes, that is, the distance to employment centers and the accessibility to given amenities. The residential equilibrium involves the spatial separation of households sharing similar incomes. Under Stone-Geary preferences, amenities and commuting are subsumed into a location-quality index. Hence, the assignment of households to locations becomes one-dimensional. Since residential choices are driven by the location-quality index, the income mapping may be fully characterized. Using a rich micro-dataset on the Netherlands, we show that household income sorting is indeed driven by amenities and commuting times
Corrected Curvature Measures
No full textInternational audienceThis paper proposes a new mathematical and computational tool for infering the geometry of shapes known only through approximations such as triangulated or digital surfaces. The main idea is to decouple the position of the shape boundary from its normal vector field. To do so, we extend a classical tool of geometric measure theory, the normal cycle, so that it takes as input not only a surface but also a normal vector field. We formalize it as a current in the oriented Grassmann bundle R^3 × S^2. By choosing adequate differential forms, we define geometric measures like area, mean and Gaussian curvatures. We then show the stability of these measures when both position and normal input data are approximations of the underlying continuous shape. As a byproduct, our tool is able to correctly estimate curvatures over polyhedral approximations of shapes with explicit bounds, even when their natural normal are not correct, as long as an external convergent normal vector field is provided. Finally, the accuracy, convergence and stability under noise perturbation is evaluated experimentally onto digital surfaces