HAL-Ecole des Ponts ParisTech
Not a member yet
42743 research outputs found
Sort by
Convex ordering for stochastic Volterra equations and their Euler schemes
No full textInternational audienceIn 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
Insider Imitation
No full textInternational audienceWe study how regulating data usage impacts innovation in digital markets. Platforms commonly use proprietary data about third-party sellers to inform their own competing offerings, dampening incentives for innovation. We model this interaction and characterize how data usage restrictions reshape these incentives. An outright ban on data usage may boost or curtail innovation, depending upon the thickness of the right tail of demand for new products. More flexible rules controlling when and what data is made available can always improve the effectiveness of regulation. Our results contribute to an ongoing policy discussion regarding competition in digital markets
Spectral correctness of the discontinuous Galerkin approximation of the first-order form of Maxwell's equations with discontinuous coefficients
No full textInternational audienceThe paper analyzes the discontinuous Galerkin approximation of Maxwell's equations written in first-order form and with non-homogeneous magnetic permeability and electric permittivity. Although the Sobolev smoothness index of the solution may be smaller than 1/2, it is shown that the approximation converges strongly and is therefore spectrally correct. The convergence proof uses the notion of involution and is based on a deflated inf-sup condition and a duality argument. One essential idea isthat the smoothness index of the dual solution is always larger than 1/2 irrespective of the regularity of the material properties
Litter in French urban areas—part 1: composition, sources, and spatio-temporal variations on urban surfaces
No full textInternational audienceUrban areas concentrate on human activities that generate large amounts of waste. A small fraction is mismanaged and ends up on urban surfaces and eventually in waterways. The fraction reaching waterways is usually estimated using poorly constrained data, while litter density on urban surfaces and its subsequent transfer dynamics are also poorly documented. This study provides new insights into litter composition, sources, and spatio-temporal variations in the urban catchments of Pin Sec and Jules Verne (Nantes, France), which are dominated by industrial/commercial, collective, and individual housing areas. Regular litter collection on selected street sections was combined with visual counting of street litter (> 1 cm). In total, 50.8 kg (dry weight) of litter were collected and 232,217 items were counted, mainly smoking and food consumption-related items. Litter densities ranged between 40,000 and 452,000 items/km 2 depending on local activities, item mobility, and land use as a driver of road and foot traffic. A median litter accumulation rate of 7 g/inhabitant/day was estimated, suggesting that 0.6% of the total amount of waste generated in public places is mismanaged. Results over space show that litter is strongly correlated with land use and that litter accumulation is promoted in green spaces. Results over time show that litter stock is quickly renewed and that items may have long residence time on urban surfaces
Two unsteady solutions of a homogeneous equilibrium model in a porous medium
No full textInternational audienceWe present in this note two reference one-dimensional unsteady solutions of a HEM model, considering possible heat source terms, and focusing on a steady porous medium. The model is recalled first, then details on exact solutions are provided. Several Equations Of State are discussed
What Makes a Satisfying Life? Prediction and Interpretation with Machine‐Learning Algorithms
No full textInternational audienceMachine Learning (ML) methods are increasingly being used across a variety of fields, and have led to the discovery of intricate relationships between variables. We here apply ML methods to predict and interpret life satisfaction using data from the UK British Cohort Study. We discuss the application of first Penalized Linear Models and then one non‐linear method, Random Forests. We present two key model‐agnostic interpretative tools for the latter method: Permutation Importance and Shapley Values. With a parsimonious set of explanatory variables, neither Penalized Linear Models nor Random Forests produce major improvements over the standard Non‐penalized Linear Model. However, once we consider a richer set of controls these methods do produce a non‐negligible improvement in predictive accuracy. Although marital status, and emotional health continue to be the most‐important predictors of life satisfaction, as in the existing literature, gender becomes insignificant in the non‐linear analysis
What Caused the US Pandemic-Era Inflation?
No full textInternational audienceWe estimate a simple dynamic model of prices, wages, and short-run and long-run inflation expectations that allows us to analyze and quantify the sources of recent US inflation. We find that, contrary to early concerns that inflation would be spurred by overheated labor markets, most of the inflation surge resulted from shocks to prices given wages. Although tight labor markets have, thus far, not been the primary driver of inflation, we find that they have a relatively more persistent effect on wage growth and inflation. Controlling inflation will, thus, ultimately require achieving a better balance of labor demand and supply
Agriculture, aquaculture et pêche : impacts des modes de production labellisés sur la biodiversité. Rapport scientifique de l'étude
No full textLa loi Climat et résilience de 2021 a instauré la mise en place d’un affichage environnemental sur les produits alimentaires afin d’informer les consommateurs du coût environnemental de leurs achats. La construction de cet affichage a suscité un important travail méthodologique ouvert aux acteurs. Un bilan intermédiaire a souligné la difficulté à appréhender toutes les dimensions de la biodiversité. C’est dans ce cadre que les ministères en charge de la transition écologique, et de l’agriculture et de l’alimentation, ainsi que l’ADEME, ont sollicité INRAE et l’Ifremer courant 2022 pour mieux documenter ce volet biodiversité, en se focalisant sur les pratiques de production. Afin d’éclairer plus largement les politiques publiques, les pouvoirs publics ont choisi de s’appuyer sur les labels dont les cahiers des charges certifient des pratiques et parce que leur développement les place au cœur de nombreux débats sur les relations entre production et consommation durables. L’étude, intitulée « BiodivLabel », a été menée par un comité pluridisciplinaire d’experts scientifiques issus d’organismes publics de recherche et d’enseignement supérieur
Recommendation of TC RILEM TC 274-TCE: 3-point bending test procedure for earthen bricks—quality control of earth bricks for structural masonry by flexural strength
No full textInternational audienceBuilding with unstabilised earth bricks (EB) as units for structural masonry walls offers a sustainable alternative to mitigate resource depletion's negative impact and global warming. Using locally sourced earth for EB production is required to achieve these benefits. This leads to large variations in material composition. Consequently, quality control becomes critical to ensure adequate mechanical performance of the masonry units. In the framework of the RILEM TC 274-TCE, the characterisation of the flexural strength of bricks has been examined. A comprehensive inter-laboratory campaign involving seven laboratories across three countries was conducted, during which flexural tests were performed on 98 bricks. This article details the TC 274-TCE recommendations on the procedure to conduct a 3-point bending test on an EB. Key test parameters such as specimen pre-conditioning, setup boundary conditions, loading rate and determination of material flexural strength are discussed. The calculation of flexural strength was evaluated by comparing results obtained from the beam theory model and a solid mechanics approach, validated through finite element modelling. The findings confirm that the 3-point bending test is a reliable method to assess the mechanical performance of EB and to control their quality
CoDEx: Combining Domain Expertise for Spatial Generalization in Satellite Image Analysis
No full textInternational audienceGlobal variations in terrain appearance raise a major challenge for satellite image analysis, leading to poor model performance when training on locations that differ from those encountered at test time. This remains true even with recent large global datasets. To address this challenge, we propose a novel domain-generalization framework for satellite images. Instead of trying to learn a single generalizable model, we train one expert model per training domain, while learning experts' similarity and encouraging similar experts to be consistent. A model selection module then identifies the most suitable experts for a given test sample and aggregates their predictions. Experiments on four datasets (DynamicEarthNet, MUDS, OSCD, and FMoW) demonstrate consistent gains over existing domain generalization and adaptation methods