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The Economics of Nation-Building: Methodological Tool Kit and Policy Lessons
No full textInternational audienceThis article reviews the recent burgeoning political economics research on nation-building. We focus on three main aspects of this body of work. First, we discuss methodological issues related to measuring nation-building outcomes and provide a synthesis of studies that employ different techniques, such as surveys on identity, lab-in-the-field methods, and direct observation of actions signaling identity. Second, we explore preconditions for effective nation-building, particularly focusing on ethnolinguistic polarization and segregation, and discuss how these factors may influence policy choices and their effectiveness. We also consider geopolitical factors. Finally, we review advances in the literature evaluating the effects of major nation-building policies, including those that encourage intergroup contact, the choice of national education curricula, propaganda, leadership, decentralization, and foreign interventions. We highlight instances in which these policies work or backfire
A quasi-interpolation operator yielding fully computable error bounds
No full textInternational audienceWe design a quasi-interpolation operator from the Sobolev space H^1_0 to its finite-dimensional finite element subspace formed by piecewise polynomials on a simplicial mesh with a computable approximation constant. The operator 1) is defined on the entire H^1_0, no additional regularity is needed; 2) allows for an arbitrary polynomial degree; 3) works in any space dimension; 4) is defined locally, in vertex patches of mesh elements; 5) yields optimal estimates for both the H^1 seminorm and the L^2 norm error; 6) gives a computable constant for both the H 1 seminorm and the L^2 norm error; 7) leads to the equivalence of global-best and local-best errors; 8) possesses the projection property. Its construction follows the so-called potential reconstruction from a posteriori error analysis. Numerical experiments illustrate that our quasi-interpolation operator systematically gives the correct convergence rates in both the H^1 seminorm and the L^2 norm and its certified overestimation factor is rather sharp and stable in all tested situations
Le modèle urbain du Transit-Oriented Development revisité par la mobilité individuelle légère émergente. Une investigation dans la région Hauts-de-France
No full textThe resurgence of interest in cycling is part of a broader transformation in mobility practices, increasingly integrated into intermodal travel chains. Within this context, this research examines the role of micromobility in Transit-Oriented Development strategies, exploring its potential to address first- and last-mile connectivity challenges in public transport and thereby reinforce the underlying urban model. The primary objective of this doctoral research is to identify the dynamics of these mobility strategies, analyze their determining factors, and assess their impacts on station-area accessibility across different spatial scales. To this end, the study extends the traditional urban model framework by incorporating micromobility, introducing the concept of Micromobility-friendly Transit-Oriented Development. This approach aims to enrich existing theoretical and operational paradigms by incorporating recent developments in the mobility landscape. Methodologically, the research adopts a mixed-methods approach applied to the Hauts-de-France region. It combines a systematic literature review ; fieldwork conducted among intermodal travelers at railway stations, including quantitative observations, a questionnaire survey, and ride-along interviews ; and a geostatistical modeling approach revisiting the Node-Place model, reinterpreted through the lens of (new) geographical proximities. The main findings underscore the emerging nature of intermodal practices at railway stations, largely driven by the rise of electric scooters. These modal combinations, still widely underestimated, triple accessibility coverage to both populations and destinations. Moreover, this investigation highlights significant gender disparities in intermodal mobility, which are exacerbated when urban environments are hostile to active travel. By establishing a classification of railway stations in the region, this research demonstrates that integrating micromobility can significantly enhance station usage without requiring major infrastructure overhauls or heavy investments. Ultimately, the development of a ”bicycle system” as a catalyst for intermodality strengthens the integration between the public transport network and the broader urban fabric.Le regain d’intérêt pour le vélo et la micro-mobilité s’inscrit dans une transformation plus large des pratiques de mobilité, intégrées dans des chaînes de déplacement intermodales. Dans ce contexte, cette recherche interroge l’intégration de la mobilité individuelle légère dans les stratégies de Transit-Oriented Development, en explorant son potentiel à répondre aux défis des « premiers et derniers kilomètres » du transport public, et ainsi à renforcer le modèle urbain sous-jacent. L’objectif central de cette recherche doctorale est d’identifier les dynamiques d’usage de ces stratégies de mobilité, d’en analyser les facteurs déterminants et d’évaluer leurs effets sur l’accessibilité des quartiers de gare, à différentes échelles spatiales. À cette fin, elle propose une extension du concept d’aménagement, en intégrant la mobilité individuelle légère à l’urbanisme ferroviaire. Cette déclinaison, désignée sous le terme de Micromobility friendly Transit-Oriented Development, vise à enrichir les cadres théoriques et opérationnels existants, en prenant en compte les évolutions récentes du paysage de la mobilité. Ce travail repose sur un dispositif méthodologique mixte, appliqué au périmètre régional des Hauts-de-France. Il combine une revue systématique de la littérature ; une enquête de terrain auprès des cyclo-voyageur·se·s en gare, incluant des séances d’observation quantitative, l’administration d’un questionnaire et la réalisation de parcours commentés ; ainsi qu’une modélisation géostatistique revisitant l’outil « nœud-lieu », à la lumière des (nouvelles) proximités géographiques. Les principaux résultats mettent en évidence le caractère émergent des pratiques intermodales en gare, en grande partie impulsé par l’essor de la trottinette électrique. Ces combinaisons modales, encore largement sous-évaluées, permettent de tripler la couverture d’accessibilité aux populations et aux destinations. Par ailleurs, cette investigation révèle des inégalités de genre marquées dans les pratiques intermodales, exacerbées lorsque les environnements urbains se révèlent hostiles à la mobilité active. En établissant une classification des gares de la région, elle démontre que l’intégration de la mobilité individuelle légère possède un potentiel considérable pour stimuler la fréquentation des nœuds, sans nécessiter de reconfiguration ou d’investissement lourds. En somme, le développement du « système vélo », en tant que catalyseur de l’intermodalité, contribue à consolider l’articulation entre le réseau de transport public et le système urbain
Exploring stratospheric aerosol composition and transport with EarthCARE ATLID and ground-based lidars
No full textInternational audienceESA’s EarthCARE satellite mission launched on 29 May 2024 and carrying Atmospheric LIDar (ATLID) provides high-resolution vertical profiling of aerosols and clouds at 355 nm. The High Spectral Resolution Technique (HSRL) exploited by ATLID enables a better SNR compared to CALIPSO lidar. We present examples of ATLID observations of various types of stratospheric aerosols and evaluate the ATLID performance in the stratosphere through cal/val exercise using ground-based lidars and comparison with limb-viewing and solar occultation satellite sensors.Fully operational since August 2024, ATLID has been witness to a significant perturbation of stratospheric aerosol budget following the eruptions of Ruang volcano (Indonesia) in late April 2024. The Ruang eruption has effectively ended the late decay of the Hunga perturbation and boosted the tropical SAOD by a factor of 3. Using ATLID together with OMPS-LP (SNPP and NOAA-21) and ISS/SAGE III satellite observations complemented by long-term groundbased lidar measurement series at various NDACC sites in both hemispheres we show that Ruang aerosols were subject to an unusually massive isentropic transport into the southern extratropics and were most probably entrained by the 2024 Antarctic polar vortex. The meridional evolution of Ruang aerosols in the stratosphere and their optical properties are compared with that of Hunga and other eruptions
Normes internationales et compétitivité des filières agroalimentaires
No full textInternational audienceLes normes de qualité, notamment les mesures sanitaires et phytosanitaires (SPS) ainsi que les obstacles techniques au commerce (OTC), sont de plus en plus utilisées par les gouvernements nationaux et donnent lieu à un nombre croissant de différends commerciaux internationaux. 1 Une étude récente (Disdier, Gaigné and Herghelegiu, 2023), analyse l’impact des normes de qualité appliquées par un pays sur la qualité des produits échangés et la compétitivité des filières
Marginal-constrained modified Wasserstein barycenters for Gaussian distributions and Gaussian mixtures
No full textThe aim of this work is to propose modified Wasserstein barycenters for probability measures defined on cartesian product sets which satisfy given marginal constraints. We focus on the specific case of Gaussian and Gaussian mixture distributions, as the proposed approach strongly relies on new results about properties of geometric means of covariance matrices.Wasserstein barycenters that respect some desired constraints on the marginals of the distributions, both for Gaussian distributions and for mixtures of Gaussian distributions. In the case of Gaussian distributions, the marginal-constrained modified Wasserstein barycenters can be analytically computed, while for Gaussian mixtures, computing the marginal-constrained barycenter consists in a postprocessing of the Gaussian mixture Wasserstein barycenter. In both cases, we provide numerical simulations illustrating the difference between Wasserstein barycenters and modified marginal-constrained Wasserstein barycenters. We moreover provide several test cases where the marginal-constrained Wasserstein barycenters interpolate better than regular Wasserstein barycenters, showcasing the practical interest of the proposed approach.As a by-product, we prove new results concerning marginal-preserving Wasserstein barycenters. Indeed,} Wasserstein barycenters do not preserve marginals in general. In this work, as a consequence of the derived properties on the geometric mean of covariance matrices, we obtain sufficient and necessary conditions for the Wasserstein barycenter between two Gaussian distributions to preserve marginals, and provide necessary conditions in the case of more than two Gaussians
SPH modelling of water flow inside a porous medium using a Riemann based formulation
No full textInternational audienceSimulating granular flows has been a major concern for thepast decades, with various environmental applications such asavalanches, landslides and scour near fluvial, coastal and off-shore constructions. These phenomena involve a porous matrixundergoing large deformations and characterized by a complexbehaviour. Thanks to its ability to handle large deformationsof the medium, SPH appears as a particularly advantageousmethod to deal with these problems. Various SPH schemesalready exist to model the granular medium behaviour, suchas the ones developed by Feng et al. [1], Bui and Nguyen [2](elastoplastic approach) or Gha¨ıtanellis [3] (elasto-viscoplasticapproach). However, to the authors’ knowledge, none of thesepapers show in their results what the water flow looks like insidethe porous structure while it deforms. Consequently, the presentwork aims at presenting a model to simulate the deformationof a granular medium as well as its infiltration by water. Theporous structure is unsaturated and is considered as a continuousmedium. Infiltrated water flows according to Darcy’s or Darcy-Forchheimer’s laws. Two different sets of particles are used forthis purpose, one for the water phase and an other one forthe porous structure, as done by Shimizu et al [4]. Riemann-based schemes have never been used yet for such purpose,though it proved to give accurate results for both fluid [6]and solid mechanics [7]. As a consequence, a new approachis proposed here by applying Riemann-based formulations onboth fluid and solid media. For the moment, the proposedmodel is not yet finished developing and only simulations withundeformable porous matrix are available for the writing of thisabstract. Results with moving, deformable porous matrix will bepresented during the conference
Resolved DEM-CFD coupling for wave-armour blocks interactions
No full textInternational audienceThe present work aims to tackle breakwater stability challenges through an innovative numerical deterministic method using a resolved DEM-CFD (Discrete Element Method—Computational Fluid Dynamics) strategy, which simulates the individual motions of armour units within a fluid solver. To achieve this, a coupling between a DEM code and a CFD code is implemented and validated. The fluids (air and water) are solved using a Eulerian–Eulerian CFD solver, and the contacts between blocks are solved using a DEM code. The solids are defined within the fluid solver using a discrete forcing approach and are therefore fully resolved. In this way, the fluid solver enables the prediction of object motions with complex shapes such as tetrapods. To couple the codes, forces exerted on the solids are calculated in the fluid solver and sent to the DEM solver. Then, contact and gravity forces are computed and added to the fluid forces. The DEM solver then computes the new positions and velocities of the bodies, which are retrieved by the fluid solver. An experimental study is performed on a fixed and instrumented idealized breakwater to evaluate the wave forces acting on a coastal structure. The experiments are then numerically reproduced to validate the numerical model. Simulations of the impact of solitary waves on a row of mobile isolated tetrapods laid on a horizontal berm are then performed using the DEM-CFD coupling. The importance of initial placement and friction parameters is investigated to show the sensitivity to these parameters
HydroModPy: A Python toolbox for deploying catchment-scale shallow groundwater models
No full textIn response to the growing demand for groundwater flow models, we present HydroModPy, an open-source toolbox designed to automate their deployment at the catchment scale. Built on top of the MODFLOW-enabling FloPy library, HydroModPy combines the robust WhiteboxTools toolbox for geospatial analysis and the well-validated MODFLOW code for groundwater modeling. This Python-based toolbox streamlines the construction, calibration, and analysis of unconfined aquifer models while adhering to FAIR (Findable, Accessible, Interoperable, and Reusable) principles. It enhances model reproducibility through editable Python code, supports multi-site deployment, and provides compatibility with alternative groundwater flow solvers. Furthermore, it integrates pre- and post-processing functionalities to simplify workflows. The toolbox enables catchment delineation and hydrological feature extraction from DEMs, followed by semi-automatic model construction and advanced visualization of hydraulic head and flow results. Users can choose from predefined aquifer structures and hydraulic properties such as exponential decay of hydraulic conductivity and porosity with depth or import complex 3D geological models. HydroModPy outputs can be exported in standard formats (e.g., raster, shapefile, netCDF), including water table elevation, water table depth, groundwater storage, groundwater-dependent hydrographic network and streamflow rates, and subsurface residence times. HydroModPy is tailored for the deployment in diverse geomorphological and hydrological settings, enabling the testing and exploration of aquifer models under varying recharge conditions. Its deployment capabilities are demonstrated in complex shallow basement and crystalline aquifers, where topography and geology primarily govern groundwater flow dynamics from hillslope to catchment scales. As an open-source toolbox, HydroModPy is designed for the community and actively encourages contributions from its users. It supports research in hydro(geo)logy and land and water management, while also providing valuable opportunities for teaching and education