HAL-Ecole des Ponts ParisTech
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Who Feels Poor? Transitions into Poverty and Subjective Well-Being
No full textThe existence of a common monetary poverty line set at 60% of the national median income, used by most OECD countries, is very useful for comparisons over time and across countries. However, this measure is primarily a convention, and thus the 60% level might be questioned in terms of targeting public policies, as it does not necessarily reflect who is poor in a given society. In this study, I attempt to establish a meaningful poverty threshold at the national level by combining the objective approach in terms of income with a subjective approach in four comparable countries—France, Australia, Germany, and the United Kingdom— using detailed panel administrative data. More precisely, I compare household income trajectories with the evolution of individuals’ well-being to identify empirical discontinuities in well-being dynamics following income shocks at the bottom of the income distribution. These discontinuities define a vulnerability zone where individuals are more impacted by transitioning below 80% of the median income in France and Australia, and 70% of the median income in Germany and the United Kingdom, than at any alternative monetary threshold. I then highlight the role of life and labor market events that occur simultaneously with households’ income shocks, as well as the differences in institutional regimes that could explain the location of these empirical discontinuities in each country. Overall, my study suggests broadening the usual monetary poverty definition by considering alternative thresholds more closely aligned with individuals’ perceptions of their situations
Collusion in Bidding Markets: The Case of the French Public Transport Industry
No full textWe explore empirically the impact of the market sharing collusive practices that were implemented in the French public transportation industry between 1994 and 1999. We build a structural model of bidding markets where innovating firms compete for the market and have the ability to spread the benefits of their innovation through all markets on which they are active. Each local competitive environment shapes the distribution of the prices (the bids) paid by public authorities to transport operators. We recover empirically the distribution of prices and innovation shocks and we show that collusive practices had overall a limited impact on prices. Firms were in reality more interested in avoiding significant financial risks inherent to the activity, as well as the high cost of preparing a tender proposal. As a by-product, we perform a counterfactual analysis that allows us to simulate how an increase in firms' innovation reduces prices significantly
Residual stress control in large format polylactic acid additive manufacturing via fast thermomechanical simulation and in-operando imaging techniques
No full textInternational audiencePolymer-based Large Format Additive Manufacturing (LFAM) is an extrusion-based technology utilizing a robotic arm-mounted nozzle to deposit large-diameter polymer beads from heated polymer pellets. However, technical challenges arise due to slower cooling rates and heat accumulation, significant deformation that should be accounted for updating the nozzle path, as well as the development of residual stresses from thermo-chemical shrinkage leading to debonding. To overcome these challenges, the study proposes to combine recent and fast thermal and mechanical approaches. This computationally efficient digital twin of the process is validated experimentally on a thin-wall structure using polylactic acid as a feedstock material. To do so, anisotropic material properties are characterized, and in-operando temperature and displacement field measurements are performed using an infrared thermal camera and backward Digital Image Correlation techniques. Numerical results are in satisfying agreement with experimental data. The validated digital twin is then utilized to characterize the effect of process parameters on the number of layers above the glass transition temperature, the formation of residual stresses and the position offset between the top surface of the structure and the nozzle. This paper presents a fast numerical tool to better design fabrication conditions and improve the quality and fabricability of LFAM-produced parts
Eyring-Kramers exit rates for the overdamped Langevin dynamics: the case with saddle points on the boundary
No full textInternational audienceLet be the stochastic process solution to the overdamped Langevin dynamics and let be the basin of attraction of a local minimum of . Up to a small perturbation of to make it smooth, we prove that the exit rates of from through each of the saddle points of on can be parametrized by the celebrated Eyring-Kramers laws, in the limit . This result provides firm mathematical grounds to jump Markov models which are used to model the evolution of molecular systems, as well as to some numerical methods which use these underlying jump Markov models to efficiently sample metastable trajectories of the overdamped Langevin dynamics
Holonic, self-organized and multi-criteria management of the Circular Supply Chain
No full textInternational audienceThe circular economy transforms the supply chain by introducing three types of feedback loops that operationalise the 10 action levers of circularity. This model aims to preserve the use value of artefacts and limit the extraction of new resources, while reducing environmental impact. Managing these circu-lar flows, which are more complex and uncertain than in a linear approach, requires an adapted and decentralised logistics organisation capable of ad-justing in real time. A holonic approach to managing this circular supply chain aims to maximise the profitability and useful life of artefacts, using a self-organised, multi-criteria approach
A Branch-Price-and-Cut Algorithm for the Kidney Exchange Problem
No full textInternational audienceWe study a Kidney Exchange Problem (KEP) with altruistic donors and incompatible patient-donor pairs. Kidney exchanges can be modelled in a directed graph as circuits starting and ending in an incompatible pair or as paths starting at an altruistic donor. For medical reasons, circuits and paths are of limited length and are associated with a medical benefit to perform the transplants. The aim of the KEP is to determine a set of disjoint kidney exchanges of maximal medical benefit or maximal cardinality.We consider a set packing formulation for the KEP with exponentially-many variables associated with circuits and paths, and develop a Branch-Price-and-Cut algorithm (BPC) to solve it.We decompose the pricing problem into a subproblem to price out the path variables and several subproblems to price out the circuit variables. We strengthen the linear relaxation via the inclusion of a family of non-robust inequalities.We perform extensive computational experiments to assess the performances of the BPC algorithm on three sets of instances from the literature and on a newly generated set of challenging instances.On the easiest instances, it yields comparable results with the literature, while on the other sets it clearly outperforms the previous results.Hence, contrary to the existing literature, the BPC algorithm is the only exact approach able to effectively solve various and difficult instances with both objective functions and long chains and cycles
Modélisation et évaluation de la solution agrivoltaïque au nexus climat-eau-énergie-alimentation dans le contexte du changement climatique dans la région euro-méditerranéenne
No full textClimate change in the Euro-Mediterranean(EUROMED) region is increasing pressure on agriculture, notably by heightening land vulnerability andreducing water availability. Agrivoltaics (AV), whichcombines photovoltaic energy production with agriculture on the same land surface, is emerging as akey solution within the water-energy-food-ecosystems(WEFE) nexus. By providing shade, AV reduces heat stress and soil evaporation, thereby improving the microclimate and the resilience of crops. However, itsperformance remains highly dependent on climate,crop type and geographical context, which calls formodelling tools suited to regional scales. To addressthis gap, we develop a regional AV model by integrating a photovoltaic module into the land surfacemodel ORCHIDEE. The model modifies solar radia-tion and wind speed from climate models, then simu-lates energy, water, carbon and nitrogen fluxes to as-sess AV impacts on agricultural soils. In a first ap-plication based on reanalysis data, two contrastingregions are studied : the Iberian Peninsula and the Netherlands. In the drier Iberian Peninsula, AV improves crop yields, food security, resource-use effi-ciency and renewable energy production, especiallyduring drought. It also enhances nitrogen-use efficiency and reduces green house gas emissions. Incontrast, in the Netherlands -wetter and less sunny-AV tends to reduce yields, offering only limited be-nefits. In a second phase, the model is applied tothe entire EUROMED region using EURO-CORDEXprojections under the RCP 8.5 scenario. The results show that the benefits of AV depend strongly on regio-nal water and climate conditions. Southern drought-prone areas are the most suitable, while more humid northern regions gain only modest advantages. This innovative, flexible and multi-scale model thus pro-vides a valuable tool to inform public policies aiming for more resilient, low-carbon agriculture and a better-integrated WEFE nexusLe changement climatique dans la région euro-méditerranéenne (EUROMED) accentue les pressions sur l’agriculture, notamment via la vulnérabilité accrue des terres et la diminution des ressources en eau. L’agrivoltaïsme (AV), qui associe production photovoltaïque et agriculture sur une même surface, apparaît comme une solution clé dans le cadre du nexus eau-énergie-alimentation-écosystèmes (EEAE). En fournissant de l’ombre, il réduit le stress thermique et l’évaporation du sol,améliorant ainsi le microclimat et la résilience des cultures. Ses performances restent cependant très dépendantes du climat, des cultures et du contexte géographique, ce qui exige des outils de modélisation adaptes aux échelles régionales. Pour combler ce manque, nous développons un modelé AV régional en intégrant un module photovoltaïque au modelé de surface ORCHIDEE. Celui-ci modifie le rayonnement solaire et la vitesse du vent issus des modelés climatiques, puis simule les flux d’énergie, d’eau, de carbone et d’azote pour évaluer les effets de l’AV sur un sol agricole. Dans une première application basée sur des données de réanalyse, deux régions contrastées sont étudies : la péninsule Ibérique et les Pays-Bas. En Ibérie, plus sèche, l’AV améliore les rendements, la sécurité alimentaire, l’efficacité des ressources et la production d’énergie renouvelable,notamment en période de sécheresse. Il augmente aussi l’efficacité d’utilisation de l’azote et réduit les émissions de gaz à effet de serre. A l’inverse, aux Pays-Bas, plus humides et moins ensoleilles, l’AV tend à diminuer les rendements avec des bénéfices limites. Dans une seconde phase, le modèle est applique à l’ensemble de la région EUROMED à partir des projections EURO-CORDEX sous RCP 8.5.Les résultats montrent que les bénéfices de l’AV dépendent fortement des conditions régionales d’eau et de climat. Les zones méridionales sèches sont les plus adaptées, tandis que les régions plus humides en tirent des gains modestes. Ce modelé innovant, flexible et multi-échelle fournit ainsi un outil précieux pour guider les politiques publiques vers une agriculture plus résiliente, faible en carbone et mieux intégrée au nexus EEA
Nexus approach to enhance water-energy-food security and ecosystems resilience under climate change in the Mediterranean
No full textInternational audienceThe Mediterranean Basin, already a water-scarcity hotspot, faces intensifying droughts and warming that strain the water–energy–food–ecosystems (WEFE) nexus. Climate impacts cascade across sectors, while siloed responses risk maladaptation. Nexus-based solutions—centred on water—can foster synergies and reduce trade-offs, with nature-based, socially inclusive, and clean energy strategies offering transformative potential. Yet governance, cooperation, and data gaps persist; closing these is vital to operationalize the nexus and advance regional sustainability
Do Billionaires Pay Taxes?
No full textWe link French households’ tax records to the corporations they control, and build a payout-policy–neutral income measure, with corresponding tax burdens including those of "billionaires": the top 0.0002%. De- fined as such, income is more concentrated than taxable income, it better predicts rich-list membership, and persists more among billionaires. Personal taxes remain progressive until the top 0.1%, but eventually decline to 2% of income. Corporate taxes are an imperfect progressive backstop, as total tax rates fall from 45% at the 0.1% threshold to 25% for billionaires. Among these, the tax burden is global and tax-efficient pyramidal control over businesses ubiquitous
Modélisation de la dispersion atmosphérique en conditions de vent faible en environnements complexes : application à une expérimentation d'émission de traceur sur un site industriel
No full textInternational audienceContext: Modeling atmospheric dispersion under low‐wind conditions in complex built environments is crucial for risk assessment near industrial sites. The combination of challenging atmospheric conditions, such as flow recirculation, turbulence anisotropy, plume meandering, and heterogeneous infrastructure makes accurate prediction of pollutant transport particularly difficult.Objective: This study aims to evaluate the performance of the high‐resolution ComputationalFluid Dynamics (CFD) model code_saturne (developed by EDF R&D and CEREA) under complexatmospheric and environmental conditions. The assessment is based on data from a controlledtracer release experiment conducted at an industrial site characterized by dense infrastructure andheterogeneous surface features