HAL-Ecole des Ponts ParisTech
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Re-analysis of ten hot-Jupiter atmospheres with disequilibrium chemistry retrieval
No full textInternational audienceContext: Constraining the chemical structure of exoplanetary atmospheres is pivotal for interpreting spectroscopic data and understanding planetary evolution. Traditional retrieval methods often assume thermochemical equilibrium or free profiles, which may fail to capture disequilibrium processes such as photodissociation and vertical mixing. This study leverages the TauREx 3.1 retrieval framework coupled with FRECKLL, a disequilibrium chemistry model, to address these challenges.Aims: The study aims to (1) assess the impact of disequilibrium chemistry on constraining metallicity and C/O ratios; (2) evaluate the role of refractory species (TiO and VO) in spectral retrievals; (3) explore consistency between transit and eclipse observations for temperature and chemical profiles; and (4) determine the effects of retrieval priors and data reduction methods.Methods: Ten hot-Jupiter atmospheres were re-analysed using Hubble Space Telescope (HST) WFC3 data in eclipse and transit. The TauREx-FRECKLL model incorporated disequilibrium chemistry calculations with a Bayesian framework to infer atmospheric properties. Retrieval scenarios included tests with and without TiO and/or VO and comparisons across different data reduction pipelines.Results: The disequilibrium approach significantly alters retrieved metallicity and C/O compared to equilibrium models, impacting insights into planet formation. TiO and/or VO additions improve fits for only two planets, with limited effect on parameter convergence. Retrievals reconcile transit and eclipse temperature profiles in deeper atmospheric layers but not in upper layers. These results are highly dependent on spectral resolution and retrieval priors, emphasising the limitations of HST data and the need for broader spectral coverage from instruments such as JWST.Conclusions: This study demonstrates the feasibility and importance of incorporating disequilibrium chemistry in atmospheric retrievals, highlighting its potential for advancing our understanding of exoplanetary atmospheres with next-generation telescopes
Mitigation or adaptation to climate change? The role of fiscal policy
No full textInternational audienceThis article examines the interplay between fiscal policy and investments in climate change mitigation and adaptation. Adaptation is funded by public revenues from taxation and public bonds, whereas households can invest in mitigation and receive subsidies. We show that adaptation and mitigation are substitutes or complements, depending on the level of economic development and fiscal policy decisions. If the capital stock is initially low, adaptation and mitigation are complements (resp. substitutes) if the mitigation subsidy is low (resp. high). When the government is in debt, we show that increasing public spending to finance adaptation and/or mitigation could be beneficial if the capital stock is high enough but could be detrimental for countries with low capital stock. Thus, we add a new argument to the debate on the optimal mix between adaptation and mitigation, namely fiscal policy and the funding schemes of these investments. Finally, we propose extensions that consider a level of adaptation proportional to pollution flow, debt financing of public investment, and public mitigation investment alongside private adaptation investment
Taille des classes et inégalités territoriales : quelle stratégie face à la baisse démographique ?
No full textInternational audienceLa baisse quasi continue de la natalité en France depuis 2010 entraîne une diminution marquée des effectifs d’élèves dans le premier degré, qui se prolongera pendant au moins une décennie. Dans un contexte de contraintes sur les finances publiques, cette évolution pose la question d’un ajustement de la dépense éducative : faut-il réduire le nombre d’enseignants pour réaliser des économies budgétaires, ou saisir cette opportunité pour améliorer les conditions d’apprentissage en réduisant la taille des classes ? Ce chapitre explore les enjeux de ce choix à partir de données détaillées et de simulations prospectives. L’étude met en lumière les arbitrages économiques associés à différents scénarios de gestion des effectifs enseignants, et souligne les risques d’accentuation des disparités territoriales en matière de taille des classes si la répartition des enseignants ne fait pas l’objet d’une planification coordonnée
From foreshock to mainshock: transient slip velocity sets nucleation time
No full textInternational audienceUnderstanding how fault slip transitions from slow, stable motion to fast, dynamic rupture is critical for improving earthquake models, yet the governing physical conditions remain uncertain. We present results from controlled laboratory experiments that simulate earthquake-like ruptures. These experiments capture a broad range of nucleation behaviors, including precursory slip and foreshock activity. We observe a consistent relationship between the characteristics of early slip events and the subsequent rupture dynamics. Specifically, transient slip rates following a foreshock predict both the duration and extent of the nucleation phase; this trend is reflected not just in the laboratory data but also along certain natural faults. Preliminary analysis suggests that these behaviors align with theoretical models incorporating velocity-dependent fracture energy and rate-and-state friction. Our findings point toward a set of parameters that may help distinguish when early slip evolves into a full rupture. This work is ongoing and contributes to a broader effort to connect lab-based rupture processes with observations from natural earthquakes
Around the World in 80 Timesteps: A Generative Approach to Global Visual Geolocation
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Exploring crystallization pressure limits via molecular simulation
No full textInternational audienceCrystallization pressure can cause significant damage to various materials, particularly cementitious materials and geomaterials. Understanding the mechanism behind this pressure is essential to preserve these materials and limit their degradation. Although the phenomenon has been known for a long time, the results from theoretical calculations and experimental observations remain very heterogeneous. The confined crystallization process relies on the presence of a nanometric wetting film at the interfaces to sustain crystal growth. The conditions for the existence and stability of these nanometric films, as well as their transport properties, remain largely unknown due to the great difficulty of studying them experimentally. In this paper, we determine by molecular simulation the limits of the crystallization pressure phenomenon at the finest scale. We perform hybrid configurational bias Monte Carlo-molecular dynamics simulations to determine the critical pressure at which the wetting film separating the crystal from the pore surface disappears under various temperature and pressure conditions. We illustrate the influence of the wetting film’s composition on the crystallization process by comparing a confined pure water film to a confined brine solution film. The obtained results enable us to establish both an upper and a lower boundary for the crystallization pressure, to define the range of applicability for the existing theoretical equations, and to identify the limiting factors affecting the transport properties in the constrained films
Distance entre métiers et transitions professionnelles des demandeurs d’emploi après une formation
No full textInternational audienceDoes vocational training help correct structural imbalances in the labour market? We propose a new measure of the skills distance between occupations, obtained by fine-tuning a large language model on a sample of job offers. Using this method, we demonstrate that the "return to employment" differential between jobseekers with and without training is driven by a reallocation of workers towards occupations that are very different from their previous posts in terms of the skills required. From a purely reallocative perspective, however, the return to employment differential associated with vocational training does not appear to be driven by more jobseekers moving to occupations where employers are struggling to recruit.La formation professionnelle contribue-t-elle à la résorption des déséquilibres structurels du marché du travail ? Nous construisons une nouvelle mesure d'écart de compétences entre métiers grâce à l'application d'un algorithme de traitement du langage à un échantillon d'offres d'emploi. En utilisant cette mesure, nous montrons que le différentiel de retour à l'emploi entre demandeurs d'emploi formés et non formés est tiré par les réallocations vers des métiers éloignés en termes de compétences par rapport à celui du dernier poste occupé. D'un point de vue purement réallocatif, le différentiel de retour à l'emploi lié à la formation professionnelle ne semble cependant pas être tiré par des redirections plus nombreuses vers des métiers en forte tension
Endogenous Innovation in a Growth Model à la Solow
No full textWe develop a dynamic endogenous-growth model with an R&D sector in which the elasticity of innovation with respect to existing knowledge can be negative. We prove the existence and uniqueness of a balanced growth path (BGP) and derive closed-form growth factors, showing that productivity and output growth are semi-endogenous and population-driven. We also establish the global stability under general production function. Under testable parameter restrictions, the economy converges to the BGP. When the knowledge elasticity is sufficiently low, a Jacobian-based condition implies instability, and an N-period innovation cycle can emerge. Comparative statics are conducted to show the role of several factors, including research efficiency, elasticity of inputs and population growth. Calibrated simulations map out transitions and mark the points at which stability is lost. They make clear when innovation frictions endanger balanced growth and provide practical guidance for R&D and demographic policy