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LONG TIME BEHAVIOUR OF ONE FACILITATED KINETICALLY CONSTRAINED MODELS: RESULTS AND OPEN PROBLEMS
No full textKinetically constrained models (KCMs) are interacting particle systems introduced in the '80s by physicists to have accessible stochastic models with glassy-type dynamics. The key mechanism behind the complex evolution of these otherwise simple models is the so-called dynamical facilitation, a feature embedded into the models via appropriate kinetic constraints. KCMs are reversible with respect to a Bernoulli product measure, and the analysis of their stationary evolution has witnessed significant progress in the last decade. Unfortunately, in the interesting regime when the equilibrium density of the facilitating vertices is small, many fundamental questions concerning the non-stationary evolution of even the simplest models remain unsolved. In this paper, we discuss some of these questions, along with partial new results and conjectures, for the one facilitated model and its variants, as well as for the biased annihilating branching process.</div
Introduction à l'ouvrage Comment les machines ont pris la terre
No full textInternational audienceLa mécanisation du travail agricole, la généralisation des pesticides de synthèse, le développement des biotechnologies furent promus comme autant de vagues successives d’amélioration de la productivité agricole. Aujourd’hui, les technologies numériques sont présentées comme un nouveau moyen de poursuivre cet objectif et de limiter ses conséquences désastreuses sur l’environnement et la santé humaine. Dans ce récit linéaire, chaque bouleversement technique viendrait en quelque sorte compenser les errements apportés par le précédent. Si la croyance dans le « progrès » ne s’exprime plus aussi naïvement que lors des « Trente Glorieuses », ce sont bien toujours les idées d’inéluctabilité, d’amélioration continue et d’impératif moral sur la nécessité de « nourrir le monde » qui sous-tendent encore cette vision, largement reprise et diffusée par les politiques publiques de soutien à l’innovation, les organisations professionnelles agricoles dominantes et les reportages à destination du grand public. Peu à peu se diffuse l’idée qu’une nouvelle génération d’équipements agricoles connectés voire « intelligents » est en train d’être mise au point grâce aux efforts conjoints de la recherche publique et de la R&D (recherche et développement) privée. Aujourd’hui, il est admis que la généralisation de l’emploi de ces matériels – drones, tracteurs autonomes, pulvérisateurs ou semoirs de précision, outils d’aide à la décision, etc. – permettra d’affronter les problèmes globaux tels que le changement climatique, la sécurité alimentaire, l’effondrement de la biodiversité et la réduction des risques pour la santé des populations, sans affecter pour autant la compétitivité de l’agriculture française sur les marchés mondiaux
Measure of maximal entropy for H-flows on non-compact manifolds
No full textIn this work, we introduce a natural class of chaotic flows on non-compact manifolds, called H-flows, which includes geodesic flows on non-compact manifolds with pinched negative curvature. We show that, under the additional assumption, called strong positive recurrence, that their entropy at infinity is strictly smaller than the topological entropy, such flows admit an invariant probability measure maximizing entropy. In particular, we compare several notions of entropy in a non-compact setting
Waiting time during admission procedures increases social inequalities in higher education
No full textInternational audienceMany domains in life require people to wait to access better outcomes, such as waiting in line to access prized tickets for a show, waiting to obtain a job offer from a selective firm, or being waitlisted for a prestigious university. Although waiting might be perceived as a fair mechanism to allocate resources, it may have unintended consequences on social inequalities as individuals from lower socioeconomic backgrounds (SES) may be less likely to wait. In this study, we investigate socioeconomic differences in waiting behavior during the higher education admission process in France. To do so, we leveraged a unique national database that recorded the admission behavior of every high schooler in France over a period of three years. During the admissions process, students faced a trade-off: They could either accept an immediate offer from a university or wait in the hope of receiving a preferred offer later. Results collected among 274,316 students reveal that low-SES students were significantly less likely to wait for preferred offers, even when controlling for objective costs and benefits of waiting. This led low-SES students to ultimately enroll in programs they liked less and that were less prestigious. These results highlight how admission procedures generating uncertainty and requiring students to wait may inadvertently exacerbate educational inequalities. Such systems, while efficient, can end up favoring students who wait more. This research contributes to current discussions on admission procedure fairness by illustrating that seemingly neutral algorithms can in fact deepen social inequalities if their design rewards patience
Analyse comparative du budget de la ville du Mans et de sa communauté urbaine (2012-2024)
No full textCette étude propose une analyse budgétaire comparative du Mans et de sa communauté urbaine, replacée dans le contexte des grandes villes françaises de plus de 100 000 habitants. En intégrant les budgets communaux et intercommunaux, l'objectif est d'évaluer la situation financière du territoire, ses équilibres, ses marges de manoeuvre, et sa soutenabilité budgétaire à moyen terme.</div
Why is the volatility of single stocks so much rougher than that of the S&P500?
No full textSoumis à "Quantitative Finance"The Nested factor model was introduced by Chicheportiche et al. in [24] to represent nonlinear correlations between stocks. Stock returns are explained by a standard factor model, but the (log)-volatilities of factors and residuals are themselves decomposed into factor modes, with a common dominant volatility mode affecting both market and sector factors but also residuals. Here, we consider the case of a single factor where the only dominant log-volatility mode is rough, with a Hurst exponent H ≃ 0.11 and the log-volatility residuals are "super-rough", with H ≃ 0. We demonstrate that such a construction naturally accounts for the somewhat surprising stylized fact reported by Wu et al. in [23], where it has been observed that the Hurst exponents of stock indexes are large compared to those of individual stocks. We propose a statistical procedure to estimate the Hurst factor exponent from the stock returns dynamics together with theoretical guarantees of its consistency. We demonstrate the effectiveness of our approach through numerical experiments and apply it to daily stock data from the S&P500 index. The estimated roughness exponents for both the factor and idiosyncratic components validate the assumptions underlying our mode
Avis du conseil scientifique du comité de bassin Seine-Normandie sur les gestions alternatives des urines et matières fécales humaines.Un potentiel d’amélioration conjointe de la gestion de l’eau et de la souveraineté alimentaire
No full textCet avis vise à remettre en débat le mode de gestion des excrétats humains (urines et matières fécales) vers des alternatives davantage sobres et circulaires, présentant des bénéfices potentiels sur les plans hydriques, environnementaux, sanitaires, économiques et de souveraineté alimentaire. Depuis plusieurs décennies, le tout-à-l’égout est le mode dominant de gestion des excrétats humains dans les villes occidentales, ce qui tend à le faire considérer comme naturel. Pourtant, les limites de ce mode de gestion, majoritairement linéaire, présentent de forts enjeux en termes de soutenabilité et de résilience. Les nombreuses alternatives à ce mode de gestion, communément nommées « séparation à la source des excrétats humains », tendent à se développer depuis dix ans sur le bassin Seine Normandie, au point que ce bassin est désormais devenu une référence mondiale en matière de séparation à la source des excrétats humains (Binz, 2024). Les filières professionnelles de gestion alternative pour une valorisation agricole sont actuellement en émergence. Il y a un intérêt stratégique à favoriser le développement de ces filières, ce qui nécessite le soutien de la puissance publique et la coordination des acteurs. À court terme, de très nombreuses opportunités « sans regret » sont à saisir. À long terme, le déploiement de la séparation à la source doit être pensé en articulation avec la remise en cause plus générale du paradigme actuel de gestion de l’eau et de l’alimentation, incompatible avec le respect des limites planétaires et les adaptations nécessaires aux changements climatiques et géopolitique
A Transformative Global Dialogue: The Race in the Marketplace (RIM) 2025 Research Forum, Cape Town, South Africa
No full textRace in the Marketplace (RIM) is an international transdisciplinary research network focused on the interactions of race in the marketplace through scholarship and practice. This article reports on the 2025 RIM Research Forum that convened in Cape Town, South Africa, in January 2025
Semiparametric posterior corrections
No full textInternational audienceAbstract We present a new approach to semiparametric inference using corrected posterior distributions. The method allows us to leverage the adaptivity, regularization, and predictive power of nonparametric Bayesian procedures to estimate low-dimensional functionals of interest without being restricted by the holistic Bayesian formalism. Starting from a conventional posterior on the whole data-generating distribution, we correct the marginal posterior for each functional of interest with the help of the Bayesian bootstrap. We provide conditions for the resulting one-step posterior to possess calibrated frequentist properties and specialize the results for several canonical examples: the integrated squared density, the mean of a missing-at-random outcome, and the average causal treatment effect on the treated. The procedure is computationally attractive, requiring only a simple, efficient postprocessing step that can be attached onto any arbitrary posterior sampling algorithm. Using the ACIC 2016 causal data analysis competition, we illustrate that our approach can outperform the existing state-of-the-art through the propagation of Bayesian uncertainty
Explicit Recursive Construction of Super-Replication Prices under Proportional Transaction Costs
No full textInternational audienceWe propose a constructive framework for the super-hedging problem of a European contingent claim under proportional transaction costs in discrete time. Our main contribution is an explicit recursive scheme that computes both the super-hedging price and the corresponding optimal strategy without relying on martingale arguments. The method is based on convex duality and a distorted Legendre-Fenchel transform, ensuring both tractability and convexity of the value functions. A numerical implementation on real market data illustrates the practical relevance of the proposed approach