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Entropic approximations of the semigeostrophic shallow water equations
No full textWe develop a discretisation of the semigeostrophic rotating shallow water equations, based upon their optimal transport formulation, which takes the form of a Moreau-Yoshida regularisation via the Wasserstein metric, whose solution provides the shallow water layer depth represented as a measure, which is the push forward of an evolving measure under the semigeostrophic coordinate transformation. First, we propose and study an entropic regularisation of the rotating shallow water equations. Second, we discretise the regularised problem by replacing both measures with weighted sums of Dirac measures, and approximating the (squared) L 2 norm of the layer depth appearing as the potential energy. We propose an iterative method to solve the discrete optimisation problem relating the two measures, and analyse its convergence. The iterative method is demonstrated numerically and applied to the solution of the time-dependent shallow water problem in numerical examples
primatoscopy-01: testing yourself amongst the animals
No full textInternational audienceI lead an art-research project at the crossroads of art and North American anthropology, where clay, a medium for creative practices, also becomes an object of knowledge. This material can be used to foster questions and considerations about our perceptual frameworks, our ways of learning, our sensory knowledge, and our relationships with other living beings, as in the research presented here, with macaques. The art-research project Primatoscopy-01 is subdivided into four distinct phases, which began with the search for comparative elements between related perceptual environments. The experiments begin with a system in which blocks of clay are scattered in enclosures at equal distances from each other and far from any equipment used in captivity conditions. This arrangement aims to delimit certain characteristics of nonhuman primates (physical strength, hierarchization, grasping, movement, etc.), but also to maximize the relationship between individuals and clay. The initial phase, although decisive, proved disappointing, leading to a complete realignment of my expectations: Japanese macaques (Macaca fuscata) carry the herpes B virus (Herpesvirus simiae), which hinders access to artifacts after they've been handled. The virus has become a constraint of the experimental protocol, as it limits my involvement in the enclosures after each phase, requires the use of Virkon® clay (a virucide, bactericide, and fungicide), and forces me to isolate the artifacts until their firing. As an archaeologist, I methodically recorded the state of the enclosures and attempted to reconstruct the activities based on the material traces, seeking to make sense of these behavioral artifacts. The results looked disastrous straight away: clay was scattered among the food and excrement; there were few marks in the clay and the blocks had hardly been handled. The primates seemed disturbed by these physical “intrusions” in their enclosure. The later phases (2 to 4) were characterized by a diversification of stimuli by introducing more “enticing” clay forms in the enclosures. The use of traditional forms, mainly Edo- and Heian-influenced vases and teabowls, as food containers, was particularly effective in tempting the macaques to handle them. A more significant understanding of behavioral patterns only emerged at the end of phase 2, revealing a separation of primate activities according to the functional divisions of their enclosures: captive macaques do not play where they eat. Analysis of the evidence has revealed a recurring pattern: the primates tended to break up the clay once it was dry, using its materiality to draw lines on the ground. The multitude of tangled lines was astonishing, because they were constant and repetitive. It seemed to be the main interest suggested to them by the clay's malleability. I have divided the lines into two categories: the lines of transportation (linear, simple, and intermittent) and the lines of persistence (localized, superimposed, and demonstrating a back-and-forth movement). The persistence lines are compared with nesting diagrams drawn by primatologists, evoking links between cognition, environment, and cultural construction. These relationships are first evident through the fusiform gyrus, a cerebral structure shared by all primates, which ensures the recognition of the contours of the environment and faces, while opening the way to alternative analogies with ancient writing systems. These reveal the continuity between the macrocosm in which we evolve and the microcosm of our inner representations, accepting our animal condition as well as the role of the imagination in the performativity of human worlds and their impact on all living things
Converging Better Response Dynamics in Sender-Receiver Games
No full textInternational audienceWe consider information transmission between a sender, who has finitely many types, and a receiver, who must choose a decision in a real interval. The payoffs depend on the sender’s type and the receiver’s decision. We assume that the payoff functions are well-behaved. We characterize the pure strategy perfect Bayesian equilibrium outcomes as incentive-compatible partitions of the sender’s types. We propose an algorithm, which starts from the finest partition. Then, at every step, if the current partition is not incentive compatible, a random type of the sender improves its payoff, and the receiver best responds. We show that every possible run of the algorithm converges to a unique incentive-compatible partition Pi*. This partition Pi* is such that any partition with more cells than Pi* is not incentive compatible, so the algorithm determines to which extent information transmission can be effective. The partition Pi* also satisfies some refinement criteria for perfect Bayesian equilibria in sender-receiver games. Furthermore, in a discrete version of a popular class of examples (namely, if the sender’s type is uniformly distributed and payoff functions are quadratic, with a constant upward bias for the sender), Pi* ex ante Pareto dominates every other incentive-compatible partition
Continuities in Policies and Turnover Among Actors: Instrument Constituencies in French Primary Care Reforms
No full textInternational audienceOver the past decade, the concept of “instrument constituency” has been proposed as a way in which to bridge studies on policy networks and policy instruments. This concept focuses on policy networks composed of diverse actors who are brought together by the shared goal of promoting a specific instrument. In this study, we examine who is involved in policy instruments development, and the extent to which they drive change within the policy process. To do so, we focus on the case of two care coordination instruments, namely, the IPEP and PEPS, used in the French healthcare system. Drawing on qualitative methods, we identify the actors involved in the development of the two instruments. Our analysis reveals the formation of two instrument constituencies around the IPEP and PEPS. This finding suggests that the continuity of primary care policies is supported through these instruments, fostering shared approaches among the actors involved.Durante la última década, se ha propuesto el concepto de “grupo de actores instrumentales” como una forma de conectar los estudios sobre redes de políticas e instrumentos de política. Este concepto se centra en redes de políticas compuestas por diversos actores unidos por el objetivo común de promover un instrumento específico. En este estudio, examinamos quiénes participan en el desarrollo de instrumentos de política y en qué medida impulsan el cambio dentro del proceso político. Para ello, nos centramos en el caso de dos instrumentos de coordinación de la atención, a saber, el IPEP y el PEPS, utilizados en el sistema de salud francés. Basándonos en métodos cualitativos, identificamos a los actores involucrados en el desarrollo de ambos instrumentos. Nuestro análisis revela la formación de dos grupos de actores instrumentales en torno al IPEP y el PEPS. Este hallazgo sugiere que la continuidad de las políticas de atención primaria se ve respaldada por estos instrumentos, fomentando enfoques compartidos entre los actores involucrados
Adjusting Manual Rates to Own Experience: Comparing the Credibility Approach to Machine Learning
No full textInternational audienceCredibility theory is the usual framework in actuarial science when it comes to reinforcing individual experience by transfering rates estimated from collective information. Based on the paradigm of transfer learning, this article presents the idea that a machine learning (ML) model pre-trained using a rich market data porfolio can improve the prediction of rates for an individual insurance portfolio. This framework consists first in training several ML models on a market portfolio of insurance data. Pre-trained models provide valuable information on relations between features and predicted rates. Furthermore, features shared with the company dataset are used to predict rates better than the same ML models trained on the insurer's dataset alone. Our approach is illustrated with classical ML models on an anonymized dataset including both market data and data from an European non-life insurance company, and is compared with a hierarchical Bühlmann-Straub credibility model. We observe the transfert learning stragegy combining company data with external market data significantly improves the prediction accuracy compared to a ML model only trained on the insurer's data and provides competitive results compared to hierarchical credibility models
Decoding CyberSecurity: How Terminology Shapes the Field
No full textInternational audienceCybersecurity stands at the forefront of protecting today's digital infrastructures and personal data. While significant technical and organizational advances have been made, it is crucial to periodically step back and question whether our current cybersecurity philosophy, concepts and models remain fit for purpose of resilience in a rapidly evolving environment. This collection of essays critically examines the prevailing understanding of cybersecurity, contrasts it with an alternative vision, and explores the foundational model on which this practice is based. Rather than offering a definitive new definition, the intention is to "shake things up" and provoke a deeper conversation on whether a shift in paradigm is warranted. By challenging the assumptions held by researchers, practitioners, and policymakers, this work aims to foster innovative thinking that can guide cybersecurity toward a more resilient and adaptive future model. Ultimately, it is a call to reassess current approaches and inspire further debate, research, and action, ensuring that our strategies remain aligned with the emerging challenges of a neverending increase interconnected digital world. This article serves as an initial exploration into the meaning of the term "cyber()security", analysing how its usage and interpretation evolve, shaped by the communities of practice that have adopted it
Dynamic off-the-grid untangling of curves with Reeds-Shepp metric.
No full textWe propose an improved strategy for point sources tracking in a temporal stack through an off-the-grid fashion, inspired by the Benamou-Brenier regularisation in the literature. We define a lifting of the problem in the higher-dimensional space of the roto-translation group. This allows us to overcome the theoretical limitation of the off-the-grid method towards tangled point source trajectories, thus enabling the reconstruction and untangling even from the numerical standpoint. We define accordingly a new regularisation based on the relaxed Reeds-Shepp metric, an approximation of the sub-Riemannian Reeds-Shepp metric, further allowing control on the local curvature of the recovered trajectories. Then, we derive some properties of the discretisation and prove a Γ-convergence result, fostering interest for practical applications of polygonal, Bézier, and piecewise geodesic discretisation. We finally test our proposed method on a localisation problem example, and give a fair comparison with the state-of-the-art off-the-grid method.</div
Signal received? Carbon price and financial–environmental performance prioritization in EU ETS firms
No full textInternational audienceUnderstanding how firms interpret and respond to carbon price signals based on their strategic priorities is crucial for aligning climate policies with corporate financial and environmental objectives. We propose a novel composite financial–environmental performance index that adjusts the emphasis on each dimension. Using a machine learning model, we evaluate the sensitivity of this index to carbon emissions allowance prices for a large sample of firms under the European Union Emissions Trading System (EU ETS) from 2008 to 2022, while controlling for a comprehensive set of potential competing predictors. Results suggest that prioritizing financial performance induces negative responses to rising carbon prices, whereas emphasizing environmental performance, without strong profitability incentives, shows limited sensitivity. By examining how carbon price signals can shape firms’ financial–environmental priorities, these findings offer actionable insights for designing policies that better balance profitability and sustainability in the low-carbon transition
EXISTENCE ET STABILITÉ DE SOLUTIONS STATIONNAIRES HORS ÉQUILIBRE D'UNE ÉQUATION DE FOKKER-PLANCK CINÉTIQUE FAIBLEMENT NON-LINÉAIRE DANS UN DOMAINE
No full textWe study a weakly non-linear Fokker-Planck equation with BGK heat thermostats in a spatially bounded domain with conservative Maxwell boundary conditions, presenting a space-dependent accommodation coefficient and a space-dependent temperature on the spatial boundary. The model is based from a problem introduced in [E. A. Carlen, R. Esposito, J. L. Lebowitz, R. Marra, and C. Mouhot. Approach to the steady state in kinetic models with thermal reservoirs at different temperatures. J. Stat. Phys., 172(2):522--543, 2018]where the authors studied the properties of the non-equilibrium steady states for non-linear kinetic Fokker-Planck equations with BGK thermostats in the torus. We generalize those results for bounded domains using the recent results presented in [K. Carrapatoso, P. Gabriel, R. Medina, and S. Mischler. Constructive krein-rutman result for kinetic Fokker-Planck equations in a domain, 2024] for the study of general kinetic Fokker-Planck equations with Maxwell boundary conditions.More precisely, in a weakly non-linear regime, we obtain the existence of a non-equilibrium steady state and its stability in the perturbative regime. .Nous étudions une équation de Fokker-Planck faiblement non linéaire avec des réservoirs de chaleur de type BGK dans un domaine spatialement borné avec des conditions aux bords de type Maxwell, et présentant un coefficient d'accommodation et une température dépendants de l'espace sur la frontière spatiale. Le modèle est basé sur un problème introduit dans [E. A. Carlen, R. Esposito, J. L. Lebowitz, R. Marra et C. Mouhot. Approach to the steady state in kinetic models with thermal reservoirs at different temperatures. J. Stat. Phys., 172(2):522--543, 2018]où les auteurs ont étudié les propriétés des états stationnaires hors équilibre pour des équations cinétiques non linéaires de type Fokker-Planck avec des réservoirs de chaleur de type BGK dans le tore. Nous généralisons ces résultats pour des domaines bornés en utilisant les résultats récents présentés dans [K. Carrapatoso, P. Gabriel, R. Medina, et S. Mischler. Constructive Krein-Rutman result for kinetic Fokker-Planck equations in a domain, 2024] pour l'étude des équations de Fokker-Planck cinétiques générales avec des conditions aux frontières de type Maxwell.Plus précisément, dans un régime faiblement non-linéaire, nous obtenons l'existence d'une solution stationnaire hors équilibré et sa stabilité dans un régime perturbatif
Trade Policy Uncertainty and the Labor Market: State-Level Evidence
No full textInternational audienceThis short paper provides U.S. state-level evidence regarding the effects of trade policy uncertainty on the labor market. We show that a higher exposure to trade policy uncertainty generates a contraction in total hours worked at the state level. The extensive margins of labor is the primary margin of employment adjustment. State-level employment is more strongly impacted by trade policy uncertainty in goods-producing industries, and more particularly in the durable goods industry. States which are more specialized in goods industries, when they face higher uncertainty, tends to postpone hiring by more, which explains the drop in total employment.>