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Two-Stage Adaptable Robust Optimization for Glass Production
No full textInternational audienceIn the glass industry, visual and thermal properties of the glass sheets are obtained via the deposit of thin layers of different materials. A standard way to perform this step is the use of a “magnetron,” in which the materials are transferred from cathodes to the sheets using a magnetic field. Since the cathodes are very expensive, activation and replacement decisions have to be carefully decided to keep the cost of the wasted materials low.The production is organized in campaigns and the activation and replacement decisions of the cathodes have to be taken before each campaign. Yet, the exact orders to process during a campaign are only revealed after the decisions have been taken. We focus here on the case of two campaigns, which we model as a two-stage robust optimization problem. We propose a method based on the finite adaptability approach of Bertsimas and Caramanis (2010) combined with the branch-and-bound of Subramanyam et al. (2020). Experiments on real instances show that our method leads to clear diminutions of the cost of wasted material in the worst cases, and—even more interesting—allow to find solutions for cases that are unfeasible with the heuristic used by the practitioners
Note pour concevoir et exploiter les réseaux de collecte de l'urine humaine dans des bâtiments
No full textRevoir la notation des élèves
No full textInternational audiencePour améliorer le système scolaire, il faut revoir le système d’évaluation. Aujourd’hui, la note informe l’enfant et ses parents. Elle récompense ou sanctionne. Surtout, elle classe et elle fige. La passion pour la notation numérique, centrée sur la moyenne, nourrit trop d’effets pervers. Il importe d’innover en distinguant les fonctions de communication et de classement
Simple visibility design in network games
No full textInternational audienceIndividuals interact through social media networks by posting contributions, comments and the like. These actions entail complementarities and generate spillovers. A social media carefully designs its platform, often with the objective of increasing users' activity. Here I study visibility strategies, which promote some individuals by making their contributions more visible than others'. Under some specifications, optimal strategies are simple, making visible the individuals whose total impact (total number of followers for example) is maximal. Comparisons with other targeting strategies are discussed
Négociation dans des environnements de choix sociaux monotones
No full textInternational audienceApplying the solutions defined in the axiomatic bargaining theory to actual bargaining problems is a challenge when the problem is not described by its Utility Possibility Set (UPS) but as a social choice environment specifying the set of alternatives and utility profile underlying the UPS. It requires computing the UPS, which is an operational challenge, and then identifying at least one alternative that actually achieves the bargained solution’s outcome. We introduce the axioms of Independence of Non-Strongly-Efficient Alternatives (resp. Weakly) and Independence of Redundant Alternatives. A solution satisfying these axioms can be applied to a simplified problem based on any reduced set of alternatives generating the strong (resp. weak) Pareto frontier of the initial problem, without changing the outcome, making the application of bargaining solutions to actual problems easier. We compare our axioms to usual independence axioms, and discuss their consistency with usual bargaining solutions. Then, we introduce monotonicity conditions corresponding to the existence of an interest group, i.e., agents ranking the alternatives in the same order. For such monotonic social choice environments, we provide a parameterized family of alternatives that generates the Pareto frontier of the bargaining problem, in line with our previous results. Our analysis illustrates that an axiomatic approach can be useful to foster the application of bargaining solutions, in complement to usual computational methods.L'application des solutions définies dans la théorie axiomatique de la négociation à des problèmes de négociation réels est un défi lorsque le problème n'est pas décrit par son ensemble de possibilités d'utilité (UPS) mais comme un environnement de choix social spécifiant l'ensemble des alternatives et le profil d'utilité sous-jacent à l'UPS. Il faut calculer l'UPS, ce qui est un défi opérationnel, puis identifier au moins une alternative qui permet d'atteindre le résultat de la solution négociée. Nous introduisons les axiomes d'indépendance des alternatives non fortement efficaces (resp. faiblement) et d'indépendance des alternatives redondantes. Une solution satisfaisant à ces axiomes peut être appliquée à un problème simplifié basé sur n'importe quel ensemble réduit d'alternatives générant la frontière de Pareto forte (resp. faible) du problème initial, sans changer le résultat, ce qui facilite l'application des solutions de négociation à des problèmes réels. Nous comparons nos axiomes aux axiomes d'indépendance habituels et discutons de leur cohérence avec les solutions de négociation habituelles. Ensuite, nous introduisons des conditions de monotonicité correspondant à l'existence d'un groupe d'intérêt, c'est-à-dire que les agents classent les alternatives dans le même ordre. Pour de tels environnements de choix sociaux monotones, nous fournissons une famille paramétrée d'alternatives qui génère la frontière de Pareto du problème de négociation, conformément à nos résultats précédents. Notre analyse montre qu'une approche axiomatique peut être utile pour favoriser l'application de solutions de négociation, en complément des méthodes informatiques habituelles
The Extraordinary March 2022 East Antarctica "Heat" Wave. Part I: Observations and Meteorological Drivers
No full textInternational audienceBetween March 15-19, 2022, East Antarctica experienced an exceptional heatwave with widespread 30-40° C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of -9.4° C on March 18 at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/mid-latitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heatwaves meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heatwave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about one hundred years, a closer recurrence of such an event is possible under future climate projections. In a subsequent manuscript, we describe the various impacts this extreme event had on the East Antarctic cryosphere
Complex systems in Ecology: A guided tour with large Lotka-Volterra models and random matrices
No full textInternational audienceEcosystems represent archetypal complex dynamical systems, often modelled by coupled differential equations of the formwhere represents the number of species and , the abundance of species . Among these families of coupled diffential equations, Lotka-Volterra (LV) equations play a privileged role, as the LV model represents an acceptable trade-off between complexity and tractability. Here, represents the intrinsic growth of species and stands for the interaction matrix: represents the effect of species over species . For large , estimating matrix is often an overwhelming task and an alternative is to draw at random, parametrizing its statistical distribution by a limited number of model features. Dealing with large random matrices, we naturally rely on Random Matrix Theory (RMT).The aim of this review article is to present an overview of the work at the junction of theoretical ecology and large random matrix theory. It is intended to an interdisciplinary audience spanning theoretical ecology, complex systems, statistical physics and mathematical biology
Le crédit dans la société et dans la sociologie : sur "la banque et sa clientèle" (Bourdieu, Boltanski, Chamboredon, 1963)
No full textInternational audienceIn 1963, a young French sociologist, Pierre Bourdieu, together with two assistants—Luc Boltanski and Jean-Claude Chamboredon—conducted the first sociological study of the credit practices of a major French bank, entitled “The Bank and Its Customers”. This article discusses the context, the findings and the legacy of this study. First, the article sketches the landscape of the emerging mass credit market in France in the early 1960s. Then, the paper summarizes and analyses the report itself. We also demonstrate how bank-customer interactions and credit continued to be a subject of interest for Bourdieu throughout his subsequent career. Finally, the paper seeks to contribute to comparative research on the varieties of national configurations of private indebtedness in relation to the level of development of the welfare state.En 1963, un jeune sociologue français - Pierre Bourdieu - et deux de ses assistants - Luc Boltanski et Jean-Claude Chamboredon - ont étudié les pratiques de crédit d'une grande banque française, et ont produit un rapport intitulé "La banque et ses clients". Cet article aborde le contexte, les résultats et l'héritage de cette enquête. Tout d'abord, l'article esquisse le paysage du marché, alors émergent, du crédit aux particuliers en France au début des années 1960, avant de résumer et analyser le rapport lui-même. Nous montrons ensuite que les interactions banque-client et le crédit ont constitué un sujet d'intérêt pour Bourdieu tout au long de sa carrière ultérieure. Enfin, l'article cherche à contribuer à la recherche comparative sur les configurations nationales de l'endettement privé en relation avec le niveau de développement de l'État providence
The Generalized System of Preferences and NGO activism
No full textInternational audienceCan NGOs contribute to the implementation of Labor Laws in a developing country? We exploit as a quasi-natural experiment the renegotiation of the Generalized System of Preferences (GSP) between the US and Indonesia in 1994, which induced the Indonesian government to raise the level of the legal minimum wage. Using data from Indonesian manufacturing firms, a diff-in-diff analysis and an event study show that the activism of workers’ rights groups helped increase firm-level average wages up to the minimum-wage level, not only inside but also outside the export sector. Labor NGO activism helped to implement the new minimum wage standards in a country that lacked strong governmental institutions
Climate Science at the Interface Between Topological Data Analysis and Dynamical Systems Theory
No full textInternational audienceThe authors are hosting an AMS sponsored Mathematics Research Community (MRC) on novel applications of topological data analysis (TDA) and dynamical systems theory to the study of climate change and weather forecasting. In this Notices article we introduce some of the big challenges in climate science, and describe how methods from TDA and dynamical systems theory can help tackle these. We hope to encourage applications to the MRC from mathematicians with a background in applied algebraic topology and scientists working on climate or meteorology, both from academia and industry