Search for an Immobile Hider on a Stochastic Network

Harry hides on an edge of a graph and does not move from there. Sally, starting from a known origin, tries to find him as soon as she can. Harry's goal is to be found as late as possible. At any given time, each edge of the graph is either active or inactive, independently of the other edges, with a known probability of being active. This situation can be modeled as a zero-sum two-person stochastic game. We show that the game has a value and we provide upper and lower bounds for this value. Finally, by generalizing optimal strategies of the deterministic case, we provide more refined results for trees and Eulerian graphs.Comment: 28 pages, 9 figure

Communicating Zero-Sum Product Stochastic Games

We study two classes of zero-sum stochastic games with compact action sets and a finite product state space. These two classes assume a communication property on the state spaces of the players. For strongly communicating on one side games, we prove the existence of the uniform value. For weakly communicating on both sides games, we prove that the asymptotic value, and therefore the uniform value, may fail to exist.Comment: 25 pages, 6 figure

Life expectancy, heavy work and return to education ; lessons for the social security reform

In most industrial countries, while the calculation of pension bene?ts is progressive, public pension systems redistribute weakly from high to low- income earners. They are close to actuarial fairness. This statement results from the following speci?city: less paid jobs are also heavier and health- damaging jobs involving losses in life expectancy. As avoiding low earnings and hard-working conditions require acquisition of skills, we study conjointly in this article the impact of social security and the work-related life ex- pectancy loss on the schooling decision. We then study macroeconomic and distributional consequences of global gain in life expectancy associated with di¤erent social security reforms, focusing particularly on spillover e¤ects pos- sibly generated by education.social security, human capital, inequality

Redistribution and the cultural transmission of the taste for fairness

Departing from mainstream economics, surveys ?rst show that individ- uals do care about fairness in their demand for redistribution. They also show that the cultural environment in which individuals grow up a¤ects their preferences about redistribution. Including these two components of the demand for redistribution, we propose in this article a mechanism of cultural transmission of the taste for fairness. Consistently with the process of socialization, the young preferences depend on collective choices through observation and imitation. Observation during childhood of redistributive policies far from what is perceived as fair results then in a lower taste for fairness. As a consequence, the model exhibits a multiplicity of history- dependent steady states which may account for the huge di¤erence of redis- tribution observed between Europe and the United States.redistribution, voting behavior, fairness, endogenous preferences

Fairness, social norms and the cultural demand for redistribution

When studying attitudes towards redistribution, surveys show that individuals do care about fairness. They also show that the cultural environment in which people grow up affects their preferences about redistribution. In this article we include these two components of the demand for redistribution in order to develop a mechanism for the cultural transmission of the concern for fairness. The preferences of the young are partially shaped through the observation and imitation of others' choices. More specifically, observing during childhood how adults have collectively failed to implement fair redistributive policies lowers the concern during adulthood for fairness or the moral cost of not supporting fair taxation. Based on this mechanism, the model exhibits a multiplicity of history-dependent stationary states that may account for the huge and persistent differences in redistribution observed between Europe and the United States. It also explains why immigrants from countries with a preference for greater redistribution continue to support higher redistribution in their destination country

Design Of An Anthropomorphic Upper Limb Exoskeleton Actuated By Ball-Screws And Cables

International audienceThis paper presents the design of ABLE, an anthropomorphic upper limb exoskeleton integrally actuated by highly reversible ball-screw and cable (SCS standing for Screw-and-Cable-System) allowing true joint torque control without force sensor. Their unique kinematics allows their integration in the structure thanks to dedicated mechanical innovations such as the shoulder articulation and the forearm-wrist. The result is an anthropomorphic, lightweight, open architecture which avoids imprisoning the human limb. Applicative projects are briefly presented in: medical rehabilitation, teleoperation and haptics (VR).Lucrarea prezintă proiectul lui ABLE, un exoschelet al braţului, integralacţionat de un sistem şurub cu cap sferic şi cablu (SSC, de la sistem cu şurub şicablu), puternic reversibil, care permite controlul real al momentului în articulaţiefără senzor de forţă. Cinematica unică permite integrarea lui în structură graţieinovaţiilor mecanice speciale, precum articulaţia umărului şi încheieturaantebraţului. Rezultatul este o arhitectură deschisă, uşoară, antropomorfică, careevită încorsetarea braţului uman. Sunt prezentate pe scurt proiecte de aplicaţii în:recuperarea medicală, telechirurgie şi interfaţare haptică (RV)

Systèmes de retraite par répartition, mode de calcul des droits à la pension et croissance

Nous présentons dans cet article un modèle à générations imbriquées avec capital humain qui permet de rendre compte de la diversité des systèmes publics de retraite par répartition. Notamment, ce modèle intègre la possibilité que les droits à pension d'une personne soient calculés soit de manière forfaitaire soit en fonction de l'historique de ses salaires et de la durée de sa période salariale. Dans ce dernier cas, de loin le plus rencontré concrètement, si la durée minimum légale de cotisation donnant droit à une pension à taux plein n'est pas trop élevée, le système de retraite peut être favorable à la croissance économique en incitant les agents à investir davantage en capital humain. Ce mode de calcul des droits à pension peut donc s'avérer économiquement profitable et dominer en tout cas le mode de calcul alternatif basé sur le versement d'une pension forfaitaire. Nous déduisons également les conséquences de ce mode de calcul sur les ajustements à opérer face à différents types de structure démographique.Systèmes de retraite, capital humain, croissance endogène

Identification dynamique de robots avec un modèle de frottement sec fonction de la charge et de la vitesse

International audienceEn robotique, les pertes dans la chaine d'actionnement articulaire des robots sont généralement prises en compte dans le modèle dynamique par un effort de frottement visqueux proportionnel à la vitesse et par un effort constant de frottement sec. Pourtant, d'après la loi de Coulomb, le frottement sec de glissement varie avec les efforts de contact dans les éléments de transmission. Ainsi, cet effet est à prendre en compte pour les systèmes mécaniques soumis à de fortes variations de charge. Cet article présente un nouveau modèle dynamique dans lequel l'effort de frottement sec est proportionnel à la charge selon un coefficient dépendant de la vitesse. Une nouvelle procédure permet d'identifier ce modèle à partir de mesures faites sur le robot réalisant diverses trajectoires avec différents cas de charge. Une validation expérimentale est réalisée sur un robot industriel