Jarosite in a Pleistocene East African saline-alkaline paleolacustrine deposit: Implications for Mars aqueous geochemistry

Jarosite occurs within altered tephra from the saline‐alkaline paleolake deposits of Pliocene‐Pleistocene Olduvai Gorge, Tanzania. Zeolites (mainly phillipsite), authigenic K‐feldspar, and Mg/Fe‐smectites dominate the mineral assemblage, indicating salinealkaline diagenetic conditions (pH > 9). As jarosite is ordinarily an indicator of acidic conditions on Earth and Mars, its association with such undisputed high‐pH indicators is unexpected. Of 55 altered tephra samples collected from the paleolake basin and margin deposits, eleven contained jarosite detectable by X‐ray Diffraction (XRD) (>0.15%). Mössbauer spectroscopy, Fourier Transform Infrared Reflectance (FTIR), Electron Probe Microanalysis (EPMA), X‐ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) analyses confirm the presence and nature of the jarosite. This paper documents this occurrence and presents mechanisms that could produce this unusual and contradictory mineral assemblage. We favor a mechanism by which jarosite formed recently, perhaps as modern ground and meteoric water interacted with and oxidized paleolacustrine pyrite, providing local and temporary acidic conditions. However, local groundwater (at modern springs) has a pH > 9. In recent studies of Mars, the presence of jarosite or other Fe or Mg sulfates is often used to indicate dominantly acidic conditions. Regardless, the current study shows that jarosite can form in sediments dominated by alkaline minerals and solutions. Its coexistence with Mg/Fe smectites in particular makes it relevant to recent observations of Martian paleolakes

Mod\'elisation multi-niveaux dans AA4MM

In this article, we propose to represent a multi-level phenomenon as a set of interacting models. This perspective makes the levels of representation and their relationships explicit. To deal with coherence, causality and coordination issues between models, we rely on AA4MM, a metamodel dedicated to such a representation. We illustrate our proposal and we show the interest of our approach on a flocking phenomenon

Construction de systèmes multi-agents par apprentissage collectif à base d'interactions

National audienceCet article se focalise sur des approches formelles pour la construction de systèmes multi-agents. Ce travail a cherché à proposer des apprentissages décentralisés pour construire les comportements d'agents sociaux. Cet article propose un formalisme original, l'interac-DEC-POMDP inspiré des modèles markoviens au sein duquel les agents peuvent interagir directement et localement entre eux. A partir de ce formalisme, cet article propose aussi un algorithme d'apprentissage décentralisé fondé sur une répartition heuristique des gains des agents au cours des interactions. Une démarche expérimentale a validé sa capacité à produire automatiquement des comportements collectifs. Les techniques présentées pourraient alors constituer des moyens permettant aux agents de décider automatiquement et de manière décentralisée comment s'organiser avec les autres pour résoudre un problème donné

Application of reinforcement learning to control a multi-agent system

Abstract: This study takes place in the context of multi-agent systems (MAS), and especially reactive ones. In such a system, interactions are essential, and trigger a collective behaviour that is not directly linked to the individual ones. Whereas the evolution of the system is unknown if not tried, the regularity of emergent structures in the system is observable and forms a global behaviour. In this paper, we propose to control the global behaviour of a MAS thanks to reinforcement learning tools applied at its global level. We also highlight the choice of the features taken into account to achieve this control, that is the information considered to decide which action to perform

Formalisme pour la construction automatique d'interactions dans les SMA réactifs - version étendue

Nous proposons un nouveau formalisme de représentation des actions et des interactions dans les SMA réactifs inspiré des processus de décision Markoviens décentralisés (DEC-MDP). Ce formalisme appelé Interac-DEC-MDP permet de représenter dans un même cadre homogène les actions individuelles et les interactions directes entre agents. Ainsi il permet de calculer automatiquement les prises de décisions des agents relativement aux actions et aux déclenchements et résolution des interactions par l'introduction de la rationalité au travers de la notion de récompense. Un premier problème simple de partage de ressources impliquant 2 agents a été modélisé selon le formalisme proposé et les comportements des agents ont été construits automatiquement par Q-learning. Les premiers résultats bien qu'obtenus avec des hypothèses limitatives montrent qu'il est possible à partir d'apprentissages simples de construire automatiquement des comportements collectifs pertinents

Teaching co-simulation basics through practice

International audienceCyber-physical system representation is one of the current challenges in Modeling and Simulation. In fact, multi-domain modeling requires new approaches to rigorously deal with it. Co-simulation, one of the approaches, lets modelers use several M&S tools in collaboration. The challenge is to find a way to enable co-simulation use for non-IT experts while being aware of assumptions and limitations involved. This paper deals with co-simulation basic principles teaching through practice. we propose an iterative and modular co-simulation process supported by a DSL-based environment for the MECSYCO co-simulation platform. Through a thermal use case, we are able to introduce co-simulation in a 4 hours tutorial destined to our students. Efficient energy management is one of this century challenges. The current trend to deal with it is to build cyber-physical system (CPS) [Kleissl and Agarwal, 2010]. CPS are physical systems monitored and supervised by one or several computers through a communication networks [Ra-jkumar et al., 2010]. Smart-grids are examples of CPS where the energy network is coupled with a communication network to enable remote monitoring and control. The Modeling and Simulation (M&S) of such systems is one of the current challenges in M&S due to the inter-disciplinary issues they raise. It requests the development of new methods which deal with multi-domain by integrating each expert point of view in the same rigorous and efficient M&S activity. Co-simulation [Gomes et al., 2018] is a way to achieve it

Multi-agent Systems as Discrete Dynamical Systems: Influences and Reactions as a Modelling Principle

Finding adequate descriptions of multi-agent systems is a central issue for modelling collective dynamics. We propose a mathematical description of multi-agent systems as discrete dynamical systems. The ground of our proposition is the influence-reaction method of Ferber and Müller. The key idea is that agents should never act directly on other components of the system (agents or environment) but release influences which are then combined to update the state of the system. We propose a method which decomposes the definitions of multi-agent system into six parts. We illustrate our method on the multi-Turmite model, also known as the multiple Langton's ants model. We exhibit two formulations of this model, which we study with three different simulation schemes. We show that for the same formulation, and the same initial conditions, the use of different simulation schemes may lead to qualitatively different evolutions of the system. As a positive spin-off of this study, we exhibit new phenomena of the multi-Turmite model such as deadlocks or gliders