Environnement Multi-agent pour la Multi-modélisation et Simulation des Systèmes Complexes

This thesis is focused on the study of complex systems through a modeling and simulation (M&S) process. Most questions about such systems requiere to take simultaneously account of several points of view. Phenomena evolving at different (temporal and spatial) scales and at different levels of resolution (from micro to macro) have to be considered. Moreover, several expert skills belonging to different scientific fields are needed. The challenges are then to reconcile these heterogeneous points of view, and to integrate each domain tools (formalisms and simulation software) within the rigorous framework of the M&S process. In order to solve these issues, we mobilise notions from multi-level modeling, hybrid modeling, parallel simulation and software engineering. Regarding these fields, we study the complementarity of the AA4MM approach and the DEVS formalism into the scope of the model-driven engineering (MDE) approach. Our contribution is twofold. We propose the operational specifications of the MECSYCO co-simulation middleware enabling the parallel simulation of complex systems models in a rigorous and decentralized way. We also define an MDE approach enabling the non-ambiguous description of complex systems models and their automatic implementation in MECSYCO. We show the properties of our approach with several proofs of concept.Ce travail de thèse porte sur l'étude des systèmes complexes par une démarche de modélisation et simulation (M&S). La plupart des questionnements sur ces systèmes nécessitent de prendre en compte plusieurs points de vue simultanément. Il faut alors considérer des phénomènes évoluant à des échelles (temporelles et spatiales) et des niveaux de résolutions (de microscopique à macroscopique) différents. De plus, l'expertise nécessaire pour décrire le système vient en général de plusieurs domaines scientifiques. Les défis sont alors de concilier ces points de vues hétérogènes, et d'intégrer l'existant de chaque domaine (formalismes et logiciels de simulation) tout en restant dans le cadre rigoureux de la démarche de M&S. Pour répondre à ces défis, nous mobilisons à la fois des notions de modélisation multi-niveau (intégration de représentations micro/macro), de modélisation hybride (intégration de formalismes discrets/continus), de simulation parallèle, et d'ingénierie logicielle (interopérabilité logiciel, et ingénierie dirigée par les modèles). Nous nous inscrivons dans la continuité des travaux de M&S existants autour de l'approche AA4MM et du formalisme DEVS. Nous étudions en effet dans cette thèse en quoi ces approches sont complémentaires et permettent, une fois combinées dans une démarche d'Ingénierie Dirigée par les Modèles (IDM), de répondre aux défis de la M&S des systèmes complexes. Notre contribution est double. Nous proposons d'une part les spécifications opérationnelles de l'intergiciel de co-simulation MECSYCO permettant de simuler en parallèle un modèle de manière rigoureuse et complètement décentralisée. D'autre part, nous proposons une approche d'IDM permettant de décrire de manière non-ambiguë des modèles, puis de systématiser leur implémentation dans MECSYCO. Nous évaluons les propriétés de notre approche à travers plusieurs preuves de concept portant sur la M&S du trafic autoroutier et sur la résolution numérique d'un système d'équations différentielles

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

Multi-level Modeling as a Society of Interacting Models

We propose to consider a multi-level representation from a multi-modeling point of view. We define a framework to better specify the concepts used in multi-level modeling and their relationships. This framework is implemented through the AA4MM meta-model, which benefits from a middleware layer. This meta-model uses the multi-agent paradigm to consider a multi-model as a society of interacting models. We extend this meta-model to consider multi-level modeling and present a proof of concept of a collective motion example where we show the ability of this approach to rapidly change from one pattern of interaction to another one by reusing some of the meta-model's components

Kinematically complete measurements of strong eld ionisation with mid-IR pulses

Recent observations of three unique peaks near 1 eV, 100 meV and 1 meV in the electron spectra generated by ionization using intense mid-IR pulses have challenged the current understanding of strong-field (SF) ionization. The results came as a surprise as they could not be reproduced by the standard version of the commonly used SF approximation. We present results showing the simultaneous measurement of all three low energy ranges at high resolution. This capability is possible due to a unique experimental combination of a high repetition rate mid-IR source, which allows probing deep in the quasi-static regime at high data rates, with a reaction microscope, which allows high resolution three dimensional imaging of the electron momentum distribution.Peer ReviewedPostprint (author's final draft

Differentiation of human induced pluripotent stem cells towards notochordal-like cells: the role of tissue source

INTRODUCTION: Notochordal cells (NCs) are linked to a healthy intervertebral disc (IVD), and they are considered an exciting target for cell-based therapy. However, NCs are scarcely available as they are lost early in life, and attempts at in vivoexpansion have failed because NCs lose their specific phenotype. The production of Notochordal-like cells (NLCs) from human induced pluripotent stem cells (iPSCs) is a viable alternative. However, current attempts have been challenged by the low differentiation efficiency into the NC lineage. Therefore, the aim of this study was to build on the tissue-specific epigenetic memory of hiPSCs derived from IVD progenitor cells (TIE2+-cells) to improve hiPSC differentiation towards mature, matrix-producing NLCs. METHODS: hiPSCs were generated from TIE2⁺ cells of three adult donors. As a comparison, donormatched minimally invasive peripheral blood mononuclear (PBM) cell-derived iPSCs were used. Firstly, the iPSCs were differentiated into mesendodermal progenitors by Wnt pathway activation (N2B27 medium + 3µM CHIR99021)¹. Thereafter, the cells were further driven towards the NClineage by transfection with synthetic NOTO mRNA¹ and further matured using a 3D pellet culture in discogenic medium containing 10ng/mL TGF-β1. Read-out parameters included cell morphology, gene and protein expression and matrix deposition. RESULTS: Both TIE2⁺ and PBM cell-derived hiPSC showed successful differentiation towards mesendodermal progenitor cells following Wnt activation on day 2, indicated by the cells moving out of the colonies after CHIR stimulation. Accordingly, a decreased gene expression of pluripotency markers (OCT4, SOX2, NANOG), and upregulation of Wnt-target genes (LEF1, NODAL) and mesendodermal markers (TBXT, FOXA2, TBX6) was observed compared to mTESR1 controls. This was confirmed by immuno-stains for FOXA2 and TBXT. At day 3, we confirmed a 9-fold increase in NOTO mRNA levels after transfection in all donor lines. At day 28, the appearance of vacuolated NLCs was observed in both TIE2⁺ and PBM cell-derived pellet cultures confirming successful commitment towards the NC-lineage. Interestingly, while DMMB-assay detected GAG deposition in both lines, a significant increase in GAG content was seen in the TIE2⁺ cell-derived pellets. DISCUSSION & CONCLUSIONS: Tissue-specific TIE2⁺ cell-derived iPSCs may allow for an improved iPSNLC differentiation efficiency, indicated by the increased potency for deposition of GAG-rich matrix. Detailed analysis of the phenotypic markers and matrix deposited at the end of the 28 day maturation is ongoing to further document the phenotype of these iPS-NLCs. Delineating which epigenetic features are retained after reprogramming of these two cell lines, could shed light on the differences in their differentiation capacity. REFERENCES: ¹Colombier et al., 202

MECSYCO: a Multi-agent DEVS Wrapping Platform for the Co-simulation of Complex Systems

Most modeling and simulation (M&S) questions about complex systems require to take simultaneously account of several points of view. Phenomena evolving at different scales and at different levels of resolution have to be considered. Moreover, expert skills belonging to different scientific fields are needed. The challenges are then to reconcile these heterogeneous points of view, and to integrate each domain tools (formalisms and simulation software) within the rigorous framework of the M&S process. To answer to this issue, we propose here the specifications of the MECSYCO co-simulation middleware. MECSYCO relies on the universality of the DEVS formalism in order to integrate models written in different formalism. This integration is based on a wrapping strategy in order to make models implemented in different simulation software inter-operable. The middleware performs the co-simulation in a parallel, decentralized and distributable fashion thanks to its modular multi-agent architecture. We detail how MECSYCO perform hybrid co-simulations by integrating in a generic way already implemented continuous models thanks to the FMI standard, the DEV&DESS formalism and the QSS method. The DEVS wrapping of FMI that we propose is not restricted to MECSYCO but can be performed in any DEVS-based platform. We show the modularity and the genericity of our approach through an iterative smart heating system M&S. Compared to other works in the literature, our proposition is generic thanks to the strong foundation of DEVS and the unifying features of the FMI standard, while being fully specified from the concepts to their implementations

Co-simulation of cyber-physical systems using a DEVS wrapping strategy in the MECSYCO middleware

International audienceMost modeling and simulation (M&S) questions about cyber-physical systems (CPS) require expert skills belonging to different scientific fields. The challenges are then to integrate each domain's tools (formalism and simulation software) within the rigorous framework of M&S process. To answer this issue, we give the specifications of the MECSYCO co-simulation middle-ware which enables to interconnect several pre-existing and heterogeneous M&S tools, so they can simulate a whole CPS together. The middleware performs the co-simulation in a parallel, decentralized and distributable fashion thanks to its modular multi-agent architecture. In order to rigorously integrate tools which use different formalisms, the co-simulation engine of MECSYCO is based on DEVS. The central idea of MECSYCO is to use a DEVS wrapping strategy to integrate each tool into the middleware. Thus, heterogeneous tools can be homogeneously co-simulated in the form of a DEVS system. By using DEVS, MECSYCO benefits from the numerous scientific works which have demonstrated the integrative power of this formalism and gives crucial guidelines to rigorously design wrappers. We demonstrate that our discrete framework can integrate a vast amount of continuous M&S tools by wrapping the FMI standard. To this end, we take advantage of DEVS efforts of the literature (namely, the DEV&DESS hybrid formalism and QSS solvers) to design DEVS wrappers for FMU components. As a side-effect, this wrapping is not restricted to MECSYCO but can be applied in any DEVS-based platform. We evaluate MECSYCO with the proof of concept of a smart-heating use-case, where we co-simulate non DEVS-centric M&S tools

Multi-agent Multi-Model Simulation of Smart Grids in the MS4SG Project

International audienceThis paper illustrates how the multi-agent approach, or paradigm, can help in the modeling and the simulation of smart grids in the context ofMS4SG (a joint project between LORIA-INRIA and EDF R&D). Smart grids simulations need to integrate together pre-existing and heterogeneous models and their simulation software; for example modeling tools of the power grids, of telecommunication networks, and of the information and decision systems. This paper describes the use of MECSYCO as a valid approach to integrate these heterogeneous models in a multi-agent smart grid simulation platform. Several use cases show the ability of MECSYCO to effectively take into account the requirements of smart grids simulation in MS4SG