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Méthodes de simulation adaptative pour l’évaluation des risques de système complexes.
No full textRisk assessment is conditioned on the knowledge and information available at the moment of the analysis. Modeling and simulation are ways to explore and understand system behavior, for identifying critical scenarios and avoiding surprises. A number of simulations of the model are run with different initial and operational conditions to identify scenarios leading to critical consequences and to estimate their probabilities of occurrence. For complex systems, the simulation models can be: i) high-dimensional; ii) black-box; iii) dynamic; and iv) computationally expensive to run, preventing the analyst from running the simulations for the multiple conditions that need to be considered.The present thesis presents advanced frameworks of simulation-based risk assessment. The methods developed within the frameworks are attentive to limit the computational cost required by the analysis, in order to keep them scalable to complex systems. In particular, all methods proposed share the powerful idea of automatically focusing and adaptively driving the simulations towards those conditions that are of interest for the analysis, i.e., for risk-oriented information.The advantages of the proposed methods have been shown with respect to different applications including, among others, a gas transmission subnetwork, a power network and the Advanced Lead Fast Reactor European Demonstrator (ALFRED).L’évaluation de risques est conditionnée par les connaissances et les informations disponibles au moment où l’analyse est faite. La modélisation et la simulation sont des moyens d’explorer et de comprendre le comportement du système, d’identifier des scénarios critiques et d’éviter des surprises. Un certain nombre de simulations du modèle sont exécutées avec des conditions initiales et opérationnelles différentes pour identifier les scénarios conduisant à des conséquences critiques et pour estimer leurs probabilités d’occurrence. Pour les systèmes complexes, les modèles de simulations peuvent être : i) de haute dimension ; ii) boite noire ; iii) dynamiques ; iv) coûteux en termes de calcul, ce qu’empêche l’analyste d’exécuter toutes les simulations pour les conditions multiples qu’il faut considérer.La présente thèse introduit des cadres avancés d’évaluation des risques basée sur les simulations. Les méthodes développées au sein de ces cadres sont attentives à limiter les coûts de calcul requis par l’analyse, afin de garder une scalabilité vers des systèmes complexes. En particulier, toutes les méthodes proposées partagent l’idée prometteuse de focaliser automatiquement et de conduire d’une manière adaptive les simulations vers les conditions d’intérêt pour l’analyse, c’est-à-dire, vers des informations utiles pour l'évaluation des risques.Les avantages des méthodes proposées ont été montrés en ce qui concerne différentes applications comprenant, entre autres, un sous-réseau de transmission de gaz, un réseau électrique et l’Advanced Lead Fast Reactor European Demonstrator (ALFRED)
Introduction to the Evolution of Physical Systems
No full textInternational audienceWe are delighted to introduce this Special Issue on the Evolution of Physical Systems, the culmination of a series of workshops organized around the topic that began with ALIFE XIII (2012) and ran through ECAL 2013, ALIFE XIV (2014) and ECAL 2015. Inspired by our mutual interests, we coined the term Evolution of Physical Systems (EPS) to describe evolutionary approaches that occur in real-world physical substrates rather than in simulation. We deliberately chose this term to be broad enough to encompass both parallel Embodied Evolution [19], in which evolution is distributed across a population of robots, as well as more classical Evolutionary Robotics work where evaluation is serialized on a single robot, such as Floreano and Mondada [5]
Experimental study of the dynamics of pulsated laminar counter-flow spray flames using optical flow and proper orthogonal decomposition
No full textInternational audienc
Power Loss in Reverberation Chambers by Antennas and Receivers
No full textInternational audienceAntennas, and more generally any equipment under test (EUT) capable of coupling to impinging electromagnetic waves, are well-known sources of power loss in reverberation chambers (RCs). As such, it is fundamental to model their contribution to an RC quality factor. The standard model available in the literature is based on power dissipated in loads connected to an antenna. This paper argues about the inaccuracy of this description, where internal dissipation within an antenna (or EUT), associated to potentially low radiation efficiencies, is neglected. An alternative model is validated by showing its self-consistency in predicting change in loading effects as opposed to the standard model. It is expected to have practical importance for tests performed in the low-frequency range of RCs, where antenna-related dissipation is the dominant loss mechanism, and in particular for EUTs which can be expected to display poor radiation efficiencies
Lightweight Ciphers and their Side-channel Resilience
No full textInternational audienceSide-channel attacks represent a powerful category of attacks against cryptographic devices. Still, side-channel analysis for lightweight ciphers is much less investigated than for instance for AES. Although intuition may lead to the conclusion that lightweight ciphers are weaker in terms of side-channel resistance, that remains to be confirmed and quantified. In this paper, we consider various side-channel analysis metrics which should provide an insight on the resistance of lightweight ciphers against side-channel attacks. In particular, for the non-profiled scenario we use the theoretical confusion coefficient and empirical optimal distinguisher. Our study considers side-channel attacks on the first, the last, or both rounds simultaneously. Furthermore, we conduct a profiled side-channel analysis using various machine learning attacks to recover 4-bit and 8-bit intermediate states of the cipher. Our results show that the difference between AES and lightweight ciphers is smaller than one would expect, and even find scenarios in which lightweight ciphers may be more resistant. Interestingly, we observe that the studied 4-bit S-boxes have a different side-channel resilience, while the difference in the 8-bit ones is only theoretically present
Difference of Convex Functions Programming Applied to Control with Expert Data
No full textThis paper reports applications of Difference of Convex functions (DC) programming to Learning from Demonstrations (LfD) and Reinforcement Learning (RL) with expert data. This is made possible because the norm of the Optimal Bellman Residual (OBR), which is at the heart of many RL and LfD algorithms, is DC. Improvement in performance is demonstrated on two specific algorithms, namely Reward-regularized Classification for Apprenticeship Learning (RCAL) and Reinforcement Learning with Expert Demonstrations (RLED), through experiments on generic Markov Decision Processes (MDP), called Garnets
Do we need a holistic approach for the design of secure IoT systems?
No full textInternational audienceIn this paper, four cryptography and security experts point out to future research directions in internet-of-things (IoT) security. Coming from different research domains, the experts address a broad range of issues related to IoT security. In preparation to a panel discussion at the International Workshop on Malicious Software and Hardware in the Internet of Things (MalIoT), they indicate which aspects are important in the design of secured IoT systems, and to which extent we need a holistic approach that integrates security measures at all levels of design abstraction
A switching mechanism to mitigate scan blindness in phased arrays
No full textInternational audienceThis paper presents a novel solution to extend the scanning range of a cavity-backed stacked-patch phased array subject to scan blindness. Two main aspects are investigated. The first section is a thorough description of the scan blindness mechanism occurring in the reported array, taking into consideration the characteristics of the associated mutual coupling scheme. The second section introduces a revised array topology that allows extending the scanning range. The proposed solution is based on the switching between two operating modes of the structure, each one covering a distinct scanning range. Taken together, they potentially allow freeing the structure from scan blindness. In the present case, the scanning capability of the array has been extended by 10° in the scanning plane of interest. © 2017 Euraap