14 research outputs found
Formal and Informal Methods for Multi-Core Design Space Exploration
We propose a tool-supported methodology for design-space exploration for
embedded systems. It provides means to define high-level models of applications
and multi-processor architectures and evaluate the performance of different
deployment (mapping, scheduling) strategies while taking uncertainty into
account. We argue that this extension of the scope of formal verification is
important for the viability of the domain.Comment: In Proceedings QAPL 2014, arXiv:1406.156
Dynamical properties and detectability of the magneto-thermal instability in the intracluster medium
Context. Amongst many plasma processes potentially relevant to the dynamics
of the intracluster medium (ICM), turbulence driven at observable scales by
internal magnetised buoyancy instabilities like the magneto-thermal instability
(MTI) stand out in the ICM outskirt, where the background temperature decreases
with radius. Aims. We characterise the statistical properties of MTI turbulence
and assess whether such magnetised dynamics would be detectable with the future
X-ray calorimeter X-IFU onboard ATHENA. Methods. We make use of scaling laws
derived by Perrone & Latter (2022a,b) to estimate the observable turbulent
saturation levels and injection length of MTI turbulence for different ICM
thermodynamic profiles, and perform a numerical MHD simulation of the dynamics
with Braginskii heat and momentum diffusion. As a prospective exercise, we use
the simulation to virtually observe MTI turbulence through the X-IFU. Results.
In bright enough regions amenable to X-ray observations, the MTI drives mild
turbulence up to 5% and 100 km/s (rms temperature fluctuation and
velocity). However, the measurable integrated temperature fluctuation and
line-of-sight velocity fields, which is essentially the azimuthal velocity
component in cluster haloes, hardly exceed 1% and 10 km/s respectively. We show
that such moderate signals would be hard to detect with upcoming X-ray
telescopes. MTI turbulence is anisotropic in the direction of the gravity. If
the fluctuation intensities were to be stronger than the current theoretical
estimates, MTI fluctuations may be detectable and their anisotropy discernible
with the X-IFU. Conclusions. Finding direct signatures of magnetised dynamics
in the ICM, even at observable scales typical of the MTI, remains challenging.
This study is a first step in this direction. Several numerical and
observational strategies are discussed to make further progress.Comment: 20 pages, 13 figures, submitted to A&
Exploration de l'espace de design assistée par ordinateur pour les systèmes multi-coeurs
The growing complexity of embedded systems calls for modeling formalisms that can be simulated and analyzed to explore the space of design alternatives. This thesis describes the development of a modeling formalism and tools for design space exploration at early design stage.We extend the classical worst-case model checking for timed automata to stochastic analysis based on a refinement of temporal uncertainty intervals into delay distribution. On one hand we introduce the formalism of Duration Probabilistic Automata (DPA) supporting analysis as well as optimization. On the other hand we provide DESPEX (DEsign SPace EXplorer), a tool for performance evaluation of high-level models of applications running on multi-core platforms. We also show its usage on several case studies.La complexité croissante des systèmes embarqués nécessite des formalismes de modélisation qui peuvent être simulés et analysés pour explorer l'espace des alternatives de conception. Cette thèse décrit le développement d'un formalisme de modélisation et des outils pour l'exploration de l'espace de design au plus tôt dans le flot de conception. Nous étendons le model-checking classique au pire cas pour les automates temporisés à l'analyse stochastique basée sur un raffinement des intervalles d'incertitude temporelle par des distributions sur les délais. D'une part, nous introduisons le formalisme des Duration Probabilistic Automata (DPA) à partir duquel nous pouvons réaliser de l'analyse ainsi que de l'optimisation. D'autre part nous présentons DESPEX (Design Space Explorer), un outil d'évaluation de performance de modèles de haut niveau des applications qui s'exécutent sur les plates-formes multi-coeurs. Nous montrons également son utilisation sur plusieurs cas d'étude
Performance Evaluation of Schedulers in a Probabilistic Setting
Invited PaperInternational audienceWe show how to evaluate the performance of solutions to finite-horizon scheduling problems where task durations are specified by bounded uniform distributions. Our computational technique, based on computing the volumes of zones, constitutes a contribution to the computational study of scheduling under uncertainty and stochastic systems in general
Dynamical properties and detectability of the magneto-thermal instability in the intracluster medium
International audienceContext. Amongst many plasma processes potentially relevant to the dynamics of the intracluster medium (ICM), turbulence driven at observable scales by internal magnetised buoyancy instabilities like the magneto-thermal instability (MTI) stand out in the ICM outskirt, where the background temperature decreases with radius. Aims. We characterise the statistical properties of MTI turbulence and assess whether such magnetised dynamics would be detectable with the future X-ray calorimeter X-IFU onboard ATHENA. Methods. We make use of scaling laws derived by Perrone & Latter (2022a,b) to estimate the observable turbulent saturation levels and injection length of MTI turbulence for different ICM thermodynamic profiles, and perform a numerical MHD simulation of the dynamics with Braginskii heat and momentum diffusion. As a prospective exercise, we use the simulation to virtually observe MTI turbulence through the X-IFU. Results. In bright enough regions amenable to X-ray observations, the MTI drives mild turbulence up to 5% and 100 km/s (rms temperature fluctuation and velocity). However, the measurable integrated temperature fluctuation and line-of-sight velocity fields, which is essentially the azimuthal velocity component in cluster haloes, hardly exceed 1% and 10 km/s respectively. We show that such moderate signals would be hard to detect with upcoming X-ray telescopes. MTI turbulence is anisotropic in the direction of the gravity. If the fluctuation intensities were to be stronger than the current theoretical estimates, MTI fluctuations may be detectable and their anisotropy discernible with the X-IFU. Conclusions. Finding direct signatures of magnetised dynamics in the ICM, even at observable scales typical of the MTI, remains challenging. This study is a first step in this direction. Several numerical and observational strategies are discussed to make further progress
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