Variants of acceptance specifications for modular system design

Les programmes informatiques prennent une place de plus en plus importante dans nos vies. Certains de ces programmes, comme par exemple les systèmes de contrôle de centrales électriques, d'avions ou de systèmes médicaux sont critiques : une panne ou un dysfonctionnement pourraient causer la perte de vies humaines ou des dommages matériels ou environnementaux importants. Les méthodes formelles visent à offrir des moyens de concevoir et vérifier de tels systèmes afin de garantir qu'ils fonctionneront comme prévu. Au fil du temps, ces systèmes deviennent de plus en plus évolués et complexes, ce qui est source de nouveaux défis pour leur vérification. Il devient nécessaire de développer ces systèmes de manière modulaire afin de pouvoir distribuer la tâche d'implémentation à différentes équipes d'ingénieurs. De plus, il est important de pouvoir réutiliser des éléments certifiés et les adapter pour répondre à de nouveaux besoins. Aussi les méthodes formelles doivent évoluer afin de s'adapter à la conception et à la vérification de ces systèmes modulaires de taille toujours croissante. Nous travaillons sur une approche algébrique pour la conception de systèmes corrects par construction. Elle définit un formalisme pour exprimer des spécifications de haut niveau et permet de les raffiner de manière incrémentale en des spécifications plus concrètes tout en préservant leurs propriétés, jusqu'à ce qu'une implémentation soit atteinte. Elle définit également plusieurs opérations permettant de construire des systèmes complexes à partir de composants plus simples en fusionnant différents points de vue d'un même système ou en composant plusieurs sous-systèmes ensemble, ainsi que de décomposer une spécification complexe afin de réutiliser des composants existants et de simplifier la tâche d'implémentation. Le formalisme de spécification que nous utilisons est basé sur des spécifications modales. Intuitivement, une spécification modale est un automate doté de deux types de transitions permettant d'exprimer des comportements optionnels ou obligatoires. Raffiner une spécification modale revient à décider si les parties optionnelles devraient être supprimées ou rendues obligatoires. Cette thèse contient deux principales contributions théoriques basées sur une extension des spécifications modales appelée " spécifications à ensembles d'acceptation ". La première contribution est l'identification d'une sous-classe des spécifications à ensembles d'acceptation, appelée " spécifications à ensembles d'acceptation convexes ", qui permet de définir des opérations bien plus efficaces tout en gardant un haut niveau d'expressivité. La seconde contribution est la définition d'un nouveau formalisme, appelé " spécifications à ensembles d'acceptation marquées ", qui permet d'exprimer des propriétés d'atteignabilité. Ceci peut, par exemple, être utilisé pour s'assurer qu'un système termine ou exprimer une propriété de vivacité dans un système réactif. Les opérations usuelles sont définies sur ce nouveau formalisme et elles garantissent la préservation des propriétés d'atteignabilité. Cette thèse présente également des résultats d'ordre plus pratique. Tous les résultats théoriques sur les spécifications à ensembles d'acceptation convexes ont été prouvés en utilisant l'assistant de preuves Coq. L'outil MAccS a été développé pour implémenter les formalismes et opérations présentés dans cette thèse. Il permet de les tester aisément sur des exemples, ainsi que d'étudier leur efficacité sur des cas concrets.Software programs are taking a more and more important place in our lives. Some of these programs, like the control systems of power plants, aircraft, or medical devices for instance, are critical: a failure or malfunction could cause loss of human lives, damages to equipments, or environmental harm. Formal methods aim at offering means to design and verify such systems in order to guarantee that they will work as expected. As time passes, these systems grow in scope and size, yielding new challenges. It becomes necessary to develop these systems in a modular fashion to be able to distribute the implementation task to engineering teams. Moreover, being able to reuse some trustworthy parts of the systems and extend them to answer new needs in functionalities is increasingly required. As a consequence, formal methods also have to evolve in order to accommodate both the design and the verification of these larger, modular systems and thus address their scalability challenge. We promote an algebraic approach for the design of correct-by-construction systems. It defines a formalism to express high-level specifications of systems and allows to incrementally refine these specifications into more concrete ones while preserving their properties, until an implementation is reached. It also defines several operations allowing to assemble complex systems from simpler components, by merging several viewpoints of a specific system or composing several subsystems together, as well as decomposing a complex specification in order to reuse existing components and ease the implementation task. The specification formalism we use is based on modal specifications. In essence, a modal specification is an automaton with two kinds of transitions allowing to express mandatory and optional behaviors. Refining a modal specification amounts to deciding whether some optional parts should be removed or made mandatory. This thesis contains two main theoretical contributions, based on an extension of modal specifications called acceptance specifications. The first contribution is the identification of a subclass of acceptance specifications, called convex acceptance specifications, which allows to define much more efficient operations while maintaining a high level of expressiveness. The second contribution is the definition of a new formalism, called marked acceptance specifications, that allows to express some reachability properties. This could be used for example to ensure that a system is terminating or to express a liveness property for a reactive system. Usual operations are defined on this new formalism and guarantee the preservation of the reachability properties as well as independent implementability. This thesis also describes some more practical results. All the theoretical results on convex acceptance specifications have been proved using the Coq proof assistant. The tool MAccS has been developed to implement the formalisms and operations presented in this thesis. It allows to test them easily on some examples, as well as run some experimentations and benchmarks

Compression of gold sub-micron crystallites: Method and experiments

Understanding and characterizing the mechanical response of individual nanostructure is of great importance for both fundamental prospects and device reliability. Higher flow stress with decreasing sample size is observed together with jerky flow. Compression of pristine submicron gold crystallites yield at very large stress in a stochastic manner, followed by large displacement bursts reaching up to 50% of the initial height [1,2]. In this work, by collecting a large set of measurements, we investigate the small and large strain behavior of crystallites loaded in compression. Large arrays of [111] oriented gold crystallites are prepared by solid state dewetting of initial cylinders of different volumes on sapphire substrates. Dedicated flat punch compression in-situ a FEG-SEM (figure 1a) has been carried out in load controlled mode [3]. Microstructure of defects is investigated using synchrotron radiation by nanoscale 3D imaging (Bragg Coherent X-ray Diffraction Imaging) [4] and Atomic Force Microscopy observations. The analysis of the plastic instability and its amount of deformation is carried out taking into account the inertial effect of the instrument, using a 1D dynamic model and Finite Element Method calculations. Simulations are made with different estimates of the shape of each individual crystallite, from an ideal cylinder of equivalent volume to the one based on SEM or AFM observations. We show that prior to the displacement burst, plastic events take place and that the sudden displacement does not necessarily relates to the onset of dislocation nucleation (figure 1b). Moreover, using the collection of measurements, we show that a unique stress-strain response can be obtained which can be used as a lower bound estimate of the mechanical response in compression of the crystallites. Please click Additional Files below to see the full abstract

Resistive-nanoindentation: contact area monitoring by real-time electrical contact resistance measurement

International audienceIn the past decades, efforts have been made to couple nanoindentation with resistive measurements in order to monitor the real-time contact area, as an alternative to the use of traditional analytical models. In this work, a novel and efficient stand-alone method is proposed to compute contact area using resistive-nanoindentation of noble metals (bulk or thin films). This method relies on three steps: tip shape measurement, setup calibration, application to the sample to be characterized. The procedure is applied to nanoindentation tests on a sample with film-on-elastic-substrate rheology and is successfully validated against experimental measurements of the contact area

Multiband Simultaneous Reception Front-End with Adaptive Mismatches Correction Algorithm

International audienceThis paper addresses the architecture of multistandard simultaneous reception receivers and aims at improving the performance-power-complexity trade-off of the front-end. To this end we propose a single front-end architecture offering lower complexity and therefore lower power consumption. In order to obtain the same performance as the state of the art receivers, a light weight adaptive method is designed and implemented. It uses a mix of two digital implemented algorithms dedicated to the correction of the frontend IQ mismatches. A study case concerning the simultaneous reception of 802.11g and UMTS signals is developed in this article

Low Power Multistandard Simultaneous Reception Architecture

International audienceIn this paper, we address the architecture of multistandard simultaneous reception receivers and we aim at improving both the complexity and the power consumption of the analog front-end. To this end we propose an architecture using the double orthogonal translation technique in order to multiplex two received signals. A study case concerning the simultaneous reception of 802.11g and UMTS signals is developed in this article

Candidate Architecture for MIMO LTE-Advanced Receivers with Multiple Channels Capabilities and Reduced Complexity and Cost

International audienceIn this paper, a candidate architecture for LTEAdvanced receiver is proposed. Based on the combination of MIMO techniques and flexible spectrum access, LTE-Advanced terminals will require an increasing complexity of the front-end part. To reduce the complexity of the analog front-end, an innovative architecture is introduced based on the merging between the double IQ and code multiplexing structure. Simulation results show that, in a Gaussian case, the bit error rate does not increase significantly when using this architecture. A complexity evaluation study reveals significantly reduced power consumption when implementing the proposed single front-end architecture

A 802.11g and UMTS Simultaneous Reception Front-End Architecture using a double IQ structure

International audienceIn this paper, we address the architecture of multistandard simultaneous reception receivers and we aim to reduce the complexity of the analog front-end. To this end, we propose an architecture using the double orthogonal translation technique in order to multiplex two signals received on different frequency bands. A study case concerning the simultaneous reception of 802.11g and UMTS signals is developed in this paper. Theoretical and simulation results show that this type of multiplexing does not significantly influence the evolution of the signal to noise ratio of the signals