Adaptive multiresolution computations applied to detonations

A space-time adaptive method is presented for the reactive Euler equations describing chemically reacting gas flow where a two species model is used for the chemistry. The governing equations are discretized with a finite volume method and dynamic space adaptivity is introduced using multiresolution analysis. A time splitting method of Strang is applied to be able to consider stiff problems while keeping the method explicit. For time adaptivity an improved Runge--Kutta--Fehlberg scheme is used. Applications deal with detonation problems in one and two space dimensions. A comparison of the adaptive scheme with reference computations on a regular grid allow to assess the accuracy and the computational efficiency, in terms of CPU time and memory requirements.Comment: Zeitschrift f\"ur Physicalische Chemie, accepte

RIOT OS Paves the Way for Implementation of High-Performance MAC Protocols

Implementing new, high-performance MAC protocols requires real-time features, to be able to synchronize correctly between different unrelated devices. Such features are highly desirable for operating wireless sensor networks (WSN) that are designed to be part of the Internet of Things (IoT). Unfortunately, the operating systems commonly used in this domain cannot provide such features. On the other hand, "bare-metal" development sacrifices portability, as well as the mul-titasking abilities needed to develop the rich applications that are useful in the domain of the Internet of Things. We describe in this paper how we helped solving these issues by contributing to the development of a port of RIOT OS on the MSP430 microcontroller, an architecture widely used in IoT-enabled motes. RIOT OS offers rich and advanced real-time features, especially the simultaneous use of as many hardware timers as the underlying platform (microcontroller) can offer. We then demonstrate the effectiveness of these features by presenting a new implementation, on RIOT OS, of S-CoSenS, an efficient MAC protocol that uses very low processing power and energy.Comment: SCITEPRESS. SENSORNETS 2015, Feb 2015, Angers, France. http://www.scitepress.or

Une autre conversion de SAT vers CSP

http://www710.univ-lyon1.fr/~csolnonCet article présente une transformation d'une formule propositionnelle du problème SAT en une autre formule propositionnelle qui, à son tour, peut être directement transformée en un problème CSP binaire. Cette transformation est basée sur une procédure de recherche de modèles locaux qui est contrôlée pour obtenir une transformation qui soit globalement polynomiale. Une méthode pour réduire la taille de la formule finale est proposée. Nous montrons également que le maintien de la k-consistance sur le problème CSP est équivalent à l'utilisation de la propagation unitaire sur une forme compilée de la formule propositionnelle correspondante dans le problème SAT. De notre point de vue, cette transformation établit un autre pont naturel entre SAT et CSP qui pourrait être bénéfique aux deux communautés

Cohérences basées sur les valeurs en échec

International audienceNon disponibl

XML Representation of Constraint Networks: Format XCSP 2.1

We propose a new extended format to represent constraint networks using XML. This format allows us to represent constraints defined either in extension or in intension. It also allows us to reference global constraints. Any instance of the problems CSP (Constraint Satisfaction Problem), QCSP (Quantified CSP) and WCSP (Weighted CSP) can be represented using this format

A long-term copper exposure on freshwater ecosystem using lotic mesocosms: Individual and population responses of three-spined sticklebacks (Gasterosteus aculeatus)

Three-spined stickleback (Gasterosteus aculeatus) was used as the highest trophic level predator in an outdoor mesocosm study assessing the effect of environmentally realistic copper concentration (0, 5, 25 and 75 μg L−1) over 18 months of continuous exposure. Condition factor, organosomatic indices (HIS, GSI and SSI) as well as copper bioaccumulation in the liver were measured at 15 days, 2, 4, 6, 10, 14 and 18 months after the beginning of the contamination. Population monitoring was realised after 6 and 18 months of contamination, allowing two reproduction periods to be measured. Results showed that condition factor was affected at medium and high copper concentrations and HSI was sporadically affected in all copper exposure, depending on the sex of the fish. GSI did not show any significant differences and SSI was lowered in the medium and high copper levels. Bioaccumulation was significantly different in males and females and fluctuated with season. A negative correlation was observed between copper bioaccumulation in the liver and fish size and a positive correlation with nominal copper concentration in the water was found. There was a negative correlation between condition factor, organosomatic indices and bioaccumulation in the liver. Population monitoring showed a significantly higher fish mean length after 6 months and a higher abundance after 18 months of exposure at the highest copper level. We conclude that indirect effects such as food and habitat availability or lower predation pressure on eggs and juveniles might have led to higher stickleback population abundances at the highest copper level. This highlights the need to study all the trophic levels when monitoring ecosystem health. Considering the population and the individual responses after 18 months of copper exposure, the NOEC for three-spined sticklebacks was 25 μg L−1 (or 20 μg L−1 if we consider the average effective concentration), with a LOEC of 75 μg L−1 (or 57 μg L−1, AEC)

A Decomposition Technique for Solving {Max-CSP}

International audienceThe objective of the Maximal Constraint Satisfaction Problem (Max-CSP) is to find an instantiation which minimizes the number of constraint violations in a constraint network. In this paper, inspired from the concept of inferred disjunctive constraints intro- duced by Freuder and Hubbe, we show that it is possible to exploit the arc-inconsistency counts, associated with each value of a net- work, in order to avoid exploring useless portions of the search space. The principle is to reason from the distance between the two best values in the domain of a variable, according to such counts. From this reasoning, we can build a decomposition technique which can be used throughout search in order to decompose the current prob- lem into easier sub-problems. Interestingly, this approach does not depend on the structure of the constraint graph, as it is usually pro- posed. Alternatively, we can dynamically post hard constraints that can be used locally to prune the search space. The practical interest of our approach is illustrated, using this alternative, with an experi- mentation based on a classical branch and bound algorithm, namely PFC-MRDAC

Substituabilité au voisinage pour le cadre WCSP

National audienceWCSP is an optimization problem for which many forms of soft local (arc) consistencies such as existential directional arc consistency (EDAC) and virtual arc consistency (VAC) have been proposed these last years. In this paper, we adopt a different perspective by revisiting the well-known property of (soft) substitutability. First, we provide a clear picture of the relationships existing between soft neighborhood substitutability (SNS) and a tractable property called $pcost$ which is based on the concept of overcost of values (through the use of so-called cost pairs). We prove that under certain assumptions, $pcost$ is equivalent to SNS but weaker than SNS in the general case since we show that SNS is coNP-hard. We also show that SNS preserves the property VAC but not the property EDAC. Finally, we introduce an optimized algorithm and we show on various series of WCSP instances, the practical interest of maintaining $pcost$ together with AC*, FDAC or EDAC, during search.WCSP est un problème d'optimisation pour lequel plusieurs formes de cohérences locales souples telles que, par exemple, la cohérence d'arc existentielle directionnelle (EDAC) et la cohérence d'arc virtuelle (VAC) ont été proposées durant ces dernières années. Dans cet article, nous adoptons une perspective différente en revisitant la propriété bien connue de la substituabilité (souple). Tout d'abord, nous précisons les relations existant entre la substituabilité de voisinage souple (SNS pour Soft Neighbourhood Substitutability) et une propriété appelée $pcost$ qui est basée sur le concept de surcoût de valeurs (par le biais de l'utilisation de paires de surcoût). Nous montrons que sous certaines hypothèses, $pcost$ est équivalent à SNS, mais que dans le cas général, elle est plus faible que SNS prouvée être coNP-difficile. Ensuite, nous montrons que SNS conserve la propriété VAC, mais pas la propriété EDAC. Enfin, nous introduisons un algorithme optimisé et nous montrons sur diverses séries d'instances WCSP l'intérêt pratique du maintien de $pcost$ avec AC*, FDAC ou EDAC, au cours de la recherche

Extension des cohérences WCSP aux tuples

National audienceDans cet article, nous présentons un nouveau type de propriétés pour les réseaux de contraintes pondérées (WCNs pour Weighted Constraint networks). Il s'agit de la cohérence de tuples (TC) dont l'établissement sur un WCN est effectué grâce à une nouvelle opération appelée TupleProject. Nous proposons également une version "optimale" de cette propriété, OTC, qui peut être perçue comme une généralisation de OSAC (Optimal Soft Arc Consistency). Le principe sous-jacent à OTC est d'appliquer de manière itérative l'opération TupleProject afin de factoriser un coût qui maximise la borne inférieure w;, sur la base de transferts de coûts entre tuples de différentes contraintes d'arité quelconque