Policy Iteration-based Conditional Termination and Ranking Functions

The final publication is available at link.springer.com.International audienceTermination analyzers generally synthesize ranking functions or relations, which represent checkable proofs of their results. In [], we proposed an approach for conditional termination analysis based on abstract fixpoint computation by policy iteration. This method is not based on ranking functions and does not directly provide a ranking relation, which makes the comparison with existing approaches difficult. In this paper we study the relationships between our approach and ranking functions and relations, focusing on extensions of linear ranking functions. We show that it can work on programs admitting a specific kind of segmented ranking functions, and that the results can be checked by the construction of a disjunctive ranking relation. Experimental results show the interest of this approach

My Corporis Fabrica Embryo: An ontology-based 3D spatio-temporal modeling of human embryo development

International audienceBackground: Embryology is a complex morphologic discipline involving a set of entangled mechanisms, sometime difficult to understand and to visualize. Recent computer based techniques ranging from geometrical to physically based modeling are used to assist the visualization and the simulation of virtual humans for numerous domains such as surgical simulation and learning. On the other side, the ontology-based approach applied to knowledge representation is more and more successfully adopted in the life-science domains to formalize biological entities and phenomena, thanks to a declarative approach for expressing and reasoning over symbolic information. 3D models and ontologies are two complementary ways to describe biological entities that remain largely separated. Indeed, while many ontologies providing a unified formalization of anatomy and embryology exist, they remain only descriptive and make the access to anatomical content of complex 3D embryology models and simulations difficult. Results: In this work, we present a novel ontology describing the development of the human embryology deforming 3D models. Beyond describing how organs and structures are composed, our ontology integrates a procedural description of their 3D representations, temporal deformation and relations with respect to their developments. We also created inferences rules to express complex connections between entities. It results in a unified description of both the knowledge of the organs deformation and their 3D representations enabling to visualize dynamically the embryo deformation during the Carnegie stages. Through a simplified ontology, containing representative entities which are linked to spatial position and temporal process information, we illustrate the added-value of such a declarative approach for interactive simulation and visualization of 3D embryos.Conclusions: Combining ontologies and 3D models enables a declarative description of different embryological models that capture the complexity of human developmental anatomy. Visualizing embryos with 3D geometric models and their animated deformations perhaps paves the way towards some kind of hypothesis-driven application. These can also be used to assist the learning process of this complex knowledge.Availability: http://www.mycorporisfabrica.org

Sea ice diatom contributions to Holocene nutrient utilization in East Antarctica

Combined high-resolution Holocene δ30Sidiat and δ13Cdiat paleorecords are presented from theSeasonal Ice Zone, East Antarctica. Both data sets reflect periods of increased nutrient utilization by diatomsduring the Hypsithermal period (circa 7800 to 3500 calendar years (cal years) B.P.), coincident with a higherabundance of open water diatom species (Fragilariopsis kerguelensis), increased biogenic silica productivity(%BSi), and higher regional summer temperatures. The Neoglacial period (after circa 3500 cal years B.P.) isreflected by an increase in sea ice indicative species (Fragilariopsis curta and Fragilariopsis cylindrus,upto50%) along with a decrease in %BSi and δ13Cdiat(< 18‰ to 23‰). However, over this period, δ30Sidiatdata show an increasing trend, to some of the highest values in the Holocene record (average of +0.43‰).Competing hypotheses are discussed to account for the decoupling trend in utilization proxies including ironfertilization, species-dependent fractionation effects, and diatom habitats. Based on mass balance calculations,we highlight that diatom species derived from the semi-enclosed sea ice environment may have a confoundingeffect upon δ30Sidowncorecompositions of the seasonal sea ice zone. A diatom composition, with approximately28% of biogenic silica derived from the sea ice environment (diat-SI) can account for the increased averagecompo sition of δ30Sidiatduring the Neoglacial. These data highlight the significant role sea ice diatoms can playwith relation to their export in sediment records, which has implications on productivity reconstructions fromthe seasonal ice zone

Proving Termination by Policy Iteration

In this paper, we explore the adaptation of policy iteration techniques to compute greatest fixpoint approximations, in order to find sufficient conditions for program termination. Restricting ourselves to affine programs and the abstract domain of template constraint matrices, we show that the abstract greatest fixpoint can be computed exactly using linear programming, and that strategies are related to the template constraint matrix used. We also present a first result on the relationships between this approach and methods which use ranking functions. Keywords: analysis. Abstract interpretation, policy iteration, template constraint matrices, termination

Comprendre l'économie collaborative et ses promesses à travers ses fondements théoriques

Airbnb, blablacar, eBay… Ces plateformes qui transforment nos économies sont le sommet du vaste iceberg appelé « économie collaborative ». Ce concept encore flou est porté par un ensemble d'acteurs constitué d'essayistes à suc-cès, de militants associatifs et d'entrepreneurs du web. À ce concept sont associées de nombreuses promesses : les pratiques collaboratives seraient une réponse à la crise du modèle de croissance, à la crise environnementale, et un moyen de refonder le lien social et les solidarités collectives. RETOUR AUX FONDEMENTS THÉORIQUES L'étude des fondements théoriques de l'économie collaborative permet de comprendre et d'analyser les promesses dont elle est porteuse. Nous identifions et discutons ici trois champs théoriques centraux mobilisés par les promoteurs de l'économie collaborative : la mouvance du libre irrigue la réflexion sur l'économie collaborative en soulignant et promouvant un changement de posture du consommateur passif vers un « consomm'ac-teur » de cette économie, ce passage se matérialisant par un accès distri-bué et universel aux connaissances, aux compétences et aux ressources matérielles ; l'économie de la fonctionnalité éclaire ce qui est au coeur de l'économie collaborative : le passage d'une logique de propriété à une logique d'usage, qui ouvre la voie à nombre de promesses environnemen-tales ; l'économie du don illustre la rupture avec l'hégémonie de l'échange marchand, en y réintégrant la dimension de l'échange symbolique basé sur le donner, recevoir et rendre. UNE POSTURE CRITIQUE VIS-À-VIS DE CES PROMESSES RESTE NÉCESSAIRE La diversité des approches théoriques mobilisées permet d'expliquer la plu-ralité des définitions de l'économie collaborative, mais aussi la diversité des promesses dont elle est porteuse. Si ces dernières doivent être prises au sérieux, elles suscitent également et à juste titre de nombreuses réserves. Les acteurs de l'économie collaborative qui veulent les concrétiser ne peuvent donc se passer d'une analyse critique, tout comme les décideurs publics qui souhaitent accompagner la diffusion des pratiques collabora-tives. Les champs théoriques identifiés ici peuvent être mobilisés à cette fin

Differential Inclusion using Matrix Exponential

[no abstract available

Multi-Objective optimization: Comparison of methods for the p-median problem

International audienc