Belief Revision, Minimal Change and Relaxation: A General Framework based on Satisfaction Systems, and Applications to Description Logics

Belief revision of knowledge bases represented by a set of sentences in a given logic has been extensively studied but for specific logics, mainly propositional, and also recently Horn and description logics. Here, we propose to generalize this operation from a model-theoretic point of view, by defining revision in an abstract model theory known under the name of satisfaction systems. In this framework, we generalize to any satisfaction systems the characterization of the well known AGM postulates given by Katsuno and Mendelzon for propositional logic in terms of minimal change among interpretations. Moreover, we study how to define revision, satisfying the AGM postulates, from relaxation notions that have been first introduced in description logics to define dissimilarity measures between concepts, and the consequence of which is to relax the set of models of the old belief until it becomes consistent with the new pieces of knowledge. We show how the proposed general framework can be instantiated in different logics such as propositional, first-order, description and Horn logics. In particular for description logics, we introduce several concrete relaxation operators tailored for the description logic \ALC{} and its fragments \EL{} and \ELext{}, discuss their properties and provide some illustrative examples

Learning Finer-class Networks for Universal Representations

Many real-world visual recognition use-cases can not directly benefit from state-of-the-art CNN-based approaches because of the lack of many annotated data. The usual approach to deal with this is to transfer a representation pre-learned on a large annotated source-task onto a target-task of interest. This raises the question of how well the original representation is "universal", that is to say directly adapted to many different target-tasks. To improve such universality, the state-of-the-art consists in training networks on a diversified source problem, that is modified either by adding generic or specific categories to the initial set of categories. In this vein, we proposed a method that exploits finer-classes than the most specific ones existing, for which no annotation is available. We rely on unsupervised learning and a bottom-up split and merge strategy. We show that our method learns more universal representations than state-of-the-art, leading to significantly better results on 10 target-tasks from multiple domains, using several network architectures, either alone or combined with networks learned at a coarser semantic level.Comment: British Machine Vision Conference (BMVC) 201

A CFH12k lensing survey of X-ray luminous galaxy clusters. II. Weak lensing analysis and global correlations

Aims. We present a wide-field multi-color survey of a homogeneous sample of eleven clusters of galaxies for which we measure total masses and mass distributions from weak lensing. This sample, spanning a small range in both X-ray luminosity and redshift, is ideally suited to determining the normalisation of scaling relations between X-ray properties of clusters and their masses (the M − T_X and the M − L_X relations) and also estimating the scatter in these relations at a fixed luminosity. Methods. The eleven clusters in our sample are all X-ray luminous and span a narrow redshift range at z = 0.21 ± 0.04. The weak lensing analysis of the sample is based on ground-based wide-field imaging obtained with the CFH12k camera on CFHT. We use the methodology developed and applied previously on the massive cluster Abell 1689. A Bayesian method, implemented in the Im2shape software, is used to fit the shape parameters of the faint background galaxies and to correct for PSF smearing. A multi-color selection of the background galaxies is applied to retrieve the weak lensing signal, resulting in a background density of sources of ~10 galaxies per square arc minute. With the present data, shear profiles are measured in all clusters out to at least 2 Mpc (more than 15 from the center) with high confidence. The radial shear profiles are fitted with different parametric mass profiles and the virial mass M_(200) is estimated for each cluster and then compared to other physical properties. Results. Scaling relations between mass and optical luminosity indicate an increase of the M/L ratio with luminosity (M/L ∝ L^(0.8)) and a LX−M_(200) relation scaling as L_X ∝ M^(0.83±0.11)_(200) while the normalization of the M_(200) ∝ T^(3/2)_X relation is close to the one expected from hydrodynamical simulations of cluster formation as well as previous X-ray analyses. We suggest that the dispersion in the M_(200) − T_X and M_(200) − L_X relations reflects the different merging and dynamical histories for clusters of similar X-ray luminosities and intrinsic variations in their measured masses. Improved statistics of clusters over a wider mass range are required for a better control of the intrinsic scatter in scaling relations

Processus discursifs dans le développement de la cohérence narrative

Nous étudions ici la capacité des enfants à parler des états internes des personages et à exprimer la fausse croyance lors de la construction d'un récit à partir d'imagesen comparant les récits produits spontanément à ceux produits après un échange construit sur la base d'un étayage clinique de type piagétien qui attire l'attention des enfants sur les causes des événements. Les résultats montrent que les enfants accroissent considérablement leurs références aux états internes des personnages, y compris leurs états épistémiques et l'expession de la fausse croyance attestant ainsi d'avoir précocément une théorie relativiste de l'esprit. Ces résultats plaident en faveur du rôle de la conversation dans le fonctionnement et de la nécessté d'une évaluation multidimensionnelle des compétences des enfants

Prise en compte de l'imperfection des tags pour la classification sémantique d'images

Session "Articles"National audienceL'annotation d'images consiste à décrire le contenu des images en utilisant un nombre fini de concepts fixés a priori. En pratique, nous utilisons deux modalités pour cela : l'image et les tags utilisateurs qui les accompagnent. Cependant, ces tags sont en général imparfaits et seulement une partie est pertinente vis-à-vis du contenu de l'image. Dans ce papier, nous nous intéressons à la prise en compte de l'imperfection des tags en vue de leur utilisation pour l'amélioration de la performance des systèmes d'annotation. Nous proposons un système de classification multimodale qui prend en compte l'imperfection des tags. L'amélioration de ~8% de classification obtenue sur la base d'images VCDT (Visual Concept detection Task) de la campagne d'évaluation ImageClef2011 montre l'intérêt de cette modélisatio

Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses

Context. Brown dwarfs represent a sizable fraction of the stellar content of our Galaxy and populate the transition between the stellar and planetary mass regime. There is however no agreement on the processes responsible for their formation. Aims. We have conducted a large survey of the young, nearby cluster IC 348, to uncover its low-mass brown dwarf population and study the cluster properties in the substellar regime. Methods. Deep optical and near-IR images taken with MegaCam and WIRCam at the Canada-France-Hawaii Telescope (CFHT) were used to select photometric candidate members. A spectroscopic follow-up of a large fraction of the candidates was conducted to assess their youth and membership. Results. We confirmed spectroscopically 16 new members of the IC 348 cluster, including 13 brown dwarfs, contributing significantly to the substellar census of the cluster, where only 30 brown dwarfs were previously known. Five of the new members have a L0 spectral type, the latest-type objects found to date in this cluster. At 3 Myr, evolutionary models estimate these brown dwarfs to have a mass of ~13 Jupiter masses. Combining the new members with previous census of the cluster, we constructed the IMF complete down to 13 Jupiter masses. Conclusions. The IMF of IC 348 is well fitted by a log-normal function, and we do not see evidence for variations of the mass function down to planetary masses when compared to other young clusters.Comment: Accepted to A&A (8 November 2012