Adaptation de maillage pour la simulation numérique du tourbillon marginal sur une aile tridimensionnelle

Phénomène physique -- Le tourbillon numérique -- Présentation de la démarche -- Schéma global du cycle solveur-remailleur -- Fonctionnement du remailleur -- Théorie sur la métrique -- Construction de l'estimateur d'erreur -- Régularité des maillages -- Algorithme pour garder le nombre d'éléments constant -- Transport de la variable d'adaption -- Critère de convergence du cycle solveur/mailleur -- Premier cas test : simulations sans le profil -- Présentation du cas test -- Analyse sans adaptation -- Adaptation -- Résultats -- Dégénérescence du tourbillon -- Simulation avec un profil -- Description du cas test -- Description de la géométrie -- Description du maillage -- Résultats sans adaptation -- Adaptation

Patient-specific anisotropic model of human trunk based on MR data

There are many ways to generate geometrical models for numerical simulation, and most of them start with a segmentation step to extract the boundaries of the regions of interest. This paper presents an algorithm to generate a patient-specific three-dimensional geometric model, based on a tetrahedral mesh, without an initial extraction of contours from the volumetric data. Using the information directly available in the data, such as gray levels, we built a metric to drive a mesh adaptation process. The metric is used to specify the size and orientation of the tetrahedral elements everywhere in the mesh. Our method, which produces anisotropic meshes, gives good results with synthetic and real MRI data. The resulting model quality has been evaluated qualitatively and quantitatively by comparing it with an analytical solution and with a segmentation made by an expert. Results show that our method gives, in 90% of the cases, as good or better meshes as a similar isotropic method, based on the accuracy of the volume reconstruction for a given mesh size. Moreover, a comparison of the Hausdorff distances between adapted meshes of both methods and ground-truth volumes shows that our method decreases reconstruction errors faster. Copyright © 2015 John Wiley & Sons, Ltd.Natural Sciences and Engineering Research Council (NSERC) of Canada and the MEDITIS training program (´Ecole Polytechnique de Montreal and NSERC)

Graphon: A Comparison of Grapheme-to-phoneme Conversion Performance between an Automated System and Primary Grade Students

Grapheme-to-phoneme conversion is a necessary part of reading, whether by an automated system or by children. Automated methods play a key role in text-to-speech and automated speech recognition systems. Children learning to read develop grapheme-to-phoneme (G2P) conversion rules that they use extensively until they build up their orthographic lexicon. Various solutions have been proposed for G2P conversion, each addressing specific problems and evaluated for different languages. In this thesis, I introduce a simple approach to G2P conversion that achieves good results, and compare these results to those of a study of children’s reading accuracy in the primary grades. The comparison highlights areas of weakness in the children’s reading skills, as well as particular phonemes for which the G2P system has difficulty. As part of the process, I also compare and discuss the wide range of discrepancies that exist between various French corpora

Comparison of semantic similarity for different languages using the Google N-gram corpus and second-order co-occurrence measures

Abstract. Despite the growth in digitization of data, there are still many languages without sufficient corpora to achieve valid measures of semantic similarity. If it could be shown that manually-assigned similarity scores from one language can be transferred to another language, then semantic similarity values could be used for languages with fewer resources. We test an automatic word similarity measure based on second-order co-occurrences in the Google n-gram corpus, for English, German, and French. We show that the scores manually-assigned in the experiments of Rubenstein and Goodenough’s for 65 English word pairs can be transferred directly into German and French. We do this by conducting human evaluation experiments for French word pairs (and by using similarly produced scores for German). We show that the correlation between the automatically-assigned semantic similarity scores and the scores assigned by human evaluators is not very different when using the Rubenstein and Goodenough’s scores across language, compared to the language-specific scores.

Numerical capture of wing tip vortex improved by mesh adaptation

This paper presents a mesh adaptation procedure linked to a finite volume solver, the goal of which is to increase the precision of the numerical simulation of a wing tip vortex flow. The adaptation scheme is applied to hexahedron meshes and hybrid meshes made up of tetrahedrons and prisms. To evaluate the ability of each type of element to capture the physics of a tip vortex, a specific test case is studied and results obtained numerically from this test case are compared with experimental results. The error estimator of the adaptation scheme is derived from a solution scalar variable. It is shown that the element anisotropy as well as the adaptation algorithms used have an impact on the precision of the solution. Adaptation of hexahedrons allows a better capture of the tip vortex far from the vortex root, even though the adaptation of those hexahedrons barely changes the number of nodes used to achieve a specified precision, contrary to the adaptation of hybrid meshes. Copyright (C) 2009 John Wiley & Sons, Ltd