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Asymptotic models of the diffusion MRI signal accounting for geometrical deformations
No full textInternational audienceThe complex transverse water proton magnetization subject to diffusion-encoding magneticfield gradient pulses can be modeled by the Bloch-Torrey partial differential equation (PDE).The associated diffusion MRI signal is the spatial integral of the solution of the Bloch-Torrey PDE. In addition to the signal, the time-dependent apparent diffusion coefficient (ADC) can be obtained from the solution of another partial differential equation, called the HADC model, which was obtained using homogenization techniques. In this paper, we analyze the Bloch-Torrey PDE and the HADC model in the context of geometrical deformations starting from a canonical configuration. To be more concrete,we focused on two analytically defined deformations: bending and twisting. We derived asymptotic models of the diffusion MRI signal and the ADC where the asymptotic parameter indicates the extent of the geometrical deformation. We compute numerically the first three terms of the asymptotic models and illustrate the effects of the deformations by comparing the diffusion MRI signal and the ADC from the canonical configuration with those of the deformed configuration. The purpose of this work is to relate the diffusion MRI signal more directly with tissue geometrical parameters
A posteriori error estimates for mixed finite element discretizations of the Neutron Diffusion equations
No full textInternational audienceWe analyse a posteriori error estimates for the discretization of the neutron diffusion equations with mixed finite elements. We provide guaranteed and locally efficient estimators on a base block equation, the one-group neutron diffusion equation. We pay particular attention to AMR strategies on Cartesian meshes, since such structures are common for nuclear reactor core applications. We exhibit a robust marker strategy for this specific constraint, the direction marker strategy
Construction de conditions transparentes pour les guides d’ondes électromagnétiques.
No full textInternational audienceWe are interested in the numerical resolution of diffraction problems in closed electromagnetic waveguides using Finite Element methods. To do this, it is necessary to truncate the domain and create a suitable transparent condition on the artificial boundary to avoid spurious reflections.Here, we show how to extend several techniques developed in acoustics or elasticity to this case. To express the transparent condition, we use a modal decomposition. Numerically, it is necessary to truncate the corresponding series. To demonstrate the convergence of our approach, we show that the problem in the truncated domain is well-posed, and that the error with the exact solution decreases exponentially with the truncation rank.We will present numerical results obtained using the XliFE++ library, which illustrate the solution of the 3D Maxwell equations using Nédélec finite elements.Nous nous intéressons à la résolution numérique de problèmes de diffraction dans des guides d’ondes électromagnétiques fermés au moyen de méthodes d’Éléments Finis. Pour ce faire, il est nécessaire de tronquer le domaine et de créer une condition transparente adaptée sur la frontière artificielle pour éviter les réflexions parasites.Nous montrons ici comment étendre à ce cas plusieurs techniques développées en acoustique ou en élasticité. Pour écrire la condition transparente, on utilise une décomposition modale. Numériquement, il est nécessaire de tronquer la série correspondante. Pour justifier la convergence de notre approche, on montre que le problème en domaine tronqué est bien posé, et que l’erreur avec la solution exacte décroît exponentiellement avec le rang de troncature.Nous montrerons des résultats numériques obtenus à l’aide de la librairie XliFE++, qui illustrent la résolution des équations de Maxwell 3D en utilisant les éléments finis de Nédélec
A hyperbolic conservative one-velocity one-pressure barotropic three-component model for fast-transient fluid-structure interaction problems
No full textInternational audienceThe present paper focuses on the simulation of compressible three-component flows interacting with surrounding deformable and immersed structures. For this purpose, a barotropic three-component model assuming instantaneous kinematic and mechanical equilibria is discussed. The mathematical properties of the system, the structure of the waves, the expression of the Riemann invariants and the existence of a mathematical entropy are thus examined. The link between the present model and the extension to three components of the Kapila model is discussed. An HLLC-type solver for the present three-component model based on the mathematical structure of the system is then described. The multi-fluid solver used is coupled with an updated Lagrangian approach used for the structural domain. Arbitrary Lagrangian-Eulerian (ALE) approach and Immersed Boundary Method (IBM) are here considered and compared for their capability to account for fluid-structure interactions (FSI). A series of Riemann problems with available analytical solutions are regarded to assess the used numerical approaches: Eulerian on fixed grids, ALE on moving grids and IBM with independent fluid and structure meshes. Finally, ALE and IBM methods are used to simulate an experimental configuration involving complex FSI problems with a multi-material flow and structural plastic deformations. The numerical results presented show a good agreement with the experimental data
Sur les effets d'inertie en flambement dynamique de colonnes sous impact longitudinal : expériences et modélisations
No full textThe objectives of this work are mainly to understand the phenomena involved in the dynamic behaviour of spacer grids under axial impact. At first, we propose to design and build a scale-up model similar to a row of the spacer grid. This design step will be accompanied by the construction of a parametric numerical model based on a one-dimensional approach of a beam with added masses. In a second step, tests, through an adapted set-up, allow to better identify the dominant behaviors during the impact. Finally, a better understanding of the physical phenomena allow to identify the main parameters of the model, whose influence has already been demonstrated in the theoretical and numerical approaches.Les objectifs de ce travail de thèse concernent principalement la compréhension des phénomènes mis en jeu dans la réponse dynamique des grilles d'assemblages combustibles en cas d'impact. Dans un premier temps, on se propose de concevoir et de réaliser une maquette de grille à échelle augmentée. Cette étape de conception s'accompagnera de la construction d'un modèle numérique paramétrique fondée sur une approche unidimensionnelle de type poutre avec masses ajoutées. Dans un second temps, des essais, à travers sur une instrumentation fine de la maquette, permettent de mieux identifier les comportements dominants pendant les phases de contact, de hiérarchiser et de caractériser les paramètres de la modélisation, dont l'influence a déjà été démontrée dans les approches théoriques et numériques
Haut potentiel intellectuel, enjeux d’un bilan psychologique intégratif en clinique de l’adolescent. À propos d’une étude de cas.
No full textInternational audienceIntroduction. – With a prevalence of 2.3% among French schoolchildren aged 6 to 16, giftedness represents a challenge in child psychiatry (Delaubier, 2002). Dys-synchronies can appear in the different domains of intelligence, associated with eclectic symptoms: hypersensitivity, anxiety, depression, attention deficit disorder with or without hyperactivity, oppositional disorder as well as conduct disorders. The psychological assessment can constitute an opportunity to identify and evaluate giftedness functioning in order to advise an adapted treatment in the guidance of these children and teenagers, and to guarantee them the most harmonious global development.Method. – The method used was that of a case study. was received within clinical research carried out at the University of Bordeaux for the realization of a psychological assessment. The objective of the assessment was to investigate and understand the polymorphic anxiety domain but also the impossibility for Minerva to attend middle school, with the result that she was home schooled with the National Center for Distance Learning (CNED). Over two half-days, we were able to successively carry out the anamnestic interview, a semi-structured interview, the K-SADS, the evaluation of cognitive functioning with the WISC-V, various projective tests such as the TAT, the Rorschach test, a drawing of a man and a family, as well as various scales in self and hetero-evaluation.Results. – The K-SADS clarified the psychopathological situation as well as the family, social and school impact of this invasive case of anxiety. The results of the WISC-V showed an intellectual potential between 117 and 129, with areas of high efficiency for the Verbal Comprehension Index (VCI = 146) and the Working Memory Index (WMI = 122). The profile, although not reaching the recommended 130 in global IQ, is consistent with high intellectual potential when the performance is impacted by the situation of parasitic anxiety and a sedative medication. The projective tests as well as the drawings of the man and the family, demonstrated the extent of the considerable rigid defense mechanisms and of avoidance, but also of the hyper investment of the intellectualization processes.Conclusion. – The screening of high intellectual potential represents a clinical challenge in view of the lack of diagnostic recommendations as well as the disparity of information accumulated in research on their characteristics. The holistic approach of the psychological assessment appears to be a solution allowing to situate the individual’s psychic functioning in a constitutive zone of the "high intellectual potential" profile, which should also be at the service of the global therapeutic management.Introduction. – La prévalence du haut potentiel intellectuel (HPI) chez les enfants français scolarisés entre 6 et 16 ans est estimée à 2,3 %, représentant ainsi un défi majeur en pédopsychiatrie (Delaubier, 2002). Des décalages peuvent se manifester dans les différents domaines de l’intelligence, associés à des symptômes variés : hypersensibilité, anxiété, dépression, trouble déficitaire de l’attention avec ou sans hyperactivité, trouble oppositionnel, et troubles des conduites. Le bilan psychologique peut constituer l’opportunité de détecter ainsi que d’évaluer le fonctionnement HPI afin de proposer un suivi adapté pour ces enfants et adolescents, dans le but de pouvoir assurer l’harmonie de leur développement global.Méthode. – La méthode retenue est celle de l’étude de cas. Minerva, 14 ans et 11 mois, fut accueillie ausein d’une recherche clinique menée à l’université de Bordeaux pour la réalisation d’un bilan psychologique. L’objectif du bilan était d’investiguer ainsi que comprendre la scène anxieuse polymorphe mais aussi l’impossibilité de se rendre au collège, ayant pour conséquence la scolarisation à domicile via le Centre National d’Enseignement a` Distance (CNED). Sur deux demi-journées, nous avons pu successivement faire l’entretien anamnestique, l’entretien semi-structuré K-SADS, l’évaluation du fonctionnement cognitif avec la WISC-V, différents tests projectifs comme le TAT, le test de Rorschach, un dessin du bonhomme et de la famille, ainsi que différentes échelles en auto- et hétéro-évaluation.Résultats. – La K-SADS a permis de clarifier la situation psychopathologique ainsi que l’impact familial, social et scolaire de cette scène anxieuse invasive. Les résultats au WISC-V ont mis en évidence un potentiel intellectuel compris entre 117 et 129, avec des zones d’efficience haute pour l’Indice de Compréhension Verbale (ICV = 146) et l’Indice de Mémoire de Travail (IMT = 122). Le profil, bien que n’atteignant pas les 130 recommandés en QI global, s’inscrit dans celui d’un haut potentiel, avec une performance impactée par la situation d’une anxiété parasite et d’une médication interférente. Les tests projectifs, ainsi que les dessins du bonhomme et de la famille, ont démontré l’étendue de la massivité des mécanismes de défenses rigides et d’évitement, mais aussi de l’hyperinvestissement du processus d’intellectualisation.Conclusion. – Le dépistage du haut potentiel intellectuel représente un défi clinique face aux manques de recommandations diagnostiques ainsi qu’à la disparité d’informations cumulées en recherche sur leurs caractéristiques. L’approche holistique du bilan psychologique apparaît néanmoins comme une solution permettant de situer les fonctionnements psychiques de l’individu dans une zone constitutive du profil de « haut potentiel intellectuel », se devant aussi d’être au service de la prise en charge thérapeutique globale
On the use of a tailored fluid-fluid Green's function to predict scattering from two-phase fluid interfaces
No full textInternational audienceIn naval applications, the precise knowledge of the acoustical behaviour of two-phase fluids is of interest. Indeed, they appear in many configurations as bubbles curtains, cavitation (along propellers and pipes) or two-phase turbulent boundary layers and wakes (gas exhaust). To model this problem, we focus on a Boundary Element/ Boundary Element coupling for low to moderate frequencies. We propose two approaches: (a) solving the Helmholtz equations in each phase by introducing the free field Green's function and (b) determining a tailored Green's function, taking into account the presence of the two-phase fluid. The determination of a tailored Green's function has two main advantages: (i) it allows a reduction of the numerical model, since it contains all the information on the fluid-fluid coupling, in particular the transmission conditions and resonances and (ii) it is sourceindependent and thus it gives directly the answer to any source. Numerical tests on the evaluation of radiated noise are performed to determine the efficiency of the approach based on a tailored Green's function compared to the free-field based one
Learning Adaptive Control of a UUV using A Bio-Inspired Experience Replay Mechanism
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Machine and Deep Learning Approaches Applied to Classify Gougerot–Sjögren Syndrome and Jointly Segment Salivary Glands
No full textInternational audienceTo diagnose Gougerot–Sjögren syndrome (GSS), ultrasound imaging (US) is a promising tool for helping physicians and experts. Our project focuses on the automatic detection of the presence of GSS using US. Ultrasound imaging suffers from a weak signal-to-noise ratio. Therefore, any classification or segmentation task based on these images becomes a difficult challenge. To address these two tasks, we evaluate different approaches: a classification using a machine learning method along with feature extraction based on a set of measurements following the radiomics guidance and a deep-learning-based classification. We propose, therefore, an innovative method to enhance the training of a deep neural network with a two phases: multiple supervision using joint classification and a segmentation implemented as pretraining. We highlight the fact that our learning methods provide segmentation results similar to those performed by human experts. We obtain proficient segmentation results for salivary glands and promising detection results for Gougerot–Sjögren syndrome; we observe maximal accuracy with the model trained in two phases. Our experimental results corroborate the fact that deep learning and radiomics combined with ultrasound imaging can be a promising tool for the above-mentioned problems