HAL-UNICE
Not a member yet
30584 research outputs found
Sort by
Low-Shapiro hydrostatic reconstruction technique for blood flow simulation in large arteries with varying geometrical and mechanical properties
No full textInternational audienceThe purpose of this work is to construct a simple, efficient and accurate well-balanced numerical scheme for one-dimensional (1D) blood flow in large arteries with varying geometrical and mechanical properties. As the steady states at rest are not relevant for blood flow, we construct two well-balanced hydrostatic reconstruction techniques designed to preserve low-Shapiro number steady states that may occur in large network simulations. The Shapiro number S h = u/c is the equivalent of the Froude number for shallow water equations and the Mach number for compressible Euler equations. The first is the low-Shapiro hydrostatic reconstruction (HR-LS), which is a simple and efficient method, inspired from the hydrostatic reconstruction technique (HR). The second is the subsonic hydrostatic reconstruction (HR-S), adapted here to blood flow and designed to exactly preserve all subcritical steady states. We systematically compare HR, HR-LS and HR-S in a series of single artery and arterial network numerical tests designed to evaluate their well-balanced and wave-capturing properties. The results indicate that HR is not adapted to compute blood flow in large arteries as it is unable to capture wave reflections and transmissions when large variations of the arteries' geometrical and mechanical properties are considered. On the contrary, HR-S is exactly well-balanced and is the most accurate hydrostatic reconstruction technique. However, HR-LS is able to compute low-Shapiro number steady states as well as wave reflections and transmissions with satisfying accuracy and is simpler and computationally less expensive than HR-S. We therefore recommend using HR-LS for 1D blood flow simulations in large arterial network simulations
Grass-Root Training: a Challenge for Ethiopian Athletics
No full textInternational audienceThis paper analyses the problem of grassroots training in Ethiopian athletics, presenting the different institutions involved in athletics and their respective reasons for the lack of interest and involvement in grass-root training activities. The overall picture provided by this description reflects the poor conditions of Ethiopian athletics and the prevalence of a predatory system of selection in lieu of a comprehensive institutional organization for the promotion of sport. The data collected for this research proceed from interviews with officials of athletics federations and sponsors over several years of professional activity of the first author and on the basis of fieldwork observations by the second author
Inner gorges incision history: A proxy for deglaciation? Insights from Cosmic Ray Exposure dating (10Be and 36Cl) of river-polished surfaces (Tinée River, SW Alps, France)
No full textInternational audienceEditor: A. Yin Keywords: river gorges incision CRE 10 Be and 36 Cl dating river polished surfaces 10 Be and 36 Cl Cosmic Ray Exposure (CRE) dating performed on river polished surfaces of river gorges in a mountain-to-sea river system in the French SW Alps highlights transient erosional events involving incision rates >10 mm a −1. These events took place during the last two major deglaciation phases following (1) the Last Glacial Maximum (LGM) at 16–14 ka, (2) the Younger Dryas at 8–11 ka, and during the warm and humid Holocene climatic optimum at 4–5 ka. These periods of high incision rates (3–>30 mm a −1) alternated with periods of low incision rates (<1 mm a −1), which probably correspond to a long-term equilibrium between incision and relative uplift. The Alpine river staircase shape profiles evidence local and transient responses that are ascribed to cumulate disequilibrium after the long-time-spanned glaciations. After each glaciation, rivers rush down to get closer to their equilibrium profile. Incision is amplified both by the sediment discharge due to the erosion of moraines and by landslides triggered by the glacier retreat
Local Controllability of the Two-Link Magneto-Elastic Micro-Swimmer
No full textInternational audienceA recent promising technique for robotic micro-swimmers is to endow them with a magnetization and apply an external magnetic field to provoke their deformation. In this note we consider a simple planar micro-swimmer model made of two magnetized segments connected by an elastic joint, controlled via a magnetic field. After recalling the analytical model, we establish a local controllability result around the straight position of the swimmer
Quelles relaxations continues pour le critère ?
No full textNational audienceFor more than two decades, several continuous (and generally separable) penalties approximating (relaxing) the l0-pseudo norm have been proposed. Although some "good" properties for such penalties have been highlighted, the choice of one relaxation rather than another one remains unclear. One approach to compare them is to investigate their fidelity to the initial problem. In other words, do they preserve global minimizers of the initial criteria without adding new local ones? Within the context of the l0 penalized least squares, we have recently studied this question resulting in a class of penalties said exact. In this communication, we present these results and complete them with a study concerning the local minimizers eliminated by such relaxations. In particular, we show that the CEL0 penalty is the one removing the largest number of local minimizers.Depuis plus de deux décennies, de nombreuses pénalités continues (et généralement séparables) ont été proposées afin d'approcher (relaxer) la pseudo-norme l0. Bien que certaines «bonnes» propriétés pour ces pénalités aient été mises en évidence, le choix d'une relaxation par rapport à une autre reste peu clair. Une approche pour les comparer est de s'intéresser à la fidélité de la relaxation au problème initial. En d'autres termes, est-ce que cette dernière préserve les minimiseurs globaux du critère initial sans en ajouter de locaux ? Dans le contexte des moindres carrés pénalisés en norme-l0, nous avons récemment étudié cette question et défini une classe de pénalités qualifiés d'exactes. Dans cette communication, nous présentons ces résultats et les complétons par une étude des minimiseurs locaux qui sont éliminés par de telles relaxations. En particulier, nous montrons que la pénalité CEL0 est celle éliminant le plus de minimiseurs locaux
Caractérisation de la source des séismes par inversion des données sismologiques et géodésiques : mécanismes au foyer, optimisation des modèles de vitesse, distribution du glissement cosismique
No full textStudies of the earthquake source are based on observations of seismic ground motions. They also depend on the quality and the density of measurements. In this present work we will present studies of the determination of focal mechanism of main aftershocks of the Les Saintes (MW 6.4, 2004) earthquake, and the determination of the coseismic slip of the L’Aquila (MW 6.3, 2009), the Miyagi-Oki (MW 7.2, 2005), ant the Sanriku-Oki (MW 7.3, 2011) earthquakes. These studies were based on two inversion methods. Different kinds of data were available (strong motion, broadband teleseismic, GPS and InSAR) depending on the earthquake studied. But the multiplicity of data is not sufficient to well describe rupture process. There are others difficulties as the data modeling of strong motion. Seismic velocity models are used to describe the characteristics of layers crossed by seismic waves. The quality of the modeling is depending on the pertinence of these seismic velocity models. The description of the rupture process is also depending on the non-uniqueness of the best solution given by global inversion methods. We propose two procedures in order to take into account these two classic issues. First, we developed a velocity model exploration procedure to obtain optimized 1D velocity models in order to improve the strong motion modeling of the L’Aquila earthquake. Then we developed a procedure to build an average rupture model from the combined results of several joint inversions, which was applied to the L’Aquila, the Miyagi-Oki, and the Sanriku-Oki earthquake. This thesis presents all these works and answers to the raised issues.La caractérisation de la source d’un séisme se fait à partir de l’analyse des mesures des déplacements transitoires et statiques du sol, et dépend de la quantité et de la qualité de ces mesures. Nous avons travaillé sur la détermination des mécanismes au foyer des répliques du séisme de Saintes (MW 6.4, 2004), et sur la détermination de la distribution spatio-temporelle du glissement cosismique des séismes de L’Aquila (Mw 6.3, 2009), et de Miyagi-Oki (Mw 7.2, 2005) et de Sanriku-Oki (Mw 7.3, 2011). Ces travaux se sont basés sur des méthodes d’inversions, et différents jeux de données (accélérométriques, large-bandes, GPS et InSAR) accessibles ou non selon le séisme considéré. La seule diversité des mesures n’est pas suffisante pour décrire la rupture. La modélisation des données se confronte à des difficultés, comme par exemple la pertinence des modèles de vitesses sismiques pour la modélisation des données accélérométriques. Une autre problématique récurrente est la non-unicité de la meilleure solution déterminée par les méthodes d’inversions pour décrire les données. Pour répondre à ces deux problématiques, nous avons d‘une part développé une procédure d’exploration de modèles de vitesse pour déterminer les valeurs optimales capables de décrire au mieux les données accélérométriques du séisme de L’Aquila. D’autre part, nous avons développé une procédure de construction d’un modèle de source moyen que nous avons appliqué pour la détermination du glissement cosismique des séismes de L’Aquila, de Miyagi-Oki, et de Sanriku-Oki. L’ensemble de ces travaux et les réponses aux problèmes soulevés sont présentés dans ce travail de thèse
Sign-changing self-similar solutions of the nonlinear heat equation with positive initial value
No full textWe consider the nonlinear heat equation on , where and . We prove that in the range , for every , there exist infinitely many sign-changing, self-similar solutions to the Cauchy problem with initial value . The construction is based on the analysis of the related inverted profile equation.In particular, we construct (sign-changing) self-similar solutions for positive initial values for which it is known that there does not exist any local, nonnegative solution
Citizenship and Diversity in Education in France: Public Controversies, Local Adaptations and Commitments
No full textInternational audienc
New insights into the chromosomal differentiation patterns among cichlids from Africa and Madagascar
No full textInternational audienceTo increase understanding of the chromosomal diversity among cichlid species, karyotypes of 19 species of Cichlidae belonging to 15 genera (Paratilapia polleni, Chromidotilapia guntheri guntheri, Hemichromis fasciatus, Steatocranus irvinei, Stomatepia pindu, Altolamprologus compressiceps, Julidochromis transcriptus, Neolamprologus tetracanthus, N. brevis, Gnathochromis permaxillaris, Eretmodus cyanostictus, Astatoreochromis alluaudi, Haplochromis callipterus, H. paludinosus, Ninzbochromis livingstonii, N. polystigma, Pseudocrenilabrus multicolor victoriae, P. philander and Ctenochromis horei) were investigated for the first time. In spite of the variation in the karyotypes of cichlid fishes (from 2n = 42 to 2n = 48 chromosomes), the modal chromosome number was 2n = 44. Cytogenetic mapping of the 18S ribosomal RNA (18S rRNA) gene was accomplished
