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Critical regularity issues for the compressible Navier--Stokes system in bounded domains
No full textWe are concerned with the barotropic compressible Navier-Stokes system in a bounded domain of (with ). In a critical regularity setting, we establish local well-posedness for large data with no vacuum and global well-posedness for small perturbations of a stable constant equilibrium state.Our results rely on new maximal regularity estimates - of independent interest - for the semigroup of the Lam\é operator, and of the linearized compressible Navier-Stokes equations
Review and Recent Developments on the Perfectly Matched Layer (PML) Method for the Numerical Modeling and Simulation of Elastic Wave Propagation in Unbounded Domains
No full textInternational audienceThis review article revisits and outlines the perfectly matched layer (PML) method and its various formulations developed over the past 25 years for the numerical modeling and simulation of wave propagation in unbounded media. Based on the concept of complex coordinate stretching, an efficient mixed displacement-strain unsplit-field PML formulation for second-order (displacementbased) linear elastodynamic equations is then proposed for simulating the propagation and absorption of elastic waves in unbounded (infinite or semi-infinite) domains. Both time-harmonic (frequency-domain) and time-dependent (timedomain) PML formulations are derived for two-and three-dimensional linear elastodynamic problems. Through the introduction of only a few additional variables governed by low-order auxiliary differential equations, the resulting mixed timedomain PML formulation is second-order in time, thereby allowing the use of standard time integration schemes commonly employed in computational structural dynamics and thus facilitating the incorporation into existing displacementbased finite element codes. For computational efficiency, the proposed timedomain PML formulation is implemented using a hybrid approach that couples a mixed (displacement-strain) formulation for the PML region with a classical (displacement-based) formulation for the physical domain of interest, using a standard Galerkin finite element method (FEM) for spatial discretization and a Newmark time scheme coupled with a finite difference (Crank-Nicolson) time scheme for time sampling. Numerical experiments show the performances of the PML method in terms of accuracy, efficiency and stability for two-dimensional linear elastodynamic problems in single-and multi-layer isotropic homogeneous elastic media
Inundation models of a potential tsunami in the plain of Martil-Tetouan (Morocco)
No full textInternational audienceThe Mediterranean coast of Morocco would by highly vulnerable if a tsunami occurred in consequence of the complex geodynamic of the Alboran sea basin. In the plain of Martil and Tetouan, in the south-east of the Gilbraltar strait, life is intrinsically linked to the touristic attractiveness which represents the first economic sector locally. Therefore, the occupation of the coast and its real estate is seasonal. A tsunami constitutes a latent threat for this developing coastal environment which the tourist numbers strongly change the extent of the exposition of population between high and low season.Protecting these human and material issues leads to increase the interest about the question of tsunami risk that is still unexpressed in the national natural risks governance (OCDE, 2016). This, using modelling tools can enhance risk apprehension by public authorities (civil protection, urban planners, etc.) and improve the awareness of resident and seasonal populations.The chosen approach to study the tetouanese coast relies on the comparison of three inundation modelling methods. The static model consists of subtracting a given water height to the local topography. The dynamic model uses numerical simulation with the Freshkiss3D computing code to appreciate the progression of the tsunami in the plain. Finally, the hybrid model subtracts the total volume of water arriving at the coast by elevation level.Their comparison highlights the heterogenous exposition of the territory. Lower and densely populated areas will need a strengthened attention in terms of evacuation planning. The spatial inundation extent obtained also lead to a precise identification of the issues exposed to the risk of tsunami, with the use of demographic criterion and a sectorial economic analysis, but mostly by analysing the capacity response of the crisis management entities in case of a tsunami
Long-term trajectory of an embankment fluvial system - The Loire River (France)
No full textInternational audienc
Analyzing Robustness of Angluin's L* Algorithm in Presence of Noise
No full textInternational audienceAngluin's L* algorithm learns the minimal (complete) deterministic finite automaton (DFA) of a regular language using membership and equivalence queries. Its probabilistic approximatively correct (PAC) version substitutes an equivalence query by a large enough set of random membership queries to get a high level confidence to the answer. Thus it can be applied to any kind of (also non-regular) device and may be viewed as an algorithm for synthesizing an automaton abstracting the behavior of the device based on observations. Here we are interested on how Angluin's PAC learning algorithm behaves for devices which are obtained from a DFA by introducing some noise. More precisely we study whether Angluin's algorithm reduces the noise and produces a DFA closer to the original one than the noisy device. We propose several ways to introduce the noise: (1) the noisy device inverts the classification of words w.r.t. the DFA with a small probability, (2) the noisy device modifies with a small probability the letters of the word before asking its classification w.r.t. the DFA, and (3) the noisy device combines the classification of a word w.r.t. the DFA and its classification w.r.t. a counter automaton. Our experiments were performed on several hundred DFAs.Our main contributions, bluntly stated, consist in showing that: (1) Angluin's algorithm behaves well whenever the noisy device is produced by a random process, (2) but poorly with a structured noise, and, that (3) almost surely randomness yields systems with non-recursively enumerable languages
P06-15 Exposure to a complex and human-relevant mixture of eight environmental toxicants during folliculogenesis alters ovarian follicular populations in the young adult female rabbit
No full textInternational audienc
PartiCitaE : Histoire et enseignement d'une expérimentation pas à pas PartiCitaE: history and lessons from a step-by-step experiment
No full textInternational audienceNous présentons ici les réflexions et expérimentations menées pour le lancement de PartiCitaE, un observatoire participatif de l'environnement urbain. Nous décrivons l'enquête de préfiguration menée en 2016, composée d'un questionnaire et de réunions participatives, qui a permis de structurer PartiCitaE en trois axes : atmosphère urbaine, ville vivante et vivre en ville. Cette enquête a également permis de développer des projets autour de la qualité de l'air et des sols urbains en réponse aux intérêts des interrogé•es. Les succès et échecs de ces projets ont nourri une réflexion autour de la co-construction pas à pas des projets avec les citadin•es et en ont fait la marque de fabrique de PartiCitaE. Dans cette co-construction, nous pensons que la posture de l'équipe porteuse laisse libre et encourage l'implication forte et transformatrice des volontaires allant jusqu'à la proposition et la mise en place de nouveaux projets dépassant le cadre de PartiCitaE. ABSTRACT. This article presents the considerations and experiments leading to the launch of PartiCitaE, a participatory observatory on the urban environment. A foreshadowing study, composed of a questionnaire and participatory meetings, was carried out in 2016. It guided us to organize PartiCitaE along three axes: urban atmosphere, living city and living in the city. This inquiry also identified air quality and urban soils as major interests and thus helped us to develop projects on these topics. The success or failure of these projects has fueled reflection on the step-by-step co-construction of projects with city dwellers, making it the hallmark of PartiCitaE. We believe that the way the team positioned itself encouraged the strong and transformative involvement of volunteers, which has resulted in the proposal and implementation of new projects beyond the framework of PartiCitaE. MOTS-CLÉS. Sciences et recherches participatives, environnement urbain, co-construction, expérimentation
A monotone numerical flux for quasilinear convection diffusion equation
No full textWe propose a new numerical 2-point flux for a quasilinear convection-diffusion equation. This numerical flux is shown to be an approximation of the numerical flux derived from the solution of a two-point Dirichlet boundary value problem for the projection of the continuous flux onto the line connecting neighboring collocation points. The later approach generalizes an idea first proposed by Scharfetter and Gummel for linear drift-diffusion equations. We establish first that the new flux satisfies sufficient properties ensuring the convergence of the associate finite volume scheme, while respecting the maximum principle. Then, we pay attention to the long time behavior of the scheme: we show relative entropy decay properties satisfied by the new numerical flux as well as by the generalized Scharfetter-Gummel flux. The proof of these properties uses a generalization of some discrete (and continuous) log-Sobolev inequalities. The corresponding decay of the relative entropy of the continuous solution is proved in the appendix. Some 1D numerical experiments confirm the theoretical results