A Fast Multipole Method formulation for 3D elastodynamics in the frequency domain

The solution of the elastodynamic equations using boundary element methods (BEMs) gives rise to fully-populated matrix equations. Earlier investigations on the Helmholtz and Maxwell equations have established that the Fast Multipole (FM) method reduces the complexity of a BEM solution to N \mbox{log}_{2}N per GMRES teration. The present Note address the extension of the FM-BEM strategy to 3D elastodynamics in the frequency domain. Its efficiency and accuracy are demonstrated on numerical examples involving up to $N=O(10^{6})$ nodal unknowns

Role of the different domains of PSD-95 in basal synaptic transmission

Die Fähigkeit des Gehirns, zu lernen und somit Information im Gedächtnis einzuspeichern, korreliert mit Veränderungen in der Stärke der synaptischen Transmission. An exzitatorischen Synapsen in der CA1-Region des Hippocampus wird die synaptische Transmission imWesentlichen durch in der postsynaptische Verdichtung befindliche AMPA-Rezeptoren reguliert. Deren Funktion wird durch PSD-95 reguliert, das zusammen mit PSD-93, SAP97 und SAP102 zur Familie der DLG-MAGUK-Proteine gehört. DLG-MAGUK-Proteine ähneln sich strukturell in der Anordnung von funktionalen Protein-Domänen. Sie haben 3 PDZ- Domänen, eine SH3- Domäne und eine indes katalytisch inaktive GK-Domäne. Von allen DLG-MAGUK-Proteinen kommt PSD-95 in reifen exzitatorischen Synapsen am häufigsten vor. PSD-95 interagiert mit mehreren anderen zellularen Proteinen. Die vorliegenden Studie verbindet zwei unterschiedliche Ansätze, um herauszufinden, ob und wie weit die Protein-Domänen für die Funktionalität des PSD-95 in der synaptischen Transmission essentiell sind. Zum einen wird die Methode des molekularen Austausch angewandt, bei dem die Expression des endogenen PSD-95 mittels Gen-Knockdown inhibiert und gleichzeitig eine genmutierte Form des PSD-95 exprimimiert wird. Der molekulare Austausch erfolgte regiospezifisch in Zellen, die zu funktionalen neuronalen Netzwerken gehören, in akuten hippokampalen Schnitten. Zum anderen wurde auch Gehirngewebe von Mäusen einer Deletionsmutate (Knockout-Linie) untersucht, bei welchen Mutanten des PSD-95 vor einem PSD-95 freien Hintergrund exprimiert wurden. Um festzustellen, welche Protein-Domäne in PSD-95 für die basale synaptische Transmission wichtig ist, wurde untersucht, ob deren Expression einzelner trunkierte Mutanten die Funktion des Proteins bei Abwesenheit von endogenem PSD-95 wiederherstellen kann. Dabei konnte gezeigt werden, daß mutiertes PSD-95, bei dem sowohl die PDZ3- als auch die SH3- und die GK-Domäne fehlte das endogene PSD-95 in bezug auf die basale synaptische Transmission n icht funktional ersetzen konnte. Die PDZ3- und SH3-Domäne allein genommen war hingegen nicht essentiell dafür, sehr wohl aber die GK- Domäne. Allerdings scheint die Essentialität der GK-Domäne von der Anwesenheit eines anderen Mitglieds der DLG-MAGUK-Proteinfamilie abzuhängen: erforderlich ist SAP102, welches synaptische Transmission in noch unreifen Synapsen reguliert. In Synapsen, die noch in Bildung begriffen sind, hängt es offenbar vom Entwicklungsstand der Synapse ab, ob die GK-Domäne des PSD-95 für die basale synaptische Transmission notwendig ist, wobei der ein Fehlen der GK-Domäne den stärksten Effekt bei unreifen Synapsen hat. Zusammenfassend zeigen die Befunde, daß die N-terminalen PDZ12-Domänen in Verbindung mit der GK-Domäne des PSD95 für die funktionale Regulation von AMPA-Rezeptoren notwendig sind, wohingegen dessen SH3- und PDZ3-Domäne dabei nur eine unterstützende Rolle zuzuordnen ist

Etude de la dégradation de la couche passive des aciers du béton armé en milieu maritime : modèle thermochimique

International audienceCette étude s'intéresse à la modélisation du processus de dépassivation des armatures d'un béton saturé exposé à de l'eau de mer. En particulier, elle tente de décrire la dégradation de la couche passive des armatures et les conditions dans lesquelles elle n'assure plus son rôle de protection. Afin d'y parvenir, un modèle couplant transport multi-espèces et thermochimie est mis en place. Le modèle prend en compte le transport par diffusion des ions contenus dans l'eau de mer ainsi que les réactions chimiques se produisant au niveau de la couche passive. Il permet d'étudier l'équilibre thermodynamique de l'oxyde de fer dans un béton pollué par l'eau de mer et de quantifier la durée au-delà de laquelle l'initiation de la corrosion peut commencer en fonction de la nature des constituants de la couche passive. Il montre, en outre, les cinétiques de dégradations de la couche passive</p

Méthode multipôle rapide multi-niveaux en visco-élastodynamique 3D

National audienceSee http://hal.archives-ouvertes.fr/docs/00/59/28/83/ANNEX/r_4VPCS0OY.pd

A new Fast Multipole formulation for the elastodynamic half-space Green's tensor

International audienceIn this article, a version of the frequency-domain elastodynamic Fast Multipole-Boundary Element Method (FM-BEM) for semi-infinite media, based on the half-space Green's tensor (and hence avoiding any discretization of the planar traction-free surface), is presented. The half-space Green's tensor is often used (in non-multipole form until now) for computing elastic wave propagation in the context of soil-structure interaction, with applications to seismology or civil engineering. However, unlike the full-space Green's tensor, the elastodynamic half-space Green's tensor cannot be expressed using derivatives of the Helmholtz fundamental solution. As a result, multipole expansions of that tensor cannot be obtained directly from known expansions, and are instead derived here by means of a partial Fourier transform with respect to the spatial coordinates parallel to the free surface. The obtained formulation critically requires an efficient quadrature for the Fourier integral, whose integrand is both singular and oscillatory. Under these conditions, classical Gaussian quadratures would perform poorly, fail or require a large number of points. Instead, a version custom-tailored for the present needs of a methodology proposed by Rokhlin and coauthors, which generates generalized Gaussian quadrature rules for specific types of integrals, has been implemented. The accuracy and efficiency of the proposed formulation is demonstrated through numerical experiments on single-layer elastodynamic potentials involving up to about $N=6 10^5$ degrees of freedom. In particular, a complexity significantly lower than that of the non-multipole version is shown to be achieved

Recent advances on the fast multipole accelerated boundary element method for 3D time-harmonic elastodynamics

International audienceThis article is mainly devoted to a review on fast BEMs for elastodynamics, with particular attention on time-harmonic fast multipole methods (FMMs). It also includes original results that complete a very recent study on the FMM for elastodynamic problems in semi-infinite media. The main concepts underlying fast elastodynamic BEMs and the kernel-dependent elastodynamic FM-BEM based on the diagonal-form kernel decomposition are reviewed. An elastodynamic FM-BEM based on the half-space Green's tensor suitable for semi-infinite media, and in particular on the fast evaluation of the corresponding governing double-layer integral operator involved in the BIE formulation of wave scattering by underground cavities, is then presented. Results on numerical tests for the multipole evaluation of the half-space traction Green's tensor and the FMM treatment of a sample 3D problem involving wave scattering by an underground cavity demonstrate the accuracy of the proposed approach. The article concludes with a discussion of several topics open to further investigation, with relevant published work surveyed in the process

A preconditioned 3-D multi-region fast multipole solver for seismic wave propagation in complex geometries

International audienceThe analysis of seismic wave propagation and amplification in complex geological structures requires efficient numerical methods. In this article, following up on recent studies devoted to the formulation, implementation and evaluation of 3-D single- and multi-region elastodynamic fast multipole boundary element methods (FM-BEMs), a simple preconditioning strategy is proposed. Its efficiency is demonstrated on both the single- and multi-region versions using benchmark examples (scattering of plane waves by canyons and basins). Finally, the preconditioned FM-BEM is applied to the scattering of plane seismic waves in an actual configuration (alpine basin of Grenoble, France), for which the high velocity contrast is seen to significantly affect the overall efficiency of the multi-region FM-BEM

Accélération des calculs de propagation d'ondes élastiques par la Méthode multipôle rapide (formulation par équations intégrales de frontière)

La résolution des équations de l'élastodynamique par la méthode des éléments de frontière (BEM) conduit à un système linéaire plein. Des travaux récents sur les équations de Helmholtz et Maxwell ont établi la capacité de la méthode multipôle rapide (FM) à réduire la complexité de la BEM à N log N par itération d'un solveur de type GMRES. Cet article présente la transposition de l'approche FM-BEM à l'élastodynamique 3D dans le domaine fréquentiel. La précision et l'efficacité de la méthode sont illustrées sur des exemples numériques mobilisant jusqu'à N=O(1 000 000) inconnues nodales

Combining NDT tools for analysing the efficiency of repair techniques of wharves: the MAREO project

ISBN: 9780415669863Repair of structures in concrete is still a challenge, especially when access and environment offer a difficult context such as the case of wharves. Concerning the repair of concrete for marine structures, European standards give the requirements in predefined and standardised conditions. However, repair of wharves is performed in harsh conditions such as access, humidity and operator position. These conditions do not enable the direct application of standards. By accounting for these requirements, the repair technique consists in rebuilding the concrete cover and in some cases using protective coating for some beams. In this paper, we focus on the concrete repair techniques. The aim of MAREO project (French project of the National competitive cluster in Civil Engineering and Eco-Building) is to compare several repair techniques carried out in the most complex area for repair: the tidal zone. The project deals with initial performance, sustainability, cost of durability and concrete properties monitoring by Destructive Testing (DT) and Non-Destructive Testing (NDT) techniques. The studied NDT techniques are: impact-echo, surface waves, multi-offset radar, and capacitive method. Both, beams placed in natural exposure and slabs specimens placed in accelerated conditions in laboratory are considered. For all the beams, the contaminated concrete was removed using high-velocity water jets (hydro-demolition). The selected techniques are wet shotcrete, dry shotcrete, formed concrete and manual repair. This paper focuses on the ability of NDT techniques to evaluate the changes of properties related to the chloride ingress in concrete both on site and in accelerated laboratory conditions. The interest of each technique and its sensitivity to several physical factors are highlighted. The need of NDT-combination is illustrated