Méthode de diagnostic à grande échelle de la vulnérabilité sismique des Monuments Historiques : Chapelles et églises baroques des hautes vallées de Savoie

The aim of this thesis is to propose a seismic vulnerability assessment method well suited to the study of a complete historical heritage, regardless of the prestige of each building. Indeed the great seismic vulnerability of the historical heritage, often in masonry, requires to act preventively in order to avoid irreparable damage. Our approach must tackle three main requirements: to develop large-scale tools of choice to prioritize the needs, to provide relevant analysis of seismic behavior on the structural scale even in the first study, and to manage the large number of uncertainties characterizing the old buildings structural assessment. To this aim, we study the baroque churches and chapels in the high valleys of the French Savoie. They witness to a particularly prosperous period in the history of Savoy and a unique artistic movement adapted to a harsh environment. In this context we have therefore developed or adapted different tools in order to handle the peculiarities of the old buildings. This way we can use the today proposed techniques for modern buildings to study these ancient buildings in rustic masonry: non-linear temporal dynamics numerical modeling, vibratory in situ measurements, non-linear multi modal analysis.L’objectif de ce travail est de proposer une méthode d’analyse de vulnérabilité sismique adaptée à l’étude d’un patrimoine historique complet très étendu, indépendamment de la renommée de chaque bâtiment. En effet la grande vulnérabilité sismique du patrimoine ancien, très souvent en maçonnerie, impose, afin d’éviter tout dommage irréparable, de se donner les moyens d’intervenir en amont. Notre démarche doit donc répondre à trois impératifs principaux: développer des outils de choix à grande échelle afin de hiérarchiser les besoins, offrir une analyse pertinente du comportement sous séisme d'une structure historique maçonnée même en première approche, et trouver des méthodes pour gérer le nombre important d’incertitudes qui caractérise le diagnostic des édifices anciens. Pour ce faire, nous étudions les églises et chapelles baroques des hautes vallées de la Savoie française, témoignages d'une période particulièrement prospère dans l'histoire de la Savoie et d'un mouvement artistique unique dans un environnement hostile. Dans ce contexte nous avons donc développé ou adapté différents outils afin de pouvoir traiter les particularités des édifices anciens et utiliser pour des édifices anciens en maçonnerie rustique les potentialités des techniques proposées pour les édifices modernes : modélisations numériques non-linéaires dynamiques temporelles, mesures vibratoires in-situ, analyse multi modale non-linéaire

Desynchronizing effect of high-frequency stimulation in a generic cortical network model

Transcranial Electrical Stimulation (TCES) and Deep Brain Stimulation (DBS) are two different applications of electrical current to the brain used in different areas of medicine. Both have a similar frequency dependence of their efficiency, with the most pronounced effects around 100Hz. We apply superthreshold electrical stimulation, specifically depolarizing DC current, interrupted at different frequencies, to a simple model of a population of cortical neurons which uses phenomenological descriptions of neurons by Izhikevich and synaptic connections on a similar level of sophistication. With this model, we are able to reproduce the optimal desynchronization around 100Hz, as well as to predict the full frequency dependence of the efficiency of desynchronization, and thereby to give a possible explanation for the action mechanism of TCES.Comment: 9 pages, figs included. Accepted for publication in Cognitive Neurodynamic

Random walk on disordered networks

Random walks are studied on disordered cellular networks in 2-and 3-dimensional spaces with arbitrary curvature. The coefficients of the evolution equation are calculated in term of the structural properties of the cellular system. The effects of disorder and space-curvature on the diffusion phenomena are investigated. In disordered systems the mean square displacement displays an enhancement at short time and a lowering at long ones, with respect to the ordered case. The asymptotic expression for the diffusion equation on hyperbolic cellular systems relates random walk on curved lattices to hyperbolic Brownian motion.Comment: 10 Pages, 3 Postscript figure

Nonlinear Diffusion Through Large Complex Networks Containing Regular Subgraphs

Transport through generalized trees is considered. Trees contain the simple nodes and supernodes, either well-structured regular subgraphs or those with many triangles. We observe a superdiffusion for the highly connected nodes while it is Brownian for the rest of the nodes. Transport within a supernode is affected by the finite size effects vanishing as $N\to\infty.$ For the even dimensions of space, $d=2,4,6,...$, the finite size effects break down the perturbation theory at small scales and can be regularized by using the heat-kernel expansion.Comment: 21 pages, 2 figures include

Fe and N self-diffusion in amorphous FeN: A SIMS and neutron reflectivity study

Simultaneous measurement of self-diffusion of iron and nitrogen in amorphous iron nitride (Fe86N14) using secondary ion mass spectroscopy (SIMS) technique has been done. In addition neutron reflectivity (NR) technique was employed to study the Fe diffusion in the same compound. The broadening of a tracer layer of 57Fe8615N14 sandwiched between Fe86N14 layers was observed after isothermal vacuum annealing of the films at different temperatures in SIMS measurements. And a decay of the Bragg peak intensity after isothermal annealing was observed in [Fe86N14/57Fe86N14]10 multilayers in NR. Strong structural relaxation of diffusion coefficient was observed below the crystallization temperature of the amorphous phase in both measurements. It was observed from the SIMS measurements that Fe diffusion was about 2 orders of magnitude smaller compared to nitrogen at a given temperature. The NR measurements reveal that the mechanism of Fe self-diffusion is very similar to that in metal-metal type metallic glasses. The structural relaxation time for Fe and N diffusion was found comparable indicating that the obtained relaxation time essentially pertain to the structural relaxation of the amorphous phase.Comment: 10 pages 12 figure

Escaping from cycles through a glass transition

A random walk is performed over a disordered media composed of $N$ sites random and uniformly distributed inside a $d$-dimensional hypercube. The walker cannot remain in the same site and hops to one of its $n$ neighboring sites with a transition probability that depends on the distance $D$ between sites according to a cost function $E(D)$. The stochasticity level is parametrized by a formal temperature $T$. In the case $T = 0$, the walk is deterministic and ergodicity is broken: the phase space is divided in a ${\cal O}(N)$ number of attractor basins of two-cycles that trap the walker. For $d = 1$, analytic results indicate the existence of a glass transition at $T_1 = 1/2$ as $N \to \infty$. Below $T_1$, the average trapping time in two-cycles diverges and out-of-equilibrium behavior appears. Similar glass transitions occur in higher dimensions choosing a proper cost function. We also present some results for the statistics of distances for Poisson spatial point processes.Comment: 11 pages, 4 figure

Large-scale seismic vulnerability assesment method for the masonry architectural heritage : baroque chapels and churches of the French Savoye

L’objectif de ce travail est de proposer une méthode d’analyse de vulnérabilité sismique adaptée à l’étude d’un patrimoine historique complet très étendu, indépendamment de la renommée de chaque bâtiment. En effet la grande vulnérabilité sismique du patrimoine ancien, très souvent en maçonnerie, impose, afin d’éviter tout dommage irréparable, de se donner les moyens d’intervenir en amont. Notre démarche doit donc répondre à trois impératifs principaux: développer des outils de choix à grande échelle afin de hiérarchiser les besoins, offrir une analyse pertinente du comportement sous séisme d'une structure historique maçonnée même en première approche, et trouver des méthodes pour gérer le nombre important d’incertitudes qui caractérise le diagnostic des édifices anciens. Pour ce faire, nous étudions les églises et chapelles baroques des hautes vallées de la Savoie française, témoignages d'une période particulièrement prospère dans l'histoire de la Savoie et d'un mouvement artistique unique dans un environnement hostile. Dans ce contexte nous avons donc développé ou adapté différents outils afin de pouvoir traiter les particularités des édifices anciens et utiliser pour des édifices anciens en maçonnerie rustique les potentialités des techniques proposées pour les édifices modernes : modélisations numériques non-linéaires dynamiques temporelles, mesures vibratoires in-situ, analyse multi modale non-linéaire.The aim of this thesis is to propose a seismic vulnerability assessment method well suited to the study of a complete historical heritage, regardless of the prestige of each building. Indeed the great seismic vulnerability of the historical heritage, often in masonry, requires to act preventively in order to avoid irreparable damage. Our approach must tackle three main requirements: to develop large-scale tools of choice to prioritize the needs, to provide relevant analysis of seismic behavior on the structural scale even in the first study, and to manage the large number of uncertainties characterizing the old buildings structural assessment. To this aim, we study the baroque churches and chapels in the high valleys of the French Savoie. They witness to a particularly prosperous period in the history of Savoy and a unique artistic movement adapted to a harsh environment. In this context we have therefore developed or adapted different tools in order to handle the peculiarities of the old buildings. This way we can use the today proposed techniques for modern buildings to study these ancient buildings in rustic masonry: non-linear temporal dynamics numerical modeling, vibratory in situ measurements, non-linear multi modal analysis