Convergence of a stochastic particle approximation for fractional scalar conservation laws

We give a probabilistic numerical method for solving a partial differential equation with fractional diffusion and nonlinear drift. The probabilistic interpretation of this equation uses a system of particles driven by L\'evy alpha-stable processes and interacting with their drift through their empirical cumulative distribution function. We show convergence to the solution for the associated Euler scheme

Correlation of Ultrasonographic Small Intestinal Wall Layering with Histology in Normal Dogs

Five intestinal layers are commonly described ultrasonographically in dogs. However, current high-frequency endosonography allows the identification of 9 layers in people. The aim of this study was to describe ex vivo small intestinal layering in dogs and correlate ultrasonographic layering with histological layers. Our hypothesis was that, similar to findings in humans, discrepancies exist in thickness and visibility of intestinal layers between histology and ultrasound in dogs. Twelve adult dogs were included in the study. They were euthanized for reasons unrelated to gastrointestinal disease, but extensive medical history was unavailable. Duodenum, jejunum and ileum samples were resected immediately after euthanasia. Ultrasonographic images were acquired post-mortem and two needles, pinned on each side of the sample, were used to denote where transverse images were acquired, and histological sections were obtained accordingly. Comparison of ultrasonographic and histological layer thicknesses was performed statistically and subjectively, and intestinal layer echogenicity as well as presence of additional ultrasonographic layers were evaluated and compared with histological findings. No significant statistical differences were noted between the ultrasonographic and histological small intestinal layer thicknesses. In addition to the five established layers, an additional hyperechoic line was observed within the muscularis of all samples, and corresponded histologically to the interface between the longitudinal and circular smooth muscle fibers of the muscularis. In 4 ileum samples, an additional hyperechoic thin mucosal line was observed parallel to the submucosa, corresponding histologically to submucosal lymphoid follicle hyperplasia (Peyer’s patches). Finally, a variably intense hyperechoic line was visible at the inner aspect of the mucosa of every sample. This ultrasonographic layer corresponded to the mucosal villi on histology, and its degree of hyperechogenicity was related to the degree of lacteal dilation observed histologically. In contrary to our hypothesis, statistical differences between ultrasonographic and histological small intestinal layers were not shown. It was also established that additional intestinal ultrasonographic layers could be observed ex vivo. Some of these layers were considered to be normal histological interfaces, such as the interface between the circular and longitudinal muscularis layers, while some were correlated with histopathological findings, such as mucosal lacteal dilation or submucosal lymphoid follicle hyperplasia

Pierre Duhem’s use of the return to the sources as a justification tool

Les origines de la statique, published in 1905 by physicist and historian of physical theories Pierre Duhem, offers not only a radically new interpretation of the history of statics but also represents a milestone in the methodology of history of science thanks to a particular form of historical reasoning as deployed by the author to justify his hypotheses. This article uses a quantitative analysis of the references contained in the book’s footnotes in order to study the way Duhem validated his assertions. We highlight in particular his relentless will to return to the original texts. This method is one of the reasons why Duhem’s book (and more generally the Duhemian methodology) had such a lasting impact on French epistemology

Existence, uniqueness and convergence of a particle approximation for the Adaptive Biasing Force process

We prove existence and uniqueness for some nonlinear stochastic differential equation used in molecular dynamics, whose nonlinearity comes from a conditional expectation term. We also introduce an interacting particle system in order to approximate this conditional expectation, providing a discretization scheme for this equation

Couplage entre simulation système et simulation aux grandes échelles pour la simulation multi-échelles de moteurs à combustion interne

The decrease of greenhouse gases and pollutant emissions (nitrous oxides, carbon oxides, particles...) for spark ignited engines goes through the development of new technologies such as direct injection, turbocharging, downsizing, etc. However, the benefits of these technologies, which complexify the engines, are limited by the phenomena they intensify such as Cyclic Combustion Variability (CCV) and abnormal combustions. A thorough understanding of these phenomena is a cornerstone for the improvement of future engines. The aim of this work is to predict acyclic and transient phenomena in increasingly complex engines through the development, the validation and the use of a coupling method between Large-Eddy Simulation (LES) and system simulation. This thesis has demonstrated that simulating a complete industrial engine in 3D with LES to study its transient behavior is possible. The methodology developed in the present work was used to study the engine of the national research agency project SGEmac and a good agreement was obtained between the experiments and the tridimensional simulations. These results are the last validation step of the coupling method and demonstrate the capacity of the coupled solver to simulate the whole engine. The coupling method is then applied to study engine load and regime transients for the national research agency project ASTRIDE. The comparison between simulations and experiments show that the coupled solver can simulate CCV and transients, thus fulfilling its initial goal.La réduction des émissions de dioxyde de carbone et de polluants réglementés (oxydes d'azote, hydrocarbures, particules...) dans les moteurs à allumage commandé est possible via l'apport de nouvelles technologies comme le downsizing, l'injection directe, la suralimentation, etc... Toutefois, les gains apportés par ces technologies, qui complexifient grandement le groupe motopropulseur, sont réduits du fait qu'elles induisent aussi une augmentation de l'intensité de certains phénomènes tels que les variations cycliques de la combustion (VCC) ou les combustions anormales. La compréhension de ces phénomènes est une clé dans l'amélioration des futurs moteurs à essence. L'objectif principal de cette thèse est de permettre la modélisation des phénomènes transitoires et acycliques dans des moteurs à structure de plus en plus complexe grâce au développement, à la validation puis à l'application d'une méthode de couplage entre la simulation aux grandes échelles (SGE ou LES pour Large-Eddy Simulation en anglais) et la simulation système. Ces travaux de thèse ont permis de démontrer qu'il est possible de simuler une configuration moteur et d'en étudier les comportements transitoires en 3D tout en prenant en compte la dynamique de tous les composants du moteur. Les simulations obtenues par cette approche pour le moteur du projet ANR SGEmac ont été comparées avec succès aux résultats expérimentaux et à des simulations tridimensionnelles : ces résultats constituent la dernière étape de validation du couplage et démontrent sa capacité à simuler des systèmes moteurs complets. Les codes couplés développés sont ensuite appliqués à l'étude des transitoires de charge et de régime pour le moteur du projet ANR ASTRIDE. La comparaison simulation/expérience montre que le solveur couplé permet bien de remplir les objectifs fixés de simulation des VCC et des transitoires

Transmission enhancement through square coaxial apertures arrays in metallic film: when leaky modes filter infrared light

We consider arrays of square coaxial apertures in a gold layer and study their diffractive behavior in the far infrared region. These structures exhibit a resonant transmission enhancement that is used to design tunable bandpass filters. We provide a study of their spectral features and show by a modal analysis that the resonance peak is due to the excitation of leaky modes of the open photonic structure. Fourier transform infrared (FTIR) spectrophotometry transmission measurements of samples deposited on Si substrate show good agreement with numerical results and demonstrate angular tolerance up to 30 degrees of the fabricated filters.Comment: 4 pages, 3 figure