120 research outputs found
Pleijel’s Theorem for Schrödinger Operators
No full textWe are concerned in this paper with the real eigenfunctions of Schrödinger operators.We prove an asymptotic upper bound for the number of their nodal domains, which implies in particular that the inequality stated in Courant’s theorem is strict, except for finitely many eigenvalues. Results of this type originated in 1956 with Pleijel’s theorem on the Dirichlet Laplacian and were obtained for some classes of Schrödinger operators by the first author, alone and in collaboration with B. Helffer and T. Hoffmann-Ostenhof. Using methods in part inspired by work of the second author on Neumann and Robin Laplacians, we greatly extend the scope of these previous results
Asymptotic behavior of generalized capacities with applications to eigenvalue perturbations: The higher dimensional case
No full textWe provide a full series expansion of a generalization of the so-called u-capacity related to the Dirichlet-Laplacian in dimension three and higher, extending the results of Abatangelo et al. (2021); Abatangelo, Lena and Musolino (2022) dealing with the planar case. We apply the result in order to study the asymptotic behavior of perturbed eigenvalues when Dirichlet conditions are imposed on a small regular subset of the domain of the eigenvalue problem. (c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Geometric bounds for the magnetic Neumann eigenvalues in the plane
No full textWe consider the eigenvalues of the magnetic Laplacian on a bounded domain Omega of R-2 with uniform magnetic field beta > 0 and magnetic Neumann boundary conditions. We find upper and lower bounds for the ground state energy lambda(1) and we provide semiclassical estimates in the spirit of Kroger for the first Riesz mean of the eigenvalues. We also discuss upper bounds for the first eigenvalue for non-constant magnetic fields beta = beta(x) on a simply connected domain in a Riemannian surface. In particular: we prove the upper bound lambda(1) infinity and consists of the semiclassical limit 2 pi k/ |Omega| plus an oscillating term.We also construct several examples, showing the importance of the topology: in particular we show that an arbitrarily small tubular neighborhood of a generic simple closed curve has lowest eigenvalue bounded away from zero, contrary to the case of a simply connected domain of small area, for which lambda(1) is always small.(c) 2023 The Author(s). Published by Elsevier Masson SAS. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/)
Subordonnées conditionnelles en Quechua Cochabambino
No full textThis record deals with the if-clauses in Quechua Cochabambino. This elicitation aims at elaborating a typology of these clauses.Cet enregistrement traite des subordonnées conditionnelles en Quechua Cochabambino. Il s'agit d'une élicitation cherchant à élaborer une typologie des conditionnelles dans cette langue
Calcul des événements climatiques extrêmes et des extrêmes de production d'énergie renouvelable à l'aide d'algorithmes d'événements rares
No full textPour atténuer le changement climatique, la part de la production renouvelable variable, principalement d'origine éolienne et solaire photovoltaïque (PV), devra fortement augmenter dans les prochaines décennies. Par conséquent, les futurs systèmes électriques, équilibrant l'offre et la demande, dépendront fortement des conditions météorologiques. Pour maîtriser ces systèmes, de nombreux défis devront être relevés, comme la gestion des événements météorologiques extrêmes. La prise en compte de ces événements est essentielle pour estimer les besoins de flexibilité, notamment en termes de stockage ou de production d'appoint, qui peuvent avoir un impact sur le coût du système électrique. Les événements les plus problématiques pourraient se produire en hiver, lorsque le faible rayonnement solaire s'accompagne d'une période sans vent avec des températures basses, entraînant une forte demande de chauffage et une faible production renouvelable. De tels événements peuvent entraîner un déséquilibre important entre l'offre et la demande. Si ce déséquilibre devait se produire à l'échelle européenne, les importations d'électricité en provenance d'autres pays seraient limitées. Dans cette thèse, nous étudions les événements extrêmes combinant une faible production d'énergie renouvelable et une forte demande en Europe, en mettant l'accent sur les événements persistants. Nous utilisons deux approches pour étudier ces événements extrêmes. Dans la première approche, basée sur une simulation climatique longue de 1000 ans, nous proposons des méthodes statistiques qui relient les événements moins extrêmes aux événements plus extrêmes. Ces méthodes, qui reposent sur des hypothèses statistiques, peuvent être utilisées pour faire des extrapolations lorsque peu de données sont disponibles, comme c'est le cas avec les données de réanalyse. Avec un processus stochastique gaussien, nous montrons que la probabilité de faible production éolienne peut être correctement estimée à l'échelle de la France pour des événements de deux semaines et à l'échelle de l'Europe pour des événements d'une durée allant d'une journée à la saison entière. Nous proposons également une hypothèse de distribution gaussienne conjointe entre les variables météorologiques et l'amplitude du déséquilibre offre-demande pour expliquer pourquoi nous observons des motifs similaires pour les événements modérément extrêmes et les plus extrêmes. Dans la seconde approche, nous utilisons un algorithme d'événements rares pour améliorer l'échantillonnage des événements extrêmes. Cet algorithme favorise l'occurrence d'événements rares en modifiant les statistiques d'échantillonnage d'un ensemble de trajectoires, chaque trajectoire étant une simulation climatique. Il nous permet d'étudier à la fois les statistiques et la dynamique des événements rares. En utilisant cet algorithme, nous échantillonnons un grand nombre d'événements extrêmes ayant une chance sur 100 ou 1000 de se produire chaque année, ce qui serait impossible à faire avec une simulation directe. Cela nous permet d'étudier leurs conditions météorologiques, qui s'avèrent très similaires à celles d'événements moins rares, associés à des téléconnexions à l'échelle de l'hémisphère nord. Enfin, nous discutons brièvement d'un travail collaboratif sur la prévision des canicules extrêmes. En utilisant une simulation très longue de 8 000 ans avec un modèle climatique de complexité intermédiaire, nous développons un réseau de neurones capable de prédire les vagues de chaleur extrêmes en France. La principale contribution de ce travail est de montrer que, pour faire de la prévision en ayant peu de données, notamment avec des réanalyses, les réseaux neuronaux fonctionnent dans un régime de manque de données.Climate change mitigation measures are expected to lead to a large increase in the share of variable renewable generation, mainly wind and solar photovoltaic (PV). As a result, future electricity systems are expected to become increasingly dependent on the weather. To manage this system, difficult challenges must be overcome, such as the management of high-impact weather-related events. Considering these events is essential to correctly design the future energy system, to understand its requirements in terms of flexibility sources such as backup and storage, and therefore, its cost. The most problematic events could occur in winter when low solar radiation is accompanied by low temperatures and wind speeds, leading to high demand for heating and low renewable production. Such events can lead to a major imbalance between supply and demand. If this imbalance were to occur on a European scale, imports of electricity from other countries to balance the electricity system would be limited. In this thesis, we consider extreme events combining low renewable production and high demand over Europe, with a focus on persistent events. We use two approaches to study these extreme events. In the first approach, based on a very long, 1000-year climate model simulation, we study the statistics of these extreme events and propose statistical methods that relate moderately extreme events to more extreme events. These methods, based on statistical hypotheses, can be used to make extrapolations when little data is available, such as with reanalysis data. With a simple Gaussian stochastic process, we show that the probability can be correctly estimated at the scale of France for two-week events, and at the scale of Europe for events lasting from one day to the whole season. We also propose a hypothesis of joint Gaussian distribution between weather variables and the amplitude of extreme events of large supply-demand imbalance to explain why we observe similar average patterns for moderately extreme and more extreme events. In the second approach, we use a rare event algorithm to improve the sampling of extreme events of low production and high demand. This algorithm favors the occurrence of rare events by modifying the sampling statistics of an ensemble of trajectories, each trajectory being a climate simulation. It allows us to study both the statistics and the dynamics of rare events, since they are actually simulated by the climate model. With the rare event algorithm, we sample a large number of extreme 1-in-100 and 1-in-1000 events, that would be impossible to study with a direct sampling approach. This allows us to study their meteorological conditions, which are found to be very similar to less rare events and are associated with hemispheric-scale teleconnection patterns. Finally, we briefly discuss a collaborative work on the prediction of extreme heatwave. Based on a very long, 8000-year simulation with a climate model of intermediate complexity, a neural network model is developed and skillfully forecasts extreme heatwaves over France. The main contribution of this work is to show that, in forecast applications with relatively little data, such as reanalyses, neural networks operate in a regime of lack of data
Irréversibilité et Turbulence
No full textSéminaire organisé par Christophe Josserand (LadHyx, CNRS et Ecole Polytechnique), Bérengère Dubrulle (PHYNX, SPEC/IRAMIS, CEA Saclay) et Yves Pomeau (CNRS) du 18 au 23 septembre 2017 Participants Jérémie Bec, Sergio Chibbaro, Pierre Coullet, Thierry Dauxois, Bérengère Dubrulle, Gregory Falkovich, Pierre Gaspard, Corentin Herbert, Christophe Josserand, Giorgio Krstulovic, Sergei Kuksin, Martine Le Berre, Xavier Leoncini, Yves Pomeau, Itamar Procaccia, Davide Proment, Alain Pumir, Sergio Rica,..
Fables d'Ésope 2: Les Hommes
No full textThis is a tight little book, 6 x 7¾. It contains eighty-six of Aesop's fables drawn from either Chambry's 1927 translation or a version done by Hachette in 1913 without attribution to an author. To go with those texts there are eleven full-page illustrations noted on 85 and a number of other designs along the way. Six of the full-page illustrations are colored. For an inexpensive edition, this book does a good job with the art! There is a T of C at the back. I am not sure that I have ever seen Aesop's work divided into animals and people before this! See the companion volume on animals.This is a hardbound book (hard cover)This book has a dust jacket (book cover)Language note: FrenchOriginal language: greTraduction, introduction et notes par Daniel Loayz
Point defect engineering in Ge
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 121-127).In 1947, the first transistor was made of germanium, but soon silicon became the core material of computer chips because of its processability. However, as the typical dimensions of transistors are getting closer to the atomic size, the traditional approach of scaling down transistors to improve performance is reaching its limits, and other elements need to be used in conjunction with silicon. Germanium is one of the key materials to empower silicon based devices because it possesses electronic and optoelectronic properties complementary to those of silicon, among them higher carrier mobilities and a direct band gap (G-valley) at 1.55 [mu]m (the telecom C-band, therefore adding new capabilities to silicon integrated microphotonics). Furthermore, good quality Ge layers can be grown epitaxially on a Si substrate, allowing a monolithic integration of devices. However, compared to silicon, little is known about the point defects in germanium. The goal of the present doctoral work is to remedy this gap. To this end, we have used radiation (gamma rays, alpha particles, and neutrons) to controllably introduce point defects in crystalline germanium, which were then characterized by Deep-Level Transient Spectroscopy (DLTS), a technique that allows the determination of the activation energy, capture cross-section, and concentration of the said defects. By studying their electronic properties, annealing kinetics, and introduction rates, we were able to separate vacancy-containing from interstitial-containing defects and gain insight on their physical nature and formation process. We especially identified a di-interstitial defect and a tri-interstitial defect. In addition, we proved that in the case of alpha particles and neutron irradiation, the fact that defects are generated in a collision cascade influences their carrier capture rates and annealing behaviors. We have also characterized the impact of radiation on commercial germanium-on-silicon photodetectors, and showed that point defects associate with dislocations in epitaxial Ge-on-Si layers. Finally, we have investigated the passivation of midgap states by implanting germanium with fluorine, and showed how the interaction between the halogen element, the amorphous/crystalline interface during the solid phase epitaxy, and the implantation damage is key in obtaining a high performance materialby Corentin Monmeyran.Ph. D
Dufour et al. Source Data.xlsx
No full textDataset used to create every graph of the paper "Phenotypic characterization of single CD4+ T cells harboring genetically intact and inducible HIV genomes" in Nature Communications
Author list: Caroline Dufour1, Corentin Richard1, Marion Pardons1, Marta Massanella1, Antoine Ackaoui1, Ben Murrell2, Bertrand Routy1, Réjean Thomas3, Jean-Pierre Routy4, Rémi Fromentin1, Nicolas Chomont1
1Centre de Recherche du CHUM and Department of Microbiology, Infectiology and Immunology, Université de Montréal, Montreal, H2X 0A9, Quebec, Canada
2Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, 171 77, Sweden
3Clinique médicale l’Actuel, Montreal, H2L 4P9, Quebec, Canada
4Division of Hematology & Chronic Viral Illness Service, McGill University Heath Centre, Montreal, H4A 3J1, Quebec, Canada</p
An Introduction to Large Deviations and Equilibrium Statistical Mechanics for Turbulent Flows
No full text- …
