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Fermi establishes classical novae as a distinct class of gamma-ray sources
No full textA classical nova results from runaway thermonuclear explosions on the surface of a white dwarf that accretes matter from a low-mass main-sequence stellar companion. In 2012 and 2013, three novae were detected in γ rays and stood in contrast to the first γ-ray-detected nova V407 Cygni 2010, which belongs to a rare class of symbiotic binary systems. Despite likely differences in the compositions and masses of their white dwarf progenitors, the three classical novae are similarly characterized as soft-spectrum transient γ-ray sources detected over 2- to 3-week durations. The γ-ray detections point to unexpected high-energy particle acceleration processes linked to the mass ejection from thermonuclear explosions in an unanticipated class of Galactic γ-ray sources
CMSR'14 proceedings
No full textInternational audienceRibonucleic acids (RNAs) play key roles in various aspects of the gene transcription and regulation processes, and are the focus of an ever-increasing interest in all areas of molecular biology. Deciphering the function of a non-protein coding RNA requires an intimate knowledge of its structure, motivating the development of structure-centric methods. This volume contains original peer-reviewed contributions and invited communications presented at "CMSR'14: Computational Methods for Structural RNAs" held on September 7, 2014 in Strasbourg. This event was hosted as an official workshop of ECCB'14: 13th European Conference on Computational Biology.Proceedings are freely downloadable at http://cmsr14.cs.mcgill.ca
Connections between Optimal Transport, Combinatorial Optimization and Hydrodynamics
No full textThere are well-established connections between combinatorial optimization, optimal transport theory and Hydrodynamics, through the linear assignment problem in combinatorics, the Monge-Kantorovich problem in optimal transport theory and the model of inviscid, potential, pressure-less fluids in Hydrodynamics. Here, we consider the more challenging quadratic assignment problem (which is NP, while the linear assignment problem is just P) and find, in some particular case, a correspondence with the problem of finding stationary solutions of Euler's equations for incompressible fluids. For that purpose, we introduce and analyze a suitable "gradient flow" equation. Combining some ideas of P.-L. Lions (for the Euler equations) and Ambrosio-Gigli-Savaré (for the heat equation), we provide for the initial value problem a concept of generalized ''dissipative'' solutions which always exist globally in time and are unique whenever theyare smooth
Les 64 premières lignes du triangle de Pascal
No full textThe 64 first lines of the Pascal's Triangle (Les 64 premières lignes du triangle de Pascal
Monument Valley au lever du Soleil
No full textMonument Valley at sunrise (Monument Valley au lever du Soleil
Développement de barrières de perméation constituées de multicouches de nitrure de silicium déposées par la technique filament chaud pour les dispositifs organiques sur substrats flexibles
No full textEfficient gas-diffusion (permeation) barriers are needed for organic optoelectronic devices because the presence of moisture or oxygen can cause strong degradation. In order for these devices to operate continuously during a long term, so to be commercialized, a reliable flexible thin film encapsulation is required, which is a major challenge. Very low water vapor transmission rates of the order of 10-5 g/m2.day are required. To reach this goal two ways have been adopted: on one hand fabricating SiNx:H / SiNx:H multilayer barriers separated by a specific Ar plasma treatment, on the other hand fabricating the conventional inorganic/organic hybrid multilayer moisture barriers. We have chosen hot-wire chemical vapor deposition (HW-CVD) as the main technique for depositing the inorganic layers and a large part of our efforts has been devoted to the complete study of the parameters controlling the plasma treatment: the energy of the ions impinging the inorganic surfaces was crucial. Several analytical (morphological, structural, optical, electrical) techniques have been necessary to assess qualitatively and quantitatively the different layers composing the moisture barriers. A physical interpretation of the plasma process treatment has been given, based on the interface atomic rearrangements induced by the low energy ions (< 40 eV). For each way of encapsulation, we have obtained very low water vapor transmission rates (4 to 7 × 10-5 g/m2.day). Combining above two encapsulation methods, we have achieved extremely low WVTR rate (6 × 10-6 g/m2.day), which seems sufficient for the utilization of organic electronic devices.Les dispositifs optoélectroniques à base de matériaux organiques nécessitent la réalisation de couches barrière de perméation car l'oxygène et l'humidité dégradent fortement ces dispositifs. Afin d'augmenter leur durée de vie et ainsi les rendre commercialement attractifs, des couches d'encapsulation sont nécessaires, ceci représente un défi majeur surtout dans le cadre des substrats flexibles comme les plastiques. Des faibles valeurs du taux de perméation sont exigées, typiquement de l'ordre de 10-5 g/m2.jour dans le cadre de l'eau. Deux voies ont été étudiées, dans le cadre de cette thèse, pour atteindre cet objectif: d'une part en fabriquant des barrières multicouches à base de nitrure de silicium amorphe, chaque couche étant séparée de la suivante par un traitement plasma d'argon, d'autre part en fabriquant des barrières hybrides alternant des couches inorganiques avec des couches organiques. Nous avons choisi la technique de dépôt chimique en phase vapeur par filament chaud (HW-CVD) pour le dépôt des couches inorganiques et nos efforts ont porté sur l'étude approfondie des paramètres contrôlant le plasma. Il ressort que l'énergie des ions impactant la surface a été le paramètre déterminant. Diverses techniques d'analyse ont été nécessaires pour évaluer précisément la qualité des couches constituant les barrières de perméation. Une interprétation physique du procédé plasma a été proposée, basée sur le réarrangement atomique induit à chaque interface par les ions de faible énergie (< 40 eV). Pour chacune des voies choisies, des très faibles taux de perméation (4 à 7 × 10-5 g/m2.jour) ont été atteints. Avec la combinaison de ces deux méthodes d'encapsulation, nous avons atteint une valeur de WVTR extrêmement faible (6 × 10-6 g/m2.jour), ce qui semble suffisant pour l'utilisation dans des dispositifs organiques
Statistical inverse method for the multiscale identification of the apparent random elasticity field of heterogeneous microstructures
No full textThe presentation is devoted to a multiscale statistical inverse problem related to materials for which the elastic heterogeneous microstructure cannot be described in terms of constituents (for instance, a biological tissue such as the cortical bone). The objective is to identify the tensor-valued elasticity random field, (apparent elasticity field) at mesoscale, using multiscale experimental data. After introducing the difficulties induced by such a problem, the multiscale identification method is presented in two steps. The first one is devoted to the mathematical construction of an advanced prior stochastic model of the apparent elasticity random field at mesoscale, introducing a family of prior stochastic models for the non-Gaussian tensor-valued random field at mesoscale, and its generator. The second one deals with the multiscale identification of the prior stochastic model using a multiscale experimental digital image correlation, at macroscale and at mesoscale. The statistical inverse problem is then formulated as a multi-objective optimization problem. Finally, an application of the method is presented for multiscale experimental measurements of cortical bone in 2D plane stresses
Feynman-Kac representation of fully nonlinear PDEs and applications
No full textThe classical Feynman-Kac formula states the connection between linear parabolic partial differential equations (PDEs), like the heat equation, and expectation of stochastic processes driven by Brownian motion. It gives then a method for solving linear PDEs by Monte Carlo simulations of random processes. The extension to (fully)nonlinear PDEs led in the recent years to important developments in stochastic analysis and the emergence of the theory of backward stochastic differential equations (BSDEs), which can be viewed as nonlinear Feynman-Kac formulas. We review in this paper the main ideas and results in this area, and present implications of these probabilistic representations for the numerical resolution of nonlinear PDEs, together with some applications to stochastic control problems and model uncertainty in finance
Carbon Radical Attack on a Pyrimidine Nitrogen. An Unusual Entry into Polycyclic Aminopyrimidones
No full textInternational audienceUnprecedented examples of a synthetically useful radical ring closure onto a pyrimidine nitrogen leading to novel, highly functionalized bi- and tricyclic pyrimidone structures are reported. An unexpected hydrogen atom translocation prior to the cyclization step was observed in some cases