3,580 research outputs found
Asymptotic global robustness in bayesian decision theory
In Bayesian decision theory, it is known that robustness with respect to the
loss and the prior can be improved by adding new observations. In this article
we study the rate of robustness improvement with respect to the number of
observations n. Three usual measures of posterior global robustness are
considered: the (range of the) Bayes actions set derived from a class of loss
functions, the maximum regret of using a particular loss when the subjective
loss belongs to a given class and the range of the posterior expected loss when
the loss function ranges over a class. We show that the rate of convergence of
the first measure of robustness is \sqrtn, while it is n for the other measures
under reasonable assumptions on the class of loss functions. We begin with the
study of two particular cases to illustrate our results.Comment: Published by the Institute of Mathematical Statistics
(http://www.imstat.org) in the Annals of Statistics
(http://www.imstat.org/aos/) at http://dx.doi.org/10.1214/00905360400000056
Topography influence on the Lake equations in bounded domains
We investigate the influence of the topography on the lake equations which
describe the two-dimensional horizontal velocity of a three-dimensional
incompressible flow. We show that the lake equations are structurally stable
under Hausdorff approximations of the fluid domain and perturbations of
the depth. As a byproduct, we obtain the existence of a weak solution to the
lake equations in the case of singular domains and rough bottoms. Our result
thus extends earlier works by Bresch and M\'etivier treating the lake equations
with a fixed topography and by G\'erard-Varet and Lacave treating the Euler
equations in singular domains
About the impact behavior of woven-ply carbon fiber-reinforced thermoplastic- and thermosetting-composites: A comparative study
This study is aimed at comparing the response of TS-based (epoxy) and TP-based (PPS or PEEK) laminates subjected to low velocity impacts. C-scan inspections showed that impact led to diamond-shaped damage resulting from different failure mechanisms: fiber breakages in warp and weft directions, more or less inter-laminar and intra-ply damage, and extensive delamination in C/PEEK and C/epoxy laminates. The permanent indentation can be ascribed to specific mechanisms which mainly depend on many factors including the ultimate out-of-plane shear strength, and the interlaminar fracture toughness in modes I–II–III. In TP-based laminates, the matrix plasticization seems to play an important role in matrix-rich areas by locally promoting permanent deformations. Fiber-bridging also prevents the plies from opening in mode I, and slows down the propagation of interlaminar and intralaminar cracks in modes II–III. Both mechanisms seem to reduce the extension of damages, in particular, the subsequent delamination for a given impact energy. In epoxy-based laminates, the debris of broken fibers and matrix get stuck in the cracks and the adjacent layers, and create a sort of blocking system that prevents the cracks and delamination from closing after impact
Tests of Sapphire Crystals Produced with Different Growth Processes for Ultra-stable Microwave Oscillators
We present the characterization of 8-12 GHz whispering gallery mode
resonators machined in high-quality sapphire crystals elaborated with different
growth techniques. These microwave resonators are intended to constitute the
reference frequency of ultra-stable Cryogenic Sapphire Oscillators. We
conducted systematic tests near 4 K on these crystals to determine the unloaded
Q-factor and the turnover temperature for whispering gallery modes in the 8-12
GHz frequency range. These characterizations show that high quality sapphire
crystals elaborated with the Heat Exchange or the Kyropoulos growth technique
are both suitable to meet a fractional frequency stability better than 1x10-15
for 1 s to 10.000 s integration times.Comment: 7 figure
Perspectives dans l'accueil collectif extrafamilial des enfants: prestation de garde ou service public ? : étude de la capacité des directions de développer des stratégies d'innovation en réponse aux enjeux sociaux actuels : exemple de la lutte contre la pauvreté et l'exclusion sociale : module Travail de Master
Depuis 2014, le Conseil fédéral a mis en place un programme national de lutte contre la pauvreté. Ce programme met en évidence différents axes d'investigation et d'action. Parmi ceux-ci, le secteur de l'accueil collectif extrafamilial des enfant figure en bonne place des mesures à développer, car les services dispensés dans ces structures sont reconnus pour une double fonction permettant d'éviter la précarisation des individus. D'une part, le placement des enfants permet aux parents de concilier leur vie familiale et leur vie professionnelle et, d'autre part, les services dispensés dans les structures d'accueil proposent des espaces de stimulation dits d'encouragement précoce, et participent ainsi à doter les enfant des compétences nécessaires à une réussite scolaire
Numerical simulation of the magnetization of high-temperature superconductors: 3D finite element method using a single time-step iteration
We make progress towards a 3D finite-element model for the magnetization of a
high temperature superconductor (HTS): We suggest a method that takes into
account demagnetisation effects and flux creep, while it neglects the effects
associated with currents that are not perpendicular to the local magnetic
induction. We consider samples that are subjected to a uniform magnetic field
varying linearly with time. Their magnetization is calculated by means of a
weak formulation in the magnetostatic approximation of the Maxwell equations
(A-phi formulation). An implicit method is used for the temporal resolution
(Backward Euler scheme) and is solved in the open source solver GetDP. Picard
iterations are used to deal with the power law conductivity of HTS. The finite
element formulation is validated for an HTS tube with large pinning strength
through the comparison with results obtained with other well-established
methods. We show that carrying the calculations with a single time-step (as
opposed to many small time-steps) produce results with excellent accuracy in a
drastically reduced simulation time. The numerical method is extended to the
study of the trapped magnetization of cylinders that are drilled with different
arrays of columnar holes arranged parallel to the cylinder axis
Natural Image Noise Dataset
Convolutional neural networks have been the focus of research aiming to solve
image denoising problems, but their performance remains unsatisfactory for most
applications. These networks are trained with synthetic noise distributions
that do not accurately reflect the noise captured by image sensors. Some
datasets of clean-noisy image pairs have been introduced but they are usually
meant for benchmarking or specific applications. We introduce the Natural Image
Noise Dataset (NIND), a dataset of DSLR-like images with varying levels of ISO
noise which is large enough to train models for blind denoising over a wide
range of noise. We demonstrate a denoising model trained with the NIND and show
that it significantly outperforms BM3D on ISO noise from unseen images, even
when generalizing to images from a different type of camera. The Natural Image
Noise Dataset is published on Wikimedia Commons such that it remains open for
curation and contributions. We expect that this dataset will prove useful for
future image denoising applications.Comment: NTIRE at CVPR 201
Influence of matrix toughness and ductility on the compression-after-impact behavior of woven-ply thermoplastic- and thermosetting-composites: A comparative study
This study was aimed at comparing the residual compressive strength and behavior of TS-based (epoxy) and TP-based (PPS or PEEK) laminates initially subjected to low velocity impacts. Provided that the impact energy is not too low, the permanent indentation is instrumental in initiating laminates local buckling under compressive loadings. CAI tests revealed that matrix toughness is not the primary parameter ruling the damage tolerance of the studied materials. However, matrix ductility seems to slow down the propagation of transverse cracks during compression thanks to plastic micro-buckling which preferentially takes place at the crimps in woven-ply laminates. It could therefore justify why the matrix toughness of TP-based laminates does not result in significantly higher CAI residual strengths. Finally, the compressive failure mechanisms of impacted laminates are discussed depending on matrix nature, with a particular attention paid to the damage scenario (buckling and propagation of 0° fibers failure)
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