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Search Results: 1 - 10 of 5348 matches for " Olivier Dubourg "
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A generalization of Snoek's law to ferromagnetic films and composites
Olivier Acher,Sébastien Dubourg
Physics , 2007, DOI: 10.1103/PhysRevB.77.104440
Abstract: The present paper establishes characteristics of the relative magnetic permeability spectrum $\mu$(f) of magnetic materials at microwave frequencies. The integral of the imaginary part of $\mu$(f) multiplied with the frequency f gives remarkable properties. A generalisation of Snoek's law consists in this quantity being bounded by the square of the saturation magnetization multiplied with a constant. While previous results have been obtained in the case of non-conductive materials, this work is a generalization to ferromagnetic materials and ferromagnetic-based composites with significant skin effect. The influence of truncating the summation to finite upper frequencies is investigated, and estimates associated to the finite summation are provided. It is established that, in practice, the integral does not depend on the damping model under consideration. Numerical experiments are performed in the exactly solvable case of ferromagnetic thin films with uniform magnetization, and these numerical experiments are found to confirm our theoretical results. Microwave permeability measurements on soft amorphous films are reported. The relation between the integral and the saturation magnetization is verified experimentally, and some practical applications of the theoretical results are introduced. The integral can be used to determine the average magnetization orientation in materials with complex configurations of the magnetization, and furthermore to demonstrate the accuracy of microwave measurement systems. For certain applications, such as electromagnetic compatibility or radar absorbing materials, the relations established herein provide useful indications for the design of efficient materials, and simple figures of merit to compare the properties measured on various materials.
Treatment for Stable Coronary Artery Disease: A Network Meta-Analysis of Cost-Effectiveness Studies
Thibaut Caruba, Sandrine Katsahian, Catherine Schramm, Ana?s Charles Nelson, Pierre Durieux, Dominique Bégué, Yves Juillière, Olivier Dubourg, Nicolas Danchin, Brigitte Sabatier
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0098371
Abstract: Introduction and Objectives Numerous studies have assessed cost-effectiveness of different treatment modalities for stable angina. Direct comparisons, however, are uncommon. We therefore set out to compare the efficacy and mean cost per patient after 1 and 3 years of follow-up, of the following treatments as assessed in randomized controlled trials (RCT): medical therapy (MT), percutaneous coronary intervention (PCI) without stent (PTCA), with bare-metal stent (BMS), with drug-eluting stent (DES), and elective coronary artery bypass graft (CABG). Methods RCT comparing at least two of the five treatments and reporting clinical and cost data were identified by a systematic search. Clinical end-points were mortality and myocardial infarction (MI). The costs described in the different trials were standardized and expressed in US $ 2008, based on purchasing power parity. A network meta-analysis was used to compare costs. Results Fifteen RCT were selected. Mortality and MI rates were similar in the five treatment groups both for 1-year and 3-year follow-up. Weighted cost per patient however differed markedly for the five treatment modalities, at both one year and three years (P<0.0001). MT was the least expensive treatment modality: US $3069 and 13 864 after one and three years of follow-up, while CABG was the most costly: US $27 003 and 28 670 after one and three years. PCI, whether with plain balloon, BMS or DES came in between, but was closer to the costs of CABG. Conclusions Appreciable savings in health expenditures can be achieved by using MT in the management of patients with stable angina.
Note sur l’atelier monétaire de Chinon du VIIe au Xe siècle Note on the mint in Chinon from the 7th to the 10th Century
Fran?oise Dumas-Dubourg
Revue Archéologique du Centre de la France , 2006,
Abstract: Chinon entre dans l’histoire de la monnaie médiévale non par une émission monétaire particulière mais par le biais d’un trésor de 81 sous d’or enfoui au VIe siècle, vers 520, composé pour l’essentiel d’imitations de monnaies impériales par divers peuples barbares : ostrogoths, burgondes et francs (Robert 1882).C’est bien plus tard que des monnaies portent le nom de Chinon : une monnaie mérovingienne d’or : un tiers de sou du VIIe siècle et deux deniers d’argent du VIIIe siècle. Le tiers de so...
Impact of routine percutaneous coronary intervention after out-of-hospital cardiac arrest due to ventricular fibrillation
Pierrick Cronier, Philippe Vignon, Koceila Bouferrache, Philippe Aegerter, Cyril Charron, Fran?ois Templier, Samuel Castro, Rami El Mahmoud, Cécile Lory, Nicolas Pichon, Olivier Dubourg, Antoine Vieillard-Baron
Critical Care , 2011, DOI: 10.1186/cc10227
Abstract: We studied 111 consecutive patients resuscitated successfully following OHCA related to shock-sensitive rhythm. They were divided into five groups according to age: < 45 years (n = 22, group 1), 45 to 54 years (n = 27, group 2), 55 to 64 years (n = 22, group 3), 65 to 74 years (n = 23, group 4) and ≥75 years (n = 17, group 5). Emergency coronary angiography was performed in hemodynamically stable patients < 80 years old, regardless of the electrocardiogram pattern. MTH was targeted to a core temperature of 32°C to 34°C for 24 hours.Most patients (73%) had coronary heart disease, although its incidence in group 1 was lower than in other groups (41% versus 81%; P = 0.01). In group 1, all patients but one underwent coronary angiography, and 33% of them underwent associated PCI. In group 5, only 53% of patients underwent a coronary angiography and 44% underwent PCI. Overall in-hospital survival was 54%, ranging between 52% and 64% in groups 1 to 4 and 24% in group 5. Time from collapse to return of spontaneous circulation was associated with mortality (odds ratio (OR) = 1.05 (25th to 75th percentile range, 1.03 to 1.08); P < 0.001), whereas PCI was associated with survival (OR = 0.30 (25th to 75th percentile range, 0.11 to 0.79); P = 0.01).We suggest that routine coronary angiography with potentially associated PCI may favorably alter the prognosis of resuscitated patients with stable hemodynamics who are treated with MTH after OHCA related to ventricular fibrillation. Although age was not an independent cause of death, the clinical relevance of this therapeutic strategy remains to be determined in older people.Coronary artery disease is the most common cause of sudden cardiac death, and ventricular fibrillation (VF) due to ischemic cardiomyopathy is responsible for more than 50% of out-of-hospital cardiac arrest (OHCA) cases [1]. In this setting, coronary angiography associated with percutaneous coronary intervention (PCI) has been recommended in the presence of ST ele
Th1 Response and Systemic Treg Deficiency in Inclusion Body Myositis
Yves Allenbach, Wahiba Chaara, Michelle Rosenzwajg, Adrien Six, Nicolas Prevel, Federico Mingozzi, Julia Wanschitz, Lucile Musset, Jean-Luc Charuel, Bruno Eymard, Benoit Salomon, Charles Duyckaerts, Thierry Maisonobe, Odile Dubourg, Serge Herson, David Klatzmann, Olivier Benveniste
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088788
Abstract: Objective Sporadic inclusion body myositis (sIBM), the most frequent myositis in elderly patients, is characterized by the presence muscle inflammation and degeneration. We aimed at characterizing immune responses and regulatory T cells, considered key players in the maintenance of peripheral immune tolerance, in sIBM. Methods Serum and muscle tissue levels of 25 cytokines and phenotype of circulating immune cells were measured in 22 sIBM patients and compared with 22 healthy subjects. Cytokine data were analysed by unsupervised hierarchical clustering and principal components analysis. Results Compared to healthy controls, sIBM patients had increased levels of Th-1 cytokines and chemokines such as IL-12 (261±138 pg/mL vs. 88±19 pg/mL; p<0.0001), CXCL-9 (186±12 pg/mL vs. 13±7 pg/mL; p<0.0001), and CXCL-10 (187±62 pg/mL vs. 13±6 pg/mL; p<0.0001). This was associated with an increased frequency of CD8+CD28? T cells (45.6±18.5% vs. 13.5±9.9%; p<0.0001), which were more prone to produce IFN-γ (45.6±18.5% vs. 13.5±9.9%; p<0.0001). sIBM patients also had a decreased frequency of circulating regulatory T cells (CD4+CD25+CD127lowFOXP3+, 6.9±1.7%; vs. 5.2±1.1%, p = 0.01), which displayed normal suppressor function and were also present in affected muscle. Conclusion sIBM patients present systemic immune activation with Th1 polarization involving the IFN-γ pathway and CD8+CD28? T cells associated with peripheral regulatory T cell deficiency.
Scikit-learn: Machine Learning in Python
Fabian Pedregosa,Ga?l Varoquaux,Alexandre Gramfort,Vincent Michel,Bertrand Thirion,Olivier Grisel,Mathieu Blondel,Peter Prettenhofer,Ron Weiss,Vincent Dubourg,Jake Vanderplas,Alexandre Passos,David Cournapeau,Matthieu Brucher,Matthieu Perrot,édouard Duchesnay
Computer Science , 2012,
Abstract: Scikit-learn is a Python module integrating a wide range of state-of-the-art machine learning algorithms for medium-scale supervised and unsupervised problems. This package focuses on bringing machine learning to non-specialists using a general-purpose high-level language. Emphasis is put on ease of use, performance, documentation, and API consistency. It has minimal dependencies and is distributed under the simplified BSD license, encouraging its use in both academic and commercial settings. Source code, binaries, and documentation can be downloaded from http://scikit-learn.sourceforge.net.
Proposition d’un modèle de tutorat pour la conception de dispositifs d’accompagnement en formation en ligne
Patricia Gounon,Pascal Leroux,Xavier Dubourg
Revue Internationale des Technologies en Pédagogie Universitaire , 2004,
Abstract: [Fran ais] Nous avons constaté dans la littérature le manque de prise en compte de l’accompagnement des apprenants dans la conception des dispositifs de formation en ligne. Ce manque nous semble très préjudiciable dans le cycle de vie d’une formation. C’est pourquoi, après avoir identifié les besoins d’accompagnement des apprenants dans une formation en ligne, nous proposons un modèle descriptif d’une activité de tutorat. Ce modèle sert de fondement pour guider la définition des spécifications du dispositif d’accompagnement des apprenants en matière de taches et d’outils supports de leurs activités. Dans la dernière partie de l’article, nous présentons la méthodologie d’application de ce modèle au cours du cycle de vie d’une formation. [English] The learners’ tutoring component in Web-based distance education is often neglected during the instructional design process. This omission is prejudicial in the life-cycle courseware. This is why we propose a descriptive tutoring model, after identifying learners support needs in a distance learning environment. This model is used as the foundation to guide specification definition of learner accompaniment environment in terms of tasks and tools supporting their activities. In the last part of this article, we present the application methodology using this model during the life-cycle courseware.
Reliability-based design optimization using kriging surrogates and subset simulation
V. Dubourg,B. Sudret,J. -M. Bourinet
Statistics , 2011, DOI: 10.1007/s00158-011-0653-8
Abstract: The aim of the present paper is to develop a strategy for solving reliability-based design optimization (RBDO) problems that remains applicable when the performance models are expensive to evaluate. Starting with the premise that simulation-based approaches are not affordable for such problems, and that the most-probable-failure-point-based approaches do not permit to quantify the error on the estimation of the failure probability, an approach based on both metamodels and advanced simulation techniques is explored. The kriging metamodeling technique is chosen in order to surrogate the performance functions because it allows one to genuinely quantify the surrogate error. The surrogate error onto the limit-state surfaces is propagated to the failure probabilities estimates in order to provide an empirical error measure. This error is then sequentially reduced by means of a population-based adaptive refinement technique until the kriging surrogates are accurate enough for reliability analysis. This original refinement strategy makes it possible to add several observations in the design of experiments at the same time. Reliability and reliability sensitivity analyses are performed by means of the subset simulation technique for the sake of numerical efficiency. The adaptive surrogate-based strategy for reliability estimation is finally involved into a classical gradient-based optimization algorithm in order to solve the RBDO problem. The kriging surrogates are built in a so-called augmented reliability space thus making them reusable from one nested RBDO iteration to the other. The strategy is compared to other approaches available in the literature on three academic examples in the field of structural mechanics.
Metamodel-based importance sampling for the simulation of rare events
V. Dubourg,F. Deheeger,B. Sudret
Statistics , 2011,
Abstract: In the field of structural reliability, the Monte-Carlo estimator is considered as the reference probability estimator. However, it is still untractable for real engineering cases since it requires a high number of runs of the model. In order to reduce the number of computer experiments, many other approaches known as reliability methods have been proposed. A certain approach consists in replacing the original experiment by a surrogate which is much faster to evaluate. Nevertheless, it is often difficult (or even impossible) to quantify the error made by this substitution. In this paper an alternative approach is developed. It takes advantage of the kriging meta-modeling and importance sampling techniques. The proposed alternative estimator is finally applied to a finite element based structural reliability analysis.
Metamodel-based importance sampling for structural reliability analysis
V. Dubourg,F. Deheeger,B. Sudret
Statistics , 2011,
Abstract: Structural reliability methods aim at computing the probability of failure of systems with respect to some prescribed performance functions. In modern engineering such functions usually resort to running an expensive-to-evaluate computational model (e.g. a finite element model). In this respect simulation methods, which may require $10^{3-6}$ runs cannot be used directly. Surrogate models such as quadratic response surfaces, polynomial chaos expansions or kriging (which are built from a limited number of runs of the original model) are then introduced as a substitute of the original model to cope with the computational cost. In practice it is almost impossible to quantify the error made by this substitution though. In this paper we propose to use a kriging surrogate of the performance function as a means to build a quasi-optimal importance sampling density. The probability of failure is eventually obtained as the product of an augmented probability computed by substituting the meta-model for the original performance function and a correction term which ensures that there is no bias in the estimation even if the meta-model is not fully accurate. The approach is applied to analytical and finite element reliability problems and proves efficient up to 100 random variables.
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