298 research outputs found
Performance of logistic regression modeling: beyond the number of events per variable, the role of data structure
No full textReply to : Steyerberg EW, Schemper M, Harrell FE. Logistic regression modeling and the number of events per variable: selection bias dominates. J Clin Epidemiol. 2011 Dec;64(12):1464-5; author reply 1463-4. doi: 10.1016/j.jclinepi.2011.06.016. PMID: 22032755. which is a comment on : Courvoisier DS, Combescure C, Agoritsas T, Gayet-Ageron A, Perneger TV. Performance of logistic regression modeling: beyond the number of events per variable, the role of data structure. J Clin Epidemiol. 2011 Sep;64(9):993-1000. doi: 10.1016/j.jclinepi.2010.11.012. Epub 2011 Mar 16. PMID: 21411281. https://archive-ouverte.unige.ch/unige:25409</a
Tailored Thienopyridine therapy: no urgency for CYP2C19 genotyping
No full textBetween 20% and 50% of cardiovascular patients treated with clopidogrel, an anti-P2Y12 drug, display high on-treatment platelet reactivity (HTPR) and are not adequately protected from major adverse cardiovascular events (MACE). Despite a minor influence of the CYP2C19*2 genetic variant on the pharmacodynamic response to clopidogrel (5% to 12%) and a limited or absent value for predicting stent thrombosis and MACE, this latter polymorphism is currently considered an important candidate to tailor anti-P2Y12 therapy during percutaneous coronary intervention. Seven studies have examined the value of CYP2C19*2 for predicting HTPR in comparison to a specific pharmacodynamic assay (VASP assay). Overall, the summarized sensitivity of the CYP2C19*2 genotype for predicting HTPR was 37.6% (95% CI: 32.2 to 43.3%), yielding a negative likelihood ratio of only 0.77 (95% CI: 0.68 to 0.86) which confirms its limited value as a routine clinical aid. A tailored anti-P2Y12 treatment strategy restricted to CYP2C19*2 carriers may be of some help, but this restrictive approach leaves out noncarriers with HTPR. As for platelet function testing, there is currently no convincing data to support that using CYP2C19*2 genotyping as a tailored anti-P2Y12 treatment would be an effective strategy and there is no urgency for CYP2C19 genotyping in clinical practice. Strategies incorporating genotyping, phenotyping, and clinical data in a stratified and sequential approach may be more promising
Entre la terre et la mer. La via Aurelia et la topographie du litoral du Latium et de la Toscane
No full textExact bifurcation analysis of the static response of a Fermi–Pasta–Ulam softening chain with short and long-range interactions
No full textThis paper is devoted to the static bifurcation of a nonlinear elastic chain with softening and both direct and indirect interactions. This system is also known as a generalized softening FPU system (Fermi–Pasta–lam nonlinear lattice) with p=2 nonlinear interactions (nonlinear direct and second-neighbouring interactions). The static response of this n-degree-of-freedom nonlinear system under pure tension loading is theoretically and numerically investigated. The mathematical problem is equivalent to a nonlinear fourth-order difference eigenvalue problem. The bifurcation parameters are calculated from the exact resolution of the fourth-order linearized difference eigenvalue problem. It is shown that the bifurcation diagram of the generalized softening FPU system depends on the stiffness ratio of both the linear and the nonlinear parts of the nonlinear lattice, which accounts for both short range and long range interactions. This system possesses both a saddle node bifurcation (limit point) and some unstable bifurcation branches for the parameters of interest. We show that for some range of structural parameters, the bifurcations in (n−1) unstable bifurcation branches prevail before the limit point. In the complementary domain of the structural parameters, the bifurcations in (n−1) unstable bifurcation branches prevail after the limit point, which means that the system becomes unstable first, at the limit point. At the border between both domains in the space of structural parameters, the bifurcation in (n−1) unstable bifurcation branches coincide with the limit point, with an addition unstable fundamental branch. This case is the hill-top bifurcation, already analysed by Challamel et al. (Int J Non-Linear Mech 156(104509): 1-11, 2023) in the case p=1 interaction. We also numerically highlight the possibility for such a generalized FPU system to possess possible imperfection sensitivity. Numerical results support the fact that the structural boundary of the hill-top bifurcation coincides with the transition between imperfection sensitive to imperfection insensitive systems
Local modal reduction in explicit dynamics with domain decomposition. Part 1: extension to subdomains undergoing finite rigid rotations
No full textWe present an extension of the dual Schur multidomain method with local linear modal reduction previously introduced by Gravouil, Combescure, Herry and Faucher to the case of modal reduction on geometrically non-linear vibrating subdomains. This first part of a two-part paper describes a new formalism, based on an original set of parameters, to represent a subdomain's finite rigid-body motion. Special attention is paid to the stability issues with time integration using the central difference scheme. The method is validated on an academic example and its efficiency is demonstrated on a large-scale example. Copyright (C) 2004 John Wiley Sons, Ltd
Flambage des nids d'abeilles en bicompaction
No full textInternational audienceLes matériaux architecturés présentent de hautes caractéristiques spécifiques grâce à leurs mésostructures élancées (poutres, plaques et coques). La nature élancée de ces géométries favorisent l’apparition de flambage à l’échelle d’une ou plusieurs cellules constitutives. Ces instabilités peuvent être mises à profit pour en tirer des propriétés fonctionnelles (comportement adoucissant, absorption d’énergie).Les essais de flambage en bicompaction sur matériaux architecturés permettent de mieux comprendre ces instabilités. Les essais de Papka & Kyriakides, montrent que plusieurs modes de flambage locaux différents peuvent apparaître. Cependant, les machines existantes de bicompaction sont souvent encore assez limitées (mesure d’effort sommaire notamment).La simulation numérique du flambage en bicompaction de tels matériaux est rendue complexe par le fait que le mode de flambage peut s’étendre sur plusieurs cellules mais également car les charges critiques de flambage sont réputées sensibles aux défauts. En utilisant un modèle sans défauts, Combescure, Elliott & Triantafyllidis ont pu démontrer l’existence de plusieurs modes de flambage, correspondants aux observations de Papka & Kyriakides.La prévision des efforts critiques théoriques obtenu par Combescure, Elliott & Triantafyllidis n’a pas encore été vérifiée expérimentalement. Le présent travail consiste à réaliser des essais de flambage en bicompaction avec une mesure fine des efforts appliqués
Local modal reduction in explicit dynamics with domain decomposition. Part 2: Specific interface treatment when modal subdomains are involved
No full textDuring the last 2 years, a multidomain formalism for structural dynamics based on a multi-time-step algorithm and local linear modal reduction was proposed by Gravouil, Combescure, Herry & Faucher. In the first part of this paper, we extended modal reduction to subdomains undergoing finite rigid-body rotations. Here, we focus on the consequences of local modal projection (either linear or geometrically non-linear) on the treatment of interface problems between subdomains. In particular, we address the issues of the invertibility and efficiency of the solution process. We illustrate our propositions with specific interpretations of the examples presented in Part 1 and present an additional example to demonstrate the properties of special sets of modes. Copyright (C) 2004 John Wiley Sons, Ltd
The problem of mutually unbiased bases in dimension 6
No full textWe outline a discretization approach to determine the
maximal number of mutually unbiased bases in dimension 6. We
describe the basic ideas and introduce the most important definitions
to tackle this famous open problem which has been open for
the last 10 years. Some preliminary results are also listed
A generalized Pauli problem and an infinite family of MUB-triplets in dimension 6
No full textWe exhibit an infinite family of triplets of mutually
unbiased bases (MUBs) in dimension 6. These triplets involve the
Fourier family of Hadamard matrices, F(a, b). However, in the
main result of the paper we also prove that for any values of the
parameters (a, b), the standard basis and F(a, b) cannot be extended
to a MUB-quartet. The main novelty lies in the method of proof
which may successfully be applied in the future to prove that the
maximal number of MUBs in dimension 6 is three
Castrum Novum (Santa Marinella, prov. de Rome)
No full textIntroduction(F. Enei, S. Nardi Combescure, G. Poccardi) Au cours du mois de septembre 2016, les recherches de terrain entreprises l’année précédente ont été poursuivies sur la colline du « Casale Alibrandi » (zone D) qui correspond au cœur de la colonie de Castrum Novum. Trois nouveaux sondages ont été ouverts : le sondage IV a permis de dégager une partie importante des remparts du IIIe siècle av. J. -C. ; le sondage V a intéressé des édifices relatifs à l’époque de fondation de la colonie ;..
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