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Asymptotic estimates for the parabolic-elliptic Keller-Segel model in the plane
No full textWe investigate the large-time behavior of the solutions of the two-dimensional Keller-Segel system in self-similar variables, when the total mass is subcritical, that is less than 8π after a proper adimensionalization. It was known from previous works that all solutions converge to stationary solutions, with exponential rate when the mass is small. Here we remove this restriction and show that the rate of convergence measured in relative entropy is exponential for any mass in the subcritical range, and independent of the mass. The proof relies on symmetrization techniques, which are adapted from a paper of J.I. Diaz, T. Nagai, and J.-M. Rakotoson, and allow us to establish uniform estimates for Lp norms of the solution. Exponential convergence is obtained by the mean of a linearization in a space which is defined consistently with relative entropy estimates and in which the linearized evolution operator is self-adjoint. The core of proof relies on several new spectral gap estimates which are of independent interest.nonnonouirechercheInternationa
Determinants of Corporate Social Disclosure in the Franchising Sector: Insights from French franchisors' websites
No full textThis paper focuses on the notion of corporate social responsibility (CSR) within the franchising sector. More specifically, a set of research hypotheses derived from Regulation Theory and Transaction Cost Analysis addresses the relationships first between the chain size and the extent of corporate social disclosure (CSD) on franchisors' websites, and then between the percentage of company-owned units within the chain and the extent of corporate social disclosure (CSD) on franchisors' websites. The empirical study encompasses a total of 136 French franchise chains. Findings reveal that 86.03% of these franchisors communicate about their CSR activities on their website. Moreover, a significant relationship exists between chain size (respectively, the percentage of company-owned units within the chain) and the extent of CSD provided on franchisors' websites.nonnonouirechercheInternationa
Introspective forgetting
No full textWe model the forgetting of propositional variables in a modal logical context where agents become ignorant and are aware of each others’ or their own resulting ignorance. The resulting logic is sound and complete. It can be compared to variable-forgetting as abstraction from information, wherein agents become unaware of certain variables: by employing elementary results for bisimulation, it follows that beliefs not involving the forgotten atom(s) remain true.nonouirechercheInternationa
Introspective Forgetting
No full textWe model the forgetting of propositional variables in a modal logical context where agents become ignorant and are aware of each others’ or their own resulting ignorance. The resulting logic is sound and complete. It can be compared to variable-forgetting as abstraction from information, wherein agents become unaware of certain variables: by employing elementary results for bisimulation, it follows that beliefs not involving the forgotten atom(s) remain true.nonouirechercheInternationa
Longitudinal deformation models, spatial regularizations and learning strategies to quantify Alzheimer's disease progression
No full textIn the context of Alzheimer's disease, two challenging issues are (1) the characterization of local hippocampal shape changes specific to disease progression and (2) the identification of mild-cognitive impairment patients likely to convert. In the literature, (1) is usually solved first to detect areas potentially related to the disease. These areas are then considered as an input to solve (2). As an alternative to this sequential strategy, we investigate the use of a classification model using logistic regression to address both issues (1) and (2) simultaneously. The classification of the patients therefore does not require any a priori definition of the most representative hippocampal areas potentially related to the disease, as they are automatically detected. We first quantify deformations of patients' hippocampi between two time points using the large deformations by diffeomorphisms framework and transport these deformations to a common template. Since the deformations are expected to be spatially structured, we perform classification combining logistic loss and spatial regularization techniques, which have not been explored so far in this context, as far as we know. The main contribution of this paper is the comparison of regularization techniques enforcing the coefficient maps to be spatially smooth (Sobolev), piecewise constant (total variation) or sparse (fused LASSO) with standard regularization techniques which do not take into account the spatial structure (LASSO, ridge and ElasticNet). On a dataset of 103 patients out of ADNI, the techniques using spatial regularizations lead to the best classification rates. They also find coherent areas related to the disease progression.nonouirechercheInternationa
The Translated Strategic Alignment Model: A Practice-Based Perspective
No full textDans cet article nous proposons de revisiter le concept d’alignement stratégique dans une approche par les pratiques. Nous proposons de nouvelles idées sur ce concept qui a été majoritairement étudié dans la littérature au travers du modèle d’alignement stratégique proposé par Henderson et Venkatraman (1993). Dans une approche enracinée, nous étudions les pratiques quotidiennes de praticiens au travers de l’étude en profondeur de trois cas d’entreprises et d’entretiens avec six consultants spécialisés en gestion des systèmes d’information (SI). Nous utilisons la théorie de l’acteur-réseau comme cadre théorique afin de nous aider à faire sens de nos données et à les interpréter. Nous proposons un nouveau modèle conceptuel, non-fonctionnaliste et qui intègre plusieurs courants de la littérature: le modèle d’alignement stratégique traduit (TSAM). Ce modèle peut aider à atteindre un niveau critique d’alignement qui apparaît comme nécessaire pour ouvrir le chemin menant à l’avantage compétitif.In this article, we propose to revisit the concept of strategic alignment in a practice-based perspective. We propose new insights on this concept which has mostly been studied in the literature through Henderson and Venkatraman’s strategic alignment model (1993). In a grounded approach, we study practitioners’ daily practices through the in-depth investigation of three corporate cases and interviews with six consultants specialized in the management of information systems (IS). We use actor-network theory as a theoretical framework to help us make sense of and interpret our data. We propose a new, conceptual, non-functionalist model, which integrates several streams of literature: the translated strategic alignment model (TSAM). This model may serve as a help to drive toward a critical level of alignment that appears as necessary to clear the path toward competitive advantage.nonouirechercheInternationa
Automatic detection and segmentation of renal lesions in 3D contrast-enhanced ultrasound images
No full textContrast-enhanced ultrasound (CEUS) is a valuable imaging modality in the detection and evaluation of different kinds of lesions. Three-dimensional CEUS acquisitions allow quantitative volumetric assessments and better visualization of lesions, but automatic and robust analysis of such images is very challenging because of their poor quality. In this paper, we propose a method to automatically segment lesions such as cysts in 3D CEUS data. First we use a pre-processing step, based on the guided filtering framework, to improve the visibility of the lesions. The lesion detection is then performed through a multi-scale radial symmetry transform. We compute the likelihood of a pixel to be the center of a dark rounded shape. The local maxima of this likelihood are considered as lesions centers. Finally, we recover the whole lesions volume with multiple front propagation based on image intensity, using a fast marching method. For each lesion, the final segmentation is chosen as the one which maximizes the gradient flux through its boundary. Our method has been tested on several clinical 3D CEUS images of the kidney and provides promising results. Copyright 2012 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. The original version of this work can be found by using the doi:10.1117/12.911103ouinonouirechercheInternationa
Geographical Diversification with a World Volatility Index
No full textThis paper proposes a new ‘World Volatility Index’, coined WVIX, by constructing the first index that approximates the aggregate volatility level of the G20 countries. The empirical analysis makes use of the factor dynamic conditional correlation model – with an automated methodology to detect the number of factors – in order to (i) sum up the information contained in the implied volatility indexes belonging to the US, the UK, the Eurozone, Japan and emerging countries, and (ii) examine the time-varying correlation between them. The results reveal that the WVIX evolves around 22%, but its activity can vary sharply depending on its exposure to various sources of geographical risks (e.g. the latest 2010-11 European debt crisis). Thus constructed as an early warning device, the methodology behind the WVIX can be replicated by market practitioners to datasets that better suit their needs.nonouirechercheInternationa
Stochastic Target Games with Controlled Loss
No full textWe study a stochastic game where one player tries to find a strategy such that the state process reaches a target of controlled-loss-type, no matter which action is chosen by the other player. We provide, in a general setup, a relaxed geometric dynamic programming for this problem and derive, for the case of a controlled SDE, the corresponding dynamic programming equation in the sense of viscosity solutions. As an example, we consider a problem of partial hedging under Knightian uncertainty.ouinonouirechercheInternationa