Search results for "Mathématiques"
showing 10 items of 88 documents
History of Mathematics: A Global Cultural Approach
2021
Double index recursive models
1994
The purpose of this document is to study the model belongs to the family of structural equation models with data varying both accross individuals (sectors) and in time. A complete theoretical analysis is developed in this work for the case of a recursive structure. Maximum likelihood estimation and Zellner's "seemingly unrelated equations" estimators (iterated or not) are presented and their asymptotic properties are carefully derived.The application of the estimation methods to the economy morocco produced statistically significant and economic meaningful results. Through a test of exogeneity, the recursivity of the system is confirmed. Policy recommendations are discussed and analyzed.
A unifying framework for specifying generalized linear models for categorical data
2013
International audience; In the context of categorical data analysis, the case of nominal and ordinal data has been investigated in depth while the case of partially ordered data has been comparatively neglected. We first propose a new specification of generalized linear models (GLMs) for categorical response variables which en- compasses all the classical models such as multinomial logit, odds proportional or continuation ratio models but also led us to identify new GLMs. This unifying framework makes the different GLMs easier to compare and combine. We then define the more general class of partitioned conditional GLMs for categorical re- sponse variables. This new class enables to take int…
GeneSys-Beet: A model of the effects of cropping systems on gene flow between sugar beet and weed beet
2008
A weedy form of the genus Beta, i.e. Beta vulgaris ssp. vulgaris (hence ''weed beet'') frequently found in sugar beet is impossible to eliminate with herbicides because of its genetic proximity to the crop. It is presumed to be the progeny of accidental hybrids between sugar beet (ssp. vulgaris) and wild beet (ssp. maritima), or of sugar beet varieties sensitive to vernalization and sown early in years with late cold spells. In this context, genetically modified (GM) sugar beet varieties tolerant to non-selective herbicides would be interesting to manage weed beet. However, because of the proximity of the weed to the crop, it is highly probable that the herbicide-tolerance transgene would b…
Adapter localement les prévisions climatiques saisonnières : désagrégation stochastique et interpolation spatiale.
2013
6 pages; International audience; Un panorama est fait des méthodes de descente d’échelles permettant de passer de prévisions climatiques saisonnières de large-échelle à des séries locales journalières. L’exemple des générateurs stochastiques de temps est appliqué à la prévision des récoltes de sorgho au Kenya, dans le cadre du programme ANR PICREVAT. Une méthode d’interpolation spatiale des paramètres des générateurs est testée, pour obtenir des séries journalières de précipitations en tout point du territoire. Les séries générées sont utilisées en entrée du modèle agronomique SARRA-H.
Glassy dynamics in monodisperse hard ellipsoids
2008
We present evidence from computer simulations for glassy dynamics in suspensions of monodisperse hard ellipsoids. In equilibrium, almost spherical ellipsoids show a first order transition from an isotropic phase to a rotator phase. When overcompressing the isotropic phase into the rotator regime, we observe super-Arrhenius slowing down of diffusion and relaxation, accompanied by two-step relaxation in positional and orientational correlators. The effects are strong enough for asymptotic laws of mode-coupling theory to apply. Glassy dynamics are unusual in monodisperse systems. Typically, polydispersity in size or a mixture of particle species is prerequisite to prevent crystallization. Here…
Isotropic-nematic interface in suspensions of hard rods: Mean-field properties and capillary waves
2006
We present a study of the isotropic-nematic interface in a system of hard spherocylinders. First we compare results from Monte Carlo simulations and Onsager density functional theory for the interfacial profiles of the orientational order parameter and the density. Those interfacial properties that are not affected by capillary waves are in good agreement, despite the fact that Onsager theory overestimates the coexistence densities. Then we show results of a Monte Carlo study of the capillary waves of the interface. In agreement with recent theoretical investigations (Eur.Phys.J. E {\bf 18} 407 (2005)) we find a strongly anistropic capillary wave spectrum. For the wave-numbers accessed in o…
Accounting for preferential sampling in species distribution models
2019
D. C., A. L. Q. and F. M. would like to thank the Ministerio de Educación y Ciencia (Spain) for financial support (jointly financed by the European Regional Development Fund) via Research Grants MTM2013‐42323‐P and MTM2016‐77501‐P, and ACOMP/2015/202 from Generalitat Valenciana (Spain). Species distribution models (SDMs) are now being widely used in ecology for management and conservation purposes across terrestrial, freshwater, and marine realms. The increasing interest in SDMs has drawn the attention of ecologists to spatial models and, in particular, to geostatistical models, which are used to associate observations of species occurrence or abundance with environmental covariates in a fi…
Removing the saturation assumption in Bank-Weiser error estimator analysis in dimension three
2020
International audience; We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes the main novelty of our study. In addition, we present a numerical comparison of the Bank-Weiser and residual estimators for a three-dimensional test case.
Les chiffres : les comprendre pour s'en dépendre
2011
C'est le regard d'une sociologue qualitativiste qui a fait l'objet de cette conférence invitée. D'un forum qui replaçait au centre des débats l'éthique et le vivre-ensemble, mais inscrit dans un atelier sur "les nombres", l'intervention d'un chercheur qualitativiste, aux côtés d'un mathématicien Thierry Duchesne (Université Laval) et de la démographe Chantal Girard (ISQ - Institut de la statistique du Québec), a fait figure de contre-emploi. La communication s'est centrée sur la remise en question de l'universalité du nombre : le nombre, dans son rapport à l'écrit est-il un sociocentrisme ? Cet universalisme supposé peut également être débattu au regard de l'usage historique du nombre (de l…