2,629 research outputs found
VILLER, Marcel, dir., CAVALLERA, Ferdinand, GUIBERT, J. de, coll., Dictionnaire de spiritualité ascétique et mystique, fascicules CIV-CV. Vide-Vocation
Gravito-inertial waves in a differentially rotating spherical shell
The gravito-inertial waves propagating over a shellular baroclinic flow
inside a rotating spherical shell are analysed using the Boussinesq
approximation. The wave properties are examined by computing paths of
characteristics in the non-dissipative limit, and by solving the full
dissipative eigenvalue problem using a high-resolution spectral method.
Gravito-inertial waves are found to obey a mixed-type second-order operator and
to be often focused around short-period attractors of characteristics or
trapped in a wedge formed by turning surfaces and boundaries. We also find
eigenmodes that show a weak dependence with respect to viscosity and heat
diffusion just like truly regular modes. Some axisymmetric modes are found
unstable and likely destabilized by baroclinic instabilities. Similarly, some
non-axisymmetric modes that meet a critical layer (or corotation resonance) can
turn unstable at sufficiently low diffusivities. In all cases, the instability
is driven by the differential rotation. For many modes of the spectrum, neat
power laws are found for the dependence of the damping rates with diffusion
coefficients, but the theoretical explanation for the exponent values remains
elusive in general. The eigenvalue spectrum turns out to be very rich and
complex, which lets us suppose an even richer and more complex spectrum for
rotating stars or planets that own a differential rotation driven by
baroclinicity.Comment: 33 pages, 14 figures, accepted for publication in Journal of Fluid
Mechanic
Multi-scale modeling of follicular ovulation as a reachability problem
During each ovarian cycle, only a definite number of follicles ovulate, while
the others undergo a degeneration process called atresia. We have designed a
multi-scale mathematical model where ovulation and atresia result from a
hormonal controlled selection process. A 2D-conservation law describes the age
and maturity structuration of the follicular cell population. In this paper, we
focus on the operating mode of the control, through the study of the
characteristics of the conservation law. We describe in particular the set of
microscopic initial conditions leading to the macroscopic phenomenon of either
ovulation or atresia, in the framework of backwards reachable sets theory
La naissance de l'ARDIST
Anniversaire 10 ans de l'ARDISTInternational audienceCet article, écrit par deux des acteurs qui ont participé à la création de l'ARDIST, décrit la naissance de l'ARDIST en 1998. Avant cette date existaient deux communautés séparées de didacticiens des sciences expérimentales, celle des sciences physiques et celle des sciences biologiques et géologiques. Le contexte de la création est rappelé et sont évoqués les problÚmes qui ont été soulevés et résolus pour aboutir à une fusion des deux communautés
A laser ranging method dedicated to path lengths equalization in diluted telescopes
International audienceWhen implementing a diluted telescope with large dimensions, one has to reach the equal path condition to the different segments of the primary mirror. In this work we suggest a way to implement a fast laser ranging method able to provide the error signal, using phase detection of the microwave modulation of a laser beam
An existence result for multidimensional immiscible two-phase flows with discontinuous capillary pressure field
International audienceWe consider the system of equations governing an incompressible immiscible two-phase flow within an heterogeneous porous medium made of two different rock types. Since the capillary pressure funciton depends on the rock type, the capillary pressure field might be discontinuous at the interface between the rocks. We prove the existence of a solution for such a flow by passing to the limit in regularizations of the problem
Introduction - Permanence et changements
Avec le web, les moteurs de recherche, les blogues et les wikis, la relation Ă lâinformation sâest transformĂ©e au point oĂč les repĂšres habituels sâĂ©moussent et doivent ĂȘtre redĂ©finis de fond en comble. Du coup, le travail des archivistes et des bibliothĂ©caires doit lâĂȘtre tout autant. Riches dâune solide tradition et conscientes des dĂ©fis posĂ©s par la modernitĂ© la plus radicale, les sciences de lâinformation se sont Ă©largies. Mais il ne sâagit plus seulement de conserver et de diffuser le savoir, il sâagit dâen repenser le traitement et lâaccĂšs.
Conçu par lâĂcole de bibliothĂ©conomie et des sciences de lâinformation (EBSI) de lâUniversitĂ© de MontrĂ©al, cet ouvrage se situe au carrefour de deux grandes traditions, amĂ©ricaine et française, et a pour ambition de fournir les clĂ©s du monde des sciences de lâinformation en se fondant sur des savoirs pratiques et concrets. Les auteurs prĂ©sentent ici un savoir Ă la fine pointe des sciences de lâinformation pour rĂ©pondre Ă la complexitĂ© des enjeux actuels et futurs.
Introduction, bibliographie, index et table des matiĂšres de lâouvrage
Oracle Inequality for Instrumental Variable Regression
We tackle the problem of estimating a regression function observed in an instrumental regression framework. This model is an inverse problem with unknown operator. We provide a spectral cut-off estimation procedure which enables to derive oracle inequalities which warrants that our estimate, built without any prior knowledge, behaves as well as, up to term, if the best model were known
Goodness-of-fit testing strategies from indirect observations
International audienceWe consider in this paper a goodness-of-fit testing problem in a density framework. In particular, we deal with an error-in-variables model where each new incoming observation is gathered with a random independent error. It is well known that in such a situation, we are faced with an inverse (deconvolution) problem. Nevertheless, following recent results in the Gaussian white noise model, we prove that using procedures containing a deconvolution step is not always necessary
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