déposer
version française rss feed


L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion d'articles scientifiques de niveau recherche, publiés ou non, et de thèses, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Derniers Dépôts 
Chimie
Économie et finance quantitative
Informatique
Mathématiques
Physique
Planète et Univers
Science non linéaire
Sciences cognitives
Sciences de l'environnement
Sciences de l'Homme et Société
Sciences de l'ingénieur
Sciences du Vivant
Statistiques
Epithelial spreading is a common and fundamental aspect of various developmental and disease-related processes such as epithelial closure and wound healing. A key challenge for epithelial tissues undergoing spreading is to increase their surface area without disrupting epithelial integrity. Here we show that orienting cell divisions by tension constitutes an efficient mechanism by which the enveloping cell layer (EVL) releases anisotropic tension while undergoing spreading during zebrafish epiboly. The control of EVL cell-division orientation by tension involves cell elongation and requires myosin II activity to align the mitotic spindle with the main tension axis. We also found that in the absence of tension-oriented cell divisions and in the presence of increased tissue tension, EVL cells undergo ectopic fusions, suggesting that the reduction of tension anisotropy by oriented cell divisions is required to prevent EVL cells from fusing. We conclude that cell-division orientation by tension constitutes a key mechanism for limiting tension anisotropy and thus promoting tissue spreading during EVL epiboly.
We search for the best possible transmission for an external occulter coronagraph that is dedicated to the direct observation of terrestrial exoplanets. We show that better observation conditions are obtained when the flux in the focal plane is minimized in the zone in which the exoplanet is observed, instead of the total flux received by the telescope. We describe the transmission of the occulter as a sum of basis functions. For each element of the basis, we numerically computed the Fresnel diffraction at the aperture of the telescope and the complex amplitude at its focus. The basis functions are circular disks that are linearly apodized over a few centimeters (truncated cones). We complemented the numerical calculation of the Fresnel diffraction for these functions by a comparison with pure circular discs (cylinder) for which an analytical expression, based on a decomposition in Lommel series, is available. The technique of deriving the optimal transmission for a given spectral bandwidth is a classical regularized quadratic minimization of intensities, but linear optimizations can be used as well. Minimizing the integrated intensity on the aperture of the telescope or for selected regions of the focal plane leads to slightly different transmissions for the occulter. For the focal plane optimization, the resulting residual intensity is concentrated behind the geometrical image of the occulter, in a blind region for the observation of an exoplanet, and the level of background residual starlight becomes very low outside this image. Finally, we provide a tolerance analysis for the alignment of the occulter to the telescope which also favors the focal plane optimization.This means that telescope offsets of a few decimeters do not strongly reduce the efficiency of the occulter.
The present book is devoted to the construction of a new theory for the elementary particles. This theory was born in order to resolve some open issues of the Standard Model, among which the research of a general equation for the description of all quantum particles in a unique way. Starting from the Pauli equation, two relativistic partial differential equations are obtained, one to the first and other to the second order, which are able to describe particles with arbitrary spin. The analysis of the energetic spectrum concerning such equations puts in evidence that the particles they describe have an imaginary mass. Then, the probability density study of these equations shows the principle of causality is not satisfied. Therefore, these equations characterize the tachyonic universe. We can see such a universe admits spontaneous symmetry breaking. In general terms, we can establish the broken symmetry might be a global characteristic of the tachyonic universe, due to its negative square energy, which made it unstable. Hence, it is possible to assume that after the hot Big-Bang there was another catastrophic cosmological event - said Big-Break - which made to break down the tachyonic universe in a positive square energy one (bradyonic universe), and from which the four fundamental interactions are probably generated. The transition from tachyonic to bradyonic universe transforms the tachyonic equations in bradyonic ones, being then able to describe elementary particles with arbitrary spin. The first order partial differential equation gives asymmetric quantum states, while the second order partial differential equation gives symmetric quantum states and so they describe different theories. In the course of this work, both these theories will be studied. Either way, only one of the two could be the right theory of the elementary particles. Since this theory follows on from the Big-Bang, from the resultant tachyonic universe and from Big-Break, it has been called α-Theory, i.e. the "beginning theory." The α-Theory may theoretically predict the experimental properties of neutrinos and anti-neutrinos and allows, thanks to the appendix A, to generalize the concepts of the Dirac sea, Pauli exclusion principle and spin-statistics theorem, thus giving rise to "s-matter" and "multi-statistics," which are able to take an interesting approach for the explanation of the Dark Matter. Furthermore, it expects on large-scale the "double inflation" mechanism, which, without the Dark Energy, could explain the acceleration of our universe (bradyonic universe). From the α-Theory, two string actions can be deduced too, by which new ideas can be developed. Practically, the α-Theory wants to be a GUT, able to describe the quantum particles and our universe in a simple and elegant way.
À l'attention du déposant 
  • Le dépôt doit être effectué en accord avec les co-auteurs et dans le respect de la politique des éditeurs
  • La mise en ligne est assujettie à une modération, la direction de HAL se réservant le droit de refuser les articles ne correspondant pas aux critères de l'archive (voir le guide du déposant)
  • Tout dépôt est définitif, aucun retrait ne sera effectué après la mise en ligne de l'article
  • Consulter le ManuHAL
  • Les fichiers textes au format pdf ou les fichiers images composant votre dépôt sont maintenant envoyés au CINES dans un contexte d'archivage à long terme.
À l'attention des lecteurs 
  • Dans un contexte de diffusion électronique, tout auteur conserve ses droits intellectuels, notamment le fait de devoir être correctement cité et reconnu comme l'auteur d'un document.
Conditions d'utilisation 
  • Les métadonnées de HAL peuvent être consultées de façon totale ou partielle par moissonage OAI-PMH dans le respect du code de la propriété intellectuelle ;
  • Pas d'utilisation commerciale des données extraites ;
  • Obligation de citer la source (exemple : hal.archives-ouvertes.fr/hal-00000001).

  Déposer
Identifiant
Mot de passe
s'inscrireretrouver son mot de passe
  Documents avec texte intégral
313359
  Evolution des dépôts
  Contact
 - support.ccsd.cnrs.fr
 - 
  Actualités
Les services modération et support pendant les vacances scolaires (10/07/2014)
Quelques nouvelles de HAL v3 (10/07/2014)
Les nouveautés de HAL v3 (27/06/2014)
La première réunion du Comité Scientifique et Technique (11/06/2014)
  À voir

tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...
tous les articles de la base du CCSd...