11,705 research outputs found
Regularity of limit sets of AdS quasi-Fuchsian groups
Limit sets of -quasi-Fuchsian groups of are
always Lipschitz submanifolds. The aim of this article is to show that they are
never , except for the case of Fuchsian groups. As a byproduct
we show that -quasi-Fuchsian groups that are not Fuchsian are
Zariski dense in
On the controllability of the Vlasov-Poisson system in the presence of external force fields
In this work, we are interested in the controllability of Vlasov-Poisson
systems in the presence of an external force field (namely a bounded force
field or a magnetic field), by means of a local interior control. We are able
to extend the results of [7], where the only present force was the
self-consistent electric field
Disaster risk financing and contingent credit : a dynamic analysis
This paper aims to assist policy makers interested in establishing or strengthening financial strategies to increase the financial response capacity of developing country governments in the aftermath of natural disasters, while protecting their long-term fiscal balance. Contingent credit is shown to increase the ability of governments to self-insure by relaxing their short-term liquidity constraints. In many situations, contingent credit is most effectively used to facilitate risk retention for middle layers, with reserves used for bottom layers and risk transfer (for example, reinsurance) for top layers. Discussions with governments on the optimal use of contingent credit instruments as part of a sovereign catastrophe risk financing strategy can be guided by the output of a dynamic financial analysis model specifically developed to allow for the provision of contingent credit, in addition to reserves and/or reinsurance. This model is illustrated with three country case studies: agricultural production risks in India; tropical cyclone risk in Fiji; and earthquake risk in Costa Rica.Insurance&Risk Mitigation,Access to Finance,Debt Markets,Bankruptcy and Resolution of Financial Distress,Financial Intermediation
Hausdorff dimension of limit sets for projective Anosov representations
We study the relation between critical exponents and Hausdorff dimensions of
limit sets for projective Anosov representations. We prove that the Hausdorff
dimension of the symmetric limit set in is bounded between two critical exponents
associated respectively to a highest weight and a simple root
Do baryons trace dark matter in the early universe?
Baryon-density perturbations of large amplitude may exist if they are
compensated by dark-matter perturbations so that the total density remains
unchanged. Big-bang nucleosynthesis and galaxy clusters allow the amplitudes of
these compensated isocurvature perturbations (CIPs) to be as large as
. CIPs will modulate the power spectrum of cosmic microwave background
(CMB) fluctuations---those due to the usual adiabatic perturbations---as a
function of position on the sky. This leads to correlations between different
spherical-harmonic coefficients of the temperature/polarization map, and it
induces B modes in the CMB polarization. Here, the magnitude of these effects
is calculated and techniques to measure them are introduced. While a CIP of
this amplitude can be probed on the largest scales with WMAP, forthcoming CMB
experiments should improve the sensitivity to CIPs by at least an order of
magnitude.Comment: 4 pages, 3 figures, updated with version published in Phys. Rev.
Lett. Results unchanged. Added expanded discussion of how to disentangle
compensated isocurvature perturbations from weak lensing of the CMB. Expanded
discussion of early universe motivation for compensated isocurvature
perturbation
Unstationnary control of a launcher using observer-based structures
This paper deals with the design of a gain-scheduled
controller for the attitude control of a launcher during
atmospheric flight. The design is characterized by classical requirements such as phase/gain margins and flexible mode attenuations as well as time-domain constraints on the response of angle of attack to a worstcase wind profile. Moreover, these requirements must be fulfilled over the full atmospheric flight envelope and must be robust against parametric uncertainties. In order to achieve this goal, we propose a method based on minimal observer-based realizations of arbitrary stabilizing compensators. An original technique to assign the closed-loop dynamics between the state-feedback dynamics and the state-estimation dynamics is presented for the H∞ compensators case. The structure is used to mix various specifications through the Cross Standard Form(CSF) and to perform a smooth gain scheduling interpolation through an Euler-Newton algorithm of continuation
De l'utilisation de la structure estimation/commande pour le pilotage instationnaire d'un lanceur spatial
Dans cet article, nous nous intéressons au développement de techniques ayant trait à la mise sous forme LQG équivalente de correcteurs stabilisants. Dans un premier temps nous nous concentrerons plus particulièrement sur la transformation de correcteurs issus d'une synthèse Hinfinty. Nous proposons une méthode originale pour effectuer le choix des dynamiques d'estimation et de commande du correcteur équivalent en s'appuyant sur les résultats d'une synthèse H2. Puis nous proposerons une définition en temps discret de la Forme Standard de Passage (CSF) qui s'appuie également sur la paramétrisation de Youla sur la structure estimation /commande. Nous la présenterons en tant qu'outil méthodologique pour la mise en forme d'un problème multi-objectif. Nous mettrons en application la CSF sur le problème de pilotage d'un lanceur et nous montrerons l'intérêt de l'utilisation de la structure estimation/commande dans le cadre de l'inter-polation de correcteur pour le pilotage instationnaire
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