62 research outputs found
The volume flux group and nonpositive curvature
We show that every closed nonpositively curved manifold with non-trivial
volume flux group has zero minimal volume, and admits a finite covering with
circle actions whose orbits are homologically essential. This proves a
conjecture of Kedra-Kotschick-Morita for this class of manifolds.Comment: 6 pages, final version, to appear in Ann. Global Analysis and
Geometr
Entropies, volumes, and Einstein metrics
We survey the definitions and some important properties of several asymptotic
invariants of smooth manifolds, and discuss some open questions related to
them. We prove that the (non-)vanishing of the minimal volume is a
differentiable property, which is not invariant under homeomorphisms. We also
formulate an obstruction to the existence of Einstein metrics on four-manifolds
involving the volume entropy. This generalizes both the Gromov--Hitchin--Thorpe
inequality and Sambusetti's obstruction.Comment: This is a substantial revision and expansion of the 2004 preprint,
which I prepared in spring of 2010 and which has since been published. The
version here is essentially the published one, minus the problems introduced
by Springer productio
A simple proof of Perelman's collapsing theorem for 3-manifolds
We will simplify earlier proofs of Perelman's collapsing theorem for
3-manifolds given by Shioya-Yamaguchi and Morgan-Tian. Among other things, we
use Perelman's critical point theory (e.g., multiple conic singularity theory
and his fibration theory) for Alexandrov spaces to construct the desired local
Seifert fibration structure on collapsed 3-manifolds. The verification of
Perelman's collapsing theorem is the last step of Perelman's proof of
Thurston's Geometrization Conjecture on the classification of 3-manifolds. Our
proof of Perelman's collapsing theorem is almost self-contained, accessible to
non-experts and advanced graduate students. Perelman's collapsing theorem for
3-manifolds can be viewed as an extension of implicit function theoremComment: v1: 9 Figures. In this version, we improve the exposition of our
arguments in the earlier arXiv version. v2: added one more grap
Les instantanés, croquis et impressions de voyage d'un métromane. T. 1 / L.-D. Bessières
Contient une table des matière
Introduction à l'étude philosophique de la phrénologie et nouvelle classification des facultés cérébrales / par le Dr G.-L. Bessières
Contient une table des matièresAvec mode text
Ocean state indicators from MyOcean altimeter products
The European MyOcean project (<a href="http://www.myocean.eu.org"http://www.myocean.eu.org"_blank">http://www.myocean.eu.org</a>) provides observations of the ocean dynamic topography from altimeter measurements. Three specific indicators have been developed, based on altimeter data only, in order to monitor the ocean state. The first ocean indicator observes the positive and negative phases of the ENSO events in the tropical Pacific, the El Niño/La Niña events, since 1992. The second ocean indicator tracks the contracted or extended state of the Kuroshio Extension. The last ocean indicator is dedicated to the Ionian Basin in the Mediterranean Sea and permits separation of "zonal-cyclonic" state (1998–2005 and since 2011 up to now) from the "anticyclonic" state (1993–1996) usually discussed in the literature. In addition, it allows identifying a third state in which both the anticyclonic circulation around the northern part of the basin and the strong zonal Mid-Ionian Jet co-exist (2008–2010)
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