57,918 research outputs found
Skinner-Rusk approach to time-dependent mechanics
The geometric approach to autonomous classical mechanical systems in terms of
a canonical first-order system on the Whitney sum of the tangent and cotangent
bundle, developed by R. Skinner and R. Rusk, is extended to the time-dependent
framework
Possible cosmological implications in electrodynamics due to variations of the fine structure constant
Astronomical observations are suggesting that the fine structure constant
varies cosmologically. We present an analysis on the consequences that these
variations might induce on the electromagnetic field as a whole. We show that
under these circumstances the electrodynamics in vacuum could be described by
two fields, the ``standard'' Maxwell's field and a new scalar field. We provide
a generalised Lorentz force which can be used to test our results
experimentally.Comment: 7 pages, no figures. Accepted for publication in Rev. Mex. Fis. (Some
extra information included, references added and small corrections made to
the original version
On the scalar curvature of constant mean curvature hypersurfaces in space forms
In this paper we study the behavior of the scalar curvature of a complete
hypersurface immersed with constant mean curvature into a Riemannian space form
of constant curvature, deriving a sharp estimate for the infimum of . Our
results will be an application of a weak Omori-Yau maximum principle due to
Pigola, Rigoli and Setti \cite{PRS}.Comment: Final version (August 2009). To appear in Journal of Mathematical
Analysis and Applications. Dedicated to Professor Marcos Dajczer on the
occasion of his 60th birthda
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