منابع مشابه
Singularities in Spatially Homogeneous, Dust-filled Cosmological Models.
Most cosmological models in general relativity have a point of singularity: There is a point, which can be reached by a geodesic of finite total length from other points of the space-time manifold, where the metric is degenerate or otherwise irregular (for example, a point where a curvature scalar is infinite). All known dust-filled models, without cosmological constant, have singular points,' ...
متن کاملCounting maps on doughnuts
Abstract. How many maps with V vertices and E edges can be drawn on a doughnut with G holes? I solved this problem for doughnuts with up to 10 holes, and my colleagues Alain Giorgetti and Alexander Mednykh counted maps by number of edges alone on doughnuts with up to 11 holes. This expository paper outlines, in terms meant to be understandable by a nonspecialist, the methods we used and those u...
متن کاملDust-Filled Axially Symmetric Universes with Cosmological Constant
Following the recent recognition of a positive value for the vacuum energy density and the realization that a simple Kantowski-Sachs model might fit the classical tests of cosmology, we study the qualitative behavior of three anisotropic and homogeneous models: Kantowski-Sachs, Bianchi type-I and Bianchi type-III universes, with dust and a cosmological constant, in order to find out which are p...
متن کاملMaking doughnuts of Cohen reals
For a ⊆ b ⊆ ω with b \ a infinite, the set D = {x ∈ [ω] : a ⊆ x ⊆ b} is called a doughnut. A set S ⊆ [ω] has the doughnut property D , if it contains or is disjoint from a doughnut. It is known that not every set S ⊆ [ω] has the doughnut property, but S has the doughnut property if it has the Baire property B or the Ramsey property R . In this paper it is shown that a finite support iteration o...
متن کاملInterrogating nanoparticles with focused doughnuts
The propagation of electromagnetic radiation in free-space is described by the source-free Maxwells equations. In contrast to conventional solutions such as infinite-energy plane waves and Gaussian pulses, there exists a family of exact solutions which represent localised transmission of finite electromagnetic energy [1]. One such solution is known as the Focused Doughnut (FD) pulse a peculiar ...
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ژورنال
عنوان ژورنال: Nature
سال: 2004
ISSN: 0028-0836,1476-4687
DOI: 10.1038/429029a