8,427 research outputs found
Existence of CMC Cauchy surfaces and spacetime splitting
In this paper, we review results on the existence (and nonexistence) of
constant mean curvature spacelike hypersurfaces in the cosmological setting,
and discuss the connection to the spacetime splittng problem. It is a pleasure
to dedicate this paper to Robert Bartnik, who has made fundamental
contributions to this area.Comment: 16 page
Nomenclatural notes on Pseudocyphellaria V : some Brazilian taxa
A new, phyllidiate, white-medulla species with yellow pseudocyphellae and a green photobiont, Pseudocyphellaria kalbii D.J.Galloway, is described from Brazilian collections, and typification and notes on P. aurora (De Not.) Vainio are presented
Studies on the lichen genus Sticta (Schreber) Ach. : 5., Australian species
Twenty five species of Sticta occur in Australia. These are: Sticta baileyi, S. brevipes, S. camarae, S. caperata, S. cyphellulata, S. diversa, S. duplolimbata, S. filix, S. flavocyphellata, S. fuliginosa, S. howei, S. hypopsiloides, S. latifrons, S. limbata, S. marginifera, S. myrioclada, S. pedunculata, S. rutilans, S. sayeri, S. stipitata, S. sublimbata, S. subtomentella, S. variabilis and S. weigelii. A key and descriptions of each taxon are given together with details of biogeography, distribution, ecology and nomenclature. Sticta baileyi, S. flavocyphellata and S. howei are newly described, and Sticta myrioloba (MĂĽll.Arg.) D.J.Galloway comb. & stat. nov., is proposed
Maximum Principles for Null Hypersurfaces and Null Splitting Theorems
A maximum principle for C^0 null hypersurfaces is obtained and used to derive
a splitting theorem for spacetimes which contain null lines. As a consequence
of this null splitting theorem, it is proved that an asymptotically simple
vacuum (Ricci flat) spacetime which contains a null line is isometric to
Minkowski space.Comment: 26 pages, latex2
Rigidity of outermost MOTS - the initial data version
In [5], a rigidity result was obtained for outermost marginally outer trapped
surfaces (MOTSs) that do not admit metrics of positive scalar curvature. This
allowed one to treat the "borderline case" in the author's work with R. Schoen
concerning the topology of higher dimensional black holes [8]. The proof of
this rigidity result involved bending the initial data manifold in the vicinity
of the MOTS within the ambient spacetime. In this note we show how to
circumvent this step, and thereby obtain a pure initial data version of this
rigidity result and its consequence concerning the topology of black holes.Comment: 8 pages; v2: minor changes; version to appear in GR
Historical development of noise exposure metrics
Some of the historical events that led to the introduction of night penalties are reported with emphasis on what happens with different kinds of day/night operations when night pentalties are employed. These effects are considered in terms of the difference between a nighttime weighting cumulative measure of noise exposure verses simply not using any night weighting at all, in decibles
dS/CFT and spacetime topology
Motivated by recent proposals for a de Sitter version of the AdS/CFT
correspondence, we give some topological restrictions on spacetimes of de
Sitter type, i.e., spacetimes with , which admit a regular past
and/or future conformal boundary. For example we show that if , , is a globally hyperbolic spacetime obeying suitable energy conditions,
which is of de Sitter type, with a conformal boundary to both the past and
future, then if one of these boundaries is compact, it must have finite
fundamental group and its conformal class must contain a metric of positive
scalar curvature. Our results are closely related to theorems of Witten and Yau
hep-th/9910245 pertaining to the Euclidean formulation of the AdS/CFT
correspondence.Comment: 16 pages, Latex2e, v2: reference corrected, v3: reference added,
material added to the introductio
Some uniqueness results for dynamical horizons
We first show that the intrinsic, geometrical structure of a dynamical
horizon is unique. A number of physically interesting constraints are then
established on the location of trapped and marginally trapped surfaces in the
vicinity of any dynamical horizon. These restrictions are used to prove several
uniqueness theorems for dynamical horizons. Ramifications of some of these
results to numerical simulations of black hole spacetimes are discussed.
Finally several expectations on the interplay between isometries and dynamical
horizons are shown to be borne out.Comment: 26 pages, 4 figures, v4: references updated, minor corrections, to
appear in Advances in Theoretical and Mathematical Physic
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