1,899 research outputs found
On the existence and convergence of polyhomogeneous expansions of zero-rest-mass fields
The convergence of polyhomogeneous expansions of zero-rest-mass fields in
asymptotically flat spacetimes is discussed. An existence proof for the
asymptotic characteristic initial value problem for a zero-rest-mass field with
polyhomogeneous initial data is given. It is shown how this non-regular problem
can be properly recast as a set of regular initial value problems for some
auxiliary fields. The standard techniques of symmetric hyperbolic systems can
be applied to these new auxiliary problems, thus yielding a positive answer to
the question of existence in the original problem.Comment: 10 pages, 1 eps figur
Can one detect a non-smooth null infinity?
It is shown that the precession of a gyroscope can be used to elucidate the
nature of the smoothness of the null infinity of an asymptotically flat
spacetime (describing an isolated body). A model for which the effects of
precession in the non-smooth null infinity case are of order is
proposed. By contrast, in the smooth version the effects are of order .
This difference should provide an effective criterion to decide on the nature
of the smoothness of null infinity.Comment: 6 pages, to appear in Class. Quantum Gra
Time asymmetric spacetimes near null and spatial infinity. I. Expansions of developments of conformally flat data
The Conformal Einstein equations and the representation of spatial infinity
as a cylinder introduced by Friedrich are used to analyse the behaviour of the
gravitational field near null and spatial infinity for the development of data
which are asymptotically Euclidean, conformally flat and time asymmetric. Our
analysis allows for initial data whose second fundamental form is more general
than the one given by the standard Bowen-York Ansatz. The Conformal Einstein
equations imply upon evaluation on the cylinder at spatial infinity a hierarchy
of transport equations which can be used to calculate in a recursive way
asymptotic expansions for the gravitational field. It is found that the the
solutions to these transport equations develop logarithmic divergences at
certain critical sets where null infinity meets spatial infinity. Associated to
these, there is a series of quantities expressible in terms of the initial data
(obstructions), which if zero, preclude the appearance of some of the
logarithmic divergences. The obstructions are, in general, time asymmetric.
That is, the obstructions at the intersection of future null infinity with
spatial infinity are different, and do not generically imply those obtained at
the intersection of past null infinity with spatial infinity. The latter allows
for the possibility of having spacetimes where future and past null infinity
have different degrees of smoothness. Finally, it is shown that if both sets of
obstructions vanish up to a certain order, then the initial data has to be
asymptotically Schwarzschildean to some degree.Comment: 32 pages. First part of a series of 2 papers. Typos correcte
Review of the Marine Monitoring Program (MMP)
The Marine Monitoring Program (MMP) monitors the condition of inshore water quality and aims to link this to changes in the health of key inshore environments (coral reefs and seagrass). This report provides a review of each of the 5 programs based on the best available information that was provided by the MMP providers at the time of the review
Brazilian vaccinia virus strains are genetically divergent and differ from the lister vaccine strain.
Vaccinia virus is responsible for an important zoonotic disease affecting dairy cattle and humans in Brazil, but little is known about the origin, epidemiology and evolution of these Brazilian Vaccinia virus strains. In this work, seven Brazilian Vaccinia virus strains and the Lister-derived Brazilian vaccine strain, named Lister-Butantan, were compared based on the sequences of ten host range and virulence related genes. Comparison of Brazilian Vaccinia virus strains with Lister-Butantan revealed several differences. Phylogenetic analyses confirmed the existence of genetically distinct Brazilian Vaccinia virus groups and has not thus far demonstrated a close relationship between Brazilian strains and Lister-Butantan. In this study, the BeAn58058 and SPAn232 strains were grouped together with the Belo Horizonte and Guarani P1 strains. Additionally, genetic polymorphisms in host range and virulence genes as well as differences in the deduced amino acid sequences were detected among Brazilian Vaccinia virus. This genetic diversity may result in a plethora of different biological properties presented by Brazilian Vaccinia virus, including differences in adaptation to the host as well as pathogenic properties. Furthermore, co-circulation of these divergent strains could increase the possibility of recombination events in nature, leading to the formation of new variants with unpredictable pathogenic potential
Boost-rotation symmetric type D radiative metrics in Bondi coordinates
The asymptotic properties of the solutions to the Einstein-Maxwell equations
with boost-rotation symmetry and Petrov type D are studied. We find series
solutions to the pertinent set of equations which are suitable for a late time
descriptions in coordinates which are well adapted for the description of the
radiative properties of spacetimes (Bondi coordinates). By calculating the
total charge, Bondi and NUT mass and the Newman-Penrose constants of the
spacetimes we provide a physical interpretation of the free parameters of the
solutions. Additional relevant aspects on the asymptotics and radiative
properties of the spacetimes considered, such as the possible polarization
states of the gravitational and electromagnetic field, are discussed through
the way
Finite-Size Scaling Studies of Reaction-Diffusion Systems Part III: Numerical Methods
The scaling exponent and scaling function for the 1D single species
coagulation model are shown to be universal, i.e. they are
not influenced by the value of the coagulation rate. They are independent of
the initial conditions as well. Two different numerical methods are used to
compute the scaling properties: Monte Carlo simulations and extrapolations of
exact finite lattice data. These methods are tested in a case where analytical
results are available. It is shown that Monte Carlo simulations can be used to
compute even the correction terms. To obtain reliable results from finite-size
extrapolations exact numerical data for lattices up to ten sites are
sufficient.Comment: 19 pages, LaTeX, 5 figures uuencoded, BONN HE-94-0
On de Sitter-like and Minkowski-like space-times
Friedrich's proofs for the global existence results of de Sitter-like
space-times and of semi-global existence of Minkowski-like space-times [Comm.
Math. Phys. \textbf{107}, 587 (1986)] are re-examined and discussed, making use
of the extended conformal field equations and a gauge based on conformal
geodesics. In this gauge the location of the conformal boundary of the
space-times is known \emph{a priori} once the initial data has been prescribed.
Thus it provides an analysis which is conceptually and calculationally simpler.Comment: 24 pages, typos corrected to match published version in CQ
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