7,768 research outputs found
Slowly rotating charged fluid balls in the presence of a cosmological constant
We examine charged slowly rotating perfect fluids in the presence of a
cosmological constant. The asymptotic form of the vacuum solutions to the
linearised Einstein-Maxwell field equations is found and the possibility of
matching this vacuum to the slow rotating Garc\'ia metric is considered. We
show that, contrary to the case of zero cosmological constant, this Garc\'ia
metric can be matched to an asymptotically de Sitter vacuum in the slow
rotation limit. We conclude the Garc\'ia metric may potentially be suitable for
describing a charged isolated rotating body in a cosmological background.Comment: 14 pages, 1 figur
Buchdahl's inequality in five dimensional Gauss-Bonnet gravity
The Buchdahl limit for static spherically symmetric isotropic stars is
generalised to the case of five dimensional Gauss-Bonnet gravity. Our result
depends on the sign of the Gauss-Bonnet coupling constant . When
, we find, unlike in general relativity, that the bound is dependent
on the stellar structure, in particular the central energy density. We find
that stable stellar structures can exist arbitrarily close to the event
horizon. Thus stable stars can exist with extra mass in this theory compared to
five dimensional general relativity. For it is found that the
Buchdahl bound is more restrictive than the general relativistic case.Comment: Matches published versio
Hadwiger Integration of Random Fields
Hadwiger integrals employ the intrinsic volumes as measures for integration
of real-valued functions. We provide a formula for the expected values of
Hadwiger integrals of Gaussian-related random fields. The expected Hadwiger
integrals of random fields are both theoretically interesting and potentially
useful in applications such as sensor networks, image processing, and cell
dynamics. Furthermore, combining the expected integrals with a functional
version of Hadwiger's theorem, we obtain expected values of more general
valuations on Gaussian-related random fields
Audiovisual preservation strategies, data models and value-chains
This is a report on preservation strategies, models and value-chains for digital file-based audiovisual content. The report includes: (a)current and emerging value-chains and business-models for audiovisual preservation;(b) a comparison of preservation strategies for audiovisual content including their strengths and weaknesses, and(c) a review of current preservation metadata models, and requirements for extension to support audiovisual files
Fusing Loop and GPS Probe Measurements to Estimate Freeway Density
In an age of ever-increasing penetration of GPS-enabled mobile devices, the
potential of real-time "probe" location information for estimating the state of
transportation networks is receiving increasing attention. Much work has been
done on using probe data to estimate the current speed of vehicle traffic (or
equivalently, trip travel time). While travel times are useful to individual
drivers, the state variable for a large class of traffic models and control
algorithms is vehicle density. Our goal is to use probe data to supplement
traditional, fixed-location loop detector data for density estimation. To this
end, we derive a method based on Rao-Blackwellized particle filters, a
sequential Monte Carlo scheme. We present a simulation where we obtain a 30\%
reduction in density mean absolute percentage error from fusing loop and probe
data, vs. using loop data alone. We also present results using real data from a
19-mile freeway section in Los Angeles, California, where we obtain a 31\%
reduction. In addition, our method's estimate when using only the real-world
probe data, and no loop data, outperformed the estimate produced when only loop
data were used (an 18\% reduction). These results demonstrate that probe data
can be used for traffic density estimation
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