5,807 research outputs found
Low-Complexity Energy-Efficient Broadcasting in One-Dimensional Wireless Networks
In this paper, we investigate the transmission range assignment for N
wireless nodes located on a line (a linear wireless network) for broadcasting
data from one specific node to all the nodes in the network with minimum
energy. Our goal is to find a solution that has low complexity and yet performs
close to optimal. We propose an algorithm for finding the optimal assignment
(which results in the minimum energy consumption) with complexity O(N^2). An
approximation algorithm with complexity O(N) is also proposed. It is shown
that, for networks with uniformly distributed nodes, the linear-time
approximate solution obtained by this algorithm on average performs practically
identical to the optimal assignment. Both the optimal and the suboptimal
algorithms require the full knowledge of the network topology and are thus
centralized. We also propose a distributed algorithm of negligible complexity,
i.e., with complexity O(1), which only requires the knowledge of the adjacent
neighbors at each wireless node. Our simulations demonstrate that the
distributed solution on average performs almost as good as the optimal one for
networks with uniformly distributed nodes.Comment: 17 page
Crossing the Phantom Divide
We consider fluid perturbations close to the "phantom divide" characterised
by p = -rho and discuss the conditions under which divergencies in the
perturbations can be avoided. We find that the behaviour of the perturbations
depends crucially on the prescription for the pressure perturbation delta-p.
The pressure perturbation is usually defined using the dark energy rest-frame,
but we show that this frame becomes unphysical at the divide. If the pressure
perturbation is kept finite in any other frame, then the phantom divide can be
crossed. Our findings are important for generalised fluid dark energy used in
data analysis (since current cosmological data sets indicate that the dark
energy is characterised by p ~ -rho so that p < -rho cannot be excluded) as
well as for any models crossing the phantom divide, like some modified gravity,
coupled dark energy and braneworld models. We also illustrate the results by an
explicit calculation for the "Quintom" case with two scalar fields.Comment: 14 pages, 10 figures, v2: updated to agree with published version:
more readable figures, slightly expanded discussion on modified gravity
models and the interpolation across w=-1, results and conclusions unchange
Cosmic Microwave Background Anisotropies from Scaling Seeds: Fit to Observational Data
We compute cosmic microwave background angular power spectra for scaling seed
models of structure formation. A generic parameterization of the energy
momentum tensor of the seeds is employed. We concentrate on two regions of
parameter space inspired by global topological defects: O(4) texture models and
the large-N limit of O(N) models. We use fitting to compare these
models to recent flat-band power measurements of the cosmic microwave
background. Only scalar perturbations are considered.Comment: LaTeX file 4 pages, 4 postscript figs. revised version, to appear in
PR
Non-uniqueness, Counterrotation, and Negative Horizon Mass of Einstein-Maxwell-Chern-Simons Black Holes
Stationary black holes in 5-dimensional Einstein-Maxwell-Chern-Simons theory
possess surprising properties. When considering the Chern-Simons coefficient
as a parameter, two critical values of appear: the
supergravity value , and the value . At
, supersymmetric black holes with vanishing horizon angular
velocity, but finite angular momentum exist. As increases beyond
a rotational instability arises, and counterrotating black
holes appear, whose horizon rotates in the opposite sense to the angular
momentum. Thus supersymmetry is associated with the borderline between
stability and instability. At rotating black holes with vanishing
angular momentum emerge. Beyond black holes may possess a negative
horizon mass, while their total mass is positive. Charged rotating black holes
with vanishing gyromagnetic ratio appear, and black holes are no longer
uniquely characterized by their global charges.Comment: 15 pages, 16 figures, MPLA style, invited review for Modern Physics
Letters
Vapor chamber fin studies. Operating characteristics of fin models
Operating characteristics and limits of vapor chamber fins or heat pipe
Vapor-chamber fin studies First quarterly report, May 28 - Aug. 28, 1965
Mechanistic model and vapor-chamber fin heat transport operation for application to space power plant radiator
Ar-40 to Ar-39 dating of pseudotachylites from the Witwatersrand basin, South Africa, with implications for the formation of the Vredefort Dome
The formation of the Vredefort Dome, a structure in excess of 100 km in diameter and located in the approximate center of the Witwatersrand basin, is still the subject of lively geological controversy. It is widely accepted that its formation seems to have taken place in a single sudden event, herein referred to as the Vredefort event, accompanied by the release of gigantic amounts of energy. It is debated, however, whether this central event was an internal one, i.e., a cryptoexplosion triggered by volcanic or tectonic processes, or the impact of an extraterrestrial body. The results of this debate are presented
Measuring the effective complexity of cosmological models
We introduce a statistical measure of the effective model complexity, called
the Bayesian complexity. We demonstrate that the Bayesian complexity can be
used to assess how many effective parameters a set of data can support and that
it is a useful complement to the model likelihood (the evidence) in model
selection questions. We apply this approach to recent measurements of cosmic
microwave background anisotropies combined with the Hubble Space Telescope
measurement of the Hubble parameter. Using mildly non-informative priors, we
show how the 3-year WMAP data improves on the first-year data by being able to
measure both the spectral index and the reionization epoch at the same time. We
also find that a non-zero curvature is strongly disfavored. We conclude that
although current data could constrain at least seven effective parameters, only
six of them are required in a scheme based on the Lambda-CDM concordance
cosmology.Comment: 9 pages, 4 figures, revised version accepted for publication in PRD,
updated with WMAP3 result
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