6,873 research outputs found
Statistical analysis of network data and evolution on GPUs: High-performance statistical computing
Network analysis typically involves as set of repetitive tasks that are particularly amenable to poor-man's parallelization. This is therefore an ideal application are for GPU architectures, which help to alleviate the tedium inherent to statistically sound analysis of network data. Here we will illustrate the use of GPUs in a range of applications, which include percolation processes on networks, the evolution of protein-protein interaction networks, and the fusion of different types of biomedical and disease data in the context of molecular interaction networks. We will pay particular attention to the numerical performance of different routines that are frequently invoked in network analysis problems. We conclude with a review over recent developments in the generation of random numbers that address the specific requirements posed by GPUs and high-performance computing needs
John Wheeler, relativity, and quantum information
In spring 1952, as John Wheeler neared the end of design work for the first thermonuclear explosion, he plotted a radical change of research direction: from particles and atomic nuclei to general relativity
Bulletin No. 346 - Irrigation Waters of Utah
Irrigation waters are never pure. All contain some dissolved salts. The amount may vary from a trace to concentrations so great that the water is unfit for use. The kind of salt in irrigation water may be even more important than the total amount. Borates in extremely low quantities, for example, may injure or kill crop plants. If the proportion of sodium in irrigation water is high, the soil may be gradually rendered unproductive. On the other hand, the salts may consist in part of essential plant nutrients or other helpful salts that aid in keeping soils productive
Parton Distributions
I discuss our current understanding of parton distributions. I begin with the
underlying theoretical framework, and the way in which different data sets
constrain different partons, highlighting recent developments. The methods of
examining the uncertainties on the distributions and those physical quantities
dependent on them is analysed. Finally I look at the evidence that additional
theoretical corrections beyond NLO perturbative QCD may be necessary, what type
of corrections are indicated and the impact these may have on the
uncertainties.Comment: Invited talk at "XXI International Symposium on Lepton and Photon
Interactions at High Energies," (Fermilab, Chicago, August 2003). 12 pages,
21 figure
Waveless Approximation Theories of Gravity
The analysis of a general multibody physical system governed by Einstein's
equations in quite difficult, even if numerical methods (on a computer) are
used. Some of the difficulties -- many coupled degrees of freedom, dynamic
instability -- are associated with the presence of gravitational waves. We have
developed a number of ``waveless approximation theories'' (WAT) which repress
the gravitational radiation and thereby simplify the analysis. The matter,
according to these theories, evolves dynamically. The gravitational field,
however, is determined at each time step by a set of elliptic equations with
matter sources. There is reason to believe that for many physical systems, the
WAT-generated system evolution is a very accurate approximation to that
generated by the full Einstein theory
Estimating the spatial and temporal distribution of species richness within Sequoia and Kings Canyon National Parks.
Evidence for significant losses of species richness or biodiversity, even within protected natural areas, is mounting. Managers are increasingly being asked to monitor biodiversity, yet estimating biodiversity is often prohibitively expensive. As a cost-effective option, we estimated the spatial and temporal distribution of species richness for four taxonomic groups (birds, mammals, herpetofauna (reptiles and amphibians), and plants) within Sequoia and Kings Canyon National Parks using only existing biological studies undertaken within the Parks and the Parks' long-term wildlife observation database. We used a rarefaction approach to model species richness for the four taxonomic groups and analyzed those groups by habitat type, elevation zone, and time period. We then mapped the spatial distributions of species richness values for the four taxonomic groups, as well as total species richness, for the Parks. We also estimated changes in species richness for birds, mammals, and herpetofauna since 1980. The modeled patterns of species richness either peaked at mid elevations (mammals, plants, and total species richness) or declined consistently with increasing elevation (herpetofauna and birds). Plants reached maximum species richness values at much higher elevations than did vertebrate taxa, and non-flying mammals reached maximum species richness values at higher elevations than did birds. Alpine plant communities, including sagebrush, had higher species richness values than did subalpine plant communities located below them in elevation. These results are supported by other papers published in the scientific literature. Perhaps reflecting climate change: birds and herpetofauna displayed declines in species richness since 1980 at low and middle elevations and mammals displayed declines in species richness since 1980 at all elevations
Update of MRST parton distributions.
We discuss the latest update of the MRST parton distributions in response
to the most recent data. We discuss the areas where there are hints
of difficulties in the global fit, and compare to some other updated sets of
parton distributions, particularly CTEQ6. We briefly discuss the issue of
uncertainties associated with partons
Folklore: An Emerging Discipline — Selected Essays of Herbert Halpert. By Martin Lovelace, Paul Smith and J. D. A. Widdowson, eds. (St. John’s: Memorial University of Newfoundland Folklore and Language Publications, 2002. Pp. xxi + 398, ISBN 0-88901-335-7)
MRST global fit update.
We discuss the impact of the most recent data on the MRST global analysis -
in particular the new high-ET jet data and their implications for the gluon and
the new small x structure function data. In the light of these new data we also
consider the uncertainty in predictions for physical quantities depending on parton
distributions, concentrating on the W cross-section at hadron colliders
The geometry of a naked singularity created by standing waves near a Schwarzschild horizon, and its application to the binary black hole problem
The most promising way to compute the gravitational waves emitted by binary
black holes (BBHs) in their last dozen orbits, where post-Newtonian techniques
fail, is a quasistationary approximation introduced by Detweiler and being
pursued by Price and others. In this approximation the outgoing gravitational
waves at infinity and downgoing gravitational waves at the holes' horizons are
replaced by standing waves so as to guarantee that the spacetime has a helical
Killing vector field. Because the horizon generators will not, in general, be
tidally locked to the holes' orbital motion, the standing waves will destroy
the horizons, converting the black holes into naked singularities that resemble
black holes down to near the horizon radius. This paper uses a spherically
symmetric, scalar-field model problem to explore in detail the following BBH
issues: (i) The destruction of a horizon by the standing waves. (ii) The
accuracy with which the resulting naked singularity resembles a black hole.
(iii) The conversion of the standing-wave spacetime (with a destroyed horizon)
into a spacetime with downgoing waves by the addition of a ``radiation-reaction
field''. (iv) The accuracy with which the resulting downgoing waves agree with
the downgoing waves of a true black-hole spacetime (with horizon). The model
problem used to study these issues consists of a Schwarzschild black hole
endowed with spherical standing waves of a scalar field. It is found that the
spacetime metric of the singular, standing-wave spacetime, and its
radiation-reaction-field-constructed downgoing waves are quite close to those
for a Schwarzschild black hole with downgoing waves -- sufficiently close to
make the BBH quasistationary approximation look promising for
non-tidally-locked black holes.Comment: 12 pages, 6 figure
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