11,933 research outputs found
A review of High Performance Computing foundations for scientists
The increase of existing computational capabilities has made simulation
emerge as a third discipline of Science, lying midway between experimental and
purely theoretical branches [1, 2]. Simulation enables the evaluation of
quantities which otherwise would not be accessible, helps to improve
experiments and provides new insights on systems which are analysed [3-6].
Knowing the fundamentals of computation can be very useful for scientists, for
it can help them to improve the performance of their theoretical models and
simulations. This review includes some technical essentials that can be useful
to this end, and it is devised as a complement for researchers whose education
is focused on scientific issues and not on technological respects. In this
document we attempt to discuss the fundamentals of High Performance Computing
(HPC) [7] in a way which is easy to understand without much previous
background. We sketch the way standard computers and supercomputers work, as
well as discuss distributed computing and discuss essential aspects to take
into account when running scientific calculations in computers.Comment: 33 page
On the distribution of career longevity and the evolution of home run prowess in professional baseball
Statistical analysis is a major aspect of baseball, from player averages to
historical benchmarks and records. Much of baseball fanfare is based around
players exceeding the norm, some in a single game and others over a long
career. Career statistics serve as a metric for classifying players and
establishing their historical legacy. However, the concept of records and
benchmarks assumes that the level of competition in baseball is stationary in
time. Here we show that power-law probability density functions, a hallmark of
many complex systems that are driven by competition, govern career longevity in
baseball. We also find similar power laws in the density functions of all major
performance metrics for pitchers and batters. The use of performance-enhancing
drugs has a dark history, emerging as a problem for both amateur and
professional sports. We find statistical evidence consistent with
performance-enhancing drugs in the analysis of home runs hit by players in the
last 25 years. This is corroborated by the findings of the Mitchell Report [1],
a two-year investigation into the use of illegal steroids in major league
baseball, which recently revealed that over 5 percent of major league baseball
players tested positive for performance-enhancing drugs in an anonymous 2003
survey.Comment: 5 pages, 5 figures, 2-column revtex4 format. Revision has change of
title, a figure added, and minor changes in response to referee comment
Linguistics
Contains reports on four research projects.National Institutes of Health (Grant MH-13390-01U. S. Air Force (Electronic Systems Division) under Contract AF 19(628)-248
Irreversible Deposition of Line Segment Mixtures on a Square Lattice: Monte Carlo Study
We have studied kinetics of random sequential adsorption of mixtures on a
square lattice using Monte Carlo method. Mixtures of linear short segments and
long segments were deposited with the probability and , respectively.
For fixed lengths of each segment in the mixture, the jamming limits decrease
when increases. The jamming limits of mixtures always are greater than
those of the pure short- or long-segment deposition.
For fixed and fixed length of the short segments, the jamming limits have
a maximum when the length of the long segment increases. We conjectured a
kinetic equation for the jamming coverage based on the data fitting.Comment: 7 pages, latex, 5 postscript figure
Application of a MHD hybrid solar wind model with latitudinal dependences to Ulysses data at minimum
In a previous work, Ulysses data was analyzed to build a complete
axisymmetric MHD solution for the solar wind at minimum including rotation and
the initial flaring of the solar wind in the low corona. This model has some
problems in reproducing the values of magnetic field at 1 AU despite the
correct values of the velocity. Here, we intend to extend the previous analysis
to another type of solutions and to improve our modelling of the wind from the
solar surface to 1 AU. We compare the previous results to those obtained with a
fully helicoidal model and construct a hybrid model combining both previous
solutions, keeping the flexibility of the parent models in the appropriate
domain. From the solar surface to the Alfven, point, a three component solution
for velocity and magnetic field is used, reproducing the complex wind geometry
and the well-known flaring of the field lines observed in coronal holes. From
the Alfven radius to 1 AU and further, the hybrid model keeps the latitudinal
dependences as flexible as possible, in order to deal with the sharp variations
near the equator and we use the helicoidal solution, turning the poloidal
streamlines into radial ones. Despite the absence of the initial flaring, the
helicoidal model and the first hybrid solution suffer from the same low values
of the magnetic field at 1 AU. However, by adjusting the parameters with a
second hybrid solution, we are able to reproduce both the velocity and magnetic
profiles observed by Ulysses and a reasonable description of the low corona,
provided that a certain amount of energy deposit exists along the flow. The
present paper shows that analytical axisymmetric solutions can be constructed
to reproduce the solar structure and dynamics from 1 solar radius up to 1 AU.Comment: 12 pages, 16 figure
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