35,952 research outputs found
The Pierre Auger Observatory: Results on Ultra-High Energy Cosmic Rays
The focus of this article is on recent results on ultra-high energy cosmic
rays obtained with the Pierre Auger Observatory. The world's largest instrument
of this type and its performance are described. The observations presented here
include the energy spectrum, the primary particle composition, limits on the
fluxes of photons and neutrinos and a discussion of the anisotropic
distribution of the arrival directions of the most energetic particles.
Finally, plans for the construction of a Northern Auger Observatory in
Colorado, USA, are discussed.Comment: Proceedings of the International Workshop on Advances in Cosmic Ray
Science, Waseda University, Shinjuku, Tokyo, Japan, March 2008; to be
published in the Journal of the Physical Society of Japan (JPSJ) supplemen
Description of Atmospheric Conditions at the Pierre Auger Observatory Using Meteorological Measurements and Models
Atmospheric conditions at the site of a cosmic ray observatory must be known
well for reconstructing observed extensive air showers, especially when
measured using the fluorescence technique. For the Pierre Auger Observatory, a
sophisticated network of atmospheric monitoring devices has been conceived.
Part of this monitoring was a weather balloon program to measure atmospheric
state variables above the Observatory. To use the data in reconstructions of
air showers, monthly models have been constructed. Scheduled balloon launches
were abandoned and replaced with launches triggered by high-energetic air
showers as part of a rapid monitoring system. Currently, the balloon launch
program is halted and atmospheric data from numerical weather prediction models
are used. A description of the balloon measurements, the monthly models as well
as the data from the numerical weather prediction are presented
An Analytical Model for the Triaxial Collapse of Cosmological Perturbations
We present an analytical model for the non-spherical collapse of overdense
regions out of a Gaussian random field of initial cosmological perturbations.
The collapsing region is treated as an ellipsoid of constant density, acted
upon by the quadrupole tidal shear from the surrounding matter. The dynamics of
the ellipsoid is set by the ellipsoid self-gravity and the external quadrupole
shear. Both forces are linear in the coordinates and therefore maintain
homogeneity of the ellipsoid at all times. The amplitude of the external shear
is evolved into the non-linear regime in thin spherical shells that are allowed
to move only radially according to the mass interior to them. We describe how
the initial conditions can be drawn in the appropriate correlated way from a
random field of initial density perturbations. By considering many random
realizations of the initial conditions, we calculate the distribution of shapes
and angular momenta acquired by objects through the coupling of their
quadrupole moment to the tidal shear. The average value of the spin parameter,
0.04, is found to be only weakly dependent on the system mass, the mean
cosmological density, or the initial power spectrum of perturbations, in
agreement with N-body simulations. For the cold dark matter power spectrum,
most objects evolve from a quasi-spherical initial state to a pancake or
filament and then to complete virialization. Low-spin objects tend to be more
spherical. The evolution history of shapes is primarily induced by the external
shear and not by the initial triaxiality of the objects. The statistical
distribution of the triaxial shapes of collapsing regions can be used to test
cosmological models against galaxy surveys on large scales.Comment: 42 pages, Tex, followed by 10 uuencoded figure
A Hierarchical Bayesian Model of Pitch Framing
Since the advent of high-resolution pitch tracking data (PITCHf/x), many in
the sabermetrics community have attempted to quantify a Major League Baseball
catcher's ability to "frame" a pitch (i.e. increase the chance that a pitch is
called as a strike). Especially in the last three years, there has been an
explosion of interest in the "art of pitch framing" in the popular press as
well as signs that teams are considering framing when making roster decisions.
We introduce a Bayesian hierarchical model to estimate each umpire's
probability of calling a strike, adjusting for pitch participants, pitch
location, and contextual information like the count. Using our model, we can
estimate each catcher's effect on an umpire's chance of calling a strike.We are
then able to translate these estimated effects into average runs saved across a
season. We also introduce a new metric, analogous to Jensen, Shirley, and
Wyner's Spatially Aggregate Fielding Evaluation metric, which provides a more
honest assessment of the impact of framing
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