690 research outputs found
Immunoglobulin production is impaired in protein-deprived mice and can be restored by dietary protein supplementation
The MIDAS telescope for microwave detection of ultra-high energy cosmic rays
We present the design, implementation and data taking performance of the
MIcrowave Detection of Air Showers (MIDAS) experiment, a large field of view
imaging telescope designed to detect microwave radiation from extensive air
showers induced by ultra-high energy cosmic rays. This novel technique may
bring a tenfold increase in detector duty cycle when compared to the standard
fluorescence technique based on detection of ultraviolet photons. The MIDAS
telescope consists of a 4.5 m diameter dish with a 53-pixel receiver camera,
instrumented with feed horns operating in the commercial extended C-Band (3.4
-- 4.2 GHz). A self-trigger capability is implemented in the digital
electronics. The main objectives of this first prototype of the MIDAS telescope
- to validate the telescope design, and to demonstrate a large detector duty
cycle - were successfully accomplished in a dedicated data taking run at the
University of Chicago campus prior to installation at the Pierre Auger
Observatory.Comment: 13 pages, 18 figure
Energy and protein requirements of 3/4 Zebu × 1/4 Holstein crossbreds fed different calcium and phosphorus levels in the diet
Avalanche Dynamics in Evolution, Growth, and Depinning Models
The dynamics of complex systems in nature often occurs in terms of
punctuations, or avalanches, rather than following a smooth, gradual path. A
comprehensive theory of avalanche dynamics in models of growth, interface
depinning, and evolution is presented. Specifically, we include the Bak-Sneppen
evolution model, the Sneppen interface depinning model, the Zaitsev flux creep
model, invasion percolation, and several other depinning models into a unified
treatment encompassing a large class of far from equilibrium processes. The
formation of fractal structures, the appearance of noise, diffusion with
anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be
related to the same underlying avalanche dynamics. This dynamics can be
represented as a fractal in spatial plus one temporal dimension. We develop
a scaling theory that relates many of the critical exponents in this broad
category of extremal models, representing different universality classes, to
two basic exponents characterizing the fractal attractor. The exact equations
and the derived set of scaling relations are consistent with numerical
simulations of the above mentioned models.Comment: 27 pages in revtex, no figures included. Figures or hard copy of the
manuscript supplied on reques
System Test of the ATLAS Muon Spectrometer in the H8 Beam at the CERN SPS
An extensive system test of the ATLAS muon spectrometer has been performed in
the H8 beam line at the CERN SPS during the last four years. This spectrometer
will use pressurized Monitored Drift Tube (MDT) chambers and Cathode Strip
Chambers (CSC) for precision tracking, Resistive Plate Chambers (RPCs) for
triggering in the barrel and Thin Gap Chambers (TGCs) for triggering in the
end-cap region. The test set-up emulates one projective tower of the barrel
(six MDT chambers and six RPCs) and one end-cap octant (six MDT chambers, A CSC
and three TGCs). The barrel and end-cap stands have also been equipped with
optical alignment systems, aiming at a relative positioning of the precision
chambers in each tower to 30-40 micrometers. In addition to the performance of
the detectors and the alignment scheme, many other systems aspects of the ATLAS
muon spectrometer have been tested and validated with this setup, such as the
mechanical detector integration and installation, the detector control system,
the data acquisition, high level trigger software and off-line event
reconstruction. Measurements with muon energies ranging from 20 to 300 GeV have
allowed measuring the trigger and tracking performance of this set-up, in a
configuration very similar to the final spectrometer. A special bunched muon
beam with 25 ns bunch spacing, emulating the LHC bunch structure, has been used
to study the timing resolution and bunch identification performance of the
trigger chambers. The ATLAS first-level trigger chain has been operated with
muon trigger signals for the first time
Yield and mineral nutrition of soybean, maize, and Congo signal grass as affected by limestone and slag
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
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