3,897 research outputs found
Atmospheric Calorimetry above 10 eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory
The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a
calorimeter to measure extensive air-showers created by particles of
astrophysical origin. Some of these particles carry joules of energy. At these
extreme energies, test beams are not available in the conventional sense. Yet
understanding the energy response of the observatory is important. For example,
the propagation distance of the highest energy cosmic-rays through the cosmic
microwave background radiation (CMBR) is predicted to be strong function of
energy. This paper will discuss recently reported results from the observatory
and the use of calibrated pulsed UV laser "test-beams" that simulate the
optical signatures of ultra-high energy cosmic rays. The status of the much
larger 200,000 km companion detector planned for the northern hemisphere
will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in
High Energy Physic
Impact of Interatomic Electronic Decay Processes on Xe 4d Hole Decay in the Xenon Fluorides
A hole in a 4d orbital of atomic xenon relaxes through Auger decay after a
lifetime of 3 fs. Adding electronegative fluorine ligands to form xenon
fluoride molecules, results in withdrawal of valence-electron density from Xe.
Thus, within the one-center picture of Auger decay, a lowered Xe 4d Auger width
would be expected, in contradiction, however, with experiment. Employing
extensive ab initio calculations within the framework of many-body Green's
functions, we determine all available decay channels in XeFn and characterize
these channels by means of a two-hole population analysis. We derive a relation
between two-hole population numbers and partial Auger widths. On this basis,
interatomic electronic decay processes are demonstrated to be so strong in the
xenon fluorides that they overcompensate the reduction in intra-atomic Auger
width and lead to the experimentally observed trend. The nature of the relevant
processes is discussed. These processes presumably underlie Auger decay in a
variety of systems.Comment: 11 pages, 5 figures, 3 tables, RevTeX4, extensively revised, the
discussion of single ionization of XeFn was published separately: J. Chem.
Phys. 119, 7763--7771 (2003), preprint arXiv: physics/030612
Resolving on 100 pc scales the UV-continuum in Lyman- emitters between redshift 2 to 3 with gravitational lensing
We present a study of seventeen LAEs at redshift 23 gravitationally
lensed by massive early-type galaxies (ETGs) at a mean redshift of
approximately 0.5. Using a fully Bayesian grid-based technique, we model the
gravitational lens mass distributions with elliptical power-law profiles and
reconstruct the UV-continuum surface brightness distributions of the background
sources using pixellated source models. We find that the deflectors are close
to, but not consistent with isothermal models in almost all cases, at the
-level. We take advantage of the lensing magnification (typically
20) to characterise the physical and morphological properties of
these LAE galaxies. From reconstructing the ultra-violet continuum emission, we
find that the star-formation rates range from 0.3 to 8.5 M yr
and that the galaxies are typically composed of several compact and diffuse
components, separated by 0.4 to 4 kpc. Moreover, they have peak star-formation
rate intensities that range from 2.1 to 54.1 M yr kpc.
These galaxies tend to be extended with major axis ranging from 0.2 to 1.8 kpc
(median 561 pc), and with a median ellipticity of 0.49. This morphology is
consistent with disk-like structures of star-formation for more than half of
the sample. However, for at least two sources, we also find off-axis components
that may be associated with mergers. Resolved kinematical information will be
needed to confirm the disk-like nature and possible merger scenario for the
LAEs in the sample.Comment: 19 pages, 7 figures, accepted for publication on MNRA
A system for online beam emittance measurements and proton beam characterization
A system for online measurement of the transverse beam emittance was
developed. It is named PrOBaM (4-Profiler Online Beam
Emittance Measurement) and was conceived to measure the emittance in a fast and
efficient way using the multiple beam profiler method. The core of the system
is constituted by four consecutive UniBEaM profilers, which are based on silica
fibers passing across the beam. The PrOBaM system was
deployed for characterization studies of the 18~MeV proton beam produced by the
IBA Cyclone 18 MeV cyclotron at Bern University Hospital (Inselspital). The
machine serves daily radioisotope production and multi-disciplinary research,
which is carried out with a specifically conceived Beam Transport Line (BTL).
The transverse RMS beam emittance of the cyclotron was measured as a function
of several machine parameters, such as the magnetic field, RF peak voltage, and
azimuthal angle of the stripper. The beam emittance was also measured using the
method based on the quadrupole strength variation. The results obtained with
both techniques were compared and a good agreement was found. In order to
characterize the longitudinal dynamics, the proton energy distribution was
measured. For this purpose, a method was developed based on aluminum absorbers
of different thicknesses, a UniBEaM detector, and a Faraday cup. The results
were an input for a simulation of the BTL developed in the MAD-X software. This
tool allows machine parameters to be tuned online and the beam characteristics
to be optimized for specific applications.Comment: published in Journal of Instrumentatio
Recent results from the Pierre Auger Observatory
The main results from the Auger Observatory are described. A steepening of
the spectrum is observed at the highest energies, supporting the expectation
that above eV the cosmic ray energies are significantly
degraded by interactions with the CMB photons (the GZK effect). This is further
supported by the correlations observed above eV with the
distribution of nearby active galaxies, which also show the potential of Auger
to start the era of charged particle astronomy. The lack of observation of
photons or neutrinos strongly disfavors top-down models, and these searches may
approach in the long term the sensitivity required to test the fluxes expected
from the secondaries of the very same GZK process. Bounds on the anisotropies
at EeV energies contradict hints from previous experiments that suggested a
large excess from regions near the Galactic centre or the presence of a dipolar
type modulation of the cosmic ray flux.Comment: 6 p., 8 figs., proceedings of the XXIII International Conference on
Neutrino Physics and Astrophysics (Neutrino 08
Inference of the Cold Dark Matter substructure mass function at z=0.2 using strong gravitational lenses
We present the results of a search for galaxy substructures in a sample of 11
gravitational lens galaxies from the Sloan Lens ACS Survey. We find no
significant detection of mass clumps, except for a luminous satellite in the
system SDSS J0956+5110. We use these non-detections, in combination with a
previous detection in the system SDSS J0946+1006, to derive constraints on the
substructure mass function in massive early-type host galaxies with an average
redshift z ~ 0.2 and an average velocity dispersion of 270 km/s. We perform a
Bayesian inference on the substructure mass function, within a median region of
about 32 kpc squared around the Einstein radius (~4.2 kpc). We infer a mean
projected substructure mass fraction at the 68
percent confidence level and a substructure mass function slope < 2.93
at the 95 percent confidence level for a uniform prior probability density on
alpha. For a Gaussian prior based on Cold Dark Matter (CDM) simulations, we
infer and a slope of =
1.90 at the 68 percent confidence level. Since only one
substructure was detected in the full sample, we have little information on the
mass function slope, which is therefore poorly constrained (i.e. the Bayes
factor shows no positive preference for any of the two models).The inferred
fraction is consistent with the expectations from CDM simulations and with
inference from flux ratio anomalies at the 68 percent confidence level.Comment: Accepted for publication on MNRAS, some typos corrected and some
important references adde
A Three-Point Cosmic Ray Anisotropy Method
The two-point angular correlation function is a traditional method used to
search for deviations from expectations of isotropy. In this paper we develop
and explore a statistically descriptive three-point method with the intended
application being the search for deviations from isotropy in the highest energy
cosmic rays. We compare the sensitivity of a two-point method and a
"shape-strength" method for a variety of Monte-Carlo simulated anisotropic
signals. Studies are done with anisotropic source signals diluted by an
isotropic background. Type I and II errors for rejecting the hypothesis of
isotropic cosmic ray arrival directions are evaluated for four different event
sample sizes: 27, 40, 60 and 80 events, consistent with near term data
expectations from the Pierre Auger Observatory. In all cases the ability to
reject the isotropic hypothesis improves with event size and with the fraction
of anisotropic signal. While ~40 event data sets should be sufficient for
reliable identification of anisotropy in cases of rather extreme (highly
anisotropic) data, much larger data sets are suggested for reliable
identification of more subtle anisotropies. The shape-strength method
consistently performs better than the two point method and can be easily
adapted to an arbitrary experimental exposure on the celestial sphere.Comment: Fixed PDF erro
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A Difference-in-Differences Approach to Assess the Effect of a Heat Action Plan on Heat-Related Mortality, and Differences in Effectiveness According to Sex, Age, and Socioeconomic Status (Montreal, Quebec).
BackgroundThe impact of heat waves on mortality and health inequalities is well documented. Very few studies have assessed the effectiveness of heat action plans (HAPs) on health, and none has used quasi-experimental methods to estimate causal effects of such programs.ObjectivesWe developed a quasi-experimental method to estimate the causal effects associated with HAPs that allows the identification of heterogeneity across subpopulations, and to apply this method specifically to the case of the Montreal (Quebec, Canada) HAP.MethodsA difference-in-differences approach was undertaken using Montreal death registry data for the summers of 2000-2007 to assess the effectiveness of the Montreal HAP, implemented in 2004, on mortality. To study equity in the effect of HAP implementation, we assessed whether the program effects were heterogeneous across sex (male vs. female), age (≥ 65 years vs. < 65 years), and neighborhood education levels (first vs. third tertile). We conducted sensitivity analyses to assess the validity of the estimated causal effect of the HAP program.ResultsWe found evidence that the HAP contributed to reducing mortality on hot days, and that the mortality reduction attributable to the program was greater for elderly people and people living in low-education neighborhoods.ConclusionThese findings show promise for programs aimed at reducing the impact of extreme temperatures and health inequities. We propose a new quasi-experimental approach that can be easily applied to evaluate the impact of any program or intervention triggered when daily thresholds are reached. Citation: Benmarhnia T, Bailey Z, Kaiser D, Auger N, King N, Kaufman J. 2016. A difference-in-differences approach to assess the effect of a heat action plan on heat-related mortality, and differences in effectiveness according to sex, age, and socioeconomic status (Montreal, Quebec). Environ Health Perspect 124:1694-1699; http://dx.doi.org/10.1289/EHP203
Results of a self-triggered prototype system for radio-detection of extensive air showers at the Pierre Auger Observatory
We describe the experimental setup and the results of RAuger, a small
radio-antenna array, consisting of three fully autonomous and self-triggered
radio-detection stations, installed close to the center of the Surface Detector
(SD) of the Pierre Auger Observatory in Argentina. The setup has been designed
for the detection of the electric field strength of air showers initiated by
ultra-high energy cosmic rays, without using an auxiliary trigger from another
detection system. Installed in December 2006, RAuger was terminated in May 2010
after 65 registered coincidences with the SD. The sky map in local angular
coordinates (i.e., zenith and azimuth angles) of these events reveals a strong
azimuthal asymmetry which is in agreement with a mechanism dominated by a
geomagnetic emission process. The correlation between the electric field and
the energy of the primary cosmic ray is presented for the first time, in an
energy range covering two orders of magnitude between 0.1 EeV and 10 EeV. It is
demonstrated that this setup is relatively more sensitive to inclined showers,
with respect to the SD. In addition to these results, which underline the
potential of the radio-detection technique, important information about the
general behavior of self-triggering radio-detection systems has been obtained.
In particular, we will discuss radio self-triggering under varying local
electric-field conditions.Comment: accepted for publication in JINS
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