112 research outputs found
Constraints on the Ultra-High Energy Neutrino Flux from Gamma-Ray Bursts from a Prototype Station of the Askaryan Radio Array
We report on a search for ultra-high-energy (UHE) neutrinos from gamma-ray
bursts (GRBs) in the data set collected by the Testbed station of the Askaryan
Radio Array (ARA) in 2011 and 2012. From 57 selected GRBs, we observed no
events that survive our cuts, which is consistent with 0.12 expected background
events. Using NeuCosmA as a numerical GRB reference emission model, we estimate
upper limits on the prompt UHE GRB neutrino fluence and quasi-diffuse flux from
to GeV. This is the first limit on the prompt UHE GRB
neutrino quasi-diffuse flux above GeV.Comment: 14 pages, 8 figures, Published in Astroparticle Physics Journa
First Constraints on the Ultra-High Energy Neutrino Flux from a Prototype Station of the Askaryan Radio Array
The Askaryan Radio Array (ARA) is an ultra-high energy ( eV) cosmic
neutrino detector in phased construction near the South Pole. ARA searches for
radio Cherenkov emission from particle cascades induced by neutrino
interactions in the ice using radio frequency antennas ( MHz)
deployed at a design depth of 200 m in the Antarctic ice. A prototype ARA
Testbed station was deployed at m depth in the 2010-2011 season and
the first three full ARA stations were deployed in the 2011-2012 and 2012-2013
seasons. We present the first neutrino search with ARA using data taken in 2011
and 2012 with the ARA Testbed and the resulting constraints on the neutrino
flux from eV.Comment: 26 pages, 15 figures. Since first revision, added section on
systematic uncertainties, updated limits and uncertainty band with
improvements to simulation, added appendix describing ray tracing algorithm.
Final revision includes a section on cosmic ray backgrounds. Published in
Astropart. Phys.
Antarctic Surface Reflectivity Measurements from the ANITA-3 and HiCal-1 Experiments
The primary science goal of the NASA-sponsored ANITA project is measurement
of ultra-high energy neutrinos and cosmic rays, observed via radio-frequency
signals resulting from a neutrino- or cosmic ray- interaction with terrestrial
matter (atmospheric or ice molecules, e.g.). Accurate inference of the energies
of these cosmic rays requires understanding the transmission/reflection of
radio wave signals across the ice-air boundary. Satellite-based measurements of
Antarctic surface reflectivity, using a co-located transmitter and receiver,
have been performed more-or-less continuously for the last few decades.
Satellite-based reflectivity surveys, at frequencies ranging from 2--45 GHz and
at near-normal incidence, yield generally consistent reflectivity maps across
Antarctica. Using the Sun as an RF source, and the ANITA-3 balloon borne
radio-frequency antenna array as the RF receiver, we have also measured the
surface reflectivity over the interval 200-1000 MHz, at elevation angles of
12-30 degrees, finding agreement with the Fresnel equations within systematic
errors. To probe low incidence angles, inaccessible to the Antarctic Solar
technique and not probed by previous satellite surveys, a novel experimental
approach ("HiCal-1") was devised. Unlike previous measurements, HiCal-ANITA
constitute a bi-static transmitter-receiver pair separated by hundreds of
kilometers. Data taken with HiCal, between 200--600 MHz shows a significant
departure from the Fresnel equations, constant with frequency over that band,
with the deficit increasing with obliquity of incidence, which we attribute to
the combined effects of possible surface roughness, surface grain effects,
radar clutter and/or shadowing of the reflection zone due to Earth curvature
effects.Comment: updated to match publication versio
Electrolyte measurements differ between point-of-care and reference analysers in dogs with hypoadrenocorticism
Introduction:
Dogs treated for hypoadrenocorticism are monitored through analysis of their blood electrolytes. This is routinely performed with pointâofâcare analysers and doses of medications are adjusted based on the results.
Objectives:
To investigate the performance of two pointâofâcare analysers (IDEXX Catalyst Dx and IDEXX VetStat) against a reference laboratory method for the measurement of blood sodium, potassium and chloride concentrations, as well as sodium: potassium ratios, in dogs diagnosed with and treated for hypoadrenocorticism.
Methods:
Fortyâeight dogs were enrolled into a prospective crossâsectional study. Paired blood samples were taken and tested on two pointâofâcare analysers and at a reference laboratory. Statistical analysis was then performed with BlandâAltman analysis and PassingâBablok regression. The clinical effects of inaccurate electrolyte analysis were investigated.
Results:
In total, 329 samples were tested on the Catalyst analyser, while another 72 samples were tested on the VetStat. PassingâBablok regression identified both proportional and constant bias for some analytes. There was poor agreement between sodium and chloride concentrations on both analysers. Both analysers tended to give higher results than the reference method for all analytes, except for potassium when measured on the VetStat.
Clinical Significance:
There are inherent differences between the electrolyte concentrations measured by these two pointâofâcare analysers and reference laboratory methods in dogs with hypoadrenocorticism
Performance of two Askaryan Radio Array stations and first results in the search for ultra-high energy neutrinos
Ultra-high energy neutrinos are interesting messenger particles since, if
detected, they can transmit exclusive information about ultra-high energy
processes in the Universe. These particles, with energies above
, interact very rarely. Therefore, detectors that
instrument several gigatons of matter are needed to discover them. The ARA
detector is currently being constructed at South Pole. It is designed to use
the Askaryan effect, the emission of radio waves from neutrino-induced cascades
in the South Pole ice, to detect neutrino interactions at very high energies.
With antennas distributed among 37 widely-separated stations in the ice, such
interactions can be observed in a volume of several hundred cubic kilometers.
Currently 3 deep ARA stations are deployed in the ice of which two have been
taking data since the beginning of the year 2013. In this publication, the ARA
detector "as-built" and calibrations are described. Furthermore, the data
reduction methods used to distinguish the rare radio signals from overwhelming
backgrounds of thermal and anthropogenic origin are presented. Using data from
only two stations over a short exposure time of 10 months, a neutrino flux
limit of is
calculated for a particle energy of 10^{18}eV, which offers promise for the
full ARA detector.Comment: 21 pages, 34 figures, 1 table, includes supplementary materia
- âŠ