1,410 research outputs found
The Non-homogeneous Poisson Process for Fast Radio Burst Rates
This paper presents the non-homogeneous Poisson process (NHPP) for modeling
the rate of fast radio bursts (FRBs) and other infrequently observed
astronomical events. The NHPP, well-known in statistics, can model changes in
the rate as a function of both astronomical features and the details of an
observing campaign. This is particularly helpful for rare events like FRBs
because the NHPP can combine information across surveys, making the most of all
available information. The goal of the paper is two-fold. First, it is intended
to be a tutorial on the use of the NHPP. Second, we build an NHPP model that
incorporates beam patterns and a power law flux distribution for the rate of
FRBs. Using information from 12 surveys including 15 detections, we find an
all-sky FRB rate of 586.88 events per sky per day above a flux of 1 Jy (95\%
CI: 271.86, 923.72) and a flux power-law index of 0.91 (95\% CI: 0.57, 1.25).
Our rate is lower than other published rates, but consistent with the rate
given in Champion et al. 2016.Comment: 19 pages, 2 figure
How do hotel and tourism students select internship employers? a segmentation approach
The major objective of this study is to segment the hotel and tourism students into groups based on their perceived importance of the criteria for selecting internship employers, which is grounded in the expectancy theory and job choice framework. Drawing from a self-administered survey of 273 hotel and tourism management college students in Hong Kong, the study used cluster analysis to generate four clusters of students, namely learning enthusiasts, social support seekers, brand seekers, and school followers. Chi-square tests showed that school followers generally do not have internship experience. Implications for educators and internship employers are discussed in the paper
Out-of-Basin Water Exports in Colorado
14 p. ; 28 cmhttps://scholar.law.colorado.edu/books_reports_studies/1118/thumbnail.jp
Out-of-Basin Water Exports in Colorado
14 p. ; 28 cmhttps://scholar.law.colorado.edu/books_reports_studies/1118/thumbnail.jp
Regulation of Wastes from the Metals Mining Industry: The Shape of Things to Come
32 p. ; 28 cmhttps://scholar.law.colorado.edu/books_reports_studies/1123/thumbnail.jp
New Options for the Lower Colorado River Basin
53 leaves ; 29 cmhttps://scholar.law.colorado.edu/books_reports_studies/1048/thumbnail.jp
Regulation of Wastes from the Metals Mining Industry: The Shape of Things to Come
32 p. ; 28 cmhttps://scholar.law.colorado.edu/books_reports_studies/1123/thumbnail.jp
A Millisecond Interferometric Search for Fast Radio Bursts with the Very Large Array
We report on the first millisecond timescale radio interferometric search for
the new class of transient known as fast radio bursts (FRBs). We used the Very
Large Array (VLA) for a 166-hour, millisecond imaging campaign to detect and
precisely localize an FRB. We observed at 1.4 GHz and produced visibilities
with 5 ms time resolution over 256 MHz of bandwidth. Dedispersed images were
searched for transients with dispersion measures from 0 to 3000 pc/cm3. No
transients were detected in observations of high Galactic latitude fields taken
from September 2013 though October 2014. Observations of a known pulsar show
that images typically had a thermal-noise limited sensitivity of 120 mJy/beam
(8 sigma; Stokes I) in 5 ms and could detect and localize transients over a
wide field of view. Our nondetection limits the FRB rate to less than
7e4/sky/day (95% confidence) above a fluence limit of 1.2 Jy-ms. Assuming a
Euclidean flux distribution, the VLA rate limit is inconsistent with the
published rate of Thornton et al. We recalculate previously published rates
with a homogeneous consideration of the effects of primary beam attenuation,
dispersion, pulse width, and sky brightness. This revises the FRB rate downward
and shows that the VLA observations had a roughly 60% chance of detecting a
typical FRB and that a 95% confidence constraint would require roughly 500
hours of similar VLA observing. Our survey also limits the repetition rate of
an FRB to 2 times less than any known repeating millisecond radio transient.Comment: Submitted to ApJ. 13 pages, 9 figure
Integrated Polarization of Sources at lambda ~1m and New Rotation Measure Ambiguities
We present an analysis of the polarization of compact radio sources from six
pointings of the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz with
35% coverage in lambda^2. After correcting for the off-axis instrumental
polarization with a simple analytical model, only a small number of 585 strong
sources have significant polarizations at these wavelengths. The median
depolarization ratio from 1.4 GHz for the strongest sources is <0.2,
reinforcing the likelihood that radio galaxies are found in magnetized
environments, even outside of rich clusters. Seven sources with significant 350
MHz polarization were selected for a more in-depth Faraday structure analysis.
We fit the observed values Q/I and U/I as a function of lambda^2 using both a
depolarizing screen and two component models. We also performed RM
Synthesis/Clean and standard fitting of polarization angle vs. lambda^2. We
find that a single rotation measure (RM), as found using polarization angle
fitting or simple screen models, commonly provides a poor fit when the
solutions are translated back into Q, U space. Thus, although a single
"characteristic" rotation measure may be found using these techniques, the
Faraday structure of the source may not be adequately represented. We also
demonstrate that RM Synthesis may yield an erroneous Faraday structure in the
presence of multiple, interfering RM components, even when cleaning of the
Faraday spectrum is performed. We briefly explore the conditions under which
rotation measures and Faraday structure results can be reliable. Many
measurements in the literature do not meet these criteria; we discuss how these
influence the resulting scientific conclusions and offer a prescription for
obtaining reliable RMs.Comment: 26 pages, 24 figures. Published in The Astronomical Journa
National Interests in Instream Flows
p. 69-86 ; 23 cmhttps://scholar.law.colorado.edu/books_reports_studies/1108/thumbnail.jp
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