133 research outputs found
The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies
Although numerous simulations have been done to understand the effects of
intense bursts of star formation on high surface brightness galaxies, few
attempts have been made to understand how localized starbursts would affect
both the color and surface brightness of low surface brightness (LSB) galaxies.
To remedy this, we have run 53 simulations involving bursts of star formation
activity on LSB galaxies, varying both the underlying galaxy properties and the
parameters describing the starbursts. We discovered that although changing the
total color of a galaxy was fairly straightforward, it was virtually impossible
to alter a galaxy's central surface brightness and thereby remove it from the
LSB galaxy classification without placing a high (and fairly artificial)
threshold for the underlying gas density. The primary effect of large amounts
of induced star formation was to produce a centralized core (bulge) component
which is generally not observed in LSB galaxies. The noisy morphological
appearance of LSB galaxies as well as their noisy surface brightness profiles
can be reproduced by considering small bursts of star formation that are
localized within the disk. The trigger mechanism for such bursts is likely
distant/weak tidal encounters. The stability of disk central surface brightness
to these periods of star formation argues that the large space density of LSB
galaxies at z = 0 should hold to substantially higher redshifts.Comment: 38 pages, 5 figures, 4 tables, tarred and compressed Also available
on http://guernsey.uoregon.edu/~kare
All-Stokes Parameterization of the Main Beam and First Sidelobe for the Arecibo Radio Telescope
We describe a scheme that characterizes the main beam and sidelobe in all
Stokes parameters employing parameters that allow reconstruction of the
complete beam patterns and, also, afford an easy way to see how the beam
changes with azimuth, zenith angle, and time. For the main beam in Stokes I the
parameters include the beam width, ellipticity and its orientation, coma and
its orientation, the point-source gain, the integrated gain (or, equivalently,
the main beam efficiency); for the other Stokes parameters the beam parameters
include beam squint and beam squash. For the first sidelobe ring in Stokes I
the parameters include an 8-term Fourier series describing the height, radius,
and radial width; for the other Stokes parameters they include only the
sidelobe's fractional polarization.
We illustrate the technique by applying it to the Arecibo telescope. The main
beam width is smaller and the sidelobe levels higher than for a
uniformly-illuminated aperture of the same effective area. These effects are
modeled modestly well by a blocked aperture, with the blocked area equal to
about 10% of the effective area (this corresponds to 5% physical blockage). In
polarized emission, the effects of beam squint (difference in pointing
direction between orthogonal polarizations) and squash (difference in beamwidth
between orthogonal polarizations) do not correspond to theoretical expectation
and are higher than expected; these effects are almost certainly caused by the
blockage. The first sidelobe is highly polarized because of blockage.Comment: 42 pages, 18 figures, accepted by PAS
HST WFPC2 Imaging of Three Low Surface Brightness Dwarf Elliptical Galaxies in the Virgo Cluster
[annotated] HST WFPC2 images were taken of three LSB dwarf elliptical
galaxies in the Virgo cluster. The intent of the observations was to determine
the small scale structure in these enigmatic galaxies, and to attempt to learn
something about the nature of their giant branch through the detection of
luminosity fluctuations. In two of the three studied galaxies, V7L3 and V1L4,
the luminosity fluctuations were unambiguously detected, yielding a density of
2 - 10 red giants/pixel. Using the observed B-V and V-I colors as a constraint,
we could find no model that would reproduce the observed fluctuation signal and
blue colors if there was a significant population of M-giants in these systems.
The third system, V2L8, did not have a detectable fluctuation signal which
possibly implies it is not in the Virgo cluster. Interestingly, this system is
highly nucleated. Our observations have resolved this nucleus and if V2L8 is in
Virgo, then we have discovered what is likely the smallest bulge measured to
date, having an effective radius of only 50 pc. This bulge is quite red (as red
as giant ellipticals) and its entirely possible that this nucleated dE galaxy,
in fact, is a very large galaxy located in the background. As such, it is
highly reminiscent of the manner in which Malin-1 was discovered. Finally, we
find no evidence for small scale clumping of stars in any of the studied
systems at this much improved spatial resolution. This implies these systems
are dynamically well-relaxed and that the physical cause of their observed low
surface brightnesses is their low density. When imaged at the high spatial
resolution of the WFPC2 (~6 pc per pixel), the galaxies are easy to look right
through without evening knowing they are present in the very middle of the
WFPC2 frame. They appear only as elevated ``sky noise''.Comment: 39 pages, 3 figures, 3 tables. Accepted for publication in AJ The
paper, full-sized figures, etc. can also be obtained via
http://guernsey.uoregon.edu/~kare
Understanding the performance and reliability of NLP tools: a comparison of four NLP tools predicting stroke phenotypes in radiology reports
BACKGROUND: Natural language processing (NLP) has the potential to automate the reading of radiology reports, but there is a need to demonstrate that NLP methods are adaptable and reliable for use in real-world clinical applications. METHODS: We tested the F1 score, precision, and recall to compare NLP tools on a cohort from a study on delirium using images and radiology reports from NHS Fife and a population-based cohort (Generation Scotland) that spans multiple National Health Service health boards. We compared four off-the-shelf rule-based and neural NLP tools (namely, EdIE-R, ALARM+, ESPRESSO, and Sem-EHR) and reported on their performance for three cerebrovascular phenotypes, namely, ischaemic stroke, small vessel disease (SVD), and atrophy. Clinical experts from the EdIE-R team defined phenotypes using labelling techniques developed in the development of EdIE-R, in conjunction with an expert researcher who read underlying images. RESULTS: EdIE-R obtained the highest F1 score in both cohorts for ischaemic stroke, ≥93%, followed by ALARM+, ≥87%. The F1 score of ESPRESSO was ≥74%, whilst that of Sem-EHR is ≥66%, although ESPRESSO had the highest precision in both cohorts, 90% and 98%. For F1 scores for SVD, EdIE-R scored ≥98% and ALARM+ ≥90%. ESPRESSO scored lowest with ≥77% and Sem-EHR ≥81%. In NHS Fife, F1 scores for atrophy by EdIE-R and ALARM+ were 99%, dropping in Generation Scotland to 96% for EdIE-R and 91% for ALARM+. Sem-EHR performed lowest for atrophy at 89% in NHS Fife and 73% in Generation Scotland. When comparing NLP tool output with brain image reads using F1 scores, ALARM+ scored 80%, outperforming EdIE-R at 66% in ischaemic stroke. For SVD, EdIE-R performed best, scoring 84%, with Sem-EHR 82%. For atrophy, EdIE-R and both ALARM+ versions were comparable at 80%. CONCLUSIONS: The four NLP tools show varying F1 (and precision/recall) scores across all three phenotypes, although more apparent for ischaemic stroke. If NLP tools are to be used in clinical settings, this cannot be performed "out of the box." It is essential to understand the context of their development to assess whether they are suitable for the task at hand or whether further training, re-training, or modification is required to adapt tools to the target task
Coherent Detector Arrays for Millimeter and Submillimeter Astronomy
Progress in many areas of astronomy requires large-area surveys and observations of
extended objects. This includes the cosmic microwave background, nearby galaxies, the
Milky Way, and regions of star-forming regions within our galaxy. The ability to carry
out such studies is critically dependent on the development of affordable high-sensitivity
focal plane arrays, for both spectral line and continuum observations. We discuss a
program for the next decade to develop such technology for ground-based and spacebased
millimeter and submillimeter astronomy. Appropriate technologies exist, but
significant effort is required to make the transition from simply replicating individual
pixels to approaching focal plane array design in an integrated fashion from feeds to
spectrometers for spectral analysis. This advance is essential to realize the full potential
of major new ground-based, suborbital, and future space facilities, and is relevant to the
RMS and EOS panels. The recommended budget for this activity is $65M
Personalization Paradox in Behavior Change Apps:Lessons from a Social Comparison-Based Personalized App for Physical Activity
Social comparison-based features are widely used in social computing apps.
However, most existing apps are not grounded in social comparison theories and
do not consider individual differences in social comparison preferences and
reactions. This paper is among the first to automatically personalize social
comparison targets. In the context of an m-health app for physical activity, we
use artificial intelligence (AI) techniques of multi-armed bandits. Results
from our user study (n=53) indicate that there is some evidence that motivation
can be increased using the AI-based personalization of social comparison. The
detected effects achieved small-to-moderate effect sizes, illustrating the
real-world implications of the intervention for enhancing motivation and
physical activity. In addition to design implications for social comparison
features in social apps, this paper identified the personalization paradox, the
conflict between user modeling and adaptation, as a key design challenge of
personalized applications for behavior change. Additionally, we propose
research directions to mitigate this Personalization Paradox
- …