471 research outputs found
Improved SAAO–2MASS photometry transformations
Near-infrared photometry of 599 stars is used to calculate transformations from the South
African Astronomical Observatory (SAAO) JHK system to the Two-Micron All-Sky Survey
(2MASS) JHKS system. Both several-term formal regression relations and simplified transformations
are presented. Inverse transformations (i.e. 2MASS to SAAO) are also given. The
presence of non-linearities in some colour terms is highlighted.Web of Scienc
What Next-Generation 21 cm Power Spectrum Measurements Can Teach Us About the Epoch of Reionization
A number of experiments are currently working towards a measurement of the 21
cm signal from the Epoch of Reionization. Whether or not these experiments
deliver a detection of cosmological emission, their limited sensitivity will
prevent them from providing detailed information about the astrophysics of
reionization. In this work, we consider what types of measurements will be
enabled by a next-generation of larger 21 cm EoR telescopes. To calculate the
type of constraints that will be possible with such arrays, we use simple
models for the instrument, foreground emission, and the reionization history.
We focus primarily on an instrument modeled after the
collecting area Hydrogen Epoch of Reionization Array (HERA) concept design, and
parameterize the uncertainties with regard to foreground emission by
considering different limits to the recently described "wedge" footprint in
k-space. Uncertainties in the reionization history are accounted for using a
series of simulations which vary the ionizing efficiency and minimum virial
temperature of the galaxies responsible for reionization, as well as the mean
free path of ionizing photons through the IGM. Given various combinations of
models, we consider the significance of the possible power spectrum detections,
the ability to trace the power spectrum evolution versus redshift, the
detectability of salient power spectrum features, and the achievable level of
quantitative constraints on astrophysical parameters. Ultimately, we find that
of collecting area is enough to ensure a very high significance
() detection of the reionization power spectrum in even the
most pessimistic scenarios. This sensitivity should allow for meaningful
constraints on the reionization history and astrophysical parameters,
especially if foreground subtraction techniques can be improved and
successfully implemented.Comment: 27 pages, 18 figures, updated SKA numbers in appendi
Current detection rates and time-to-detection of all identifiable BRCA carriers in the Greater London population.
BACKGROUND: BRCA carrier identification offers opportunities for early diagnoses, targeted treatment and cancer prevention. We evaluate BRCA- carrier detection rates in general and Ashkenazi Jewish (AJ) populations across Greater London and estimate time-to-detection of all identifiable BRCA carriers. METHODS: BRCA carrier data from 1993 to 2014 were obtained from National Health Service genetic laboratories and compared with modelled predictions of BRCA prevalence from published literature and geographical data from UK Office for National Statistics. Proportion of BRCA carriers identified was estimated. Prediction models were developed to fit BRCA detection rate data. BRCA carrier identification rates were evaluated for an 'Angelina Jolie effect'. Maps for four Greater London regions were constructed, and their relative BRCA detection rates were compared. Models developed were used to predict future time-to-identify all detectable BRCA carriers in AJ and general populations. RESULTS: Until 2014, only 2.6% (3072/111 742 estimated) general population and 10.9% (548/4985 estimated) AJ population BRCA carriers have been identified in 16 696 608 (AJ=190 997) Greater London population. 57% general population and 54% AJ mutations were identified through cascade testing. Current detection rates mirror linear fit rather than parabolic model and will not identify all BRCA carriers. Addition of unselected ovarian/triple-negative breast cancer testing would take >250 years to identify all BRCA carriers. Doubling current detection rates can identify all 'detectable' BRCA carriers in the general population by year 2181, while parabolic and triple linear rates can identify 'detectable' BRCA carriers by 2084 and 2093, respectively. The linear fit model can identify 'detectable' AJ carriers by 2044. We did not find an Angelina Jolie effect on BRCA carrier detection rates. There was a significant difference in BRCA detection rates between geographical regions over time (P<0.001). CONCLUSIONS: The majority of BRCA carriers have not been identified, missing key opportunities for prevention/earlier diagnosis. Enhanced and new strategies/approaches are needed
Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
The Epoch of Reionization (EoR) is an uncharted era in our Universe's history
during which the birth of the first stars and galaxies led to the ionization of
neutral hydrogen in the intergalactic medium. There are many experiments
investigating the EoR by tracing the 21cm line of neutral hydrogen. Because
this signal is very faint and difficult to isolate, it is crucial to develop
analysis techniques that maximize sensitivity and suppress contaminants in
data. It is also imperative to understand the trade-offs between different
analysis methods and their effects on power spectrum estimates. Specifically,
with a statistical power spectrum detection in HERA's foreseeable future, it
has become increasingly important to understand how certain analysis choices
can lead to the loss of the EoR signal. In this paper, we focus on signal loss
associated with power spectrum estimation. We describe the origin of this loss
using both toy models and data taken by the 64-element configuration of the
Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER).
In particular, we highlight how detailed investigations of signal loss have led
to a revised, higher 21cm power spectrum upper limit from PAPER-64.
Additionally, we summarize errors associated with power spectrum error
estimation that were previously unaccounted for. We focus on a subset of
PAPER-64 data in this paper; revised power spectrum limits from the PAPER
experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.)
and supersede results from previously published PAPER analyses.Comment: 25 pages, 18 figures, Accepted by Ap
A Technique for Primary Beam Calibration of Drift-Scanning, Wide-Field Antenna Elements
We present a new technique for calibrating the primary beam of a wide-field,
drift-scanning antenna element. Drift-scan observing is not compatible with
standard beam calibration routines, and the situation is further complicated by
difficult-to-parametrize beam shapes and, at low frequencies, the sparsity of
accurate source spectra to use as calibrators. We overcome these challenges by
building up an interrelated network of source "crossing points" -- locations
where the primary beam is sampled by multiple sources. Using the single
assumption that a beam has 180 degree rotational symmetry, we can achieve
significant beam coverage with only a few tens of sources. The resulting
network of crossing points allows us to solve for both a beam model and source
flux densities referenced to a single calibrator source, circumventing the need
for a large sample of well-characterized calibrators. We illustrate the method
with actual and simulated observations from the Precision Array for Probing the
Epoch of Reionization (PAPER).Comment: 10 pages, 9 figures, 1 table, revised to match version accepted by A
Validating the FLASH Code: Vortex-Dominated Flows
As a component of the Flash Center's validation program, we compare FLASH
simulation results with experimental results from Los Alamos National
Laboratory. The flow of interest involves the lateral interaction between a
planar Ma=1.2 shock wave with a cylinder of gaseous sulfur hexafluoride (SF_6)
in air, and in particular the development of primary and secondary
instabilities after the passage of the shock. While the overall evolution of
the flow is comparable in the simulations and experiments, small-scale features
are difficult to match. We focus on the sensitivity of numerical results to
simulation parameters.Comment: 10 pages, 5 figures, presented at the 5th International Conference on
High Energy Laboratory Astrophysics, Tucson, AZ, March 10-13, 200
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