313 research outputs found
HIRAX:A Probe of Dark Energy and Radio Transients
The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a new
400-800MHz radio interferometer under development for deployment in South
Africa. HIRAX will comprise 1024 six meter parabolic dishes on a compact grid
and will map most of the southern sky over the course of four years. HIRAX has
two primary science goals: to constrain Dark Energy and measure structure at
high redshift, and to study radio transients and pulsars. HIRAX will observe
unresolved sources of neutral hydrogen via their redshifted 21-cm emission line
(`hydrogen intensity mapping'). The resulting maps of large-scale structure at
redshifts 0.8-2.5 will be used to measure Baryon Acoustic Oscillations (BAO).
HIRAX will improve upon current BAO measurements from galaxy surveys by
observing a larger cosmological volume (larger in both survey area and redshift
range) and by measuring BAO at higher redshift when the expansion of the
universe transitioned to Dark Energy domination. HIRAX will complement CHIME, a
hydrogen intensity mapping experiment in the Northern Hemisphere, by completing
the sky coverage in the same redshift range. HIRAX's location in the Southern
Hemisphere also allows a variety of cross-correlation measurements with
large-scale structure surveys at many wavelengths. Daily maps of a few thousand
square degrees of the Southern Hemisphere, encompassing much of the Milky Way
galaxy, will also open new opportunities for discovering and monitoring radio
transients. The HIRAX correlator will have the ability to rapidly and
eXperimentciently detect transient events. This new data will shed light on the
poorly understood nature of fast radio bursts (FRBs), enable pulsar monitoring
to enhance long-wavelength gravitational wave searches, and provide a rich data
set for new radio transient phenomena searches. This paper discusses the HIRAX
instrument, science goals, and current status.Comment: 11 pages, 5 figure
Graphical modeling of binary data using the LASSO: a simulation study
Background: Graphical models were identified as a promising new approach to modeling high-dimensional clinical data. They provided a probabilistic tool to display, analyze and visualize the net-like dependence structures by drawing a graph describing the conditional dependencies between the variables. Until now, the main focus of research was on building Gaussian graphical models for continuous multivariate data following a multivariate normal distribution. Satisfactory solutions for binary data were missing. We adapted the method of Meinshausen and Buhlmann to binary data and used the LASSO for logistic regression. Objective of this paper was to examine the performance of the Bolasso to the development of graphical models for high dimensional binary data. We hypothesized that the performance of Bolasso is superior to competing LASSO methods to identify graphical models. Methods: We analyzed the Bolasso to derive graphical models in comparison with other LASSO based method. Model performance was assessed in a simulation study with random data generated via symmetric local logistic regression models and Gibbs sampling. Main outcome variables were the Structural Hamming Distance and the Youden Index. We applied the results of the simulation study to a real-life data with functioning data of patients having head and neck cancer. Results: Bootstrap aggregating as incorporated in the Bolasso algorithm greatly improved the performance in higher sample sizes. The number of bootstraps did have minimal impact on performance. Bolasso performed reasonable well with a cutpoint of 0.90 and a small penalty term. Optimal prediction for Bolasso leads to very conservative models in comparison with AIC, BIC or cross-validated optimal penalty terms. Conclusions: Bootstrap aggregating may improve variable selection if the underlying selection process is not too unstable due to small sample size and if one is mainly interested in reducing the false discovery rate. We propose using the Bolasso for graphical modeling in large sample sizes
Farmersâ perceptions of climate change : identifying types
Ambitious targets to reduce greenhouse gas (GHG) emissions from agriculture have been set by both national governments and their respective livestock sectors. We hypothesize that farmer self-identity influences their assessment of climate change and their willingness to im- plement measures which address the issue. Perceptions of climate change were determined from 286 beef/sheep farmers and evaluated using principal component analysis (PCA). The analysis elicits two components which evaluate identity (productivism and environmental responsibility), and two components which evaluate behavioral capacity to adopt mitigation and adaptation measures (awareness and risk perception). Subsequent Cluster Analyses reveal four farmer types based on the PCA scores. âThe Productivistâ and âThe Countryside Stewardâ portray low levels of awareness of climate change, but differ in their motivation to adopt pro-environmental behavior. Conversely, both âThe Environmentalistâ and âThe Dejectedâ score higher in their awareness of the issue. In addition, âThe Dejectedâ holds a high sense of perceived risk; however, their awareness is not conflated with an explicit understanding of agricultural GHG sources. With the exception of âThe Environmentalistâ, there is an evident disconnect between perceptions of agricultural emission sources and their contribution towards GHG emissions amongst all types. If such linkages are not con- ceptualized, it is unlikely that behavioral capacities will be realized. Effective communication channels which encour- age action should target farmers based on the groupings depicted. Therefore, understanding farmer types through the constructs used in this study can facilitate effective and tai- lored policy development and implementation
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