12,006 research outputs found
Cauchy Annealing Schedule: An Annealing Schedule for Boltzmann Selection Scheme in Evolutionary Algorithms
Boltzmann selection is an important selection mechanism in evolutionary
algorithms as it has theoretical properties which help in theoretical analysis.
However, Boltzmann selection is not used in practice because a good annealing
schedule for the `inverse temperature' parameter is lacking. In this paper we
propose a Cauchy annealing schedule for Boltzmann selection scheme based on a
hypothesis that selection-strength should increase as evolutionary process goes
on and distance between two selection strengths should decrease for the process
to converge. To formalize these aspects, we develop formalism for selection
mechanisms using fitness distributions and give an appropriate measure for
selection-strength. In this paper, we prove an important result, by which we
derive an annealing schedule called Cauchy annealing schedule. We demonstrate
the novelty of proposed annealing schedule using simulations in the framework
of genetic algorithms
Efficient implementation of the adaptive scale pixel decomposition algorithm
Context. Most popular algorithms in use to remove the effects of a
telescope's point spread function (PSF) in radio astronomy are variants of the
CLEAN algorithm. Most of these algorithms model the sky brightness using the
delta-function basis, which results in undesired artefacts when used on image
extended emission. The adaptive scale pixel decomposition (Asp-Clean) algorithm
models the sky brightness on a scale-sensitive basis and thus gives a
significantly better imaging performance when imaging fields that contain both
resolved and unresolved emission.
Aims. However, the runtime cost of Asp-Clean is higher than that of
scale-insensitive algorithms. In this paper, we identify the most expensive
step in the original Asp-Clean algorithm and present an efficient
implementation of it, which significantly reduces the computational cost while
keeping the imaging performance comparable to the original algorithm. The PSF
sidelobe levels of modern wide-band telescopes are significantly reduced,
allowing us to make approximations to reduce the computing cost, which in turn
allows for the deconvolution of larger images on reasonable timescales.
Methods. As in the original algorithm, scales in the image are estimated
through function fitting. Here we introduce an analytical method to model
extended emission, and a modified method for estimating the initial values used
for the fitting procedure, which ultimately leads to a lower computational
cost.
Results.The new implementation was tested with simulated EVLA data and the
imaging performance compared well with the original Asp-Clean algorithm. Tests
show that the current algorithm can recover features at different scales with
lower computational cost.Comment: 6 pages; 4 figure
Advances in Calibration and Imaging Techniques in Radio Interferometry
This paper summarizes some of the major calibration and image reconstruction
techniques used in radio interferometry and describes them in a common
mathematical framework. The use of this framework has a number of benefits,
ranging from clarification of the fundamentals, use of standard numerical
optimization techniques, and generalization or specialization to new
algorithms
Microbial carbon use efficiency predicted from genome-scale metabolic models
Respiration by soil bacteria and fungi is one of the largest fluxes of carbon (C) from the land surface. Although this flux is a direct product of microbial metabolism, controls over metabolism and their responses to global change are a major uncertainty in the global C cycle. Here, we explore an in silico approach to predict bacterial C-use efficiency (CUE) for over 200 species using genome-specific constraint-based metabolic modeling. We find that potential CUE averages 0.62 ± 0.17 with a range of 0.22 to 0.98 across taxa and phylogenetic structuring at the subphylum levels. Potential CUE is negatively correlated with genome size, while taxa with larger genomes are able to access a wider variety of C substrates. Incorporating the range of CUE values reported here into a next-generation model of soil biogeochemistry suggests that these differences in physiology across microbial taxa can feed back on soil-C cycling.Published versio
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