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The main objective of this work is to accelerate the Maximum-Likelihood (ML) estimation procedure for radio interferometric direction dependent self-calibration. We introduce the OS-SAGE radio interferometric calibration method, as a combination of the Ordered-Subsets (OS) method with the Space Alternating Generalized Expectation maximization (SAGE)(More)
We present the GPU based acceleration of two well known nonlinear optimization routines: Levenberg-Marquardt (LM) and Limited Memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) in radio interferometric calibration. Radio interferometric calibration is a heavily compute intensive operation where the same nonlinear optimization problem has to be solved over many(More)
—An efficient hybrid method is presented to obtain the current distribution of both non-uniformly linear and planar arrays by sampling the array factor of a desired radiation pattern. The proposed method provides Fourier coefficients and uses the Least Mean Square method (LMS) to solve the system of equations in order to obtain current distribution in(More)
This paper introduces an amendment to radio interferometric calibration of sources below the noise level. The main idea is to employ the information of the stronger sources' measured signals as a plug-in criterion to solve for the weaker ones. For this purpose, we construct a number of source clusters, with centroids mainly near the strongest sources,(More)
Aims. This paper discusses the spectral occupancy for performing radio astronomy with the Low-Frequency Array (LOFAR), with a focus on imaging observations. Methods. We have analysed the radio-frequency interference (RFI) situation in two 24-h surveys with Dutch LOFAR stations, covering 30– 78 MHz with low-band antennas and 115–163 MHz with high-band(More)
Cloud computing is a computer model that tries to facilitate the users' access based on their request for the information and computing sources. In recent years, making the cloud against the attacks has become significantly important. One of the security methods is the use of intrusion detection systems. In these systems, when a suspicious event that(More)
LOFAR is the LOw-Frequency Radio interferometer ARray located at midlatitude (52 ∘ 53 ′ N). Here we present results on ionospheric structures derived from 29 LOFAR nighttime observations during the winters of 2012/2013 and 2013/2014. We show that LOFAR is able to determine differential ionospheric total electron content values with an accuracy better than(More)
We investigate the feasibility of detecting 21 cm absorption features in the afterglow spectra of high redshift long Gamma Ray Bursts (GRBs). This is done employing simulations of cosmic reionization, together with estimates of the GRB radio afterglow flux and the instrumental characteristics of the LOw Frequency ARray (LOFAR). We find that absorption(More)