The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
M. G. Mingaliev - One of the best experts on this subject based on the ideXlab platform.
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Spectral characteristics and variability of Radio Sources near the north celestial pole
Astronomy Reports, 2009Co-Authors: M. G. Mingaliev, Yu. V. Sotnikova, N. S. Kardashev, M. G. LarionovAbstract:We present the results of our observations of compact extragalactic Radio Sources near the north celestial pole (+75° ≤ δ ≤ +88°) obtained on the RATAN-600 Radio telescope. Our sample consists of 51 Radio Sources with spectra that are either flat or inverted (growing toward shorter wavelengths) and with flux densities at 1.4 GHz S _ ν ≥ 200 mJy. We observed the Sources at 1–21.7 GHz. Multi-frequency instantaneous spectra are presented for 1999–2007. We observed 33 of our sample source daily for 30 days in August 2007. As a result, we revealed 15 objects exhibiting rapid variations on time scales of a day. The multi-frequency instantaneous spectra of these Sources indicate that Radio flux variations on one-day timescales are characteristic of objects of various spectral types. More than half the Sources exhibiting rapid variations demonstrate a growth in the variability amplitude with increasing frequency. For some of the objects, the variability amplitude is virtually independent of frequency.
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Optical identifications and spectra of Radio Sources
Astronomy Reports, 2009Co-Authors: V. L. Afanas’ev, S. N. Dodonov, A. V. Moiseev, A. G. Gorshkov, V. K. Konnikova, M. G. MingalievAbstract:We present classifications, optical identifications, and Radio spectra for eight Radio Sources from three flux-density-complete samples in the following declination ranges: 4°–6° (B1950), S _3.9 > 200 mJy; 10°–12°30′ (J2000), S _4.85 > 200 mJy; 74°−75° (J2000), S _4.85 > 100 mJy. For all these samples, the right ascensions are 0^h–24^h and the Galactic latitudes, | b | > 15°. Our optical observations at 4000–7500 ° were made with the 6-m telescope of the Special Astrophysical Observatory; we also observed at 0.97–21.7 GHz with the RATAN-600 Radio telescope of the Special Astrophysical Observatory. We classify four of the objects as quasars and four as galaxies. Five of the Radio Sources have power-law spectra at 0.97–21.7 GHz, while two objects have flat spectra. The quasar J2358+0430 virtually did not vary during 23 years.
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Spectral characteristics of Radio Sources near the North Celestial Pole
Astronomy Reports, 2007Co-Authors: M. G. Mingaliev, Yu. V. Sotnikova, N. N. Bursov, N. S. Kardashev, M. G. LarionovAbstract:We have used the RATAN-600 Radio telescope to study the spectral characteristics of a uniform sample of 504 Radio Sources from the NVSS catalog near the North Celestial Pole at six frequencies from 1.1 to 21.7 GHz, with the aim of selecting Sources possessing inverted spectra near 22 GHz, to be included in the program of the Radio Astron future space VLBI mission. We found 17 Radio Sources with the desired spectral characteristics. Data from spectral studies over a wide wavelength range testify that the spectral behavior of our sample differs from that for a complete sample of Sources with the same initial parameters but selected at 20 GHz. We find a 6% deficit of inverted-spectrum Sources, which can be explained as an effect of the spectral characteristics of “sub-threshold” Sources that were not included in the initial sample at 1.4 GHz.
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Radio and optical spectra of objects from three complete samples of Radio Sources
Astronomy Reports, 2006Co-Authors: V. L. Afanas’ev, S. N. Dodonov, A. V. Moiseev, A. G. Gorshkov, V. K. Konnikova, M. G. MingalievAbstract:We present classifications, optical identifications, and Radio spectra for 19 Radio Sources from three complete samples, with declinations 4°–6° (B1950, S _3.9 GHz > 200 mJy), 10°–12°30′ (J2000, S _4.85 GHz > 200 mJy), and 74°–75° (J2000, S _4.85 GHz > 100 mJy). We also present corresponding information for the Radio source J0527+0331. The right ascensions are 0–24^h and the Galactic latitudes | b | > 15° for all the samples. Our observations were obtained with the 6 m telescope from the Special Astrophysical Observatory in the range 4000–9000 Å or 4000–7500 Å and the RATAN-600 Radio telescope at frequencies in the range 0.97–21.7 GHz. We obtained flux densities for the Radio Sources and optical spectra for their optical counterparts. Nine objects were classified as quasars with redshifts from z = 1.029 to 3.212; nine objects are emission-line galaxies with redshifts from 0.172 to 0.546, and one is a galaxy with burstlike star formation at z = 0.156, and one is a BL Lac object with z = 0.509. The spectra of five Radio Sources were decomposed into extended and compact components. The Radio source J0527+0331, identified with a BL Lac object, displays significant variations of time scales from several days to several years. Data on flux variations are presented for 11 Radio Sources, as well as their spectra at several epochs.
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Classification of optical identifications of Radio Sources from complete samples
Astronomy Reports, 2002Co-Authors: V. Chavushyan, A. G. Gorshkov, V. K. Konnikova, R. Mujica, J. R. Valdes, M. G. MingalievAbstract:Classifications of the optical counterparts and Radio spectra of nine Radio Sources are presented. The observations were carried out using the 2.1-m optical telescope in Cananea (Mexico) at 4200–9000 Å and the RATAN-600 Radio telescope at 0.97–21.7 GHz. Five objects have been classified as quasars (three have redshifts z >2), two as BL Lac objects, one as an elliptical galaxy, and one as an absorption-line galaxy.
Jingang Yi - One of the best experts on this subject based on the ideXlab platform.
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Simultaneous Localization of Multiple Unknown and Transient Radio Sources Using a Mobile Robot
IEEE Transactions on Robotics, 2012Co-Authors: Dezhen Song, Jingang YiAbstract:We report system and algorithm developments that utilize a single mobile robot to simultaneously localize multiple unknown transient Radio Sources. Because of signal source anonymity, short transmission durations, and dynamic transmission patterns, the robot cannot treat the Radio Sources as continuous Radio beacons. To deal with this challenging localization problem, we model the Radio source behaviors using a novel spatiotemporal probability occupancy grid that captures transient characteristics of Radio transmissions and tracks posterior probability distributions of Radio Sources. As a Monte Carlo method, a ridge walking motion planning algorithm is proposed to enable the robot to efficiently traverse the high-probability regions to accelerate the convergence of the posterior probability distribution. We also formally show that the time to find a Radio source is insensitive to the number of Radio Sources, and hence, our algorithm has great scalability. We have implemented the algorithms and extensively tested them in comparison with two heuristic methods: a random walk and a fixed-route patrol. The localization time of our algorithms is consistently shorter than that of the two heuristic methods.
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Localization of Unknown Networked Radio Sources Using a Mobile Robot with a Directional Antenna
2007 American Control Conference, 2007Co-Authors: Dezhen Song, Jingang Yi, Zane GoodwinAbstract:In this paper, we present algorithmic developments for a single mobile robot equipped with a directional antenna to localize unknown networked Radio Sources. We assume that the robot only senses Radio transmissions at the physical layer and that the network has a carrier sense multiple access (CSMA)-type medium access control (MAC) layer. The total number of Radio Sources are assumed unknown. We first formulate the localization problem and then propose a particle filter-based localization algorithm. The algorithm combines a new CSMA model and a new directional antenna model. The new CSMA model provides network configuration data, such as the network size and the probability of collision, when listening to network traffic. The directional antenna model enhances the efficiency of robot motion. The new combined sensing model is capable of handling transmission collisions during localization. The overall algorithm runs in O(nm) time for n particles and m Radio Sources at each step. The numerical results show that the algorithm can localize unknown networked Radio Sources effectively.
Dezhen Song - One of the best experts on this subject based on the ideXlab platform.
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Simultaneous Localization of Multiple Unknown and Transient Radio Sources Using a Mobile Robot
IEEE Transactions on Robotics, 2012Co-Authors: Dezhen Song, Jingang YiAbstract:We report system and algorithm developments that utilize a single mobile robot to simultaneously localize multiple unknown transient Radio Sources. Because of signal source anonymity, short transmission durations, and dynamic transmission patterns, the robot cannot treat the Radio Sources as continuous Radio beacons. To deal with this challenging localization problem, we model the Radio source behaviors using a novel spatiotemporal probability occupancy grid that captures transient characteristics of Radio transmissions and tracks posterior probability distributions of Radio Sources. As a Monte Carlo method, a ridge walking motion planning algorithm is proposed to enable the robot to efficiently traverse the high-probability regions to accelerate the convergence of the posterior probability distribution. We also formally show that the time to find a Radio source is insensitive to the number of Radio Sources, and hence, our algorithm has great scalability. We have implemented the algorithms and extensively tested them in comparison with two heuristic methods: a random walk and a fixed-route patrol. The localization time of our algorithms is consistently shorter than that of the two heuristic methods.
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Localization of Unknown Networked Radio Sources Using a Mobile Robot with a Directional Antenna
2007 American Control Conference, 2007Co-Authors: Dezhen Song, Jingang Yi, Zane GoodwinAbstract:In this paper, we present algorithmic developments for a single mobile robot equipped with a directional antenna to localize unknown networked Radio Sources. We assume that the robot only senses Radio transmissions at the physical layer and that the network has a carrier sense multiple access (CSMA)-type medium access control (MAC) layer. The total number of Radio Sources are assumed unknown. We first formulate the localization problem and then propose a particle filter-based localization algorithm. The algorithm combines a new CSMA model and a new directional antenna model. The new CSMA model provides network configuration data, such as the network size and the probability of collision, when listening to network traffic. The directional antenna model enhances the efficiency of robot motion. The new combined sensing model is capable of handling transmission collisions during localization. The overall algorithm runs in O(nm) time for n particles and m Radio Sources at each step. The numerical results show that the algorithm can localize unknown networked Radio Sources effectively.
E M Sadler - One of the best experts on this subject based on the ideXlab platform.
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extragalactic peaked spectrum Radio Sources at low frequencies
The Astrophysical Journal, 2017Co-Authors: E M Sadler, J R Callingham, R D Ekers, B M Gaensler, J Line, N Hurleywalker, S J TingayAbstract:This document is the Accepted Manuscript of the following article: J.R. Callingham, et al, 'Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies', The Astrophysical Journal, 836 (2), (28pp), first published online 17 February 2017. DOI: https://doi.org/10.3847/1538-4357-836/2/174. © 2017, The American Astronomical Society. All rights reserved. Data tables, and the appendix containing all of the SEDs, are available from the journal and on request to the author
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crates an all sky survey of flat spectrum Radio Sources
Astrophysical Journal Supplement Series, 2007Co-Authors: S E Healey, Roger W Romani, G B Taylor, E M Sadler, R Ricci, Tara Murphy, James S Ulvestad, Joshua N WinnAbstract:We have assembled an 8.4 GHz survey of bright, flat-spectrum ({alpha} > -0.5) Radio Sources with nearly uniform extragalactic (|b| > 10{sup o}) coverage for Sources brighter than S{sub 4.8 GHz} = 65 mJy. The catalog is assembled from existing observations (especially CLASS and the Wright et al. PMN-CA survey), augmented by reprocessing of archival VLA and ATCA data and by new observations to fill in coverage gaps. We refer to this program as CRATES, the Combined Radio All-sky Targeted Eight GHz Survey. The resulting catalog provides precise positions, sub-arcsecond structures, and spectral indices for some 11,000 Sources. We describe the morphology and spectral index distribution of the sample and comment on the survey's power to select several classes of interesting Sources, especially high energy blazars. Comparison of CRATES with other high-frequency surveys also provides unique opportunities for identification of high-power Radio Sources.
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the properties of extragalactic Radio Sources selected at 20 ghz
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: E M Sadler, R Ricci, Tara Murphy, R D Ekers, Jennifer A Ekers, P J Hancock, C A Jackson, M J Kesteven, Chris Phillips, R F ReinfrankAbstract:We present some first results on the variability, polarization and general properties of Radio Sources selected at 20 GHz, the highest frequency at which a sensitive Radio survey has been carried out over a large area of sky. Sources with flux densities above 100 mJy in the Australia
M. G. Larionov - One of the best experts on this subject based on the ideXlab platform.
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Spectral characteristics and variability of Radio Sources near the north celestial pole
Astronomy Reports, 2009Co-Authors: M. G. Mingaliev, Yu. V. Sotnikova, N. S. Kardashev, M. G. LarionovAbstract:We present the results of our observations of compact extragalactic Radio Sources near the north celestial pole (+75° ≤ δ ≤ +88°) obtained on the RATAN-600 Radio telescope. Our sample consists of 51 Radio Sources with spectra that are either flat or inverted (growing toward shorter wavelengths) and with flux densities at 1.4 GHz S _ ν ≥ 200 mJy. We observed the Sources at 1–21.7 GHz. Multi-frequency instantaneous spectra are presented for 1999–2007. We observed 33 of our sample source daily for 30 days in August 2007. As a result, we revealed 15 objects exhibiting rapid variations on time scales of a day. The multi-frequency instantaneous spectra of these Sources indicate that Radio flux variations on one-day timescales are characteristic of objects of various spectral types. More than half the Sources exhibiting rapid variations demonstrate a growth in the variability amplitude with increasing frequency. For some of the objects, the variability amplitude is virtually independent of frequency.
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Spectral characteristics of Radio Sources near the North Celestial Pole
Astronomy Reports, 2007Co-Authors: M. G. Mingaliev, Yu. V. Sotnikova, N. N. Bursov, N. S. Kardashev, M. G. LarionovAbstract:We have used the RATAN-600 Radio telescope to study the spectral characteristics of a uniform sample of 504 Radio Sources from the NVSS catalog near the North Celestial Pole at six frequencies from 1.1 to 21.7 GHz, with the aim of selecting Sources possessing inverted spectra near 22 GHz, to be included in the program of the Radio Astron future space VLBI mission. We found 17 Radio Sources with the desired spectral characteristics. Data from spectral studies over a wide wavelength range testify that the spectral behavior of our sample differs from that for a complete sample of Sources with the same initial parameters but selected at 20 GHz. We find a 6% deficit of inverted-spectrum Sources, which can be explained as an effect of the spectral characteristics of “sub-threshold” Sources that were not included in the initial sample at 1.4 GHz.
