scholarly journals An Atlas of Extragalactic Radio Sources

1996 ◽  
Vol 175 ◽  
pp. 157-158 ◽  
Author(s):  
J.P. Leahy ◽  
A.H. Bridle ◽  
R.G. Strom
Keyword(s):  
High Resolution ◽  
Line Emission ◽  
Radio Sources ◽  
X Rays ◽  
Complete Sample ◽  
High Quality ◽  
Extragalactic Radio Sources ◽  
Optical Line

Our Atlas of Extragalactic Radio Sources will present high-quality images of the nearer half of “3CRR”, the sample defined by Laing, Riley & Longair (1983). This is the best-studied complete sample of extragalactic radio sources. All 173 members have secure redshifts and most have been imaged in the radio at high resolution. There is also copious information on their optical line emission, and many have been detected in the sub-mm, FIR, and in X-rays. 3CRR is widely used as a baseline against which fainter, higher-redshift samples can be compared to define the evolution of the population (e.g. Neeser et al. 1995; Law-Green, this conference).

scholarly journals VLBI Survey of a Complete Sample of Active Nuclei and Quasars

1984 ◽  
Vol 110 ◽  
pp. 15-24 ◽  
Author(s):  
T. J. Pearson ◽  
A.C.S. Readhead
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Complete Sample ◽  
Limited Sample ◽  
Extragalactic Radio Sources ◽  
5 Ghz ◽  
Number Of Classes ◽  
Compact Sources ◽  
Continuous Range

We have conducted a VLBI survey of a complete, flux-density limited sample of 65 extragalactic radio sources, selected at 5 GHz. We have made hybrid maps at 5 GHz of all of the sources accessible to the Mark-II system. The sources can be divided provisionally into a number of classes with different properties: central components of extended double sources, steep-spectrum compact sources, very compact (almost unresolved) sources, asymmetric sources (sometimes called “core-jet” sources), and “compact double” sources. It is not yet clear whether any of these classes is physically distinct from the others, or whether there is a continuous range of properties.

Survey of a complete sample of southern extragalactic radio sources

1993 ◽  
Vol 105 ◽  
pp. 1680 ◽  
Author(s):  
M. Tornikoski ◽  
E. Valtaoja ◽  
H. Terasranta ◽  
M. Lainela ◽  
M. Bramwell ◽  
...  
Keyword(s):  
Radio Sources ◽  
Complete Sample ◽  
Extragalactic Radio Sources

scholarly journals Intensity Variations in Extragalactic Radio Sources at 13 cm

1972 ◽  
Vol 44 ◽  
pp. 224-224 ◽  
Author(s):  
G. D. Nicolson
Keyword(s):  
Low Frequency ◽  
Secular Change ◽  
Radio Sources ◽  
Complete Sample ◽  
Frequency Spectra ◽  
Extragalactic Radio Sources ◽  
The Relationship

Results of a three-year investigation into the variability of 55 Parkes sources at 13 cm are presented. Thirty-six of the sources comprise a complete sample of QSS with fluxes exceeding 2 flux units. The remaining sources include most other known or likely variables stronger than 2 flux units. The relationship between spectra and variability in QSS is investigated and it is confirmed that variables generally have flat low frequency spectra. A possible relationship between redshift and specific types of intensity variations is considered. Limits on the secular change in the intensity of non-variable QSS are set and are generally found to be ± 1.5% p.a. at 13 cm. Results for the remaining 19 sources are discussed and some preliminary findings of an extension patrol to include weaker sources in the range 1-2 flux units are given.

scholarly journals Noise-residue learning convolutional network model for magnetic resonance image enhancement

2021 ◽  
Vol 2089 (1) ◽  
pp. 012029
Author(s):  
Ram Singh ◽  
Lakhwinder Kaur
Keyword(s):  
Magnetic Resonance ◽  
High Resolution ◽  
Magnetic Resonance Image ◽  
Motion Artifacts ◽  
Tumor Segmentation ◽  
X Rays ◽  
High Quality ◽  
High Resolution Mri ◽  
Segmentation Image ◽  
Filter Noise

Abstract Magnetic Resonance Image (MRI) is an important medical image acquisition technique used to acquire high contrast images of human body anatomical structures and soft tissue organs. MRI system does not use any harmful radioactive ionized material like x-rays and computerized tomography (CT) imaging techniques. High-resolution MRI is desirable in many clinical applications such as tumor segmentation, image registration, edges & boundary detection, and image classification. During MRI acquisition, many practical constraints limit the MRI quality by introducing random Gaussian noise and some other artifacts by the thermal energy of the patient body, random scanner voltage fluctuations, body motion artifacts, electronics circuits impulse noise, etc. High-resolution MRI can be acquired by increasing scan time, but considering patient comfort, it is not preferred in practice. Hence, postacquisition image processing techniques are used to filter noise contents and enhance the MRI quality to make it fit for further image analysis tasks. The main motive of MRI enhancement is to reconstruct a high-quality MRI while improving and retaining its important features. The new deep learning image denoising and artifacts removal methods have shown tremendous potential for high-quality image reconstruction from noise degraded MRI while preserving useful image information. This paper presents a noise-residue learning convolution neural network (CNN) model to denoise and enhance the quality of noise-corrupted low-resolution MR images. The proposed technique shows better performance in comparison with other conventional MRI enhancement methods. The reconstructed image quality is evaluated by the peak-signal-to-noise ratio (PSNR) and structural similarity index (SSIM) metrics by optimizing information loss in reconstructed MRI measured in mean squared error (MSE) metric.

scholarly journals The Evolution of Linear Sizes

1982 ◽  
Vol 97 ◽  
pp. 401-410
Author(s):  
V. K. Kapahi ◽  
C. R. Subrahmanya
Keyword(s):  
Strong Correlation ◽  
Angular Size ◽  
Inverse Correlation ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Complete Sample ◽  
Extragalactic Radio Sources ◽  
Rule Out

Possible evidence that the linear sizes of extragalactic radio sources were smaller at earlier epochs was first provided by the angular size redshift (θ-z) relation for double radio quasars (Legg 1970, Miley 1971, Wardle and Miley 1974). But because of the strong correlation between redshift (z) and radio luminosity (P) in flux limited radio samples, it is hard to decide if the observed decrease in sizes with z is caused by an epoch dependence of linear sizes (ℓ) or by an inverse correlation between P and ℓ. Several authors (eg. Stannard and Neal 1977, Wardle and Potash 1977, Hooley ET AL. 1978, Wills 1979, Masson 1980) have attempted to separate the two effects by comparing the properties of quasars from the 3CR survey with those from the 4C and Parkes samples. Although most of these studies appear to marginally favour a P-ℓ correlation, none of them can rule out even a fairly strong evolution in ℓ with z. Apart from the small numbers involved, the difficulty is that 3C and 4C quasars do not differ a great deal in their redshifts or luminosities. A complete sample of quasars at much weaker flux levels would be quite valuable in this regard.

scholarly journals Multi-Frequency Polarization Studies of Radio Galaxies

1982 ◽  
Vol 97 ◽  
pp. 53-54
Author(s):  
G. G. Pooley
Keyword(s):  
High Resolution ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Frequency Range ◽  
Extragalactic Radio Sources ◽  
High Resolution Mapping ◽  
New Instrument ◽  
Resolution Mapping ◽  
Polarization Studies ◽  
The One

This is a brief report on some of the work in progress at Cambridge, with emphasis on studies of extragalactic radio sources using the One-mile and 5-km telescopes; together with the 6C survey and a new instrument now being commisioned at 151 MHz, we have a frequency range of 100:1 available for high-resolution mapping. The 6C survey has resulted in the discovery of a number of giant radio galaxies, most notably NGC 6251. At 151 MHz, the beautiful jet is not prominent; we have mapped it with the One-mile and 5-km instruments and a paper (by Saunders et al.) will shortly appear in Monthly Notices. Dr Willis will speak later on the structure of this source.

A search for hard X-rays from five strong extragalactic radio sources

1977 ◽  
Vol 212 ◽  
pp. 22 ◽  
Author(s):  
R. F. Mushotzky ◽  
W. A. Baity ◽  
L. E. Peterson
Keyword(s):  
Radio Sources ◽  
X Rays ◽  
Extragalactic Radio Sources
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