scholarly journals High resolution VLBI observations of the nuclei of bright galaxies and quasars at 327 MHz

1986 ◽  
Vol 119 ◽  
pp. 169-170
Author(s):  
S. Ananthakrishnan ◽  
V.K. Kulkarni
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
The Other ◽  
Radio Sources ◽  
Interplanetary Scintillation ◽  
Ss 433 ◽  
Vlbi Observations ◽  
Nearby Galaxies ◽  
Compact Sources ◽  
3C 120

An intercontinental VLBI experiment at 327 MHz involving the Ooty Radio Telescope and telescopes at Jodrell Bank, Westerbork, Torun and Crimea was carried out during December 8–12, 1983. The purpose of the experiment was to (i) establish the feasibility of performing MKII VLBI observations from India and (ii) to study the low frequency structure of nearby galaxies, quasars and some other well known radio sources at metre wavelengths. The sources observed were NGC 262, 315, 1052, 1068, 1265, 1275, 4151, 4486, 7674 and 3C 120; PKS 1055+018, 1148−001 and CTA 102; 3C 237 and SS 433. The bright NGC galaxies chosen were selected from an Interplanetary Scintillation survey of 150 nearby galaxies (Bagri and Ananthakrishnan 1983); they were found to have a flux density greater than about 0.2 Jy in subarcsec components at 327 MHz and have high frequency VLBI observations. The quasars chosen are amongst the most compact sources known at metrewavelengths. The other objects were the well known sources which have been studied extensively at higher frequencies.

scholarly journals Interplanetary Scintillation with the Murchison Widefield Array V: An all-sky survey of compact sources using a modern low-frequency radio telescope

2019 ◽  
Vol 36 ◽  
Author(s):  
J. S. Morgan ◽  
J.-P. Macquart ◽  
R. Chhetri ◽  
R. D. Ekers ◽  
S. J. Tingay ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Low Frequency ◽  
Radio Sources ◽  
Interplanetary Scintillation ◽  
Complementary Information ◽  
Imaging Arrays ◽  
Sky Survey ◽  
Murchison Widefield Array ◽  
Celestial Sphere ◽  
Compact Sources

AbstractWe describe the parameters of a low-frequency all-sky survey of compact radio sources using Interplanetary Scintillation, undertaken with the Murchison Widefield Array. While this survey gives important complementary information to low-resolution survey, providing information on the sub-arsecond structure of every source, a survey of this kind has not been attempted in the era of low-frequency imaging arrays such as the Murchison Widefield Array and LOw Frequency Array. Here we set out the capabilities of such a survey, describing the limitations imposed by the heliocentric observing geometry and by the instrument itself. We demonstrate the potential for Interplanetary Scintillation measurements at any point on the celestial sphere and we show that at 160 MHz, reasonable results can be obtained within 30° of the ecliptic (2π str: half the sky). We also suggest some observational strategies and describe the first such survey, the Murchison Widefield Array Phase I Interplanetary Scintillation survey. Finally we analyse the potential of the recently upgraded Murchison Widefield Array and discuss the potential of the Square Kilometre Array-low to use Interplanetary Scintillation to probe sub-mJy flux density levels at sub-arcsecond angular resolution.

Ion-cyclotron modes in weakly relativistic plasmas

1994 ◽  
Vol 51 (3) ◽  
pp. 371-379 ◽  
Author(s):  
Chandu Venugopal ◽  
P. J. Kurian ◽  
G. Renuka
Keyword(s):  
Dispersion Relation ◽  
High Frequency ◽  
Low Frequency ◽  
Dispersion Relations ◽  
The Other ◽  
Larmor Radius ◽  
Relativistic Plasmas ◽  
Ion Plasma ◽  
Maxwellian Plasma ◽  
Relativistic Dispersion

We derive a dispersion relation for the perpendicular propagation of ioncyclotron waves around the ion gyrofrequency ω+ in a weaklu relaticistic anisotropic Maxwellian plasma. These waves, with wavelength greater than the ion Larmor radius rL+ (k⊥ rL+ < 1), propagate in a plasma characterized by large ion plasma frequencies (). Using an ordering parameter ε, we separated out two dispersion relations, one of which is independent of the relativistic terms, while the other depends sensitively on them. The solutions of the former dispersion relation yield two modes: a low-frequency (LF) mode with a frequency ω < ω+ and a high-frequency (HF) mode with ω > ω+. The plasma is stable to the propagation of these modes. The latter dispersion relation yields a new LF mode in addition to the modes supported by the non-relativistic dispersion relation. The two LF modes can coalesce to make the plasma unstable. These results are also verified numerically using a standard root solver.

P3392Potential of imaging-guided PCI for event suppression in Japanese acute myocardial infarction patients: J-MINUET substudy

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
T Yamashita ◽  
K Sakamoto ◽  
K Tsujita ◽  
K Nakao ◽  
Y Ozaki ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
High Frequency ◽  
Low Frequency ◽  
The Other ◽  
Intravascular Imaging ◽  
Clinical Events ◽  
Coronary Imaging ◽  
Usage Frequency ◽  
Moderate Frequency ◽  
Event Rates

Abstract Background Intravascular ultrasound (IVUS) and Optical Coherence Tomography (OCT) has been widely used in clinical settings. Although favorable results of imaging-guided percutaneous coronary intervention (PCI) compared with angio-guided PCI were observed in several studies, impacts of institutional-based usage frequency, about imaging-guided PCI, have not been well elucidated. Methods To elucidate the impact of imaging-guided PCI and the effects of frequency of its usage, we analyzed data of the Japanese registry of acute Myocardial INfarction diagnosed by Universal dEfiniTion (J-MINUET). This was a prospective and multicenter registry consisting of 3,283 AMI patients, who were hospitalized within 48 hours of onset from July 2012 to March 2014. Clinical follow-up data was obtained for 3 years. In this sub-study, a total of 2,788 patients who underwent urgent PCI having detailed procedural information were enrolled. We analyzed the differences of utilization rates of imaging-guided PCI among the participating institutions and the impacts for the clinical events. The participating institutions were divided into 3 groups by the frequency of IVUS usage: low frequency institutions: under 50%; moderate frequency institutions: 50% to 90%; and, high frequency institutions: over 90%. Results In this cohort registry, patients were enrolled from 28 institutions. The utilization rate of coronary imaging varied widely depending on each institution from 15.4% to 100% (mean 85.7%±24.3, median 97.4%). When the institutions were divided into 3 groups by the frequency of intravascular imaging usage, four low frequency institutions enrolled 295 patients, five moderate frequency institutions enrolled 624 patients, and 19 high frequency institutions enrolled 1,491 patients. Although the incidence of MACE (death, MI, stroke, cardiac failure, or revascularization for unstable angina) decreased stepwise (33.2%, 23.7%, and 19.7%) (gray bar in the Figure), the event rates of the imaging-guided PCI cases among the 3 groups were comparable (21.6%, 21.9%, and 19.6%) (white bar in the Figure). On the other hand, a gradual event reduction between the 3 groups was observed in the angio-guided PCI cases (black bar in the Figure). In comparison of MACE rate between imaging-guided and angio-guided PCI, there were statistically significant differences in the low frequency and moderate frequency institutions (p=0.001 and p=0.012, respectively). In contrast, comparable event rates were observed in the high frequency institutions (p=0.441). MACE rate by imaging usage frequency Conclusions In Japanese ACS patients treated with imaging-guided PCI, better suppression of clinical events during 3-year was found in the institutions with the more frequent use of intravascular imaging, mainly due to stepwise event suppression in the cases of angio-guided PCI. On the other hand, the clinical benefit of coronary imaging was obtained independently of the frequency of use and its experience.

scholarly journals Optimizing smoke alarm signals: Testing the effectiveness of children’s smoke alarms for sleeping adults

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Gary A. Smith ◽  
Sandhya Kistamgari ◽  
Mark Splaingard
Keyword(s):  
Median Time ◽  
High Frequency ◽  
Low Frequency ◽  
The Other ◽  
Wilcoxon Test ◽  
Smoke Alarm ◽  
Smoke Alarms ◽  
Alarm Signals ◽  
Frequency Tone ◽  
Residential Fire

Abstract Background Being asleep is an important risk factor for death during a residential fire; however, the high-frequency tone smoke alarms in many homes will not adequately awaken children who are old enough to self-rescue. In a series of previous studies, we identified smoke alarm signals that effectively awaken children 5–12 years old and prompt their escape. Because it is impractical to have separate alarms for children and adults in a household, the purpose of this study is to test whether alarms that are effective in awakening children and prompting their escape are also effective among adults. Methods Using a randomized, non-blinded, repeated measures design, 150 adults 20–49 years old were exposed during stage 4 sleep to four different smoke alarms. Statistical tests included the Kaplan-Meier estimator, generalized Wilcoxon test, and hazard ratios with Wald’s 95% confidence intervals. Results The median age of study subjects was 30.0 years and 67.3% were female. Almost all (n = 149) subjects awakened and performed the escape procedure to all four alarms; one individual did not awaken or escape to the high-frequency tone alarm. The median time-to-awaken was 2.0 s for the high-frequency tone alarm and 1.0 s for the other three alarms. The median time-to-escape for the high-frequency tone alarm was 12.0 s, compared with 10.0 s for the low-frequency tone alarm and 9.0 s each for the female and male voice alarms. All pairwise comparisons between the high-frequency tone alarm and each of the other three alarms were statistically significant for the probability functions for time-to-awaken and time-to-escape. There were no significant differences in these outcome measures between the latter three alarms, except for female voice versus low-frequency tone alarms for time-to-escape. Conclusions All alarms performed well, demonstrating that smoke alarms developed for the unique developmental requirements of sleeping children are also effective among sleeping adults. Compared with a high-frequency tone alarm, use of these alarms may reduce residential fire-related injuries and deaths among children, while also successfully alerting adult members of the household.

scholarly journals Radio Source Surveys

2002 ◽  
Vol 199 ◽  
pp. 3-10
Author(s):  
J. J. Condon
Keyword(s):  
Radio Source ◽  
Source Parameters ◽  
Low Frequency ◽  
Low Frequencies ◽  
Cluster Emission ◽  
New Class ◽  
Basic Source ◽  
Nearby Galaxies ◽  
Source Populations ◽  
Compact Sources

The primary goal of radio source surveys is to generate flux-limited samples. Sources selected at very low frequencies are dominated by unbeamed emission and give the only unbiased view of the parent populations used by “unification” models to account for the diversity of sources seen at high frequencies. Low-frequency surveys favor sources with exceptionally steep spectra. They include radio galaxies at high redshifts, radio halos of nearby galaxies, relic radio sources, diffuse cluster emission, pulsars that may be missed by traditional pulse searches, and a new class of unidentified compact sources. Flux densities from low-frequency surveys extend the spectra of known source populations to frequencies at which free-free and synchrotron absorption become significant and constrain basic source parameters. Finally, telescope fields-of-view scale ∝ λ2, so gridded surveys can be more efficient than directed observations of individual targets. This review covers recent and proposed low-frequency source surveys and their astronomical uses.

scholarly journals Unveiling the high-frequency radio source population with the AT20G survey

2013 ◽  
Vol 9 (S304) ◽  
pp. 205-208
Author(s):  
Elizabeth K. Mahony
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Sources ◽  
Source Population ◽  
Frequency Source ◽  
Galaxy Population ◽  
5 Ghz

AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

scholarly journals THE AGRO-PASTORAL CONFLICTS AND FORAGE SPECIES PRIZED BY CATTLE: CASE OF THE NORTHERN PERIPHERY OF THE MBAM AND DJEREM NATIONAL PARK (ADAMAOUA-CAMEROON)

2021 ◽  
Vol 9 (02) ◽  
pp. 965-985
Author(s):  
Marie Mvu Njoya ◽  
◽  
Ambahe Duplex Rufin ◽  
Keyword(s):  
High Frequency ◽  
National Park ◽  
Low Frequency ◽  
Partial Solution ◽  
The Other ◽  
Survey Method ◽  
Other Hand ◽  
Forage Species ◽  
The One ◽  
The Relationship

In the outskirts of the northern periphery of Mbam and Djerem National Park, agro-pastoral conflicts have become very frequent in recent years. The resulting damage is so surprising that it leaves no one indifferent. Unfortunately, many writings analyze the causes of these agro-pastoral conflicts without, however, dwelling on the fodder resources which constitute not only the staple food of cattle but also one of the primary factors of these antagonisms. To overcome this knowledge gap, the authors adopted the survey method in order to identify, on the one hand, the attributes of agro-pastoral conflicts and the plant species consumed in all seasons by cattle on the northern periphery of the PNMD and, on the other hand, the relationship between these forage species with the frequency of agro-pastoral conflicts according to the protagonists and the seasons. Thus, from field observations and a questionnaire sent to 44 breeders and 103 farmers in four control villages, it results, after processing the data, that the high frequency of conflicts experienced by the farmers in the dry season (35.9 %) and especially by the breeders (70.5%) is due to the location of the forage species prized in this season at the bottom of the valleys where the herds are concentrated and compete. On the other hand, the low frequency of conflicts experienced during the rainy season especially by breeders, except in Mbitom, is more justified by the extension of fodder registers to woody leaves from the start of this season. Finally, the fodder fields of Brachiaria constitute a partial solution to the shortage of pastures even if it sometimes gives rise to new conflicts between herders.

scholarly journals Australian Journal of Physics Astrophysical Supplement

1976 ◽  
Vol 29 (5) ◽  
pp. 471
Author(s):  
JN Clarke ◽  
AG Little ◽  
BY Mills
Keyword(s):  
Flux Density ◽  
High Frequency ◽  
Magellanic Clouds ◽  
Australian Journal ◽  
The Other ◽  
Optical Data ◽  
Radio Sources ◽  
Angular Extent

The fourth catalogue of radio sources observed at 408 MHz with the Molonglo radiotelescope is presented. A total of 1349 sources is listed to a limiting flux density of 0�2 Jy, the catalogue being largely complete above 0� 25 Jy. The area of sky surveyed includes the Magellanic Clouds as well as a comparison region of similar angular extent. Detailed notes are provided on some of the Cloud sources, and maps are given for complex sources in the region of the Clouds. Those sources for which high-frequency or optical data are available are classified into two lists, one of Cloud members and the other of 'unidentified nonthermal sources', presumably not Cloud members.

scholarly journals Evolution of low-frequency contribution in emission of steep-spectrum radio sources

2014 ◽  
Vol 11 (S308) ◽  
pp. 631-635
Author(s):  
Alla P. Miroshnichenko
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Unified Model ◽  
Linear Size ◽  
Radio Sources ◽  
Mean Values ◽  
Spectrum Radio ◽  
Size Characteristic ◽  
The Mean

AbstractWe consider evolution properties of galaxies and quasars with steep radio spectrum at the decametre band from the UTR-2 catalogue. The ratios of source's monochromatic luminosities at the decametre and high-frequency bands display the dependence on the redshift, linear size, characteristic age of examined objects. At that, the mean values of corresponding ratios for considered galaxies and quasars have enough close quantities,testifying on the unified model of sources. We analyse obtained relations for two types of steep-spectrum sources (with linear steep spectrum (S) and low-frequency steepness after a break (C+)) from the UTR-2 catalogue.

scholarly journals Radio and optical observations of “optically quiet quasars”

1986 ◽  
Vol 119 ◽  
pp. 113-115
Author(s):  
W. D. Cotton ◽  
F. N. Owen ◽  
M. J. Mahoney
Keyword(s):  
Large Particle ◽  
Low Frequency ◽  
Optical Emission ◽  
Optical Observations ◽  
Radio Sources ◽  
Optical Counterpart ◽  
Vlbi Observations ◽  
Compact Radio Source ◽  
Weak Magnetic Fields ◽  
Sky Survey

In recent years a number of very steep spectrum, compact radio sources have been discovered (e.g. Cotton 1983, Cotton and Owen 1985, Ulvestad 1985) which have no optical counterpart to the limit of the Palomar Sky Survey. VLBI observations of a number of these have confirmed the very compact (<10 mas) nature of several of these sources. Analysis of the available data in terms of the standard synchrotron modal suggest that they contain very weak magnetic fields, large particle densities and may emit detectable infrared and optical emission by inverse Campton scattering in the compact radio source (Cotton 1983). This paper will report on an analysis including new VLBI observations, infrared and optical imaging at KPNO and low frequency radio observations at CLRO of a number of these objects.

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