scholarly journals Low frequency observations of radio relics and halos

2018 ◽  
Vol 14 (S342) ◽  
pp. 37-43
Author(s):  
Ruta Kale
Keyword(s):  
Galaxy Clusters ◽  
Low Frequency ◽  
Relativistic Electrons ◽  
Physical Processes ◽  
Low Frequencies ◽  
Origin And Evolution ◽  
Extended Sources ◽  
Low Mass ◽  
Statistical Studies

AbstractDiffuse radio emission from galaxy clusters in the form of radio halos and relics are tracers of the shocks and turbulence in the intra-cluster medium. The imprints of the physical processes that govern their origin and evolution can be found in their radio morphologies and spectra. The role of mildly relativistic population of electrons may be crucial for the acceleration mechanisms to work efficiently. Low frequency observations with telescopes that allow imaging of extended sources over a broad range of low frequencies (<2 GHz) offer the best tools to study these sources. I will review the Giant Metrewave Radio Telescope (GMRT) observations in the past few years that have led to: i) statistical studies of large samples of galaxy clusters, ii) opening of the discovery space in low mass clusters and iii) tracing the spectra of seed relativistic electrons using the Upgraded GMRT.

Role of intracellular calcium and metabolites in low-frequency fatigue of mouse skeletal muscle

1997 ◽  
Vol 272 (2) ◽  
pp. C550-C559 ◽  
Author(s):  
E. R. Chin ◽  
C. D. Balnave ◽  
D. G. Allen
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Low Frequency ◽  
Single Muscle ◽  
Low Frequencies ◽  
Time Integral ◽  
Metabolic Component ◽  
Dependent Component ◽  
Low Frequency Fatigue

We have examined the extent to which prolonged reductions in low-frequency force (i.e., low-frequency fatigue) result from increases in intracellular free Ca2+ concentration ([Ca2+]i) and alterations in muscle metabolites. Force and [Ca2+]i were measured in mammalian single muscle fibers in response to short, intermediate, and long series of tetani that elevated the [Ca2+]i-time integral to 5, 17, and 29 microM x s, respectively. Only the intermediate and long series resulted in prolonged (>60 x min) reductions in Ca2+ release and low-frequency fatigue. When fibers recovered from the long series of tetani without glucose, Ca2+ release was reduced to a greater extent and force was reduced at high and low frequencies. These findings indicate that the decrease in sarcoplasmic reticulum Ca2+ release associated with fatigue has at least two components: 1) a metabolic component, which, in the presence of glucose, recovers within 1 h, and 2) a component dependent on the elevation of the [Ca2+]i-time integral, which recovers more slowly. It is this Ca2+-dependent component that is primarily responsible for low-frequency fatigue.

scholarly journals A Single-Case, Mixed Methods Study Exploring the Role of Music Listening in Vibroacoustic Treatment

2019 ◽  
Vol 19 (2) ◽  
pp. 27 ◽  
Author(s):  
Elsa Campbell ◽  
Birgitta Burger ◽  
Esa Ala-Ruona
Keyword(s):  
Chronic Pain ◽  
Pain Relief ◽  
Mood Disorders ◽  
Single Case ◽  
Low Frequency ◽  
Music Listening ◽  
Low Frequencies ◽  
Therapeutic Interaction ◽  
Treatment Context

Chronic pain is a widespread issue accompanied commonly by depression and anxiety. Chronic pain has been shown to alter brain processing within the emotional and reward circuits, pointing towards a possible link between pain and comorbid mood disorders. Pain relief may be achieved by alleviating depressive and anxious symptoms. Relaxation is important for pain relief and eliciting relaxation through music listening is shown to relieve pain, depression, anxiety, and discomfort among others. In addition to auditory stimuli, Vibroacoustic treatment – the tactile application of low frequency sinusoidal sound vibration, plus music listening and therapeutic interaction – has been shown to be beneficial for relieving these symptoms. Although the combination of music listening and low frequencies has been previously explored, the role of the music listening within the vibroacoustic treatment context is unknown. A single-case, mixed method crossover study was conducted with a client suffering from chronic pain and comorbid mood disorders, four sessions with music listening, and four sessions without. Quantitative outcomes showed the client was more relaxed, less anxious, and had less pain after the music sessions. Qualitative findings showed that the client at first could not relax without the music listening because of her severe anxiety, but learned to use music as a distractor from her thoughts to relax, but also that silence was equally important for her; these hinged on her making the choice based on her needs, which had previously been difficult for her.

The Role of Spatial-Frequency Channels in the Perception of Local and Global Structure

Perception ◽  
1986 ◽  
Vol 15 (3) ◽  
pp. 259-273 ◽  
Author(s):  
Gordon L Shulman ◽  
Marc A Sullivan ◽  
Ken Gish ◽  
William J Sakoda
Keyword(s):  
Reaction Time ◽  
Spatial Frequency ◽  
Low Frequency ◽  
Global Structure ◽  
Global Processing ◽  
Low Frequencies ◽  
Subsequent Performance ◽  
Spatial Frequencies

Adaptation and reaction-time techniques were used to examine the role of different spatial-frequency channels in the perception of local and global structure. Subjects were shown figures consisting of a large C composed of smaller Cs and asked to identify the orientation of either the global C or its local elements. Prior to performing the task subjects were adapted to different spatial frequencies and the effect on subsequent performance was assessed. Two main results were found. First, the adapting frequency that most affected the global task was often lower than that most affecting the local task, suggesting that high and low frequencies independently code the structure of an image. Second, reaction time to global figures was often faster than to local figures at all levels of detectability, again suggesting a role of low-frequency channels in global processing.

scholarly journals A low frequency study of linear polarization in radio galaxies

2020 ◽  
Author(s):  
V H Mahatma ◽  
M J Hardcastle ◽  
J Harwood ◽  
S P O’Sullivan ◽  
G Heald ◽  
...  
Keyword(s):  
Flux Density ◽  
Angular Size ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Low Frequencies ◽  
Sky Survey ◽  
Linearly Polarized ◽  
Low Mass ◽  
The Magnetic Field ◽  
Cent Detection

Abstract Radio galaxies are linearly polarized – an important property that allows us to infer the properties of the magnetic field of the source and its environment. However at low frequencies, Faraday rotation substantially depolarizes the emission, meaning that comparatively few polarized radio galaxies are known at low frequencies. Using the LOFAR Two Metre Sky Survey at 150 MHz and at 20 arcsec resolution, we select 342 radio galaxies brighter than 50 mJy and larger than 100 arcsec in angular size, of which 67 are polarized (18 per cent detection fraction). These are predominantly Fanaroff Riley type II (FR-II) sources. The detection fraction increases with total flux density, and exceeds 50 per cent for sources brighter than 1 Jy. We compare the sources in our sample detected by LOFAR to those also detected in NVSS at 1400 MHz, and find that our selection bias toward bright radio galaxies drives a tendency for sources depolarized between 1400 and 150 MHz to have flatter spectra over that frequency range than those that remain polarized at 150 MHz. By comparing observed rotation measures with an analytic model we find that we are preferentially sensitive to sources in low mass environments. We also infer that sources with one polarized hotspot are inclined by a small angle to the line of sight, while sources with hotspots in both lobes lie in the plane of the sky. We conclude that low frequency polarization in radio galaxies is related to a combination of environment, flux density and jet orientation.

scholarly journals LOW-MASS BINARY X-RAY SOURCES: MONITORING WITH VARIOUS SATELLITES

2014 ◽  
Vol 54 (3) ◽  
pp. 248-253
Author(s):  
Vojtěch Šimon
Keyword(s):  
Light Curve ◽  
Spectral Region ◽  
Large Amplitude ◽  
Single Band ◽  
Intensity Curve ◽  
Physical Processes ◽  
Strong Activity ◽  
X Ray ◽  
Low Mass

We show the importance of observing low-mass binary (LMXB) X-ray sources with the X-ray monitors onboard satellites. This enables us to study the physical processes governing the longterm activity of LMXBs. They are excellent targets for monitoring because of their strong activity. We recall that various physical processes operating in LMXBs produce specific large-amplitude variations of X-ray luminosity which can be investigated even in a single-band X-ray light curve as often provided by the monitors. We also emphasize the role of the spectral region of the X-ray monitor. Choosing the spectral region often strongly influences the profile of the observed intensity curve because different emission components may dominate in different X-ray energy ranges. We show several examples of LMXBs which undergo various types of unpredictable activity (e.g. outbursts, superorbital cycles).

scholarly journals Mutation Landscape of SARS COV2 in Africa

2020 ◽  
Author(s):  
Angus A. Nassir ◽  
Clarisse Musanabaganwa ◽  
Ivan Mwikarago
Keyword(s):  
Disease Burden ◽  
Severe Disease ◽  
Experimental Studies ◽  
Low Frequency ◽  
The United States ◽  
Sub Saharan Africa ◽  
Single Nucleotide ◽  
Low Frequencies ◽  
Sub Saharan

ABSTRACTCOVID-19 disease has had a relatively less severe impact in Africa. To understand the role of SARS CoV2 mutations on COVID-19 disease in Africa, we analysed 282 complete nucleotide sequences from African isolates deposited in the NCBI Virus Database. Sequences were aligned against the prototype Wuhan sequence (GenBank accession: NC_045512.2) in BWA v. 0.7.17. SAM and BAM files were created, sorted and indexed in SAMtools v. 1.10 and marked for duplicates using Picard v. 2.23.4. Variants were called with mpileup in BCFtools v. 1.11. Phylograms were created using Mr. Bayes v 3.2.6. A total of 2,349 single nucleotide polymorphism (SNP) profiles across 294 sites were identified. Clades associated with severe disease in the United States, France, Italy, and Brazil had low frequencies in Africa (L84S=2.5%, L3606F=1.4%, L3606F/V378I/=0.35, G251V=2%). Sub Saharan Africa (SSA) accounted for only 3% of P323L and 4% of Q57H mutations in Africa. Comparatively low infections in SSA were attributed to the low frequency of the D614G clade in earlier samples (25% vs 67% global). Higher disease burden occurred in countries with higher D614G frequencies (Egypt=98%, Morocco=90%, Tunisia=52%, South Africa) with D614G as the first confirmed case. V367F, D364Y, V483A and G476S mutations associated with efficient ACE2 receptor binding and severe disease were not observed in Africa. 95% of all RdRp mutations were deaminations leading to CpG depletion and possible attenuation of virulence. More genomic and experimental studies are needed to increase our understanding of the temporal evolution of the virus in Africa, clarify our findings, and reveal hot spots that may undermine successful therapeutic and vaccine interventions.

scholarly journals The Challenges of Low-Frequency Radio Polarimetry: Lessons from the Murchison Widefield Array

2017 ◽  
Vol 34 ◽  
Author(s):  
E. Lenc ◽  
C. S. Anderson ◽  
N. Barry ◽  
J. D. Bowman ◽  
I. H. Cairns ◽  
...  
Keyword(s):  
Imaging Techniques ◽  
Low Frequency ◽  
Field Of View ◽  
Wide Field ◽  
Low Mass Stars ◽  
Future Directions ◽  
Low Frequencies ◽  
Wide Field Of View ◽  
Low Mass ◽  
Murchison Widefield Array

AbstractWe present techniques developed to calibrate and correct Murchison Widefield Array low-frequency (72–300 MHz) radio observations for polarimetry. The extremely wide field-of-view, excellent instantaneous (u, v)-coverage and sensitivity to degree-scale structure that the Murchison Widefield Array provides enable instrumental calibration, removal of instrumental artefacts, and correction for ionospheric Faraday rotation through imaging techniques. With the demonstrated polarimetric capabilities of the Murchison Widefield Array, we discuss future directions for polarimetric science at low frequencies to answer outstanding questions relating to polarised source counts, source depolarisation, pulsar science, low-mass stars, exoplanets, the nature of the interstellar and intergalactic media, and the solar environment.

scholarly journals 2-D and 3-D models of convective turbulence and oscillations in intermediate-mass main-sequence stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 540-543
Author(s):  
Joyce A. Guzik ◽  
T. H. Morgan ◽  
N. J. Nelson ◽  
C. Lovekin ◽  
K. Kosak ◽  
...  
Keyword(s):  
Main Sequence ◽  
Convection Zone ◽  
Low Frequency ◽  
Main Sequence Stars ◽  
Low Frequencies ◽  
Rotation Rates ◽  
Multidimensional Modeling ◽  
Core Convection ◽  
Radiative Zone

AbstractWe present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the Sun, using three separate approaches: 1) Using the 3-D planar StellarBox radiation hydrodynamics code to model the envelope convection zone and part of the radiative zone. Our goals are to examine the interaction of stellar pulsations with turbulent convection in the envelope, excitation of acoustic modes, and the role of convective overshooting; 2) Applying the spherical 3-D MHD ASH (Anelastic Spherical Harmonics) code to simulate the core convection and radiative zone. Our goal is to determine whether core convection can excite low-frequency gravity modes, and thereby explain the presence of low frequencies for some hybrid γ Dor/δ Sct variables for which the envelope convection zone is too shallow for the convective blocking mechanism to drive gravity modes; 3) Applying the ROTORC 2-D stellar evolution and dynamics code to calculate evolution with a variety of initial rotation rates and extents of core convective overshooting. The nonradial adiabatic pulsation frequencies of these nonspherical models are calculated using the 2-D pulsation code NRO. We present new insights into pulsations of 1-2 M⊙ stars gained by multidimensional modeling.

scholarly journals Diffuse Extragalactic Emission at Low Frequencies within the Epoch of Reionization 0-hour Field

2021 ◽  
Author(s):  
◽  
Stefan Duchesne
Keyword(s):  
Radio Emission ◽  
Sample Size ◽  
Galaxy Clusters ◽  
Low Frequency ◽  
Small Sample ◽  
Point Sources ◽  
Scaling Relations ◽  
Low Frequencies ◽  
Cluster Emission ◽  
Radio Halo

<p>Low-frequency radio imaging of the southern sky has become available with the advent of the Murchison Widefield Array (MWA). The topic of this thesis is the study of extended, low-frequency radio emission, with a primary focus on the non-thermal synchrotron emission associated with the intra-cluster medium (ICM) of galaxy clusters. We do not limit the study to such emission, however, and investigate a small sample of other interesting and extended radio emission from objects in the southern sky.   A significant portion of this work is invested in detecting, and characterising, extended, diffuse radio emission from galaxy clusters within a 45 degree by 45 degree region of the southern sky centred on R.A. = 0 hours, decl. = -27 degrees. This field is chosen as a deep MWA image has been made available which is sensitive to extended structures. Within the field we search for low-frequency, diffuse cluster emission, previously detected or otherwise. In doing so we find 34 diffuse radio sources, 3 of which are newly detected haloes, 1 newly detected relic with many new candidates of each. Further, we detect a new phoenix candidate as well as 2 candidate dead radio galaxies at the centre of clusters. We confirm previous observations of such emission as well, and measure properties such as their integrated flux densities, spectral indices, and sizes where possible. We compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power with the cluster X-ray luminosity and mass. We find that both scaling relations are consistent with previous findings despite the increase in sample size, though note that the raw scatter in the data for best-fitting parameters increases with increase in sample size. In this, we demonstrate the utility of low-frequency radio telescopes like the MWA in detecting such emission, showing that the MWA is pushing into higher-redshift, lower-mass systems, though we caution that the low resolution of the MWA can work against us.  We follow-up on two galaxy clusters found to host extended emission - Abell S1136 and Abell S1063. In the case of Abell S1136 we observe the emission at its centre with the Australia Telescope Compact Array (ATCA) and determine the presence of a core, suggesting the emission to be that of an ancient episode of an active galactic nucleus in the central elliptical of the cluster, ESO 470-G020. After reducing archival ATCA data for Abell S1063 we find no evidence of a halo and consider the source to be constructed of blended point sources. We close with a description of a strong double-lobed radio source associated with a non-elliptical host ESO 472-G013, likely a spiral or irregular galaxy, that was found serendipitously whilst searching for diffuse cluster emission. We explore the host within the context of star-formation, and consider the possible origins of the AGN and lobes due to interaction with either the nearby spiral, ESO 472-G012, or a past or ongoing merger event.</p>

scholarly journals Particle re-acceleration in the ICM and low-frequency observations

2006 ◽  
Vol 2 (14) ◽  
pp. 374-375
Author(s):  
Gianfranco Brunetti
Keyword(s):  
Radio Emission ◽  
Galaxy Clusters ◽  
Low Frequency ◽  
Radio Observations ◽  
Low Frequencies

AbstractThe particle reaceleration model is one of the most promising possibilities to explain the Mpc-scale diffuse radio emission detected in a number of galaxy clusters. Ongoing and future radio observations at low frequencies may help in constraining and testing this model.

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