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.

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 Modelling Time-Dependent Diffusion in Am Star Envelopes

1993 ◽  
Vol 137 ◽  
pp. 272-274 ◽  
Author(s):  
G. Alecian
Keyword(s):  
Diffusion Process ◽  
Mass Loss ◽  
Main Sequence ◽  
Convection Zone ◽  
Time Dependent ◽  
Radiative Zone

AbstractWe study the diffusion process occurring just below the superficial convection zone of Am stars, improving the methods used sofar. We are now able to compute, in a more realistic way, the evolution of the concentrations during the stay of the stars on the main sequence for a large number of elements. This allows to better constrain the different properties (mass loss, depth of the superficial convection zone, transition between convection and radiative zone) entering the modelling of Am stars in the framework of a diffusion-dominant description.

scholarly journals Rotation of Pre-Main Sequence Stars from High S/N Spectroscopy

1988 ◽  
Vol 132 ◽  
pp. 95-98
Author(s):  
J. Bouvier
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Spectroscopic Studies ◽  
Main Sequence Stars ◽  
Rotation Rates ◽  
Large Samples ◽  
Stellar Formation ◽  
Low Mass ◽  
Pms Stars ◽  
Large Telescopes

Until 1980, only a handful of low-mass, active pre-main sequence (pms) stars had known rotation velocities (vsini) /1/. Since then, increasingly sensitive detectors coupled to large telescopes led to high–resolution (a few 104) spectroscopic studies of these faint stars (mv = 10–13), with S/N ratio of the order of 100. The measurement of vsini for large samples of pms stars that resulted brought new insights on various pressing questions related to stellar formation and early stellar evolution : how do the rotation rates of pms stars compare with those expected from models of stellar formation ? how does the stellar angular momentum change during pms evolution ? is pms activity linked with rotation as would be expected if activity were triggered by magnetic processes ?

MAIN SEQUENCE-LIKE STARS WITH SOLITONIC CORES IN EFFECTIVE GRAVITY MODELS

1999 ◽  
Vol 08 (06) ◽  
pp. 695-703
Author(s):  
NIMMI ROOPRAI ◽  
DAKSH LOHIYA
Keyword(s):  
Main Sequence ◽  
Gravity Models ◽  
Main Sequence Stars ◽  
Effective Gravity ◽  
Normal Star ◽  
Astrophysical Objects ◽  
Generic Class ◽  
Radiative Zone ◽  
Characteristic Features

Lee–Wick type nontopological solitons (NTS's) are known to arise in a generic class of nonminimally coupled theories. Size of these solutions depend upon the nature and the amount of their associated conserved charge. Such NTS's would have characteristic features and would represent novel astrophysical objects. We explore the possibility of having main sequence stars condensing around small NTS's. In particular, if such an NTS is embedded in the radiative zone of a star, the exterior attributes could be indistinguishable from those of a normal star. Possible application to stellar modeling is explored.

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.

scholarly journals Light elements in massive single and binary stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 411-420 ◽  
Author(s):  
N. Langer ◽  
I. Brott ◽  
M. Cantiello ◽  
S. E. de Mink ◽  
R. G. Izzard ◽  
...  
Keyword(s):  
Binary Stars ◽  
Main Sequence ◽  
Diagnostic Value ◽  
Light Elements ◽  
Main Sequence Stars ◽  
Mixing Processes ◽  
Transfer Event ◽  
Internal Mixing ◽  
Early Type Stars

AbstractWe highlight the role of the light elements (Li, Be, B) in the evolution of massive single and binary stars, which is largely restricted to a diagnostic value, and foremost so for the element boron. However, we show that the boron surface abundance in massive early type stars contains key information about their foregoing evolution which is not obtainable otherwise. In particular, it allows to constrain internal mixing processes and potential previous mass transfer event for binary stars (even if the companion has disappeared). It may also help solving the mystery of the slowly rotating nitrogen-rich massive main sequence stars.

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.

scholarly journals Bipolar flows and jets from stars of different spectral types: Observations

1987 ◽  
Vol 122 ◽  
pp. 39-50
Author(s):  
Martin Cohen
Keyword(s):  
Main Sequence ◽  
Cataclysmic Variables ◽  
Circumstellar Disks ◽  
Red Giants ◽  
Main Sequence Stars ◽  
Hot Stars

The fact that bipolar flows are widespread among stars of very different spectral types is emphasized. First, the stars associated with the phenomenon are divided into broad types: protostars and pre-main-sequence stars; red giants; symbiotic objects; protoplanetaries; planetaries; novae and cataclysmic variables; and peculiar hot stars. Second, the evidence for circumstellar “disks” or toroids is considered among these different categories of star. Finally, the possible role of binarity is discussed.

scholarly journals Emission line spectropolarimetry and circumstellar structures

2014 ◽  
Vol 10 (S305) ◽  
pp. 288-292
Author(s):  
Jorick S. Vink
Keyword(s):  
Emission Line ◽  
Accretion Disks ◽  
Main Sequence ◽  
Gamma Ray ◽  
Young Stars ◽  
Main Sequence Stars ◽  
Current Sensitivity ◽  
Luminous Blue Variables ◽  
3D Monte Carlo

AbstractWe discuss the role of linear emission-line polarimetry in a wide set of stellar environments, involving the accretion disks around young pre-main sequence stars, to the aspherical outflows from O stars, luminous blue variables and Wolf-Rayet stars, just prior to explosion as a supernova or a gamma-ray burst. We predict subtle QU line signatures, such as single/double QU loops for un/disrupted disks. Whilst there is plenty of evidence for single QU loops, suggesting the presence of disrupted disks around young stars, current sensitivity (with S/N of order 1000) is typically not sufficient to allow for quantitative 3D Monte Carlo modeling. However, the detection of our predicted signatures is expected to become feasible with the massive improvement in sensitivity of extremely large mirrors.

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