scholarly journals Turbulent radiative diffusion and turbulent Newtonian cooling

2021 ◽  
Vol 33 (9) ◽  
pp. 095125
Author(s):  
Axel Brandenburg ◽  
Upasana Das
Keyword(s):  
2005 ◽  
Vol 9 (3) ◽  
pp. 515-548 ◽  
Author(s):  
J. R. Nanduri ◽  
C. J. Sung ◽  
J. S. T'Ien

2003 ◽  
Vol 189 (2) ◽  
pp. 539-556 ◽  
Author(s):  
T.M. Evans ◽  
T.J. Urbatsch ◽  
H. Lichtenstein ◽  
J.E. Morel

2020 ◽  
Vol 494 (1) ◽  
pp. 1463-1469
Author(s):  
G V Vereshchagin ◽  
I A Siutsou

ABSTRACT Photospheric emission may originate from relativistic outflows in two qualitatively different regimes: last scattering of photons inside the outflow at the photospheric radius or radiative diffusion to the boundary of the outflow. In this work, the measurement of temperature and flux of the thermal component in the early afterglows of several gamma-ray bursts along with the total flux in the prompt phase is used to determine initial radii of the outflow as well as its Lorentz factors. Results indicate that in some cases the outflow has relatively low Lorentz factors (Γ < 10), favouring cocoon interpretation, while in other cases Lorentz factors are larger (Γ > 10), indicating diffusive photospheric origin of the thermal component, associated with an ultrarelativistic outflow.


2019 ◽  
Vol 24 (1) ◽  
pp. 31
Author(s):  
Nazish Shahid

An investigation of how the velocity of elasto-viscous fluid past an infinite plate, with slip and variable temperature, is influenced by combined thermal-radiative diffusion effects has been carried out. The study of dynamics of a flow model leads to the generation of characteristic fluid parameters ( G r , G m , M, F, S c and P r ). The interaction of these parameters with elasto-viscous parameter K ′ is probed to describe how certain parametric range and conditions could be pre-decided to enhance the flow speed past a channel. In particular, the flow dynamics’ alteration in correspondence to the slip parameter’s choice, along with temperature provision to the boundary in temporal pattern, is determined through uniquely calculated exact expressions of velocity, temperature and mass concentration of the fluid. The complex multi-parametric model has been analytically solved using the Laplace and Inverse Laplace transform. Through study of calculated exact expressions, an identification of variables, adversely (M, F, S c and P r ) and favourably ( G r and G m ) affecting the flow speed and temperature has been made. The accuracy of our results have also been tested by computing matching numerical solutions and by graphical reasoning. The verification of existing results of Newtonian fluid with varying boundary condition of velocity and temperature has also been completed, affirming the veracity of present results.


1993 ◽  
Vol 138 ◽  
pp. 517-527 ◽  
Author(s):  
Thierry Lanz ◽  
Ivan Hubeny

AbstractSo far, neither chromospheres nor stellar winds have been directly detected in main-sequence A stars. While radiative diffusion requires extremely weak stellar winds to reproduce chemical anomalies (10−15 to 10−12M⊙yr−1), two independent direct searches for mass loss set up upper limits to 10−10 M⊙yr−1, which is still several orders of magnitude higher. We discuss some new recent possibilities to detect chromospheres which arise thanks to new NLTE model atmospheres. In the near future, some progress is also expected from new observations of Lyman α with HST and from the increased sensitivity of ROSAT in the X-ray domain.


1931 ◽  
Vol 50 ◽  
pp. 225-242 ◽  
Author(s):  
O. F. T. Roberts

SummaryThe processes of long-wave low-temperature radiation in the atmosphere have been studied with a view to investigating the extent to which they may be regarded as diffusion-like; the decrease of water-vapour with height is taken to be exponential, that of temperature to be constant up to the tropopause, and then to be zero. Full allowance is made for the radiation being diffuse, involving the functions ; such properties of these functions as are required in the further work are studied. The expression for the upward flow of radiation is obtained in the form of a power series in the temperature gradient in the troposphere; the coefficient of the first power of the temperature gradient is defined as the “coefficient of radiative diffusion.” There is shown to be a certain amount of ambiguity about the coefficient so defined.A model atmosphere resembling fairly well the conditions in N.W. Europe is considered: the upward flow of radiation and the coefficient of radiative diffusion are calculated; for this purpose we require Hettner's measurements of water-vapour absorption as modified by Simpson.The effect of the heating of the ground during the day to a temperature above that of the air near by is then considered; it is shown that the study of the results of this factor which are of importance in the interpretation of continuous temperature records near the ground requires measurements of the absorption of water-vapour for the wave-lengths for which it is particularly opaque; these do not appear to exist.


2014 ◽  
Vol 35 (1) ◽  
pp. 135-151 ◽  
Author(s):  
T. Gallouët ◽  
R. Herbin ◽  
A. Larcher ◽  
J.-C. Latché

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