scholarly journals Onset of plane layer magnetoconvection at low Ekman number

2015 ◽  
Vol 27 (10) ◽  
pp. 106602 ◽  
Author(s):  
Kélig Aujogue ◽  
Alban Pothérat ◽  
Binod Sreenivasan
Keyword(s):  
Plane Layer ◽  
Ekman Number

Convection-driven dynamos in a rotating plane layer

2000 ◽  
Vol 404 ◽  
pp. 311-343 ◽  
Author(s):  
CHRIS A. JONES ◽  
PAUL H. ROBERTS
Keyword(s):  
Simple Model ◽  
Three Dimensional ◽  
Plane Layer ◽  
Dynamo Model ◽  
Ekman Number ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
Dynamo Mechanism ◽  
Diffusivity Ratio

The plane layer Childress–Soward dynamo model, consisting of a rotating layer of electrically conducting fluid between horizontal planes heated from below, is studied. Solutions periodic in the horizontal directions are sought, with electrically insulating boundary conditions applied. The large Prandtl number limit is used.Fully three-dimensional convection-driven dynamos have been studied numerically for this problem. Both the kinematic and the magnetically saturated regimes are studied, and a simple model of the dynamo mechanism is proposed. The dependence of the dynamo on the Rayleigh number, Ekman number and diffusivity ratio is studied, and the role of Taylor's constraint in low Ekman number convection-driven dynamos is considered.

A New Technique for the Light and Electron Microscopic Study of Individual Cerebro-Spinal Fluid Cells in a Mona Plane Layer

1976 ◽  
Vol 34 ◽  
pp. 362-363
Author(s):  
L.A. Dell
Keyword(s):  
Microscopic Study ◽  
Electron Microscopic Study ◽  
Plane Layer ◽  
Ultrastructural Level ◽  
Spinal Fluid ◽  
Electron Microscopic Level ◽  
Electron Microscopic ◽  
Easy Method ◽  
Cell Pellet ◽  
A New Technique

A new method has been developed which readily offers the microscopist a possibility for both light and electron microscopic study of selected cells from the cerebrospinal fluid. Previous attempts to examine these cells in the spinal fluid at the ultrastructural level were based on modifications of cell pellet techniques developed for peripheral blood. These earlier methods were limited in application by the number of cells in spinal fluid required to obtain a sufficient size pellet and by the lack of an easy method of cellular identification between the light and electron microscopic level. The newly developed method routinely employs microscope slides coated with Siliclad and tungsten oxide for duplicate cytocentrifuge preparations of diagnostic spinal fluid specimens. Work done by Kushida and Suzuki provided a basis for our use of the metal oxide.

scholarly journals Cosmic-Ray Driven Outflows to Mpc Scales from L* Galaxies

2020 ◽  
Author(s):  
Philip F Hopkins ◽  
T K Chan ◽  
Suoqing Ji ◽  
Cameron B Hummels ◽  
Dušan Kereš ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
Plane Layer ◽  
Equilibrium Density ◽  
Pressure Gradients ◽  
Low Velocity ◽  
Star Forming ◽  
Stellar Feedback ◽  
Massive Halos ◽  
Halo Masses

Abstract We study the effects of cosmic rays (CRs) on outflows from star-forming galaxies in the circum and inter-galactic medium (CGM/IGM), in high-resolution, fully-cosmological FIRE-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/CR diffusion and streaming, and CR losses). We showed previously that massive (Mhalo ≳ 1011 M⊙), low-redshift (z ≲ 1 − 2) halos can have CR pressure dominate over thermal CGM pressure and balance gravity, giving rise to a cooler CGM with an equilibrium density profile. This dramatically alters outflows. Absent CRs, high gas thermal pressure in massive halos “traps” galactic outflows near the disk, so they recycle. With CRs injected in supernovae as modeled here, the low-pressure halo allows “escape” and CR pressure gradients continuously accelerate this material well into the IGM in “fast” outflows, while lower-density gas at large radii is accelerated in-situ into “slow” outflows that extend to >Mpc scales. CGM/IGM outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disk to >Mpc. The CR-driven outflows are primarily cool (T ∼ 105 K) and low-velocity. All of these effects weaken and eventually vanish at lower halo masses (≲ 1011 M⊙) or higher redshifts (z ≳ 1 − 2), reflecting the ratio of CR to thermal+gravitational pressure in the outer halo. We present a simple analytic model which explains all of the above phenomena. We caution that these predictions may depend on uncertain CR transport physics.

Hydromagnetic convective instability of a rotating, self-gravitating fluid sphere containing a uniform distribution of heat sources

1977 ◽  
Vol 353 (1673) ◽  
pp. 145-162 ◽  
Keyword(s):  
Cylindrical Shell ◽  
Uniform Distribution ◽  
Critical Rayleigh Number ◽  
Plane Layer ◽  
Fluid Sphere ◽  
Dynamo Model ◽  
Planar Geometry ◽  
Heat Sources ◽  
Curvature Effects ◽  
The Waves

The desire to understand better the magneto-hydrodynamics of the Earth's and planetary interiors has recently motivated a number of studies on convective motions in hydromagnetic rotating systems. These studies have, however, been restricted to planar geometry, the convective layer being confined between two horizontal planes in externally applied uniform gravitational and magnetic fields. This paper takes a step further to the geophysical and astrophysical contexts by restoring curvature effects. The linear stability of a uniformly rotating, self-gravitating fluid sphere in the presence of a co-rotating zonal magnetic field is studied when buoyancy is provided by a uniform distribution of heat sources. The analysis is limited to the case where the Chandrasekhar number, Q , and the Taylor number, λ 2 , are both large. (These are, respectively, dimension-less measures of Lorentz and Coriolis forces relative to the viscous forces.) It is shown that for all values of λ and Q the motions appearing at marginal convection are necessarily time-dependent and associated with a temperature fluctuation which is always symmetric with respect to the equatorial plane. The critical Rayleigh number R c ( λ, Q ), which is a dimensionless measure of the temperature contrast necessary for the onset of convection, is found to be qualitatively the same as for the planar model only when λ ≥ O(Q) , although even in this case certain characteristic curvature effects arise. The motions prevalent at marginal stability, when O ( Q 3/2 ) ≥ λ ≫ Q , occur in the form of a thin cylindrical shell of thickness O (( Q/λ ) 2/3 ) and whose distance from the axis of rotation varies between 0.4 and 0.6 spherical radii depending on the value of q , which is the ratio of the thermal to the magnetic diffusivities. The waves will drift westward or eastward according to whether q ≶ 2.5. (The cause of disagreement in this result with Busse (1975 b ) is explained in an appendix). For λ = O(Q) convection occurs in the whole volume of the sphere and the waves drift westward for all values of q . When λ ≪ Q , not only is R c incorrectly given by that for the plane layer model but also modal degeneracies of convection in the plane layer are removed by the curvature and boundedness of the system. For this range of λ and Q convection again fills the whole sphere but all forms of diffusion are concentrated in multiple boundary layers on the surface of sphere. The waves drift westward. The results are compared with parellel studies, including Braginsky's MAC waves (i. e. Hide's slow magnetohydrodynamic waves) and Busse's recent dynamo model. In particular, it is argued that the last of these may not be representative of planetary magnetism because of a convective growth of field (not considered by Busse) associated with convection patterns occuring in the whole sphere rather than in a cylindrical shell.

Combined Conduction and Radiation Heat Transfer in Porous Materials Heated by Intense Solar Radiation

1985 ◽  
Vol 107 (1) ◽  
pp. 29-34 ◽  
Author(s):  
L. K. Matthews ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Heat Transfer ◽  
Radiation Heat Transfer ◽  
Plane Layer ◽  
Single Scattering ◽  
Dominant Mode ◽  
Radiative Properties ◽  
Maximum Temperature ◽  
Transfer Model ◽  
Radiation Heat ◽  
Flux Approximation

An analysis is presented to predict the heat transfer characteristics of a plane layer of a semitransparent, high-temperature, porous material which is irradiated by an intense solar flux. A transient, combined conduction and radiation heat transfer model, which is based on a two-flux approximation for the radiation, is used to predict the temperature distribution and heat transfer in the material. Numerical results have been obtained using thermophysical and radiative properties of zirconia as a typical material. The results show that radiation is an important mode of heat transfer, even when the opacity of the material is large (τL > 100). Radiation is the dominant mode of heat transfer in the front third of the material and comparable to conduction toward the back. The semitransparency and high single scattering albedo of the zirconia combine to produce a maximum temperature in the interior of the material.

Sign in / Sign up

Export Citation Format

Share Document