Search results for "Convection"

General treatment of vortical, toroidal, and compression modes

2011

The multipole vortical, toroidal, and compression modes are analyzed. Following the vorticity concept of Ravenhall and Wambach, the vortical operator is derived and related in a simple way to the toroidal and compression operators. The strength functions and velocity fields of the modes are analyzed in $^{208}$Pb within the random-phase-approximation using the Skyrme force SLy6. Both convection and magnetization nuclear currents are taken into account. It is shown that the isoscalar (isovector) vortical and toroidal modes are dominated by the convection (magnetization) nuclear current while the compression mode is fully convective. The relation between the above concept of the vorticity to …

Fully Developed Mixed Magnetohydrodynamic Convection in a Vertical Square Duct

2008

The fully developed flow of an electrically conducting, internally heated fluid in a vertical square duct under the influence of buoyancy and magnetohydrodynamic forces is studied. The flow being parallel, the governing equations are two-dimensional and linear; an analytical solution exists for temperature, while velocity and electric potential are computed by a finite difference technique under different electric boundary conditions, forced to natural convection intensity ratios and values of the magnetic induction. Limiting values of pressure gradient and mean velocity are determined for the flow to be unidirectional throughout the duct's section; recirculation occurs for intermediate val…

Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun

2017

The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we continue studies Gorobets, A. Y., Borrero, J. M., & Berdyugina, S. 2016, ApJL, 825, L18 of the temporal stochasticity of the magnetic field on the solar surface without relying either on the concept of magnetic features or on subjective assumptions about their identification and interaction. We propose a data analysis method to quantify fluctuations of the line-of-sight …

Activity, Rotation And Convection in Orion: Are the Data Inconsistent with the MS Activity-Rossby Number Relation?

2004

A relation between activity and rotation in young ~ 1Myr PMS in often not observed, suggesting that the mechanism responsible for the X-ray emission may differ from the α - ω dynamo. We re-investigate the matter utilizing recent X-ray and rotational data on the Orion Nebula Cluster (ONC).

Spatial distribution and statistical properties of small-scale convective vortex-like motions in a quiet-Sun region

2011

High-resolution observations of a quiet Sun internetwork region taken with the Solar 1-m Swedish Telescope in La Palma are analyzed. We determine the location of small-scale vortex motions in the solar photospheric region by computing the horizontal proper motions of small-scale structures on time series of images. These plasma convectively-driven swirl motions are associated to: (1) downdrafts (that have been commonly explained as corresponding to sites where the plasma is cooled down and hence returned to the interior below the visible photospheric level), and (2) horizontal velocity vectors converging into a central point. The sink cores are proved to be the final destination of passive …

Convection in the Surface Layers of Neutron Stars

1997

During some phases of a neutron star's evolution, the temperature gradient in the surface layers, calculated assuming only radiative and conductive transport, may exceed the adiabatic gradient. This superadiabatic gradient is the necessary (but not sufficient) condition for convective instability. The present paper examines the sufficiency condition for the onset of convection in neutron stars in the presence of a strong magnetic field. It is shown that the large fields typically found in neutron stars—about 1011 to 1013 G—stabilize the atmosphere against convection. Convective instability can arise only in neutron stars with very weak magnetic fields, ≤108-109 G. Convective motions in such…

Poincaré's role in the Crémieu-Pender controversy over electric convection

1989

Summary In the course of 1901, V. Cremieu published the results of some experiments carried out to test the magnetic effects of electric convection currents. According to Cremieu, his experiments had proved that convection currents had no magnetic effects and consequently they were not equivalent to conduction currents, that is they were not ‘real’ electric currents. These negative results conflicted with those of well-known experiments carried out by other researchers, in particular with Rowland's experiments, and with Maxwell's, Hertz's and Lorentz's theories, which was more shocking. The publication of Cremieu's experiments raised a controversy which involved directly or indirectly some …

Influence of a Magnetic Field on Liquid Metal Free Convection in an Internally Heated Cubic Enclosure

2002

The buoyancy‐driven magnetohydrodynamic flow in a cubic enclosure was investigated by three‐dimensional numerical simulation. The enclosure was volumetrically heated by a uniform power density and cooled along two opposite vertical walls, all remaining walls being adiabatic. A uniform magnetic field was applied orthogonally to the gravity vector and to the temperature gradient. The Prandtl number was 0.0321 (characteristic of Pb–17Li at 300°C), the Rayleigh number was 104, and the Hartmann number was made to vary between 0 and 2×103. The steady‐state Navier–Stokes equations, in conjunction with a scalar transport equation for the fluid's enthalpy and with the Poisson equation for the electr…

Matrix solutions of diffusion equation

2002

Adiabatic eigenflows in a vertical porous channel

2014

AbstractThe existence of an infinite class of buoyant flows in a vertical porous channel with adiabatic and impermeable boundary walls, called adiabatic eigenflows, is discussed. A uniform heat source within the saturated medium is assumed, so that a stationary state is possible with a net vertical through-flow convecting away the excess heat. The simple isothermal flow with uniform velocity profile is a special adiabatic eigenflow if the power supplied by the heat source is zero. The linear stability analysis of the adiabatic eigenflows is carried out analytically. It is shown that these basic flows are unstable. The only exception, when the power supplied by the heat source is zero, is th…