78,150 research outputs found
Simulations of the interaction of cold gas with radio jets
A new scenario for the interaction of a jet with a background medium with
cold clouds is investigated by means of hydrodynamic turbulence simulations
with cooling. The idea is that the cold clouds are overtaken by a radio cocoon
and stirred up by turbulence in this cocoon. The 2D multiphase turbulence
simulations contain all the three gas phases and have a number of interesting
properties. The produced power spectrum is proportional to the inverse square
of the wavevector. The Mach number - density relation may explain the observed
velocities in emission line gas associated with radio galaxies. The model also
explains the increased optical visibility within the radio structures, the
correlation between emission line and radio luminosity, and the evolution of
the alignment effect with source size. I also propose this to be a useful model
for the recently discovered neutral outflows in nearby radio sources.Comment: Contribution to the proceedings of "The Fate of Gas in Galaxies",
Dwingeloo, July 2006, 8 pages 6 figures. To appear in New Astronomy Reviews,
Vol. 51 (2007), eds. Morganti, Oosterloo, Villar-Martin & van Gorko
Radio Observations of the Magnetic Fields in Galaxies
After a short introduction on how we get information of the magnetic fields
from radio observations I discuss the results concerning the magnetic field
structure in galaxies: Large-scale regular magnetic field pattern of spiral
structure exist in grand-design spirals, flocculent and even irregular
galaxies. The regular field in spirals is aligned along the optical spiral arms
but strongest in the interarm region, sometimes forming 'magnetic arms'. The
strongest total field is found in the optical arms, but mainly irregular. The
large-scale regular field is best explained by some kind of dynamo action. Only
a few galaxies show a dominant axisymmetric field pattern, most field
structures seem to be a superposition of different dynamo modes or rather
reveal more local effects related to density waves, bars or shocks.
Observations of edge-on galaxies show that the magnetic fields are mainly
parallel to the disk except in some galaxies with strong star formation and
strong galactic winds as e.g. NGC 4631.Comment: 9 pages with 4 figures. To be published in Acta Astronomica Sinica
Vol. 44, 2003 (Conf. Proc. "Radio Studies of Galactic Objects, Galaxies and
AGNs", eds. J.L. Han et al.). Final published version also available at
http://www.bao.ac.cn/bao/hjl/xian/proceedings
Energy conserving Anisotropic Anhysteretic Magnetic Modelling for Finite Element Analysis
To model ferromagnetic material in finite element analysis a correct
description of the constitutive relationship (BH-law) must be found from
measured data. This article proposes to use the energy density function as a
centrepiece. Using this function, which turns out to be a convex function of
the flux density, guarantees energy conservative modelling. The magnetic field
strength can be seen as a derivative with respect to the flux density.
Especially for anisotropic materials (from lamination and/or grain orientation)
this method has advantages. Strictly speaking this method is only valid for
anhysteretic and thermodynamically stable material
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