18,095 research outputs found
On the MHD load and the MHD metage
In analogy with the load and the metage in hydrodynamics, we define
magnetohydrodynamic load and magnetohydrodynamic metage in the case of
magnetofluids. They can be used to write the magnetic field in MHD in Clebsch's
form. We show how these two concepts can be utilised to derive the magnetic
analogue of the Ertel's theorem and also, how in the presence of non-trivial
topology of the magnetic field in the magnetofluid one may associate the
linking number of the magnetic field lines with the invariant MHD loads. The
paper illustrates that the symmetry translation of the MHD metage in the
corresponding label space generates the conservation of cross helicity.Comment: Some issues in the paper are yet to be addressed. Constructive
critisicms are most welcom
Analysis of radial segregation of granular mixtures in a rotating drum
This paper considers the segregation of a granular mixture in a rotating
drum. Extending a recent kinematic model for grain transport on sandpile
surfaces to the case of rotating drums, an analysis is presented for radial
segregation in the rolling regime, where a thin layer is avalanching down while
the rest of the material follows rigid body rotation. We argue that segregation
is driven not just by differences in the angle of repose of the species, as has
been assumed in earlier investigations, but also by differences in the size and
surface properties of the grains. The cases of grains differing only in size
(slightly or widely) and only in surface properties are considered, and the
predictions are in qualitative agreement with observations. The model yields
results inconsistent with the assumptions for more general cases, and we
speculate on how this may be corrected.Comment: 12 pages inclusive of 10 PostScript (*.eps) figures, uses svjour,
psfrag and graphicx. Submitted for publication to Euro. Phys. J.
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