3,158 research outputs found
Magnetic induction and diffusion mechanisms in a liquid sodium spherical Couette experiment
We present a reconstruction of the mean axisymmetric azimuthal and meridional
flows in the DTS liquid sodium experiment. The experimental device sets a
spherical Couette flow enclosed between two concentric spherical shells where
the inner sphere holds a strong dipolar magnet, which acts as a magnetic
propeller when rotated. Measurements of the mean velocity, mean induced
magnetic field and mean electric potentials have been acquired inside and
outside the fluid for an inner sphere rotation rate of 9 Hz (Rm 28). Using the
induction equation to relate all measured quantities to the mean flow, we
develop a nonlinear least square inversion procedure to reconstruct a fully
coherent solution of the mean velocity field. We also include in our inversion
the response of the fluid layer to the non-axisymmetric time-dependent magnetic
field that results from deviations of the imposed magnetic field from an axial
dipole. The mean azimuthal velocity field we obtain shows super-rotation in an
inner region close to the inner sphere where the Lorentz force dominates, which
contrasts with an outer geostrophic region governed by the Coriolis force, but
where the magnetic torque remains the driver. The meridional circulation is
strongly hindered by the presence of both the Lorentz and the Coriolis forces.
Nevertheless, it contributes to a significant part of the induced magnetic
energy. Our approach sets the scene for evaluating the contribution of velocity
and magnetic fluctuations to the mean magnetic field, a key question for dynamo
mechanisms
On the endomorphism algebra of modular Gelfand-Graev representations
We study the endomorphism algebras of a modular Gelfand-Graev representation
of a finite reductive group by investigating modular properties of
homomorphisms constructed by Curtis and Curtis-Shoji.Comment: 25 page
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