64 research outputs found
Scattering Polarization in the Presence of Magnetic and Electric Fields
The polarization of radiation by scattering on an atom embedded in combined
external quadrupole electric and uniform magnetic fields is studied
theoretically. Limiting cases of scattering under Zeeman effect and Hanle
effect in weak magnetic fields are discussed. The theory is general enough to
handle scattering in intermediate magnetic fields (Hanle-Zeeman effect) and for
arbitrary orientation of magnetic field. The quadrupolar electric field
produces asymmetric line shifts and causes interesting level-crossing phenomena
either in the absence of an ambient magnetic field or in its presence. It is
shown that the quadrupolar electric field produces an additional depolarization
in the profiles and rotation of the plane of polarization in the
profile over and above that arising from magnetic field itself. This
characteristic may have a diagnostic potential to detect steady state and time
varying electric fields that surround radiating atoms in Solar atmospheric
layers.Comment: 41 pages, 6 figure
Existence of global strong solutions to a beam-fluid interaction system
We study an unsteady non linear fluid-structure interaction problem which is
a simplified model to describe blood flow through viscoleastic arteries. We
consider a Newtonian incompressible two-dimensional flow described by the
Navier-Stokes equations set in an unknown domain depending on the displacement
of a structure, which itself satisfies a linear viscoelastic beam equation. The
fluid and the structure are fully coupled via interface conditions prescribing
the continuity of the velocities at the fluid-structure interface and the
action-reaction principle. We prove that strong solutions to this problem are
global-in-time. We obtain in particular that contact between the viscoleastic
wall and the bottom of the fluid cavity does not occur in finite time. To our
knowledge, this is the first occurrence of a no-contact result, but also of
existence of strong solutions globally in time, in the frame of interactions
between a viscous fluid and a deformable structure
- …