4,603 research outputs found
Gravity-driven instability in a spherical Hele-Shaw cell
A pair of concentric spheres separated by a small gap form a spherical
Hele-Shaw cell. In this cell an interfacial instability arises when two
immiscible fluids flow. We derive the equation of motion for the interface
perturbation amplitudes, including both pressure and gravity drivings, using a
mode coupling approach. Linear stability analysis shows that mode growth rates
depend upon interface perimeter and gravitational force. Mode coupling analysis
reveals the formation of fingering structures presenting a tendency toward
finger tip-sharpening.Comment: 13 pages, 4 ps figures, RevTex, to appear in Physical Review
Geodesics around line defects in elastic solids
Topological defects in solids, usually described by complicated boundary
conditions in elastic theory, may be described more simply as sources of a
gravity- like deformation field in the geometric approach of Katanaev and
Volovich. This way, the deformation field is described by non-Euclidean metric
that incorporates the boundary imposed by the defects. A possible way of
gaining some insight into the motion of particles in a medium with topological
defects (e.g., electrons in a dislocated metal) is to look at the geodesics of
the medium around the defect. In this work, we find the exact solution for the
geodesic equation for elastic medium with a generic line defect, the
dispiration, that can either be a screw dislocation or a wedge disclination for
particular choices of its parameters.Comment: 10 pages, Latex, 4 figures, accepted for publication in Phys. Lett.
Using torsion to manipulate spin currents
We address the problem of quantum particles moving on a manifold
characterised by the presence of torsion along a preferential axis. In fact,
such a torsion may be taylored by the presence of a single screw dislocation,
whose Burgers vector measures the torsion amplitude. The problem, first treated
in the relativistic limit describing fermions that couple minimally to torsion,
is then analysed in the Pauli limit We show that torsion induces a geometric
potential and also that it couples generically to the phase of the wave
function, giving rise to the possibility of using torsion to manipulate spin
currents in the case of spinor wave functions. These results emerge as an
alternative strategy for using screw dislocations in the design of
spintronic-based devices
- …