126 research outputs found
Stability of giant vortices in quantum liquids
We show how giant vortices can be stabilized in strong external potential
Bose-Einstein condensates. We illustrate the formation of these vortices thanks
to the relaxation Ginzburg-Landau dynamics for two typical potentials in two
spatial dimensions. The giant vortex stability is studied for the particular
case of the rotating cylindrical hard wall. The minimization of the perturbed
energy is simplified into a one dimensional relaxation dynamics. The giant
vortices can be stabilized only in a finite frequency range. Finally we obtain
a curve for the minimum frequency needed to observe a giant vortex for a given
nonlinearity
Curvature singularity and film-skating during drop impact
We study the influence of the surrounding gas in the dynamics of drop impact
on a smooth surface. We use an axisymmetric 3D model for which both the gas and
the liquid are incompressible; lubrication regime applies for the gas film
dynamics and the liquid viscosity is neglected. In the absence of surface
tension a finite time singularity whose properties are analysed is formed and
the liquid touches the solid on a circle. When surface tension is taken into
account, a thin jet emerges from the zone of impact, skating above a thin gas
layer. The thickness of the air film underneath this jet is always smaller than
the mean free path in the gas suggesting that the liquid film eventually wets
the surface. We finally suggest an aerodynamical instability mechanism for the
splash.Comment: 5 figure
Wrinkles, folds and plasticity in granular rafts
We investigate the mechanical response of a compressed monolayer of large and
dense particles at a liquid-fluid interface: a granular raft. Upon compression,
rafts first wrinkle; then, as the confinement increases, the deformation
localizes in a unique fold. This characteristic buckling pattern is usually
associated to floating elastic sheets and as a result, particle laden
interfaces are often modeled as such. Here, we push this analogy to its limits
by comparing the first quantitative measurements of the raft morphology to a
theoretical continuous elastic model of the interface. We show that although
powerful to describe the wrinkle wavelength, the wrinkle-to-fold transition and
the fold shape, this elastic description does not capture the finer details of
the experiment. We describe an unpredicted secondary wavelength, a compression
discrepancy with the model and a hysteretic behavior during compression cycles,
all of which are a signature of the intrinsic discrete and frictional nature of
granular rafts. It suggests also that these composite materials exhibit both
plastic transition and jamming dynamics.Comment: 10 pages, including Supplementary Information. Submitted to Physical
Review Material
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