83 research outputs found
Dissipative dynamics of superfluid vortices at non-zero temperatures
We consider the evolution and dissipation of vortex rings in a condensate at
non-zero temperature, in the context of the classical field approximation,
based on the defocusing nonlinear Schr\"odinger equation. The temperature in
such a system is fully determined by the total number density and the number
density of the condensate. A vortex ring is introduced into a condensate in a
state of thermal equilibrium, and interacts with non-condensed particles. These
interactions lead to a gradual decrease in the vortex line density, until the
vortex ring completely disappears. We show that the square of the vortex line
length changes linearly with time, and obtain the corresponding universal decay
law. We relate this to mutual friction coefficients in the fundamental equation
of vortex motion in superfluids.Comment: 4 pages, 3 figure
Critical packing in granular shear bands
In a realistic three-dimensional setup, we simulate the slow deformation of
idealized granular media composed of spheres undergoing an axisymmetric
triaxial shear test. We follow the self-organization of the spontaneous strain
localization process leading to a shear band and demonstrate the existence of a
critical packing density inside this failure zone. The asymptotic criticality
arising from the dynamic equilibrium of dilation and compaction is found to be
restricted to the shear band, while the density outside of it keeps the memory
of the initial packing. The critical density of the shear band depends on
friction (and grain geometry) and in the limit of infinite friction it defines
a specific packing state, namely the \emph{dynamic random loose packing}
Endothelial dysfunction and diabetes: roles of hyperglycemia, impaired insulin signaling and obesity
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