4 research outputs found
A Hydrodynamic model for a dynamical jammed-to-flowing transition in gravity driven granular media
Granular material on an inclined plane will flow like a fluid if the angle
the plane makes with the horizontal is large enough. We employ a
modification of a hydrodynamic model introduced previously to describe Couette
flow experiments to describe chute flow down a plane. In this geometry, our
model predicts a jammed-to-flowing transition as is increased even
though it does not include solid friction, which might seem necessary to
stabilize a state without flow. The transition is driven by coupling between
mean and fluctuating velocity. In agreement with experiments and simulations,
it predicts flow for layers with a thickness H larger than a critical value
and absence of flow for
Wandering of a contact line at thermal equilibrium
We reconsider the problem of the solid-liquid-vapour contact-line on a
disordered substrate, in the collective pinning regime. We go beyond scaling
arguments and perform an analytic computation, through the replica variational
method, of the fluctuations of the line. We show how gravity effects must be
included for a proper quantitative comparison with available experimental data
of the wetting of liquid helium on a caesium substrate. The theoretical result
is in good agreement with experimental findings for this case.Comment: 24 laTex pages with 5 EPS figures included. submitted to Phys. Rev
Disordered Type-II Superconductors: A Universal Phase Diagram for Low-T Systems
A universal phase diagram for weakly pinned low-T type-II superconductors
is revisited and extended with new proposals. The low-temperature ``Bragg
glass'' phase is argued to transform first into a disordered, glassy phase upon
heating. This glassy phase, a continuation of the high-field equilibrium vortex
glass phase, then melts at higher temperatures into a liquid. This proposal
provides an explanation for the anomalies observed in the peak effect regime of
2H-NbSe and several other low-T materials which is independent of the
microscopic mechanisms of superconductivity in these systems.Comment: 23 pages, 9 figure
Phase Behavior of Type-II Superconductors with Quenched Point Pinning Disorder: A Phenomenological Proposal
A general phenomenology for phase behaviour in the mixed phase of type-II
superconductors with weak point pinning disorder is outlined. We propose that
the ``Bragg glass'' phase generically transforms via two separate thermodynamic
phase transitions into a disordered liquid on increasing the temperature. The
first transition is into a glassy phase, topologically disordered at the
largest length scales; current evidence suggests that it lacks the long-ranged
phase correlations expected of a ``vortex glass''. This phase has a significant
degree of short-ranged translational order, unlike the disordered liquid, but
no quasi-long range order, in contrast to the Bragg glass. This glassy phase,
which we call a ``multi-domain glass'', is confined to a narrow sliver at
intermediate fields, but broadens out both for much larger and much smaller
field values. The multi-domain glass may be a ``hexatic glass''; alternatively,
its glassy properties may originate in the replica symmetry breaking envisaged
in recent theories of the structural glass transition. Estimates for
translational correlation lengths in the multi-domain glass indicate that they
can be far larger than the interline spacing for weak disorder, suggesting a
plausible mechanism by which signals of a two-step transition can be obscured.
Calculations of the Bragg glass-multi-domain glass and the multi-domain
glass-disordered liquid phase boundaries are presented and compared to
experimental data. We argue that these proposals provide a unified picture of
the available experimental data on both high-T and low-T materials,
simulations and current theoretical understanding.Comment: 70 pages, 9 postscript figures, modified title and minor changes in
published versio