94 research outputs found
Density waves in dry granular media falling through a vertical pipe
We report experimental measurements of density waves in granular materials
flowing down in a capillary tube. The density wave regime occurs at
intermediate flow rates between a low density free fall regime and a high
compactness slower flow.Comment: LaTeX file, 17 pages, 6 EPS figures, Phys.Rev.E (Feb.1996
Shock waves in two-dimensional granular flow: effects of rough walls and polydispersity
We have studied the two-dimensional flow of balls in a small angle funnel,
when either the side walls are rough or the balls are polydisperse. As in
earlier work on monodisperse flows in smooth funnels, we observe the formation
of kinematic shock waves/density waves. We find that for rough walls the flows
are more disordered than for smooth walls and that shock waves generally
propagate more slowly. For rough wall funnel flow, we show that the shock
velocity and frequency obey simple scaling laws. These scaling laws are
consistent with those found for smooth wall flow, but here they are cleaner
since there are fewer packing-site effects and we study a wider range of
parameters. For pipe flow (parallel side walls), rough walls support many shock
waves, while smooth walls exhibit fewer or no shock waves. For funnel flows of
balls with varying sizes, we find that flows with weak polydispersity behave
qualitatively similar to monodisperse flows. For strong polydispersity, scaling
breaks down and the shock waves consist of extended areas where the funnel is
blocked completely.Comment: 11 pages, 15 figures; accepted for PR
Granular discharge and clogging for tilted hoppers
We measure the flux of spherical glass beads through a hole as a systematic
function of both tilt angle and hole diameter, for two different size beads.
The discharge increases with hole diameter in accord with the Beverloo relation
for both horizontal and vertical holes, but in the latter case with a larger
small-hole cutoff. For large holes the flux decreases linearly in cosine of the
tilt angle, vanishing smoothly somewhat below the angle of repose. For small
holes it vanishes abruptly at a smaller angle. The conditions for zero flux are
discussed in the context of a {\it clogging phase diagram} of flow state vs
tilt angle and ratio of hole to grain size
Properties of layer-by-layer vector stochastic models of force fluctuations in granular materials
We attempt to describe the stress distributions of granular packings using
lattice-based layer-by-layer stochastic models that satisfy the constraints of
force and torque balance and non-tensile forces at each site. The inherent
asymmetry in the layer-by-layer approach appears to lead to an asymmetric force
distribution, in disagreement with both experiments and general symmetry
considerations. The vertical force component probability distribution is robust
and in agreement with predictions of the scalar q model while the distribution
of horizontal force components is qualitatively different and depends on the
details of implementation.Comment: 18 pages, 12 figures (with subfigures), 1 table. Uses revtex,
epsfig,subfigure, and cite. Submitted to PRE. Plots have been bitmapped.
High-resolution version is available. Email [email protected] or
download from http://rainbow.uchicago.edu/~mbnguyen/research/vm.htm
The Hubble Space Telescope PanCET Program:An Optical to Infrared Transmission Spectrum of HAT-P-32Ab
A new current algebra and the reflection equation
We establish an explicit algebra isomorphism between the quantum reflection
algebra for the R-matrix and a new type of current algebra.
These two algebras are shown to be two realizations of a special case of
tridiagonal algebras (q-Onsager).Comment: 14 pages; v2: More details in Section 4; Typos corrected; References
added; To appear in Lett. Math. Phy
Classical Yang-Mills Black hole hair in anti-de Sitter space
The properties of hairy black holes in Einstein–Yang–Mills (EYM) theory are reviewed, focusing on spherically symmetric solutions. In particular, in asymptotically anti-de Sitter space (adS) stable black hole hair is known to exist for frak su(2) EYM. We review recent work in which it is shown that stable hair also exists in frak su(N) EYM for arbitrary N, so that there is no upper limit on how much stable hair a black hole in adS can possess
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