2,179 research outputs found
Bose-Einstein Correlations and the Equation of State of Nuclear Matter
Within a relativistic hydrodynamic framework, we use four different equations
of state of nuclear matter to compare to experimental spectra from CERN/SPS
experiments NA44 and NA49. Freeze-out hypersurfaces and Bose-Einstein
correlation functions for identical pion pairs are discussed. We find that
two-pion Bose-Einstein interferometry measures the relationship between the
temperature and the energy density in the equation of state during the late
hadronic stage of the fireball expansion. Little sensitivity of the
light-hadron data to a quark-gluon plasma phase-transition is seen.Comment: 4 pages, including 4 figures. You can also download a PostScript file
of the manuscript from http://p2hp2.lanl.gov/people/schlei/eprint.htm
Model for the Scaling of Stresses and Fluctuations in Flows near Jamming
We probe flows of soft, viscous spheres near the jamming point, which acts as
a critical point for static soft spheres. Starting from energy considerations,
we find nontrivial scaling of velocity fluctuations with strain rate. Combining
this scaling with insights from jamming, we arrive at an analytical model that
predicts four distinct regimes of flow, each characterized by rational-valued
scaling exponents. Both the number of regimes and values of the exponents
depart from prior results. We validate predictions of the model with
simulations.Comment: 4 pages, 5 figures (revised text and one new figure). To appear in
Phys. Rev. Let
Stresses in Smooth Flows of Dense Granular Media
The form of the stress tensor is investigated in smooth, dense granular flows
which are generated in split-bottom shear geometries. We find that, within a
fluctuation fluidized spatial region, the form of the stress tensor is directly
dictated by the flow field: The stress and strain-rate tensors are co-linear.
The effective friction, defined as the ratio between shear and normal stresses
acting on a shearing plane, is found not to be constant but to vary throughout
the flowing zone. This variation can not be explained by inertial effects, but
appears to be set by the local geometry of the flow field. This is in agreement
with a recent prediction, but in contrast with most models for slow grain
flows, and points to there being a subtle mechanism that selects the flow
profiles.Comment: 5 pages, 4 figure
Counting and Sequential Information Processing in Mechanical Metamaterials
Materials with an irreversible response to cyclic driving exhibit an evolving
internal state which, in principle, encodes information on the driving history.
Here we realize irreversible metamaterials that count mechanical driving cycles
and store the result into easily interpretable internal states. We extend these
designs to aperiodic metamaterials which are sensitive to the order of
different driving magnitudes, and realize 'lock and key' metamaterials that
only reach a specific state for a given target driving sequence. Our strategy
is robust, scalable and extendable, and opens new routes towards smart sensing,
soft robotics and mechanical information processing.Comment: 5 pages, 4 figure
The tail of the contact force distribution in static granular materials
We numerically study the distribution P(f) of contact forces in frictionless
bead packs, by averaging over the ensemble of all possible force network
configurations. We resort to umbrella sampling to resolve the asymptotic decay
of P(f) for large f, and determine P(f) down to values of order 10^{-45} for
ordered and disordered systems in two and three dimensions. Our findings
unambiguously show that, in the ensemble approach, the force distributions
decay much faster than exponentially: P(f) ~ exp(-f^{\alpha}), with alpha
\approx 2.0 for 2D systems, and alpha \approx 1.7 for 3D systems.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Critical jamming of frictional grains in the generalized isostaticity picture
While frictionless spheres at jamming are isostatic, frictional spheres at
jamming are not. As a result, frictional spheres near jamming do not
necessarily exhibit an excess of soft modes. However, a generalized form of
isostaticity can be introduced if fully mobilized contacts at the Coulomb
friction threshold are considered as slipping contacts. We show here that, in
this framework, the vibrational density of states (DOS) of frictional discs
exhibits a plateau when the generalized isostaticity line is approached. The
crossover frequency to elastic behavior scales linearly with the distance from
this line. Moreover, we show that the frictionless limit, which appears
singular when fully mobilized contacts are treated elastically, becomes smooth
when fully mobilized contacts are allowed to slip.Comment: 4 pages, 4 figures, submitted to PR
Sheared force-networks: anisotropies, yielding and geometry
A scenario for yielding of granular matter is presented by considering the
ensemble of force networks for a given contact network and applied shear stress
. As is increased, the probability distribution of contact forces
becomes highly anisotropic, the difference between average contact forces along
minor and major axis grows, and the allowed networks span a shrinking subspace
of all force-networks. Eventually, contacts start to break, and at the yielding
shear stress, the packing becomes effectively isostatic. The size of the
allowed subspace exhibits simple scaling properties, which lead to a prediction
of the yield stress for packings of arbitrary contact number.Comment: 4 pages, 4 figure
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