1,574 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
Critical scaling in linear response of frictionless granular packings near jamming
We study the origin of the scaling behavior in frictionless granular media
above the jamming transition by analyzing their linear response. The response
to local forcing is non-self-averaging and fluctuates over a length scale that
diverges at the jamming transition. The response to global forcing becomes
increasingly non-affine near the jamming transition. This is due to the
proximity of floppy modes, the influence of which we characterize by the local
linear response. We show that the local response also governs the anomalous
scaling of elastic constants and contact number.Comment: 4 pages, 3 figures. v2: Added new results; removed part of
discussion; changed Fig.
Sources and sinks separating domains of left- and right-traveling waves: Experiment versus amplitude equations
In many pattern forming systems that exhibit traveling waves, sources and
sinks occur which separate patches of oppositely traveling waves. We show that
simple qualitative features of their dynamics can be compared to predictions
from coupled amplitude equations. In heated wire convection experiments, we
find a discrepancy between the observed multiplicity of sources and theoretical
predictions. The expression for the observed motion of sinks is incompatible
with any amplitude equation description.Comment: 4 pages, RevTeX, 3 figur
Force network ensemble: a new approach to static granular matter
An ensemble approach for force distributions in static granular packings is
developed. This framework is based on the separation of packing and force
scales, together with an a-priori flat measure in the force phase space under
the constraints that the contact forces are repulsive and balance on every
particle. We show how the formalism yields realistic results, both for
disordered and regular ``snooker ball'' configurations, and obtain a
shear-induced unjamming transition of the type proposed recently for athermal
media.Comment: 4 pages, 4 figures, changed conten
Forecasting the SST space-time variability of the Alboran Sea with genetic algorithms
We propose a nonlinear ocean forecasting technique based on a combination of
genetic algorithms and empirical orthogonal function (EOF) analysis. The method
is used to forecast the space-time variability of the sea surface temperature
(SST) in the Alboran Sea. The genetic algorithm finds the equations that best
describe the behaviour of the different temporal amplitude functions in the EOF
decomposition and, therefore, enables global forecasting of the future
time-variability.Comment: 15 pages, 3 figures; latex compiled with agums.st
Universal and wide shear zones in granular bulk flow
We present experiments on slow granular flows in a modified (split-bottomed)
Couette geometry in which wide and tunable shear zones are created away from
the sidewalls. For increasing layer heights, the zones grow wider (apparently
without bound) and evolve towards the inner cylinder according to a simple,
particle-independent scaling law. After rescaling, the velocity profiles across
the zones fall onto a universal master curve given by an error function. We
study the shear zones also inside the material as function of both their local
height and the total layer height.Comment: Minor corrections, accepted for PRL (4 pages, 6 figures
Direct Emission of multiple strange baryons in ultrarelativistic heavy-ion collisions from the phase boundary
We discuss a model for the space-time evolution of ultrarelativistic
heavy-ion collisions which employs relativistic hydrodynamics within one region
of the forward light-cone, and microscopic transport theory (i.e. UrQMD) in the
complement. Our initial condition consists of a quark-gluon plasma which
expands hydrodynamically and hadronizes. After hadronization the solution
eventually changes from expansion in local equilibrium to free streaming, as
determined selfconsistently by the interaction rates between the hadrons and
the local expansion rate. We show that in such a scenario the inverse slopes of
the -spectra of multiple strange baryons (, ) are practically
unaffected by the purely hadronic stage of the reaction, while the flow of
's and 's increases. Moreover, we find that the rather ``soft''
transverse expansion at RHIC energies (due to a first-order phase transition)
is not washed out by strong rescattering in the hadronic stage. The earlier
kinetic freeze-out as compared to SPS-energies results in similar inverse
slopes (of the -spectra of the hadrons in the final state) at RHIC and SPS
energies.Comment: 4 pages, 3 figures, statistics for Omegas improved, slight revision
of the manuscript (expansion of hadronization volume more emphasized,
pi-Omega scattering is discussed very briefly
Bounds on the shear load of cohesionless granular matter
We characterize the force state of shear-loaded granular matter by relating
the macroscopic stress to statistical properties of the force network. The
purely repulsive nature of the interaction between grains naturally provides an
upper bound for the sustainable shear stress, which we analyze using an
optimization procedure inspired by the so-called force network ensemble. We
establish a relation between the maximum possible shear resistance and the
friction coefficient between individual grains, and find that anisotropies of
the contact network (or the fabric tensor) only have a subdominant effect.
These results can be considered the hyperstatic limit of the force network
ensemble and we discuss possible implications for real systems. Finally, we
argue how force anisotropies can be related quantitatively to experimental
measurements of the effective elastic constants.Comment: 17 pages, 6 figures. v2: slightly rearranged, introduction and
discussion rewritte
Ensemble Theory for Force Networks in Hyperstatic Granular Matter
An ensemble approach for force networks in static granular packings is
developed. The framework is based on the separation of packing and force
scales, together with an a-priori flat measure in the force phase space under
the constraints that the contact forces are repulsive and balance on every
particle. In this paper we will give a general formulation of this force
network ensemble, and derive the general expression for the force distribution
. For small regular packings these probability densities are obtained in
closed form, while for larger packings we present a systematic numerical
analysis. Since technically the problem can be written as a non-invertible
matrix problem (where the matrix is determined by the contact geometry), we
study what happens if we perturb the packing matrix or replace it by a random
matrix. The resulting 's differ significantly from those of normal
packings, which touches upon the deep question of how network statistics is
related to the underlying network structure. Overall, the ensemble formulation
opens up a new perspective on force networks that is analytically accessible,
and which may find applications beyond granular matter.Comment: 17 pages, 17 figure
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