743 research outputs found
Pressure and Motion of Dry Sand -- Translation of Hagen's Paper from 1852
In a remarkable paper from 1852, Gotthilf Heinrich Ludwig Hagen measured and
explained two fundamental aspects of granular matter: The first effect is the
saturation of pressure with depth in a static granular system confined by silo
walls -- generally known as the Janssen effect. The second part of his paper
describes the dynamics observed during the flow out of the container -- today
often called the Beverloo law -- and forms the foundation of the hourglass
theory. The following is a translation of the original German paper from 1852.Comment: 4 pages, accepted for publication in Granular Matter, original
article (German) can be found under http://www.phy.duke.edu/~msperl/Janssen
Surface Magnetization of Aperiodic Ising Quantum Chains
We study the surface magnetization of aperiodic Ising quantum chains. Using
fermion techniques, exact results are obtained in the critical region for
quasiperiodic sequences generated through an irrational number as well as for
the automatic binary Thue-Morse sequence and its generalizations modulo p. The
surface magnetization exponent keeps its Ising value, beta_s=1/2, for all the
sequences studied. The critical amplitude of the surface magnetization depends
on the strength of the modulation and also on the starting point of the chain
along the aperiodic sequence.Comment: 11 pages, 6 eps-figures, Plain TeX, eps
An alternative order parameter for the 4-state Potts model
We have investigated the dynamic critical behavior of the two-dimensional
4-state Potts model using an alternative order parameter first used by
Vanderzande [J. Phys. A: Math. Gen. \textbf{20}, L549 (1987)] in the study of
the Z(5) model. We have estimated the global persistence exponent by
following the time evolution of the probability that the considered
order parameter does not change its sign up to time . We have also obtained
the critical exponents , , , and using this alternative
definition of the order parameter and our results are in complete agreement
with available values found in literature.Comment: 6 pages, 6 figure
A comparative study of the dynamic critical behavior of the four-state Potts like models
We investigate the short-time critical dynamics of the Baxter-Wu (BW) and
Turban (3TU) models to estimate their global persistence exponent . We conclude that this new dynamical exponent can be useful in detecting
differences between the critical behavior of these models which are very
difficult to obtain in usual simulations. In addition, we estimate again the
dynamical exponents of the four-state Potts (FSP) model in order to compare
them with results previously obtained for the BW and 3TU models and to decide
between two sets of estimates presented in the current literature. We also
revisit the short-time dynamics of the 3TU model in order to check if, as
already found for the FSP model, the anomalous dimension of the initial
magnetization could be equal to zero
Granular packings with moving side walls
The effects of movement of the side walls of a confined granular packing are
studied by discrete element, molecular dynamics simulations. The dynamical
evolution of the stress is studied as a function of wall movement both in the
direction of gravity as well as opposite to it. For all wall velocities
explored, the stress in the final state of the system after wall movement is
fundamentally different from the original state obtained by pouring particles
into the container and letting them settle under the influence of gravity. The
original packing possesses a hydrostatic-like region at the top of the
container which crosses over to a depth-independent stress. As the walls are
moved in the direction opposite to gravity, the saturation stress first reaches
a minimum value independent of the wall velocity, then increases to a
steady-state value dependent on the wall-velocity. After wall movement ceases
and the packing reaches equilibrium, the stress profile fits the classic
Janssen form for high wall velocities, while it has some deviations for low
wall velocities. The wall movement greatly increases the number of
particle-wall and particle-particle forces at the Coulomb criterion. Varying
the wall velocity has only small effects on the particle structure of the final
packing so long as the walls travel a similar distance.Comment: 11 pages, 10 figures, some figures in colo
Confined granular packings: structure, stress, and forces
The structure and stresses of static granular packs in cylindrical containers
are studied using large-scale discrete element molecular dynamics simulations
in three dimensions. We generate packings by both pouring and sedimentation and
examine how the final state depends on the method of construction. The vertical
stress becomes depth-independent for deep piles and we compare these stress
depth-profiles to the classical Janssen theory. The majority of the tangential
forces for particle-wall contacts are found to be close to the Coulomb failure
criterion, in agreement with the theory of Janssen, while particle-particle
contacts in the bulk are far from the Coulomb criterion. In addition, we show
that a linear hydrostatic-like region at the top of the packings unexplained by
the Janssen theory arises because most of the particle-wall tangential forces
in this region are far from the Coulomb yield criterion. The distributions of
particle-particle and particle-wall contact forces exhibit
exponential-like decay at large forces in agreement with previous studies.Comment: 11 pages, 11 figures, submitted to PRE (v2) added new references,
fixed typo
Molecular epidemiology of apparent outbreak of invasive aspergillosis in ahematology ward
During a 2-month period, five patients suffering from invasive infections
caused by Aspergillus flavus or Aspergillus fumigatus were identif
Percolating granular superconductors
We investigate diamagnetic fluctuations in percolating granular
superconductors. Granular superconductors are known to have a rich phase
diagram including normal, superconducting and spin glass phases. Focusing on
the normal-superconducting and the normal-spin glass transition at low
temperatures, we study he diamagnetic susceptibility and the mean
square fluctuations of the total magnetic moment of large
clusters. Our work is based on a random Josephson network model that we analyze
with the powerful methods of renormalized field theory. We investigate the
structural properties of the Feynman diagrams contributing to the
renormalization of and . This allows us to determine
the critical behavior of and to arbitrary order in
perturbation theory.Comment: 18 pages, 2 figure
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