120 research outputs found
Collapsing granular suspensions
A 2D contact dynamics model is proposed as a microscopic description of a
collapsing suspension/soil to capture the essential physical processes
underlying the dynamics of generation and collapse of the system. Our physical
model is compared with real data obtained from in situ measurements performed
with a natural collapsing/suspension soil. We show that the shear strength
behavior of our collapsing suspension/soil model is very similar to the
behavior of this collapsing suspension soil, for both the unperturbed and the
perturbed phases of the material.Comment: 7 pages, 5 figures, accepted for publication in EPJ
Collapsing granular suspensions
A 2D contact dynamics model is proposed as a microscopic description of a collapsing suspension/soil to capture the essential physical processes underlying the dynamics of generation and collapse of the system. Our physical model is compared with real data obtained from in situ measurements performed with a natural collapsing/suspension soil. We show that the shear strength behavior of our collapsing suspension/soil model is very similar to the behavior of this collapsing suspension soil, for both the unperturbed and the perturbed phases of the materia
Granular packings of cohesive elongated particles
We report numerical results of effective attractive forces on the packing properties of two-dimensional elongated grains. In deposits of non-cohesive rods in 2D, the topology of the packing is mainly dominated by the formation of ordered structures of aligned rods. Elongated particles tend to align horizontally and the stress is mainly transmitted from top to bottom, revealing an asymmetric distribution of local stress. However, for deposits of cohesive particles, the preferred horizontal orientation disappears. Very elongated particles with strong attractive forces form extremely loose structures, characterized by an orientation distribution, which tends to a uniform behavior when increasing the Bond number. As a result of these changes, the pressure distribution in the deposits changes qualitatively. The isotropic part of the local stress is notably enhanced with respect to the deviatoric part, which is related to the gravity direction. Consequently, the lateral stress transmission is dominated by the enhanced disorder and leads to a faster pressure saturation with dept
Pore Stabilization in Cohesive Granular Systems
Cohesive powders tend to form porous aggregates which can be compacted by
applying an external pressure. This process is modelled using the Contact
Dynamics method supplemented with a cohesion law and rolling friction. Starting
with ballistic deposits of varying density, we investigate how the porosity of
the compacted sample depends on the cohesion strength and the friction
coefficients. This allows to explain different pore stabilization mechanisms.
The final porosity depends on the cohesion force scaled by the external
pressure and on the lateral distance between branches of the ballistic deposit
r_capt. Even if cohesion is switched off, pores can be stabilized by Coulomb
friction alone. This effect is weak for round particles, as long as the
friction coefficient is smaller than 1. However, for nonspherical particles the
effect is much stronger.Comment: 10 pages, 15 figure
Frictional coupling between sliding and spinning motion
We show that the friction force and torque, acting at a dry contact of two
objects moving and rotating relative to each other, are inherently coupled. As
a simple test system, a sliding and spinning disk on a horizontal flat surface
is considered. We calculate, and also measure, how the disk is slowing down,
and find that it always stops its sliding and spinning motion at the same
moment. We discuss the impact of this coupling between friction force and
torque on the physics of granular materials.Comment: 4 pages, 5 figures; submitte
Granular packings of cohesive elongated particles
We report numerical results of effective attractive forces on the packing
properties of two-dimensional elongated grains. In deposits of non-cohesive
rods in 2D, the topology of the packing is mainly dominated by the formation of
ordered structures of aligned rods. Elongated particles tend to align
horizontally and the stress is mainly transmitted from top to bottom, revealing
an asymmetric distribution of local stress. However, for deposits of cohesive
particles, the preferred horizontal orientation disappears. Very elongated
particles with strong attractive forces form extremely loose structures,
characterized by an orientation distribution, which tends to a uniform behavior
when increasing the Bond number. As a result of these changes, the pressure
distribution in the deposits changes qualitatively. The isotropic part of the
local stress is notably enhanced with respect to the deviatoric part, which is
related to the gravity direction. Consequently, the lateral stress transmission
is dominated by the enhanced disorder and leads to a faster pressure saturation
with depth.Comment: 6 pages, 6 figure
Particle and particle pair dispersion in turbulence modeled with spatially and temporally correlated stochastic processes
In this paper we present a new model for modeling the diffusion and relative
dispersion of particles in homogeneous isotropic turbulence. We use an
Heisenberg-like Hamiltonian to incorporate spatial correlations between fluid
particles, which are modeled by stochastic processes correlated in time. We are
able to reproduce the ballistic regime in the mean squared displacement of
single particles and the transition to a normal diffusion regime for long
times. For the dispersion of particle pairs we find a -dependence of the
mean squared separation at short times and a -dependence for long ones. For
intermediate times indications for a Richardson law are observed in
certain situations. Finally the influence of inertia of real particles on the
dispersion is investigated.Comment: 10 pages, 7 figures, 1 tabl
Electronic Scattering Effects in Europium-Based Iron Pnictides
In a comprehensive study, we investigate the electronic scattering effects in
EuFe(AsP) by using Fourier-transform infrared
spectroscopy. In spite of the fact that Eu local moments order around
\,K, the overall optical response is strikingly similar
to the one of the well-known Ba-122 pnictides. The main difference lies within
the suppression of the lower spin-density-wave gap feature. By analysing our
spectra with a multi-component model, we find that the high-energy feature
around 0.7\,eV -- often associated with Hund's rule coupling -- is highly
sensitive to the spin-density-wave ordering, this further confirms its direct
relationship to the dynamics of itinerant carriers. The same model is also used
to investigate the in-plane anisotropy of magnetically detwinned
EuFeAs in the antiferromagnetically ordered state, yielding a
higher Drude weight and lower scattering rate along the crystallographic
-axis. Finally, we analyse the development of the room temperature spectra
with isovalent phosphor substitution and highlight changes in the scattering
rate of hole-like carriers induced by a Lifshitz transition
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