1,344 research outputs found
Compaction of anisotropic granular materials : experiments and simulations
We present both experimental and numerical investigations of compaction in
granular materials composed of rods. As a function of the aspect ratio of the
particles, we have observed large variations of the asymptotic packing volume
fraction in vertical tubes. The relevant parameter is the ratio between the rod
length and the tube diameter . Even the compaction dynamics remains
unchanged for various particle lengths, a 3d/2d phase transition for grain
orientations is observed for . A toy model for the compaction of
needles on a lattice is also proposed. This toy model gives a complementary
view of our experimental results and leads to behaviors similar to experimental
ones.Comment: 5 pages, 10 figure
Experimental study of the compaction dynamics for 2D anisotropic granular materials
We present an experimental study of the compaction dynamics for
two-dimensional anisotropic granular systems. Compaction dynamics is measured
at three different scales : (i) the macroscopic scale through the packing
fraction , (ii) the mesoscopic scale through both fractions of aligned
grains and ideally ordered grains , and (iii) the
microscopic scale through both rotational and translational grain mobilities
. The effect of the grain rotations on the compaction dynamics has
been measured. At the macroscopic scale, we have observed a discontinuity in
the late stages of the compaction curve. At the mesoscopic scale, we have
observed the formation and the growth of domains made of aligned grains. From a
microscopic point of view, measurements reveal that the beginning of the
compaction process is essentially related to translational motion of the
grains. The grains rotations drive mainly the process during the latest stages
of compaction.Comment: 8pages, 11 figure
Networks of equities in financial markets
We review the recent approach of correlation based networks of financial
equities. We investigate portfolio of stocks at different time horizons,
financial indices and volatility time series and we show that meaningful
economic information can be extracted from noise dressed correlation matrices.
We show that the method can be used to falsify widespread market models by
directly comparing the topological properties of networks of real and
artificial markets.Comment: 9 pages, 8 figures. Accepted for publication in EPJ
A fountain of droplets
A vessel is plunged upside down into a pool of 50 cSt silicone oil. An air
bell is then created. This bell is vertically shaken at 60 Hz that leads to the
oscillation of the air/oil interface. The edges of the immersed vessel generate
surface waves that propagate towards the center of the bell. When the amplitude
of the oscillation increases, wave amplitude increases. We study the influence
of the angle between successive sides on the wave patterns. Two kinds of vessel
have been studied: a triangular and a square prism. The shape of the air/oil
meniscus depends on the angle between the sides of the considered prism. As the
amplitude of the oscillation is increased, the triple line, which is the
contact line between the solid and the air/oil interface, moves up and down.
Above a given acceleration that depends on the immersion depth and on the shape
vessel, wave goes under the corner edge of the bell. During the oscillation,
the wave generates at the edges presents a singularity that leads eventually to
a jet and a drop ejection. A drop is ejected at each oscillation. More
complicated ejection can be produced with further increase of the amplitude.
This is a sample arXiv article illustrating the use of fluid dynamics videos.Comment: 3 pages, 2 figures, 2 movies (high-res and low-res
Drop on a Bent Fibre
Inspired by the huge droplets attached on cypress tree leaf tips after rain,
we find that a bent fibre can hold significantly more water in the corner than
a horizontally placed fibre (typically up to three times or more). The maximum
volume of the liquid that can be trapped is remarkably affected by the bending
angle of the fibre and surface tension of the liquid. We experimentally find
the optimal included angle () that holds the most water.
Analytical and semi-empirical models are developed to explain these
counter-intuitive experimental observations and predict the optimal angle. The
data and models could be useful for designing microfluidic and fog harvesting
devices
Diffusive foam wetting process in microgravity
We report the experimental study of aqueous foam wetting in microgravity. The
liquid fraction along the bubble edges is measured and is found to be a
relevant dynamical parameter during the capillary process. The penetration of
the liquid in the foam, the foam inflation, and the rigidity loss are shown all
to obey strict diffusion processes.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
Flow of magnetic repelling grains in a two-dimensional silo
During a typical silo discharge, the material flow rate is determined by the
contact forces between the grains. Here, we report an original study concerning
the discharge of a two-dimensional silo filled with repelling magnetic grains.
This non-contact interaction leads to a different dynamics from the one
observed with conventional granular materials. We found that, although the flow
rate dependence on the aperture size follows roughly the power-law with an
exponent found in non-repulsive systems, the density and velocity
profiles during the discharge are totally different. New phenomena must be
taken into account. Despite the absence of contacts, clogging and intermittence
were also observed for apertures smaller than a critical size determined by the
effective radius of the repulsive grains.Comment: 6 pages, 8 figure
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