1,079 research outputs found
Labyrinthic granular landscapes
We have numerically studied a model of granular landscape eroded by wind. We
show the appearance of labyrinthic patterns when the wind orientation turns by
. The occurence of such structures are discussed. Morever, we
introduce the density of ``defects'' as the dynamic parameter governing
the landscape evolution. A power law behavior of is found as a function
of time. In the case of wind variations, the exponent (drastically) shifts from
2 to 1. The presence of two asymptotic values of implies the
irreversibility of the labyrinthic formation process.Comment: 3 pages, 3 figure, RevTe
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
Ripple and kink dynamics
We propose a relevant modification of the Nishimori-Ouchi model [{\em Phys.
Rev. Lett.} {\bf 71}, 197 (1993)] for granular landscape erosion. We explicitly
introduce a new parameter: the angle of repose , and a new process:
avalanches. We show that the parameter leads to an asymmetry of the
ripples, as observed in natural patterns. The temporal evolution of the maximum
ripple height is limited and not linear, according to recent
observations. The ripple symmetry and the kink dynamics are studied and
discussed.Comment: 7 pages, 10 figure, RevTe
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
Ontogenic and ecological control of metamorphosis onset in a carapid fish, <i>Carapus homei</i>: experimental evidence from vertebra and otolith comparisons
In Carapus homei, reef colonisation is associated with a penetration inside a sea cucumber followed by heavy transformations during which the length of the fish is reduced by 60%. By comparing vertebral axis to otolith ontogenetic changes, this study aimed (i) to specify the events linked to metamorphosis, and (ii) to establish to what extent these fish have the ability to delay it. Different larvae of C. homei were caught when settling on the reef and kept in different experimental conditions for at least 7 days and up to 21 days: darkness or natural light conditions, presence of sea cucumber or not, and food deprivation or not. Whatever the nutritional condition, a period of darkness seems sufficient to initiate metamorphosis. Twenty-one days in natural light conditions delayed metamorphosis, whereas the whole metamorphosis process is the fastest (15 days) for larvae living in sea cucumbers. Whether the metamorphosis was initiated or not, otoliths were modified with the formation of a transition zone, whose structure varied depending on the experimental conditions. At day 21, larvae maintained in darkness had an otolith transition zone with more increments (around 80), albeit wider than those (more or less 21) of individuals kept under natural lighting. These differences in otolith growth could indicate an increased incorporation rate of released metabolites by metamorphosing larvae. However, the presence of a transition zone in delayed-metamorphosis larvae suggests that these otolith changes record the endogenously-induced onset of metamorphosis, whereas body transformations seem to be modulated by the environmental conditions of settlement
Effect of an electric field on an intermittent granular flow
Granular gravity driven flows of glass beads have been observed in a silo
with a flat bottom. A DC high electric field has been applied perpendicularly
to the silo to tune the cohesion. The outlet mass flow has been measured. An
image subtraction technique has been applied to visualize the flow geometry and
a spatiotemporal analysis of the flow dynamics has been performed. The outlet
mass flow is independent of voltage, but a transition from funnel flow to
rathole flow is observed. This transition is of probabilistic nature and an
intermediate situation exists between the funnel and the rathole situations. At
a given voltage, two kinds of flow dynamics can occur : a continuous flow or an
intermittent flow. The electric field increases the probability to observe an
intermittent flow.Comment: Accepted for publication in PRE on Apr 9, 201
Block to granular-like transition in dense bubble flows
We have experimentally investigated 2-dimensional dense bubble flows
underneath inclined planes. Velocity profiles and velocity fluctuations have
been measured. A broad second-order phase transition between two dynamical
regimes is observed as a function of the tilt angle . For low
values, a block motion is observed. For high values, the velocity
profile becomes curved and a shear velocity gradient appears in the flow.Comment: Europhys. Lett. (2003) in pres
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