93 research outputs found
Flow and Jamming of Granular Suspensions in Foams
The drainage of particulate foams is studied under conditions where the
particles are not trapped individually by constrictions of the interstitial
pore space. The drainage velocity decreases continuously as the particle volume
fraction increases. The suspensions jam - and therefore drainage
stops - for values which reveal a strong effect of the particle
size. In accounting for the particular geometry of the foam, we show that
accounts for unusual confinement effects when the particles pack
into the foam network. We model quantitatively the overall behavior of the
suspension - from flow to jamming - by taking into account explicitly the
divergence of its effective viscosity at . Beyond the scope of
drainage, the reported jamming transition is expected to have a deep
significance for all aspects related to particulate foams, from aging to
mechanical properties
Mechanical probing of liquid foam aging
We present experimental results on the Stokes experiment performed in a 3D
dry liquid foam. The system is used as a rheometric tool : from the force
exerted on a 1cm glass bead, plunged at controlled velocity in the foam in a
quasi static regime, local foam properties are probed around the sphere. With
this original and simple technique, we show the possibility of measuring the
foam shear modulus, the gravity drainage rate and the evolution of the bubble
size during coarsening
An experimental study of the breakage of liquid bridges at stability limit of minimum volume
An experimental apparatus to study the breaking process of axisymmetric liquid bridges has been developed, and the breaking sequences of a large number of liquid bridge configurations at minimum-volume stability limit have been analyzed. Experimental results show that very close to the breaking moment the neck radius of the liquid bridge varies as t1/3, where t is the time to breakage, irrespective of the value of the distance between the solid disks that support the liquid column
Angle of repose and segregation in cohesive granular matter
We study the effect of fluids on the angle of repose and the segregation of
granular matter poured into a silo. The experiments are conducted in two
regimes where: (i) the volume fraction of the fluid is small and it forms
liquid bridges between particles, and (ii) the particles are completely
immersed in the fluid. The data is obtained by imaging the pile formed inside a
quasi-two dimensional silo through the transparent glass side walls. In the
first series of experiments, the angle of repose is observed to increase
sharply with the volume fraction of the fluid and then saturates at a value
that depends on the size of the particles. We systematically study the effect
of viscosity by using water-glycerol mixtures to vary it over at least three
orders of magnitude while keeping the surface tension almost constant. Besides
surface tension, the viscosity of the fluid is observed to have an effect on
the angle of repose and the extent of segregation. In case of bidisperse
particles, segregation is observed to decrease and finally saturate depending
on the size ratio of the particles and the viscosity of the fluid. The sharp
initial change and the subsequent saturation in the extent of segregation and
angle of repose occurs over similar volume fraction of the fluid. In the second
series of experiments, particles are poured into a container filled with a
fluid. Although the angle of repose is observed to be unchanged, segregation is
observed to decrease with an increase in the viscosity of the fluid.Comment: 9 pages, 12 figure
Nonlinear atom optics and bright gap soliton generation in finite optical lattices
We theoretically investigate the transmission dynamics of coherent matter
wave pulses across finite optical lattices in both the linear and the nonlinear
regimes. The shape and the intensity of the transmitted pulse are found to
strongly depend on the parameters of the incident pulse, in particular its
velocity and density: a clear physical picture for the main features observed
in the numerical simulations is given in terms of the atomic band dispersion in
the periodic potential of the optical lattice. Signatures of nonlinear effects
due the atom-atom interaction are discussed in detail, such as atom optical
limiting and atom optical bistability. For positive scattering lengths, matter
waves propagating close to the top of the valence band are shown to be subject
to modulational instability. A new scheme for the experimental generation of
narrow bright gap solitons from a wide Bose-Einstein condensate is proposed:
the modulational instability is seeded in a controlled way starting from the
strongly modulated density profile of a standing matter wave and the solitonic
nature of the generated pulses is checked from their shape and their
collisional properties
Wet Granular Materials
Most studies on granular physics have focused on dry granular media, with no
liquids between the grains. However, in geology and many real world
applications (e.g., food processing, pharmaceuticals, ceramics, civil
engineering, constructions, and many industrial applications), liquid is
present between the grains. This produces inter-grain cohesion and drastically
modifies the mechanical properties of the granular media (e.g., the surface
angle can be larger than 90 degrees). Here we present a review of the
mechanical properties of wet granular media, with particular emphasis on the
effect of cohesion. We also list several open problems that might motivate
future studies in this exciting but mostly unexplored field.Comment: review article, accepted for publication in Advances in Physics;
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Capillary Bridge Formation and Breakage: A Test to Characterize Antiadhesive Surfaces
In order to characterize very weak adhesive surfaces, we have developed a
quantitative test inspired by the Johnson, Kendall, and Roberts adhesion test
for soft adhesives, which relies on the formation and then the rupture of a
capillary bridge between the surface to be tested and a liquid bath. Both the
shape and the kinetics of breakage of the capillary bridge for various coatings
put into contact with liquids of various viscosities and surface tensions have
been studied. Several pull off regimes can be distinguished. For low pull off
velocities, a quasi-static regime is observed, well described by capillary
equations and sensitive to the hysteresis of the contact angle of the fluid on
the coating. Above a critical pull off velocity that depends on the fluid
viscosity, a dynamic regime is observed, characterized by the formation of a
flat pancake of fluid on the coating that recedes more slowly than the
capillary bridge itself. After the breakage of the capillary bridge, a small
drop can remain attached to the surface. The volume of this drop depends on the
dynamical regime and is strongly affected by very small differences between the
coatings. The aptitude of this test in characterizing very weakly adhesive
surfaces is exemplified by a comparison between three different perfluorinated
coatings
Square Packing and Structural Arrangement of ABC Triblock Copolymer Spheres in Thin Films
Copepod distribution in surface waters of the Drake Passage using Continuous Plankton Recorder and a Pump-Net onboard system
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