15 research outputs found
Dense bubble flow in a silo: an unusual flow of a dispersed medium
The dense flow of air bubbles in a two-dimensional silo (through an aperture
D) filled with a liquid is studied experimentally. A particle tracking
technique has been used to bring out the main properties of the flow:
displacements of the bubbles, transverse and axial velocities. The behavior of
the air bubbles is observed to present similarities with non-deformable solid
grains in a granular flow. Nevertheless, a correlation between the bubble
velocities and their deformations has been evidenced. Moreover, a new discharge
law (Beverloo-like) must be considered for such a system, where the flow rate
is observed to vary as D^{1/2} and depends on the deformability of the
particles.Comment: 5 pages, 6 figure
Experimental evidences of a structural and dynamical transition in fish school
We have developed a video tracking system in order to determine all the trajectories of young fish (Oreochromis niloticus L.) within a school. Both individual and collective behaviours have been studied as a function of the number of fish per unit area. By studying distributions of distances between fish and distributions of relative orientations, structural effects and cooperative motions have been evidenced. Signatures of a phase transition have been found, as predicted by some numerical models. This work opens new perspectives in the study of collective phenomena in biological systems since it is the first time that such measurements are possible
Advantages and limits of a video multitracking system for quantification of individual behavior in a large fish shoal
peer reviewedbourse FRI
Fish lateral system is required for accurate control of shoaling behaviour
In teleost fishes, the lateral system is assumed to contribute, among other roles, to maintaining schooling behaviour. Sight is also assumed to play a role in schooling, as fish with a cut lateral line do not stop schooling unless they are also blinded. This conclusion, however, was based on experiments where only the trunk lateral line was inactivated, leaving the head lateral system intact. Here the aim was to test how inactivation of the whole lateral system affects the fish shoaling behaviour. Groups of firehead tetras, Hemigrammus bleheri, were video-recorded before and after inactivation of their whole lateral system with aminoglycoside antibiotics (and also in sham-treated specimens). Shoaling behaviour was characterized by: nearest distance to the first, second, and third neighbour, shoal radius, shoal order parameter, and the number of collisions between individuals. SEM observations showed damage to most superficial neuromasts as a result of antibiotic treatment. Importantly, the antibiotic-treated fish proved unable to maintain a shoal. After the end of the treatment, however, they recovered both a normal tissue morphology and normal shoaling behaviour within about a month. The lateral system is thus more crucial to shoaling behaviour than previously believed