Hervé Caps

Comparing the EthoVision 2.3 system and a new computerized multitracking prototype system to measure the swimming behavior in fry fish

Coming from the framework of unmarked fry tracking, we compared the capacities, advantages, and disadvantages of two recent video tracking systems: EthoVision 2.3 and a new prototype of multitracking. The EthoVision system has proved to be impressive for tracking a fry using the detection by gray scaling. Detection by subtraction has given less accurate results. Our video multitracking system is able to detect and track more than 100 unmarked fish by gray scaling technique. It permits an analysis at the group level as well as at the individual level. The multitracking program is able to attribute a number to each fish and to follow each one for the whole duration of the track. Our system permits the analysis of the movement of each individual, even if the trajectories of two fish cross each other. This is possible thanks to the theoretical estimation of the trajectory of each fish, which can be compared with the real trajectory (analysis with feedback). However, the period of the track is limited for our system (about 1 min), whereas EthoVision is able to track for numerous hours. In spite of these limitations, these two systems allow an almost continuous automatic sampling of the movement behaviors during the track.

Rolling and slipping motion of Euler's disk.

We present an experimental study of the motion of a circular disk spun onto a table. With the help of a high speed video system, the temporal evolutions of (i) the inclination angle

Foam imbibition in microgravity: An experimental study

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Fluid instabilities in the birth and death of antibubbles

, (ii) the angular velocity

Granular size segregation in underwater sand ripples.

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Bubble splitting in oscillatory flows on ground and in reduced gravity

and (iii) the precession rate

Long lasting instabilities in granular mixtures

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Foam stability in microgravity

are studied. The influence of the mass of the disk and the friction between the disk and the supporting surface are considered. %The motions of disks with different masses and over different surfaces are studied. The inclination angle

Effect of a capillary meniscus on the Faraday instability threshold

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Hybrid wetting state on micro-waffle textures

and the angular velocity are observed to decrease according to a power law. We also show that the precession rate