Stéphane Dorbolo

Avalanches of Popping Bubbles in Collapsing Foams

We report acoustic experiments on foam systems. We have recorded the sound emitted by crackling cells during the collapsing of foams. The sound pattern is then analyzed using classical methods of statistical physics. Fundamental processes at the surface of the collapsing foam are found. In particular, size is not a relevant parameter for exploding bubbles.

Resonant and rolling droplet

When an oil droplet is placed on a quiescent oil bath, it eventually collapses into the bath due to gravity. The resulting coalescence may be eliminated when the bath is vertically vibrated. The droplet bounces periodically on the bath, and the air layer between the droplet and the bath is replenished at each bounce. This sustained bouncing motion is achieved when the forcing acceleration is higher than a threshold value. When the droplet has a sufficiently low viscosity, it significantly deforms: spherical harmonic Ylm modes are excited, resulting in resonant effects on the threshold acceleration curve. Indeed, a lower acceleration is needed when l modes with m=0 are excited. Modes m≠0 are found to decrease the bouncing ability of the droplet. A break of degeneracy is observed for the m parameter. In particular, when the mode l=2 and m=1 is excited, the droplet rolls on the vibrated surface without touching it, leading to a new self-propulsion mode.

Dynamics of a Bouncing Dimer

We investigate the dynamics of a dimer bouncing on a vertically oscillated plate. The dimer, composed of two spheres rigidly connected by a light rod, exhibits several modes depending on initial and driving conditions. The first excited mode has a novel horizontal drift in which one end of the dimer stays on the plate during most of the cycle, while the other end bounces in phase with the plate. The speed and direction of the drift depend on the aspect ratio of the dimer. We employ event-driven simulations based on a detailed treatment of frictional interactions between the dimer and the plate in order to elucidate the nature of the transport mechanism in the drift mode.

Controlling the partial coalescence of a droplet on a vertically vibrated bath.

A method is proposed to stop the cascade of partial coalescences of a droplet laid on a liquid bath. The strategy consists of vibrating the bath in the vertical direction in order to keep small droplets bouncing. Since large droplets are not able to bounce, they partially coalesce until they reach a critical size. The system behaves as a low pass filter: droplets smaller than the critical size are selected. This size has been investigated as a function of the acceleration and the frequency of the bath vibration. Results suggest that the limit size for bouncing is related to the first mode of the droplet deformation.

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

Magnetic ghosts and monopoles

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Dancing droplets onto liquid surfaces

, (ii) the angular velocity

Fluid instabilities in the birth and death of antibubbles

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Hysteretic behavior in metallic granular matter

and (iii) the precession rate

Magnon-polaron and spin-polaron signatures in the specific heat and electrical resistivity of La0.6Y0.1Ca0.3MnO3 in zero magnetic field and the effect of Mn - O - Mn bond environment

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