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

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 \boldmath{$Y_{\ell}^m$} modes are excited, resulting in resonant effects on the threshold acceleration curve. Indeed, a lower acceleration is needed when $\ell$ modes with $m=0$ are excited. Modes $m \ne 0$ are found to decrease the bouncing ability of the droplet. When the mode $\ell=2$ and $m=1$ is excited, the droplet rolls on the vibrated surface without touching it, leading to a new self-propulsion mode.Comment: 4 pages, 6 figure

Measurement of the ⁴He(⁶He,⁶He)⁴He cross section with a ⁴He-implanted Al target

In order to obtain information on a possible two-neutron component in the 6He wavefunction, we investigated the 4He(6He, 6He)4He elastic scattering at beam energies of 29.1, 29.6 and 40 MeV and at center-of-mass angles between 20 and 163 degrees. The experiments were performed at the ARENAS3 Radioactive Ion Beam Facility in Louvain-La-Neuve. We used a4He-implanted aluminium foil as a target. A 4He thickness of about 2-3 × 1017 particles/cm2 was obtained implanting 4He nuclei at energies between 20 and 80 keV in 0.7-μm-thick foils. Data collected in a larger angular range than previous measurements give additional evidence for the 2n-transfer process to take place in the 4He(6He, 6He)4He scattering. Our results demonstrate the possibility of using a 4He-implanted target in experiments with low-intensity beams, like radioactive beams, where deterioration of the target is irrelevant.</p