Convection in molecular fluids is provided by the competition between gravity and an adverse temperature gradient (two thermostats, the hotter below, the colder above). In a granular gas it can be achieved by a single thermostat at the base, for instance a vibrating piston. Energy dissipation provides the “second thermostat” which spontaneously forms gradient and may stabilize a convective state. Here we have demonstrated that even the simple dissipation in the collision between grains and lateral walls is sufficient to trigger convection, without any critical threshold.… Read the rest
We have reproduced the self propulsion of bacteria and animals with 3d-printed “active granular particles”. Those small artificial insects walk on a rough vibrated plate because of a subtle interplay between material elastic properties and solid-on-solid friction. The advantage of 3d-printed objects is in the possibility to tune certain features (here the inclination of “legs”) in order to verify theoretical predictions and establish an optimal shape for running.… Read the rest
Caging is the typical microscopic phenomenon that “traps” molecules in a liquid at low temperature. The usual Brownian Motion of a tracer experiences a temporary “dynamical arrest” which eventually is broken restoring normal diffusion. In this work we have shown that at intermediate densities and temperature the same phenomenon occurs in granular liquids. At large densities and lower temperatures the late normal diffusion is replaced with superdiffusion.… Read the rest
Since July 2010, the Granular Dynamics Laboratory is operative – originally in room “010” and (from november 2012) – in room “012” (ground floor of Fermi Building of the Physics Department) at the Sapienza unit of ISC. The laboratory includes two main experimental setups:
- Vertical vibration (2d and 3d granular experiments): an electrodynamic shaker LDS V455, which can reach a maximum acceleration of 105g, powered by a PA1000L power amplifier.