Granes in pills
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Dipartimento Fisica Nuovo Edifico Università La Sapienza – P.le Aldo Moro, 5 – 00185 Roma
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When is a lubricant effective?
in Granular SystemsA plate shearing an interstitial granular medium and driven by an always ongoing spring feels less fricion when only few layers are present. Adding more layers results in an increase of friction,
nevertheless the plate slides more often. The ease of slipping is not determined by friction alone?
M A Annunziata, A Baldassarri, F Dalton, A Petri and G Pontuale, Increasing ‘ease of sliding’ also increases friction: when is a lubricant effective?… Read the rest
Differential and absolute negative mobility in steady laminar flows
in Granular SystemsThermal convection in granular gases with dissipative lateral walls
in Granular SystemsConvection 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
Heat, temperature and Clausius inequality in a model for active brownian particles
in Granular SystemsMechanism of self-propulsion in 3D-printed active granular particles
in Granular SystemsCages and anomalous diffusion in vibrated dense granular media
in Granular SystemsCaging 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
Brownian Ratchet in a Thermal Bath Driven by Coulomb Friction
in Granular SystemsA Brownian Ratchet is a small engine which is conceived to extract work from molecular fluctuations. Examples of Brownian Ratchets occur in the cell, see for instance this nice movie about kinesin.
As well explained by Richard Feynmann, a Brownian Ratchet cannot perform its own task in an equilibrium environment, i.e. the fluctuations feeding energy to the ratchet cannot originate from a single thermal bath, in accordance with the second principle of thermodynamics.… Read the rest
Shaken Granular Lasers
in Granular Systems