Differential and absolute negative mobility in steady laminar flows

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  Nonlinear response in out-of-equilibrium systems can show counter-intuitive behaviors, for instance cases where the force increases but the response decreases (negative differential mobility). Sometimes the response crosses zero and changes sign with respect to the force (absolute negative mobility). In classical physics this is usually observed within complicate models with obstacles and traps. We have demonstrated such complex non-linear phenomena in a much simpler and realistic system, ie.… Read the rest

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Thermal convection in granular gases with dissipative lateral walls

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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

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Heat, temperature and Clausius inequality in a model for active brownian particles

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Living matter at the microscale, many kinds of cells, bacteria and other organisms, self-propel through a viscous fluid which acts as a thermal bath, dissipating the energy provided by the internal motor (pseudopoda, flagella, etc.). This energetic balance is ruled by non-equilibrium thermodynamics, as for heat engines. In this theoretical work we have given a mesoscopic description of this process, which allows to measure a local heat dissipation and a local non-equilibrium temperature (associated to self-propulsion and to the forces driving the active particle) which together provide a definition of active entropy production which satisfies the Clausius inequality.… Read the rest

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Mechanism of self-propulsion in 3D-printed active granular particles

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 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

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In the news: Re-entrant DNA gels in Nature Communications

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Francesco Sciortino and his group published Re-entrant DNA gels in Nature Communications, showing that bulk quantities of colloidal nanoparticles that can be used for designing and realizing self-assembled soft materials with unconventional properties.… Read the rest

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Verbale del Consiglio di Istituto dell’Istituto dei Sistemi Complessi (ISC) del 28 settembre 2016

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Verbale firmato Consiglio di Istituto 28 settembre 2016… Read the rest

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ISC meeting – Diffusion Processes

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An ISC-meeting on diffusion processes took place in Sesto Fiorentino (Florence) on Sept. 27th and 28th.
It was the occasion to highlight the variety of ISC research fields where diffusion plays a relevant role:

If brownian motion has been a milestone to understand the atomistic nature of matter, diffusion processes are so widespread because diffusion is one of the main “way of transport”, as we learn from the kinetic theory.… Read the rest

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