Nonlinear Response of Inertial Tracers in Steady Laminar Flows: Differential and Absolute Negative Mobility.
We study the mobility and the diffusion coefficient of an inertial tracer advected by a two-dimensional incompressible laminar flow, in the presence of thermal noise and under the action of an external force. We show, with extensive numerical simulations, that the force-velocity relation for the tracer, in the nonlinear regime, displays complex and rich behaviors, including negative differential and absolute mobility. These effects rely upon a subtle coupling between inertia and applied force that induces the tracer to persist in particular regions of phase space with a velocity opposite to the force. The relevance of this coupling is revisited in the framework of nonequilibrium response theory, applying a generalized Einstein relation to our system. The possibility of experimental observation of these results is also discussed.
CNR-ISC and Dipartimento di Fisica, Sapienza Università di Roma, piazzale A. Moro 2, 00185 Roma, Italy.
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Sarracino
CNR-ISC and Dipartimento di Fisica, Sapienza Università di Roma, piazzale A. Moro 2, 00185 Roma, Italy.
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Cecconi
CNR-ISC and Dipartimento di Fisica, Sapienza Università di Roma, piazzale A. Moro 2, 00185 Roma, Italy.
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Puglisi
Dipartimento di Fisica, Sapienza Università di Roma, piazzale A. Moro 2, 00185 Roma, Italy.
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Vulpiani