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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

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Published on: December 4, 2017

Nonequilibrium Brownian motion beyond the effective temperature.

Andrea Gnoli¹, Andrea Puglisi¹, Alessandro Sarracino²

¹Istituto dei Sistemi Complessi - Consiglio Nazionale delle Ricerche, Rome, Italy; Dipartimento di Fisica, Università "Sapienza", Rome, Italy.

|April 10, 2014

Summary

This summary is machine-generated.

Researchers explored fluctuations in granular media, finding Einstein's relation breaks down in dense systems. A Generalized Fluctuation-Dissipation Theorem (GFDT) explains this by strong intruder-fluid coupling, not effective temperatures.

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Area of Science:

Physics
Soft Matter Physics
Non-equilibrium Systems

Background:

Thermal equilibrium simplifies fluctuation theories, like Einstein's relation for Brownian motion.
Recent theories explore non-equilibrium systems, introducing effective temperatures or Generalized Fluctuation-Dissipation Theorem (GFDT).
Mixed timescales in active or granular fluids challenge the concept of a single temperature.

Purpose of the Study:

To experimentally investigate the mixed timescale regime in Brownian motion.
To study fluctuations and linear response in a vibro-fluidized granular medium with a rotating intruder.
To analyze the breakdown of Einstein's relation and the applicability of GFDT.

Main Methods:

Experimental study of a rotating intruder in a vibro-fluidized granular medium.
Systematically varying packing fraction to transition between single- and multiple-timescale regimes.
Measuring fluctuations and linear response, and comparing with Einstein's relation and GFDT.

Main Results:

Einstein's relation holds in dilute, single-timescale regimes.
Einstein's relation is violated in denser, multiple-timescale regimes.
The violation is explained by GFDT due to strong intruder-fluid coupling, not effective temperatures.
Spatial correlations develop with increasing density.

Conclusions:

The study experimentally validates GFDT in mixed timescale regimes.
It highlights the breakdown of equilibrium concepts in dense granular systems.
Strong coupling and emergent spatial correlations are key features of these non-equilibrium systems.