This brief offers a concise presentation of granular fluids from the point of view of non-equilibrium statistical physics. The emphasis is on fluctuations, which can be large in granular fluids due to the small system size (the number of grains is many orders of magnitude smaller than in molecular fluids).

Firstly, readers will be introduced to the most intriguing experiments on fluidized granular fluids. Then granular fluid theory, which goes through increasing levels of coarse-graining and emerging collective phenomena, is described. Problems and questions are initially posed at the level of kinetic theory, which describes particle densities in full or reduced phase-space. Some answers become clear through hydrodynamics, which describes the evolution of slowly evolving fields. Granular fluctuating hydrodynamics, which builds a bridge to the most recent results in non-equilibrium statistical mechanics, is also introduced. Further and more interesting answers come when the dynamics of a massive intruder are discussed. Such non-equilibrium stochastic process offers a more precise and compact picture of the features foreseen at the more detailed levels of description. The dynamics of an intruder diffusing in a granular fluid reveal the clearest connection with recent theories on stochastic energetics and stochastic thermodynamics.

Includes supplementary material: sn.pub/extras

Autorentext

Massimo Cencini graduated in Physics from the Sapienza University of Rome in 1996 and gained his Ph.D. there in 2000. He then became a postdoc at the Max Planck Institute for Complex Systems in Dresden and at the Observatory of Nice. Currently, he is senior researcher at the Institute of Complex Systems of the National Research Council in Rome, where he works since 2008. His scientific interests include chaos and complexity in dynamical systems, statistical theories of turbulence, and turbulent transport. In recent years, he has also become interested in theoretical population dynamics. Dr. Cencini has written about 90 scientific papers in international peer-reviewed journals and a monograph on chaos and dynamical systems. Andrea Puglisi graduated from Sapienza University of Rome in 1998 and gained a Ph.D. in Physics in 2002. Then, he has been a Marie Curie fellow at Orsay, Paris (2003-2004) and a postdoc at Sapienza University (2005-2008). He is senior researcher at the Institute of Complex Systems of the National Research Council in Rome (CNR-ISC), where he works since 2008. His interests are granular materials (theory and experiments), non-equilibrium statistical mechanics, and computational cognitive science. He has co-authored more than 100 scientific papers on international journals and one book: Transport and Fluctuations in Granular Fluids (Springer 2014). Davide Vergni graduated in Physics from the Sapienza University of Rome in 1997 and gained his Ph.D. there in 2001. He is currently a senior researcher at the Institute for Calculus Applications "Mauro Picone" of the National Research Council of Italy, and since 2015 he is a member of the technical-scientific board of experts at the Department of the Treasury. His scientific interests lie within applied mathematics, in particular reactive systems in heterogeneous media, population dynamics, combinatorial aspects in bioinformatics, and management and optimization in financial systems (public debt, pension funds, energy market). He has co-authored more than 50 scientific publications, including peer-reviewed papers in international journals, book chapters, and proceedings. Angelo Vulpiani graduated from Rome University in 1977, where his supervisor was Gianni Jona-Lasinio. He subsequently became a CNR fellow (1978-1981), Assistant Professor at Rome University (1981-1988), and Associate Professor at first the University of L'Aquila (1988-1991) and then the University of Rome (1991-2000). At present, he is Professor of Theoretical Physics in the Physics Department of Sapienza University of Rome and a fellow of the Institute of Physics. He has been a visiting fellow at several research institutes and universities in France, Belgium, Sweden, Denmark, and the USA. His scientific interests include chaos and complexity in dynamical systems, statistical mechanics of non-equilibrium and disordered systems, developed turbulence, phenomena of transport and diffusion, and foundations of physics. He has written about 250 scientific papers in international journals and nine books, including most recently Reductionism, Emergence and Levels of Reality (Springer, 2014; co-authors: S. Chibbaro and L. Rondoni).

Inhalt

Introduction.- 1 Granular fluids: from everyday life to the lab.- Boltzmann equation: a gas of grains.- Hydrodynamics: a sea of grains.- Tracer's diffusion: swimming through the grains.- The arrow of time: past and future of grains.- Conclusion and perspectives.- Expansion of the first two moments of the transition rates for large mass of the tracer.- Index.