3 pm in Howey Physics Lecture Room 5
Georgia Tech School of Physics Colloquium
Mark Shattuck
Benjamin Levich Institute and Physics Department
The City College of New York
"Granular Equilibrium: Shaken, Not Stirred"
Thermodynamics is generally not applicable to systems with energy
input and dissipation present, and identifying relevant tools for
understanding these far-from-equilibrium systems poses a serious
challenge. Excited granular materials have become a canonical system
to explore such ideas since they are inherently dissipative due to
inter-particle frictional contacts and inelastic collisions. Granular
materials also have far reaching practical importance in a number of
industries, but accumulated ad-hoc knowledge is often the only design
tool.
An important feature of driven granular systems is that the energy
input and dissipation mechanisms can be balanced such that a
Non-Equilibrium Steady-State (NESS) is achieved. This NESS shares
many properties of systems in thermodynamic equilibrium. In
particular, the structure and dynamics of the NESS are almost
identical to equilibrium systems. Further, we present strong
experimental evidence for a NESS first-order phase transition in a
vibrated two-dimensional granular fluid. The phase transition between
a gas and a crystal is characterized by a discontinuous change in both
density and temperature and exhibits rate dependent hysteresis.
Finally, we measure a free energy-like function for the system,
whose minimum determines the state of the system.
