We focus on soft condensed matter and non-linear systems.

Janssen Effect in 2D Friction-Driven Systems

Sphere Packing and the Jamming Transition

Until recently, the jamming of hard spheres has been described using only mechanics. Below jamming, mechanical properties like pressure, energy, force, stress, and strain are nonexistent, and so it becomes difficult to characterize the transition. Our group has found that the same phase transition is seen in the statistics of the network of nearest neighbors, which can be defined over all of phase space. This phase transition, however, is qualitatively different from the mechanical one, and so we attempt to characterize it.

Construction of a Pseudo-Thermal Bath

Two-dimensional thermal systems are very difficult to create and observe.  We use chaotic Faraday waves, which result from vertical oscillation of a fluid beyond some critical amplitude, to macroscopically produce thermal-like behavior on the surface of water.  Since the chaotic waves are isotropic and uncorrelated, an object floating on the surface will experience random kicks from all directions, much like a particle in a gas, thus creating an environment analogous to a two-dimensional thermal bath.  This pseudo-thermal system then becomes a playground on which we explore interparticle potentials and self-assembly on a two-dimensional substrate.

Fluctuation Dissipation Theory

Mechanical Properties of Proteins

Proteins are little more than chains of nearly identical molecules linked together head to tail, yet when they fold, they form compact and stable structures with wildly varying forms and functions.  The ground state structures of these folded proteins have been extensively studied through x-ray scattering, however, little is known about their dynamical response to changing environments.  Through the use of a highly optimized atomic force microscope, we intend to study the dynamic response of proteins to changing mechanical stresses.  In so doing we hope to learn about the mechanisms that allow proteins to function reliably in ever-changing biological systems.