Sidney R. Nagel
The University of Chicago,
James Franck Institute L-115,
Tel: (773)-702-7190
Fax: (773)-702-5863
e-mail: s-nagel@uchicago.edu
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Sidney R. Nagel The University of Chicago,
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Ph.D., Princeton, 1974.
Stein-Freiler Distinguished Service Prof., Dept. Physics, James Franck
Inst., and the College
Experimental physics, condensed-matter physics, non-linear dynamics.
Many complex phenomena are so familiar that we forget to ask whether or not they are understood. Indeed, some effects are so ubiquitous that we hardly realize that they defy our normal intuition about why they occur. Examples of poorly understood classical physics include the anomalous flow of granular material, the long messy tendrils left by honey spooned from one dish to another, and the pesky rings deposited by spilled coffee on a table after the liquid evaporates. These are all non-linear hydrodynamic phenomena which not only are of technological importance but can also lead the inquisitive into new realms of physics. It is problems such as these which have fueled much of my research effort.
Another emphasis of my work can be classified as an attempt to understand the properties of disordered materials. I have worked on several different projects which involve a range of disciplines from conventional solid-state physics to non-linear dynamics with some applications to geophysics.
I list here a few of the topics on which my group is currently working:
Granular Materials. In collaboration with the group of Heinrich Jaeger, we have been studying the properties of granular media. Despite their ubiquity around us and the simplicity with which we can describe them, we understand very little about how these materials (e.g., sand) behave. In these studies we enter a new area of physics in which we are studying a statistical system of many particles but where the temperature is totally irrelevant. Thus, these systems are unavoidably always out of equilibrium, and we must come up with new concepts in order to understand and predict their properties.
Glass Transition. The glass transition has been called "the deepest and most interesting unsolved problem in solid state theory." We have been studying this transition using a variety of techniques including neutron diffraction, specific heat spectroscopy, computer simulation, dielectric susceptibility, shear modulus. We have managed to produce a master curve onto which all the dielectric data from all samples over 15 decades in frequency can be scaled. Such scaling has important implications for the nature of the glass transition.
Jamming. In an effort to deal with diverse phenomena where systems become stuck in a region far from equilibrium (e.g., at the glass transition and in clogged granular materials flowing - unsuccessfully - through a pipe), I have been investigating, along with Andrea Liu at UCLA, whether there can be a more general way of looking at these systems in terms of a "Jamming Phase Diagram." We proposed such a diagram and are currently investigating its utility in connecting a wide range of observed phenomena.
Singularities in Free-surface Flows. A drop falling from a faucet is a common example of a liquid fissioning into two or more pieces. The cascade of structure that is produced in this process is of uncommon beauty. As the drop falls, a long neck, connecting two masses of fluid, stretches out and then breaks. What is the shape of the drop at the instant of breaking apart? Something dire must happen to the mathematical description of the liquid at that point since the drop undergoes a topological transition where it starts out as a single, connected fluid and ends up in two or more separate pieces. This is an example of a finite-time singularity since the drop breakup occurs in a short time after the drop becomes unstable and starts to fall. At the transition, a singularity occurs since the radius of the neck holding the drop to the nozzle becomes vanishingly thin. As its radius goes to zero, the curvature diverges and the surface tension forces become infinite. How can such dramatic dynamics occur in something which had such smooth and innocuous initial conditions and forcing terms? Using photographic techniques, we have been studying transitions such as these to understand how the non-linearities in the governing equations (in this case the Navier-Stokes equations) can be tamed and understood. Singularities of this kind occur in many areas of physics from stellar structure to turbulence to bacterial colony growth. This drop breakup problem is one of the simplest places to start an experiment which directly probes the singularity itself.
Encapsulation of Biological Cells for Transplantation. Using the fluid experiments of the kind described above, in collaboration of Milan Mrksich in our Chemistry Department we have invented a new procedure for encapsulating small particles. This method may be particularly useful for coating biological cells for transplantation or for coating drugs for controlled time-release.
Crumpling. How does a sheet of paper crumple into a small ball? If you squeeze a sheet of paper very hard by hand, nearly 80% of the volume is still filled by air. What gives the crumpled ball its strength? We have been attacking this question experimentally in connection with the theoretical investigations of Tom Witten. We have found surprising time dependence and histeresis in the response.
Honors