Sidney R. Nagel

One part of my research deals with how a fluid loses its ability to flow. This can happen, for example, to a supercooled liquid as the temperature is lowered so that it becomes increasingly sluggish and forms a glass. It can also happen in a granular fluid when it becomes jammed. I have been searching for common aspects that relate these transitions between flowing and dynamically arrested states. Another area of interest has to do with exploring the nature of the singularities that occur in the interfaces of fluids. 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 is changing from a single entity into two disconnected pieces. Exploring the nature of the singularities in this situation is relevant for understanding singularities in many other dynamical contexts.