A Hele-Shaw system (consisting of two glass plates separated by a small gap) was used by University of Chicago MRSEC researchers, Sidney Nagel and Heinrich Jaeger and their research groups, to explore the zero-order-surface-tension properties of granular "fluids."
Theoretically, it had been predicted by Paul Wiegmann, also at the University of Chicago, that fluid fingering in the zero-surface-tension limit in these types of systems should lead to singular cusp structure locally and fractal geometry globally.
Granular flow provides the first experimental evidence for the coexistence of these two singular featues. High speed videos taken while nitrogen was slowly blown into a small hole at the center of the sand-filled glass plates, shows how the local cusps evolve into a global fractal.
Summer REU student, Aaron Patterson from Morehouse College, conducted the preliminary experiments for this study.
Work made possible through the NSF MRSEC program, DMR-0213745.
- "Towards the zero-surface-tension limit in granular fingering instability," Xiang Cheng, Lei Xu, Aaron Patterson, Heinrich M. Jaeger, and Sidney R. Nagel, Nature Physics, 4, 234-237 (2008).