PROFESSOR S. BHATTACHARYA

A monolayer of granular spheres in a cylindrical vial, driven continuously by an orbital shaker and subjected to a symmetric confining centrifugal potential, self-organizes to form a distinctively asymmetric structure which occupies only the rear half-space. It is marked by a sharp leading edge at the potential minimum and a curved rear. The area of the structure obeys a power-law scaling with the number of spheres. Imaging shows that the regulation of motion of individual spheres occurs via toggling between two types of motion, namely, rolling and stumbling into sliding. Experiments further suggest that because the coefficients of rolling and sliding friction differ substantially, the spheres acquire a local time-averaged coefficient of friction with a large range of intermediate values. Experiments demonstrate and simulations confirm that the global features of the structure are maintained robustly by auto-tuning of friction through internal dynamical states of rolling and sliding, providing a route to self-organization of a many-body system. Recent results show that when the system is restricted to a quasi-2 D space, this self-organization leads to crystallization. Usefulness of this paradigm in understanding the phenomenon of stampede in moving crowds and its prevention will be speculated on. *Work done at TIFR in collaboration with Deepak Kumar, Anit Sane, Soham Bhattacharya, Nitin Nitsure and Shankar Ghosh.