Nonlinear Dynamics and Pattern Formation in Physics and Biology

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9812526 Goldstein This award supports research on nonlinear dynamics and pattern formation in physical and biological systems. Theoretical research well connected with experiment will focus on the areas of cell growth and motion, and on an alternative explanation of the Rayleigh instability in fluid mechanics. Work in the first area focuses on understanding the physical mechanisms of cell growth in the bacterium B. subtilis and on the mechanism of directed swimming in peritrichously flagellated bacterial cells. The proposed work would elucidate the physical processes that lead to the formation of the supercoiled structure of B. subtilis that results when cell separation fails to occur after cell division, and related physical biology associated with moving filamentary structures. Work in the second area seeks to elucidate the mechanism for directed swimming that results when co-rotating helical flagella bundle together. Inquiry will focus on the hydrodynamic interactions that occur when this happens and on collective behavior recently observed in suspensions of swimming microorganisms. The PI seeks a description that melds the areas of elasticity and hydrodynamics at low Reynolds number to elucidate the physical mechanisms by which microorganisms swim. Recent experiments on shape instabilities of membrane vesicles induced by optical traps that have shown that front propagation may occur in such tension driven instabilities. Motivated by these experiments, the PI will study the circumstances under which an analogous `propagating topological transition' might occur in viscous two-phase flow. Of particular interest are convective instabilities of jets and plumes, buckling phenomena in jets, and the role of viscoelasticity and shear. %%% This talented PI will carry out theoretical research in areas at the interface between physics and biology. The physical mechanisms by which microorganisms swim and a better understanding of kinds of fluid flow peculiar t o biological systems are a major focus of the research. ***