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Dr. Anupam Sengupta: Emergent topological landscapes - from liquid crystals in flow to living systems under stress

Datum objave: 18. 1. 2016
Seminar fizike mehkih snovi
Petek, 22. 1. 2016 ob 10:15, Kuščerjev seminar, FMF, Jadranska 19, Ljubljana

Emergent topological landscapes - from liquid crystals in flow to living systems under stress

Anupam Sengupta,

Massachusetts Institute of Technology, Ralph M Parsons Laboratory for Environmental Engineering, USA & ETH Zurich, Institute for Environmental Engineering, Switzerland

Topological defects exist in a range of ordered systems with broken symmetries. In this talk, I will present two vignettes that elucidate emergence of topological landscapes under disparate physical conditions. In the first part, I will show how intrinsic order in liquid crystals (LCs) - mesogenic phases of matter which combine liquid fluidity with crystalline solid properties, can lead to a hierarchical buildup of topological defect(s) under symmetric cross-flow conditions. Topological defects of strength higher than 1, stably exist as multiples of integer defect, but get spatially locked at a stationary arrangement. However, the arrangement could be “unlocked” by perturbing the flow parameters, suggesting a possible degeneracy in the free energy levels of the system. In the second part, I will present how topological landscapes emerge (or actively bypassed) in a proliferating colony of anisometric bacterial cells. Here, the growth-induced stresses hinder formation of a global ordered nematic phase, nor does it result in a purely disordered (isotropic) phase. Instead, different sizes of domains relative to the colony size, in which cells are highly aligned at specific orientations, are found. I will discuss how the cell-to-colony morphology evolves over time, and highlight the role of stress propagation on the emergent topological landscape therein.