Seminars & Discussions
Week beginning 24 April 2016
Monday 25 Apr 16 - 1:00pm
Biological evolution in microbial colonies
Bartek Waclaw (University of Edinburgh)
Biological evolution is not only of theoretical but also of immense practical significance (e.g. the evolution of antibiotic resistance). In the last few years I have been trying to find out how biological evolution depends on physical interactions between organisms and their environment. In this talk I will discuss one such example: the fate (fixation/extinction at the front) of a new mutant bacterium in an expanding microbial colony. I will show some cool experimental images, demonstrate how they can be explained using computer simulations and theory, and list some new predictions which I would like to test experimentally in the future.
Friday 29 Apr 16 - 11:30am
Diffusion of Ellipsoids in Bacterial Suspensions
Authors: Yi Peng, Lipeng Lai, Yi-Shu Tai, Kechun Zhang, Xinliang Xu, Xiang Cheng
Speaker: Nick Koumakis
Active fluids such as swarming bacteria and motile colloids exhibit exotic properties different from conventional equilibrium materials. As a peculiar example, a spherical tracer immersed inside active fluids shows an enhanced translational diffusion, orders of magnitude stronger than its intrinsic Brownian motion. Here, rather than spherical tracers, we investigate the diffusion of isolated ellipsoids in a quasi-twodimensional bacterial bath. Our study shows a nonlinear enhancement of both translational and rotational diffusions of ellipsoids. More importantly, we uncover an anomalous coupling between particles' translation and rotation that is strictly prohibited in Brownian diffusion. The coupling reveals a counterintuitive anisotropic particle diffusion, where an ellipsoid diffuses fastest along its minor axis in its body frame. Combining experiments with theoretical modeling, we show that such an anomalous diffusive behavior arises from the generic straining flow of swimming bacteria. Our work illustrates an unexpected feature of active fluids and deepens our understanding of transport processes in microbiological systems.
article 068303 (2016) pdf version
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