Seminário da Física 24/11/2020

Título: Active mixtures in a narrow channel: Motility diversity changes cluster sizes 
Palestrante: Pablo de Castro (Universidad de Chile) 
Data: 24/11/2020 às 16 horas via Google Meet

Resumo: The persistent motion of bacteria produces clusters with a stationary cluster size distribution (CSD). Here we develop a minimal model for bacteria in a narrow channel to assess the relative importance of motility diversity (i.e. polydispersity in motility parameters) and confinement. A mixture of run-and-tumble particles with a distribution of tumbling rates is considered on a 1D lattice. Particles facing each other cross at constant rate, rendering the lattice quasi-1D. To isolate the role of diversity, the global average tumbling rate stays fixed. For a binary mixture with no particle crossing, the average cluster size increases with the diversity as lower-tumbling-rate particles trap higher-tumbling-rate ones for longer. At finite crossing rate, particles escape from the clusters sooner, making the average cluster size smaller and the diversity less important, even though crossing can enhance demixing of particle types between the cluster and gas phases. If the crossing rate is increased further, the clusters become controlled by particle crossing. We also consider an experiment-based continuous distribution of tumbling rates, revealing similar physics. Using parameters fitted from experiments with Escherichia coli bacteria, we predict that the error in estimating the average cluster size without accounting for polydispersity is around 60%. We discuss how to find a binary system with the same CSD as the fully polydisperse mixture. An effective theory is developed and shown to give accurate expressions for the CSD, the effective tumbling rate, and the average fraction of mobile particles. We give reasons why our qualitative results are expected to be valid for other active matter models and discuss the changes that would result from polydispersity in the active speed rather than in the tumbling rate.

Referências:

https://arxiv.org/abs/2011.08905

Link de acesso Google Meet: https://meet.google.com/wgq-yuci-ygz

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