12:15–1:15 pm
KPTC 206 https://compinsci.psd.uchicago.edu/
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"A fast-swimming bacterium collides with a hard surface" |
The sediment-dwelling bacterium \textit{Thiovulum majus}, which swims at a speed of $600\,\mu$m/s, is one of the fastest known bacteria. When such a cell collides with a hard surface it either escapes rapidly into the bulk fluid or else becomes hydrodynamically bound to the wall. We first show that these dynamics preserve a memory of the cell's trajectory before the collision, which is gradually erased by contact with the surface. This erasure of information is consistent with a first-passage problem. Next, we investigate the two-dimensional motion of cells that are hydrodynamically bound to the surface. These cells diffuse laterally over the surface. When two cells diffuse within a critical distance of one another, they form a stable dimer of co-rotating cells. These dimers grow into two-dimensional active crystals composed of hundreds of cells. We analyze the large-scale motion of these crystals and their stability.