How swimming microorganisms displace fluid particles

Abstract:

As fish, microorganisms, or other bodies move through a fluid, they stir their surroundings.  This can be beneficial to some fish, since the plankton they eat depends on a well-stirred medium to feed on nutrients.  Bacterial colonies also stir their environment, and this is even more crucial for them since at small scales there is no turbulence to help mixing.  I will discuss a simple model of the stirring action of moving bodies through a fluid.  An attempt will be made to explain existing data on the displacements of small particles, which exhibit probability densities with exponential tails.  The simple model matches the data remarkably well, with a single adjustable parameter.