Rotating Bacteria
(a) Still image of a rotating group of bacteria (B. subtilis)
with a magnification of 500 times original size, and (b) the corresponding velocity field
obtained by digitizing a series of images. The way in which this group of bacteria lines themselves up and chooses to move in a single direction amidst multiple possibilities is reminiscent of how a bird flock selects a single direction to move, even though there are many choices (Courtesy Andras Czirok and Tamas Vicsek.)
Source: A. Czirok, E. Ben-Jacob, I. Cohen, O. Shochet and T.
Vicsek, "Formation of complex bacterial colonies via self generated
vortices," Physical Review E 54 , 1791 (1996)
