Self_organization of gas bubbles
  Self_organization of hydrogen bubbles is reported under etching of metallic Aluminum in a weakly basic solution. The ascending gas bubbles drift to the areas with higher density of bubbles due to pressure difference. As a result, ascending bubbles form various stationary structures whose symmetry is determined by the symmetry of the etched area. The process is modeled on the basis of numerical solution of Bernoulli equation. 
M.E. Shcherbina, E.V. Barmina, P.G. Kuzmin, and G.A. Shafeev
cond-mat.other