Foams out of stable equilibrium: cell elongation and side swapping
The evolution of a liquid foam usually mixes quasi-equilibrium topological and geometrical features in an intricate way. We take advantage of special properties of ferro ̄uid froths and of constrained area evolution simulations, to distinguish the eects of side swapping (T1 processes) from other rearrangements in the froth. Cell elongation characterizes the froth and its deviation from mechanical equilibrium as robustly as the usually measured total wall length, that is surface energy. §
Reverse draining of a magnetic soap film.
We investigate the draining of a vertical magnetic soap film in the presence of a strong, nonuniform magnetic field. A colloidal suspension of magnetic nanoparticles in a regular soap solution yields a magnetic soap solution, from which a soap film is formed across an isolated frame. Experiments demonstrate that with a strong magnet placed above the frame, the film may be made to flow upward against gravity. The amount of film draining upward is altered by varying the distance between the frame and magnet. A first mathematical model is developed for the evolution of the film. Simulations demonstrate qualitative agreement with the experiment.
Archaeology and mud wall decay in a West African village
Abstract A detailed study of the processes of deterioration of mud walls and of the physical evolution and devolution of a contemporary West African village is seen to facilitate the location of decayed mud structures at a nearby archaeological site. Various climatic and pedological conditions at the site make it unlikely that such walls will be discerned. The archaeologist wishing to obtain the fullest and least biased picture of the settlement configuration of the ancient community should therefore heed all the inferential lessons to be had from a focused ethnographic investigation. Given similar climatic situations and practices of house construction, taphonomy and ethnographic analogies may both be necessary for a valid reconstruction of an archaeological settlement.