The
Belousov-Zhabotinskii reaction (or BZ reaction) is performed
using a mixture of sodium bromate, malonic acid, sulphuric acid,
and ferroin. This creates a complex oxidising reaction that changes
colour periodically. The oscillations start with the formation
in a red solution of small blue dots that expand into ever-widening
concentric blue rings. Sometimes these will become expanding
Archimedean spirals; the patterns intermix and become increasingly
complex towards the end of the reaction. These waves are not
mechanical in the same sense a ripple can be considered; instead
these waves show information traveling.
The
reaction was discovered in 1951, but more recently the reaction
has been used to study the possibly applications of liquid
computers using chemical waves.
" Similar
Spiral Patterns have been observed in dishes of social amoebae
in a slime mould. Individual cells communicate in spiral
waves at a certain stage in their life cycles when they synthesise
and hoard molecules of a hormone called cAMP, to be suddenly
released in an abrupt ‘sneeze’. Professor Winfree
suggests that this cAMP diffusion is perhaps in effect "a
living fossil replaying events that were common during evolution
from unicellular to multi cellular organisms two billion
years ago". The spirals rotate at about the same period
as the chemical wave in the B-Z reaction, with about the
same speed and spacing. The tiny rotating source at the core
of a spiral wave is called a ‘rotor’, and the
term ‘pacemaker’refers to the variably longer-period
sources of concentric ring wave s..." http://people.musc.edu/~alievr/BZ/BZexplain.html
Computer simulations, which allow exploration of five different
cellular automata "All of them use a 2-dimensional array
of cells which can vary in size from 33x33 to 528x528. "Periodic
boundary conditions" are used, meaning that the left edge
of the array wraps around to contact the right edge, and the
top edge of the array wraps around to contact the bottom edge.
The structure is thus that of a tours, although it is easier
to think of a 2-dimensional plane in which an unlimited number
of copies of the square array are reproduced next to, and above
and below, each other (and each copy changes in the same way)."