  Experiments with networks of discrete reactive bistable electrochemical
elements organized in regular and nonregular tree networks are presented to
confirm an alternative to the Turing mechanism for the formation of
self-organized stationary patterns. The results show that the pattern formation
can be described by the identification of domains that can be activated
individually or in combinations. The method also enabled the localization of
chemical reactions to network substructures and the identification of critical
sites whose activation results in complete activation of the system. Although
the experiments were performed with a specific nickel electrodissolution
system, they reproduced all the salient dynamic behavior of a general network
model with a single nonlinearity parameter. Thus, the considered
pattern-formation mechanism is very robust, and similar behavior can be
expected in other natural or engineered networked systems that exhibit, at
least locally, a treelike structure.
