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ORDER OUT OF CHAOS 152<br />

were known to mathematicians as the "attractors" of stable<br />

systems. What is new is their application to chemical systems.<br />

It is worth noting that the first paper dealing with instabilities<br />

in reaction-diffusion systems was published by Thring in 1952.<br />

In recent years new types of attractors have been identified.<br />

They appear only when the number of independent variables<br />

increases (there are two independent variables in the Brusselator,<br />

the variables X and Y). In particular, we can get "strange<br />

attractors" that do not correspond to periodic behavior.<br />

Figure 8, which summarizes some calculations by Hao Bailin,<br />

gives an idea of such very complicated attractor lines calculated<br />

for a model generalizing the Brusselator through the<br />

addition of an external periodic supply of X. What is remarkable<br />

is that most of the possibilities we have described have<br />

been observed in in<strong>org</strong>anic chemistry as well as in a number of<br />

biological situations.<br />

In in<strong>org</strong>anic chemistry the best-known example is the<br />

Belousov-Zhabotinsky reaction discovered in the early 1960s.<br />

The corresponding reaction scheme, the Oregonator, introduced<br />

by Noyes and his colleagues, is in essence similar to the<br />

Brusselator though more complex. The Belousov-Zhabotinsky<br />

reaction consists of the oxidation of an <strong>org</strong>anic acid (malonic<br />

acid) by a potassium bromate in the presence of a suitable catalyst,<br />

cerium, manganese, or ferroin.<br />

INFLOW<br />

MALONIC . ::: ...rP U ::- M :: P :

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