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Fig. 6.3 Benard cells (a)
and scheme of the liquid
motion in them (b)
In 1900 an article of the French scientist Benard was published. He showed that
when a layer of mercury poured into a flat wide vessel was heated from the bottom,
the entire layer spontaneously broke up into identical vertical hexagonal prisms. In
the central part of each cell the liquid rises and near vertical faces it sinks
(Fig.
6.3b
). That is, convective flows appear in the vessel, which raise the heated
liquid up and lower the cold liquid down. Subsequently, these cells were called
Benard cells.
5. Interesting phenomena of spontaneous development of the structure are
observed in bacterial environments. One example is the study of the evolution of
the colonies of the bacterium
Paenibacillus alvei
. Colonies were grown in petri
dishes containing agar with some peptone added. Peptone is a product obtained by
partial protein hydrolysis, which is used as a nutrient in bacterial media. During
evolution bacterial media spontaneously formed complex spatial distributions of
bacteria (Fig.
6.4
). In this case, the distribution varied depending on the concentra-
tions of agar and peptone.
6. Suppose that in the closed habitat (e.g., on the island which has no connection
to the mainland), a population of creatures leaves. The evolution of its population
over time will be determined primarily by the reproducibility parameter
, i.e., the
average number of the offsprings produced by one individual. We will use a
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