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Fig. 5.4 Simulation of a
chemical diode
local change in the dynamic mode in the selected areas of the medium. As an
example let us consider a concentration pulse bending around a hindrance and
passing through a hole (see Fig.
4.9
in the previous chapter). In this case a
homogeneous Belousov-Zhabotinsky medium was used in which two divergent
linear impulses were initially excited. After that a hindrance was projected onto the
surface of the medium by intense radiation that was supposed to be bent around by
the left pulse and a band with two holes through which the right impulse was
supposed to pass. Intense radiation, projected over the entire duration of the
impulses, transferred the medium in these areas into an inactive state (see zero
isoclines in Fig.
5.2
), which was equivalent to a solid impermeable hindrance
introduced into the medium.
A second example is the creation of the “chemical diode” configuration in a
reaction-diffusion medium. In 1996 the Japanese researcher Prof. Yoshikawa with
colleagues proposed the idea of a device in which unidirectional passage of
concentration waves generated in the Belousov-Zhabotinsky reaction takes place.
The device, called chemical diode, is a thin gap, inactive for the Belousov-
Zhabotinsky reaction, between linear (P-side) and converging to the gap (
-side)
boundaries (Fig.
5.4
). Experimentally, this system was implemented as a set of two
square plates made of microporous glass, with the apex of one of them directed
toward the middle of the side of the other plate. The plates were impregnated with a
solution of the reaction catalyst—ferroin—and placed into the solution of the
remaining components of the reaction. Since ferroin was contained only in the
porous glass, the reaction could only take place on the surface of the plates. It was
shown that the passage of concentration waves in the direction P
!
C and C
!
Pis
not adequate. Given a gap of a certain width, the wave moves in the direction P
!
C
and does not pass in the opposite direction C
!
P. Yoshikava and colleagues also
showed that a variety of logic circuits can be constructed based on elementary
chemical diodes.
A major shortcoming of the experimental device used in this work was high
labor intensity of its manufacturing and rather low reliability. However, if one
controls the modes of the Belousov-Zhabotinsky reaction by light radiation, a
simple experimental scheme can be proposed that facilitates forming both a geo-
metrically arbitrary structure of the diode and a variety of devices based on it. In a
homogeneous photosensitive medium, a concentration wave can be excited, and
during the entire time of its passage through the device, the structure of the diode
С
