MCB111: Mathematics in Biology (Fall 2019)


week 13:

Diffusion-Reaction patterns

The Brusselator on steroids


Figure 1. The Brusselator + diffusion model. Adapted from K. Sims (http://www.karlsims.com/rd.html).

In class, we showed how the Gray-Scott model is a two-species system that in two dimensions can produce striking spatial patterns. Here, we are going to look at another two-species model that also produces interesting patters.

The Brusselator is just a theoretical model, and it got its name because it was proposed by investigators at the Universite libre de Bruxelles. The Brusselator is a purely reaction process, and it is interesting on its own because it can produce oscillations, thus the name Brusselator.

These are the reactions that define the Brusselator. There are two species and such that,

that is, transforms to , and transforms to but this last reaction can only occur in the presence of two additional molecules

But here, we are not going to study the Brusselator reactions alone, but the result of combining the Brusselator with a diffusion process. The and in addition to being subject to the Brusselator’s reactions, they can diffuse in both the and directions with diffusion coefficients and respectively.

We will workout this exercise in class, but that we need to do is


Figure 2. Brusselator-diffusion patterns. The top figure depicts the initial conditions for species A. The bottom figure depicts the concentration of A after some time. Parameters values are described in the text. The concentration of species B is a mirror image of that of A.

Do not forget the four conditions necessary to convert the system from a steady state of the Brusselator alone, into pattern-forming when including the diffusion terms,

where is a steady state of the Brusselator alone.

Here are some possible sets of parameters and initial conditions that in my hands produced cool patterns. I used a square of length , and . I run it until , with .


Figure 3. Brusselator-diffusion patterns. The top figure depicts the initial conditions for species A. The bottom figure depicts the concentration of A after some time. Parameters values are described in the text. The concentration of species B is a mirror image of that of A.

I know you will be creative, and for sure will get more interesting patterns than mine.