Paper 1, Section I, B

Mathematical Biology
Part II, 2011

A proposed model of insect dispersal is given by the equation

nt=Dx[(n0n)nx]\frac{\partial n}{\partial t}=D \frac{\partial}{\partial x}\left[\left(\frac{n_{0}}{n}\right) \frac{\partial n}{\partial x}\right]

where n(x,t)n(x, t) is the density of insects and DD and n0n_{0} are constants.

Interpret the term on the right-hand side.

Explain why a solution of the form

n(x,t)=n0(Dt)βg(x/(Dt)β),n(x, t)=n_{0}(D t)^{-\beta} g\left(x /(D t)^{\beta}\right),

where β\beta is a positive constant, can potentially represent the dispersal of a fixed number n0n_{0} of insects initially localised at the origin.

Show that the equation (1) can be satisfied by a solution of the form (2) if β=1\beta=1 and find the corresponding function gg.