In this paper we study a nonlocal, semilinear, parabolic problem. The existence and uniqueness of a maximal solution is proved for bounded domains, in arbitrary dimensions, using the Schauder fixed-point theorem. In the one-dimensional case, we give a result of positivity and a comparison principle for the integral of the solution. The proofs are based on the decomposition of the solutions in an appropriate spectral basis.

We study the limiting behavior as $\varepsilon$ tends to zero of the solution of a system arising in the microphase separation of diblock copolymers. This system involves a fourth-order parabolic equation. We consider the case of spherical symmetry, and we show the convergence to a free-boundary Hele--Shaw-type problem.

We study the porous medium equation with sign changes and examine the way sign changes disappear. We give a formal classification of self-similar and non-self-similar scenarios for their disappearance, for $N>1,$ restricting attention to the radial case. The results we present on the classification of similarity solutions are rigorous except where indicated otherwise.