“…on x = L. In particular, the fact that Z > 0 close to the free boundary, so that phase is shrinking, makes it similar to a supercooled Stefan problem, for which blow-up can be a typical feature (for a review on non-standard Stefan problems see [7]). A rather comprehensive analysis of the phenomenon of blow-up for parabolic free boundary problems with data of Cauchy type (like (67)) or of supercooled (superheated) Stefan type (like (68)) has been performed in a series of papers [9,13,14], but only in case of constant coefficients. We note for instance that in (68) the source is not constant and even has variable sign, and the 'latent heat', though of constant sign, is non-constant (although, by assumption, it is bounded away from zero in the time interval considered).…”