The quadratic isoperimetric inequality for mapping tori of free group automorphisms (with M.R. Bridson). Memoirs of the AMS, 203 (2010), no. 955. .pdf

Abstract If F is a finitely generated free group and \phi is an automorphism of F then F \rtimes_\phi Z satisfies a quadratic isoperimetric inequality.

(This is essentially the two papers with the same title, along with the paper `Free-group automorphisms, train tracks and the beaded decomposition', turned into a single monograph).