Generalized $\beta$-expansions, substitution tilings, and local   finiteness
  For a fairly general class of two-dimensional tiling substitutions, we prove that if the length expansion $\beta$ is a Pisot number, then the tilings defined by the substitution must be locally finite. We also give a simple example of a two-dimensional substitution on rectangular tiles, with a non-Pisot length expansion $\beta$, such that no tiling admitted by the substitution is locally finite. The proofs of both results are effectively one-dimensional and involve the idea of a certain type of generalized $\beta$-transformation. 
Natalie Priebe Frank (Vassar College) and E. Arthur Robinson, Jr.   (George Washington University)