Sjoerd Crans has mainly worked on aspects of the algebraic definition of higher categories, notably on clarifying the right monoidal structure on globular ω-categories that achieves the analogous effect that the simple cartesian product does on simplicial sets. This is now known as the Crans-Gray tensor product.
Crans also made an influential contribution to the theory of models for ∞-stack (∞,1)-toposes in his study of the model structure on simplicial sheaves.
A collection of articles by Sjoerd Crans is here: