P. Hackney and M. Robertson, "On the Category of Props," Applied Categorical Structures: DOI 10.1007/s10485-014-9369-4. arXiv version.
The Homotopy Theory of Simplicially Enriched Multicategories, arXiv version. Part of my Ph.D thesis. This result was independently obtained by Ieke Moerdijk and Denis-Charles Cisinski in their paper http://arxiv.org/abs/1109.1004.
Spaces of Operad Structures, arXiv version. (Replacement in progress)