I'm sorry, I was busy finishing edits on a paper with Brendan Fong - the referee had demanded major revisions, and we've been working on this for months, and now it's done (I hope):

* [A compositional framework for passive linear networks.](http://math.ucr.edu/home/baez/circuits.pdf)

Hypergraph categories, decorated cospan categories, decorated corelation categories - lots of nice category theory, all in the service of electrical engineering.

I'm dying to tell you about how to compose enriched profunctors, and I'll do it tomorrow - Thursday! In the meantime you could read about quantales in the book.