[ook]

http://www.tara.tcd.ie/handle/2262/77562 - "Design and implementation of an ahead-of-time compiler for PHP" is the PhD thesis in question.

A google tech talk related to this work is on youtube https://www.youtube.com/watch?v=kKySEUrP7LA

You can find multiple other papers on google scholar where Paul was an author all related to programming languages, compilers etc.