There's been an interesting discussion on mouthpiece physics at the 
Sax On The Web mouthpiece forum: 

http://forum.saxontheweb.net/forum_rmpc.html

I asked a question about the dynamics going on with mouthpieces, 
especially aerodynamics and airflow, and got some pretty good 
feedback.  It seems that there hasn't been much definitive study on 
this, so it's trial and error for now... until this can be modelled 
accurately in a computer... 

Thanks Keith for the link to the Gary Scavone paper.  He had some 
really interesting things to say about mouthpiece design:

http://ccrma-www.stanford.edu/~gary/thesis.html