\acknow{Special thanks to Dr.\ P.\ E.\ Cantrell, whose guidance
and patience made this thesis possible. I would also like to thank
Drs. R.\ M.\ Feldman, J.\ D.\ Gibson, and K.\ Watson for their time
and useful comments in reviewing this document.

I am indebted to Dr.\ G.\ M.\ Clark of Ohio State University 
for help in implementing his
approximation method.}
