Arguably (b) is more formal, but both are acceptable in pretty much any context.
(a) is also correct (“University” is used attributively).
When referring to “a university”, the word “university” should not be capitalised (as it is not a proper name). “the University” is normally OK when referring to a specific institution, but I don’t think I would capitalise it in “the university structure”. This is not clear cut, however.