Complex sentence: He worked as Professor at the Department of Mathematics until 2000, is now professor of Mechanics of Materials at the Department of Materials Science (University of Ioannina) and has worked as Visiting Professor at the Trinity College, Dublin (1989--1990).
Split into simpler sentences: He worked as Professor at the Department of Mathematics until 2000 when he was appointed professor of Mechanics of Materials at the Department of Materials Science (University of Ioannina). Professor Massalas has worked as Visiting Professor at the Trinity College, Dublin (1989--1990).