Complex sentence: Previously he was the J. Erik Jonsson 22 Professor of Science at Rensselaer Polytechnic Institute, where he had joint appointments in the Department of Physics, Applied Physics and Astronomy, and the Department of Electrical Computer, and System Engineering.
Split into simpler sentences: Previously he was the J. Erik Jonsson 22 Professor of Science at Rensselaer Polytechnic Institute. He has joint appointments in the Department of Physics, Applied Physics and Astronomy, and the Department of Electrical Computer, and System Engineering.