Complex sentence: He was a visiting scientist in Chemical Physiology of Plants, Institut fuer Pflanzenphysiologie, University of Vienna in 1997, and a visiting scholar at the University of California at San Diego in 2004 and 2013-present.
Split into simpler sentences: He was a visiting scientist in Chemical Physiology of Plants, Institut fuer Pflanzenphysiologie, University of Vienna in 1997. Obendorf was a visiting scholar at the University of California at San Diego in 2004 and 2013-present.