Passage: Jürgen Kurths (born 11 March 1953 in Arendsee/Altmark) is a German physicist and mathematician. He is a chair of the research domain Transdisciplinary Concepts of the Potsdam Institute for Climate Impact Research, a Professor of Nonlinear Dynamics at the Institute of Physics at the Humboldt University, Berlin, and a 6th-century chair for Complex Systems Biology at the Institute for Complex Systems and Mathematical Biology at Kings College, Aberdeen University (UK). His research is mainly concerned with nonlinear physics and complex systems sciences and their applications to challenging problems in Earth system, physiology, systems biology and engineering.

Question: Which fields did Jurgen Kurths focus his research on?
nonlinear physics and complex systems sciences