In the autumn of 1928, Oppenheimer visited Paul Ehrenfest 's institute at the University of Leiden in the Netherlands, where he impressed by giving lectures in Dutch, despite having little experience with the language. There, he was given the nickname of Opje, later anglicized by his students as "Oppie". From Leiden, he continued on to the Swiss Federal Institute of Technology (ETH) in Zurich to work with Wolfgang Pauli on quantum mechanics and the continuous spectrum. Oppenheimer respected and liked Pauli and may have emulated his personal style as well as his critical approach to problems.