sentences:  In 1927 Eckart received a Guggenheim Fellowship to do postdoctoral study and research with Arnold Sommerfeld at the Ludwig Maximilian University of Munich, one of the three main centers for the development of quantum mechanics, the others being Göttingen under Born and the University of Copenhagen under Niels Bohr.Also at Munich simultaneous with Eckart were Rudolf Peierls, and two other Guggenheim Fellows, Edwin C. Kemble and William V. Houston.In Munich, Eckart worked on the quantum mechanical behavior of simple oscillators using the Schrödinger equation and on operator calculus related to the matrix formulation of quantum mechanics.