sentences:  He also applied his work to the theory of electrons and the conductivity of metals using Fermi statistics, and he co-authored a paper on the subject with Sommerfeld and William V. Houston.Returning to the United States in 1928, Eckart was appointed Assistant Professor in the Physics Department at the University of Chicago, where he continued his work on quantum mechanics for another 14 years.Noteworthy was a paper co-authored with Helmut Hönl, who received his doctorate under Sommerfeld in 1926; the paper, on the foundations of quantum mechanics, dealt with the role of group theory in quantum dynamics in monatomic systems and comparisons of the nuclear theories of Werner Heisenberg and Eugene Wigner.