sentences:  Dennison arrived at the Institute of Theoretical Physics at the University of Copenhagen, in October 1924.During his three years in Europe, he mostly did postdoctoral research in Copenhagen, where he had associations with other visiting physicists working there, such as Paul Dirac, Samuel Abraham Goudsmit, Werner Heisenberg, Walter Heitler, Ralph H. Fowler, Friedrich Hund, Hendrik Anthony Kramers, Yoshio Nishina, Wolfgang Pauli, and George Eugene Uhlenbeck.In the last half of 1925, Heisenberg and Max Born published their matrix mechanics formulation of quantum mechanics.