The dual nature of 5f electrons and origin of heavy fermions in U   compounds
  We develop a theory for the electronic excitations in UPt$_3$ which is based on the localization of two of the $5f$ electrons. The remaining $f$ electron is delocalized and acquires a large effective mass by inducing intra-atomic excitations of the localized ones. The measured deHaas-vanAlphen frequencies of the heavy quasiparticles are explained as well as their anisotropic heavy mass. A model calculation for a small cluster reveals why only the largest of the different $5f$ hopping matrix elements is operative causing the electrons in other orbitals to localize. 
G Zwicknagl (1) and P. Fulde (2) ((1) Institut f\"ur Mathematische   Physik, Technische Universit\"at Braunschweig, Germany ...