  We study the isolated resonances occurring in conductance fluctuations of
ballistic electron systems with a classically mixed phase space. In particular,
we calculate the conductance and Wigner-Smith time as well as scattering states
and eigenstates of the open and closed cosine billiard, respectively. We
demonstrate that the observed isolated resonances and their scattering states
can be associated with eigenstates of the closed system. They can all be
categorized as hierarchical or regular, depending on where in a phase space
representation the corresponding eigenstates are concentrated.
