We generalize the notion of partial dynamical symmetry (PDS) to a system of interacting bosons and fermions. In a PDS, selected states of the Hamiltonian are solvable and preserve the symmetry exactly, while other states are mixed. As a first example
of such novel symmetry construction, spectral features of the odd-mass nucleus $^{195}$Pt are analyzed.
In this paper a review is given of a class of sub-models of both approaches, characterized by the fact that they can be solved exactly, highlighting in the process a number of generic results related to both the nature of pair-correlated systems as w
ell as collective modes of motion in the atomic nucleus.
The case of U(5)--$hat{Q}(chi)cdothat{Q}(chi)$ mixing in the configuration-mixed Interacting Boson Model is studied in its mean-field approximation. Phase diagrams with analytical and numerical solutions are constructed and discussed. Indications for
first-order and second-order shape phase transitions can be obtained from binding energies and from critical exponents, respectively.
