  Correlation effects in nuclear matter at finite temperatures are studied for
subnuclear densities ($\rho<\rho_0$) and medium excitation energy, where a
nonrelativistic potential approach is possible. A quantum statistical approach
is given, where clusters are treated under the influence of a clustered medium
treated within a mean field approximation. Spectral functions, in-medium cross
sections, and reaction rates are considered as well as the formation of a
quantum condensate. In particluar, exploratory calculations are shown with
respect to the pseudo gap in the nucleon level density close to the superfluid
phase transition. Estimates of isospin singlet pairing and quartetting in
nuclear binding energies are given.
