  Deuteron-deuteron elastic scattering and transfer reactions in the energy
regime above four-nucleon breakup threshold are described by solving exact
four-particle equations for transition operators. Several realistic nuclear
interaction models are used, including the one with effective many-nucleon
forces generated by the explicit $\Delta$-isobar excitation; the Coulomb force
between protons is taken into account as well. Differential cross sections,
deuteron analyzing powers, outgoing nucleon polarization, and
deuteron-to-neutron polarization transfer coefficients are calculated at 10 MeV
deuteron energy. Overall good agreement with the experimental data is found.
The importance of breakup channels is demonstrated.
