  Analytic expressions describe universal elastic and reactive rates of
quasi-two-dimensional and quasi-one-dimensional collisions of highly reactive
ultracold molecules interacting by a van der Waals potential. Exact and
approximate calculations for the example species of KRb show that stability and
evaporative cooling can be realized for spin-polarized fermions at moderate
dipole and trapping strength, whereas bosons or unlike fermions require
significantly higher dipole or trapping strengths.
