  Elastic and spin-changing inelastic collision cross sections are presented
for cold and ultracold magnetically trapped NH. The cross sections are obtained
from coupled-channel scattering calculations as a function of energy and
magnetic field. We specifically investigate the influence of the intramolecular
spin-spin, spin-rotation, and intermolecular magnetic dipole coupling on the
collision dynamics. It is shown that $^{15}$NH is a very suitable candidate for
evaporative cooling experiments. The dominant trap-loss mechanism in the
ultracold regime originates from the intermolecular dipolar coupling term. At
higher energies and fields, intramolecular spin-spin coupling becomes
increasingly important. Our qualitative results and conclusions are fairly
independent of the exact form of the potential and of the size of the channel
basis set.
