  It is well known that under plastic deformation, dislocations are not only
created but also move through the crystal, and their mobility is impeded by
their interaction with the crystal structure. At high stress and temperature,
this `drag' is dominated by phonon wind, i.e. phonons scattering off
dislocations. Employing the semi-isotropic approach discussed in detail in Ref.
[arXiv:1804.01586], we discuss here the approximate functional dependence of
dislocation drag $B$ on dislocation velocity in various regimes between a few
percent of transverse sound speed $c_t$ and $c_t$ (where $c_t$ is the effective
average transverse sound speed of the polycrystal). In doing so, we find an
effective functional form for dislocation drag $B(v)$ for different slip
systems and dislocation characters at fixed (room) temperature and low
pressure.
