  We show using molecular dynamics simulations that simple diatomic molecules
in the glassy state exhibit only limited participation in the Johari-Goldstein
(JG) relaxation process. That is, with sufficient cooling local reorientations
are essentially frozen for some molecules, while others continue to change
their orientation significantly. Thus, the "islands of mobility" concept is
valid for these molecular glass-formers; only near the glass transition
temperature does every molecule undergo the JG process. In contrast, for a
linear polymer this dichotomy in the distribution of JG relaxation strengths is
absent - if any segments are changing their local orientation, all segments
are.
