  Certain areas of scientific research flourish while others lose advocates and
attention. We are interested in whether structural patterns within citation
networks correspond to the growth or decline of the research areas to which
those networks belong. We focus on three topic areas within optical physics as
a set of cases; those areas have developed along different trajectories: one
continues to expand rapidly; another is on the wane after an earlier peak; the
final area has re-emerged after a short waning period. These three areas have
substantial overlaps in the types of equipment they use and general
methodology; at the same time, their citation networks are largely independent
of each other. For each of our three areas, we map the citation networks of the
top-100 most-cited papers, published pre-1999. In order to quantify the
structures of the selected articles' citation networks, we use a modified
version of weak tie theory in tandem with entropy measures. Although the
fortunes of a given research area are most obviously the result of accumulated
innovations and impasses, our preliminary study provides evidence that these
citation networks' emergent structures reflect those developments and may shape
evolving conversations in the scholarly literature.
