  We examine the time dependent defect fluctuations and lifetimes for a
bidisperse disordered assembly of Yukawa particles. At high temperatures, the
noise spectrum of fluctuations is white and the coordination number lifetimes
have a stretched exponential distribution. At lower temperatures, the system
dynamically freezes, the defect fluctuations exhibit a 1/f spectrum, and there
is a power law distribution of the coordination number lifetimes. Our results
indicate that topological defect fluctuations may be a useful way to
characterize systems exhibiting dynamical heterogeneities.
