1086/382905. Watkins, L. L.; et al, Substructure revealed by RR Lyraes in SDSS Stripe82, Monthly Notices of the Royal Astronomical Society, 2009, 398 (4): 1757–70
Kimball, A.; Sesar, B.; Westman, D. Modeling the Time Variability of SDSS Stripe82 Quasars as a Damped Random Walk. The Astrophysical Journal. October 2010