@Article{SCI:Kno2009b,
  author =    "A. Knoll and Y. Hijazi and C.D. Hansen and I. Wald
              and H. Hagen",
  title =     "Fast Ray Tracing of Arbitrary Implicit Surfaces
              with Interval and Affine Arithmetic",
  journal =   "Computer Graphics Forum",
  volume =    "28",
  number =    "1",
  pages =     "26--40",
  year =      "2009",
  keywords =  "rt, irt, interactive ray-tracing",
  url =       "http://www.sci.utah.edu/publications/knoll09/CGF-implicits-2009.pdf",
}