@TechReport{SCI:Sch2008d,
  author =    "M. Schott and V. Pegoraro and C.D. Hansen and K.
              Boulanger and J. Stratton and K. Bouatouch",
  title =     "A Directional Occlusion Shading Model for
              Interactive Direct Volume Rendering",
  number =    "UUSCI-2008-009",
  year =      "2008",
  institution = "University of Utah Scientific Computing and
              Imaging Institute",
  type =      "SCI Technical Report",
  keywords =  "volume rendering",
  url =       "http://www.sci.utah.edu/publications/SCITechReports/UUSCI-2008-009.pdf",
}