@Article{SCI:Ber2001d,
  author =    "M. Berzins",
  title =     "Modified Mass Matrices and Positivity Preservation
              for Hyperbolic and Parabolic {PDE}s",
  journal =   "Communications in Numerical Methods in
              Engineering",
  volume =    "17",
  pages =     "659--666",
  year =      "2001",
  url =       "http://www.sci.utah.edu/publications/berzins01/austpapv3.pdf",
}