@Article{Riv92a,
  author =       { Ronald L. Rivest },
  title =        { Vortex air rings },
  pages =        { 199--200 },                  
  doi =          { 10.1038/356199b0 },                  
  journal =      { Nature (Scientific Correspondence) },
  OPTyear =      { 1992 },                  
  OPTmonth =     { March 19, },                  
  date =         { 1992-03-19 },                    
  volume =       { 356 },
}