P. T. Callaghan, A. Coy, D. MacGowan, K. J. Packer, and F. O. Zelaya.
  <b>Diffraction-like Effects in NMR Diffusion Studies of Fluids
  in Porous Solids</b>.
  <i>Nature</i>, 351:467-469, 1991.
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Callaghan-1991-DEN.bib">(bibtex:
  Callaghan-1991-DEN)</A>.<br />