H. Y. Carr and E. M. Purcell.
  <b>Effects of diffusion on free precession in nuclear magnetic
  resonance experiments</b>.
  <i>Phys. Rev.</i>, 94:630, 1954.
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Carr-1954-EDF.bib">(bibtex:
  Carr-1954-EDF)</A>.<br />