Matthias Schroeter, Sibylle Naegle, Charles Radin and Harry Swinney
Phase transition in a static granular system
(763K, postscript)

ABSTRACT.  We have measured the force needed by a rod to penetrate a static 
column of grains for different well-defined particle volume fractions 
$\phi$. Measurements on our system reveal a phase transition at $\phi 
= 0.590 \pm 0.003$.