Nov. 8, 1999 DURHAM, N.C. -- Researchers at Duke University have
shown in careful experiments that not all sandpiles are the
same. The pressures under some are highest at their centers. But
the stresses under others get shifted outwardly much like loads
are transferred from the walls of some medieval cathedrals. It
all depends on how the sand heaps are formed, and the take-home
message is that "small changes in the history of preparation
have an extraordinarily dramatic effect," said Robert Behringer,
a Duke professor of physics. These experiments, which were
supported by the National Science Foundation, have practical
importance because unbalanced distributions of stresses can lead
to the self destruction of structures like coal and grain silos,
he said. Coal, like sand, is a granular material, a class that
includes objects as diverse as breakfast cereals and ice
crystals. Behringer, who recently became chairman of Duke's
department of physics, is a long-time investigator of granular
materials, which are reg