years after Einstein’s landmark work on Brownian motion,
physicists have discovered a new concept of temperature
that could be the key to explaining how ice and snow
particles flow during an avalanche, and could also
lead to a better way of handling tablets in the pharmaceutical
industry. This research is reported today in a special
Einstein Year issue of the New Journal of Physics
(www.njp.org) published jointly by the Institute of
Physics and the German Physical Society (Deutsche
from powdery snow to desert sands, from salt to corn
flakes are granular materials. Physicists have known
for many years that granular materials have many perplexing
properties that make them behave at times like solids,
liquids, and even gases. This new research reveals
for the first time how to measure a concept called
“granular temperature” – that could be the key to
explaining how they behave.
the solid snow covering a ski slope, for instance”,
suggests lead author of the paper Patrick Mayor of
the EPFL in Lausanne, Switzerland. “While it stays
still it is a solid, but as soon as it starts flowing
downhill as happens during an avalanche the flowing
material is behaving more like a liquid. Similarly,
during a desert storm, sand grains are whipped up
and behave like molecules in a gas, rather than as
most materials are usually described as solid, liquid
or gases, granular systems do not seem to fall into
any of these categories and are often considered a
separate state of matter of their own," says
Mayor, "The diverse behaviour of granular materials
makes it extremely difficult to establish a general
theory that accounts for the observed phenomena."
and his colleagues, Gianfranco D'Anna, Alain Barrat,
Vittorio Loreto, have shown that shaken granular matter
behaves in a way related to Einstein's theory of Brownian
motion, first published in 1905.
temperature of an object reflects the random motion
of its constituent parts. For instance, the faster
the molecules in a gas or liquid are moving around
the higher the temperature of the material.
also measures the degree of agitation of molecules
in a liquid or a gas. Mayor and his colleagues have
now devised a thermometer that can measure the temperature
of a granular material based on the degree of agitation
of its component particles. The researchers also discovered
that, unlike usual liquids, temperature varies depending
on which way and how far they insert the "thermometer"
into the granular material.
able to measure "granular temperature" might
allow researchers to better understand the peculiar
properties of a granular material, which is of crucial
importance to industries that handle powders and particulate
materials from pharmaceutical pills and food powders
to sand and cement in the construction industry.
For further information contact:
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(0)20 7470 4815, Mobile: 07946 321473, E-mail: firstname.lastname@example.org.
paper will be published on Monday 31st January 2005
in New Journal of Physics (www.njp.org) as part of
a celebratory focus issue on "Brownian Motion
and Diffusion in the 21st Century" (http://stacks.iop.org/1367-2630/7/i=1/a=E01).
The paper can be downloaded free of charge from 31st
January at http://stacks.iop.org/1367-2630/7/28. Reference:
P Mayor et al. New J. Phys. 7 (2005) 28.
Mayor and Gianfranco D'Anna
Institut de Physique de la Matiere Complexe, Faculte
des Sciences de Base, Ecole Polytechnique Fédérale
de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
Laboratoire de Physique Theorique, Unite Mixte de
Recherche UMR 8627, Batiment 210, Universite de Paris-Sud,
91405 Orsay Cedex, France
Universit`a degli Studi di Roma La Sapienza, Dipartimento
di Fisica, and INFM, Center for Statistical Mechanics
and Complexity, Piazzale A.
Moro 5, 00185 Rome, Italy
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