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Avalanches, Hysteresis, and Crackling Noises
Motivation
Recently, physicists have realized that it is their job to understand systems
which crackle. Wood crackles as it is twisted apart; magnets (and magnetic
tapes!) have jumps in their magnetization as the field from the tape head is
increased (Barkhausen noise); paper crackles as it is crumpled; continental
plates have jerky, irregular motions as they slide across one another
(earthquakes). These avalanches often span many decades of length and time
scales, and are therefore collective, many body physics.
Existing Research Simulations
Sethna's group has proposed a new model for studying hysteresis (the
zero-temperature random-field Ising model), and has developed new algorithms
for running large-scale simulations which simultaneously conserve computer
time (O(N)) and memory (one bit per domain). This was necessary for running
large-scale simulations on the SP2: even at one bit per spin (plus overhead
scaling more slowly than O(N)) a 10003 system barely fits on a
2 GB machine and takes four days to run half of one hysteresis loop. Such
large simulations are necessary for extracting accurate critical exponents
(in 2, 3, 4, and 5 dimensions. However "Little Models" with modest
803 and 4002 lattices can be used by the
students either on the client or timeshared servers to provide data with
higher quality and more dynamic range than many published experiments.
Web resources
An introduction
to hysteresis and avalances is available on the Laboratory of Atomic and Solid State Physics
(LASSP) server at Cornell. Current work
for this module is available:
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This page is maintained by Simeon Warner
Last updated 3 June 1996