100 research outputs found
Random Field Ising Model In and Out of Equilibrium
We present numerical studies of zero-temperature Gaussian random-field Ising
model (zt-GRFIM) in both equilibrium and non-equilibrium. We compare the
no-passing rule, mean-field exponents and universal quantities in 3D (avalanche
critical exponents, fractal dimensions, scaling functions and anisotropy
measures) for the equilibrium and non-equilibrium disorder-induced phase
transitions. We show compelling evidence that the two transitions belong to the
same universality class.Comment: 4 pages, 2 figures. submitted to Phys. Rev. Let
No-passing Rule in the Ground State Evolution of the Random-Field Ising Model
We exactly prove the no-passing rule in the ground state evolution of the
random-field Ising model (RFIM) with monotonically varying external field. In
particular, we show that the application of the no-passing rule can speed up
the calculation of the zero-temperature equilibrium curve dramatically.Comment: 7 pages, 4 figure
Transforming mesoscale granular plasticity through particle shape
When an amorphous material is strained beyond the point of yielding it enters
a state of continual reconfiguration via dissipative, avalanche-like slip
events that relieve built-up local stress. However, how the statistics of such
events depend on local interactions among the constituent units remains
debated. To address this we perform experiments on granular material in which
we use particle shape to vary the interactions systematically. Granular
material, confined under constant pressure boundary conditions, is uniaxially
compressed while stress is measured and internal rearrangements are imaged with
x-rays. We introduce volatility, a quantity from economic theory, as a powerful
new tool to quantify the magnitude of stress fluctuations, finding systematic,
shape-dependent trends. For all 22 investigated shapes the magnitude of
relaxation events is well-fit by a truncated power law distribution , as has been proposed within the context of plasticity
models. The power law exponent for all shapes tested clusters around
1.5, within experimental uncertainty covering the range 1.3 - 1.7. The
shape independence of and its compatibility with mean field models
indicate that the granularity of the system, but not particle shape, modifies
the stress redistribution after a slip event away from that of continuum
elasticity. Meanwhile, the characteristic maximum event size changes by
two orders of magnitude and tracks the shape dependence of volatility. Particle
shape in granular materials is therefore a powerful new factor influencing the
distance at which an amorphous system operates from scale-free criticality.
These experimental results are not captured by current models and suggest a
need to reexamine the mechanisms driving mesoscale plastic deformation in
amorphous systems.Comment: 11 pages, 8 figures. v3 adds a new appendix and figure about event
rates and changes several parts the tex
Determination of the universality class of crystal plasticity
Although scaling phenomena have long been documented in crystalline
plasticity, the universality class has been difficult to identify due to the
rarity of avalanche events, which require large system sizes and long times in
order to accurately measure scaling exponents and functions. Here we present
comprehensive simulations of two-dimensional dislocation dynamics under shear,
using finite-size scaling to extract scaling exponents and the avalanche
profile scaling function from time-resolved measurements of slip-avalanches.
Our results provide compelling evidence that both the static and dynamic
universality classes are consistent with the mean-field interface depinning
model.Comment: 6 pages, 4 figures. Figure 4 inset has been corrected as compared to
the EPL publication. We thank Michael Zaiser for bringing its incorrect
caption to our attention. The correction leaves all results unaffecte
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