56 research outputs found
Force networks and the dynamic approach to jamming in sheared granular media
Diverging correlation lengths on either side of the jamming transition are
used to formulate a rheological model of granular shear flow, based on the
propagation of stress through force chain networks. The model predicts three
distinct flow regimes, characterized by the shear rate dependence of the stress
tensor, that have been observed in both simulations and experiments. The
boundaries separating the flow regimes are quantitatively determined and
testable. In the limit of jammed granular solids, the model predicts the
observed anomalous scaling of the shear modulus and a new relation for the
shear strain at yield
The jamming transition and new percolation universality classes in particulate systems with attraction
We numerically study the jamming transition in particulate systems with
attraction by investigating their mechanical response at zero temperature. We
find three regimes of mechanical behavior separated by two critical
transitions--connectivity and rigidity percolation. The transitions belong to
different universality classes than their lattice counterparts, due to force
balance constraints. We also find that these transitions are unchanged at low
temperatures and resemble gelation transitions in experiments on colloidal and
silica gels.Comment: 4 pages, 2 figures, 2 table
A percolation model for slow dynamics in glass-forming materials
We identify a link between the glass transition and percolation of mobile
regions in configuration space. We find that many hallmarks of glassy dynamics,
for example stretched-exponential response functions and a diverging structural
relaxation time, are consequences of the critical properties of mean-field
percolation. Specific predictions of the percolation model include the range of
possible stretching exponents and the functional
dependence of the structural relaxation time and exponent
on temperature, density, and wave number.Comment: 4 pages, 1 figur
Long Range Correlation in Granular Shear Flow II: Theoretical Implications
Numerical simulations are used to test the kinetic theory constitutive
relations of inertial granular shear flow. These predictions are shown to be
accurate in the dilute regime, where only binary collisions are relevant, but
underestimate the measured value in the dense regime, where force networks of
size are present. The discrepancy in the dense regime is due to
non-collisional forces that we measure directly in our simulations and arise
from elastic deformations of the force networks. We model the non-collisional
stress by summing over all paths that elastic waves travel through force
networks. This results in an analytical theory that successfully predicts the
stress tensor over the entire inertial regime without any adjustable
parameters
Reliable protein folding on non-funneled energy landscapes: the free energy reaction path
A theoretical framework is developed to study the dynamics of protein
folding. The key insight is that the search for the native protein conformation
is influenced by the rate r at which external parameters, such as temperature,
chemical denaturant or pH, are adjusted to induce folding. A theory based on
this insight predicts that (1) proteins with non-funneled energy landscapes can
fold reliably to their native state, (2) reliable folding can occur as an
equilibrium or out-of-equilibrium process, and (3) reliable folding only occurs
when the rate r is below a limiting value, which can be calculated from
measurements of the free energy. We test these predictions against numerical
simulations of model proteins with a single energy scale.Comment: 13 pages, 9 figure
- …