259 research outputs found
Fragilities of Liquids Predicted from the Random First Order Transition Theory of Glasses
A microscopically motivated theory of glassy dynamics based on an underlying
random first order transition is developed to explain the magnitude of free
energy barriers for glassy relaxation. A variety of empirical correlations
embodied in the concept of liquid "fragility" are shown to be quantitatively
explained by such a model. The near universality of a Lindemann ratio
characterizing the maximal amplitude of thermal vibrations within an amorphous
minimum explains the variation of fragility with a liquid's configurational
heat capacity density. Furthermore the numerical prefactor of this correlation
is well approximated by the microscopic calculation. The size of heterogeneous
reconfiguring regions in a viscous liquid is inferred and the correlation of
nonexponentiality of relaxation with fragility is qualitatively explained. Thus
the wide variety of kinetic behavior in liquids of quite disparate chemical
nature reflects quantitative rather than qualitative differences in their
energy landscapes.Comment: 10 pages including 4 eps figure
Statistical Mechanics of a Cat's Cradle
It is believed that, much like a cat's cradle, the cytoskeleton can be
thought of as a network of strings under tension. We show that both regular and
random bond-disordered networks having bonds that buckle upon compression
exhibit a variety of phase transitions as a function of temperature and
extension. The results of self-consistent phonon calculations for the regular
networks agree very well with computer simulations at finite temperature. The
analytic theory also yields a rigidity onset (mechanical percolation) and the
fraction of extended bonds for random networks. There is very good agreement
with the simulations by Delaney et al. (Europhys. Lett. 2005). The mean field
theory reveals a nontranslationally invariant phase with self-generated
heterogeneity of tautness, representing ``antiferroelasticity''.Comment: 4 pages, 4 figure
Effective temperature and glassy dynamics of active matter
A systematic expansion of the many-body master equation for active matter, in
which motors power configurational changes as in the cytoskeleton, is shown to
yield a description of the steady state and responses in terms of an effective
temperature. The effective temperature depends on the susceptibility of the
motors and a Peclet number which measures their strength relative to thermal
Brownian diffusion. The analytic prediction is shown to agree with previous
numerical simulations and experiments. The mapping also establishes a
description of aging in active matter that is also kinetically jammed.Comment: 2 figure
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