604 research outputs found
Dynamical Heterogeneity close to the Jamming Transition in a Sheared Granular Material
The dynamics of a bi-dimensional dense granular packing under cyclic shear is
experimentally investigated close to the jamming transition. Measurement of
multi-point correlation functions are produced. The self-intermediate
scattering function, displaying slower than exponential relaxation, suggests
dynamic heterogeneity. Further analysis of four point correlation functions
reveal that the grain relaxations are strongly correlated and spatially
heterogeneous, especially at the time scale of the collective rearrangements.
Finally, a dynamical correlation length is extracted from spatio-temporal
pattern of mobility. Our experimental results open the way to a systematic
study of dynamic correlation functions in granular materials.Comment: 4 pages, final version accepted for publication in Phys. Rev. Let
Confinement as a tool to probe amorphous order
We study the effect of confinement on glassy liquids using Random First Order
Transition theory as framework. We show that the characteristic length-scale
above which confinement effects become negligible is related to the
point-to-set length-scale introduced to measure the spatial extent of amorphous
order in super-cooled liquids. By confining below this characteristic size, the
system becomes a glass. Eventually, for very small sizes, the effect of the
boundary is so strong that any collective glassy behavior is wiped out. We
clarify similarities and differences between the physical behaviors induced by
confinement and by pinning particles outside a spherical cavity (the protocol
introduced to measure the point-to-set length). Finally, we discuss possible
numerical and experimental tests of our predictions.Comment: 5 pages, 3 figures and EPAPS (4 pages, 1 figure
Are defect models consistent with the entropy and specific heat of glass-formers?
We show that point-like defect model of glasses cannot explain thermodynamic
properties of glass-formers, as for example the excess specific heat close to
the glass transition, contrary to the claim of J.P. Garrahan, D. Chandler
[Proc. Natl. Acad. Sci. 100, 9710 (2003)]. More general models and approaches
in terms of extended defects are also discussed.Comment: 4 pages, version to appear in J. Chem. Phys with a Note Adde
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