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

Comment on ``Stripe Glasses: Self-Generated Randomness in a Uniformly Frustrated System''

comment on J. Schmalian and P. Wolynes, Phys. Rev. Lett. {\bf 85}, 836 (2000).Comment: 1 page, 1 Figure, accepted in Phys. Rev. Letter

Locally preferred structure in simple atomic liquids

We propose a method to determine the locally preferred structure of model liquids. This latter is obtained numerically as the global minimum of the effective energy surface of clusters formed by small numbers of particles embedded in a liquid-like environment. The effective energy is the sum of the intra-cluster interaction potential and of an external field that describes the influence of the embedding bulk liquid at a mean-field level. Doing so we minimize the surface effects present in isolated clusters without introducing the full blown geometrical frustration present in bulk condensed phases. We find that the locally preferred structure of the Lennard-Jones liquid is an icosahedron, and that the liquid-like environment only slightly reduces the relative stability of the icosahedral cluster. The influence of the boundary conditions on the nature of the ground-state configuration of Lennard-Jones clusters is also discussed.Comment: RevTeX 4, 17 pages, 6 eps figure

Aging and response properties in the parking-lot model

An adsorption-desorption (or parking-lot) model can reproduce qualitatively the densification kinetics and other features of a weakly vibrated granular material. Here we study the the two-time correlation and response functions of the model and demonstrate that their behavior is consistent with recently observed memory effects in granular materials. Although the densification kinetics and hysteresis are robust properties, we show that the aging behavior of the adsorption-desorption model is different from other models of granular compaction. We propose an experimental test to distinguish the possible aging behaviors.Comment: 9 pages, 7 figures, to appear in Eur. Phys. Jour.