Search

We show that memory can be encoded in a model amorphous solid subjected to athermal oscillatory shear deformations, and in an analogous spin model with disordered interactions, sharing the feature of a deformable energy landscape. When these systems are subjected to oscillatory shear deformation, they retain memory of the deformation amplitude imposed in the training phase, when the amplitude is below a "localization" threshold. Remarkably, multiple, persistent, memories can be stored using such an athermal, noise-free, protocol. The possibility of such memory is shown to be linked to the presence of plastic deformations and associated limit cycles traversed by the system, which exhibit avalanche statistics also seen in related contexts., 5 pages, 4 figures

We study the statistical properties of the potential energy landscape of a system of particles interacting via a very short-range square-well potential (of depth $-u_0$), as a function of the range of attraction $\Delta$ to provide thermodynamic insights of the Noro and Frenkel [ M.G. Noro and D. Frenkel, J.Chem.Phys. {\bf 113}, 2941 (2000)] scaling. We exactly evaluate the basin free energy and show that it can be separated into a {\it vibrational} ($\Delta$-dependent) and a {\it floppy} ($\Delta$-independent) component. We also show that the partition function is a function of $\Delta e^{\beta u_o}$, explaining the equivalence of the thermodynamics for systems characterized by the same second virial coefficient. An outcome of our approach is the possibility of counting the number of floppy modes (and their entropy)., Comment: 4 pages, 4 figures accepted for publication on PRE

We discuss the situation where attractive and repulsive portions of the inter-particle potential both contribute significantly to glass formation. We introduce the square-well potential as prototypical model for this situation, and {\it reject} the Baxter as a useful model for comparison to experiment on glasses, based on our treatment within mode coupling theory. We present explicit results for various well-widths, and show that, for narrow wells, there is a useful analytical formula that would be suitable for experimentalist working in the field of colloidal science. We raise the question as to whether, in a more exact treatment, the sticky sphere limit might have an infinite glass transition temperature, or a high but finite one., 17 pages, 5 figures

We discuss features of simple inter-particle potentials which are able to generate low-packing fraction arrested states, i.e. gels, in the absence of a macroscopic phase separation phenomenon. We suggest that the ratio between surface and bulk free energy is crucial in favoring ideal gel states. Two possible models for gels, one based on the competition of short range attraction and long range repulsions and the other on local constraints disfavoring packed local structures are discussed. © 2005 Elsevier B.V. All rights reserved.

We studied the phase behavior of a model binary mixture of eye lens crystallin proteins using first-order thermodynamic perturbation theory. The instability boundary, or spinodal surface, was found to be very sensitive to the strength of the attraction between the two proteins, and also to respond to this interprotein attraction strength in a non-monotonic fashion. In particular, in the case of either weak or strong attractions, these eye lens solutions become thermodynamically unstable. Interestingly, attraction strengths that correspond closely to those of proteins isolated from the living lens fall right within the stable region of the phase diagram. This non-monotonic stability suggests new molecular mechanisms for eye lens opacification in cataract.

Extensive molecular dynamics simulation studies of particles interacting via a short-ranged attractive square-well potential arc reported. The calculated loci of constant diffusion coefficient D in the temperature-packing fraction plane show a reentrant behavior, i.e., an increase of diffusivity on cooling, confirming an important part of the high volume-fraction dynamical-arrest scenario earlier predicted by theory for particles with short-ranged potentials. The more efficient localization mechanism induced by the short-range bonding provides, on average, additional free volume as compared to the hard-sphere case and results in faster dynamics. © 2002 The American Physical Society.

We derive an analytical expression for the effective force between a pair of macrospheres immersed in a sea of microspheres, in the case where the interaction between the two unlike species is assumed to be a square well or a square shoulder of given range and depth (or height). This formula extends a similar one developed in the case of hard core interactions only. Qualitative features of such effective force and the resulting phase diagram are then analyzed in the limit of no interaction between the small particles. Approximate force profiles are then obtained by means of integral equation theories (PY and HNC) combined with the superposition approximation and compared with exact ones from direct Monte Carlo simulations., 34 pages