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A general jamming scenario has been recently proposed to understand the nonequilibrium behavior of a broad class of amorphous materials as diverse as colloidal suspensions, emulsions, foams, gels, polymeric melts, supercooled liquids, biological tissues, or granular matter which share common features near the so-called jamming transition. The dynamics of this wide class of physical systems is governed by the presence of kinematical constraints, induced by both interactions and geometry, which may be able to suppress their temporal relaxation and thus their ability to explore the space of configurations. On the other hand, they flow like a viscous fluid above the so-called yield stress value. Shear yielding is thus another feature they have in common, together with other characteristics of their intriguing rheology.

Recent progress in the understanding of yielding and jamming of colloids, based on extensions of the mode coupling theory (MCT) of glasses, is reviewed. This includes schematic extensions to shear-thickening fluids based on the ad-hoc introduction of a stress-dependent vertex in MCT. The possible distinction between dynamic and static yield stress, and its implications for shear-banding and other instabilities, is considered. Finally, what we know about systems where steady stress leads to unsteady flow or vice versa (“rheochaos”) is briefly summarised.

In this lecture we review several aspects of the thermal noise properties in two aging materials: a polymer and a colloidal glass. The measurements have been performed after a quench for the polymer and during the transition from a fluid-like to a solid-like state for the gel. Two kind of noise has been measured: the electrical noise and the mechanical noise. For both materials we have observed that the electric noise is characterized by a strong intermittency, which induces a large violation of the Fluctuation Dissipation Theorem (FDT) during the aging time, and may persist for several hours at low frequency. The statistics of these intermittent signals and their dependance on the quench speed for the polymer or on sample concentration for the gel are studied. The results are in a qualitative agreement with recent models of aging, that predict an intermittent dynamics. For the mechanical noise the results are unclear. In the polymer the mechanical thermal noise is still intermittent whereas for the gel the violation of FDT, if it exists, is extremely small.

We review some recent results on Statistical Mechanics approach to dense granular media. In particular, by analytical mean field investigation we derive the phase diagram of a monodisperse system. We show that “jamming” corresponds to a phase transition from a “.uid” to a “glassy” phase. The nature of such a “glassy” phase turns out to be the same found in mean field models for glass formers. This gives quantitative evidence to the idea of a unified description of the “jamming” transition in granular media and thermal systems, such as glasses.

A common property of jammed systems is a yield stress they have to overcome in order to start to flow. In rheology it is generally assumed that the corresponding solid-liquid transition is continuous, the steady state viscosity progressively decreasing from infinity to a finite value as the applied shear stress is increased beyond the yield stress. Recent experiments with various materials such as colloidal suspensions, foams, emulsions, or polymer gels, show that this transition is in fact abrupt: in steady state, at a critical stress the material viscosity abruptly turns from infinity to a finite value. This phenomenon corresponds to another effect observed from MRI-rheometry tests: in steady state such pasty materials either flow at a sher rate larger than a critical, finite value, associated to a critical stress, or do not flow at all. This phenomenon has also a dynamic character, which is in particular illustrated by the “viscosity bifurcation” in time under controlled stress: below the critical stress value the shear rate progressively decreases until reaching stoppage; beyond this critical stress the shear rate increases and reaches a finite value. Moreover for a material initially at rest the interface between the sheared and unsheared regions, i.e. the slope break, progressively reaches its asymptotic position in time. From these results we deduce that usual macroscopic observations basically reflect complex space and time evolutions of flow and material characteristics in the rheometer gap, rather than local time-dependent properties.

In these notes we present a brief review of the dynamical properties of interfaces in a disordered environment. We focus in particular on the response of such systems to a very small external force, and the corresponding very slow motion it entails, so called creep. We discuss various general theoretical aspects of this problem and consider in detail the case of a one dimensional interface (domain wall).

The magnetic flux line lattice in type II superconductors serves as a useful system in which to study condensed matter flow, as its dynamic properties are tunable. Recent studies have shown a number of puzzling phenomena associated with vortex motion, including: low-frequency noise and slow voltage oscillations; a history-dependent dynamic response, and memory of the direction, amplitude duration and frequency of the previously applied current; high vortex mobility for alternating current, but no apparent vortex motion for direct currents; negative resistance and strong suppression of an a.c. response by small d.c. bias. A generic edge contamination mechanism that comprehensively accounts for these observations is based on a competition between the injection of a disordered vortex phase at the sample edges, and the dynamic annealing of this metastable disorder by the transport current. For an alternating current, only narrow regions near the edges are in the disordered phase, while for d.c. bias, most of the sample is in the disordered phase-preventing vortex motion because of more efficient pinning. The resulting spatial dependence of the disordered vortex system serves as an active memory of the previous history. Random injection of the strongly pinned metastable disordered vortex phase through the sample edges and its subsequent random annealing into the weakly pinned ordered phase in the bulk results in large critical current fluctuations causing strong vortex velocity fluctuations. The resulting excess low frequency flux-flow voltage noise displays pronounced reentrant behavior. In the Corbino geometry the injection of the metastable phase is prevented and, accordingly, the excess noise is absent.

The purpose of the present work is to introduce a limited set of kinetic equations which describe the out-of-equilibrium relaxation of a structural glass and its response to shear deformation. It was originally motivated by recent theories for the plasticity of amorphous solids, [4, 5] in an attempt to incorporate glassy relaxation at an elementary level. [8, 9] A quite simple picture emerges, which accounts for important properties of glassy materials, while its premises may hold for general classes of complex fluids; [7] it echoes early theories of structural relaxation [1,10,11,14] in a much more systematic framework, and provides theoretical grounding for phenomenological rateand- state equations. [2]

We review in these notes the dynamics of extended condensed matter systems, such as vortex lattices in type-II superconductors and charge density waves in anisotropic metals, driven over quenched disorder. We focus in particular on the case of strong disorder, where topological defects are generated in the driven lattice. In this case the response is plastic and the depinning transition may become discontinuous and hysteretic.

Complex systems such as glasses, gels, granular materials, and systems far from equilibrium exhibit violation of the ergodic hypothesis (EH) and of the fluctuation-dissipation theorem (FDT). Recent investigations in systems with memory [1] have established a hierarchical connection between mixing, the EH and the FDT. They have shown that a failure of the mixing condition (MC) will lead to the subsequent failures of the EH and of the FDT. Another important point is that such violations are not limited to complex systems: simple systems may also display this feature. Results from such systems are analytical and obviously easier to understand than those obtained in complex structures, where a large number of competing phenomena are present. In this work, we review some important requirements for the validity of the FDT and its connection with mixing, the EH and anomalous diffusion in onedimensional systems. We show that when the FDT fails, an out-of-equilibrium system relaxes to an effective temperature different from that of the heat reservoir. This effective temperature is a signature of metastability found in many complex systems such as spin-glasses and granular materials.