Transient dynamics of a 2D granular pile

International audienceWe investigate by means of Contact Dynamics simulations the transient dynamics of a 2D granular pile set into motion by applying shear velocity during a short time interval to all particles. The spreading dynamics is directly controlled by the input energy whereas in recent studies of column collapse the dynamics scales with the initial potential energy of the column. As in column collapse, we observe a power-law dependence of the runout distance with respect to the input energy with nontrivial exponents. This suggests that the power-law behavior is a generic feature of granular dynamics, and the values of the exponents reflect the distribution of kinetic energy inside the material. We observe two regimes with different values of the exponents: the low-energy regime reflects the destabilization of the pile by the impact with a runout time independent of the input energy whereas the high-energy regime is governed by the input energy. We show that the evolution of the pile in the high-energy regime can be described by a characteristic decay time and the available energy after the pile is destabilized

Basic science of osteoarthritis

Osteoarthritis (OA) is a prevalent, disabling disorder of the joints that affects a large population worldwide and for which there is no definitive cure. This review provides critical insights into the basic knowledge on OA that may lead to innovative end efficient new therapeutic regimens. While degradation of the articular cartilage is the hallmark of OA, with altered interactions between chondrocytes and compounds of the extracellular matrix, the subchondral bone has been also described as a key component of the disease, involving specific pathomechanisms controlling its initiation and progression. The identification of such events (and thus of possible targets for therapy) has been made possible by the availability of a number of animal models that aim at reproducing the human pathology, in particular large models of high tibial osteotomy (HTO). From a therapeutic point of view, mesenchymal stem cells (MSCs) represent a promising option for the treatment of OA and may be used concomitantly with functional substitutes integrating scaffolds and drugs/growth factors in tissue engineering setups. Altogether, these advances in the fundamental and experimental knowledge on OA may allow for the generation of improved, adapted therapeutic regimens to treat human OA.(undefined

Initiation of immersed granular avalanches

By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure. © 2014 American Physical Society

Scaling behavior of immersed granular flows

The shear behavior of granular materials immersed in a viscous fluid depends on fluid properties (viscosity, density), particle properties (size, density) and boundary conditions (shear rate, confining pressure). Using computational fluid dynamics simulations coupled with molecular dynamics for granular flow, and exploring a broad range of the values of parameters, we show that the parameter space can be reduced to a single parameter that controls the packing fraction and effective friction coefficient. This control parameter is a modified inertial number that incorporates viscous effects

IN SEARCH OF CREATIVE EXPRESSION: THE DIALECTICS OF RACE, POLITICS, AND LITERATURE IN CARIBBEAN DUB POETRY / IEŠKANT KŪRYBINĖS IŠRAIŠKOS: RASĖS, POLITIKOS IR LITERATŪROS DIALEKTIKA KARIBŲ DUB ŽANRO POEZIJOJE

This article examines dub poetry as an artistic form located along several borderlines, both spatial and cultural. Formulated by poets of African descent, the creative language of dub poets was often conceptualized through the framework of identity politics and an anti-colonial approach. Yet from the 1980s, dub poetry became institutionalized simultaneously within the pop culture industry and in “respectable” venues such as academic research, a process that calls its initial political orientation into question. In light of its differentiated formations, audiences, mediating devices, and forms of reception, however, we might view and evaluate dub poetry not exclusively through the prism of political speech, but also as a cultural form. Based on texts, recordings and performance analysis this article is a call to acknowledge dub poetry, and artistic expression in general, as the result of aesthetic decisions rather than exclusively moral ones. Santrauka Straipsnyje tyrinėjama dub žanro poezija kaip meninė forma, vyraujanti ties kai kuriais paribiais – tiek erdviniais, tiek kultūriniais. Formuluota Afrikos nuosmukio laikotarpio poetų, kūrybinė dub žanro poetų kalba politikos ir antikolonijiniu požiūriais dažnai buvo konceptualizuojama ieškant tapatumo. Nuo XX a. 9-ojo dešimtmečio dub poezija tapo institucionalizuota tiek popkultūros industrijoje, tiek „gerbiamose“ srityse, tokiose kaip akademiniai tyrimai – tai procesas, kvestionuojantis savąją vidinę politinę orientaciją. Šio proceso diferencijuotų formacijų, auditorijų, medijuojančių priemonių ir priėmimo formų fone vis dėlto galima į dub poeziją žvelgti ir ją vertinti ne išimtinai per politinės kalbos prizmę, bet ir kaip kultūrinę formą. Pagrįstas tekstų, įrašų ir performansų analize, šis straipsnis – tai kvietimas pripažinti dub poeziją ir meninę išraišką apskritai ne tiek kaip išskirtinai moralinių, kiek estetinių sprendimų rezultatą. Reikšminiai žodžiai: juodumas, Karibų dub žanro poezija, Jamaika, performansas, rasė, regis