Granular flow down a rough inclined plane: transition between thin and thick piles

The rheology of granular particles in an inclined plane geometry is studied using molecular dynamics simulations. The flow--no-flow boundary is determined for piles of varying heights over a range of inclination angles $\theta$. Three angles determine the phase diagram: $\theta_{r}$, the angle of repose, is the angle at which a flowing system comes to rest; $\theta_{m}$, the maximum angle of stability, is the inclination required to induce flow in a static system; and $\theta_{max}$ is the maximum angle for which stable, steady state flow is observed. In the stable flow region $\theta_{r}<\theta<\theta_{max}$, three flow regimes can be distinguished that depend on how close $\theta$ is to $\theta_{r}$: i) $\theta>>\theta_{r}$: Bagnold rheology, characterized by a mean particle velocity $v_{x}$ in the direction of flow that scales as $v_{x}\propto h^{3/2}$, for a pile of height $h$, ii) $\theta\gtrsim\theta_{r}$: the slow flow regime, characterized by a linear velocity profile with depth, and iii) $\theta\approx\theta_{r}$: avalanche flow characterized by a slow underlying creep motion combined with occasional free surface events and large energy fluctuations. We also probe the physics of the initiation and cessation of flow. The results are compared to several recent experimental studies on chute flows and suggest that differences between measured velocity profiles in these experiments may simply be a consequence of how far the system is from jamming.Comment: 19 pages, 14 figs, submitted to Physics of Fluid

Reliability of fecal coliforms and fecal enterococci as indicator of microbial contamination of groundwater in carbonate aquifers

A research is in progress since January 2001 in order to analyze the effect of grazing and manure spreading on microbial pollution of groundwater in carbonate aquifers. The research is carrying out through laboratory and field experiments in different test sites of Southern Italy. The results suggest that fecal enterococci are more reliable than fecal coliforms as indicator organisms of microbial contamination of groundwater. In carbonate Southern Apennines this difference in reliability is strongly conditioned by meteorological and pedological factors. The soil medium, which has a pyroclastic origin, causes a retention of fecal coliforms higher than that of fecal enterococci. This phenomenon is non-uniform at field scale and can reach a difference of an order of magnitude. It often produces the absence of fecal coliforms in spring water samples characterized by low concentrations of fecal enterococci. Both freezing and freeze-thaw intervals will cause a significant decrease in population (3 orders of magnitude, at least) of fecal coliforms while fecal enterococci are temporary inhibited. Each water year this phenomenon determine the absence of fecal coliforms in spring water samples contaminated by fecal enterococci during winter and spring, before the beginning of the new seasonal grazin

Aproximation of continuous media models for granular systems using cellular automata

In this paper a new cellular automata model suitable for granular systems simulation is presented. The proposed model is shown to be equivalent to a particularization of the well known BCRE model of granular systems and a correspondence between the parameters of the presented model and the BCRE model is also set, allowing to fit these parameters for a given system. The model has the advantage over other cellular automata models of being more realistic in the behavior of the surface of heaps and slopes. The dynamics of the CA is analyzed in order to confirm that it also has one of the most important features of these systems, 1/f noise

Active Remembering, Selective Forgetting, and Collective Identity: The Case of Bloody Sunday

Bloody Sunday. Derry, Northern Ireland, January 30, 1972, in which 13 Catholic civilians were shot dead by the British army has evoked two contesting memories - an 'official' or elite memory and a folk memory among the Nationalist community that, it is argued, has been omitted from dominant memory discourses. The official memory of this life- destroying historical event is encoded in the report of the Widgery Tribunal established by the British government in the aftermath of bloody Sunday. A second popular memory has emerged in resistance to this that carries the remembrances of the victims'families and of the wider Nationalist community in Northern Ireland. I explore the mediums through which this unofficial memory has been established and maintained, the meanings associated with it, and how and why these have changed over time. Traditionally, it has been invested with a negative meaning associated with sectarianism, colonialism, and victimization. In recent times, the folk memory has been framed within a broader global context with a focus on its healing and reconciliation potential, which, together with institutional statements such as the Dowling Street Declaration and the Good Friday Agreement, points to the emergence of a more inclusivist understanding of collective identity-formation in Northern Ireland