Gago, P.A. (Paula A.)
- Publications
- item.page.relationships.isContributorAdvisorOfPublication
- item.page.relationships.isContributorOfPublication
5 results
Search Results
Now showing 1 - 5 of 5
- Experimental proof of faster-is-slower in systems of frictional particles flowing through constrictions(2015) Pugnaloni, L.A. (Luis A.); Parisi, D.R. (D. R.); Zuriguel-Ballaz, I. (Iker); Peralta, J.P. (Juan Pablo); Martín-Gómez, C. (César); Pastor-Gutierrez, J.M. (José Martín); Ferrer, L.M. (Luis Miguel); Maza-Ozcoidi, D. (Diego); Montero, Á. (Ángel); Gago, P.A. (Paula A.)The “faster-is-slower” (FIS) effect was first predicted by computer simulations of the egress of pedestrians through a narrow exit [D. Helbing, I. J. Farkas, and T. Vicsek, Nature (London) 407, 487 (2000)]. FIS refers to the finding that, under certain conditions, an excess of the individuals’ vigor in the attempt to exit causes a decrease in the flow rate. In general, this effect is identified by the appearance of a minimum when plotting the total evacuation time of a crowd as a function of the pedestrian desired velocity. Here, we experimentally show that the FIS effect indeed occurs in three different systems of discrete particles flowing through a constriction: (a) humans evacuating a room, (b) a herd of sheep entering a barn, and (c) grains flowing out a 2D hopper over a vibrated incline. This finding suggests that FIS is a universal phenomenon for active matter passing through a narrowing.
- Clogging transition of many-particle systems flowing through bottlenecks(2014) Clement, E. (E.); Pugnaloni, L.A. (Luis A.); Parisi, D.R. (D. R.); Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Peralta, J.P. (Juan Pablo); Cruz-Hidalgo, R. (Raúl); Ferrer, L.M. (Luis Miguel); Lozano, C. (Celia); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel); Gago, P.A. (Paula A.)
- Relevance of system size to the steady-state properties of tapped granular systems(American Physical Society, 2015) Pugnaloni, L.A. (Luis A.); Maza-Ozcoidi, D. (Diego); Gago, P.A. (Paula A.)We investigate the steady-state packing fraction ϕ and force moment tensor Σ of quasi-two-dimensional granular columns subjected to tapping. Systems of different height h and width L are considered. We find that ϕ and Σ, which describe the macroscopic state of the system, are insensitive to L for L>50d (with d the grain diameter). However, results for granular columns of different heights cannot be conciliated. This suggests that comparison between results of different laboratories on this type of experiments can be done only for systems of same height. We show that a parameter ɛ=1+(Aω)^{2}/(2gh), with A and ω the amplitude and frequency of the tap and g the acceleration of gravity, can be defined to characterize the tap intensity. This parameter is based on the effective flight of the granular bed, which takes into account the h dependency. When ϕ is plotted as a function of ɛ, the data collapses for systems of different h. However, this parameter alone is unable to determine the steady state to be reached since different Σ can be observed for a given ɛ if different column heights are considered.
- Ergodic-nonergodic transition in tapped granular systems: the role of persistent contacts(2016) Pugnaloni, L.A. (Luis A.); Maza-Ozcoidi, D. (Diego); Gago, P.A. (Paula A.)Static granular packs have been studied in the last three decades in the frame of a modified equilibrium statistical mechanics that assumes ergodicity as a basic postulate. The canonical example on which this framework is tested consists in the series of static configurations visited by a granular column subjected to taps. By analyzing the response of a realistic model of grains, we demonstrate that volume and stress variables visit different regions of the phase space at low tap intensities in different realizations of the experiment. We show that the tap intensity beyond which sampling by tapping becomes ergodic coincides with the forcing necessary to break all particle-particle contacts during each tap. These results imply that the well-known "reversible" branch of tapped granular columns is only valid at relatively high tap intensities.
- Towards a relevant set of state variables to describe static granular packings(The American Physical Society, 2010-11-04) Damas, J. (José); Pugnaloni, L.A. (Luis A.); Zuriguel-Ballaz, I. (Iker); Maza-Ozcoidi, D. (Diego); Sánchez, I. (Iván); Gago, P.A. (Paula A.)We analyze, experimentally and numerically, the steady states, obtained by tapping, of a two-dimensional granular layer. Contrary to the usual assumption, we show that the reversible (steady state branch) of the density-acceleration curve is nonmonotonous. Accordingly, steady states with the same mean volume can be reached by tapping the system with very different intensities. Simulations of dissipative frictional disks show that equal volume steady states have different values of the force moment tensor. Additionally, we find that steady states of equal stress can be obtained by changing the duration of the taps; however, these states present distinct mean volumes. These results confirm previous speculations that the volume and the force moment tensor are both needed to describe univocally equilibrium states in static granular assemblies.