Garcimartín-Montero, Á. (Ángel)
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- Clogging and unclogging of many-particle systems passing through a bottleneck(EDP Sciences, 2017) Zuriguel-Ballaz, Í. (Íker); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Garcimartín-Montero, Á. (Ángel)When a group of discrete particles pass through a narrowing, the flow may become arrested due to the development of structures that span over the size of the aperture. Then, it is said that the system is clogged. Here, we will discuss about the existence of a phase diagram for the clogged state that has been recently proposed, arguing on its usefulness to describe different systems of discrete bodies ranging from granular materials, to colloidal suspensions and live beings. This diagram is built based on the value of a flowing parameter which characterizes the intermittent flow observed in all these discrete systems provided that there is an external or internal energy supply. Such requirement, which is necessary to destabilize the clogging arches, is absent in a standard static silo, which is therefore examined as a particular case. This view will help to understand some a priori inconsistencies concerning the role of driving force in the clogging process that have been found in the last years.
- Granular Matter Under Microgravity(2008) Garrabos, Y. (Y.); Beysens, D.A. (Daniel A.); Garcimartín-Montero, Á. (Ángel); Vandewalle, N. (N.); Evesque, P. (P.)
- Pedestrian collective motion in competitive room evacuation(2017) Parisi, D.R. (D. R.); Zuriguel-Ballaz, Í. (Íker); Gómez, C. (Carlos); Pastor-Gutierrez, J.M. (José Martín); Garcimartín-Montero, Á. (Ángel)When a sizable number of people evacuate a room, if the door is not large enough, an accumulation of pedestrians in front of the exit may take place. This is the cause of emerging collective phenomena where the density is believed to be the key variable determining the pedestrian dynamics. Here, we show that when sustained contact among the individuals exists, density is not enough to describe the evacuation, and propose that at least another variable -such as the kinetic stress- is required. We recorded evacuation drills with different degrees of competitiveness where the individuals are allowed to moderately push each other in their way out. We obtain the density, velocity and kinetic stress fields over time, showing that competitiveness strongly affects them and evidencing patterns which have been never observed in previous (low pressure) evacuation experiments. For the highest competitiveness scenario, we detect the development of sudden collective motions. These movements are related to a notable increase of the kinetic stress and a reduction of the velocity towards the door, but do not depend on the density.
- Stability of clogging arches in a silo submitted to vertical vibrations(2015) Zuriguel-Ballaz, Í. (Íker); Lozano, C. (Celia); Garcimartín-Montero, Á. (Ángel)We present experimental results on the endurance of arches that block the outlet of a two-dimensional silo when subjected to vertical vibration. In a recent paper [C. Lozano et al., Phys. Rev. Lett. 109, 068001 (2012)], it was shown that the arch resistance against vibrations is determined by the maximum angle among those formed between each particle in the bridge and its two neighbors: the larger the maximum angle is, the weaker the bridge. It has also been reported that the breaking time distribution shows a power-law tail with an exponent that depends on the outlet size, the vibration intensity, and the load [I. Zuriguel et al., Sci. Rep. 4, 7324 (2014)]. Here we connect these previous works, demonstrating the importance of the maximum angle in the arch on the exponent of the breaking time distribution. Besides, we find that the acceleration needed to break an arch does not depend on the ramp rate of the applied acceleration, but it does depend on the outlet size above which the arch is formed. We also show that high frequencies of vibration reveal a change in the behavior of the arches that endure very long times. These arches have been identified as a subset with special geometrical features. Therefore, arches that cannot be broken by means of a given external excitation might exist.
- Local Marangoni number at the onset of hydrothermal waves(American Physical Society, 2000) Burguete-Mas, F.J. (Francisco Javier); Pelacho, M.A. (M.A.); Garcimartín-Montero, Á. (Ángel)We report the results of an experiment in which a layer of fluid, placed in a container open to the air, is subjected to a horizontal temperature difference DT. The fluid height h is kept constant and both the horizontal temperature difference and the horizontal dimensions of the fluid layer are changed. In this configuration, when DT goes beyond a certain threshold, waves propagating from the cold to the hot side appear ~hydrothermal waves! with a determined group velocity. We study the influence of the container geometry on these waves. Close to the threshold, they are spatially localized near the hot side and a local Marangoni number is defined to describe this behavior. If DT is further increased, the waves fill the whole fluid layer. We also find an agreement between our experimental results and theoretical works and simulations.
- Experimental evidence of the ‘Faster Is Slower’ effect(Elsevier, 2014) Parisi, D.R. (D. R.); Zuriguel-Ballaz, Í. (Íker); Martín-Gómez, C. (César); Pastor-Gutierrez, J.M. (José Martín); Garcimartín-Montero, Á. (Ángel)The Faster-Is-Slower effect (Helbing et al (2000)) is an important instance of self-organized phenomenon in pedestrian dynamics. Despite this, an experimental demonstration is still lacking. We present controlled tests where a group of students are asked to exit a room through a door. Instead of just measuring the evacuation times, we have analyzed the probability distribution of the time lapses between consecutive individuals. We show how it displays a power-law tail. This method displays clearly the Faster Is Slower effect, and also allows to assess the impact of several tactics that can be put in place to alleviate the problem.
- 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, Í. (Íker); Peralta, J.P. (Juan Pablo); Martín-Gómez, C. (César); Pastor-Gutierrez, J.M. (José Martín); Ferrer, L.M. (Luis Miguel); Maza-Ozcoidi, D. (Diego); Garcimartín-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.
- Role of driving force on the clogging of inert particles in a bottleneck(2014) Zuriguel-Ballaz, Í. (Íker); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Garcimartín-Montero, Á. (Ángel)
- Fluctuations of grains inside a discharging two-dimensional silo(American Physical Society, 2011-09-26) Zuriguel-Ballaz, Í. (Íker); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Garcimartín-Montero, Á. (Ángel)We present experimental data corresponding to a two-dimensional dense granular flow, namely, the gravitydriven discharge of grains from a small opening in a silo. We study the local velocity field at the scale of single grains at different places with the help of particle-tracking techniques. From these data, the velocity profiles can be obtained and the validity of some long-standing approaches can be assessed. Moreover, the fluctuations of the velocities are taken into consideration to characterize the features of the advective motion (due to the gravity force) and the diffusive motion, which shows nontrivial behavior.
- Hydrothermal waves in Marangoni convection in a cylindrical container(American Physical Society, 1993) Burguete-Mas, F.J. (Francisco Javier); Perez-Garcia, C. (C.); Garcimartín-Montero, Á. (Ángel); Mancini-Maza, H. L. (Hector Luis); Ezersky, A. (A.)