Facultad de Ciencias
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- A Glossary for Research on Human Crowd Dynamics(Forschungszentrum Julich, Zentralbibliothek, 2019) Ronchi, E. (Enrico); Köster, G. (Gerta); Toschi, F. (Federico); Neville, F. (Fergus); Fu, Z. (Zhijian); Wijermans, N. (Nanda); Michalareas, G. (Georgios); Schadschneider, A. (Andreas); Kneidl, A. (Angelika); Adrian, J. (Juliane); Zuriguel-Ballaz, I. (Iker); Beermann, M. (Mira); Corbetta, A. (Alessandro); Spearpoint, M. (Michael); Zanlungo, F. (Francesco); Amos, M. (Martyn); Drury, J. (John); Küpper, M. (Mira); Hunt, A. (Aoife); Seyfried, A. (Armind); Boltes, M. (Maik); Sieben, A. (Anna); Dezecache, G. (Guillaume); Sullivan, G.B. (Gavin Brent); Wal, N. (Natalie) van der; Bode, N. (Nikolai); Reicher, S. (Stephen); Kanters, T. (Tinus); Schadewijk, F. (Frank) van; Krüchten, C. (Cornelia) von; Shipman, A. (Alastair); Templeton, A. (Anne); Hofinger, G. (Gesine); Baratchi, M. (Mitra); Geraerts, R. (Roland); Yücel, Z. (Zeynep); Ntontis, E. (Evangelos); Gwynne, S. (Steve); Konya, K. (Krisztina)This article presents a glossary of terms that are frequently used in research on human crowds. This topic is inherently multidisciplinary as it includes work in and across computer science, engineering, mathematics, physics, psychology and social science, for example. We do not view the glossary presented here as a collection of finalised and formal definitions. Instead, we suggest it is a snapshot of current views and the starting point of an ongoing process that we hope will be useful in providing some guidance on the use of terminology to develop a mutual understanding across disciplines. The glossary was developed collaboratively during a multidisciplinary meeting. We deliberately allow several definitions of terms, to reflect the confluence of disciplines in the field. This also reflects the fact not all contributors necessarily agree with all definitions in this glossary.
- Redefining the role of obstacles in pedestrian evacuation(2018) Parisi, D.R. (D. R.); Zuriguel-Ballaz, I. (Iker); Gómez, C. (Carlos); Pastor-Gutierrez, J.M. (José Martín); Maza-Ozcoidi, D. (Diego); Montero, Á. (Ángel)The placement of obstacles in front of doors is believed to be an effective strategy to increase the flow of pedestrians, hence improving the evacuation process. Since it was first suggested, this counter-intuitive feature is considered a hallmark of pedestrian flows through bottlenecks. Indeed, despite the little experimental evidence, the placement of an obstacle has been hailed as the panacea for solving evacuation problems. In this work, we challenge this idea and experimentally demonstrate that the pedestrians flow rate is not necessarily altered by the presence of an obstacle. This result-which is at odds with recent demonstrations on its suitability for the cases of granular media, sheep and mice- differs from the outcomes of most of existing numerical models, and warns about the risks of carelessly extrapolating animal behaviour to humans. Our experimental findings also reveal an unnoticed phenomenon in relation with the crowd movement in front of the exit: in competitive evacuations, an obstacle attenuates the development of collective transversal rushes, which are hazardous as they might cause falls.
- Invited review: clogging of granular materials in bottlenecks(2014) Zuriguel-Ballaz, I. (Iker)During the past decades, notable improvements have been achieved in the understanding of static and dynamic properties of granular materials, giving rise to appealing new concepts like jamming, force chains, non-local rheology or the inertial number. The 'saltcellar' can be seen as a canonical example of the characteristic features displayed by granular materials: an apparently smooth flow is interrupted by the formation of a mesoscopic structure (arch) above the outlet that causes a quick dissipation of all the kinetic energy within the system. In this manuscript, I will give an overview of this field paying special attention to the features of statistical distributions appearing in the clogging and unclogging processes. These distributions are essential to understand the problem and allow subsequent study of topics such as the influence of particle shape, the structure of the clogging arches and the possible existence of a critical outlet size above which the outpouring will never stop. I shall finally offer some hints about general ideas that can be explored in the next few years.
- Experimental evidence of the ‘Faster Is Slower’ effect(Elsevier, 2014) Parisi, D.R. (D. R.); Zuriguel-Ballaz, I. (Iker); Martín-Gómez, C. (César); Pastor-Gutierrez, J.M. (José Martín); 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.
- Silo clogging reduction by placing an obstacle above the outlet(AIP Publishing, 2013) Zuriguel-Ballaz, I. (Iker); Lozano, C. (Celia); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel)We present an experimental study of the effect that an obstacle above the outlet of a silo has on the clogging probability. Both, the size of the ori ce and the obstacle position are varied for a chosen obstacle size and shape. If the position of the obstacle is properly selected the clogging probability can be importantly reduced. Indeed, as the outlet size is increased – and we approach the critical size above which there is not clogging – the obstacle effect is enhanced. For the largest outlet size studied, the clogging probability is reduced by a factor of more than one hundred. We will show, using numerical simulations, that the physical parameter behind the reduction of the silo clogging seems to be the decrease of the vertical pressure at the outlet proximities.
- Avoiding clogs: the shape of arches and their stability against vibrations(AIP Publishing, 2013) Zuriguel-Ballaz, I. (Iker); Lumay, G. (G.); Lozano, C. (Celia); Montero, Á. (Ángel)A distinctive feature of discrete solids is their ability to form arches. These mechanically stable structures alter the isotropy of granular packings and can arrest the motion of grains when, for example, they flow through a bottleneck. Breaking arches can be achieved by means of an external vibration, which effectively eliminates clogging. Indeed, these phenomena and procedures are quite common in industrial applications. Nevertheless, there are not rigorous, well founded criteria to determine the most efficient way to break arches and restore the flow of grains. This happens in part because it is not known which are the relevant characteristics that boost the arch strength. In the experiment presented here, we have carried out a statistical analysis of the arches that block the exit orifice at the bottom of a two dimensional silo, and described their geometrical properties. We then submit the silo to an external vibration. We find that the larger the outlet size, the weaker the arches that clog it. This dependence is just the outcome of a more complicated process that involves geometrical defects inthe arch. The defects a are quantitatively defined in terms of contact angles and we show that this is a key factor regarding the endurance of arches.