arXiv subjects

C. O. Dorso

Publications and source records attributed to C. O. Dorso.

At least 19 recordsLinked to original sources

arXiv2022

Microscopic dynamics at the Running of the Bulls (San Fermin Festival) in the context of the Social Force Model

This research explores the dynamics of the emergency evacuation during the "Running of the Bulls" festival (Spain, 2013). As people run to escape from danger, many pedestrians stumble and fall down, while others will try to pass over them. We carefully examined three specific recordings of the running, that show this kind of behavior. We developed a microscopic model mimicking the stumbling mechanism in the context of the Social Force Model (SFM). In our model, "moving" individuals can suddenly switch to a "fallen" state when they are in the vicinity of a fallen individual. We arrived to the conclusion that the presence of a fallen pedestrian increases dramatically the falling probability of the pedestrians nearby. Also, the product between the local density gradient and the velocity of each pedestrian appears as a relevant indicator for an imminent fall. We call this the pedestrian "falling susceptibility (f_s)".

physics.soc-ph↗

arXiv2022

Faster and safer evacuations induced by closed vestibules

Improving emergency evacuations is a top priority in human safety and in pedestrian dynamics. In this paper, we use the social force model, in order to optimize high-anxiety pedestrian evacuations. We explore two architectural layouts, the 1-door vestibule, and the 2-doors vestibule. The "vestibule" is defined as the room next to the exit door and it is characterized by two structural parameters: the vestibule width ($d$) and the vestibule door width ($w$). We found that, specific values of $d$ and $w$, can almost double the evacuation flow compared to the no-vestibule scenario. The key to this achievement is that the density (close to the exit door) can be controlled by $d$ and $w$. Therefore, it is possible to tune these parameters to a density that maximizes the available space while preventing the formation of blocking clusters at the exit door ($ρ\sim 2.5\,$p/m$^2$). As opposed to the optimal condition, low-density values ($ρ\sim 1\,$p/m$^2$) lead to suboptimal flow since there is unused space left; while higher density values ($ρ\sim 4\,$p/m$^2$) also lead to suboptimal flow due to the presence of blocking clusters at the exit. Moreover, we take into account the usually foreseen fact that high pressures can actually be reached at the exit, threatening the health of pedestrians. Therefore, we studied the crowd pressure using the agents' overlap as an indicative. We found that the explored vestibules reduce the crowd pressure compared to the no-vestibule situation. In particular, we show that the 2-doors vestibule scenario performs better than the 1-door vestibule, because it reduces the overall local density (by enforcing the crowd to spread out more).

physics.soc-ph↗

arXiv2021

Improving competitive evacuations with a vestibule structure designed from panel-like obstacles

It has been shown that placing an obstacle in front of an exit door has proven to be a successful method to improve pedestrian evacuations. In this work, we will focus on the space limited by the exit and the obstacles (i.e. the vestibule structure). We analyzed two different types of vestibules: the two-entry vestibule (which consists of a single panel-like obstacle) and the three-entry vestibule (which consists of two panel-like obstacles). In the former, we studied the effects of varying the walls' friction coefficient $κ_w$ and the distance from the obstacle to the exit door $d$. In the latter, we varied the space between the two panels (gap). We found that the three above mentioned parameters control the vestibule's density, which subsequently affects the evacuation flow (fundamental diagram). We have also found that reducing the distance $d$ or increasing the friction facilitates the formation of blocking clusters at the vestibule entries, and hence, diminishes the density. If the density is too large or too low, the evacuation flow is suboptimal, whereas if the density is around $2 \pm 2$, the flow is maximized. Our most important result is that the density (and therefore the evacuation flow) can be precisely controlled by $κ_w$, $d$, and the gap. Moreover, the three-entry vestibule produced the highest evacuation flow for specific configurations of the gap and the distance from the panels to the door.

physics.soc-ph↗

arXiv2020

Microscopic dynamics of the evacuation phenomena

We studied the room evacuation problem within the context of the Social Force Model. We focused on a system of 225 pedestrians escaping from a room in different anxiety levels, and analyzed the clogging delays as the relevant magnitude responsible for the evacuation performance. We linked the delays with the clusterization phenomenon along the "faster is slower" and the "faster is faster" regimes. We will show that the "faster is faster" regime is characterized by the presence of a giant cluster structure (composed by more than 15 pedestrians), although no long lasting delays appear within this regime. For this system, we found that the relevant structures in the "faster is slower" regime are those blocking clusters that are somehow attached to the two walls defining the exit. At very low desired velocities, very small structures become relevant (composed by less than 5 pedestrians), but at intermediate velocities (vd = 3 m/s) the pedestrians involved in the blockings increases (not exceeding 15 pedestrians).

physics.soc-ph↗

arXiv2020

Social Force Model parameter testing and optimization using a high stress real-life situation

The escape panic version of the Social Force Model (SFM) is a suitable model for describing emergency evacuations. In this research, we analyze a real-life video, recorded at the opening of a store during a Black Friday event, which resembles an emergency evacuation (November 2017, South Africa). We measure the flow of pedestrians entering the store and found a higher value ($\langle J \rangle =6.7 \pm 0.8\,$p/s) than the usually reported in ``laboratory'' conditions. We performed numerical simulations to recreate this event. The empirical measurements were compared against simulated evacuation curves corresponding to different sets of parameters currently in use in the literature. The results obtained suggest that the set of parameters corresponding to calibrations from laboratory experiments (involving pedestrians in which the safety of the participants is of major concern) or situations where the physical contact is negligible, produce simulations in which the agents evacuate faster than in the empirical scenario. To conclude the paper, we optimize two parameters of the model: the friction coefficient $k_t$ and the body force coefficient $k_n$. The best fit we found could replicate the qualitative and quantitative behavior of the empirical evacuation curve. We also found that many different combinations in the parameter space can produce similar results in terms of the goodness of fit.

physics.soc-ph↗

arXiv2019

A re-examination of the role of friction in the original Social Force Model

The fundamental diagram of pedestrian dynamics gives the relation between the density and the flow within a specific enclosure. It is characterized by two distinctive behaviors: the free-flow regime (for low densities) and the congested regime (for high densities). In the former, the flow is an increasing function of the density, while in the latter, the flow remains on hold or decreases. In this work, we perform numerical simulations of the pilgrimage at the entrance of the Jamaraat bridge (pedestrians walking along a straight corridor) and compare flow-density measurements with empirical measurements made by Helbing[1]. We show that under high density conditions, the basic Social Force Model (SFM) does not completely handle the fundamental diagram reported in empirical measurements. We use analytical techniques and numerical simulations to prove that with an appropriate modification of the friction coefficient (but sustaining the SFM) it is possible to attain behaviors which are in qualitative agreement with the empirical data. Other authors have already proposed a modification of the relaxation time in order to address this problem. In this work, we unveil the fact that our approach is analogous to theirs since both affect the same term of the reduced-in-units equation of motion. We show how the friction modification affects the pedestrian clustering structures throughout the transition from the free-flow regime to the congested regime. We also show that the speed profile, normalized by width and maximum velocity yields a universal behavior regardless of the corridor dimensions.

physics.soc-ph↗

arXiv2018

Panic contagion and the evacuation dynamics

Panic may spread over a crowd in a similar fashion as contagious diseases do in social groups. People no exposed to a panic source may express fear, alerting others of imminent danger. This social mechanism initiates an evacuation process, while affecting the way people try to escape. We examined real life situations of panic contagion and reproduced these situations in the context of the Social Force Model. We arrived to the conclusion that two evacuation schemes may appear, according to the \textit{stress} of the panic contagion. Both schemes exhibit different evacuation patterns and are qualitatively visible in the available real life recordings of crowded events. We were able to quantify these patterns through topological parameters. We further investigated how the panic spreading gradually stops if the source of danger ceases.

physics.soc-ph↗

arXiv2018

Phase transitions and symmetry energy in nuclear pasta

Cold and isospin-symmetric nuclear matter at sub-saturation densities is known to form the so-called pasta structures, which, in turn, are known to undergo peculiar phase transitions. Here we investigate if such pastas and their phase changes survive in isospin asymmetric nuclear matter, and whether the symmetry energy of such pasta configurations is connected to the isospin content, the morphology of the pasta and to the phase transitions. We find that indeed pastas are formed in isospin asymmetric systems with proton to neutron ratios of x=0.3, 0.4 and 0.5, densities in the range of 0.05 1/fm$^3$<$ρ$< 0.08 1/fm$^3$, and temperatures T<2 MeV. Using tools (such as the caloric curve, Lindemann coefficient, radial distribution function, Kolmogorov statistic, and Euler functional) on the composition of the pasta, determined the existence of homogeneous structures, tunnels, empty regions, cavities and transitions among these regions. The symmetry energy was observed to attain different values in the different phases showing its dependence on the morphology of the nuclear matter structure.

nucl-th↗

arXiv2017

Beyond the "faster is slower" effect

The "faster is slower" effect raises when crowded people push each other to escape through an exit during an emergency situation. As individuals push harder, a statistical slowing down in the evacuation time can be achieved. The slowing down is caused by the presence of small groups of pedestrians (say, a small human cluster) that temporary blocks the way out when trying to leave the room. The pressure on the pedestrians belonging to this blocking cluster raises for increasing anxiety levels and/or larger number of individuals trying to leave the room through the same door. Our investigation shows, however, that very high pressures alters the dynamics in the blocking cluster, and thus, changes the statistics of the time delays along the escaping process. It can be acknowledged a reduction in the long lasting delays, while the overall evacuation performance improves. We present results on this novel phenomenon taking place beyond the "faster is slower" regime.

physics.soc-ph↗

arXiv2017

The Neutrino Opacity of Neutron Star Inner Crust

The study of neutron rich matter, present in neutron star, proto-neutron stars and core-collapse supernovae, can lead to further understanding of the behavior of nuclear matter in highly asymmetric nuclei. Heterogeneous structures are expected to exist in these systems, often referred to as nuclear pasta. We have carried out a systematic study of neutrino opacity for different thermodynamic conditions in order to assess the impact that the structure has on it. We studied the dynamics of the neutrino opacity of the heterogeneous matter at different thermodynamic conditions with semiclassical molecular dynamics model already used to study nuclear multifragmentation. For different densities, proton fractions and temperature, we calculate the very long range opacity and the cluster distribution. The neutrino opacity is of crucial importance for the evolution of the core-collapse supernovae and the neutrino scattering.

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arXiv2017

Fragmentation of Neutron Star Matter

Background: Neutron stars are astronomical systems with nucleons submitted to extreme conditions. Due to the long range coulomb repulsion between protons, the system has structural inhomogeneities. These structural inhomogeneities arise also in expanding systems, where the fragment distribution is highly dependent on the thermodynamic conditions (temperature, proton fraction, ...) and the expansion velocity. Purpose: We aim to find the different regimes of fragment distribution, and the existence of infinite clusters. Method: We study the dynamics of the nucleons with a semiclassical molecular dynamics model. Starting with an equilibrium configuration, we expand the system homogeneously until we arrive to an asymptotic configuration (i. e. very low final densities). We study the fragment distribution throughout this expansion. Results: We found the typical regimes of the asymptotic fragment distribution of an expansion: u-shaped, power law and exponential. Another key feature in our calculations is that, since the interaction between protons is long range repulsive, we do not have always an infinite fragment. We found that, as expected, the faster the expansion velocity is, the quicker the infinite fragment disappears. Conclusions: We have developed a novel graph-based tool for the identification of infinite fragments, and found a transition from U-shaped to exponential fragment mass distribution with increasing expansion rate.

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arXiv2017

High pressures in room evacuation processes and a first approach to the dynamics around unconscious pedestrians

Clogging raises as the principal phenomenon during many evacuation processes of pedestrians in a panic situation. As people push to escape from danger, compression forces may increase to harming levels. Many individuals might fall down, while others will try to dodge the fallen people, or, simply pass through them. We studied the dynamics of the crowd for these situations, in the context of the "social force model". We modeled the unconscious (fallen) pedestrians as inanimate bodies that can be dodged (or not) by the surrounding individuals. We found that new morphological structures appear along the evacuating crowd. Under specific conditions, these structures may enhance the evacuation performance. The pedestrian's willings for either dodging or passing through the unconscious individuals play a relevant role in the overall evacuation performance.

physics.soc-ph↗

arXiv2016

Room evacuation through two contiguous exits

Current regulations demand that at least two exits should be available for a safe evacuation during a panic situation. Although the "faster is slower" effect is expected to take place near the exits, the evacuation time will improve because of the additional exits. However, rooms having contiguous doors not always reduce the leaving time as expected. We investigated the relation between the doors separation and the evacuation performance. We found that there exists a separation distance range that does not really improve the evacuation time, or it can even worsen the process performance. To our knowledge, no attention has been given to this issue in the literature. This work reports how the pedestrians dynamics differ when the separation distance between two exit doors changes and how this affects the overall performance.

physics.soc-ph↗

arXiv2014

Vaccination and public trust: a model for the dissemination of vaccination behavior with external intervention

Vaccination is widely recognized as the most effective way of immunization against many infectious diseases. However, unfounded claims about supposed side effects of some vaccines have contributed to spread concern and fear among people, thus inducing vaccination refusal. For instance, MMR vaccine coverage has undergone an important decrease in a large part of Europe and US as a consequence of erroneously alleged side effects, leading to recent measles outbreaks. In this work, we propose a general agent-based model to study the spread of vaccination behavior in social networks, not as an isolated binary opinion spreading on it, but as part of a process of cultural dissemination in the spirit of Axelrod's model. We particularly focused on the impact of a small anti-vaccination movement over an initial population of pro-vaccination social agents. Additionally, we have considered two classes of edges in the underlying social network: personal edges able to spread both opinions and diseases; and the non-personal ones representing interactions mediated by information technologies, which only allow opinion exchanges. We study the clustering of unvaccinated agents as a dynamical outcome of the model, together with its direct relation with the increase of the probability of occurrence and the final size of measles outbreaks. Finally, we illustrate the mitigating effect of a public health campaign, represented by an external field, against the harmful action of anti-vaccination movements. We show that the topological characteristics of the clusters of unvaccinated agents determine the scopes of this mitigating effect.

physics.soc-ph↗

arXiv2014

Memory effects induce structure in social networks with activity-driven agents

Activity-driven modeling has been recently proposed as an alternative growth mechanism for time varying networks, displaying power-law degree distribution in time-aggregated representation. This approach assumes memoryless agents developing random connections, thus leading to random networks that fail to reproduce two-nodes degree correlations and the high clustering coefficient widely observed in real social networks. In this work we introduce these missing topological features by accounting for memory effects on the dynamic evolution of time-aggregated networks. To this end, we propose an activity-driven network growth model including a triadic-closure step as main connectivity mechanism. We show that this mechanism provides some of the fundamental topological features expected for social networks. We derive analytical results and perform extensive numerical simulations in regimes with and without population growth. Finally, we present two cases of study, one comprising face-to-face encounters in a closed gathering, while the other one from an online social friendship network.

physics.soc-ph↗

arXiv2014

Finite size effects in Neutron Star and Nuclear matter simulations

In this work we study molecular dynamics simulations of symmetric nuclear matter using a semi-classical nucleon interaction model. We show that, at sub-saturation densities and low temperatures, the solutions are non-homogeneous structures reminiscent of the ``nuclear pasta'' phases expected in Neutron Star Matter simulations, but shaped by artificial aspects of the simulations. We explore different geometries for the periodic boundary conditions imposed on the simulation cell: cube, hexagonal prism and truncated octahedron. We find that different cells may yield different solutions for the same physical conditions (i.e. density and temperature). The particular shape of the solution at a given density can be predicted analytically by energy minimization. We also show that even if this behavior is due to finite size effects, it does not mean that it vanishes for very large systems and it actually is independent of the system size: The system size sets the only characteristic length scale for the inhomogeneities. We then include a screened Coulomb interaction, as a model of Neutron Star Matter, and perform simulations in the three cell geometries. In this case, the competition between competing interactions of different range produces the well known nuclear pasta, with (in most cases) several structures per cell. However, we find that the results are affected by finite size in different ways depending on the geometry of the cell. In particular, at the same physical conditions and system size, the hexagonal prism yields a single structure per cell while the cubic and truncated octahedron show consistent results with more than one structure per cell. In this case, the results in every cell are expected to converge for systems much larger than the characteristic length scale that arises from the competing interactions.

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arXiv2013

Effect of Coulomb Screening Length on Nuclear Pasta Simulations

We study the role of the effective Coulomb interaction strength and length on the dynamics of nucleons in conditions according to those in a neutron star's crust. Calculations were made with a semi-classical molecular dynamics model, studying isospin symmetric matter at sub-saturation densities and low temperatures. The electrostatic interaction between protons interaction is included in the form of a screened Coulomb potential in the spirit of the Thomas-Fermi approximation, but the screening length is artificially varied to explore its effect on the formation of the non-homogeneous nuclear structures known as "nuclear pasta". As the screening length increases, we can a transition from a one-per-cell pasta regime (due exclusively to finite size effects) to a more appealing multiple pasta per simulation box. This shows qualitative difference in the structure of neutron star matter at low temperatures, and therefore, special caution should be taken when the screening length is estimated for numerical simulations.

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arXiv2013

Cold nuclear matter

The behavior of nuclear matter is studied at low densities and temperatures using classical molecular dynamics with three different sets of potentials with different compressibility. Nuclear matter is found to arrange in crystalline structures around the saturation density and in non-homogeneous (i.e. pasta-like) structures at lower densities. Similar results were obtained with a simple Lennard-Jones potential. Finite size effects are analysed and the existence of the non-homogeneous structures is shown to be inherent to the use of periodic boundary conditions and the finitude of the system. For large enough systems the non-homogeneous structures are limited to one sphere, one rod or one slab per simulation cell, which are shown to be minimal surface structures under cubic periodic boundary conditions at the corresponding volume fraction. The relevance of these findings to the simulations of neutron star and supernovae matter is discussed.

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