9,796 research outputs found
Redefining the role of obstacles in pedestrian evacuation
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 counterintuitive 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.Fil: Garcimartín, A.. Universidad de Navarra; EspañaFil: Maza, D.. Universidad de Navarra; EspañaFil: Pastor, J. M.. Focke Meler Gluing Solutions S.A.; EspañaFil: Parisi, Daniel Ricardo. Instituto Tecnológico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Martín Gómez, C.. Universidad de Navarra; EspañaFil: Zuriguel, I.. Universidad de Navarra; Españ
Complex networks created by aggregation
We study aggregation as a mechanism for the creation of complex networks. In
this evolution process vertices merge together, which increases the number of
highly connected hubs. We study a range of complex network architectures
produced by the aggregation. Fat-tailed (in particular, scale-free)
distributions of connections are obtained both for networks with a finite
number of vertices and growing networks. We observe a strong variation of a
network structure with growing density of connections and find the phase
transition of the condensation of edges. Finally, we demonstrate the importance
of structural correlations in these networks.Comment: 12 pages, 13 figure
Statistical analysis of 22 public transport networks in Poland
Public transport systems in 22 Polish cities have been analyzed. Sizes of
these networks range from N=152 to N=2881. Depending on the assumed definition
of network topology the degree distribution can follow a power law or can be
described by an exponential function. Distributions of paths in all considered
networks are given by asymmetric, unimodal functions. Clustering, assortativity
and betweenness are studied. All considered networks exhibit small world
behavior and are hierarchically organized. A transition between dissortative
small networks N=500 is observed.Comment: 11 pages, 17 figures, 2 tables, REVTEX4 forma
Elementary transitions and magnetic correlations in two-dimensional disordered nanoparticle ensembles
The magnetic relaxation processes in disordered two-dimensional ensembles of
dipole-coupled magnetic nanoparticles are theoretically investigated by
performing numerical simulations. The energy landscape of the system is
explored by determining saddle points, adjacent local minima, energy barriers,
and the associated minimum energy paths (MEPs) as functions of the structural
disorder and particle density. The changes in the magnetic order of the
nanostructure along the MEPs connecting adjacent minima are analyzed from a
local perspective. In particular, we determine the extension of the correlated
region where the directions of the particle magnetic moments vary
significantly. It is shown that with increasing degree of disorder the magnetic
correlation range decreases, i.e., the elementary relaxation processes become
more localized. The distribution of the energy barriers, and their relation to
the changes in the magnetic configurations are quantified. Finally, some
implications for the long-time magnetic relaxation dynamics of nanostructures
are discussed.Comment: 19 pages, 6 figure
Critical load and congestion instabilities in scale-free networks
We study the tolerance to congestion failures in communication networks with
scale-free topology. The traffic load carried by each damaged element in the
network must be partly or totally redistributed among the remaining elements.
Overloaded elements might fail on their turn, triggering the occurrence of
failure cascades able to isolate large parts of the network. We find a critical
traffic load above which the probability of massive traffic congestions
destroying the network communication capabilities is finite.Comment: 4 pages, 3 figure
Social inertia in collaboration networks
This work is a study of the properties of collaboration networks employing
the formalism of weighted graphs to represent their one-mode projection. The
weight of the edges is directly the number of times that a partnership has been
repeated. This representation allows us to define the concept of "social
inertia" that measures the tendency of authors to keep on collaborating with
previous partners. We use a collection of empirical datasets to analyze several
aspects of the social inertia: 1) its probability distribution, 2) its
correlation with other properties, and 3) the correlations of the inertia
between neighbors in the network. We also contrast these empirical results with
the predictions of a recently proposed theoretical model for the growth of
collaboration networks.Comment: 7 pages, 5 figure
Steady-State Dynamics of the Forest Fire Model on Complex Networks
Many sociological networks, as well as biological and technological ones, can
be represented in terms of complex networks with a heterogeneous connectivity
pattern. Dynamical processes taking place on top of them can be very much
influenced by this topological fact. In this paper we consider a paradigmatic
model of non-equilibrium dynamics, namely the forest fire model, whose
relevance lies in its capacity to represent several epidemic processes in a
general parametrization. We study the behavior of this model in complex
networks by developing the corresponding heterogeneous mean-field theory and
solving it in its steady state. We provide exact and approximate expressions
for homogeneous networks and several instances of heterogeneous networks. A
comparison of our analytical results with extensive numerical simulations
allows to draw the region of the parameter space in which heterogeneous
mean-field theory provides an accurate description of the dynamics, and
enlights the limits of validity of the mean-field theory in situations where
dynamical correlations become important.Comment: 13 pages, 9 figure
Corrections to scaling in the forest-fire model
We present a systematic study of corrections to scaling in the self-organized
critical forest-fire model. The analysis of the steady-state condition for the
density of trees allows us to pinpoint the presence of these corrections, which
take the form of subdominant exponents modifying the standard finite-size
scaling form. Applying an extended version of the moment analysis technique, we
find the scaling region of the model and compute the first non-trivial
corrections to scaling.Comment: RevTeX, 7 pages, 7 eps figure
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