33 research outputs found
Joint effect of ageing and multilayer structure prevents ordering in the voter model
The voter model rules are simple, with agents copying the state of a random
neighbor, but they lead to non-trivial dynamics. Besides opinion processes, the
model has also applications for catalysis and species competition. Inspired by
the temporal inhomogeneities found in human interactions, one can introduce
ageing in the agents: the probability to update decreases with the time elapsed
since the last change. This modified dynamics induces an approach to consensus
via coarsening in complex networks. Additionally, multilayer networks produce
profound changes in the dynamics of models. In this work, we investigate how a
multilayer structure affects the dynamics of an ageing voter model. The system
is studied as a function of the fraction of nodes sharing states across layers
(multiplexity parameter q ). We find that the dynamics of the system suffers a
notable change at an intermediate value q*. Above it, the voter model always
orders to an absorbing configuration. While, below, a fraction of the
realizations falls into dynamical traps associated to a spontaneous symmetry
breaking in which the majority opinion in the different layers takes opposite
signs and that due to the ageing indefinitely delay the arrival at the
absorbing state.Comment: 10 pages, 8 figure
Optimization of transport protocols with path-length constraints in complex networks
We propose a protocol optimization technique that is applicable to both
weighted or unweighted graphs. Our aim is to explore by how much a small
variation around the Shortest Path or Optimal Path protocols can enhance
protocol performance. Such an optimization strategy can be necessary because
even though some protocols can achieve very high traffic tolerance levels, this
is commonly done by enlarging the path-lengths, which may jeopardize
scalability. We use ideas borrowed from Extremal Optimization to guide our
algorithm, which proves to be an effective technique. Our method exploits the
degeneracy of the paths or their close-weight alternatives, which significantly
improves the scalability of the protocols in comparison to Shortest Paths or
Optimal Paths protocols, keeping at the same time almost intact the length or
weight of the paths. This characteristic ensures that the optimized routing
protocols are composed of paths that are quick to traverse, avoiding negative
effects in data communication due to path-length increases that can become
specially relevant when information losses are present.Comment: 8 pages, 8 figure
A generalized vector-field framework for mobility
Trip flow between areas is a fundamental metric for human mobility research.
Given its identification with travel demand and its relevance for
transportation and urban planning, many models have been developed for its
estimation. These models focus on flow intensity, disregarding the information
provided by the local mobility orientation. A field-theoretic approach can
overcome this issue and handling both intensity and direction at once. Here we
propose a general vector-field representation starting from individuals'
trajectories valid for any type of mobility. By introducing four models of
spatial exploration, we show how individuals' elections determine the
mesoscopic properties of the mobility field. Distance optimization in long
displacements and random-like local exploration are necessary to reproduce
empirical field features observed in Chinese logistic data and in New York City
Foursquare check-ins. Our framework is an essential tool to capture hidden
symmetries in mesoscopic urban mobility, it establishes a benchmark to test the
validity of mobility models and opens the doors to the use of field theory in a
wide spectrum of applications.Comment: 13 pages, 8 figures, Appendice
American cultural regions mapped through the lexical analysis of social media
Cultural areas represent a useful concept that cross-fertilizes diverse
fields in social sciences. Knowledge of how humans organize and relate their
ideas and behavior within a society helps to understand their actions and
attitudes towards different issues. However, the selection of common traits
that shape a cultural area is somewhat arbitrary. What is needed is a method
that can leverage the massive amounts of data coming online, especially through
social media, to identify cultural regions without ad-hoc assumptions, biases
or prejudices. This work takes a crucial step in this direction by introducing
a method to infer cultural regions based on the automatic analysis of large
datasets from microblogging posts. The approach presented here is based on the
principle that cultural affiliation can be inferred from the topics that people
discuss among themselves. Specifically, regional variations in written
discourse are measured in American social media. From the frequency
distributions of content words in geotagged Tweets, the regional hotspots of
words' usage are found, and from there, principal components of regional
variation are derived. Through a hierarchical clustering of the data in this
lower-dimensional space, this method yields clear cultural areas and the topics
of discussion that define them. It uncovers a manifest North-South separation,
which is primarily influenced by the African American culture, and further
contiguous (East-West) and non-contiguous divisions that provide a
comprehensive picture of today's cultural areas in the US.Comment: 13 pages, 5 figures; contains Supplementary Informatio
Multilingual Societies from Twitter Data: Empirical Analysis and Theoretical Modelling
Purpose: Cultural diversity encoded within the languages of the world is at
risk, as many languages have become endangered in the last decades in the context of
growing globalization. To preserve this diversity, it is first necessary to understand what
drives language extinction, and which mechanisms might enable coexistence
Endemic infectious states below the epidemic threshold and beyond herd immunity
In the recent COVID-19 pandemic we assisted at a sequence of epidemic waves
intertwined by anomalous fade-outs with periods of low but persistent epidemic
prevalence. These long-living epidemic states complicate epidemic control and
challenge current modeling approaches as classical epidemic models fail to
explain their emergence. Inspired by this phenomenon, we propose a simple
mechanism able to reproduce several features observed in real data.
Specifically, here we introduce a modification of the
Susceptible-Infected-Recovered (SIR) model in a meta-population framework where
a small inflow of infected individuals accounts for undetected internal or
imported cases. Focusing on a regime where this external seeding is so small
that cannot be detected from the analysis of epidemic curves, we find that
outbreaks of finite duration percolate in time resulting in overall low but
long-living epidemic states below and above the epidemic threshold. Using a
two-state description of the local dynamics, we can extract analytical
predictions for the phase space. The comparison with epidemic data demonstrates
that our model is able to reproduce some critical signatures observed in
COVID-19 spreading in England. Finally, our findings defy our understanding of
the concept of epidemic threshold and its relationship with outbreaks survival
for disease control.Comment: Corrected typo
Migrant mobility flows characterized with digital data
Monitoring migration flows is crucial to respond to humanitarian crisis and to design efficient policies. This information usually comes from surveys and border controls, but timely accessibility and methodological concerns reduce its usefulness. Here, we propose a method to detect migration flows worldwide using geolocated Twitter data. We focus on the migration crisis in Venezuela and show that the calculated flows are consistent with official statistics at country level. Our method is versatile and far-reaching, as it can be used to study different features of migration as preferred routes, settlement areas, mobility through several countries, spatial integration in cities, etc. It provides finer geographical and temporal resolutions, allowing the exploration of issues not contemplated in official records. It is our hope that these new sources of information can complement official ones, helping authorities and humanitarian organizations to better assess when and where to intervene on the ground