97,403 research outputs found
Diffusion-annihilation processes in complex networks
We present a detailed analytical study of the
diffusion-annihilation process in complex networks. By means of microscopic
arguments, we derive a set of rate equations for the density of particles
in vertices of a given degree, valid for any generic degree distribution, and
which we solve for uncorrelated networks. For homogeneous networks (with
bounded fluctuations), we recover the standard mean-field solution, i.e. a
particle density decreasing as the inverse of time. For heterogeneous
(scale-free networks) in the infinite network size limit, we obtain instead a
density decreasing as a power-law, with an exponent depending on the degree
distribution. We also analyze the role of finite size effects, showing that any
finite scale-free network leads to the mean-field behavior, with a prefactor
depending on the network size. We check our analytical predictions with
extensive numerical simulations on homogeneous networks with Poisson degree
distribution and scale-free networks with different degree exponents.Comment: 9 pages, 5 EPS figure
Diffusion-annihilation processes in complex networks
We present a detailed analytical study of the
diffusion-annihilation process in complex networks. By means of microscopic
arguments, we derive a set of rate equations for the density of particles
in vertices of a given degree, valid for any generic degree distribution, and
which we solve for uncorrelated networks. For homogeneous networks (with
bounded fluctuations), we recover the standard mean-field solution, i.e. a
particle density decreasing as the inverse of time. For heterogeneous
(scale-free networks) in the infinite network size limit, we obtain instead a
density decreasing as a power-law, with an exponent depending on the degree
distribution. We also analyze the role of finite size effects, showing that any
finite scale-free network leads to the mean-field behavior, with a prefactor
depending on the network size. We check our analytical predictions with
extensive numerical simulations on homogeneous networks with Poisson degree
distribution and scale-free networks with different degree exponents.Comment: 9 pages, 5 EPS figure
Detecting the Influence of Spreading in Social Networks with Excitable Sensor Networks
Detecting spreading outbreaks in social networks with sensors is of great
significance in applications. Inspired by the formation mechanism of human's
physical sensations to external stimuli, we propose a new method to detect the
influence of spreading by constructing excitable sensor networks. Exploiting
the amplifying effect of excitable sensor networks, our method can better
detect small-scale spreading processes. At the same time, it can also
distinguish large-scale diffusion instances due to the self-inhibition effect
of excitable elements. Through simulations of diverse spreading dynamics on
typical real-world social networks (facebook, coauthor and email social
networks), we find that the excitable senor networks are capable of detecting
and ranking spreading processes in a much wider range of influence than other
commonly used sensor placement methods, such as random, targeted, acquaintance
and distance strategies. In addition, we validate the efficacy of our method
with diffusion data from a real-world online social system, Twitter. We find
that our method can detect more spreading topics in practice. Our approach
provides a new direction in spreading detection and should be useful for
designing effective detection methods
Activation thresholds in epidemic spreading with motile infectious agents on scale-free networks
We investigate a fermionic susceptible-infected-susceptible model with
mobility of infected individuals on uncorrelated scale-free networks with
power-law degree distributions of exponents
. Two diffusive processes with diffusion rate of an infected
vertex are considered. In the \textit{standard diffusion}, one of the
nearest-neighbors is chosen with equal chance while in the \textit{biased
diffusion} this choice happens with probability proportional to the neighbor's
degree. A non-monotonic dependence of the epidemic threshold on with an
optimum diffusion rate , for which the epidemic spreading is more
efficient, is found for standard diffusion while monotonic decays are observed
in the biased case. The epidemic thresholds go to zero as the network size is
increased and the form that this happens depends on the diffusion rule and
degree exponent. We analytically investigated the dynamics using quenched and
heterogeneous mean-field theories. The former presents, in general, a better
performance for standard and the latter for biased diffusion models, indicating
different activation mechanisms of the epidemic phases that are rationalized in
terms of hubs or max -core subgraphs.Comment: 9 pages, 4 figure
Bosonic reaction-diffusion processes on scale-free networks
Reaction-diffusion processes can be adopted to model a large number of
dynamics on complex networks, such as transport processes or epidemic
outbreaks. In most cases, however, they have been studied from a fermionic
perspective, in which each vertex can be occupied by at most one particle.
While still useful, this approach suffers from some drawbacks, the most
important probably being the difficulty to implement reactions involving more
than two particles simultaneously. Here we introduce a general framework for
the study of bosonic reaction-diffusion processes on complex networks, in which
there is no restriction on the number of interacting particles that a vertex
can host. We describe these processes theoretically by means of continuous time
heterogeneous mean-field theory and divide them into two main classes: steady
state and monotonously decaying processes. We analyze specific examples of both
behaviors within the class of one-species process, comparing the results
(whenever possible) with the corresponding fermionic counterparts. We find that
the time evolution and critical properties of the particle density are
independent of the fermionic or bosonic nature of the process, while
differences exist in the functional form of the density of occupied vertices in
a given degree class k. We implement a continuous time Monte Carlo algorithm,
well suited for general bosonic simulations, which allow us to confirm the
analytical predictions formulated within mean-field theory. Our results, both
at the theoretical and numerical level, can be easily generalized to tackle
more complex, multi-species, reaction-diffusion processes, and open a promising
path for a general study and classification of this kind of dynamical systems
on complex networks.Comment: 15 pages, 7 figure
Phase transitions in contagion processes mediated by recurrent mobility patterns
Human mobility and activity patterns mediate contagion on many levels,
including the spatial spread of infectious diseases, diffusion of rumors, and
emergence of consensus. These patterns however are often dominated by specific
locations and recurrent flows and poorly modeled by the random diffusive
dynamics generally used to study them. Here we develop a theoretical framework
to analyze contagion within a network of locations where individuals recall
their geographic origins. We find a phase transition between a regime in which
the contagion affects a large fraction of the system and one in which only a
small fraction is affected. This transition cannot be uncovered by continuous
deterministic models due to the stochastic features of the contagion process
and defines an invasion threshold that depends on mobility parameters,
providing guidance for controlling contagion spread by constraining mobility
processes. We recover the threshold behavior by analyzing diffusion processes
mediated by real human commuting data.Comment: 20 pages of Main Text including 4 figures, 7 pages of Supplementary
Information; Nature Physics (2011
Communities, Knowledge Creation, and Information Diffusion
In this paper, we examine how patterns of scientific collaboration contribute
to knowledge creation. Recent studies have shown that scientists can benefit
from their position within collaborative networks by being able to receive more
information of better quality in a timely fashion, and by presiding over
communication between collaborators. Here we focus on the tendency of
scientists to cluster into tightly-knit communities, and discuss the
implications of this tendency for scientific performance. We begin by reviewing
a new method for finding communities, and we then assess its benefits in terms
of computation time and accuracy. While communities often serve as a taxonomic
scheme to map knowledge domains, they also affect how successfully scientists
engage in the creation of new knowledge. By drawing on the longstanding debate
on the relative benefits of social cohesion and brokerage, we discuss the
conditions that facilitate collaborations among scientists within or across
communities. We show that successful scientific production occurs within
communities when scientists have cohesive collaborations with others from the
same knowledge domain, and across communities when scientists intermediate
among otherwise disconnected collaborators from different knowledge domains. We
also discuss the implications of communities for information diffusion, and
show how traditional epidemiological approaches need to be refined to take
knowledge heterogeneity into account and preserve the system's ability to
promote creative processes of novel recombinations of idea
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