3,869 research outputs found
Epidemic spreading on interconnected networks
Many real networks are not isolated from each other but form networks of
networks, often interrelated in non trivial ways. Here, we analyze an epidemic
spreading process taking place on top of two interconnected complex networks.
We develop a heterogeneous mean field approach that allows us to calculate the
conditions for the emergence of an endemic state. Interestingly, a global
endemic state may arise in the coupled system even though the epidemics is not
able to propagate on each network separately, and even when the number of
coupling connections is small. Our analytic results are successfully confronted
against large-scale numerical simulations
Modular networks emerge from multiconstraint optimization
Modular structure is ubiquitous among complex networks. We note that most
such systems are subject to multiple structural and functional constraints,
e.g., minimizing the average path length and the total number of links, while
maximizing robustness against perturbations in node activity. We show that the
optimal networks satisfying these three constraints are characterized by the
existence of multiple subnetworks (modules) sparsely connected to each other.
In addition, these modules have distinct hubs, resulting in an overall
heterogeneous degree distribution.Comment: 5 pages, 4 figures; Published versio
Promiscuity and the Evolution of Sexual Transmitted Diseases
We study the relation between different social behaviors and the onset of
epidemics in a model for the dynamics of sexual transmitted diseases. The model
considers the society as a system of individual sexuated agents that can be
organized in couples and interact with each other. The different social
behaviors are incorporated assigning what we call a promiscuity value to each
individual agent. The individual promiscuity is taken from a distributions and
represents the daily probability of going out to look for a sexual partner,
abandoning its eventual mate. In terms of this parameter we find a threshold
for the epidemic which is much lower than the classical fully mixed model
prediction, i.e. (basic reproductive number) . Different forms for
the distribution of the population promiscuity are considered showing that the
threshold is weakly sensitive to them. We study the homosexual and the
heterosexual case as well.Comment: 6 pages, 4 figure
Statistics of Certain Models of Evolution
In a recent paper, Newman surveys the literature on power law spectra in
evolution, self-organised criticality and presents a model of his own to arrive
at a conclusion that self-organised criticality is not necessary for evolution.
Not only did he miss a key model (Ecolab) that has a clear self-organised
critical mechanism, but also Newman's model exhibits the same mechanism that
gives rise to power law behaviour as does Ecolab. Newman's model is, in fact, a
``mean field'' approximation of a self-organised critical system. In this
paper, I have also implemented Newman's model using the Ecolab software,
removing the restriction that the number of species remains constant. It turns
out that the requirement of constant species number is non-trivial, leading to
a global coupling between species that is similar in effect to the species
interactions seen in Ecolab. In fact, the model must self-organise to a state
where the long time average of speciations balances that of the extinctions,
otherwise the system either collapses or explodes. In view of this, Newman's
model does not provide the hoped-for counter example to the presence of
self-organised criticality in evolution, but does provide a simple, almost
analytic model that can used to understand more intricate models such as
Ecolab.Comment: accepted in Phys Rev E.; RevTeX; See
http://parallel.hpc.unsw.edu.au/rks/ecolab.html for more informatio
Shift of percolation thresholds for epidemic spread between static and dynamic small-world networks
The aim of the study was to compare the epidemic spread on static and dynamic
small-world networks. The network was constructed as a 2-dimensional
Watts-Strogatz model (500x500 square lattice with additional shortcuts), and
the dynamics involved rewiring shortcuts in every time step of the epidemic
spread. The model of the epidemic is SIR with latency time of 3 time steps. The
behaviour of the epidemic was checked over the range of shortcut probability
per underlying bond 0-0.5. The quantity of interest was percolation threshold
for the epidemic spread, for which numerical results were checked against an
approximate analytical model. We find a significant lowering of percolation
thresholds for the dynamic network in the parameter range given. The result
shows that the behaviour of the epidemic on dynamic network is that of a static
small world with the number of shortcuts increased by 20.7 +/- 1.4%, while the
overall qualitative behaviour stays the same. We derive corrections to the
analytical model which account for the effect. For both dynamic and static
small-world we observe suppression of the average epidemic size dependence on
network size in comparison with finite-size scaling known for regular lattice.
We also study the effect of dynamics for several rewiring rates relative to
latency time of the disease.Comment: 13 pages, 6 figure
A statistical network analysis of the HIV/AIDS epidemics in Cuba
The Cuban contact-tracing detection system set up in 1986 allowed the
reconstruction and analysis of the sexual network underlying the epidemic
(5,389 vertices and 4,073 edges, giant component of 2,386 nodes and 3,168
edges), shedding light onto the spread of HIV and the role of contact-tracing.
Clustering based on modularity optimization provides a better visualization and
understanding of the network, in combination with the study of covariates. The
graph has a globally low but heterogeneous density, with clusters of high
intraconnectivity but low interconnectivity. Though descriptive, our results
pave the way for incorporating structure when studying stochastic SIR epidemics
spreading on social networks
The Social Behavior and the Evolution of Sexually Transmitted Diseases
We introduce a model for the evolution of sexually transmitted diseases, in
which the social behavior is incorporated as a determinant factor for the
further propagation of the infection. The system may be regarded as a society
of agents where in principle anyone can sexually interact with any other one in
the population. Different social behaviors are reflected in a distribution of
sexual attitudes ranging from the more conservative to the more promiscuous.
This is measured by what we call the promiscuity parameter. In terms of this
parameter, we find a critical behavior for the evolution of the disease. There
is a threshold below what the epidemic does not occur. We relate this critical
value of the promiscuity to what epidemiologist call the basic reproductive
number, connecting it with the other parameters of the model, namely the
infectivity and the infective period in a quantitative way. We consider the
possibility of subjects be grouped in couples. In this contribution only the
homosexual case is analyzed.Comment: 4 pages, 4 figure
Multi-state epidemic processes on complex networks
Infectious diseases are practically represented by models with multiple
states and complex transition rules corresponding to, for example, birth,
death, infection, recovery, disease progression, and quarantine. In addition,
networks underlying infection events are often much more complex than described
by meanfield equations or regular lattices. In models with simple transition
rules such as the SIS and SIR models, heterogeneous contact rates are known to
decrease epidemic thresholds. We analyze steady states of various multi-state
disease propagation models with heterogeneous contact rates. In many models,
heterogeneity simply decreases epidemic thresholds. However, in models with
competing pathogens and mutation, coexistence of different pathogens for small
infection rates requires network-independent conditions in addition to
heterogeneity in contact rates. Furthermore, models without spontaneous
neighbor-independent state transitions, such as cyclically competing species,
do not show heterogeneity effects.Comment: 7 figures, 1 tabl
Transmission of severe acute respiratory syndrome in dynamical small-world networks
The outbreak of severe acute respiratory syndrome (SARS) is still threatening
the world because of a possible resurgence. In the current situation that
effective medical treatments such as antiviral drugs are not discovered yet,
dynamical features of the epidemics should be clarified for establishing
strategies for tracing, quarantine, isolation, and regulating social behavior
of the public at appropriate costs. Here we propose a network model for SARS
epidemics and discuss why superspreaders emerged and why SARS spread especially
in hospitals, which were key factors of the recent outbreak. We suggest that
superspreaders are biologically contagious patients, and they may amplify the
spreads by going to potentially contagious places such as hospitals. To avoid
mass transmission in hospitals, it may be a good measure to treat suspected
cases without hospitalizing them. Finally, we indicate that SARS probably
propagates in small-world networks associated with human contacts and that the
biological nature of individuals and social group properties are factors more
important than the heterogeneous rates of social contacts among individuals.
This is in marked contrast with epidemics of sexually transmitted diseases or
computer viruses to which scale-free network models often apply.Comment: 4 figure
Aortic Insufficiency in LVAD Patients
Aortic insufficiency (AI) is a common complication that increases morbidity and mortality in patients with left ventricular assist devices (LVAD). Significant AI during LVAD support creates a substantial regurgitant flow loop, negatively affecting cardiac recovery and exposing blood to longer residence time and higher shear stress. The mechanism of AI development and progression is linked to a lack of aortic valve opening, which alters the valvular tissue mechanics. Pre-existing AI also worsens following LVAD implantation, interfering with the pump benefits. This chapter will evaluate AI development with LVAD support compared with naturally occurring AI and present the features, mechanisms, and links to clinical treatment options
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