1,217 research outputs found
Reactive immunization on complex networks
Epidemic spreading on complex networks depends on the topological structure
as well as on the dynamical properties of the infection itself. Generally
speaking, highly connected individuals play the role of hubs and are crucial to
channel information across the network. On the other hand, static topological
quantities measuring the connectivity structure are independent on the
dynamical mechanisms of the infection. A natural question is therefore how to
improve the topological analysis by some kind of dynamical information that may
be extracted from the ongoing infection itself. In this spirit, we propose a
novel vaccination scheme that exploits information from the details of the
infection pattern at the moment when the vaccination strategy is applied.
Numerical simulations of the infection process show that the proposed
immunization strategy is effective and robust on a wide class of complex
networks
Controlling edge dynamics in complex networks
The interaction of distinct units in physical, social, biological and
technological systems naturally gives rise to complex network structures.
Networks have constantly been in the focus of research for the last decade,
with considerable advances in the description of their structural and dynamical
properties. However, much less effort has been devoted to studying the
controllability of the dynamics taking place on them. Here we introduce and
evaluate a dynamical process defined on the edges of a network, and demonstrate
that the controllability properties of this process significantly differ from
simple nodal dynamics. Evaluation of real-world networks indicates that most of
them are more controllable than their randomized counterparts. We also find
that transcriptional regulatory networks are particularly easy to control.
Analytic calculations show that networks with scale-free degree distributions
have better controllability properties than uncorrelated networks, and
positively correlated in- and out-degrees enhance the controllability of the
proposed dynamics.Comment: Preprint. 24 pages, 4 figures, 2 tables. Source code available at
http://github.com/ntamas/netctr
Effect of correlations on network controllability
A dynamical system is controllable if by imposing appropriate external
signals on a subset of its nodes, it can be driven from any initial state to
any desired state in finite time. Here we study the impact of various network
characteristics on the minimal number of driver nodes required to control a
network. We find that clustering and modularity have no discernible impact, but
the symmetries of the underlying matching problem can produce linear, quadratic
or no dependence on degree correlation coefficients, depending on the nature of
the underlying correlations. The results are supported by numerical simulations
and help narrow the observed gap between the predicted and the observed number
of driver nodes in real networks
Multiple Scale-Free Structures in Complex Ad-Hoc Networks
This paper develops a framework for analyzing and designing dynamic networks
comprising different classes of nodes that coexist and interact in one shared
environment. We consider {\em ad hoc} (i.e., nodes can leave the network
unannounced, and no node has any global knowledge about the class identities of
other nodes) {\em preferentially grown networks}, where different classes of
nodes are characterized by different sets of local parameters used in the
stochastic dynamics that all nodes in the network execute. We show that
multiple scale-free structures, one within each class of nodes, and with
tunable power-law exponents (as determined by the sets of parameters
characterizing each class) emerge naturally in our model. Moreover, the
coexistence of the scale-free structures of the different classes of nodes can
be captured by succinct phase diagrams, which show a rich set of structures,
including stable regions where different classes coexist in heavy-tailed and
light-tailed states, and sharp phase transitions. Finally, we show how the
dynamics formulated in this paper will serve as an essential part of {\em
ad-hoc networking protocols}, which can lead to the formation of robust and
efficiently searchable networks (including, the well-known Peer-To-Peer (P2P)
networks) even under very dynamic conditions
Highly intensive data dissemination in complex networks
This paper presents a study on data dissemination in unstructured
Peer-to-Peer (P2P) network overlays. The absence of a structure in unstructured
overlays eases the network management, at the cost of non-optimal mechanisms to
spread messages in the network. Thus, dissemination schemes must be employed
that allow covering a large portion of the network with a high probability
(e.g.~gossip based approaches). We identify principal metrics, provide a
theoretical model and perform the assessment evaluation using a high
performance simulator that is based on a parallel and distributed architecture.
A main point of this study is that our simulation model considers
implementation technical details, such as the use of caching and Time To Live
(TTL) in message dissemination, that are usually neglected in simulations, due
to the additional overhead they cause. Outcomes confirm that these technical
details have an important influence on the performance of dissemination schemes
and that the studied schemes are quite effective to spread information in P2P
overlay networks, whatever their topology. Moreover, the practical usage of
such dissemination mechanisms requires a fine tuning of many parameters, the
choice between different network topologies and the assessment of behaviors
such as free riding. All this can be done only using efficient simulation tools
to support both the network design phase and, in some cases, at runtime
Predicting link directions via a recursive subgraph-based ranking
Link directions are essential to the functionality of networks and their
prediction is helpful towards a better knowledge of directed networks from
incomplete real-world data. We study the problem of predicting the directions
of some links by using the existence and directions of the rest of links. We
propose a solution by first ranking nodes in a specific order and then
predicting each link as stemming from a lower-ranked node towards a
higher-ranked one. The proposed ranking method works recursively by utilizing
local indicators on multiple scales, each corresponding to a subgraph extracted
from the original network. Experiments on real networks show that the
directions of a substantial fraction of links can be correctly recovered by our
method, which outperforms either purely local or global methods.Comment: 6 pages, 5 figures; revised arguments for methods section; figures
replotted; minor revision
- …