553 research outputs found
Exact solution of bond percolation on small arbitrary graphs
We introduce a set of iterative equations that exactly solves the size
distribution of components on small arbitrary graphs after the random removal
of edges. We also demonstrate how these equations can be used to predict the
distribution of the node partitions (i.e., the constrained distribution of the
size of each component) in undirected graphs. Besides opening the way to the
theoretical prediction of percolation on arbitrary graphs of large but finite
size, we show how our results find application in graph theory, epidemiology,
percolation and fragmentation theory.Comment: 5 pages and 3 figure
Adaptive networks: coevolution of disease and topology
Adaptive networks have been recently introduced in the context of disease
propagation on complex networks. They account for the mutual interaction
between the network topology and the states of the nodes. Until now, existing
models have been analyzed using low-complexity analytic formalisms, revealing
nevertheless some novel dynamical features. However, current methods have
failed to reproduce with accuracy the simultaneous time evolution of the
disease and the underlying network topology. In the framework of the adaptive
SIS model of Gross et al. [Phys. Rev. Lett. 96, 208701 (2006)], we introduce an
improved compartmental formalism able to handle this coevolutionary task
successfully. With this approach, we analyze the interplay and outcomes of both
dynamical elements, process and structure, on adaptive networks featuring
different degree distributions at the initial stage.Comment: 11 pages, 8 figures, 1 appendix. To be published in Physical Review
Strategic tradeoffs in competitor dynamics on adaptive networks
Recent empirical work highlights the heterogeneity of social competitions
such as political campaigns: proponents of some ideologies seek debate and
conversation, others create echo chambers. While symmetric and static network
structure is typically used as a substrate to study such competitor dynamics,
network structure can instead be interpreted as a signature of the competitor
strategies, yielding competition dynamics on adaptive networks. Here we
demonstrate that tradeoffs between aggressiveness and defensiveness (i.e.,
targeting adversaries vs. targeting like-minded individuals) creates
paradoxical behaviour such as non-transitive dynamics. And while there is an
optimal strategy in a two competitor system, three competitor systems have no
such solution; the introduction of extreme strategies can easily affect the
outcome of a competition, even if the extreme strategies have no chance of
winning. Not only are these results reminiscent of classic paradoxical results
from evolutionary game theory, but the structure of social networks created by
our model can be mapped to particular forms of payoff matrices. Consequently,
social structure can act as a measurable metric for social games which in turn
allows us to provide a game theoretical perspective on online political
debates.Comment: 20 pages (11 pages for the main text and 9 pages of supplementary
material
Modeling the dynamical interaction between epidemics on overlay networks
Epidemics seldom occur as isolated phenomena. Typically, two or more viral
agents spread within the same host population and may interact dynamically with
each other. We present a general model where two viral agents interact via an
immunity mechanism as they propagate simultaneously on two networks connecting
the same set of nodes. Exploiting a correspondence between the propagation
dynamics and a dynamical process performing progressive network generation, we
develop an analytic approach that accurately captures the dynamical interaction
between epidemics on overlay networks. The formalism allows for overlay
networks with arbitrary joint degree distribution and overlap. To illustrate
the versatility of our approach, we consider a hypothetical delayed
intervention scenario in which an immunizing agent is disseminated in a host
population to hinder the propagation of an undesirable agent (e.g. the spread
of preventive information in the context of an emerging infectious disease).Comment: Accepted for publication in Phys. Rev. E. 15 pages, 7 figure
Propagation dynamics on networks featuring complex topologies
Analytical description of propagation phenomena on random networks has
flourished in recent years, yet more complex systems have mainly been studied
through numerical means. In this paper, a mean-field description is used to
coherently couple the dynamics of the network elements (nodes, vertices,
individuals...) on the one hand and their recurrent topological patterns
(subgraphs, groups...) on the other hand. In a SIS model of epidemic spread on
social networks with community structure, this approach yields a set of ODEs
for the time evolution of the system, as well as analytical solutions for the
epidemic threshold and equilibria. The results obtained are in good agreement
with numerical simulations and reproduce random networks behavior in the
appropriate limits which highlights the influence of topology on the processes.
Finally, it is demonstrated that our model predicts higher epidemic thresholds
for clustered structures than for equivalent random topologies in the case of
networks with zero degree correlation.Comment: 10 pages, 5 figures, 1 Appendix. Published in Phys. Rev. E (mistakes
in the PRE version are corrected here
Le raisonnement à base de logique propositionnelle à l'appui de la fusion et de la révision de bases de données géospatiales
Le but de ce mémoire était d’effectuer, dans un contexte géospatial, une comparai- son d’une approche de raisonnement qualitatif basée sur le PROLOG avec une autre approche reposant sur l’ASP. La principale question que nous posons est la suivante : Le moteur de raisonnement Smodels rendant possible la mise en oeuvre du raisonnement non monotone poussé et faisant intervenir le concept de modèle stable peut-il nous permettre de résoudre des problèmes de vérification de cohérence ontologique et des problèmes de révision dans le contexte de la géomatique ? Pour y répondre, nous avons procédé à une série de tests sur un échantillon de la Base nationale de données topographiques (BNDT). À la lumière des résultats obtenus, cette approche se montre très efficace et contribue à l’amélioration de la cohérence de l’information géospatiale et du raisonnement spatial réalisé à partir de cette dernière.The objective of this thesis is to make a comparison between a qualitative reasoning approach based on PROLOG with another approach based on ASP. Our principal research question was the following : Can the Smodels reasoning engine, allowing for advanced non monotonic reasoning and introducing the stable model concept, allow us to solve ontological consistency checking problems as well as revision problems in a geomatic context ? To answer this question, we carried out a series of tests on a cross-section from the National Topographical Database (NTDB). In the light of the results obtained, this approach has proven very effective and contributes to the amelioration of geospatial information consistency and to the resultant improvement in spatial reasoning
SensLAB Very Large Scale Open Wireless Sensor Network Testbed
International audienceThis paper presents a precise description of SensLAB: Very Large Scale Open Wireless Sensor Network Testbed that has been developed and deployed in order to allow the evaluation of scalable wireless sensor network protocols and applications. SensLAB's main and most important goal is to o er an accurate open access multi-users scienti c tool to support the design, development, tuning, and experimentation of real large-scale sensor network applications. The SensLAB testbed is composed of 1024 nodes and it is distributed among 4 sites. Two sites o er access to mobile nodes. Every sensor node is also able to be con gured as a sink node and can exchange data with any other sink node of the whole SensLAB testbed (locally or remotely) or any computer on the Internet. The hardware designed on purpose and software architectures that allow to reserve, con gure, deploy embedded software, boot wireless sensor nodes and gather experimental data and monitoring information are described in details. We also present short demonstration examples to illustrate the use of the SensLAB testbed
CARACTERISATION PERCEPTIVE DES VARIETES HYBRIDES CHINOISES DU MAÏS : LA SÉLECTIVITÉ SENSORIELLE EST-ELLE DÉTERMINANTE AU BÉNIN ?
Agricultural researches usually advocate high yielding competitive crop varieties in order to supply foodstuff to the increasing population. However, this is not to care for the social dimension of adoption in the technology transfer process. That is why the present paper acknowledges actors like producers, food processors, marketers and others, whose perception with respect to growing, harvesting and processing stages of maize, to be included in the perceptive evaluation of Chinese hybrid varieties at the research centers. Four new varieties of maize are promoted: T2 (Guidan 162), T3 (Jinguyuan 688), T4 (Jinyu No.8) and T5 (Xianyu 335). Actors compare new Chinese varieties of maize to their traditional ones. On the basis of a comparative appraisal index (CAI), ie. a new variety is likely to be adopted if the differences of score between its descriptors and those of the traditional variety are greater than zero. In terms of results, T2 and T4 are the most likely to be adopted in the South and the Center. In the North, on the contrary, T5 is substituted to T4. Because of a low performance on various descriptors, T3 is unlikely to be adopted. While in the south and the center of Benin, sensorial descriptors remain decisive in the adoption profile, agromorphological and harvest stage descriptors are more likely to affect adoption in the North. Based on the increasing economic importance of maize, actors’ perception in the North significantly matters in the process of adoption of new varieties
Propagation on networks: an exact alternative perspective
By generating the specifics of a network structure only when needed
(on-the-fly), we derive a simple stochastic process that exactly models the
time evolution of susceptible-infectious dynamics on finite-size networks. The
small number of dynamical variables of this birth-death Markov process greatly
simplifies analytical calculations. We show how a dual analytical description,
treating large scale epidemics with a Gaussian approximations and small
outbreaks with a branching process, provides an accurate approximation of the
distribution even for rather small networks. The approach also offers important
computational advantages and generalizes to a vast class of systems.Comment: 8 pages, 4 figure
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