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Bogotá, Colombia

Mejia M.,University of Los Andes, Colombia | Pena N.,University of Los Andes, Colombia | Munoz J.L.,Polytechnic University of Catalonia | Esparza O.,Polytechnic University of Catalonia | Alzate M.A.,University Distrital
Journal of Network and Computer Applications | Year: 2011

Cooperation among nodes is fundamental for the operation of mobile ad hoc networks (MANETs). In such networks, there could be selfish nodes that use resources from other nodes to send their packets but that do not offer their resources to forward packets for other nodes. Thus, a cooperation enforcement mechanism is necessary. Trust models have been proposed as mechanisms to incentive cooperation in MANETs and some of them are based on game theory concepts. Among game theoretic trust models, those that make nodes' strategies evolve genetically have shown promising results for cooperation improvement. However, current approaches propose a highly centralized genetic evolution which render them unfeasible for practical purposes in MANETs. In this article, we propose a trust model based on a non-cooperative game that uses a bacterial-like algorithm to let the nodes quickly learn the appropriate cooperation behavior. Our model is completely distributed, achieves optimal cooperation values in a small fraction of time compared with centralized algorithms, and adapts effectively to environmental changes. © 2010 Elsevier Ltd. All rights reserved. Source

Mejia M.,University Militar Nueva Granada | Mejia M.,University of Los Andes, Colombia | Pena N.,University of Los Andes, Colombia | Munoz J.L.,Polytechnic University of Catalonia | And 2 more authors.
Ad Hoc Networks | Year: 2012

The scarce resources of a mobile ad hoc network (MANET) should not be wasted attending selfish nodes (those nodes that use resources from other nodes to send their own packets, without offering their own resources to forward other nodes' packets). Thus, rational nodes (those nodes willing to cooperate if deemed worthy) must detect and isolate selfish nodes in order to cooperate only among themselves. To achieve this purpose, in this paper we present a new game theoretic trust model called DECADE (Distributed Emergent Cooperation through ADaptive Evolution). The design of DECADE is shown by first, analyzing a simple case of packet forwarding between two nodes, and then the results are extended to bigger networks. In DECADE, each node seeks individually to maximize its chance to deliver successfully their own packets, so that the cooperation among rational nodes and the isolation of selfish nodes appear as an emergent collective behavior. This behavior emerges as long as there is a highly dynamic interaction among nodes. So, for those cases where the mobility alone does not suffice to provide this interaction, DECADE includes a sociability parameter that encourages nodes to interact among them for faster learning and adaptability. Additionally, DECADE introduces very low overhead on computational and communication resources, achieving close to optimal cooperation levels among rational nodes and almost complete isolation of selfish nodes. © 2012 Elsevier B.V. All rights reserved. Source

Gaona-Barrera A.,University of Barcelona | Gaona-Barrera A.,University Distrital | Moreno-Arostegui J.M.,University of Barcelona
Computers and Electrical Engineering | Year: 2015

This paper introduces a new approach for the implementation of randomly interconnected neural networks on hardware taking into account the length of the synapses. We divide the synapses into Long and Short according to the distance between the source and target neurons in a 2D mesh, and we demonstrate that it is possible to guarantee the latency of the Long synapses when they are routed through an additional layer which is based on hierarchical structures of Networks on Chip (NoC). The connection scheme consists in grouping neurons into four regions and communicating their sets of synapses between a pair of them, using circuit switching. In order to validate the interconnection scheme, we simulated the operation of this additional layer for two regions in a neuronal network with grid structure arrangement comprising 1.03×106 neurons, with a firing rate of 100Hz and an average of 104 synapses per neuron. This pair of regions can support an average of 562 Long synapses per neuron, which is equivalent to managing 5% of the traffic generated by the grouped neurons, with the advantage of having the latency of the synapses guaranteed. A node of the one region has 30,528 neurons and operates with a throughput of 2.95 Millions of spikes per second (Mspk/s) approximately. In a complete operation, the additional layer has four regions and it would support 58 Mspk/s and 520,672 neurons of the network. © 2015 Elsevier Ltd. Source

Cortes-B. R.C.-B,University Distrital | Motley T.J.,Old Dominion University
Phytotaxa | Year: 2015

The Henriquezieae-Posoquerieae-Sipaneeae clade (Rubiaceae) is centered in the Guayana Region of Northern South America. The Henriquezieae and Sipaneeae contain a large number of taxa that are endemic to the Guayana Region, while the Posoquerieae exhibits a wider distribution throughout the Neotropics. In order to evaluate the phylogenetic relationships within this clade, and assess the evolution of selected morphological characters potentially important in its diversification, we performed parsimony analyses of ITS, trnL-F, rps16 and morphology, Bayesian Markov chain Monte Carlo analyses of the molecular data, and optimized six morphological characters on cpDNA trees. Results confirm the monophyly of each of the tribes, and that of the genera included in the study. The Sipaneeae are the earliest diverging lineage, sister to a well-supported Henriquezieae-Posoquerieae clade. Henriquezieae have many traits unique or atypical in Rubiaceae, a tendency observed in other lineages endemic to the Guayana Region, suggesting strong selection for morphological novelties necessary to colonize the extremely poor soils of this region. The pollen catapult mechanism originated in the Molopanthera-Posoqueria clade is perhaps unique in angiosperms, and may represent a novel strategy that played an important role in the early divergence that gave rise to both genera, and to the early radiation of the genus Posoqueria. Diversification of Posoqueria outside the Guayana Region probably was accompanied by a shift from capsular to baccate fruits that facilitated colonization of understory forests. Habit specialization may be considered a consistent factor in the diversification of the Guayanan-centered clade of the Rubiaceae. © 2015 Magnolia Press Source

Unsolicited bulk email (spam) nowadays accounts for nearly 75% of daily email traffic, a figure that speaks strongly for the need of finding better protection mechanisms against its dissemination. A clever trick recently exploited by email spammers in order to circumvent textual-based filters, involves obfuscation of black-listed words with visually equivalent text substitutions from non-alphabetic symbols, in such a way it still conveys the semantics of the original word to the human eye (e.g. masking viagra as v1@gr@ or as v-i-a-g-r-a). In this paper we discuss how a simple-yet-effective adaptation of a classical algorithm for string matching may meet this stylish challenge to effectively reveal the similarity between genuine spam-trigger terms with their disguised alpha-numeric variants. Source

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