Bogotá, Colombia
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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


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.


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.


Melgarejo R.M.A.,University Distrital | Obregon N.N.,Pontifical Xavierian University
2014 IEEE Conference on Norbert Wiener in the 21st Century: Driving Technology's Future, 21CW 2014 - Incorporating the Proceedings of the 2014 North American Fuzzy Information Processing Society Conference, NAFIPS 2014, Conference Proceedings | Year: 2014

This paper presents a design approach for a fuzzy cellular automaton based on an inverse entropy optimization principle. The cells of the automaton are characterized by two state variables computed by dynamic TSK fuzzy systems. The state variables of the cells are understood as spatial information sources so that the entropy of the binary sequences produced by the cells is maximized in a given instant. An evolutionary mechanism like the Differential Evolution Algorithm has been used to solve the optimization problem effectively since entropy reveals a convex landscape. Results show different regimes of operation for the fuzzy automata can be obtained. Among these regimes, there is one in which the cell entropy fluctuates over the maximum limit and the automata exhibit interesting behaviors so that it can be used as a model of several complex phenomena. © 2014 IEEE.


Pinzon C.M.,University Distrital | Rojas-Galeano S.,University Distrital
2015 10th Colombian Computing Conference, 10CCC 2015 | Year: 2015

User-generated text is the primary source of interaction in virtual communities on Web2.0 applications such as forums, blogs or social networks. Unfortunately some users abuse this freedom of speech liberty to disseminate non-authorised profanity content (foul language, insults, advertisement, boosting or denigration of a name or a trademark). Naïve filters based on literal comparisons against black-lists of forbidden terms, fail to detect variations obtained by character transliteration or masking (e.g. writing piss as P!55 or p.i.s.s). Recent approaches to this problem inspired in sequence alignment methods from comparative genomics in bioinformatics, have shown promise in preventing overlooking such variants. Building upon those results we have developed an experimental Web forum allowing users to generate text that is screened against transliterated profanity. In this paper we introduce the software (ForumForte) and describe briefly the technique and engineering behind it. We anticipate this kind of tools might prove beneficial for content moderation in mainstream applications such as newspaper forums and micro-blogging social networking sites. Our software is open-source under the New BSD License and is available at: http://tinyurl.com/ForumForte. © 2015 IEEE.


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.


Cortes R.,University Distrital
Novon | Year: 2014

Retiniphyllum francoanum Cortés-Ballén (Rubiaceae), a species restricted to the westernmost limit of the Guayana Shield in Colombia, is described. It differs from the other known species of the genus by the ovaries with seven or eight locules, and from its closest relative, R. secundiflorum Bonpl., by the shorter inflorescences, bracteole shape, colleters inside bracteoles, longer corolla tube, turbinate ovary, and by the winged and smaller pyrenes.


Barrera M.A.R.,University Distrital | Carpes W.P.,Jr.
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Year: 2016

Walter Pereira Carpes Jr,Purpose - The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach - In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings - Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-Term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were implemented with the ECM and compared with those obtained via Ansys - high frequency structure simulator commercial software simulations. Originality/value - The lack of a model of dielectric effective permittivity for the ECM causes a restricted search space in the stochastic FSS design process limited to only geometric parameters, as it is reported in the available literature. The proposed approach simplifies and makes more flexible the design process, and allows guiding the FSS design to unit cell surface and/or dielectric thickness of small dimensions. © Emerald Group Publishing Limited.


Chamorro H.R.,University of Los Andes, Colombia | Diaz N.L.,University Distrital
45th North American Power Symposium, NAPS 2013 | Year: 2013

With the increasing rate of Renewable Energy Sources (RES) installed and the different Microgrids schemes implemented around the world, it has done necessary to develop intelligent and autonomous control strategies to deal with the power flow and load sharing requirements. In this document, a hierarchical controller based on a Multi-agents Systems (MAS) methodology applied to low voltage Microgrids is proposed. The control strategy designed regulates the active and reactive power flow in both operation modes: grid connected and standalone, where is located some local controllers designed with fuzzy logic. Global multi-agent strategy can reconfigure and synchronize the system under new load states, supervising the Voltage Source Converter (VSC) units providing bidirectional energy flow by managing the modulation signals. Different cases are studied in simulation demonstrating the methodology adaptability and flexibility control. Conclusions and future work are given. © 2013 IEEE.


Rojas H.,National University of Colombia | Cortes C.,National University of Colombia | Santamaria F.,University Distrital
2012 31st International Conference on Lightning Protection, ICLP 2012 | Year: 2012

In recent years, several activities have been carried out by EMC-UNC (research group) to measure, study and classify the parameters of lightning electric fields signals in Bogotá, Colombia. However, measurements are distorted and exhibit significant noise levels caused by undesired signals from the electromagnetic environment together with other types of disturbances produced by the measuring system, which inevitably introduces noise in signal measurements. This paper shows the results of applying the fractional Fourier transform (FRFT) as an alternative technique to reduce the presence of noise and also of undesired signal components within a set of electric field signatures. Basic conditions to carry out the filtering process in the fractional Fourier domain (FRFd) are presented. Afterwards, some lightning electric field temporal characteristics are analyzed by using the processed signatures. Important differences between processed and measured waveforms are observed. © 2012 IEEE.

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