Optimal map of the modular structure of complex networks

Modular structure is pervasive in many complex networks of interactions observed in natural, social and technological sciences. Its study sheds light on the relation between the structure and function of complex systems. Generally speaking, modules are islands of highly connected nodes separated by a relatively small number of links. Every module can have contributions of links from any node in the network. The challenge is to disentangle these contributions to understand how the modular structure is built. The main problem is that the analysis of a certain partition into modules involves, in principle, as many data as number of modules times number of nodes. To confront this challenge, here we first define the contribution matrix, the mathematical object containing all the information about the partition of interest, and after, we use a Truncated Singular Value Decomposition to extract the best representation of this matrix in a plane. The analysis of this projection allow us to scrutinize the skeleton of the modular structure, revealing the structure of individual modules and their interrelations.Comment: 21 pages, 10 figure

Propuesta de Educación Ambiental incluyente para personas con discapacidad visual, en el Jardín Botánico de la Universidad Tecnológica de Pereira.

La educación ambiental como herramienta para la concientización de la población en torno a la problemática ambiental local y mundial, permite integrar a todo tipo de público, desde niños hasta personas mayores y de todas las razas. En Colombia, la Política Nacional de Educación Ambiental promueve la integración de diferentes grupos de personas en los procesos educativos. El Jardín Botánico Universidad Tecnológica de Pereira es reconocido a nivel regional por su compromiso con la educación ambiental teniendo como referentes los programas educativos que se desarrollan para la protección del Bosque Andino sus especies de flora y fauna. Es así como la Propuesta de Educación Ambiental incluyente para personas con discapacidad visual, en el Jardín Botánico de la Universidad Tecnológica de Pereira, pretende acercar el proceso a personas con discapacidad visual, a través de las estrategias Senderos Amigables para la comunidad Invidente, Herramientas didácticas y Audiodescripción

A proof of uniform convergence over time for a distributed particle filter

Distributed signal processing algorithms have become a hot topic during the past years. One class of algorithms that have received special attention are particles filters (PFs). However, most distributed PFs involve various heuristic or simplifying approximations and, as a consequence, classical convergence theorems for standard PFs do not hold for their distributed counterparts. In this paper, we analyze a distributed PF based on the non-proportional weight-allocation scheme of Bolic et al (2005) and prove rigorously that, under certain stability assumptions, its asymptotic convergence is guaranteed uniformly over time, in such a way that approximation errors can be kept bounded with a fixed computational budget. To illustrate the theoretical findings, we carry out computer simulations for a target tracking problem. The numerical results show that the distributed PF has a negligible performance loss (compared to a centralized filter) for this problem and enable us to empirically validate the key assumptions of the analysis.This work was supported by Ministerio de Economia y Competitividad of Spain (project COMPREHENSION TEC2012 38883 C02 01), Comunidad de Madrid (project CASI CAM CM S2013/ICE 2845) and the Office of Naval Research Global (award no. N62909 15 1 2011

On the use of the channel second-order statistics in MMSE receivers for time- and frequency-selective MIMO transmission systems

Equalization of unknown frequency- and time-selective multiple input multiple output (MIMO) channels is often carried out by means of decision feedback receivers. These consist of a channel estimator and a linear filter (for the estimation of the transmitted symbols), interconnected by a feedback loop through a symbol-wise threshold detector. The linear filter is often a minimum mean square error (MMSE) filter, and its mathematical expression involves second-order statistics (SOS) of the channel, which are usually ignored by simply assuming that the channel is a known (deterministic) parameter given by an estimate thereof. This appears to be suboptimal and in this work we investigate the kind of performance gains that can be expected when the MMSE equalizer is obtained using SOS of the channel process. As a result, we demonstrate that improvements of several dBs in the signal-to-noise ratio needed to achieve a prescribed symbol error rate are possible

Importance sampling with transformed weights

The importance sampling (IS) method lies at the core of many Monte Carlo-based techniques. IS allows the approximation of a target probability distribution by drawing samples from a proposal (or importance) distribution, different from the target, and computing importance weights (IWs) that account for the discrepancy between these two distributions. The main drawback of IS schemes is the degeneracy of the IWs, which significantly reduces the efficiency of the method. It has been recently proposed to use transformed IWs (TIWs) to alleviate the degeneracy problem in the context of population Monte Carlo, which is an iterative version of IS. However, the effectiveness of this technique for standard IS is yet to be investigated. The performance of IS when using TIWs is numerically assessed, and showed that the method can attain robustness to weight degeneracy thanks to a bias/variance trade-off.This work was supported by the Ministerio de Economía y Competitividad of Spain (projects TEC2012-38883-C02-01 and TEC2015-69868-C2-1-R) and the Office of Naval Research Global (award no. N62909-15-1-2011

Degradación fotocatalítica de la fluoresceína

El color ha tenido un gran significado en las diversas sociedades humanas desde que el hombre comenzó a teñir sus ropas y otros objetos; este fenómeno es el resultado de una compleja serie de respuestas fisiológicas a las radiaciones de longitud de onda situadas en el intervalo 400-750nm, cuando estas inciden en la retina del ojo [8]. En la naturaleza se pueden distinguir gran diversidad de colores, entre ellos los del colibrí o las plumas del pavo real, los cuales se originan por la difracción de la luz en ellos, gracias a la estructura única de las plumas, pero la mayor parte de los colores que se ven en la naturaleza se deben a la absorción de ciertas longitudes de onda de luz visible por los compuestos orgánicos, tales como los colorantes los cuales son sustancias coloreadas que se utilizan para dar color a un objeto determinado o a una tela. [8] El vertido incontrolado de residuos industriales y municipales a ríos y lagos, está causando serios problemas a los recursos hídricos de muchas regiones [15]. La composición de las aguas residuales causa graves impactos cuando se enfrenta a las áreas naturales; un alto contenido de materia orgánica origina el agotamiento del oxígeno disuelto, que tiene un efecto inverso sobre el sistema ecológico. El nitrógeno y el fósforo también conducen a un agotamiento del oxígeno disuelto (es decir, eutrofización) [10], por esto la contaminación del agua reviste gran importancia ya que los contaminantes pueden afectar el equilibrio silvestre y por ende la salud humana.[11] La problemática ambiental planteada a escala mundial por la presencia de altas concentraciones de contaminantes de todo tipo en aguas, [15] ha llevado a que el desarrollo industrial de los países requieran de una constante investigación dirigida hacia la implementación de una tecnología actualizada y adecuada a las 8 necesidades que se plantean en cada momento, tanto de carácter económico, como social y ambiental

Algoritmo genético para solucionar el problema de dimensionamiento y programación de lotes con costos de alistamiento dependientes de la secuencia

The main purpose of this paper is to develop a hybrid genetic algorithmin order to determine the lot sizes and their production scheduling in asingle machine manufacturing system for multi-item orders, the objectivefunction minimizes the sum of holding costs, tardy costs and setup costs.The problem considers a set of orders to be processed each one with itsown due date. Each order must be delivered complete. In the schedulingare considered sequence dependent setup times. The proposed hybridgenetic algorithm has embedded a heuristic that is used to calculate itsfitness function. The heuristic method presents a modification on theoptimal timming algorithm in which are involved sequence dependentset up times. A design of experiments is developed in order to assess thealgorithm performance, which is also tested using random-generateddata and results are compared with those generated by an exact method.The results show that the algorithm achieves a good performance in bothsolution quality and time especially for large instances.El objetivo de este artículo es desarrollar un algoritmo genético el cualpermita determinar los tamaños de lote de producción y su programaciónen un sistema de manufactura de una máquina para órdenesmultiproducto, cuya función objetivo minimiza la suma de los costosde inventario por terminaciones tardías y de alistamiento. El problemacontempla un conjunto de órdenes a ser procesadas con sus respectivasfechas de entrega. Cada orden debe ser entregada en su totalidad. Dentrode la programación de los trabajos se consideran tiempos de alistamientodependientes de la secuencia. En la metaheurística implementada se utilizade manera embebida un método heurístico para el cálculo de la funciónde adaptación. El método heurístico presentado es una variación delOptimal Timming Algorithm el cual involucra los tiempos de alistamientodependientes de la secuencia. Se desarrolla un diseño de experimentospara probar el desempeño del algoritmo utilizando instancias generadasde forma aleatoria y comparando sus soluciones contra las encontradaspor un método exacto. Los resultados muestran que el algoritmo lograun buen desempeño tanto en tiempo de ejecución como en calidad de lasolución especialmente en instancias grandes.

Active learning in Operations Management: interactive multimedia software for teaching JIT/Lean Production

Purpose: Information & Communication Technologies (ICT) can be a fundamental aid for the design of new teaching methods that better adapt to the framework of the European Higher Education Area. In this context, this study aims to develop and assess a complex and truly interactive ICT-based teaching tool for instruction in OM. Design/methodology/approach: A multimedia application for Just-in-Time (JIT) / Lean Production has been conceived, designed and assessed. A constructivist focus was followed in its conception and design to encourage active and flexible learning adapted to each individual’s own requirements. Using empirical research the tool has been assessed by students and compared to the traditional teaching methods. Findings: The interactive multimedia application has been clearly valued for the way it conveys information and for its usability, for the way the application is structured and the improvements to students’ understanding of the knowledge. Students are also in favour of ICT being incorporated into teaching over more traditional methods. The assessment took students’ gender and the average overall mark on their academic records as control variables but, broadly-speaking, no significant differences were found. Research limitations/implications: The study was carried out in a controlled environment and not in the normal on-site university teaching process. Conclusions could be extended to OM and other related subjects, especially if they make use of similar tools to the one described in this paper. Practical implications: This study provides a contribution that allows reflections to be made on the design of specific software for OM and students’ perceptions when using it. Originality/value: Through this paper we contribute to an improvement in learning methods in general and to higher education in OM in particular.Peer Reviewe