The Spread of Opinions and Proportional Voting

Election results are determined by numerous social factors that affect the formation of opinion of the voters, including the network of interactions between them and the dynamics of opinion influence. In this work we study the result of proportional elections using an opinion dynamics model similar to simple opinion spreading over a complex network. Erdos-Renyi, Barabasi-Albert, regular lattices and randomly augmented lattices are considered as models of the underlying social networks. The model reproduces the power law behavior of number of candidates with a given number of votes found in real elections with the correct slope, a cutoff for larger number of votes and a plateau for small number of votes. It is found that the small world property of the underlying network is fundamental for the emergence of the power law regime.Comment: 10 pages, 7 figure

Determinación de vitaminas del Complejo B en Arthrospira maxima por cromatografía líquida de alta resolución

Se diseñan dos métodos para la extracción de las vitaminas del complejo B en muestras de Arthrospira maximacubana. Para la determinación, se emplea un sistema HPLC formado por una columna de octadecilsilano y fasesmóviles de metanol - agua - ácido fosfórico 0.1 mol/L (20:79.5:0.5) para el análisis de la cianocobalamina y (30:69.5:0.5)para el resto de las vitaminas, empleando hexanosulfonato sódico 5 mM en ambos casos. Las velocidades de flujoson de 1 y 0.8 mL/min respectivamente. La determinación se realiza a 362 y 270 nm. Se observó que la Arthrospiramaxima cultivada en Cuba constituye una rica fuente de vitaminas del grupo B presentando un contenido promediode 3.1 mg/10g de tiamina, 4.0 mg/10g de riboflavina, 9.0 mg/10g de piridoxina, 0.29 mg/10g de cianocobalamina, 21mg/10g de ácido nicotínico y 26 mg/10g de nicotinamida

Fast Community Identification by Hierarchical Growth

A new method for community identification is proposed which is founded on the analysis of successive neighborhoods, reached through hierarchical growth from a starting vertex, and on the definition of communities as a subgraph whose number of inner connections is larger than outer connections. In order to determine the precision and speed of the method, it is compared with one of the most popular community identification approaches, namely Girvan and Newman's algorithm. Although the hierarchical growth method is not as precise as Girvan and Newman's method, it is potentially faster than most community finding algorithms.Comment: 6 pages, 5 figure

A systematic comparison of supervised classifiers

Pattern recognition techniques have been employed in a myriad of industrial, medical, commercial and academic applications. To tackle such a diversity of data, many techniques have been devised. However, despite the long tradition of pattern recognition research, there is no technique that yields the best classification in all scenarios. Therefore, the consideration of as many as possible techniques presents itself as an fundamental practice in applications aiming at high accuracy. Typical works comparing methods either emphasize the performance of a given algorithm in validation tests or systematically compare various algorithms, assuming that the practical use of these methods is done by experts. In many occasions, however, researchers have to deal with their practical classification tasks without an in-depth knowledge about the underlying mechanisms behind parameters. Actually, the adequate choice of classifiers and parameters alike in such practical circumstances constitutes a long-standing problem and is the subject of the current paper. We carried out a study on the performance of nine well-known classifiers implemented by the Weka framework and compared the dependence of the accuracy with their configuration parameter configurations. The analysis of performance with default parameters revealed that the k-nearest neighbors method exceeds by a large margin the other methods when high dimensional datasets are considered. When other configuration of parameters were allowed, we found that it is possible to improve the quality of SVM in more than 20% even if parameters are set randomly. Taken together, the investigation conducted in this paper suggests that, apart from the SVM implementation, Weka's default configuration of parameters provides an performance close the one achieved with the optimal configuration

Accelerating networks

Evolving out-of-equilibrium networks have been under intense scrutiny recently. In many real-world settings the number of links added per new node is not constant but depends on the time at which the node is introduced in the system. This simple idea gives rise to the concept of accelerating networks, for which we review an existing definition and -- after finding it somewhat constrictive -- offer a new definition. The new definition provided here views network acceleration as a time dependent property of a given system, as opposed to being a property of the specific algorithm applied to grow the network. The defnition also covers both unweighted and weighted networks. As time-stamped network data becomes increasingly available, the proposed measures may be easily carried out on empirical datasets. As a simple case study we apply the concepts to study the evolution of three different instances of Wikipedia, namely, those in English, German, and Japanese, and find that the networks undergo different acceleration regimes in their evolution.Comment: 12 pages, 8 figure

Loose Leaf Lettuce Quality Grown in Two Production Systems

Horticultural crops have a strong impact on human nutrition. Lettuce is the most important leafy vegetable in Argentina and it is cultivated mainly in green belts, in greenhouses or open field. The aim of this study was to evaluate growth and phytonutrients concentration of leaf lettuce under greenhouse and field production. Crop establishment was made from seedlings produced in a commercial greenhouse. Loose lettuce cv. Brisa was used for field and greenhouse growth. Experimental design with complete random block with 4 replicates per treatment was used. Fresh and dry weights of shoot, number of leaves, color, ascorbic acid, chlorophyll content were measured. Absolute and relative growth rate and commercial yield were calculated. Lettuce grown under greenhouse system showed, as expected, a higher value of fresh and dry weight, number of leaves, leaf area, yield and absolute and relative growth rate. Ascorbic acid value of the leaves decreased during lettuce growth in both production systems. Chlorophyll content was higher in the greenhouse cultivation but the antioxidant capacity was lower in lettuce leaves from greenhouse than the leaves grown on open field