Reciprocity of Networks with Degree Correlations and Arbitrary Degree Sequences

Although most of the real networks contain a mixture of directed and bidirectional (reciprocal) connections, the reciprocity $r$ has received little attention as a subject of theoretical understanding. We study the expected reciprocity of networks with an arbitrary degree sequence and a broad class of degree correlations by means of statistical ensemble approach. We demonstrate that degree correlations are crucial to understand the reciprocity in real networks and a hierarchy of correlation contributions to $r$ is revealed. Numerical experiments using novel network randomization methods show very good agreement to our analytical estimations.Comment: 8 pages, 3 figures, added a new table and a new figure, accepted for publication in Phys.Rev.

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

Order patterns networks (orpan) - A method to estimate time-evolving functional connectivity from multivariate time series

Complex networks provide an excellent framework for studying the function of the human brain activity. Yet estimating functional networks from measured signals is not trivial, especially if the data is non-stationary and noisy as it is often the case with physiological recordings. In this article we propose a method that uses the local rank structure of the data to define functional links in terms of identical rank structures. The method yields temporal sequences of networks which permits to trace the evolution of the functional connectivity during the time course of the observation. We demonstrate the potentials of this approach with model data as well as with experimental data from an electrophysiological study on language processing

From modular to centralized organization of synchronization in functional areas of the cat cerebral cortex

Recent studies have pointed out the importance of transient synchronization between widely distributed neural assemblies to understand conscious perception. These neural assemblies form intricate networks of neurons and synapses whose detailed map for mammals is still unknown and far from our experimental capabilities. Only in a few cases, for example the C. elegans, we know the complete mapping of the neuronal tissue or its mesoscopic level of description provided by cortical areas. Here we study the process of transient and global synchronization using a simple model of phase-coupled oscillators assigned to cortical areas in the cerebral cat cortex. Our results highlight the impact of the topological connectivity in the developing of synchronization, revealing a transition in the synchronization organization that goes from a modular decentralized coherence to a centralized synchronized regime controlled by a few cortical areas forming a Rich-Club connectivity pattern.Comment: 24 pages, 8 figures. Final version published in PLoS On

Exfoliated graphite flakes as soft-electrodes for precisely contacting nanoobjects

This is the post-peer reviewed version of the following article: P. ares et al. “Exfoliated graphite flakes as soft-electrodes for precisely contacting nanoobjects”. 2D Matererials, 2015, 2(3): 035008. Which has been published in final form at:http://dx.doi.org/10.1088/2053-1583/2/3/035008We introduce a simple, clean and reliable method to transfer exfoliated graphite flakes as soft-electrodes for the electrical contacts of nano-objects. The microelectrodes thus produced exhibit extremely well-defined and thin edges and can be placed at any sample location with sub-micrometer precision. The procedure is carried out under ambient conditions and does not require chemical agents. We present electrical characterization of relevant examples including carbon nanotubes, metal-organic MMX nanoribbons, reduced graphene sheets and damaged circuit repair. The quality of the electrical contacts thus obtained is as good as those fabricated with conventional techniques. This technique is particularly relevant for conductive atomic force microscopy (AFM) studiesThis work was supported by Consolider CSD2010-0024, MAD2D-CM, S2013/MIT-3007 and MAT2013-46753-C2-1 and

Perception Analysis for the Selection of Postgraduate Programs in Presential and Virtual Modality

The research proposed in this paper focuses on the analysis of perception for the selection of postgraduate programs in face-to-face and virtual modality in the Directorate of Postgraduate and Continuing Education of the ESPAM MFL. Although it is true, face-to-face education is of vital importance for the formation of a student, since it fixes their attention in place, time, and space, promoting social interaction that becomes a key to success in learning. However, in the last three years, in the face of adverse and unexpected situations, virtual university education has prepared to revolutionize the concept of learning beyond face-to-face learning. The objective of this research is inclined toward the description of the appreciation of students who have received master’s classes in both virtual and face-to-face modalities. In order to obtain the data that allowed defining the results and conclusions, a survey was applied through a Google Forms questionnaire with a total of 13 questions that determined the perception that 87 students have when selecting a postgraduate program, and it raised a descriptive investigation to represent the data found. Finally, with the information obtained, it was possible to show that the applicants reflect a favorable attitude toward learning in virtual environments, because it allows them to continue with their other activities and foster skills with the use of technological tools that contribute to creativity, innovation, and arouse interest in learning. Keywords: fourth level, education, face-to-face, online. Resumen La investigación planteada en el presente trabajo, se centra en el análisis de percepción para la selección de programas de posgrado en modalidad presencial y virtual en la Dirección de Posgrado y Educación Continua de la ESPAM MFL. Si bien es cierto, la educación presencial es de vital importancia para la formación de un estudiante, ya que esta fija su atención en lugar, tiempo y espacio, promoviendo la interacción social que se convierte en una clave de éxito para el aprendizaje; no obstante, en los últimos tres años, frente a situaciones adversas e inesperadas, mediante la educación virtual universitaria se logró revolucionar el concepto del aprendizaje más allá de la presencialidad. El objetivo de esta investigación, se inclina en la descripción de las apreciaciones de los estudiantes que han recibido clases de maestría tanto en modalidad virtual como presencial. Para la obtención de los datos que permitieron definir los resultados y las conclusiones, se aplicó una encuesta mediante un cuestionario de Google Forms con un total de 13 preguntas que definen la percepción que tienen 87 estudiantes al momento de seleccionar un programa de posgrado y se planteó una investigación descriptiva para representar los datos encontrados. Finalmente, con la información obtenida se pudo evidenciar que los postulantes reflejan una actitud favorable con el aprendizaje en entornos virtuales, debido a que les permite continuar con sus demás actividades y fomentar las habilidades con el uso de herramientas tecnológicas que contribuyen a la creatividad, innovación y despiertan el interés de aprender. Palabras Clave: cuarto nivel, educación, presencial, en línea

Espécies arbóreas nativas da amazônia ocidental brasileira com potencial para arborização de pastagens.

Esta revisão teve como objetivo reunir informações sobre algumas espécies de árvores nativas da Amazônia Ocidental tomando como base a lista apresentada por Franke (1999) e enfatizando características intrínsecas de cada espécie e de fácil visualização com o intuito de auxiliar técnicos, pesquisadores e estudantes na identificação das mesmas no campo. Jacarandá copaia (Aubl) D. Donbitstream/CPAF-RO-2010/13296/1/doc127-arborizacaodepastagens.pd