70 research outputs found
Algorithms for nonuniform networks
In this thesis, observations on structural properties of natural networks are taken as a starting point for developing efficient algorithms for natural instances of different graph problems. The key areas discussed are sampling, clustering, routing, and pattern mining for large, nonuniform graphs. The results include observations on structural effects together with algorithms that aim to reveal structural properties or exploit their presence in solving an interesting graph problem.
Traditionally networks were modeled with uniform random graphs, assuming that each vertex was equally important and each edge equally likely to be present. Within the last decade, the approach has drastically changed due to the numerous observations on structural complexity in natural networks, many of which proved the uniform model to be inadequate for some contexts.
This quickly lead to various models and measures that aim to characterize topological properties of different kinds of real-world networks also beyond the uniform networks. The goal of this thesis is to utilize such observations in algorithm design, in addition to empowering the process of network analysis. Knowing that a graph exhibits certain characteristics allows for more efficient storage, processing, analysis, and feature extraction.
Our emphasis is on local methods that avoid resorting to information of the graph structure that is not relevant to the answer sought. For example, when seeking for the cluster of a single vertex, we compute it without using any global knowledge of the graph, iteratively examining the vicinity of the seed vertex. Similarly we propose methods for sampling and spanning-tree construction according to certain criteria on the outcome without requiring knowledge of the graph as a whole.
Our motivation for concentrating on local methods is two-fold: one driving factor is the ever-increasing size of real-world problems, but an equally important fact is the nonuniformity present in many natural graph instances; properties that hold for the entire graph are often lost when only a small subgraph is examined.reviewe
Agrupamiento local en grafos dirigidos
En este trabajo se presenta un método de agrupamiento local en grafos dirigidos: dado un vértice semilla, se determinó el grupo de vértices al que pertenece de tal forma que los vértices seleccionados sean estructuralmente cercanos de la semilla. A un grafo dirigido se le puede asociar una cadena de Markov que corresponde a una caminata aleatoria ciega en el grafo. Se aprovechó esta conexión para expresar cercanía estructural en términos de los tiempos de absorción para detectar vértices que son “cercanos” al vértice semilla. Se detectó el grupo de un vértice a través de caminatas aleatorias cortas repetidas desde el vértice semilla, analizando la frecuencia de visitas a los otros vértices. Se experimentó con grafos pequeños para comparar el resultado los tiempos exactos de absorción. El agrupamiento local puede ser aplicado a diferentes fenómenos reales, por ejemplo, en propagación de epidemias, balanceo de carga, etc
Studying the effects of instance structure in algorithm performance
the amount of resources consumed in the worst case. However, it has become evident that the instance size by itself is an insufficient measure and that the worst-case scenario is often unin-formative in practice. As a complementary analysis, we propose the examination of structural properties present in the instances and the effects they have on algorithm performance; our goal is to characterize complexity in terms of instance structure. We propose a framework for identifying and characterizing hard instances based on algorithm behaviour as well as a case study applying the framework on the graph coloring problem
Sequência didática da divisão no conjunto dos números naturais
Este artigo é um recorte da pesquisa Inovando o Currículo de Matemática através da Incorporação das Novas Tecnologias, do Grupo de Estudos Curriculares de Educação Matemática (GECEM), da ULBRA, em convênio com o Grupo de Tecnologias Educativas, da Universidade de La Laguna, Tenerife, Espanha. Esta parceria desenvolveu o Sistema Integrado de Ensino e Aprendizagem (SIENA) que é um sistema inteligente para apoio ao desenvolvimento do processo de ensino e aprendizagem de um conteúdo qualquer. O SIENA é composto por um grafo, onde cada nodo está ligado a um teste adaptativo, que gera o mapa individualizado das dificuldades do estudante, e uma sequência didática, que visa à recuperação das dificuldades de cada aluno. Foi desenvolvido, nessa pesquisa, o ambiente de investigação, no sistema SIENA, com o tema Divisão nos Números Naturais, para o 4º, 5º e 6º anos do Ensino Fundamental, visando desenvolver atividades para alunos que apresentam Necessidades Educativas Especiais (NEE), ou seja, alunos que necessitam de recuperação de conteúdos. O conceito de divisão está desenvolvido conforme as indicações metodológicas de Vergnaud (1991). Todo o trabalho com o tema proposto está implementado no sistema SIENA, no servidor da Matemática da Universidade Luterana do Brasil (ULBRA)
Assortative and modular networks are shaped by adaptive synchronization processes
Modular organization and degree-degree correlations are ubiquitous in the connectivity structure of biological, technological, and social interacting systems. So far most studies have concentrated on unveiling both features in real world networks, but a model that succeeds in generating them simultaneously is needed. We consider a network of interacting phase oscillators, and an adaptation mechanism for the coupling that promotes the connection strengths between those elements that are dynamically correlated. We show that, under these circumstances, the dynamical organization of the oscillators shapes the topology of the graph in such a way that modularity and assortativity features emerge spontaneously and simultaneously. In turn, we prove that such an emergent structure is associated with an asymptotic arrangement of the collective dynamical state of the network into cluster synchronization
Panel 1. The audio description process
Same film, different audio descriptions? On audience design and purpose of AD / Iwona Mazur (Adam Mickiewicz University) ; The impact of pre-recorded audio description on the description process for theatre / Nina Reviers (University of Antwerp) ; Analyzing translation process of professional and novice audiodescribers / Alexandra Frazão Seoane (State University of Ceará), Paula Lenz Costa Lima (State University of Ceará) ; Is audio describing writing or translating? / Anna Jankowska (University of Antwerp) ; The French-German TADS project: a multi method approach to the translation of AD scripts / Nathalie Mälzer (Stiftung Universität Hildesheim) ; Eva Schaeffer-Lacroix (Stiftung Universität Hildesheim ), Maria Wünsche (Stiftung Universität Hildesheim) ; Upcycling audio descriptions: towards a more sustainable model / Estel·la Oncins (Universitat Autònoma de Barcelona). Chair: Elisa Perego (University of Trieste
- …