Navegando por Palavras-chave "Graph"

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    Decreased centrality of subcortical regions during the transition to adolescence: A functional connectivity study
    (Elsevier B.V., 2015-01-01) Sato, Joao Ricardo [UNIFESP]; Salum, Giovanni Abrahao; Gadelha, Ary [UNIFESP]; Vieira, Gilson; Zugman, Andre [UNIFESP]; Picon, Felipe Almeida; Pan, Pedro Mario [UNIFESP]; Hoexter, Marcelo Queiroz [UNIFESP]; Anes, Mauricio; Moura, Luciana Monteiro [UNIFESP]; Gomes Del'Aquilla, Marco Antonio [UNIFESP]; Crossley, Nicolas; Amaro Junior, Edson; Mcguire, Philip; Lacerda, Acioly L. T. [UNIFESP]; Rohde, Luis Augusto; Miguel, Euripedes Constantino; Jackowski, Andrea Parolin [UNIFESP]; Bressan, Rodrigo Affonseca [UNIFESP]; Universidade Federal do ABC (UFABC); Univ Fed Rio Grande do Sul; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP); Kings Coll London; CNPq
    Investigations of brain maturation processes are a key step to understand the cognitive and emotional changes of adolescence. Although structural imaging findings have delineated clear brain developmental trajectories for typically developing individuals, less is known about the functional changes of this sensitive development period. Developmental changes, such as abstract thought, complex reasoning, and emotional and inhibitory control, have been associated with more prominent cortical control. the aim of this study is to assess brain networks connectivity changes in a large sample of 7- to 15-year-old subjects, testing the hypothesis that cortical regions will present an increasing relevance in commanding the global network. Functional magnetic resonance imaging (fMRI) data were collected in a sample of 447 typically developing children from a Brazilian community sample who were submitted to a resting state acquisition protocol. the fMRI data were used to build a functional weighted graph from which eigenvector centrality (EVC) was extracted. for each brain region (a node of the graph), the age-dependent effect on EVC was statistically tested and the developmental trajectories were estimated using polynomial functions.Our findings show that angular gyrus become more central during this maturation period, while the caudate; cerebellar tonsils, pyramis, thalamus; fusiform, parahippocampal and inferior semilunar lobe become less central. in conclusion, we report a novel finding of an increasing centrality of the angular gyrus during the transition to adolescence, with a decreasing centrality of many subcortical and cerebellar regions. (C) 2014 Elsevier Inc. All rights reserved.
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    Measuring network's entropy in ADHD: A new approach to investigate neuropsychiatric disorders
    (Elsevier B.V., 2013-08-15) Sato, João Ricardo; Takahashi, Daniel Yasumasa; Hoexter, Marcelo Queiroz [UNIFESP]; Massirer, Katlin Brauer; Fujita, André; Fed Univ ABC; Princeton Univ; Universidade Federal de São Paulo (UNIFESP); Universidade Estadual de Campinas (UNICAMP); Universidade de São Paulo (USP)
    The application of graph analysis methods to the topological organization of brain connectivity has been a useful tool in the characterization of brain related disorders. However, the availability of tools, which enable researchers to investigate functional brain networks, is still a major challenge. Most of the studies evaluating brain images are based on centrality and segregation measurements of complex networks. in this study, we applied the concept of graph spectral entropy (GSE) to quantify the complexity in the organization of brain networks. in addition, to enhance interpretability, we also combined graph spectral clustering to investigate the topological organization of sub-network's modules. We illustrate the usefulness of the proposed approach by comparing brain networks between attention deficit hyperactivity disorder (ADHD) patients and the brain networks of typical developing (TD) controls. the main findings highlighted that GSE involving sub-networks comprising the areas mostly bilateral pre and post central cortex, superior temporal gyrus, and inferior frontal gyri were statistically different (p-value = 0.002) between ADHD patients and TO controls. in the same conditions, the other conventional graph descriptors (betweenness centrality, clustering coefficient, and shortest path length) commonly used to identify connectivity abnormalities did not show statistical significant difference. We conclude that analysis of topological organization of brain sub-networks based on GSE can identify networks between brain regions previously unobserved to be in association with ADHD. (C) 2013 Elsevier Inc. All rights reserved.
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    Uma nova heurística para o problema de minimização de trocas de ferramentas
    (Universidade Federal de São Carlos, 2012-01-01) Chaves, Antonio Augusto [UNIFESP]; Senne, Edson Luiz França; Yanasse, Horacio Hideki [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Universidade Estadual Paulista (UNESP); Instituto Nacional de Pesquisas Espaciais
    The minimization of tool switches problem (MTSP) seeks a sequence to process a set of jobs so that the number of tool switches required is minimized. This study presents a new heuristic for the MTSP. This heuristic has two phases: a constructive phase, based on a graph where the vertices correspond to tools and there is an arc k = (i, j) linking vertices i and j if and only if the tools i and j are required to execute some job; and an improvement phase, based on an Iterated Local Search. Computational results show that the proposed heuristic has a good performance on the instances tested contributing to a significant reduction in the number of nodes generated by an enumerative algorithm.