Sznajd Complex Networks

The Sznajd cellular automata corresponds to one of the simplest and yet most interesting models of complex systems. While the traditional two-dimensional Sznajd model tends to a consensus state (pro or cons), the assignment of the contrary to the dominant opinion to some of its cells during the system evolution is known to provide stabilizing feedback implying the overall system state to oscillate around null magnetization. The current article presents a novel type of geographic complex network model whose connections follow an associated feedbacked Sznajd model, i.e. the Sznajd dynamics is run over the network edges. Only connections not exceeding a maximum Euclidean distance $D$ are considered, and any two nodes within such a distance are randomly selected and, in case they are connected, all network nodes which are no further than $D$ are connected to them. In case they are not connected, all nodes within that distance are disconnected from them. Pairs of nodes are then randomly selected and assigned to the contrary of the dominant connectivity. The topology of the complex networks obtained by such a simple growth scheme, which are typically characterized by patches of connected communities, is analyzed both at global and individual levels in terms of a set of hierarchical measurements introduced recently. A series of interesting properties are identified and discussed comparatively to random and scale-free models with the same number of nodes and similar connectivity.Comment: 10 pages, 4 figure

The rich-club phenomenon across complex network hierarchies

The so-called rich-club phenomenon in a complex network is characterized when nodes of higher degree (hubs) are better connected among themselves than are nodes with smaller degree. The presence of the rich-club phenomenon may be an indicator of several interesting high-level network properties, such as tolerance to hub failures. Here we investigate the existence of the rich-club phenomenon across the hierarchical degrees of a number of real-world networks. Our simulations reveal that the phenomenon may appear in some hierarchies but not in others and, moreover, that it may appear and disappear as we move across hierarchies. This reveals the interesting possibility of non-monotonic behavior of the phenomenon; the possible implications of our findings are discussed.Comment: 4 page

Strategic CSR shifts towards adaptive food governance under environmental change: A comparison between South African and Brazilian retailers

Governance in the food system has become a key topic of discussion in light of the 2007-08 food price crisis. Of special importance has been the shift to include the role that non-state actors are likely to play in achieving food security under global environmental change (GEC). This paper aims to compare private sector food system governance trends in two emerging economies, Brazil and South Africa. It focuses on practices around adaptation, an area largely neglected in climate change discussion, yet a critical factor in coping with the societal consequences of GEC. This study identifies several processes, particularly within the retail sector, that could indicate normative mechanisms through which 'good governance' can be translated into practice

Complex networks: the key to systems biology

Though introduced recently, complex networks research has grown steadily because of its potential to represent, characterize and model a wide range of intricate natural systems and phenomena. Because of the intrinsic complexity and systemic organization of life, complex networks provide a specially promising framework for systems biology investigation. The current article is an up-to-date review of the major developments related to the application of complex networks in biology, with special attention focused on the more recent literature. The main concepts and models of complex networks are presented and illustrated in an accessible fashion. Three main types of networks are covered: transcriptional regulatory networks, protein-protein interaction networks and metabolic networks. The key role of complex networks for systems biology is extensively illustrated by several of the papers reviewed.FAPESPCNP

Transient dynamics for sequence processing neural networks: effect of degree distributions

We derive a analytic evolution equation for overlap parameters including the effect of degree distribution on the transient dynamics of sequence processing neural networks. In the special case of globally coupled networks, the precisely retrieved critical loading ratio $\alpha_c = N ^{-1/2}$ is obtained, where $N$ is the network size. In the presence of random networks, our theoretical predictions agree quantitatively with the numerical experiments for delta, binomial, and power-law degree distributions.Comment: 11 pages, 6 figure

Cabeças femorais de grande diâmetro em próteses totais primárias da anca – um estudo comparativo

Introdução As próteses totais primárias da anca tem vindo a registar avanços significativos, nomeadamente no que diz respeito ao seu desenho e dimensões dos implantes. Assim, o diâmetro da cabeça femoral é um factor a levar em linha de conta, uma vez que os grandes diâmetros podem contribuir para um risco mais baixo de luxação no período de convalescença. Para além da estabilidade articular, outras variáveis são influenciadas pelo diâmetro da cabeça femoral, em que se incluem, o desgaste dos componentes, o conflito tipo “cam”, a mobilidade articular, a restauração da biomecânica natural, a propriocepção e a dor localizada à região nadegueira. O objetivo deste trabalho foi, comparar as taxas de luxação após prótese total primária da anca, em doentes com cabeças femorais de grandes diâmetros e de pequenos diâmetros. Material e Métodos Trata-se de um estudo comparativo, onde se consideraram dois grupos, doentes submetidos a prótese total primária da anca com recurso a pequeno diâmetro (grupo I, n=40) e grande diâmetro (grupo II, n=40). Consideraram-se as cabeças de pequeno diâmetro para tamanhos de 28 e 32 mm, sendo que as de grande diâmetro correspondem a 36 e 38 mm. Colheram-se dados do processo clínico sobre a causa etiológica, idade, lateralidade, tempo médio de recuo, perdas hemáticas, técnica cirúrgica, complicações e via de abordagem. A via de abordagem preconizada neste estudo foi a via de Moore. Resultados No grupo I, a idade média foi de 64,9± 7,3 (32-82) anos , o tempo médio de recuo foi de 1059,8± 120,4 dias e as perdas hemáticas médias foram de 2,7± 0,9 (0,6-4,1) g/dL. A coxartrose primária foi a causa mais frequente de intervenção cirúrgica (n=28). Foi realizada a cimentação de ambos os componentes protéticos em 28 doentes. A anca esquerda foi intervencionada em 21 doentes. No grupo II, a idade média foi de 53,3± 9,7 (27-76) anos , o tempo médio de recuo foi de 974,7± 178,7 dias e perdas hemáticas médias foram de 3,5± 1,0 (0,9-5,6) g/dL. Em 23 doentes a coxartrose era de causa secundária. Não se observou prevalência na lateralidade da anca submetida a artroplastia. Optou-se pela realização de uma artroplastia total primária não cimentada em 33 doentes. A complicação mais frequente foi a luxação posterior (cinco casos no grupo I e apenas um caso no grupo II). Discussão A escolha do tamanho da cabeça femoral, a adotar durante a realização de uma prótese total primária da anca, depende não só do tamanho do acetábulo, mas também da “filosofia” que defende a utilização de grandes diâmetros com o objetivo de reduzir a incidência de luxações após a cirurgia. O risco de luxação da anca e de conflito (que promove um aumento do desgaste dos componentes), contribuiu para a introdução no mercado de cabeças femorais com diâmetros cada vez mais elevados. Os doentes do grupo I (pequenos diâmetros) apresentavam uma idade média mais avançada e uma menor taxa de sangramento (perdas sanguíneas) no pós-operatório. Os doentes do grupo II (grandes diâmetros), em média mais jovens, foram submetidos na sua maioria a próteses totais primárias não cimentadas por coxartrose de causa secundária, registando-se apenas um caso de luxação da prótese. Conclusão As próteses totais primárias da anca em que se usaram cabeças femorais de grande diâmetro mostraram uma taxa de luxação protética muito aceitável. Contudo, embora as cabeças femorais de grande diâmetro contribuam para a redução do risco pós-operatório de instabilidade articular, é de ressalvar a componente multifatorial da luxação protética

Intermittent exploration on a scale-free network

We study an intermittent random walk on a random network of scale-free degree distribution. The walk is a combination of simple random walks of duration $t_w$ and random long-range jumps. While the time the walker needs to cover all the nodes increases with $t_w$, the corresponding time for the edges displays a non monotonic behavior with a minimum for some nontrivial value of $t_w$. This is a heterogeneity-induced effect that is not observed in homogeneous small-world networks. The optimal $t_w$ increases with the degree of assortativity in the network. Depending on the nature of degree correlations and the elapsed time the walker finds an over/under-estimate of the degree distribution exponent.Comment: 12 pages, 3 figures, 1 table, published versio

Performance of networks of artificial neurons: The role of clustering

The performance of the Hopfield neural network model is numerically studied on various complex networks, such as the Watts-Strogatz network, the Barab{\'a}si-Albert network, and the neuronal network of the C. elegans. Through the use of a systematic way of controlling the clustering coefficient, with the degree of each neuron kept unchanged, we find that the networks with the lower clustering exhibit much better performance. The results are discussed in the practical viewpoint of application, and the biological implications are also suggested.Comment: 4 pages, to appear in PRE as Rapid Com

Learning about knowledge: A complex network approach

This article describes an approach to modeling knowledge acquisition in terms of walks along complex networks. Each subset of knowledge is represented as a node, and relations between such knowledge are expressed as edges. Two types of edges are considered, corresponding to free and conditional transitions. The latter case implies that a node can only be reached after visiting previously a set of nodes (the required conditions). The process of knowledge acquisition can then be simulated by considering the number of nodes visited as a single agent moves along the network, starting from its lowest layer. It is shown that hierarchical networks, i.e. networks composed of successive interconnected layers, arise naturally as a consequence of compositions of the prerequisite relationships between the nodes. In order to avoid deadlocks, i.e. unreachable nodes, the subnetwork in each layer is assumed to be a connected component. Several configurations of such hierarchical knowledge networks are simulated and the performance of the moving agent quantified in terms of the percentage of visited nodes after each movement. The Barab\'asi-Albert and random models are considered for the layer and interconnecting subnetworks. Although all subnetworks in each realization have the same number of nodes, several interconnectivities, defined by the average node degree of the interconnection networks, have been considered. Two visiting strategies are investigated: random choice among the existing edges and preferential choice to so far untracked edges. A series of interesting results are obtained, including the identification of a series of plateaux of knowledge stagnation in the case of the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure

CO013. PREVALÊNCIA DE SÍNDROME METABÓLICA EM CRIANÇAS E ADOLESCENTES COM DIABETES MELLITUS TIPO 1

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