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### Navegando por Autor "Ferreira, Ronan Silva"

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Item Analisando ementas curriculares usando redes complexas.(2020) Pinto, Suzane F.; Ferreira, Ronan SilvaMostrar mais Analisamos as grades curriculares do ciclo básico das engenharias em nosso instituto usando ferramentas da física estatística de redes complexas. Naturalmente, uma grade curricular estrutura-se em forma de rede (ordenamento temporal e pré-requisitos). Nessa abordagem, cada tópico dentro de uma ementa é associado a um nó que, por sua vez, são conectados por links que representam a dependência de um certo tema para a compreensão de um outro, em uma disciplina diferente. Como uma grade curricular é uma estrutura tempo-dependente, evoluindo semestre após semestre, propomos um modelo simples para assinalar ligações entre pares de nós levando em conta apenas dois ingredientes do processo de ensino-aprendizagem: a recursividade e o acúmulo de conhecimentos. Como já conhecemos nossas grades curriculares, nosso primeiro objetivo é verificar se o modelo proposto é capaz de capturar as particularidades de cada uma delas e identificar as implicações que diferentes sequenciamentos do setor de física possam ter no aprendizado dos estudantes. Nosso modelo pode ser usado como uma ferramenta sistemática auxiliando na construção de uma grade curricular interdisciplinar, articulando entre os saberes das disciplinas iniciais da graduação em ciências exatas.Mostrar mais Item Droplet finite-size scaling of the contact process on scale-free networks revisited.(2023) Alencar, David Santana Marques; Alves, Tayroni Francisco de Alencar; Ferreira, Ronan Silva; Alves, Gladstone de Alencar; Macedo Filho, Antonio de; Lima, Francisco Welington de SousaMostrar mais We present an alternative finite-size scaling (FSS) of the contact process on scale-free networks compatible with mean-field scaling and test it with extensive Monte Carlo simulations. In our FSS theory, the dependence on the system size enters the external field, which represents spontaneous contamination in the context of an epidemic model. In addition, dependence on the finite size in the scale-free networks also enters the network cutoff. We show that our theory reproduces the results of other mean-field theories on finite lattices already reported in the literature. To simulate the dynamics, we impose quasi-stationary states by reactivation. We insert spontaneously infected individuals, equivalent to a droplet perturbation to the system scaling as N⁻¹. The system presents an absorbing phase transition where the critical behavior obeys the mean-field exponents, as we show theoretically and by simulations. However, the quasi-stationary state gives finite-size logarithmic corrections, predicted by our FSS theory, and reproduces equivalent results in the literature in the thermodynamic limit. We also report the critical threshold estimates of basic reproduction number R₀ λc of the model as a linear function of the network connectivity inverse 1/z, and the extrapolation of the critical threshold function for z→∞ yields the basic reproduction number R₀ = 1 of the complete graph, as expected. Decreasing the network connectivity increases the critical R₀ for this model.Mostrar mais Item Epidemic outbreaks on random Voronoi–Delaunay triangulations.(2020) Alencar, David Santana Marques; Alves, Tayroni Francisco de Alencar; Alves, Gladstone de Alencar; Macedo Filho, Antonio de; Ferreira, Ronan SilvaMostrar mais We study epidemic outbreaks on random Delaunay triangulations by applying the Asynchronous SIR (susceptible–infected–removed) dynamics coupled to two-dimensional Voronoi–Delaunay triangulations. In order to investigate the critical behavior of the model, we obtain the cluster size distribution by using Newman–Ziff algorithm, allowing to simulate random inhomogeneous lattices and measure any desired observable related to percolation. We numerically calculate the order parameter, defined as the wrapping cluster density, the mean cluster size, and Binder cumulant ratio defined for percolation in order to estimate the epidemic threshold. Our findings suggest that the system falls into two-dimensional dynamic percolation universality class and the quenched random disorder is irrelevant, in agreement with results for classical percolation.Mostrar mais Item Epidemic outbreaks on two-dimensional quasiperiodic lattices.(2020) Santos, G. B. M.; Alves, Tayroni Francisco de Alencar; Alves, Gladstone de Alencar; Macedo Filho, Antonio de; Ferreira, Ronan SilvaMostrar mais We present a novel kinetic Monte Carlo technique to study the susceptible-infected-removed model in order to simulate epidemic outbreaks on two quasiperiodic lattices, namely, Penrose and Ammann-Beenker. Our analysis around criticality is performed by investigating the order parameter, which is defined as the probability of growing a spanning cluster formed by removed sites, evolving from an initial system configuration with a single random chosen infective site. This system is studied by means of the cluster size distribution, obtained by the Newman-Ziff algorithm. Additionally, we obtained the mean cluster size, and a cumulant ratio to estimate the epidemic threshold. In spite of the quasiperiodic order moves the transition point, compared to periodic lattices, this is not able to alter the universality class of the model, leading to the same critical exponents. In addition, our technique can be generalized to study epidemic outbreaks in networks and diffusing populations.Mostrar mais Item Metastable localization of diseases in complex networks.(2016) Ferreira, Ronan Silva; Costa, Rui A. da; Dorogovtsev, Sergey; Mendes, José Fernando FerreiraMostrar mais We describe the phenomenon of localization in the epidemic susceptible-infective-susceptible model on highly heterogeneous networks in which strongly connected nodes (hubs) play the role of centers of localization. We find that in this model the localized states below the epidemic threshold are metastable. The longevity and scale of the metastable outbreaks do not show a sharp localization transition; instead there is a smooth crossover from localized to delocalized states as we approach the epidemic threshold from below. Analyzing these long-lasting local outbreaks for a random regular graph with a hub, we show how this localization can be detected from the shape of the distribution of the number of infective nodes.Mostrar mais Item Opinion dynamics systems on barabási-albert networks : biswas-chatterjee-sen model.(2023) Alencar, David Santana Marques; Alves, Tayroni Francisco de Alencar; Alves, Gladstone de Alencar; Macedo Filho, Antonio de; Ferreira, Ronan Silva; Lima, Francisco Welington de Sousa; Plascak, João AntônioMostrar mais A discrete version of opinion dynamics systems, based on the Biswas–Chatterjee–Sen (BChS) model, has been studied on Barabási–Albert networks (BANs). In this model, depending on a pre-defined noise parameter, the mutual affinities can assign either positive or negative values. By employing extensive computer simulations with Monte Carlo algorithms, allied with finite-size scaling hypothesis, second-order phase transitions have been observed. The corresponding critical noise and the usual ratios of the critical exponents have been computed, in the thermodynamic limit, as a function of the average connectivity. The effective dimension of the system, defined through a hyper-scaling relation, is close to one, and it turns out to be connectivity-independent. The results also indicate that the discrete BChS model has a similar behavior on directed Barabási–Albert networks (DBANs), as well as on Erdös–Rènyi random graphs (ERRGs) and directed ERRGs random graphs (DERRGs). However, unlike the model on ERRGs and DERRGs, which has the same critical behavior for the average connectivity going to infinity, the model on BANs is in a different universality class to its DBANs counterpart in the whole range of the studied connectivities.Mostrar mais Item q-Weibull distributions describing commercial service routes.(2020) Ferreira, Ronan Silva; Silva, Priscila Caroline Albuquerque daMostrar mais We present an investigation of the mode of road transport in Brazil combining tools of complex networks and real-data. Our analysis involves a dataset based on the service routes inscribed on the Brazilian Transport Agency database. Although connectivity distributions of road networks worldwide are usually claimed as described by a power-law fashion, we report a better fit for the Brazilian case offered by the q-Weibull distribution. In our approach nodes assume the role of localities, whereas links represent service routes among them. Interestingly, a rapid drop takes place on the tail of the data distribution for a particular range of the number of outgoing connections. The mechanism responsible for driving this drop is revealed by investigating the spectral centrality of the network and different patterns of disassortative mixture, for both incoming and outgoing distributions. Besides a discussion about a power law description, we report a contrast with two different distributions. They are interpolated by the q-Weibull one: the Weibull and the q-exponential distributions. Moreover, we study the reciprocity of this network, which reflects the influence of mutual links over dynamical processes. This kind of analysis is indispensable for studies on human mobility, shipping, and a multi-modal perspectiveMostrar mais Item The diffusive epidemic process on Barabasi–Albert networks.(2021) Alves, Tayroni Francisco de Alencar; Alves, Gladstone de Alencar; Macedo Filho, Antonio de; Ferreira, Ronan Silva; Lima, Francisco Welington de SousaMostrar mais We present a modified diffusive epidemic process (DEP) that has a finite threshold on scale-free graphs, motivated by the COVID-19 pandemic. The DEP describes the epidemic spreading of a disease in a non-sedentary population, which can describe the spreading of a real disease. Our main modification is to use the Gillespie algorithm with a reaction time tmax, exponentially distributed with mean inversely proportional to the node population in order to model the individuals’ interactions. Our simulation results of the modified model on Barabasi–Albert networks are compatible with a continuous absorbing-active phase transition when increasing the average concentration. The transition obeys the mean-field critical exponents β = 1, γ = 0 and ν⊥ = 1/2. In addition, the system presents logarithmic corrections with pseudo-exponents β = γ = −3/2 on the order parameter and its fluctuations, respectively. The most evident implication of our simulation results is if the individuals avoid social interactions in order to not spread a disease, this leads the system to have a finite threshold in scale-free graphs.Mostrar mais