Browsing by Author "Freitas, Vander Luis de Souza"

Now showing 1 - 7 of 7
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    Complex networks approach for dynamical characterization of nonlinear systems.
    (2019) Freitas, Vander Luis de Souza; Lacerda, Juliana Cestari; Macau, Elbert Einstein Nehrer
    Bifurcation diagrams and Lyapunov exponents are the main tools for dynamical systems char- acterization. However, they are often computationally expensive and complex to calculate. We present two approaches for dynamical characterization of nonlinear systems via the generation of an undirected complex network that is built from their time series. Periodic windows and chaos can be detected by analyzing network statistics like average degree, density and betweenness centrality. Results are assessed in two discrete time nonlinear maps.
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    Flood risk map from hydrological and mobility data : a case study in São Paulo-Brazil.
    (2022) Tomás, Lívia Rodrigues; Soares, Giovanni Guarnieri; Jorge‬, ‪Aurelienne Aparecida Souza; Mendes, Jeferson Feitosa; Freitas, Vander Luis de Souza; Santos, Leonardo Bacelar Lima
    Cities increasingly face flood risk primarily due to exten-sive changes of the natural land cover to built-up areas with impervious surfaces. In urban areas, flood impacts come mainly from road interruption. This article proposes an urban flood risk map from hydrological and mobility data, considering the megacity of São Paulo, Brazil, as a case study. We estimate the flood susceptibility through the Height Above the Nearest Drainage algorithm; and the potential impact through the exposure and vulnerability components. We aggregate all variables into a regular grid and then classify the cells of each component into three classes: Moderate, High, and Very High. All components, except the flood susceptibility, have few cells in the Very High class. The flood susceptibility component reflects the presence of watercourses, and it has a strong influence on the location of those cells classified as Very High.
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    Robustness analysis in an inter-cities mobility network : modeling municipal, state and federal initiatives as failures and attacks toward SARS-CoV-2 containment.
    (2020) Freitas, Vander Luis de Souza; Moreira, Gladston Juliano Prates; Santos, Leonardo Bacelar Lima
    We present a robustness analysis of an inter-cities mobility complex network, motivated by the challenge of the COVID-19 pandemic and the seek for proper containment strategies. Brazilian data from 2016 are used to build a network with more than five thousand cities (nodes) and twenty-seven states with the edges representing the weekly flow of people between cities via terrestrial transports. Nodes are systematically isolated (removed from the network) either at random (failures) or guided by specific strategies (targeted attacks), and the impacts are assessed with three metrics: the number of components, the size of the giant component, and the total remaining flow of people. We propose strategies to identify which regions should be isolated first and their impact on people mobility. The results are compared with the so-called reactive strategy, which consists of isolating regions ordered by the date the first case of COVID-19 appeared. We assume that the nodes’ failures abstract individual municipal and state initiatives that are independent and possess a certain level of unpredictability. Differently, the targeted attacks are related to centralized strategies led by the federal government in agreement with municipalities and states. Removing a node means completely restricting the mobility of people between the referred city/state and the rest of the network. Results reveal that random failures do not cause a high impact on mobility restraint, but the coordinated isolation of specific cities with targeted attacks is crucial to detach entire network areas and thus prevent spreading. Moreover, the targeted attacks perform better than the reactive strategy for the three analyzed robustness metrics.
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    Synchronization-based symmetric circular formations of mobile agents and the generation of chaotic trajectories.
    (2021) Freitas, Vander Luis de Souza; Yanchuk, Serhiy; Zaks, Michael; Macau, Elbert Einstein Nehrer
    The self-organization of multiple autonomous mobile agents is a trending topic nowadays with applications in robotics, aerospace engineering, and satellite formations. We investigate a model of particles with coupled-oscillators dynamics focusing on the particular case of agents grouping in symmetric clusters while moving in concentric circular trajectories. Our results reveal that certain regions of the parameter space are more suitable for the onset of such clusters. Additionally, we study the effects of adding and removing agents from already formed clusters, prescribe a strategy to properly switch from one formation to another, and finally introduce an approach to obtain chaotic almost-circular trajectories and symmetric clusters with non-overlapping particles.
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    The correspondence between the structure of the terrestrial mobility network and the spreading of COVID-19 in Brazil.
    (2020) Freitas, Vander Luis de Souza; Konstantyner, Thais Cláudia Roma de Oliveira; Mendes, Jeferson Feitosa; Sepetauskas, Cátia Souza do Nascimento; Santos, Leonardo Bacelar Lima
    The inter-cities mobility network is of great importance in understanding outbreaks, especially in Brazil, a continental-dimension country. We adopt the data from the Brazilian Ministry of Health and the terrestrial flow of people between cities from the Brazilian Institute of Geography and Statistics database in two scales: cities from Brazil, without the North region, and from the São Paulo State. Grounded on the complex networks approach, and considering that the mobility network serves as a proxy for the SARS-CoV-2 spreading, the nodes and edges represent cities and flows, respectively. Network centrality measures such as strength and degree are ranked and compared to the list of cities, ordered according to the day that they confirmed the first case of COVID-19. The strength measure captures the cities with a higher vulnerability of receiving new cases. Besides, it follows the interiorization process of SARS-CoV-2 in the São Paulo State when the network flows are above specific thresholds. Some countryside cities such as Feira de Santana (Bahia State), Ribeirão Preto (São Paulo State), and Caruaru (Pernambuco State) have strength comparable to states’ capitals. Our analysis offers additional tools for understanding and decision support to inter-cities mobility interventions regarding the SARS-CoV-2 and other epidemics.
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    The effects of time-delay and phase lags on symmetric circular formations of mobile agents.
    (2021) Freitas, Vander Luis de Souza; Yanchuk, Serhiy; Grande, Helder Luciani Casa; Macau, Elbert Einstein Nehrer
    The mobile agents’ circular formation problem is driven by applications that require a desired spatial and temporal separation, such as data collection or satellite constellations. There are numerous strategies to assign the cluster number and spacing, the radius of the trajectory, communication network, and other parameters. In this numerical study, we are particularly interested in the effects of time-delay and phase lag on circular formations with symmetric clusters in a first-order model with all-to-all interaction. When the information exchange time-delay exceeds some critical value, it leads to either incoherent or alternative symmetric arrangements. Besides, we show that formations can be effectively controlled using phase lags. As a paradigmatic example, we consider identical phase lags for half of the agents, while the other half receives an opposite phase lag. As a result, the system reaches more complicated stable arrangements. For instance, the agents can split into asymmetric clusters, each of them creating a symmetric formation.
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    Vulnerability analysis in complex networks under a flood risk reduction point of view.
    (2023) Santos, Leonardo Bacelar Lima; Soares, Giovanni Guarnieri; Garg, Tanishq; Jorge, Aurelienne Aparecida Souza; Londe, Luciana de Resende; Reani, Regina Tortorella; Bacelar, Roberta Baldo; Oliveira, Carlos Eduardo S. de; Freitas, Vander Luis de Souza; Sokolov, Igor Mikhailovich
    The measurement and mapping of transportation network vulnerability to natural hazards constitute subjects of global interest for a sustainable development agenda and as means of adaptation to climate change. During a flood, some elements of a transportation network can be affected, causing the loss of lives. Furthermore, impacts include damage to vehicles, streets/roads, and other logistics services - sometimes with severe economic consequences. The Network Science approach may offer a valuable perspective considering one type of vulnerability related to network-type critical infrastructures: the topological vulnerability. The topological vulnerability index associated with an element is defined as reducing the network’s average efficiency due to removing the set of edges related to that element. In this paper, we present the results of a systematic literature overview and a case study applying the topological vulnerability index for the highways in Santa Catarina (Brazil). We produce a map considering that index and areas susceptible to urban floods and landslides. Risk knowledge, combining hazard and vulnerability, is the first pillar of an Early Warning System and represents an important tool for stakeholders of the transportation sector in a disaster risk reduction agenda.