Cristiano M Silva | Universidade Federal de São João del Rei (original) (raw)

Papers by Cristiano M Silva

Expert Systems with Applications

Anais do III Workshop sobre as Implicações da Computação na Sociedade (WICS 2022)

O assunto metaverso tem se tornado onipresente e o principal impulso para que o tema ganhe repres... more O assunto metaverso tem se tornado onipresente e o principal impulso para que o tema ganhe representatividade e interesse das pessoas é sua capacidade de trazer para o dia a dia das pessoas a vivência de uma realidade que até então só tínhamos contato em obras de ficção científica. Por tratar-se de algo novo, surgem novas perguntas em relação a como será o uso e aplicação da tecnologia, quais são as mudanças que essa nova tecnologia promoverá em nossas vidas e como nossa percepção do mundo pode mudar com a intensificação de seu uso constante. Com um potencial de impactar diversos aspectos de nossas vidas, o estudo tem o objetivo de avaliar impactos em relação a questões psicológicos, econômicas e tecnológicas, avaliando como esse novo ambiente onde podemos viver e fazer negócios pode influenciar nossa vida real.

VII ENPI - Encontro Nacional de Propriedade Intelectual, Oct 16, 2021

A tecnologia par-a-par encontra-se emergindo como um novo paradigma para sistemas distribuidos. A... more A tecnologia par-a-par encontra-se emergindo como um novo paradigma para sistemas distribuidos. A continuidade de seu crescimento depende do desenvolvimento de mecanismos que garantam a escalabilidade da rede. Este trabalho analisa a utilizacao de sistemas de replicacao no ambiente par-a-par de forma a reduzir a utilizacao da banda de rede e latencia percebida pelo usuario, aumentando a disponibilidade dos servicos. Alem de prover conteudo em um ambiente par-a-par especifico, tal sistema de replicacao pode atuar (tambem) como um interligador de diversos sistemas par-a-par, tornando possivel que clientes de um sistema tenham acesso aos recursos disponiveis em quaisquer dos sistemas conectados ao replicador. A arquitetura de replicacao projetada atende a todos estes requisitos, tendo sido aplicada a tres populares redes par-a-par: FreeNet, DirectConnect e eDonkey. Os resultados experimentais mostram que esta estrategia de replicacao permite a reducao da latencia percebida pelo usuario e o aumento da disponibilidade dos recursos. Atraves dos experimentos utilizando dados reais de um provedor brasileiro de acesso Internet de grande porte, e possivel verificar que a utilizacao de sistemas de replicacao para o ambiente par-a-par oferece taxas de acerto de ate 87%. De forma a atingir essa taxa, o repositorio de replicacao deve ser dimensionado como 50% da soma do tamanho de todos os arquivos distintos requisitados pelos usuarios.

2017 IEEE Symposium on Computers and Communications (ISCC), 2017

Video streaming now amounts to the majority of traffic in the Internet. Media streaming relies on... more Video streaming now amounts to the majority of traffic in the Internet. Media streaming relies on large-scale content distribution networks (CDNs), that incur significant costs to build or use. P2P distribution of video content reduce reliance on CDNs and costs. Unfortunately, P2P distribution is fraught with QoE problems, specially during flash crowds or in scenarios where users have limited bandwidth to contribute to the overlay. In this paper, we propose a new P2P overlay construction mechanism to speed up peer joining during flash crowd events while preserving QoE for peers already in the overlay. We also show that our techniques work on resource-constrained overlays where a fraction of peers lack resources to contribute to the overlay, e.g., users on mobile devices and metered connections.

Bitcoin e a criptomoeda de maior popularidade na atualidade. Sua operacao se da a partir de uma r... more Bitcoin e a criptomoeda de maior popularidade na atualidade. Sua operacao se da a partir de uma rede P2P descentralizada que busca manter um livro razao de transacoes distribuido pela rede. A notoriedade dessa rede motiva o desenvolvimento desse trabalho, onde investiga-se a evolucao da rede em termos de blocos, transacoes, enderecos e saldos. Sao analisados mais de 500 mil blocos de dados correspondendoa 1,54 bilhoes de transacoes que envolveram 368 milhoes de enderecos Bitcoin distribuidos pelo mundo. Os resultados demonstram que o volume de dados armazenado no blockchain cresce, atualmente,a taxa de 5GB ao mes, sendo processados 10 milhoes de transacoes mensais. A quantidade de enderecos criados por mes cresce em proporcao quadratica, embora 74% deles tenha o tempo de vida de apenas um dia. Mais de 85% dos enderecos realizam apenas duas transacoes e 1,7% dos enderecos receberam 90% dos Bitcoins transacionados ao longo de 2017.

European Journal of Epidemiology, 2021

BackgroundBrazil became the epicenter of the COVID-19 epidemic in a brief period of a few months ... more BackgroundBrazil became the epicenter of the COVID-19 epidemic in a brief period of a few months after the first officially registered case. The knowledge of the epidemiological/clinical profile and the risk factors of Brazilian COVID-19 patients can assist in the decision making of physicians in the implementation of early and most appropriate measures for poor prognosis patients. However, these reports are missing. Here we present a comprehensive study that addresses this demand.MethodsThis data-driven study was based on the Brazilian Ministry of Health Database (SIVEP-Gripe, 2020) regarding notified cases of hospitalized COVID-19 patients during the period from February 26 to August 10, 2020. Demographic data, clinical symptoms, comorbidities and other additional information of patients were analyzed.ResultsThe hospitalization rate was higher for male gender (56.56%) and for older age patients of both sexes. Overall, the mortality rate was quite high (41.28%) among hospitalized p...

Research, Society and Development, 2022

Nas últimas décadas, o papel das Universidades vem se alterando para, além do ensino e da pesquis... more Nas últimas décadas, o papel das Universidades vem se alterando para, além do ensino e da pesquisa, atuar como facilitadora da transferência de tecnologia e incentivadora do desenvolvimento econômico local e regional. Nesse contexto, o empreendedorismo acadêmico tem recebido atenção crescente nas áreas de ensino superior, pois passou a ser considerado um mecanismo-chave para novos avanços inovadores e desenvolvimentos econômicos regionais. Dessa forma, o presente estudo teve por objetivo investigar e discutir as ações que o Núcleo de Empreendedorismo e Inovação Tecnológica da Universidade Federal de São João del Rei tem desenvolvido para apoiar e incentivar a formação empreendedora bem como mapear os empreendimentos afiliados à universidade, na qual ele está situado. Mais especificamente foram estudadas as atividades de formação empreendedora, incubação de empresas e o mapeamento de empresas-filhas. Para alcance do objetivo geral, a pesquisa se caracteriza com uma abordagem qualitat...

2017 IFIP/IEEE Symposium on Integrated Network and Service Management (IM), 2017

2021 IEEE Latin-American Conference on Communications (LATINCOM), 2021

This work studies computational heuristics in the search for urban mobility solutions for the 21s... more This work studies computational heuristics in the search for urban mobility solutions for the 21st century society. The Delta Network, which is a metric to characterize the performance of vehicular networks, is discussed and two heuristics that perform the allocation of roadside communication units in urban centers (based on the Delta Network) are proposed. The first heuristic operates greedily, making allocations to locations that result in the best momentary performance. The second heuristic uses a genetic algorithm with local search to perform the allocation. The choice of some parameters for the execution of the genetic algorithm, as well as the most promising locations for the deployment of the roadside communication units are studied throughout this work. The proposed heuristics are compared to the intuitive strategy of allocating roadside units at the most popular areas of the road network. The results show that the heuristics achieve better results than the intuitive strategy for all scenarios. The proposed heuristics are also compared with each other, and the results show that the genetic algorithm achieves results slightly superior to the greedy algorithm in the studied scenarios, which indicates that the greedy decisions are well designed to the problem.

The first officially registered case of COVID-19 in Brazil was on February 26, 2020. Since then, ... more The first officially registered case of COVID-19 in Brazil was on February 26, 2020. Since then, the situation has worsened with more than 672, 000 confirmed cases and at least 36, 000 reported deaths at the time of this writing. Accurate diagnosis of patients with COVID-19 is extremely important to offer adequate treatment, and avoid overloading the healthcare system. Characteristics of patients such as age, comorbidities and varied clinical symptoms can help in classifying the level of infection severity, predict the disease outcome and the need for hospitalization. Here, we present a study to predict a poor prognosis in positive COVID-19 patients and possible outcomes using machine learning. The study dataset comprises information of 13, 690 patients concerning closed cases due to cure or death. Our experimental results show the disease outcome can be predicted with a ROC AUC of 0.92, Sensitivity of 0.88 and Specificity of 0.82 for the best prediction model. This is a preliminary...

2021 7th International Conference on Signal Processing and Intelligent Systems (ICSPIS)

NOMS 2016 - 2016 IEEE/IFIP Network Operations and Management Symposium

In this work we investigate the benefits of an hybrid architecture integrating both mobile roadsi... more In this work we investigate the benefits of an hybrid architecture integrating both mobile roadside units, and stationary roadside units supporting the operation of vehicular networks. Since traffic fluctuates, an architecture employing just stationary roadside units might not be able to properly support the network operation all the time. Similarly, an architecture composed just of mobile roadside units may lack part of the robustness provided by stationary roadside units. Furthermore, the traffic fluctuations are limited by the underlying road network, and the road networks do not change so often as traffic does. Thus, it seems straight full to assume that a set of roadside units will always be left stationary, while other roadside units will need to roam along the road network. As major roads counts on a higher transportation capacity, they tend to be very popular routes, and they are natural candidates for receiving the stationary roadside units. On the other hand, we may rely on mobile roadside units for handling roads presenting a high traffic variation. In this work we use the realistic vehicular mobility trace of Cologne, Germany, and we model the allocation of the roadside units as a Maximum Coverage Problem. Our results demonstrate the hybrid deployment increases the number of covered vehicles up to 45%.

2017 IEEE 85th Vehicular Technology Conference (VTC Spring), 2017

In this work, we propose a GRASP+VNS algorithm for solving the allocation of Roadside Units (RSUs... more In this work, we propose a GRASP+VNS algorithm for solving the allocation of Roadside Units (RSUs) in a Vehicular Network. Our main objective is to find the minimum set of RSUs to meet a Deployment Delta (ρ1,ρ2). The Deployment Delta (ρ1,ρ2) is a metric for specifying minimal communication guarantees from the infrastructure supporting the Vehicular Network. We compare GRASP+VNS to some baseline algorithms: (i) Delta-g; (ii) Delta-r and, (iii) the optimal value. Our results demonstrate that our approach requires up to 90% less Roadside Units to meet the QoS required by Deployment Delta (ρ1,ρ2) metric. Besides, different from the baseline algorithms, our approach find results that differ no more than 17% from the optimal values for all tested instances.

2021 IEEE Latin-American Conference on Communications (LATINCOM)

Este trabalho considera a deposicao de unidades de comunicacao (RSUs) em redes veiculares. Basica... more Este trabalho considera a deposicao de unidades de comunicacao (RSUs) em redes veiculares. Basicamente, tem-se o objetivo de promover encontros regulares de veiculos com a infraestrutura, permitindo que os veiculos continuem recebendo midia da infraestrutura durante sua locomocao. Em termos de parâmetros de QoS, sao considerados: (a) a fracao de veiculos que recebera a transmissao de midia, (b) a taxa de recepcao de dados da infraestrutura para os veiculos, e (c) a taxa de consumo de dados dentro dos veiculos. Apos a formulacao do problema, este trabalho apresenta a estrategia de deposicao Sigma-N que utiliza o algoritmo evolucionario multiobjetivo NSGA-II. Sigma-N e comparada com a estrategia intuitiva de se alocar unidades de comunicacao em pontos de maior concentracao de fluxo. Os resultados mostram que Sigma-N requer menos RSUs para atingir a mesma cobertura, enquanto fornece similar qualidade de servico.

2018 IEEE Symposium on Computers and Communications (ISCC), 2018

In this work we consider the deployment of roadside units (RSUs) for communication in vehicular n... more In this work we consider the deployment of roadside units (RSUs) for communication in vehicular networks. Basically, we intend to promote regular vehicle-to-infrastructure encounters allowing vehicles to continuously receive media from roadside units while driving. In terms of QoS parameters, we consider (a) the share of vehicles demanding the streaming service, (b) the data download rate from roadside units to vehicles, and (c) the data consumption rate inside vehicles. After formulating the problem, we present the GMOA strategy that uses the NSGA-II evolutionary multiobjective algorithm. We compare GMOA to the intuitive strategy of placing roadside units at the densest locations of the road network. Results show that GMOA uses much less roadside units (economy may reach 44%), while providing the same network QoS.

Multim. Tools Appl., 2021

2019 IEEE Latin-American Conference on Communications (LATINCOM), 2019

This work presents DESTINy, a traffic management solution for vehicular network using V2V ad V2I ... more This work presents DESTINy, a traffic management solution for vehicular network using V2V ad V2I communication. Considering a number of RoadSide Units (RSUs) deployed in the road infrastructure, DESTINy divides the city map into regions and each RSU is responsible to store information about traffic conditions of its responsible roads. When necessary, each vehicle requests information to the closest RSU and using the travel time information of the roads inside the region where the vehicle is, it calculates alternative routes with lower travel time. When forwarding the response message, the vehicles also update their local database in order to reduce the number of transmitted messages. Our solution was evaluated considering different literature solutions and presents better results considering network and traffic metrics, providing a reduction of number of message of approximately 70 % as well as, a reduction in the average travel time about 26%.