CT - DCA - Artigos publicados em periódicos
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Artigo NPi-Cluster: a Low Power Energy-Proportional Computing Cluster Architecture(Institute of Electrical and Electronics Engineers, 2017-08-09) Filho, Sebastião Emidio Alves; Burlamaqui, Aquiles Medeiros Filgueira; Aroca, Rafael Vidal; Gonçalves, Luiz Marcos GarciaThis paper presents the NPi-Cluster, an energy proportional computing cluster that automatically powers ON or OFF the number of running machines according to the actual processing demand. A theoretical model is proposed, discussed, and implemented on a cluster composed of Raspberry Pi computer boards designed and built in order to test the proposed system architecture. Experimental results show adequate performance of the proposed platform when compared with other web servers running on traditional server architectures, but with considerably less power consumption. The power consumption of the entire cluster is about 14 W when running at maximum performance. In this situation, the system is able to handle more than 450 simultaneous requests, with about 1000 transactions per second, making it possible to be used as a server capable of handling real web workloads with acceptable quality of service. When the requests demand is reduced to a minimum, the power consumption is dynamically reduced until less than 2 W. Additionally, the proposed cluster architecture also provides high availability by reducing single points of failure on the systemArtigo A review of dynamic data envelopment analysis: state of the art and applications(Wiley, 2017-11-01) Mariz, Fernanda B. A. Rocha; Almeida, Mariana Rodrigues de; Aloise, DanielThis article reports the evolution of the literature on Dynamic Data Envelopment Analysis (DDEA) models from 1996 to 2016. Systematic searches in the databases Scopus and Web of Science were performed to outline the state of the art. The results enabled the establishment of DDEA studies as the scope of this article, analyzing the transition elements to represent temporal interdependence. The categorization of these studies enabled the mapping of the evolution of the DDEA literature and identification of the relationships between models. The three most widely adopted studies to conduct DDEA research were classified as structuring models. Mapping elucidated the literature behavior through three phases and showed an increase in publications with applications in recent years. The analysis of applications indicated that most studies address evaluations in the agriculture and farming, banking and energy sectors and consider the facilities as transition elements between analysis periodsArtigo Using virtual reality and percolation theory to visualize fluid flow in porous media(Springer, 2012-10-23) Lima, Carlos Magno de; Gonçalves·, Luiz Marcus Garcia; Bentes, Cristiana; Farias, RicardoThe study of the fluid flow process through porous media can bring valuable contributions in areas like oil exploration and environmental research. In this work, we propose an interactive tool, named VRFluid, that allows visual interpretation of the three-dimensional data generated by the simulation of the fluid flow the porous media. VRFluid comprises a virtual reality engine that provides stereo visualization of the three-dimensional data, and a simulation engine based on a dynamic percolation method to model the fluid flow. VRFluid is composed of two independent main threads, the percolation simulator and the rendering server, that can operate in parallel as a pipeline. We tested our tool on a region of a mature field database, supervised by geophysicists, and obtained images of the interior of the percolation data, providing important results for the interpretation and cluster formation processArtigo Single image highlight removal for real-time image processing pipelines(IEEE, 2019-12-30) Ramos, Vítor S.; Silveira Júnior, Luiz Gonzaga de Q.; Silveira, Luiz Felipe de Q.This paper presents a fully automatic method for the separation of diffuse and specular reflection components from a single image. Overall, the mechanisms in which the available methods operate on are computationally costly and do not translate well to modern hardware-implemented image processing pipelines, such as the ones present in consumer electronics. Consequently, the objective of this article is to introduce a simple yet effective method for specular highlight removal. It is based on the dichromatic reflection model and operates through histogram matching in the YCbCr color space. The proposed method performs in real-time. It only uses global image statistics and point-wise intensity transformations. Experimental evaluation shows that the proposed approach has competitive results in comparison to state-of-the-art methods. Limitations of the proposed approach are seldom and are common to most methods available. The proposed method, however, achieves better quality results with much less computational cost, thus enabling feasibility in systems with limited processing powerArtigo A Versatile method for depth Data error estimation in RGB-D sensors(MDPI, 2018-09-13) Avila, Elizabeth Viviana Cabrera; Fernandez, Luiz Enrique Ortiz; Slva, Bruno Marques Ferreira a; clua, Esteban Walter G.; Goncalves, Luiz Marcos GarciaWe propose a versatile method for estimating the RMS error of depth data provided by generic 3D sensors with the capability of generating RGB and depth (D) data of the scene, i.e., the ones based on techniques such as structured light, time of flight and stereo. A common checkerboard is used, the corners are detected and two point clouds are created, one with the real coordinates of the pattern corners and one with the corner coordinates given by the device. After a registration of these two clouds, the RMS error is computed. Then, using curve fittings methods, an equation is obtained that generalizes the RMS error as a function of the distance between the sensor and the checkerboard pattern. The depth errors estimated by our method are compared to those estimated by state-of-the-art approaches, validating its accuracy and utility. This method can be used to rapidly estimate the quality of RGB-D sensors, facilitating robotics applications as SLAM and object recognitionArtigo Performance evaluation of multi-UAV network applied to scanning rocket impact area(MDPI, 2019-11-09) Silva, Maurício R.; Souza, Elitelma S.; Alsina, Pablo Javier; Leite, Deyvid Lucas; Morais, Mateus Rodrigues de; Pereira, Diego S.; Nascimento, Luís B. P.; Medeiros, Adelardo Adelino Dantas de; Cunha Junior, Francisco H.; Nogueira, Marcelo Borges; Albuquerque, Glauberto Leilson Alves de; Dantas, João B. D.This paper presents a communication network for a squadron of unmanned aerial vehicles (UAVs) to be used in the scanning rocket impact area for Barreira do Inferno Launch Center—CLBI (Rio Grande do Norte, Brazil), aiming at detecting intruder boats. The main features of communication networks associated with multi-UAV systems are presented. This system sends information through Wireless Sensor Networks (WSN). After comparing and analyzing area scanning strategies, it presents the specification of a data communication network architecture for a squadron of UAVs within a sensor network using XBee Pro 900HP S3B modules. A brief description is made about the initial information from the construction of the system. The embedded hardware and the design procedure of a dedicated communication antenna to the XBee modules are presented. In order to evaluate the performance of the proposed architecture in terms of robustness and reliability, a set of experimental tests in different communication scenarios is carried out. Network management software is employed to measure the throughput, packet loss and other performance indicators in the communication links between the different network nodes. Experimental results allow verifying the quality and performance of the network nodes, as well as the reliability of the communication links, assessing signal received quality, range and latencyArtigo Distributed-Memory load balancing with cyclic token-based work-stealing applied to reverse time migration(Institute of Electrical and Electronics Engineers, 2019) Martins, Idalmis Milian Sardina; Assis, Ítalo Augusto Souza; Oliveira, Antônio D. S.; Barros, Tiago; Bianchini, Calebe P.; Souza, Samuel Xavier deReverse time migration (RTM) is a prominent technique in seismic imaging. Its resulting subsurface images are used in the industry to investigate with higher confidence the existence and the conditions of oil and gas reservoirs. Because of its high computational cost, RTM must make use of parallel computers. Balancing the workload distribution of an RTM is a growing challenge in distributed computing systems. The competition for shared resources and the differently-sized tasks of the RTM are some of the possible sources of load imbalance. Although many load balancing techniques exist, scaling up for large problems and large systems remains a challenge because synchronization overhead also scales. This paper proposes a cyclic token-based work-stealing (CTWS) algorithm for distributed memory systems applied to RTM. The novel cyclic token approach reduces the number of failed steals, avoids communication overhead, and simplifies the victim selection and the termination strategy. The proposed method is implemented as a C library using the one-sided communication feature of the message passing interface (MPI) standard. Results obtained by applying the proposed technique to balance the workload of a 3D RTM system present a factor of 14.1 % speedup and reductions of the load imbalance of 78.4 % when compared to the conventional static distributionArtigo A wearable mobile sensor platform to assist fruit grading(MDPI, 2013-05-10) Aroca, Rafael Vidal; Gomes, Rafael Beserra; Dantas, Rummenigge Rudson; Calbo, Adonai G.; Gonçalves, Luiz Marcos GarciaWearable computing is a form of ubiquitous computing that offers flexible and useful tools for users. Specifically, glove-based systems have been used in the last 30 years in a variety of applications, but mostly focusing on sensing people’s attributes, such as finger bending and heart rate. In contrast, we propose in this work a novel flexible and reconfigurable instrumentation platform in the form of a glove, which can be used to analyze and measure attributes of fruits by just pointing or touching them with the proposed glove. An architecture for such a platform is designed and its application for intuitive fruit grading is also presented, including experimental results for several fruitsArtigo Global optimization workshop 2012(Springer, 2014-07-24) Rocha, Caroline Thennecy de Medeiros; Aloise, Daniel; Hansen, PierreThe Global Optimization Workshop 2012 (GOW 2012) was the eleventh of a series of meetings, organized to be a forum for both academic and industrial communities to present and discuss the latest results and challenges in global optimizationArtigo A model for clustering data from heterogeneous dissimilarities(Elsevier, 2016-09-16) Santi, Éverton; Aloise, Daniel; Blanchard, Simon J.Clustering algorithms partition a set of n objects into p groups (called clusters), such that objects assigned to the same groups are homogeneous according to some criteria. To derive these clusters, the data input required is often a single n × n dissimilarity matrix. Yet for many applications, more than one instance of the dissimilarity matrix is available and so to conform to model requirements, it is common practice to aggregate (e.g., sum up, average) the matrices. This aggregation practice results in clustering solutions that mask the true nature of the original data. In this paper we introduce a clustering model which, to handle the heterogeneity, uses all available dissimilarity matrices and identifies for groups of individuals clustering objects in a similar way. The model is a nonconvex problem and difficult to solve exactly, and we thus introduce a Variable Neighborhood Search heuristic to provide solutions efficiently. Computational experiments and an empirical application to perception of chocolate candy show that the heuristic algorithm is efficient and that the proposed model is suited for recovering heterogeneous data. Implications for clustering researchers are discussedArtigo Sinais e sistemas definidos sobre aritmética intervalar complexa(Sociedade Brasileira de Matemática Aplicada e Computacional, 2012-03-17) Santana, Fabiana Tristão de; Santana, Fágner Lemos; Doria Neto, Adrião Duarte; Santiago, Regivan Hugo NunesNeste trabalho, é feita a fundamentação para os conceitos de sinais e sistemas intervalares complexos, fazendo-se o uso da aritmética complexa retangular e do conceito de intervalo de números complexos feito com auxílio da chamada ordem de Kulisch-Miranker para complexos. É apresentado também o conceito de representação intervalar e é definida a representação canônica intervalar (CIR) de funções complexas. A partir de um sistema f que opere sobre sinais cujos valores sejam números complexos, usando a função CIR, encontra-se um sistema intervalar F o qual preserva, no ambiente intervalar, as propriedades de f, tais como estabilidade, invariância no tempo, aditividadade, homogeneidade e linearidadeArtigo Uma ferramenta computacional par o agendamento de operações do programa de acessibilidade especial porta a porta - PRAE(SOBRAPO, 2014) Rocha, Caroline Thennecy de Medeiros; Dantas, Saulo de Tarso Alves; Aloise, Daniel; Galvão, José Claudio; Martins, Ana Maria da SilvaEm todo o mundo, a demanda por serviços de transporte para pessoas portadoras de necessidades especiais, idosos, e pessoas com mobilidade reduzida vêm crescendo nos últimos anos. A população está envelhecendo, os governos precisam se adaptar a esta realidade, e este fato pode significar oportunidade de negócios para as companhias. Dentro deste contexto está inserido o Programa de Acessibilidade Especial porta a porta – PRAE do município de Natal-RN. A pesquisa presente neste trabalho procura desenvolver um modelo de programação capaz de auxiliar o processo de tomada de decisão dos gestores deste serviço de transporte. Para tanto, foi criado um algoritmo baseado em métodos de geração de soluções aproximativas conhecidas como heurísticas. O objetivo do modelo é incrementar o número de pessoas atendidas pelo PRAE, dada a frota disponível, gerando programações de roteiros otimizadas. O PRAE consiste em um problema de roteirização e programação de veículos do tipo dial-a-ride – DARP, um dos tipos mais complexos dentre os problemas de roteirização. A validação do método de resolução foi feita mediante a comparação entre os resultados auferidos pelo modelo computacional e a programação manual real atual. Os resultados mostraram que o modelo idealizado neste trabalho foi capaz de elevar a capacidade de atendimento deste serviço de transporteArtigo Column generation bounds for numerical microaggregation(Springer, 2014-02-18) Rocha, Caroline Thennecy de Medeiros; Aloise, Daniel; Hansen, Pierre; Santi, ÉvertonThe biggest challenge when disclosing private data is to share information contained in databases while protecting people from being individually identified. Microaggregation is a family of methods for statistical disclosure control. The principle of microaggregation is that confidentiality rules permit the publication of individual records if they are partitioned into groups of size larger or equal to a fixed threshold value, where none is more representative than the others in the same group. The application of such rules leads to replacing individual values by those computed from small groups (microaggregates), before data publication. This work proposes a column generation algorithm for numerical microaggregation in which its pricing problem is solved by a specialized branch-and-bound. The algorithm is able to find, for the first time, lower bounds for instances of three real-world datasets commonly used in the literature. Furthermore, new best known solutions are obtained for these instances by means of a simple heuristic method with the columns generatedArtigo A simple and effective genetic algorithm for the two-stage capacitated facility location problem(Elsevier, 2014) Fernandes, Diogo Robson Montes; Rocha, Caroline Thennecy de Medeiros; Aloise, Daniel; Ribeiro, Glaydston M.; Santos, Enilson Medeiros dos; Silva, AllysonThis paper presents a simple and effective Genetic Algorithm (GA) for the two-stage capacitated facility location problem (TSCFLP). The TSCFLP is a typical location problem which arises in freight transportation. In this problem, a single product must be transported from a set of plants to meet customers demands, passing out by intermediate depots. The objective is to minimize the operation costs of the underlying two-stage transportation system thereby satisfying demand and capacity constraints of its agents. For this purpose, a GA is proposed and computational results are reported comparing the heuristic results with those obtained by two state-of-the-art Lagrangian heuristics proposed in the literature for the problemArtigo Wi-Bio: management policy aimed at the establishment of networks for patient monitoring using IEEE 802.11(Sociedade Brasileira de Engenharia Biomédica, 2014) Souza, Vinícius Samuel Valério de; Valentim, Ricardo Alexsandro de Medeiros; Brandão, Gláucio Bezerra; Silveira, Luiz Felipe de Queiroz; Dantas, Marcel da Câmara Ribeiro; Souza, Pedro Thiago Valério deINTRODUCTION: Patient monitoring will tend to decline in the coming years due to a shortage of physical and human resources in hospitals. Therefore, several studies define alternatives to improve patient monitoring using wireless networks. In these studies, a wireless network is used to transfer data generated by medical sensors without interacting with the traffic in the data network of the hospital. However, this approach should be avoided because there are demands for integration between user applications and patient monitoring. Therefore, this paper defines a patient monitoring system, called Wi-Bio, directed to the establishment of IEEE 802.11 networks that allows traffic generated by user applications. METHODS: The formal validation of Wi-Bio was made through the design of Petri nets, and performance analysis was performed through simulations of the Network Simulator 2 tool. The adoption of this approach is justified by the fact that Petri nets allow verification of logical correctness of the designed systems, while simulations allow behavioral analysis of Wi-Bio in overload scenarios where many patients are monitored. RESULTS: The results confirmed the validity of the designed Petri nets and showed that Wi-Bio is able to accomplish the temporal goals imposed by medical sensors, thereby promoting efficient integration of traffic present in the data network and the patient monitoring network. CONCLUSION: As described, Wi-Bio fulfilled its objectives and motivates future studies aimed at complementing the obtained resultsArtigo A Versao 2006 da Equipe POTI de Futebol de Robos o(II JRI - Jornada de Robótica Inteligente, 2006) Cerqueira, Auciomar C. T.; Lins, Filipe C. A.; Medeiros, Adelardo Adelino Dantas de; Alsina, Pablo J.Artigo A survey of control architectures for autonomous mobile robots(Journal of the Brazilian Computer Society, 1998-04) Medeiros, Adelardo Adelino Dantas de