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Da Silva M.F.,Federal Institute of Bahia | De Area Leao Pereira E.J.,Federal Institute of Maranhao | De Castro A.P.N.,Computational Modeling Program SENAI CIMATEC | Garcia Vivas Miranda J.,Federal University of Bahia | Zebende G.F.,Computational Modeling Program SENAI CIMATEC
Physica A: Statistical Mechanics and its Applications | Year: 2015

The objective of this paper is to demonstrate the influence of the blue-chips companies in the stock market. In this, we apply the detrended cross-correlation coefficient ρDCCA at the São Paulo stock market (Ibovespa, Brazil). Initially we found that there is a positive cross-correlation between these companies and the index. Afterwards, we show that the cross-correlation coefficient value depends on the time scale and the specific company (blue-chips). Thus, this type of analysis lets to infer what is the most adherent company with Ibovespa. Also, in this paper we analyze, in the point of view of ρDCCA, the 2008 financial crisis (before/after). Altogether, the results show that there is more cross-correlation between Ibovespa index the blue-chips after the 2008 crisis. © 2015 Elsevier B.V. All rights reserved.


Amaral F.M.,University of Sao Paulo | Amaral F.M.,Federal Institute of Bahia | Alberto L.F.C.,University of Sao Paulo
International Journal of Robust and Nonlinear Control | Year: 2011

The behavior of stability regions of nonlinear autonomous dynamical systems subjected to parameter variation is studied in this paper. In particular, the behavior of stability regions and stability boundaries when the system undergoes a type-zero sadle-node bifurcation on the stability boundary is investigated in this paper. It is shown that the stability regions suffer drastic changes with parameter variation if type-zero saddle-node bifurcations occur on the stability boundary. A complete characterization of these changes in the neighborhood of a type-zero saddle-node bifurcation value is presented in this paper. © 2010 John Wiley & Sons, Ltd.


Silva F.G.S.,Federal Institute of Bahia | de Lima R.N.,Federal University of Bahia | Freire R.C.S.,Federal University of Campina Grande
Microwave and Optical Technology Letters | Year: 2016

In this article, the design and implementation of a dual-band power amplifier using multiresonant networks is presented. The measurement results have shown 50.7% and 37.2% of PAE peak efficiency at 29.6 dBm and 26.5 dBm output power, respectively, at 433 and 865 MHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2807–2811, 2016. © 2016 Wiley Periodicals, Inc.


Simas Filho E.F.,Federal University of Rio de Janeiro | Simas Filho E.F.,Federal Institute of Bahia | de Seixas J.M.,Federal University of Rio de Janeiro | CalOba L.P.,Federal University of Rio de Janeiro
Neurocomputing | Year: 2010

The nonlinear independent component analysis (NLICA) is an extension of the standard ICA model that does not restrict the mixing system to be linear. Different algorithms have been proposed to solve the NLICA problem, but, as the dimension of the problem increases, most of them present limitations such as poor accuracy and high computational cost. In this work, a novel structural model is proposed for the overdetermined NLICA problem (when there exist more sensors than sources), by adding a signal compaction block to the standard post-nonlinear (PNL) de-mixing model. The proposed methodology proves to be efficient in the feature extraction phase of a challenging high-dimensional online neural discrimination problem. © 2010 Elsevier B.V.


Novais R.L.,Federal University of Bahia | Novais R.L.,Federal Institute of Bahia | De F. Carneiro G.,Federal University of Bahia | Simoes Jr. P.R.M.,Federal University of Bahia | Mendonca M.G.,Federal University of Bahia
Lecture Notes in Business Information Processing | Year: 2012

Software evolution is one of the most important topics in modern software engineering research. This activity requires the analysis of large amounts of data describing the current software system structure as well as its previous history. Software visualization can be helpful in this scenario, as it can summarize this complex data into easy to interpret visual scenarios. This paper presents an interactive differential approach for visualizing software evolution. The approach builds multi-view structural descriptions of a software system directly from its source code, and uses colors to differentiate it from any other previous version. This differential approach is highly interactive allowing the user to quickly brush over many pairs of versions of the system. As a proof of concept, we used the approach to analyze eight versions of an open source system and found out it was useful to quickly identify hot spot and code smell candidates in them. © 2012 Springer-Verlag.


Aquino A.L.L.,Federal University of Alagoas | Junior O.S.,Pontifical Catholic University of Minas Gerais | Frery A.C.,Federal University of Alagoas | De Albuquerque E.L.,Federal Institute of Bahia | Mini R.A.F.,Pontifical Catholic University of Minas Gerais
IEEE Transactions on Computers | Year: 2014

A wireless sensor network can be used to collect and process environmental data, which is often of multivariate nature. This work proposes a multivariate sampling algorithm based on component analysis techniques in wireless sensor networks. To improve the sampling, the algorithm uses component analysis techniques to rank the data. Once ranked, the most representative data is retained. Simulation results show that our technique reduces the data keeping its representativeness. In addition, the energy consumption and delay to deliver the data on the network are reduced. © 1968-2012 IEEE.


Novais R.L.,Federal University of Bahia | Novais R.L.,Federal Institute of Bahia | Torres A.,Federal University of Bahia | Mendes T.S.,Federal University of Bahia | And 4 more authors.
Information and Software Technology | Year: 2013

Background Software evolution is an important topic in software engineering. It generally deals with large amounts of data, as one must look at whole project histories as opposed to their current snapshot. Software visualization is the field of software engineering that aims to help people to understand software through the use of visual resources. It can be effectively used to analyze and understand the large amount of data produced during software evolution. Objective This study investigates Software Evolution Visualization (SEV) approaches, collecting evidence about how SEV research is structured, synthesizing current evidence on the goals of the proposed approaches and identifying key challenges for its use in practice. Methods A mapping study was conducted to analyze how the SEV area is structured. Selected primary studies were classified and analyzed with respect to nine research questions. Results SEV has been used for many different purposes, especially for change comprehension, change prediction and contribution analysis. The analysis identified gaps in the studies with respect to their goals, strategies and approaches. It also pointed out to a widespread lack of empirical studies in the area. Conclusion Researchers have proposed many SEV approaches during the past years, but some have failed to clearly state their goals, tie them back to concrete problems, or formally validate their usefulness. The identified gaps indicate that there still are many opportunities to be explored in the area. © 2013 Elsevier B.V. All rights reserved.


Isidio De Lima J.J.,Federal University of Bahia | Caetano Da Silva J.,Federal Institute of Bahia | Rodriguez-Esquerre V.F.,Federal University of Bahia
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The absorption and reflection characteristics of multilayered nanoplasmonic gratings with sub wavelength sizes are analyzed in details by using an efficient finite element method. The multilayered structures are composed by several layers of nanoparticles of metals such as Silver, Gold and Aluminum embedded in dielectric such as amorphous silicon over a metallic substrate. The propagations characteristics for several geometrical configurations are obtained and a broadband reflection or absorption covering the near infrared wavelengths has been observed. The proposed nanoplasmonic structures have a great potential for applications in photovoltaic cells or polarizers by improving their reflection or absorption efficiency. Peaks of reflection or absorption larger than 80% were obtained and their performance over the near infrared can be improved by adequately tuning their geometrical parameters, the refractive index and thickness of the layers as well as the nanoparticles shape and size. © 2015 SPIE.


Novais R.L.,Federal Institute of Bahia | Nunes C.,Pontifical Catholic University of Rio de Janeiro | Garcia A.,Pontifical Catholic University of Rio de Janeiro | Mendonca M.,Federal University of Bahia
IEEE International Conference on Software Maintenance, ICSM | Year: 2013

Program comprehension is an essential activity to perform software maintenance and evolution. Comprehensibility often encompasses the analysis of individual logical units, called features, which are often scattered through many program modules. Understanding how the feature code is implemented along the software evolution history is essential, for instance, to perform refactoring activities. However, existing tools do not provide means to comprehend the feature code evolution. To overcome this shortcoming, this paper presents a tool called Source Miner Evolution (SME) that provides multiple interactive and coordinated views to comprehend feature code evolution. SME implements a feature-sensitive comparison of multiple program versions. Our usability assessment with experienced developers indicated that SME allows them to efficiently perform recurring comprehension tasks on evolving feature code. The developers' performance was influenced by the combination of visual SME mechanisms, such as colors, tool tips and menu-popup interactions over the features' code elements. © 2013 IEEE.


Pitangueira A.M.,Federal University of Bahia | Pitangueira A.M.,Federal Institute of Bahia | Maciel R.S.P.,Federal University of Bahia | De Oliveira Barros M.,Post graduate Information Systems Program | Andrade A.S.,Federal University of Bahia
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013

Selection and prioritization of software requirements represents an area of interest in Search-Based Software Engineering (SBSE) and its main focus is finding and selecting a set of requirements that may be part of a software release. This paper uses a systematic review to investigate which SBSE approaches have been proposed to address software requirement selection and prioritization problems. The search strategy identified 30 articles in this area and they were analyzed for 18 previously established quality criteria. The results of this systematic review show which aspects of the requirements selection and prioritization problems were addressed by researchers, the methods approaches and search techniques currently adopted to address these problems, and the strengths and weaknesses of each of these techniques. The review provides a map showing the gaps and trends in the field, which can be useful to guide further research. © 2013 Springer-Verlag.

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