Brasília, Brazil
Brasília, Brazil

Time filter

Source Type

Santana E.,Federal University of Maranhão | Principe J.C.,University of Florida | Santana E.,State University of Maranhão | Kardec Barros A.,National Agency of Petroleum
Signal Processing | Year: 2012

This paper addresses the problem of semi-blindly extracting one single desired signal using a priori information about its higher order temporal structure. Our approach is based on the maximization of the autocorrentropy function for a given time delay. The a priori information is quantified as a time delay and a size for a Gaussian kernel to set the free parameters in the correntropy function. Those values provide information which allows the proposed method to adapt a demixing vector to extract the desired signal without the indeterminacy of the permutation problem in blind source separation. Moreover, this method is different from those for Independent Component Analysis that separate all the available sources, which, in some problems, is not desirable or computationally possible. Since correntropy can be interpreted as a generalization of correlation, we demonstrate that it is a suitable measure for studying the temporal behavior of higher order statistics of a signal. Also, the flexibility brought by the kernel size selection allows the user to choose the range of statistics he is interested in. We show in simulations that correntropy achieve better or equal separation than other linear methods proposed in the literature for source extraction based on temporal structures. © 2012 Elsevier B.V. All rights reserved.

Santana E.,Federal University of Maranhão | Principe J.C.,University of Florida | Santana E.E.,State University of Maranhão | Freire R.C.S.,Federal University of Campina Grande | Barros A.K.,National Agency of Petroleum
IEEE Transactions on Signal Processing | Year: 2010

This work derives and evaluates a method for Blind Source Extraction (BSE) in a reproducing kernel Hilbert space (RKHS) framework. The a priori information about the autocorrelation function of the signal under study is translated in a linear transformation of the Gram matrix of the transformed data in Hilbert space. Our method proved to be more robust than methods presented in the literature of BSE with respect to ambiguities in the available a priori information of the signal to be extracted. The approach here introduced can also be seen as a generalization of Kernel principal component analysis (KPCA) to analyze autocorrelation matrices at specific time lags. © 2010 IEEE.

Lucena F.,Nagoya University | Lucena F.,Federal University of Maranhão | Barros A.K.,Federal University of Maranhão | Barros A.K.,National Agency of Petroleum | And 2 more authors.
PLoS ONE | Year: 2011

The heart integrates neuroregulatory messages into specific bands of frequency, such that the overall amplitude spectrum of the cardiac output reflects the variations of the autonomic nervous system. This modulatory mechanism seems to be well adjusted to the unpredictability of the cardiac demand, maintaining a proper cardiac regulation. A longstanding theory holds that biological organisms facing an ever-changing environment are likely to evolve adaptive mechanisms to extract essential features in order to adjust their behavior. The key question, however, has been to understand how the neural circuitry self-organizes these feature detectors to select behaviorally relevant information. Previous studies in computational perception suggest that a neural population enhances information that is important for survival by minimizing the statistical redundancy of the stimuli. Herein we investigate whether the cardiac system makes use of a redundancy reduction strategy to regulate the cardiac rhythm. Based on a network of neural filters optimized to code heartbeat intervals, we learn a population code that maximizes the information across the neural ensemble. The emerging population code displays filter tuning proprieties whose characteristics explain diverse aspects of the autonomic cardiac regulation, such as the compromise between fast and slow cardiac responses. We show that the filters yield responses that are quantitatively similar to observed heart rate responses during direct sympathetic or parasympathetic nerve stimulation. Our findings suggest that the heart decodes autonomic stimuli according to information theory principles analogous to how perceptual cues are encoded by sensory systems. © 2011 Lucena et al.

Braga L.P.,National Agency of Petroleum | Szklo A.S.,Federal University of Rio de Janeiro
Journal of World Energy Law and Business | Year: 2014

The Brazilian regulatory framework for petroleum exploration and production activities was significantly altered after the discovery of pre-salt province. In addition to Act No. 9.478, of 6 August 1997, four new Laws were launched since 2010, creating a new oil company-Pre-Sal Petroleo S.A. (PPSA)-and establishing two other types of international petroleum agreement-production sharing contract (PSC) and onerous assignment agreement. This article aims to explain the new rules launched, and also assess the role of the agents involved and their competences. Present article will also analyse the three petroleum agreements provided by Brazilian Law: concession agreements, onerous assignment and PSC. © The Authors 2013. Published by Oxford University Press on behalf of the AIPN. All rights reserved.

Braga J.W.B.,University of Brasilia | Junior A.A.D.S.,University of Brasilia | Junior A.A.D.S.,National Agency of Petroleum | Martins I.S.,National Agency of Petroleum
Fuel | Year: 2014

In order to ensure the quality of the lubricants, the productive sector and the regulatory agencies require a robust and accurate method to monitor the quality parameters of the lubricant oils. Multivariate methods based on infrared spectroscopy have been proposed as an alternative for quality control analysis of lubricants. However, to the best of our knowledge, no studies or methods were reported covering a significant number of samples of different manufacturers or oil brands that prove their performance and robustness for routine analysis in quality control monitoring by regulatory agencies. Therefore, the present paper describes the development and validation of a method for determination of the viscosity index (VI) of lubricant oils that could be applied for 81 different producers/brands. The 1085 samples used for development and validation were collected from all regions of Brazil by the monitoring program of the National Agency of Petroleum of the Brazil, so that the dataset is representative of the variation in most of the lubricant market in Brazil. The results indicate that the method can be applied for VI determination taking into account the variation in a high number of lubricant producers/brands, different kinds of lubricating oils, regarding the origin of the base oils (mineral or synthetic) and the API and SAE classifications. The method was also simpler than the reference method, fast, required a lower amount of sample and produced fewer chemical residuals. © 2013 Elsevier Ltd. All rights reserved.

Santos A.G.D.,Federal University of Rio Grande do Norte | Araujo A.S.,Federal University of Rio Grande do Norte | Caldeira V.P.S.,Federal University of Rio Grande do Norte | Fernandes Jr. V.J.,Federal University of Rio Grande do Norte | And 2 more authors.
Thermochimica Acta | Year: 2010

Model-free kinetic studies for volatilization of Brazilian sunflower oil and its respective biodiesel were carried out. The biodiesel was obtained by the methylic route using potassium hydroxide as catalyst. Both sunflower oil and biodiesel were characterized by physicochemical analyses, gas chromatography, simulated distillation and thermogravimetry. The physicochemical properties indicated that the oil and biodiesel samples are in accordance with the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP). Gas chromatography indicated that the biodiesel was obtained with a content of ester of ca. 97.35 wt%. The TG curves indicated that the temperatures for volatilization of biodiesel are lower than for sunflower oil, which is explained by their different compositions and properties. The value of the apparent activation energy for the volatilization process, as determinated by the Vyazovkin Method, was higher for sunflower oil than for biodiesel. © 2010 Elsevier B.V. All rights reserved.

Santos A.G.D.,Federal University of Rio Grande do Norte | Caldeira V.P.S.,Federal University of Rio Grande do Norte | Farias M.F.,Federal University of Rio Grande do Norte | Araujo A.S.,Federal University of Rio Grande do Norte | And 2 more authors.
Journal of Thermal Analysis and Calorimetry | Year: 2011

In this study, the physico-chemistry characterization and kinetic study of the thermal decomposition of sunflower oil and its biodiesel were carried out. Sunflower biodiesel was synthesized by the methanol route and basic homogeneous catalysis. The physicochemical characterization of the sunflower oil and biodiesel were performed according to standards set out in the ANP resolution, and both are in accordance to the specifications. The chromatographic analysis was obtained by GC-FID. The yield of conversion of 97.4 wt% of sunflower oil in methyl esters confirms the efficiency of the conversion of the fatty acids into esters. The thermal analysis was performed on a thermobalance, using heating rates of 5, 10, and 20 °C min -1. In these three rates, we observed a single well-defined step of mass loss that describes the volatilization and decomposition of the sunflower oil and the biodiesel. The kinetic study was performed using equations of approximation and integration methods such as Coats-Redfern, Van Krevelen, and Horowitz-Metzger. The kinetic parameters reaction order (n) and apparent activation energy (E a), obtained by applying these method were correlated. © 2011 Akadémiai Kiadó, Budapest, Hungary.

De Almeida A.G.,National Agency of Petroleum
5th CCPS Latin American Conference on Process Safety 2013, LACPS 2013 | Year: 2013

Despite efforts in search alternative sources of energy, the growth in demand for petroleum natural gas is a reality [1] [2]. However, accidents such as that occurred at Piper Alpha platform in 1988 in the UK, at P-36 platform in 2001 in Brazil and Deepwater Horizon drilling rig in the U.S. in 2010 produced a negative impact in oil and gas offshore exploration and production activities. Accidents like these are mainly result of a poorly implemented or nonexistent process safety management system in a company that results in large losses of human lives and environmental impact [3]. In this context, regulators have a special role to enforce the use of good risk management practices in their overview position. For this purpose and to help regulators' decision safety indicators are used to follow performance, show deviations and the need to implement or demand corrective actions to ensure that all efforts are going in a right direction [4]. This study aims to analyze different indicator's programs from regulators and other organizations, select and apply methods to normalize and compose global indicator. Using obtained information related to risk management system and incidents from 67 oil and gas production platforms in Brazil, the results show a new method to follow offshore performance and its companies, in lagging and leading focuses, showing a powerful tool to improve Regulator's overview. It provides to Regulators important information to improve allocation of preventive actions to avoid major accidents. © (2013) by AIChE.

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