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Kyriazis G.A.,National Institute of Metrology of Brazil
IEEE Transactions on Instrumentation and Measurement | Year: 2011

A Bayesian approach to spectrum analysis using approximations based on the posterior mode is applied here to waveform metrology. A simple algorithm for obtaining accurate estimates of signal parameters and their associated uncertainties is presented. It is assumed that the data can be modeled with trigonometric equations. The algorithm can be easily implemented with those commercial laboratory software packages routinely used by metrologists for controlling instrumentation and reporting measurement results. Its performance has been confirmed through several experimental setups. © 2006 IEEE. Source


Kyriazis G.A.,National Institute of Metrology of Brazil
IEEE Transactions on Instrumentation and Measurement | Year: 2013

A simple method for estimating the parameters of complex modulated signals from digital sampling data is proposed. It can be employed with advantage to analyze the modulation functions of commercial arbitrary waveform (AW) generators. Although this problem of inference has many applications in communication technology, it has also become a concern to the power industry in issues related to mains flicker measurements. Prior information available to metrologists about AW carriers or modulating signals allows the reduction of the dimensionality of the search algorithm with consequent time savings. © 1963-2012 IEEE. Source


Mikhailov M.D.,National Institute of Metrology of Brazil | Freire A.P.S.,Mechanical Engineering Program
Powder Technology | Year: 2013

An accurate model for the drag coefficient (CD) of a falling sphere is presented in terms of a non-linear rational fractional transform of the series of Goldstein (Proc. Roy. Soc. London A, 123, 225-235, 1929) to Oseen's equation. The coefficients of the six polynomial terms are improved through a direct fit to the experimental data of Roos and Willmarth (AIAA J., 9:285-290, 1971). The model predicts CD up to Reynolds number 100,000 with a standard deviation of 0.04. Results are compared with eight different formulations of other authors. © 2012 Elsevier B.V. Source


Da Silva T.F.,National Institute of Metrology of Brazil
Applied Optics | Year: 2016

Single-photon avalanche photodiodes (SPADs) are instruments capable of measuring light at the single-photon level. Some important features of these devices must be correctly characterized for reliable application. In this paper, I present a high-resolution self-triggered method for characterization of SPADs based on the analysis of the time intervals between consecutive detection events with the detector under continuous-wave illumination. The self-triggered method is employed for characterization of the detection dead time - a limiting feature for the maximum counting rate achievable under free-running or gated modes - and of the temporal gate width - an important parameter when the detector is operated under gated mode. The measurement results are presented and the method is experimentally validated. © 2016 Optical Society of America. Source


Barbieri Gonzaga F.,National Institute of Metrology of Brazil | Pereira Sobral S.,National Institute of Metrology of Brazil
Talanta | Year: 2012

A new method is proposed for determining the acid number (AN) of biodiesel using coulometric titration with potentiometric detection, basically employing a potentiostat/galvanostat and an electrochemical cell containing a platinum electrode, a silver electrode, and a combination pH electrode. The method involves a sequential application of a constant current between the platinum (cathode) and silver (anode) electrodes, followed by measuring the potential of the combination pH electrode, using an isopropanol/water mixture as solvent and LiCl as the supporting electrolyte. A preliminary evaluation of the new method, using acetic acid for doping a biodiesel sample, showed an average recovery of 100.1%. Compared to a volumetric titration-based method for determining the AN of several biodiesel samples (ranging from about 0.18 to 0.95 mg g -1), the new method produced statistically similar results with better repeatability. Compared to other works reported in the literature, the new method presented an average repeatability up to 3.2 times better and employed a sample size up to 20 times smaller. © 2012 Elsevier B.V. All rights reserved. Source

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