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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


Campos-Delgado J.,Catholic University of Louvain | Cancado L.G.,Federal University of Minas Gerais | Achete C.A.,National Institute of Metrology of Brazil | Jorio A.,Federal University of Minas Gerais | Raskin J.-P.,Catholic University of Louvain
Nano Research | Year: 2013

Bilayer graphene with a twist angle θ between the layers generates a superlattice structure known as a Moiré pattern. This superlattice provides a θ-dependent q wavevector that activates phonons in the interior of the Brillouin zone. Here we show that this superlattice-induced Raman scattering can be used to probe the phonon dispersion in twisted bilayer graphene (tBLG). The effect reported here is different from the widely studied double-resonance in graphene-related materials in many aspects, and despite the absence of stacking order in tBLG, layer breathing vibrations (namely ZO' phonons) are observed. © 2013 Tsinghua University Press and Springer-Verlag Berlin Heidelberg. 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

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