P. J. Almeida

Learn More
The analysis of E-2-nonenal is of considerable interest for the brewery industry as this compound is claimed to be responsible for a paper/cardboard unpleasant flavour. Usually, the presence of E-2-nonenal can be noticed in aged beers at levels higher than 0.1 microg/l. In this work, an analytical method was developed to determine E-2-nonenal in beer(More)
The main results of this paper are twofold: the first one is a matrix theoretical result. We say that a matriz is superregular if all of its minors that are not trivially zero are nonzero. Given a a × b, a ≥ b, superregular matrix over a field, we show that if all of its rows are nonzero then any linear combination of its columns, with nonzero coefficients,(More)
We experimentally demonstrate the use of saw-tooth optical pulses, which are shaped using a fiber Bragg grating, to achieve robust and high performance time-domain add-drop multiplexing in a scheme based on cross-phase (XPM) modulation in an optical fiber, with subsequent offset filtering. As compared to the use of more conventional pulse shapes, such as(More)
The key factors that influence the population growth rate can be identified with sensitivity analysis. Caswell presented an algorithm based on vector calculus that speeds up, and improves the practicality of the application of the sensitivity analysis, by calculating the derivatives of the explicit elements from the population Leslie matrix. Despite the(More)
In this paper, we describe compact laser sources based on high-power amplification in Yb-doped silica fibers of ultra-stable mode-locked pulses from an all-fiber oscillator. The interplay between third-order nonlinearity, gain and chromatic dispersion in the polarization-maintaining fiber amplifier is engineered to produce high-quality, high-energy pulses(More)
A method for the simultaneous determination of E-2-nonenal and beta-damascenone in beer by reversed-phase liquid chromatography using UV detection is presented. The method consists of beer steam distillation, followed by an extraction/concentration step using Sep-Pak Plus C18 RP cartridges and determination by HPLC at 226 nm UV-absorption maximum. The(More)
This paper deals with the problem of constructing superregular matrices that lead to MDP convolutional codes. These matrices are a type of lower block triangular Toeplitz matrices with the property that all the square submatrices that can possibly be nonsingular due to the lower block triangular structure are nonsingular. We present a new class of matrices(More)
Let H(x) = ∑ n≤x φ(n) n − 6 π2x. Motivated by a conjecture of Erdös, Lau developed a new method and proved that #{n ≤ T : H(n)H(n + 1) < 0} T. We consider arithmetical functions f(n) = ∑ d|n bd d whose summation can be expressed as ∑ n≤x f(n) = αx+P (log(x))+E(x), where P (x) is a polynomial, E(x) = − ∑ n≤y(x) bn n ψ ( x n ) + o(1) and ψ(x) = x− bxc − 1/2.(More)
Résumé. Soit H(x) = ∑ n≤x φ(n) n − 6 π2x. Motivé par une conjecture de Erdös, Lau a développé une nouvelle méthode et il a démontré que #{n ≤ T : H(n)H(n + 1) < 0} T. Nous considérons des fonctions arithmétiques f(n) = ∑ d|n bd d dont l’addition peut être exprimée comme ∑ n≤x f(n) = αx+ P (log(x)) + E(x). Ici P (x) est un polynôme, E(x) = − ∑ n≤y(x) bn n ψ(More)
  • 1