Browsing by Author "Gonzalez, L"

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    Automated testing of aluminum castings using classifier fusion strategies
    (AMER SOC NONDESTRUCTIVE TEST, 2005) Mery, D; Chacon, M; Gonzalez, L; Munoz, L
    Generally, discontinuity detection in automated visual testing consists of two steps: identification of potential discontinuities using image processing techniques and classification of potential discontinuities into discontinuities and regular structures (false alarms) using a pattern recognition methodology. In the second step, since several features cyan be extracted from the potential discontinuities, a feature selection must be performed. In this paper, several known classifiers are studied in automated visual testing: threshold, euclidean, mahalanobis, polynomial, support vector machine and neural network classifiers. First, the performance of the classifiers is assessed individually. Second, the classifiers are combined in order to improve their performance. Seven fusion strategies in the combination were tested: and, or, majority vote, product, sum, maximum and median. The proposed methodology was tested on real data acquired from 50 noisy radiographic images of aluminum wheels, where 23 000 potential discontinuities (with only 60 real discontinuities) were segmented and 405 features were extracted for each potential discontinuity. Using fusion of classifiers, a very good performance was achieved, yielding a sensitivity of 100% and specificity of 99.97%.
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    Study of the iron catechin complexes in dimethyl sulphoxide. Redox chemistry and interaction with superoxide radical anion in this medium.
    (2001) Bodini, ME; Del Valle, MA; Tapia, R; Leighton, F; Gonzalez, L
    The redox chemistry of catechin (catH(2)) and its iron complexes has been studied in dimethyl sulphoxide. In the absence of base a one-to-one iron (II)-catechin complex is formed which exhibits oxidation processes at 0.28, 0.66, and 0.92 V vs SCE. These processes correspond to the oxidation of Fe(II) to Fe(III), the formation of the quinonic form of the catechol moiety and the oxidation of another hydroxy group to a radical. In the presence of base a stable 1:1 complex is formed with oxidation processes that show up at +0.25, +0.64, and +0.88 V vs SCE. The voltammetric and spectroscopic characterization of the species produced after the oxidation processes is described. Upon interaction of the complex with superoxide radical anion in dimethyl sulphoxide, the basic character of this radical anion causes the formation of the monoanion of catechin leading to a more stable complex of iron(II). The protonated superoxide disproportionates to molecular oxygen and peroxide, causing the oxidation of the metal ion. The addition of a second equivalent of superoxide oxidizes bound catechin to the corresponding semiquinone. The formation of hydroxy radicals through Fenton chemistry does not take place because peroxide is consumed and the metal ion remains as a stable iron(III) complex.