Navegando por Autor "OLIVEIRA, Terezinha Ferreira de"

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Acesso aberto (Open Access)
Evaluation via multivariate techniques of scale factor variability in the rietveld method applied to quantitative phase analysis with X ray powder diffraction
(2006-12) OLIVEIRA, Terezinha Ferreira de; AVILLEZ, Roberto Ribeiro de; EPPRECHT, Eugenio Kahn; QUEIROZ, Joaquim Carlos Barbosa
The present work uses multivariate statistical analysis as a form of establishing the main sources of error in the Quantitative Phase Analysis (QPA) using the Rietveld method. The quantitative determination of crystalline phases using x ray powder diffraction is a complex measurement process whose results are influenced by several factors. Ternary mixtures of Al2O3, MgO and NiO were prepared under controlled conditions and the diffractions were obtained using the Bragg-Brentano geometric arrangement. It was possible to establish four sources of critical variations: the experimental absorption and the scale factor of NiO, which is the phase with the greatest linear absorption coefficient of the ternary mixture; the instrumental characteristics represented by mechanical errors of the goniometer and sample displacement; the other two phases (Al2O3 and MgO); and the temperature and relative humidity of the air in the laboratory. The error sources excessively impair the QPA with the Rietveld method. Therefore it becomes necessary to control them during the measurement procedure.
Acesso aberto (Open Access)
HS-SPME as an efficient tool for discriminating chemotypes of Lippia Alba(Mill.) N. E. Brown
(Universidade Federal do Pará, 2017-01) SILVA, Aiêrta Cristina Carrá da; BARBOSA, Francisco Geraldo; MAFEZOLI, Jair; OLIVEIRA, Maria da Conceição Ferreira de; OLIVEIRA, Terezinha Ferreira de
Lippia alba (Mill.) N. E. Brown (Verbenaceae) is a medicinal plant for which several biological activities are reported, such as sedative, anxiolytic, anti-ulcer, antifungal, antimicrobial, antioxidant, antispasmodic, anti-nociceptive and anti-inflammatory. It is characterized by the production of essential oils which have been used to classify the plant in different chemotypes. In the Northeast region of Brazil, the presence of three chemotypes are reported: myrcene-citral (chemotype I), limonene-citral (chemotype II) and carvone-limonene (chemotype III). In this work, headspace-solid phase microextraction (HS-SPME) was used on the analysis of the volatile organic compounds (VOCs) of three chemotypes of L. alba from the Northeast region of Brazil, and compared to the essential oils of the plants extracted by hydrodistillation. Volatile compounds from each chemotype were more effectively differentiated when extracted by HS-SPME than by hydrodistillation.
Acesso aberto (Open Access)
Modelo de efeitos fixos com medida repetida aplicado em experimentos de melhoramento genético do cupuaçuzeiro
(Universidade Federal do Pará, 2015-12) ALVES, Rafael Moysés; TAVARES, Maria Regina Madruga; TAVARES, Héliton Ribeiro; LOBATO, Tarcísio da Costa; OLIVEIRA, Terezinha Ferreira de
This study was conducted to evaluate vegetative performance of cupuassu progenies, in the immaturity phase, through analysis of repeated measures. The experimental area was installed in the municipality of Tomé Açu, Northeast of the state of Para. We employed 25 full-sib progeny of cupuassu, who had vegetative growth (height and diameter of the plant), monitored for three years. Because of the nature of longitudinal observations it was assessed primarily through Mauchly sphericity test, which type of statistical analysis should be applied. For the variable diameter, sphericity condition was not violated, therefore, proceeded to review the design scheme of split plot. For the height variable, the test was significant, indicating necessarily evaluate the best structure to explain the correlation of errors, being chosen the covariance structure Heterogeneous Composed Symmetry. Differences were found between the progenies only in the third year of evaluation, and the variable diameter of the plant allowed better discriminate the progenies.