889 resultados para Minor Component Analysis


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O objetivo deste trabalho foi relacionar as características da anatomia foliar de Brachiaria decumbens (capim-braquiária) e Brachiaria plantaginea (capim-marmelada), em três estádios de desenvolvimento da planta, com a sensibilidade a herbicidas. A semeadura foi feita em vasos plásticos, contendo solo, mantidos em casa de vegetação. Foi amostrada a porção mediana do limbo da terceira folha expandida, a partir da base do colmo, compreendendo três estádios de desenvolvimento da planta: estádio 1 (com 4-6 folhas), estádio 2 (com 3-4 perfilhos) e estádio 3 (plantas adultas no início do florescimento). Foram quantificados os seguintes descritores anatômicos das regiões da quilha (nervura central) e da asa (porção entre a nervura central e a margem do limbo): área da secção transversal; porcentagens de epiderme das faces adaxial e abaxial, esclerênquima, bainha do feixe vascular, feixe vascular e parênquima; espessura da folha; distância entre os feixes vasculares; comprimento do estômato; e número de estômatos e de tricomas (curtos e longos). Os valores obtidos foram submetidos aos testes estatísticos multivariados de Análise de Agrupamento e Análise dos Componentes Principais. Os descritores avaliados permitiram diferenciar o estádio 3 de desenvolvimento da planta em relação aos demais, o qual pode ser considerado o menos sensível à ação dos herbicidas aplicados em pós-emergência.

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As espécies Commelina benghalensis, C. villosa, C. diffusa e C. erecta são conhecidas como trapoeraba e, freqüentemente, são confundidas entre si, dificultando o controle químico, o que pode provocar prejuízos econômicos e danos ambientais. O presente trabalho teve como objetivo selecionar características morfológicas que possibilitem facilitar a identificação dessas espécies, utilizando a técnica de análise multivariada. Foram avaliadas 12 características morfológicas descritivas e 13 quantitativas, utilizando-se os métodos de análise de agrupamento e análise de componentes principais. As espécies apresentaram alto grau de dissimilaridade, sobretudo em relação às características descritivas, destacando-se: hábito da planta, pilosidade do caule e da folha, entre outros. As características quantitativas também mostraram poder discriminatório. Características que apresentaram alto valor taxonômico foram selecionadas para compor a chave de identificação para as quatro espécies de Commelina.

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This paper aims to study the ecological system of the Pardo River, at the source and lower-order passages, which are in the Botucatu area, São Paulo State, Brazil. This study was carried out to determine water quality with some chemical-physical indicators, coliforms, and chemical species of samples taken monthly, 1995/02-1996/01, from eight sampling stations sited along the Pardo River. The results in the river monitoring are discussed based on annual averages, analysis of variance, and compared to Tukey's Studentized Range-HSD, and principal component analysis (PCA) was applied to normalize data to assess association between variables. We can conclude that the variables used are very efficient for identifying and that the dry season shows the worst water quality. These were caused by organic matter, nutrients (originate) from anthropogenic sources (spatial sources) and mainly municipal wastewater, affecting the quality and hydrochemistry of the river water, which have been differentiated and assigned to polluting sources. Meanwhile, the degree of degradation of the Pardo River is low (sewage treatment carried out by the city of Pardinho is efficient), leaving the water of the river suitable for use by the population of Botucatu, after conventional treatment (Conama, Resolucao No. 20, CONAMA, Brazilia DF, 09-23, 1986-the water of the Pardo river is classified as level 03). (C) 2001 Elsevier B.V. Ltd. All rights reserved.

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A biometric study of caste development was carried out using Nasutitermes sp., by measuring the height, width, and length of the head, the length and width of the pronotum and mesonotum, and the length of the posterior tibia. These measurements were taken on 200 individuals, including larvae, nymphs, workers, pre-soldiers and soldiers. For instar separation, it was verified that the Principal Component Analysis (P.C.A.) was the most efficient methodology. Results of this analysis showed that Nasutitermes coxipoensis follows the general pattern of development presented by other Nasutitermes.

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A number of attempts have been made to obtain a clear definition of biological stress. However, in spite of the efforts, some controversies on the concept of plant stress remain. The current versions are centered either on the cause (stress factor) or on the effect (stress response) of environmental stress. The objective of this study was to contribute to the definition of stress, using a hierarchical approach. Thus, we have performed an analysis of the most usual stress concepts and tested the relevance of considering different observation scales in a study on plant response to water deficit. Seedlings of Eucalyptus grandis were grown in vitro at water potentials ranging from -0.16 to -0.6 MPa, and evaluated according to growth and biochemical parameters. Data were analyzed through principal component analysis (PCA), which pointed to a hierarchical organization in plant responses to environmental disturbances. Growth parameters (height and dry weight) are more sensitive to water deficit than biochemical ones (sugars, proline, and protein), suggesting that higher hierarchical levels were more sensitive to environmental constraints than lower hierarchical ones. We suggest that before considering an environmental fluctuation as stressful, it is necessary to take into account different levels of plant response, and that the evaluation of the effects of environmental disturbances on an organism depends on the observation scale being used. Hence, a more appropriate stress concept should consider the hierarchical organization of the biological systems, not only for a more adequate theoretical approach, but also for the improvement of practical studies on plants under stress.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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We investigate the solution of the gap equation for mixed order parameter symmetry states as a function of filling using a two-dimensional tight-binding model incorporating second-neighbor hopping for tetragonal and orthorhombic lattice, the principal (major) component of the order parameter is taken to be of the d(x2-y2) type, As suggested in several investigations the minor component of the order parameter is taken to be of the d(xy) type. Both the permissible mixing angles 0 and pi/2 between the two components are considered. As a function of filling pronounced maxima of d(x2-y2) order parameter is accompanied by minima of the d(xy) order parameter. At fixed filling. The temperature dependence of the two components of the order parameter is also studied in all cases. The variation of critical temperature T, with filling is also studied and T-c is found to increase with second-neighbor hopping. (C) 2001 Elsevier B.V. B.V. All rights reserved.

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