[pt] Em análises efetuadas através de Métodos de Elementos de Contorno, o procedimento de integração exerce um papel fundamental, já que faz-se necessária a avaliação de integrais singulares e quase-singulares que introduzem erros numéricos nos resultados quando não são devidamente avaliadas. Nos últimos anos, vários pesquisadores sugeriram diferentes técnicas de integração para tratar os problemas de integração de uma forma adequada. Este trabalho inicia apresentando alguns conceitos básicos e uma revisão bibliográfica das principais técnicas sugeridas. Em seguida, apresenta-se uma técnica de integração unificada, que possui uma forma simples e oferece resultados com excelente precisão. A técnica proposta foi aplicada para integrais singulares ou quase- singulares possuindo pólos simples ou múltiplos, sendo que tanto integrais unidimensionais quanto integrais bidimensionais foram consideradas.Paralelamente ao estudo das integrais, foi desenvolvido um programa computacional em linguagem orientada a objetos (C++), destinado a implementar simultaneamente a formulação convencional e as formulações híbridas dos Métodos de Elementos de Contorno. Da forma em que foi planejado, a implementação suporta diferentes aplicações de análises de engenharia. Este programa resultou de um trabalho conjunto realizado com pesquisadores da Universidade de Stuttgart. Por fim, apresentam-se diversos exemplos numéricos e resultados de análises, ressaltando o bom desempenho da técnica proposta e a influência do procedimento de integração em análises através de Métodos de Elementos de Contorno. / [en] In Boundary Element Method analysis, the integration procedure is one of the most important tasks, since one has to deal with singular and quasi-singular integrals which introduce numerical errors in the results, if they are not evaluated adequately. In the last years, several researchers have suggested different techniques with the aim of handling the problem adequately. This work begins presenting some basic concepts and a review of the most important work published before. Following, it introduces a unified integration technique which has a simple form and provides highly accurate results. The proposed scheme also deals with one- or two-dimensional singular or quasi- singular integrals having single or multiple poles. Besides the study of the integrals, a computational code was developed using an objectoriented computer language (C++). This code takes into account the conventional and hybrid formulations of the Boundary Element Method and supports different types of engineering analysis. This computer program was developed in a frame of a joint project with some researchers from the University of Stuttgart.Finally, several numerical examples and analysis results are displayed, showing the good performance of the proposed technique and the influence of the integration task in analysis using Boundary Element Methods.

From Introduction: With the rapidly growing knowledge on trace elements and their influence on plant nutrition the need for accurate and rapid methods for their determination arose. The essential plant nutrients are usually divided into two groups. The major or macronutrient elements, necessary in comparatively large amounts, and the trace or micro-nutrient elements. In the case of plants, the first group includes Sulphur, Phosphorus, Potassium, Magnesium, Calcium and Nitrogen. The essential trace elements are Iron, manganese, Boron, Copper, Zinc, Molybdenum and Chlorine. Cobalt is essential for animal nutrition as a constituent of Vitamin B₁₂, but its essentiality for plants has not yet been proved. The latter group consists of metals which are catalysts in enzyme reactions and whose presence in the plant in minute amount determines whether the plant will be able to complete the vegetative or reproductive stage of its life cycle. Molybdenum may be quoted as an example of an essential trace element. It is generally recognised to be the catalyst responsible for the fixation of Nitrogen.

Micrometer-thin rims of hydrothermally altered zircon preserve significant geological information regarding the timing and nature of fluid infiltration. The research presented in this thesis details an investigation of the isotopic and geochemical composition zircon rims from deformed Archean meta-sedimentary rocks proximal to the world class Musselwhite gold deposit. A continuous ablation Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb technique is proposed in conjunction with Secondary Ion Mass Spectrometry (SIMS) U-Pb and LA-ICP-MS REE depth profile methods. These techniques are capable of identifying and analyzing isotopic and chemical modification of zircon rims that are <5 μm thick by ablating directly into the surface of unpolished crystals. The age of analyzed rims is >100 m.y younger than crystal interiors and corresponds to periods of regional magmatism and hydrothermal activity. The measured thickness of rims is variable across single grains and between grain suites suggesting that they do not form as a uniform mantle around the crystal interior. Instead the interacting fluids exploit pre-existing structural weaknesses caused by sedimentary transport and the α-decay of uranium. A novel LA-ICP-MS single element grain 2-dimension mapping technique for unpolished zircon demonstrates preferential element mobility along fractures and in isolated patches. Pressure-temperature experiments were conducted on a zircon reference material under lower greenschist facies conditions to better understand the low temperature incorporation of REEs into the zircon structure. LA-ICP-MS element mapping of unpolished grains reveals that zircon are chemically modified under these conditions, as characterized by an increase in Ce and Y concentration (up to an order of magnitude enrichment) in CePO4-bearing and YPO4-bearing experiments, respectively, when compared with the concentrations of unaltered primary grains. The integration of these micro-analytical techniques on unpolished zircon can provide insight into the timing of low- to moderate-temperature history of supracrustal rocks which would remain otherwise undefined.

M.Sc.

This comparative study attempts to determine the importance of soil fertility in determining how much of an element a plant absorbs.

Waveguides are used to transmit electromagnetic signals.Their geometry is typically long and slender their particularshape can be used in the design of computational methods. Onlyspecial modes are transmitted and eigenvalue and eigenvectoranalysis becomes important. We develop a .nite-element code for solving theelectromagnetic .eld problem in closed waveguides .lled withvarious materials. By discretizing the cross-section of thewaveguide into a number of triangles, an eigenvalue problem isderived. A general program based on Arnoldi’s method andARPACK has been written using node and edge elements toapproximate the .eld. A serious problem in the FEM was theoccurrence of spurious solution, that was due to impropermodeling of the null space of the curl operator. Therefore edgeelements has been chosen to remove non physical spurioussolutions that arises. Numerical examples are given for homogeneous andinhomogeneous waveguides, in the homogeneous case the resultsare compared to analytical solutions and the right order ofconvergence is achieved. For the more complicated inhomogeneouswaveguides with and without striplines, comparison has beendone with results found in literature together with gridconvergence studies. The code has been implemented to be used in an industrialenvironment, together with full 3-D time and frequency domainsolvers. The2-D simulations has been used as input for full3-D time domain simulations, and the results have been comparedto what an analytical input would give. / NR 20140805

The instrumentation and methodology for real-time computer controlled scanning potential coulometry for multi-component trace analysis is described. The sensitivity limit was determined to be 10^-8 F for electrochemically reversible constituents. The sensitivity limit could be extended if measures were taken to compensate for the periodic signal found on the electrolysis current. Non-linear least squares curve fitting methods accurately resolved iron-platinum and silver-iron interferences to give accurate determinations for iron and silver. The resolving capability of this method was tested using theoretically generated scanning potential coulograms. The computer resolved sample constituents with a 1 to 100 concentration ratio and a formal potential separation of 10 millovolts. It also accurately resolved sample constituents with a 1 to 1000 concentration ratio, one with 1 equivalent per and the other with 2 equivalents per mole, but with no formal potential separation.

Caenorhabditis Elegans genome maintains active H3K36me3 chromatin domains interspersed with repressive H3K27me3 domains on the autosomes’ distal ends. The mechanisms stabilizing these domains and the prevention of position-effect variegation remains unknown as no insulator elements have been identified in C. elegans. De-novo motif discovery applied on mes-4 binding sites links the H3K36me3-specific methyltransferase to a class of non-coding DNA known as Periodic An/Tn Clusters (PATCs). PATCs display characteristics of insulator elements such as local nucleosome depletion and their restriction to genes with specific expression profiles and chromatin marks. Finally, I describe a set of experiments to further investigate the role of PATCs and mes-4 in the maintenance of stable chromatin domains using a synthetic biology approach.

The distribution and speciation of trace metals in natural waters is only slightly, at best, understood. Interactions with organic substances can effectively distribute the metals throughout many ill-defined physical and chemical. To better comprehend the complexity of metal-organic interactions this work focused on the delineation of trace iron species present in a natural system. The separation of Fe(II) and Fe(III) was successfully accomplished using a variation of an ion exchange method involving resin-loaded filter paper. The quantitation of the various iron species was determined using linear scan voltammetry and atomic absorption. The total iron concentration, determined as the sum of the various separate species, compares favorably with the total iron concentration as determined directly using atomic absorption methods.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Nuclear Engineering. / Microfiche copy available in Archives and Science. / Vita. / Includes bibliographical references. / by George Charman Allen, Jr. / Ph.D.