Green operators on manifolds with edges are known to be an ingredient of parametrices of elliptic (edge-degenerate) operators. They play a similar role as corresponding operators in boundary value problems. Close to edge singularities the Green operators have a very complex asymptotic behaviour. We give a new characterisation of Green edge symbols in terms of kernels with discrete and continuous asymptotics in the axial variable of local model cones.

We study elliptic boundary value problems in a wedge with additional edge conditions of trace and potential type. We compute the (difference of the) number of such conditions in terms of the Fredholm index of the principal edge symbol. The task will be reduced to the case of special opening angles, together with a homotopy argument.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 188-196).

Habitat loss and fragmentation have been identified as the main drivers of biodiversity loss. These drivers increase the proportion of habitat edges and change the configuration of landscapes. Habitat edges are known to affect ecological patterns and processes, however, is still unknown how these boundaries affect the assemblage of interactions among species within a community, and particularly its structure. Food webs depict not only the composition of the community, but also the feeding links, which represent a measure of energy flow. Therefore, they can inform about the relationships among community diversity, stability, and ecosystem functions. This thesis explores the effects of habitat edges across native vs. managed forests on the food web of a tri-trophic system comprising plants, herbivores (Lepidoptera larvae) and predators (parasitoids). Particularly, it addresses three main objectives: 1) how food webs at habitat edges are assembled from the species and interactions present in the adjoining habitats; 2) how phylogenetic diversity and the coevolutionary signal among interacting species change across a habitat edge gradient; and 3) whether the mechanisms driving community-wide consumption rates and the ecosystem service of pest control are related to structural characteristics of the food webs. The key findings of this thesis are that, despite the composition of species and interactions of native and managed habitats merging at their interface, food-web structure did not arise as a simple combination of its adjacent habitat webs, potentially due to differential responses of organisms to habitat edges. Moreover, beyond taxonomic composition, the phylogenetic diversity and signal of coevolution among interacting species also change between habitat types, even though this did not translate to changes in consumption rates. Consumption rates and their stability increased with complementarity and redundancy in resource-use among predators. This reflects how environmental changes such as habitat fragmentation can have an effect beyond composition per se, affecting the assemblage of species interactions and even potentially interfering with natural evolutionary processes. Therefore, using interaction-network approaches for determining the impacts of changes may shed light on the underlying mechanisms driving such changes, and help to develop landscape management plans that reduce negative effects on species assemblages.

The performance of various designs of outdoor noise barrier has been investigated using numerical modelling and full scale experiments. The numerical modelling has been performed using a two-dimensional boundary element method. The model has been extended to allow the efficient simulation of barrier arrangements on ground having two distinct impedance values and cross-sections incorporating cuttings. It has been reported previously that the performance of a plane screen can be enhanced by adding a device to the top of the barrier to induce destructive interference. Full scale modelling and boundary element simulations have been performed on one such commercially available device. It has been shown that, taking the height increase into account, the major contribution to the improved performance is the presence of two diffracting edges rather than any interference effects generated. It is known that the performance of a single barrier is degraded following the introduction of a barrier on the opposite side of a source. Boundary element simulations of such parallel arrangements have been performed. Modifications have been proposed to reduce the over-estimation of multiple reflections within the model, together with a method for converting predictions to the equivalent point source values. Sound absorptive, tilted and median barriers have been shown to be effective in reducing the degradation. A multiple-edge barrier configuration is known to offer improved screening performance over a plane screen. Reported in-situ measurements have suggested the behaviour to be influenced by site geometry. Boundary element calculations have been performed to identify a more efficient variant of the device. The results suggest the addition of an inclined base panel to be most effective. The boundary element model has been used to investigate the effect of shape and surface treatment upon railway noise barriers. The model has been adapted to allow the use of dipole sources characteristic of railway noise. The cross-section of the rolling stock has been shown to affect the performance of rigid barriers. If the upper edges are coincident, the results suggest that simple absorptive barriers provide better screening than tilted designs. The addition of multiple edges further enhances performance.

Boundary-layer flows near leading edges of generally curved obstacles have been studied for a long time. Apart from having many practical applications, the theory and approaches prevailing in this area stimulate development of a variety of computational tools and form a ground for testing them. The specific aim of this work is to study two-dimensional laminar boundary layer flows near the leading edges of airfoils and other elongated bodies, and to explore geometries for which boundary layer separation can be avoided. This class of problems is relevant to optimal design of wings, aircraft and projectile noses, laminar flow control methods and adaptive wing technology. One of the findings of this work suggests that local modifications to parabolic wing noses can yield up to 11% increase in the unseparated angle of attack. Another result obtained here is the set of shortest possible generalised elliptic noses of long symmetric bodies which allow unseparated flow. Methods adopted in this work are based on the combined use of numerically solved Prandtl equations written in Gortler variables, and inviscid solutions obtained semi-analytically by the conformal mapping method. The resulting technique being reliable, fast and computationally inexpensive, can complement or test the results obtained using a comprehensive CFD approach. / Thesis (Ph.D.)--School of Mathematical Sciences, 2002.

The accelerated edges erosion in bass course of the river San Francisco s became of the actions sponsored for the man and development politics gone back to construction and barrages operations and energy generation. This work had as objective the Oportunity Cost Method for monetary valuation of ambient recovery, through cost-benefit and to quantify the economic losses of bass San Francisco s edges right, caused by marginal erosion in the space of the irrigated perimeter Cotinguiba/Pindoba . The loss of hectares in the period from 1975 to 2005 approximately 76 hectares , what it results an annual medium damage of 2,5 hectares . The oportunity cost in the environmental recovery of the researched area was R$ 396.796,00 and the rude value is R$ 101.040,52. If we verify for a cost-benefit analysis in the stated period of ten years, applied in a tax discount of 15% translated for the present value, we would have a liquid benefit of R$ 61.598,65. The agents causers of marginal erosion are recognized by the retreat of ciliary forest for the implantation of the perimeter Cotinguiba /Pindoba by the construction of diverse barrages to the long one of river course. The gotten data will serve of alert and for subsidy for the decisions linked to planning and environmental administration of the area with intention of minimizing externalidades . / A acelerada erosão das margens no Baixo curso do rio São Francisco é fruto das ações antrópicas e das políticas de desenvolvimento voltadas para construção e operação de barragens e geração de energia. Este trabalho teve como objetivo a aplicação do método custo de oportunidade para mostrar que o investimento em recuperação ambiental é economicamente viável. Através da análise benefício-custo, quantificamos as perdas econômicas do Perímetro Irrigado Cotinguiba/Pindoba, localizado no margem direita do São Francisco em seu baixo curso, causadas pela erosão marginal. A quantidade de hectares degradados, no período de 1975 a 2005, foi de aproximadamente 76 ha, o que resulta em um prejuízo anual médio de 2,5 hectares. O nosso custo oportunidade foi a produção da área não-recuperada, estimada em R$ 101.040,52. O valor da recuperação ambiental da superfície degradada foi de R$ 396.796,00. Aplicando como ferramenta a análise benefício-custo, num período de dez anos, utilizando uma taxa de desconto de 15% e, traduzindo ao valor presente, teríamos um beneficio liquido de R$ 61.598,65. Os agentes antrópicos causadores da erosão marginal são reconhecidos quando da retirada de mata ciliar para implantação do Perímetro Irrigado Cotinguiba/Pindoba e pela construção de diversas barragens ao longo do curso do rio. Os dados obtidos servirão de alerta e subsídio para a tomada de decisões, ligadas ao planejamento e gestão ambiental da região, com o intuito de minimizar as externalidades.

nÃo hà / Modelos baseados em splats tÃm ganhado crescente atenÃÃo devido a seu potencial para renderizaÃÃes de modelos geomÃtricos complexos de forma eficiente e com alta qualidade. A ausÃncia de informaÃÃes de conectividade desses modelos permite operaÃÃes de modelagem complexas, como operaÃÃes booleanas, e fraturas em simulaÃÃes fÃsicas. Entretanto, essas operaÃÃes geralmente geram modelos com arestas e cantos que nÃo podem ser representados corretamente com um nÃmero finito de splats sem que um tratamento seja feito. Neste trabalho, um grafo de vizinhanÃa utiliza uma estimativa que garante a conexÃo de todos os splats presentes em lados opostos de uma descontinuidade e que precisam ser recortados uns contra os outros. ApÃs utilizar um mÃtodo de detecÃÃo de descontinuidades no grafo gerado, os vizinhos que participam do recorte de um splat, os clip partners, sÃo determinados e classificados para que recortem o splat de forma a adaptÃ-lo à curva da descontinuidade. Outro problema encontrado na renderizaÃÃo de modelos baseados em splats à reconstruÃÃo de superfÃcies intersectantes. Nas proximidades de interseÃÃes de superfÃcies, as superfÃcies sÃo misturadas, resultando em artefatos. Para tratar esses casos, um algoritmo de segmentaÃÃo realiza a separaÃÃo das diversas superfÃcies presentes no modelo, identificando os splats que as formam e impedindo que eles sejam combinados em Ãreas prÃximas de interseÃÃes de superfÃcies na etapa de reconstruÃÃo da superfÃcie em espaÃo de imagem / Splats based models have gained increasing attention due to its potential for rendering complex geometric models efficiently and with high quality. The absence connectivity information of these models allows complex modeling operations, as Boolean operations, and fractures in physics simulations. However, these operations often generate models with edges and corners that can not be represented correctly with a finite number of splats without a treatment to be done. In this work, a neighborhood graph uses an estimate which ensures the connection of all these splats on opposite sides a discontinuity and that need to be clipped against each other. After using a method for detecting discontinuities in the generated graph, the neighbors participating in the a splat clipping, clip partners are determined to cut out and sorted splat so as to adapt it to the curve of discontinuity. Another problem encountered in rendering models based on reconstruction of splats is intersecting surfaces. Close intersections of surfaces, the surfaces are mixed, resulting in artifacts. to treat these cases, a segmentation algorithm performs separation of the various surfaces present in the model, identifying the splats that form and hold them to be combined into areas near the intersections of surfaces in the surface reconstruction phase space image

Made available in DSpace on 2014-06-12T18:02:43Z (GMT). No. of bitstreams: 2 arquivo4052_1.pdf: 1926198 bytes, checksum: a394edbf4f303fa7b25af920df83cf25 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho propõe uma técnica não-paramétrica para detecção de bordas em imagens speckle. As imagens SAR ("Synthetic aperture Radar"), sonar, B-ultrasound e laser são corrompidas por um ruído não aditivo chamado speckle. Vários modelos estatísticos foram propostos para desrever este ruído, levando ao desenvolvimento de técnicas especiais para melhoramento e análise de imagens. A distribuição G0 é um modelo estatístico que consegue descrever uma ampla gama de áreas, como, por exemplo, em dados SAR, pastos (lisos), florestas (rugosos) e áreas urbanas (muito rugosos). O objetivo deste trabalho é estudar ténicas alternativas na detecção de imagens speckled, tomando como ponto de partida Gambini et al. (2006, 2008). Um novo detector de borda baseado no teste de Kruskal Wallis é proposto. Os nossos resultados numéricos mostram que esse detector é uma alternativa atraente ao detector de M. Gambini, que é baseado na função de verossimilhançaa. Neste trabalho fornecemos evidências de que a técnica de M. Gambini pode ser substituída om sucesso pelo método Kruskal Wallis. O ganho reside em ter um algoritmo 1000 vezes mais rápido, sem omprometer a qualidade dos resultados

This dissertation aims to challenge the existing built thresholds that are in place between South Africa and its neighbouring countries. In the words of Heidegger, “ A boundary is not that at which something stops, but as the Greeks recognised, the boundary is that from which something begins it’s prescencing.”¹ Boundaries and edges need to be created. They need to be made strong. They need to dominate and control. But borders must not be barriers. This study sets out to investigate the design of a border complex as a transition zone between two countries. It intends to encourage international connectivity, and encourage fair trade and travel, by addressing the functional requirements expectant of a border post, and ensuring the necessary control. Emphasis is also placed on movement through a site where many challenging physical constraints call for innovative design solutions, and where a harsh climate needs to be addressed. / Dissertation (MArch (Prof))--University of Pretoria, 2007. / Architecture / unrestricted