In this study, I examined the effect of watershed urbanization on the invasion of alien woody species in riparian forests. This study was conducted in three major steps: 1) estimating the degree of watershed urbanization using impervious surface maps extracted from remote sensing images; 2) examining the effect of urbanization on hydrologic regime; and 3) investigating a relationship between watershed urbanization and ecosystem invasibility of a riparian forest. I studied twelve riparian forests along urban-rural gradients in Austin, Texas. Hydrologic regimes were quantified by transfer function (TF) models using four-year daily rainfall-streamflow data in two study periods (10/1988-09/1992 and 10/2004-09/2008) between which Austin had experienced rapid urbanization. For each study period, an impervious surface map was generated from Landsat TM image by a support vector machine (SVM) with pairwise coupling. SVM more accurately estimated impervious surface than other subpixel mapping methods. Ecosystem invasibilities were assessed by relative alien cover (RAC) of riparian woody species communities. The results showed that the effects of urbanization differ by hydrogeologic conditions. Of the study watersheds, seven located in a hillslope region experienced the diminishing peakflows between the two study periods, which are contrary to current urban hydrologic model. I attributed the decreased peakflows to land grading that transformed a hillslope into a stair-stepped landscape. In the rest of the watersheds, peakflow diminished between the two study periods perhaps due to the decrease in stormwater infiltration and groundwater pumpage that lowered groundwater level. In both types of watersheds, streamflow rising during a storm event more quickly receded as watershed became more urbanized. This study found a positive relationship between RAC and watershed impervious surface percentage. RAC was also significantly related to flow recession and canopy gap percentages, both of which are indicators of hydrologic disturbance. These results suggest that urbanization facilitated the invasion of alien species in riparian forests by intensifying hydrologic disturbance. The effects of urbanization on ecosystems are complex and vary by local hydrologeologic conditions. These results imply that protection of urban ecosystems should be based on a comprehensive and large-scale management plan.

This thesis focuses on experimentally measuring the response of varying dilatation ratio bluff body flames under harmonic excitation. Such flames are often encountered in jet engine afterburners and are susceptible to combustion instabilities. Previous work has been done modeling such flames, however, only limited experimental data has been obtained at these conditions and is the motivation for this thesis. The focus of this work is to measure the transfer function of longitudinally forced, varying dilatation ratio bluff body flames. The transfer function is obtained by measuring flame position and flame luminosity fluctuations at the forcing frequency. Specifically, the amplitude and phase of the fluctuations are characterized as a function of flow velocity, axial location, and perturbation amplitude. These measurements are also compared to available theoretical predictions, showing that qualitative measured trends are consistent with theory. In addition, a detailed quantitative comparison is performed at one condition, showing good agreement between predictions and measurements in the near and mid-field of the flame response. However, agreement is not obtained in the far-field, indicating that continued theoretical work is needed to understand the flame response characteristics in this region.

Large scale linear time invariant (LTI) systems arise in many physical and technical fields. An approximation, e.g. with model order reduction techniques, of this large systems is crucial for a cost efficient simulation. In this thesis we focus on a model order reduction method based on modal approximation, where the LTI system is projected onto the left and right eigenspaces corresponding to the dominant poles of the system. These dominant poles are related to the most dominant parts of the residue expansion of the transfer function and usually form a small subset of the eigenvalues of the system matrices. The computation of this dominant poles can be a formidable task, since they can lie anywhere inside the spectrum and the corresponding left eigenvectors have to be approximated as well. We investigate the subspace accelerated dominant pole algorithm and the two-sided and alternating Jacobi-Davidson method for this modal truncation approach. These methods can be seen as subspace accelerated versions of certain Rayleigh quotient iterations. Several strategies that admit an efficient computation of several dominant poles of single-input single-output LTI systems are examined. Since dominant poles can lie in the interior of the spectrum, we discuss also harmonic subspace extraction approaches which might improve the convergence of the methods. Extentions of the modal approximation approach and the applied eigenvalue solvers to multi-input multi-output are also examined. The discussed eigenvalue algorithms and the model order reduction approach will be tested for several practically relevant LTI systems.

The study was aimed at developing a simple methodology for flow prediction in ungauged basins using existing data resources. For this purpose, the streamflow measurements across the Kentucky River Basin located in Kentucky, USA were obtained from United States Geological Survey (USGS) archive. The flow transferring characteristics of the subbasins of the Kentucky River Basin were obtained by combining downstream and upstream stream gauges. The flow transferring function thus derived were related to watershed, channel and flow characteristics of the subbasins by multiple regression analysis. The gauge pairs were divided into two classes of subbasins representing Upper and Lower Kentucky, which were characterized mainly by the geology of the watersheds. The regression models corresponding to the two groups of subbasins were applied to example gauge pairs to evaluate the efficiency of the proposed model to predict streamflow in downstream channel. The estimated hydrographs agreed with the observed hydrographs with the performance efficiency of greater than 90%. The proposed method was tested for its applicability in first-order streams in the Goose Creek, a tributary to the Kentucky River. The overland flow component for the first-order streams was determined using TOPMODEL with topography, soil and climatic factors as inputs. The overland flow was routed to the Goose Creek outlet using the transfer function obtained from measured flow records. The simulated hydrographs were reproduced with 80% accuracy when compared with the observed hydrographs. The flow prediction of first-order ungauged streams was automated by the back-calibration algorithm. The algorithm is supported by the Shuffled Complex Evolution - University of Arizona algorithm for its optimization routine. The back-calibration procedure optimizes each first-order stream with the aid of the flow transferring function. The back-calibration procedure was imbedded in a Visual Basic.NET environment to automatically predict flow on a daily time scale and predicted was published on the internet using ESRI Arc Internet Mapping Server (ArcIMS). The project thus provides daily streamflow estimation for streams on a first-order level on every day basis, which will facilitate flow prediction of streams regardless of the size of the watersheds.

This thesis resulted in the development of robust chironomid-based transfer-functions for February mean air temperature and the concentration of total nitrogen (TN) in lake-water. The New Zealand transfer-functions for both variables compare favourably with chironomid-based transfer-functions for equivalent variables from elsewhere in the world, and diatom-based transfer-functions for nutrients and lake production from New Zealand. The application of the temperature and TN transfer-functions provided insight into New Zealand climate conditions during the last glacial and served as validation for the reconstructions. Chironomid-based Temperature reconstructions from lake silts preserved in the banks of Lyndon Stream indicate a maximum cooling of ca 4 ℃ between 26.6 and 24.5 ka BP, which is consistent with estimates based on beetles and plant macrofossils. A cooling of 4 ℃ is insufficient to explain the lack of canopy tree pollen in many New Zealand pollen records at this time. Other environmental parameters additional to temperature may have limited the expansion forest cover. The chironomid-based TN reconstructions infer a trend of rapidly deteriorating water-quality in a small doline in north-west Nelson, in the South Island of New Zealand following deforestation immediately surrounding the lake ca. 1970 AD. The overall trend and timing of eutrophication inferred from the chironomids was consistent with other biological proxies and actual observations of changes in lake water quality. The chironomid-based transfer-functions provide a valuable new tool for the study of longterm climate variability and improving our understanding of the response of aquatic ecosystems to long-term natural and human induced environmental change in New Zealand lakes. I have identified some possibilities for future research which should improve the performance of these transfer-functions. The improvement of the chironomid taxonomy and the expansion of the training set should be the highest priorities.

O projeto de funções de transferência é um interessante problema que recebe muita atenção da comunidade de visualização. Diversas pesquisas tem sido conduzidas para criar melhores ferramentas e técnicas que trabalham com dados volumétricos. Existem duas grandes classes de dados: volumes estruturados e volumes não-estruturados. A maioria dos trabalhos anteriores apenas se refere a dados estruturados. Este trabalho possui dois grupos de contribuições. O primeiro diz respeito ao problema clássico de especificação de funções de transferência. Primeiramente é desenvolvido o conceito de Ensembles, que são funções de transferência desenvolvidas a partir da combinação de funções anteriores e mais simples. Também é apresentada uma abordagem de key-framing para manipular dados que variam no tempo. O segundo grupo de contribuições é um estudo aprofundado sobre o comportamento de dados não-estruturados. Problemas críticos foram descobertos e tratados para permitir uma integração quase perfeita de ferramentas usadas para dados estruturados em dados não-estruturados. Os resultados mostram a melhoria de qualidade de histogramas, e também o sistema de desenvolvimento de funções de transferência. Trabalhos futuros são sugeridos para utilizar a versão melhorada do histograma de gradiente-magnitude, assim como a exploração de novos modelos de bordas. / Transfer function design is an important problem that receives much attention from the visualization community. Several researches have inspired the creation of better tools and techniques to deal with volumetric datasets. There are two major classes of datasets, namely structured and unstructured grids. Most of the previous work has only addressed structured data. This work presents two groups of contributions of different nature. The first contribution is related to the general problem of transfer function design. It introduces the concept of ensembles, which are complex transfer functions created from standard types. It also presents a key-frame based approach to handle time-varying sequences. The second group of contributions is related with a study on several characteristics of unstructured data. Problems have been discovered and addressed to allow a seamless integration of classical structured grids tools to unstructured data. This work includes results that show improvements on a statistical analysis of the data, as well as the developed transfer function design system. Further work is suggested to take advantage of the enhanced version of the gradient-magnitude histogram, and explore different boundary model.

Técnicas de visualização volumétrica direta são utilizadas para visualizar e explorar volumes de dados complexos. Dados volumétricos provêm de diversas fontes, tais como dispositivos de diagnóstico médico, radares de sensoriamento remoto ou ainda simulações científicas assistidas por computador. Um problema fundamental na visualização volumétrica é a especificação de Funções de Transferência (FTs) que atribuem cor e opacidade aos valores escalares que compõem o volume de dados. Essas funções são importantes para a exibição de características e objetos de interesse do volume, porém sua definição não é trivial ou intuitiva. Abordagens tradicionais permitem a edição manual de pontos de controle que representam a FT a ser utilizada no volume. No entanto, essas técnicas acabam conduzindo o usuário a um processo de “tentativa e erro” para serem obtidos os resultados desejados. Considera-se também que técnicas automáticas que excluem o usuário do processo não são consideradas as mais adequadas, visto que o mesmo deve possuir algum controle sobre o processo de visualização. Este trabalho apresenta uma ferramenta semi-automática e interativa destinada a auxiliar o usuário na geração de FTs de cor e opacidade. A ferramenta proposta possui dois níveis de interação com o usuário. No primeiro nível são apresentados várias FTs candidatas renderizadas como thumbnails 3D, seguindo o método conhecido como Design Galleries (MARKS et al., 1997). São aplicadas técnicas para reduzir o escopo das funções candidatas para um conjunto mais razoável, sendo possível ainda um refinamento das mesmas. No segundo nível é possível definir cores para a FT de opacidade escolhida, e ainda refinar essa função de modo a melhorála de acordo com as necessidades do usuário. Dessa forma, um dos objetivos desse trabalho é permitir ao usuário lidar com diferentes aspectos da especificação de FTs, que normalmente são dependentes da aplicação em questão e do volume de dados sendo visualizado. Para o rendering do volume, são exploradas as capacidades de mapeamento de textura e os recursos do hardware gráfico programável provenientes das plácas gráficas atuais visando a interação em tempo real. Os resultados obtidos utilizam volumes de dados médicos e sintéticos, além de volumes conhecidos, para a análise da ferramenta proposta. No entanto, é dada ênfase na especificação de FTs de propósito geral, sem a necessidade do usuário prover um mapeamento direto representando a função desejada. / Direct volume rendering techniques are used to visualize and explore large scalar volumes. Volume data can be acquired from many sources including medical diagnoses scanners, remote sensing radars or even computer-aided scientific simulations. A key issue in volume rendering is the specification of Transfer Functions (TFs) which assign color and opacity to the scalar values which comprise the volume. These functions are important to the exhibition of features and objects of interest from the volume, but their specification is not trivial or intuitive. Traditional approaches allow the manual editing of a graphic plot with control points representing the TF being applied to the volume. However, these techniques lead the user to an unintuitive trial and error task, which is time-consuming. It is also considered that automatic methods that exclude the user from the process should be avoided, since the user must have some control of the visualization process. This work presents a semi-automatic and interactive tool to assist the user in the specification of color and opacity TFs. The proposed tool has two levels of user interaction. The first level presents to the user several candidate TFs rendered as 3D thumbnails, following the method known as Design Galleries (MARKS et al., 1997). Techniques are applied to reduce the scope of the candidate functions to a more reasonable one. It is also possible to further refine these functions at this level. In the second level is permitted to define and edit colors in the chosen TF, and refine this function if desired. One of the objectives of this work is to allow users to deal with different aspects of TF specification, which is generally dependent of the application or the dataset being visualized. To render the volume, the programmability of the current generation of graphics hardware is explored, as well as the features of texture mapping in order to achieve real time interaction. The tool is applied to medical and synthetic datasets, but the main objective is to propose a general-purpose tool to specify TFs without the need for an explicit mapping from the user.

O projeto de funções de transferência é um interessante problema que recebe muita atenção da comunidade de visualização. Diversas pesquisas tem sido conduzidas para criar melhores ferramentas e técnicas que trabalham com dados volumétricos. Existem duas grandes classes de dados: volumes estruturados e volumes não-estruturados. A maioria dos trabalhos anteriores apenas se refere a dados estruturados. Este trabalho possui dois grupos de contribuições. O primeiro diz respeito ao problema clássico de especificação de funções de transferência. Primeiramente é desenvolvido o conceito de Ensembles, que são funções de transferência desenvolvidas a partir da combinação de funções anteriores e mais simples. Também é apresentada uma abordagem de key-framing para manipular dados que variam no tempo. O segundo grupo de contribuições é um estudo aprofundado sobre o comportamento de dados não-estruturados. Problemas críticos foram descobertos e tratados para permitir uma integração quase perfeita de ferramentas usadas para dados estruturados em dados não-estruturados. Os resultados mostram a melhoria de qualidade de histogramas, e também o sistema de desenvolvimento de funções de transferência. Trabalhos futuros são sugeridos para utilizar a versão melhorada do histograma de gradiente-magnitude, assim como a exploração de novos modelos de bordas. / Transfer function design is an important problem that receives much attention from the visualization community. Several researches have inspired the creation of better tools and techniques to deal with volumetric datasets. There are two major classes of datasets, namely structured and unstructured grids. Most of the previous work has only addressed structured data. This work presents two groups of contributions of different nature. The first contribution is related to the general problem of transfer function design. It introduces the concept of ensembles, which are complex transfer functions created from standard types. It also presents a key-frame based approach to handle time-varying sequences. The second group of contributions is related with a study on several characteristics of unstructured data. Problems have been discovered and addressed to allow a seamless integration of classical structured grids tools to unstructured data. This work includes results that show improvements on a statistical analysis of the data, as well as the developed transfer function design system. Further work is suggested to take advantage of the enhanced version of the gradient-magnitude histogram, and explore different boundary model.

abstract: The utilization of power cables is increasing with the development of renewable energy and the maintenance replacement of old overhead power lines. Therefore, effective monitoring and accurate fault location for power cables are very important for the sake of a stable power supply. The recent technologies for power cable diagnosis and temperature monitoring system are described including their intrinsic limitations for cable health assessment. Power cable fault location methods are reviewed with two main categories: off-line and on-line data based methods. As a diagnostic and fault location approach, a new passive methodology is introduced. This methodology is based on analyzing the resonant frequencies of the transfer function between the input and output of the power cable system. The equivalent pi model is applied to the resonant frequency calculation for the selected underground power cable transmission system. The characteristics of the resonant frequencies are studied by analytical derivations and PSCAD simulations. It is found that the variation of load magnitudes and change of positive power factors (i.e., inductive loads) do not affect resonant frequencies significantly, but there is considerable movement of resonant frequencies under change of negative power factors (i.e., capacitive loads). Power cable fault conditions introduce new resonant frequencies in accordance with fault positions. Similar behaviors of the resonant frequencies are shown in a transformer (TR) connected power cable system with frequency shifts caused by the TR impedance. The resonant frequencies can be extracted by frequency analysis of power signals and the inherent noise in these signals plays a key role to measure the resonant frequencies. Window functions provide an effective tool for improving resonant frequency discernment. The frequency analysis is implemented on noise laden PSCAD simulation signals and it reveals identical resonant frequency characteristics with theoretical studies. Finally, the noise levels of real voltage and current signals, which are acquired from an operating power plant, are estimated and the resonant frequencies are extracted by applying window functions, and these results prove that the resonant frequency can be used as an assessment for the internal changes in power cable parameters such as defects and faults. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2015

Técnicas de visualização volumétrica direta são utilizadas para visualizar e explorar volumes de dados complexos. Dados volumétricos provêm de diversas fontes, tais como dispositivos de diagnóstico médico, radares de sensoriamento remoto ou ainda simulações científicas assistidas por computador. Um problema fundamental na visualização volumétrica é a especificação de Funções de Transferência (FTs) que atribuem cor e opacidade aos valores escalares que compõem o volume de dados. Essas funções são importantes para a exibição de características e objetos de interesse do volume, porém sua definição não é trivial ou intuitiva. Abordagens tradicionais permitem a edição manual de pontos de controle que representam a FT a ser utilizada no volume. No entanto, essas técnicas acabam conduzindo o usuário a um processo de “tentativa e erro” para serem obtidos os resultados desejados. Considera-se também que técnicas automáticas que excluem o usuário do processo não são consideradas as mais adequadas, visto que o mesmo deve possuir algum controle sobre o processo de visualização. Este trabalho apresenta uma ferramenta semi-automática e interativa destinada a auxiliar o usuário na geração de FTs de cor e opacidade. A ferramenta proposta possui dois níveis de interação com o usuário. No primeiro nível são apresentados várias FTs candidatas renderizadas como thumbnails 3D, seguindo o método conhecido como Design Galleries (MARKS et al., 1997). São aplicadas técnicas para reduzir o escopo das funções candidatas para um conjunto mais razoável, sendo possível ainda um refinamento das mesmas. No segundo nível é possível definir cores para a FT de opacidade escolhida, e ainda refinar essa função de modo a melhorála de acordo com as necessidades do usuário. Dessa forma, um dos objetivos desse trabalho é permitir ao usuário lidar com diferentes aspectos da especificação de FTs, que normalmente são dependentes da aplicação em questão e do volume de dados sendo visualizado. Para o rendering do volume, são exploradas as capacidades de mapeamento de textura e os recursos do hardware gráfico programável provenientes das plácas gráficas atuais visando a interação em tempo real. Os resultados obtidos utilizam volumes de dados médicos e sintéticos, além de volumes conhecidos, para a análise da ferramenta proposta. No entanto, é dada ênfase na especificação de FTs de propósito geral, sem a necessidade do usuário prover um mapeamento direto representando a função desejada. / Direct volume rendering techniques are used to visualize and explore large scalar volumes. Volume data can be acquired from many sources including medical diagnoses scanners, remote sensing radars or even computer-aided scientific simulations. A key issue in volume rendering is the specification of Transfer Functions (TFs) which assign color and opacity to the scalar values which comprise the volume. These functions are important to the exhibition of features and objects of interest from the volume, but their specification is not trivial or intuitive. Traditional approaches allow the manual editing of a graphic plot with control points representing the TF being applied to the volume. However, these techniques lead the user to an unintuitive trial and error task, which is time-consuming. It is also considered that automatic methods that exclude the user from the process should be avoided, since the user must have some control of the visualization process. This work presents a semi-automatic and interactive tool to assist the user in the specification of color and opacity TFs. The proposed tool has two levels of user interaction. The first level presents to the user several candidate TFs rendered as 3D thumbnails, following the method known as Design Galleries (MARKS et al., 1997). Techniques are applied to reduce the scope of the candidate functions to a more reasonable one. It is also possible to further refine these functions at this level. In the second level is permitted to define and edit colors in the chosen TF, and refine this function if desired. One of the objectives of this work is to allow users to deal with different aspects of TF specification, which is generally dependent of the application or the dataset being visualized. To render the volume, the programmability of the current generation of graphics hardware is explored, as well as the features of texture mapping in order to achieve real time interaction. The tool is applied to medical and synthetic datasets, but the main objective is to propose a general-purpose tool to specify TFs without the need for an explicit mapping from the user.