The following thesis demonstrates two isotope tracing experiments that measure oxygen transport through electrochemically polarized solid oxides. Cathode-symmetric ‘button’ cells with yttria stabilized zirconia(YSZ) electrolytes and either strontium doped lanthanum manganate(LSM) or composite LSM/YSZ cathodes were studied. The first experiment measured the residence time distributions(RTD) of 34O2. The measured RTDs were compared at different temperatures(700-800°C) and applied potentials(-2 to -8V). Comparisons with simulated RTDs revealed that oxygen transport was laterally heterogeneous. Delamination of the counter electrode is likely the source of the heterogeneity. The second experiment measured a wave of 18O by exposing an interior cross section and applying ToF-SIMS analysis. A depth profile was produced that spans the cathode and electrolyte interface. The depth profile was compared with a variety of limiting oxygen activation scenarios predicted by a simple 1-D model. Comparisons demonstrated that oxygen activation is likely not restricted to the cathode and electrolyte interface.

Tables have been used for working and studying for years, and people continue using tables to work with digital artifacts. Collaborative tabletop activities such as planning, designing, and scheduling are common on traditional tables, but digital tables still face a variety of design issues to facilitate doing the same tasks. For example, due to the high cost of digital tables, it is unclear how large a digital table must be to support collaborative problem solving. This thesis examines the impact of physical features, in particular the table size, on collaborative tasks. This research leverages findings of previous studies of traditional and digital tables, and focuses on exploring the interaction of table size and users’ seating arrangement in collaborative problem solving. An experimental study is used to observe the behaviors of two-member groups while doing problem-solving tasks. Two tasks, storytelling and travel planning, were selected for this study, and the experiments were performed on two traditional tables, one small and one large. Although working on digital and traditional tables differs, investigating the impact of physical features in traditional tables can help us better understand how these features interact with workspace awareness and external cognition factors during taskwork. In the empirical study, external cognitive behaviors of participants were deeply analyzed to understand how physical settings of the table and seating arrangement affect the way people manipulate artifacts in the table workspace. Collaborators passed through different stages of problem solving using varied strategies, and the data analysis revealed that they manipulated material on the tabletop for understanding, organizing and solution making through visual separation, cognitive tracing and piling. Table size, task type and user seating arrangement showed strong effects on the external cognition of collaborators. In particular, the accessibility of sufficient space on the table influenced how much users could distribute their materials to improve workspace awareness and cognitive tracing. On the other hand, lack of space or inaccessible space forced people to use the space above the table—by holding materials in their hands—or to pile materials to compensate for space limitations. The insights gained from this research inform design decisions regarding size and seating arrangement for tabletop workspaces. For cases in which there is insufficient space, design alternatives are recommended to improve accessibility to artifacts to compensate for space limitations. These solutions aim to enhance the external cognition of users when space is insufficient to work with artifacts in problem-solving tasks.

Successful integration of daylighting systems requires the ability to predict their performance for given climates. In this dissertation, a bottom-up approach is applied to evaluate the optical performance of a selection of daylighting systems. The evaluations are based on the optical properties of the included materials, and part of the dissertation focuses on developing new optical characterization methods. The work on characterization techniques uses an integrating sphere method to characterize the transmittance of light scattering samples more accurately. The method's principle is to reduce the discrepancy in light distribution between the reference and the sample scans by using an entry port beam diffuser. For samples exhibiting distinct light scattering patterns, the benefits of improved uniformity outweigh the errors introduced by the diffusing material. The method is applicable to any integrating sphere instrument, and its simplicity makes it suitable for standard measurements. In addition to normal-hemispherical properties, many daylighting applications require knowledge of the system's spatial light distribution. This dissertation presents a method combining experimental techniques and ray tracing simulations to assess the light distribution from a Venetian blind system. The method indicates that ray tracing based on simplified optical data is inadequate to predict the light distribution for slat materials exhibiting both specular and diffuse properties. Ray tracing is a promising complement to experimental methods used to characterize light guiding or light redirecting systems. Here, spectrophotometric measurements of a scaled mirror light pipe validate a ray tracing model. The model shows excellent agreement with experimental results for both direct and diffuse incident light. The spectral evaluation shows no dramatic color changes for the transmitted light. The ray tracing model is used to evaluate four daylighting systems for a selection of Swedish locations. The percentage of occupied time when the studied systems achieve full design illuminance is relatively low, but the systems provide a valuable contribution to the required illuminance. Additionally, this dissertation provides an overview of available energy efficient windows and illustrates the importance of including the solar energy transmittance when evaluating window energy performance. Overall, this dissertation presents optical characterization techniques for improved performance evaluations of daylighting systems.

The use of High-Frequency (HF) radio-wave propagation in the ionosphere remains prevalent for applications such as long-range communication, target detection and commercial broadcasting. The ionosphere presents a challenging channel for radio-wave propagation as it is a varying medium dependent on a number of external factors. Of the many adverse effects of ionospheric propagation, signal fading is one of the most difficult to eliminate due to its unpredictable nature. Increase in the knowledge of how the ionospheric channel affects the propagating signals, in particular fading of the signals, will drive the continual improvements in the reliability and performance of modern wide-bandwidth HF systems. This is the underlying motivation for the study of signal fading of HF radio-waves propagating through the ionosphere, from both the theoretical and experimental perspectives, with the focus of application to modern wide bandwidth HF systems. Furthermore, it is the main objective of this investigation to address the lacking in the current literature of a simple analytical signal fading model for wideband HF systems that relates the physics of the ionospheric irregularities to the observable propagation effects due to the irregularities, and one that is verified by experimental observations. An original approach was taken in the theoretical investigation to develop an analytical model that combines the effects of signal fading and directly relating them to the ionospheric irregularities that are causing the fading. The polarisation fading model (PFM) is a combination of geometric optics, perturbation techniques and frequency offset techniques to derive expressions for the Faraday rotation of the radio-wave propagating in the ionosphere. Using the same notation as the PFM, the amplitude fading model (AFM) extends the Complex Amplitude concept using perturbation techniques and Green’s functions solution to arrive at a set of expressions that describes the focussing and defocussing effects of the wave. The PFM and AFM, together with expressions for combining the effects of multiple propagation paths, provide a simple analytic model that completely describes the fading of the signal propagating in the ionosphere. This theoretical model was implemented into an efficient ionospheric propagation simulator (IPS) from which simulations of wide bandwidth HF signals propagating through the ionosphere can be undertaken. As an example of the type of results produced by the IPS, for a typical 1200km path in the north-south direction with the ionospheric channel under the influence of a travelling ionospheric disturbance (TID), a 10 MHz radio-wave signal in one-hop path is shown to be affected by polarisation fading with fading periods in the order of minutes, and a fading bandwidth in the order of 100 kHz. Further results generated by the IPS have shown to be consistent with the results reported elsewhere in the literature. The experimental investigation involves the study of signal fading from observations of real signals propagating in the ionosphere, a major part of which is the development of a digital compact channel probe (CCP) capable of operating in dual-polarisation mode, and the characterisation of such systems to ensure that data collected are not compromised by the non-idealities of the individual devices contained within the system. The CCP was deployed in experiments to collect transmissions of HF frequency-modulated continuouswave (FMCW) radio signals from the Jindalee Over-the-Horizon radar (OTHR) in dualpolarisation. Analyses of the collected data showed the full anatomy of fading of signals propagating in the ionosphere for both horizontal and vertical polarisations, the results of which are consistent with that from the IPS and thus verifying the validity of the theoretical model of fading. Further experimental results showed that in majority of the observations polarisation fading is present but can be masked by multi-path fading, and confirming that periods of rapid signal fading are associated with rapid changes in the ionospheric channel. From the theoretical and experimental investigations, the major achievement is the successful development of an efficient propagation simulator IPS based on the simple analytical expressions derived in the PFM and AFM theoretical models of signal fading, which has produced sensible signal fading results that are verified by experimental observations. One of the many outcomes of this investigation is that polarisation diversity has the potential to bring improvements to the quality of wide-bandwidth HF signals in a fading susceptible propagation channel. The combination of an efficient propagation simulator IPS based on theoretical signal fading model and the experimental data collection by the dual-polarisation CCP is a major step in allowing one to fully understand the different aspects of fading of signals propagating in the ionosphere, which sets a solid foundation for further research into the design of wide bandwidth HF systems and the possible fading mitigation techniques. / Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2008

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 78-81).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references and index.

Thesis (D.P.H.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed on June 23, 2009). Includes bibliographical references.

Techn. University, Diss., 2004--Braunschweig.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Airborne seeker antennas are usually enclosed within a dielectric radome for protection against their harsh operational environment. However the presence of a radome can introduce serious degrading effects on the radiation and electrical performance of the enclosed antenna. The degradation effect studied in this report is that of Bore Sight Error (BSE). BSE is a squint in the pointing accuracy of the antenna due to the enclosing radome. A ray-tracing approach is presented that is able to analyse the BSE of seeker radomes in general and is especially suited to electrically large radomes where other computational electromagnetic techniques become overly computationally intensive. The ray-tracing algorithm is wrapped in a GUI which, given the radome, antenna, polarisation and incidence plane parameters will compute the BSE for any set of requested scan angles. Close agreement was obtained with measured BSE performance available in literature. Due to easy setup and fast computation time it is demonstrated that the GUI can be efficiently used for iterative radome design and optimisation. / AFRIKAANSE OPSOMMING: Luggedrae soekantennes is normaalweg omhul binne ‘n dielektriese antennekoepel vir beskerming teen ‘n strawwe omgewing. Die teenwoordigheid van ‘n antennakoepel kan egter ernstige nadelige effekte op die straling en elektriese werkverrigting van die omhulde antenne hê. Die nadelige effek wat in hierdie verslag ondersoek word, is dié van die “Bore Sight Error (BSE).” BSE is ‘n afwyking in die akkuraatheid van die antenna se rigtingwysing as gevolg van die antennakoepel. Straal-natrekking wat die BSE van soek-antennekoepels in die algemeen kan analiseer word beskryf. Hierdie tegniek is veral gepas vir elektries groot antennekoepels waar die berekenige vir EM tegnieke te intensief raak. Die straalnatrekkingsalgoritme word omvat in ‘n grafiese gebruikerskoppelvlak. Gegee die parameters van die antennekoepel, antenne, polarisasie en invallende vlak, sal die BSE vir enige stel skandeerhoeke bereken word. Goeie ooreenstemming was verkry, vergeleke met gemete BSE vanuit die literatuur. Die eenvoudige opstel van die koppelvlak en vinnige berekeningstyd wys daarop dat die koppelvlak doeltreffend gebruik kan word vir iteratiewe antennekoepel ontwerp en optimering.

BARRETO, Isaac Moreira. Cálculo do fator-de-forma exato entre áreas diferencial e finita usando CSG. 2008. 62 f. Dissertação (Mestrado em ciência da computação)- Universidade Federal do Ceará, Fortaleza-CE, 2008. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-07-11T16:45:40Z No. of bitstreams: 1 2008_dis_imbarreto.pdf: 752627 bytes, checksum: 2c1a97d41785e527e97633cc6c7e9756 (MD5) / Approved for entry into archive by Rocilda Sales (rocilda@ufc.br) on 2016-07-18T13:45:29Z (GMT) No. of bitstreams: 1 2008_dis_imbarreto.pdf: 752627 bytes, checksum: 2c1a97d41785e527e97633cc6c7e9756 (MD5) / Made available in DSpace on 2016-07-18T13:45:29Z (GMT). No. of bitstreams: 1 2008_dis_imbarreto.pdf: 752627 bytes, checksum: 2c1a97d41785e527e97633cc6c7e9756 (MD5) Previous issue date: 2008 / The Ray-Tracing and Radiosity methods are the main representatives of the method that solve the global illumination problem. In both mthods it is necessary to know the energy tranfer ratio between two areas. This ratio, called form factor, is one of the key concepts in Radiosity methods and is being more frequently used in Ray-Tracing methods with finite area light sources. There are many methods for the computation of the form factor, most of them are approximative due to a matter of performance, but, in some specific cases, the extra computational effort needed to compute the exact value of the form factor can improve the overall performance of the illumination method. In general, in these cases, the computational effort needed to obtain an acceptable approximation of the form factor outweighs the effort necessary to compute the exact value. Furthermore there are situation, for example, shadow boundary shading, in which a high precision is far more important than a performance gain. In this work we present a method to compute the exact form factor between a finite area and a differential area which uses CSG techniques to identify the ooccluded areas of the source. / Os métodos de Ray-Tracing e Radiosidade são os principais representantes dos métodos existentes para resolver o problema de iluminação global. Em ambos os métodos se faz necessário saber a taxa de transferência de energia luminosa entre duas áreas. Essa taxa de transferência, chamada de fator-de-forma, é um dos pontos principais no método de Radiosidade e vem sendo usado cada vez com mais frequência em métodos de Ray-Tracing com fontes luminosas de área finita. Existem vários métodos para o cálculo do fator-de-forma, a maioria deles são aproximativos por uma questão de desempenho. Porém, em casos específicos, o trabalho extra para calcular o valor exato do fator-de-forma pode melhorar o desempenho global do método. Em geral, nesses casos, o esforço necessário para se obter uma aproximação aceitável do valor do fator-de-forma supera o esforço necessário para calcular o valor exato em si. Além disso, existem situações, tais como a renderização nas áreas de fronteiras de sombras, em que uma alta precisão é mais importante do que um ganho no desempenho. Nessas situações, é desejável que o método tenha ao seu dispor uma maneira de calcular o valor exato do fator-de-forma. Neste trabalho é apresentado um método para calcular o fator-de-forma exato entre uma área finita e uma área diferencial que utiliza de técnicas CSG para identificar as áreas ocluídas do polígono emissor.