Thesis advisor: Michael J. Naughton / Surface plasmon polaritons (SPPs) are hybridized quasiparticles of photons and electron density waves. They are confined to propagate along metal-dielectric interfaces, and decay exponentially along the direction perpendicular to the interfaces. In the past two decades, SPPs have drawn intensive attention and undergone rapid development due to their potential for application in a vast range of fields, including but not limited to subwavelength imaging, biochemical/biomedical sensing, enhanced light trapping for solar cells, and plasmonic logic gates. These applications utilize the following intrinsic properties of SPPs: (1) the wavelength of SPPs is shorter (and can be much shorter) than that of free photons with the same frequency; (2) the local electric field intensity associated with SPPs can be orders of magnitude larger than that of free photons; and (3) SPPs are bound to metal surfaces, and are thus easily modulated by the geometry of those surfaces. Here, we present studies on SPPs along metal surfaces with novel structures, including the following: (1) SPP standing waves formed along circular metal surfaces that lead to a "plasmonic halo" effect; (2) directional reflectionless conversion between free photons and SPPs in asymmetric metal-insulator-metal arrays; and (3) broadband absorbance enhancement of embedded metallic nanopatterns in a photovoltaic absorber layer. These works may prove useful for new schemes for SPP generation, plasmon-photon modulation, ultrasensitive dielectric/bio sensing, and high efficiency thin film solar cells. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

O trabalho apresentado nesta dissertação consiste do estudo do comportamento direcional de um veículo comercial de 2 eixos, classificando-o quanto a sua estabilidade (Oversteer, Understeer ou Neutral Steer) e predizendo em que condições sua instabilidade torna-se crítica. para esta finalidade, o veículo foi modelado desenvolvendo uma trajetória curvilínea de raio constante em situação de regime permanente e uma rotina de cálculos representa sua dinâmica lateral. O recurso computacional utilizado (software Excel) foi propositadamente escolhido tendo como premissa ser o mais simples possível, para que os custos e tempo envolvidos fossem mínimos. Foram realizadas algumas medições com o veículo em questão e, levando-se em conta todas as simplificações implementadas, os resultados práticos e teóricos demonstraram correlação satisfatória. Desta maneira, então, pode-se dizer que o instrumento desenvolvido neste trabalho pode ser aplicado como um recurso valioso durante a fase inicial de conceituação da suspensão de um veículo de 2 eixos, principalmente tratando-se de uma avaliação comparativa com veículos semelhantes já testados. / The work presented consists of a 2 axles light truck directional behavior evaluation, where computational resources applied are very simple and easy hand (software excel). Steady state cornering concept was used to get its stability classification (Oversteer, Understeer or Neutral Steer) and show in which moment its behavior become unstable. Experimental measurements took place and the practical (measured) and theoretical (came from the developed model) results showed theirselves satisfactory, considering all the simplifications. Thus, this procedure might be useful during a two axle light truck suspension development, ultimately if is adopted to compare with another one already known. Costs and time are saved in this way.

Este trabalho envolve dois diferentes aspectos da estimação de espectros direcionais de onda a partir de movimentos de 1a ordem da embarcação. Sendo a estimação do espectro de ondas feita por meio de um método Bayesiano, existe a necessidade da calibração dos hiperparâmetros derivados da modelagem Bayesiana. O primeiro assunto abordado é a determinação de uma metodologia de calibração dos hiperparâmetros necessários à estimação do espectro direcional de ondas. Desenvolve-se ao longo deste uma primeira análise de um método aplicável a qualquer embarcação do tipo FPSO para a determinação a priori de valores de dois hiperparâmetros de controle da suavização da estimativa. Obtém-se resultados indicativos de que é possível definir valores destes hiperparâmetros dependentes de quantidades observáveis como calado da embarcação e período das ondas, de modo que os erros de estimação ainda se mantém muito próximos aos encontrados por valores ótimos dos hiperparâmetros. Isto leva à conclusão de que na abordagem atual, com valores fixos a cada calado, erros excessivos e desnecessários podem ocorrer no processo de estimação. O segundo tema trata da estimação paramétrica de espectros, utilizando modelos paramétricos de descrição de espectros como forma de obtenção de estatísticas de mar. Abordam-se também os assuntos de mares cruzados, donde se faz necessária a identificação da bimodalidade dos espectros para a estimação correta das estatísticas de mar. / In this work, two differents aspects of directional wave spectra estimation from 1st order ship motions are presented. As the estimation of wave spectrum is made by means of a Bayesian method, it is necessary to calibrate the hyperparameters derived from Bayesian modeling. The first addressed subject is the determination of a calibration methodology of the hyperparameters needed for the directional wave spectrum estimation. It is developed through this work a first analysis of an applicable method to any vessel of FPSO type for the prior determination of values for this two hyperparameters depending on observable quantities, such as draft of the vessel and wave period, in such a way that the estimation errors are still very close to those found by optimum values of the hyperparameters. This leads to the conclusion that in the current approach excessive and unnecessary errors can occur on the estimation process. The second subject addresses the parametric estimation of spectra, using parametric models of spectrum description to acquire the sea statistics. For this purpose, it became necessary the study of crossed-sea states, which was employed in the bimodal spectrum identification for the correct estimation of sea statistics.

Vários estudos sobre ontogenia e assimetria foram e vêm sendo realizados com cetáceos odontocetos através da utilização da morfometria convencional. Frequentemente compara-se o tamanho de estruturas do sistema respiratório de ambos os lados do crânio para avaliar a assimetria de tamanho e analisa-se o aumento de tamanho do corpo com a idade para avaliar ontogenia. Porém, através da morfometria convencional nem sempre é possível descrever ou representar a variabilidade de forma dos organismos, sendo que informações sobre a forma craniana dos odontocetos são bastante escassas. A morfometria geométrica é uma técnica que vem sendo amplamente utilizada em estudos de comparação da forma dos organismos, a qual leva em consideração o caráter geométrico das formas biológicas e analisa estatisticamente sua variação. Além disso, possibilita a realização de descrições independentes de forma e tamanho, o que permite que os mesmos sejam analisados separadamente. Sendo assim, este estudo se propôs a investigar as alterações ontogenéticas na forma e tamanho do crânio do boto-cinza, Sotalia guianensis, buscando alterações cranianas entre indivíduos de diferentes classes etárias, além de verificar a existência e analisar a assimetria direcional na forma e tamanho craniano para esta espécie. Para isso, os crânios foram digitalizados através de um braço digitalizador e depois de um tratamento geométrico as configurações geradas foram analisadas estatisticamente, a partir dos seus componentes de forma e tamanho. Foi observada assimetria de tamanho e forma para muitas das estruturas cranianas estudadas, notando-se diferenças com relação à assimetria entre as subunidades de desenvolvimento do crânio. Com relação à ontogenia, verificou-se um padrão semelhante para a alteração da forma e do tamanho com a idade, evidenciando que, tanto a forma como o tamanho craniano, se estabilizam por volta dos oito anos de idade. / Several studies exploring the ontogeny and asymmetry involving the skull and skeleton of the species of the Suborder Odontoceti have been performed using traditional morphometric techniques. Ontogenetic studies are usually based on the relationship between body size and age, while those focusing on the existence and degree of asymmetry compare the size of skull elements related to the respiratory tract. However, traditional morphometrics can not describe or represent adequately the variability of shape between organisms and therefore information about shape of dolphin skulls are very scarce. Geometric Morphometrics is a toolbox of techniques that is been widely applied in studies comparing the shape of organisms taking into consideration the biological shapes and analyzing their variation statistically. In addition, this technique allows to independently describe both shape and size separately, as well as exploring their relationship. The main objective of this study is to investigate the changes in skull shape and size during the ontogeny for the estuarine dolphin, Sotalia guianensis, characterizing the shape of the skull among different age groups. The second goal is to verify and analyze directional asymmetry in skull size and shape for this species. Dolphin skulls were scanned using a Microscribe-3D digitizer, statistically analyzing size and shape of the configurations created after translating, rotating and rescaling the original variables. Asymmetry in size and shape was detected for some cranial structures. There were also differences in asymmetry degree between the development subunits of the skull. For the ontogenetic trajectory it was detected a similar pattern of changes in shape and in size with age, in which both are stabilizing around eight years old for this species.

Structures made of plate-like components are common in a variety of industries where the impacts of structural failures are severe. In many cases these structures are surrounded and only partially accessible, such as storage tanks and bridges, making them difficult to inspect frequently. The application of ultrasonic Guided Waves (GWs) in the evaluation and monitoring of relatively large plate-like structures is evermore a feasible option with the continuous development of transducer arrays. The use of transducer arrays is however complex due to directional control and the existence of many GW modes. Aimed at the evaluation of plate-like structures, in this research two piezoelectric transducer arrays respectively capable of omnidirectional and unidirectional control of the fundamental GW shear mode in plates (SH0) with above 20 dB mode purity are successfully designed, produced and validated. Omnidirectionality facilitates full structural evaluation coverage and can lead to defect mapping of large volumes with relatively few transducers. A unidirectional beam with relatively high mode purity facilitates evaluation of specific structural locations. Preference to the SH0 mode was given because of its non-dispersive and in-plane propagation properties making it more suitable than other GW modes to propagation in structures surrounded by fluid material. To enable the array development, a number of monolithic piezoelectric thickness-shear transducers of varied area were characterised with respect to GW mode directionality, amplitude and SH0 mode purity. The characterisation of each thickness-shear transducer allows for optimised superposition manipulation for specific applications. A single characterised shear transducer was selected for use in the development of omnidirectional and unidirectional SH0 mode transducer arrays. To aid development a linear superposition analysis model was produced and used to predict for a circular array design the optimum parameters for omnidirectional SH0 mode transmission with significant mode purity. A range of parameter combinations were evaluated and their predicted influence on array performance was characterised. The same method was employed to optimise a dual row linear array design for the unidirectional transducer array. All results were validated by FE models and later with empirical data. Both developed transducer arrays were characterised with respect to GW mode directionality, magnitude and SH0 mode purity. Both their detection sensitivity to pertinent defects and structures was validated, demonstrating relevance to Non Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) applications.

Wave tank tests facilitate the understanding of how complex sea conditions influence the dynamics of man-made structures. If a potential deployment location is known, site data can be used to improve the relevance and realism of the test conditions, thus helping de-risk device development. Generally this data is difficult to obtain and even if available is used simplistically due to established practices and limitations of test facilities. In this work four years of buoy data from the European Marine Energy Centre is characterised and simulated at the FloWave Ocean Energy Research Facility; a circular combined wave-current test tank. Particular emphasis is placed on the characterisation and validation processes, aiming to preserve spectral and directional complexity of the site, whilst proving that the defined representative conditions can be effectively created. When creating representative site-specific sea states, particular focus is given to the application of clustering algorithms, which enable the entire spectral (frequency or directional) form to be considered in the characterisation process. This enables the true complex nature of the site to be considered in the data reduction process. Prior to generating and measuring the resulting sea states, issues with scaling are explored, the facility itself is characterised, and emphasis is placed on developing measurement strategies for the validation of directional spectra. Wave gauge arrays are designed and used to characterise various elements of the FloWave tank, including reflections, spatio-temporal variability and wave shape. A new method for directional spectrum reconstruction (SPAIR) is also developed, enabling more effective measurement and validation of the resulting directional sea states. Through comparison with other characterisation methods, inherent method-induced trade-offs are understood, and it is found that there is no absolute favourable approach, necessitating an application specific procedure. Despite this, a useful set of 'generic' sea states are created for the simulation of both production and extreme conditions. For sea state measurement, the SPAIR method is proven to be significantly more effective than current approaches, reducing errors and introducing additional capability. This method is used in combination with a directional wave gauge array to effectively measure, correct, and validate the resulting directional wave conditions. It is also demonstrated that site-specific wave-current scenarios can be effectively re-created, thus demonstrating that truly complex ocean conditions can be simulated at FloWave. This ability, along with the considered characterisation approach used, means that representative site-specific sea states can be simulated with confidence, increasing the realism of the test environment and helping de-risk device development.

O trabalho apresentado nesta dissertação consiste do estudo do comportamento direcional de um veículo comercial de 2 eixos, classificando-o quanto a sua estabilidade (Oversteer, Understeer ou Neutral Steer) e predizendo em que condições sua instabilidade torna-se crítica. para esta finalidade, o veículo foi modelado desenvolvendo uma trajetória curvilínea de raio constante em situação de regime permanente e uma rotina de cálculos representa sua dinâmica lateral. O recurso computacional utilizado (software Excel) foi propositadamente escolhido tendo como premissa ser o mais simples possível, para que os custos e tempo envolvidos fossem mínimos. Foram realizadas algumas medições com o veículo em questão e, levando-se em conta todas as simplificações implementadas, os resultados práticos e teóricos demonstraram correlação satisfatória. Desta maneira, então, pode-se dizer que o instrumento desenvolvido neste trabalho pode ser aplicado como um recurso valioso durante a fase inicial de conceituação da suspensão de um veículo de 2 eixos, principalmente tratando-se de uma avaliação comparativa com veículos semelhantes já testados. / The work presented consists of a 2 axles light truck directional behavior evaluation, where computational resources applied are very simple and easy hand (software excel). Steady state cornering concept was used to get its stability classification (Oversteer, Understeer or Neutral Steer) and show in which moment its behavior become unstable. Experimental measurements took place and the practical (measured) and theoretical (came from the developed model) results showed theirselves satisfactory, considering all the simplifications. Thus, this procedure might be useful during a two axle light truck suspension development, ultimately if is adopted to compare with another one already known. Costs and time are saved in this way.

Novas rotas para obtenção de silício grau solar a partir de silício grau metalúrgico estão em desenvolvimento e a solidificação direcional é uma etapa presente em todos os processos propostos. O refino de silício por solidificação direcional baseia-se no fenômeno de macrossegregação das impurezas. Experimentos de solidificação direcional transiente foram realizados em condições estáticas utilizando um equipamento projetado no âmbito desse trabalho. A partir de um experimento de referência, foram avaliadas as influências da alteração do material da base do cadinho, altura do lingote e condição de resfriamento do forno. Para estudo das condições de solidificação e dos mecanismos envolvidos no fenômeno de macrossegregação de solutos foi proposto e implementado um modelo matemático. Esse modelo considera as equações gerais de transporte no caso unidirecional e o transporte de espécies químicas por difusão macroscópica e convecção. A convecção foi tratada a luz da teoria da camada estagnada a frente da interface sólido-líquido. Variáveis como velocidade da interface sólido-líquido, gradiente de temperatura, perfis de concentração de soluto e de fração de sólido foram obtidos com o modelo matemático utilizando as temperaturas medidas no silício durante os experimentos de solidificação como condições de contorno do modelo. Os resultados experimentais mostraram que sob algumas condições foram obtidos lingotes com macroestrutura típica de solidificação unidirecional e, além disso, as microestruturas mostraram evidências de macrossegregação de solutos. Os resultados do modelo matemático mostraram que a solidificação ocorreu em diferentes condições de velocidade da interface sólido-líquido e gradiente de temperatura nos experimentos. Os resultados obtidos com a utilização do modelo matemático mostraram que a convecção teve papel fundamental no fenômeno de macrossegregação de solutos. / New process routes are under development to obtain solar grade silicon from metallurgical grade one, and the directional solidification is an essential step in all proposed process routes. The silicon refining by directional solidification is based on the impurities macrosegregation phenomena. Transient solidification experiments were conducted under a static condition in a furnace projected for this work. From a reference experiment it was analyzed the effects of the changing the material of the crucible base, the ingot height and the cooling condition of the furnace. A mathematical model was proposed and implemented in order to study the solidification conditions and the main mechanisms regarding the macrosegregation phenomena. The mathematical model considers the conservation equations in one direction and the transport of chemical species occurs by diffusion and convection. The convection was treated using the diffusion layer theory. The velocity of solid-liquid interface, temperature gradient and profiles of solute concentration and solid fraction were obtained using the temperatures on silicon during the solidification experiments as boundaries conditions of the model. The experimental results showed that under some conditions it was obtained ingots with typical unidirectional macrostructure and, besides, showed in the microstructure evidences of macrosegregation. The mathematical model results showed that the solidification took place under different conditions of solid-liquid interface velocities and temperature gradient in the experiments. The results from the mathematical model showed that convection plays an essential role in the macrosegregation phenomena.

Energy-based acoustic quantities provide vital information about acoustic fields and the characterization of acoustic sources. Recently, the phase and amplitude gradient estimator (PAGE) method has been developed to reduce error and extend bandwidth of energy-based quantity estimates. To inform uses and applications of the method, analytical and experimental characterizations of the method are presented. Analytical PAGE method bias errors are compared with those of traditional estimation for two- and three-microphone one-dimensional probes. For a monopole field when phase unwrapping is possible, zero bias error is achieved for active intensity using three-microphone PAGE and for specific acoustic impedance using two-microphone PAGE. A method for higher-order estimation in reactive fields is developed, and it is shown that a higher-order traditional method outperforms higher-order PAGE for reactive intensity in a standing wave field. Extending the applications of PAGE, the unwrapped phase gradient is used to develop a method for directional sensing with improved bandwidth and arbitrary array response.

In this dissertation, we will study solvent-vapor induced spherulitic growth in multicomponent thin films modeled as prestressed elastic solids. The interface between the crystalline phase and the amorphous phase will be treated as an evolving thermodynamic system and no diffusion of any component will be considered. The dissertation is divided into three parts. In Part I we will determine necessary conditions of thermodynamic equilibrium between the two solid phases, the inter- face, and the vapor. In Part II we will derive the thermodynamic driving force for spherulitic growth in multicomponent elastic thin films. In Part III we will investigate the effect of prestress on the directional dependence of the growth. There a formula that delineates how the prestress affects the shape of the spherulite will be proposed.