This thesis makes contributions to the solution of Hadamard's problem through an examination of the question of the validity of Huygens'principle for the non-self-adjoint scalar wave equation on a Petrov type D spacetime. The problem is split into five further sub-cases based on the alignment of the Maxwell and Weyl principal spinors of the underlying spacetime. Two of these sub-cases are considered, one of which is proved to be incompatible with Huygens' principle, while for the other, it is shown that Huygens' principle implies that the two principal null congruences of the Weyl tensor are geodesic and shear-free. Furthermore, an unpublished result of McLenaghan regarding symmetric spacetimes of Petrov type D is independently verified. This result suggests the possible existence of counter-examples of the Carminati-McLenaghan conjecture.

In any research program we begin with a hypothesis and when our expected results do not concur with the observed results we must try and understand the dynamics behind the changed process. In this study we were trying to understand the flux between regional groundwater systems, surface waters and sedimentation processes in order to predict the fate of contaminants entering one of the larger bodies of water in the world- Lake Ontario. This lake has increased levels of tritium due to anthropogenic inputs. Our first approach to the problem was to look at tritium fluxes within the system . Hydrological balances were constructed and a series of sediment cores were taken longitudinally and laterally across the lake. The second approach was to quantify the sediment accumulation rate (SAR) within the depositional basins and zones of erosion in order to improve the linkage between erosion control (sedimentation) and the water quality program. In the last chapter the movement of tritium, by molecular diffusion, through the clayey-silts of Lake Ontario is quantified in terms of an effective diffusion coefficient. In these sediments effective diffusion equals molecular diffusion. In a laboratory experiment four cores of lake sediment were spiked with tritium . The resulting concentration gradient changes in the sediment porewaters after six weeks could be modeled by an analytical one- dimensional diffusive transport equation. Results calculated the average lab diffusion coefficient to be 2. 7 x 10 - 5cm 2. sec -1 which is twice that determined by Wang et al, 1952 but still reasonable. Short cores (50 cm) from lake Ontario had observed tritium concentrations with depth that reflected a variable diffusive profile. The increases and decreases in tritium with depth could be correlated between cores. Monthly tritium emission data was obtained and correlations between peaks in the tritium profile and emissions were observed. Monthly variations in release emissions corresponded to approximately a one centimeter slice of core. An average calculated diffusion coefficient of theses cores was 1. 0 x 10 -5 cm 2. sec -1 which compares to Wang's coefficient of 1. 39 x 10 -5 cm 2. sec -1. This implies that tritium is moving through the sediment column at a rate equal to diffusion. The results were obtained for smoothed values. It was not possible to model the perturbations of the data with a one dimensional model. The dynamics of the system imply that tritium could be used as a biomonitor for reactor emissions, mixing time and current direction scenarios and that a better understanding of this process could be gained by future coring studies and a new hypothesis.

Tese (doutorado) - Universidade Federal de Santa Catarina, Programa de Pós-Graduação em Educação Científica e Tecnológica, Florianópolis, 2010 / Made available in DSpace on 2012-10-25T09:11:36Z (GMT). No. of bitstreams: 1 280245.pdf: 1612359 bytes, checksum: 1b3de2f576a2b4cb937a97d23262e13a (MD5) / A presente pesquisa de Tese explora os potenciais didáticos do contexto histórico de Huygens para a educação científica. Na física escolar, as contribuições científicas de Christiaan Huygens (século XVII) expressam um exemplo de reconstrução didática dos fatos históricos. Esta abordagem resignifica as idéias deste cientista em termos de uma interpretação ondulatória atual. Ao Princípio de Huygens, agrega-se a idéia de superposição de ondas, em um modelo de ondas periódicas, por oposição à versão originalmente proposta em seu Tratado da Luz. de 1690. A fim de evidenciar uma possível intencionalidade didática nas reconstruções históricas do Princípio de Huygens, na física escolar, analisamos alguns livros didáticos do ensino superior. Com base nesse exemplo de resignificação didática, discorremos sobre os obstáculos presentes na transposição didática de episódios históricos ao contexto educativo. Isso porque, os documentos históricos, produzidos pelos historiadores, do mesmo modo que os textos originais dos cientistas, não podem, simplesmente, lançarem-se na ciência escolar. O que torna imprescindível delinear uma intencionalidade didática inequívoca do conteúdo histórico (do conteúdo de ensino) quando se pensa em sua transposição para a realidade educativa. Exploramos, assim, as possíveis faces da intencionalidade didática, presente na transposição didática tradicional, que descontextualiza, dessincretiza e despersonaliza, de modo dogmático, os fatos históricos da ciência. Esta análise mostrou a insuficiência do modelo freqüentemente dedicado à abordagem da física escolar. Por não favorecer o processo de conceitualização escolar que se caracteriza por um movimento contínuo e gradativo de significação e resignificação de conceitos, conforme delineado por estudos da psicologia cognitiva. Transpomos esta análise ao caso de Huygens. Exploramos, assim, a fragilidade da distorção histórica do modelo desse cientista para uma aprendizagem efetiva dos conceitos físicos presentes nos fenômenos ondulatórios. Em particular, porque essa abordagem é insuficiente para problematizar os equívocos dos estudantes quanto ao papel do meio na propagação das ondas mecânicas e suas idéias confusas de superposição de ondas. Expomos, então, como contribuição original da pesquisa uma estratégia didática que apresenta os potenciais didáticos do modelo de ondas mecânicas genuinamente proposto por Huygens.

This study argues for a more widely-conceived cultural sphere that allows the complex and multifarious interactions of both English and Dutch cultures in the early modern period to be explored more fully. My lenses are the works of John Milton and Andrew Marvell, and the relations that they and their work had with the United Provinces and its people. The thesis has a two-part structure. The first half introduces Dutch contexts, being a brief introduction to major areas of early modern Dutch culture, while the second shows how these contexts were influential on, and reflected by, Milton and Marvell. The first four chapters therefore consider areas that had an impact on England and its political and literary writers. These include, in Chapter I, stereotypes and first impressions of the Dutch Republic in English travelogues; representations of the Dutch in these works often surfaced in satirical work on the Dutch during the Anglo-Dutch Wars. Another concern is the literary milieu of the United Provinces, including print culture, literary circles, and ideas of educational reform. Other chapters in Part I discuss two highly influential aspects of Dutch religious life, Arminianism and toleration - both of which had repercussions for Protestantism in England - politics and trade, in particular works on Dutch republicanism and trade, in which England became the United Provinces’ greatest rival. Part II then explores Dutch culture, nation and stereotyping in Milton and Marvell. It demonstrates the far-reaching involvement of Dutch printing culture, especially visible in the publication history of Milton’s Defenses. It also interrogates literary similarities in the works of two Dutch authors, Constantijn Huygens and Joost van den Vondel, with Milton’s Paradise Lost and Marvell’s Upon Appleton House, respectively. The last two chapters identify traces of Dutch Arminianism and toleration in Milton’s Samson Agonistes, Marvell’s Remarks, and Rehearsal Transpros’d, part I and II; and compare versions of republicanism in Samson Agonistes and Vondel’s Samson, of Heilige Wraak, as well as discussing Anglo-Dutch rivalry in their works. This thesis demonstrates the deep and abiding importance of Anglo-Dutch relations to the works of two canonical English authors. Literary, intellectual and politico-religious exchange between England and the United Provinces was more entrenched than it has previously been portrayed.

L'atmosphère de Saturne subit d'importantes variations saisonnières d'insolation, à cause de son obliquité, de son excentricité et de l'ombre de ses anneaux. Dans la stratosphère (de 20 hPa à 10-4 hPa), les échelles de temps photochimiques et radiatives sont du même ordre de grandeur que la période de révolution de Saturne (29,5 ans). On s'attend donc à mesurer des variations saisonnières et méridiennes significatives de la température et des espèces produites par la photochimie (en particulier C2H6, C2H2 et C3H8) dans cette région. Grâce à sa durée (2004-2017), la mission Cassini est l'occasion inédite de suivre l'évolution saisonnière de l'atmosphère de Saturne.Au cours de ma thèse, j'ai analysé des observations au limbe Cassini/CIRS car elles permettent de sonder à la fois la structure méridienne et verticale de la stratosphère de Saturne. Ainsi, j'ai mesuré les variations saisonnières de la température et des abondances de C2H6, C2H2 et C3H8. J'ai également contribué au développement d'un modèle radiatif-convectif et d'un GCM (Global Climate Model) de l'atmosphère de Saturne. Les prédictions de ces modèles sont comparées avec les températures mesurées avec CIRS, de façon à étudier les processus radiatifs et dynamiques qui contribuent à l'évolution saisonnière. Les simulations numériques réalisées avec ce GCM m'ont également permis d'étudier la propagation des ondes atmosphérique ainsi que les effets de l'ombre des anneaux sur l'atmosphère de Saturne. Par ailleurs, la comparaison entre les distributions de C2H6, C2H2 et C3H8 et des modèles photochimiques (Moses et Greathouse 2005, Hue et al. 2015) donne des indications sur le transport méridien. / Saturn's atmosphere undergoes important seasonal variations of insolation, due to its obliquity, its eccentricity and the shadow of its rings. In the stratosphere (from 20 hPa to 10-4 hPa), radiative and photochemical timescales are in the same order as Saturn's revolution period (29.5 ans). Hence, significative seasonal and meridional variations of temperature and photochemical by-products (especially C2H6, C2H2, and C3H8) are expected. Because of its duration (2004-2017), the Cassini mission is an unprecedented opportunity to monitor the seasonal evolution of Saturn's atmosphere. During my PhD, I analysed Cassini/CIRS limb observations as they probe the meridional and vertical structure of Saturn's stratosphere. Hence, I measured seasonal variations of temperature and abundances of C2H6, C2H2, and C3H8. I also contributed to the development of a radiative-convective model and a GCM (Global Climate Model) of Saturn's atmosphere. The predictions of these models are compared with the temperatures measured from CIRS observations, in order to study the radiative and dynamical processes which contribute to the seasonal evolution. Numerical simulations performed with the GCM also allowed me to study atmospheric waves propagation and the effects of rings shadowing in Saturn's atmosphere. Besides, comparison between C2H6, C2H2, and C3H8 distributions and photochemical models (Moses and Greathouse 2005, Hue et al., 2015) give insights on meridional transport.

When an electrically small antenna is conceived, designed, simulated, and tested, the main emphasis is usually placed immediately on its impedance bandwidth and radiation efficiency. All too often it is assumed that its directivity will only be that of a Hertzian dipole and, hence, its directivity becomes a minor consideration. This is particularly true if such a compact antenna radiates in the presence of a large ground plane. Attention is typically focused on the radiator and its size, while the ground plane is forgotten. This has become a too frequent occurrence when antennas, such as patch antennas that have been augmented with metamaterial structures, are explored. In this paper, it is demonstrated that while the ground plane has little impact on the resonance frequency and impedance bandwidth of patch antennas or metamaterial-inspired three-dimensional magnetic EZ antennas, it has a huge impact on their directivity performance. Moreover, it is demonstrated that with both a metamaterial-inspired two-element array and a related Huygens dipole antenna, one can achieve broadside-radiating electrically small systems that have high directivities. Several common and original designs are used to highlight these issues and to emphasize why a fundamental figure of merit such as directivity should never be overlooked.

Saturn’s moon, Titan, has been a scientific marvel since Cassini’s flyby discovered methane-ethane lakes in the northern hemisphere. Several science missions to explore these lakes have been proposed, but none have been launched. Using these previous mission designs, as well as the success of the Huygens probe, this paper will discuss the development of a deployable multi-buoy system with the intent of studying the methane-ethane lakes. The buoys will study the chemical makeup of the lakes, determine meteorology of Titan atmosphere, and map the depth and floor of the targeted lakes. This thesis is a concept study on the multi-buoy system that reviews briefly the concept and design.

A study is undertaken of the numerical reconstruction of acoustic and electromagnetic (EM) localized waves (LWs). The latter are carrier-free ultra-wideband pulses characterized by large focusing depths and extended ranges of localization. Special emphasis is placed on finite energy LWs that can be generated by dynamic aperture antennas with independently addressable elements. The reconstruction techniques are based on Huygens and Rayleigh-Sommerfeld integral I and II representations, both in the time and frequency domains. In contradistinction to the Weyl representation,they lend themselves to the physical realization of space-time aperture sources capable of generating localized wave solutions propagating away from the aperture plane. A detailed comparison of the three reconstruction techniques has been carried out in connection with LW solutions to the scalar wave equation, especially with respect to their handling of acausal components incorporated in the aperture excitation fields. In addition, a study is presented of the characteristic properties of LWs propagating through dispersive media modeled by the Klein-Gordon equation. It is demonstrated that contrary to expectation, the depletion of the spectral components of the LW Klein-Gordon field may be slower than that associated with the free space scalar field. Previous work by Power et al. [73] is extended by studying the acoustic bistatic scattering of a modified power spectrum (MPS) pulse from rigid and compressible spheres. The analysis allows the extraction of the radius of a sphere from the backscattered data. Finally, a special class of electromagnetic (EM) LWs, referred to as azimuthally polarized X waves (APXWs), is derived and their reconstruction is addressed, both in the time and frequency domains. / Ph. D.

Laser-based photo-thermal therapies can provide minimally-invasive treatment of cancers. Their effectiveness is limited by light penetration depth in tissue due to its highly scattering properties. The highly disordered refractive index distribution in tissue leads to multiple-scattering of incident light. It has been hypothesized that mechanical compression has a great potential to enhance the capabilities of laser therapy by inducing localized water transport, decreasing the refractive index mismatch, and decreasing the scattering coefficient of tissue. To better understand this process, we investigated the refractive index change of ex-vivo dog skin during mechanical compression using a swept-source optical coherence tomography (OCT) device built in our lab. The Lorentz-Lorenz rule of mixtures was applied to evaluate the water and protein weight fraction of tissue simultaneously. Results show that the refractive index of skin increased from 1.38 to 1.52 during compression and water content decreased about 60%-70% when the skin sample was compressed by 70%. In addition, we conducted compression experiments on human finger, palm, back of hand, and front of forearm in vivo. OCT images of these skin sites before and after compression by 1 minute were compared. Optical thickness of epidermis and light penetration depth in the dermis were measured. The extended Huygens-Fresnel model was applied to measure the scattering coefficient μs of skin specimens. μs of skin was measured to be about 10-17 mm-1 before compression and decreased 60%-80% after compression, which increases the averaged light intensity by 2-7 dB and almost doubles light penetration depth in dermis. It is quite significant in laser therapies especially for treating epithelia cancers which originate at 1-2 mm beneath the tissue surface. In the OCT imaging of skin dehydration experiment, we conclude that dehydration is an important mechanism of mechanical clearing. / Master of Science

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