Energias de ligação do estado fundamental de doadores rasos em super-redes são consideradas teoricamente com o auxílio de um procedimento variacional que leva em conta a mistura do contínuo de estados da minibanda à qual o mesmo está associado. Os cálculos são realizados para um grande número de parâmetros de super-rede e qualquer posição da impureza na mesma. É mostrado que a dependência da energia de ligação com os vários parâmetros envolvidos pode ser completamente explicada em termos de um modelo simples unidimensional (tight-binding) onde a largura da respectiva minibanda de condução e a energia de ligação no Limite de poço isolado são os únicos parâmetros relevantes. A extrema concordância quantitativa entre as energias de ligação derivadas deste modelo e as obtidas pelo método variacional mais rigoroso vem enfatizar o papel fundamental desempenhado pela largura de minibanda com o único parâmetro relevante ao se levar em conta os efeitos de tunelamento existentes nas super-redes. / A variational procedure which takes into account the mixing of a continuum of subband states has been used to investigate the binding energies of shallow donors in superlattices. The calculations where performed for a wide range of superlattices parameters and impurity positions. It is shown that the dependence of the binding energy upon the various superlattice parameters can be completely explained in terms of a simple onedimensional tight-binding model where the bandwidth of the respective conduction subband and the binding energy in the isolated quantum well are the only relevant parameters. The quantitative overall agreement between the binding energies derived from this model and those found variationally is excellent and emphasizes the fundamental role played by the bandwidth as the only relevant parameter accounting for the tunneling effects.

Este trabalho realizou um estudo sobre a aplicação de algoritmos de inversão da forma de onda completa (FWI) sobre dados de sísmica de reflexão em uma escala rasa ( 0 100 m de profundidade). A FWI foi estudada com o fim de melhorar as velocidades estimadas através do processamento de reflexão PP e PS convencional. Para um melhor entendimento da resposta obtida por este tipo de problema, a inversão foi avaliada sobre dados sintéticos por métodos de busca global e local. Na busca global foi utilizado o algoritmo de Evolução Diferencial que é uma variante de um algoritmo genético. O intuito da busca global foi avaliar a sensibilidade da função objetivo para cada parâmetro do modelo em diferentes janelas de afastamentos em relação à fonte. Na busca local foi utilizado um algoritmo de gradiente conjugado para a estimativa 2D dos parâmetros do meio. Dentre os principais resultados têm-se que a função objetivo é mais sensível aos parâmetros em janelas de afastamentos próximas da fonte. Em tais janelas, dominadas por ondas superficiais, a velocidade da onda S é facilmente estimada. Entretanto, mesmo em janelas mais afastadas a velocidade da onda S é o parâmetro do modelo que se destaca em relação aos demais. Já a busca por todos os parâmetros concomitantemente mostrou-se difícil e implicaria na necessidade de mais iterações do algoritmo de inversão. O método também foi aplicado em dados reais adquiridos no terreno do Instituto de Física da USP. A FWI foi aplicada nestes dados buscando apenas pelos valores de Vs, mantendo os valores de Vp e densidade fixos. A aplicação do algoritmo 2D nestes dados resultaram em valores de Vs coerentes com as velocidades observadas em um ensaio downhole na área. Concluindo, os resultados apresentados na tese mostram que a FWI é aplicável para a melhoria do modelo de velocidade da onda S obtido através do processamento de eventos de reflexão PP e PS. / This work carried out a study on the application of full waveform inversion algorithms (FWI) on reflection seismic data on a shallow scale (0 - 100 m depth). FWI has been studied in order to improve estimated velocities through conventional PP and PS reflection processing. For a better understanding of the response obtained by this type of problem the inversion was evaluated by global and local search methods. In the global search the algorithm employed was the Differential Evolution which is a variant of a genetic algorithm. The aim of the global search was to evaluate the sensitivity of the objective function for each parameter of the model in different windows of distance from the source. In the local search a conjugate gradient algorithm was used for a 2D estimate of the medium parameters. Among the main results is the fact that in a suitable window, for a reflection data acquisition the sensitivity is reduced in relation to a window with geophones closer to the source. However, even in more distant windows the velocity of the S wave is the parameter of the model that stands out in relation to the others. The concomitant search for all parameters at the same time is still difficult and implies the need for more iterations of the inversion algorithm. The method was also applied in a data acquired in the field of the Institute of Physics of USP. The results of the application of the 2D algorithm for this data showed modifications of the provided initial model for a velocity of the S wave coherent with the observed velocities in downhole and lithological informations from this area. In conclusion, the results found that FWI is applicable to improve the S-wave velocity model obtained by processing PP and PS reflection events.

Visando estudo do método de sísmica multicomponente (3C) na investigação rasa, foram adquiridos dados em duas áreas urbanas da cidade de São Paulo, Brasil, com características geológicas diferentes: Campus da Universidade de São Paulo (USP), situado na zona oeste do município e área da estrutura de Colônia, situada na região de Parelheiros, na zona periférica do município. Na aquisição foram empregados geofones de 3 componentes com frequência natural de 10 Hz e, como fontes sísmicas, o compactador e o impacto de uma marreta. Para realizar o processamento dos dados foi utilizado o pacote Seismic Unix (CWP/SU). Foi observada uma marcada diferença nas respostas dos subsolos entre os dois sítios. Nos dados adquiridos no Campus da USP foram observadas tanto as ondas PP como as ondas convertidas (PSv), no entanto, nos dados obtidos em área de Colônia, não foi possível visualizar as ondas convertidas. A partir das secções da onda PP e da onda PS foi estimada a razão Vp/Vs assim como o coeficiente de Poisson para a área da USP. / In order to study the multicomponent seismic method (3C) to shallow investigation, two data sets were acquired in urban areas of São Paulo city, Brazil, with different geological characteristics. The area of the Campus of São Paulo University (USP) is located in the western part of the city and the area of the structure of Colônia is located in the region of Parelheiros, a peripheral zone of São Paulo. For the data acquisition, it were employed 3C-geophones of 10 Hz and, as seismic sources, hand-operated surface compactor and sledge hammer. For processing were used the Seismic Unix package (CWP / SU). It was observed a marked difference in the subsoil responses between the two sites. In the data acquired in the Campus of USP, both PP waves and converted waves (PSv) was observed; however, in the data obtainedin the Colônia area, it was not possible to visualize the converted waves. For the USP area, the Vp / Vs ratio and Poisson ratio were estimated.

Hydraulic structures such as dykes and groynes are commonly used to help control river flows and reduce flood risk. The present research aims to develop an idealized model of the hydrodynamics in the vicinity of a large river bend, and the advection and mixing processes where groynes are located. In this study a curvilinear model of shallow water equations is applied to investigate chaotic advection of particles in a river bend similar in dimensions to a typical bend in the River Danube, Hungary. First, a curvilinear grid generator is developed based on Poisson-type elliptic partial differential equations. The grid generator is verified for benchmark tests concerning a circular domain and for distorted grids in a rectangular domain. It is found that multi-grid (MG) and conjugate gradient (CG) methods performed better computationally than successive over-relaxation (SOR) in generating the curvilinear grids. The open channel hydrodynamics are modelled using the shallow water equations (SWEs) derived by depth-averaging the continuity and Navier-Stokes momentum equations. Both Cartesian and curvilinear forms of the shallow water equations are presented. Both sets of equations are discretized spatially using finite differences and the solution marched forward in time using fourth-order Runge-Kutta scheme. The shallow water solvers are verified and validated for uniform flow in the rectangular channel, wind-induced set up in rectangular and circular basins, flow past a sidewall expansion, and Shallow flow in a rectangular channel with single groyne. A Lagrangian particle tracking model is used to predict the trajectories of tracer particles, and bilinear interpolation is used to provide a representation of the continuous flow field from discrete results. The particle tracking model is verified for trajectories in the flow field of a single free vortex and in the alternating flow field of a pair of blinking vortices. Excellent agreement is obtained with analytical solutions, previously published results in the literature. The combined shallow flow and Lagrangian particle tracking model is then used to simulate particle advection in the flow past a side-wall cavity containing a groyne and reasonable agreement is obtained with published experimental and alternative numerical data. Finally, the combined model is applied to simulate the shallow flow hydrodynamics, advection and mixing processes in the vicinity of groynes in river bend, the dimensions representative of a typical bend in the Danube River, Hungary.

A presença abundante de gás nos sedimentos quaternários do substrato da Lagoa dos Patos, detectada através de perfis sísmicos de alta resolução (3,5 kHz) tem sido evidenciada (Weschenfelder,2005; Weschenfelder et al. 2005; Vasconcellos, 2006). Com a crescente necessidade e procura por novos reservatórios de hidrocarbonetos, a Lagoa dos Patos, localizada na Bacia de Pelotas, merecer ser avaliada mais cuidadosamente com relação ao gás presente em seu substrato, fato esse, até recentemente desconhecido. O estudo tem por finalidade o reconhecimento e mapeamento das acumulações de gás raso na Região da Lagoa dos Patos, assim como estabelecer modelos de formação e reconhecer os fatores que condicionam as acumulações. A análise sísmica de alta resolução (3,5 kHz), juntamente com um sistema de posicionamento por satélite dos perfis levantados, mostra-se um importante instrumento para o mapeamento das feições indicativas de gás raso presentes em perfis sísmicos, sendo notadas por sua impedância acústica anômala, configuração interna quase sempre caótica e terminações laterais abruptas, características desse tipo de gás. É possível diferenciar duas formas principais de acumulações, que são os bolsões de gás e o gás disseminado no sedimento. O objetivo do estudo é integrar dados do projeto temático em geologia “Acumulações de Gás Raso no substrato da Lagoa dos Patos reveladas por sísmica de alta resolução: Caracterização, Mapeamento e Fatores Condicionantes” com dados sísmicos inéditos, adquiridos na campanha intitulada “Operação LAGUPATOS II” do projeto de pesquisa “Levantamento sísmico da Laguna dos Patos na caracterização dos depósitos sedimentares com presença de gás no fundo lagunar”; realizado em julho de 2006. Quer-se aqui desenvolver mapas que reflitam a distribuição do gás raso, diferenciando suas variadas formas de acumulações no sedimento e ainda determinar os processos que geraram as camadas selantes e reservatórias, paleotopografia, assim como outros fatores que propiciaram a geração e armazenamento e, por vezes, o escape do gás. Devido a atual importância do gás natural na economia nacional e ao provável potencial da Bacia de Pelotas como geradora de gás, é importante localizar suas reservas, mesmo que estas acumulações estejam a pequenas profundidades. Diferenciar, através da sísmica, as propriedades acústicas das acumulações para a determinação de possíveis alvos de interesse econômico e ambiental é outro fator importante de aplicação deste trabalho. / The abundant presence of gas in the Quaternary sediments of the substrate of the Patos Lagoon, detected by high resolution seismic profiles (3.5 kHz) has been evidenced (Weschenfelder, 2005; Weschenfelder et al. 2005; Vasconcellos, 2006). With the growing need and demand for new reservoirs of hydrocarbons, the Patos Lagoon, located in the Pelotas Basin, deserve to be evaluated more carefully with respect to the gas present in the substrate, a fact that, until recently unknown. The study aims at the recognition and mapping of shallow gas accumulations in the region of Lagoa dos Patos and establishes generation models and recognizes the factors that influence the accumulations. The analysis of high resolution seismic (3.5 kHz), with a global positioning system satellite of the raised profiles, show an important tool for mapping the indicative features of shallow gas present in seismic profiles and is noted for its anomalous acoustic impedance, internal configuration almost always chaotic and abrupt lateral terminations, characteristics of this type of gas. It is possible to distinguish two main forms of accumulation, which are pocket gas and disseminated gas in the sediment. The objective is to integrate data in geology theme “Acumulações de Gás Raso no substrato da Lagoa dos Patos reveladas por sísmica de alta resolução: Caracterização, Mapeamento e Fatores Condicionantes" with unpublished seismic data acquired in the campaign entitled "Operação LAGUPATOS II "the research project "Levantamento sísmico da Laguna dos Patos na caracterização dos depósitos sedimentares com presença de gás no fundo lagunar”, held in July 2006. The objective of the study is to develop maps that reflect the distribution of shallow gas, differentiating its various forms of accumulation in sediment and also determine the processes that generated the sealant layers and reservoirs, paleotopography as well as other factors that contributed to the generation and storage, and sometimes the gas seeps. The current importance of natural gas in the national economy and the likely potential of the Pelotas Basin as a generator of gas, it is important to locate their stores, even if these accumulations are in small depths. Differentiate, through the seismic, the acoustic properties of the accumulations to determine possible targets of economic and environmental interest is another important application of this work.

Os escorregamentos translacionais rasos são freqüentes na região da Serra do Mar, principalmente quando associados a eventos pluviométricos extremos, como em Janeiro de 1985 (380 mm, em 2 dias). Quando deflagrados de forma generalizada, podem ser catastróficos causando danos para a sociedade. Inúmeros métodos vêm sendo propostos para compreender a ocorrência destes processos na paisagem. O objetivo deste trabalho é avaliar a suscetibilidade a escorregamentos translacionais rasos na Serra do Mar por meio da aplicação de um modelo matemático em bases físicas, tendo como resultado um índice de estabilidade, que aponta, em forma de perigo relativo, áreas passíveis de instabilizações. As etapas de trabalho dividiramse na construção do Modelo Digital de Terreno e em produtos derivados (ângulo da encosta, curvatura, aspecto e área de contribuição), no mapeamento das cicatrizes de 1985 e na simulação dos cenários de suscetibilidade. Os mapas dos parâmetros topográficos, assim como, os mapas de suscetibilidade foram correlacionados com o mapa de cicatrizes e avaliados utilizando-se dos índices de Concentração de Cicatrizes (CC) e Potencial de Escorregamento (PE). Foram mapeadas 216 cicatrizes para uma área de 2,5 km² com uma produção de sedimentos estimado em 135,525m³. Os resultados apontam que encostas com ângulos entre 30° e 40° e com formato retilíneo foram as mais suscetíveis. A área foi considerada instável, segundo o modelo, em todos os cenários, tendo a melhor calibração para o cenário C2. O emprego de diferentes métodos demonstrou-se bastante satisfatório e concordante na análise do resultado final. Além disso, podem auxiliar como ferramentas de apoio de decisão no planejamento do uso do solo, principalmente em regiões onde é freqüente a ocorrência de movimentos de massa. Portanto, o resultado da avaliação a susceptibilidade a escorregamentos rasos na Serra do Mar pode direcionar ações mitigadoras político-administrativas e ambientais, tendo em vista minimizar o impacto sócio-ambiental de eventos futuros. / The shallow landslides are frequent in the Serra do Mar, especially when associated with intense rainfall events, as in January 1985 (380 mm in 2 days). When triggered generalized, causing damage to society. Several methods have been proposed to understand the occurrence of these processes in the landscape. The aim of this study is to evaluate the susceptibility to shallow landslides in the Serra do Mar by applying a physically based models, resulting in a stability index, which points in the form of relatively hazard and susceptible areas. The stages of his research were divided in building the Digital Terrain Model in their products derived (angle of slope, curvature, aspect and area of contribution), mapping the scars of 1985 and simulation of susceptibility scenarios. The maps of the parameters topographic, as well as the susceptibility maps were correlated with the scars map and evaluated using the indices of Scars Concentration (SC) and Landslide Potential (LP). 216 scars were mapped into here area of 2.5 km² with an estimated production of 135.525 m³ sediments. The results show that slopes with angles between 30° and 40° with rectilinear curvature were the most susceptible. The area was considered unstable, according to the model in all scenarios, with the best calibration for scenario C2. The use of different methods showed to be satisfactory and consistent when analyzing with these results. Moreover they can assist as tools for decision support in planning the soil use and, especially in regions where much frequent the occurrence of mass movement. Therefore, the result of susceptibility to shallow landslides in the Serra do Mar can help in the mitigation actions and politicaladministrative environment, aiming minimizes the environmental and social impact of future events.

Visando estudo do método de sísmica multicomponente (3C) na investigação rasa, foram adquiridos dados em duas áreas urbanas da cidade de São Paulo, Brasil, com características geológicas diferentes: Campus da Universidade de São Paulo (USP), situado na zona oeste do município e área da estrutura de Colônia, situada na região de Parelheiros, na zona periférica do município. Na aquisição foram empregados geofones de 3 componentes com frequência natural de 10 Hz e, como fontes sísmicas, o compactador e o impacto de uma marreta. Para realizar o processamento dos dados foi utilizado o pacote Seismic Unix (CWP/SU). Foi observada uma marcada diferença nas respostas dos subsolos entre os dois sítios. Nos dados adquiridos no Campus da USP foram observadas tanto as ondas PP como as ondas convertidas (PSv), no entanto, nos dados obtidos em área de Colônia, não foi possível visualizar as ondas convertidas. A partir das secções da onda PP e da onda PS foi estimada a razão Vp/Vs assim como o coeficiente de Poisson para a área da USP. / In order to study the multicomponent seismic method (3C) to shallow investigation, two data sets were acquired in urban areas of São Paulo city, Brazil, with different geological characteristics. The area of the Campus of São Paulo University (USP) is located in the western part of the city and the area of the structure of Colônia is located in the region of Parelheiros, a peripheral zone of São Paulo. For the data acquisition, it were employed 3C-geophones of 10 Hz and, as seismic sources, hand-operated surface compactor and sledge hammer. For processing were used the Seismic Unix package (CWP / SU). It was observed a marked difference in the subsoil responses between the two sites. In the data acquired in the Campus of USP, both PP waves and converted waves (PSv) was observed; however, in the data obtainedin the Colônia area, it was not possible to visualize the converted waves. For the USP area, the Vp / Vs ratio and Poisson ratio were estimated.

The marine shallow-water hydrothermal vent system of Tutum Bay, Ambitle Island, PNG discharges hot, acidic, arsenic-rich, chemically reduced fluid into cool, alkaline, oxygenated seawater. Gradients in temperature, pH, total arsenic (TAs) and arsenic species, among others, are established as the two aqueous phases mix. Hydrous ferric oxides (HFO) are precipitated around focused venting, and coat the surrounding sediments visibly to 150 m away. HFO coatings, mechanical transport and weathering of volcanoclastic sediments, as well as dissolution of carbonate sediments nearer to venting, combine to alter sediment chemistry substantially. Tutum Bay surface sediments have a mean As concentration of 527 mg/kg. Arsenic at concentrations up to 50 mg/kg (mean = 19.7 mg/kg) was extracted from the easily extractable fraction of surface sediments. Arsenic is elevated in surface seawaters (8 µg/L) directly over hydrothermal vents, and As(III) is substantially enriched in both surface and bottom seawater throughout Tutum Bay. Surprisingly, aqueous As(V) far exceeded aqueous As(III) at almost all distances and depths investigated for Tutum Bay pore waters. These data indicate that throughout Tutum Bay, chemical disequilibria among As species provides potential metabolic energy for arsenite oxidizing and arsenate reducing microorganisms, and that As is bioavailable from two major environments: 1) easily-exchangeable As from surface sediments, and 2) in surface seawaters, which may allow for biological uptake and trophic transfer through plankton. The soft coral Clavularia sp., the calcareous algae Halimeda sp., and the tunicate Polycarpa sp. were collected and analyzed to assess bioaccumulation and biotransformation patterns. All organisms collected from the hydrothermal area displayed higher (2 to 20 times) TAs. Concentrations of arsenic species in their tissues were also elevated compared to the control site. Increased concentrations were observed near focused venting. Distinct arsenic speciation patterns in Clavularia and Polycarpa collected from near hydrothermal venting suggest rapid methylation/detoxification of arsenic, with enhanced bioaccumulation of dimethylarsenate and arsenobetaine as products of the organisms metabolic pathways. Elevated concentrations of As(III) in Halimeda suggest that this organism is not as efficient at methylating inorganic arsenic. The presence of arsenobetaine in Halimeda suggests the biomethylation pathway for calcareous algae is different from commonly studied seaweeds.

Flux gradient terms and source terms are two fundamental components of hyperbolic systems of balance law. Though having distinct mathematical natures, they form and maintain an exact balance in a special class of solutions, which are called steady-state solutions. In this dissertation, we are interested in the construction of well-balanced schemes, which are the numerical methods for hyperbolic systems of balance laws that are capable of exactly preserving steady-state solutions on the discrete level. We first introduce a well-balanced scheme for the Euler equations of gas dynamics with gravitation. The well-balanced property of the designed scheme hinges on a reconstruction process applied to equilibrium variables---the quantities that stay constant at steady states. In addition, the amount of numerical viscosity is reduced in the areas where the flow is in (near) steady-state regime, so that the numerical solutions under consideration can be evolved in a well-balanced manner. We then consider the shallow water equations with friction terms, which become very stiff when the water height is close to zero. The stiffness in the friction terms introduces additional difficulty for designing an efficient well-balanced scheme. If treated explicitly, the stiff friction terms impose a severe restriction on the time step. On the other hand, a straightforward (semi-) implicit treatment of the stiff friction terms can greatly enhance the efficiency, but will break the well-balanced property of the resulting scheme. To this end, we develop a new semi-implicit Runge-Kutta time integration method that is capable of maintaining the well-balanced property under the time step restriction determined exclusively by non-stiff components in the underlying equations. The well-balanced property of our schemes are tested and verified by extensive numerical simulations, and notably, the obtained numerical results clearly indicate that the well-balanced property plays an important role in achieving high resolutions when a coarse grid is used. / acase@tulane.edu

The widespread use of laser line scanners (LLS) aboard unmanned underwater vehicles in the last decade has opened a unique window to a series of ecological and military applications. Variability of underwater light fields and complexity of light contributions reaching the receiver pose a challenge for target detection of LLS under different environmental conditions. The interference of photons not originating at the target (e.g. water path, bottom) can often be minimized (e.g., time-gated systems) but not excluded. Radiative transfer models were developed to better discriminate noise components from signal contributions at the receiver for two continuous LLS: Real-time Ocean Bottom Optical Topographer (ROBOT) and Fluorescence Imaging Laser Line Scanner (FILLS). Numerical experiments using forward Monte Carlo methods were designed to explore the effects of diverse water turbidities and bottom reflectances on ROBOT and FILLS measurements. Interference due to solar light on LLS target detection was also examined. Reliability of radiative transfer models was tested against standard models (Hydrolight) and aquarium measurements. In general a green laser was the best all around choice to detect targets using both LLS sensors. Based on signal-to-noise (S/N) values, performance of ROBOT for target detection was greater (two-fold) than FILLS because of the lower contribution of path photons in ROBOT than FILLS. When ROBOT was located at 1 m above the target, path radiance contributions (noise) were reduced up to 25-fold in clear waters (0.3 mg m-3) with respect to turbid waters (5 mg m-3). Since ROBOT was more discriminative of bottom reflectance discontinuities (high-contrast transitions) than FILLS, algorithms are proposed to retrieve contrasting man-made targets such mines.