Continual technology innovations make it possible to fabricate electronic devices on the order of 10nm. In this nanoscale regime, quantum physics becomes critically important, like energy quantization effects of the narrow channel and the leakage currents due to tunneling. It has also been utilized to build novel devices, such as the band-to-band tunneling field-effect transistors (FETs). Therefore, it presages accurate quantum transport simulations, which not only allow quantitative understanding of the device performances but also provide physical insight and guidelines for device optimizations. However, quantum transport simulations usually require solving repeatedly the Green’s function or the wave function of the whole device region with open boundary treatment, which are computationally cumbersome. Moreover, to overcome the short-channel effects, modern devices usually employ multi-gate structures that are three-dimensional, making the computation very challenging. It is the major target of this thesis to enhance the simulation efficiency by proposing several fast numerical algorithms. The other target is to apply these algorithms to study the physics and performances of some emerging electronic devices. First, an efficient method is implemented for real space simulations with the effective mass approximation. Based on the wave function approach, asymptotic waveform evaluation combined with a complex frequency hopping algorithm is successfully adopted to characterize electron conduction over a wide energy range. Good accuracy and efficiency are demonstrated by simulating several n-type multi-gate silicon FETs. This technique is valid for arbitrary potential distribution and device geometry, making it a powerful tool for studying n-type silicon nanowire (SiNW) FETs in the presence of charged impurity and surface roughness scattering. Second, a model order reduction (MOR) method is proposed for multiband simulation of nanowire structures. Employing three- or six-band k.p Hamiltonian, the non-equilibrium Green’s function (NEGF) equations are projected into a much smaller subspace constructed by sampling the Bloch modes of each cross-section layer. Together with special sampling schemes and Krylov subspace methods for solving the eigenmodes, large cross-section p-type SiNW FETs can be simulated. A novel device, junctionless FET, is then investigated. It is found that its doping density, channel orientation, and channel size need to be carefully optimized in order to outperform the classical inversion-mode FET. With a spurious band elimination process, the MOR method is subsequently extended to the eight-band k.p model, allowing simulation of band-to-band tunneling devices. In particular, tunneling FETs with indium arsenide (InAs) nanowire channel are studied, considering different channel orientations and configurations with source pockets. Results suggest that source pocket has no significant impact on the performances of the nanowire device due to its good electrostatic integrity. At last, improvements are made for open boundary treatment in atomistic simulations. The trick is to condense the Hamiltonian matrix of the periodic leads before calculating the surface Green’s function. It is very useful for treating leads with long unit cells. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / I would like to acknowledge a number of people who contributed towards the completion of this thesis. Firstly, I thank my supervisor Professor Montaz Ali for his patience, enthusiasm, guidance and teachings. The skills I have acquired during this process have infiltrated every aspect of my life. I remain forever grateful. Secondly, I would like to say a special thank you to Professor Jan Snyman for his assistance, which contributed immensely towards this thesis. I would also like to thank Professor Dominque Orban for his willingness to assist me for countless hours with the installation of CUTEr, as well as Professor Jose Mario Martinez for his email correspondence. A heartfelt thanks goes out to my family and friends at large, for their prayers, support and faith in me when I had little faith in myself. Thank you also to my colleagues who kept me sane and motivated, as well as all the support staff who played a pivotal roll in this process. Above all, I would like to thank God, without whom none of this would have been possible.

The objectives of this thesis is to explore different approaches of modelling clustered correlated data in the form of repeated or longitudinal counts data leading to a replicated Poisson process. The specific application is from repeated epileptic seizure time to events data. Two main classes of models will be considered in this thesis. These are the marginal and subject or cluster specific effects models. Under the marginal class of models the generalized estimating equations approach due to Liang and Zeger (1986) is first considered. These models are concerned with population averaged effects as opposed to subject-specific effects which include random subject-specific effects such that multiple or repeated outcomes within a subject or cluster are assumed to be independent conditional on the subject−specific effects. Finally we consider a distinct class of marginal models which include three common variants namely the approach due to Anderson and Gill (1982), Wei et al (1989) and Prentice et al. (1981) / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

<p>Rock groundwater has always caused major problems when tunnelling. Water leaking into tunnels can cause large problems, not only on the construction itself but also on the environment. A continuous water leakage can lead to a declining water supply, and geotechnical problems can occur as subsidence in the ground. Therefore it is of great importance to predict the consequences that can appear in the surroundings due to a declining groundwater surface.</p><p>The aim of the study was to investigate different methods for predicting leakage and changes in groundwater level due to tunnelling excavations in rock. This thesis was performed by comparing mathematical methods, actual groundwater changes and results from preliminary investigations.</p><p>Investigations were made for three railway tunnels planned by Botniabanan AB. Varvsbergstunneln (2 km), Åsbergstunneln (1 km) and Strannebergstunneln (1.4 km) all situated in the surroundings of Örnsköldsvik. During the time this thesis was performed, all tunnels have been fully excavated.</p><p>This thesis has emphasised difficulties in predicting groundwater behaviour as tunnelling excavations are made in rocks. The reason is the complex characteristics of rocks. The conductivity seems to be the parameter that is most difficult to determine with a high accuracy, and hence the accuracy shows in the results. Also the result is affected by the chosen mathematical method. Although careful preliminary investigations are made, it is hard to determine the rock characteristics with such accuracy that leakage and groundwater level changes can be predicted with high precision. However, mathematical methods are a good supplement when determining groundwater influences around railway tunnels in rock.</p> / <p>Vatten i berg har ofta inneburit stora problem vid tunnelbyggen. Vatten som läcker in i tunnlar kan orsaka stora problem på såväl konstruktionen som miljön och dessutom kan ett stort inflöde medföra stabilitetsproblem. Om vatten läcker in kontinuerligt kan omgivningarna dräneras så att vattentillgången minskar och geotekniska problem kan uppstå i form av sättningar i marken. Det är därför av stor vikt att prediktera inläckaget och de konsekvenser som kan uppstå på omgivningen till följd av en grundvattensänkning.</p><p>Syftet med arbetet har varit att undersöka olika metoder för att förutspå inläckage och nivåförändring av grundvatten i samband med tunnelbygge i berggrund. Arbetet utfördes genom att en jämförelse gjordes mellan matematiska metoder, verkliga grundvattenförändringar samt resultat från förundersökningar.</p><p>Undersökningar gjordes för tre järnvägstunnlar som är projekterade av Botniabanan AB. Varvsbergstunneln (2 km), Åsbergstunneln (1 km) samt Strannebergstunneln (1.4 km) som alla är belägna i närheten av Örnsköldsvik. Under examensarbetets gång har man hunnit driva igenom samtliga tre tunnlar.</p><p>Examensarbetet har påvisat svårigheterna i att förutspå grundvattnets beteende vid tunnelbyggen i berggrund. Detta beror på att berggrunden är ett komplext byggnadsmaterial vars egenskaper är svåra att bestämma. Konduktiviteten tycks vara den parameter som är svårast att bestämma med hög noggrannhet, och noggrannheten avspeglas i resultatet. Dessutom beror resultatet av vilken beräkningsmetod som väljs. Trots utförliga förundersökningar är det alltså svårt att bestämma bergets egenskaper med sådan noggrannhet att inläckage och nivåförändring av grundvatten kan förutspås med stor precision. Dock är matematiska metoder bra hjälpmedel för att bestämma grundvattenpåverkan kring järnvägstunnlar i berg.</p>

Orientador: Renata Zotin Gomes de Oliveira / Resumo: Este trabalho concentra-se no estudo do comportamento elástico de materiais através da análise das matrizes de rigidez e flexibilidade de estruturas elementares. Baseado em conceitos da disciplina Resistência dos Materiais e nas propriedades elásticas dos materiais são apresentadas e demonstradas relações matemáticas que refletem as associações entre as tensões normais e de cisalhamento atuantes e as deformações e distorções decorrentes. Essas relações são ilustradas computacionalmente, através do software Geogebra. Transformações de coordenadas possibilitam a determinação de tensões em planos diferentes dos originais de forma analítica ou gráfica. Estes conceitos são aplicados a materiais compósitos ortotrópicos sujeitos a carregamento plano, configuração característica de uma lâmina de material compósito empregada em estruturas mais complexas, possibilitando a determinação das propriedades elásticas de uma lâmina em direções diferentes das chamadas direções principais, alinhadas ou ortogonais à direção das fibras. / Abstract: This essay focuses on the study of the elastic behavior of materials through the analysis of the stiffness and flexibility matrices of elementary structures. Based on the concepts of the Material Resistance discipline and the elastic properties of the materials, mathematical relationships are presented and demonstrated that reflect the associations between the acting normal and shear stresses and the resulting deformations and distortions. These relationships are computationally illustrated through Geogebra software. Coordinate transformations allow the determination of stresses in different planes of the originals in an analytical or graphical way. These concepts are applied to orthotropic composites subjected to flat loading, characteristic configuration of a composite material blade used in more complex structures, making it possible to determine the elastic properties of a blade in different directions of the so-called main directions, aligned or orthogonal to the direction of the fibers. / Mestre

Casimir forces originating from vacuum fluctuations of the electromagnetic fields are of increasing importance in many scientific and technological areas. The manifestations of these long-range forces at the nanoscale have led to the need of better understanding of their contribution in relation to the stability of different physical systems as well as the operation of various technological components and devices. This dissertation presents mathematical and theoretical methods to calculate the Casimir interaction in various infinitely long cylindrical nanostructures. A dielectric-diamagnetic cylindrical layer immersed in a medium is first considered. The layer has a finite thickness characterized with specific dielectric and magnetic properties. Another system considered is that of perfectly conducting concentric cylindrical shells immersed in a medium. The electromagnetic energy between two infinitely long straight parallel dielectric-diamagnetic cylinders immersed in a medium is also considered. The mode summation method is used to calculate the Casimir energy of all these systems. The energy dependence on the cylindrical radial curvature and dielectric response of the cylinders is investigated. The fundamental effects of these long range interactions are studied in the form of exciton-plasmon interactions in carbon nanotubes and this is achieved by looking at the dielectric response of carbon nanotubes.

The current work deals with modelling longitudinal or repeated non-Gaussian measurements for a respiratory disease. The analysis of longitudinal data for non-Gaussian binary disease outcome data can broadly be modeled using three different approaches; the marginal, random effects and transition models. The marginal type model is used if one is interested in estimating population averaged effects such as whether a treatment works or not on an average individual. On the other hand random effects models are important if apart from measuring population averaged effects a researcher is also interested in subject specific effects. In this case to get marginal effects from the subject-specific model we integrate out the random effects. Transition models are also called conditional models as a general term. Thus all the three types of models are important in understanding the effects of covariates and disease progression and distribution of outcomes in a population. In the current work the three models have been researched on and fitted to data. The random effects or subject-specific model is further modified to relax the assumption that the random effects should be strictly normal. This leads to the so called hierarchical generalized linear model (HGLM) based on the h-likelihood formulation suggested by Lee and Nelder (1996). The marginal model was fitted using generalized estimating equations (GEE) using PROC GENMOD in SAS. The random effects model was fitted using PROC GLIMMIX and PROC NLMIXED in SAS (generalized linear mixed model). The latter approach was found to be more flexible except for the need of specifying initial parameter values. The transition model was used to capture the dependence between outcomes in particular the dependence of the current response or outcome on the previous response and fitted using PROC GENMOD. The HGLM was fitted using the GENSTAT software. Longitudinal disease outcome data can provide real and reliable data to model disease progression in the sense that it can be used to estimate important disease i parameters such as prevalence, incidence and others such as the force of infection. Problem associated with longitudinal data include loss of information due to loss to follow up such as dropout and missing data in general. In some cases cross-sectional data can be used to find the required estimates but longitudinal data is more efficient but may require more time, effort and cost to collect. However the successful estimation of a given parameter or function depends on the availability of the relevant data for it. It is sometimes impossible to estimate a parameter of interest if the data cannot its estimation. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Orientador: Meuris Gurgel Carlos da Silva / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-14T21:12:02Z (GMT). No. of bitstreams: 1 Kleinubing_SirleiJaiana_D.pdf: 11340317 bytes, checksum: a992fa50589d93601c1046723bfdc324 (MD5) Previous issue date: 2009 / Resumo: Estudos no campo da biotecnologia ambiental tem buscado encontrar materiais alternativos para o tratamento de efluentes industriais, dentre os quais se destacam as algas marinhas marrons. O alginato e o seu principal polissacarídeo e a presença dos ácidos manuronico (M) e guluronico (G) neste biopolimero esta diretamente relacionada a capacidade de bioadsorcao de íons metálicos. As propriedades de adsorção de diferentes espécies metálicas individuais vem sendo largamente estudadas, embora a maioria dos efluentes industriais contenha varias espécies metálicas em mistura. Este trabalho teve como objetivo investigar o fenômeno de bioadsorcao em sistemas simples e binário, constituídos dos íons Cu2+ e Ni2+, utilizando alginatos comerciais e alga marinha Sargassum filipendula como bioadsorventes. O estudo com alginatos comerciais visou auxiliar na compreensão dos mecanismos envolvidos no processo de bioadsorcao pelas algas marrons. Dois tipos de alginatos com diferentes relações M/G foram avaliados em sistemas monocomponentes. O alginato com menor relação M/G apresentou maior capacidade de bioadsorcao de ambos os íons metálicos. Seguiu-se então o estudo com a alga marinha Sargassum filipendula como bioadsorvente. Inicialmente, foi feita a extração do acido alginico e sua caracterização quanto a relação M/G. Em seguida, foi realizada a identificação dos grupos funcionais presentes na alga que poderiam estar envolvidos no processo de bioadsorcao. Verificou-se que os grupos carboxílicos e álcoois presentes no alginato, grupos sulfatos presentes na fucoidana, e grupos aminos nos aminoácidos, são responsáveis pelas ligações com estes íons. Para a obtenção dos dados de equilíbrio, foram realizados experimentos de remoção individual e da mistura dos íons Cu2+ e Ni2+ pela alga marinha Sargassum filipendula em coluna de leito fixo. Diferentes modelos foram aplicados para ajustar o equilíbrio e o modelo desenvolvido por Silva (2001) para simular a dinâmica de bioadsorcao. A bioadsorcao dos íons metálicos quando puros em solução apresentou capacidades adequadas tanto para o Cu2+ como para o Ni2+. Para a condição binária, o fenômeno de troca seqüencial foi observado, onde o íon Cu2+ desloca o Ni2+ anteriormente bioadsorvido. O modelo de Silva (2001) se ajustou aos dados experimentais obtidos tanto na condicao simples como na binária. Foram estudados, ainda, três ciclos de bioadsorção/dessorção, sendo verificado que a alga manteve suas características de bioadsorcao, assim como o efeito competitivo entre os íons durante os três ciclos avaliados. / Abstract: Environmental biotechnology studies have been conducted using alternative materials in order to eliminate heavy metal ions from industrial effluents. Brown algae are an attractive materials, due to their large availability and their reduced participation in the vital functions of marine ecosystems. The main structural polysaccharide of the brown algae is alginate, constituted of two uronic acids, mannuronic (M) e guluronic (G), and these groups are directly related to its bioadsorption capacity. The adsorption of different heavy metal ions in single systems has been investigated. However, in real systems it is more common to observe several ions in solution, which may interfere and compete for adsorption sites. The aim of this work was to study the bioadsorption of Cu2+ and Ni2+ ions on Sargassum filipendula seaweed and on commercial alginate (single and binary systems), in order to evaluate the competition of different metallic ions for the adsorption sites of bioadsorbents. Two types of alginates with different M / G ratio were evaluated in single component systems. Alginate with the lower M / G ratios showed a higher biosorption capacity of both metal ions. Next, a study with the seaweed Sargassum filipendula as biosorbent was performed. Initially, the alginic acid was extracted and its M / G ratio was characterized. The functional groups present in the algae that could be involved in the process of biosorption were identified. These results indicated that the alcohols and carboxylic groups present in alginate, sulphate groups present in fucoidan, and amino groups in amino acids, are responsible for binding these ions. To obtain equilibrium data, experiments were carried out to remove ions Cu2+ and Ni2+ individuales or in mixture by Sargassum filipendula seaweed in fixed bed column. Different equilibrium models were used to adjust the experimental data and the model developed by Silva (2001) was employed to simulate the dynamic of biosorption. The biosorption of pure ions in solution showed adequate capacity for Cu2+ and Ni2+. For the binary condition, the phenomenon of sequential exchange was observed, where the Cu2+ ion displaces the previously bioadsorbed Ni2+ ion. The mathematical model of Silva (2001) was able to describe satisfactorily the experimental data obtained for single and binary conditions. With regard to biosorption performance for sorption/desorption cycles, metal uptake remained practically unaltered as well as the competition effect between the ions during three successive cycles. / Doutorado / Engenharia de Processos / Doutor em Engenharia Química

Structurally precision graphene nanoribbons (GNRs) are promising candidates for next-generation nanoelectronics due to their intriguing and tunable electronic structures. GNRs with hybrid edge structures often confer them unique geometries associated with exotic physicochemical properties. Herein, a novel type of cove-edged GNRs with periodic short zigzag-edge segments is demonstrated. The bandgap of this GNR family can be tuned using an interplay between the length of the zigzag segments and the distance of two adjacent cove units along the opposite edges, which can be converted from semiconducting to nearly metallic. A family member with periodic cove-zigzag edges based on N = 6 zigzag-edged GNR, namely 6-CZGNR-(2,1), is successfully synthesized in solution through the Scholl reaction of a unique snakelike polymer precursor (10) that is achieved by the Yamamoto coupling of a structurally flexible S-shaped phenanthrene-based monomer (1). The efficiency of cyclodehydrogenation of polymer 10 toward 6-CZGNR-(2,1) is validated by FT-IR, Raman, and UV–vis spectroscopies, as well as by the study of two representative model compounds (2 and 3). Remarkably, the resultant 6-CZGNR-(2,1) exhibits an extended and broad absorption in the near-infrared region with a record narrow optical bandgap of 0.99 eV among the reported solution-synthesized GNRs. Moreover, 6-CZGNR-(2,1) exhibits a high macroscopic carrier mobility of ∼20 cm2 V–1 s–1 determined by terahertz spectroscopy, primarily due to the intrinsically small effective mass (m*e = m*h = 0.17 m0), rendering this GNR a promising candidate for nanoelectronics.

Orientador: Wladimir Seixas / Banca: Manoel Borges Ferreira Neto / Banca: Henrique Lazari / Resumo: Esta dissertação tem a proposta de organizar, discutir e apresentar de maneira precisa os conceitos matemáticos de variedade diferenciável e de tensores envolvidos no estudo da Cosmologia sob o ponto de vista da Teoria da Relatividade Geral para o modelo de Friedmann-Lemaître-Robertson-Walker. Busca-se assim apresentar um texto didático que possa ser utilizado tanto nos cursos de graduação em Matemática como de Física para uma disciplina optativa de Introdução Matemática à Cosmologia / Abstract: The goal of this dissertation is to organize and discuss in a rigorous way the mathematical concepts of manifolds and tensors needed to the study of Cosmology and the Friedmann-Lemaître-Robertson-Walker model under the point of view of the General Relativity. In this way, this dissertation was written as textbook that could be used in an undergraduate course of Physics and Mathematics / Mestre