Dissertations / Theses on the topic 'Field defect'

For many years, the theoretical and experimental study of eddy current non-destructive evaluation (NDE) has been conducted separately, as most models were not suited to practical industrial applications. The aim of this work is to bridge this gap by investigating the relationship between magnetic fields and defects using both modelling and experimental study and to link these results to quantitative NDE. In this work, 3D FEM numerical simulations are used to predict the response of an eddy current probe being scanned over the area of a defect and understand the underlying change in magnetic field due to the presence of the defect. Experimental investigations are performed to study the feasibility of the proposed magnetic field measurement techniques for defect detection. This experimental work investigates the inspection of both surface and subsurface defects, the use of rectangular (directional) probes and the measurement of complex magnetic field values, as the response in these cases has been found to have a greater correlation with the shape of the defect being studied. As well as the detection of defects, both frequency spectrum and transient information from pulsed eddy current responses are used to reconstruct the profile (depth and width) of a slot shaped defect. The work concludes that the use of magnetic field measurements provides useful information for defect detection and quantification. This will have applications in both industrial and research areas, including visualisation of defects from magnetic field measurements, which can be applied to the monitoring of safety critical components.

Electron beam induced current (EBIC) and atom probe tomography (APT) were used in this study to determine electrical activities and impurity compositions at extended defects in multicrystalline silicon (mc-Si) samples. The results provide, for the first time, information regarding the chemical species present at defects whose electrical activity has previously been measured. A new APT specimen fabrication process was developed with the ability to select a specific defect for APT analysis. Development of the APT specimen fabrication process proceeded by first selecting and optimising the preferential etching for nano-scale defect delineation. Three etchants were evaluated, namely Secco, Sirtl and Dash, from which the Secco etch was selected. Three parameters were optimised to produce etch pits with geometries that meet the requirements imposed by APT specimen fabrication methods. The optimum parameters were 0.05M potassium dichromate concentration, 20°C etch temperature, and 30sec etch time. In the second stage, marking techniques were developed in order for the defects to be located throughout the APT specimen fabrication process. However, it became apparent that the conventional APT specimen fabrication method could not be used to fabricate APT specimens containing selected defects in a mc-Si sample. This led to the development of a novel APT specimen fabrication approach which allowed APT specimens to be fabricated, reproducibly, containing grain boundaries and isolated dislocations. In order to evaluate accurately iron contamination in mc-Si, four atom probe parameters were optimised to maximise detection sensitivity: the evaporation rate, the laser beam energy, the pulse repetition rate and the specimen temperature. The optimisation process can be divided in to two parts. In the first part, a matrix of pre-sharpened single-crystal silicon specimens was subjected to a variety of experimental parameters. The optimised parameters were determined to be 0.3% evaporation rate, 0.5nJ beam energy, 160kHz repetition rate and 55K specimen temperature. The second part was to determine the iron detection efficiency –the percentage of detected Fe ions that can be correctly identified as Fe– and sensitivity using these parameters to analyse a specially prepared iron calibration specimen. The values were determined to be a detection efficiency of about 35% and sensitivity of 54ppm or 2.70x10¹⁸ atom/cm³. The APT specimen fabrication process and the optimised APT analysis parameters were used to analyse four extended defects in mc-Si samples subjected to three different processing conditions, namely gold-contaminated, as-grown and phosphorus diffusion gettering (PDG). The important aspects of the analysis are listed below: • Gold was not detected at the grain boundary and its associated dislocations in the gold-contaminated specimen. The binding enthalpy of gold to such defects is thus less than 0.63eV. • Iron was not detected in any specimen. • Copper was observed at the grain boundary in the as-grown specimen in the form of individual atoms as well as clusters with diameters ranging between 4nm and 9nm. The electrical activity of the grain boundary was about 58%. • Nickel and carbon were detected at the grain boundary in the post-PDG specimen with the former having platelet structures with diameters and thicknesses ranging between 4nm-7nm and 2nm-4nm, respectively. The recombination strength of the defect was about 22%. • Two nickel clusters were found at the isolated dislocation in the post-PDG specimen. The clusters were spherical with an average diameter of 10nm. The distance between the two clusters was 35nm. The recombination strength of the defect was about 4%.

DNA methylation is increasingly recognised as a significant epigenetic event that may initiate and drive the process of neoplasia in humans. In the colon, DNA methylation of key genes is common in a subset of colorectal cancers. The extent to which DNA methylation at various genes contributes to initiation of colorectal neoplasms is less clear. This study sought to clarify the biological and clinicopathological significance of methylation of various genes in the development of sporadic and familial colorectal neoplasia. Quantitative methylation-specific PCR (qMSP) assays (capable of detecting down to a measureable proportion of 0.1% of the total input DNA) were developed to determine the presence of CpG methylation at a given gene. Methylation of MLH1-C was found in the apparently normal mucosa samples from seven of 104 (7%) of individuals with sporadic colorectal cancer (CRC) showing microsatellite instability (MSI). No methylation of MLH1-C was found in the biological samples of individuals with microsatellite stable (MSS) counterparts (n=131). MLH1-C methylation may be a field defect that predisposes to the development of sporadic colorectal neoplasia, particularly those demonstrating MSI. Methylation of three of five genes within the 3p22 region including AB002340, MLH1, ITGA9, PLCD1 and DLEC1 (regional 3p22 methylation) was found in 83% of sporadic MSI (n=86) and 12% of MSS cancers demonstrating BRAF V600E mutation (n=42). Regional 3p22 correlated strongly with CpG island methylator phenotype (CIMP), and other clinicopathological characteristics typical of CIMP. Thus, regional 3p22 methylation and CIMP may be overlapping phenomena. Regional 3p22 methylation and the BRAF V600E mutation were found in normal colonic mucosa of four individuals with sporadic MSI CRC, and these cases also had multiple synchronous serrated polyps. These molecular aberrancies may predispose some individuals to the development of metachronous serrated neoplasia. Germline epimutations of APC do not contribute towards the development of FAP, AFAP, or hyperplastic polyposis syndromes. However, APC methylation in normal colonic mucosa of these individuals may represent a field defect in the development of futher neoplasms. In conclusion, different patterns of DNA methylation in normal colonic mucosa may represent a field defect important in the development of different subtypes of colorectal neoplasia.

Purpose: Glaucoma diagnosis and monitoring would benefit from a quantitative visual field (VF) classification system like VF archetypal analysis, where Elze et al. showed that any VF can be represented as a weighted sum of 17 archetype (AT) patterns. We assessed the clinical construct validity of this system by testing for clinical correlates of VF ATs. Methods: From 30,995 reliable Humphrey VFs (24-2), 243 patients were retrospectively selected, comprising the 10 to 20 patients whose VFs had the highest decomposition coefficients for each AT. Corresponding patient systemic and ocular characteristics were obtained and compared between each AT and all others using the two-tailed t-test or Fisher exact test. Results: Mean deviation and pattern standard deviation varied with VF loss severity and focality respectively. Cup-to-disc ratio was more often ≥0.7 for AT6 (central island; P=0.002), AT14 (superior paracentral defect; P=0.016), and AT16 (inferior paracentral defect; P=0.016). Other associations included: AT6 (central island): African ancestry (P<0.001) and younger age (P<0.0001); AT13 (diffuse inferior defect): African ancestry (P=0.006) and chronic angle closure glaucoma (P=0.005); and AT16 (inferior paracentral defect): female sex (P=0.017). Conclusions: Several expected clinical associations support computationally derived VF ATs’ clinical construct validity. New associations identified by exploratory analysis may merit further investigation.

Orientador: Prof. Dr. Ivo Alexandre Hümmelgen
Tese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Curso de Pós-Graduação em Física. Defesa: Curitiba, 15/12/2017
Inclui referências : f. 93-102
Resumo: O trabalho atual investiga a melhoria das propriedades de transporte de carga em transistores de efeito de campo de baixa tensão (FETs), que utilizam poli(3-hexiltiofeno-2,5-diil) (P3HT) não-100% e 100% regioregular como os semicondutores orgânicos, e poli(álcool vinílico) reticulado (cr-PVA) como isolante. O trabalho de pesquisa realizado durante o projeto pode ser dividido em duas partes. A primeira parte investiga a melhoria das propriedades de transporte de carga na interface cr-PVA/P3HT, e a influência de defeitos de regioregularidade de P3HT nas propriedades da interface. A segunda parte demonstra a preparação de filmes finos que consistem em moléculas alinhadas de P3HT 100% regioregular e, consequentemente, a aplicação desses filmes alinhados para o desenvolvimento de dispositivos de alto desempenho. No caso da primeira parte, o problema essencial é que o transporte de carga na interface de cr-PVA/P3HT está limitado pela presença de armadilhas na interface que correspondem aos dipolos de superfície de cr-PVA. Esses dipolos de superfície possuem a capacidade de modificar a distribuição de carga em moléculas adjacentes de P3HT, o que pode levar à localização e a captura de cargas. Isso representa um problema fisico complexo, sendo que a variação de energia potencial na interface depende da posição e orientação das armadilhas dipolares em relação às moléculas de P3HT. No entanto, a solução é conceitualmente simples, pois, em princípio, é apenas necessário passivar as armadilhas. Para conseguir isso, é apresentada uma técnica experimental econômica, na qual a superfície de cr-PVA é tratada com um surfactante catiônico, brometo de hexadeciltrimetilamónio (CTAB). As cabeças hidrofílicas carregadas positivamente de CTAB visam a passivação das armadilhas carregadas negativamente da superfície de cr-PVA. A deposição de CTAB sobre o cr-PVA, em relação ao cr-PVA somente, resulta em aumento significativo na capacitância do isolanate (Ci), e as imagens de microscopia de força atômica (AFM) mostram que a superfície de cr-PVA é coberta com grãos de surfactante bem conectados. Em caso de dispositivos baseados em P3HT não-100% regioregular, este tratamento resulta em uma melhora da mobilidade de efeito de campo (?FET) por um fator de ~3 (?FET médio de 0.44 cm2/V.s) quando comparado aos dispositivos não tratados. Para investigar como o tratamento do surfactante modifica o transporte de carga na interface, a variação de ?FET em função da espessura efetiva do gargalo do canal (l0) também é analisada e discutida detalhadamente. Curiosamente, ao contrário dos dispositivos baseado em P3HT não-100% regioregular, o tratamento com surfactante em dispositivos baseado em P3HT 100% regioregular resulta em degradação de ?FET e do desempenho geral dos dispositivos. Isso indica que a interação de defeitos de regioregularidade e armadilhas de superfície de cr-PVA é um fator crítico que afeta as propriedades de transporte de carga na interface cr-PVA/P3HT. Para investigar este assunto, a interação das moléculas de P3HT não-100% e 100% regioregular com dipolos de superfície de cr-PVA é investigada usando espectroscopia de absorbância, AFM e cálculos de química quântica. Observa-se que, dependendo da presença ou ausência de defeitos de regioregularidade de P3HT (e, portanto, da planaridade molecular), o contato entre as moléculas de P3HT e os dipolos de superfície de cr-PVA afeta a ordem molecular do P3HT de forma diferente. Por causa dos defeitos de regioregularidade, as moléculas de polímero não-100% regioregular produzem momentos de dipolo mais altos em comparação com moléculas 100% regioregular. Consequentemente, discute-se como a interação de moléculas de P3HT não-100% e 100% regioregular com dipolos de cr-PVA contribuem à desordem energética na interface cr-PVA/P3HT. Neste caso, o transporte de carga em dispositivos de FET é investigado para quatro espessuras diferentes de P3HT não-100% e 100% regioregular. Os resultados elétricos mostram que o comportamento de ?FET × l0 e a dependência de ?FET na espessura do canal são uma função forte da presença ou ausência de defeitos de regioregularidade de P3HT. Neste trabalho, os dispositivos (não tratados) baseados em P3HT 100% regioregular demonstram ?FET tão alto quanto 1.20 cm2/V.s. Esses valores tornam esses dispositivos reconhecíveis para a integração em várias aplicações comerciais. No entanto, um desenho de circuitos para muitas outras aplicações de alto desempenho impõem um requisito de ?FET mais rigoroso (> 5 cm2/V.s). Para alcançar este marco, na segunda parte do projeto de pesquisa, está apresentada uma técnica de deposição simples (chamado, floating-film transfer method, em inglês), que permite o alinhamento supra-molecular das moléculas de P3HT 100% regioregular. A aplicação de filmes de polímero alinhados em FETs resulta em valores de ?FET de até 8 cm2/V.s, que é o valor mais alto reportado até agora para os FETs baseados em P3HT. Palavras-chaves: Transistores orgânicos de efeito de campo, poli(3-hexiltiofeno-2,5-diil) livre de defeitos, regioregularidade, poli(álcool vinílico) reticulado, interface isolante/semicondutor, armadilhas dipolares.
Abstract: The current work investigates the improvement of charge transport properties in low-voltage organic field-effect transistors (OFETs) that utilize non-100% and 100% regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) as the organic semiconductors, and cross-linked poly(vinyl alcohol) (cr-PVA) as the gate insulator. The essential research work performed during the project can be divided into two parts. The first part investigates the improvement of charge transport properties at the cr-PVA/P3HT interface, and the influence of regioregularity defects of P3HT on interface properties. The second part demonstrates the development of high performance OFETs based on supra-molecularly aligned thin films of 100% regioregular P3HT. In the case of the first part, the essential problem in hand is that charge transport at the cr-PVA/P3HT interface is limited by the presence of charge traps at the interface corresponding to the surface dipoles of cr-PVA. These surface dipoles hold the ability to modify charge distribution on adjacent P3HT molecules, which can lead to localization and trapping of otherwise mobile charge carriers. This presents a physically complex problem, since the potential energy variations at the interface depends on the position and orientation of the dipolar traps with respect to P3HT molecules. However, the solution is conceptually simple since, in principle, it is only required to passivate the traps. In order to achieve this, a cost-effective experimental technique is presented, in which the cr-PVA surface is treated with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). The positively charged hydrophilic heads of CTAB are aimed at passivating the negatively charged traps of the cr-PVA surface. The deposition of CTAB over cr-PVA leads to significant enhancement in gate insulator capacitance (Ci), and the atomic force microscopy (AFM) images show that the cr-PVA surface is covered with well-connected surfactant grains. In the case of non-100% regioregular P3HT OFETs, this treatment results in an improvement of field-effect mobility (?FET) by a factor of ~3 (average ?FET of 0.44 cm2/V.s) when compared to untreated devices. In order to investigate how the surfactant treatment modifies charge transport at the interface, variation of ?FET as a function of the effective bottleneck thickness of the conducting channel (l0) is also analyzed and thoroughly discussed. Quite interestingly, contrary to non-100% regioregular P3HT devices, the surfactant treatment in 100% regioregular P3HT devices leads to degradation of ?FET and overall device performance. This indicates that the interaction of regioregularity defects and cr-PVA surface traps is a crucial factor affecting charge transport properties at the cr-PVA/P3HT interface. In order to address this issue, the interaction of non-100% and 100% regioregular P3HT molecules with cr-PVA surface dipoles is investigated using UV-vis absorbance spectroscopy, AFM and quantum chemical calculations. It is observed that, depending on the presence or absence of regioregularity defects of P3HT (and thus the molecular planarity); the intimate contact between P3HT molecules and cr-PVA surface dipoles affects the molecular order of P3HT differently. Because of the regioregularity defects, the non-100% regioregular polymer molecules produce higher dipole moments compared to 100% regioregular molecules. Consequently, it is discussed how the interaction of non-100% and 100% regioregular P3HT molecules with cr-PVA surface dipoles contribute differently to the potential energy variations at the cr-PVA/P3HT interface. In this case, the charge transport in FET devices is investigated for four different thicknesses of both non-100% and 100% regioregular P3HT. The electrical results reveal that the behavior of ?FET × l0 and the dependence of ?FET on channel thickness are a strong function of the presence/absence of the regioregularity defects of P3HT. In this project, the untreated 100% regioregular P3HT devices demonstrate ?FET as high as 1.20 cm2/V.s. Such high values make these devices recognizable for translation to various commercial applications. However, the circuit designs of many other high performance applications impose a more stringent ?FET requirement (> 5 cm2/V.s). In order to achieve this landmark, in the second part of the research project, a simple and cost-effective deposition technique (floating-film transfer method) is presented, which allows supra-molecular alignment of 100% regioregular P3HT molecules. The application of aligned polymer films in FET devices leads to the demonstration of ?FET values as high as 8 cm2/V.s, which is the highest value reported so far for P3HT based OFETs. Keywords: Organic field-effect transistors, defect-free poly(3-hexylthiophene-2,5-diyl), regioregularity, cross-linked poly(vinyl alcohol), insulator/semiconductor interface, dipolar charge traps.

General ideas in the conformal bootstrap program are covered. Both numerical and analytical approaches to the bootstrap equation are reviewed to show how it can be manipulated in different ways. Further analytical approaches are studied for theories with defects. We consider the three-dimensional CFT at the corresponding WF fixed point in the O(N) \phi^4 model with a co-dimension two, monodromy defect. Anomalous dimensions for bulk- and defect-local fields as well as one of the OPE coefficients are found to the first loop order. Implications of inserting this defect and constraints that arises from symmetries of the theory are investigated.

Quick mass production of homogeneous thin film material is required in paper, plastic, fabric, and thin film industries. Due to the high feed rates and small thicknesses, machine vision and other nondestructive evaluation techniques are used to ensure consistent, defect-free material by continuously assessing post-production quality. One of the fastest growing inspection areas is for 0.5-500 micrometer thick thin films, which are used for semiconductor wafers, amorphous photovoltaics, optical films, plastics, and organic and inorganic membranes. As a demonstration application, a prototype roll-feed imaging system has been designed to inspect high-temperature polymer electrolyte membrane (PEM), used for fuel cells, after being die cast onto a moving transparent substrate. The inspection system continuously detects thin film defects and classifies them with a neural network into categories of holes, bubbles, thinning, and gels, with a 1.2% false alarm rate, 7.1% escape rate, and classification accuracy of 96.1%. In slot die casting processes, defect types are indicative of a misbalance in the mass flow rate and web speed; so, based on the classified defects, the inspection system informs the operator of corrective adjustments to these manufacturing parameters. Thickness uniformity is also critical to membrane functionality, so a real-time, full-field transmission densitometer has been created to measure the bi-directional thickness profile of the semi-transparent PEM between 25-400 micrometers. The local thickness of the 75 mm x 100 mm imaged area is determined by converting the optical density of the sample to thickness with the Beer-Lambert law. The PEM extinction coefficient is determined to be 1.4 D/mm and the average thickness error is found to be 4.7%. Finally, the defect inspection and thickness profilometry systems are compiled into a specially-designed graphical user interface for intuitive real-time operation and visualization.

There are several reasons to be interested in conformal field theories in two dimensions. Apart from arising in various physical applications, ranging from statistical mechanics to string theory, conformal field theory is a class of quantum field theories that is interesting on its own. First of all there is a large amount of symmetries. In addition, many of the interesting theories satisfy a finiteness condition, that together with the symmetries allows for a fully non-perturbative treatment, and even for a complete solution in a mathematically rigorous manner. One of the crucial tools which make such a treatment possible is provided by category theory. This thesis contains results relevant for two different classes of conformal field theory. We partly treat rational conformal field theory, but also derive results that aim at a better understanding of logarithmic conformal field theory. For rational conformal field theory, we generalize the proof that the construction of correlators, via three-dimensional topological field theory, satisfies the consistency conditions to oriented world sheets with defect lines. We also derive a classifying algebra for defects. This is a semisimple commutative associative algebra over the complex numbers whose one-dimensional representations are in bijection with the topological defect lines of the theory. Then we relax the semisimplicity condition of rational conformal field theory and consider a larger class of categories, containing non-semisimple ones, that is relevant for logarithmic conformal field theory. We obtain, for any finite-dimensional factorizable ribbon Hopf algebra H, a family of symmetric commutative Frobenius algebras in the category of bimodules over H. For any such Frobenius algebra, which can be constructed as a coend, we associate to any Riemann surface a morphism in the bimodule category. We prove that this morphism is invariant under a projective action of the mapping class group ofthe Riemann surface. This suggests to regard these morphisms as candidates for correlators of bulk fields of a full conformal field theories whose chiral data are described by the category of left-modules over H.

Thesis (PhD (Physics))--Stellenbosch University, 2008.
The advent of high intensity short pulse lasers has opened the door to investigating buried solid-solid interfaces through the technique of optical second harmonic generation (SHG). This has led to extensive study of technologically important systems such as the Si/SiO2 interface. In this study, SHG is employed to study the interface between highly boron doped p+-type Si and its native oxide layer (SiO2). Previous studies from this laboratory have extensively investigated the photo-induced charge transfer process across the Si/SiO2 interface in the case of undoped natively oxidized Si by means of SHG, with initial SHG measurements being performed on boron doped p+-type Si. The natively oxidized p+-type Si/SiO2 sample was placed on a computer controlled positioning system which allowed for translation of the sample and rotation around the azimuth. The laser system employed was characterized in terms of spectral composition, pulse duration, pulse repetition rate, spatial pro le and pulse energy in order to ensure quantitative measurements. The SHG signal generated from the sample interface was recorded in re ection. Under the applied irradiation conditions, defects are created at the interface by the near infra red (NIR) femtosecond radiation from the laser. These defects are then populated via multi-photon processes by electrons and to a lesser extent holes. The charge transfer across the interface induces an interfacial electric eld. This photo-induced electric eld is in addition to the built-in interfacial electric eld caused by positive ionization of naturally occurring interfacial defects due to the strong doping of the bulk Si. It is this interfacial electric eld, consisting of the built-in doping induced eld and the photo-induced electron and hole elds, that is probed by SHG. The SHG signal is strongly dependent on the magnitude of this interfacial electric eld as the electric eld induced second harmonic (EFISH) signal dominates all other contributions to the observed SHG signal in the case of the Si/SiO2 system. The temporal evolution of the SHG signal is recorded for di erent intensities from virgin as well as the pre-irradiated samples. This yields information about the time scales on which the charge separation occurs as well as the in- uence of existing photo-induced trap sites on the charge separation process, since the strength of the SHG signal is an indirect measure of the interfacial electric eld strength. The angular dependence of the SHG signal (SH rotational anisotropy measurements) for both the initial signal (when the doping induced electric eld dominates) and the saturated signal (when the electron induced electric eld dominates) is measured. Both these measurements show a four fold symmetry but with a relative 45 phase shift between them. This iii is taken as con rmation of the reversal of the interfacial electric eld direction. The initial SHG signal as a function of intensity is also recorded for di erent incident wavelengths. The variation in the non-quadratic dependence of the initial SHG signal on the incident intensity is attributed to a resonant enhancement of two-photon absorption and subsequent screening of the interfacial electric eld by charge carriers. The measurement performed and the results obtained contribute to the understanding of the photo-induced charge separation process across buried solid-solid interfaces, speci cally as it applies to the important Si/SiO2 interface.

BACKGROUND:Cancers often arise within an area of cells (e.g. an epithelial patch) that is predisposed to the development of cancer, i.e. a "field of cancerization" or "field defect." Sporadic colon cancer is characterized by an elevated mutation rate and genomic instability. If a field defect were deficient in DNA repair, DNA damages would tend to escape repair and give rise to carcinogenic mutations.PURPOSE:To determine whether reduced expression of DNA repair proteins Pms2, Ercc1 and Xpf (pairing partner of Ercc1) are early steps in progression to colon cancer.RESULTS:Tissue biopsies were taken during colonoscopies of 77 patients at 4 different risk levels for colon cancer, including 19 patients who had never had colonic neoplasia (who served as controls). In addition, 158 tissue samples were taken from tissues near or within colon cancers removed by resection and 16 tissue samples were taken near tubulovillous adenomas (TVAs) removed by resection. 568 triplicate tissue sections (a total of 1,704 tissue sections) from these tissue samples were evaluated by immunohistochemistry for 4 DNA repair proteins. Substantially reduced protein expression of Pms2, Ercc1 and Xpf occurred in field defects of up to 10 cm longitudinally distant from colon cancers or TVAs and within colon cancers. Expression of another DNA repair protein, Ku86, was infrequently reduced in these areas. When Pms2, Ercc1 or Xpf were reduced in protein expression, then either one or both of the other two proteins most often had reduced protein expression as well. The mean inner colon circumferences, from 32 resections, of the ascending, transverse and descending/sigmoid areas were measured as 6.6 cm, 5.8 cm and 6.3 cm, respectively. When combined with other measurements in the literature, this indicates the approximate mean number of colonic crypts in humans is 10 million.CONCLUSIONS:The substantial deficiencies in protein expression of DNA repair proteins Pms2, Ercc1 and Xpf in about 1 million crypts near cancers and TVAs suggests that the tumors arose in field defects that were deficient in DNA repair and that deficiencies in Pms2, Ercc1 and Xpf are early steps, often occurring together, in progression to colon cancer.

This thesis outlines methods for generating new integrable defects in affine Toda field theory. These methods are grounded in the hypothesis that defects have a particle-like classification with as many species of fundamental defect existing in a particular affine Toda theory as there are species of soliton. The methods employed are: 1. Defect fusing rules, linking different species of defect in the same theory. Defect fusing rules are used in this thesis to find transmission matrices for a new, species 2, defect in a^(1)_3. 2. Folding, linking defects in simply laced theories to defects in non-simply laced theories. Folding is used in this thesis to find defects in the c^(1)_n, d^(2)_n and a^(2)_2n affine Toda field theories.

This thesis expands previous work on defects appearing in classical integrable field theories, with a generalised form for momentum conserving defects being found. It is shown that the defect equations can always be augmented to give a Bäcklund transformation for the bulk theory, and new momentum conserving defects are found for the Br and Dr ATFTs. Momentum conservation is shown to be a necessary condition if the system is to have an infinite number of conserved quantities for all defects in ATFTs. The D4 defect in particular is investigated, with the system shown to have a zero curvature representation and soliton-defect interactions being investigated.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Nesta tese discutimos as propriedades de integrabilidade das teorias de campo clássicas em duas dimensões na presença de descontinuidades ou defeitos tipo-II, principalmente usando a linguagem do formalismo do espalhamento inverso. Um método geral para calcular a função geradora de um conjunto infinito de grandezas conservadas modificadas para qualquer equação de campo integrável é apresentado, uma vez que seus respetivos problemas lineares associados são dados e suas correspondentes matrices do defeito são calculadas. O método é aplicado no cálculo das contribuições dos defeitos para a energia e o momento para vários modelos e mostramos a relação entre as condições de defeito integráveis e suas respevtivas transformações de Bäcklund para cada modelo
In this thesis we discuss the integrability properties of two-dimensional classical field theories in the presence of discontinuities or type-II defects, mainly using the language of the inverses cattering approach. We present a general method to compute the generating function of an infinite set of modified conserved quantities for any integrable field equation givent heir associated linear problems and computing their corresponding defect matrices. We apply this method to derive in particular defect contributions to the energy and momentum for several models and show the relationship between the integrable defect conditions and the Bäcklund transformations for each model

Orientador: Abraham Hirsz Zimerman
Banca: Clisthenis Ponce Constantinidis
Banca: Harold Socrates Blas Achic
Banca: Andrei Mikhailov
Banca: Marcio José Martins
Resumo: Nesta tese discutimos as propriedades de integrabilidade das teorias de campo clássicas em duas dimensões na presença de descontinuidades ou defeitos tipo-II, principalmente usando a linguagem do formalismo do espalhamento inverso. Um método geral para calcular a função geradora de um conjunto infinito de grandezas conservadas modificadas para qualquer equação de campo integrável é apresentado, uma vez que seus respetivos problemas lineares associados são dados e suas correspondentes matrices do defeito são calculadas. O método é aplicado no cálculo das contribuições dos defeitos para a energia e o momento para vários modelos e mostramos a relação entre as condições de defeito integráveis e suas respevtivas transformações de Bäcklund para cada modelo
Abstract: In this thesis we discuss the integrability properties of two-dimensional classical field theories in the presence of discontinuities or type-II defects, mainly using the language of the inverses cattering approach. We present a general method to compute the generating function of an infinite set of modified conserved quantities for any integrable field equation givent heir associated linear problems and computing their corresponding defect matrices. We apply this method to derive in particular defect contributions to the energy and momentum for several models and show the relationship between the integrable defect conditions and the Bäcklund transformations for each model
Doutor

The infinite-dimensional symmetry algebra of a conformal field theory (CFT), the Virasoro algebra, is generated by the holomorphic and anti-holomorphic part of the stress tensor. Besides such 'chiral symmetries' the CFT also has an integrable symmetry, that is, infinite families of commuting conserved charges. In this thesis a step towards combining these two symmetries into a single formalism is taken, by identifying integrable stuctures of a CFT through studying the representation category of the underlying chiral algebra. Then by introducing defects in the system, conserved charges can be constructed by perturbing certain conformal defects. Starting from an abelian rigid braided monoidal category C one defines an abelian rigid monoidal category C_F which captures some aspects of perturbed conformal defects in two-dimensional CFT. Namely, for V a rational vertex operator algebra one considers the charge-conjugation CFT constructed from V (the Cardy case). Then C = Rep(V) and an object in C_F corresponds to a conformal defect condition together with a direction of perturbation. To each object in C_F one assigns a perturbed defect operator on the space of states of the CFT and then shows that the assignment factors through the Grothendieck ring of C_F. This allows one to find functional relations between perturbed defect operators. Such relations are interesting because they contain information about the integrable structure of the CFT.

Das erste Thema dieser Dissertation ist der Defekt projektiver Hyperflächen. Es scheint, dass Hyperflächen mit Defekt einen verhältnismäßig großen singulären Ort besitzen. Diese Aussage wird im ersten Kapitel der Dissertation präzisiert und für Hyperflächen mit beliebigen isolierten Singularitäten über einem Körper der Charakteristik null, sowie für gewisse Klassen von Hyperflächen in positiver Charakteristik bewiesen. Darüber hinaus lässt sich die Dichte von Hyperflächen ohne Defekt über einem endlichen Körper abschätzen. Schließlich wird gezeigt, dass eine nicht-faktorielle Hyperfläche der Dimension drei mit isolierten Singularitäten stets Defekt besitzt. Das zweite Kapitel der Dissertation behandelt Bertini-Sätze über endlichen Körpern, aufbauend auf Poonens Formel für die Dichte glatter Hyperflächenschnitte in einer glatten Umgebungsvarietät. Diese wird auf quasiglatte Hyperflächen in simpliziellen torischen Varietäten verallgemeinert. Die Hauptanwendung ist zu zeigen, dass Hyperflächen mit einem in Relation zum Grad großen singulären Ort die Dichte null haben. Weiterhin enthält das Kapitel einen Bertini-Irreduzibilitätssatz, der auf einer Arbeit von Charles und Poonen beruht. Im dritten Kapitel werden ebenfalls Dichten über endlichen Körpern untersucht. Zunächst werden gewisse Faserungen über glatten projektiven Basisvarietäten in einem gewichteten projektiven Raum betrachtet. Das erste Resultat ist ein Bertini-Satz für glatte Faserungen, der Poonens Formel über glatte Hyperflächen impliziert. Der letzte Abschnitt behandelt elliptische Kurven über einem Funktionskörper einer Varietät der Dimension mindestens zwei. Die zuvor entwickelten Techniken ermöglichen es, eine untere Schranke für die Dichte solcher Kurven mit Mordell-Weil-Rang null anzugeben. Dies verbessert ein Ergebnis von Kloosterman.
The first topic of this dissertation is the defect of projective hypersurfaces. It is indicated that hypersurfaces with defect have a rather large singular locus. In the first chapter of this thesis, this will be made precise and proven for hypersurfaces with arbitrary isolated singularities over a field of characteristic zero, and for certain classes of hypersurfaces in positive characteristic. Moreover, over a finite field, an estimate on the density of hypersurfaces without defect is given. Finally, it is shown that a non-factorial threefold hypersurface with isolated singularities always has defect. The second chapter of this dissertation deals with Bertini theorems over finite fields building upon Poonen’s formula for the density of smooth hypersurface sections in a smooth ambient variety. This will be extended to quasismooth hypersurfaces in simplicial toric varieties. The main application is to show that hypersurfaces admitting a large singular locus compared to their degree have density zero. Furthermore, the chapter contains a Bertini irreducibility theorem for simplicial toric varieties generalizing work of Charles and Poonen. The third chapter continues with density questions over finite fields. In the beginning, certain fibrations over smooth projective bases living in a weighted projective space are considered. The first result is a Bertini-type theorem for smooth fibrations, giving back Poonen’s formula on smooth hypersurfaces. The final section deals with elliptic curves over a function field of a variety of dimension at least two. The techniques developed in the first two sections allow to produce a lower bound on the density of such curves with Mordell-Weil rank zero, improving an estimate of Kloosterman.

Dans les alliages multiphasés, la cohérence des interfaces entre des phases en désaccord paramétrique génère des champs élastiques internes à longue distance et généralement anisotropes. L'interaction de ces champs affecte fortement la cinétique des transformations de phase diffusives, et influence la forme et l'arrangement spatial des précipités. Dans la microstructure des superalliages monocristallins à base de nickel, obtenue par précipitation de la phase γ’ ordonnée L12 dans la matrice CFC γ, l'élasticité conduit à la formation d'alignements quasi-périodiques des précipités γ’ cuboïdaux. La microstructure γ/ γ’ possède cependant des défauts systématiques d'alignement des précipités: des branches, des macro-dislocations et des motifs en chevrons. Nous nous intéressons à l'origine de ces défauts d'alignement. Nous conduisons des analyses de stabilité de l'arrangement périodique de précipités en interactions élastiques. Contrairement à la stabilité attendue, les calculs semi-analytiques ont révélé l'instabilité de la distribution périodique de précipités γ’ cubiques, vis-à-vis de certains modes de perturbation. Les principales instabilités sont le mode longitudinal [100] et le mode transverse [110], et leur domaine d'instabilité est analysé vis-à-vis de l'anisotropie élastique. Le développement de ces modes instables est étudié par une méthode de champ de phase classique, en simulant l'évolution de microstructures périodiques soumises à des légères perturbations initiales. Nous montrons que l'expression des instabilités d'arrangement procède essentiellement par l'évolution de la forme des précipités, et conduit à la formation de motifs qui ont pu être reliés à des microstructures expérimentales. En particulier, le mode transverse [110] conduit à la formation de motifs en chevrons. Nous étudions l'influence du taux de phase γ’ et de l'inhomogénéité du module élastique C’, et nous montrons le rôle qu'ils jouent dans la stabilisation de l'arrangement périodique. Dans des simulations réalisées dans des études antérieures, la dynamique des défauts est analysée au moyen de paramètres topologiques issus de la phénoménologie des structures hors-équilibre. Au cours d'un recuit isotherme, nous observons que les branches et les macro-dislocations migrent dans la microstructure selon des mécanismes de montée et de glissement. Nous utilisons ensuite une nouvelle formulation des modèles de champ de phase, intrinsèquement discrète, dans laquelle les interfaces sont résolues essentiellement avec un pas de grille sans friction de réseau et avec une invariance par rotation précise. Cette approche, appelée Sharp Phase Field Method (S-PFM), est implémentée sur une grille CFC, et avec une description des quatre variants de translation des précipités γ’. Nous montrons que la S-PFM permet la modélisation de microstructures à grande échelle, avec plusieurs milliers de précipités à deux et trois dimensions, et donne ainsi accès à des informations statistiques sur l'évolution de la microstructure et sur la dynamique des défauts d'alignement. Nous discutons finalement la perspective de modéliser l'évolution de la microstructure γ/γ’ à une échelle supérieure par une description de la dynamique des défauts d'alignement des précipités
In multiphase alloys, internal elastic fields often arise as a result of a coherently adjusted misfit between the lattices of coexisting phases. Given their long-range and usually anisotropic nature, the interaction of these fields is known to significantly alter the kinetics of diffusion-controlled phase transformations, as well as influence the shapes and spatial arrangement of the misfitting precipitates. In the microstructure of single-crystal nickel-base superalloys, obtained by precipitation of the L12-ordered γ’ phase in the FCC γ matrix, elasticity leads to the formation of nearly periodic alignments of the cuboidal γ’ precipitates. However, the γ/γ’ microstructure systematically displays defects in the precipitate alignment: branches, macro-dislocations and chevron patterns. We first address the question of the origin of these alignment defects. Stability analyses of the periodic arrangement of elastically interacting precipitates are carried out. Contrary to the expected stability, the semi-analytical calculations revealed the periodic distribution of cubic γ‘ precipitates to be unstable against specific perturbation modes. The main instabilities are the [100] longitudinal mode and the [110] transverse mode, and their instability range is analyzed with respect to the elastic anisotropy. The consequences of these unstable modes are investigated using a classic phase field method, by modeling the evolution of periodic microstructures undergoing small initial perturbations. We show the expression of the instabilities mainly proceeds by the evolution of the precipitate shapes, and leads to the formation of patterns which were related to experimental microstructures. Specifically, the [110] transverse instability is responsible for the formation of chevron patterns. The effects of the volume fraction and of an inhomogeneity on the C’ shear modulus on the stability of the arrangement are studied, and we show the role they play in the partial stabilization of the periodic distribution, though the [100] longitudinal mode always remains unstable. In phase field calculations carried out in previous studies, the dynamics of alignment defects are analyzed by means of topological parameters derived from pattern formation theory. During annealing, branches and macro-dislocations were observed to migrate in the microstructure according to climbing and gliding mechanisms. We then use a new formulation of phase field models, intrinsically discrete, in which the interfaces are resolved with essentially one grid point with no pinning on the grid and an accurate rotational invariance. This approach, known as the Sharp Phase Field Method (S-PFM), is implemented on a FCC grid and accounts for the four translational variants of the γ’ precipitates. We show that the S-PFM allows for the modeling of large-scale microstructures, with several thousand precipitates both in two and three dimensions, and provides access to statistical information on the microstructure evolution and on the the dynamics of alignment defects. We finally discuss the perspective of modeling the evolution of the γ/γ’ microstructure at the macroscale by means of a description of the defect dynamics in the precipitate alignments

Point defects control many properties of technological importance in intermetallic compounds such as atomic diffusion, creep, hardness, mechanical properties and sintering. Farther, since intermetallic compounds are characterized by long range atomic order, the point defects in these compounds can be qualitatively different from those in pure metals and disordered alloys. In the present study, we have chosen β-NiAl for our point defect studies since it is a potential candidate for high temperature applications and a model system for the study of basic phenomena in ordered alloys. We have used a mean field formulation for studying point defect concentrations. The outline of the formulation is as follows: We divide the rigid, body centred cubic lattice into two interpenetrating cubic sublattices called α and j3 which are made up of the cube corners and body centres respectively. We write a generic free energy function (G) that involves the temperature T and the six sublattice occupancies viz., the A (Ni), B (Al) and vacancies (V) on the two sublattices α andβ. We use the constraints on the number of α and β sublattice sites viz., the number of α sublattice sites is equal to the number of β sublattice sites, to write G as a function of four of the six sublattice occupancies and T. We define three auxiliary parameters η1, η2 and η3 which correspond to the vacancy concentration, the differential B species population on the two sublatices (the chemical or atomic order), and the differential vacancy population on the two sublattices, respectively. We then rewrite G as a function of T, xB and ηi. The G can now be minimized with respect to the three auxiliary variables so that we recover the free energy (G) as a function of XB and T only. The formulation requires as inputs the Ni-Ni, Al-Al, Ni-Al, Ni-V and Al-V interaction energies in the nn and nnn shells. We have obtained the Ni-Ni, Al-Al and Ni-Al interaction energies from the effective pair potentials reported in the literature. For the Ni-V and Al-V interaction energies we have used a bond breaking model in which we have assumed that the Ni-V and Al-V interaction energies in the nnn shell to be zero. Using the above interaction parameters in our mean field formulation we have determined the concentrations of various types of point defects in β-NiAL We have specifically chosen the temperature range of 800 - 2000 K and the composition range of 45 - 55 atomic% Al. Our results can be summarised as follows: 1.The predominant defect in the stoichiometric alloy is a combination of an Ni-antisite defect and two vacancies on the Ni sublattice. 2.The Al-rich alloys of composition (50 + ∆) atomic% contain 2∆% vacancies;since the alloys are almost perfectly ordered, these vacancies predominantly occupy the Ni sublattice. Similarly, the Ni-rich alloys of composition (50 — ∆)atomic% contain ∆% Ni antisites. 3.Both the vacancies on the Ni sublattice (in Al-rich alloys) and Ni-antisites (in Ni-rich alloys) show negligible temperature dependence, and hence owe their origin to the off-stoichiometry. 4.In all the alloys, the Al-antisites have the lowest concentration (of the order 10-6 even at 2000 K) and the concentration of the vacancies on the β sublattice is the next lowest. Thus, our results support the view that β-NiAl is a triple defect B2 and, if we consider constitutional vacancies as those which have a little or no temperature dependence, there exist constitutional vacancies in Al-rich β-NiAl. This conclusion is in agreement with some of the experimental results. However, it must be pointed out that there is considerable disagreement among experimental results from different groups.

In this thesis, we examine the construction and characteristics of generalised reflection matrices, within the a_1^(1), a_2^(1) and a_2^(2) integrable affine Toda field theories. In doing so, we generalise the existing finite-dimensional reflection matrices because our construction involves the dressing of an integrable boundary with a defect. Within this framework, an integrable defect's ability to store an unlimited amount of topological charge is exploited, therefore all generalised solutions are intrinsically infinite-dimensional and exhibit interesting features. Overall, further evidence of the rich interplay between integrable defects and boundaries is provided. It is hoped that the generalised solutions presented in this thesis are potential quantum analogues of more general classical integrable boundary conditions.

In the first part of this thesis algebro-geometric solutions for the sine-Gordon and KdV equations in the presence of a type I integrable defect are found, generalising the previously known soliton solutions. Elliptic (genus one) solutions where the defect induces only a phase shift are obtained via ansätze for the fields on each side of the defect. Algebro-geometric solutions for arbitrary genus and involving soliton emission by the defect are constructed using a Darboux transformation, exploiting the fact that the defect equations have the form of a Bäcklund transformation at a point. All the soliton and phase-shifted elliptic solutions to the defect equations are recovered as limits of the algebro-geometric solutions constructed in this way. Certain energy and momentum conserving defects for the Kadomtsev-Petviashvili equation are then presented as a first step towards the construction of integrable defects in higher dimensions. Algebro-geometric solutions to the sine-Gordon equation on the half-line with an integrable two parameter boundary condition are obtained by imposing a corresponding restriction on the Lax pair eigenfunction or, alternatively, as a Darboux transformation of the known algebro-geometric solution for the Dirichlet boundary. Finally, the collision of sine-Gordon solitons with a Robin type boundary is examined. This boundary is typically non-integrable but becomes an integrable Neumann or Dirichlet boundary for certain values of a boundary parameter. Depending on the boundary parameter and initial velocity an antikink may be reflected into various combinations of kinks, antikinks and breathers. The soliton content of the field after the collision is numerically determined by computing the discrete scattering data associated with the inverse scattering method. A highlight of this investigation is the discovery of an intricate structure of resonance windows caused by the production of a breather which can collide multiple times with the boundary before escaping as a lighter breather or antikink.

We are coming to realize that there is an urgent need to reduce energy usage in buildings and it has to be done in a sustainable way. This thesis focuses on the performance of the building envelope; more precisely thermal performance of walls and super insulation material in the form of vacuum insulation. However, the building envelope is just one part of the whole building system, and super insulators have one major flaw: they are easily adversely affected by other problems in the built environment.  Vacuum Insulation Panels are one fresh addition to the arsenal of insulation materials available to the building industry. They are composite material with a core and an enclosure which, as a composite, can reach thermal conductivities as low as 0.004 W/(mK). However, the exceptional performance relies on the barrier material preventing gas permeation, maintaining a near vacuum into the core and a minimized thermal bridge effect from the wrapping of barrier material round the edge of a panel. A serpentine edge is proposed to decrease the heat loss at the edge. Modeling and testing shows a reduction of 60% if a reasonable serpentine edge is used. A diffusion model of permeation through multilayered barrier films with metallization coatings was developed to predict ultimate service life. The model combines numerical calculations with analytical field theory allowing for more precise determination than current models. The results using the proposed model indicate that it is possible to manufacture panels with lifetimes exceeding 50 years with existing manufacturing. Switching from the component scale to the building scale; an approach of integrated testing and modeling is proposed. Four wall types have been tested in a large range of environments with the aim to assess the hygrothermal nature and significance of thermal bridges and air leakages. The test procedure was also examined as a means for a more representative performance indicator than R-value (in USA). The procedure incorporates specific steps exposing the wall to different climate conditions, ranging from cold and dry to hot and humid, with and without a pressure gradient. This study showed that air infiltration alone might decrease the thermal resistance of a residential wall by 15%, more for industrial walls. Results from the research underpin a discussion concerning the importance of a holistic approach to building design if we are to meet the challenge of energy savings and sustainability. Thermal insulation efficiency is a main concept used throughout, and since it measures utilization it is a partial measure of sustainability. It is therefore proposed as a necessary design parameter in addition to a performance indicator when designing building envelopes. The thermal insulation efficiency ranges from below 50% for a wood stud wall poorly designed with incorporated VIP, while an optimized design with VIP placed in an uninterrupted external layer shows an efficiency of 99%, almost perfect. Thermal insulation efficiency reflects the measured wall performance full scale test, thus indicating efficiency under varied environmental loads: heat, moisture and pressure. The building design must be as a system, integrating all the subsystems together to function in concert. New design methodologies must be created along with new, more reliable and comprehensive measuring, testing and integrating procedures. New super insulators are capable of reducing energy usage below zero energy in buildings. It would be a shame to waste them by not taking care of the rest of the system. This thesis details the steps that went into this study and shows how this can be done.
QC 20120228

Vigabatrin, a GABA (γ-aminobutyric acid) agonist is a drug widely prescribed in Europe and Asia between 1989 and 1997 for drug resistant, partial epilepsy and has been associated with visual field defects. Uncertainity in the effect of Vigabatrin on vision resulted in decreased prescriptions. However, there has been poor reproducibility in previous studies due to many factors, especially poor sensitivity and specificity of tests for Vigabatrin associated visual dysfunction. The wide field multifocal electroretinogram (WF-mfERG) can objectively measure discrete areas of retinal function up to 90 degrees. The results of 204 patients with epilepsy divided into four groups are presented. A subgroup of 89 patients had repeat investigations. The patients were divided into four groups. Group 1.The Vigabatrin group comprised patients who had been taking Vigabatrin for at least 1 year (56 patients). Group 2. Forty nine patients who had previously taken Vigabatrin for at least 1 year but had stopped taking this treatment for at least 2 years comprised the ex-Vigabatrin group. Group 3.The GABA group had 46 patients who used other anti-epileptic drugs (AED) with GABA action other than Vigabatrin. Group 4. Fifty three patients who had never used an AED with GABA action including Vigabatrin made up the non-GABA group. Surprisingly, the percentage of patients with visual field defects were high in all groups investigated (Vigabatrin group 59%, ex-Vigabatrin group 46%, GABA group 30.2% and non-GABA group 21.2%). However, abnormal bilateral WF-mfERG responses were only found in the Vigabatrin group (48%) and the ex-Vigabatrin group (22%). The study suggests that there are probably different causes of visual field abnormalities in patients with epilepsy not related to Vigabatrin. We propose that the most sensitive and specific tests that can be used to detect visual dysfunction associated with Vigabatrin is the WF-mfERG

Glaucoma is a progressive disease of the optic nerve that can result in irreversible loss of visual function and impairment in everyday visual tasks. The experimental studies described in this thesis primarily aim to investigate the performance of people with glaucoma on search and other visual tasks whilst simultaneously monitoring eye movements, making comparison with age-related visually healthy people. In an experiment focussing on visual search, a patient group (n=30) took significantly longer on average to find a target in images of everyday scenes than controls (n=30). Furthermore, comparison of eye movements made by the participants during this task revealed there was a statistically significant reduction (6%) in saccade rate in the patients compared to the controls, and that saccade rate correlated with performance. Similar differences in eye movements were observed when the same groups passively viewed a selection of images in a slideshow. A bivariate contour ellipse (BCE) analysis revealed that, on average, patients viewed smaller regions of the images compared to the controls. Eye movement differences between patients and controls were also examined in a different cohort of people with glaucoma (n=14) and visually healthy controls (n=22) whilst they watched a selection of Hazard Perception Test driving films. Saccade rate of the patients was found to increase by 9%, though results from the BCE analysis suggested the average size of viewing area was similar in both groups. Finally, a novel interview-based study of 50 people with glaucoma provides evidence that patients do not perceive their visual field defect as a black ‘tunnel’ effect, or as ‘black patches’, but more like blurred regions: this finding may, for example, impact on how glaucomatous visual field loss is depicted in patient information about the condition. In conclusion, the results from this thesis show how visual loss from glaucoma influences how patients perceive and react to their visual environment. The principal findings from the studies described in this thesis also show, for the first time, that eye movement analysis could provide a window into the functional deficits associated with glaucoma.

The theory and computation of line defects are discussed in the context of both solids and liquid crystals. This dissertation includes four parts. The Generalized Disclination theory is discussed and applied to numerous interfacial and bulk line defect problems. An augmented Oseen-Frank energy as well as a novel 2D-model is proposed and demonstrated for disclination dynamics in liquid crystal. A model based on kinematics and thermodynamics is devised to predict tactoid dynamics during the process of the isotropic-nematic phase transition in LCLC. In the first part of the thesis, the utility of the notion of generalized disclinations in materials science is discussed within the physical context of modeling interfacial and bulk line defects. The Burgers vector of a disclination dipole in linear elasticity is derived, clearly demonstrating the equivalence of its stress field to that of an edge dislocation. An explicit formula for the displacement jump of a single localized composite defect line in terms of given g.disclination and dislocation strengths is deduced based on the Weingarten theorem for g.disclination theory at finite deformation. The Burgers vector of a g.disclination dipole at finite deformation is also derived. In the second part, a numerical method is developed to solve for the stress and distortion fields of g.disclination systems. Problems of small and finite deformation theory are considered. The fields of various line defects and grain/phase boundary problems are approximated. It is demonstrated that while the far-field topological identity of a dislocation of appropriate strength and a disclinationdipole plus a slip dislocation comprising a disconnection are the same, the latter microstructure is energetically favorable. This underscores the complementary importance of all of topology, geometry, and energetics (plus kinetics) in understanding defect mechanics. It is established that finite element approximations of fields of interfacial and bulk line defects can be achieved in a systematic and routine manner, thus contributing to the study of intricate defect microstructures in the scientific understanding and predictive design of materials. In the third part, nonsingular disclination dynamics in a uniaxial nematic liquid crystal is modeled within a mathematical framework where the kinematics is a direct extension of the classical way of identifying these line defects with singularities of a unit vector field representing the nematic director. We devise a natural augmentation of the Oseen-Frank energy to account for physical situations where infinite director gradients have zero associated energy cost, as would be necessary for modeling half-integer strength disclinations within the framework of the director theory. A novel 2D-model of disclination dynamics in nematics is proposed, which is based on the extended Oseen-Frank energy and takes into account thermodynamics and the kinematics of conservation of defect topological charge. We validate this model through computations of disclination equilibria, annihilation, repulsion, and splitting. In the fourth part, the isotropic-nematic phase transition in chromonic liquid crystals is studied. We simulate such tactoid equilibria and dynamics with a model using degree of order, a variable length director as state descriptors, and an interfacial descriptor. We introduce an augmented Oseen-Frank energy, with non-convexity in both interfacial energy and the dependence of the energy on the degree of order. A strategy is devised based on continuum kinematics and thermodynamics. The model is used to predict tactoid dynamics during the process of phase transition. We reproduce observed behaviors in experiments and perform an experimentally testable parametric study of the effect of bulk elastic and tactoid interfacial energy constants on the interaction of interfacial and bulk fields in the tactoids.

This thesis will focus on the residual function and visual and attentional deficits in human patients, which accompany damage to the visual cortex or its thalamic afferents, and plastic changes, which follow it. In particular, I will focus on homonymous visual field defects, which comprise a broad set of central disorders of vision. I will present experimental evidence that when the primary visual pathway is completely damaged, the only signal that can be implicitly processed via subcortical visual networks is fear. I will also present data showing that in a patient with relative deafferentation of visual cortex, changes in the spatial tuning and response gain of the contralesional and ipsilesional cortex are observed, which are accompanied by changes in functional connectivity with regions belonging to the dorsal attentional network and the default mode network. I will also discuss how cortical plasticity might be harnessed to improve recovery through novel treatments. Moreover, I will show how treatment interventions aimed at recruiting spared subcortical pathway supporting multisensory orienting can drive network level change.

Several approaches have been developed to help patients with partial visual field defects to cope with their visual loss, and the most effective are those that encourage the person to move their eyes more efficiently. This thesis sought to examine the efficacy of a multiplatform compensatory training called Durham Reading and Exploration (DREX) in the rehabilitation of these individuals. Overall, the thesis focuses on two primary aims which include establishing whether the DREX training app completed on either a computer or a touchscreen tablet can be an effective treatment for homonymous visual field defects (HVFDs) caused by brain injury, as well as validating the assessment tasks that have been incorporated into the app. The results from Studies 1 to 3 show that DREX training is clinically effective for HVFD rehabilitation, and the training effect in patients trained using a touchscreen tablet is equivalent to patients trained with a computer, with a meaningful improvement in the quality of life which remains stable over a period of three months. In Studies 4 to 6, the built-in assessments tasks are found to be reliable and valid and can be used confidently to monitor the training progression and outcomes. Study 7 explores the novel observation that DREX training is also beneficial for patients with other types of partial visual field defects like tunnel vision and central visual field loss, demonstrating that this training could potentially be offered to a wider low vision population. Finally, studies 8 and 9 explore whether the blurring of vision, a common comorbid visual impairment in patients with visual field defect, could affect the visual exploration performance and the outcomes of visual exploration training. From these results it is clear that blurring of vision did reduce the search efficacy, but searching behaviour can still be improved with the training. Taken together, the findings from this suite of studies indicate that DREX is an effective and inexpensive treatment for visual field defects in a variety of etiologies, however the comorbid impairments that could affect the rehabilitation should be identified to maximise efficacy of this treatment.

Rehabilitation for patients with homonymous visual field defects (HVFDs) is important for helping to improve their quality of life. Various therapies have been developed, most notably vision restoration training (VRT), optical aids and compensatory training. Studies utilising modem optical aids have reported promising results but the extent to which these aids can reliably reduce the patients' visual disability has yet to be confirmed. Restorative approaches are the most ambitious and controversial, aiming to restore vision to portions of the lost visual field. Whilst early studies suggested that VRT could reduce the visual field defect. recent studies using more reliable methods to monitor the patients' fixation coulc not confirm this effect.

The integration of defence companies in Europe and the U.S. has in the defence market’s environment for a long time received considerable interest. Companies see business opportunities and attractive technology on the other side of the Atlantic Ocean. Governments advocate in a public discourse that transatlantic defence industry integration is highly desirable and that it would benefit all concerned. This supportive discourse is compared to the action; the corporate integration that has occurred. The aim of the thesis is to understand and explain the level and nature of the transatlantic defence industry integration and its driving forces and inhibitors. A combination of three focal theoretical concepts has been used: integration, discourse and organizational field. The thesis shows that there is a marked discrepancy between the discourse for and the actual extent of transatlantic defence industry integration. This discrepancy and the nature of the corporate integration is analyzed and explained through the combination of discourse and integration within an organizational field. The thesis shows that defence companies’ in transatlantic acquisitions achieve very limited influence over the acquired company’s strategy and operations, and that synergies and rationalization are strongly disencouraged by governments. The processual integration within trans-national groups and in transatlantic defence materiel collaboration is highly restricted by governments. The thesis also shows that the defence innovation largely is separated between the U.S. and Europe. The defence market is an example of a political market showing a very different corporate rationality compared to ideal models of corporate rationality as the SCP paradigm. The findings suggest that defence companies’ strategy and integration appear non-rational in isolation, but become rational when understood through the lens of the defence market seen as an organizational field – a perspective that emphasizes the influence of the government field. If you want to understand, analyze or engage in transatlantic defence industry integration, you should benefit from this study. It should be of interest to researchers who study the defence industry, defence procurement, political markets, organizational fields, regulatory governance and corporate integration. It should be of interest to policymakers and others engaged in the discourse that concerns reforms of political markets in general, and of the defence market in particular. Martin Lundmark is a researcher at the Center for Marketing, Distribution and Industry Dynamics at the Stockholm School of Economics. His research focuses on the defence market, defence procurement, Europeanization and the transformation within political markets. Martin also works as defence market and defence procurement analyst and deputy research director at the Swedish Defence Research Agency (FOI).
Diss. Stockholm : Handelshögskolan i Stockholm, 2011

This thesis addresses the behaviour of artificial magnetic square spin ice patterns in response to applied magnetic fields and thermal activation. Two main points of focus are the access of well-defined statistical states and the properties of fractionalised “monopole” charge defects. Experimental investigations are conducted using magnetic force microscopy of athermal remanent states. Magnetic reversal of a square ice subject to magnetic fields applied slightly off a diagonal symmetry axis is found to mediate via incremental sublattice-independent processes. Dipolar correlations manifest as charge defect propagation and ordering, along and between adjacent flipped moment chains respectively. Quenched disorder, while allowing for bulk defect nucleation, is responsible for strongly suppressing correlations. A constant magnitude rotating field protocol is investigated. The acquisition of strong ground state ordering via highly correlated edgenucleated reversal processes, as recently predicted, is not found, attributable to the enhancement of bulk processes by quenched disorder. An optimally tuned field allows for efficient demagnetisation towards the ground state. A study of as-fabricated states is presented, magnetically self-ordered following formation of magnetic elements via evaporative vacuum deposition. Compelling evidence is presented, in a case study of a sample closely approaching the ground state, for superparamagnetism during early deposition stages which is subsequently arrested. Large ground state domains are observed sustaining Boltzmann factor weighted monopole excitations. Evidence is present for monopole interactions playing a role in thermal ordering, as excitations explore a dipolar energy band structure. Further, order is found to increase with interaction strength, and preliminary results suggest that quenched disorder acts to suppress it. Statistical mechanical calculations show that states achieved correspond closely to arrested thermal equilibrium. Consideration of an effective thermodynamic model presented for ac field demagnetised states is given. Comparison allows for discussion of the general role of quenched disorder and the effective temperature of a “frozen” state.

Even though silicon technology is dominant today, the physics (quantum electron tunneling effect), design (power dissipation, wire delays) and the manufacturing (lithography resolution) limitations of CMOS technology are pushed towards the scaling end. These issues motivated us towards a new paradigm that contributes to a continued advancement in terms of performance, density, and cost. The magnetic field coupled computing (MFC) paradigm, which is one of the regimes where we leverage and utilize the neighbor interaction of the nanomagnets to order the single-domain magnetic cells to perform computational tasks. The most important and attractive features of this technology are: 1) room temperature operation, which has been a limitation in electrostatic field coupled devices, 2) high density and nonetheless 3) low static power dissipation. It will be intriguing to address queries like, what are the challenges posed by the technology with such exotic features? Answer to such questions would become the focus of this doctoral research. The fundamental problem with magnetic field coupled devices is the directional flow of information from input to output. In this work, we have proposed a novel spatially moving Landauer clock system for MFC nanomagnet array which has an advantage over existing adiabatic clock system. Extensive simulation studies were done to model and validate the clock for different length, size, and shape of nanomagnet array. Another key challenge is the manufacturing defect, which leads to uncertainty and unreliability issues. We studied the different dominant types of geometric defects (missing material, missing cell, spacing, bulge, and merging) in array (used as interconnects) based on our fabrication experiments. We also studied effect of these defects on different segments (locations) of the array with spatially moving clock. The study concluded that a spatially moving clock scheme constitutes a robust MFC architecture as location of defect and length of arrays does not play any role in error masking as opposed to conventional clock. Finally, the work presents the study on the 2D nanomagnet array for boolean logic computation and vision logic computation. The effect of dipole-dipole interaction on magnetization state transition in closely spaced 2D array of ferromagnetic circular nanomagnet was explored. The detailed design space to demarcate the boundary between single domain state and vortex state reveals that the single domain state space is desirable for Boolean logic computation while the space around the boundary would be appropriate for vision logic computing.

Electrically detected magnetic resonance (EDMR) is a sensitive spectroscopic technique, which can be used to readout few to single electron spins in semiconductor and carbon nanodevices for applications in solid state quantum information processing (QIP). Since only electrically active defects contribute to the EDMR signal, this technique can be used further to investigate defects and impurities in photovoltaic devices, in which they limit the sunlight-to-energy conversion efficiency significantly. Here, I employ X-band EDMR for semiconductor defect analysis and identify the most important recombination centres in Czochralski silicon with oxide precipitates, which can be intentionally grown to confine detrimental metallic impurities to inactive regions of the wafer in order to serve as a defect-free substrate for modern silicon photovoltaic devices. Those experiments show that oxide precipitation is accompanied by the formation of silicon dangling bonds. Furthermore, I describe a very promising route towards the fabrication and readout of few to single electron spins in carbon nanotube devices, which can be characterised structurally via transmission electron microscopy in order to relate their electrical and spin properties with their structure. Finally, I employ EDMR to read out electron spin states in donor-doped silicon field-effect transistors as a prerequisite for their application in QIP. I report on a novel cryogenic probe head for EDMR experiments in resonant microwave cavities operating at 0.35 T (9.7 GHz, X-band) and 3.34 T (94 GHz, W-band). This approach overcomes the inherent limitations of conventional X-band EDMR and permits the investigation of paramagnetic states with a higher spectroscopic resolution and signal intensity. Both advantages are demonstrated and discussed. I further report on a novel mechanism giving rise to the EDMR effect in donor-doped silicon field-effect transistors, which is capable of explaining why the EDMR signal intensities of the conduction electrons are enhanced by a factor of ∼100, while the donor resonance signals increase by a factor of ∼20 from X- to W-band only. The spin-relaxation and dephasing times are extracted from a series of pulsed-EDMR measurements and confirm this model. The author gratefully acknowledges funding from Trinity College Oxford, Department of Materials, EPSRC DTA, and Konrad-Adenauer-Stiftung e.V. (Begabtenförderung).

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Stress migration of point and open-volume defects in materials is an important problem in a wide variety of applications, such as degradation of metallic interconnects in semiconductor devices, metal fatigue, and radiation damage profiles in ion implantation and surface modification. From a fundamental research view point, this study aims to contribute to a better understanding of the basic processes underlying the effect of stress assisted diffusion of foreign interstitial atoms under stress fields, using the Rutherford backscattering to obtain depth profiles, and synchroton radiation diffraction for the determination of stress fields. This has been achieved by creating a well designed model system of krypton implanted polycrystalline titanium.

The prevalence of concrete and cement-based materials in the civil infrastructure plus the risk of failure makes structural health monitoring an important issue in the understanding of the complete life cycle of civil structures. Correspondingly, the field of nondestructive evaluation (NDE) has been maturing and now concentrates on the detection of flaws and defects, as well as material damage in early stages of degradation. This defect detection is typically usually done by looking at the impulse response of the medium in question such as a cement-based material. The impulse response of a solid can be used to image a complex medium. Classically, the waveform is obtained by an active setup: an ultrasonic signal is generated at one location and recorded at another location. The waveform obtained from imaging can be used to quantitatively characterize the medium, for example by calculating the material's diffusivity coefficient or dissipation rate. In recent years, a different monitoring technique has been developed in seismology to measure the velocity of different kinds of waves, the Coda Wave Interferometry (CWI). In this CWI technique, the main focus is given to the late part of the recorded waveform, the coda. CWI is now successfully used in seismology and acoustics. In the current research, CWI is applied on concrete in different damage states to develop basic knowledge of the behavior of the wave velocity, and how it can be used to characterize cement-based materials. By comparing two impulse responses, the relative velocity change between the two impulse responses is used to characterize damage. Because of the stress-dependency of the velocity change, the calculations can also be used to directly calculate the Murnaghan's and Lam´e's coefficients. The newer technique of CWI is applied - the Stretching Technique (ST) [27]. The first goal of this research is to establish the viability of using CWI in cement-based materials. Next, we use the ST in the application of stress as we compress concrete samples for the detection of thermal damage, ASR-damage and mechanical softening.