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This work addresses the growth of ultrathin magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) films and their thorough structural, electronic, and magnetic characterization. In a first step, ultrathin Fe3O4 films are grown on SrTiO3(001) substrates by reactive molecular beam epitaxy (RMBE) and the substrate-induced anomalous strain behavior of the films is investigated by complementary high-resolution transmission electron microscopy (HRTEM) and (grazing incidence) X-ray diffraction [(GI)XRD] measurements. Next, an additional CoO film is deposited on similar Fe3O4/SrTiO3(001) heterostructures to demonstrate an alternative route for the synthesis of cobalt ferrite films through the thermally mediated interdiffusion of both oxide films. The evolution from the initial bilayer stacks to completely reacted cobalt ferrite films is extensively monitored by soft and hard X-ray photoelectron spectroscopy (soft XPS and HAXPES) and (GI)XRD. Complete intermixing and formation of single cobalt ferrite films is confirmed by angular-resolved HAXPES (AR-HAXPES) and X-ray reflectivity (XRR). The study of the cationic distribution resulting from this novel synthesis technique and its effects on the magnetic properties of the cobalt ferrite films is the subject of the subsequent part. Here, X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry serve as key investigation techniques, which are further complemented by AR-HAXPES and atomic force microscopy (AFM) measurements. In a final step, highly crystalline cobalt ferrite films with different cationic stoichiometries are grown on MgO substrates using RMBE while their growth behavior is captured in real-time using operando XRD. Further structural characterization of the films is carried out by low-energy electron diffraction and XRR, whereas HAXPES and SQUID provide fundamental information on the electronic, chemical, and magnetic properties of the films.

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With reference to some figures reproduced in this thesis: "Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society." / We report on the growth and characterization of strontium ruthenate (214) (Sr2RuO4) and strontium rhodate (214) (Sr2RhO4) in efforts to test their agreement with Landau-Fermi liquid theory using optical measurements. We begin by reviewing the theory of Landau-Fermi liquids and the frequency and temperature dependent conductivities. We review existing work on both Sr2RuO4 and Sr2RhO4 including evidence of agreement with Landau-Fermi liquid theory. We also describe optical floating zone crystal growth and the exact procedures we used to prepare samples of both Sr2RuO4 and Sr2RhO4 via optical floating zone. The resulting Sr2RuO4 crystals were characterized using AC susceptibility measurements and Sr2RhO4 by powder diffraction, single crystal diffraction, and SQUID magnetization measurements. Finally, early optical reflectivity measurements at low temperatures are presented. / Thesis / Master of Science (MSc) / Crystals of Sr2RuO4 and Sr2Rho4 were grown by the author in an effort to study changes of their resistivity with varying temperature and frequency at low temperatures. The crystals were characterized using a variety of x-ray and other techniques, so as to measure their purity. Past work on these materials is discussed and analyzed. Preliminary measurements of the resistivity are presented.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Assessing the quality of fruit has become vitally important for farmers and growers. With retailers placing ever stricter requirements on fresh produce, growers have to spend a greater amount of time and effort sorting and grading their harvest. Increasingly, vendors are placing requirements not only on external factors like colour, and firmness, but on internal quality factors such as sugar content and acidity, because, although consumers buy fruit based on their external appearances, the taste of the fruit is what determines whether the consumer will buy again. Different techniques exist that probe the internal quality of fruit non-destructively. The technique most widely used today is Near Infrared Spectroscopy. This technique is powerful, but has certain limitations such as poor reliability and the need for constant recalibration. This thesis suggests an alternative method for evaluating internal fruit quality based on low-field nuclear magnetic resonance detected by superconducting quantum interference devices. It introduces the theory of SQUIDs and NMR, and evaluates the use of SQUID detected NMR spectroscopy as a method for determining the internal quality of fruit. The fabrication techniques and processes are explained in detail and a design for a SQUID detected NMR spectrometer is given. Relevant simulations and simulation results are also given. No working SQUID could be fabricated and, as such, no working NMR spectrometer was demonstrated. This thesis serves as a reference work for future research. / AFRIKAANSE OPSOMMING: Bepaling van die gehalte van vrugte het vir boere uiters belangrik geword. Met kleinhandelaars wat al strenger vereistes plaas op vars produkte moet boere meer tyd en inspanning bestee met die sortering en gradering van hul oes. Handelaars plaas nie net vereistes op eksterne kwaliteitsfaktore soos kleur en fermheid nie, maar begin al hoe strenger vereistes plaas op interne kwaliteitsfaktore soos suikerinhoud en suurgehalte, want, hoewel verbruikers vrugte koop op grond van hul eksterne kwaliteitsfaktore, is dit die smaak van die vrug wat bepaal of die verbruiker weer die vrug sal koop. Verskillende tegnieke bestaan wat die interne kwaliteit van vrugte op ’n nie-destruktiewe manier kan bepaal. Die mees algemene tegniek is Naby Infrarooi Spektroskopie. Hierdie tegniek is kragtig maar het sekere beperkings soos swak betroubaarheid en die noodsaaklikheid van konstante herkalibrasie. Hierdie tesis stel ’n alternatiewe metode vir die evaluering van interne vrugkwaliteit gebaseer op lae-veld kernmagnetiese resonans waargeneem deur supergeleidende kwantum inmenging toestelle voor. Dit stel die teorie van SKWITs en KMR bekend, en evalueer die gebruik van SKWIT-bespeurde KMR spektroskopie as ’n metode vir die bepaling van die interne kwaliteit van vrugte. Die fabrikasie tegnieke en prosesse word in detail verduidelik en ’n ontwerp vir ’n SWKIT opgevangde KMR spektrometer word gegee. Toepaslike simulasies en simulasie resultate word ook gegee. Geen werkende SKWIT kon vervaardig word nie en as gevolg daarvan kon geen werkende KMR spektrometer gedemonstreer word nie. Hierdie tesis dien as ’n naslaan werk vir toekomstige navorsing.

As principais propriedades físico-químicas da quitosana dependem da massa molar média, grau médio de acetilação (<span style=\"text-decoration: overline\">GA) e do parâmetro de acetilação (PA) que expressa o padrão de distribuição das unidades 2-acetamido-2-desoxi-D-glucopiranose (GlcNAc) e 2-amino-2-desoxi-D-glucopiranose ( GlcN) ao longo de suas cadeias. A distribuição alternada, randômica ou em blocos das unidades GlcN e GlcNAc ao longo das cadeias poliméricas está diretamente relacionada com as condições de preparação da quitosana, sendo que as reações executadas em condições homogêneas geram quitosanas em cujas cadeias há o predomínio da distribuição randômica, enquanto que nas quitosanas produzidas em condições heterogêneas a distribuição em blocos predomina. Neste trabalho &beta;-quitina extraída de gládios de lulas (Loligo sp) foi submetida a 3 etapas consecutivas do processo de desacetilação assistida por irradiação de ultrassom de alta intensidade (processo DAIUS), resultando em quitosana extensivamente desacetilada (<span style=\"text-decoration: overline\">GA &asymp; 2%) e de elevada massa molar média viscosimétrica (<span style=\"text-decoration: overline\">Mv &asymp; 354000 g/mol) comparada a quitosanas obtidas por outros métodos. Essa amostra, denominada amostra QSo, foi dissolvida em ácido acético aquoso e então submetida à reação de N-acetilação por 24 h à temperatura ambiente. A ocorrência de O-acetilação foi evitada pela adição de 1,2-propanodiol ao meio reacional e a variação da razão molar anidrido acético/grupos amino permitiu a obtenção de cinco amostras de quitosanas N-acetiladas, as quais foram caracterizadas por espectroscopia de RMN 1H, espectroscopia na região do infravermelho, difração de raios X, viscosimetria capilar, microscopia eletrônica de varredura e análise termogravimétrica. O parâmetro de acetilação (PA) das quitosanas N-acetiladas foi determinado a partir dos espectros de RMN 1H de modo a permitir a avaliação do tipo de distribuição de unidades 2-acetamido-2-desoxi-D-glucopiranose (GlcNAc) e 2-amino-2-desoxi-D-glucopiranose (GlcN) predominante nos produtos. As reações de N-acetilação foram executadas em duplicata gerando as amostras dos conjuntos 1 e 2, as quais apresentaram <span style=\"text-decoration: overline\">GA variando no intervalo 25%&lt; <span style=\"text-decoration: overline\">GA &lt;55%, sendo constatada variação linear de <span style=\"text-decoration: overline\">GA com a razão molar anidrido acético/grupos amino. As quitosanas N-acetiladas apresentaram parâmetro de acetilação variando com 0,9&lt;PA&lt;1,5, indicando o predomínio da distribuição randômica das unidades GlcNAc e GlcN. As quitosanas N-acetiladas apresentaram maior estabilidade térmica em comparação com a quitosana de partida (amostra QSo), devido a porcentagem de unidades GlcNAc nas cadeias dos polímeros que provocaram alterações na sua estrutura cristalina. Os ângulos de Bragg característicos de &beta;-quitina (amostra QTo) extraída de gládios de lulas foram identificados nos difratogramas das quitosanas N-acetiladas com 30%&lt; <span style=\"text-decoration: overline\">GA &lt;55%, o que sugere que essas amostras adquiriram características semelhantes a da &beta;-quitina. Outra evidência desse fato foi comprovada através da análise das micrografias das amostras de quitosana N-acetiladas, que revelaram que as características das superfícies das partículas das amostras mais acetiladas são semelhantes a da &beta;-quitina. / The main physichochemical properties of chitosan rely on its average molar mass, average degree of acetylation (<span style=\"text-decoration: overline\">GA) and the parameter of acetylation (PA), which expresses the distribution pattern of 2-deoxy-2-acetamido-D-glucopyranose (GlcNAc) and 2-deoxy-2-amino-D-glucopyranose (GlcN) units along its chains. The occurrence of alternated, random or block-like distribution of GlcN and GlcNAc along the polymer chains is directly related to preparation conditions of chitosan. When homogeneous conditions are applied chitosan chains exhibiting random distribution are produced, while the chitosan generated from heterogeneous reactions presents block-like distribution. In this work, &beta;-chitin extracted from squid pens (Loligo sp.) was submitted to three consecutive steps of ultrasound-assisted deacetylation process (USAD process), resulting in an extensively deactylated chitosan (DA=2%) with high viscosity average molar mass (<span style=\"text-decoration: overline\">Mv= 354,000 g/mol) compared to chitosan obtained by other methods. This chitosan, named sample CSo, was dissolved in aqueous acetic acid and then it was submitted to N-acetylation reaction for 24 hours at room temperature. The occurrence of O-acetylation was prevented by adding 1,2-propanediol to the reaction nedium and the variation of the molar ratio acetic anhydride/amino groups allowed the preparation of five N-acetylated chitosans, named as samples RCSon, which were characterized by 1H NMR spectroscopy, infrared spectroscopy, X-ray diffraction, viscometry, scanning electron microscopy and thermogravimetric analysis. The parameter of acetylation (PA) of N-acetylated chitosans was determined from the 1H NMR spectra, allowing the assessment to the distribution pattern of GlcNAc and GlcN units. The N-acetylation reactions were carried out in duplicate, generating two independent sets of N-acetylated chitosans whose average degree of acetylation ranged as 25% &lt; DA &lt; 55%, a linear increase of DA with increasing molar ratio acetic anhydride/amino groups being observed. The N-acetylated chitosans presented parameter of acetylation ranging as 0,9 &lt; PA &lt; 1,5, indicating the predominance of random distribution of GlcNAc and GlcN units. The N-acetylated chitosans showed higher thermal stability as compared to the parent chitosan (CSo sample), probably due to the changes in the degree of order resulting from the higher content of GlcNAc units present in former samples. The Bragg angles characteristic of beta-chitin (CTo sample) were identified in the XRD patterns of N-acetylated chitosans, suggesting that these samples acquired similar characteristics as beta-chitin. Further evidence of this fact was observed through the SEM analyses, which revealed that the characteristics of particle\'s surfaces of N-acetylated chitosans are similar to those of beta-chitin.

The New Zealand (NZ) sea lion Phocarctos hookeri is the only pinniped endemic to NZ with a population of approximately 12,000 individuals. Its breeding range is currently restricted to NZ sub-Antarctic islands, and it has failed to recolonise its pristine distribution around the NZ main islands despite its protection since 1881. The current hypothesis is that the population growth of this pinniped is limited by the distribution of suitable prey on the Auckland Islands (50°30'S, 166°E) shelf, and by the direct and indirect pressure exerted by the arrow squid Nototodarus sloani fishery. However, this hypothesis has not been fully tested to date as there has been limited information on the diet of the NZ sea lion and their potential prey. The objective of this thesis is to analyse the diet of NZ sea lions over several years with particular emphasis on the most reproductively important segment of the population: lactating females. This thesis provides the first quantification by percentage mass of the diet of NZ sea lion using a combination of stomach content analysis, qualitative fatty acid (FA) analysis, and quantitative FA signature analysis (QFASA). Stomach contents and blubber FAs were analysed from 121 individuals incidentally caught (by-caught) in the southern arrow squid fishery from the years 1997 to 2006. The blubber FAs of 78 freeranging lactating females captured at Enderby Island, Auckland Islands, were also examined during January and February of 2000 to 2005. Data obtained from both stomach analysis and QFASA indicate that arrow squid, rattails Macrouridae, hoki Macruronus novaezelandiae and red cod Pseudophycis bachus are key prey species for NZ sea lions in the Auckland Islands region. Because these prey species live mostly at depths greater than 200 m, lactating females must undertake long foraging trips and dive regularly to greater depths than other sea lion species. Data from QFASA indicates that this foraging pattern is conducted over an extended period through the summer and autumn. The daily food requirement of a lactating female was estimated by a simple energetic model to be greater than 20% of its body mass. During years of low arrow squid recruitment such as 1999 and 2001, the amounts of squid required by the NZ sea lion population may have been similar to the amount harvested by the fishery, suggesting that resource competition is likely to occur between the arrow squid fishery and NZ sea lions in years of low squid abundance. Half of the fishing activity of the southern squid fishery occurs in the north of the Auckland Islands shelf where NZ sea lions forage, leading to incidental captures every year. This research emphasises that management of the NZ sea lion must not only consider the direct interactions with the arrow squid fishery, but also the likelihood of food resource competition between the fishery and NZ sea lions.

L'objectif de cette thèse est d'étudier les corrélations entre les propriétés morphologiques, structurales et magnétiques de nanoparticules à base de cobalt et platine. L'importance de cette étude tient au fait que les nanoparticules de CoPt constituent un matériau potentiellement utilisable dans le domaine de l'enregistrement magnétique. Il est donc essentiel de déterminer les liens entre les propriétés magnétiques et l'organisation atomique des nanoparticules. Pour cela, nous avons d'abord étudié la structure et la morphologie de ces objets à l'aide de techniques complémentaires : la microscopie électronique, la diffusion et l'absorption des rayons X. Les résultats montrent des transitions structurales dépendantes de paramètres comme la température, la taille ou le mode de croissance des nanoparticules. Ainsi, lors de la croissance atome par atome, des transitions de structure icosaédrique vers cubique à faces centrées sont observées. En revanche, la coalescence permet la formation d'une structure intermédiaire décaédrique. La structure chimiquement ordonnée qui est la plus intéressante pour le stockage de l'information a été obtenue par recuit à une température de 630 °C. Dans un second temps nous avons étudié les propriétés magnétiques des nanoparticules par magnétométrie SQUID et par dichroïsme magnétique circulaire des rayons X. L'analyse des résultats fait apparaître des liens clairs entre leurs structures et leurs propriétés magnétiques. Ces études ont été menées sur des particules alliées et coeur / coquille. Des effets d'interface ont été mis en évidence et les échantillons recuits ont montré une très forte augmentation du moment magnétique.

Nous avons étudié la dynamique quantique d'un circuit supraconducteur constitué d'un SQUID dc couplé à un transistor à paires de Cooper fortement asymétrique (ACPT). Le SQUID dc est un qubit de phase contrôlé par un courant de polarisation et un champ magnétique. L'ACPT est un qubit de charge contrôlé par un courant de polarisation, un champ magnétique et une tension de la grille.<br /><br />Nous avons mesuré par spectroscopie micro-onde les premiers niveaux d'énergie du circuit couplé en fonction des paramètres de contrôle. Les mesures des états quantiques des qubits de charge et de phase sont réalisées par une mesure d'échappement du SQUID dc avec une impulsion de flux nanoseconde appliquée dans celui-ci. La mesure de l'ACPT utilise un nouveau processus quantique : l'état excité de l'ACPT est transféré adiabatiquement vers l'état excité du SQUID durant l'impulsion de flux.<br /><br />Notre circuit permet de manipuler indépendamment chaque qubit tout comme il permet d'intriquer les états quantiques des deux circuits. Nous avons observé des anti-croisements des niveaux d'énergie des deux qubits lorsqu'ils sont mis en résonance. Le couplage a été mesuré sur une large gamme de fréquence, pouvant varier de 60 MHz à 1.1 GHz. Nous avons réussi à obtenir un couplage variable entre le qubit de charge et le qubit de phase. Nous avons analysé théoriquement la dynamique quantique de notre circuit. Cette analyse a permis de bien expliquer le couplage variable mesuré par une combinaison entre un couplage Josephson et un couplage capacitif entre les deux qubits.