This thesis explores the theory of electron energy-loss spectroscopy (EELS) in atomic resolution electron microscopy. / The first unequivocal evidence of the effective nonlocal potential in momentum-transfer-resolved EELS is presented. For suitable geometries, the nonlocal potential can be well approximated by a local potential. In scanning transmission electron microscopy (STEM) the validity of this is mainly influenced by the detector size and, contrary to conventional wisdom, a thin annular detector does not allow direct image interpretation. It is found that the best way to ensure the potential is well approximated by a local potential is to use a detector with a large collection angle. / To simplify computation and interpretation it is desirable to make the single-channelling approximation. In this approximation only the elastic scattering of the probe before the ionisation event is modelled. It is shown how this approximation breaks down for the small detectors used in momentum-transfer-resolved EELS and this is confirmed with experimental results. Double-channelling calculations, where the channelling of the probe both before and after the ionisation event are modelled, can also be simulated. An alternative approximation for small detectors that includes double channelling and is more applicable for momentum-transfer-resolved EELS is also presented. / Beyond chemical information, the fine structure of an absorption edge gives bonding and electronic information. Incorporating fine structure into channelling theory allows the exploration of the effects of channelling on fine structure. The weighting of the two different spectra in graphite, as a function of incident probe tilt in momentum-transfer-resolved EELS, is calculated using double-channelling simulations. This is combined with experimental data and multivariate statistical analysis to extract the two physical spectra, greatly simplifying the analysis of a large data set. / The effect of the nonlocal potential and channelling on site-specific electronic structure analysis by channelling EELS is examined. It is found that using a large on-axis detector can make the interaction effectively local, leading to a greater change in the spectra as a function of sample tilt. Alternatively offsetting the detector can achieve similar results but at the cost of greater statistical noise. Channelling calculations were combined with the program FEFF and the full energy differential cross section was calculated from first principles for the aluminium K edge as a function of sample tilt in nickel aluminate spinel. Qualitative agreement with experiment was found but quantitative agreement will require further investigation. / The theory of fine structure in STEM was examined, using strontium titanate to see how the high spatial resolution of STEM can be used in conjunction with energy-loss near-edge spectroscopy measurements. The possibility of imaging unoccupied electron molecular orbitals using STEM was also examined.

Copper-alumina composites were developed for testing in abrasive wear applications. The composites featured a porous continuous ceramic-preform network infiltrated by a liquid metal to form the final consolidated composite. The liquid metal phase was pure copper. Six different ceramic preform variants were tested. Ceramic volume fractions of 40, 50 and 60% were used, of two preform types; one pure-alumina, and one with additional 2wt% copper(I) oxide (CU20), functioning as an infiltration aid, the effects of which were determined in a previous study; the copper-oxide reduced infiltration pressure and allowed the use of higher ceramic phase volume fraction in the final composite. Abrasive wear tests against two automotive braking system materials were conducted. Grey cast iron of alloy type GG15 was used to establish a baseline for behaviour of the six different composite samples and compare them. Following this, the three volume fraction variants of samples using the copper-oxide infiltration aid were trialled against a commercially-available European passenger vehicle brake pad friction material; ABEX 6091. Wear tests were conducted on a pin-on-disc tribometer. Hemispherical-headed pins were made from the composite and tested against rotating discs of the grey cast iron and the ABEX friction material. Contact velocity was kept constant at Ims-?? at room temperature in air, and contact loads up to 15N were used. Test loads of 1-4N were used against grey cast iron, and 15N against the ABEX friction material. Optical micrography was used to monitor the wear rate of samples tested against grey cast iron. Scanning electron microscopy (SEM) was used to characterise bulk microstructures and evaluate surface wear features. Transmission electron microscopy (TEM) was used for further microstructural investigation of the sintering and interfacial features of the undamaged pin samples, as well as damage zones and tribofilm compositions. Focussed ion beam (FIB) milling was used to create subsurface cross-sections of wear regions and prepare TEM samples. The wear performance of the different sample types was compared by ceramic content and preform additives. It was found that the wear resistance of pure-alumina preform composites was dependent on ceramic volume fraction. Increasing ceramic content lead to increased wear resistance. The lower sinter temperature of the samples with the copper oxide additive led to reduced wear resistance compared with the monolithic alumina preforms and changes in ceramic volume fractions were not discernable in wear resistance against grey cast iron. This could be further supported by qualitative micrographic observations. All tests against grey cast iron were dominated by tribochemical film formation, which was determined to be oxidation of the iron which formed at the composite pin contact surface. Further testing of the copper-oxide containing samples against the ABEX friction material revealed a mixed result; the 50 and 60% ceramic volume samples produced near-identical wear performance, while the 40% sample suffered poor wear resistance. The dominant wear mechanism of composite pins tested against the ABEX friction material was abrasive wear. Sub-surface analysis of wear pins revealed a prominent damage layer forming at the contact surface of all pin samples which progressively grew into the bulk material. This layer was believed to have an important effect on the wear behaviour of the materials.

Thesis (MSc.(Anatomy)--Faculty of Health Sciences)-University of Pretoria, 2007. / Includes bibliographical references.

Three types of electrodes: carbon paste electrodes modified with nanoparticles of metallophthalocyanines (MPcNP-CPEs, M = Mn, Fe, Ni, Co), basal plane pyrolytic graphite electrodes modified with iron or nickel phthalocyanine nanoparticles and multiwalled carbon nanotube composites (FePcNP/MWCNT-BPPGE or NiPcNP/MWCNT-BPPGE),and basal plane pyrolytic graphite electrodes modified with multiwalled carbon nanotubes and electropolymerized metal tetra-aminophthalocyanines (poly-MTAPc-MWCNT-BPPGE), where M is Mn, Fe, Ni or Co, were prepared. Electrochemical characterizations showed that faster electron transfer kinetics occurred at the NiPcNP/MWCNT-BPPGE than at the FePcNP/MWCNT-BPPGE surface. SEM and electrochemical characterizations of poly-MTAPc-MWCNT-BPPGE showed that MTAPc had been deposited on the MWCNTBPPGE surface, and that the poly-CoTAPc-MWCNT-BPPGE exhibited the fastest electron transfer kinetics of all the poly-MTAPc-MWCNT-BPPGEs. Using amitrole and asulam as test analytes, electrochemical experiments showed that, amongst the CPEs, the FePcNP-CPE and NiPcNP-CPE displayed the most electrocatalytic behavior towards amitrole and asulam oxidation, respectively, and further experiments were done to obtain the electrochemical parameters associated with these electrodes and the corresponding analytes. Although, the FePcNP/MWCNT- BPPGE displayed electrocatalytic behavior towards amitrole oxidation in comparison with the bare BPPGE, it was less electrocatalytic than the FePcNP-CPE in terms of detection potential. The NiPcNP/MWCNT-BPPGE displayed the same detection potential as the NiPcNP-CPE. The poly-FeTAPc-MWCNT-BPPGE exhibited the most electrocatalytic behavior towards amitrole, of all the electrodes investigated, and the poly-CoTAPc-MWCNT-BPPGE displayed the best electrocatalytic behavior towards asulam, amongst the poly-MTAPc-MWCNT-BPPGEs.

Made available in DSpace on 2014-10-09T12:27:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:51Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

abstract: A piezoelectric transducer, comprised of electroded and active pad PZT layer atop a backing PZT layer and protected with an acoustic matching layer, and operating under a pulse-echo technique for longitudinal ultrasonic imaging, acts as both source and detector. Ultrasonic transducer stacks (modules), which had failed or passed during pulse-echo sensitivity testing, were received from Consortium X. With limited background information on these stacks, the central theme was to determine the origin(s) of failure via the use of thermal and physicochemical characterization techniques. The optical and scanning electron microscopy revealed that contact electrode layers are discontinuous in all samples, while delaminations between electrodes and pad layer were observed in failed samples. The X-ray diffraction data on the pad PZT revealed an overall c/a ratio of 1.022 ratio and morphotropic boundary composition, with significant variations of the Zr to Ti ratio within a sample and between samples. Electron probe microanalysis confirmed that the overall Zr to Ti ratio of the pad PZT was 52/48, and higher amounts of excess PbO in failed samples, whereas, inductively coupled plasma mass spectrometry revealed the presence of Mn, Al, and Sb (dopants) and presence of Cu (sintering aid) in in this hard (pad) PZT. Additionally, three exothermic peaks during thermal analysis was indicative of incomplete calcination of pad PZT. Moreover, transmission electron microscopy and scanning transmission electron microscopy revealed the presence of parylene at the Ag-pad PZT interface and within the pores of pad PZT (in failed samples subjected to electric fields). This further dilutes the electrical, mechanical, and electromechanical properties of the pad PZT, which in turn detrimentally influences the pulse echo sensitivity. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

Made available in DSpace on 2014-10-09T12:27:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:51Z (GMT). No. of bitstreams: 0 / Fibras são definidas como o conjunto formado de filamentos orientados na direção da cadeia molecular e são parte fundamental na vida diária do ser humano, encontradas de várias formas, tais como filamentos, fios, feixes, cordas, tecidos, compósitos, revestimentos, entre outras. Elas abrangem diversas áreas, tais como civil, mecânica, elétrica, eletrônica, militar, naval, náutica, aeronáutica, saúde, medicina, ambiental, comunicação, segurança, espacial, entre outras. A fibras são divididas em duas classes distintas, naturais e químicas, que compõem as subclasses sintéticas e artificiais. Podem ser produzidas de vários materiais, tais como lã, algodão, raion, linho, seda, rocha, náilon, poliéster, polietileno, polipropileno, aramida, vidro, carbono, aço, cerâmica, entre outros. Em nível global, as fibras químicas correspondem a 59,9% do mercado, sendo as fibras sintéticas tipo poliéster as mais utilizadas, com 63%. Necessidades vitais têm levado ao desenvolvimento de fibras multifuncionais e o foco mudou nos últimos dez anos com a utilização da nanotecnologia para fibras de responsabilidade ambiental e fibras inteligentes. O estudo das propriedades mecânicas e dos mecanismos de fratura das fibras é de grande importância para caracterização e entendimento das causas de falhas. Para este propósito foram selecionados tecidos fabricados com fibras sintéticas de alto desempenho do tipo náilon e poliéster, utilizadas em produtos de engenharia tais como pneus, correias, mangueiras e molas pneumáticas, as quais foram analisadas em cada etapa de processamento. Amostras das fibras foram retiradas de cada etapa de processamento para análise por ensaios destrutivos de tração e microscopia eletrônica de varredura. Os resultados de análise das propriedades mecânicas mostraram perda de resistência por temperatura e tensões multiaxiais durante as etapas de processamento da fibra. Por meio de ensaios de microscopia foi possível determinar contaminações, manchas superficiais, deformações plásticas, delaminações, variações nas faces de fratura dos filamentos e analisar, na interface fibra-borracha, o nível de adesão. Estas irregularidades e variações são causadas durante as etapas inerentes ao processo de fabricação. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The small intestine mucosa is known to be able to adapt itself to several kinds of both physiological and pathological conditions. The adaptive patterns of the structure of the enterocytes, particularly their apical surface (brush border), were studied in three models: (1) in rats, subjected to antrectomy or antral exclusion, combined with gastroduodenostomy and gastrojejunostomy; (2) in rats with alloxan dia­betes; (3) in children with coeliac disease; a) in its active phase; b) after long-term treatment with gluten-free diets; c) after long-term challenge with dietary gluten following treatment; d) after short-term elimination of dietary gluten. Gut mucosa from fasting or fed, normal or sham-operated rats, fasting cats, and short-statured children with no signs of gastrointestinal disease served as controls. - The specimens were prepared for light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Quantitation of structural variables was achieved by means of LM and TEM morphometrical procedures. Differentiation of the rat enterocytes from the base to the crest of the villi was structurally reflected by doubling of their apical cell area, an increase in cell height, and a decrease of both nuclear and mitochondrial volume densities. In mature normal rat enterocytes, high-power SEM showed regularly arranged, nude microvilli in thir apical surfaces, whereas in cat and man the apical surfaces were covered by a thick glycocalyx. - Fasting for 24 hours decreased the total length of the rat small intestine and the height of the enterocytes. Antrectomy and antral exclusion with gastrojejunostomy produced an increase of the apical surfaces of the enterocytes of the seif-emptying duodenal blind loop, whereas no changes occurred after antrectomy with gastroduodeno­stomy. In the jejunum, the apical surface area was reduced both after antrectomy and antral exclusion. In the diabetic rats a slight decrease of the apical surface area, together with an elongation of both the vil­li and the crypts, was observed in the jejunum, whereas no structural changes occurred in the duodenal mucosa. Both in active coeliac disease and after long-term challenge with dietary gluten, SEM analyses showed uniformly destructed villi. The api­cal surfaces of the enterocytes were frequently convex and irregular in size and delineation (the surface of the normal enterocytes was polygo­nal and flat). Ultrastructurally, the apical surfaces were severely damaged with a distortion of the glycocalyx and with marked irregularity of the microvilli. - After gluten elimination, the surface ultrastructu­re of the enterocytes in the coeliac gut mucosa generally showed a rapid, clear-cut restoration despite a remaining severe atrophy of the villi. Successful dietary treatment (after about one year of gluten-free diet) restored the small intestine mucosa to normal as assessed both by LM and low-power SEM. In contrast, high-power SEM often disclosed per­sisting lesions of the enterocytes. Another provocation with gluten for up to 9 days in clinically healed coeliac mucosa did not significantly alter the surface ultrastructure of the enterocytes. / <p>S. 1-52: sammanfattning, s. 53-138: 5 uppsatser</p> / digitalisering@umu

Magister Pharmaceuticae - MPharm / The aim of this study was to investigate the mechanism of fenfluramine-induced pulmonary phospholipidosis, by comparing the profile and levels of induced phospholipids in the rat and the mode of phospholipase inactivation, both relative to that produced by chlorphentermine. Wistar and BD9 rats were injected with fenfluramine (FF) and chlorphentermine (CP) intra-peritoneally daily over a six week period to induce phospholipidosis. The lungs isolated from such treated and untreated animals, were grouped into unlavaged lungs and lungs to be lavaged and from the latter group the alveolar macrophages were isolated. Small sections of the unlavaged lungs were microscopically examined to verify the induction of phospholipidosis. Further the levels of phosphatidyl choline (PC), spingomyelin (SPM), phosphatidyl ethanolamine (PE), phosphatidyl glycerol (PG), phosphatidyl inositol (PI), phosphatidyl serine (PS) and phosphatidic acid (PA) were determined in both groups of lungs using a TLC method. To assess whether the drug-mediated inactivation of the phospholipases (PL) occurred via direct inhibition of the enzymes or via the drug-phospholipid complex, the hydrolysis of the above phospholipids by PL-A or PL-C were monitored using colorimetric methods. The feasibility of the phospholipid-drug complex-mediated mechanism was further explored, by assessing the effect the two drugs had on the phase transition temperature of the phospholipids. Electron microscopy revealed the presence of hypertrophied and elevated counts of alveolar macrophages in the treated-Wistar and -BD9 rats. In the FF- and CP treated Wistar and BD9 rats there were, compared to the saline-treated rats, a 200 % and 235 % increase in macrophage counts, respectively, for the FF-treated rats and a 700 % and 965 % increase in macrophage counts, respectively, for the CP treated rats. The levels of all the phospholipids in the unlavaged lungs of both rat strains were elevated, except that for PG, PS and PA. In both rat strains following the treatment with both drugs the PG levels were not elevated and the PS levels were not elevated following CP treatment. Following the treatment for both drugs, the PA levels were also not elevated in the BD9 rats. Relative to the levels found in the unlavaged lungs of the control rats, the increases ranged from a minimum of 9 to a maximum of 216 %. In general, Wistar rats appeared to be more susceptible to both FF and CP treatment. In both rat strains, lavaging of the lungs considerably reduced the levels of phospholipids remaining in the lung and the differences between the treated and untreated animals became less striking. The addition of FF or CP, whether directly to the enzyme, or in the form of the drug phospholipid complex, resulted in significant decreases in the PL-A-mediated or PL-C-mediated hydrolysis of virtualy all the test phospholipids. The average decrease ranged from 0.811 to 4.04 ,.,.FFAbbb ,.,.1-1sample min-I, for the PL-A activity and 0.023 to 0.827 ,.,.gIp'CC100 ,.,.1-1 sample min-I, for the PL-C activity. In the case of FF, the inhibition of PL-A activity could not be ascribed exclusively to either direct inhibition of the enzyme or reduced susceptibility of the phospholipid substrate-drug complex. The PL-C activity appeared to be inhibited to a greater extent via the phospholipid substrate-drug complex rather than by direct inhibition. On the other hand, CP induced a small, but significantly greater degree of inhibition of PL-A activity, more via direct inhibition, rather than by the phospholipid substrate-drug complex. The PL-C activity appeared to be inhibited to a greater extent via phospholipid substrate-drug complexation than by direct inhibition. From the above data, considered collectively, it was not possible to declare either of the two possible mechanisms as the more likely one for FF or CP-induced inhibition of the phospholipases. The feasibility of the indirect mode was further explored, by determining the phase transition temperatures for the phospholipid-drug complexes of each drug. The addition of each drug caused a depression of the phase transition temperature of all the phospholipids with a .1T'dd ranging from 0.52 to 15.73 °C. This appears to support the notion that both drugs bind to the phospholipids and the differences in the extent of the phase transition temperature depression of the individual phospholipids may indicate differences in the binding capacities of these drugs. The following major conclusions may be drawn from the results of this investigation. Fenfluramine induces a phospholipidosis syndrome in the lungs of Wistar and BD9 rats that are histologically similar to that induced by CP. It induces the elevation of essentially the same phospholipids as CP, primarily in the alveolar spaces and macrophages, and by implication, most likely via similar mechanisms. For both FF and CP, both direct inhibition and phospholipid-drug complex-mediated inhibition of phospholipases were found to be a viable mechanism for this syndrome. The mechanism for FF-induced pulmonary phospholipidosis thus appears to be similar to that of CP; small quantitative differences in essentially similar mechanisms, may explain the differences in the levels of induced phospholipidosis found in this study.

Proton-Exchange Membrane Fuel Cells are an alternative source of electricity generation for automobiles and stationary power plants. With increasing concerns on environmental issues, recent research has focused on maximizing the efficiency and durability as well as minimizing the costs of fuel cells. One of the main areas of research is optimizing the structure of the cathode catalyst layer. The main driving force of this thesis was the effective visualization of nanostructure of the ionomer, which is responsible for proton conduction in the cathode catalyst layer. However, challenges regarding sample preparation and radiation damage still need to be well understood. Different sample preparation techniques of catalyst inks and catalyst coated membranes were used for Scanning and Transmission Electron Microscopy, such as freeze fracturing, ultramicrotomy and Focused Ion Beam. Comparisons of the microstructure and chemical differences of all components, especially the ionomer, prepared by ultramicrotomy and Focused Ion Beam, was done with Transmission Electron Microscopy and Scanning Transmission X-ray Microscopy applied to the same catalyst coated membrane sample. Detailed spectroscopic information regarding components in both specimens was compared with C 1s and F 1s near edge X-ray absorption spectra recorded in a Scanning Transmission X-ray Microscope. Focused Ion Beam causes extensive damage to the carbon support and ionomer but prepares thinner sections than ultramicrotomy. This work makes it possible to understand the limitations of each sample preparation and compositional analysis technique in order to later apply one of them to image the ionomer in the catalyst layer at the nanoscale, hopefully using tomography techniques. / Thesis / Master of Materials Science and Engineering (MMatSE)