Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 58-59). Also available in electronic version. Access restricted to campus users.

Nanoparticles possess unique physical, chemical, optical and electronic properties stemming from their nanoscale dimensions and are currently used in catalysis, microelectronics, drug delivery, as well as other applications. However, due to their large surface area-to-volume ratio, nanoparticles have a strong tendency to coalesce and sinter during processing or usage over short time scales and at low temperatures, which lead to significant changes in behavior and performance. In this work, in-situ transmission electron microscopy (TEM) heating has been used to investigate the effects of particle size, temperature and carbon capping layers on sintering in face-centered cubic (FCC) metallic nanoparticles. For the first time, we make direct and real-time measurements of nanoparticle size, neck growth, dihedral angle and grain boundary motion during sintering, which are then used to calculate fundamental material transport parameters such as surface diffusivity and grain boundary mobility. We observe that carbon surface coatings typically present on most commercial nanoparticles can significantly inhibit sintering in nanoparticles. Also, a new mechanism for coalescence in nanoparticles is shown where small clusters on the support can initiate neck growth by forming a bridge between the nanoparticles consisting of individual atoms or small clusters of atoms. In-situ TEM experiments provide critical and valuable real-time dynamic information for direct investigation of the link between the evolution of sintering and controlling mechanisms, which conventional experiments such as post-mortem TEM observations are not capable of conveying. / text

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Abstract The properties of starch nanoparticles (SNPs) labeled with the fluorescent dye pyrene (Py-SNPs) were probed by using fluorescence quenching, pyrene excimer formation, and transmission electron microscopy (TEM). Pyrene labeling of the SNPs was achieved by reacting 1-pyrenebutyric acid with the hydroxyl groups of the SNPs under basic conditions and in the presence of diisopropylcarbodiimide. This procedure did not degrade the SNPs as confirmed by dynamic light scattering (DLS) and afforded a means to generate a pyrene labeling level ranging from 0.5 to 5.0 mol% of the glucose units making up the SNPs. A polymeric quencher was also synthesized to probe the accessibility of the interior of the Py-SNPs by using fluorescence quenching measurements. The polymeric quencher was a 2K poly(ethylene glycol) terminated at one end with a methyl group and a nitropropane group at the other. Unfortunately these quenching experiments were abandoned when it was found that the polymeric quencher synthesized for these experiments absorbed too strongly where pyrene absorbs. Intramolecular pyrene excimer formation in the Py-SNPs was investigated by steady-state and time-resolved fluorescence. These experiments demonstrated that the Py-SNPs contract but do not overlap like linear polymers do in the semi-dilute regime. They also showed that despite the inherent rigidity of starch, the Py-SNPs deformed in water to allow their hydrophobic pyrene labels to cluster toward the center of the SNPs to minimize pyrene-solvent contacts. This segregation of the hydrophobic pyrene labels led to a distinct core-shell structure for the Py-SNPs which was illustrated in TEM images acquired on films prepared with the Py-SNPs. In summary, this thesis has uncovered some unexpected properties of the SNPs. Their branched structure makes their interpenetration difficult in the semi-dilute regime which forces them to contract. SNPs are thus deformable and their deformation can be probed quantitatively by using fluorescence and TEM.

Over the last few years, TEM has become a powerful technique to study cracks and specially crack tips. However, the number of publications including TEM results has not grown as it was expected. The main reason for this might be difficulties in the sample preparation. In this work we present a novel FIB sample preparation technique which has proved to be an ideal tool for preparing cross sectional samples containing crack tips. The morphology of intergranular stress corrosion cracking (IGSCC) has been investigated in Alloy 600 subjected to constant load and slow strain rate tests in simulated primary circuit pressurized water reactor conditions. Cracks were observed to nucleate at high-angle grain boundaries and propagate to depths of a few tens of micrometer along such boundaries, still in the initiation stage. Electron diffraction, energy dispersive x-ray (EDX) and electron energy loss spectroscopy (EELS) have been used to identify the different corrosion products and precipitates. Elemental mapping was employed to reveal changes in composition in the crack tip area. Major observations at cracks and grain boundaries include: the presence of different oxides in different locations, differences in grain boundary oxides and open crack/free surface oxides. These observations suggest that IGSCC involves oxygen diffusion through a porous oxide region along grain boundaries to the bare metal. This is a novel concept that offers an alternative to previous mechanisms proposed in the literature e.g. H embrittlement, slip-dissolution, etc., for which no supporting evidence has been found.

Most living eukaryotes are currently classified into one of five or six ‘supergroups’, which are in turn often divided between two assemblages: ‘unikonts’ and ‘bikonts’. This thesis explores the cytoskeletal morphology and phylogeny of three lineages that do not belong to any supergroup: ancyromonads, apusomonads, and breviates, likely relatives of supergroups Opisthokonta and Amoebozoa. It also investigates the phylogeny of malawimonads (basal members of supergroup Excavata) and collodictyonids (another unaffiliated lineage). Serial-section transmission electron microscopy was used to model the flagellar apparatus cytoskeletons of the ancyromonad Ancyromonas sigmoides, the breviate Breviata anathema, and the apusomonad Thecamonas trahens. Each has two main posterior microtubular roots and at least one anterior root (two in Ancyromonas). All three possess splitting posterior right microtubular roots and supernumerary singlets, features also characteristic of basal members of the supergroup Excavata (‘typical excavates’). One peripheral microtubule system in Ancyromonas, and the ‘right ribbon’ in Thecamonas, are likely homologous to dorsal fans in Breviata and ‘typical excavates’, and to the ‘r2’ root of myxogastrid Amoebozoa. One of the branches of the splitting root in Breviata and Thecamonas joins the right and intermediate roots, similarly to some myxogastrids. This implies that myxogastrids, and not the simpler pelobionts, represent the ancestral state for Amoebozoa. A phylogenomic analysis was performed focussing on apusomonads breviates, ancyromonads, and the problematic ‘typical excavate’ malawimonads, based on new transcriptomic data from Ancyromonas and an undescribed malawimonad. Rapid-site- removal analyses recover the ‘unikont’/‘bikont’ partition, and do not support the previously demonstrated affiliation between breviates and the ‘unikont’ supergroup Amoebozoa. Specifically, they group apusomonads with the ‘unikont’ supergroup Opisthokonta, and ancyromonads with breviates. Taxon-removal analyses group ancyromonads, breviates, and apusomonads together. Most analyses group malawimonads (perhaps with collodictyonids, another problematic group) between ‘unikonts’ and (other) ‘bikonts’, while other excavates are in a basal position amongst other ‘bikonts’. Combining these morphological and phylogenetic results suggests that splitting right roots, supernumerary intermediate singlets, and dorsal fans are found in multiple ‘basal’ lineages in both ‘unikont’ and ‘bikont’ portions of the eukaryotic tree, are likely characters of the last common ancestor of most or all living eukaryotes.

Leukocytes play a central role in protecting the body against infectious organisms and their research is essential for understanding the mechanisms of immunity. By studying leukocytes across a range of species, insights are provided into differing strategies employed to ensure resistance to disease. Surprisingly, the structure and function of marsupial leukocytes has received very limited study. Marsupials represent a major evolutionary pathway with distinct differences in reproduction and development from placental mammals. These differences in the life history of marsupials place unique challenges on the immune system, and differences in leukocyte structure and function could be reasonably expected. In this thesis, studies were undertaken to examine the cytochemical, ultrastructural and functional features of leukocytes from species of marsupials, belonging to the family Macropodidae (kangaroos and wallabies). The aim of these studies was to elucidate the characteristics of macropodid leukocytes and to compare and contrast these features with the known characteristics of other mammalian leukocytes. Leukocytes from two species of macropodid, the tammar wallaby (Macropus eugenii) and the western grey kangaroo (Macropus fuliginosis), formed the basis of this study with additional material provided from quokka (Setonix brachyurus), woylie (Bettongia pencillata) and red kangaroo (Macropus rufus). Staining characteristics of cells were examined following reaction with Sudan black B, peroxidase, chloroacetate esterase, naphthyl butyrate esterase, alkaline phosphatase and periodic acid-Schiff. Peroxidase and Sudan Black B reactions were similar to domestic animal species but chloroacetate esterase and naphthyl butyrate esterase were unreliable as markers for macropodid neutrophils and monocytes, respectively. Significant variation in staining for alkaline phosphatase was seen between species of macropodid. Tammar wallabies and quokka demonstrated strong neutrophil alkaline phosphatase activity whereas western grey kangaroos, red kangaroos and woylies contained no activity within their leukocytes. Peroxidase and alkaline phosphatase cytochemistry were also assessed at the ultrastructural level with transmission electron microscopy. This allowed the identification of distinct granule populations within macropodid neutrophils. Two subcellular compartments containing alkaline phosphatase activity were identified within tammar wallaby neutrophils. These were considered equivalent to secretory vesicles and a subpopulation of specific granules. Tubular vesicles containing alkaline phosphatase were also identified within the eosinophils of tammar wallabies. These structures were a novel finding having not been reported previously in the eosinophils of other animal species. In addition to cytochemistry, the general ultrastructure of leukocytes from tammar wallabies and western grey kangaroos were reported. Results were similar to previous reports for other marsupial species. The current body of knowledge was extended by the first detailed description of the ultrastructure of basophils in a marsupial. To assess functional aspects of macropdid neutrophils, flow cytometric assays were performed examining oxidative burst responses and phagocytosis. Reactive oxygen species were generated by neutrophils from tammar wallabies and western grey kangaroos in response to phorbol 12-myristate 13-acetate but not N-formyl-Met-Leu-Phe or opsonised bacteria. Phagocytosis of opsonised bacteria was also measured in neutrophils from tammar wallabies, which was poor in contrast to ovine neutrophils. However, flow cytometric studies were limited by sample preparation. Further optimisation of isolation methods for tammar wallaby leukocytes should be undertaken before dogmatic conclusions are drawn. Overall, the results of this thesis demonstrate that, in the areas examined, the general characteristics of leukocyte structure and function of mammals are present in macropodids. However differences were identified both within and outside of the macropodid group. These differences have important ramifications for the use of ‘model’ species in the study of leukocyte biology in marsupials. The results also provide potentially useful tools for the clinical diagnosis of haematological disease in macropodids and may be of interest to those studying comparative and evolutionary aspects of leukocyte structure and function.

Thesis (M.S.)--Ball State University, 2009. / Title from PDF t.p. (viewed on Apr. 16, 2010). Includes bibliographical references (p. 36-37).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.