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The aim of my study was to create a Drosophila line lacking the expression of all Sirtuin genes, check its developmental phenotype and characterise its response in stress conditions. The flies had bigger weight than controls, they had decreased fertility and fecundity and they developed more slowly. They showed a trend towards increased resistance to chill coma, but they did not show a significant difference in starvation or oxidative stress assay. Its effect on lifespan is being investigated.

Group-III nitride materials are increasingly important, because of their semiconducting properties and bandgaps tuneable across a wide range from the infrared to ultraviolet. They are of particular interest for optoelectronic and power electronic applications. The studies on nitride materials are comprehensive, and one way to categorise them is based on the scale of the material, namely: (a) 3D bulk materials, for example the development of 3D bulk nitride substrate; (b) epitaxial layers, for example GaN/InGaN 2D quantum well based light emitting diodes (LEDs); (c) 1D nitride nanowires and (d) 0D quantum dots, for example InGaN quantum dot based single photon sources. This thesis uses a multimicroscopy concept to investigate various group-III nitride nanowires and hillocks. Multiple different microscopy techniques were applied to the same specific nanostructure or defect. This allows the properties of the materials of interest to be linked directly to the nanostructures or defects, providing a more complete picture of the samples that have been studied. The multiple microscopy techniques used to conduct the work in this thesis include (scanning) transmission electron microscopy ((S)TEM), cathodoluminescence (CL), focused ion beam (FIB) and atomic force microscopy (AFM). Specifically, AFM was used to characterise the morphology of the sample on a sub-nanometer scale. The crystalline structures were characterised using (S)TEM, and the in-situ energy dispersive X-ray spectroscopy (EDS) was used to conduct compositional analysis of the selected sites. CL was used to reveal the optoelectronic properties by analysing the emission wavelengths of the materials, excited by the electron beam. FIB was the technique used to prepare site-specific samples to be measured in (S)TEM. A detailed explanation of these characterisation techniques was also included. In the context of the studies on nitride materials, nitride nanowires and their heterostructures are a particular research focus. They combine the unique properties of III-nitride materials together with the advantages induced by the nanowire geometry. This thesis explores three different nanowire systems: a GaN nanowire structure incorporating a GaN/Sc$_x$Ga$_{1-x}$N axial heterostructure grown by molecular beam epitaxy (MBE); GaN/InGaN core-shell nanowires fabricated by a hybrid approach combining metalorganic vapour phase epitaxy (MOVPE) and dry etching techniques; and AlGaN nanowires on free standing AlGaN substrates fabricated by MBE and inductively coupled plasma (ICP) etching. The optoelectronic properties, compositions and structures of these nanowires were studied in detail. Moreover, a comprehensive review on the properties, growth methods and applications of group-III nitride nanowires is also included in this thesis. Apart from nanowires, a lot of effort has been focusing on the improvement of the quality of epitaxial layers of GaN and its alloys, and they currently have an even wider perspective than nitride nanowires. The understanding of defects within the epitaxial layers is crucial in order to mitigate the their adverse effects, leading to the increased emphasis on defect analysis. Hillocks are a type of defects found on GaN epilayers, which are less well studied than other defects such as dislocations and stacking faults. As a consequence, the formation mechanisms of hillocks remain controversial. In this context, after a review on the past studies on GaN hillocks, this thesis also investigates two types of hillocks, i.e. hillocks on GaN p-i-n diodes and hillocks on GaN grown on patterned sapphire substrates (PSS). Their nanoscale structures, properties and formation mechanisms are studied.

Polyacrylamide is widely used as a flocculant but the influence of the molecular mass distribution upon flocculant activity is poorly understood. This thesis outlines the successful characterisation of ultrahigh molecular mass polyacrylamide solutions in terms of discrete solvated polymer coils and coil agglomerates. These features were correlated with the observed flocculation, demonstrating a number of solution state features required to improve flocculation activity.Aqueous solutions of polyacrylamide exhibit time-dependant behaviour affecting viscosity and polymer agglomeration. Improving the solvation of the polymer suppressed the agglomerates, as did manipulation of hydrogen bonding through the presence of salts. Limiting agglomeration through improved solvation apparently lowers a barrier to polymer interaction, such that the coils disperse but become more susceptible to reagglomeration under mild shear. These solvent modifications did not fully suppress the agglomerates.To fractionate polyacrylamide into a molecular mass distribution, flow field-flow fractionation (flow FFF) was chosen, coupled to a multi-angle laser light scattering (MALLS) photometer and a differential refractometer for molecular mass and concentration sensitive detection, respectively. For the first time, the analysis of high molecular mass polyacrylamides in water using the flow FFF-MALLS technique has been reported. However, a number of difficulties needed to be overcome, including shear artefacts, sample agglomeration and polymer-membrane interactions.Both polyacrylamide standards and commercial flocculants were amenable to the technique. Commercial flocculants were found to vary not only with regard to viscosity and mean molecular mass, but also with sub- and supramicron size agglomerates. The flow FFF technique is size-sensitive, which for some low molecular mass samples displayed an ++ / unusually wide elution profile, in apparent conflict with the molecular mass sensitive MALLS detector. It was concluded that polyacrylamide in solution exists simultaneously in three states: discrete polymer coils, entanglements of a several coils, and agglomerates with supramicron diameters.This thesis concluded with a comparison between the characterised polyacrylamides and observed flocculation activity on a standard kaolin substrate. Results show polymer with supramicron agglomerates produce the largest and most shear-resistant kaolin aggregates with a definite optimum agitation intensity. Higher molecular mass flocculants with less agglomeration bind fine particles under more gentle conditions but are deficient under increasing stress. Flocculants exhibiting coil entanglements showed poor activity and formed only small aggregates. A modified flocculation mechanism was proposed, in which supramicron polymer agglomerates play a critical role.

<p>The demands on decreased environmental impact from vehicles force the automotive industry to develop engines with reduced engine oil and fuel consumption. Engine oil consumption is recognized to be a significant source of pollutant emissions. Unburned or partially burned oil in the exhaust gases contribute directly to hydrocarbon and particulate emissions. Engine oil and fuel consumption are to a great extend controlled by the topography of the cylinder liner surface.</p><p>Recent engine tests have shown a promising reduction in oil consumption when using cylinder liners with a smoother finish than the current plateau honing.</p><p>One approach to produce smoother liner surfaces is to replace SiC ceramic honing stones with diamond tools. However, event though the diamond honing process results in higher productivity, improved demands of quality control is needed to monitor the degree of cold worked material - “blechmantel” (German), and the resulting risk of increased wear and scuffing.</p><p>A number of petrol and diesel engine cylinder liners have been mapped to be able to verify the quality and consequences, in terms of wear and function, of the honing process. A new mapping method, combining SEM images and quantitative image analysis with traditional 2D profilometry has been developed and tested in this study. The liners where tested in a reciprocating rig of 8 mm stroke and with a frequency of 10 Hz, simulating the top-dead center conditions in a running engine. </p><p>The tests where carried out in high- and low pressure conditions with smooth respectively rough liner roughnesses against PVD coated piston rings. The developed surface mapping method was employed before and after the test to study effect of running-in wear on the surface, features characterized with the SEM- and the 2D profilometer.</p><p>The results show that combining SEM- and profilometric methods gives a good picture of the effects of varying the cylinder liner pressure and roughness. The roughness of the core decreases more for diesel liners than for petrol liners. In average (rough and smooth liners) the diesel core roughness decreases 265% while the petrol liners average on a 60% decrease. Blechmantel- and Irregularities ratio show a high sensitivity to varying conditions and decrease 1180% to 100% for the diesel liners while the parameters increase between 106% to 18% for all the petrol liners. A probable cause is the more severe diesel high pressure run-in conditions are able to effectively “truncate” the plateaux and remove residing plastically deformed un-cut honing residues while the less severe petrol liner conditions not manage to remove the blechmantel and irregularities in an important extent.</p>

The demands on decreased environmental impact from vehicles force the automotive industry to develop engines with reduced engine oil and fuel consumption. Engine oil consumption is recognized to be a significant source of pollutant emissions. Unburned or partially burned oil in the exhaust gases contribute directly to hydrocarbon and particulate emissions. Engine oil and fuel consumption are to a great extend controlled by the topography of the cylinder liner surface. Recent engine tests have shown a promising reduction in oil consumption when using cylinder liners with a smoother finish than the current plateau honing. One approach to produce smoother liner surfaces is to replace SiC ceramic honing stones with diamond tools. However, event though the diamond honing process results in higher productivity, improved demands of quality control is needed to monitor the degree of cold worked material - “blechmantel” (German), and the resulting risk of increased wear and scuffing. A number of petrol and diesel engine cylinder liners have been mapped to be able to verify the quality and consequences, in terms of wear and function, of the honing process. A new mapping method, combining SEM images and quantitative image analysis with traditional 2D profilometry has been developed and tested in this study. The liners where tested in a reciprocating rig of 8 mm stroke and with a frequency of 10 Hz, simulating the top-dead center conditions in a running engine. The tests where carried out in high- and low pressure conditions with smooth respectively rough liner roughnesses against PVD coated piston rings. The developed surface mapping method was employed before and after the test to study effect of running-in wear on the surface, features characterized with the SEM- and the 2D profilometer. The results show that combining SEM- and profilometric methods gives a good picture of the effects of varying the cylinder liner pressure and roughness. The roughness of the core decreases more for diesel liners than for petrol liners. In average (rough and smooth liners) the diesel core roughness decreases 265% while the petrol liners average on a 60% decrease. Blechmantel- and Irregularities ratio show a high sensitivity to varying conditions and decrease 1180% to 100% for the diesel liners while the parameters increase between 106% to 18% for all the petrol liners. A probable cause is the more severe diesel high pressure run-in conditions are able to effectively “truncate” the plateaux and remove residing plastically deformed un-cut honing residues while the less severe petrol liner conditions not manage to remove the blechmantel and irregularities in an important extent.

Chromatography media (resins) are very important for and widely used by the biopharma industry in large scale production of biopharmaceuticals, e.g. monoclonal antibodies. Today there are several hundred biopharmaceuticals released globally on the healthcare market. This thesis discusses various strategies and methods for the characterisation of chemical and functional stability of chromatography media. In addition, various analytical techniques used in these areas were evaluated and applied. Further, more specific physical and chemical characterisation methods were evaluated and applied to explore different properties of various chromatography media. In Papers I-III, established methodologies for performing chemical and functional stability studies were used. Mainly agarose-based chromatography media were investigated. For fast screening of the chemical stability, the total organic carbon analysis technique was evaluated and applied. This technique that measures the carbon leakage from the chromatography media at different conditions, proved to be very suitable and robust. For detection and/or identification of leakage compounds responsible for or for part of the measured carbon leakage, different methods such as (high performance) liquid chromatography and gas chromatography mass spectrometry were used. In Papers IV-VII, different properties (i.e. functional performance, ligand content and surface chemistry) were evaluated for different agarose-based chromatography media. Standard chromatographic methods (ion exchange chromatography) and spectroscopic methods (e.g. Fourier transform infrared spectroscopy and time-of-flight secondary ion mass spectrometry) were evaluated and applied. Chemometric methods were used for efficient evaluation of data. Information of chemical, functional and leakage data of chromatography media are valuable and important for the biopharmaceutical companies to be able to fulfil the regulatory requirements of biopharmaceuticals. In addition, information of various chemical, functional and physical properties of chromatography media is likewise important during development and set up of new biopharmaceutical processes.

A gel permeation chromatography (GPC) system, using two concentration detectors and a low angle laser light scattering (LALLS) detector, has been investigated for use in characterising copolymers. At each elution volume, the system allows the calculation of molecular weight, average composition, and compositional heterogeneity. Overall molecular weight, composition, and heterogeneity parameters can also be calculated. This characterisation method yields heterogeneity information previously unobtainable without the use of cross fractionation techniques which are far more time consuming but ultimately more thorough.

This study concerned the synthesis of modified terephthalic acid monomers and branched dialcohols for the synthesis of polyesters with different properties. Monomers were prepared by esterification of terephthalic acid (TPA) and the alkylation of the ester dimethyl terephthalate (DMT). If alkylation was unsucessful, TPA was brominated using N-bromosuccinimide (NBS) and other brominating agents. However, the bromination reactions were also unsuccessful. Therefore, oxidation reactions of 2-bromoparaxylene were conducted as an attempt to obtain the desired monomers, however a mixture of products was produced that were difficult to separate. Subsequently, the brominated TPA was bought, and the alkylation reactions were performed using tetramethyltin and other alkylating agents; however the alkylation reaction was once again unsuccessful. Despite the difficulties encountered during monomer synthesis, polymerization of the obtained monomers was investigated. Polymer synthesised by the technique of condensation polymerization of branched diols and the brominated TPA. The unbranched diol monomers and unsubstituted DMT were used to synthesize reference polymers for comparison with the novel polymers produced in this study. The following diols were used: 1,2-propanediol, 2-methyl-1,3-propanediol, and 3-methyl-1,5-pentanediol. A batch reactor equipped with a mechanical stirrer connected to the vacuum pump was used as polymerization vessel. The polyesters were synthesised and they were characterised using IR and NMR. Additional polymer analysis was performed using Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), Gel permeation Chromatography (GPC) and Scanning Electron Microscopy (SEM). The results of the analyses indicated that the polymers became flexible and softer with an increasing number of methylene units in the main chain. Consequently, the melting point of the polymer decreased when there was branching present. SEM analyses showed that polymers were softer and had no hard edges, and the SEM also showed the catalyst inside the polymers. The decomposition temperature changed very slightly with alkyl substitution or the presence of bromide in benzene ring. It was concluded that the benzene ring did not become activated as a number of methods were attempted unsuccessfully to facilitate reaction by either alkylation or bromination. The methyl branches on the diols were not held responsible for any changes in the properties of the polyesters. Bromination of the monomers resulted in polymers that were structurally amorphous and that demonstrated a low tensile strength. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015