<p dir="ltr">The technological drive of humanity to explore the cosmos, travel at hypersonic speeds, and pursue clean energy solutions requires ceramic scientists and engineers to constantly push materials to their functional, behavioral, and chemical extremes. Ultra-high temperature ceramics, and particularly transition metal carbides, are promising materials to meet the demands of extreme environment materials with their >4000 °C melting temperature and impressive thermomechanical behaviors in extreme conditions. The advent of the 2D version of these transition metal carbides, known as MXenes, added a new direction to design transition metal carbides for energy, catalysis, flexible electronics, and other applications. Toward extreme conditions, although MXenes remain yet unexplored, we believe that the ~1 nm flakes of MXenes gives ceramics scientists and engineers the ability to truly engineer transition metal carbides layer-by-layer at the nanoscale to endure the extreme conditions required by future harsh environment technology. Although MXenes have this inherent promise, fundamental study of their behavior in high-temperature environments is necessary to understand how their chemistry and 2D nature affects the high-temperature stability and phase behavior of MXenes toward application in extreme environments.</p><p dir="ltr">In this dissertation, we investigate the high-temperature phase behavior of 2D MXenes in high temperature inert environments to understand the stability and phase transition behavior of MXenes. In this work, we demonstrate that 1) MXenes’ transition at high-temperatures is to highly textured transition metal carbides is due to the homoepitaxial growth of these phases onto ~1-nm-thick MXenes’ highly exposed basal plane, 2) the MXene to MXene interface plays a major role in the phase behavior of MXenes, particularly toward building layered transition metal carbides using MXenes as ~1-nm-thick building blocks, and 3) Defects are the primary site at which atomic migration begins during phase transition of MXenes into these highly textured transition metal carbides, and these defects can be engineered for different phase stability of MXenes. To do so, we investigate the phase behavior of Ti₃C₂T_<em>x</em>, Ta₄C₃T_<em>x</em>, Mo₂TiC₂T_<em>x</em>, and other MXenes using a combination of <i>in situ</i> x-ray diffraction and scanning transmission electron microscopy and other <i>ex situ</i> methods, such as secondary ion mass spectrometry and x-ray photoelectron spectroscopy, with other methods. By investigating the fundamentals of the high-temperature phase behavior of MXenes, we hope to establish the basic principles behind use of MXenes as the ideal material for application in future extreme environments.</p>

<p dir="ltr">Shape memory alloys (SMAs) belong to the category of smart materials due to their unique shape memory properties induced by a thermomechanically-triggered phase transformation. This phase changing process is also associated with a pronounced energy dissipation capacity. In recent years, the shape-recovery and energy-dissipating capabilities of SMAs have been object of extensive studies with particular focus on the opportunities they offer for the design of smart composites. The restoring stress of constrained SMAs as well as the modulus change, following thermal loading, can be leveraged to improve the static and dynamic performance, such as the pre/post-bulking behavior, the aerodynamic stability, and the impact resistance of composite materials embedded with SMA wires or fibers. The nonlinear damping resulting from the nonlinear material behavior associated with the ferro-elastic and pseudo-elastic phases was explored in a few studies focusing on vibration suppression in composites. Nonetheless, existing research mainly focused on either SMA wire or fiber reinforced composites, while the understanding of the dynamics of hybrid composites integrating SMA layers still presents several unexplored areas. In part, this technological gap might be explained by the fact that the most common SMA alloy, the so-called Nitinol, is expensive and hence not amenable to be deployed in large scale applications. With the most recent advancements in low-cost SMAs (e.g. Fe-based and Cu-based alloys), new applications that make more extensive use of SMAs are becoming viable. It follows that the understanding of the dynamic response of composites integrating SMA laminae becomes an important topic in order to support the development of innovative hybrid composite structures.</p><p dir="ltr">This dissertation explores the design and the nonlinear dynamic response of hybrid composites integrating SMA laminae, with a particular emphasis on the damping performance under different operating conditions. The dynamic properties of SMA monolithic beams and hybrid composite beams integrated with SMA laminae are investigated via one-dimensional constitutive models. Monolithic SMA beams are investigated to understand the fundamental aspects of the damping capacity of the material as well as possible bifurcation phenomena occurring under different types of harmonic excitations and different levels of pre-strain. The study then focuses on hybrid composite beams, highlighting the effects of design parameters, such the thickness, position, and pre-strain level of SMA layers on the transient and forced dynamic characteristics.</p><p dir="ltr">To further explore the potential of embedding SMA laminae to tailor the damping capacity of the hybrid composite and optimize the distribution of SMA materials, hybrid composite plates (HCPs) assembled by stacking fiber composites and SMA layers (either monolithic or patterned) are explored. The damping capacity of the HCP is assessed under different operating conditions, with emphasis on the effect of pre-strain levels in the SMA layers. The optimization study focuses on understanding the distribution of SMA materials and the synergistic role of patterning and pre-straining individual SMA layers within the HCP. The damping capacity of the HCP is also estimated as a function of the SMA total transformed volume fraction in order to identify the types of patterns and the pre-strain profiles capable of improving the overall damping capacity of the HCP.</p><p dir="ltr">The investigation on the dynamics of SMA hybrid composites continues with the optimal design of sandwich composite beams with elastic face sheets and SMA cellular cores. A deep learning-based surrogate model is proposed to efficiently predict the nonlinear mechanical response of the SMA sandwich beams subject to transverse loading, hence enabling the optimization of the SMA cellular core. The multi-objective optimization of the energy-dissipating capacity and of the overall stiffness is then performed by taking advantage of evolutionary algorithms. Once the optimal geometric parameters of the SMA cellular cores are obtained, finite element simulations are conducted to numerically validate the optimal configurations of the sandwich beams.</p><p dir="ltr">Finally, the numerical models are validated via experimental measurements conducted on monolithic SMA beams. Tests include both tensile and vibration measurements in both the ferro-elastic and pseudo-elastic regimes. The stress-strain relations obtained from tensile tests are used to calibrate the constitutive model of SMAs. Subsequently, experimental vibration tests are performed on clamped-clamped SMA beams to assess the effect of pre-strain levels on the damping capacity of SMA beams via a dedicated experimental setup to apply and maintain the pre-strain levels. The theoretical, numerical, and experimental results provided in this dissertation can serve as important guidelines to design lightweight SMA smart composites with customizable dynamic behavior.</p>

Bacteria are known to adhere to surfaces, which allows for the formation of biofilms, possibly causing a surge in hospital-offset infections, perilous diseases, and in some cases, death. Although certain bacteria are present in the natural flora of the human skin, some present extreme clinical significance due to the ability to transmit and adhere, and can be resistant to antibiotics. They also evolve over time to survive in harsh environmental conditions. Current research reveals that design of plastic surfaces containing submicron structures, is becoming a popular approach to tackle issues concerning infection transmission, with inspiration being derived from biomimetics and self-cleaning surfaces, such as the surface of a gecko skin, and the hydrophobic wax layer of forest leaves. Main barriers to adoption include that these surfaces alone are difficult to manufacture on 3D products, expensive to fabricate on a large scale and do not last long when subjected to environmental wear. Replication of nano-scale ridges was carried out using micro-injection, and the various samples were characterised using a range of tools to determine physical and biomechanical parameters. The sample surfaces were then cultured with the pathogenic bacterium Staphylococcus aureus under several environmental conditions, and the results were statistically analysed to reveal that anti-fouling LIPSS (laser induced periodic surface structures) ridges perform better to reduce bacteria cell-substrate adhesion, when compared to flat surfaces, or surfaces containing dual structures (anti-fouling ridges combined with anti-wear walls). It was therefore demonstrated that nanotextured polymeric surfaces with hydrophobic characteristics have exceptional non-fouling properties, preventing S. aureus, a very significant bacterial strain, from initial adhesion, a critical primary mechanism in its ability to proliferate. Collectively, the findings of this study strongly support the literature, suggesting that the bacteria struggle to adhere onto polymeric topography with increased water contact angles and simple nanostructures. However, the addition of certain anti-wear micro-features increased bacterial adhesion, reducing the efficacy of the non-fouling nanostructures from preventing biofilm formation.

[ES] La presente Tesis Doctoral se centra en la síntesis de nanoestructuras híbridas de TiO2/ZnO para su utilización como fotoelectrocatalizadores durante la producción de hidrógeno a partir de la rotura de la molécula de agua mediante fotoelectrocatálisis y la degradación fotoelectrocatalítica de pesticidas. La principal ventaja de las nanoestructuras híbridas de TiO2/ZnO frente a otros fotocatalizadores basados en materiales semiconductores radica en su capacidad para formar heterouniones en las que se intercalan las bandas de valencia y conducción de ambos semiconductores. Este fenómeno produce una disminución del ancho de banda del fotoelectrocatalizador y de los procesos de recombinación de los pares electrón-hueco fotogenerados y un aumento del rango de absorción de la luz, lo que mejora sus propiedades como fotoelectrocatalizadores. Las nanoestructuras híbridas de TiO2/ZnO obtenidas en la presente Tesis Doctoral se sintetizaron mediante electrodeposición de ZnO sobre nanoesponjas de TiO2. Las nanoesponjas de TiO2 se formaron mediante anodizado electroquímico de titanio en condiciones hidrodinámicas y, posteriormente, se electrodepositó ZnO sobre la superficie de las nanoesponjas de TiO2 modificando la concentración de precursor (Zn(NO3)2 0.5-60 mM), la temperatura (25-75 °C) y el tiempo (15-60 min). Además, se estudió la influencia de electrodepositar ZnO sobre nanoesponjas de TiO2 amorfo o nanoesponjas de TiO2 cristalino, observándose una mejora significativa de la actividad fotoelectrocatalítica de las nanoestructuras híbridas de TiO2/ZnO electrodepositadas sobre nanoesponjas de TiO2 cristalino. Las nanoestructuras híbridas de TiO2/ZnO sintetizadas tuvieron morfología en forma de nanoesponjas, nanobarras hexagonales, nanobarras sin definir y nanoláminas, estudiando la influencia de la concentración de Zn(NO3)2, temperatura y tiempo durante el proceso de electrodeposición de ZnO sobre su comportamiento como fotoelectrocatalizadores. Las nanoestructuras híbridas de TiO2/ZnO sintetizadas se caracterizaron mediante Microscopía Electrónica de Barrido de Emisión de Campo (FE-SEM), Espectroscopía de Energía Dispersiva de Rayos X (EDX), Microscopía Electrónica de Transmisión (TEM), Microscopía de Fuerza Atómica (AFM), Difracción de Rayos X (DRX), Espectroscopía UV-Visible y mediciones de la banda prohibida. Además, se caracterizaron fotoelectroquímicamente mediante ensayos de rotura de la molécula de agua mediante fotoelectrocatálisis y estabilidad frente a la fotocorrosión y electroquímicamente mediante Espectroscopía de Impedancia Fotoelectroquímica (PEIS) y ensayos de Mott-Schottky. Los resultados evidenciaron que las nanoestructuras híbridas de TiO2/ZnO electrodepositadas sobre TiO2 cristalino a 75 °C durante 15 minutos con una concentración de Zn(NO3)2 de 30 mM fueron las más favorables para llevar a cabo aplicaciones fotoelectroquímicas debido a que ofrecieron buena estabilidad frente a la fotocorrosión, elevada respuesta fotoelectroquímica (177 % superior a la de las nanoesponjas de TiO2), baja resistencia a la transferencia de carga y elevada densidad de portadores de carga, en comparación con las nanoesponjas de TiO2. Por último, las nanoestructuras híbridas de TiO2/ZnO óptimas se emplearon como fotoelectrocatalizadores en aplicaciones energéticas y medioambientales. Por un lado, se evaluó la producción teórica de hidrógeno que se obtendría al utilizar las nanoestructuras híbridas de TiO2/ZnO sintetizadas en la presente Tesis Doctoral como fotoánodos durante el proceso de rotura de la molécula de agua mediante fotoelectrocatálisis. Por otro lado, se evaluó la utilización de las nanoestructuras híbridas de TiO2/ZnO óptimas en la degradación fotoelectrocatalítica de pesticidas (Imazalil) en agua, obteniéndose un porcentaje de degradación del 99.6 % llevando a cabo la degradación fotoelectrocatalítica de 10 ppm de Imazalil en Na2SO4 0.1 M durante 24 horas aplicando un potencial de 0.6 V (Ag/AgCl(KCl 3M)). / [CA] La present tesi doctoral se centra en la síntesi de nanoestructures híbrides de TiO2/ZnO per a utilitzar-les com a fotoelectrocatalitzadors durant la producció d'hidrogen a partir del trencament de la molècula d'aigua mitjançant fotoelectrocatàlisi i la degradació fotoelectrocatalítica de pesticides. El principal avantatge de les nanoestructures híbrides de TiO2/ZnO enfront d'altres fotocatalitzadors basats en materials semiconductors radica en la seua capacitat per a formar heterojuncions en les quals s'intercalen les bandes de valència i conducció de tots dos semiconductors. Aquest fenomen produeix una disminució de l'ample de banda del fotoelectrocatalitzador i dels processos de recombinació dels parells electró-forat fotogenerats, i un augment del rang d'absorció de la llum, la qual cosa millora les seues propietats com a fotoelectrocatalitzadors. Les nanoestructures híbrides de TiO2/ZnO es van sintetitzar mitjançant electrodeposició de ZnO sobre nanosponges de TiO2. Les nanosponges de TiO2 es van formar mitjançant anodització electroquímica de titani en condicions hidrodinàmiques i, posteriorment, es va electrodepositar ZnO sobre la superfície de les nanosponges de TiO2 modificant la concentració del precursor (Zn(NO3)2 0.5-60 mm), la temperatura (25-75 °C) i el temps d'electrodeposició (15-60 min). A més, es va estudiar la influència d'electrodepositar ZnO sobre nanosponges de TiO2 amorf o nanosponges de TiO2 cristal·lí, i es va observar una millora significativa de l'activitat fotoelectrocatalítica de les nanoestructures híbrides de TiO2/ZnO en dur a terme el procés d'electrodeposició de ZnO sobre nanosponges de TiO2 cristal·lí. Les nanoestructures híbrides de TiO2/ZnO sintetitzades van tindre morfologia en forma de nanosponges, nanobarres hexagonals, nanobarres sense definir i nanolàmines, i es va estudiar la influència de la concentració de Zn(NO3)2, la temperatura i el temps durant el procés d'electrodeposició de ZnO sobre el seu comportament com a fotoelectrocatalitzadors. Les nanoestructures híbrides de TiO2/ZnO es van caracteritzar mitjançant microscòpia electrònica d'escombratge d'emissió de camp, espectroscòpia de raigs X per dispersió d'energia, microscòpia electrònica de transmissió, microscòpia de força atòmica, difracció de raigs X, espectroscòpia UV visible i mesuraments de la banda prohibida. D'altra banda, es van caracteritzar fotoelectroquímicament mitjançant assajos de trencament de la molècula d'aigua mitjançant fotoelectrocatàlisi i estabilitat enfront de la fotocorrosió, i electroquímicament mitjançant espectroscòpia d'impedància fotoelectroquímica i assajos de Mott-Schottky. Els resultats van evidenciar que les nanoestructures híbrides de TiO2/ZnO electrodepositades sobre TiO2 cristal·lí a 75°C durant 15 minuts amb una concentració de Zn(NO3)2 de 30 mm van ser les més favorables per a dur a terme aplicacions fotoelectroquímiques, pel fet que van oferir bona estabilitat enfront de la fotocorrosió, elevada resposta fotoelectroquímica (un 177 % superior a la de les nanosponges de TiO2), baixa resistència a la transferència de càrrega i elevada densitat de portadors de càrrega, en comparació amb les nanosponges de TiO2. Finalment, les nanoestructures híbrides de TiO2/ZnO òptimes es van emprar com a fotoelectrocatalitzadors en aplicacions energètiques i mediambientals. D'una banda, es va avaluar la producció teòrica d'hidrogen que s'obtindria en utilitzar les nanoestructures híbrides de TiO2/ZnO sintetitzades en la present tesi doctoral com a fotoànodes durant el procés de trencament de la molècula d'aigua mitjançant fotoelectrocatàlisi. D'altra banda, es va avaluar la utilització de les nanoestructures híbrides de TiO2/ZnO òptimes en la degradació fotoelectrocatalítica de pesticides (Imazalil) en aigua, i es va obtenir un percentatge de degradació del 99.6% duent a terme la degradació fotoelectrocatalítica de 10 ppm d'Imazalil en Na2SO4 0.1 M durant 24 h aplicant un potencial de 0.6 V (Ag/AgCl(KCl 3M)). / [EN] This Doctoral Thesis focuses on synthesizing TiO2/ZnO hybrid nanostructures to be used as photoelectrocatalysts in energy and environmental applications, particularly hydrogen production from water splitting by photoelectrocatalysis and photoelectrocatalytic degradation of pesticides. The main advantage of TiO2/ZnO hybrid nanostructures over other photocatalysts based on semiconductor materials is their ability to form heterojunctions in which the valence and conduction bands of both semiconductors are intercalated. This phenomenon produces a decrease in the band gap of the nanostructures, the recombination processes of the photogenerated electron-hole pairs, and an increase in the light absorption range, which improves their properties as photoelectrocatalysts. The TiO2/ZnO hybrid nanostructures formed in this Doctoral Thesis were synthesized by electrodeposition of ZnO on TiO2 nanosponges. First, TiO2 nanosponges were formed by electrochemical anodization of titanium under hydrodynamic conditions (3000 rpm) and, subsequently, ZnO was electrodeposited on the surface of the TiO2 nanosponges by modifying the precursor concentration (Zn(NO3)2 0.5 - 60 mM), the temperature (25 - 75 °C) and the electrodeposition time (15 - 60 min). In addition, the influence of performing the ZnO electrodeposition on amorphous TiO2 nanosponges (before the thermal treatment) or crystalline TiO2 nanosponges (after the thermal treatment) was studied, showing a significant improvement in the photoelectrocatalytic activity of TiO2/ZnO hybrid nanostructures by carrying out the ZnO electrodeposition process on crystalline TiO2 nanosponges. In this Doctoral Thesis, TiO2/ZnO hybrid nanostructures with morphologies of nanosponges, hexagonal nanorods, undefined nanorods, and nanosheets were synthesized by studying the influence of Zn(NO3)2 concentration, temperature and time during the ZnO electrodeposition process. In addition, the performance of TiO2/ZnO hybrid nanostructures as photoelectrocatalysts was studied. The synthesized TiO2/ZnO hybrid nanostructures were characterized morphologically, photoelectrochemically, and electrochemically. On the one hand, they were morphologically characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Diffraction X-Ray (XRD), UV-Visible Spectroscopy and band gap measurements. On the other hand, they were characterized photoelectrochemically by e water splitting and stability against photocorrosion tests and electrochemically by Photoelectrochemical Impedance Spectroscopy (PEIS) and Mott-Schottky tests. The results showed that TiO2/ZnO hybrid nanostructures electrodeposited on crystalline TiO2 at 75 °C for 15 minutes with a Zn(NO3)2 concentration of 30 mM were the most favourable for carrying out photoelectrochemical applications because they offered good stability against photocorrosion, high photoelectrochemical response (177 % higher than that of TiO2 nanosponges), low resistance to charge transfer and high density of charge carriers, compared to TiO2 nanosponges. Finally, the optimal TiO2/ZnO hybrid nanostructures were used as photoelectrocatalysts in energy and environmental applications. On the one hand, the theoretical hydrogen production obtained with the TiO2/ZnO hybrid nanostructures synthesized in this Doctoral Thesis during the water splitting tests was evaluated. On the other hand, the use of the optimal TiO2/ZnO hybrid nanostructures as photoelectrocatalysts in the photoelectrocatalytic degradation of pesticides (Imazalil) in water was evaluated, obtaining a degradation percentage of 99.6 % carrying out the photoelectrocatalytic degradation of 10 ppm of Imazalil in Na2SO4 0.1 M for 24 hours applying a potential of 0.6 VAg/AgCl (3M KCl). / Agradezco al Ministerio de Ciencia e Innovación la concesión de la subvención proporcionada por el Sistema Nacional de Garantía Juvenil (PEJ2018- 003596-A-AR), al Ministerio de Economía, Industria y Competitividad la concesión del proyecto CTQ2016-79203-R y al Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación la concesión del proyecto PID2019-105844RB- I00/MCIN/AEI/ 10.13039/501100011033, en los cuales he podido participar durante el desarrollo de la presente Tesis Doctoral. / Navarro Gázquez, PJ. (2023). Desarrollo de nuevos electrodos basados en nanoestructuras híbridas de óxidos metálicos semiconductores para aplicaciones energéticas y medioambientales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/194708

Since the development of the ruthenium containing precatalysts Grubbs 1 (1) and Grubbs 2 (2), there was an increase in the development of new precatalysts. The NMR characterization could not cope with this. The NMR characterization mainly consists of 1H, 31P, COSY and rarely 13C. Due to the high natural abundance of 1H and 31P (99.98% and 100%), these experiments could be carried out quickly and easily. The only change that had to be made was to the spectral width, to accommodate the carbene signal (Ru=CH) between δ 20.02 and δ 17.32 ppm. The lack of 13C characterization is attributed to the low natural abundance of these nuclei that is only 1.10% and the lack of published parameters. Furthermore, the broad spectral width of 300 ppm increases the difficulty because the number of scans has to be increased to increase the sensitivity of the spectra and obtain useful data. In this study the precatalyst 1 was used to learn the NMR technique as well as to acquire the NMR parameters. 2 and two other commercial Grubbs-type precatalysts 3 and 4 underwent NMR characterization so that acquired values could be compared with the literature. Six other non-commercial Grubbs-type precatalysts 5-10 were synthesized and characterized. Due to the instability of the precatalysts and taking into account the duration of these experiments, the characterization was done over three steps. The first step was to do the following experiments: 1H, COSY, HSQC and HMBC, which took four hours. The next step was the DEPT135 experiment of three hours, and finally the 13C experiment of seven hours. The maximum amount of information could be obtained in this way. The combined NMR parameters for this study was obtained and used to characterize the Grubbs-type precatalysts 5-10 partially. Due to the large amount of overlapping peaks in the aromatic and alkane areas the resolution was not sufficient for full characterization. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Since the development of the ruthenium containing precatalysts Grubbs 1 (1) and Grubbs 2 (2), there was an increase in the development of new precatalysts. The NMR characterization could not cope with this. The NMR characterization mainly consists of 1H, 31P, COSY and rarely 13C. Due to the high natural abundance of 1H and 31P (99.98% and 100%), these experiments could be carried out quickly and easily. The only change that had to be made was to the spectral width, to accommodate the carbene signal (Ru=CH) between δ 20.02 and δ 17.32 ppm. The lack of 13C characterization is attributed to the low natural abundance of these nuclei that is only 1.10% and the lack of published parameters. Furthermore, the broad spectral width of 300 ppm increases the difficulty because the number of scans has to be increased to increase the sensitivity of the spectra and obtain useful data. In this study the precatalyst 1 was used to learn the NMR technique as well as to acquire the NMR parameters. 2 and two other commercial Grubbs-type precatalysts 3 and 4 underwent NMR characterization so that acquired values could be compared with the literature. Six other non-commercial Grubbs-type precatalysts 5-10 were synthesized and characterized. Due to the instability of the precatalysts and taking into account the duration of these experiments, the characterization was done over three steps. The first step was to do the following experiments: 1H, COSY, HSQC and HMBC, which took four hours. The next step was the DEPT135 experiment of three hours, and finally the 13C experiment of seven hours. The maximum amount of information could be obtained in this way. The combined NMR parameters for this study was obtained and used to characterize the Grubbs-type precatalysts 5-10 partially. Due to the large amount of overlapping peaks in the aromatic and alkane areas the resolution was not sufficient for full characterization. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Chapter 1 outlines the aim of the study, research methodology, delimitation of scope and the definition of some terms. This is followed by a list of Zulu short stories which Ntuli has already contributed. His other contributions in circles outside the writing of fiction are also acknowledged. Finally, tribute is paid to some contributions made by Ntuli as an endeavour to uplift the standard of Zulu writing. In Chapter 2 plot structure is discussed. This is followed by an in-depth semiotic analysis of some short stories. Chapter 3 deals with the different narration techniques employed by the author in his short stories. Chapter 4 differentiates between actors and characters. Different methods of character portrayal are investigated. Chapter 5 concludes this dissertation by summarising the main finding of this study. It also brings forth some conclusions with regard to literary merit of Ntuli's short stories and his contribution to Zulu literature. / African Languages / M.A. (African Languages)

Early written Shona narratives like Solomon Mutswairo's Feso [Thorn; name of main character, 1982] evince fantasy since they emanated from folktales, a genre that abounds in this element. Contrary to this, Charles Mungoshi attempts to portray life faithfully in Makunun'unu Maodzamwoyo [Brooding breeds despair, 1977], Ndiko Kupindana Kwamazuva [How time passes, 1975] and Kunyarara Hakusi Kutaura? [Is silence not a form of speech? 1983]. This study attempts to show how this realism manifests itself in the components that constitute each of the works: setting, plot, characterisation, theme and style. Mungoshi's characters, for instance, are not one-sided supernatural beings who perform fabulous acts. Instead, they have strengths and limitations like people in everyday life. Their actions and speech are consistent with their social backgrounds. By injecting realism into the Shona narrative, Mungoshi has contributed towards its development. Due to this realism, the works deserve the label "novels" as opposed to "romances". / African Languages / M.A. (African languages)

The future of human embryonic stem cell (hESC) research with regards to their applicability in a therapeutic setting, relies on the development and standardisation of consistent and robust methods to demonstrate their defining characteristics; their pluripotent ability to form all three germ layers and their capacity for self-renewal. Although much research has been carried out to investigate new methods of culturing hESCs, many of these studies have not robustly concluded the impact of prolonged culture on genetic and genomic stability nor have they examined in any comparative detail the impact of the culture conditions such as differences in feeders used or the media composition in which the stem cells are cultured in. The aim of this thesis therefore was to investigate and evaluate methods for improving the uniform and robust culture and characterisation of hESCs over prolonged periods in culture. Four hESC lines ( RH5, HUES9, SHEF1 and NCL5) were chosen on the basis that they had not previously been well characterised and therefore could potentially benefit the wider stem cell community by increasing diversity, rather than continue to use the already small subset of well publicised lines. The RH5, HUES9, SHEF1 and NCL5 cells were subjected to long term passaging using recombinant enzyme TrypLE™ Express, on human feeders, mouse feeders and feeder free matrix Matrigel in combination with defined media mTeSR1, for uniform scale up. Changes in characteristic stem cell surface markers were compared using two techniques; flow cytometry and quantitative in situ fluorescence microscopy. Genomic stability was assessed by real time PCR. Chromosomal integrity was monitored using array genomic hybridisation (aCGH). Array genomic hybridisation analysis of cells cultured for 20 passages by enzymatic passaging revealed changes in copy number variations in all the stem cell lines. Aberrations on chromosomes 12, 17 and 20, appeared most commonly as a result of long term culture. Although no significant differences were seen between hESCs cultured on mouse and human feeders, cultures on Matrigel showed fewer detected chromosomal aberrations. Expression of cell surface stemness markers SSEA3, SSEA4, TRA1-60 and TRA1-81 were maintained by hESC cultured on all matrices and confirmed by the use of flow cytometry and high throughput quantitative immunofluorescence imaging using the TissueFaxs™ cell analysis microscopy system. In depth imaging revealed subtle but important differences in the way in which hESCs attach and proliferate on different matrices. Genetic profiling of each of the stem cell lines using Taqman Low density array cards to assess the expression of 96 genes by Real Time PCR, demonstrated the continued expression of stemness genes 21 at late passage, and low level expression of differentiation genes, inherent to particular stem cell lines. Although both mouse and human feeders and Matrigel support the undifferentiated growth of hESCs, subtle differences from the hESCs were seen as a result of their use, most obviously, changes in morphology and how they proliferate. This was further explored in the stem cell line NCL5, as it demonstrated a readiness to adapt to new matrices, better chromosomal stability and higher expression of cell surface markers compared with the other hESC lines. Using in vitro differentiation assays to all three germ layers, NCL5 cultured to late passage (p+20) on human feeder iMRC5, mouse feeder iMEF and feeder free matrix Matrigel, demonstrated the ability to differentiate to ectoderm, endoderm and mesoderm progenitors after induction using three 7 day flat based directed differentiation protocols. Altered differentiation patterns were detected by Real Time PCR and TissueFaxs™ imaging and quantitative analysis, as a consequence of the prolonged culture on the specific matrices used. Such key findings allude to the strong influences of microenvironment and will help to improve the standardisation of in vitro differentiation assays. From these studies, chromosomal changes had no impact on NCL5 stem cell lines‘ ability to form progenitors, however small genetic instabilities may still play a role in terminal differentiation of germ lineage specific cell types. The findings of the programme of work described has led to the successful culture methods and characterisation testing validated in this project being incorporated into routine culture and banking of research grade hESCs at the UK Stem Cell Bank. These protocols will now be made more widely available and should assist stem cell researchers in adopting the most suitable and optimum conditions for culturing stem cells in the undifferentiated and stable state. With the huge surge in stem cell research over the past decade, the development of robust characterisation and culture methods will undoubtedly have significant impact on the exploitation of these cells for regenerative medicine and to assist with this a future aim of the stem cell bank will be to standardise methodologies for clinical grade banking.

Polyethylene Terephthalate (PET) is one of the most important polymers in use today for packaging due to its outstanding properties. The usage of PET has grown at the highest rate compared with other plastic packaging over the last 20 years, and it is anticipated that the increase in global demand will be around 6% in the 2010-2015 period. The rheological behaviour, thermal properties, tensile modulus, permeability properties and degradation phenomena of PET/clay nanocomposites have been investigated in this project. An overall, important finding is that incorporation of nanoclays in PET gives rise to improvements in several key process and product parameters together - processability/ reduced process energy, thermal properties, barrier properties and stiffness. The PET pellets have been compounded with carefully selected nanoclays (Somasif MAE, Somasif MTE and Cloisite 25A) via twin screw extrusion to produce PET/clay nanocomposites at various weight fractions of nanoclay (1, 3, 5, 20 wt.%). The nanoclays vary in the aspect ratio of the platelets, surfactant and/or gallery spacing so different effect are to be expected. The materials were carefully prepared prior to processing in terms of sufficient drying and re-crystallisation of the amorphous pellets as well as the use of dual motor feeders for feeding the materials to the extruder. The rheological properties of PET melts have been found to be enhanced by decreasing the viscosity of the PET i.e. increasing the 'flowability' of the PET melt during the injection or/and extrusion processes. The apparent shear viscosity of PETNCs is show to be significantly lower than un-filled PET at high shear rates. The viscosity exhibits shear thinning behaviour which can be explained by two mechanisms which can occur simultaneously. The first mechanism proposed is that some polymer has entangled and few oriented molecular chain at rest and when applying high shear rates, the level of entanglements is reduced and the molecular chains tend to orient with the flow direction. The other mechanism is that the nanoparticles align with the flow direction at high shear rates. At low shear rate, the magnitudes of the shear viscosity are dependent on the nanoclay concentrations and processing shear rate. Increasing nanoclay concentration leads to increases in shear viscosity. The viscosity was observed to deviate from Newtonian behaviour and exhibited shear thinning at a 3 wt.% concentration. It is possible that the formation of aggregates of clay is responsible for an increase in shear viscosity. Reducing the shear viscosity has positive benefits for downstream manufacturers by reducing power consumption. It was observed that all ii three nanoclays used in this project act as nucleation agents for crystallisation by increasing the crystallisation temperature from the melt and decreasing the crystallisation temperature from the solid and increasing the crystallisation rate, while retaining the melt temperature and glass transition temperatures without significant change. This enhancement in the thermal properties leads to a decrease in the required cycle time for manufacturing processes thus potentially reducing operational costs and increasing production output. It was observed that the nanoclay significantly enhanced the barrier properties of the PET film by up to 50% this potentially allows new PET packaging applications for longer shelf lives or high gas pressures. PET final products require high stiffness whether for carbonated soft drinks or rough handling during distribution. The PET/Somasif nanocomposites exhibit an increase in the tensile modulus of PET nanocomposite films by up to 125% which can be attributed to many reasons including the good dispersion of these clays within the PET matrix as shown by TEM images as well as the good compatibility between the PET chains and the Somasif clays. The tensile test results for the PET/clay nanocomposites micro-moulded samples shows that the injection speed is crucial factor affecting the mechanical properties of polymer injection moulded products.