3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Probing heavy-quark production vs charged-particle multiplicity in pp collisions at √ s = 5.02 TeV with ALICE(2024) Mdhluli, Joyful ElmaThe differential heavy-flavour (charm and beauty quark) production as a function of the charged-particle multiplicity is investigated in pp collisions at √ s = 5.02 TeV. The heavy-quark production cross section as a function of transverse momentum (pT) and pseudorapidity (η) is also evaluated. The measurement of the inclusive yield of heavy quarks via the single-muon (µ) decay channel is done in the muon spectrometer at forward pseudorapidity (−4 < η < −2.5) and the charged-particle multiplicity using the Silicon Pixel Detector at central pseudorapidity (|η| < 1). These measurements are important in order to gain more insight into which processes are involved in the collision at a partonic level as well as provide information on the interplay between hard and soft mechanisms during particle production. Reference data taken during Run 2 in 2015 and 2017 in pp collisions at √ s = 5.02 TeV are analyzed for measurements of the inclusive heavy-flavour decay muon differential cross-section and heavy-flavour decay muon yield as a function of the charged-particle multiplicity. A total number of 102.7 M (21.34 M) events for the single muon low (high)- pT triggers are analyzed for both measurements. Minimum bias triggered events with multiplicity tracklets > 0 are used for multiplicity estimation. Two methodologies are utilized, the data-driven method and the ”Official Framework”. Results of inclusive heavy-flavour decay muon differential cross-section measured as a function of pT are compared with the theoretical model FONLL, the data and theoretical model are in agreement within systematic uncertainties. The results are also compared with measurements in pp collisions at √ s = 7 TeV, an energy dependence is observed. Results of inclusive heavy-flavour decay muon yield as a function of the charged-particle multiplicity indicated an approximately faster than linear correlation. Comparisons with other heavy-quark measurements vs charged-particle multiplicity is made and the measurements are in agreement at low charged-particle multiplicities. This thesis also reports on the Service Task work done. This entailed tests performed on detector elements of the Muon Chambers (MCH) that suffered high-voltage trips that were repaired during the long shutdown (LS2). The detector elements were successfully repaired and are currently stored as spares for the Run 3 data-taking period.Item In vitro assessment of the toxicity of gold nanoparticles(2019) Vetten, Melissa AnneThe hazard identification of gold nanoparticles forms an essential part of their risk assessment; however, the test methodologies used should be appropriate and applicable to ensure reliable results. In this study, various in vitro testing methodologies used for hazard identification were investigated for their applicability in the testing of gold nanoparticles. Preferable assays were identified, in particular, the use of label-free methodologies, such as the cell impedance based xCELLigence and the CytoViva HSI systems, were found to be ideal in order to avoid optical interference of the nanoparticles with the testing methodology. The recommended tests were then implemented to investigate the effect of size, surface charge and different functional groups in the bronchial epithelial cell line BEAS-2B. Two citrate stabilized gold nanoparticles of 14 nm and 20 nm in diameter were tested. Moreover, the 14 nm polyethylene glycol-liganded AuNPs with either hydroxyl, carboxyl, biotin, nitrilotriacetic acid, or azide negatively charged functional groups, and the positively charged 14 nm polyethylene glycol-liganded AuNP with amine functional group were investigated. The characterization of the physicochemical characteristics and sterility of these nanoparticles were performed prior to the assessment of their toxicity, intracellular uptake and localization, and the mechanism of uptake. The gold nanoparticles tested were not toxic or genotoxic to the BEAS-2B cells, regardless of cellular internalisation. These cellular effects were not influenced by their size or surface charge. On the other hand, surface functionalization influenced uptake, which was shown to be through a caveolin-mediated endocytosis pathway followed by accumulation within vesicles and in the cytosol. However, additional work needs to be conducted to establish the link between different functional groups and their role in endocytosis and subsequent localization and toxicity. In conclusion, the possibility exists for the interference of nanoparticles with in vitro assays and this should be tested prior to their implementation. However, most importantly, the physicochemical characterization of nanoparticles is of utmost importance, which should precede the hazard identification of nanomaterials using these in vitro assays. These in turn, will allow the establishment of the relationship between these characteristics and any observed toxicity, which will aid not only the risk assessment of nanomaterials but also in the establishment of predictive models in the toxicity of newly synthesised nanomaterials.Item High temperature packed bed thermal storage for solar gas turbines(2016) Klein, PeterSolar powered gas micro-turbines present opportunities for off-grid power generation. Due to the intermittent nature of the solar energy supply, existing Solar Gas Turbine (SGT) plants employ hybridisation with fossil fuels to generate dispatchable power. In this work sensible heat and latent heat storage solutions are investigated as a means of increasing the solar share of a SGT cycle, thus reducing the consumption of diesel fuel. The sensible heat storage concept was based on a pressurised packed bed of spherical ceramic particles, using air as the heat transfer fluid. An axisymmetric, two-phase heat transfer model of the system was developed, based on the continuous solid phase approach. The model was successfully validated against experimental data from a packed bed of alumino-silicate particles over the temperature ranges of gas turbine cycles (350-900 °C and 600-900 °C). The validated numerical model was utilised to conduct a parametric design study of a six hour (1.55 MWhth) storage system for a gas micro-turbine. The results show that a high storage efficiency and high utilisation factor can be achieved when combining sensible heat storage in alumina with fossil fuel hybridisation, with somewhat lower values without hybridisation. An analysis of different inventory geometries showed that a packed bed of spherical particles is best suited to pressurised sensible heat storage. The latent heat storage concept was based on a pressurised packed bed of Encapsulated Phase Change Material (EPCM) particles. Sodium sulphate was identified as a suitable phase change material for the gas turbine cycle. The sensible heat storage model was extended to account for intra-particle temperature gradients and phase change within the particles. The intra-particle phase change model was validated against published experimental data for a single EPCM sphere heated and cooled by convection. The full EPCM storage model was further successfully validated against experimental data from a packed bed of macro- encapsulated sodium sulphate particles with alumina shells, up to a temperature of 950 °C. A comparison of the two storage concepts for a 7 m3 bed shows that a packed bed of en- capsulated sodium sulphate particles would have a 36% lower energy storage capacity than a bed of solid alumina particles. This is due to the limited melt fraction in the EPCM bed when a temperature limit is placed on the base. Increasing the packed bed volume to 10.5 m3 would provide a comparable thermal performance to the 7 m3 solid alumina bed, at a 12% lower storage mass. A hybrid three-layer packed bed is proposed to increase the volumetric energy storage density. Modelling shows that this concept could provide a small increase of 5.3% in the amount of energy discharged above 850 °C, compared to the solid alumina particles only.