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Die herkoms en die sosiale, ekonomiese en opvoedkundige aspekte van die lewe van die Kleurlinge van Eersterust
(University of Pretoria, 1968-06) Coertze, P.J.; Jacobs, Paul Petrus
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Mineralogy of the lower part of the upper zone, eastern Bushveld Complex : implications for ore-forming processes
(University of Pretoria, 1991) Von Gruenewaldt, G. (Gerhard), 1942-; Harney, Dirk M.W.
English: The lower part of the upper zone in the eastern Bushveld Complex was subjected to a detailed mineralogical investigation, aimed at gaining a better understanding of processes that led to the formation of the main magnetite layer (MML), sulfide-enriched horizons and possible concentrations of platinum-group elements (PGE). The most prominent rock types in the investigated stratigraphic sequence are anorthosites, containing variable amounts of magnetite, which are interlayered with gabbronorites, leuco-gabbronorites and magnetite layers. Elevated sulfide concentrations are commonly associated with magnetite layers. The highest values were found in an anorthosite directly below the MML, and the sulfide assemblage typically contains pyrrhotite, chalcopyrite, cubanite and pentlandite in decreasing order of abundance. PGE are not enriched in specific stratigraphic horizons, as in those known from the critical zone. However, a local concentration of Pt and Pd has been encountered in the sulfide-bearing anorthositic footwall of lower magnetite layer 2. Several Pt-Pd-Bi-Te minerals were found, namely michenerite, moncheite, merenskyite and froodite, and textural as well as compositional evidence indicates that these platinum-group minerals are of hydrothermal origin. Post-magmatic hydrothermal processes also affected the mineralogy and composition of sulfides above the MML. Pentlandite, in particular, reflects such hydrothermal activity and displays varying, but considerably elevated, Co concentrations. Changes in the Sr content and the Sr/Al 2o3 ratio of plagioclase, the whole-rock PGE concentration pattern and possibly also the composition of pyroxene at the level of the MML show that the MML formed in response to a magma mixing event between the resident and a less differentiated magma. Magma mixing resulted either from a breakdown of density stratified liquid layers or an influx of a small volume of new magma (up to 30 % of the hybrid). In addition to the formation of the MML, magma mixing is also believed to have caused the segregation of sulfides associated with that layer. It is concluded that the evolution of the upper zone does not reflect simple differentiation, but that it was interrupted by magma mixing events which occurred at the level of the MML and possibly also at other levels during crystallization of the upper zone. Afrikaans: Die onderste gedeelte van die bosone in die oostelike Bosveldkom-pleks is mineralogies noukeurig ondersoek met die doel om 'n beter begrip te vorm van die prosesse wat aanleiding gegee het tot die ontstaan van die hoofmagnetietlaag (HML), sulfied-verrykte lae en konsentrasies van die platinum-groep elemente (PGE). Die mees algemene gesteente tipes in die stratigrafiese suksessiewat ondersoek is, is anortosiete met varierende hoeveelhede magnetiet, wat tussengelaagd is met gabbronoriet, leukogabbronoriet en magnetietlae. Verhoogde sulfiedkonsentrasies is meestal geassosieer met magnetietlae. Die hoogste konsentrasies kom in 'n anortosietlaag direk onderkant die HML voor. Die mees algemene sulfiedassosiasie bevat, in volgorde van afnemende hoeveelheid, pirrhotiet, chalkopiriet, kubaniet en pentlandiet. Die PGE is nie in enige van die sulfiedgemineraliseerde lae verryk nie. Lokale verryking van Pt en Pd is egter teegekom in die sulfied-draende anortosiet net onder die laer magnetietlaag 2. Verskeie Pt-Pd-Bi-Te minerale is teegekom, te wete micheneriet, moncheiet, merenskyiet en froodiet. Tekstuur en samestelling dui daarop dat hierdie platinumminerale van hidrotermale oorsprong is. Na-magmatiese hidrotermale prosesse het ook die sulfied-mineralogie en samestelling bokant die HML geaffekteer. Veral pentlandiet reflekteer sodanige hidrotermale aktiwiteit en toon varierende, maar aansienlik verhoogde, Co konsentrasies. Veranderings in die Sr-inhoud en die Sr/Al 2o3 verhouding van plagioklaas, die heelgesteente PGE konsentrasiepatroon en moontlik ook die samestelling van pirokseen by die posisie van die HML dui daarop dat hierdie laag moontlik ontstaan het as gevolg van magmavermenging tussen die kristalliserende magma en 'n minder gedifferensieerde een. Magmavermenging kan of die gevolg wees van die ineenstorting van digtheidsgestratifiseerde vloeistoflae, of die gevolg van die invloei van 'n klein volume nuwe magma (tot 30 % van die hibriede produk). Bykomstig tot die ontstaan van die HML, word magmavermenging ook beskou as die oorsaak te wees vir die segregasie van sulfiede geassosieer met die laag. Daar word tot die slotsom gekom dat die ontstaan van die bosone nie die gevolg van 'n eenvoudige differensiasie is nie, maar dat dit onderbreek was deur episodes van magmavermenging soos byvoorbeeld by die HML en moontlik ook op ander tye tydens kristallisasie van die bosone.
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Paternal factors affecting under-five immunization status in Sub-Saharan Africa : a systematic review and meta-analysis
(Elsevier, 2025-10) Musuka, Godfrey; Moyo, Enos; Mano, Oscar; Madziva, Roda; Pierre, Gashema; Iradukunda, Patrick Gad; Sayem, Abu Sadat Mohammad; Dhliwayo, Tapiwa; Herrera, Helena; Mutata, Constantine; Dzinamarira, Tafadzwa
Please read abstract in the article.
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Numerical thermohydraulic investigation of developing mixed convective laminar flow through horizontal tubes with a uniform wall temperature
(Elsevier, 2025-09) Steyn, Deniel; Everts, Marilize; Craig, K.J. (Kenneth)
A numerical investigation of simultaneously developing laminar mixed convective flow in a horizontal tube under a uniform wall temperature (UWT) boundary condition was conducted. Two numerical models were created to examine the differences between experimental and numerical approaches. The first replicated an experimental UWT setup, while the second implemented an ideal UWT boundary condition. Simulations were performed in ANSYS Fluent with temperature-dependent water properties. The Reynolds number and Grashof number ranges were 500-2000 and 0.18×103-9.43×103, respectively. Length-to-diameter ratios varied between 1020 and 1632. The circulation strength of buoyancy-driven vortices was calculated to quantify free convection effects. Higher Grashof numbers intensified the circulation strength and shifted the peak circulation strength upstream. Increased Reynolds numbers delayed the occurrence of peak circulation strength without altering its magnitude. A boundary layer analysis indicated longer thermal and hydrodynamic entrance lengths with higher Grashof numbers or Reynolds numbers. Furthermore, the local Nusselt number decreased from a maximum at the tube inlet to a trough and then increased to a peak before declining to a value of 3.66. Elevated Grashof numbers amplified these trends and shifted the troughs and peaks upstream, whereas increasing Reynolds numbers delayed these extrema points without significantly affecting their magnitudes. Based on circulation strength and boundary layer behaviour, seven thermohydraulic regions were defined: (1) hydrodynamic-merge, (2) free convection increasing, (3) free convection dominating, (4) free convection settling, (5) sustained free convection, (6) hydrodynamically fully developed forced convective flow, and (7) thermally fully developed forced convective flow. HIGHLIGHTS • Seven distinct thermohydraulic regions defined for laminar UWT mixed convective flow. • Thermal and hydrodynamic boundary layer analysis for developing UWT flow. • Quantification of mixed convective flow using circulation strength of buoyancy-induced vortices. • Mathematical justification of increasing local Nusselt numbers for mixed convective flow. • Influence of Grashof and Reynolds number on local Nusselt numbers of mixed convective UWT flow.
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Mixed convective laminar flow through non-circular channels heated at a constant heat flux
(Elsevier, 2025-04) Chen, Qi; Harris, Nikha; Craig, K.J. (Kenneth); Everts, Marilize
Together with the need to improve the thermal efficiency, there is a continuous drive towards miniaturisation and compact heat exchangers using non-circular channels are commonly employed. In this study, mixed convective laminar flow through non-circular channels was numerically investigated using Ansys Fluent 2024R1. The hydraulic diameter of the channels was chosen as 4 mm, 8 mm, and 11.5 mm with aspect ratios (AR) of ½, 1, and 2, while the Reynolds number and heat flux ranges were 1000–1800 and 1–3 kW/m2, respectively. Special attention was given to the local Nusselt number trends, velocity and temperature profiles, and circulation strength along the channels. In general, the local Nusselt numbers increased with increasing hydraulic diameter and heat flux, and decreasing Reynolds number, due to increased buoyancy effects and circulation strength. While an increase in channel height enhanced the secondary flow velocity, an increased in channel width enabled the formation of a secondary vortex pair, which significantly enhanced the thermal performance. The relationship between the circulation strength and Nusselt number was identified, and the local Nusselt numbers increased with increasing heat flux and decreasing Reynolds number. At a fixed circulation strength, improved cross-sectional mixing led to higher Nusselt numbers. The Nusselt numbers increased with decreasing aspect ratio and overall AR = ½ provided the best heat transfer performance for mixed convective flow through non-circular channels. When comparing the single channels results to counterflow multi-channel heat exchangers, the results correlated very well, indicating potential savings in computational costs. HIGHLIGHTS • Decreasing the aspect ratios enhanced circulation strength and mixed convective heat transfer • The formation of secondary vortex pairs leads to increased heat transfer enhancement • Channel width is the key factor determining the formation of secondary vortex pairs • Heat transfer performance increases with increased cross-sectional mixing • Best heat transfer performance obtained using an aspect ratio of ½ • Single channel results can be translated to larger multi-channel systems