https://vital.seals.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://vital.seals.ac.za/vital/access/manager/Repository/vital:28265 Wed 13 Mar 2024 14:17:24 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41606 Wed 13 Mar 2024 09:37:38 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27363 Wed 13 Mar 2024 09:16:24 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10495 Wed 12 May 2021 23:47:26 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38621 Wed 12 May 2021 23:43:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27041 Wed 12 May 2021 23:25:12 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38164 Wed 12 May 2021 23:20:52 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20556 Wed 12 May 2021 22:55:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10458 Wed 12 May 2021 22:50:44 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26408 Wed 12 May 2021 22:39:17 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10453 Wed 12 May 2021 22:30:17 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10358 Wed 12 May 2021 22:29:58 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10557 Wed 12 May 2021 22:24:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10423 Wed 12 May 2021 22:17:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10759 Wed 12 May 2021 20:37:37 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10665 Wed 12 May 2021 20:35:59 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10504 Wed 12 May 2021 20:21:45 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:32585 Wed 12 May 2021 20:18:08 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29403 Wed 12 May 2021 20:17:42 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:11078 Wed 12 May 2021 20:13:43 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:39653 Wed 12 May 2021 19:57:13 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29452 Wed 12 May 2021 19:56:02 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27135 Wed 12 May 2021 19:53:02 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10466 Wed 12 May 2021 19:44:39 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30935 Wed 12 May 2021 19:36:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10620 Wed 12 May 2021 19:31:50 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10472 Wed 12 May 2021 19:25:08 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10727 Wed 12 May 2021 19:20:42 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31131 Wed 12 May 2021 19:16:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26370 Wed 12 May 2021 19:14:02 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10375 Wed 12 May 2021 19:10:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10307 Wed 12 May 2021 18:40:02 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10533 Wed 12 May 2021 18:34:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10306 Wed 12 May 2021 18:28:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10688 Wed 12 May 2021 17:58:04 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:21236 Wed 12 May 2021 17:57:20 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:33029 10 and TPI between -1 and 1. Landslides are less pronounced on slope zones where slope gradient is <15˚ and >45˚, profile curvature <0, TWI <8 and >18, SPI <10 and TPI >1. Deep soil profiles ranging between 2.5 and 7 meters are a major characteristic of the study area. Soils are characterized by clay pans at a depth ranging between 0.75 and 3 meters within the profiles. The study area is dominated by clay texture, except for the uppermost surface horizons, which are loamy sand. All surface horizons analysed had the percentage of sand, silt and clay ranging from 33 to 55%, 22 to 40% and 10 to 30% respectively. In the deeper horizons, sand was observed to reduce drastically to less than 23%, while clay increased to greater than 50%. The clay content is very high in the deeper horizons exceeding 35%. By implication, such soils with a very high clay content and plasticity index are considered as Vertisols, with a profound influence in the occurrence of landslides. The top soil predominantly contains more quartz, while subsurface horizons have considerable amounts of illite/muscovite as the dominant clay minerals, ranging from 43% to 47 %. The liquid limit, plasticity index, computed weighted plasticity index (PIw), expansiveness (ɛex) and dispersion ranging from 50, 22, 17, 10 and 23 to 66, 44,34,54 and 64, respectively also have strong implications for landslide occurrence. Landslides are not normally experienced during or immediately after extreme rainfall events but occur later in the rainfall season. By implication, this time lag in landslide occurrence and rainfall distribution, is due to the initial infiltration through quartz dominated upper soil layers, before illite/muscovite clays in the lower soil horizons get saturated. Whereas forest cover reduced from 40 % in 1985 to 8% in 2015, cultivated land and settlements increased from 16% and 11% to 52% and 25% respectively during the same period. The distribution of cultivated land decreased in lower slope sections within gradient group < 15˚ by 59%. It however increased in upper sections within gradient cluster 25˚ to 35˚ by over 85% during the study period. There is a shift of cultivated land to the steeper sensitive upper slope elements associated with landslides in the study area. More than 50% of the landslides are occurring on cultivated land, 20% on settlements while less than 15 % and 10% are occurring on grassland and forests with degraded areas respectively. Landslides in Kigezi highlands are triggered by a complex interaction of multiple- factors, including dynamic triggers and ground condition variables. Topographic hollows are convergence zones within the landscape where all the parameters interact to cause landslides. Topographic hollows are therefore potential and actual landslide sites in the study area. Characterized by deep soil horizons with high clay content dominated by illite/muscovite minerals in the sub soils and profile concave forms with moderately steep slopes, topographic hollows are the most vulnerable slope elements to landslide occurrence. The spatial temporal patterns of landslide occurrence in the study area has changed due to increased cultivation of steep middle and upper slopes. Characterized by deep soil horizons with high clay content dominated by illite/muscovite minerals in the sub soils and profile concave forms with moderately steep slopes, topographic hollows are the most vulnerable slope elements to landslide occurrence. The spatial-temporal patterns of landslide occurrence in the study area has changed due to increased cultivation of steep middle and upper slopes. A close spatial and temporal correlation between land use/cover changes and landslide occurrence is discernible. The understanding of these topographical, pedological and land use/cover parameters and their influence on landslide occurrence is important in land management. It is now possible to identify and predict actual and potential landslide zones, and also demarcate safer zones for community activities. The information generated about the area’s topographic, pedological and land cover characteristics should help in vulnerability mitigation and enhance community resilience to landslide hazards in this fragile highland ecosystem. This can be done through designating zones for community activities while avoiding potential landslide zones. It is also recommended that, tree cover restoration be done in the highlands and the farmers encouraged to re-establish terrace farming while avoiding cultivation of sensitive steep middle and upper slope sections.]]> Wed 12 May 2021 17:50:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10510 Wed 12 May 2021 17:48:52 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20613 500 oC) resulted in a lower rate of reaction and selectivity than when slightly lower temperatures are used (<350 oC) in both reactors, although much difference was noticed in the packed bed flow tubular reactor. Synthesis in the batch reactor needed longer silicon-catalyst activation time, higher pre-heating temperature and higher catalyst amounts as compare to the packed bed flow tubular reactor. Reaction temperature and alcohol flow rate influenced the reaction in both methods. The optimum reaction temperature range and alcohol flow rate was comparable in both reactors (230 to 240 oC) and 0.1mL/min respectively. The effect of alcohol R-group (C1 to C4) on the reaction revealed that conversion and selectivity generally decrease with an increase in carbon chain length in both methods. Ethanol showed highest selectivity (>95% in batch and >97% in flow) and conversion (about 88% in batch and about 64% in flow) as compared to all other alcohols studied showing that it could be the most efficient alkoxylation alcohol for this reaction. Overally, the packed bed flow tubular reactor resulted in higher selectivity to trialkoxysilanes than the batch system. Performing the reaction under pressure resulted in increased conversion but selectivity to the desire trialkoxysilane diminished. Synthesis in a continuous flow falling film tubular reactor was not successful as it resulted in very poor conversion and selectivity. Monosilane was successfully synthesized from the disproportionation of triethoxysilane using homogeneous and heterogeneous catalysts in batch mode. The results obtained from homogeneous catalysis showed that the reaction can be conducted at room temperature. The heterogeneous catalysis method resulted in slow conversion at room temperature but mild heating up to 55 oC greatly improved the reaction. Conducting the reaction under neat conditions produced comparable results to reactions which were carried out using solvents. The disproportionation reaction was best described by the first order kinetic model. The results obtained in this research indicate that the packed bed flow tubular reactor can be utilized with future modifications for continuous flow synthesis of alkoxysilanes as feedstock for the solar-grade silicon production.]]> Wed 12 May 2021 17:32:11 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:39655 Wed 12 May 2021 17:18:59 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:36921 Wed 12 May 2021 17:12:16 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10446 Wed 12 May 2021 16:46:44 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10494 Wed 12 May 2021 16:38:46 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10604 300 cm) Rhizophora trees at Mngazana Estuary. Mortality of Avicennia marina individuals (51-150 cm) was related to tree density indicating intraspecific competition and self thinning. Selective harvesting of particular size classes of Rhizophora mucronata was recorded when comparing length of harvested poles (~301 cm) and the size class distribution of individuals. Taking into account the differences in growth rate for each size class for this species it will take approximately 13 years to attain a height of 390 cm which is the height at which trees are selected for harvesting at this estuary. This is 2.6 times slower than those individuals growing in Kenya. The feasibility of harvesting is dependent on the growth rate of younger size classes to replace harvested trees as well as the rate of natural recruitment feeding into the population. Different harvesting intensity scenarios tested within a matrix model framework showed that limits should be set at 5 percent trees ha-1 year-1 to maintain seedling density at > 5 000 ha-1 for R. mucronata. However harvesting of Bruguiera gymnorrhiza should be stopped due to the low density of this species at Mngazana Estuary. Harvesting of the tallest trees of Avicennia marina can be maintained at levels less than 10 percent ha-1 year-1. Effective management of mangrove forests in South African is important to maintain the current state, function and diversity of these ecosystems. Management recommendations should begin with determining the freshwater requirements of the estuaries to maintain the mouth dynamics and biotic communities and deter the harvesting of (whole) adult trees particularly those species that do not coppice. Further management is needed to ensure that forests are cleared of pollutants (plastic and industrial), and any further developments near the mangroves should be minimized.]]> Wed 12 May 2021 16:26:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10677 Wed 12 May 2021 16:26:06 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10482 Wed 12 May 2021 16:04:46 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:24320 Wed 12 May 2021 15:57:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10489 Wed 12 May 2021 15:51:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10345 Wed 12 May 2021 15:49:56 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41618 Wed 12 May 2021 15:10:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:40886 Wed 12 May 2021 15:09:39 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:40839 Wed 12 May 2021 15:08:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41620 Wed 12 May 2021 15:05:32 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41605 Wed 12 May 2021 14:32:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:40526 Wed 12 May 2021 14:26:38 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:42329 Wed 12 May 2021 14:19:44 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41615 Wed 12 May 2021 14:17:26 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:40885 Wed 12 May 2021 14:15:50 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41598 150 K) a divalent acceptor is extracted with an activation energy varying between samples based on compensation in a range of 90 meV to 70 meV. Photoluminescence measurements show four peaks with recombination mechanisms linked to the native acceptor identified in literature as either the gallium antisite and/or vacant gallium site. A fifth peak observed is attributed to the longitudinal phonon of the native acceptor. InAs and InAsSb epilayer are all grown at a temperature of 600 °C and cell pressure of 600 Torr. InAs is grown at a V/III ratio of 9.5 on GaAs substrate. Photoluminescence of the InAs layer shows two distinct peaks, one of which is an extrinsic band to band recombination. The other is attributed to free electron to acceptor or a donor-acceptor pair transition. An additional weak peak is also observed which is assigned to the longitudinal phonon of the band to band. InAsSb growth was conducted under a range of V/III ratios of 4.8 to 5, with a vapour phase composition of 0.4 to 0.435. Structural analysis via X-ray diffraction showed a 6 % to 12 % solid antimony content. Photoluminescence exhibited a single broad peak for all samples, with extended band tails. Temperature and power dependant analysis of luminescence indicated a convolution of extrinsic band to tail and band to band recombinations. Hall measurements indicated the InAsSb was n-type material with an apparent measured maximum mobility at 120 K of 9.5 × 103 cm2/V.s. and a room temperature apparent mobility of 7.5 × 103 cm2/V.s. Analysis of hall results using a two-layer model calculated a true bulk mobility of the epilayer at room temperature with an increased value of 15.4 × 103 cm2/V.s. The two-layer model details the effects of the surface conduction. From photoconductivity measurements and further analysis a resultant effective lifetime, at room temperature, was found to be on same order of magnitude as that of InAs materials. Application of a single Einstein oscillator extrapolated 0 K energy gaps for two samples of solid Sb contents of 6 % and 12 %, of 354 meV and 332 meV, respectively. Finally consideration was given to the growth of aluminium containing compounds, particularly AlGaSb. Multiple phases were observed under scanning electron microscope showing growth of GaSb regions surrounded by amorphous solid aluminium and/or aluminium oxide phases. The failure of the aluminium to incorporate into the desired crystal structure is speculated to be due to impure precursor introducing oxygen into the films. Additionally, the effectiveness of the gallium precursor compared to the aluminium precursor in helping the removal of the methyl groups at the growth surface, could also promote a preference for GaSb growth.]]> Wed 12 May 2021 13:53:32 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30786 Thu 13 May 2021 13:38:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29284 Thu 13 May 2021 13:20:37 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:36926 Thu 13 May 2021 12:45:50 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:37048 Thu 13 May 2021 08:47:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10339 Thu 13 May 2021 07:36:07 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:36664 NSN2 (148.55 mg/g) > NNN1 (131.88 mg/g) > NNN2 (75.87 mg/g). The bis-benzimidazole derivatives preference for metal ions was further investigated with a multi-element solution containing Rh(III), Ir(III), Pt(II), Pd(II) and Ni(II). The bis-benzimidazole derivatives showed the following order of loading capacity: NSN1 (47.28 mg/g) > NSN2 (23.89 mg/g) > NNN1 (17.47 mg/g) > NNN2 (14.91 mg/g) for Rh(III); NSN2 (10.64 mg/g) > NNN2 (6.84 mg/g) > NSN1 (5.74 mg/g) > NNN1 (5.02 mg/g) for Ir(III); NNN2 (33.96 mg/g) > NSN1 (30.95 mg/g) > NSN2 (19.95 mg/g) > NNN1 (14.92 mg/g) for Pt(II); NNN1 (47.94 mg/g) > NNN2 (28.90 mg/g) > NSN1 (16.22 mg/g) > NSN2 (15.83 mg/g) for Pd(II). Bis-benzimidazole derivatives showed no uptake of nickel(II) under these conditions. It was observed the ligand-selectivity order for Rh(III) was similar in both single-element and multi-element studies. This order showed that the bis-benzimidazoles containing a sulfur atom showed a high preference for rhodium(III) compared to Pt(II) which had a high preference for NNN2 as well as Pd(II) which had a high preference for NNN1. Ir(III) generally had a lower preference for the ligands presumably due to its higher kinetic inertness compared with Rh(III). Column sorption of [IrCl6]2- and [RhCl5(H2O)]2- on nanofibers functionalized with diammonium cations was carried out and the loading capacities of [IrCl6]2- were obtained. [RhCl5(H2O)]2- was not adsorbed by the sorbent materials while [IrCl6]2- was loaded onto the column. The loading capacities of [IrCl6]2- with the quaternary diammonium sorbent materials increased in the order of F-QuatDMDAMeBnz (60.29 mg/g) < F-QuatDMDABnz (67.61 mg/g) < F-QuatDMDACF3Bnz (107.59 mg/g) < F-QuatDMDANO2Bnz (140.47 mg/g). The loading capacity for Ir(IV) with quaternary diammonium cationic nanofibers increased with an increase in the electron-withdrawing nature of the quaternizing group. The charge delocalizing ability of the nitrobenzyl group resulted in the best interaction of the diammonium cation with [IrCl6]2-. Batch equilibrium studies were carried out to assess the efficiency of bis-benzimidazole chelating derivatives as adsorbents using a multi-metal solution (Rh(III), Ir(III), Pt(II), Pd(II) and Ni(II)) in 0.5 M HCl. The efficiency of the quaternary diammonium cations was tested using a binary metal solution (Ir(IV) and Rh(III)) in 6 M HCl. The isothermal batch adsorption studies of a multi-metal solution with bis-benzimidazoles derivatives fitted the Langmuir isotherm model which confirmed monolayer adsorption onto a homogeneous surface. The Langmuir isotherm parameter (qe (mg/g)), using functionalized nanofibers, showed the order of NNN2 (128.21 mg/g) > NSN1 (99.01 mg/g) > NSN2 (91.74 mg/g) > NNN1 (84.03 mg/g) for Pt(II); NNN1 (66.23 mg/g) > NNN2 (5.89 mg/g) > NSN1 (1.40 mg/g) > NSN2 (0.59 mg/g) for Pd(II); NSN2 (10.64 mg/g) > NNN2 (6.84 mg/g) > NSN1 (5.74 mg/g) > NNN1 (5.02 mg/g) for Ir(III); NSN1 (140.85 mg/g) > NSN2 (109.89 mg/g) > NNN1 (104.17 mg/g) > NNN2 (91.74 mg/g) for Rh(III). The pseudo-first-order kinetics model was found to be the best fit to describe the adsorption kinetics of all metal ions onto all the sorbent materials. K1 (min-1) value in pseudo-first-order kinetics showed the same order of adsorption as observed in the Langmuir isotherms. The isothermal batch adsorption studies of [IrCl6]2- and [RhCl5(H2O)]2- with quaternary diammonium cations fitted the Freundlich isotherm model and confirmed to be effective for multiple-layered adsorption onto a heterogeneous surface. The Freundlich isotherm parameter (kf (mg/g)) using functionalized quaternary diammonium cationic nanofibers increased in the order of F-QuatDMDANO2Bnz (794.33 mg/g) > F-QuatDMDACF3Bnz (185.35 mg/g) > F-QuatDMDABnz (156.32 mg/g) > F-QuatDMDAMeBnz (112.46 mg/g) for Ir(IV) uptake. F-QuatDMDANO2Bnz resin showed the highest adsorption than that of F-QuatDMDAMeBnz, F-QuatDMDABnz and F-QuatDMDACF3Bnz and this order is similar to what was observed in column studies. The quaternary diammonium cations were shown to have the highest adsorption capacity for Ir(IV) compared with Rh(III). The adsorption of Rh(III) was also observed to increase in the order of F-QuatDMDANO2Bnz (177.83 mg/g) > F-QuatDMDACF3Bnz (40.37 mg/g) > F-QuatDMDABnz (36.98 mg/g) > F-QuatDMDAMeBnz (12.71 mg/g). The pseudo-second-order kinetic model was found to be the best fit to describe the adsorption kinetics of both metal ions onto all the sorbent materials. K2 (g.mg-1min-1) value in pseudo-second-order kinetics showed the same order of adsorption as observed in the Freundlich isotherms. The adsorption studies showed adsorption takes place via chemisorption process. This thesis presents PGMs and iridium-specific materials that could be applied in solutions of secondary PGMs sources containing rhodium, platinum and palladium with bis-benzimidazoles as well as in feed solutions from ore processing with diammonium cations for iridium recovery.]]> Thu 13 May 2021 07:20:28 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:21137 Thu 13 May 2021 07:18:53 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10641 Thu 13 May 2021 07:16:53 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10338 Thu 13 May 2021 07:01:58 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26925 Thu 13 May 2021 06:52:01 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20441 Thu 13 May 2021 06:50:39 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:32266 Thu 13 May 2021 06:46:04 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38169 Thu 13 May 2021 06:45:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20793 Thu 13 May 2021 06:37:01 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10321 sCD23>derCD23) for IgE, upon increasing length of the proximal CD23 “stalk” domain. These findings highlight the differences in both the structural basis and affinity of the three physiological fragments of human CD23 for the ligands CD21 and IgE and underscore the complexity of CD23-mediated regulatory networks. It was found that B-cells only make up ~5% of the PBMC population, and that these cells were able to be activated, via STAT-6 phosphorylation, to enter class switch recombination (CSR) by the addition of switch factors (IL-4 and anti-CD40). Titration experiments dictated that 25 ng/mL of CD23 was the most efficient concentration to up-regulate IgE synthesis in PBMCs; furthermore, soluble CD23 proteins were incubated with PBMCs in the presence and absence of CD21 SCR 1-2 to investigate the effect that these recombinant proteins have on IgE synthesis. Results showed that the influence of recombinant proteins (both CD23 and CD21) on IgE synthesis was slight. It was shown that while derCD23 had no significant effect, monomeric sCD23 down-regulated, and the mixture of monomeric and oligomeric exCD23 up-regulated IgE synthesis. On addition of CD21 SCR 1-2 to the cells switched and treated with soluble CD23, it was found that in both cases for sCD23 and exCD23, IgE synthesis was increased, while for derCD23, there was no noticeable difference in IgE synthesis. This confirmed previous data showing the lack of binding between derCD23 and CD21 SCR 1-2. The exact binding site for CD21 on the CD23 molecule is unknown, and incompletely represented in the NMR and crystal structures. It is thought that CD21 binds to the C-terminal tail section, not present in derCD23. It is therefore likely that only a negative-feedback mechanism operates with derCD23 to regulate IgE synthesis. Further investigation of the binding of CD23 fragments to SCR 5-8 of CD21 and the effect of this on IgE synthesis may lead to a potential therapeutic role for derCD23 in the treatment of allergic disease. Data accumulated in this study suggests that investigating the modulation of oligomeric state and thus the activity of soluble CD23 fragments may be important in the construction of new regulators of IgE synthesis.]]> Thu 13 May 2021 05:44:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31347 Thu 13 May 2021 05:31:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31640 Thu 13 May 2021 05:23:01 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:33442 Thu 13 May 2021 05:11:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:34276 Thu 13 May 2021 05:07:10 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29504 Thu 13 May 2021 05:06:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30537 B ± 0.1ᵒ and (111) ± 0.1ᵒ] using similar growth conditions yielded a higher dot density on the (100) substrate compared to the (111) substrate. This was attributed to the presence of terraces/atomic steps induced by the misorientation on the (100) substrate, which invariably gives rise to increased adsorption and an enhanced sticking coefficient of adatoms. Studies on the influence of a buffer layer on the morphology of uncapped dots showed that the shape and size of the dots are sensitive to the thickness of the buffer layer. In some case a corrugated buffer surface resulted, which introduced order in the arrangement of the dots, which formed preferentially inside the troughs. An increase in the V/III ratio from 1.0 to 3.0 was found to reduce the areal density of the QDs, while an analysis of the diameter histograms showed a narrowing of the size distribution with an increase in V/III ratio. The larger size distribution at low V/III was ascribed to the increase in indium species and the increased indium adatom migration length. This leads to increased dot density and nucleation sites, and thus triggers an increase in the conversion of tiny QDs into thermodynamically more suitable larger dots via coalescence. However, as the V/III ratio increased, the number of indium adatoms available for growth on the surface reduced, which automatically led to a decrease in the migration length of indium species which is unfavourable for the production of nucleation sites and to a decrease in dot density. Low growth rates were found to be beneficial for the growth of a high density (~5×1010cm-2) of QDs. Photoluminescence (PL) analysis of the capped samples at low temperature (~10 K), using an excitation power of 2 mW, showed a PL peak at ∼732 meV. Upon an increase in laser power to 120 mW, a blue shift of ∼ 8 meV was noticed. This emission typically persisted up to 60–70 K. An increase in the number of InSb QD-layers, was observed to cause an increase in the luminescence spectral line width and a long-wavelength shift of the PL lines, together with an enhancement in the strength of the PL emission. However, high resolution transmission electron microscopy (HRTEM) of the capped dots revealed the formation of an InGaSb quantum well-like structure, ∼10 nm thick, which was responsible for the PL signal mentioned above. The absence of QDs in the capped sample was attributed to inter-diffusion of Ga and In during the deposition of the cap layer, giving rise to a quantum well (QW) instead of the intended QDs. The presence of threading dislocations and stacking faults were also observed in the TEM micrographs of the samples containing multilayers, which can account for the fast quenching of the PL emission with increasing temperature from these samples. Theoretical simulations of the band alignment, wave functions and energy levels were in good agreement with the data collected from the PL spectra of the samples.]]> Thu 13 May 2021 04:56:31 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:33941 Thu 13 May 2021 04:07:46 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28900 Thu 13 May 2021 03:48:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:33447 Thu 13 May 2021 03:47:57 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:11093 Thu 13 May 2021 03:35:04 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29731 Thu 13 May 2021 03:32:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:34124 Thu 13 May 2021 02:13:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10376 Thu 13 May 2021 01:56:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29817 m-toluidine > o-toluidine) and the cresols (p-cresol > m-cresol > o-cresol). Each guest mixture was selected based on data from experiments using either the industrial significance of its separation or because the mixture would add to the knowledge base of the host compound’s preferences and selectivities. In a separate study, TETROL and its derivative, (–)-(2R,3R)-2,3-dimethoxy-1,1,4,4- tetraphenylbutane-1,4-diol (DMT), were also allowed to compete for the inclusion of the guest cyclohexanone, where TETROL demonstrated superior ability. This host, in addition, showed potential for the separation of cis- and trans- 2-methylcyclohexanol.]]> Thu 13 May 2021 01:55:11 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38163 Thu 13 May 2021 01:42:53 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26866 Thu 13 May 2021 01:38:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10643 Thu 13 May 2021 01:30:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10340 Thu 13 May 2021 01:22:10 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10368 99.9 % certainty) potential in two of the semi-organic mixtures formulated while the organic mixture showed a relatively good growth rate as compared to the control (pure tap water). According to statistical analysis (ANOVA) comparison, two of the semi-organic mixtures performed considerably better than the two commercial samples evaluated. Potential benefits profoundly associated with these nutrient mixtures as compared to similar liquid fertilizer products on the market is that most nutrients are chelated and dissolved in solution. Also, the mixtures contain all necessary nutrients including plant growth substances required for healthier plant growth. The most important socioeconomic impact is the value addition to the technology chain in the citrus industry. The use of fluid fertilizers in significant quantities is less than twenty years old. Nevertheless, growth has been so rapid that in South Africa demand for mixed liquid fertilizer has greatly increased from 90 000 tons NPK & blended micronutrients in 1955 to more than 600 000 per annum tons today (Report 41/2003, Department of Minerals and Energy). The liquid fertilizers market is sparsely specialized with major competitors like Omnia, Kynoch and Foskor supplying more than 50 % of the market demand. Amongst the nutrient mixtures formulated, mixture one is an NPK (1-1-2) based nutrient mixture containing both secondary nutrients (0.5 % Mg & 1.0 % Ca) and seven micronutrients (0.1 % Fe, 0.05 % Cu, 0.05 % Zn, 0.05 % Mn, 0.02 % B, 0.0005 % Mo and 0.0005 % Co). The composition of this mixture offers the formula a potential to be used as a general purpose (all stages of plant growth) fertilization mixture in view of its balanced composition (containing all essential plant nutrients). Mixture two contains essentially the micronutrients and in higher concentrations (0.3 % Fe, 0.3 % Cu, 0.1 % Zn, 0.2 % Mn, 0.02 % B, 0.0005 % Mo and 0.0005 % Co) as compared to mixture one except for boron, molybdenum and cobalt. The concentration of the micronutrients contained in this mixture is adequately high which offers a potential for it to be used in supplementing nutrition in plants with critical micronutrient-deficient symptoms. Mixture three is very similar to mixture two (1.0 % Fe, 0.05 % Cu, 0.05 % Zn, 0.05 Mn, 0.05 % B, 0.0005 % Mo and 0.0005 % Co) except that the concentrations of all seven micronutrients are considerably less than those of contained in mixture two. However, the concentration of iron in this mixture is as high as 1.0 %. The mixture has a potential to be used in high iron-deficient situations. Mixture four is an organic formula with relatively low nutrient concentrations (NPK-0.02-0.02-1, 0.27 % Mg, 0.02 % Ca, 0.008 % Fe, 0.26 % Cu, 0.012 % Zn, 0.009 % Mn). Nevertheless, this mixture is appealing for organically grown crops where the use of chemicals is prohibited by standards. These lemon juice-based nutrient mixtures were further characterized and tested for stability and storability over a period of eight weeks. This study revealed no major change in the physical quality (colour, pH and “salt out” effect). The basic formulation methodology is a two-step procedure that involves filtration of the lemon juice to remove membranous materials, mixing at ambient temperature and stabilization of the nutrient mixtures. However, for the organic nutrient formula mix, filtration follows after extraction of nutrients from plant materials using the lemon juice.]]> Thu 13 May 2021 01:15:13 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10542 Thu 13 May 2021 00:41:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10425 Thu 13 May 2021 00:38:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:34047 Thu 13 May 2021 00:29:28 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38922 Thu 13 May 2021 00:25:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:10537 580 ˚C) growth temperatures reduce the Mg incorporation. High VI/II ratios also decrease the Mg incorporation, as evidenced by the red-shift of the donor bound exciton (D°X) line. This is ascribed to a stronger premature reaction between (MeCp)2Mg and the oxidant or a preferential heterogeneous interaction between the Mg and oxygen species on the growth front. For both oxidizing agents (O2 and TBOH), the growth at 420 ˚C and a VI-II ratio of 60 on c-Al2O3 gave optimal quality layers in terms of their optical and structural quality. A comparison of films grown using TBOH and O2 gas as oxidizing agent shows no major difference in terms of Mg incorporation. The effect of annealing, the inclusion of a buffer layer and the influence of growth rate on the properties MgxZn1-xO thin films are also reported.]]> Thu 13 May 2021 00:01:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29314 Mon 22 Aug 2022 14:58:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:36669 Fri 15 Mar 2024 13:06:48 SAST ]]>