http://vital.seals.ac.za:8080/vital/access/manager/Index ${session.getAttribute("locale")} 5 http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:28265 Wed 13 Mar 2024 14:17:24 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:41619 80 μg∙L-1, ≥ 2781 H. akashiwo cells∙mL-1). Dissolved oxygen differed significantly by bloom state, with the highest dissolved oxygen concentrations. Larval fish density, diversity and community structure variability were lower during hypereutrophic blooms compared to standard blooms and bloom absence, albeit statistically insignificant. Estuarine resident larval density was negatively correlated with dissolved oxygen concentration (P < 0.001). Dominant prey copepod of G. aestuaria larvae, P. hessei, was less abundant and variable during hypereutrophic blooms (mean: 664, range: 4-4301 individuals per m3) compared to standard blooms (mean: 950, range: 2-5237 individuals per m3) and bloom absence (mean: 1182, range: 23-7259 individuals per m3). Although HABs did not appear to drive a mismatch between prey and G. aestuaria larvae, early juvenile larvae made only a small contribution to the assemblage (0.2-1.8%). In terms of predator effects, yolk sac larvae were negatively related to R. terranatalis (P < 0.05). A significant positive relationship was found between prey, P. hessei and G. aestuaria preflexion (P < 0.001), flexion (P < 0.001) and postflexion (P < 0.05) larvae. In a world first, the effects of HABs were investigated on a larval fish species, Gilchristella aestuaria, using biochemical body condition analyses. During severe bloom conditions, G. aestuaria larvae were smaller and the assemblage consisted of mainly early developmental stages (stats). Body condition (RNA per dry weight) was poorest in the presence of hypereutrophic blooms (P < 0.001). A bell-curved relationship between RNA/DW and dissolved oxygen concentration was also produced in a 3-day time-lagged GAM (P < 0.001). In conclusion, hypereutrophic bloom conditions appeared to trigger adult G. aestuaria spawning in the upper mesohaline zone of the estuary in response to heightened primary productivity which occurs during the early bloom stage. However, reductions in copepod abundance (P. hessei) and unfavourable oxygen concentrations interfered with grow-out of G. aestuaria larvae. This research showed that HABs can alter nursery properties to the detriment of G. aestuaria larvae can have serious knock-on effects up the food chain. The loss in abundance of adult, juvenile and larval G. aestuaria, a key forage fish in South African estuaries, has major implications for estuarine food webs, especially in reduced prey availability to juvenile fishes and birds. There is still much to learn about the effects of HABs on the physiological and behavioural aspects on plankton communities worldwide.]]> Wed 13 Mar 2024 14:10:51 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:32483 Wed 13 Mar 2024 11:50:54 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20443 Wed 13 Mar 2024 11:43:41 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:41606 Wed 13 Mar 2024 09:37:38 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27363 Wed 13 Mar 2024 09:16:24 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:30786 Thu 13 May 2021 13:38:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20677 Thu 13 May 2021 13:21:29 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:29284 Thu 13 May 2021 13:20:37 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:36926 Thu 13 May 2021 12:45:50 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10430 Thu 13 May 2021 11:17:38 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26423 Thu 13 May 2021 08:53:16 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26827 Thu 13 May 2021 08:53:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10532 Thu 13 May 2021 08:50:32 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:37048 Thu 13 May 2021 08:47:30 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10329 Thu 13 May 2021 08:22:46 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:32396 80 mm) showed a greater component of invertebrates in previously unexplored habitats, which proves their omnivorous diet related to ontogenetic niche use. Knowledge of fine-scale habitat use by fishes is essential for conservation planning as exclusion zones can be optimised to limit anthropogenic influence on nursery use patterns in fishes. The availability of shallow water habitats (<60 cm) was assessed as an additional driver to explain the species diversity and richness of juvenile fishes within the lower reaches. These habitats are known as important nursery habitats providing numerous marine and estuarine spawned fishes with adequate refuge and food supply. This shallow water volume was measured by means of a two-man kayak using both the spring high and low tides in the lower reaches of these systems to assess juvenile assemblages. It was clear from the results that aquatic vegetation significantly adds to the volume of these areas and as a result, much greater fish density and species richness were observed. Generalized additive models showed that marine spawned species were particularly reliant on the availability of this shallow water along with submerged vegetation and additional environmental variables. The presence of structurally submerged vegetation typically characterized within shallow estuarine waters is commonly believed to reduce predation risk resulting in elevated densities of biota. Based on the current stock status and percentage of pristine breeding stock, five fish species classified as collapsed/overexploited was consistently found within these systems with an additional 14 species currently classified as exploited/vulnerable. Based on the current species richness and diversity, available habitat cover and knowledge regarding important recreational species, priority areas that require some form of legal protection in order to meet potential biodiversity targets, could be identified. It is a legal requirement in South Africa that all estuaries require management plans that should be based on good knowledge of priority habitats for fauna and flora. The identification of estuarine protected areas is seen as a mechanism for protecting a representative sample of the biodiversity accompanied by a complete range of environmental gradients and habitat types at a reasonable scale in order to maximize the protection of estuarine species.]]> Thu 13 May 2021 08:20:19 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27888 Thu 13 May 2021 08:19:50 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26960 Thu 13 May 2021 07:38:12 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10339 Thu 13 May 2021 07:36:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10637 7 days) but could survive submergence of short duration (< 7 days) through continuous underwater photosynthesis, accumulation of osmolytes such as oxalic acid and carotenoid, and maintenance of relative water content and succulence within control levels. When considered together, results showed that the two upper intertidal species were sensitive to waterlogging and would not survive complete submergence, whereas the lower intertidal species could in addition to its natural range, thrive in conditions typical of the upper intertidal range, namely prolonged dry conditions and high sediment salinity. These results have important implications for the future management of salt marshes under predicted climate change conditions. In permanently open South African estuaries, a landward migration of salt marsh will be possible if coastal squeeze is limited and the rate of landward recruitment is on par with sea level rise. In this case salt marsh species would retain their current zonation while shifting inland. Increased sea storms and saltwater intrusion could lead to high salinity concentration in the sediment and significantly reduce growth of salt-sensitive plants. In estuaries that are temporarily open to the sea, reduced freshwater inflow will result in an increase in mouth closure, high water levels, prolonged submergence, and consequently die back of salt marsh vegetation. On the other hand increased abstraction and drought would result in low water levels and high sediment salinity which would decrease growth and survival of salt marsh. This research has provided new knowledge on the ecophysiology of salt marsh plants which can be used to predict the responses of plants to climate change.]]> Thu 13 May 2021 07:33:25 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:35989 Thu 13 May 2021 07:31:09 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10391 Thu 13 May 2021 07:30:13 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27835 Thu 13 May 2021 07:25:57 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26968 _D 2 suffciently large, a non-constant positive solution is generated, that is, stationary patterns emerge, depicting dispersal of species. Predators were observed to occupy habitats surrounding prey. However, super-predators were observed to alternate their habitats, from staying away from prey to invading prey habitat. In the investigation, strategies to determine ways in which the predator species could be saved from extinction and its population improved were devised, and these included isolation of the predator from the super-predator.]]> Thu 13 May 2021 07:24:20 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:39314 Thu 13 May 2021 07:23:53 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10598 Thu 13 May 2021 07:20:35 SAST ]]> http://vital.seals.ac.za:8080/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 ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10427 Thu 13 May 2021 07:20:06 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10670 Thu 13 May 2021 07:19:36 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21137 Thu 13 May 2021 07:18:53 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10559 Thu 13 May 2021 07:18:21 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10641 Thu 13 May 2021 07:16:53 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10449 Thu 13 May 2021 07:13:00 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10507 Thu 13 May 2021 07:05:24 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10406 Thu 13 May 2021 07:03:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10672 Thu 13 May 2021 07:02:31 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10338 Thu 13 May 2021 07:01:58 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26925 Thu 13 May 2021 06:52:01 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20441 Thu 13 May 2021 06:50:39 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:30432 Thu 13 May 2021 06:47:35 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:32266 Thu 13 May 2021 06:46:04 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:38169 Thu 13 May 2021 06:45:15 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20793 Thu 13 May 2021 06:37:01 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21071 Thu 13 May 2021 06:31:44 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:30854 Thu 13 May 2021 06:20:56 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10603 Thu 13 May 2021 06:19:11 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10607 Thu 13 May 2021 06:16:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10979 Thu 13 May 2021 06:15:42 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:36231 Thu 13 May 2021 06:13:26 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21141 Thu 13 May 2021 06:11:45 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10550 Thu 13 May 2021 05:57:43 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:30585 Thu 13 May 2021 05:45:06 SAST ]]> http://vital.seals.ac.za:8080/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 ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26433 0.3. The possibility that Si could become a DX-centre in AlxGa1-xN was then investigated. However, Hall effect measurements showed that the Si activation energy increased in good agreement with the model of a shallow effective mass state donor, with no sudden increase in ED being observed up to x = 0.4. It was then suggested that the increase in the E1 and E2 activation energies, as well as the exciton localisation energies, could be due to the 9 7 valence band crossover, which occurs at roughly the same composition. However, due to the scarcity of reports on the valence band structure in AlxGa1-xN no conclusions could be made at this stage as to the effect of the 9 7 valence band crossover on the PL properties of AlxGa1-xN.]]> Thu 13 May 2021 05:42:11 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:31374 Thu 13 May 2021 05:35:24 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:30579 Thu 13 May 2021 05:34:31 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:31347 Thu 13 May 2021 05:31:19 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21001 Thu 13 May 2021 05:30:49 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10613 Thu 13 May 2021 05:28:58 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10397 Thu 13 May 2021 05:26:59 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:32669 Thu 13 May 2021 05:24:44 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:31640 Thu 13 May 2021 05:23:01 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10502 Thu 13 May 2021 05:15:37 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:33442 Thu 13 May 2021 05:11:34 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:34276 Thu 13 May 2021 05:07:10 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:29504 Thu 13 May 2021 05:06:49 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10444 Thu 13 May 2021 05:01:05 SAST ]]> http://vital.seals.ac.za:8080/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 ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27153 Thu 13 May 2021 04:53:06 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10506 (Kw + $) −W . This result shows that the warthog’s equilibrium population density is bounded above by population thresholds, i.e., W < (Kw+$). Besides showing the occurrence under parameter space of the so-called paradox of enrichment, early indicators of chaos can also be deduced. In addition, numerical results revealed stable oscillatory behaviour and stable spirals of the species as predator fertility rate, mortality rate and prey threshold were varied. The stabilising effect of prey refuge due to variations in predator fertility and proportion of prey in the refuge was studied. Formulation and analysis of a robust mathematical model for two predators having an overlapping dietary niche were also done. The Beddington-DeAngelis functional and numerical responses which are relevant in addressing the Principle of Competitive Exclusion as species interact were incorporated in the model. The stabilizing effect of additional food in relation to the relative diffusivity D, and wave number k, was investigated. Stability, dissipativity, permanence, persistence and periodicity of the model were studied using the routine and limit cycle perturbation methods. The periodic solutions (b 1 and b 3), which influence the dispersal rate (') of the interacting species, have been shown to be controlled by the wave number. For stability, and in order to overcome predator natural mortality, the nutritional value of predator additional food has been shown to be of high quality that can enhance predator fertility gain. The threshold relationships between various ecosystem parameters and the carrying capacity of the game park for the prey species were also deduced to ensure ecosystem persistence. Besides revealing irregular periodic travelling wave behaviour due to predator interference, numerical results also show oscillatory temporal dynamics resulting from additional food supplements combined with high predation rates.]]> Thu 13 May 2021 04:45:04 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21109 Thu 13 May 2021 04:42:08 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:33939 Thu 13 May 2021 04:32:53 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10303 Thu 13 May 2021 04:27:58 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10606 Thu 13 May 2021 04:26:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:36280 Thu 13 May 2021 04:21:00 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10544 Thu 13 May 2021 04:18:24 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10548 Thu 13 May 2021 04:10:03 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:11085 Thu 13 May 2021 04:09:09 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:33941 Thu 13 May 2021 04:07:46 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10404 Thu 13 May 2021 04:05:40 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10538 Thu 13 May 2021 04:03:36 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10668 Thu 13 May 2021 03:57:49 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:28258 Thu 13 May 2021 03:57:46 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10711 Thu 13 May 2021 03:54:12 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10323 Thu 13 May 2021 03:53:26 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10555 Thu 13 May 2021 03:51:44 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:28900 Thu 13 May 2021 03:48:41 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:33447 Thu 13 May 2021 03:47:57 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:39320 0oC, and partly due to the thermodynamic equilibrium between two stereoisomers. An economically alternative process was developed, evaluated and scaled-up in a 2l reactor. The project was initiated with a specific limitation in terms of the starting material that comprised a mixture of plant sterols, which necessitated a study of the isolation and purification of the desired product from a rather complex reaction mixture. The use of silver as halide acceptor for the Koenigs-Knorr synthesis did not give statistically significant different results from the same approach but using cadmium as halide acceptor instead. However, using the direct O-glucosylation approach not only gave statistically significant higher results, but also resulted in a much more convenient procedure. Under optimum conditions, a yield of approximately 83% (isolated) of 2,3,4,6- tetra-О-acetyl-β-sitosterol-D-glucoside could be achieved, which was substantially higher than that achieved with the traditional Koenigs-Knorr methodology and above reported yields in the literature (60-80%) for direct glycosylation. Separation of 2,3,4,6-tetra-О-acetyl-β-sitosterol-D-glucoside (BSSGT) from a reaction mixture that contains 2,3,4,6-tetra-О-acetyl-campesterol-D-glucoside (CSGT), 2,3,4,6-tetra-О-acetyl campestanol-glucoside (CSSGT), and 2,3,4,6-tetra-О-acetyl-sitostanol-Dglucoside (SSGT) was investigated using column chromatography. When using silica gel particles, very good separation efficiency and product recovery could be achieved using hexane/ethyl hexane as eluent. The isolated 2,3,4,6-tetra-О-acetyl-β-sitosterol-Dglucoside was easily hydrolysed to β-sitosterol-D-glucoside in high yields (79%) using methanolic KOH. The process for the production of β-sitosterol-D-glucoside was scaled-up from the laboratory bench scale (250 cm3) to a laboratory scale of 2 l using the direct Oglycosylation method. The overall yields of the scaled reaction for β-sitosterol-D-glucoside was slightly above the literature reported values (59%, 8/92) for the KnoenigsKnorr synthesis and compares well above (62%, 0/100) the current production process (less than 20% yields). When using catalogue prices, the material costs (without recycling) for the direct Oglucosylation route is approximately 57% less for the synthesis of 1kg of β-sitosterol-Dglucoside compared to the Koenigs-Knorr route. Given further savings for recycling, the direct O-glucosylation route provides an attractive alternative route for the synthesis ofthe target compound.]]> Thu 13 May 2021 03:47:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10322 Thu 13 May 2021 03:37:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:11093 Thu 13 May 2021 03:35:04 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:29731 Thu 13 May 2021 03:32:14 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10372 Thu 13 May 2021 03:30:44 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21162 Thu 13 May 2021 03:15:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10981 Thu 13 May 2021 03:10:28 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:29314 Mon 22 Aug 2022 14:58:54 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:36669 Fri 15 Mar 2024 13:06:48 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:33371 Fri 15 Mar 2024 09:15:47 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:28280 Fri 15 Mar 2024 08:55:07 SAST ]]>