Faculty of Applied Sciences
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Item Higher-dimensional radiating black holes in Einstein-Gauss-Bonnet gravity(American Physical Society (APS), 2019-07-01) Brassel, Byron P.; Maharaj, Sunil D.; Goswami, RituparnoThe higher order curvature corrections in Einstein-Gauss-Bonnet gravity play a significant role in the dynamics of gravitational collapse. We extend the gravitational collapse of radiating shells of matter in Einstein-Gauss-Bonnet gravity to higher dimensions, in the context of the cosmic censorship conjecture. In five dimensions the final collapse terminates with the formation of an extended and weak conical, naked singularity in the central region. For dimensions N>5, we determine that collapse terminates with a strong curvature singularity which may or may not be naked. Cosmic censorship is affected by higher-order curvature corrections. A comparison with the higher-dimensional general relativity counterpart is also given, where the dynamics are affected by the higher dimensions.Item A relativistic heat conducting model(Springer Science and Business Media LLC, 2018-11-27) Govender, Gabriel; Brassel, Byron P.; Maharaj, Sunil D.The interior dynamics of a relativistic fluid in a shear-free spherically symmetric spacetime are investigated. The isotropic matter distribution is an imperfect fluid with a nonvanishing heat flux which is in the radial direction. The pressure isotropy condition is a second-order nonlinear ordinary differential equation with variable coefficients in the gravitational potentials. We impose a particular on these potentials and a new class of solutions are obtained, containing those of Bergmann and Modak. A physical analysis is then performed where the matter variables are graphically plotted and the energy conditions are shown to be satisfied. Causality is also shown not to be violated. An analysis of the temperature profiles indicates that closed form expressions can be generated for both the noncausal and causal cases.Item Extended naked conical singularity in radiation collapse in Einstein-Gauss-Bonnet gravity(American Physical Society (APS), 2018-09-11) Brassel, Byron P.; Maharaj, Sunil D.; Goswami, RituparnoIn this paper, we investigate the continual gravitational collapse of a spherically symmetric radiation shell in five-dimensional Einstein-Gauss-Bonnet gravity. We show that the final fate of such a collapse is an extended and weak curvature naked conical singularity at the centre, which then subsequently becomes covered by an apparent horizon. This process is entirely different from the five dimensional general relativity counterpart, where a strong curvature singularity develops at the centre. Since the singularity in the case of Einstein-Gauss-Bonnet gravity is sufficiently weak, we argue that the spacetime can be extended through it, which gives us an elegant way of constructing regular black holes in higher dimensions without violating any energy conditions. We also extend our study to spacetimes with null and string fluids, which are the counterpart of generalized Vaidya spacetimes in general relativity. We show that similar end states are also possible in those cases. Higher-dimensional spacetimes are then considered.Item Collapsing radiating stars with various equations of state(American Physical Society (APS), 2017-06-28) Brassel, Byron P.; Goswami, Rituparno; Maharaj, Sunil D.We study the gravitational collapse of radiating stars in the context of the cosmic censorship conjecture. We consider a generalized Vaidya spacetime with three concentric regions. The local internal atmosphere is a two-component system consisting of standard pressure-free, null radiation and an additional string fluid with energy density and nonzero pressure obeying all physically realistic energy conditions. The middle region is purely radiative which matches to a third region which is the Schwarzschild exterior. We outline the general mathematical framework to study the conditions on the mass function so that future-directed nonspacelike geodesics can terminate at the singularity in the past. Mass functions for several equations of state are analyzed using this framework and it is shown that the collapse in each case terminates at a locally naked central singularity. We calculate the strength of these singularities to show that they are strong curvature singularities which implies that no extension of spacetime through them is possible.Item Diffusive and dynamical radiating stars with realistic equations of state(Springer Science and Business Media LLC, 2017-03) Brassel, Byron P.; Maharaj, Sunil D.; Goswami, RituparnoWe model the dynamics of a spherically symmetric radiating dynamical star with three spacetime regions. The local internal atmosphere is a two-component system consisting of standard pressure-free, null radiation and an additional string fluid with energy density and nonzero pressure obeying all physically realistic energy conditions. The middle region is purely radiative which matches to a third region which is the Schwarzschild exterior. A large family of solutions to the field equations are presented for various realistic equations of state. We demonstrate that it is possible to obtain solutions via a direct integration of the second order equations resulting from the assumption of an equation of state. A comparison of our solutions with earlier well known results is undertaken and we show that all these solutions, including those of Husain, are contained in our family. We then generalise our class of solutions to higher dimensions. Finally we consider the effects of diffusive transport and transparently derive the specific equations of state for which this diffusive behaviour is possible.Item The effect of a two-fluid atmosphere on relativistic stars(Springer Science and Business Media LLC, 2015-07-11) Govender, Gabriel; Brassel, Byron P.; Maharaj, Sunil D.We model the physical behaviour at the surface of a relativistic radiating star in the strong gravity limit. The spacetime in the interior is taken to be spherically symmetrical and shear-free. The heat conduction in the interior of the star is governed by the geodesic motion of fluid particles and a nonvanishing radially directed heat flux. The local atmosphere in the exterior region is a two-component system consisting of standard pressureless (null) radiation and an additional null fluid with nonzero pressure and constant energy density. We analyse the generalised junction condition for the matter and gravitational variables on the stellar surface and generate an exact solution. We investigate the effect of the exterior energy density on the temporal evolution of the radiating fluid pressure, luminosty, gravitational redshift and mass flow at the boundary of the star. The influence of the density on the rate of gravitational collapse is also probed and the strong, dominant and weak energy conditions are also tested. We show that the presence of the additional null fluid has a significant effect on the dynamical evolution of the star.Item Bioaugmentation efficiency of diesel degradation by Bacillus pumilus JLB and Acinetobacter calcoaceticus LT1 in contaminated soils(2010-10-11) Pillay, Charlene; Lin, JohnsonThe abilities of diesel-degrading Bacillus pumilus JLB and Acinetobacter calcoaceticus LT1 were tested in contaminated soils. The effect of nutrient supplementation on bioaugmented samples was also examined. The results show that bio-augmentation and biostimulation accelerated significantly (p < 0.05) the diesel degradation in the contaminated loam soil and sea sand. Supplementing fertilizers to the augmented loam samples did not result in a significantly higher degradation rate. Furthermore, A. calcoaceticus LT1 alone failed to stimulate higher degradation rates in sea sand unless further supplementation of fertilizer. The results from environmental scanning electron microscopy demonstrate the population increases, then decreases in augmented samples corresponding to the level of diesel degradation. Fungi-like microorganisms became dominant in contaminated loam soil at the end of the study but not in sea sand. The study shows that it is critical not only to understand the physiology of the inoculum but also how it affects microbial community structure and function before the microorganism being introduced in the contaminated soil.Item In vitro efficacy of temperature and preservatives on fast food bacilli, and their antibiotic susceptibility profile(2017-06-20) Aruwa, Christiana Eleojo; Akinyosoye, Felix AkinsolaBackground and Objective: Species within the Bacillus genus are ubiquitous, and cause food infections and intoxications. Bacillus species are however rarely assayed for in convenience foods. Furthermore, consumer health protection as it relates to the keeping quality of convenience/fast foods (prior to sale to consumers), remain a subject of global concern. Therefore, this study focused on the in vitro efficacy of temperature and preservatives on fast food bacilli. Materials and Methods: A study of chemical preservative and thermal effect on test bacilli isolates was done, with spectrophotometric measurement of optical density at 600nm. Several concentrations of chemical preservatives (0.1-1% for potassium metabisulphite, sodium nitrite, sodium benzoate, and sorbic acid; and 1-10% for sodium chloride) were prepared. Test Bacillus species were subjected to the concentrations, incubated over a 72-hrs and readings taken periodically. Statistical analysis was carried out using one way ANOVA in SPSS version 15 package for separation of means at 95% confidence interval. Results: Findings showed that at 60oC holding temperature growth of test bacilli were effectively inhibited. Also, 8% sodium chloride, 0.3% sorbic acid, 0.4% sodium benzoate, 0.3% sodium nitrite and 0.4% potassium metabisulphite effectively inhibited all test bacilli. Antibiotic susceptibility results showed that B. megaterium and B. stearothermophilus were resistant to vancomycin, while B. cereus, B. subtilis and B. thuringiensis were susceptible to vancomycin. Other test bacilli were resistant to clindamycin except B. cereus and B. stearothermophilus. Conclusion: This study showed the importance of heat and chemical preservatives in the inactivation of Bacillus species. Holding temperatures (55-60oC) and/or preservatives (at minimum inhibitory levels) could improve the shelf life and quality of ready-to-eat foods prior to purchase, and ensure consumer health protection. Antibiotic susceptibility profile of test species would be efficacious in alleviating symptoms of Bacillus related food borne illness.Item Hollow fibre liquid phase microextraction of pharmaceuticals in water and Eichhornia crassipes(2019) Mlunguza, Nomchenge Yamkelani; Madikizela, Lawrence Mzukisi; Chimuka, Luke; Mahlambi, Precious N.This work describes a simple and rapid method for the simultaneous isolation, enrichment, and quantitation of selected pharmaceuticals in aqueous environmental samples and Eichhornia crassipes. This was achieved by developing a hollow fiber liquid phase microextraction (HF-LPME) technique coupled with ultra-high-pressure liquid chromatography-high resolution mass spectrometry for the simultaneous extraction, pre- concentration and quantitation of four non-steroidal anti-inflammatory drugs (NSAIDs) and three antiretroviral drugs (ARVDs) from aqueous matrices and different segments of water hyacinth plant species. The target compounds for NSAIDs were naproxen (NAP), fenoprofen (FENO), diclofenac (DICLO) and ibuprofen (IBU) whereas the selected ARVDs included emtricitabine (FTC), tenofovir disoproxil (TD) and efavirenz (EFV). A multivariate approach by means of a half-fractional factorial design was used to optimize the HF-LPME technique focusing on six factors; donor phase (DP) pH, acceptor phase (AP) pH, extraction time, stirring rate, supported liquid membrane carrier composition (SLM carrier comp.) and salt content. Four of these factors (DP pH, AP pH, stirring rate and extraction time) were identified as vital for an enhanced enrichment of each of the selected NSAIDs and four of the previously mentioned vital factors including the SLM carrier composition were classified as significant for the selected ARVDs from aqueous samples into the hollow fiber. These essential factors were further paired according to their level of significance. The paired significant factors were then optimized using central composite designs (CCD) where empirical quadratic response models were used to visualize the response surface through contour plots, surface plots and optimization plots of the response outputs. The optimized factors for individual analytes belonging to each class were then altered to universal conditions for their simultaneous extraction from same sample solution. The acceptability of the universal conditions was defined using desirability studies. A composite desirability value of 0.7144 was obtained when the optimum factors of the three ARVDs were applied for their simultaneous extraction while a simultaneous extraction of NSAIDs had a desirability value of 0.7735. This implied that the set conditions were ideal for a combined extraction of the target compounds from the donor phase into the acceptor phase across a supported liquid membrane impregnated with a carrier molecule. For the simultaneous extraction of ARVDs, the universal optimum HF- LPME conditions were found to be DP pH of 4, AP HCl conc. of 200 mM (pH = 0.4) with SLM carrier comp. set at 4.5 (%w/w) and stirring at 1000 rpm. Under optimum conditions, the enrichment factors (EF) for ARVDs from aqueous phase were 78 (FTC), 111 (TD) and 24 (EFV). These conditions yielded recoveries in the range of 96 to 111%. The sensitivity of the analytical method through limits of quantification (LOQ) for the selected ARVDs in wastewater samples were 0.033 μg L-1 (FTC), 0.10 μg L-1 (TD) and 0.53 μg L-1 (EFV). The LOQ values were computed for surface water samples using the same target ARVDs were 0.169 μg L-1 (FTC), 0.018 μg L-1 (TD) and 0.113 μg L-1 (EFV). For NSAIDs, the overall conditions were DP pH of 10, AP pH of 3 at an extraction time of 60 min with stirring rate at 1000 rpm. The recoveries yielded under these optimum conditions for the target compounds ranged from 86 to 116%. The EF for the target NSAIDs from aqueous media were 49 (NAP), 126 (FENO), 93 (DICLO) and 156 (IBU). The LOQ values for each target NSAID in wastewater samples were 0.47 μg L-1 (NAP), 0.09 μg L-1 (FENO), 0.59 μg L-1 (DICLO) and 0.49 μg L-1 (IBU). The specific universal conditions were then used in the analysis of ARVDs in wastewater and surface water whereas for NSAIDs analysis, only wastewater samples were analysed. The surface water samples were obtained from North of Johannesburg in Hartbeespoort dam and the wastewater samples were collected from various wastewater treatment plants located in Durban, KwaZulu-Natal. The technique was also applied in the analysis of the target compounds in plant samples obtained from Hartbeespoort dam in North of Johannesburg, Umgeni river located in Springfield (Durban in KwaZulu-Natal) and Mbokodweni river located in south of Durban city, KwaZulu-Natal. The plant samples were first cut and separated into different segments (roots, stems and leaves) and the target analytes then extracted into 20 mL water using an optimized microwave assisted extraction technique (MAE). The HF-LPME technique initially optimized for water samples was then applied for pre-concentration of the target pharmaceuticals from the MAE water extract. Factors that were optimized for MAE technique were irradiation time and temperature for ARVDs whereas irradiation time and solvent volume were optimized for the extraction of NSAIDs. For extraction of both ARVDs and NSAIDs, the optimum irradiation time was 20 min while the irradiation temperature was set at 90 ̊C during the extraction of ARVDs and 100 ̊C for NSAIDs. Generally, the studied ARVDs were all detected in most samples with concentrations for FTC (0.11 – 3.10), TD (0.10 – 0.25) and EFV (1.09 up to 37.3) μg L-1 recorded in wastewater samples. EFV had the highest concentration of 37.3 μg L-1 in the wastewater effluent. The concentration of ARVDs in the roots of the water hyacinth ranged from 7.4 to 29.6 μg kg-1, 0.97 to 11.42 μg kg-1 in the stem and 0.98 to 9.98 μg kg-1 in the leaves of the aquatic plant. Roots of the water hyacinth plant had higher concentrations of the investigated ARVDs. Lastly, the NSAIDs were also detected in various wastewater samples with concentration for NAP (1.15 to 3.30) μg L-1, FENO (Item Development of a third-generation electrochemical enzyme-based biosensor for a scalable detection of oxygen in power generation cells(2019-12) Jiyane, Sphumelele Nomnontho; Bisetty, Krishna; Sabela, M. I.; Kanchi, S.Pencil graphite electrodes (PGEs) are another form of carbon electrodes with good mechanical strength and comparable electrical properties. Moreover. their low cost makes them an excellent alternative to more conventional electrodes. especially in disposable applications. In this study. the PGEs were constructed with a 2 mm diameter pencil graphite with hardness 4H. HB. and 4B. The electrodes were cleaned and modified with 1 mg/ml of graphene oxide (GO) to enhance the surface area of the electrodes. The PGE-GO was further reduced electrochemically using Na2S2O4 from -1.2 V to 0.8 V at 50 mV/s for 50 cyclic voltammetry scans in the presence of oxygen. using K3Fe(CN)6 / K4Fe(CN)6 as a redox couple. The performance of the PGE was evaluated with multi-walled carbon nanotubes and nanomaterials with various linking agents. A further evaluation was conducted with multi-copper oxidase (MCO) enzymes (Bilirubin oxidase (BOx) and Laccase oxidase) applied for the bio-catalytic reduction of oxygen. The outcome of this study showed that the modification with GO revealed redox peaks 3.6 times higher than the bare PGE. The immobilization of MCO was confirmed by cyclic voltammetry in the presence of a phosphate buffer. Furthermore. the amperometric measurements of O2 at a reducing potential of +0.34 V. showed linearity up to 0.36 mM and sensitivity of 520 μA/(mM.cm2) to O2. Furthermore. computational adsorption studies were performed for the layer-by-layer electrode modification steps. The adsorption simulations revealed a lowering of the energy favored between the designed electrode layers. suggesting a most favorable interaction for the GO/MWCNTs/PBSE/BOx layer. Overall the computational data correlated well with experimental work. Notably. the layer-by-layer adsorption of the GO/MWCNTs/PBSE/BOx showed excellent affinity 11.4 M−1 between PBSE and the enzyme interaction. The direct electron transfer (DET) of the enzymatic reaction integrated with nanotechnology. has led to a small. portable and renewable power generating device. Thus this study addresses the demand for implantable medical devices. in the absence of an external power source.