Research Publications (Applied Sciences)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/213
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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 An efficient, lung-targeted, drug-delivery system to treat asthma via microparticles(Dove Medical Press, 2019-12-27) Nagaraja, SreeHarsha; Venugopala, Katharigatta Narayanaswamy; Anroop, Nair; Roopashree, Srinivasa; Mahesh, Attimarad; Jagadeesh, Hiremath; Bandar, Al-Dhubiab; Chandramouli, Ramnarayanan; Pottathil, Shinu; Mukund, Handral; Micheline, Haroun; Christophe, TratratBackground: Chronic diseases such as diabetes, asthma, and heart disease are the leading causes of death in developing countries. Public health plays an important role in preventing such diseases to improve individuals’ quality of life. Conventional dosage schemes used in public health to cure various diseases generally lead to undesirable side effects and renders the overall treatment ineffective. For example, a required concentration of drug cannot reach the lungs using conventional methods to cure asthma. Microspheres have emerged as a confirmed drug-delivery system to cure asthma. Method: In this paper, a salbutamol-loaded poly lactic acid-co-glycolic acid-polyethylene glycol (PLGA-PEG) microsphere (SPP)-based formulation was prepared using a Buchi B-90 nanospray drier. Face-centered central composite design (CCD) was applied to optimize the spray-drying process. Results: The drug content and product yield were found to be 72%±0.8% and 86%±0.4%, respectively; drug release (91.1%) peaked for up to 12 hrs in vitro. Microspheres obtained from the spray dryer were found to be shriveled. The experiments were carried out and verified using various groups of rabbits. In our study, the particle size (8.24 μm) was observed to be an essential parameter for drug delivery. The in vivo results indicated that the targeting efficacy and drug concentration in the lung was higher with the salbutamolloaded PLGA-PEG SPP formulation (1,410.1±10.11 μg/g, 15 mins), as compared to the conventional formulation (92±0.56 μg/g, 10 min). The final product was stable under 5°C±2°C, 25°C±2°C, and 40°C±2°C/75%±5% relative humidity. In addition, these co-polymers have a good safety profile, as determined by testing on human alveolar basal epithelium A549 cell lines. Conclusion: Our results prove that microspheres are an alternative drug-delivery system for lung-targeted asthma treatments used in public health.Item Interstitial Fe in MgO(AIP Publishing, 2014-01) Mølholt, Torben Esmann; Mantovan, R.; Gunnlaugsson, H.P.; Svane, A.; Masenda, Hilary; Naidoo, D.; Bharuth-Ram, Krish; Fanciulli, M.; Gíslason, H.P.; Johnston, K.; Langouche, G.; Ólafsson, S.; Sielemann, R.; Weyer, G.Isolated Fe-57 atoms were studied in MgO single-crystals by emission Mossbauer spectroscopy following implantation of Mn-57 decaying to Fe-57. Four Mossbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe2+ and Fe3+, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.