Faculty of Science (Research Outputs)
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Item An inertial-type method for solving image restoration problems(Springer, 2023-07) Izuchukwu, Chinedu; Shehu, Yekini; Reich, SimeonWe first establish weak convergence results regarding an inertial Krasnosel’skiĭ-Mann iterative method for approximating common fixed points of countable families of nonexpansive mappings in real Hilbert spaces with no extra assumptions on the considered countable families of nonexpansive mappings. The method of proof and the imposed conditions on the iterative parameters are different from those already available in the literature. We then present some applications to the Douglas–Rachford splitting method and image restoration problems, and compare the performance of our method with that of other popular inertial Krasnosel’skiĭ-Mann methods which can be found in the literature.Item Numerical simulation of nanofluid flow due to a stretchable rotating disk(Elsevier, 2023-05) Ayano, Mekonnen S.; Otegbeye, Olumuyiwa; Mathunjwa, Jochonia S.In this study, a steady magnetohydrodynamic (MHD) flow due to stretchable rotating disk in the presence of gyrotactic microorganisms is investigated. The governing equations modeling the flow are solved numerically using the newly introduced simple iteration method (SIM) that seeks to linearize a system using relaxation technique that effectively decouples the system. To verify the convergence and accuracy of the method, solution error and residual error analysis are carried out, respectively. The obtained results suggest that the SIM is a highly efficient method that produces convergent and highly accurate solutions. The effects of various parameters as well as combined parameter effects on the solution profiles are also investigated. An increase in the Hall and permeability parameters leads to a corresponding rise in the microorganism’s density and nanoparticle volume fraction.Item Projecting Podocarpaceae response to climate change: we are not out of the woods yet(Oxford University Press, 2023-06) Twala, Thando C.; Fisher, Jolene T.; Glennon, Kelsey L.Under the changing climate, the persistence of Afrotemperate taxa may be threatened as suitable habitat availability decreases. The unique disjunct ranges of podocarps in southern Africa raise questions about the persistence of these species under climate change. Here, we identified likely environmental drivers of these distributions, characterized the current and future (2070) environmental niches, and projected distributions of four podocarp species in South Africa. Species distribution models were conducted using species locality data for Afrocarpus falcatus, Podocarpus latifolius, Pseudotropheus elongatus and Podocarpus henkelii and both historical climate data (1970–2000) and future climate scenarios (Representative Concentration Pathway [RCP] 4.5 and 8.5, 2061–2080) to estimate the current and future distributions. We also used this opportunity to identify the most important climatic variables that likely govern each species’ distribution. Using niche overlap estimates, a similarity test, and indices of niche expansion, stability and unfilling, we explored how niches change under different climate scenarios. The distribution of the study species was governed by the maximum temperature of the warmest month, temperature annual range, mean temperature of the wettest quarter, and precipitation of the wettest, driest and warmest quarters. The current distribution of A. falcatus was predicted to expand to higher elevations under RCP 4.5 and RCP 8.5. Podocarpus henkelii was predicted to lose most of its suitable habitat under RCP 4.5 and expand under RCP 8.5; however, this was the opposite for P. elongatus and P. latifolius. Interestingly, P. elongatus, which had the smallest geographic distribution, showed the most vulnerability to climate change in comparison to the other podocarps. Mapping the distribution of podocarps and understanding the differences in their current and future climate niches provide insight into potential climate drivers of podocarp persistence and the potential for adaptation of these species. Overall, these results suggest that P. elongatus and P. henkelii may expand to novel environmental niches.Item Stakeholder perceptions reveal obstacles and opportunities to change lethal methods of protecting bathers from sharks(2023-09) Atkins, Shanan; Mann-Lang, Judy; Cliff, Geremy; Pillay, Neville; Cantor, MauricioBather protection gear—shark nets and baited hooks—is set to catch and kill sharks to protect bathers at popular swimming beaches. This lethal practice contributes to human well-being and safeguards beach tourism, a valuable income-generator. However, it is costly—financially and environmentally. Here we identify obstacles and opportunities to change this lethal method of bather protection in KwaZulu-Natal, South Africa, by assessing the knowledge of people closely involved in this bather-shark conflict. We conducted semi-structured interviews with 29 stakeholders from various organisations—KwaZulu-Natal Sharks Board which manages the gear, three government levels (local, provincial, national), and tourism and conservation organisations—to identify their perceptions about how the gear works, its advantages and disadvantages, and the possibility of changing this method of protecting bathers. Half the interviewees were unaware that the gear intentionally kills sharks. Barriers to changing the 70-year status quo include: mindsets regarding sharks and bather protection in KwaZuluNatal (compared to other places); government officials’ fear of negative consequences of change; politicians prioritising constituents’ short-term well-being; lack of proven alternatives; high cost of potential alternatives; challenging surf conditions; and slow progress of innovation. Opportunities included promising technologies, research and education to rectify misconceptions. We recommend assessing the obstacles and opportunities for change to governance structures (institutions, policies, systems) to implement a programme that accelerates the development and testing of alternatives in KwaZulu-Natal, coupled with a well-designed communication campaign. It is crucial to revisit this long-standing bather protection programme and make it safe for both humans and sharks.Item Extensions and variations of Andrews–Merca identities(Springer, 2023-07) Nyirenda, Darlison; Mugwangwavari, BeaullahRecently, Andrews and Merca have given a new combinatorial interpretation of the total number of even parts in all partitions of n into distinct parts. We generalise this result and consider many more variations of their work. We also highlight some connections with the work of Fu and Tang.Item Precipitation gradients drive high tree species turnover in the woodlands of eastern and southern Africa(Wiley, 2023-07) Davies, Robert W.; Ryan, Casey M.; Harrison, Rhett D.; Dexte, Kyle G.; Ahrends, Antje; te Beest, Mariska; Benitez, Lorena; Brade, Thom K.; Carreiras, Joao M. B.; Druce, Dave J.; Fayolle, Adeline; Finckh, Manfred; Godlee, John L.; Gonclaves, Francisco M.; Grundy, Isla M.; Hoche, T.; Holdo, Ricardo M.; Makungwa, Steve; McNicol, Iain M.; Mograbi, Penelope J.; Muchawona, Anderson; Muhate, Aristidies; Muledi, Jonathan; Pritchard, Rose; Revermann, Rasmus; Ribeiro, Natasha S.; Siampale, Abel; Staver, A. Carla; Syampungani, Stephen; Williams, Mathew; Swemmer, Anthony M.; Edwards, David P.Savannas cover one-fifth of the Earth’s surface, harbour substantial biodiversity, and provide a broad range of ecosystem ser-vices to hundreds of millions of people. The community composition of trees in tropical moist forests varies with climate, butwhether the same processes structure communities in disturbance-driven savannas remains relatively unknown. We investigatehow biodiversity is structured over large environmental and disturbance gradients in woodlands of eastern and southern Africa.We use tree inventory data from the Socio-Ecological Observatory for Studying African Woodlands (SEOSAW) network, cov-ering 755 ha in a total of 6780 plots across nine countries of eastern and southern Africa, to investigate how alpha, beta, andphylogenetic diversity varies across environmental and disturbance gradients. We find strong climate-richness patterns, withprecipitation playing a primary role in determining patterns of tree richness and high turnover across these savannas. Savannaswith greater rainfall contain more tree species, suggesting that low water availability places distributional limits on species,creating the observed climate-richness patterns. Both fire and herbivory have minimal effects on tree diversity, despite theirrole in determining savanna distribution and structure. High turnover of tree species, genera, and families is similar to turnoverin seasonally dry tropical forests of the Americas, suggesting this is a feature of semiarid tree floras. The greater richness andphylogenetic diversity of wetter plots shows that broad-scale ecological patterns apply to disturbance-driven savanna systems.High taxonomic turnover suggests that savannas from across the regional rainfall gradient should be protected if we are tomaximise the conservation of unique tree communities.Item Medicinal plants trade in Harare's urban markets diversity conservation status and economic significance(Biomed Central) Muvengwi, Justice ; Mbiba, MonicahBackground: Urban markets serve as crucial centres for trading traditional medicinal plants, yet there is limited research on the diversity, geographic origins, and socio-economic contributions of these plants. Therefore, this study aimed at understanding the species composition and diversity, conservation status, and economic importance of medicinal plants in urban markets of Harare, Zimbabwe, to provide insights into their sustainability and cultural significance. Methods: This study surveyed medicinal plant vendors in three major urban markets in Harare, Mbare, Highfield, and the Central Business District (CBD) in 2019 over a period of three months. Data were collected through semi-structured questionnaires to inventory medicinal plant species, document vendors' districts of origin, and assess harvesting practices. Species diversity was analysed using Shannon–Wiener and Simpson diversity indices, while Non-metric Multidimensional Scaling (NMDS) was used to compare species composition across markets. The informant consensus factor (ICF) was calculated to determine the level of agreement among vendors on the medicinal use of plant species. Results: A total of 64 medicinal plant species were identified, with Fabaceae being the most represented family. Sixty-one species were in the least concern IUCN Red List category. Key species with high use reports included Entada goetzei (62), Cassia abbreviata (58), Pterocarpus angolensis (40), and Albizia anthelmintica (31). Roots were the most sold plant part, followed by bark and leaves. Mbare exhibited the highest species richness (54), followed by Highfield (34), while the CBD recorded the lowest richness (23). Non-metric Multidimensional Scaling (NMDS) analysis revealed distinct differences in species composition among the three markets (R = 0.492), with Highfield displaying a unique suit of medicinal plant species. Vendors primarily originated and sourced their medicinal plants from eastern Zimbabwe, particularly Chipinge, highlighting a strong link between plant sourcing and geographic origin. The ICF was highest for gastrointestinal disorders (0.807), women’s health (0.778), sexually transmitted infections (0.746), and labour-related ailments (0.842). Medicinal plant trade contributed significantly to vendors' livelihoods, with monthly incomes ranging from US$150 to $300. Conclusion: This study underscores the high diversity of medicinal plants and their socio-economic importance in Harare’s urban markets. This shows that traditional medicine is still considered important in primary health care in the city of Harare. However, the reliance on distant districts (~ ≥ 100 km) for plant sourcing raises concerns about the possibility of unknowingly overharvesting.Item Impacts of African elephants and other environmental drivers on trees nested in by critically endangered whitebacked vultures(Nordic Society Oikos) Cook, Robin; Witkowski, Edward; Henley, MichelleThe decline of white-backed vultures Gyps africanus (hereafter termed vultures) across Africa highlights the need to understand their habitat and nesting requirements, especially in protected areas where African elephants Loxodonta africana can impact the trees in which vultures build their nests. Our study aimed to assess the impact that elephants have on trees containing vulture nests in the Associated Private Nature Reserves (APNR) of South Africa's savanna system through three separate but interlinked assessments. We first assessed the tree species used by vultures for nesting and compared their size and elephant impact scores between riparian and woodland habitats. We assessed how elephant presence or absence affects the size of Senegalia nigrescens, a key tree species, and compared vulture nests in an adjacent elephant-free area. Lastly, we modeled environmental factors influencing vulture nest and tree persistence using data from 2008–2020. Vultures utilised 10 tree species, with riparian trees supporting nests being significantly taller, with larger DBHs, and experienced lower elephant impact compared to woodland trees, which were more heavily impacted by elephants. Less robust species like S. nigrescens were more vulnerable to elephant damage, primarily bark-stripping, and less likely to host vulture nests. Our results show that vultures prefer the largest, least impacted trees for nesting, favouring those with greater stability and longevity. We suggest that although elephants influence the overall height range of trees to vultures, strong gusts of wind have a strong negative contribution on vulture nest persistence and that only a relatively small number of trees died during the 12-year study in comparison to fallen nests. We recommend further research into elephant impact thresholds on trees and vulture nest selection. Monitoring treefall and regeneration rates will help predict when vultures may face a shortage of suitable nesting trees.Item The Crystal and Molecular Structure of Nmethylephedrinium 4nitrobenzoate I II Racemic Mimic Part 5Bernal, Ivan; Lalancette, Roger A.Ephedrine is an ancient Chinese medicine drug used on patients with asthma, bronchitis and hay fever. In more recent times, it is used to prevent low blood pressure during anesthesia and to treat narcolepsy and obesity. It seemed important to understand the interaction of this drug with as large a variety of substrates as possible to get hints as to its modus operandi. It was, therefore, of interest that it appeared to crystallize as a Racemic Mimic in the form of its 4-nitrobenzoate derivative as determined by the cell parameters of that salt when it crystallized in both racemic and Sohncke space groups. Below, we describe the procedure used to prove that ephedrine belongs in that class and to illustrate the nature of the intra- and intermolecular interactions between the constituent moieties in that monoclinic (P21 and P21/c) pair. Both crystal structures,obtained from the literature, were determined at 123 K and refined, respectively, to R-factors of 3.73 and 5.51%.Item The life and mathematics of Ismail MohamedKikianty, Eder ; Nongxa, LoyisoIsmail Mohamed’s major contributions, which were in collaboration with Hermann Heineken, was to provide a procedure for constructing groups with prescribed characteristics. In particular, they constructed examples of non-nilpotent groups in which every subgroup is subnormal and nilpotent. These have become known as the Heineken–Mohamed groups. This construction led to settling a few questions posed, in the 1940s, by Kurosh and Cernikov in their survey of various generalisations of nilpotency. He also studied properties of series of subgroups of a group G that are constructed from arbitrary subgroups of automorphisms of a group.