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Synthesis and characterisation of lanthanide complexes with O,O-donor ligands: towards a new generation of hydrophonsphonylation catalysts
No full textThis study investigates the coordination behaviour of potentially bi- and tridentate O,O- and O,N,O-donor Schiff base ligands with trivalent lanthanide ions. The reactions of lanthanide nitrates with 2-((E)-(tert-butylimino)methyl)-6-methoxyphenol (HL1) have yielded five complexes that are described by the general formula [Ln(HL1)2(NO3)3] (Ln = Ce, Nd, Gd, Ho and Er) and were characterised using physico-chemical techniques including single-crystal X-ray diffraction spectroscopy. The cerium complex crystallised in a triclinic (P-1) space group, while the rest of the complexes crystallised in the monoclinic (P21/c) space group. All the complexes are ten-coordinate adopting a tetradecahedron geometry with two HL1 molecules coordinated through the phenolic and methoxy oxygen atoms. The coordination sphere is completed by six oxygen atoms from three bidentately coordinated nitrate ligands. Electronic data reveals that only the neodymium, holmium and erbium complexes exhibit weak f-f transitions in the visible region. The redox behaviour of the complexes was also investigated and reported. Five novel complexes were prepared by reacting 2-((E)-(tert-butylimino)methyl)phenol (HL2) with [Ln(NO3)3∙xH2O] (Ln = Gd and Dy ; x = 5 or 6) and [LnCl3∙6H2O] (Ln = Nd, Gd and Dy). The crystal structures of the former two complexes are isostructural and the coordination sphere is composed of three HL2 ligands bonded to the metal centre through the phenolic oxygen atom and three nitrate ions coordinated in a bidentate fashion. Both complexes are nine-coordinate and SHAPE analysis reveals that they adopted a muffin geometry. The average Ln-Onitrate and Ln-Ophenolate bond lengths are 2.5078 and 2.2814 Å, respectively. The complexes derived from the chloride salts exhibited an octahedral geometry with four monodentate ligands [Ln-Ophenolate distances range from 2.224(4) to 2.2797(17) Å] coordinating in the equatorial positions and two chloride ions [average Ln-Cl bond length is 2.6527 Å, and average Cl-Ln-Cl angles is 180o] in axial positions. The ligand coordinated through the phenolic oxygen with the phenolic proton migrating to the imino nitrogen to give a zwitterionic form of the ligand. There are weak C-H∙∙∙Cl interactions present and O-H∙∙∙N hydrogen bonds are also observed in the crystal packing. The synthesis of lanthanide complexes with methoxy-6-((E)-(phenylimino)methyl)phenol (HL3) was carried out in methanol to yield two mononuclear complexes with the formulae [Nd(HL3)2(NO3)3] and [Ho(HL3)(NO3)3(DMF)(H2O)]. Single-crystal crystallographic studies shows that the neodymium complex contains two HL3 ligands coordinated bidentately through its methoxide and phenolic oxygen atoms, with three nitrate ions also bonded to the metal in a bidentate manner. The coordination geometry in the holmium complex is composed of only oxygen atoms from the various ligands. Both complexes are ten-coordinate and exhibit a tetradecahedron geometry.National Research Foundatio
Diplomatic negotiations in international disputes
No full textSouth Africa‟s participation in international peace missions is guided by the White Paper of 1998 and premised specifically on the country‟s foreign policy objectives based on its vision of “a better South Africa, a better Africa and a better world”. South Africa recognises itself as an integral part of the African continent and therefore sees its national interests as being intrinsically linked to Africa‟s stability, unity and prosperity. Since 1994, South Africa has placed itself at the forefront of Africa's peace and security endeavours, trying to transform itself from international villain during apartheid years to Pan-Africanist peacemaker. The country has played an instrumental role in both shaping and setting the normative agenda of the African Union and Southern African Development Community. South Africa‟s participation in conflict resolution and peace missions in Africa is informed by an understanding of the nexus that exists between peace, security and sustainable development. This research focuses on South Africa‟s diplomatic and peacekeeping engagement in Lesotho, covering the constitutional and electoral crises from 1994 - 2015 constitutional crisis. The author shows the importance and way forward to resolve conflicts before they become escalated and deadly. The study calls for a „timely‟ reaction to disputes and conflicts on the African continent via preventive diplomacy, conflict provention and addressing of underlying issues that give rise to disputes and conflict.National Research Foundatio
Dynamics in hybrid and organic-inorganic light harvesting thin films followed with femtosecond transient absorption spectroscopy
No full textNational Research Foundatio
Statistical classification in high-dimensional scenarios with a focus on microarray data sets
No full textHigh-dimensional data analysis characterises many contemporary problems in statistics and arise in many application areas. This thesis focuses on very high-dimensional problems in which the input predictor variables are gene expression measurements in microarray studies. Accurate analysis of microarray data sets can provide new insight into cancer diagnosis using gene expression profiles and can result in breakthroughs in medical research.
K-nearest neighbours (KNN), fastKNN, linear discriminant analysis (and variants thereof), nearest shrunken centroids (NSC) and support vector machines (SVMs) are investigated in this thesis as binary (and multi-class) classification procedures on microarray data sets.
The important problem of eliminating redundant input variables before implementing classification procedures in high-dimensional data sets is addressed in this thesis. Several variable selection and dimension reduction procedures suitable for microarray data sets are discussed, with the focus on implementing sure independence techniques, NSC and fastKNN feature engineering in the empirical study. Principal component analysis and supervised principal component analysis are implemented as the two main dimension reduction techniques in this thesis.
The performance of the classification procedures is evaluated on three real and three synthetic high-dimensional microarray data sets. The comparison of the different classification methods in the empirical study led to the conclusion that SVMs prove to be the most accurate procedure on the binary data sets considered, whilst NSC is the most accurate procedure on the multi-class data set.National Research Foundatio
Gender related morphometric differences in mature and nestling Crowned Eagles, with comments on ringing of eagle nestlings in KwaZulu-Natal, South Africa.
No full textAlthough most raptor species are sexually dimorphic, many species are non-discrete in some metrics. A limited amount of existing data for southern Africa suggests that Crowned Eagles Stephanoaetus coronatus exhibit non-discrete sexual dimorphism. Consequently, we investigated gender-related morphometric data of Crowned Eagles with corresponding genetic avian sex tests. Immature (n = 13) and adult (n = 5) Crowned Eagles were trapped, measured and released in KwaZulu-Natal, South Africa from 2012 to 2015. Our results show that tarsus width, body mass, and DI claw (hallux) measurements are suitable for discriminating between sexes of mature Crowned Eagles. We comment on the use of South African Ringing Scheme (SAFRING) and colour read-rings as a marking technique in Crowned Eagles. Furthermore, we suggest suitable parameters for accessing nests and marking nestlings. To aid in the age estimates of nestling eagles, a reference of growth of known-age nestlings is provided.National Research Foundation (South Africa
Love grows with sex: Teenagers negotiating sex and gender in the context of HIV and the implications for sex education
No full textHow do teenagers located in the KwaZulu-Natal province of South Africa, the epicentre of the HIV pandemic, give meaning to sexuality? This paper examines teenage black Africans investments in sex and sexuality and the gendered dynamics through which sexuality is articulated. Whilst unequal gender relations of power continue to feature prominently within relationship dynamics fuelling the gendering of HIV, attention to the micro-processes through which relationships are forged remain significant in illustrating the complex connections between love, sex and gender. Drawing on empirical findings with teenagers between the ages of 16 and 17 years old, the paper shows how relationships are conceptualised based on discourses of love. Love is inextricably bound up with sex and when teenagers talk about love and sex they also talk about condom use, multiple sexual partners and gender inequalities. What teenagers were interested in for their sexual relationships was not raised in sex education programmes at school. Implications for addressing teenage constructions of sexuality are discussed in the conclusionNational Research Foundation (South Africa
Estimating δ15N fractionation and adjusting the lipid correction equation using Southern African freshwater fishes
No full textStable isotope analysis is an important tool for characterising food web structure; however, interpretation of isotope data can often be flawed. For instance, lipid normalisation and trophic fractionation values are often assumed to be constant, but can vary considerably between ecosystems, species and tissues. Here, previously determined lipid normalisation equations and trophic fractionation values were re-evaluated using freshwater fish species from three rivers in the Upper Zambezian floodplain ecoregion in southern Africa. The parameters commonly used in lipid normalisation equations were not correct for the 18 model species (new D and I parameters were estimated as D = 4.46‰ [95% CI: 2.62, 4.85] and constant I = 0 [95% CI: 0, 0.17]). We suggest that future isotopic analyses on freshwater fishes use our new values if the species under consideration do not have a high lipid content in their white muscle tissue. Nitrogen fractionation values varied between species and river basin; however, the average value closely matched that calculated in previous studies on other species (δ15N fractionation factor of 3.37 ± 1.30 ‰). Here we have highlighted the need to treat stable isotope data correctly in food web studies to avoid misinterpretation of the data
Optimising invasive fish management in the context of invasive species legislation in South Africa
No full textBACKGROUND: South Africa hosts a large number of non-native freshwater fishes that were introduced for various industries. Many of these species are now listed under the National Environmental Management: Biodiversity Act (NEM:BA) Alien and Invasive Species (A&IS) lists and regulations, though the practical options available to conservation agencies to effectively manage these fishes vary greatly among species and regions.
OBJECTIVES & METHODS: We assessed the history and status of national legislation pertaining to invasive freshwater fishes, and the practical implications of the legislation for managing different species with contrasting distributions, impacts and utilisation value.
RESULTS: The smallmouth bass, despite being a potential conflict-generating species, is fairly straightforward to manage based on current legislation. Two species of trout, which remain absent from the NEM:BA A&IS lists because of ongoing consultation with stakeholders, continue to be managed in regions like the Western Cape province using existing provincial legislation. To maximise the limited capacity for management within conservation agencies, we proposed a decision-support tool that prioritises invasive fish populations that represent high environmental risk and low potential for conflict with stakeholders. Using three case studies, we demonstrated how the tool can be used to set management goals of 'eradicate', 'manage against impacts and further spread' and 'continue to monitor population' as the most pragmatic solutions given the state of an invasion, its socio-economic impact and the capacity of the responsible agency to act.
CONCLUSION: By choosing a pragmatic management strategy, conservation agencies can maximise the effective deployment of limited resources, while minimising avoidable conflicts with stakeholders
Leapfrogging into new territory: How Mascarene ridged frogs diversified across Africa and Madagascar to maintain their ecological niche
No full textThe Mascarene ridged frog, Ptychadena mascareniensis, is a species complex that includes numerous lineages occurring mostly in humid savannas and open forests of mainland Africa, Madagascar, the Seychelles, and the Mascarene Islands. Sampling across this broad distribution presents an opportunity to examine the genetic differentiation within this complex and to investigate how the evolution of bioclimatic niches may have shaped current biogeographic patterns. Using model-based phylogenetic methods and molecular-clock dating, we constructed a time-calibrated molecular phylogenetic hypothesis for the group based on mitochondrial 16S rRNA and cytochrome b (cytb) genes and the nuclear RAG1 gene from 173 individuals. Haplotype networks were reconstructed and species boundaries were investigated using three species-delimitation approaches: Bayesian generalized mixed Yule-coalescent model (bGMYC), the Poisson Tree Process model (PTP) and a cluster algorithm (SpeciesIdentifier). Estimates of similarity in bioclimatic niche were calculated from species-distribution models (maxent) and multivariate statistics (Principal Component Analysis, Discriminant Function Analysis). Ancestral-area reconstructions were performed on the phylogeny using probabilistic approaches implemented in BioGeoBEARS. We detected high levels of genetic differentiation yielding ten distinct lineages or operational taxonomic units, and Central Africa was found to be a diversity hotspot for these frogs. Most speciation events took place throughout the Miocene, including "out-of-Africa" overseas dispersal events to Madagascar in the East and to São Tomé in the West. Bioclimatic niche was remarkably well conserved, with most species tolerating similar temperature and rainfall conditions common to the Central African region. The P. mascareniensis complex provides insights into how bioclimatic niche shaped the current biogeographic patterns with niche conservatism being exhibited by the Central African radiation and niche divergence shaping populations in West Africa and Madagascar. Central Africa, including the Albertine Rift region, has been an important center of diversification for this species complex
The ecology of fish in the surf zones of ocean beaches: A global review
No full textThe surf zones of ocean beaches provide habitat for a diversity of fishes and are prime sites for recreational angling and commercial net fisheries. Here, we review the global literature (152 studies) on surf fish ecology to better inform fisheries management and coastal conservation planning. These studies suggest that surf zones support diverse fish assemblages, which are characterized by high numerical dominance (10 species typically comprise 95% of catches), but also show that few families are especially common. The composition of assemblages is highly variable, changing with fluctuations in water temperature, wave climate and the biomass of drifting algae or seagrass. Fish use surf zones as feeding habitats and transit routes, but these areas might not be widely used as spawning sites or juvenile nurseries. These systems are under escalating human pressures, most notably from coastal urbanization and recreational angling. Despite the recognized ecological and economic importance of surf‐zone fishes, few studies have tested for impacts of urbanization or fishing. The benefits of marine reserves for fish in surf zones are also rarely measured. We suggest that progress will be made by moving from largely descriptive studies to hypothesis‐driven research, which is guided by contemporary ecological theory and adapts modern techniques from research in other ecosystems. A key challenge is to obtain empirical data that are needed to improve the effectiveness of fisheries management and underpin conservation planning for coastal waters