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Showing papers by "University of the Witwatersrand published in 1998"


Journal ArticleDOI
TL;DR: To test the application of a clinical definition of severe acute maternal morbidity, a large number of patients with confirmed or suspected cases of maternal death in the second trimester of pregnancy are randomly selected to undergo a EMT procedure.

384 citations


Journal ArticleDOI
TL;DR: It is inferred that one of the oldest events in the nested cladistic analysis was a range expansion out of Africa which resulted in the complete replacement of Y chromosomes throughout the Old World, a finding consistent with many versions of the Out of Africa Replacement Model.
Abstract: We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544 individuals from Africa, Asia, Europe, Oceania, and the New World Phylogenetic analyses of these nine sites resulted in a tree for 10 distinct Y haplotypes with a coalescence time of approximately 150,000 years The 10 haplotypes were unevenly distributed among human populations: 5 were restricted to a particular continent, 2 were shared between Africa and Europe, 1 was present only in the Old World, and 2 were found in all geographic regions surveyed The ancestral haplotype was limited to African populations Random permutation procedures revealed statistically significant patterns of geographical structuring of this paternal genetic variation The results of a nested cladistic analysis indicated that these geographical associations arose through a combination of processes, including restricted, recurrent gene flow (isolation by distance) and range expansions We inferred that one of the oldest events in the nested cladistic analysis was a range expansion out of Africa which resulted in the complete replacement of Y chromosomes throughout the Old World, a finding consistent with many versions of the Out of Africa Replacement Model A second and more recent range expansion brought Asian Y chromosomes back to Africa without replacing the indigenous African male gene pool Thus, the previously observed high levels of Y chromosomal genetic diversity in Africa may be due in part to bidirectional population movements Finally, a comparison of our results with those from nested cladistic analyses of human mtDNA and beta-globin data revealed different patterns of inferences for males and females concerning the relative roles of population history (range expansions) and population structure (recurrent gene flow), thereby adding a new sex-specific component to models of human evolution

370 citations


Journal ArticleDOI
TL;DR: The main Karoo Basin of South Africa is a Late Carboniferous-Middle Jurassic retroarc foreland fill, developed in front of the Cape Fold Belt (CFB) in relation to subduction of the palaeo-Pacific plate underneath the Gondwana plate.
Abstract: The main Karoo Basin of South Africa is a Late Carboniferous–Middle Jurassic retroarc foreland fill, developed in front of the Cape Fold Belt (CFB) in relation to subduction of the palaeo-Pacific plate underneath the Gondwana plate. The Karoo sedimentary fill corresponds to a first-order sequence, with the basal and top contacts marking profound changes in the tectonic setting, i.e. from extensional to foreland and from foreland to extensional, respectively. Sedimentation within the Karoo Foreland Basin was closely controlled by orogenic cycles of loading and unloading in the CFB. During orogenic loading, episodes of subsidence and increase in accommodation adjacent to the orogen correlate to episodes of uplift and decrease in accommodation away from the thrust-fold belt. During orogenic unloading the reverse occurred. As a consequence, the depocentre of the Karoo Basin alternated between the proximal region, during orogenic loading, and the distal region, during orogenic unloading. Orogenic loading dominated during the Late Carboniferous–Middle Triassic interval, leading to the accumulation of thick foredeep sequences with much thinner forebulge correlatives. The Late Triassic–Middle Jurassic interval was dominated by orogenic unloading, with deposition taking place in the distal region of the foreland system and coeval bypass and reworking of the older foredeep sequences. The out of phase history of base-level changes generated contrasting stratigraphies between the proximal and distal regions of the foreland system separated by a stratigraphic hinge line. The patterns of hinge line migration show the flexural peripheral bulge advancing towards the craton during the Late Carboniferous–Permian interval in response to the progradation of the orogenic front. The orogenward migration of the foreland system recorded during the Triassic–Middle Jurassic may be attributed to piggyback thrusting accompanied by a retrogradation of the centre of weight within the orogenic belt during orogenic loading (Early Middle Triassic) or to the retrogradation of the orogenic load through the erosion of the orogenic front during times of orogenic unloading (Late Triassic–Middle Jurassic).

354 citations


Journal ArticleDOI
TL;DR: Gilbert et al. as discussed by the authors identify some of the issues associated with the role of models in scientific explanations and identify some characteristics of explanations sought and provided for and by scientists, science curricula, teachers of science and students of science.
Abstract: This is the first of two papers which seeks to identify some of the issues associated with the role of models in scientific explanations. Starting from a broad definition, a typology of explanations is developed and the notion of ‘appropriateness’ in scientific explanations is explored. Some characteristics of explanations sought and provided for and by scientists, science curricula, teachers of science and students of science are identified. Finally, the nature of models and their contribution to explanations are explored. In Part 2 (Gilbert et al. 1998), the understandings generated from provided explanations are discussed, together with an appraisal of those explanations which are not commonly sought or attempted.

313 citations


Journal ArticleDOI
TL;DR: The phenomenon called ecosystem engineering is considered with a case study of the mound building termite Macrotermes michaelseni, and it is argued that this species acts as an ecosystem engineer across a range of spatial scales.
Abstract: Many organisms create or alter resource flows that affect the com- position and spatial arrangement of current and future organismal diversity. The phenomenon called ecosystem engineering is considered with a case study of the mound building termite Macrotermes michaelseni. It is argued that this species acts as an ecosystem engineer across a range of spatial scales, from alteration of local infiltration rates to the creation of landscape mosaics, and that its impacts accrue because of the initiation of biophysical processes that often include feedback mech- anisms. These changes to resource flows are likely to persist for long periods and constrain the biological structure of the habitat. The value of ecosystem engineer- ing is discussed as a holistic way of understanding the complexity of tropical ecology.

306 citations


Journal ArticleDOI
TL;DR: In this article, a thermal model is presented to constrain the emplacement and crystallization times of basaltic magmatism in the Bushveld Complex, showing that large intrusions were not emplaced in a single pulse, but which permits the investigation of the rate of cooling of magma in an intrusion repeatedly subjected to magma addition (and subresult from multiple magma injection).
Abstract: The Bushveld Complex formed by the crystallization of successive basaltic magmatism may be of the order of several million years. For example, the Columbia River Basalts (Hooper, injections of magma, which were sufficiently closely spaced in time that each previous magma had not cooled and differentiated 1988) were erupted in the period 17–12 Ma, with minor eruptions for a further 5 my, although most outpouring significantly before the addition of the next one. To constrain the emplacement and crystallization times, a thermal model is presented occurred within the first 2 my. It is now recognized that large intrusions were not emplaced in a single pulse, but which permits the investigation of the rate of cooling of magma in an intrusion repeatedly subjected to magma addition (and subresult from multiple magma injection. The question is how rapidly were magma chambers, such as the BC, traction). Such modelling indicates that magmas injected into the Bushveld Complex were emplaced within 75 000 years. At that filled and how much magma was involved. Answers are relevant to the dynamics of melt production, storage and time injection into the Complex ceased. The volume of rock in the Eastern and Western limbs is 370 000–600 000 km. However, transport in the mantle and crust. This paper describes a thermal modelling technique (not previously applied a quantitative evaluation of the Cr budget in the formation of chromitite layers indicates that large volumes of magma cannot be to magma chambers) which can be used to analyse this process, and to obtain an estimate of the emplacement accounted for in the preserved rock sequence. Similarly, an evaluation of the incompatible trace-element abundances, such as those for Zr time. To present this model it is necessary to discuss the stratigraphy, size, and connectivity of the different limbs and K, suggests that the chamber was open and that large volumes of differentiated magma escaped. The volume of magma therefore of the Bushveld Complex, and to consider the extent of tapping of the magma chamber as well as its filling. greatly exceeded the preserved volume of cumulate rocks, giving an estimated magma volume of over 1× 10 km. An average The term ‘Bushveld Complex’ has been given several meanings in the literature, and according to the South emplacement rate of 13 km/year is indicated by these calculations. African Commission on Stratigraphy (1980) includes not only the ultramafic–mafic layered rocks, but also the sills beneath the intrusion, volcanic rocks which pre-date the

257 citations


Journal Article
TL;DR: Risperidone is of equivalent efficacy to lithium and haloperidol in the management of acute mania and the Global Assessment of Functioning and Clinical Global Impression data showed a similar pattern of improvement.
Abstract: Case reports and studies of other neuroleptics suggest the efficacy of risperidone in the treatment of mania. Forty-five inpatients with DSM-IV mania were studied in a 28-day randomized, controlled, double-blind trial of either 6 mg daily of risperidone, 10 mg daily of haloperidol, or 800 to 1200 mg daily of lithium. The patients in all three groups showed a similar improvement on the total score for all rating scales at day 28 (Brief Psychiatric rating scale; lithium 9.1, haloperidol 4.9, risperidone 6.5, F = 1.01, df = 2, p = 0.37; Mania rating scale; lithium 15.7, haloperidol 10.2, risperidone 12.4, F = 1.07, df = 2, p = 0.35 [analysis of variance]). The Global Assessment of Functioning and Clinical Global Impression data showed a similar pattern of improvement. This study suggests that risperidone is of equivalent efficacy to lithium and haloperidol in the management of acute mania. The extrapyramidal side effects of risperidone and haloperidol were not significantly different.

246 citations


Journal ArticleDOI
TL;DR: Low birth weight in conjunction with rapid childhood gains in weight especially as subcutaneous fat, produces poor glucose tolerance in 7-year-old children and can make them susceptible to the development of Type II diabetes later in life.
Abstract: A number of studies have shown that glucose tolerance falls with decreasing birth weight and that people with low birth weight and high body mass index (BMI) as adults are those at greatest risk of developing Type II (non-insulin-dependent) diabetes mellitus. No such studies have been carried out in African populations. Therefore we investigated the relation between glucose tolerance and birth weight in a group of 7-year-old black South Africans for whom longitudinal anthropometric data were available. Oral glucose tolerance tests (OGTTs) were carried out on 152 subjects and inverse correlations were found between birth weight and the total amount of insulin secreted during the first 30 min (r = –0.19, p = 0.04) and last 90 min (r = –0.19, p = 0.04) of the oral glucose tolerance test and also between birth weight and the 30 min glucose concentrations (r = –0.20, p = 0.02). Children born with low birth weights but who had high weights at 7 years had higher insulin concentrations and indices of obesity compared with those with low birth weights and low weights at 7 years. There were also positive correlations between weight velocity and BMI (r = 0.24, p = 0.02) and weight velocity and insulin resistance (r = 0.18, p = 0.04) as measured using homeostasis model assessment (HOMA). Thus, low birth weight in conjunction with rapid childhood gains in weight especially as subcutaneous fat, produces poor glucose tolerance in 7-year-old children and can make them susceptible to the development of Type II diabetes later in life. [Diabetologia (1998) 41: 1163–1167]

240 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa.
Abstract: We investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa. Aerosol samples were collected on glass fiber filters and on stacked filter units, consisting of a Nuclepore prefilter for particles larger than ∼1–2 μm and a Teflon second filter stage for the submicron fraction. The samples were analyzed for soluble ionic components, organic carbon, and black carbon. Onboard the research aircraft, particle number and volume distributions as a function of size were determined with a laser-optical particle counter and the black carbon content of the aerosol with an aethalometer. We determined the emission ratios (relative to CO2 and CO) and emission factors (relative to the amount of biomass burnt) for the various aerosol constituents. The smoke aerosols were rich in organic and black carbon, the latter representing 10–30% of the aerosol mass. K+ and NH4+ were the dominant cationic species in the smoke of most fires, while Cl− and SO42− were the most important anions. The aerosols were unusually rich in Cl−, probably due to the high Cl content of the semiarid vegetation. Comparison of the element budget of the fuel before and after the fires shows that the fraction of the elements released during combustion is highly variable between elements. In the case of the halogen elements, almost the entire amount released during the fire is present in the aerosol phase, while in the case of C, N, and S, only a small proportion ends up as particulate matter. This suggests that the latter elements are present predominantly as gaseous species in the fresh fire plumes studied here.

229 citations


Journal ArticleDOI
TL;DR: It is suggested that pentoxifylline improves symptoms and left-ventricular systolic function in patients with idiopathic dilated cardiomyopathy and these results must be confirmed in larger-scale trials.

210 citations


Journal ArticleDOI
TL;DR: A new measure of the amount of overall disequilibrium shows least disequ equilibrium in African populations, somewhat more in European populations, and the greatest amount in East Asian and Amerindian populations.
Abstract: A four-site haplotype system at the dopamine D2 receptor locus (DRD2) has been studied in a global sample of 28 distinct populations. The haplotype system spans about 25 kb, encompassing the coding region of the gene. The four individual markers include three TaqI restriction site polymorphisms (RSPs) -- TaqI "A", "B", and "D" sites -- and one dinucleotide short tandem repeat polymorphism (STRP). All four of the marker systems are polymorphic in all regions of the world and in most individual populations. The haplotype system shows the highest average heterozygosity in Africa, a slightly lower average heterozygosity in Europe, and the lowest average heterozygosities in East Asia and the Americas. Across all populations, 20 of the 48 possible haplotypes reached a frequency of at least 5% in at least one population sample. However, no single population had more than six haplotypes reaching that frequency. In general, African populations had more haplotypes present in each population and more haplotypes occurring at a frequency of at least 5% in that population. Permutation tests for significance of overall disequilibrium (all sites considered simultaneously) were highly significant (P<0.001) in all 28 populations. Except for three African samples, the pairwise disequilibrium between the outermost RSP markers, TaqI "B" and "A", was highly significant with D' values greater than 0.8; in two of those exceptions the RSP marker was not polymorphic. Except for those same two African populations, the 16-repeat allele at the STRP also showed highly significant disequilibrium with the TaqI "B" site in all populations, with D' values usually greater than 0.7. Only four haplotypes account for more than 70% of all chromosomes in virtually all non-African populations, and two of those haplotypes account for more than 70% of all chromosomes in most East Asian and Amerindian populations. A new measure of the amount of overall disequilibrium shows least disequilibrium in African populations, somewhat more in European populations, and the greatest amount in East Asian and Amerindian populations. This pattern seems best explained by random genetic drift with low levels of recombination, a low mutation rate at the STRP, and essentially no recurrent mutation at the RSP sites, all in conjunction with an "Out of Africa" model for recent human evolution.

Journal ArticleDOI
TL;DR: In this study, brain temperature was higher than abdominal temperature throughout exercise; that is, selective brain cooling did not occur when body temperature was below the level limiting exercise.
Abstract: We measured brain and abdominal temperatures in eight male Sprague-Dawley rats (350–450 g) exercising voluntarily to a point of fatigue in two hot environments. Rats exercised, at the same time of ...

Journal ArticleDOI
TL;DR: Groups were discriminated from each other more clearly with outline methods than with landmark-based analyses, and the summaries of shape complexity provide good discrimination of groups.
Abstract: We examined and compared several morphometric methods for describing complex shapes. W e chose the leaves of maples ( Acer) and other tree species because they can all be visually discriminated from each other solely by leaf shape. W e digitized the leaf outlines with a video camera and then examined the outlines with several morphometric methods to deter- mine the extent to which margin details could be quanti® ed and compared. Elliptic Fourier analysis provides complete and accurate descriptions of complex outlines and can be used to reconstruct images accurately. We compared several metrics that summarize overall shape complexity. A new measure of margin roughness is useful for quantifying and comparing margin detail independently of overall shape. Fractal dimension is highly correlated with the ratio of perimeter to area (dissection index) and reveals little additional information about shape. In combination, the summaries of shape complexity provide good discrimination of groups. W e used canonical discriminant analysis to compare methods for outlines to tradi- tional morphometric analysis of measurements taken between landmark points. Groups were discriminated from each other more clearly with outline methods than with landmark-based analyses. (Acer, Fourier analysis, fractal dimension, landmark analysis, leaf shape, margin roughness, Liquidambar , morphometrics, Quercus.)

Journal ArticleDOI
TL;DR: Extensions of the temporal ranges of several lineages of diapsids into the Late Permian suggests that more groups of terrestrial reptiles survived the end-Permian mass extinction than thought previously.
Abstract: Restudy of the unique diapsid reptile Mesosuchus browni Watson, from the Cynognathus Assemblage Zone (late Early Triassic to early Middle Triassic) of the Burgersdorp Formation (Tarkastad Subgroup; Beaufort Group) of South Africa, confirms that it is the most plesiomorphic known member of the Rhynchosauria. A new phylogenetic analysis of basal taxa of Archosauromorpha indicates that Choristodera falls outside of the Sauria, Prolacertiformes is a paraphyletic taxon with Prolacerta sharing a more recent common ancestor with Archosauriformes than with any other clade, Megalancosaurus and Drepanosaurus are sister taxa in the clade Drepanosauridae within Archosauromorpha, and are the sister group to the clade Tanystropheidae composed of Tanystropheus , Macrocnemus , and Langobardisaurus . Combination of the phylogenetic relationships of basal archosauromorphs and their known stratigraphic ranges reveals significant gaps in the fossil records of Late Permian and Triassic diapsids. Extensions of the temporal ranges of several lineages of diapsids into the Late Permian suggests that more groups of terrestrial reptiles survived the end-Permian mass extinction than thought previously.

Journal ArticleDOI
TL;DR: Three classes of genes have been examined for their contribution to normal human color variation through the production of hypopigmented phenotypes or by genetic association with skin type and hair color.
Abstract: There is no doubt that visual impressions of body form and color are important in the interactions within and between human communities. Remarkably, it is the levels of just one chemically inert and stable visual pigment known as melanin that is responsible for producing all shades of humankind. Major human genes involved in its formation have been identified largely using a comparative genomics approach and through the molecular analysis of the pigmentary process that occurs within the melanocyte. Three classes of genes have been examined for their contribution to normal human color variation through the production of hypopigmented phenotypes or by genetic association with skin type and hair color. The MSH cell surface receptor and the melanosomal P-protein are the two most obvious candidate genes influencing variation in pigmentation phenotype, and may do so by regulating the levels and activities of the melanogenic enzymes tyrosinase, TRP-1 and TRP-2.

Journal ArticleDOI
TL;DR: In this article, immigrants and asylum seekers from two countries, Nigeria and the Democratic Republic of Congo, have experienced significant antagonism and prejudice from the local population, more especially from black South Africans, who are often easily distinguishable due to their physical features, distinctive dress and inability to speak the indigenous languages.
Abstract: Xenophobia in post-apartheid South Africa has become a major issue Much of the hostility is directed at Africans from countries north of Southern Africa who are often easily distinguishable due to their physical features, distinctive dress and inability to speak the indigenous languages This article focuses on immigrants and asylum seekers from two countries, Nigeria and the Democratic Republic of Congo Both groupings have experienced significant antagonism and prejudice from the local population, more especially from black South Africans The article describes and analyses the interaction of the two groupings in question with the local populace and authorities What is argued is that during the apartheid era the restrictions on black immigration meant that the number of black foreigners was limited Since 1990, however, there has been a substantial increase in illegal and legal migration from Southern African countries and countries further north This increase, in a context of growing unempl

Journal ArticleDOI
TL;DR: All of the genes known to be directly involved in the repair of oxidative and alkylative damage are present in M. tuberculosis, which has potentially significant implications with respect to genome stability, strain variability at repeat loci and the emergence of chromosomally encoded drug resistance mutations.
Abstract: The genome sequence of Mycobacterium tuberculosis was analysed by searching for homologues of genes known to be involved in the reversal or repair of DNA damage in Escherichia coli and related organisms. Genes necessary to perform nucleotide excision repair (NER), base excision repair (BER), recombination, and SOS repair and mutagenesis were identified. In particular, all of the genes known to be directly involved in the repair of oxidative and alkylative damage are present in M. tuberculosis. In contrast, we failed to identify homologues of genes involved in mismatch repair. This finding has potentially significant implications with respect to genome stability, strain variability at repeat loci and the emergence of chromosomally encoded drug resistance mutations.

Journal ArticleDOI
TL;DR: The pattern of haplotype diversity and linkage disequilibrium observed supports a recent African-origin model of modern human evolution and suggests that the original mutation event that gave rise to DM-causing alleles arose in a population ancestral to non-Africans prior to migration of modern humans out of Africa.
Abstract: Haplotypes consisting of the (CTG)n repeat, as well as several flanking markers at the myotonic dystrophy (DM) locus, were analyzed in normal individuals from 25 human populations (5 African, 2 Middle Eastern, 3 European, 6 East Asian, 3 Pacific/Australo-Melanesian, and 6 Amerindian) and in five nonhuman primate species. Non-African populations have a subset of the haplotype diversity present in Africa, as well as a shared pattern of allelic association. (CTG)18-35 alleles (large normal) were observed only in northeastern African and non-African populations and exhibit strong linkage disequilibrium with three markers flanking the (CTG)n repeat. The pattern of haplotype diversity and linkage disequilibrium observed supports a recent African-origin model of modern human evolution and suggests that the original mutation event that gave rise to DM-causing alleles arose in a population ancestral to non-Africans prior to migration of modern humans out of Africa.

Journal ArticleDOI
TL;DR: New discoveries of A. africanus fossils from Member 4 Sterkfontein reveal a body form quite unlike earlier Australopithecus species, and postcranial material reveals an apparently primitive morphology of relatively large forelimb and small hindlimb joints resembling more the pongid than the human pattern.

Journal ArticleDOI
TL;DR: Evidence is presented support of a variation of the developmental hypothesis that adventitial cystic disease is a developmental condition occurring in the nonaxial blood vessels.

Journal ArticleDOI
TL;DR: Frequent, but not necessarily high, rainfall appears to be essential for germination and seedling survival over the first 7 weeks of four African savanna tree species.

Journal ArticleDOI
TL;DR: It is concluded that dietary iron overload may contribute to the development of HCC in Black Africans.

Journal ArticleDOI
TL;DR: The influence of ambient temperature on daily activity level was assessed for greater kudus observed in two study areas in South Africa, suggesting that foraging activity was effectively constrained by thermal tolerance on only about one day in seven.
Abstract: The influence of ambient temperature on daily activity level was assessed for greater kudus observed in two study areas in South Africa. Active time proportion for adult females and subadults of both sexes was significantly negatively correlated with maximum daily temperature, but uninfluenced directly by cloud cover. However, maximum temperature differences between days accounted for only a quarter of the variability in active time. On most days the overall activity level and hence daily foraging time allocation were somewhat lower than the maximum levels observed for the prevailing temperature conditions. The upper limit to the distribution of active time was lower during the mild dry season than over the hot wet season, probably due to a seasonal change in pelage by kudus. Temperature influences were strongest during the early growing season, when food availability was low and conditions frequently hot. The active and foraging times of kudus during daylight hours appeared to be restricted below the target level only when maximum daily temperature exceeded 36 °C in the wet season, and 30 °C in the dry season. Only 15% of days exceeded these levels during the respective mid-seasonal periods, suggesting that foraging activity was effectively constrained by thermal tolerance on only about one day in seven. Optimal foraging models that assume thermal stress to be a consistent daily constraint on foraging time may be misleading.

Journal ArticleDOI
TL;DR: The Okavango Delta is a large, low gradient (ca. 1:3400), alluvial fan situated in a graben structure which is an extension of the East African Rift system as discussed by the authors.
Abstract: SUMMARY The Okavango Delta is a large, low gradient (ca. 1:3400), alluvial fan situated in a graben structure which is an extension of the East African Rift system. The catchment is situated in sub-tropical central Angola (rainfall ca. 1000 mm/a), and is underlain by Kalahari sand. Okavango River water therefore has a very low dissolved solid content (ca. 40 ppm), and a very low suspended load. The main clastic sediment load consists of eroded Kalahari sand, which is transported as bedload. Base flow in the river sustains about 4000 km2 of permanent swamps in the Panhandle and upper fan. The latter are flanked by seasonal swamps, which become inundated during advance of the seasonal flood wave. This flood wave takes four months to traverse the 250 km length of the fan. The extent of seasonal flooding is variable and can exceed 12 000 km2. The fan is situated in a semiarid region (rainfall 513 mm/a), in which evapotranspiration exceeds rainfall by a factor of three. Only 15% of inflow plus rainfall leaves ...

Journal Article
TL;DR: The state of knowledge on the tectonic and geomorphological evolution of southern Africa during the post-Gondwana period is reviewed in the context of Alex du Toit's fundamental contributions to these fields of geology as mentioned in this paper.
Abstract: The state of knowledge on the tectonic and geomorphological evolution of southern Africa during the post-Gondwana period is reviewed in the context of Alex du Toit9s fundamental contributions to these fields of geology. Basic to an understanding of post-rifting events are, firstly, the high elevation which much of Africa possessed prior to rifting; secondly, the erosion of one to three kilometres from its surface during the Cretaceous; and thirdly, the role of Neogene uplift in re-establishing high elevations, particularly within the eastern half of the subcontinent. This history is traced through the massive denudation of the early Cretaceous, which was followed by the establishment of a dense, integrated drainage net on a well-planed land surface from the Santonian onwards. The configuration of the Upper Cretaceous river system is fundamental to a comprehension of the present distribution of alluvial diamonds and of gems transported into the sea via these conduits. Equally significant for an appreciation of the present macro-geomorphology of southern Africa is the continent-wide planation surface--known as the African Surface--generated by the multi-phase cycle of Cretaceous erosion. This surface forms a readily identifiable datum across the high plains because of the widespread preservation of deep weathering and massive cappings of laterite and silcrete on remnants which have survived later dissection. The African silcretes reflect a world-wide shift to greater aridity at the beginning of the Palaeocene. The evidence for large-scale Neogene uplift, particularly within the eastern half of the subcontinent, is now beyond question and argues for the late development of at least the southern part of the African Superswell. The largest movements post-date the Miocene and have contributed both to the anomalous elevations of the eastern hinterland and to the strong east-west climatic gradient across southern Africa. Controversies surrounding the mechanisms underlying these recent movements appear to have been resolved in favour of buoyancy forces originating from a massive low-density anomaly in the Earth9s mantle below East and southern Africa.

Journal Article
TL;DR: Using this approach it is now possible to detect individuals homozygous or heterozygous for the HFE gene using a simple polymerase chain reaction-based test, which promises to provide fresh insights into the range of phenotypic expression in hereditary hemochromatosis.

Journal ArticleDOI
TL;DR: In this article, new identities relating the Euler-Lagrange, Lie-Backlund and Noether operators are obtained, and the symmetry based results deduced from the new identities are used to construct Lagrangians for partial differential equations.
Abstract: New identities relating the Euler–Lagrange, Lie–Backlund and Noether operators are obtained Some important results are shown to be consequences of these fundamental identities Furthermore, we generalise an interesting example presented by Noether in her celebrated paper and prove that any Noether symmetry is equivalent to a strict Noether symmetry, ie a Noether symmetry with zero divergence We then use the symmetry based results deduced from the new identities to construct Lagrangians for partial differential equations In particular, we show how the knowledge of a symmetry and its corresponding conservation law of a given partial differential equation can be utilised to construct a Lagrangian for the equation Several examples are given

Journal ArticleDOI
TL;DR: The effect of postnatal administration of the long‐acting progestogen contraceptive, norethisterone enanthate, on postnatal depression and on serum hormone concentrations, and their association with depression are studied.

Journal ArticleDOI
TL;DR: This article explored particular organisational dimensions of school failure with a view to understanding how they have affected the operation of schools, why schools have broken down and what interventions may remedy this breakdown.
Abstract: > A prominent and problematical legacy of apartheid education, which requires transformation, is the poor functioning of a large number of previously black schools (commonly termed ‘the breakdown of the culture of teaching and learning'). While the causes of breakdown may be traced back to the years of opposition to apartheid and the resistance struggle waged within schooling from 1976 onwards, it is less clear what may be done to remedy the situation. This article explores particular organisational dimensions of school failure with a view to understanding how they have affected the operation of schools, why schools have broken down and what interventions may remedy this breakdown. It moves beyond rational theories of organisation to argue that perspectives derived from psychoanalytical approaches to organisation may be useful in planning strategies for intervention to transform teaching and learning in these schools.

Journal ArticleDOI
04 Jun 1998-Nature
TL;DR: The cranium was found in a succession of fluvio-deltaic and lacustrine deposits and is associated with a rich mammalian fauna of early to early-middle Pleistocene age, which means the human remains can be dated at ∼1 million years before present.
Abstract: One of the most contentious topics in the study of human evolution is that of the time, place and mode of origin of Homo sapiens1,2,3. The discovery in the Northern Danakil (Afar) Depression, Eritrea, of a well-preserved Homo cranium with a mixture of characters typical of H. erectus and H. sapiens contributes significantly to this debate. The cranium was found in a succession of fluvio-deltaic and lacustrine deposits and is associated with a rich mammalian fauna of early to early-middle Pleistocene age. A magnetostratigraphic survey indicates two reversed and two normal magnetozones. The layer in which the cranium was found is near the top of the lower normal magnetozone, which is identified as the Jaramillo subchron. Consequently, the human remains can be dated at ∼1 million years before present.