Showing papers by "University of the Witwatersrand published in 1992"
TL;DR: The Kaapvaal craton of South Africa, which formed and stabilized between 3.7 and 2.7 Gyr ago, is one of the oldest reasonably sized examples of these continental fragments as mentioned in this paper.
Abstract: About 30% of the Earth is covered by continents, but only about 10 small kernels of these continentsae—known as Archaean cratonsae—are continental fragments formed before 2.5 Gyr ago. The Kaapvaal craton of South Africa, which formed and stabilized between 3.7 and 2.7 Gyr ago, is one of the oldest reasonably sized examples of these continental fragments. It consists of a mosaic of subdomains that have been welded together by processes similar to those of modern-day plate tectonics. The earliest subdomains may have owed their origin to the onset of efficient recycling from the Earth's hydrosphere into the mantle.
700 citations
261 citations
TL;DR: The authors reported on 18 months of action research that monitored British pupils' learning about the nature of science, using some aspects of history of science for the purpose and found some areas of substantial progress in the pupils' understanding of the nature science, and others where little change seems to have been effected.
Abstract: This article reports on 18 months of action research that monitored British pupils' learning about the nature of science, using some aspects of history of science for the purpose. The action research took place within five classrooms and involved practicing teachers who used a set of historical materials specially written for this study. Preliminary findings about the common perceptions of the nature of science held by middle school pupils (age 11–14 years) guided the work, which was carried out using a variety of methodologies. The results obtained show some areas of substantial progress in the pupils' understanding of the nature of science, and others where little change seems to have been effected.
251 citations
TL;DR: In an effort to use more of the information available in the image, the present approach evaluates two-dimensional entropies based on the 2D (grey-level/local average grey-level) “histogram” or scatterplot.
248 citations
TL;DR: An improved HB cross is established and evaluated to combine the high bioactivation capacity with the ease of scoring the wings using the same criteria as for the standard cross, and has a sensitivity to the direct-acting alkylating agent ethyl nitrosourea equal to that of the standardCross.
Abstract: The two tester strains of the high bioactivation (HB) cross for the wing somatic mutation and recombination test (SMART) in Drosophila melanogaster developed by Frolich and Wurgler possess high metabolic capacity to activate promutagens. These strains contain chromosomes 1 and 2 of the DDT-resistant stock Oregon R(R) which exhibits a high constitutive level of cytochrome P450. However, they show several disadvantages for routine application, such as disturbed wing hair patterns in certain areas of the wing, making spot classification difficult, and a delay in development of the larvae. We have established and evaluated an improved HB cross (ORR; flr3 females and mwh males) producing ORR heterozygous individuals. These develop normally and have a normal, undisturbed wing hair pattern while exhibiting high bioactivation. The hybrid larvae of the improved HB cross show P450-dependent bioactivation capacity equal to or even slightly higher than those of the original HB cross. This was demonstrated by measuring the genotoxic activity of the promutagens diethylnitrosamine, 7,12-dimethylbenz[a]anthracene, N-nitrosopyrrolidine, and urethane. In addition, the improved HB cross has a sensitivity to the direct-acting alkylating agent ethyl nitrosourea equal to that of the standard cross. The main advantage of the improved HB cross is to combine the high bioactivation capacity with the ease of scoring the wings using the same criteria as for the standard cross.
197 citations
TL;DR: A study of the avulsion of a major distributory channel on the alluvial fan (22 000 km2 in area) of the Okavango River in northern Botswana has revealed that channels serve as arterial systems distributing water which sustains large areas of permanent swamp.
Abstract: A study of the avulsion of a major distributory channel on the alluvial fan (22 000 km2 in area) of the Okavango River in northern Botswana has revealed that channels serve as arterial systems distributing water which sustains large areas of permanent swamp. The channels are vegetatively confined. A primary channel, defined here as a channel which receives water and sediment directly from the fan apex, aggrades vertically as a result of bedload deposition. The rate of aggradation increases downchannel and may exceed 5 cm yr−1 in the distal reaches. Rapid aggradation is associated with a decline in flow velocity. This initiates a series of feedback mechanisms involving invasion of the channel by aquatic plants which trap floating plant debris, further reducing flow rate and causing the channel water surface to become elevated, thereby increasing rate of water loss from the channel, accelerating blockage and aggradation. The channel ultimately fails. Enhanced water loss from the channel promotes the growth of flanking swamp vegetation, which confines the failing channel. Increased flow through the swamp erodes pre-existing hippopotamus trails, producing a secondary channel system which overlaps but does not connect directly to the failing reach of the primary channel. The region of failure of the primary channel migrates upstream, accompanied by headward propagation of the secondary channel system. The swamp distal to the failed primary channel dessicates and is destroyed by peat fires. Secondary channels are stable and not prone to blockage. Comparison with avulsions described in other river systems indicates that the influence of plants in the Okavango River system is exceptionally strong.
192 citations
TL;DR: In this paper, the exact nature of climatic change in southern Africa over the past two millennia has been investigated based on oxygen isotope analyses of cave speleothems, and the results showed that relatively little was known of the exact evolution of climate change in the region.
Abstract: Until recently, relatively little was known of the exact nature of climatic change in southern Africa over the past two millennia. New research based on oxygen isotope analyses of cave speleothems ...
188 citations
TL;DR: A conceptual model is presented to determine situations in which the Principle of Least Effort may, or may not, apply, and helps identify when the PLE may be a useful model for interpretation of appropriate data sets.
179 citations
TL;DR: Resistance to penicillin among South African strains of Streptococcus pneumoniae increased from 4.9% in 1979 to 14.4% in 1990, and antigenic homology was found in PBPs 1A and 2B of strains belonging to these species.
Abstract: Resistance to penicillin among South African strains of Streptococcus pneumoniae increased from 4.9% in 1979 to 14.4% in 1990. Except for resistance to co-trimoxazole (44%), resistance to other antimicrobial agents remained relatively low. Multiply resistant strains belonged mainly to serovars 6B, 19A, 14, and, more recently, 23F. Use of chloramphenicol to treat meningitis caused by strains relatively resistant to penicillin proved to be unsatisfactory, probably because of the inadequate bactericidal activity of chloramphenicol against these strains. Spread of penicillin-resistant nasopharyngeal strains in pediatric wards was most common among children who received antimicrobial therapy. Penicillin-binding protein (PBP) patterns were shown to vary in resistant clinical strains. Interspecies transfer of penicillin resistance between Streptococcus mitis and S. pneumoniae was demonstrated and antigenic homology was found in PBPs 1A and 2B of strains belonging to these species. Restriction enzyme mapping following DNA amplification of the PBP 2B gene revealed six arrangements among South African strains within serogroup 19. Despite extensive studies in South Africa and several other countries, many questions with regard to the global problem of antimicrobial resistance among S. pneumoniae strains remain unanswered, especially those that relate to prevalence in developing regions of the world.
177 citations
TL;DR: When compared to a group of normal ovulating women, however, REM sleep time decreased during the last two months of pregnancy and, although there was no change in sleep onset latency, the time spent awake during the first six hours of sleep was increased.
Abstract: We conducted a longitudinal polysomnographic study in five healthy primiparous subjects, whose sleep was first recorded between 8 and 16 weeks of gestation, then every 2 months until parturition and at 1 month postpartum. The first 6 hours of sleep were used for statistical analysis. In contrast to previous studies, we found no reduction in stage 4 sleep with pregnancy. Slow-wave sleep (comprising stages 3 and 4), was significantly higher at 27-39 weeks of gestation than at 8-16 weeks, as predicted by the restorative theory of sleep. There was no significant difference in rapid eye movement (REM) sleep time. When compared to a group of normal ovulating women, however, REM sleep time decreased during the last two months of pregnancy and, although there was no change in sleep onset latency, the time spent awake during the first six hours of sleep was increased. Future research into the effects of cortisol and progesterone is indicated.
157 citations
TL;DR: Evidence is provided that the biologic activity of osteogenin can be restored and delivered by a substratum other than the organic collagenous matrix, inducing rapid bone differentiation in calvarial defects of adult nonhuman primates.
Abstract: Osteogenin, a bone morphogenetic protein, in conjunction with insoluble collagenous bone matrix initiates local endochondral bone differentiation by induction in vivo. This study, by exploiting the affinity of native osteogenin for hydroxyapatite, was designed to construct a delivery system for the expression of the biologic activity of osteogenin in nonhealing calvarial defects of adult primates. After exposure of the calvaria, 64 cranial defects, 25 mm in diameter, were prepared in 16 adult male baboons (Papio ursinus). Defects were implanted with disks of porous nonresorbable and resorbable hydroxyapatite substrata obtained after hydrothermal conversion of calcium carbonate exoskeletons of corals. In each animal, one disk of each hydroxyapatite preparation was treated with osteogenin isolated and purified from baboon bone matrix after sequential chromatography on heparin-Sepharose, hydroxyapatite, and Sephacryl S-200 gel filtration columns. The remaining two defects were implanted with one disk of each hydroxyapatite preparation without osteogenin as control. Histomorphometry on decalcified sections prepared on days 30 and 90 showed superior osteogenesis in osteogenin-treated nonresorbable hydroxyapatite specimens as compared with controls. On day 90, substantial bone formation also had occurred in control nonresorbable hydroxyapatite specimens. On day 90, but not on day 30, significantly greater amounts of bone had formed in osteogenin-treated resorbable specimens as compared with resorbable controls. Overall, resorbable substrata performed poorly when compared with nonresorbable substrata, perhaps due to a premature dissolution of the implants. These results provide evidence that the biologic activity of osteogenin can be restored and delivered by a substratum other than the organic collagenous matrix, inducing rapid bone differentiation in calvarial defects of adult nonhuman primates. The adsorption strategy of osteogenin on porous inorganic nonimmunogenic substrata may help to design appropriate osteogenic delivery systems for craniofacial and orthopedic applications in humans.
TL;DR: Arguments for and against traditional healers in health care are presented, and alternatives which could be chosen are outlined.
TL;DR: The origins of the Group Areas Act have been the subject of some speculations but no serious research; the same applies to examination of the specific nature of the changes which it introduced.
Abstract: In the early months of 1990, as the excitement of F.W. de Klerk's change of direction captured international attention, government television in South Africa offered its white viewers a new serial which revealed that those previously 'disqualified' people, showing an increasing tendency to move in next door, might even be 'People Like Us'.' This crude, if entertaining, ideological manipulation provided an extraordinary antithesis to earlier National Party contortions. Exactly forty years before, when Dr T.E. Donges introduced the Group Areas Bill in the House of Assembly, his staff had to cast around for evidence of the popularity of generalised, compulsory urban racial segregation. In doing so they found many examples of demands for, moves towards and attempts at enforced separation of 'race groups' in urban areas. Some of these Donges cited during the lengthy parliamentary debates on the Group Areas Bill. But what were the forces pushing for comprehensive segregation? Who contributed to the framing of the Bill? Was there a preconceived scheme to impose a master plan for internal urban apartheid? Our inability to answer these questions stems from the fact that the creation of 'group areas', usually considered to lie at the very core of urban apartheid, has not yet been studied by scholars. The origins of the Group Areas Act have been the subject of some speculations but no serious research; the same applies to examination of the specific nature of the changes which it introduced, and to the
TL;DR: The ethnic background and traditional usage of these remedies was researched and a literature survey revealed that 57 different plants were used in herbal remedies during pregnancy and childbirth.
TL;DR: In this paper, the anatomically modern status and a Last Interglacial or later age for the human fossils enjoy general support, issues related to the definition of the Middle Stone Age, its dating, and the interpretation of human behavior lack consensus.
Abstract: Current interest in the origins of anatomically modernHomo sapiens has focused attention on early modern human remains and related archaeological materials associated with the southern African Middle Stone Age. While the anatomically modern status and a Last Interglacial or later age for the human fossils enjoy general support, issues related to the definition of the Middle Stone Age, its dating, and the interpretation of human behavior lack consensus. Available evidence suggests that the anatomically modern human skeleton appeared well before many aspects of the subsistence and symbolic behavior that characterize recent foragers and that Middle Stone Age technology persisted longer in southern Africa than its northern hemisphere counterpart.
TL;DR: Heterogeneity analyses are consistent with the hypothesis that MHS can be caused in humans by any one of at least three distinct genetic loci and preliminary linkage data suggesting the localization of a gene in human MHS to 17q11.2-q24 (MHS2), with a gene frequency approximately equal to that of the MHS1 locus on 19q.1.
TL;DR: In this article, the authors obtained upper and lower bounds for Christoffel functions for Freud weights by relatively new methods, including a new way to estimate discretization of potentials.
Abstract: We obtain upper and lower bounds for Christoffel functions for Freud weights by relatively new methods, including a new way to estimate discretization of potentials. We then deduce bounds for orthogonal polynomials onℝ thereby largely resolving a 1976 conjecture of P. Nevai. For example, let W:=e−Q, whereQ:ℝ→ℝ is even and continuous inℝ, Q" is continuous in (0, ∞) andQ'>0 in (0, ∞), while, for someA, B,
$$1< A \leqslant \frac{{(d/dx)(xQ'(x))}}{{Q'(x)}} \leqslant B,x \in (0,\infty )$$
TL;DR: Prostate cancer rates are very low among those living traditionally, however, rates rise in urban populations in transition, associated with changes in diet and other aspects of life-style.
Abstract: nean countnes, such as Greece. In the same country. as in the UK (Cancer Statistics Group, 1982). rates vary regionally. Thev can also vary even between adjacent districts. as in Scotland (Kemp et al.. 1985). Incidence and mortality rates are rising in many countries (Davis et al.. 1990: Dofl, 1990). However, survival rates are improving (Bonnett et al.. 1988). In Third World populations. prostate cancer rates are very low among those living traditionally. However, rates rise in urban populations in transition, associated with changes in diet and other aspects of life-style (Parkin, 1986). In rural Africa, rates are very low (Gilpin et al.. 1989; Bah et al.. 1990): but are higher in those living in big cities (Cancer Registry of South Africa, 1988). According to this Registry.
TL;DR: A mutant of one of these strains was isolated which had lost azo-dye decolorizing ability and the strain was used to clone DNA conferring this ability, by screening a BclI library constructed from DNA of a decolorized strain.
Abstract: Azo dye are recalcitrant pollutants. Two sulfonated azo dyes, Orange II and Amino black, are effectively decolorized by certain noncardioform strains of the genus Rodococcus. A mutant of one of these strains was isolated which had lost azo-dye decolorizing ability and the strain was used to clone DNA conferring this ability, by screening of Bc/I library constructed from DNA of a decolorizing strain. The relevant genetic information was located on a 6.3-kb fragment of DNA.
TL;DR: In this paper, the authors compared the ethical beliefs of managers operating in South Africa and Australia and found that despite differences in socio-cultural and political factors there are no statistically significant differences between the two groups regarding their own ethical beliefs.
Abstract: Academic literature addressing the topic of business ethics has paid little attention to cross-cultural studies of business ethics. Uncertainty exists concerning the effect of culture on ethical beliefs. The purpose of this research is to compare the ethical beliefs of managers operating in South Africa and Australia. Responses of 52 managers to a series of ethical scenarios were sought. Results indicate that despite differences in socio-cultural and political factors there are no statistically significant differences between the two groups regarding their own ethical beliefs. Results thus support the view that culture has little or no impact on ethical beliefs.
TL;DR: Findings in adult primates establish a primary role for osteogenin in initiation and promotion of osteogenesis, and imply a potential therapeutic application based on cell biology of extracellular matrix-cell interactions.
TL;DR: In this article, the authors present a generale de travaux concernant la preparation and the structure moleculaire of complexes halogenes, acyles, avec des coordinats contenant de l'oxygene, soufre ou phosphore, des metallocenes ainsi que des composes metallocycliques.
TL;DR: The histogenesis of lateral periodontal cysts is uncertain but it is favoured origin from reduced enamel epithelium, while the unicystic and multicystic varieties are distinguished.
Abstract: Lateral periodontal cysts account for 0.8% of all jaw cysts seen in our department. Published reports have indicated that they occur most frequently in the 5th to 7th decades, that there is a male preponderance and that they are located mainly in the mandibular canine-premolar region. In our own series of 20 cases, 10 were found in the anterior maxilla. We have distinguished unicystic and multicystic (including botryoid) varieties. They were lined predominantly or exclusively by thin reduced enamel epithelium-like tissue which contained many clear cells and epithelial thickenings referred to as plaques. Glycogen was present in the epithelium of two-thirds of our cases although not exclusively in the clear cells, many of which showed no positivity. Two of our examples of the botryoid variety were different histologically, being lined predominantly by non-keratinizing stratified squamous epithelium with crowded and pyknotic nuclei and no clear cells. One case contained melanin while another showed epithelial crypt formation and superficial palisaded low columnar cells as seen in the glandular odontogenic cyst. This raised the question of whether the latter may form part of the clinico-pathologic spectrum of lateral periodontal cyst. The histogenesis of lateral periodontal cysts is uncertain but we favour origin from reduced enamel epithelium.
TL;DR: In this paper, the electrodissolution of copper in hydrochloric acid solutions at the rotating ring disk elec- trode was found to be controlled by both mass transfer and reaction in the apparent-Tafel region in HCl concentrations of between 1 and 10 M.
TL;DR: Autonomic testing revealed AD in each patient, while symptoms were experienced by 33 of them, and the potential role of AD in the pathogenesis of SSc deserves further study.
TL;DR: It is suggested that neurotensin has an important regulatory function in the growth of colonic mucosa; however, the mode of action, at the cellular level, appears to be different depending on age.
TL;DR: In this article, the phlobaphenes formation and precipation during sulphite/water extraction of pine tannins from pine bark was minimized by blocking tannin self-condensation by the addition of small amounts of a strong nucleophile such as phloroglucinol, m-phenylenediamine and urea, the latter due to its low cost for industrial application.
Abstract: The phlobaphenes formation and precipation during sulphite/water extraction of pine tannins from pine bark was minimized by blocking tannin self-condensation by the addition of small amounts of a strong nucleophile such as phloroglucinol, m-phenylenediamine and urea, the latter due to its low cost for industrial application. These inhibitors reacted preferentially with the reaction intermediates formed in the tannins self-condensation mechanism, stopping the reaction reaching the molecular rearranged precipates known as phlobaphenes. The principle of inhibition appears to be effective at both the laboratory and industrial level. The results of laboratory and industrial extractions and the results of the adhesives from the modified pine tannin extract/urea adducts obtained are presented. The pine tannin/urea extracts proved to yield good thermosetting wood adhesives for panel products. The minimization of phlobaphenes precipitation increased the yield from 19% to 25% industrial scale.
TL;DR: In the Limpopo Orogeny, the authors of as discussed by the authors found that the charnoenderbite and enderbite were derived from a crustal precursor and the granodiorite and granite of the Matok Pluton were intruded at approximately the same time, between ∼ 2667 Ma and ∼ 2664 Ma ago.
TL;DR: In this article, the structure of the central Kaapvaal Craton of southern Africa has been investigated by deep seismic sounding, using mine tremors as energy sources, and the traveltimes and amplitudes interpreted using 2-D ray-tracing techniques.
Abstract: SUMMARY The structure of the central Kaapvaal Craton of southern Africa has been investigated by deep seismic sounding, using mine tremors as energy sources. Seismometers were deployed at approximately 10 km intervals on two profiles stretching between major mine tremor source regions. Mine tremors are rich in shear energy enabling joint interpretation of P- and S-waves and produce substantial energy at frequencies as low as 1 Hz. Record sections are presented for both P- and S-waves, and the traveltimes and amplitudes interpreted using 2-D ray-tracing techniques. Synthetic seismograms computed for a 1-D velocity model by the reflectivity method compare well with the observed data. A generalized seismic model of the Kaapvaal Craton has the following features: supracrustal strata 0-10 km thick; upper crystalline basement with P-wave velocities of 6.0-6.2 km s-’; the boundary between upper and lower crust at a depth of 14-18 km; a lower crust with a relatively uniform seismic velocity in the range 6.4-6.7 kms-’; and the crust/mantle transition over 1-3 km with the Moho at a depth of about 35 km. The lower crust is found to be seismically attenuating and has a Poisson’s ratio of about 0.28. It is also known to be electrically conductive. These observations are in accord with the presence of hydrated mantle rock at the base of the crust. The velocity-depth model of the Kaapvaal Craton is similar to models derived for other Archaean cratons. The Proterozoic provinces adjacent to the Kaapvaal craton are significantly thicker, and have an intermediate- to high-velocity layer developed at the base of the crust. This is interpreted to indicate a change in the process of crustal growth, with basaltic underplating becoming more important since the Archaean. This change is attributed to a change in the composition of the upper mantle. The higher temperatures in the Archaean mantle led to the eruption of komatiitic lavas, resulting in an ultradepleted mantle unable to produce significant volumes of basaltic melt. Proterozoic crust developed above fertile mantle, and subsequent partial melting resulted in basaltic underplating and crustal inflation.
TL;DR: Water consumption and discharge in industrial water systems are currently minimised, but fluid dynamics and their effect on biofouling control programmes have been well reported in the literature, and remains an aspect which is neglected by industry in terms of practical applications.