Showing papers by "University of the Witwatersrand published in 1983"

The effects of organic acids, phytates and polyphenols on the absorption of iron from vegetables.

Abstract: 1. Non-haem iron absorption from a variety of vegetable meals was studied in parous Indian Women, using the erythrocyte utilization of radioactive Fe method.2. The studies were undertaken to establish whether Fe absorption could be correlatedwith the chemical composition of the foodstuff.3. Addition of the following organic acids commonly found in vegetables, improved the geometric mean Fe absorption from a basic rice meal as follows: from 0·028 to 0·085 with 1 g citric acid, from 0·031 to 0·081 with 15 mg ascorbic acid, from 0·048 to 0·095 with 1 g L-malic acid, from 0·041 to 0·096 with 1 g tartaric acid. The only exception was oxalic acid; the addition of 1 g calciumoxalate to cabbage (Brassica oleraceae) was associated with some depression in Fe absorption from 0·320 to 0·195.4. There was a marked inhibition of the geometric mean absorption when 500 mg tannic acid was added to a broccoli (Brassica oleraceae) meal (0·015 v. 0·297). Sodium phytate (2 g) caused a similar, though less profound inhibition (0·035 to 0·152).5. When 3 mg ferrous sulphate was added to different vegetables the geometric mean absorption varied widely. Vegetables of low Fe bioavailability were wheat germ (Triticum aestivum) 0·007, aubergine (Solanum melongena) 0·007, butter beans (Phaseolus lunatus) 0·012, spinach (Spinacea oleraceae) 0·014, brown lentils (Lens culinaris) 0·024, beetroot greens (Beta vulgaris) 0·024 and green lentils (Lens culinaris) 0·032. In contrast, bioavailability was moderate or good with carrot (Daucus carota) 0·098, potato (Solanum tuberosum) 0·115, beetroot (Beta vulgaris) 0·185, pumpkin (Cucurbita mixta) 0·206, broccoli 0·260, tomato (Lycopersicon esculentum) 0·224, cauliflower (Brassica oleraceae) 0·263, cabbage 0·320, turnip (Brassica rapa) 0·327 and sauerkraut 0·327.6. All the vegetables associated with moderate or good Fe bioavailability contained appreciable amounts of one or more of the organic acids, malic, citric and ascorbic acids.7. Poor Fe bioavailability was noted in vegetables with high phytate contents (e.g. wheat germ 0·007, butter beans 0·012, brown lentils 0·024 and green lentils 0·032).8. The fact that a number of vegetables associated with low Fe-absorption turned bluish-black when Fe was added to them, suggested that the total polyphenol content in them was high. The vegetables included aubergine spinach, brown lentils, green lentils and beetroot greens. When the total polyphenol content in all the vegetables tested was formally measured, there was a significant inverse correlation (r 0·859, P < 0·001) between it and Fe absorption. The inverse correlation between the non-hydrolysable polyphenol content and Fe absorption was r 0·901 (P < 0·001).9. The major relevance of these findings is the fact that the total absorption of non-haem-Fe from a mixed diet may be profoundly influenced by the presence of single vegetables with either marked enhancing or inhibiting effects on Fe bioavailability.

Pb, Sr and Nd isotopic evidence for sources of southern African Cretaceous kimberlites

Abstract: Previously reported initial 87Sr/86Sr and 143Nd/144Nd ratios of non-micaceous southern African Cretaceous kimberlites indicate that their mantle source rocks are undifferentiated to slightly depleted relative to the bulk Earth1–6. Anomalously radiogenic Pb isotopic ratios of these kimberlites, on the other hand, are smilar to those of oceanic island basalts and indicate that the source regions have had high U/Pb ratios7. Some micaceous kimberlites have a different Sr and Pb isotopic character, reflecting different source regions characterized by higher Rb/Sr, but lower U/Pb ratios1,2,7. Nd isotopic analyses have not been reported for the micaceous kimberlites. I present here new whole-rock Pb, Sr and Nd isotopic analyses of examples of both types of kimberlite which, in conjunction with previously published data, confirm the existence of both depleted and enriched upper mantle sources for southern African Cretaceous kimberlites.

Effect of instruction using students' prior knowledge and conceptual change strategies on science learning.

Abstract: One of the factors affecting students' learning in science is their existing knowledge prior to instruction. The students' prior knowledge provides an indication of the alternative conceptions as well as the scientific conceptions possessed by the students. This study is concerned primarily with students' alternative conceptions and with instructional strategies to effect the learning of scientific conceptions; i.e., to effect conceptual change from alternative to scientific conceptions. The conceptual change model used here suggests conditions under which alternative conceptions can be replaced by or differentiated into scientific conceptions and new conceptions can be integrated with existing conceptions. The instructional strategy and materials were developed for a particular student population, namely, black high school students in South Africa, using their previously identified prior knowledge (conceptions and alternative conceptions) and incorporate the principles for conceptual change. The conceptions involved were mass, volume, and density. An experimental group of students was taught these concepts using the special instructional strategy and materials. A control group was taught the same concepts using a traditional strategy and materials. Pre- and posttests were used to assess the conceptual change that occurred in the experimental and control groups. The results showed a significantly larger improvement in the acquisition of scientific conceptions as a result of the instructional strategy and materials which explicitly dealt with student alternative conceptions.

Self-Efficacy Beliefs and Sales Performance

Abstract: Self-efficacy theory predicts that people will perform better when they believe they have the skills necessary for success. It also suggests, however, that believing in long-term rewards for success ("response-outcome expectations") does not correlate with adequate performance. This paper supports the generality of self-efficacy theory and provides evidence that self-efficacy beliefs predict insurance sales performance, whereas response-outcome expectations did not. A questionnaire was developed to measure self-efficacy beliefs and response-outcome expectations using 200 insurance sales representatives. Regression analyses were computed on a different sample of 97 insurance sales representatives using four separate dependent variables (calls-per-week; number of policies sold; sales revenue and a composite performance index on which actual sales commission was based). (1) These analyses established a correlation (but no causal relationship) between self-efficacy beliefs and sales performance. (2) The gener...

Marxism, Feminism and South African Studies

Abstract: (1983). Marxism, feminism and South African studies. Journal of Southern African Studies: Vol. 9, No. 2, pp. 139-171.

Self-efficacy beliefs and tennis performance

Abstract: Theoretical and methodological aspects of self-efficacy theory are assessed in this study, and the tennis performance of 40 active players (M age = 26.6 years) serves as the criterion variable. On a theoretical level, only self-efficacy beliefs, and not response-outcome expectations or the valence thereof, were consistently and significantly related to 12 dimensions of tennis performance. This phenomenon pertained to the relationship of the self-rating of performance as well as to the average of two judges' external ratings of performance and efficacy beliefs, even though the 12 behavioral criteria used were different from the items on the self-efficacy scale. Although Pearson correlations rather than microanalyses were computed to assess the relationship between self-efficacy and performance, the correlations were all positive and significant. Theoretical and empirical implications are suggested.

On Spatial Justice

Abstract: This essay reflects on the desirability and possibility of fashioning a concept of spatial justice from notions of social justice and territorial social justice. The contested meaning, rival formul...

Effects of low intermittent concentrations of nitrous oxide on the developing rat fetus

Abstract: Five groups of 12 gravid female rats were exposed, during their entire gestation, intermittently for 6 h a day, 5 days per week, to 0.5% (5000 p.p.m.), 0.1% (1000 p.p.m.), 0.05% (500p.p.m.) and 0.025% (250p.p.m.) nitrous oxide-air mixtures (v/v), respectively. After killing the gravid rats on the 19th day of their pregnancies the numbers of corpora lutea of pregnancy were counted. Each uterus was examined for placentation sites and embryonic remnants and a detailed examination of the fetuses was undertaken. A significant reduction in mean litter size occurred only in the group exposed to 0.5% nitrous oxide in air (v/v). The mean litter sizes of the control and other exposed groups were comparable. No signs of fetal resorption or skeletal malformation were found in any group. The threshold of pollution for reduction in litter size has been shown in this study to lie between 0.1% and 0.5% nitrous oxide in air (v/v). A previous study on continuous exposure reported the threshold pollution to lie between 0.05% and 0.1% nitrous oxide in air (v/v). This investigation confirms that intermittent exposure to nitrous oxide-air mixtures increases the threshold for reproductive effects in rats.

Experimental data at 3 kbars pressure on parental magma to the Bushveld Complex

Abstract: Experimental studies, mainly under 3 kbars pressure, have been undertaken on representative samples to determine if any of these compositions could be parental magma to the Bushveld Complex. One such composition, with 12.5% MgO, Mg/(Mg + Fe) of 0.72 and quartz-normative, crystallizes olivine, Fo88, as liquidus mineral, at about 1,300° C, followed at only slightly lower temperature by orthopyroxene at 3 kbars pressure. There is a temperature drop of over 100° C before the appearance of plagioclase and finally clinopyroxene. This crystallization sequence is in excellent agreement with the observed sequence in the lower part of the Bushveld Complex.

Infections in children with severe protein-energy malnutrition.

Abstract: SUMMARYThe infections occuring in 68 black children admitted to hospital with kwashiorkor, marasmus or marasmic-kwashiorkor were studied prospectively. Fifteen episodes of bacteraemia, most commonly due to Gram-negative enteric bacilli, occurred in 13 children (19%), six of these episodes being nosocomial. Urinary tract infection, diagnosed on suprapubic urine specimens and all due to Escherichia coli, occurred in five out of 16 cases (31%). In the 48 cases admitted with gastro-enteritis and 18 with pneumonia, a causative organism was found in the minority. Fifteen episodes of nosocomial infection occurred in 14 children (20·6%), of whom four died. Of the 14 deaths, eight were associated with bacteraemia. Skin infections were due mainly to staphylococci and streptococci. Infections in severely malnourished children appear to be due largely to the same microorganisms as cause infection in well-nourished children of the same community. Nosocomial infections pose a major threat to these children.

The effect of microstructure and stress state on the fracture behaviour of wood

Abstract: Based on a general fracture mechanics approach, this paper attempts to correlate macroscopic fracture properties with micromechanical behaviour in wooD. In the first part, the influence of orientation, cell size and other structural features of wood on toughness, fatigue resistance and fracture morphology is described. Subsequently, experimental observations of crack tunnelling effects are reported which, coupled with direct crack tip strain measurements and a verification of the influence of specimen thickness on fracture properties, confirm the existence of stress state variations across a crack front in wood, and the corresponding effects on fracture behaviour. Irreversible crack-tip deformation modes are identified, involving intercellular debonding, cell twisting and buckling, and the role of stress triaxiality is discussed. A strain criteria for the fracture of pre-notched bulk wood specimens is developed, based on an observed linear relationship between notch root radius and crack opening displacement for fracture initiation.

Mating behavior and the evolution of drosophila mauritiana

Abstract: Drosophila mauritiana is closely related to D. melanogaster and D. simulans, from which it differs obviously morphologically in having narrow posterior lobes of the male genital arches (Tsacas and David, 1974). Studies of allozyme frequencies (Gonzailez et al., 1982), some DNA components (see Dover, 1982), polytene chromosome banding sequences (Lemeunier and Ashburner, 1976), and hybrid fertility (David et al., 1974) indicate that it is most closely related to simulans. Drosophila mauritiana is endemic to the island of Mauritius, from which simulans and melanogaster are absent. They are however present on the neighboring island of Reunion from which mauritiana is absent (David and Tsacas, 1975). Mauritius and Reunion are approximately 320 km apart, and 960 km and 720 km from Madagascar, respectively. The only other melanogaster group species on Mauritius are D. ananassae and D. parabipectinata (David and Tsacas, 1975). Their courtships differ considerably from those of the melanogaster subgroup (Narda, 1968; Hegde and Krishnamurthy, 1979). In addition to interest in how its courtship has changed from that of its muchstudied sibling species, mauritiana may provide a test of two evolutionary questions. The first is whether changes in mating behavior, narrow variability of courtship signals, and specificity of mating responses can evolve and be maintained in complete allopatry, i.e., in a solely intraspecific context. This is therefore partly a test of Mayr's (1970 p. 67) prediction

A corundum and sapphirine paragenesis from the Limpopo Mobile Belt, southern Africa

Abstract: An assemblage consisting of corundum, sapphirine, spinel, cordierite, garnet, biotite and bronzite is described from the Messina area of the Limpopo Mobile Belt, and consideration given to its petrogenesis. Various geothermometers and geobarometers have been applied in an attempt to determine the temperatures and pressures of metamorphism. A former coexistence of garnet and corundum is suggested to have developed during the earliest high pressure phase of the metamorphism, where temperatures exceeded 800°C and pressures as high as 10kbar may have been experienced. Subsequently, continuous retrograding reactions from medium pressure granulite facies at about 800°C and 8kbar towards amphibolite facies generated spinel, cordierite, sapphirine and possibly also bronzite. The most notable reaction was probably of the form: garnet + corundum = cordierite + sapphirine + spinel.

Psychosocial factors and obstetric complications.

Abstract: A number of studies have attempted to explain obstetric difficulties on the basis of psychosocial conditions which exist during pregnancy. In addition, recent research in the field of life event stress has indicated that life experiences occurring prior to a pregnancy may influence pregnancy outcome. The present study examines the ability of life event stress as well as a variety of medical, social and psychological variables to predict complications of pregnancy. In contrast to previous small-sample research, the present study examines 782 subjects. Multivariate statistical techniques are employed to analyse the numerous variables measured. Results suggest that ‘age at birth of first child’, ‘education level’, ‘menstrual history’, ‘attitudes to pregnancy’ and ‘age at menstruation’ best predict obstetric difficulties. However, only a small percentage of the variance of pregnancy complication scores is explained by these factors.

Distribution of water in deep gold mines in South Africa

Abstract: Gold mines in South Africa use large volumes of water for cooling and other purposes underground. The mines are often at great depths, for example 3600 metres below surface level. Water piped down the shaft can therefore be at high pressures unless a system of pressure reducing dams or valves is installed. Modern practice is to utilize the high water pressures wherever possible. Examples of the use of water pressure include driving turbines for power generation, moving ore by means of high pressure jets and there is the future possibility of driving mining machinery using the water. The operation and analysis of water reticulation systems is complex owing to the complex distribution system and the number of possible operating conditions. Computer programs for the optimum design of such distribution systems and for the hydraulic analysis of such pipe flow systems have been compiled. The high pressures also pose problems in the design of pipework and equipment.

The behaviour of mine tailings during hydraulic deposition

Abstract: The environmentally acceptable disposal of fine-particled mining and industrial wastes by the formltion of hydraulic- fill slimes dams is becoming an increasingly important aspect of the total mining endeavour. Relatively little is known of the behaviour of waste slurries during deposition. This paper descriptionbes and analyses the following aspects of slurry behaviour: (i) the relationship between viscosity, shear strength, and water content, (ii) the slope assumed by a thickened slurry, (iii) particle-size sorting on a hydraulic-fill beach, (iv) gradients of hydraulic-fill beaches, and (v) internal erosion during the deposition of slurry.

Biological groups within the Lycaenidae (Lepidoptera)

Abstract: The biological groups within the Lycaenidae created by Hinton (195 I) are resurrected and updated. The life histories of Durbania amakosa natalensis van Son, iolaus trimeni Wallengren, PoecUmit;s aureus van Son, Spindasis phanes (Tri­ men), "Hoeides den/atis (Swierstra), Lepidochrysops ignota (Trimen) are described in detail for the first time and additional observations are made on several other species. The importance of larval stages to the higher classification of the Lycaenidae is discussed.