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Showing papers by "University of the Witwatersrand published in 1981"


Journal ArticleDOI
TL;DR: In this paper, a model of learning as conceptual change is developed, which investigates the conditions under which an individual holding a set of conceptions of natural phenomena, when confronted by new experiences, will either keep his or her conceptions substantially unaltered in the process of incorporating these experiences, or have to replace them because of their inadequacy.
Abstract: Summaries English Learning science is complex‐‐a student has at different times to acquire new information, reorganize existing knowledge and even discard cherished ideas. In addressing this issue, the analogy between individual learning and conceptual change in scientific disciplines has been fruitful in providing aspects of a suitableframework for analysing science learning. In this paper a model of learning as conceptual change is developed. It investigates the conditions under which an individual holding a set of conceptions of natural phenomena, when confronted by new experiences will either keep his or her conceptions substantially unaltered in the process of incorporating these experiences, or have to replace them because of their inadequacy. The model illuminates the importance of addressing an individual's existing conceptions. It also pinpoints the importance of an individual's metaphysical commitments in influencing scientific learning.

446 citations


Journal ArticleDOI
TL;DR: It is suggested that a large proportion of proteoglycans from normal disc have undergone a degree of degradation in the hyaluronate binding region and that proteoglycan synthesis in this tissue is slower than in degenerate tissue.

306 citations


Journal ArticleDOI
TL;DR: DNA extracts from hepatocellular carcinomas of 13 patients from South Africa suggest that integration of HBV‐DNA into the human genome occurs in conjunction with malignant transformation.

196 citations


Journal ArticleDOI
TL;DR: Direct and indirect evidence suggests that emergent Homo (though not Australopithecus ) possessed at least the rudiments of a speech faculty about 2 Ma ago, and biological and cultural evolution were in a positive reciprocal feedback relationship.
Abstract: Transformations of the nervous, masticatory, locomotor and manipulatory systems, with accompanying functional changes, marked the emergence of the Hominidae and of the genus Homo . Various systems evolved in a mosaic fashion. The manipulatory and locomotor systems hominized early, probably with the emergence of the hominid family. Major changes of brain form and size occurred later, with the emergence of Homo . The functional counterpart of brain change is often thought of as cultural behaviour (material and non-material). However, the evolution of a propensity for culture would not alone have ensured the perpetuation of culture. Only an advanced mechanism for social transmission could have handed on the culture itself: evolving speech was such an advanced mechanism. Direct and indirect evidence suggests that emergent Homo (though not Australopithecus ) possessed at least the rudiments of a speech faculty about 2 Ma ago. Thereafter, biological and cultural evolution were in a positive reciprocal feedback relationship. In this autocatalytic system, speech was a crucial component: by making possible spoken teaching and learning, it enabled culture to evolve beyond what could be conveyed by grunts, snorts or nudges.

165 citations


Journal ArticleDOI
11 Dec 1981-Science
TL;DR: Sleep recordings were carried out on athletes on four successive nights after completing a 92-kilometer road race and significant increases in total sleep time and slow-wave sleep were found.
Abstract: Sleep recordings were carried out on athletes on four successive nights after completing a 92-kilometer road race. Significant increases in total sleep time and slow-wave sleep were found after this metabolic stress. The results show a definite exercise effect on sleep and support sleep-restoration hypotheses.

151 citations



Journal ArticleDOI
TL;DR: A method of blocking the brachial plexus using an infraclavicular approach is described and compared with the axillary approach a higher level of analgesia can be obtained and a potentially septic area is not traversed.
Abstract: A method of blocking the brachial plexus using an infraclavicular approach is described. Compared with the supraclavicular approach, pulmonary complications do not occur and compared with the axillary approach a higher level of analgesia can be obtained and a potentially septic area is not traversed. However, the level of anaesthesia is at a lower level than that obtained from the supraclavicular approach.

123 citations


Journal ArticleDOI
TL;DR: In contrast to Africa's holistic approach the framework of bigoted rationalism and fanatic adherence to outer physical reality, characteristic of western society, has created a dehumanized psychology, particularly apparent in South Africa as mentioned in this paper.
Abstract: Psychology grew out of the European and North American soil, which, according to several African authors, is impoverished in soul and poor in spirit. It is to such psychology that we in South Africa bow our heads. In doing so we do ourselves a disservice, for there is in sub-Sahara Africa a psychological dimension which has a great deal to offer the rest of the world. Southern Africa's psychological potential is especially apparent with respect to the holistic principle — the importance of the majority of her people attach to the physical, spiritual and interpersonal dimensions of being.In contrast to Africa's holistic approach the framework of ‘bigoted rationalism and fanatic adherence to outer physical reality’, characteristic of western society, has created a dehumanized psychology, particularly apparent in South Africa. Not only is there no understanding or need to understand and know about the psychological principles underlying life in Africa, but psychology seems to be oblivious to the immense huma...

120 citations


Journal ArticleDOI
TL;DR: In this paper, the authors explain variations in rainfall over southern Africa in terms of variations in pressure and circulation patterns, and suggest that the 10-11 year rainfall oscillation of the southern Cape may be forced by longitudinal changes in the position of the first ridge of standing wave 3 which may oscillate with a similar quasi-periodicity.
Abstract: Variations in rainfall over southern Africa are explained in terms of variations in pressure and circulation patterns. The extended wet spells of the quasi 18-year oscillation in rainfall that have affected the subcontinent are shown to have occurred in association with increased pressures in the region where the subtropical ridge of the first zonal standing wave in the 500-mb surface has its expression in the southern hemisphere, in association with the eastwards displacement or weakening of the Indian Ocean high and a probable lowering of pressure over the subcontinental interior. It is further suggested that the 10-11 year rainfall oscillation of the southern Cape may be forced by longitudinal changes in the position of the first ridge of standing wave 3 which may oscillate with a similar quasi-periodicity.

105 citations


Journal ArticleDOI
TL;DR: In this article, ground acceleration was recorded at a depth of about 3 km in the East Rand Proprietary Mines, South Africa, for tremors with −1 ≦ M L ≦ 2.38 · M L.
Abstract: Ground acceleration was recorded at a depth of about 3 km in the East Rand Proprietary Mines, South Africa, for tremors with −1 ≦ M L ≦ 2.6 in the hypocentral distance range 50 m R ≦ 1.6 km. The accelerograms typically had predominant frequencies of several hundred Hertz and peak accelerations, a , as high as 12 g . The peak accelerations show a dependence on magnitude, especially when expressed as dynamic shear-stress differences, defined as σ˜ = ρRa , where ρ is density. For the mine tremors, σ˜ varies from 2 to 500 bars and depends on magnitude according to log σ˜ = 1.40 + 0.38 · M L . Accelerograms for 12 events were digitized and then processed to determine velocity and, for seven events with especially good S/N , displacement and seismic source parameters. Peak ground velocities v ranged up to 6 cm/sec and show a well-defined dependence one earthquake size as measured by M L or by seismic moment, M o . On the basis of regression fits to the mine data, with −0.76 ≦ M L ≦ 1.45, log Rv = 3.95 + 0.57 M L , where Rv is in cm 2 /sec, and log Rv = −4.68 + 0.49 log M o . These regression lines agree excellently with the corresponding data for earthquakes of M L up to 6.4 or M o to 1.4 × 10 26 dyne-cm. At a given value of M L or M o , a , at fixed R , shows considerably greater variation than v and appears to depend on the bandwidth of the recording system. The peak acceleration at small hypocentral distances is broadly consistent with ρRa = 1.14 Δτ r o f s / β , where Δτ is stress drop, r o is the source radius, β is shear velocity, and f s is the bandwidth of the recording system. The peak velocity data agree well with Rv = 0.57 β Δτ r o /μ, where μ is the modulus of rigidity; both expressions follow from Brune9s model of the seismic source and were compared with data for events in the size range 5 × 10 16 ≦ M o ≦ 1.4 × 10 26 dyne-cm. Measurements of the source parameters indicated that, as for earthquakes, the stress drops for the tremors range from 1 to 100 bars and show no consistent dependence on M o down to M o = 5 × 10 16 dyne-cm.

103 citations


Journal ArticleDOI
15 Jan 1981-Lithos
TL;DR: In this paper, four distinct ages of sills intrude the floor rocks under the Bushveld Complex, including metadolerite, hypersthene microgabbro and doleritic sills.


Journal ArticleDOI
TL;DR: It is suggested that the psychological parameter of muscle endurance to a large, but unknown, extent depends on the physiological parameter of isometric contractile activity but also individual psychological factors seem to play a role.
Abstract: Maximal voluntary isometric contractions of the elevator jaw muscles, with the mandible in the position of maximal intercuspation of the natural teeth, can induce fatigue and weak as well as severe pains in the jaw muscles of children and adults. A subjective sensation of muscle fatigue appears after about 0.5 min of clenching, and it seems as if the psychological parameter of fatigue onset to a large, but unknown, extent is determined by the physiological parameter of the amount of isometric contractile activity, and perhaps also the original strength of the muscle; however, also individual psychological factors seem to play a role. Pains in the elevator jaw muscles appear after about 1 min of clenching. Although isometric contractions are necessary to cause onset of jaw muscle pains, it is conceivable that perception of the moment of onset of pains to a large, but unknown, extent depends on psychological factors, perhaps the intensity of pains; however, also physiological factors may play a role. The severe muscle pains and gradually increasing subjective exhaustion of the elevator jaw muscles can be endured for about 2 min of maximal voluntary tooth clenching. It is suggested that the psychological parameter of muscle endurance to a large, but unknown, extent depends on the physiological parameter of isometric contractile activity but also individual psychological factors seem to play a role.

Journal ArticleDOI
TL;DR: Fe(III)EDTA may be a useful compound for food fortification of cereals because the Fe is well absorbed and utilized for haemoglobin synthesis and the mechanism whereby it forms a common pool with intrinsic food Fe differs from that occurring with simple Fe salts.
Abstract: 1. The modification of iron absorption from Fe(III)EDTA by agents known to promote or inhibit absorption was examined in 101 volunteer multiparous Indian women. Fe absorption from Fe(III)EDTA was compared with absorption of intrinsic food Fe in a further twenty-eight subjects. Finally the urinary excretion of radio-Fe after oral administration of 59Fe(III)EDTA was studied in twenty-four subjects and evidence of intraluminal exchange of Fe was examined. 2. Fe absorption from maize porridge fortified with Fe(III)EDTA was more than twice that from porridge fortified with FeSO4 . 7H2O. 3. Although bran decreased Fe absorption from FeSO4 . 7H2O approximately 11-fold, it had no significant effect on Fe absorption from Fe(III)EDTA. Nevertheless tea, which is a more potent inhibitor of Fe absorption, decreased absorption from Fe(III)EDTA 7-fold. 4. Fe absorption from Fe(III)EDTA given in water was only increased 40% by addition of 3 mol ascorbic acid/mol Fe but by 7-fold when the relative proportions were increased to 6:1. This enhancing effect was blunted when the Fe(III)EDTA was given with maize porridge. In these circumstances, an ascorbate:iron value of 3:1 (which doubles absorption from FeSO4 . 7H2O) produced no significant increase in Fe absorption, while a value of 6:1 produced only a 2 . 5-fold increase. 5. Fe absorption from Fe(III)EDTA was not altered by addition of maize porridge unless ascorbic acid was present. 6. Less than 1% of 59Fe administered as 59Fe(III)EDTA was excreted in the urine and there was no inverse relationship between Fe absorption and the amounts excreted (r 0 . 58, P less than 0 . 05). 7. Isotope exchange between 59Fe(III)EDTA and 59FeSO4 . 7H2O was demonstrated by finding a similar relative value for the two isotopes in urine and erythrocytes when the two labelled compounds were given together orally. This finding was confirmed by in vitro studies, which showed enhanced 59Fe solubilization from 59FeSO4 . 7H2O in maize porridge when unlabelled Fe(III)EDTA was added. 8. Although Fe absorption from Fe(III)EDTA was marginally higher it appeared to form a common pool with intrinsic food iron in most studies. It is postulated that the mechanism whereby Fe(III)EDTA forms a common pool with intrinsic food Fe differs from that occurring with simple Fe salts. When Fe is present in the chelated form it remains in solution and is relatively well absorbed because it is protected from inhibitory ligands. Simple Fe salts, however, are not similarly protected and are absorbed as poorly as the intrinsic food Fe. 9. It is concluded that Fe(III)EDTA may be a useful compound for food fortification of cereals because the Fe is well absorbed and utilized for haemoglobin synthesis. The substances in cereals which inhibit absorption of simple Fe salts do not appear to inhibit absorption of Fe from Fe(III)EDTA.


Journal ArticleDOI
TL;DR: In this article, the effect of flexible working hours on employee satisfaction and performance was investigated in a field experiment conducted in a federal agency among 64 clerical employees who were randomly assigned to either flexible or fixed working hours for 6 months.
Abstract: The effect of flexible working hours on employee satisfaction and performance was investigated in a field experiment conducted in a federal agency among 64 clerical employees who were randomly assigned to either flexible or fixed working hours for 6 months. The results indicated that flexitime caused a significant increase in satisfaction but had negligible effects on performance, whether assessed by ratings or output. Future research should aim to uncover the reasons for the positive effect of flexitime on employee feelings about their jobs. As part of a general trend to reexamine patterns of working hours, an increasing number of work organizations have introduced flexible working hours for their employees. The essential feature of such schemes is that "the starting and quitting times are flexible for the employee, but that he or she must be there during a core working time" (Glickman & Brown, 1974, p. 34). Typically, organizations that adopt flexible working hours define a core time period during which all employees are expected to work and then allow a range of time before and after this period during which employees can decide on their own arrival and departure times. Despite its widespread adoption by many organizations, however, the actual effect of flexible working hours on employee morale and productivity has yet to be demonstrated. With the notable exception of the studies by Golembiewski, Hilles, and Kagno (1974) and by Schein, Maurer, and Novak (1977), most of the information regarding the effects of flexible working hours has not been based on controlled studies but instead on managerial judgments, single case studies, and surveys of employee opinion (cf. Baum & Young, 1974). In their longitudinal study based on preattitudinal and postattitudinal measures, Golembiewski et al. found employee reactions to the installation of flexible working hours to be generally positive. In their study among insurance clerks in five different working units, Schein et al. found a significant increase in productivity following the initiation of flexitime in two of the units but no change in the other three units. As the researchers of both these studies admit, however, no "clearcut conclusions" regarding the actual effect of flexible working hours can be made from their


Journal ArticleDOI
TL;DR: The mechanisms of the adsorption and elution processes have not yet been established unequivocally as mentioned in this paper, despite the efforts of investigators over a period of almost 70 years, but the literature relating to them is reviewed here.
Abstract: Exciting new developments are taking place in the extractive metallurgy of gold, which are based upon the adsorption of the metal or its complexes on carbon and subsequent elution. Despite the efforts of investigators over a period of almost 70 years, however, the mechanisms of the adsorption and elution processes have not yet been established unequivocally. The literature relating to them is reviewed here.

Journal ArticleDOI
TL;DR: The results indicate that both anions and cations can affect the lability of the two sites and suggest that the ionic composition serum may play an important role in determining the observed distribution of iron among the sites.

Journal ArticleDOI
TL;DR: During hospitalization on a normal ward diet containing approximately 1200 mg calcium/day, the radiological bone lesions healed, serum PTH, 1,25-(OH) 2 D and alkaline phosphatase concentrations returned to normal, and urinary calcium excretion increased.

Journal ArticleDOI
07 May 1981-Nature
TL;DR: In this article, a comparison of clinopyroxene megacrysts with existing kimberlite data was made, and it was shown that low crystal-liquid partition coefficients for the rare earths are plausible.
Abstract: Kimberlites are characterized by a high concentration of incompatible elements, including light rare earths. However, Nd isotopic evidence indicates that their source regions do not have a long history of enrichment. If kimberlites can be generated from non-enriched mantle sources by simple partial melting processes, this implies that crystal–liquid partition coefficients for some trace elements are lower for kimberlitic liquids than for basalts or andesites. From a comparison of clinopyroxene megacrysts (regarded as equilibrated with kimberlite at depth) with existing kimberlite data we argue here that low crystal–liquid partition coefficients for the rare earths are plausible.

Journal ArticleDOI
TL;DR: In this paper, the results of electron microprobe studies of minerals from two-pyroxene, cordierite-orthopyroxene (-gedrite) (-sapphirine) and garnet and/or Cordierite parageneses from Namaqualand, in the N.W. Cape Province of South Africa were reported.
Abstract: The northwestern part of South Africa and southern South-West Africa/Namibia is amongst the most extensive granulite terranes in Africa. This work reports the results of electron microprobe studies of minerals from two-pyroxene, cordieriteorthopyroxene (-gedrite) (-sapphirine) and garnet and/or cordierite parageneses from Namaqualand, in the N.W. Cape Province of South Africa. Determined PT conditions of prograde metamorphism based on thermodynamic calculations are 800°–900° C and ca. 6–7 Kb; and it is argued that rocks of unusual composition, notably cordierite-orthopyroxene rocks, are restites after the extraction of granitic liquid from former argillites. This interpretation is consistent with previously published data on similar rocks, and with McCarthy's (1976) suggestion of extensive partial melting in the quartzofeldspathic rocks in the area.

Journal ArticleDOI
TL;DR: The distribution of gastrin-, cholecystokinin-, glucagon, secretin, vasoactive intestinal polypeptide, glucagon and substance P was studied in samples from the following regions: proventriculus, gizzard, pylorus, duodenum, upper and lower ileum, caeca and rectum.
Abstract: The distribution of gastrin-, cholecystokinin-, glucagon-, secretin-, vasoactive intestinal polypeptide-, substance P-, bombesin-, neurotensin-, motilin-, somatostatin- and avian pancreatic polypeptide-like cells, demonstrated by indirect immunocytochemistry, was studied in samples from the following regions: proventriculus, gizzard, pylorus, duodenum, upper and lower ileum, caeca and rectum. The pylorus is particularly rich in gastrin-, neurotensin- and somatostatin-like cells. No cells immunoreactive for gastric inhibitory polypeptide or insulin were detected. In a number of instances the same cells were found to stain with antisera raised to different gut peptides. This happened with antisera detecting gastrin- and neurotensin-like cells, with antisera to avian pancreatic polypeptide and glucagon and with antisera to secretin, vasoactive intestinal polypeptide, glucagon and substance P. The possibility that antigenic determinants to more than one peptide are contained in certain endocrine-like cells is considered.

Journal ArticleDOI
TL;DR: Ophiolite complexes in southern Chile represent the remnants of the mafic portion of the floor of a Cretaceous back-arc basin which widened markedly from north to south over a length of 600 km.

Journal ArticleDOI
TL;DR: The crown morphology of 202 dental casts from living Lengua Indians shows a high Mongoloid component with little effects of possible European admixture, thus supporting the theory that despite early Franciscan and Jesuit attempts at missionization, much of the Paraguayan Chaco has remained genetically and culturally relatively intact well into the present century.
Abstract: The crown morphology of 202 dental casts from living Lengua Indians is described and compared with other Amerind, Melanesian, and Caucasoid samples. The Lengua dentition shows a high Mongoloid component with little effects of possible European admixture, thus supporting the theory that despite early Franciscan and Jesuit attempts at missionization, much of the Paraguayan Chaco has remained genetically and culturally relatively intact well into the present century. A finding of note was the apparent sexual dimorphism of the Carabelli cusp, which questions earlier assumptions that no correction for sex need be made in population studies when dealing with this trait. Since mandibular canines show proportionately less wear in the canine distal accessory ridge area than maxillary canines, the value of the incidence of this trait in population and microevolutionary studies is questioned.

Journal ArticleDOI
TL;DR: A 1600m succession of quartz arenites and associated shaley deposits comprising the Hospital Hill Subgroup at the base of the Witwatersrand Supergroup is considered to have been deposited largely under the influence of tidal processes as discussed by the authors.

Journal ArticleDOI
TL;DR: A major increase in the absolute number of glycosaminoglycans and oligosaccharides attached to core protein was detected during the third trimester of fetal life and no further changes in substitution occurred in early postnatal life.

Journal ArticleDOI
12 Jan 1981-Ethology
TL;DR: Data from the present study and others indicated that urine washing did not function as an olfactory sign marking territorial boundaries, and it was suggested that in this species it facilitated grip.
Abstract: A wild, female Galago senegalensis molohi (lesser bushbaby) was radio collared and followed for 139 h. The occurrence of ‘urine washing’, wetting the hands and feet with urine, was recorded and analysed in terms of when and where it took place and with what other behaviours it was associated. Data from the present study and others indicated that urine washing did not function as an olfactory sign marking territorial boundaries. It was suggested that in this species it facilitated grip.

Journal ArticleDOI
TL;DR: Comparisons of food toughness measures, previously reported data on human maximum bite forces, and maximum bite force values hypothesized for Australopithecus africanus suggest that although these fossil hominids would have been able to prepare orally many of the tough food species, it also appears likely that they would have had to process artifactually the toughest of these food items to assure their survival in this environment.

Journal ArticleDOI
TL;DR: In this paper, the effects of performance accomplishments, modeling, locus of control, and their interaction were investigated on 504 children's [Mage = 11 years 7 months] self-efficacy beliefs.
Abstract: Two studies assessed the determinants of children's academic self-efficacy beliefs. First, the effects of performance accomplishments, modeling, locus of control, and their interaction were investigated on 504 children's [Mage = 11 years 7 months)self-efficacy beliefs. Contrary to theoretical predictions, performance accomplishments did not account for any of the variance in self-efficacy beliefs, although modeling was highly significant. The significant modeling ×attributional style interaction showed that externally oriented children were more amenable to modeling effects. The second study assessed whether contextual factors together with performance accomplishments and modeling account for more of the variance in self-efficacy beliefs. Modeling was again the most significant predictor of self-efficacy beliefs. However, when performance accomplishments reflected the self-rating of continuous participation in the classroom, self-efficacy was predicted significantly. In addition, a contextual factor, Rule Specification, also predicted self-efficacy beliefs significantly. In general, theoretical predictions were supported, although the hypothesized order of the importance of performance accomplishments and modeling was reversed, and this was attributed to the age of the present sample.