Showing papers by "University of the Witwatersrand published in 1982"

Prediction of aggressive behavior in basal cell carcinoma.

Abstract: In this study, a series of aggressively behaving basal cell carcinomas has been contrasted with a series of the nonaggressive type (metastasizing lesions were not considered in this study). Aggressive tumors were characteristically more likely to be ulcerative and infiltrative. They were composed of small groups of cells often displaying an irregular spiky appearance; infiltration of cells in cords, only one or two cells thick, could be seen. There was loss of peripheral palisading: the cells tended not to show differentiation. Hyalinization of the stroma was more common in the aggressive tumors. It is postulated that by utilizing these criteria, the pathologist can confidently diagnose the majority of cases and forewarn the clinician that a particular tumor is potentially aggressive. Adequate treatment and careful follow-up then become feasible.

A Case Study of Conceptual Change in Special Relativity: The Influence of Prior Knowledge in Learning‡

Abstract: Summaries English It is widely accepted that a person's existing knowledge plays a critical role in learning science. Two different aspects of this role are illuminated by the research reported in this paper. A graduate tutor in freshman physics was interviewed on three separate occasions. The first interview was used to determine what metaphysical commitments he held in relation to special relativity theory and showed the significant role his commitments played in his acceptance of counter‐intuitive aspects of the theory. The second interview was used to show the stability of his commitments four months later and to present the metaphysics underlying the theory in comparison and contrast with his own. The third interview, ten days later, repeated parts of the first interview and showed that significant changes in his metaphysical commitments had occurred. This case study demonstrates firstly the importance of the learner's metaphysical commitments as components of existing knowledge and secondly the effe...

Porcine Stress Syndromes

Abstract: Publisher Summary This chapter discusses that porcine stress syndrome (PSS) is characterized by acute death induced by natural stressors—such as—transport, high ambient temperature, exercise, fighting, service, and parturition. Malignant hyperthermia (MH) is a pharmacogenetic disease. Identification of pigs susceptible to any of the stress syndromes is of great importance. The chapter discusses that serological tests have focused on the measurement of serum enzymes. Hematological tests have analyzed platelet function, blood groups, and erythrocyte fragility in attempts to find a predictive test. In general, the rationale has promised much, but the results have been disappointing. In man, susceptibility to MH is well correlated with clinical myopathies. There is no doubt that sympathetic nerve activity associated with stress causes the release of adrenaline and nonadrenaline. It is well recognized that thyroid hormones regulate tissue metabolic rates. Hypermetabolism of tissues and hyperthermia are characteristic of PSS and MH, and a priori link between thyroid hormone activity and stress seems likely. The chapter discusses that although it is possible for clinically normal pigs to develop stress syndromes, the data presented here argue that pigs most likely to develop MH and PSS have a “homozygote” genetic defect involving a single gene. A whole range of responses to stress or drugs can, therefore, be envisaged and breed variations and the difficulty of finding unequivocal predictive tests all can be accounted for by variation in the severity of the inherited defect.

Prevalence of albinism in the South African negro.

Abstract: Two hundred and six individuals (113 males and 93 females) affected with oculocutaneous albinism have been ascertained in 126 Black (South African Negro) families living in Soweto, Johannesburg. The prevalence is approximately 1/3 900 and the carrier rate about 1/32. Autosomal recessive inheritance has been demonstrated for the condition and consanguinity had been shown to be an important factor in the different prevalences found in the different ethnic groups represented in the study. The sex ratio of 1,21 is not significantly different from unity for a sample of this size.

Mate recognition and mechanical isolation in enallagma damselflies (odonata: coenagrionidae).

Abstract: The concept of mechanical isolation, first mooted by Dufour (1844), became popular when Dobzhansky (1940, 1951) developed fully the theory of speciation by reinforcement. Very little empirical evidence was produced however, and as a result, both Mayr (1963, 1970) and Dobzhansky (1970) concluded that mechanical isolation was relatively unimportant in the maintenance of species integrity. This concept remains valid, however, within the theory of speciation by reinforcement, and the isolation concept of species (Paterson, 1980). Furthermore, it is still discussed and sometimes advocated by recent writers of books on speciation and evolution (e.g., Maynard Smith, 1975; Dobzhansky et al., 1977; Grant, 1977; Stansfield, 1977; White, 1978; Futuyma, 1979). The mating behavior of many Odonata has previously been explained in terms of mechanical isolation (Williamson, 1906; Johnson, 1962a; Paulson, 1974). This group of insects is particularly suited to this explanation because their copulation involves two separate points of contact. When a male encounters a female, he grasps her thorax with his legs and then clasps the female's prothorax with his anal appendages, thus achieving the tandem position (Fig. 1). The second stage of mating involves female choice or recognition, when she cooperates with the male in bending her abdomen under him to make contact with his accessory genitalia on the second abdominal segment, and so achieves the copula position (Fig. 2). Mechanical isolation may operate at either stage, but the attainment of tandem is usually thought to be the more probable site. The best evidence for this theory was provided by Paulson (1974). He pinned live females of a number of species of coenagrionid damselflies to sedge stems and presented them to males of the various species. He then scored whether the male approached and attempted to clasp the female, and whether he was successful in clasping her. The degree of mechanical isolation could then be expressed as the proportion of attempted tandem linkages which were unsuccessful. Of the seven intrageneric species-pairs (in which the males almost always attempted to clasp the female), four showed nearly complete, two partial and one very little mechanical isolation. Thus, for most of these species, reproductive isolation is normally maintained by the inability of males to clasp non-conspecific females with their anal appendages, presumably because their differently shaped and sized appendages are not compatible with the thoracic structures of the non-conspecific females. Since Paulson only discussed how males are reproductively isolated from non-conspecific females, he did not offer an explanation for how the integrity of the speciespair which showed very little mechanical isolation is maintained in the sympatric situation he studied. This might be explained by the work of Loibl (1958) and Krieger and Krieger-Loibl (1958). They, especially Loibl, concluded that in the genera Lestes (Lestidae) and Ischnura (Coenagrionidae), females recognized conspecific males by the tactile stimulation of the anal appendages when clasped in tandem. They observed that in both genera males would readily attempt and sometimes attain tandem linkage with non-conspecific females. These females then refused to cooperate in achieving copulation, and were eventually released. Furthermore, Loibl found that in Lestes, females

Muonium in diamond

Abstract: Two muonium states have been found in diamond. "Normal" muonium shows an isotropic hyperfine interaction with a coupling constant $\frac{A}{h}=3711\ifmmode\pm\else\textpm\fi{}21$ MHz. "Anomalous" muonium is described by a $〈111〉$ axially symmetric spin Hamiltonian with coupling constants extrapolated to 0 K $\frac{|{A}_{\ensuremath{\parallel}}|}{h}=167.98\ifmmode\pm\else\textpm\fi{}0.06$ MHz and $\frac{|{A}_{\ensuremath{\perp}}|}{h}=392.59\ifmmode\pm\else\textpm\fi{}0.06$ MHz. ${A}_{\ensuremath{\parallel}}$ and ${A}_{\ensuremath{\perp}}$ are of opposite sign, and they exhibit a temperature dependence describable by a Debye model. The amplitudes of the three anomalous muonium hyperfine transitions is zero applied field increase with increasing temperature and show relative variations which give information about muonium formation and indicate that anomalous muonium is the most stable state for muons in diamond. These diamond results are compared with those from the isostructural materials silicon and germanium.

Termites of a South African savanna : II. Densities and populations of smaller mounds, and seasonality of breeding

Abstract: The commonest epigeal termite mounds at Nylsvley Reserve, northern Transvaal, are constructed by Cubitermes pretorianus and shared by other termites and by ants. Two surveyed areas had the equivalents of 385 and 496 mounds ha-1 (328 and 432 ha-1 respectively with live Cubitermes). Counts of all termite species and stages in 13 mounds are given. Nests contained up to 15,000 Cubitermes workers (of which up to 0.7% were parasitised by nematodes). Egg-laying was seasonal, with a peak early in the wet season and few eggs in the nest in late autumn (and hence few larvae in winter). Soldier production showed two peaks per year, one at swarming and one in mid-dry season. Aganotermes workers sharing the mounds showed seasonal (over winter) abdominal storage of food reserves. Counts of populations and stored forage in two small Trinervitermes rhodesiensis mounds are also given.

Packing efficiency in sunflower heads

Abstract: In the mathematical description given by Vogel [1], the seeds on a sunflower head are centered at points on a “cyclotron spiral,” with constant divergence angle between any two successive seeds. It is shown that the divergence angle occurring in nature (and leading to the appearance of the Fibonacci numbers) gives the theoretically most efficient packing of the seeds. The inadequacy of Vogel's explanation for the occurrence of the Fibonacci angle is also discussed.

Common birth defects in South African Blacks.

Abstract: The prevalence rates of some of the common birth defects have been ascertained in a Black population in South Africa. The births of 29,633 infants were studied retrospectively from hospital records. The commonest defect was found to be polydactyly (10,4/1,000 births), and the other defects investigated were talipes equinovarus (1,55/1000 births), hydrocephalus (1,3/1,000 births), spina bifida and anencephaly (0,78 and 0,40/1,000 births respectively) and facial clefts (0,30/1,000 births). These rates were compared with those found in other population groups in South Africa and, in some cases, in other African countries and in Negro groups in the USA and Canada.

Studies of the effects of outliers and data transformation on variogram estimates for a base metal and a gold ore body

Abstract: Variograms for gold and lead values from the Loraine and Prieska mines, respectively, indicate that data outliers can seriously distort and/or mask the real variogram patterns. Studies show that this problem is best overcome for these mines by logarithmic transformation of the data, and/or a suitable screening out of such outliers, and/or more robust variogram estimation procedures; the benefits are particularly significant when the basic data is limited.

Black Townships in South Africa: Terra Incognita for Urban Geographers

Abstract: The paper provides urban geographers with an introduction to the growing volume of scholarly work that reflects the concern of other social sciences with the Black urban residents of South Africa. Particular reference is made to the emergence of ‘Locations’ and other segregated areas such as the Black freehold townships of Sophiatown, Martindale and Newc1are, and to the slumyards of Johannesburg. Against this background the emergence of controlled “labour pools” in the form of the townships of Soweto is discussed.

The dynamics and trophic ecology of grasshoppers (Acridoidea) in a South African savanna

Abstract: 1. A grasshopper population was monitored for three seasons in broad leaved savanna in South Africa. The biomass at corresponding times in successive seasons varied by up to a factor of four. Climatic factors may have been responsible. 2. The energetics of the grasshopper population are described for one year of intensive study. In this year a mean grasshopper biomass of 0.73 kg ha-1 ingested 94 kg ha-1 of plant material. In addition, 36 kg ha-1 was wasted in the course of feeding. Grasshoppers removed 16% of grass production, but this dropped to about 7% in the following year. 3. Production efficiency and ecological efficiency were lower than those measured for grasshoppers in other systems. Reasons are suggested. 4. Grasshopper diets were examined by epidermal analysis of crop fragments. All grasshopper species examined fed from a wide range of plant species, but diets could be grouped according to the physical characteristics of the food items. There was limited dietary overlap between the whole grasshopper population and large grazing mammals. 5. Vegetation structure is more significant than species composition as a determinant of habitat selection within the savanna type.

Penetrating injuries of the diaphragm

Abstract: Thirty-two cases of penetrating injuries of the diaphragm are reviewed. The problems of clinical and radiological diagnosis are outlined and the pitfalls of barium contrast studies are illustrated. Thoracoscopy is advised in all cases seen within 24 hours of the injury. Surgical access via laparotomy is recommended in both acute and chronic cases and where additional thoracotomy is necessary, separate abdominal and thoracic incisions are advised. The presence of colonic injury is shown to increase the risk of both wound sepsis and empyema postoperatively, whilst other visceral injuries do not appear to affect postoperative morbidity.

Success and failure of banding and bonding. A clinical study.

Abstract: A clinical study on the failure rate of 882 bands and 1194 directly bonded brackets placed on the teeth of 100 consecutively completed orthodontic patients treated with the Begg light wire technique showed an overall adhesion failure rate of 4.7%. This was significantly lower than the 7% recorded in a comparable study by Mizrahi in 1979 using only bands. The reduction was due primarily to a much lower failure rate of directly bonded brackets compared to bands on the maxillary cuspids and incisors. These results indicate that the lowest attachment failure rate during orthodontic treatment can be achieved by using bands on molars and bicuspids, directly bonded brackets on maxillary cuspids and incisors, and either on lower anterior teeth.

Geostatistical case studies of the advantages of lognormal-de Wijsian kriging with mean for a base metal mine and a gold mine

Abstract: Parallel variogram analyses, block kriging, and follow-up studies were effected for the lead content of part of the Prieska copper-zinc ore body and for the gold content of the highly variable Breef in a section of the Loraine gold mine, based first on untransformed values and second on logarithmically transformed values using the lognormal-de Wijsian model. For both models the effect was also analyzed of using the population mean or ignoring it. Practical follow-up comparisons confirm theoretical considerations and show that on these mines conditional biases can be eliminated conveniently by kriging with mean; also that the lognormal-de Wijsian model with mean gives the best results.