Showing papers by "University of the Witwatersrand published in 1984"
TL;DR: The rapidity and ease of performance as well as the low costs of the test necessitate a high priority for validation of this promising Drosophila short-term test.
Abstract: A novel test system for the detection of mutagenic and recombinogenic activity of chemicals is described in detail. Drosophila melanogaster larvae trans-heterozygous for the mutations multiple wing hairs (mwh) and flare (flr) are exposed to the test compounds for various periods of time ranging from 96 hr to 1 hr. Induced mutations are detected as single mosaic spots on the wing blade of surviving adults that show either the multiple wing hairs or flare phenotype. Induced recombination leads to mwh and flr twin spots and also to a certain extent, to mwh single spots. Recording of the frequency and the size of the different spots allows for a quantitative determination of the mutagenic and recombinogenic effects. This and earlier studies with a small set of well-known mutagens indicate that the test detects monofunctional and polyfunctional alkylating agents (ethyl methanesulfonate, diepoxybutane, mitomycin C, Trenimon), mutagens forming large adducts (aflatoxin B1), DNA breaking agents (bleomycin), intercalating agents (5-aminoacridine, ICR-170), spindle poisons (vinblastine), and antimetabolites (methotrexate). In addition, the test detects mutagens unstable in aqueous solution (beta-propiolactone), gaseous mutagens (1,2-dibromoethane), as well as promutagens needing various pathways of metabolic activation (aflatoxin B1, diethylnitrosamine, dimethylnitrosamine, mitomycin C, and procarbazine). The rapidity and ease of performance as well as the low costs of the test necessitate a high priority for validation of this promising Drosophila short-term test.
641 citations
TL;DR: This article examined conceptual conflict in the light of an epistemological model of learning as conceptual change and showed that the conceptual change model provides an explanation of conceptual conflict which is sufficiently detailed to allow it to be used in the design of instruction.
Abstract: Conceptual conflict has long been recognized as a factor that could facilitate student learning. Due, however, to the lack of a convincing explanation of why it occurs, and how it can be resolved, it has seldom been used in instructional design. Its potential use in instruction is particularly relevant in the light of the recent, well-documented finding that students' existing conceptions frequently constitute a barrier to effective learning. This article examines conceptual conflict in the light of an epistemological model of learning as conceptual change. This analysis shows that the conceptual change model provides an explanation of conceptual conflict which is sufficiently detailed to allow it to be used in the design of instruction. The results of two studies, the first of which addressed the concepts of mass, volume, and density, and the second, the concept of speed, show that instruction, designed in this way, is effective in changing students' existing conceptions.
436 citations
TL;DR: In this paper, the authors proposed two summary statistics: an unweighted median and a weighted median, which are more efficient but less robust than the weighted median and the unweighting median, respectively.
Abstract: The outlying tendency of any case in a multiple regression of p predictors may be estimated by drawing all subsets of size p from the remaining cases and fitting the model. Each such subset yields an elemental residual for the case in question, and a suitable summary statistic of them can be used as an estimate of the case's outlying tendency. We propose two such summary statistics: an unweighted median, which is of bounded influence, and a weighted median, which is more efficient but less robust. The computational load of the procedure is reduced by using random samples in place of the full set of subsets of size p. As a byproduct the method yields useful information on the influence (or leverage) of cases and the mutual masking of high leverage points.
297 citations
TL;DR: The ferricenium compounds are the first iron complexes for which antineoplastic activity has now been shown, and represent a new type of antitumor agent insofar as they differ fundamentally from known inorganic and organometallic antitumors.
Abstract: The antitumor activity of a series of iron complexes, i.e., of ferrocene [Cp2Fe], of tetrachloroferrates(III) [R4N]+[FeCl4]-, and of ferricenium complexes [Cp2Fe]+X- (X- = [FeCl4]-, 1/2 [Cl3FeOFeCl3]2-, [H5Mo7O24]- X 2H2O, [2,4,6-(NO2)3C6H2O]-, or [CCl3COO]- X 2 CCl3COOH) was investigated against EAT in CF1 mice. Whereas ferrocene and the ammonium tetrachloroferrates(III) did not show recognizable tumor-inhibiting activity, such activity was exhibited by the water-soluble, salt-like ferricenium complexes; the best antineoplastic properties, with optimum cure rates of 100%, were found for ferricenium picrate and ferricenium trichloroacetate. The ferricenium compounds are the first iron complexes for which antineoplastic activity has now been shown. They represent a new type of antitumor agent insofar as they differ fundamentally from known inorganic and organometallic antitumor agents (a) by their ionic, salt-like character, which is responsible for their high water solubility, and (b) by the absence of a cis-dihalometal moiety; this moiety has been recognized as important for the intracellular action of other known inorganic cytostatics.
214 citations
TL;DR: Smode principal component analysis has been applied to standardized monthly South African rainfall fields and the synoptic systems represented on the higher eigenvectors identified by matching the spatial distribution of rainfall on each component with that of the various weather systems as revealed by satellite imagery as mentioned in this paper.
Abstract: S-mode principal component analysis has been applied to standardized monthly South African rainfall fields and the synoptic systems represented on the higher eigenvectors identified by matching the spatial distribution of rainfall on each component with that of the various weather systems as revealed by satellite imagery. Summer systems identified include cloud bands connecting the tropical and temperate circulations, tropical and subtropical cyclones, coastal depressions, cyclones on the continental west coast and troughs associated with cold fronts on the east coast. The new classification is contrasted with earlier equivalent schemes. The uses of the results in terms of the search for geophysical controls on the development of each of the identified systems are discussed.
185 citations
TL;DR: The difference in the pattern of transmission of this virus between the Far East and Africa seems to centre mainly on the differences in the HBeAg status of the mothers in these two regions.
173 citations
TL;DR: Non-haem-iron absorption from a variety of cereal and fibre meals was measured in parous Indian women, using the erythrocyte utilization of radioactive Fe method to establish whether alteration of the phytate and polyphenol contents of sorghum affected Fe absorption from Sorghum meals, and to assess the influence of fibre on Fe absorption.
Abstract: Non-haem-iron absorption from a variety of cereal and fibre meals was measured in parous Indian women, using the erythrocyte utilization of radioactive Fe method. The present study was undertaken to establish whether alteration of the phytate and polyphenol contents of sorghum (Sorghum vulgare) affected Fe absorption from sorghum meals, and to assess the influence of fibre on Fe absorption. Removing the outer layers of sorghum grain by pearling reduced the polyphenol and phytate contents by 96 and 92% respectively. This treatment significantly increased the geometric mean Fe absorption from 0.017 to 0.035 (t 3.9, P less than 0.005). The geometric mean Fe absorption from a sorghum cultivar that lacked polyphenols (albino sorghum) was 0.043, which was significantly greater than the 0.019 absorbed from bird-proof sorghum, a cultivar with a high polyphenol content (t 2.83, P less than 0.05). Fe was less well absorbed from the phytate-rich pearlings of the albino sorghum than from the pearled albino sorghum (0.015 v. 0.035 (t 8.4, P less than 0.0005]. Addition of sodium phytate to a highly Fe-bioavailable broccoli (Brassica oleracea) meal reduced Fe absorption from 0.185 to 0.037. The geometric mean Fe absorption from malted sorghum porridge was 0.024 when 9.5 mg ascorbic acid were added and 0.094 when the ascorbic acid was increased to 50 mg (t 3.33, P less than 0.005). This enhancing effect of 50 mg ascorbic acid was significantly depressed to 0.04 by tea (t 38.1, P less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)
159 citations
152 citations
143 citations
TL;DR: In the anorexic and bulimic groups a significant correlation was found between the degree of overestimation after mirror confrontation and progress in treatment, as measured on a specially devised rating scale.
Abstract: Using an apparatus which provides a continuous horizontal slit of light of variable length, self-estimations of 4 body widths were carried out before and after a mirror confrontation procedure on 4 groups of young female subjects – anorexic, bulimic, emotionally disturbed and normal. The results confirm that anorexic subjects overestimate body size, although in this study the hip diameter was frequently underestimated. Bulimic and emotionally disturbed subjects overestimate to much the same degree as anorexics, whereas normal subjects are remarkably accurate with the exception of the head width. Mirror confrontation resulted in reduced estimations in the majority of subjects, but significant differences were found in the degree to which this occurred in the 4 groups; anorexic subjects showed the greatest change and normal subjects the least. This relative instability of the anorexic subject's body image cannot be explained simply on the basis of a self-correcting experience, as many estimations which were initially below actual width were even lower on re-testing. In the anorexic and bulimic groups a significant correlation was found between the degree of overestimation after mirror confrontation and progress in treatment, as measured on a specially devised rating scale. Possible explanations for these findings and their diagnostic and prognostic implications are discussed.
136 citations
TL;DR: It is demonstrated that insemination triggers ovarian activity, and colonies of the ponerine Ophthalmopone berthoudi reproduce by means of a large number of unspecialized egglayers.
Abstract: The control of oviposition in insect colonies is fundamental to the structure of their social systems. In most ant societies a distinct female caste performs the reproductive function, while the worker caste is sterile, or at the most produces trophic or unfertilized (male) eggs. Winged males and virgin queens are seasonally produced, and leave their nests on nuptial flights [1]. Thus a trend towards reproductive specialization and monogyny has accompanied the evolution of the division of labour. In contrast to this, we have found that colonies of the ponerine Ophthalmopone berthoudi reproduce by means of a large number of unspecialized egglayers. Wheeler and Chapman [2] recognized two distinct evolutionary patterns in the ponerines, one leading to the development of wingless ergatoid (=worker-like) queens as in Leptogenys, and the other associated with the complete disappearance of the queen caste and its replacement with fertile workers [3]. It is the latter unusual reproductive pattern to which we wish to direct attention. Wheeler and Chapman [2] observed a normal male copulating with a worker in Diacamma, a genus in which there are no queens. The fertile workers may be called gamergates ("married workers") to distinguish them from ergatoids. Work on a number of species with gamergates [4, 5] has documented that in each colony there may be one or more fertile workers which supply the eggs that develop into workers and males. Many features of such a reproductive system are still unknown, e.g. how are gamergates differentiated, can all workers mate and if so, what is the proportion of gamergates in a colony? Ophthalmopone berthoudi is an African species in which winged queens have never been found; it occurs in semi-arid regions and feeds on termites. Field observations in Mkuzi Game Reserve, South Africa, have shown that colonies consist of a number of distinct nests separated by various distances. Colony integration is maintained through the frequent transfer of adults and brood between the nests along non-chemical trails. Workers are produced for most of the year (with a hiatus in egg production before winter) and this results in a nest population with individuals of various ages. Single nests and nest complexes of O. berthoudi were excavated at different times of the year, and a large sample of ants from each unit was dissected. This included a sample of 100 above-ground ants which were all found to be non-reproductive. Dissection of 350 cocoons containing pharate adults never yielded any winged females. In each nest there are various numbers of egg-laying workers, all of which are indistinguishable from sterile workers by simple visual inspection. These fertile workers were found to have 3 enlarged ovarioles per ovary, with short strings of developing oocytes and very seldom more than two large fully formed eggs per individual. The ovarian apparatus of sterile workers was the same as that of reproductive ones, but the 6 ovarioles were undeveloped. Thus there are no distinct female castes. Examination of spermathecae revealed that ants with active ovaries had been inseminated, while ants with undeveloped ovaries had not been inseminated (Table 1). These data demonstrate that insemination triggers ovarian activity. This is not simply a correlation between the occurrence of the two events, since the male data reported below indicate that the relationship is a causal one. Were ovarian activity to be responsible for changes in worker behaviour which lead to mating, we would expect to find unmated workers with developed ovaries. None have been found at any time of the year. Indeed we can state that the haploid eggs which develop into males are laid by inseminated gamergates. Insemination also produced a change in the chemical composition of the mandibular gland pheromone of these ants and in their behaviour. The mated ants remained inside their nests for the rest of their lives, except when they were carried from one nest to another. They are removed from the normal sequence ' of age polyethism exhibited by their non-reproductive sisters. Males were only active above ground for a few weeks of the year (February to the beginning of March). Every day during this period a few males left their nests and flew off. They were seen to enter other nests and copulation occurred underground. Any ant that had not become active above ground prior to the period of male activity had a high probability of becoming inseminated and hence reproductive; this accounts for the large number of garnergates found in the nests sampled at this period (Table 1). Thus the sharp increase in the gamergate to worker ratio seen from February to March can be correlated with the pattern of male activity. During the rest of the year the proportion of gamergates usually decreased through the emergence of new non-mated ants. However, the wide variations over a one-year period seen
TL;DR: Cell culture results suggest that although the essential fatty acids suppress proliferation, eicosanoids of all 3 series may be involved, and the proliferation suppressive effect of docosahexaenoic acid suggests that other aspects than only eicOSanoid activity may also be important in the suppression of cancer cell proliferation.
Journal Article•
TL;DR: It is concluded that alcohol abuse is associated with: uncoupling of bone resorption and bone formation; reduced trabecular bone volume and thickness; and a mild mineralization defect.
Abstract: In this study bone morphometric findings in 19 heavy or moderate drinkers are compared with those in 43 non-drinkers (22 non-osteoporotic patients with osteo-arthritis (OA) and 21 osteoporotic patients with femoral neck fractures (FNFs). Transiliac bone biopsy specimens were examined for assessment of trabecular bone volume and thickness, bone resorption and formation, osteoid seam length and width and the mineralization front by quantitative histomorphometry and microradiography. Trabecular bone volume and thickness were significantly diminished in the drinking group when compared with those in the 22 non-drinking patients with OA (P less than 0,005 and P less than 0,0001 respectively). Bone formation was significantly lower in the drinkers than in the OA group (P less than 0,0005), and bone resorption was significantly greater in the drinkers than in the OA (P less than 0,005) and FNF (P less than 0,01) groups. In heavy drinkers bone formation was significantly lower (P less than 0,05) than in moderate drinkers. The extent of the mineralization front was significantly lower in the drinking group than in the OA (P less than 0,005) and FNF (P less than 0,0005) groups. Osteoid seam length and width did not differ in the three groups. The presence of abnormal liver function test results did not significantly affect any of the parameters. It is concluded that alcohol abuse is associated with: (i) uncoupling of bone resorption and bone formation; (ii) reduced trabecular bone volume and thickness; and (iii) a mild mineralization defect.
TL;DR: It is postulated that the initiating process of the aneurysmal bone cyst is the microcyst, which forms as a result of intercellular oedema in a primary lesion with loose, unsupported stroma.
TL;DR: In this article, the authors used principal component analysis to identify the most important statistically uncorrelated pressure patterns accounting for the variance of the annual pressure field over South Africa and adjacent oceans.
Abstract: Differences in annual geopotential heights at the 850 and 500 mb levels between 16 pairs of stations have been submitted to principal component analysis to identify the most important statistically uncorrelated pressure patterns accounting for the variance of the annual pressure field over South Africa and adjacent oceans. By correlating component scores for the period 1958/9 to 1977/8 with annual rainfall an attempt has been made to determine the regional rainfall responses to variations in different circulation types. Regional variations in annual rainfall are shown to be significantly linked to variations in both low latitude forcing, associated with tropical easterly airflow and cyclonic wave perturbations therein, and mid-latitude forcing, associated with a variety of both cyclonic and anti-cyclonic perturbations in the westerlies. It has been shown that it is primarily variations in the atmospheric field of motion at the 500 mb level that are responsible for year-to-year differences in annual rainfall totals.
TL;DR: The granulites of southern Malawi and Tete (Mozambique) typically comprise prograde two-pyroxene ± garnet ± hornblende ± biotite parageneses.
TL;DR: It is concluded that the learning styles of delinquents may be qualitatively different and that early learning difficulties may provide a indicator of risk for later delinquency.
Abstract: The association between school failure and antisocial behavior has been the focus of much discussion but little consensus. In the present study, 53 delinquent adolescents and 51 junior high school students were compared on the basis of their learning profiles. An educational battery was devised to evaluate quality of learning style and error clusters in addition to traditional grade-equivalents. Significant differences were found in the type and prevalence of multiple error clusters within each of the eight educational skill areas and across the eight combined skills. In a second part of the study early school records and parent questionnaires were reviewed. Results indicated a significantly higher prevalence of school problems among the delinquents as early as kindergarten. By second grade, 45% of the delinquents were already delayed in reading and 36% in handwriting, in contrast to only 14% of the comparison group (p < .001). Finally, the prevalence of special education services recommended or provided ...
TL;DR: In this paper, a comprehensive description of the physical behavior of the froth phase of the flotation process has been provided by two mathematical models, which are formulated in terms of familiar design and control variables (e.g., cell dimensions, froth depth, gas rate).
TL;DR: It is concluded that regression of the female reproductive system was the result of discontinued male stimulation and the nature and implications of the obligatory relationship between male and female S. mansoni are discussed.
TL;DR: A clinicopathological study has been performed on a series of 42 well-documented examples of aneurysmal bone cyst of the jaws recorded in the literature, and 4 additional personally observed cases.
TL;DR: In this article, the existence of substantial inter-bar laminar currents in large three phase squirrel cage induction motors with broken bars and/or rings was analyzed and the effect of these tangential currents on the production of very large axial vibrations were shown.
Abstract: An analysis is developed which describes the existence of substantial inter-bar laminar currents in large three phase squirrel cage induction motors with broken bars and/or rings. Results of experimental measurements are presented which verify the theoretical model. Also the effect of these tangential currents on the production of very large axial vibrations are shown.
TL;DR: In this article, the efficiency of separation for fine coal in a 150 mm dia. dense-medium hydrocyclone has been determined, and the results lead to an accurate predictive model for the calculation of the partition curve as a function of coal particle size and medium specific gravity.
TL;DR: These studies in vitro suggest that the reduced total peripheral resistance and hypotension seen in obstructive jaundice cannot be explained by a spasmolytic effect of some of the bile salts on smooth muscle.
Abstract: Summary 1. We have examined the effects of bile duct ligation on vascular and extravascular smooth muscle responsiveness to noradrenaline and tyramine using isolated rat hindlimb perfusion, and portal vein and vas deferens preparations. 2. Bile duct ligation reduced the contractile responses to noradrenaline of vascular and extravascular smooth muscle. 3. Exposure of smooth muscle to some bile salts caused a reduction in contractility. 4. This effect was dependent upon bile salt type and concentration. 5. These studies in vitro suggest that the reduced total peripheral resistance and hypotension seen in obstructive jaundice cannot be explained by a spasmolytic effect of some of the bile salts on smooth muscle.
Abstract: Drepanophycus spinaeformis Goppert is a long ranging Devonian plant. Although reported from numerous localities, it is far from well understood. Observations on specimens from the Emsian Strathmore Group of Scotland have revealed variation in forms of branching including root-like axes on branches interpreted as rhizomes. The anatomy of the xylem is described from uncompressed pyrite permineralisations. Cuticle characteristics are also described and discussed. The systematic position of the plant is debated since, although the morphology of the leaves, leaf traces, roots and xylem indicate an affinity with the lycopods, there is some doubt as to whether sporangial position permits inclusion in this group.
TL;DR: In this paper, it was shown that the gradual disappearance of staurolite is due to a shift of the 3-phase AFM assemblage stau-rolite-garnetsapphirine to more Fe-rich compositions according to probably prograde reactions between stourolite and garnet to form sapphirines together with either quartz or gedrite, and the local equilibria now frozen in indicate minimum pressures of 7-8 kbar and temperatures in excess of about 800° C.
Abstract: Unusually Mg-rich staurolite with F=Fe/(Fe+ Mg) = 0.51 occurs in a peraluminous silica-deficient sapphirine-garnet-gedrite-spinel-corundum-phlogopite rock as relic inclusions within pyrope-almandine garnet (F=0.43–0.48), from which it is generally separated by sapphirine (F=0.19). Gedrite has F=0.24–0.27, phlogopite 0.19, and spinel 0.43. The gradual disappearance of staurolite is due to a shift of the 3-phase AFM assemblage staurolite-garnetsapphirine to more Fe-rich compositions according to probably prograde reactions between staurolite and garnet to form sapphirine together with either quartz or gedrite. Thus still more Mg-rich staurolite seems to have existed in the rock at earlier stages of metamorphism characterized by lower temperatures and perhaps higher pressures. The local equilibria now frozen in indicate minimum pressures of 7–8 kbar and temperatures in excess of about 800° C.
TL;DR: The differing ratio of ANLL:ALL, some of the distinctive clinical features, and the high frequency of detectable chromosome abnormalities in black children may be reflections of a particular oncogenic agent within their environmental background that could be responsible for the initiation of the leukemic process.
TL;DR: The non-verbal communication of eleven aphasic patients was investigated within a dyadic communication framework and results were compared with those of standardised aphasia measures.
Abstract: The non-verbal communication of eleven aphasic patients was investigated within a dyadic communication framework. Results were then compared with those of standardised aphasia measures. Appropriateness and functions of the non-verbal behaviours were found to differ among patients and to correlate poorly with other test measures. Case examples are provided and neurological and clinical implications are discussed.
TL;DR: The present study analyzes a sample of 63 cases from the literature together with 7 personally observed cases to derive a histological classification based on that of Rosai (1981) for fibrous histiocytoma of the oral and maxillofacial regions.
Abstract: Fibrous histiocytomas of the oral and maxillofacial regions are rare. The present study analyzes a sample of 63 cases from the literature together with 7 personally observed cases. Age, sex, site, size, clinical behaviour, treatment and survival were evaluated and related to a histological classification based on that of Rosai (1981). Lesions were assessed for histological criteria which would place them in one of 2 groups: fibrous histiocytoma (FH) or pleomorphic fibrous histiocytoma (PFH). Within these 2 histological groups the cases were subdivided into clinically benign, aggressive or malignant lesions. Thirty-nine cases (56.0%) were classified as FH and 31 cases (44.0%) as PFH. The mean age of male patients with PFH was significantly higher than female patients with FH (t = 3.05; d.f. 37; p less than 0.0025). Lesions in the PFH group involved bone more frequently than those in the FH group (Yate's Chi2 = 16.66; d.f. 1; p less than 0.00025). Lesions involving bone for both histological groups were more likely to be aggressive or malignant than soft-tissue lesions (Yate's Chi2 = 29.9; d.f. 1; p less than 0.00025). Soft-tissue lesions were usually less than 5 cm in greatest diameter. Radiographic features of malignancy for lesions with bone involvement is of prognostic importance regardless of the histological appearance of the lesion. The majority of the lesions under study were from the deep tissues of the oral and maxillofacial regions.