Showing papers by "University of Port Elizabeth published in 1991"
TL;DR: The energy yield of the seeds calculated here, in conjunction with rodent population energy requirements and dietary data, may be used to estimate potential granivore impact on the seed production of the plant community.
Abstract: Knowledge of the basis upon which granivores select seeds is crucial to the understanding of granivory. In this study the preferences of three rodent granivores among seeds of 11 plants from the semi-arid Karoo of South Africa were estimated, and related to the physical and chemical attributes of the seeds. Seed weights and calorific, moisture, protein, polyphenol, ash, lipid and silica contents were estimated and cell contents, soluble ash and soluble carbohydrate contents were derived from these values. These attributes were determined for both the intact seeds and the portion of the seed that is ingested by the mice. The efficiency with which mice ingested the seeds (in terms of time and mass) was recorded. All three mouse species ranked the seeds similarly, and the two species for which handling efficiency was measured did not differ in this regard. Preference hierachies were highly correlated with the rate of energy intake, as predicted by optimal foraging theory. There was no correlation between rodent preferences and the gross energy content of the seeds, emphasising the importance of measuring relevant parameters. The energy yield of the seeds calculated here, in conjunction with rodent population energy requirements and dietary data, may be used to estimate potential granivore impact on the seed production of the plant community.
104 citations
TL;DR: The distinguishing feature of coastal dunes is their connection to the shore and this maritime influence results in most coastal dunefields exhibiting a marked shore-normal gradient of decreasing physical stress and increasing complexity and vegetation cover landwards.
86 citations
TL;DR: Comparisons in the patterns of granivory in the semi-arid Karoo contrast those in Israeli and North American deserts, and are convergent with those in Australian and SouthAmerican deserts, despite the Karoo rodent fauna having taxonomic and morphological affinities with that of Israeli andNorth American deserts.
81 citations
TL;DR: The copepod, Pseudodiaptomus hessie, was studied over 1 year in the Sundays River estuary and found females took longer to reach maturity than males and high production estimates can be linked to high summer temperatures.
Abstract: The copepod, Pseudodiaptomus hessie, was studied over 1 year in the Sundays River estuary. Maximum abundance occurred during summer in the upper half of the estuary. Nauplii and copepodid stages attained peak abundance higher up in the estuary compared with adults. Development time and body size were inversely related to temperature and varied between instars. Females took longer to reach maturity than males. Reproduction was continuous. Production estimates integrated over 1 year varied from 0·3 g dry mass m−3 at the estuary mouth to 4·3 g dry mass m−3 in the upper estuary. Annual P/B ratios varied between 78·5 and 100·2 for the same regions. High production estimates can be linked to high summer temperatures.
71 citations
49 citations
TL;DR: In this article, the authors measured over a period of up to 38 years at Cape Town, Port Elizabeth and Durban, and investigated the coastal wind field around South Africa; diurnal variability is excluded.
Abstract: Wind data measured over a period of up to 38 years at Cape Town, Port Elizabeth and Durban are analyzed in an investigation of the coastal wind field around South Africa; diurnal variability is excluded. Principal axes are established, and show the orientation of the wind parallel to the local coastline. A marked seasonal variability is found, in particular in the easterly component winds. The three sites display different characteristics, with Durban having the weakest winds, and Cape Town the most energy at longer periods.
41 citations
TL;DR: In this paper, the interaction between combinations of sulfur, stearic acid, and zinc stearate was studied by differential scanning calorimetry in the absence of rubber.
Abstract: The interaction between combinations of sulfur, stearic acid, and ZnO were studied by differential scanning calorimetry in the absence of rubber. The only reaction observed was between ZnO and stearic acid. A small amount of zinc stearate formed as soon as the stearic acid melted, but the solid product blocked further reaction, which was only completed at 154°C. Water played a major role in the reaction, and in the presence of water, the reaction went to completion at lower temperatures. Sulfur, too, affected the temperature of the ZnO/stearic acid reaction. The preparation of zinc stearate by a number of routes was investigated.
38 citations
TL;DR: In this paper, the authors described the need to contribute to the limited amount of sociological research into the phenomenon of black teenage pregnancy in South Africa, and described the research described in this paper.
Abstract: Few research studies have been conducted in South Africa into the incidence of, and possible social and medical factors associated with, black teenage pregnancy. The research described in this paper was prompted by the need to contribute to the limited amount of sociological research into the phenomenon.
38 citations
TL;DR: In this article, problems of family disorganization and problems of teenage pregnancy in South Africa and the rest of Africa are examined and recommendations to prevent further deterioration of quality of life for ‘chil...
Abstract: Black teenage pregnancy in South Africa and the rest of Africa is discussed. Problems of family disorganization are examined. An increasing number of, female-headed single parent families; out-of-wedlock children; unwanted and abandoned babies; street children; adolescents with sexuality transmitted disease and teenage pregnancies attest to this. Particular reference is made to a research study by Boult and Cunningham (1991) of Black Teenage Pregnancy in Port Elizabeth. The study demonstrates that teenage pregnancy is associated with disorganized family structure; disregard of traditional cultural norms; low education; lack of knowledge and use of contraception and, a correlation between age at onset of menarche and onset of sexual activity. It is associated with a negative response to the pregnancy from the teenager, her sexual partner and her family. There is a lack of realistic planning on her and her child's behalf. Recommendations to prevent further deterioration of quality of life for ‘chil...
35 citations
TL;DR: The different refuge strategies result in habitat segregation and may be an important means of partitioning resources between these two sympatric rodents which have comparable body sizes, adtivitym dietary and thermoregulatory patterns.
Abstract: The possibility of different refuge strategies resulting in habitat segregation in two sympatric rodents, the bush Karoo rat, O unisulcatus and the whistling rat, P brantsii was investigated The rodents' habitats were characterized by using the multivariate analysis procedures: ordination diagrams and hierarchical classification The most important environmental variables were identified
Otomys unisulcatus was restricted to areas with high percentage plant cover (606%) and dense foliage compared to P brantsii habitat (plant cover=348%) The high percentage plant cover is necessary for nest construction Parotomys brantsii habitat was characterized by deep Soil (769+15cm) with larger soil particles (031+02mm) compared to 475+303 cm soil depth and 015+01 mm soil particles in O unisulcatus habitat A suitable substratum therefore determines distribution of P brantsii
The different refuge strategies result in habitat segregation and may be an important means of partitioning resources between these two sympatric rodents which have comparable body sizes, adtivitym dietary and thermoregulatory patterns
27 citations
TL;DR: Activity rhythms of Eurydice longicornis, Pontogeloides latipes and Excirolana natalensis, three intertidal cirolanid isopods co-existing on South African sandy beaches, were studied in the field and under constant darkness in infra-red actographs in the laboratory.
TL;DR: In this paper, the interaction of combinations of sulfur, tetramethylthiuram disulfide (TMTD), ZnO, and stearic acid were investigated by differential scanning calorimetry in the absence of rubber.
Abstract: The interaction of combinations of sulfur, tetramethylthiuram disulfide (TMTD), ZnO, and stearic acid were investigated by differential scanning calorimetry in the absence of rubber. TMTD decomposed partially to tetramethylthiuram monosulphide on liquefaction. Sulfur and TMTD reacted at vulcanization temperatures, and although the exact composition of all the products was not established, several features involving DSC and HPLC analysis were interpreted in terms of the formation of tetramethylthiuram polysulfides (TMTP). TMTD decomposed much faster to volatile products such as Me2NH, CS2, and CS when heated in the presence of stearic acid. Contrary to literature reports on the facile reaction of TMTD and ZnO to yield zinc perthiomercaptides (or zinc dimethyldithiocarbamate), the TMTD/ZnO reaction was found to be extremely sluggish under a variety of conditions. In the presence of sulfur, too, the TMTD/ZnO reaction was of negligible importance. It was inferred that several reactions occurred concurrently on heating a TMTD/stearic acid/ZnO system. These reactions were not observed for the sulfur/TMTD/stearic acid/ZnO mixture per se, but, instead, the stearic acid/ZnO reaction was very prominent. The formation of zinc stearate occurred at temperatures as low as 77°C in the quadruple system. TMTD and zinc stearate were virtually unreactive at vulcanization temperatures. None of the reactions involving ZnO could be attributed to the formation of a zinc perthiomercaptide, generally accepted to be a precursor in thiuram vulcanization.
TL;DR: The Group Areas Act in South Africa has been one of the most controversial pieces of legislation of the second half of the 20th century as discussed by the authors and has been subject to marked variations as the priorities of the government have changed.
TL;DR: Differences in dietary patterns are not critical for niche separation but are the result of habitat segregation, according to a function of food availability in the different habitats.
Abstract: Differences and overlap in the diets of two sympatric, herbivorous rodents Otomys unisulcatus and Parotomys brantsii were investigated. Frequency of occurrence of plant species in the diets were compared with availability of the plants in the rodents' habitats. Both rodents are generalist herbivores, eating plants species in proportion to the availability in their habitats. Dietary patterns, diversity of diet and degree of overlap between rodent's diets are a function of food availability in the different habitats. It is suggested that these rodents separate niches on a spatial rather than trophic basis. Differences in dietary patterns are therefore not critical for niche separation but are the result of habitat segregation.
TL;DR: The only known ideal-hereditary radicals in the variety of o-symmetric near-rings were J 2, the Brown-McCoy radical or radicals based on these two.
TL;DR: Three-weekly transects were done over a 14-month period at Sundays River Beach, a high energy beach in Algoa Bay, South Africa, to determine the life histories, breeding patterns, and fecundities of three intertidal cirolanid isopods.
Abstract: . Three-weekly transects were done over a 14-month period at Sundays River Beach, a high energy beach in Algoa Bay, South Africa, to determine the life histories, breeding patterns, and fecundities of three intertidal cirolanid isopods. Eurydice longicornis. Pontogeloides latipes, and Excirolana naialensis. E. longicornis exhibits an annual, multivoltine life history with a more extended breeding period than the other two species. P. latipes and E. natalensis both have biennial. univoltine life histories with lower fecundities than E. longicornis.
Journal Article•
TL;DR: In a study involving 137 outpatients receiving digoxin 55 patients (40%) were found to be non-compliant, patients who experienced communication problems and who lacked a meaningful relationship with their doctor showed a marked deterioration in compliance.
Abstract: Non-compliance has a major influence on the successful outcome of a therapeutic regimen. It also unnecessarily increases the costs of health care. In a study involving 137 outpatients receiving digoxin 55 patients (40%) were found to be non-compliant. Patients who experienced communication probiems and who lacked a meaningful relationship with their doctor showed a marked deterioration in compliance. An applied pharmacokinetic approach was used to predict the serum digoxin concentration for each patient. The creatinine clearance was determined and the degree of severity of heart failure was assessed. Total body clearance was then calculated. The predicted concentration was also calculated and compared with the measured digoxin concentration enabling an objective assessment of compliance. Twentyfour of the non-compliant patients who had subtherapeutic levels of digoxin « 0,8 ng/ml) had signs of cardiac failure. Eighteen of these patients were receiving additional medication (1,7 ± 0,5 items) for the treatment of cardiac failure.
TL;DR: In this article, the interaction among various combinations of sulfur, tetramethylthiuram monosulphide (TMTM), ZnO, and stearic acid were studied by differential scanning calorimetry in the absence of rubber.
Abstract: The interaction among various combinations of sulfur, tetramethylthiuram monosulphide (TMTM), ZnO, and stearic acid were studied by differential scanning calorimetry in the absence of rubber. Sulfur and TMTM reacted to form tetramethylthiuram disulphide, and the ternary eutectic mixture melted at about 80°C. The absence of the Sγ Sμ transition in sulfur/TMTM mixes was related to a sulfur/TMTM interaction, wherein the eightmembered sulfur rings were opened at temperatures well below 170°C. The interaction of stearic acid with TMTM led to the decomposition of TMTM, but the reaction was largely suppressed when both ZnO and sulfur were present in the mixture. No evidence was found for the formation of a zinc-accelerator complex of the type normally attributed a role in the accelerated sulfur vulcanization.
TL;DR: In this paper, the interaction of combinations of sulfur, 2,2′-dibenzothiazole (MBTS), ZnO, and stearic acid were studied by differential scanning calorimetry.
Abstract: The interaction of combinations of sulfur, 2,2′-dibenzothiazole (MBTS), ZnO, and stearic acid were studied by differential scanning calorimetry. A MBTS/stearic acid interaction was indicated as evidenced by the effect the MBTS/stearic acid combination had on the melting of sulfur, the Sα Sβ transition being suppressed in favor of a Sα Sγ transition. The dissolution/interaction of MBTS in molten sulfur was also delayed by the MBTS/stearic acid interaction, which, it is proposed, involved protonation of the N atom in MBTS by stearic acid. MBTS did not affect the formation of zinc stearate from ZnO and stearic acid, but when sulfure was added to the mixture, the ZnO/stearic acid reaction did not go to completion. No direct evidence for the formation of 2,2′-dibenzothiazole polysulphides was found, but the absence of the Sγ Sμ transition in sulfur/MBTS mixes was interpreted as indirect evidence of a reaction between these curatives. There was no evidence for the formation of a sulfur/MBTS/ZnO compound of the type generally attributed the role of an active sulfurating agent in accelerated sulfur vulcanization.
TL;DR: Une population de Tylos capensis a ete surveillee pendant un an sur un champ de dunes cotieres en arriere d'un plage exposee en fevrier-mai, indiquant une ponte estivale.
Abstract: Une population de Tylos capensis a ete surveillee pendant un an sur un champ de dunes cotieres en arriere d'un plage exposee. Les animaux etaient concentres pres de la plage et les juveniles etaient incorpores dans la population a une taille de 1-2 mm en fevrier-mai, indiquant une ponte estivale. Les femelles reproductives etaient inactives et produisaient environ 11 embryons par ponte. La croissance continuait jusqu'a l'âge de 4 ou 5 ans et jusqu'a une largueur de 14 mm environ. Le taux de mortalite specifiquement lie a l'âge etait de 0,77 y-1 et la biomasse de population de 3,55 g sans cendres par m de littoral. Le rapport estime P/B etait de 1,38-1 et la valeur energetique moyenne de 7,8 kJ.g-1.
TL;DR: The results support the use of the Career Decision Scale—High School version of Hartman and Hartman as a differential measure of career indecision and indicate that the number and structure of factors can change across populations.
Abstract: A factor analytic study of the Career Decision Scale-High School version of Hartman and Hartman on 312 white South African adolescents from Grades 11 and 12 was undertaken. A simple two-factor structure emerged which accounted for 47.36% of the total variance in the scores. These results support the use of the version as a differential measure of career indecision and indicate that the number and structure of factors can change across populations. The implications of these results for research in South Africa are considered.
TL;DR: In this paper, the structure of UBr4(tpyrpo)2 has been determined by X-ray crystallography and the compound is monoclinic, space group C2/c, with a=17.226, b=11.883, c=18.372, β=109.30(3)°; Dc=2.005(5)g cm−3.
TL;DR: The authors developed a systemic measure instrument, consiting of 45 tenets of community life, which was tested on rural communities consisting mostly of illiterate farm labourers, with great success.
Abstract: The authors developed a systemic measure instrument, consiting of 45 tenets of community life, which was tested on rural communities consisting mostly of illiterate farm labourers. The measurement was done by community members them-selves, with very little guidance, but with great success, especially due to the fact that they were involved and could see changes as well as problems that needed further attention.
TL;DR: The Stereotype Reduction Workshop as discussed by the authors is an organizational intervention in intergroup relations, which is described in detail in the paper "Organizational Intervention in Intergroup Relations: Stereotypes Reduction Workshop".
Abstract: In this paper an organizational intervention in intergroup relations, the Stereotype Reduction Workshop, is described. Outlines of the content, group dynamic processes, theoretical underpinnings and impact of the Stereotype Reduction Workshop are presented.
TL;DR: In this paper, the vegetation of bushpockets in the active coastal dunefields of the eastern Cape, South Africa, and provides an inventory of the bushes of the area.
TL;DR: In this article, the extraction of cobalt(II) from a chloride medium (pH 1 to 5) by N,N,N1,N 1-tetra-n octylethylenediamine, N, N-di-n-octyl-2-(aminomethyl)pyridine, Alamine 336 and Aliguat 336 dissolved in 5% isodecanol - benzene was investigated.
Abstract: The extraction of cobalt(II) from a chloride medium (pH 1 to 5) by N,N,N1,N1-tetra-n-octylethylenediamine, N,N-di-n-octyl-2-(aminomethyl)pyridine, Alamine 336 and Aliguat 336 dissolved in 5% isodecanol - benzene was investigated. The protonation constants of the tertiary amine extractants are reported. They were obtained using the program SUPERQUAD in conjunction with the electrode calibration program MAGEC. The nature of the extracted complexes was elucidated using spectrophotometric methods, including the program TRIANG. Extraction equilibria are proposed based on these results. Gaussian analysis was employed to resolve the spectra of the extracted complexes in order to obtain estimates of the concentrations of the individual extracted complexes. These estimates were utilized in a non-linear least squares curve-fitting procedure to obtain extraction constants for the proposed extraction equilibria.
TL;DR: Three forms of N-acetyl-beta-D-glucosaminidase were separated from baboon kidney using Con A-Sepharose and DEAE-Trisacryl chromatography and further purified into two forms A-1 and A-2, which were homogeneous on SDS-PAGE and anodic PAGE but microheterogeneous on PAG-IEF.
TL;DR: In this article, the effect of thermal treatment on the formation of microsplits and damage rafts in hydrogen implanted (1 × 10 16) and annealed (700 and 800°C) GaAs was studied.
Abstract: Transmission electron microscopy has been used to study the effect of thermal treatment on the formation of microsplits and damage rafts in hydrogen implanted (1 × 10 16 and 5 × 10 16 H + cm -2 ) and annealed (700 and 800°C) GaAs. The results show that microsplit and damage raft formation in implanted samples may be prevented if the samples are first given a pre-anneal heat treatment for 15 minute intervals at 300, 350, 400 and 450°C, during which the hydrogen concentration is reduced without allowing vacancy coalescence to take place.
TL;DR: In this paper, the trans-ReOCl3(PPh3)2 reacts with potentially bidentate N,O- and N,S-donor benzimidazolyl alcohols and benzimidsylthiols (HL) in ethanol to produce the compounds ReOGl2(L) or ReOCl(OEt)(L) depending on the reaction conditions.
Abstract: The complex trans-ReOCl3(PPh3)2 reacts with potentially bidentate N,O- and N,S-donor benzimidazolylalcohols and benzimidazolylthiols (HL) in ethanol to produce the compounds ReOGl2(L)(PPh3) or ReOCl(OEt)(L)(PPh3), depending on the reaction conditions. The complexes were characterized by elemental analysis, NMR, vibrational and optical spectroscopy. Mechanisms for the formation reactions and probable configurations of the products are proposed, and these are supported by qualitative studies and spectroscopy.