Showing papers by "University of Port Elizabeth published in 1992"
TL;DR: For the entire mangrove area, a total of 75t of frasse enters the estuary per annum and increases leaf turnover an estimated four-fold, which is considerable contribution to the detrital pool of the Estuary and increases Leaf turnover four- fold.
153 citations
TL;DR: The Tierberg Karoo Research Centre near Prince Albert in the southern Karoo is intended for long-term ecological monitoring and manipulative studies as discussed by the authors and includes preliminary checklists of 189 vascular plant species, 25 ant, 90 bird, 18 reptile and 18 mammal species known to occur on the 1 km2 study site.
Abstract: SUMMARY The Tierberg Karoo Research Centre near Prince Albert in the southern Karoo is intended for long-term ecological monitoring and manipulative studies. This paper summarizes information on the management history, geology, soils, climate and vegetation and includes preliminary checklists of 189 vascular plant species, 25 ant, 90 bird, 18 reptile and 18 mammal species known to occur on the 1 km2 study site. In comparison with arid shrublands in North America, Australia. Israel and elsewhere in southern Africa, grasses and annual forbs are scarce, succulents abundant and there are few alien taxa.
76 citations
TL;DR: In this investigation the antimicrobial effect of two antioxidants and zinc ions, both separately and combined, was determined against three organisms at 37°C, with the exception of Escherichia coli at low zinc concentrations.
Abstract: The potentiation of action of antimicrobial preservatives/antiseptics by, respectively, antioxidants and metal ions has been established. In this investigation the antimicrobial effect of two antioxidants (Butylated hydroxyanisole and Propyl Gallate) and zinc ions, both separately and combined, was determined against three organisms at 37 degrees C. With the exception of Escherichia coli at low zinc concentrations, definite potentiation occurred, as reflected by a decrease in killing times.
66 citations
TL;DR: This model may explain the conflicting reports on the impact of livestock grazing on desert small mammals, with small mammal diversity decreasing with grazing below the peak, and increasing with grazing above the peak.
Abstract: The understanding of the determinants of small mammal community structure in arid and semiarid ecosystems is of importance, both in the light of the role that small mammals play, and the impact of livestock grazing on the flora of these systems. In a study aimed at identifying these determinants, small mammal assemblages and environmental features were quantified at six localities (a gradient of floristic structure, with constant annual rainfall) across the southern Karoo, South Africa. Stepwise variable regression indicated that small mammal diversity was correlated with plant and rock cover, as well as plant cover and horizontal foliage diversity at intermediate heights (40–60 cm). Initially, small mammal diversity increased with increasing plant cover, but decreased at cover levels greater than 30%. This relationship is similar to that found in other desert systems, although the peak in diversity found here is at higher levels of plant cover than found previously. I suggest that this higher peak may be owing to the lack of reliance on granivory by these animals, which are relatively omnivorous. This model may therefore explain the conflicting reports on the impact of livestock grazing on desert small mammals, with small mammal diversity decreasing with grazing below the peak, and increasing with grazing above the peak.
51 citations
TL;DR: The results presented here (including the first analysis of the diet of M. typica) indicate a greater emphasis on herbivory than previously described for these species, which is similar to that of South American, Australian and other southern African semi-arid communities.
Abstract: The feeding habits of a community of small mammals from the semi-arid Karoo, South Africa were analysed by microscopic examination of the stomach contents of animals caught during a 13-month snap-trapping study. The community comprised eight rodent species (Gerbillurus paeba, Mus minutoides, Rhabdomys pumilio, Otomys unisulcatus, Saccostomus campestris, Desmodillus auricularis, Malacothrix typica, Mastomys natalensis) and a single macroscelid elephant shrew (Macroscelides proboscideus.) The rodents were all predominantly herbivorous, while the elephant shrew ate mainly insects. No granivores or omnivores were represented in this community. The results presented here (including the first analysis of the diet of M. typica) indicate a greater emphasis on herbivory than previously described for these species. Limited dietary overlap was recorded between these species, although some instances of potential dietary competition that deserve further study were identified. The paucity of granivorous small mammals in the semi-arid Karoo contrasts the patterns of trophic specialization for North American and Israeli semi-arid communities, but is similar to that of South American, Australian and other southern African semi-arid communities.
40 citations
TL;DR: The authors investigated the understandings of electric current held by Australian primary science teachers, third year education students and South African primary school teachers teaching science through a second language (English), reveal very similar views shared within and between groups.
Abstract: Investigations of the understandings of electric current held by Australian primary science teachers, third‐year education students and South African primary school teachers teaching science through a second language (English), reveal very similar views shared within and between groups. These views are also very similar to the understandings of electric current held by 11‐year‐old pupils in New Zealand and Australian primary schools. Previous research has shown that participation in a teaching sequence wherein alternative conceptions were made explicit, challenge activities provided and a firm commitment to an explanation solicited, results in a shift towards ‘more scientifically acceptable’ understandings of electric current by pupils. This study shows this approach to be equally successful in changing teachers’ understandings of electric current.
40 citations
TL;DR: In this paper, the authors investigated the characteristics of the second decay process on a natural exposed dissipative beach, including its magnitude and dual dependence on local mean water depth and distance from the breaker line.
28 citations
TL;DR: Moonlight had a significant influence on the distribution of the copepodPseudodiaptomus hessei in the water column, and the strongest decrease in abundance was displayed by ovigerous females.
Abstract: Moonlight had a significant influence on the distribution of the copepodPseudodiaptomus hessei in the water column. Copepod samples were taken between March 1986 and March 1987 in the Sundays River estuary. South Africa. Late copepodid stages and adults showed vertical differences in abundance on moonlit nights, with more animals in bottom waters, but not on dark nights. Numbers of adults present in the water column were markedly lower on full moon nights compared with new moon nights. The strongest decrease in abundance was displayed by ovigerous females. These observed distribution patterns support published predation hypotheses.
27 citations
TL;DR: The first tris-bidentate cationic complex of technetium has been characterized in this article, which has a TcO bond distance of 1.668(7) A, that is typical for monooxotechnetium(V) square-pyramidal complexes.
26 citations
TL;DR: These findings refute the hypothesis that as a result of the harshness and similarity of physical conditions in deserts, the properties of desert communities are convergent, and raises the question as to why granivory varies between these systems.
Abstract: Annual seed consumption by a small mammal community in the semi-arid Karoo, South Africa, was calculated using population, biomass and dietary estimates and published estimates of field metabolic rate. The community comprised a macroscelid elephant shrew Macroscelides proboscideus, and two rodents Gerbillurus paeba and Desmodillus auricularis. Only G. paeba consumed seed during the study, and then in low amounts (annual mean = 0.4% of diet, insects = 53%, herbage = 47%), with M. proboscideus and D. auriocularis consuming mainly insects (88%) and herbage (90%), respectively. Energy requirements for the G. paeba population averaged 568 kJ ha−1 day−1. Total seed consumption was estimated to be ≈ 140 g ha−1, or 155 000 seeds ha−1 which represents ≈0.5% of the annual seed production for this site. These levels of granivory by small mammals are significantly lower than those recorded for North American deserts, and raises the question as to why granivory varies between these systems. These findings also refute the hypothesis that as a result of the harshness and similarity of physical conditions in deserts, the properties of desert communities are convergent.
26 citations
TL;DR: The nest of O. unisulcatus, with less temperature variation in winter and lower temperatures in summer, was less dependent of TA than P. brantsii's warren, and the use of these refuges contributes to the survival of these mesic rodents in a semi-arid region.
Abstract: We investigated microclimates of the nest of Otomys unisulcatus Cuvier, 1829 and the warren of Parotomys brantsii (Smith, 1834) during two seasons and correlated these with the rodents' physiology. In both rodents' refuges, temperature varied less than ambient temperature (TA). In winter, temperatures in the O. unisulcatus nest at 40 cm below the nest apex, and in the P. brantsii warren 15 cm below the soil surface, were higher than nocturnal TA. In summer, during the hours of highest TA, refuges were cooler than TA. Vapour pressure (v.p.) in the refuges varied less and was higher than ambient v.p. In the humid refuges, heat loss by conduction rather than evaporative water loss is suggested. The nest of O. unisulcatus, with less temperature variation in winter and lower temperatures in summer, was less dependent of TA than P. brantsii's warren. The use of these refuges therefore contributes to the survival of these mesic rodents in a semi-arid region.
TL;DR: In this paper, the reaction of the trans-ReOCl3(PPh3)2 with potentially bidentate N,O-donor benzimidazolyl-alcoholate ligands (HL) in the presence of triethylamine in ethanol and benzene produces the complexes ReO(OEt)(L)2 and ReOCl(L) 2, respectively.
Abstract: The reaction of the complex trans-ReOCl3(PPh3)2 with potentially bidentate N,O-donor benzimidazolyl-alcoholate ligands (HL) in the presence of triethylamine in ethanol and benzene produces the complexes ReO(OEt)(L)2 and ReOCl(L)2, respectively. These compounds were characterized by elemental analysis, NMR, vibrational and optical spectroscopy. Mechanisms for the formation reactions and probable configurations of the complexes are proposed, and these are supported by qualitative and spectroscopic studies.
TL;DR: The tetramethylthiuram disulfide (TMTD) and zinc dimethyldithiocarbamate (ZDMC) related vulcanization of cis-1,4-polyisoprene (IR) were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and electron spin resonance (ESR) as mentioned in this paper.
Abstract: The tetramethylthiuram disulfide (TMTD) and zinc dimethyldithiocarbamate (ZDMC) related vulcanization of cis-1,4-polyisoprene (IR) were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and electron spin resonance (ESR). The progress of the reactions in a given compound was monitored by analyzing the vulcanizate at selected points along the DSC curing curve. Full details of the analysis procedures are given. Analysis were mainly concerned with measurement of the crosslink densities, percentage of polysulfidic crosslinks, and the types and quantities of extractable compounds by thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC).
TL;DR: N-terminal amino acid sequences were determined for one chymotrypsinogen and one trypsin and the enzymes differed in amino acid composition as well as in specific activities towards synthetic amidase and esterase substrates.
TL;DR: Investigation of small mammal communities in the semi-arid Karoo, South Africa found that the energy demands of the small mammals are highest in winter when plant production is depressed, and small mammal energy requirements need to be taken into account in ecosystem models for the Karoo and when evaluating the impact of livestock on vegetation.
TL;DR: Cooper et al. as discussed by the authors reported that the Caspian tern Sterna caspia occurs along the whole southern African coastline and on large river systems and water bodies away from the coast.
Abstract: Summary Cooper, J., Brooke, R.K., Cyrus, D.P., Martin, A.P., Taylor, R.H. & Williams, A.J. 1992. Distribution, population size and conservation of the Caspian Tern Sterna caspia in southern Africa. Ostrich 63: 58–67. The Caspian Tern Sterna caspia occurs along the whole southern African coastline and on large river systems and water bodies away from the coast. A total of 28 definite breeding localities has been recorded in southern Africa. Breeding has occurred recently at at least 14 coastal localities between Swakopmund, Namibia, and Lake St Lucia, Natal, South Africa. Inland breeding has been recorded in recent years at Sua Pan, Botswana and Kalkfonteindam, Orange Free State, South Africa. Based on censuses conducted between 1980 and 1991, the southern African breeding population is estimated to be of the order of 500 pairs, 91% of which breed coastally and 89% breed on islands. Up to 290 pairs (58%) bred at Lake St Lucia. Seventyone per cent of the 1980–1991 breeding population falls within eight natu...
Journal Article•
TL;DR: In this paper, selected outcrops along the Baakens valley and coastal strip east of Sardinia Bay were used to determine the overall structure of the Table Mountain Group (TMG) close to Port Elizabeth.
Abstract: Selected outcrops along the Baakens valley and coastal strip east of Sardinia Bay were used to determine the overall structure of the Table Mountain Group (TMG) close to Port Elizabeth. A large recumbent fold (nappe?) structure is interpreted to be the result of an early phase of shortening. Pelitic horizons were subsequently smeared out along thrusts in the TMG. This caused repeated stacking, resulting in an unusually thick sequence of quartzites. The last phase of tectonism was extensional. An 8 km broad graben formed between two prominent west-northwest-striking fault zones, the Moregrove and Chelsea-Noordhoek faults
TL;DR: A detailed account of the mechanism of crosslinking in the cis-1,4-polyisoprene (IR)-tetramethylthluram disulfide (TMTD)-ZnO system is given in this article.
Abstract: A detailed account of the mechanism of crosslinking in the cis-1,4-polyisoprene (IR)-tetramethylthluram disulfide (TMTD)–ZnO system is given. Many experimental observations were harmonized in terms of a radical mechanism, rather than an ionic mechanism. Electron spin resonance (ESR) spectra on the IR–TMTD–ZnO system, recorded at 120°C, inter alia revealed resonance lines in the vicinity of g = 2.02. These were related to the rapid formation of thiuram persulphenyl radicals XS, on the homolytic splitting of tetramethylthiuram polysulfides. The Moore–Trego efficiency E dropped from 11.5 (at 140.0°C) to 3.5 (at 146.9°C), indicating that a substantial part of the sulfur atoms was initially to be associated with pendent groups. The formation of these pendent groups could be viewed as an irreversible, concerted reaction without the formation of a true alkenyl radical intermediate. Crosslinks would form by either a disproportionation reaction between two α-methylic or α-methylenic pendent groups RSxX or a reaction between a pendent groups RSxX (R = polyisoprenyl, x ≥ 2, X = Me2NC(S)) and the unsaturated polymer chain. The latter crosslink formation reactions were regarded as rate determining in the vulcanization sequence. A mechanism is proposed that does not require the participation of ZnO in the formation of the active sulfurating agent.
TL;DR: In this paper, the interaction of curatives in the systems cis-1,4-polyisoprene (IR) -sulfur, ZnO, IR-tetramethylthiuram disulphide (TMTD), and TMTD were studied.
Abstract: The interaction of curatives in the systems cis-1,4-polyisoprene (IR)–sulfur, IR–sulfur–ZnO, IR–tetramethylthiuram disulphide (TMTD), and IR–sulfur–TMTD were studied. Thermal events observed in the differential scanning calorimetry curing curves characteristic of these systems were explained in terms of the melting/liquefaction of compounds, the evaporation of gases, and the vulcanization process itself. The similarity of the IR–sulfur and IR–sulfur–ZnO curing curves suggested that sulfur and ZnO were unreactive during vulcanization. On heating the IR–TMTD and IR–sulfur–TMTD systems, gases such as Me2NH and CS2 formed easily. Although the maximum crosslink densities in the latter systems were low, the crosslink formation was found to be strongly exothermic. The sulfur efficiency parameter E was estimated for the IR–sulfur–TMTD system and decreased steeply from 37.5 (at 143.2°C) to 16.6 (at 151.0°C). This was taken as evidence that much of the bound sulfur was initially combined in pendent groups. Then E increased dramatically toward the advanced stages of cure, emphasizing the extraordinary inefficient manner in which sulfur was utilized to form crosslinks.
TL;DR: In this article, the mechanism of vulcanization in the synthetic cis-1,4-polyisoprene (IR)-sulfur-tetramethylthiuram disulphide (TMTD)-ZnO system was harmonized.
Abstract: Several aspects on the mechanism of vulcanization in the synthetic cis-1,4-polyisoprene (IR)-sulfur-tetramethylthiuram disulphide (TMTD)–ZnO system were harmonized. The differential scanning calorimetry (DSC) thermograms showed that the vulcanization processes became better resolved on increasing the curative loading in the compound. Two major crosslinking reactions occurred consecutively in the IR (100)–sulfur (9.46)–TMTD (8.86)–ZnO (3.00) mixture, viz the IR–sulfur–TMTD–ZnO and IR–sulfur–zinc dimethyldithiocarbamate (ZDMC) (or IR–sulfur–ZDMC–ZnO) reactions. In the first process poly-and disulfidic pendent groups RSxSX (R = polyisoprenyl, X = Me2NC (S), x ≥ 1) formed via the IR–XSSxSX reaction, and in the second via the IR–XSSxZnSSX reaction. Thermogravimetric analysis (TGA) and high-pressure liquid chromatography (HPLC) data showed that dimethyldithiocarbamic acid liberated during the IR–sulfur–TMTD–ZnO reaction was trapped by ZnO to yield ZDMC. Hence ZDMC was a product, and not precursor, of this crosslinking process. A comparison of reactions in IR–sulfur–TMTD–ZnO and poly(ethylene-co-propylene)–sulfur–TMTD–ZnO mixtures showed that the participation of IR molecules was essential for ZDMC formation. The ZDMC concentration remained constant at ∼ 38.4 mol % during the later stages of cure, showing that it did not participate in the desulfuration reactions of polysulfidic links. In the presence of stearic acid the stearic acid–ZnO reaction occurred at 87°C as was manifested by an intense crystallization peak of zinc stearate. The vulcanization processes were the same both in the presence and absence of stearic acid.
TL;DR: In this article, a factor analysis of 190 South African university undergraduates' responses to the Commitment to Career Choices Scale showed considerable similarity of factors with those in Blustein et al.'s 1989 work and supported the construct validity of the scale.
Abstract: Factor analysis of 190 South African university undergraduates' responses to the Commitment to Career Choices Scale showed considerable similarity of factors with those in Blustein, et al.'s 1989 work and supports the construct validity of the scale. However, omission of certain items from the two dimensions is recommended.
TL;DR: In this paper, a vulcanization of cis-1,4-polyisoprene (IR) with thiruam-related curing systems, dimethyldithiocarbamic acid (DMDCA) is formed as a byproduct, in the formation of either pendent groups or crosslinks.
Abstract: During the vulcanization of cis-1,4-polyisoprene (IR) with thiruam-related curing systems, dimethyldithiocarbamic acid (DMDCA) is formed as a byproduct, in the formation of either pendent groups or crosslinks. DMDCA is unstable, and decomposes instantly to Me2NH and CS2 in the absence of ZnO. The facile reaction of Me2NH and thiuram-related molecules such as tetramethylthiuram polysulfides, tetramethylthiuram disulfide (TMTD), tetramethylthiuram monosulfide and pendent groups caused (i) increased induction periods, (ii) lower maximum crosslink densities, and (iii) the excessive formation of tetramethylthiourea (TMTU). A most important function of ZnO was to trap the DMDCA via the formation of zinc dimethyldithiocarbamate and water, thereby preventing the detrimental reactions above. The IR/TMTD/ZnO and IR/sulfur/TMTD/ZnO systems were therefore characterized by (i) shorter induction periods, (ii) higher maximum crosslink densities, and (iii) the absence of TMTU.
06 May 1992
TL;DR: In this article, an interpretation of James Cameron's films, The Terminator and Terminator II - Judgment Day, is presented, where the paradoxical time-structure of the film-narrative is explored in terms of Heidegger's analysis of temporarily with its emphasis on the primacy of the future in relation to the past and the present.
Abstract: This article is an interpretation of James Cameron’s films, The Terminator and Terminator II - Judgment Day . As instances of popular art, they are first situated in the context of Habermas's conviction that art has a specific function in the public sphere, viz. to provide an enlightening experience for people who are normally excluded from the specialized discourse of aesthetics and an criticism. The interpretation of the joint film narrative of Terminator I and II is then articulated in two stages. First, the paradoxical time -structure of the film-narrative is explored in terms of Heidegger’s analysis of temporarily, with its emphasis on the primacy of the future in relation to the past and the present. Secondly, the fact that these film s were made possible by a combination of film art and advanced film technology, is thematized along lines suggested by Heidegger's critique of technology. This leads to the insight, finally , that the Terminator film s exemplify Heidegger’s contention that the threat posed by technology is averted by a liberating force from within itself
TL;DR: In this article, the special radical classes of near-rings are defined and investigated, and it is shown that their approach does cater for all the well-known radicals of a near-ring.
Abstract: Special radical classes of near-rings are defined and investigated. It is shown that our approach, which differs from previous ones, does cater for all the well-known radicals of near-rings. Moreover, most of the desirable properties from their ring theory counterpart are retained. The relationship between the special radical of a near-ring and the corresponding matrix near-ring is given.
TL;DR: Gel electrophoresis on SDS-PAGE revealed relative molecular masses of 202,900 and 208,600 for the active catalase and peroxidase molecules respectively (nonreducing conditions), as compared to 56,800 and 49,800 for the monomers under reducing conditions, thus indicating the likelihood of tetramers in the intact state.
TL;DR: In this article, six-coordinate cationic complexes of rhenium and technetium with tridentate N-(2-oxidophenyl)-salicylideneiminate (OPhsal2-) and the bidentate aromatic nitrogen-donor ligands 2,2′-dipyridine, 1,10-phenanthroline, 2, 2-2′ -phenanthusine and bis(2-pyridyl)ketone (NN) have been prepared.
Abstract: Six-coordinate cationic complexes of rhenium(V) and technetium(V) with the tridentate N-(2-oxidophenyl)-salicylideneiminate (OPhsal2-) and the bidentate aromatic nitrogen-donor ligands 2,2′-dipyridine, 1,10-phenanthroline, 2,2′-dipyridylamine and bis(2-pyridyl)ketone (NN) have been prepared. Complexes of general formula [MO(OPhsal)(NN)]X (M = Re, Tc; X = Cl, PF6) were isolated by the reaction of ReOCl(OPhsal)(PPh3) and TcOCl(O Phsal) with the bidentate nitrogen-donor ligands. The reaction of TcOCl(O Phsal) with bis(2-pyridyl)ketone (dpk) in ethanol produced the complex [TcO(OPhsal)-(dpk.EtOH)]Cl, in which alcoholation of ethanol across the ketone double bond of dpk has occurred. Spectroscopic and analytical results obtained for all the isolated complexes suggest terdentate coordination of OPhsal2- in the equatorial plane cis to the oxo oxygen, with the bidentate pyridyl nitrogen-donor ligands bridging the fourth equatorial site and the position trans to the oxo group.
TL;DR: The germination potential of Atriplex nummularia (Lind.) was investigated under laboratory conditions and gibberellic acid treatment showed the greatest stimulation of germination.
TL;DR: In this paper, it is shown that an ideal A of a near-ring is equiprime if and only if it is the annihilator of an equip-rime TV-group G. This concept was shown in subsequent work to lead to a very satisfactory theory of special radicals for near-rings.
Abstract: Equiprime near-rings, which generalize the concept of prime-ness in rings, were defined by the present authors, together with S. Veldsman. This concept was shown in subsequent work to lead to a very satisfactory theory of special radicals for near-rings. In the current paper, we define equiprime N-groups for a near-ring N. It is shown that an ideal A of N is equiprime if and only if it is the annihilator of an equiprime TV-group G. Special classes of near-ring modules are defined, and a module-theoretic characterization of special radicals of near-rings is established, similar to that given by Andrunakievich and Rjabuhin for special radicals of rings.
TL;DR: In this article, the nucleation and growth of undoped gallium arsenide (GaAs) epitaxial layers, grown by metallo-organic vapour phase epitaxy (MOVPE) on Si (001) substrates, were investigated by transmission electron microscopy (TEM).
TL;DR: In this article, the authors investigated the mechanism of zinc dimethyldithiocarbamate (ZDMC)-accelerated sulfur vulcanization and found that crosslinking is preceded by the formation of pendent groups RSxSX [R = polyisoprenyl, X = Me2NC(S)].
Abstract: Aspects of the mechanism of zinc dimethyldithiocarbamate (ZDMC)-accelerated sulfur vulcanization were discussed. The trends in the efficiency parameter E, confirmed that crosslinking is preceded by the formation of pendent groups RSxSX [R = polyisoprenyl, X = Me2NC(S)] in ZDMC-based systems. The index x in RSxX was calculated as 5.82 in the cis-1,4-polyisoprene (IR)/sulfur/ZDMC/ZnO compound at the initial stages of curing, compared to 3.23 in the absence of ZnO. The high value of x supports the postulation that elemental sulfur and ZDMC react at the early stages of vulcanization, to form the active sulphurating agent XSxSZnSSX. Crosslinks form by either a disproportionation reaction between two α-methylic or α-methylenic pendent groups RSxX, or a reaction between a pendent group RSxX and the rubber chain—these routes are the same as that suggested for the IR/tetramethylthiuram disulfide (TMTD)/ZnO compound. The beneficial role of ZnO and zinc stearate is shown, as in the case of ZnO in the IR/TMTD/ZnO system, to be related to their ability to trap dimethyldithiocarbamic acid, which formed in the generation of pendent groups and crosslinks. ZnS is inactive in this regard. The formation of ZnS is characteristic of natural rubber/sulfur/ZDMC/ZnO systems, as opposed to IR/TMTD/ZnO mixtures where little ZnS forms.