Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320070002&lang=en vol. 103 num. 3-4 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>AfrOBIS: A marine biogeographic information system for sub-Saharan Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200001&lng=en&nrm=iso&tlng=en AfrOBIS is one of 11 global nodes of the Ocean Biogeographic Information System (OBIS), a freely accessible network of databases collating marine data in support of the Census of Marine Life. Versatile graphic products, provided by OBIS, can be used to display the data. To date, AfrOBIS has loaded about 3.2 million records of more than 23 000 species located mainly in the seas around southern Africa. This forms part of the 13.2 million records of more than 80 000 species currently stored in OBIS. Scouting for South African data has been successful, whereas locating records in other African countries has been much less so. <![CDATA[<b>Correlations between advertising and R&D expenditures: Dealing with important intangibles</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200002&lng=en&nrm=iso&tlng=en Expenditures on research and experimental development (R&D) and advertising by companies are forms of capital investment in intangible commodities as opposed to capital investment in tangible commodities such as plant and equipment. The amounts spent on both advertising (adspend) and R&D are positively related to the profitability of commercial enterprises. Various studies have recorded the links between R&D and adspend at the level of firms, sub-sectors and sectors of industry for particular countries. However, no analyses appear to have been published on the associations between these two kinds of investment either at national level or in international comparisons. The findings presented here indicate that the most-developed countries spend between two and six times more on R&D per capita than on advertising. In less R&D-intensive economies, however, adspend may equal or exceed R&D expenditure per capita. In four countries examined, that have the lowest investment in R&D as a percentage of GDP-namely South Africa, Greece, Portugal and Poland-adspend actually exceeds gross expenditure on R&D. I focus on the link between R&D and adspend in South Africa between 1989 and 2004, for which a highly significant correlation (r = 0.99) was found. I also examine international comparisons of reliable data and indicator series concerning these factors in 17 other countries between 1995 and 2004. In the majority of EU and other countries for which relevant advertising and R&D data were available, significant correlations were also found between these two variables. Because total advertising figures tend to be published within the first quarter of the following year, it may be possible to use these statistics to forecast national R&D expenditure. The benefits for businesses to continue investing in both advertising and R&D, even under adverse economic conditions, are also discussed. <![CDATA[<b>Frank Nabarro: A journey through science and society</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200003&lng=en&nrm=iso&tlng=en Expenditures on research and experimental development (R&D) and advertising by companies are forms of capital investment in intangible commodities as opposed to capital investment in tangible commodities such as plant and equipment. The amounts spent on both advertising (adspend) and R&D are positively related to the profitability of commercial enterprises. Various studies have recorded the links between R&D and adspend at the level of firms, sub-sectors and sectors of industry for particular countries. However, no analyses appear to have been published on the associations between these two kinds of investment either at national level or in international comparisons. The findings presented here indicate that the most-developed countries spend between two and six times more on R&D per capita than on advertising. In less R&D-intensive economies, however, adspend may equal or exceed R&D expenditure per capita. In four countries examined, that have the lowest investment in R&D as a percentage of GDP-namely South Africa, Greece, Portugal and Poland-adspend actually exceeds gross expenditure on R&D. I focus on the link between R&D and adspend in South Africa between 1989 and 2004, for which a highly significant correlation (r = 0.99) was found. I also examine international comparisons of reliable data and indicator series concerning these factors in 17 other countries between 1995 and 2004. In the majority of EU and other countries for which relevant advertising and R&D data were available, significant correlations were also found between these two variables. Because total advertising figures tend to be published within the first quarter of the following year, it may be possible to use these statistics to forecast national R&D expenditure. The benefits for businesses to continue investing in both advertising and R&D, even under adverse economic conditions, are also discussed. <![CDATA[<b>HIV/AIDS in South Africa revisited</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200004&lng=en&nrm=iso&tlng=en Expenditures on research and experimental development (R&D) and advertising by companies are forms of capital investment in intangible commodities as opposed to capital investment in tangible commodities such as plant and equipment. The amounts spent on both advertising (adspend) and R&D are positively related to the profitability of commercial enterprises. Various studies have recorded the links between R&D and adspend at the level of firms, sub-sectors and sectors of industry for particular countries. However, no analyses appear to have been published on the associations between these two kinds of investment either at national level or in international comparisons. The findings presented here indicate that the most-developed countries spend between two and six times more on R&D per capita than on advertising. In less R&D-intensive economies, however, adspend may equal or exceed R&D expenditure per capita. In four countries examined, that have the lowest investment in R&D as a percentage of GDP-namely South Africa, Greece, Portugal and Poland-adspend actually exceeds gross expenditure on R&D. I focus on the link between R&D and adspend in South Africa between 1989 and 2004, for which a highly significant correlation (r = 0.99) was found. I also examine international comparisons of reliable data and indicator series concerning these factors in 17 other countries between 1995 and 2004. In the majority of EU and other countries for which relevant advertising and R&D data were available, significant correlations were also found between these two variables. Because total advertising figures tend to be published within the first quarter of the following year, it may be possible to use these statistics to forecast national R&D expenditure. The benefits for businesses to continue investing in both advertising and R&D, even under adverse economic conditions, are also discussed. <![CDATA[<b>Nitrous oxide and carbon dioxide: Their similar and contrasting biological effects</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200005&lng=en&nrm=iso&tlng=en The similar and contrasting biological properties of CO2 and N2O appear to reflect fundamental biological processes in both very simple and the most complex organisms. <![CDATA[<b>Biogenic volatile organic compounds: The state of knowledge in southern Africa and the challenges for air quality management</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200006&lng=en&nrm=iso&tlng=en Emissions of biogenic volatile organic compounds (BVOCs) on an urban and regional scale compare with those from anthropogenic sources, both in magnitude and in their role in atmospheric photochemistry and in the formation of ozone. Despite this, research on BVOC emissions in southern Africa has been limited to relatively few plant species in savannas, woodlands and shrublands. Extrapolation of these values provides an estimated annual emission of 80 Tg C for the subcontinent. Isoprene and monoterpene emissions vary widely according to plant species, temperature, foliar density and photosynthetically active radiation, and also diurnally and with season. Savanna trees such as Acacia nigrescens and Burkea africana are high isoprene emitters, and monoterpene emissions from Colophospermum mopane and Acacia tortilis are significant. By comparison, some tree species, such as Combretum molle and Sclerocarya birrea, emit neither compound. The legal prerequisite for holistic air quality management in South Africa, together with the dearth of information on BVOC emissions and an understanding of their role in the formation of ozone, poses significant challenges for policy-makers, air quality managers and scientists in southern Africa. <![CDATA[<b>Functional characterization of heterotrophic denitrifying bacteria in activated sludge</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200007&lng=en&nrm=iso&tlng=en Wastewater treatment facilities are largely accountable for the detrimental enrichment of water bodies with nitrogenous compounds, resulting in eutrophication. Denitrification is of interest as a means of removing nitrates and nitrites from water supplies because they are also hazardous to human health. The integration of biological nutrient removal into conventional wastewater treatment processes has, however, failed to take into sufficient consideration the role of key microorganisms present, specifically denitrifying bacteria. The purpose of the study reported here was to group such heterotrophic denitrifying bacteria using a series of biochemical and molecular analyses, to achieve an improved understanding of their functions. The role of the denitrifying bacteria in reducing nitrate and nitrite was monitored using the colorimetric nitrate reduction test. The genetic diversity of the culture collection was investigated by the use of denaturing gradient gel electrophoresis (DGGE), which enabled the creation of a microbial population profile of eight predominant isolates. Batch experiments were conducted on these isolates, the results of which ultimately confirmed their classification according to their respective functions, namely, incomplete denitrifiers, true denitrifiers, sequential denitrifiers, and exclusive nitrite reducers. <![CDATA[<b>Documenting lichen-induced mechanical weathering of quartzitic sandstone at Kaapsehoop, Mpumalanga</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200008&lng=en&nrm=iso&tlng=en The role of lichens in rock weathering is difficult to quantify and its study is still in its infancy. Here we highlight some biologically induced weathering processes observed on sandstone samples taken in a field of boulders located at Kaapsehoop in Mpumalanga province, South Africa. Light microscopy and scanning electron microscopy were used to investigate the interaction between lichen colonies and sandstone surfaces. The biological structures of lichens were observed for their effect on the rock surface, and variations in pore size, angularity and sorting of sandstone micro-granules were assessed. We demonstrate that the interlacing of lichen hyphae between sandstone grains contributes to the dislodgement and movement of these granules. We also found that lichen-induced weathering at Kaapsehoop produces smaller and more angular micro-granular sandstone surface structures than on the adjacent lichen-free surfaces. <![CDATA[<b>Plant regeneration from seed-derived callus of <i>Arctotis arctotoides, </i>a medicinal herb of the family Asteraceae</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200009&lng=en&nrm=iso&tlng=en We have devised a procedure for in vitro plant regeneration, from seed-derived callus, of Arctotis arctotoides, a plant noted for its medicinal uses among the rural people of the Eastern Cape province of South Africa. Callus formation was induced in basal MS salt supplemented with 3% sucrose and 1% agar at different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D). After two weeks, morphogenic responses were evident in cultures and deeply stained, light-yellow calluses were produced. The highest percentage (68%) of seed explants that induced callus formation was obtained on MS medium supplemented with 2.0 mg l(-1)2,4-D in the dark. When callus material was repeatedly subcultured in ½MS basal medium with a 16-h photoperiod without any hormonal supplement, adventitious shoots were produced eight weeks after the start of culture. The shoots rooted two weeks later. This is the first record of the in vitro regeneration of A arctotoides and could serve as a foundation for further research on tissue culture, micropropagation and germplasm conservation of this noteworthy medicinal plant. <![CDATA[<b>Discovery of an alien invasive, predatory insect in South Africa: The multicoloured Asian ladybird beetle, <i>Harmonia axyridis </i>(Pallas) (Coleoptera: Coccinellidae)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200010&lng=en&nrm=iso&tlng=en The Asian ladybird beetle, Harmonia axyridis (HA) (Insecta: Coleoptera: Coccinellidae), is a generalist predator long valued as a biocontrol agent of pestiferous aphids and other invertebrates. However, HA has become highly invasive in North America and Europe. The beetle is eurytopic, broadly polyphagous, very dispersive and pheno-typically highly plastic. In the United States and Europe, this pest is implicated in adverse ecological impacts involving changes in invaded communities through interspecific competition and intraguild predation. Additionally, HA can be a household nuisance, and affect human health and agricultural production. The beetle has now reached South Africa. A founder population has become established in the Western Cape province, and the species has also been collected in the Eastern Cape province. We present illustrated diagnoses of HA and selected resident South African Coccinellidae with which it may be confused. There is reason to suspect that HA will spread rapidly through much of South Africa and beyond and bring to bear its negative consequences here. The early detection of this incursion presents a rare opportunity to study an anticipated biological invasion virtually from its beginning. <![CDATA[<b>On the development of a new nonhydrostatic atmospheric model in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200011&lng=en&nrm=iso&tlng=en With the advent of ever faster computers, the operational use of nonhydrostatic atmospheric models at resolutions beyond the hydrostatic limit has become a reality. A renewed global research effort is being made to formulate and improve nonhydrostatic models. In this paper, the status of numerical atmospheric modelling research in South Africa is briefly reviewed. We then report on the development of a new, nonhydrostatic atmospheric model at the University of Pretoria. The dynamic kernel of the model is based on a novel, split semi-Lagrangian formulation of a set of quasi-elastic equations in a terrain-following vertical coordinate based on the full pressure field. The main features of the model dynamics and numerics are discussed, and it is noted that the governing equation set presented here has not been applied in atmospheric modelling before. The model may be used to perform state-of-the-art research in numerical model development, for instance, for the derivation of new equation sets, numerical techniques and vertical coordinate systems. The model's ability to simulate highly nonlinear and nonhydrostatic flow is illustrated by means of a convective bubble experiment, where an updraft interacts with vertical shear of the horizontal wind. This experiment illustrates the potential of the new model to be used in the study of thunderstorm dynamics. <![CDATA[<b>An investigation into the extent of uncertainty surrounding estimates of the impact of HIV/AIDS in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200012&lng=en&nrm=iso&tlng=en HIV/AIDS statistics have been the source of much controversy in South Africa, but often the extent of uncertainty around these estimates is ignored. There is need for an assessment of the range of uncertainty around often-quoted HIV/AIDS statistics. This analysis determines ranges of uncertainty around the inputs and outputs of the ASSA2002 AIDS and Demographic model of the South African HIV/AIDS epidemic, using a generalized likelihood uncertainty estimation approach. A sample of 500 parameter combinations was drawn by weighting randomly generated parameter combinations by likelihood functions defined on the basis of four South African HIV/AIDS data sets. The estimated number of HIV infections in mid-2005 was 5.1 million (95% prediction interval: 4.2-6.0 million), equivalent to an HIV prevalence rate of 11.1% (9.1-13.1%). Between mid-2004 and mid-2005, the estimated number of new HIV infections was 490 000 (370 000-590 000) and the estimated number of AIDS deaths was 320 000 (270 000-380 000). The posterior mean HIV survival time was estimated to be 11.5 years (95% credibility interval: 10.0-12.9 years), longer than estimated for elsewhere in the developing world. This analysis confirms that South Africa is experiencing a severe HIV/AIDS epidemic, and suggests that HIV/AIDS epidemiology in the country probably differs from that elsewhere in Africa. <![CDATA[<b>Status of seedling establishment pests of <i>Acacia mearnsii </i>De Wild. (Mimosaceae) in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200013&lng=en&nrm=iso&tlng=en There are about 106 690 ha of Acacia mearnsii (wattle) plantations in South Africa. Wattle was previously grown mainly for the commercial potential of its bark (a source of tannin extract) but is now also managed on a short rotation for pulpwood. Clear-felled sites are continually being regenerated. Although considerable research has been done on the post-establishment insect pests of wattle, little is known about the incidence and status of seedling establishment pests. Fourteen trials were planted, on previous wattle sites, over six growing seasons from 1990/91 to 1999/00. Seedlings were evaluated monthly after planting for one year. Stressed, damaged and dead seedlings were uprooted and inspected to determine the cause of death. About 9% to 51% of seedlings failed to establish during wattle regeneration, and the incidence of damage by seedling pests ranged from about 2% to 30%. At sites where the plantation residue was windrowed and burnt, the average incidence of seedling establishment pests was about 20%, and the average total failure of wattle seedlings to establish was about 34%. Whitegrubs (larvae of Coleoptera: Scarabaeidae: Melolonthinae, Rutelinae) were the dominant and economically most important seedling establishment pests (average incidence of about 13%), followed by cutworms (larvae of Lepidoptera: Noctuidae) whose average incidence of about 4% was similar to that of grasshoppers (Orthoptera: Acrididae, Pyrgomorphidae) (about 2%) and millipedes (Diplopoda: Juliformia) (about 1%). Other seedling establishment pests included termites (Isoptera: Termitidae, Hodotermitidae), tipulid larvae (Diptera: Tipulidae), wireworms (Coleoptera: Elateridae), false wireworms (Coleoptera: Tenebrionidae), crickets (Orthoptera: Gryllidae), ants (Hymenoptera: Formicidae) and nematodes (Nematoda: Heteroderidae, Trichodoridae). Nematodes were sporadically important (about 12%) in an old arable wattle site. Although the prophylactic and corrective application of insecticides was widely used to control these pests at planting, their routine use in certified plantations now contravenes the Forest Stewardship Council guidelines. <![CDATA[<b>Importance value of landscapes, flora and fauna to Tsonga communities in the rural areas of Limpopo province, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200014&lng=en&nrm=iso&tlng=en Many parts of the former homeland areas of South Africa are believed to be experiencing environmental scarcity, and are increasingly vulnerable to resource over-exploitation. Frequently, these areas are adjacent to formally protected areas and present unique challenges in integrating biodiversity conservation and sustaining livelihoods, especially for resource-dependent rural communities. Although studies have been undertaken on the use of various plants by Tsonga communities, and the economic value of specific taxa, no investigation on the relative importance value that considers both wild flora and fauna, together with landscapes, has been carried out previously in the former Gazankulu homeland. We used a weighted ranking exercise for nine focus groups within three rural villages bordering the Kruger National Park, which are largely dependent on wild resources, to assess the relative importance of landscape units and species-level biodiversity. Landscape units, particularly forest/bush and river/stream, were found to be extensively used in meeting community needs, across a range of resource use categories including maintaining socio-cultural norms. Moreover, landscape units vary among villages and age/gender regarding how they contribute to sustaining livelihoods. In total, 162 taxa were identified, with two taxa (Sclerocarya birrea subsp. caffra; Ficus spp.) exploited in up to seven use categories. Sclerocarya birrea, Combretum imberbe and Colophospermum mopane were the most highly valued species among those surveyed, contributing 22% to the overall value of wild flora and fauna in the area. Of those identified, 28 faunal (60%) and 10 floral (8.7%) taxa are listed in either IUCN, national or provincial protected species schedules. Based on combined Local Users Value scores, over 20% of all biodiversity value for local communities comes from protected tree species. Similarly, faunal taxa with enhanced protection constitute almost 12% of all local biodiversity value. In developing strategies for resource conservation, it is necessary to recognize this widespread use of the natural environment and the wild products, including those under formal protection, exploited by local people. <![CDATA[<b>New theories of </b><b>α</b><b>-radioactivity</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200015&lng=en&nrm=iso&tlng=en We review the radioactive decay of nuclei via emission of α-particles using three different theoretical approaches. The half-lives of the radioactive nuclei, calculated using these three methods, are compared with each other and with available experimental data. The results show that the superasymmetric fission model with the double-folding procedure for obtaining the α-nucleus potential is the most reliable among the three models studied. <![CDATA[<b>Human and automatic accent identification of Nguni and Sotho Black South African English</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200016&lng=en&nrm=iso&tlng=en It is well established that accent can have a detrimental effect on the performance of automatic speech recognition (ASR) systems. Whereas accents can be labelled in terms of a speaker's mother tongue, it remains to be determined if and when this distinction is appropriate for the development of ASR technology. This study compares the varieties of South African English produced by mother-tongue speakers of the Nguni and Sotho languages, who account for over 70% of the country's population. The aim of the investigation was to determine whether these two accent groups should be treated as a single variety by ASR systems, or whether it is better to consider them separately. To this end, two sets of experiments were carried out. First, a perceptual experiment was performed in which human listeners were required to classify different English accents. Subsequently, automatic speech recognition experiments were conducted to determine how the accuracy of an automatic accent identification system compares with these perceptual results, and whether the acoustic models benefit from the incorporation of Nguni/Sotho accent classifications. The results of the perceptual experiment indicated that most listeners could not correctly identify a speaker's mother tongue based on their English accent. This finding was supported by the results of the automatic accent identification and speech recognition experiments. <![CDATA[<b>Dithiocarbonate and trithiocarbonate interactions with pyrite</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200017&lng=en&nrm=iso&tlng=en Dithiocarbonate (xanthate) collectors have been the workhorse of the sulphide flotation industry for more than 80 years. More recently, some flotation plants have started to use a new collector, trithio-carbonate (TTC). Extensive research has been conducted on the interaction of different substrates with xanthates, which adsorb electrochemically and are present as a chemisorbed xanthate, metal xanthate or dixanthogen. The work reported here is the first detailed, fundamental evaluation of a long-chain trithiocarbonate collector for sulphide minerals. The results show that this collector-unlike the widely used xanthate collector-has a strong non-electrochemical collection action in addition to an electrochemical one. The non-electrochemical action opens up significant possibilities of changing mill conditions (specifically regarding the propensity of sulphide minerals to oxidize), to obtain better sulphide recovery. <![CDATA[<b>Enhanced drought tolerance in transgenic potato expressing the <i>Arabidopsis thaliana </i>Cu/Zn superoxide dismutase gene</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200018&lng=en&nrm=iso&tlng=en All aerobic organisms must possess the means to protect themselves from the toxic effects of reduced oxygen species generated during the normal metabolic activity of cells or as a result of environmental stresses such as drought. Cells are protected from the deleterious effects of free oxygen radicals by Cu/Zn superoxide dismutase (SOD), which catalyses the initial step in neutralizing activated oxygen species. In the study reported here, the potato cultivar Aviva was transformed with a cytosolic Cu/Zn superoxide dismutase gene from Arabidopsis thaliana using Agrobacterium-mediated gene transformation. Four transgenic potato lines were identified and evaluated for drought tolerance in the greenhouse. Two transformed lines could withstand drought in the greenhouse for two weeks longer than the untransformed plants and one week longer than two other transformed lines. These findings were confirmed by data from enzyme activity as well as by 2,3,5-triphenyltetrazolium chloride reduction. <![CDATA[<b>The effect of coarse edge on wool spinning performance and yarn properties</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532007000200019&lng=en&nrm=iso&tlng=en The interrelationship of natural fibre, yarn and fabric properties is both important and complex, and has attracted considerable research. An area which has received little attention is that concerning the effect of fibre diameter distribution, notably of relatively coarse fibres, on processing behaviour and yarn and fabric properties, except for their well-known effect on handle and prickle (scratchiness). Prickle is an unpleasant sensation sometimes experienced with garments worn next to the skin. The effect of fibre diameter distribution, of coarse fibres (or coarse edge, CE) in particular, on spinning performance and yarn properties, was investigated for 400 different wools. Multiple regression analyses were carried out to quantify the relationships between all the main fibre properties, including CE, on the one hand, and the spinning performance and yarn properties on the other hand. We found that CE had no significant effect on spinning performance and yarn properties, except for yarn neps and yarn hairiness. These findings are important for sheep breeding practices as well as for selecting the most appropriate wools when yarn of a specified quality is to be processed, because attention needs be paid only to fibre diameter, not to coarse edge.