Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320100002&lang=en vol. 106 num. 3-4 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<B>The National Research Foundation scores an own goal for South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200001&lng=en&nrm=iso&tlng=en <![CDATA[<B>Assessing the hunting practices of Namibia's commercial seal hunt</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200002&lng=en&nrm=iso&tlng=en <![CDATA[<B>The colonial legacy in African plant taxonomy</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200003&lng=en&nrm=iso&tlng=en <![CDATA[<B>International astronomer Phil Charles meets the ire of the National Research Foundation</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200004&lng=en&nrm=iso&tlng=en <![CDATA[<B>New hominin fossils from Malapa</B>: <B>the unveiling of <I>Australopithecus sediba</B></I>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200005&lng=en&nrm=iso&tlng=en <![CDATA[<B>The importance of the greater Agulhas Current is increasingly being recognised</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200006&lng=en&nrm=iso&tlng=en <![CDATA[<B>Sheep, soil and stability</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200007&lng=en&nrm=iso&tlng=en <![CDATA[<B>The intimate politics of the Cape Floral Kingdom</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200008&lng=en&nrm=iso&tlng=en <![CDATA[<B>A review of scientific linkages and interactions between climate change and air quality, with implications for air quality management in South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200009&lng=en&nrm=iso&tlng=en In recent years there has been considerable advancement in our scientific understanding of the linkages and interactions between climate change and air quality. A warmer, evolving climate is likely to have severe consequences for air quality due to impacts on pollution sources and meteorology. Climate-induced changes to sources of tropospheric ozone precursor gases and to atmospheric circulation are likely to lead to changes in both the concentration and dispersion of near-surface ozone that could act to offset improvements in air quality. The control of air pollutants through air quality management is also likely to impact on climate change, with reductions in ozone, particulate matter and sulphur dioxide being of particular interest. The improved understanding of the relationship between air quality and climate change provides a scientific basis for policy interventions. After a review of the scientific linkages, the potential to include climate change considerations in air quality management planning processes in South Africa was examined. <![CDATA[<B>Khat (<I>Catha edulis</I>)</B>: <B>the herb with officio-legal, socio-cultural and economic uncertainty</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200010&lng=en&nrm=iso&tlng=en Khat (Catha edulis) is a plant of uncertain and highly controversial status grown in the countries around the Red Sea and on the eastern coast of Africa. The chewing of khat leaves has a deep-rooted religious and socio-cultural tradition. Khat is considered a cash crop and its cultivation is a source of economic value to the societies and nations involved. There have, however, been reports of negative economic effects on the individuals engaging in the habit of khat chewing. The increasing use of khat worldwide, along with the negative international attention that this has garnered, has led to the present status of uncertainty of the once indigenous practice of khat chewing. Scientists, mostly western Europeans, have tended to focus on problems related to khat with little attention to the positive role of khat chewing in society and the world at large. In addition, no report has directly associated khat with any organised crime, violence or antisocial activity, particularly in countries where khat is legalised. This paper reviewed the various areas of uncertainty and controversy relating to khat. Based on the findings of the review, further qualitative and quantitative research is required and a positive international approach to khat use at economic, religious and socio-cultural levels is advocated. <![CDATA[<B>Channel and delay estimation for base-station-based cooperative communications in frequency flat-fading channels</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200011&lng=en&nrm=iso&tlng=en Base-station-based cooperative communication is an asynchronous cooperative communication system. The challenge therein is to estimate the relative delay between the transmitters in the system. A channel and delay estimation algorithm based on the distributed Alamouti scheme has been previously discussed for the asynchronous cooperative system. The algorithm only makes accommodation for positive delay, that is, when data from Transmitter one always arrives at the receiver before data from Transmitter two. In reality, the data from Transmitter one does not always arrive at the receiver before data from Transmitter two in the asynchronous cooperative system, because of the constantly changing mobile environment in the system. This paper extends the algorithm to accommodate both positive and negative delays, which is when the data from Transmitter one arrives at the receiver before or after data from Transmitter two, in a Rayleigh block flat-fading channel. Simulation results show that the Cramér-Rao lower bound for channel and delay estimation is achieved for different delay values. The symbol error rate performance is also achievable compared to the channel and the delay is known at the receiver. <![CDATA[<B>Determining the relationship between invasive alien species density and a country's socio-economic status</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200012&lng=en&nrm=iso&tlng=en We explored the relationships between various socio-economic variables and the prevalence and density of invasive alien species (IAS) on a global scale using country-level data sets. We did this by testing the hypothesis that the abundance and distribution of populations of IAS are correlated with various socio-economic indicators, with the direction of causality being that the state of IAS is determined by socio-economic conditions. We found a positive and statistically significant relationship between the prevalence and density of IAS and the human development index (HDI), the satisfaction with life index and the gross domestic product (GDP) among all the countries tested. Additionally, the density of IAS increased significantly with human-population density, total geographic area, GDP and HDI. We also found a positive relationship between the density of IAS and the top 10 road networks of the world. This provides some insight into the development of renewed policies and management strategies for invasive species across both continents and countries. We do caution, however, that the results are likely to be influenced by the sampling factor, whereby affluent countries have more resources to measure and monitor IAS than poorer countries and hence have better records of such, which then indicates a stronger relationship with the level of development. <![CDATA[<B>Characterisation of South African isolates of <I>Fusarium oxysporum</I> f.sp. <I>cubense</I> from Cavendish bananas</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200013&lng=en&nrm=iso&tlng=en Fusarium wilt, caused bythe soil-borne fungusFusarium oxysporum f.sp. cubense (Foc), is a serious vascular disease of bananas in most subtropical and tropical regions of the world. Twenty-four vegetative compatibility groups (VCGs) and three pathogenic races have been identified in Foc, reflecting a relatively high genetic diversity for an asexual fungus. To characterise a South African population of Foc, a collection of 128 isolates from diverse geographic origins were isolated from diseased Cavendish bananas and subjected to VCG analysis and sequencing of the translation elongation factor 1-α (TEF) gene region. The presence of mating type genes was also determined using MAT-1 and MAT-2 specific primers. VCG 0120 was established as the only VCG of Foc present in the South African population studied. Only the MAT-2 idiomorph was present in all the local isolates of Foc. A phylogenetic analysis of DNA sequences of the TEF gene region revealed that the South African isolates grouped closely with VCG 0120 isolates from Australia and Asia. These results suggest that the South African population of Foc was most likely introduced in a limited number of events and that it had spread with infected planting material within the country. The presence of only one mating type and the limited diversity in this pathogen render it unlikely to rapidly overcome disease management strategies involving host resistance. <![CDATA[<B>No 'free ride' for African women</B>: <B>a comparison of head-loading versus back-loading among Xhosa women</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200014&lng=en&nrm=iso&tlng=en Although contrasting evidence exists in the literature as to the economy of head-loading, there is a notion that head-loading is an extremely economical method of load carriage. This has become known as the 'free ride' hypothesis and, although untested, it is widely accepted. The purpose of this study was to test the 'free ride' hypothesis for head-load carriage among African women by comparing the relative economy of head-loading and back-loading. Twenty-four Xhosa women walked on a level treadmill, attempting to carry loads of between 10% and 70% of their body mass (BM) using both a backpack and a head basket. All 24 women carried at least 25% of their BM in both conditions. The relative economy of load carriage was calculated for loads of 10% to 25% of BM. Results indicated that the 'free ride' was not a generalisable phenomenon, with both methods realising economy scores close to unity (1.04 ± 0.19 and 0.97 ± 0.15 for head-loading and back-loading, respectively). The results did, however, reveal significant individual differences in economy scores and it is suggested that analysis of such individual differences in future may well be instructive in understanding mechanisms associated with greater economy in load carriage. <![CDATA[<B>Salinity and temperature tolerance of the invasive freshwater gastropod <I>Tarebia granifera</B></I>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200015&lng=en&nrm=iso&tlng=en Invasive aquatic species, such as the gastropod Tarebia granifera, can cause ecological disturbances and potentially reduce biodiversity by displacing indigenous invertebrates. In South Africa, T. granifera was first recorded in an estuarine environment in the St Lucia Estuary. Its tolerance to salinity and temperature was investigated through the experimental manipulation of these factors. T. granifera can tolerate temperatures between 0 ºC and 47.5 ºC, allowing it to survive high temperature extremes. The species may also survive cold snaps and invade higher altitude areas. More remarkably, this snail survives high salinity for a relatively long time, as LS50 (lethal salinity for 50% of the population) was reached at 30 psu over 65-75 days. However, higher salinity adversely affected the T. granifera population. Snails acclimated to freshwater conditions and suddenly transferred to 30 psu experienced 100% mortality within 48 h. Snail activity also declined with increasing salinity. T. granifera's environmental tolerance and parthenogenetic characteristics are the keys to successful introduction and establishment. Therefore, the management of T. granifera may prove difficult in the short to medium term. The present findings constitute a contribution to the knowledge of biological invasions in Africa and to the understanding of estuarine invasions by T. granifera. <![CDATA[<B>The production and use of citric acid for the removal of potassium from the iron ore concentrate of the Sishen Iron Ore Mine, South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200016&lng=en&nrm=iso&tlng=en The depletion of the richer iron ore worldwide has made it necessary to process lower quality iron ore. Certain substances, such as potassium, contained within the lower quality iron ore, have a detrimental effect on the smelting process during steel manufacturing. Therefore, international steel-making companies charge penalties when purchasing iron ore concentrates containing high concentrations of potassium. To date, lower quality iron ore has been blended with high quality iron ore in an attempt to alleviate the potassium concentrations in the export iron ore; however, the ratio of low quality iron ore to high quality iron ore is increasing, thereby becoming an escalating problem within the economic functioning of the Sishen Iron Ore Mine. It has, therefore, become necessary to develop an economically viable and environmentally friendly process to reduce the high potassium concentrations contained in the iron ore concentrate of the Sishen Iron Ore Mine. In this study, we compared solid substrate and submerged fermentation using Aspergillus niger for the production of citric acid, which is used for the chemical leaching of potassium from the iron ore concentrate. It was found that submerged fermentation proved to be more economical and efficient, producing a maximum citric acid concentration of 102.3 g/L in 96 h of fermentation. 'Heap leaching' simulation experiments were found to be uneconomical, due to the required addition of fungal growth medium every 5 days as a result of growth factor depletion within this time; however, this process removed 17.65% of the potassium from the iron ore concentrate. By contrast, chemical leaching of potassium from the iron ore concentrate proved to be most efficient when using a 1 mol citric acid leaching solution at 60 ºC, removing 23.53% of the potassium contained within the iron ore concentrate. Therefore, the most economical and efficient process for the removal of potassium from the iron ore concentrate of the Sishen Iron Ore Mine involved a two-stage process whereby citric acid was produced by A. niger, followed by the chemical leaching of the potassium from the iron ore concentrate using a 1 mol citric acid leaching solution at 60 ºC. <![CDATA[<B>A South African research agenda to investigate the potential environmental, health and safety risks of nanotechnology</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200017&lng=en&nrm=iso&tlng=en The South African perspective on nanotechnology, recently articulated through its national strategy, envisages nanotechnology to provide solutions to some of the country's key development challenges, such as the provision of safe water and the innovative delivery of health services. The adoption of nanotechnology is therefore being encouraged and nanomaterials are being manufactured on a small scale for research and development purposes. The national strategy places the most emphasis on supporting the design, manufacture, synthesis and characterisation of nanomaterials and developing human capital and infrastructure. However, South Africa has yet to develop a national research strategy to investigate the environmental, health and safety risks of nanotechnology. This paper provides a brief overview of the risk-related research challenges that have been reported internationally. These challenges form the basis of a research framework and a prioritised agenda is proposed to take research forward in the South African context. Ultimately, a greater understanding of the environmental, health and safety risks will help to ensure the long-term sustainability of nanotechnologies. <![CDATA[<B>Academic freedom statement from the Academy Of Science Of South Africa (Assaf)</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000200018&lng=en&nrm=iso&tlng=en The South African perspective on nanotechnology, recently articulated through its national strategy, envisages nanotechnology to provide solutions to some of the country's key development challenges, such as the provision of safe water and the innovative delivery of health services. The adoption of nanotechnology is therefore being encouraged and nanomaterials are being manufactured on a small scale for research and development purposes. The national strategy places the most emphasis on supporting the design, manufacture, synthesis and characterisation of nanomaterials and developing human capital and infrastructure. However, South Africa has yet to develop a national research strategy to investigate the environmental, health and safety risks of nanotechnology. This paper provides a brief overview of the risk-related research challenges that have been reported internationally. These challenges form the basis of a research framework and a prioritised agenda is proposed to take research forward in the South African context. Ultimately, a greater understanding of the environmental, health and safety risks will help to ensure the long-term sustainability of nanotechnologies.