Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320110005&lang=en vol. 107 num. 9-10 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>The decline of the humanities and social sciences in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500001&lng=en&nrm=iso&tlng=en <![CDATA[<b>How effective and safe is <i>Bt</i>-maize in South Africa?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500002&lng=en&nrm=iso&tlng=en <![CDATA[<b>Challenges of reducing emissions from deforestation and forest degradation (REDD+) on the African continent</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500003&lng=en&nrm=iso&tlng=en <![CDATA[<b>Juggling the demands of a career and motherhood</b>: <b>Perspectives of an academic in science</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500004&lng=en&nrm=iso&tlng=en <![CDATA[<b>Johann Lutjeharms</b>: <b>Oceanographer (1944-2011)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500005&lng=en&nrm=iso&tlng=en <![CDATA[<b>Deserts as laboratories of evolution</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500006&lng=en&nrm=iso&tlng=en <![CDATA[<b>African medicinal flora in the limelight</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500007&lng=en&nrm=iso&tlng=en <![CDATA[<b>Increased structure and active learning</b>: <b>can we bridge the achievement gap in South African science?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500008&lng=en&nrm=iso&tlng=en <![CDATA[<b>Internet access constrains science development and training at South African universities</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500009&lng=en&nrm=iso&tlng=en <![CDATA[<b>A fossilised humerus of a lovebird tells little of the Pleistocene habitat of <i>Australopithecus robustus</i></b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500010&lng=en&nrm=iso&tlng=en <![CDATA[<b>Past approaches and future challenges to the management of fire and invasive alien plants in the new Garden Route National Park</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500011&lng=en&nrm=iso&tlng=en The recently established Garden Route National Park (GRNP) along the Cape south coast of South Africa occurs in a landscape where indigenous forests, fire-prone fynbos shrublands and fire-sensitive plantations of alien invasive trees are interspersed. We used the area as a case study in the challenges facing conservation managers in the achievement of biodiversity goals in a fire-prone environment. We explored the context within which fire management was practised during the past century by interviewing former catchment managers and reviewing forestry and catchment management policies. Mountain fynbos adjacent to plantations was subjected to burning regimes aimed at the protection of commercial timber resources rather than the preservation of fynbos biodiversity. Prescribed burning of fynbos adjacent to the plantations was typically done in multiple belt systems at rotations of about 4-8 years during spring, summer and autumn, to avoid the winter berg wind season. Such short-rotation and low-intensity fires favour resprouting graminoids over slow-maturing reseeders, and likely account for the compositional impoverishment observed in fynbos near plantations. Current and future challenges faced by the GRNP include (1) balancing conflicting fire management requirements for plantation safety against fynbos conservation; (2) the continual invasion of fynbos by fire-propagated alien pines sourced from plantations; (3) inadequate resources to redress the 'invasion debt' caused by the socio-economic legacy and past management neglect; and (4) fragmentation of land use between conservation and forestry threatening the sustainability of the region at large. We provide recommendations for management actions and research priorities to address these challenges. <![CDATA[<b>Ensuring the security and privacy of information in mobile health-care communication systems</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500012&lng=en&nrm=iso&tlng=en The sensitivity of health-care information and its accessibility via the Internet and mobile technology systems is a cause for concern in these modern times. The privacy, integrity and confidentiality of a patient's data are key factors to be considered in the transmission of medical information for use by authorised health-care personnel. Mobile communication has enabled medical consultancy, treatment, drug administration and the provision of laboratory results to take place outside the hospital. With the implementation of electronic patient records and the Internet and Intranets, medical information sharing amongst relevant health-care providers was made possible. But the vital issue in this method of information sharing is security: the patient's privacy, as well as the confidentiality and integrity of the health-care information system, should not be compromised. We examine various ways of ensuring the security and privacy of a patient's electronic medical information in order to ensure the integrity and confidentiality of the information. <![CDATA[<b>Screening South African potato, tomato and wheat cultivars for five carotenoids</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500013&lng=en&nrm=iso&tlng=en In South Africa malnutrition is of great concern. Vitamin A deficiency is one of the leading causes of infections as a result of micronutrient malnutrition. Although supplementation and food fortification programmes exist, these either are not available or are unaffordable to communities in remote rural areas. The selection of crops that are naturally rich in provitamin A (β-carotene) and other carotenoids that can be recommended to small-scale farmers for breeding and for food production, could be an effective way to address vitamin A deficiencies and associated diseases. The aim of this study was to profile two cultivars each of potato, tomato, bread wheat and durum wheat, which are highly consumed crops in South Africa, for their carotenoid content using high-performance liquid chromatography. To this effect, reliable extraction and quantification of five carotenoids - lutein, zeaxanthin, canthaxanthin, β-carotene and lycopene - were performed for these crops. Lutein and zeaxanthin were found to be the major carotenoids in potato, whilst lycopene was the major carotenoid in tomato. In durum wheat, only lutein and zeaxanthin were identified whilst bread wheat contained lutein, zeaxanthin and β-carotene. The methodology used proved to be robust and suitable to screen a large number of potato, tomato and wheat cultivars for their carotenoid content. <![CDATA[<b>Solar flares detected by the new narrowband VLF receiver at SANAE IV</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500014&lng=en&nrm=iso&tlng=en A narrowband receiver was installed at the SANAE IV base in Antarctica to monitor specific very low frequency (VLF) radio signals from transmitters around the world. VLF waves propagating through the Earth-Ionosphere Waveguide are excellent probes of the varying properties of the lower region of the ionosphere. This paper describes the set-up of the narrowband system and demonstrates its capabilities with data from a set of solar flares on 08 February and 12 February 2010. <![CDATA[<b>Effects of non-thermal mobile phone radiation on breast adenocarcinoma cells</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500015&lng=en&nrm=iso&tlng=en Mobile phone usage currently exceeds landline communication in Africa. The extent of this usage has raised concerns about the long-term health effects of the ongoing use of mobile phones. To assess the physiological effects of radiation from mobile phones in vitro, MCF-7 breast adenocarcinoma cells were exposed to 2W/kg non-thermal 900-MHz mobile phone radiation. The effects investigated were those on metabolic activity, cell morphology, cell cycle progression, phosphatidylserine (PS) externalisation and the generation of reactive oxygen species and nitrogen species. Statistically insignificant increases in mitochondrial dehydrogenase activity were observed in irradiated cells when compared to controls. Fluorescent detection of F-actin demonstrated an increase in F-actin stress fibre formation in irradiated MCF-7 cells. Cell cycle progression revealed no statistically significant variation. A small increase in early and late apoptotic events in irradiated MCF-7 cells was observed. No statistically significant changes were observed in reactive oxygen and reactive nitrogen species generation. In addition, quantitative and qualitative analyses of cell cycle activity and nuclear and cytosolic changes, respectively, revealed no significant changes. In conclusion, exposure to 1 h of 900-MHz irradiation induced an increase in PS externalisation and an increase in the formation of F-actin stress fibres in MCF-7 cells. Data obtained from this study, and their correlation with other studies, provides intriguing links between radio frequency radiation and cellular events and warrant further investigation. <![CDATA[<b>Understanding pathogen transmission dynamics in waterbird communities</b>: <b>at what scale should interactions be studied?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500016&lng=en&nrm=iso&tlng=en Pathogen transmission in animal populations is contingent on interactions between and within species. Often standard ornithological data (e.g. total counts at a wetland) are the only data available for assessing the risks of avian pathogen transmission. In this paper we ask whether these data can be used to infer fine-scale transmission patterns. We tested for non-randomness in waterbird assemblages and explored waterbird interactions using social network analysis. Certain network parameter values were then compared to a data set on avian influenza prevalence in southern Africa. Our results showed that species associations were strongly non-random, implying that most standard ornithological data sets would not provide adequate information on which to base models of pathogen spread. In both aquatic and terrestrial networks, all species regularly associated closely with other network members. The spread of pathogens through the community could thus be rapid. Network analysis together with detailed, fine-scale observations offers a promising avenue for further research and management-oriented applications. <![CDATA[<b>Accurate measurement of microscopic forces and torques using optical tweezers</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500017&lng=en&nrm=iso&tlng=en It is now well known that matter may be trapped by optical fields with high intensity gradients. Once trapped, it is then possible to manipulate microscopic particles using such optical fields, in so-called optical tweezers. Such optical trapping and tweezing systems have found widespread application across diverse fields in science, from applied biology to fundamental physics. In this article we outline the design and construction of an optical trapping and tweezing system, and show how the resulting interaction of the laser light with microscopic particles may be understood in terms of the transfer of linear and angular momentum of light. We demonstrate experimentally the use of our optical tweezing configuration for the measurement of microscopic forces and torques. In particular, we make use of digital holography to create so-called vortex laser beams, capable of transferring orbital angular momentum to particles. The use of such novel laser beams in an optical trapping and tweezing set-up allows for the control of biological species at the single-cell level. <![CDATA[<b>Caricain</b>: <b>a basis for enzyme therapy for coeliac disease</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500018&lng=en&nrm=iso&tlng=en It is now well known that matter may be trapped by optical fields with high intensity gradients. Once trapped, it is then possible to manipulate microscopic particles using such optical fields, in so-called optical tweezers. Such optical trapping and tweezing systems have found widespread application across diverse fields in science, from applied biology to fundamental physics. In this article we outline the design and construction of an optical trapping and tweezing system, and show how the resulting interaction of the laser light with microscopic particles may be understood in terms of the transfer of linear and angular momentum of light. We demonstrate experimentally the use of our optical tweezing configuration for the measurement of microscopic forces and torques. In particular, we make use of digital holography to create so-called vortex laser beams, capable of transferring orbital angular momentum to particles. The use of such novel laser beams in an optical trapping and tweezing set-up allows for the control of biological species at the single-cell level. <![CDATA[<b>Effects of internal heat generation, thermal radiation and buoyancy force on a boundary layer over a vertical plate with a convective surface boundary condition</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000500019&lng=en&nrm=iso&tlng=en In this paper we analyse the effects of internal heat generation, thermal radiation and buoyancy force on the laminar boundary layer about a vertical plate in a uniform stream of fluid under a convective surface boundary condition. In the analysis, we assumed that the left surface of the plate is in contact with a hot fluid whilst a stream of cold fluid flows steadily over the right surface; the heat source decays exponentially outwards from the surface of the plate. The similarity variable method was applied to the steady state governing non-linear partial differential equations, which were transformed into a set of coupled non-linear ordinary differential equations and were solved numerically by applying a shooting iteration technique together with a sixth-order Runge-Kutta integration scheme for better accuracy. The effects of the Prandtl number, the local Biot number, the internal heat generation parameter, thermal radiation and the local Grashof number on the velocity and temperature profiles are illustrated and interpreted in physical terms. A comparison with previously published results on similar special cases showed excellent agreement.