Scielo RSS http://www.scielo.org.za/rss.php?pid=0038-235320110001&lang=en vol. 107 num. 1-2 lang. en http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100001&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100002&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100003&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100004&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100005&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100006&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100007&lng=en&nrm=iso&tlng=en Scientific reports, articles, strategies and plans in South Africa (and elsewhere) are often written in unnecessarily confusing, complex and obscure language. While this is often unintended, it can be used by some to assert authority and discourage inquiry or dissent. Specialist styles of writing and jargon used by business, management or socio-economic development professionals are often copied or echoed in other contexts where their meaning is less clear. Although there is some very clear scientific writing in South Africa, confusing and obscure writing is common and may even be a growing problem. This style of writing may act as a barrier to entry for speakers of English as a second language (the majority of South Africans), who must devote extra time to mastering the medium rather than the content of science writing. The problem is even found in some school textbooks aimed specifically at speakers of English as a second language. The various uses of poor language in science in South Africa have unwanted and potentially serious implications, including supporting unwanted power and institutional hierarchies, alienating the general public, confusing decision-makers, hampering efforts towards transformation, discouraging debate, and diverting time and energy away from scientific work and cooperation. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100008&lng=en&nrm=iso&tlng=en Nickel oxide (NiO) is a versatile wide band gap semiconductor material. At present, transparent conducting oxide films find application as transparent electrodes and window coatings for opto-electronic devices but most are n-type. However p-type conducting films, of which NiO is one, are required as optical windows for devices where minority carrier injection is required. In this study, nickel (Ni) was resistively deposited on glass substrates and oxidised (isochronally) in oxygen at temperatures ranging from 300 ºC to 600 ºC. The oxidised Ni layers were subsequently characterised using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible photospectrometry in the range 200 nm - 1000 nm. The four point probe method (van der Pauw geometry) was used to determine the sheet resistances of the oxidised films. SEM results of the surface revealed a strong dependence of the surface texture and particle size on the oxidation temperature and time. XRD performed on the oxidised Ni indicated progressive transformation from nanograined polycrystalline Ni to NiO at elevated temperatures. Film thicknesses, particle sizes, energy band gap and wavelength-dependent refractive indices were determined from transmission and absorbance data. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100009&lng=en&nrm=iso&tlng=en The National Curriculum Statement for matric physical science places strong emphasis on the development of critical thinking and reasoning abilities of pupils. The successful implementation of this curriculum therefore requires teachers who are competent in the cognitive (intellectual) skills and strategies needed for learning science effectively. Testing of teachers' competence in this aspect is therefore important. I therefore analysed teachers' answers to questions that were carefully designed to test competence in some basic intellectual strategies that are important for problem solving in physical science courses. A total of 73 matric physical science teachers, from about 50 Dinaledi schools in the North West and KwaZulu-Natal provinces in South Africa, were tested in five intellectual strategies: clear representation of problems, identifying and focusing on the goal, identification and use of relevant principles, use of equations for deductions and proceeding step-by-step with the solution. The teachers' competence was poor in all the intellectual strategies tested. About 60% (the average performance in all 13 questions used for testing) of teachers tested were unable to solve the questions correctly. An important objective of the curriculum is the development of critical thinking, scientific reasoning and strategies of pupils. This study shows that the achievement of this objective will be seriously handicapped because of the lack of competence of many teachers in intellectual strategies. There is therefore a need to train teachers in order to increase their competence in this aspect. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100010&lng=en&nrm=iso&tlng=en The paper examines the change in volume of South African publications as indexed to the Web of Science over the periods 1990-1994 and 2004-2008. It was noted that publication volumes have increased sharply even while the stock of researchers has remained static. A number of factors may account for the rise including the increase in the Department of Education publication subsidy, the increase in the number of South African journals indexed to the Web of Science and a shift in focus to fields with higher publication propensity. For example, it was noted that a new growth area has emerged in the field of infectious diseases. The publication count by author institution showed that collaboration with foreign authors has increased considerably across the two periods and it is suggested that it is this factor that best accounts for the rise in volume. The concentration by subject area permitted some judgement to be made regarding the prospects for the five grand challenges of the Ten Year Innovation Plan. Lastly, it was noted that if it is collaboration that is driving the volume increase, the system is vulnerable to offshore changes. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100011&lng=en&nrm=iso&tlng=en Fusarium spp. produce fumonisins - mycotoxins that are of importance to maize production in South Africa. Fumonisins have been associated with human oesophageal cancer and cause various diseases in animals that are of concern to the animal feed industry. Maize samples, collected from subsistence farm fields in the Eastern Cape, KwaZulu-Natal, Limpopo and Mpumalanga provinces of South Africa during the 2006 and 2007 growing seasons, were analysed for Fusarium spp. and contamination with fumonisins. Fusariumverticillioides was the most common Fusarium species in maize followed by F. subglutinans and F. proliferatum. Levels of contamination with fumonisins ranged from 0 µg/g to 21.8 µg/g, depending on the region where samples were collected. Levels of fumonisins were highest in northern KwaZulu-Natal (Zululand) where 52% and 17% of samples collected in 2006 and 2007, respectively, exceeded 2 µg/g. Regression analyses showed a positive correlation between fumonisin-producing Fusarium spp. determined by real-time polymerase chain reaction and concentration of fumonisins (r = 0.93). Many samples from Zululand, and some from Mokopane (Limpopo) and Lusikisiki (Eastern Cape), contained fumonisins at levels well above the maximum levels of 2 µg/g set by the Food and Drug Administration (USA) and therefore also the limit of 1 µg/g set by the European Union for food intended for direct human consumption. Regulations governing contamination of grain with fumonisins are not yet implemented in South Africa. The high incidence of fumonisins in subsistence farming systems indicates the need for awareness programmes and further research. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100012&lng=en&nrm=iso&tlng=en Channel adaptive M-ary quadrature amplitude modulation (M-QAM) schemes have been developed to provide higher average link spectral efficiency by taking advantage of the time-varying nature of wireless fading channels. Much of the earlier work on such schemes uses the assumption that thresholds designed for additive white Gaussian noise (AWGN) channels can be directly applied to slowly varying block-fading channels. The thresholds are calculated with a commonly used approximation bit error rate (BER) expression in these schemes. The first aim of this paper was to investigate the accuracy of using this common BER expression in a fading channel. This was done by comparing the result of the average BER expression derived using the approximate expression with results of simulations over a Nakagami-m block-fading channel. The second aim was to show that the inaccuracy in the threshold values determined using the closed form approximation expression would lead to inappropriate operation of the adaptive M-QAM scheme in a fading channel. This was done by comparing expected theoretical values with the simulation results. Two alternative approximate BER expressions for M-QAM in AWGN were then presented and used to determine the average M-QAM of BER over a Nakagami-m fading channel. The comparison between the average BER expressions and the simulation showed a much closer match. More accurate thresholds for the adaptive M-QAM system were then determined using one of the two average BER expressions and the accuracy of these threshold points was then verified using simulation results. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100013&lng=en&nrm=iso&tlng=en There are four extant species of Gerbilliscus, formally classified as Tatera, native to the southern African subregion, each exhibiting varying degrees of environmental tolerance. These species are also routinely reported from many of the palaeontological and archaeological sites in the region. We used a geographic information systems analysis to examine the distribution of modern Gerbilliscus by georeferencing museum specimens. The distribution of Gerbilliscus was then compared to the latest treatment of the vegetation of South Africa, Lesotho and Swaziland in order to quantify the genus's environmental tolerances and propose a new niche model for this taxon. Palaeoenvironmental reconstructions are made possible by defining the tolerance limits of modern taxa that have persisted relatively unchanged throughout the Plio-Pleistocene. Tolerance limits can then be applied to fossil-bearing localities where these taxa are known to have occurred in the past. Results from our analysis indicated that Gerbilliscus exhibits a wide range of environmental tolerances that must be considered when reconstructing palaeoenvironments. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100014&lng=en&nrm=iso&tlng=en Diverse natural and anthropogenic activities in the Highveld of South Africa contribute to elevated levels of inorganic and organic gaseous pollutant species. The primary aims of this investigation were to determine spatial and temporal distributions of nitrogen dioxide (NO2), sulphur dioxide (SO2) and ozone (O3), as well as benzene, toluene, ethylbenzene and xylene (BTEX) in this area. Sampling was conducted on a monthly basis for a year at eight strategically selected sites. The highest NO2, SO2 and BTEX concentrations were measured at sites with significant local sources and/or sites impacted by more remote sources, as indicated by overlay back trajectories. O3 concentrations were found to be lower at sites with high levels of NO2, SO2 and BTEX. NO2 and SO2 peaked during winter, while O3 peaked in spring. NO2 and SO2 temporal concentration variations were ascribed to differences in seasonal meteorological conditions, as well as additional sources in winter. The O3 peak coincided with a seasonal CO peak, which was identified as an important precursor for O3 formation. No distinct seasonal trend was observed for BTEX. The annual average concentrations for SO2, NO2, O3 and benzene were below the South African annual standards at all sites. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100015&lng=en&nrm=iso&tlng=en The role of endothelin-1 (ET-1) and its receptors (ET-RA and ET-RB) in tumour development and progression involves complex interactions. ET-1, produced by tumours and associated cells like endothelial cells, functions in an autocrine and paracrine manner to promote tumour angiogenesis. Thus, we hypothesised that endothelin, released into the tumour milieu by both tumours and the tumour vasculature, would influence angiogenesis. Therefore, this preliminary study aimed to investigate changes in ET1, ET-RA and ET-RB in breast tumour and microvascular endothelial cultures when each cell type was exposed directly to the other (co-culture model) as well as to the conditioned-medium metabolites of the other (challenge model). ET-1 secretion was measured by an enzyme-linked immunosorbent assay and ET-1, ET-RA and ET-RB expression investigated by the linked streptavidin-biotin method. In challenge experiments, endothelial metabolites significantly increased secretion of breast tumour ET-1. Tumour metabolites promoted endothelial membrane projections with no effect on ET-1 secretion. ET-1 and its receptors were immunolocalised in both cell types, including in projections. Increasing cancer cell conditioned medium resulted in decreased endothelial ET-RA and increased ET-RB staining. Co-cultures demonstrated ET proteins in projections of both cell types as well as at heterogeneous contact points. The findings support a role for the endothelin system in endothelial cell and breast cancer cell invasion. It is tempting to consider that early endothelial and tumour cell alterations may be promoted by ET-1 produced by both cell types. Further work is required that will examine localised cellular gene expression of the endothelin system as well as its pro-invasive and angiogenic effects in breast cancer models. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100016&lng=en&nrm=iso&tlng=en Simple cosmic ray diffusion in magnetic fields is often discussed in terms of a characteristic scattering mean free path or equivalent diffusion coefficient. This assumes very simple properties of the structure of astrophysical magnetic fields. A better approximation is to assume that the magnetic structure has fractal properties and there is then the possibility of including very short and very long interaction lengths when modelling the propagation. Results of modelling such propagation in a fractal medium are discussed. Values of the propagation parameter (α) less than 2 were obtained and confirm the plausibility of the hypothesis that supernova are the origin of galactic cosmic rays in the energy range below the knee in the spectrum. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000100017&lng=en&nrm=iso&tlng=en Abundant vertebrate fossils have been recorded from the Early Pliocene locality, Langebaanweg, South Africa. This study documents the pathologies evident in the 5 million-year-old fossil phocid seal assemblage. Careful anatomical assessment of the remains revealed that 0.73% showed evidence of disease and/or trauma. The majority of the ailments were forms of osteoarthritis, although periodontitis and osteomyelitis were also evident. Some bones also showed healed fractures, suggesting that the individuals survived the traumatic event. Two cases of dental pathologies were also noted.