Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320120002&lang=en vol. 108 num. 3-4 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Research chairs initiative fails to increase doctoral student numbers</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200001&lng=en&nrm=iso&tlng=en <![CDATA[<b>Funding drought hits experimentally based South African researchers and their graduate students</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200002&lng=en&nrm=iso&tlng=en <![CDATA[<b>Investigation of a credible report by a US Marine on the location of the missing Peking Man fossils</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200003&lng=en&nrm=iso&tlng=en <![CDATA[<b>National Senior Certificate results belie conceptual and skill limitations of school-leavers</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200004&lng=en&nrm=iso&tlng=en <![CDATA[<b>Southern Ocean Seasonal Cycle Experiment 2012</b>: <b>seasonal scale climate and carbon cycle links</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200005&lng=en&nrm=iso&tlng=en <![CDATA[<b>Friedrich Paul Cilliers</b>: <b>philosopher (1956-2011)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200006&lng=en&nrm=iso&tlng=en <![CDATA[<b>Solved problems in classical mechanics</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200007&lng=en&nrm=iso&tlng=en <![CDATA[<b>Is the master's degree being neglected in the discourse on postgraduate education?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200008&lng=en&nrm=iso&tlng=en http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200009&lng=en&nrm=iso&tlng=en <![CDATA[<b>Global geopotential models from Satellite Laser Ranging data with geophysical applications</b>: <b>a review</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200010&lng=en&nrm=iso&tlng=en The launch of artificial satellites (as early as in 1957), specifically the launch of the first laser tracked satellite, Beacon-B, in 1964, has provided data sets which have allowed researchers to probe the long to medium components of the gravitational field of the Earth. In particular, observational data recorded at satellite laser ranging tracking stations have since been used to develop models that quantify the global long-wavelength and medium-wavelength gravity field of the Earth. Currently, literature reviewing gravity field models with geophysical applications is scarce and not up to date. The most recent review paper was published more than a decade ago. In the interim, there has been an unprecedented increase in gravity field modelling, which can be attributed to the deployment of new and dedicated satellite missions. As a result, a number of existing geopotential models have been improved and new models have been developed. Each of these models differs in accuracy and spatial-temporal scale. This review extends the earlier review of gravity field models, by incorporating up-to-date research efforts in geopotential modelling with geophysical applications in oceanography, hydrology, geodesy and solid Earth science. <![CDATA[<b>Factors influencing the crystallisation of highly concentrated water-in-oil emulsions</b>: <b>A DSC study</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200011&lng=en&nrm=iso&tlng=en Highly concentrated emulsions are used in a variety of applications, including the cosmetics, food and liquid explosives industries. The stability of these highly concentrated water-in-oil emulsions was studied by differential scanning calorimetry. Crystallisation of the emulsions was initiated by exposing the emulsions to a low temperature. The effects of surfactant type, electrolyte concentration and electrolyte composition in the aqueous phase on emulsion crystallisation temperature were studied. Surfactant type affected the emulsion crystallisation temperature in the following order: PIBSA-MEA=PIBSA-UREA<PIBSA-MEA/SMO<PIBSA-IMIDE<SMO. These results are in the same sequence as results obtained for the stability of these emulsions in aging studies, that is, PIBSA-MEA was the most stable with age and SMO was the least. The effect of the surfactant type on emulsion crystallisation can probably be attributed to the differing strengths of the surfactant-electrolyte interactions, which result in different molecular packing geometry and differing mobility of the surfactant lipophilic portion at the interface. These results enhance our understanding of the factors that affect the stability of explosive emulsions. <![CDATA[<b>New hominin fossils from Kanapoi, Kenya, and the mosaic evolution of canine teeth in early hominins</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200012&lng=en&nrm=iso&tlng=en Whilst reduced size, altered shape and diminished sexual dimorphism of the canine-premolar complex are diagnostic features of the hominin clade, little is known about the rate and timing of changes in canine size and shape in early hominins. The earliest Australopithecus, Australopithecus anamensis, had canine crowns similar in size to those of its descendant Australopithecus afarensis, but a single large root alveolus has suggested that this species may have had larger and more dimorphic canines than previously recognised. Here we present three new associated dentitions attributed to A. anamensis, recently recovered from the type site of Kanapoi, Kenya, that provide evidence of canine evolution in early Australopithecus. These fossils include the largest mandibular canine root in the hominin fossil record. We demonstrate that, although canine crown height did not differ between these species, A. anamensis had larger and more dimorphic roots, more like those of extant great apes and Ardipithecus ramidus, than those of A. afarensis. The canine and premolar occlusal shapes of A. anamensis also resemble those of Ar. ramidus, and are intermediary between extant great apes and A. afarensis. A. afarensis achieved Homo-like maxillary crown basal proportions without a reduction in crown height. Thus, canine crown size and dimorphism remained stable during the early evolution of Australopithecus, but mandibular root dimensions changed only later within the A. anamensis-afarensis lineage, coincident with morphological changes in the canine-premolar complex. These observations suggest that selection on canine tooth crown height, shape and root dimensions was not coupled in early hominin evolution, and was not part of an integrated adaptive package. <![CDATA[<b>The lightning climatology of South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200013&lng=en&nrm=iso&tlng=en In 2005, the South African Weather Service installed a state-of-the-art cloud-to-ground lightning detection network across the country. The data recorded by this network in 2006 was utilised in the development of an initial lightning climatology of South Africa. Until 2010, this climatology was based on data from a single year. This paper updates this climatology with the lightning data for the 2006-2010 period, which is the first actual lightning climatology by the South African Weather Service based on data covering 5 years. A number of different maps were created from these lightning data. These were lightning ground flash density, median peak kiloampere, percentage positive and average flash multiplicity maps. These four maps were in turn used to develop lightning intensity risk, positive lightning risk and total lightning risk maps. Analysis of the maps showed that the highest concentrations of lightning are found over the central to northern interior of the country, with areas along the northern parts of the eastern escarpment experiencing the highest flash densities and falling within the extreme risk category. Both the positive and total lightning risks are severe for almost the entire country. Only towards the west of the country does the lightning risk decrease. This lightning climatology can now be used throughout South Africa for various disciplines. It will be especially useful for setting lightning safety standards and identifying priority areas for installing lightning conductors and conducting public awareness campaigns. <![CDATA[<b>Detection and molecular identification protocols for <i>Phyllosticta citricarpa</i> from citrus matter</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200014&lng=en&nrm=iso&tlng=en Strict quarantine measures for the export of South African citrus fruit to European and US markets require the development of sensitive and accurate detection methods for the pathogen Phyllosticta citricarpa - a fungus causing citrus black spot disease. Because of the presence of other, non-pathogenic Phyllosticta species, rapid and accurate verification of the Phyllosticta species present on exported citrus fruit is important to producers, exporters and regulatory authorities to prevent unnecessary losses. We have analysed over 800 samples collected over 7 years and have compared sample preparation and detection protocols applied in different environments: nurseries, production systems including phytosanitary inspections in orchards, pack houses and export terminals in order to compile protocols for the detection of P. citricarpa. Standard procedures of sample preparation and DNA extraction were adapted to suit diverse inoculum sources. Low pathogen numbers in symptomless green leaves, for example, obliged the use of a wet-dry enrichment technique constituting the stimulation of fungal growth for easier detection. Physical maceration was adapted for sturdy material using liquid nitrogen or bead beating. The use of a two-step polymerase chain reaction (PCR) with nested primers significantly increased both the sensitivity and the specificity of the PCR performed on soil samples, overcoming problems with relatively impure DNA extracts and low pathogen numbers. The assays have proven to be highly consistent, thereby providing a reliable, reproducible and highly sensitive detection and diagnostic service to the southern African citrus industries in order to sustain market access. <![CDATA[<b>Leaving rates and reasons for leaving in an Engineering faculty in South Africa</b>: <b>A case study</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200015&lng=en&nrm=iso&tlng=en This paper describes a case study undertaken at the Faculty of Engineering of the University of KwaZulu-Natal to determine the leaving rates from the faculty both by a cohort analysis (over the existence of the university from 2005 to 2010) and by a 1-year population balance over the whole faculty in 2009. Students who had left the faculty who could have continued were identified from the population balance and interviewed to determine the common reasons for leaving. The cohort analysis showed that from 2005 through to 2008, the leaving rate from first-year cohorts was reduced year on year (from over 22% to below 14%). This reduction coincided with stabilisation of the faculty after a merger process and increased academic support. In 2009, however, an increase in the proportion of first-year students who left (to over 17%) was identified, which may be linked to the entry of students who had taken the new National Senior Certificate in South African high schools. The population balance over the year 2009 showed an academic exclusion rate of approximately 6% of the total undergraduate student body, and, more significantly, an academic leaving rate of about 14% of the total student body. The exclusion rate remained fairly static across three semesters whilst voluntary leavers increased over the same period. An analysis and interviews with a sample of the students who left showed that financial reasons played a significant role in these rates, with 49% of non-academically excluded students having financial difficulties, and that a significant proportion of students continue their studies at universities of technology. Although this is a case study within one institution, it is hoped that the findings can inform the current debate surrounding increasing throughput in Science and Engineering within the country. <![CDATA[<b>The evolution of cranial form in mid-Pleistocene <i>Homo</i></b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200016&lng=en&nrm=iso&tlng=en Interactions of the brain and cranium in archaic populations remain poorly understood. Hominin fossils from Middle Pleistocene localities in Africa and Europe have been allocated to one or more species distinct from Homo erectus, the Neanderthals and modern humans, based on the assumption that characters of the vault and face are developmentally independent. However, it is possible that increased frontal width, parietal lengthening, midvault expansion and occipital rounding all reflect encephalisation occurring within the H. erectus lineage. If specimens from Broken Hill and Elandsfontein (in southern Africa) and Sima de los Huesos and Petralona (in Europe) differ from H. erectus only in brain volume, then it will be difficult to distinguish and diagnose Homo rhodesiensis or Homo heidelbergensis adequately. In this study, correlation analysis showed that the brain fails to influence vault breadth within either H. erectus or the mid-Pleistocene sample. Instead, the (large) cranial base has a major effect on width. Variation in brain volume is not associated with frontal flattening. In H. erectus and in individuals such as Bodo and Petralona, the massive face seems to override the brain as a determinant of frontal curvature. Small H. erectus crania have rounded occipitals, whilst larger individuals show greater flexion. Later hominins do not follow this trend, and encephalisation cannot explain the occipital rounding that is present. Few of the vault characters considered diagnostic for the mid-Pleistocene fossils can be attributed to increasing brain volume. The situation is complex, as of course the brain must influence some traits indirectly. The cranial base is also an instrument of change. Discriminant analysis identified basicranial breadth as critical to distinguishing individuals such as Broken Hill, Sima de los Huesos and Petralona from H. erectus. <![CDATA[<b>Validation of remote sensing and weather model forecasts in the Agulhas ocean area to 57°S by ship observations</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200017&lng=en&nrm=iso&tlng=en The region south of South Africa, encompassing the Agulhas Current and Retroflection, and part of the Southern Ocean, is known for its severe meteorological conditions. Because of these conditions, in-situ observations are rare. Consequently, remote-sensing satellite observations and high-resolution regional weather forecasts at the ocean surface are difficult to assess. However, atmospheric data collected in the southern hemisphere summer of 2008 during the International Polar Year-BONUS-GoodHope campaign were used to validate two satellite data sets: the twice daily QuikSCAT winds and the daily OAflux data set of latent and sensible heat fluxes. The surface winds and heat fluxes forecasts produced by a regional atmospheric model were also assessed along the ship track. In this study, we have shown that the two data sets exhibited a very good accordance with daily in-situ observations. During the campaign, the correlation coefficients for wind speed and direction were 0.97 and 0.91, respectively, and those for latent and sensible heat fluxes were 0.92 and 0.90, respectively. The QuikSCAT wind speed was underestimated by 1.37 m/s relative to in-situ data, south of the Subtropical Front. Large differences in heat fluxes in both OAflux and the atmospheric model were observed when crossing the Subtropical Front and a warm eddy, as well as during a storm, when gale force winds reached more than 20 m/s. The two data sets were then used to assess the regional model forecasts over a larger area south of South Africa, not limited to the ship track. Most of the model errors were located in a region north of the Subtropical Front, where the sea surface temperature used by the model was not accurate enough to reproduce the relevant mesoscale oceanic features driving the spatial variability of the surface winds and heat fluxes. Finally, compared to in-situ and remote sensing observations, the numerical modelling weather forecast produced realistic atmospheric conditions over the sea south of the Subtropical Front. <![CDATA[<b>Educational outcomes</b>: <b>Pathways and performance in South African high schools</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200018&lng=en&nrm=iso&tlng=en We analysed the pathways and performances in mathematics of high (secondary) school students in South Africa using a panel-like data set of Grade 8 students who participated in the 2002 Trends in International Mathematics and Science Study (TIMSS) and who were tracked to Grade 12 examination data sets. We examined the relationship between TIMSS mathematics performance and reaching Grade 12, the selection of and performance in Grade 12 mathematics, and success rates in the matriculation examination. The progression of students from schools serving middle-class (Subsystem M) and poorer students (Subsystem P, the majority) was compared. Firstly, mathematics achievement scores in South Africa are low and different performance patterns were shown between the two subsystems. Secondly, students who started with similar Grade 8 mathematics scores had different educational outcomes 4 years later. In Subsystem M schools, Grade 8 mathematics scores were a good indicator of who would pass matric, whilst this relationship was not as strong in Subsystem P schools. Thirdly, there was a stronger association between TIMSS Grade 8 scores and subject choice of matric mathematics in Subsystem M schools than in Subsystem P schools. Fourthly, there was a strong correlation between Grade 8 mathematics performance and matric mathematics achievement. Mathematics performance in the earlier years predicted later mathematics performance. To raise exit level outcomes, mathematics scores need to be raised by Grade 8 or earlier. To improve educational and labour market outcomes, the policy priority should be to build foundational knowledge and skills in numeracy. <![CDATA[<b>A theoretical model for substance abuse in the presence of treatment</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200019&lng=en&nrm=iso&tlng=en The production and use of addictive stimulants has been a major problem in South Africa. Although research has shown increased demand for drug abuse treatment, the actual size of the drug-abusing population remains unknown. Thus the prevalence of drug abuse requires estimation through available tools. Many questions remain unanswered with regard to interventions, new cases of substance abuse and relapse in recovering persons. A six-state compartmental model including a core and non-core group, with fast and slow progression to addiction, was formulated with the aim of qualitatively investigating the dynamics of substance abuse and predicting drug abuse trends. The analysis of the model was presented in terms of the substance abuse epidemic threshold R0. Numerical simulations were performed to fit the model to available data for methamphetamine use in the Western Cape and to determine the role played by some key parameters. The model was also fitted to data on methamphetamine users who enter rehabilitation using the least squares curve fitting method. It was shown that the model exhibits a backward bifurcation where a stable drug-free equilibrium coexists with a stable drug-persistent equilibrium for a certain defined range of values of R0. The stabilities of the model equilibria were ascertained and persistence conditions established. It was found that it is not sufficient to reduce R0 below unit to control the substance abuse epidemic. The reproduction number should be brought below a determined threshold, R0c. The results also suggested that the substance abuse epidemic can be reduced by intervention programmes targeted at light drug users and by increasing the uptake rate into treatment for those addicted. Projected trends showed a steady decline in the prevalence of methamphetamine abuse until 2015. <![CDATA[<b>Characterising agrometeorological climate risks and uncertainties</b>: <b>Crop production in Uganda</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200020&lng=en&nrm=iso&tlng=en Uganda is vulnerable to climate change as most of its agriculture is rain-fed; agriculture is also the backbone of the economy, and the livelihoods of many people depend upon it. Variability in rainfall may be reflected in the productivity of agricultural systems and pronounced variability may result in adverse impacts on productivity. It is therefore imperative to generate agronomically relevant seasonal rainfall and temperature characteristics to guide decision-making. In this study, historical data sets of daily rainfall and temperature were analysed to generate seasonal characteristics based on monthly and annual timescales. The results show that variability in rainfall onset dates across Uganda is greater than the variability in withdrawal dates. Consequently, even when rains start late, withdrawal is timely, thus making the growing season shorter. During the March-May rainy season, the number of rainy days during this critical period of crop growth is decreasing, which possibly means that crops grown in this season are prone to climatic risks and therefore in need of appropriate adaptation measures. A time-series analysis of the maximum daily temperature clearly revealed an increase in temperature, with the lower limits of the ranges of daily maximums increasing faster than the upper limits. Finally, this study has generated information on seasonal rainfall characteristics that will be vital in exploiting the possibilities offered by climatic variability and also offers opportunities for adapting to seasonal distribution so as to improve and stabilise crop yields. <![CDATA[<b>Waterford Formation in the south-eastern Karoo</b>: <b>Implications for basin development</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532012000200021&lng=en&nrm=iso&tlng=en Extensive research on the rocks of the Karoo Supergroup has shown that this sequence, which contains an unsurpassed record of Permian-Jurassic tetrapods, records a largely unbroken stratigraphic succession from 300 Ma to 180 Ma. This Gondwanan succession was deposited in a changing environmental setting reflecting glacial marine through deltaic to fluvial and aeolian desert conditions. The contact between the Ecca and Beaufort Groups (at the top of the Waterford Formation of the Ecca Group) in the southern and western Karoo represents a change in depositional environment from a subaqueous to a subaerial delta plain. By contrast, the Waterford Formation has not yet been recognised in the south-eastern Karoo Basin, which might imply that a major unconformity is present between the Fort Brown Formation of the Ecca Group, deposited in a prodelta environment, and the overlying fluvially deposited Koonap Formation of the Beaufort Group. From careful documentation of lithofacies and sedimentological data, it can be demonstrated that the Waterford Formation is indeed present in the south-eastern part of the basin and that no major unconformity is present - a fact that has implications for the mapping of Karoo rocks in the Eastern Cape Province of South Africa, for understanding the depositional environment of 'reptilian' fossils from the lowermost Beaufort in this part of the Karoo basin, and for basin development models.