Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320080005&lang=en vol. 104 num. 9-10 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<B>Visitors' views on alien animal species in national parks</B>: <B>a case study from South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500001&lng=en&nrm=iso&tlng=en Little information exists globally on the levels of awareness of visitors to national parks about the role of these parks, in part, to protect ecosystems. An exploratory study, involving a questionnaire survey, supported by interviews, examined visitors' views on the hypothetical presence of alien (that is, non-indigenous) animal species in the Addo Elephant National Park (AENP), South Africa. Correlations between responses and respondents' country of origin, level of education and age were investigated. The majority (c. 62%) of the respondents, who interpreted the questions correctly, were not aware of the fact that the presence of alien species would be at odds with the vision of the AENP, insofar as it refers to protecting the integrity of its ecosystems; this indicates the need for a focused education campaign for park visitors. Foreign respondents, and those who possessed a high level of tertiary education, were more opposed to the presence of alien species than South African respondents and those with lower levels of education. Respondents opposed to such a presence (c. 38%) form a relatively large segment of the growing ecotourism market in South Africa; research needs to be conducted to determine whether this group may be lost to the industry if alien species continue to be stocked in some state-run and private conservation areas. Little progress appears to have been made in the past 25 years in South Africa regarding the level of knowledge of park visitors about alien species, ecological and environmental interrelationships and the goals of park management. <![CDATA[<B>The first oceanographic survey of the Conrad Rise</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500002&lng=en&nrm=iso&tlng=en This article presents data collected during the first hydrographic survey of the Conrad Rise, South-West Indian Ocean. Past investigations have shown that the Conrad Rise acts as an obstacle to the flow of the Antarctic Circumpolar Current (ACC). Numerical modelled data suggest that two eastward-flowing jets are formed on the northern and southern extremities of the rise as a result of the bifurcation of the ACC. Hydrographic data collected during the research cruise corroborate the model findings and provide a wealth of empirical data for further investigation of this dynamic ocean region. Counts of seabirds conducted during the cruise revealed unusually large numbers of penguins and diving petrels associated with the frontal jets, suggesting that the area is important for the large populations of penguins breeding at the Prince Edward and Crozet islands farther north. <![CDATA[<B>First hominoid from the Late Miocene of Niger</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500003&lng=en&nrm=iso&tlng=en Since the discovery of Orrorin tugenensis in the Late Miocene Lukeino Formation, Tugen Hills, Kenya, it is generally admitted that the origin of bipedal hominids occurred earlier than 6 Myr ago and that the adaptation to bipedal stance and locomotion initially occurred in a forested or well-wooded setting. In Africa, eight localities aged between 13 and 5.5 Myr have yielded hominoid fossils belonging to nine species. We here report the occurrence of a Late Miocene hominoid in Niger, associated with a restricted fauna which indicates an age of c. 11-8 Myr. The Niger fossil locality is 940 km north of the nearest known extant hominoids, and 1000 km west of the nearest recorded fossil hominoid from Chad. The scientific value of the Niger specimen resides in its discovery locus far from any other known fossil hominoids, its Late Miocene age and the attention that it will focus on the Neogene fossil record of West Africa, currently almost unknown. <![CDATA[<B>Prevalence of asymptomatic intestinal coccidian parasite infections among non-diarrhoeic HIV-positive children in Zaria, Nigeria</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500004&lng=en&nrm=iso&tlng=en Opportunistic coccidian parasites, amongst other infections, frequently complicate human immunodeficiency virus (HIV) infection by causing chronic diarrhoea. The magnitude of these parasitic infections in HIV-positive patients requires careful attention in developing countries. There have been inadequate studies addressing this problem in Nigeria. The investigation reported here was conducted at Ahmadu Bello University Teaching Hospital, Zaria, Nigeria, with the objective of determining the prevalence of these parasitic infections among HIV-positive children. Eighty-eight stool samples were collected during the wet humid months of July and August 2006 from 60 non-diarrhoeic, HIV-positive and 28 HIV-negative children less than 10 years old. The samples were examined for intestinal coccidian parasites by microscopy and modified Kinyoun's acid fast staining methods. Coccidian parasites, Cyclospora cayetanensis, Cryptosporidium parvum and Isospora belli, were identified in 51% (45/88) of all the stool samples examined. The parasite oocysts were identified in 68% (41/60) of the HIV-positive patients presenting at the hospital and in 14% (4/28) of the controls (P < 0.01). The HIV patients were found to be thirteen times more likely to have been infected with coccidian parasites than the control children (odds ratio = 13.0, 95% CI = 3.9-42.6). Cyclospora cayetanensis was the most prevalent parasite identified in the study (36%). Dual infections caused by C. cayetanensis and C. parvum were found in 17% of HIV-positive patients. Female children were found to have more (53%: 25/47) coccidian oocysts in their stools than the boys (49%: 20/41) (P > 0.05). We found an increase in parasite prevalence with age of the patient. This study indicates that coccidian parasites may be important opportunistic infection agents in non-diarrhoeic HIV-infected children. The prevalence of these parasites and their potential for compounding the health problems of HIV-infected patients suggest that the diagnosis and treatment of coccidian parasites should be a part of routine HIV care. <![CDATA[<B>Gough Island 500 years after its discovery</B>: <B>a bibliography of scientific and popular literature 1505 to 2005</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500005&lng=en&nrm=iso&tlng=en Opportunistic coccidian parasites, amongst other infections, frequently complicate human immunodeficiency virus (HIV) infection by causing chronic diarrhoea. The magnitude of these parasitic infections in HIV-positive patients requires careful attention in developing countries. There have been inadequate studies addressing this problem in Nigeria. The investigation reported here was conducted at Ahmadu Bello University Teaching Hospital, Zaria, Nigeria, with the objective of determining the prevalence of these parasitic infections among HIV-positive children. Eighty-eight stool samples were collected during the wet humid months of July and August 2006 from 60 non-diarrhoeic, HIV-positive and 28 HIV-negative children less than 10 years old. The samples were examined for intestinal coccidian parasites by microscopy and modified Kinyoun's acid fast staining methods. Coccidian parasites, Cyclospora cayetanensis, Cryptosporidium parvum and Isospora belli, were identified in 51% (45/88) of all the stool samples examined. The parasite oocysts were identified in 68% (41/60) of the HIV-positive patients presenting at the hospital and in 14% (4/28) of the controls (P < 0.01). The HIV patients were found to be thirteen times more likely to have been infected with coccidian parasites than the control children (odds ratio = 13.0, 95% CI = 3.9-42.6). Cyclospora cayetanensis was the most prevalent parasite identified in the study (36%). Dual infections caused by C. cayetanensis and C. parvum were found in 17% of HIV-positive patients. Female children were found to have more (53%: 25/47) coccidian oocysts in their stools than the boys (49%: 20/41) (P > 0.05). We found an increase in parasite prevalence with age of the patient. This study indicates that coccidian parasites may be important opportunistic infection agents in non-diarrhoeic HIV-infected children. The prevalence of these parasites and their potential for compounding the health problems of HIV-infected patients suggest that the diagnosis and treatment of coccidian parasites should be a part of routine HIV care. <![CDATA[<b>A target for South Africa's business expenditure on research and development based on industry structure</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500006&lng=en&nrm=iso&tlng=en Opportunistic coccidian parasites, amongst other infections, frequently complicate human immunodeficiency virus (HIV) infection by causing chronic diarrhoea. The magnitude of these parasitic infections in HIV-positive patients requires careful attention in developing countries. There have been inadequate studies addressing this problem in Nigeria. The investigation reported here was conducted at Ahmadu Bello University Teaching Hospital, Zaria, Nigeria, with the objective of determining the prevalence of these parasitic infections among HIV-positive children. Eighty-eight stool samples were collected during the wet humid months of July and August 2006 from 60 non-diarrhoeic, HIV-positive and 28 HIV-negative children less than 10 years old. The samples were examined for intestinal coccidian parasites by microscopy and modified Kinyoun's acid fast staining methods. Coccidian parasites, Cyclospora cayetanensis, Cryptosporidium parvum and Isospora belli, were identified in 51% (45/88) of all the stool samples examined. The parasite oocysts were identified in 68% (41/60) of the HIV-positive patients presenting at the hospital and in 14% (4/28) of the controls (P < 0.01). The HIV patients were found to be thirteen times more likely to have been infected with coccidian parasites than the control children (odds ratio = 13.0, 95% CI = 3.9-42.6). Cyclospora cayetanensis was the most prevalent parasite identified in the study (36%). Dual infections caused by C. cayetanensis and C. parvum were found in 17% of HIV-positive patients. Female children were found to have more (53%: 25/47) coccidian oocysts in their stools than the boys (49%: 20/41) (P > 0.05). We found an increase in parasite prevalence with age of the patient. This study indicates that coccidian parasites may be important opportunistic infection agents in non-diarrhoeic HIV-infected children. The prevalence of these parasites and their potential for compounding the health problems of HIV-infected patients suggest that the diagnosis and treatment of coccidian parasites should be a part of routine HIV care. <![CDATA[<b>Where are our universities going? A review, twenty years later</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500007&lng=en&nrm=iso&tlng=en Opportunistic coccidian parasites, amongst other infections, frequently complicate human immunodeficiency virus (HIV) infection by causing chronic diarrhoea. The magnitude of these parasitic infections in HIV-positive patients requires careful attention in developing countries. There have been inadequate studies addressing this problem in Nigeria. The investigation reported here was conducted at Ahmadu Bello University Teaching Hospital, Zaria, Nigeria, with the objective of determining the prevalence of these parasitic infections among HIV-positive children. Eighty-eight stool samples were collected during the wet humid months of July and August 2006 from 60 non-diarrhoeic, HIV-positive and 28 HIV-negative children less than 10 years old. The samples were examined for intestinal coccidian parasites by microscopy and modified Kinyoun's acid fast staining methods. Coccidian parasites, Cyclospora cayetanensis, Cryptosporidium parvum and Isospora belli, were identified in 51% (45/88) of all the stool samples examined. The parasite oocysts were identified in 68% (41/60) of the HIV-positive patients presenting at the hospital and in 14% (4/28) of the controls (P < 0.01). The HIV patients were found to be thirteen times more likely to have been infected with coccidian parasites than the control children (odds ratio = 13.0, 95% CI = 3.9-42.6). Cyclospora cayetanensis was the most prevalent parasite identified in the study (36%). Dual infections caused by C. cayetanensis and C. parvum were found in 17% of HIV-positive patients. Female children were found to have more (53%: 25/47) coccidian oocysts in their stools than the boys (49%: 20/41) (P > 0.05). We found an increase in parasite prevalence with age of the patient. This study indicates that coccidian parasites may be important opportunistic infection agents in non-diarrhoeic HIV-infected children. The prevalence of these parasites and their potential for compounding the health problems of HIV-infected patients suggest that the diagnosis and treatment of coccidian parasites should be a part of routine HIV care. <![CDATA[<B>South African research in the context of Africa and globally</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500008&lng=en&nrm=iso&tlng=en The quality and quantity of research publications are used as benchmarks to monitor the performance of South Africa's national system of innovation. The indicators are pertinent to the policies of the Department of Education, which distributes funds for research at institutions of higher education by measuring the volume of research outputs. In this article, we present a scientometric assessment of research in South Africa in the context of the rest of Africa and in comparison with Brazil and India-two countries with which South Africa aims to develop strong scientific ties. We find that South Africa has published a significant number of papers in all 22 disciplines represented in the ISI's Essential Science Indicators. The largest numbers of journal articles in a 10-year period (1996-2005) were published in the categories Clinical Medicine, and in Plant and Animal Sciences, with over 7000 papers each. Three groupings, namely, Chemistry, Geosciences, and Environmental/Ecology, form the second cluster of disciplines in terms of the highest number of publications (2966, 2488 and 2386, respectively). In all 22 subject categories, India and Brazil are rated higher than South Africa in terms of number of publications, but South Africa is ranked above these countries in relation to citations per paper in all disciplines. Egypt outranked South Africa in three disciplines in the period 1995-2004, namely, Chemistry, Engineering, and Materials Science, as did Nigeria in Agriculture in 1996-2005. In addition to the three disciplines in the earlier period, Egypt outranked South Africa in 1996-2005 in Physics, Agricultural Sciences, and Pharmacology/ Toxicology. However, South Africa scored higher than both African countries in all disciplines in terms of citations per paper. <![CDATA[<B>South Africa's bioprospecting, access and benefit-sharing legislation</B>: <B>current realities, future complications, and a proposed alternative</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500009&lng=en&nrm=iso&tlng=en Globally, many nations are legislating access for bioprospecting purposes to their biological and genetic resources. South Africa, as a megadiverse country, has recently regulated bioprospecting, access and benefit-sharing activities in accordance with its obligations as a ratifying party to the Convention on Biological Diversity. The context and process of key legislation developments in South Africa are discussed, prior to our presenting a critique which emphasizes the practical impacts, especially on drug discovery, arising from the newly introduced systems. Probable effects on existing bioresource-based industries within South Africa, together with current as well as future bioprospecting activities, are assessed. Several practicalities of bioprospecting methods have been poorly accommodated, resulting in the development of impracticable and unnecessarily restrictive regulations. We conclude that though well-intentioned, these non-facilitative regulations have placed a dead hand on value-addition to South Africa's biodiversity. Bioprospectors will find it difficult to continue with broad-scale screening programmes given their user insecurity, legal uncertainty, and cost-inefficiency. Existing bioresource-based industries within South Africa face potential closure in view of onerous bioprospecting permit application requirements. An alternative, practical, CBD-compliant model on which to base urgently required legislative reforms is presented. <![CDATA[<B>Application of active biomonitoring within an integrated water resources management framework in South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500010&lng=en&nrm=iso&tlng=en Because waste water and runoff from surrounding catchments are a main source of direct and continuous input of pollutants in aquatic ecosystems, the study of the effects of in-stream exposure on organisms has a high ecological relevance. However, correlating observed effects with specific pollutants or even classes of pollutants remains difficult, due to the usually unknown, complex and often highly variable composition of these source waters. By integrating multiple endpoints at different ecologically relevant levels of organization within one test organism, it is possible to gain an understanding of how different levels of organization within this organism respond to toxic exposure, and how responses at these different levels are interrelated. The use of biological markers in transplanted organisms, referred to as active biomonitoring (ABM), is demonstrated in this paper. The correct choice of bioindicator organism and suite of biomarkers makes it possible to assess the effects of wastewater and runoff water in terms of known environmental effects (such as effluents containing endocrine-disrupting chemicals or pulp mill effluent) as well as runoff water with an uncharacterized composition of contaminants (for instance storm-water runoff from industrial complexes). The applicability of ABM as a cause-effect assessment protocol is demonstrated through a case study in South Africa that relates to stressor identification within a system exposed to urban and industrial waste water. This paper proposes a multi-tiered framework that allows for the incorporation of ABM within the existing South African integrated water resources management framework. <![CDATA[<B>Frequency dependence of dispersive phonon images</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500011&lng=en&nrm=iso&tlng=en In the past, lattice dynamics models have been used in interpreting dispersive phonon focusing patterns of crystals. They have had mixed success in accounting for observed images and, moreover, different models applied to the same crystal tend to differ significantly in their predictions. In this paper we interpret observed phonon focusing images of two cubic crystals, germanium and silicon, through an extension of continuum elasticity theory that takes into account the first deviation from linearity of the phonon dispersion relation. This is done by incorporating fourth-order spatial derivatives of the displacement field in the wave equation. The coefficients of the higher-order derivatives are determined by fitting to phonon dispersion relations for the acoustic branches measured by neutron scattering in the [100], [111] and [110] symmetry directions. With this model we simulate phonon images of Si and Ge projected onto the (100), (110) and (111) observation planes. These are able to account well for the observed phonon images. <![CDATA[<B>The role of frictional stress on the generation of misfit dislocations</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500012&lng=en&nrm=iso&tlng=en The concept of misfit strain driving dislocations to an interface between two different phases leads to a residual strain that is not accommodated by the misfit dislocations. The residual strain occurs when the misfit stress is reduced to a value insufficient to generate further misfit-accommodating dislocations at the interface. This idea has been applied to epitaxial films to account for the relaxation of strain with increasing film thickness. It is here extended to the case of endotaxial interfaces between a solid matrix and precipitate. This paper builds upon work of Nabarro published in 1940 and the frictional stress to be overcome to move dislocations into the interface. <![CDATA[<B>Enhanced efficiency of a parabolic solar trough system through use of a secondary radiation concentrator</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500013&lng=en&nrm=iso&tlng=en Solar electric energy is not yet economically competitive with fossil fuels. Apart from large capital outlay, solar systems suffer from low efficiency of converting solar energy to electric power. In this paper, a receiver for a solar trough was investigated in which the dominant radiation losses were suppressed by reducing the radiation area. The concentration ratio of the primary concentrator (a parabolic mirror) was enhanced by use of a simple secondary concentrator (an optical funnel), which minimized the width of the focal line. The resultant radiation losses were significantly reduced (by 22%). The novel aspect in this work was the design and modelling of a solar radiation receiver with secondary concentrator and black-body chamber. An initial model of this receiver showed an improvement of overall efficiency of about 1% for solar to electric power generation as compared to conventional receivers. Application of a receiver built on this model could reduce heat losses and costs of a solar trough system. <![CDATA[<B>A single-element plane-wave solid-state laser rate equation model</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500014&lng=en&nrm=iso&tlng=en A numerical rate equation model has been developed to describe the dynamics of a solid-state laser during continuous wave or Q-switched operation. The model allows the optimization of parameters such as the output coupler transmission percentage, crystal length and beam diameters, with the aim of improving the laser output performance. To validate the model, it was applied to a Nd:YLF laser, and proved successful in predicting and explaining the laser dynamics. It also satisfied our objective of creating a useful laser design tool. <![CDATA[<B>The effect of nitrogen on the co-segregation with molybdenum in a Fe-3.5wt%Mo-N(100) single crystal</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500015&lng=en&nrm=iso&tlng=en In this study, the co-segregation of molybdenum and nitrogen to the (100) surface of an iron single crystal was investigated by studying a Fe-3.5wt%Mo-N single crystal. Ternary segregation systems are considerably more complex than binary systems in the sense that there are seven unknown segregation parameters to determine, as opposed to three for a binary system. A novel approach was undertaken to minimize the number of unknown variables and thus reduce the calculation time needed for the ternary system, by first analysing the segregation behaviour of molybdenum in a binary system [Fe-3.5 wt%Mo(100)] that was exposed to a nitrogen ambient. Exposing the binary crystal to nitrogen at high temperatures, the molybdenum segregated to the surface. The segregation profiles of the two systems were acquired at constant temperatures in the range 797-888 K using Auger electron spectroscopy (AES). The segregation profiles were fitted with the modified Darken model and the segregation parameters, namely, the pre-exponential factor (D0), activation energy (E), segregation energy (ΔG) and the interaction energies (ΩFe-Mo, ΩFe-N, and ΩMo-N) for molybdenum and nitrogen, were determined. For the binary system the segregation parameters for molybdenum were: D0,Mo = 2.4 ×10(0&plusmn;1) m² s-1, E Mo = 323 &plusmn; 16kJ mol-1, and ΔG Mo = -38 &plusmn; 5 kJ mol-1. These segregation parameters were then used as initial values to fit the experimental data of the ternary system. The segregation parameters for molybdenum in the ternary system were determined as: D0,Mo = 1.9 ×10-4&plusmn;1 m² s-1, E Mo =271 &plusmn; 11kJ mol-1 and ΔG Mo= -32 &plusmn; 5 kJ mol-1. The segregation parameters for nitrogen in the ternary system were D0,N = 2.8 ×10-0&plusmn;3 m² s-1, E N = 323 &plusmn; 43 kJ mol-1 and ΔG N = -19 &plusmn; 3 kJ mol-1. The interaction energy between molybdenum and nitrogen was ΔΩMo-N = -19 &plusmn;3 kJ mol-1. <![CDATA[<B>Photoluminescence properties of SiO<SUB>2</SUB> surface-passivated PbS nanoparticles</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500016&lng=en&nrm=iso&tlng=en SiO2:PbS nanoparticle phosphors were successfully prepared by a sol-gel process. The crystallized lead sulphide (PbS) nanoparticles inside the amorphous silicon dioxide (silica, SiO2) matrix were examined by X-ray diffraction and transmission electron microscopy (TEM) to estimate the particle size and distribution. The particles were in the size range of 10-50 nm. The TEM diffraction patterns showed the PbS particles to be cubic in structure. Two strong broad photoluminescence emission bands were observed, namely blue (450 nm) from the SiO2 matrix and yellow-orange (560 nm) from the PbS nanoparticles. In bulk PbS emission occurs at ~3200 nm, and the blue shift to the much shorter wavelength reported here is ascribed to quantum effects in the PbS nanoparticles. The emission spectra were strongly dependent on the excitation wavelength. <![CDATA[<B>Parameter extraction from dark current-voltage characteristics of solar cells</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500017&lng=en&nrm=iso&tlng=en Electrical properties derived from the dark current-voltage (I-V) characteristics of solar cells provide essential information necessary in the analysis of performance losses and device efficiency. Device parameters of crystalline silicon solar cells were determined using the one-diode and two-diode models. The parameters extracted from the dark I-V curve of the solar cells were series resistance, shunt resistance, saturation currents and ideality factors. Iteration and approximation techniques were used to determine the device parameters of the solar cells. The method, which considered a finite shunt resistance in the high current region of the curve, made the implementation different from other techniques. Standard deviation, R² values and a fitting routine that provides a graphical representation of the output were implemented to determine the best set of parameters. Comparison of the extracted device parameters against the simulated values suggests that the two-diode model is more suitable than the one-diode model in describing the behaviour of the dark I-V curve. The two-diode model also provides more information necessary to explain the mechanisms governing the I-V curve under dark conditions. <![CDATA[<B>The earliest primate (<I>Parapapio </I>sp.) from the Cradle of Humankind World Heritage site (Waypoint 160, Bolt's Farm, South Africa)</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000500018&lng=en&nrm=iso&tlng=en Waypoint 160 is a breccia occurrence in a dolomite solution cavity on Bolt's Farm on the southern margin of the Cradle of Humankind World Heritage site in South Africa. The calcified breccia has yielded microfauna that has been dated between 4.0 and 4.5 million years. Here we present the first evidence for Parapapio, an extinct monkey, from Waypoint 160. This site is of particular interest as Parapapio is associated with Pliocene or Pleistocene hominids in Africa, for example at Sterkfontein, Taung, Kromdraai, Swartkrans and Makapansgat in South Africa, as well as at Lothagam in East Africa.