Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320080004&lang=en vol. 104 num. 7-8 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<B>Defining waste in South Africa</B>: <B>moving beyond the age of 'waste'</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400001&lng=en&nrm=iso&tlng=en The legal definition of waste can often be vague and dependent on factors other than the composition or possible after-use of the material. The European Court of Justice has stated that the term 'waste', in European Union legislation, implies 'discard'. In South Africa, there is currently more than one legal definition of waste. This not only complicates the classification of material as waste, but also creates confusion amongst industry and government dealing with waste management issues. This hinders the successful implementation of the waste hierarchy that aims at diverting waste away from landfill by promoting sustainable waste recycling and re-use. The aim of this paper is to provide a critical analysis of the definition of waste and the shift to waste as resource, and the implications thereof for the implementation of government policies, strategies and legislation on waste re-use and recycling. Special emphasis is placed on the South African situation where new waste legislation is currently under development. <![CDATA[<b>Taxonomic research in South Africa</b>: <b>the state of the discipline</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400002&lng=en&nrm=iso&tlng=en The legal definition of waste can often be vague and dependent on factors other than the composition or possible after-use of the material. The European Court of Justice has stated that the term 'waste', in European Union legislation, implies 'discard'. In South Africa, there is currently more than one legal definition of waste. This not only complicates the classification of material as waste, but also creates confusion amongst industry and government dealing with waste management issues. This hinders the successful implementation of the waste hierarchy that aims at diverting waste away from landfill by promoting sustainable waste recycling and re-use. The aim of this paper is to provide a critical analysis of the definition of waste and the shift to waste as resource, and the implications thereof for the implementation of government policies, strategies and legislation on waste re-use and recycling. Special emphasis is placed on the South African situation where new waste legislation is currently under development. <![CDATA[<B><I>Dasineura rubiformis</I> (Diptera: Cecidomyiidae), a new biological control agent for <I>Acacia mearnsii</I> in South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400003&lng=en&nrm=iso&tlng=en Acecidomyiid midge, Dasineura rubiformis, is the most recent addition to the suite of biological control agents that have been deployed in South Africa against invasive Australian Acacia species. This insect is associated with Acacia mearnsii (black wattle), which is extremely invasive, but also an important agro-forestry species, in South Africa. It induces development of galls in the flowers of A. mearnsii, thereby preventing pod development and reducing the reproductive capacity of the plants. The useful attributes of this economically important plant species should not be affected by the introduction of D. rubiformis. The midge is established in the vicinity of Stellenbosch, where it is increasing in abundance. Studies have been initiated to (i) evaluate the performance of the midge; (ii) confirm that galling does not cause a reduction in vegetative growth of A. mearnsii; and (iii) determine the potential effectiveness of D. rubiformis as a biological control agent of A. mearnsii. All indications are that the insect has the potential to become an excellent seed-reducing biological control agent of A. mearnsii. <![CDATA[<B>Prediction of cotton yield in Kenya</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400004&lng=en&nrm=iso&tlng=en COTTON YIELD IS ONE OF THE INDICATORS for describing agricultural efficiency from different resource management methods in the cotton-growing industry. Selected cotton-growing cost factors were used to design an artificial neural network model to predict cotton yield in Kenya. This neural network model was able to predict cotton yield with a satisfactory performance error of 0.204 kg/ha and a regression correlation coefficient between network output and actual yield of 0.945. <![CDATA[<B>First use of geological radar to assess the conservation condition of a South African rock art site</B>: <B>Game Pass Shelter (KwaZulu-Natal)</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400005&lng=en&nrm=iso&tlng=en WE PRESENT THE RESULTS OF A SURVEY of the main panels of Game Pass Shelter, a major painted rock art site in the KwaZulu-Natal Drakensberg mountain range, using ground penetrating radar. The investigation depth in the Clarens Formation sandstones lies between four and 80 cm, adequate to determine whether the rock wall presents any potentially unstable discontinuities. By identifying such areas and determining the depth of alteration zones at the major discontinuities, the radar helps in the precision mapping of the state of conservation of the rock art panels. The best results are obtained when discontinuities consist of thin clayey layers and are saturated with infiltrating water or are open widely. The radar analysis demonstrated the major role of the thin clayey sedimentary joints as potential source of instability and damage to the art. Thus, non-destructive and technically simple ground penetrating radar is especially useful for the investigation of the stability of rock art sites. <![CDATA[<B>Rheo-processing of semi-solid metal alloys</B>: <B>a new technology for manufacturing automotive and aerospace components</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400006&lng=en&nrm=iso&tlng=en The latest trend in the automotive industry to produce fuel-efficient vehicles has resulted in the increased use of aluminium and magnesium alloys. Liquid metal high pressure die-casting (HPDC) currently satisfies the bulk of the automotive industry's needs in this regard. Growing demands for improved quality and weight reduction, however, have been driving the development of new processing technologies. Problems inherently associated with liquid metal HPDC have resulted in enhanced interest in semi-solid metal (SSM) casting processes. The CSIR has developed and patented a novel SSM rheocasting process and equipment for semi-solid casting described here. <![CDATA[<B>A role for barcoding in the study of African fish diversity and conservation</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400007&lng=en&nrm=iso&tlng=en Africa has a rich diversity of marine and freshwater fishes, but very little taxonomic expertise or funding to describe it. New approaches to using modern technology, such as DNA barcoding, can facilitate collaboration between field biologists, reference collections and sequencing facilities to speed up the process of species identification and diversity assessments, provided specimen vouchers, tissues, photographs of the specimen and DNA sequences (barcodes) are clearly linked. The FISH-BOL project in Africa aims to establish a collaborative Pan-African regional working group to facilitate barcoding of fish across the continent and the surrounding FAO marine regions. This is being established through existing African biodiversity networks and global biodiversity programmes that are already in place. Barcoding is expected to inform African fisheries management and conservation through more accurate identification of species and their different life-history stages, by speeding up biodiversity assessments. Barcoding is an important development, contributing towards an evolutionary history perspective on which to base Africa's conservation strategies. <![CDATA[<B>Particle acceleration with lasers</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400008&lng=en&nrm=iso&tlng=en Within less than a decade, scientists have learned how to use high-intensity lasers to accelerate electrons within a few millimetres to 1 GeV and how to produce ultrashort pulsed proton beams with extremely small emittances. Laser science has touched upon applications in accelerator and synchrotron physics, in hot dense matter and nuclear physics, and one has started to speculate on the feasibility of hitherto experimentally inaccessible nonlinear quantum electrodynamical effects like, for example, photon-photon scattering. Today's acceleration of charged particles by lasers has evolved from the large programmes on inertial confinement fusion that have long been conducted in France and the United States. As fusion laser installations have grown to the size of several soccer fields, however, they place limits on the flexibility of systematic fundamental research. But with the advent of compact, ultra-intense and ultrashort pulsed laser systems, the field of relativistic laser plasma physics has exploded in recent years. <![CDATA[<B>The spinning pipe gas lens revisited</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400009&lng=en&nrm=iso&tlng=en The graded index (GRIN-like) medium generated by gas inside a heated steel pipe when rotated about its longitudinal axis has the ability to focus a laser beam. While the effective focal length of such a system has previously been studied, there is little information on optical phase aberrations and no study to date on the propagation parameters of the laser beam, but has rather remained rooted in the domain of ray optics. We revisit the spinning pipe gas lens in this paper with new perspectives on the propagation of optical waves, and show how the position of the focus is not a measure of the focal length of the lens. We make use of both the intensity and phase information carried by waves to accurately measure the salient parameters of the lens, and complement our experimental findings with a computational fluid dynamics model. <![CDATA[<B>Improvement in the modelling of geomagnetically induced currents in southern Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400010&lng=en&nrm=iso&tlng=en One of the consequences of the geomagnetic storms resulting from adverse space weather is the induction of geomagnetically induced currents (GICs) in power lines. The GICs that flow in a power transmission network are driven by the induced electric field at the Earth's surface. The electric field, in turn, is affected by the changing magnetic field during a magnetic storm. These GICs can cause extensive and expensive damage to transformers in the power transmission system. Understanding the behaviour of the magnetic field during a magnetic storm is a crucial step in modelling and predicting the electric field and ultimately the GICs in a power transmission network. We present a brief overview of the present status of GIC modelling in southern Africa and then discuss whether it is sufficient to use geomagnetic data from a single magnetic observatory alone to model GICs over the subcontinent. A geomagnetic interpolation method is proposed to improve the modelling of GICs in southern Africa. This improved model is one step closer to our being able to predict GICs accurately in the subcontinent, which will enable power distribution companies to take the necessary precautions to minimize possible transformer damage. <![CDATA[<b>Ectomycorrhizas in association with <i>Pinus patula</i> in Sabie, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400011&lng=en&nrm=iso&tlng=en Forestry is an economically important industry in South Africa, involving extensive exotic plantations of Eucalyptus, Pinus and Acacia species. These tree species have fungal associations, such as ectomycorrhizas, that have become locally naturalized. The forestry industry is increasingly faced with problems of long-term sustainability, increasing soil acidity and depletion of soil nutrients. It is, therefore, essential that the fundamental importance of the ectomycorrhizal (ECM) symbioses in the nutrient cycling, growth, health and survival of these tree species should not be ignored. Research on the species diversity of ECM fungi associated with forestry plant species has been hampered by the difficulty of identifying the fungi involved in the symbiosis. This investigation focused on the ECM fungi associated with Pinus patula (Schlecht. et Cham.) grown in managed plantations in the Sabie region, Mpumalanga province, South Africa. ECM roots were morphotyped and DNA was extracted. The internal transcribed spacer (ITS) region was amplified using the ITS 1F and ITS 4 primers. The sequences were BLASTed using the GenBank and UNITE databases. Twenty-seven extractions were successfully amplified representing 17 different morphotypes. Of the 27 sequences, 21 were identified as ECM fungi and, from the BLAST results, eleven different ECM species could be identified. Selected ECM root types were morphologically and anatomically described according to root morphology, mantle structure, specialized hyphae and rhizomorph arrangement. Seven dominant field types were described and identified as two Amanita species, Scleroderma citrinum, a suilloid species, Thelephora terrestris, a tometelloid species and one resembled an Albatrellus species. <![CDATA[<B>Predicting action potential characteristics of human auditory nerve fibres through modification of the Hodgkin-Huxley equations</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400012&lng=en&nrm=iso&tlng=en In 1952, Hodgkin and Huxley published an empirical set of equations describing changes in the neural membrane potential of the squid giant axon during the application of depolarizing or hyperpolarizing stimuli. As these equations were derived for an unmyelinated nerve fibre, there are reservations about their applicability to describe action potential propagation adequately in myelinated mammalian nerve fibres. This study proposes possible modifications of the Hodgkin-Huxley equations to describe action potentials generated in the Ranvier node of a human sensory nerve fibre, as applied specifically to the prediction of temporal characteristics of the human auditory system. Simulations of the effects of these modifications were performed in Matlab. Results suggest that the temporal characteristics of the human auditory system may be predicted better by using the modified set of equations. This finding is of value in creating more realistic neural models of the electrically stimulated human auditory system. Refractory periods were similar to those of general sensory nerve fibres of the same calibre. Relative refractory periods decreased with progressive retrograde nerve fibre degeneration. Chronaxie times decreased and rheobase current values increased when retrograde nerve fibre degeneration was simulated. Rheobase currents were also greater for straight array compared with contour array stimulation. Mean latencies decreased with progressive retrograde nerve fibre degeneration and agreed well with neural response telemetry. They also decreased with an increase in stimulus intensity. <![CDATA[<B>A broad host range reporter plasmid for the analysis of divergent promoter regions</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400013&lng=en&nrm=iso&tlng=en Although many vectors exist for Escherichia coli and closely related species, there are few broad host range vectors that can be conjugated into a large variety of Gram-negative bacteria. We have constructed a broad host range vector, pMJ445, that facilitates the analysis of divergent promoters in Gram-negative bacteria. The vector was validated using two intergenic regions derived from gene clusters involved in hydantoin hydrolysis, from the environmental isolates Pseudomonas putida and Agrobacterium tumefaciens. The DNA sequences analysed were capable of activating expression of the reporter enzymes, β-glucuronidase and β-galactosidase, present on pMJ445, indicating the presence of divergent promoters in the sequences selected. In addition, we demonstrated that pMJ445 can be applied to gene regulation studies. <![CDATA[<B>Long-term effects of a low dosage of grape seed proanthocyanidin extract on blood pressure in spontaneously hypertensive rats</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400014&lng=en&nrm=iso&tlng=en Most studies on the antihypertensive effects of bioflavonoids have reported short-term effects (within 7 weeks) at high concentrations (40-100 mg kg-1 day-1). The present study by contrast has investigated long-term effects of low concentrations of bioflavonoids on arterial blood pressure and left ventricular performance in spontaneously hypertensive rats (SHR). Spontaneously hypertensive rats were divided into a treated (n = 16) and a control (n = 16) group. The treated group received daily a grape seed proanthocyanidin extract (GSPE) at a concentration of 4 mg kg-1 day-1 over six months. Arterial blood pressure (ABP) was measured once monthly on six randomly selected rats from both groups using an indirect tail-cuff method. After three months, the remaining rats underwent catheterizations to measure left ventricular performance and aortic pressure. The possible role of nitric oxide (NO) in the effects of GSPE was investigated by blocking NO synthase with N-nitro-L-arginine methyl ester (L-NAME). Animals in the treated group had significantly lower arterial end-diastolic pressures (AEDP) after three months of treatment compared with control animals, and this trend continued until six months. In the treated group, left ventricular systolic pressures (LVSP) were reduced by 16.6% (P = 0.005), their dP/dt max (left ventricular pressures) were reduced by 19.7% (P = 0.050), and cardiac work was reduced by 22.0% (P = 0.045) at the end of three months. Treatment with L-NAME suggested a contribution of NO to the effects of GSPE on blood pressure. A low concentration of GSPE administered over six months lowered AEDP significantly, and the L-NAME response suggested that NO is involved. The decreased AEDP had a lowering effect on left ventricular dynamics of hypertensive rats. <![CDATA[<B>Skeletochronology of the endangered side-neck turtle, <I>Podocnemis expansa</B></I>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400015&lng=en&nrm=iso&tlng=en Previous preliminary mark-recapture studies, and assessment of carapace length and annuli of the endangered giant Amazonian river turtle, Podocnemis expansa, have provided some insight into various aspects of their population structure and overall biology. Many questions still remain, however, particularly pertaining to the attainment of sexual maturity, nesting age of females, and longevity of individuals. The current study examines the feasibility of using skeletochronology on the bones of Podocnemis expansa, to obtain data pertaining to these questions, as well as to acquire individual ontogenetic age data. Material for the analysis was opportunistically obtained from 'kitchen remains' and leftovers of natural predators. Our results showed that even after being subjected to such harsh treatment, all the bones in our sample preserved histological detail. By the application of skeletochronology, we estimate the individual ages of all specimens and these compared favourably with age data obtained previously. In spite of our limited sample size, we found a positive relationship between the number of growth rings and carapace length, a slower increase in body size for the larger individuals, and we tentatively suggest that sexual maturity may have occurred at about 5-6 years of age. On the basis of the findings of this pilot study, we suggest that skeletochronology can be effectively used on this endangered taxon. Furthermore, as skeletochronology can also reliably permit deductions about the age profile of individuals that fall prey to predators, it also has the potential of assisting in the development of effective conservation strategies. <![CDATA[<B>Comparison of lipid and fatty acid profiles of commercially raised pigs with laboratory pigs and wild-ranging warthogs</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400016&lng=en&nrm=iso&tlng=en The perception that commercial livestock meat products have adverse nutritional effects, especially from the point of view of lipids and cardiovascular disease, is linked to assumptions concerning their inherent lipid profile. However, when commercially reared domestic pig meat samples were compared with those from laboratory pigs or wild-ranging warthogs, the warthog and laboratory pig samples shared similar lipid profiles, whereas the commercially reared pig samples were different. Pork is not inherently high in saturated fatty acids, unless this has been induced by the current intensive agricultural practices employed in raising the animal. We conclude that problems of high saturated fatty acid content in commercially raised pork could be ameliorated by appropriate changes to current intensive animal production methods. <![CDATA[<B>Neutralization of acid mine drainage using fly ash, and strength development of the resulting solid residues</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400017&lng=en&nrm=iso&tlng=en Acid mine drainage (AMD) from a South African coal mine was neutralized with fly ash (FA) from a local power station. An immediate increase in pH and subsequent decrease in the electrical conductivity (EC) values were observed with the addition of FA. A pH buffering region was observed for all the AMD:FA ratios investigated. This was attributed to precipitation and hydrolysis of the main AMD constituents such as Al and Fe and adsorption of the precipitates upon the ash particles. A high percentage of major, minor and trace elements and SO4(2-) attenuation was achieved after contact of AMD with FA in solution; this removal depended on the final pH of the product water. Most of the contaminants were removed to acceptable levels in one simple procedure by contacting the AMD with FA in suitable ratios. Solid residues (SR) recovered from neutralization reactions were tested for unconfined compressive strength and elastic modulus in order to assess their suitability as backfill material. Strength testing was carried out for 410 days with and without the addition of ordinary Portland cement. The SR with a pozzolanic binder added gained 300% greater strength than without, both of which increased in strength over time. The implementation of this FA treatment process would not only be environmentally beneficial but also would be to the advantage of coal mines and power stations as a way of constructively using the large volumes of waste that they generate. <![CDATA[<b>Sterols and sterolins in <i>Hypoxis hemerocallidea</i> (African potato)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000400018&lng=en&nrm=iso&tlng=en Commercially available health supplements and herbal remedies containing sterols and sterolins, either from African potato (Hypoxis hemerocallidea) alone, or whether enriched with sterols and sterolins, are claimed to be efficacious in the treatment of a variety of ailments. Sterols and sterolins in African potato are purported to be the relevant constituents that are required for the therapeutic claims of such products. A patent describing the extraction of sterolins from African potato plant material has claimed that approximately 9 mg sterolins can be isolated from 100 g of an enriched aqueous African potato extract. Our analysis of African potato plant material and its sterol and sterolin content, when similarly prepared, shows that the measureable content of sterols and sterolins in African potato is far less than the amounts of these compounds that have been claimed to be necessary for therapeutic benefit. We conclude that therapeutic claims relating to sterol and sterolin content in African potato are unsubstantiated, in view of the extremely low content of such compounds that we have isolated from our plant material, and in products containing African potato, or extracts thereof.