Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320090005&lang=pt vol. 105 num. 9-10 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Will South Africa's hosting of the twelfth TWAS Conference make a difference?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500001&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>Modern behaviour in ancient South Africans</b>: <b>evidence for the heat treatment of stones in the Middle Stone Age</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500002&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>Universities in a time of change</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500003&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>South Africa's gold production and reserves</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500004&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>A change of the seaward boundary of Goukamma Marine Protected Area could increase conservation and fishery benefits</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500005&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>Reflections on AIDS denialism in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500006&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>How Many Things by Season Season'd Are</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500007&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>Were environmental or demographic factors the driving force behind Middle Stone Age innovations in southern Africa?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500008&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>The evolution of fire and invasive alien plant management practices in fynbos</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500009&lng=pt&nrm=iso&tlng=pt The history and development of fire and invasive alien plant management policies in fynbos during the 20th century are reviewed. Fire was initially condemned outright as a destructive force, but as its vital role became better understood, management policies switched from protection to active burning in 1968. During the 1970s, large, coordinated research programmes were established, resulting in a solid basis of knowledge on which to develop fire management policies. Despite policies of prescribed burning, wild fires remain the dominant feature of the region, fortunately driving a variable fire regime that remains broadly aligned with conservation objectives. The problem of conserving fire-adapted fynbos is complicated by invading alien trees that are also fire-adapted. Research results were used to demonstrate the impacts of these invasions on water yields, leading to the creation of one of the largest alien plant control programmes globally. Despite improvements in control methods, alien trees, notably pines, continue to spread almost unchecked. Biological control offered some hope for controlling pines, but was ruled out as too high a risk for these commercially-important trees. Failure to address this problem adequately will almost certainly result in the severe degradation of remaining fynbos ecosystems. <![CDATA[<b>The evolution of fire management practices in savanna protected areas in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500010&lng=pt&nrm=iso&tlng=pt The history and development of ecologically-based fire management policies in savanna protected areas during the 20th century are reviewed. Research on fire in savannas began in the 1950s, and from the 1980s onwards, managers of savanna protected areas experimented on large scales with different management approaches. New ecological paradigms that embraced variability in space and time, and management goals that broadened from single-species to biodiversity conservation, precipitated significant changes to management approaches in the 1990s. Many lessons have been learnt in the process, allowing for the derivation of general principles regarding both the effects of fire and managerial ability to influence fire regimes on a large scale. Significant challenges remain; these include dealing with increasing CO2 concentrations in the atmosphere, and with interactions between fire and increasing elephant numbers in protected areas. The ability of savanna managers to deal with these challenges in the context of an imperfect understanding will be determined by how well, and how fast, they can learn from experience. <![CDATA[<b>Environmental and resource economics in South Africa</b>: <b>status quo and lessons for developing countries</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500011&lng=pt&nrm=iso&tlng=pt We review the potential contributions of environmental and resource economics (ERE) to the achievement of sustainable development in developing countries; and highlight the limitations associated with applying ERE within a developing-country context, using examples from South Africa. We fInd that ERE has much to offer in helping to overcome the challenges associated with sustainable development in developing countries, but that the developing-country context needs to be taken into account before applying tools and methods that were designed with the developed-country context in mind. In particular, the unique and often complex socioecological context of developing countries needs to be considered and integrated into policy and management prescriptions. <![CDATA[<b>Possible trace fossils of putative termite origin in the Lower Jurassic (Karoo Supergroup) of South Africa and Lesotho</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500012&lng=pt&nrm=iso&tlng=pt Complex structures in the sandstones of the Lower Jurassic aeolian Clarens Formation (Karoo Supergroup) are found at numerous localities throughout southern Africa, and can be assigned to five distinct architectural groups: (1) up to 3.3-m high, free-standing, slab-shaped forms of bioturbated sandstones with elliptical bases, orientated buttresses and an interconnecting large burrow system; (2) up to 1.2-m high, free-standing, irregular forms of bioturbated sandstones with 2-cm to 4-cm thick, massive walls, empty chambers and vertical shafts; (3) about 0.15-m to 0.25-m high, mainly bulbous, multiple forms with thin walls (<2 cm), hollow chambers with internal pillars and bridges; (4) about 0.15-m to 0.2-m (maximum 1-m) high, free-standing forms of aggregated solitary spheres associated with massive horizontal, orientated capsules or tubes, and meniscate tubes; and (5) about 5 cm in diameter, ovoid forms with weak internal shelving in a close-fitting cavity. Based on size, wall thickness, orientation and the presence of internal chambers, these complex structures are tentatively interpreted as ichnofossils of an Early Jurassic social organism; the different architectures are reflective of the different behaviours of more than one species, the history of structural change in architectural forms (ontogenetic series) or an architectural adaptation to local palaeoclimatic variability. While exact modern equivalents are unknown, some of these ichnofossils are comparable to nests (or parts of nests) constructed by extant termites, and thus these Jurassic structures are very tentatively interpreted here as having been made by a soil-dwelling social organism, probably of termite origin. This southern African discovery, along with reported Triassic and Jurassic termite ichnofossils from North America, supports previous hypotheses that sociality in insects, particularity in termites, likely evolved prior to the Pangea breakup in the Early Mesozoic. <![CDATA[<b>Experimental response of an optical sensor used to determine the moment of blast by sensing the flash of the explosion</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500013&lng=pt&nrm=iso&tlng=pt The Council for Scientific and Industrial Research (CSIR) conducts research into the effect of underwater explosions on maritime structures and equipment. One of the parameters that are required to be measured to a large degree of accuracy is the shock wave velocity in close proximity (10-120 charge radii) of the explosion, without having to revert to the streak photography method. This distance is in the region where the near field crosses over to the far field, and it would be expected that the distance-time curve would not be linear. The streak photography method produces accuracy in the very near field of the explosion, but is not recommended for accurate measurements at distances beyond 20 charge radii. We investigated the response of an optical sensor constructed to measure the light flash of an underwater blast to determine the moment of explosion. By measurement of the time taken between this moment and the time when the shock wave reaches the pressure sensors, accurate measurements of the distance-time history (and hence shock wave velocity) could be calculated. Twelve general purpose phototransistors were used in a parallel configuration to enhance the sensitivity of the sensor. These transistors were connected directly to a conditioning amplifier which formed the interface between the transistors and the data acquisition equipment. The results that were obtained confirmed that the light intensity of the flash of the explosion increased to a maximum within several microseconds. Measurements of the average velocity of the shock wave propagation, based on the flash measurement as a marker, correlated to within 0.1%, meaning that this method of marking the moment of explosion to within several microseconds had been successful. This method can therefore be used in similar underwater blast measurement applications when a measurement marker of the moment of explosion is required. <![CDATA[<b>Application of Numenta<sup>® </sup>Hierarchical Temporal Memory for land-use classification</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500014&lng=pt&nrm=iso&tlng=pt The aim of this paper is to present the application of memory-prediction theory, implemented in the form of a Hierarchical Temporal Memory (HTM), for land-use classification. Numenta®HTM is a new computing technology that replicates the structure and function of the human neocortex. In this study, a photogram, received by a photogrammetric UltraCamD® sensor of Vexcel, and data on 1 513 plots in Manzanilla (Huelva, Spain) were used to validate the classification, achieving an overall classification accuracy of 90.4%. The HTM approach appears to hold promise for land-use classification. <![CDATA[<b>Femtosecond pump probe spectroscopy for the study of energy transfer of light-harvesting complexes from extractions of spinach leaves</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500015&lng=pt&nrm=iso&tlng=pt Measurements of ultrafast transient processes, of temporal durations in the picosecond and femtosecond regime, are made possible by femtosecond pump probe transient absorption spectroscopy. Such an ultrafast pump probe transient absorption setup has been implemented at the CSIR National Laser Centre and has been applied to investigate energy transfer processes in different parts of photosynthetic systems. In this paper we report on our first results obtained with Malachite green as a benchmark. Malachite green was chosen because the lifetime of its excited state is well known. We also present experimental results of the ultrafast energy transfer of light-harvesting complexes in samples prepared from spinach leaves. Various pump wavelengths in the range 600-680 nm were used; the probe was a white light continuum spanning 420-700 nm. The experimental setup is described in detail in this paper. Results obtained with these samples are consistent with those expected and achieved by other researchers in this field. <![CDATA[<b>The applicability of existing topside ionospheric models to the South African region</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500016&lng=pt&nrm=iso&tlng=pt The modelling of the electron density profile (Ne) for the topside ionosphere is challenging due to the limited availability of measured data. Over the past few years, a range of approaches to topside ionospheric modelling and representation of the Ne variation over the topside altitude range have been developed. This paper presents various topside ionospheric modelling efforts and describes their applicability for the South African region. <![CDATA[<b>Is there evidence for a Congo peafowl (<i>Afropavo congensis</i>) in the Middle Stone Age of South Africa?</b>: <b>comments on Stidham (2008)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000500017&lng=pt&nrm=iso&tlng=pt Recently, a fossil Congo peafowl (Afropavo congensis) was described from Middle Stone Age Plovers Lake Cave, South Africa.¹ Because this species is now restricted to rainforests in the Congo Basin, it was concluded that the fossil indicates forested, or even rainforest, habitats in the vicinity of Plovers Lake Cave during the Pleistocene.¹ The correct identification of the fossil specimen is, however, questionable, and the hypothesis of densely forested areas in this area 71 000 years ago is at odds with manifold evidence that grasslands and open woodlands predominated the palaeoenvironment in Pleistocene southern Africa.