Scielo RSS <![CDATA[South African Journal of Science]]> vol. 103 num. 11-12 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>The National Research Foundation's rating system</b>: <b>why scientists let their ratings lapse</b>]]> <![CDATA[<b>Approximation of a biological species constant?</b>]]> <![CDATA[<b>Preliminary data on the nutritional composition of the edible stink-bug, <i>Encosternum delegorguei</i> Spinola, consumed in Limpopo province, South Africa</b>]]> THE EDIBLE STINK-BUG, ENCOSTERNUM (Haplosterna) delegorguei Spinola (Heteroptera, Hemiptera), is a traditional delicacy of the Venda people in South Africa's Limpopo province. Selling the insects at Thohoyandou and other markets provides a valuable income for harvesters. In this article we report the first nutritional information on these insects. Dried bugs consist of 35% protein, 51% fat, with an energy content of 2600 kJ/100 g. Amino-acid concentrations varied from 0.82 mg/100 g (for threonine) to 1.32 mg/100 g (valine). Mineral content was 1.2 g/100 g. The stink-bugs are therefore a source of proteins, fats, amino acids, minerals and vitamins. The conservation and sustainable harvesting of these insects is highly desirable. Further investigation of their nutritional and medicinal properties is recommended, as well as research on their conservation and more efficient use as a food source. <![CDATA[<b>Hyraceum, the fossilized metabolic product of rock hyraxes (<i>Procavia capensis</i>)</b>: <b>shows GABA-benzodiazepine receptor affinity</b>]]> HYRACEUM, AN ACCRETION OF URINE AND dung of rock hyraxes (also known as rock dassies), when fossilized with age, has been used in South Africa for the traditional treatment of epilepsy. We report on tests of 14 hyraceum samples, collected at various geographical locations in South Africa, and assayed for GABA-benzodiazepine receptor affinity. Ethanolic extracts of four of the hyraceum samples assayed positive, whereas all aqueous extracts were inactive. Qualitative TLC resolution of the ethanolic extracts shows a complex mixture of constituents, with no feature being a distinguishing pattern for all four active samples. These preliminary results are not in conflict with the traditional use of hyraceum as a treatment for epilepsy by the settlers of Gamkaskloof. <![CDATA[<b>Geo-information pyramids for up-to-date and flexible conservation plans</b>: <b>a case study for Transfrontier Conservation Areas</b>]]> The initiative to link habitat and parks across political borders, to form large Transfrontier Conservation Areas (TFCAs), has gained momentum in Africa and the world. TFCAs hold many advantages, one of them being the restoration of habitat connectivity in order to conserve ecosystem functioning. A feasibility study in 2002 highlighted 22 sites as potential TFCAs in southern Africa, and the Peace Parks Foundation is facilitating the implementation of eight of them. This paper describes a methodological framework with which to map remaining large, natural habitat fragments (or remnants) in southern Africa, the distribution, shape and size of which will provide the foundation and stakeholders with information on possible coarse-scale landscape linkages. This framework, which maps remnants, was designed to be transparent, systematic and dynamic to facilitate easy updating as TFCA projects mature, or updated data become available. This is intended to be the first in a series of studies towards developing an integrated, systematic framework for TFCA planning at a sub-continental scale. It does not aim to prioritize remnants or linkages. <![CDATA[<b>What is an address in South Africa?</b>]]> Addresses come in many forms as they have a variety of uses. In this paper we illustrate the need for standardized addresses in South Africa by describing scenarios where they are required, or where standardized addresses would improve the current situation. We present the eleven address types described in the current draft South African address standard (SANS 1883), which has been developed under the auspices of the South African Bureau of Standards. We go on to show that these address types represent an all-encompassing description of an address in South Africa. The address types have to accommodate the current situation where there are no mandated authorities that assign standardized addresses according to a set of guidelines, and we provide a critical evaluation of this situation. Our contribution is threefold: it illustrates the need for standardized addresses, shows that there is an all-encompassing description for an address in South Africa, and describes the potential adverse effect of the current lack of mandated authorities on unambiguous address specification and the benefits that address standardization would bring. <![CDATA[<b>Performance of a quasi-synchronous four-dimensional super-orthogonal WCDMA modulator for next generation wireless applications</b>]]> This paper presents the bit-error-rate (BER) performance of an upwards-expandable spectral and power efficient quasi-synchronous multi-layer-modulated (MLM) four-dimensional super-orthogonal wideband code-division multiple access (QS-4D-SO-WCDMA) modem, suitable for application in next generation WLAN and wireless cellular systems. The unique combination of the 4D-WCDMA modem configuration and super-orthogonal families of root-of-unity filtered (RUF) constant-envelope generalized-chirp-like complex spreading sequences (SO-CE-GCL-CSS), renders a spectrally and power efficient output signal with data throughput rates equivalent to that of a 16-ary quadrature amplitude modulated (16-QAM) WCDMA modulation scheme, but with the BER performance equivalent to that of BPSK/QPSK in both AWGN and fading multipath channel scenarios. <![CDATA[<b>The distribution and spread of the invasive alien common myna, <i>Acridotheres tristis</i> L. (Aves: Sturnidae), in southern Africa</b>]]> The common myna is an Asian starling that has become established in many parts of the world outside of its native range due to accidental or deliberate introductions by humans. The South African population of this species originated from captive birds that escaped in Durban in 1902. A century later, the common myna has become abundant throughout much of South Africa and is considered to pose a serious threat to indigenous biodiversity. Preliminary observations suggest that the common myna's distribution is closely tied to that of humans, but empirical evidence for this hypothesis is lacking. We have investigated the relationships between common myna distribution, human population size and land-transformation values at a quarter-degree resolution in South Africa. Common mynas were found more frequently than expected by chance in areas with greater human population numbers and land-transformation values. We also investigated the spatial relationship between the bird's range and the locations of South Africa's protected areas at the quarter-degree scale. These results indicate that, although there is some overlap, the common myna distribution is not closely tied to the spatial arrangement of protected areas. We discuss the original introduction, establishment and rate of spread of the common myna in South Africa and neighbouring countries and contrast the current distribution with that presented in The Atlas of Southern African Birds. We also discuss the factors that affect the common myna's success and the consequences that invasion by this species is likely to have, specifically in protected areas. <![CDATA[<b>Cooling layers in rectangular heat-generating electronic regions for two boundary condition types</b>: <b>a comparison with a traditional approach</b>]]> This paper investigates the cooling ability of embedded solid-state, high-conductive layers in electronics applications. A numerical approach is used to determine and compare steady-state thermal characteristics of this internal heat transfer augmentation scheme for two thermal boundary condition types. The boundary conditions under investigation represent cases where a rectangular three-dimensional solid-state heat generating volume is externally cooled from its surface in either one or two orthogonal directions. Various material property and geometric parameters are considered. The numeric results are compared with predictions of a traditional planar conductivity approach. It is shown that a planar approach used for obtaining the thermal characteristics of a laminated composite structure over-simplifies the problem and only supplies an indication of the ultimate ideal cooling efficiency, which may be achieved, with cooling layers. This paper presents trends, which may be used to predict thermal characteristics more accurately for conditions where no thermal interfacial resistance is present. <![CDATA[<b>Constructal design</b>: <b>geometric optimization of micro-channel heat sinks</b>]]> This paper reports numerical optimization results for three-dimensional heat and fluid flow in a rectangular micro-channel heat sink using water as the cooling fluid. The conducting heat sink consists of silicon wafer. Numerical simulation was conducted on a unit cell which is a micro-channel heat sink with a fixed volume of 0.9 mm³ and a fixed axial length of 10 mm. Geometric optimization was carried out to determine the optimal aspect ratio of a unit cell of a heat sink that minimized the overall maximum temperature and thus maximized the overall global thermal conductance. The effect of total volume fraction of the silicon wafer on the optimal aspect ratio and minimized maximum temperature was also studied. Results show that as the pressure drop increases, the minimized peak temperature decreases, and suggests that there is an optimal allocation of solid volume fraction for a fixed pressure drop. The behaviour of the optimized volume is in agreement with the constructal design method, where the objective is to minimize the peak temperature, subject to the constraints of fixed total volume and solid (silicon wafer) material. <![CDATA[<b>Shelf sediments off the Thukela River mouth</b>: <b>complex interaction between fluvial and oceanographic processes</b>]]> The shelf off the Thukela River has a unique geological and oceanographic setting within the KwaZulu-Natal continental margin. High terrestrial sediment input from the Thukela is delivered to this unusually wide shelf, resulting in deposits that exhibit both deltaic and submarine fan characteristics, the latter initiated during flood events. The Inner shelf (0 to -30 m) is dominated by well-sorted sands reworked by fair-weather processes. The Mid-shelf (-30 to -60 m) comprises poorly sorted sands subjected to ocean storm processes and redistribution by the semi-permanent KwaZulu-Natal Gyre. The Outer shelf (-60 to -100 m) is characterized by gravels and large bedforms produced by the southerly-flowing Agulhas Current. During fair-weather conditions, the Mid-shelf is dominated by the KwaZulu-Natal Gyre and the Outer shelf by the Agulhas Current. During extreme flood events, sedimentation extends further offshore, building the submarine fan, overprinting the typical outer-shelf sediment distribution. This model provides a basis for the effective assessment and management of the biological communities and commercial prawn industry in the area. <![CDATA[<b>Observations on the population dynamics of the invasive freshwater snail <i>Aplexa marmorata</i> (Pulmonata: Physidae) in Durban, South Africa</b>]]> The invasive freshwater snail Aplexa marmorata was shown to exhibit a univoltine reproductive pattern in two ecologically different habitats, a stable ornamental pond and a small, unstable lake. Generation times and the timing of egg-laying periods did, however, differ between these two sites. It is suggested that the retention of a univoltine pattern in the lake, despite a prolonged drop in water level, may be evidence that A. marmorata is not as reproductively flexible as Physa acuta, the other physid invader in South Africa. Such a lack of reproductive flexibility may explain why A. marmorata has not invaded rivers whereas P. acuta, which is known to adopt a multivoltine pattern following repeated disturbances to its habitat, has done so. <![CDATA[<b>Further evidence for eagle predation of, and feeding damage on, the Taung child</b>]]> We present new evidence supporting the hypothesis that a large raptor was responsible for the death of the c. 2.0-Myr-old Taung child, holotype of the early hominin species Australopithecus africanus. We compare the Taung child's skull with those of monkeys killed and eaten by modern crowned eagles, Stephanoaetus coronatus, in the Ivory Coast's Tai Forest. Close inspection of primate feeding remains from these large, powerful raptors reveals scratch marks in the orbital, frontal, temporal, parietal and occipital regions. Scratches similar in size and distribution are also present on the Taung child's skull. The new taphonomic evidence, combined with previously recognized similarities in breakage patterns and other assemblage characteristics, bolsters the case that a large bird of prey was responsible for the death of the juvenile hominin from Taung. <![CDATA[<b>Return period of extreme rainfall at George, South Africa</b>]]> The torrential rains of August 2006 in the southern Cape of South Africa were the most intense observed in the region. Here we use the longest-available daily rainfall series at George (from 1941 to 2006), in the vicinity of which the most destructive floods were observed, together with an extreme value model to estimate the return period of such an extreme event. According to this model, the greatest annual maximum daily rainfall of 230 mm, observed at the town on 1 August 2006, has a return period of 1222 years, whereas the second-largest observed annual maximum daily rainfall (132 mm in September 1964) has a return period of 23 years. This shows that the August 2006 extreme rainfall at George can be considered as a particularly rare event. <![CDATA[<b>Reliability stochastic optimization for an <i>n</i>-stage series system with <i>m</i> chance constraints</b>]]> This paper addresses the chance constraints reliability stochastic optimization (CCRSO) problem, for which the objective is to maximize system reliability for the given chance constraints. A method is illustrated to determine optimal solutions to an n-stage series system with m chance constraints of the redundancy allocation problem, incorporating the concepts of chance constraints techniques. One can quickly reach an exact real number solution closest to the optimal solution by this means. Once the real number solution is obtained, the branch-and-bound (B&B) technique is used to obtain the integer solution. We illustrate this approach for a 4-stage series system with two chance constraints. <![CDATA[<b>Fusarium populations in the household food gardens of a peri-urban community</b>]]> Toxigenic Fusarium species, studied mainly for the damage they cause to commercial crops, have received scant research attention in the context of small-scale food production. In this regard home gardens are an important source of nutrition for resource-poor urban families in Africa. We have investigated the presence of Fusarium in household food gardens in a peri-urban setting in the Rustenburg district of South Africa. Standard techniques were employed for the isolation and morphological species identification of Fusarium species from various sources, namely, maize, soil, air and naturally growing morogo vegetables, thepe and lerotho. Nine Fusarium species with mycotic and mycotoxigenic potential were specifically targeted for detection: F. verticillioides, F. proliferatum, F. solani, F. subglutinans and F. oxysporum were predominantly isolated from maize, air, soil and morogo vegetables. All species were isolated in significantly higher numbers from localities in proximity to maize. Fusarium chlamydosporum, F. semitectum and F. equiseti were not retrieved where maize was absent, whereas F. verticillioides and F. proliferatum were predominantly isolated from maize cobs. These results have public-health implications. All nine Fusarium species retrieved from peri-urban food gardens produce toxins and, except for F. poae, have been implicated in opportunistic infections in immune-suppressed individuals. <![CDATA[<b>Linear and nonlinear sea-level changes at Durban, South Africa</b>]]> The tide record between 1970 and 2003 for Durban, South Africa, is analysed to determine the extent of recent linear and nonlinear sea-level trends in the light of predicted global sea-level rise. Given the stability of the adjacent land mass, Durban is ideally suited to test global sea-level change. The linear trends of monthly mean sea level revealed a sea-level rise of 2.7 ± 0.05 mm/yr and the yearly mean sea-level trend revealed a rise of 2.4 ± 0.29 mm/yr. Nonlinear trends varied between -1 mm and +8 mm/yr. These findings are similar to recently published results of global sea-level rise calculations over the last ten years derived from worldwide tide gauge and TOPEX/Poseidon altimeter measurements, which range between 2.4 and 3.2 mm/yr.