1834 research outputs found
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Lead optimisation of an indole based HIV-1 non-nucleoside reverse transcriptase inhibitor
No full textNational Research Foundatio
The edible museum : exploring foodways as sociomuseological practice in Kayamandi, South Africa
No full textNational Research Foundatio
Using genetics to prioritise headwater stream fish populations of the Marico barb, Enteromius motebensis Steindachner 1894, for conservation action
No full textSouth Africa has a relatively large number of threatened freshwater fish species and limited resources to implement conservation programs. Enteromius motebensis was regionally prioritised for action because of its conservation status and flagship status in a nationally important aquatic ecosystem. Genetic diversity of E. motebensis in headwater refugia of the Groot Marico River Catchment was assessed to determine if genetic diversity is important for conservation planning for this species. The results of the genetic analysis indicate that some prioritisation was possible, with two populations showing evidence of recent isolation.
Conservation implications: We recommend that at least three populations be prioritised for conservation action to ensure maintenance of most of the remaining genetic diversity of the species
A review of the influence of biogeography, riverine linkages, and marine connectivity on fish assemblages in evolving lagoons and lakes of coastal southern Africa
No full textThe Holocene evolution of eight South African coastal lakes and lagoons is examined and related to changes in fish composition over that period. Historical and current connectivity with riverine and marine environments are the primary determinants of present‐day fish assemblages in these systems. A small and remarkably consistent group of relict estuarine species have persisted in these coastal lakes and lagoons. The loss or reduction of connectivity with the sea has impacted on the diversity of marine fishes in all eight study systems, with no marine fishes occurring in those water bodies where connectivity has been completely broken (e.g. Sibaya, Groenvlei). In systems that have retained tenuous linkages with the sea (e.g., Verlorenvlei, Wilderness lakes), elements of the marine fish assemblage have persisted, especially the presence of facultative catadromous species. Freshwater fish diversity in coastal lakes and lagoons is a function of historical and present biogeography and salinity. From a freshwater biogeography perspective, the inflowing rivers of the four temperate systems reviewed here contain three or fewer native freshwater fishes, while the subtropical lakes that are fed by river systems contain up to 40 freshwater fish species. Thus, the significantly higher fish species diversity in subtropical versus temperate coastal lakes and lagoons comes as no surprise. Fish species diversity has been increased further in some systems (e.g., Groenvlei) by alien fish introductions. However, the impacts of fish introductions and translocations have not been studied in the coastal lakes and lagoons of South Africa. In these closed systems, it is probable that predation impacts on small estuarine fishes are significant. The recent alien fish introductions is an example of the growing threats to these systems during the Anthropocene, a period when human activities have had significant negative impacts and show potential to match the changes recorded during the entire Holocene
Antibacterial activities of bacteria isolated from the marine sponges isodictya compressa and higginsia bidentifera collected from algoa bay, South Africa
No full textDue to the rise in multi-drug resistant pathogens and other diseases, there is renewed interest in marine sponge endosymbionts as a rich source of natural products (NPs). The South African marine environment is rich in marine biota that remains largely unexplored and may represent an important source for the discovery of novel NPs. We first investigated the bacterial diversity associated with five South African marine sponges, whose microbial populations had not previously been investigated, and select the two sponges (Isodictya compressa and Higginsia bidentifera) with highest species richness to culture bacteria. By employing 33 different growth conditions 415 sponge-associated bacterial isolates were cultured and screened for antibacterial activity. Thirty-five isolates showed antibacterial activity, twelve of which exhibited activity against the multi-drug resistant Escherichia coli 1699, implying that some of the bioactive compounds could be novel. Genome sequencing of two of these isolates confirmed that they harbour uncharacterized biosynthetic pathways that may encode novel chemical structures
Body temperature patterns of a small endotherm in an extreme desert Environment.
No full textMost desert small mammals use mechanisms to avoid overheating or dehydration during summer (e.g. nocturnality or torpor), but some are apparently able to cope with higher body temperatures (Tb) than normally recorded for mammals (i.e. hyperthermia). In winter, some small desert mammals use torpor to conserve energy during cool periods. Still, surprisingly few studies have reported field body temperature patterns in small terrestrial mammals inhabiting deserts, so it is unclear how common hyperthermia and torpor are in desert mammals. We measured Tb of a murid rodent, the Libyan jird (Meriones libycus), during both summer and winter in Saudi Arabia. Modal, minimum, and maximum Tbs were higher in summer than in winter, with maximum Tbs near 42 °C during summer, among the highest Tbs ever recorded in wild mammals. Variation in Tb was significantly higher during summer than winter, which was mostly related to passive warming throughout the day as ambient temperatures regularly exceeded 45 °C during summer. Conversely, during winter, Tbs were highest during the nocturnal active period. While the summer Tbs we recorded are among the highest ever for either murids or small desert mammals, we suspect this represents a lack of data on free-ranging small mammals more than unique adaptations by this speciesNational Research Foundation (South Africa
Development of phosphate-based inorganic wood composite materials
No full textIn a world constantly driven by change, developing new composite products requires moving beyond
the traditional approach to more environmentally benign processes and products. This study investigates
the application of magnesium-based phosphate cement and calcium-based phosphate cement in the
development of natural fibre composite products. The magnesium phosphate cement was prepared from
a heavy magnesium oxide (MgO) and monopotassium phosphate (KH2PO4), while the calcium
phosphate cement was prepared from unslaked lime (CaO), calcium silicate (CaSiO3) and
monopotassium phosphate (KH2PO4). These phosphate cements were used to produce composite panels
using bio-based industrial residues. The residues utilized include sugarcane bagasse (Saccharum
officinarum), hemp hurds (Cannabis sativa), pine sawdust (Pinus elliottii), paper mill sludge and waste
paper. Additionally, forest biomass waste from the clearing of locally occurring invasive alien species
including Black wattle (Acacia mearnsii), Long-leaved wattle (A. longifolia), Port Jackson (A. saligna),
Rooikrans (A. cyclops), Blue gum (Eucalyptus globulus), Sekelbos (Dichrostachys cinerea) and
Deurmekaarbos (Ehretia rigida) were used.
The study utilized a central composite statistical design, whereupon the following factors were
considered i.e. KH2PO4: MgO ratio, KH2PO4: CaO + CaSiO3 ratio, CaO: CaSiO3 ratio and the amount
of wood/fibre as a ratio of wood/fibre to the total inorganic content. Additionally, the use of coal fly
ash as a complementary material in the composite was investigated. Fitted response surface
methodology plots were used to show the relationship between the variable factors on the desired
responses. The effect of the main factors and their interactions on the measured board properties were
evaluated using Pareto analysis of variance. Response surface models were developed to predict the
parameters yielding the optimum board properties. While the physical properties of the panels met the
minimum requirements for cement bonded particleboard (EN 634-2:2007) and LD-1 grade particle
board (ANSI A208.1:1999), the strength properties needed to be improved to offer more flexibility in
terms of application.
Three biomass materials were selected for further study aimed at enhancing the properties of the boards.
These materials were subjected to three different treatments, namely alkalization, acetylation and hot
water extraction. The effect of each of the treatments on the fibre materials was evaluated using HPLC,
SEM and FTIR. These materials were used to manufacture composite panels and µCT was used to
characterize the microstructure of the composite samples. A numerical technique was used to quantify
the phases in the composites, namely cement matrix, filler and void spaces. All treatments improved
the fibre characteristics and did not significantly reduce the fibre yield. In magnesium phosphate bonded
panels, the mean modulus of rupture was 0.74 MPa for untreated, 1.03 MPa for hot water extracted,
1.20 MPa for acetylated and 1.66 MPa for alkalized black wattle panels. In calcium phosphate bonded
panels, the mean modulus of rupture was 0.88 MPa for untreated, 0.83 MPa for hot water extracted, 0.73 MPa for acetylated and 1.18 MPa for alkalized black wattle panels. Boards made with alkali treated
fibres had the best properties. The study concluded that bio-based residues can be incorporated into
formulated phosphate cement binders to produce durable products that are comparable to current
cement bonded products.National Research Foundatio
Improvement of the Thermodynamic description of polar molecules and their mixtures in the SAFT framework
No full textNational Research Foundatio
The bio-geochemistry of bio-active trace elements cadmium and cobalt in the Southern Ocean, Atlantic sector
No full textNational Research Foundatio
Improving feeding efficiencies of black soldier fly larvae, Hermetia illucens (L., 1758) (Diptera: Stratiomyidae: Hermetiinae) through manipulation of feeding conditions for industrial mass rearing
No full textThe human population is rapidly expanding and raises several concerns in terms of food security and
waste management. To feed the human population, we need to start expanding our horizons in terms of
what we eat. Insects may be the answer to this. But due to our many other problems, it helps to create
multiple solutions from single ideas that promote green industry and help ‘heal’ our planet rather than
only taking from it. This is where the black soldier fly, Hermetia illucens (L., 1758) (Diptera:
Stratiomyidae: Hermetiinae) may offer such a solution.
Hermetia illucens is a non-pestilent fly that has spread worldwide due to its many innovative uses, for
example used as a type of biological control agent for some filth fly species, recycle 1.3 billion tonnes
of annual organic waste globally, create high-grade biodiesel and replace (or at least alleviate the
demand) for fish or legume-based animal feeds and lipids. However, very little is known about how the
protein and lipid rich larvae can be mass reared for industrial purposes.
This thesis answers questions about the feeding environment and density of H. illucens larvae in an
industrial setting (i.e. food waste, and larger population sizes). By investigating how feed depth and
particle size, feed provisioning rations (i.e. larval densities), and population sizes effect the ability of
larvae to develop, survive and feed.
The results of this thesis were finding the optimal feed depths (i.e. 5-10 cm), provisioning rations
(125 mg/larva/day) and population sizes (5 000-50 000 larvae per container) of H. illucens larvae when
fed kitchen wastes. Additionally, two new measures of feeding efficiencies were described (i.e.
provisioning ration change and optimal bioconversion deficit) and values for larval aggregation heat were
also recorded for the first time. Future recommendations and research that came up during this study is
also given to continue furthering an industry capitalising on US$ 750 million lost annually in all waste
streams worldwide.National Research Foundatio