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Cytotoxic activity of marine sponge extracts from the sub–Antarctic islands and the Southern Ocean
No full textOver the past 50 years, marine invertebrates, especially sponges, have proven to be a valuable source of new and/or bioactive natural products that have the potential to be further developed as lead compounds for pharmaceutical applications. Although marine benthic invertebrate communities occurring off the coast of South Africa have been explored for their biomedicinal potential, the natural product investigation of marine sponges from the sub-Antarctic Islands in the Southern Ocean for the presence of bioactive secondary metabolites has been relatively unexplored thus far. We report here the results for the biological screening of both aqueous and organic extracts prepared from nine specimens of eight species of marine sponges, collected from around Marion Island and the Prince Edward Islands in the Southern Ocean, for their cytotoxic activity against three cancer cell lines. The results obtained through this multidisciplinary collaborative research effort by exclusively South African institutions has provided an exciting opportunity to discover cytotoxic compounds from sub-Antarctic sponges, whilst contributing to our understanding of the biodiversity and geographic distributions of these cold-water invertebrates. Therefore, we acknowledge here the various contributions of the diverse scientific disciplines that played a pivotal role in providing the necessary platform for the future natural products chemistry investigation of these marine sponges from the sub-Antarctic Islands and the Southern Ocean.
SIGNIFICANCE:
• This study will contribute to understanding the biodiversity and geographic distributions of sponges in the Southern Ocean.
• This multidisciplinary project has enabled the investigation of marine sponges for the presence of cytotoxic compounds.
• Further investigation will lead to the isolation and identification of cytotoxic compounds present in the active sponge extracts.National Research Foundation (South Africa
Synthesis and Evaluation of Substituted 4-(N-Benzylamino)cinnamate Esters as Potential Anti- Cancer Agents and HIV-1 Integrase Inhibitors.
No full textEncouraging selectivity and low micromolar activity against HeLa cervical carcinoma (IC50 ⩾ 3.0 μM) and the aggressive MDA-MB-231 triple negative breast carcinoma (IC50 ⩾ 9.6 μM) cell lines has been exhibited by a number of readily accessible 4-(N-benzylamino)cinnamate esters. The potential of the ligands as HIV-1 integrase inhibitors has also been examinedNational Research Foundation (South Africa
Urban roost temperatures of large-spotted-genets: The effect of anthropogenic structures
No full textGenerally, large-spotted genets (Genetta tigrina) use tree hollows and canopies as daytime roosts during their inactive phase. However, there has been an increasing tendency for individuals to make use of anthropogenic structures, such as roofs, within urban landscapes in KwaZulu-Natal, South Africa. This study investigated the roosting thermal dynamics of large-spotted genets within the urban suburbs of Kloof. Roost temperatures were recorded with i-Button® temperature loggers at known large-spotted genet roosts in anthropogenic structures as well as in natural roost sites. Over the seasons, temperatures varied significantly between months and among different roosts. However, anthropogenic roost temperatures were higher than ambient temperatures throughout the study period. Furthermore, anthropogenic roosts had higher temperatures (with lower variability) than natural roost sites. This study highlighted the importance of anthropogenic structures as daytime roosts for large-spotted genets within an urban mosaic. However, high temperatures experienced during the summer can be detrimental to juvenile large-spotted genets resulting in plasticity of breeding behaviour and a switch to producing young in cooler months.National Research Foundation (South Africa
Differences in the carcinogenic evaluation of glyphosate between the International Agency for Research on Cancer (IARC) and the European Food Safety Authority (EFSA).
No full textThe International Agency for Research on Cancer (IARC) Monographs Programme identifies chemicals, drugs, mixtures, occupational exposures, lifestyles and personal habits, and physical and biological agents that cause cancer in humans and has evaluated about 1000 agents since 1971. Monographs are written by ad hoc Working Groups (WGs) of international scientific experts over a period of about 12 months ending in an eight-day meeting. The WG evaluates all of the publicly available scientific information on each substance and, through a transparent and rigorous process,1 decides on the degree to which the scientific evidence supports that substance's potential to cause or not cause cancer in humans.
For Monograph 112,2 17 expert scientists evaluated the carcinogenic hazard for four insecticides and the herbicide glyphosate.3 The WG concluded that the data for glyphosate meet the criteria for classification as a probable human carcinogen.
The European Food Safety Authority (EFSA) is the primary agency of the European Union for risk assessments regarding food safety. In October 2015, EFSA reported4 on their evaluation of the Renewal Assessment Report5 (RAR) for glyphosate that was prepared by the Rapporteur Member State, the German Federal Institute for Risk Assessment (BfR). EFSA concluded that ‘glyphosate is unlikely to pose a carcinogenic hazard to humans and the evidence does not support classification with regard to its carcinogenic potential’. Addendum 1 (the BfR Addendum) of the RAR5 discusses the scientific rationale for differing from the IARC WG conclusion.
Serious flaws in the scientific evaluation in the RAR incorrectly characterise the potential for a carcinogenic hazard from exposure to glyphosate. Since the RAR is the basis for the European Food Safety Agency (EFSA) conclusion,4 it is critical that these shortcomings are corrected.National Research Foundation (South Africa
Adaptive observer based MLPNN and sliding mode for wearable robots: application to an active joint orthosis
No full textThis paper deals with the design of an adaptive observer based both on a Multi-Layer Perceptron Neural Network (MLPNN) and a sliding mode technique. Its main objective is to construct the complete state of a given exoskeleton worn by a human subject. The observer we propose in this paper can be used for any application: rehabilitation, assistance, etc. The dynamic model of the global system composed of the exoskeleton and the human is complex and supposed completely unknown. The MLPNN chosen for its characteristic of universal approximation has been used here to identify the unknown dynamic. Its parameters have been adjusted by taking into account the structure of the dynamic model of the considered system and the closed-loop stability based on Lyapunov׳s approach. A Taylor series expansion allows resolving the non-linearity problem present in the MLPNN. Besides the fact that the proposed adaptive observer can be integrated in a control scheme, it also allows us to study the behavior of the exoskeleton before any application on the human subject. The proposed study has been validated both in simulation and in experimentation. The obtained results show the effectiveness of the proposed adaptive approach.National Research Foundation (South Africa
Defining invasiveness and invasibility in ecological networks
No full textThe success of a biological invasion is context dependent, and yet two key concepts—the invasiveness of species and the invasibility of recipient ecosystems—are often defined and considered separately. We propose a framework that can elucidate the complex relationship between invasibility and invasiveness. It is based on trait-mediated interactions between species and depicts the response of an ecological network to the intrusion of an alien species, drawing on the concept of community saturation. Here, invasiveness of an introduced species with a particular trait is measured by its per capita population growth rate when the initial propagule pressure of the introduced species is very low. The invasibility of the recipient habitat or ecosystem is dependent on the structure of the resident ecological network and is defined as the total width of an opportunity niche in the trait space susceptible to invasion. Invasibility is thus a measure of network instability. We also correlate invasibility with the asymptotic stability of resident ecological network, measured by the leading eigenvalue of the interaction matrix that depicts trait-based interaction intensity multiplied by encounter rate (a pairwise product of propagule pressure of all members in a community). We further examine the relationship between invasibility and network architecture, including network connectance, nestedness and modularity. We exemplify this framework with a trait-based assembly model under perturbations in ways to emulate fluctuating resources and random trait composition in ecological networks. The maximum invasiveness of a potential invader (greatest intrinsic population growth rate) was found to be positively correlated with invasibility of the recipient ecological network. Additionally, ecosystems with high network modularity and high ecological stability tend to exhibit high invasibility. Where quantitative data are lacking we propose using a qualitative interaction matrix of the ecological network perceived by a potential invader so that the structural network stability and invasibility can be estimated from the literature or from expert opinion. This approach links network structure, invasiveness and invasibility in the context of trait-mediated interactions, such as the invasion of insects into mutualistic and antagonistic networks.National Research Foundation (South Africa
Performance characterisation of a separated heat-pipe-heat-recovery-heat-exchanger for the food drying industry
No full textIn light of the ever increasing demand for energy efficiency, waste heat recovery has become an important engineering design consideration. Heat-pipe-Heat-Exchangers (HPHE’s) are waste-heat-recovery-units (WHRU’s) that utilise heat pipes/thermosyphons that contain a working fluid as the heat transfer mechanism from the high temperature waste stream to the low temperature stream. To prevent cross contamination for the food industry, the exhaust and inlet streams are often far apart. However, performance correlations for separated-HPHE’s are difficult to find.
For this reason, the thermal performance of an air-to-air separated-HPHE is investigated and characterised. The investigation involved the theoretical and numerical modelling of the separated-HPHE. The models were then compared to the experimental results for validation purposes. It is also important to use energy efficiently, hence the effect of air temperature and flow rate on the drying times of various materials were also investigated.
To develop the HPHE model, outside and inside heat transfer coefficients for the HPHE are required. The outside heat transfer coefficients were obtained by passing hot air over a HPHE filled with cold water and of similar geometry to the HPHE’s used for the separated-HPHE. The inside heat transfer coefficients for the separated-HPHE were determined with R600a, R134a and R123 as working fluids. The experiments were undertaken at various temperatures and flow rates. The results showed that R600a works the most effectively in the temperature range considered and this is expected since R600a is less dense and has a higher latent heat of vaporisation than both R134a and R123. As an example, the R600a charged separated-HPHE yielded heat transfer rates in the region of 9352 W compared to the 7017 W and 4555 W yielded for R134a and R123 respectively at an air temperature difference of 27 °C and mass flow rate of 0.841 kg/s.
The predicted inside heat transfer coefficients correlate the experimentally obtained heat transfer coefficients reasonably well. However, it is found that theoretical models correlated by previous researchers do not correspond to the predicted values obtained from the correlations found from the testing of the separated-HPHE. The differences are attributed to the poor manifold design and the fact that the researchers conducted their experiments on a single thermosyphon, whereas the entire heat exchanger was used in this case.
The main objective of the thesis was because the as-tested separated-HPHE was shown to worked effectively (recovering up to 90 % of the of the dryer exhaust heat) for typical food industry drying temperatures of between 25-80 °C. Additionally, the theoretical simulation models for the HPHE was validated in as much that its energy saving performance was within 12 % of the as-tested experimental models; and thus it was demonstrated that substantial energy cost saving could be realised using standard heat exchanger manufacturing technology. If the heat exchanger is installed in a plant, charged with R600a and is operated with an inlet air temperature of approximately 80 °C and mass flow rate of 0.841 kg/s, the heat recovered is 13.828 kW in an environment of 13 °C. At these conditions, the potential payback period of installing the heat exchanger specified for this study is 3.22 years.
It is recommended that notwithstanding accuracies of roughly 22 % obtained by the theoretically predicted correlations to the experimental work, the heat exchanger design should be optimised to allow better refrigerant flow and various performance parameters like liquid fill charge ratio and condenser/evaporator length dependencies should be further investigated.National Research Foundatio
Plant functional types on Marion Island
No full textA database was compiled of structural and physiological traits for 25 vascular species and 17 bryophyte species on Marion Island (sub-Antarctic). The structural traits included leaf, stem and root characteristics and the physiological traits are all associated with photosynthetic responses to light and were measured using chlorophyll fluorescence quenching analysis. The data were subjected to principal component analysis and clustering analysis to construct a suite of plant functional types (PFTs). The correspondences between the PFTs and plant habit/taxonomy (forb, graminoid, fern, moss and liverwort), status (native to the island or introduced alien) and habitat (oligotrophic, manured or saline) were investigated using correspondence analysis.
There were significant differences in most of the structural traits, but in only one of the photosynthetic traits, between sites at the same altitude and between altitudes. The between-site differences could not be explained since site characteristics were not measured, but the between site differences were often species-dependent; a particular species might show its lowest value for a particular trait at the same site where another species showed the highest value for that trait. The between-altitude differences in structural trait values could be ascribed to the effect of greater wind speed at higher altitude (lower stature, tougher leaves and stems). High altitude plants have greater specific root length, probably a response to low soil nutrient status and hence a need for foraging roots. However, plants in saline coastal habitats also show a high specific root length, probably in response to the inhibitory effect of high salt concentration on nutrient and water uptake. All the species except Azorella selago, the archetypical vascular species of high altitude were more stunted and showed greater signs of stress at high altitude than at low altitude.
Native species tend to show greater values for those traits indicative of structural strength (tough, thick leaves, strong stems), and allocate a greater proportion of their biomass aboveground, than human-introduced alien species. Alien graminoids also have higher stomatal densities (but lower chlorophyll concentrations on a leaf area basis) than native species. There are no consistent differences in photosynthetic capacity between natives and aliens, except that native species tend to show a sharper photosynthetic response to increasing light at low levels, possibly an adaptation to the consistently low light regime at the island.
Maximum photosynthetic electron transport rate varies greatly (by an order of magnitude) between the island’s vascular species and by almost an order of magnitude between the Stellenbosch University https://scholar.sun.ac.za
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bryophyte species. Species with high electron transport rate also tend to have a high effective quantum yield and show electron transport saturation at high light – all indicative of high photosynthetic capacity sun species, most of which are forbs. The shade-adapted, lowest photosynthetic capacity species are mostly ferns, mosses and liverworts. Graminoids tend to be moderate photosynthetic capacity species but some of the forb species also have moderate, and even low, photosynthetic capacity.
Only two structural traits were measured on bryophytes so in grouping both the vascular and bryophyte species together into functional types only the photosynthetic traits were considered. This yielded eight photosynthetic functional groups, together representing three levels of photosynthetic capacity - high, moderate or low capacity. Forbs predominate in the two highest photosynthetic capacity groups, graminoids (with one hepatic) in the moderate to moderately high capacity groups, graminoids, ferns and some bryophytes in the low to moderate capacity groups and bryophytes and shade-adapted ferns in the very low to low capacity groups. Mosses tend to have a higher capacity than hepatics although four of the six species in the very lowest capacity group are mosses. At each level of photosynthetic capacity – the high, moderate or low capacity groups – the species are divided into subgroups based on their capability for photoprotection at high light and how sharply photosynthesis responds to increasing light at low levels.
Previous studies at the island have unequivocally shown that habitats influenced by seal and seabird manuring have higher soil and plant nutrient status, greater plant vitality and higher productivity. It was expected that species restricted to, or that attain maximum cover in manured habitats would be in the group with highest photosynthetic capacity. However, a surprising finding of the study is that those species occur in all the photosynthetic capacity groups except the highest capacity one.
Further research into plant functional traits and functional types at the island should consider phenological, reproductive, and a wider suite of physiological, traits, especially the temperature responses of, and desiccation effects on, photosynthesis, photorespiration and respiration. Since wind is such a dominant factor at the island, its effects on plant morphology, architecture, growth and physiology also need to be addressed.National Research Foundatio
Design of an ironless doublee-rotor radial flux air-cored permanent magnet machine
No full textThis thesis presents research on the Ironless Double-rotor Radial Flux Permanent
Magnet (IDRFPM) machine. The machine is characterised by a rotor
topology consisting of magnets with no iron yoke, which aims to reduce weight
and improve overall torque density. Tangentially magnetized inter-pole magnets
complete the flux path as would normally be done by the steel yoke.
The design also features air-cored concentrated windings which eliminate core
losses and cogging torque while reducing copper losses.
The research was preceded by initial work which produced a crude but
functional aluminium prototype. A primary focus is to improve the topology
used in the first prototype and construct a new prototype with improved torque
density. The new prototype will serve as a propulsion motor for a Shell Eco
Marathon (SEM) vehicle, since the lightweight characteristic suits a small
vehicle application. However, the IDRFPM design is derived from steel-yoke
machines used in wind power generation applications. As such, this research
aims to gain insights to later be applied to wind technology, particularly for
applications in vertical axis wind turbines (VAWTs).
Electromagnetic, structural and thermal analysis was performed as part of
a multi-physics design approach. The electromagnetic design concluded that
best performance is achieved with an in-line segmented quasi-Halbach magnet
array with pole and inter-pole magnets of equal width. To maximize torque
density, advanced carbon fibre reinforced plastic (CFRP) was selected to comprise
the frame components. Detailed mechanical design was completed and
ANSYS Mechanicalr software was used to assess structural integrity. Thermal
analysis was performed to verify the maximum safe operating point. A
basic theoretical model was created by approximating the machine as an intricate
thermal resistance network. A prototype fit to function as a SEM vehicle
propulsion motor was successfully manufactured and tested. While efficiency
was slightly lower than anticipated, the machine achieved good torque density.
The prototype contains a low percentage structural mass while providing a
frame on which a 20” bicycle tire can be directly mounted.National Research Foundatio
Taxonomy and diversity of the sponge fauna from walters shoal, a shallow seamount in the western indian ocean region
No full textSeamounts are poorly understood ubiquitous undersea features, with less than 4% sampled for scientific purposes globally. Consequently, the fauna associated with seamounts in the Indian Ocean remains largely unknown, with less than 300 species recorded. One such feature within this region is Walters Shoal, a shallow seamount located on the South Madagascar Ridge, which is situated approximately 400 nautical miles south of Madagascar and 600 nautical miles east of South Africa. Even though it penetrates the euphotic zone (summit is 15 m below the sea surface) and is protected by the Southern Indian Ocean Deep-Sea Fishers Association, there is a paucity of biodiversity and oceanographic data. Thus, a multidisciplinary cruise was initiated in May 2014 on the FRS Algoa as a component of the African Coelacanth Ecosystem Programme. The research presented here focuses exclusively on the diversity, bathymetric distribution patterns and biogeographic affiliations of the sponge fauna of this seamount. Sponges were sampled using SCUBA and a roughed epibenthic sled, from the peak and down
two opposing slopes of the seamount, to a depth of 500 m. Two hundred and fifty-five sponge specimens were collected, comprising 78 operational taxonomic units (OTU’s), 23 of which are known to science, 26 which are possibly new, 16 that could only be identified to higher taxonomic levels and 13 that could only be designated as morphospecies. Thirteen OTU’s are formally described here, four which are known, and nine possibly new to science. Sponge assemblages demonstrated no significant difference according to location on the shoal, with several species shared by both the western and eastern flanks. In contrast, sponge
assemblages differed significantly according to depth, with the mesophotic zone (31 – 150 m) acting as a transition between the shallow (15 – 30 m) and submesophotic (> 150 m) zones. Species richness and the number of putative new species was highest in the submesophotic zone. Biogeographical affiliations were found with both the Western Indo-Pacific and Temperate Southern African realms based on the 23 known species recorded. No affiliations were found with the West Wind Drift Island Province, as has been documented previously for the fish fauna of this seamount, possibly due to the incomplete nature of the online database
(World Porifera Database) used to assess affinities. Thirty-nine percent of the known sponge species found at Walters Shoal Seamount are widely distributed in the Indian Ocean, 35% are found exclusively within the Western Indian Ocean region, with this study representing the southernmost distribution record for several of these, and 26% have a restricted distribution around South Africa.National Research Foundatio