Center for Scientific and Industrial Research

South Africa

Center for Scientific and Industrial Research

South Africa
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Lain L.R.,University of Cape Town | Bernard S.,University of Cape Town | Bernard S.,Center for Scientific and Industrial Research | Matthews M.W.,University of Cape Town | Matthews M.W.,CyanoLakes Pty Ltd.
Optics Express | Year: 2017

The accurate description of a water body's volume scattering function (VSF), and hence its phase functions, is critical to the determination of the constituent inherent optical properties (IOPs), the associated spectral water-leaving reflectance, and consequently the retrieval of phytoplankton functional type (PFT) information. The equivalent algal populations (EAP) model has previously been evaluated for phytoplankton-dominated waters, and offers the ability to provide phytoplankton population-specific phase functions, unveiling a new opportunity to further understanding of the causality of the PFT signal. This study presents and evaluates the wavelength dependent, spectrally variable EAP particle phase functions and the subsequent effects on water-leaving reflectance. Comparisons are made with frequently used phase function approximations e.g. the Fournier Forand formulation, as well as with phase functions inferred from measured VSFs in coastal waters. Relative differences in shape and magnitude are quantified. Reflectance modelled with the EAP phase functions is then compared against measured reflectance data from phytoplankton-dominated waters. Further examples of modelled phytoplankton-dominated waters are discussed with reference to choice of phase function for two PFTs (eukaryote and prokaryote) across a range of biomass. Finally a demonstration of the sensitivity of reflectance due to the choice of phase function is presented. The EAP model phase functions account for both spectral and angular variability in phytoplankton backscattering i.e. they display variability which is both spectral and shape-related. It is concluded that phase functions modelled in this way are necessary for investigating the effects of assemblage variability on the ocean colour signal, and should be considered for model closure even in relatively low scattering conditions where phytoplankton dominate the IOPs. © 2017 Optical Society of America.

Alexandre K.B.,South African National Institute for Communicable Diseases | Gray E.S.,South African National Institute for Communicable Diseases | Pantophlet R.,Simon Fraser University | Moore P.L.,South African National Institute for Communicable Diseases | And 5 more authors.
Journal of Virology | Year: 2011

The glycans on HIV-1 gp120 play an important role in shielding neutralization-sensitive epitopes from antibody recognition. They also serve as targets for lectins that bind mannose-rich glycans. In this study, we investigated the interaction of the lectin griffithsin (GRFT) with HIV-1 gp120 and its effects on exposure of the CD4-binding site (CD4bs). We found that GRFT enhanced the binding of HIV-1 to plates coated with anti-CD4bs antibodies b12 and b6 or the CD4 receptor mimetic CD4-IgG2. The average enhancement of b12 or b6 binding was higher for subtype B viruses than for subtype C, while for CD4-IgG2, it was similar for both subtypes, although lower than observed with antibodies. This GRFT-mediated enhancement of HIV-1 binding to b12 was reflected in synergistic neutralization for 2 of the 4 viruses tested. The glycan at position 386, which shields the CD4bs, was involved in both GRFT-mediated enhancement of binding and neutralization synergism between GRFT and b12. Although GRFT enhanced CD4bs exposure, it simultaneously inhibited ligand binding to the coreceptor binding site, suggesting that GRFT-dependent enhancement and neutralization utilize independent mechanisms. This study shows for the first time that GRFT interaction with gp120 exposes the CD4bs through binding the glycan at position 386, which may have implications for how to access this conserved site. © 2011, American Society for Microbiology.

Lain L.R.,University of Cape Town | Bernard S.,University of Cape Town | Bernard S.,Center for Scientific and Industrial Research | Evers-King H.,University of Cape Town
Optics Express | Year: 2014

There is a pressing need for improved bio-optical models of high biomass waters as eutrophication of coastal and inland waters becomes an increasing problem. Seasonal boom conditions in the Southern Benguela and persistent harmful algal production in various inland waters in Southern Africa present valuable opportunities for the development of such modelling capabilities. The phytoplankton-dominated signal of these waters additionally addresses an increased interest in Phytoplankton Functional Type (PFT) analysis. To these ends, an initial validation of a new model of Equivalent Algal Populations (EAP) is presented here. This paper makes a first order comparison of two prominent phytoplankton Inherent Optical Property (IOP) models with the EAP model, which places emphasis on explicit bio-physical modelling of the phytoplankton population as a holistic determinant of inherent optical properties. This emphasis is shown to have an impact on the ability to retrieve the detailed phytoplankton spectral scattering information necessary for PFT applications and to successfully simulate reflectance across wide ranges of physical environments, biomass, and assemblage characteristics. © 2014 Optical Society of America.

Dharmadhikari A.S.,Harvard University | Basaraba R.J.,Colorado State University | Van Der Walt M.L.,South African Medical Research Council | Weyer K.,WHO | And 8 more authors.
Tuberculosis | Year: 2011

A natural TB infection model using guinea pigs may provide useful information for investigating differences in transmission efficiency and establishment of active disease by clinical TB strains in a highly susceptible host under controlled environmental conditions. We sought to examine the capacity of naturally transmitted multidrug-resistant Mycobacterium tuberculosis to establish infection and produce active disease in guinea pigs. Guinea pigs were continuously exposed for 4 months to the exhaust air of a 6-bed multidrug-resistant tuberculosis inpatient hospital ward in South Africa. Serial tuberculin skin test reactions were measured to determine infection. All animals were subsequently evaluated for histologic disease progression at necropsy. Although 75% of the 362 exposed guinea pigs had positive skin test reactions [≥6 mm], only 12% had histopathologic evidence of active disease. Reversions (≥6 mm change) in skin test reactivity were seen in 22% of animals, exclusively among those with reactions of 6-13 mm. Only two of 86 guinea pigs with reversion had histological evidence of disease compared to 47% (31/66) of guinea pigs with large, non-reverting reactions. Immunosuppression of half the guinea pigs across all skin test categories did not significantly accelerate disease progression. In guinea pigs that reverted a skin test, a second positive reaction in 27 (33%) of them strongly suggested re-infection due to ongoing exposure. These results show that a large majority of guinea pigs naturally exposed to human-source strains of multidrug-resistant tuberculosis became infected, but that many resolved their infection and a large majority failed to progress to detectable disease. © 2011 Elsevier Ltd. All rights reserved.

Rambau G.,Tshwane University of Technology | Popoola P.,Tshwane University of Technology | Mathebula T.,Tshwane University of Technology | Mathebula T.,Center for Scientific and Industrial Research | And 2 more authors.
ICALEO 2012 - 31st International Congress on Applications of Lasers and Electro-Optics | Year: 2012

Light metals have found intense use in the automobile industry, however, the surface properties of aluminium is still unsatisfactory for many purposes. The corrosion performance of aluminium laser alloyed with a combination of zirconium and stellite-6 powders were investigated. Laser surface alloying was carried out using Nd: YAG solid state laser. Characterization of the resultant microstructure was carried out by optical and scanning electron microscopes. Experimental results revealed novel properties due to the microstructure evolved. The addition of these powders to aluminium solid solution retarded the ingress of destructive chloride ions onto the aluminium matrix. This action increased the electrode potential; decreased the anodic activation and promoted the formation of stable passivation on the surface of aluminium. Significant increase in the corrosion performance of the substrate was achieved.

Rambau T.G.,Tshwane University of Technology | Popoola A.P.I.,Tshwane University of Technology | Loto C.A.,Tshwane University of Technology | Mathebula T.,Tshwane University of Technology | And 2 more authors.
International Journal of Electrochemical Science | Year: 2013

Excellent display of surface dependent properties by metals and alloys are pre-requisite for efficient engineering operations in the industry. In this work, AA1200 laser alloyed surface was investigated for its hardness, wear and corrosionbehaviour at different laser processing conditions. Stellite-6 and zirconium powders were used as ceramic and metallic reinforcement materials respectively; these were chosen in order that all required surface properties are improved. A continuous wave Rofin Sinar Nd:YAG laser emitting 1.064 μm wavelength was utilized for the fabrication process. The microstructures of the developed composites were characterized by optical (OM) and scanning electron microscopes (SEM/EDS). Equally, x-ray diffractometer (XRD) was used to identify the phases present. The addition of alloying elements increased the hardness, wear and corrosion resistances. The improvement of these properties was attributed to the formation of new phases and the microstructures evolved on the surface of the laser alloyed aluminium AA1200. © 2013 by ESG.

Adebiyi D.I.,Tshwane University of Technology | Fedotova T.,Tshwane University of Technology | Pityana S.L.,Tshwane University of Technology | Pityana S.L.,Center for Scientific and Industrial Research | Popoola A.P.I.,Tshwane University of Technology
International Journal of Physical Sciences | Year: 2011

The improvement in hardness of X12CrNiMo martensitic stainless steel laser alloyed with 99.9% pure titanium carbide, stellite 6 and two cases of premixed ratio of titanium carbide and stellite 6 [TiC (30 wt.%)- stellite 6 (70 wt.%) and TiC (70 wt.%)- stellite 6 (30 wt.%)] were examined. The powders were supplied through a pneumatically driven powder delivery system with a 4.4 kW continuous wave (CW) Nd:YAG laser. The microstructures of the alloyed zones were investigated by x-ray diffractometer (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The alloyed zones obtained by alloying with premixed ratio of 70 wt.% TiC and 30 wt.% stellite 6 were free from dilution and crack that were in those of pure stellite 6. A significant increase in Vickers hardness value compared with that of the substrate was achieved with the powders and their premixed ratios; 608 HVN for TiC and 503 HVN for stellite 6, 763 HVN for 30 wt.% TiC and 1025 HVN for 70 wt.% TiC. © 2011 Academic Journals.

Popoola A.P.,Tshwane University of Technology | Pityana S.,Tshwane University of Technology | Pityana S.,Center for Scientific and Industrial Research
29th International Congress on Applications of Lasers and Electro-Optics, ICALEO 2010 - Congress Proceedings | Year: 2010

The present work deals with the development of Aluminium metal matrix composite (MMC) using Ti2 reinforcement. The aim is to improve the microhardness property of the substrate. The surface of the aluminium was sand blasted to improve its laser energy absorption and simultaneous deposition of the ceramic powder onto the surface of the substrate was carried out using a Rofin Nd: YAG laser with an Argon shield environment to prevention oxidation. The laser processing parameters were varied. The characterization of the alloyed surfaces MMC was carried out by Optical Microscopy (OPM), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The microstructure of the alloyed layer shows that the ceramic powder was well dispersed within the Al-matrix. Good metallurgical bonds were evident. Microhardness measurements were carried out. The maximum depth attained was 1.17 mm. There was a microhardness increase from that of substrate which is 24±0.4 HV to that of the MMC layer 58.0±0.2 HV.

Adebiyi D.I.,Tshwane University of Technology | Popoola A.P.I.,Tshwane University of Technology | Pityana S.L.,Tshwane University of Technology | Pityana S.L.,Center for Scientific and Industrial Research
Optics and Laser Technology | Year: 2014

Multiple track laser alloying is characterised by additional heat treatment and differences in the amount of powder deposited at the overlap regions. These result in different microstructural and phase evolution at these regions, which are not obtainable in the single tracks. X12CrNiMo steel has been laser alloyed with TiC using a 4.4 kW continuous wave (CW) Nd:YAG laser. The process parameters were first optimised after which they were kept constant for overlap ratios of 50% and 75%. The depths of the alloyed zone, the mcrostructural evolution, metallurgical structures and compositions are different for the 50% and 75% overlap. The 75% overlap sample has an alloying depth of 4233 μm (about two times that of the 50% overlap). The XRD of the 50% overlap sample reveals the presence of complex carbides, which are absent in that of the 75% overlap. Although both overlap samples have retained martensite, diffractographs show that the martensite of the 75% is richer in carbide. These are attributed to differences in powder catchment, heat build-up and depth of alloying. ©2014 Published by Elsevier Ltd.

Cundill G.,University of South Africa | Cundill G.,Center for Scientific and Industrial Research | Fabricius C.,University of South Africa
Ecology and Society | Year: 2010

The governance outcomes of natural resource co-management have been neither systematically monitored nor rigorously assessed. We identified system attributes and key variables that could form the basis for monitoring the governance dimension of adaptive co-management. A methodology for collaboratively monitoring these system attributes and key variables was tested in four localities in South Africa. Our results suggest that creating the conditions that facilitate self-organization, and particularly cross-scale institutional linkages, is the major challenge facing attempts to initiate adaptive co-management. Factors requiring greater attention include community perceptions of support from outside agencies, access to long-term funding for adaptive decision making, and access to reliable information about changes in natural resources and legal options for the formation of decision-making bodies. Long-term and well-funded social facilitation is key to achieving this. © 2010 by the author(s).

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