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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 | 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. Source

Popoola P.A.I.,Tshwane University of Technology | Pityana S.L.,Tshwane University of Technology | Pityana S.L.,Center for Scientific and Industrial Research | Fedotova T.,Tshwane University of Technology | Popoola O.M.,Tshwane University of Technology
Materials Science- Poland | Year: 2011

As the reports in the literature regarding corrosion performance of Al/TiB 2 MMC are rather contradictory, the optimization of laser surface alloying parameters for these composite coatings seems to be necessary. The characterization of the MMC was carried out by optical microscopy (OM), scanning electron microscopy (SEM/EDS) and x-ray diffraction (XRD). Partial melting of the alloying powder occurred and the chemical reactions with the α-Al in the matrix led to the formation of AlTi and AlB 2 phases. Eutectics of TiB 2/Al and TiB 2/Ti were observed. The results of the tests indicate that TiB 2 reinforcement does not give significant increase in microhardness of aluminium. The corrosion resistance of a single laser trackline MMC in a 3.65 % NaCl solution was improved, especially for the sample produced at high scan speed, with the lowest volume fraction of TiB 2 particles. © Wroclaw University of Technology. Source

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. Source

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. Source

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). Source

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