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Pretoria, South Africa

The University of Pretoria is a multi campus public research university located in Pretoria, the administrative and de facto capital of South Africa. The university was established in 1908 as the Pretoria campus of the Johannesburg based Transvaal University College and is the fourth South African insitution in continuous operation to be awarded university status. Wikipedia.

Jacobs J.P.,University of Pretoria
IEEE Transactions on Antennas and Propagation | Year: 2012

The modeling of microwave antennas and devices typically requires that non-linear input-output mappings be determined between a set of variable parameters (such as geometry dimensions and frequency), and the corresponding scattering parameter(s). Support vector regression (SVR) employing an isotropic Gaussian kernel has been widely used for such tasks; this kernel has one tunable hyperparameter that can be optimized (along with the penalty constant $C$) using a standard procedure that involves a parameter grid search combined with cross-validation. The isotropic kernel however suffers from limited expressiveness, and might provide inadequate predictive accuracy for nonlinear mappings that involve multiple tunable input variables. The present study shows that Bayesian support vector regression using the inherently more flexible Gaussian kernel with automatic relevance determination (ARD) is eminently suitable for highly non-linear modeling tasks, such as the input reflection coefficient magnitude S-{11}\vert$ of broadband and ultrawideband antennas. The Bayesian framework enables efficient training of the multiple kernel ARD hyperparametersa task that would be computationally infeasible for the grid search/cross-validation approach of standard SVR. © 2012 IEEE. Source

Eriksson P.G.,University of Pretoria | Condie K.C.,New Mexico Institute of Mining and Technology
Gondwana Research | Year: 2014

The ca. 2.45-2.0. Ga supracratonic record of six cratonic terranes (Superior Province, Hearne Domain, Fennoscandian crustal segment, and São Francisco, Pilbara and Kaapvaal cratons) is investigated. A <~2415-2420 basal unconformity appears pervasive, floored by basement lithologies for the three "Kenorland-related" terranes (Superior, Hearne and Fennoscandian) and by passive margin chemical sedimentary platform deposits for the apparently "non-amalgamated" cratons. Palaeosols are locally associated with this unconformity, and glacigenic lithologies, for all of the "non-amalgamated" cratons as well as for Superior. A relatively complete sedimentary record is recorded for the three Kenorland supercontinent terranes, including at least two glacial events, whereas hiatuses characterise the Pilbara and São Francisco cratons, with an incomplete record for Kaapvaal. Evidence for geodynamic reactivation at ca. 2.2. Ga includes widespread mafic dykes and volcanics, orogenies in Pilbara and São Francisco, glaciation in Kaapvaal and Pilbara, and significant transgressions thereafter on many of the cratonic terranes. While the overall ca. 2.45-2.2. Ga records studied here are at least compatible with the postulated global magmatic slowdown of Condie et al. (2009), distinct differences between the records associated with "Kenorland-related" and "non-amalgamated" cratons might reflect thermal subsidence and associated sedimentation accompanying the slowdown for the former group (where thermal blanketing likely played a role), while elevated freeboard and concomitant erosive regimes accompanied the inferred slowdown for the latter group. © 2012 International Association for Gondwana Research. Source

Du Plessis C.,University of Pretoria
Building Research and Information | Year: 2012

The concept of regenerative design and development is situated within the broader theoretical context of sustainability. The emerging regenerative paradigm is contrasted with the two current sustainability paradigms - internationally negotiated idealistic public policy and private sector Ecological Modernization - that seek to maintain the status quo. Each of these sustainability paradigms is explained though a brief historical narrative to illustrate their response to broader social pressures, the main critiques of each and some commonalities. It is argued that the dominant sustainability paradigms are reaching the limitations of their usefulness due to their conceptual foundation in an inappropriate mechanistic worldview and their tacit support of a modernization project that prevents effective engagement with a complex, dynamic and living world. The regenerative paradigm provides an alternative that is explicitly designed to engage with a living world through its emphasis on a co-creative partnership with nature based on strategies of adaptation, resilience and regeneration. It provides a foundation for a sustainability paradigm that is relevant to an ecological worldview. © 2012 Taylor & Francis. Source

Six D.L.,University of Montana | Wingfield M.J.,University of Pretoria
Annual Review of Entomology | Year: 2011

The idea that phytopathogenic fungi associated with tree-killing bark beetles are critical for overwhelming tree defenses and incurring host tree mortality, herein called the classic paradigm (CP), has driven research on bark beetle-fungus symbiosis for decades. It has also strongly influenced our views of bark beetle ecology. We discuss fundamental flaws in the CP, including the lack of consistency of virulent fungal associates with tree-killing bark beetles, the lack of correspondence between fungal growth in the host tree and the development of symptoms associated with a successful attack, and the ubiquity of similar associations of fungi with bark beetles that do not kill trees. We suggest that, rather than playing a supporting role for the host beetle (tree killing), phytopathogenicity performs an important role for the fungi. In particular, phytopathogenicity may mediate competitive interactions among fungi and support survival and efficient resource capture in living, defensive trees. © 2011 by Annual Reviews. All rights reserved. Source

Inglesi R.,University of Pretoria
Applied Energy | Year: 2010

In 2008, South Africa experienced a severe electricity crisis. Domestic and industrial electricity users had to suffer from black outs all over the country. It is argued that partially the reason was the lack of research on energy, locally. However, Eskom argues that the lack of capacity can only be solved by building new power plants. The objective of this study is to specify the variables that explain the electricity demand in South Africa and to forecast electricity demand by creating a model using the Engle-Granger methodology for co-integration and Error Correction models. By producing reliable results, this study will make a significant contribution that will improve the status quo of energy research in South Africa. The findings indicate that there is a long run relationship between electricity consumption and price as well as economic growth/income. The last few years in South Africa, price elasticity was rarely taken into account because of the low and decreasing prices in the past. The short-run dynamics of the system are affected by population growth, too. After the energy crisis, Eskom, the national electricity supplier, is in search for substantial funding in order to build new power plants that will help with the envisaged lack of capacity that the company experienced. By using two scenarios for the future of growth, this study shows that the electricity demand will drop substantially due to the price policies agreed - until now - by Eskom and the National Energy Regulator South Africa (NERSA) that will affect the demand for some years. © 2009 Elsevier Ltd. All rights reserved. Source

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