Research Outputs

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Analysing the disciplinary power of proactive monitoring bodies
(Emerald, 2025-07) Flowers, Kevin; van Zijl, Wayne; Ram, Jaywant; Warren Maroun
Purpose – The important role of regulatory monitoring bodies in enhancing financial statement quality is increasingly being studied. Prior research focuses on developed economies and often adopts a relatively unproblematic regulatory perspective to explain how these bodies foster compliance. This paper adopts a more critical approach by investigating the forces and processes at work by utilising a Foucauldian disciplinary power perspective on the proactive monitoring unit (PMU) regulating South African listed companies on the Johannesburg Stock Exchange. Design/methodology/approach – Seventeen semi-structured, open-ended interviews were conducted with expert financial statement preparers, auditors, regulators and academics. Open, axial and selective coding were used to analyse the interview data. Findings – The PMU isindicative of an enclosure mechanism that monitors and controlsthe financial reporting space of listed companies. Consequently, preparers and auditors resemble well-trained individuals who follow the PMU’s guidance without question. The PMU’s constant gaze, combined with the negative reputational impact of an adverse review for individual preparers and auditors, results in them presenting their financial statements in conformity with the PMU’sinterpretation. However, complete panoptic control is not achieved, as there is some resistance. Originality/value – This is one of the first studies to examine how an external monitoring body, the PMU, functions in a real-world setting. There is a limited understanding of what drives companies to comply with monitoring bodies that do not enjoy the direct force of law. This paper makes use of the novel Foucauldian framework to contribute towards understanding the disciplinary power that may be applied by the PMU.
Testing the suitability of portable X-Ray Fluorescence (pXRF) analysis of dried herbarium specimens to detect Ni hyperaccumulators in South Africa
(Elsevier, 2023-07) Balkwill, Kevin; Samojedny Jr. Thomas J.; Rajakaruna, Nishanta; Siebert, Stefan J.
Metal hyperaccumulators accumulate particular metals or metalloids in their leaves to concentrations hundreds or thousands of times greater than is normal for most plants. Globally, Ni is the most often hyperaccumulated metal, with 532 hyperaccumulator species documented to date. Hyperaccumulators have attracted much attention as potential candidates for green technologies, including phytoremediation and agromining. In South Africa, six serpentinite-associated plants in the genera Berkheya and Senecio hyperaccumulate Ni (to > 0.1% of leaf tissue dry weight). It is surprising that only six of about 70 Berkheya and 290 Senecio species native to South Africa hyperaccumulate Ni, given about ∼10–20% of taxa from each genus occur on serpentinite. While it is costly and time consuming to field collect and chemically analyze leaves of all species in these genera, a novel method (portable X-Ray Fluorescence or pXRF analysis of herbarium specimens) allows for rapid (100 s of specimens/day) and non-destructive measurement of Ni in dry herbarium specimens. We tested the accuracy of this approach on known Ni hyperaccumulators vouchered at two South African herbaria (C.E. Moss Herbarium (J) of the University of the Witwatersrand and A.P. Goossens Herbarium (PUC) from North-West University). While the absolute concentrations of Ni determined by ICP-MS and pXRF were not always directly in agreement, we had 100% success in confirming those that were known to hyperaccumulate Ni with those that did not. We propose pXRF as a cheap, effective, and efficient approach to rapidly screen herbarium specimens across South Africa to discover additional metal hyperaccumulators for much-needed remediation purposes.
The valorisation of platinum group metals from flotation tailings: A review of challenges and opportunities
(Elsevier, 2023-06) Gibson, Borbor A.K.K.; Nwaila, Glen; Manzi, Musa; Ndlovu, Sehliselo; Ghorbani, Yousef; Petersen, Jochen
Flotation tailings from South Africa’s platinum group minerals (PGM) represent complex polymetallic orebodies comprising a low-grade platinum group elements (PGE) content and complex mineralogical composition. Nevertheless, given the valuable mineral potential in the tailings, it is understandable that the substantial historic tailings deposits and sizeable annual production volume from primary processes represent a potential secondary resource. For several decades, valorising the PGM tailing materials received very little interest due to limitations associated with extractive metallurgical technology to achieve economically viable PGE extraction. The early 21st century saw the coming online of technologies, including but not limited to ultrafine grinding, suitable to meet challenges in primary metallurgical treatment processes to recover valuable minerals from ultrafine particle fractions, which could not otherwise be recovered. More so, such processes were critical in improving the liberation of partially liberated particles without compromising additional ultrafine generation. These technologies led to the development of re-treatment pilot tests and subsequent industrial re-treatment recovery processes. The current industrial re-treatment approach – via tertiary scavenging flotation circuits – renders profit in small increments up to 1 ~ 2% additional recovery relative to the primary plant head grade. These small increments relate to about ~12–30% PGE recovery of the feed grade to the re-treatment circuit, thereby enhancing the primary plant’s overall economics as well as aiding the supply of critical metals to meet global demands. With a focus on South Africa, this review provides an overview of (a) the current and future drivers of the precious metals global demand; (b) proffers discussion on the PGM characteristic mineralogy and the metallurgical value chain; (c) relates the parent orebodies (“reefs”) mineral characteristics to the inherent processed tailings; (d) estimates the economic potential these massive processed waste materials contain, (e) provides an overview of existing technologies that are industrially used in tailing re-treatment plants; and (f) outlines a comprehensive understanding of the nature of value minerals rejection to tailings.
Performance of the Biomark HD real-time qPCR System (Fluidigm) for the detection of nasopharyngeal bacterial pathogens and Streptococcus pneumoniae typing
(Nature Research, 2019-04) Olwagen, Courtney P.; Adrian, Peter V.; Madhi, Shabir A.
Traditional qPCR assays for pneumococcal detection and serotype characterization require large sample volume, is expensive and labor intensive. We aimed to develop a quantitative nanofuidic Fluidigm assay to overcome some of these shortcomings. A quantitative Fluidigm assay was established to detect 11 bacterial pathogens, 55 pneumococcal serotypes and 6 serotypes of H. infuenzae. The Fluidigm assay results were compared to conventional qPCR and culture. All reactions in the Fluidigm assay efectively amplifed their respective targets with high sensitivity and specifcity compared to qPCR. There was excellent concordance between qPCR and Fluidigm for detection of carriage prevalence (kappa>0.75) and density (Rho>0.95). Fluidigm identifed an additional 7 (4.2%) serotypes over those detected by qPCR. There was a modest concordance between culture and Fluidigm for the majority of reactions detecting S. pneumoniae serotypes/serogroups (kappa>0.6), with Fluidigm identifying an additional 113 (39.1%) serotypes. Discordant results between the three methods were associated with a low carriage density. The Fluidigm assay was able to detect common pneumococcal serotypes, H. infuenzae serotypes, and other common nasopharyngeal bacterial organisms simultaneously. Deployment of this assay in epidemiological studies could provide better insight into the efect of PCV immunization on the nasopharyngeal microbiota in the community
Generalized hot attractors
(Springer, 2019-03) Goldstein, Kevin; Jejjala, Vishnu; Mashiyane, James Junior; Nampuri Suresh
Non-extremal black holes are endowed with geometric invariants related to their horizon areas. We extend earlier work on hot attractor black holes to higher dimensions and add a scalar potential. In addition to the event and Cauchy horizons, when we complexify the radial coordinate, non-extremal black holes will generically have other horizons as well. We prove that the product of all of the horizon areas is independent of variations of the asymptotic moduli further generalizing the attractor mechanism for extremal black holes. In the presence of a scalar potential, as typically appears in gauged supergravity, we find that the product of horizon areas is not necessarily the geometric mean of the extremal area, however. We outline the derivation of horizon invariants for stationary backgrounds.
Characterization of putative DD-carboxypeptidase-encoding genes in Mycobacterium smegmatis
(Nature Research, 2019-03) Ealand, Christopher S.; Asmal, Rukaya; Mashigo, Lethabo; Campbell, Lisa; Kana, Bavesh D.
Penicillin binding proteins (PBPs) are the target of numerous antimicrobial agents that disrupt bacterial cell wall synthesis. In mycobacteria, cell elongation occurs through insertion of nascent cell wall material in the sub-polar region, a process largely driven by High Molecular Weight PBPs. In contrast, the function of DD-carboxypeptidases (DD-CPases), which are Low Molecular Weight Class 1C PBPs, in mycobacteria remains poorly understood. Mycobacterium smegmatis encodes four putative DD-CPase homologues, which display homology to counterparts in Escherichia coli. Herein, we demonstrate that these are expressed in varying abundance during growth. Deletion of MSMEG_1661, MSMEG_2433 or MSMEG_2432, individually resulted in no defects in growth, cell morphology, drug susceptibility or spatial incorporation of new peptidoglycan. In contrast, deletion of MSMEG_6113 (dacB) was only possible in a merodiploid strain expressing the homologous M. tuberculosis operon encoding Rv3627c (dacB), Rv3626c, Rv3625c (mesJ) and Rv3624c (hpt), suggestive of essentiality. To investigate the role of this operon in mycobacterial growth, we depleted gene expression using anhydrotetracyclineresponsive repressors and noted reduced bipolar peptidoglycan synthesis. These data point to a possible role for this four gene operon, which is highly conserved across all mycobacterial species, in regulating spatial localization of peptidoglycan synthesis.
A tunable Josephson platform to explore many-body quantum optics in circuit-QED
(Nature Research, 2019-02) Snyman, Izak; Martínez, Javier Puertas; Léger, Sébastien; Gheeraert, Nicolas; Dassonneville, Rémy; Planat, Luca; Foroughi, Farshad; Krupko, Yuriy; Buisson, Olivier; Naud, Cécile; Hasch-Guichard, Wiebke; Florens, Serge; Roch, Nicolas
The interaction between light and matter remains a central topic in modern physics despite decades of intensive research. Coupling an isolated emitter to a single mode of the electromagnetic field is now routinely achieved in the laboratory, and standard quantum optics provides a complete toolbox for describing such a setup. Current efforts aim to go further and explore the coherent dynamics of systems containing an emitter coupled to several electromagnetic degrees of freedom. Recently, ultrastrong coupling to a transmission line has been achieved where the emitter resonance broadens to a significant fraction of its frequency, and hybridizes with a continuum of electromagnetic (EM) modes. In this work we gain significantly improved control over this regime. We do so by combining the simplicity and robustness of a transmon qubit and a bespoke EM environment with a high density of discrete modes, hosted inside a superconducting metamaterial. This produces a unique device in which the hybridisation between the qubit and many modes (up to ten in the current device) of its environment can be monitored directly. Moreover the frequency and broadening of the qubit resonance can be tuned independently of each other in situ. We experimentally demonstrate that our device combines this tunability with ultrastrong coupling and a qubit nonlinearity comparable to the other relevant energy scales in the system. We also develop a quantitative theoretical description that does not contain any phenomenological parameters and that accurately takes into account vacuum fluctuations of our large scale quantum circuit in the regime of ultrastrong coupling and intermediate non-linearity. The demonstration of this new platform combined with a quantitative modelling brings closer the prospect of experimentally studying many-body effects in quantum optics. A limitation of the current device is the intermediate nonlinearity of the qubit. Pushing it further will induce fully developed many-body effects, such as a giant Lamb shift or nonclassical states of multimode optical fields. Observing such effects would establish interesting links between quantum optics and the physics of quantum impurities
Spin-3/2 dark matter in a simple t-channel model
(Springer Open, 2018-11) Khojali, Mohammed Omer; Kumar, Mukesh; Cornell, Alan S.; Goyal, Ashok
We consider a spin-3/2 fermionic dark matter (DM) particle interacting with the Standard Model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple t-channel model. It is found that for the vector mediator case, almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. No such bounds exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The collider bounds put a lower limit on the allowed DM masses.
Dimethylformamide is a novel nitrilase inducer in Rhodococcus rhodochrous
(Springer, 2018-09) Chhiba-Govindjee, V. P.; Brady, D.; Mathiba, K.; van der Westhuyzen, C. W.; Steenkamp, P.; Rashamuse, J. K.; Stoychev, S.
Nitrilases are of commercial interest in the selective synthesis of carboxylic acids from nitriles. Nitrilase induction was achieved here in three bacterial strains through the incorporation of a previously unrecognised and inexpensive nitrilase inducer, dimethylformamide (DMF), during cultivation of two Rhodococcus rhodochrous strains (ATCC BAA-870 and PPPPB BD1780), as well as a closely related organism (Pimelobacter simplex PPPPB BD-1781). Benzonitrile, a known nitrilase inducer, was ineffective in these strains. Biocatalytic product profiling, enzyme inhibition studies and protein sequencing were performed to distinguish the nitrilase activity from that of sequential nitrile hydratase-amidase activity. The expressed enzyme, a 40-kDa protein with high sequence similarity to nitrilase protein Uniprot Q-03217, hydrolyzed 3-cyanopyridine to produce nicotinic acid exclusively in strains BD-1780 and BD-1781. These strains were capable of synthesising both the vitamin nicotinic acid as well as β-amino acids, a compound class of pharmaceutical interest. The induced nitrilase demonstrated high enantioselectivity (>99%) in the hydrolysis of 3-amino-3-phenylpropanenitrile to the corresponding carboxylic acid.
Free field primaries in general dimensions: counting and construction with rings and modules
(Springer, 2018-08) de Mello Koch, Robert
We define lowest weight polynomials (LWPs), motivated by so(d, 2) representation theory, as elements of the polynomial ring over d × n variables obeying a system of first and second order partial differential equations. LWPs invariant under Sn correspond to primary fields in free scalar field theory in d dimensions, constructed from n fields. The LWPs are in one-to-one correspondence with a quotient of the polynomial ring in d × (n − 1) variables by an ideal generated by n quadratic polynomials. The implications of this description for the counting and construction of primary fields are described: an interesting binomial identity underlies one of the construction algorithms. The product on the ring of LWPs can be described as a commutative star product. The quadratic algebra of lowest weight polynomials has a dual quadratic algebra which is non-commutative. We discuss the possible physical implications of this dual algebra.

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