Faculty of Science (Research Outputs)

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A Technique to Solve a Parabolic Equation by Point Symmetries that Incorporate Initial Data
(Springer, 2025-03) Jamal, Sameerah; Maphanga, Rivoningo
In this paper, we show how transformation techniques coupled with a convolution integral can be used to solve a generalised option-pricing model, including the Black–Scholes model. Such equations are parabolic and the special convolutions are extremely involved as they arise from an initial value problem. New symmetries are derived to obtain solutions through an application of the invariant surface condition. The main outcome is that the point symmetries are effective in producing exact solutions that satisfy a given initial condition, such as those represented by a call-option.
Accurate hyperspectral imaging of mineralised outcrops: An example from lithium-bearing pegmatites at Uis, Namibia
(Elsevier Inc, 2021) Booysen, René; Nex, Paul A.M.; Lorenz, Sandra; Thiele, Samuel T.; Fuchsloch, Warrick C.; Marais, Timothy; Gloaguen, Richard
Efficient, socially acceptable and rapid methods of exploration are required to discover new deposits and enable the green energy transition. Sustainable exploration requires a combination of innovative thinking and new technologies. Hyperspectral imaging (HSI) is a rapidly developing technology and allows for fast and systematic mineral mapping, facilitating exploration of the Earth’s surface at various scales on a variety of platforms. Newly available sensors allow data capture over a wide spectral range, and provide information about the abundance and spatial location of ore and pathfinder minerals in drill-core, hand samples and outcrops with mm to cm precision. Conversely, the complex geometries of the imaged surfaces affect the spectral quality and signal-to-noise ratio (SnR) of HSI data at these very narrow spatial samplings. Additionally, the complex mineral assemblages found in hydrothermally altered ore deposits can make interpretation of spectral results a challenge. In this contribution, we propose an innovative approach that integrates multiple sensors and scales of data acquisition to help disentangle complex mineralogy associated with lithium and tin mineralisation in the Uis pegmatite complex, Namibia. We train this method using hand samples and finally produce a three-dimensional (3D) point cloud for mapping lithium mineralisation in the open pit. We were able to identify and map lithium-bearing cookeite and montebrasite at outcrop scale. The accuracy of the approach was validated by drill-core data, XRD analysis and LIBS measurements. This approach facilitates efficient mapping of complex terrains, as well as important monitoring and optimisation of ore extraction. Our method can easily be adapted to other minerals relevant to the mining industry.
Analysis of urban sprawl dynamics using machine learning, CA-Markov chain, and the Shannon entropy model: a case study in Mbombela City, South Africa
(SpringerOpen, 2024) Mhangara, Paidamwoyo; Gidey, Eskinder; Rabia Manjoo
Over half of the world’s population resides in urban areas. We anticipate that this pattern will become more evident, notably in South Africa. Therefore, research on urban spirals, both past and projected, is necessary for efficient urban land use planning and management. This study aims to assess the spatio-temporal urban sprawl dynamics from 2003 to 2033 in Mbombela, South Africa. We employed robust approaches such as machine learning, the cellular automata-Markov chain, and the Shannon entropy model to look at how urban sprawl changes over time using both the Landsat 4–5 Thematic Mapper and the 8 Operational Land Imagers. We conducted this study to bridge the gaps in existing research, which primarily focuses on past and current urban growth trends rather than future trends. The findings indicated that the coverage of built-up areas and vegetation has expanded by 1.98 km2 and 13.23 km2 between the years 2003 and 2023. On the other hand, the amount of land continues to decrease by -12.56 km2 and − 2.65 km2 annually, respectively. We anticipate an increase in the built-up area and vegetation to a total of 7.60 km2 and 0.57 km2, respectively, by the year 2033. We anticipate a total annual decline of -7.78 km2 and − 0.39 km2 in water bodies and open land coverage, respectively. This work has the potential to assist planners and policymakers in improving sustainable urban land-use planning.
Assessing runs of Homozygosity: a comparison of SNP Array and whole genome sequence low coverage data
(BMC, 2018) Ceballos, Francisco C.; Hazelhurst, Scott; Ramsay, Michèle
Background: Runs of Homozygosity (ROH) are genomic regions where identical haplotypes are inherited from each parent. Since their first detection due to technological advances in the late 1990s, ROHs have been shedding light on human population history and deciphering the genetic basis of monogenic and complex traits and diseases. ROH studies have predominantly exploited SNP array data, but are gradually moving to whole genome sequence (WGS) data as it becomes available. WGS data, covering more genetic variability, can add value to ROH studies, but require additional considerations during analysis. Results: Using SNP array and low coverage WGS data from 1885 individuals from 20 world populations, our aims were to compare ROH from the two datasets and to establish software conditions to get comparable results, thus providing guidelines for combining disparate datasets in joint ROH analyses. By allowing heterozygous SNPs per window, using the PLINK homozygosity function and non-parametric analysis, we were able to obtain non-significant differences in number ROH, mean ROH size and total sum of ROH between data sets using the different technologies for almost all populations. Conclusions: By allowing 3 heterozygous SNPs per ROH when dealing with WGS low coverage data, it is possible to establish meaningful comparisons between data using SNP array and WGS low coverage technologies.
Batch and semi-continuous fermentation with Parageobacillus thermoglucosidasius DSM 6285 for H2 production
(BMC, 2025) de Maayer, Pieter; Ardila, Magda S.; Aliyu, Habibu; Neumann, Anke
Background Parageobacillus thermoglucosidasius is a facultatively anaerobic thermophile that is able to produce hydrogen (H2) gas from the oxidation of carbon monoxide through the water–gas shift reaction when grown under anaerobic conditions. The water–gas shift (WGS) reaction is driven by a carbon monoxide dehydrogenase– hydrogenase enzyme complex. Previous experiments exploring hydrogenogenesis with P. thermoglucosidasius have relied on batch fermentations comprising defned media compositions and gas atmospheres. This study evaluated the efects of a semi-continuous feeding strategy on hydrogenogenesis. Results A batch and two semi-continuous fermentations, with feeding of the latter fresh media (with glucose) in either 24 h or 48 h intervals were undertaken and H2 production, carbon monoxide dehydrogenase (CODH) activity, and metabolite consumption/production were monitored throughout. Maximum H2 production rates (HPR) of 0.14 and 0.3 mmol min−1, were observed for the batch and the semi-continuous fermentations, respectively. Daily feeding attained stable H2 production for 7 days, while feeding every 48 h resulted in high variations in H2 production. CODH enzyme activity correlated with H2 production, with a maximum of 1651 U mL−1 on day 14 with the 48 h feeding strategy, while CODH activity remained relatively constant throughout the fermentation process with the 24 h feeding strategy. Conclusions The results emphasize the signifcance of a semi-continuous glucose-containing feed for attaining stable hydrogen production with P. thermoglucosidasius. The semi-continuous fermentations achieved a 46% higher HPR than the batch fermentation. The higher HPRs achieved with both semi-continuous fermentations imply that this approach could enhance the biohydrogen platform. However, optimizing the feeding interval is pivotal to ensuring stable hydrogen production.
Chemical analysis of low grade gold from mine tailings after size fractionation and acid digestion using reverse aqua regia
(Nature Research, 2025-03) Chimuka, Luke; Tshilongo, James; Mashale, Kedibone Nicholine; Sehata, James; Ntsasa, Napo Godwill
The growing interest in reprocessing mine tailings for gold recovery requires a suitable quantification method that is accurate, rapid, and not harsh to the environment. Acid digestion is often used to determination of gold; however, it often faces the challenge of incomplete digestion due to the presence of minerals such as quartz, and homogeneity is compromised due to small sample masses, which can result in low bias. This study investigated a shorter acid digestion method employing reverse aqua regia, both in the presence and absence of hydrofluoric acid. Before digestion, the sample was subjected to gold depot analysis, which showed that 78% was free-milling gold and that only 0.8% was associated with pyrite, increasing the chances of accurate quantifications. Furthermore, the size screening test showed that most of the gold could be recovered on the −38 μm screen. This proposed method provided good linearity (5–100 µg. L−1) and low detection limits (0.139–0.183 µg.kg−1). The concentrations obtained by the acid digestion was 0.258 g.t−1 with the recoveries ranging between 80% and 82%, which fit the criteria set. The method also worked well for the certified reference materials (CRM), AMIS 610 (accurate value=0.068 g.t−1) and AMIS 646 (accurate value=0.166 g.t−1), which are of a similar matrix and are also lower in grade compared to the sample. The method was also evaluated for uncertainty (±value) using the bottom-up approach, and the expanded uncertainty (k=2) was reported to be 0.258±0.092 g.t−1, which was comparable to that offered by the fire assay with the ICP‒OES finish, which was 0.28±0.10 g.t−1. This implies that the acid digestion method is suitable for quantifying gold from mine tailings without large uncertainties.
Compositions with a fixed number of inversions
(Springer, 2018-05) Knopfmacher, A.; Mays, M. E.; Wagner, S.
A composition of the positive integer n is a representation of n as an ordered sum of positive integers n = a1 + a2 + ··· + am. There are 2n−1 unrestricted compositions of n, which can be sorted according to the number of inversions they contain. (An inversion in a composition is a pair of summands {ai, aj} for which i aj .) The number of inversions of a composition is an indication of how far the composition is from a partition of n, which by convention uses a sequence of nondecreasing summands and thus has no inversions. We count compositions of n with exactly r inversions in several ways to derive generating function identities, and also consider asymptotic results.
Confocal microscopy and molecular analyses reveal anal secretory apparatus in immatures and recover transcontinental Clade of Gall Mites (Eriophyoidea) from Tamarisks
(MDPI, 2024-04) Sivu, Situngu; Chetverikov , Philipp E.; Ngubane-Ndhlovu, Nompumelelo P.; Elhalawan, Ashraf; Amrine, James
Tamarisk is an invasive evergreen shrub native to arid regions of Africa and Eurasia and is considered a weed in some countries with dry climates. The complex of gall mites from tamarisks includes fourteen species from four genera of the family Eriophyidae. We reinvestigated the type species of the genus Dicruvasates, D. tamaricis from Egypt, described D. ngubani n. sp. from Tamarix usneoides from South Africa, and revised the generic concept of Dicruvasates. This genus possesses cuticular plates marking longitudinal opisthosomal ridges typical of various phyllocoptine genera, e.g., Echinacrus. We sequenced three genes of Dicruvasates and Phyllocoptes mites from Tamarix and Echinacrus from Frangula, combined our sequences with the data from GenBank, and performed single-gene phylogenetic analyses. All analyses inferred the following: (1) a transcontinental clade Tam comprising Dicruvasates + Aceria + Phyllocoptes from Tamarix; (2) Echinacrus distantly related to Dicruvasates, suggesting the homoplastic nature of the cuticular plates on the opisthosomal ridges, and (3) polyphyly of the genera Aceria and Phyllocoptes. We also investigated partially cleared specimens of Dicruvasates under CLSM and, for the first time, visualized a well-developed anal secretory apparatus (ASA) in the immatures of gall mites, which was previously shown to be a specialized system evolved in Eriophyoidea for silk production. We hypothesize that the ASA contributes to finding nymphs by conspecific males and advocate for the importance of the future molecular biology studies of gall mite silk for developing new methods for controlling mites based on the knowledge of their ecology, behavior, and silk gene genetics.
Deep-crustal layered mafic complexes in the Mesoproterozoic oceanic-arc of the Tugela Terrane, South Africa
(Elsevier, 2025-03) Wilson, Allan H.
Layered mafic intrusions are important in understanding the generation of continental crust in oceanic arcs. The Mesoproterozoic (c. 1200 Ma) Tugela Terrane in southeast South Africa is made up of a series of thrust slices of varied rock-types purported to have been derived in oceanic arcs prior to accretion onto the southern margin of the Archean Kaapvaal Craton. They are not ophiolites. Mafic intrusions in two adjacent thrust slices are known as the Tugela Rand and Mambula Complexes. Both intrusions are intensely layered on scales of centimetres to several tens of metres but clear cyclic units are not apparent and crystal fractionation is limited indicating these were open systems with magma chamber through-flow. Tugela Rand is made up of dominantly olivine-bearing rocks ranging from dunite and pyroxenite to gabbro. In contrast, Mambula is dominantly gabbroic with only rare olivine-bearing rocks and is more evolved with layers of titaniferous-magnetite. Primary magmatic structures in both complexes include graded bedding, slumping and erosion features. Relatively high pressure of formation is indicated by the aluminous nature of the pyroxenes and corona textures by reaction between plagioclase and olivine. Chromitites in Tugela Rand range from massive to podiform with the rare orbicular variety indicating complex controls on chromite accretion. They include the high-Al compositional variety. There are no other similar chromitite occurrences in South Africa. The complexes, together with their enclosing rock-types, draw striking parallels with the lower arc crust observed in the late Cretaceous Kohistan arc complex in NE Pakistan. The Tugela Rand Complex shares many similarities with the Chilas Complex in that terrane, while the Mambula Complex is considered to be a more evolved derivative of the same magma. This study shows that generation of juvenile continental crust formation in mature island arc systems may have been firmly established by the Mesoproterozoic.
Detection of REEs with lightweight UAV‑based hyperspectral imaging
(Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations., 2020) Booysen, René; Nex, Paul A.M.; Zimmermann, Robert; Loren, Sandra; Kirsch, Moritz; Jackish, Robert; Gloaguen, Richard
Rare earth elements (REEs) supply is important to ensure the energy transition, e-mobility and ultimately to achieve the sustainable development goals of the United Nations. Conventional exploration techniques usually rely on substantial geological field work including dense in-situ sampling with long delays until provision of analytical results. However, this approach is limited by land accessibility, financial status, climate and public opposition. Efficient and innovative methods are required to mitigate these limitations. The use of lightweight unmanned aerial vehicles (UAVs) provides a unique opportunity to conduct rapid and non-invasive exploration even in socially sensitive areas and in relatively inaccessible locations. We employ drones with hyperspectral sensors to detect REEs at the earth’s surface and thus contribute to a rapidly evolving field at the cutting edge of exploration technologies. We showcase for the first time the direct mapping of REEs with lightweight hyperspectral UAV platforms. Our solution has the advantage of quick turn-around times (< 1 d), low detection limits (< 200 ppm for Nd) and is ideally suited to support exploration campaigns. This procedure was successfully tested and validated in two areas: Marinkas Quellen, Namibia, and Siilinjärvi, Finland. This strategy should invigorate the use of drones in exploration and for the monitoring of mining activities.
Developing a density functional theory model of glassy carbon via carbon defect induction and relaxation
(Elsevier, 2025-01) Falch, A.; Meerholz, K.; van Sittert, C.G.C.E.
Glassy Carbon (GC) is a non-graphitising carbon known for its thermal stability, conductivity, and resistance to chemical attack, making it valuable in industrial and scientific applications, especially as an electrode substrate in catalysis research. Despite its widespread use, GC’s precise structural characteristics is unclear due to synthesis variability. This study developed and validated a computational model to simulate GC’s structure. Starting from the R3-carbon allotrope, density functional theory calculations were used to construct a representative GC model, incorporating induced defects to mimic its structural imperfections. Multiple GC slab models were created for comparative analysis. Validation involved comparing theoretical X-ray diffraction data with published data, confirming the model’s accuracy in representing the GC’s structure. The model showed high correlation with existing models, particularly those by Jurkiewicz et al., emphasizing the effect of formation temperature on GC’s structural evolution. These findings enhance the understanding of GC’s structural complexities, providing a solid foundation for future research and applications in material science, especially for robust and conductive substrates used in electrocatalysis.
Draft genome sequence of the fungal pathogen Penicillium expansum (PPRI25879) isolated in South Africa
(Elsevier, 2025-02) Chan, Wai Yin; Rauwane, Molemi; Figlan, Sandiswa; Ntushelo, Khayalethu
Objectives: Penicillium expansum, a necrotrophic plant pathogen with a wide range of fruit hosts, is an important causal agent of blue mold rot. The fruit business suffers significant financial losses because of blue mold rot that occurs during fruit storage, transportation, and sale. The objective of this work was to generate a high-quality draft genome assembly of P. expansum, which will contribute to enhancing the management of blue mold, especially in stone and pome fruits, including grapes, by improving our understanding of the epidemiology of the pathogen and its interactions with the host. Data description: Here, we describe the genome sequence of Penicillium expansum isolate PPRI25879, one of the most virulent strains isolated from grapes in South Africa. Sequencing reads from P. expansum produced approximately 3.5 Gb. The assembly generated a draft genome of size 32.1 Mb, consisting of 1648 contigs, with an N50 of 508 KB. Examination of the genome completeness with Benchmarking Universal Single-Copy Orthologs (BUSCO) showed the draft genome carries 97.9% of the 746 genes in the Eurotiomycetes_odb10 database. The draft genome sequence will allow improved genomic comparisons among the most important pathogens belonging to the Penicillium genus, with the aim of improving our knowledge of their plant-pathogen interactions, population biology, and control.
Entanglement beating in free space through spin–orbit coupling
(Springer Nature, 2018) Rosales-Guzmán, Carmelo; Denz, Cornelia; Otte, Eileen; Ndagano, Bienvenu; Forbes, Andrew
It is well known that the entanglement of a quantum state is invariant under local unitary transformations. This rule dictates, for example, that the entanglement of internal degrees of freedom of a photon remains invariant during free-space propagation. Here, we outline a scenario in which this paradigm does not hold. Using local Bell states engineered from classical vector vortex beams with non-separable degrees of freedom, the so-called classically entangled states, we demonstrate that the entanglement evolves during propagation, oscillating between maximally entangled (purely vector) and product states (purely scalar). We outline the spin–orbit interaction behind these novel propagation dynamics and confirm the results experimentally, demonstrating spin–orbit coupling in paraxial beams. This demonstration highlights a hitherto unnoticed property of classical entanglement and simultaneously offers a device for the on-demand delivery of vector states to targets, for example, for dynamic laser materials processing, switchable resolution within stimulated emission depletion (STED) systems, and a tractor beam for entanglement.
Evidence for igneous differentiation in Sudbury Igneous Complex and impact-driven evolution of terrestrial planet proto-crusts
(Nature Research, 2019-01) Latypov, Rais; Chistyakova, Sofya; Grieve, Richard; Huhma, Hannu
Bolide impact is a ubiquitous geological process in the Solar System, which produced craters and basins filled with impact melt sheets on the terrestrial planets. However, it remains controversial whether these sheets were able to undergo large-scale igneous differentiation, or not. Here, we report on the discovery of large discrete bodies of melanorites that occur throughout almost the entire stratigraphy of the 1.85-billion-year-old Sudbury Igneous Complex (SIC) – the best exposed impact melt sheet on Earth – and use them to reaffirm that conspicuous norite-gabbro-granophyre stratigraphy of the SIC is produced by fractional crystallization of an originally homogeneous impact melt of granodioritic composition. This implies that more ancient and compositionally primitive Hadean impact melt sheets on the Earth and other terrestrial planets also underwent large-volume igneous differentiation. The near-surface differentiation of these giant impact melt sheets may therefore have contributed to the evolution and lithological diversity of the proto-crust on terrestrial planets.
Forward scattering on the line with a transfer condition
(SpringerOpen [Commercial Publisher], 2013-12) Currie, Sonja; Nowaczyk, Marlena; Watson, Bruce A.
We consider scattering on the line with a transfer condition at the origin. Under suitable growth conditions on the potential, the spectrum consists of a finite number of eigenvalues which are negative real numbers, while the remainder is continuous spectrum which is comprised of the positive real axis. Asymptotics are provided for the Jost solutions. Conditions which characterize transfer conditions resulting in self-adjoint problems are found. Properties are given of the scattering coefficient linking it to the spectrum.
Geological Remote Sensing
(Acdemic Press, United Kingdom, 2021) Booysen, René; Nex, Paul A.M.; Gloaguen, Richard; Lorenz, Sandra; Zimmermann, Robert; Alderton, David; Elias, Scott A.
The field of remote sensing has recently witnessed major innovations that have been translated to Earth science applications. Before they can be used, remote sensing data must be corrected for effects originating from the sensors, the platforms on which they are deployed, atmospheric characteristics, and geometrical constraints. When the data are calibrated and geolocated, they can be used either as physical quantities, such as reflectance and temperatures, or as images. The recent development of new sensors has permitted the remote measurement of a large area of the Earth's surface, with direct geological applications. Additionally, advances in machine vision, machine learning and artificial intelligence, combined with an unprecedented increase in computer processing power, have led to innovative remote sensing data processing techniques that simplify the handling of large amounts of complex data. As a consequence, it is now possible to characterize the geological settings of large areas with precision and even their changes through time. Remote sensing data are now directly integrated into modelling algorithms that describe surface and subsurface processes at different scales. Geological remote sensing currently encompasses multi temporal, multi-source and multi scale approaches. The retrieval of big data in disseminated archives, as well as (near) real time processing are the challenges that remain to be solved. These new applications in geology ensure cost efficient, safe, and rapid surveys and monitoring that not only benefit the research community but society at large.
Insights into the genetics of blood pressure in black South African individuals: the Birth to Twenty cohort
(BMC, 2018) Hendry, Liesl M.; Sahibdeen, Venesa; Choudhury, Ananyo; Norris, Shane A.; Ramsay, Michèle; Lombard, Zané
Background: Cardiovascular diseases (CVDs) are the leading cause of non-communicable disease deaths globally, with hypertension being a major risk factor contributing to CVDs. Blood pressure is a heritable trait, with relatively few genetic studies having been performed in Africans. This study aimed to identify genetic variants associated with variance in systolic (SBP) and diastolic (DBP) blood pressure in black South Africans. Methods: Genotyping was performed using the Metabochip in a subset of participants (mixed sex; median age 17.9) and their adult female caregivers (median age 41.0) from the Birth to Twenty cohort (n = 1947). Data were analysed as a merged dataset (all participants and caregivers together) in GEMMA (v0.94.1) using univariate linear mixed models, incorporating a centered relatedness matrix to account for the relatedness between individuals and with adjustments for age, sex, BMI and principal components of the genotype information. Results: Association analysis identified regions of interest in the NOS1AP (DBP: rs112468105 - p = 7.18 × 10−5 and SBP: rs4657181 - p = 4.04 × 10−5), MYRF (SBP: rs11230796 - p = 2.16 × 10−7, rs400075 - p = 2.88 × 10−7) and POC1B (SBP: rs770373 - p = 7.05 × 10−5, rs770374 - p = 9.05 × 10−5) genes and some intergenic regions (DACH1|LOC440145 (DBP: rs17240498 - p = 4.91 × 10−6 and SBP: rs17240498 - p = 2.10 × 10−5) and INTS10|LPL (SBP: rs55830938 - p = 1.30 × 10−5, rs73599609 - p = 5.78 × 10−5, rs73667448 - p = 6.86×10−5)). Conclusions: The study provided further insight into the contribution of genetic variants to blood pressure in black South Africans. Future functional and replication studies in larger samples are required to confirm the role of the identified loci in blood pressure regulation and whether or not these variants are African-specific.
Knock-down of LRP/LR promotes apoptosis in early and late stage colorectal carcinoma cells via caspase activation
(BioMed Central, 2018-05) Vania, Leila; Rebelo, Thalia M.; Ferreira, Eloise; Weiss, Stefan F. T.
Background: Cancer remains one of the leading causes of death around the world, where incidence and mortality rates are at a constant increase. Tumourigenic cells are characteristically seen to over-express the 37 kDa/67 kDa laminin receptor (LRP/LR) compared to their normal cell counterparts. This receptor has numerous roles in tumourigenesis including metastasis, angiogenic enhancement, telomerase activation, cell viability and apoptotic evasion. This study aimed to expose the role of LRP/LR on the cellular viability of early (SW-480) and late (DLD-1) stage colorectal cancer cells. Methods: siRNA were used to down-regulate the expression of LRP/LR in SW-480 and DLD-1 cells which was assessed using western blotting. Subsequently, cell survival was evaluated using the MTT cell survival assay and confocal microscopy. Thereafter, Annexin V-FITC/PI staining and caspase activity assays were used to investigate the mechanism underlying the cell death observed upon LRP/LR knockdown. The data was analysed using Student’s ttest with a confidence interval of 95%, with p-values of less than 0.05 seen as significant. Results: Here we reveal that siRNA-mediated knock-down of LRP led to notable decreases in cell viability through increased levels of apoptosis, apparent by compromised membrane integrity and significantly high caspase-3 activity. Down-regulated LRP resulted in a significant increase in caspase-8 and -9 activity in both cell lines. Conclusions: These findings show that the receptor is critically implicated in apoptosis and that LRP/LR downregulation induces apoptosis in early and late stage colorectal cancer cells through both apoptotic pathways. Thus, this study suggests that siRNA-mediated knock-down of LRP could be a possible therapeutic strategy for the treatment of early and late stage colorectal carcinoma.
Kondo effect and enhanced magnetic properties in gadolinium functionalized carbon nanotube supramolecular complex
(Nature Research, 2018-05) Ncube, S.; Coleman, C.; Strydom, A.; Flahaut, E.; de Sousa, A.
We report on the enhancement of magnetic properties of multiwalled carbon nanotubes (MWNTs) functionalized with a gadolinium based supramolecular complex. By employing a newly developed synthesis technique, we find that the functionalization method of the nanocomposite enhances the strength of magnetic interaction, leading to a large effective moment of 15.79µB and nonsuperparamagnetic behavior, unlike what has been previously reported. Saturating resistance at low temperatures is ftted with the numerical renormalization group formula, verifying the Kondo effect for magnetic impurities on a metallic electron system. Magnetoresistance shows devices fabricated from aligned gadolinium functionalized MWNTs (Gd-Fctn-MWNTs) exhibit spin-valve switching behaviour of up to 8%. This study highlights the possibility of enhancing magnetic interactions in carbon systems through chemical modification, moreover, we demonstrate the rich physics that might be useful for developing spin based quantum computing elements based on one-dimensional (1D) channels.
A metagenomic viral discovery approach identifies potential zoonotic and novel mammalian viruses in Neoromicia bats within South Africa
(Public Library of Science, 2018-03) Geldenhuys, M.; Mortlock, M.; Weyer, J.; Bezuidt, O.; Seamark, E.C.J.; Kearney, T.
Species within the Neoromicia bat genus are abundant and widely distributed in Africa. It is common for these insectivorous bats to roost in anthropogenic structures in urban regions. Additionally, Neoromicia capensis have previously been identified as potential hosts for Middle East respiratory syndrome (MERS)-related coronaviruses. This study aimed to ascertain the gastrointestinal virome of these bats, as viruses excreted in fecal material or which may be replicating in rectal or intestinal tissues have the greatest opportunities of coming into contact with other hosts. Samples were collected in five regions of South Africa over eight years. Initial virome composition was determined by viral metagenomic sequencing by pooling samples and enriching for viral particles. Libraries were sequenced on the Illumina MiSeq and NextSeq500 platforms, producing a combined 37 million reads. Bioinformatics analysis of the high throughput sequencing data detected the full genome of a novel species of the Circoviridae family, and also identified sequence data from the Adenoviridae, Coronaviridae, Herpesviridae, Parvoviridae, Papillomaviridae, Phenuiviridae, and Picornaviridae families. Metagenomic sequencing data was insufficient to determine the viral diversity of certain families due to the fragmented coverage of genomes and lack of suitable sequencing depth, as some viruses were detected from the analysis of reads-data only. Follow up conventional PCR assays targeting conserved gene regions for the Adenoviridae, Coronaviridae, and Herpesviridae families were used to confirm metagenomic data and generate additional sequences to determine genetic diversity. The complete coding genome of a MERS-related coronavirus was recovered with additional amplicon sequencing on the MiSeq platform. The new genome shared 97.2% overall nucleotide identity to a previous Neoromicia-associated MERS-related virus, also from South Africa. Conventional PCR analysis detected diverse adenovirus and herpesvirus sequences that were widespread throughout Neoromicia populations in South Africa. Furthermore, similar adenovirus sequences were detected within these populations throughout several years. With the exception of the coronaviruses, the study represents the first report of sequence data from several viral families within a Southern African insectivorous bat genus; highlighting the need for continued investigations in this regard.