27 research outputs found

    Identifying important differences in mass spectra generated by secondary ion mass spectrometry (TOF-SIMS) in a tribochemical study

    Get PDF
    In order to better understand the lubricating properties of diesel fuel, species that were present on tribological surfaces were investigated using secondary ion time-of-flight mass spectrometry (TOF–SIMS). Traditionally, only certain species that are expected to be present at the interface are investigated and their presence or absence is used to make conclusions regarding the mechanism of lubrication. In this work, an alternative and complementary approach to data analysis and interpretation is proposed, previously demonstrated for TOF–SIMS and based on multivariate analysis methods, where the mass spectral data are investigated more comprehensively. The main objective was to interpret variation within and between different areas of a tested surface and ultimately to contribute to the understanding of the tribochemical reactions that occur at the interface. The validity of this approach was confirmed when the palmitate ion (which would normally be targeted) was shown to contribute significantly (together with other ions) to chemical differences between scratched and unscratched areas of the surface.Sasol (Sasol Technology,Fuels Research) and the National Research Foundation (DAAD-NRF).http://link.springer.com/journal/112492015-10-31hb201

    A metabolomics-guided exploration of the phytochemical constituents of Vernonia fastigiata with the aid of pressurized hot water extraction and liquid chromatography-mass spectrometry

    Get PDF
    CITATION: Masike, K., et al. 2017. A metabolomics-guided exploration of the phytochemical constituents of Vernonia fastigiata with the aid of pressurized hot water extraction and liquid chromatography-mass. Molecules, 22(8):1200, doi:10.3390/molecules22081200.The original publication is available at http://www.mdpi.comVernonia fastigiata is a multi-purpose nutraceutical plant with interesting biological properties. However, very little is known about its phytochemical composition and, thus the need for its phytochemical characterization. In the current study, an environmentally friendly method, pressurized hot water extraction (PHWE), was used to extract metabolites from the leaves of V. fastigiata at various temperatures (50 °C, 100 °C, 150 °C and 200 °C). Ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry (UHPLC-qTOF-MS) analysis in combination with chemometric methods, particularly principal component analysis (PCA) and liquid/gas chromatography mass spectrometry (XCMS) cloud plots, were used to descriptively visualize the data and identify significant metabolites extracted at various temperatures. A total of 25 different metabolites, including hydroxycinnamic acid derivatives, clovamide, deoxy-clovamide and flavonoids, were noted for the first time in this plant. Overall, an increase in extraction temperature resulted in an increase in metabolite extraction during PHWE. This study is the first scientific report on the phytochemical composition of V. fastigiata, providing insight into the components of the chemo-diversity of this important plant.http://www.mdpi.com/1420-3049/22/8/1200Publisher's versio

    Human rights in diverse education contexts

    Get PDF
    The focus of this publication is on answering the central research question: How can Human Rights be advanced with regard to different kinds of diversities, and in different educational settings? The publication pays special attention to the advancement of human rights in a variety of education-related contexts, in keeping with human rights as a declared national priority for both society at large and the education system. One strategic priority of the Faculty of Education is research based on market requirements and needs. This book strives towards meeting this expectation by directly aiming at building human rights and social justice in the South African society, public schools and higher education institutions. Adjudication in the education context of the constitutional values of dignity, equality and freedom focusses regularly on learners. The book highlights the value of education for full-fledged citizenship by delineating what schooling should entail to inspire learners towards both claiming equal freedoms and rights and taking accountability for the responsibilities attached to citizenship

    Drug-associated adverse events and their relationship with outcomes in patients receiving treatment for extensively drug-resistant tuberculosis in South Africa

    Get PDF
    BACKGROUND: Treatment-related outcomes in patients with extensively drug-resistant tuberculosis (XDR-TB) are poor. However, data about the type, frequency and severity of presumed drug-associated adverse events (AEs) and their association with treatment-related outcomes in patients with XDR-TB are scarce. METHODS: Case records of 115 South-African XDR-TB patients were retrospectively reviewed by a trained researcher. AEs were estimated and graded according to severity [grade 0 = none; grade 1-2 = mild to moderate; and grade 3-5 = severe (drug stopped, life-threatening or death)]. FINDINGS: 161 AEs were experienced by 67/115(58%) patients: 23/67(34%) required modification of treatment, the offending drug was discontinued in 19/67(28%), reactions were life-threatening in 2/67(3.0%), and 6/67(9.0%) died. ∼50% of the patients were still on treatment at the time of data capture. Sputum culture-conversion was less likely in those with severe (grade 3-5) vs. grade 0-2 AEs [2/27(7%) vs. 24/88(27%); p = 0.02]. The type, frequency and severity of AEs was similar in HIV-infected and uninfected patients. Capreomycin, which was empirically administered in most cases, was withdrawn in 14/104(14%) patients, implicated in (14/34) 41% of the total drug withdrawals, and was associated with all 6 deaths in the severe AE group (renal failure in five patients and hypokalemia in one patient). CONCLUSION: Drug-associated AEs occur commonly with XDR-TB treatment, are often severe, frequently interrupt therapy, and negatively impact on culture conversion outcomes. These preliminary data inform on the need for standardised strategies (including pre-treatment counselling, early detection, monitoring, and follow-up) and less toxic drugs to optimally manage patients with XDR-TB

    Self-Directed Learning in the era of the COVID-19 pandemic

    Get PDF
    The COVID-19 pandemic severely impacted teaching and learning at higher education institutions (HEIs), and this book disseminates research findings on a series of cross-campus online initiatives of the North-West University (NWU) to ensure high-quality self-directed learning, whilst simultaneously attending to the need for inclusion and diversity in this challenging context. The golden thread running through the 13 chapters is how this HEI responded to the pandemic in a creative way through its investment in online virtual student excursions, based on problem-based, cooperative learning and gamification principles to support self-directed learning. Whereas virtual excursions usually refer to learning opportunities where ‘a museum, author, park or monument is brought to the student’ (Hehr 2014:1), the virtual excursion in our context is an activity system (Engeström 1987) where students’ learning is scaffolded across the zone of proximal development (Vygotsky 1978) and where their ‘social and pedagogical boundaries are stretched or expanded’ (De Beer & Henning 2011:204). Students engage as Homo ludens, the playing human (Huizinga 1955), in learning activities embedded in an ill-structured problem, and through reflective activities, they are encouraged to reflect on their own naïve understandings or biases. This ‘tension’, or in Veresov (2007) parlance, ‘dramatical collisions’, provides a fertile learning space for self-directed learning

    Self-Directed Learning in the era of the COVID-19 pandemic

    Get PDF
    The COVID-19 pandemic severely impacted teaching and learning at higher education institutions (HEIs), and this book disseminates research findings on a series of cross-campus online initiatives of the North-West University (NWU) to ensure high-quality self-directed learning, whilst simultaneously attending to the need for inclusion and diversity in this challenging context. The golden thread running through the 13 chapters is how this HEI responded to the pandemic in a creative way through its investment in online virtual student excursions, based on problem-based, cooperative learning and gamification principles to support self-directed learning. Whereas virtual excursions usually refer to learning opportunities where ‘a museum, author, park or monument is brought to the student’ (Hehr 2014:1), the virtual excursion in our context is an activity system (Engeström 1987) where students’ learning is scaffolded across the zone of proximal development (Vygotsky 1978) and where their ‘social and pedagogical boundaries are stretched or expanded’ (De Beer & Henning 2011:204). Students engage as Homo ludens, the playing human (Huizinga 1955), in learning activities embedded in an ill-structured problem, and through reflective activities, they are encouraged to reflect on their own naïve understandings or biases. This ‘tension’, or in Veresov (2007) parlance, ‘dramatical collisions’, provides a fertile learning space for self-directed learning

    Analise van diesel-monsters deur middel van omvattende twee-dimensionele gaschromatografie (GCXGC/TOFMS) om die smeerbaarheid van hierdie brandstof fundamenteel-chemies beter te probeer verstaan

    Get PDF
    <div style="font-size: 12px; font-family: serif; left: 226.427px; top: 410.205px; transform: scale(1.12462, 1); transform-origin: 0% 0% 0px;" dir="ltr">Smeerbaarheid is die vermoë van ’n vloeistof om skawing te voorkom in ’n sisteem waar twee</div><div style="font-size: 12px; font-family: serif; left: 226.427px; top: 426.201px; transform: scale(1.10929, 1); transform-origin: 0% 0% 0px;" dir="ltr">metaaloppervlakke in noue kontak is. Die smeerbaarheid van diesel is baie belangrik, aangesien die brandstofinspuitsisteem slegs deur die diesel gesmeer word.</div

    Characterisation of the chemical classes present in diesel fuel to identify the components that contribute to lubricity

    Get PDF
    Lubricity is the ability of a substance to prevent wear in a system where interacting surfaces are in close contact with each other. Some critical components in high pressure diesel injection systems are dependent on diesel fuel for lubrication and thus the lubricating properties of diesel fuel are very important. The relationship between the chemical composition and lubricating properties of diesel fuel were investigated, in an attempt to identify chemical classes and components in diesel that could improve lubricity. From literature, hetero-atom containing compounds and aromatic hydrocarbons were thought to be important. The chemical compositions of diesel fuels were determined using comprehensive twodimensional gas chromatography coupled to time of flight mass spectrometry. Four different column combinations were investigated and compared for the separation of these samples. The separations obtained for each column combination were compared graphically and mathematically. Better compound separation was achieved as the polarity of the stationary phase in the first dimension increased. Using a column with an ionic liquid stationary phase in the first dimension presented unique separations of aliphatic hydrocarbons but the improved compound separation resulted in the overlap of certain compound classes. The best class separation was achieved by using a polyethylene glycol column in the first dimension. Multivariate statistical analysis was used to investigate the relationship between the chemical compositions and the measured lubricities of these fuels. A provisional model was determined, which showed that lubricity improved as the relative amount of aromatic hydrocarbons and oxygenates increased. The model also showed that oxygenates play a more important role than aromatic hydrocarbons in improving lubricity. The influence of chain length was also investigated and less volatile oxygenated compounds seem to contribute more to lubricity.Dissertation(MSc)--University of Pretoria, 2011Chemistr

    Class separation of the trace polar species present in diesel using hydrophilic interaction chromatography and high resolution mass spectrometry

    Get PDF
    The analysis of fuels is not straightforward, due to its complex nature, and many different techniques have been developed to address this complexity. This paper reports on the use of hydrophilic interaction liquid chromatography (HILIC) as a complementary and green method for classifying diesel fuel composition. For comparative reasons, analyses with and without chromatographic preseparation were performed. Selective ionization of polar species was achieved with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). High resolution time-of-flight mass spectrometry (TOFMS) was used to summarize the fuel composition in terms of compound classes based on accurate mass based elemental compositions. These compound classes showed different retention characteristics and were separated to a certain extent under hydrophilic interaction conditions. In normal phase liquid chromatography, the separation is based on heteroatom content, whereas alkylation (chain length) and degree of unsaturation (or double bond equivalents, DBE) play an important role in reversed phase liquid chromatography. The separation achieved with the proposed HILIC method depended on heteroatom content, DBE as well as hydrogen bonding, while alkylation did not influence retention significantly. This work therefore presents an alternative and complementary method for fuel analysis, compared to traditional reverse and normal phase liquid chromatography, by considering specific advantages and limitations.Sasol (Sasol Energy, Energy Technology), the Deutscher Akademischer Austauschdienst (DAAD), and the National Research Foundation (NRF).http://pubs.acs.org/journal/enfuem2019-08-27hj2018Chemistr
    corecore