The condition monitoring of the passive harmonic filters in rail way DC sub stations

The condition monitoring of the passive 12th and 24th harmonic filters in the DC sub station employing 12 pulse passive rectification plays the vital role of suppressing generated harmonics. The railway service of South Africa (Transnet) is confronted by the introduction of complex loads the sub stations was never designed for. In recent years the suppression of harmonics has become increasingly important due to penalties incurred from the energy supplier and the influence harmonics has on sensitive equipment supplied from the same grid. The condition monitoring of harmonic filters can thus be used to control harmonic energy. Due to the fact that these filters are passive they have to be monitored to ensure efficiency. The efficiency of the filter is dependant on the filter components being within specification to ensure accurate attenuation of generated harmonics. The investigation of the document aims to address the condition monitoring of the passive filter components for various operating conditions to establish whether these components are still operating in an efficient manner. In the short term the proper functioning of the harmonic filters will reduce power factor quality penalties and in the long term the life expectancy of systems supplied by the DC grid will be prolonged. The monitoring of the harmonic filters may even aid in diagnosing faulty components that have harmonics as a results that influence the operation of the harmonic filters. The investigation in this research report involves the development of a method to practically measure the voltage harmonics (600 and 1200 Hz) generated by DC sub station components. The investigation deals with the simulation of the DC sub station during various operating conditions and the actual measurement of sub stations in order to calibrate the findings. The report aims to investigate the feasibility of monitoring the condition of the DC sub station passive harmonic filters without entering the DC sub station

The relationship between graduate employability and work performance in the mining industry in South Africa

In a rapid changing environment mining companies have to change the way in which they do business, while employees have to manage their careers and ensure they are multi-skilled. Organisations are looking to employ individuals who are career driven, highly adaptable and flexible and display the necessary employability skills. The main purpose of this study was to determine if any relationship exists between the different factors of graduate employability and work performance in the mining industry in South Africa. A cross-sectional quantitative research approach was followed. A simple random sample was drawn from graduate male and female employees between the ages of 18 – 30 years with any post-matric qualification employed in the mining industry in South Africa. Through the process of exploratory factor analysis, six graduate employability factors and four work performance factors were identified. The graduate employability factors included career self-management drive, cultural competence, career resilience, emotional literacy, career literacy and self-efficacy. The work performance factors included the supervisor role, employee role, recognition and organisation support. Correlation and regression analyses were conducted. The results indicated a relationship between graduate employability and work performance. Strong, positive correlations were found between graduate employability and work performance with career self-management drive being the strongest predictor of work performance. Recommendations for the mining industry focused on how employability could be enhanced to improve work performance.Human Resource ManagementM. Com. (Human Resource Management

Eclipse, transit and occultation geometry of planetary systems at exo-syzygy

Although conjunctions and oppositions frequently occur in planetary systems, eclipserelated phenomena are usually described from an Earth-centric perspective. Space missions to different parts of the Solar system, as well as the mounting number of known exo-planets in habitable zones and the possibility of sending featherweight robot spacecraft to them, prompt broader considerations. Here, we derive the geometry of eclipses, transits and occultations from a primarily exo-Earth viewpoint, and apply the formulation to the Solar system and three types of three-body extrasolar planetary systems: with 1 star and 2 planets (Case I), with 2 stars and 1 planet (Case II), and with 1 planet, 1 star and 1 moon (Case III). We derive the general conditions for total, partial and annular eclipses to occur at exo-syzygy, and implement them in each case in concert with stability criteria. We then apply the formalism to the TRAPPIST-1, Kepler-444 and Kepler-77 systems – the first of which contains multiple potentially habitable planets – and provide reference tables of both Solar system and TRAPPIST- 1 syzygy properties. We conclude by detailing a basic algebraic algorithm which can be used to quickly characterize eclipse properties in any three-body system

The Origin of UV-optical Variability in AGN and Test of Disc Models: XMM-Newton and ground based observations of NGC4395

The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of observational programmes, particularly of NGC5548 with Swift, have shown that the UV/optical variations lag behind the X-ray variations in a manner strongly supportive of X-ray reprocessing. Somewhat surprisingly the implied size of the accretion disc is ~3x greater than expected from a standard, smooth, Shakura-Sunyaev thin disc model. Although the difference may be explained by a clumpy accretion disc, it is not clear whether the difference will occur in all AGN or whether it may change as, eg, a function of black hole mass, accretion rate or disc temperature. Measurements of interband lags for most AGN require long timescale monitoring, which is hard to arrange. However for low mass (<1 million solar mass) AGN, the combination of XMM-Newton EPIC (X-rays) with the optical monitor in fast readout mode allows an X-ray/UV-optical lag to be measured within a single long observation. Here we summarise previous related observations and report on XMM-Newton observations of NGC4395 (mass ~100x lower and accretion rate ~20x lower than for NGC5548). We find that the UVW1 lags the X-rays by ~470s. Simultaneous observations at 6 different ground based observatories also allowed the g-band lag (~800s) to be measured. These observations are in agreement with X-ray reprocessing but initial analysis suggests that, for NGC4395, they do not differ markedly from the predictions of the standard thin disc model.Comment: 6 pages, 16 figures, accepted for publication in Astronomische Nachrichte

Correlated X-ray/Ultraviolet/Optical variability in the very low mass AGN NGC 4395

We report the results of a one year Swift X-ray/UV/optical programme monitoring the dwarf Seyfert nucleus in NGC 4395 in 2008-2009. The UV/optical flux from the nucleus was found to vary dramatically over the monitoring period, with a similar pattern of variation in each of the observed UV/optical bands (spanning 1900 - 5500 {\AA}). In particular, the luminosity of NGC 4395 in the 1900 {\AA} band changed by more than a factor of eight over the monitoring period. The fractional variability was smaller in the UV/optical bands than that seen in the X-rays, with the X-ray/optical ratio increasing with increasing flux. Pseudo-instantaneous flux measurements in the X-ray and each UV/optical band were well correlated, with cross correlation coefficients of >0.7, significant at 99.9 per cent confidence. Archival Swift observations from 2006 sample the intra-day X-ray/optical variability on NGC 4395. These archival data show a very strong correlation between the X-ray and b bands, with a cross-correlation coefficient of 0.84 (significant at >99 per cent confidence). The peak in the cross correlation function is marginally resolved and asymmetric, suggesting that X-rays lead the b band, but by 1 hour. In response to recent (August 2011) very high X-ray flux levels from NGC4395 we triggered Swift ToO observations, which sample the intra-hour X-ray/UV variability. These observations indicate, albeit with large uncertainties, a lag of the 1900 {\AA} band behind the X-ray flux of ~400 s. The tight correlation between the X-ray and UV/optical lightcurves, together with the constraints we place on lag time-scale are consistent with the UV/optical variability of NGC 4395 being primarily due to reprocessing of X-ray photons by the accretion disc.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRA

Stakeholder views of educational governance after a change in ownership of independent schools

Independent schools became part of South Africa in 1994. The new educational system contributed to the freedom of the choice of language medium of education as well as the freedom of religion in education. In the last 10 years, many independent schools have become part of corporate companies which have invested in small, sometimes poor, independent schools including them as part of a larger business organisation. This corporate company investment has resulted in a change from educational governance to corporate governance in these schools. One of the concerns relating to this change is that the focus of governance could move from educational development to the increase of profit. The purpose of this study was to understand the views of some stakeholders when their schools changed from not-for-profit governance to a profit-driven governance. The primary question addressed was: What are the views of stakeholders in formerly independent not-for-profit schools of governance after a change of ownership to a listed organisation? A multiple case study design was used. Semi-structured interviews were used to try to understand how the stakeholders viewed this change. The King III Report (2009) presented certain characteristics of good governance: responsibility, accountability, fairness and transparency. These characteristics were used as a conceptual framework to obtain sufficient information on how different stakeholders viewed the change in governance. The stakeholders mentioned changes that were not anticipated beforehand and the differences in experiences regarding the different stakeholders were inevitable. This thesis recommends that changes from not-for-profit governance to profit-driven governance need to be planned, monitored and supervised very carefully. Governors need to know and acknowledge that a school is a community. Compassion and empathy need to be shown to all stakeholders of the school. Attention needs to be given to communication with stakeholders, especially the teachers and parents. Relationships of trust take time to develop and need to be established between stakeholders. The psychological effect of a transformation like this on all stakeholders, including the children and their families, needs to be addressed. Key words: Independent Schools, Governance, Corporate Governance, Stakeholders.Thesis (PhD)--University of Pretoria, 2022.Education Management and Policy StudiesPhDUnrestricte