Browsing by Author "Van der Merwe, S."

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    Comparison of infant-feeding practices in two health subdistricts with different baby-friendly status in Mpumalanga province
    (MedPharm Publications, 2015) Van der Merwe, S.; Du Plessis, L.; Jooste, H.; Nel, D.
    Objectives: The objective of the study was to compare the infant-feeding practices of two subdistricts with different baby-friendly status in Mpumalanga province, South Africa. Design: This was a cross-sectional, descriptive, observational study with an analytical component. Eighteen fieldworkers assisted with the data collection, utilising two sets of interviewer-administered questionnaires – one on socio-demographic information and the other on infantfeeding practices. Subjects: Mothers with infants from birth to six months old, attending postnatal care at public sector primary health care facilities in Emalahleni and Mbombela health subdistricts on the days of data collection were included. A total of 435 mother and infant pairs were included in the study. Outcome measures: Five infant-feeding indicators were used, namely the early initiation of breastfeeding, exclusive breastfeeding, exclusive replacement feeding and mixed feeding rates, as well as the age at which complementary food was introduced. Results: There was a significantly higher early initiation of breastfeeding (57% vs. 43%), exclusive breastfeeding rates (60% vs 48%), and a lower exclusive replacement feeding rate (18% vs. 33%) in Emalahleni subdistrict, where all the public sector maternity facilities are accredited as being baby friendly, compared to that in Mbombela subdistrict, where none of the public sector maternity facilities are baby friendly. The mixed feeding rate (19% vs. 15%) and the mean age of the introduction of complementary foods (50 days versus 35 days) did not differ significantly between the two subdistricts. Conclusion: Implementation of the Baby-Friendly Hospital Initiative (BFHI) in a health subdistrict was associated with more optimal infant feeding practices in mothers with infants aged six months and younger. It is concluded that strengthening practices prescribed within the BFHI would improve infant-feeding practices at community level.
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    Modelling and performance evaluation of a three-phase capacitive voltage sensor topology
    (Stellenbosch : University of Stellenbosch, 2006-12) Van der Merwe, S.; Vermeulen, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    This research project investigates the design, modelling and application of an open-air capacitive voltage sensor assembly for the measurement of wideband High Voltage signals on three-phase transmission lines. The advantages and disadvantages of conventional methods used to measure these voltages are reviewed and the advantages of the open-air capacitive sensor are established. The main research objective of this project involves extending the application of previously developed single-phase capacitive sensor topologies to three-phase applications. A three-phase set of mobile, compact and relatively inexpensive capacitive voltage sensors for open-air application under overhead transmission lines are designed and constructed, including a data acquisition triggering system for the measurement of transient waveforms. Equivalent circuit models, using a Thévenin equivalent approach, are developed for the three-phase sensor topology and the associated three-phase transmission line configuration. A number of different methods for simplifying the associated Thévenin equivalent impedance and voltage equations are evaluated. The decoupling of the voltage waveforms measured by the individual sensors for a three-phase transmission line configuration is subsequently examined with the view to derive mathematical relationships for determining the phase conductor voltages from the measured sensor voltages. The performance of the sensor assembly is experimentally evaluated under laboratory conditions as well as field conditions. An outdoor HV test facility, representing a scaled three-phase flat transmission line structure, is developed for evaluation of the three-phase sensor topology in a controlled environment. The methodology for decoupling the phase voltages and reconstructing the phase conductor voltages from the voltages induced on the sensors is evaluated using measured data obtained with this HV test facility. It is shown that the three-phase capacitive voltage sensor topology as applied in the test facility delivers good results for the measurement of three-phase transient voltage waveforms.