132,237 research outputs found
Die skrywer (Esta Steyn)
No full textDie skrywer.Esta Steyn. Kaapstad: Tafelberg, 2012. 214 pp. ISBN: 978-0-624-05441-2
Genital schistosomiasis presenting as suspected ectopic pregnancy in the Western Cape
No full textCITATION: Schneider, D. & Steyn, D. W. 2000. Genital schistosomiasis presenting as suspected ectopic pregnancy in the Western Cape. South African Medical Journal, 90(6):609.The original publication is available at http://www.samj.org.za[No abstract available]Publisher’s versio
Steyn en die krisisjare, 1896-1899
No full textOmslagtitel: President Steyn en die krisisjare, 1896-1899.Proefskrif (D. Ph.) -- Universiteit van Stellenbosch, [1939].Full text to be digitised and attached to bibliographic record
How diverse are our diets?
No full textFor many South Africans, particularly those living in rural areas and informal settlements, our diet is simply not diverse enough, find DEMETRE LABADARIOS, NELIA PATRICIA STEYN and JOHANNA NEL.
How diverse are our diets?
No full textFor many South Africans, particularly those living in rural areas and informal settlements, our diet is simply not diverse enough, find DEMETRE LABADARIOS, NELIA PATRICIA STEYN and JOHANNA NEL.
Describing the stochastic dynamics of neurons using Hamilton’s equations of classical mechanics
No full textWe consider the most likely behaviour of neuron models by formulating them in terms of Hamilton’s equations. Starting from a Lagrangian for a stochastic system, we describe how Hamilton’s equations of classical mechanics can be used to derive an equivalent description in terms of canonical co-ordinates and momenta. We give physical meaning to these generalized momenta; specifically they are linear combinations of the noise terms in the stochastic model. Pseudo-kinetic energy and potential energy terms are also derived. The conjugate momenta can be considered as growing modes, and by implication the most likely noise input to a system will grow exponentially at large times; this surprising prediction agrees with existing experimental work on a single neuron. For many-neuron models, multiple growing modes will exist, and the numerical analysis of these is more complicated; however, the approach may still provide insight on the more detailed dynamics of these systems
A piezoelectric microvalve for compact high frequency high differential pressure micropumping systems
No full textA piezoelectrically driven hydraulic amplification microvalve for use in compact high-performance hydraulic pumping systems was designed, fabricated, and experimentally characterized. High-frequency, high-force actuation capabilities were enabled through the incorporation of bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. Large valve stroke at the microscale was achieved with an hydraulic amplification mechanism that amplified (40/spl times/-50/spl times/) the limited stroke of the piezoelectric material into a significantly larger motion of a micromachined valve membrane with attached valve cap. These design features enabled the valve to meet simultaneously a set of high frequency (/spl ges/1 kHz), high pressure(/spl ges/300 kPa), and large stroke (20-30 /spl mu/m) requirements not previously satisfied by other hydraulic flow regulation microvalves. This paper details the design, modeling, fabrication, assembly, and experimental characterization of this valve device. Fabrication challenges are detailed
Hypertension in pregnancy : round-table discussion: part 1: cardiovascular profile
No full textAuthors: Brink, A.; Akande, W.; Moodley, J.; Hague, W.; Hall, D.; Steyn, W.; Dekker, G.; Odendaal, H
Whose story is it anyway? The ethics of narration and the narration of ethics in Summertime and Die Sneeuslaper
No full textIncludes bibliographical references.This dissertation analyses and compares the narrative strategies in J.M. Coetzee’s Summertime and Marlene van Niekerk’s Die sneeuslaper and considers the implications of these strategies for the authors’ exploration of the ethics of writing. Much has been written about the literary oeuvres of both Coetzee and Van Niekerk, including studies of the translations of Van Niekerk’s Afrikaans novels into English. There are few “interlingual” comparative studies of contemporary works in Afrikaans and English, however, and certainly none to my knowledge which compares the work of Coetzee and Van Niekerk. My contribution to the conversation about Coetzee’s and Van Niekerk’s work, but also to an increasingly multilingual and interconnected South African literary criticism, will be a comparison of one recent work by each of these two authors, written in English and Afrikaans respectively. I draw on the theories of Bakhtin, Barthes and Levinas to consider the ethical dimension of texts in which “double-voicedness”, a questioning not only of existence, but of the self is fore grounded in the content and narrative structure; where there is a shift in focus from the author to the reader (“the birth of the reader”) and “utterances” are made with the response of “the other” in mind
Investigation and Modelling of Fetal Sheep Maturation
No full textIn this thesis, I study the maturational changes of the fetal sheep ECoG (electrocorticogram) in its third-trimester of gestation (95-140 days of gestation), investigate three continuum models for electrical behaviour of the cortex, and tune the parameters in one of these models to generate the discontinuous EEG waves in the immature cortex. Visual inspection of the ECoG time-series shows that the third-trimester of fetal sheep is comprised of two stages: early third-trimester characterised by bursting activity separated by silent intervals, and late third-trimester with well-defined SWS (slow wave sleep) and REM (rapid eye movement) sleep states. For the late third-trimester, the results of power, correlation time, and SVD (singular value decomposition) entropy analysis demonstrate that the sleep state change is a cortical phase transition—with SWS-to-REM transition being a first-order transition, and REM-to-SWS second-order. Further analyses by correlation time, SVD entropy, and spectral edge frequency display that the differentiation of the two distinct SWS and REM sleep states occurs at about 125 dGA (day gestational age). Spectral analysis divides the third-trimester into four stages in terms of the frequency and amplitude variations of the major resonances. Spindle-like resonances only occur in the first stage. A power surge is observed immediately prior to the emergence of the two sleep states. Most significant changes of the spectrum occur during the fourth stage for both SWS (in amplitude) and REM (in frequency) sleep states. For the modelling of the immature cortex, different theoretical descriptions of cortical behaviour are investigated, including the ccf (cortical column field) model of J. J. Wright, and the Waikato cortical model. For the ccf model at centimetric scale, the time-series, fluctuation power, power law relation, gamma oscillation, phase relation between excitatory and inhibitory elements, power spectral density, and spatial Fourier spectrum are quantified from numerical simulations. From these simulations, I determined that the physiologically sophisticated ccf model is too large and unwieldy for easy tuning to match the electrical response of the immature cortex. The Waikato near-far fast-soma model is constructed by incorporating the back-propagation effect of the action potential into the Waikato fast-soma model, state equations are listed and stability prediction are performed by varying the gap junction diffusion strength, subcortical drive, and the rate constants of the near- and far-dendritic tree. In the end, I selected the classic and simpler Waikato slow-soma mean-field model to use for my immature cortex simulations. Model parameters are customised based on the physiology of the immature cortex, including GABA (an inhibitory neurotransmitter in adult) excitatory effect, number of synaptic connections, and rate constants of the IPSPs (inhibitory postsynaptic potential). After hyperpolarising the neuron resting voltage sufficiently to cause the immature inhibitory neuron to act as an excitatory agent, I alter the rate constant of the IPSP, and study the stability of the immature cortex. The bursting activity and quiet states of the discontinuous EEG are simulated and the gap junction diffusion effect in the immature cortex is also examined. For a rate constant of 18.6 s-1, slow oscillations in the quiet states are generated, and for rate constant of 25 s-1, a possible cortical network oscillation emerges. As far as I know, this is the first time that the GABA excitatory effect has been integrated into a mean-field cortical model and the discontinuous EEG wave successfully simulated in a qualitative way
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