Accurate transistor models are important in wireless and microwave circuit design. Large-signal field-effect transistor (FET) models are generally extracted from current-voltage (IV) characteristics, small-signal S-parameters, and large-signal measurements. This dissertation describes improved characterization and measurement validation techniques for FET models that correctly account for thermal and trapping effects. Demonstration of a customized pulsed-bias, pulsed-RF S-parameter system constructed by the author using a traditional vector network analyzer is presented, along with the design of special bias tees to allow pulsing of the bias voltages. Pulsed IV and pulsed-bias S-parameter measurements can provide results that are electrodynamically accurate; that is, thermal and trapping effects in the measurements are similar to those of radio-frequency or microwave operation at a desired quiescent bias point. The custom pulsed S-parameter system is benchmarked using passive devices and advantages and tradeoffs of pulsed S-parameter measurements are explored. Pulsed- and continuous-bias measurement results for a high-power transistor are used to validate thermal S-parameter correction procedures. A new implementation of the steepest-ascent search algorithm for load-pull is presented. This algorithm provides for high-resolution determination of the maximum power and associated load impedance using a small number of measured or simulated reflection-coefficient states. To perform a more thorough nonlinear model validation, it is often desired to find the impedance providing maximum output power or efficiency over variations of a parameter such as drain voltage, input power, or process variation. The new algorithm enables this type of validation that is otherwise extremely tedious or impractical with traditional load-pull. A modified nonlinear FET model is presented in this work that allows characterization of both thermal and trapping effects. New parameters and equation terms providing a trapping-related quiescent-bias dependence have been added to a popular nonlinear ("Angelov") model. A systematic method for fitting the quiescent-dependence parameters, temperature coefficients, and thermal resistance is presented, using a GaN high electron-mobility transistor as an example. The thermal resistance providing a good fit in the modeling procedure is shown to correspond well with infrared measurement results.

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Due to the current research needs and the lack of commercial multi-channel, multi-constellation GNSS receivers, a two-board solution has been developed so it can be mated with and take advantage of the processing power of the FPGA board branded as MicroZed. In order to achieve the proposed goals, an initial phase for assessing and updating the older design, building, and testing of SiGe modules (including both the electronics and casings) has been carried out. The results included demonstrate performances at logging GPS-L1 data with similar C/N0 and AGC values as the previous versions of the modules and offering navigation solutions with accuracies of a few meters. Secondly, a first iteration and design proposal for the new generation receiver has been proposed for GPS and GLONASS L1 and L2, which has been manufactured and tested. Partial tests have been performed due to the flaws of the current revision of the MicroZed Board in regards to its communication peripherals, and the results have validated the receiver’s design provided certain modifications are considered for future iterations. Furthermore, voltage and frequency tests have provided results with an error of less than 7%, and signal tests have provided C/N0 values similar to those of the SiGe modules of around 47[dB-Hz] which will be a useful baseline for future iterations. Finally, a design proposal for an Interface Board used between the older NT1065_PMOD Board and other FPGA boards carrying the standardized FMC connectors has been added to the report and negotiations with manufacturers have been engaged.

Leaflet replacement in aortic valve repair (AVr) is associated with increased long-term repair failure. Hemodynamic performance and mechanical stress levels were investigated after porcine AVr with 5 types of clinically relevant replacement materials to ascertain which material(s) would be best suited for repair. Porcine aortic roots with intact aortic valves were placed in a left-heart simulator mounted with a high-speed camera for baseline valve assessment. Then, the non-coronary leaflet was excised and replaced with autologous porcine pericardium (APP), glutaraldehyde-fixed bovine pericardial patch (BPP; Synovis™), extracellular matrix scaffold (CorMatrix™), or collagen-impregnated Dacron (HEMASHIELD™). Hemodynamic parameters were measured over a range of cardiac outputs (2.5–6.5L/min) post-repair. Material properties of the above materials along with St. Jude Medical™ Pericardial Patch with EnCapTM Technology (SJM) were determined using pressurization experiments. Finite element models of the aortic valve and root complex were then constructed to verify the hemodynamic characteristics and determine leaflet stress levels. This study demonstrates that APP and SJM have the closest profiles to normal aortic valves; therefore, use of either replacement material may be best suited. Increased stresses found in BPP, HEMASHIELD™, and CorMatrix™ groups may be associated with late repair failure.

Leaflet replacement in aortic valve repair (AVr) is associated with increased long-term repair failure. Hemodynamic performance and mechanical stress levels were investigated after porcine AVr with 5 types of clinically relevant replacement materials to ascertain which material(s) would be best suited for repair. Porcine aortic roots with intact aortic valves were placed in a left-heart simulator mounted with a high-speed camera for baseline valve assessment. Then, the non-coronary leaflet was excised and replaced with autologous porcine pericardium (APP), glutaraldehyde-fixed bovine pericardial patch (BPP; Synovis™), extracellular matrix scaffold (CorMatrix™), or collagen-impregnated Dacron (HEMASHIELD™). Hemodynamic parameters were measured over a range of cardiac outputs (2.5–6.5L/min) post-repair. Material properties of the above materials along with St. Jude Medical™ Pericardial Patch with EnCapTM Technology (SJM) were determined using pressurization experiments. Finite element models of the aortic valve and root complex were then constructed to verify the hemodynamic characteristics and determine leaflet stress levels. This study demonstrates that APP and SJM have the closest profiles to normal aortic valves; therefore, use of either replacement material may be best suited. Increased stresses found in BPP, HEMASHIELD™, and CorMatrix™ groups may be associated with late repair failure.

The researcher investigated the management of multi-grade teaching for optimal learning in Gauteng West primary schools. Ten participants, including school principals, heads of departments and educators participated in individual and focus group interviews and in observation of multi-grade classroom contexts. Findings revealed that educators involved in multi-grade teaching feel overwhelmed by challenging work conditions pertaining to large learner numbers and a lack of adequate didactical resources. This is exacerbated by a lack of professional development by means of tailor-made training for multi-grade teaching and the presumption that educators teaching such classes must merely change the monograde teaching format of the curriculum themselves for applicable implementation in a multi-grade teaching context. This leaves educators socially, emotionally and professionally isolated. Recommendations include the involvement of seasoned educators with expert knowledge and experience of multi-grade teaching to present training sessions constituting advice and support to inexperienced educators involved in said teaching. / Die navorser het die bestuur van meergraadonderrig by laerskole in Wes-Gauteng vir optimale leer ondersoek. Afgesien van individuele en fokusgroeponderhoude met skoolhoofde, departementshoofde en opvoeders, is waarneming in meergraadklaskamers gedoen. Volgens die bevindings bemoeilik groot klasse en ʼn gebrek aan didaktiese hulpmiddels meergraadopvoeders se taak. Meergraadopvoeders voel hulle geensins opgewasse teen hierdie werksomstandighede nie. ʼn Gebrek aan opleiding in meergraadonderrig en die veronderstelling dat opvoeders die eengraadformaat van die kurrikulum in ʼn meergraadformaat kan omskakel, vererger sake. Opvoeders is van mening dat hulle maatskaplik, emosioneel en professioneel in die steek gelaat word. Daar word aanbeveel dat gesoute opvoeders met kennis van en ervaring in meergraadonderrig onervare opvoeders oplei en adviseer. / Monyakisisi o dirile dinyakisiso ka ga go ruta dikereiti tse fapanego go fihlelela bokgoni le tsebo tikologong ya go thekga dinyakwa tsa baithuti dikolong tsa phoraemari go la Gauteng Bodikela. Batseakarolo ba lesome, go akaretswa dihlogo tsa dikolo, dihlogo tsa dikgoro le barutisi ba tseere karolo ditherisanong ka botee le dihlopha tseo di nepisitswego gape le temogo dikemong tsa diphaposi tsa dikereiti tse di fapanego. Dikhwetso di utollotse gore barutisi bao ba rutago dikereiti tse fapanego ba imelwa ke maemo a modiro wo o nyakago gore ba ntshe bokgoni bja bona ka moka ka lebaka la dipalo tse ntsi tsa baithuti le tlhokego ya dithusi tsa thuto tse di lekanego. Se se thatafiswa ke tlhokego ya tlhabollo ya profesene ye ka go fa tlhahlo yeo e lebanego ya go ruta dikreiti tse fapanego le kgopolo ya go re barutisi bao ba rutago ba swanela go no fetola popego ya lenaneothuto la kereiti e tee ka bobona go re ba le dirise kemong ya go ruta dikereiti tse fapanego. Se se dira gore barutisi ba ikhwetse ba se na kgokagano le setshaba leagong, ba hloka bao ba ka llelago go bona le go se be le bao ba nago le kgahlego go profesene ya bona. Ditshisinyo di akaretsa go ba gona ga barutisi bao e lego kgale ba ruta ba nago le maitemogelo le botsebi go ruta dikereiti tse fapanego go hlagisa dipaka tsa tlhahlo tseo di fago maele le thuso go barutisi bao ba se nago maitemogelo. / Educational Management and Leadership / M. Ed. (Education Management)