A thesis submitted in fulfilment of the requirements of the degree Doctor of Philosophy in the Department of Curriculum and Instructional Studies, Faculty of Education, 2018. / Writing remains central to effective learning. It is through writing that learners are able to access knowledge, express their ideas and thoughts in different subjects across the curriculum. Through writing, learners are also expected to display the acquired knowledge in their assessments and examinations. Competency in writing is therefore crucial for learners, especially in the last three years of schooling, prior to them entering the demanding writing contexts of higher education. Despite this, writing continues to be a challenge for the majority of learners in South Africa, especially those learners writing in their second language in which they are not competent and confident. Thus, this calls for the special attention to how writing is taught and learnt, specifically at the FET levels. This study, therefore, investigated the nature and pedagogical implication of English First Additional Language Learners (EFAL) writing among Further Education and Training (FET) phase learners in the Pinetown District. Guided by the Socio-cultural Learning Theory, I observed the writing lessons, analysed the types of writing produced by learners and explored the quality of writing among FET learners to understand the extent to which the writing practices and pedagogy meet the expectations of the curriculum. Five FET schools in the Pinetown District were purposively selected to participate in this study. Underpinned by the qualitative framework, the study employed the interpretative paradigm to understand the human experiences of writing within the natural classroom contexts. To gain insights into the writing activities and classroom pedagogy, five writing lessons were observed and recorded using a video camera. To understand the types of writing and the quality of learners’ writing, learners’ written tasks were collected and analysed. Findings from the analysis of the sample of written tasks collected from the five schools indicated that learners produced different types of writing: narrative essays, formal letters, friendly letters, formal letters, obituaries, diary entries, directions, interviews, invitation cards and covering letters. The study also found that this is in line with the curriculum which suggests that learners should be exposed to different types of texts to develop their cognitive and creative writing skills. The study found ii that the learners’ writing contained recurring incorrect spelling, misuse of capitalisation, violation of punctuation rules and incorrect use of tenses. Even though the analysis of the learners’ written tasks revealed that such incorrect use of writing mechanics does not necessarily affect comprehension or meaning of the learners’ texts, they, however, affect the overall judgement of the learners’ writing. Data from classroom observations, lesson analyses and analysis of the curriculum show that, at most, the writing approaches used by the teachers were in line with the writing approach suggested by the curriculum. Findings from the analyses of the writing lessons indicate that teachers mostly used the question and answer method to teach writing in the five schools. This method entails the teachers controlling the interactions in the classrooms through nomination-response cycle. The findings from the analyses of lessons suggest that teachers creatively employed code-switching for pedagogical and pastoral purposes. The study found code-switching to enhance learners’ understanding and thus fulfils an academic purpose, especially in situations where switching to isiZulu explained concepts better. The study concludes that the effectiveness of any curriculum and pedagogy depends on the teachers’ knowledge and understanding of writing and approaches to writing. For the effective development of the learners’ writing, teachers must, firstly, understand their curriculum and implement it in their classrooms. Secondly, the researcher believes that successful teaching and learning of writing also depends on the effective instruction methods that embrace the socio-cultural learning perspectives. Lastly, the researcher found code-switching to be inevitable in second language writing classrooms where the teachers and learners are competent in more than one language. The study recommends collaborative writing activities in the learners’ Zone of Proximal Development (ZPD) and the recognition of learners’ home language for the learning of second language writing skills.

Interior walls are one of the biggest environmental culprits in office renovations. With this project I want to consider a new way to radically alter the layout of public spaces without producing waste.  The purpose of this project is to investigate the potential for using brickwork as an inspiration for adaptable walls in offices and public spaces. I will explore how sustainable, lightweight materials such as hemp or wool can be used to create lightweight “bricks” with acoustic properties. These bricks are assembled in an accordion-like structure that allows the wall to be extended, folded and to create various shapes.  By rethinking the interior wall, I have created a circular system of semi-permanent walls that can transform offices, workspaces and meeting rooms at will, and allows for an affordable and sustainable alternative to costly and disruptive renovations. With a leasing system the walls are part of a circular business model. Using brickwork as an inspiration, and a way to connect innovations to architectural history, this project explores the possibilities inherent in the modularity of bricks.

A new multiple-gate transistor, the SOI MOS-JFET, is presented. This device combines the MOS field effect and junction field effect within one transistor body. Measured I-V characteristics are provided to illustrate typical modes of operation and the functionality associated with each gate. Two-dimensional simulations of the device?s cross-section will be presented to illustrate various conduction modes under different bias conditions. Test results indicate the MOS-JFET is well suited for both high-voltage and low-voltage circuit demands for systems-on-a-chip applications on SOI technology. Analog building-block circuits based the MOS-JFET are also presented.

No description available.

No description available.

The ultimate goal for power electronics is to convert one form of raw electrical energy into a usable power source with the lowest amount of loss. A considerable portion of these losses are due to the use of switching devices themselves. Device losses can be apportioned to conduction loss and switching loss. It is commonly known and practiced that conduction loss can be reduced by driving MOSFETs and IGBTs harder with gate voltages closer to the maximum rating. This lowers the voltage across the device in the path of the amplified current and ultimately reduces power dissipated by the device. However, switching losses of these devices are not as easily characterized or intuitive for power electronics designers. This is mainly due to the fact that the parasitic reactive elements are nonlinear and not as readily documented as I-V characteristics of a given power device. For example, non-linear parasitic capacitances in the device are given for a fixed frequency across a voltage sweep. Parasitic inductance is typically not even mentioned in the datasheet. The switching losses of these devices depend on these mysterious reactances. A functional way to obtain estimates of switching loss is to test the device under the conditions the device will be used. However, this task must be approached carefully in order to accurately measure the voltage and current of the device. Measurement devices also have parasitic impedances of their own that can add or subtract to switching energy during turn on or turn off and create misleading results. Preliminary testing was performed on multiple devices. After preliminary testing and deliberation, a device-measurement printed circuit board was made to easily replace switching devices of the same package. This thesis presents switching loss measurements of medium-power capable devices in the tens of kW range. It also aims to attribute characteristics of switching voltage and current waveforms to the internal structure of the devices. The device tester designed is versatile since the output buffer of the gate drive is comprised of D-PAK totem pole BJTs. This is able to drive both current and voltage driven devices, i.e. SiC J-FETs (current-driven) and other voltage-driven devices (i.e. MOSFETs and IGBTs). It also allows for TO-220 and TO-247 packaged power diodes. / Master of Science

Investigations performed in order to understand the electronic and optoelectronic properties of field effect transistors based on few layers of 2D Copper Indium Selenide (CuIn7Se11) are reported. In general, field effect transistors (FETs), electric double layer field effect transistors (EDL-FETs), and photodetectors are crucial part of several electronics based applications such as tele-communication, bio-sensing, and opto-electronic industry. After the discovery of graphene, several 2D semiconductor materials like TMDs (MoS2, WS2, and MoSe2 etc.), group III-VI materials (InSe, GaSe, and SnS2 etc.) are being studied rigorously in order to develop them as components in next generation FETs. Traditionally, thin films of ternary system of Copper Indium Selenide have been extensively studied and used in optoelectronics industry as photoactive component in solar cells. Thus, it is expected that atomically thin 2D layered structure of Copper Indium Selenide can have optical properties that could potentially be more advantageous than its thin film counterpart and could find use for developing next generation nano devices with utility in opto/nano electronics. Field effect transistors were fabricated using few-layers of CuIn7Se11 flakes, which were mechanically exfoliated from bulk crystals grown using chemical vapor transport technique. Our FET transport characterization measurements indicate n-type behavior with electron field effect mobility µFE ≈ 36 cm^2 V^-1 s^-1 at room temperature when Silicon dioxide (SiO2) is used as a back gate. We found that in such back gated field effect transistor an on/off ratio of ~ 10^4 and a subthreshold swing ≈ 1 V/dec can be obtained. Our investigations further indicate that Electronic performance of these materials can be increased significantly when gated from top using an ionic liquid electrolyte [1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6)]. We found that electron field effect mobility µFE can be increased from ~ 3 cm^2 V^-1 s^-1 in SiO2 back gated device to ~ 18 cm^2 V^-1 s^-1 in top gated electrolyte devices. Similarly, subthreshold swing can be improved from ~ 30 V/dec to 0.2 V/dec and on/off ratio can be increased from 10^2 to 10^3 by using an electrolyte as a top gate. These FETs were also tested as phototransistors. Our photo-response characterization indicate photo-responsivity ~ 32 A/W with external quantum efficiency exceeding 10^3 % when excited with a 658 nm wavelength laser at room temperature. Our phototransistor also exhibit response times ~ tens of µs with specific detectivity (D*) values reaching ~ 10^12 Jones. The CuIn7Se11 phototransistor properties can be further tuned & enhanced by applying a back gate voltage along with increased source drain bias. For example, photo-responsivity can gain substantial improvement up to ~ 320 A/W upon application of a gate voltage (Vg = 30 V) and/or increased source-drain bias. The photo-responsivity exhibited by these photo detectors are at least an order of magnitude better than commercially available conventional Si based photo detectors coupled with response times that are orders of magnitude better than several other family of layered materials investigated so far. Further photocurrent generation mechanisms, effect of traps is discussed in detail.

This work builds on a semester project 2 from the winter semester of this academic year. The aim of this thesis is the design of converter using semiconductor components based on SiC technology. This converter is used in the construction of quick charger for electric vehicles. The design of this converter must be based on the requirements for compliance voltage safety. It describes the design of power components used in the construction of this facility, the determination of their losses and determines the overall efficiency of the converter. There is also proposed mathematical model of high-frequency transformer and made his simulation in Matlab-Simulink.

Die vorliegende Arbeit befasst sich mit der Anwendbarkeit von transparenter Elektronik basierend auf oxidischen Halbleitern in Multielektrodenarrays zur Messung von neuronalen Signalen. Im ersten experimentellen Kapitel werden auf Zinkoxid basierende Bauelemente untersucht. Verschiedene Varianten von Feldeffekttransistoren (FETs) werden charakterisiert und ihre Eignung zur Detektion von Zellsignalen überprüft. Die Anwendbarkeit physikalischer Modelle zur Beschreibung von ZnO-basierten Metal-Halbleiter-FETs (MESFETs) wird behandelt. Weiterhin wird die Eignung von einfachen Inverterschaltungen zur Spannungsverstärkung diskutiert. Das zweite Kapitel thematisiert Rauschmessungen an unterschiedlichen ZnO-basierten Proben, darunter Dünnfilme, Mikronadeln, MESFETs und Inverter. Darauf aufbauend wird die Auswirkung des gemessenen Stromrauschens auf die Sensitivität der Bauelemente nachvollzogen und theoretisch modelliert. Im dritten Kapitel wird das Verhalten der Bauelemente im Kontakt mit Elektolyt beschrieben. Die Signalübertragung von Spannungsänderungen im Elektrolyt auf die Chipelektronik wird mit verschiedenen Messmethoden charakterisiert. Dabei kommt teilweise ein selbstgebauter Vorverstärker zum Einsatz, dessen Aufbau ebenfalls beschrieben wird. Die Stabilität der verwendeten Materialien in physiologischen Salzlösungen und ihre Biokompatibilität wird überprüft. Darüber hinaus werden FETs mit Elektrolytgate und Zinkzinnoxid-Kanal vorgestellt.:1. Introduction 2. Measurement Setup and Sample Fabrication 2.1. Device Fabrication 2.2. Measurement Methods 2.3. Current Amplifier with Offset Compensation 3. Oxide Semiconductor Based Devices 3.1. Theoretical Description 3.2. Thin Films 3.4. Simple Inverter 3.5. Test Circuit for Active Matrix Configurations 4. Noise 4.1. Noise Sources 4.2. Contributions from Measurement Setup 4.3. Homogenous ZnO Samples 4.4. ZnO Based Devices 5. Experiments in Electrolyte and with Cells 5.1. Cell-Transistor Coupling 5.2. Materials in Electrolytical and Biological Environment 5.3. Electrode Arrays with Field-Effect Transistors 5.4. Electrode Arrays with Simple Inverters 5.5. Electrode Arrays with Solution Gated Transistors 6. Conclusion and Outlook Appendices Bibliography Symbols and Abbreviations List of Own and Contributed Articles Acknowledgements

Dentro de los sistemas de comunicación han adquirido gran importancia las aplicaciones en alta frecuencia, lo que conlleva un gran desarrollo en este tipo de tecnologías; aplicaciones bajo ruido, potencia monolítico, etc. Este tipo de tecnologías precisan un conocimiento no lineal de los circuitos. Por ello el presente trabajo se ha orientado hacia la resolución de tres problemas no lineales fundamentales que son: modelización física, análisis no lineal de sistemas activos autónomos trabajando en microondas y el desarrollo de una formulación matemática compacta dirigida hacia la optimización gran señal de sistemas activos a transistor Mesfet. El trabajo se completa con una verificación experimental de los comportamientos simulados teóricamente lo que confiere a los métodos matemáticos un amplio rango de validez