We invistegated the characteristic of GaN nanostructure grown on£^-LiAlO2 substrate by molecular epitaxy beam. We observed the c-plane GaN pillar and M-plane GaN terraces assembled at the LiAlO2 substrate. It was found that the [0001 ¡Â] disk was established with the capture of N atoms by most-outside Ga atoms, while the pyramid was obtained due to the missing of most-outside N atoms. To continue, the photointensity of cathode luminescence excited from the pillar structure was one order of amplitude greater than that from M-plane.

The paper describes major features of an unmanned aerial vehicle, designed undersafety and performance requirements for missions of aerial photography and remotesensing in precision agriculture. Unmanned aerial vehicles have vast potential asobservation and data gathering platforms for a wide variety of applications. The goalof the project was to develop a small, low cost, electrically powered, unmanned aerialvehicle designed in conjunction with a payload of imaging equipment to obtainremote sensing images of agricultural fields. The results indicate that this conceptwas feasible in obtaining high quality aerial images.

Thesis (MScEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: South Africa has a signi cant potential resource for electrical power generation in the Agulhas Current on the southeast coast. The Ocean Current Energy Convertor studied in this project was designed to generate power from this current. The feasibility of this device was investigated by analysing the dynamic stability and controllability of the convertor, when acted upon by hydrodynamic forces while harvesting energy from the current. A simulation model was developed to predict the dynamic behaviour using the Simulink software suite. A scale model of the prototype was built and tested in the Towing Tank at Stellenbosch University, and the experimental results were compared against the simulation results. A control algorithm was designed, using the mathematical model, to control the roll angle and deployment depth. The control algorithm was tested in simulation. The results indicated that the simulation model accurately predicted the behaviour of the prototype in testing, and results showed that the device is both stable and controllable. It was concluded that this OCEC design concept warrants further investigation. The recommendations are that the experimental model be improved to ensure reliable experimental results, that further complexity be added to the simulation model, and that the control algorithm be tested on the improved prototype in the towing tank. / AFRIKAANSE OPSOMMING: Die Agulhas-seestroom aan die suidooskus van Suid-Afrika bied 'n aansienlike potensiële hulpbron vir elektriese kragopwekking. Die seestroomenergieomsetter (SEO) wat in hierdie projek bestudeer is was ontwikkel om krag uit hierdie seestroom te genereer. Die doenlikheid van hierdie toestel is ondersoek deur die dinamiese stabiliteit en beheerbaarheid van die omsetter onder die invloed van hidrodinamiese kragte te analiseer terwyl dit energie van die stroom inwin. 'n Simulasiemodel is met behulp van Simulink-sagteware ontwikkel om die dinamiese gedrag te voorspel. 'n Skaalmodel van die prototipe was gebou en in die sleeptenk by Universiteit Stellenbosch getoets en die eksperimentele resultate met die simulasie se resultate vergelyk. 'n Beheer-algoritme is daarna ontwerp, deur middel van die wiskundige model, om die rolhoek en diepte van ontplooiing te beheer.Hierdie algoritme is tydens simulasie getoets. Die resultate het aangedui dat die simulasiemodel akkuraat die gedrag van die prototipe tydens toetse voorspel het, en die resultate het gewys dat die toestel beide stabiel en beheerbaar is. Die gevolgtrekking is gemaak dat die SEO se ontwerpkonsep verdere studie regverdig. Die aanbevelings is dat die eksperimentele model verbeter word om betroubare eksperimentele resultate te verseker, dat verdere kompleksiteit by die simulasiemodel gevoeg word, en dat die beheer-algoritme op die verbeterde model in die sleeptenk getoets word.

General lighting with InGaN light emitting diodes (LEDs) as light sources is of particular interest in terms of energy savings and related environmental benefits due to high lighting efficiency, long lifetime, and Hg-free nature. Incandescent and fluorescent light sources are used for general lighting almost everywhere. But their lighting efficiency is very limited: only 20-30 lm/W for incandescent lighting bulb, approximately 100 lm/W for fluorescent lighting. State-of-the-art InGaN LEDs with a luminous efficacy of over 200 lm/W at room temperature have been reported. However, the goal of replacing the incandescent and fluorescent lights with InGaN LEDs is still elusive since their lighting efficiency decreases substantially when the injection current increases beyond certain values (typically 10-50 Acm-2). In order to improve the electroluminescence (EL) performance at high currents for InGaN LEDs, two approaches have been undertaken in this thesis. First, we explored the preparation and characterization of non-polar and semi-polar GaN substrates (including a-plane, m-plane and semi-polar planes). These substrates serve as promising alternatives to the commonly used c-plane, with the benefit of a reduced polarization-induced electric field and therefore higher quantum efficiency. It is demonstrated that LEDs on m-plane GaN substrates have inherently higher EL quantum efficiency and better efficiency retention ability at high injection currents than their c-plane counterparts. Secondly, from a device structure level, we explored the possible origins of the EL efficiency degradation at high currents in InGaN LEDs and investigated the effect of hot electrons on EL of LEDs by varying the barrier height of electron blocking layer. A first-order theoretical model is proposed to explain the effect of electron overflow caused by hot electron transport across the LED active region on LED EL performance. The calculation results are in agreement with experimental observations. Furthermore, a novel structure called a “staircase electron injector” (SEI) is demonstrated to effectively thermalize hot electrons, thereby reducing the reduction of EL efficiency due to electron overflow. The SEI features several InyGa1-yN layers, with their In fraction (y) increasing in a stepwise manner, starting with a low value at the first step near the junction with n-GaN.