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A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2015 / Electrical utilities are tasked with managing large numbers of assets that have long useful lives and are fairly expensive to replace. With emphasis on medium voltage vacuum circuit breakers, a key challenge is determining when circuit breakers are close to their end-of-life and what the appropriate action at that point in time should be. Condition-based maintenance, intended to “do only what is required, when it is required,” has been reported as the most effective maintenance strategy for circuit breakers. This dissertation provides an overview, together with laboratory measurements, on non-intrusive technologies and analytics that could reduce maintenance costs, unplanned outages, catastrophic failures and even enhance the reliability and lifetime of circuit breakers by means of a real-time condition monitoring and effective failure prevention maintenance approach. The key areas of research are the condition assessment of the mechanical mechanism based on coil current signature diagnosis, degradation detection of the main interrupting contacts through thermal monitoring and interrupter vacuum integrity assessment based on magnetron atmospheric condition (MAC) testing. The information from test results allows both immediate onsite analysis and trending of key parameters which enables informed asset management decisions to be taken. / GS2016

The nervous system is a complex organ that functions in most metazoans to sense and respond to a constantly changing world. How the nervous system does this is a major focus of systems-level neuroscience. This dissertation investigates the neural basis of the sensorimotor transformation underlying a spatial orientation strategy in the nematode Caenorhabditis elegans. Motile organisms rely on spatial orientation strategies to navigate to environments that are conducive to organismal fitness and comfort, e.g. environments with the correct temperature, light level, or access to food and mates. As such, spatial orientation strategies as a class represent a key behavior common to most forms of life on earth. To explore the behavioral mechanism used by C. elegans for spatial orientation, we designed and manufactured a microfluidic device that breaks the feedback loop between self-motion and environmental change by partially restraining the animal. The device takes advantage of laminar flow at small scale to provide distinct environments across the dorsoventral undulation that constitutes locomotion in this animal without using a physical barrier. This device allowed us to conclude that worms use the change in chemical concentration sensed between lateral extremes of the locomotion cycle to direct forward locomotion toward a favorable stimulus, an orientation strategy termed klinotaxis. We then investigated the neuronal basis of this behavior using laser ablation, calcium imaging, and optogenetic stimulation. We found a minimal neuronal network for klinotaxis to sodium chloride including the ASE, AIY, AIZ, and SMB neuron classes that displays left/right asymmetry across the sensory neuron, interneuron, and motor neuron levels. We extended these results by ablating other neurons that have been implicated in klinotaxis in other studies. Finally, we imaged the ASE neurons during klinotaxis in microfluidic device and found that these neurons are active on the timescale of individual head swings. Additionally, we found anecdotal evidence that photostimulation of ASE neurons expressing the light sensitive ion channel Channel Rhodopsin (CHR2) is sufficient to stimulate klinotaxis behavior. This dissertation includes previously published co-authored material.

by Fan Chun-Wah. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 90-[91]). / Abstract also in Chinese. / Chapter CHAPTER 1: --- INTRODUCTION --- p.1 / Chapter CHAPTER 2: --- BACKGROUND OF INJECTION LOCKING --- p.3 / Chapter 2.1 --- Basics of Injection Locking --- p.3 / Chapter 2.2 --- Analytical Methods for Injection Locking --- p.6 / Chapter 2.2.1 --- Analysis of Fundamental Mode Injection Locking --- p.6 / Chapter 2.2.2 --- Analysis of Ha rmonic/Subharmonic Injection Locking --- p.9 / Chapter 2.4 --- Numerical Methods --- p.11 / Chapter CHAPTER 3: --- THE VOLTERRA SERIES METHOD FOR NONLINEAR CIRCUIT ANALYSIS --- p.13 / Chapter 3.1 --- Volterra Expansion --- p.14 / Chapter 3.2 --- Evaluation of Nonlinear Transfer Function --- p.16 / Chapter 3.2.1 --- Probing Method --- p.16 / Chapter 3.2.2 --- Nonlinear Current Method --- p.17 / Chapter 3.2.3 --- Higher order nonlinear current --- p.20 / Chapter 3.2.4 --- Voltage response by using nonlinear transfer function --- p.20 / Chapter 3.3 --- Advantage of Volterra Series --- p.21 / Chapter 3.4 --- Volterra Series Simulator(VSS) Implementation --- p.22 / Chapter 3.4.1 --- Admittance Matrix Formulation --- p.22 / Chapter 3.4.2 --- Evaluation of Nonlinear Response --- p.26 / Chapter 3.4.3 --- Local Cache and Global Cache --- p.26 / Chapter 3.4.4 --- Components Library --- p.27 / Chapter 3.4.5 --- Verification of Simulator --- p.27 / Chapter CHAPTER 4: --- VOLTERRA SERIES GENERAL INJECTION-LOCKED OSCILLATOR FORMULATION --- p.28 / Chapter 4.1 --- Volterra Series Approach to Analysis of Autonomous System --- p.29 / Chapter 4.1.1 --- Chua and Tang's work --- p.29 / Chapter 4.1.2 --- Cheng and Everard's work --- p.29 / Chapter 4.1.3 --- Huang and Chu 's work --- p.30 / Chapter 4.2 --- A Novel Approach --- p.33 / Chapter 4.3 --- Derivation of Determining Equation --- p.35 / Chapter 4.4 --- Injection Lock vector and circuit synthesis --- p.38 / Chapter 4.5 --- Modification to Volterra Series Simulator (VSS) --- p.40 / Chapter CHAPTER 5: --- CIRCUIT MODELING AND PARAMETER EXTRACTION --- p.42 / Chapter 5.1 --- Forward-Bias Gate Measurement --- p.42 / Chapter 5.2 --- Low FREQUENCY S-PARAMETER MEASUREMENT --- p.50 / Chapter 5.3 --- Parameter Extraction from High Frequency S-Parameter Data --- p.52 / Chapter 5.3.1 --- Direct Extraction Method --- p.52 / Chapter 5.3.2 --- Estimation of lead inductance --- p.56 / Chapter 5.4 --- Large Signal Characterization and Extraction --- p.59 / Chapter 5.4.1 --- Large Signal Model --- p.59 / Chapter 5.4.2 --- Extraction of g2 and g3 --- p.60 / Chapter 5.5 --- Equivalent circuit model for inductor and capacitor --- p.67 / Chapter CHAPTER 6: --- APPLICATION TO 1/3 ANALOG FREQUENCY DIVIDER --- p.68 / Chapter 6.1 --- Oscillator design by negative resistance approach --- p.68 / Chapter 6.2 --- Simulation of Free Running Oscillation by VSS --- p.73 / Chapter 6.3 --- Simulation of injection locked oscillator by VSS --- p.75 / Chapter 6.4 --- Injection Locking Experiment --- p.77 / Chapter 6.5 --- Injection Lock Vector --- p.80 / Chapter CHAPTER 7: --- CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK --- p.85 / Chapter 7.1 --- Conclusions --- p.85 / Chapter 7.2 --- Recommendations for Future Work --- p.86 / APPENDIX 1: REFERENCES --- p.87 / APPENDIX 2: PUBLICATION --- p.91

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The adaptation of standard integrated circuit (IC) technology for biosensors in drug discovery pharmacology, neural interface systems, environmental sensors and electrophysiology requires electrodes to be electrochemically stable, biocompatible and affordable. Unfortunately, the ubiquitous IC technology, complementary metal oxide semiconductor (CMOS), does not meet the first of these requirements. For devices intended only for research, modification of CMOS by post-processing using cleanroom facilities has been achieved by others. However, to enable adoption of CMOS as a basis for commercial biosensors, the economies of scale of CMOS fabrication must be maintained by using only low-cost post-processing techniques. The scope of this work was to develop post-processing methods that meet the electrochemical and biocompatibility requirements but within the low-cost constraint. Several approaches were appraised with the two most promising designs taken forward for further investigation. Firstly, a process was developed whereby the corrodible aluminium is anodised to form nanoporous alumina and further processed to optimise its impedance. A second design included a noble metal in the alumina pores to enhance further the electrical characteristics of the electrode. Experiments demonstrated for the first time the ability to anodise CMOS metallisation to form the desired electrodes. Tests showed the electrode addressed the problems of corrosion and presented a surface that was biocompatible with the NG108-15 neuronal cell line. Difficulties in assessing the influence of alumina porosity led to the development of a novel cell adhesion assay that showed for the first time neuronal cells adhere preferentially to large pores rather than small pores or planar aluminium. It was also demonstrated that porosity can be manipulated at room temperature by modifying the anodising electrolyte with polyethylene glycol. CMOS ICs were designed as multiple electrode arrays and optimised for neuronal recordings. This utilised the design incorporating a noble metal deposited into the porous alumina. Deposition of platinum was only partially successful, with better results using gold. This provided an electrode surface suitable for electric cell-substrate impedance sensors (ECIS) and many other sensor applications. Further processing deposited platinum black to improve signal-to-noise ratio for neuronal recordings. The developed processes require no specialised semiconductor fabrication equipment and can process CMOS ICs on laboratory or factory bench tops in less than one hour. During the course of electrode development, new methods for biosensor packaging were assessed: firstly, a biocompatible polyethylene glycol mould process was developed for improved prototype assembly. Secondly, a commercial ‘partial encapsulation’ process (Quik-Pak, U.S.) was assessed for biocompatibility. Cell vitality tests showed both methods were biocompatible and therefore suitable for use in cell-based biosensors. The post-processed CMOS electrode arrays were demonstrated by successfully recording neuronal cell electrical activity (action potentials) and by ECIS with a human epithelial cell line (Caco2). It is evident that these developments may provide a missing link that can enable commercialisation of CMOS biosensors. Further work is being planned to demonstrate the technology in context for specific markets.