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CIVINS / CIVINS

The method of electrodeless conductivity measurement using two coils wound on toroidal ferrite cores in close proximity, coupled by the induced current in the electrolyte and operating in the audio range of frequencies has been used in process control since its introduction in the 1950s. It presents several advantages over the traditional method of measuring conductivity most important of which are stability, ruggedness, and maintenance free operation. Its major disadvantage is the large sample size required for correct operation. Despite its long established use in industry with various configurations of probe design, there is no published theory of its operation. A model of the probe operation is presented which takes into account the pattern of current flow induced in the electrolyte. This allows the electrolyte to be modelled as a resistance and the effect of geometrical factors upon this resistance is described. The operation of the probe can be represented by an equivalent circuit and theoretical expressions for the cell constant are derived. The correctness of this theory is confirmed by practical measurements. Factors affecting the performance of the probe such as operating frequency, cable length and coupling have been examined. The design and development of a conductivity meter which operates with an existing electrodeless sensor is described. It comprises analog circuitry which interfaces the sensor to a microcontroller. The microcontroller provides synchronisation, analog circuit control, calculations, display update, and interfacing with a small keyboard. A requirement that the meter be portable necessitated the minimisation of component count, cost and power consumption. Addition of reference curves for various chemicals stored in the microcontroller's EEPROM allows the instrument to be used as a concentration meter.

Approved for public release; distribution is unlimited / An evaluation was conducted of the various propulsion motors being considered for electric ship propulsion. The benefit of such an evaluation is that all of the propulsion options being considered by the U.S. Navy have been described in one document. The AC induction motor, AC synchronous motor, High Temperature Superconducting (HTS) motor and Superconducting DC Homopolar Motor (SDCHM) are examined. The properties, advantages, and disadvantages of each motor are discussed and compared. The power converters used to control large propulsion motors are also discussed. The Navy’s IPS program is discussed and the results of concept testing are presented. Podded propulsion is introduced and the benefits are discussed. The final chapter presents the simulation results of a volts/Hertz controlled 30 MW induction motor. The evaluation revealed that the permanent magnet motor is the best propulsion motor when considering mature technology, power density, and acoustic performance. HTS motors offer significant volume reductions and improved acoustic performance as compared to conventional motors. This includes both AC and DC HTS motors. The main obstacle for the SDCHM remains the unavailability of high current capacity brushes. / Ensign, United States Navy

M.Ing. / During mineral exploration a whole lot of different exploration techniques can be applied. In this thesis the instrumentation used for electromagnetic surveying, which is only one of the prospecting techniques, is inspected. In particular the thesis will be about the transmitter of the single transmitter wide band receiver airborne electromagnetic prospecting system. A new power electronic topology is proposed in order to improve this transmitter. Before this is done a reference is first established. This is done in the form of the exponential transition inverter, which is the inverter that is currently applied as transmitter in South-Africa. Another reason for looking at this circuit topology is because it is the simplest way to realize the transmitter. During the analysis of this inverter topology all the proporties of the transmitter as a whole is also investigated. The main component of the transmitter, namely the transmitter coil is also discussed. This is followed by a summary of the properties of the exponential transition inverter in which the main shortcomings of this transmitter is discussed. The greatest of which is surely that pliable frequency spectra cannot be obtained. Subsequently resonance is viewed as a solution to the shortcomings. The main contribution of this is that the pliability of the frequency spectrum can be increased, because the capasitor in this circuit can easily be changed. It is however shown that a purely resonant circuit on it's own, also is not the solution. This leads to the improved inverter topology for the transmitter, namely the Kwasi resonant inverter. It is shown in detail that the Kwasi resonant inverter is a much beter option as transmitter then the exponential transient inverter. Since this circuit also has a capacitor in it, it is shown that pliable frequency spectra can be obtained. It is futher shown how the pliability of the frequency spectrum can be improved even more by deviating from conventional methods of switch control. Mathematical analysis, as well as an experimental setup, of the different inverter topologies, are used to illustrate all of the above mentioned. As a conclusion the only drawback of the Kwasi resonant inverter, namely high voltage peaks, is addressed. A solution to this problem is proposed in the form of two different voltage clamps. The best one of the two is identified and also implemented.

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A general scheme for time-delay control systems is presented so that with particular choice of system elements and loop gain many of the existing time-delay systems can be recovered. The effects of imperfections in the system model for time-delay systems are described and analysed. Sensitivity expressions are obtained and their relationship with the structure of time-delay systems are explored. Sensitivity Analysis for a time-delay system is extended to Adaptive Control of time-delay systems. An adaptive control system for Smith's Predictor and an LOP Optimal Control scheme are investigated analytically and by simulation. Delay-free optimal control methods are extended to systems with delay for LQP and parametric optimisation. For parametric optimal control, we explore, in particular, cases where deliberate mismatch leads to improvement, and the improvement of delay-free systems by addition of delay is also investigated. Various cases of LQP are discussed and the sub-optimality of published schemes, induced by mismatch is exposed. The method is also extended to time-varying systems with time-delay.

All of the single sideband systems currently being considered for the land mobile radio service transmit a pilot tone in addition to the wanted information. The pilot is required in the receiver for automatic gain control and automatic frequency control. In particular, a phase-locked loop is often employed to perform receiver frequency control. This thesis begins by presenting background information on phase-locked receiver design and the problem caused by excess time delay introduced into the loop of a conventional phaselocked receiver. A novel phase-locked loop configuration is introduced and shown to overcome the effects of the excess time delay. The same technique is shown to greatly improve the adjacent channel selectivity performance of a phase-locked receiver. Random phase and amplitude variations are impressed upon a signal transmitted through the land mobile multipath environment. After discussing several models of the propagation medium, some of the limitations it imposes on phase-locked SSB receiver performance are introduced.

Yeung Kai-hau, Alan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references. / ACKNOWLEDGMENTS --- p.iv / ABSTRACT --- p.v / Chapter CHAPTER 1 --- Introduction --- p.1 / Chapter 1.1 --- The Information Age --- p.2 / Chapter 1.2 --- The Importance of Input/Output --- p.3 / Chapter 1.3 --- Redundant Arrays of Inexpensive Disks --- p.5 / Chapter 1.4 --- Outline of the Thesis --- p.7 / References --- p.8 / Chapter CHAPTER 2 --- Selective Broadcast Data Distribution Systems --- p.10 / Chapter 2.1 --- Introduction --- p.11 / Chapter 2.2 --- The Distributed Architecture --- p.12 / Chapter 2.3 --- Mean Block Acquisition Delay for Uniform Request Distribution --- p.16 / Chapter 2.4 --- Mean Block Acquisition Delay for General Request Distributions --- p.21 / Chapter 2.5 --- Optimal Choice of Block Sizes --- p.24 / Chapter 2.6 --- Chapter Summary --- p.25 / References --- p.26 / Chapter CHAPTER 3 --- Dynamic Multiple Parity Disk Arrays --- p.28 / Chapter 3.1 --- Introduction --- p.29 / Chapter 3.2 --- DMP Disk Array --- p.31 / Chapter 3.3 --- Average Delay --- p.37 / Chapter 3.4 --- Maximum Throughput --- p.47 / Chapter 3.5 --- Simulation with Precise Disk Model --- p.53 / Chapter 3.6 --- Chapter Summary --- p.58 / References --- p.59 / Appendix --- p.61 / Chapter CHAPTER 4 --- Dynamic Parity Logging Disk Arrays --- p.69 / Chapter 4.1 --- Introduction --- p.70 / Chapter 4.2 --- DPL Disk Array Architecture --- p.73 / Chapter 4.3 --- DPL Disk Array Operation --- p.79 / Chapter 4.4 --- Performance of DPL Disk Array --- p.83 / Chapter 4.5 --- Chapter Summary --- p.91 / References --- p.92 / Appendix --- p.94 / Chapter CHAPTER 5 --- Performance Analysis of Mirrored Disk Array --- p.101 / Chapter 5.1 --- Introduction --- p.102 / Chapter 5.2 --- Queueing Model --- p.103 / Chapter 5.3 --- Delay Analysis --- p.104 / Chapter 5.4 --- Numerical Examples and Simulation Results --- p.108 / References --- p.109 / Chapter CHAPTER 6 --- State Reduction in the Exact Analysis of Fork/Join Queues --- p.110 / Chapter 6.1 --- Introduction --- p.111 / Chapter 6.2 --- State Reduction For Closed Fork/Join Queueing Systems --- p.113 / Chapter 6.3 --- Extension To Open Fork/Join Queueing Systems --- p.118 / Chapter 6.4 --- Chapter Summary --- p.122 / References --- p.123 / Chapter CHAPTER 7 --- Conclusion and Future Research --- p.124 / Chapter 7.1 --- Summary --- p.125 / Chapter 7.2 --- Future Researches --- p.126

This thesis presents research into reducing microphone artefacts in live sound with no prior knowledge of the sources or microphones. Microphone artefacts are defined as additional sounds or distortions that occur on a microphone signal that are often undesired. We focus on the proximity effect, comb filtering and microphone bleed. In each case we present a method that either automatically implements human sound engineering techniques or we present a novel method that makes use of audio signal processing techniques that goes beyond the skills of a sound engineer. By doing this we can show that a higher quality mix of a live performance can be achieved. Firstly we investigate the proximity effect which occurs on directional microphones. We present a method for detecting the proximity effect with no prior knowledge of the source to microphone distance. This then leads to a method for reducing the proximity effect which employs a dynamic filter informed by audio analysis. Comb filtering occurs when the output of microphones reproducing the same source are mixed together. We present a novel analysis of how the accuracy of a technique to automatically estimate the correct delay of the source between each microphone is affected by source bandwidth and the windowing function applied to the data. We then present a method for reducing microphone bleed in the multiple source, multiple microphone case, both in determined and overdetermined configurations. The proposed method is extended from prior research in noise cancellation, which has not previously been applied to musical sound sources. We then present a method for simulating microphone bleed in synthesised drum recordings, where bleed enhances the realism of the output. Through subjective listening tests and objective measures each proposed method is shown to succeed at reducing the microphone artefacts while preserving the original sound source.