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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Development of a system to measure marine turbulence

Main, Ian Cameron January 1989 (has links)
Bibliography: leaves 109-113. / Various transducers have been developed turbulent shear in the ocean. The airfoil probe with it's piezoceramic beam encapsulated in a rubber airfoil has the simplest electronic processing system. However, the beam is very fragile and displays unpredictable thermal effects. An airfoil probe with semiconductor strain gauges on an aluminium cantilever beam has been developed as an alternative to the piezoceramic beam. The probe was calibrated by exciting it with a known shear generated by the water flow from an oscillating nozzle. During the calibration the thermal sensitivity of the probe was established to be -1.7 % °C-1• The probe, along with it's high gain, low noise processing system, is fitted to a tethered free-fall vehicle. A solid state data logger situated in the vehicle is used to record the data generated by the turbulence probe and a pressure transducer. Field trials at St.Helena Bay and Hout Bay showed that the sensitivity of the system is 20 dB lower than that of similar systems using piezoceramic beams. The system is able to resolve turbulent dissipation levels above 10-8 W kg-1, making it useful in regions characterised by a typical mixed layer (dissipation level of 10-W kg-1); however, it's sensitivity is not adequate for deep sea measurements where dissipation levels may be as low as 10-10 W kg-1.
32

An investigation into a DSP implementation of partial response signaling for 4800 bits per second full-duplex data communications over M.1020 telephone lines

Horwitz, Russel January 1990 (has links)
Includes bibliographical references. / This thesis investigates high-speed digital transmission over a conditioned, voice-grade telephone circuit (M.1020), using a technique known as partial response signaling, or PRS. In particular, the case where 4800 bps, full-duplex transmission is required in a CCI'PT V. 22 type format is investigated. The main v.22 criterion to be adhered to, is that frequency-division multiplexing (FDM) is to be used as the means of separating thetransmit and receive channels. The carrier frequencies should be 1200 Hz and 2400 Hz respectively. The investigation concerns the modulation and demodulation sections only.
33

Development and implementation of a finite element program for static electromagnetic field problems

Gopal, G January 1990 (has links)
Bibliography: leaves 102-106. / A program is presented for the solution of static electromagnetic fields in bounded and unbounded 2- dimensional domains. The program comprises of a mesh generator which descretises the domain into triangular finite elements or if applicable into special elements, called infinite elements which model the bounded and unbounded domains respectively. The potential function is solved for, using a special solution technique which enhances the speed of the program. The program outputs data in the form of potential or flux component distributions along lines of interest.
34

H to infinity optimal control of a counter-current process

Olivier, Brendan January 1991 (has links)
Bibliography: leaves 156-160. / The extraction of gold from ore that has been mined is the most important part of the process which eventually produces gold bullion. The process most commonly used today is that of carbon-in-pulp gold extraction (CIP). One of the main reasons for this is that it is the most economically efficient method of extracting gold from ore. The process uses activated carbon to absorb gold from a cyanide leach solution. Slurry containing the gold bearing ore and the activated carbon flow in a counter-current fashion. This counter-current flow enables a high percentage of the gold to be recovered. Gold can then be recovered through an elution process. Large amounts of activated carbon are used in the process and a formal multi variable control study of the adsorption section of the CIP process could provide further economic savings by extracting more gold with controlled amounts of carbon. A study was performed to identify the chemical mechanisms involved in the adsorption section of a CIP plant. It was felt that the workings of the process could best be established by designing a simple simulator of the process. The simulator was designed with four reactor tanks, in which the carbon absorbs gold from the leached slurry. The simulator uses a continuous transfer of carbon. In order to fully understand the operation of the HERIG, a simulation study was performed. This simulated model was a simplified version of the actual rig. The level changes of COLD water in the tanks were assumed to be instantaneous and the heat transfer coefficients were assumed to be the same for all four of the tanks. The calculation of the heat transfer coefficients was investigated thoroughly and care was taken to obtain accurate values. The simulator designed was a lumped parameter model. The pipes containing the HOT stream were divided into many small section, in each of which a constant temperature was assumed. A sum of the contributions of all the sections submerged under the COLD water was used to calculate the heat transferred into the COLD water. The COLD water in the tank is stirred continuously and is assumed to be at a constant temperature. The level of COLD water in each tank on the HERIG represents the mass of carbon in each of the tanks on a CIP plant. A change in the HOT water pipe temperature (concentration of Au in slurry) was examined as a function of a change in the level of COLD water in a tank (mass of carbon in a reactor). A steady state and dynamic analysis verified that trends observed from the CIP model were in fact mimicked by the trends observed on the HERIG. It was then decided to perform a formal control study of the HERIG, since the numerous similarities found between the CIP and HERIG enabled relevant conclusions to be drawn about the control of CIP from the control of the HERIG.
35

The investigation and design of a machine vision system for the detection and control of the separation in a spinal ore concentrator

Gold, David January 1991 (has links)
Includes bibliography. / The objectives of the project were firstly, to propose and implement the hardware needed for a Machine Vision System that is to operate on the Spiral Ore Concentrator. Secondly, to propose and implement an algorithm that would operate together with the hardware, to find the transition point between the two types of material, also to find the optimum position for the blade separator, while the system operates in a continuous repetitive mode. Finally, to have an on line analysis of the efficiency of the refinement process in the Spiral Ore Concentrator. The hardware of the Machine Vision System was implemented and tested in the laboratory. The hardware included a video recorder, through which a video signal was obtained from the play-back of video material taken of the ore flow in the Spiral Ore Concentrator. The video signal was used as input to an RGB decoder in order to remove the colour modulation. A black and white frame grabber digitized the video signal which was then analyzed by a computer. Based on the fundamental theory of edge detection used in computer vision systems, an algorithm was designed and implemented to detect the transition point between the two types of material. This algorithm was used to find the difference of averages of grey levels between two global neighborhoods within a specified area of interest window. The algorithm gave consistent results and was robust towards surface irregularities. The algorithm, operating in a continuous repetitive mode, gave rapid fluctuations in the determined edge position. Because a motor with a slow response time would be used to control the movement of the blade separator, the determined edge position signal was smoothed by a filter. Based on periodogram analysis of the edge position signal, a smoothing filter was implemented which incorporates a median filter, followed by a fading-memory polynomial filter. These filters gave sufficient smoothing with little lag to step changes in ore concentration. The efficiency of the ore separation was monitored by the determination of losses. These losses consist of, the percentage of black material loss and percentage of white material contamination. Two types of losses could be identified, they were Spraying losses and Filter losses, these were combined to give Total losses. From the true edge position curve, which was obtained by finding the edge position every second pixel point, the Nyquist sampling frequency could be determined. Because of the slow sampling rate, an error in the calculation of the losses was determined from the true edge curve, and the sub-sampled edge curve. Based on this error, it was shown that the machine vision system could multiplex multiple camera inputs.
36

A low cost tellurometer

Marsden, Mark January 1987 (has links)
Bibliography: leaves 94-96. / This thesis describes the development of a low-cost microwave electronic distance measurement instrument using the Tellurometer phase-measurement principle. In a simplified form the instrument can be configured as a full-duplex 9 600 Baud datalink. The Tellurometer was invented in 1957 by the late Dr. Trevor Wadley of the National Institute of Telecommunications Research. Since then there has been a continuous development of Tellurometers that are used world-wide in the surveying profession. Sophisticated instruments are now available, but this development has been accompanied by increased costs and complexity. There is a growing need in underdeveloped countries for a simple low-cost microwave Tellurometer with good performance and maintainability. These countries survey with low budgets and cannot afford expensive equipment and do not necessarily require all the features and performance of today's instruments. To meet this need it has been the objective of this work to develop a Tellurometer with a range of 1O m to 15 km, with an accuracy in the order of 3 cm, and to keep the materials cost to within R700 per instrument. This has been reached by reducing circuit complexity, current consumption, and cost to a minimum, without compromising the required performance. Only essential features have been included, except where their inclusion has not compromised the cost. The use of a single -chip microprocessor, a simple narrow-band pattern-synthesiser, a low-cost microwave source, low-power technology and a very simple mechanical arrangement has resulted in a cheap simple instrument. Built-in test features of the software allow sophisticated maintenance with a minimum of test equipment.
37

A simulation of the single scan accuracy of a two-dimensional pulsed surveillance radar

Bras, Johan J January 1991 (has links)
Bibliography: leaves 194-198. / The following dissertation considers the single-scan two-dimensional positional accuracy of a pulsed surveillance radar. The theoretical aspects to the positional accuracy are considered and a generalized analytical approach is presented. Practical position estimators are often complex, and theoretical predictions of their performance generally yield unfriendly mathematical equations. In order to evaluate the performance of these estimators, a simulation method is described based on replicating the received video signal. The accuracy of such a simulation is determined largely by the accuracy of the models applied, and these are considered in detail. Different azimuth estimation techniques are described, and their performances are evaluated with the aid of the signal simulation. The best azimuth accuracy performance is obtained with the class of analogue processing estimators, but they are found to be more susceptible to interference than their binary processing counterparts. The class of binary processing estimators offer easily implemented techniques which are relatively insensitive to radar cross-section scintillation characteristics. A hybrid estimator, using both analogue and binary processing, is also evaluated and found to give an improved accuracy performance over the binary processing method while still maintaining the relative insensitivity to radar cross-section fluctuation.
38

Broadband, low-noise and power microwave amplifiers

Hall, Andrew D January 1986 (has links)
The design of Broadband, Low-Noise and Power Microwave Amplifiers using microstrip softboard technology is investigated. The software program TOUCHSTONE (TM) by EEsof is used extensively as a basic design tool. The characterisation of the GaAs Field Effect Transistors, used for the amplifiers, is carried out. These characterisations are then used by the program in its circuit analysis. A determination of the validity of using the manufacturer's data, for the designs, is determined by comparing it to the measured data. Source-Pull and Load-Pull measurements were performed for the Power GaAs FET characterisation. The noise-parameter device characterisation is carried out in a similar way to that for Load-Pull data. Each amplifier required final tuning adjustments in order to peak the performances. The Broadband Maximum Gain Amplifier had a 10 ± 1.5dB gain over a bandwidth from 2- to 6-GHz. The Low-Noise amplifier achieved 5dB Noise-Figure and 5.4 ± 1. 4dB gain over the 2- to 6-GHz band. The Power amplifier Output Power was 390mW over the 3.7- to 4.2-GHz band. Techniques of broadband matching are investigated, with Double-Stub matching producing the widest bandwidth. A literature survey is presented on aspects of broadband microwave amplifiers, as well as a survey on Computer-aided-design at microwave frequencies and techniques of Large-Signal Transistor characterisation.
39

Ore sorting using microwave resonant cavities

Radebe, Kelvin G January 1992 (has links)
Bibliography: leaves 71-73.
40

Switched capacitor networks : a novel prewarping procedure

Campbell, Charles Robert Weston January 1985 (has links)
Bibliography: leaves 152-157. / Novel methods for prewarping filter specifications prior to realization. in Switched Capacitor (SC) form are presented. These allow the design of arbitrary response requirements, exhibiting a low amount of error that normally results from the frequency warping associated with sampled-data networks. Adjustment is applied to the pole and zero locations of a reference filter, using three distinct approaches (Center frequency "CF", Selectivity "S" and Complex Mapping "CM" pole/zero prewarping), developed for both the Lossless Discrete Integrator (LOI) and Bilinear (Bil) analog to digital transformations. The derivation of the prewarping expressions is explained with reference to these mappings, and the effect they have on the apparent pole and zero locations of an SC filter realization.

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