The development of new imaging technologies has made the understanding of differences between observers even more demanding. The factors that influence the outcomes of cross-media colour-matching experiments were investigated in this study. In total.six cross media colour matching experiments were implemented, between physical samples and LCD monitors. The first experiment. implemented the use of a 46" LCD TV display and two sets of physical samples to perform colour matching tasks. The outcomes of this experiment are presented and discussed in two parts, each corresponding to the nature of the physical sample set. The first part, Part A, involved colour matching of the ColorChecker Chart. The second part, Part B, involved 5 garments. The garments were chosen to reflect dominant hues of the CIELAB colour space axes including red, green, yellow, blue and an achromatic grey. On both experimental parts the observers used a custom designed software interface to match the colour of the presented physical stimulus against its real size digital reproduction on the display screen. The results showed a similar magnitude of the inter-observer variations between the two experimental parts and better intra-observer performance in Part 2. The second experiment involved colour matching of solid colour printed surfaces on a desktop 20" LCD display. The printed samples were shown to two separate age groups of 10 observers under 4 different viewing angle conditions. The measured colour-matches from the LCD screen provided a dataset to estimate the inter-observer magnitude and the influence of age and viewing size factors. The dataset was used to test the newly proposed colorimetry methods using individual colour matchinq functions. On one hand the CIE2006 colorimetry framework was implemented and on the other Sarkar's Observer categories were used. The outcomes indicated the change in stimulus size as well the age of observers should be taken into consideration in colour-matching experiments. The use of the newly developed method for implementing individual colour matching functions indicated a better performance in fitting observer variability than that of the CIE Standard Observer.

As a great deal of the present analyses of the single phase-locked loop locks both accuracy and theoretical validity it is not considered adequate in describing phase-locked loop dynamics. A simplified mathematical model of the single phase locked loop is built by making use of experimentally obtained data concerning the relative magnitudes of the harmonic components of the voltage-controlled oscillator control voltage. The derived general equation governing the dynamic behavior of the phase-looked loop is then applied to an analogue computer. The characteristic non-sinusoidal beat-note waveform obtained as the output from the phase-detector, comfirms the practical validity of the derived equation. A close correlation is also obtained between the analogue computer results for the pull-in range and pull-in time, and experimentally obtained results. However in order to extend the scope of a computer analysis of the single phase-looked loop two mathematical models were constructed for application to a digital computer. The first model ('PLOPIT') made great use of empirically derived formula and subsequently was rather limited in its overall application. The second model ('TOPPLL') however, was more theoretically founded and subsequently found greater application to all the common orders of phase-looked loops. The rapid means efforded to a system disgner for obtaining reliable information on many different phase-looked loops by use of 'TOPPLL' is regarded as a significant contribution to the design and analysis of the phase-looked loop. Simple empirically derived expressions governing the pull-in and look-in ranges of the phase looked loop have also been obtained. These expressions are regarded as significant contributions to phase-looked loops design as they have been found to be accurate and reliable and may be used in all types of phase-looked loops.

This thesis is focused on the growth of narrow band gap semiconductor nanowires (NWs) on silicon and graphite by droplet epitaxy. First, the growth conditions of In droplets suitable for the nucleation of NWs was identified. Vertically-aligned and non-tapered InAs NWs were then realized on bare Si. It is shown that the diameter and areal density of NWs are defined by the geometry of pre-deposited In droplets. The NWs exhibit a dominant PL peak associated with the band to band (BtB) emission in addition to a distinct BtB temperature dependent red-shift, strong emission efficiency (up to 2500C) and record narrow spectral linewidth of ~20 meV (at 10K) which is relatively smaller than previously reported values. This demonstrates the high optical properties of the droplet epitaxy grown InAs NWs. Vertically-aligned and non-tapered InAs1-xSbx NWs have been demonstrated on Si without the commonly used NWs stems. In addition, the effect of Sb addition to the morphology of self-catalyzed InAsSb NWs grown directly on Si is systematically investigated for the first time. It is shown that trace Sb flux significantly promotes lateral NWs growth while at the same time suppressing axial growth. Furthermore, Sb-induced crystal phase evolution is elucidated as a function of Sb content. Although, pure InAs NWs show a mixture of Wurtzite (WZ) and Zinc-Blende (ZB) phases, a crystal phase evolution from a highly polytypic InAs to a quasi-pure WZ InAsSb NWs (2-4% Sb content) and a quasi-pure ZB InAsSb NWs crystals (~10% Sb content) is demonstrated in addition to a significant reduction in the stacking fault density in as-grown NWs with increasing Sb content. The recent discovery of flexible graphene has triggered a new wave of optoelectronic revolution. In order to fully exploit the enormous potential of functional monolithic NWs/graphene hybrid structures, the optimal growth conditions for realizing morphologically and structurally superior InAs NWs on graphitic substrates has been identified. Vertically well-aligned and thin InAs NWs were obtained in a narrow growth window of 420-450oC while a high yield of NWs was realized within a restricted domain of growth rate and V/III flux ratio. Compared to the growths on Si, the graphitic substrate is shown to enhance adatom mobility and enable growth at high growth rate which is highly promising for cost-effective devices. In addition, the NWs on graphite show a significantly reduced density of defect in comparison to the growth on conventional Si substrates owing to van der Waals epitaxy growth technique resulting from the absence of dangling bonds. Moreover, high aspect ratio NWs are essential for functional device applications however, the growth of thin InAs1-xSbx NWs is extremely challenging owing to Sb-induced lateral growth. The growth of ultra-high aspect ratio InAs1-xSbx NWs (0 ≤ x ≤ 0.12) on graphite is demonstrated for the first time at highly As-rich conditions with potential for applications in ultra-sensitive, eco-friendly, flexible and cost-effective infrared photodetectors. It is shown that the graphitic thin film promotes Sb incorporation and is more favourable for InAsSb NWs growth in comparison to Si substrates. Finally, a morphological evolution from InN NCs to three dimensional (3D) InN islands is demonstrated with increasing growth temperature attributable to lowered surface free energy of the growing crystals with disproportionate growth velocities along different growth fronts.

No description available.

Nowadays, Carbon Nanotubes (CNTs) and Graphene Oxide (GO) have attracted enormous interest in various applications such as thin film transistors, chemical sensors, field emission devices and transparent conductive coatings. In this report, thin films of CNT and GO networks were fabricated as a two-terminal device for gas sensing applications. These devices were fabricated using vacuum filtration and drop casting methods at room temperature in order to get a thin and uniform film. The electrical measurement was conducted in order to investigate the film resistance as the solution concentration increased. The multi – walled carbon nanotubes (MWCNTs) solutions were acid treated by attaching carboxylic acid (-COOH) groups, in order to form a stable aqueous suspension with a neutral pH. The conductivity of the networks film was increased as the solution concentration increased where the sheet resistance at the highest concentration (0.125 mg/ml) was around 7.09 kΩ/sq. The single – walled carbon nanotubes (SWCNTs) suspension was produced using an organic dye in order to improve its solubility in water. Raman spectroscopy showed that no damage to the structure of SWCNTs was occurred. The GO suspension was produced by the chemical exfoliation of graphite through oxidation. The basal plane and edges of GO were decorated by oxygen functional groups, hence improving its solubility in water. To decrease the concentration of solutions, the solutions were diluted with methanol or water and various concentrations were achieved. The extreme sensitivity to changes in CNTs and GO local chemical environment makes them an ideal candidate for gas sensing application. The devices were tested by exposure to gasses such as NO2 and NH3. Results show a tremendous sensitivity towards NO2 and NH3 gasses. The sensitivities of the MWCNTs sensor device were ranging from 2 to 20 %. Whereas for the SWCNTs sensor device, the sensitivities were ranging from 20 to 50 %. For the GO sensor devices, the optimum sensitivity was achieved when the device was exposed at room temperature. The changes in resistance of the devices reflected the interaction mechanism that happened between exposure gasses (NO2 and NH3) and the materials.

No description available.

The parallel operation of voltage fed converters can be used in many applications, such as aircraft, aerospace, and wind turbines, to increase the current handling capability, system efficiency, flexibility, and reliability through providing redundancy. Also, the maintenance of low power parallel connected units is lower than one high power unit. Significant performance improvement can be attained with parallel converters employing interleaving techniques where small passive components can be used due to harmonic cancellation. In spite of the advantages offered by parallel connected converters, the circulating current problem is still a major concern. The term circulating current describes the uneven current sharing between the units. This circulating current leads to: current distortion, unbalanced operation, which possibly damages the converters, and a reduction in overall system performance. Therefore, current sharing control methods become necessary to limit the circulating current in a parallel connected converter system. The work in this thesis proposes four active current sharing control schemes for two equally rated, directly paralleled, AC/DC/AC converters. The first scheme is referred to as a “time sharing approach,” and it divides the operation time between the converters. Accordingly, in the scheme inter-module reactors become unnecessary, as these are normally employed at the output of each converter. However, this approach can only be used with a limited number of parallel connected units. To avoid this limitation, three other current sharing control schemes are proposed. Moreover, these three schemes can be adopted with any pulse width modulation (PWM) strategy and can be easily extended to three or more parallel connected units since they employ a modular architecture. The proposed current sharing control methods are employed in two applications: a current controller for three-phase RL load and an open loop V/f speed control for a three-phase induction motor. The performance of the proposed methods is verified in both transient and steady state conditions using numerical simulation and experimental testing.

The subject of study was the growth and nucleation of sol-gel deposited lead zirconate titanate (PZT) films of composition Pb(Zr0_52,Ti0_4g)O3 (PZT52/48). This particular composition is on a phase boundary between titanium-rich tetragonally structured PZT and the zirconium-rich rhombohedral phase. The coexistence and relative instability of these phases is thought to be one of the origins of high piezoelectric coefficients exhibited by films of this composition. The aims of this study were to investigate variables affecting the piezoelectric coefficients in sol-gel deposited PZT52/48 thin films. Control of preferred orientation if PZT52/48 films on platinum-coated substrates was accomplished by manipulating processing conditions, specifically pyrolysis temperature. Corona poling was investigated as an alternative to contact poling. Attempts were made to find a set of poling parameters which yielded consistent results. Piezoelectric coefficients are highly dependant on poling conditions, with coefficient being lower in insufficiently poled films or those damaged by field induced sample cracking. It was observed that (001)/(100)-oriented samples with small grains had significantly lower piezoelectric coefficients and were harder to pole than coarser-grained (00l)/(l00)- oriented samples. Samples with a more irregular grain structure and a wide distribution of grain size had the lowest piezoelectric coefficients, irrespective of preferred orientation. The impact of grain size on piezoelectric coefficients was confirmed using the FWHM of the (200) reaction. Films with more irregular grain structures had higher FWHM than those with more uniform grains and had lower d33,f and e31,f. Values of e31,f and d33f were plotted against (001) intensity a determined from xray diffraction. It was difficult to determine any correlation between piezoelectric coefficients and (001) intensity. I comparison, there was a definite inverse correlation between d33,f, e31,f and FWHM, indicating that defect concentration has much more of an impact on piezoelectric coefficients in polycrystalline thin films than (001) intensity as a result of defect-induced domain pinning.

No description available.

No description available.