In this thesis, the recently discovered Soft Gamma Ray Repeaters SGR J1833-0832, SWIFT J1822.3-1606 and SWIFT J1834.9-0846 are analysed using the archival Swift, RXTE, Chandra and XMM-Newton observations. The period fluctuations and timing noise properties of these sources are investigated. Spectral characteristics and long term frequency evolution of these sources are presented. Investigation for timing noise structure of these magnetars has shown a correlation between first frequency derivative of the spin frequency and torque noise strength.

The usefulness of vibrotactile feedback as a channel to communicate information has been widely recognized. However, most of the recent work on this subject uses actuators that are either too expensive or too large for many practical applications. This thesis explores the generation of vibrotacatile feedback patterns using a simple, inexpensive eccentric-mass motor that is constrained to use a constant voltage and a low on/off switching frequency. In particular, it explores the pulse timing method, which utilizes the slow transient response of the eccentric-mass motor to calculate pulse and rest times for an arbitrary envelope waveform shape. Several hardware tests were performed to (1) obtain a model of the transient response and (2) to verify that the resulting vibrations match the patterns predicted by the pulse timing method. Two custom built devices consisting of an eccentric-mass motor and a rigid housing were used in addition to a Wii remote. Vibrations for each device were measured and compared to the pattern predicted by the pulse timing method when the device was sitting on a table top and when the device was held in the hand. Results indicate that the vibrations match the predicted patterns very well in both cases. It was also determined that error in the motor's transient response model will result in some error between the measured and predicted vibrations. To assess whether this error affects perception of the intended envelope waveform, a study was performed in which users were asked to identify the envelope waveform of vibration patterns created using curve-fit models that contained various levels of error. An analysis of variance revealed that error in the curve-fit will have an effect on the perception of the envelope waveform if the error is large. Two more user studies were performed to determine the perceptual space of patterns generated using the pulse timing method, and to determine whether users could identify the meanings encoded within vibration features. The Perceptual Space study used a cluster-sorted Multi-Dimensional Scaling analysis to determine that envelope waveform, roughness (deviation from the envelope waveform), and amplitude are vibration features that may be used to encode information. Using these features, participants were presented with vibrations that contained GPS navigation instructions similar to those used in a car, and were asked to identify the associated meaning. Users were able to correctly identify all three features with an average accuracy of 80.6%, and were able to correctly identify the envelope waveform and roughness with accuracies of 96.9% and 94.5% respectively. These results are evidence that the pulse timing method (and eccentric-mass motors in general) are capable of generating complex vibrotactile feedback patterns that can be uniquely identified.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / Although the Class D topology offers several advantages, its use in audio amplification has previously been limited by the lack of competitiveness in fidelity compared to its linear counterparts. During the past decade, technological advances in semiconductor technology have awakened new interest since competitive levels of distortion could now be achieved. The output stage of such an amplifier is the primary limiting factor in its performance. In this dissertation, four non-ideal effects existing in this stage are identified and mathematically analysed. The analytical analysis makes use of a well-established mathematical model, based on the double Fourier series method, to model the imperfections introduced into a naturally sampled pulsewidth modulated waveform. The analysis is complemented by simulation using a strategy based on Newton’s numerical method. The theory is verified by a comparison between the analytical-, simulated- and experimental results.

In this thesis, X-ray and optical observations of accretion powered pulsars are presented. By using archival RXTE observations we work on the X-ray spectral and pulse timing analysis of 4U 1538-52, 4U 1907+09, SMC X-1 to have more detailed information about their orbital and spin parameters. For 4U 1538-52 and SMC X-1, we determined new orbital epochs. By using long term pulse history of 4U 1907+09, we were able to work spin-down trend of the system and also calculate the change in the spin-down rate. Using Fermi/GBM observations we can monitor bright accreting pulsar systems. We are producing long term histories of pulse frequency and flux of 20 continuosly monitoring systems. Adding Swift/BAT observations to GBM observations, for 4U 1626-67, we did reveal the characteristics belong to spin-down trend before and spin-up behaviour after torque reversal seen in 2008 February. Two newly discovered IGRJ06074+2205 and IGRJ01583+6713 sources are identified as X-ray binary systems and we found parameters of them like distance, magnitudes, by using both optical photometric and spectroscopic observations.