"April 1996." / Includes bibliographical references.

Thesis (Ph.D.)--Victoria University (Melbourne, Vic.), 2009.

This thesis describes the theoretical development of a new ionospheric sounding system. The different types of ionosonde, their prime objectives, and their relative merits and demerits are discussed. The various types of code and their correlation functions are described. The essential requirements of the new system are listed, and suitable codes are found for it. Computer calculations and mathematical derivations demonstrate the (theoretical) suitability of these codes under all conditions. Essentials of the mode of operation of the system and details of its design are specified, and computer simulations are used to examine relevant aspects of its operation. Finally, since the construction of the system is not complete and results cannot therefore be presented, the present state of construction of the system is described

In passive sonar systems, knowledge of low-frequency shipping noise is an important factor for target detection performance. However, an accurate model for the shipping noise structure is difficult to obtain, due to the varying distributions of ships and complicated underwater environment. This work characterizes low-frequency distant shipping noise observed in deep water environments as a function of receiver depth and vertical arrival structure for the case of a receiver below the conjugate depth. Surface shipping noise is examined using Monte Carlo simulations using a normal mode propagation model based on random distribution of ships and realistic parameters. The depth dependence of the simulated distant shipping noise is in agreement with published experimental measurements. A Vertical Line Array (VLA) is used to produce vertical beams that isolate the surface interference from nearby targets. Simulation results quantifying the beamformer output as a function of ocean environment, receiver aperture, and frequency are presented for both conventional and adaptive beamformers. The results suggest that conventional beamforming could detect the noisy target from both direct arrival and bottom bounce in the presence of distant shipping interferers and wind noise. However, the beamwidth of conventional beamforming is wider than that of adaptive beamforming. Once the motion effects of nearby ship interferences are considered, the adaptive beamforming using diagonal loading provides better detection performance. Preliminary adaptive beamforming results corresponding to different snapshot times show that motion effects can be minimized by using short observation times.

The holomorphology of ll life stages of 20 western Nearctic Isoperla and one Cascadoperla was studied over the 3-year period 1975-1978. One monotypicgenus new to science, Cascadoperla, is described, and Cascadoperla tricture (Hoppe) designated as the type species. The nymph, adult male and female, and ova are described and illustrated.

No description available.

No description available.

This thesis concerns the potential use of auditory virtual reality (A VR) in safety-critical situations. Localization accuracy is essential in many VR situations, such as simulated cockpits, where vision is fully occupied and targets must be signified acoustically. However, the errors reported for localizing 3D sounds varies considerably in the literature and some (e.g. Wightman & Kistler, 1989; Wenzel et aI, 1993) report fairly large errors. This thesis consists of an evaluation of the use of acoustic cues to indicate the location of certain targets. A Knowles Electronic Manikin for Acoustic Research (KEMAR) was used to examine the effects of individualized pinnae on localization accuracy. The results showed that using our own pinnae over foreign pinnae provides little or no benefit. More surprisingly, substantial errors were observed in this study. This initial result drove the fundamental investigation into the large angle errors. The method of eliciting subject responses was investigated. The findings established response method as an important methodological feature in localization experiments from the significant effect it has on the results. Error values can be halved when using a categorical method, compared to an unguided (non-categorical) method, possibly because it constrains the subjects' response options. A further possible constraint on subject responses is the effect of memory in absolute judgement tasks. If the memory of one sound impinges on subsequent sounds then the subject's judgement is constrained and the measurement of error may be contaminated. This effect was studied by introducing variable delays that should affect memory .(0 a different extent. No obvious differences in accuracy were noted. This rules out 'interstimulus interval' as a cause for the variability of reported angle errors. Stimulus types were varied in an effort to maximise acuity. Although broadband sounds are purported to give the smallest errors (e.g. Stevens & Newman, 1936; Sandel et aI, 1955), this investigation offered a unique comparison of long and shortduration broadband and complex sounds. But consistently high angle errors forced the inclusions of non-acoustic cues such as vision and head movements, which decreased the error to between 0° and 7°. III The implicatioos for VR in light of the importance of vision (demonstrated by this work), are that it is 'not advisable to implement an auditory cueing system that may conflict or fail to be guided by vision. Where high levels of accuracy are required, as is paramount in safety-criticalsituations, auditory localizatioo is not sufficient as a sole cue to target location. Scientific conclusion: The acoustic cues alone (independent of context) cannot support accurate auditory localization. Applications conclusion: It is not advisable to implement an auditory cueing system that is not guided by vision.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science, 1969.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Includes bibliographical references.