No description available.

The following is a thesis for a Master's degree in Electrical Engineering. It presents the design of an FPGA coprocessor for real-time bathymetric synthetic aperture sonar. Bathymetry is the process of finding the height of the seafloor; a problem that requires the computation of a large number of short-length correlations and runs slowly on a conventional microprocessor architecture. It is desirable to generate the seafloor bathymetry in real time for use as a visual aid during data gathering, thus the development of a customised coprocessor is required. The design presented utilises the system-on-chip (SoC) approach to FPGA programming, with a microprocessor, memory, communication cores and custom hardware all contained within a single chip. The merits of SoC design are examined and the details of this implementation are presented. The coprocessor communicates with a host computer over a USB link, receiving raw data as it is collected and sending processed data back to be displayed on-screen. The system was successful as a proof-of-concept, capable of processing an eighth of the area imaged by the sonar in real-time. The results for a simulated scene are presented and the performance of the current system examined with a view to improving its capabilities. While further work is required to implement a complete solution to the problem, the work carried out thus far has provided a solid base for future research.

No description available.

No description available.

Bats are social organisms that live in large colonies. However, reliance upon echolocation in order to hunt and navigate, means that bats also face pressing acoustic challenges due to overlap with surrounding noise. Bats also possess fine control over the properties of their echolocation pulses. This study's goal was to determine how bats are able to effectively function in large groups despite the interfering noise generated by conspecifics. Mexican free-tailed bats (Tadarida brasiliensis) were exposed to both artificially generated interfering noises and noise generated by conspecifics, and the temporal characteristics of their resulting echolocation calls were analyzed. In addition, bats were given injections of dopaminergic and serotonergic drugs, in an effort to determine which monoamine(s) were capable of altering vocal motor timing and to determine which regions of the brain play a role in regulating the timing of echolocation. I hypothesized that bats would alter the timing of emission of their own echolocation pulses in response to noise, and that drugs affecting the 5HT2A receptor would shift the timing of emission of echolocation pulses. The first part of this dissertation describes a novel temporal alteration behavior that occurs in response to artificially generated intermittent noise, and is characterized by a period of pulse suppression followed by a gradual return to normal call rates. Bats alter the timing of emission of their echolocation pulses to avoid overlap with noise and call within silent periods. The second part of this study investigated whether dopamine or serotonin, or both, could alter the timing of this vocal behavior. The results of this study were inconclusive, although I found some evidence that 5HT2A agonists can produce faster responses. Finally, I show that echolocating bats suppress pulse emission in nearby conspecifics. The resulting decrease in call rate leads to an overall increase in information throughput. This study also demonstrates that bats respond to continuous noise by increasing their call rate, and that the switch between the responses to intermittent noise and continuous noise occurs at a duty cycle of 50% or higher. Overall, this dissertation establishes that bats alter the timing of emission of their echolocation calls in response to noise, and that these mechanisms may be regulated by serotoninergic mechanisms.

Thesis (Ph. D.)--University of Canterbury, 2007. / Typescript (photocopy). "January 2007." Includes bibliographical references (p. [209]-223). Also available via the World Wide Web.

Thesis (Ph. D.)--University of California, San Diego, 1997. / Vita. Includes bibliographical references (p. 304-311).

"April 1996." / Includes bibliographical references.

Thesis (M.S. in Computer Science and M.S. in Electrical Engineering) Naval Postgraduate School, March 1996. / Thesis advisor(s): D.P. Brutzman, Xiaoping Yun. "March 1996." Includes bibliographical references (p. 55-56). Also available online.

Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "June 2006." Includes bibliographical references (p. [169]-182) and index. Also available via the World Wide Web.