Insects use an estimate of the angular speed of the visual image across the eye (termed optic flow) for a wide variety of behaviors including flight speed control, visual navigation, depth estimation, grazing landings, and visual odometry. Despite the behavioral importance of visual speed estimation, the neuronal mechanisms by which the brain extracts optic flow information from the retinal image remain unknown. This dissertation investigates the underlying neuronal mechanisms of visual speed estimation via three complementary strategies: the development of neuronally-based computational models, testing of the models in a behavioral simulation framework, and behavioral experiments using bumblebees. Using these methods I demonstrate the sufficiency of two non-directional models of motion detection for reproducing real-world, speed dependent behaviors, propose potential neuronal circuits by which these models may be physiologically implemented, and predict the expected responses of these neurons to a range of visual stimuli.

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This work describes the design, development and testing of a portable charge-coupled device detector system to be used for the simultaneous collection of X-ray diffraction and X-ray fluorescence data from powdered samples. The detector was designed for both terrestrial and extra-terrestrial applications that require in-situ analysis of samples, where access to a laboratory instrument is restricted. The detector system incorporates 4 e2v technologies CCD30-11 devices, employing multi-phase pinned technology for low noise operation. Geometrical calculations and thermal studies concerning the design of the detector are presented, with particular emphasis on motivations for the chosen geometry. Initial characterisation and calibration of the detector was performed in a laboratory environment using a purpose built test facility. The test facility included a high brightness X-ray micro-source from Bede Scientific Instruments, coupled with an XOS polycapillary collimating optic, which was used to deliver a focused beam of low divergent X-rays to the sample. The design of the test facility is discussed and the spectra and flux produced by the X-ray micro-source are investigated. The operational performance of the detector is highlighted and the use of the instrument in different applications is described, namely the planetary sciences and pharmaceuticals sector. Finally, based on the knowledge gained from initial testing of the instrument, improvements to the detector design are outlined, which greatly enhance the combined X-ray diffraction/X-ray fluorescence performance of the instrument.

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Thesis advisor: Thomas N. Seyfried / GM1 gangliosidosis is a glycosphingolipid lysosomal storage disease caused by a genetic deficiency of acid b-galactosidase (β-gal), the enzyme that catabolyzes GM1 within lysosomes. Accumulation of GM1 and its asialo form (GA1) occurs primarily in the brain, leading to progressive neurodegeneration and brain dysfunction. Less information is available on the neurochemical pathology in optic nerve and sciatic nerve of GM1- gangliosidosis. Here we analyzed the lipid content and myelin structure in optic and sciatic nerve in 7 and 10 month old normal β-gal (+/?) and GM1-gangliosidosis β-gal (-/-) mice. Optic nerve weight was lower in the β-gal -/- mice than in unaffected β-gal +/? mice, but no difference was seen between the normal and the β-gal -/- mice for sciatic nerve weight. The concentrations of GM1 and GA1 were significantly higher in optic nerve and sciatic nerve in the β-gal -/- mice than in β-gal +/? mice. The content and composition of myelin-enriched cerebrosides, sulfatides, plasmalogen ethanolamines were significantly lower in optic nerve of β-gal -/- mice than in β-gal +/? mice, however cholesteryl esters were enriched in the β-gal -/- mice. No significant abnormalities in these myelin enriched lipids were detected in sciatic nerve of the β-gal -/- mice. The abnormalities in GM1 and myelin lipids in optic nerve of β-gal -/- mice were also associated with abnormalities in the X-ray diffraction pattern including myelin content in fresh nerves [M/(M +B)] and periodicity (d). With the exception of a slight reduction in myelin content, no abnormalities in the X-ray diffraction pattern were observed in sciatic nerve of β-gal -/- mice. The results indicate that neurochemical pathology is greater in optic nerve than in sciatic nerve of β-gal -/- mice. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.