D.Phil. Faculty of Health Sciences, University of the Witwatersrand, 2009 / In this thesis I describe the development of an animal model of sustained hyperalgesia induced by exposure to ultraviolet (UV) A light to the rat’s tail, and the role of the Cfibre barrage and peripheral afferent fibre sensitization in this model of hyperalgesia. Exposure of rats’ tails to UVA-light caused hyperalgesia to a noxious thermal challenge, immersion of the rats’ tails into 49°C water, and a noxious mechanical challenge, application of a static force of 3.9N by a bar algometer onto the rats’ tails. The hyperalgesia to the thermal challenge lasted eight days and hyperalgesia to the mechanical challenge continued for up to 16 days. Despite the sustained hyperalgesia, rats exposed to UVA-light showed no overt signs of morbidity as they gained weight normally and were mobile throughout the study. Histological examination of rat tail tissue showed mild, chronic inflammation in rats exposed to UVA-light and in rats that had their tails covered with a protective layer of aluminium foil during UVA-light exposure. This inflammation was therefore not responsible for the behavioural hyperalgesia. To investigate the role of C-fibre barrage in the development of hyperalgesia after UVA-light exposure, I pre-emptively blocked C-fibre activation during UVA-light exposure with the local anaesthetic bupivacaine. Injection of bupivacaine (1ml of 0.5%), into the base of the tail prevented the development of thermal hyperalgesia to tail immersion in 49°C water. However, it did not prevent the development of hyperalgesia to a noxious punctate challenge. Thus the sustained mechanical hyperalgesia did not depend on the activation of the C-fibre barrage, but thermal hyperalgesia did depend on the activation of a C-fibre barrage during the conditioning event of UVA-light exposure. Lastly, in rats anaesthetised with enflurane, I examined the responses of coccygeal primary afferent fibres to noxious thermal and mechanical stimulation after UVA-light exposure of their receptive fields on the tail. I investigated only pure nociceptive afferents and ignored those afferents that responded to challenges in the noxious and non-noxious ranges. The peak firing rates and areas under the curve of post-challenge histograms, a measure of neuronal firing over time, of Ad- and C-fibres were increased when noxious blunt and punctate challenges were applied to the rats’ tails after UVA-light exposure, showing that Ad- and C-fibres that encode for noxious mechanical challenges were sensitized. The peak firing rate of C-fibres that were responsive to noxious thermal challenges were not increased after UVA-light exposure. Therefore, thermal hyperalgesia was probably mediated by sensitization of central nervous system neurones. In summary, I developed a model of sustained mechanical and thermal hyperalgesia caused by UVA-light exposure of the rat tail. The thermal hyperalgesia was initiated by the C-fibre barrage, while mechanical hyperalgesia did not depend on the C-fibre barrage and peripheral afferent sensitization of Ad- and C-fibres could account for the mechanical hyperalgesia.

by Chan Chi-Ming. / Chinese title in romanization: Zai zhong zi-r she xian hun he chang zhong, yong you ji shan yue ti ce liang zhong zi tong liang di fang fa. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1987. / Bibliography: leaves 142-149.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

When one takes an x-ray, one learns how much material is along the line between the x-ray source and the x-ray sensor. The goal of tomography is to learn what one can about an object, by knowing how much material is on a collection of lines or rays passing through that object. Mathematically, this is a collection of line integrals of density function of the object. In this paper, we provide and prove reconstructions for a class of convex objects of uniform density using x-rays from three point sources.

Despite many years of research dedicated to elucidating the conditions in which cosmic rays (CRs) are accelerated, there is still great uncertainty about exactly how such particles are accelerated up to energies of 1 TeV (1 TeV= 10¹² eV) and well beyond. Additionally, there is also great uncertainty about the structure and amplitude of the Galactic magnetic field which necessarily has a great impact upon the movement and interaction of CRs in the Galaxy. This thesis deals with a number of ways in which Gigahertz (GHz) frequency radio continuum observations can be used with GeV–TeV γ-ray observations to explore (i) the CR spectrum and (ii) the magnetic field amplitude in the Galaxy. An accurate knowledge of the CR spectrum and amplitude of the magnetic field has important consequences for a wide range of phenomena, such as particle acceleration and even star formation within the Galaxy. We present a simple static, single-zone model of secondary electron and positron production from CR protons and heavier nuclei interacting with ambient matter. We then apply this model, assuming a local CR spectrum, to predict the synchrotron emission from two cold, dense, massive molecular cores which are relatively nearby using a prescription for the magnetic field which scales as the (approximate) square-root of the hydrogen number density. Radio continuum observations with the Australia Telescope Compact Array (ATCA) are then used to search for this emission and, due to the lack of detection, upper limits to the magnetic fields within these cores are obtained. We find that these limits are not inconsistent with the prescription used in the theoretical modeling. We also present observations of a giant molecular cloud located in the Galactic centre (GC) region, Sagittarius B2 (Sgr B2), chosen because of the expectation of a higher CR flux (than that observed at the top of the earth’s atmosphere). Based on previous work, the simple model presented in this thesis is then extended to include effects of CR diffusion into the Sgr B2 cloud parameterized by a “diffusion transport suppression” factor (and based on a molecular distribution – obtained from NH₃ spectral line emission studies – that can modeled as a three-dimensional Gaussian distribution). Our results show that the complex nature of the environment severely hampers the separation of the thermal and non-thermal emission so that no spectral, polarized or morphological evidence is found for non-thermal emission due to secondary electrons and positrons. Analysis of the radial brightness distribution from the centre of the main complex of Sgr B2 allowed us to place limits on the diffusion of GeV energy CRs into the cloud. This leads to a relative deficit of CRs at the centre of the cloud and a morphology which is reminiscent of a ‘limb-brightening’ of synchrotron emission from secondary electrons and positrons. This is in contrast to to the TeV energy γ-rays from which a good correlation with molecular matter in the GC region is observed. This is interpreted by us as evidence of the exclusion of GeV energy CRs from the densest molecular environments in this region, whilst the TeV (or higher) CRs are able to freely penetrate these regions leading to the γ-ray -molecular line emission correlation observed by the HESS telescopes. Serendipitously, observations of this region uncovered evidence of non-thermal emission from a source to the south of the main complex of emission within Sgr B2. Analysis of archival XMM-Newton X-ray observations revealed an X-ray source located approximately 20” from the non-thermal radio source whose spectrum is strongly suggestive of a SNR. The non-thermal radio spectrum, X-ray source and spectrum were then used in concert with NH3 line emission to argue that this source is a SNR of approximately 3000 years of age which had exploded in this dense region. A large gradient in the NH₃ line emission towards the X-ray source suggests that any SNR shell would expand towards this region of lower density. Analysis of higher resolution 1720 MHz ATCA data revealed a weak source whose extension is coincident with the X-ray source. Finally, the observations of the Sgr B2 region were then expanded to explore the nature of the magnetic field amplitude on large scales in the region, of which there is a two orders of- magnitude uncertainty. Based on earlier work, which showed a large (6° x 2°) region of synchrotron emission at the GC, we assembled single-dish and interferometric observations of this region. The objective of this was to explore the possibility that a ‘spectral downturn’ existed at GHz frequencies, which is due to the gradual dominance towards lower energies of the bremsstrahlung cooling rate over the synchrotron cooling rate. After the removal of appropriate background and the consideration of limitations at GeV and TeV energies, we found significant statistical evidence for a spectral break at ~ 2 GHz, which implies a magnetic field amplitude of 100 μG in a density of ~ 100 cm ⁻³. An amplitude this high, on such large scales will have a large impact on processes such as particle acceleration, star-formation and gas-dynamics in the region. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1456598 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

In this thesis, synchrotron radiography was utilized to image liquid water distributions in the porous polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs). GDLs were compressed in an ex situ flow field apparatus with 1mm x 1mm channels, and injected with liquid water to study the effect of current density and microstructure on through-plane GDL liquid water distributions. The effect of the size of the water inlet on GDL liquid water distribution was also investigated. Micro-computed tomography was employed to characterize the effect of flow field compression on commercial and non-commercial GDLs. Porosity distributions of compressed GDLs were compared with those of uncompressed GDLs, and the effect of microstructure on the porosity was discussed. The experimental techniques documented in this thesis will inform future research, while the results will help modellers generate realistic GDL pore structures for multiphase flow simulations and validate their models.

In this thesis, synchrotron radiography was utilized to image liquid water distributions in the porous polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs). GDLs were compressed in an ex situ flow field apparatus with 1mm x 1mm channels, and injected with liquid water to study the effect of current density and microstructure on through-plane GDL liquid water distributions. The effect of the size of the water inlet on GDL liquid water distribution was also investigated. Micro-computed tomography was employed to characterize the effect of flow field compression on commercial and non-commercial GDLs. Porosity distributions of compressed GDLs were compared with those of uncompressed GDLs, and the effect of microstructure on the porosity was discussed. The experimental techniques documented in this thesis will inform future research, while the results will help modellers generate realistic GDL pore structures for multiphase flow simulations and validate their models.

Licenciatavhandling Uppsala : Sveriges lantbruksuniversitet, 2009. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Michigan, 1938. / Cover title. "Reprinted from the Physical review, vol. 54, no. 12, December 15, 1938."