School of Physics - Theses
Permanent URI for this collection
Search Results
1 - 6 of 6
-
ItemStructure of dark matter in galaxies( 2004-12)The origin, nature and distribution of dark matter in the universe form some of the biggest questions in modern astrophysics. Dark matter is distributed on a wide range of scales in the universe. This thesis concentrates on galactic scales, attempting to lower the veil and probe the structure of dark matter in galaxies. (For complete abstract open document)
-
ItemThe structure of galaxies and AGN using gravitational lensing( 2004-12)A new software tool, Lensview, is developed for the analysis of resolved gravitational lens images. Based on the LensMEM algorithm, the software iteratively finds the best fitting lens model and source brightness distribution incorporating a maximum entropy constraint. Some significant improvements to LensMEM are made, including a different ‘inner loop’ which improves both the accuracy and speed of the algorithm. (For complete abstract open document)
-
ItemStudy of B to rho pi decays with the Belle detector( 2004)This thesis presents an investigation of the charged B meson decay to the pseudoscalar-vector final state p°π±..The results presented in this thesis have been published in Physics Letters B, Volume 542, Issues 3-4, 29 August 2002, Pages 183-192.
-
ItemQuantum chaos: spectral analysis of Floquet operators( 2004-12)The Floquet operator, defined as the time-evolution operator over one period, plays a central role in the work presented in this thesis on periodically perturbed quantum systems. Knowledge of the spectral nature of the Floquet operator gives us information on the dynamics of such systems. The work presented here on the spectrum of the Floquet operator gives further insight into the nature of chaos in quantum mechanics. After discussing the links between the spectrum, dynamics and chaos and pointing out an ambiguity in the physics literature, I present a number of new mathematical results on the existence of different types of spectra of the Floquet operator. I characterise the conditions for which the spectrum remains pure point and then, on relaxing these conditions, show the emergence of a continuous spectral component. The nature of the continuous spectrum is further analysed, and shown to be singularly continuous. Thus, the dynamics of these systems are a candidate for classification as chaotic. A conjecture on the emergence of a continuous spectral component is linked to a long standing number-theoretic conjecture on the estimation of finite exponential sums.
-
ItemHolographic imaging of cold atoms( 2004-08)This thesis presents a new optical imaging technique which measures the structure of objects without the use of lenses. Termed diffraction-contrast imaging (DCI), the method retrieves the object structure from a Fresnel diffraction pattern of the object, using a deconvolution algorithm. DCI is particularly adept at imaging highly transparent objects and this is demonstrated by retrieving the structure of an almost transparent cloud of laser-cooled atoms. Applied to transparent Bose-Einstein condensates, DCI should allow the non-destructive imaging of the condensate while requiring only the minimum possible apparatus of a light source and a detector. (For complete abstract open document)
-
ItemThe study of defect and trapping levels in CVD polycrystalline diamond with applications to ultraviolet dosimetry( 2004-05)The unique properties of diamond make it an excellent material for electronic and optical applications. It is particularly attractive for ultraviolet radiation dosimetry due to its intrinsic properties, which include biological tissue equivalence and visible blindness. Importantly, the advent of synthetic diamond, especially Chemical Vapour Deposition (CVD) diamond, has made it more economically viable for such applications. A thorough understanding of the electronic properties of diamond is needed before these applications can be fully explored. Consequently, this thesis investigates charge carrier trapping states in CVD polycrystalline diamond for the optimization of ultraviolet radiation dosimetry. The technique of Thermally Stimulated Conductivity (TSC) is used to probe electrically active defects and is also applied for dosimetric read-out. A range of as-grown CVD polycrystalline diamond films are studied to determine attributes that favour dosimetric-related TSC. In doing so, we establish that dosimetric TSC in these films originate from defects at the grain boundaries with a correlation to high crystalline quality. With this finding in hand, we then investigate the possibility of optimising diamond for dosimetry by controllably introducing extrinsic dosimetric defects using ion implantation. However, it is shown that these defects are not suitable for dosimetry and have a detrimental effect on the indigenous TSC signal. This study verifies the importance of crystalline quality on the indigenous dosimetric properties of CVD polycrystalline diamond. The possibility of doping CVD diamond during growth is also investigated as a means for intentionally introducing extrinsic dosimetric defects. Sulphur is selected as the dopant based on the theoretical energy levels formed by this defect, and because the prospect of S doping in diamond remains an actively debated issue in the literature. We report for the first time defect levels extracted from TSC analysis of S-doped CVD diamond and find consistency with theoretical predications. In addition, the dominant TSC trap level in S-doped diamond shows promise for radiation dosimetry with certain properties exceeding many current radiation dosimeters. The experimental results in this thesis lead to a deeper understanding of defect and trapping mechanisms in CVD polycrystalline diamond and establish attributes that favour TSC and related dosimetric properties in such films. This knowledge is fundamental to the realisation of diamond for ultraviolet dosimetry.