<p>The investigation of the feasibility of a bone mineral measurement technique based on coherent scattering of gamma rays was performed using a HPGe detector.</p> <p>Considerations of detector efficiency and resolution, absorbed dose to bone, spectral separation between coherent and Compton peaks, variation of differential coherent cross section and scattering volume with scattering angle led to the selection of a photon soruce energy of 103.2 keV (Sm153) and a scattering angle of 40 degree.</p> <p>Bone phantoms (aqueous solutions of K2HPO4) were used to examine how the coherent intensity emanating from a scattering volume at the centre of an object varied with object dimensions and solution effective atomic number. Simulation and experimental measurements with solutions in cylindrical polyethylene containers of varying sizes indicated that the ratio of the coherent count rate to the transmission count rate was independent of container dimensions (at least up to 7 cm diameter). For ease of comparison, all the ratios at different concentrations were normalised to that of water obtained in an identical measurement geometry. The normalised coherent-to-transmission ratios were related to solution effective atomic number by a power function with a exponent of 3.30 plus minus 0.15.</p> <p>When the rate of change of the normalised ratio with effective atomic number is used as an indicator of the sensitivity of the technique, the coherent-to-transmission method is almost twice as sensitive as a coherent-to-Compton technique.</p> <p>In-citro bone mineral measurements were made in the calcaneus (heel bone), an easily accessible site in which 90% of bone mineral is trabecular. Prior to the measurements the spatial distribution of mineral was investigated with a Norland 278-A single photon absorptiometry (SPA) machine in slices of several calcanei. Cortical bone was restricted to a thin peripheral region of the calcaneus.</p> <p>Three whole calcanei, one of which had its calcium content deliberately reduced by soaking overnight in hydrochloric acid, were selected for measurement using the coherent-to-transmission technique. For the first measurement each bone was submerged in water only. For the second measurement the trabeculae were filled with corn oil, to simulate marrow fate, and again each bone were submerged in water. The latter measurements were about 50% lower than the first, indicating a large "marrow fat" effect. However, both sets of results can by explained by assuming a power relationship between the normalised coherent-to-transmission ratio and the effective atomic number of the scattering volume contents.</p> <p>Cuboid samples of side approximately 16 mm were cut out of the posterior region of each calcaneus and ashed. A plot of the normalised coherent-to-transmission ratio versus the ashed weight per unit volume (bone mineral density) of the three calcanei yielded a straight line. While this indicates that the normalised coherent-to-transmission ratio is an indicator of bone mineral, a larger number of samples will be required to establish a robust calibration curve.</p> / Doctor of Philosophy (PhD)

The research is concerned with atmospheric chemistry & physics, and analyzing the environment with respect to the quantity of molecules is in the air we breathe. Fourier Transform Infrared Spectroscopy is used to identify the IR active molecules in our atmosphere. FTIR Spectrometer determines the intensity loss for molecules that have absorbed IR light. The FTIR spectroscopy is performed using the light from the sun or a carbon rod light source in the lab. A Sun-tracking device was employed to direct the sunlight into the spectrometer. Open-path measurements were made using multiple mirror reflections of the carbon rod light source over the top of the SERF (Science and Engineering Research Facility) building. From the Open-path measurements it was determined that the CO and N2O change concentrations during the day and night. Two different open path setups were employed with good success. Time-dependence of the IR spectra for many of the greenhouse gases are presented. In addition, we have performed Gaussian 03 calculations of the IR spectra for many of the greenhouse gases as well as for the nitroethane molecule.

The mechanical breakage of tobacco mosaic virus (TMV) due to the action of acoustic transients has been investigated. The acoustic transients were produced by transient heating of a Prussian blue dye solution (attenuation coefficient of 1000 per cm) when a ruby laser light (20 x 106 watts) was incident on the dye surface. A quartz piezoelectric transducer was used to determine the amplitude and form of the acoustic wave. The production of acoustic waves by transient heating is discussed, and the theoretical form of the acoustic wave determined for various boundary and initial conditions are compared to the experimentally measured values. The electron microscope was used to compare particle length distributions of control TMV solutions and solutions exposed to the acoustic transients. Two conditions of exposure have been studied by varying the boundary conditions of the TMV solutions. In one case the TMV solution was exposed to a single acoustic transient whereas in the other case the solution was exposed to an acoustic transient which was reflected within the solution. Significantly greater breakage was produced in the latter case demonstrating the importance of boundary conditions in the biological effects of pressure transients. Calculations were made of the magnitude of hydrodynamical forces producing tensions in the TMV particle. A laser intensity of 1.6 x 108 watts per cm2 incident on the absorbing dye solution was found to be sufficient to cause significant breakage at the 5 percent level (Kolmogorov-Smirnov test). The corresponding tension on the TMV particle was calculated to be 6.3 x 10-5 dynes.

A visible and Infrared (IR) range dual beam frequency comb Fourier transform spectrometer was developed. Using dual mode-locked Ti:Sapphire lasers a comb-interferogram was generated in the visible range. This spectrum was calculated and used to measure the transmittance of a Nd-doped crystal. The system was further developed to generate an IR interferogram by Difference Frequency Generation (DFG) using a Gallium Selenide (GaSe) crystal placed in the mode-locked pump beam. Numerical work was done to calculate the expected DFG spectrum confirming the necessary IR range can be reached. This has been conducted in support of an IR holographic spectroscopic microscopy spatial and spectral resolving platform for applications in cell biology and biomedical applications.

Intensity modulated proton therapy (IMPT) in the form of pencil beam scanning (PBS) has shown improvement in treatment plan quality as compared to conventional proton and photon-based radiotherapy techniques. However, in IMPT maintaining a sharp lateral dose falloff is crucial for sparing organs at risk (OARs), especially when they are in close proximity to the target volume. The most common approach to improve lateral dose falloff is through the use of physical beam shaping devices, such as brass apertures or collimator-based systems. This work has shown that IMPT can be further improved by implementation of advanced spot placement techniques by moving away from traditional grid-based placements to boundary contoured techniques. We have developed a new optimized spot placement algorithm that provides robust spot distributions inside the target volume by making use of various geometric construction techniques in other fields and developed a unique spot placement technique that provides both high conformality and uniformity in a robust manner for arbitrarily complex target geometries. This approach achieves the boundary conformity of a recently proposed concentric-contours based approach and uses a fast-iterative method to distribute the interior spots in a highly uniform fashion in an attempt to improve both the lateral dose falloff and uniformity. We performed the treatment plan quality comparison for five spot placement techniques using customized homogeneous phantoms. These include two grid-based (rectilinear/hexagonal) and three boundary-contoured (concentric-contours, hybrid and optimized) techniques. Treatment plans were created for two different target volumes, (conical and spherical). An optimal set of planning parameters was defined for all treatment plans and the impact of spot placement techniques on the plan quality was studied in terms of lateral & distal dose falloff, normal tissue sparing, conformity & homogeneity of dose distributions, and total number of spots. For grid-based spot placement techniques, dose conformity is dependent on the target cross sectional shape, which changes for each proton energy. This variable conformity problem is shown to be mitigated by using boundary contoured techniques. However, in the case of concentric contours, the conformity is improved but at the cost of decreased homogeneity. Hybrid and optimized spot placement techniques show more uniform dose distributions while maintaining the improved dose conformity. The optimized spot placement technique is shown to provide robust treatment plans with improved target coverage, homogeneity of dose, and minimal spots count. These results highlight that plan quality in PBS proton therapy may be improved for many patients, without the need for expensive delivery equipment updates, simply by providing additional spot placement techniques in commercial treatment planning software (TPS).

Alzheimer's disease (AD) is the major cause of dementia and is characterized by neuronal death and brain atrophy. The amyloid ß (Aß) peptide is tightly associated with neuronal dysfunction during AD, but the molecular mechanism underlying the neurotoxic effect of Aß is poorly understood. Extracellular fibrillar deposits (plaques) of Aß were initially believed to be the cause of AD, but currently there is overwhelming evidence that the prefibrillar Aß oligomers are the major toxic entities. Structural characterization of Aß oligomers and fibrils is important for understanding the structural features determining the toxic potency of the peptide. This project has studied the aggregation and accompanying structural transitions of Aß, a naturally occurring hypertoxic species, i.e. pyroglutamylated Aß, and their combination, using biophysical approaches (circular dichroism, fluorescence, infrared spectroscopy). In addition, aggregation and structure of overlapping peptide fragments have been studied to identify the specific stretch of Aß that serves as seeding region initiating the aggregation and fibril formation by the full-length Aß peptide. These studies elucidate the structural features of Aß responsible for the peptide's neurotoxic action

<p>The magnetic properties of the heavy rare earth titanium oxides RTiO₃, R=Tb, Dy, Ho, Er, Tm, Yb and Lu, have been investigated. The RTiO₃ develop a spontaneous magnetization below critical temperatures ranging from 28 K to 64 K. Both the rare earth and titanium moments order at the same temperature. The field dependence of the magnetization at 4.2K indicates that the magnetocrystalline anisotropy is very large. The paramagnetic susceptibility of the materials formed with R=Tb-Tm is analyzed with molecular field theory to obtain the molecular field coupling constants λTi-Ti, λR-Ti and λR-R. The magnetic structures are determined for RTiO₃, R=Tb-Tm with the technique of neutron diffraction. The erbium and thulium moments form a ferromagnetic array along the orthorhombic c cxis and the terbium, dysprosium and holmium moments have both ferromagnetic and antiferromagnetic components in the ab plane, giving rise to a canted structure. The titanium moments are in a ferromagnetic array which is directed antiparallel to the ferromagnetic component of the rare earth moment. The preferred direction of the rare earth magnetization with respect to the orthorhombic c axis is discussed in terms of the interaction between 4f electrons on the rare earth and the crystalline environment. Calculations are presented which support this hypothesis.</p> / Doctor of Philosophy (PhD)

Tumor biologist have long appreciated that both cell to cell and cell to extracellular matrix (ECM) interactions are involved in the invasive and metastatic events that are characteristic of malignancy. Cancer cell attachment to and invasion of an ECM has been associated with metastatic potential of cell lines of the Dunning rat prostate model. It was postulated that differences observed in the metastatic potential of four Dunning cell lines may correlate with cell-matrix interactions. Four cell lines, highly metastatic ML, MLL, AT-3 and non-metastatic AT-1 were studied. The adhesive, invasive and chemoinvasive capability of each cell line was compared. Cell adhesion was examined by plating the cells on plastic dishes coated with various components of the ECM (fibronectin, laminin and collagen) as well as EHS Natrix (a natural ECM) . Invasion was determined by examining cells ability to traverse a matrigel barrier. Correlations were found between the cells' adhesive and invasive abilities in response to the ECM. These observations suggest that ECM components are highly involved in prostate cancer cell activities and loss may contribute to tumor progression and metastasis.

Single molecule nanopore spectroscopy is a label-free method for characterizing a wide variety of water-soluble molecules. Recently there have been efforts to expand nanopore sensing to new areas of study. Forensic investigators require an easy to deploy method to identify an unknown number of contributors in a solution. Currently there is no easily available method to distinguish between a single or multiple contributor solution of DNA before being processed by more advanced analytical techniques which has led to wasted time and resources increasing the backlog of samples waiting to be processed. In this work we present a new nanopore technique capable of distinguishing between single and multiple contributors with an easy to deploy infrared heating laser. Previous cluster-nanopore enhancement interaction studies, produced by this group, have found that polymers in the presence of a gold-nanopore complex spend longer periods of time inside the pore. This is of great interest to the nanopore sensing community because longer residence times enable more accurate statistics on single polymers. In order to understand why x some polymers see large enhancements in the residence times (i.e. 20x) while other polymers see much less enhancement (i.e. 3x) a more complete picture of the free energy components is required. By using a IR heating laser, we construct an Eyring transition graph to extract the enthalpic and entropic energy components to find entropy plays a more important role than previously thought when a polymer interacts with a the nanopore. For nanoconfined polymers, entropy plays an important role on how a polymer will interact with the cluster-nanopore structure which in turn may lead to an increase or decrease of the residence time enhancement factor. This work shows with the addition of an infrared laser heater to a nanopore system a new tool has been added to the field. The IR laser coupled to a nanopore system allows for precise adjustments to residence times of events and extracts the free energy components without the need to physically modify the nanopore.

No description available.