The purpose of this thesis is to develop an optimized and effective iterative reconstruction algorithm and hardware acceleration methods that work synonymously together through reconstruction in proton computed tomography, which accurately maps the electron density.

Abstract not available

The research presented here is a study to determine the effect of shear reinforcement corrosion on the shear capacity in conventionally reinforced concrete (CRC) bridge elements. A total of 14 CRC beams were tested using three stirrup spacings (8, 10, and 12-inch). Six of the beams included the influence of a 4-inch thick deck, and both positive and negative moment regions were considered. The CRC beams were subjected to an accelerated corrosion process to produce the damage states. Inspection techniques were used to visually correlate corrosion damage with actual structural performance. Severe corrosion damage was shown to have significant effect on the shear performance of the CRC beams. Findings indicate that current inspection ratings for corrosion damage may not adequately identify the extent of structural deterioration. / Graduation date: 2003

Plant cell walls compose the largest source of sugars on earth and are a potential source after conversion for liquid transportation fuels. However, the crystalline region of cellulose and the lignin that incases it present significant obstacles for enzymes to digest. This lowers the sugar yield, which ultimately decreases the production efficiency of bioethanol. A pretreatment that could help lowering the amount of crystallinity; meanwhile, breakdown the matrix of lignin and polysaccharides that cover cellulose fibers would be ideal. Here we propose a physical pretreatment strategy of electron beam irradiation that could potentially decrease cellulose crystallinity as well as unzip the lignin structure. Four types of biomass: cellulose, yellow pine, yellow poplar, and switchgrass were irradiated with a 12 MeV electron beam (Sterigenics, Inc.) at dosages of 0, 54, 80, 148 and 403 kGy. By combining the result from the wet chemical analysis of percent weight glucose/ cellulose from the HPLC, percent crystallinity from the Wide Angle X-Ray Diffraction (WAX) and the change of chemical functionality from Fourier Transform Infrared Spectrometer (FTIR), a promising effect is obtained in pine and yellow poplar but not in cellulose and switchgrass. A significant increase in percent glucose is observed for pine at higher doses as shown by (r = 0.97, P< 0.0076) which are 9.4 and 27% at 0 and 403 kGy. The amount of glucose considerably changes from all different types of biomass over time (P< 0.0001). A strong correlation of decreasing in percent crystallinity was found in poplar (r = -0.89, P< 0.05) from 32.4% to 17.4% and related to an average increase in percent glucose produced from 30 to 55% comparing between 0 and 403 kGy.

Magnetic properties of cobalt clusters (20 N 200) were studied in molecular beams. The magnetization of cobalt clusters is studied at a broad range of temperatures, magnetic fields and clusters sizes. It is shown that the agnetization of ferromagnetic clusters in a cluster beam can be understood as an adiabatic process using the avoided crossing theory. Besides the ground state that bears magnetic moment of about 2 Bohr magneton per atom, an excited state that has 1 Bohr magneton per atom was discovered for every cobalt cluster observed. The energy separations between the two states was investigated by photo-ionization experiments. The ionization threshold shows that the energy gap between the two states is on the order of 0.1 eV for small clusters (N 100) and vanishes for larger clusters. Experiments also show that the polarizability of the excited state is lower than that of the ground state, which indicates a significant electronic tructure difference between the two states. Two states are also found for iron clusters (20 N 200) for which the magnetic moments per atom are about 3 Bohr magneton for the ground state and 1 Bohr magneton for the excited states. This explains the fractional magnetic moments as well as the local magnetic order observed above the Curie temperatures for iron group ferromagnets. Further experiments show two states for manganese clusters for which the ground state has magnetic moment of 1 Bohr magneton per atom in about the same size range. This suggests that the two states are a universal phenomenon of 3d transition metal clusters, which originate from the interaction between 3d and 4s electrons.

Plant cell walls compose the largest source of sugars on earth and are a potential source after conversion for liquid transportation fuels. However, the crystalline region of cellulose and the lignin that incases it present significant obstacles for enzymes to digest. This lowers the sugar yield, which ultimately decreases the production efficiency of bioethanol. A pretreatment that could help lowering the amount of crystallinity; meanwhile, breakdown the matrix of lignin and polysaccharides that cover cellulose fibers would be ideal. Here we propose a physical pretreatment strategy of electron beam irradiation that could potentially decrease cellulose crystallinity as well as unzip the lignin structure. Four types of biomass: cellulose, yellow pine, yellow poplar, and switchgrass were irradiated with a 12 MeV electron beam (Sterigenics, Inc.) at dosages of 0, 54, 80, 148 and 403 kGy. By combining the result from the wet chemical analysis of percent weight glucose/ cellulose from the HPLC, percent crystallinity from the Wide Angle X-Ray Diffraction (WAX) and the change of chemical functionality from Fourier Transform Infrared Spectrometer (FTIR), a promising effect is obtained in pine and yellow poplar but not in cellulose and switchgrass. A significant increase in percent glucose is observed for pine at higher doses as shown by (r = 0.97, P< 0.0076) which are 9.4 and 27% at 0 and 403 kGy. The amount of glucose considerably changes from all different types of biomass over time (P< 0.0001). A strong correlation of decreasing in percent crystallinity was found in poplar (r = -0.89, P< 0.05) from 32.4% to 17.4% and related to an average increase in percent glucose produced from 30 to 55% comparing between 0 and 403 kGy.

Split Concrete Model (SCM) is a unified approach towards modeling shear behavior in concrete. SCM is essentially a rational model which is evaluated and modified using a large experimental database.The shear strength of the concrete beam is modeled as the sum of the contribution of concrete, transverse reinforcement, longitudinal reinforcement and bond between concrete and longitudinal reinforcement. Concrete does not contribute to the shear strength after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the second branch of the critical crack while computing the contribution of concrete towards shear strength of the beam. Formation of the second branch of the critical crack and immediate subsequent failure of the beam has been compared to the split-cylinder test, which forms the conceptual basis of SCM.SCM computes the concrete contribution using the split tensile strength and the area under compression of the concrete beam. For cases where a split-cylinder test is not performed, a mathematical model is proposed to compute the split tensile strength using the compressive strength of concrete available from experimental results. This model is proposed using advanced statistical methods, including weighted residuals and Box-Cox transformation and is validated using various statistical procedures. The transverse reinforcement contributes to the shear strength of the concrete beam only after the formation of the crack. In SCM, this is shown to be accurately modeled by only considering the first branch of the critical crack while computing the contribution of the transverse reinforcement towards shear strength of the beam, instead of the conventional approach of considering the entire length of the crack. The contribution of the longitudinal steel and bond between concrete and longitudinal steel and concrete is accurately modeled unlike the conventional approaches which do not consider this contribution.Evaluation using the database shows that SCM can predict accurate results for all ranges of strength, depth, reinforcement ratio, and shear span to depth ratio of the beam. This shows that all the influencing parameters for concrete shear strength have been correctly modeled in SCM. SCM gives more accurate results as compared to current codified approaches as verified with design examples. Finally, specific recommendations have been made indicating how the shear design requirements in the current ACI code can be modified.

The non-corrodible nature of FRP bars along with their high strength, light weight and ease of installation made it attractive as reinforcement especially for structures exposed to aggressive environment. In addition, the transparency of FRP bars to magnetic and electrical fields makes them an ideal alternative to traditional steel reinforcement in applications sensitive to electromagnetic fields such as magnetic resonance imaging (MRI) units. Continuous concrete beams are commonly-used elements in structures such as parking garages and overpasses, which might be exposed to extreme weather conditions and the application of de-icing salts. In such structures, using the non-corrodible FRP bars is a viable alternative to avoid steel-corrosion problems. However, the linear-elastic behaviour of FRP materials makes the ability of continuous beams to redistribute loads and moments questionable. The objective of this research project is to investigate the flexural behaviour of continuous concrete beams reinforced with FRP and their capability of moment redistribution. An experimental program was conducted at the University of Manitoba to realize the research objectives. Ten full-scale continuous concrete beams were constructed and tested to failure in the laboratory. The specimens had a rectangular cross-section of 200×300 mm and continuous over two spans of 2,800 mm each. The main investigated parameters were the amount and material of longitudinal reinforcement, the amount and material of transverse reinforcement and the spacing of used stirrups. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible if the reinforcement configuration is chosen properly, and is improved by increasing the amount of transverse reinforcement. A finite element investigation was conducted using ANSYS-software. A 3-D model was created to simulate the behaviour of continuous beams reinforced with FRP. The model was verified against the experimental results obtained from the present study. This verified model was used to investigate the effect of the concrete compressive strength, longitudinal reinforcement ratio, midspan-to-middle support reinforcement ratio and the amount of transverse reinforcement on the behaviour of FRP-reinforced beams. The analytical results of this parametric investigation along with the experimental results were used to propose an allowable limit for moment redistribution in FRP-reinforced continuous concrete beams.

Treatment delivery verification is an essential step of radiotherapy. The purpose of this thesis is to develop new methods to improve the verification of photon and electron beam radiotherapy treatments. This is achieved through developing and testing (1) a way to acquire portal images during electron beam treatments, (2) a method to reconstruct the dose delivered to patients during photon beam treatments and (3) a technique to improve image quality in kilovoltage (kV) cone beam computed tomography (CBCT) by correcting for scattered radiation. The portal images were acquired using the Varian CL21EX linac and the Varian aS500 electronic portal imaging device (EPID). The EGSnrc code was used to model fully the CL21EX, the aS500 and the kV CBCT system. / We demonstrate that portal images of electron beam treatments with adequate contrast and resolution can be produced using the bremsstrahlung photons portion of the electron beam. Monte Carlo (MC) calculations were used to characterize the bremsstrahlung photons and to obtain predicted images of various phantoms. The technique was applied on a head and neck patient. / An algorithm to reconstruct the dose given to patients during photon beam radiotherapy was developed and validated. The algorithm uses portal images and MC simulations. The primary fluence at the detector is back-projected through the patient. CT geometry to obtain a reconstructed phase space file. The reconstructed phase space file is used to calculate the reconstructed dose to the patient using MC simulations. The reconstruction method was validated in homogeneous and heterogeneous phantoms for conventional and IMRT fields. / The scattered radiation present in kV CBCT images was evaluated using MC simulations. Simulated predictions of the scatter distribution were subtracted from CBCT projection images prior to the reconstruction to improve the reconstructed image quality. Reducing the scattered radiation was found to improve contrast and reduce shading artifacts. / MC simulations, in combination with experimental techniques, have been shown to be valuable tools in the development of treatment verification methods. The three novel methods presented in this thesis contribute to the improvement of radiotherapy treatment verification. They can potentially improve treatment outcome by ensuring a better target coverage.

The non-corrodible nature of FRP bars along with their high strength, light weight and ease of installation made it attractive as reinforcement especially for structures exposed to aggressive environment. In addition, the transparency of FRP bars to magnetic and electrical fields makes them an ideal alternative to traditional steel reinforcement in applications sensitive to electromagnetic fields such as magnetic resonance imaging (MRI) units. Continuous concrete beams are commonly-used elements in structures such as parking garages and overpasses, which might be exposed to extreme weather conditions and the application of de-icing salts. In such structures, using the non-corrodible FRP bars is a viable alternative to avoid steel-corrosion problems. However, the linear-elastic behaviour of FRP materials makes the ability of continuous beams to redistribute loads and moments questionable. The objective of this research project is to investigate the flexural behaviour of continuous concrete beams reinforced with FRP and their capability of moment redistribution. An experimental program was conducted at the University of Manitoba to realize the research objectives. Ten full-scale continuous concrete beams were constructed and tested to failure in the laboratory. The specimens had a rectangular cross-section of 200×300 mm and continuous over two spans of 2,800 mm each. The main investigated parameters were the amount and material of longitudinal reinforcement, the amount and material of transverse reinforcement and the spacing of used stirrups. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible if the reinforcement configuration is chosen properly, and is improved by increasing the amount of transverse reinforcement. A finite element investigation was conducted using ANSYS-software. A 3-D model was created to simulate the behaviour of continuous beams reinforced with FRP. The model was verified against the experimental results obtained from the present study. This verified model was used to investigate the effect of the concrete compressive strength, longitudinal reinforcement ratio, midspan-to-middle support reinforcement ratio and the amount of transverse reinforcement on the behaviour of FRP-reinforced beams. The analytical results of this parametric investigation along with the experimental results were used to propose an allowable limit for moment redistribution in FRP-reinforced continuous concrete beams.