The DMPO type spin trap 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) and the exceptionally similar spin trap 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-l-oxide (EMPO) are widely studied in computational and theoretical works. This particular study examines the addition reactions that both these molecules undergo with the carcinogenic hydroxyl radical. This work used a relatively new approximation method, called the correlation consistent composite approach or ccCA, for carrying out quantum mechanical calculations to give the free energies of the products and reactants of the reactions. The free energies are to be used to extrapolate the rate constants of the reactions from the Arrhenius equation. Though both the spin traps studied have been widely examined and assessed in both theoretical and experimental work, accurately calculated rate constants have not been previously obtained using computational methods. The results obtained here will help to assess the efficiency and the accuracy of the ccCA method, as well as lead to the design of better, more novel spin traps.

Molecular modeling, using both ab initio and semi-empirical methods has been undertaken for a series of dirhodium complexes in order to improve the understanding of the nature of the chemical bonding in this class of homogeneous catalysts. These complexes, with carboxylamidate and carboxylate ligands, are extremely functional metal catalysts used in the synthesis of pharmaceuticals and agrochemicals. The X-ray crystallography shows anomalies in the bond angles that have potential impact on understanding the catalysis. To resolve these issues, minimum energy structures of several examples (e.g. Rh2(NHCOCH3)4, Rh2(NHCOCH3)4NC, Rh2(CO2CH3)4, Rh2(CO2CH3)4NC, Rh2(CHO2)4, and Rh2(CHO2)4NC) were calculated using Hatree-Fock and Density Functional Theory/B3LYP with the LANL2DZ ECP (Rh), and cc-pVDZ (all other atoms) basis sets.

A 1D numerical reaction-transport model (RTM) that is a coupled system of partial differential equations is created to simulate prominent physical and biogeochemical processes and interactions in limnological environments. The prognostic variables considered are temperature, horizontal velocity, salinity, and turbulent kinetic energy of the water column, and the concentrations of phytoplankton, zooplankton, detritus, phosphate (H3PO4), nitrate (NO3-), ammonium (NH4+), ferrous iron (Fe2+), iron(III) hydroxide (Fe(OH)3(s)), and oxygen (O2) suspended within the water column. Turbulence is modelled using the k-e closure scheme as implemented by Gaspar et al. (1990) for oceanic environments. The RTM is used to demonstrate how it is possible to investigate limnological trophic states by considering the problem of eutrophication as an example. A phenomenological investigation of processes leading to and sustaining eutrophication is carried out. A new indexing system that identifies different trophic states, the so-called Self-Consistent Trophic State Index (SCTSI), is proposed. This index does not rely on empirical measurements that are then compared to existing tables for classifying limnological environments into particular trophic states, for example, the concentrations of certain species at certain depths to indicate the trophic state, as is commonly done in the literature. Rather, the index is calculated using dynamic properties of only the limnological environment being considered and examines how those properties affect the sustainability of the ecosystem. Specifically, the index is calculated from a ratio of light attenuation by the ecosystem’s primary biomass to that of total light attenuation by all particulate species and molecular scattering throughout the entire water column. The index is used to probe various simulated scenarios that are believed to be relevant to eutrophication: nutrient loading, nutrient limitation, overabundance of phytoplankton, solar-induced turbulence, and wind-induced turbulence.

The first two chapters are dedicated to the modeling and implementation of a stock-flow consistent framework that incorporates real estate as an asset in the portfolio of the household. The third chapter investigates the main determinants of mortgage repayment of Canadian households. This first chapter presents a five-sector stock-flow consistency growth model where the portfolio decision of the households includes their choice of how much real estate they are interested in holding. The primary aim of the chapter is to model the housing market using the stock-flow consistent approach to explain the current global financial problem triggered by the housing market. The model is then simulated to predict the behaviour of various variables and propose appropriate solutions to the financial problem in the hope of returning the economy to a suitable equilibrium. Households' portfolio consists of money deposits, bills, bank equities and real estate. The other sectors that interact with the household sector are the production firms, the banks, the central bank and the government. Aside from the household sector, the banking sector ends up holding some real estate equivalent to the amount of mortgages defaulted by the households. The supply of real estate from the production sector is therefore augmented by the additional ones held by the banks. The second chapter presents the implementation of the stock-flow consistency model of first chapter. The purpose of the chapter is to run a simulation of the model and experiment with shocks to determine the path of the economic variables of the model. Another objective in performing the experiments is to find policies for mitigating the housing crisis. The model is implemented using the Eviews computer modeling software and runs until a stationary steady state is achieved. Various shocks are applied to the baseline stationary state. The results of the monetary policy show that the mortgage rate shock is more effective in influencing the growth rate of the economy as well as controlling the real estate market. Government fiscal policy is also effective in regulating the housing market. A one-period temporary fiscal policy shock is even capable of generating permanent long run growth effects. Household expectations in future housing price increases or future high rates of housing returns have the effect of heating the real estate market without comparable increases in economic growth. Policy makers must keep these expectations in check. The third chapter analyzes the determinants of mortgage repayment options in Canada. With the freedom that comes with being debt-free and owning a home one will assume that households pay off their mortgages as soon as possible. However, there are factors that inhibit households from carrying out these payoffs. The study uses Canadian micro-level data to examine factors that drive households to default, prepay or continue to make regular mortgage payments. The research methodology uses multinomial (polytomous) logistic regression analyzes. The empirical results establish that the traditional mortgage related predictor variables for repayment are statistically significant with the expected signs. The results relating to the provinces are not significantly different from each other. The results did not however provide any significance in relation to mortgage rates and the number of children in the household.

A 1D numerical reaction-transport model (RTM) that is a coupled system of partial differential equations is created to simulate prominent physical and biogeochemical processes and interactions in limnological environments. The prognostic variables considered are temperature, horizontal velocity, salinity, and turbulent kinetic energy of the water column, and the concentrations of phytoplankton, zooplankton, detritus, phosphate (H3PO4), nitrate (NO3-), ammonium (NH4+), ferrous iron (Fe2+), iron(III) hydroxide (Fe(OH)3(s)), and oxygen (O2) suspended within the water column. Turbulence is modelled using the k-e closure scheme as implemented by Gaspar et al. (1990) for oceanic environments. The RTM is used to demonstrate how it is possible to investigate limnological trophic states by considering the problem of eutrophication as an example. A phenomenological investigation of processes leading to and sustaining eutrophication is carried out. A new indexing system that identifies different trophic states, the so-called Self-Consistent Trophic State Index (SCTSI), is proposed. This index does not rely on empirical measurements that are then compared to existing tables for classifying limnological environments into particular trophic states, for example, the concentrations of certain species at certain depths to indicate the trophic state, as is commonly done in the literature. Rather, the index is calculated using dynamic properties of only the limnological environment being considered and examines how those properties affect the sustainability of the ecosystem. Specifically, the index is calculated from a ratio of light attenuation by the ecosystem’s primary biomass to that of total light attenuation by all particulate species and molecular scattering throughout the entire water column. The index is used to probe various simulated scenarios that are believed to be relevant to eutrophication: nutrient loading, nutrient limitation, overabundance of phytoplankton, solar-induced turbulence, and wind-induced turbulence.

Hexagonal closed packed (hcp) materials, in contrast to cubic materials, possess several processing challenges due to their anisotropic structural response, the wide variety of deformation textures they exhibit, and limited ductility at room temperature. The aim of this work is to investigate, both experimentally and theoretically, the effect os severe plastic deformation, ultrafine grain sizes, crystallographic textures and number of phases on the flow stress anisotropy and tension compression asymmetry, and the mechanisms responsible for these phenomena in two hcp materials: AZ31B Mg alloy consisting of one phase and Zn-8wt.% Al that has an hcp matrix with a secondary facecentered cubic (fcc) phase. Mg and its alloys have high specific strength that can potentially meet the high demand for light weight structural materials and low fuelconsumption in transportation. Zn-Al alloys, on the other hand, can be potential substitutes for several ferrous and non-ferrous materials because of their good mechanical and tribological properties. Both alloys have been successfully processed using equal channel angular extrusion (ECAE) following different processing routes in order to produce samples with a wide variety of microstructures and crystallographic textures for revealing the relationship between microstructural parameters, crystallographic texture and resulting flow stress anisotropy at room temperature. For AZ31B Mg alloy, the texture evolution during ECAE following conventional and hybrid ECAE routes was successfully predicted using visco-plastic self-consistent (VPSC) crystal plasticity model. The flow stress anisotropy and tension-compression (T/C) asymmetry of the as received and processed samples at room temperature were measured and predicted using the same VPSC model coupled with a dislocation-based hardening scheme. The governing mechanisms behind these phenomena are revealed as functions of grains size and crystallographic texture. It was found that the variation in flow stress anisotropy and T/C asymmetry among samples can be explained based on the texture that is generated after each processing path. Therefore, it is possible to control the flow anisotropy and T/C asymmetry in this alloy and similar Mg alloys by controlling the processing route and number of passes, and the selection of processing conditions can be optimized using VPSC simulations. In Zn-8wt.% Al alloy, the hard phase size, morphology, and distribution were found to control the anisotropy in the flow strength and elongation to failure of the ECAE processed samples.

<p>This thesis is part of an effort to enable large-scale Hartree-Fock/Kohn-Sham (HF/KS) calculations. The objective is to model molecules and materials containing thousands of atoms at the quantum mechanical level. HF/KS calculations are usually performed with the Self-Consistent Field (SCF) method. This method involves two computationally intensive steps. These steps are the construction of the Fock/Kohn-Sham potential matrix from a given electron density and the subsequent update of the electron density usually represented by the so-called density matrix. In this thesis the focus lies on the representation of potentials and electron density and on the density matrix construction step in the SCF method. Traditionally a diagonalization has been used for the construction of the density matrix. This diagonalization method is, however, not appropriate for large systems since the time complexity for this operation is σ(n³). Three types of alternative methods are described in this thesis; energy minimization, Chebyshev expansion, and density matrix purification. The efficiency of these methods relies on fast matrix-matrix multiplication. Since the occurring matrices become sparse when the separation between atoms exceeds some value, the matrix-matrix multiplication can be performed with complexity σ(n).</p><p>A hierarchic sparse matrix data structure is proposed for the storage and manipulation of matrices. This data structure allows for easy development and implementation of algebraic matrix operations, particularly needed for the density matrix construction, but also for other parts of the SCF calculation. The thesis addresses also truncation of small elements to enforce sparsity, permutation and blocking of matrices, and furthermore calculation of the HOMO-LUMO gap and a few surrounding eigenpairs when density matrix purification is used instead of the traditional diagonalization method.</p>

Economic policy in the EU faces a trilemma of solving three challenges simultaneously - growth, distribution, and the environment. In order to assess policies that address these issues simultaneously, economic models need to account for both sector-sector and sector-environment feedbacks within a single framework.This paper presents a multi-sectoral stock-flow consistent (SFC) macro model where a demand-driven economy consisting of multiple institutional sectors - firms, energy, households, government, and financial - interacts with the environment. The model is calibrated for the EU region and five policy scenarios are evaluated; low consumption, a capital stock damage function, carbon taxes, higher share of renewable energy, and technological shocks to productivity. Policy outcomes are tracked on overall output, unemployment, income and income distributions, energy, and emission levels. Results show that investment in mitigation technologies allows for absolute decoupling and ensures that the above three issues can be solved simultaneously. (author's abstract) / Series: Ecological Economic Papers

Polymer Nanocomposites (PNC) are a new class of materials characterized by their large interfacial areas between the host polymer and nanofiller. This unique feature, due to the size of the nanofiller, is understood to be the cause of enhanced mechanical, electrical, optical, and barrier properties observed of PNCs, relative to the properties of the unfilled polymer. This interface can determine the miscibility of the nanofiller in the polymer, which, in turn, influences the PNC's properties. In addition, this interface alters the polymer's structure near the surface of the nanofiller resulting in heterogeneity of local properties that can be expressed at the macroscopic level. Considering the polymer-nanoparticle interface significantly influences PNC properties, it is apparent that some atomistic level of detail is required to accurately predict the behavior of PNCs. Though an all-atom simulation of a PNC would be able to accomplish the latter, it is an impractical approach to pursue even with the most advanced computational resources currently available. In this contribution, we develop (1) an equilibrium coarse-graining method to predict nanoparticle dispersion in a polymer melt, (2) a dynamic coarse-graining method to predict rheological properties of polymer-nanoparticle melt mixtures, and (3) a numerical approach that includes interfacial layer effects and polymer rigidity when predicting barrier properties of PNCs. In addition to the above, we study how particle and polymer characteristics affect the interfacial layer thickness as well as how the polymer-nanoparticle interface may influence the entanglement network in a polymer melt. More specifically, we use a mean-field theory approach to discern how the concentration of a semiflexible polymer, its rigidity and the particle's size determine the interfacial layer thickness, and the scaling laws to describe this dependency. We also utilize molecular dynamics and simulation techniques on a model PNC to determine if the polymer-nanoparticle interaction can influence the entanglement network of a polymer melt. / text

Zr-2.5Nb is currently used for pressure tubes in the CANDU (CANada Deuterium Uranium) reactor. A complete understanding of the deformation mechanism of Zr-2.5Nb is important if we are to accurately predict the in-reactor performance of pressure tubes and guarantee normal operation of the reactors. This thesis is a first step in gaining such an understanding; the deformation mechanism of ZrNb alloys at room temperature has been evaluated through studying the effect of texture and microstructure on deformation. In-situ neutron diffraction was used to monitor the evolution of the lattice strain of individual grain families along both the loading and Poisson’s directions and to track the development of interphase and intergranular strains during deformation. The following experiments were carried out with data interpreted using elasto-plastic modeling techniques: 1) Compression tests of a 100%Zr material at room temperature. 2) Tension and compression tests of hot rolled Zr-2.5Nb plate material. 3) Compression of annealed Zr-2.5Nb. 4) Cyclic loading of the hot rolled Zr-2.5Nb. 5) Compression tests of ZrNb alloys with different Nb and oxygen contents. The experimental results were interpreted using a combination of finite element (FE) and elasto-plastic self-consistent (EPSC) models. The phase properties and phase interactions well represented by the FE model, the EPSC model successfully captured the evolution of intergranular constraint during deformation and provided reasonable estimates of the critical resolved shear stress and hardening parameters of different slip systems under different conditions. The consistency of the material parameters obtained by the EPSC model allows the deformation mechanism at room temperature and the effect of textures and microstructures of ZrNb alloys to be understood. This work provides useful information towards manufacturing of Zr-2.5Nb components and helps in producing ideal microstructures and material properties for pressure tubes. Also it is helpful in guiding the development of new materials for the next generation of nuclear reactors. Furthermore, the large data set obtained from this study can be used in evaluation and improving current and future polycrystalline deformation models. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-09-05 13:51:30.42