Wall shear stresses are thought to have an influence on the formation of deposits of blood fats on the linings of the arteries, in atherosclerosis. Measuring velocities close to an artery wall to determine wall shears is difficult in view of the thinness of the boundary layer. Analytical solutions are limited to simple geometries and numerical analyses of three-dimensional, unsteady blood flows are expensive in terms of computational time. In the present study, finite element analyses of blood flow in models representative of the human aorta are based on two-dimensional sections in order to reduce the computational requirement.

Five new genes apparently involved in the metabolism of cell wall peptidoglycan by Escherichia coli are described. One of these, designated murH, was mapped at 99 min on the E. coli linkage map. The murH1 mutant exhibited temperature- sensitive (ts) growth which was associated with a block in a late step in peptidoglycan synthesis and with peptidoglycan hydrolase-mediated lysis at the restrictive temperature. The murH locus could not be cloned in multicopy vectors but was readily cloned in a single copy phasmid vector derived from phage λ. The instability of murH in multicopy prevented its further characterization. As an alternative approach to characterizing the murH function, extragenic mutations which suppressed the murH1 ts lysis phenotype were isolated. One suppressor mutation, designated smh-A1, (25 min on the genetic linkage map) restored temperature resistance in murH1 mutants but otherwise had no distinguishable phenotype. A second extragenic murH1 suppressor, smhB1 (13 min) conferred a ts lysis phenotype by itself. Interestingly, a combination of murH1 and smhB1 resulted in cosuppression of their lysis phenotypes. The suppressor activities of the smhA1 and smhB1 alleles were relatively specific in that they failed to suppress lysis caused by either mutational (murE or murF) or antibiotic-induced blocks in peptidoglycan synthesis. Two additional ts lysis mutations, lytD1 (mapped at 13 min) and lytE1 (25 min), arose spontaneously in smhB1 and smhA1 backgrounds, respectively. The smhA1 allele suppressed the lysis phenotype of lytE1 but not of lytD1. Furthermore, the combination of smhB1 with either lytD1 or lytE1 resulted in cosuppression of their lysis phenotype. The specificity of the suppressor activities, combined with the similarities in the phenotypes of the mutants representing this collection of loci, suggested functional relationships between the murH, smhA, smhB, lytD, and lytE loci. Four clones which complemented the lytD1 mutation were obtained by screening an E. coli gene library, but it is shown that the complementing activity did not represent the E. coli chromosomal lytD locus. It is shown instead that 2 phage λ genes, identified as cro and cI, accounted for the lytD1 complementing activities in these clones. Evidence is presented which suggests that these clones were derived from phage λ DNA which was fortuitously present as a contaminant in the vector preparation used for construction of the gene library. Since the λ Cro and CI proteins are DNA-binding proteins which bind to identical 17 base-pair recognition sequences (the λ right operator sequences), it is hypothesized that LytD encodes a DNA-binding protein with a similar specificity (i.e., which binds to a λ right operator-like sequence) which regulates, probably negatively, the expression of a gene(s) involved in some way with peptidoglycan hydrolysis. / Graduate

The main objective of the study is to verify the accuracy of the approximate hand calculation method used extensively by the engineers for the calculation of the rigidity of shear walls with openings. Different types of shear walls are considered varying in the dimensions and positions of the opening, however, maintaining the same basic material properties. The results obtained by the hand calculation are compared to the finite element approach to check for the discrepancy. The finite element analysis software NISA/DISPLAY IV and SAP2000 is considered for the purpose.

M.Sc. / An increasing problem in subtropical regions, such as South Africa, is the susceptibility of various banana varieties to Fusarium wilt by the soil borne pathogen Fusarium oxysporum tsp. cubense (FOC). In this study the problem of fungal susceptibility of banana was addressed by investigating the biochemical aspects of cell wall strengthening in banana roots. Defence responses were induced in both adult and tissue culture tolerant Goldfinger and susceptible Williams banana cultivars by treatment of the plants with a heat-released elicitor preparation from the mycelial cell walls of FOC race 4 and the crude filtrate. Banana plants were maintained in a hydroponic system, before being inoculated with the elicitor and crude filtrate preparation. Differences in lignin content, callose deposition, phenolics and the enzymes involved in cell wall strengthening; (PAL, CAD, POD and PPO) between the tolerant and susceptible banana cultivars were investigated. Differences in defence responses after treatment with elicitor and with crude filtrate were observed, but it was shown that the former is a more efficient experimental system for the characterisation of susceptible and tolerant responses in banana cultivars. An elicitor concentration of 45 4g/m1 greatly induced cellular POD, PPO, PAL and CAD activity in Goldfinger, whereas no significant increase was observed for Williams. Lignin content increased significantly in Goldfinger compared to Williams. The quantitative determination of induced total phenolics, phenolic glycosides, phenolic esters and cell wall-bound phenolic acids were higher in Goldfinger than in Williams. These increases in the four phenolic subfractions were clearly confirmed by reverse phase HPLC. No significant increase in callose accumulation was observed for both cultivars. The obtained results indicate an important role for cell wall strengthening as an inducible defence mechanism of banana roots against FOC race 4.

no abstract provided by author / Master of Engineering

The plant cell wall is a vitally important interface connecting plant cells to their outside environment and neighboring cells. Acting as a hub for defense, signaling, and physiological processes, the plant cell wall was a crucial innovation in plant evolution. Current cell wall models are largely based on what has been observed in plants like Arabidopsis, Pisum sativum, Nicotiana tabacum, and Phaseolus vulgaris. These models are unable to consider the variety of polymers in a given wall, the mechanical and functional properties such polymers impart, and the complexity of interactions among polymeric cell wall constituents. This work deepened the understanding of wall composition of specialized walls that fall outside of the scope of current plant cell wall models. A detailed survey of cell wall polymer distribution in the transfer cell walls in three key bryophyte species the model moss Physcomitrium patens, hornwort Phaeoceros carolinianus, and liverwort Marchantia polymorpha was done utilizing histochemical techniques in the light and florescent microscopes coupled with immunocytochemical localization with monoclonal antibodies (MAbs) in the transmission electron microscope (TEM). This work demonstrated that the occurrence, abundance, and types of polymers differ among taxa and between the two generations, are more influenced by developmental and life history needs than the similar function of the cells in individual taxa. A notable difference between generations was seen in M. polymorpha with the LM2 and JIM13 MAbs targeting AGP epitopes. However, findings in P patens appear to lack the differential labeling observed in both M. polymorpha and P. carolinianus. Using these same techniques, the walls and matrices involved in the process of spermatogenesis were examined in the moss P. patens and noted differences in abundance and location of cell wall polymers during sperm cell differentiation. Another notable finding of this work was that high concentrations of arabinose as components of AGP and pectins are important in the walls of P. patens during the process of spermatogenesis. The final study focused on utilizing herbarium specimens to explore the application of immunogold localization on dried collections of the moss Polytrichum up to 100 years old. The studies compiled in this dissertation demonstrate that the major cell wall components, cellulose, pectins, hemicelluloses, and callose, are constituents of special walls in three bryophytes, but they are differentially expressed within cell types and across these plants. Taken together, these works contribute significant new data on the composition of plant cell walls by focusing on bryophytes and the unique cell walls vital to the life history processes of spermatogenesis and placental function. These findings also show that both field-collected and herbarium samples are successfully labeled with MAbs at the TEM level, unlocking the potential for further studies across time and taxa using plant collections.

In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.

A parametric study was performed to determine the effect of flexible foundations on the response of timber shear walls. Timber shear walls, which typically consist of structural-use panels, such as plywood or oriented strand board (OSB), attached to a frame made from dimension lumber with dowel-type fasteners such as nails, provide resistance to lateral loading for many low-rise structures in North America. Research performed on shear walls has assumed that a wall is supported by a relatively stiff foundation, such as a concrete block wall, along the entire length of the wall. However, walls are sometimes supported by a relatively flexible foundation, such as a floor joist, which would alter the stiffness, and therefore the response of the wall. Research on flexible foundations is limited at best, and there is a string need to examine the behavior of shear walls on flexible foundations. The study consisted of creating a shear wall numerical model, varying the conditions at the foundation of the model, and analyzing the model when subjected to both monotonic and dynamic loading for each foundation. The system modeled corresponded to a 2.4 m (8 ft) high by 3.7 m (12 ft) long shear wall supported by and parallel to a 7.3 m (24 ft) long joist with hold-downs at each chord of the wall. The joist was supported at each end, with one chord of the wall at an end of the joist and the other chord located at the center of the joist. Eleven joist cross-sections, with sizes determined based on deflection criteria ranging from L/180 to L/720, and a rigid base were included in the study, along with three different hold-down bolt sizes, for a total of thirty-six different foundations. The wall model was analyzed using WALSEIZ1, which is a modified version of the finite element program WALSEIZ (White and Dolan, 1995). Maximum displacements, internal forces, and maximum load were recorded when the model was subjected to monotonic loading, while the maximum displacements and base shear were recorded when the model was subjected to dynamic loading. Results from the study were examined to determine if modifications to the current design practices should be considered. / Master of Science

<p> An investigation of domain walls in some uniaxial magnetic materials is reported in this thesis. Firstly, a method for measuring the wall energy anisotropy in orthoferrites, which causes cylindrical magnetic (bubble) domains to be elliptical is described. In Sm0.55Tb0.45FeO3 a measured anisotropy energy of 1.7% of the wall-energy density at room temperature is responsible for eccentricities as large as 0.4 at average bubble radii equal to 85% of the bubble strip-domain transition radius. The relationship between material parameters and wall-energy anisotropy is discussed. The hypothesis that in orthoferrites walls parallel to the a axis are Bloch walls while walls parallel to the b axis are Néel walls is investigated by measuring the wall anisotropy as a function of the quality factor of the material by varying the temperature of the sample. The measurements seem to verify the predicted dependence of wall anisotropy on the quality factor and thus the hypothesis.</p> <p> A method for measuring the temperature dependence of the wall-energy density in orthoferrites and the saturation magnetization in garnets is described. The advantage of the method is that it uses a single isolated bubble domain without the need to destroy the bubble in order to obtain the measurements. This method led to the derivation of the temperature sensitivities of bubble domains in orthoferrites and garnets in terms of the material parameters. Optimum plate thicknesses to minimize the variation of bubble diameter with temperature are considered. Also, the condition for zero temperature sensitivity of bubbles in some uniaxial materials is derived in terms of the material parameters.</p> <p> Finally, a study of the current requirement to cut a bubble domain from a strip domain or another bubble in uniaxial plates is reported in this thesis.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.