Bacterial membranes act as protective barriers and help to regulate molecular interactions between a cell and its surrounding environment. External chemical and physical influences have the potential to alter the properties of bacterial membranes and therefore impact the viability of the cell. This can stem from natural or seasonal changes to the local environment (e.g., temperature, pH, and salinity), or even deliberate application of an antimicrobial agent. Regardless, understanding exactly how such external stimuli influence bacterial membrane properties is of fundamental importance, both in terms of basic microbiology as well as for designing pharmaceutical interventions. Experimentally, this is a non-trivial task as this requires selective isolation of a signal arising from the membrane, which is typically buried in the overwhelming background response of the surrounding bulk environment. In particular, our lab has previously developed the surface-sensitive nonlinear optical method, second harmonic light scattering (SHS), as a means of interrogating molecular interactions at the membrane surfaces of living cells, even for multimembrane systems (e.g., Gram-negative bacteria). In this dissertation, time-resolved SHS was employed to study a variety of membrane properties across two separate projects, including 1) chemical and physical induced changes in membrane permeability and 2) temperature-induced membrane permeability changes. Specifically, in the first project (Chapter 4), the influence of the signaling molecule, indole, on the permeability of the bacterial cytoplasmic membrane was quantified. It was revealed that the interaction of indole with the tryptophan specific transporting protein, Mtr permease, resulted in enhanced passive diffusion across the membrane. For the second project (Chapter 5), we examined the influence of temperature on the rate of passive diffusion across a membrane, both in model systems (liposomes) and in living cells (E. coli). For both bacterial and liposome systems, increasing temperatures resulted in a modest increase in passive diffusion rates across the membrane. However, when the temperature range included a phase transition, passive diffusion increased by an order of magnitude. Therefore, by monitoring transport rate in relation to temperature, membrane phase transitions can be quantitatively determined based on the characteristic discontinuities in the measured trend. / Chemistry

Parrotfeather [Myriophyllum aquaticum (Vellozo) Verdecourt] is a non-native aquatic plant from South America that was introduced into the United States in the 1890's. Research was conducted to elucidate seasonal life history, starch allocation patterns, and key environmental factors that may affect plant growth. Environmental factors identified in field studies were used to develop a conceptual model to display relationships between growth and environmental factors. The conceptual model served as a broad-based hypothesis to parameterize growth limiting factors as it related to M. aquaticum growth. Mesocosm experiments were then conducted to test relationships depicted in the model and define the growth requirements of this species. Emergent shoot biomass, submersed shoot biomass, and sediment root biomass were related to light transmittance. Submersed shoot biomass was also related to water temperature. Stolons accounted for 40-95% of total biomass. Starch allocation was also greatest in stolons (78.1 g m-2); where up to 16.3% of total starch was stored. Low points in biomass and starch occurred from October to March. Biomass was greater when plants were grown in 30% shade, whereas plant length was greatest when plants were grown in 50% shade, with reductions observed in full sunlight. Biomass increased by 53% when nitrogen and phosphorus were added to the water column at 1.80 and 0.01 mg L-1, respectively. Myriophyllum aquaticum yield response was positively related (r2 = 0.82) to increasing nitrogen content and a critical concentration of 1.80% nitrogen and 0.20% phosphorus was identified for M. aquaticum growth. Plants grown at 0 cm water depth had 96% greater biomass than plants grown at water depths of 137 cm. Total length was 25% greater when plants were grown at water levels from 0-77 cm. Winter drawdowns reduced biomass by 99% at 4 weeks when compared to pre drawdown biomass. Summer drawdown efficacy was more rapid where biomass was reduced by 98% at 2 weeks when compared to pre drawdown biomass. Subsurface herbicide applications were not more efficacious than herbicides applied to the foliage. The foliar application of 2,4-D was the only herbicide and application method that resulted in ¡Ý90% biomass reduction of M. aquaticum.

<p>  </p> <p>Maternal smoking during pregnancy (MSDP) is still occurring in the United States, as of 2021, at an average rate of 6% (CDC, WONDER). This proximal exposure to MSDP has been associated with decreased fetal head size, increased risk of SIDS, and increased risk for low birthweight (Abraham et al., 2017, Avsar et al., 2021; Knopik et al., 2016b) in infants exposed to MSDP compared to infants not exposed to MSDP. Additionally, MSDP has been associated with epigenetics in the form of differential DNA methylation (DNAm) in children and adolescents who were exposed to MSDP. Among these studies, there has been consistency in gene-specific findings of differential methylation in global DNAm (across the genome), <em>AHRR, CYP1A1, CNTNAP2, MYOIG, </em>and<em> GFI1 </em>(Ladd-Acosta et al., 2015; Lee et al., 2015; Richmond et al., 2015; Rzehak et al., 2016)<em>.</em> Using the frameworks of the Developmental Origins of Health and Disease, as well as Ecological Systems Theory, the current study aims to (1) test the effect of MSDP on global DNAm (across the genome) cross-sectionally in 8-17 y/o children and adolescents, (2) attempt to replicate and analyze the MSDP impacts on <em>AHRR, CYP1A1, CNTNAP2, MYOIG, </em>and<em> GFI1, </em>and (3) adjust for several prenatal and postnatal covariates (second-hand smoke and particulate matter (PM2.5), specifically) in an attempt to isolate the MSDP exposure on DNAm analysis. In a sample of 325 8-17 y/o children whose sibling was exposed to more or less MSDP compared to them, it was found that higher child-specific MSDP was associated with more global methylation and less <em>CNTNAP2</em> methylation, possibly suggesting evidence for a partially causal pathway between MSDP and DNAm for these genetic outcomes. Both child-specific and family-average MSDP were associated with<em> CYP1A1</em> and <em>MYO1G</em> methylation. There were also various findings related to child sex and age covariates, as well as postnatal PM2.5. Future studies focused on replication of these findings in a longitudinal genetic design could further confirm the associations found in the current study.</p>

<p>The purpose of this dissertation was to use an integrative theoretical framework to examine the individual and environmental factors associated with leisure-time physical activity (LTPA) for persons living with spinal cord injury (SCI). Using a systematic approach, three studies were conducted to: (1) survey the accessibility and availability of physical activity facilities for Canadians living with mobility disabilities, (2) test an integrative, theoretical framework for understanding LTPA among people with SCI, and (3) implement a theory-based intervention that focuses on helping beginner exercisers living with SCI cope with salient individual and environmental LTPA barriers. </p> <p>Study 1 involved two sub-studies. Study lA used a modified version of the AIMFREE instrument (Rimmer et al., 2004) and provided evidence of the limited accessibility of fitness and recreational facilities (n=44) for persons with mobility disabilities. Study lB applied a geographical technique, Geographical Information Systems (GIS), to develop an objective proximity measure specific to persons with SCI. Results indicated a small, negative association between the objective presence of physical activity facilities and L TPA in a sample of persons with SCI (n=50), suggesting that living in close proximity to a facility which provides adaptive programming and equipment does not necessarily translate into greater LTPA for persons with SCI.</p> <p>As an extension of Study 1, Study 2 used structural equation modeling to conduct a cross-sectional examination of whether an environmental factor --neighbourhood perceptions--could enhance the Theory of Planned ehaviour's (TPB; Ajzen, 1985) ability to explain LTPA intentions and behaviour in persons with SCI (n=246). Results indicated a small, negative association between perceived wheeling infrastructure and LTPA intentions. However, perceptions of neighbourhood aesthetics and wheeling infrastructure did not explain significant variance in either L TPA intentions or behaviour, beyond that accounted for by the TPB constructs, suggesting that these eighbourhood factors do not enhance the TPB's ability to explain LTPA behaviour.</p> <p>Lastly, Study 3 used a randomized, controlled design to examine the effects of a 10-week action and coping planning intervention on enhancing LTPA and coping self efficacy in exercise intenders living with SCI (n=47). Results indicated greater LTPA for participants who formed action plans and coping plans (A+C condition) than for the participants who only formed action plans (A condition). Furthermore, the A+C condition had greater confidence to schedule their L TPA and overcome L TPA-related barriers than the A condition. These findings provide evidence of the benefits of supplementing action plans with coping plans for enhancing L TP A and coping self-efficacy beliefs among exercise intenders living with SCI. </p> <p>Together, these three studies provide a broader understanding of L TPA correlates and determinants in people with SCI, and provide evidence of the efficacy of multiple planning strategics for promoting L TPA in persons with SCI. The results provide an impetus for extending the scope of the research on the physical environment and LTPA towards persons with mobility disabilities. Moreover, the findings demonstrate the value of theory-based research for identifying the multidimensional correlates and determinants of LTPA, and for designing effective LTPA-enhancing interventions in persons with SCI. </p> / Thesis / Doctor of Philosophy (PhD)

<p> The vegetational colonization and development preceding the establishment of lichen-heath was examined on a Hudson Bay coastal raised-beach system. A continuous and directional developmental sequence of approximately 200 years was quantified on both a coastal intraridge sample sequence and on an inland interridge sample sequence. Increasing gradients of elevation, soil peat thickness and soil organic matter coincide with the vegetational development, however no appreciable changes in soil pH or concentrations of available nutrients were detected and it is concluded that these parameters have little influence on the development of lichen-heath at this site. Community composition over the ridge profile forms a second major vegetational gradient which appears to be affected primarily by environmental factors related to ridge morphology and orientation. The interactions of environmental factors in the development of lichen-heath are discussed.</p> / Thesis / Master of Science (MSc)

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No description available.

No description available.

Structural Health Monitoring (SHM) is the implementation of damage detection and characterization algorithms using in vitro sensing and actuation for rapidly determining faults in structural systems before the damage leads to catastrophic failure. SHM systems provide near real time information on the state of the integrity of civil, mechanical and aerospace structures. A roadblock in implementing SHM systems in practice is the possibility of false positives introduced by environmental changes. In particular, temperature changes can cause many SHM algorithms to indicate damage when no damage exists. While several experimentally based efforts have been attempted to alleviate temperature effects on SHM algorithms, fundamental research on the effects of temperature on SHM has not been investigated. The work presented in this dissertation composes of two main parts: the first part focuses on the experimental studies of different mechanical structures of aluminum beams, lug samples and railroad switch bolts. The experimental study of the aluminum lug samples and beams is done to propose and examine methods and models for in situ interrogation and detection of damage (in the form of a fatigue crack) in these specimen and to quantify the smallest detectable crack size in aluminum structures. This is done by applying the electrical impedance-based SHM method and using piezoceramic sensors and actuators. Moreover, in order to better extract the damage features from the measured electrical impedance, the ARX non-linear feature extraction is employed. This non-linear feature extraction, compared to the linear one, results in detection of damages in the micro-level size and improves the early detection of fatigue cracks in structures. Experimental results also show that the temperature variation is an important factor in the structural health monitoring applications and its effect on the impedance-based monitoring of the initiation and growth of fatigue cracks in the lug samples is experimentally investigated. The electrical impedance-based SHM technique is also applied in monitoring the loosening of bolted joints in a full-scale railroad switch and the sensitivity of this technique to different levels of loosening of the bolts is investigated. The second part of the work presented here focuses on the analytical study and better understanding of the effect of temperature on the vibration-based SHM. This is done by analytical modeling of the vibratory response of an Euler-Bernoulli beam with two different support conditions of simply supported and clamped-clamped and with a single, non-breathing fatigue crack at different locations along the length of the beam. The effect of temperature variations on the vibratory response of the beam structure is modeled by considering the two effects of temperature-dependent material properties and thermal stress formations inside the structure. The inclusion of thermal effects from both of these points of view (i.e. material properties variations and generation of thermal stresses) as independent factors is investigated and justified by studying the formulations of Helmholtz free energy and stresses inside a body. The effect of temperature variations on the vibratory response of the cracked beam are then studied by integrating these two temperature-related effects into the analytical modeling. The effect of a growing fatigue crack as well as temperature variations and thermal loadings is then numerically studied on the deflection of the beam and the output voltage of a surface-bonded piezoceramic sensor. / Ph. D.

Damage detection in mechanical and aerospace structures is critical to maintaining safe and optimal performance. The early detection of damage increases safety and reduces cost of maintenance and repair. Structural Health Monitoring (SHM) integrates sensor networks and structures to autonomously interrogate the structure and detect damage. The development of robust SHM systems is becoming more vital as aerospace structures are becoming more complex. New SHM methods that can determine the health of the structure without using traditional non-destructive evaluation techniques will decrease the cost and time associated with these investigations. The primary SHM method uses the signals recorded on a pristine structure as a reference and compares operational signals to the baseline measurement. One of the current limitations of baseline SHM is that environmental factors, such as temperature and stress, can change the system response so the algorithm indicates damage when there is none. Many structures which can benefit from SHM have multiple components and often have connections and interfaces that also can change under environmental conditions, thus changing the dynamics of the system. This dissertation addresses some of the current limitations of SHM. First the changes that temperature variations and applied stress create on Lamb wave propagation velocity in plates is analytically modeled and validated. Two methods are developed for the analytical derivative of the Lamb wave velocity; the first uses assumes a thermoelastic material while the second expands thermoelastic theory to include thermal expansion and the associated stresses. A model is developed so the baseline measurement can be compensated to eliminate the false positives due to environmental conditions without storage of dispersion curves or baseline signals at each environmental state. Next, a wave based instantaneous baseline method is presented which uses the comparison of simultaneously captured real time signals and can be used to eliminate the influence of environmental effects on damage detection. Finally, wave transmission and conversion across interfaces in prestressed bars is modeled to provide a better understanding of how the coupled axial and flexural dynamics of a non-ideal preloaded interface change with applied load. / Ph. D.