Biofouling is the accumulation of sessile marine organisms, such as algae, tube worms and barnacles on man-made substrata and has negative economic and ecological implications. Ship hulls are readily fouled, which significantly increases drag while decreasing ship fuel efficiency when moving through water. Fouled hulls have also become important vectors of invasive species. These problems are minimized when hulls are painted with a toxic anti-fouling or non-toxic foul-release coating. Due to recent restrictions of anti-fouling paint use, research and development of non-toxic alternatives has increased. Novel hull coating efficiency is often quantified by the critical removal stress value of barnacles from the coating. Barnacle adhesive cement protein content is thought to be responsible for barnacles’ incredible ability to adhere underwater. The expression level and type of adhesive proteins has eluded scientists due to their extreme insolubility within cured barnacle cement. Identification of these proteins may provide insight to the adhesion of fouling species and aid coating development. Barnacles are a cosmopolitan organism, able to withstand a wide range of environmental conditions, yet foul-release coating research had not previously incorporated environmental factors as variables in determining coating performance. Temperature is known to affect protein structure and function and is also a formative factor of barnacle larvae survival and development. Even so, the interaction between temperature and barnacle adhesion to has not previously been explored. We examined the effect of temperature on barnacle adhesion to foul-release coatings. After observing differences in critical removal stress due to temperature, we attempted to attribute these differences to specific proteins within the adhesive using 2D SDS PAGE. Gel image analysis determined that there were significant differences in cement protein expression between barnacles raised within different temperatures. Preliminary protein identification with Mass Spectronomy (MALDI TOF/TOF) was performed, however further research and a larger barnacle genomic database is needed to elucidate barnacle cement protein sequences.

<P> There is a growing interest in magnesium and its alloys due to their high strength to weight ratio. Magnesium is of particular interest to the automotive industry as a consequence of the current pressure to reduce green house gas emissions from the transportation sector through vehicle weight reduction. However, there is a lack of knowledge concerning the formability of magnesium. As a result, the application of magnesium as a commercial material has not been fully exploited. Much has been learned from the constitutive modeling of materials such as aluminum and steel. Therefore, this thesis considers the constitutive modeling of magnesium and its alloys. </p> <p> Based on this motivation, polycrystal plasticity theories that have been established and used to characterize aluminum and steel are studied. The validity of these theories is examined with respect to magnesium and its alloys. The magnesium system is composed of the hexagonal closed-packed (HCP) crystal structure. Therefore, a strong plastic anisotropy is induced in magnesium crystals due to the limited number of slip systems that may be activated with ease. The models proposed by Taylor and Sachs neglect strain and stress heterogeneities respectively. As a result, the models are either too stiff or too soft to study magnesium due to the anisotropic nature of the crystal structure. The intermediate models; self-consistent models, which are able to consider the heterogeneities among the grains in polycrystals, are believed to be more suitable to study magnesium and its alloys. Therefore, a large strain elastic-viscoplastic self-consistent (EVPSC) model is developed for polycrystalline materials. Both rate sensitive slip and twinning are included as mechanisms of plastic deformation, while elastic anisotropy is accounted for in the elastic modulus. The transition from single crystal plasticity to polycrystal plasticity is based on a completely self-consistent approach. It is shown that the differences in the predicted stress-strain curves and texture evolutions based on the EVPSC and the viscoplastic self-consistent (VPSC) model proposed by Lebensohn and Tome (1993) are negligible at large strains for monotonic loadings. For the deformations involving unloading and strain path changes, the EVPSC predicts a smooth elasto-plastic transition, while the VPSC model gives a discontinuous response because the model is incapable of modeling elastic deformation. In addition, it is demonstrated that the EVPSC model can capture some important experimental features which cannot be simulated by using the VPSC model. </p> <p> Various self-consistent schemes exist for EVPSC and VPSC models. However, the evaluations of these models are not complete. Therefore, an examination of various polycrystal plasticity models is made, based on comparisons of the predicted and experimental stress responses as well as the R values, to assess their validity. It is established that, among the models examined, the self-consistent models with grain interaction stiffuess values halfway between those of the limiting Secant (stiff) and Tangent (compliant) approximations give the best results. Among the available options, the Affine self-consistent scheme results in the best overall performance. Furthermore, it is demonstrated that the R values under uniaxial tension and compression within the sheet plane show a strong dependence on the imposed strain. This suggests that the development of anisotropic yield functions using measured R values, must account for the strain. dependence. </p> <p> The recently developed large strain elastic visco-plastic self-consistent (EVPSC) model, which incorporates both slip and twinning deformation mechanisms, is used to study .the lattice strain evolution in extruded magnesium alloy AZ31 under uniaxial tension and compression. The results are compared against in-situ neutron diffraction measurements done on the same alloy. For the first time, the effects of stress relaxation and strain creep on lattice strain measurements in respectively displacement controlled and load controlled in-situ tests are numerically assessed. It is found that the stress relaxation, has a significant effect on the lattice strain measurements. It is also observed that although the creep does not significantly affect the trend of the lattice strain evolution, a better agreement with the experiments is found if creep is included in the simulations. </p> <p> In conjunction with the M-K approach developed by Marciniak and Kuczynski (1967), the EVPSC model is applied to study the sheet metal formability of magnesium alloys in terms of the forming limit diagram (FLO). The role of crystal plasticity models and the effects of basal texture on formability of magnesium alloy AZ31 B sheet are studied numerically. It is observed that formability in HCP polycrystalline materials is very sensitive to the intensity of the basal texture. The path-dependency of formability is examined based on different non-proportional loading histories, which are combinations of two linear strain paths. It is found that while the FLO in strain space is very sensitive to strain path changes, the forming limit stress diagram (FLSO) in stress space is much less path-dependent. It is suggested that the FLSO is much more favourable than the FLO in representing forming limits in the numerical simulation of sheet metal forming processes. The numerical results are found to be in good qualitative agreement with experimental observations. </p> / Thesis / Doctor of Philosophy (PhD)

Anthropogenic impacts to the environment are unavoidable currently; however, my research investigates a potential mitigation method for amphibians dealing with poor health outcomes caused by detrimental anthropogenic changes to their wetlands. Environmental stressors such as antibiotics leeching from manure of domesticated farm animals into local wetlands can cause a dysbiosis of the gastrointestinal bacterial flora within tadpoles. Dysbiosis of gastrointestinal bacteria during early tadpole development is associated with a decrease in development rate, decrease in body mass accumulation, and other poor health outcomes. I investigated if increasing the indigestible fiber (prebiotic) content in wood frog tadpole’s alfalfa based diet could return tadpoles with stripped microbiomes (dysbiotic gastrointestinal bacterial community composition) to the same phenotype of healthy control tadpoles. I also did a pilot study to see if diet could help in increasing survival post infection with Ranavirus, and from both studies, I created NGSS aligned curriculum and activities. I found that a 10% corn starch enriched alfalfa diet significantly increased the body mass accumulation and development rate of stripped tadpoles. I found there was an association with metabolism and gut dysbiosis. Unfortunately, the connection in regards to corticosterone release was unclear. There was an association with diet and survival, but it needs to be repeated with a larger sample size.

ABSTRACT In the context of increasing incidence of stroke (but also an increasing rate of survival), non-invasive brain stimulation techniques (NIBS) are more frequently used for patients with post-stroke aphasia (PWA) and post-stroke depression (PSD). NIBS techniques, modulating brain plasticity, might offer valid, alternative therapeutic strategies. The aim is to reach a better outcome because treatment of aphasia can also improve post-stroke depression and vice versa. Based on two literature reviews on NIBS effects on PSD and post-stroke aphasia the conclusion is that, although the field is relatively new, and many more investigations with larger samples of patients are required, transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) clinical application is well tolerated, safe, and feasible. Starting from these encouraging data, we used a combination of TMS and electroencephalography (EEG) to explore the excitability modulation before and after active (20 sessions) and sham (20 sessions) tDCS in a double-blind crossover experiment. Four chronic non fluent PWA underwent 8 weeks of verbal exercises coupled with tDCS over the perilesional areas close to the left inferior frontal gyrus. To evaluate changes induced by tDCS, TMS-EEG responses over Brodmann area 6 (BA6) were computed using five different parameters. In addition, these data were compared with those recorded from a matched control group. The results indicated a slight improvement after tDCS stimulation (as compared to sham) for patients with Broca’s aphasia, but not for those with global aphasia. Also, TMS-evoked EEG responses recorded from the ipsilesional hemisphere were abnormal in individuals with chronic post-stroke aphasia (slower and simple responses with higher amplitudes) when compared to responses from the contralesional hemisphere and from the control group. Critically, the Global Mean Field Power (GMFP), Local Mean Field Power (LMFP) and Natural Frequency values were modulated by anodal tDCS. Despite these interesting results, further data are needed in order the obtain more direct, stronger evidence linking behavioral tDCS effects and neurophysiological data.

Historically, the ability of crystal plasticity to incorporate the Schmid’s law at each integration point has been a powerful tool to simulate and predict the slip behavior at the grain level and the succeeding heterogeneous stress/strain localization and texture evolution at the macroscopic level. Unfortunately, this remarkable capability has not been replicated for materials where twinning becomes a noticeable deformation mechanism, namely in the case of low-stacking fault energy cubic, orthorhombic, and hexagonal close packed structures. This dissertation is an attempt to gain understanding on the heterogeneous deformation due to twinning through various techniques including micromechanics, discrete dislocation dipole loops, and digital image correlation (DIC) analyses, and then bring the collected small scale information up to the fullield crystal plasticity scale using fast Fourier Trans- forms. Results indicate that the twin spacing depends primarily upon the height of the twin, and the stress relaxation from the twinning depends upon the thickness of the twin. Furthermore, in a homogenous stress state, discrete dislocation dipole loop-based twinning model showed that the lenticular shape has the minimum stable energy rather than the lamellar or ellipsoidal twin morphology. Our study on the evolution of twinning under three-point bending condition in strongly basal textured magnesium alloy allowed us to build a strategy to incorporate characteristic twin spacing parameter in the crystal plasticity framework. Inspired by results from molecular dynamics (MD) simulations stressing the effect of shuffles on twin nucleation and disconnection core width, we developed an explicit twinning nucleation criterion based on hydrostatic stress gradient and volume fraction of twin inside a grain. Characteristic twin spacing parameter is used as a function of twin height to determine site specific nucleation points in case of multiple twinnings. This ap- proach offered a good reproduction of the microstructure evolution as affected by twinning in a tri-crystal system.

A mulitscale approach is used to model the coalescence of voids. At the microscale, cylindrical and spherical voids in nickel and the magnesium alloy AM60 are simulated through finite element analyses. The nickel cylindrical void simulations are compared to a set of experiments to validate this micromechanical finite element approach used to study void coalescence. At the macroscale, the coalescence portion of a microstructure-property material model is modified to reflect the behavior of three-dimensional spherical voids using results from the micromechanical simulations. An analysis of an automotive component illustrates the influence of void coalescence at the structural scale.

In this work, a crystal elasto-viscoplastic model was modified to account for the anisotropic mechanical response of magnesium aluminum alloys. Crystal plasticity may offer new understanding of these alloys by explicitly modeling the texture development that profoundly affects the properties of magnesium. The model is able to account for the individual slip systems of both the cubic and hexagonal phases. The constants of the model were determined from published experimental AZ31 data, and the plastic hardening response is shown to match these results well using a modification to the hardening rule to approximate the kinetics of twinning. Model aggregates were created with aluminum compositions representative of common magnesium structural alloys. This approach allows the effect of varying percentage of cubic phase on the hexagonal magnesium alloy aggregate to be studied both in terms of macroscopic response and the crystallographic changes occurring within the system.

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