Graduate Theses & Dissertations

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Daphnia pulicaria responses to temperature and nutrients stress
Warming climates have had various consequences on terrestrial and aquatic food webs that are expected to persist. There is evidence suggesting that certain organisms are better equipped to handle changing climates compared to others. Therefore, the purpose of my thesis was to study the adaptability of Daphnia under temperature stress and nutrient limitation. First, to examine the effects of dietary phosphorus limitation and temperature on daphniid life-history and population growth, a series of experiments were conducted in the laboratory. In general, I found that Daphnia body growth rates and life-history traits to food carbon to phosphorus (C:P) ratios change with temperature. Next, I identified a protocol to limit the genomic DNA (gDNA) from ribonucleic acid (RNA) extractions. I found that using a modified phenol-chloroform extraction protocol was the most effective way to remove gDNA from extracted Daphnia RNA samples. Overall, results from this study show that temperature and food quality interactions are more complicated than previously thought. Furthermore, the RNA extraction protocol developed will be useful in future studies examining gene expression responses in Daphnia. Author Keywords: ecological stoichiometry, gene expression, life-history, nutrient limitation, RNA puritiy, temperature
Cognitive Inefficiencies in Adolescents with Eating Disorders
Eating Disorders (ED) are notoriously difficult to treat due, in part, to commonly observed inefficiencies in cognitive flexibility and central coherence, which are believed to maintain disordered cognitions and behaviours and negatively impact prognosis. Cognitive remediation therapy (CRT) has recently been used effectively with adults with ED; however, evidence among adolescents is limited. The present study explored change in flexibility and central coherence in a group of 23 adolescent ED inpatients (M = 16 years, SD = 0.95). All participants received a comparable dose of ED treatment. Participants were split into two groups for comparison: the CRT group (n = 15) received CRT in addition to TAU; and a TAU group for control (TAU; n = 8). Improvements in flexibility and central coherence were superior in the CRT group, suggesting that CRT is a potentially useful treatment for adolescents with AN as part of an overall psychosocial rehabilitation program. Author Keywords: anorexia nervosa, central coherence, cognitive flexibility, cognitive remediation, eating disorders, set shifting
Temporal variation of dissolved organic matter and diffusive gradient in thin films-labile mercury in the Quesnel river, BC, and the Goose Creek tributary of Churchill river, MB
This study examined dissolved organic matter (DOM) and labile Mercury (from diffusive gradient in thin films (DGT)) in the Quesnel river, British and the Goose creek tributary of the Churchill river, Manitoba. DOM properties were measured with optical measurements of absorption coefficient (a254), spectral slopes (S275-295, SR) and fluorescence indices (HIX, BIX, FI). The DOC proxy measurements (a254) were almost 10 times higher at the Churchill site (Mean a254 116.77 cm-1) compared with the Quesnel river site (Mean a254 12.06 cm-1) during the study periods. While DGT labile Hg concentrations at the Quesnel site (2.17 to 98.97ppt) were almost 10 times more than the levels reported at the Churchill site (0.03 to 9.06 ppt). Fluorescence indices and the rise of labile Hg concentrations in spring indicated mostly terrestrial sources of DOM at both the sites. Spectral slopes and fluorescence indices substantiated that Churchill site had high molecular weight, complex and more humic DOM compared with Quesnel. DOM at both the sites was prone to temporal variation and affected by environmental conditions. Correlation between DGT labile-Hg and DOM parameters suggested that DGT collected Hg-organic complexes along with inorganic labile-Hg complexes. Author Keywords: Churchill, Diffusive gradient in thin films, Dissolved organic matter, Labile Hg, Mercury, Quesnel
Solving Differential and Integro-Differential Boundary Value Problems using a Numerical Sinc-Collocation Method Based on Derivative Interpolation
In this thesis, a new sinc-collocation method based upon derivative interpolation is developed for solving linear and nonlinear boundary value problems involving differential as well as integro-differential equations. The sinc-collocation method is chosen for its ease of implementation, exponential convergence of error, and ability to handle to singularities in the BVP. We present a unique method of treating boundary conditions and introduce the concept of the stretch factor into the conformal mappings of domains. The result is a method that achieves great accuracy while reducing computational cost. In most cases, the results from the method greatly exceed the published results of comparable methods in both accuracy and efficiency. The method is tested on the Blasius problem, the Lane-Emden problem and generalised to cover Fredholm-Volterra integro-differential problems. The results show that the sinc-collocation method with derivative interpolation is a viable and preferable method for solving nonlinear BVPs. Author Keywords: Blasius, Boundary Value Problem, Exponential convergence, Integro-differential, Nonlinear, Sinc
Assessing limnological characteristics of subarctic Québec thaw ponds and mercury methylation and methylmercury demethylation within their sediments
Thawing permafrost due to increasingly warm temperatures in northern subarctic regions is releasing mercury. The consequent formation of thaw ponds in the peatland palsa valley of the Sasapimakwananisikw (SAS) river in Whapmagoostui-Kuujjuarapik, Québec may provide a pool for MMHg formation and a potential risk to aquatic and human life, if these ponds facilitate MMHg export through hydrological connections to nearby waterways. Hg methylation and MMHg demethylation activities were examined in thaw pond sediments using a Hg tracer isotope incubation experiment. Analysis by coupling gas chromatography cold-vapor atomic fluorescence spectrophotometry (GC-CVAFS) with inductively coupled mass spectrometry (ICP-MS) techniques showed that MMHg was produced at a higher rate and within the first 2 h of incubation for both summer and winter seasons. For thaw ponds SAS1A, SAS1B and SAS2A, MMHg was formed at 0.0048 % h-1, 0.0012 % h-1, and 0.0008 % h-1, respectively during winter and at 0.0001 % h-1, 0.0016 % h-1, and 0.0010 % h-1, respectively during summer. Detection of MMHg losses were not as expected likely due to limitations of the combined tracer spike and overestimation of the in situ ambient mercury levels. Physical and chemical properties vary within ponds, among ponds and between winter and summer. SAS1B’s location nearby an organic carbon rich palsa may be ideal to study DOC – Hg interactions. Variability in pond characteristics including depth, surface area, age, pH, temperature, colour, oxygen concentration, total dissolved and suspended solids, conductivity, carbon, mercury, ammonium, calcium, magnesium, sulfate, total phosphorous, potassium, and sodium between seasons indicate the challenge of predicting future environmental impacts of climate change related thaw pond creation in the north. Author Keywords: demethylation, mercury, methylation, methylmercury, SAS, thaw ponds
Use Of Rapid Amygdala Kindling With Corticosterone Supplementation As A Model Of Epilepsy-Depression Comorbidity
Temporal lobe epilepsy increases risk for developing major depression, and conversely, depression increases risk for development of epilepsy. The mechanisms responsible for the widely observed bi-directional relationship between epilepsy and depression are currently poorly understood. One reason why our understanding of shared etiology has had little improvement is due to the lack of availability of a reliable animal model for inducing depression in epileptic animals. The development of a reliable model of epilepsy-depression comorbidity would greatly improve the ability to mechanistically evaluate shared pathophysiology between the conditions. Recently there has been evidence that rapid kindling of the basolateral amygdala can evoke a behavioural phenotype that is comparable to the symptoms of anxiety and depression observed in depressed epileptic patients. However, this work has yet to be replicated, leaving question as to whether or not the behavioural phenotype can be reliably evoked. In the following series of experiments we assessed rapid amygdala kindling as a potential model of epilepsy-depression comorbidity and sought to improve the model with inclusion of the glucocorticoid corticosterone. Our findings may improve our understanding of the unique relationships between epilepsy and depression. Author Keywords: animal models, depression, hippocampus, kindling, stress, temporal lobe epilepsy
Influence of Action Potentiation on the Perception of Objects Presented Near Hand
For currently-debated reasons, perception of visual stimuli is enhanced in near-hand space compared to far-hand space. According to the action potentiation hypothesis, near-hand effects result from automatically generated potential motor responses produced upon viewing objects presented in near-hand space. This hypothesis was tested by crossing hand manipulations with two separate techniques designed to elicit action potentiation. The first series of experiments presented participants with a cueing task where images of handled objects served as the cue, and its handle compatibility was manipulated. A consistent near-hand effect was observed, but there was no evidence that the images potentiated action as there was no handle-compatibility effect. The second experiment used a visuomotor competition reaching task, which required participants to initiate reaches toward a distractor display and adjust their trajectory on the fly so as to end the reach at a later indicated target location. For every distractor presented simultaneous and competing motor responses were generated, and differences in how hand presence influenced the resolution of this competition were examined. Based on predictions made, action potentiation is unlikely to be the root cause of the near-hand effect; however, was not possible to rule out this explanation entirely. The findings of these experiments shed light both on the importance and consistency of the near-hand effect, and the difficulties associated with uncovering its nature in human populations. Author Keywords:
Predictive Digital Mapping of Soils in Kitimat, British Columbia
Soil is an essential natural resource that supports provisioning services such as agriculture, silviculture, and mining. However, there is limited knowledge on forest soil properties across Canada. Digital soil mapping may be used to fill these data gaps, as it can predict soil properties in areas with limited observations. The focus of this study was to develop predictive maps of select soil physicochemical properties for the Kitimat Valley, British Columbia, and apply these maps to assess the potential impacts of sulphur dioxide emissions from an aluminum smelter, on soil properties in the Valley. Exchangeable [Ex.] magnesium, organic matter, pH, coarse fragment, Ex. potassium, bulk density, Ex. calcium, Ex. acidity, and Ex. sodium were all mapped with acceptable confidence. Time to depletion of base cation pools showed that ~240 km2 of the study area had a depletion time of 50 years or less. However, sources of base cations such as atmospheric deposition and mineral weathering were not considered. Author Keywords: acidification, buffering capacity, Digital soil mapping, predictive mapping, regression kriging, soil properties
Fraud Detection in Financial Businesses Using Data Mining Approaches
The purpose of this research is to apply four methods on two data sets, a Synthetic dataset and a Real-World dataset, and compare the results to each other with the intention of arriving at methods to prevent fraud. Methods used include Logistic Regression, Isolation Forest, Ensemble Method and Generative Adversarial Networks. Results show that all four models achieve accuracies between 91% and 99% except Isolation Forest gave 69% accuracy for the Synthetic dataset. The four models detect fraud well when built on a training set and tested with a test set. Logistic Regression achieves good results with less computational eorts. Isolation Forest achieve lower results accuracies when the data is sparse and not preprocessed correctly. Ensemble Models achieve the highest accuracy for both datasets. GAN achieves good results but overts if a big number of epochs was used. Future work could incorporate other classiers. Author Keywords: Ensemble Method, GAN, Isolation forest, Logistic Regression, Outliers
Problem-Solving and Cognitive Flexibility in Older Adolescents and Young Adults
Ill-structured problems have changing components that solvers need to adapt their solutions to. Well-structured problems have strict, well-defined procedures, and solvers must know which procedures to apply and when. Research has suggested that these two types of problems utilize different problem-solving skills. The current study focused on the relation between ill-structured interpersonal problem solving, novel well-structured problem-solving, and cognitive flexibility in young adults and older adolescents. It was predicted that because of the changing components of ill-structured problems, cognitive flexibility would more strongly predict these compared to well-structured problems. The current study sample consisted of 73 undergraduates with an average age of 20.43 years. The results showed that cognitive flexibility is equally associated with ill-structured problem-solving and well-structured problem-solving. This suggests that cognitive flexibility may support the perspective coordination involved in solving ill-structured problems and that cognitive flexibility may support switching between search strategies when solving a novel well-structured problem. Author Keywords: adolescent, adult, cognitive flexibility, ill-structured problem-solving, novel problems, well-structured problem-solving
role of Cln5 in autophagy, using a Dictyostelium discoideum model of Batten disease
This thesis investigated the role of the neuronal ceroid lipofuscinosis protein, Cln5, during autophagy. This was accomplished by performing well-established assays in a Dictyostelium cln5 knockout model (cln5-). In this study, cln5- cells displayed a reduced maximum cell density during growth and impaired cell proliferation in autophagy-stimulating media. cln5- cells had an increased number of autophagic puncta (autophagosomes and lysosomes), suggesting that autophagy is induced when cln5 is absent. cln5- cells displayed increased amounts of ubiquitin-positive proteins but had no change in proteasome protein abundance. During the development of cln5- cells, fruiting bodies developed precociously and cln5- slug size was reduced. Lastly, when cln5- cells were developed on water agar containing ammonium chloride (NH4Cl), a lysosomotropic agent, the formation of multicellular structures was impaired, and the small slug phenotype was exaggerated. In summary, these results indicate that Cln5 plays a role in autophagy in Dictyostelium. The cellular processes that regulate autophagy in Dictyostelium are similar to those that regulate the process in mammalian cells. Thus, this research provides insight into the undefined pathological mechanism of CLN5 disease and could identify cellular pathways for targeted therapeutics. Author Keywords: Autophagy, Batten disease, Cln5, Dictyostelium discoideum, NCL
Tracking Mercury and Mercury Stable Isotopes Throughout the Wabigoon/English River System
In the Wabigoon/English River system, mercury concentrations downstream from Dryden, ON, where there was a former chlor-alkali plant, remain elevated in sediments and biota. Understanding the current extent and severity of mercury contamination downstream from the former chlor-alkali plant is of great interest in furthering the clean-up of mercury within the traditional territory of Asubpeeschoseewagong Netum (Grassy Narrows) First Nation. The objective of this study was to evaluate the current level and extent of mercury contamination within sediments, crayfish, Hexagenia mayflies, yellow perch, spottail shiner and walleye in the Wabigoon/English River system. An additional objective was to use mercury stable isotope analysis to distinguish between legacy mercury from the former chlor-alkali plant and mercury from geogenic sources. Mercury contamination within surface sediments and biota at locations as far as 178 kms downstream of the historical source of mercury contamination are elevated relative to the reference lake, Wabigoon Lake. Isotope ratios in young of the year fish and sediments collected from within the system were distinct from fish from the reference lake, Wabigoon Lake, indicating that anthropogenic mercury contamination is distinguishable from geogenic mercury. Author Keywords:

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Graduate student theses produced at Trent University. You may also browse theses and dissertations by year, program, or author.

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1973 - 2033
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