Graduate Student Research

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This community holds theses and dissertations submitted to the Faculty of Graduate Studies. For more information please consult the Faculty of Graduate Studies website http://www.uvic.ca/graduatestudies/resourcesfor/students/thesis/index.php

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1-D and 2-D digital filters design using model reduction and optimization methods for broadband beamforming and interference rejection
(2025) Omar, Abdussalam; Agathoklis, Panajotis; Shpak, Dale John
This thesis presents several design algorithms for nearly linear-phase one-dimensional (1-D) and two-dimensional (2-D) infinite impulse response (IIR) digital filters. Optimization techniques as well as model order reduction (MOR) filter design methods are considered in this study. For 1-D, finite impulse response (FIR) filters can achieve perfectly linear phase which makes them important in applications such as the field of audio signal processing where a flat delay characteristic may be desired. However, in most applications a perfectly linear phase response is not required and filters that have nearly linear phase response are quite acceptable. In such cases, IIR filters are more attractive than FIR filters. The design of IIR filters is more challenging than that of FIR filters because it results in a highly nonlinear objective function that requires sophisticated optimization methods. The 1-D optimization method proposed here solves the problem of approximating specified magnitude and linear-phase responses simultaneously. Since IIR filters can be designed to have nearly linear phase response in the passband, their passband group delay is usually considerably smaller than the delay of linear-phase FIR filters with equivalent magnitude responses. Meeting a required minimum stopband attenuation or a minimum deviation from the desired magnitude and phase responses in the passbands are common design constraints that can be handled by the proposed optimization method for 1-D IIR filter. Also, an important constraint in the design of IIR filters is the prescription of a maximum pole radius, which allows to guarantee the stability margin and low coefficient selectivity for the obtained filter for finite-precision implementations. These design specifications are consistent with the constraints which often arise in practical filter design problems. In this research work, an optimization method for solving this constrained 1-D IIR design problem is presented. The above optimization method used for designing 1-D IIR filters is extended to 2-D separable-denominator IIR digital filters with nearly linear phase in the passband. During the development of the proposed design techniques for 2-D digital filters, a special emphasis has been placed on their computational efficiency and a method for the design of 2-D IIR digital filters based on a balanced realization (BR) model order reduction technique is proposed. In this method, the initial design is a linear phase 2-D FIR filter realized in a 2-D state space model, which leads to a stable 2-D separable-denominator IIR filter with nearly linear phase in the passband. The model reduction method is based on structured controllability Ps and structured observability Qs gramians. These gramians are block-diagonal positive-definite matrices satisfying 2-D Lyapunov inequalities. An efficient general algorithm is developed to compute these matrices by minimizing the trace of Ps and the trace of Qs under Linear Matrix Inequalities (LMI) constraints. The use of these gramians ensures that the resulting 2-D IIR filter is a 2-D stable filter. Furthermore, the obtained nearly linear-phase 2-D IIR filter is more economical and computationally more efficient than the original 2-D FIR filter. Numerical examples using MATLAB show that the proposed method provides a good compromise between the filter selectivity and computational complexity when compared to existing techniques, making the results of this dissertation directly applicable to many practical applications. For example, in the field of array signal processing, 2-D digital filters having a fan-shaped filter in the passband emerge as powerful tools, particularly when employed as beamformers in scenarios where the Direction of Arrivals (DOAs) of the desired broadband Plane Waves (PWs) are known. In such cases, the designed 2-D FIR and IIR filters having a fan-shaped filter passband in the 2-D frequency domains are used as beamformers. Benefiting from the knowledge of DOAs of the desired broadband PWs, these filters are used to extract the signal of interest (SOI), suppress the interference, and reduce the noise corrupting the SOI. The successful implementation of 2-D FIR and IIR fan filters as beamformers not only enhances the rejection of the interference but also demonstrates its capability to reduce the effect of AWGN. This dual functionality holds significant implications for practical applications in digital signal processing, in which robustness against interference and noise is important. Simulation results demonstrate a good performance of the proposed beamformers and confirmed that the filters obtained using the proposed methods are capable of extracting and enhancing the desired 2-D broadband signals according to their directions of arrival under severe interference and noise.
10,000 Steps a Day to Decrease Chronic Disease Risk Factors and Increase Aerobic Physical Activity Levels Among Capital Regional District Office Workers in Victoria, BC.
(2013-04-30) Delaney, Kara; Stuart-Hill, Lynneth A.
The mixed method design examined the impact of a 6-week pedometer based 10,000 moderate-vigorous steps a day employee workplace wellness challenge on aerobic fitness, chronic disease markers, and self-reported physical activity. The study used prompts to both educate and facilitate the intervention. Pre and post-test data analyzed self-report physical activity and sedentary time, sub max aerobic walking levels, and anthropometric measures. Participants logged their step count across the intervention and were challenged to increase their steps throughout. Participants were on average unable to achieve the goal step count and thus no statistically significance was found between pre-post tests. Qualitatively, three themes emerged from discussions with participants about their experiences: awareness of physical activity (PA) levels, demands of both work and family, and the frequency and content of the information given as prompts. The combination of prompts and the pedometer created an awareness of PA levels among participants but failed to fully motivate them to hit their target step count.
10,000 years later: body shape and evolution in threespine stickleback
(2009-12-08T23:14:28Z) Spoljaric, Mark A.; Reimchen, T. E.
Descent with modification (Darwin, 1859) overwhelmingly occurs through the process of natural selection on genetically variable traits. Following deglaciation in the Pleistocene, morphologically conservative marine stickleback (Gasterosteus aculeatus) from two distinct mitochondrial DNA lineages colonized freshwater habitats on the Haida Gwaii archipelago. These freshwater populations have radiated in response to a diverse selective landscape on the archipelago and exhibit morphological diversity that equals or exceeds the known range for the species in the circumboreal distribution. I investigated the body shape of 3808 stickleback from 125 isolated populations from Haida Gwaii using geometric morphometrics. Relative warp and discriminant function analysis were used to quantify lateral shape differences based on partial warp scores. which were generated from twelve homologous landmarks digitally placed on each specimen's image. The possibility of ontogenetic shifts and sexual dimorphism of body shape were examined for each population on the archipelago. Stickleback body-shape changes during ontogeny were highly variable, and cannot be predicted by the volume and water clarity of the habitat. I found a slight sexual dimorphism in adult body shape, the magnitude of which could not be predicted by habitat volume and clarity. A number of comparisons were made to elucidate the possible causes for selection for divergence of adult body shape among Haida Gwaii populations. Body shape of parapatric lake-river stickleback populations differed significantly in concordance with hydrodynamic principles. Comparing the body shape of Haida Gwaii populations to the shape of sympatric benthic-limnetic species pairs from southwestern British Columbia. I found that benthic and limnetic body-shape ecotypes differ by up to 56% of the total variation among Haida Gwaii populations. Tests for phenotypic plasticity of body shape were conducted with two morphologically distinct stickleback populations that had been transplanted into two separate experimental ponds that were the ecological opposites of the respective source lakes. I found evidence for some phenotypic plasticity in body shape; the difference between each source and experimental population was approximately 11% of the total variation in body shape among populations throughout the archipelago. Throughout the islands adult body shape and size can be predicted by both abiotic and biotic factors of the habitat. Populations with derived shape (CV1+), including thicker peduncles, posteriad and closely spaced dorsal spines, anteriad pelvis, short dorsal and anal fins, and smaller body size occur in small, shallow, stained ponds, and populations with less derived shape (CVI-). with smaller narrow peduncles. anteriad and widely spaced dorsal spines. posteriad pelvis. longer dorsal and anal fins, and larger size occur in large, deep. clear lakes. There were large-bodied populations with derived shape (CV2-). including smaller heads and shallower elongate bodies in open water habitats of low productivity, and populations with smaller size and less derived shape (CV2±), with larger heads and deeper bodies, in higher productivity, structurally complex habitats. Populations with robust defensive adaptations have less derived shape (CV1-) and larger size, in response to salmonid predation, while populations with weak defences had derived shape (CV 1+), in response to bird/invertebrate predators. The ecomorphological relationships were consistent between mitochondrial lineages and replicated in each geographical region on the archipelago among geographically distant populations, suggesting the parallel evolution of body shape governed by the hydrodynamic constraints of each habitat. Although initially colonized by ancestors with conserved morphology, the stickleback populations on Haida Gwaii exhibit body shapes suited to the hydrodynamic landscape of the habitat, demonstrating the predictability of natural selection in adaptive radiations.
A 100-year retrospective and current carbon budget analysis for the Sooke Lake Watershed: Investigating the watershed-scale carbon implications of disturbance in the Capital Regional District’s water supply lands
(2015-05-01) Smiley, Byron; Trofymow, J. A.; Niemann, K. O.
Northern forest ecosystems play an important role in global carbon (C) cycling and are considered to be a net C sink for atmospheric C (IPCC, 2007; Pan, et al., 2011). Reservoir creation is a common cause of deforestation and when coupled with persistent harvest activity that occurs in forest ecosystems, these disturbance events can significantly affect the C budget of a watershed. To understand the effects of these factors on carbon cycling at a landscape level, an examination of forest harvest and reservoir creation was carried out in the watershed of the Sooke Lake Reservoir, the primary water supply for the Greater Victoria area in British Columbia. Covering the period between 1910 and 2012, a detailed disturbance and forest cover dataset was generated for the Sooke Lake Watershed (SLW) and used as input into a spatially-explicit version of the Carbon Budget Model of the Canadian Forest Sector 3 (CBM-CFS3). The model was modified to include export of C out of the forest system in the form of dissolved organic C (DOC) into streams. The fraction of decaying C exported through this mechanism was tuned in the model using DOC measurements from three catchments within the SLW. Site-specific growth and yield curves were also generated for watershed forest stand types, in part, by using LiDAR-derived site indices. C transfers associated with disturbances were adjusted to reflect the disturbance types that occurred during the 100-year study period. Due to the removal of C resulting from wildfire, logging and residue burning, as well as deforestation disturbances, total ecosystem C stocks dropped from 700 metric tonnes of C per hectare (tC ha-1) in 1910 to their current (2012) level of ~550 tC ha-1 across the SLW. Assuming no change in management priorities and negligible effects of climate change, total ecosystem C stocks will not recover to 1910 levels until 2075. The cumulative effect of reservoir creation and expansion on the C budget resulted in 14 tC ha-1 less being sequestered (111,217 tC total) across the watershed by 2012. In contrast, sustained yield forestry within the Capital Regional District’s tenure accounts for a 93 tC ha-1 decrease by 2012, representing an impact six times greater than deforestation associated with reservoir creation. The proportionally greater impact of forestry activity is partly due to current C accounting rules (Intergovernmental Panel on Climate Change) that treats C removed from the forest in the form of Harvested Wood Products as C immediately released to the atmosphere as carbon dioxide. Cumulative DOC export to the Sooke Lake reservoir was ~30,660 tC by 2012, representing a substantial pathway for C leaving the forest ecosystem. However, more research is required to understand what fraction of terrestrially-derived DOC is sequestered long term in lake sediment. The results of this study will assist forest manager decision making on the appropriate management response to future forest disturbance patterns that could result from climate change and to improve climate change mitigation efforts.
11 Years and Beyond: A Visual Exploration of Collective Arts for Climate Justice
(2020-05-25) Gelderman, Hannah; Clover, Darlene
As we collectively navigate the interconnected climate and inequality crises and fight for a just and habitable future, the arts and creative practices have a critical role to play. In 11 Years and Beyond: A Visual Exploration of Collective Arts for Climate Justice I focus specifically on the role of locally produced, participatory visual arts as a response to both the drivers and the impacts of the climate crisis. From a climate communications perspective participatory visual arts have already proven effective in engaging people in climate solutions (Burke, Ockwell, & Whitmarsh, 2018; Roosen, Klöckner, & Swim, 2018). In addition to improving climate change communications, participatory visual arts offer us a platform to envision a different world (Galafassi et al., 2018), strengthen our activism (Duncombe & Lambert, 2018), build community connection (Berman, 2017), and increase our resiliency (Huss, Kaufman, Avgar & Shuker, 2016) which all help us to navigate, resist and transform our current capitalist, colonial paradigm. Artists, organizers and others who facilitate participatory art projects have an important role to play in these processes, but I have found that there is a lack of resources for those seeking to make change at the intersection of art and activism. To fill this gap I have used arts-based research methods (thus leveraging the power of the arts in my own research) to create Collective Arts for Climate Justice, an illustrated guide in zine format, that advocates for the use of locally produced, participatory visual art practices as a necessary part of our response to our current crises. Because "arts-based forms have the potential to reach wider audiences, including nonacademic audiences" (Leavy & Harris, 2019, p. 216) I have illustrated all my background information (e.g., my literature review), as well as the zines, to ensure that all my research can be as accessible as possible. Through this I hope to invite organizers, artists, and others to utilize community based visual arts to further expand our collective and community capacity to respond to the climate crisis. The growth of participatory art practices can help invigorate and strengthen us as we fight for climate justice, renew our relationships with the land, and build the world we want to live in.
13,000 years of fire activity in a temperate rainforest on the Central Coast of British Columbia, Canada
(2018-04-10) Hoffman, Kira M.; Starzomsk, Brian M.
While wildfire is globally most common in the savanna-grassland ecotone, the flammability of coastal temperate rainforests is considered low and little is known regarding historic fire activity. Reconstructing historical fire activity typically requires dendrochronological records from fire-scarred trees and post-fire cohorts, but this type of information is rare in perhumid temperate rainforests, which are dominated by dense fuels with high year-round moisture content. I reconstructed historic fire activity using fire scars, tree rings, soil charcoal, and remote sensing techniques in a 2000 km2 island group located within the Hakai Lúxvbálís Conservancy on the coastal margin of central British Columbia. I broadly assessed 13,000 years of fire activity with charcoal deposited in soils, and reconstructed late Holocene fire events with a 700-year chronology built from living fire-scarred trees and stand establishment data. I used a weight of evidence approach to hypothesize the origins of fires and whether First Nations intentionally utilized fire for resource management. Low-severity fires occurred most frequently in forests surrounding former First Nations habitation sites, and lightning strikes do not occur often enough to explain the observed temporal or spatial patterns of fire activity in the study area. Low-severity fires occurred approximately every 39 years, and were 25 times more likely to occur than previously estimated. Fires influenced the composition and structure of vegetation by creating a mosaic of vegetation types in different stages of succession, and thus increased the abundance of culturally important food plants. Fire events have not occurred in the study area since 1893, which also coincides with the reduction of First Nations activities in their traditional territories. My data are consistent with the hypothesis that humans intentionally used fire to manage resources, though further research and ethnographic data collected elsewhere in the region is required to corroborate these findings. Ecological legacies of historic fires remain visible on the present day landscape, and by reconstructing the historic range of fire cycle variability we gain a better understanding of human-driven fire activity and the abrupt changes that occurred in the 20th century.
19F NMR investigation of CF3 motion in solid zinc trifluoromethylsulfonate
(1987) Sun, Jiankang
2 to 1 embeddings of grids into hypercubes
(1993) Manke, Dennis L.
We consider two-to-one embeddings of grids into the next smaller Hypercube and derive novel two-to-one embedding techniques that achieve optimal dilation 1 for many grids, where in some cases no previous solutions were known. In particular, dilation 1, two-to-one embeddings into the next smaller Hypercube can be found for grids that are: - square. - close to square. - of height within one of a power of 2.
2-D and 3-D viscoelastic finite element models for subduction earthquake deformation
(2008-04-10T05:57:27Z) Hu, Yan.; Wang, Kelin
2-D digital filter analysis and application with DEDIP
(1994) Keddy, William Alfred Lyle
Two-dimensional (2-0) digital signal processing is applied in many areas including digital image processing, medicine, geography, geology and robotics. In many of these applications 2-D linear, shift invariant (LSI) digital filtering is used and it is desirable to be able to analyze all types of 2-D, LSI filters (finite-duration impulse response (FIR), infinite-duration impulse response (IIR) and separable versions of both) and evaluate their performance by applying them to real images. Though many digital image processing (DIP) packages are available, they lack the capability for 2-D filtering beyond simple convolution. The work presented here describes an environment for developing DIP algorithms with particular emphasis on the 2-D LSI digital filtering applications. DEDIP, a Developmental Environment for Digital Image Processing, has been developed using the traditional two level programming approach. The low level is a C-language software library of DIP and system management functions. The high level is a set of digital image processing and file management tools operating under UNIX. Through representation-dependent system management functions, the data and file structures are hidden. These functions perform access and modification, file input and output, and dynamic memory al location on an image which is treated as a single data object. This hides the details of the implementation from the programmer and forms the base of a hierarchical library. The library's top level of DIP functions, built using the system management functions, are data and file structure independent which enhances the portability, reusability and reliability of DEDIP. The DIP algorithms available in DEDIP can be grouped by the operation types of point, intensity and filter. Point operations such as negation and addition of two images are performed on individual pixels. Intensity operations include histogram equalization and linear contrast stretching that modify the histogram of an image. Filter operations include the application of FIR, IIR, separable FIR and separable IIR filter coefficient masks to images as well as the analysis of filter mask characteristics which include the impulse, step, magnitude and phase responses, and the group delays. The capabilities of DEDIP for the implementation of 2-D LSI digital filters are demonstrated through examples of FIR lowpass, IIR lowpass and FIR fan filters, first directional-derivative edge-detection operators and the Laplacian of a Gaussian second derivative edge-detection operator. In each example the particular filter coefficient mask is analyzed, the filtering operation on a test image is pe1fo1med and the filtering result is discussed.
2-dipath and proper 2-dipath k-colourings
(2011-05-02) Young, Kailyn M.; MacGillivray, Gary
A 2-dipath k-colouring of an oriented graph G is an assignment of k colours, 1,2, . . . , k, to the vertices of G such that vertices joined by a directed path of length two are assigned different colours. The 2-dipath chromatic number is the minimum number of colours needed in such a colouring. There are two possible models, depending on whether adjacent vertices must also be assigned different colours. For both models of 2-dipath colouring we develop the basic theory, including characterizing the oriented graphs that can be 2-dipath coloured using a small number of colours, finding bounds on the 2-dipath chromatic number, determining the complexity of deciding the existence of a 2-dipath k-colouring, describing a homomorphism model, and showing how to determine the 2-dipath chromatic number of tournaments and bipartite tournaments.
2-limited broadcast domination on grid graphs
(2021-07-29) Slobodin, Aaron; MacGillivray, Gary; Ruskey, Frank
Suppose there is a transmitter located at each vertex of a graph G. A k-limited broadcast on G is an assignment of the integers 0,1,...,k to the vertices of G. The integer assigned to the vertex x represents the strength of the broadcast from x, where strength 0 means the transmitter at x is not broadcasting. A broadcast of positive strength s from x is heard by all vertices at distance at most s from x. A k-limited broadcast is called dominating if every vertex assigned 0 is within distance d of a vertex whose transmitter is broadcasting with strength at least d. The k-limited broadcast domination number of G is the minimum possible value of the sum of the strengths of the broadcasts in a k-limited dominating broadcast of G. We establish upper and lower bounds for the 2-limited broadcast domination number of various grid graphs, in particular the Cartesian products of two paths, a path and a cycle, and two cycles. The upper bounds are derived by explicit broadcast constructions for these graphs. The lower bounds are obtained via linear programming duality by finding lower bounds for the fractional 2-limited multipacking number of these graphs. Finally, we present an algorithm to improve the lower bound for the 2-limited broadcast domination number of special sub-families of grids. We conclude this thesis with suggested open problems in broadcast domination and multipackings.
A 2122-year tree-ring chronology of Douglas-fir and spring precipitation reconstruction at Heal Lake, southern Vancouver Island, British Columbia
(1996) Zhang, Qibin
A 2122-year tree-ring chronology was developed from living and submerged logs of Douglas-fir at Heal Lake, near Victoria, southern Vancouver Island, British Columbia. Correlations between the tree-ring indices and monthly mean temperature and monthly total precipitation indicated that the radial growth of Douglas-fir was strongly correlated with the spring and early summer (April-July) precipitation and the previous years' growth. A transfer function was established using tree-ring indices to predict the weighted 5 years' effective precipitation. The reconstructed precipitation history for the last two millennia exhibited eight distinct climatic intervals involving long periods of wetness and drought and extreme events. The result showed that the Little Ice Age was featured by wetness in the interval AD. 1567-1765 and there were occurrences of wet episodes before and after this interval. There was no evidence of Medieval Warm Period in the area. Comparison with other studies in the nearby regions showed general agreement and demonstrated a regional climatic control. The result can be applied in a broad range from the fundamental understanding of the climate system to the practical management of our natural resources.
21st century competencies: the effect on teacher workload
(2015-04-27) Arksey, Lori; Milford, Todd
This project is a proposed strategic plan for districts, schools and individual teachers to aid in the successful implementation of 21st century competencies, specifically Critical Thinking, Problem Solving and Decision Making and Lifelong Learning, Personal Management and Well-being, while keeping in mind teacher workload. The proposed strategic plans allow for the breakdown of new initiatives into manageable goals, while keeping in mind government mandates and teacher attrition. Included is an exemplar plan for all levels and stakeholders who include the school district, schools and individual teachers. This was created in the wake of a mandate letter from Alberta Education (2010) which specified that teachers must teach students the competencies as well as the original curriculum, in all grades across all subject levels and grades.
A 258-year record of precipitation as snow from tree-rings, Southern Coast Mountains, British Columbia
(2017-01-03) MacKinnon, Stuart James; Smith, Daniel J.
In Pacific North America, a substantial amount of the streamflow available during the dry summer months originates from melting mountain snowpacks. Since the start of the twenty-first century, these mountain snowpacks have been declining due to the impacts of global climate change and could have severe implications for future water availability in many regions. To develop robust predictive models of future water availability derived from mountainous snowpacks, the longest possible data record is required. However, instrumental data for snow measurements, when available, are limited to a length of only five or six decades in most regions of Pacific North America. In this study, tree-rings from snow-depth sensitive tree species (mountain hemlock (Tsuga mertensiana (Bong.) Carrière) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.)) were used as a proxy to develop a 258-year record of precipitation as snow (PAS) for the southern Coast Mountains of British Columbia. Four snow models were evaluated based on a suite of dendroclimatological model diagnostics. From these, one PAS reconstruction was carried out. The reconstruction was unable to properly validate using the leave-one-out cross validation method. This result is attributed to the combination of a short calibration period, a potentially weak climate signal, and the absence of signal enhancement. Despite this outcome the research resulted in number of inferences and recommendations useful for future research.
2SLGBTQ recreational sport participation: Mental health, social support and community connection
(2025) Wells, Gordon A.; Lachowsky, Nathan; Souleymanov, Rusty
Community sport participation is increasingly promoted as a strategy to support people’s health and wellbeing. Without strategies that account for the harassment and marginalization that many Two-Spirit, lesbian, gay, bisexual, transgender and queer (2SLGBTQ) people experience in sport, the promotion of community sport may further compound health disparities experienced by 2SLGBTQ people. Despite these experiences of harassment and marginalization, 2SLGBTQ people have created their own 2SLGBTQ recreational community sports teams and leagues to exercise, socialize and play with other 2SLGBTQ people. In this dissertation I conducted a series of analyses to understand the relationship between 2SLGBTQ recreational sports participation and the mental health and sense of community connection of 2SLGBTQ people in Canada. My first analysis is of data from the Momentum study, a longitudinal prospective cohort study on the health of gay and bisexual men (GBM) in Metro Vancouver, comparing self-reported questionnaire findings on those who participated in 2SLGBTQ recreational sports with those who did not. I also compared outcomes between those who saw a change in their 2SLGBTQ sports participation (e.g. started or stopped 2SLGBTQ sport participation). I found no significant differences in mental health measures, but GBM who participated in 2SLGBTQ sports reported more social support and were less likely to report being in poorer health. GBM who started participating in 2SLGBTQ sports reported higher community participation and were less likely to report being in worse health. Lastly, GBM who stopped participating were less likely to have depression scores in the normal range. The second analysis sought to understand if transgender, nonbinary and gender diverse (trans) people’s participation in 2SLGBTQ recreational sports is associated with improved mental health, social support and sense of connection with 2SLGBTQ communities. My analysis is conducted on data drawn from the 2019 and 2022 cycles of the community-based, cross-sectional Sex Now study. Compared with those who did not participate in 2SLGBTQ recreational sports, trans people did not report a significant difference in anxiety symptoms, but did report lower depressive symptoms and higher satisfaction with their relationship to the 2SLGBTQ community. My final analysis is of data from the Our Health study, a cross-sectional, community health survey on 2SLGBTQ people across Canada. I sought to understand the relationship between 2SLGBTQ recreational sport participation and 2SLGBTQ people’s mental health, social support and sense of 2SLGBTQ community connection. I also sought to understand if age moderated any of these potential associations. I found that while participants of 2SLGBTQ recreational sports reported similar levels of anxiety and depression symptoms as non-participants, they demonstrated significantly higher social support and 2SLGBTQ community connection. These associations held for younger and older 2SLGBTQ people. My research has found a strong relationship between 2SLGBTQ people’s participation in 2SLGBTQ sport and improved mental health, social support and sense of connection to 2SLGBTQ communities. This dissertation provides insights for social service and healthcare policy and practice to engage 2SLGBTQ recreational sport to support the health and wellbeing of 2SLGBTQ people across Canada.
3-D seismic investigations of northern Cascadia marine gas hydrates
(2018-10-23) Riedel, Michael; Hyndman, R. D.
This dissertation presents results from 3-D (parallel 2-D) high resolution seismic surveys and associated studies over an area with deep sea gas hydrate occurrence. The study area is located on the accretionary prism of the northern Cascadia subduction zone offshore Vancouver Island, Canada. The major objectives of this study were the imaging of a gas/fluid vent field found in the study area and detailed mapping of the tectonic setting and geological controls on fluid/gas venting. Secondary objectives were the characterization of the gas hydrate occurrence and constraints on the seismic nature of the bottom-simulating reflector (BSR) and its spatial distribution. The main grid was 40 lines at 100 m spacing with eight perpendicular crossing lines of multichannel and single channel seismic reflection, and 3.5 kHz subbottom profiler data. In addition to the main 3-D seismic grid, two smaller single channel grids (25 m spacing) were collected over the vent field. The multichannel seismic data acquired with the Canadian Ocean Acoustic Measurement System (COAMS) streamer required correction for irregular towing depth and shot point spacing. A new array element localization (AEL) technique was developed to calculate receiver depth and offset. The individual receiver depths along the COAMS streamer varied between 10-40 m, which resulted in the occurrence of a prominent receiver ghost that could not be completely removed from the seismic data. The ghost resulted in limited vertical resolution and a coarse velocity depth function. The vent field is characterized by several blank zones that are related to near-surface deformation and faulting. These zones are 80-400 m wide and can be traced downward through the upper 100-200 m thick slope sediment section until they are lost in the accreted sediments that lack coherent layered reflectivity. The blank zones are also characterized by high amplitude rims that are concluded to result from the interference effect of diffractions. These diffractions result due to relatively sharp discontinuities in the sediment physical properties at the blank zone boundary. 2-D vertical incidence seismic modeling suggests an increase in P-wave velocity inside of the blank zone with only minor changes in density. Blanking is believed to be mainly the effect of increased hydrate formation within the fault planes. The faults are conduits for upward migrating fluids and methane gas that is converted into hydrate once it reaches the hydrate stability field. Carbonate formations at the seafloor can also contribute to blanking especially at higher frequencies. Free gas may be present in case of full hydrate saturation or strong fluid flow. Geochemical analyses of pore water and water-column samples carried out in cooperation with Scripps Institute of Oceanography indicate relatively low fluid fluxes of less than 1 mm/yr and there is no heat flow anomaly present over the vent field. Methane concentrations of 20 n-moles/L (about 8 times the ocean background concentration) were detected in water-column samples of the first 100-200 m above the main blank zone of the vent field. Venting is also believed to be strongly episodic with a recently more quiet time. However, the observed carbonate crusts indicate a long-term activity of the vents.
3-D travel time tomography of the gas hydrate area offshore Vancouver Island based on OBS data
(2009-11-24T23:04:46Z) Zykov, Mikhail Mikhailovich; Chapman, N. Ross
This dissertation presents results from a complex seismic study using Ocean Bot¬tom Seismometers (OBS) conducted at a site of deep sea gas hydrate occurrence. The site is located on the accretionary margin of the northern Cascadia subduction zone offshore Vancouver Island. Canada. The major objectives for this study were the construction of a 3-D velocity model around the Bullseye vent zone by the means of travel time inversion tomography and the analysis of the amplitude data for reflections from the water-sediment interface and the bottom simulating reflector (BSR). Secondary objectives included the integration of the results from this study with previous knowledge about the vent zone for further clarification of its structure and evolution. The OBS seismic data set consisted of 22 parallel lines at 200 in spacing with three perpendicular crossing lines recorded on five OBS stations. Multichannel and single channel conventional seismic data along these lines were also acquired. The OBS experiment geometry required corrections for the coordinates of sources and receivers initially obtained in the field. A new comprehensive source and receiver localization technique was developed for the case of stationary hydrophones and multiple seismic lines. The horizontal size of the created 3-D velocity model is 3 km x 2.7 km. The modelled volume is limited by the seafloor at the top and by the BSR at the bottom. The size of a grid cell is 50 m x 50 m x 20 m. The uncertainty for the velocity value of individual cells was as low as 20 m/s. although the resolution of the model was reduced by the sparse receiver geometry. The inversion results indicate a fairly uniform velocity field around and inside the vent zone. Velocities are nearly equal to values expected for sediments containing no hydrate, which supports the idea that the bulk concentrations of gas hydrates are low at the site. The largest velocity anomaly with an amplitude of +25 m/s is spatially associated with the limits of the blank zone. The anomaly suggests greater gas hydrate concentrations inside the vent zone than outside. Low vertical resolution of the model did not provide information on the depth distribution of the hydrate. However, the combination of the information from the velocity inversion with previous studies suggests that the zone of high hydrate concentration (15-20% of the pore space) associated with a hydrate lens, located at the top of the sediment section. The vent site is characterized by a negative anomaly of the seafloor reflection coefficient, outlined by a high amplitude rim. The low reflection coefficient is believed to be the result of the processes taking place above the hydrate lens, methane venting in particular. and the high amplitude rim to be the effect of carbonate formation. The seafloor reflection coefficient zonation appears to be correlated with the distribution of low magnetic susceptibility zone in the first 8 in of the sediment section. Both phenomena can be related to the distribution of upward fluid flow at the vent site. The cause of the blanking phenomena is likely different for different frequencies of the seismic signal. The blanking at high frequencies is an effect of near-surface disturbed sediments due to active venting and, possibly. free gas presence at the top of the vent zone. The blanking for the middle range of seismic frequencies is mostly the effect of reduced impedance contrast between the sediment layers inside the blank zone due to local presence of gas hydrates in small concentrations (2-3%). It is concluded that. the Bullseye vent zone, which shows very low activity presently, was probably much more active in the past (similar to a mud volcano). The past ac¬tivity may have led to the formation of the bathymetric expression of the vent site (a mound), together with the hydrate lens and authigenic carbonates.
A 3-D visualization system for serial microscope images
(2018-07-18) Li, Jianping; Agathoklis, Panajotis
A three-dimensional (3-D) visualization system for serial microscope images is developed with special reference to its application in microscopy and cell biology. The 3-D visualization system involves three process stages, namely data acquisition, volume data modeling and object rendering. The data acquisition part deals with collecting serial microscope images and is carried out by optical sectioning which records serial microscope images from the top to the bottom of a specimen. A new algorithm is proposed to computationally remove out-of-focus information from each recorded image of a specimen. This algorithm processes serial images independently and thus avoids computationally expensive 3-D convolution and 3-D Fourier transforms. Further, an extensive study of imaging properties of defocused microscopes is carried out in the thesis. The defocused point spread functions and optical transfer functions of transmitted light microscopes have been analyzed. An extensive comparison of the two approaches of obtaining these functions, namely direct measurements and theoretical calculations. is conducted. An interesting observation is made that the results of these two approaches correspond well with each other only for low magnification and low numerical aperture objective lenses. Modeling of serial microscope images is carried out by an isosurface modeling algorithm. This algorithm is based on the marching-cube algorithm with two modifications proposed in the thesis. One modification is to detect and prevent the redundancy existing in the original marching-cube algorithm. The other modification is to use the middle-point algorithm to avoid linear interpolation to locate the vertex of a polygon. Results show that the modified marching-cube algorithm proposed in the thesis significantly reduces the number of polygons generated and thus greatly increases the computation efficiency for surface generation and object rendering. Object rendering, which is to generate a realistic image, is carried out by using a C library SImple Polygon Processor (SIPP). A graphic user-interface is designed and implemented to facilitate the modeling and rendering processes. It offers various user-friendly functions, such as rotation, zooming and cutting, for close examination of the objects under study and can be used for visualizing various volume data. The interactive system together with the data acquisition algorithm form a 3-D visualization system for serial microscope images. The results of visualization show that the 3-D visualization system developed in this thesis realistically and efficiently reconstructs objects of interest from serial microscope images as well as from various volume data such as Computer Tomography (CT) and Magnetic Resonance Imaging (MRI) medical images.
3-manifolds algorithmically bound 4-manifolds
(2019-08-27) Churchill, Samuel; Mehlenbacher, Alan; Budney, Ryan David
This thesis presents an algorithm for producing 4–manifold triangulations with boundary an arbitrary orientable, closed, triangulated 3–manifold. The research is an extension of Costantino and Thurston’s work on determining upper bounds on the number of 4–dimensional simplices necessary to construct such a triangulation. Our first step in this bordism construction is the geometric partitioning of an initial 3–manifold M using smooth singularity theory. This partition provides handle attachment sites on the 4–manifold Mx[0,1] and the ensuing handle attachments eliminate one of the boundary components of Mx[0,1], yielding a 4-manifold with boundary exactly M. We first present the construction in the smooth case before extending the smooth singularity theory to triangulated 3–manifolds.

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