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Physiological costs of altered hydrothermal conditions in harvested forests
Full text linkAmphibians are among the most rapidly declining vertebrate groups worldwide, with habitat modification and climate change driving widespread population declines. Much work on amphibian vulnerability focuses on gradual shifts of climate change. While in many landscapes, habitat-altering disturbances such as clearcutting introduce sudden shifts in thermal and hydric environments on timescales far shorter than those of potential local adaptation and potentially removing critical microhabitat refugia. Such changes may be particularly relevant for amphibians, whose behaviour and ecological performance is linked to both body temperature and dehydration status. However, predicting the impacts of harvesting on amphibian hydrothermal physiology is not straightforward as higher temperatures (up to thermal optima) may increase performance, while dehydration will decrease it. To untangle these effects, I compared hydrothermal performance curves for Dryophytes versicolor with water loss rates and operative temperatures of replica frogs in harvested, edge, and unharvested boreal forest across four time-since-cut stages. Replica frog water loss was significantly correlated with real frog water loss (R2 = 0.86). I found performance declines past 15-20% dehydration and that baseline performance was lower at cooler temperatures and higher dehydrations. Clearcut environments reduced performance for gray treefrogs during overnight activity periods, particularly in uncovered microhabitats, across all time-since-cut groups, indicating that the increased hydrothermal vulnerability from harvesting is maintained through succession. By examining the relationship between performance, hydration, and temperature, we can begin to understand how removal or alteration of key microhabitats may impact individual fitness and population persistence within disturbed landscapes
A novel current source converter-based ultra-high-power offshore wind energy conversion system
Full text linkIn medium voltage (MV) ultra-high-power (over 10 MW) offshore wind energy
conversion systems (WECS), current source converter (CSC)-based series-connected
configurations are a good candidate. However, existing CSC-based WECS use the
bulky low-frequency transformer (LFT), have high rotor torque ripple or require the
active rectifier, which entails higher costs, lower reliability and efficiency, and larger
size and weight than the diode rectifier. To address these issues, this thesis proposes a
novel CSC-based series-connected MV WECS, combining the six-phase generator
connected to two diode rectifiers with two medium frequency transformers (MFTs)-
based modular converters on the generator side and using the dual-bridge current source
inverters (CSIs) on the grid side. The proposed WECS effectively mitigates rotor torque
ripple caused by diode rectifiers and retains all the advantages of existing MFTs-based
WECS. Additionally, the modular converter in the proposed WECS has voltage and
current imbalance issues, so a corresponding control scheme is proposed to address
these issues. Furthermore, online selective harmonic elimination (SHE) modulation is
applied to the grid-side CSIs. This approach significantly reduces the memory
requirements of the digital controller, thereby lowering costs while retaining all the
advantages of conventional SHE techniques. The feasibility and effectiveness of the
proposed WECS, its control scheme, and the online SHE modulation are validated
through simulation results
Being/becoming a neurodiverse student
Full text linkThis SSHRC-funded autoethnographic portfolio explores the lived experiences of a neurodiverse university student through transformative multimedia story-making. Drawing from the researcher's personal journey with anxiety, ADHD, autism, and memory disability, the portfolio challenges dominant deficit-oriented discourses that frame neurodiversity in academia as inherently problematic. By employing an interpretive disability studies (IDS) framework and Re•Storying methodologies, the research articulates how inclusive pedagogical and socio-cultural environments can affirm the agency and belonging of neurodiverse students. The written narrative and multimedia short film (Where I Sit: A Narrative of Being and Becoming) critically examine how ableism and (in)visibility intersect with academic identity, while also highlighting the role of ensemble, space, and relational trust in shaping a positive university experience for neurodiverse students. This portfolio contributes to the growing field of (invisible) disability and neurodiversity scholarship by providing rich data from an insider perspective that affirms neurodiversity as an important aspect of identity with transformative potential within academic communities rather than an unfortunate burden to be carried and overcome
Nonlinear dynamics and vortex mechanics for energy harvesting from fluttering wings
Full text linkThis research investigates the nonlinear aeroelastic dynamics and energy harvesting performance of a two-degrees-of-freedom NACA 0012 wing under varying reduced velocities and electrical load resistances. In the first part of this work related to two-dimensional computational simulations, nonlinear oscillations emerge near the critical reduced velocity U∗r=6, with large amplitude limit-cycle oscillations forming around U∗r=8 in the absence of an electrical loading. As the electrical resistance increases, this transition is delayed, indicating the damping effect of the energy extraction mechanism. Fourier spectral analysis reveals the presence of both odd and even superharmonics in the aerodynamic lift force, highlighting the strong nonlinear fluid-structure coupling, which becomes less prominent at higher resistances. Phase portraits and Poincare maps demonstrate clear transitions between periodic and chaotic states, particularly under low resistance conditions. The voltage output is strongly correlated with fluctuations in the lift force, reaching a maximum at intermediate resistance before declining due to nonlinear suppression. Flow visualizations uncover a range of vortex shedding patterns, including single, paired, and multi-pair vortex configurations that weaken at high resistances and lower U∗r . Building upon the insights gained from two-dimensional simulations, this study is extended to three-dimensional configurations by systematically increasing the wing's spanwise length to 0.3c, 0.6c, and 0.9c. The three-dimensional analysis focuses on the conditions that yielded optimal voltage output in the two-dimensional simulation results, particularly at U∗r=10 for different load resistances. The objective is to examine how variations in spanwise length influence fluid-structure interactions, alter vortex formation and organization, and impact the onset and intensity of nonlinear behaviors. Also, the comparative analysis of the 3D and 2D results highlight the influence of spanwise flow instabilities on the energy harvesting performance. These findings provide valuable insights for identifying optimal spanwise length and operational parameters that enhance power generation efficiency in flutter-based energy harvesting systems
Demethylation of sulfobutylated kraft lignin and its application as phenol-formaldehyde adhesives
No full textThe shift toward sustainable and eco-friendly adhesives has led to increased research into renewable alternatives for petroleum-derived components in phenol-formaldehyde (PF) resins. Lignin, a natural phenolic polymer, presents a promising option due to its structural similarity to phenol. However, its high molecular weight, structural heterogeneity, and low reactivity hinder its direct incorporation into adhesive formulations. To overcome these limitations, this study investigates a two-step chemical modification—sulfobutylation followed by demethylation—to improve lignin’s solubility and performance in PF resins.
The sulfobutylation (SB) step resulted in a decrease in methoxy and hydroxyl groups while increasing molecular weight, sulfur content, solubility, and charge density, significantly improving lignin’s aqueous compatibility. Demethylation of sulfobutylated lignin (DSB) further decreased methoxy content, with a slight increase in hydroxyl groups compared to SB lignin. Additionally, demethylation led to higher molecular weight and a reduction in sulfur content back to levels observed in kraft lignin (KL) while maintaining solubility. These changes were attributed to an increase in β-O-4 interunit linkages, which contributed to improved reactivity. The demethylated sulfobutylated lignin-PF (DSBPF) resins retained the PF resin’s molecular structure but exhibited more reactive formaldehyde adducts. Increasing the lignin content led to higher MW and viscosity, which enhanced bonding strength but reduced thermal stability. The β-O-4 linkages in DSB contributed to improved adhesive properties, increasing bonding strength by 19% in DSBPF20 and 25% in DSBPF60. However, the resins also exhibited higher free formaldehyde emissions, exceeding safety limits. Additionally, while pH and non-volatile content remained stable, water absorption increased, potentially impacting long-term durability. Despite these challenges, the modified resins showed enhanced fire resistance and adhesion performance compared to conventional PF resins.
Future research should focus on optimizing resin synthesis parameters, including NaOH catalyst amount, reaction time and temperature, and curing conditions, to improve performance while reducing emissions. Furthermore, incorporating enhancers such as melamine, urea, or furfural could help maintain or improve adhesive properties while minimizing formaldehyde content. This study provides valuable insights into lignin-based PF resins, contributing to the development of more sustainable, high-performance adhesives and reducing reliance on petroleum-based materials
Effect of enhanced efficiency nitrogen fertilizers and ANVOL™ on winter wheat yield and protein content
Full text linkNitrogen (N) plays a critical role in agricultural production, particularly in cereal crops such as winter wheat (Triticum aestivum L.), where it influences both yield and grain quality. However, managing nitrogen efficiently remains a challenge in many regions, including Northwestern Ontario, where suboptimal nitrogen use often results in reduced yields and lower plant protein content. This study evaluated the effectiveness of enhanced efficiency nitrogen fertilizers (EEFs), such as Environmentally Smart Nitrogen (ESN), SUPERUTM, and urea treated with ANVOLTM, in improving winter wheat production under the agroclimatic conditions of Thunder Bay, Ontario. The overarching goal was to determine whether these advanced fertilizers could enhance N use efficiency and address the issue of low plant protein content. The experiment was conducted at the Lakehead University Agricultural Research Station (LUARS; https://www.lakeheadu.ca/centre/luars) using N application rate of 120 kg N/ha either from individual N fertilizers or their blends with additional treatments of SUPERUTM at 100 kg ha-1, urea at 160 kg N ha, and a no-N reference treatment. Key parameters such as plant and stem counts, plant heights through critical stages, chlorophyll content, grain yield, and plant protein content were assessed to evaluate treatment performance. Nitrogen source had minor effects on chlorophyll content, with marginal differences in leaf pigmentation among treatments. Similarly, phenotypic traits and grain characteristics showed no substantial variation across N sources or application rates. Grain yields were, however, significantly higher in treated plots compared to reference plots without N. This suggests that EEFs, while aimed at improving N use efficiency, did not translate into higher yields than urea alone under Thunder Bay's specific environmental and soil conditions (pre-seeding nitrate N: 14 ppm and ammoniacal N: 5 ppm). These results underscore the complexity of N management in winter wheat and suggest that factors beyond N application may have a more pronounced impact on yield in this region, in this case a dry summer. Despite the lack of yield improvement, the central question remains whether EEFs can enhance plant protein content—a critical quality determinant for wheat.
Keywords: Nitrogen management, enhanced efficiency fertilizers (EEFs), Environmentally Smart Nitrogen (ESN), SUPERUTM, ANVOL, winter wheat, plant protein content, yield, nitrogen use efficiency, chlorophyll content, Thunder Bay, Northwestern Ontario
Improving performance of NOMA and RSMA systems with improper Gaussian signaling
Full text linkWith the new wave of beyond fifth generation (B5G) and sixth generation (6G) communication systems, there is a perpetual demand for more wireless services with higher data rates,
lower latency, and greater connectivity. In order to meet these growing expectations, new candidate technologies (e.g., small cells, millimeter wave, and massive multiple-input multiple-output)
have been introduced. Non-orthogonal multiple access (NOMA) has been presented among the
most promising strategies for wireless applications due to its effectiveness in supporting heavily-
loaded systems by serving users with diverse channel conditions in the same time-frequency
resources. NOMA makes it possible to allocate one resource (frequency, time, code, or spatial)
to serve multiple users at once by employing superposition coding at the transmitter side and
successive interference cancellation (SIC) at the receiver side, resulting in more spectral-efficient
and energy-efficient systems.
Recently, rate-splitting multiple access (RSMA) has emerged as a more generalized multiple
access technique than NOMA which can serve various under-loaded and over-loaded wireless
applications by taking advantage of the common streams to better manage the interference.
RSMA offers a flexible interference management technique by enabling an intelligent combination of transmitter-side and receiver-side interference mitigation rather than fully mitigating
the interference at the receiver side as in NOMA. The RSMA strategy involves splitting user
messages and employing a non-orthogonal transmission scheme, where common messages are
decoded by multiple users, and private messages are decoded by their respective users. This
approach enhances performance across a broader range of network loads, improving spectral and
energy efficiency as well as user fairness.
Improper Gaussian signalling (IGS) has emerged as a signal processing tool and potential alternative to the proper Gaussian signalling (PGS) to improve the spectral efficiency of
interference-limited 5G and beyond networks. IGS achieves higher degrees of freedom than PGS
due to its capability to control the interference signal dimension. IGS can be viewed as a type
of interference alignment, where interference is effectively eliminated by confining it to a single
orthogonal signal space dimension, allowing the desired signal to be decoded from the remaining
orthogonal dimension.
In this thesis, we investigate the potential performance merits of using IGS in the downlink interference-limited NOMA systems assuming practical scenarios including SIC imperfection in
point-to-point NOMA systems and imperfect self-interference cancellation in cooperative full-
duplex NOMA systems etc. We also investigate the potential performance merits of using IGS
in RSMA as a generalization scheme of NOMA system.
In the first part of this thesis, a point-to-point downlink NOMA system is studied, where the
IGS strategy is adopted to compensate for the performance loss caused by imperfect SIC. New
closed-form expressions for achievable user rates are derived when users employ the IGS strategy.
Joint optimization problems are then formulated to maximize the overall spectral efficiency and
energy efficiency of a two-user NOMA system, subject to minimum user-rate requirements and
total power constraints. Sub-optimal solutions for the IGS circularity coefficients and power
allocation are derived for the formulated problems. Additionally, improper constellation diagrams are designed using widely linear transformation (WLT) with the predefined optimized
IGS coefficients to analyze the impact of IGS on throughput and error performance.
In the second part of this thesis, a downlink cooperative full-duplex NOMA (FD-NOMA)
system employing IGS under imperfect self-interference cancellation is analyzed. Optimization
problems are formulated and solved to maximize the sum rate, achieve max-min rate fairness,
and enhance energy efficiency. These problems involve the joint optimization of the circularity
coefficients of the IGS and the power allocation at the base station, subject to each user’s
rate constraints. We propose iterative algorithms based on solving the Karush-Kuhn-Tucker
(KKT) conditions to derive sub-optimal solutions to the formulated problems. Additionally, we
illustrate the impact of the IGS circularity coefficient on the constellation diagram of each user.
In the third part of this thesis, we consider a downlink cellular system using RSMA transmission scheme at the base-station with IGS to serve multiple users. We first derive the achievable
user private rate and user common rate considering IGS is used for the common message. Then,
we maximize the private sum rate of the users’ private rates subject to certain minimum users’
common rate constraint. In this optimization problem, we optimize the IGS circularity coefficients and power allocation.
The thesis results show that the performance of IGS-based NOMA/RSMA system outperforms its counterpart PGS-based NOMA/RSMA system under the realistic hardware imperfections
Induction of actinobacterial enzymes for enhanced biological depolymerization of polyethylene terephthalate plastics
No full textPolyethylene terephthalate (PET), a widely used plastic, has been accumulating in the environment at an alarming rate, posing significant ecological challenges. This research addresses PET pollution through a biological depolymerization-based approach, involving three integrated strategies: (1) physicochemical modification of PET to enhance degradability, (2) optimization of carbon sources and inducer sources for cutinase enzyme production by Thermobifida fusca YX, and (3) an in silico investigation to identify and characterize potential PET-hydrolyzing enzymes (PHEs) in the bacterium.
The first phase of the study focused on improving PET biodegradability through pretreatment techniques, including ultraviolet (UV) photooxidation, thermal oxidation, and size reduction of PET films. These treated samples were subjected to enzymatic depolymerization using both commercial immobilized enzymes and free (non-immobilized) enzymes derived from T. fusca YX. Analytical techniques such as Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) revealed that higher temperatures (above 80 °C) favored whole-cell biological depolymerization, while lower temperatures were more suitable for free enzyme-mediated depolymerization. Reduced particle size was also found to significantly improve biological depolymerization efficiency.
Following these findings, cutinase production by T. fusca YX was optimized to increase enzyme yield. Various carbon sources (including sodium acetate, sodium butyrate, and sodium lactate) and natural cutin inducers (extracted from Roma tomatoes, Royal Gala apples, and watermelon peels) were tested. Using Response Surface Methodology (RSM), enzyme production was enhanced by 42%, demonstrating a viable strategy for scalable and cost-effective cutinase generation for industrial applications.
In the final phase, an in silico analysis was conducted to explore the genomic potential of T. fusca YX for PET depolymerization. Six candidate cutinase enzymes were identified: three extracellular, two membrane-associated, and one intracellular. Molecular docking studies were performed to analyze their binding affinities with PET and cutin ligands, representing the first structural investigation of such interactions in T. fusca YX.
Overall, this study offers a comprehensive approach to improving PET biological depolymerization under environmentally benign conditions, while reducing reliance on harsh chemical depolymerization processes. The use of a naturally occurring microbial strain highlights the potential for further biotechnological advancements in sustainable plastic waste management.
Keywords
Polyethylene terephthalate, physicochemical pretreatments, chemical hydrolysis, biological depolymerization, cutinase, Thermobifida fusca YX, response surface methodology, central composite rotatable design, bioinformatics, PET-hydrolyzing enzyme
“As you’re able”: exploring perceptions of culturally-inclusive physical activity classes among older adults
Full text linkCulturally-inclusive physical activity (CIPA) encompasses initiatives designed to promote movement while accommodating diverse cultural backgrounds. Within this, group dynamics play an important role in fostering a sense of belonging and can improve physical activity participation. While studies on the benefits of CIPA-based programming exist, limited research on how CIPA influences engagement for older adults is available, especially through a group dynamics lens. Older adults face unique challenges when it comes to physical activity adherence which makes them an important population to research. Having more insight into the experience of group-based CIPA engagement could prove useful for identifying avenues to promote adherence, thereby impacting the health of participants positively. Thus, this qualitative study explored the perspectives of older adults (aged 60+) with CIPA program experience (e.g., BollyFit, Yoga, Tai Chi) from the Greater Toronto Area. A descriptive design integrating semi-structured interviews was used to gather information on participant’s facilitators and barriers to engagement, as well as group dynamics principles. Twelve older adults were interviewed (Mage = 70.16; n = 8 females). Deductive and inductive thematic analysis were used to identify recurring themes, and several strategies were employed to enhance data trustworthiness. Overall, program accessibility, health benefits, and opportunities for personal growth served as key facilitators to engagement, while programmatic issues, physical/mental barriers, and language challenges hindered participation. Notably, group dynamics themes — including social connections, role modeling, and support in various capacities — emerged as central to fostering belongingness and adherence. In sum, these findings illustrate the potential of CIPA to enhance engagement and well-being among older adults by fostering inclusivity and harnessing cultural diversity when creating supportive environments. Findings can be used to inform equitable and diverse movement opportunities for older adults and contribute to the growing discourse on culturally-sensitive approaches used for physical activity.
Keywords: Culturally-Inclusive Physical Activity, Older Adults, Physical Activity Engagement, Qualitative, Group Dynamics, Belongingnes
Optimal and global autonomous navigation in environments with convex obstacles
Full text linkMotion planning for autonomous navigation in unknown environments cluttered with
obstacles is a fundamental challenge in robotics, requiring efficient, safe, and reliable
strategies for path planning. This thesis introduces two novel autonomous navigation
strategies for vehicles operating in static, unknown n-dimensional environments clut-
tered with convex obstacles. The first strategy proposes a continuous feedback controller
that steers a vehicle safely to a target destination in a quasi-optimal manner within a
“sphere world,” where each obstacle is enclosed by a sphere-shaped boundary. Under this
approach, the robot avoids obstacles by navigating along the shortest path on the sur-
face of the cone enclosing the obstacle and proceeds directly toward the target when no
obstacles obstruct the line of sight. This controller guarantees almost global asymptotic
stability in two-dimensional (2D) environments under specific obstacles configurations.
An extension of this method is also developed for real-time navigation in unknown, static
2D environments with sufficiently curved convex obstacles, maintaining the same stability
guarantees. Simulation and experimental results demonstrate the practical effectiveness
of this approach in navigating real-world environments.
While the first strategy ensures almost global asymptotic stability only under specific
conditions related to the obstacles configuration and for 2D environments, the second
strategy aims to provide a more robust solution with stronger stability guarantees. This
second strategy introduces a hybrid feedback controller designed to navigate a vehicle in
static n-dimensional Euclidean spaces cluttered with spherical obstacles. This approach
ensures safe convergence to a predefined destination from any initial position within the
obstacle-free workspace while optimizing obstacle avoidance. A novel switching mecha-
nism is proposed to alternate between two operational modes: the motion-to-destination
mode and the obstacle-avoidance mode, ensuring global asymptotic stability regardless
of the obstacles’ configuration. Numerical simulations in both known and unknown 2D
and 3D environments, along with experimental validation in a 2D setting, demonstrate
the effectiveness the proposed approach.
These strategies provide robust solutions for autonomous navigation in static, un-
known environments, contributing to the advancement of safe, efficient, and optimal
motion planning techniques for robotic systems in complex, obstacle-laden spaces