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Development of Poly(Hindered Urea) Network for Self-healable Triboelectric Nanogenerators
Get PDFIn recent years healable electronics have garnered significant attention for their scope in next-generation electronic devices. In particular, triboelectric nanogenerators (TENGs) which are capable of harvesting energies from mechanical motions have been explored as a promising power source for self-powered devices. TENGs possess the benefits of high performance, convenience, eco-friendliness, and low cost and require great strength and functionality to perform. The incorporation of self-healability into the design of TENG systems could improve their lifetime and durability as well as their energy harvesting capabilities. Dynamic covalent chemistries have been utilized extensively for the development of covalent adaptive networks exhibiting self-healability and reprocessability. However, most approaches require the use of external stimuli to establish the reversibility of broken networks. Therefore, the development of a new strategy for the synthesis of robust networks with the balanced properties of void-filling and mechanical strength is required for value-added applications such as flexible electronics.
Hindered urea bond (urea with a bulky substituent, attached to its nitrogen atom) is a promising dynamic covalent chemistry which undergoes dynamic exchange reaction at mild temperature, with no catalysts. The reaction of a bulky amine with isocyanate allows for a simple design of a polyurea self-healing network, further broadening the scope of applications for these materials.
My Ph.D. research has aimed to study self-healing mechanisms of hindered urea chemistry and to design and synthesize new materials that can undergo catalyst-free dynamic exchange reactions and thus autonomously repair cracks and starches at lower temperatures as well as exhibit reprocessability. Furthermore, the developed networks were evaluated for TENG performances to better understand the design principles of self-healable TENGs
Friction and Wear Behavior of Thermally Sprayed Oxide Coatings
Get PDFConventional alloys and composites are widely used as coating materials in various contacting interfaces within gas turbine engines. These alloys form in-situ lubricious oxides during sliding at high temperatures, which help to reduce friction and wear. However, the formation of an oxide film on the contact zones requires time and depends on the chemical nature of the materials as well as the contact conditions and environment. In most cases, the running-in period for traditional alloys or composites is relatively long, which ultimately causes an overall increase in wear. Since the lubricious oxide is responsible for low wear and steady-state friction coefficient at high temperatures, it could be beneficial to replace the conventional alloys/composites and use such oxides instead. Based on prior work, ionic potential, and interaction parameters, which emphasis the lubricity at high temperatures, examples of such oxides include CuO, Ta2O5, CoO, NiO, Co-Ni-O.
In this dissertation, CuO, Ta2O5, CoO, NiO, Co-Ni-O oxides were sprayed to produce thick coatings with dense, homogeneous microstructures using Suspension Plasma Spray (SPS) and High Velocity Oxygen Fuel (HVOF). The effects of spray parameters on the composition and microstructure of the coatings were investigated. The CuO and NiO coatings produced by SPS partially reduced to Cu2O, Cu and Ni, respectively. On the other hand, CoO, Ta2O5, and Co-Ni-O coatings remained single phase.
The thermally sprayed coatings were tested on a ball vs flat tribometer with dry sliding reciprocating condition at various temperatures (i.e., 25°C, and 450°C) against an alumina counterface. CuO and CoO were found to have low coefficients of friction at high temperatures compared to other oxides (i.e., Ta2O5, NiO, Co-Ni-O). On the other hand, CoO and Co0.75Ni0.25O were found to be superior in terms of wear resistance at high temperatures.
Scanning electron microscopy (SEM), electron channeling contrast imaging (ECCI), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman analysis, and focused ion beam (FIB) were used to characterize the coatings and the corresponding wear tracks to determine the dominant wear mechanisms. In general, brittle fracture, cracking, and tribofilm delamination were found to be the main wear mechanisms leading to high wear of the oxides at room temperature. In contrast, the formation of a relatively ductile, smeared tribofilm, grain refinement, and amorphous layer closer to the wear track surface contributed to friction and wear reduction at high temperatures.
In addition, a low interaction parameter of the oxides, regardless of the microstructure of the oxide coatings, led to the low friction. Such a correlation was not observed with the high interaction parameter and ionic potential. Furthermore, the high sintering ability or diffusion coefficient of the oxides could play a role in reducing friction and wear at high temperature
Praxis Abraxas: How Tradition, Canonical Reading, and Craft Shape the Poetics of Translation
Get PDFExamining methodologies of translating poetry developed from an interdisciplinary approach, namely a combination of research creation (Creative Writing, MA 2015), history, theory (Dept of English), and Translation Studies, in combination with insights gained from over a decade as a Greek Orthodox nun in monasteries in Greece, Jerusalem, Russia and South Korea, as well as my experience translating poetry and liturgical works from modern and Hellenistic Greek (Cambridge Theological Federation, UK, 2001), this thesis presents techniques and identifies specialized forms of knowledge and craft that address the very specific task of translating poetry
well. After a discussion of the tradition and importance of translation in developing one's own poetic praxis, I offer a timeline of English translation of Greek drama and its expansion to include an impressive array of women now leading the field. A detailed chapter on Sacred Poetics, the translation of sacred texts from Greek to English, and the challenges and solutions
offered by the Anglican tradition, is followed by an analysis of Seamus Heaney's contribution to the translation of poetry and Greek drama, and the effects this had on real-world politics, as well as his own development as a poet. Finally, I offer my own translation and an exegesis of my methods using a section from a modern Greek translation of Aeschylus' Seven Against Thebes. I conclude with a summary integrating the five chapters, to demonstrate an understanding of the spectrum of skills and knowledge required for the successful translation of poetry, and the criteria connected with a poetics of translation in terms of what the future of both poetry and
translation can be if it is adopted, as once was standard, as a poetic praxis for poets today
Prevalence of musculoskeletal disorders and postural analysis of beekeepers
Get PDFWork-related musculoskeletal disorders (WRMSDs) lead to fatigue and decreased productivity in workers, resulting in the need for many affected individuals to seek medical treatment annually. Beekeepers, like other agricultural workers, are susceptible to WRMSDs due to the continuous demands of their work and the repetitive movements involved. Thus, the objective of this study is to determine the prevalence of WRMSDs and assess the level of risk associated with different postures among beekeepers to improve their musculoskeletal health. To achieve this, a cross-sectional study was conducted involving 33 beekeepers, consisting of two stages. Firstly, the Nordic Questionnaire was utilized to assess the prevalence of WRMSDs. Subsequently, the Ovako Working Posture Analysis System (OWAS) was employed to analyze and categorize the riskiest postures into four levels of corrective measures. The findings indicate that the most commonly affected areas were the back (51.5%) and waist (45.4%). The occurrence of WRMSDs in various body regions was significantly associated with the beekeepers’ years of experience and weekly working hours. Additionally, the prevalence of neck and back pain was significantly related to their body mass index (BMI). The OWAS postural analysis revealed that the back (36.75%) and arm (21.08%) regions required corrective measures as soon as possible (level III), while the back (26.47%) and legs (14.70%) fell under the category of corrective measures needed in the near future (level II). Combining the postural analysis results, 28.43% were classified as Action Levels (AL) II, 37.73% as level III, and 0.98% as level IV. This study demonstrates that WRMSDs are relatively common among beekeepers, primarily due to their extensive work experience and the adoption of awkward postures during their tasks. As a result, recommendations regarding ergonomics and physiotherapy are provided to alleviate pain and reduce the strain on critical posture
A Passionate, Virginal Chapel, Moving Us to Kneel: Marian Iconography and Lesbian Desire in Select Works by Romaine Brooks and Renée Vivien, 1900-1915
Get PDFThis thesis examines a select group of works by the poet Renée Vivien (née Pauline Tarn, 1877-1909) and the painter Romaine Brooks (1874-1970) created between the years 1900 and 1915. Catholic iconography, and in particular Madonna figures, reoccur in both of their works from this period. While their work is part of a longer lineage of Decadent artists using Catholic iconography, and indeed, the influence of the Decadent movement is seen in both women’s work, in this thesis I argue that their use of Marian iconography enabled Brooks and Vivien to confront heternoromative, patriarchal ideals and express lesbian desire, and to work through their complex relationships to their mothers. Using a queer Freudian psychoanalytic lens, drawn especially from Teresa de Lauretis’ positive reading of Sigmund Freud’s theories on perversion, I suggest that Vivien and Brooks’ mothers inscribed a narcissistic wound on their daughters which continued to affect their adult relationships with women, and this is expressed through the works I discuss. However, these are also works which explicitly depict lesbian desire, and their use of Marian iconography is linked with both of these ideas. The complex nature of these works therefore reflects how Brooks and Vivien were using their work to address issues within their own psyche, while simultaneously they are an attempt to envision a society in which lesbian desire was not only accepted, but celebrated
Determinants of Survival and Success among Nascent Entrepreneurs: A Cohort Analysis
Get PDFThis paper explores determining factors of startups’ survival rate and subsequent factors that play a role in the growth of those start-ups into established firms. We use data from the Panel Study of Entrepreneurial Dynamics (PSED) of five cohorts of 3,910 nascent ventures across four countries; the United States, Australia, Sweden, and China. Our results indicate that (1) survival within the first year seems mainly determined by select procedural activities such as employee recruitment and initiation of financial projections, as well as the age of the team leader and cohort of the firm; (2) gender, education, and growth preference of the firms’ leader appear as the biggest predictors of performance after five years; and (3), a positive innovation-performance relationship through R&D prioritization, patenting, and product novelty may exist
Minimizing Energy Consumption in Data Centers Using Embedded Sensors and Machine Learning
Get PDFCloud Data Centers (DCs) consume extensive amounts of energy, making a significant
contribution to environmental concerns. Moreover, with the emergence of 5G and future
B5G networks, which are increasingly inclined towards software orientation and reliant
on cloud computing, there is an urgent requirement for optimizing the energy consumption
of DCs. We address this issue by proposing an energy-aware Virtual Machine (VM)
placement solution for energy minimization.
In the first part of this study, we propose a highly accurate model for predicting the
dynamic power consumption of cloud computing devices. Our proposal takes advantage
of the various sensors that are now embedded in physical machines, or more generally in
cloud server machines, as well as Performance Monitoring Counters (PMCs) to implement
a highly accurate Machine Learning (ML) power prediction model. The core part of this
study then integrates the novel feature space of real-time sensors’ measurements and the
predictive power model to propose a scalable placement algorithm, enabling proactive and
energy-aware Virtual Machine placements. In addition, it utilizes a new set of temperature-related
features that enables proactive hotspot avoidance.
Our ML predictive models, as well as our proposed placement algorithm, were extensively
evaluated on a cluster of real physical machines and demonstrated a significantly
higher performance as compared to the implemented reference models and algorithms, reducing
energy consumption by up to 7%, CPU temperature by 2%, and overloading by 28%
A Non-Uniform Cellular Automata Approach for the Design Optimization of Truss Structures
Get PDFCellular automata (CA) paradigm has been successfully applied to solve the topology and sizing optimization problems of truss structures and continuum bodies. In a conventional uniform Cellular Automata (CA) model, a unit cell's behavior is updated based on information from its eight immediate neighboring nodes (in 2D configuration). However, this neighborhood system may not always be suitable for representing real truss structures. To address this limitation, a non-uniform CA approach has been proposed in this research study for the optimization of truss structures.
The proposed non-uniform CA approach is based on non-identical cells, each of which is defined by a center node and members connecting the center node of the cell to all other nodes in its immediate neighborhood. This differs from the Moore neighborhood concept used in the conventional uniform CA approach, which only considers the eight immediate neighboring nodes. It has been shown that the proposed non-uniform CA approach provides a more realistic representation of truss structures and improves the optimization process.
Moreover, conventional CAs rely on a fixed grid, thus with respect to design optimization of discrete structures, they can only be used for sizing and topology of the structure while the layout optimization cannot be conducted as the coordinates of the nodes remain unchanged throughout the optimization process. In this research study, a novel non-uniform CA design optimization algorithm has been formulated to solve the general problem of topology, sizing and layout optimization of truss structures subject to both stress and displacement constraints. Several benchmark case studies have been provided to demonstrate the efficiency and accuracy of the proposed design optimization methodology
Environmentally-induced circadian disruption and alcohol consumption: shared and distinct effects in female rats
Get PDFThe disruption of daily rhythms in physiology is a widespread concern in modern society and affects individuals across the entire population. Repeated rhythm disruption has detrimental effects on health and is known to be a risk factor for the development of mental conditions, including alcohol abuse and mood disorders. This results in an intricate clinical picture, as affective disorders are often comorbid with pathological alcohol consumption. Furthermore, affective behavior may also induce alcohol consumption or relapse, and both factors can affect daily rhythms in physiology, which may exacerbate the conditions ultimately. While there is accumulating evidence on the negative consequences of circadian disruption in males, knowledge in females is limited. This project aims to bridge this gap by investigating the association between circadian desynchronization and alcohol consumption, focusing on behavior and physiology in female rats.
To model environmentally-induced circadian disruption, we exposed female rats to either a short-day light cycle or repeated shifts of the light/dark cycle and investigated alcohol drinking behavior, mood-related behavioral changes, and physiology to study the effect of chronodisruption. Moreover, we analyzed changes in gene expression in brain regions associated with the reward system following circadian disruption and alcohol consumption to understand the underlying mechanism of displayed behaviors.
The results demonstrate that exposure to aberrant light conditions disrupts the circadian system and impairs physiological processes such as the estrous cycle. Strikingly, the sole effects of the light conditions on mood-related behavior and alcohol consumption were minor, despite changes in gene expression in the brain regions related to reward processing. However, chronodisrupted females displayed changes in mood-related behavior under alcohol abstinence, indicating that the combined impact of circadian desynchrony and stressors like abstinence are risk factors in the development of mental conditions, that may affect drinking behavior or relapse subsequently.
The outcomes of this thesis expand our understanding of the effects of chronodisruption in females and establish a foundation to further explore the complex relationship between circadian disruption, alcohol consumption, and their effects on mental health. This knowledge can guide future studies and interventions targeting mood disorders and alcohol misuse in females, especially in the context of shiftwork
Analysis and Topology Optimization of Adaptive Sandwich Plates treated with Magnetorheological Elastomer core layer
Get PDFStructural vibration control is a promising method for mitigating the detrimental effects of excessive vibration in structures. It involves monitoring the dynamic behavior of a structure and implementing control strategies to reduce the vibration levels of the structure. Among various control methodologies, the semi-active control method adeptly combines the reliability characteristic of passive systems with the adaptability inherent in fully active systems, without requiring complex control hardware. Smart materials play a crucial role in implementing semi-active vibration control, and among them, magnetorheological (MR) materials have garnered substantial attention for their remarkable properties, including rapid response times and low energy consumption. Compared with MR fluids (MRFs) which can only provide variable damping, Magnetorheological elastomers (MREs) have field dependent viscoelastic properties in which both stiffness and damping properties can be effectively altered using the applied magnetic field. By incorporating MREs into the core of sandwich plates, it becomes possible to modify the continuous plate's vibration characteristics on-demand through application of an external magnetic field. Although employing complete coverage of the MRE core layer within a sandwich plate is likely to yield the best results in reducing vibration levels, it is essential to consider practical factors like mass limitations. Therefore, optimizing the topology of the MRE layer with a constrained volume fraction is of practical importance. The goal of the topology optimization process is to attain the desired vibration control performance while concurrently minimizing the mass or volume of the MRE layer. This enables the efficient utilization of MRE-based vibration control systems in real-world applications, where optimizing resources is crucial.
To achieve this end, first a finite element model has been formulated to evaluate the vibration behavior of MRE-based sandwich plate under dynamic loading. The plate is discretized with rectangular elements, each having 28 degrees of freedom and 4 nodes, enabling accurate estimation of the MRE-based sandwich plate's vibration characteristics.
An optimization problem based on the method of moving asymptotes (MMA), is subsequently formulated to identify the optimal topology of the MRE layer within the sandwich plate to minimize dynamic compliance yielding reduction in vibration amplitude. For material properties interpolation, an MRE-based penalization (MREP) model, based on solid isotropic material with penalization (SIMP) method, has been developed. To validate the accuracy of the proposed methodology, several numerical examples considering MRE-based sandwich plates under different loading and boundary conditions are provided. These examples illustrate the effectiveness of the proposed design optimization methodology for topology optimization of MRE-based sandwich panels to mitigate the vibration