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Novel Auxiliary RISE (ARISE) Robust Control Approaches for Nonsmooth or Switched Nonlinear Systems
No full textTo deal with uncertainties in a dynamic system, many nonlinear control approaches have
been considered. Unique challenges arise from uncertainties that are bounded by constants,
which led to the development of both continuous and discontinuous control methods. One
such approach that yields a favorable transient performance is sliding mode (SM) control.
However, SM control requires rapid switching within the control input due to a discontinuous
signum function in the control architecture, which introduces chattering during real-world
application. To address the limitations of SM control while still exploiting its advantages
and robustness, a class of continuous robust controllers named Robust Integral of the Sign
of the Error (RISE) was developed. RISE controllers include an integral of the signum
function, not a signum function, in the control law. Filtering the signum function with an
integral makes the signum function continuous and thereby mitigates chatter that would
result from a discontinuous SM term. Even though RISE controllers exhibit a significant
level of robustness, it is limited to classes of smooth nonlinear dynamic models.
In the first part of this thesis, a novel auxiliary RISE (ARISE) controller is proposed
to prevent chattering and deal with uncertainties (even those bounded by constants) for
general, switched, and nonsmooth control-affine nonlinear systems. The ARISE control
system includes a unique auxiliary error that is designed to inject a discontinuous SM term
directly into the error system without including a SM term in the controller itself akin to the
RISE control architecture. Consequently, the ARISE control law minimizes the chattering
effect that results from discontinuous SM terms. The proposed ARISE control system is
augmented with an adaptive update law to deal with the unknown control effectiveness
matrix in the dynamic model. To prove the effectiveness of the ARISE controller, a nonlinear
stability analysis was conducted and resulted in semi-global exponential tracking towards an
ultimate bound. Furthermore, the performance of the proposed controller was evaluated and
compared against a traditional SM controller through simulations using a switched Van der
Pol oscillator model. The simulations were conducted in Matlab/Simulink, and the results
of the comparisons are shown in various graphs. It is concluded that the proposed ARISE
controller performs better for a switched system than the SM controller. The improved
performance of the ARISE controller was consistent across different dynamic parameters
and disturbances.
In the second part of this thesis, the ARISE controller is modified to account for the
physical limitations of actuators. Specifically, to enhance the applicability of the ARISE
control approach, a saturated hyperbolic tangent function is incorporated into the control
input to allow the controller to be bounded a priori, which will account for the limitations
of physical actuators during real-world applications. A nonsmooth Lyapunov-like stability
analysis is performed for the proposed saturated ARISE control system to prove that the
closed-loop error system is uniformly ultimately bounded for a switched dynamic model.
A series of numerical simulations were performed to compare the performance of the saturated ARISE controller with a standard saturated SM controller across different dynamic parameters and disturbances
Surviving the Storm: Labor Market Resilience in Small Businesses During the Pandemic
No full textThis dissertation highlights the importance of social distancing policies and targeted financial interventions, such as the Paycheck Protection Program (PPP), in influencing labor market outcomes and business survival during economic shocks. During the COVID-19 pandemic, policymakers implemented social distancing policies to limit the spread of the virus. These health policies significantly affect labor market outcomes, especially for small businesses. We start by exploring the direct (emergency implementation) and indirect (business closure policy) impacts of health policies on small business operations. Next, we examine how political partisanship affects health and labor market outcomes. Additionally, we show the effectiveness of the PPP that was implemented to help mitigate the adverse effects of the pandemic on small businesses by preventing job loss, supporting existing businesses, and encouraging new business formation. Using a unique dataset of hourly employee information for over one million U.S. small businesses and loan-level microdata for all PPP loans, our analysis shows the resilience of small businesses during the pandemic. The results indicate that small businesses faced severe impacts from employment contractions and closures at the beginning of the pandemic. Social distancing policies have reduced the number of employees, weekly hours worked, and weekly wages. Prolonged social distancing led to fewer workers engaging in voluntary stay-at-home behavior. Interestingly, our findings highlight that Republican-leaning counties show no difference in compliance based on the state governor’s political affiliation. The results suggest that the average level of political mismatch affects outcomes, and how blue or red a county is does not matter. PPP was implemented to boost employment and safeguard small businesses from exiting the market. Using a dynamic difference–in–difference (DDID) event study methodology, we estimate the impact of PPP on employment, wages, and the operational status of establishments and firms. The findings reveal that PPP have a significant and positive impact on employment, wages, and operational status. The results underscore the immediate and long-lasting benefits of PPP, including positive spillover effects on local business activities and new business formation. The results underscore the necessity for public policies to increase employment, protect small businesses, and promote resilience and economic growth
Experiencing a Safe Classroom: A Critical Phenomenological Study of Graduate Teaching Assistants in Counselor Education who Teach Diversity and Social Justice Courses
Get PDFThe classroom is a gathering of individuals with diverse backgrounds and perspectives. When course content focuses on diversity and social justice content, discussions can invite dialogue with the potential to damage perceptions of psychological safety in the classroom. As Counselor Education programs continue to emphasize diversity, equity, and inclusion educators must navigate critical dialogue and ensure classroom safety. This research sought to understand the experiences of GTAs (graduate teaching assistants) in Counselor Education who created safe classroom environments while teaching content focused on diversity and social justice. Using a critical phenomenological framework of qualitative inquiry, the research found that GTAs felt confident to create safe classrooms when they received sufficient training and support for teaching diversity and social justice content. When GTAs felt confident to create safe classrooms they acted as involved instructors that practiced self-awareness, maintained boundaries around classroom discussions, and navigated nuanced moments of conflict. GTAs reported using self-disclosure of personal experiences as a tool for creating feelings of classroom safety and using classroom discussions as a measurement for cohesion and learning. Special attention should be paid to support GTAs who hold marginalized identities and who may experience microaggressions while teaching. Findings from this research may be used to inform how doctoral students and GTAs in Counselor Education are trained to educate counselors-in-training on diversity and social justice content
A Programmatic Evaluation of Four-Year Equine Degree Programs in the United States
Get PDFThe equine industry is a vast and growing segment of the United States economy that is supported by equine educational programs at the post-secondary level. The purpose of this study is to provide a programmatic evaluation of the four-year equine degree programs currently in operation. The potential for this study to inform and influence existing and emerging programs with their curricula and resource offerings could improve both the sustainability and relevance of equine programs nationwide. The quantitative data for this study was collected through the use of an online survey instrument. The instrument was sent to a department head or senior faculty member for each of the 77 institutions identified as offering a four-year equine degree program option. The data collected included the program type and objectives, curricular offerings, supporting resources, graduation rates, and characteristics of both the student and faculty populations. The findings indicate that the main objectives of a four-year equine degree program, regardless of type, should be to produce students with foundational knowledge in equine health, care, and handling, who are knowledgeable about what is currently happening in the equine industry, with the personal and professional skills needed for employment beyond academia, and who have a mindset for continued learning and education. To do this, equine programs need to offer students the time to put their theoretical knowledge into practice with hands on activities. Twenty course topics were evaluated for student success upon graduation, the two highest ranked courses were equine care and management and communications and the two lowest ranked courses for success were general reproduction and genetics. Overall, participating institutions believed that an equine industry internship was the most valuable experience a student could participate in, and that the most needed resources were horses and industry specific teaching professionals. Graduation rates were similar across programs and career paths varied only slightly in terms of primary equine employment or employment in the animal science or agricultural industries outside of equine specific occupations. The information found will inform stakeholders of the key curricula and resource needs of successful post-secondary institutions and serve as a foundation for future studies involving equine educational degree programs
Exploring the Impacts of Training, Exercise, and Obesity on Cognition in Companion Dogs
No full textExecutive functions, like working memory, attention, inhibitory control, and cognitive flexibility, are cognitive abilities that allow dogs to regulate their behavior and are important for the ability of companion dogs to successfully live as a companion to humans. Research into
factors that impact executive functioning and cognitive abilities in dogs is important for understanding how best to curate the life experiences and health of dogs to optimize their executive function abilities, and may lead to understanding of preventative measures for cognitive dysfunction in old age. In this study, pet dogs over one year of age were recruited to participate in a cognitive test battery designed to assess executive function and the potential impacts of aging, training, exercise, and obesity/body condition were explored. These tasks included the Spatial Working Memory Task, the Detour Reversal Task (also called the A-not-B Barrier Task), the Eye Gaze Task, and the Cylinder Task. We found that age negatively impacted performance across all the utilized tasks. Training positively influenced performance in the
Detour Reversal Task and the Cylinder Task, but not the Memory or Eye Gaze tasks. Interaction effects between age and training in some of the tasks suggested that training may be protective against cognitive decline. Higher exercise and fitness was associated with better performance in the Detour Reversal and Cylinder tasks. We also found interaction effects between age and training in those as well as the Memory task that suggested that exercise may be protective against cognitive decline. We found mixed results of body condition/obesity, with obesity being associated with worse task performance in the Cylinder Task but better performance in the Eye
Gaze Task. There were also sex-specific differences that highlight the need for a nuanced approach when looking at executive function in dogs. The findings in this study provide a basis for some under-studied but important factors that may impact canine cognitive health
Physiological and Molecular Responses to Environmental Stressors in Emerging Eco-molecular Models
No full textThe perception of stress and the stress responses of animals are complex. My dissertation examines stress response in the context of different environmental stressors. Ecosystems host a multitude of stressors that impact the organisms inhabiting them. It is understood that different environmental stressors can elicit varied effects on these organisms. This raises the question: To what degree is the stress response uniform, or is the stress response specifically adapted to each type of stressor? Research on vertebrates shows that in response to many different stressful situations, levels of corticosterone/cortisol produced by the endocrine system will rise in a similar manner. However, stress responses are multifaceted, involving numerous biological levels, with the endocrine system being just one component. My dissertation aims to characterize sources of variation in stress response using diverse approaches in both vertebrate and invertebrate organisms.
I utilize the Eastern fence lizard, Sceloporus undulatus, in my second and third chapters. The fence lizard is an emerging ecological model organism used to understand the molecular and physiological mechanisms of stress response and how ectotherms respond to their environments through climate change or invasive species. In the second chapter, I aim to investigate the relative effects of acute heat exposure and inadvertent stress from experimental procedures on female fence lizards using two experiments. In the first experiment, lizards were exposed to a temperature of 42.5°C for up to 1.5 hours, followed by a 1-hour recovery period without heat exposure. We predicted that increased exposure duration at high temperatures would elevate corticosterone (CORT) levels, which would then decrease during the recovery period.Contrary to our predictions, CORT levels remained elevated and showed significant variation between individuals. To further understand these results, I conducted a secondary experiment testing the hypothesis that stress from general experimental procedures, such as handling, in part explains the CORT response. In this experiment, lizards were exposed to a control temperature of 30°C or a heat stress temperature of 43°C, with exposure times set to either 60 minutes or 90 minutes. The results indicated that control temperatures alone raised CORT levels above baseline, suggesting that the experimental procedure itself induced a measurable stress response. I identified heat shock protein gene expression as a specific biomarker for heat stress, noting an elevation in heat shock protein 70 (HSP70) levels, suggesting the presence of heat stress in the animals. These data support the concept that while CORT may serve as a general indicator of stress, future research should focus on more precise biomarkers tailored to the specific stressors being investigated in experiments to understand if their treatments have an effect.
The findings and experimental approach from chapter two lay the groundwork for my third chapter, whose aim was to identify shared and unique responses to two ecologically relevant stressors—acute heat and fire ant envenomation—in male fence lizards. At the endocrine level, both stressors showed a shared response of elevated CORT. At the liver transcriptome level, I found a very robust response to heat stress, having many differentially expressed genes, such as heat shock proteins. However, the response was relatively mild in the fire ant group compared to the control, supporting the idea of unique responses. Several commonly expressed genes associated with the upregulation of CORT were identified in both treatment groups, including NR4A1, FOS, and DUSP1. These genes were further validated through their significant correlation with the CORT-linked module identified via weighted gene correlation network analysis (WGCNA). At the pathway level, stress-induced cellular pathways like the P53 pathway and Tumor Necrosis Factor Alpha (TNFA) signaling were shared across both treatment groups. Interestingly, the fire ant treatment downregulated pathways related to immune responses, such as the complement system. Meanwhile, glycolysis—a process for the metabolic breakdown of glucose to produce energy—was upregulated in the heat treatment group. Glucocorticoid receptor motifs were identified in promoter regions of differentially expressed genes and regions of the genome that became accessible due to heat stress. To investigate the heat stress response further, ATAC-seq was used for differential peak analysis to identify genome regions accessible for transcription. We overlapped the glucocorticoid response element (GRE) sites, differentially expressed genes, and differentially accessible regions. This analysis suggests that in response to heat stress, epigenetic modifications facilitate genome accessibility, enabling the glucocorticoid receptor (GR) to bind to the GRE and modulate the transcription of adjacent genes by either upregulating or downregulating their expression. These methodologies examine the transcriptomic and epigenetic responses to these two independent natural stressors and support the idea that stress responds at multiple biological levels and at the genomic level these responses can be largely unique.
In the fourth chapter, we shift our focus from examining how animals respond to stressors to exploring the interactions between genotype and environments and the divergence in stress responses among animals with different genetic backgrounds. Daphnia is a well-known model organism in ecology and eco-toxicology, predominantly found in freshwater habitats such as lakes and ponds, and they can survive extreme environments like acidic swamps. Due to its phenotypic plasticity, this organism is extensively utilized to study both natural and anthropogenic environmental stressors. The diverse phenotypes exhibited by Daphnia are strongly influenced by their environment, making it an ideal model for addressing evolutionary genomic questions. Strains of Daphnia pulicaria show varying levels of tolerance to the toxic cyanobacterium Microcystis aeruginosa, which is known for producing hepatotoxins called microcystins. D. pulicaria strains from nutrient-rich lakes have greater tolerance to M. aeruginosa compared to their counterparts from nutrient-poor lakes, which are more susceptible to microcystins. This chapter aimed to assess the effect of microcystins on lifespan and reproduction across different strains of D. pulicaria. I hypothesized that the toxin-produced by M. aeruginosa will reduce the lifespan and reproductive rates of D. pulicaria strains. I predicted tolerant strains would exhibit better survival and reproductive outcomes than susceptible strains. I conducted two replicate experiments where I tested four strains of D. pulicaria, two characterized as tolerant and two as susceptible, exposing them to either a strain of M. aeruginosa that was previously reported to produce the microcystin or a strain for which the microcystin gene was knocked out and could not produce the microcystin, measuring survival, time to reproduction, and lifetime fitness. While the M. aeruginosa microcystin treatment demonstrated the predicted results, interestingly, we observed a significant decrease in life-history traits for all D. pulicaria strains when exposed to the M. aeruginosa that could NOT produce the microcystin. I conclude there may be a molecular component other than general microcystins (toxins) produced by the M. aeruginosa that led to significant mortality in D. pulicaria strains. Future directions of this project will involve investigating the genetic components of both M. aeruginosa genomes to identify potential drivers responsible for the observed decline in fitness within “nontoxic” Microcystis strains.
My dissertation investigated stress in a vertebrate model by comparing different types of stressors and in an invertebrate model by examining evolved differences in stress responses across genotypes. Exploring stress responses at multiple biological levels provides a deeper understanding of stress and how organisms interact with their complex environments
A Feminist-Informed Autoethnographic Study Troubling My Motivations for Peer Leadership in Higher Education
No full textThe purpose of this study was to trouble my own motivations for serving as a peer leader while in college. As a unit director for a student support office at a large, land-grant institution of higher education, I have worked over 15 years in the field of higher education alongside peer leaders as a graduate assistant, a program coordinator, and unit director. More so, I served as a first-year seminar peer leader and resident mentor (routinely called resident assistant) while an undergraduate student in college. I engaged in an autoethnographic study and applied emotional recall, journaling, timelining and kinship mapping to meet the needs of the study. As a critically-informed study, I applied feminism as an epistemological stance and incorporated Crenshaw’s (1988) concept of perspectivelessness to serve as a conceptual lens. Through a series of vignettes and found poetry, findings problematize the role of trauma, my socialization from childhood and into college, and my motivations for peer leadership as a vehicle for safety and as a way to feel valuable while in college. Implications of this study include 1) helping practitioners trouble the varying motivations for students serving as peer leaders, 2) building nuanced and power-informed understandings of the systems and structures that inform peer leaders’ experiences while in college, and 3) challenging practitioners’ own assumptions and beliefs associated with peer peers and peer leadership programs
Reliability of the Distal Upper Extremity Tool (Duet)
No full textMusculoskeletal disorders (MSDs) are medical conditions affecting muscles, tendons, vertebrae, and nerves. These disorders, particularly those affecting the upper extremities, are a significant concern for industries due to their prevalence and the high costs associated with treating them. Several ergonomic exposure assessment tools are available for assessing occupational exposure to physical risk factors associated with upper extremity MSDs. A promising observational risk assessment tool that applies material fatigue failure theory to address MSDs of the distal upper extremity is the Distal Upper Extremity Tool (DUET).
For occupational safety and health practitioners to use an exposure assessment tool most effectively, it must be reliable. Although DUET’s cumulative damage measure showed strong associations with upper extremity outcomes using data collected in a cross-sectional epidemiological study, the tool’s reliability has not been assessed. The objectives of this dissertation were to 1) complete a thorough reliability analysis of DUET; 2) investigate the tool’s usability and identify potential improvements to improve rater reliability; and 3) introduce a mobile application version of DUET and evaluate its usability.
Results indicated that the web-based version of DUET suffers from usability weaknesses, leading to poor inter- and intra-rater reliability among both expert and novice users. Consequently, a mobile application was developed to address these weaknesses. While the mobile application showed improved performance over the web-based version, the improvements were modest. The primary finding of this dissertation is that DUET has poor reliability, requiring additional development and evaluation. Practical implications and recommendations for future work are discussed
The Principalship through the eyes of Former Assistant Principals
Get PDFThe assistant principalship is meant to be a steppingstone for aspiring principals. The experience in the assistant principalship should prepare them to be effective principals. However, there is little to no research from sitting principals to assert this claim. The purpose of this study was to examine the assistant principalship through the perspective of sitting principals. The study is a multiple cross-case analysis of four former assistant principals that are within their first three years of the principalship. The central question for this study was “what is their perception of their preparation through their former positions as assistant principals? “
I examined each case study using Clandenin and Connelly’s (2000) three dimensions of narrative inquiry – continuity, interaction, and situation. According to the researchers, the lived experience of each participant will reveal significant events to the participants. Each of these events shape how the participants perceive their daily lives and their experiences. The results from the study revealed that each sitting principal was prepared for the principalship through their experience in the assistant principalship. Some of the main themes revealed importance of mentoring, experiential learning, relationships, and students. The findings of this study are significant to further principal preparation with implications for sitting principals and current assistant principals
Effects of a Heated Environment and Exercise on Firefighter Response Time and Gait: An Exploratory Analysis
No full textFirefighters are often required to work in high-temperature environments, which can lead to an elevated core temperature. Prolonged exposure to heat can have significant physiological impacts, potentially affecting both cognitive and physical performance. While previous research has examined the effects of heat on general occupational tasks, there is limited information on how these conditions specifically affect firefighters' response times and gait characteristics, such as step length, swing time, stance time, double support time, and velocity. Understanding these impacts is crucial for improving safety and performance in firefighting operations. This study aims to explore the effects of an elevated core temperature on response time and gait parameters in firefighters.
A repeated measures randomized design was implemented for this study to evaluate the effects that an increased core temperature may have on response time and gait in firefighters. The independent variable for this study was time with two levels (pre-heat exposure, and post-heat exposure). The dependent variables were response time which was assessed using a Go/No-Go task administered via a laptop, and gait (step length, swing time, stance time, velocity, and double support time) which was analyzed via a GAITRite walkway. Participants completed all of the required tasks while wearing their full personal protective equipment (hood, helmet, gloves, jacket, pants, and boots). Additionally, participants completed the exercise protocol in an environmental chamber set to 110 ℉ and 50% relative humidity. Statistical analyses were performed using R Studios version 3.6.0 (R Studio Team, Boston, MA, USA). A paired samples t-test was used to assess changes in gait and response time as a result of prolonged exposure to a heated environment. An a priori alpha level of 0.05 was used to determine statistical significance of the results.
15 Firefighters from the East Alabama area were recruited to participate in this research study. Results from the paired samples t-test indicated no significant change in response time between pre-heat exposure and post-heat exposure (t (14) =.2242, p= 0.8258, mean difference = 5.48 ms). Additionally, results from the paired samples t-test for the gait variables indicated no significant change between pre-heat and post-heat exposure (step length: left foot, t(14)=1.0216, p=0.3243, mean difference = 2.26 cm; right foot: t(14)=1.4094, p=0.1805, mean difference = 2.33 cm; swing time: left foot, t(14)= -0.471, p=0.6446, mean difference = -0.012 seconds; right foot: t(14)=1.0852, p=0.2961, mean difference seconds = 0.011; stance time: left foot, t(14)=-0.36779, p=0.7185, mean difference = -0.007 seconds; right foot: t(14)=-0.3246, p=0.7503, mean difference =-0.0054 seconds; double-support time: left foot, t(14)= -1.6731, p=0.1165, mean difference = -0.0492 seconds; right foot: t(14)= -1.325, p= 0.2064, mean difference = -0.0294 seconds; velocity: t(14)= 0.62386, p=0.5428, mean difference = 2.42 m/s).
The results from this research study are exploratory and not confirmatory in nature. Due to the small sample size for this study, no conclusive statements can be made regarding the effect of a heated environment on response time and gait in firefighters. Further research studies should be conducted to continue to analyze how a heated environment impacts firefighter occupational performance