ScholarWorks@UMassAmherst
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Recent Submissions
Publication CASCADING CONSERVATION: ASSESSING THE REPEATED SPAWNING MIGRATIONS AND FRESHWATER MUSSEL HOST POTENTIAL OF BLUEBACK HERRING (ALOSA AESTIVALIS)(2025-02)Anadromous blueback herring (Alosa aestivalis) interact with numerous species during their spawning migrations between marine and freshwater systems. As such, the drastic declines in blueback herring populations and altered population dynamics over the last centuries may be affecting not only the stability of blueback herring, but also the species they interact with, including freshwater mussels. Effectively evaluating the impacts of blueback herring population changes on freshwater mussels requires unbiased demographic assessments of blueback herring data, such as age and number of spawning events, and a robust understanding of blueback herring as hosts for mussels. To assess the quality of spawning mark data, I examined the precision and bias between paired spawning estimates of 8,698 blueback herring collected by the U.S. Fish and Wildlife Service (USFWS) over the last decade. Systematic bias was found in 70% of years, and 30% showed coefficient of variation (CV) values >10% indicating imprecision. Bias was absent and precision was highest in most recent years where new training requirements and reference collections were used. These findings support future spawning estimation improvements through standardized precision thresholds and uniform training. To explore freshwater mussel use of blueback herring as hosts within the Connecticut River, the frontmost gills of 1,011 fish from the 2023 USFWS survey were examined for mussel glochidia (larvae). I observed 18,738 glochidia from four genera, including a species not known to inhabit the watershed (Utterbackia imbecillis), and a 64% infection prevalence (i.e. # of infected fish / # of total fish examined). Water temperature significantly affected the prevalence on blueback herring, with prevalence peaking at 14.2 ºC for alewife floater (Utterbackiana implicata) and 18.8 ºC for eastern elliptio (Elliptio complanata). For U. implicata, higher infection prevalence was related to higher densities of blueback herring, highlighting the linkage between these two species. Maximum infection intensities were predicted for smaller fish that were female and virgin spawners, which may be primarily explained by temporal patterns in migrating blueback herring and correspondence to glochidia release by mussels. These results highlight the value of understanding and monitoring organisms with unique, coupled life cycles toward developing effective, comprehensive conservation strategies.Publication Muscle Fatigue's Impact on Gait Mechanics and Neuromuscular Control in Individuals with Knee Osteoarthritis(2025-02)Fatigue, defined here as a lack of physical and/or mental energy, is a commonly-reported symptom of osteoarthritis (OA) that may limit physical capacity and contribute to disability. In healthy older adults, muscle fatigue (acute decrement in muscle power) has been proposed as a key contributor to symptoms of fatigue. Knee extensor muscle dysfunction, including lower isometric and isokinetic torques and altered muscle activation patterns, are common with knee osteoarthritis (KOA). Together these changes in neuromuscular function may increase locomotor muscle fatigue in KOA compared to age-matched controls, as a greater percentage of the muscle’s capacity must be used for daily activities such as walking. To date, evidence to explain whether and how muscle fatigue may alter control and coordination of movement in KOA is limited. Our working hypothesis was that KOA-related neuromuscular changes may exacerbate locomotor muscle fatigue (Aim 1) and alter the neuro-mechanical response to muscle fatigue during gait (Aim 2), thereby contributing to mobility declines. To assess and compare the mechanisms for loss of force with a prolonged walk in individuals with KOA we used high density EMG (Aim 3). We collected data on 2 groups of 19 participants (9 male, 10 female): KOA (65-80 years) and older healthy controls (70-80 years). We implemented a 30-minute treadmill walk (30MTW) to induce knee extensor muscle fatigue and quantified the response with measures of gait mechanics, electromyography, physical performance, and motor unit behavior. We found that knee extensor peak power during dynamic contractions is lower in individuals with KOA compared to older healthy, however, muscle fatigue in response to a 30MTW is not different between groups, and intramuscular fat negatively is associated with poorer mobility. We also found that individuals with KOA do not experience greater performance fatigability (6m walk test) than age and sex matched controls, but they do alter gait mechanics and muscle activation in response to a 30MTW. Finally, individuals with KOA do not have impaired force steadiness as compared to older healthy controls and that only the recruitment threshold is impacted by a 30MTW in individuals with or without KOA. The results of this study suggest that individuals with and without KOA experience measurable knee extensor fatigue in response to 30MTW and individuals with KOA adapt to this fatigue with a gait strategy aimed at maintaining joint stability and attenuating load on the knee joint.Publication Three Essays Pertaining to Organizing for Value Creation in Professional Service Firms(2025-02)Professional service firms (PSFs) including law firms, consulting firms, hospitals, and universities, have become an increasingly important fixture in the global economy. It is broadly accepted that due to their human capital intensity, knowledge intensity, and the professionalization of their workforce, such firms are imbued with several distinct management challenges that complicate organizing for value creation. In this dissertation, I develop three essays pertaining to organizing in PSFs. In essay one, I endeavor to make sense of the different ways in which client-based knowledge impacts PSF value creation and capture. Despite the consensus that client-based knowledge contributes to PSF performance and competitive advantage, the ubiquity of the concept has meant that there is little precision regarding what we are talking about in any given instance. Thus, I develop a taxonomy of different client-based knowledge types according to its explicitness and relative specificity. In essay two, I develop and test a model linking elements of a PSF’s structure to its ability to effectively create value via the acquisition and integration of strategically valuable knowledge. Specifically, I argue that as a PSF adopts a more generalist strategy, the cultivation and integration of client-based knowledge – relatively more idiosyncratic than problem-based knowledge – becomes more critical to PSF competitive advantage, necessitating the use of specific practices (lateral partner hiring, hiring for client overlap, a job rotation program, and a practice of mandating multiple client ties) to enhance firm growth. Finally, in essay three I develop an integrative review of what we know of how PSFs get the right resources to the right place at the right time to create value for clients. Specifically, I synthesize insights generated by coordination scholars, knowledge and human capital scholars, and strategic human capital scholars. The review reveals that each of these communities of practice follows a similar trajectory in their perspective, including elaborating the mechanisms that enable interdependent work and expounding on the relational dimension of organizing. It also reveals several shared assumptions and critical gaps that serve as the basis for a proposed agenda for future research on organizing for value creation in these firms.Publication LEARNING FROM THE PAST TO INFORM FUTURE ACTION: LEARNING CURVE INNOVATIONS(2025-02)We present the work in three essays in the manuscript. Each essay will include methodology and results. Our work will focus on renewable energy technologies and water recycling technologies. Estimating the future cost of technologies that play a significant role in the energy transition can help design robust and cost-effective policies to promote a carbon-neutral, sustainable economic system. These forecasts are important inputs to a number of analyses, including energy-economic models. For the first essay, we develop a hypothesis around the impact of a related technology on the development of an experience curve. We explore the implications of this hypothesis in the case of wind energy, which has been historically developed onshore and is currently experiencing rapid growth in deployment offshore. We look at the impact of modeling offshore wind as (1) a fully new technology, (2) a direct offshoot of onshore wind, and (3) a hybrid. Focusing on the levelized cost of electricity of offshore wind, we find that assumptions about its relatedness to onshore wind are equally important as assumptions about future growth scenarios. This research highlights a previously neglected factor in experience curve analysis, which may be especially important for technologies, such as offshore wind energy, that are expected to contribute significantly to climate change mitigation. For the second essay, we investigate in more detail data underlying learning curves. We disaggregate the error between projected technology costs and realized costs, to determine how much of the error comes from projecting cumulative experience and how much from projecting the amount of learning in response to cumulative experience. We apply this method to energy technologies, using actual observed data, projections based on authoritative reports, and expert forecasts. The disaggregation analyses can tell us how much of a surprise in cost is due to higher or lower than expected increases in cumulative experience in the form of installed capacity; or higher or lower than expected learning per unit capacity. Lastly, for the third essay, we investigate the choice of metrics used in learning curves. We apply this analysis to learning curves of water recycling technologies. This pilot study and analysis, which focuses on the impact of the metric choices in learning curves, will build knowledge for a larger study in the future. We systematically examine a range of studies to gain insights into the metrics utilized for experience and performance in assessing the learning rates of energy technologies. Existing literature broadly suggests that energy technologies that are more investment-reliant rather than process and labor reliant are better represented by cumulative capacity. We develop and focus on a case study for California; assemble a dataset of costs and capacities; and construct an experience curve of water recycling in wastewater treatment plants. We illustrate how metric choice impacts the shape and forecasts of the learning curves.Publication Investigating the Type 3 Secretion System Translocon in Pseudomonas aeruginosa: Establishing a Functional Assay for Translocon Assembly and Mapping the Topology of PopB(2025-02)The Type III Secretion System (T3SS) is a crucial virulence factor employed by Pseudomonas aeruginosa to inject effector proteins into the host cells. Despite its significance in pathogenesis, the assembly mechanism and structure of the T3SS translocon, formed by PopB and PopD proteins, remain poorly understood. This dissertation elucidates key aspects of T3SS translocon assembly and structure through innovative methodologies. A cell-based split luciferase complementation assay was developed to monitor T3SS translocon assembly. This assay, utilizing a P. aeruginosa PAK strain expressing NLuc10-PopD and HeLa cells stably expressing NLuc1-9, demonstrated robust performance with Z' factors of 0.67 and 0.23 in manual and automated formats, respectively. A pilot screen of 776 FDA-approved compounds validated the assay's efficacy in identifying potential inhibitors. To investigate the membrane topology of PopB, a novel dual-tagging strategy combining SpyCatcher-SpyTag labeling, and GSK-tag phosphorylation was employed. This approach revealed that both the N-terminal region and the region between two hydrophobic segments of PopB are exposed to the host cell cytosol, challenging previous models. Notably, PopB exhibited distinct conformations in functional versus non-functional translocons, highlighting its interdependence with PopD. These findings provide crucial insights into T3SS translocon structure and assembly, paving the way for novel therapeutic strategies against P. aeruginosa infections. The methodologies developed herein, particularly the dual-tagging approach for membrane protein topology studies, may find broad applicability in investigating other complex membrane protein systems, laying a foundation for future T3SS research and anti-virulence strategies.
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