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Statistics of extremes-based analytics of geometrical defects and the effect on fatigue scattering in laser powder bed fusion
No full textCompared to traditional subtractive manufacturing processes, laser-based powder bed fusion (LPBF) shows promise for making complex metal parts with design freedom, short development time, and environmental sustainability. However, there is a consensus within the additive manufacturing (AM) community that the random geometrical defects (e.g., porosity, lack-of-fusion) produced in LPBF processes impose a great challenge to fabricating load-bearing parts, particularly under dynamic loading conditions.
Fatigue performance is a critical design specification for any manufacturers of mechanical components under dynamic loading (e.g., aerospace, automotive, military). Many researchers have shown random scattering of fatigue life for materials produced with LPBF. This uncertainty is largely caused by the random geometrical defects with random shapes, sizes, and locations within parts that act as stress concentrations. Therefore, it is imperative to quantify defect sizes and distributions to predict the critical, life-limiting defect size that significantly reduces fatigue life.
Furthermore, the bulk literature is limited to gross fatigue fracture while the fatigue initiation and development process is poorly understood due to the constraint of available online fatigue monitoring techniques. It is more practical to monitor the fatigue damage process in metal AM components rather than solely rely on fatigue model predictions because monitoring adds safety to a design by providing physical evidence of component damage before reaching critical levels. Fatigue monitoring has been researched for decades in a variety of applications. Only in this past decade has fatigue monitoring been applied to AM materials and only in the past several years has machine learning (ML) been applied to predicting the fatigue performance of AM materials. There is thus a great opportunity to explore physics-informed ML models for AM fatigue prediction, which can leverage the monitoring data to improve the fatigue learning process.
Addressing these challenges is critical to qualify LPBF as a standard industrial process for fabricating load-bearing metal parts. This work addresses the challenges of characterization of geometrical defect size and distribution, fatigue monitoring, and fatigue scattering due to geometrical defects, all in the context of materials made by LPBF. The objective of this study is to obtain data from throughout the LPBF design cycle to lay the foundation for future work in modeling the process-quality-fatigue (PQF) causal relationship. First, the state-of-the-art fatigue monitoring and analytics in metal AM are reviewed. This is followed by two consecutive studies on geometrical defects in LPBFed SS-316L material. The first study presents a statistics-of-extreme methodology for predicting the maximum expected defect size in a part. The second study adopts a scientific point of view to quantify the effect of a wide range of porosity on fatigue performance.
The key conclusions are the following. The quality of LPBF material can be described by its maximum expected defect size, which can be extrapolated from a sampled distribution of defect sizes. At a minimum, hundreds of defect sizes should be sampled to obtain an accurate representation of the actual defect size distribution. Several different distribution functions (well-correlated to the dataset) should also be compared to select a realistic extrapolated maximum defect size (i.e., larger than the maximum measured defect but not too large). In-situ fatigue monitoring techniques can provide data on the entire fatigue process (i.e., crack initiation, crack propagation, rapid fracture) that can be leveraged as a fatigue process signature for fatigue modeling. The scattering of fatigue life and fatigue limit mainly impacted by random porosity in LPBF materials are characterized by normal distributions. Resonant fatigue frequency and machine power consumption act as fatigue process signatures.M.S.Includes bibliographical reference
An elastic robotic platform with tendon-driven actuation for scrubbing and cleaning
No full textThere is a lack of cleaning robots which can scrub adhesive stains from contaminated surfaces. Contaminated surfaces in domestic and industrial settings typically require manual scrubbing which can be expensive, time-consuming, or pose a health risk. To address the opportunity to automate the scrubbing of contaminated surfaces, this work investigates the use of series elastic actuators which can apply consistent trajectories of scrubbing force. Robotic scrubbing-based cleaning requires force control at the interface between the scrubbing tool and the substrate. Typical force measurements during scrubbing are noisy and require a complex controller to minimize disturbances. This work models the application of a serial manipulator with low-stiffness joints to improve the rejection of disturbances in force measurements during dynamic contact with a surface. This study uses an elastic serial manipulator with a hybrid force-position controller to perform scrubbing with consistent force trajectories. The robotic platform and controller in this work has the potential for future deployment in homes, hospitals, food-processing plants, and other settings where cleanliness of surfaces is important.Ph.D.Includes bibliographical reference
Novel sources of semiochemicals to manipulate spotted-wing drosophila behavior in blueberries
No full textSpotted-wing drosophila (SWD), Drosophila suzukii (Matsumura), is an invasive pest that causes severe damage to soft-skinned fruits including blueberries. Presently, the predominant method of control involves scheduled insecticide sprays, but the emergence of resistance poses a considerable challenge. As an alternative approach, my thesis focuses on researching the manipulation of SWD behavior using semiochemicals. First, I explored the use of elicitors of plant defenses and a crop sterilant to induce a defense response in blueberries against SWD or impede the growth of a mutualistic yeast. The aim was to render the fruits less attractive to the flies. Observations were recorded at intervals of 1, 3, 7, and 10 days post-treatment to assess any residual effects. Additionally, I investigated the impact of specific volatiles emitted from anthracnose-infected blueberries as potential repellents or oviposition deterrents for SWD. In semi-field and large field cage trials, neither elicitors nor a crop sterilant demonstrated a reduction in blueberry attractiveness or deterrence of oviposition. However, among 14 differentially emitted volatiles, nine compounds exhibited repellency in multiple-choice assays. In dual-choice assays, two of these volatiles displayed excellent repellency. These two compounds exhibited dose-dependent effects on behavior and antennal response, consistently diminishing attraction and oviposition in field studies. The findings presented in this thesis offer valuable insights for the further development of behavioral manipulation tactics to control SWD in blueberry fields.M.S.Includes bibliographical reference
Stress or enrichment? A study of the effects of zoo visitors on captive spider monkey behavior and welfare at a New Jersey zoo
No full textMillions of people visit zoos across the world annually, and these facilities help educate the public about important topics such as conservation and wildlife ecology, as well as aid in maintaining threatened species. However, while zoos provide many useful benefits, several issues also arise, such as unethical enclosure designs, unnatural diets, and the zoo visitor effect, the process in which captive animals will exhibit pathological patterns of behavior and physiology indicative of stress, based on fluctuating welfare states, stemming from the presence and activity of large numbers of unfamiliar human visitors. This study investigates the zoo visitor effect on a troop (n = 4) of zoo-housed, black-handed spider monkeys (Ateles geoffroyi). Using behavioral observations and a combination of quantitative and qualitative data analysis, results seem to indicate a negative effect assessed by an increase in negative behaviors. Individuals displayed high levels of resting and vigilance in their overall activities, yet increased rates of locomotion and repetitive, abnormal behaviors in the presence of human visitors. These results suggest that a form of stressful excitement arises in response to the presence of human visitors, reflecting similar results from other studies conducted on captive Ateles. This study emphasizes the importance of ethical animal management and techniques for alleviating potential issues, with a focus on an understudied species of primate in captivity.M.A.Includes bibliographical reference
Combining mouse molecular genetics and computer vision tools to probe spinal cord circuits of locomotion
No full textLocomotion is a complex motor behavior facilitated by spinal networks of sensory neurons, interneurons, and motor neurons that code for the timing and cyclical coordination of flexor and extensor muscles. The rhythmic activity of locomotion is separated into two phases: stance, when the foot is on the ground, and swing, when the foot lifts off the ground and moves forward in the air. To investigate how spinal circuits integrate sensory information to modulate these rhythmic motor outputs, we utilize mouse molecular genetics to enable genetic ablation, silencing, or activation of distinct neuronal populations in vivo. To quantify the functional implications of these manipulations, we use computer vision to derive meaningful information from our behavioral recordings with pose estimation by detecting and tracking anatomical landmarks, such as hindlimb joints. By combining mouse molecular genetics with computer vision I show that manipulation of a distinct population of spinal inhibitory interneurons during treadmill locomotion alters hindlimb kinematics, particularly at the phase transition from stance to swing. Beyond these studies, I provide a validated, proof of principle to couple nearly instantaneous pose tracking with optogenetic stimulation of sensory neurons at user-defined instances. To a greater extent, integrating real-time pose estimation with closed-loop optogenetic manipulation of sensory neuron activity enables us to tease apart the functional role of neurons that may be involved in the phase-dependent modulation of locomotion and offers unprecedented sensitivity to broadly probe neural activity at user defined instances.M.S.Includes bibliographical reference
From heart rhythms to scheduled motor milestones: a novel approach to early-stage neurodevelopmental monitoring
No full textRecent decades have seen an uptick in neurodevelopmental disorders, yet the detection of developmental abnormalities remains rooted in the assessment of social and emotional behaviors through observation, often missing subtle, spontaneous movements present from birth. This research delves into the intricate changes occurring in the postnatal period, focusing on heart rate variability (HRV) as a reflection of the infant's autonomic nervous system and its influence on the mother-infant dyad. By analyzing a unique dataset of naturalistic HRV recordings from 18 mother-infant pairs, we identify distinctive clusters of autonomic regulation, revealing a significant influence of infant HRV on maternal states. This work demonstrates the feasibility of utilizing HRV as a marker for early development, offering insights into the autonomic foundations of mother-infant interactions. We underscore the transformative power of integrating cutting-edge technologies with traditional cardiac analytics to enrich our comprehension of neurodevelopmental dynamics within the naturalistic confines of home life.
Concurrently, using wearable motion sensors, and pose estimation technology to engage parents in cognitive developmental research, we capture the nuanced evolution of movements. We present a novel approach that combines longitudinal data from parent submitted videos to map the maturation of motor behaviors that underpin later social interactions, potentially flagging atypical patterns that could indicate neurodevelopmental disorders. Through the convergence of longitudinal sensor data, clinical video validation, and parent-submitted footage, the research unveils a nuanced portrayal of neuromotor evolution from birth. By merging innovative data acquisition techniques with established and newly developed analytic methods, this thesis advances the understanding of neuromotor control in neonates and proposes a comprehensive model for the early detection of neurodevelopmental derailments. The integration of video-based assessments with HRV analysis in naturalistic settings represents a leap forward in the quest for early indicators of neurodevelopmental trajectories, paving the way for interventions that could foster development during the most formative stages of life.Ph.D.Includes bibliographical reference
"Let people tell their stories": becoming a caring doctor
No full textThis dissertation examines the stories of medical students and recent graduates from diverse backgrounds advocating a community-driven healthcare system in the United States while having difficulties navigating the U.S. healthcare system. Drawing on feminist epistemologies of care, decolonizing healthcare, and science technology studies (STS), this dissertation complicates medical knowledge production processes in the U.S. healthcare system in three ways: First, by conceptualizing care as a vital part of medical knowledge production, I intervene in the hegemonic biomedical approach of medicine. Second, by focusing on positionalities and co-production of medical knowledge between physicians and patients, I offer a counternarrative to an elitist, “detached” medical expertise. Third, I suggest a patchwork methodology by interweaving the personal and political stories of caring future doctors as change agents; this methodological intervention changes the focus from structural limitations to possibilities of change in the medical field. Throughout my dissertation, I use mixed qualitative methods, analyzing 40 semi-structured, in-depth interviews with medical school students and recent graduates who take part and advocate for community health and social justice in the healthcare system in the U.S. I also did participant observation following their community outreach/engagements as well as textual analysis of their personal statements for medical school admissions and residencies. The COVID-19 pandemic changed my plans, and I continued my participant observations on online platforms. As part of digital ethnography, I analyzed these medical students’ tweets on medical education, becoming a physician, and social change between 2020 and 2022 using NVivo. Then, I did five reflexive interviews with the research participants I had interviewed earlier to get their feedback on my findings. This dissertation is about listening to the stories of people, giving space to these stories to tell what is wrong with the U.S. medical system and how to transform medical care as caring healers. “Letting them speak their realities” is the method and finding of my dissertation. I developed these findings from multiple sources: from personal experiences of caring future doctors, from the stories of myself, my parents, and grandparents, from my positionalities, from my affective fieldnotes, from deep connections with the research participants, and the interviews in which they tell their journeys to become a doctor, and their struggles to change the system. I aim to contextualize and order these stories so that I theorize sociologically like a streetwalker. I let them simultaneously theorize their own stories of social change by foregrounding their voices.Ph.D.Includes bibliographical reference
Perceptions of economic inequality at the intersection of race and gender
No full textLittle previous work has investigated public perceptions of economic inequality at the intersection of race and gender, for both Asian and Black identities. This thesis study sought to fill this gap in the literature and identify whether intersectional inequality estimates followed a pattern based on identity prototypicality (i.e., intersectional invisibility), or an additive identity model (i.e., double jeopardy). An online survey study asked U.S. participants (N = 589) to estimate the annual earnings (in the year 2022) for targets with different racial, gender, or intersectional identities against a differently identified target serving as a baseline. Participants estimated significant earnings gaps only for some racial and intersectional identity targets, and not for those based on Asian racial identity or gender alone. In terms of accuracy against objective U.S. Census Bureau data, respondents overestimated the size of earnings gaps for Asian targets and underestimated the size of earnings gaps for Black targets. Finally, the results did not lend definitive support for either an intersectional invisibility or a double jeopardy model for intersectional identities. Further investigation is needed to determine an appropriate theoretical framework for understanding intersectional inequality perceptions.M.S.Includes bibliographical reference
Implementation of an interdisciplinary system to assess time spent in upright and ambulant positions during the first stage of labor
No full textPurpose: This quality improvement pilot project developed and implemented a provider-focused educational program and created and implemented a patient-focused guide/visual aid to assess the time spent in upright and ambulant positions during early labor for low-risk, term, gravid women.
Methodology: The project applied a post-implementation assessment design and took place in a 519-bed urban teaching hospital in Essex County, New Jersey where approximately 1,200 births occur annually. Convenience sampling and purposive recruitment were used to target participation by low-risk, term, singleton, and gravid women whose fetus was in the cephalic position. The project encompassed unit-based education for the labor and delivery providers, distribution of educational flyers to laboring persons, displaying instructional and reminder posters in the labor and delivery suites, and implementation of an assessment form to track the time spent in various ambulant and upright positions during the first stage labor.
Results: Assessment forms successfully tracked the amount of time spent taking upright and ambulant positions and the various positions taken during the first stage of labor. Time spent standing/walking ranged from 17 to 135 (n=4, mean 56.75) minutes. The range of time spent sitting was 25 to 270 minutes (n=4, mean 91.25) minutes. The range of time spent using a birthing ball was zero to 95 minutes (n=4, mean 51.25) minutes. The time spent in these various positions was preference-based.
Implications for Practice: This project encouraged healthcare personnel to assess time spent in upright and ambulant positions and raised awareness of physiologic best birthing practices. With the use of the visual guides and new birthing balls on the unit, nursing and ancillary providers were able to aid patients to various positions and track the time they are spending in non-recumbent positions.D.N.P.Includes bibliographical reference
Managing non-specific chronic low back pain with steps in a patient-driven program using pedometer walking intervention
No full textPurpose of the Project: This quality improvement project was initiated to improve the overall functionality, quality of life, and pain severity of patients with chronic low back pain (CLBP) by maximizing physical activity through pedometer walking intervention.
Methodology: Participants engaged in a six-week pedometer-driven walking project. This project was implemented in the care plan of all patients 18 years and older for CLBP management through a retrospective chart review. Two pain management providers at the clinic were recruited to motivate CLBP patients to use walking to treat and manage their low back pain. A tracking sheet was used to monitor the patient’s participation by providing them with a weekly walking diary log to track steps taken.
Results: A total of 10 patients were included. A paired sample correlation coefficient was used to compare the self-reported pain severity pre/post-intervention. The hypothesis testing revealed the significance of the changes in the continuous outcomes. In self-reported pain severity pre-intervention (M = 2.400, SD = 1.776), t-value (4.272) with a corresponding p-value of <.002. While in post-intervention (M =4.272, SD = 1.776), t-value (9) = 9.000, p = 0.002. Evaluating physical function pre-intervention (M = -3.00, SD = 0.483) and post-intervention (M = -1.964, SD = 0.483), t-value (9) = -1.964, p <.081. While quality of life pre-intervention (M = -1.100, SD = 0.568) and post-intervention (M = -6.128, SD = 0.568), t-value (9) = -6.128, p < .001.
Implications for Practice: Findings support the role and benefits of a walking intervention as a management strategy for CLBP. Incorporating a pedometer walking intervention into the care plan treatment can maximize patients' quality of life with CLBP.D.N.P.Includes bibliographical reference