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Advancing High-Performance Bio-Inspired Propulsion: Investigating the Physics of Non-Uniform Flexibility, Unsteady Ground Effect, and Schooling Interactions
No full textUtilizing non-uniform flexibility, unsteady ground effect and in-line schooling in bio-inspired propulsion can enhance the propulsive performance of underwater propulsors. Moreover, the physics of stable positions (also known as stable equilibrium altitudes in unsteady ground effect) can be used to control the relative spacing between a bio-inspired propulsor and a boundary or between two or more bio-inspired propulsors. These stable arrangements are purely driven by fluid-mediated forces that arise in boundary and schooling interactions. By altering stable positions the hydrodynamics and propulsive performance of the bio-inspired propulors can also be significantly affected. In order to enhance propulsive efficiency and design/control stable positions in bio-inspired propulsion, the physics of non-uniform flexibility, unsteady ground effect and in-line schooling were examined.For the study of non-uniform flexibility, measurements of thrust, power and amplitude were conducted on non-uniformly flexible pitching foils fabricated with a rigid leading section joined to a flexible trailing section. This construction enables us to vary the bending pattern and resonance condition of the foils independently. It is discovered that non-uniformly flexible foils achieve high propulsive efficiencies around and greater than 50%, which makes them outperform their rigid and uniformly flexible counterparts. There is an optimal flexion ratio from 0.4 < lambda < 0.7 that maximizes the efficiency. Furthermore, this optimal range coincides with the flexion ratios observed in nature.A classic lift decomposition in Von Karman and Sears (1938) is conducted on potential flow simulations of a near-ground pitching hydrofoil to identify fundamental competing forces behind the equilibrium altitude of unsteady ground effect. It is discovered that previously observed stable and unstable equilibrium altitudes are generated by a balance between positive wake-induced lift and negative quasi-steady lift while the added mass lift doesn\u27t play a role. Scaling laws for the quasi-steady lift, wake-induced lift and the stable equilibrium altitude are discovered.In terms of in-line schooling, potential flow simulations were conducted on two pitching hydrofoils unconstrained in the streamwise direction. Suppressing leading-edge separation of the simulations show that in-line stable positions are only formed when leading-edge separation occurs. The effects of common design and control variables such as the Lighthill number, pitching amplitude, and phase difference on the stable positions and propulsive efficiency at those positions were investigated. The actual wake wavelength, lambda_{a}, which is determined from an isolated foil, is found to scale in-line stable positions of both varying Lighthill number and pitching amplitude. Along with constrained experiments, it is found that the stable positions of freely swimming foils using matched pitching kinematics do not lie in the optimal efficiency band discovered in previous constrained studies, but are in fact near the edge of the band. Implementing unmatched kinematics by giving the leader a larger amplitude relative to the follower can push the freely swimming foils into the optimal efficiency band and also increase the efficiency enhancement of the band and its neighborhood. In this manner, the efficiency of freely swimming foils at in-line stable positions can be enhanced, and the gap between constrained and unconstrained studies of in-line schooling is bridged
Cumulative Trauma Among Latine Individuals: Exploring Post-Traumatic Growth as a Coping Mediator Using Structural Equation Modeling
No full textResearch suggests that Latine individuals are more likely to experience multiple traumatic events throughout their lifetimes, a phenomenon known as Cumulative Trauma (CT). A CT framework also acknowledges how collective identity and developmental traumas may significantly impact the mental health and well-being outcomes for Latine individuals. Research and theorists suggest that subjective well-being (SWB) can be negatively impacted by traumatic life events. On the other hand, traumatic events can also lead to meaningful and adaptive changes known as Post-traumatic Growth (PTG). Although PTG has often been studied as an outcome of trauma, evidence suggests that perceptions of PTG may also serve as a significant coping mechanism. The current study aimed to explore the role of PTG in relation to CT and SWB using structural equation mediation models. A coping mediation model was proposed, and a competing moderation model was also tested following SEM best practices. Given the evidence to suggest that the relationship between CT and SWB may differ for Latinas compared to their male counterparts, a multi-group analysis was also used to test potential gender differences in the current research sample. Data was collected using Amazon Mturk, and a sample of 235 Latine participants was included in the analyses. Results supported the majority of the hypotheses in the current study. A coping mediation model was found to better fit the current Latine participant sample compared to the moderation model. PTG was found to partially mediate and weaken the relationship between CT and SWB. Although the path between CT and SWB was significant and negatively related, there were no significant gender differences. Implications and future directions are discussed for researchers and practitioners
Changing Times, Changing Reputation: An Organizational History of William Allen High School, 1960-2020
No full textWilliam Allen High School (WAHS) was once a pillar of success. From a growing student body to a successful vocational wing, the high school was the epicenter of the district and the city for over a century. Today, however, WAHS evokes a different image. Between 1960 and 2020, WAHS evolved from a predominately White and high-achieving institution, to one synonymous with failing academics and a majority-minority student body. The current study utilized Dan Duke\u27s (1995) proposed steps for writing an organizational history. Analysis of primary and secondary sources identified four critical incidents- urban renewal, the migration of Puerto Rican residents, the collapse of industry, and the funding formula defined and implemented by Pennsylvania\u27s public schools. These events worked both individually, and collectively, to create impacts which challenged the academic performance of the WAHS. Through the use of organizational history, critical incidents were tracked between 1960 and 2020, along with the response, or lack thereof, by the school to these external pressures. Document analysis revealed that WAHS\u27s internal responses to each critical incident were inadequate, contributing to the decline of the school\u27s academics over a 60-year period. Urban renewal, while not directly impacting the internal structure of WAHS, relocated Allentonians of color into the downtown district and laid the foundation for a city segregated by race and socioeconomic status. As the city experienced a rapidly growing Puerto Rican population beginning in the 1970s, it also faced the simultaneous decline of Allentown industries. Each event, while external to WAHS, required the school to respond to a changing demographic and economic base within the city. As the population within the school continued to evolve throughout the 21st century, WAHS was unable to provide the instructional programs and supports necessary for its increasing number of high-needs students. The funding formula defined and implemented by Pennsylvania\u27s public schools forced WAHS to rely heavily on a local tax base that remained unable to generate adequate revenue to support the instructional needs of the school
Microfluidic Engineering of on-Chip Vascular Models for Preclinical Biomedical Investigation
No full textVascular system is involved in various essential life activities, including both normal embryonic organ development and pathological processes, such as tumorigenesis. In addition to exchanging nutrients, oxygen, and metabolites with organs, blood vessels are also involved in many important immune responses and signaling pathways. In recent years, microfluidic chips and organoid technologies have become more and more advanced, and small-dimensional organ tissues can be replicated in vitro for regenerative medicine development and drug candidate screening research. However, without timely vascularization, the organ tissue at a certain size will develop a necrotic inner core, causing overall apoptosis finally. Therefore, understanding vascular biology and rational introduction of vascular structures in the microenvironment is particularly important for reproducing realistic functional tissue models.Here, we report three different forms of microfluidic vascular models for periclinal physiological investigation research and drug screening purpose, respectively. In chapter 1, a blood vessel lumen with hundreds of microns in diameter was constructed on microfluidic chip to study the vessel-circulating tumor cells (CTCs) interaction during cancer metastasis. In chapter 2, on-chip capillary micro vessel network was restored to support microfluidic droplet-fabricated tumor spheroids, enabling high-fidelity restoration of the tumor microenvironment and high-throughput preclinical drug screening. In chapter 3, acoustofluidic patterning is presented for on-demand and facile engineering of the in vitro vessel model in a high-resolution manner
Mê: Room of Fixations and Reinstatement
No full textThe word "Mê" in Vietnamese is attributed to those being enchanted or fixated by specific interests or passions; and often, these interests are rooted in childhood experiences. The concept of my project will revisit my childhood fixations which are clay and sewing crafts, particularly those related to food and toys. The project will also pay homage to how I entered my artistic journey by recreating an installation of a children\u27s play room through a contemporary and psychologically responsive lens. Delving into my Vietnamese heritage as well, I will investigate and explore the themes of childhood psychology, accessibility of materials, creativity found in play, deficit of culture, early hyperfixations, and reflection from an adulthood standpoint
Tedhi Growth: Queer Childhood in Ismat Chughtai\u27s The Crooked Line
No full textThis paper theorizes tedhi growth in Ismat Chughtai\u27s novel, Tedhi Lakeer or The Crooked Line in order to explore the diverse queer potentialities in children and their "coming-of-age" narratives. Tedhi Lakeer, I contend, is a novel about children—their strangeness, queerness, and tedhi (crooked) growth. Growing up is a concept couched in a heteronormative sense of "progress." It signifies a straight growth that follows linear time and conventions. Tedhi growth, on the other hand, suggests queer growth, where the heteronormative "progress" is halted by a temporal stasis or circularity. The tedhi growth in Chughtai\u27s context refuses to ascribe a singular direction to queer temporality in a postcolonial space. It enables a multiplicity of queer growths. By centering non-normativity, it also complicates the genre of Bildungsroman. Instead of favoring a linear growth in which the protagonist comes of age, the genre is queered. The first section of my paper theorizes and deploys tedhi growth in order to expand the politics of colonized queer children and their narratives. Following the theorization of tedhi growth, the second part of my paper deals more conceptually with the formal structure of a postcolonial and queer Bildungsroman.</p
Controlling Lubricated Sliding Friction for Soft Solids
No full textLubricated contacts in soft materials are common in various engineering and natural systems. Three major regimes are elastohydrodynamic lubrication (EHL), in which solid surfaces are fully separated by a fluid film, mixed lubrication (ML), in which there is partial solid-to-solid contact and boundary regime, in which the contact region is dry. ML-boundary and EHL-ML regime transitions govern the maximum and minimum sliding friction achievable for a certain system and are thus very important in various engineering and natural settings such as tires, haptic applications, bio-inspired systems, contact lenses, and the fabrication of soft electronic devices. However, the insufficient understanding of transitions between these regimes impedes desired control of lubricated sliding friction for soft solids.Generally, the transition from EHL to ML regimes is believed to occur when the thickness of the lubricant layer is comparable with the amplitude of surface roughness. We performed lubricated sliding experiments on smooth polydimethylsiloxane (PDMS) substrates under various normal load, sliding velocity, and lubricant conditions. We found that for smooth soft surfaces, the transition from EHL to ML regimes can occur when the thickness of the liquid layer is much larger than the height of asperities, that is, the conventional criterion is highly inaccurate. By direct visualization of the "contact" region during sliding experiments, we demonstrate that the transition corresponds to the formation of wave-like surface wrinkles at the leading contact edge and associated fingering instabilities at the trailing contact edge. We believe these instabilities are peculiar to soft solids and is accompanied by the transition from EHL to ML regime. Our results change the fundamental understanding of what governs the important EHL-ML transition in lubricated sliding of soft solids. To further investigate the mechanisms controlling lubrication regime transitions, we explored the roles of wettability and adhesion played in the lubricated sliding for soft materials. We adopted the ultraviolet light-ozone (UV-Ozone) cleaner to change the wettability of glycerol on polydimethylsiloxane (PDMS) surface and adhesion between glass indenter and PDMS. By combining friction tests and visualizations, we demonstrate that the transition from ML to BL regime is dominated by the wettability of the lubricant as increasing wettability of glycerol can maintain a liquid layer more easily in the contact region. EHL-ML transition is related to a series of events with increasing normal load, which are thinning of lubricant layer, sudden contact between a glass indenter over a few hundreds of nanometers, and elastic instabilities. The morphology of elastic instabilities is determined by the competition between the wettability of the liquid and the adhesion of two solid surfaces. These results provide a comprehensive understanding of the frictional behavior of a soft material and elaborate the maximum and minimum friction achievable of a soft system.</p
Towards Safe Learning and Perception-based Networked Control Systems: A Risk-aware Approach
No full textNetworked control systems, rooted in networked control theory, tackle collective behavior and coordination among interconnected entities. This concept, which is crucial in robotics, social networks, and distributed computing, aims to achieve consensus among diverse agents. Understanding and guiding such systems toward coherent states is pivotal for developing resilient and adaptive systems capable of autonomous decision-making and control. However, bridging the gap between theoretical constructs and real-world applications poses challenges, particularly in networked control systems. Incorporating factors like input noise and communication time-delay is essential for a nuanced understanding and effective deployment of control systems in uncertain environments.A significant focus lies on investigating cascading failures within networked control systems, triggered by the failure of a single component propagating through the entire network. Understanding and mitigating cascading effects are imperative for safeguarding critical infrastructure and enhancing system resilience. Through theoretical analyses and simulation studies, researchers aim to characterize the dynamics of cascading failures and develop robust frameworks to mitigate their impact, thereby enhancing the stability and reliability of networked control systems. In the next stage, the challenge will emerge when the statistics of the noise are not exactly known. As a result, the ambiguity of the uncertainty will be introduced into the existing system and make the behavior of the system even less predictable. To address this issue, we adopt the concept of distributionally robust risk measures and optimization to solve the robustified version of the original problem. These methodologies aim to enhance the robustness of the system against the ambiguity of uncertainty, providing a framework to make decisions that are resilient to variations in the underlying distribution of the noise.Lastly, instead of considering the dynamics of the system obtaining a linear closed-form, we delve into the intricate realm of real-world perception models to enhance the capabilities of robots. We explore problems including 3D scene understanding via Neural Radiance Fields (NeRF) models, traffic sign classification with risk-aware decision-making, and map classification via a team of communicating aerial robots. In these applications, we examine the impact of uncertainties on the safety, decision-making, and task completion of autonomous robot systems.</p