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Room-Temperature Electrochemical Healing of Structural Metals
No full textFor over 6,000 years, repairing high-strength metallic materials has required high temperatures and large energy inputs. Likewise, recent innovations in self-healing and repairable metals have remained limited by the need for heating, the small size of repairable cracks, and the low strength and constrained chemical composition of healed metals. While welding remains the most widely used approach to repair metals, the increasing ubiquity of digital manufacturing and “unweldable” alloys call for radically different approaches. This thesis pioneers a new approach for repairing structural metals at room-temperature, termed “electrochemical healing”. First, by mimicking the transport-mediated healing of bone, selective nickel electrodeposition enables rapid, effective, low-energy, and room-temperature healing of a cellular metal. A polymer coating restricts electrodeposition only at fracture or high stress sites, and a statistical method quantifies and predicts the probability of a target recovery of tensile strength based on energy input. This thesis extends room-temperature healing to low-carbon steel, a widely used structural metal, by elucidating how ion transport and electrolyte chemistry influence growth morphology and strength in fractured steel wires repaired with nickel electrodeposition. Pulsed electroplating and electrolyte chemistry selection improve nickel adhesion and enable fully fractured steel wires to recover up to 69% of their pristine strength. Finally, this thesis presents a framework for effective room temperature electrochemical healing based on a quantitative model that links geometric, mechanical, and electrochemical parameters to the recovery of tensile strength in repaired metals. This framework enables full recovery of tensile strength in a variety of structural metals, including “unweldable” alloys and a 3D-printed difficult-to-weld funicular shellular structure, as well as over 100% recovery of toughness in an aluminum alloy. The model reveals scaling relationships for the energetic, financial, and time costs of repairing metals that facilitate the practical adoption of electrochemical healing. Room-temperature electrochemical healing could open exciting possibilities for the scalable, autonomous, repeatable, and prophylactic repair of metalsin structures and robots, enable cellular materials that respond to environmental stimulus with growth and morphogenesis, and advance the life cycle sustainability of structural metals
Novel Models of XCI Maintenance Reveal Cell Type Specific Modes of Regulation
No full textRegulation of X-linked gene dose between females(XX) and males(XY) is critically necessary to prevent disease associated over-expression in females. X-linked equilibrium is achieved by X-Chromosome Inactivation (XCI), initiated by Xist RNA to inactivate one allele (Xi). Silencing of the Xi is maintained across all cell divisions by retention of Xist RNA transcripts and maintenance of a condensed, bipartite allele. However, our lab made a seminal discovery that naïve, quiescent B lymphocytes express Xist, but lack Xist RNA at the Xi. Upon lymphocyte activation, Xist RNA dynamically re-localizes to the Xi. Lymphocytes are the first cell type to display dynamic XCI, thus how differential localization of Xist RNA impacts Xi silencing and regulation of Xi-specific structure is unknown. Further, this finding implores us to ask whether other cell types, particularly quiescent cells, could show unique XCI regulation. Here, I utilize various primary cells to ask whether XCI maintenance has cell-type specific regulatory mechanisms outside of lymphocytes, and how varied Xist RNA localization could influence XCI maintenance. Examination of Xist RNA localization across adult stem cells determined that dispersed Xist RNA is not directly linked to quiescence. Further, we identify a new cell type, satellite cells, with dynamic XCI maintenance upon activation. In AT2 stem cells of the lung, we observe loss of localized Xist RNA coupled with a significant number of XCI escape genes. The results from these studies suggest that varied XCI maintenance is a more widespread, cell-type specific phenomenon with implications for sex-differences in stem cell function. Finally, upon B lymphocyte activation, the Xi displays TAD-like structures with increased interactions that appear independent from escape gene expression. Xist RNA re-localizes to the Xi in parallel to activation induced Xi remodeling, thus we hypothesized that Xist RNA maintains Xi structure in stimulated B cells. Remarkably, we find that Xist RNA is required to prevent extensive activation-induced Xi remodeling, but surprisingly also prevents modulation to Xi structure in naïve B cells. Together, this work challenges the paradigms of XCI maintenance and lays the foundation for further work in which to understand the connections between varied XCI maintenance and sex-biased cellular functions
Understanding Cellular Plasticity within the Intestinal Epithelium
No full textThe intestinal epithelium exhibits a rapid and efficient regenerative response to injury. Emerging evidence supports a model where plasticity of differentiated cells, particularly those in the secretory lineages, contributes to epithelial regeneration upon ablation of injury-sensitive stem cells. However, such facultative stem cell activity is rare within secretory populations. Here we ask whether specific functional properties predict facultative stem cell activity. We utilize in vivo labeling combined with ex vivo organoid formation assays to evaluate how cell age and autophagic state contribute to facultative stem cell activity within secretory lineages. Strikingly, we find that cell age (time elapsed since cell cycle exit) does not correlate with secretory cell plasticity. Instead, high autophagic activity predicts plasticity and resistance to DNA damaging injury independently of cell lineage. Our findings indicate that autophagic status prior to injury serves as a lineage-agnostic marker for the prospective identification of facultative stem cells. In contrast to the dedifferentiation of committed secretory cells, other studies suggest that a population of dedicated, quiescent, facultative stem cells drives intestinal regeneration. Our group has previously determined that the Msi family of RNA-binding proteins are both necessary and sufficient for activation of this pool of facultative intestinal stem cells. Here we present a novel mouse model utilizing HyperTRIBE technology to identify Msi2 RNA binding partners in rare intestinal epithelial cell populations, and possibly even single cells
A Delicate Balance Between the Artist and His Work: Preserving Isaiah Zagar\u27s Public Mosaic Murals
Get PDFOutsider artists are artists driven by the compulsion to create immense spaces separate and distinct from the politics of everyday life and the ordinary and mundane aspects of the built environment. For over half a century, artist Isaiah Zagar has committed his life to city beautification; creating over 220 mosaic murals in Philadelphia. One can argue that Isaiah Zagar has transformed Philadelphia into a folk art environment through his public and private mosaic murals that have long been ingrained in the city’s urban fabric. While this research does not address the entire scope of his work, it aims to provide the basis for addressing preservation issues in the context of outsider art, and Philadelphia. Zagar’s mosaic murals remain at risk to a lack of regular maintenance caused by ambiguities in ownership, and protection from demolition. This thesis will examine the preservation of Isaiah Zagar’s public mosaic murals, his connection to outsider art, and the complex relationship between public art and private property while focusing on the mosaics entitled 4,000 Poets. This particular grouping of mosaics are located in the Bella Vista/ Southwark neighborhood on Schell Street between the Eyes Gallery and Philadelphia’s Magic Gardens; the site that fostered the South Street Renaissance in the 1960s
How Does the Built Environment Influence Car and Motorcycle Ownership and Use in Metro Manila?
Get PDFMetro Manila is the Philippines’ political and economic capital. With 20 million inhabitants and a land area of only 550 sq. miles, it is Southeast Asia’s most densely populated megacity. In many ways, Metro Manila’s urban development mirrors the challenges faced by rapidly urbanizing cities: economic opportunities are disproportionately concentrated in the capital, rising land values in the urban core have pushed residents towards the fringes, weak planning and enforcement have resulted in unchecked development, and unreliable public transportation coupled with a growing middle class have increased motorization rates.
To address these challenges, cities have turned to land use strategies, which have the potential to influence travel and ownership behavior. While several studies have explored this relationship, research on how the built environment’s effect varies across private motorized modes remains limited. To fill this gap, I sought to answer the following research questions: What is the relationship between the built environment and car ownership and use in Metro Manila? How does this relationship differ for motorcycle ownership and use?
Using data from the 2015 Metro Manila Urban Transportation Integration Study Home Interview Survey, I find that the built environment influences vehicle ownership and use differently. Population, job, and intersection densities as well as the land use mix influence car ownership, while population and job densities and distance to the central business district are correlated with motorcycle ownership and use. Proximity to a railway station and diverse land uses influence both motorcycle and car use. These findings could help inform strategies for reducing motorization rates and shifting towards more sustainable transportation in Metro Manila
Mapping Urban Infrastructure: Temporal Metropolitan Geographies of Nonprofit Human Service Organizations
Get PDFAcross the United States, planning for human services relies largely upon public-private partnerships with nonprofit organizations as the result of decades of federal retrenchment. The locational patterns of nonprofit human services organizations (NHSOs) have been studied in the nonprofit literature, but there is little scholarship on this topic in the realm of city planning. This research connects these two disciplines while answering two questions: 1) Where do NHSOs cluster over time within metropolitan statistical areas (MSAs)? 2) Are NHSOs locating in response to community needs, resources, or conditions? In order to establish generalizable results across space and time, this study used a multi-site analysis of eight MSAs in 2010 and 2018: Austin, TX; Buffalo, NY; Cleveland, OH; Indianapolis, IN; Philadelphia, PA; Research Triangle, NC; Sacramento, CA; and Seattle, WA. Two quantitative methods explored these questions. First, a spatial analysis used density-based clustering to identify clusters of NHSOs throughout each MSA. Then linear regression modeling revealed relationships between the NHSO landscape and various socioeconomic and built environment variables. The results of this analysis demonstrated evidence of NHSO clustering that warrants further investigation. Furthermore, the evidence confirmed previous findings that NHSO patterns are more related to resources and community conditions than need. While this study contributes to a growing body of research in the nonprofit field, there are theoretical frameworks, practical tools, and policy solutions that should prompt city planners to take interest in this subject as well
An Organizational Guide to Leveraging Military Veteran Human Capital
Get PDFMilitary veterans possess a unique set of nontechnical skills from military training and operation that transfer into the civilian workforce. If leveraged appropriately, these nontechnical skills create an economic advantage for organizations and an engaged veteran workforce. The last two decades have built a resource-rich foundation to assist veterans during their military-to-civilian transition and a clear business case that supports hiring them. Unfortunately, organizations can overlook and underutilize these nontechnical skills after veteran employees are hired and onboarded. What can organizations do to leverage the human capital of their veterans during the entire employee lifecycle? This appreciative inquiry is designed around 27 qualitative interviews with military veterans of different ranks and military branches, currently employed in the civilian workforce. Veteran interview responses across nine different industries provided a summary of their nontechnical skills to be: Creativity & Collaboration, Adaptability & Resilience, Servant Leadership, Effectiveness under Pressure, and Visibility into Diverse Work Teams. Using a thematic analysis, the responses were mapped to four organizational engagement drivers that can be measured and improved by managers and organizations: CHALLENGE, MOTIVATION, COMMUNITY, and COMMUNICATION. This paper explores the “why” behind these nontechnical skills, the “how” of what civilian organizations are doing to leverage these skills, and the “what” that can be done to improve the future of work for this demographic. This research can be used both as a tool for organizations and for the veteran community to market the transferable value of their military service
Repeated Jumping with the REBOund: Self-Righting Jumping Robot Leveraging Bistable Origami-Inspired Design
Get PDFRepeated jumping is crucial to the mobility of jumping robots. In this paper, we extend upon the REBOund jumping robot design, an origami-inspired jumping robot that uses the Reconfigurable Expanding Bistable Origami (REBO) pattern as its body. The robot design takes advantage of the pattern\u27s bistability to jump with controllable timing. For jump repeatedly, we also add self-righting legs that utilize a single motor actuation mechanism. We describe a dynamic model that captures the compression of the REBO pattern and the REBOund self-righting process and compared it to the physical robot. Our experiments show that the REBOund is able to successfully self-right and jump repeatedly over tens of jumps.
Supplemental video: https://youtu.be/LoCXcwIxCg
TrussBot: Modeling, Design, and Control of a Compliant, Helical Truss of Tetrahedral Modules
Get PDFModular and truss robots offer the potential of high reconfigurability and great functional flexibility, but common implementations relying on rigid components often lead to highly complex actuation and control requirements. This paper introduces a new type of modular, compliant robot: TrussBot. TrussBot is composed of 3D-printed tetrahedral modules connected at the corners with compliant joints. We propose a truss geometry, analyze its deformation modes, and provide a simulation framework for predicting its behavior under applied loads and actuation. The TrussBot is geometrically constrained, thus requiring compliant joints to move. The TrussBot can be actuated through a network of tendons which pinch vertices together and apply a twisting motion due to the structure\u27s connectivity. The truss was demonstrated in a physical prototype and compared to simulation results.
Supplemental video: https://youtu.be/bcvFMq40Ez
Statistical Learning for System Identification, Estimation, and Control
No full textDespite the recent widespread success of machine learning, we still do not fully understand its fundamental limitations. Going forward, it is crucial to better understand learning complexity, especially in critical decision making applications, where a wrong decision can lead to catastrophic consequences. In this thesis, we focus on the statistical complexity of learning unknown linear dynamical systems, with focus on the tasks of system identification, prediction, and control. We are interested in sample complexity, i.e. the minimum number of samples required to achieve satisfactory learning performance. Our goal is to provide finite-sample learning guarantees, explicitly highlighting how the learning objective depends on the number of samples. A fundamental question we are trying to answer is how system theoretic properties of the underlying process can affect sample complexity. Using recent advances in statistical learning, high-dimensional statistics, and control theoretic tools, we provide finite-sample guarantees in the following settings. i) System Identification. We provide the first finite-sample guarantees for identifying a stochastic partially-observed system; this problem is also known as the stochastic system identification problem. ii) Prediction. We provide the first end-to-end guarantees for learning the Kalman Filter, i.e. for learning to predict, in an offline learning architecture. We also provide the first logarithmic regret guarantees for the problem of learning the Kalman Filter in an online learning architecture, where the data are revealed sequentially. iii) Difficulty of System Identification and Control. Focusing on fully-observed systems, we investigate when learning linear systems is statistically easy or hard, in the finite sample regime. Statistically easy to learn linear system classes have sample complexity that is polynomial with the system dimension. Statistically hard to learn linear system classes have worst-case sample complexity that is at least exponential with the system dimension. We show that there actually exist classes of linear systems, which are hard to learn. Such classes include indirectly excited systems with large degree of indirect excitation. Similar conclusions hold for both the problem of system identification and the problem of learning to control