71446 research outputs found
Sort by
Rising from the Ashes: How the Milky Way Got Its Scars
No full textUnderstanding ancient events in the Milky Way's history is essential for building a consistent picture of galaxy formation and evolution, bridging stellar and chemical evolution models with the extragalactic population. Our galaxy experienced three simultaneous, transformative events 8 Gyr ago: our last major merger, the formation of a bar, and a transition chemical enrichment leading to an alpha-element bimodality. The history of these events is encoded in the present-day observable properties of stars: dynamics (positions and velocities), chemical compositions, and ages. In this thesis, we will make use of numerical simulations tailored to understanding how these historical processes of the Milky Way led to its present-day properties. First, we will propose a solution to the mystery of why the bar rotates rapidly when it is old enough to have slowed down by now. Second, we will propose that our last major merger led to the emergence of the alpha-bimodality via a metallicity-dependent halt in star formation. Finally, we will demonstrate that the formation of the bar might have triggered the formation of the bimodality through the same mechanism. This work demonstrates the rich understandings that can be gleaned from idealized simulations specifically tailored to the Milky Way.Astronom
The Fine-Grained Complexity of Min-Distance Problems in DAGs
No full textThe min-distance between two nodes u and v is the minimum of the shortest path distances from u to v and from v to u. Min-distance is a natural measure of distance in DAGs (directed acyclic graphs), and many classically studied graph distance parameters can be redefined in terms of mindistance. This thesis presents several new results on the fine-grained complexity of approximating min-distance parameters such as min-diameter, min-radius, and min-eccentricities, concentrating primarily (though not exclusively) on the special case of DAGs. In particular, we develop new approximation algorithms for these parameters, with runtimes polynomially faster than the standard All-Pairs Shortest Paths algorithm. Our algorithms improve on the approximation factors achieved in prior work, and in several cases, we obtain approximation factors that are conditionally tight, in the sense that they match lower bounds implied by hardness hypotheses such as the Orthogonal Vectors Conjecture and the Hitting Set Conjecture. We also obtain new several conditional lower bounds for min-distance problems, including a new lower bound for min-diameter conditioned on the OV Conjecture. Lastly, we present the first study of approximating bichromatic min-diameter.Mathematic
Harnessing the Capital of the Poor: Assessing the Acceptability of Community Based Health Insurance in Zimbabwe
No full textMost people in Zimbabwe face financial risk when seeking healthcare. Similar to other low- and middle-income countries, the population is largely informally employed or unemployed, with only 10% covered by private health insurance or limited government programs. Without health insurance or strong financial risk pooling mechanisms, both rural and urban populations must pay out-of-pocket, and the government collects insufficient tax revenue to fund equitable healthcare and achieve its goal of Universal Health Coverage (UHC).
Community-based health insurance (CBHI) has been proposed as a viable path toward providing high quality health services and financial protection for the population in low- and middle-income countries like Zimbabwe. CBHI involves forming local risk pools through community-managed insurance schemes that rely on voluntary contributions and social capital—trust and solidarity within communities. This social capital is essential for CBHI’s success.
Faith-based organizations (FBOs), long trusted within communities, have been identified as well-positioned to help organize CBHI programs. This project aimed to assess the acceptability of FBO-led CBHI in predominantly rural communities near mission hospitals in Zimbabwe. The Old Mutare community, surrounding the United Methodist Church’s Old Mutare Mission Hospital, was selected for the study.
Using a qualitative design, researchers conducted focus group discussions and key informant interviews. The Adapted Cooperative Healthcare framework was used to identify enablers and barriers to CBHI acceptance.
Findings suggest that CBHI is indeed acceptable to the Old Mutare community. FBOs can play a critical enabling role by offering financial and technical support. However, the study found that those interviewed felt the church should not lead the initiative outright. When CBHI is perceived solely as an FBO initiative, it may trigger mistrust in the community that could undermine success. Instead, strong community ownership and oversight will be essential.
Acceptability studies like this one are an important first step in CBHI development. Early community engagement and buy-in can build the foundation for long-term sustainability and contribute meaningfully to Zimbabwe’s progress toward UHC.Public Healt
The Promise and Paradox of Public Higher Education: Institutional Logics, Organizational Action, and Mission Fulfillment
No full textPublic higher education has long served as a vehicle for upward mobility in American society.
However, public colleges are experiencing difficulties in getting students across the finish line and struggle with persistently low degree completion rates. Integrating and building on key concepts of institutional and organizational theories, my dissertation investigates why public higher education is struggling to fulfill a core component of its mission and deliver on its promise of material value.
In Paper 1, I examine why colleges do not adopt or pursue organizational actions known to improve degree completion. Drawing on and extending both institutional and organizational theories, I develop a multi-level theoretical model that accounts for competing institutional logics at the macro-level, embedded organizational attributes at the meso-level, and interactions at the individual-level. In Paper 2, my co-author and I investigate how, in an institutional environment defined by pluralism, actors within a public university system are enabled or hindered from pursuing actions that align with public higher education’s democratic mission with constrained resources. Drawing on unique interview data of actors and students at a large, less-selective, public university system, we introduce the concept of structural filtering to describe the process by which organizational attributes lead actors to perceive certain kinds of organizational conduct as appropriate, resulting in an unequal provision of support. In my final paper, I explore the origins and drivers of the disconnect between the material value higher education promises and the organizational conditions that make delivering on that promise challenging for public colleges. In this historical case study and document analysis of the City University of New York (CUNY), I find that conflicting logics were adopted in response to two distinct institutional environments, which shaped its organizational characteristics in ways that remain embedded today. This has created a value-gap, where CUNY’s egalitarian-shaped characteristics communicate and reinforce its material value. Yet, CUNY’s austerity-shaped characteristics constrain its ability to deliver on its promised and expected value.
Together, these papers suggest that organizational conditions and complexity can—and do—obfuscate the democratic missions of public institutions. Moreover, I demonstrate how, if society still wants, expects, or needs higher education to be a vehicle for upward mobility and not stratification, a reinvestment and corresponding organizational transformation is necessary.Educatio
The molecular origins and implications of genomic structural variation in deer mice
No full textUnderstanding the origins and evolution of genome architecture is a central goal in biology. Nonetheless, genomic structural variation within species remains poorly characterized in natural populations and the molecular mechanisms underlying variation in genome architecture are largely obscure. Here, I apply theory of genetic conflict, state-of-the-art sequencing techniques and recently developed bioinformatics methods to investigate the origins of genome architecture and characterize genomic structural variation in the deer mouse (Peromyscus maniculatus), a mammalian model system for studying natural variation. In Chapter 1, I show that endogenization and subsequent invasion of divergent retroviruses ultimately gave rise to a unique genomic repeat landscape in the deer mouse relative to nearly all other studied mammals. In Chapter 2, by sequencing and comparing chromosome-level genome assemblies within deer mouse populations, I elucidate how various genomic repeats contribute to the formation of massive chromosomal rearrangements resulting in widespread intraspecific karyotype variation. Finally, in Chapter 3, I use newly developed pangenomic methods to characterize structural variation in ecologically and biogeographically diverse deer mouse populations, revealing striking gene copy number variation with likely implications in adaptation. Together this work characterizes several novel patterns of genome evolution in a mammal, providing important insight into the processes that give rise to variation in mammalian genome structure.Biology, Organismic and Evolutionar
High-Performance Photonic and Acoustic Interfaces for Qubits
No full textSolid-state-based quantum information technology has advanced significantly in recent years, with platforms such as diamond defect centers (e.g., silicon-vacancy and nitrogen-vacancy centers) playing a central role. Alongside the exploration of fundamental science, practical quantum applications demand scalable, efficient devices with ultra-low loss, high integrability, and robust fabrication processes.
This thesis focuses on the fabrication and demonstration of novel devices, motivated by the need for better quantum interfaces. Key contributions include developing methods to confine and manipulate phonons in diamond, fabricating state-of-the-art photonic crystal cavities, demonstrating novel 2D diamond devices, and integrating diamond with other materials like lithium niobate for hybrid quantum systems. Additionally, the work on compact microcavities offers the potential for diverse applications, including quantum networking, lasers, and precision sensing.
These innovations focus on different aspects of high-performance photonic and acoustic interfaces for qubits, pushing the boundaries of nanofabrication and quantum device performance and enabling scalable and practical solutions for emerging quantum technologies.Engineering and Applied Sciences - Applied Physic
The Pattern Recognizers: Surveillance, Security, and the Making of Identity in 20th Century America
No full textThis dissertation considers the historical relationship between science and surveillance in the 20th century in the United States. It centers its study on the emergence and development of pattern recognition as a scientific methodology and as a surveillance technique for recognizing identity. Across seven chapters, the dissertation shows how social scientific and technical research transformed patterns into a scientific object primed for classification. The dissertation begins with research in cultural anthropology in the early 20th century. It examines how, at the nexus of methodological, professional, and political concerns, anthropologists developed the notion that culture contains patterns. Throughout World War II, cultural anthropologists brought notions of patterning and their recognition into U.S. government agencies. Following the war, in response to existing research in anthropology and psychology, cyberneticists developed pattern perception mechanisms. While engaging with this work, in the 1950s scientists developed computers that could recognize patterns with formalized rules. Pattern recognition researchers soon advocated to U.S. intelligence agencies that their techniques could solve problems of surveillance. By the end of the 1960s, pattern recognition research had changed how intelligence agencies could conduct surveillance. Machine-classifiable patterns had become a ubiquitous object of scientific knowledge and object of surveillance. The dissertation foregrounds the often-mundane ways in which scientists have shaped the practice of surveillance, as well as how problems of surveillance have shaped the practice of science. More generally, the dissertation bridges historical epistemology with surveillance studies to excavate the historical conditions of possibility for surveillance practices today.History of Scienc
New Age
No full textNew Age is a memoir about growing up as a witness for my mother, an atheist Jew, who rejects a terminal cancer diagnosis by embracing non-western healing modalities transforming into an occult feminist, living each day full of gratitude, joy, and music.
The scene is 1980s Boston, which happens to be the perfect place for a terrible tragedy to unfold. Not only is Boston home to cutting edge western medicine, but it is also open-minded enough to support expansive, new age healing modalities, coop grocery stores, a thriving music scene and a non-western spiritual community. The story starts in December 1970, with the beginnings of my music education in utero, and chronicles the ups and downs of my family’s life through psychotic breaks, divorce, a terminal cancer diagnosis, a groundbreaking lawsuit, a major miracle, a hugging saint, and the daily traumas and magic one might expect growing up with a very non-traditional mother and the constant threat of impending death.
New Age contains many short vignettes or essay chapters which flow back and forth from past to present as I uncover buried memories and try to connect my children to the grandmother they never met. I do this work through a ketamine assisted psychotherapy session and by reconnecting with some of the esoteric healing modalities and people that helped my mother in the 1980s.
The story is told from a few points of view. There are three flavors of first-person: adult narrator talking about the present, adult narrator looking back, remembering, and child narrator, sharing the moment with the reader. There’s some third person, mostly used to give some background on my parent’s lives, to round out their characters. These chapters are usually events that I was either not alive for or too young to participate in. There’s one chapter that uses second person, where I speak directly to my mother. In addition to all of those, I include excerpts from my mother’s writing which consist of journal entries, poetry, and some prose from my personal archive.
New Age is a memoir about memory, grief, connection, music, healing, and being present in the moment.Extension Studie
Statistical Inference and Learning in Complex Experimental Settings
No full textThis thesis presents three self-contained chapters: a powerful approach to partial conjunction hypothesis testing, an online reinforcement learning algorithm for scarce resource allocation in public health settings, and an experimental design for anytime valid inference on adaptive experiments.
In Chapter 1, we propose a new method for partial conjunction hypothesis (PCH) testing, called the Conditional Partial Conjunction Hypothesis (cPCH) test. PCH tests are necessary to address important statistical questions in a diverse array of fields, from the analysis of causal graphs to the evaluation of scientific replicability. The cPCH test is less conservative, and hence, more powerful than existing approaches, and achieves particular power gains in low-signal regimes commonly encountered in applications such as genetic analysis.
In Chapter 2, we propose a new experimental design for adaptive experiments that enables continuous inference on the Average Treatment Effect (ATE), with guarantees on statistical validity and power. In contrast to existing work, our approach does not require the treatment assignment probabilities of the adaptive assignment algorithm to be bounded away from zero and one, making it applicable to nearly any adaptive experimental design, including many common multi-armed bandit algorithms like Thompson sampling and the Upper Confidence Bound method. We empirically show that our design improves the power of ATE inference while maintaining valid finite-sample coverage across a wide array of experimental settings while paying relatively little cost in reward.
In Chapter 3, we present a new online reinforcement learning algorithm for allocating scarce interventions in health program. By utilizing hierarchical Bayesian modeling approaches, our algorithm shares information within and across the program participants to learn the underlying transition dynamics quickly, even the algorithm only has a limited time horizon to interact with the system. Through an extensive simulation study, including one setting developed from real data from a mobile health service program in India, we showcase our algorithm’s ability to significantly improve retention in health program settings.Statistic
Masticatory Function and Cognitive Health: Investigating a Molecular Connection Between Oral Tissues and the Brain
No full textBackground: Amongst the rapidly growing elderly population, there is increasing need for comprehensive prosthodontic treatment to address impaired masticatory function of many etiologies3. Compromised oral health may contribute to a myriad of systemic pathologies, including cognitive decline. Several studies have observed an association between poor masticatory function in elderly patients and impaired cognitive function6. Previously, we identified a novel retrograde transport mechanism of exosomal neprilysin, a neuroprotective enzyme, from the masseter muscle to the hippocampus through the trigeminal nerve4.
Aim: This study aims to identify additional neurotrophic agents that are produced in various oral tissues (OT) and retrogradely transported to the brain.
Project-design: This study evaluates: 1) neurotrophic mRNA expression profiles in murine cells from submandibular-glands (SMG), dental-pulp (DP), brain-astrocytes (AST), and neuronal cell line (CATHa) using next-generation-sequencing; 2) protein expression of brain-derived growth factor (BDNF) and nerve growth factor (NGF) in SMG/DP cells versus AST/CATHa-cells via Western blot; and 3) the growth support of CATHa by exosomes isolated from other cells.
Preliminary-results:
- Neurotrophic mRNAs were significantly overexpressed in SMG/DP cells versuss AST/CATHa.
- Western blot analysis of BDNF/NGF protein expression in SMG/DP cells was abundant, but minimal in AST/CATHa.
Conclusion: OT-cells exhibit higher neurotrophic mRNA expression than brain-cells, with corresponding proteins abundant in OT-derived exosomes. This suggests that OTs may play a crucial role in supplying essential biomolecules to the brain. Results from this ongoing study further highlight the impact of masticatory function and oral health on systemic health and provides hope for development of therapeutics.Prosthodontic