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ESSAYS ON COMPLEX HEALTH INNOVATIONS FOR CHILDREN AND ADOLESCENTS IN FRAGILE AND CONFLICT-AFFECTED COUNTRIES
No full textFragile and conflict-affected countries (FCAS) encounter unique healthcare delivery challenges due to political instability, weak infrastructures, and often scarce resources, making traditional health service models frequently inadequate (World Health Organization [WHO], 2020). According to WHO, FCAS is a broad term describing a range of situations including humanitarian crises, protracted emergencies, and armed conflicts (WHO, 2020). These regions often deal with disrupted medical services, damage to healthcare facilities, and significant population displacement (Witter et al., 2020). FCAS lag behind more stable contexts in meeting international health goals (Burt, 2014; Organization for Economic Co-Operation and Development [OECD], 2015). Despite the significant decline in child and maternal mortality over the last 20 years, estimates indicate 60% of preventable maternal deaths, 53% of deaths in children under five, and 45% of neonatal deaths take place in FCAS (UN IGME, 2024, Zeid et al., 2015). According to the Fragile States Index, 9 FCV countries were classified as “very high alert” or “high alert”, with maternal mortality rates (MMRs) ranging from 30 (the Syrian Arab Republic) to 1223 (South Sudan) in 2020 (Fragile States Index [FSI], 2020; WHO, 2023a). Immunization rates are also critically low in these areas; five of the ten countries with the lowest coverage for the three recommended doses of diphtheria, tetanus, and pertussis vaccine (DTP3) were among the top ten countries on the Fragile States Index in 2021 (WHO & UNICEF, 2022). Approximately, 49% of children who are not vaccinated or only partially vaccinated reside in FCAS countries, making them highly susceptible to diseases, especially in these precious environments (UNICEF Data, 2023). In almost two-thirds of countries, women are more likely than men to report food insecurity, which is fueled by conflict and climate change (World Food Programme [WFP], 2021).
There is a growing focus on developing resilient health systems that can withstand ongoing conflicts and crises. A resilient health system can absorb shocks, adapt to changing conditions, and transform in ways that ensure sustainable improvements in health and well-being (Blanchet et al., 2017; Campbell, 2015; Lebel et al., 2006; Thomas et al., 2013). In FCAS, resilience in health systems is critical to ensure continuous delivery of essential health services amidst instability and violence (Truppa et al., 2024). One significant innovation is the One Health Workforce Next Generation initiative in the Democratic Republic of the Congo (DRC), which focuses on training public health leaders using mobile training units and online learning platforms to reach remote and conflict-prone areas (Kerlin, 2019; USAID, 2023). Task shifting in Nigeria is another critical strategy where community health workers are trained to perform duties typically handled by doctors, addressing workforce shortages and maintaining healthcare delivery in conflict zones (Okoroafor et al., 2023). This approach is supported by findings that CHWs in fragile settings improve service delivery to vulnerable populations, leveraging their community ties and cultural understanding (Miller et al., 2020). Technological advancements, such as telemedicine in South Sudan, have facilitated remote diagnostics and consultations, providing essential healthcare services when traditional infrastructures are compromised (WHO, 2021). In Somalia, mobile health technologies and portable diagnostic tools improve disease surveillance and data management, enabling a more efficient response to health emergencies (Exemplars in Global Health Partner Network, 2021; WHO, 2024). Additionally, the use of digital health records in the South of Chad has proven vital for maintaining continuity of care for frequently displaced populations, ensuring that patient information is accessible and up-to-date despite frequent relocations (Léchenne et al., 2024).
Despite these advancements, significant gaps remain in research and implementation in health systems within these fragile areas, primarily due to the complex nature of these environments (Blanchet et al., 2013). Implementing established health strategies and technologies is particularly challenging in FCAS compared to other equally impoverished but more stable countries (Newbrander et al., 2011). Health systems research (HSR) in FCAS is underdeveloped due to inherent difficulties such as ethical issues, field access, security concerns, data quality, local research capacity, and terminology problems (Woodward et al., 2017). Although there is limited research on adapting proven health interventions in FCAS, evidence is not always applied optimally, often because the findings become rapidly outdated due to the changing nature of these environments (Woodward et al., 2017). HSR must often be designed specifically for the unique conditions of FCAS rather than merely conducted within them (Health System Global, 2013; Newbrander et al., 2011; Swanson et al., 2015; Warsame, 2014; Woodward et al., 2017). Therefore, there is a need for innovative and customized approaches to research design and implementation in FCAS. For example, using longitudinal studies can be crucial for understanding long-term impacts on health systems (Bowling et al., 2014). Additionally, mixed methods approaches that combine quantitative data with qualitative insights can provide a comprehensive understanding of health system dynamics (Creswell & Plano Clark, 2017). Participatory action research (PAR) engages local communities and stakeholders in the research process, ensuring that the findings are contextually relevant and actionable (Baum, MacDougall, & Smith, 2006). Collaborating with local researchers and institutions enhances in-country research capacity and ensures the sustainability of research efforts (Sitthi-amorn & Somrongthong, 2000). These strategies are essential for adapting research methodologies to the complexities of FCAS and generating robust, applicable insights for health system strengthening.
Chad and Mali exemplify the severe implications of conflict on healthcare systems. Chad is grappling with political instability, frequent violence, and a lack of infrastructure, which has led to dire health outcomes for its population of approximately 18 million (World Bank Data, 2023). The country’s healthcare challenges are compounded by severe poverty and insufficient healthcare facilities, which limit access to essential services (Jaeger et al., 2018; Nassirou et al., 2005). Particularly concerning are Chad's low immunization rates and high infant mortality (Samaké-Roman, 2022; Gavi, 2023). Only a small fraction of children receives all the recommended vaccines, leading to outbreaks of preventable diseases such as measles and polio (Gavi, 2023). Additionally, Chad has one of the highest rates of infant mortality in the world, with many deaths attributed to malnutrition and preventable diseases (UNICEF, 2023). Mali, on the other hand, faces continuous security threats from insurgent groups that have destabilized the northern regions, affecting around 23 million inhabitants (Baldaro, 2019; International Peace Institute [IPI], 2019; World Bank Data, 2023). This instability hampers healthcare delivery and exacerbates issues such as high maternal and infant mortality rates and limited access to essential health services (Ataullahjan et al., 2020; Degni et al., 2015; Masset, 2022; Tsujimoto & Kijima, 2020). In addition to these challenges, Mali struggles with endemic diseases such as malaria and tuberculosis, which thrive in conditions where healthcare access is sporadic, and the population is frequently displaced (Debarre, 2018; WHO, 2023b). The ongoing conflict has also led to significant mental health issues, with a large portion of the population experiencing trauma and stress without adequate psychological support services (Debarre, 2018; Poudiougou et al., 2021; Sekou et al., 2012; WHO, 2022). Both Chad and Mali exemplify the severe implications of conflict on healthcare systems and the urgent need for tailored health interventions that address both the immediate and long-term needs of their populations.
Present dissertation papers
This dissertation integrates three distinct papers, each exploring innovative approaches to healthcare in medically challenging and socio-politically complex environments. The overarching problem addressed is the introduction and implementation of complex health innovations in fragile settings, where both the innovation and the context present significant complexities. Through various methods and different tracers, these papers collectively aim to shed light on health innovations impacting child and adolescent outcomes. The collective goal of these papers is to provide a framework for the design, integration, and expansion of such interventions in countries affected by fragility and conflicts. It addresses key issues related to the implementation and scale-up of complex innovations in these settings, contributing to the broader discourse on improving healthcare systems under conditions of uncertainty and adversity.
As previously noted, conventional healthcare delivery systems fall short of meeting the population’s needs in FCAS (WHO, 2020). Innovative and adaptive healthcare strategies are essential to ensure continuous healthcare services. One such approach is the proactive community case management (ProCCM) strategy, which has shown potential in improving child health outcomes in Mali (Johnson et al., 2018). ProCCM involves training and deploying community health workers (CHWs) to actively seek out and treat common childhood illnesses, rather than waiting for patients to seek care (Whidden et al., 2019). This strategy is particularly effective in Mali, where access to formal healthcare facilities is limited. By bringing healthcare services directly to the community, ProCCM addresses both the access and availability issues prevalent in FCAS. This innovative approach is vital in FCAS because they utilize the trust and local knowledge inherent in CHWs (Grant et al., 2017). These workers are often community members themselves, which typically results in higher levels of trust compared to external health providers, an essential element in areas where skepticism towards outsiders may be prevalent due to ongoing conflicts or socio-political unrest (Shepard, 2016). Additionally, the local knowledge CHWs bring to their roles allows them to tailor health interventions in culturally sensitive ways, enhancing both receptiveness and effectiveness. This adaptability is crucial for addressing the specific health challenges and barriers that communities in conflict zones face (Miller et al., 2020). However, CHWs encounter several challenges. Logistically, they often operate in environments with underdeveloped infrastructure, complicating efforts to reach patients or deliver supplies (Miller et al., 2020). Security concerns are paramount, as CHWs can be at risk of harm while fulfilling their responsibilities in unstable regions (Miller et al., 2020). Moreover, they often lack sufficient professional support from the formal healthcare system and may face high levels of stress and fatigue, leading to potential burnout due to their demanding roles and the critical nature of their work (Johnson et al., 2022). As for the numbers and coverage of CHWs in Mali, the country has taken significant steps to expand its network of community health workers to tackle widespread health access issues (Oliphant et al., 2022). Mali's community health program is designed to provide extensive coverage, especially in rural and underserved areas, with thousands of CHWs trained and deployed throughout the nation (Ministère de la Santé et de l’Hygiène Publique [MSHP], 2015). These workers handle various tasks, from maternal and child health to managing non-communicable diseases and preventive care (MSHP, 2015). Despite these efforts, the CHW-to-population ratio remains variable and is influenced by several factors, including funding, regional health priorities, and ongoing security challenges (MSHP, 2015). The need for a more systematic approach to scaling up and evaluating the impact of CHWs in Mali is a critical part of ongoing public health discussions in the country (MSHP, 2015).
Building on this, my first dissertation paper is motivated by the need to improve healthcare delivery in FCAS and addresses the gap in evidence by providing insights into the operational dynamics and impact of CHW programs, specifically, assessing the effectiveness of ProCCM on reducing all-cause under-five mortality (U5MR) compared to a traditional iCCM, which involves a fixed, site-based passive workflow, delivered by CHWs. This study, structured as a pragmatic, cluster-randomized controlled trial in the Bankass health district of the Mopti region in Mali, aims to fill the gap by estimating the intervention effects using a mixed-effects logistic regression model on the intention-to-treat population. The findings highlight the challenges of implementing and evaluating complex health interventions in FCAS. The insights from this study provide crucial guidance for the optimal deployment of CHWs, not only in Mali but across similar settings in sub-Saharan Africa, potentially informing the design and scale-up of analogous CHW initiatives.
Digital solutions are increasingly recognized as a transformative tool for improving health outcomes in sub-Saharan Africa (Ibeneme et al., 2022; Jousset et al., 2023; Kipruto et al., 2022; Rinke de Wit, 2022; Olu et al., 2019). Specifically, digital health technologies are essential for enhancing healthcare access in FCAS (Pattanshetty et al., 2024). The use of suitable and customized digital tools can improve the quality, accessibility, and availability of healthcare services (Marwaha et al., 2022). Additionally, digital payments facilitate the secure and transparent transfer of funds, crucial for mobilizing resources and ensuring that they reach the intended recipients without delays and risks associated with cash transfers (Nimpagaritse et al., 2020; Pazarbasioglu et al., 2020). Moreover, digital payment platforms enable better tracking and accountability of funds, vital in settings where corruption and mismanagement are prevalent (Pazarbasioglu et al., 2020). However, challenges such as unreliable infrastructure, including intermittent internet and power supply, often hinder their effectiveness (Ibeneme et al., 2022). By integrating technology into healthcare delivery, this approach streamlines the process of payment for workers. Although there is increasing focus on payment digitization, there is limited rigorous evidence on the impacts on health system outcomes (Joshi et al., 2020; Muralidharan et al., 2017). Nevertheless, the deployment of these systems must consider the local context to address specific barriers such as financial literacy and access to mobile technology, ensuring that digital payment solutions are accessible to all members of affected communities (Cambaza, 2023; Klapper & Bull, 2023).
In the context of limited evidence on the experiences of health workers and managers in rolling out digital payment systems, my second dissertation paper investigates the implementation of a digital payment system for immunization workers in Chad. This research assesses the relationship between the intervention and job motivation and satisfaction. Employing a mixed-methods approach, this study combines a quantitative one-time survey with qualitative semi-structured interviews to provide a comprehensive analysis of the intervention's implementation. The novelty of this study is two-pronged: (1) the application of expectancy theory to understand the complex mechanisms by which digital payment systems influence health workers’ motivation and job; and (2) the use of mixed methods, which are particularly suited and necessary for understanding the multifaceted challenges in FCAS. These insights will inform policymakers and health administrators aiming to implement digital payment systems to strengthen health services and improve public health outcomes in low- and middle-income countries (LMICs).
Even with significant strides in lowering new HIV infections and improving access to effective treatments, governments face substantial difficulties in addressing HIV care in FCAS (UNAIDS, 2019; UNAIDS, 2024). Individuals in these regions often face severe difficulties, including reduced or complete loss of access to HIV prevention, treatment, care and support services (UNAIDS, 2024). For example, less than 20% of people in FCAS receive antiretroviral therapy (ART) (Ferreyra, 2014). In Chad, the HIV epidemic disproportionately affects youth, with stark disparities in access to treatment and testing (UNAIDS, 2023). According to UNAIDS (2023), in 2022, an estimated 26.3% of new HIV infections in Chad were in youth (ages 15-24 years) (UNAIDS, 2023). Additionally, young women continue to suffer disproportionately from the epidemic, more specifically due to the HIV triple threat from the combination of new HIV infections, sexual and gender-based violence (SGBV), and adolescent pregnancies (Global Communities, 2022). In 2022, young women had HIV infection rates four times as high as men, accounting for 19.5% of all new infections in Chad (UNAIDS, 2023). Despite efforts to improve health education and services, only a fraction of HIV-positive children and adolescents receive the necessary retroviral treatment, and there is a lack of consistent supply of antiretrovirals (ARVs) and adequate healthcare infrastructure (Chad DHS 2014-15, 2015). For instance, only 22% of HIV-positive children in Chad have access to necessary treatment, with reported irregular availability of ARV drugs and insufficient pediatric care provisions (UNICEF, 2023b). Overall, the data underscores the need for Chad to intensify efforts for addressing the HIV epidemic among young populations, emphasizing gender-sensitive approaches and improving healthcare access and quality to curb the epidemic’s impact on adolescents (UNICEF, 2023b; UNICEF, 2023c). To optimize HIV services for adolescents in Chad, there needs to be a concerted effort to make these services more accessible, confidential, and tailored to the diverse needs of young people.
My third dissertation paper is a secondary data analysis from a parent study employing grounded theory design to understand youth’s sensemaking and service utilization in the context of SRH and HIV care in Chad (Bedingar et al., 2024). This study focuses on the pathways to care for youth in Chad from diagnosis to ART adherence. We analyze the data collected using thematic analysis to identify barriers and facilitators to HIV care. The novelty of this study lies in its grounded theory approach and youth-centric focus, providing a comprehensive and in-depth understanding of the specific needs and challenges of adolescents in accessing HIV care in Chad. Research on HIV in youth in sub-Saharan Africa, especially in FCAS, is lacking. The findings suggest that tailored interventions that are culturally sensitive and context-specific are likely to be more effective. These interventions could serve as models for similar settings in sub-Saharan Africa, contributing to improved HIV care and outcomes for youth across the region.
These examples underscore the urgent need for innovative healthcare strategies in FCAS. The findings from the three papers demonstrate that by addressing specific challenges and integrating both local insights and global health innovations, we can identify promising strategies to enhance health outcomes in some of the world’s most challenging environments.Population Health Science
Selective Elimination of Vibrio Pathogens via the Synergy of a Type Six Secretion System and a Natural Phenazine Antibiotic
No full textVibrio species are most often studied in the context of human disease; multiple Vibrio species, including Vibrio cholerae, are widespread mammalian pathogens. In this work, we describe the isolation of a vibriocidal strain of Aeromonas dhakensis, named A603. We determine that its vibriocidal activity comes from a synergy between A603’s Type Six Secretion System and a synthesized phenazine antibiotic, AdPhen. Remarkably, non-Vibrio taxa resist this killing. We identify 3 systems in Vibrio strains that confer increased AdPhen resistance. However, A603’s T6SS activity overcomes efflux-mediated AdPhen resistance in newly generated V. cholerae mutants, likely through membrane potential dissipation and disruption of essential cation gradients. A603 uses both AdPhen and its T6SS to protect the host from invading Vibrio pathogens, like AHPND strains of V. parahaemolyticus. A603 guards aquatic hosts from AHPND-related microbiome disruptions without significant host colonization or changes to native flora. A603’s easy application, low colonization of hosts, and minimal alteration of microbiome composition or function makes it a promising new probiotic for prevention of vibriosis in aquatic hosts. While A603 itself cannot colonize mammalian hosts, the lessons learned from its activity can be leveraged to improve prophylaxis and treatment of Vibrio diseases, including cholera.Biological and Biomedical Science
Propensity Scores for Causal Inference under Partial Interference
No full textIn observational studies across fields like public health, education, and social science, treatment assignments often influence each other. While recent research in causal inference has focused more extensively on spillover effects, where one person's treatment affects another person's outcomes, far less attention has been paid to how treatment assignments themselves might interact. This oversight is particularly problematic in settings where peer influence is likely to occur, as resulting causal inferences may be significantly biased or flawed.
This thesis develops novel methods for modeling dependent binary treatment assignments under partial interference, a setting where units only interact within known clusters, although our approach can be extended to arbitrary known networks. We propose a flexible Ising model framework that captures pairwise treatment dependencies as functions of observed covariates, generalizing standard logistic regression and including mixed-effects logistic regression as a special case. To address computational challenges, we develop a maximum pseudo-likelihood estimator (MPLE) with theoretical consistency guarantees and explore approximation techniques like loopy belief propagation for computing joint distributions.
Through extensive simulations and an empirical analysis of COVID-19 vaccination data from Nigeria, we demonstrate that models neglecting within-cluster dependencies produce biased and high-variance estimates. Our Ising model consistently outperforms standard approaches, offering robust performance across prediction, treatment effect estimation, and individualized policy learning tasks. To help with efficient predictions, we also introduce a novel algorithm for computing the most likely cluster-level treatment assignment under mixed-effects logistic regression.Computer Scienc
Comparing Bite Force Distribution to Periodontal Support Markers of Lower Anterior Teeth in Orthodontically Untreated Adults using T-scan
No full textA crucial challenge for orthodontists is to fully analyze the components of a patient's malocclusion and address the needs of the patient by providing orthodontic treatment that adjusts the individual's natural balance harmoniously. To meet targeted objectives such as esthetics, function, and stability by positioning the teeth within the dentoalveolar housing, it is critical to expand our understanding of bite force distribution as it can significantly improve treatment planning and mechanotherapy of orthodontic patients. Digital occlusion analysis systems can offer this information rapidly and accurately at the initial patient visit. Conventional methods, such as the use of occlusal marking paper and intraoral scanners, deliver an incomplete record in comparison. The objective of this investigation was to identify a relationship between bite force distribution in centric relation and periodontal health. T-scan technology was utilized to record premature contacts, heavy forces, and right, left, anterior, posterior, and single tooth force distribution. For the study, a sample of 26 orthodontically untreated adults aged 18 to 40 was recruited during consultations for comprehensive treatment at the Orthodontic clinic at Harvard School of Dental Medicine. Inclusion criteria for participants required them to be within the skeletal range of -7°°, to be in permanent dentition. Exclusion criteria included patients with a history of orthodontic care, those with craniofacial defects, musculoskeletal disorders, and participants whose wisdom teeth were involved in occlusion. The null hypothesis posited that bite force distribution would not correlate directly with markers of periodontal health. To analyze periodontal support, the study focused on collecting ultrasound measurements of the buccal bone and soft tissue surrounding the six mandibular anterior teeth. The positioning of these specific teeth has long since been regarded as crucial for establishing a healthy and well-balanced occlusion. Additionally, cephalometric indicators of lower anterior tooth positioning, such as IMPA and L1-NB, were analyzed to assess their role in the interplay between occlusion and periodontal support. In our study, we could not identify a statistically significant correlation between bite force distribution and the measurements of periodontal tissue thickness. However, analyses suggest potential relationships between the cephalometric positioning of the lower incisors and the robustness of the soft tissue housing. Future research will need larger sample sizes to more thoroughly explore the relationship between bite force equilibrium and periodontal support.Orthodontic
Lagos: The Forms and Dissolutions of a Postcolonial Megacity
No full text“Lagos is a complex entity that subverts common expectations. It is not just its demographic size that makes it a megacity, but also its social and cultural contradictions … a mega-slum and megacity -- in that order.”
-- Oka Obono (2007)
The sociologist Oka Obono’s characterization of Lagos brings to the forefront the opposing realities of (post)colonial African urbanisms more generally: abundance as opposed to scarcity, colonial hegemony as opposed to cultural diversity, and crippling elitism as opposed to the lived experiences of the vast majority of urban dwellers experiencing poverty. Urban landscapes are inevitably marked by the fluidity of the spaces produced by contradictions like these—a fluidity that, in Lagos, is marked by the richness of culture and vibrancy of peoples while at the same time making manifest oppression, suffering, and collective trauma. The interaction of group identity and physical space here is simultaneously reciprocal and contested, uniting and fracturing.
With Lagos as its focus, this dissertation addresses the interaction of group identity and physical space by bringing several disciplinary perspectives into conversation: urban planning, preservation, anthropology, religion, and postcolonial theory. It takes as its subject a city whose constituent parts, which are bound by water, serve as the unstable container for dramatic ethnic and religious differences, for competing narratives of cultural identity, and for profound socioeconomic divide. Indeed, ethnic and religious contestation, marginalization, and inequality in Lagos exemplify the non-neutrality of physical spaces in which they are made visible. The built environment is both the container of inequality and the stage on which colonial pasts, cultural hierarchies, and social exclusions continuously play out. So, what are the means of describing Lagos in all this complexity? How might such a description lead to a better understanding of the urban environment and to proposals for a more equitable and just city?
The dissertation is structured by a sequence of chapters in which the aforementioned non-neutrality of physical space is foregrounded at different urban scales: first, how the traces of colonial urbanism leave their imprint on modern networks; second, how the urban governance and planning interact with current social hierarchies in contexts such as outdoor markets; and, finally, how the physical manifestation of urban informalization offers up forms of resistance. These chapters and the scales they offer as objects of study—the urban grid, the streetscape, and the informalized district—speak in different ways to broader issues of social inequality, the physical unfolding of the urban fabric, and the ways in which this urban fabric shapes and reflects identity, hierarchy, culture, and exclusion. They exemplify the different modalities that construct various political narratives of place in Lagos, resulting in vastly unequal distributions of capital and services.Advanced Studies Progra
Volatility and Resilience in Islamic vs. Conventional Equity Markets: A Time-Frequency Analysis of Sharia-Compliant Firms
No full textWe investigate the impact of sharia-compliancy on firm-level and market-level resilience during periods of economic stress, using the 2014-2016 oil price collapse as a case study. We evaluate financial and liquidity performance across a panel of firms representing markets with a spectrum of permeance of Islamic finance. In parallel, we implement state-space multitaper spectral analysis, GARCH volatility modeling and Markov regime switching models to examine the time-frequency behavior of stock returns and transitions across volatility regimes. Our findings suggest that Sharia-compliant firms maintain better liquidity ratios in the post-shock period and display distinctive volatility dynamics, including lower persistence in higher-volatility regimes and a faster return to baseline states. However, there exists a trade-off as they also demonstrate increased reactivity to price fluctuations as compared to their conventional counterparts.Applied Mathematic
Pathways to Progress: The Role of Academic and Technical High Schools in Black Economic Advancement, 1900-1940
No full textThis thesis examines the role of high school education in stimulating Black economic progress from 1900-1940 by tracing the outcomes of Blacks who attended high school in the Jim Crow South. By utilizing linkages of people across Census years and a novel hand-classified dataset of 1,500 Black high schools built in the South between 1900 and 1940, I estimate the returns to schooling for Blacks who attended academic versus technical high schools along the lines of wages, white-collar labor force participation, and migration. I find that Blacks who attended academic high schools earned higher wages, worked white-collar jobs with higher frequency, and migrated with less frequency compared to Blacks who attended technical high schools. This thesis contributes to an important literature on the relationship between school quality and earnings and the muted progress of Blacks in the 20th Century relative to other racial groups. By allowing Black Americans to have a more general and adaptable education, I argue that academic schools helped Blacks retain their skills in the face of technological change, and greater access to academic high schools would have accelerated Black economic progress during this period.Applied Mathematic
Graph Embeddings for Harvard Widener Library Data
No full textIn this project, I consider complications with retrieval of resources in a database, particularly library entries and a catalog, and consider how graph machine learning can aid in that retrieval pro- cess. Typical retrieval systems are exclusively text-based. This means that they will rely on natural language models only when making determinations about which resources might be relevant for the user. Natural language data is indispensable and at the core of how search engines operate. One can embed the query and all entries in a coordinate space and then find the closest entries based on some distance metric to get the most relevant search results. However, limiting the model to just this natural language data is letting go to waste one of the most powerful tools for understanding the relationships between entries: keywords.
By including keywords in the model, we can understand the hierarchical nature of the relationships between entries and keywords and among the keywords themselves, and this gives us additional information about the extent to which entries might be related when the text might be deceiving at face value. This introduces a new complication, however, as the keywords and entries are related in a graph structure. The keywords and entries are nodes and relations indicate the connection between an entry and a keyword that describes that entry. Since computers cannot look at a graph and make sense of it like humans can, we must use graph machine learning techniques to embed the graph into a coordinate space. Then, we can use the coordinates to make conclusions about the relatedness of entries and the relevance of search results. This gives use a new way to approach retrieval and can be paired with the common natural language model approach to enhance retrieval and return more relevant results to the user.Computer Scienc
Seeking the Brain’s Compensatory Healing Mechanisms: A Clinical Application of Neuroplasticity-based Tools to Advance Neurorehabilitation
No full textPaper 1: Clinical Characteristics Associated with the PLP-PLS Index, a New Potential Metric to Phenotype Phantom Limb Pain
Abstract
Background: Phantom limb pain (PLP) is highly prevalent after amputation. However, the influence of non-painful sensations (PLS) remains unclear. This study examines the PLP-PLS index as a novel tool to differentiate PLP from PLS and explores the association of clinical factors with the index.
Methods: We conducted a cross-sectional analysis of baseline data from 112 participants in a previous factorial trial in patients with unilateral traumatic lower limb amputation. Linear regression models were used to examine the associations between the index and various demographic, psychological and clinical factors. Logistic and Poisson regression, and e-value calculation were utilized for sensitivity analyses.
Results: Adjusted multivariable linear regression models demonstrated significant associations of phantom movement sensation (β: -1.532; 95% CI: -2.615 to -0.449; p = 0.006) and time since amputation (β: 0.005; 95% CI: 0.0006 to 0.0101; p = 0.026) with the PLP-PLS index. These findings were confirmed by multivariable logistic regression (phantom movement sensation OR: 0.469; 95% CI: 0.200 to 1.099, p = 0.082; time since amputation OR: 1.003; 95% CI: 1.00003 to 1.007; p = 0.048) and sensitivity analyses.
Conclusions: Time since amputation and phantom movement sensation likely reflect distinct phenotypes and potential mechanisms for PLP and PLS. The PLP-PLS index is a promising clinical tool for selecting therapies to prevent/treat PLP and for measuring treatment effects to modulate phantom pain. These findings emphasize the importance of understanding the mechanisms underlying PLP and PLS for improving clinical management and guiding future research.
Paper 2: A Salutogenic Signature of the Placebo Effect in Brain Oscillations: A systematic review and meta-analysis
Abstract
Background: The placebo effect is increasingly acknowledged as a component of rehabilitation interventions, however its characterization and quantification remain poorly explored. This study investigates brain oscillatory activity as a biomarker for the placebo effect's neural mechanisms.
Methodology: A systematic literature review up to January 2025 searched PubMed, Embase, and Cochrane databases for randomized controlled and cross-over trials reporting brain oscillations in resting state from placebo-controlled neurorehabilitation trials in healthy and subjects with neurological disorders. The analysis included a semi-quantitative (albatross plots), and quantitative meta-analysis (Hedge’s g), focusing on the effect sizes of power differences between placebo and active groups.
Results: We included 63 studies with 180 healthy subjects and 1,758 neurological disorder patients. In healthy subjects, placebo showed an increase in alpha power compared to no intervention (g = 0.45, 95% CI [0.09; 0.8]). In patients, sham interventions elevated alpha power in frontal (g = 0.08, 95% CI [0.07; 0.08] ), central (g = 0.55, 95% CI [0.47; 0.65]), and parietal areas (g = 0.28, 95% CI [0.18; 0.44]), as well as beta (g = 1.31, 95% CI [1.06; 1.63]) and theta central (g = 0.58, 95% CI [0.46; 0.72]). However, these effects were non-significant when compared to active interventions.
Conclusion: Alpha oscillations in fronto-central regions are the primary biomarkers of the placebo effect, with beta and theta oscillations also indicative, especially in patients with neurological disorders. These effects were reversed when compared to active interventions, suggesting that active rehabilitation also encompass the placebo effect. Intriguingly, these placebo effects vary based on baseline brain activity, highlighting a tendency towards more stable, salutogenic rhythms in different populations.Medical Scienc
Spin-Phonon Coupling in Nanodevices
No full textMany physical implementations of quantum bits interact to varying degrees with mechanical
vibrations. The ability to nanostructure a qubit’s local environment presents new opportunities
to utilize mechanical modes in a coherent spin-phonon interface, and to connect different types
of quantum systems. Some solid-state spin qubits like the silicon vacancy center (SiV) in diamond
have notably large strain susceptibilities. Integrating SiV centers with engineered wavelength scale
nanomechanical resonators can provide the high quality factors and small mode volumes required to
enhance the strength of spin-phonon interactions towards the quantum coherent regime.
This thesis details the characterization of high Q factor optomechanical crystal (OMC) resonators
in diamond with coupled intracavity SiV centers. We make use of the resonant SiV-optical
cavity spin-photon interface to probe the spin’s coherence properties and to observe spectroscopic
signatures of spin-phonon coupling when the mechanical modes of the structure are near their motional
ground state. We independently probe the frequency and intrinsic linewidth of the mechanical
swelling mode of the OMC via the optomechanical interaction. We observe that mechanical
dissipation currently limits the cooperativity of the spin-phonon interface. We discuss how future
devices could eventually reach the quantum coherent coupling regime.Engineering and Applied Sciences - Engineering Science