Alliance One Tobacco (Malawi)
Academic Research Repository at the Institute of Developing EconomiesNot a member yet
52305 research outputs found
Sort by
The Quest for Educational Equity in Mexico
No full textAbstract
I examine the dynamics of implementing at-scale reforms to provide meaningful educational opportunities to disadvantaged students in Mexico. To effectively reduce social inequality and exclusion, education policies need a mix of system-wide and targeted efforts that are implemented at scale and sustained long enough to become institutionalized. The resiliency of those policies requires an elusive balance between system-wide and targeted efforts, alignment between federal and state initiatives, and supportive politics. However, the politics of implementing system-wide reforms are more contentious than those involving targeted efforts because they disrupt entrenched interests, making such efforts harder to sustain. Targeted policies, while easier to implement, reinforce the segregation of students into different educational tracks of varying quality
Genome-wide association analyses identify 95 risk loci and provide insights into the neurobiology of post-traumatic stress disorder
No full textPosttraumatic stress disorder (PTSD) genetics are characterized by lower discoverability than most other psychiatric disorders. The contribution to biological understanding from previous genetic studies has thus been limited. We performed a multi-ancestry meta-analysis of genome-wide association studies across 1,222,882 individuals of European ancestry (137,136 cases) and 58,051 admixed individuals with African and Native American ancestry (13,624 cases). We identified 95 genome-wide significant loci (80 novel). Convergent multi-omic approaches identified 43 potential causal genes, broadly classified as neurotransmitter and ion channel synaptic modulators (e.g., GRIA1, GRM8, CACNA1E ), developmental, axon guidance, and transcription factors (e.g., FOXP2, EFNA5, DCC ), synaptic structure and function genes (e.g., PCLO, NCAM1, PDE4B ), and endocrine or immune regulators (e.g., ESR1, TRAF3, TANK ). Additional top genes influence stress, immune, fear, and threat-related processes, previously hypothesized to underlie PTSD neurobiology. These findings strengthen our understanding of neurobiological systems relevant to PTSD pathophysiology, while also opening new areas for investigation.Accepted Manuscrip
Integrating Spin Defects with Thin-Film Silicon Carbide Devices
No full textThin film silicon carbide (SiC) is a material used in commercial power electronics, and finding application in quantum information processing, microelectromechanical systems, photonics, and harsh environment sensors. Desirable in these applications is obtaining thin film-suspended device layers of undoped silicon carbide, which could be used as the basis of SiC-on-insulator (SiCOI) or for suspended photonics. It is an open challenge to obtain scalable thin films of single crystal silicon carbide, a challenge addressed in detail in this dissertation by implementing a dopant free photoelectrochemical (PEC) etching of SiC. In this dissertation we examine several incarnations of suspended SiC devices, and examine their potential for use in spin defect control, mechanical oscillators, and optical cavities.
In initial experiments, the photoluminescence and spin properties of ensembles of color centers in silicon carbide are enhanced by fabricating optically isolated slab waveguide structures using a doped PEC process and carefully controlling annealing and cooling conditions. We find that the photoluminescence signal of an ensemble of implanted defects is enhanced in slab waveguides by an order of magnitude over identically implanted bulk defects. The slab waveguide-enhanced photoluminescence of several defect species is used to study recombination and diffusion in the presence of thermal annealing with both rapid quench cooling and a longer return to ambient conditions. The confined mechanical geometry of a thin film is exploited to measure the spin-strain coupling of the negatively charged silicon monovacancy. The methods in this work can be used to exercise greater control on near-surface emitters in silicon carbide and better understand and control the effects of strain on spin measurements of silicon carbide based color centers. On the basis of these results we conclude that the properties of defects and devices are likely strongly degraded by the use of heavily doped epilayers.
Consequently, we reexamine in detail and then redesign the photoelectrochemical etching process used to suspend the devices to be compatible with a fully undoped device layer of SiC. PEC etching is a simple, rapid means of wet processing SiC, including the use of dopant selective etch stops that take advantage of mature SiC homoepitaxy. However, dopant selective photoelectrochemical etching typically relies on highly doped material, which poses challenges for device applications such as quantum defects and photonics that benefit from low doping to produce robust emitter properties and high optical transparency. In this work, we develop a selective photoelectrochemical etching process that relies not on high doping but on the electrical depletion of a fabricated diode structure, allowing the selective etching of an n-doped substrate wafer versus an undoped epitaxial (carrier density of 1(10)^{14}\unit{\cm}^{-3}) device layer. We characterize the photo-response and photoelectrochemical etching behavior of the diode under bias and use those insights to suspend large (100\unit{\um}\times100\unit{\um}) undoped membranes of SiC. We further characterize the compatibility of membranes with quantum emitters, performing comparative spin spectroscopy between undoped and highly doped membrane structures, finding the use of undoped material improves ensemble spin lifetime by . Furthermore, we examine these use of these films in the initial incarnations of photonic crystal cavities and mechanical "trampoline" type oscillators. This work enables the fabrication of high-purity suspended thin films suitable for scalable photonics, mechanics, and quantum technologies in SiC.
Next, we consider electrically driven mechanical oscillators fabricated using a front-side back-side dry etch, known as Lateral Overtone Bulk Acoustic Resonators (LOBARs) and the coupling of their dynamic strain to defect centers in the SiC. Here we report acoustic spin control of naturally occurring negatively charged silicon monovacancies in a lateral overtone bulk acoustic resonator that is based on 4H silicon carbide. We show that acoustic driving can be used at room temperature to induce coherent population oscillations. Spin acoustic resonance is shown to be useful as a frequency-tuneable probe of bulk acoustic wave resonances, highlighting the dynamical strain distribution inside a bulk acoustic wave resonator at ambient operating conditions. Our approach could be applied to the characterization of other high quality-factor micro-electro-mechanical systems and has the potential to be used in mechanically addressable quantum memory.
Finally, we consider an unconventional means of introducing defects into already suspended material through the process of energetic laser irradiation (referred to here as "laser-writing"). High-yield engineering and characterization of cavity-emitter coupling is an outstanding challenge in developing scalable quantum network nodes. Ex-situ defect formation systems prevent real-time analysis, and previous in-situ methods are limited to bulk substrates or require further processing to improve emitter properties. Here, we demonstrate direct laser-writing of cavity-integrated spin defects using a nanosecond-pulsed above-bandgap laser. Photonic crystal cavities in 4H-silicon carbide serve as a nanoscope monitoring silicon monovacancy defect formation within the approximately 200\unit{\nm}^3 cavity mode volume. We observe spin resonance, cavity-integrated photoluminescence, and excited-state lifetimes consistent with conventional defect formation methods, without need for post-irradiation thermal annealing. We further find an exponential reduction in excited-state lifetime at fluences approaching the cavity amorphization threshold and show single-shot annealing of intrinsic background defects at silicon monovacancy formation sites. This real-time in-situ method of localized defect formation, paired with cavity-integrated defect spins, is necessary towards engineering cavity-emitter coupling for quantum networking.
The proceeding work establishes a basis for the fabrication of integrated quantum systems using silicon carbide and the defects therein, from the incorporation of defects through laser writing, to the creating of nanofabricated geometries using PEC etching, to the control and read-out of their ground state spins using mechanical resonators. Though the experiments herein often investigate different devices, defects, and techniques, the underlying theme is same: improving the integration of spin defects in SiC with realistic devices that could lead to their use in quantum sensing and information processing.Engineering and Applied Sciences - Applied Physic
How the Evolution of American Society Has Made the American Populace Less Likely to Survive Should Nuclear War Occur
No full textThe “end” of the Cold War along with the technological and societal changes
which occurred thereafter within the United States, especially following the terrorist
attacks of September 11, 2001 have had an undeniable impact on the likelihood that
American citizens and American society as a whole could survive nuclear attacks on the
American homeland. While the Cold War required the American populace to face the
realities of the potential for nuclear war with the Soviet Union, and potentially the
People’s Republic of China, the post-September 11th era required Americans to shift their
focus to the realities of the potential for terrorist attacks on American soil. Although this
shift in priorities seemed justified following the terrorist attacks at the turn of the
millennium and has been further justified by subsequent attacks, both in the United States
and abroad, the threat posed by nuclear weapons has not dissipated nor disappeared. With
the Russian invasion of Ukraine and Vladimir Putin’s nuclear saber rattling directed
towards the West, and the United States in particular, paired with the tensions and
conflicts in the Middle East and the reality that Iran could obtain nuclear weapons in an
alarmingly short time span, it is clear that the importance and potential threat of nuclear
weapons was not relegated to the 20th century.
The shift from being concerned about nuclear weapons to being concerned about
terrorism was justified. However, in making this transition the American populace and
government have neglected to remember the important lessons of the Cold War and the
threat that nuclear weapons will pose, for as long as they exist. Thus, it is necessary to
better understand how American society has changed since the early days of the Cold
War so that it can be understood if America is prepared to survive a nuclear conflict
should it occur. The existence of nuclear weapons denotes the possibility of nuclear war
and this is an inescapable reality of the world we live in. The nuclear taboo is simply that,
a taboo, and there is nothing guaranteeing that nuclear weapons will not be used in any
war or conflict, either ongoing or upcoming, if the participants are nuclear powers. The
threat of nuclear war has not dissipated with time, yet our readiness for such a catastrophe has
Real Bubbles, Synthetic Traders: AI-Agent-Based Simulations of the Speculative Market
No full textWith the rise of agentic AI comes a powerful opportunity to rethink how we model
economic complexity and nonlinear systems. I create an extensible, AI-agent-based
market simulation sandbox for exploring behavioral finance questions and speculative
dynamics. This paper presents the first AI-agent-based simulation of a speculative
stock market built on a general-purpose agentic framework—a high-quality, consumerfacing software development kit (SDK) rather than a bespoke, special-purpose scaffold
around a LLM using chat completions API features. The framework is fully customizable, enabling researchers to design and run experiments by defining trader archetypes,
injecting news shocks, testing different market microstructures, and observing interactions—including those via a simulated social platform, enabling rich experimentation
with speculation, herding, pricing dynamics, and financial stability. Empirical simulation results echo findings from prior literature while introducing new nuance. Across
markets with varying share of trader archetypes, results show that trading volume
negatively predicts future returns when irrational agents dominate, suggesting that
high-volume events can signal upcoming price reversals. In contrast, even though results show that rationalists reduce momentum overall, when they do trade in high
volume, it’s often with conviction, which can support trend continuation (i.e., real
momentum). These findings point to a possibly more nuanced relationship between
volume and returns — one distinctly modulated by the rationality of market participants. Notably, this does not imply that rational markets exhibit more volume
overall (simply because prices may appear more supported); rather, it reflects a shift
in the informational character of volume—from noise to signal—as market composition
increases in rational agents. Lastly, volume and rationality in my simulations are uncorrelated, suggesting their separate influences on price dynamics are not confounded
— but rather, arise endogenously from the system’s own emergent complexity. This
study demonstrates the viability of AI-agent-based simulations and their potential to
generate nuanced insight into enduring financial economics questions.Applied Mathematic
Growth Through Inclusion in South Africa
No full textIt is painfully clear that South Africa is performing poorly, exacerbating problems such as inequality and exclusion. The economy’s ability to create jobs is slowing, worsening South Africa’s extreme levels of unemployment and inequality. South Africans are deeply disappointed with social progress and dislike the direction where the country seems to be heading. Despite its enviable productive capabilities, the national economy is losing international competitiveness. As the economy staggers, South Africa faces deteriorating social indicators and declining levels of public satisfaction with the status quo. After 15 years, attempts to stimulate the economy through fiscal policy and to address exclusion through social grants have failed to achieve their goals. Instead, they have sacrificed the country's investment grade, increasing the cost of capital to the whole economy, with little social progress to show for it. The underlying capabilities to achieve sustained growth by leveraging the full capability of its people, companies, assets, and knowhow remain underutilized. Three decades after the end of apartheid, the economy is defined by stagnation and exclusion, and current strategies are not achieving inclusion and empowerment in practice.
This report asks the question of why. Why is the economy growing far slower than any reasonable comparator countries? Why is exclusion so extraordinarily high, even after decades of various policies that have aimed to support socio-economic transformation? What would it take for South Africa to include more of its people, capabilities, assets, and ideas in the functioning of the economy, and why aren’t such actions being undertaken already? The Growth Lab has completed a deep diagnostic of potential causes of South Africa’s prolonged underperformance over a two-year research project. Building on the findings of nine papers and widespread collaboration with government, academics, business and NGOs, this report documents the project’s central findings. Bluntly speaking, the report finds that South Africa is not accomplishing its goals of inclusion, empowerment and transformation, and new strategies and instruments will be needed to do so. We found two broad classes of problems that undermine inclusive growth in the Rainbow Nation: collapsing state capacity and spatial exclusion.Version of Recor
Words Speak As Loudly As Actions: Deep Learning Methods For Stance-Based Ideal Points From Congressional Speeches
No full textThis thesis presents a framework for analyzing text data to extract ideological positions, with a particular application to estimating legislators’ ideal points from their speeches. Traditional vote-based methods such as DW-NOMINATE capture limited information from binary roll-call votes, while existing text-based methods rely solely on the lexical co-occurrence of words, leaving a gap in leveraging the rich semantic content of legislative discourse. To address this, we introduce the first theoretical formulation for stance-based ideal points and develop computational methods for their estimation directly from the Congressional Record using language models and contextual embeddings.
Our contributions include: (1) a comprehensive new dataset linking congressional speeches to the bills they discuss; (2) BARTExpan, a novel topic taxonomy generation method that discovers topics from speeches and organizes them in a hierarchical taxonomy of increasing specificity; (3) StrideStance, a state-of-the-art zero-shot stance detection model that identifies legislators’ stances on these topics; and (4) an integrated framework that combines all of these methodological developments to estimate new stance-based ideal points that reveal patterns not captured in voting data.
Applied to the 117th Congress (2021-2023), we validate our method against existing measures, and show that it captures fiscal and economic issues along the primary dimension as well as contemporary social flashpoints on issues such as abortion and civil rights along secondary dimensions. Furthermore, we use these ideal points to illustrate the strategic behavior of swing-district representatives who moderate their speeches while ultimately voting with the party line, as well as to examine the political positions of non-voting delegates.
Beyond Congress, our framework provides a broadly applicable methodology for estimating ideological positions across a diversity of textual domains, including judicial opinions and news media.Computer Scienc
A Multilevel Investigation of Transgender and Nonbinary Adolescent and Young Adult Mental Health: Classification and Assessment of Structural and Interpersonal Determinants
No full textMental health disparities, including depression and suicidality, among transgender and/or nonbinary (TNB) youth and college students are of high public health concern. Understanding the risk factors and population patterning of mental health disparities can shape intervention efforts at various levels to improve the mental health of TNB individuals. Caregivers of TNB youth have the ability to provide emotional support and access resources that are key to reducing disparities in TNB mental health. Colleges too have the ability to provide unique forms of institutional support to TNB students to facilitate reductions in mental health outcomes. Despite this, little is known about caregiver experiences of parenting TNB youth, the policy environments experienced by TNB college students, or the intersectional disparities in TNB college student mental health outcomes. This dissertation explores these key risk factors and disparities with the goal of informing intervention development for TNB youth and college students.
The first study (Chapter 2) utilizes the social ecological model to contextualize experiences of 48 caregivers of TNB youth in semi-structured interviews using thematic analysis and immersion crystallization. Chapter 3 utilizes quantitative intersectional modeling to characterize the population patterning of mental health outcomes among US college students across intersections of gender identity, race/ethnicity, and socioeconomic status. Finally, Chapter 4 empirically classifies the distribution of 12 TNB-supportive policies across 311 US colleges using latent class analysis.
Among caregivers, we found opportunities for gender affirmation and social connections, stressors between youth and caregivers, and associations between caregiver labor and stress. Among college students, we found first generation biracial Black and Indigenous TNB students had the poorest predicted mental health outcomes. Lastly, in examining college campus policy environments, we found associations between the probability of having a more supportive policy environment for TNB students and indicators of a college’s access to resources.
This dissertation discusses opportunities and recommendations for intersectional interventions across levels of the social ecological model, especially interventions at the community, organizational, and societal levels.Population Health Science
The Present-Day Effects of the 1921 Tulsa Race Massacre and Moving Towards Healing
No full textIn 1921, a terrible race massacre was perpetrated upon the prosperous Black Greenwood neighborhood in Tulsa, Oklahoma. An estimated 300 Black Tulsans were murdered and the entire Black neighborhood full of homes and businesses were looted and burned to the ground by a white mob enabled and deputized by local law enforcement. Prohibitive building codes enacted and the refusal of the city, the state, the country, and insurance companies to take responsibility after the massacre made it difficult for Tulsans to rebuild. Racial redlining, urban renewal projects, and continued racial discrimination that has occurred well after the massacre continue to negatively affect Black Tulsans. The purpose of this thesis is to asses the current situation in Tulsa as a result of the massacre and what steps can be taken to help heal the community.
I evaluated research that has been done about the massacre as well as statistical data about Tulsa. Black Tulsans and the once vibrant Greenwood neighborhood are still being negatively affected by the massacre and the lack of remedy and continuing harm to survivors and descendants of the massacre and the Black neighborhood as a whole.
Much recent work has been done to attempt healing for Tulsa, including the Road to Repair initiative recently announced by Tulsa’s first Black mayor on the event’s 104th anniversary. Ultimately, I believe much healing can be done by those companies and families that might have profited from or historically been responsible for the massacre to consider the steps they can take to heal the community and to assist with Tulsa Mayor Nichol’s Road to Repair plan.Extension Studie
The Disputation of America’s Moral Authority in Nuremberg (sample chapter)
No full textThe Disputation of America’s Moral Authority in Nuremberg constitutes a chapter in the monograph entitled Service in the Shadow of Justice: The Legacy of the Black American Military Court Guards in the Nuremberg Military Tribunals. The full work demonstrates that the assignment of Black troops to security details at the historic Nuremberg Trials was both symbolic and significant in the Long Civil Rights Movement and within the activism surrounding the desegregation of the U.S. military. Dim perceptions surrounding the performance of the U.S. Army’s Black troops (pejoratively termed “the Negro Problem”) during WWII and the continuation of Jim Crow policies in the European Theater were factors in excluding these servicemen from earlier duty at the Trials which ran from 1945-1949. By 1946, Nuremberg had become a symbol for the strivings of American racial justice while the verdicts delivered at the International Military Tribunal precipitated calls for anti-lynching legislation. A confluence of events, including slowly staged advocacy work by the Black press and by antiracists from within the U.S. military, eventually brought Black troops into the courtroom as sentries while the service window and stakes in the Nuremberg legacy waned. America was at its finest postwar display in the Palace of Justice while simultaneously revealing a tension between its democratic ideals and actions. The Black U.S. military court guards of Nuremberg are situated in this complex and historic legacy.Author's Origina