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Essays on Macroeconomics
Get PDFThe first chapter examines the role of return migration in driving innovation within India’s tech startup ecosystem, using a novel dataset constructed from web scraping of startup profiles, LinkedIn data, and patent databases. By capturing founders’ international experience, education, and innovation outcomes, the analysis reveals that returnees significantly contribute to higher inno- vation levels, particularly through patent filings. Returnee-founded startups exhibit an 18% higher rate of patent filings compared to those led by locals. The study employs OLS, Poisson regression, Coarsened Exact Matching (CEM), and Instrumental Variables (IV) to address selection bias and endogeneity concerns. U.S. immigration policy changes provide causal evidence of returnees’ impact, estimating an elasticity of substitution between returnees and locals of 1.41. This research sheds light on the critical role of returnees in fostering innovation in emerging markets. The second chapter investigates the impact of military expenditures on Foreign Direct In- vestment (FDI) inflows in low- and middle-income countries from 1990 to 2018, focusing on how armed conflict influences this relationship. Using the Arellano-Bond estimator to address dynamic panel bias and endogeneity, the analysis finds that military expenditures do not significantly affect FDI inflows in non-conflict settings. However, during conflicts, increased military spending attracts FDI, supporting the ”geoeconomic favoritism hypothesis,” which suggests that foreign investors perceive higher military expenditures as a commitment to security. The study also reveals that military spending has an immediate positive effect on FDI when a country transitions from peace to conflict but shows no significant impact when transitioning from conflict to peace. Additionally, the findings highlight that military spending attracts FDI during low-intensity conflicts but has a weaker and less robust effect during major conflicts. These results have policy implications for conflict-affected countries, emphasizing the importance of strategic military investments as a signal of security commitments to potential investors
Investigate the Use of Nucleic Acids as Pesticides to Manage Major Pests and Pathogens of Crops in South Carolina
Get PDFThe sugarcane aphid (SCA, Melanaphis sorghi), first discovered on grain sorghum in late 2013, has gradually become a major insect pest of sorghum. It inflicts significant damage to the crop year after year, causing millions of dollars in losses throughout the sorghum-producing regions of the United States. Similarly, Armillaria root rot—also referred to as oak root rot—is a major cause of decline in peach (Prunus persica) production in the southeastern United States. This disease is caused by Armillaria mellea and Armillaria tabescens. Current management practices for controlling M. sorghi include the use of synthetic pesticides, resistant varieties, and regular scouting. In contrast, management options for Armillaria species are limited, as no specific fungicides are available apart from systemic treatments like propiconazole. Integrated pest management approaches, such as tree removal, above-ground root collar excavation, and the use of resistant germplasm, are commonly employed. The primary insecticides used to manage M. sorghi are Sivanto Prime and Transform. However, their continued application is expected to result in the development of resistant M. sorghi strains. Additionally, these insecticides can negatively impact pollinators. Therefore, to meet the growing demand for greener (environmentally benign), target-specific, and safer alternatives for managing M. sorghi in sorghum and Armillaria species in peach, this project evaluates the potential of small nucleic acid molecules complementary to essential pest and pathogen gene transcripts in preventing their growth in laboratory, greenhouse, and field settings. To address these challenges, we assessed the potential of dsRNA-induced gene silencing targeting the acetylcholinesterase gene (AChE) in M. sorghi and the fungal cytochrome P450 lanosterol C-14α-demethylase (CYP51) gene in Armillaria mellea and A. tabescens. We compared various dsRNA delivery methods for M. sorghi and found that dsRNA is absorbed through the body surface, with mortality increasing significantly when combined with leaf painting and excess diet. To enhance dsRNA stability, it was conjugated with chitosan and liposomes or replaced with 2′-deoxy-2′-fluoro-d-arabinonucleic acid antisense oligonucleotides (FANA-ASO). Our studies suggest that chitosan conjugation notably improves dsRNA stability and enhances gene silencing efficiency in aphids. In contrast, in fungi, conjugation iii with chitosan or liposomes had little effect on gene silencing efficiency compared to unconjugated dsRNA. Overall, our results indicate that dsRNA-induced gene silencing targeting the AChE gene in M. sorghi and the CYP51 genes in Armillaria mellea and A. tabescens offers a potential option to chemical treatments in control of these pests and pathogens
Borders and Burdens: Three Essays on Inter-jurisdictional Tax Policy in America
Get PDFIndividuals, firms, and governments make decisions about the tradeoffs of different tax policies at jurisdictional borders, such as those between states, nations, or local governments; those choices shape the burden of taxation. This dissertation examines the effects of three distinct changes in tax policy: for state corporate income tax apportionment, colonial tobacco tariffs, and tax abatements for data centers. Chapter 1 examines how changes to the corporate income tax base formula affect state tax revenues. Chapter 2 analyzes how colonial era export and import tariffs on tobacco impacted trade volumes, raised revenue, and the distribution of the tax burden between producers and consumers. Chapter 3 estimates the effect of attracting a data center to a locality through tax abatements on public sector activity. These essays provide insight into how tax policy affects government revenue, economic incentives, and inter-jurisdictional choice.
Across settings as varied as colonial era empires and modern state and local governments, these chapters show how borders, whether geographic or political, shape the burden of taxation. Tax policy decisions at and within these borders determine how revenue is raised, and by extension where economic activity occurs and which taxpayers bear the greater burden of those decisions. At its core, the study of taxation is about choices—and choices involve tradeoffs. The effects of these choices are, and will continue to be, a relevant focus of economic research
Understanding Conversion of Long Chain Fatty Acids in Anaerobic Digestion Systems
Get PDFAnaerobic co-digestion with fats, oils, and grease (FOG) waste can increase energy production due to the high methane potential of lipids. However, adding FOG can lead to operational issues caused by accumulating saturated long-chain fatty acids (LCFA). My research explored why saturated LCFAs are often the primary intermediate that accumulates and the microbial sensitives of the populations responsible for their degradation. In each batch or semi-continuous experiment, all intermediates of FOG degradation, including LCFAs, volatile fatty acids (VFAs), Hydrogen gas (H2), and endpoint methane production, were paired with temporal quantitative polymerase chain reaction (qPCR) of the Syntrophomonas genus, a known LCFA b-oxidizing microorganism, or 16S ribosomal ribonucleic acid (rRNA) sequencing. Monitoring all potential intermediates, including H2 partial pressure, was a novel addition to FOG anaerobic co-digestion studies. The prevailing explanation in literature of why palmitic acid accumulates revolves around increased H2 partial pressure leading to non-spontaneous b-oxidation.
The research analyzed the pH sensitivity of anaerobic co-digestion of FOG. Buffering the pH as a strategy to mitigate the inhibitory effects of FOG was explored with a semi-continuous experiment. Also, a batch study investigated the pH sensitivity of species belonging to the Syntrophomonas genus and palmitic acid degradation, the primary analyte observed in inhibited anaerobic co-digesters. Apparent first-order growth rate constants for palmitic acid and growth rate constants for Syntrophomonas sp. were calculated. Results indicated that microbes involved in lipid anaerobic digestion, specifically the genus Syntrophomonas, are highly sensitive to even small changes in pH and that buffering can help overcome the inhibitory effects associated with LCFA accumulation by promoting the growth of Syntrophomonas sp. during co-digester start-up or LCFA overloaded conditions.
The research also explored the biochemical pathways of five common saturated and unsaturated LCFAs observed in wastewater. All intermediates produced from myristic, palmitic, stearic, oleic, and linoleic acid were monitored in batch study to identify differences in the degradation pathways of unsaturated vs saturated LCFA degradation and differences in the microbial communities involved. Specifically, the batch study allowed exploration of whether unsaturated LCFA degradation requires hydrogenation and whether species belonging to Syntrophomonas genus are involved in that step. Unsaturated LCFA degradation most likely involves an initial hydrogenation step, as the dominant b-oxidizing genus present, Syntrophomonas, experienced a lag in growth while unsaturated LCFAs were converted to saturated LCFAs. My results indicated that unsaturated LCFAs do not directly enter the b-oxidation cycle and the Syntrophomonas genus were not involved in unsaturated degradation to saturated LCFAs. The research also supported the conclusion that saturated LCFA accumulation was not due to H2 partial pressure, as concentrations never reached high enough levels to cause a positive Gibbs free energy.
Saturated LCFAs, primarily palmitic acid, are the primary analyte observed in stalled anaerobic co-digesters despite FOG waste containing predominantly unsaturated fatty acid tails. Saturated LCFAs degrade rapidly under ideal conditions when fed as the substrate; however, they accumulate when produced from unsaturated LCFAs. My research explored if the presence of unsaturated LCFAs inhibited the degradation of palmitic acid and the growth of Syntrophomonas sp. through a batch study. Assays were spiked with palmitic acid and oleic, linoleic, or stearic acid. Palmitic and stearic acid are saturated LCFAs, while oleic and linoleic acid are unsaturated LCFAs. The study revealed significantly smaller first-order palmitic acid degradation rate constants in the presence of oleic and linoleic acid compared to stearic acid, indicating that unsaturated LCFAs inhibit b-oxidation. Syntrophomonas sp. concentrations also initially decreased during hydrogenation within the first two days of the experiment. These results indicated potentially different inhibition mechanisms between unsaturated and saturated LCFAs. Unsaturated LCFAs could promote permanent toxicity due to lysing and the ultimate decay of cells. Saturated LCFAs could promote temporary inhibition due to adsorption to cells, limiting substrate transport and nutrient uptake. H2 partial pressure never reached concentrations high enough to create a positive Gibbs free energy for b-oxidation. However, the presence of unsaturated LCFA in digester feed causing decay of b-oxidizers like Syntrophomonas sp. could be a potential explanation of why saturated LCFAs are the primary bottleneck.
Finally, VFAs are an alternative resource to methane generated from lipid-rich waste streams like FOG. Adding acetic acid, a VFA, can enhance biological nutrient removal at water resource reclamation facilities (WRRF). Excess methane not used to heat digesters or provide onsite electricity is often flared, resulting in CO2 emissions. VFAs from onsite FOG fermentation would reduce the chemical costs and greenhouse gas emissions (GHG). VFA production from FOG requires manipulating the lipid anaerobic food web to enhance b-oxidation and inhibit methane production. VFA production of lipids under slightly acidic, pH 6.7, and basic conditions, pH 8.2, was explored as a potential means of promoting the growth of b-oxidizers such as Syntrophomonas sp. while inhibiting methanogens. Apparent first-order growth rate constants of Syntrophomonas sp. and apparent first-order degradation rate constants of palmitic acid at pH 6.7 and 8.2 were calculated in a batch study. Both apparent first-order degradation rate constants of palmitic acid and growth rate constants of Syntrophomonas sp. were greater at pH 8.2 compared to pH 6.7. Another batch study spiked with FOG was used to determine if efficient b-oxidation of LCFAs produced from lipid hydrolysis is possible at pH 8.2 or 6.7. My study showed acetate as the primary VFA produced from the FOG and that at pH 8.2, there was a point at which acetate concentrations reached 80-100% of the influent COD added. A semi-continuous study further analyzed VFAs produced from FOG fermentation, pH control for methane inhibition, and solids residence time (SRT) selection. Caproate was the dominant VFA produced in both pH 6.7 and pH 8.2 FOG fermentation reactors, most likely due to the biological conversion of glycerol into caproic acid via chain elongation. VFA production efficiency was similar between pH 6.7 and 8.2. Semi-continuous buffering was not effective in controlling the pH in either fermentation reactor. A continuous experimental design would be necessary to identify the best pH and SRT selection, as continuous buffering and pH adjustment would allow for better stabilization at the desired reactor conditions
Collecting Human Subject Data for Modeling Maximum Potential Power at Specific Cadence and Fatigue Levels
Get PDFThe overarching goal of this research project was to investigate the relationship between a participant\u27s maximum power (Watts) at a given cadence (RPM) on a specific fatigue level. Before conducting any experiments, we hypothesized that maximum power and cadence would decay linearly with fatigue. To do this, six days of testing for each of 4 human subjects were split across two phases. The first 4 days were devoted to Phase one, which focuses on determining the physical abilities of each unique participant and finding metabolic constants such as Critical Power and Anaerobic Work Capacity. Phase two then tests maximal power at various fatigue levels. This protocol was repeated twice to verify the results. Finally, an overarching goal of this research was to remove the human mind and its unconscious pacing. The mind is a beautiful thing, but when it comes to participant-based athletic research, it is an uncontrollable variable. The mind unconsciously limits the body to ensure some energy is always left. This limit causes a significant issue when the goal is to analyze the maximal performance. In an all-out exercise, for instance, a participant may unconsciously save energy at first, which will cause them to finish with unexpended reserves. To limit mental influence, a constant power method was used to determine critical power and anaerobic work capacity
