VictorJuiz/thesis huggingface dataset:
Statistics, Formation and Stability of Exoplanetary Systems

Over the past two decades scientists have detected thousands of exoplanets, and their collective properties are now emerging. This thesis contributes to the exoplanet field by analyzing the statistics, formation and stability of exoplanetary systems. The first part of this thesis conducts a statistical reconstruction of the radius and period distributions of Kepler planets. Accounting for observation and detection biases, as well as measurement errors, we calculate the occurrence of planetary systems, including the prevalence of Earth-like planets. This calculation is compared to related works, finding both similarities and differences. Second, the formation of Kepler planets near mean motion resonance (MMR) is investigated. In particular, 27 Kepler systems near 2:1 MMR are analyzed to determine whether tides are a viable mechanism for transporting Kepler planets from MMR. We find that tides alone cannot transport near-resonant planets from exact 2:1 MMR to their observed locations, and other mechanisms must be invoked to explain their formation. Third, a new hybrid integrator HERMES is presented, which is capable of simulating N-bodies undergoing close encounters. HERMES is specifically designed for planets embedded in planetesimal disks, and includes an adaptive routine for optimizing the close encounter boundary to help maintain accuracy. We find the performance of HERMES comparable to other popular hybrid integrators. Fourth, the longterm stability of planetary systems is investigated using machine learning techniques. Typical studies of longterm stability require thousands of realizations to acquire statistically rigorous results, which can take weeks or months to perform. Here we find that a trained machine is capable of quickly and accurately classifying longterm planet stability. Finally, the planetary system HD155358, consisting of two Jovian-sized planets near 2:1 MMR, is investigated using previously collected radial velocity data. New orbital parameters are derived using a Bayesian framework, and we find a high likelihood that the planets are in MMR. In addition, formation and stability constraints are placed on the HD155358 system.

Keywords: Exoplanets
Machine Learning
Numerical Methods
Physics
Planetary Science
Statistics
Advisor: Rein, Hanno
Seller Organizations, Market Brokers and Brokerage in the Context of U.S. Venture Capital Market

Market intermediaries – brokers – play a critical role in making markets by bridging the buyer-seller informational interface. This role is particularly valuable for sellers who often lack information about buyers. In this dissertation, I explore when sellers need brokers and their resources and to what extent sellers gain benefits from them. To date, most of brokerage research has built theories and empirical evidence about actors who broker. This dissertation complements to extant research by taking the perspective of the brokered – actor who connects to a broker. I develop and test my theoretical arguments in the context of the U.S. venture capital market in which start-ups as sellers choose to use law firms as market brokers for their venture capital financing. In the first study, I explore the brokering roles of law firms in the venture capital market. I specify two types of roles, connection-making and coordination, based on qualitative and quantitative analyses. Building on the first study, the second study explores brokerage motivations for sellers. I examine when sellers choose to rely on brokers for their connection-making and coordination roles. In parallel with these roles, I test and find support for catalysis and coordination conditions that increase incentives to use brokers: (1) when they struggle to secure financing deals, (2) when they form deals with buyers that have highly embedded brokerage routines and (3) when they form deals with multiple buyers. In the third study, I explore brokerage outcomes for sellers. I propose that brokers develop a portfolio of clients (buyers), exploiting alternatives to create new matches in attempts that meet both profit motivation and reputation building effort. I hypothesize and find support that brokers maintain strong ties with some buyers by repetitive representation, while they utilize other buyers to create matches for sellers that they represent. I conclude by integrating the three studies to elaborate on the studies’ common themes and to make implications on research concerning market brokerage and research concerning entrepreneurship.

Advisor: Mitchell, Will
Rowley, Tim
CNS hormonal and nutritional regulation of glucose and energy homeostasis

The mediobasal hypothalamus (MBH) and the dorsal vagal complex (DVC) regions contain a leaky blood-brain barrier and therefore act as critical sites of action for circulating hormones and nutrients on glucose and energy homeostasis. For example, hormones such as insulin, leptin and glucagon and nutrients such as lipids, glucose and amino acids act in the MBH and DVC to regulate hepatic glucose production, glucose tolerance, food intake and body weight, but the underlying CNS sensory mechanisms in rodents and humans remain elusive. The current dissertation unveils novel mechanisms for glucagon action in the MBH and glycine sensing in the DVC in rats and mice that maintain glucose and energy homeostasis. In Study 1, we discovered that KATP channel is necessary for MBH glucagon action to exert glucose control. In Study 2, we found that pharmacological and molecular manipulation of glycine transporter 1 in the DVC enhances glycine sensing and potently regulates glucose and energy homeostasis. In conclusion, I have discovered novel mechanisms for glucagon and glycine sensing in the brain that regulate glucose and energy homeostasis, and have unveiled CNS therapeutic targets for diabetes and obesity.

Keywords: Diabetes
Dorsal Vagal Complex
Glucose Homeostasis
Hypothalamus
Metabolism
Obesity
Advisor: Lam, Tony TKT
Self-Assembled Carbon-Polyoxometalate Composites for Electrochemical Capacitors

The development of high performance yet cost effective energy storage devices is critical for enabling the growth of important emerging sectors from the internet of things to grid integration of renewable energy. Material costs are by far the largest contributor to the overall cost of energy storage devices and thus research into cost effective energy storage materials will play an important role in developing technology to meet real world storage demands. In this thesis, low cost high performance composite electrode materials for supercapacitors (SCs) have been developed through the surface modification of electrochemically double layer capacitive (EDLC) carbon substrates with pseudocapacitive Polyoxometalates (POMs). Significant fundamental contributions have been made to the understanding of all components of the composite electrode including the POM active layer, cation linker, and carbon substrate. The interaction of different POM chemistries in solution has been studied to elucidate the novel ways in which these molecules combine and the mechanism underlying this combination. A more thorough understanding regarding the cation linkerâ s role in electrode fabrication has been developed through examining the linker properties which most strongly affect electrode performance. The development of porosity in biomass derived carbon materials has also been examined leading to important insights regarding the effect of substrate porosity on POM modification and electrochemical properties. These fundamental contributions enabled the design and performance optimization of POM-carbon composite SC electrodes. Understanding how POMs combine in solution, allowed for the development of mixed POM molecular coatings with tunable electrochemical properties. These molecular coatings were used to modify low cost biomass derived carbon substrates that had been structurally optimized to accommodate POM molecules. The resulting electrode composites utilizing low cost materials fabricated through simple scalable techniques demonstrated (i) high capacitance (361 F g-1), (ii) close to ideal pseudocapacitive behavior, (iii) stable cycling, and (iv) good rate performance.

Keywords: biochar
carbon
energy storage
polyoxometalates
supercapacitors
surface-modification
Advisor: Lian, Keryn
The Socio-Economics of Neighbourhoods and Cities: Papers in Urban Economics

This thesis explores the socio-economics of neighbourhoods and cities and the role that changes to labour market opportunities and access to amenities play in determining housing demand and demographic shifts. Many cities are experiencing a spatial inversion in terms of neighbourhood demographics -- city centers are becoming both wealthier and more expensive while peripheral, suburban neighbourhoods are becoming both poorer and less expensive. In a dynamic context, I consider the social and economic processes that contribute to neighbourhood change. Chapter 1 contributes to the literature on neighbourhood change by providing a comprehensive characterization of the dynamics of New York City neighbourhoods. Using a structural breakpoint analysis I provide evidence of which neighbourhoods have changed, when they changed, and the magnitude of the change. I show a clear spatial and temporal pattern to neighbourhood change and I present several results: price increases are larger than price decreases; increases in housing demand precede increases in price growth; and downtown neighbourhoods are increasingly wealthier and a greater fraction white. Chapter 2 explores the extent to which changing labour market characteristics contribute to the patterns of neighbourhood change. I construct a spatial-Bartik instrumental variable as an exogenous measure of neighbourhood labour demand, which is then used to generate predicted income growth rates and house price growth rates. I find that in New York City 21% of the variation in income growth rates and 41% of the variation in house price growth rates between 1990 and 2010 can be explained by exogenous labour demand shocks. Chapter 3 focuses on the influence of the built environment on social behaviours. I find a strong and positive cross-sectional relationship between the built environment and social interactions. Once I address the endogenous decision of where to live, the significant effects found in the cross-section disappear. This implies that there is sorting of relatively social individuals into more walkable neighbourhoods. I find some evidence that this sorting is correlated with life-cycle changes that may affect both residential decisions and social relationships.

Advisor: Strange, William
Social interactions and racial inequality

A large body of evidence suggests that social interactions causally influence individuals' economic decisions (e.g. Duo and Saez, 2003; Bayer, Ross and Topa, 2008; Dahl, Loken and Mogstad, 2014). This finding implies that differences in the social environment faced by members of different races â in particular, differences in social norms and in the characteristics of social networks - may help perpetuate racial inequality. In this dissertation, I present two papers that attempt to understand how these differences in the social environment are created and reinforced. In the first chapter, I assess the influence of media role models on black educational attainment by examining the impact of a popular 1980's sitcom: The Cosby Show. The show portrayed an upper-middle class black family, and frequently emphasized the importance of a college education. If role model effects exist, young black people should have responded more strongly to this message. I test this hypothesis by relating educational attainment to city-level Cosby ratings, using Thursday NBA games and very warm Thursdays as instruments. I find that Cosby increased years of education by 0.2-5.0% among black youth, but had no effect on white youth. In the second chapter, I examine a determinant of social segregation by race in the United States: physical distance. Because U.S. cities are highly segregated, the time cost of interacting with a member of another race is typically higher than the cost of interacting with a same-race friend. My goal in this chapter is to quantitatively assess the importance of this channel in explaining why people typically interact with members of their own race. I argue that the causal effect of distance on social interactions is captured by consumers' distaste for travel. Based on external estimates of this parameter, I simulate the frequency of cross-racial interactions that would occur if only distance mattered in determining individuals' choice of interaction partners. I compare the simulation results to a new measure of the actual frequency of inter-racial interactions based on Flickr photographs. I estimate that 25-30% of social segregation for whites in the U.S. is attributable to physical distance alone.

Advisor: Benjamin, Dwayne
Multiplexed Microfluidics for the Study of Photosynthetic Microorganisms

The ability of large datasets of simple metrics (i.e. growth rate, lipid accumulation) to contribute to the understanding of microalgal photosynthesis is explored in this thesis. Specifically, three tools were developed, (i) a microfluidic multiplexed irradiance assay, which was composed of a microfluidic chip and a liquid crystal display; (ii) a second order mathematical model which can predict the growth under fluctuating light for periods ranging from a day to one under second and; (iii) a combinatorial assay for studying the mixed effect of light and nitrogen on growth and lipid accumulation. The multiplexed microfluidic irradiance assay (Microalgae on display) was capable of producing a large number of independent light treatments (200+), while avoiding the self-shading typical of flask-scale experiments. A set of linear ordinary differential equations were capable of capturing a second order behavior of photosynthetic growth, specifically a penalty at intermediate frequencies. This behavior lies outside the prevailing understanding of a high and low frequency limit. Lastly, the interplay between irradiance intensity and ammonium was resolved, showing that ammonium concentration plays a role at high light intensities only.

Keywords: Algae
Microfluidics
Photosynthesis
Advisor: Sinton, David
Oral Glucocorticoids: Fracture Risk and Benefit of Osteoporosis Pharmacotherapy

Oral glucocorticoids are potent anti-inflammatory and immunosuppressant agents used to treat and control several conditions. However, oral glucocorticoid exposure leads to an osteoporotic state characterized by increased bone loss and fracture risk. Bone loss is rapid upon oral glucocorticoid exposure, particularly in the vertebra. Osteoporosis treatment are often recommended for patients receiving oral glucocorticoids to prevent fracture. However, osteoporosis drug benefit in randomized controlled trials and observational studies is not yet established among oral glucocorticoid users. This research aimed to estimate fracture rates among new and ongoing oral glucocorticoid users and assess the benefit of osteoporosis drugs. First, meta-analytic methods were leveraged to pool fracture data from randomized clinical trials and examine fracture rates by oral glucocorticoid exposure history. Second, network meta-analysis was used to estimate the relative efficacy of osteoporosis drugs among oral glucocorticoid users. Third, using Ontario administrative healthcare data, three cohort analyses were conducted to assess the effectiveness of alendronate, etidronate, and risedronate in reducing fracture risk among chronic oral glucocorticoid users. Results of the meta-analytic analyses (study 1) showed that vertebral and non-vertebral fracture rates are higher among patients starting a new oral glucocorticoid treatment course than patients with ongoing use. These findings are consistent with higher bone loss among glucocorticoid initiators than ongoing users. The network meta-analysis (study 2) showed etidronate, risedronate, and teriparatide as efficacious in preventing vertebral fracture; teriparatide was identified as the most efficacious treatment followed by risedronate. No treatment was associated with a reduction in hip fracture risk, yet the data were limited to small pooled samples of heterogeneous patients in clinical trials. Results of the large population-based observational research (study 3) support the effectiveness of alendronate and risedronate to reduce hip fracture risk, and all three oral bisphosphonates to reduce vertebral fracture risk. The findings of this dissertation draw attention to the high fracture risk among new oral glucocorticoid users and provide evidence of the benefit of osteoporosis drugs early upon oral glucocorticoid exposure to reduce fracture risk. Further research is required to examine fracture risk by different glucocorticoid exposure patterns and estimate the comparative effectiveness between osteoporosis drugs.

Keywords: Drug effectiveness
Fracture risk
Glucocorticoid-induced osteoporosis
Meta-analytic methods
Pharmacoepidemiology
Advisor: Cadarette, Suzanne M
A Learning Based Robot Interaction System for Multi-User Activities

The population of the world is rapidly aging and there is presently an increasing demand for residential care facilities to provide care for older adults. Understimulation can be a major concern in such facilities due to high resident-to-staff ratios and a decreasing number of healthcare staff to facilitate cognitive, social, and physical activities for older adults. Currently, socially assistive robots are being developed to assist in providing such stimulation. However, the existing robots are limited to only facilitating a set of activities that have been pre-programmed on the robot and cannot be customized to the needs of a facility. Furthermore, the majority consider only one-on-one activities, rather than providing stimulation to groups of users at the same time. This thesis focused on developing a learning based interaction system for socially assistive robots to: 1) autonomously facilitate multi-user activities while providing individualized assistance; 2) learn new customized activities from caregivers; and 3) personalize robot assistive behaviours to obtain user compliance. Numerous human-robot interaction experiments were conducted with the system integrated into the socially assistive robot Tangy for the multi-user activity of Bingo. The participants for the experiments consisting of caregivers and older adults. The results showed that: 1) participants had positive attitudes towards interacting with the robot and found it easy to use, 2) older adults were engaged during the activity and complied with the robotâ s behaviours, and 3) caregivers were able to successfully teach a new activity to the robot with moderately low perceived workload.

Keywords: Human-Robot Interaction
Learning from Demonstration
Socially Assistive Robotics
Advisor: Nejat, Goldie
Essays in the Economics of Violence and Conflict

Chapter 1 studies the impact of the arrival of displaced individuals on the wages of residents at receiving locations. To do this, the study employs an enclave IV strategy, which exploits both social distance between origin and destination locations and forced migration. I compare the effects on four different subgroups of the population, partitioned by skill (low-skilled versus high-skilled) and by gender. The analysis suggests that a conflict-induced increase in population leads to a short-run negative impact on wages, but that subsequent out-migration from receiving municipalities helps to mitigate these effects. Chapter 2 studies the relationship between political violence and congressional decision-making. I examine how politicians and their constituents respond to attacks by FARC, Colombia's largest rebel group, using data from politicians' Twitter accounts and roll-call voting records, and employing both an event study and a difference-in-differences research design. The analysis finds that tweets from incumbent politicians and tweets which exhibit "right-wing" language receive higher user engagement (a proxy for popular support) following rebel attacks. In congress, politicians were more likely to align their legislative votes with the right-leaning ruling party following an attack, before the government started negotiations with the rebels in 2012. However, this relationship breaks down after the start of the peace process. The empirical results are consistent with a political economy model of legislative behaviour in which events that shift median voter preferences, and the presence of rally 'round the flag effects, elicit different politician responses depending on the policy position of the ruling party. Chapter 3, joint work with Gustavo Bobonis and Roberto Castro, provides evidence of the long-term relationship between male-to-female spousal violence and the Oportunidades conditional cash transfer program in rural Mexico. It uses data from three nationally representative surveys that include detailed information on the prevalence of spousal abuse and threats of violence against women. Constructing comparable groups of beneficiary and nonbeneficiary households within each village to minimize potential selection biases, the analysis finds that, in contrast to short-run estimates, physical and emotional abuse rates over the long term do not differ significantly between existing beneficiary and nonbeneficiary couples.

Keywords: Applied Microeconomics
Development Economics
Political Economy
Advisor: Bobonis, Gustavo J
Design of Force-Sensing Sleeve for Minimal Access Surgical Instruments

Due to the nature of Minimal Access Surgery (MAS), surgeons are faced with multiple challenges including: (1) lack of direct hand-eye coordination, (2) loss of depth perception, (3) fixed access points, (4) long surgical instruments, and (5) reduced access to the surgical site. These challenges ultimately affect the surgeon's ability to sense the forces between the laparoscopic instrument and tissue. Improper force control can lead to poor clinical outcomes such as tissue necrosis, infection, and scarring. Currently, minimal literature exists on the benefit of force metrics in training and clinical environments. Moreover, existing MAS force-sensing technologies prevent researchers and surgeons from conducting extensive MAS force studies due to their limited applications in MAS training or the operating room, and/or complex manufacturing processes. This thesis work describes the design of a novel force sensor for a broad range of standard MAS instruments and procedures. The proposed Force-Sensing Sleeve (FSS) design utilizes a flexible printed circuit and multiple strain gauges to determine distal instrument forces from mechanical deformations measured in the MAS tool's exterior shaft. The FSS acts as a minimally disruptive add-on and can be applied to standard MAS instruments in a simple and low-cost assembly process. A supporting-system for the FSS was also developed to provide the full force-sensing solution capable of wirelessly measuring, logging, and displaying force data in real-time. A standard MAS needle holder was equipped with the FSS system and tested in a realistic surgical training environment of the most complex Fundamentals of Laparoscopic Surgery (FLS) task (Intracorporeal Suture Knot Task (ISKT)); this proof of concept study's preliminary findings demonstrated the potential use of ISKT mean force measurements as a first approximation of surgical expertise, however more sophisticated dynamic force metrics are likely required for the further classification of surgeon expertise. The FSS system's ability to leverage existing operating room instruments and potential to be used in both standardized MAS training programs and surgical environments creates the opportunity for extensive force investigations in standard MAS tasks to determine how force metrics can benefit the surgical community and enhance patient safety and care.

Keywords: Force
Instrument
Minmal Access Surgery
Surgery
Advisor: Gerstle, Justin T
Drake, James