The Coronavirus (COVID-19) pandemic has created a crisis in the tourism and hospitality industry. As the people began following social distance protocols and stay-at-home orders, how would this affect consumer behavior in the short-term rental market? Airbnb data from New York City was used to determine factors that influence Airbnb prices after the onset of COVID-19. Exploratory data analysis was used to select useful features to model the rental prices. Random Forest, Linear Regression, and XGBoost models would be evaluated on their overall performance using RMSE and R2 as metrics. Topic modeling, perceived cleanliness, and polarity analysis were used to determine how reviewers could influence the listings. The number of listings and the prices significantly dropped during the onset of COVID-19. Hosts were more interested in long-term guests in their stays. XGBoost, the highest performing model, weighted renting the entire home/apartment and number of accommodations as the most important factors in Airbnb price prediction.

In this presented thesis, we delve into the dynamics between metals and soil organic matter. Metals are vital micronutrients essential for plant homeostasis, dynamically interacting within the ecosystem. Many studies typically analyze metal content by quantifying total levels using destructive methods; these approaches can be intrusive and overlook the comprehensive chemical picture, including chemical speciation and binding interactions with organic elements in the soil system. This research presents efforts to design new methods to address this gap by assessing metal availability, extracellular H2O2 in algae media, and flavonoid persistence in the presence of soil organic matter.Chapter One offers background and insights into the current state of research on soil chemistry, metals in soil environments, and how the interconnectivity between the two properties are crucial for the survival of organisms like plants. Chapter Two discusses the optimization of a zinc and copper chelator assay using the chromophoric molecules zincon and pyrocatechol violet under plant physiological conditions, considering variables such as temperature and pH. The assay yielded the desired results when tested with a known chelator, EDTA, demonstrating reduced metal binding to the chromophores when analyzed under a high throughput plate reader assay. Chapter Three implements the colorimetric chelator assay in soil systems, beginning with humic substances at various pH values. Initial tests revealed metal-ligand binding competition between the chelators, humic acids, and fulvic acids, showcasing variability in ligand exchange based on pH. Chapter Four complements the UV-Vis based assays in the preceding chapters and describes efforts to establish LC-MS-based strategies to assess flavonoid persistence in soil systems, including the optimization of soil extractions containing flavonoids. While the results were not as expected, it was complementary toward tool development for analyzing flavonoid persistence in soil environments. Chapter Five focuses on employing an H2O2-responsive bioluminescence probe in algae media, revealing differences in extracellular H2O2 with growth and feed conditions. Overall, this thesis describes initial efforts to uncover the dynamics of metals ions in soil through the development and assessment of a range of analytical methods for studying metal ion speciation in complex mixtures.

Defects are a key component in fine tuning the behavior of materials for technological applications. In this thesis, we explore the effect of planar (in the form of surfaces and grain boundaries) and point defects on material properties. We will use density functional theory (DFT) calculations to uncover the physics behind defect modified material properties and develop high-throughput databases. This thesis is broadly divided into three topics.

The first topic (Chapters~\ref{surface_energy_section} and~\ref{work_function_section}) focuses on developing a high-throughput database for surface energy and work function. This study covers elemental crystalline solids of over 100 polymorphs and over 70 elements. Our database is rigorously validated against previous experimental and computational data where available. We propose a weighted work function and surface energy based on the Wulff shape that can be compared to measurements from polycrystalline specimens. We show that the weighted work function can be modeled empirically using simple atomic parameters. Finally, we analyze work function anisotropy with simple bond breaking rules for metallic systems.

The second topic (Chapters~\ref{TaC_section} and~\ref{Mo_GB_section}) is an investigation of the role of metallic dopant segregation in the planar defects of refractory materials with the intention of reducing room temperature brittleness. We use DFT calculations in conjunction with experimental results to demonstrate dopant induced nanocube formaiton in \ch{TaC} which is useful for reducing material porosity during sintering. We also investigate the strengthening/embrittling effects of 29 dopants at the grain boundaries of Mo using DFT and empirical continuum models and assessed several simple atomic parameters as predictors for segregation and embrittlement.

The third topic (Chapters~\ref{V2O3_section} and~\ref{SmNiO3_section}) investigates the role of point defects on the metal insulator transition (MIT) of quantum materials for the purpose of developing energy-efficient neuromorphic devices. Using the PBE+$U$ functional, we explore the effect of intrinsic point defects on temperature and electric field induced MIT in \ch{V2O3}. In corroboration with experimental results, we also investigate the use of H-doping to tune the Ni valency of \ch{SmNiO3} which has broad implications in its MIT properties.

The heart is a vital organ that pumps blood throughout the body by constantly, cyclically contracting. Unfortunately, the heart can be vulnerable a wide range of diseases and injuries. In order to truly predict, prevent, or treat diseases in the heart, the myocardial environment and how it affects myocardial repair and pathways that lead to cardiac diseases should be thoroughly investigated. However, the complex structure, genetic and environmental factors, and inaccessibility in vivo make it difficult to fully elucidate the mechanisms behind cardiac remodeling and repair. Thus, to truly study the heart, it is necessary to develop in vitro models that can closely recapitulate the myocardial environment to methodically investigate the isolated mechanisms.

The heart has a unique dynamic mechanical environment that is closely linked to its highly organized structure and specialized cells. This mechanical environment is contributed to the unique composition of cell types and the resultant structure of the tissue. Interestingly, in some heart diseases, this organization and cellular composition is disrupted, which results in loss of efficient heart function. Additionally, as the heart contracts, all the resident cells are also exposed to unique mechanical strains which can affect their function and organization. To create an accurate in vitro model of the myocardium, the mechanical strains and cellular composition of the heart should be considered. However, it is not fully known what cells contribute to the highly organized structure of the heart and how the cells are affected by mechanical strain.

To address these problems, we recapitulated in vitro both the dynamic mechanical environment of the heart and its cellular composition to demonstrate how these factors can affect the organization, morphology, and viability of cardiac cells. In order to understand how cardiac cells organize in healthy or pathological heart tissue, we applied cyclic strain to co-cultures of the two most dominant cell types within the heart, cardiomyocytes and fibroblasts. Our results illustrates that cardiomyocytes and fibroblasts do influence the organization of one another. Additionally, to recreate in vitro the organization or lack thereof observed in healthy and fibrotic heart tissue respectively, we examined tissue exposed to cyclic strain with various densities of cardiomyocytes and fibroblasts. Furthermore, when we investigated if intercellular junctions could affect organization, there were no changes in the overall orientation of the two cell types when junction formation was inhibited with drugs. Thus, either these intercellular junctions are more important in the myocardium or they play a secondary role in organization relative to the amount of cells present.

Additionally, in this dissertation we examined how mechanics mimicking the myocardial environment affects cells with and without a LMNA mutation. To investigate this, we used patient specific cells and subjected them to cyclic strains before quantifying the cell viability/proliferation, cytoskeleton and extracellular matrix organization, proportion of dysmorphic nuclei, and nuclear shape. Though our results indicated that cyclic strain alone was insufficient to cause any significant differences that could explain the mechanisms that lead to heart diseases in these patients with LMNA mutations, we were able to observe these differences in cells with a severe type of the LMNA mutation.

Overall, our results highlight the influence that different cell types have on heart tissue organization. Additionally, we emphasize the importance of the unique mechanical environment of the heart when examining cardiac tissue organization and cells with genetic mutations. The work done in this dissertation will serve as a foundation for future models of the heart that study cardiac remodeling, repair, and diseases.