Electronic Thesis or Dissertation

The objective of this thesis is to study the proper placement and denoising of Total Field Magnetometers (TFM) installed on an Autonomous Underwater Vehicle (AUV), in support of a long-term goal to perform geophysical navigation based on total field magnetic sensing. This new form of navigation works by using the magnetic field of the Earth as a source of reference to find the desired heading. The primary tools used in this experiment are a REMUS 100 AUV, a QuSpin scalar magnetometer, and a TwinLeaf vector magnetometer. The Earth’s magnetic field was measured over periods of several hours to determine the range of values it provides under natural conditions. Digital filters were created to digitally reduce fluctuations caused by sources of external interference and sources of internal interference. To mitigate the issue of platform based interference, two methods were examined. These methods involved the use of the Tolles-Lawson model and Wavelet Multiresolution Analysis. The Tolles-Lawson model is used to determine the compensation coefficients from a calibration mission to mitigate the effects from the permanently detected magnetic field, the induced magnetic field, eddy currents. and the geomagnetic field. Wavelet multiresolution analysis follows the same basic steps as Fourier transformations and is used to analyze time series with power sources in motion over a frequency spectrum. Several acquisitions were run with the QuSpin in various locations around and along REMUS, and it was concluded that placing the sensor at the very front of the vessel which is approximately 1.8 [m] from the DC motor, with assistance from wavelet analysis was acceptable for the project.

H. P. Lovecraft has been a significant influence in horror fiction, but most of the attention paid to Lovecraft’s work focuses on his Cthulhu Mythos. This thesis examines a group of fantasy stories from Lovecraft’s Dream Cycle, overlooked in favor of his horror tales. I argue these stories merit attention for their presentation of an ideological conflict central to much of Lovecraft’s work: reality, knowledge, and science vs. fantasy, imagination, and dreams. Lovecraft demonstrates the limitations and importance of one’s perspective, illustrating the need to be flexible in one’s beliefs and viewpoints. I also argue that this understanding of perspective encourages alternative readings of Lovecraft’s other work, as well as enabling a greater understanding of horror and fear of the unknown.

Emerging insights on the role of microbiomes in the sustainability of ecosystems and plant cover are transforming knowledge-driven agro-environmental management practices. For more than a century, the Brazilian pepper tree -BP (Schinus terebinthifolius), a category 1 invasive plant in Florida has defied numerous conventional control measures directed at its well-known ecology. This dissertation is one of the pioneer studies designed to determine whether microorganisms play a role in the aggressive invasion of BP in Florida and examine potential mechanisms with the goal of creating supplemental restoration tools. To test the hypothesis that enhanced mutualism of Brazilian pepper tree with microbes, compounded by relatively low biotic resistance of Florida soils is a critical driver of its invasion, plant biomass indices, metagenomics analysis of microbial community shifts, electron microscopy of endomycorrhizal infection and qPCR of key rhizobacterial taxa were measured. A multifactorial grow-room experiment was conducted simulating invasion with BP and two Florida natives (Pinus elliottii and Bidens alba) in a sterile, bioinoculant supplemented, and non-sterile control soils with various plant combinations.

This dissertation investigates the consequences of stock repurchase programs on long-term shareholders and bondholders. In the first essay, I present evidence that stock buybacks reduce investment inefficiencies associated with short-term ownership. For a sample of U.S. firms from 1988 to 2018, I first document that stock buybacks are associated with lower and short-term investors with higher corporate investment and net hiring. However, contrary to the conventional view, I find that buybacks reduce overinvestment related to short-term owners rather than increasing underinvestment. I conclude that firms have been using buybacks as an efficient mechanism to align the interest of short-term and long-term investors. Results are robust to alternative measures of stock repurchase and ownership investment horizon and to endogeneity concern
In the second essay, I test the signaling and wealth transfer hypotheses for share repurchase announcements using daily bond and stock returns. I distinguish between governance mechanisms protecting shareholders or bondholders and between internal and external shareholder governance strength. I find that stock and bond returns react positively to buyback announcements only at companies with strong internal shareholder governance mechanisms. Moreover, I reveal the positive impact of internal governance on the relation between stock and bond return is more pronounced in the firms where managerial compensation is more tied to stock performance and where the wealth transfer is expected. I found no evidence that high short-term oriented ownership increases the wealth transfer in repurchase announcements. Finally, I show that bonds with distribution covenants are negatively impacted by repurchase announcements, which supports the view that the market punishes these bonds when firms are likely to use repurchase stocks
to bypass their covenants.

Turbulent flow is a complex three dimensional system of velocity and pressure fluctuations in a fluid that creates vorticity, eddies and other flow structures. In this study we are specifically concerned with the surface pressure fluctuations below a turbulent boundary layer which is one of the primary sources of panel vibration on aircraft fuselages and ship hulls as well a major issue in ship hydrodynamics. The most accepted analytical approaches to describe the surface pressure fluctuations are the Chase model [1] for the surface pressure wavenumber spectrum and Goody’s model [2] for the pressure spectrum at a point. The most accurate numerical approach to use is Direct Numerical Simulations (DNS) [3]. In this study we compared Chase and Goody’s models against DNS of a turbulent channel flow in the space–time and wavenumber-frequency domains and estimated regions of convergence between the analytical models and the DNS data.

The ocular lens is comprised of an epithelial cell population that undergoes a continuous process of cellular remodeling and differentiation to form elongated transparent fiber cells. This lens differentiation process is hallmarked by the complete elimination of organelles at the center of the lens, elongation of lens fiber cells, and production of lens fiber-cell specific crystallin proteins to form the mature functional structure of the transparent ocular lens. To date, our understanding of the mechanisms that drive the lens differentiation process is incomplete. This dissertation sought to elucidate the potential roles of both hypoxia and epigenetic chromatin remodeling processes as novel regulators of lens differentiation.
The lens lacks a direct blood supply and thus resides in a hypoxic microenvironment. Previous studies revealed the presence of a decreasing oxygen gradient in the region of the lens where cellular remodeling and organelle elimination occur to form mature transparent lens fiber cells. Thus we hypothesized that the hypoxic environment of the lens itself, was required to induce gene expression changes to drive the lens differentiation process. We utilized a multimoics analysis combining CUT&RUN and RNAseq high-throughput sequencing technologies to identify a role for the hypoxia-inducible transcription factor HIF1a as a novel regulator of lens gene expression during lens differentiation.

Marine sponges are one of the most prolific sources of chemical compounds with pharmaceutical importance. To establish a supply of such compounds large enough for clinical development, in vitro production methodology was investigated. Since all sponge cells do not divide in culture, it was hypothesized that the fusion of rapidly dividing cells of a sponge that does not produce any compounds of interest with cells of a nondividing but compound-producing sponge would result in a hybridoma that produces the compound of interest. In this study, hybridomas have been produced with cells of two marine sponges, Axinella corrugata, which produces the antitumor compound stevensine, and Geodia neptuni, which divides rapidly in a nutrient medium optimized for sponge cell culture. Successful hybridization and subsequent cell division and in vitro stevensine production may unlock the potential for sustainable mass production of other sponge-derived compounds.

Cryptography relies on hard mathematical problems that current conventional computers cannot solve in a feasible amount of time. On the other hand, quantum computers, with their quantum mechanic construction, are presumed to be able to solve some of these problems in a reasonable amount of time. More specifically, the current hard problems that public key cryptography relies upon are expected to be easily broken during the quantum era, a time when large-scale quantum computers are available. To address this problem ahead of time, researchers and institutions have proposed post-quantum cryptography (PQC), which is an area of research that focuses on quantum-resistant public key cryptography algorithms. One of the candidates in the NIST PQC standardization process is SIKE, an isogeny-based candidate. The main advantage of SIKE is that it provides the smallest key size out of all the NIST PQC candidates at the cost of performance. Therefore, the development of hardware accelerators for SIKE is very important to achieve high performance in time-constrained applications. In this thesis, we implement several accelerators for SIKE and its primitives using different design approaches, all of which are suitable for different applications. We deliver significant enhancements to SIKE’s most expensive component, the modular multiplier. We design SIKE using a hardware-based approach and a software-hardware codesign approach, the latter of which utilizes a RISC-V processor. We also design SIKE with multi-level security level support for applications that require support of multiple security levels with minimal area usage. We enclose our performance and area results, which provide a reference to evaluate our work with other implementations.

Significant reduction in space, weight, power, and cost (SWAP-C) of imaging hardware has induced a paradigm shift in remote sensing where unmanned platforms have become the mainstay. However, mitigating the degraded visual environment (DVE) remains an issue. DVEs can cause a loss of contrast and image detail due to particle scattering and distortion due to turbulence-induced effects. The problem is especially challenging when imaging from unmanned platforms such as autonomous underwater vehicles (AUV) and unmanned ariel vehicles (UAV).
While single-frame image restoration techniques have been studied extensively in recent years, single image capture is not adequate to address the effects of DVEs due to under-sampling, low dynamic range, and chromatic aberration. Significant development has been made to employ multi-frame image fusion techniques to take advantage of spatial and temporal information to aid in the recovery of corrupted image detail and high-frequency content and increasing dynamic range.

High-profile police use-of-force events, like the deaths of Trevon Martin, Freddie Gray, Alton Sterling, and George Floyd, have increased scrutiny towards law enforcement, and many believe that racial disparities in the justice system are caused by biased decision-making. The subsequent protests and civil unrest have furthered the divide between the police and members of the public, which has damaged police legitimacy and led to depolicing and militarization. This study pilot tests the impact of implicit bias on decision-making for a student sample with a decision-making simulator and an experimental design with random assignment. Simulated police-public contacts, substantively, were found to be very complex and largely guided by legal factors; however, stressful stimuli can affect decision-making. The forthcoming protocol and methodology, moreover, provide insight to decision-making and create a framework to guide future research.