Archives: Portfolios

I use a combination of novel and published fossil occurrence data to investigate ecological changes in marine paleocommunities during intense ecosystem changes in the Ordovician Period (~487–443 million years ago) of Earth’s history. My work focuses on trilobites, an extinct group of marine arthropods, and how they distributed themselves across different habitat types during the prolonged ecosystem restructuring of the Ordovician Radiation, as well as their response to the more abrupt end-Ordovician mass extinction. The fossil record contains many examples of climate change-induced mass extinction events, but only a few are associated with the transition from an “icehouse” to an “ice-free” world. The end-Ordovician event is one such instance and therefore can provide useful context for the ongoing biodiversity crisis and associated ecosystem changes.

My research has two primary aims. First, I am investigating the reorganization of trilobite communities across depth-related habitat types in response to the climate change-driven end-Ordovician mass extinction, which eliminated over 50% of global trilobite diversity at higher taxonomic levels. Within-habitat (alpha) species diversity remained unaffected by the extinction event, which suggests that a dissimilarity component of diversity may have been altered. I am investigating the between-habitat (beta) diversity response of trilobites to determine if local (alpha) diversity was maintained by reducing taxonomic dissimilarity among habitat types. Additionally, I am examining the habitat associations of taxonomic lineages that survived, and did not survive, the extinction event to assess if habitat preference, or changes to it over time, was linked to extinction likelihood.

Initial results from Laurentia (most of present-day North America) support a decline in between-habitat dissimilarity following the end-Ordovician mass extinction. This mechanism appears to have at least partially maintained local diversities, potentially buffering against wider ecosystem changes in the wake of the extinction. Ongoing research will determine if this reorganization was unique to Laurentia and if the pattern holds up to additional examination.

Be stars are a type of star that rotate so rapidly that the centrifugal force causes their equators to bulge outward. If they rotate fast enough, they can eject material into an orbiting disk. To form such a disk, these stars must be spinning near their critical velocity (the speed where the centrifugal force at the equator throwing material outwards balances the force of gravity pulling material inwards). However, spectroscopic observations of Be stars show that they are only rotating at about 70% critical, which isn’t fast enough to eject material into orbit and create the disks we see. These observations have assumed that the stars rotate as solid bodies. The goal of my project is to investigate whether differential rotation along the surface (meaning that different parts of the surface rotate at different rates) could explain why spectroscopic observations might underestimate the true rotation rate. To test this, I have calculated the shape and rotation rate of a rotating star and used a library of spectral data to simulate the total spectra produced by the star. I have successfully applied this method to a few test cases, such as an ellipsoid-shaped star, and verified that the effects of rotation on the resulting spectra match my expectations. I plan on applying this method to a differentially rotating star to see what effects the differential rotation has on the spectra. 

The Astrophysics Division of NASA’s SMD emphasizes the development of precision X-ray optics to study the hot X-ray emitting plasma associated with faint celestial sources. Additionally, modern diffraction-limited storage rings and X-ray free-electron laser beamlines have enabled extremely bright and coherent X-ray beams that require precisely shaped optics focus these beamlines so as to not degrade their performance. This research project will mature the readiness of adjustable X-ray optics for use in astronomy and X-ray beamlines. This technology will enable the production of thin mirrors without compromising their focusing capability. These mirrors employ a set of discrete, thin-film piezoelectric actuators that when supplied a set of voltages induce a deterministic figure change to the mirror. This can correct for a variety of distortions and improve mirror angular resolution. This project will include designing an electronic control system and optical alignment configuration to test adjustable mirrors of different geometries and actuator materials. Interferometry will be used to measure the surface correctability of these mirrors on the scale of nanometers. Different optimization techniques will be explored to understand how to better calculate the voltages necessary to induce figure changes that yields the best angular resolution.

This work focuses on advancing the integration of autonomous aircraft into civilian airspace, a key component of NASA’s Urban Air Mobility (UAM) initiative. Previously, I developed a cooperative planning and control framework that ensures collision avoidance and energy-efficient autonomous flight using optimal control and formal safety guarantees. This framework provides mathematically rigorous methods for generating safe trajectories in constrained and dynamic environments. Building on this foundation, I am now investigating how neural networks can enhance trajectory generation by improving adaptability to dynamic airspace conditions. Traditional optimal control methods, while effective, often face computational challenges when applied in real-time. By integrating data-driven techniques, I aim to develop a framework that enables computationally efficient trajectory generation for autonomous aircraft in complex environments.

My research focuses on the synthesis and drawing of thin film glassy solid electrolytes for use in solid-state batteries.  I am working to synthesize large-scale rectangular glass preforms of highly ionically conductive glasses that will be reheated until they are viscous liquids and then pulled, stretched, and cooled, thinning the preform down from 6 millimeters to around 100 microns. I am working to optimize this process, to prevent crystallization of the glass during the reheating, and to generate films that are as thin as possible.  I have just recently drawn the first sample of a highly conductive lithium glassy solid electrolyte down to around 100 microns ever.  I hope to continue thinning these glassy ribbons, while further testing their electrochemical behavior through testing with lithium metal anodes, and in the future, sulfur cathodes.  This project relates to the NASA Space Technology Directorate through the need of highly energy-dense, and safe batteries in nearly every aspect of space missions.

To evaluate the habitability of other worlds, we must understand how the early biosphere evolved and developed on Earth and how Earth’s geochemistry impacted those processes. Environmental abundances of redox-sensitive metals such as iron (Fe) and molybdenum (Mo) have shifted over geological history as the Earth’s oceans transformed from largely anoxic to oxic production. This would have impacted microbial processes such as photosynthesis and nitrogen (N) acquisition which rely on bioavailable Fe and Mo, potentially modulating early primary production. I am evaluating whether Archean Ocean concentrations of Mo limit microbial productivity by measuring how Mo additions impact nitrate (NO₃^–) assimilation and Mo uptake among bacteria in Deming Lake which is a modern analog for the Archean Oceans. To address this, I am conducting incubation experiments with isotopically labeled NO₃^– and varying concentrations of Mo to determine whether early N assimilation was limited by Mo. Additionally, I will be doing transcriptomics to measure the microbial response to Mo additions. Expected results will provide insights into the role of Mo in regulating microbial productivity, thereby deepening our understanding of the metal requirements for life, the feedback between life and the environment, and where to search for extraterrestrial life.

I’m working to build and test magnetometers that can measure magnetic fields in the upper ionosphere, to better understand turbulence, electron precipitation, and Alfvén waves. These magnetometers have been used on balloons and suborbital rockets, meaning we have a good understanding of the sensor’s performance on short-time scales. In the future, we are targeting a long-duration multi-year application, such as a space weather monitoring instrument at the first Lagrangian point between Earth and the Sun. We would greatly benefit from knowing the performance of our magnetometers over longer durations of time. Testing a magnetometer for several days to a few weeks would help better define the limits of these devices and make known where improvements can be made. An important step to this future project is knowing the limits of our sensors, and how they vary over time. My project is to better understand the characterization and stability of our mini-T magnetometers. With the support of this grant, I would go to Goddard Space Flight Center and test our sensor in a high-grade facility for a longer duration than previous missions, to further strengthen and inform the short-term testing we do at the University of Iowa. A multi-week calibration at the GSFC facility would help us qualify our instrument design for long-term space weather forecasting applications.

Pacti is a design-time tool for engineers that lets them create Assume Guarantee contracts with components in their system. Currently used by NASA and many others. R2U2 or the Realizable Responsible Unobtrusive Unit is a very powerful runtime verification tool currently used by NASA and others that is a mission time tool. The integration here is to have R2U2 monitors generated from the contracts generated by Pacti. This allows for verifying the system operates in real-time exactly the way the engineer designed it. Without the need to learn a whole new formal methods language and how to use a new tool. By empowering a broader range of users, this tool has the potential to detect mission-critical issues early, reducing the risk of mission failure. 

My research project goal is to produce a glassy solid electrolyte (GSE) that is stable and competitive with currently available liquid-based electrolytes. These GSEs in next-generation batteries present a safer, higher-performance alternative to liquid electrolytes, which can then be used in demanding environments, including vehicular and space technologies. The project’s initial scope focused on determining how to best design a GSE for bulk processing, which included developing a method to characterize the thin film drawability of GSEs utilizing crystallization and viscosity models. Once the metrics for drawability were determined, GSE compositions were explored to synthesize a viable candidate that met the drawability metric without compromising the ionic conductivity and stability of the GSE. Continuous efforts have been made to further understand the structure of the produced GSEs and their relationship to beneficial properties, focusing on spectroscopic, electrochemical, and thermal characterization methods. Key structural units have been identified and are being iteratively targeted in candidate GSEs to refine their performance further.