Organic matter, a complex mixture of organic compounds, is responsible for the cycling of global carbon and nutrients in aquatic and terrestrial ecosystems. Understanding the sorption and desorption dynamics of organic matter on mineral surface is then important in determining the mechanisms of carbon, pollutants and nutrients cycling in the environment. This project assess the energetics and dynamics of sorption and desorption of natural organic matter from different sources with 2-line ferrihydrite. To understand how theses interaction occur on mineral surfaces, we studied the sorption and desorption behavior of various fraction of organic matter such as humic acid, fulvic acid, natural organic matter as well as water-extracted organic matter from charred plant biomass. Result thus far show the differences in energy, quantity and the kinetics of sorption and desorption involved in these interactions. The energy and rate involved in the binding and de-binding of natural organic matter with the surface of 2-line ferrihydrite is greater than those associated with charred ashe juniper. Additionally, the energy of sorption and desorption decrease with increasing pH conditions. In contrast, the rate of reaction increase with increasing pH. This presentation will link the chemical properties of organic matter as well as the surface properties of ferrihydrite and their influence on the sorption and desorption dynamics across different environmentally relevant pH conditions.

A flow adsorption microcalorimtery-UVvis spectroscopy method was used to directly measure high temporal resolution energetics and energy dynamics of Adenosine triphosphate disodium (ATP) at the ferrihydrite-water interface. Ferrihydrite is amongst the most reactive and ubiquitous form of Fe-oxide minerals in the geosphere known to exhibit controlling effects on the bioavailability and cycling of nutrients such as Phosphorous. Fe-oxide minerals are known catalysts in the phase transformation from organic phosphate (Po) to inorganic phosphate (Pi) depending on the surface and organic molecule speciation. Interactions of ATP and ferrihydrite at pH 2, 5, and 8 were conducted to quantify the effect of pH on energetics and energy dynamics. At pH 2, 5, and 8 where the speciation of ATP was cation, uncharged, and anion respectively, its interactions with nitrate (NO3-) saturated ferrihydrite were exothermic with 13.8 J g-1, 11.4 J g-1, and 8.7 J g-1 respectively. Nitrate’s interactions with ATP saturated ferrihydrite were endothermic with 13.8 J g-1, 11.5 J g-1, and 45. 4 J g-1 at pH 2, 5, and 8 respectively. Post ATP anion exchange indicated that the interaction of ATP and ferrihydrite decreased by a factor of ≈ 1.8 (6.51 ± 0.38 J g-1 to 3.63 ± 0.23 Jg-1), ≈ 1.6 (0.13 ± 0.01 J g-1 to 0.08 ± 0.02 Jg-1 ), ≈ 2 (0.15 ± 0.05 J g-1 to 0.07 ± 0.02 Jg-1 ) at pH 2, 5, and 8 respectively. In addition to ATP’s speciation and ferrihydrite’s surface charge, differences in interaction energetics and dynamics were attributable to the Pi produced by hydrolysis of ATP. A decrease in post ATP anion exchange suggested partial reversibility by NO3- pointing to inner sphere interactions with ferrihydrite. The presentation will further discuss the molar heats of inner sphere interactions of the ATP and Pi with ferrihydrite at pH 2, 5, and 8.

Beginning in the Late Mississippian to Early Pennsylvanian, southern Laurentia experienced a major tectonic regime change. Progressive closure of the Rheic Ocean and collision between Laurentia and Gondwana along the Ouachita-Marathon fold and thrust belt drove deformation and subsidence within a series of basins along the southern Laurentian margin. Few provenance studies in the Ardmore Basin have been conducted mainly based on facies distribution, and heavy mineral and petrographic analyses. There are two opposing ideas regarding regional sediment deposition; 1.) a transcontinental system with headwaters from the Appalachian Orogen region and minor inputs from uplifts associated with the Ouachita Orogen, and 2.) a dominant transport from a southern source, likely accreted Gondwanan terranes. Here I propose a detailed U-Pb detrital zircon geochronology study to document the provenance of major upper Mississippian (Chesterian) to lower Pennsylvanian (Atokan) sandstones in the Ardmore Basin. I hypothesize that due to increased regional tectonic activity to the east and south, the Ardmore Basin experienced a major source shift from the Late Mississippian to Early Pennsylvanian with sediment transitioning from mature sand, mainly derived from Laurentia, to less mature sediments likely sourced from the Appalachian and Ouachita Orogens and local uplifts. Results of this study will provide critical evidence for the debate between previously proposed transcontinental vs. locally-derived sediment dispersal models, and contribute to the understanding of paleogeography during the collision of Laurentia and Gondwana.

Meander bend theory has been around since Albert Einstein popularized it in the 1920s. Since then, many geologists and physicists have grappled to understand the mechanics and concepts that cause rivers to meander in the ways that they do. Through the years, scientists have learned that bedload, slope, and flow velocity are all major drivers of cutbank erosion and bar building. However, one answer that has eluded scientists to this point is whether bar building (bar push) or bank scour (bank pull) causes meander bend migration. This study aims to analyze meander bend patterns in an 88 Km unchannelized stretch of the Missouri River between Yankton, SD and Sioux City, IA. Landsat images of this stretch over the last 30 years have been processed in remote sensing software to track bank, bar, and channel changes over this span of time. Extensive remote sensing processing (ESRI ArcMap and ArcGIS Pro) and statistical analyses will be performed on the river with respect to bank vs. bar movement, mid-channel bar migration, bar growth, and bar life cycles.

The Red River of the South is a highly understudied fluvial system with limited mapping. Early work, however, did map four fluvial terraces along the flanks of the modern river valley. These terraces record a period of time in which the ancestral Pleistocene Red River was a continent-scale river, sourcing from the Rockies and the volcanic uplands of New Mexico and depositing into the Gulf of Mexico. The ages of these terraces, though, are poorly understood. With these four known terraces, spanning the “terrace zone” (a ~5 km radius from the modern valley), and with surface areas of the terraces ranging between ~3 km2 and ~8.8 km2—there exists the potential to document the deposits of these four distinct periods of lateral migration—as well as to characterize various paleochannels and other fluvial features preserved within these terraces through hand auger sampling.

I aim to track the evolution of the Red River both physiologically and geochronologically, utilizing allostratigraphic methods to reconstruct some of the River’s past through the floodplain’s lithology and optically stimulated luminescence (OSL) dating of preserved terraces. I aim to construct detailed cross-sections of the valley fill by sampling the deposits of each of the various ancient terraces, as well as the modern floodplain, running roughly perpendicular to the axis of the current stretch of the Red River. Ideally, I would encounter paleochannels while drilling so as to potentially assess the features of the paleochannel belt. To maximize the likelihood of encountering paleochannels and related assemblages, I have begun to process and analyze Lidar and satellite data in an effort to identify remnants of these paleo-structures. I will collect sealed samples containing silica grains to send for OSL dating. In doing so, I can ascertain definitive dates on when the deposits associated with specific terraces were laid down.

Mathematical modeling of viral kinetics can be used to gain further insight into the viral replication cycle and virus-host interactions. However, many of the virus dynamics models do not incorporate the cell-to-cell heterogeneity of virus yield or the time-dependent factor of virus replication. A recent study of vesicular stomatitis virus (VSV) kinetics in single BHK cells determined that both virus production rate and yield of virus particles varies widely between individual cells of the same cell population. Here we use the results of the previously mentioned study to determine the distribution that best describes the time course of viral production within the single cells. We determined a list of eight potential distributions that are commonly used in viral kinetics models to fit to each data set by minimizing the sum of squared residuals. The model of best fit for each individual cell was determined using Akaike’s Information Criterion (AICC ). Results of this study show that the distribution that best describes viral production varies from cell to cell. This finding could have further reaching implications for incorporating time-dependent viral production into a standard model of virus kinetics in order to better reproduce the diversity of viral replication that occurs over time within a population of cells.

This report presents a novel approach to increase the detection sensitivity of trace amounts of DNA in a sample by employing Förster Resonance Energy Transfer (FRET) between intercalating dyes. Two intercalators that present efficient FRET were used to enhance sensitivity and improve specificity in detecting minute amounts of DNA. Comparison of steady-state acceptor emission spectra with and without the donor allows for simple and specific detection of DNA (acceptor bound to DNA) down to 100 pg/ul. When utilizing as an acceptor a dye with a significantly longer lifetime (e.g., Ethidium Bromide bound to DNA), multi-pulse pumping and time-gated detection enable imaging/visualization of picograms of DNA present in a microliter of an unprocessed sample or DNA collected on a swab or other substrate materials.

We studied room temperature phosphorescence of tryptophan (TRP) embedded in poly (vinyl alcohol) [PVA] films. With UV (285 nm) excitation, the phosphorescence spectrum of TRP appears at about 460 nm. We also observed the TRP phosphorescence with blue light excitation at 410 nm, well outside of the S0→S1 absorption. This excitation reaches the triplet state of TRP directly without the involvement of the singlet excited state. The phosphorescence lifetime of TRP is in the sub-millisecond range. The long-wavelength direct excitation to the triplet state results in high phosphorescence anisotropy which can be useful in macromolecule dynamics study via time-resolved phosphorescence.

The first stars in the Universe, Pop III stars, formed out of the primordial hydrogen and helium sometime during the first billion years of cosmic time. Their formation ended the Cosmic Dark Ages. Despite their critical role in kick starting the formation of all “metals,” (ie. the carbon in our bodies and the oxygen we breathe), we do not know how massive these first stars were, and when and how the era of the first stars ended. While Pop III stars are too faint for a direct detection, their deaths are potentially visible by James Webb Space Telescope (JWST). A subset of Pop III stars end their lives as Pair Instability Supernova (PISN), explosions 100 times more powerful than a typical supernova. However, determining the astrophysics of the first stars will require combining the detection of PISN with theoretical work on the mass distribution of Pop III stars. In this theoretical work, we need to fully explore the range of mass distribution of Pop III stars to determine how dependent the PISN rate is on the masses of Pop III stars. In this work, we present results from a new model which explores the distribution of Population III masses with a set free parameters. We find an order magnitude difference in the PISN rates for various Pop III mass distribution. In addition, we find that PISN rates may provide one of the first independent probes of the maximum mass of Pop III stars.

It has been well established that ZnO is a versatile material with multiple existing and potential applications owing to its numerous and unique properties. ZnO in the nano- and microscale forms has been a focus of attention in recent years due to demonstrated utilities in pharmaceutics, bioengineering and medical diagnostics. Of particular interest is the utilization of ZnO as an antibacterial agent. With growth inhibition observed for both gram-positive and gram-negative bacteria as well as antibiotic strains, the antibacterial action of ZnO is well documented. Yet, there exists much debate over the fundamental mechanisms underlying the antibacterial action of ZnO. Commonly proposed mechanisms include the generation of various reactive oxygen species, release of Zn ions, surface-to-surface interactions, etc. In this work, we investigate the surface and near-surface optoelectronic properties of ZnO microcrystals as they relate to the antibacterial figures of merit. As microscale ZnO particles exhibit comparable antibacterial action to those at the nanoscale, while minimizing effects related to internalization, they are well-suited to serve as a platform to investigate the role of the crystalline free surfaces in this behavior. A bottom-up hydrothermal growth method was employed to synthesize ZnO microcrystals with tunable morphology and a well-controlled relative abundance of polar and non-polar surfaces. The quality of the crystalline lattice and free surfaces as well as the predominant morphology of these samples were confirmed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface photovoltage spectroscopy. The antibacterial efficacy of these particles was characterized via minimum inhibitory concentration assays, performed using Staphylococcus Aureus in a Mueller Hinton broth media. We performed a series of optoelectronic experiments including temperature dependent photoluminescence spectroscopy as well as spectroscopic and transient surface photovoltage as a means to observe changes occurring at the ZnO surface during these assays. We detected significant spectral changes due to interactions with bacteria and growth media. In particular, we showed that interactions with s.aureus resulted in considerable modifications of the excitonic luminescence.